AbstractsComputer Science

Exploiting multiuser diversity with contention-based opportunistic feedback in wireless communication systems

by Hang Li

Institution: University of Western Australia
Degree: PhD
Year: 2013
Keywords: Multiuser diversity; Outage; Capture effect; Opportunistic feedback; Queuing analysis; Multiple-input multiple-output; User identification approach; Orthogonal frequency-division multiplexing
Record ID: 1032194
Full text PDF: http://repository.uwa.edu.au:80/R/?func=dbin-jump-full&object_id=35132&local_base=GEN01-INS01


For multi-user wireless communications, information theory has demonstrated that system performance can be significantly improved by exploiting multi-user diversity, where the channel is always scheduled to the user with the best instantaneous channel gain. For achieving the benefit of multi-user diversity, conventionally, all users' channel state information (CSI) must be available at the Base Station (BS), thereby inducing enormous system overhead. In a wireless communication system with a large number of users, the overhead induced by polling CSIs may overshadow the multiuser diversity gain. The first part of this dissertation (Chapters 2 and 3) proposes a user identification approach (UIDA) to handle the overhead issue in a generic wireless network exploiting multiuser diversity, and demonstrates two user identification (UID) design methods and application in the orthogonal frequency-division multiplexing (OFDM) system and the multiple-input multiple-output OFDM (MIMO-OFDM) system. Then, we present a theoretical upper bound of the throughput of the system with the UIDA over general channels. In addition, a modified UIDA is proposed to effectively trade off throughput and fairness performances. In comparison with Medium Access Diversity and Multiuser Diversity with Capture (two alternative approaches in the literature for exploiting multiuser diversity), the proposed UIDA achieves better throughput performance when there are a reasonably large number of users. Following the above work, a simplified UIDA for multiuser diversity with enhanced throughput is proposed in Chapter 3 to reduce the overhead further by allowing a small degree of outage to occur. In view of the opportunistic feedback protocol proposed in the literature, the second part of this dissertation (Chapters 4-6) analyses the system performances further by considering the following conditions, respectively: (1) The capture effect and the effect of the overhead on system throughput, (2) Fairne and capacity performances for maximum throughput (MT) or proportional fair (PF) scheduling [Signal-to-noise ratios (SNRs) with independent but not necessarily identical distributions], (3) The finite-length queuing effect. Our work investigates and improves the system performances of the opportunistic feedback protocol in a practical wireless environment. In the third part of this dissertation (Chapter 7), a cluster-based feedback protocol is proposed for multiuser orthogonal frequency-division multiple access (OFDMA) systems, where the capture effect is employed in each cluster to reduce the enormous system overhead induced by polling CSIs. This work in Chapter 7 is an extension of our previous protocol (Multiuser Diversity with Capture). Our previous protocol is a special case of the proposed one, i.e., the number of clusters is 1. The proposed one additionally exploits multiuser diversity in the frequency domain, thereby achieving better throughput with the increase of the number of clusters. For multi-user wireless communications, information…