On optimizing CSMA for wide area ad hoc networks

The recent deployment of data‐rich smart phones has led to a fresh impetus for understanding the performance of wide area ad hoc networks. The most popular medium access mechanism for such ad hoc networks is CSMA/CA with RTS/CTS. In CSMA‐like mechanisms, spatial reuse is achieved by implementing energy‐based guard zones. We consider the problem of simultaneously scheduling the maximum number of links that can achieve a given signal to interference ratio (SIR). In this paper, using tools from stochastic geometry, we study and maximize the medium access probability of a typical link. Our contributions are two‐fold: (i) We show that a simple modification to the RTS/CTS mechanism, viz., changing the receiver yield decision from an energy‐level guard zone to an SIR guard zone, leads to performance gains; and (ii) We show that this combined with a simple modification to the transmit power level–setting it inversely proportional to the square root of the link gain–leads to significant improvements in network throughput. Further, this simple power‐level choice is no worse than a factor of two away from optimal over the class of all ‘local’ power level selection strategies for fading channels, and further is optimal in the non‐fading case. The analysis relies on an extension of the Matérn hard core point process which allows us to quantify both these SIR guard zones and this power control mechanism.