A new tracking loop for direct sequence spread spectrum systems on frequency-selective fading channels

A new tracking loop is proposed for direct-sequence spread-spectrum signaling on a frequency-selective fading channel. By exploiting the inherent multipath diversity of the channel, the new tracking loop overwhelmingly outperforms a traditional noncoherent delay-locked loop (DLL) for all cases under consideration. Linear and nonlinear (based on the renewal process approach) methods are employed to analyze the new tracking loop with perfect channel estimation. Although the analytical methods are developed under the guise of a slowly time-varying channel, the analytical and simulation results show close agreement for channels with a code Doppler shift β_D as large as 0.117598 (Doppler shift f_D=83 Hz). Consequently, the analytical methods, especially those based on linear methods, can be easily employed to characterize the new tracking loop. The performance degradation caused by imperfect channel estimation is determined by computer simulations. Over a range of signal-to-noise-ratios (SNRs) of practical interest, the simulation results show a degradation of about 2 dB and 1 dB for β_D=0.0117598 (f_D=8.3 Hz) and β_D =0.117598 (f_D=83 Hz), respectively