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Cyber Journals: Multidisciplinary Journals in Science and Technology, Journal of Selected Areas in Telecommunications (JSAT), May Edition, 2011 Throughput Performance Enhancement for MUDiv/OFDMA using MMSE Equalization without Guard Interval Yuta Ida†, Chang-Jun Ahn, Takeshi Kamio, Hisato Fujisaka, and Kazuhisa Haeiwa many users in the same channel at the same time [7], [8]. Abstract—Recently, to achieve a high data rate and a high quality WiMAX is one of the next generation mobile networks multimedia service, orthogonal frequency division multiplexing designed to support a high capacity and a high data rate. (OFDM) and orthogonal frequency division multiplexing access In a wireless network, the transmitted signal of each user has (OFDMA) are widely studied. In a wireless network, the independent channel fluctuation characteristics. By using such transmitted signal of each user has independent channel fluctuation characteristics. By using such characteristic, a characteristic, the diversity that exists between users is called multiuser diversity (MUDiv) for OFDMA has been proposed. In a multiuser diversity (MUDiv) and can be exploited by the sender multipath fading environment, inter-symbol interference (ISI) is to enhance the capacity of a wireless network [9]-[11]. caused. In OFDM systems, the ISI is eliminated by inserting the Therefore, the MUDiv technique achieves dramatically guard interval (GI). On the other hand, this operation is degraded increased the system throughput and the spectral efficiency [12]. the maximum throughput. In this paper, we propose to enhance In a MUDiv for OFDMA, the exploiting channel fluctuation the throughput performance for a MUDiv/OFDMA without GI. diversity is in essence done by selecting the user with the strong subcarrier channels. Index Terms—OFDMA, multiuser diversity, guard interval, In a multipath fading environment, inter-symbol interference MMSE, throughput (ISI) and inter-carrier interference (ICI) are caused due to the previous symbol and different subcarrier, respectively. In OFDM systems, the ISI is eliminated by inserting the guard I. INTRODUCTION interval (GI) longer than the delay spread channel. However, O rthogonal frequency division multiplexing (OFDM) systems have recently attracted considerable attention as a fourth generation mobile communication system due to the this operation is degraded the maximum throughput due to the extended packet length. To mitigate this problem, the several methods without GI have been proposed [13]-[15]. For example, parallel signal transmission using many subcarriers that are [13] improves the performance in the short GI. However, the mutually orthogonal [1]. Moreover, since the frequency spacing system performance without GI is significantly degraded. [14] of each subcarrier minimum, OFDM can treat a frequency mitigates the complexity by using the time domain equalizer selective fading as a flat fading for each subcarrier [2], [3]. (TDE). However, TDE is degraded the system performance in Furthermore, OFDM has been chosen for several broadband the rugged environment as a frequency selective fading. [15] WLAN standard like IEEE802.11a, IEEE802.11g, and adapts the overlap-frequency domain equalization (FDE). European HIPERLAN/2. In addition, terrestrial digital audio However, the noise enhancement due to the residual ISI is not broadcasting (DAB) and digital video broadcasting (DVB) have considered by using the perfect channel estimation. Previously, also proposed for broadband wireless multiple access system we have proposed the ISI and ICI compensation methods for such as IEEE802.16 wireless MAN standard and interactive multiple-input multiple-output (MIMO) systems [16]. To DVB-T [4]-[6]. OFDM allows only one user on the channel at mitigate above-mentioned problems, in this paper, we propose a any given time. To accommodate multiple users, orthogonal MUDiv/OFDMA without GI using the ISI and ICI cancellation frequency division multiple access (OFDMA) has been to enhance the throughput performance. In Section II, we proposed [6]. OFDMA combines OFDM and frequency present a MUDiv/OFDMA system. The configuration of the division multiple access (FDMA), and provides each user with a proposed system is described in Section III. In Section IV, we fraction of the available number of subcarriers. Worldwide show the computer simulation results. Finally, the conclusion is interoperability for microwave access (WiMAX) as given in Section V. IEEE802.16 standard is applied an OFDMA to accommodate Manuscript received May 10, 2011. II. MUDIV/OFDMA SYSTEM Y. Ida, T. Kamio, H. Fujisaka, and K. Haeiwa are with the Graduate School of Information Sciences, Hiroshima City University, 3-4-1 Ozukahigashi, Asaminami-ku, Hiroshima, 731-3194 Japan. A. Channel Model C. Ahn is with the Graduate School of Engineering, Chiba University, 1-33 We assume that a propagation channel consists of L discrete Yayoi-cho, Inage-ku, Chiba, 263-8522 Japan. paths with different time delays. The impulse response hm(τ, t) e-mail: y.ida@chiba-u.jp† 74 for user m is represented as 10 L 1 hm , t hm.l t m,l , (1) 5 l 0 where hm,l, τm,l are the complex channel gain and the time delay 0 of the lth propagation path for user m, and L 1 E hm,l 1 , 2 l 0 -5 where E denotes the ensemble average operation. The channel transfer function Hm(f, t) is the Fourier transform of -10 hm(τ, t) and is given by -15 H m f , t hm , t exp j 2f d 0 (2) -20 L 1 hm,l t exp j 2f m,l . User 1 User 2 l 0 -25 0 5 10 15 20 Frequency bandwidth [MHz] Fig. 1. Magnitude of the channel transfer function for a radio channel with B. Subcarrier Selection multipath. Figure 1 shows the magnitude of the channel transfer function for different users in a single cell. Subcarriers fade differently from user to user in OFDMA systems. The diversity that exists C. MUDiv/OFDMA between users is called multiuser diversity (MUDiv) and can be The transmitter block diagram of the proposed system is exploited by the transmitter to enhance the capacity of a wireless shown in Fig. 2(a). Firstly, the coded data is modulated and Np network. In a MUDiv/OFDMA, exploiting channel fluctuation pilot symbols are appended at the beginning of the sequence. diversity is in essence done by selecting the user with the strong The MUDiv/OFDMA transmitted signal for user m can be subcarrier channels. In this case, the selection scheme is very expressed in its equivalent baseband representation as important to select subcarriers with the highest SNR and to N p N d 1 2S N c 1 guarantee all users the same quality of service (QoS). The s m t g t iT um k , i (6) i 0 N c k 0 subcarrier selection criteria for each user is given by exp j 2 t iT k Ts , Nu 1 Nc 1 1 allocation Z H k m ,k , m ,k 2 (3) m where Nd and Np are the number of data and pilot symbols, Ts is m 0 k 0 0 no allocation , the effective symbol length, S is the average transmission power, and T is the OFDM symbol length, respectively. The frequency where αm,k is the selection parameter, Nc is the number of separation between adjacent orthogonal subcarriers is 1/Ts and subcarriers, and Nu is the number of users, respectively. From can be expressed, by using the kth subcarrier of the ith Eq. (3), the subcarrier is selected for the maximization of Z. In modulation symbol dm(k, i) with |dm(k, i)|=1 for Np ≤ i ≤ Np+Nd-1, this case, one subcarrier is selected at once and users do not as share the same subcarriers. Therefore, the MUDiv technique promises dramatically increased the system throughput and the um k , i cPN k d m k , i , (7) spectral efficiency. On the other hand, Eq. (3) requires large complexity for calculating subcarrier assignment. To mitigate where cPN is a long pseudo-noise (PN) sequence as a scrambling the complexity, the block selection method is considered. In the code to reduce the peak average power ratio (PAPR). Moreover, block selection, the block for each user is given by the kth subcarrier dm(k, i) is given by Nb 1 x N b q, i for k N b 1 H m q k d m k , i q0 m 1 2 H m q , (4) k 0 Nb 0 otherwise, (8) where Nb is the block length, β is N c N b , and y denotes where xm(k, i) is the kth subcarrier of the ith symbol for user m. the largest integer less than or equal to y, respectively. By using In general, the GI is inserted in order to eliminate the ISI due to Eq. (4), the block selection criteria for each user is given by a multipath fading, and hence, we have Nu 1 1 1 allocation Z H q m ,q , m ,q 2 (5) m 0 q 0 m 0 no allocation . T Ts Tg , (9) where, Tg is the GI length. In Eq. (6), the transmission pulse g(t) is given by 75 User#Nu-1 Data/FEC Interleaver Mod. Mux S/P Scrambling IFFT P/S Pilot generation User#0 (a) Transmitter (MS) Channel Side information estimation User#0 P/S MMSE detector Descrambling FFT S/P FEC/Data Deinterleaver User#Nu-1 Interference S/P IFFT FFT cancellation (b) Receiver (BS) Fig. 2. Proposed system. c PN k ~ 1 for Tg t Ts r k , i r k , i g t (10) c PN k 2 (14) 0 otherwise. N u 1 H k Ts , iT d m k , i nk , i , 2S ˆ The receiver structure is illustrated in Fig. 2(b). By applying Nc m 0 the FFT operation, the received signal r(t) is resolved into Nc where (∙)* is a complex conjugate and cPN k cPN k is the 2 subcarriers. The received signal r(t) in the equivalent baseband representation can be expressed as descrambling operation, respectively. For Eq. (14), we can see N u 1 that the received signal has the frequency distortion arising from r t h , t s t d nt , m (11) a frequency selective fading. To mitigate this frequency m 0 distortion, the frequency equalization combining is necessary. where n(t) is additive white Gaussian noise (AWGN) with a For the channel estimation scheme using Np pilot symbols, the single sided power spectral density of N0. The kth subcarrier channel response of the kth subcarrier is given by ~k , i is given by r N p 1 H k Ts r k , i , ~ 1 (15) r t exp j 2 t iT k Ts dt iT Ts ~ k , i 1 r Ts iT N p 2P N c i 0 N u 1N c 1 where P is the transmitted pilot signal power. Here, the u m e, i exp j 2 2S 1 Ts Nc m 0 e 0 Ts 0 combining weight for the kth subcarrier is denote by ω(k, i). After the frequency equalization combining, the received e k t Ts h , t iT g t (12) detected data symbol for user m can be written as d m k , i r k , i k , i ~ exp j 2e Ts d dt nk , i , ˆ H k Ts , iT d m k , i k , i nk , i k , i 2S ˆ Nc where nk , i is AWGN noise with zero-mean and a variance of ˆ for k N b 1. (16) 2N0/Ts. After abbreviating, Eq. (12) can be rewritten as N u 1N c 1 From Eq. (16), the decision variable of the kth subcarrier and ~ k , i 1 u m e, i exp j 2 2S Ts r the ith data symbol for user m is obtained by Ts Nc m 0 e0 0 Nb 1 ~ k , i d N q, i for k N b 1. (17) ~ e k t Ts h , t iT g t (13) xm m b q 0 exp j 2e Ts d dt nt ˆ N u 1 H k Ts , iT u m k , i nk , i . 2S ˆ Nc m 0 After descrambling, the output signal r(k, i) is given by 76 III. PROPOSED SYSTEM ~ N u 1 R i R i λ isi,ici FDi , m ˆ m 0 (22) A. MUDiv/OFDMA without GI N u 1 In the proposed system, we have Eq. (9) as λFD m 0 i,m Ni , T Ts . (18) where λ is the time domain channel matrix and N i is the noise In this case, the received signal r(k, i) after the pilot signal term with the residual ISI and residual ICI, respectively. After separation contains the ISI and ICI. In this paper, we eliminate the FFT operation, the ICI equalized signal Di, m is generated the ISI and ICI in the time domain. Firstly, the received signal r(k, i) after the IFFT operation is rewritten the time domain by using Eq. (15). Observing Eqs. (21) and (22), the proposed matrix form as method using the orthogonality reconstruction with inserting the subtracted signal due to the ISI compensation can mitigate the N u 1 Ri λ m 0 isi, i 1 FDi 1, m λ ici ,i FDi , m N i , (19) enhancement of the noise term. Therefore, the detected signal Di, m is accurately detected compared with Di, m . Next, we where λisi,i-1 and λici,i are the Nc×Nc ISI and ICI channel matrices explain that the frequency equalization combining using Eq. (15). for the (i - 1)th and the ith symbols, F is the IFFT operation, and Ni is the Nc×1 noise matrix, respectively. In next subsection, we explain the ISI and ICI compensation methods. D. Zero Forcing (ZF) The ZF weight ωzf(k, i) is given by B. ISI and ICI Equalization zf k , i ~ 1 (23) . In general, the first data symbol of the received signal has no H k T the ISI [16]. Hence, the received signal of Eq. (19) for i = 0 is expressed as Here, the time domain matrix R i after the FFT operation is rewritten the kth subcarrier r k , i . By using Eq (23), the N u 1 R0 λ m0 ici , 0 FD0, m N 0 . (20) detectd signal d zf , m k , i can be written as For i > 0, we eliminate the ISI and ICI. The ISI equalization is d zf ,m k , i r k , i zf k , i performed by using the previous detected signal Di,m . ~ N u 1 H k T , iT d m k , i zf k , i 2S ~ Therefore, the time domain signal R i to eliminate the ISI is Nc m 0 obtained by n k , i zf k , i N u 1 N u 1 n k , i k , i d k , i H k T ~ ~ 2S Ri Ri λ isi,ici FDi 1,m ˆ m0 (21) Nc m 0 zf m ~ N u 1 ~ for k N b 1, (24) λ ici FD i , m N i , m 0 where zf k , i H k T , i H k T and n k , i is the noise ~ ˆ where λ isi,ici is the estimated ISI and ICI channel matrix and term, respectively. From Eq. (24), the decision variable is ~ ˆ obtained by N i is the noise term with the residual ISI, respectively. λ isi,ici N b 1 is consisted the estimated channel impulse responses for Eq. x zf , m k , i d zf , m N b q, i for k N b 1. (15) after the IFFT operation. After the FFT operation, the ISI q 0 equalized signal Di, m is generated by using Eq. (15). (25) Observing Eq. (21), the ISI is eliminated. However, since the The ZF scheme can restore the orthogonality, but it enhances the ICI is remained, the noise component is enhanced. Therefore, noise term due to the residual ISI and ICI. we mitigate the noise enhancement due to the ICI. E. Minimum Mean Square Error (MMSE) C. Replica Signal Insertion based on ICI Equalization The MMSE weight is given by To avoid the noise enhancement due to the ICI, we consider k , i ~ H k 2T , ~ the orthogonality reconstruction with inserting the eliminated (26) mm signal due to the ISI compensation. The ICI equalized signal H k T 2 ~ R i with inserting eliminated the part of the signal using ~ previous detected signal Di, m is given by where 2 is the estimated noise power. In this paper, by using the detected signal d zf , m k , i , 2 is obtained by ~ 77 Nu 1 N d 1 r k , i H k T d k , i 0 1 ~ 2 10 2 ~ zf ,m . (27) With GI (Nb=16, ZF) Nd m 0 i 0 Without GI (Nb=16, ZF) With GI (Nb=16, MMSE) By using Eq. (26), the detected signal d mm, m k , i can be -1 10 Without GI (Nb=16, MMSE) written as -2 10 d mm ,m k , i r k , i mm k , i N u 1 H k T , iT d m k , i mm k , i -3 2S 10 Nc m 0 n k , i mm k , i 10 -4 n k , i H k T N u 1 ~ mm k , i d m k , i ~ 2S H k T 2 2 -5 Nc m 0 ~ 10 for k N b 1, (28) -6 10 H k T 0 5 10 15 20 25 where mm k , i H k T , T H k T ~ ~ 2 2 . ~ Eb/N0 [dB] Fig. 3. The BER of the conventional MUDiv/OFDMA with the GI and without Observing the noise term of Eqs. (24) and (28), the MMSE the GI at Doppler frequency of 10 Hz. scheme can mitigate the noise enhancement due to the residual ISI and ICI. Therefore, the MMSE scheme is accurately 0 10 detected to compare with the ZF scheme. Finally, the decision With GI (Nb=16, ZF) variable is obtained by With GI (Nb=16, MMSE) Without GI (Nb=16, MMSE) -1 10 ISI cancellation (Nb=16, MMSE) N b 1 xmm, m k , i d N b q, i Proposed method (Nb=16, MMSE) mm , m for k N b 1. Proposed method (Nb=8, MMSE) q 0 -2 10 (29) -3 10 IV. COMPUTER SIMULATED RESULTS In this section, we show the performance of the proposed 10 -4 method. Figure 2 shows a simulation model of the proposed system. On the transmitter, the data stream is encoded. Here, -5 10 convolutional codes (rate R = 1/2, constrain length K = 7) with interleaving used. These have been found to be efficient for transmission of an OFDM signal over a frequency selective 10 -6 0 5 10 15 20 25 fading channel. The coded bits are QPSK modulated, and then Eb/N0 [dB] the pilot signal and the data signal are multiplexed. After serial Fig. 4. The BER of the conventional methods and the proposed method for Nb to parallel (S/P) converted, the OFDM signal is allocated based = 8, 16 at Doppler frequency of 10 Hz. on Eq. (5). The scrambling operation is adapted to reduce the PAPR with a PN code. The OFDM time signal is generated by an IFFT. The transmitted signal is subject to broadband channel maximum Doppler frequency is 10 Hz. In the receiver, the propagation. In this simulation, we assume that OFDM symbol received signal is S/P converted. The parallel sequences are period is 8.96 s, and L = 5 path Rayleigh fadings have passed to the FFT operator and convert the signal back to the exponential shapes and a path separation Tpath = 140 ns. The frequency domain. The frequency domain data signal is detected and demodulated. Since the detected signal contains TABLE I the ISI and ICI, it is necessary to eliminate them. The ISI SIMULATION PARAMETERS. equalization is performed with the previous detected signal as Data modulation QPSK Eq. (21). Moreover, to restrict the orthogonality, the ICI Data detection Coherent equalization is performed to insert the replica signal as Eq. (22). Symbol duration 8.96 s Frame size Np = 2, Nd = 20 Finally, the MMSE equalization is performed to mitigate the FFT size 64 noise enhancement due to the residual ISI and ICI as Eq. (28). Number of carriers 64 After the detection, bits are decoded by using the Vitebi soft Number of users 4 decoding algorithm. The packet consists of Np = 2 and Nd = 20 Guard interval 16 sample times data symbols. Table I shows the simulation parameters. Fading 5 path Rayleigh fading Fig. 3 shows the BER of the conventional MUDiv/OFDMA Doppler frequency 10 Hz FEC Convolutional code with and without GI at Doppler frequency of 10 Hz. For (R = 1/2, K = 7) inserting GI, MMSE shows about 5 dB gain compared with ZF. 78 0 -4 10 10 With GI (Nb=16, MMSE) Without GI (Nb=16, MMSE) ISI cancellation (Nb=16, MMSE) -1 10 Proposed method (Nb=16, MMSE) -5 10 -2 10 -3 -6 10 10 -4 10 -7 10 10 -5 With GI (ZF) With GI (MMSE) Without GI (MMSE) ISI cancellation (MMSE) -6 Proposed method (MMSE) 10 10 -8 0 5 10 15 20 25 0 2 4 6 8 10 12 14 16 Eb/N0 [dB] Block length Nb Fig. 5. The BER of the conventional methods and the proposed method for Nb Fig. 7. The BER versus the block length Nb for the conventional methods and = 16 in the perfect channel at Doppler frequency of 10 Hz. the proposed method with Eb/N0 = 18 dB at Doppler frequency of 10 Hz. 0 10 7 With GI (Nb=1, ZF) Without GI (Nb=1, ZF) With GI (Nb=16, MMSE) -1 10 Without GI (Nb=16, MMSE) 6 Proposed method (Nb=16, MMSE) Proposed method (Nb=8, MMSE) -2 5 10 4 -3 10 3 -4 10 2 -5 With GI (Nb=16, ZF) 10 With GI (Nb=16, MMSE) 1 Without GI (Nb=16, MMSE) ISI cancellation (Nb=16, MMSE) Proposed method (Nb=16, MMSE) -6 10 Proposed method (Nb=8, MMSE) 0 5 10 15 20 25 0 Eb/N0 [dB] 0 5 10 15 20 Eb/N0 [dB] Fig. 6. The BER of the conventional methods and the proposed method for Nb = 1, 8, 16 at Doppler frequency of 10 Hz. Fig. 8. The throughput of the conventional methods and the proposed method for Nb = 8, 16 at Doppler frequency of 10 Hz. Moreover, MMSE shows about 8 dB gain compared with ZF diversity can enhance the BER performance. In Fig. 5, the BER without inserting GI. Therefore, the MMSE equalization can performance is improved under the perfect channel estimation. enhance the BER performance both inserting GI and without This is because the channel response of Eq. (15) is not contained GI. the noise and the noise enhancement is mitigated. Therefore, the Figs. 4, 5, and 6 show the BER of the conventional methods proposed method shows the approximately same BER and the proposed method at Doppler frequency of 10 Hz. In Fig. performance compared with inserting the case with GI in the 4, the BER performance of ISI cancellation without GI shows same block length. In Fig. 6, the BER of Nb = 1 shows a good about 6 times improvement compared with not inserting GI performance, but large complexity is required. The BER since ISI is eliminated. Moreover, the ISI cancellation shows performance of Nb = 1 with ZF shows about 67 times compared about 2 times improvement compared with inserting GI with ZF. with MMSE of Nb = 16 for not inserting GI. On the other hand, The BER performance of the proposed method for Nb = 16 the proposed method of Nb = 8 shows the approximately same shows about 6 times improvement compared with ISI BER performance compared with ZF for Nb = 1 with inserting cancellation without GI. However, the proposed method of Nb = GI. Therefore, the proposed method of Nb = 8 achieves the same 16 shows about 3 dB penalty compared with inserting GI with BER performance compared with ZF for Nb = 1with inserting MMSE since the noise is enhanced due to the residual ISI and GI. ICI. On the other hand, the proposed method of Nb = 8 shows the Fig. 7 shows the BER versus the block length Nb for the best BER performance. It means that a strong multiuser conventional methods and the proposed method with Eb/N0 = 18 79 dB at Doppler frequency of 10 Hz. For Nb = 16, the proposed on OFDM access in IEEE802.16”, IEEE Commun. Mag., vol. 40, pp. 96- 103, April 2002. method shows about 7 times improvement compared with ZF [7] WiMax Forum, http://www.wimaxforum.org/ with inserting GI. However, this shows about 9 times penalty [8] S. J. Vaughan-Nichols, “Mobile WiMax: the next wireless battleground?”, compared with inserting GI of MMSE. For Nb ≤ 8, the BER of IEEE Computer Society, vol. 41, no. 6, pp. 16-18, June 2008. proposed method approaches the BER performance of MMSE [9] W. Seo, H. Song, J. Lee, and D. Hong, “A new asymptotic analysis of with inserting GI. Therefore, a multiuser diversity is effective to throughput enhancement from selection diversity using a high SNR approach in multiuser systems”, IEEE Trans. on Wireless Commun., pp. mitigate the ISI and ICI for Nb ≤ 8. 55-59, vol. 8, no. 1, Jan. 2009. Fig. 8 shows the throughput of the conventional methods and [10] S. Kwack, H. Seo, and B. G. Lee, “Suitability-based subcarrier allocation the proposed method at Doppler frequency of 10 Hz. The for multicast services employing layered video coding in wireless OFDM throughput Ttp is defined as System”, Proc. of VTC2007, pp. 1752-1756, Oct. 2007. [11] J. Hui and Y. Zhou, “Enahanced rate adaptive resource allocation scheme Nd Nc C R in downlink OFDMA system”, Proc. of VTC2006, vol. 5, pp. 2464-2468, Ttp N p N d T 1 Pper , (30) May 2006. [12] C. Ahn, “Reinforced multiuser diversity using frequency symbol spreading and adaptive subcarrier block selection for OFDMA”, IEICE where C is the modulation level and Pper is the packet error rate , Technical Report, vol. 109, no. 266, CS2009-44, pp. 13-18, Nov. 2009. respectively. In this simulation, we assume that the GI length is [13] S. Trautmann and N. J. Fliege, “Perfect equalization for DMT systems without guard interval”, IEEE Journal on Selected Areas in Commun., pp. Ts/4. In this case, the symbol duration T is 11.2 μs, and the 987-996, nol 20, no. 5, June 2002. maximum throughput with GI would be 20 % degraded from Eq. [14] G. Mkrtchyan, K. Naito, K. Mori, and H. Kobayashi, “ML time domain (30). Thus, the maximum throughput of the proposed method channel estimation and equalization for OFDM without guard interval”, for Nb = 16 shows the improvement of about 20 % compared Proc. of ECTI-CON2005, pp. 473-476, May 2005. [15] T. Kobori and F. Takehata, “An application of frequency diversity to with inserting GI. Therefore, the proposed method of Nb = 16 OFDM transmission based on overlap-FDE”, IEICE Trans. Commun., achieves the enhancement of the maximum throughput. vol. J93-B, no. 12, pp. 1651-1659, Dec. 2010. Moreover, the proposed method of Nb = 8 shows the best [16] Y. Ida, C. Ahn, K. Kamio, H. Fujisaka, and K. Haeiwa, “Large delay throughput performance. This means that a strong multiuser spread cancellation based on replica signal for HTRCI-MIMO/OFDM”, Proc. of WPMC’09, S-11-4, pp. 1-5, Sep. 2009. diversity also enhances the throughput performance. V. CONCLUSION In this paper, we have proposed the ISI and ICI compensations to enhance the throughput performance for a MUDiv/OFDMA without GI. When the GI is not inserted, the system performance is significantly degraded due to the ISI and ICI. Therefore, we have performed ISI and ICI compensations. From the simulation results, the proposed method shows the approximately same BER performance compared with the case with inserting GI. For the throughput performance, the proposed method improves about 20 % compared with the case with inserting GI. As a result, the proposed method achieves the enhancement of the maximal throughput. Moreover, the proposed method of Nb = 8 shows the best performance both the BER and the throughput. Therefore, a strong multiuser diversity enhances the BER and the throughput performances. REFERENCES [1] 2010 White paper information and communications in Japan, http://www.soumu.go.jp/johotsusintokei/whitepaper/ja/h22/pdf/index.ht ml [2] L. Cimini, “Analysis and simulation of digital mobile channel using OFDM”, IEEE Trans. Commun., vol. 33, no. 7, pp. 666-675, July 1985. [3] J.A.C. Bingham, “Multicarrier modulation for data transmission: an idea whose time has come”, IEEE Commun. Mag., vol. 28, pp. 5-14, May 1990. [4] ETSI ETS 301 958, “Digital video broadcasting (DVB); interaction channel for digital terrestrial television (RCT) incorporating multiple access OFDM”, ETSI, Tech. Rep., March 2002. [5] “IEEE draft standard for local and metropolitan area network-part 16: Air interface for fixed broadband wireless access systems - medium access control modifications and additonal physical layer specifications for 2- 11GHz”, IEEE LAN MAN Standards Committee, 2002. [6] I. Koffman and V. Roman, “Broadband wireless access solutions based 80

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