A modified PN code tracking loop for direct-sequence spread-spectrum communication over arbitrarily correlated multipath fading channels

A modified fully digital pseudonoise code tracking loop is proposed in this paper for direct-sequence spread-spectrum communication. By taking advantage of the inherent diversity, a modified code tracking loop is embedded into a RAKE receiver in order to avoid problems caused by unstable locked points of error signals. Such unsteadiness of locked points often occurs with a conventional code tracking loop because the error signals may be randomly biased by multipath fading. Thus, a robust pull-in capability can be provided over a time-variant fading channel where multiple propagation paths are arbitrarily correlated. Furthermore, an effective multipath interference regeneration and cancellation technique is also proposed to improve the error characteristics of the proposed technique. Analytical expressions of the error characteristics and error signals are derived and then confirmed by means of extensive computer simulation results. In addition, several simulation results for the timing jitter and the mean time to lose lock are also presented in this paper. Very attractive behaviors obtained using the proposed technique are verified.