Study On Key Techniques In Wireless Underground Sensor Network For Farmland Soil Water Content Monitoring

Wireless underground sensor network(Wireless Underground Sensor Networks, WUSN) is that most wireless sensor nodes are buried in the underground soil, and only a few gateways that provide information exchange for public communication network are set on the ground.In the paper, the node and transmission characteristics, communication protocol and topology control and node location algorithm of wireless underground sensor network for farmland soil water content monitoring was seemed as the research object, the WUSN support signal transmission theory and network system technology were studied through computer simulation through the theoretical model analysis, computer simulation, unit system structure and indoor and outdoor tests. The WUSN node was designed and developed, 433 MHz electromagnetic wave communication characteristic was identified in the soil, the WUSN communication protocol was proposed, node positioning and deployment algorithm were established and WUSN unit testing system was implemented. The following results were obtained:(1) A kind of low-power nodes based on 433 MHz frequency was developed.The software and hardware system of wireless underground sensor network node were designed. The design requirements of wireless underground sensor network node were put forward basis on farmland soil water content, the electromagnetic wave transmission characteristics and node properties. Combining with computer simulation, the node circuit was demonstrated and designed, the wireless underground sensor network node that consists of 433 MHz, MSP430, XR61-TDR2 etc. hardware was developed.(2) The basic characteristic of WUSN electromagnetic wave under 433 MHz frequency transmission in the soil were established.When WUSN node frequency was 433 MHz, the comprehensive effects of nodes burial depth, the horizontal inter-nodes distance and the soil water content on communication were studied. Three dimensional relation of the nodes burial depth, the horizontal inter-nodes distance, the soil water content and the received signal strength, communication error rate were obtained, and the basic characteristic of the electromagnetic wave transmission in the soil was established.(3) The wireless underground sensor network routing protocol and topology control were studied and put forward.433MHz electromagnetic wave was adopted as signal carrier, wireless underground sensor network system clustering routing protocol was proposed and simulated through research and analysis of energy routing protocol, data center routing protocol and the logical layered routing protocol three routing mechanism. In addition, wireless underground sensor network topology algorithm was studied, the mixed topology control algorithm was presented based on the GAF algorithm and improved GAF algorithm to realize the wireless underground sensor network system communication load balance.(4) The wireless underground sensor network node location algorithm was studied and determined.The location algorithm based on distance and the location algorithm that has nothing to do with the distance were analyzed according to WUSN coverage and connectivity. The mixed node location algorithm of RSSI location algorithm based on the distance and maximum likelihood estimation method was presented and determined through algorithm research, optimization and validation.(5) The wireless underground sensor network unit test system was established.The plane hierarchical wireless underground sensor network verification unit with four underground sensor nodes and cluster head was built in farmland. The results were basically consistent through the test of the soil moisture content, and compared with soil moisture content data of the WUSN underground sensor nodes surrounding that were measured by drying method.Wireless underground sensor network is a relative new research direction. There are a lot of contents available for study about node design, network communication protocol, topology control algorithm and the node localization and deployment. The paper is only an exploratory research on the WUSN key technology, the whole establishment technology of network system has not been formed and further studies in the key technology, support theory and hardware design, etc are needed in the future.