Kazuaki Takeda

Tohoku University, Sendai-shi, Miyagi-ken, Japan

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Publications (40)3.05 Total impact

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    ABSTRACT: Multi-user single-carrier multiple-input multiple-output (MU SC-MIMO) multiplexing can increase the uplink capacity of a cellular system without expanding the signal bandwidth. It is practically important to make clear an extent to which the MU SC-MIMO multiplexing combined with frequency-domain equalization (FDE) and transmit power control (TPC) can increase the uplink capacity in the presence of the co-channel interference (CCI). Since the theoretical analysis is quite difficult, we resort to the computer simulation to investigate the uplink capacity. In this paper, frequency-domain zero-forcing detection (ZFD) and frequency-domain minimum mean square error detection (MMSED) are considered for MU signal detection. It is shown that ZFD and MMSED provide almost the same uplink capacity and that an advantage of fast TPC over slow TPC diminishes. As a result, MU SC-MIMO using computationally efficient ZFD can be used together with slow TPC instead of using MMSED. With 8 receive antennas and slow TPC, MU SC-MIMO multiplexing using ZFD can achieve about 1.5times higher uplink capacity than SU SC-SIMO diversity. KeywordsMulti-user MIMO–Single-carrier–Frequency-domain equalization–Cellular system–Uplink-capacity
    Wireless Personal Communications 06/2011; 58(3):455-468. · 0.43 Impact Factor
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    ABSTRACT: Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can increase the downlink bit error rate (BER) performance of DS-CDMA beyond that possible with conventional rake combining in a frequency-selective fading channel. FDE requires accurate channel estimation. Recently, we proposed a pilot-assisted channel estimation (CE) based on the MMSE criterion. Using MMSE-CE, the channel estimation accuracy is almost insensitive to the pilot chip sequence, and a good BER performance is achieved. In this paper, we propose a channel estimation scheme using one-tap recursive least square (RLS) algorithm, where the forgetting factor is adapted to the changing channel condition by the least mean square (LMS)algorithm, for DS-CDMA with FDE. We evaluate the BER performance using RLS-CE with adaptive forgetting factor in a frequency-selective fast Rayleigh fading channel by computer simulation.
    IEICE Transactions. 01/2009; 92-B:1457-1465.
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    Yohei Kojima, Kazuaki Takeda, Fumiyuki Adachi
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    ABSTRACT: Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can provide better downlink bit error rate (BER) performance of direct sequence code division multiple access (DS-CDMA) than the conventional rake combining in a frequency-selective fading channel. FDE requires accurate channel estimation. In this paper, we propose a new 2-step maximum likelihood channel estimation (MLCE) for DS-CDMA with FDE in a very slow frequency-selective fading environment. The 1st step uses the conventional pilot-assisted MMSE-CE and the 2nd step carries out the MLCE using decision feedback from the 1st step. The BER performance improvement achieved by 2-step MLCE over pilot assisted MMSE-CE is confirmed by computer simulation.
    IEICE Transactions. 01/2009; 92-B:2065-2071.
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    Kazuaki Takeda, Yohei Kojima, Fumiyuki Adachi
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    ABSTRACT: Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can provide a better bit error rate (BER) performance than rake combining. However, the residual inter-chip interference (ICI) is produced after MMSE-FDE and this degrades the BER performance. Recently, we showed that frequency-domain ICI cancellation can bring the BER performance close to the theoretical lower bound. To further improve the BER performance, transmit antenna diversity technique is effective. Cyclic delay transmit diversity (CDTD) can increase the number of equivalent paths and hence achieve a large frequency diversity gain. Space-time transmit diversity (STTD) can obtain antenna diversity gain due to the space-time coding and achieve a better BER performance than CDTD. Objective of this paper is to show that the BER performance degradation of CDTD is mainly due to the residual ICI and that the introduction of ICI cancellation gives almost the same BER performance as STTD. This study provides a very important result that CDTD has a great advantage of providing a higher throughput than STTD. This is confirmed by computer simulation. The computer simulation results show that CDTD can achieve higher throughput than STTD when ICI cancellation is introduced.
    IEICE Transactions. 01/2009; 92-B:2882-2890.
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    ABSTRACT: In next generation wireless network, significantly higher rate data services of close to 1 Gpbs are expected. The wireless channels for such a broadband data transmission become severe frequency-selective. Frequency-domain equalisation (FDE) technique may play an important role for broadband data transmission using multi-carrier (MC)- and direct-sequence code division multiple access (DS-CDMA). The performance can be further improved by the use of multi-input/multi-output (MIMO) antenna diversity technique. The downlink performance is significantly improved with FDE. However, the uplink performance is limited by the multiple access interference (MAI). To remove the MAI while gaining the frequency diversity effect through the use of FDE, two-dimensional (2D) block spread CDMA can be used. Recently, particular attention has been paid to MIMO space division multiplexing (SDM) to significantly increase the throughput without expanding the signal bandwidth. In this paper, we present a comprehensive performance comparison of MC- and DS-CDMA using FDE. Copyright © 2008 John Wiley & Sons, Ltd.
    European Transactions on Telecommunications 08/2008; 19:553-560. · 1.05 Impact Factor
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    ABSTRACT: Recently, multi-carrier code division multiple access (MC-CDMA) has been attracting much attention as a broadband wireless access technique for the next generation mobile communications systems. Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can take advantage of the channel frequency-selectivity and improve the average bit error rate (BER) performance due to frequency-diversity gain. The conventional FDE requires the insertion of the guard interval (GI) to avoid the inter-block interference (IBI), resulting in the transmission efficiency loss. In this paper, an overlap FDE technique, which requires no GI insertion, is presented for MC-CDMA transmission. An expression for the conditional bit error rate (BER) is derived for the given set of channel gains. The average BER performance in a frequency-selective Rayleigh fading channel is evaluated by Monte-Carlo numerical computation method using the derived conditional BER and is confirmed by computer simulation of the MC-CDMA signal transmission. Keyword− Frequency-selective fading channel, Overlap FDE, MC-CDMA.
    IEICE Transactions on Communications 03/2008; 91-B:795-804. · 0.31 Impact Factor
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    ABSTRACT: Recently, a new frequency-domain equalization (FDE) technique, called overlap FDE, that requires no GI insertion was proposed. However, the residual inter/intra-block interference (IBI) cannot completely be removed. In addition to this, for multicode direct sequence code division multiple access (DS-CDMA), the presence of residual interchip interference (ICI) after FDE distorts orthogonality among the spreading codes. In this paper, we propose an iterative overlap FDE for multicode DS-CDMA to suppress both the residual IBI and the residual ICI. In the iterative overlap FDE, joint minimum mean square error (MMSE)-FDE and ICI cancellation is repeated a sufficient number of times. The bit error rate (BER) performance with the iterative overlap FDE is evaluated by computer simulation.
    IEICE Transactions. 01/2008; 91-B:1942-1951.
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    Koichi Ishihara, Kazuaki Takeda, Fumiyuki Adachi
    IEICE Transactions on Communications 05/2007; 90-B:1152-1161. · 0.31 Impact Factor
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    Koichi Ishihara, Kazuaki Takeda, Fumiyuki Adachi
    IEICE Transactions on Communications 05/2007; 90-B:1171-1180. · 0.31 Impact Factor
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    IEICE Transactions on Communications 03/2007; 90-B:597-606. · 0.31 Impact Factor
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    Ryoko Kawauchi, Kazuaki Takeda, Fumiyuki Adachi
    IEICE Transactions on Communications 03/2007; 90-B:591-596. · 0.31 Impact Factor
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    Kazuaki Takeda, Fumiyuki Adachi
    IEICE Transactions. 01/2007; 90-B:260-268.
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    ABSTRACT: Turbo coded hybrid ARQ (HARQ) is known as one of the promising error control techniques for high speed wireless packet access. However, in a severe frequency-selective fading channel, the HARQ throughput performance significantly degrades for direct sequence code division multiple access (DS-CDMA) system using rake combining. This problem can be overcome by replacing the rake combining by the frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion. In a system with the conventional FDE, the guard interval (GI) is inserted to avoid the inter-block interference (IBI). The insertion of GI reduces the throughput. Recently, overlap FDE that requires no GI insertion was proposed. In this paper, we apply overlap FDE to HARQ and derive the MMSE-FDE weight for packet combining. Then, we evaluate the throughput performance of DS-CDMA HARQ with overlap FDE. We show that overlap FDE provides better throughput performance than both the rake combining and conventional FDE regardless of the degree of the channel frequency-selectivity.
    01/2007;
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    Kazuaki TAKEDA, Fumiyuki ADACHI
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    ABSTRACT: Frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion can replace the conventional rake combining to significantly improve the bit error rate (BER) performance in a frequency-selective fading channel. MMSE-FDE requires an accurate estimate of the channel transfer function and the signal-to-noise power ratio (SNR). Direct application of pilot-assisted channel estimation (CE) degrades the BER performance, since the frequency spectrum of the pilot chip sequence is not constant over the spreading bandwidth. In this paper, we propose a pilot-assisted decision feedback frequency-domain MMSE-CE. The BER performance with the proposed pilot-assisted MMSE-CE in a frequency-selective Rayleigh fading channel is evaluated by computer simulation. It is shown that MMSE-CE always gives a good BER performance irrespective of the choice of the pilot chip sequence and shows a high tracking ability against fading. For a spreading factor SF of 16, the E b / N 0 degradation for BER=10−4 with MMSE-CE from the ideal CE case is as small as 0.9 dB (including an E b / N 0 loss of 0.28 dB due to the pilot insertion).
    01/2007;
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    ABSTRACT: Recently, frequency-domain pre-equalization (pre-FDE) transmission has been attracting attention for improving the broadband DS-CDMA (or single carrier (SC)) transmission performance in a frequency-selective fading channel. To further improve the transmission performance, antenna diversity technique is very effective. However, so far the joint use of pre-FDE and the receive diversity has not been fully discussed. Recently, we proposed the space-time block coded-joint transmit/receive diversity (STBC-JTRD) for the narrowband transmission in a frequency-nonselective fading channel. STBC-JTRD allows an arbitrary number of transmit antennas while limiting the number of receive antennas to 4. In this paper, we extend the STBC-JTRD to the case of frequency-selective fading channel and propose the frequency-domain STBC-JTRD for the SC transmission in a frequency-selective fading channel. The average bit error rate (BER) performance of the SC transmission with frequency-domain STBC-JTRD is evaluated by the computer simulation
    Communication systems, 2006. ICCS 2006. 10th IEEE Singapore International Conference on; 11/2006
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    Kazuaki Takeda, Fumiyuki Adachi
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    ABSTRACT: Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can replace the conventional rake combining with significantly improved bit error rate (BER) performance of multicode DS-CDMA in a frequency-selective fading channel. However, the presence of residual inter-chip-interference (ICI) after MMSE-FDE produces the orthogonality distortion among the spreading codes and the BER performance degrades as the number of multiplex order increases. Recently, we have proposed a frequency-domain ICI cancellation to improve the uncoded performance. To further improve the BER performance, in this paper, we propose MMSE turbo equalization. In the proposed scheme, MMSE-FDE and ICI cancellation are incorporated into iterative maximum a posteriori (MAP) decoding, resulting in an MMSE turbo equalization. MMSE weight taking into account the residual ICI is updated in each iteration. The effect of MMSE turbo equalization is confirmed by computer simulation
    Communication systems, 2006. ICCS 2006. 10th IEEE Singapore International Conference on; 11/2006
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    ABSTRACT: High speed packet access is the core technology of the next generation mobile communication systems. Turbo coded hybrid ARQ (HARQ) is known as one of the promising error control techniques. For direct sequence code division multiple access (DS-CDMA), frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion can replace the well known rake combining with much improved transmission performance. However, the insertion of guard interval (GI), which is required for conventional FDE, reduces the throughput. Recently, overlap FDE that requires no GI insertion was proposed for DS-CDMA. In this paper, we evaluate the throughput of DS-CDMA HARQ with overlap FDE
    Communication systems, 2006. ICCS 2006. 10th IEEE Singapore International Conference on; 11/2006
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    IEICE Transactions. 01/2006; 89-B:2189-2195.
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    Koichi Ishihara, Kazuaki Takeda, Fumiyuki Adachi
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    ABSTRACT: SUMMARY Frequency-domain equalization (FDE) based on the min- imum mean square error (MMSE) criterion can significantly improve the BER performance of DS- and MC-CDMA systems in a severe frequency- selective fading channel. However, since the frequency-distorted signal cannot be completely equalized, the residual inter-code interference (ICI) limits the BER performance improvement. 4G systems must support much higher variable rate data services. Orthogonal multicode transmission tech- nique has flexibility in offering variable rate services. However, the BER performance degrades as the number of parallel codes increases. In this paper, we propose an iterative frequency-domain soft interference cancel- lation (IFDSIC) scheme for multicode DS- and MC-CDMA systems and their achievable BER performances are evaluated by computer simulation.
    IEICE Transactions. 01/2006; 89-B:3344-3355.
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    ABSTRACT: Recently, frequency-domain equalization (FDE) has been attracting much attention is an effective equalization technique for the single-carrier (SC) transmission in a frequency-selective fading channel. However, when the time delays of the propagation paths are fractionally spaced, the inter-symbol interference (ISI) is produced for the SC transmission using the Nyquist filters. In this paper, we examine, by computer simulation, the impact of the presence of fractionally spaced time delays on the bit error rate (BER) performance in a frequency-selective Rayleigh fading channel. Keyword Frequency-selective fading channel, fractionally spaced time delays, Nyquist filter, frequency-domain equalization, pilot assisted channel estimation, single-carrier transmission
    01/2006;