射频功放预失真技术的研究

发布时间：2018-10-11 07:00

【摘要】：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,引起邻道干扰外,还会造成带内信号失真,提高误码率。本文对高功率放大器的线性化技术进行了系统的研究。首先介绍了功率放大器的非线性特性和常见的各种线性化技术,其中数字基带预失真技术是校正效果最好、最容易实现和最具发展潜力的线性化技术。在数字基带预失真技术中,对当前出现的各种预失真方案进行了分析总结,并分别提出了针对无记忆功放和有记忆功放的预失真方法。在无记忆功放预失真技术中着重研究了查找表预失真技术与预失真自适应算法,文中分别使用弦截法与牛顿迭代法自适应算法结合查找表预失真技术构建了预失真系统并仿真验证了两种不同算法的性能。然而弦截法的收敛精度不够高、稳态误差比较大,针对此点不足文中使用插值法代替差商法求导方式对弦截法进行了改进,仿真验证该改进算法可以在原弦截法基础上使得信号带外扩展降低6dB。在目前的通信系统中,OFDM等宽带信号的应用使得放大器的记忆效应不能忽略,所以文章对记忆功放的预失真技术也进行了详细的研究,首先介绍了记忆功放的行为模型,针对不同的模型介绍了两种不同的记忆功放预失真系统,记忆多项式预失真系统与Hammerstein预失真系统。并对Hammerstein预失真系统以及递归最小二乘法自适应算法进行了重点研究,递归最小二乘算法有着非常好的收敛特性,然而其固定的遗忘因子限制了其性能的进一步提高,对此文章引入了可变遗忘因子的理念,在算法复杂度稍有增加的前提下可使的遗忘因子能够随着系统特性的变化而变化,这样就使得改进后算法不仅具有很快的收敛速度而且能够保持很小的稳态误差。在信号功率谱密度的仿真中可使得带外扩展进一步降低7dB之多。
[Abstract]:Power amplifier is a necessary part of wireless communication system. Its nonlinear distortion will not only cause spectrum spread out of the band and cause adjacent channel interference, but also cause in-band signal distortion and improve bit error rate (BER). The linearization technology of high power amplifier is studied systematically in this paper. Firstly, the nonlinear characteristics of power amplifier and various linearization techniques are introduced. Among them, digital baseband predistortion is the most effective, easy to realize and the most potential linearization technology. In the digital baseband predistortion technology, the current predistortion schemes are analyzed and summarized, and the predistortion methods for memoryless and memorized power amplifiers are proposed respectively. In the memoryless power amplifier predistortion technique, the look-up table predistortion technique and the predistortion adaptive algorithm are studied. In this paper, the predistortion system is constructed by using the chord truncation method and the Newton iterative adaptive algorithm combined with the look-up table predistortion technique, and the performance of the two different algorithms is verified by simulation. However, the convergence accuracy of the chord truncation method is not high enough, and the steady-state error is relatively large. The interpolation method is used instead of the differential quotient method to solve the problem in this paper. The simulation results show that the improved algorithm can reduce the out-of-band spread of the signal by 6 dB on the basis of the original chord truncation method. In the present communication system, the memory effect of amplifier can not be ignored because of the application of wideband signal such as OFDM, so the predistortion technology of memory power amplifier is studied in detail in this paper. Firstly, the behavior model of memory power amplifier is introduced. Two kinds of memory amplifier predistortion system, memory polynomial predistortion system and Hammerstein predistortion system are introduced for different models. The Hammerstein predistortion system and the recursive least square adaptive algorithm are studied in detail. The recursive least squares algorithm has a very good convergence property, but its fixed forgetting factor limits the performance of the algorithm. In this paper, the idea of variable forgetting factor is introduced, and the forgetting factor can be changed with the change of system characteristics when the complexity of the algorithm is slightly increased. In this way, the improved algorithm not only has a fast convergence rate, but also can maintain a very small steady-state error. In the simulation of signal power spectral density, the out-of-band spread can further reduce the number of 7dB.
【学位授予单位】：辽宁工程技术大学
【学位级别】：硕士
【学位授予年份】：2011
【分类号】：TN722.75

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