Kazuki Takeda

Tohoku University, Miyagi, Japan

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Publications (43)10.35 Total impact

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    ABSTRACT: In this paper, we propose joint cooperative-transmit/receive frequency-domain equalization (cooperative-Tx/Rx FDE) with incremental relaying (IR) for broadband single-carrier (SC) transmission under the total and individual transmit power constraint at a source node (S) and a relay node (R). We derive the optimum cooperative-Tx/Rx FDE weights to minimize the mean square error (MSE) after packet combining at a destination node (ssr D). We show that the optimum cooperative-Tx FDE weights allocate the transmit power in the minimum MSE (MMSE) sense in the frequency domain and in the maximal ratio transmission (MRT) sense in the spatial domain. To relax the condition that the complete channel state information (CSI) needs to be shared among all nodes, selection-based suboptimum cooperative-Tx FDE weights are derived. Computer simulation verifies the effectiveness of the proposed schemes and shows that the 5%-outage throughput of the system can be increased by around 30% over the conventional IR with only Rx FDE.
    IEEE Transactions on Vehicular Technology 01/2013; 62(1):1-13. DOI:10.1109/TVT.2012.2219566 · 2.64 Impact Factor
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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 03/2012; E95.B(3):924-932. DOI:10.1587/transcom.E95.B.924 · 0.33 Impact Factor
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    ABSTRACT: Multi-user multi-input multi-output (MIMO) system has been attracting much attention due to its high spectrum efficiency. Nonlinear MIMO signal detection methods with less computational complexity have been widely studied for single-user MIMO systems. In this paper, we investigate how a lattice reduction (LR)-aided detection and a maximum likelihood detection (MLD) employing the QR decomposition and M-algorithm (QRM-MLD), which are commonly known as non-linear MIMO signal detection methods, improve the uplink capacity of a multi-user MIMO-OFDM cellular system, compared to simple linear detection methods such as zero-forcing detection (ZFD) and minimum mean square error detection (MMSED). We show that both LR-aided linear detection and QRM-MLD can achieve higher uplink capacity than simple linear detection at the cost of moderate increase of computational complexity. Furthermore, QRM-MLD can obtain the same uplink capacity as MLD.
    IEICE Transactions on Communications 01/2012; 95-B(1):198-205. DOI:10.1587/transcom.E95.B.198 · 0.33 Impact Factor
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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 12/2011; 11(12):1551-1563. DOI:10.1002/wcm.1212 · 1.29 Impact Factor
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    ABSTRACT: In this paper, we propose an iterative minimum mean square error detection with interference cancellation (MMSED-IC) for frequency-domain filtered single carrier (SC)-frequency-division multiple-access (FDMA) uplink transmission. The use of a square-root Nyquist transmit filter reduces the peak-to-average power ratio (PAPR) while increases the frequency-diversity gain. However, if carrier-frequency separation among multiple-access users is kept the same as the one used for the case of roll-off factor alpha=0 (i.e., brick-wall filter), then the adjacent users' spectra will overlap and multi-user interference (MUI) occurs. The proposed MMSED-IC can sufficiently suppress the MUI from adjacent users while achieving the maximum frequency-diversity gain. We apply the proposed MMSED-IC to a packet access using filtered SC-FDMA, multi-input multi-output (MIMO) multiplexing, and hybrid automatic repeat request (HARQ). It is shown by computer simulation that filtered SC-FDMA with alpha = 1 can achieve higher throughput than orthogonal frequency division multiple access (OFDMA).
    IEICE Transactions on Communications 12/2011; 94-B(12):3559-3568. DOI:10.1587/transcom.E94.B.3559 · 0.33 Impact Factor
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    ABSTRACT: Broadband single-carrier frequency division multiple access (SC-FDMA) uplink using frequency-domain square-root Nyquist filtering is considered. The peak-to-average power ratio (PAPA) of filtered SC signals can be reduced by increasing the filter roll-off factor a. Furthermore, an additional frequency diversity gain can be obtained by making use of the excess bandwidth introduced by the transmit root Nyquist filtering. However, if the carrier-frequency separation is kept the same as in the case of alpha = 0, the adjacent users' signal spectra overlap with the desired users' spectrum and the multiuser interference (MUI) is produced. In this paper, we propose two frequency-domain iterative MUI cancellation schemes which can achieve the frequency diversity gain through spectrum combining. The achievable bit error rate (BER) and throughput performances are evaluated by computer simulation.
    IEICE Transactions on Communications 10/2011; 94-B(10):2847-2856. DOI:10.1587/transcom.E94.B.2847 · 0.33 Impact Factor
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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. DOI:10.1007/s11277-010-0130-5 · 0.98 Impact Factor
  • Kazuki Takeda, Fumiyuki Adachi
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    ABSTRACT: In this paper, we propose a novel iterative transmit/receive equalization technique for single-carrier (SC) block transmission in a severe frequency-selective fading channel. Iterative frequency-domain inter-symbol interference (ISI) cancellation (FDIC) is introduced to the previously proposed joint iterative transmit/receive frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion. 1-tap FDE is employed at the transmitter. At the receiver, a 1-tap FDE and FDIC are jointly used and they are updated in an iterative manner. The transmit FDE weight is derived based on the MMSE criterion by taking into account the reduction of residual ISI in the receiver. To derive the weight, the transmitter assumes that the receiver can partially reduce the residual ISI after the FDIC. We conduct a computer simulation to investigate the achievable bit error rate (BER) performance to confirm the effectiveness of our proposed technique.
    IEICE Transactions on Communications 05/2011; 94-B(5):1396-1404. DOI:10.1587/transcom.E94.B.1396 · 0.33 Impact Factor
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    ABSTRACT: Recently, assuming ideal brick-wall transmit filtering, we proposed a frequency-domain block signal detection (FDBD) with maximum likelihood detection employing QR decomposition and M-algorithm (called QRM-MLD) for the reception of single-carrier (SC) signals transmitted over a frequency-selective fading channel. QR decomposition (QRD) is applied to a concatenation of the propagation channel and discrete Fourier transform (DFT). However, a large number of surviving paths is required in the M-algorithm to achieve sufficiently improved bit error rate (BER) performance. The introduction of filtering can achieve improved BER performance due to larger frequency diversity gain while keeping a lower peak-to-average power ratio (PAPR) than orthogonal frequency division multiplexing (OFDM). In this paper, we develop FDBD with QRM-MLD for filtered SC signal reception. QRD is applied to a concatenation of transmit filter, propagation channel, and DFT. We evaluate BER and throughput performances by computer simulation. From performance evaluation, we discuss how the filter roll-off factor affects the achievable BER and throughput performances and show that as the filter roll-off factor increases, the required number of surviving paths in the M-algorithm can be reduced.
    IEICE Transactions on Communications 05/2011; 94-B(5):1386-1395. DOI:10.1587/transcom.E94.B.1386 · 0.33 Impact Factor
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    ABSTRACT: Frequency-domain equalization (FOE) based on minimum mean square error (MMSE) is considered as a promising equalization technique for a broadband single-carrier (SC) transmission. When a square-root Nyquist filter is used at a transmitter and receiver to limit the signal bandwidth, the presence of timing offset produces the inter-symbol interference (ISI) and degrades the bit error rate (BER) performance using MMSE-FDE. In this paper, we discuss the mechanism of the BER performance degradation in the presence of timing offset. Then, we propose joint MMSE-FDE & spectrum combining which can make use the excess bandwidth introduced by transmit filter to achieve larger frequency diversity gain while suppressing the negative effect of the timing offset.
    IEICE Transactions on Communications 05/2011; 94-B(5):1366-1375. DOI:10.1587/transcom.E94.B.1366 · 0.33 Impact Factor
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    ABSTRACT: Recently, overlap frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion which requires no guard interval (GI) insertion was proposed for signal transmission using multi-code direct sequence code division multiple access (DS-CDMA) in a frequency-selective fading channel. Another promising equalization technique is time-domain sliding-window chip equalization (SWCE). In this paper, the bit error rate (BER) performances achievable with overlap FDE and SWCE are compared. It is shown that, by extending the fast Fourier transform (FFT) block size, overlap FDE can achieve almost the same BER performance as SWCE with much less computational complexity than SWCE.
    IEICE Transactions on Communications 03/2011; 94-B(3):750-757. DOI:10.1587/transcom.E94.B.750 · 0.33 Impact Factor
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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: 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: In this paper, joint water filling and maximal ratio transmission (joint WF-MRT) downlink transmit diversity for a single-carrier distributed antenna network (SC DAN) is proposed. The joint WF-MRT transmit weight allocates the transmit power in both transmit antenna dimension and frequency dimension, i.e., the power allocation is done both across frequencies based on WF theorem and across transmit antennas based on MRT strategy. The cumulative distribution function (CDF) of the channel capacity achievable by joint WF-MRT transmit diversity is evaluated by Monte-Carlo numerical computation method. The channel capacities achievable with joint WF-MRT, MRT, and WF transmit weight (WF transmit weight is done across transmit antennas and frequencies based on WF theorem) are compared. It is shown that the joint WF-MRT transmit weight provides the highest channel capacity among three transmit weights.
    IEICE Transactions on Communications 10/2010; 93-B(10):2753-2760. DOI:10.1587/transcom.E93.B.2753 · 0.33 Impact Factor
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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 on Communications 08/2010; 93-B(8):2104-2112. DOI:10.1587/transcom.E93.B.2104 · 0.33 Impact Factor
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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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    ABSTRACT: In the future wireless communication systems, the broadband wireless technology which enables Giga-bps class data services is demanded. Broadband wireless channels become extremely frequency-selective and cause severe inter-symbol interference (ISI). Furthermore, the average received signal power changes in a random manner because of the shadowing and path losses according to the movement of a mobile terminal (MT). Accordingly, the transmission performance severely degrades. Development of some advanced equalization and networking is necessary to overcome the performance degradation. Among them, promising are the frequency-domain equalization (FDE) and distributed antenna network (DAN). The former takes advantage of channel frequency-selectivity to obtain the frequency-diversity gain. In DAN, a group of distributed antennas serve each user to mitigate the negative impact of shadowing and path losses. This article will introduce the recent advances in FDE and DAN for the broadband single-carrier (SC) transmissions.
    Information, Communications and Signal Processing, 2009. ICICS 2009. 7th International Conference on; 01/2010
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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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    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.
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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.