Adaptive Digital Feedback Predistortion Technique for Linearizing Power Amplifiers

We have developed a new adaptive digital predistortion (DPD) linearization technique based on analog feedback predistortion (FBPD). The lookup-table-based feedback input can remove the bandwidth limitation of the feedback circuit related to the loop delay, and suppress feedback oscillation by accurate digital control of the feedback signal. Moreover, the predistortion (PD) signal can be extracted very efficiently. By combining the feedback linearization and DPD linearization techniques, the performance of the predistorter is enhanced significantly compared to the conventional DPD. To clearly visualize the characteristics of digital FBPD (DFBPD), we have compared it to the conventional DPD based on the recursive least square algorithm using Matlab simulation. The results clearly show that the new method is a good linearization algorithm, better than a conventional DPD. For the demonstration, a Doherty power amplifier with 180-W peak envelope power is linearized using the proposed DFBPD. For a 2.14-GHz forward-link wideband code-division multiple-access signal, the adjacent channel leakage ratio at 2.5-MHz offset is -58 dBc, which is improved by 15 dB at an average output power of 43 dBm     

Analysis of Adaptive Digital Feedback Linearization Techniques

A new lookup-table linearization technique is developed based on the digital feedback and digital feedback/predistortion (DFBPD) concepts. The linearization characteristics are investigated through system simulation of a real power-amplifier model with 90-W peak envelope power. The DFB suppresses forward-path nonlinear distortion as a gain reduction due to the FB effect, and this technique enhances the system tolerance without any bandwidth limitation. As the PD network is added to the FB loop, the linearization performance and system tolerance are further improved because of more accurate PD signal extraction. In addition, the gain is purely determined by the FB path, so the gain fluctuation in the forward path, including amplifier aging and temperature effects, is suppressed. The analysis and simulation allow experimental evaluation of the linearization mechanism and performance of the DFBPD technique for an 802.16e mobile Worldwide Interoperability for Microwave Access signal.      

功率放大器的自适应预失真线性化技术

重点介绍了几种主要的功率放大器的自适应预失真技术,包括基带预失真、中频预失真及射频预失真技术,以及几种自适应预失真工作函数的产生方法,并利用多项式产生工作函数的方法对功率放大器进行预失真调整,使其线性度得到明显改善。     

A Method to Reduce Sampling Rate of the ADC in Feedback Channel for Wideband Digital Predistortion

This paper presents a new digital predistortion (DPD) solution for wideband signals with low feedback sampling rate. To reduce the minimum sampling rate of the analog-to-digital converter (ADC) for wideband digital predistortion, the proposed method uses a bandpass filter to form a narrowband signal before the ADC. Then, a deconvolution operation is performed to recover the original wideband signal from the ADC samples. The proposed method is evaluated with an international mobile telecommunication-advanced signal with 100 MHz bandwidth. The simulation results show that the recovered signal of the proposed method closely approximates to the original signal in the passband of the filter, and the mean square error of the deconvolution decreases as the signal-to-noise ratio increases. The proposed algorithm can reduce the sampling rate of the ADC from 1105.92 million samples per second (MSPS) to 368.64 MSPS, and improve the adjacent channel power ratio more than 20 dB, which is merely 5.6 dB less than the conventional DPD with 1105.92 MSPS sampling rate.     

关于自适应预失真射频功率放大器线性化研究

介绍新的带外信号检测方法和自适应模拟预失真线性化技术,并应用于CDMA直放站的5W自适应射频线性功率放大器.为了有效抑制临信道频谱再生,通过自适应检测和自适应预失真控制使输出信号的3阶和5阶交调失真分别改善8dBc和6dBc.     

单路反馈射频功放预失真线性化方法

该文基于记忆多项式模型,提出一种采用单路反馈的射频功放预失真线性化新方法,只需用正交解调后的IQ信号中的一路,就可完成对预失真器模型参数的获取。该方法可消除使用正交解调器所带来的增益和相位不平衡问题,且节省了一路反馈采样电路,在降低成本、简化设计的同时还能提高预失真线性化的性能。仿真和物理实验结果表明,该文提出的方法是正确的,能达到比较好的线性化效果。     

使用自适应RF预失真技术改善放大器线性的研究

RF功率放大器对信号造成的非线性失真会产生邻道干扰，并降低信号质量，因此宽带通信系统对功率放大器的线性提出了严格的要求。本文提出了可以改善功率放大器线性的自适应RF预失真电路的模型，描述了自适应RF预失真的实现过程；介绍了现有的一些自适应预失真技术，具体分析了常用的矩形功函数预失真技术和最小功率自适应方法；通过仿真进一步证明了预失真技术可大大提高RF功率放大器的线性度。     

基于自适应射频预失真的多载波功率放大器线性化技术

用高功率放大器放大线性调制信号 (包络波动变化 ) ,必然会产生失真和互调成分。而基于扩频技术的第三代无线通信系统中的功率放大器必须要有很好的线性性能。本文提出一种线性化射频多载波高功率放大器的自适应射频预失真器。     

微波回传系统发射机数字预失真线性化

微波回传系统是宽带无线通信基站信号回传的主要手段之一.对19GHz微波回传系统发射机的非线性特性进行了实验测试与分析研究,采用基于查找表(LUT)的数字预失真技术对其进行线性化以满足大容量无线基站信号传输的需求.利用指数加权移动平均算法(EWMA)提取发射机的静态非线性特性以构建数字预失真查找表.使用3载波WCDMA信号进行实验验证,实验结果表明采用查找表数字预失真器对该被测发射机进行线性化,3阶互调失真(IMD3)最大可以改善23dB.因此通过简单的查找表数字预失真技术可以有效地提高微波回传系统发射机的线性度,同时可以使微波功率放大器工作在较高的输出功率,增大回传距离,降低生产成本.     

Derivative Derivative-Based Envelope Design Technique for Wideband Envelope Tracking Power Amplifier with Digital Predistortion

A novel envelope design for an envelope tracking(ET)power amplifier(PA)based on its derivatives is proposed,which can trade well off between bandwidth reduc-tion and tracking accuracy.This paper theoretically analyzes how to choose an envelope design that can track the original envelope closely and reduce its bandwidth,and then demonstrates an example to validate this idea.The generalized memory polynomial(GMP)model is applied to compensate for the nonlinearity of ET PA with the proposed envelope design.Experiments are carried out on an ET system that is operated with the center fre-quency of 3.5 GHz and excited by a 20 MHz LTE signal,which show that the proposed en-velope design can make a good trade-off between envelope bandwidth and efficiency,and satisfactory linearization performance can be realized.     

自适应预失真线性化技术的延时补偿研究

引言 现代无线通信系统中,出于对更高的传输速率和频谱效率的要求,线性调制技术如QPSK、64QAM及多载波调制技术如OFDM等,正得到越来越广泛的应用。由于线性调制或多载波调制信号的包络是起伏波动的,这些波动经过非线性的射频功率放大器后将产生交调分量,从而产生邻道干扰。为了解决这个问题,一般的方法是采用大功率放大器进行功率回退,使放大器工作在线性放大区。这种情况下,大功率器件只能输出很小的有效功率,其本身潜力不能充分发挥,造成整机成本提高。     

非均匀采样率并发双频数字预失真技术

5G通信的高速发展对发射机支持多模式多频带并发有了新的需求.考虑非均匀采样率并发双频场景下发射机的线性化方案,针对低采样率频段失真频谱超过采样带宽,从而恶化建模精度这一问题,提出一种混叠消除的并发双频数字预失真(DPD)方案.该方案通过在高采样率下构造模型基函数,然后通过低通滤波器来滤除超出采样带宽的频谱分量,再降采样...     

使用多智能体反馈神经网络实现的数字预失真器

近年来,深度学习（Deep Learning,DL）在通信场景中的应用逐渐兴起,其中就包括射频发射机的数字预失真（Digital Predistortion,DPD）处理。然而,由于射频功率放大器（Power Amplifier,PA）固有的非线性失真和记忆效应特点,如果直接应用传统DL算法去实现DPD会出现拟合效果不佳、自适应性差等现象。针对这个问题,本文提出了一种由多智能体反馈神经网络实现的数字预失真器（Multi-Agent Feedback Enabled Neural Network for Digital Predistortion,MAFENN-DPD）,该网络引入了具有高纠错能力的反馈智能体结构,其主要特点是基于Stackelberg博弈理论去加速网络训练和收敛,同时我们还应用信息瓶颈理论指导网络超参数设计以增强MAFENN-DPD对PA记忆效应变化的动态适应能力。我们进行了一系列的实验来验证MAFENN-DPD的有效性。与使用典型前馈网络实现的DPD方案相比,基于MAFENN-DPD的方案在相邻信道功率比（Adjacent Channel Power Ratio,ACPR）指标上提高了约5 dB。同时,在没有通信过程中的大量先验知识的情况下,MAFENN-DPD实现了与使用记忆多项式方法建模的DPD方案十分接近的ACPR性能。仿真结果说明MAFENN-DPD相比传统神经网络可进一步提升ACPR性能,同时相比记忆多项式方法具有更好的自适应建模能力和通用性,并且具有多智能体反馈结构特征的神经网络未来在其他的通信场景中也具有应用推广的潜力。      

射频功率放大器数字预失真技术及其发展趋势

3G无线通信系统对功率放大器的设计提出了更加严格的要求。为了有效地利用宝贵的频谱资源,功率放大器既要保证高线性度以减小带外发射功率以及误码率,又要有较高的效率以减少电源消耗。在众多功放线性化高效率技术中,数字预失真技术被认为是最有效的解决方案,受到越来越多的关注。本文对数字预失真技术作了详细介绍,结合实例分析了当前主要的几种预失真模型和对应的预失真方案,并展望了Doherty放大器技术与数字预失真结合的应用方向。     

自适应数字预失真的FPGA实现

数字预失真技术在软件仿真方面已取得长足进步,但在硬件实现上还存在着很大的不足。利用设计的实验平台,在窄带通信系统中不考虑记忆效应的情况下,提出了一种基于查询表的能够有效抑制器件噪声的自适应数字预失真方案。经FPGA实现该方案后,可以明显降低噪声和交调干扰,实验结果较为理想。     

宽带Chrip信号激励下功放数字预失真补偿

功率放大器(power amplifiers, PAs)会对输入的宽带线性调频信号(linear frequency modulated, LFM)引入幅度失真和相位失真,这将导致接收机脉冲压缩处理后的输出信号主瓣展宽,旁瓣电平抬高,从而恶化雷达距离分辨率甚至产生虚假目标。文中提出采用有限冲击响应滤波器(finite impulse response, FIR)模型对宽带LFM信号激励下的功放进行行为建模和数字预失真(digital predistortion, DPD)补偿。利用宽带测试平台对500 MHz 瞬时带宽LFM信号激励下峰值功率15 W 的S波段功放进行验证。实验结果表明,浅饱和和深饱和情况下FIR模型都能准确建模功放的失真特性,浅饱和情况下DPD能够补偿幅度失真和相位失真,而深饱和情况下只能补偿相位失真,经过DPD补偿脉冲压缩后的峰值旁瓣电平都明显降低。     

数字电视发射机自适应预失真技术

本文介绍了国外应用在数字电视发射机中的自适应预失真技术 ,着重介绍了笛卡尔环的工作原理、高功放产生互调失真的原理以及预失真的工作原理。     

5G光载无线通信前传系统数字预失真线性化研究

第五代移动通信系统新空口(5G NR)的信号带宽、调制度和峰均比相比4G信号高很多。用于小蜂窝或微蜂窝基站组网的光载无线通信(Radio-over-Fiber, RoF)前传系统的非线性失真也更加严重。为了使5G NR信号线性传输,采用记忆多项式(Memory Polynomial, MP)和广义记忆多项式(Generalized Memory Polynomial, GMP)模型构建数字预失真器,矫正5G RoF前传系统的非线性。在实验中搭建了2 km光纤的RoF前传系统,并采用100 MHz带宽5G NR信号作为测试信号对其进行线性化测试。实验结果表明,采用MP和GMP数字预失真器进行线性化时,5G RoF前传系统的邻信道功率比(Adjacent Channel Power Ratio, ACPR)可分别改善13 dB和17 dB以上。这说明MP和GMP数字预失真器对5G RoF前传系统的非线性具有显著的抑制作用。因此基于MP和GMP两个模型的数字预失真器均可用于5G RoF前传系统的线性化,而且GMP预失真器比MP预失真器对该系统线性化的能力更强。     

查找表联合记忆效应补偿技术的宽带自适应预失真算法

为了能够对记忆型功率放大器线性化处理,并能一定程度克服其记忆效应,该文介绍一种自适应数字预失真器。该数字预失真器采用查找表与记忆效应补偿技术相结合的方法,并且利用内插值方法有效减小了查找表幅度量化过程产生的误差。相比记忆多项式预失真器,这种预失真器的计算复杂度较小,却能够得到与其相近的线性化效果。基于功率放大器记忆多项式模型,利用OFDM(Orthogonal Frequency Division Multiplexing)宽带信号验证该文提出的预失真器对记忆型非线性功率放大器的良好线性化效果。     

A Low-Voltage 5-GHz Downconversion Mixer Employing A Second Harmonic Injection Linearization Technique

In this paper, a low-voltage CMOS mixer topology, appropriate for operation in the 5-GHz frequency band, is presented. The mixer combines several design techniques in order to achieve high linearity performance with minimum current consumption in a restricted 1-V supply. The proposed mixer utilizes an integrated transformer to improve the high frequency performance and to achieve large LO to RF isolation. In addition, a novel linearization technique based on second harmonic injection, is introduced to optimize linearity performance. The design is being implemented in a 0.13-mum CMOS technology.