• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.9C
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• pp.734-742
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• 2008

In spatially multiplexed MIMO systems that enable high data rate transmission over wireless communication channels, the spatial demultiplexing at the receiver is a challenging task and various demultiplexing methods have been developed. Among the previous methods, maximum likelihood detection with QR decomposition and M-algorithm (QRM-MLD), sphere decoding (SD), QOC, and MOC schemes have been reported to achieve a (near) maximum likelihood (ML) hard decision performance. In general, however, the reliability of soft output of these schemes is not satisfactory. In this paper, we propose a method which enhances the reliability of soft output. By computer simulations, we demonstrate the improved performance by the proposed method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.2A
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• pp.115-120
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• 2008

We propose a cooperative transmission scheme that uses Hurwitz-Radon space-time code for the relays which help the source to transmit signals to the destination, the full utilization here is that the destination utilizes the broadcast symbols from the source. We present the 2 transmit antennas case in detail because of its simplicity and high data rate. Analysis and simulations show that the proposed scheme achieves full diversity order of 3. The maximum likelihood receiver is also derived and the combining scheme is shown to be very simple.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12A
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• pp.1205-1213
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• 2006

In this paper, we analyze the IQ(In-phase/Quadrature) imbalance effects at both transmitter and receiver side of OFDM(Orthogonal Frequency Division Multiplexing) and show that IQ imbalance is the parameter to improve the performance using ML and OSIC scheme. Especially, we can archive the diversity gain due to the IQ imbalance in multipath fading environment. In addition, new preamble format is proposed, which enable estimation of the channel and IQ imbalance parameters to maximize the diversity gain. Significant performance improvement is achieved by using the ML(Maximum Likelihood)and OSIC(Ordered Successive Interference Cancellation) with compensation compared to a standard receiver with no compensation for IQ imbalance and proposed channel estimation scheme achieves the better performance improvement than conventional.

• ETRI Journal
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• v.40 no.2
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• pp.218-226
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• 2018

Multiuser detection (MUD) and channel estimation techniques in space-division multiple-access aided orthogonal frequency-division multiplexing systems recently has received intensive interest in receiver design technologies. The maximum likelihood (ML) MUD that provides optimal performance has the cost of a dramatically increased computational complexity. The minimum mean-squared error (MMSE) MUD exhibits poor performance, although it achieves lower computational complexity. With almost the same complexity, an MMSE with successive interference cancellation (SIC) scheme achieves a better bit error rate performance than a linear MMSE multiuser detector. In this paper, hybrid ML-MMSE with SIC adaptive multiuser detection based on the joint channel estimation method is suggested for signal detection. The simulation results show that the proposed method achieves good performance close to the optimal ML performance at low SNR values and a low computational complexity at high SNR values.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.8
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• pp.32-41
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• 2010

We propose the use of multi-preambles using Gold codes and analyze its performance. The multi-preamble is a way of utilizing different codes for preambles according to operation modes or applications in a system. The receiver can be easily implemented using the maximum likelihood algorithm. The performance is robust against noise due to the good correlation characteristic of the Gold codes. We use 128-bit-long multi-preambles generated by 127 bit Gold codes in deriving the detection error probability and in verifying the validity through computer simulation. The results show that the theory and the experiment are in good agreement within the approximation error.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.10 s.352
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• pp.1-7
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• 2006

Lattice decoding concept has been proposed for the implementation of the Maximum-Likelihood detection which is the optimal receiver from the viewpoint of the BER (Bit Error Rate) performance for MIMO (Multiple Input Multiple Output) systems. Sphere decoding algorithm and K-best decoding algorithm are based on the lattice decoding concept. A K-best decoding algorithm shows a good BER performance with relatively low complexity. However, with small K value, the error propagation effect severely degrades the performance. In this paper, we propose an adaptive K-best decoding algorithm which has lower average complexity and better BER performance than conventional K-best decoding algorithm.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.11
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• pp.5305-5321
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• 2016

In wireless communication, the multiple-input multiple-output (MIMO) system is a well-known approach to improve the reliability as well as the data rate. In MIMO systems, channel state information (CSI) is typically required at the receiver to detect transmitted signals; however, in practical systems, the CSI is imperfect and contains errors, which affect the overall system performance. In this paper, we propose a novel maximum likelihood (ML) scheme for MIMO systems that is robust to the CSI errors. We apply an optimization method to estimate an instantaneous covariance matrix of the CSI errors in order to improve the detection performance. Furthermore, we propose the employment of the list sphere decoding (LSD) scheme to reduce the computational complexity, which is capable of efficiently finding a reduced set of the candidate symbol vectors for the computation of the covariance matrix of the CSI errors. An iterative detection scheme is also proposed to further improve the detection performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.10A
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• pp.1000-1010
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• 2002

Partial response maximum-likelihood (PRML) and fixed-delay tree search with decision feedback (FDTS/DF) yield a sub-optimum performance in storage systems. However, they suffer from the inevitable complexity problems. this paper focuses on detection schemes to overcome the drawbacks of the sequence detections by exploiting minimum run-length d=2. It is expected that the proposed systems yield substantial reductions of both processing speed and receiver complexity. When combined with a decision feedback equalization (DFE), they prove to keep pace with the FDTS/DF with ${\tau}$=2 and even outperform the PR(1111)ML at normalized density S>5.6.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.05a
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• pp.447-450
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• 2009

In this paper, binary pulse-antipodal modulation (2PAM) direct-sequence (DS) ultra-wideband (UWB) system is applied to multiple input multiple output (MIMO) system using vertical bell lab layered space-time (V-BLAST) structure to achieve high-data-rate communications over indoor wireless channels. The relationship between antenna dimension and BER performance of 2PAM DS UWB MIMO system is discussed. In the receiver of UWB-MIMO system, various MIMO detection algorithms such as zero-forcing (ZF), ZF-ordered successive interference cancellation (OSIC), minimum-mean-square-error (MMSE), MMSE-OSIC and maximum likelihood (ML) are comparatively studied.

• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.41-45
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• 2007

Multi-input multi-output (MIMO) system can increase data rate, capacity and bit error rate (BER) performance compare to traditional single antenna system. However MIMO technique is pointed out the problem that has high complexity to design receiver. So a recent trend of research on the MIMO system pays more attention to simplified implementation of receiver structure. In this paper, we propose differential space time block code (STBC) for MIMO system with cyclic delay diversity (CDD). This structure can provide a very close performance to that of the conventional diversity scheme with maximum likelihood (ML) detection without channel estimation block while the receiver structure is highly simplified. Bit error rate (BER) performance of the proposed system is simulated for an AWGN channel by theoretical and simulated approaches. The results of this paper can be applicable to the 4G mobile multimedia communication systems.