| Summary: | 博士 === 國立臺灣科技大學 === 電子工程系 === 91 === In this dissertation, a new multiple access communication system based on finite field wavelet spread signature (FFWSS) is proposed. The comparisons of traditional multiple access schemes with single user or multiuser detection and the FFWSS-CDMA system are presented. In addition to the function of frequency diversity and multiple access, which are typically provided by traditional spreading codes, the FFWSS spreads data symbols in time, resulting in robustness against frequency selective slow fading. Using the FFWSS to spread a data symbol so that it is overlapped with neighboring symbols, an FFWSS-CDMA system is developed. It is observed that the ratio of the maximum nontrivial value of periodic correlation function to the code length of FFWSS is the same as that of a Sidelnikov sequence. Using RAKE-based receivers, simulation results show that the proposed FFWSS-CDMA system yields lower bit error rate (BER) than conventional DS-CDMA and multitone-CDMA (MT-CDMA) systems in multipath-fading channels.
Besides single-user detection schemes, the use of multiuser detection for BER improvement in fading channels is also investigated. It is well known that the BER performance of parallel interference cancellation (PIC) is superior to that of successive interference cancellation (SIC) in the situation of approximately equal received powers among different users. On the contrary, the SIC scheme outperforms PIC when the received powers are dissimilar in a fading channel. Due to the parallel-transmitting structure of every user in FFWSS-CDMA, we employ the merit of PIC in the situation of equal received powers and that of SIC in a fading channel to design the hybrid successive and intracode interference cancellation (HSIIC) scheme. Therefore, a scheme with HSIIC is developed for data detection, besides a conventional RAKE receiver used in the FFWSS-CDMA system. The interference cancellation efficiently suppresses both intracode and multiple access interference of FFWSS-CDMA. Simulation results show that the proposed FFWSS-CDMA system with the HSIIC yields lower BER than the DS/MT-CDMA with SIC/HSIIC system in a multipath-fading channel.
|
|---|
