Fair Coexistence MAC Protocol for Contention-Based Heterogeneous Networks

This paper proposes a contention-based fair coexistence mechanism among heterogeneous networks that have different transmission power and/or coverage. First, we show that the existing carrier sensing multiple access (CSMA) mechanism, that is a prevailing contention-based protocol, results in significant unfairness in channel access when heterogeneous networks coexist; a system with lower transmission power hardly occupies the shared channel due to interference from a system with higher transmission power. We analyze the causes of unfairness in terms of (i) the asymmetry of carrier sensing and (ii) the blindness of binary exponential backoff mechanism and the link adaptation mechanism, and we derive an analytical model of per-system throughput to investigate the effects of these causes.To resolve this problem, we propose a fair coexistence CSMA protocol consisting of access etiquette and interference-aware backoff. The former adaptively controls the contention window size so that the high-power system allows transmission opportunities to the low-power system in a fair and efficient manner. The latter differentiates between the response to transmission failure caused by collision and the response to failure caused by interference. The simulation results confirm that the proposed scheme effectively mitigates the unfairness of channel sharing while attaining high spectral efficiency.