Wireless network coding with improved opportunistic listening

Network coding has been shown to be a very promising technique for increasing the throughput in wireless ad hoc networks. In this paper, we set to define simple extensions for distributed medium access control (MAC) protocols that optimize the transmission of network-coded packets independently of the actual network coding algorithm. The main characteristic of the proposed protocol is that it improves the efficiency of coding decisions and allows verifying the decodability of packets before they are transmitted. The aforementioned goals are achieved first by adopting minor extensions to the channel access scheme, and second by introducing a new algorithm that manages intelligently the data packets that are stored at the MAC queue of each network node. The later algorithm improves the knowledge of a node regarding the available correct coding opportunities by the use of opportunistic acknowledgments, and by maintaining virtual buffers for the overheard data packets. For the proposed protocol, we also develop an analytical performance model that is used for evaluating its performance in conjunction with simulations. Extensive simulations are presented for several ad hoc network topologies that test all the features of the proposed protocol. Significant throughput improvement can be observed when our protocol is compared with network coding schemes that do not exploit the full potential of opportunistic listening.