Research On The Construction Method Of QC-LDPC Codes In Indoor VLC Systems

Indoor visible light communication(VLC)is a indoor wireless optical communication that uses visible light for data transmission.Like traditional communication,indoor VLC needs to introduce forward error correction(FEC)technology to improve system reliability.Quasi-cyclic low-density parity-check(QC-LDPC)codes are kinds of FEC codes with good error correction performance and low coding complexity.In order to improve the performance of indoor VLC system,the three aspects of error correction performance,coding complexity and code length flexibility of QC-LDPC codes are mainly discussed,and the structured construction method for constructing QC-LDPC codes suitable for indoor VLC systems is studied.The main research work is as follows:1.In order to solve the problem that the poor error correction performance caused by the short girth of the QC-LDPC codes,a construction method of QC-LDPC codes with girth-8 based on the Hoey sequence is proposed.The QC-LDPC codes constructed by this method can change the code length and code rate flexibly,and it is theoretically proved that the check matrix of the QC-LDPC codes do not contain 4-cycles or 6-cycles.The H-QC-LDPC(1536,768)code constructed by the proposed method is compared with the other three code patterns with the same code length and code rate in the same indoor VLC system simulation environment.Simulation results show that when the bit error rate(BER)is 10-6,the coding gain of H-QC-LDPC(1536,768)code has increased compared with the other three code patterns.2.In order to further reduce the coding complexity of QC-LDPC codes applied in indoor VLC system,a construction method of QC-LDPC codes with girth-8 and fast encoding based on Hoey sequence is proposed.The check matrix of the basis matrix of QC-LDPC codes constructed by this method is a square matrix with quasi-diagonal structure,so that the QC-LDPC codes can be coded quickly by using the check matrix directly,which further reduces the encoding complexity of the QC-LDPC codes,and it is theoretically proved that the check matrix of the QC-LDPC codes do not contain 4-cycles or 6-cycles.The HF-QC-LDPC(1536,768)code constructed by the proposed method is compared with the other three code patterns with the same code length and code rate in the same indoor VLC system simulation environment.Simulation results show that whenthe BER is 10-6,the coding gain of HF-QC-LDPC(1536,768)code has increased compared with the other three code patterns.3.In order to improve the error correction performance of QC-LDPC codes with fast encoding in indoor VLC system,a construction method of QC-LDPC codes with girth-8 and fast encoding is proposed based on the Greatest Common Divisor(GCD)algorithm.The check matrix of the QC-LDPC codes constructed by this method is a square matrix with quasi-diagonal structure,and it is theoretically proved that the QC-LDPC codes do not contain 4-cycles or 6-cycles.The GL-QC-LDPC(2650,1325)code constructed by the proposed method is compared with the other four code patterns with the same code length and code rate in the same indoor VLC system simulation environment.Simulation results show that when the BER is 10-6,the GL-QC-LDPC(2650,1325)code has better error correction performance than the other four code patterns.