Adaptive Network Coding Based Cooperative Medium Access for Wireless Networks

Ever since the introduction of network coding (NC) technique, several Medium Access Control (MAC) protocols based on NC have been developed for wireless networks of three node topology as well as `X' topology, considering that the information flows originate from the source (or reaches the relay) simultaneously. However, there are cases when these information flows do not occur simultaneously. In this context, a new medium access mechanism which is a modified version of CSMA/CA based IEEE 802.11 protocol is proposed in this paper, considering `X' topology based wireless network. It consists of two independent sources, transmitting to the same pair of destinations with the help of a relay node. The relay node of an ongoing cooperative transmission checks for NC opportunity before forwarding the packet to the destinations. If NC opportunity exists, then the relay initiates packet exchange with the other potential source. If not, it continues with the procedures of existing protocol. A suboptimal method of relay selection is also discussed. The proposed method is analyzed in terms of throughput and packet delay and the performance is compared with that of IEEE 802.11 based cooperative MAC protocol. Results show that the proposed protocol shows an improved performance.