Optimum Network Coding for Delay Sensitive Applications in WiMAX Unicast

MAC layer random network coding (MRNC) was proposed as an alternative to HARQ for reliable data transmission in WiMAX unicast. It has been shown that MRNC achieves a higher transmission efficiency than HARQ as it avoids the problem of ACK/NAK packet overhead and the additional redundancy resulting from their loss. However, it did not address the problem of restricting the number of transmissions to an upper bound which is important for delay sensitive applications. In this paper, we investigate a more structured MAC layer coding scheme that achieves the optimum performance in the delay sensitive traffic context while achieving the same overhead level as MRNC. We first formulate the delay sensitive traffic satisfaction, in such an environment, as a minimax optimization problem over all possible coding schemes. We then show that the MAC layer systematic network coding (MSNC), which transmits the packets once uncoded and employs random network coding for retransmissions, achieves the optimum performance for delay sensitive applications while achieving the same overhead level as MRNC.