A Study On LDPC Coding Construction And Cooperative Transmission Application

The reliability and stability of wireless communication systems are critical to the development of today's wireless communication services.In the wireless signal transmission process,multipath effects,channel fading,and path loss will affect the signal transmission process.Distortion causes the receiver to fail to receive valid information.Channel coding technology and cooperative communication technology can effectively suppress the influence of signal fading,but due to the defects such as high coding and decoding complexity of each channel coding,reliable information correction cannot be achieved.The cooperative communication technology also has the problems of low information transmission efficiency,low reliability of information transmission,and high complexity.To deal with these problems,This dissertation focuses on the optimization of Low-Density Parity-Check(LDPC)code and its innovative application in Coded Cooperation.The main tasks are as follows:(1)First introduced the basic principles of cooperative communication technology and the model of collaborative communication system.Then the diversity combining techniques are introduced,including Selective Consolidation(SC),Equal Gain Consolidation(EGC)and Maximum Ratio Consolidation(MRC).Next,relay protocols such as AF and DF are introduced,and the outage probability and SER of AF and DF relay systems are deduced.Simulations show that when the SER is 10-1,the AF protocol and the DF protocol have about 5d B and 5.5d B performance improvement over the link direct transmission method;when the equal power is distributed,the relay node is in the source node to the destination node.At the midpoint,the system performs best at this time.(2)Aiming at the influence of the short cycle existing in the LDPC code check matrix on the decoding error correction performance,an improved method for constructing the high order circular quasi loop low density parity check(QC-LDPC)code is proposed.In view of the quasi-cyclic characteristics of QC-LDPC codes and the ease of coding and other advantages,the QC-LDPC codes are eliminated using the incremental characteristics of the Dayan sequences,and the QC-LDPC code can be constructed to have a girth of at least 8 and10 respectively.The simulation results show that the QC-LDPC codes based on higher-order derivatives constructed by the high-order derivatives have obvious performance advantages over other traditional construction methods.When BER is 10-5,the QC-LDPC codes with a girth of at least 8 constructed based on the Dayan sequence have performance gains of about 0.5d B,0.65 d B,1.3d B,and 2.3d B respectively compared with the differential sequence construction code,PEG construction code,Mackay construction code,and array code.(3)Aiming at the defect that cooperative partners in Coded Cooperation(CC)systems only decide to participate in cooperative forwarding when they are correctly decoded,a Link Adaptive Regeneration Coded Cooperation(LAR-CC)scheme is proposed.Proposing LDPC code as channel coding method based on two-user model,The link adaptive regeneration(LAR)protocol is introduced into the CC system.By comparing the quality of the channels at both ends of the trunk to adjust the relay forwarding information power.which effectively solves the disadvantages of collaborative partner decoding errors in the CC system resulting in the termination of cooperation.Simulations show that LAR-CC scheme can obtain more obvious system performance advantage than traditional CC scheme.When BER is 10-4,LAR-CC scheme has about 4d B performance gains compared with traditional CC scheme.This paper improve LDPC code and the optimization of LDPC code-based Coded Cooperation,improving the performance of the cooperative communications.And the improvement points are easy to apply to actual environment with significant application value.