小麦田中天线高度对2.4GHz无线信道传播特性的影响

探索农田环境下无线信道传播特性，将为无线传感器网络部署与功率控制方面的研究打下基础。该研究在小麦田地中实地测试了不同生育期 2.4GHz 无线信号的功率衰减情况和丢包率，进而得出传输范围及路径损耗，并用MATLAB对路径损耗进行了回归分析。研究表明，小麦田中，信号衰减的速度随天线高度的变化单调递减，而传输距离随天线高度的变化单调递增，因此，天线的较优位置应略高于成熟植株（1.2 m左右）。同一天线高度下，小麦生长后期无线信号的衰减大于前期。2.4GHz 无线信号的衰减情况可用对数距离路径损耗模型来预测，理论值与测量值的相关系数在0.961～0.996之间。路径损耗指数与天线高度呈现对数衰减趋势；在同一天线高度下，路径损耗指数随着小麦的生长而增大。

Impact of antenna height on propagation characteristics of 2.4 GHz wireless channel in wheat fields

It will provide the foundation for researches on wireless sensor network deployment and power control to study the wireless channel propagation characteristics in cropland environments. The power attenuation and the packet loss rate (PLR) of 2.4GHz radio signals were measured in wheat fields at different growth stages with the transmission ranges of nodes and the path loss further attained, and then the path loss model was built through regression analysis using MATLAB. The results showed that the attenuation speed of signal power monotonically decreased, and transmission range monotonically increased with the increase of antenna height, respectively. Therefore, the optimal height of antenna was about 1.2 m, which was a little bit higher than that of mature wheat plants. The signal attenuation at later growth stages of wheat was larger than that at earlier stages when the antenna height was kept unchanged. In addition, 2.4GHz wireless channel loss in wheat fields could be predicted by the logarithm distance path loss model, and the correlation coefficients between computational values and measurement values were between 0.961 and 0.996. Path loss index decreased logarithmically with the increased of antenna height, and increased with the growth of wheat plants.