Analysis of Network Coding in Slotted ALOHA with Two-Hop Bidirectional Traffic

This paper deals with two representative bidirectional traffic cases in two-hop wireless relay access systems employing network coding and a slotted ALOHA protocol. Network coding is a recent and highly regarded technology for capacity enhancement of multiple unicast and multisource multicast networks. The relay nodes are generally involved with unbalanced multidirectional traffic, but the impact of the unbalanced traffic on network coding has not been analyzed. This paper provides closed-form expressions for the throughput and packet delay for two-hop bidirectional traffic cases both with and without network coding even if the buffers on nodes are unsaturated. The analytical results are mainly derived by solving queueing systems for the buffer behavior at the relay node. The results show that the transmission probability of the relay node is a design parameter that is crucial for maximizing the achievable throughput of slotted ALOHA systems with network coding in two-hop bidirectional traffic cases.