Semi-blind channel estimation in HSDPA systems

In this paper we propose a semi-blind channel estimator for High Speed Downlink Packet Access (HSDPA) systems that use multicode transmission to obtain high data rates. In these systems spreading factors are small. Therefore, severe interference caused by multipath propagation may be experienced. The quality of the conventional channel estimates obtained using only pilot signal may not be sufficient. In this paper we propose a semi-blind channel estimator for HSDPA systems. It combines a blind and conventional pilot assisted channel estimate in a novel way. Semi-blind method has larger sample support since the information from both the pilot signal and known spreading codes is used. Consequently, the variance of the estimates is smaller. The performance of the proposed method is compared in simulation to conventional pilot assisted estimator. The proposed method provides significant performance gains over the pilot-based method. Moreover, it allows reducing the pilot power.