带记忆效应的射频功放数字基带预失真

在无线通信系统中，射频大功率器是产生非线性失真的主要器件，预失真技术因其成本低廉、自适应能力强、效率高等优势成为最有发展潜力的线性化技术。本文介绍了射频功放的记忆效应及用于识别HPA记忆效应的数字预失真器的结构和特点,提出了基于Wiener模型预失真器的相关算法。通过计算机仿真验证了该算法的有效性以及基于Wiener模型的数字预失真技术能够有效改善记忆功放的线性化，从而提高发射机的整体性能。     

数字预失真技术在空间通信系统中的应用研究

针对空间通信中非恒定包络调制信号的传输对功率放大器的高线性度和高效率的需求,提出了一种应用于空间通信系统的数字预失真器方案。基于FPGA硬件平台、结合Matlab软件的仿真结果,采用最小二乘算法拟合出非线性功放归一化输入/输出功率特性曲线的反函数实现的数字预失真器,使得非恒包络调制信号经非线性射频功放后具有良好的线性特性。数字预失真器实现了60MHz中频输出、最大码率为1 Mb/s时,将预失真前EVM值为4.71%的SRRC-OQPSK调制信号变换为EVM值为9.09%的信号,经非线性功放后调制信号的EVM值小于5%。     

自适应宽带数字预失真理论分析和仿真

研究优化宽带性能问题,在多载波调制系统中,具有较大峰均比的宽带线性调制信号经过射频功率放大器会产生非线性失真和记忆效应.为了消除功放非线性带来的影响,提出了宽带自适应数字预失真技术,采用间接学习结构设计预失真系统,记忆多项式模型进行功放辨识,并运用递推最小二乘算法更新预失真器参数.仿真结果表明,预失真器改善带外频谱抑制25dB左右,有效地补偿了功放的非线性失真和记忆效应,提高了功放效率,对通信传输质量有了提高,并为优化设计提供了参考.     

基于直接学习法的一种新预失真器

为了克服宽带信号经过记忆放大器的非线性失真,针对有记忆非线性功放的多项式模型,提出了一种新的基于直接学习法的自适应算法.该算法采用无记忆预失真器的级联扩展,具有横向滤波器结构,与记忆多项式有相似的线性化效果.并且针对信号噪声对自适应算法的扰动和收敛速度慢等缺点,采用归一化LMS算法加以改进.在非线性功放的记忆多项式模型下,通过宽带信号验证了基于直接学习法的记忆型预失真器算法的有效性.     

一种高效的功放自适应预失真器设计

在对高功率放大器(HPA)进行自适应预失真过程中,为提高自适应算法运用的灵活性和自适应的收敛速率,解决幅度自适应预处理过程中对幅度过度压缩而影响功放输出功率和效率的问题,设计出一种高效的HPA自适应预失真器。该方案中幅度、相位预失真器相级联,对幅度预失真器采用间接自适应结构进行训练;相位预失真器直接对功放幅度-相位(AM-PM)特性进行辨识,然后取反得到,AM-PM特性辨识器同时又是相位预失真器,能够提高HPA自适应预失真过程中自适应算法运用的灵活性和自适应收敛速率;幅度预失真器基于正弦函数系模型,自适应预失真过程可以同时兼顾功放效率、输出功率和线性度3项重要指标。最后以M-QAM和双音信号为例进行仿真测试,验证了该方法的优势。     

基于数字预失真技术的有记忆功放线性化研究

现代通信系统中,具有较大峰均比和带宽的线性调制信号经过大功率功放会产生非线性失真和记忆效应.针对高峰均比的宽带输入信号,提出一套联合峰均比抑制技术和基带自适应预失真技术来改善功放非线性失真的可行方案.并仿真了峰值抵消算法和自适应预失真算法,结果表明对于峰均比为7.6dB的输入信号,经过1dB的削峰处理后,预失真器改善带外频谱抑制25dB左右,有效的补偿了功放的非线性失真和记忆效应,提高了功放效率,对功放线性化技术有一定的实用价值.     

基于自适应扩展卡尔曼滤波与神经网络的HPA预失真算法

针对强记忆功放的非线性问题,提出一种基于自适应扩展卡尔曼滤波与神经网络的高功放(High power amplifier, HPA)预失真算法.采用实数固定延时神经网络(Real-valued focused time-delay neural network, RVFTDNN)对间接学习结构预失真系统中的预失真器和逆估计器进行建模,扩展卡尔曼滤波(Extended Kalman filter, EKF)算法训练神经网络,从理论上指出Levenberg-Marquardt(LM)算法是EKF算法的特殊情况,并用李亚普诺夫稳定性理论分析EKF算法的稳定收敛条件,推导出测量误差矩阵的自适应迭代公式.结果表明:自适应EKF算法的训练误差和泛化误差均比LM算法更低,预失真后的邻道功率比(Adjacent channel power ratio, ACPR)比LM算法改善了2dB.     

基于SOPC的数字预失真器设计与实现

目前数字预失真技术的研究多偏重在不同算法的仿真方面,对具体实现技术的研究较少。为此,设计一种基于可编程片上系统(SOPC)的自适应数字预失真器。采用多项式查找表电路来实现预失真功能,用现场可编程门阵列(FPGA)内的EDK工程完成系数计算,以避免全硬件实现带来的复杂性。以IP核的形式下载到Xilinx FPGA上,并在测试平台对其进行验证,结果表明,该预失真器能改善功放的线性度,对于8MHz带宽的OFDM信号和doherty结构的GaN功放,ACPR可改善8dB,并且具备自适应功能,可较好地应用到实际工作环境中。     

一种具有普适性的功放线性化预失真方案

为解决功率放大器的非线性问题,提高功放效率,提出了一种能够应用于多种类型功放的间接结构多项式数字基带预失真方案。采取间接预失真结构规避了功放的辨识过程,选择记忆多项式模型作为预失真器能够线性化多种类型的功放,同时采用改进的抑制牛顿算法减少了参数的迭代次数和运算量。以64QAM信号作为输入,对几种典型的功放模型进行数字预失真处理,通过MATLAB仿真分析预失真前后信号的功率谱变化以及ACPR值的改变,表明该方案能够取得比较理想的预失真效果,同时证明了此预失真方案具有一定的普适性。     

基于自适应模糊神经网络的功放预失真新方法

针对无线通信系统中记忆非线性功率放大器预失真结构不足和精度不高等问题,提出了一种基于模糊神经网络模型识别的双环学习结构自适应预失真方法。该方法以实数延时模糊神经网络模型为基础,采用改进的简化粒子群优化（Simplified Particle Swarm Optimization,SPSO）算法进行间接学习结构离线训练模糊神经网络来确定模型参数,作为预失真器的初值,再利用最小均方（Least Mean Square,LMS）算法进行直接学习结构在线微调整预失真器参数,拟合功放的非线性和记忆效应。该方法结构简单,收敛速度快且精度高,避免了局部最优。实验结果表明,该方案邻信道功率比经典的双环结构预失真方法约改善7 dB,功放的线性化性能明显提高,由此验证了其可行性。     

One‐bit in‐phase observation for direct learning‐based digital predistortion with modified frequency‐domain delay estimation and alignment

This article proposes a novel digital predistortion (DPD) implementation method for RF power amplifiers. The new approach adopts only one 1‐bit comparator in the feedback path to observe the in‐phase (I) or the quadrature (Q) component of the error signal between the input and the output signals. To this end, the theoretical derivation of the in‐phase observation based on direct learning architecture (DLA) DPD is first given in this article, by combining the existing 1‐bit method and the low‐cost in‐phase observation. To facilitate the delay estimation and alignment, a modified iterative frequency‐domain delay estimation is presented, which only acquires either I or Q components of the output signal to achieve satisfied delay estimation. Experimental results show that the proposed DPD method decreased the normalized mean square error (NMSE) and the adjacent channel power ratio (ACPR) to less than ?42 and ?51 dB, respectively, which indicates that the proposed DPD system can achieve comparable performance as the existing DPD identification techniques with lower implementation complexity.     

A digital predistorter for wireless transmitters

A novel digital baseband predistorter with improved reduction of spectral regrowth is proposed and investigated. The improvements are achieved by using a proposed predistortion technique and extended power amplifier (PA) fundamental‐frequency modeling. The digital baseband predistortion (DPD), known for its simplicity of realization, low cost and integrability; however, it suffers from poor linearizing performances. We incorporate baseband iterative injection of in‐band distortion components into the baseband DPD to enhance the nonlinearity compensation. General formulas for the fundamental‐frequency output of a PA with n‐order nonlinearity and recursive formulas for calculating the injected components for different number of iterations are developed. The proposed iterative digital baseband predistorter is verified experimentally with a wireless PA and measured results are presented to demonstrate feasibility of the proposed concept. The spectral regrowth suppression of 20 dB is achieved for a 3.5 MHz digitally modulated signal. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

预失真多合体功率放大器ACLR与反馈通道带宽的关系

针对TI公司数字预失真芯片GC5322和Xilinx公司的数字预失真知识产权核(IP Core),考虑输入九载波TD-SCDMA信号,测试了数字预失真多合体功率放大器的反馈通道带宽与邻道及次邻道泄漏功率比(ACLR)的关系。测试结果表明,当反馈通道带宽大于信号带宽1.7倍时,再增加反馈通道带宽,ACLR的改善量变化不明显,在±1.3 dB范围内波动;当反馈通道带宽小于信号带宽1.7倍以下时,再降低反馈通道带宽,ACLR的改善量恶化明显。该结果对工程实现时选取最低反馈通道带宽,降低系统对模数转换器(ADC)的指标要求和器件成本,具有重要的参考和应用价值。     

A novel distortion elimination method of power amplifier in wideband OFDM system

The nonlinear,memory and saturate distortion caused by power amplifier lead to low BER per-formance and low power efficiency in wideband OFDM system.To solve the related problems,a novel power amplifier based on combined amplification with multi power amplifiers is proposed in this paper.In addition,a novel simplified filter look-up table predistorter is proposed.The novel predistorter connects to a memoryless predistorter subsystem with an adaptive filter subsystem in cascade,and can eliminate the nonlinear memory distortion effectively.The simulation results indicate that the power efficiency and BER performance will be improved by using the novel amplifier structure together with the novel predistorter.     

宽频二阶程控低通滤波器的设计

设计了一种宽频二阶程控低通滤波器.二阶低通滤波电路由模拟乘法器、电流反馈运算放大器、可编程电阻网络及电容构成,充分利用了模拟乘法器和电流反馈运算放大器的优点,并通过主控电路调节数模转换电路的输出电压和低通滤波电路可编程电阻网络的值,实现截止频率程控.该滤波器具有截止频率高、信号处理范围宽、速度高等特点.     

Adaptive Predistortion and Postdistortion for Nonlinear Channel

This paper proposes a new adaptive predistortion-postdistortion scheme based on a recurrent neural network to reduce nonlinear distortion introduced by a high power amplifier in the amplitude and phase of received Quadrature Phase Shift Keying (QPSK) signals in a digital microwave system. The recurrent neural network structure is inspired by the model proposed by Williams and Zipser, with a modified backpropagation algorithm. The input signal is processed by a nonlinear predistorter which reduces the warping effect. The received output signal is passed through a postdistorter to compensate for the warping and clustering effects produced by an amplifier. The proposed scheme yields a significant improvement when it is compared to the system without predistortion-postdistortion, perform-ance is evaluated in terms of the bit error rate and output signal constellation.     

一种宽带信号调理通道设计

在高速数据采集系统中,对模拟信号调理通道带宽的要求越来越高。本文结合无源衰减网络、高增益可变增益放大器（VGA）、高速电流反馈放大器（CFA）,设计并实现了一种宽带模拟信号调理电路,并给出了实验结果与分析。该电路具有高带宽、动态范围大、低噪声等特性,能满足数据采集系统高带宽的要求,也可以应用于宽带电子测量仪器的前端信号调理电路。     

热处理炉温控制系统设计

以单片机为核心的热处理炉温控制系统使温度控制指标得到了大幅度提高.硬件部分由AT89C51单片机、温度检测电路、电源电路、信号放大电路、AD模数转换电路、键盘输入电路、显示电路及执行电路等组成.其中信号放大电路将温度检测电路输出的0～41 mV的信号放大到0～10V.AD模数转换电路将采集的模拟量转换为数字量后输入到单片机,给定值和采样值通过大林算法处理得到控制量,经输出口控制固态继电器,来调节炉的温度.软件部分包括主程序,温度采样子程序,滤波子程序,标度变换子程序,显示子程序,大林算法子程序等.经过仿真软件验证,可以精确的控制电阻炉的温度.     

Digital techniques to mitigate feedback impairment and noise of look‐up table digital predistortion

In this article, some new effects of feedback impairment and noise on look‐up table (LUT) digital predistortion (DPD) are presented. Several digital techniques are proposed to mitigate these effects. A smoothing filter (SMF) for LUTs is used to eliminate fluctuations of the transfer function of the overall DPD amplification system. By combining SMF method with iterative average (IA) method, the LUTs iterative process becomes stable and well converged. A postcompensator is established according to the proposed two‐box model for feedback impairment. For the demonstration, both simulation and experiments are carried out based on a Hammerstein‐type PA. Simulation results give some preliminary cognition of these new effects and the effectiveness of proposed techniques. Experimental tests are performed on an S‐band amplifier excited with single‐carrier WCDMA signal. The adjacent channel power ratio (ACPR) at 5‐MHz offset is ?48 dBc after DPD with SMF method and postcompensator. A total of 8 dB extra improvement of ACPR is obtained compared with that with neither SMF nor postcompensator. The result clearly shows that the proposed digital techniques are qualified for LUT DPD system, especially when it suffers significant feedback impairment and noise. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.