As 5G New Radio (NR) is being rolled out, research effort is being focused on the evolution of what is to come in the post-5G era. In order to meet the diverse requirements of future wireless communication in terms of increased capacity and reduced latency, technologies such as distributed massive Multiple-Input Multiple-Output (MIMO), sub-millimeter wave and Tera-hertz spectrum become technology components of interest. Furthermore, to meet the demands on connectivity anywhere at anytime, non-terrestrial satellite networks will be needed, which brings about challenges both in terms of implementation as well as deployment. Finally, scaling up massive Internet-of-Things (IoT), energy harvesting and Simultaneous Wireless Information and Power Transfer (SWIPT) is foreseen to become important enablers when deploying a large amount of small, low-power radios. In this paper, we will discuss some of the important opportunities these technologies bring, and the challenges faced by the microwave and wireless communication communities.

This invited paper presents potential solutions for tackling some of the main underlying challenges toward developing sustainable Internet-of-things (IoT) devices with a focus on eco-friendly manufacturing, sustainable powering, and wireless connectivity for next-generation IoT devices. The diverse applications of IoT systems, such as smart cities, wearable devices, self-driving cars, and industrial automation, are driving up the number of IoT systems at an unprecedented rate. In recent years, the rapidly-increasing number of IoT devices and the diverse application-specific system requirements have resulted in a paradigm shift in manufacturing processes, powering methods, and wireless connectivity solutions. The traditional cloud-centering IoT systems are moving toward distributed intelligence schemes that impose strict requirements on IoT devices, e.g., operating range, latency, and reliability. In this article, we provide an overview of hardware-related research trends and application use cases of emerging IoT systems and highlight the enabling technologies of next-generation IoT. We review eco-friendly manufacturing for next-generation IoT devices, present alternative biodegradable and eco-friendly options to replace existing materials, and discuss sustainable powering IoT devices by exploiting energy harvesting and wireless power transfer. Finally, we present (ultra-)low-power wireless connectivity solutions that meet the stringent energy efficiency and data rate requirements of future IoT systems that are compatible with a batteryless operation.

Wireless power transmission (WPT) is an emerging technology that is gaining increased visibility in recent years. Efficient WPT circuits, systems and strategies can address a large group of applications spanning from batteryless systems, battery-free sensors, passive RF identification, near-field communications, and many others. WPT is a fundamental enabling technology of the Internet of Things concept, as well as machine-to-machine communications, since it minimizes the use of batteries and eliminates wired power connections. WPT technology brings together RF and dc circuit and system designers with different backgrounds on circuit design, novel materials and applications, and regulatory issues, forming a cross disciplinary team in order to achieve an efficient transmission of power over the air interface. This paper aims to present WPT technology in an integrated way, addressing state-of-the-art and challenges, and to discuss future R&D perspectives summarizing recent activities in Europe.

In this article, the different challenges and open issues regarding WPT systems have been presented considering both the transmitting and receiving ends. The challenges in the receiving side include the accurate modeling of the rectifying elements, the adequate selection of the rectifier topology, and the joint optimization of antenna and rectifier circuit. The challenges in the transmitting side are mainly in the improvement of the dc-to-RF conversion efficiency and in the selection of the optimum transmitted signal waveform. The final goal of most of these challenges is to take advantage of the nonlinear nature of the rectifying elements in order to maximize the RF-to-dc conversion efficiency in the receiving end of WPT systems.

This paper presents a comprehensive analysis of nonlinear intermodulation distortion (IMD) behavior in RF CMOS power amplifiers (PAs). Separate analyses are presented for small- and large-signal operation regimes. Especially, a new, simple, large-signal behavioral IMD analysis method is presented that allows the mechanisms dominant for IMD generation to be identified and their individual contributions to be studied. By combining these analyses, typical IMD versus input power characteristics of MOSFET PAs can be predicted and understood for different classes of operation. Various measurements made on a 950-MHz RF CMOS PA are used to demonstrate typical behavior and validate the proposed theory. Prediction of IMD using a standard CMOS transistor model is also evaluated and is shown to give good agreement with the measurements.