Research On LDPC Coding And Decoding In 5G URLLC Data Channel

The fifth generation of mobile communication system(5G)Ultra Reliable Low Latency Communication(URLLC)is a key technology to solve the reliability and delay problems of future industrial scenarios.Channel coding is important to ensure system performance.At present,the coding scheme adopted by the URLLC data channel is still not determined.Considering the excellent performance of Low Density Parity Check(LDPC)code in short code design,code length flexibility,code rate compatibility and retransmission adaptability,LDPC code is a very competitive candidate.In this paper,using transmission performance as an indicator,the LDPC code encoding and decoding algorithm based on 5G NR system is studied.The specific research content and achievements are:(1)In this paper,based on the communication protocols TS38.211 and TS38.212,a channel coding simulation link platform is built to transmit LDPC code with different code lengths and bit rates in 5G standard.In order to explore coding and decoding algorithms that are more suitable for high reliability and low delay communication scenarios,bit error rate and block error rate are used to quantify the reliability indexes that URLLC scenarios pay most attention to,and the average number of iterations and the total number of iterations are used to quantify the delay indexes that URLLC scenarios focus on.(2)In order to reduce the bit error rate and improve the decoding convergence speed,a dynamic scheduling hierarchical iterative decoding algorithm based on node reliability is proposed.This algorithm uses the iterative decoding method of hierarchical scheduling to reduce the decoding complexity.The traditional decoding algorithm updates the node information in a natural order,resulting in slow convergence rate and too many iterations.In order to solve this problem,this algorithm proposes an approximate representation equation of the reliability of the check nodes,reorders the reliability of the check nodes in ascending order according to the representation equation,and performs hierarchical iterative decoding in this order.In order to avoid incorrect decoding caused by inaccurate information of approximate representation equation,the approximate representation equation in this algorithm is only used to determine the order of message update,while the exact probability value is still used in the calculation of message update.The simulation results show that this algorithm can combine the advantages of hierarchical decoding algorithm and dynamic scheduling,improve the transmission reliability,reduce the number of iterations,speed up the convergence and reduce the decoding delay.(3)In order to improve the transmission performance of LDPC code with low signal-to-noise ratio(SNR),an improved iterative decoding algorithm based on Incremental Redundancy Hybrid Automatic re Quest(IR-HARQ)is proposed.In order to solve the problem of high bit error rate in the case of low SNR,a retransmission mechanism is introduced,a 5G IR-HARQ system is constructed,and a transmission scheme is determined.In order to solve the problems of the large number of iterations and high decoding delay of the traditional retransmission decoding algorithm,this algorithm makes effective use of the decoding results of the last iteration.Simulation results show that the proposed decoding algorithm can reduce the number of total iterations and thus reduce the time delay without increasing the complexity.It is particularly advantageous to improve the transmission performance in the low SNR environment,so it can improve the system performance in the URLLC communication scenario when the channel environment is not ideal.