• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.3A
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• pp.260-268
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• 2010

Channel inversion is one of the simplest techniques for multiuser downlink systems with single-antenna users. In this paper, we extend the regularized channel inversion technique developed for the single-antenna user case to multiuser multiple-input multiple-output (MIMO) channels with multiple-antenna users. We first employ the multiuser preprocessing to project the multiuser signals near the null space of the unintended users based on the MMSE criterion, and then the single-user preprocessing is applied to the decomposed MIMO interference channels. In order to reduce the complexity, we focus on non-iterative solutions for the multiuser transmit beamforming and use a linear receiver based on an MMSE criterion. Simulation results show that the proposed scheme outperforms existing joint iterative algorithms in most multiuser configurations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.10A
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• pp.980-986
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• 2008

Spatial multiuser access is investigated for the reverse link of multiuser multiple-input multiple-output (MIMO) systems. In particular, we consider two alternative a aches to spatial multiuser access that adopt the same detection algorithm at the base station: one is a closed-loop approach based on singular value decomposition (SVD) of the channel matrix, whereas the other is an open-loop approach based in space-time block coding (STBC). We develop multiuser detection algorithms for these two spatial multiuser access schemes based on the minimum mean square error (MMSE) criterion. Then, we compare the bit error rate (BER) performance of the two schemes and a single-user MIMO scheme. Interestingly, it is found that the STBC approach can provide much better BER performance than the SVD approach as well as than a single-user MIMO scheme.

• ETRI Journal
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• v.30 no.6
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• pp.765-773
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• 2008

Spatial correlation is a result of insufficient antenna spacing among multiple antenna elements, while temporal correlation is caused by Doppler spread. This paper compares the effect of spatial and temporal correlation in order to investigate the performance of multiuser scheduling algorithms in multiple-input multiple-output (MIMO) broadcast channels. This comparison includes the effect on the ergodic capacity, on fairness among users, and on the sum-rate capacity of a multiuser scheduling algorithm utilizing statistical channel state information in spatio-temporally correlated MIMO broadcast channels. Numerical results demonstrate that temporal correlation is more meaningful than spatial correlation in view of the multiuser scheduling algorithm in MIMO broadcast channels. Indeed, the multiuser scheduling algorithm can reduce the effect of the Doppler spread if it exploits the information of temporal correlation appropriately. However, the effect of spatial correlation can be minimized if the antenna spacing is sufficient in rich scattering MIMO channels regardless of the multiuser scheduling algorithm used.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.5
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• pp.1-9
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• 1996

In this paper, we propose an efficient computational algorithm that can reduce significantly the computational complexity of the ML optimum multiuser detector known as the most excellent detector in synchronous code division multiple access channels. The proposed detector uses the sequential detection algorithm based on the alternating maximization appraoch to obtain the ML estimates. As initial estimates for this sequential algorithm, we can use the estimated values obtained by the conventional single-user detector, the linear decorrelating multiuser detector, or the decorrelating decision-feedback muliuser detector, the linear decorrelating multiuser detector, or the decorrelating decision-feedback multiuser detector. We have performed computer simulations in order to see the convergence behaviors and the detection performance of the propsoed algorithm in terms of initial algorithms and the number of users, and then to compare the computational complexity with that of the ML optimum multiuser detector. From the results, we have seen that the proposed alternating maximization detector has nearly equal detction performance with that of the ML optimum multiuser detctor in only a few iteration.

• Journal of electromagnetic engineering and science
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• v.6 no.4
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• pp.222-228
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• 2006

In this paper, the performance of a multiuser diversity system combined with a multi-element transmit antenna system is analyzed under the assumption of independent Rayleigh fading. A measure of system .level performance is an average channel capacity as a function of the number of users and antennas. Average channel capacity is obtained from the instantaneous signal-to-noise ratio(SNR) distribution combined by both transmit diversity(TD) at each link and multiuser diversity at system level. Numerical results show that closed-loop antenna techniques provide an additional gain with multiuser diversity system due to array gain, even though space diversity gain reduces multiuser diversity gain. On the other hand, the space-time block coding(STBC) that provides full order space diversity gain only has a destructive influence on multiuser diversity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.6C
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• pp.481-489
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• 2005

In this letter, we propose an efficient training sequence structure for adaptive linear multiuser detectors in space-time block coded multiuser systems, by exploiting a particular property of the minimum mean square error multiuser detectors used in these systems. The proposed structure wastes less overall system capacity than the straightforward training structure, without any corresponding loss of performance, as confirmed by the simulation results.

• Journal of Communications and Networks
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• v.10 no.4
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• pp.444-450
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• 2008

This paper studies the performance of multiuser data networks with transmit diversity under correlated fading channels. Previous work shows that correlated fading reduces the link performance of multiple antenna systems, but how correlated fading affects the throughput of multiuser data networks is still unknown since the throughput depends not only on the link performance but also on the multiuser diversity. We derive the throughput of the multiuser data networks with various transmit diversity schemes under correlated fading channels. The impact of correlated fading on the throughput is investigated. Analytical and simulation results show that, although correlated fading is harmful for link performance, it increases the throughput of the multiuser data networks if the transmit scheme is appropriately selected.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.12-16
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• 2008

In this paper, we study precoding techniques for co-channel interference suppression in multiuser MIMO systems. DPC is optimal techniques to achieve the system capacity of multiuser MIMO downlink channels. DPC is not proper in practical wireless systems because complexity is very high. So block diagonal precoding for multiuser MIMO downlink channel is studied. The block diagonal precoding is used to suppress co-channel interference between multiuser. Block diagonal precoding method, whose complexity is reduced by modified null space operation, change multiuser MIMO channel to multiple single-user MIMO channel. We also use V-BLAST decoder in receiver. V-BLAST decoder can achieve increased system capacity in proportion to the number of users. We show improved system performance by using computer simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.2C
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• pp.184-190
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• 2006

In this paper, we propose the blind multiuser detector which is robust against the effects of near-far and multiuser interference. The proposed detector is composed of the partial IC(interference canceller) and the blind MOE(minimum output energy) multiuser detector. The partial IC partially eliminates interference components from the received signal then the output of partial IC is fed into the input of multiuser detector. Simulation results show that the proposed detector has the robust property but the performance of conventional MOE multiuser detector is rapidly degraded in case of existing both near far and multiuser. Thus, the proposed partial IC BMUD(blind multiuser detection) technique has better performance than the conventional MOE.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.9
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• pp.1573-1595
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• 2011

In this paper, the outage performance of multiuser multiple-input single-output (MISO) systems exploiting joint spatial and multiuser diversities is investigated for Rayleigh fading channels with outdated feedback. First, we derive closed-form exact outage probabilities for the joint diversity schemes that combine user scheduling with different spatial diversity techniques, including: 1) transmit maximum-ratio combining (TMRC); 2) transmit antenna selection (TAS); and 3) orthogonal space-time block coding (OSTBC). Then the asymptotic outage probabilities are analyzed to gain more insights into the effect of feedback delay. It is observed that with outdated feedback, the asymptotic diversity order of the multiuser OSTBC (M-OSTBC) scheme is equal to the number of transmit antennas at the base station, while that of the multiuser TMRC (M-TMRC) and the multiuser TAS (M-TAS) schemes reduce to one. Further by comparing the asymptotic outage probabilities, it is found that the M-TMRC scheme outperforms the M-TAS scheme, and the M-OSTBC scheme can perform best in the outage regime of practical interest when the feedback delay is large. Theoretical analysis is verified by simulation results.