Research And Optimization Of OFDM Performance Under Millimeter Wave

In order to widen the communication bandwidth,academia and industry gradually focused on the millimeter wave band for the fifth-generation mobile communication network(5G).However,it brings new challenges to the waveform design of air interface as the spectrum range expands.In the previous work,Orthogonal Frequency Division Multiplexing(OFDM)is excellent in terms of transceiver structure,compatibility with large-scale multi-input and multi-output,and sensitivity to phase noise.However,in the millimeter-wave frequency band,OFDM systems still have more serious high Peak to Average Power Ratio(PAPR)problems,as well as inter-carrier interference(ICI)due to Doppler effect and phase noise.Those problems lead to OFDM limited in practical applications.Therefore,this thesis mainly proposes corresponding optimization solutions for the two problems,i.e.PAPR and ICI of OFDM system in the millimeter wave band.The main contents of this article are summarized as follows:1.Aiming at the problem of ICI of OFDM system,firstly the change of the ICI in the millimeter wave band is analyzed from the perspective of phase noise and Doppler effect,and carrier to interference ratio is used to quantify the ICI.Then an optimization scheme based on self-cancellation is proposed.This scheme modulates the data onto a group of mirror subcarriers,and adds artificial phase and conjugate processing.In order to further reduce ICI,the signal is received through a corresponding linear combination,and finally the optimal phase is solved.The simulation results show that in OFDM and its optimized system,the optimization scheme proposed in this thesis can obtain better the carrier to interference ratio under high frequency deviation,and slightly improve the bit error rate of the system.2.For the problem of rising PAPR in the millimeter wave band,this thesis sets a dynamic threshold on the traditional Partial Transmit Sequence(PTS)method,and performs PTS processing on signals higher than the threshold.The candidate factors are regarded as the form of a matrix,and the elements of the matrix are optimally searched by gradient descent algorithm.In order to further reduce the complexity of searching,the precoding scheme is introduced to optimize the matrix.Simulation results show that,compared with traditional solutions,the algorithm in this thesis can achieve better PAPR optimization effect without affecting the complexity.