Distributed joint source-channel code design for GMAC using irregular LDPC codes

Separate source and channel coding is known to be sub-optimal for communicating correlated sources over a Gaussian multiple access channel (GMAC). This paper presents an approach to designing distributed joint source-channel (DJSC) codes for encoding correlated binary sources over a two-user GMAC, u...

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Vydané v:EURASIP journal on wireless communications and networking Ročník 2014; číslo 1; s. 1 - 15
Hlavní autori: Shahid, Iqbal, Yahampath, Pradeepa
Médium: Journal Article
Jazyk:English
Vydavateľské údaje: Cham Springer International Publishing 09.01.2014
Predmet:
Channels
Coding
Communications Engineering
Computer simulation
Correlation
Engineering
Error correcting codes
Gaussian
Information Systems Applications (incl.Internet)
Mathematical models
Networks
Parity
Signal,Image and Speech Processing
EXIT analysis
Gaussian multiple-access channels
LDPC codes
Distributed joint source-channel coding
ISSN:1687-1499, 1687-1472, 1687-1499
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Shrnutí:Separate source and channel coding is known to be sub-optimal for communicating correlated sources over a Gaussian multiple access channel (GMAC). This paper presents an approach to designing distributed joint source-channel (DJSC) codes for encoding correlated binary sources over a two-user GMAC, using systematic irregular low-density parity check (LDPC) codes. The degree profile defining the LDPC code is optimized for the joint source probabilities using extrinsic information transfer (EXIT) analysis and linear programming. A key issue addressed is the Gaussian modeling of log-likelihood ratios (LLRs) generated by nodes representing the joint source probabilities in the combined factor graph of the two LDPC codes, referred to as source-channel factor (SCF) nodes. It is shown that the analytical expressions based on additive combining of incoming LLRs, as done in variable nodes and parity check nodes of the graph of a single LDPC code, cannot be used with SCF nodes. To this end, we propose a numerical approach based on Monte-Carlo simulations to fit a Gaussian density to outgoing LLRs from the SCF nodes, which makes the EXIT analysis of the joint decoder tractable. Experimental results are presented which show that LDPC codes designed with the proposed approach outperforms previously reported DJSC codes for GMAC. Furthermore, they demonstrate that when the sources are strongly dependent, the proposed DJSC codes can achieve code rates higher than the theoretical upper-bound for separate source and channel coding.
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ISSN:1687-1499
1687-1472
1687-1499
DOI:10.1186/1687-1499-2014-3