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

摘要

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 R 2 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