Multiuser space-time channel estimation for CDMA under reduced-rank constraint

This paper addresses the problem of estimating the multi-user channels in CDMA systems when using a linear array of antennas. The training sequences to be used for multi-user channel estimation have limited lengths. In order to control the errors of the (unstructured) estimate of space-time (S-T) channel here we propose to reduce the complexity when parameterizing the channel. This is achieved by constraining each matrix that models the S-T channel of each user to have a low-rank. The rank of the matrix accounts for the degrees of space and/or time diversity in S-T channel. Here we propose to estimate the reduced-rank channel simultaneously for all the users so as to control the multiaccess interference (i.e., all the users are considered signals for each other). The co-variance matrix of intercell interference is constrained accordingly. Simulation results for realistic propagation/interference environments confirm the expected benefits.