Effects of Medium Access Control on the Capacity of Mobile Ad Hoc Networks

Abstract

As various wireless networks evolves into the next generation to provide better services, a key technology, mobile ad hoc networks (MANETs), has emerged recently. The dynamic topology, multi-hop transmission, and the nature of wireless channels create many challenging research topics in the area of MANETs. Recently, there has been work on determining the capacity of MANETs. The effects of some factors, such as node mobility, number of nodes, and transmission range, on the capacity of MANETs have been considered. In this work, we define and investigate the capacity of MANETs, considering the effects of medium access control (MAC). Since all the nodes in MANETs use a single or multiple channels to communicate, MAC plays an important role in coordinating channel access among nodes so that information gets through from one node to another. The MAC affects the capacity of MANETs in two aspects: collisions and spatial reuse. Three basic mechanisms are adopted to eliminate the incidence of collisions and maximize spatial reuse, i.e., carrier sense, handshake, and back-off. We define and use persistent probability, sensing range and back-off time to represent the effect of these mechanisms. The characteristics of MAC are thoroughly examined and an analytical solution for capacity evaluation is proposed. Numerical results are presented to demonstrate the effects of MAC, including carrier sense, handshake and back-off mechanism on the capacity of MANETs in terms of persistent probability, sensing range, and back-off time.