Code tracking of DS-CDMA systems in the presence of multiuser interference and additive noise

The code tracking performance of a noncoherent digital delay-locked loop for DS-CDMA systems is investigated in the presence of multiuser interference and additive noise. Following the description of the code tracking loop, the tracking discriminator characteristics are theoretically analyzed. A detailed theoretical analysis of the steady-state probability density function (PDF) and variance of the tracking jitter is performed by solving the first-order Fokker-Planck equation, and the mean loss-of-lock time of the loop is derived. Numerical evaluation of the PDF is done and compared to the Gaussian distribution. Numerical results of the variance of the tracking jitter and the mean time to lose lock are also presented to illustrate the tracking performance for Gold code sequences. Optimal performance is evaluated minimizing the variance of the tracking jitter, by proper selection of the loop offset.