A Study on Receiver Architecture Design for CDMA Systems

• Main Authors: Chun-Chyuan Chen, 陳俊全
• Other Authors: Chia-Chi Huang
• Format: Others
• Language: en_US
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/88976311205503205176

博士 === 國立交通大學 === 電信工程系 === 89 === Code division multiple access (CDMA) is considered to be a promising technology for future wireless communications. In this dissertation, we proposed a receiver architecture for CDMA systems. The receiver architecture includes a low-IF architecture which translates the RF signal to the digital baseband signal, and a digital RAKE receiver which demodulates the CDMA signal. The performances of both the low-IF architecture and the digital RAKE receiver are evaluated by computer simulations. In the low-IF architecture, we proposed a hybrid image rejection method. The hybrid image rejection method includes a modified Hartley image rejection mixer and a baseband digital image rejection processor. The modified image rejection mixer has similar performance as the original Hartley image rejection receiver but provides two digital outputs. In one output it enhances the desired signal and in the other output it enhances the image signal. The digital image rejection processor first measures the mismatching effect in the analog devices and then suppresses the image signal by compensating for the mismatching effect. We also propose a simplified implementation method for the hybrid image rejection receiver to reduce its computation complexity. Computer simulation was used to evaluate the performance of this simplified implementation method including the quantization effect of the A/D converters. Simulation results show that the proposed hybrid image rejection receiver achieves much better image rejection ratio than the original Hartley image rejection receiver. The adoption of this architecture greatly relaxes the matching requirements in the analog devices. In the digital RAKE receiver, we proposed a RAKE receiver with a new multipath search scheme. In this new multipath search scheme, we employ a fast searcher and a heuristic path selector to estimate a predetermined number of the code phase delays for the multipath fading channel. Besides, a sounding subsystem which utilizes a feedforward channel sounding technique is used to track the rapidly changing impulse response. The fast searcher detects the code phase delays coarsely and the heuristic path selector which is operated on a heuristic path selection algorithm decides a more reliable set of the code phase delays according to both the outputs of the fast searcher and the sounding subsystem. In the RAKE receiver, we adopt a pilot interference cancellation technique to improve the system performance. Both the transient performance of the new multipath search scheme and the average BER performance of the RAKE receiver were evaluated by computer simulations. The simulation results show that the proposed RAKE receiver performs well in a radio mobile channel. In overall, the proposed receiver architecture for CDMA systems has both a good performance and a low complexity for IC implementation.