柿园无线传感器网络信号传输损耗研究

Loss research on wireless sensor network signal transmission in persimmon orchard

为探究柿园无线传感器网络信号传输特性,该文研究了在2.4 GHz无线信道下柿树处于萌芽期、幼叶期和花期3种时期时无线网络信号传输的衰减情况。试验中分别在柿子树萌芽期、幼叶期和花期3个生长时期下选择一列长势均匀的柿树,通过调节子节点和汇聚节点装置的高度和距离测量柿子树从距离地面3个高度冠层底部(0.8 m)、冠层最密部(1.8 m)和冠层顶部(2.8 m)处各8个距离点的链路质量指示值(link quality indicator,LQI),并对试验数据进行分析。结果表明LQI值随着距离的变化呈正弦曲线式衰减趋势。萌芽期时子节点和汇聚节点的高度均位于冠层顶部时,节点间距38 m时是最佳位置;幼叶期时子节点和汇聚节点的高度均位于冠层顶部,节点间距32 m时是最佳位置;花期时子节点和汇聚节点的高度均位于冠层顶部时,节点间距26 m时是最佳位置。通过对3次数据进行曲线拟合分析分别建立了在2.4 GHz信道下信号衰减模型,其中3种生长时期下均是三次多项式模型决定系数R2最大,为最适模型。果园中无线传感器网络信号传输损耗的研究为在果园中无线传感器网络节点部署提供了技术基础。

To explore a wireless sensor network （WSN） system and node deployment in persimmon orchards, this paper focused on the wireless network signal transmission under the 2.4 GHz radio channel in the persimmon orchard when it was in the germination stage, young leaves stage, and flowering stage, three growth periods. A row of persimmon tress in the growth period was selected. By adjusting the height and distance of the node and father node, the distance from three different heights from 0.80 meters at the bottom of the tree and 1.80m at the most luxuriant foliage location to 2.80 meters at the top of the canopy wee measured. Persimmon trees were measured for each growth period resulting in 72 groups of data. Results showed the LQI value with the change of the distance, the sine curve type attenuation trend, and the difference was obvious in the three growth periods. The radio signal attenuation data measured the worst minimal in the flowering stage, because the branches and leaves of signal reflection, refraction, and absorption was the most serious in this period. It is showed that the best effective transmission distance of each column of trees was 38m when child nodes and father nodes are on the top of the canopy （2.80 m） in germination, while in the young leaves stage, the height of the child nodes and father nodes are located in the top of the canopy, when the node is the best place to pitch 32m. In the flowering stage, child nodes and father nodes are on the top of the canopy, and the best distance is 26m. In the case when plant height is not very high, when the device is placed on top of the node, the wireless sensor networks optimal signal transmission distance changes as the degree of lush foliage plants is smaller and smaller. During the experiment, because the orchard in the wild environment was susceptible to the wind, the corresponding external factors, such as the difference of the instantaneous value, sometimes the LQI was big. Based on two data sets, curve fittings were established in the 2.4GHz channel signal attenuation model, which cubic polynomial model maximum correlation was coefficient R squared for an optimal model. A model of R value was the biggest of all. In the germination stage, R squared was 0.754-0.958;in the young leaves stage it was 0.805-0.979;and in the flowering stage it was 0.758-0.991. Wireless sensor network research on orchard signal transmission loss provided the technical basis for the deployment of wireless sensor network nodes in orchards.