Throughput Performance of Iterative Frequency-domain SIC with 2D MMSE-FDE for SC-MIMO Multiplexing Akinori Nakajima † and Fumiyuki Adachi ‡ Dept. of Electrical and Communications Engineering, Graduated school of Engineering, Tohoku University, Sendai, Japan †nakajima@mobile.ecei.tohoku.ac.jp, ‡adachi@ecei.tohoku.ac.jp Abstract— Broadband wireless packet access will be the core technology of the next generation mobile communication systems. For very high-speed and high-quality packet transmissions in a limited bandwidth, the joint use of multiple- input multiple-output (MIMO) multiplexing and hybrid ARQ (HARQ) is an effective method. However, if single-carrier (SC) transmission is used, the transmission performance significantly degrades due to a large inter-symbol interference (ISI) resulting from a severe frequency-selective fading. In this paper, we propose an iterative frequency-domain successive interference cancellation (SIC) with two dimensional (2D) MMSE-FDE. At each iteration stage, the successive signal detection/cancellation is performed according to the descending order of the signal reliability. However, since the interference from the other transmit antennas can be only partially cancelled by performing SIC, the residual interference is present at the output of SIC. In this paper, we propose to update the 2D MMSE-FDE weights at each signal detection in order to suppress simultaneously the ISI and the interference from other antennas while obtaining antenna and frequency diversity gain. However, since a single use of SIC with 2D MMSE-FDE is insufficient, it is repeated a sufficient number of times. The bit error rate (BER) and HARQ throughput performance in a frequency-selective Rayleigh fading channel are evaluated by computer simulation. Keywords- SC-MIMO multiplexing, Iterative frequency- domain SIC, 2D MMSE-FDE, RCPT-HARQ I. INTRODUCTION Recently, there have been tremendous demands for high- speed data transmissions higher than few tens of Mbps in mobile communications [1]. However, for such high-speed data transmissions, the channel consists of many resolvable paths with different time delays, resulting in a severely frequency-selective fading channel. The transmission performance of SC transmission significantly degrades due to a severe inter-symbol interference (ISI) [2]. Recently, it has been shown that the use of frequency-domain equalization (FDE) can significantly improve the SC transmission performance [3,4]. For wireless communication, however, the available bandwidth is limited, so some highly spectrum- efficient transmission technique is required for the next generation mobile communication systems. One of the promising techniques is the multiple-input multiple-output (MIMO) multiplexing [5], that uses multiple transmit and receive antennas. Packet access will be the core technology of the next generation mobile communication systems. For very high-speed and high-quality packet transmissions in a limited bandwidth, the joint use of MIMO multiplexing and hybrid automatic repeat request (HARQ) is very effective. In MIMO multiplexing, the transmit data sequence is transformed into parallel sequences and each sequence is transmitted from a different transmit antenna at the same time with the same carrier frequency. Therefore, the total transmission data rate increases in proportion to the number of transmit antennas without requiring additional bandwidth. At a receiver, it is necessary to separate the signals transmitted from different antennas. A lot of research attention has been paid to develop the signal separation schemes, which provide a performance close to that of maximum likelihood detection (MLD) but with reduced complexity, like vertical-Bell laboratories layered space-time architecture (V-BLAST) [6] (which is a version of successive interference cancellation (SIC)), MLD using QR decomposition [7] and so on. Recently, we had proposed an iterative frequency-domain parallel interference cancellation (PIC) with two dimensional minimum mean square error (2D MMSE)-FDE for single carrier (SC)-MIMO multiplexing in a frequency-selective fading channel [8,9]. In 2D MMSE-FDE, the FDE weight is considered for each pair of transmit antenna and receive antenna. However, in PIC, all interference replicas are generated at the same time and therefore, an interference replica having low reliability limits the performance improvement. Another cancellation scheme is successive interference cancellation (SIC). In SIC, signal detection/cancellation is performed according to the descending order of the signal reliability. Therefore, the interference replica is more reliable than in PIC and hence, SIC provides better performance than PIC. In this paper, we propose an iterative frequency-domain SIC with 2D MMSE- FDE for SC-MIMO multiplexing in a frequency-selective fading channel. For the separation of the transmitted signals, the successive signal detection/cancellation is performed at each iteration stage according to the descending order of the signal reliability. However, since SIC can cancel only partially the interference from the other transmit antennas, the residual interference is present at the output of SIC. In this paper, the 2D MMSE-FDE weights are updated, by using the signals which have already been detected, at every signal detection in order to suppress simultaneously the ISI and the residual interference from other antennas while obtaining antenna and frequency diversity gain. However, since the initial iteration stage can not sufficiently suppress the interference, frequency- domain SIC with 2D MMSE-FDE is repeated a sufficient number of times. We evaluate, by computer simulation, the bit error rate (BER) performance and the throughput performance of rate compatible punctured turbo coded (RCPT) HARQ [10] of SC-MIMO multiplexing using iterative frequency-domain SIC with 2D MMSE-FDE in a frequency-selective Rayleigh fading channel. We then compare the BER and throughput performances of the proposed SIC with those of PIC [8,9]. The remainder of this paper is organized as follows. Section II describes the iterative frequency-domain SIC with 2D MMSE-FDE. In section III and IV, the system model and RCPT-HARQ are explained, respectively. Section V presents the computer simulation results of the BER and throughput performances. Section VI concludes this paper. 1-4244-0063-5/06/$2000 (c) 2006 IEEE