Pilot diversity channel estimation in power-controlled CDMA systems

In this paper, we consider a channel estimator in code-division multiple-access (CDMA) systems, where both the common pilot channel (CPICH), which is not power controlled, and the dedicated physical channel (DPCH), which is power controlled, exist. The proposed channel estimator estimates the channel gain by combining the common pilot symbols in CPICH symbols and the dedicated pilot symbols, which are inserted in DPCH. We derive the maximum likelihood (ML) estimator and present the approximate ML estimator, which can be readily used for fast and accurate online channel estimation. We also derive the Cramer-Rao lower bound (CRLB) of the proposed method and compare it with the CRLB of the method using the CPICH symbols only. End-to-end full-downlink signal-processing worksystem-based simulations have been run and the results confirm that significant gains can be achieved in power-controlled CDMA systems. The resulting estimator can be applied to open- and closed-loop transmit diversity cases as well as the single-antenna case. A similar concept can be applied to other wireless communication systems, where the pilot symbols are used as a reference signal, such as frequency offset estimation.