Performance Analysis of Threshold Relaying with Random Channel Access over Non-Identically Distributed Rayleigh-Fading Channels

In a cooperative ad hoc network, cooperating nodes are randomly distributed and hence coordinating them in a centralized manner becomes costly and inefficient. Developing relaying schemes that allow network nodes to cooperate distributively is thus critically important. While instantaneous channel state information (CSI) available at the receiver is commonly employed as the basis for making cooperation decisions, most of the previous works rely on a centralized mechanism to collect the required CSI. Besides, performance analysis on cooperative networks is usually limited to the symmetric topology. In this paper, we propose a fully distributed relaying scheme, called distributed threshold relaying (DTR) for cooperative wireless ad hoc networks. In DTR, each relay measures signal-to-noise ratios (SNRs) of source-relay and relay-destination channels using broadcast messages sent from source and destination, respectively. The decision on cooperation is made at each relay by performing two threshold tests. In addition, the cooperation among multiple relays is coordinated via a distributive medium access control (MAC) protocol based on a discrete random backoff algorithm. We derive closed-form expressions for the average outage probability and the average delay for independent but not necessarily identically distributed (i.n.i.d.) flat Rayleigh fading channels. Using numerical results and comparing DTR with well-known opportunistic relaying (OR) and selection relaying (SR), we can show the tradeoff relation between reliability and delay in distributed cooperative relaying.