Iterative multi-user MMSE receiver for space-time trellis coded CDMA systems over frequency selective channels

In this paper, we explore code division multiple access (CDMA) systems with multiple transmit and receive antennas combined with space-time trellis codes over a frequency selective channel. The conventional multi-user minimum mean square error (MMSE) detector is generalized to deal with multiple antennas and multiple paths and, then, extended to include the turbo principle in an iterative fashion, allowing interference regeneration and cancellation at the receiver. Iterative multi-user MMSE receivers employing chip level and symbol level detectors are derived and their equivalence is demonstrated. Computer simulations show that the proposed iterative MMSE equalizer completely remote the interference of the other users and transmit antennas in the system, providing a significant improvement compared to the conventional non-iterative multi-user MMSE detector and effectively achieving the single-user performance, even in a fully loaded system.