A fair and Adaptive Contention Resolution Algorithm for time-slotted MAC protocol designs

This paper addresses the fairness of Medium Access Control (MAC) protocols that are capable of handling interference on the physical layer to a varying extent. The variation addressed is thereby not based on different physical layer techniques applied, but on differing attribute levels of the same physical layer technique. This can e.g., be a varying number of antennas at each node in case of Multiple Input Multiple Output (MIMO). Fair contention resolution in such protocols becomes a trade off between on the one hand avoiding a permanent overwhelming of low level devices with interference, and on the other hand blocking of all spatial reuse by these low level devices. The latter one would restrain the better equipped terminals from taking advantage of their excellent equipment. In order to balance both aspects, we propose the Fair and Adaptive Contention Resolution Algorithm (FACRA). The algorithm is fully distributed and requires only the exchange of a single parameter value between competing terminals. We show by means of simulations that the algorithm significantly increases the spatial reuse by avoiding frequent blocking by low level devices, without disadvantaging these devices significantly.