ITR: Characterization and Linearization of Nonlinear Memory Effects in RF Power Amplifiers

现代移动通信系统努力使系统内的容量最大化。系统处理多个用户的能力受到相邻信道干扰（ACI）的不利影响。ACI是由发射机功率放大器（PA）产生的非线性失真造成的。这对于蜂窝基础设施中的高功率基站pa来说尤其成问题。这种失真会产生带外信号，干扰其他用户的接收。因此，ACI有效地提高了噪声底限，迫使这些用户降低比特率和/或增加传输功率。随着用于互联网接入的中速数据服务被引入蜂窝系统，对服务的容量和质量提出了更高的要求。由于这些原因，最小化ACI是非常重要的，这需要在基站基础设施中进行PA线性化。市售的最先进的基站PAs采用前馈线性化。虽然这种方法在提高ACI方面是有效的，但该体系结构需要额外的组件以及高功率组合。这些增加的元件，以及它们在直流和射频功率中引入的损耗，往往会使基于前馈方法的PAs成本高昂且效率低下。预失真线性化是另一种线性化方法。这种方法比前馈线性化更具成本效益，因为信号处理是数字完成的，并且PA之后没有浪费功率的组件。然而，预失真的性能通常不如前馈线性化，因为必须提取接近完美的放大器模型，并制定预失真器模型来抵消失真机制。当前模型存在缺陷的一个领域是描述记忆效应。文献中已经对无记忆预失真进行了深入的研究，但是对于高峰均比信号，如多载波CDMA或OFDM信号，会产生自热效应，在失真中产生延迟响应，表现为记忆效应。一般来说，高功率放大器，例如用于基站的放大器，比用于低功率移动设备的放大器更容易受到记忆效应的影响。本提案将概述一个研究计划，该计划将调查PA记忆效应的建模，以及表现出这种效应的PA的线性化。作者提出了一项研究计划，该计划将开发PA表征和建模的新方法，并推进最先进的预失真线性化，以达到或超过以前仅使用昂贵且低效的前馈技术所见的性能水平。

Modern mobile communication systems strive to maximize capacity within the system. The capacity of the system to handle multiple subscribers is adversely affected by adjacent channel interference (ACI). ACI results from nonlinear distortion created by the transmitter power amplifier (PA). This is especially problematic for high power base station PAs within the cellular infrastructure. Such distortion produces out-of-band signals that interfere with other subscribers' reception. Thus ACI, effectively raises the noise floor forcing lower bit rates and/or increased transmit power for those subscribers. As medium rate data services for internet access are being introduced into the cellular systems, higher demands are being placed on both capacity and quality of service. For these reasons, minimization of ACI, which requires PA linearization in basestation infrastructure, is of great importance.Commercially available state-of-the-art base station PAs use feed-forward linearization. While this method is effective in improving ACI, the architecture needs additional components as well as a high power combining. These added components, and the losses they introduce in both DC and RF power, tend to make PAs based on the feed-forward method both costly and inefficient.Predistortion linearization is another method of linearization. This approach is more cost effective than feed-forward linearization, because the signal processing is done digitally, and there are no components following the PA that waste power. However, the performance of predistortion is generally not as good as feed-forward linearization, because a near perfect model of the amplifier must be extracted and a predistorter model formulated to counteract the distortion mechanisms. One area in which current models are deficient is in characterizing memory effects. Memoryless predistortion has been thoroughly investigated in the literature, but for high peak-to-average signals, such as multicarrier CDMA or OFDM signals, self-heating effects arise, creating delay responses in the distortion that manifest themselves as memory effects. In general, higher power amplifiers, such as those used in basestations, are more susceptible to memory effects than those used in lower power mobile equipment.This proposal will outline a research program that will investigate modeling of PA memory effects, as well as linearization of PAs that exhibit such effects. The authors propose a research program that will develop new methods in PA characterization and modeling, as well as advance the state-of-the-art in predistortion linearization to achieve or exceed performance levels previously seen only using costly and inefficient feed-forward techniques.