A low-complexity iterative interference suppressor for coded aperiodic spreading CDMA systems

An uplink scenario incorporating an antenna array in DS-CDMA systems with long (aperiodic) pseudorandom (PN) spreading codes is addressed in this paper. When received at the base station, the desired user\´s modulated data sequence suffers from both the ISI induced by the dispersive channel environment and the presence of MAI from the other users. A "turbo-principle" alike chip-level 2D-RAKE receiver, employing a space-time processing technique, coupled with a bank of SISO channel decoders, is proposed to combat the ISI and MAI simultaneously without strict power control limitations. The estimated symbol for each user is performed by collecting a corresponding chip-level estimated sequence, which is the output through the soft interference suppressor and the instantaneous linear vector filter, prior to conducting the despreading operation. In the simulations, the performance improvements at moderate system load and low SNRs under frequency-selective Rayleigh fading and near-far limited environments are demonstrated when compared to the conventional non-iterative 2D-RAKE receiver, justifying the efficacy of the addressed iterative space-time multiuser demodulator in the long-code CDMA system. A comparison to a coded receiver which combines a hard-decision multiuser detector with a bank of Viterbi decoders in a manner of low computational complexity is also manifested.