Research ArticleOptical Frequency Upconversion Technique for Transmission ofWireless MIMO-Type Signals over Optical Fiber
R Q Shaddad12 A B Mohammad1 S A Al-Gailani13 and A M Al-Hetar2
1 Lightwave Communications Research Group Infocomm Research Alliance Universiti Teknologi Malaysia (UTM)81310 Johor Malaysia
2 Communication and Computer Engineering Department Faculty of Engineering and Information TechnologyTaiz University Taiz Yemen
3 Industrial Technical Institute Mallaa Aden Yemen
Correspondence should be addressed to R Q Shaddad rqs2006gmailcom
Received 28 August 2013 Accepted 2 February 2014 Published 16 March 2014
Academic Editors C-W Chow and E Stevens-Navarro
Copyright copy 2014 R Q Shaddad et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
The optical fiber is well adapted to pass multiple wireless signals having different carrier frequencies by using radio-over-fiber(ROF) technique However multiple wireless signals which have the same carrier frequency cannot propagate over a single opticalfiber such as wireless multi-input multi-output (MIMO) signals feeding multiple antennas in the fiber wireless (FiWi) system Anovel optical frequency upconversion (OFU) technique is proposed to solve this problem In this paper the novel OFU approachis used to transmit three wireless MIMO signals over a 20 km standard single mode fiber (SMF) The OFU technique exploits oneoptical source to produce multiple wavelengths by delivering it to a LiNbO
3external optical modulatorThe wireless MIMO signals
are then modulated by LiNbO3optical intensity modulators separately using the generated optical carriers from the OFU process
These modulators use the optical single-sideband with carrier (OSSB+C) modulation scheme to optimize the system performanceagainst the fiber dispersion effect Each wireless MIMO signal is with a 24GHz or 5GHz carrier frequency 1 Gbs data rate and16-quadrature amplitude modulation (QAM) The crosstalk between the wireless MIMO signals is highly suppressed since eachwireless MIMO signal is carried on a specific optical wavelength
1 Introduction
Next generation access networks are planned to providecustomers with high data rate broadband multiple servicesand flexible communication There is strong competitionbetween optical access technologies and wireless access tech-nologies to achieve these requirements since the bandwidthdemand of the end-users has become larger nowadays [1]Theoptical fiber access networks provide high-bandwidth digitalservices and long-distance communication but they are lessubiquitous The wireless access networks provide flexibleand ubiquitous communication with a low deployment costHowever its deployment scalability is limited by spectrumand range [2 3] The FiWi access network is powerful hybridarchitecture of optical backhaul and wireless front-end Thishybrid FiWi access network supports high data rates andthroughput with minimal time delay [4]
Figure 1 shows architecture of a FiWi access networkTheoptical backhaul is a tree network connecting the centraloffice (CO) and wireless front-end The optical backhaulis comprised of an optical line terminal (OLT) at the COan SMF a remote node (RN) and multiple access points(APs) The wireless front-end consists of widespread APs topenetrate numerous wireless end users (WEUs) There aretwo main methods to transmit the wireless signals over theFiWi systems ROF transmission and digitized radio-over-fiber (DROF) transmission [5 6]
For wireless broadband transmission the MIMO radiosystem has been defined as multiple transmitreceive anten-nas The MIMO system is designed to improve transmissionrangereliability and deliver higher data transmission ratesthan the single-input single-output (SISO) system The wire-lessMIMO signals are transmitted over fiber to get a powerfulintegrated FiWi system The optical fiber is well adapted
Hindawi Publishing Corporatione Scientific World JournalVolume 2014 Article ID 170471 14 pageshttpdxdoiorg1011552014170471
2 The Scientific World Journal
Wireless front-endOptical backhaul
CO
RN
ONUAP
CO central officeOLT optical line terminalRN remote node
AP access pointWEUs wireless end-usersONU optical network unit
WEUs
OLT
ONUAP
ONUAP
ONUAP
ONUAP
ONUAP
RN
Figure 1 FiWi access network architecture
to pass multiple wireless signals having different carrierfrequencies by using ROF technique However multiplewireless signalswhich have the same carrier frequency cannotpropagate over a single optical fiber such as MIMO signalsfeeding multiple antennas in the FiWi system The problemstarts once multiple MIMO signals are combined and thenupconverted by a single optical carrier Individual MIMOsignals could not be separated and recovered thereafter withregular electrical filtering The simple approach to solve thisproblem is by transporting eachMIMOsignal over individualoptical fiber However this approach will not be cost-effectivewhen many MIMO signals are transmitted over severaloptical fibers An approach to solve this problem by usingwavelength division multiplexing (WDM) and subcarriersmultiplexing (SCM) techniques has also been proposed [78] These techniques are not cost-effective since multipleoptical sources and photodetectors are required When SCMtechnique is used all except one of the MIMO radio signalsare translated to different frequency bands to transport themover fiber Many frequency converters are then used totranslate the delivered signal back to the original frequencyband So the cost and complexity are high in this approachespecially when the number of MIMO signals is large
The phase quadrature double-sideband frequency-translation technique has been proposed to transport MIMOradio signals over single optical fiber [9] The achievedmodulation symbol rate was limited because the phase andamplitude of the double sidebands were not sufficiently
matched due to the dispersion and frequency response of theoverall system [9]
Transmission of three MIMO radio signals all with244GHz carrier frequency over an optical fiber was pro-posed and demonstrated using an electrical single-sidebandfrequency translation (ESSB-FT) technique [10] The tech-nique used here [10] improves the system performance [9]where the phase and amplitude of the single sidebands weremore matched The proposed approach decreased the max-imum crosstalk level between the different MIMO channelsas compared to transporting the same signals by using SCMtechnique In addition it could be applied to work withexisting commercially available ROF systems which weredesigned to carry just SISO radio signals
Recently threewireless 16-QAMMIMOsignals were pro-posed to be transmitted over a 20 km SMF using the opticalsingle-sideband frequency translation (OSSB-FT) technique(which is considered as OFU technique) [11] These wirelessMIMO signals weremodulated using the carrier frequency of244GHz and optically modulated using the optical double-sideband (ODSB) modulation scheme The ODSB modu-lation scheme is affected by the dispersion effects of thefiber segment The fiber chromatic dispersion also increasesdirectly proportional with increasing radio frequency (RF)modulating frequency [1] In terms of the spectral efficiencythe ODSBmodulation scheme is not attractiveThe proposedcommunication system achieved a bit error rate (BER) of10minus5
The Scientific World Journal 3
In this paper the OFU technique is proposed to solve theproblem of wireless MIMO signals transmission over fibersince it does not need low-frequency local oscillators (LOs)at the transmitter and the receiver as compared to [10] Thecrosstalk is highly suppressed between the different wirelessMIMO signals with the same carrier frequency since eachwireless MIMO signal is carried on specific optical wave-length By using the OFU technique one optical dual-armmodulator (DAM) is derived by one optical source to producemultiple wavelengths which convey multiple wireless MIMOsignals over the optical fiber The FiWi system based onthe new approach can also support the wavelength reusetechnique so one optical source is enough to generate theoptical carrier which is reused at theAP as uplinkwavelengthand multiple wavelengths which convey multiple wirelessMIMO signals over the SMF [12] The principles and thesimulation design of the OFU technique to transport wirelessMIMO signals over fiber are discussed in Section 3
The novel OFU approach is used to transmit three wire-less MIMO signals over a 20 km SMF The OFU techniqueexploits one optical source to produce multiple wavelengthsby delivering it to a DAM The parameters of the DAMare adjusted to produce number of wavelengths accordingto the number of the wireless MIMO signals The wirelessMIMO signals are then optically modulated by opticalintensity modulators separately using the produced opticalcarriers from the OFU process All these optical modulatorsare LiNbO
3Mach-Zehnder modulators (LN-MZMs) Each
wireless MIMO signal is with a 24GHz or 5GHz carrierfrequency 1 Gbs data rate and 16-QAM The crosstalkbetween the wireless MIMO signals is highly suppressedsince each wireless MIMO signal is carried on a specificoptical wavelength The system performance is evaluatedin terms of BER error vector magnitude (EVM) and eyediagrams for different RF carriers optical link distances andchannel spacings The novel technique provides a spectralefficient and reliable FiWi system
This paper is organized as follows Section 2 outlinesthe operation of the OFU technique Principles and designof the proposed system are demonstrated in Section 3 InSection 4 the mathematical model of the proposed systemillustrates how the OFU approach operates in the proposedsystem Section 5 analyzes and discusses the system perfor-mance Section 6 suggests how the proposed approach canbe extended to transport a higher number of wireless MIMOsignals Finally conclusions are given in Section 7
2 Optical Frequency Upconversion Technique
OFU technique is a prime technique in many fields of opticalcommunication External frequency modulators such as LN-MZMs can be used as a light-wave frequency upconverterin fiber optics [13] The LN-MZM is a DAM which can beused as an optical frequency upconverter when its dual-armsare supplied by a sinusoidal RF signal The LN-MZM is alsoused as an optical modulator for digital base-band signalsor modulated RF signals when these signals drive its dual-arms For broadband communication applications externalLN-MZMs provide broadband operation and minimize the
dispersion effects Moreover the external LN-MZMs offerhigh stability very low bias-voltage drift rates and bias-freedevices [14 15] The frequency conversion efficiency of theLN-MZMs can be increased by using low values of half-wavevoltage (119881
120587)
In this study the OFU technique is proposed to generatemultiple optical carriers which are used to modulate multiplewireless signals separately at many optical external intensitymodulators (IMs) The modulated optical signals can thenbe multiplexed together to the optical fiber since theyhave no overlapping adjacent spectral bands The DAM isset to generate first-order signal component (at the centersinusoidal RF frequency) and other higher-order modulatedcomponents around it The higher-order components areneglected since they have small amplitude compared tothe lower-order components In this approach the WDMinterleaver (WDM IL) is used after the DAM to separate thegenerated dominant wavelengths [16]
Generation of multiple wavelengths from one laser diode(LD) using OFU technique is illustrated in Figure 2 Oneoptical source LD with optical carrier frequency 119891
119901supplies
a DAM which is driven by a sinusoidal clock frequency 119891119898
(RFmodulating frequency)TheDAM is adjusted to generatemultiple frequency components first-order component withthe center optical carrier frequency 119891
119901and upper and lower
single sidebands components around the center frequencyThe lower single sideband components have the opticalfrequencies (119891
119901minus 119891119898 119891119901minus 2119891119898 119891119901minus 3119891119898 etc) At the
output the upper single sideband components will have theoptical frequencies (119891
119901+ 119891119898 119891119901+ 2119891119898 119891119901+ 3119891119898 etc) From
Figure 2 there are a number (five) of frequency componentsexceeding the other higher-order components which havesmall magnitudes as compared to their magnitudes Thesefrequency components are called dominant wavelengths orfrequencies which are interleaved separately by using WDMIL The channel frequency space (or wavelength interleave)between the generated wavelengths is 119891
119898 The dominant
wavelengths will be used as downlink wavelengths to conveythe multiple wireless MIMO signals over optical fiber
3 Principles and Design ofthe Proposed System
The block diagram of the OFU technique for transmissionof three wireless MIMO signals over a single optical fiberis shown in Figure 3(a) At the transmitter three wirelessMIMO signals MIMO
1 MIMO
2 and MIMO
3are generated
and modulated using M-QAM at the same carrier frequency119891119888
= 24GHz The spectra of these three wireless signalsare shown in Figure 3(b) in the insets ((i)ndash(iii)) A DAMwith the ODSB modulation technique is used to generatethree downlink wavelengths from one LD with a wavelength120582119889
= 155252 nm (193100 THz) as shown in Figure 3(b)the inset (iv) The three generated downlink wavelengths areshown in Figure 3(b) as the inset (v) Two ILs are used afterthe DAM to separate the three downlink wavelengths whichare the two single-sideband wavelengths 120582
1198891= 155232 nm
(193125 THz) and 1205821198892
= 155273 nm (193075 THz) and theoptical carrier frequency 120582
1198893= 155252 nm (193100 THz)
4 The Scientific World Journal
DAM
Clockfrequency
fm
fm
DC biasvoltage
Opticalcarrier
fp
fp
fp
fp minus fmfp minus 2fmfp minus 3fm
WDMIL
fp + 2fmfp + fm
fp + fm
fp + 3fm
Dominantwavelengths
fp
fp minus fm
fp minus 2fm
fp + 2fm
Figure 2 Generation of multiple wavelengths using OFU technique
The channel spacing between these wavelengths Δ120582 equalsthe frequency of the sinusoidal clock 119891
119900= 25GHz (02 nm)
which is used in the DAM An optical attenuator is used inthe path of the downlink wavelength 120582
1198893to equilibrate its
power with the generated power from the other downlinkwavelengths 120582
1198891and 120582
1198892
The downlink wavelengths 1205821198891 1205821198892 and 120582
1198893are used to
modulate the three wirelessMIMO signalsMIMO1 MIMO
2
and MIMO3by external IMs respectively The wireless
MIMO signals are firstly biased to be compatible with thenature of the optical signals and then optically modulated bythe IMs These IMs use the OSSB+C modulation scheme tooptimize the system performance against the fiber dispersioneffectThe three modulated optical signals with the downlinkwavelengths 120582
1198891 1205821198892 and 120582
1198893are coupled together as shown
in Figure 3(b) inset (vi) and then propagated along a 20 kmSMFwith attenuation of 02 dBkm and dispersion coefficientof 17 psnmkm
The receiver receives the optical downstream and theninterleaves it into three modulated optical signals with thewavelengths 120582
1198891 1205821198892 and 120582
1198893 as shown in Figure 3(b)
in the insets ((vii)ndash(ix)) The receiver then downconvertsthe three modulated optical signals directly to the suitable
electrical signals by using an optical receiver for each signalThe electrical signals are then band-pass filtered accordingto the allocated RF carrier frequency 119891
119888= 24GHz by
using bandpass filters (BPFs) to get the wireless MIMOsignalsMIMO
1MIMO
2 andMIMO
3The crosstalk between
the received wireless MIMO signals which have the samefrequency is highly suppressed because each signal is carriedon an independent wavelength with a large channel spacing(25GHz) as compared to the carrier frequency (24GHz) Inthis simulation the PIN photodiodes with power sensitivityof minus20 dBm are used in the optical receivers
In the simulation design the OFU technique is used totransport three wireless MIMO signals with the same RFcarrier frequency of 24GHz or 5GHz over fiberThewirelessMIMO signals are modulated by using 16-QAM modulationto investigate the performance of this ROF system at differentaccess distances and different wavelength interleaves
4 Mathematical Model of the Proposed System
The optical field of the output signal 119864out(119905) from the DAMcan be expressed as [17 18]
Figure 3 Transport of wireless MIMO signals over optical fiber using the OFU technique (a) block diagram of the proposed technique and(b) power spectra of the signals according to the indicated insets
119864out (119905) = 120572119864in (119905) (1 minus 120574) 119890(119895120587V1(119905)119881120587RF+1198951205871198811198871119881120587DC)
Here119864in(119905) is the input optical signal to theDAMfrom theLD V1(119905) and V
2(119905) are the RF modulating electrical voltage
with the carrier frequency 119891119898
= 1205961198982120587 119881
1198871and 119881
1198872are
the DC bias voltages applied to the arms of the DAM 119881120587RF
and 119881120587DC are the switching RF and switching bias voltages
respectivelyThe parameter 120572 is given by
120572 = 10minus(Ω20)
(2)
Here Ω is the insertion loss in dB (It is assigned as 5 dBin this design) 120574 designates the power splitting (combining)ratio of arm two for the input (output resp) 119884-branchwaveguide 120574 is given by
120574 =(1 minus 1radic120576
119903)
2 (3)
where 120576119903= 10(Extinction Ratio10)
= 100 so 120574 asymp 12 in this workIn the simulation design the values of 119881
120587RF and 119881120587DC are
set to 4V and the bias voltages of 1198811198871and 119881
1198872are assigned as
minus1 V and 1V respectively In addition the generated opticalsignal from the LD can be expressed as 119864in(119905) = 119864
119901119890119895120596119901119905 and
the modulating electrical signals can be expressed as V1(119905) =
+1198723(119905 minus 1199051198893) 119890119895[(120596119901+120596119888)119905+120573(120596
119901+120596119888)119911]
(12)
where 119905119889119894(119894 = 1 2 or 3) is the time delay of the 119894th optical
downlink signal The time delay is calculated by the firstderivative of 120573(120596) since 119905
119889119894= 1205731015840(120596119889119894
+ 120596119888) and 120596
119894is the
120596p120596p minus 120596m 120596p + 120596m
120596
Am
plitu
de
USSB2 USSB3 USSB1
fd2 fd3 fd1
Figure 4 The propagated lightwave signal over the optical fiber
119894th optical downlink carrier frequency The output lightwaveat the end of fiber is considered as three optical signals withdifferent downlink frequencies of 120596
119901+ 120596119898 120596119901minus 120596119898 and 120596
119901
which convey the three wireless MIMO signals in their uppersingle sidebands (USSBs) as shown in Figure 4
The optical receiver receives the transmitted optical sig-nals and separates them according to their downlink wave-lengths by using optical ILs as shown in Figure 3 Each opticaldownlink signal is then directly detected by a photodetector(PD) so the photocurrent for each detectedMIMOsignal canbe written as the following equation according to the square-law PD [18]
Figure 5 The fiber nonlinearity effect on the system performance
The wireless end-user will receive the three MIMO signalsand demodulate them using the suitable QAMdemodulationand MIMO decoding techniques
5 System Performance Evaluation
In this work the communication system is designed toprovide a data rate of 1 Gbs for each 16-QAMwirelessMIMOsignal Figure 3 in the inset (vi) shows the input opticalpower to the optical fiber where the three modulated opticalsignals with the downlink wavelengths 120582
1198891 1205821198892 and 120582
1198893
are coupled to propagate through 20 km optical fiber Thetotal input power of the three optical signals is 1626 dBmaccording to the simulation calculations for both RF carrierfrequencies of 24GHz and 5GHzThis power is suitable to belaunched to avoid the nonlinear effects along the optical linkFigure 5 shows the system performance at different launchedoptical powers Nonlinearity of the fiber negatively affects thesystem performance when the launched optical powers aregreater than 108 dBm and 79 dBm at the carrier frequenciesof 24GHz and 50GHz respectively
To evaluate the performance of the proposed techniqueFigures 6(a) and 6(b) show the BER performance versus thereceived optical power at the receiver for the three wirelessMIMO signals (MIMO
1 MIMO
2 andMIMO
3) at the carrier
frequencies 24GHz and 5GHz respectively The powersensitivity differences of the receivers for the three MIMOsignals are small especially between the two MIMO signals(MIMO
1and MIMO
2) The maximum power penalties of
347 dB and 4 dB are recorded at BER of 10minus9 for the carrierfrequencies of 24GHz and 5GHz receptively
Figure 7 shows the system performance at three differentfiber lengths (20 km 30 km and 50 km) of the optical fiber Inthe proposed system the fiber length of 50 kmhas slight effecton the performance of the transmitted optical signals whichcarry the wireless MIMO signals The system performance
deteriorates progressively when the access distance becomeslonger than 50 km
In addition the system performance is analyzed by usingdifferent wavelength interleaves between the optical carrierfrequency (or RF clock frequency 119891
119900) Figure 8 shows the
systemperformance at differentwavelength interleaves (Δ119891 =
15 25 and 50GHz which are compatible with Δ120582 = 01202 and 04 nm resp) When the wavelength interleaves aresmaller than 15GHz the system performance will degradeand the error floor clearly appears
Figures 9(a)ndash9(c) show 1Gbs 16-QAM constellationdiagrams for the received MIMO signals MIMO
1 MIMO
2
and MIMO3 respectively at 24GHz Clear scatter-plots are
achieved at EVM values of minus208780 dB minus202873 dB andminus212961 dB for MIMO
1 MIMO
2 and MIMO
3 respectively
So the proposed technique has achieved a good performanceof transmitting wireless MIMO signals over the optical fiberat the carrier frequencies 24GHz and 5GHz The EVMs arecalculated considering the following equation [21]
EVM (dB) = 10 sdot log10[sum119872
119896=1
1003816100381610038161003816119878119905119909119896 minus 119878119903119909119896
where EVM is the value of the difference between a collectionof received symbols and transmitted or ideal symbols 119878
119905119909119896
is the corresponding transmitted symbol of the constellationassociated with the 119896th symbol 119878
119903119909119896is the received symbol
associated with 119878119905119909119896
and119872 is the number of the symbols forthe inphase-quadrature constellation
Figures 10(a)ndash10(c) show the eye diagrams of the 119868-branch of the received 16-QAMbaseband signals forMIMO
1
MIMO2 and MIMO
3 respectively Also Figures 11(a)ndash11(c)
show the eye diagrams of the 119876-branch of the received 16-QAM baseband signals for MIMO
1 MIMO
2 and MIMO
3
respectively The eye diagrams of both 119868-branch and 119876-branch of the received wireless MIMO signals at the receivershow slight differences and good quality communicationsystem at a BER around of 10minus9 The BER are calculatedaccording to (15) [22]
where 119876 is the number of signal levels within each branchof the constellation diagram log
2119872 is the amount of bits
encoded into one QAM symbol and 119896 is a modulationformat-dependent factor giving the relationship betweenmaximum field magnitude and average overall119872 field mag-nitudes defined by the constellation diagram for the chosenmodulation formatThis factor is calculated according to (15)
Figure 7The system performance at different lengths of the opticalfiber
to be 6(radic5+2) for 16-QAMThe 119878119905119909119894
is the ideal transmittedfield vector and 119878
119905119909max is the field vector of the outermostconstellation point In this paper the performance of EVMand the BER is evaluated for the 16-QAM MIMO signalswithout using forward error correction (FEC) techniques
6 Transmission of More Wireless MIMOSignals over Optical Fiber
Figure 12 shows the proposed OFU technique to transmitfive wireless MIMO signals over fiber At the OLT the DAM
Received optical powerminus20 minus18 minus16 minus14 minus12 minus10 minus8 minus6
10minus20
10minus18
10minus16
10minus14
10minus12
10minus10
10minus8
10minus6
10minus4
10minus2
100
BER
Δf = 15GHzΔf = 25GHzΔf = 50GHz
Figure 8 The system performance at different wavelength inter-leaves
is injected by LD with the wavelength 120582119889 The DAM is a
LN-MZM Adjusting the parameters of the DAM to suitablevalues can generate multiple wavelengths The dominantwavelengths are considered and the remaining outside wave-lengths are neglected because of their very small magnitudesThe OLT allocates five downlink wavelengths (120582
1198891 1205821198892 1205821198893
1205821198894 and 120582
1198895) which are used for downstream modulation
To generate five dominant wavelengths the values of DAMparameters are configured as minus05 V 05 V DC bias voltagesare applied to respectively first and second arms of theLN-MZM the RF clock voltage with frequency of 119891
119900drives
10 The Scientific World Journal
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(a)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)(b)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(c)
Figure 9 Constellation diagrams of the demodulated 16-QAMMIMO signals (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
to the DAM and the DC and RF switching voltages areset to 4V and 2V respectively The wavelength interleavesbetween the five generatedwavelengthswhich are equal to thefrequency of the sinusoidal clock 119891
119900 The power magnitudes
of the fivewavelengths are approximately equal and the centerwavelength 120582
1198893has maximum value The difference between
this and the others is around 6 dB To get balanced powermagnitudes an optical attenuator is used in path of the centerwavelength after IL as shown in Figure 12 Each generatedwavelengthmodulates theMIMO signal by using IMThefive
modulated optical signals propagate along the same opticalfiber
The receiver receives the optical downstream and theninterleaves it into the five modulated optical signals withthe wavelength 120582
1198891 1205821198892 1205821198893 1205821198894 and 120582
1198895as shown in
Figure 12The receiver then downconverts the fivemodulatedoptical signals directly to the suitable electrical signals byusing an optical receiver for each signalThe electrical signalsare then band-pass filtered according to the allocated RFcarrier frequency 119891
119888by using BPFs to get the original five
The Scientific World Journal 11
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 10 Eye diagrams of the 119868-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
wireless MIMO signals MIMO1 MIMO
2 MIMO
3 MIMO
4
and MIMO5
7 Conclusions
The novel OFU technique is proposed to solve the problemof wireless MIMO signals transmission over a single opticalfiberThree wireless 16-QAMMIMO signals have been trans-mitted over a 20 km SMF using the OFU technique Thesewireless MIMO signals were modulated using the carrier
frequency of 24GHz or 5GHz at data rate of 1 Gbs for eachsignal The physical layer performance has been reported interms of the BER at different RF carrier frequencies differentaccess distances and different wavelength interleaves Inaddition the EVM and the eye diagrams are analyzed in thisstudy
The proposed approach highly suppressed the crosstalkbetween different MIMO signals with the same RF carrierfrequency since each MIMO signal is carried on a spe-cific optical wavelength While the ESSB-FT technique [10]
12 The Scientific World Journal
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 11 Eye diagrams of the 119876-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
requires a number of low-frequency LOs and electrical BPFsat the transmitter and the receiver the OFU technique doesnot require low-frequency LOs at the transmitter and thereceiver or electrical BPFs at the transmitter Less numberof electrical BPFs is required at the receiver in the proposedtechnique However a number of PDs are required at thereceiver which is equal to the number of MIMO signals Theproposed system supports many wavelengths for carrying
multiple wireless MIMO signals over the fiber using singleLD The novel technique provides a spectral efficient andreliable FiWi system
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
The Scientific World Journal 13
IM
IM
IM
IM
IM
DAM
fo
120582d3
120582d4
120582d5
Transmitter
120582d
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
120582d1
120582d2
Bias
Bias
Bias
Bias
Bias
AWG
RF amplifier
RF amplifier
RF amplifier
RF amplifier
RF amplifier
fc
fc
fc
fc
fc
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalfiber
BPF
BPF
BPF
BPF
BPF
IL
IL
Receiver
LD 120582d3
120582d4
120582d5
120582d1
120582d2
Optical attenuator
+
+
+
+
+minus70
minus50
minus30
minus10
0
minus20
minus40
minus60
1929T 193T 1931T 1932T 1933T
Pow
er (d
Bm)
Frequency (Hz)
Figure 12 Transmission of five wireless MIMO signals over fiber using the novel approach
Acknowledgments
This work is supported by Universiti Teknologi Malaysia(UTM) under the Postdoctoral fellowship scheme Theauthors greatly appreciate UTM and Photonics ResearchLaboratory for providing the facilities which enabled themto accomplish this work They would also like to thank theMinistry of Science Technology and Innovation (MOSTI)Malaysia for sponsoring this work under Project vote no73720
References
[1] L Kazovsky S-W Wong T Ayhan K M Albeyoglu MR N Ribeiro and A Shastri ldquoHybrid optical-wireless accessnetworksrdquo Proceedings of the IEEE vol 100 no 5 pp 1197ndash12252012
[2] R Q Shaddad A B Mohammad and AM Al-hetar ldquoAnalysisof physical layer performance of hybrid optical-wireless accessnetworkrdquo Optics Communications vol 284 no 20 pp 4894ndash4899 2011
[3] R Q Shaddad A Bakar Mohammad and A M Al-hetar ldquoPer-formance evaluation for optical backhaul andwireless front-endin hybrid optical-wireless access networkrdquo Optoelectronics andAdvanced Materials Rapid Communications vol 5 no 4 pp376ndash380 2011
[4] C Lim A Nirmalathas M Bakaul et al ldquoFiber-wirelessnetworks and subsystem technologiesrdquo Journal of LightwaveTechnology vol 28 no 4 pp 390ndash405 2010
[5] A Nirmalathas P A Gamage C Lim D Novak and RWaterhouse ldquoDigitized radio-over-fiber technologies for con-verged optical wireless access networkrdquo Journal of LightwaveTechnology vol 28 no 16 pp 2366ndash2375 2010
[6] Z Jia J Yu G Ellinas and G-K Chang ldquoKey enablingtechnologies for optical wireless networks optical millimeter-wave generation wavelength reuse and architecturerdquo Journalof Lightwave Technology vol 25 no 11 pp 3452ndash3471 2007
[7] A Zelst ldquoSystem for transporting multiple radio frequencysignals of a multiple input multiple output wireless communi-cation system tofrom a central processing base stationrdquo USpatent application 20040017785A1 2004
[8] I Seto H Shoki and S Ohshima ldquoOptical subcarrier mul-tiplexing transmission for base station with adaptive arrayantennardquo IEEE Transactions on Microwave Theory and Tech-niques vol 49 no 10 pp 2036ndash2041 2001
[9] C-P Liu and A Seeds ldquoTransmission of MIMO radio signalsover fibre using a novel phase quadrature double sidebandfrequency translation techniquerdquo in Proceedings of the IEEEInternational Meeting on Microwave Photonics Jointly Held withthe Asia-Pacific Microwave Photonics Conference pp 23ndash26Gold Coast Australia October 2008
[10] C-P Liu and A J Seeds ldquoTransmission of wireless MIMO-type signals over a single optical fiber without WDMrdquo IEEETransactions on Microwave Theory and Techniques vol 58 no11 pp 3094ndash3102 2010
[11] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgailani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overoptical fiberrdquo in Proceedings of the 3rd International Conferenceon Photonics (ICP rsquo12) Penang Malaysia 2012
[12] R Shaddad A Mohammad and A Al-hetar ldquoSpectral efficienthybrid wireless optical broadband access network (WOBAN)based on transmission of wireless MIMO OFDM signals overWDM PONrdquo Optics Communications vol 285 no 20 pp4059ndash4067 2012
[13] K Shimizu T Horiguchi and Y Koyamada ldquoFrequency trans-lation of light waves by propagation around an optical ringcircuit containing a frequency shifter 1 Experimentrdquo AppliedOptics vol 32 pp 6718ndash6726 1993
[14] E L Wooten K M Kissa A Yi-Yan et al ldquoA review of lithiumniobate modulators for fiber-optic communications systemsrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 6no 1 pp 69ndash82 2000
[15] P Yao R Shireen J Macario C A Schuctz S Shi and D WPrather ldquoDesign fabrication and characterization of LiNbO
3
optical modulator for high-sensitivity mmW imaging systemrdquoin Passive Millimeter-Wave Imaging Technology XI vol 6948 ofProceedings of SPIE March 2008
[16] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgeelani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overfiber-wireless systemrdquo Optics amp Laser Technology vol 47 pp347ndash354 2013
14 The Scientific World Journal
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
CO central officeOLT optical line terminalRN remote node
AP access pointWEUs wireless end-usersONU optical network unit
WEUs
OLT
ONUAP
ONUAP
ONUAP
ONUAP
ONUAP
RN
Figure 1 FiWi access network architecture
to pass multiple wireless signals having different carrierfrequencies by using ROF technique However multiplewireless signalswhich have the same carrier frequency cannotpropagate over a single optical fiber such as MIMO signalsfeeding multiple antennas in the FiWi system The problemstarts once multiple MIMO signals are combined and thenupconverted by a single optical carrier Individual MIMOsignals could not be separated and recovered thereafter withregular electrical filtering The simple approach to solve thisproblem is by transporting eachMIMOsignal over individualoptical fiber However this approach will not be cost-effectivewhen many MIMO signals are transmitted over severaloptical fibers An approach to solve this problem by usingwavelength division multiplexing (WDM) and subcarriersmultiplexing (SCM) techniques has also been proposed [78] These techniques are not cost-effective since multipleoptical sources and photodetectors are required When SCMtechnique is used all except one of the MIMO radio signalsare translated to different frequency bands to transport themover fiber Many frequency converters are then used totranslate the delivered signal back to the original frequencyband So the cost and complexity are high in this approachespecially when the number of MIMO signals is large
The phase quadrature double-sideband frequency-translation technique has been proposed to transport MIMOradio signals over single optical fiber [9] The achievedmodulation symbol rate was limited because the phase andamplitude of the double sidebands were not sufficiently
matched due to the dispersion and frequency response of theoverall system [9]
Transmission of three MIMO radio signals all with244GHz carrier frequency over an optical fiber was pro-posed and demonstrated using an electrical single-sidebandfrequency translation (ESSB-FT) technique [10] The tech-nique used here [10] improves the system performance [9]where the phase and amplitude of the single sidebands weremore matched The proposed approach decreased the max-imum crosstalk level between the different MIMO channelsas compared to transporting the same signals by using SCMtechnique In addition it could be applied to work withexisting commercially available ROF systems which weredesigned to carry just SISO radio signals
Recently threewireless 16-QAMMIMOsignals were pro-posed to be transmitted over a 20 km SMF using the opticalsingle-sideband frequency translation (OSSB-FT) technique(which is considered as OFU technique) [11] These wirelessMIMO signals weremodulated using the carrier frequency of244GHz and optically modulated using the optical double-sideband (ODSB) modulation scheme The ODSB modu-lation scheme is affected by the dispersion effects of thefiber segment The fiber chromatic dispersion also increasesdirectly proportional with increasing radio frequency (RF)modulating frequency [1] In terms of the spectral efficiencythe ODSBmodulation scheme is not attractiveThe proposedcommunication system achieved a bit error rate (BER) of10minus5
The Scientific World Journal 3
In this paper the OFU technique is proposed to solve theproblem of wireless MIMO signals transmission over fibersince it does not need low-frequency local oscillators (LOs)at the transmitter and the receiver as compared to [10] Thecrosstalk is highly suppressed between the different wirelessMIMO signals with the same carrier frequency since eachwireless MIMO signal is carried on specific optical wave-length By using the OFU technique one optical dual-armmodulator (DAM) is derived by one optical source to producemultiple wavelengths which convey multiple wireless MIMOsignals over the optical fiber The FiWi system based onthe new approach can also support the wavelength reusetechnique so one optical source is enough to generate theoptical carrier which is reused at theAP as uplinkwavelengthand multiple wavelengths which convey multiple wirelessMIMO signals over the SMF [12] The principles and thesimulation design of the OFU technique to transport wirelessMIMO signals over fiber are discussed in Section 3
The novel OFU approach is used to transmit three wire-less MIMO signals over a 20 km SMF The OFU techniqueexploits one optical source to produce multiple wavelengthsby delivering it to a DAM The parameters of the DAMare adjusted to produce number of wavelengths accordingto the number of the wireless MIMO signals The wirelessMIMO signals are then optically modulated by opticalintensity modulators separately using the produced opticalcarriers from the OFU process All these optical modulatorsare LiNbO
3Mach-Zehnder modulators (LN-MZMs) Each
wireless MIMO signal is with a 24GHz or 5GHz carrierfrequency 1 Gbs data rate and 16-QAM The crosstalkbetween the wireless MIMO signals is highly suppressedsince each wireless MIMO signal is carried on a specificoptical wavelength The system performance is evaluatedin terms of BER error vector magnitude (EVM) and eyediagrams for different RF carriers optical link distances andchannel spacings The novel technique provides a spectralefficient and reliable FiWi system
This paper is organized as follows Section 2 outlinesthe operation of the OFU technique Principles and designof the proposed system are demonstrated in Section 3 InSection 4 the mathematical model of the proposed systemillustrates how the OFU approach operates in the proposedsystem Section 5 analyzes and discusses the system perfor-mance Section 6 suggests how the proposed approach canbe extended to transport a higher number of wireless MIMOsignals Finally conclusions are given in Section 7
2 Optical Frequency Upconversion Technique
OFU technique is a prime technique in many fields of opticalcommunication External frequency modulators such as LN-MZMs can be used as a light-wave frequency upconverterin fiber optics [13] The LN-MZM is a DAM which can beused as an optical frequency upconverter when its dual-armsare supplied by a sinusoidal RF signal The LN-MZM is alsoused as an optical modulator for digital base-band signalsor modulated RF signals when these signals drive its dual-arms For broadband communication applications externalLN-MZMs provide broadband operation and minimize the
dispersion effects Moreover the external LN-MZMs offerhigh stability very low bias-voltage drift rates and bias-freedevices [14 15] The frequency conversion efficiency of theLN-MZMs can be increased by using low values of half-wavevoltage (119881
120587)
In this study the OFU technique is proposed to generatemultiple optical carriers which are used to modulate multiplewireless signals separately at many optical external intensitymodulators (IMs) The modulated optical signals can thenbe multiplexed together to the optical fiber since theyhave no overlapping adjacent spectral bands The DAM isset to generate first-order signal component (at the centersinusoidal RF frequency) and other higher-order modulatedcomponents around it The higher-order components areneglected since they have small amplitude compared tothe lower-order components In this approach the WDMinterleaver (WDM IL) is used after the DAM to separate thegenerated dominant wavelengths [16]
Generation of multiple wavelengths from one laser diode(LD) using OFU technique is illustrated in Figure 2 Oneoptical source LD with optical carrier frequency 119891
119901supplies
a DAM which is driven by a sinusoidal clock frequency 119891119898
(RFmodulating frequency)TheDAM is adjusted to generatemultiple frequency components first-order component withthe center optical carrier frequency 119891
119901and upper and lower
single sidebands components around the center frequencyThe lower single sideband components have the opticalfrequencies (119891
119901minus 119891119898 119891119901minus 2119891119898 119891119901minus 3119891119898 etc) At the
output the upper single sideband components will have theoptical frequencies (119891
119901+ 119891119898 119891119901+ 2119891119898 119891119901+ 3119891119898 etc) From
Figure 2 there are a number (five) of frequency componentsexceeding the other higher-order components which havesmall magnitudes as compared to their magnitudes Thesefrequency components are called dominant wavelengths orfrequencies which are interleaved separately by using WDMIL The channel frequency space (or wavelength interleave)between the generated wavelengths is 119891
119898 The dominant
wavelengths will be used as downlink wavelengths to conveythe multiple wireless MIMO signals over optical fiber
3 Principles and Design ofthe Proposed System
The block diagram of the OFU technique for transmissionof three wireless MIMO signals over a single optical fiberis shown in Figure 3(a) At the transmitter three wirelessMIMO signals MIMO
1 MIMO
2 and MIMO
3are generated
and modulated using M-QAM at the same carrier frequency119891119888
= 24GHz The spectra of these three wireless signalsare shown in Figure 3(b) in the insets ((i)ndash(iii)) A DAMwith the ODSB modulation technique is used to generatethree downlink wavelengths from one LD with a wavelength120582119889
= 155252 nm (193100 THz) as shown in Figure 3(b)the inset (iv) The three generated downlink wavelengths areshown in Figure 3(b) as the inset (v) Two ILs are used afterthe DAM to separate the three downlink wavelengths whichare the two single-sideband wavelengths 120582
1198891= 155232 nm
(193125 THz) and 1205821198892
= 155273 nm (193075 THz) and theoptical carrier frequency 120582
1198893= 155252 nm (193100 THz)
4 The Scientific World Journal
DAM
Clockfrequency
fm
fm
DC biasvoltage
Opticalcarrier
fp
fp
fp
fp minus fmfp minus 2fmfp minus 3fm
WDMIL
fp + 2fmfp + fm
fp + fm
fp + 3fm
Dominantwavelengths
fp
fp minus fm
fp minus 2fm
fp + 2fm
Figure 2 Generation of multiple wavelengths using OFU technique
The channel spacing between these wavelengths Δ120582 equalsthe frequency of the sinusoidal clock 119891
119900= 25GHz (02 nm)
which is used in the DAM An optical attenuator is used inthe path of the downlink wavelength 120582
1198893to equilibrate its
power with the generated power from the other downlinkwavelengths 120582
1198891and 120582
1198892
The downlink wavelengths 1205821198891 1205821198892 and 120582
1198893are used to
modulate the three wirelessMIMO signalsMIMO1 MIMO
2
and MIMO3by external IMs respectively The wireless
MIMO signals are firstly biased to be compatible with thenature of the optical signals and then optically modulated bythe IMs These IMs use the OSSB+C modulation scheme tooptimize the system performance against the fiber dispersioneffectThe three modulated optical signals with the downlinkwavelengths 120582
1198891 1205821198892 and 120582
1198893are coupled together as shown
in Figure 3(b) inset (vi) and then propagated along a 20 kmSMFwith attenuation of 02 dBkm and dispersion coefficientof 17 psnmkm
The receiver receives the optical downstream and theninterleaves it into three modulated optical signals with thewavelengths 120582
1198891 1205821198892 and 120582
1198893 as shown in Figure 3(b)
in the insets ((vii)ndash(ix)) The receiver then downconvertsthe three modulated optical signals directly to the suitable
electrical signals by using an optical receiver for each signalThe electrical signals are then band-pass filtered accordingto the allocated RF carrier frequency 119891
119888= 24GHz by
using bandpass filters (BPFs) to get the wireless MIMOsignalsMIMO
1MIMO
2 andMIMO
3The crosstalk between
the received wireless MIMO signals which have the samefrequency is highly suppressed because each signal is carriedon an independent wavelength with a large channel spacing(25GHz) as compared to the carrier frequency (24GHz) Inthis simulation the PIN photodiodes with power sensitivityof minus20 dBm are used in the optical receivers
In the simulation design the OFU technique is used totransport three wireless MIMO signals with the same RFcarrier frequency of 24GHz or 5GHz over fiberThewirelessMIMO signals are modulated by using 16-QAM modulationto investigate the performance of this ROF system at differentaccess distances and different wavelength interleaves
4 Mathematical Model of the Proposed System
The optical field of the output signal 119864out(119905) from the DAMcan be expressed as [17 18]
Figure 3 Transport of wireless MIMO signals over optical fiber using the OFU technique (a) block diagram of the proposed technique and(b) power spectra of the signals according to the indicated insets
119864out (119905) = 120572119864in (119905) (1 minus 120574) 119890(119895120587V1(119905)119881120587RF+1198951205871198811198871119881120587DC)
Here119864in(119905) is the input optical signal to theDAMfrom theLD V1(119905) and V
2(119905) are the RF modulating electrical voltage
with the carrier frequency 119891119898
= 1205961198982120587 119881
1198871and 119881
1198872are
the DC bias voltages applied to the arms of the DAM 119881120587RF
and 119881120587DC are the switching RF and switching bias voltages
respectivelyThe parameter 120572 is given by
120572 = 10minus(Ω20)
(2)
Here Ω is the insertion loss in dB (It is assigned as 5 dBin this design) 120574 designates the power splitting (combining)ratio of arm two for the input (output resp) 119884-branchwaveguide 120574 is given by
120574 =(1 minus 1radic120576
119903)
2 (3)
where 120576119903= 10(Extinction Ratio10)
= 100 so 120574 asymp 12 in this workIn the simulation design the values of 119881
120587RF and 119881120587DC are
set to 4V and the bias voltages of 1198811198871and 119881
1198872are assigned as
minus1 V and 1V respectively In addition the generated opticalsignal from the LD can be expressed as 119864in(119905) = 119864
119901119890119895120596119901119905 and
the modulating electrical signals can be expressed as V1(119905) =
+1198723(119905 minus 1199051198893) 119890119895[(120596119901+120596119888)119905+120573(120596
119901+120596119888)119911]
(12)
where 119905119889119894(119894 = 1 2 or 3) is the time delay of the 119894th optical
downlink signal The time delay is calculated by the firstderivative of 120573(120596) since 119905
119889119894= 1205731015840(120596119889119894
+ 120596119888) and 120596
119894is the
120596p120596p minus 120596m 120596p + 120596m
120596
Am
plitu
de
USSB2 USSB3 USSB1
fd2 fd3 fd1
Figure 4 The propagated lightwave signal over the optical fiber
119894th optical downlink carrier frequency The output lightwaveat the end of fiber is considered as three optical signals withdifferent downlink frequencies of 120596
119901+ 120596119898 120596119901minus 120596119898 and 120596
119901
which convey the three wireless MIMO signals in their uppersingle sidebands (USSBs) as shown in Figure 4
The optical receiver receives the transmitted optical sig-nals and separates them according to their downlink wave-lengths by using optical ILs as shown in Figure 3 Each opticaldownlink signal is then directly detected by a photodetector(PD) so the photocurrent for each detectedMIMOsignal canbe written as the following equation according to the square-law PD [18]
Figure 5 The fiber nonlinearity effect on the system performance
The wireless end-user will receive the three MIMO signalsand demodulate them using the suitable QAMdemodulationand MIMO decoding techniques
5 System Performance Evaluation
In this work the communication system is designed toprovide a data rate of 1 Gbs for each 16-QAMwirelessMIMOsignal Figure 3 in the inset (vi) shows the input opticalpower to the optical fiber where the three modulated opticalsignals with the downlink wavelengths 120582
1198891 1205821198892 and 120582
1198893
are coupled to propagate through 20 km optical fiber Thetotal input power of the three optical signals is 1626 dBmaccording to the simulation calculations for both RF carrierfrequencies of 24GHz and 5GHzThis power is suitable to belaunched to avoid the nonlinear effects along the optical linkFigure 5 shows the system performance at different launchedoptical powers Nonlinearity of the fiber negatively affects thesystem performance when the launched optical powers aregreater than 108 dBm and 79 dBm at the carrier frequenciesof 24GHz and 50GHz respectively
To evaluate the performance of the proposed techniqueFigures 6(a) and 6(b) show the BER performance versus thereceived optical power at the receiver for the three wirelessMIMO signals (MIMO
1 MIMO
2 andMIMO
3) at the carrier
frequencies 24GHz and 5GHz respectively The powersensitivity differences of the receivers for the three MIMOsignals are small especially between the two MIMO signals(MIMO
1and MIMO
2) The maximum power penalties of
347 dB and 4 dB are recorded at BER of 10minus9 for the carrierfrequencies of 24GHz and 5GHz receptively
Figure 7 shows the system performance at three differentfiber lengths (20 km 30 km and 50 km) of the optical fiber Inthe proposed system the fiber length of 50 kmhas slight effecton the performance of the transmitted optical signals whichcarry the wireless MIMO signals The system performance
deteriorates progressively when the access distance becomeslonger than 50 km
In addition the system performance is analyzed by usingdifferent wavelength interleaves between the optical carrierfrequency (or RF clock frequency 119891
119900) Figure 8 shows the
systemperformance at differentwavelength interleaves (Δ119891 =
15 25 and 50GHz which are compatible with Δ120582 = 01202 and 04 nm resp) When the wavelength interleaves aresmaller than 15GHz the system performance will degradeand the error floor clearly appears
Figures 9(a)ndash9(c) show 1Gbs 16-QAM constellationdiagrams for the received MIMO signals MIMO
1 MIMO
2
and MIMO3 respectively at 24GHz Clear scatter-plots are
achieved at EVM values of minus208780 dB minus202873 dB andminus212961 dB for MIMO
1 MIMO
2 and MIMO
3 respectively
So the proposed technique has achieved a good performanceof transmitting wireless MIMO signals over the optical fiberat the carrier frequencies 24GHz and 5GHz The EVMs arecalculated considering the following equation [21]
EVM (dB) = 10 sdot log10[sum119872
119896=1
1003816100381610038161003816119878119905119909119896 minus 119878119903119909119896
where EVM is the value of the difference between a collectionof received symbols and transmitted or ideal symbols 119878
119905119909119896
is the corresponding transmitted symbol of the constellationassociated with the 119896th symbol 119878
119903119909119896is the received symbol
associated with 119878119905119909119896
and119872 is the number of the symbols forthe inphase-quadrature constellation
Figures 10(a)ndash10(c) show the eye diagrams of the 119868-branch of the received 16-QAMbaseband signals forMIMO
1
MIMO2 and MIMO
3 respectively Also Figures 11(a)ndash11(c)
show the eye diagrams of the 119876-branch of the received 16-QAM baseband signals for MIMO
1 MIMO
2 and MIMO
3
respectively The eye diagrams of both 119868-branch and 119876-branch of the received wireless MIMO signals at the receivershow slight differences and good quality communicationsystem at a BER around of 10minus9 The BER are calculatedaccording to (15) [22]
where 119876 is the number of signal levels within each branchof the constellation diagram log
2119872 is the amount of bits
encoded into one QAM symbol and 119896 is a modulationformat-dependent factor giving the relationship betweenmaximum field magnitude and average overall119872 field mag-nitudes defined by the constellation diagram for the chosenmodulation formatThis factor is calculated according to (15)
Figure 7The system performance at different lengths of the opticalfiber
to be 6(radic5+2) for 16-QAMThe 119878119905119909119894
is the ideal transmittedfield vector and 119878
119905119909max is the field vector of the outermostconstellation point In this paper the performance of EVMand the BER is evaluated for the 16-QAM MIMO signalswithout using forward error correction (FEC) techniques
6 Transmission of More Wireless MIMOSignals over Optical Fiber
Figure 12 shows the proposed OFU technique to transmitfive wireless MIMO signals over fiber At the OLT the DAM
Received optical powerminus20 minus18 minus16 minus14 minus12 minus10 minus8 minus6
10minus20
10minus18
10minus16
10minus14
10minus12
10minus10
10minus8
10minus6
10minus4
10minus2
100
BER
Δf = 15GHzΔf = 25GHzΔf = 50GHz
Figure 8 The system performance at different wavelength inter-leaves
is injected by LD with the wavelength 120582119889 The DAM is a
LN-MZM Adjusting the parameters of the DAM to suitablevalues can generate multiple wavelengths The dominantwavelengths are considered and the remaining outside wave-lengths are neglected because of their very small magnitudesThe OLT allocates five downlink wavelengths (120582
1198891 1205821198892 1205821198893
1205821198894 and 120582
1198895) which are used for downstream modulation
To generate five dominant wavelengths the values of DAMparameters are configured as minus05 V 05 V DC bias voltagesare applied to respectively first and second arms of theLN-MZM the RF clock voltage with frequency of 119891
119900drives
10 The Scientific World Journal
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(a)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)(b)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(c)
Figure 9 Constellation diagrams of the demodulated 16-QAMMIMO signals (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
to the DAM and the DC and RF switching voltages areset to 4V and 2V respectively The wavelength interleavesbetween the five generatedwavelengthswhich are equal to thefrequency of the sinusoidal clock 119891
119900 The power magnitudes
of the fivewavelengths are approximately equal and the centerwavelength 120582
1198893has maximum value The difference between
this and the others is around 6 dB To get balanced powermagnitudes an optical attenuator is used in path of the centerwavelength after IL as shown in Figure 12 Each generatedwavelengthmodulates theMIMO signal by using IMThefive
modulated optical signals propagate along the same opticalfiber
The receiver receives the optical downstream and theninterleaves it into the five modulated optical signals withthe wavelength 120582
1198891 1205821198892 1205821198893 1205821198894 and 120582
1198895as shown in
Figure 12The receiver then downconverts the fivemodulatedoptical signals directly to the suitable electrical signals byusing an optical receiver for each signalThe electrical signalsare then band-pass filtered according to the allocated RFcarrier frequency 119891
119888by using BPFs to get the original five
The Scientific World Journal 11
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 10 Eye diagrams of the 119868-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
wireless MIMO signals MIMO1 MIMO
2 MIMO
3 MIMO
4
and MIMO5
7 Conclusions
The novel OFU technique is proposed to solve the problemof wireless MIMO signals transmission over a single opticalfiberThree wireless 16-QAMMIMO signals have been trans-mitted over a 20 km SMF using the OFU technique Thesewireless MIMO signals were modulated using the carrier
frequency of 24GHz or 5GHz at data rate of 1 Gbs for eachsignal The physical layer performance has been reported interms of the BER at different RF carrier frequencies differentaccess distances and different wavelength interleaves Inaddition the EVM and the eye diagrams are analyzed in thisstudy
The proposed approach highly suppressed the crosstalkbetween different MIMO signals with the same RF carrierfrequency since each MIMO signal is carried on a spe-cific optical wavelength While the ESSB-FT technique [10]
12 The Scientific World Journal
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 11 Eye diagrams of the 119876-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
requires a number of low-frequency LOs and electrical BPFsat the transmitter and the receiver the OFU technique doesnot require low-frequency LOs at the transmitter and thereceiver or electrical BPFs at the transmitter Less numberof electrical BPFs is required at the receiver in the proposedtechnique However a number of PDs are required at thereceiver which is equal to the number of MIMO signals Theproposed system supports many wavelengths for carrying
multiple wireless MIMO signals over the fiber using singleLD The novel technique provides a spectral efficient andreliable FiWi system
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
The Scientific World Journal 13
IM
IM
IM
IM
IM
DAM
fo
120582d3
120582d4
120582d5
Transmitter
120582d
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
120582d1
120582d2
Bias
Bias
Bias
Bias
Bias
AWG
RF amplifier
RF amplifier
RF amplifier
RF amplifier
RF amplifier
fc
fc
fc
fc
fc
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalfiber
BPF
BPF
BPF
BPF
BPF
IL
IL
Receiver
LD 120582d3
120582d4
120582d5
120582d1
120582d2
Optical attenuator
+
+
+
+
+minus70
minus50
minus30
minus10
0
minus20
minus40
minus60
1929T 193T 1931T 1932T 1933T
Pow
er (d
Bm)
Frequency (Hz)
Figure 12 Transmission of five wireless MIMO signals over fiber using the novel approach
Acknowledgments
This work is supported by Universiti Teknologi Malaysia(UTM) under the Postdoctoral fellowship scheme Theauthors greatly appreciate UTM and Photonics ResearchLaboratory for providing the facilities which enabled themto accomplish this work They would also like to thank theMinistry of Science Technology and Innovation (MOSTI)Malaysia for sponsoring this work under Project vote no73720
References
[1] L Kazovsky S-W Wong T Ayhan K M Albeyoglu MR N Ribeiro and A Shastri ldquoHybrid optical-wireless accessnetworksrdquo Proceedings of the IEEE vol 100 no 5 pp 1197ndash12252012
[2] R Q Shaddad A B Mohammad and AM Al-hetar ldquoAnalysisof physical layer performance of hybrid optical-wireless accessnetworkrdquo Optics Communications vol 284 no 20 pp 4894ndash4899 2011
[3] R Q Shaddad A Bakar Mohammad and A M Al-hetar ldquoPer-formance evaluation for optical backhaul andwireless front-endin hybrid optical-wireless access networkrdquo Optoelectronics andAdvanced Materials Rapid Communications vol 5 no 4 pp376ndash380 2011
[4] C Lim A Nirmalathas M Bakaul et al ldquoFiber-wirelessnetworks and subsystem technologiesrdquo Journal of LightwaveTechnology vol 28 no 4 pp 390ndash405 2010
[5] A Nirmalathas P A Gamage C Lim D Novak and RWaterhouse ldquoDigitized radio-over-fiber technologies for con-verged optical wireless access networkrdquo Journal of LightwaveTechnology vol 28 no 16 pp 2366ndash2375 2010
[6] Z Jia J Yu G Ellinas and G-K Chang ldquoKey enablingtechnologies for optical wireless networks optical millimeter-wave generation wavelength reuse and architecturerdquo Journalof Lightwave Technology vol 25 no 11 pp 3452ndash3471 2007
[7] A Zelst ldquoSystem for transporting multiple radio frequencysignals of a multiple input multiple output wireless communi-cation system tofrom a central processing base stationrdquo USpatent application 20040017785A1 2004
[8] I Seto H Shoki and S Ohshima ldquoOptical subcarrier mul-tiplexing transmission for base station with adaptive arrayantennardquo IEEE Transactions on Microwave Theory and Tech-niques vol 49 no 10 pp 2036ndash2041 2001
[9] C-P Liu and A Seeds ldquoTransmission of MIMO radio signalsover fibre using a novel phase quadrature double sidebandfrequency translation techniquerdquo in Proceedings of the IEEEInternational Meeting on Microwave Photonics Jointly Held withthe Asia-Pacific Microwave Photonics Conference pp 23ndash26Gold Coast Australia October 2008
[10] C-P Liu and A J Seeds ldquoTransmission of wireless MIMO-type signals over a single optical fiber without WDMrdquo IEEETransactions on Microwave Theory and Techniques vol 58 no11 pp 3094ndash3102 2010
[11] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgailani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overoptical fiberrdquo in Proceedings of the 3rd International Conferenceon Photonics (ICP rsquo12) Penang Malaysia 2012
[12] R Shaddad A Mohammad and A Al-hetar ldquoSpectral efficienthybrid wireless optical broadband access network (WOBAN)based on transmission of wireless MIMO OFDM signals overWDM PONrdquo Optics Communications vol 285 no 20 pp4059ndash4067 2012
[13] K Shimizu T Horiguchi and Y Koyamada ldquoFrequency trans-lation of light waves by propagation around an optical ringcircuit containing a frequency shifter 1 Experimentrdquo AppliedOptics vol 32 pp 6718ndash6726 1993
[14] E L Wooten K M Kissa A Yi-Yan et al ldquoA review of lithiumniobate modulators for fiber-optic communications systemsrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 6no 1 pp 69ndash82 2000
[15] P Yao R Shireen J Macario C A Schuctz S Shi and D WPrather ldquoDesign fabrication and characterization of LiNbO
3
optical modulator for high-sensitivity mmW imaging systemrdquoin Passive Millimeter-Wave Imaging Technology XI vol 6948 ofProceedings of SPIE March 2008
[16] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgeelani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overfiber-wireless systemrdquo Optics amp Laser Technology vol 47 pp347ndash354 2013
14 The Scientific World Journal
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
In this paper the OFU technique is proposed to solve theproblem of wireless MIMO signals transmission over fibersince it does not need low-frequency local oscillators (LOs)at the transmitter and the receiver as compared to [10] Thecrosstalk is highly suppressed between the different wirelessMIMO signals with the same carrier frequency since eachwireless MIMO signal is carried on specific optical wave-length By using the OFU technique one optical dual-armmodulator (DAM) is derived by one optical source to producemultiple wavelengths which convey multiple wireless MIMOsignals over the optical fiber The FiWi system based onthe new approach can also support the wavelength reusetechnique so one optical source is enough to generate theoptical carrier which is reused at theAP as uplinkwavelengthand multiple wavelengths which convey multiple wirelessMIMO signals over the SMF [12] The principles and thesimulation design of the OFU technique to transport wirelessMIMO signals over fiber are discussed in Section 3
The novel OFU approach is used to transmit three wire-less MIMO signals over a 20 km SMF The OFU techniqueexploits one optical source to produce multiple wavelengthsby delivering it to a DAM The parameters of the DAMare adjusted to produce number of wavelengths accordingto the number of the wireless MIMO signals The wirelessMIMO signals are then optically modulated by opticalintensity modulators separately using the produced opticalcarriers from the OFU process All these optical modulatorsare LiNbO
3Mach-Zehnder modulators (LN-MZMs) Each
wireless MIMO signal is with a 24GHz or 5GHz carrierfrequency 1 Gbs data rate and 16-QAM The crosstalkbetween the wireless MIMO signals is highly suppressedsince each wireless MIMO signal is carried on a specificoptical wavelength The system performance is evaluatedin terms of BER error vector magnitude (EVM) and eyediagrams for different RF carriers optical link distances andchannel spacings The novel technique provides a spectralefficient and reliable FiWi system
This paper is organized as follows Section 2 outlinesthe operation of the OFU technique Principles and designof the proposed system are demonstrated in Section 3 InSection 4 the mathematical model of the proposed systemillustrates how the OFU approach operates in the proposedsystem Section 5 analyzes and discusses the system perfor-mance Section 6 suggests how the proposed approach canbe extended to transport a higher number of wireless MIMOsignals Finally conclusions are given in Section 7
2 Optical Frequency Upconversion Technique
OFU technique is a prime technique in many fields of opticalcommunication External frequency modulators such as LN-MZMs can be used as a light-wave frequency upconverterin fiber optics [13] The LN-MZM is a DAM which can beused as an optical frequency upconverter when its dual-armsare supplied by a sinusoidal RF signal The LN-MZM is alsoused as an optical modulator for digital base-band signalsor modulated RF signals when these signals drive its dual-arms For broadband communication applications externalLN-MZMs provide broadband operation and minimize the
dispersion effects Moreover the external LN-MZMs offerhigh stability very low bias-voltage drift rates and bias-freedevices [14 15] The frequency conversion efficiency of theLN-MZMs can be increased by using low values of half-wavevoltage (119881
120587)
In this study the OFU technique is proposed to generatemultiple optical carriers which are used to modulate multiplewireless signals separately at many optical external intensitymodulators (IMs) The modulated optical signals can thenbe multiplexed together to the optical fiber since theyhave no overlapping adjacent spectral bands The DAM isset to generate first-order signal component (at the centersinusoidal RF frequency) and other higher-order modulatedcomponents around it The higher-order components areneglected since they have small amplitude compared tothe lower-order components In this approach the WDMinterleaver (WDM IL) is used after the DAM to separate thegenerated dominant wavelengths [16]
Generation of multiple wavelengths from one laser diode(LD) using OFU technique is illustrated in Figure 2 Oneoptical source LD with optical carrier frequency 119891
119901supplies
a DAM which is driven by a sinusoidal clock frequency 119891119898
(RFmodulating frequency)TheDAM is adjusted to generatemultiple frequency components first-order component withthe center optical carrier frequency 119891
119901and upper and lower
single sidebands components around the center frequencyThe lower single sideband components have the opticalfrequencies (119891
119901minus 119891119898 119891119901minus 2119891119898 119891119901minus 3119891119898 etc) At the
output the upper single sideband components will have theoptical frequencies (119891
119901+ 119891119898 119891119901+ 2119891119898 119891119901+ 3119891119898 etc) From
Figure 2 there are a number (five) of frequency componentsexceeding the other higher-order components which havesmall magnitudes as compared to their magnitudes Thesefrequency components are called dominant wavelengths orfrequencies which are interleaved separately by using WDMIL The channel frequency space (or wavelength interleave)between the generated wavelengths is 119891
119898 The dominant
wavelengths will be used as downlink wavelengths to conveythe multiple wireless MIMO signals over optical fiber
3 Principles and Design ofthe Proposed System
The block diagram of the OFU technique for transmissionof three wireless MIMO signals over a single optical fiberis shown in Figure 3(a) At the transmitter three wirelessMIMO signals MIMO
1 MIMO
2 and MIMO
3are generated
and modulated using M-QAM at the same carrier frequency119891119888
= 24GHz The spectra of these three wireless signalsare shown in Figure 3(b) in the insets ((i)ndash(iii)) A DAMwith the ODSB modulation technique is used to generatethree downlink wavelengths from one LD with a wavelength120582119889
= 155252 nm (193100 THz) as shown in Figure 3(b)the inset (iv) The three generated downlink wavelengths areshown in Figure 3(b) as the inset (v) Two ILs are used afterthe DAM to separate the three downlink wavelengths whichare the two single-sideband wavelengths 120582
1198891= 155232 nm
(193125 THz) and 1205821198892
= 155273 nm (193075 THz) and theoptical carrier frequency 120582
1198893= 155252 nm (193100 THz)
4 The Scientific World Journal
DAM
Clockfrequency
fm
fm
DC biasvoltage
Opticalcarrier
fp
fp
fp
fp minus fmfp minus 2fmfp minus 3fm
WDMIL
fp + 2fmfp + fm
fp + fm
fp + 3fm
Dominantwavelengths
fp
fp minus fm
fp minus 2fm
fp + 2fm
Figure 2 Generation of multiple wavelengths using OFU technique
The channel spacing between these wavelengths Δ120582 equalsthe frequency of the sinusoidal clock 119891
119900= 25GHz (02 nm)
which is used in the DAM An optical attenuator is used inthe path of the downlink wavelength 120582
1198893to equilibrate its
power with the generated power from the other downlinkwavelengths 120582
1198891and 120582
1198892
The downlink wavelengths 1205821198891 1205821198892 and 120582
1198893are used to
modulate the three wirelessMIMO signalsMIMO1 MIMO
2
and MIMO3by external IMs respectively The wireless
MIMO signals are firstly biased to be compatible with thenature of the optical signals and then optically modulated bythe IMs These IMs use the OSSB+C modulation scheme tooptimize the system performance against the fiber dispersioneffectThe three modulated optical signals with the downlinkwavelengths 120582
1198891 1205821198892 and 120582
1198893are coupled together as shown
in Figure 3(b) inset (vi) and then propagated along a 20 kmSMFwith attenuation of 02 dBkm and dispersion coefficientof 17 psnmkm
The receiver receives the optical downstream and theninterleaves it into three modulated optical signals with thewavelengths 120582
1198891 1205821198892 and 120582
1198893 as shown in Figure 3(b)
in the insets ((vii)ndash(ix)) The receiver then downconvertsthe three modulated optical signals directly to the suitable
electrical signals by using an optical receiver for each signalThe electrical signals are then band-pass filtered accordingto the allocated RF carrier frequency 119891
119888= 24GHz by
using bandpass filters (BPFs) to get the wireless MIMOsignalsMIMO
1MIMO
2 andMIMO
3The crosstalk between
the received wireless MIMO signals which have the samefrequency is highly suppressed because each signal is carriedon an independent wavelength with a large channel spacing(25GHz) as compared to the carrier frequency (24GHz) Inthis simulation the PIN photodiodes with power sensitivityof minus20 dBm are used in the optical receivers
In the simulation design the OFU technique is used totransport three wireless MIMO signals with the same RFcarrier frequency of 24GHz or 5GHz over fiberThewirelessMIMO signals are modulated by using 16-QAM modulationto investigate the performance of this ROF system at differentaccess distances and different wavelength interleaves
4 Mathematical Model of the Proposed System
The optical field of the output signal 119864out(119905) from the DAMcan be expressed as [17 18]
Figure 3 Transport of wireless MIMO signals over optical fiber using the OFU technique (a) block diagram of the proposed technique and(b) power spectra of the signals according to the indicated insets
119864out (119905) = 120572119864in (119905) (1 minus 120574) 119890(119895120587V1(119905)119881120587RF+1198951205871198811198871119881120587DC)
Here119864in(119905) is the input optical signal to theDAMfrom theLD V1(119905) and V
2(119905) are the RF modulating electrical voltage
with the carrier frequency 119891119898
= 1205961198982120587 119881
1198871and 119881
1198872are
the DC bias voltages applied to the arms of the DAM 119881120587RF
and 119881120587DC are the switching RF and switching bias voltages
respectivelyThe parameter 120572 is given by
120572 = 10minus(Ω20)
(2)
Here Ω is the insertion loss in dB (It is assigned as 5 dBin this design) 120574 designates the power splitting (combining)ratio of arm two for the input (output resp) 119884-branchwaveguide 120574 is given by
120574 =(1 minus 1radic120576
119903)
2 (3)
where 120576119903= 10(Extinction Ratio10)
= 100 so 120574 asymp 12 in this workIn the simulation design the values of 119881
120587RF and 119881120587DC are
set to 4V and the bias voltages of 1198811198871and 119881
1198872are assigned as
minus1 V and 1V respectively In addition the generated opticalsignal from the LD can be expressed as 119864in(119905) = 119864
119901119890119895120596119901119905 and
the modulating electrical signals can be expressed as V1(119905) =
+1198723(119905 minus 1199051198893) 119890119895[(120596119901+120596119888)119905+120573(120596
119901+120596119888)119911]
(12)
where 119905119889119894(119894 = 1 2 or 3) is the time delay of the 119894th optical
downlink signal The time delay is calculated by the firstderivative of 120573(120596) since 119905
119889119894= 1205731015840(120596119889119894
+ 120596119888) and 120596
119894is the
120596p120596p minus 120596m 120596p + 120596m
120596
Am
plitu
de
USSB2 USSB3 USSB1
fd2 fd3 fd1
Figure 4 The propagated lightwave signal over the optical fiber
119894th optical downlink carrier frequency The output lightwaveat the end of fiber is considered as three optical signals withdifferent downlink frequencies of 120596
119901+ 120596119898 120596119901minus 120596119898 and 120596
119901
which convey the three wireless MIMO signals in their uppersingle sidebands (USSBs) as shown in Figure 4
The optical receiver receives the transmitted optical sig-nals and separates them according to their downlink wave-lengths by using optical ILs as shown in Figure 3 Each opticaldownlink signal is then directly detected by a photodetector(PD) so the photocurrent for each detectedMIMOsignal canbe written as the following equation according to the square-law PD [18]
Figure 5 The fiber nonlinearity effect on the system performance
The wireless end-user will receive the three MIMO signalsand demodulate them using the suitable QAMdemodulationand MIMO decoding techniques
5 System Performance Evaluation
In this work the communication system is designed toprovide a data rate of 1 Gbs for each 16-QAMwirelessMIMOsignal Figure 3 in the inset (vi) shows the input opticalpower to the optical fiber where the three modulated opticalsignals with the downlink wavelengths 120582
1198891 1205821198892 and 120582
1198893
are coupled to propagate through 20 km optical fiber Thetotal input power of the three optical signals is 1626 dBmaccording to the simulation calculations for both RF carrierfrequencies of 24GHz and 5GHzThis power is suitable to belaunched to avoid the nonlinear effects along the optical linkFigure 5 shows the system performance at different launchedoptical powers Nonlinearity of the fiber negatively affects thesystem performance when the launched optical powers aregreater than 108 dBm and 79 dBm at the carrier frequenciesof 24GHz and 50GHz respectively
To evaluate the performance of the proposed techniqueFigures 6(a) and 6(b) show the BER performance versus thereceived optical power at the receiver for the three wirelessMIMO signals (MIMO
1 MIMO
2 andMIMO
3) at the carrier
frequencies 24GHz and 5GHz respectively The powersensitivity differences of the receivers for the three MIMOsignals are small especially between the two MIMO signals(MIMO
1and MIMO
2) The maximum power penalties of
347 dB and 4 dB are recorded at BER of 10minus9 for the carrierfrequencies of 24GHz and 5GHz receptively
Figure 7 shows the system performance at three differentfiber lengths (20 km 30 km and 50 km) of the optical fiber Inthe proposed system the fiber length of 50 kmhas slight effecton the performance of the transmitted optical signals whichcarry the wireless MIMO signals The system performance
deteriorates progressively when the access distance becomeslonger than 50 km
In addition the system performance is analyzed by usingdifferent wavelength interleaves between the optical carrierfrequency (or RF clock frequency 119891
119900) Figure 8 shows the
systemperformance at differentwavelength interleaves (Δ119891 =
15 25 and 50GHz which are compatible with Δ120582 = 01202 and 04 nm resp) When the wavelength interleaves aresmaller than 15GHz the system performance will degradeand the error floor clearly appears
Figures 9(a)ndash9(c) show 1Gbs 16-QAM constellationdiagrams for the received MIMO signals MIMO
1 MIMO
2
and MIMO3 respectively at 24GHz Clear scatter-plots are
achieved at EVM values of minus208780 dB minus202873 dB andminus212961 dB for MIMO
1 MIMO
2 and MIMO
3 respectively
So the proposed technique has achieved a good performanceof transmitting wireless MIMO signals over the optical fiberat the carrier frequencies 24GHz and 5GHz The EVMs arecalculated considering the following equation [21]
EVM (dB) = 10 sdot log10[sum119872
119896=1
1003816100381610038161003816119878119905119909119896 minus 119878119903119909119896
where EVM is the value of the difference between a collectionof received symbols and transmitted or ideal symbols 119878
119905119909119896
is the corresponding transmitted symbol of the constellationassociated with the 119896th symbol 119878
119903119909119896is the received symbol
associated with 119878119905119909119896
and119872 is the number of the symbols forthe inphase-quadrature constellation
Figures 10(a)ndash10(c) show the eye diagrams of the 119868-branch of the received 16-QAMbaseband signals forMIMO
1
MIMO2 and MIMO
3 respectively Also Figures 11(a)ndash11(c)
show the eye diagrams of the 119876-branch of the received 16-QAM baseband signals for MIMO
1 MIMO
2 and MIMO
3
respectively The eye diagrams of both 119868-branch and 119876-branch of the received wireless MIMO signals at the receivershow slight differences and good quality communicationsystem at a BER around of 10minus9 The BER are calculatedaccording to (15) [22]
where 119876 is the number of signal levels within each branchof the constellation diagram log
2119872 is the amount of bits
encoded into one QAM symbol and 119896 is a modulationformat-dependent factor giving the relationship betweenmaximum field magnitude and average overall119872 field mag-nitudes defined by the constellation diagram for the chosenmodulation formatThis factor is calculated according to (15)
Figure 7The system performance at different lengths of the opticalfiber
to be 6(radic5+2) for 16-QAMThe 119878119905119909119894
is the ideal transmittedfield vector and 119878
119905119909max is the field vector of the outermostconstellation point In this paper the performance of EVMand the BER is evaluated for the 16-QAM MIMO signalswithout using forward error correction (FEC) techniques
6 Transmission of More Wireless MIMOSignals over Optical Fiber
Figure 12 shows the proposed OFU technique to transmitfive wireless MIMO signals over fiber At the OLT the DAM
Received optical powerminus20 minus18 minus16 minus14 minus12 minus10 minus8 minus6
10minus20
10minus18
10minus16
10minus14
10minus12
10minus10
10minus8
10minus6
10minus4
10minus2
100
BER
Δf = 15GHzΔf = 25GHzΔf = 50GHz
Figure 8 The system performance at different wavelength inter-leaves
is injected by LD with the wavelength 120582119889 The DAM is a
LN-MZM Adjusting the parameters of the DAM to suitablevalues can generate multiple wavelengths The dominantwavelengths are considered and the remaining outside wave-lengths are neglected because of their very small magnitudesThe OLT allocates five downlink wavelengths (120582
1198891 1205821198892 1205821198893
1205821198894 and 120582
1198895) which are used for downstream modulation
To generate five dominant wavelengths the values of DAMparameters are configured as minus05 V 05 V DC bias voltagesare applied to respectively first and second arms of theLN-MZM the RF clock voltage with frequency of 119891
119900drives
10 The Scientific World Journal
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(a)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)(b)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(c)
Figure 9 Constellation diagrams of the demodulated 16-QAMMIMO signals (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
to the DAM and the DC and RF switching voltages areset to 4V and 2V respectively The wavelength interleavesbetween the five generatedwavelengthswhich are equal to thefrequency of the sinusoidal clock 119891
119900 The power magnitudes
of the fivewavelengths are approximately equal and the centerwavelength 120582
1198893has maximum value The difference between
this and the others is around 6 dB To get balanced powermagnitudes an optical attenuator is used in path of the centerwavelength after IL as shown in Figure 12 Each generatedwavelengthmodulates theMIMO signal by using IMThefive
modulated optical signals propagate along the same opticalfiber
The receiver receives the optical downstream and theninterleaves it into the five modulated optical signals withthe wavelength 120582
1198891 1205821198892 1205821198893 1205821198894 and 120582
1198895as shown in
Figure 12The receiver then downconverts the fivemodulatedoptical signals directly to the suitable electrical signals byusing an optical receiver for each signalThe electrical signalsare then band-pass filtered according to the allocated RFcarrier frequency 119891
119888by using BPFs to get the original five
The Scientific World Journal 11
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 10 Eye diagrams of the 119868-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
wireless MIMO signals MIMO1 MIMO
2 MIMO
3 MIMO
4
and MIMO5
7 Conclusions
The novel OFU technique is proposed to solve the problemof wireless MIMO signals transmission over a single opticalfiberThree wireless 16-QAMMIMO signals have been trans-mitted over a 20 km SMF using the OFU technique Thesewireless MIMO signals were modulated using the carrier
frequency of 24GHz or 5GHz at data rate of 1 Gbs for eachsignal The physical layer performance has been reported interms of the BER at different RF carrier frequencies differentaccess distances and different wavelength interleaves Inaddition the EVM and the eye diagrams are analyzed in thisstudy
The proposed approach highly suppressed the crosstalkbetween different MIMO signals with the same RF carrierfrequency since each MIMO signal is carried on a spe-cific optical wavelength While the ESSB-FT technique [10]
12 The Scientific World Journal
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 11 Eye diagrams of the 119876-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
requires a number of low-frequency LOs and electrical BPFsat the transmitter and the receiver the OFU technique doesnot require low-frequency LOs at the transmitter and thereceiver or electrical BPFs at the transmitter Less numberof electrical BPFs is required at the receiver in the proposedtechnique However a number of PDs are required at thereceiver which is equal to the number of MIMO signals Theproposed system supports many wavelengths for carrying
multiple wireless MIMO signals over the fiber using singleLD The novel technique provides a spectral efficient andreliable FiWi system
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
The Scientific World Journal 13
IM
IM
IM
IM
IM
DAM
fo
120582d3
120582d4
120582d5
Transmitter
120582d
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
120582d1
120582d2
Bias
Bias
Bias
Bias
Bias
AWG
RF amplifier
RF amplifier
RF amplifier
RF amplifier
RF amplifier
fc
fc
fc
fc
fc
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalfiber
BPF
BPF
BPF
BPF
BPF
IL
IL
Receiver
LD 120582d3
120582d4
120582d5
120582d1
120582d2
Optical attenuator
+
+
+
+
+minus70
minus50
minus30
minus10
0
minus20
minus40
minus60
1929T 193T 1931T 1932T 1933T
Pow
er (d
Bm)
Frequency (Hz)
Figure 12 Transmission of five wireless MIMO signals over fiber using the novel approach
Acknowledgments
This work is supported by Universiti Teknologi Malaysia(UTM) under the Postdoctoral fellowship scheme Theauthors greatly appreciate UTM and Photonics ResearchLaboratory for providing the facilities which enabled themto accomplish this work They would also like to thank theMinistry of Science Technology and Innovation (MOSTI)Malaysia for sponsoring this work under Project vote no73720
References
[1] L Kazovsky S-W Wong T Ayhan K M Albeyoglu MR N Ribeiro and A Shastri ldquoHybrid optical-wireless accessnetworksrdquo Proceedings of the IEEE vol 100 no 5 pp 1197ndash12252012
[2] R Q Shaddad A B Mohammad and AM Al-hetar ldquoAnalysisof physical layer performance of hybrid optical-wireless accessnetworkrdquo Optics Communications vol 284 no 20 pp 4894ndash4899 2011
[3] R Q Shaddad A Bakar Mohammad and A M Al-hetar ldquoPer-formance evaluation for optical backhaul andwireless front-endin hybrid optical-wireless access networkrdquo Optoelectronics andAdvanced Materials Rapid Communications vol 5 no 4 pp376ndash380 2011
[4] C Lim A Nirmalathas M Bakaul et al ldquoFiber-wirelessnetworks and subsystem technologiesrdquo Journal of LightwaveTechnology vol 28 no 4 pp 390ndash405 2010
[5] A Nirmalathas P A Gamage C Lim D Novak and RWaterhouse ldquoDigitized radio-over-fiber technologies for con-verged optical wireless access networkrdquo Journal of LightwaveTechnology vol 28 no 16 pp 2366ndash2375 2010
[6] Z Jia J Yu G Ellinas and G-K Chang ldquoKey enablingtechnologies for optical wireless networks optical millimeter-wave generation wavelength reuse and architecturerdquo Journalof Lightwave Technology vol 25 no 11 pp 3452ndash3471 2007
[7] A Zelst ldquoSystem for transporting multiple radio frequencysignals of a multiple input multiple output wireless communi-cation system tofrom a central processing base stationrdquo USpatent application 20040017785A1 2004
[8] I Seto H Shoki and S Ohshima ldquoOptical subcarrier mul-tiplexing transmission for base station with adaptive arrayantennardquo IEEE Transactions on Microwave Theory and Tech-niques vol 49 no 10 pp 2036ndash2041 2001
[9] C-P Liu and A Seeds ldquoTransmission of MIMO radio signalsover fibre using a novel phase quadrature double sidebandfrequency translation techniquerdquo in Proceedings of the IEEEInternational Meeting on Microwave Photonics Jointly Held withthe Asia-Pacific Microwave Photonics Conference pp 23ndash26Gold Coast Australia October 2008
[10] C-P Liu and A J Seeds ldquoTransmission of wireless MIMO-type signals over a single optical fiber without WDMrdquo IEEETransactions on Microwave Theory and Techniques vol 58 no11 pp 3094ndash3102 2010
[11] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgailani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overoptical fiberrdquo in Proceedings of the 3rd International Conferenceon Photonics (ICP rsquo12) Penang Malaysia 2012
[12] R Shaddad A Mohammad and A Al-hetar ldquoSpectral efficienthybrid wireless optical broadband access network (WOBAN)based on transmission of wireless MIMO OFDM signals overWDM PONrdquo Optics Communications vol 285 no 20 pp4059ndash4067 2012
[13] K Shimizu T Horiguchi and Y Koyamada ldquoFrequency trans-lation of light waves by propagation around an optical ringcircuit containing a frequency shifter 1 Experimentrdquo AppliedOptics vol 32 pp 6718ndash6726 1993
[14] E L Wooten K M Kissa A Yi-Yan et al ldquoA review of lithiumniobate modulators for fiber-optic communications systemsrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 6no 1 pp 69ndash82 2000
[15] P Yao R Shireen J Macario C A Schuctz S Shi and D WPrather ldquoDesign fabrication and characterization of LiNbO
3
optical modulator for high-sensitivity mmW imaging systemrdquoin Passive Millimeter-Wave Imaging Technology XI vol 6948 ofProceedings of SPIE March 2008
[16] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgeelani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overfiber-wireless systemrdquo Optics amp Laser Technology vol 47 pp347ndash354 2013
14 The Scientific World Journal
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
Figure 2 Generation of multiple wavelengths using OFU technique
The channel spacing between these wavelengths Δ120582 equalsthe frequency of the sinusoidal clock 119891
119900= 25GHz (02 nm)
which is used in the DAM An optical attenuator is used inthe path of the downlink wavelength 120582
1198893to equilibrate its
power with the generated power from the other downlinkwavelengths 120582
1198891and 120582
1198892
The downlink wavelengths 1205821198891 1205821198892 and 120582
1198893are used to
modulate the three wirelessMIMO signalsMIMO1 MIMO
2
and MIMO3by external IMs respectively The wireless
MIMO signals are firstly biased to be compatible with thenature of the optical signals and then optically modulated bythe IMs These IMs use the OSSB+C modulation scheme tooptimize the system performance against the fiber dispersioneffectThe three modulated optical signals with the downlinkwavelengths 120582
1198891 1205821198892 and 120582
1198893are coupled together as shown
in Figure 3(b) inset (vi) and then propagated along a 20 kmSMFwith attenuation of 02 dBkm and dispersion coefficientof 17 psnmkm
The receiver receives the optical downstream and theninterleaves it into three modulated optical signals with thewavelengths 120582
1198891 1205821198892 and 120582
1198893 as shown in Figure 3(b)
in the insets ((vii)ndash(ix)) The receiver then downconvertsthe three modulated optical signals directly to the suitable
electrical signals by using an optical receiver for each signalThe electrical signals are then band-pass filtered accordingto the allocated RF carrier frequency 119891
119888= 24GHz by
using bandpass filters (BPFs) to get the wireless MIMOsignalsMIMO
1MIMO
2 andMIMO
3The crosstalk between
the received wireless MIMO signals which have the samefrequency is highly suppressed because each signal is carriedon an independent wavelength with a large channel spacing(25GHz) as compared to the carrier frequency (24GHz) Inthis simulation the PIN photodiodes with power sensitivityof minus20 dBm are used in the optical receivers
In the simulation design the OFU technique is used totransport three wireless MIMO signals with the same RFcarrier frequency of 24GHz or 5GHz over fiberThewirelessMIMO signals are modulated by using 16-QAM modulationto investigate the performance of this ROF system at differentaccess distances and different wavelength interleaves
4 Mathematical Model of the Proposed System
The optical field of the output signal 119864out(119905) from the DAMcan be expressed as [17 18]
Figure 3 Transport of wireless MIMO signals over optical fiber using the OFU technique (a) block diagram of the proposed technique and(b) power spectra of the signals according to the indicated insets
119864out (119905) = 120572119864in (119905) (1 minus 120574) 119890(119895120587V1(119905)119881120587RF+1198951205871198811198871119881120587DC)
Here119864in(119905) is the input optical signal to theDAMfrom theLD V1(119905) and V
2(119905) are the RF modulating electrical voltage
with the carrier frequency 119891119898
= 1205961198982120587 119881
1198871and 119881
1198872are
the DC bias voltages applied to the arms of the DAM 119881120587RF
and 119881120587DC are the switching RF and switching bias voltages
respectivelyThe parameter 120572 is given by
120572 = 10minus(Ω20)
(2)
Here Ω is the insertion loss in dB (It is assigned as 5 dBin this design) 120574 designates the power splitting (combining)ratio of arm two for the input (output resp) 119884-branchwaveguide 120574 is given by
120574 =(1 minus 1radic120576
119903)
2 (3)
where 120576119903= 10(Extinction Ratio10)
= 100 so 120574 asymp 12 in this workIn the simulation design the values of 119881
120587RF and 119881120587DC are
set to 4V and the bias voltages of 1198811198871and 119881
1198872are assigned as
minus1 V and 1V respectively In addition the generated opticalsignal from the LD can be expressed as 119864in(119905) = 119864
119901119890119895120596119901119905 and
the modulating electrical signals can be expressed as V1(119905) =
+1198723(119905 minus 1199051198893) 119890119895[(120596119901+120596119888)119905+120573(120596
119901+120596119888)119911]
(12)
where 119905119889119894(119894 = 1 2 or 3) is the time delay of the 119894th optical
downlink signal The time delay is calculated by the firstderivative of 120573(120596) since 119905
119889119894= 1205731015840(120596119889119894
+ 120596119888) and 120596
119894is the
120596p120596p minus 120596m 120596p + 120596m
120596
Am
plitu
de
USSB2 USSB3 USSB1
fd2 fd3 fd1
Figure 4 The propagated lightwave signal over the optical fiber
119894th optical downlink carrier frequency The output lightwaveat the end of fiber is considered as three optical signals withdifferent downlink frequencies of 120596
119901+ 120596119898 120596119901minus 120596119898 and 120596
119901
which convey the three wireless MIMO signals in their uppersingle sidebands (USSBs) as shown in Figure 4
The optical receiver receives the transmitted optical sig-nals and separates them according to their downlink wave-lengths by using optical ILs as shown in Figure 3 Each opticaldownlink signal is then directly detected by a photodetector(PD) so the photocurrent for each detectedMIMOsignal canbe written as the following equation according to the square-law PD [18]
Figure 5 The fiber nonlinearity effect on the system performance
The wireless end-user will receive the three MIMO signalsand demodulate them using the suitable QAMdemodulationand MIMO decoding techniques
5 System Performance Evaluation
In this work the communication system is designed toprovide a data rate of 1 Gbs for each 16-QAMwirelessMIMOsignal Figure 3 in the inset (vi) shows the input opticalpower to the optical fiber where the three modulated opticalsignals with the downlink wavelengths 120582
1198891 1205821198892 and 120582
1198893
are coupled to propagate through 20 km optical fiber Thetotal input power of the three optical signals is 1626 dBmaccording to the simulation calculations for both RF carrierfrequencies of 24GHz and 5GHzThis power is suitable to belaunched to avoid the nonlinear effects along the optical linkFigure 5 shows the system performance at different launchedoptical powers Nonlinearity of the fiber negatively affects thesystem performance when the launched optical powers aregreater than 108 dBm and 79 dBm at the carrier frequenciesof 24GHz and 50GHz respectively
To evaluate the performance of the proposed techniqueFigures 6(a) and 6(b) show the BER performance versus thereceived optical power at the receiver for the three wirelessMIMO signals (MIMO
1 MIMO
2 andMIMO
3) at the carrier
frequencies 24GHz and 5GHz respectively The powersensitivity differences of the receivers for the three MIMOsignals are small especially between the two MIMO signals(MIMO
1and MIMO
2) The maximum power penalties of
347 dB and 4 dB are recorded at BER of 10minus9 for the carrierfrequencies of 24GHz and 5GHz receptively
Figure 7 shows the system performance at three differentfiber lengths (20 km 30 km and 50 km) of the optical fiber Inthe proposed system the fiber length of 50 kmhas slight effecton the performance of the transmitted optical signals whichcarry the wireless MIMO signals The system performance
deteriorates progressively when the access distance becomeslonger than 50 km
In addition the system performance is analyzed by usingdifferent wavelength interleaves between the optical carrierfrequency (or RF clock frequency 119891
119900) Figure 8 shows the
systemperformance at differentwavelength interleaves (Δ119891 =
15 25 and 50GHz which are compatible with Δ120582 = 01202 and 04 nm resp) When the wavelength interleaves aresmaller than 15GHz the system performance will degradeand the error floor clearly appears
Figures 9(a)ndash9(c) show 1Gbs 16-QAM constellationdiagrams for the received MIMO signals MIMO
1 MIMO
2
and MIMO3 respectively at 24GHz Clear scatter-plots are
achieved at EVM values of minus208780 dB minus202873 dB andminus212961 dB for MIMO
1 MIMO
2 and MIMO
3 respectively
So the proposed technique has achieved a good performanceof transmitting wireless MIMO signals over the optical fiberat the carrier frequencies 24GHz and 5GHz The EVMs arecalculated considering the following equation [21]
EVM (dB) = 10 sdot log10[sum119872
119896=1
1003816100381610038161003816119878119905119909119896 minus 119878119903119909119896
where EVM is the value of the difference between a collectionof received symbols and transmitted or ideal symbols 119878
119905119909119896
is the corresponding transmitted symbol of the constellationassociated with the 119896th symbol 119878
119903119909119896is the received symbol
associated with 119878119905119909119896
and119872 is the number of the symbols forthe inphase-quadrature constellation
Figures 10(a)ndash10(c) show the eye diagrams of the 119868-branch of the received 16-QAMbaseband signals forMIMO
1
MIMO2 and MIMO
3 respectively Also Figures 11(a)ndash11(c)
show the eye diagrams of the 119876-branch of the received 16-QAM baseband signals for MIMO
1 MIMO
2 and MIMO
3
respectively The eye diagrams of both 119868-branch and 119876-branch of the received wireless MIMO signals at the receivershow slight differences and good quality communicationsystem at a BER around of 10minus9 The BER are calculatedaccording to (15) [22]
where 119876 is the number of signal levels within each branchof the constellation diagram log
2119872 is the amount of bits
encoded into one QAM symbol and 119896 is a modulationformat-dependent factor giving the relationship betweenmaximum field magnitude and average overall119872 field mag-nitudes defined by the constellation diagram for the chosenmodulation formatThis factor is calculated according to (15)
Figure 7The system performance at different lengths of the opticalfiber
to be 6(radic5+2) for 16-QAMThe 119878119905119909119894
is the ideal transmittedfield vector and 119878
119905119909max is the field vector of the outermostconstellation point In this paper the performance of EVMand the BER is evaluated for the 16-QAM MIMO signalswithout using forward error correction (FEC) techniques
6 Transmission of More Wireless MIMOSignals over Optical Fiber
Figure 12 shows the proposed OFU technique to transmitfive wireless MIMO signals over fiber At the OLT the DAM
Received optical powerminus20 minus18 minus16 minus14 minus12 minus10 minus8 minus6
10minus20
10minus18
10minus16
10minus14
10minus12
10minus10
10minus8
10minus6
10minus4
10minus2
100
BER
Δf = 15GHzΔf = 25GHzΔf = 50GHz
Figure 8 The system performance at different wavelength inter-leaves
is injected by LD with the wavelength 120582119889 The DAM is a
LN-MZM Adjusting the parameters of the DAM to suitablevalues can generate multiple wavelengths The dominantwavelengths are considered and the remaining outside wave-lengths are neglected because of their very small magnitudesThe OLT allocates five downlink wavelengths (120582
1198891 1205821198892 1205821198893
1205821198894 and 120582
1198895) which are used for downstream modulation
To generate five dominant wavelengths the values of DAMparameters are configured as minus05 V 05 V DC bias voltagesare applied to respectively first and second arms of theLN-MZM the RF clock voltage with frequency of 119891
119900drives
10 The Scientific World Journal
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(a)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)(b)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(c)
Figure 9 Constellation diagrams of the demodulated 16-QAMMIMO signals (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
to the DAM and the DC and RF switching voltages areset to 4V and 2V respectively The wavelength interleavesbetween the five generatedwavelengthswhich are equal to thefrequency of the sinusoidal clock 119891
119900 The power magnitudes
of the fivewavelengths are approximately equal and the centerwavelength 120582
1198893has maximum value The difference between
this and the others is around 6 dB To get balanced powermagnitudes an optical attenuator is used in path of the centerwavelength after IL as shown in Figure 12 Each generatedwavelengthmodulates theMIMO signal by using IMThefive
modulated optical signals propagate along the same opticalfiber
The receiver receives the optical downstream and theninterleaves it into the five modulated optical signals withthe wavelength 120582
1198891 1205821198892 1205821198893 1205821198894 and 120582
1198895as shown in
Figure 12The receiver then downconverts the fivemodulatedoptical signals directly to the suitable electrical signals byusing an optical receiver for each signalThe electrical signalsare then band-pass filtered according to the allocated RFcarrier frequency 119891
119888by using BPFs to get the original five
The Scientific World Journal 11
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 10 Eye diagrams of the 119868-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
wireless MIMO signals MIMO1 MIMO
2 MIMO
3 MIMO
4
and MIMO5
7 Conclusions
The novel OFU technique is proposed to solve the problemof wireless MIMO signals transmission over a single opticalfiberThree wireless 16-QAMMIMO signals have been trans-mitted over a 20 km SMF using the OFU technique Thesewireless MIMO signals were modulated using the carrier
frequency of 24GHz or 5GHz at data rate of 1 Gbs for eachsignal The physical layer performance has been reported interms of the BER at different RF carrier frequencies differentaccess distances and different wavelength interleaves Inaddition the EVM and the eye diagrams are analyzed in thisstudy
The proposed approach highly suppressed the crosstalkbetween different MIMO signals with the same RF carrierfrequency since each MIMO signal is carried on a spe-cific optical wavelength While the ESSB-FT technique [10]
12 The Scientific World Journal
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 11 Eye diagrams of the 119876-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
requires a number of low-frequency LOs and electrical BPFsat the transmitter and the receiver the OFU technique doesnot require low-frequency LOs at the transmitter and thereceiver or electrical BPFs at the transmitter Less numberof electrical BPFs is required at the receiver in the proposedtechnique However a number of PDs are required at thereceiver which is equal to the number of MIMO signals Theproposed system supports many wavelengths for carrying
multiple wireless MIMO signals over the fiber using singleLD The novel technique provides a spectral efficient andreliable FiWi system
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
The Scientific World Journal 13
IM
IM
IM
IM
IM
DAM
fo
120582d3
120582d4
120582d5
Transmitter
120582d
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
120582d1
120582d2
Bias
Bias
Bias
Bias
Bias
AWG
RF amplifier
RF amplifier
RF amplifier
RF amplifier
RF amplifier
fc
fc
fc
fc
fc
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalfiber
BPF
BPF
BPF
BPF
BPF
IL
IL
Receiver
LD 120582d3
120582d4
120582d5
120582d1
120582d2
Optical attenuator
+
+
+
+
+minus70
minus50
minus30
minus10
0
minus20
minus40
minus60
1929T 193T 1931T 1932T 1933T
Pow
er (d
Bm)
Frequency (Hz)
Figure 12 Transmission of five wireless MIMO signals over fiber using the novel approach
Acknowledgments
This work is supported by Universiti Teknologi Malaysia(UTM) under the Postdoctoral fellowship scheme Theauthors greatly appreciate UTM and Photonics ResearchLaboratory for providing the facilities which enabled themto accomplish this work They would also like to thank theMinistry of Science Technology and Innovation (MOSTI)Malaysia for sponsoring this work under Project vote no73720
References
[1] L Kazovsky S-W Wong T Ayhan K M Albeyoglu MR N Ribeiro and A Shastri ldquoHybrid optical-wireless accessnetworksrdquo Proceedings of the IEEE vol 100 no 5 pp 1197ndash12252012
[2] R Q Shaddad A B Mohammad and AM Al-hetar ldquoAnalysisof physical layer performance of hybrid optical-wireless accessnetworkrdquo Optics Communications vol 284 no 20 pp 4894ndash4899 2011
[3] R Q Shaddad A Bakar Mohammad and A M Al-hetar ldquoPer-formance evaluation for optical backhaul andwireless front-endin hybrid optical-wireless access networkrdquo Optoelectronics andAdvanced Materials Rapid Communications vol 5 no 4 pp376ndash380 2011
[4] C Lim A Nirmalathas M Bakaul et al ldquoFiber-wirelessnetworks and subsystem technologiesrdquo Journal of LightwaveTechnology vol 28 no 4 pp 390ndash405 2010
[5] A Nirmalathas P A Gamage C Lim D Novak and RWaterhouse ldquoDigitized radio-over-fiber technologies for con-verged optical wireless access networkrdquo Journal of LightwaveTechnology vol 28 no 16 pp 2366ndash2375 2010
[6] Z Jia J Yu G Ellinas and G-K Chang ldquoKey enablingtechnologies for optical wireless networks optical millimeter-wave generation wavelength reuse and architecturerdquo Journalof Lightwave Technology vol 25 no 11 pp 3452ndash3471 2007
[7] A Zelst ldquoSystem for transporting multiple radio frequencysignals of a multiple input multiple output wireless communi-cation system tofrom a central processing base stationrdquo USpatent application 20040017785A1 2004
[8] I Seto H Shoki and S Ohshima ldquoOptical subcarrier mul-tiplexing transmission for base station with adaptive arrayantennardquo IEEE Transactions on Microwave Theory and Tech-niques vol 49 no 10 pp 2036ndash2041 2001
[9] C-P Liu and A Seeds ldquoTransmission of MIMO radio signalsover fibre using a novel phase quadrature double sidebandfrequency translation techniquerdquo in Proceedings of the IEEEInternational Meeting on Microwave Photonics Jointly Held withthe Asia-Pacific Microwave Photonics Conference pp 23ndash26Gold Coast Australia October 2008
[10] C-P Liu and A J Seeds ldquoTransmission of wireless MIMO-type signals over a single optical fiber without WDMrdquo IEEETransactions on Microwave Theory and Techniques vol 58 no11 pp 3094ndash3102 2010
[11] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgailani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overoptical fiberrdquo in Proceedings of the 3rd International Conferenceon Photonics (ICP rsquo12) Penang Malaysia 2012
[12] R Shaddad A Mohammad and A Al-hetar ldquoSpectral efficienthybrid wireless optical broadband access network (WOBAN)based on transmission of wireless MIMO OFDM signals overWDM PONrdquo Optics Communications vol 285 no 20 pp4059ndash4067 2012
[13] K Shimizu T Horiguchi and Y Koyamada ldquoFrequency trans-lation of light waves by propagation around an optical ringcircuit containing a frequency shifter 1 Experimentrdquo AppliedOptics vol 32 pp 6718ndash6726 1993
[14] E L Wooten K M Kissa A Yi-Yan et al ldquoA review of lithiumniobate modulators for fiber-optic communications systemsrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 6no 1 pp 69ndash82 2000
[15] P Yao R Shireen J Macario C A Schuctz S Shi and D WPrather ldquoDesign fabrication and characterization of LiNbO
3
optical modulator for high-sensitivity mmW imaging systemrdquoin Passive Millimeter-Wave Imaging Technology XI vol 6948 ofProceedings of SPIE March 2008
[16] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgeelani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overfiber-wireless systemrdquo Optics amp Laser Technology vol 47 pp347ndash354 2013
14 The Scientific World Journal
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
Figure 3 Transport of wireless MIMO signals over optical fiber using the OFU technique (a) block diagram of the proposed technique and(b) power spectra of the signals according to the indicated insets
119864out (119905) = 120572119864in (119905) (1 minus 120574) 119890(119895120587V1(119905)119881120587RF+1198951205871198811198871119881120587DC)
Here119864in(119905) is the input optical signal to theDAMfrom theLD V1(119905) and V
2(119905) are the RF modulating electrical voltage
with the carrier frequency 119891119898
= 1205961198982120587 119881
1198871and 119881
1198872are
the DC bias voltages applied to the arms of the DAM 119881120587RF
and 119881120587DC are the switching RF and switching bias voltages
respectivelyThe parameter 120572 is given by
120572 = 10minus(Ω20)
(2)
Here Ω is the insertion loss in dB (It is assigned as 5 dBin this design) 120574 designates the power splitting (combining)ratio of arm two for the input (output resp) 119884-branchwaveguide 120574 is given by
120574 =(1 minus 1radic120576
119903)
2 (3)
where 120576119903= 10(Extinction Ratio10)
= 100 so 120574 asymp 12 in this workIn the simulation design the values of 119881
120587RF and 119881120587DC are
set to 4V and the bias voltages of 1198811198871and 119881
1198872are assigned as
minus1 V and 1V respectively In addition the generated opticalsignal from the LD can be expressed as 119864in(119905) = 119864
119901119890119895120596119901119905 and
the modulating electrical signals can be expressed as V1(119905) =
+1198723(119905 minus 1199051198893) 119890119895[(120596119901+120596119888)119905+120573(120596
119901+120596119888)119911]
(12)
where 119905119889119894(119894 = 1 2 or 3) is the time delay of the 119894th optical
downlink signal The time delay is calculated by the firstderivative of 120573(120596) since 119905
119889119894= 1205731015840(120596119889119894
+ 120596119888) and 120596
119894is the
120596p120596p minus 120596m 120596p + 120596m
120596
Am
plitu
de
USSB2 USSB3 USSB1
fd2 fd3 fd1
Figure 4 The propagated lightwave signal over the optical fiber
119894th optical downlink carrier frequency The output lightwaveat the end of fiber is considered as three optical signals withdifferent downlink frequencies of 120596
119901+ 120596119898 120596119901minus 120596119898 and 120596
119901
which convey the three wireless MIMO signals in their uppersingle sidebands (USSBs) as shown in Figure 4
The optical receiver receives the transmitted optical sig-nals and separates them according to their downlink wave-lengths by using optical ILs as shown in Figure 3 Each opticaldownlink signal is then directly detected by a photodetector(PD) so the photocurrent for each detectedMIMOsignal canbe written as the following equation according to the square-law PD [18]
Figure 5 The fiber nonlinearity effect on the system performance
The wireless end-user will receive the three MIMO signalsand demodulate them using the suitable QAMdemodulationand MIMO decoding techniques
5 System Performance Evaluation
In this work the communication system is designed toprovide a data rate of 1 Gbs for each 16-QAMwirelessMIMOsignal Figure 3 in the inset (vi) shows the input opticalpower to the optical fiber where the three modulated opticalsignals with the downlink wavelengths 120582
1198891 1205821198892 and 120582
1198893
are coupled to propagate through 20 km optical fiber Thetotal input power of the three optical signals is 1626 dBmaccording to the simulation calculations for both RF carrierfrequencies of 24GHz and 5GHzThis power is suitable to belaunched to avoid the nonlinear effects along the optical linkFigure 5 shows the system performance at different launchedoptical powers Nonlinearity of the fiber negatively affects thesystem performance when the launched optical powers aregreater than 108 dBm and 79 dBm at the carrier frequenciesof 24GHz and 50GHz respectively
To evaluate the performance of the proposed techniqueFigures 6(a) and 6(b) show the BER performance versus thereceived optical power at the receiver for the three wirelessMIMO signals (MIMO
1 MIMO
2 andMIMO
3) at the carrier
frequencies 24GHz and 5GHz respectively The powersensitivity differences of the receivers for the three MIMOsignals are small especially between the two MIMO signals(MIMO
1and MIMO
2) The maximum power penalties of
347 dB and 4 dB are recorded at BER of 10minus9 for the carrierfrequencies of 24GHz and 5GHz receptively
Figure 7 shows the system performance at three differentfiber lengths (20 km 30 km and 50 km) of the optical fiber Inthe proposed system the fiber length of 50 kmhas slight effecton the performance of the transmitted optical signals whichcarry the wireless MIMO signals The system performance
deteriorates progressively when the access distance becomeslonger than 50 km
In addition the system performance is analyzed by usingdifferent wavelength interleaves between the optical carrierfrequency (or RF clock frequency 119891
119900) Figure 8 shows the
systemperformance at differentwavelength interleaves (Δ119891 =
15 25 and 50GHz which are compatible with Δ120582 = 01202 and 04 nm resp) When the wavelength interleaves aresmaller than 15GHz the system performance will degradeand the error floor clearly appears
Figures 9(a)ndash9(c) show 1Gbs 16-QAM constellationdiagrams for the received MIMO signals MIMO
1 MIMO
2
and MIMO3 respectively at 24GHz Clear scatter-plots are
achieved at EVM values of minus208780 dB minus202873 dB andminus212961 dB for MIMO
1 MIMO
2 and MIMO
3 respectively
So the proposed technique has achieved a good performanceof transmitting wireless MIMO signals over the optical fiberat the carrier frequencies 24GHz and 5GHz The EVMs arecalculated considering the following equation [21]
EVM (dB) = 10 sdot log10[sum119872
119896=1
1003816100381610038161003816119878119905119909119896 minus 119878119903119909119896
where EVM is the value of the difference between a collectionof received symbols and transmitted or ideal symbols 119878
119905119909119896
is the corresponding transmitted symbol of the constellationassociated with the 119896th symbol 119878
119903119909119896is the received symbol
associated with 119878119905119909119896
and119872 is the number of the symbols forthe inphase-quadrature constellation
Figures 10(a)ndash10(c) show the eye diagrams of the 119868-branch of the received 16-QAMbaseband signals forMIMO
1
MIMO2 and MIMO
3 respectively Also Figures 11(a)ndash11(c)
show the eye diagrams of the 119876-branch of the received 16-QAM baseband signals for MIMO
1 MIMO
2 and MIMO
3
respectively The eye diagrams of both 119868-branch and 119876-branch of the received wireless MIMO signals at the receivershow slight differences and good quality communicationsystem at a BER around of 10minus9 The BER are calculatedaccording to (15) [22]
where 119876 is the number of signal levels within each branchof the constellation diagram log
2119872 is the amount of bits
encoded into one QAM symbol and 119896 is a modulationformat-dependent factor giving the relationship betweenmaximum field magnitude and average overall119872 field mag-nitudes defined by the constellation diagram for the chosenmodulation formatThis factor is calculated according to (15)
Figure 7The system performance at different lengths of the opticalfiber
to be 6(radic5+2) for 16-QAMThe 119878119905119909119894
is the ideal transmittedfield vector and 119878
119905119909max is the field vector of the outermostconstellation point In this paper the performance of EVMand the BER is evaluated for the 16-QAM MIMO signalswithout using forward error correction (FEC) techniques
6 Transmission of More Wireless MIMOSignals over Optical Fiber
Figure 12 shows the proposed OFU technique to transmitfive wireless MIMO signals over fiber At the OLT the DAM
Received optical powerminus20 minus18 minus16 minus14 minus12 minus10 minus8 minus6
10minus20
10minus18
10minus16
10minus14
10minus12
10minus10
10minus8
10minus6
10minus4
10minus2
100
BER
Δf = 15GHzΔf = 25GHzΔf = 50GHz
Figure 8 The system performance at different wavelength inter-leaves
is injected by LD with the wavelength 120582119889 The DAM is a
LN-MZM Adjusting the parameters of the DAM to suitablevalues can generate multiple wavelengths The dominantwavelengths are considered and the remaining outside wave-lengths are neglected because of their very small magnitudesThe OLT allocates five downlink wavelengths (120582
1198891 1205821198892 1205821198893
1205821198894 and 120582
1198895) which are used for downstream modulation
To generate five dominant wavelengths the values of DAMparameters are configured as minus05 V 05 V DC bias voltagesare applied to respectively first and second arms of theLN-MZM the RF clock voltage with frequency of 119891
119900drives
10 The Scientific World Journal
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(a)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)(b)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(c)
Figure 9 Constellation diagrams of the demodulated 16-QAMMIMO signals (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
to the DAM and the DC and RF switching voltages areset to 4V and 2V respectively The wavelength interleavesbetween the five generatedwavelengthswhich are equal to thefrequency of the sinusoidal clock 119891
119900 The power magnitudes
of the fivewavelengths are approximately equal and the centerwavelength 120582
1198893has maximum value The difference between
this and the others is around 6 dB To get balanced powermagnitudes an optical attenuator is used in path of the centerwavelength after IL as shown in Figure 12 Each generatedwavelengthmodulates theMIMO signal by using IMThefive
modulated optical signals propagate along the same opticalfiber
The receiver receives the optical downstream and theninterleaves it into the five modulated optical signals withthe wavelength 120582
1198891 1205821198892 1205821198893 1205821198894 and 120582
1198895as shown in
Figure 12The receiver then downconverts the fivemodulatedoptical signals directly to the suitable electrical signals byusing an optical receiver for each signalThe electrical signalsare then band-pass filtered according to the allocated RFcarrier frequency 119891
119888by using BPFs to get the original five
The Scientific World Journal 11
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 10 Eye diagrams of the 119868-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
wireless MIMO signals MIMO1 MIMO
2 MIMO
3 MIMO
4
and MIMO5
7 Conclusions
The novel OFU technique is proposed to solve the problemof wireless MIMO signals transmission over a single opticalfiberThree wireless 16-QAMMIMO signals have been trans-mitted over a 20 km SMF using the OFU technique Thesewireless MIMO signals were modulated using the carrier
frequency of 24GHz or 5GHz at data rate of 1 Gbs for eachsignal The physical layer performance has been reported interms of the BER at different RF carrier frequencies differentaccess distances and different wavelength interleaves Inaddition the EVM and the eye diagrams are analyzed in thisstudy
The proposed approach highly suppressed the crosstalkbetween different MIMO signals with the same RF carrierfrequency since each MIMO signal is carried on a spe-cific optical wavelength While the ESSB-FT technique [10]
12 The Scientific World Journal
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 11 Eye diagrams of the 119876-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
requires a number of low-frequency LOs and electrical BPFsat the transmitter and the receiver the OFU technique doesnot require low-frequency LOs at the transmitter and thereceiver or electrical BPFs at the transmitter Less numberof electrical BPFs is required at the receiver in the proposedtechnique However a number of PDs are required at thereceiver which is equal to the number of MIMO signals Theproposed system supports many wavelengths for carrying
multiple wireless MIMO signals over the fiber using singleLD The novel technique provides a spectral efficient andreliable FiWi system
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
The Scientific World Journal 13
IM
IM
IM
IM
IM
DAM
fo
120582d3
120582d4
120582d5
Transmitter
120582d
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
120582d1
120582d2
Bias
Bias
Bias
Bias
Bias
AWG
RF amplifier
RF amplifier
RF amplifier
RF amplifier
RF amplifier
fc
fc
fc
fc
fc
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalfiber
BPF
BPF
BPF
BPF
BPF
IL
IL
Receiver
LD 120582d3
120582d4
120582d5
120582d1
120582d2
Optical attenuator
+
+
+
+
+minus70
minus50
minus30
minus10
0
minus20
minus40
minus60
1929T 193T 1931T 1932T 1933T
Pow
er (d
Bm)
Frequency (Hz)
Figure 12 Transmission of five wireless MIMO signals over fiber using the novel approach
Acknowledgments
This work is supported by Universiti Teknologi Malaysia(UTM) under the Postdoctoral fellowship scheme Theauthors greatly appreciate UTM and Photonics ResearchLaboratory for providing the facilities which enabled themto accomplish this work They would also like to thank theMinistry of Science Technology and Innovation (MOSTI)Malaysia for sponsoring this work under Project vote no73720
References
[1] L Kazovsky S-W Wong T Ayhan K M Albeyoglu MR N Ribeiro and A Shastri ldquoHybrid optical-wireless accessnetworksrdquo Proceedings of the IEEE vol 100 no 5 pp 1197ndash12252012
[2] R Q Shaddad A B Mohammad and AM Al-hetar ldquoAnalysisof physical layer performance of hybrid optical-wireless accessnetworkrdquo Optics Communications vol 284 no 20 pp 4894ndash4899 2011
[3] R Q Shaddad A Bakar Mohammad and A M Al-hetar ldquoPer-formance evaluation for optical backhaul andwireless front-endin hybrid optical-wireless access networkrdquo Optoelectronics andAdvanced Materials Rapid Communications vol 5 no 4 pp376ndash380 2011
[4] C Lim A Nirmalathas M Bakaul et al ldquoFiber-wirelessnetworks and subsystem technologiesrdquo Journal of LightwaveTechnology vol 28 no 4 pp 390ndash405 2010
[5] A Nirmalathas P A Gamage C Lim D Novak and RWaterhouse ldquoDigitized radio-over-fiber technologies for con-verged optical wireless access networkrdquo Journal of LightwaveTechnology vol 28 no 16 pp 2366ndash2375 2010
[6] Z Jia J Yu G Ellinas and G-K Chang ldquoKey enablingtechnologies for optical wireless networks optical millimeter-wave generation wavelength reuse and architecturerdquo Journalof Lightwave Technology vol 25 no 11 pp 3452ndash3471 2007
[7] A Zelst ldquoSystem for transporting multiple radio frequencysignals of a multiple input multiple output wireless communi-cation system tofrom a central processing base stationrdquo USpatent application 20040017785A1 2004
[8] I Seto H Shoki and S Ohshima ldquoOptical subcarrier mul-tiplexing transmission for base station with adaptive arrayantennardquo IEEE Transactions on Microwave Theory and Tech-niques vol 49 no 10 pp 2036ndash2041 2001
[9] C-P Liu and A Seeds ldquoTransmission of MIMO radio signalsover fibre using a novel phase quadrature double sidebandfrequency translation techniquerdquo in Proceedings of the IEEEInternational Meeting on Microwave Photonics Jointly Held withthe Asia-Pacific Microwave Photonics Conference pp 23ndash26Gold Coast Australia October 2008
[10] C-P Liu and A J Seeds ldquoTransmission of wireless MIMO-type signals over a single optical fiber without WDMrdquo IEEETransactions on Microwave Theory and Techniques vol 58 no11 pp 3094ndash3102 2010
[11] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgailani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overoptical fiberrdquo in Proceedings of the 3rd International Conferenceon Photonics (ICP rsquo12) Penang Malaysia 2012
[12] R Shaddad A Mohammad and A Al-hetar ldquoSpectral efficienthybrid wireless optical broadband access network (WOBAN)based on transmission of wireless MIMO OFDM signals overWDM PONrdquo Optics Communications vol 285 no 20 pp4059ndash4067 2012
[13] K Shimizu T Horiguchi and Y Koyamada ldquoFrequency trans-lation of light waves by propagation around an optical ringcircuit containing a frequency shifter 1 Experimentrdquo AppliedOptics vol 32 pp 6718ndash6726 1993
[14] E L Wooten K M Kissa A Yi-Yan et al ldquoA review of lithiumniobate modulators for fiber-optic communications systemsrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 6no 1 pp 69ndash82 2000
[15] P Yao R Shireen J Macario C A Schuctz S Shi and D WPrather ldquoDesign fabrication and characterization of LiNbO
3
optical modulator for high-sensitivity mmW imaging systemrdquoin Passive Millimeter-Wave Imaging Technology XI vol 6948 ofProceedings of SPIE March 2008
[16] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgeelani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overfiber-wireless systemrdquo Optics amp Laser Technology vol 47 pp347ndash354 2013
14 The Scientific World Journal
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
Figure 3 Transport of wireless MIMO signals over optical fiber using the OFU technique (a) block diagram of the proposed technique and(b) power spectra of the signals according to the indicated insets
119864out (119905) = 120572119864in (119905) (1 minus 120574) 119890(119895120587V1(119905)119881120587RF+1198951205871198811198871119881120587DC)
Here119864in(119905) is the input optical signal to theDAMfrom theLD V1(119905) and V
2(119905) are the RF modulating electrical voltage
with the carrier frequency 119891119898
= 1205961198982120587 119881
1198871and 119881
1198872are
the DC bias voltages applied to the arms of the DAM 119881120587RF
and 119881120587DC are the switching RF and switching bias voltages
respectivelyThe parameter 120572 is given by
120572 = 10minus(Ω20)
(2)
Here Ω is the insertion loss in dB (It is assigned as 5 dBin this design) 120574 designates the power splitting (combining)ratio of arm two for the input (output resp) 119884-branchwaveguide 120574 is given by
120574 =(1 minus 1radic120576
119903)
2 (3)
where 120576119903= 10(Extinction Ratio10)
= 100 so 120574 asymp 12 in this workIn the simulation design the values of 119881
120587RF and 119881120587DC are
set to 4V and the bias voltages of 1198811198871and 119881
1198872are assigned as
minus1 V and 1V respectively In addition the generated opticalsignal from the LD can be expressed as 119864in(119905) = 119864
119901119890119895120596119901119905 and
the modulating electrical signals can be expressed as V1(119905) =
+1198723(119905 minus 1199051198893) 119890119895[(120596119901+120596119888)119905+120573(120596
119901+120596119888)119911]
(12)
where 119905119889119894(119894 = 1 2 or 3) is the time delay of the 119894th optical
downlink signal The time delay is calculated by the firstderivative of 120573(120596) since 119905
119889119894= 1205731015840(120596119889119894
+ 120596119888) and 120596
119894is the
120596p120596p minus 120596m 120596p + 120596m
120596
Am
plitu
de
USSB2 USSB3 USSB1
fd2 fd3 fd1
Figure 4 The propagated lightwave signal over the optical fiber
119894th optical downlink carrier frequency The output lightwaveat the end of fiber is considered as three optical signals withdifferent downlink frequencies of 120596
119901+ 120596119898 120596119901minus 120596119898 and 120596
119901
which convey the three wireless MIMO signals in their uppersingle sidebands (USSBs) as shown in Figure 4
The optical receiver receives the transmitted optical sig-nals and separates them according to their downlink wave-lengths by using optical ILs as shown in Figure 3 Each opticaldownlink signal is then directly detected by a photodetector(PD) so the photocurrent for each detectedMIMOsignal canbe written as the following equation according to the square-law PD [18]
Figure 5 The fiber nonlinearity effect on the system performance
The wireless end-user will receive the three MIMO signalsand demodulate them using the suitable QAMdemodulationand MIMO decoding techniques
5 System Performance Evaluation
In this work the communication system is designed toprovide a data rate of 1 Gbs for each 16-QAMwirelessMIMOsignal Figure 3 in the inset (vi) shows the input opticalpower to the optical fiber where the three modulated opticalsignals with the downlink wavelengths 120582
1198891 1205821198892 and 120582
1198893
are coupled to propagate through 20 km optical fiber Thetotal input power of the three optical signals is 1626 dBmaccording to the simulation calculations for both RF carrierfrequencies of 24GHz and 5GHzThis power is suitable to belaunched to avoid the nonlinear effects along the optical linkFigure 5 shows the system performance at different launchedoptical powers Nonlinearity of the fiber negatively affects thesystem performance when the launched optical powers aregreater than 108 dBm and 79 dBm at the carrier frequenciesof 24GHz and 50GHz respectively
To evaluate the performance of the proposed techniqueFigures 6(a) and 6(b) show the BER performance versus thereceived optical power at the receiver for the three wirelessMIMO signals (MIMO
1 MIMO
2 andMIMO
3) at the carrier
frequencies 24GHz and 5GHz respectively The powersensitivity differences of the receivers for the three MIMOsignals are small especially between the two MIMO signals(MIMO
1and MIMO
2) The maximum power penalties of
347 dB and 4 dB are recorded at BER of 10minus9 for the carrierfrequencies of 24GHz and 5GHz receptively
Figure 7 shows the system performance at three differentfiber lengths (20 km 30 km and 50 km) of the optical fiber Inthe proposed system the fiber length of 50 kmhas slight effecton the performance of the transmitted optical signals whichcarry the wireless MIMO signals The system performance
deteriorates progressively when the access distance becomeslonger than 50 km
In addition the system performance is analyzed by usingdifferent wavelength interleaves between the optical carrierfrequency (or RF clock frequency 119891
119900) Figure 8 shows the
systemperformance at differentwavelength interleaves (Δ119891 =
15 25 and 50GHz which are compatible with Δ120582 = 01202 and 04 nm resp) When the wavelength interleaves aresmaller than 15GHz the system performance will degradeand the error floor clearly appears
Figures 9(a)ndash9(c) show 1Gbs 16-QAM constellationdiagrams for the received MIMO signals MIMO
1 MIMO
2
and MIMO3 respectively at 24GHz Clear scatter-plots are
achieved at EVM values of minus208780 dB minus202873 dB andminus212961 dB for MIMO
1 MIMO
2 and MIMO
3 respectively
So the proposed technique has achieved a good performanceof transmitting wireless MIMO signals over the optical fiberat the carrier frequencies 24GHz and 5GHz The EVMs arecalculated considering the following equation [21]
EVM (dB) = 10 sdot log10[sum119872
119896=1
1003816100381610038161003816119878119905119909119896 minus 119878119903119909119896
where EVM is the value of the difference between a collectionof received symbols and transmitted or ideal symbols 119878
119905119909119896
is the corresponding transmitted symbol of the constellationassociated with the 119896th symbol 119878
119903119909119896is the received symbol
associated with 119878119905119909119896
and119872 is the number of the symbols forthe inphase-quadrature constellation
Figures 10(a)ndash10(c) show the eye diagrams of the 119868-branch of the received 16-QAMbaseband signals forMIMO
1
MIMO2 and MIMO
3 respectively Also Figures 11(a)ndash11(c)
show the eye diagrams of the 119876-branch of the received 16-QAM baseband signals for MIMO
1 MIMO
2 and MIMO
3
respectively The eye diagrams of both 119868-branch and 119876-branch of the received wireless MIMO signals at the receivershow slight differences and good quality communicationsystem at a BER around of 10minus9 The BER are calculatedaccording to (15) [22]
where 119876 is the number of signal levels within each branchof the constellation diagram log
2119872 is the amount of bits
encoded into one QAM symbol and 119896 is a modulationformat-dependent factor giving the relationship betweenmaximum field magnitude and average overall119872 field mag-nitudes defined by the constellation diagram for the chosenmodulation formatThis factor is calculated according to (15)
Figure 7The system performance at different lengths of the opticalfiber
to be 6(radic5+2) for 16-QAMThe 119878119905119909119894
is the ideal transmittedfield vector and 119878
119905119909max is the field vector of the outermostconstellation point In this paper the performance of EVMand the BER is evaluated for the 16-QAM MIMO signalswithout using forward error correction (FEC) techniques
6 Transmission of More Wireless MIMOSignals over Optical Fiber
Figure 12 shows the proposed OFU technique to transmitfive wireless MIMO signals over fiber At the OLT the DAM
Received optical powerminus20 minus18 minus16 minus14 minus12 minus10 minus8 minus6
10minus20
10minus18
10minus16
10minus14
10minus12
10minus10
10minus8
10minus6
10minus4
10minus2
100
BER
Δf = 15GHzΔf = 25GHzΔf = 50GHz
Figure 8 The system performance at different wavelength inter-leaves
is injected by LD with the wavelength 120582119889 The DAM is a
LN-MZM Adjusting the parameters of the DAM to suitablevalues can generate multiple wavelengths The dominantwavelengths are considered and the remaining outside wave-lengths are neglected because of their very small magnitudesThe OLT allocates five downlink wavelengths (120582
1198891 1205821198892 1205821198893
1205821198894 and 120582
1198895) which are used for downstream modulation
To generate five dominant wavelengths the values of DAMparameters are configured as minus05 V 05 V DC bias voltagesare applied to respectively first and second arms of theLN-MZM the RF clock voltage with frequency of 119891
119900drives
10 The Scientific World Journal
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(a)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)(b)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(c)
Figure 9 Constellation diagrams of the demodulated 16-QAMMIMO signals (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
to the DAM and the DC and RF switching voltages areset to 4V and 2V respectively The wavelength interleavesbetween the five generatedwavelengthswhich are equal to thefrequency of the sinusoidal clock 119891
119900 The power magnitudes
of the fivewavelengths are approximately equal and the centerwavelength 120582
1198893has maximum value The difference between
this and the others is around 6 dB To get balanced powermagnitudes an optical attenuator is used in path of the centerwavelength after IL as shown in Figure 12 Each generatedwavelengthmodulates theMIMO signal by using IMThefive
modulated optical signals propagate along the same opticalfiber
The receiver receives the optical downstream and theninterleaves it into the five modulated optical signals withthe wavelength 120582
1198891 1205821198892 1205821198893 1205821198894 and 120582
1198895as shown in
Figure 12The receiver then downconverts the fivemodulatedoptical signals directly to the suitable electrical signals byusing an optical receiver for each signalThe electrical signalsare then band-pass filtered according to the allocated RFcarrier frequency 119891
119888by using BPFs to get the original five
The Scientific World Journal 11
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 10 Eye diagrams of the 119868-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
wireless MIMO signals MIMO1 MIMO
2 MIMO
3 MIMO
4
and MIMO5
7 Conclusions
The novel OFU technique is proposed to solve the problemof wireless MIMO signals transmission over a single opticalfiberThree wireless 16-QAMMIMO signals have been trans-mitted over a 20 km SMF using the OFU technique Thesewireless MIMO signals were modulated using the carrier
frequency of 24GHz or 5GHz at data rate of 1 Gbs for eachsignal The physical layer performance has been reported interms of the BER at different RF carrier frequencies differentaccess distances and different wavelength interleaves Inaddition the EVM and the eye diagrams are analyzed in thisstudy
The proposed approach highly suppressed the crosstalkbetween different MIMO signals with the same RF carrierfrequency since each MIMO signal is carried on a spe-cific optical wavelength While the ESSB-FT technique [10]
12 The Scientific World Journal
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 11 Eye diagrams of the 119876-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
requires a number of low-frequency LOs and electrical BPFsat the transmitter and the receiver the OFU technique doesnot require low-frequency LOs at the transmitter and thereceiver or electrical BPFs at the transmitter Less numberof electrical BPFs is required at the receiver in the proposedtechnique However a number of PDs are required at thereceiver which is equal to the number of MIMO signals Theproposed system supports many wavelengths for carrying
multiple wireless MIMO signals over the fiber using singleLD The novel technique provides a spectral efficient andreliable FiWi system
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
The Scientific World Journal 13
IM
IM
IM
IM
IM
DAM
fo
120582d3
120582d4
120582d5
Transmitter
120582d
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
120582d1
120582d2
Bias
Bias
Bias
Bias
Bias
AWG
RF amplifier
RF amplifier
RF amplifier
RF amplifier
RF amplifier
fc
fc
fc
fc
fc
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalfiber
BPF
BPF
BPF
BPF
BPF
IL
IL
Receiver
LD 120582d3
120582d4
120582d5
120582d1
120582d2
Optical attenuator
+
+
+
+
+minus70
minus50
minus30
minus10
0
minus20
minus40
minus60
1929T 193T 1931T 1932T 1933T
Pow
er (d
Bm)
Frequency (Hz)
Figure 12 Transmission of five wireless MIMO signals over fiber using the novel approach
Acknowledgments
This work is supported by Universiti Teknologi Malaysia(UTM) under the Postdoctoral fellowship scheme Theauthors greatly appreciate UTM and Photonics ResearchLaboratory for providing the facilities which enabled themto accomplish this work They would also like to thank theMinistry of Science Technology and Innovation (MOSTI)Malaysia for sponsoring this work under Project vote no73720
References
[1] L Kazovsky S-W Wong T Ayhan K M Albeyoglu MR N Ribeiro and A Shastri ldquoHybrid optical-wireless accessnetworksrdquo Proceedings of the IEEE vol 100 no 5 pp 1197ndash12252012
[2] R Q Shaddad A B Mohammad and AM Al-hetar ldquoAnalysisof physical layer performance of hybrid optical-wireless accessnetworkrdquo Optics Communications vol 284 no 20 pp 4894ndash4899 2011
[3] R Q Shaddad A Bakar Mohammad and A M Al-hetar ldquoPer-formance evaluation for optical backhaul andwireless front-endin hybrid optical-wireless access networkrdquo Optoelectronics andAdvanced Materials Rapid Communications vol 5 no 4 pp376ndash380 2011
[4] C Lim A Nirmalathas M Bakaul et al ldquoFiber-wirelessnetworks and subsystem technologiesrdquo Journal of LightwaveTechnology vol 28 no 4 pp 390ndash405 2010
[5] A Nirmalathas P A Gamage C Lim D Novak and RWaterhouse ldquoDigitized radio-over-fiber technologies for con-verged optical wireless access networkrdquo Journal of LightwaveTechnology vol 28 no 16 pp 2366ndash2375 2010
[6] Z Jia J Yu G Ellinas and G-K Chang ldquoKey enablingtechnologies for optical wireless networks optical millimeter-wave generation wavelength reuse and architecturerdquo Journalof Lightwave Technology vol 25 no 11 pp 3452ndash3471 2007
[7] A Zelst ldquoSystem for transporting multiple radio frequencysignals of a multiple input multiple output wireless communi-cation system tofrom a central processing base stationrdquo USpatent application 20040017785A1 2004
[8] I Seto H Shoki and S Ohshima ldquoOptical subcarrier mul-tiplexing transmission for base station with adaptive arrayantennardquo IEEE Transactions on Microwave Theory and Tech-niques vol 49 no 10 pp 2036ndash2041 2001
[9] C-P Liu and A Seeds ldquoTransmission of MIMO radio signalsover fibre using a novel phase quadrature double sidebandfrequency translation techniquerdquo in Proceedings of the IEEEInternational Meeting on Microwave Photonics Jointly Held withthe Asia-Pacific Microwave Photonics Conference pp 23ndash26Gold Coast Australia October 2008
[10] C-P Liu and A J Seeds ldquoTransmission of wireless MIMO-type signals over a single optical fiber without WDMrdquo IEEETransactions on Microwave Theory and Techniques vol 58 no11 pp 3094ndash3102 2010
[11] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgailani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overoptical fiberrdquo in Proceedings of the 3rd International Conferenceon Photonics (ICP rsquo12) Penang Malaysia 2012
[12] R Shaddad A Mohammad and A Al-hetar ldquoSpectral efficienthybrid wireless optical broadband access network (WOBAN)based on transmission of wireless MIMO OFDM signals overWDM PONrdquo Optics Communications vol 285 no 20 pp4059ndash4067 2012
[13] K Shimizu T Horiguchi and Y Koyamada ldquoFrequency trans-lation of light waves by propagation around an optical ringcircuit containing a frequency shifter 1 Experimentrdquo AppliedOptics vol 32 pp 6718ndash6726 1993
[14] E L Wooten K M Kissa A Yi-Yan et al ldquoA review of lithiumniobate modulators for fiber-optic communications systemsrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 6no 1 pp 69ndash82 2000
[15] P Yao R Shireen J Macario C A Schuctz S Shi and D WPrather ldquoDesign fabrication and characterization of LiNbO
3
optical modulator for high-sensitivity mmW imaging systemrdquoin Passive Millimeter-Wave Imaging Technology XI vol 6948 ofProceedings of SPIE March 2008
[16] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgeelani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overfiber-wireless systemrdquo Optics amp Laser Technology vol 47 pp347ndash354 2013
14 The Scientific World Journal
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
+1198723(119905 minus 1199051198893) 119890119895[(120596119901+120596119888)119905+120573(120596
119901+120596119888)119911]
(12)
where 119905119889119894(119894 = 1 2 or 3) is the time delay of the 119894th optical
downlink signal The time delay is calculated by the firstderivative of 120573(120596) since 119905
119889119894= 1205731015840(120596119889119894
+ 120596119888) and 120596
119894is the
120596p120596p minus 120596m 120596p + 120596m
120596
Am
plitu
de
USSB2 USSB3 USSB1
fd2 fd3 fd1
Figure 4 The propagated lightwave signal over the optical fiber
119894th optical downlink carrier frequency The output lightwaveat the end of fiber is considered as three optical signals withdifferent downlink frequencies of 120596
119901+ 120596119898 120596119901minus 120596119898 and 120596
119901
which convey the three wireless MIMO signals in their uppersingle sidebands (USSBs) as shown in Figure 4
The optical receiver receives the transmitted optical sig-nals and separates them according to their downlink wave-lengths by using optical ILs as shown in Figure 3 Each opticaldownlink signal is then directly detected by a photodetector(PD) so the photocurrent for each detectedMIMOsignal canbe written as the following equation according to the square-law PD [18]
Figure 5 The fiber nonlinearity effect on the system performance
The wireless end-user will receive the three MIMO signalsand demodulate them using the suitable QAMdemodulationand MIMO decoding techniques
5 System Performance Evaluation
In this work the communication system is designed toprovide a data rate of 1 Gbs for each 16-QAMwirelessMIMOsignal Figure 3 in the inset (vi) shows the input opticalpower to the optical fiber where the three modulated opticalsignals with the downlink wavelengths 120582
1198891 1205821198892 and 120582
1198893
are coupled to propagate through 20 km optical fiber Thetotal input power of the three optical signals is 1626 dBmaccording to the simulation calculations for both RF carrierfrequencies of 24GHz and 5GHzThis power is suitable to belaunched to avoid the nonlinear effects along the optical linkFigure 5 shows the system performance at different launchedoptical powers Nonlinearity of the fiber negatively affects thesystem performance when the launched optical powers aregreater than 108 dBm and 79 dBm at the carrier frequenciesof 24GHz and 50GHz respectively
To evaluate the performance of the proposed techniqueFigures 6(a) and 6(b) show the BER performance versus thereceived optical power at the receiver for the three wirelessMIMO signals (MIMO
1 MIMO
2 andMIMO
3) at the carrier
frequencies 24GHz and 5GHz respectively The powersensitivity differences of the receivers for the three MIMOsignals are small especially between the two MIMO signals(MIMO
1and MIMO
2) The maximum power penalties of
347 dB and 4 dB are recorded at BER of 10minus9 for the carrierfrequencies of 24GHz and 5GHz receptively
Figure 7 shows the system performance at three differentfiber lengths (20 km 30 km and 50 km) of the optical fiber Inthe proposed system the fiber length of 50 kmhas slight effecton the performance of the transmitted optical signals whichcarry the wireless MIMO signals The system performance
deteriorates progressively when the access distance becomeslonger than 50 km
In addition the system performance is analyzed by usingdifferent wavelength interleaves between the optical carrierfrequency (or RF clock frequency 119891
119900) Figure 8 shows the
systemperformance at differentwavelength interleaves (Δ119891 =
15 25 and 50GHz which are compatible with Δ120582 = 01202 and 04 nm resp) When the wavelength interleaves aresmaller than 15GHz the system performance will degradeand the error floor clearly appears
Figures 9(a)ndash9(c) show 1Gbs 16-QAM constellationdiagrams for the received MIMO signals MIMO
1 MIMO
2
and MIMO3 respectively at 24GHz Clear scatter-plots are
achieved at EVM values of minus208780 dB minus202873 dB andminus212961 dB for MIMO
1 MIMO
2 and MIMO
3 respectively
So the proposed technique has achieved a good performanceof transmitting wireless MIMO signals over the optical fiberat the carrier frequencies 24GHz and 5GHz The EVMs arecalculated considering the following equation [21]
EVM (dB) = 10 sdot log10[sum119872
119896=1
1003816100381610038161003816119878119905119909119896 minus 119878119903119909119896
where EVM is the value of the difference between a collectionof received symbols and transmitted or ideal symbols 119878
119905119909119896
is the corresponding transmitted symbol of the constellationassociated with the 119896th symbol 119878
119903119909119896is the received symbol
associated with 119878119905119909119896
and119872 is the number of the symbols forthe inphase-quadrature constellation
Figures 10(a)ndash10(c) show the eye diagrams of the 119868-branch of the received 16-QAMbaseband signals forMIMO
1
MIMO2 and MIMO
3 respectively Also Figures 11(a)ndash11(c)
show the eye diagrams of the 119876-branch of the received 16-QAM baseband signals for MIMO
1 MIMO
2 and MIMO
3
respectively The eye diagrams of both 119868-branch and 119876-branch of the received wireless MIMO signals at the receivershow slight differences and good quality communicationsystem at a BER around of 10minus9 The BER are calculatedaccording to (15) [22]
where 119876 is the number of signal levels within each branchof the constellation diagram log
2119872 is the amount of bits
encoded into one QAM symbol and 119896 is a modulationformat-dependent factor giving the relationship betweenmaximum field magnitude and average overall119872 field mag-nitudes defined by the constellation diagram for the chosenmodulation formatThis factor is calculated according to (15)
Figure 7The system performance at different lengths of the opticalfiber
to be 6(radic5+2) for 16-QAMThe 119878119905119909119894
is the ideal transmittedfield vector and 119878
119905119909max is the field vector of the outermostconstellation point In this paper the performance of EVMand the BER is evaluated for the 16-QAM MIMO signalswithout using forward error correction (FEC) techniques
6 Transmission of More Wireless MIMOSignals over Optical Fiber
Figure 12 shows the proposed OFU technique to transmitfive wireless MIMO signals over fiber At the OLT the DAM
Received optical powerminus20 minus18 minus16 minus14 minus12 minus10 minus8 minus6
10minus20
10minus18
10minus16
10minus14
10minus12
10minus10
10minus8
10minus6
10minus4
10minus2
100
BER
Δf = 15GHzΔf = 25GHzΔf = 50GHz
Figure 8 The system performance at different wavelength inter-leaves
is injected by LD with the wavelength 120582119889 The DAM is a
LN-MZM Adjusting the parameters of the DAM to suitablevalues can generate multiple wavelengths The dominantwavelengths are considered and the remaining outside wave-lengths are neglected because of their very small magnitudesThe OLT allocates five downlink wavelengths (120582
1198891 1205821198892 1205821198893
1205821198894 and 120582
1198895) which are used for downstream modulation
To generate five dominant wavelengths the values of DAMparameters are configured as minus05 V 05 V DC bias voltagesare applied to respectively first and second arms of theLN-MZM the RF clock voltage with frequency of 119891
119900drives
10 The Scientific World Journal
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(a)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)(b)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(c)
Figure 9 Constellation diagrams of the demodulated 16-QAMMIMO signals (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
to the DAM and the DC and RF switching voltages areset to 4V and 2V respectively The wavelength interleavesbetween the five generatedwavelengthswhich are equal to thefrequency of the sinusoidal clock 119891
119900 The power magnitudes
of the fivewavelengths are approximately equal and the centerwavelength 120582
1198893has maximum value The difference between
this and the others is around 6 dB To get balanced powermagnitudes an optical attenuator is used in path of the centerwavelength after IL as shown in Figure 12 Each generatedwavelengthmodulates theMIMO signal by using IMThefive
modulated optical signals propagate along the same opticalfiber
The receiver receives the optical downstream and theninterleaves it into the five modulated optical signals withthe wavelength 120582
1198891 1205821198892 1205821198893 1205821198894 and 120582
1198895as shown in
Figure 12The receiver then downconverts the fivemodulatedoptical signals directly to the suitable electrical signals byusing an optical receiver for each signalThe electrical signalsare then band-pass filtered according to the allocated RFcarrier frequency 119891
119888by using BPFs to get the original five
The Scientific World Journal 11
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 10 Eye diagrams of the 119868-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
wireless MIMO signals MIMO1 MIMO
2 MIMO
3 MIMO
4
and MIMO5
7 Conclusions
The novel OFU technique is proposed to solve the problemof wireless MIMO signals transmission over a single opticalfiberThree wireless 16-QAMMIMO signals have been trans-mitted over a 20 km SMF using the OFU technique Thesewireless MIMO signals were modulated using the carrier
frequency of 24GHz or 5GHz at data rate of 1 Gbs for eachsignal The physical layer performance has been reported interms of the BER at different RF carrier frequencies differentaccess distances and different wavelength interleaves Inaddition the EVM and the eye diagrams are analyzed in thisstudy
The proposed approach highly suppressed the crosstalkbetween different MIMO signals with the same RF carrierfrequency since each MIMO signal is carried on a spe-cific optical wavelength While the ESSB-FT technique [10]
12 The Scientific World Journal
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 11 Eye diagrams of the 119876-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
requires a number of low-frequency LOs and electrical BPFsat the transmitter and the receiver the OFU technique doesnot require low-frequency LOs at the transmitter and thereceiver or electrical BPFs at the transmitter Less numberof electrical BPFs is required at the receiver in the proposedtechnique However a number of PDs are required at thereceiver which is equal to the number of MIMO signals Theproposed system supports many wavelengths for carrying
multiple wireless MIMO signals over the fiber using singleLD The novel technique provides a spectral efficient andreliable FiWi system
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
The Scientific World Journal 13
IM
IM
IM
IM
IM
DAM
fo
120582d3
120582d4
120582d5
Transmitter
120582d
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
120582d1
120582d2
Bias
Bias
Bias
Bias
Bias
AWG
RF amplifier
RF amplifier
RF amplifier
RF amplifier
RF amplifier
fc
fc
fc
fc
fc
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalfiber
BPF
BPF
BPF
BPF
BPF
IL
IL
Receiver
LD 120582d3
120582d4
120582d5
120582d1
120582d2
Optical attenuator
+
+
+
+
+minus70
minus50
minus30
minus10
0
minus20
minus40
minus60
1929T 193T 1931T 1932T 1933T
Pow
er (d
Bm)
Frequency (Hz)
Figure 12 Transmission of five wireless MIMO signals over fiber using the novel approach
Acknowledgments
This work is supported by Universiti Teknologi Malaysia(UTM) under the Postdoctoral fellowship scheme Theauthors greatly appreciate UTM and Photonics ResearchLaboratory for providing the facilities which enabled themto accomplish this work They would also like to thank theMinistry of Science Technology and Innovation (MOSTI)Malaysia for sponsoring this work under Project vote no73720
References
[1] L Kazovsky S-W Wong T Ayhan K M Albeyoglu MR N Ribeiro and A Shastri ldquoHybrid optical-wireless accessnetworksrdquo Proceedings of the IEEE vol 100 no 5 pp 1197ndash12252012
[2] R Q Shaddad A B Mohammad and AM Al-hetar ldquoAnalysisof physical layer performance of hybrid optical-wireless accessnetworkrdquo Optics Communications vol 284 no 20 pp 4894ndash4899 2011
[3] R Q Shaddad A Bakar Mohammad and A M Al-hetar ldquoPer-formance evaluation for optical backhaul andwireless front-endin hybrid optical-wireless access networkrdquo Optoelectronics andAdvanced Materials Rapid Communications vol 5 no 4 pp376ndash380 2011
[4] C Lim A Nirmalathas M Bakaul et al ldquoFiber-wirelessnetworks and subsystem technologiesrdquo Journal of LightwaveTechnology vol 28 no 4 pp 390ndash405 2010
[5] A Nirmalathas P A Gamage C Lim D Novak and RWaterhouse ldquoDigitized radio-over-fiber technologies for con-verged optical wireless access networkrdquo Journal of LightwaveTechnology vol 28 no 16 pp 2366ndash2375 2010
[6] Z Jia J Yu G Ellinas and G-K Chang ldquoKey enablingtechnologies for optical wireless networks optical millimeter-wave generation wavelength reuse and architecturerdquo Journalof Lightwave Technology vol 25 no 11 pp 3452ndash3471 2007
[7] A Zelst ldquoSystem for transporting multiple radio frequencysignals of a multiple input multiple output wireless communi-cation system tofrom a central processing base stationrdquo USpatent application 20040017785A1 2004
[8] I Seto H Shoki and S Ohshima ldquoOptical subcarrier mul-tiplexing transmission for base station with adaptive arrayantennardquo IEEE Transactions on Microwave Theory and Tech-niques vol 49 no 10 pp 2036ndash2041 2001
[9] C-P Liu and A Seeds ldquoTransmission of MIMO radio signalsover fibre using a novel phase quadrature double sidebandfrequency translation techniquerdquo in Proceedings of the IEEEInternational Meeting on Microwave Photonics Jointly Held withthe Asia-Pacific Microwave Photonics Conference pp 23ndash26Gold Coast Australia October 2008
[10] C-P Liu and A J Seeds ldquoTransmission of wireless MIMO-type signals over a single optical fiber without WDMrdquo IEEETransactions on Microwave Theory and Techniques vol 58 no11 pp 3094ndash3102 2010
[11] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgailani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overoptical fiberrdquo in Proceedings of the 3rd International Conferenceon Photonics (ICP rsquo12) Penang Malaysia 2012
[12] R Shaddad A Mohammad and A Al-hetar ldquoSpectral efficienthybrid wireless optical broadband access network (WOBAN)based on transmission of wireless MIMO OFDM signals overWDM PONrdquo Optics Communications vol 285 no 20 pp4059ndash4067 2012
[13] K Shimizu T Horiguchi and Y Koyamada ldquoFrequency trans-lation of light waves by propagation around an optical ringcircuit containing a frequency shifter 1 Experimentrdquo AppliedOptics vol 32 pp 6718ndash6726 1993
[14] E L Wooten K M Kissa A Yi-Yan et al ldquoA review of lithiumniobate modulators for fiber-optic communications systemsrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 6no 1 pp 69ndash82 2000
[15] P Yao R Shireen J Macario C A Schuctz S Shi and D WPrather ldquoDesign fabrication and characterization of LiNbO
3
optical modulator for high-sensitivity mmW imaging systemrdquoin Passive Millimeter-Wave Imaging Technology XI vol 6948 ofProceedings of SPIE March 2008
[16] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgeelani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overfiber-wireless systemrdquo Optics amp Laser Technology vol 47 pp347ndash354 2013
14 The Scientific World Journal
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
Figure 5 The fiber nonlinearity effect on the system performance
The wireless end-user will receive the three MIMO signalsand demodulate them using the suitable QAMdemodulationand MIMO decoding techniques
5 System Performance Evaluation
In this work the communication system is designed toprovide a data rate of 1 Gbs for each 16-QAMwirelessMIMOsignal Figure 3 in the inset (vi) shows the input opticalpower to the optical fiber where the three modulated opticalsignals with the downlink wavelengths 120582
1198891 1205821198892 and 120582
1198893
are coupled to propagate through 20 km optical fiber Thetotal input power of the three optical signals is 1626 dBmaccording to the simulation calculations for both RF carrierfrequencies of 24GHz and 5GHzThis power is suitable to belaunched to avoid the nonlinear effects along the optical linkFigure 5 shows the system performance at different launchedoptical powers Nonlinearity of the fiber negatively affects thesystem performance when the launched optical powers aregreater than 108 dBm and 79 dBm at the carrier frequenciesof 24GHz and 50GHz respectively
To evaluate the performance of the proposed techniqueFigures 6(a) and 6(b) show the BER performance versus thereceived optical power at the receiver for the three wirelessMIMO signals (MIMO
1 MIMO
2 andMIMO
3) at the carrier
frequencies 24GHz and 5GHz respectively The powersensitivity differences of the receivers for the three MIMOsignals are small especially between the two MIMO signals(MIMO
1and MIMO
2) The maximum power penalties of
347 dB and 4 dB are recorded at BER of 10minus9 for the carrierfrequencies of 24GHz and 5GHz receptively
Figure 7 shows the system performance at three differentfiber lengths (20 km 30 km and 50 km) of the optical fiber Inthe proposed system the fiber length of 50 kmhas slight effecton the performance of the transmitted optical signals whichcarry the wireless MIMO signals The system performance
deteriorates progressively when the access distance becomeslonger than 50 km
In addition the system performance is analyzed by usingdifferent wavelength interleaves between the optical carrierfrequency (or RF clock frequency 119891
119900) Figure 8 shows the
systemperformance at differentwavelength interleaves (Δ119891 =
15 25 and 50GHz which are compatible with Δ120582 = 01202 and 04 nm resp) When the wavelength interleaves aresmaller than 15GHz the system performance will degradeand the error floor clearly appears
Figures 9(a)ndash9(c) show 1Gbs 16-QAM constellationdiagrams for the received MIMO signals MIMO
1 MIMO
2
and MIMO3 respectively at 24GHz Clear scatter-plots are
achieved at EVM values of minus208780 dB minus202873 dB andminus212961 dB for MIMO
1 MIMO
2 and MIMO
3 respectively
So the proposed technique has achieved a good performanceof transmitting wireless MIMO signals over the optical fiberat the carrier frequencies 24GHz and 5GHz The EVMs arecalculated considering the following equation [21]
EVM (dB) = 10 sdot log10[sum119872
119896=1
1003816100381610038161003816119878119905119909119896 minus 119878119903119909119896
where EVM is the value of the difference between a collectionof received symbols and transmitted or ideal symbols 119878
119905119909119896
is the corresponding transmitted symbol of the constellationassociated with the 119896th symbol 119878
119903119909119896is the received symbol
associated with 119878119905119909119896
and119872 is the number of the symbols forthe inphase-quadrature constellation
Figures 10(a)ndash10(c) show the eye diagrams of the 119868-branch of the received 16-QAMbaseband signals forMIMO
1
MIMO2 and MIMO
3 respectively Also Figures 11(a)ndash11(c)
show the eye diagrams of the 119876-branch of the received 16-QAM baseband signals for MIMO
1 MIMO
2 and MIMO
3
respectively The eye diagrams of both 119868-branch and 119876-branch of the received wireless MIMO signals at the receivershow slight differences and good quality communicationsystem at a BER around of 10minus9 The BER are calculatedaccording to (15) [22]
where 119876 is the number of signal levels within each branchof the constellation diagram log
2119872 is the amount of bits
encoded into one QAM symbol and 119896 is a modulationformat-dependent factor giving the relationship betweenmaximum field magnitude and average overall119872 field mag-nitudes defined by the constellation diagram for the chosenmodulation formatThis factor is calculated according to (15)
Figure 7The system performance at different lengths of the opticalfiber
to be 6(radic5+2) for 16-QAMThe 119878119905119909119894
is the ideal transmittedfield vector and 119878
119905119909max is the field vector of the outermostconstellation point In this paper the performance of EVMand the BER is evaluated for the 16-QAM MIMO signalswithout using forward error correction (FEC) techniques
6 Transmission of More Wireless MIMOSignals over Optical Fiber
Figure 12 shows the proposed OFU technique to transmitfive wireless MIMO signals over fiber At the OLT the DAM
Received optical powerminus20 minus18 minus16 minus14 minus12 minus10 minus8 minus6
10minus20
10minus18
10minus16
10minus14
10minus12
10minus10
10minus8
10minus6
10minus4
10minus2
100
BER
Δf = 15GHzΔf = 25GHzΔf = 50GHz
Figure 8 The system performance at different wavelength inter-leaves
is injected by LD with the wavelength 120582119889 The DAM is a
LN-MZM Adjusting the parameters of the DAM to suitablevalues can generate multiple wavelengths The dominantwavelengths are considered and the remaining outside wave-lengths are neglected because of their very small magnitudesThe OLT allocates five downlink wavelengths (120582
1198891 1205821198892 1205821198893
1205821198894 and 120582
1198895) which are used for downstream modulation
To generate five dominant wavelengths the values of DAMparameters are configured as minus05 V 05 V DC bias voltagesare applied to respectively first and second arms of theLN-MZM the RF clock voltage with frequency of 119891
119900drives
10 The Scientific World Journal
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(a)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)(b)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(c)
Figure 9 Constellation diagrams of the demodulated 16-QAMMIMO signals (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
to the DAM and the DC and RF switching voltages areset to 4V and 2V respectively The wavelength interleavesbetween the five generatedwavelengthswhich are equal to thefrequency of the sinusoidal clock 119891
119900 The power magnitudes
of the fivewavelengths are approximately equal and the centerwavelength 120582
1198893has maximum value The difference between
this and the others is around 6 dB To get balanced powermagnitudes an optical attenuator is used in path of the centerwavelength after IL as shown in Figure 12 Each generatedwavelengthmodulates theMIMO signal by using IMThefive
modulated optical signals propagate along the same opticalfiber
The receiver receives the optical downstream and theninterleaves it into the five modulated optical signals withthe wavelength 120582
1198891 1205821198892 1205821198893 1205821198894 and 120582
1198895as shown in
Figure 12The receiver then downconverts the fivemodulatedoptical signals directly to the suitable electrical signals byusing an optical receiver for each signalThe electrical signalsare then band-pass filtered according to the allocated RFcarrier frequency 119891
119888by using BPFs to get the original five
The Scientific World Journal 11
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 10 Eye diagrams of the 119868-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
wireless MIMO signals MIMO1 MIMO
2 MIMO
3 MIMO
4
and MIMO5
7 Conclusions
The novel OFU technique is proposed to solve the problemof wireless MIMO signals transmission over a single opticalfiberThree wireless 16-QAMMIMO signals have been trans-mitted over a 20 km SMF using the OFU technique Thesewireless MIMO signals were modulated using the carrier
frequency of 24GHz or 5GHz at data rate of 1 Gbs for eachsignal The physical layer performance has been reported interms of the BER at different RF carrier frequencies differentaccess distances and different wavelength interleaves Inaddition the EVM and the eye diagrams are analyzed in thisstudy
The proposed approach highly suppressed the crosstalkbetween different MIMO signals with the same RF carrierfrequency since each MIMO signal is carried on a spe-cific optical wavelength While the ESSB-FT technique [10]
12 The Scientific World Journal
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 11 Eye diagrams of the 119876-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
requires a number of low-frequency LOs and electrical BPFsat the transmitter and the receiver the OFU technique doesnot require low-frequency LOs at the transmitter and thereceiver or electrical BPFs at the transmitter Less numberof electrical BPFs is required at the receiver in the proposedtechnique However a number of PDs are required at thereceiver which is equal to the number of MIMO signals Theproposed system supports many wavelengths for carrying
multiple wireless MIMO signals over the fiber using singleLD The novel technique provides a spectral efficient andreliable FiWi system
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
The Scientific World Journal 13
IM
IM
IM
IM
IM
DAM
fo
120582d3
120582d4
120582d5
Transmitter
120582d
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
120582d1
120582d2
Bias
Bias
Bias
Bias
Bias
AWG
RF amplifier
RF amplifier
RF amplifier
RF amplifier
RF amplifier
fc
fc
fc
fc
fc
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalfiber
BPF
BPF
BPF
BPF
BPF
IL
IL
Receiver
LD 120582d3
120582d4
120582d5
120582d1
120582d2
Optical attenuator
+
+
+
+
+minus70
minus50
minus30
minus10
0
minus20
minus40
minus60
1929T 193T 1931T 1932T 1933T
Pow
er (d
Bm)
Frequency (Hz)
Figure 12 Transmission of five wireless MIMO signals over fiber using the novel approach
Acknowledgments
This work is supported by Universiti Teknologi Malaysia(UTM) under the Postdoctoral fellowship scheme Theauthors greatly appreciate UTM and Photonics ResearchLaboratory for providing the facilities which enabled themto accomplish this work They would also like to thank theMinistry of Science Technology and Innovation (MOSTI)Malaysia for sponsoring this work under Project vote no73720
References
[1] L Kazovsky S-W Wong T Ayhan K M Albeyoglu MR N Ribeiro and A Shastri ldquoHybrid optical-wireless accessnetworksrdquo Proceedings of the IEEE vol 100 no 5 pp 1197ndash12252012
[2] R Q Shaddad A B Mohammad and AM Al-hetar ldquoAnalysisof physical layer performance of hybrid optical-wireless accessnetworkrdquo Optics Communications vol 284 no 20 pp 4894ndash4899 2011
[3] R Q Shaddad A Bakar Mohammad and A M Al-hetar ldquoPer-formance evaluation for optical backhaul andwireless front-endin hybrid optical-wireless access networkrdquo Optoelectronics andAdvanced Materials Rapid Communications vol 5 no 4 pp376ndash380 2011
[4] C Lim A Nirmalathas M Bakaul et al ldquoFiber-wirelessnetworks and subsystem technologiesrdquo Journal of LightwaveTechnology vol 28 no 4 pp 390ndash405 2010
[5] A Nirmalathas P A Gamage C Lim D Novak and RWaterhouse ldquoDigitized radio-over-fiber technologies for con-verged optical wireless access networkrdquo Journal of LightwaveTechnology vol 28 no 16 pp 2366ndash2375 2010
[6] Z Jia J Yu G Ellinas and G-K Chang ldquoKey enablingtechnologies for optical wireless networks optical millimeter-wave generation wavelength reuse and architecturerdquo Journalof Lightwave Technology vol 25 no 11 pp 3452ndash3471 2007
[7] A Zelst ldquoSystem for transporting multiple radio frequencysignals of a multiple input multiple output wireless communi-cation system tofrom a central processing base stationrdquo USpatent application 20040017785A1 2004
[8] I Seto H Shoki and S Ohshima ldquoOptical subcarrier mul-tiplexing transmission for base station with adaptive arrayantennardquo IEEE Transactions on Microwave Theory and Tech-niques vol 49 no 10 pp 2036ndash2041 2001
[9] C-P Liu and A Seeds ldquoTransmission of MIMO radio signalsover fibre using a novel phase quadrature double sidebandfrequency translation techniquerdquo in Proceedings of the IEEEInternational Meeting on Microwave Photonics Jointly Held withthe Asia-Pacific Microwave Photonics Conference pp 23ndash26Gold Coast Australia October 2008
[10] C-P Liu and A J Seeds ldquoTransmission of wireless MIMO-type signals over a single optical fiber without WDMrdquo IEEETransactions on Microwave Theory and Techniques vol 58 no11 pp 3094ndash3102 2010
[11] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgailani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overoptical fiberrdquo in Proceedings of the 3rd International Conferenceon Photonics (ICP rsquo12) Penang Malaysia 2012
[12] R Shaddad A Mohammad and A Al-hetar ldquoSpectral efficienthybrid wireless optical broadband access network (WOBAN)based on transmission of wireless MIMO OFDM signals overWDM PONrdquo Optics Communications vol 285 no 20 pp4059ndash4067 2012
[13] K Shimizu T Horiguchi and Y Koyamada ldquoFrequency trans-lation of light waves by propagation around an optical ringcircuit containing a frequency shifter 1 Experimentrdquo AppliedOptics vol 32 pp 6718ndash6726 1993
[14] E L Wooten K M Kissa A Yi-Yan et al ldquoA review of lithiumniobate modulators for fiber-optic communications systemsrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 6no 1 pp 69ndash82 2000
[15] P Yao R Shireen J Macario C A Schuctz S Shi and D WPrather ldquoDesign fabrication and characterization of LiNbO
3
optical modulator for high-sensitivity mmW imaging systemrdquoin Passive Millimeter-Wave Imaging Technology XI vol 6948 ofProceedings of SPIE March 2008
[16] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgeelani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overfiber-wireless systemrdquo Optics amp Laser Technology vol 47 pp347ndash354 2013
14 The Scientific World Journal
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
Figure 7The system performance at different lengths of the opticalfiber
to be 6(radic5+2) for 16-QAMThe 119878119905119909119894
is the ideal transmittedfield vector and 119878
119905119909max is the field vector of the outermostconstellation point In this paper the performance of EVMand the BER is evaluated for the 16-QAM MIMO signalswithout using forward error correction (FEC) techniques
6 Transmission of More Wireless MIMOSignals over Optical Fiber
Figure 12 shows the proposed OFU technique to transmitfive wireless MIMO signals over fiber At the OLT the DAM
Received optical powerminus20 minus18 minus16 minus14 minus12 minus10 minus8 minus6
10minus20
10minus18
10minus16
10minus14
10minus12
10minus10
10minus8
10minus6
10minus4
10minus2
100
BER
Δf = 15GHzΔf = 25GHzΔf = 50GHz
Figure 8 The system performance at different wavelength inter-leaves
is injected by LD with the wavelength 120582119889 The DAM is a
LN-MZM Adjusting the parameters of the DAM to suitablevalues can generate multiple wavelengths The dominantwavelengths are considered and the remaining outside wave-lengths are neglected because of their very small magnitudesThe OLT allocates five downlink wavelengths (120582
1198891 1205821198892 1205821198893
1205821198894 and 120582
1198895) which are used for downstream modulation
To generate five dominant wavelengths the values of DAMparameters are configured as minus05 V 05 V DC bias voltagesare applied to respectively first and second arms of theLN-MZM the RF clock voltage with frequency of 119891
119900drives
10 The Scientific World Journal
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(a)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)(b)
minus20m
minus10m
0
10m
20m
minus20m minus10m 0 10m 20mAmplitude-I (au)
Am
plitu
de-Q
(au
)
(c)
Figure 9 Constellation diagrams of the demodulated 16-QAMMIMO signals (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
to the DAM and the DC and RF switching voltages areset to 4V and 2V respectively The wavelength interleavesbetween the five generatedwavelengthswhich are equal to thefrequency of the sinusoidal clock 119891
119900 The power magnitudes
of the fivewavelengths are approximately equal and the centerwavelength 120582
1198893has maximum value The difference between
this and the others is around 6 dB To get balanced powermagnitudes an optical attenuator is used in path of the centerwavelength after IL as shown in Figure 12 Each generatedwavelengthmodulates theMIMO signal by using IMThefive
modulated optical signals propagate along the same opticalfiber
The receiver receives the optical downstream and theninterleaves it into the five modulated optical signals withthe wavelength 120582
1198891 1205821198892 1205821198893 1205821198894 and 120582
1198895as shown in
Figure 12The receiver then downconverts the fivemodulatedoptical signals directly to the suitable electrical signals byusing an optical receiver for each signalThe electrical signalsare then band-pass filtered according to the allocated RFcarrier frequency 119891
119888by using BPFs to get the original five
The Scientific World Journal 11
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 10 Eye diagrams of the 119868-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
wireless MIMO signals MIMO1 MIMO
2 MIMO
3 MIMO
4
and MIMO5
7 Conclusions
The novel OFU technique is proposed to solve the problemof wireless MIMO signals transmission over a single opticalfiberThree wireless 16-QAMMIMO signals have been trans-mitted over a 20 km SMF using the OFU technique Thesewireless MIMO signals were modulated using the carrier
frequency of 24GHz or 5GHz at data rate of 1 Gbs for eachsignal The physical layer performance has been reported interms of the BER at different RF carrier frequencies differentaccess distances and different wavelength interleaves Inaddition the EVM and the eye diagrams are analyzed in thisstudy
The proposed approach highly suppressed the crosstalkbetween different MIMO signals with the same RF carrierfrequency since each MIMO signal is carried on a spe-cific optical wavelength While the ESSB-FT technique [10]
12 The Scientific World Journal
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 11 Eye diagrams of the 119876-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
requires a number of low-frequency LOs and electrical BPFsat the transmitter and the receiver the OFU technique doesnot require low-frequency LOs at the transmitter and thereceiver or electrical BPFs at the transmitter Less numberof electrical BPFs is required at the receiver in the proposedtechnique However a number of PDs are required at thereceiver which is equal to the number of MIMO signals Theproposed system supports many wavelengths for carrying
multiple wireless MIMO signals over the fiber using singleLD The novel technique provides a spectral efficient andreliable FiWi system
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
The Scientific World Journal 13
IM
IM
IM
IM
IM
DAM
fo
120582d3
120582d4
120582d5
Transmitter
120582d
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
120582d1
120582d2
Bias
Bias
Bias
Bias
Bias
AWG
RF amplifier
RF amplifier
RF amplifier
RF amplifier
RF amplifier
fc
fc
fc
fc
fc
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalfiber
BPF
BPF
BPF
BPF
BPF
IL
IL
Receiver
LD 120582d3
120582d4
120582d5
120582d1
120582d2
Optical attenuator
+
+
+
+
+minus70
minus50
minus30
minus10
0
minus20
minus40
minus60
1929T 193T 1931T 1932T 1933T
Pow
er (d
Bm)
Frequency (Hz)
Figure 12 Transmission of five wireless MIMO signals over fiber using the novel approach
Acknowledgments
This work is supported by Universiti Teknologi Malaysia(UTM) under the Postdoctoral fellowship scheme Theauthors greatly appreciate UTM and Photonics ResearchLaboratory for providing the facilities which enabled themto accomplish this work They would also like to thank theMinistry of Science Technology and Innovation (MOSTI)Malaysia for sponsoring this work under Project vote no73720
References
[1] L Kazovsky S-W Wong T Ayhan K M Albeyoglu MR N Ribeiro and A Shastri ldquoHybrid optical-wireless accessnetworksrdquo Proceedings of the IEEE vol 100 no 5 pp 1197ndash12252012
[2] R Q Shaddad A B Mohammad and AM Al-hetar ldquoAnalysisof physical layer performance of hybrid optical-wireless accessnetworkrdquo Optics Communications vol 284 no 20 pp 4894ndash4899 2011
[3] R Q Shaddad A Bakar Mohammad and A M Al-hetar ldquoPer-formance evaluation for optical backhaul andwireless front-endin hybrid optical-wireless access networkrdquo Optoelectronics andAdvanced Materials Rapid Communications vol 5 no 4 pp376ndash380 2011
[4] C Lim A Nirmalathas M Bakaul et al ldquoFiber-wirelessnetworks and subsystem technologiesrdquo Journal of LightwaveTechnology vol 28 no 4 pp 390ndash405 2010
[5] A Nirmalathas P A Gamage C Lim D Novak and RWaterhouse ldquoDigitized radio-over-fiber technologies for con-verged optical wireless access networkrdquo Journal of LightwaveTechnology vol 28 no 16 pp 2366ndash2375 2010
[6] Z Jia J Yu G Ellinas and G-K Chang ldquoKey enablingtechnologies for optical wireless networks optical millimeter-wave generation wavelength reuse and architecturerdquo Journalof Lightwave Technology vol 25 no 11 pp 3452ndash3471 2007
[7] A Zelst ldquoSystem for transporting multiple radio frequencysignals of a multiple input multiple output wireless communi-cation system tofrom a central processing base stationrdquo USpatent application 20040017785A1 2004
[8] I Seto H Shoki and S Ohshima ldquoOptical subcarrier mul-tiplexing transmission for base station with adaptive arrayantennardquo IEEE Transactions on Microwave Theory and Tech-niques vol 49 no 10 pp 2036ndash2041 2001
[9] C-P Liu and A Seeds ldquoTransmission of MIMO radio signalsover fibre using a novel phase quadrature double sidebandfrequency translation techniquerdquo in Proceedings of the IEEEInternational Meeting on Microwave Photonics Jointly Held withthe Asia-Pacific Microwave Photonics Conference pp 23ndash26Gold Coast Australia October 2008
[10] C-P Liu and A J Seeds ldquoTransmission of wireless MIMO-type signals over a single optical fiber without WDMrdquo IEEETransactions on Microwave Theory and Techniques vol 58 no11 pp 3094ndash3102 2010
[11] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgailani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overoptical fiberrdquo in Proceedings of the 3rd International Conferenceon Photonics (ICP rsquo12) Penang Malaysia 2012
[12] R Shaddad A Mohammad and A Al-hetar ldquoSpectral efficienthybrid wireless optical broadband access network (WOBAN)based on transmission of wireless MIMO OFDM signals overWDM PONrdquo Optics Communications vol 285 no 20 pp4059ndash4067 2012
[13] K Shimizu T Horiguchi and Y Koyamada ldquoFrequency trans-lation of light waves by propagation around an optical ringcircuit containing a frequency shifter 1 Experimentrdquo AppliedOptics vol 32 pp 6718ndash6726 1993
[14] E L Wooten K M Kissa A Yi-Yan et al ldquoA review of lithiumniobate modulators for fiber-optic communications systemsrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 6no 1 pp 69ndash82 2000
[15] P Yao R Shireen J Macario C A Schuctz S Shi and D WPrather ldquoDesign fabrication and characterization of LiNbO
3
optical modulator for high-sensitivity mmW imaging systemrdquoin Passive Millimeter-Wave Imaging Technology XI vol 6948 ofProceedings of SPIE March 2008
[16] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgeelani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overfiber-wireless systemrdquo Optics amp Laser Technology vol 47 pp347ndash354 2013
14 The Scientific World Journal
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
Figure 9 Constellation diagrams of the demodulated 16-QAMMIMO signals (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
to the DAM and the DC and RF switching voltages areset to 4V and 2V respectively The wavelength interleavesbetween the five generatedwavelengthswhich are equal to thefrequency of the sinusoidal clock 119891
119900 The power magnitudes
of the fivewavelengths are approximately equal and the centerwavelength 120582
1198893has maximum value The difference between
this and the others is around 6 dB To get balanced powermagnitudes an optical attenuator is used in path of the centerwavelength after IL as shown in Figure 12 Each generatedwavelengthmodulates theMIMO signal by using IMThefive
modulated optical signals propagate along the same opticalfiber
The receiver receives the optical downstream and theninterleaves it into the five modulated optical signals withthe wavelength 120582
1198891 1205821198892 1205821198893 1205821198894 and 120582
1198895as shown in
Figure 12The receiver then downconverts the fivemodulatedoptical signals directly to the suitable electrical signals byusing an optical receiver for each signalThe electrical signalsare then band-pass filtered according to the allocated RFcarrier frequency 119891
119888by using BPFs to get the original five
The Scientific World Journal 11
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 10 Eye diagrams of the 119868-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
wireless MIMO signals MIMO1 MIMO
2 MIMO
3 MIMO
4
and MIMO5
7 Conclusions
The novel OFU technique is proposed to solve the problemof wireless MIMO signals transmission over a single opticalfiberThree wireless 16-QAMMIMO signals have been trans-mitted over a 20 km SMF using the OFU technique Thesewireless MIMO signals were modulated using the carrier
frequency of 24GHz or 5GHz at data rate of 1 Gbs for eachsignal The physical layer performance has been reported interms of the BER at different RF carrier frequencies differentaccess distances and different wavelength interleaves Inaddition the EVM and the eye diagrams are analyzed in thisstudy
The proposed approach highly suppressed the crosstalkbetween different MIMO signals with the same RF carrierfrequency since each MIMO signal is carried on a spe-cific optical wavelength While the ESSB-FT technique [10]
12 The Scientific World Journal
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 11 Eye diagrams of the 119876-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
requires a number of low-frequency LOs and electrical BPFsat the transmitter and the receiver the OFU technique doesnot require low-frequency LOs at the transmitter and thereceiver or electrical BPFs at the transmitter Less numberof electrical BPFs is required at the receiver in the proposedtechnique However a number of PDs are required at thereceiver which is equal to the number of MIMO signals Theproposed system supports many wavelengths for carrying
multiple wireless MIMO signals over the fiber using singleLD The novel technique provides a spectral efficient andreliable FiWi system
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
The Scientific World Journal 13
IM
IM
IM
IM
IM
DAM
fo
120582d3
120582d4
120582d5
Transmitter
120582d
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
120582d1
120582d2
Bias
Bias
Bias
Bias
Bias
AWG
RF amplifier
RF amplifier
RF amplifier
RF amplifier
RF amplifier
fc
fc
fc
fc
fc
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalfiber
BPF
BPF
BPF
BPF
BPF
IL
IL
Receiver
LD 120582d3
120582d4
120582d5
120582d1
120582d2
Optical attenuator
+
+
+
+
+minus70
minus50
minus30
minus10
0
minus20
minus40
minus60
1929T 193T 1931T 1932T 1933T
Pow
er (d
Bm)
Frequency (Hz)
Figure 12 Transmission of five wireless MIMO signals over fiber using the novel approach
Acknowledgments
This work is supported by Universiti Teknologi Malaysia(UTM) under the Postdoctoral fellowship scheme Theauthors greatly appreciate UTM and Photonics ResearchLaboratory for providing the facilities which enabled themto accomplish this work They would also like to thank theMinistry of Science Technology and Innovation (MOSTI)Malaysia for sponsoring this work under Project vote no73720
References
[1] L Kazovsky S-W Wong T Ayhan K M Albeyoglu MR N Ribeiro and A Shastri ldquoHybrid optical-wireless accessnetworksrdquo Proceedings of the IEEE vol 100 no 5 pp 1197ndash12252012
[2] R Q Shaddad A B Mohammad and AM Al-hetar ldquoAnalysisof physical layer performance of hybrid optical-wireless accessnetworkrdquo Optics Communications vol 284 no 20 pp 4894ndash4899 2011
[3] R Q Shaddad A Bakar Mohammad and A M Al-hetar ldquoPer-formance evaluation for optical backhaul andwireless front-endin hybrid optical-wireless access networkrdquo Optoelectronics andAdvanced Materials Rapid Communications vol 5 no 4 pp376ndash380 2011
[4] C Lim A Nirmalathas M Bakaul et al ldquoFiber-wirelessnetworks and subsystem technologiesrdquo Journal of LightwaveTechnology vol 28 no 4 pp 390ndash405 2010
[5] A Nirmalathas P A Gamage C Lim D Novak and RWaterhouse ldquoDigitized radio-over-fiber technologies for con-verged optical wireless access networkrdquo Journal of LightwaveTechnology vol 28 no 16 pp 2366ndash2375 2010
[6] Z Jia J Yu G Ellinas and G-K Chang ldquoKey enablingtechnologies for optical wireless networks optical millimeter-wave generation wavelength reuse and architecturerdquo Journalof Lightwave Technology vol 25 no 11 pp 3452ndash3471 2007
[7] A Zelst ldquoSystem for transporting multiple radio frequencysignals of a multiple input multiple output wireless communi-cation system tofrom a central processing base stationrdquo USpatent application 20040017785A1 2004
[8] I Seto H Shoki and S Ohshima ldquoOptical subcarrier mul-tiplexing transmission for base station with adaptive arrayantennardquo IEEE Transactions on Microwave Theory and Tech-niques vol 49 no 10 pp 2036ndash2041 2001
[9] C-P Liu and A Seeds ldquoTransmission of MIMO radio signalsover fibre using a novel phase quadrature double sidebandfrequency translation techniquerdquo in Proceedings of the IEEEInternational Meeting on Microwave Photonics Jointly Held withthe Asia-Pacific Microwave Photonics Conference pp 23ndash26Gold Coast Australia October 2008
[10] C-P Liu and A J Seeds ldquoTransmission of wireless MIMO-type signals over a single optical fiber without WDMrdquo IEEETransactions on Microwave Theory and Techniques vol 58 no11 pp 3094ndash3102 2010
[11] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgailani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overoptical fiberrdquo in Proceedings of the 3rd International Conferenceon Photonics (ICP rsquo12) Penang Malaysia 2012
[12] R Shaddad A Mohammad and A Al-hetar ldquoSpectral efficienthybrid wireless optical broadband access network (WOBAN)based on transmission of wireless MIMO OFDM signals overWDM PONrdquo Optics Communications vol 285 no 20 pp4059ndash4067 2012
[13] K Shimizu T Horiguchi and Y Koyamada ldquoFrequency trans-lation of light waves by propagation around an optical ringcircuit containing a frequency shifter 1 Experimentrdquo AppliedOptics vol 32 pp 6718ndash6726 1993
[14] E L Wooten K M Kissa A Yi-Yan et al ldquoA review of lithiumniobate modulators for fiber-optic communications systemsrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 6no 1 pp 69ndash82 2000
[15] P Yao R Shireen J Macario C A Schuctz S Shi and D WPrather ldquoDesign fabrication and characterization of LiNbO
3
optical modulator for high-sensitivity mmW imaging systemrdquoin Passive Millimeter-Wave Imaging Technology XI vol 6948 ofProceedings of SPIE March 2008
[16] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgeelani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overfiber-wireless systemrdquo Optics amp Laser Technology vol 47 pp347ndash354 2013
14 The Scientific World Journal
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
Figure 10 Eye diagrams of the 119868-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
wireless MIMO signals MIMO1 MIMO
2 MIMO
3 MIMO
4
and MIMO5
7 Conclusions
The novel OFU technique is proposed to solve the problemof wireless MIMO signals transmission over a single opticalfiberThree wireless 16-QAMMIMO signals have been trans-mitted over a 20 km SMF using the OFU technique Thesewireless MIMO signals were modulated using the carrier
frequency of 24GHz or 5GHz at data rate of 1 Gbs for eachsignal The physical layer performance has been reported interms of the BER at different RF carrier frequencies differentaccess distances and different wavelength interleaves Inaddition the EVM and the eye diagrams are analyzed in thisstudy
The proposed approach highly suppressed the crosstalkbetween different MIMO signals with the same RF carrierfrequency since each MIMO signal is carried on a spe-cific optical wavelength While the ESSB-FT technique [10]
12 The Scientific World Journal
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(a)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(b)
0 05 1
minus20m
minus10m
0
10m
20m
Am
plitu
de (a
u)
0 05 1
Time (bit period)
(c)
Figure 11 Eye diagrams of the 119876-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
requires a number of low-frequency LOs and electrical BPFsat the transmitter and the receiver the OFU technique doesnot require low-frequency LOs at the transmitter and thereceiver or electrical BPFs at the transmitter Less numberof electrical BPFs is required at the receiver in the proposedtechnique However a number of PDs are required at thereceiver which is equal to the number of MIMO signals Theproposed system supports many wavelengths for carrying
multiple wireless MIMO signals over the fiber using singleLD The novel technique provides a spectral efficient andreliable FiWi system
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
The Scientific World Journal 13
IM
IM
IM
IM
IM
DAM
fo
120582d3
120582d4
120582d5
Transmitter
120582d
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
120582d1
120582d2
Bias
Bias
Bias
Bias
Bias
AWG
RF amplifier
RF amplifier
RF amplifier
RF amplifier
RF amplifier
fc
fc
fc
fc
fc
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalfiber
BPF
BPF
BPF
BPF
BPF
IL
IL
Receiver
LD 120582d3
120582d4
120582d5
120582d1
120582d2
Optical attenuator
+
+
+
+
+minus70
minus50
minus30
minus10
0
minus20
minus40
minus60
1929T 193T 1931T 1932T 1933T
Pow
er (d
Bm)
Frequency (Hz)
Figure 12 Transmission of five wireless MIMO signals over fiber using the novel approach
Acknowledgments
This work is supported by Universiti Teknologi Malaysia(UTM) under the Postdoctoral fellowship scheme Theauthors greatly appreciate UTM and Photonics ResearchLaboratory for providing the facilities which enabled themto accomplish this work They would also like to thank theMinistry of Science Technology and Innovation (MOSTI)Malaysia for sponsoring this work under Project vote no73720
References
[1] L Kazovsky S-W Wong T Ayhan K M Albeyoglu MR N Ribeiro and A Shastri ldquoHybrid optical-wireless accessnetworksrdquo Proceedings of the IEEE vol 100 no 5 pp 1197ndash12252012
[2] R Q Shaddad A B Mohammad and AM Al-hetar ldquoAnalysisof physical layer performance of hybrid optical-wireless accessnetworkrdquo Optics Communications vol 284 no 20 pp 4894ndash4899 2011
[3] R Q Shaddad A Bakar Mohammad and A M Al-hetar ldquoPer-formance evaluation for optical backhaul andwireless front-endin hybrid optical-wireless access networkrdquo Optoelectronics andAdvanced Materials Rapid Communications vol 5 no 4 pp376ndash380 2011
[4] C Lim A Nirmalathas M Bakaul et al ldquoFiber-wirelessnetworks and subsystem technologiesrdquo Journal of LightwaveTechnology vol 28 no 4 pp 390ndash405 2010
[5] A Nirmalathas P A Gamage C Lim D Novak and RWaterhouse ldquoDigitized radio-over-fiber technologies for con-verged optical wireless access networkrdquo Journal of LightwaveTechnology vol 28 no 16 pp 2366ndash2375 2010
[6] Z Jia J Yu G Ellinas and G-K Chang ldquoKey enablingtechnologies for optical wireless networks optical millimeter-wave generation wavelength reuse and architecturerdquo Journalof Lightwave Technology vol 25 no 11 pp 3452ndash3471 2007
[7] A Zelst ldquoSystem for transporting multiple radio frequencysignals of a multiple input multiple output wireless communi-cation system tofrom a central processing base stationrdquo USpatent application 20040017785A1 2004
[8] I Seto H Shoki and S Ohshima ldquoOptical subcarrier mul-tiplexing transmission for base station with adaptive arrayantennardquo IEEE Transactions on Microwave Theory and Tech-niques vol 49 no 10 pp 2036ndash2041 2001
[9] C-P Liu and A Seeds ldquoTransmission of MIMO radio signalsover fibre using a novel phase quadrature double sidebandfrequency translation techniquerdquo in Proceedings of the IEEEInternational Meeting on Microwave Photonics Jointly Held withthe Asia-Pacific Microwave Photonics Conference pp 23ndash26Gold Coast Australia October 2008
[10] C-P Liu and A J Seeds ldquoTransmission of wireless MIMO-type signals over a single optical fiber without WDMrdquo IEEETransactions on Microwave Theory and Techniques vol 58 no11 pp 3094ndash3102 2010
[11] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgailani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overoptical fiberrdquo in Proceedings of the 3rd International Conferenceon Photonics (ICP rsquo12) Penang Malaysia 2012
[12] R Shaddad A Mohammad and A Al-hetar ldquoSpectral efficienthybrid wireless optical broadband access network (WOBAN)based on transmission of wireless MIMO OFDM signals overWDM PONrdquo Optics Communications vol 285 no 20 pp4059ndash4067 2012
[13] K Shimizu T Horiguchi and Y Koyamada ldquoFrequency trans-lation of light waves by propagation around an optical ringcircuit containing a frequency shifter 1 Experimentrdquo AppliedOptics vol 32 pp 6718ndash6726 1993
[14] E L Wooten K M Kissa A Yi-Yan et al ldquoA review of lithiumniobate modulators for fiber-optic communications systemsrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 6no 1 pp 69ndash82 2000
[15] P Yao R Shireen J Macario C A Schuctz S Shi and D WPrather ldquoDesign fabrication and characterization of LiNbO
3
optical modulator for high-sensitivity mmW imaging systemrdquoin Passive Millimeter-Wave Imaging Technology XI vol 6948 ofProceedings of SPIE March 2008
[16] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgeelani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overfiber-wireless systemrdquo Optics amp Laser Technology vol 47 pp347ndash354 2013
14 The Scientific World Journal
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
Figure 11 Eye diagrams of the 119876-branch of the demodulated 16 QAM baseband signals for (a) MIMO1 (b) MIMO
2 and (c) MIMO
3
requires a number of low-frequency LOs and electrical BPFsat the transmitter and the receiver the OFU technique doesnot require low-frequency LOs at the transmitter and thereceiver or electrical BPFs at the transmitter Less numberof electrical BPFs is required at the receiver in the proposedtechnique However a number of PDs are required at thereceiver which is equal to the number of MIMO signals Theproposed system supports many wavelengths for carrying
multiple wireless MIMO signals over the fiber using singleLD The novel technique provides a spectral efficient andreliable FiWi system
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
The Scientific World Journal 13
IM
IM
IM
IM
IM
DAM
fo
120582d3
120582d4
120582d5
Transmitter
120582d
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
MIMO1
MIMO2
MIMO3
MIMO4
MIMO5
120582d1
120582d2
Bias
Bias
Bias
Bias
Bias
AWG
RF amplifier
RF amplifier
RF amplifier
RF amplifier
RF amplifier
fc
fc
fc
fc
fc
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalreceiver
Opticalfiber
BPF
BPF
BPF
BPF
BPF
IL
IL
Receiver
LD 120582d3
120582d4
120582d5
120582d1
120582d2
Optical attenuator
+
+
+
+
+minus70
minus50
minus30
minus10
0
minus20
minus40
minus60
1929T 193T 1931T 1932T 1933T
Pow
er (d
Bm)
Frequency (Hz)
Figure 12 Transmission of five wireless MIMO signals over fiber using the novel approach
Acknowledgments
This work is supported by Universiti Teknologi Malaysia(UTM) under the Postdoctoral fellowship scheme Theauthors greatly appreciate UTM and Photonics ResearchLaboratory for providing the facilities which enabled themto accomplish this work They would also like to thank theMinistry of Science Technology and Innovation (MOSTI)Malaysia for sponsoring this work under Project vote no73720
References
[1] L Kazovsky S-W Wong T Ayhan K M Albeyoglu MR N Ribeiro and A Shastri ldquoHybrid optical-wireless accessnetworksrdquo Proceedings of the IEEE vol 100 no 5 pp 1197ndash12252012
[2] R Q Shaddad A B Mohammad and AM Al-hetar ldquoAnalysisof physical layer performance of hybrid optical-wireless accessnetworkrdquo Optics Communications vol 284 no 20 pp 4894ndash4899 2011
[3] R Q Shaddad A Bakar Mohammad and A M Al-hetar ldquoPer-formance evaluation for optical backhaul andwireless front-endin hybrid optical-wireless access networkrdquo Optoelectronics andAdvanced Materials Rapid Communications vol 5 no 4 pp376ndash380 2011
[4] C Lim A Nirmalathas M Bakaul et al ldquoFiber-wirelessnetworks and subsystem technologiesrdquo Journal of LightwaveTechnology vol 28 no 4 pp 390ndash405 2010
[5] A Nirmalathas P A Gamage C Lim D Novak and RWaterhouse ldquoDigitized radio-over-fiber technologies for con-verged optical wireless access networkrdquo Journal of LightwaveTechnology vol 28 no 16 pp 2366ndash2375 2010
[6] Z Jia J Yu G Ellinas and G-K Chang ldquoKey enablingtechnologies for optical wireless networks optical millimeter-wave generation wavelength reuse and architecturerdquo Journalof Lightwave Technology vol 25 no 11 pp 3452ndash3471 2007
[7] A Zelst ldquoSystem for transporting multiple radio frequencysignals of a multiple input multiple output wireless communi-cation system tofrom a central processing base stationrdquo USpatent application 20040017785A1 2004
[8] I Seto H Shoki and S Ohshima ldquoOptical subcarrier mul-tiplexing transmission for base station with adaptive arrayantennardquo IEEE Transactions on Microwave Theory and Tech-niques vol 49 no 10 pp 2036ndash2041 2001
[9] C-P Liu and A Seeds ldquoTransmission of MIMO radio signalsover fibre using a novel phase quadrature double sidebandfrequency translation techniquerdquo in Proceedings of the IEEEInternational Meeting on Microwave Photonics Jointly Held withthe Asia-Pacific Microwave Photonics Conference pp 23ndash26Gold Coast Australia October 2008
[10] C-P Liu and A J Seeds ldquoTransmission of wireless MIMO-type signals over a single optical fiber without WDMrdquo IEEETransactions on Microwave Theory and Techniques vol 58 no11 pp 3094ndash3102 2010
[11] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgailani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overoptical fiberrdquo in Proceedings of the 3rd International Conferenceon Photonics (ICP rsquo12) Penang Malaysia 2012
[12] R Shaddad A Mohammad and A Al-hetar ldquoSpectral efficienthybrid wireless optical broadband access network (WOBAN)based on transmission of wireless MIMO OFDM signals overWDM PONrdquo Optics Communications vol 285 no 20 pp4059ndash4067 2012
[13] K Shimizu T Horiguchi and Y Koyamada ldquoFrequency trans-lation of light waves by propagation around an optical ringcircuit containing a frequency shifter 1 Experimentrdquo AppliedOptics vol 32 pp 6718ndash6726 1993
[14] E L Wooten K M Kissa A Yi-Yan et al ldquoA review of lithiumniobate modulators for fiber-optic communications systemsrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 6no 1 pp 69ndash82 2000
[15] P Yao R Shireen J Macario C A Schuctz S Shi and D WPrather ldquoDesign fabrication and characterization of LiNbO
3
optical modulator for high-sensitivity mmW imaging systemrdquoin Passive Millimeter-Wave Imaging Technology XI vol 6948 ofProceedings of SPIE March 2008
[16] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgeelani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overfiber-wireless systemrdquo Optics amp Laser Technology vol 47 pp347ndash354 2013
14 The Scientific World Journal
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
Figure 12 Transmission of five wireless MIMO signals over fiber using the novel approach
Acknowledgments
This work is supported by Universiti Teknologi Malaysia(UTM) under the Postdoctoral fellowship scheme Theauthors greatly appreciate UTM and Photonics ResearchLaboratory for providing the facilities which enabled themto accomplish this work They would also like to thank theMinistry of Science Technology and Innovation (MOSTI)Malaysia for sponsoring this work under Project vote no73720
References
[1] L Kazovsky S-W Wong T Ayhan K M Albeyoglu MR N Ribeiro and A Shastri ldquoHybrid optical-wireless accessnetworksrdquo Proceedings of the IEEE vol 100 no 5 pp 1197ndash12252012
[2] R Q Shaddad A B Mohammad and AM Al-hetar ldquoAnalysisof physical layer performance of hybrid optical-wireless accessnetworkrdquo Optics Communications vol 284 no 20 pp 4894ndash4899 2011
[3] R Q Shaddad A Bakar Mohammad and A M Al-hetar ldquoPer-formance evaluation for optical backhaul andwireless front-endin hybrid optical-wireless access networkrdquo Optoelectronics andAdvanced Materials Rapid Communications vol 5 no 4 pp376ndash380 2011
[4] C Lim A Nirmalathas M Bakaul et al ldquoFiber-wirelessnetworks and subsystem technologiesrdquo Journal of LightwaveTechnology vol 28 no 4 pp 390ndash405 2010
[5] A Nirmalathas P A Gamage C Lim D Novak and RWaterhouse ldquoDigitized radio-over-fiber technologies for con-verged optical wireless access networkrdquo Journal of LightwaveTechnology vol 28 no 16 pp 2366ndash2375 2010
[6] Z Jia J Yu G Ellinas and G-K Chang ldquoKey enablingtechnologies for optical wireless networks optical millimeter-wave generation wavelength reuse and architecturerdquo Journalof Lightwave Technology vol 25 no 11 pp 3452ndash3471 2007
[7] A Zelst ldquoSystem for transporting multiple radio frequencysignals of a multiple input multiple output wireless communi-cation system tofrom a central processing base stationrdquo USpatent application 20040017785A1 2004
[8] I Seto H Shoki and S Ohshima ldquoOptical subcarrier mul-tiplexing transmission for base station with adaptive arrayantennardquo IEEE Transactions on Microwave Theory and Tech-niques vol 49 no 10 pp 2036ndash2041 2001
[9] C-P Liu and A Seeds ldquoTransmission of MIMO radio signalsover fibre using a novel phase quadrature double sidebandfrequency translation techniquerdquo in Proceedings of the IEEEInternational Meeting on Microwave Photonics Jointly Held withthe Asia-Pacific Microwave Photonics Conference pp 23ndash26Gold Coast Australia October 2008
[10] C-P Liu and A J Seeds ldquoTransmission of wireless MIMO-type signals over a single optical fiber without WDMrdquo IEEETransactions on Microwave Theory and Techniques vol 58 no11 pp 3094ndash3102 2010
[11] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgailani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overoptical fiberrdquo in Proceedings of the 3rd International Conferenceon Photonics (ICP rsquo12) Penang Malaysia 2012
[12] R Shaddad A Mohammad and A Al-hetar ldquoSpectral efficienthybrid wireless optical broadband access network (WOBAN)based on transmission of wireless MIMO OFDM signals overWDM PONrdquo Optics Communications vol 285 no 20 pp4059ndash4067 2012
[13] K Shimizu T Horiguchi and Y Koyamada ldquoFrequency trans-lation of light waves by propagation around an optical ringcircuit containing a frequency shifter 1 Experimentrdquo AppliedOptics vol 32 pp 6718ndash6726 1993
[14] E L Wooten K M Kissa A Yi-Yan et al ldquoA review of lithiumniobate modulators for fiber-optic communications systemsrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 6no 1 pp 69ndash82 2000
[15] P Yao R Shireen J Macario C A Schuctz S Shi and D WPrather ldquoDesign fabrication and characterization of LiNbO
3
optical modulator for high-sensitivity mmW imaging systemrdquoin Passive Millimeter-Wave Imaging Technology XI vol 6948 ofProceedings of SPIE March 2008
[16] R Q Shaddad A B Mohammad A M Al-hetar and S AAlgeelani ldquoA novel optical single-sideband frequency transla-tion technique for transmission of wireless MIMO signals overfiber-wireless systemrdquo Optics amp Laser Technology vol 47 pp347ndash354 2013
14 The Scientific World Journal
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
[17] J C Cartledge ldquoPerformance of 10Gbs lightwave systemsbased on lithium niobate Mach-Zehnder modulators withasymmetric Y-branch waveguidesrdquo IEEE Photonics TechnologyLetters vol 7 no 9 pp 1090ndash1092 1995
[18] J Ma J Yu C Yu X Xin J Zeng and L Chen ldquoFiberdispersion influence on transmission of the optical millimeter-waves generated using LN-MZM intensitymodulationrdquo Journalof Lightwave Technology vol 25 no 11 pp 3244ndash3256 2007
[19] A Cuyt V B Petersen B Verdonk H Waadeland and W BJones Handbook of Continued Fractions for Special FunctionsSpringer Berlin Germany 2008
[20] J Ma L Chen X Xin et al ldquoTransmission of a 40GHzoptical millimeter wave generated by quadrupling a 10GHzlocal oscillator via a Mach-Zehnder modulatorrdquo Journal ofOptics A Pure and Applied Optics vol 11 no 6 pp 1ndash7 2009
[21] A Moscoso-Martir I Molina-Fernandez and A Ortega-Monux ldquoSignal constellation distortion and BER degradationdue to hardware impairments in six-port receivers with analogIQ generationrdquo Progress in Electromagnetics Research vol 121pp 225ndash247 2011
[22] D Hillerkuss R Schmogrow T Schellinger et al ldquo26 Tbit sminus1line-rate super-channel transmission utilizing all-optical fastFourier transform processingrdquo Nature Photonics vol 5 no 6pp 364ndash371 2011
