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Frequency Reuse and Relay Selection in Wireless Relay Networks

Author: Liang
Tutor: YangDaCheng
School: Beijing University of Posts and Telecommunications
Course: Communication and Information System
Keywords: cooperative relay user cooperation opportunistic relaying frequency reuse relay selection
CLC: TN925
Type: PhD thesis
Year: 2010
Downloads: 670
Quote: 3
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Abstract

Cooperative relay has been proposed as a way to form virtual antenna arrays that provide dramatic gains in slow fading wireless environments. However, most of the proposed solutions require simultaneous relay transmissions at the same frequency bands, using distributed space-time coding algorithms. Careful design of distributed space-time coding for the relay channel is usually based on global knowkedge of some network parameters or is usually left for future investigation, if there is more than one cooperative relay. We adopt opportunistic relaying that elimates the need for space-time coding and provides diversity gains on the order of the number of relays in the network. This scheme first selects the best relay from a set of M available relays and then uses this "best" relay for cooperation between the source and destination. Information theoretic analysis of outage probability shows that this scheme achieves the same diversity-multiplexing gain tradeoff as achieved by more complex schemes, where coordination and distributed space-time coding for M relay nodes is required. Cooperative relay is based on the broadcast nature of the wireless medium, which can promote the capacity, coverage and reliability without requiring significant infrastructure deployment costs. Hence, cooperative relay has been widely used in wireless sensor networks, wireless Ad Hoc networks, wireless Mesh networks and mobile cellular networks. Focus on wireless relay networks, we study the frequency reuse and relay selection these two wireless resource management techniques in this thesis.The cooperation between source and destination in wireless relay networks requires more wireless resources because of the relay links. Reducing frequency reuse factor is an effective way to improve spectral efficiency. For example, different relay nodes in the same cell serve their mobile stations by using the same frequency bands. However, these frequency reuse methods induce serious co-channel interference in wireless relay networks. We address this problem and propose a novel static frequcny reuse method for two-hop cellular relay networks with fixed relay stations. In this method, inter-cell interference is eliminated and intra-cell interference is minimized by special frequency bands allocation in divided regions and usage of directional antennas. This method is expounded and analyzed under two different relay reuse factors. Additionally, a key parameter, relay stations and base stations transmission power ratio r, is found in the signal to interference plus noise ratio (SINR) expressions of one-hop and two-hop mobile stations. When optimal r is used, the proposed frequency reuse method can achieve significant improvement on spectral efficiency compared to existing methods.Since cooperative diversity in wireless relay networks is accomplished by the cooperation among nodes, cooperative strategy is crucial to the system performance. Cooperative strategy is composed of cooperative mode and relay selection. The former one determines cooperative condition and cooperative manner, and the latter one determines cooperative objects. Cooperative strategy design should consider performance and fairness of nodes as well as system performance according to the application instances. We address the relay selection in wireless relay networks based on relay cooperation and user cooperation, separately.Firstly, we propose a decentralized relay selection method for two-hop cellular relay networks with fixed relay stations. By utilizing the results of non-cooperative power allocation game via pricing, i.e., power-utility pairs, joint optimation of transmission power and data rate is done under terminal energy consumption minimization and data rate maximization these two optimization objectives, in which load balancing solution is integrated. Simulations verify that the two proposed relay selection algorithms perform more advantages depending on the desired optimization objectives rather than the SINR-based relay selection algorithm, respectively.Secondly, beginning with the derivation of a tight threshold-based sufficient condition on the feasibility of a relay node, i.e., ensure that user relaying via the node can achieve its target rate, two semi-distributed relay selection algorithms with different system overhead are proposed for user cooperation based wireless relay networks. Both algorithms minimize outage probability and ensure the fairness among sources with low computational complexity and system overhead. The algorithm with high system overhead has better capacity than the one with low system overhead. Then, we apply these two algorithms in two-hop cellular relay networks with fixed relay stations. In these two application instances, both algorithms can decrease outage probability significantly; ensure the sources’fairness and keep capacity at least compared to existing algorithms.

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