1328 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 29, NO. 6, JUNE 2011

Performance Evaluation of 5 Gbit/s and 10 Gbit/sMobile Optical Wireless Systems Employing Beam

Angle and Power Adaptation with DiversityReceivers

Mohammed T. Alresheedi and Jaafar M.H. Elmirghani, Senior Member IEEE

Abstract—Over the last two decades, indoor optical wireless(OW) systems have operated typically at 30 Mbit/s to 155 Mbit/s.Here, we propose and evaluate for the first time a mobile OWsystem that operates at 5 Gbit/s and 10 Gbit/s. The improvementsin data rates and channel bandwidth are achieved through theintroduction of three approaches: angle diversity, beam angle andbeam power adaptation. We propose a mobile OW system thatemploys beam angle and beam power adaptation in a line stripmultibeam spot diffusing system configuration in conjunctionwith an angle diversity receiver (APA-LSMS) to mitigate thedegradation due to ambient light noise, multipath dispersionand mobility. The performance of our proposed system wasinvestigated through channel and noise modelling. Our resultsshow that the proposed APA-LSMS at a bit rate of 30 Mbit/sachieves about 45 dB signal-to-noise ratio (SNR) gain over apower adaptive line strip multibeam system (PA-LSMS) andoffers 60 dB SNR gain over a conventional diffuse system (CDS)at a 6 m horizontal separation between the transmitter and thereceiver. The SNR is independent of the transmitter location andwhen our methods (angle diversity, beam angle and beam poweradaptations) are implemented, the SNR can be maximized atthe receiver for every transmitter location. The results showan increase in channel bandwidth from 36 MHz (CDS) toapproximately 7.2 GHz in our proposed system (APA-LSMS).These improvements enhance our system and enable it to operateat higher data rates of 5 Gbit/s and 10 Gbit/s.

Index Terms—optical wireless, signal-to-noise ratio (SNR), an-gle diversity detection, beam angle and beam power adaptation.

I. INTRODUCTION

INFRARED (IR) wireless local area network (LAN) sys-tems are attractive due to their potentially high speed

and their use of inexpensive optoelectronic devices such aslight emitting diodes (LEDs) and silicon detectors [1, 2]. OWsystems can support the increased growth of portable wirelessdevices. They use infrared radiation for indoor wireless com-munication. IR offers some potential advantages over radiofrequency (RF) systems, including a huge bandwidth that isunregulated worldwide, and the fact that optical signals donot penetrate walls, which offers a degree of privacy at thephysical layer and reduces interference between neighbouringrooms in different parts of a building. Additionally, OW

Manuscript received 1 June 2010; revised 1 December 2010.M. Alresheedi and J. Elmirghani are with the School of Electronic &

Electrical Engineering, University of Leeds, Leeds, LS2 9JT, UK (e-mail:{ml07mta, j.m.h.elmirghani}@leeds.ac.uk).Digital Object Identifier 10.1109/JSAC.2011.110620.

systems are free from fading [1] and optical transceiver com-ponents (LEDs, PIN detectors) are low in cost compared toradio components. However, there are two major impairmentsassociated with the OW system. When intensity modulationwith direct detection (IM/DD) is employed, the impairmentsinclude shot noise and multipath dispersion. Furthermore, theimpairments connected with an OW channel are not the onlyfactors that limit the OW system; the transmission power inthe OW system is restricted so as to comply with eye and skinsafety regulations [3, 4]

OW transmission links can be classified into two categoriesbased on the path between the transmitter and the receiver:direct LOS systems and non-LOS (diffuse systems). In directLOS systems there is always a direct path between thetransmitter and the receiver, whereby the transmitted signalsreach the receiver directly. Direct-LOS links provide highpower efficiency, and minimize power consumption as wellas multipath dispersion. However, direct LOS links must bealigned prior to use and require an uninterrupted LOS pathbetween the transmitter and the receiver, thus making themsusceptible to shadowing. On the other hand, diffuse or non-LOS systems rely on diffuse reflections from the walls andceiling. They do not rely on the existence of a direct pathbetween the transmitter and the receiver and mitigate shadow-ing through the use of light reflections. Diffuse systems offerboth robust links and protection against direct beam blockage.However, the transmitted signal in the diffuse system reachesthe receiver through a number of different paths which resultsin pulse spread, which in turn leads to inter-symbol inter-ference (ISI). The effects of multipath propagation can bereduced by employing a multibeam transmitter, which can alsobe used to enhance the performance of the OW system [3]. Themultibeam transmitter was first proposed by Yun and Kevhardin order to provide multiple diffusing spots pointed in differentdirections in a room, thus mitigating the multipath distortionand maximising the SNR at the receiver [5]. Spot diffusingbeams can be produced by using a holographic diffuser infront of the emitter. This produces multiple diffusing spotswhich act as secondary transmitters [3, 5]. Previous workin this area has shown that significant improvements can beachieved by employing a line strip multibeam system (LSMS)transmitter or a beam clustering method (BCM) transmitter [6,7]. Moreover, diversity detection is considered to be one of

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ALRESHEEDI and ELMIRGHANI: PERFORMANCE EVALUATION OF 5 GBIT/S AND 10 GBIT/S MOBILE OPTICAL WIRELESS SYSTEMS 1329

the most efficient and simplest techniques that can be usedin order to reduce the impact of pulse spread as well asdirectional ambient light noise. Furthermore, it has been shownthat beam steering using a ferroelectric liquid crystal spatiallight modulator (SLM) in a free space adaptive optical settingis feasible at 1.25 Gb/s [8].Link performance is adversely affected by mobility, thus

there is significant interest in identifying methods to mitigatethe effect of mobility on OW systems. Previous studies [9,10] have shown that adaptively distributing the power amongthe beams in conjunction with diversity detection can signif-icantly improve the SNR in a real environment (where thereis mobility, ambient light noise and multipath propagation).However, despite these studies having achieved significant im-provements, the SNR still degrades due to transmitter mobility(where the transmitter and receiver are placed far away fromeach other) and shadowing. In these studies, the positions ofthe spots are fixed. In the case of the adaptive beam clusteringmethod (ABCM), when the transmitter and the receiver arefar from each other, the spots are only distributed near thetransmitter; on the ceiling and the corner adjacent to thetransmitter. In this case, the fixed beam angle associated withbeam power adaptation does not help much. To overcomethis problem, as well as mitigate the SNR degradation dueto transmitter mobility, ’angle adaptation’ is introduced toprovide a degree of freedom in order to optimize the positionof spots (redistribute spots near the receiver position regardlessof the transmitter position).In this work, we introduce beam angle and beam power

adaptations in conjunction with angle diversity. Our goal isto optimize the distribution of spots in a room, employing amultibeam transmitter whose beam angles and beam powerscan be adapted and controlled by a digital signal processor(DSP). This can reduce the negative effect of mobility aswell as improve the performance of the system in a realenvironment. Our simulation results showed that beam powerand beam angle adaptations coupled with diversity receiverscan significantly improve the bandwidth efficiency of OWsystems. Beam angle adaptation can help to identify theoptimum spot location for the receiver by using a single spotand scanning this spot along a number of locations on theceiling and the walls. We model two OW configurations, aPA-LSMS and an APA-LSMS, coupled with three branchedangle diversity receivers. For comparison purposes, a CDSand a LSMS, with three branched angle diversity receiversare modelled and compared to our system. All the systemsare simulated at a 30 Mbit/s bit rate to facilitate comparisonwith results in the literature. The PA-LSMS and APA-LSMSare also simulated at 5 Gbit/s and 10 Gbit/s bit rates. TheAPA-LSMS in conjunction with three diversity receivers offersalmost a 45 dB SNR gain over the PA-LSMS in a worst casescenario. Furthermore, the proposed APA-LSMS offers a 60dB SNR gain over the CDS at a 6m horizontal separationbetween the transmitter and the receiver. The proposed APA-LSMS can also reduce the delay spread by a factor of 60compared to the CDS. A significant improvement in channelbandwidth from 36 MHz (CDS) to 7.2 GHz can be achievedby our proposed system. These significant improvements inSNR, delay spread and channel bandwidth enable our system

to operate at higher data rates, i.e., 5 Gbit/s and 10 Gbit/s.Section II of this paper presents a channel model for the OWsystem. The angle diversity receiver is discussed in SectionIII. The proposed APA-LSMS is summarized in Section IV.Simulation results are presented and conclusions are drawn inSections V and VI, respectively.

II. OW SYSTEM MODEL

For OW communication links, IM/DD is considered to bethe most viable method, in which the desired waveform ismodulated onto the instantaneous power. The indoor OWIM/DD channel can be fully characterized by its impulseresponse h(t). It can be modelled as a baseband linear system[11] given by

I(t, Az,El) =M∑m=1

Rx(t) ⊗ hm +M∑m=1

nm(t, Az,El) (1)

where t is the absolute time, Az and El are the directionsof arrival in the azimuth and elevation, respectively,M is thetotal number of receiving elements, x(t) is the transmittedinstantaneous optical power, ⊗ denotes convolution, R is thephotodetector responsivity (R = 0.54 A/W) and I(t, Az,El)is the received instantaneous current in the photodetector ata particular position due to M reflecting elements. Finally,n(t, Az,El) is the background noise which is independent ofthe received signal. Several parameters can be derived fromthe impulse response including the 3dB channel bandwidthand delay spread. The root mean square (rms) delay spread isa good measure of the signal pulse spread due to multipathpropagation. The delay spread can be written as [11]

D =

√∑(ti − μ)2P 2

ri∑P 2ri

, where μ =∑tiP

2ri∑

P 2ri

(2)

where the time delay ti is associated with the received powerPri (Pri reflects the impulse response h(t) behaviour) and μis the mean delay. In order to examine the effects of ambientlight noise and multipath dispersion and their impact on thereceived data stream, simulations were conducted in an emptyrectangular room (without furnishings) with dimensions of8m × 4m × 3m (length × width × height). Previous workhas found that the power reflected by elements either on theceiling or walls is in a form close to a Lambertian function [1].Therefore, the reflecting elements from the walls, ceiling andfloor were treated as small emitters that diffuse the receivedsignal in the form of a Lambertian pattern with a reflectivityof 0.8 for ceiling and walls, and 0.3 for the floor. In thiswork, we considered reflections from doors and windowsto be the same as reflections from walls. These reflectingelements are formed by subdividing the walls and ceilinginto small elements (square-shaped reflecting elements) whichact as secondary transmitters. The accuracy of the receivedimpulse response profile is controlled by the size of thesereflecting elements. Therefore, surface elements of 5cm×5cmfor first order reflections and 20cm× 20cm for second orderreflections are used for all configurations. These values havebeen selected to keep the computation time within reasonablelimits. Previous research has found that most of the transmittedpower is within the first and second reflections but that when

1330 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 29, NO. 6, JUNE 2011

it goes beyond the second order it is highly attenuated [1, 4].Therefore, reflections up to the second order are considered inour simulator (we however evaluate the impact of third orderreflections on our high bit rate systems and show that thirdorder reflections have little impact on our adaptive (beam angleand beam power) systems).A simulation tool similar to the one developed by Barry

et al. [4] is used to obtain the received optical power andproduce the impulse response. In order to determine thereceived optical power at the receiver, a ray tracing algorithmwas implemented. The received optical power on a reflectingelement (either walls or ceiling) with an area dA′ can bemodelled as:

dP =n+ 12πR2

1

× PS × cosn(α) × cos(β) × dA′, (3)

where PS is the average transmitted optical power, R1 is thedistance between the transmitter and reflecting element, α isthe angle of incidence with respect to the transmitter’s normal,β is the angle between the reflecting element’s normal andthe incident ray, and n is the mode number that describesthe shape of the transmitted beam. The reflecting elementthen becomes a secondary emitter, where the radiated powerof the reflecting element depends on its reflection coefficient(ρ). Since the reflecting element emits radiation in an idealLambertian distribution, the received power at the detector(non-imaging) is given by (4), where R2 is the distancebetween the reflecting element and the receiver, γ is the anglebetween the reflected ray and the reflecting element’s normaland δ is the angle between the normal to the surface of thedetector and the incident ray. TC is the transmission factorof the concentrator. We compared our simulator results in thecase of the CDS with the experimental and theoretical resultsreported in [4], which showed that there was a good match,giving confidence in the capability of our simulator to evaluateother systems.To quantify our system’s performance under mobility, four

configurations were considered: CDS, LSMS, PA-LSMS andAPA-LSMS in conjunction with different detection techniques.The transmitter was placed in an upright position at twodifferent locations on the communication floor (CF), i.e.,(2m, 4m, 1m) and (2m, 7m, 1m), and emitted 1 W totaloptical power with an ideal Lambertian radiation pattern.Computer-generated holograms can be used to produce staticmultibeam intensities. Power adaptation among the beams canbe implemented by using a liquid crystal device. Liquid crystaldevices can also vary the beam angle if they are used togenerate the 2D holograms. These devices have μs to msresponse time [12]. A feedback channel can be provided byusing one of the beams at low data rate. In order to assessthe system’s performance as well as examine the advantagesof having beam angle and power adaptation with differentreception techniques, for example a diversity receiver, eightspotlights are used (’Philips PAR 38 Economic’ (PAR38)) inour systems which represent one of the most corruptive opticalinterference sources. Each lamp emits an optical power of65 W radiated in the form of a narrow beam-width whichis modelled as a Lambertian radiant intensity with order n =33.1. The spotlights are placed on the ceiling at positions (1m,

1m, 3m), (1m, 3m, 3m), (1m, 5m, 3m), (1m, 7m, 3m), (3m,1m ,3m), (3m, 3m, 3m), (3m, 5m, 3m) and (3m, 7m, 3m).These lamps produced a well-illuminated environment. We donot consider the interference of daylight through windows inthis work. An angle diversity receiver is used to reduce theimpact of background noise as well as multipath dispersion.Angle diversity receivers are discussed in Section III. Moresimulation parameters are given in Table I.

III. ANGLE DIVERSITY RECEIVER

In contrast to the single wide field-of-view (FOV) receiver,angle diversity receivers exploit the fact that the desired signalarrives from different directions than the undesired noise[13]. The design of the angle diversity receivers incorporatesmultiple detectors that are pointed in different directions. Thenarrow FOVs of these detectors are chosen so as to confinethe optical signal and limit the background noise. The receivedoptical signal in each detector can be treated separately, andcan be processed using selection or combining techniques.As illustrated in Fig.1, the three photodetectors are placedon square pyramidal faces. Each branch points in a certaindirection which can be defined by two angles: azimuth (Az)angle and elevation (El) angle. The El of two photodetectorsremains at 35◦ and the detector facing up is set at 90◦. TheAz angles for the three branches are 0◦, 180◦, and 0◦. TheFOVs of these branches are set as follows: two are restrictedto 35◦, whereas the detector facing up is set to 20◦. Thevalues of El, Az and FOV were selected in order to achievethe best SNR [14]. Furthermore, each photodetector employsa compound-parabolic concentrator (CPC), which can collectand concentrate the light from a large input area down into asmaller detector area. The CPC is a non-image concentratorand has an acceptance semi-angle of ψa < 90◦ . Whenthe reception angle δ exceeds the acceptance semi-angle, thetransmission factor (Tc) of the concentrator approaches zero.The transmission factor of the concentrator is given by

Tc(δ) = T

[1 +

(δ

ψa

)2R]−1

, (5)

where T = 0.9 and R = 13 [15]. The CPC has a refractiveindex of N = 1.7 and the entrance area is A = 9π

4 cm2. The

exit area of the CPC is A′ = Asin2(ψa)N2 . In our analysis, each

photodetector is assumed to employ a CPC. The photodetectorfacing up employs a CPC with an acceptance semi-angle ofψa = 20◦ whereas the acceptance semi-angle of each sidephotodetector was restricted to 35◦. Each photodetector isassumed to fit exactly into its corresponding concentrator’sexit area. Therefore, the photodetector facing up has photo-sensitive area of 0.28cm2 whereas each side photodetector hasphotosensitive area of 0.8cm2.

IV. TRANSMITTER CONFIGURATIONS

In this section, three different multibeam transmitter config-urations (LSMS, APA-LSMS, PA-LSMS) in conjunction withangle diversity are presented, evaluated and compared in orderto identify the best geometry for indoor OW under mobility.In addition, the proposed APA-LSMS is compared with theCDS.

ALRESHEEDI and ELMIRGHANI: PERFORMANCE EVALUATION OF 5 GBIT/S AND 10 GBIT/S MOBILE OPTICAL WIRELESS SYSTEMS 1331

dP1 ={ n+1

2π2R21R

22× PS × dA′ × ρ× TC(δ) ×A× cosn(α) × cos(β) × cos(γ) × cos(δ), 0 ≤ δ ≤ ψa

0, δ > ψa(4)

TABLE ISIMULATION PARAMETERS

A. CDS

The conventional diffuse system (CDS) is the basicconfiguration used in diffuse transmission and reception andhas been widely discussed in [1, 16]. It does not rely on adirect path between the transmitter and the receiver. Althoughit can reduce the impact of shadowing through the use oflight reflections, this process causes multipath dispersion.The pure diffuse system uses a single beam transmitter witha wide FOV receiver. The receiver collects the signal after ithas undergone one or more reflections from the ceiling, wallsand room objects. For comparison purposes, a conventionaldiffuse system was simulated determining its channel impulseresponse, 3dB channel bandwidth, delay spread and SNR.

B. LSMS

The LSMS achieves performance improvements overthe CDS by employing multiple beams in OW systems.Multibeam spot diffusing methods have been investigated in[7, 17]. The LSMS in conjunction with an angle diversityreceiver reduces the impact of background noise as well asmultipath dispersion. The LSMS is assumed to produce equalintensity beams, 80× 1, aimed at the middle of the ceiling inthe form of a line strip with 10cm spacing between adjacent

Fig. 1. Physical structure of an angle diversity receiver.

spots on the ceiling when the transmitter is at the centreof the room. These spots operate as secondary transmitters.The positions of the spots change according to transmittermovement. The analysis of LSMS mobility is detailed in [18].

C. PA-LSMS

In contrast to the LSMS, where the transmitter distributesthe total power among the beams equally, the PA-LSMS isbased on an adaptive approach that adjusts the distribution ofthe transmitter power among the beams. These adjustmentsare based on information about the signal quality fed backto the transmitter by the receiver at each location. Beampower adaptation can improve the performance of the spotdiffusing transmitter, especially the mobile transmitter. Insteadof distributing the transmission power (1 W) equally among80 beams (12.5 mW per beam) in the LSMS, the PA-LSMStransmitter varies the power distribution among the beams inorder to optimize the SNR at the receiver. The beam poweradaptation algorithm adapts the transmission power among thebeams based on the following algorithm:

1) Equally distribute the total power among the beams andcompute the received power as well as the SNR at thediversity receiver.

2) Individually turn on each spot.3) Compute the SNR at the three detectors and the SNR af-ter combining the signals using maximum ratio combing(MRC) weights, send a control feedback signal at lowrate to the transmitter about the SNR associated witheach spot.

4) Use the SNR in step 3 as the SNR associated with thespot.

5) Repeat steps 2, 3 and 4 for all the spots.6) Redistribute the transmit power among the spots basedon the SNR ratio among the spots.

1332 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 29, NO. 6, JUNE 2011

The algorithm increases the power allocated to those spotsthat produce higher SNR at the receiver. This algorithm appliesto the single user scenario where the spots nearest to thereceiver are allocated more power. Different methods can beused in a multiuser scenario such as opportunistic scheduling[19]. The adaptive transmission algorithm can be practicallyimplemented by using a liquid crystal device. Liquid crystaldevices readily offer the capability to modulate the beamwithin tens or hundredths of microseconds [12]. The SNRmeasured by the receiver is conveyed to the transmitter viaa feedback link at a low data rate for reliability. This can bea diffuse link, for example implemented by using a separatesource or by using one of the beams.

D. APA-LSMS

An excessively large distance between the nearest diffusingspot on the ceiling or walls and the receiver can lead tosignificant performance degradation. In order to reduce theimpact of this problem we introduce APA-LSMS in conjunc-tion with angle diversity receivers. Previous work has shownthat significant improvement in the OW system SNR can beachieved by employing a power adaptive BCM (ABCM) witha seven-branch diversity receiver [9]. However, despite theSNR being maximized, degradation remains in the systemunder mobility (for example when the transmitter and receiverare at the opposite ends of the room). Beam angle adaptationhelps identify the optimum locations of spots that maximizethe SNR at the receiver. Fig. 2 shows the APA-LSMS mobileOW communication system where the transmitter is placed at(2m, 7m, 1m), multibeam angle and beam power adaptationsare employed and the receiver is placed in the corner (1m,1m, 1m) and utilizes angle diversity with three branches. Thebeam angle and beam power adaptations can be implementedby an adaptive hologram that produces spots whose locationsand intensities can be varied with transmission angles (δx, δy)in the x− y directions.These angles can be varied between (-90◦, 90◦) with respectto the transmitter’s normal in both directions (x−y). They canidentify the optimum locations of the spots, which significantlyenhances the receiver’s SNR. The adaptive hologram producesa single spot which is scanned along a range of rows andcolumns in the ceiling and walls to identify the best SNRlocation for the receiver. This location is used as the centreof the line strip. This technique helps to identify the strongestpath between the transmitter and the receiver. The algorithmused to implement beam angle and beam power adaptations issimilar to the one used for an imaging receiver [18]. However,here we introduce, for the first time, the idea of beam angleand beam power adaptations (APA-LSMS) in conjunction withan angle diversity receiver. The APA-LSMS algorithm, whichis depicted in Fig. 3, adapts the beam angles and beam powersfor a single transmitter and a single receiver as follows:

1) The adaptive hologram generates a single spot whichscans the walls and ceiling by changing the beam angleassociated the spot between −90◦ and 90◦ in steps of2.86◦ (in each step the spot moves 10cm which resultsin a total of 8000 possible locations (40 × 80 locationsin the ceiling, 40×20 locations in the wall xz(y=0,y=8m)

and 80 × 20 locations in the wall yz(x=0,x=4m) )). Ifeach SNR computation is carried out in 1μs, then thetotal adaption time when the receiver moves is 8ms.Pedestrians move typically at a speed of 1m/sec. Ifthe receiver moves by 1m, the SNR penalty (Fig. 12)incurred as a result of using the old beam power and oldbeam angle is less than 3 dB. As such the hologramscan adapt every 1 second (or slightly more frequently ifthe SNR penalty is to be reduced). The 8ms adaptationtime therefore represents an overhead of 0.8% in termsof transmission time. If an SNR penalty lower than 3 dBis desired then Fig. 12 shows how often the system hasto adapt its settings. For example for the SNR penaltyto be below 1 dB, the system has to adapt the beampowers every 0.4m approximately which correspondsto 0.4 second adaptation frequency, which increases theoverhead to 2% which is still acceptable. It should benoted that this adaptation has been done at the rate atwhich the environment changes not at the system’s bitrate. Holograms based on liquid crystal devices capableof adapting within ms times are feasible.

2) It computes the SNR at the receiver for each stepand sends a control feedback signal at low rate to thetransmitter about the SNR associated with each step.

3) It records the transmission angles (δxc, δyc) that maxi-mize the receiver’s SNR, and determines the spot loca-tion (xc, yc, zc).

4) A line strip of spots (80 × 1) is generated with equalpower distribution among the beams whose centre is(xc, yc, zc) starting with an angle of 0.28◦ between thebeams (all spots touch each other in the line, each spothas a diameter of 1cm).

5) It individually turns on each spot, and then computesthe SNR associated with the spot.

6) A control feedback signal is sent at low rate to thetransmitter about the SNR associated with the spot.

7) The SNR in step 5 is used as the SNR associated withthe spot.

8) Steps 5, 6, and 7 are repeated for all the spots.9) The transmit power is redistributed among the spotsbased on the SNR ratio among the spots.

10) The angle between the beams is increased by0.57◦(notice that the angles between the beams areequal), and steps 5 to 9 are repeated.

11) The algorithm stops when the angle between the beamsreaches 2.86◦.

12) The transmitter is specified so that it operates at theoptimum beam angles and powers.

In order to perform steps 5-10, the medium access control(MAC) protocol should include a repetitive training period.This training is required at the low rate at which the environ-ment (channel) changes. The algorithm for beam angle andbeam power adaptations is applied to every single transmitterand single receiver position during-mobility. For beam powerand angle adaptations, we propose that the receiver periodi-cally (namely at 1 second intervals) re-evaluates its SNR andif this has changed significantly (compared to a threshold)

then this change initiates transmitter adaptation. In Fig. 12, anSNR penalty is calculated based on the transmitter using its old

ALRESHEEDI and ELMIRGHANI: PERFORMANCE EVALUATION OF 5 GBIT/S AND 10 GBIT/S MOBILE OPTICAL WIRELESS SYSTEMS 1333

Fig. 2. The APA-LSMS OW communication system.

angle and power settings while in motion. The results showthe SNR penalty incurred as a result of mobility (distancemoved, x-axis) and non-adaptation of weights. The systemdesign should allow a link margin. For example with a linkpower margin of 3 dB, Fig. 12 shows that adaptation has to bedone every time the receiver moves by 1m approximately. Ata pedestrian speed of 1m/s, this corresponds to re-adaptationevery 1 second which is feasible. The transmitter and receiverorientation may affect the line strip system performance.However, during the initialization of the proposed systems,the angle adaptation algorithm turns on one spot and scansthe room to find the optimum location and orientation ofthe spots that maximizes the SNR. The power and angleadaptation algorithms therefore offer a degree of robustnessagainst changes in the receiver orientation however this canbe investigated further.

V. SIMULATION RESULTS

In this section, we examine the performance of all theconfigurations: CDS, LSMS, PA-LSMS and APA-LSMS inthe presence of background noise, multipath propagation andmobility. The results are presented for two different loca-tions when the transmitter is placed on the communicationfloor(CF): at (2m, 4m, 1m) and (2m, 7m, 1m). The resultsof our simulation are compared with the experimental andtheoretical results for the simple CDS reported in [4] and theresults for the LSMS reported in [17]. Good agreement wasobserved, giving confidence in the capability of our simulator.Our results are presented in terms of impulse response, delayspread, 3dB channel bandwidth and SNR.

A. Impulse Response and Delay Spread

The impulse response of three configurations (CDS, LSMSand PA-LSMS in conjunction with an angle diversity receiver)when the transmitter is placed at the centre of the room (2m,4m, 1m) and the receiver is placed in the corner (1m, 1m,

1m) is shown in Fig. 4. Fig. 4 compares the received powerprofile (μW ) as a function of time (ns). In practice, theimpulse response of the OW system is continuous; however,the simulator subdivides reflecting surfaces (ceiling, wallsand floor) into small elements. In order to reduce the effectof discretization, we grouped the received power using a timebin (0.5 ns duration) into a single received power, hence thesmoothness seen in the impulse response. Moreover, a smallertime bin of 0.01 ns was also considered for higher datarates. Reflective elements of 2.5cm × 2.5cm for first orderreflections and 10cm × 10cm for second order reflectionswere used for higher data rates.

The result indicates that the adaptive multibeam transmitter,coupled with the angle diversity receiver is significantly betterthan both the CDS and LSMS. As depicted in Fig. 4, thepower level (μW ) of the PA-LSMS increases by a factorof 3 compared with the LSMS in conjunction with threeangle diversity receivers. This is due to assigning higherpowers to the spots near the receiver, thus increasing thedirect-LOS components at the receiver. This factor can befurther increased by employing ABCM with a seven-branchdiversity receiver. However, power adaptation among thebeams may not help much under mobility. Fig. 5 showsthe impulse responses of the APA-LSMS and PA-LSMS ina worst case scenario (6 m horizontal separation betweentransmitter and receiver). A significant increase is obtained inthe power level by employing beam angle and beam poweradaptations. Previous work [10] has shown that the ABCMin conjunction with a seven-branch diversity receiver canincrease the power level from 0.1 μW (LSMS) to 1 μWin the worst case scenario. As can be seen in Fig. 5, ourproposed APA-LSMS significantly increased the power levelby a factor of 27 compared with ABCM.

For delay spread assessment, Fig. 6 compares the delayspread performance of the CDS, LSMS, PA-LSMS and APA-

1334 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 29, NO. 6, JUNE 2011

Fig. 3. Block diagram of the beam angle and power adaption algorithm.

Fig. 4. Impulse response of the three configurations: CDS, LSMS and PA-LSMS when the transmitter is placed at (2m, 4m, 1m) and the receiver is at(1m, 1m, 1m).

LSMS when the transmitter is stationary at the centre of theroom (2m, 4m, 1m) and the receiver moves along the y-axis inan x=1m line.The CDS shows much more signal delay spreaddue to diffuse transmission and the wide receiver FOV. Thereis a significant reduction in the signal spread for the APA-LSMS. The result shows that the APA-LSMS can reduce thedelay spread from the 0.45 ns offered by the PA-LSMS to 0.04ns. Moreover, the APA-LSMS reduces the delay spread by afactor of 5 compared to the ABCM reported in [10]. Fig. 7shows the delay spread of APA-LSMS with different time binsof 0.5 ns and 0.01 ns. A smaller time bin (0.01 ns) resultedin a slightly higher delay spread compared with a time bin of0.5 ns.

Fig. 5. Impulse response of two configurations: PA-LSMS and APA-LSMSat a transmitter-receiver horizontal separation of 6m.

Fig. 6. Delay spread of four configurations: CDS, LSMS, PA-LSMS andAPA-LSMS when the transmitter is placed at (2m, 4m, 1m) and the receivermoves along x=1m line.

ALRESHEEDI and ELMIRGHANI: PERFORMANCE EVALUATION OF 5 GBIT/S AND 10 GBIT/S MOBILE OPTICAL WIRELESS SYSTEMS 1335

Fig. 7. Delay spread of APA-LSMS using different time bins: 0.5ns and0.01ns.

B. 3dB Channel Bandwidth

The 3 dB channel bandwidth of four configurations whenthe transmitter is stationary at the centre of the room andthe receiver moves along an x = 1m line is depicted inFig. 8. The results demonstrate that, when compared withother systems, the proposed APA-LSMS provides the largestbandwidth. This is due to three factors. Firstly, optimizationof the spots positions in an area on the ceiling and/or walls,whereby the receiver can collect a strong signal through directLOS components from the spots. Secondly, allocation of ahigh power level to the spots nearest to the receiver, whichresults in a strong received power. Thirdly, employment of adiversity receiver which significantly reduces the backgroundnoise collected. The CDS is the basic configuration andwas first investigated in 1979 [1].Our proposed APA-LSMSincreases the bandwidth from the 25.5 MHz offered by theCDS to about 7.2 GHz, see Fig. 9. Our simulation resultsshow that the CDS with a wide FOV at a 6 m transmitter-receiver separation achieves 25.5 MHz bandwidth, which isin good agreement with previous work [4]. The multibeamtransmitter in conjunction with an angle diversity receiverincreases the communication channel bandwidth from thebandwidth offered by the CDS to almost 600 MHz, whichis in good agreement with that reported in [9], see Fig.8.Previous work [20] has shown that adopting a multibeamtransmitter coupled with 7◦ field of view angle diversityreceiver can provide 3dB channel bandwidths of more than2 GHz. Furthermore, recent work has demonstrated anexperimental 1.25Gbit/s OW line of sight system with anangle diversity receiver [21]. However these studies do not useangle and power adaptations in conjunction with the diversityreceiver. When the PA-LSMS replaces the conventionalLSMS, there is significant bandwidth improvement, from 600MHz to approximately 4.2 GHz. This significant increase inchannel bandwidth is due to assigning higher power to thespots nearest to the receiver, which results in high direct LOScomponents from the diffusing spots to the receiver, and isalso due to limiting the rays accepted by employing a narrowfield of view diversity receiver. We assumed that the journey

Fig. 8. 3dB channel bandwidth of four configurations: CDS, LSMS, PA-LSMS and APA-LSMS when the transmitter is placed at (2m, 4m, 1m) andthe receiver moves along x=1m line.

of the beam from the transmitter to the spot location is anideal journey where no power is lost and where the pulsewidth does not increase. This is acceptable since the beamsforming the spots are highly confined. It can be seen thatdistributing the power among the beams equally can resultin wasting power in those spots that are far away from thereceiver, hence limiting the channel bandwidth. Therefore,beam angle and beam power adaptations help to identify theoptimum locations of the spots and assign high powers to thespots nearest to the receiver, thus significantly increasing thechannel bandwidth from 25.5 MHz (CDS with wide FOV) to7.2 GHz in a worst case scenario with APA-LSMS, as shownin Fig. 8. This significant increase in channel bandwidthenables our proposed system to operate at higher data rates,i.e., 5 Gbit/s and 10 Gbit/s. In an optical direct detectionsystem, the optimum receiver bandwidth is 0.7 times the bitrate. This means that a 10 Gbit/s data rate requires a 7 GHzreceiver bandwidth (the 0.7 figure is based on Personik’soptical receiver design [22]).Our proposed APA-LSMS canalready offer a bandwidth of more than 7 GHz, which enablesit to support operations at 5 Gbit/s and 10 Gbit/s.

Third order reflections are also considered at two differentreceiver locations (1m, 1m, 1m) and (1m, 4m, 1m). Table IIshows the delay spread and the channel bandwidth of the pro-posed APA-LSMS with and without third order reflections. Ascan be seen from Table II, the reduction in receiver bandwidthis very small when third order reflections are included.Thisis attributed to beam angle and beam power adaptation whichalign the beam angle and power such that the receiver receivesa strong direct component directly from one or more diffusingspots. This is an important distinction between our proposedsystems and conventional diffuse systems where in the latterthird order reflections may play a significant role at high datarates.

C. SNR Performance Analysis

Indoor OW communication links are strongly impaired bythe shot noise in the receiver’s electronics induced by ambientlight. On-off keying (OOK) is considered to be the simplestmodulation technique for OW systems. OOK employs a rect-angular pulse with duration equal to the bit period. The SNR

1336 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 29, NO. 6, JUNE 2011

Fig. 9. Impulse response and frequency response of CDS and APA-LSMS.

TABLE IIDELAY SPREAD AND 3DB CHANNEL BANDWIDTH OF OUR PROPOSED

APA-LSMS

associated with the received signal can be computed by takinginto account Ps1 and Ps0, the powers associated with logic 1and 0, respectively. The SNR is given by [23]

SNR =(R(Ps1 − Ps0)σ0 + σ1

)2

, (6)

where σ0 and σ1 are the noises associated with the signal andcan be computed from

σ0 =√σ2pr + σ2

bn + σ2s0 and σ1 =

√σ2pr + σ2

bn + σ2s1,

(7)where σpr represents the preamplifier noise component, σbnrepresents the background shot noise component and σso andσs1 represent the shot noise associated with the received signal(Ps0 and Ps1) respectively. This signal-dependent noise (σ2

si)

is very small and can be neglected based on the experimentalresults reported in [24]. In this study, we used the p-i-n FETtransimpedance preamplifier used in [25]. The gate leakageand 1/f noise of the FET were neglected. Therefore, thepreamplifier shot noise is given by [25]

σpr =

√4kTRf

I2B +16π2kTΓ

gm+ (Cd + Cg)2I3B3, (8)

where k is the Boltzmann’s constant, T is the absolutetemperature, Rf is the feedback resistance, I2 = 0.562, andB is the bit rate. The first term in (8) represents thermalnoise from the feedback resistor, whereas the second termin (8) represents thermal noise from the FET channelresistance. Γ is the noise factor of the FET channel, gm isthe transconductance of the FET, I3 = 0.0868, Cd is thedetector capacitance and Cg is FET gate capacitance. Weassumed that the receiver bandwidth is equal to the bit rateand Cg � Cd.

These assumptions require the condition Rf = G/2πBCd.G is the open loop voltage gain. The photodetector capacitanceis proportional to the photodetector area A′, i.e. Cd = ηA′,where η is a fixed capacitance per unit area. Therefore, thepreamplifier shot noise can be rewritten as

σpr =

√8πkTG

ηA′I2B2 +16π2kTΓ

gm+ η2A′2I3B3, (9)

ALRESHEEDI and ELMIRGHANI: PERFORMANCE EVALUATION OF 5 GBIT/S AND 10 GBIT/S MOBILE OPTICAL WIRELESS SYSTEMS 1337

This preamplifier is used for a bit rate of 30Mbit/s. Inour calculations, we chose the same parameters valuesused in [25]: Γ = 1.5 , T = 295K , R = 0.54A/W ,G = 10, gm = 30ms and, η = 112pF/cm2. Higher bitrates of 5 Gbit/s and 10 Gbit/s are also considered. Weused the p-i-n FET design proposed by Kimber et al. [26].This preamplifier has a noise current spectral density of10pA/

√Hz and a bandwidth of 10 GHz. The preamplifier

bandwidth can be limited to 3.5 GHz and 7 GHz throughthe use of appropriate filters for the 5Gbit/s and 10Gbit/ssystems respectively. The optimum receiver bandwidth is 0.7times the bit rate (Personick’s analysis [22]). The detectorcapacitance is directly proportional to its area, i.e. a largerphotosensitive area means a large capacitance, which resultsin a restriction on the attainable bandwidth. At a higherdata rate our proposed system used photodetector areas of0.05cm2 and 0.01cm2. Although the detector area has beenreduced, the receiver design in [26] has to be improved,circuit design techniques, such as bootstrapping, can be usedto reduce the effect of the large area detector capacitance [29].

The background shot noise can be calculated from itsrespective associated power level Pbn as:

σbn =√

2 × q ×R× Pbn ×BW, (10)

where q, Pbn and BW represent the electron charge, receivedbackground power, and receiver bandwidth respectively.

Substituting equation (7) in (6), the SNR can be written as

SNR =

⎛⎝ R(Ps1 − Ps0)√

σ2pr + σ2

bn + σ2s0 +

√σ2pr + σ2

bn + σ2s1

⎞⎠

2

.

(11)For angle diversity receivers, we consider two schemes:

selection combing (SC) and maximum ratio combing (MRC).SC considers a simple diversity approach. The receiver sim-ply selects the branch with the largest SNR among all thebranches. The SC SNR is given by (12).In contrast to the SC approach, MRC utilizes all the

branches. The output signals of all the branches are combinedthrough an adder circuit. Each input to the circuit is addedwith a weight (proportional to its SNR) in order to maximizethe SNR. The weight of each branch is obtained as

wk =R(Ps1k − Ps0k)(σ0k + σ1k)2

, 1 ≤ k ≤ 3. (13)

The SNR computed using MRC is

SNRMRC =(∑3

k=1R(Ps1k − Ps0k)wk)2∑3k=1(σ0k + σ1k)2w2

k

(14)

giving,

SNRMRC =(∑3

k=1 R(Ps1k − Ps0k)R(Ps1k−Ps0k)(σ0k+σ1k)2 )2∑3

k=1(σ0k + σ1k)2(R(Ps1k−Ps0k)(σ0k+σ1k)2 )2

=3∑

k=1

(R(Ps1k − Ps0k)σ0k + σ1k

)2

=3∑

k=1

SNRk.

(15)

The performances of the LSMS, PA-LSMS and APA-LSMSoperating at 30 Mbit/s are investigated under backgroundshot noise, multipath dispersion and mobility. The SNR ofthese three configurations is compared with that of the CDSat a bit rate of 30 Mbit/s when the transmitter is placed at(2m, 4m,1m) and (2m, 7m, 1m). The SNR calculationswere performed for seven different locations along the y-axisat a constant x = 1m which scans the peak and troughs ofbackground noise, based on MRC. The results are depictedin Fig. 10 and Fig. 11. Our simulation results indicate thatthe angle diversity LSMS offers a 23 dB SNR gain overthat of the CDS. This result is in agreement with previousfindings [3]. A significant improvement can be achievedby employing PA-LSMS, which assigns high powers to thespots nearest to the receiver, thus providing about 13 dBSNR gain over the LSMS SNR. Our proposed APA-LSMSachieved an approximately 16 dB SNR gain over PA-LSMS.Degradation in the LSMS and the PA-LSMS is observedwhen the transmitter is mobile, as depicted in Fig. 11(transmitter moved to (2m, 7m, 1m) and receiver moved tothe corner (1m, 1m, 1m)). However, this SNR degradation,which is attributed to transmitter mobility, can be mitigatedby replacing the LSMS and the PA-LSMS with our proposedAPA-LSMS. Our proposed APA-LSMS with three diversityreceivers achieves about a 45 dB SNR gain over PA-LSMSand 60 dB SNR gain over the CDS. The results depictedin Fig. 10 and Fig. 11 show that the APA-LSMS SNR iscompletely independent of the transmitter location. Therefore,a significant improvement in SNR is obtained at everytransmitter and receiver location. It should be noted that if asingle beam system is used the improvement in the channelbandwidth and the SNR may be desirable, however, such asystem can be affected by beam blockage, and shadowing,and may violate eye safety regulations if all the transmitpower is allocated to the single beam. Other approaches canbe adopted where for example three clusters of beams areused and are independently steered to areas in the ceilingnear each of the receiver detectors, however this is morecomplex. Further work in this area is however warranted.It should also be noted that the beam power and angleadaptations have been done at the rate at which theenvironment changes not at the system bit rate. The systemdesign can allow an SNR margin, e.g. 3dB. This margin willensure that the beam power and angle adaptations do not haveto be repeated frequently. A 3dB SNR margin correspondsto a distance of 1m, see Fig 12. Hence adaptation has tobe done every 1 second for a pedestrian speed of 1m/s.

1338 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 29, NO. 6, JUNE 2011

SNRSC = max1≤k≤3

⎛⎝ R(Ps1 − Ps0)√

σ2pr + σ2

bn + σ2s0 +

√σ2pr + σ2

bn + σ2s1

⎞⎠

2

k

(12)

Fig. 10. OW CDS, LSMS, PA-LSMS and APA-LSMS systems SNR at 30Mbit/s, when the transmitter is placed at (2m, 4m, 1m) and the receiver movesalong x=1m line, with a total transmit power of 1W.

Fig. 11. OW CDS, LSMS, PA-LSMS and APA-LSMS systems SNR at 30Mbit/s, when the transmitter-receiver separation is 6m, with a total transmitpower of 1 W.

Therefore the overhead of our proposed system is 0.8% asmentioned earlier if 8ms are needed for the adaptation.

Significant improvement in SNR is achieved in conjunctionwith excess channel bandwidth, as shown in Fig. 8, whichconfirms that our proposed system is extremely useful inincreasing the data rate. At a higher data rate our proposedsystem used photodetector areas of 0.05cm2 and 0.01cm2 witha 7◦ FOV instead of 0.8cm2 (35◦ FOV). The 0.01cm2 detectorwill collect 19 dB less power than the 0.8cm2 detector. This ishowever compensated for by increasing the concentrator gainfrom 9.4 dB for a 35◦ FOV to about 22.9 dB by reducing

Fig. 12. The SNR Penalty of our proposed system when the receiver movesfrom the optimum location of the spots at (2m, 1m, 1m) along y axis.

its FOV to 7◦. The narrower receiver FOV is possible in oursystem since the beam angle adaptation method introducedis able to identify the optimum location of the spots as seenby the receiver. Our proposed system thus has a concentratorgain of 22.9 dB corresponding to a 7◦ FOV [27, 28]. Wehave compensated for the remaining 5.5 dB link marginthrough proposing the use of error correction codes. Note thatalternatively (or in addition) an imaging system with more thanthree receivers and with maximum ratio combining (MRC)can be used to further improve the link budget. For examplean MRC imaging receiver with 200 pixels can improve thelink budget by 18 dB compared to the three detector diversityreceiver, but is more complex. We have added new results toshow that the link budget is feasible. Figure 13 shows the SNRof the PA-LSMS and APA-LSMS operating at 5 Gbit/s and 10Gbit/s with photodetector areas of 0.05cm2 and 0.01cm2 whenthe systems operate under background noise and multipathdispersion impairments. The transmitter is placed at (2m, 7m,1m) and the receiver moves at a constant x = 1 m along they-axis over the communication floor. Fig. 13 shows that ourAPA-LSMS achieves a consistent 37 dB and 34.5 dB SNRat 5 Gbit/s and 10 Gbit/s, respectively, in the presence ofbackground shot noise, multipath dispersion and mobility. At10 Gbit/s our APA-LSMS system with a photodetector area of0.01cm2 obtained about 21 dB SNR, still achieving a BER of10−9, see Fig.13. With 60mW transmit power, 10 Gbit/s and0.05cm2 detector area the SNR was about 10dB, see Fig.14,FEC can be used to reduce the BER here to below 10−9.The SNR improvement obtained through the combination of

beam angle and power adaptations, spot-diffusing and anglediversity detection allows us to reduce the transmit powerbelow the current 1 W level. To investigate our proposedsystem (with a photodetector area of 0.05cm2) with respect to

ALRESHEEDI and ELMIRGHANI: PERFORMANCE EVALUATION OF 5 GBIT/S AND 10 GBIT/S MOBILE OPTICAL WIRELESS SYSTEMS 1339

Fig. 13. OW PA-LSMS and APA-LSMS systems SNR at 5 Gbit/s and10 Gbit/s, with two detection areas (0.05cm2 and 0.01cm2), when thetransmitter-receiver separation is 6m, with a total transmit power of 1 W.

eye safety regulations, we used a total transmit power of 60mW (0.75 mW per beam) and introduced a limitation in thepower adaptation algorithm such that no single beam power isallowed to exceed 1 mW following power adaptation (whichis an eye safety limit). We have also reduced the size of thespot from a diameter of 1 cm to 0.5 cm which allows moreflexibility in clustering the spots closely if needed.The SNRsachieved in our proposed system in this case were about 13dB and 10 dB at 5 Gbit/s and 10 Gbit/s, respectively,underthe impact of background noise, multipath dispersion and

mobility, see Fig. 14. These degradations are due to thereduction in the total transmit power from 1 W to 60 mW, andalso due to the 1mW power restriction in our algorithm. At10 Gbit/s the SNR is still greater than 9.5 dB (BER < 10−3

). Therefore forward error correction (FEC) can be used tofurther reduce the BER from 10−3 to 10−9 in our proposedsystem (10 Gbit/s with an area of 0.05cm2, 60 mW transmitpower and less than 1mW per beam).The shape and the size of the transmitter have to be consideredhowever to determine if the human eye can see more thanone beam. The higher date rates of the PA-LSMS and theAPA-LSMS are shown to be feasible through a combinationof the methods of spot diffusion, beam angle and beam poweradaptation. The APA-LSMS is able to achieve BER of 10−9

while operating at 5 Gbit/s and 10 Gbit/s. We believe theseare useful results for wireless communications.

VI. CONCLUSIONS

Mobility can degrade the link performance of the CDS,LSMS and PA-LSMS. In this paper, we designed and in-vestigated an APA-LSMS coupled with a diversity receiverto mitigate the SNR degradation under background noise,multipath dispersion and mobility. The SNR results show thatbeam angle and beam power adaptations in conjunction withangle diversity can help reduce the impact of backgroundnoise, multipath dispersion and mobility. At a bit rate of 30Mbit/s, our proposed APA-LSMS offers SNR improvement:45 dB SNR gain over PA-LSMS and 60 dB SNR gain over

Fig. 14. The SNR performance our proposed system operating at 30Mbit/s,5 Gbit/s and 10 Gbit/s, with a total transmit power of 60 mW and detectionarea of 0.05cm2 for high data rates and 0.8cm2 for 30 Mbit/s.

CDS in a worst case scenario. This improvement is achievedby introducing three methods: angle diversity, beam angle andbeam power adaptations. Beam angle adaptation can help thetransmitter to target its diffusing-spot at an area where thereceiver can achieve a strong signal through direct-LOS com-ponents. Beam power adaptation can enable the transmitter toallocate more power to the spots nearest to the receiver thusincreasing the SNR at the receiver. These methods coupledwith angle diversity are extremely effective in increasingchannel bandwidth from 36 MHz (conventional CDS) to 7.2GHz (APA-LSMS with angle diversity). Furthermore, theproposed APA-LSMS offers a reduction in the delay spreadby a factor of more than 60 compared with the CDS. Thesesignificant improvements in SNR, delay spread and channelbandwidth enhance the performance of our system enabling itto operate at higher data rates. Higher data rates of 5 Gbit/s and10 Gbit/s were shown to be feasible through the combinationof spot diffusing, angle diversity and beam power adaptation.The APA-LSMS is able to achieve BER of 10−9 at 5Gbit/sand 10 Gbit/s.

ACKNOWLEDGMENT

The authors would like to thank Amer Albargi for his helpwith LATEX.

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Mohammed T. Alresheedi received a B.Sc degreein Electrical Engineering from King Saud Univer-sity, Riyadh, Saudi Arabia, in 2006 and an MSCdegree in Communication Engineering from LeedsUniversity, United Kingdom, in 2009. He is cur-rently pursuing the Ph.D. degree in Electronic andElectrical Engineering at Leeds University, UnitedKingdom. His research interests include adaptivetechniques for OW, OW systems design, and indoorOW networking.

Jaafar Elmirghani is a Fellow of the Institute ofPhysics, a Senior Member of IEEE, and the Directorof the Institute of Integrated Information Systemswithin the School of Electronic and Electrical Engi-neering, University of Leeds, UK. He joined Leedsin 2007, and prior to that (2000-2007), as chair inoptical communications at the University of WalesSwansea he founded, developed, and directed theInstitute of Advanced Telecommunications and theTechnium Digital (TD), a technology incubator/spin-off hub.He has provided outstanding leadership in a

number of large research projects at the IAT and TD. He was Chairman of theIEEE Comsoc Transmission Access and Optical Systems technical committeeand the IEEE Comsoc Signal Processing and Communications Electronicstechnical committee and was an editor of IEEE Communications Magazine.Hewas a founding Chair of the Advanced Signal Processing for CommunicationSymposium that started at IEEE GLOBECOM’ 99 and has continued sinceat every ICC and GLOBECOM. Dr. Elmirghani was also a founding Chair ofthe first IEEE ICC/ GLOBECOM optical symposium at GLOBECOM’00,the Future Photonic Network Technologies, Architectures and ProtocolsSymposium. He chaired this symposium, which continues to date underdifferent names. He received the IEEE Communications Society Hal Sobolaward, the IEEE Comsoc Chapter Achievement award for excellence inchapter activities (both in 2005), the University of Wales Swansea OutstandingResearch Achievement Award 2006, and the IEEE Communications SocietySignal Processing and Communication Electronics outstanding service award2009. He has coauthored the book Photonic Switching Technology: Systemsand Networks, published by Wiley, and has published over 300 papers. Hehas research interests in optical systems and networks and signal processing.