E.I. Balunin1, A.P. Ratushin2, D.S. Khrapkov3, M.V. Vlasov4

1–4 Military University of Radio Electronics (Cherepovets, Russia)

Shannon’s theorems state that source coding and channel coding can be optimized separately, while maintaining the optimality of the entire system as the length of the codeword tends to infinity. However, for finite length codes, the redundancy left by the source code can be used by the channel decoder to correct errors introduced by the communication channel. In order to efficiently use the channel bandwidth and achieve high corrective capacity, modern communication systems are optimized through the use of distributed code structures (DCS).

Distributed code structures of digital signals in the article are understood as schemes that implement joint source and channel coding. The study of the holistic mutual arrangement of code symbols of heterogeneous codes and the presence of stable relationships between them makes DCS a promising direction for further development and implementation in modern communication systems.

The article presents an analytical model of the code word of a joint low-density source and channel code (D-LDPC), which makes it possible to further describe the procedures for forming the structure of the DCS based on protographs and to study these schemes. The conducted studies have shown that the source message can be reconstructed at the receiver by a joint maximum likelihood decoder, where the source decoder and the channel decoder work in parallel and exchange information. In order to achieve high information transfer rates for sources with high entropy, it is possible to compensate for the redundancy introduced by the channel encoder by the result of compression. It has been established that it is possible to compress and protect the original sequence from interference in one step using the combined D-LDPC matrix. It is noted that in D-LDPC the initial information sequence is not transmitted over the communication channel, but only check blocks are transmitted, due to which an increase in the throughput of the communication channel is achieved.

A graphical model of a joint decoder is presented in the form of a double bipartite Tanner graph. The correction capability of the scheme with a joint decoder and the scheme with separate channel and source decoding is compared. The resulting difference in performance of the circuits is explained by the cooperative operation of the D-LDPC decoders, where the redundancy of the source encoder gives additional information to the channel encoder to evaluate the correct source sequence.

The effectiveness of the described scheme makes DCS a promising direction for further development and implementation in modern communication systems, for example, in fifth generation mobile networks (5G). But all these developments are conceptually based on the D-LDPC system.

Balunin E.I., Ratushin A.P., Khrapkov D.S., Vlasov M.V. Procedure for generating and decoding codewords of a joint low-density source and channel code. Electromagnetic waves and electronic systems. 2023. V. 28. № 3. P. 28−37. DOI: https://doi.org/10.18127/ j15604128-202303-04 (in Russian)

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