Spatial TDMA and CSMA with preamble sampling for low power ad hoc wireless sensor networks

Wireless sensor networks are a class of wireless ad hoc networks for which low power consumption is a major requirement. This paper presents an analysis of the performances of low power multiple access protocols designed for a network of wireless sensors. It considers the use of spatial TDMA for the transport of regular and frequent traffic and of a low power version of the nonpersistent CSMA protocol for the transport of rare signaling traffic. The low power version of CSMA is obtained by combining it with a preamble sampling technique. The delay performances and associated power consumption and lifetime are computed analytically. The power consumption of TDMA is computed as well, taking into account the power cost of keeping synchronized two nodes which have imprecise clocks. The lifetime that can be expected by a node with a single alkaline LR6 battery is given as a function of the desired average time interval between collision free transmissions on the TDMA and on the contention channels.