Research On Time Difference Measurement And Passive Localization Algorithms

The localization based on time difference of arrival(TDOA) measurements is an important topic in the passive localization technology. The indirect localization method is usually employed in the traditional passive localization systems based on TDOA, where TDOAs are measured in the first step, then position of emitter is estimated according to the TDOA localization equations. In the indirect localization method, the accuracy of TDOA estimation directly affects the localization performance of emitter. Given this, the TDOA estiamtion methods are detailed discussed. In addition, with the increasing ability of the integrated circuit operation, the direct localization method, owning higher computational complexity as well as higher localization accuracy, is concerned by researchers recently. The position of emitter is estimated through directly using observed signals rather than TDOA measurements. In the direct localization method, the independence of the between TDOA measurement and position determination is avoid, thus the localization performance can be improved. On account of this, research on the direct localization method is focused in this dissertation. The briefly introduction of the main research results and contributions about TDOA estimation and direct localization methods is given in the following.1. In the multipath propagation environment, the high-resolution time difference estimation algorithm using the normalized cross-spectral and subspace concept is proposed.This algorithm improve the operation efficiency of high resolution delay estimation algorithm because that does not need to estimate source signal waveform and power spectrum.2. A TDOA estimation method based on blind beamforming is proposed in the frequency domain. The proposed method improves the accuracy of time difference estimation in low signal-to-noise ratio(SNR) because of the using of the constraint relationship between the actual time difference and geometrical structure of the positioning scenario.3. The CRLB of joint estimation of clock error and TDOA is derived, and the CRLB of TDOA estimation considering phase noise is also derived. These derived results not only indicate the direction for improving TDOA estimation performance, and they also provide the foundation for selecting the clock device according to the target of the accuracy of TDOA measurement.4. In a incoherent reception scenarios, the joint estimation of mixing error and TDOA is proposed. Furthermore, under the assumption of the mixing clock and sampling clock originated from the common system clock, the joint maximum likelihood(ML) estimation of system clock error and TDOA is proposed. The joint estimation method not only improves the time difference estimate performance, and system clock error estimation results can also be used for clock calibration.5. Considering the incoherent reception and multipath propagation, The multipath time delay estimation based on Gibbs sampling is proposed. The accuracy of the time delay estimation of the proposed method is superior to the conventional methods, and the number of multipath can be also accurately estimated.6. A minimum-joint-entropy-based direct position determination approach of flat spectral radiation source is proposed. The localization performance of the proposed method is inferior to the ML direct localization method, but superior to the traditional indirect localization method. And the resolution of the proposed method is higher than the ML direct localization method.7. In order to reduce the computing complexity of direct localization methods, an adaptive direct position determination method is proposed. In the proposed adaptive algorithm, the emitter position not only can be automatically sought out according to gradient descent principle, and relationship among the SNRs of the observed signals can be also revealed.