Pseudo-Noise Code Acquisition For Direct Sequence Spread Spectrum Systems on Multipath Fading Channels
| Autor: | Huan-Chun Wang, 王煥宗 |
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| Rok vydání: | 1999 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 87 Many code acquisition techniques with different types of searching strategies and detector structures have been proposed, analyzed and employed in practical Direct-Sequence Spread-Spectrum (DS/SS) systems. In this thesis, the noncoherent code acquisition systems with different test methods (fixed dwell-time or sequential) and correlators (active or passive) are investigated for AWGN channels and multipath fading channels. For AWGN channels, a new method is explored to evaluate the performance of the sequential code acquisition systems to any desired accuracy. Starting from Albert''s integral equations, the method evaluates the detection probability, false alarm probability and the moments of the sample number very efficiently and accurately by using polynomial interpolations. Numerical examples show that the new method is much more efficient and/or accurate than the known methods, including the Wald''s approximation. For multipath fading channels, the exact analysis of the code acquisition system becomes extremely difficult because of the channel memory incurred by multipath fading. In this research, we first investigate a code acquisition based on multiple-dwell or sequential linear test with the active correlator on multipath Rayleigh fading channels. By assuming the time between correct cells detections is larger than the channel coherence time, a novel method is developed to evaluate the mean acquisition time of the acquisition systems to any desired accuracy. The effects of multipath fading are evaluated, and comparisons are made between the multiple-dwell and sequential linear tests. Numerical results show that the multipath fading may result in 1-4 dB loss in performance and the sequential linear test can outperform the multiple-dwell test by a margin of 1-2.5dB. The analytical results are verified by computer simulations. In addition, a unified analysis is proposed for accurate evaluation of the acquisition performance on multipath Rayleigh fading channels without imposing the assumption that the time between correct cells detections is larger than the channel coherence time. Since the homogeneous Markov chain model, used to characterize the acquisition process over additive white Gaussian noise (AWGN) channels, is no longer valid due to the correlations between cell detections incurred by fading. The traditional direct and flow-graph approaches for performance evaluation of an acquisition system are not applicable to this fading channel.Hence, some new theory are required in this analysis. This analysis is quite general and can include various search strategies, correlators and test methods with different performance measures: probability mass function (PMF) and/or moments of the acquisition time. Analytical and computer simulation results show that the new method predicts the acquisition performance very accurately. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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