基于并联FIR滤波器组的Hammerstein预失真器

采用预失真技术对功率放大器的记忆非线性失真进行补偿的关键是预失真器建模的准确性,尤其是模型对功率放大器逆记忆特性的描述能力。针对目前预失真器模型对功率放大器逆记忆效应描述不充分的问题,提出了将查找表(LUT)级联一个具有并联结构的有限长单位冲激响应(FIR)滤波器组作为实现形式的Hammerstein预失真器,以提高传统Hammerstein预失真器的补偿性能,并采用一种两步算法对其参数进行辨识。仿真实验表明,提出的Hammerstein预失真器能更好地补偿带强记忆效应的功率放大器的非线性失真。     

广义改进型Hammerstein预失真器的实现方法及验证

射频功率放大器与生俱来的非线性是无线通信前端设计需要解决的核心问题之一。根据广义改进型Hammerstein功率放大器非线性模型,提出一种应用于射频功放线性化的新型数字预失真器——广义改进型Hammerstein(Generalized Augmented Hammerstein, GAH)预失真器,并给出了该预失真器的实现方法。另外,为了精确分析GAH 预失真器的性能,采用实际功放的输入输出数据进行仿真和实验。被测功放为中心频率1960 MHz,带宽40 MHz, 输出功率45 dBm的Doherty功放。仿真和实验证明：提出的数字预失真器不仅计算复杂度远低于记忆多项式（Memory Polynomial,MP）和分数阶记忆多项式（Fractional Memory Polynomial, FMP）预失真器,而且其线性化能力也强于AH、MP及FMP等预失真器。     

一种新的用于Hammerstein预失真器的自适应结构

针对目前的自适应预失真结构不利于高效的最小二乘算法直接对Hammerstein预失真器参数进行更新的问题,该文提出了一种新的自适应预失真结构。应用该结构可以得到Hammerstein预失真器中两个子系统的误差,因此可使用高效的最小二乘算法直接对Hammerstein预失真器进行自适应更新,避免了结构误差以及子系统误差不精确对预失真器性能的影响。仿真结果表明:该文提出的自适应结构可使Hammerstein预失真器快速高效地补偿带记忆效应功率放大器的非线性失真。     

双分支Hammerstein-Wiener射频功放行为建模及预失真

提出一种新的双分支Hammerstein-Wiener模型,对功放进行非线性行为建模及数字预失真研究.利用飞思卡尔半导体公司的MRF7S21170晶体管进行功放电路设计,从ADS中导出输入输出数据进行模型验证和预失真分析.仿真结果表明,该模型性能优于Hammerstein,Wiener和记忆多项式模型,具有较高的精度,能够精确模拟功率放大器的特性,经过数字预失真后,能抑制功放非线性引起的带内失真和频谱再生,对功放线性化技术的发展具有重要的应用价值.     

一种改进的用于Hammerstein预失真器的自适应结构

针对目前的自适应结构不利于Hammerstein预失真器进行参数更新,尤其是不利于线性子系统参数更新的问题,该文在间接学习结构的基础上提出了一种改进的自适应预失真结构。应用该结构能够得到Hammer-stein预失真器中待识别线性子系统的误差,使得高效的最小二乘算法能够直接对其参数进行更新,进而提高了整个预失真器的线性化性能。仿真结果表明：应用文中自适应结构,Hammerstein预失真器可以高效地补偿带记忆效应功率放大器的非线性失真。     

一种级联两箱通用数字预失真器及其辨识算法

提出了一种由单形规范线性分段(SCPWL)函数与记忆多项式级联的数字预失真器,并给出了复数域两步最小二乘参数辨识算法。不同于以往一种预失真器适用一种功放模型的情况,所提的预失真算法利用SCPWL函数的分段特性以及记忆多项式的非线性记忆特性,在完成参数辨识的同时自动地调整结构,可适用于传统以及强非线性新型功放模型的线性化补偿。将所提预失真器分别应用于传统记忆多项式、两箱模型以及新型包络跟踪功放。经过计算机仿真,功放输出的幅频特性和频谱曲线表明所提预失真器能够有效地补偿多种功放的非线性特性。算法仿真比较结果也表明,针对包络跟踪功放,所提复数两步最小二乘算法的邻道泄漏比(ACLR)可改善约35 dB,性能优于最小均方(LMS)类算法约30 dB。     

改进型Hammerstein动态非线性模型的Doherty射频功放线性化

采用改进型Hammerstein动态非线性模型来设计数字预失真器,用于矫正Doherty射频功放的动态非线性,从而获得一个适合于诸如WCDMA、CDMA2000和WiMAX这样的新型宽带无线通信系统的高效线性射频功率放大系统.文中使用频率间隔5MHz的两载波3GPP-FDD WCDMA信号作为测试信号,设计了一个16W 峰值输出功率的L波段Doherty射频功率放大器.实验表明基于改进型Hammerstein动态非线性模型的数字预失真器可以很好地抑制Doherty射频功放的动态非线性引起的频谱再生,从而有效地降低了邻道干扰.     

数字电视发射机功放的预失真技术研究

介绍了一种可识别HPA记忆效应的数字预失真器的结构、特点,以Hammerstein预失真器为例仿真了可识别功放记忆效应的基带数字预失真器,并在数字电视发射机功放线性化中加以应用,结果表明记忆效应预失真结构应用在数字电视发射机功放的线性化中可以取得令人满意的效果.     

一种新的用于有记忆功放的查找表预失真器

 针对有记忆非线性功放提出了一种新的基于查找表的记忆型预失真器.该记忆型预失真器采用无记忆预失真器的级联扩展,其横向滤波器结构相比记忆多项式方法降低了复杂度,却能够得到与其相近的线性化效果.并且针对查找表固有的量化误差大和自适应收敛速度慢的缺点,分别采用线性内插和加权窗迭代更新的方法加以改进.在非线性功放的记忆多项式模型下,通过多载波WCDMA宽带信号和OFDM宽带信号验证了基于查找表的记忆型预失真器的良好线性化效果和改进方法的有效性.     

Wiener功率放大器的分离预失真方法

Hammerstein(以下简称H)系统能实现对Wiener功率放大器的预失真,文章从其结构特点出发,提出了分离预失真方法,将放大器中的记忆和非线性因素分离,并独立地得到各自的预失真模块,从而组成能对WienerPA进行线性化的H系统,克服了以往在对H系统各参数的辨识中,由于没有排除记忆和非线性因素的相互干扰而导致的算法较为复杂,收敛速度缓慢,收敛精度不高的问题。仿真表明,该方法在收敛速度和收敛精度上都有明显提高。     

GaN逆F类高效率功率放大器及线性化研究

效率和线性度是功率放大器的重要指标,也是设计的技术难点。该文设计了2.5-2.6 GHz高效率GaN逆F类功率放大器,其输入输出谐波匹配网络由解析的方法设计得到。单音测试结果表明,在2.55 GHz处,功放的漏极效率超过75%。为了建立逆F类功放的行为模型进行数字预失真,对传统的Hammerstein模型进行了改进,提升了模型拟合精度,对20 MHz带宽、峰均功率比为9.6 dB的16-QAM OFDM调制信号,结合峰值因子降低技术和数字预失真技术对逆F类功放进行线性化后,功放的相邻信道功率比(ACPR)优于-48 dBc。     

An accurate digital baseband predistorter design for linearization of RF power amplifiers by a genetic algorithm based Hammerstein structure

In this paper, a novel digital predistorter design based on the Hammerstein structure is proposed in order to linearize radio frequency power amplifiers. A genetic algorithm optimization method has been proposed to accurately identify the coefficients of a Wiener model for the power amplifier. Digital predistorter design based on the proposed Hammerstein model has been carried out according to the accurate Wiener model. The validation of the suggested model is carried out using the simulation of the power amplifier and the digital predistortion excited by 64QAM signals in the advanced design system software. According to the simulation results, the criterion of an adjacent channel power ratio decreased by about 16 dB. The simulation results show the adjacent channel power ratio of almost ??46 dBc. In order to assess the feasibility of the proposed predistorter, it is completely implemented in the Kintex FPGA using Vivado HLS. This proposed model enables a more accurate modeling of nonlinear distortion and memory effects compared to the previous linearization methods. This paper presents the new linearization method using the genetic algorithm based Hammerstein structure.     

Wiener功率放大器预失真中LMS Newton算法的研究

基于Wiener模型构建的功率放大器和Hammerstein模型构建的预失真器,在现有的LMS算法基础上,结合预失真系统模型,推导出NFLMS(Nonlinear Filtered LMS)预失真算法.在此基础上,提出NFLMS Newton预失真算法的概念,为了达到实用目的,本文提出并推导了一种改进型NFLMS Newton预失真算法.仿真结果表明,改进型NFLMS Newton预失真算法和NFLMS预失真算法相比明显加快了收敛速度,并且快速降低了算法的剩余误差.     

非线性信道的LMS Newton均衡算法的研究

本文使用Hammerstein模型和维纳模型代替Volterra级数模型来模拟非线性结构以降低运算复杂度,提出了一个由Hammerstein模型和维纳模型构建成的非线性信道传输系统的模型,由此模型给出并推导出了基于该信道模型的NCLMS算法、改进1型NCLMS Newton算法和改进2型NCLMS Newton算法.仿...     

基于SoC的可重构短波功放数字预失真线性化

在对功率放大器的非线性放大特性研究的基础上,提出了在SoC为核心的硬件平台上对短波功放进行可重构预失真线性化的方法。文章重点对改进型Hammerstein 模型进行了改进,修改后的模型不仅在硬件上易于实现,而且具备模式切换功能,可以根据需求选择不同的有记忆模型或无记忆模型。实验结果证实了修改后的模型能有效地抑制短波功放的带外寄生辐射。提出的基于SoC 硬件平台的预失真线性化实现方案可以很方便地实现各种不同的预失真非线性模型,节省系统硬件资源,具有重要的工程实际应用价值。     

非线性信道的均衡算法研究

本文使用Hammerstein模型和维纳模型代替Volterra级数模型来模拟非线性结构以降低运算复杂度,提出了一个由Hammerstein模型和维纳模型构建成的非线性信道传输系统的模型.基于该系统模型,分别提出并推导了三种非线性信道的均衡算法:NCRLS算法、NCKalman算法和NCRPEM算法,并对这三种新算法的性能进行了比较.仿真结果表明,在剩余均方误差方面三种算法中NCKalman算法最小,NCRPEM算法次之,NCRLS算法较差;在收敛速度方面NCRPEM算法收敛最快,NCRLS算法次之,NCKalman算法较差.     

A Generalized Memory Polynomial Model for Digital Predistortion of RF Power Amplifiers

Conventional radio-frequency (RF) power amplifiers operating with wideband signals, such as wideband code-division multiple access (WCDMA) in the Universal Mobile Telecommunications System (UMTS) must be backed off considerably from their peak power level in order to control out-of-band spurious emissions, also known as “spectral regrowth.” Adapting these amplifiers to wideband operation therefore entails larger size and higher cost than would otherwise be required for the same power output. An alternative solution, which is gaining widespread popularity, is to employ digital baseband predistortion ahead of the amplifier to compensate for the nonlinearity effects, hence allowing it to run closer to its maximum output power while maintaining low spectral regrowth. Recent improvements to the technique have included memory effects in the predistortion model, which are essential as the bandwidth increases. In this paper, we relate the general Volterra representation to the classical Wiener, Hammerstein, Wiener–Hammerstein, and parallel Wiener structures, and go on to describe some state-of-the-art predistortion models based on memory polynomials. We then propose a new generalized memory polynomial that achieves the best performance to date, as demonstrated herein with experimental results obtained from a testbed using an actual 30-W, 2-GHz power amplifier.     

Wiener predistorter for nonlinear satellite downlinks

The nonlinear power amplifier and the analogue output channel filter with nonconstant group delay add nonlinear and linear distortions to the satellite transmitted signal, respectively. Recently, there has been growing interest in using Wiener predistorters, consisting of separate nonlinear and linear components, to compensate for these distortions in the satellite downlinks. The Wiener predistorter has been shown to effectively deal with signal distortions and has lower complexity compared to other state-of-the-art methods. In this paper, we argue that fully compensating the nonconstant group-delay distortion degrades the overall performance of the Wiener predistortion systems. This is primarily due to the increased peak-to-average power ratio of the signal at the output of the linear predistorter. We show that the overall performance of the Wiener predistorter can be improved by undercompensating the group-delay distortion. We propose two optimizations to address the PAPR growth problem and show using simulations that our approach leads to significant improvement in predistortion performance. Using our Wiener predistorter, the total degradation gap to the ideal limiter channel can be reduced to merely 0.34 dB for 64-APSK modulated signals.     

Quantifying and cancelation memory effects in high power amplifier for OFDM systems

A modeling approach to power amplifier design for implementation in OFDM radio units is presented. The power amplifier model assesses the impact of linear memory effects within the system using a Wiener representation, and employs a linear novel parametric estimation technique using Hilbert space. In addition, in order to model the nonlinear memory effects the previous topology is generalized by inserting the truncated Volterra filter before the static nonlinearity. Predistortion based on the Hammerstein model is introduced to deal with the nonlinear response. The new general algorithm is proposed to evaluate the Hammerstein model parameters for an OFDM system. A representative test bed was designed and implemented. The assessment of the new methods for PA and PD modeling are confirmed by experimental measurements. The measurement results reveal the preference of the new techniques over the existing approaches.