Propagation characteristics of 2.4 GHz wireless channel at different heights in apple orchard

For configuring WSN system and node deployment in apple orchards, the paper focused on signal strength attenuation and packet loss rate of 2.4 GHz wireless channel in different heights in apple orchard when the apples were mature. The field test was conducted along a line of apple trees with the height from 0.5 meters at the trunk level to the top of canopy about 3 meters high. At each height, receiving signal strength and packet loss rate were tested for ten different distances. Regression analysis results showed that 2.4 GHz wireless channel loss accords with logarithm distance path loss model, and the correlation coefficients between computational values and measurement values were between 0.915 and 0.983. When the height was between 1 and 2.25 meters, the signal attenuation rate was larger than the other heights. When the height was higher than 2.25 meters, the signal attenuation rate became slower with the increase of height until 3 meters when the signal attenuation rate was the smallest. So in apple orchard, it's best to place the antennas at the top of the canopy or above of it, followed at higher place above 2.25 meters. Besides, a model used for calculating the received signal strength of 2.4 GHz transmitting through mature apple orchard was constructed. Validation results show that the model can better predict the received signal strength at different distance point at different height. This research can provide a reference for WSNs application.