Research On The Construction Of Rate-compatible LDPC Codes Based On LTC-QC Structure

LDPC codes is a low-density linear block codes, the low density characteristics of thiscodes make it have the excellent performance of approaching the Shannon limit. Since it hadbeen rediscovered, it has been the research focus of the coding profession and has beenapplied in many fields. As a research hotspot in the LDPC codes, rate compatible coding alsogets the attention of the coding profession which achieve signal in the time-varying fadingchannel transmission. One of its main directions is how to construct the check matrix of rate-compatible LDPC codes.This paper first systematically analysis and researches on LDPC codes, and then on thebasis of this does further research about the construction of rate-compatible LDPC codes.Based on the LDPC codes which is prescribed by the IEEE802.16e protocol, this paperresearches on the check matrix of the constructed RC-LDPC code, and then does short ringdetection in this parity check matrix. This paper uses a new method to delete four rings, and anew method to delete six rings of fixed shape, getting a short loop optimization of LTC-QC-LDPC codes. For the shortspot of the above matrix existing four rings and needing a largespace to store the parity check matrix. This paper uses a QC-LDPC codes matrix having nofour rings and anti-diagonal pairs to construct a new RC-LDPC codes having no four ringsand the encoding of this code words can also be achieved in linear time.This paper gives the BER performance simulation diagram of the above two methods inAWGN channel with BP decoding algorithm, and constructs semi-random LDPC codescomparing with different bit rate of rate compatible LDPC codes with no four rings. Researchand simulation results show that the LTC-QC-LDPC codes after a short ring optimized has agood code performance. Compared with the codes having four rings, it has better BERperformance. The newly constructed RC-LDPC codes can construct different rates no fourring check matrix because of the reasonable structure design, and makes the code well appliedin time-varying channel and achieves better BER performance.