Opportunistic relaying in wireless networks

Document Type

Article

Publication Date

11-10-2009

Abstract

Relay networks having n source-to-destination pairs and m half-duplex relays, all operating in the same frequency band and in the presence of block fading, are analyzed. This setup has attracted significant attention, and several relaying protocols have been reported in the literature. However, most of the proposed solutions require either centrally coordinated scheduling or detailed channel state information (CSI) at the transmitter side. Here, an opportunistic relaying scheme is proposed that alleviates these limitations, without sacrificing the system throughput scaling in the regime of large n. The scheme entails a two-hop communication protocol, in which sources communicate with destinations only through half-duplex relays. All nodes operate in a completely distributed fashion, with no cooperation. The key idea is to schedule at each hop only a subset of nodes that can benefit from multiuser diversity. To select the source and destination nodes for each hop, CSI is required at receivers (relays for the first hop, and destination nodes for the second hop), and an index-valued CSI feedback at the transmitters. For the case when n is large and m is fixed, it is shown that the proposed scheme achieves a system throughput of m/2 bits/ s/Hz. In contrast, the information-theoretic upper bound of (m/2) log log n bits/s/Hz is achievable only with more demanding CSI assumptions and cooperation between the relays. Furthermore, it is shown that, under the condition that the product of block duration and system bandwidth scales faster than log n log log n, the achievable throughput of the proposed scheme scales as Θ(log n). Notably, this is proven to be the optimal throughput scaling even if centralized scheduling is allowed, thus proving the optimality of the proposed scheme in the scaling law sense. Simulation results indicate a rather fast convergence to the asymptotic limits with the system's size, demonstrating the practical importance of the scaling results. © 2009 IEEE.

Identifier

70350743185 (Scopus)

Publication Title

IEEE Transactions on Information Theory

External Full Text Location

https://doi.org/10.1109/TIT.2009.2030435

ISSN

00189448

First Page

5121

Last Page

5137

Issue

11

Volume

55

Grant

CNS-0626611

Fund Ref

National Science Foundation

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