Collision-minimizing CSMA and its applications to wireless sensor networks

Abstract

Recent research in sensor networks, wireless location systems, and power-saving in ad hoc networks suggests that some applications' wireless traffic be modeled as an event-driven workload: a workload where many nodes send traffic at the time of an event, not all reports of the event are needed by higher level protocols and applications, and events occur infrequently relative to the time needed to deliver all required event reports. We identify several applications that motivate the event-driven workload and propose a protocol that is optimal for this workload. Our proposed protocol, named CSMA/p*, is nonpersistent carrier sense multiple access (CSMA) with a carefully chosen nonuniform probability distribution p* that nodes use to randomly select contention slots. We show that CSMA/p* is optimal in the sense that p* is the unique probability distribution that minimizes collisions between contending stations. CSMA/p* has knowledge of N. We conclude with an exploration of how p* could be used to build a more practical medium access control protocol via a probability distribution with no knowledge of N that approximates p*.