Adaptive non coherent DLLs for DS-SS chip tracking in slow and fast fading environments

RAKE receivers are the most common receiver schemes adopted in W-CDMA systems. For the operation of the RAKE receiver it is necessary to track multipaths in their phase and position in time (i.e. code space). Previous results (De Gaudenzi 1999) show that the non-coherent DLLs outperform the coherent DLLs in terms of demodulator losses caused by unresolvable multipath components. The present paper's focus is on non-coherent DLL jitter in dynamic frequency selective fading channels. A rank reduced adaptive two stage filtering strategy operating on a code multiplexed pilot channel is proposed. The filtering is decomposed in a coherent stage and a filter on the squared envelopes. A joint cost function is used in order to tune the filters to the environment's propagation conditions. The air interface used to evaluate the performance is UTRA FDD mode. The results have been experimentally confirmed in controlled laboratory conditions.