Radio Spectrum Research Articles

Low-profile robust circularly polarized textile patch antenna for WBAN and ISM applications

In this research, a conformal circularly polarized (CP) antenna has been developed employing polyester textile as its substrate material. The proposed antenna configuration demonstrates its efficacy across multiple frequency bands—specifically 3 GHz and 4.5 GHz of WBAN and 5.8 GHz of ISM radio bands. The antenna’s distinctive design is developed on a rectangular plane as its primary radiating component, with a ground structure ingeniously arranged counter-positioning to the antenna’s patch. Electrical conductivity was widely achieved by employing adhesive copper and silver tape, conductive fabric, stitching conductive threads and copper paint, conventionally applied through brush painting techniques. The copper paint fabrication methodology has been chosen for its ability to confer conformability upon the antenna while minimizing its dimensions, ensuring lightweight attributes, and endowing it with remarkable resilience to environmental factors while preserving its optimal radiating performance. The CP polyester antenna showcases noteworthy peak gains: 3.91 dBi at 3 GHz, 5.86 dBi at 4.5 GHz and 6.62 dBi at 5.8 GHz (ISM). These gains highlight the antenna’s ability to efficiently capture and transmit signals within the aforementioned frequency bands, affirming its potential for robust wireless communication.

Superluminal Proper Motion in the X-Ray Jet of Centaurus A

The structure of the jet in Cen A is likely better revealed in X-rays than in the radio band, which is usually used to investigate jet proper motions. In this paper, we analyze Chandra Advanced CCD Imaging Spectrometer observations of Cen A from 2000 to 2022 and develop an algorithm for systematically fitting the proper motions of its X-ray jet knots. Most of the knots had an apparent proper motion below the detection limit. However, one knot at a transverse distance of 520 pc had an apparent superluminal proper motion of 2.7 ± 0.4c. This constrains the inclination of the jet to be i < 41° ± 6° and the velocity of this knot to be β > 0.94 ± 0.02. This agrees well with the inclination measured in the inner jet by the Event Horizon Telescope but contradicts previous estimates based on jet and counterjet brightness. It also disagrees with the proper motion of the corresponding radio knot, of 0.8 ± 0.1c, which further indicates that the X-ray and radio bands trace distinct structures in the jet. There are four prominent X-ray jet knots closer to the nucleus, but only one of these is inconsistent with being stationary. A few jet knots also have a significant proper-motion component in the nonradial direction. This component is typically larger closer to the center of the jet. We also detect brightness and morphology variations at a transverse distance of 100 pc from the nucleus.

Secrecy Performance Review for IoT-based Cognitive Farming System

Abstract: Smart farm management has complex challenges; therefore, there is a need to improve the overall adaptability, profitability, and environmental soundness of the farming systems. Agricultural production can be enhanced with the help of IoT-based cognitive tools. The rapid increase in IoT-based smart systems has raised critical concerns about efficiently utilizing the wireless spectrum. To drastically bring the improvement in the utilization of the wireless spectrum, cognitive radio (CR) has emerged as an effective solution. The inherent openness and broadcast nature of the wireless medium have given rise to many security issues in cooperative networks. Informationtheoretic security or physical layer security (PLS) is evolved as an efficacious wireless prototype for reliable transmissions to avert the eavesdropper from expropriating transmittal data on the wireless connections. Security is the key factor in these networks as they are exposed and active in behavior, thus, are susceptible to fraudulent activities. We investigated the performance of the CR system in terms of secrecy and also examined the system in terms of diversity receipt and selection of relay. The secrecy outcome of channel state information at the sender was also studied. The detrimental effects of fading in cooperative networks were also extensively discussed. Cooperative diversity was examined by deploying MRC and SC strategies at receptors. It has been deduced that CSI knowledge at the sender also has an eloquent concussion on the secrecy of the cognitive system.

Integrated Sensing and Communication Signal Processing Based on Compressed Sensing Over Unlicensed Spectrum Bands

Integrated Sensing and Communication Signal Processing Based on Compressed Sensing Over Unlicensed Spectrum Bands

Association of the IceCube neutrinos with blazars in the CGRaBS sample

The origin of high-energy (HE) astrophysical neutrinos has remained an elusive hot topic in the field of HE astrophysics for the past decade. Apart from a handful of individual associations, the vast majority of HE neutrinos arise from unknown sources. While there are theoretically motivated candidate populations, such as blazars – a subclass of active galactic nuclei with jets pointed toward our line of sight – they have not been convincingly linked to HE neutrino production yet. Here, we perform a spatio-temporal association analysis between a sample of blazars (from the CGRaBS catalog) in the radio and optical bands and the most up-to-date IceCube HE neutrino catalog. We find that if the IceCube error regions are enlarged by 1° in quadrature, to account for unknown systematic errors at a maximal level, a spatio-temporal correlation between the multiwavelength light curves of the CGRaBS blazars and the IceCube HE neutrinos is hinted at, least at a 2.17σ significance level. On the other hand, when the IceCube error regions are taken as their published values, we do not find any significant correlations. A discrepancy in the blazar-neutrino correlation strengths, when using such minimal and enlarged error region scenarios, was also obtained in a recent study by the IceCube collaboration. In our study, this difference arises because several flaring blazars – coinciding with a neutrino arrival time – happen to narrowly miss the published 90%-likelihood error region of the nearest neutrino event. For all of the associations driving our most significant correlations, the flaring blazar is much less than 1° away from the published error regions. Therefore, our results indicate that the question of the blazar-neutrino connection is highly sensitive to the reconstruction of the neutrino error regions, whose reliability is expected to improve with the next generation of neutrino observatories.

Origin of the Very High Energy Gamma Rays in the Low-luminosity Active Galactic Nucleus NGC 4278

NGC 4278, a low-luminosity active galactic nucleus, is generally classified as a low-ionization nuclear emission-line region (LINER). Recently, it has been reported to be associated with a very high energy γ-ray source 1LHAASO J1219+2915 in the first Large High Altitude Air Shower Observatory source catalog. However, no associated counterpart has been detected by analyzing the data collected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. By analyzing its X-ray observation data from Swift-XRT, we find that NGC 4278 is in a high-flux state on MJD 59546, with the X-ray flux more than one order of magnitude higher than that observed ∼11.7 yr earlier by Chandra. Interestingly, this Swift-XRT observation was conducted during the active phase of the γ-ray source 1LHAASO J1219+2915. We propose that the detection of very high energy γ-rays from NGC 4278 may be attributed to the presence of an active nucleus in its center. To reproduce the spectral energy distribution (SED) of NGC 4278, we employ a one-zone leptonic model, typically used for fitting broadband SEDs of BL Lacs, and find that a smaller magnetic field strength is required than that of typical TeV BL Lacs. Furthermore, NGC 4278 exhibits significantly lower luminosity in both radio and TeV bands when compared with typical TeV BL Lacs. In the radio luminosity versus Eddington ratio plane, NGC 4278 shows greater similarity to Seyfert galaxies and LINERs than to BL Lacs; however, it still roughly follows the extension toward lower luminosity seen in BL Lacs.

From 100 MHz to 10 GHz: Unveiling the spectral evolution of the X-shaped radio galaxy in Abell 3670

Context. X-shaped radio galaxies (XRGs) are characterised by two pairs of misaligned lobes: active lobes hosting radio jets and the wings. None of the formation mechanisms proposed thus far are able to exhaustively reproduce the diverse features observed among XRGs. Emerging evidence has proposed the existence of sub-populations of XRGs forming via different processes. Aims. The brightest cluster galaxy (BCG) in Abell 3670 (A3670) is a dumbbell system hosting the XRG MRC 2011-298. The morphological and spectral properties of this interesting XRG were first characterised based on Karl G. Jansky Very Large Array (JVLA) data at 1–10 GHz. In the present work, we follow up on MRC 2011-298 with the upgraded Giant Metrewave Radio Telescope (uGMRT) at 120–800 MHz to further constrain its properties and origin. Methods. We carried out a detailed spectral analysis sampling different spatial scales. Integrated radio spectra, spectral index maps, radio colour-colour diagrams, and radiative age maps of both the active lobes and prominent wings were employed to test the origin of the source. Results. We confirm a progressive spectral steepening from the lobes to the wings. The maximum radiative age of the source is ~80 Myr, with the wings being older than the lobes by ≳30 Myr in their outermost regions. Conclusions. The observed properties are in line with an abrupt reorientation of the jets by ~90 deg from the direction of the wings to their present position. This formation mechanism is further supported by the comparison with numerical simulations in the literature, which additionally highlight the role of hydrodynamic processes in the evolution of large wings such as those of MRC 2011-298. It is plausible that the coalescence of supermassive black holes could have triggered the spin-flip of the jets. Moreover, we show that the S-shape of the radio jets is likely driven by precession with a period of P ~ 10 Myr.

An Improved Phase Noise Reduction in Millimeter-Wave FBMC Systems

The next generation mobile network needs to have a spectrum above the 30 GHz radio band. The 5G system is a promising technology for future communication systems. It has been used in Device-to-Device (D2D) communications, IoT, Machine type communications (MTC), and wireless backhaul. The 5G is expected to have speeds of hundreds of times and satisfy the requirements of larger traffic density, low latency, connective density, higher capacity &amp; reliability, data rate, super high mobility, etc. It is expected to have applications such as HD video, virtual reality &amp; augmented reality, online games, and cloud desktops. For this, Millimeter wave (Mmwave) has been used for fifth-generation mobile networks. The millimeter wave has a frequency range from 30 to 300 GHz. When the usage of frequency is above 60 GHz, the band will acquire RF impairments such as PAPR, Phase noise, non-linearity, and phase and quadrature timing mismatch (IQTM). This article shows the Phase noise reduction in MIMO FBMC systems using Extended Kalman filter techniques.

Millimeter wave frequency generation based on variations in coupling coefficients of a silicon add-drop microring resonator

A microwave photonic system with silicon add-drop microring resonator as the core photonic device is analyzed for microwave/millimeter wave frequency generation. The primary concept of the proposed study relies on varying the coupling coefficients of the silicon add-drop microring resonator. Unequal coupling coefficients between the ring cavity and bus waveguides are one of the parameters which are responsible for generating second, third order sidebands in the radio frequency spectrum generated at the photodetector. Another parameter of interest is the phase difference between the two radio frequency signals which are fed to the Mach–Zehnder modulators of the proposed system. A 1 GHz sinusoidal signal with 1V peak-to-peak amplitude results in a third order sideband generation whose frequency corresponds to 3 GHz. The coupling coefficients in this case are 0.2 and 0.8, between ring cavity, top and bottom waveguides respectively. It is also observed that, phase difference of 90◦ between the input radio frequency signals results in highest power of the third order sideband generated in the output radio frequency spectrum whose frequency corresponds to the multiple of input radio frequency.

Small-Size Eight-Element MIMO Metamaterial Antenna with High Isolation Using Modal Significance Method.

This article presents a symmetrical reduced-size eight-element MIMO antenna array with high electromagnetic isolation among radiators. The array utilizes easy-to-build techniques to cover the n77 and n78 new radio (NR) bands. It is based on an octagonal double-negative metamaterial split-ring resonator (SRR), which enables a size reduction of over 50% for the radiators compared to a conventional disc monopole antenna by increasing the slow-wave factor. Additionally, due to the extreme proximity between the radiating elements in the array, the modal significance (MS) method was employed to identify which propagation modes had the most impact on the electromagnetic coupling among elements. This approach aimed to mitigate their effect by using an electromagnetic barrier, thereby enhancing electromagnetic isolation. The electromagnetic barriers, implemented with strip lines, achieved isolation values exceeding 20 dB for adjacent elements (<0.023 λ) and approaching 40 dB for opposite ones (<0.23 λ) after analyzing the surface current distribution by the MS method. The elements are arranged in axial symmetry, forming an octagon with each antenna port located on a side. The array occupies an area of 0.32 λ2 at 3.5 GHz, significantly smaller than previously published works. It exhibits excellent performance for MIMO applications, demonstrating an envelope correlation coefficient (ECC) below 0.0001, a total active reflection coefficient (TARC) lower than -10 dB for various incoming signals with random phases, and a diversity gain (DG) close to 20 dB.

SUB-6 5G NETWORKS: DESIGN OF BUTTON MUSHROOM MIMO ANTENNA AND IT’S INVESTIGATION

The unlicensed National Information Infrastructure radio band (n77, n78, and n46) is taken into consideration for this research work's "Multiple-input-multiple-output (MIMO)" antenna with dual band features. Gradually, the form design of simple single-patch MIMO antennas gives way to four-element MIMO antennas. Four microstrip antennas are integrated using button-like circular caps on the main patches. Reduced ground is also used in the construction of many band characteristics. Excellent isolation can be achieved by using Rectangular Metallic Strip (RMS). The suggested MIMO antenna has the advantage of covering two significant frequency bands. At 3.07 GHz and 6.31 GHz, the antenna system resonates with a total bandwidth of 2.43 GHz. The antenna design uses a FR4 substrate measuring 35 mm by 49 mm by 1.6 mm in thickness. For simulation purposes, Teflon and a specially made SMA connector with a perfect electrical conductor (PEC) are used to enhance impedance matching. An 8.2 mm feed line with an inset feed is also utilized. Research and investigation are conducted on radiation properties, including mean effective gain, envelope correction coefficient, reflection coefficient, and more. Both the reflection and isolation coefficients have values of less than -10 dB, with the former being less than -15 dB. It is a 16.30 dB increase overall. 5G applications will greatly benefit from having this smaller, four-element MIMO antenna.

SUB-6 5G NETWORKS: DESIGN OF BUTTON MUSHROOM MIMO ANTENNA AND IT’S INVESTIGATION

The unlicensed National Information Infrastructure radio band (n77, n78, and n46) is taken into consideration for this research work's "Multiple-input-multiple-output (MIMO)" antenna with dual band features. Gradually, the form design of simple single-patch MIMO antennas gives way to four-element MIMO antennas. Four microstrip antennas are integrated using button-like circular caps on the main patches. Reduced ground is also used in the construction of many band characteristics. Excellent isolation can be achieved by using Rectangular Metallic Strip (RMS). The suggested MIMO antenna has the advantage of covering two significant frequency bands. At 3.07 GHz and 6.31 GHz, the antenna system resonates with a total bandwidth of 2.43 GHz. The antenna design uses a FR4 substrate measuring 35 mm by 49 mm by 1.6 mm in thickness. For simulation purposes, Teflon and a specially made SMA connector with a perfect electrical conductor (PEC) are used to enhance impedance matching. An 8.2 mm feed line with an inset feed is also utilized. Research and investigation are conducted on radiation properties, including mean effective gain, envelope correction coefficient, reflection coefficient, and more. Both the reflection and isolation coefficients have values of less than -10 dB, with the former being less than -15 dB. It is a 16.30 dB increase overall. 5G applications will greatly benefit from having this smaller, four-element MIMO antenna.

The AllWISE Catalog as an Infrared Celestial Reference Frame in the Gaia Era

The launch of Gaia in 2013 December ushered in a new era of space astrometry, allowing for fundamental reference research at an unprecedented level of precision. The international celestial reference frames in the radio band and the Gaia celestial reference frame in the optical band have been established and are consistent within several microarcseconds for axes orientation. To bridge the gap between the visual and radio bands, an infrared reference frame should be investigated. We present a study aimed at constructing an infrared reference frame using the observations from the AllWISE catalog. It is compared with Gaia DR3 for approximately 0.57 million extragalactic sources and for a full set of 273 million sources. Systematic differences in positions and proper motions, such as magnitude or color equations and vector spherical harmonics, are derived. These systematic differences are comparable to the random errors of AllWISE measurements and can be used to improve the AllWISE source positions and proper motions, making the AllWISE catalog a valuable all-sky reference frame in the infrared band. Our investigation of the AllWISE catalog reveals that extragalactic sources and stars exhibit different astrometric properties. The global difference between the extragalactic source reference frame and the stellar reference frames is found to be 8.6 mas and 13.7 mas for global rotation and glide amplitudes, respectively. Such internal inconsistency should be considered when using AllWISE as an infrared reference frame. Finally, we determine the orientation of the mean Galactic plane using the calibrated source distribution of the AllWISE catalog.

Priority-based band sharing for secondary users in cognitive radio networks

To improve wireless spectrum utilization, cognitive radio networks (CRNs) allow secondary users (SUs) opportunistic access to the frequency bands owned by primary users (PUs), when such PUs are inactive. A fully distributed CRN architecture is quite favorable, as it does not require any centralized scheduling, nor does it require coordination between SUs via a common control channel. This can reduce cost and avoid single point-of-failure issues. However, uncoordinated access to the spectrum by competing SUs, if not done judiciously, can cause excessive collisions and limit performance, which can be detrimental to the usefulness of CRNs, especially if some SUs have urgent traffic to send. Hence, we present a novel protocol to support traffic with multiple classes of priority within a fully distributed CRN. In such protocol, competing SUs attempt to access the spectrum autonomously, but rationally, based on their priority level, opting to transmit their packets when it is beneficial to both the SU itself and also to the overall system performance. Simulations confirm that the proposed protocol achieves excellent overall network performance, while ensuring that higher priority packets experience higher throughput and smaller delay compared to lower priority packets.

Adiabatic spectrum of radio emission of plasma clouds, emitted by the Sun during solar flares, and inhomogeneities of the spectrum of radio emission of clouds

It is known that so-called solar flares systematically occur in the area of sunspots. They are accompanied by radiation in almost all frequency ranges and sometimes by the emission of hot plasma. Observations on the RATAN-600 radio telescope have shown that the radio emission spectrum of plasma clouds heated to values of the order of 106K erupted from the solar flare region turned out to be adiabatic. The high correlation of the inhomogeneities of the radio emission spectra of active formation over a group of sunspots indicates the stable presence of recombination radio lines in the radiation of active formation. However, the radio emission spectra of hot plasma clouds ejected from the region of solar flares occurring in this group of spots do not show any correlation.

NDN multicast over wireless networks: A survey on fundamentals, challenges, and open issues

Wireless devices have shown remarkable growth in data demand in the last decade due to the proliferation of smart devices and the emergence of bandwidth-hungry applications. This increasing data traffic demand is overcrowding the radio frequency spectrum, leading wireless multicast schemes to become a popular research topic again, as they provide efficient data dissemination. NDN supports multicast communication by design. It is a networked system formed by named entities that adopt a communication model focusing on the content rather than its location. The architecture follows a receiver-driven communication model through which content consumers retrieve data through semantically meaningful names instead of specific destinations. Its properties are essential for multicast communication on ad hoc networks, as its features provide enhanced support for dynamic topologies, decentralized control, and the self-organization of participant nodes that communicate without needing a pre-existing network infrastructure. However, despite the wireless medium being broadcast by nature, NDN multicast is still challenging in wireless scenarios, especially in ad hoc environments, due to the node’s high mobility, link instability, constant handovers, and data transmission over a shared medium. Hence, this survey discusses the benefits of NDN for mobile scenarios through an in-depth analysis of NDN multicast features, focusing on fundamentals, challenges, and open issues when applied to wireless networking.

Monitoring and enhancing the co-operation of IoT network rhrough scheduling function based punishment reward strategy

The Internet of Things (IoT) has revolutionized the connectivity of physical devices, leading to an exponential increase in multimedia wireless traffic and creating substantial demand for radio spectrum. Given the inherent scarcity of available spectrum, Cognitive Radio (CR)-assisted IoT emerges as a promising solution to optimize spectrum utilization through cooperation between cognitive and IoT nodes. Unlicensed IoT nodes can opportunistically access licensed spectrum bands without causing interference to licensed users. However, energy constraints may lead to reduced cooperation from IoT nodes during the search for vacant channels, as they aim to conserve battery life. To address this issue, we propose a Punishment-reward-based Cooperative Sensing and Data Forwarding (PR-CSDF) approach for IoT data transmission. Our method involves two key steps: (1) distributing sensing tasks among IoT nodes and (2) enhancing cooperation through a reward and punishment strategy. Evaluation results demonstrate that both secondary users (SUs) and IoT nodes achieve significant utility gains with the proposed mechanism, providing strong incentives for cooperative behaviour.

An adaptive approach for integrating primary user behavior in compressive spectrum sensing

Compressive sensing (CS) has been widely used to sense the wideband spectrum with fewer measurements by taking advantage of radio spectrum underutilization. As new smart devices, such as IoT devices, smart home devices, and wearables, use batteries and have limited memory, more research is needed to reduce the overuse of cognitive radio (CR) resources through spectrum sensing. To reduce the number of compressive measurements required for spectrum recovery, researchers proposed approaches like weighted and sequential compressive sensing. In this paper, we estimate the primary user’s (PU) behavior statistics and use the estimated information in a novel weighted sequential compressive spectrum sensing approach. Our proposed approach can reduce and adapt the number of measurements and the sensing time to the changing number of active channels in a dynamically changing wideband spectrum.

Energy‐efficient channel selection algorithm with reduced collision probability in cognitive radio networks

AbstractThe growing demand for radio spectrum, driven by widespread communication devices, has led to spectrum congestion. Cognitive radio networks (CRNs) offer a solution by allowing secondary users (SUs) to access primary users' (PUs) channels without causing interference. This paper presents an energy‐efficient channel selection algorithm aimed at reducing collision probability and energy consumption during spectrum sensing. A prediction‐based model forecasts PU channel availability, enabling selective sensing. The results show a significant reduction in energy consumption, with the proposed method consuming 57.9% energy compared to 63.7% for a recent existing method. The proposed approach enhances spectrum management in next‐generation wireless systems by minimizing interference and optimizing energy use.

Multi-objective optimization in order to allocate computing and telecommunication resources based on non-orthogonal access, participation of cloud server and edge server in 5G networks

Mobile edge processing is a cutting-edge technique that addresses the limitations of mobile devices by enabling users to offload computational tasks to edge servers, rather than relying on distant cloud servers. This approach significantly reduces the latency associated with cloud processing, thereby enhancing the quality of service. In this paper, we propose a system in which a cellular network, comprising multiple users, interacts with both cloud and edge servers to process service requests. The system assumes non-orthogonal multiple access (NOMA) for user access to the radio spectrum. We model the interactions between users and servers using queuing theory, aiming to minimize the total energy consumption of users, service delivery time, and overall network operation costs. The problem is mathematically formulated as a multi-objective, bounded non-convex optimization problem. The Structural Correspondence Analysis (SCA) method is employed to obtain the global optimal solution. Simulation results demonstrate that the proposed model reduces energy consumption, delay, and network costs by approximately 50%, under the given assumptions.