A near optimum adaptive iterative MMSE receiver for interference suppression in W-CDMA systems

In this paper, we propose a near optimum adaptive iterative equalizer receiver for interference suppression in convolutionally coded wideband CDMA (W-CDMA) systems. In the proposed near-far resistant receiver, conventional matched filter front end is replaced by adaptive minimum mean-square error (MMSE) filter, for the generation of sufficient statistics. The receiver employs an adaptive soft-input soft-output (SISO) multiuser detector and a bank of single user SISO channel decoders. In the first iteration, multiuser detector processes received samples from chip-matched filter (CMF) and provides soft bit estimates. After deinterleaving, these bit estimates are decoded by SISO channel decoders. We have used optimum maximum a posteriori (MAP) decoders. The soft output decoders provide soft outputs for both decoded and coded bits. The soft estimates of coded bits are then fed to a symbol spaced adaptive MMSE equalizer in second or higher iterations, which further provides soft interference cancellation. Using simulations, it is shown that through an iterative process the effects of multiple-access interference (MAI) and inter-symbol interference (ISI) can almost be completely overcome and near optimum performance can be obtained