A Simple Probabilistic Relay Selection Protocol for Asynchronous Multi-Relay Networks Employing Rateless Codes

Cooperative communication with rateless codes has attracted much attention recently because it combines spatial diversity of multiple nodes and high bandwidth efficiency of rateless codes. However, relay selection for asynchronous relaying, which shows great potential for practical applications, has not been carefully studied yet. In this paper, based on rateless codes, we propose a simple probabilistic relay selection protocol for asynchronous multi-relay networks, where no symbol-level inter-node synchronization or multiuser detection is needed. In such asynchronous networks, a decoding relay can help the other relays which have not decoded the message yet. Moreover, the tradeoff between the first hop and the second hop can be controlled by setting the decoding relay threshold. We analyze the average end-to-end throughput and find an optimal decoding relay threshold to maximize the throughput. Simulation results show the superiority of the proposed protocol at low Signal-to-Noise Ratios (SNRs) when the relays are close to the source.