RF Propagation Patterns at 915 MHz and 2.4 GHz Bands for In-Field Wireless Sensor Networks

Abstract

Abstract. The objective of this study was to evaluate and compare in-field radio frequency signal propagation and data transmission performance of a wireless sensor network (WSN) in the 915 MHz and 2.4 GHz bands in a wheat field. Two types of wireless sensor nodes using 915 MHz and 2.4 GHz carrier frequencies were tested. Two nodes with the same carrier frequency were wirelessly connected, one as a receiver and another as a transmitter. Indexed packets transmitted from the transmitter were captured by a spectrum analyzer to measure path-loss and simultaneously received by the receiver to calculate packet delivery rate (PDR). Field experiments were conducted on a research farm at Oklahoma State University where wheat was planted. Impact factors on RF signal propagation considered included: plant canopy height, carrier frequency, transmitter height, receiver height, and transmitter-to-receiver distance (T-R distance). Analysis of impact factors’ influences on path-loss indicated that in-field RF signal path-loss was more subject to all separate impact factors as well as their interactions when using the higher carrier frequency. Pearson’s correlation results indicated that path-loss and PDR were more correlated with each other when the plants between the transmitter and receiver were higher than both types of nodes. Estimated marginal means plots indicated that for all plant canopy heights, the lowest path-loss could be achieved when the transmitter was installed at a height of 2 m and the receiver was installed at a height of 3 m using both types of nodes. At distances of 80 and 70 m, data communication was stable for the 915 MHz and 2.4 GHz nodes, respectively, for wheat field WSN applications when the transmitter and receiver antennas were at a minimum height of 1.0 m above ground and the wheat had a maximum plant height of 0.8 m.