Low complexity iterative receivers for space-time block coded MC-CDMA downlink systems

Multi-carrier code division multiple access (MC-CDMA) and space-time block coding (STBC) are two promising techniques to fulfill the high-speed and spectral efficiency requirements of fourth generation mobile communication systems. In this contribution we present an iterative receiver for the downlink of STBC MC-CDMA systems, that aims to mitigate the effects of multiple access interference (MAI) by jointly optimizing multiuser detection and channel decoding. Our proposal is a two-stage parallel interference canceller (PIC), where soft information in the form of log-likelihood ratios (LLRs) is exchanged between the multiuser detector (MUD) and individual channel decoders for successive refinement. In the first iteration a minimum mean square error (MMSE) equalizer, adapted to the equivalent channel as seen after space-time combining, is used for multiuser detection, whereas for the second and successive iterations a bank of MMSE filters adapted to each user and optimized for the quasi MAI free case is employed.