Design and experiment based on wireless sensor network with 780 MHz in greenhouse

Abstract: In recent years, a wireless sensor network (WSN) technique was widely applied in the field of agriculture, which detects, senses, and collects information of various environments or objectives in the network area, and at the same time sends and receives data through wireless and self-organizing multi-hop routing links. Due to the complexity of the agricultural environment and various factors like barriers, weather condition, structure, materials, and the layout of facility agriculture that all affect the WSN communication quality, wireless sensor networks adapt dissimilarly to agricultural environment. Therefore, how to achieve the best networking to different agricultural environment conditions, minimize the cost and energy consumption, and improve the performance of the network transmission turn out to be the key issue in the studying of agricultural wireless sensor networks. Aiming at the problems of previous agricultural wireless sensor networks, such as high cost, high-energy consumption, and non-ideal transmission performance, this paper designed, with chips of AT86RF212 and C8051F920 a new type of wireless sensor network which works on a Chinese dedicated band of 780MHz and is compatible with the IEEE802.15.4c standard for a greenhouse. This paper briefly described the structure of wireless sensor network node, mainly introduced the hardware design of a 780MHz wireless sensor network, and also tested and analyzed the received signal strength index (RSSI) and the average packet loss rate (PLR) of the wireless sensor network node in 433 MHz, 780 MHz, and 2.4 GHz bands by changing the wireless communication distance in a typical northern solar greenhouses working as the experimental environment. The experimental results showed that RSSI of wireless transceiver modules in the three different bands decreased with the increasing of the communication distance. The RSSI values of the three wireless transceiver modules were similar to each other when the communication distance in a greenhouse was less than 20m. When the distance reached 40-90m, the module in 780MHz showed a slightly larger RSSI value than the 433MHz module while the .4GHz module had the smallest RSSI. Within the 90m communication distance range in a greenhouse, packet loss rates (PLR) of both 780MHz and 433MHz modules were 0. For the 2.4GHz module, packet loss took place at a distance of 80m and when it went to 90m, the maximal PLR was 5%. When the communication distance was 50-90m between greenhouses, the RSSI of the 780MHz and 433MHz modules were close. The RSSI value of the 780MHz module was higher than that of the 433MHz module when the wireless communication distance exceeded 90m. For the 2.4GHz wireless module, the RSSI value was lower than both the 780MHzand 433MHz modules' when communication distance between greenhouses was 50-140m. Packet loss occurred to the 433MHz module when the distance was over 100m, and when it went to 140 m, the maximal PLR was 11%. Packet loss took place to the 2.4GHz module if the communication distance between greenhouses exceeded 70m, and when it was over 135m, the PLR reached 100%. For the 780MHz band wireless module, packet loss took place when the communication distance between greenhouses was over 125m, and when the distance was 140m, the maximal PLR was smaller than 6%, which allows the reliable wireless transmission between greenhouses to proceed. Above all, the transmission characteristics of the wireless sensor networks in the 433MHz and 780MHz bands were obviously better than the WSN of a 2.4GHz band in the application of greenhouse environmental monitoring. The 780MHz band WSN was even superior as to transmission and communication quality performance.