Evaluation of 920 MHz Radio Wave Propagation Characteristics for Wireless Sensor Networks in a Farm

Abstract

To implement reliable wireless sensor networks suitable for use in “smart agriculture”, it is important to understand the radio propagation characteristics in the farm environment. In a farm field, crops and structures such as glasshouses or vinyl houses that lie between transmitter and receiver nodes affect radio wave propagation. Owing to multipath effects that arise from reflections of radio waves from crops, the ground, and other obstacles, slight differences among the node positions can affect the received signal strength indicator (RSSI). In addition, crops that are shaken by the wind introduce temporal variation into RSSI. In this paper, we measured RSSI based on radio propagation characteristics in the 920 MHz band, which is used in the Wi-SUN standard for smart agriculture, in a farm field, inside a vinyl house, and between the base station and farm fields, and evaluated signal attenuation as a function of distance and the variability of RSSI by analyzing signal data. We measured the decay characteristics of the signal in a farm where crops and other obstacles exist along the radio wave’s propagation path. In addition, we characterized the variation of RSSI in a farm, where obstacles exist near the transmitter or receiver nodes and crops exist along the radio wave’s propagation path.