Robustness and Optimality in CSMA Wireless Networks

It has recently been shown that distributed queuebased adaptation of CSMA’s contention aggressiveness can provably optimize network utility. However, such an approach is fragile, and was shown to suffer high performance degradation under conditions of frequent occurrence, namely; asymmetric channels, heterogeneous traffic, and packet collisions. In this work, we address the main sources of performance degradation in optimal CSMA to design a distributed system for proportionalfair throughput that delivers high performance in a wide-range of network conditions. First, we propose a generalized version of prior optimal CSMA models to incorporate individual perlink modulation and coding rates. With such a model, we derive adaptive principles that maximize utility under arbitrary channel capacities. Second, we propose a novel structure that can be used in the place of queues to provide optimal CSMA adaptation. As such a structure does not use traffic backlog to operate, the resulting adaptation is optimal for the set of backlogged flows under general traffic arrival patterns. Third, we propose a robustness function that reduces access in high contention scenarios to avoid high performance degradation due to collisions. By evaluating these three solutions against prior designs, we observe vast performance gains, of up to 68% higher logarithmic utility by our approach, on average over randomly-generated scenarios that incorporate the three main sources of performance degradation.