Physical Layer Effect on MAC Performance in Ad-hoc Wireless Networks

R. Negi and A. Rajeswaran (USA)


-- Wireless communications, ad-hoc networks, physical layer, MAC, graph coloring.


-- In wireless ad hoc networks, every device (node) has a transmission radius and may communicate successfully with any node lying within a disk of radius . However, a node also has an interference radius , which determines contention between links. The relation between the transmission and interference radius depends on the underlying physical layer. Pair-wise interference between two links in ad-hoc networks has been previously modeled by disk graphs, allowing the application of graph theoretic results. However, these geometric models do not accurately represent the physical layer. In this paper, geometric conditions for contention between links are derived by analyzing the physical layer and utilizing the relationship between and . This analysis results in geometric conditions significantly different from the existing disk graph models. A bound on MAC performance is derived based on the physical layer model, by specifying a graph coloring heuristic. This bound is very different from that derived for disk-graph models, thus demonstrating the importance of the physical layer when evaluating MAC performance.

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