Reliable multicast in wireless networks using network coding

Abstract

Reliable multicast in wireless networks has been well studied in the sense to solve the feedback implosion issue, which, however, can not reduce the number of retransmissions in order to recover all lost packets at receivers. Most recently, it has been proposed to use network coding for reliable multicast in wireless LANs to reduce the number of retransmissions. In this paper, we propose two new models to further reduce the number of retransmissions for reliable multicast. In the first model, each retransmission encoding decision is made according to the latest ldquowantedrdquo packet set at all receivers. Thus, the maximum number of receivers can potentially decode out one ldquowantedrdquo packet from each encoded retransmission packet. Such a model is referred to as dynamic multicast retransmission encoding (DMRE) model. This model is a memoryless model where a receiver will not buffer encoded retransmission packets for later use. In the second model, a receiver will buffer all received encoded retransmission packets and decode out their ldquowantedrdquo packets at the end of the retransmission batch. Such a model is referred to as cache-based multicast retransmission encoding(CMRE) model. The problem to minimize the number of retransmissions under both DMRE and CMRE models are NP-hard. Effective heuristic algorithms are proposed in this paper. We analyze the impact of packet delivery ratio on the gain of network coding. We derive the lower bound of the expected number of retransmissions using network coding, which provides the insights of the maximum potential gain using network coding in reliable multicast.