• Journal of KIISE:Information Networking
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• v.36 no.3
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• pp.243-250
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• 2009

Channel diversity is exploited to increase multiuser diversity gains in IEEE 802.11 WLANs. To this end, we propose an opportunistic channel switching method and evaluate this with different number of stations, number of channels, switching latency, and the average channel condition of stations.

• 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.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.11C
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• pp.1111-1118
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• 2007

This paper presents our study of throughput enhancement achieved by selection diversity in a multiuser system, called multiuser diversity (MUDiv), using a new asymptotic approach. The MUDiv gain is evaluated by deriving an asymptotic formula for the throughput enhancement from the MUDiv gain as a simple closed form introducing a Puiseux series. The formula shows that the MUDiv gain is independent of the signal-to-noise ratio (SNR). This concept can be extended to analysis applicable to scheduling algorithms, such as Max C/I and proportional fair scheduling. The MUDiv gain throughput analysis is verified using Monte-Carlo simulations.

• Information and Communications Magazine
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• v.25 no.5
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• pp.23-29
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• 2008

기지국이 셀 내에 있는 여러 사용자에게 신호를 전송하는 하향링크에서 셀 전체 채널 용량을 달성하기 위해서는 채널상태가 가장 좋은 사용자에게만 전송해야 한다. 무선 페이딩 채널에서 여러 사용자 중에 채널이 좋은 사용자를 선택하면, 다중 사용자 다이버시티 이득을 얻을 수 있다. 본 고에서는 이런 다중 사용자 다이버시티를 얻으면서도 사용자 간에 공평하게 자원을 할당하는 여러 방식에 대해서 알아본다.

• Information and Communications Magazine
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• v.25 no.5
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• pp.38-46
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• 2008

협력 다이버시티 기술은 최근 수년간 MIMO(Multiple-Input-Multiple-Output) 기술의 실질적인 대안으로, 애드 혹 네트워크에서의 MIMO 기술로, 셀룰러 시스템에서의 커버리지 확장 기술로 주목을 받아 왔다. 따라서, 협력 다이버시티 기술은 응용 목표에 따라 방식이 다르게 존재하게 된다. 이 논문에서는 기존의 협력 다이버시티 기술들을 몇 가지 일관된 기준으로 분류하여 보고, 이 분야에서 미진한 연구방향으로 다중사용자 환경에서의 협력 다이버시티 기술과 다중 안테나 노드를 위한 협력 다이버시티 기술을 제시한다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.2
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• pp.293-300
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• 2015

Recently, multiuser diversity(MUD) technique is used to improve the performance of OFDM transmission systems. With STBC antenna diversity technique, the performance of OFDM systems can be also improved. Pilot symbol is used for the channel estimation in OFDM systems. However, imperfect channel estimates in this systems degrade the performance. The performance of MUD STBC OFDM systems using pilot symbol, gauged by the bit error rate, is analyzed considering the channel estimation error. Result shows that MUD can improve the required power by a factor of approximately 5 dB for users number 32.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2008.11a
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• pp.103-105
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• 2008

차세대 양방향데이터방송 (BIFS: BInary Format for Scenes) 서비스에서는 하향링크(downlink) 데이터 전송률에 상응하는 높은 상향링크(uplink) 데이터 전송률이 요구되고 있다. 이에 무선 전송 채널의 한정된 자원 환경 속에서 상향링크 전송용량 증대를 위한 주파수 효율성 제고 기술의 필요성이 대두되고 있다. 본 논문에서는 차세대 양방향데이터방송을 위한 다중 모바일(mobile) 사용자의 클러스터(cluster) 기반 상향링크 협동 다이버시티(cooperative diversity) 기법을 제안한다. 제안된 기법은 하나의 단일 안테나(single antenna) 방송 기지국과 다수의 단일 안테나 모바일 사용자가 있는 상향링크 시분할다중접속 (TDMA: Time Division Multiple Access) 시스템에서 데이터 지연허용(delay-tolerant)에 따라 클러스터를 구성하고 제곱 다이버시티 차수(square diversity order)의 협동 프로토콜(cooperative protocol)을 통해 높은 공간다이버시티 이득(spatial diversity gain)을 얻는다. 또한, 비대칭(asymmetric) 무선 채널 환경에서 공정성(fairness)을 보장한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12A
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• pp.1223-1228
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• 2006

Closed-form expressions for capacity bounds of multiuser diversity combined with maximum ratio transmission (MRT) and maximum ratio combining (MRC) at each link are presented under the assumption of independent and quasi-static flat multiple-input multiple-output (MIMO) Rayleigh fading channels. The analysis results precisely agree with the numerical verification results and clearly show the impact of MRT/MRC on multiuser diversity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3A
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• pp.248-255
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• 2008

In an OFDMA system the performance of multi-user scheduling in the frequency domain is affected by the frequency selectivity of the channel. If the channel is too flat in the frequency domain, the multi-user scheduling gain might be degraded. On the contrary, if the frequency selectivity is too high and the magnitude of the frequency response severely fluctuates on the allocation bandwidth, it is also hard to get sufficient scheduling gain. For maximizing the multi-user scheduling gain, a cyclic delay diversity technique can be used to adjust the frequency selectivity of the channel. This paper proposes a method to determine the optimal delay value of cyclic delay diversity according to the allocation bandwidth and the channel characteristics.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.6A
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• pp.474-480
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• 2005

In this paper, we present a new scheduling scheme for MIMO OFDM Multiuser Diversity System. This scheduling scheme maximizes the system throughput, and at the same time fairly shares the resources based on the feedback information from the receivers and the queue information. To show the effectiveness of the proposed algorithm, we evaluate the performance of the proposed algorithm as compared to K&H and RR algorithms.