Low density parity check (LDPC) code is a linear block code with sparse check matrix, which was proposed by Gallager in 1963. However, due to the lack of computing power, it has been ignored for the next 30 years. In 1996, D. MacKay, M. Neal and others re-studied it and found that LDPC codes have excellent performance close to Shannon limit. It has the characteristics of low decoding complexity, parallel decoding and detectable decoding errors, and has become a new research hotspot in channel coding theory.
Irregular LDPC codes proposed by Mckay and Luby extend the concept of LDPC codes. The performance of irregular LDPC code is not only better than regular LDPC code, but also better than Turbo code, and it is the closest code known at present.
Richardson and Urbank have also made great contributions to the development of LDPC codes. First, they proposed a new coding algorithm, which greatly reduced the huge calculation and storage requirements of randomly constructed LDPC codes. Secondly, they invented the density evolution theory, which can effectively analyze the decoding threshold of a large class of LDPC decoding algorithms. The simulation results show that this is a compact decoding threshold. Finally, the density evolution theory can also be used to guide the design of irregular LDPC codes in order to obtain the best possible performance.
Structure diagram of LDPC watermarking system LDPC codes have great application potential and will be widely used in deep space communication, optical fiber communication, satellite digital video, digital watermarking, magnetic/optical/holographic storage, mobile and fixed wireless communication, cable modems and digital subscriber line (DSL).
Chiain et al. evaluated the performance of LDPC codes in memory fading channels. B.Myher proposed a rate-adaptive LDPC coded modulation scheme for slowly changing flat fading channels, which can also be used in FEC-ARQ systems.
The Flash-OFDM mobile wireless chipset integrated with V-DLPC developed by Flarino can be used in IP-based mobile broadband networks. Sound technology. Ltd proposed an asymmetric LDPC/Turbo solution for WLAN, that is, the downlink uses LDPC codes and the uplink uses turbo codes. The research shows that the battery life of IEEE 802.11a/b/gwlan mobile terminal can be extended to four times after adopting this scheme.
Industry also produces LDPC coding and decoding chips. Among them, the vector LDPC solution based on ASIC introduced by Flarion Company, which is in the leading position, uses about 2.6 million gates, and can support the maximum code length of 50,000, the code rate of 0.9, and the maximum number of iterations 10. The throughput of the decoder can reach 10 Gbps, and its performance is very close to Shannon limit, which can meet the needs of most communication services at present. AHA Company and Digital Fountain Company also launched their own codec solutions.