Exploiting Network Coding for Pseudo Bidirectional Relay in Wireless LAN

Network coding is an effective method to improve forwarding efficiency in multi-hop wireless networks. Previous network coding schemes proposed for unicast transmissions focus on scheduling where paths are already established, and assume a fixed rate for all links, neglecting link rate heterogeneity. In this paper we study a network coding based pseudo bidirectional relay scheme for wireless LAN, taking link quality into account. We first show when network coding based relay improves channel efficiency and how to select such a relay in a distributed way. Then we enhance network coding based transmissions from three aspects: (i) Coordinated rate adaptation is adopted to reduce the probability with which a priori packet is missing in times of network decoding. (ii) The retransmission scheduling completely solves the lack-of-a-priori problem. (iii) Piggybacking receiving status in ACK/NAK further enables opportunistic reception and avoids unnecessary transmissions. Simulation results confirm that compared with direct transmissions, the proposed relay scheme can reduce per-packet transmission time by up to 39% in Rayleigh fading environment.