Study Of Some Key Techniques In Wireless Underground Sensor Networks

Wireless Underground Sensor Network(WUSN) is the sensor network that most sensor nodes are buried in the soil. The nodes communicate with each other and devices aboveground through the radio. WUSN has a great potential in applications. It is helpful to monitor the soil material content, the underground animal den, the situation of the in-soil construction and the motion of the objects above ground, which can offer a lot of useful information for agriculture management, environment supervision, research work and security surveillance. Compared to using wired sensors monitor underground situation, WUSN has several outstanding advantages in concealment, in-time data, reliability and scalability.The technique of WUSN is a novel area in the Wireless Sensor Network. This paper is the first work to roundly study the fundamental and key problems in WUSN, including the network architecture, underground electromagnetic(EM) wave propagation, underground channel model, soil dielectric properties and its variation rules, as well as sensor node deployment schemes. The creative works of this paper include the following aspects:1. Based on the WUSN technique speciality, WUSN architectures for two different application scenarios are proposed. One is a self learned network for Intelligent Transportation System(ITS), which gets the transportation information timely and provides it to drivers in real time. The other is the network for outside court or near-surface soil maintenance. For kinds of applications environments, an information sharing platform is proposed to integrate the wireless sensor network resources. It can resolve the problems of information sharing caused by the proprietary of wireless sensor networks.2. The propagation modes of EM wave both under ground and above ground are analyzed based on the electromagnetic theory. The vertical electric dipole produces a spherical wave and it propagates in soil. When it reaches the ground surface, a reflected wave and a lateral wave are created. Part of the spherical wave traverses the ground surface and enters the air, resulting in a refraction wave and a wave similar to the lateral wave. The path losses of the EM waves in soil air are analyzed and simulated. The simulation results verify the feasibility of WUSN by using hundreds MHz EM wave.3. Through analyzing the underground environment and analogizing the under-water channel, the underground channel modelis is proposed, which is based on latent path and multi-path Rayleigh fading effect. After analyzing channel characteristics, the Bit Error Rate (BER) of WUSN is simulated, and the result provides the reference values for the system performance analysis of network and above layers. With the dry and wet demo places, the variation rule of soil dielectric properties and its affecting factors are studied. Through simulations and analysis, the rule of soil dielectric properties influencing underground channel is gained.4. The sensor nodes deployment problem of WUSN is explored. Under the considerations of that the communication range of WUSN is limited and the communication quality of WUSN changes spatially, the frame of the sensor nodes deployment scheme is proposed. And two sensor node selection algorithms are brought forward. They aim to use minimum sensors meet the demand of coverage as well as maintaining the full connectivity of the network. The simulation results show that the new algorithm use less than half of the number of sensors compared to existing sensor node deployment algorithms.