190 research outputs found
Enhancing Near-Field Sensing and Communications with Sparse Arrays: Potentials, Challenges, and Emerging Trends
As a promising technique, extremely large-scale (XL)-arrays offer potential
solutions for overcoming the severe path loss in millimeter-wave (mmWave) and
TeraHertz (THz) channels, crucial for enabling 6G. Nevertheless, XL-arrays
introduce deviations in electromagnetic propagation compared to traditional
arrays, fundamentally challenging the assumption with the planar-wave model.
Instead, it ushers in the spherical-wave (SW) model to accurately represent the
near-field propagation characteristics, significantly increasing signal
processing complexity. Fortunately, the SW model shows remarkable benefits on
sensing and communications (S\&C), e.g., improving communication multiplexing
capability, spatial resolution, and degrees of freedom. In this context, this
article first overviews hardware/algorithm challenges, fundamental potentials,
promising applications of near-field S\&C enabled by XL-arrays. To overcome the
limitations of existing XL-arrays with dense uniform array layouts and improve
S\&C applications, we introduce sparse arrays (SAs). Exploring their potential,
we propose XL-SAs for mmWave/THz systems using multi-subarray designs. Finally,
several applications, challenges and resarch directions are identified
Holographic MIMO Communications: Theoretical Foundations, Enabling Technologies, and Future Directions
Future wireless systems are envisioned to create an endogenously
holography-capable, intelligent, and programmable radio propagation
environment, that will offer unprecedented capabilities for high spectral and
energy efficiency, low latency, and massive connectivity. A potential and
promising technology for supporting the expected extreme requirements of the
sixth-generation (6G) communication systems is the concept of the holographic
multiple-input multiple-output (HMIMO), which will actualize holographic radios
with reasonable power consumption and fabrication cost. The HMIMO is
facilitated by ultra-thin, extremely large, and nearly continuous surfaces that
incorporate reconfigurable and sub-wavelength-spaced antennas and/or
metamaterials. Such surfaces comprising dense electromagnetic (EM) excited
elements are capable of recording and manipulating impinging fields with utmost
flexibility and precision, as well as with reduced cost and power consumption,
thereby shaping arbitrary-intended EM waves with high energy efficiency. The
powerful EM processing capability of HMIMO opens up the possibility of wireless
communications of holographic imaging level, paving the way for signal
processing techniques realized in the EM-domain, possibly in conjunction with
their digital-domain counterparts. However, in spite of the significant
potential, the studies on HMIMO communications are still at an initial stage,
its fundamental limits remain to be unveiled, and a certain number of critical
technical challenges need to be addressed. In this survey, we present a
comprehensive overview of the latest advances in the HMIMO communications
paradigm, with a special focus on their physical aspects, their theoretical
foundations, as well as the enabling technologies for HMIMO systems. We also
compare the HMIMO with existing multi-antenna technologies, especially the
massive MIMO, present various...Comment: double column, 58 page
Real-Time Beamforming Using High-Speed FPGAs at the Allen Telescope Array
The Allen Telescope Array (ATA) at the Hat Creek Radio Observatory (HCRO) is a wide‐field panchromatic radio telescope currently consisting of 42 offset‐Gregorian antennas each with a 6 m aperture, with plans to expand the array to 350 antennas. Through unique back‐end hardware, the ATA performs real‐time wideband beamforming with independent subarray capabilities and customizable beam shaping. The beamformers enable science observations requiring the full gain of the array, time domain (nonintegrated) output, and interference excision or orthogonal beamsets. In this paper we report on the design of this beamformer, including architecture and experimental results. Furthermore, we address some practical considerations in large‐N wideband beamformers implemented on field programmable gate array platforms, including device utilization, methods of calibration and control, and interchip synchronization
Towards versatile access networks (Chapter 3)
Compared to its previous generations, the 5th generation (5G) cellular network features an additional type of densification, i.e., a large number of active antennas per access point (AP) can be deployed. This technique is known as massive multipleinput multiple-output (mMIMO) [1]. Meanwhile, multiple-input multiple-output (MIMO) evolution, e.g., in channel state information (CSI) enhancement, and also on the study of a larger number of orthogonal demodulation reference signal (DMRS) ports for MU-MIMO, was one of the Release 18 of 3rd generation partnership project (3GPP Rel-18) work item. This release (3GPP Rel-18) package approval, in the fourth quarter of 2021, marked the start of the 5G Advanced evolution in 3GPP. The other items in 3GPP Rel-18 are to study and add functionality in the areas of network energy savings, coverage, mobility support, multicast broadcast services, and positionin
1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface
A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance
Beam scanning by liquid-crystal biasing in a modified SIW structure
A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium
Advanced Radio Frequency Antennas for Modern Communication and Medical Systems
The main objective of this book is to present novel radio frequency (RF) antennas for 5G, IOT, and medical applications. The book is divided into four sections that present the main topics of radio frequency antennas. The rapid growth in development of cellular wireless communication systems over the last twenty years has resulted in most of world population owning smartphones, smart watches, I-pads, and other RF communication devices. Efficient compact wideband antennas are crucial in RF communication devices. This book presents information on planar antennas, cavity antennas, Vivaldi antennas, phased arrays, MIMO antennas, beamforming phased array reconfigurable Pabry-Perot cavity antennas, and time modulated linear array
A Vision to Smart Radio Environment: Surface Wave Communication Superhighways
Complementary to traditional approaches that focus on transceiver design for
bringing the best out of unstable, lossy fading channels, one radical
development in wireless communications that has recently emerged is to pursue a
smart radio environment by using software-defined materials or programmable
metasurfaces for establishing favourable propagation conditions. This article
portraits a vision of communication superhighways enabled by surface wave (SW)
propagation on "smart surfaces" for future smart radio environments. The
concept differs from the mainstream efforts of using passive elements on a
large surface for bouncing off radio waves intelligently towards intended user
terminals. In this vision, energy efficiency will be ultra-high, due to much
less pathloss compared to free space propagation, and the fact that SW is
inherently confined to the smart surface not only greatly simplifies the task
of interference management, but also makes possible exceptionally localized
high-speed interference-free data access. We shall outline the opportunities
and associated challenges arisen from the SW paradigm. We shall also attempt to
shed light on several key enabling technologies that make this realizable. One
important technology which will be discussed is a software-controlled fluidic
waveguiding architecture that permits dynamic creation of high-throughput data
highways.Comment: 7 pages, 6 figure
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