Study On Ranging And Positioning Technology In Wireless Sensor And Actuator Network

Wireless Sensor and Actuator Network is a new type of wireless network which can sense and feed back to control the external environment. In WSAN, the sensor nodes mainly sense events which occur in the physical world, while actuators make decisions based on the occurrence of the event so as to complete the corresponding task. A large number of studies have found that it doesn’t make sense that the data is sensed by sensor nodes without location information in practical application of WSAN. so the node positioning technology is an important application of the supporting technology.Currently, two hotspots in the research of node positioning technology are based on range-free positioning technology and range-based positioning technology. The former is less demanding on the hardware of node, low cost, but the estimated accuracy is not high, there is mostly theoretical research, usability is poor; the latter demands on high power, the node’s hardware requirements are relatively high, but the estimated accuracy is higher to realize relatively accurate positioning. So in the light of the characteristics of WSAN, this thesis focuses on two kinds of more active ranging techniques, and explores effective methods of improvement.Firstly in this thesis, the architecture as well as node positioning technology of WSAN is outlined, the fundamental principles of ranging positioning technology and the quality of the evaluation criteria is introduced.Next, four common ranging algorithms based on the Chinese Remainder Theorem in WSAN are theoretically analyzed and applied to ranging between network nodes. This thesis gives specific ranging steps,and through simulation experiments, the performance is analyzed and compared in the ranging accuracy, computational complexity and robustness aspects.Then, Aiming at nodes deployment in wireless sensor and actuator network as well as network characteristics, a kind of ranging based on improved Chinese remainder theorem and node localization algorithm of locating residual error correction is put forward. Firstly, the algorithm applies the improved Chinese remainder theorem to ranging between nodes, using the maximum likelihood estimation method to locate the unknown node in the first round calculates its estimated distance, then according to the residual between the estimated and the measured values, positioning is optimized by the greedy algorithm to obtain the minimum mean square residual, which achieves correction refinement of the initial positioning results. The validity of the method is verified by simulation and performance analysis.In the end, Based on RSSI ranging positioning algorithm in the wireless sensor and actuator network is explained in detail. Aiming at these deficiencies such as prerequisite for a minimum region signal propagation loss model parameter estimation methods in real time is demanding, requirement that the unknown node is located in the minimum region which is composed of its nearest three neighbor anchor nodes and so on, based on the actual situation of sparse node deployment in wireless sensor and actuator network, this thesis proposes an improved algorithm. The core idea of the algorithm is when the unknown node is not located in the minimum region, the minimum region is sub-optimized by searching of the latest third anchor node. Simulation results show that under the premise to ensure accuracy node positioning coverage rate has improved significantly.