Research On The Application Of Wavelets Theory To Channel Transmission

This dissertation researches on wavelet theory applied to information transmission, including CDMA spreading code design, waveform coding in digital modulation, over-saturated multi-access communication, diversity techniques for multi-path fading channels, and Peak-to-Average Power Ratio (PAPR) reducing methods for the wavelet packet modulation signals, etc.. The major contributions of the dissertation are as follows:1.It is well known that the multi-value CDMA spreading codes can be designed by means of a pair of mirror multi-rate filter-banks based on some optimizing criteria. The dissertation indicates that there exists a theoretical bound in the performance of its circular correlation property, which can be described by an explicit expression. Based on this analysis, a criterion of maximizing entropy is proposed to design such codes. Experimental result of computer simulation suggests that the resulted codes behave better than the conventional binary balance Gold codes for an asynchronous CDMA system.2.introducing the bi-orthogonal-wavelet-based waveform coding techniques in digital modulation, the dissertation proposes a modified method, where a bi-orthogonal scale function of approximating Gaussian function is used for waveform coding. We have proved that the waveform not only has very good performance in time-frequency centralization but also coincides with the Nyquist criterion 1. Experimental results of computer simulation also show that it can get very high spectrum efficiency. It would be very useful for some special cases although its power efficiency appears to be slightly lower than that of the conventional methods.3.The dissertation explores over-saturated multi-access communication techniques based on wavelet packet. After analyzing the performance of the coherent Tree-Structured Optimal Joint Detection (TSOJD) for QPSK signals and deriving a non-coherent multi-user weight/phase estimator, the dissertation proposes a low complexity non-coherent multi-user weight/phase optimal joint detection algorithm. Besides, the dissertation proposes a partial coherent multi-user/Ivweight/phase optimal joint detection algorithm and some useful conclusions are obtained in comparison experiments.4.In the research on the diversity techniques for fast fading multi-path channels, the dissertation proposes a time-scale RAKE receiver, and analyzes its performance with the conception of Auto- Wavelet-Transform (AWT) and time--scale resolution. Both theoretical analysis and computer simulation show that the performance of the time-scale RAKE receiver is better than that of the conventional RAKE receiver for fast fading multi-path channels.5.In the research on reducing PAPR of wavelet packet modulation signals, the dissertation proposes a new method-æ¡°terative-Shifting Linear-Searching. The new method is a modified PTS method, and can make good compromise between performance and computational complexity. The dissertation explores, by means of computer simulation, how the conventional method based on amplitude-limiting and filtering affects the performances of wavelet packet modulation signals, and presents a new method, namely, Selective Mapping/Amplitude Limiting/Filtering method, which proves to be effective, simple, and have better BER performance.