Radio Path-Loss Modeling for a 2.4 GHz In-Field Wireless Sensor Network

Abstract

Wireless sensor network (WSN) technology is a promising solution for large-scale, real-time, and continuous soil property data acquisition. However, the applications are still very limited due to a lack of understanding of in-field data transmission performance of a WSN. In this study, commercial 2.4 GHz wireless sensor modules (referred to as motes) and a hand-held spectrum analyzer were used to set up a test platform to evaluate radio propagation performance. Indexed packets transmitted from a module were captured by the spectrum analyzer to measure path-loss through received signal strength (RSS) and synchronously received by another module, called the base station, to calculate packet delivery rate (PDR). Experiments were conducted in a wheat field of an experimental farm of Oklahoma State University. Canopy height, transmitter height, receiver height, and transmitter-to-receiver distance (T-R distance) were considered as impact factors on radio propagation. Correlation analysis was used to evaluate the relationship between path-loss and PDR. The results indicated that, as plant height increased, path-loss and PDR became more correlated with each other. A distance of 70 m was defined as a stable communication distance for 2.4 GHz in-field WSN applications. Four models were developed to predict the path-loss based on the log of T-R distance and transmitter and receiver heights under conditions of clear line-of-sight and three different plant canopy heights. The R2 values of the models were 0.601, 0.599, 0.674, and 0.776, respectively. Their standard errors of the estimate were 3.761, 3.199 3.518, and 2.889, respectively.