MMSE based turbo equalization for chip space-time block coded downlink CDMA

Space-time (ST) block coding based transmit diversity is included in the 3G mobile telecommunication specification for CDMA downlink transmission. On the other hand, Turbo (iterative) equalization can be used in channel coded broadband wireless systems to enhance the performance. Hence, in this paper, we develop a linear MMSE-based Turbo equalization scheme for downlink ST block coded CDMA to achieve high capacity gains over multipath fading channels. The proposed unified CDMA system model considers both conventional and block spreading. However, block spreading is more desirable as confirmed by the simulation results. Both ST encoding and ST decoding are performed at the chip-block level. Turbo equalization is performed after ST decoding. Furthermore, we also consider computationally-efficient implementations of the proposed Turbo equalization scheme. Simulation results demonstrate that high performance can be achieved using the proposed iterative equalizer.