The Research On Wideband Digital Predistorton Method For 5G/6G

With the rapid development of wireless communication technology,in the fifth-generation mobile communication system(5G),in order to meet the increasing demand of users for data transmission rate,the bandwidth of signals needs to be wider.And in order to transmit more information in a limited frequency band and improve spectrum utilization,the modulation efficiency of wireless signals also needs to be higher.Such a complex wideband signal will make the RF power amplifier show strong nonlinearity,which is very unfavorable to the communication quality.While power amplifier is an essential part of wireless communication,the linearity of power amplifier determines the quality of wireless communication to a certain extent.And high efficiency and high linearity power amplifier is particularly important.Digital predistortion(DPD),as a simple,flexible and excellent linearization method of power amplifier,is a research hotspot at present.In this paper,firstly,the predistortion method to reduce the complexity of predistortion model and improve the linearization ability in wideband situation is studied.Secondly,aiming at the high cost of feedback loop analog-to-digital converter in broadband situation,the band-limited predistortion method in ADC with low sampling rate is studied.The main contents and innovations are as follows:1.In this paper,a modified magnitude-selective affine function-based digital predistortion for power amplifiers(M-MSA model)is proposed,which has low complexity,high modeling accuracy and strong linearization ability.Compared with the I-MSA model,this model omits the original phase solving process and reduces the number of coefficients by(M+1)·K.The experimental results show that the ACPR of M-MSA model is about-52.7dBc,which is improved by 20.5dB and NMSE is-42.7 1dB compared with that without predistortion.Compared with ACPR of MP model,it is optimized by about 2dB,and NMSE is optimized by 4.2dB;Compared with ACPR of GMP model,it is optimized by 1.2dB,and NMSE is optimized by about 2dB;Compared with ACPR of I-MSA model,it is optimized by 0.7dB,and NMSE is optimized by about 1.2dB.M-MSA model has the best predistortion performance,the lowest complexity,and the shortest simulation time in existing models.Using M-MSA model for linearization compensation can obtain more accurate modeling results and better linearization effect with low complexity.2.This paper proposes a band-limited predistortion model based on amplitude-selective affine function with out-of-band compensation.In this paper,the M-MSA model is derived into the band-limited system,and a band-limited M-MSA model with out-of-band compensation is proposed.The predistortion process is roughly as follows:the coefficients of the forward model are obtained by the band-limited M-MSA model,then the output of the whole band is estimated by the M-MSA model,and finally the input signal and the estimated output signal are used for predistortion.It can be seen from the test results of single carrier 80MHz signal that the performance of band-limited M-MSA model is better than other band-limited models when the bandwidth of feedback loop is the same.When the feedback loop bandwidth is 1.25 times of the signal bandwidth,the band-limited M-MSA model has a good linearization effect.Compared with the case without predistortion,the ACPR is improved by 17dB,optimized by 2.2dB compared with the band-limited MP model,optimized by 1.6dB compared with the band-limited DDR model and optimized by 1.05dB compared with the band-limited CPWL model.When the feedback loop bandwidth increases by 1.5 times the signal bandwidth,the ACPR of the band-limited M-MSA model is improved by 18dB,optimized by 2.55dB compared with the band-limited MP model,optimized by 1.45dB compared with the band-limited DDR model and optimized by 1dB compared with the band-limited CPWL model.The results show that the band-limited M-MSA model can achieve good linearization effect in the whole band at low sampling rate.In the current 5G and future 6G,the bandwidth of a single signal can reach 100MHz or even 1000MHz.The M-MSA model proposed in this paper has a broad prospect in such wideband signal predistortion.The band-limited M-MSA model proposed in this paper also has important reference value for reducing ADC sampling rate under such wideband conditions.