Rate diverse network coding: Breaking the broadcast bottleneck

An inherent limitation of the existing digital wireless network coding is that the relay node has to settle for a single broadcast rate for the coded packet transmission. Since the selected rate should be supported on the worst quality links to the intended receivers, the throughput gain by network coding is essentially bound to the capacity of the worst link. Worse yet, the bottleneck capacity diminishes as the diversity of links increases, which generally happens when the nodes participating in network coding operation grow in number. In this paper, we solve this "broadcast bottleneck" by using a novel symbol-level network coding scheme called Rate Diverse Network Coding (RDNC). With RDNC, the relay node can deal with receivers under disparate channel conditions with a single coded data stream, eliminating the single-rate broadcast bottleneck. Through extensive simulation, we find that RDNC significantly boosts the coding gain and the throughput, more when the given topology provides richer opportunities for coding. Specifically, RDNC is as good as COPE in the worst case, but can achieve up to 2.5 times the coding gain if the network topology permits.