Design and experiment of locating system for facilities agricultural vehicle based on wireless sensor network

Some problems of facility agriculture machinery locating system still exist now, such as poor stability, low positioning accuracy and high cost. In addition, agricultural machinery navigation and positioning system based on Global Position System (GPS) is widely used at home and abroad. But it is not applicable to the agricultural facilities and the scenes of more buildings. In order to resolve these problems, a wireless sensor network (WSN) locating system based on NanoPAN5375 module was designed. NanoPAN5375 module is based on the technology of chirp spread spectrum (CSS); it not only has advantages of reliable communication, good stability, long transmission distance, low system power consumption, and so on, but also adopts the principle of the time difference of arrival (TDOA) to calculate the distance between nodes, so that its ranging accuracy is high. Therefore, NanoPAN5375 module was chosen as positioning node of facility agriculture vehicle. In the locating system, the 3 beacon nodes were responsible for the wireless ranging, and the car installed with location node was responsible for the wireless ranging and location coordinates calculation. WD5032N module based on NanoPAN5375 was used as WSN node. And microprocessor STM32F103CB and NanoPAN5375 module were integrated on WD5032N module. NanoPAN5375 communicated with the microprocessor through the serial peripheral interface (SPI), so it could realize the function of wireless communication and wireless ranging. A power supply backplane circuit of WD5032N module was designed to meet the power supply requirement of its microprocessor and NanoPAN5375 module, and location coordinates X and Y were displayed in real time through the serial port communicating with liquid crystal display (LCD). The node software, which was compiled by C Language taking the Keil MDK as development environment, could complete data acquisition and processing, wireless transmission, serial communication and other functions. The distances between unknown nodes and each beacon node were calculated by using Symmetrical double-sided two way ranging (SDSTWR) algorithm which was based on CSS technology in location node. And then the coordinate information of the unknown node was calculated by the triangle centroid localization algorithm. Finally in order to resolve the effects of measurement noise on positioning accuracy, the iterating based on Kalman filter algorithm was applied to observed values of target state. The antennas of 3 and 5 DB were respectively used on WD5032N to do ranging and positioning experiments in the indoor and outdoor. On one hand, the results of ranging experiments have shown that the ranging accuracy of the nodes based on NanoPAN5375 module is high. Within the scope of the appropriate distance, point-to-point ranging accuracy between the nodes can reach 1.02 m or less. On the other hand, the results of positioning experiments indicate that the stability of WSN positioning system based on NanoPAN5375 is good and the positioning accuracy is high. And the positioning precision could reach about less than 1 m within the scope of 3 edges of equilateral triangle formed by 3 beacon nodes. And the positioning accuracy was about 1-2 m close to the outside of the triangle edges. So it can satisfy the requirement of positioning accuracy of general facility agriculture vehicle, and can be applied to other agricultural machines' positioning.