基于无线传感器网络的设施农业车辆定位系统设计与试验

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

为解决目前设施农业机械定位系统稳定性差、定位精度低和成本高等问题,该文设计了一套基于Nano PAN5375模块的无线传感器网络（wireless sensor network,WSN）定位系统。该定位系统的3个信标节点负责和定位节点的无线测距,安装有定位节点的车辆构成的移动节点负责无线测距和定位坐标的计算。WSN节点采用的是基于Nano PAN5375的WD5032N模块。Nano PAN5375模块通过串行外设接口和微处理器进行通信,实现无线通信和无线测距的功能。设计了WD5032N模块的供电底板电路,满足其微处理器和Nano PAN5375模块的供电要求,以及通过串口和液晶显示屏模块通信实时显示定位坐标X和Y。节点软件以Keil MDK为开发环境,采用单片机C语言开发,实现节点数据采集与处理、无线传输和串口通信等功能。在定位节点上,采用基于线性调频扩频技术的对称双向双边测距算法来计算定位节点到各个信标节点之间的距离,并使用三边质心定位算法计算出未知节点的坐标位置信息,最后使用卡尔曼滤波算法对目标状态的观测值进行迭代,解决因为测量噪声对于定位精度造成的影响。在WD5032N上分别采用3DB天线和5DB天线进行室内和室外测距和定位试验,结果表明,基于Nano PAN5375的WSN定位系统稳定性好,定位精度高,在3个信标节点组成的合适的等边三角形3条边线范围内定位精度能达到1 m左右,而在接近三角形边线外侧的位置定位精度是1-2 m左右,可以满足一般设施农业车辆的定位精度要求。该文为农业机械精确定位的深入研究提供了参考。

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.