Comparative performance evaluation of MAC protocols in ad hoc networks with bandwidth partitioning

This paper considers the performance of the MAC protocols ALOHA and CSMA in wireless ad hoc networks, where the total system bandwidth may be divided into smaller subbands. In the network model used, the arrival of users/packets follows a Poisson point process, communication between nodes is continuous in time, selection of a subband to transmit across is made randomly at each transmitter, and the outage assessments made in the network are based on SINR measurements. Accurate bounds on the probability of outage for the MAC protocols are derived, and evaluated with respect to the number of subbands. It is observed that there exists an optimal number of subbands for each protocol, for which the probability of outage is minimized. For ALOHA, we obtain an analytical expression for this optimal value, while in CSMA, the optimal value is observed through simulations. Furthermore, we improve the performance of CSMA by introducing channel sensing across all subbands, in order to decrease the probability that a packet is in outage upon arrival. The obtained results are used to compare the performance of the two MAC protocols. Finally, we also evaluate the performance of our network in terms of sum capacity.