Research And Realization On Localization Technology For In-field Wireless Sensor Networks

As one of hot research spots in current time, wireless sensor network( WSN) technology is a way to realize real-time monitoring of all kinds of object information in network distribution areas, which has a broad prospect of application in the future. Location information, as a basic issue of applications of wireless sensor network, is the premise for wireless sensor network’s widely use. As an important application field of wireless sensor network, node positioning technology of wireless sensor network is of great importance to the application of this technology in agricultural environment and it is necessary to make more deeply research in this field. Range-based localization technology of wireless sensor network was researched in the paper and wheat environment was chosen as the application field. Path loss modeling of wireless channel and positioning algorithm were mainly explored. Meanwhile, the feasibility of the algorithm was verified based on the ZigBee network. The main work and research results are as following:Firstly, starting from the development status of wireless sensor networks and its positioning technology, the basic principle and application scenarios of several main positioning technologies were introduced based on the range-based and range-free classification methods respectively. At the respect of range-based localization technology, the distance measurement methods including the TOA, TDOA, AOA and RSSI methods were introduced respectively and then three kinds of range-based localization mechanisms were discussed respectively, including the trilateral positioning method, multilateral maximum likelihood estimation method and angle measurement method. At the respect of range-free localization technology, the basic principle of the DV-HOP, the Amorphous, the APIT and the centroid localization algorithms were discussed respectively. The advantages and limitations were analyzed after the introduction of characteristics of various kinds of positioning technologies.Secondly, for exploring the signal propagation principle of wireless sensor network, 2.4 GHz wireless channel path loss was measured based on the ZigBee network node built by CC2530 EM in wheat fields, based on which the trend of path loss was analyzed. And then the measured data were compared with the path loss predicted by the free space model and the two-ray model respectively. What’s more, the one-slope log-distance model and the two-slope log-distance model were applied to perform regressions for the measured data of path loss based on the least square method respectively. The results showed that there were big differences between the path loss predicted by the first two models and the measured data, and thus the first two models cannot be used to predict path loss directly in the environment. both of the latter two models were applicable for path loss modeling in wheat fields and the two-slope log-distance model had a better accuracy.Thirdly, based on comparison and analysis of a variety of wireless signal propagation model, the one-slope log-distance model was chosen as the model to model 2.4 GHz wireless signal path loss in wheat field and the optimal antenna height was determined. Based on this model, a new localization algorithm was proposed combining the trilateral positioning algorithm and centroid localization algorithm and the algorithm process, the specific calculation method and parameters were proposed. The proposed algorithm was simulated by the MATLAB software and the simulation result showed that compared with the traditional trilateral positioning algorithm and centroid localization algorithm, this algorithm could get smaller positioning error.Finally, based on hardware platform of CC2530 EM, the proposed localization algorithm was developed combined with the ZigBee protocol stack and the positioning software was developed to display the result with a graphic interface. What’s more, a ZigBee network was built in wheat field to verify the localization method and system. The experimental results showed that the algorithm could realize real-time positioning, the proposed algorithm had high stability and accuracy and the localization platform could work stably.