The thesis focuses on fast acquisition techniques for spread spectrum packet radio communications systems. Matched filters are often used to achieve fast acquisitions. A new synchronizer using multiple acquisition detection is designed to achieve a highly reliable synchronization with a very simple receiver structure. Since PN codes, in practice, cannot be made too long due to the difficulty of manufacturing long matched filters and the limitation on the bandwidth of the frequency spectrum for the system, the reliable synchronization can be only obtained by repeating the transmission of the acquisition code at the beginning of each packet. The verification or coincidence detection is done by means of a marker detection following an acquisition. A hard-limiting synchronizer is also examined combined with the multiple acquisition detection. The hard-limiting synchronizer is simpler to implement and suitable for receiving signals with a large SNR dynamic range, but it cannot work well when multi-user interference and multi-path interference are present. For this reason, a new linear Automatic Threshold Control (ATC) synchronizer is developed for detecting signals with a large amplitude dynamic range while preserving good performance in multi-path and multi-user interference. The idea of the ATC scheme is to adjust the receiver acquisition threshold level according to the SNR of the received signal such that the largest (or the most likely) correlation peak in a short time period is selected for the synchronization alignment. Therefore false acquisitions caused by strong correlation side-lobes during the acquisition can be eliminated. For the more realistic situation where the multi-user interference or near-far effect causes severe performance degradation, we proposed a novel non-linear multi-user detector or multistage detector which is suitable for both the synchronous and asynchronous CDMA systems. This sub-optimal detector is able to achieve the performance of the optimal detector with very small computation complexity. The near-far effect will no longer exist because the interference from the unexpected users is considered to be not always harmful for the detection of a specific users' message. To apply this detection technique to asynchronous CDMA systems, acquisition for each users' PN codes becomes more critical, because during the acquisition, the information from the other users' PN code is usually not available, which means that acquisition still suffers the near-far effect. The proposed acquisition scheme based on interference cancellation technique and the ATC scheme can alleviate the near-far effect significantly, and provide the necessary condition for the appropriate operations of multi-user detectors. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/9661 |
| Date | 10 July 2018 |
| Creators | Shi, Zhen-Liang |
| Contributors | Driessen, Peter F. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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