Design And Implementation Of Digital Predistortion Based On F-OFDM System

The orthogonal frequency division Multiplexing technology widely used in the fourth generation mobile communication technology(4G)can not meet the needs of future mobile wireless communication,because of its large sidelobe,high peak-to av-erage ratio,low spectrum resource utilization and poor anti-carrier interference ability.Filtered orthogonal frequency division multiplexing(F-OFDM)is one of the candidate technologies for some technical scenarios of 5G,its basic principle is to divide the spectrum bandwidth into several subbands,each subband is configured with different parameters according to different service requirements.It is an extension of traditional OFDM.It can better use of frequency spectrum by adding subband filters,and flexibly changing parameters such as cyclic prefix length,transmission time interval and sub-carrier interval,but it also has the disadvantage of high peak average power ratio(PAPR).The signal with the high PAPR is more sensitive to the nonlinearity of the power amplifier(PA).In order to ensure the quality of the transmitting signal,the re-quirement of linearity of PA is higher,so the linearization techniques have been well developed,and the digital predistortion(DPD)technology has become the mainstream linearization technology because of its good optimization effect,high flexibility and low relative cost.In this paper,digital predistortion(DPD)technology is studied under the background of F-OFDM signals,combined with the crest factor reduction(CFR)techniques.The specific work and research contents of the paper are listed as follows:(1)We propose a new structure of DPD combined CFR based on feedback term to compensate the nonlinear characteristics of the PA.The proposed digital predistorter module adopts the polynomial adaptive predistortion technology based on the short-term output information of the feedback term.Joint partial transmission sequence(PTS)and companding transform(CT)are used as the CFR algorithm,which can restrain PAPR of input signal,so that the working area of the power amplifier is infinitely close to the saturation area.The simulations show that the proposed new model structure can truly capture the nonlinear characteristics and memory effects,effectively reduce out-of-band spectrum expansion and nonlinear distortion,and alleviate the amplitude and phase distortion.(2)The design and implementation of digital predistortion system based on iter-ative clipping revision(ICR)algorithm are studied,and its feasibility is verified in MATLAB.Firstly,iterative clipping revision algorithm is used to limit the signals that exceed the set threshold,then the model coefficient is adjusted by the adaptive model parameter calculation algorithm through the polynomial digital predistortion module,and the output signal is amplified by the power amplifier cascaded with the predistor-tion module.The design solution finally solves the problem of high PAPR of input signal and slow convergence speed of adaptive predistortion algorithm.The simulation results show that the ACPR is improved,and the PAPR of the output signal is reduced by about 1.1 dB compared with that of the original signal by using the secondary clip-ping revision algorithm.