Over-Complete Source-Mapping Aided AMR-WB MIMO Transceiver Using Three-Stage Interative Detection

Abstract

-In this paper we propose an iteratively detected Sphere Packing (SP) aided Differential Space-Time Spreading (DSTS) scheme using a Recursive Systematic Convolutional (RSC) code, for protecting the soft-bit assisted Adaptive Multi Rate Wideband (AMR-WB) decoder's bitstream, which is also protected by a novel over-complete source-mapping scheme. The convergence behaviour of the Multiple-Input Multiple-Output (MIMO) transceiver advocated is investigated with the aid of both threedimensional (3D) and two-dimensional (2D) Extrinsic Information Transfer (EXIT) charts. The proposed system exhibits an E b /N0 gain of about 2.5 dB in comparison to the benchmark scheme carrying out iterative source-and channel-decoding as well as DSTS aided SP-demodulation, but dispensing with the over-complete source-mapping, when using I system = 3 system iterations. MOTIVATION AND BACKGROUNDThe employment of joint source and channel coding techniques has been motivated by the fact that the classic Shannonian source and channel coding separation theorem [1] has limited applicability in practical speech systems [2]. This is due to the delay-and complexity constraints of practical speech transmission systems. For example, iterative turbo decoding can be used to exploit the residual redundancy found in the encoded bitstream of finite-delay lossy speech codecs. This residual redundancy is inherently present owing to the limitedcomplexity, limited-delay source encoders' failure to remove all the redundancy from the correlated speech source signal.Vary and his team [3,4] developed the concept of soft speech bits exploiting the residual redundancy. Their work culminated in the formulation of iterative source and channel decoding (ISCD) [5]. More explicitly, in order to improve the overall system performance, extrinsic information is exchanged between the constituent decoders including the source decoder. As a further development, in [6] and [7] the inherent residual redundancy of the encoded bitstream was deliberately increased using redundant index assignments and multi-dimensional mapping schemes, which resulted in an enhanced soft-bit source decoder performance.In [6], the iterative decoding behaviour of an ISCD scheme was studied using Extrinsic Information Transfer (EXIT) charts [8], for characterizing the achievable performance of the ISCD scheme exploiting the residual redundancy inherent in the source encoded bitstream. In this contribution we propose and investigate the jointly optimised ISCD scheme of Figure 1 by using the novel Over-Complete source-Mapping (OCM) of [10], which is protected by a Recursive Systematic Convolutional (RSC) code. The resultant bitstream is transmitted using Differential SpaceTime Spreading (DSTS) combined with Sphere Packing (SP) modulation [11] over a temporally correlated narrowband Rayleigh fading channel. More explicitly, in the resultant multi-stage scheme extrinsic information is exchanged amongst the three constituent decoders, namely the source decoder, the channel decoder and the DSTS-...

Over-Complete Source-Mapping Aided AMR-WB Using Iteratively Detected Differential Space-Time Spreading

“…Recently, it was demonstrated in [6] that the performance of the proposed scheme can be further improved by employing an enhanced Over-Complete source-Mapping (OCM) aided soft-bit assisted AMR-WB decoder. By contrast, in this contribution we propose and investigate the jointly optimised ISCD scheme of Figure 1 by partitioning the total available bit-rate budget between the source and channel codecs.…”