LDPC Code-polar Code Parallel Concatenated Codes With Medium And Short Code Lengths

Low density parity check（LDPC）code and polar code are adopted as the data channel and control channel coding schemes in the enhanced mobile broadband scenario in the fifth generation mobile communication system respectively.Their performance is not that good with medium and short code length.In view of the excellent performance of parallel concatenated code,this paper attempts to take LDPC code and polar code as parallel concatenated code’s component codes.This paper studies the encoding and decoding scheme of parallel concatenated code with medium and short code length.First of all,this paper propose a parallel concatenated code of polar code and LDPC code.Because the polar code is a non-system code,it can not distinguish its information bits and redundant bits,so the parallel concatenated codeword contains all the bits of the polar codeword and the redundant bits in the LDPC codeword.During the decoding process,the decoding information is reduced and an adapter is added to make full use of the decoding information.The simulation results show that the decoding performance of（1024,256）parallel concatenated code of polar code and LDPC code is better than that of serial concatenated code of polar code and LDPC code with the same code length and same code rate.Increasing the number of external iterations to 5 can further improve the parallel concatenated code’s decoding performance.When the bit error rate is 10^-5,the parallel concatenated code of polar code and LDPC code can achieve a coding gain of about 0.6 d B compared with that without external iteration.Secondly,through the reassign of polarization channel of polar code,the polar code with improved decoding performance can further improve the overall performance of parallel concatenated code of polar code and LDPC code.With medium and short code length,the channel polarization of polar code is insufficient.The polarization characteristics of polar code channel in this case are analyzed and summarized,and the selection criteria for insufficient polarization channel is proposed.Taking the column weight of generation matrix corresponding to polarization channel and the change of channel parameters as the selection criteria,these insufficient polarization channels are reassigned,which can improve the decoding performance of polar code without changing its code length and code rate.The bit error rate of parallel concatenated code can be further reduced by applying the reassign polarization channel polar code to the parallel concatenated code.The simulation results show that after 5 external iterations,when the bit error rate is 10^-6,the（1024,256）parallel concatenated code of reassign polarization channel polar code and LDPC code can achieve a coding gain of about0.2d B compared with the previously proposed parallel concatenated code of polar code and LDPC code.Finally,in order to reduce the negative impact of code rate loss on concatenated codes,a parallel concatenated code of polar code and LDPC code with information bit partial protection is proposed.With medium and short code length,due to insufficient channel polarization,there are some polarization channel with low reliability for transmitting information bits.These polarization channels with low reliability are selected according to the large column weight of generation matrix and the decreasing trend of channel parameters.The information bits transmitted by these polarization channels are encoded and protected by LDPC code.The polar code protects all the information bits.It reduces the number of redundant bits of LDPC codeword and the code length of the parallel concatenated code,and reduces the code rate loss.The simulation results show that after 5 external iterations,the（533,256）parallel concatenated code of polar code and LDPC code with information bit partial protection can achieve a coding gain of about 0.4 d B compared with that without external iteration when the bit error rate is 10^-5.