适用于宽带功率放大器的自适应数字预失真技术研究

【作者】 王栋；

【导师】 王晶琦；

【作者基本信息】 南京理工大学 ， 电磁场与微波技术， 2017， 硕士

【摘要】 随着通信频带的扩展,通信系统对功率放大器在线性度和效率上提出了更高的要求。数字预失真技术是补偿宽带功率放大器非线性特性和记忆效应最有效的方式。近年来,宽带功率放大器的数字预失真技术受到了国内外学者的广泛关注,开展针对其特性的预失真技术研究迫在眉睫。本文主要研究适用于宽带功率放大器的功放建模和预失真技术。首先介绍了功率放大器行为模型,重点介绍了正交多项式模型及其对强记忆深度宽带功放模型的改善作用;其次介绍了功放数字预失真技术,着重介绍了预失真器的参数提取算法,包括最小二乘法(Least Squares,LS)、递归最小二乘法(Recursive Least Squares,RLS)、最小均方算法(Least Mean Squares,LMS)及其改进算法,首次提出并分析了输入矩阵条件数对RLS算法的影响,证明了使用基于正交多项式模型的功放预失真器,进行RLS参数估计,可避免因宽带功放强记忆效应导致的输入矩阵相关性上升问题,提高了建模精度;然后讨论了 RLS-LMS结合算法,提出了一种基于多模型数据融合的新型参数提取算法,将收敛后的RLS解作为静态参数,LMS解作为动态参数,利用最大似然函数实现数据融合,最终输出适用于宽带功放预失真器的高精度参数估计值。仿真结果表明,均方根误差(Root Mean Square Error,RMSE)降低了 4.2dB,融合算法有效提高了预失真器的收敛速度和精度;文章最后介绍了基于正交多项式模型和数据融合参数提取算法的宽带功放数字预失真系统方案,对其进行仿真测试,验证了其有效性,并最终通过实验验证平台对其进行了性能测试,实测激励信号为100MHz带宽OFDM信号,功放为工作频率1.95GHz的Doherty宽带功放,实测结果表明使用常规预失真方案,功放输出ACPR可从-31.29dBc改善至-41.16dBc,而使用新型预失真方案,可将功放输出ACPR进一步改善至-44.37dBc,验证了该方案的有效性。更多还原

【Abstract】 Digital predistortion is the most effective way to compensate the nonlinearity and memory effects of wideband power amplifiers.In recent years,the digital pre-distortion technology of wideband power amplifier has gained great attention of scholars all over the world.Therefore,it’s imminent to carry out the pre-distortion technology research for its characteristic.This paper focuses on the power amplifier modeling and predistortion techniques applicable to wideband power amplifiers.Firstly,the behavior model of power amplifier is introduced.The orthogonal polynomial model and its improvement for the deep memory power amplifier model are demonstrated.Secondly,the digital predistortion technique for power amplifier and the parameter extraction algorithms for the pre-distorter,such as Least Squares(LS),Recursive Least Squares(RLS),Least Mean Squares(LMS),are presented.It is provedthat by using the orthogonal polynomial model,the conditional number increasing of the input matrix in RLS algorithm,caused by the memory effect of the broadband power amplifier,can be effectively avoided.Then a new parameter extraction algorithm based on multi-model data fusion method is proposed,which using the maximum likelihood function to achieve data fusion,and is suitable for wideband power amplifier.Simulation results show that the root mean square error(RMSE)is reduced by 4.2dB.At last,a brand new digital predistortion scheme for wideband power amplifier based on orthogonal polynomial model and data fusion parameter extraction algorithm is presented.The simulation results show that the proposed scheme is effective and the performance of the system is verified by the experimental verification platform.The bandwidth of excitation OFDM signal used for measurement is 100MHz,and the test power amplifier is a 1.95GHz Doherty wideband power amplifier.Measurement results show that the output ACPR can be improved from-31.29dBc-41.16dBc by using normal predistortion scheme,meanwhile,by employing the new predistortion scheme,the output ACPR of power amplifier can be further improved to-44.37dBc.更多还原