Distributed Admission Control for IEEE 802.11 Ad Hoc Networks

IEEE 802.11 has very poor performance in terms of throughput and transmission delay when the traffic load reaches the saturation condition. Admission control must be provided in order to guarantee the service of existing traffic. Unfortunately, the normalized saturation throughput is variable corresponding to different traffic statistics (i.e. bit-rate and average packet length) . Therefore it does not perform well if the station admits traffic simply based on certain threshold of the normalized throughput. Most existing analytical models for IEEE 802.11 MAC adopt quite strict assumptions of saturation conditions and simplified traffic scenarios. Nevertheless, it is more realistic to analyze the non-saturation condition under heterogeneous traffic scenarios. Moreover, an accurate analytical model under non-saturation condition is critical for the correctness of admission control decisions. In this paper, (1) we propose a unified analytical model which is the first model capable of analyzing performance under both non-saturation and saturation conditions; (2) we then introduce a new performance criterion, saturation coefficient Cn,sat, which reflects the degree of saturation experienced by any specific station; (3) finally we propose a distributed admission control scheme for IEEE 802.11 based on this criterion. With this scheme, any station can make local decision on whether admitting/rejecting a new traffic. The accuracy of the proposed analytical model and performance of the proposed admission control scheme are validated by simulations.