Design And Application Of QC-LDPC Code In Coding And Cooperation System

With the advancement of technology,the demand for mobile communication in society is increasing.At the same time,people pay more and more attention to the quality of communication services.Channel coding techniques and spatial diversity-based cooperation techniques can improve the reliability and effectiveness of communication systems respectively.By combining the two techniques,Quasi-cyclic low density parity check(QC-LDPC)coded cooperation system not only obtains the coding gain brought by the QC-LDPC code,but also obtains the diversity gain brought by the cooperation technology.This system can improve the quality of communication services effectively and meet the needs of the times.In this thesis,we investigate the joint design and application of QC-LDPC codes in multi-source multi-relay coded cooperation system.The main contents of this thesis are summarized as follows:(1)The QC-LDPC coded cooperation system is investigated.Firstly,three implementation methods of cooperation technology are investigated.Meanwhile,the advantages and disadvantages of each technology are analyzed.Secondly,the system model and coding implementation of QC-LDPC coded cooperation system are given based on the theory of LDPC code.Then the parity-check matrix and Tanner graph corresponding to the destination are derived.Based on this,the joint belif prooagation(BP)decoding algorithm adopted by the destination is explained.Finally,the point-to-point transmission model corresponding to the QC-LDPC coded cooperation system is set up by introducing the concept of the average signal-to-noise ratio(SNR)of received signal in the destination.Also,the simulations are performed over the additive white gaussian noise(AWGN)channel.(2)For the problem of high coding complexity and prolonged coding delay of the relay in the girth-8 QC-LDPC coded cooperation system,a joint design scheme of special QC-LDPC code based on generator matrix is investigated.This scheme combines the characteristics of generation-matrix-based LDPC(G-LDPC)code and QC-LDPC code,which can directly implement fully parallel coding.So,it can greatly reduce the coding complexity and coding delay of the relay.Firstly,an explicit construction algorithm of girth-8 regular QC-LDPC code is introduced.Then,the joint parity-check matrix,equivalent joint Tanner graph and joint Min Sun(MS)iterative decoding algorithm corresponding to the destination are derived based on the coding implementation of the system.Secondly,a joint design scheme of parity-check matrix is proposed to eliminate all girth-4 and girth-6 cycles in it so as to improve the bit error rate(BER)performance of the system.Finally,The BER performance of the girth-8 QC-LDPC coded cooperation system with different modulation modes and available number of nodes is compared over AWGN channel.(3)The construction method of QC-LDPC code based on the greatest common divisor(GCD)theorem in multi-source multi-relay QC-LDPC coded cooperation system is investigated.Firstly,a kind of QC-LDPC code based on GCD theorem is introduced.Compared with the traditional QC-LDPC code,it has the flexible code length and code rate,which matches the QC-LDPC coded cooperation system very well.Secondly,the girth-8 QC-LDPC coded cooperation system based on GCD theorem is further investigated in the case of multi-source multi-relay situation.Meanwhile,the joint parity-check matrix and equivalent joint Tanner graph corresponding to the destination are derived based on its coding implementation.Then,the codewords adopted by each node are jointly designed to eliminate the short girth cycles in parity-check matrix so as to improve the BER performance of the system.Otherwise,the decoding complexity of the system under the joint design scheme is analyzed.Finally,the BER performance of multi-source multi-relay QC-LDPC coded cooperation system is compared under different conditions and channels.Theoretical analysis and simulation results show that the BER performance of the multi-source multi-relay QC-LDPC coded cooperation system based on GCD theorem is better than the corresponding point-to-point system and the system using general QC-LDPC code.At the same time,the BER performance of the system is significantly improved with the increasing of the number of receiving antennas under different modulation modes.