Date Added: Jul 2010
Wireless sensor networks for environmental monitoring and agricultural applications often face long-range requirements at low bit-rates together with large numbers of nodes. This paper presents the design and test of a novel wireless sensor network that combines a large radio range with very low power consumption and cost. The asymmetric sensor network uses ultra-low-cost 40 MHz transmitters and a sensitive software defined radio receiver with multichannel capability. Experimental radio range measurements in two different outdoor environments demonstrate a single-hop range of up to 1.8 km. A theoretical model for radio propagation at 40 MHz in outdoor environments is proposed and validated with the experimental measurements.