tailieunhanh - Báo cáo hóa học: " A Kalman-Filter Approach to Equalization of CDMA Downlink Channels"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: A Kalman-Filter Approach to Equalization of CDMA Downlink Channels | EURASIP Journal on Applied Signal Processing 2005 5 611-625 2005 Hindawi Publishing Corporation A Kalman-Filter Approach to Equalization of CDMA Downlink Channels Hoang Nguyen Nokia Research Center San Diego CA 92131 USA Email Jianzhong Zhang Nokia Research Center Irving TX 75039 USA Email Balaji Raghothaman Nokia Research Center San Diego CA 92131 USA Email Received 31 July 2003 Revised 26 February 2004 An efficient method for equalization of downlink CDMA channels is presented. By describing the observed signal in terms of a state-space model the method employs the Kalman filter KF to achieve an unbiased signal estimate satisfying the linear minimum mean-squared error LMMSE criterion. The state-space model is realized at the symbol and chip levels. With the symbollevel model the KF is used to estimate the transmitted chips that correspond to each symbol interval whereas at the chip level the transmitted chips are estimated individually. The symbol-level KF has a built-in tracking capability that takes advantage of the a priori known scrambling sequence which renders the transmitted signal nonstationary. The chip-level KF reduces the complexity of the symbol-level KF significantly by ignoring the nonstationarity introduced by scrambling. A simple method for further reducing the KF complexity is also presented. The computational complexity of the proposed technique is analyzed and compared with that of several linear approaches based on finite-impulse response FIR filtering. Simulations under realistic channel conditions are carried out which indicate that the KF-based approach is superior to FIR equalizers by 1-2 dBs in error-rate performance. Keywords and phrases Kalman filter CDMA single-user detection oversampling color noise state-space models. 1. INTRODUCTION The existence of dispersive effects of the channel such as multipath destroys the orthogonality of the spreading codes in CDMA