Iteratively Detected Three-Stage Multi-Dimensional Sphere Packing Modulation Aided Multi-Functional MIMO

This paper presents a novel multi-functional MultipleInput Multiple-Output (MIMO) scheme that combines the benefits of the Vertical Bell Labs Layered Space-Time (V-BLAST) scheme, of SpaceTime Codes (STC) as well as of beamforming. To further enhance the attainable system performance and to maximise the coding advantage of the proposed transmission scheme, the system is also combined with multi-dimensional Sphere Packing (SP) modulation. Additionally, further system performance improvements can be attained by serially concatenated convolutional coding combined with a Unity-Rate Code (URC) employed as an inner code. Then, at the receiver side, iterative decoding is invoked by exchanging extrinsic information between the three constituent decoders, i.e. the outer convolutional code´s decoder, the inner URC´s decoder as well as the SP demapper. Moreover, the convergence behaviour of the proposed scheme is evaluated with the aid of both three-dimensional (3D) and two-dimensional (2D) Extrinsic Information Transfer (EXIT) charts. Finally, we quantify the maximum achievable rate of the system based on EXIT charts and demonstrate that the iterative-detection-aided system is capable of operating within 0.6 dB from the maximum achievable rate limit. Explicitly, the proposed iteratively detected three-stage LSSTC-SP scheme is capable of attaining at least 4.8 dB gain at a BER of 10^-5 over the conventional iterativedetection aided two-stage scheme, where the extrinsic information is limited to the SP demapper and the outer code´s decoder.