Receiver Design for Spread Spectrum Systems over Frequency-Selective Fading Channels

• Main Authors: Tsung-Hua Tsai, 蔡宗樺
• Other Authors: Tsan-Ming Wu
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/31659338080143916553

博士 === 中原大學 === 電機工程研究所 === 100 === In this thesis, the receiver design of the spread spectrum (SS) communications system over wireless fading environments, including the digital code tracking loop and the successive interference cancellation for multicode direct-sequence code-division multiple access systems, is evaluated. 1. For band-limited pseudo-noise signals, a non-coherent digital delay-lock loop (DDLL) equipped with a discrete automatic gain control algorithm under a RAKE scheme over frequency-selective fading channels is studied. Its associated statistical characteristics are analyzed based on the Nakagami-m stochastic process. The transition timing error probability density function (pdf) of the Chapman-Kolmogorov equation is evaluated to drive an analytical expression for the steady-state timing error pdf. The mean time to lose lock and the mean square tracking error with its corresponding Cram’er-Rao lower bound under frequency-selective Nakagami-m fading environments are scrutinized, while their numerical results are confirmed by time-domain computer simulations. Moreover, the tracking performance of the DDLL in the presence of Doppler shifts is also examined. 2. Noncoherent and coherent multicode direct-sequence code-division multiple access (DS-CDMA) systems with successive interference cancellation (SIC) for multimedia reverse links over frequency-selective fading channels are studied. Followed by a RAKE receiver, the SIC scheme is applied for combating the multiple access interference. The bit error rate (BER) using the SIC technique over Nakagami-m fading channels is derived. Simulation results show that the multicode DS-CDMA system with SIC has demonstrated better performance than that without SIC under the multipath fading environment, while their corresponding numerical results from performance analyses are also provided for verifications. Furthermore, the coherent receiver could achieve a more satisfactory BER than the noncoherent counterpart at the expense of synchronization.