Reduced rank channel estimation and rank order selection for CDMA systems

This paper investigates the problem of channel estimation in the uplink of CDMA systems with base station antenna array. The estimation is based on the transmission of training sequences with limited length. In order to improve multiuser receiver performance it is proposed to reduce the number of the unknowns in the channel estimation by constraining the space-time channel matrix of each user to be low rank. The rank-order is estimated according to the MDL criterion as this method provides the best trade-off between distortion (due to under-parametrization) and variance (due to the limited training length).