Wide-area long-range unidirectional sensor (WALRUS) network

Networks consisting of low-cost wireless sensors have been the subject of extensive research, with applications ranging from environmental monitoring to building control systems, to name a few. In this paper we consider networks intended to provide wide area coverage of one or more physical, chemical or biological parameters. We envision a target average data rate per sensor of 1-5 bps and transmission ranges of up to 100 m. Unlike conventional networks, the goal of wide-area parameter characterization can be achieved even with less than 100% node reliability, a feature that allows us to propose a novel ultra-low-cost architecture based on redundant sensors. To achieve the low-cost goal, sensor nodes include no receivers, and they transmit their information to a central reader using radio backscatter. This communication modality makes it possible to achieve a few years of battery life with small and inexpensive batteries. Performance impact due to absence of individual reception acknowledgement in this unidirectional communication channel is offset mainly by transmitter spatial diversity achieved through deployment of additional nodes. We describe the design of the system and its components, and analyze its performance characteristics.