苹果园中2.4 GHz无线信道在不同高度的传播特性

为解决苹果园中无线传感器网络的规划和部署问题,该文研究了苹果成熟时苹果园中2.4GHz无线信道在不同高度的信号衰减和丢包率情况。通过实地试验测量了沿着一列果树由距离地面高度0.50m主干处至3.00m处冠层顶部9个高度下各10个距离点的接收信号强度和丢包率,并对试验数据进行回归分析。研究表明:在不同高度层,2.4GHz信号衰减均符合对数路径损耗模型,模拟的相关系数在0.915～0.983之间;高度1.00～2.25m之间信号衰减均较快。高度大于2.25m时,衰减速度随着高度的增加递减,在冠层顶部高3m处达到最小值。因此,苹果园中天线最宜部署在高约3.00m处的冠层顶部或略高于此,其次为高度大于2.25m的冠层上部且较高的位置。同时,建立了用于预测2.4GHz信号在成熟期果园中的信号衰减模型并用额外的数据进行了验证。结果表明:该模型能较好地预测不同高度处不同传输距离点的接收信号强度,为苹果园中无线传感器网络的应用提供了技术支持。

Propagation characteristics of 2.4 GHz wireless channel at different heights in apple orchard

For configuring WSN system and node deployment in apple orchards, the paper focused on signal strength attenuation and packet loss rate of 2.4 GHz wireless channel in different heights in apple orchard when the apples were mature. The field test was conducted along a line of apple trees with the height from 0.5 meters at the trunk level to the top of canopy about 3 meters high. At each height, receiving signal strength and packet loss rate were tested for ten different distances. Regression analysis results showed that 2.4 GHz wireless channel loss accords with logarithm distance path loss model, and the correlation coefficients between computational values and measurement values were between 0.915 and 0.983. When the height was between 1 and 2.25 meters, the signal attenuation rate was larger than the other heights. When the height was higher than 2.25 meters, the signal attenuation rate became slower with the increase of height until 3 meters when the signal attenuation rate was the smallest. So in apple orchard, it's best to place the antennas at the top of the canopy or above of it, followed at higher place above 2.25 meters. Besides, a model used for calculating the received signal strength of 2.4 GHz transmitting through mature apple orchard was constructed. Validation results show that the model can better predict the received signal strength at different distance point at different height. This research can provide a reference for WSNs application.