NCAPQ: Network Coding-Aware Priority Queueing for UDP Flows over COPE

We are interested in UDP unicast flows over coded wireless networks with constructive inter-session network coding, such as COPE [1]. In prior work, we developed independently two mechanisms: (i) network coding-aware queue management (NCAQM) aimed at creating more network coding opportunities in the presence of congestion [2]; and (ii) network coding-aware MAC level packet prioritization (NCAPP), which assigned higher priority to coded than to uncoded packets [3]. In this paper, we compare the two mechanisms and we show that they achieve similar throughput benefits but work in complementary ways. We improve and combine them into a novel network coding-aware priority queuing scheme, which we refer to as NCAPQ. The proposed scheme improves throughput compared to COPE (by a factor of 10, in our simulations) and, even more importantly, compared to each individual scheme alone (by a factor of 2). Furthermore, we show that this significant increase in throughput comes without significant loss in fairness. The modifications we propose are minimal on top of COPE, thus making the scheme suitable for practical deployment.