Research On The Technologies For Node Localization In Wireless Sensor Network

Wireless sensor network (WSN) can be applied to many fields significantly, while node localization is the needed prerequisite part for WSN to carry out certain applications. Due to the high precision ranging ability and the low implementation complexity, impulse radio ultra-wideband (IR-UWB) is now regarded as the most appropriate physical layer technology for WSN. In the IR-UWB based WSNs, to utilize the fine time resolution of the signal most, node localization is realized based on the ranging of TOA estimation.Researches on the key technologies of node localization for IR-UWB wireless sensor network are taken in this dissertation. Based on the analysis of research status quo at home and abroad, problems and defects of the existent researches on localization system are pointed out. These problems and defects exist both in the internal mechanisms and the external communications of the three modules of localization system--the ranging module, NLOS processing module and the positioning module. The purpose of this dissertation is just to carry out some improvements on these problems and defects, so that the theoretic system can be consummated to certain extent. Principal contents of this dissertation are summarized as follows.Firstly, researches on the TOA estimation algorithms for the ranging module are carried out. An energy detection based non-coherent TOA estimation algorithm that suit for the current node hardware level are proposed. The normalized detection threshold of ED-TC-VSR can be optimally set based on the VSR value that extracted from the received energy samples. Though the simulation we can learn that this algorithm outperforms the other existent non-coherent TOA estimation algorithms at nearly all SNR range.At the same time, effects of the source end parameter settings on ranging and reliability of the output results of ranging module are studied. The source end parameters, including the pulse shape, pulse bandwidth and pulse repetition interval. Effects of the settings of every parameter on ranging are qualitatively predicted through theoretic analysis. The method of reliability evaluation adopted in this dissertation is to classify the TOA estimation results into different reliability levels according to the threshold setting metric.Secondly, researches are conducted on how to handle the NLOS problem. The proposed NLOS channel identification method directly extract the product of DP-to-average and peak-to-average from the received signal segment samples as the identification metric, and likelihood ratio test on the metric is conducted to identify the channel state.Thirdly, the single node positioning algorithm and the network cooperative positioning method for the positioning module are studied. In this dissertation, an integrative ranging-positioning platform is built, where the range estimation results used by the positioning algorithms are obtained from the processing of ranging module on the received ranging signal. Three different positioning algorithms which differently utilize the reliability information and the NLOS state information are proposed. The advantage of network cooperative positioning over single node positioning is that the positioning coverage can be enlarged and the NLOS effects can be greatly mitigated.