The performance of a direct sequence spread spectrum PN code tracking system for frequency selective channels

In frequency selective channels, the delay-lock loop, and tracking systems derived from it are not ideal candidates for PN code tracking. This is because they are primarily designed for the AWGN channel. A tracking system designed specifically for use in frequency selective channels is presented. It is shown that with the knowledge of the channel response of the first few resolvable paths, an extended Kalman filter can be used to generate estimates of the PN code delay from the output of baseband inphase and quadrature early-late detectors, similar to those used in delay-lock loops. From computer simulation results of a practical model of the tracking system, it is shown that the tracking system is quite robust to errors in the parameters used to describe the PN code timing process. It is also shown that a simple channel noise estimation system can be used to provide the extended Kalman algorithm with reliable estimates of the channel noise. The performance of the tracking system in PN code clock drift situations is also presented.