WCDMA系统中基于查找表的预失真技术的研究

在无线通信系统中,高功率放大器因其非线性,导致AM／PM效应使得微分相位、微分增益和互调失真变坏。高质量的通信系统设计应尽可能减小功率放大器的AM／PM效应。因此,针对宽带码分多址（WCDMA）功放非线性失真问题,采用一种基于查找表（LUT）的自适应预失真方法,改善功放的非线性失真。仿真表明．该方法能有效补偿放大器产生的AM—AM、AM-PM失真,并将功放的邻道功率泄漏比（ACPR）改善到30dB左右。     

一种基于双查找表自适应预失真结构的射频功率放大器线性化方法

同其它使用简单函数实现数据查找表索引的自适应预失真结构不同，本文采用专门的地址查找表来实现数据查找表索引，组成了双查找表结构的自适应预失真器。仿真结果表明，采用本文方法可以使得射频功率放大器对相邻信道的干扰得到25dB以上的性能改善。     

基于多项式与查找表的预失真技术研究

为补偿功率放大器固有的非线性,提出了一种新型的预失真器。该预失真器结合查找表和多项式两种常用的预失真方法实现,在查找表中存储分段低阶多项式系数,根据输入信号的幅度查表得到相应的多项式系数对输入信号进行预失真处理。仿真结果表明,该预失真器对互调失真（IMD）的改善优于多项式预失真器,能有效改善信号因功放非线性失真而导致的信号星座图扭曲及频谱再生,提高通信系统的性能。     

基于预失真技术的短波功率放大器线性化系统设计

本文提出了一种基于预失真技术的短波功率放大器线性化系统的设计方案,该方案采用查找表技术,且使用了一种独特的放大特性测量方法,具有很强的实用性。     

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。     

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.     

基于查找表的功放数字预失真方法

对功率放大器的失真原理进行了数学分析，描述了三阶，五阶互调的产生机理。介绍了基于查找表的数字预失真的两种算法，并对算法进行了仿真，分析了算法的有效性。     

功放的数字基带预失真技术研究

在射频通信中,大功率放大器是无线通信系统中的必要组成部分,它的非线性失真除了会造成信号带外的频谱扩展,引起临道干扰外,还会造成带内信号失真,提高误码率.因此,如何克服功放的非线性就成了通信领域的一个重要课题和研究热点.本文采用基于查找表的自适应算法,设计了自适应数字基带预失真器并进行了仿真和综合.结果表明自适应数字基带预失真方法可有效地提高功放线性度,从而提高系统性能.     

线性功放中数字预失真方法的实验研究

对数字预失真线性功放中两种主要的数字预失真方法:多项式拟合法和查找表构建预失真器法进行研究;首先针对两种方法所对应的不同预失真器结构,就预失真精度、算法复杂性、所需存储空间和自适应能力等进行分析对比;然后采用cdma2000调制信号源对两种方法预失真效果作ADS仿真分析和实验测试,验证了两种方法的可行性,并对两种方法预失真能力作进一步讨论;最后总结了两种预失真方法在功放线性化应用的优缺点和适用范围.     

数字基带预失真自适应算法改进与性能分析

文章首先介绍了数字基带预失真的自适应算法,针对基于多项式的实现方式分析比较了LMS和RLS算法,然后研究基于查找表的各种自适应算法,提出了一种改进的查找表预失真组合算法。仿真结果表明,这种算法可以很好地满足查找表预失真自适应环节的要求。     

WCDMA功放预失真发生器的研究

针对宽带码分多址(WCDMA)功放的非线性失真问题,提出了一种简单有效的解决方案,即通过预失真发生器对幅度-幅度(AM-AM)及幅度-相位(AM-PM)曲线进行调整,以补偿功放的非线性失真.这种方案主要是通过利用二极管的非线性特性设计出的预失真发生器来实现的.实验证明,将预失真发生器与WCDMA功放配合使用,能将功放的邻道功率泄漏比(ACPR)改善5 dB.     

A data predistortion technique with memory for QAM radio systems

The authors present an efficient data predistortion technique with memory for compensation of high-power amplifier (HPA) nonlinearities in digital microwave radio systems employing quadrature amplitude modulation (QAM) signal formats. A practical implementation method is described which trades off performance against complexity and which makes it possible to implement this kind of predistorter in 256-QAM, and higher-level QAM systems. Using the 16-, 64-, and 256-QAM signal constellations, it is shown that the proposed technique achieves a considerably higher performance than that of conventional memoryless data predistortion of the predistortion technique with memory based on finite-order inverses of nonlinear systems. Specifically, numerical results show that the proposed technique achieves a gain that is in excess of 2 dB over conventional memoryless data predistortion     

一种基于BOC信号的导航发射信道预失真技术

由于卫星导航系统中导航卫星发射信道的记忆非线性效应,使带宽受限的二进制偏移载波（BOC）调制信号失真加剧,导航系统性能将受到严重影响。针对这个问题,建立并分析了导航发射信道模型,提出将等效简化信道模型的主体部分（HPA及其前后置滤波器）等效为Wiener—Hammerstein模型的思想,同时设计了一种针对此模型的基于直接学习结构的自适应LMS预失真方案。仿真结果表明,该方案能有效抑制BOC信号的带外频谱扩展,优化星座图,可以很好地消除导航信道对BOC信号的失真影响,在卫星导航系统中有着重要的意义和良好的应用前景。     

Multi-order predistortion of power amplifiers using a second harmonic based technique

A novel multi-order predistortion linearizer is proposed to achieve independent control of the third- and fifth-order intermodulation products in high power amplifier. The approach is based on a combination of the second harmonic technique and the difference frequency technique. The second harmonic and difference frequency terms are generated using an envelope detector and two frequency multipliers. The RF predistorter has the advantage of low insertion loss and the requirement of a short delay line. Experimental results demonstrate an adjacent channel power ratio (ACPR) reduction of 11 dB for W-CDMA, at 2140 MHz.     

WCDMA系统中结合导频与信息码的信道估计方法

研究了快衰落环境中第三代移动通信空中接口WCDMA(FDD),基于时分复用的导频信号辅助衰落信道下的信道估计。提出了同时根据导频信号及数据信号估计信道参数的信道估计方法,该方法将信道估计分为根据导频信号和数据信号两部分进行并由其加权合并完成。计算了最小均方误差下的合并系数。仿真结果表明该方法能快速跟踪信道的衰落,有效地估计出各时隙中数据段的信道参数。利用该算法,尤其在高速运动情况下,接收机的性能可得到显著的改善。     

WCDMA系统中基于多普勒频移估计的信道估计方法

Rake接收机是CDMA系统抗多径的有效手段，信道估计对其性能有很大的影响。传统方法是利用连续多个时隙的导频段估计出的信道参数，再对估计值进行平均。这种固定平均的方法不适合3G系统信道变化范围大的环境。本文提出了直接利用每个导频段的信道参数的包络来估计最大多普勒频移，再运用指数平滑法来调整各被估计时隙的权值的信道估计方法。仿真结果表明，该方法能准确有效地估计出信道参数，改善系统性能。     

An improved look-up table predistortion technique for HPA with memory effects in OFDM systems

It is well known that HPAs (High Power Amplifiers) are inherently nonlinear devices and many researches have focused on the predistortion for memoryless HPAs. However, memory effects of HPAs can no longer be ignored when communication systems have wider bandwidth. Memoryless predistortion techniques proposed previously seldom have satisfactory effectiveness for typical wideband applications such as OFDM (Orthogonal Frequency Division Multiplexing) systems. In this paper, an improved adaptive predistortion method called 2D LUT (2-dimension look-up table) with different accuracy levels is presented to linearize HPAs with memory effects. Simulation and experimental results show that 2D LUT implements excellent performance in mitigating the signal deterioration caused by memory effects, both rectifies the signal constellation distortion and suppresses the spectrum emission. Large scale matrix computation is also avoidable in these adaptive algorithms, which makes them feasible when a real-time system is necessary.     

Optimum design of a predistortion RF power amplifier for multicarrier WCDMA applications

This paper provides a design guide for optimum design of an RF power amplifier with a predistortion linearizer. For a two-tone signal, three performance degradation factors, higher order terms, amplitude, and phase mismatches are analyzed quantitatively. The results are implemented to the design of optimized predistortion power amplifier for a WCDMA signal application. For the experiments, a 2.4-GHz class-AB power amplifier is fabricated using an LDMOSFET with a 30-W peak envelope power. A simple third-order predistorter is used to measure the relative phases of the harmonics, as well as to linearize the amplifier. The performance of the optimized predistortion power amplifier is excellent for an IS-95 code-division-multiple-access signal. Finally, a method for reducing the memory effects of the amplifier is devised to get a good cancellation performance for a wide-band signal, and the performance degradation caused by the memory effects is analyzed. For a forward-link four-carrier WCDMA signal, the predistortion power amplifier delivers an adjacent channel leakage ratio of -46 dBc at a 4-W average output power with a cancellation of 13.4 dB.     

Adaptive digital/RF predistortion using a nonuniform LUT indexing function with built-in dependence on the amplifier nonlinearity

This paper reports on an integrated adaptive digital/RF predistorter using a nonuniform spaced lookup table (LUT) and in-phase/quadrature (I/Q) RF vector multiplier (VM). The LUT contents are directly deduced from the baseband input and output signals of the power amplifier (PA). In addition, a new nonlinear indexing function of the predistortion LUT with built-in dependence on the PA nonlinearity is proposed. This function is made to be robust to the input signal statistics. A comparison of this new indexation method with conventional approaches, namely, power and logarithmic power indexation functions, is carried out. The superiority of the proposed scheme is demonstrated in particular for class-AB amplifiers where the gain of the PA varies over the whole input range of the drive signal. The measured output spectrum of a linearized 90-W peak lateral double-diffused metal-oxide-semiconductor PA reveals a significant reduction of the power emission at the adjacent channels of approximately 15 dB under IS95, single-carrier, and multicarrier wide-band code-division multiple-access signals. The experimental evaluation is carried out using an RF/digital predistorter prototype that mainly includes an envelope detector, a linear I/Q RF VM, field-programmable gate array and digital signal processor, and fast analog/digital and digital/analog converters.