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1. Reconfigurable Radios Employing Ferroelectrics: Recent Progress on Reconfigurable RF Acoustic Devices Based on Thin-Film Ferroelectric Barium Strontium Titanate

   Milad Koohi, Amir Mortazawi ( May 2020 , IEEE microwave magazine)

   null (Ed.)

   Wireless communication has become an integral part of our lives, continuously improving the quality of our everyday activities. A multitude of functionalities are offered by recent generations of mobile phones, resulting in a significant adoption of wireless devices and a growth in data traffic, as reported by Ericsson [1] in Figure 1. To accommodate consumers' continuous demands for high data rates, the number of frequency bands allocated for communication by governments across the world has also steadily increased. Furthermore, new technologies, such as carrier aggregation and multiple-input/multiple-output have been developed. Today's mobile devices are capable of supporting numerous wireless technologies (i.e., Wi-Fi, Bluetooth, GPS, 3G, 4G, and others), each having its own designated frequency bands of operation. Bandpass filters, multiplexers, and switchplexers in RF transceivers are essential for the coexistence of different wireless technologies and play a vital role in efficient spectrum usage. Current mobile devices contain many bandpass filters and switches to select the frequency band of interest, based on the desired mode of operation, as shown in Figure 2. This figure presents a schematic of a generic RF front end for a typical mobile device, where a separate module is allocated for the filters. Each generation of mobile devices demands a larger number of RF filters and switches, and, with the transition toward 5G and its corresponding frequency bands, the larger number of required filters will only add to the challenges associated with cell-phone RF front-end design. 

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2. Non-volatile RF and mm-wave Switches Based on Monolayer hBN

   https://doi.org/10.1109/IEDM19573.2019.8993470  

   Kim, Myungsoo ; Pallecchi, Emiliano ; Ge, Ruijing ; Wu, Xiaohan ; Avramovic, Vanessa ; Okada, Etienne ; Lee, Jack C. ; Happy, Henri ; Akinwande, Deji ( December 2019 , IEEE IEDM)

   Non-volatile radio-frequency (RF) switches based on hexagonal boron nitride (hBN) are realized for the first time with low insertion loss (≤ 0.2 dB) and high isolation (≥ 15 dB) up to 110 GHz. Crystalline hBN enables the thinnest RF switch device with a single monolayer (~0.33 nm) as the memory layer owing to its robust layered structure. It affords ~20 dBm power handling, 10 dB higher compared to MoS 2 switches due to its wider bandgap (~6 eV). Importantly, operating frequencies cover the RF, 5G, and mm-wave bands, making this a promising low-power switch for diverse communication and connectivity front-end systems. Compared to other switch technologies based on MEMS, memristor, and phase-change memory (PCM), hBN switches offer a promising combination of non-volatility, nanosecond switching, power handling, high figure-of-merit cutoff frequency (43 THz), and heater-less ambient integration. Our pioneering work suggests that atomically-thin nanomaterials can be good device candidates for 5G and beyond. 

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3. Blind source separation with integrated photonics and reduced dimensional statistics

   https://doi.org/10.1364/OL.409474  

   Ma, Philip_Y ; Tait, Alexander_N ; Zhang, Weipeng ; Karahan, Emir_Ali ; Ferreira_de_Lima, Thomas ; Huang, Chaoran ; Shastri, Bhavin_J ; Prucnal, Paul_R ( November 2020 , Optics Letters)

   Microwave communications have witnessed an incipient proliferation of multi-antenna and opportunistic technologies in the wake of an ever-growing demand for spectrum resources, while facing increasingly difficult network management over widespread channel interference and heterogeneous wireless broadcasting. Radio frequency (RF) blind source separation (BSS) is a powerful technique for demixing mixtures of unknown signals with minimal assumptions, but relies on frequency dependent RF electronics and prior knowledge of the target frequency band. We propose photonic BSS with unparalleled frequency agility supported by the tremendous bandwidths of photonic channels and devices. Specifically, our approach adopts an RF photonic front-end to process RF signals at various frequency bands within the same array of integrated microring resonators, and implements a novel two-step photonic BSS pipeline to reconstruct source identities from the reduced dimensional statistics of front-end output. We verify the feasibility and robustness of our approach by performing the first proof-of-concept photonic BSS experiments on mixed-over-the-air RF signals across multiple frequency bands. The proposed technique lays the groundwork for further research in interference cancellation, radio communications, and photonic information processing.

    

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4. On the wireless virtualization with QoE constraints

   https://doi.org/10.1002/ett.3573  

   Rawat, Danda B. ; Alsulami, Bassma Saleh ; Chaudhary, Vijay ( February 2019 , Transactions on Emerging Telecommunications Technologies)

   Wireless virtualization is emerging as a new paradigm to improve wireless spectrum utilization by subleasing radio frequency (RF) channels through slicing. This paper investigates wireless virtualization where wireless resources for virtual wireless networks adapted based on availability of leasable RF slices as well as the demands from the users of virtual wireless networks. The user utilities are subject to quality‐of‐experience requirements such as coverage, rate, mobility, and delay requirements. With the help of software defined network controller, wireless infrastructure providers (WIPs) slice their RF bands to sublease those slices to mobile virtual network operators (MVNOs). In wireless virtualization, MVNOs work as independent service provides, and thus, the end users negotiate directly to MVNOs regardless of WIPs used behind the scene (this concept is analogous to the Uber being a taxi company without owning any vehicles). The performance of the proposed approach is evaluated with the help of numerical results obtained from simulations by using different metrics such as percentage of RF band of WIP, outage probability, and data rate.

    

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5. Mobile near-field terahertz communications for 6G and 7G networks: Research challenges

   https://doi.org/10.3389/frcmn.2023.1151324  

   Petrov, Vitaly ; Bodet, Duschia ; Singh, Arjun ( March 2023 , Frontiers in Communications and Networks)

   Following the current development of the wireless technology landscape, and with respect to the constant growth in user demands, it is inevitable that next-generation mobile wireless networks will use new frequency bands located in the sub-terahertz and terahertz (THz) spectrum to complement the existing microwave and millimeter wave (mmWave) channels. The feasibility of point-to-point stationary THz communication links has already been experimentally demonstrated. To build upon this breakthrough, one of the pressing research targets is making THz communication systems truly mobile. Achieving this target is especially complicated because mobile THz wireless systems (including WLANs and even cellular access) will often operate in the near-field due to the very large (even though physically small) electrical size of the high-gain antenna systems required for making high-rate communication links feasible at such frequencies. This perspective article presents several key prospective research challenges envisioned on the way to designing efficient mobile near-field THz wireless access as a part of 6G and 7G wireless landscapes. 

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