A Suboptimal Modified Code Tracking Loop for Synchronous DS-CDMA Systems

This paper presents a suboptimal modified code tracking loop (SO-MCTL) that mitigates the effect of multiple- access interference (MAI) for synchronous direct-sequence code division multiple access (DS-CDMA) systems. Weighted linear combinations of the interfering users´ signals are introduced into the local signals to facilitate the optimization of the tracking performance. Instead of search for the optimal weighting vectors that yields the minimum mean square tracking error, the mean square tracking error is minimized with respect to the weighting parameters given the constraints that ensure a stable bias-free S-curve. Simulations based on Gold codes compare the S-curve and root-mean-square (rms) tracking error of the SO-MCTL and traditional modified code tracking loop (T-MCTL). It is shown that SO-MCTL outperforms T-MCTL greatly in that it provides unbiased code tracking with reduced mean square tracking error and near-far resistance.