Mitigating the Impact of Asynchronous ACKs on the Performance of Opportunistic Network Coding
Existing opportunistic network coding architectures relies on pseudobroadcast to deliver a coded packet to multiple receivers in a single transmission. In such situation, there is only one primary receiver who acknowledges the reception by synchronous MAC-layer ACKnowledgements (ACKs) and the other receivers receive it by overhearing and acknowledge the reception by asynchronous ACKs, which are usually piggybacked in outgoing data packets. This may cause a large amount of unnecessary retransmissions if asynchronous ACKs are dropped due to packet losses or they arrive late. Moreover, a large number of redundant retransmissions in IP layer easily cause congestion losses, especially under heavy traffic and thus compromise the throughput gain brought by network coding.