Distributed Opportunistic Channel Access in Wireless Relay Networks

In this paper, the problem of distributed opportunistic channel access in wireless relaying is investigated. A relay network with multiple source-destination pairs and multiple relays is considered. All source nodes contend through a random access procedure. A winner source may give up its transmission opportunity if its link quality is poor. In this research, we apply the optimal stopping theory to analyze when a winner source should give up its transmission opportunity. By assuming the winner source has channel state information (CSI) of links from itself to relays and from relays to its destination, the existence of an optimal stopping strategy is rigorously proved. The optimal stopping strategy has a pure-threshold structure. The case when a winner source does not have CSI of links from relays to its destination is also studied. Two stopping problems exist, one in the main layer (for channel access of sources), and the other in the sub-layer (for channel access of relays). An intuitive stopping strategy, where the main layer (for the first hop) and sub-layer (for the second hop) maximize their throughput respectively, is derived. The intuitive stopping strategy is shown to be non-optimal. An optimal stopping strategy is then derived theoretically. In either the intuitive stopping strategy or the optimal stopping strategy, the main-layer stopping rule has a pure-threshold structure, while the sub-layer stopping rule has a threshold determined by the channel realization in the preceding first-hop transmission. Our research reveals that multi-user (including multi-source and multi-relay) diversity and time diversity can be utilized in a relay network by our proposed strategies. The effectiveness of the strategies is validated by numerical and simulation results.