Robustness of practical downlink wideband CDMA channel estimation algorithms to delay estimation errors

Wideband CDMA systems employ pilot symbols for coherent detection. When the pilot symbols are time-multiplexed with data symbols, their number is usually limited, due to overhead considerations and rate matching requirements. Therefore, channel estimation based only on the pilot symbols is usually not accurate enough. It was shown previously that, in the absence of code synchronization errors, a pilot-aided decision-directed (PADD) approach exhibits better BER performance than pilot-aided estimation over fading channels, because it uses both pilot and data symbols for channel estimation. This paper shows the impact of the delay estimation errors on the PADD algorithm. The multipath delays are estimated using pilot-aided (PA), non-data aided (NDA), or decision-directed (DD) algorithms, and the comparison with ideal channel estimation case is done via simulation. The PADD algorithm in the presence of multipath delay errors is also compared with the pilot-aided plus linear interpolation channel estimation. The simulation results show that the PADD algorithm is not very sensitive to the delay estimation errors when the delays are estimated via an NDA or DD approach, and it exhibits better performance than the traditional pilot-aided methods also when the delay estimation errors are present.