农田土壤无线地下传感器网络节点设计与通信试验

为了揭示电磁波信号在农田土壤中的传输特性、科学部署传感器节点，以关中地区农田土壤为研究对象，采用模块化设计思想，将传感器、无线数传、处理器和能量供应等模块集于一体，设计了无线地下传感器网络（Wireless underground sensor networks，WUSN）节点和汇聚节点。采用单因素试验方法，分析了土壤含水率、WUSN节点埋深、节点间水平距离对WUSN节点信号传输的影响，建立了接收信号强度和误码率预测模型。结果表明，当WUSN节点信号在地下垂直方向上传输时，土壤含水率增加2.5个百分点，接收信号强度降低4~6dBm，通信误码率增加3~5个百分点；WUSN节点埋深增加5cm，接收信号强度降低3~5dBm，通信误码率增加3~4.5个百分点。当WUSN节点信号在地下水平方向上传输时，土壤含水率增加2.5个百分点，接收信号强度降低5~7dBm，通信误码率增加4~5个百分点；节点间水平距离在10~90cm范围内，节点间水平距离增加10cm，接收信号强度降低6~8dBm，通信误码率增加6.5~8个百分点；节点间水平距离在90~190cm范围内，节点间水平距离增加10cm，接收信号强度降低约1dBm，通信误码率增加1~1.5个百分点WUSN节点信号在垂直、水平两种传输方向上误码率和接收信号强度预测模型拟合优度R2最高为0.982，均方根误差RMSE为1.7%，拟合优度R2最低为0.942，均方根误差RMSE为5.136dBm。WUSN节点信号在土壤中传输受到土壤含水率、WUSN节点埋深和节点间水平距离的严重影响。

Design and Test of Wireless Underground Sensor Network Nodes

In order to reveal the general characteristics of electromagnetic wave signal transmission in farmland soil and scientifically deploy sensor nodes, taking the farmland soil in Guanzhong region as the research object, adopted the modular design idea, integrated sensor, wireless data transmission, processor and energy supply module into one. Wireless underground sensor networks (WUSN) nodes and sink nodes were designed. The influences of soil moisture content, buried depth of WUSN nodes and horizontal distance between nodes on signal transmission of WUSN nodes were analyzed by single factor test method, and the prediction model of received signal strength and bit error rate was established. The experimental results showed that when the WUSN node signal was transmitted vertically underground, the soil moisture content was increased by 2.5 percentage points, the received signal strength was decreased by 4~6dBm, and the bit error rate was increased by 3~5 percentage points. The buried depth of WUSN node was increased by 5cm, the received signal strength was decreased by 3~5dBm, and the bit error rate was increased by 3~4.5 percentage points. When the WUSN node signal was transmitted in the horizontal direction underground, the soil moisture content was increased by 2.5 percentage points, the received signal strength was decreased by 5~7dBm, and the bit error rate was increased by 4~5 percentage points. When the horizontal distance between nodes was within the range of 10~90cm, the received signal strength was decreased by 6~8dBm when the horizontal distance between nodes was increased by 10cm, and the bit error rate was increased by 6.5~8 percentage points. When the horizontal distance between nodes was within the range of 90~190cm, the received signal strength was decreased by about 1dBm when the horizontal distance between nodes was increased by 10cm. The bit error rate would be increased by 1~1.5 percentage points. The best fit R2 and root mean square error of WUSN node bit error rate and signal receiving strength prediction model in two transmission directions were 0.982 and 1.7%, respectively, and the best fit R2 and root mean square error were 0.942 and 5.136dBm, respectively. In conclusion, the signal transmission of WUSN nodes in soil was seriously affected by soil moisture content, buried depth of WUSN nodes and horizontal distance between nodes. The received signal strength and bit error rate can be accurately calculated by using this prediction model, and then the maximum buried depth and maximum horizontal distance of WUSN nodes can be obtained. At the same time, the general conclusion of WUSN signal transmission in farmland soil was given.