Iteratively Detected Generalised MC DS-CDMA Using Layered Steeered Space-Time Spreading

Abstract

We present a novel tri-functional Multiple-Input Multiple-Output (MIMO) scheme that intrinsically amalgamates Space-Time Spreading (STS), the Vertical Bell Labs Layered Space-Time (V-BLAST) scheme and beamforming with generalised MultiCarrier Direct Sequence Code Division Multiple Access (MC DS-CDMA). Further system performance improvements can be attained by employing channel coding, where the source bits are serial-to-parallel converted to two layers, each constituted by a serial concatenation of an outer code amalgamated with a unity-rate code for the sake of improving the convergence behaviour of the proposed system. Additionally, the convergence behaviour of the iteratively detected scheme is evaluated with the aid of Extrinsic Information Transfer (EXIT) charts. We also propose a novel Logarithmic Likelihood Ratio (LLR) postprocessing technique for improving the iteratively detected system's performance. Explicitly, after I=10 decoding iterations and employing an interleaver depth of Dint=160, 000 bits, the proposed system supporting K=4 users attains a BER below 10 −5 for E b /N0 values in excess of −2.8 dB.