Quasi-coherent delay-locked loops for fading channels

The most widely used delay estimators in DS-CDMA receivers are based on the delay-locked loops (DLL). In a coherent RAKE receiver the complex channel coefficient estimate can be used to attain the phase coherency in DLL and the effect of data modulation can be removed via decision feedback. The resulting algorithms are called quasi-coherent delay-locked loops (QCDLL). The performance of four variations for QCDLLs based on lead-lag phase-locked loops has been analyzed by computer simulations. All the loops performed satisfactorily in a fading channel, but the quasi-coherent sample-correlate-choose-largest (QCSCCL) loop had 5-6 dB better performance than the other schemes.