Research On Coding And Modulation Techniques For Satellite-terrestrial Communication

Under the vision of global coverage of the new generation mobile communication,the integration of satellites and terrestrial communication networks is a powerful way to build a space-air-ground integrated communication network.Recently,LDPC codes,which exhibition flexible structure as well as excellent error correction performance,are adopted by DVB-S2 and 5G as the channel coding scheme.Due to their wide application and outstanding performance,LDPC codes gradually enter the field of vision of satellite-terrestrial high-speed communication systems.This thesis studies the iterative decoding algorithm,matrix structure optimization and various coding modulation techniques of the concatenated code system based on the DVBS2 standard.Starting from the satellite communication standard,the corresponding system frame structure is realized in accordance with the requirements of all code lengths and rates in the DVB-S2 standard.Aiming at the “BCH + LDPC” concatenated codes in the standard,the hard decision BM algorithm and the GMD algorithm with the soft information are adopted to reduce the error-rate floor region for the BCH decoding.Simulation results show that the performance of the two decoding algorithms can meet the standard waterfall region performance,and lower the floor region.Then the encoding and decoding process of the LDPC codes are discussed mainly based on the check matrix.In practice,a simple and effective coding scheme is adopted,where a more flexible and regular code structure is obtained by transforming the check matrix.In this structure,the LDA is used to greatly improve the iterative efficiency and reduce the decoding complexity.At the same time,pipeline conflicts and memory access conflicts are discussed,and effective solutions for efficient hardware implementation are proposed.In order to improve the spectral efficiency of the system,the adaptive coding modulation(ACM)technology is considered in the DVB-S2 standard,which can support a variety of high-order modulations,compared with the QPSK modulation in DVB-S.In this thesis,the performance of 24 kinds of coding modulation schemes in DVB-S2 standard under the short frame is simulated,and the results obtained can be used to select the optimal coding and modulation scheme in different system conditions.For satellite-terrestrial communications,this thesis constructs a class of MR-QC-LDPC codes with the better structure and performance than the current DVB-S2 concatenated code.In view of the successful application of QC-LDPC codes in 5G communications,the proposed QC-LDPC codes are based on two basis matrices of 5G LDPC codes,which satisfy the requirements of DVB-S2 standard and solve the shortcomings of concatenated codes in that,such as multiple edges,complex structure and rate loss.The scheme combines with the advantages of the exponent matrix that can support multiple lifting sizes,uses methods such as extension,puncturing,shortening,and superposition,and selects the appropriate base matrix and lifting size according to the metric.The designed multirate QC-LDPC codes have excellent performance,strong structure and hardware-friendly high reliability,providing a achievable coding scheme for satellite-terrestrial communication.