A PN code tracking system for direct sequence spread spectrum operation in a frequency selective fading environment

The delay-locked loop and other tracking systems derived from it are inadequate for PN code tracking in a frequency selective environment. In this paper a PN code tracking system for frequency selective fading channels is presented. It is shown that the extended Kalman filter, aided by a RAKE receiver, is well suited to estimating the PN code delay after the quadrature down-converted received signal has been pre-processed by early-late structures, similar to the delay-locked loop but excluding any output squaring. The performance of a practical implementation of the tracking system is evaluated using computer simulation. The results show that the system performs well in practice and also highlights the advantages of using a RAKE receiver in frequency selective environments