The Research On Rate-Compatible LDPC Codes

With the high development of wireless communication, people’s requirements of the communication system are higher. Low density parity check(LDPC) code become the hotspot of channel coding in recent years because of its feature of very close to Shannon limit. In order to solve the problem of time-varying channel state in mobile communication system, a lot of research works about rate-compatible LDPC codes have been started. So that communication system can adapt the dynamic channels. It means that under the assurance of reliability, the communication can increase the utilization of the power and spectrum resource.Rate-compatible LDPC codes are studied in this paper, major work includes:(1) Analyzed and compared the advantage and disadvantage of traditional method of designing rate-compatible LDPC codes. Aimed at solving the shortcoming of traditional method of ignoring the effects by the internal structure of LDPC codes and channel, we designed a set of puncturing scheme based on important sampling technique to find internal structure harmful to the LDPC decoding performance. The designed puncturing scheme effectively overcomes the effects of harmful internal structure of LDPC codes, especially the effect for rate-compatible LDPC codes decoding performance in high-rate.(2) Aimed at solving the shortcoming of traditional puncturing scheme of greedy choice based on the puncturing degree distribution, we designed an ungrudging puncturing scheme by defining a new of tree to find a best puncturing degree distribution. The puncturing degree distribution made by the ungrudging puncturing scheme is superior to degree distribution made by traditional method. The decoding performances of overall rate-compatible LDPC codes are improved.(3) Designed an adaptive coding and modulation system based on non-binary rate-compatible LDPC codes and higher-order modulation. By using the designed adaptive coding and modulation system, two adaptive coding and modulation schemes over independent and correlative fading channels were proposed. In theproposed schemes, the LDPC encoder can provide a flexible code-rate range from 1/3to 5/6, and can provide a flexible transmission rate ranger from 0.33bit/s/Hz to5bit/s/Hz. By designing the adaptive coding and modulation scheme, complexity of system is lower and the thoughtput of communication system is increased.