Encoded Packet-Assisted Retransmission for Multiple Unicast Flows in Wireless Networks

In this paper, we address the problem of reliable unicast transmission across wireless networks with a packet erasure channel. It has been proven that network coding (NC) can offer significant advantages over conventional approaches for this problem. However, existing NC schemes do not always fully exploit the potential of NC due to the lack of understanding of the use of the encoded packets that receivers cannot decode. To overcome this limitation, we propose an NC framework called encoded packet-assisted retransmission (EAR). EAR develops an improved opportunistic listening mechanism that allows receivers to store all heard undecodable NC packets and to report periodically the reception status to the sender. Thus, the sender can directly xor these encoded packets with other packets to take full advantage of all the available coding opportunities. We also formulate a packet-scheduling problem that aims at maximizing the utilization of coding opportunity in the network. By solving it, we design a simple and efficient scheduler that prioritizes packets according to their contribution to the overall transmission performance. Then, the sender determines a packet that should be transmit next and selects packets to be encoded, i.e., based on the priority class. In addition, we investigate the performance of our approach from a theoretical perspective. From simulation results, it is seen that EAR can significantly reduce the total number of retransmissions and provide more efficient bandwidth utilization compared with existing schemes.