A turbo RAKE receiver for space-time block coded frequency selective CDMA systems

A turbo receiver that combines the concepts of RAKE combining, turbo detection and space-time block coding is proposed for multipath CDMA systems. The proposed system combines the decorrelating RAKE (DRAKE) receiver developed for frequency selective CDMA channels with the iterative soft interference cancellation and minimum mean square error (MMSE) filtering proposed for convolutionally coded CDMA, and extends these ideas to the case where the system also employs space-time block coding (STBC) in addition to the convolutional channel coding. A novelty of the new receiver is that the space-time decoding is performed along each resolvable multipath direction. Simulation results show that, while in some cases a non-iterative space-time coded system may have inferior performance compared to a system without space-time coding in a multipath channel, the proposed iterative scheme always significantly outperforms systems without space-time coding even with only two iterations.