基于动态有理函数的功放模型及预失真应用

针对现代无线通信系统中射频功率放大器的非线性与记忆效应,提出一种新的低复杂度的动态有理函数模型,该模型简化了有理函数模型,通过两个多项式的比进行建模,但分子是包络记忆多项式的形式,分母由无记忆多项式构成.通过模型仿真和预失真应用系统验证,结果表明:与记忆多项式模型相比,动态有理函数模型所需的系数要少30.6％,模型精度却与其相近,邻信道功率比(ACPR)改善约20 dB,而与有理函数模型相比,所需系数要少21.9％,模型精度改善2.4 dB,ACPR改善约15 dB.由此证明了该模型在复杂度和精确度上的优越性,对功放预失真的研究具有重要的参考价值.     

新型功率放大器PLTC行为模型及预失真应用

为提高通信质量,针对功率放大器的记忆效应和动态非线性特征,提出一种新型的三箱PLTC ( parallel-LUT-TMP-CIMT)模型。该模型由查找表、三角记忆多项式和记忆时刻信号交叉项并联构成。 PLTC模型用于功率放大器的行为模型建模以及数字预失真的应用,使用16 QAM信号驱动一个强非线性Doherty功放来验证模型的性能,把PLTC模型应用在预失真中,经过PLTC预失真后,邻信道功率比减少大约22 dB。将PLTC模型与多项式MP模型、一般多项式GMP模型和LMEC模型这3种模型进行精度与计算系数复杂度的比较,结果表明,PLTC模型能够达到较好的精度,同时可以大幅降低计算系数。     

基于分段线性函数的功放模型及数字预失真应用

为了克服通信系统中功率放大器的非线性和记忆效应,数字预失真技术成为研究的热点。提出一种基于分段线性函数的多项式模型,与广义记忆多项式模型相比,我们把多项式中的高阶项转换为分段求和项,消除了高阶相乘带来的不稳定性,同时由于分段阈值的存在,该模型的适用性和稳定性均有所提高。把功放模型应用于数字预失真结构中的实验结果表明:与广义记忆多项式模型相比,分段线性函数模型所需系数要少40%,邻信道功率比提高约1dB,归一化均方误差提高约8dB,因此该模型在数字预失真方面具有较好的效果。     

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。     

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。     

稀疏的归一化功放模型及预失真应用*

针对射频功放的非线性特性进行了研究,提出一种新的稀疏化的Volterra级数模型。该模型基于压缩感知算法,将稀疏系统的辨识等效为信号的重构问题,利用正则正交匹配（ROMP）算法对核系数进行稀疏化并选择出活跃的核系数。将提出的模型与记忆多项式（MP）模型、通用记忆多项式（GMP）模型进行比较,较MP模型的建模精度提升10.7dB,模型系数减少25%,较GMP模型的建模精度提升3.9dB,但模型系数减少84.58%。仿真结果表明：提出的方法实现良好的预失真线性化性能,极大地降低模型系数,优于传统的功放行为模型。由此验证对功放的线性化技术发展具有参考价值。     

宽带GaN功率放大器的建模与预失真

对正交频分复用传输系统中宽带GaN功率放大器的建模与预失真线性化方法进行研究。应用一个带有记忆的多项式模型来建模GaN功率放大器及其逆特性,并通过递推最小二乘法(RLS)辨识模型参数,然后利用预失真间接结构实现了GaN功率放大器的预失真器。最后,仿真验证预失真方法的有效性,结果表明记忆多项式模型可以对GaN功率放大器进行建模并实现线性化。     

模拟预失真射频功率放大器设计

本文介绍了一种WCDMA频段模拟预失真功率放大器的设计。在设计中采用预失真技术对幅度一幅度（AM—AM）和幅度一相位（AM—PM）曲线进行校正,以补偿功率放大器的非线性失真。实现了在输出功率为39dBm时信号带宽内偏离第一个5MHz信道的ACPR值优于-53dB。     

功放非线性特性及预失真模型研究

针对功率放大器的非线性特性问题进行研究,分别根据无记忆和有记忆两种类型的功放特性曲线用最小二乘法拟合出功放模型,根据线性化原则以及输出幅度限制和功率最大化约束,建立预失真模型.以误差函数和工程可实现性为评价指标,从不同模型中分别选出无记忆和有记忆最优模型.仿真测试表明被选取的多项式预失真模型能够有效的改善功率放大器的非线性具有较好的抗噪性,对工程实践中预失真器的设计具有一定的指导意义.     

一种宽带OFDM系统中记忆非线性功放的预失真方法*

针对宽带OFDM系统中功放的记忆非线性失真问题,提出一种新的频域预失真方案。该方案在频域建立具有自适应更新的幅度、相位预失真矩阵,对信号幅度和相位分别进行多次预失真处理。为提高自适应预失真收敛速度,提出一种新的预失真矩阵自适应更新算法,即Linear Convergence算法。仿真结果表明,发送信号频谱旁瓣较二维查表法压低6dB。误码率为时,该方法比二维查表法约有2dB的信噪比增益。此外,Linear Convergence更新算法收敛速度比二维查表法中的更新算法提高75%。本文提出的频域预失真方案能够有效提高收敛精度和收敛速度。     

An accurate physical knowledge‐based model for behavioral modeling and digital predistortion of power amplifiers

The objective of this article is to present an accurate model for behavioral modeling and digital predistortion of power amplifiers (PAs) using physical knowledge. Starting with the physically meaningful block model, we present a novel approach to simplify the block model and propose a simplified physical knowledge‐based (SPK) model. The SPK model's performance was experimentally assessed by two types of PAs (a LDMOS Doherty PA and a GaN Doherty PA) and two signals (a single carrier 16QAM signal and a 2‐carrier WCDMA signal). All experimental results prove the superiority of the SPK model. Compared with the 1st‐dynamic deviation reduction (DDR) approach and the 2nd‐simplified DDR approach, the SPK approach achieves average ACPR improvements of 4.4 dB and 2.5 dB, respectively. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 23: 682–689, 2013.     

Frequency domain data based model extraction for band‐limited digital predistortion of wideband RF power amplifiers

Bandwidth constraints pose significant challenges to linearization of wideband RF power amplifiers (PAs) with digital predistortion (DPD). A recently proposed band‐limited DPD scheme uses a band‐limited modeling technique to eliminate the bandwidth constraints and reduce DPD implementation cost. However, time consuming convolution operations are involved for model extraction in this time domain data based band‐limited modeling method. In this article, band‐limited model extraction is formulated as a generalized least squares problem and investigated from a frequency domain perspective. A frequency domain data based model extraction method is proposed, which greatly reduces the computational complexity for extracting band‐limited DPD model parameters. A 10 W GaN HEMT inverse class‐F PA excited by a 20 MHz four‐carrier WCDMA signal and a 40 MHz two‐carrier LTE signal is tested to validate the method. Experimental results show that the computationally efficient frequency domain data based model extraction method for band‐limited DPD provides as good linearization performance as the time domain data based method. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:412–420, 2014.     

An open‐loop digital predistorter based on memory polynomial inverses for linearization of RF power amplifier

Digital Predistorter is a cost‐effective solution to compensate for the nonlinear distortions appearing in the RF power amplifiers (PAs). The indirect learning scheme is widely implemented because of its flexibility to eliminate the requirement for building a closed‐loop real time system, which dramatically reduces the complexity for measurement setup. However, such scheme is sensitive to the measurement noise that may cause biasing in the coefficients estimation. To minimize the influence of measurement noise and simultaneously enable the open‐loop implementation, we propose a predistortion technique that first model the PA and then generates predistorted signal iteratively through a feedback configured structure to avoid using the noisy signal when performing the inverse model estimation. Unlike the indirect learning which estimates the postinverse of the PA, our predistortion is based on the preinverse of the PA. Both simulations and measurements show that utilizing the proposed predistortion can obtain adjacent channel power ratio (ACPR) improvement in wideband code division multiple access (WCDMA) signal test compared with the conventional memory polynomial predistortion based on indirect learning. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

面向TD-LTE通信系统的功放新模型

鉴于参数辨识过程简单的优点,记忆多项式模型已被广泛用于模拟功率放大器的行为。在记忆多项式功放模型的基础上,提出了一种面向TD-LTE通信系统的有理函数功放新模型。该模型通过基于两个记忆多项式模型的比率,在保证模拟小信号输入功放特性的同时还能够对大信号驱动下的功放行为进行准确预测,应用最小二乘法技术提取模型参数。利用NXP功放管设计Doherty功放电路,在ADS环境下导出强非线性输入输出信号数据实现模型性能验证。结果表明,提出的新模型性能优于传统的记忆多项式模型,具有更高精度,能够精确模拟功率放大器特性,对射频功放行为建模的研究与发展具有重要参考价值。     

Low complexity output generalized memory polynomial model for digital predistortion of RF power amplifiers

A novel output generalized memory polynomial (OGMP) behavioral model was proposed in this article, which is based on the previous output signal for digital predistortion (DPD) of power amplifiers (PA). Traditional MP or GMP model use polynomials of the previous input signal to characterize memory effect. Although the OGMP model use polynomials of the previous output signal to characterize memory effect. Using the previous output signal to characterize polynomials of the previous input signal, the number of coefficients will decrease. Measurement results show that the proposed OGMP model can achieve the similar effect with less coefficients. In detail, the complexity of OGMP model reduced by about 50% comparing with MP model. Compared with GMP model, the complexity of OGMP model reduced by about 60% with the similar effect.     

Volterra series‐based model for concurrent dual‐band power amplifier using dynamic memory depth

In this article, a dynamic dual‐band baseband equivalent Volterra (DDBE) model is proposed to compensate the nonlinear distortions of the concurrent dual‐band power amplifier (PA). The DDBE model is obtained by improving the discretized dual‐band baseband equivalent Volterra model which can describe the output characteristics of concurrent dual‐band PA completely in theory but is lack of practicability. Three simplification rules are proposed in the article, and the relevance between in‐band intermodulation and in‐band cross modulation is employed to simplify the establishment complexity of the model. Then the dynamic kernels are categorized into three groups, and based on this, DDBE models with different level dynamical kernels are derived. In addition, draw on the experience of single‐band PA behavioral model, even‐order kernels are introduced into DDBE models. Digital predistortion performances of a wideband PA, which works in concurrent dual‐band mode, are evaluated to verify the feasibility and advantages of the proposed model.