Low-bit-rate joint source-channel decoding aided wireless video communications

Abstract

Detailed wireless video structures employing novel channel coding schemes for enhancing the achievable performance are designed. Although there is a plethora of papers on both robust video transmission, iterative detection and video telephony, there is a paucity of up-to-date research studies on the unified treatment of the topic of near capacity multimedia communication systems using iterative detection aided joint source-channel decoding employing sophisticated transmission techniques. Therefore in this thesis we focus our attention not only on the source and channel coding but also on their iterative decoding and transmission. Initially, we investigated the H.264 codec’s error sensitivity. The perceptually more important bits were provided with more strong protection relative to less important bits using Unequal Error Protection (UEP) by applying different-rate Recursive Systematic Convolutional (RSC) codes.

We then further improved the attainable performance of a Data-Partitioned (DP) H.264 coded video transmission system using UEP based IrRegular Convolutional Codes (IRCC). An iterative detection aided combination of IRCC and a rate-1 precoder was used to improve the overall BER performance and to enhance the objective video quality expressed in terms of the Peak Signal-to-Noise Ratio (PSNR)1. More specifically, we exploited the innate UEP capability and high design flexibility of IRCCs, which are constituted by different-rate subcodes capable of maintaining an excellent iterative decoding performance. In contrast to regular convolutional codes, which encode the entire segment of the source signal using the same code, the IRCCs introduced encode the source signal by splitting it into segments having specifically designed lengths, each of which is encoded by a code having an appropriately designed code-rate. A novel Extrinsic Information Transfer (EXIT) chart matching procedure was used for the design of our specific IRCC which allowed us to design near-capacity schemes.

Additionally, we developed a novel Unequal Source-Symbol Probability Aided (USSPA) design, which is capable of further enhancing the subjective video quality by exploiting the residual redundancy that remains in the source-coded stream after encoding. Furthermore, we proposed a family of Short Block Codes (SBCs) designed for guaranteed convergence in Iterative Source-Channel Decoding (ISCD). The DP H.264 source coded video stream was used to evaluate the performance of our system using SBCs in conjunction with RSCs for transmission over correlated narrowband Rayleigh fading channels. The effect of different SBC schemes having diverse minimum Hamming distances (dH,min) and code rates on the attainable system performance was quantified, when using iterative SBSD and channel decoding, while keeping the overall bit-rate budget constant by appropriately partitioning the total available bit rate budget between the source and channel codecs. EXIT charts were used for analysing the attainable system performance and it was observed from the EXIT-chart analysis that the convergence behaviour of ISCD is substantially improved with the aid of SBCs.

The above-mentioned investigations evolved further by designing more sophisticated non-coherent-detection aided space time coding based Multiple-Input Multiple-Output (MIMO) schemes for near-capacity video transmissions without the need for any high-complexity MIMO channel estimation. Space time coding constitutes an effective transmit diversity technique of compensating the effects of wireless channels by exploiting the independent fading of the signal transmitted from multiple antennas. Space-time coding is capable of achieving a substantial diversity and power gain relative to its single-input and single-output counterpart, which is attained without any bandwidth expansion. More specifically, we proposed a new near-capacity Sphere Packing (SP) modulation aided Differential Space Time Spreading (DSTS) design for the transmission of the video coded stream. SP modulation is a specific scheme, which maintains the highest possible Euclidean distance of the modulated symbols, while constitutes DSTS a low-complexity MIMO technique that does not require any channel estimation, since it relies on non-coherent detection.

Finally, in order to circumvent the BER floor imposed by conventional two-stage turbo-detection schemes, we considered jointly optimised three-stage source and channel decoding arrangements employing serially concatenated and iteratively decoded SBCs combined with a URC and multi-dimensional SP modulation. The mutual information between the SBC, URC and SP constituent components is iteratively exploited in a turbo process in order to improve the overall BER and objective video quality in terms of the PSNR. The resultant coded signal was transmitted using a non-coherently detected DSTS MIMO-aided transceiver designed for near capacity JSCD. The performance of the system was evaluated by considering interactive video telephony using the H.264/AVC source codec. Again, the convergence behaviour of the MIMO transceiver advocated was investigated with the aid of EXIT charts.

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Identifiers

ORCID for Lajos Hanzo: orcid.org/0000-0002-2636-5214

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