Joint Optimization of Iterative Source and Channel Decoding Using Over-Complete Source-Mapping

Abstract

Abstract-The intentionally imposed or inherent unintentional residual redundancy found in source encoded bitstreams can be exploited for supporting joint SoftBit-Source Decoding and Channel Decoding, which has the potential of improving both the error correcting capability as well as the subjective audio or video quality of communication systems. As a potent error concealment technique, the softbit-based source decoding, proposed by Adrat, Vary and Spittka exploits the residual redundancy or correlation inherent in the source codec parameters for mitigating the effects of transmission errors. However, when using efficient source encoders, limited source redundancy is left in the sourceencoded bitstream. In this scenario the SoftBit-Source Decoder (SBSD) may have a limited extrinsic information contribution, which results in no system performance improvements beyond two decoding iterations.In our novel approach, we partition the total available bit-rate budget between the source and channel codecs in order to improve the attainable error correcting capability and hence to maximize the overall system's performance. More explicitly, the inherent redundancy in the encoded bitstream is intentionally increased with the aid of over-complete mapping, and EXtrinsic Information Transfer (EXIT) charts are used for designing a suitable mapping of the source-coded bits to the modulated symbols, leading to an approximately 2dB signal-to-noise gain.

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

“…speech codec [7] exploiting the intentionally increased residual redundancy of the AMR-WB encoded bitstream by using the novel OCM of [8]. The resultant OCM aided bit-stream is protected by a Recursive Systematic Convolutional (RSC) code and transmitted using Differential Space-Time Spreading (DSTS) aided Sphere Packing (SP) modulation [9] for attaining a diversity gain without the need for any high-complexity MIMO channel estimation.…”

“…The AMR-WB speech codec is capable of supporting nine different bit rates [7]. Each AMR-WB frame represents 20 ms of speech, producing 461 bits at the bit rate of 23.05 kbps.In the advocated system we employ the over-complete sourcemapping philosophy of [8]. More explicitly, the AMR-WB encoded bit-stream is divided into M bits/symbol sequence using the OCM of rate M/N , where N denotes the number of bits corresponding to an OCM symbol.…”

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

“…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.…”

“…Recently, in [12] the soft-bit assisted AMR-WB codec exploiting the concept of soft speech bits was employed in a multi-stage turbo detection process, which resulted in an enhanced Bit Error Ratio (BER) performance. By contrast, in this paper we study the achievable performance of the AMR-WB speech codec exploiting the intentionally increased residual redundancy of the AMR-WB encoded bitstream using over-complete source-mapping [10], while employing a three-dimensional (3D) EXIT-chart based procedure and its two-dimensional (2D) EXIT-chart projection technique [13,14] for designing the optimum combination of receiver components. We will refer to this three-stage system as the DSTS-SP-RSC-AMRWB-OCM scheme.…”

“…However, in the advocated system we employ the over-complete source-mapping [10] using a rate of R mapping =8/9. Thus, the AMR-WB encoded bitstream is divided into 8-bit source symbolsṽ…”