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ABSTRACT: In this paper, we address spatially multiplexed (SM) multiple-input-multiple-output (MIMO) systems that are expected to be used in next-generation mobile communication systems that require high-speed data transmission. The data-transmission rate of an SM MIMO system increases in proportion to the number of spatial streams it transmits. However, it is hard to implement large numbers of spatial streams due to the spatial limits of mobile units and the high cost of installing many antennas. In this paper, we focus on the case of two spatial streams and propose a novel signal-detection technique. We first define the bidirectional detectability of a 2-D complex vector, and using the fact that only a small number of vectors, including the maximum-likelihood (ML) solution vector, satisfy the bidirectional detectability, we reduce the search space, thereby enabling efficient ML signal detection at the receiver.
IEEE Transactions on Vehicular Technology 03/2010; · 1.92 Impact Factor
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ABSTRACT: In this paper, the effect of the time difference of arrival (TDoA) on synchronous types or asynchronous types of OFDMA-based multi-hop relay (MR) systems is investigated. Effective SINRs for downlinks and uplinks are defined to measure the degree of interference due to TDoA in asymmetric MR systems. A path selection technique based on the effective SINR is then proposed to determine the optimal paths for the uplink and downlink independently. It is shown that asymmetric routing can improve the performance of OFDMA-based MR systems when the proposed technique is applied to the path selection of the uplink taking into account the effect of the TDoA.
Personal, Indoor and Mobile Radio Communications, 2009 IEEE 20th International Symposium on; 10/2009
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ABSTRACT: This brief proposes a new signal detection method called QR ordered successive interference cancellation (OSIC) with candidates (QOC) method for spatially multiplexed multiple-input-multiple-output (MIMO) systems. By using the OSIC algorithm and the maximum-likelihood (ML) metric, the proposed method achieves near-ML performance without requiring a large number of candidates. Although the proposed method can be used for both hard and soft decoding systems, it is particularly useful for soft decoding systems since the log-likelihood-ratio (LLR) values for all the bits can efficiently be computed without using LLR estimation. The proposed method is also suitable for very large scale integration (VLSI) implementation since it leads to a fixed throughput system. A QOC detector for a 4 times4 16-quadrature-amplitude-modulation (16-QAM) MIMO system has been designed and synthesized with a 0.13-mum complimentary metal-oxide-semiconductor (CMOS) technology. The implementation results show that the proposed detector reduces the hardware complexity by 73% relative to a K-best detector.
Circuits and Systems II: Express Briefs, IEEE Transactions on 06/2009; · 1.41 Impact Factor
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Proceedings of the 70th IEEE Vehicular Technology Conference, VTC Fall 2009, 20-23 September 2009, Anchorage, Alaska, USA; 01/2009
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IEICE Transactions. 01/2009; 92-B:1365-1368.
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IEICE Transactions. 01/2009; 92-B:3487-3490.
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IEICE Transactions. 01/2009; 92-B:3533-3536.
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ABSTRACT: Although the maximum-likelihood decision-feedback equalization (ML-DFE) detection method for multi-input multi- output (MIMO) system leads to a good compromise between the performance and the complexity, the computational complexity of the ML part in the ML-DFE is still large. This paper describes a modified maximum-likelihood (MML) algorithm, which reduces the computational complexity of the original ML algorithm significantly without degrading the performance. Then, based on the MML algorithm, we propose the MML-DFE, which has the same performance as the ML-DFE but has much lower complexity. Both the ML-DFE block and MML-DFE block for 4times4 MIMO system have been implemented in field-programmable gate array to verify the functional correctness and the complexity advantage.
Circuits and Systems II: Express Briefs, IEEE Transactions on 08/2008; · 1.41 Impact Factor
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ABSTRACT: In spatially multiplexed MIMO systems that enable high-data-rate transmission over wireless communication channels, spatial demultiplexing at the receiver is a challenging task. Thus, various demultiplexing methods have been developed by many researchers. In this paper, a novel signal detection method that achieves near-ML performance in a computationally efficient manner is proposed. The proposed method is based on the well-known minimum mean squared error (MMSE) ordered successive interference cancellation (OSIC) method. However, unlike the conventional MMSE-OSIC, a number of candidates are selected at each layer, hence, it has been termed MMSE-OSIC with candidates (MMSE-OSIC<sup>2</sup>). In this study, it is demonstrated via a series of computer simulations that the MMSE-OSIC<sup>2</sup> achieves near-ML performance while requiring a complexity comparable to that of the conventional MMSE- OSIC. Also shown here is that the log likelihood ratio (LLR) values are successfully generated via the proposed method.
Vehicular Technology Conference, 2008. VTC Spring 2008. IEEE; 06/2008
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Conference Proceeding:
MMSE-OSIC
Proceedings of the 67th IEEE Vehicular Technology Conference, VTC Spring 2008, 11-14 May 2008, Singapore; 01/2008
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Proceedings of the 65th IEEE Vehicular Technology Conference, VTC Spring 2007, 22-25 April 2007, Dublin, Ireland; 01/2007
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ABSTRACT: This letter compares orthogonal space time codes and quasi-orthogonal codes when the wireless channels are fast fading. It is well known that a orthogonal space-time code is better than a quasi-orthogonal code in high signal-to-noise ratio (SNR) range and that a quasi-orthogonal code is better in low SNR range. In this letter, we show that a quasi-orthogonal space-time code is a better choice even in high SNR range when the channels are fast fading.
