Research On GFDM Transmission Technology In Double-selected Channel Communication System

In this era of the information network,with its swift growth,air and earth are now being integrated.The requirements for high-speed business development are constantly increasing.Therefore,the low-orbit satellite communication system with low orbit and low transmission delay has been paid more and more attention.Generalized Frequency Division Multiplexing(GFDM)is a non-orthogonal multi-carrier technology based on data block modulation.Compared to other multicarrier transmission techniques,it has a relatively lower peak-to-average power ratio,lower out-of-band radiation,and higher spectral efficiency.As a new multi-carrier transmission technology,it provides a new idea for the next Leo satellite communication system development.Although GFDM transmission technology is one of the best multi-carrier transmission systems at present,the non-orthogonal characteristics of its carriers bring self-interference and timing asynchronism to the signal,which affects the transmission and reception of the signal.Therefore,in view of these problems,this paper studies the GFDM system under a high-speed environment,proposes improved technology,and carries out theoretical verification and simulation analysis.Firstly,the basic framework of OFDM and GFDM systems is introduced.The modulation principle in the transmitter and the demodulation principle in the receiver of GFDM are described in detail.The double selective fading channel is time selective fading and frequency selective fading.The advantages and disadvantages of the two Basic Extra Models(BEM)are analyzed,and the two models are compared by simulation.Finally,the channel estimation model which is more suitable for this paper is selected.Then we analyze the performance of OFDM and GFDM under different environmental conditions,which are white Gaussian noise channel,multipath channel,and doppler channel respectively.Aiming at the influence of time delay and frequency offset caused by these environments on GFDM transmission technology,combined with the characteristics of GFDM technology,an improved time-frequency synchronization algorithm is proposed.Through simulation verification,the improved algorithm can effectively improve the time delay and frequency offset problems,to lay the foundation for the following channel estimation.Finally,considering that the non-orthogonal characteristics of each subcarrier of GFDM will affect the channel estimation based on the pilot,this paper designs a method to put zero elements on the adjacent subcarriers of pilot insertion.The principle is that the product of zero elements and any symbol is equal to zero,that is,the inner product of zero and any number is zero.Therefore,in theory analysis,this method can avoid the interference caused by the non-orthogonal subcarriers of GFDM on the channel estimation at the pilot,and also overcome the subcarrier interference and inter-subsymbol interference caused by the double selective fading channel.The simulation results show that the proposed method can effectively improve the channel estimation performance of GFDM system technology under the condition of a double selective fading channel.