Research On Wideband Digital Predistortion Based On Low Sampling Rate ADC

Power amplifier is the main energy-consuming device in the wireless communication base station.In order to obtain maximum efficiency,power amplifiers need to work near the critical point of the gain compression zone.Signals with high peak-to-average power ratios will cause the power amplifier to enter the gain compression zone,causing distortion in the output signal.Digital predistortion has the advantages of simple structure,high efficiency and low cost,and has become the most widely used power amplifier linearization technology currently.With the increase of communication bandwidth,wideband digital predistortion places extremely high requirements on the sampling rate of the ADC in the feedback loop.The high-speed ADC manufacturing process is complex and costly,which greatly increases the application cost of digital predistortion.This article aims to achieve wideband digital predistortion with low sampling rate ADCs.The traditional under-sampling restoration digital predistortion scheme(USR-DPD)needs to adopt a double loop structure,which has low computational efficiency and limited down-sampling factors.MATLAB simulation results show that in order to achieve a good predistortion effect,the USR-DPD scheme needs to extract the pre-distorter parameters three times,and iteratively perform 5 times of down-sampling restoration in each pre-distorter parameter extraction.The down-sampling factor of the USR-DPD scheme can only reach 4,and the ACPR suppression in the output signal of the power amplifier after predistortion is31.76 d B.This article proposes a digital predistortion scheme(TFNW-DPD)that transitions from narrowband to wideband.The MATLAB simulation results show that the TFNW-DPD scheme only needs to extract the parameters of the wideband pre-distorter once on the basis of the narrowband digital predistortion,and the under-sampling restoration only needs to be iteratively performed twice.When the down-sampling factor in the TFNW-DPD scheme is 4,the ACPR suppression in the output signal of the power amplifier after predistortion can reach 32.29 d B,and the calculation efficiency is about 3.6 times that of the USR-DPD scheme.In addition,the TFNW-DPD scheme has stronger down-sampling capabilities.When the down-sampling factor is 10,the ACPR suppression in the output signal of the power amplifier after predistortion can still reach 30.03 dB.