MAC protocols and transport capacity in ad hoc wireless networks: Aloha versus PR-CSMA

Ad hoc wireless networks represent a new communication paradigm and could be an important means of providing ubiquitous communication in the future. Based on a recently developed communication-theoretic framework, in which the interaction between the medium access control (MAC) layer and the physical layer is taken into account, we investigate the performance of circuit switched ad hoc wireless networks. Upon the introduction of the concept of effective transport capacity, which represents the "actual" rate-distance product carried by the network and the maximum of which is the transport capacity of the network, an intuitive and simple approach for the evaluation of this quantity is proposed. In particular, two MAC protocols are considered: Aloha and perroute carrier sense multiple access (PR-CSMA). Numerical results indicate that for low values of the network traffic load the effective transport capacity achievable with Aloha is almost equal to that obtained in the ideal case without internode interference (INI). We also show the existence of a threshold value of the traffic load below which Aloha outperforms PR-CSMA, and above which the opposite is true.