The Propagation Characteristics of Radio Frequency Signals for Wireless Sensor Networks in Large-Scale Farmland

For configuring wireless sensor network and deploying nodes, the propagation characteristics of wireless channel at frequency of 433 MHz and 2.4 GHz are investigated. Through the analysis of the received signal strength indicator (RSSI) and packet loss rate (PLR), we find that the RSSI (PLR) decreases (increases) as the transceiver nodes distance increases. It is also found that the path loss decreases with the antenna height increasing, and the path loss at 2.4 GHz is more serious than that at 433 MHz. Through the regression analysis in Matlab, we find that the optimal fitting model is the parametric exponential decay (OFPED) model, and the second-best is the linear logarithmic model. For OFPED model, the values of R-2 vary from 0.9347 to 0.9893, and the values of root mean square error (RMSE) range from 0.7469 to 2.243 at frequency of 433 MHz; while at frequency of 2.4 GHz, the values of R-2 change from 0.9612 to 0.9857, and the values of RMSE range from 1.375 to 3.181. Moreover, we make a comparison analysis with several modified exponential decay (MED) models, and the validation results show that the MED models can be used as conservative upper and lower bounds of path loss, at least for wheat field.