System Design and Analysis of MIMO SFBC CI-OFDM System against the Nonlinear Distortion and Narrowband Interference
Heung-Gyoon Ryu Member, IEEE
Abstract – The CI-OFDM (carrier interferometry
orthogonal frequency division multiplexing) system has been widely studied in the multi-carrier communication system. This CI-OFDM system spreads each information symbol across all N sub-carriers using orthogonal CI spreading codes. The CI-OFDM system can show the advantage of PAPR (peak to average power ratio) reduction and frequency diversity gains without any loss in the communication throughput. On the other hand, a great attention has been devoted to MIMO (multiple input multiple output) antenna array systems and space-time-frequency processing. In this paper, focusing on the two Tx (transmit) / one Rx (receive) antennas and two Tx / two Rx antennas configuration, we evaluate the performance of MIMO OFDM and MIMO CI-OFDM system. SFBC (space frequency block coding) coding is applied into both MIMO OFDM system and MIMO CI-OFDM system. For CI-OFDM realization, digital implemented CI-OFDM structure is used in which CI code spreading operation and carrier allocation are separately processed by simple IFFT type operation. From the simulation results, it is shown that MIMO SFBC CI-OFDM reduces PAPR significantly compared with MIMO SFBC-OFDM system. The out-of band re-growth of signal spectrum in MIMO SFBC CI-OFDM system is much smaller than MIMO SFBC OFDM. In the NBI (narrow band interference) channel MIMO SFBC CI-OFDM system achieves considerable BER improvement, compared with the MIMO SFBC-OFDM system in which error floor occurs in most of SNR range. So, it can be expected that MIMO SFBC CI-OFDM system is very useful for the high speed communication system in the situation of nonlinear HPA (high power amplifier) and NBI channel.
Keyword: OFDM, CI (carrier interferometry), PAPR, MIMO, SFBC
I. INTRODUCTION OFDM (orthogonal frequency division multiplexing)
technique has been adopted as the standards in the several high data rate applications, such as Europe DAB/DVB (digital audio and video broadcasting) system, high-rate WLAN (wireless local area networks) such as IEEE802.11x, HIPERLAN II and MMAC (multimedia mobile access communications), and terrestrial DMB (digital multimedia broadcasting) system. OFDM system transmits information data by many sub-carriers, where sub-carriers are orthogonal to each other and sub-channels are overlapped so that the spectrum efficiency may be enhanced.
Heung-Gyoon Ryu is the Department of Electronic Engineering, Chungbuk National University, 12 Kaesin-dong, Cheongju, Chungbuk, 361-763, Republic of KOREA. (email: [email protected])
OFDM can be easily implemented by the IFFT (inverse fast
Fourier transform) and FFT (fast Fourier Transform) process in digital domain, and has the property of high-speed broadband transmission and robustness to multi-path interference, frequency selective fading. However, OFDM signal has high PAPR (peak to average power ratio) because of the superimposition of multi-carrier signals with large number of sub-carriers. The high PAPR makes the signal more sensitive to the nonlinearities of the HPA (high power amplifier) and result in signal distortion when the peak power exceeds the dynamic range of the amplifier. To transmit the high PAPR signal without distortion requires more expensive power amplifier with high linearity and wider dynamic range. Besides, the non-linear distortions due to clipping and amplification effects in the transmitted signal will lead to both in-band and out-of band emissions. The former provokes BER degradation whereas the later results in spectral spreading.
Recently, a new kind of technique called CI-OFDM (carrier interferometry orthogonal frequency division multiplexing) has been widely studied [1-4]. In the CI-OFDM technique, each information symbol is sent simultaneously over all carriers and the each carrier for the symbol is assigned a corresponding orthogonal CI spreading code. This CI/OFDM system not only can reduce PAPR problem significantly but also achieve frequency diversity gains without any loss in throughput.
Besides, a great deal attention has been devoted to MIMO (multiple-input multiple-output) antenna array systems and space-time-frequency processing [5-7]. MIMO diversity technique which exist diversity gain and coding gain can resolve the high link budget problem in the high data rate transmission, especially in the multi-path fading channel. Besides, the space-time-frequency processing, especially Alamouti’s diversity technique offers significant increase in performance at a low decoding complexity. Alamouti’s STBC (space-time block coding) method is very efficient when delay spread is big or channel’s time variation is very small during the coded continuous OFDM symbols and OFDM sub carrier number is small. On the other hand, when Doppler spread is big or channel’s time variation is large and channel is non frequency selective, so the inter-sub carrier’s channel frequency response is nearly constant in the OFDM system with many sub carriers, the SFBC (space-frequency block coding) method is more efficient for the high quality transmission.
Several researches have been studied in the area of CI-OFDM system with MIMO type transceiver [8-10]. There, STBC method is applied in some researches. And, MIMO CI-OFDM system is utilized to compensate the BER penalty caused by Doppler frequency or frequency selective fading.
368 IEEE Transactions on Consumer Electronics, Vol. 54, No. 2, MAY 2008
Authorized licensed use limited to: NATIONAL INSTITUTE OF TECHNOLOGY CALICUT. Downloaded on June 29, 2009 at 04:42 from IEEE Xplore. Restrictions apply.
In this paper, focused on the two transmit (Tx) / one receive (Rx) antenna and two Tx / two Rx antenna configuration, we evaluate the performance of MIMO OFDM and MIMO CI-OFDM system on the basis of MIMO technique theoretical analysis when HPA nonlinearity or NBI(narrow band interference) are existed. SFBC coding is applied in both MIMO OFDM system and MIMO CI-OFDM system. For CI-OFDM realization, digital implemented CI-OFDM structure is used in which CI code spreading operation and carrier allocation are separately processed by simple IFFT type operation [11]. As results, MIMO CI-OFDM system outperforms MIMO OFDM significantly in the existence of both HPA nonlinearity and NBI.
II. SYSTEM DESCRIPTION In this paper, SFBC transmit diversity technique is applied
into the OFDM system. Simply, the 2Tx/1Rx and 2Tx/2Rx antenna configuration are considered to compare the system performance of the MIMO OFDM and MIMO CI-OFDM system. First, we discuss the traditional MIMO SFBC OFDM structure with 2Tx/1Rx and 2Tx/2Rx antenna.
A) 2Tx-1Rx SFBC OFDM system
Fig. 1. MIMO SFBC OFDM transceiver diagram with 2 x 1 diversity. When 2 Tx antennas and 1 Rx antenna are considered,
assuming the system transmits data symbols
1110 ...,,,...,,, −+ Nkk XXXXX on carriers 1...,,1,...,,1,0 −+ Nkk , respectively, the encoding algorithm is
21
**1
1
1
TxTx
kk
kk
k
k
XXXX
ff
⎥⎦
⎤⎢⎣
⎡− +
+
+.
Channel description between the Tx antennas and Rx
antenna is as Fig.2.
2H1H
Fig. 2. Channel definition in 2 x 1 diversity scheme.
Received signals at the Rx antenna is defined as
Rx antenna 1 kth carrier kR
thk 1+ carrier 1+kR So, received signal in frequency domain can be
⎥⎦
⎤⎢⎣
⎡+⎥
⎦
⎤⎢⎣
⎡⎥⎦
⎤⎢⎣
⎡
−=+=⎥
⎦
⎤⎢⎣
⎡=
+++++*
11*1
1*2
1
21
*1 k
k
k
k
kk
kk
k
k
NN
XX
HHHH
NHXRR
R
(1) Let’s assume that adjacent two carriers have same channel
characteristic, such as ,11
11 HHH kk == + .22
12 HHH kk == +
Then, decoding algorithm is as follows.
⎥⎦
⎤⎢⎣
⎡
⎥⎥⎦
⎤
⎢⎢⎣
⎡
−==
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡=
++
*1
1*2
2*1
^
1
^^
k
kH
k
k
RR
HHHHRH
R
RR
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡+⎥
⎦
⎤⎢⎣
⎡⋅+=
++
~
1
~
1
2221 )(k
k
k
k
N
NXX
HH (2)
where HH means the conjugate transpose of H , and
⎥⎦
⎤⎢⎣
⎡
⎥⎥⎦
⎤
⎢⎢⎣
⎡
−=
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡
++
*1
1*2
2*1
~
1
~
k
k
k
k
NN
HHHH
N
N. (3)
B) 2Tx-2Rx SFBC OFDM system
22H11H
12H 21H
Fig. 3. Channel definition in 2 x 2 diversity scheme.
H.-G. Ryu: System Design and Analysis of MIMO SFBC CI-OFDM System against the Nonlinear Distortion and Narrowband Interference 369
Authorized licensed use limited to: NATIONAL INSTITUTE OF TECHNOLOGY CALICUT. Downloaded on June 29, 2009 at 04:42 from IEEE Xplore. Restrictions apply.
Fig. 4. MIMO SFBC OFDM transceiver diagram with 2 x 2 diversity. When there are 2 Tx antennas and 2 Rx antennas, channel
between the Tx and Rx antennas is described as Fig.3. Received signals at the two Rx antennas are defined as
Rx antenna 1 Rx antenna 2 kth carrier 1
kR 2kR
thk 1+ carrier 11+kR 2
1+kR So, received signals in frequency domain are expressed as
follows.
⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢
⎣
⎡
+⎥⎦
⎤⎢⎣
⎡
⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢
⎣
⎡
−
−=+=
⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢
⎣
⎡
=
+
+
+
+
+
+
+
+
+
*21
2
*11
1
1*12
1
22
*111
21
*221
12
*211
11
*21
2
*11
1
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
k
NN
NN
XX
HHHH
HHHH
NHX
RR
RR
R
(4) Suppose adjacent two carriers have same channel
characteristic, such as ,1111
111 HHH kk == + ,1212
112 HHH kk == +
,22221
22 HHH kk == + .21211
21 HHH kk == + Then decoding algorithm is as follows.
⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢
⎣
⎡
⎥⎥⎦
⎤
⎢⎢⎣
⎡
−−==
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡=
+
+
+ *21
2
*11
1
12
22
*22
*12
11
21
*21
*11
^
1
^^
k
k
k
k
H
k
k
RR
RR
HH
HH
HH
HHRH
R
RR
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡+⎥
⎦
⎤⎢⎣
⎡⋅+++=
++
~
1
~
1
221212222211 )(k
k
k
k
N
NXX
HHHH
(5)
where
⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢
⎣
⎡
⎥⎥⎦
⎤
⎢⎢⎣
⎡
−−=
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡
+
+
+ *21
2
*11
1
12
22
*22
*12
11
21
*21
*11
~
1
~
k
k
k
k
k
k
NN
NN
HH
HH
HH
HH
N
N.
(6)
III. MIMO SFBC CI-OFDM SYSTEM In the MIMO SFBC CI-OFDM system, the CI spreading
process can be expressed as follows.
∑−
=
ΔΔ ⋅=1
0
2)(N
k
kjtfkji
ieetC θπ
1......,1,0,2 −==Δ NiiNiπθ (7)
where, j = 1− , N is the total number of sub-carriers, fΔ
means the carrier spacing and iθΔ is the assigned base spreading phase offset for the i th parallel data. Here, for general expression, we define CI spreading sequence series for the i th parallel data as
{ }⎭⎬⎫
⎩⎨⎧
==−⋅⋅− )1(2122
11 ,...,,,...,,][Ni
Nji
Njoi
NjN
iioii eeecccc
πππ
.
Before passing through nonlinear HPA, the lth Tx transmitted signal for one entire MIMO SFBC CI-OFDM symbol is as follows.
∑∑−
=
−
=
ΔΔ ⋅⋅⋅⋅=1
0
1
0
22 )()(N
k
N
i
tfjkjtfkjlk
l tpeeextS ci πθπ
∑−
=
Δ⋅⋅=1
0
22N
k
tfkjlk
tfj ese c ππ (8)
where, lkx is the time domain SFBC coded data on the k th
carrier and lth Tx antenna, cf is the center frequency and
)(tP is the pulse shaping for the bit duration bT . Besides,
here, ikjN
i
li ex θΔ
−
=
⋅∑1
0
is defined as lks .
0je
ije θΔ
iNje θΔ− )1(
ikje θΔ
Fig. 5. CI codes spreading block.
370 IEEE Transactions on Consumer Electronics, Vol. 54, No. 2, MAY 2008
Authorized licensed use limited to: NATIONAL INSTITUTE OF TECHNOLOGY CALICUT. Downloaded on June 29, 2009 at 04:42 from IEEE Xplore. Restrictions apply.
0je−
kje θΔ−
kNje θΔ−− )1(
kkje θΔ−
Fig. 6. CI codes despreading block.
Fig. 7. MIMO SFBC CI-OFDM Transceiver diagram (2Tx-2Rx).
Theoretically, in the MIMO SFBC CI-OFDM receiver side, the jth Rx received signal can be expressed as follows.
)()(1
1
0
22 tneshetR ljL
l
N
k
tfkjlk
ljk
tfjj c +⋅⋅⋅= ∑∑=
−
=
Δππ
)(1
1
0
22 tneese ljL
l
jN
k
tfkjlk
ljk
tfj ljkc +⋅⋅⋅⋅= ∑∑
=
−
=
Δ φππ α
)(1
1
0
1
0
22 tnexeee ljL
l
N
i
kjlk
jN
k
tfkjljk
tfj iljkc +⋅⋅⋅⋅⋅= ∑ ∑∑
=
−
=
Δ−
=
Δ θφππ α
)(1
1
0
1
0
22 tneeeex ljL
l
N
k
N
i
jtfjkjtfkjlk
ljk
ljkci +⋅⋅⋅⋅⋅=∑∑∑
=
−
=
−
=
ΔΔ φπθπα
(9) where L is the total transmit antenna number and here supposed to 2=L . )(tR j is the jth Rx antenna received
signal, ljkh is the time domain channel response of the kth
carrier from lth Tx antenna to jth Rx antenna when channel is frequency selective fading channel, lj
kα and ljkφ are the fade
parameter and phase offset of ljkh respectively, and )(tnlj is
the AWGN (additive white Gaussian noise) with a power spectral density equal to 20N from lth Tx antenna to jth Rx antenna.
The above received signal is separated into its N orthogonal sub-carriers through FFT process. After channel state estimation, each symbol stream’s phase offset due to spreading is removed from each carrier by CI codes despreading. The obtained vectors from each carrier are then combined by certain combining strategy. The combining strategy is employed to help restore orthogonality between symbol streams, maximize frequency diversity benefits, and minimize interference and noise. In AWGN or flat fading channel, EGC (equal gain combining) can be used. In the frequency selective channel, MMSEC (minimum mean-square error combining) can be used to minimize inter-symbol-interference from other spreading codes and noise [1, 8].
IV. PAPR and HPA
Consider the MIMO OFDM system with L transmit antennas
that uses N sub-carriers. In the case of two transmit antennas,
the each of N-dimensional OFDM symbol is transmitted from
antenna 1 and antenna 2 respectively. Generally, the PAPR of
the transmitted OFDM signal is defined as:
⎥⎦⎤
⎢⎣⎡
≡<≤
2
2
0 )(
)(max
tSE
tSPAPR
l
l
Tt
l (10)
where l means the transmit antenna number and [ ]•E means
the expectation operation.
When calculating PAPR using discrete sampled signals, we
cannot find the accurate PAPR because the true peak of
continuous-time OFDM signal may be missed in the Nyquist
sampling. So, we use 4 times over-sampling to improve
accuracy of discrete PAPR. Besides, to show statistical
characteristics of PAPR, we use CCDF (complementary
cumulative distribution function), which is the probability that
PAPR of OFDM signal exceeds a certain threshold 0PAPR .
The CCDF is defined as
)Pr( 0PAPRPAPRCCDF ll >=
)Pr(1 0PAPRPAPR l ≤−=
H.-G. Ryu: System Design and Analysis of MIMO SFBC CI-OFDM System against the Nonlinear Distortion and Narrowband Interference 371
Authorized licensed use limited to: NATIONAL INSTITUTE OF TECHNOLOGY CALICUT. Downloaded on June 29, 2009 at 04:42 from IEEE Xplore. Restrictions apply.
∏= ⎥
⎥⎦
⎤
⎢⎢⎣
⎡×−−−=
N
nl
n
lavg
PP
PAPR1
0 )exp(11
( )( ) NoPAPR α−−−= exp11 (11)
where lnP is the average sample power of lth transmit
antenna signal, ∫=T ll
avg dttSTP0
2)()/1( is the average
power of lth transmit antenna signal, here, when over-
sampling is done, lavg
ln PP = is nearly satisfied. Commonly,
α is 2.8 in most cases. We define the observed CCDF of
MIMO transmitter is
( )lCCDFLl
CCDF≤<
=0
max . (12)
HPA inputs signal )(tS l of lth transmit antenna side can be
expressed as
)()()( tjll l
etytS ϕ= . (13)
Distorted HPA output signal )(tY l is
)]]([)([])([)( tyFtjlA
l lP
l
etyFtY += ϕ . (14)
where, )]([ tyF lA and )]([ tyF l
P are AM/AM and AM/PM
characteristics of nonlinear HPA of lth transmit antenna. Here,
we consider SSPA (solid-state power amplifier) model, SSPA
are assumed to be memory-less.
SSPA are as follows
ppl
ll
A
Aty
tytyF 2/12
0
)(1
)()]([
⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛+
=
0)]([ =tyF lP . (15)
0A is saturation voltage, p is a smoothness factor.
V. PERFORMANCE ANALISES AND DISCUSSION
Based on the above theoretical analysis, in order to compare the transmission performance both in the MIMO SFBC OFDM and MIMO SFBC CI-OFDM system, we evaluate the PAPR and BER of MIMO SFBC OFDM and MIMO SFBC CI-OFDM when SSPA is used as each transmitter’s HPA or
NBI is inserted to the data carriers. 2Tx-1Rx and 2Tx-2Rx MIMO scheme is considered. HPA backoff is supposed to 2, 3 and 6. Total sub-carrier number interrupted by NBI is defined as p and supposed p=8, besides, JSR of NBI is supposed to 0dB or 1dB. AWGN channel is considered through the whole evaluation. The total sub carrier number is supposed to 1024 and 16QAM modulation is used in the whole simulation.
Fig.8. PAPR in MIMO SFBC OFDM and MIMO SFBC CI-OFDM (N=1024, 16QAM).
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
f/B
PS
D(d
Br)
MIMO SFBC OFDM(N=1024)MIMO SFBC CI-OFDM(N=1024)
Fig.9. Spectrum in MIMO SFBC OFDM and MIMO SFBC CI-OFDM (N=1024, 16QAM).
372 IEEE Transactions on Consumer Electronics, Vol. 54, No. 2, MAY 2008
Authorized licensed use limited to: NATIONAL INSTITUTE OF TECHNOLOGY CALICUT. Downloaded on June 29, 2009 at 04:42 from IEEE Xplore. Restrictions apply.
Fig.8 is the PAPR of MIMO SFBC OFDM and MIMO SFBC CI-OFDM system and Fig.9 is the signal spectrum of two kinds MIMO system. As seen from Fig.8, there is about 2dB PAPR gain at 110− in the MIMO SFBC CI-OFDM system compared with MIMO SFBC OFDM system when total sub-carrier number is supposed to 1024. Besides, the out of band spectrum re-growth is reduced significantly in the MIMO SFBC CI-OFDM system compared with MIMO SFBC OFDM system as seen in Fig.9.
Fig.11. BER in MIMO SFBC OFDM and MIMO SFBC CI-OFDM when SSPA back-off=6 or 3 (N=1024, 16QAM, AWGN channel).
Fig.10 is the BERs of MIMO SFBC OFDM and MIMO SFBC CI-OFDM when SSPA with 2 backoff is considered as the transmitter HPA. As seen in Fig.10, about 17dB and 13.5dB SNR are required at 410− of BER in the 2Tx-1Rx SFBC CI-OFDM and 2Tx-2Rx SFBC CI-OFDM system, but worse than 210− of BERs are achieved at SNR of 17dB both in the 2Tx-1Rx SFBC OFDM and 2Tx-2Rx SFBC OFDM system, and error floors occur in the two kinds of MIMO SFBC OFDM systems.
Fig.13. BER in MIMO SFBC OFDM and MIMO SFBC CI-OFDM with SSPA and NBI (p=8, N=1024, 16QAM, AWGN channel).
H.-G. Ryu: System Design and Analysis of MIMO SFBC CI-OFDM System against the Nonlinear Distortion and Narrowband Interference 373
Authorized licensed use limited to: NATIONAL INSTITUTE OF TECHNOLOGY CALICUT. Downloaded on June 29, 2009 at 04:42 from IEEE Xplore. Restrictions apply.
Fig.11 is the BER of MIMO SFBC OFDM and MIMO SFBC CI-OFDM when SSPA with certain back-off is considered as transmitter HPA. As seen in Fig.11, when back-off of 6 and 3 are supposed respectively in the 2Tx-1Rx SFBC CI-OFDM and 2Tx-2Rx SFBC CI-OFDM system, SSPA nonlinearity is almost compensated completely. However, in 2Tx-1Rx SFBC OFDM system, about 2.5dB SNR penalty is observed at BER of 410− , and in the 2Tx-2Rx SFBC OFDM system, error floor occurs even if at SNR of 30dB.
Fig.12 is the BER of MIMO SFBC OFDM and MIMO SFBC CI-OFDM when NBI is inserted to the data carriers. As seen from the figure, MIMO SFBC CI-OFDM system can nearly compensate all the NBI affect when p is equal to 8 and JSR is 0 or 1 respectively. Only About 1dB SNR penalty is observed at BER of 410− in the 2Tx-1Rx SFBC CI-OFDM system, and even if 2dB SNR gain is observed in the 2Tx-2Rx SFBC CI-OFDM system compared with theory without NBI. However, worse than 310− of BER are achieved in the 2Tx-1Rx SFBC OFDM and 2Tx-2Rx SFBC OFDM system, and error floors occur in the both of MIMO SFBC OFDM systems.
Fig.13 is the BER of MIMO SFBC OFDM and MIMO SFBC CI-OFDM when SSPA with 2 back-off is considered as transmitter HPA and also NBI is inserted to the data carriers. As seen from the figure, about 18dB and 15dB SNR are required at 310 − of BER in the 2Tx-1Rx SFBC CI-OFDM and 2Tx-2Rx SFBC CI-OFDM system respectively, but worse than 2102 −× of BER are achieved in the 2Tx-1Rx SFBC OFDM and 2Tx-2Rx SFBC OFDM system, and error floors occur in the both of MIMO SFBC OFDM systems.
VI. CONCLUSION
In this paper, focused on the two Tx/one Rx antenna and two Tx/two Rx antenna configurations, we evaluate the system performance of MIMO SFBC OFDM and MIMO SFBC CI-OFDM system on the basis of MIMO technique theoretical analysis. SFBC coding is applied in both MIMO OFDM system and MIMO CI-OFDM system. For CI-OFDM realization, digital implemented CI-OFDM structure is used, in which CI codes spreading operation and carrier allocation are separately processed by simple IFFT type operation.
1) From the simulation results, it is found that MIMO SFBC CI-OFDM reduces PAPR significantly compared with MIMO SFBC-OFDM system. The carefully selected CI codes result in one symbol stream’s power reaching a maximum, when the powers of the remaining N-1 symbol streams are at a minimum. Therefore, a more stable envelope, average PAPR and standard deviation of PAPR far smaller than traditional schemes can be achieved.
2) The out-of band re-growth of signal spectrum in MIMO SFBC CI-OFDM system is much smaller than MIMO SFBC OFDM.
3) When the Narrow band interference exists, MIMO SFBC CI-OFDM system achieves considerable BER improvement compared with the MIMO SFBC-OFDM system in which error floor occurs even in high SNR. It is because that CI-OFDM method has frequency diversity benefit so that it brings robustness to the narrow band interference.
4) Much better system performance can be expected by using MIMO SFBC CI-OFDM method than MIMO SFBC-OFDM in the situation of existing both nonlinear HPA and NBI.
Overall, MIMO SFBC CI-OFDM system outperforms MIMO SFBC OFDM significantly when system is interrupted by the HPA nonlinearity or NBI. Therefore, the MIMO SFBC CI-OFDM method can be further applicable to the any kinds of MIMO type multi-carrier communication systems with many sub-carriers.
[2] Wiegandt, D.A., Nassar, C.R., and Wu, Z., “The elimination of peak-to-average power ratio concerns in OFDM via carrier interferometry spreading codes: a multiple constellation analysis,” Proceedings of the Thirty-Sixth Southeastern Symposium on System Theory, 2004, pp.323 – 327, 2004.
[3] Zhiquang Wu, Nassar, C.R. and Xiaoyao Xie, “Narrowband interference rejection in OFDM via carrier interferometry spreading codes,” Global Telecommunications Conference, 2004 GLOBECOM '04. IEEE, Vol.4, pp.2387 – 2392, 29 Nov. – 3 Dec. 2004.
[4] Wiegandt, D.A., Wu, Z. and Nassar, C.R.; “High-performance carrier interferometry OFDM WLANs: RF testing,” ICC '03. IEEE International Conference on Communications, Vol. 1, pp.203 – 207, 11-15 May 2003.
[5] Alamouti, S.M., “A simple transmit diversity technique for wireless communications,” IEEE Journal on Selected Areas in Communications, Vol. 16, Issue 8, pp.1451 – 1458, Oct. 1998.
[6] Lee, K.F. and Williams, D.B., “A space-frequency transmitter diversity technique for OFDM systems,” Global Telecommunications Conference, 2000. GLOBECOM '00. Vol.3, pp.1473 – 1477, 27 Nov.-1 Dec. 2000.
[7] Suto, K. and Ohtsuki, T., “Performance evaluation of space-time-frequency block codes over frequency selective fading channels,” IEEE 56th Vehicular Technology Conference, 2002. VTC 2002-Fall. 2002, Vol.3, pp.1466 - 1470, 24-28 Sept. 2002.
[8] Barbosa, P.R., Zhiqiang Wu and Nassar, C.R., “High-performance MIMO-OFDM via carrier interferometry,” Global Telecommunications Conference, 2003. GLOBECOM '03 Vol.2, pp.853 – 857, 1-5 Dec. 2003.
[9] Maehara, F. and Kuchenbecker, H.-P., “Performance of space diversity reception for coded carrier interferometry OFDM,” IEEE 59th Vehicular Technology Conference, 2004. VTC 2004-Spring 2004, Vol.1, pp.520 – 524, 17-19 May 2004.
[10] Wanwoo Seo and Yeonho Chung, “Comparative study of OFDM system with carrier interferometry code and STBC in flat fading channels,” The 6th International Conference on Advanced Communication Technology, 2004, Vol. 1, pp.376 – 379, 2004.
[11] Heung-Gyoon Ryu and Yingshan Li, “Digital Implementation and Performance Evaluation of the CI-OFDM Structure with Low Complexity,” submitted to the EEE Transaction on Consumer Electronics, May 2005.
[12] S. Sampei, Applications of Digital Wireless Technologies to Global Wireless Communications, Prentice-Hall, 1997.
[13] John G. Proakis, Digital Communications, McGraw-Hill, 2000. [14] Anwar, K and Yamamoto, H., ”A new design of carrier interferometry
OFDM with FFT as spreading codes,” 2006 IEEE Radio and Wireless Symposium, pp.543-546, 17-19 Jan. 2006.
374 IEEE Transactions on Consumer Electronics, Vol. 54, No. 2, MAY 2008
Authorized licensed use limited to: NATIONAL INSTITUTE OF TECHNOLOGY CALICUT. Downloaded on June 29, 2009 at 04:42 from IEEE Xplore. Restrictions apply.
[15] Xu, Fang; Xu, Ru and Sun, Haixin, “Implementation of Carrier Interferometry OFDM by Using Pulse Shaping Technique in Frequency Domain,” 2007 IEEE International Workshop on Anti-counterfeiting, Security, Identification, pp. 319 – 323, 16-18 April 2007.
Heung-Gyoon Ryu (M’88) was born in Seoul, Republic of Korea in 1959. He received the B.S. and M.S. and Ph.D. degrees in electronic engineering from Seoul National University in 1982, 1984 and 1989. Since 1988, he has been with Chungbuk National University, Korea, where he is currently Professor of Department of Electrical, Electronic and Computer Engineering in Chungbuk National University. And he worked as Chief of RICIC (research institute of computer, information
communication center) in Chungbuk National University from March 2002 to Feb 2004. His main research interests are digital communication systems, communication circuit design, spread spectrum system and communication signal processing. Since 1999, he has worked as reviewer of the IEEE transaction paper. He was a winner of ‘2002 ACADEMY AWARD’ from the Korea Electromagnetic Engineering Society, Korea.
H.-G. Ryu: System Design and Analysis of MIMO SFBC CI-OFDM System against the Nonlinear Distortion and Narrowband Interference 375
Authorized licensed use limited to: NATIONAL INSTITUTE OF TECHNOLOGY CALICUT. Downloaded on June 29, 2009 at 04:42 from IEEE Xplore. Restrictions apply.
