Blind channel estimation for downlink CDMA systems

The problem of channel estimation in code division multiple access (CDMA) systems are considered. Using only the spreading code of the user of interest, a technique is proposed to identify the impulse response of the multipath channel from the received data sequence. While existing blind methods suffer from high computational complexity and sensitivity to accurate knowledge of the noise subspace rank, the proposed method overcomes both problems. In particular we estimate the noise subspace by a simple matrix power that is computationally efficient and requires no knowledge of the noise subspace rank. Once an estimate of the noise subspace is available the channel impulse response can be directly identified through a small size SVD or a least squares approach. Extensive simulations demonstrate similar performance of our method as compared to the existing schemes but a considerably lower computational cost.