DS-CDMA RAKE receiver with time-window control loop (TWCL) in multipath fading environment

This paper presents a code synchronization scheme-the time-window control l oop (TWCL)-for postdetection RAKE receiver systems that offers the path-div ersity effect. Laboratory test results from a postdetection RAKE receiver s ystem with TWCL under a frequency-selective fading environment are introduc ed. RAKE combining methods, a simple integral demodulation method within a time window and a recursive least squares (RLS) demodulation method within the time window that uses the RLS algorithm to realize maximal ratio combin ing, are investigated. It is found that TWCL performance,vith delay paths ( double-spike frequency-selective Rayleigh-fading model) surpasses the perfo rmance of both acquisition and tracking without delay paths (nonfrequency-s elective Rayleigh-fading model) because of the path-diversity effect. The l aboratory results show that TWCL provides good acquisition and tracking per formance under the fading conditions experienced with maximum Doppler frequ encies of 5 or 80 Hz, It is also shown that the signal energy per bit to no ise-power spectral-density ratio (E-b/N-0) required to achieve the bit erro r rate (BER) of 10(-3) under the double-spike frequency-selective Rayleigh- fading model is reduced by 10 dB compared to the nonfrequency-selective Ray leigh-fading model. The difference in path-diversity effect between the two RAKE combining methods is only 1 dB, From a structural viewpoint, the simp le integral demodulation method supports miniaturization and high-speed dat a-transmission.