Joint transmitter and receiver carrier sensing capability of CSMA in MANETs

This paper considers the performance of the CSMA protocol with joint transmitter-receiver sensing in a wireless mobile ad hoc network. In our network model, packets belonging to specific transmitters arrive randomly in space and time according to a 3-D Poisson point process, and are then transmitted to their intended destinations using a fully-distributed CSMA MAC protocol. A packet transmission is considered successful if the received SINR is above a predefined threshold for the duration of the packet. Approximate expressions are derived for the outage probability of CSMA, and the role of joint transmitter-receiver sensing is evaluated. Furthermore, the optimal sensing thresholds for both the transmitter and receiver are derived, and shown to yield significant performance improvement. An understanding is established on the inherent hidden and exposed node problems of CSMA, and we illustrate how an optimization of the sensing thresholds can efficiently balance between these two problems. It is shown that the optimal choice for the sensing threshold of the receiver is the communication threshold, whereas the optimal sensing threshold of the transmitter is found numerically as a function of the communication threshold.