Low-complexity Detection And Diversity Technology Design For GFDM

Generalized Frequency Division Multiplexing(GFDM)is currently considered as a potential multi-carrier transmission technology for future wireless communication systems,due to its advantages which the unique system architecture brought,such as high spectrum efficiency,low out of band radiation,well flexibility,and low latency.However,GFDM system uses a non-orthogonal transmit pulse that yields self-interference,resulting in higher receiver complexity and lower system reliability.This thesis mainly studies low-complexity detection and diversity technology for GFDM systems under multi-path Rayleigh fading channel.The main contributions of this thesis are as follows:1.The principle of GFDM system and three kinds of receiver detection techniques are introduced in detail,they are matched filter(MF)detection,zero forcing(ZF)detection,and minimum mean square error(MMSE)detection,and the performance is evaluated by simulations.2.The characteristics of GFDM frequency domain modulation matrix is deeply studied,and its structure is found to be block tri-diagonal and sparse.Then the singularity of GFDM modulation matrix is studied.The problem of the GFDM modulation matrix is irreversible under certain conditions is solved by increasing the up-sampling factor,which makes the GFDM system configuration more flexible and the performance more stable.Based on above studies,a frequency-domain equivalent channel model is established,and low-complexity ZF and MMSE detection methods for the GFDM systems in the frequency domain is designed.The method which makes use of sparse matrix multiplication and fast inversion algorithm of block(cycle)tri-diagonal matrices reduce the complexity of receiver.Finally,it is proved that the frequency domain GFDM detection method can reduce the receiver complexity by10~10~3 without causing the symbol error rate performance loss.3.The MMSE receiver with low complexity based on fast inversion algorithm of block diagonal matrices is only applicable to the case where the number of sub-symbols in GFDM system is small,an iterative algorithm based on L-BFGS is proposed to reduce the complexity of MMSE receiver,which using the conjugate symmetry of autocorrelation matrix of frequency domain equivalent channel.The method converts the operations between matrices into operations between vectors,further complexity of MMSE receiver is reduced by10~10~5,and also saves storage space.The simulation results demonstrate that the method will result in approximately 1dB of symbol error rate performance loss,but it is acceptable.It is worth mentioning that when the number of up-sampling multiple is greater than the number of sub-carriers,the MMSE receiver under this algorithm can bring lower complexity and better symbol error rate performance.4.A GFDM frequency diversity transmission method is proposed on the basis of quasi-orthogonal codes.The interference between sub-carriers is eliminated by designing the signal coding scheme and using of the symmetry of the raised cosine filter,and a signal decoding scheme is designed to eliminate the interference between sub-symbols.The analysis and simulations demonstrate that the system can obtain diversity gain,and improve its reliability.