Performance evaluation of distributed co-ordination function for IEEE 802.11 wireless LAN protocol in presence of mobile and hidden terminals

摘要

This paper investigates the performance of IEEE 802.11 wireless local area network (WLAN) protocol's distributed coordination function (DCF) in the presence of mobile and hidden terminals. In order to study the joint effect of hidden terminals and user mobility on the performance of IEEE 802.11 DCF, we extend Tobagi and Kleinrock's (1975) hearing graph framework to model hidden terminals in a static environment. We derive a combined mobility and hidden terminal model using a Markov chain from the hearing graph of a given physical layout. The simple model uses two parameters: /spl alpha/, which controls the number of hidden terminals in the steady state, and /spl lambda/, which controls the rate of mobility of each terminal. By varying the values of /spl alpha/ and /spl lambda/ we can systematically generate scenario with different number of hidden terminals and different mobility rates for a particular physical layout with static obstructions. We have developed a discrete event simulator which uses the parameterized model to obtain the throughput and blocking probability behavior of an IEEE 802.11 based ad hoc network in the presence of certain static obstructions. Our simulations suggest that the IEEE 802.11 DCF protocol is robust enough to handle moderate conditions of hidden terminals and mobility, but the performance may degrade under extreme conditions. Carefully selecting protocol parameters (RTS and fragmentation threshold) can help improve the performance even under extreme conditions.