生猪养殖场无线传感器网络路径损耗模型的建立与验证

研究无线信号在生猪养殖环境中的传播特性，可以对无线传感器网络的路径损耗进行预测，从而为网络的部署奠定基础。研究采用ZigBee无线传感网络技术，通过在生猪养殖场中实际测试了有障碍物情况下，无线信号的丢包率和接收信号的功率强度，进而得出路径损耗值，以及障碍物的衰减因子，并进行了回归分析。研究表明，墙体衰减因子随墙壁数量增加而增大，植株衰减因子随天线架设高度升高而减小。最终模型的路径损耗参数为2.02，路径损耗的基础损耗为63.602，以混凝土墙为障碍物时，其衰减因子大小为2.64。将障碍物的衰减因子综合添加在经验模型中，可以有效的预测路径损耗值。

Modeling and validation on path loss of WSN in pig breeding farm

Abstract: In order to build a path loss model and optimize the deployment of ZigBee nodes, in this study, how the characteristic affecting the wireless signal propagation in pig farm environment is evaluated. The research is based on ZigBee wireless sensor network technology. Depend on the environment of pig farm, we consider piggery wall and plant growing between piggeries as the two mainly barriers which affect the wireless signal propagation greatly. During the research, packet loss rate (PLR) of wireless signal and received signal strength indicator (RSSI) are the most important parameters being used to evaluate transmission characteristics. We chose direct ray model as the basic path loss model and designed three groups of experiment to measure the parameters used in the model. Firstly, we tested RSSI value changed with the distance between transmitter and receiver in the case of no obstacle for 12 times. Based on the data obtained by regression analysis, the path loss exponent value was 2.02 and the correlation coefficient was higher than 0.9. Secondly, the influence of barrier was taken in count. The thickness of piggery wall was 0.4 m and the antenna height was set at 1.2 m for avoiding the effect of other obstacles. By increasing the number of wall, the rate of packet loss obviously changed. Result showed that one or two walls have no influence on PLR value, but it turns to 17.75% when the number of walls increases to 3 and when the number of walls added to 5, with PLR value reaches 100%. The influence of wall is transformed into the wall attenuation factor that added into the path loss model, and its value is computed to be 2.64. There are plants growing between the piggeries, which can be divided into three groups, 40, 80 and 120 cm. We set 4 groups of antenna heights for each kind of plant, which is depending on their own height. At each antenna height, we tested RSSI value with the changes of distance between transmitter and receiver, and then get the varying pattern of plant attenuation factor with the antenna height based on the regression analysis. Results showed that plant attenuation factor decreased with the rising of the height of installing antenna. Finally, prediction path loss model with the wall attenuation factor 2.64 and the plant attenuation factor, we use multi stage function to express when the plant height is 40, 80 and 120 cm, were obtained. In order to test the accuracy and practicability of the model, the integrated experiments with both wall and plant as the barriers in the pig farm environment were investigated, and the model was verified according to the field-test result. In the model, the path loss exponent is 2.02 and the basic path loss value is 63.602 dBm and other parameters change with the plant height or antenna height. The model is a comprehensive model that can be used for predicting the path loss value of ZigBee wireless signal in the pig farm environment. On the basic of the prediction path loss model, we can optimize the node deployment for increasing the network coverage rate and connectivity.