Distributed joint source-channel coding and modulation for wireless communications

Abstract

Distributed Source Coding (DSC) schemes rely on separate encoding but joint decoding of statistically dependent sources, which exhibit correlation. DSC has numerous promising applications ranging from reduced-complexity handheld video communications to onboard hyperspectral image coding under computational limitations. The concept of separate encoding at the first sight compromises the attainable encoding performance. However, DSC theory proves that independent encoding can in fact be designed as efficiently as joint encoding, as long as joint decoding is allowed. More specifically, Distributed Joint Source-Channel coding (DJSC) is associated with the scenario, where the correlated source signals are transmitted through a noisy channel. A series of Turbo Trellis-Coded Modulation (TTCM) aided DJSC-based cooperative transmission schemes are proposed.

An iterative Joint Source-coding, Channel-coding and Modulation (JSCM) scheme relying on the intrinsic amalgamation of Variable Length Code (VLC) and TTCMwas proposed for two-wayaided transmission. The system advocated was designed for improving the attainable throughput, reliability and coverage area compared to that of conventional one-way relaying. Briefly, a pair of users exchange their information with the aid of a twin-antenna aided Relay Node (RN). We quantify the Discrete-input Continuous-output Memoryless Channel (DCMC) capacity of the corresponding two-way relay channel. The semi-analytical EXtrinsic Information Transfer Characteristics (EXIT) charts are employed for investigating the decoding convergence of the joint source and channel decoder as well as for assisting the overall system design. Furthermore, our iterative scheme employs a novel low-complexity source coding technique that significantly reduces the number of states in the bit-based trellis before invoking it for robust image and video transmission.

Then, an adaptive DJSC scheme is conceived for the transmission of a pair of correlated sources to a Destination Node (DN). The first source sequence is TTCMencoded and then it is compressed before it is transmitted both over a Rayleigh fading and Nakagami-m fading channels, where the second source signal is assumed to be perfectly decoded side-information at the DN for the sake of improving the achievable decoding performance of the first source. The proposed scheme is capable of performing reliable communications for various levels of correlation near to the theoretical Slepian-Wolf/Shannon (SW/S) limit. Additionally, its encoder is capable of accommodating arbitrary time-variant short-term correlation between the two sources.

Pursuing our objective of designing practical DJSC schemes, we further extended the abovementioned arrangement to a more realistic cooperative communication system, where the pair of correlated sources are transmitted to a DN with the aid of a RN. Explicitly, the two correlated source sequences are TTCMencoded and compressed before transmission over a Rayleigh fading Multiple Access Channel (MAC). The RN transmits both users’ signal with the aid of a powerful Superposition Modulation (SPM) technique that judiciously allocates the transmit power between the two signals. The correlation is beneficially exploited at both the RN and the DN using our powerful iterative joint decoder, which is optimised using EXIT charts. We further conceive a so-called Block Syndrome Decoding (BSD) approach for our DJSC scheme, which reduces the decoding complexity, whilst additionally providing an accurate correlation estimate.

As a further new cooperative technique, our DJSC scheme invokes RN-aided Network Coding (NC) which is capable of improving the overall throughput without increasing the energy dissipation. To investigate our DJSC in the context of diverse environments, our NC-based schemes are also appraised in the context of slow fading effects that might be imposed by obstacles blocking the line-of-sight transmission links. Our proposed scheme is shown to achieve substantial performance gains over its conventional non-cooperative counterpart.

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Identifiers

ORCID for Soon Xin Ng: orcid.org/0000-0002-0930-7194

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