Signal Design and Optimization for Wireless Communication Systems Employing Nonlinear RF Energy Harvesting

无线系统的节点需要能量来传输通信信号以及执行侦听和处理任务。传统上，这种能量一直由电线或电池提供。然而，电线严重限制了节点的移动性，电池需要手动充电或更换。这两种解决方案都不适合具有许多小节点或无法访问的节点的应用(例如，部署在危险地形中的传感器、物联网设备等)。对于这样的应用，射频(RF)无线功率传输作为向无线节点提供能量的替代解决方案已经引起了极大的关注。为了最大限度地提高依赖于射频能量采集的无线网络的性能，需要对用于无线通信和无线能量传输的信号进行联合设计。几乎所有关于这一主题的现有工作都假设接收到的射频功率与收获的能量之间存在线性关系。然而，这种大大简化了设计和分析的假设是不合理的，因为能量采集电路本身就是非线性的。因此，基于简单的线性能量收集模型设计的射频能量收集的无线通信系统可能会遭受较大的性能损失。使用非线性射频能量采集电路的无线通信系统的信号设计和优化是本项目的重点，是具有很强的实用性和理论挑战性的问题。在我们前期工作的基础上，在这个项目中，我们将为使用多个二极管的能量采集电路的输入输出特性开发精确的、数学上易于处理的非线性模型。利用这些模型和现有的单二极管能量采集电路的非线性模型，我们将设计和优化具有射频能量采集节点的不同基本无线网络架构的发射波形，包括多用户系统、多输入多输出系统和基于中继的系统。对于每种情况，将研究最优信号设计，并将其与次优的、可能不太复杂的解决方案进行比较，以评估无线功率传输和无线信息传输之间的内在权衡，为实际系统的设计制定指导方针，并评估无线功率传输对未来无线通信网络的潜力。

The nodes of wireless systems require energy for transmitting communication signals and for performing sensing and processing tasks. Traditionally, this energy has been supplied by electrical wires or batteries. However, wires severely constrain the mobility of the nodes and batteries require manual recharging or replacement. Both solutions are unsuitable for applications with many small or inaccessible nodes (e.g. sensors deployed in hazardous terrain, Internet-of-Things devices, etc.). For such applications, radio frequency (RF) wireless power transfer has gained significant attention as an alternative solution for providing energy to wireless nodes. To maximize the performance of wireless networks relying on RF energy harvesting, a joint design of the signals used for wireless communication and wireless power transfer is needed. Almost all of the existing work on this topic assumes a linear relationship between the received RF power and the harvested energy. However, this assumption, which considerably simplifies design and analysis, is not justified as energy harvesting circuits are inherently nonlinear. Hence, wireless communication systems with RF energy harvesting designed based on a simplistic linear energy harvesting model may suffer from large losses in performance. The signal design and optimization for wireless communication systems employing nonlinear RF energy harvesting circuits, which are the focus of this project, are highly practical and theoretically challenging problems. Building upon our preliminary work, in this project, we will develop accurate yet mathematically tractable nonlinear models for the input-output characteristic of energy harvesting circuits employing multiple diodes. Using these models and the existing nonlinear models for single diode energy harvesting circuits, we will design and optimize the transmit waveforms for different fundamental wireless network architectures with RF energy harvesting nodes, including multiuser systems, multiple-input multiple-output systems, and relay-based systems. For each case, the optimal signal design will be investigated and compared with suboptimal, possibly less complex solutions in order to evaluate the inherent tradeoff between wireless power transfer and wireless information transfer, to develop guidelines for the design of practical systems, and to evaluate the potential of wireless power transfer for future wireless communication networks.