Design And Implementation Of Digital Predistortion For 5G Wireless Communication System

With the rapid development of wireless communication technology,the fifth generation(5G)wireless communication that has been commercialized in China still uses cyclic prefix orthogonal frequency division multiplexing(CP-OFDM)waveform for transmission,but it has limitations such as low spectrum utilization and lack of flexibility.Filtered orthogonal frequency division multiplexing(F-OFDM)has great hope to be applied in the later versions of wireless communication system because of its advantages such as its sub-band can set different parameters according to different application scenarios and low out-of-band emission(OOBE).However,due to the use of orthogonal modulation,it will bring the disadvantage of higher peak to average power ratio(PAPR).Meanwhile,in communication system,the efficiency of power amplifier(PA)is one of the important factors affecting the system efficiency,and the nonlinear of PA will cause nonlinear distortion,which will bring system error.Digital predistortion(DPD)technology is a linearization technology that can effectively improve PA nonlinearity.In this paper,for 5G wireless communication system,F-OFDM waveform is used for the research and design of digital pre-distortion.Because high PAPR value means more peak signals,and the greater the amplitude of PA input signal,the more serious the nonlinear distortion will be.Hence,in this paper,the combination of digital predistortion and PAPR reduction technology in the communication system is studied.The main innovation points and contents are as follows:1.A structure combining DPD and PAPR reduction technology is proposed for FOFDM system.In this system,PA will produce nonlinear distortion because it works in the saturated region and has high PAPR value.DPD based on reduced PAPR structure can compensate the nonlinearity caused by PA.Firstly,in order to reduce PAPR,a low complexity Iterative Partial Transmit Sequence(IPTS)algorithm combined with Iterative Clipping Revision(ICR)algorithm was introduced.On this basis,the joint structure of DPD and IPTS-ICR is proposed.Simulation results show that,compared with only use IPTS algorithm or ICR algorithm,the combined IPTS-ICR algorithm can better improve the PAPR suppression performance of F-OFDM system,by 1.9d B and0.13 d B,respectively.The combined structure can also effectively improve the nonlinear distortion of F-OFDM system,and reduce the normalized mean square error(NMSE)and error vector amplitude(EVM)of the system.2.A new polynomial digital predistortion model,which is a fractional polynomial,is proposed,and output feedback and short-term memory effect are added.In order to better verify the performance of the model,the polynomial digital predistortion model is combined with IPTS algorithm and companding transform(CT),and compared with other digital predistortion models.Theoretical analysis and experimental results show that when using different PAPR reduction techniques,the proposed model has better performance,while the IPTS-CT algorithm with the polynomial digital predistortion model can reduce PAPR and PA linearization of the best effect,after using the joint scheme,the NMSE performance is improved about 2 d B than traditional memory polynomial model,the PAPR value is reduced by 6d B compared with the signals do not use PAPR reduction technology.