Impact of fading on the performance of ALOHA and CSMA

This paper considers the performance of the ALOHA and CSMA MAC protocols in wireless ad hoc networks in the presence of fading. Increasing the rate of successful reception of packets is our objective, and thus, outage probability is used as the performance evaluation metric. 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 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 ALOHA and the different flavors of CSMA, namely CSMA with transmitter sensing, receiver sensing, and joint transmitter-receiver sensing. The introduction of fading adds to the hidden and exposed node problems of CSMA, resulting in an up to 75\% increase in the outage probability. Interestingly, however, the relative difference between the protocols remains unchanged.