温室高湿环境下433 MHz无线信道传播特性研究

Propagation Characteristics of 433 MHz Wireless Channel in Greenhouse under High Humidity

为解决温室高湿环境下无线传感器网络的规划和部署问题,探究了高湿环境、通讯距离、天线高度对无线信号传播特性的影响,以433MHz为载波频率,研究无线信号在不同湿度及不同高度下的传播特性,通过两组试验测取了接收信号强度及丢包率,并通过MatLab对试验数据进行回归分析。结果表明:在不同湿度和高度下,433 MHz无线信道传播特性符合路径损耗模型,拟合决定系数在0. 892 0～0. 965 8之间;湿度对无线信号具有一定影响,尤其是湿度在80%以上时,对在冠层中传播的无线信号具有较大影响。同时,建立了路径损耗指数n与湿度之间的二次多项式关系模型,并根据此模型对路径损耗模型进行修正,建立了湿度系数修正模型。经验证,该模型均可有效地预测3种高度水平下的接收信号强度。

In order to solve the problem of WSN planning and deployment in greenhouse under humid environment,investigate the effect of humid environment,communication distance and the height of the antenna on the wireless signal propagation characteristics,we chose 433 MHz as carrier frequency and studied on propagation characteristics of 433 MHz wireless channel in different humidity and heights,received signal strength indicator and packet loss rate were measured through two experiments,and experimental data were analyzed with multivariable linear regression in MATLAB. The results show that in different humidity and heights,propagation characteristics of 433 MHz wireless channel is accord with logarithm distance path loss model,and fitting coefficient of determination are between 0. 892 0 and 0. 965 8. Humidity has an impact on wireless signals,especially when humidity is over 80%,it has a significant influence on the wireless signals which transmitted in the canopy of plant. A polynomial relation model between the path loss exponent and humidity is established,and the path loss model is revised according to the model. The humidity coefficient correction model was established. And the model can be used to predict the received signal strength indicator in three kinds of heights effectively after verification.