Analysis of topology-unaware TDMA MAC policies for ad-hoc networks under diverse traffic loads

Abstract

The ever-changing nature of the ad-hoc networks, makes the design of efficient Medium Access Control (MAC) policies challenging. Topology-unaware MAC policies, that allocate slots deterministically or probabilistically have been proposed in the past and evaluated under heavy traffic assumptions. In this paper, the heavy traffic assumption is relaxed and the system throughput achieved by these policies is derived as a function of the traffic load. The presented analysis establishes the conditions and determines the values of the access probability for which the system throughput under the probabilistic policy is not only higher than that under the deterministic policy but it is also close to the maximum achievable, provided that the traffic load and the topology density of the network are known. In case the traffic load and/or the topology density are not known (which is commonly the case in ad-hoc networks), alternative values for the access probability are also derived which, although not the optimal (maximizing the system throughput), they do lead to a system throughput higher than that under the Deterministic Policy. Simulation results for a variety of topologies with different characteristics support the claims and the expectations of the analysis and show the comparative advantage of the Probabilistic Policy over the Deterministic Policy.