Delay performance of opportunistic network coding for a bidirectional relaying link

Using network coding (NC) in wireless networks can potentially improve the throughput and energy efficiency. On the other hand, it may result in longer delay because packets arriving early at the relay node have to wait to be network coded with other packets. In contrast, using traditional relaying allows the data packets to be forwarded as soon as possible, while its overall lower throughput (compared to that using NC) may result in longer average delay of the transmitted data packages. Opportunistic scheduling that takes advantages of both the high efficiency of NC and promptness of the traditional relay may help reduce the packet transmission delay. In this paper we propose an opportunistic packet scheduling scheme that allows the relay node to adaptively decide using one-way (traditional) or two-way (network coded) relaying, and analyze the average two-hop transmission delay performance. By considering both the buffer occupancy at the relay node and the link conditions to the end nodes, the proposed opportunistic scheduling achieves much lower average packet transmission delay, compared to pure one-way and pure two-way relaying. In addition, the simulation results verify the accuracy of the analytical model.