Interference Analysis And Modulation Structure Optimization Design For FP-OFDM Systems

With the gradual popularization of 5G networks and the continuous changes in production and daily needs,people’s requirements for the next generation mobile communication network are also increasing.As the core technology of 5G networks,the filtered orthogonal frequency division multiplexing(f-OFDM)system can still able to be used in the next generation mobile communication network.But the complexity of system implementation will become a significant constraint,due to the increase in data volume.Therefore,further research on f-OFDM is needed to meet the needs of next-generation mobile communication.The scholars have further proposed Filtered Prefix Orthogonal Frequency Division Multiplexing(FP-OFDM)on the basis of f-OFDM.Compared with f-OFDM,FPOFDM has lower implementation complexity and smaller in-band distortion.However,according to existing research,there has been no theoretical derivation of interference analysis for FP-OFDM systems and quantitative analysis of system interference in the presence of non ideal synchronization factors.The processing range is only limited to the transmitting end.After reading relevant literature,it was found that there is no matched filtering at the receiving end.This is because once the in-band fluctuation of subcarrier weighting is smoothed by increasing the degree of freedom of the intra passband weighting coefficient setting,it will result in inconsistent frequency domain weighting coefficients and Crest Factor Reduction(CFR)of the filter for cyclic prefix partial filtering.That will make it impossible to generate spectral filter coefficients and naturally unable to perform receive filtering,which is precisely a necessary step in multi user communication.The innovation of this thesis is reflected in two aspects.Firstly,based on previous research,a mathematical derivation of the received signal of the FP-OFDM system was conducted based on the signal processing process of the sender and receiver of the FP-OFDM system,that is,signal interference analysis was performed on the FP-OFDM system.The time-domain signal at the receiving end is transformed into a frequency-domain signal through discrete Fourier transform.Based on the types of interference generated by different types of subcarrier signals,the received frequency-domain signal will be divided into three parts: useful signal,In Band Interference(INBI),and Inter subband Interference(ITBI).Assuming that the average power of the transmitted signal is 1,derive the power expression for the three parts of the received frequency-domain signal.The derivation and verification will be conducted by making a comparison of program simulation results and formula calculation results.The simulation result shows that the formula calculation results are consistent with the program simulation results,which indicates that the mathematical expressions and power expressions of the three parts of the received signal are correct.The second innovation is to conduct in-depth research on the optimal solutions of the weighted coefficients and filter coefficients in FP-OFDM systems.Due to the simultaneous impact of these two factors on system performance,during the optimization process,one factor will be fixed and the other factor will be optimized for solution.The optimization is mainly divided into two steps: firstly,under the condition of constant weighting coefficients,construct a filter coefficient optimization model with the objective function of minimum signal interference ratio or average symbol error rate of the subband;Then construct a weighted coefficient optimization model with the objective function of minimum signal interference ratio or average symbol error rate of the subband when the filter coefficients are given.The ultimate step is to jointly optimize the weighted coefficients and filter coefficients with the average symbol error rate of the subband as the objective function.The SCA algorithm is used to solve the optimization model,and the optimal solution that achieves the maximum or minimum value of the objective function is found through multiple iterative processes.The optimized filter coefficients reduce out of band leakage and interference to other subbands,thereby reducing SER and improving system performance.The weighting coefficient achieves performance improvement by reducing in band distortion,but it will cause discontinuity between the CP and data parts,increasing out of band leakage.Finally,the impact of other non ideal synchronization factors on the FP-OFDM system is analyzed,and the stability of the FP-OFDM system in various environments is studied.The research process is similar to the previous interference analysis process.In the presence of phase noise and Doppler frequency shift interference,the received frequency-domain signal expression and its power expression are derived and verified by comparing the program simulation results with the formula calculation results.The simulation result shows that the derivation of signal and power expressions for the FP-OFDM system under non ideal synchronous interference is consistent with the program simulation results,which indicates the correctness of the derivation.