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Research On Time Delay Estimation Technologies For Extremely Weak Signal In Multipath Environments

Posted on:2010-03-10Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y Y LiFull Text:PDF
GTID:1118360275486788Subject:Communication and Information System
Abstract/Summary:PDF Full Text Request
This dissertation focuses on the issue of the target scatting signal's time delay estimation, which is one of the key technologies for passive radar systems based on the civil transmitter of opportunity. Methods of time delay estimation of scatted signal (multipath signal) are discussed. Several theoretically methods and practically valued methods are proposed and derived for time delay estimation in multipath signal environment, including cause analysis and settlement ways of determining the performance of multipath time delay estimation, methods of time delay estimation based on correlation analysis, methods of super-resolution time delay estimation and methods of space-time joint processing time delay estimation. Computer simulations and theirs results are given to verify the efficiency of these proposed methods. The main contributions of this dissertation can be concluded as follows:1,After the variance theory low bound (Cramer-Rao Lower Bound, CRLB) of time delay estimation of two path signal is derived, the parameters of variance low bound of time delay estimation in multipath signal environment is deduced. The multipath signal simulation model is built base on the parameters. Signal model are verified with power spectrum analyses and time delay experiment2,The methods of time delay estimation based on correlation analysis are comprehensive analyzed, including the method such as correlation, spectral estimation, interpolation, EM and Wrleax. Sem (Spline EM) method, a method for estimating the multipath time delay of signals is proposed. The new method is based on the dimension reduction idea of EM method. To avoid truncation effect reducing the performance, using Fourier transform in Wrelax method is replace with interpolation. The performance of the new method is higher than reference method. The resolving power of time delay estimation method based on correlation is anglicized in theory and the way of improving performance of time delay estimation is advised. Computer simulation show that the proposed method can work well in weak multipath signal environment.3,The principle of Time delay estimation using spectral estimation is briefly introduced. Fast time delay MUSIC method and beam-forming time delay MUSIC method are proposed. The computational complexity of fast time delay MUSIC method is two orders of magnitude lower than tradition MUSIC method by rebuild received signal covariance matrix. The later proposed method build switched beam matrix according to time distribution of signal time delay, and then use Fast time delay MUSIC method to estimate time delay. The function of switch beam matrix is equivalent to time band-pass filter. The beam cover area is pass band of the filter and the noise outside the area is removed. Therefore, the later proposed method has more excellent resolving power of time delay estimation in low signal-to-noise ratio (SNR). The feasibility of the two proposed methods is verified by computer simulation.4,A single receiving station passive radar system framework based on Software Defined Radio is proposed. Receiving directly signal (reference signal), scatted signal use an array antenna simultaneously in the radar system. Therefore, the hardware structure of the system is simplified, Maneuvering and Flexible design are improved. Reference signal Extraction and scattered signals detection, receiving and time delay estimation in the radar system are introduced in detail. A new reference signal extraction method is proposed. The method use digital control beam-forming technology to filter background clutter signal and abstain purely direct signal as reference signal. A extremely weak scatter signal detection method is proposed. The new method use spatial filtering and coherent detection technology to realize extremely weak signal detection and reception and the time correlative accumulation is far less than the reference detection method. The feasibility of the two proposed methods is verified by computer simulation.
Keywords/Search Tags:Time delay estimation, Multipath signal, Weak signal detection, Array antenna, Passive radar
PDF Full Text Request
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