• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.10A
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• pp.1540-1547
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• 2000

In this paper, the performance of the MMSE multiuser detector is compared with the conventional detector with respect to the signal-to-noise ratio, the number of users and the Nakagami parameter under AWGN as well as Nakagami fading channel. The results show that the MMSE multiuser detector is superior to the conventional detector with respect to cancelling the multiple access interference. However, its drawback is the hardware's complexity. To solve this drawback, the advanced MMSE multiuser detector is presented, and its performance is analyzed. The number of taps in the advanced MMSE multiuser are independent of the processing gain. Thus, the system engineer can choose the appropriate number of taps in the detector to achieve a optimal trade-off between the hardware complexity and the performance of system.

• Journal of information and communication convergence engineering
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• v.20 no.2
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• pp.73-78
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• 2022

Based on experimental measurements conducted on many different practical wireless communication systems, ambient noise has been shown to be decidedly non-Gaussian owing to impulsive phenomena. However, most multiuser detection techniques proposed thus far have considered Gaussian noise only. They may therefore suffer from a considerable performance loss in the presence of impulsive ambient noise. In this paper, we consider a large-scale multiuser multiple-input multiple-output system in the presence of non-Gaussian noise and propose a genetic algorithm (GA) based detector for large-dimensional multiuser signal detection. The proposed algorithm is more robust than linear multi-user detectors for non-Gaussian noise because it uses a multi-directional search to manipulate and maintain a population of potential solutions. Meanwhile, the proposed GA-based algorithm has a comparable complexity because it does not require any complicated computations (e.g., a matrix inverse or derivation). The simulation results show that the GA offers a performance gain over the linear minimum mean square error algorithm for both non-Gaussian and Gaussian noise.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.9A
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• pp.1273-1281
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• 2000

In this paper we studied for multi-user detection system, which hold the merit of CDMA system and can enhance the system capacity. We designed actually realizable quasi-optimal multiuser detection system by use of linear equalizer on the concept that multiuser detection algorithm can be reduced by combining TDMA with CDMA. we call this the hybrid TDMA/CDMA system. And we proposed multiuser detection system, which can use PSAD and MSDD channel estimation method. As a result of performance analysis we acquired equal or much better performance by use of linear multichannel equalizer in the case of not so many user. And on the occasion of many user within cell we can also acquired much better performance in comparison with conventional single user detection system by use of hybrid TDMA/CDMA system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3B
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• pp.472-486
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• 2000

This paper analysis the performance of joint receiving structure consisting of the decorrelating multiuser detection and beamfromenr-RAKE receive for DS-CDMA communication systems. In asynchronous transmission as the number of simultaneous users increase. the capacity of CDMA system becomes severly reduced due to the nonideal orthogonality between user-assigned PN sequences and improper power control. Accordingly, the CDMA receiving system becomes vulnerable to the multiple access interferences and the near-far problem under multipath fading channel environment. To withstand these undesired performance degradations, this paper proposes the new type of multiuser detection which has a form of the hybrid structure of concatenating beamformer-RAKE receiver and decorrelating multiuser detection. the beam former-RAKE receiver performs temporal and spatial diversity combining with alleviating fading effect and suppressing undesired interferences, and the multiuser detection plays a role of making the receiver robust to the near-far problem. Regarding the individual merit on the usage of either multiuser detection or beamformer-RAKE receiver, the hybrid one is expected to produce the enhanced performance in multipath fading CDMA channel. However major drawback of using decorrelating multiuser detection for practical deployment is arised from its computational complexity , which is exponentially increased as more number of users and transmitted symbols involve. To diminish the computational complexity, this paper exploits an efficient block Toeplitz inversion technique using matrix Levinson polynomial will be introduced. And this paper provided the mathematical analysis to show the efficiency of the proposed joint structure under the multipath propagation environment. And results of a series of exhaustive computer simulations are presented in order to demonstrate the overall performance of the proposed hybrid structure in multipath fading CDMA channel.

• Journal of Communications and Networks
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• v.1 no.3
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• pp.182-188
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• 1999

The optimal joint maximum-likelihood sequence estima-for using an array of antennas is derived for synchronous direct sequence-code division multiple access (DS-CDMA) system. Each user employs a rate 1/n convolutional code for channel coding for the additive white Gaussian noise (AWGN) channel. The array re-ceiver structure is composed of beamformers in the users' direc-tions followed by a bank of matched filters. The decoder is imple-mented using a Viterbi algorithm whose states depend on the num-ber of users and the constraint length of the convolutional code. The asymptotic array multiuser coding gain(AAMCG)is defined to encompass the asymptotic multiuser coding gain and the spatial information on users' locations in the system. We derive the upper and lower bounds of the AAMCG. As an example, the upper and lower bounds of AAMCG are obtained for the two user case where each user employes the maximum free distance convolutional code with rate 1/2. The enar-far resistance property is also investigated considering the number of antenna elements and user separations in the space.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.175-185
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• 2008

In this paper, we investigate the effect of cooperative and selection relaying schemes on multiuser diversity in downlink cellular systems with fixed relay stations (RSs). Each mobile station (MS) is either directly connected to a base station (BS) and/or connected to a relay station. We first derive closed-form solutions or upper-bound of the ergodic and outage capacities of four different downlink data relaying schemes: A direct scheme, a relay scheme, a selection scheme, and a cooperative scheme. The selection scheme selects the best access link between the BS and an MS. For all schemes, the capacity of the BS-RS link is assumed to be always larger than that of RS-MS link. Half-duplex channel use and repetition based relaying schemes are assumed for relaying operations. We also analyze the system capacity in a multiuser diversity environment in which a maximum signal-to-noise ratio (SNR) scheduler is used at a base station. The result shows that the selection scheme outperforms the other three schemes in terms of link ergodic capacity, link outage capacity, and system ergodic capacity. Furthermore, our results show that cooperative and selection diversity techniques limit the performance gain that could have been achieved by the multiuser diversity technique.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.7
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• pp.3010-3025
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• 2016

Lattice reduction (LR) has been used widely in conventional multiple-input multiple-output (MIMO) systems to enhance the performance. However, LR is hard to be applied to the relay systems which are important but more complicated in the wireless communication theory. This paper introduces a new viewpoint for utilizing LR in multiuser MIMO relay systems. The vector precoding (VP) is designed along with zero force (ZF) criterion and minimum mean square error (MMSE) criterion and enhanced by LR algorithm. This implementable precoder design combines nonlinear processing at the base station (BS) and linear processing at the relay. This precoder is capable of avoiding multiuser interference (MUI) at the mobile stations (MSs) and achieving excellent performance. Moreover, it is shown that the amount of feedback information is much less than that of the singular value decomposition (SVD) design. Simulation results show that the proposed scheme using the complex version of the Lenstra--Lenstra--Lovász (LLL) algorithm significantly improves system performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6C
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• pp.423-428
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• 2008

We consider the use of cooperative diversity in a multiuser wireless data network. This paper provides an analysis of the interaction between cooperative diversity and multiuser diversity on downlink channels. By using approximation of the signal-to-noise ratio (SNR) distribution of each cooperative diversity link by Gamma distribution, an analytic expression is derived for the average throughput of a single-cell wireless system with multiple cooperative diversity links combined with a fair-access scheduler. The proposed analytic approach is verified through comparisons with simulated results and shows that cooperative diversity makes the detrimental impacts on multiuser diversity.

• Journal of Communications and Networks
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• v.5 no.2
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• pp.150-156
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• 2003

In this paper, an uplink MC-CDMA system incorporating multiuser detection and smart antennas has been considered. The performance of asynchronous as well as synchronous system is studied over a correlated Rayleigh multipath slow fading channel. A simplified array-processing algorithm suitable for slow fading situation is investigated to overcome the heavy computational complexity associated with Eigen solutions. The effect of variable data rate in the system performance is considered and effectiveness of antenna array to handle high data rate is discussed. A brief investigation on the system performance degradation due to correlated channel is also carried out. Based on the extensive simulation carried out, the performance of the asynchronous uplink system is found dramatically improved with antenna array and multiuser detection. Asynchronicity and channel correlation are found to affect the system performance significantly. The investigated simpli- fied algorithm produces similar results as Eigen solutions in slow fading situation with much reduced complexity.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.7
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• pp.6-12
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• 2009

In this paper, we propose the opportunistic channel state information feedback scheme for eigen based scheduling in multiuser MIMO systems. According to 3GPP SMC channel model, the system capacity of MU-MIMO systems is severly degraded, since the antennas are highly correlated in urban macro cell. Although the eigen based scheduling scheme mitigates the adverse effect of the antenna correlation, it achieves only small amount of the multiuser diversity gain. Since the opportunistic channel state information scheme can achieve sufficient multiuser diversity gain, the system capacity of MU-MIMO systems can be improved. The system capacity improvement is verified by the computer simulation results.