The Research On Propagation Characteristics Of433MHz Wireless Sensor Network Signal In Agriculuture Application

How to improve the agricultural production efficiency, economic and environmental benefits with constraint of the limited resources has become an important issue needed to be addressed in the development of fine agricultural in China. Advanced information technology has become an important means to achieve this goal, and wireless sensor network technology is one of the most popular research direction for agricultural modernization.The wireless sensor network technologies include sensor technology, MEMS technology, wireless communication technology, embedded computing technology, and distributed information processing technology. The common requirement for them is low power consumption which leads to a smaller coverage range compared to traditional wireless systems. When the application environment is different, the covering performance of wireless sensor networks will be very different. Considering this characteristics, this paper studied the propagation characteristics of wireless signals in farmland environment. Firstly, we measured the pathloss in three typical growing periods of winter wheat by using wireless sensor nodes with433MHz transmit signals and spectrum analyzer, and then analyzed the measurement results by using curve fitting and regression method, from which we obtained the propagation model for433MHz wireless signals in agriculture environment. We also compared this model with typical outdoor and indoor propogation models so that we could observe the impact of farmland environment. Secondly, we designed a multipath delay measurement system based on GNU radio platform and USRP for small scale radio propogation characterisitics of433MHz signals. One USRP sender sends M sequence, and another USRP receiver uses the same M sequence to accomplish the correlate operation, then we calculated sliding correlation to the received signal in order to get the power delay profile (PDP) of small scale propogation, based on which we can deduce the multipath delay of the transmitted signal. We used this system to measure the PDP of433MHz wireless signals in Lab639, teaching building3at the Beijing University of Posts and Telecommunications campus.