Kazuki Takeda

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

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Publications (35)1.29 Total impact

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    ABSTRACT: In the conventional iterative superimposed pilot-assisted channel estimation (SI-PACE), simple averaging of the instantaneous channel estimates obtained by using the pilot over several single-carrier (SC) blocks (called the frame in this paper) is taken in order to reduce the interference from data symbols. Therefore, the conventional SI-PACE has low tracking ability against fading time variations. To solve the tracking problem, Wiener filtering (WF)-based averaging can be used instead of simple averaging. However, WF incurs high computational complexity. Furthermore, the estimation error of the fading autocorrelation function significantly degrades the channel estimation accuracy. In order to improve the channel estimation accuracy while keeping the computational complexity low, a new iterative SI-PACE using sliding WF (called iterative SWFSI-PACE) is proposed. The channel estimation is done by sliding a WF having a shorter filter size than the measurement interval. The bit error rate (BER) and throughput performances of SC-FDE using iterative SWFSI-PACE are investigated by computer simulation to show that the proposed scheme achieves good BER and throughput performances while keeping the computational complexity low irrespective of the fading rate (or maximum Doppler frequency).
    IEICE Transactions on Communications. 01/2012; E95.B(3):924-932.
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    ABSTRACT: Uplink Capacity of OFDM Multi-User MIMO Using Near-ML Detection in a Cellular System
    IEICE Transactions. 01/2012; 95-B:198-205.
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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: In this paper, we investigate how a distributed antenna network (DAN) offers better throughput performance than a conventional cellular network (CN). In DAN, a group of multiple antennas are distributed in each cell of the CN in order to mitigate the adverse effect of path loss. Moreover, antenna diversity technique can make use of shadowing and multipath fading to improve the transmission performance due to a large spatial diversity gain. In this paper, we consider frequency-domain space-time block coded-joint transmit/ receive diversity (FD-STBC-JTRD) for downlink transmission of single-carrier (SC) DAN. FD-STBC-JTRD uses frequency-domain pre-equalization (pre-FDE) instead of receive FDE to keep the mobile terminal's complexity low, and achieves the full-diversity gain. We show by computer simulation that the transmit power for achieving the required throughput can be significantly reduced compared to the conventional CN.
    Proceedings of the 74th IEEE Vehicular Technology Conference, VTC Fall 2011, 5-8 September 2011, San Francisco, CA, USA; 01/2011
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    ABSTRACT: Joint MMSE-FDE & Spectrum Combining for a Broadband Single-Carrier Transmission in the Presence of Timing Offset
    IEICE Transactions. 01/2011; 94-B:1366-1375.
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    ABSTRACT: For the realization of future wireless networks, gigabit wireless technology, which can achieve higher-than-1 Gbps data transmission with extremely low transmit power, is indispensable. We have been studying the distributed antenna network (DAN) and the frequency domain wireless signal processing. In DAN, many antennas or clusters of antennas are spatially distributed over a service area, and they are connected by means of optical fiber links with DAN signal processing center. A number of distributed antennas cooperatively serve mobile users using spatial multiplexing, diversity, array, or relaying technique. In this paper, the recent advances in single-carrier DAN are introduced. Copyright © 2011 John Wiley & Sons, Ltd.
    Wireless Communications and Mobile Computing 01/2011; 11:1551-1563. · 0.86 Impact Factor
  • Kazuki Takeda, Fumiyuki Adachi
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    ABSTRACT: Joint Iterative Transmit/Receive FDE & FDIC for Single-Carrier Block Transmissions
    IEICE Transactions. 01/2011; 94-B:1396-1404.
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    ABSTRACT: Iterative MMSE-FDE/MUI Cancellation and Antenna Diversity for Frequency-Domain Filtered SC-FDMA Uplink
    IEICE Transactions. 01/2011; 94-B:2847-2856.
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    ABSTRACT: Transmission Performance of Frequency-Domain Filtered Single-Carrier Transmission Using Frequency-Domain Block Signal Detection with QRM-MLD
    IEICE Transactions. 01/2011; 94-B:1386-1395.
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    ABSTRACT: Performance Comparison of Overlap FDE and Sliding-Window Chip Equalization for Multi-Code DS-CDMA in a Frequency-Selective Fading Channel
    IEICE Transactions. 01/2011; 94-B:750-757.
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    ABSTRACT: Iterative MMSE Detection with Interference Cancellation for Up-Link HARQ Using Frequency-Domain Filtered SC-FDMA MIMO Multiplexing
    IEICE Transactions. 01/2011; 94-B:3559-3568.
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    ABSTRACT: We propose an incremental relaying scheme using joint Tx/Rx frequency-domain equalization (FDE) for single-carrier (SC) transmission. If a packet sent by a source node (S) has been correctly decoded at a relay node (R), but not at the destination node (D), retransmission is cooperatively done by S and R. Assuming that the channel state information (CSI) is shared by S, R, and D, joint Tx/Rx FDE is performed. We derive a set of optimal/suboptimal Tx/Rx FDE weights among S, R, and D, based on the minimum mean square error (MMSE) criterion under total transmit power constraint of S and R. Computer simulation verifies the effectiveness of the proposed scheme.
    Proceedings of the 74th IEEE Vehicular Technology Conference, VTC Fall 2011, 5-8 September 2011, San Francisco, CA, USA; 01/2011
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    ABSTRACT: Single carrier (SC) signal transmission has a property of low peak-to-average power ratio (PAPR) and achieves the frequency diversity gain by the use of frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion. In this paper, Nyquist filtered broadband SC transmission is considered. As the transmit filter roll-off factor α increases, the signal bandwidth increases and the PAPR reduces. MMSE-FDE using spectrum combining was proposed in [15]. An additional frequency diversity gain can be obtained by making use of the excess bandwidth introduced by the transmit filter and by using spectrum combining. In this paper, we thoroughly investigate how α affects PAPR, BER performance, and throughput performance.
    Vehicular Technology Conference (VTC 2010-Spring), 2010 IEEE 71st; 06/2010
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    Kazuki Takeda, Fumiyuki Adachi
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    ABSTRACT: In the next generation high-speed wireless packet access systems, hybrid automatic repeat request (HARQ) is necessary to achieve higher throughput performance. An HARQ with Chase combining (CC) transmits the same coded packet until it is correctly received. The received packets are combined to achieve the time-diversity gain. Recently, we proposed a joint transmit/receive frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion for a broadband single-carrier (SC) signal transmission in a frequency-selective channel. In this paper, we consider SC-HARQ using joint transmit/receive MMSE-FDE and derive a suboptimal set of transmit and receive FDE weights for packet combining. We show by computer simulation that the joint transmit/receive MMSE-FDE offers improved throughput compared to the conventional receive MMSE-FDE.
    Proceedings of the 71st IEEE Vehicular Technology Conference, VTC Spring 2010, 16-19 May 2010, Taipei, Taiwan; 01/2010
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    ABSTRACT: One-tap frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can significantly improve the bit error rate (BER) performance of single-carrier (SC) transmission in a frequency-selective fading channel. However, a big performance gap from the theoretical lower bound still exists due to the presence of residual inter-symbol interference (ISI) after MMSE-FDE. In this paper, we point out that the frequency-domain received SC signal can be expressed using the matrix representation similar to the multiple-input multiple-output (MIMO) multiplexing and therefore, signal detection schemes developed for MIMO multiplexing, other than simple one-tap MMSE-FDE, can be applied to SC transmission. Then, for the reception of SC signals, we propose a new signal detection scheme, which combines FDE with MIMO signal detection, such as MMSE detection and Vertical-Bell Laboratories layered space-time architecture (V-BLAST) detection (we call this frequency-domain block signal detection). The achievable average BER performance using the proposed frequency-domain block signal detection is evaluated by computer simulation.
    IEICE Transactions. 01/2010; 93-B:2104-2112.
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    ABSTRACT: Joint Water Filling-MRT Downlink Transmit Diversity for a Broadband Single-Carrier Distributed Antenna Network
    IEICE Transactions. 01/2010; 93-B:2753-2760.
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    Kazuki Takeda, Fumiyuki Adachi
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    ABSTRACT: In this paper, we propose a new joint transmit/receive equalization technique for single-carrier (SC) block transmissions in a severe frequency-selective fading channel. An iterative frequency-domain inter-symbol interference cancellation (FDIC) is introduced to the joint transmit/receive (Tx/Rx) frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion which was previously proposed by authors. At a receiver, a 1-tap FDE and FDIC are jointly used and they are updated in an iterative manner to achieve larger frequency diversity gain. Since the transmit FDE weight cannot be updated, we introduce a virtual receiver having a receive FDE & FDIC into the transmitter. In the virtual receiver at the transmitter, the same degree of the residual ISI cancellation is assumed to compute the transmit FDE weight, based on the MMSE criterion, matched to the receive FDE & FDIC. The computer simulation results show that the bit error rate (BER) performance is significantly improved by using our proposed scheme.
    Proceedings of the 6th International Wireless Communications and Mobile Computing Conference, IWCMC 2010, Caen, France, June 28 - July 2, 2010; 01/2010
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    Kazuki Takeda, Fumiyuki Adachi
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    ABSTRACT: In this paper, we discuss how the channel estimation (CE) error affects the bit error rate (BER) performance of single-carrier (SC) block transmission using a previously proposed joint transmit/receive (Tx/Rx) frequency-domain equalization (FDE). First, the set of FDE weights is derived based on the minimum mean square error (MMSE) criterion by taking into account the CE error. The CE error is approximated as a zero-mean complex random Gaussian variable. We show by computer simulation that the proposed joint Tx/Rx MMSE-FDE is robust against the CE error. We consider pilot-assisted channel estimation (PACE) for joint Tx/Rx MMSE-FDE. A first order linear interpolation and extrapolation are introduced to achieve higher tracking ability against the time-variation of the channel gain. We discuss the impact of normalized Doppler frequency on the BER performance.
    01/2010;
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    ABSTRACT: Single-carrier distributed antenna network (SC-DAN), in which a group of multiple antennas are distributed in a cell serve a user, can mitigate adverse impacts of path loss, shadowing loss and multipath fading. Frequency-domain space-time block coded-joint transmit/ receive diversity (FD-STBC-JTRD) is attractive for downlink transmission since an arbitrary number of distributed transmit antennas can be used. FD-STBC-JTRD requires the channel state information (CSI) only at the transmitter side and therefore, the complexity problem of mobile terminals can be alleviated. In this paper, we investigate, by computer simulation, the bit error rate (BER) distribution of the SC-DAN downlink. We discuss the impact of the number of distributed antennas involved in FD-STBC-JTRD on the BER outage probability.
    01/2010;
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    ABSTRACT: Distributed antenna network (DAN) is a promising wireless network to solve the problems arising from shadowing and path lesses as well as frequency-selective fading. Many anntennas are spatially distributed around each base station (BS) so that with a high probability, some antennas can always be visible from a mobile station (MS). Recently, we proposed a 2-dimensional water-filling (2D-WF) transmit diversity for single-carrier (SC) DAN downlink transmission. An MS having single receive antenna was considered. In this paper, we extend the 2D-WF transmit diversity to the case of MS having multiple receive antennas to implement frequency-domain space-time block coded-joint transmit/receive diversity (FD-STBC-JTRD). The channel capacity distribution is evaluated by Monte-Carlo numerical computation method. It is shown that the use of 2 receive antennas maximize the downlink channel capacity while the use of around 5 distributed transmit antennas is sufficient.
    01/2010;