| LDPC code is a channel code with decoding performance close to the Shannon limit,it is widely used in the field of communication and storage.Aerocraft data-link is a communication link used in wireless ad hoc network,there are services with different information types and transmission rates in the network,the information length and code rate of LDPC codec are required to be configurable.Aiming at the problem of low compatibility rate of different modes leading to high consumption of hardware resources,this paper analyzes the multi-rate LDPC technology,and combines with the 5G standard extended LDPC code to design and implement a multi-rate LDPC codec.The codec supports 2 kinds of information lengths and 4 kinds of code rates,and it is compatible with 8 modes to match the requirements of data-link.The research work of this paper is mainly divided into the following aspects:First,the scene is analyzed and the information length and code rate are selected.This paper combines with the application scenarios of the ad hoc network and the structural characteristics of the 5G standard LDPC code.According to the short frame and long frame with different information lengths in data-link,it is determined to realize the two information lengths of 320 bits and 1280 bits.According to the requirements of the variable transmission rate of the long frame in the data-link,it is determined to realize four code rates of 1 3,1 2,2 3,5 6,corresponding to the four transmission rates and decoding thresholds,respectively.Second,a multi-rate LDPC encoder is designed and implemented.This paper analyzes the complexity of the encoding algorithm based on generator matrix and check matrix,and combines the structure of the quasi-cyclic approximate lower triangular matrix to design a encoding scheme based on cyclic shift vectors.This paper describes the implementation method of the encoding module,an optimization method is proposed to solve the problems of codeword storage,shift length and matrix dimension compatibility,which effectively reduces the resource utilization of the multi-rate encoder.Third,a multi-rate LDPC decoder is designed and implemented.This paper analyzes the decoding performance of different algorithms.Based on the Belief Propagation(BP)algorithm,the Normalized Minimum Sum(NMS)algorithm with low complexity is selected,and the performance loss is within 0.2dB.We consider the performance and resources to determine the normalization factor,number of iterations,and quantization bit width parameters in the decoding algorithm.The multi-rate decoder is realized through expanding matrix,and a feasible solution is given to the problem that the node information storage unit and node update unit are compatible with different modes.Fourth,multi-rate LDPC codec was tested on the verification platform.We evaluate the codec from three aspects of function,performance and resources.The performance loss of the codec is less than 0.1dB compared with the simulation performance,and the information processing rate is higher than 25 Mbps.We implement an 8 modes compilation codec by reusing the single mode codec resources of 1280 bits information length and 1 3 code rate,flip floap takes less than 5% and resource utilization is less.This paper designs and implements the multi-rate LDPC codec of the aerocraft datalink on FPGA,which has reference value for the compatible solutions of different information lengths and code rates,and is valuable for engineering. |
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