Research On Time Delay Estimation In Highly Precise Localization Based On Spread Spectrum Signal

Location information is becoming more and more important in the modern society,the location demand has been extended from the initial military purpose to commercialand civil field, which greatly promotes the development of wireless location technology.Due to the excellent nature, especially the ranging ability, spread spectrum system iswidely used in wireless location. Time delay is the key to determining distance, therefore,the paper focuses on time delay estimation problem in wireless location system. Timedelay estimation is determined by using PN code synchronization technology in spreadspectrum technology, so the PN code synchronous technology is discussed and studied inthe paper. In addition, the paper discusses the application of carrier phase has also donein-depth research information to determine the time delay.Firstly, the related theory of the wireless location technology and spread spectrumcommunication is analyzed and deduced by formula, the pseudo random is the majorresearch, and the type of PN code is determined and its performance is discussed.Secondly, the typical algorithm of time-delay estimation in location system is studiedand deduced, including PN code acquisition and tracking, the results of simulation andperformance analysis are given.Again, in order to improve the precision of time delay, the paper focuses on themethod of PN code phase measurement. When sampling rate divided by the pseudo-coderate is an integer, the precision of time delay estimation is decided by sampling rate andthe problem of sampling illegibility has arisen. In this case, PN code tracing algorithm innon-commensurate sampling (NCS) technology based on least-square is studied anddeduced in mathematical method. Without increasing the sampling rate, the time delaymeasurement precision is improved greatly, and the influence of noise can be alsoeliminated effectively.Finally, this paper also studied a method to further determine the signal delay usingreceived signal carrier phase information. With the relationship between carrier phasesreceived of different base stations, the non-integer part of time delay to carrier cyclebetween base stations is determined. Because carrier cycle is very small, the time delay difference determined is more precise. The result proves that the location error can bereduced using carrier phase measurement combined with PN code phase measurement.