Sony (Sweden)

Low-cost, resource-constrained, mainte-nance-free, and energy-harvesting (EH) Internet of Things (IoT) devices, referred to as zero-energy devices (ZEDs), are rapidly attracting attention from industry and academia due to their myriad of applications. To date, such devices remain primar-ily unsupported by modern IoT connectivity solutions due to their intrinsic fabrication, hardware, deployment, and operation limitations, while lacking clarity on their key technical enablers and prospects. Herein, we address this by discussing the main characteristics and enabling technologies of ZEDs within the next generation of mobile networks, specifically focusing on unconventional EH sources, multi-source EH, power management, energy storage solutions, manufacturing material and practices, backscattering, and low-complexity receivers. Moreover, we highlight the need for lightweight and energy-aware computing, communication, and scheduling protocols, while discussing potential approaches related to tiny machine learning (TinyML), duty cycling, and infrastructure enablers like radio frequency wire-less power transfer and wake-up protocols. Chal-lenging aspects and open research directions are identified and discussed in all the cases. Finally, we showcase an experimental ZED proof-of-con-cept related to ambient cellular backscattering.

As 6G emerges, cellular systems are envisioned to integrate sensing with communication capabilities, leading to multi-faceted communication and sensing (JCAS). This paper presents a comprehensive cross-layer overview of the Hexa-X-II project's endeavors in JCAS, aligning 6G use cases with service requirements and pinpointing distinct scenarios that bridge communication and sensing. This work relates to these scenarios through the lens of the cross-layer physical and networking domains, covering models, deployments, resource allocation, storage challenges, computational constraints, interfaces, and innovative functions.

Recent advances in sensor technology are expected to lead to a greater use of wireless sensor networks (WSNs) in industry, logistics, healthcare, etc. On the other hand, advances in artificial intelligence (AI), machine learning (ML), and deep learning (DL) are becoming dominant solutions for processing large amounts of data from edge-synthesized heterogeneous sensors and drawing accurate conclusions with better understanding of the situation. Integration of the two areas WSN and AI has resulted in more accurate measurements, context-aware analysis and prediction useful for smart sensing applications. In this paper, a comprehensive overview of the latest developments in context-aware intelligent systems using sensor technology is provided. In addition, it also discusses the areas in which they are used, related challenges, motivations for adopting AI solutions, focusing on edge computing, i.e., sensor and AI techniques, along with analysis of existing research gaps. Another contribution of this study is the use of a semantic-aware approach to extract survey-relevant subjects. The latter specifically identifies eleven main research topics supported by the articles included in the work. These are analyzed from various angles to answer five main research questions. Finally, potential future research directions are also discussed.

Reflective reconfigurable intelligent surface (RIS) technology is regarded as an innovative, cost- and power-effective solution that aims at influencing the wireless channel through controlled scattering. The technology can be realized by using metamaterials and/or resonant elements that scatter electromagnetic waves with a configurable phase shift. Most of the previous work on beamforming techniques for RIS assumes ideal hardware and, thus, continuous phase shifts. However, hardware constraints limit the phase shift resolution, manifested into the amount of discrete phase shifts that can be configured into each RIS element. This paper aims to offer a discrete phase shift beamforming algorithm for reflective RISs that targets minimization of the quantization error resulting from discretization of continuous phase shifts. The beamforming solution proves to be optimal under perfect channel knowledge for any discrete set of uniformly distributed phase shifts. The required complexity to find the optimal beamforming vector for our approach is found to be linear with the number of RIS elements, the minimum needed to obtain optimal results. Simulated behavior is validated by measurements, showing robustness against angle misalignments and distance variations.

In this paper, a method to reduce the metal-frame obstruction to the radiation of endfire mm-wave arrays with wideband operation is presented. A 7 mm-wide frame is chosen to emulate the current commercial bezel thickness. Slots of three different sizes are etched on the frame to ensure the wideband endfire behavior. The proposed solution allows the mm-wave array to radiate through the metal frame from 27.27 GHz to 37.43 GHz, which corresponds to a fractional bandwidth of 31.4 %. The presented design is compared with the free space mm-array and with the array with a normal unmodified frame. The results show that the proposed solution provides similar performance to the free space counterpart, while a 15 dBi gain improvement of the antenna array comparing to a normal frame is obtained. A good beam-steering performance can also be supported with the proposed slotted-frame structure of the mm-wave array.

The exposure to electromagnetic field (EMF) from phased antenna arrays integrated into wireless devices operating at the millimeter-wave (mmWave) part of the spectrum should be evaluated in terms of power density (PD). Two aspects related to test reduction when evaluating the radiation from handset antenna arrays are considered. First, the peak PD decay with the distance from 4-elements antenna arrays is analyzed. The focus is on finding the size of the volume around the handset beyond which the PD is so low that its measurement can be omitted. By limiting the measurements to the inside of the exposed volume, the total test time is reduced. Antenna configurations that are representative for current trends in handset technology are chosen: arrays of half-wavelength dipoles and patches operating at 26 GHz, 28 GHz, and 39 GHz, and having inter-element spacing either 0.5λ or 0.9λ. The second investigation aims to determine the critical distance between two 4-elements phased arrays for which the peak PD when the two arrays operate simultaneously is similar to the peak PD when only one array operates at the time. The study shows the configurations for which the number of tests can be reduced while having sufficiently accurate results.

Massive multiple-input multiple-out (MIMO) technology is vital in millimeter-wave (mmWave) bands to obtain large array gains. However, there are practical challenges, such as high hardware cost and power consumption in such systems. A promising solution to these problems is to adopt a hybrid beamforming architecture. This architecture has a much lower number of transceiver (TRx) chains than the total antenna number, resulting in cost- and energy-efficient systems. In this paper, we present a real-time mmWave (28GHz) massive MIMO testbed with hybrid beamforming. This testbed has a 64-antenna/16-TRx unit for beam-selection, which can be expanded to larger array sizes in a modular way. For testing everything from baseband processing algorithms to scheduling and beam-selection in real propagation environments, we extend the capability of an existing 100-antenna/100-TRx massive MIMO testbed (below 6GHz), built upon software-defined radio technology, to a flexible mmWave massive MIMO system.

The use of ultra-low power wake-up receivers (WuRx) can significantly reduce idle listening energy cost. To tailor a WuRx scheme to orthogonal frequency division multiplexing (OFDM) based systems, such as LTE-MTC or IEEE 802.11, the wake-up signal (WUS) also needs to follow OFDM principles to avoid interfering with other transmissions in the same shared bandwidth. Here, we address this particular issue and propose an approach where the OFDM transmitter is modified to also transmit WUSs designed for non-coherent low-power WuRxs, on a subset of the carriers, thus embedding the WUS correctly and ensuring orthogonality. The approach is evaluated for different system parameters and channel conditions. Its applicability across a wide range of OFDM-based systems is examined.

This paper presents a new SIW horn antenna with high performance in the mm-wave bands for the next generation mobile devices. The proposed antenna is integrated in a double layer of Rogers RO4003C substrate and requires a clearance of only 3 mm. Air vias are etched in the substrate in a specific portion of the horn aperture, in order to correct the phase of the electromagnetic wave and allow the beam pointing in the desired direction. Moreover, a tapered ladder transition is placed at the horn aperture to improve the impedance matching and enhance the radiation performance. Simulation results prove that the 6 dB bandwidth is wider than 40 GHz in the frequency range 24-64 GHz. In particular, the same beam pointing is guaranteed over the whole bandwidth with realized gain of 6.4, 8.5 and 8.7 dBi at 28, 38 and 60 GHz respectively. Simulations including two symmetric elements pointing opposite directions and a central element show that the angle of 90° can be covered with peak gain of 7.5 dBi at 28 GHz.

In this paper, we investigate the unwanted scattering that exists within the multipath simulator (MPS) array antennas employed in over the air (OTA) testing of mobile terminals. The impact of scattering is evaluated in terms of the measurement uncertainty of the average received power and the Ricean <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$K$</tex> </formula> -factor. The maximum ratio combining diversity is investigated for a generic device under test comprising two half-wavelength dipole antennas. We provide closed-form expressions for the uncertainties of the average received power and the Ricean <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$K$</tex></formula> -factor for a uniform circular array of MPS antennas and a 2-D uniformly distributed angle-of-arrival spectrum. We also derive the maximum number of MPS antennas and the minimum ring radius of the MPS system as a function of the separation between the most distant antenna elements if the device under test employs a uniform linear array. As a result, we provide design guidelines for MPS array in terms of the number antennas, the radius of the MPS array and the wavelength of the carrier frequency.