Investigation Of Anti-multipath Time-delay Estimation Algorithms Based On Frequency Domain Subspace For CDMA Mobile Location

This thesis aims at the research of time based CDMA mobile location techniques in multipath environment. Because of the multipath interference problem in wireless location systems, time delay estimation can be biased to some degree, and this becomes a key factor and bottleneck to restrain the location accuracy of wireless location systems. In this thesis the multipath interference problem is studied based on the application of TDOA techniques in CDMA multipath environment, the investigation is focused on how to cancel the disadvantageous influence of multipath interference to the precision of time delay estimation parameters, so as to improve the location accuracy.Based on the analysis to research status of wireless location techniques, TDOA techniques and several time delay estimation algorithms, the frequency domain subspace based time delay estimation algorithms are determined to be the main research item. The traditional algorithm for time-delay estimation is cross correlation method, which is characterized of simplicity, explicity, and approaching CRLB theory bound in the case of a single path. However, the cross correlation method cannot identify multipath signals within one chip interval, and this leads to the location precision is degraded dramatically under multipath environments. Therefore this thesis pays more attention to the reseach of high-resolution frequency domain subspace based techniques known as MUSIC, ESPRIT and their performance analysis in CDMA location systems, besides, several improvement suggestions to these algorithms are proposed. Considering highly correlated signals created by mutipath environment can reduce the performance of MUSIC algorithm, data smoothing isused to decorrelate the signals. In order to enhance the precision and reduce the computation cost, a time-shift based ESPRIT algorithm is proposed. Moreover, multipath power delay profile is introduced to restrain white Gussian noise effectively. Based on the formation of moderate multipath channel model, the performance of MUSIC and ESPRIT algorithms are simulated in detail, simulation results verify the efficiency of the proposed algorithms. Finally, based on above research, the applicability and feature of above algorithms are compared and analyzed, projects of applying the anti-multipath time delay estimation algorithms to two CDMA location systems are proposed, and the corresponding scheme is discussed.