Sub-6 GHz Bands Research Articles

Circularly polarized metalens antenna design for 5G NR sub-6 GHz communication systems

5G NR (new radio) FR1 range refers to as Sub-6 GHz band (410–7125 MHz and 3.4–6 GHz). In this paper, the frequency range of interest is from 3.4 to 6 GHz, as many cellular companies are focusing on this Sub-6 GHz band. A wideband circularly polarized (CP) antenna radiator is designed with diamond shape patches, fed by a microstrip line at the bottom through a rectangular shape wide slot on a ground plane. The proposed CP antenna covering a −10 dB bandwidth of 21.52 % (5.0–6.3 GHz) with 3-dB axial ratio (AR) bandwidth of 12.48 % (5.1–5.8 GHz). Furthermore, a metasurface-based lens (metalens) is designed for gain enhancement and fed by 3 × 1 array of the proposed CP antennas for multibeam operation. The lightweight dual-layer metasurface structure consisting of circular shape unit cell elements are used to implement the lens. For the proof-of-concept, the array of radiating elements is implemented and experimentally validated, which gives a ±18° beam scanning range with a maximum gain of 13dBic at 5.6 GHz.

Higher-Frequency Permeability Measurement by Harmonic Resonance Cavity Perturbation Method

A new combination of electric field antenna and coupling hole plates are introduced to extend the measurable frequency range of rectangular waveguide type harmonic resonator to evaluate complex relative permeability of magnetic composites by perturbation method from 18 GHz to 38 GHz (K/Ka-band). The noise suppression performance parameter ωμ”=2πfμ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ” [kΩ/m] is useful to estimate the performance of magnetic powder composite sheets especially beyond 10 GHz range where relative permeability is as small as 0-2. The ωμ” exhibited the maximum of 166 kΩ/m at 27 GHz for a carbonyl iron powder composite sheet, and as high as 510 at 38 GHz for Sendust sheet. These values meet ωμ”≥100 kΩ/m criteria that some commercially available noise suppression sheets exhibit in their recommended frequency range. These performance match Sub-6 GHz band and 28 GHz band used for 5G telecommunication equipment.

High Isolation Wideband MIMO Antenna without Decoupling Technique for IoT Applications

This paper presents a method a high isolation wideband MIMO antenna without using any decoupling technique. This is achieved by transforming a strip line to a 1 ×2 MIMO antenna using Hilbert transform and Defected Ground structure is used in the antenna to resonate the antenna in for IOT and 5G sub-6 GHz bands. The proposed antenna has a size of 50 × 49.8 × 1.6 mm 3 and operates in the frequency band of 4.6 GHz to 5.94 GHz. The antenna simulated in ANSYS HFSS showed that its parameters Envelope correlation coefficient (ECC), Total Active Reflection Coefficient (TARC), Diversity gain (DG) and Channel Capacity Loss (CCL) are less than 0.04, -25 dB, 9.98 to 10 dB and less than 0.4 bits/s/Hz respectively. The radiation pattern of the antenna in both E-plane and H-plane has been simulated which the uniform distribution of power in the space.

Deep learning assisted fractal slotted substrate MIMO antenna with characteristic mode analysis (CMA) for Sub-6 GHz n78 5 G NR applications: design, optimization and experimental validation

This article presents the design and optimization of a Deep Learning assisted MIMO antenna for 5 G New Radio (NR) applications in Sub-6 GHz band. The Prototype of the simulated geometry has been practically modelled and experimentally tested to validate the theoretical results. The optimized two-port MIMO antenna of 48 × 24 mm2 size is designed using fractal slotted substrate geometry. The concept of characteristic mode analysis (CMA) method is performed to characterize the performance of the proposed slotted substrate monopole MIMO Antenna. Usually, Optimization techniques based on traditional electromagnetic simulation tools (CST, HFSS, etc) are time-consuming for the design purpose of complex MIMO antenna geometries. The simulation studies using electromagnetic simulation tools are needed to be performed repeatedly to evaluate the optimum geometrical parameters for achieving better acceptable performance. In order to solve this issue, Deep Learning (DL) method-based design optimization approach is considered as an effective technique for determining the optimum physical parameters. In this article, Deep learning method based Dual-Channel type Deep Neural Network (DC-DNN) optimization technique is suggested to estimate the S-parameters. The generated data is fed to DC-DNN acting as a surrogate model to map the input features with the reflection and transmission coefficients, thereby enabling the search for the optimum design parameters to obtain the best performance. The diversity parameters are observed within acceptable limits and the characteristic parameters related to impedance and radiation performance are best suitable for lower sub-6 GHz n78 (3300–3800 MHz) 5 G NR network applications.

Broadband Dual-Polarized Phased Array With Dynamic Scanning Control for Intelligent Mobile Communication Application

This work investigates a low-cost, broadband, dual-polarized, beamwidth reconfigurable phased array for dynamic beam-scanning control. Both the beamwidth in the E-plane and H-plane are synchronously extended by introducing the vertically polarized (VP) field components. Then, by exploring a switch-loaded omnidirectional source, a novel dual-polarized wide/narrow beamwidth switchable or reconfigurable method is proposed. To meet the demand for intelligent mobile communication for dynamic beam steering, the dual-polarized beamwidth reconfigurable radiator as the array element is used for the phased array or MIMO designs. As a proof of concept, an interesting four-element reconfigurable dual-polarized phased array is implemented in the Sub-6 GHz band. By controlling the switch states of each element, this array can be operated in two modes: <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">wide-angle scanning coverage (V2V connection) and long-distance high-gain scanning (V2I communication)</i> . In wide-angle scanning mode, the main lobe of the array can scan from -60° to +55°, and its peak gain is 9.1 dBi. In long-distance high-gain scanning, this array can scan the beam in the range of [-35°, +35°] with a peak gain of 11.2 dBi. Besides, the isolation between different elements or polarization is greater than 13 dB. This reconfigurable phased array demonstrates the advantages of low-cost, broadband, and flexible beam-steering capability. It is expected to find broad applications in intelligent vehicular communication and low-cost phased array.

Opportunities and Challenges of LoRa 2.4 GHz

Internet of Things (IoT) technologies are increasingly used in our daily life. Among these technologies, LoRa is widely used for low power IoT data collection in wide areas. LoRa typically operates in sub-GHz bands which are region-specific, and thus has limited world-wide applications. The version of LoRa developed for the 2.4 GHz ISM band has spurred recent interest in the scientific community, as it enables the use of worldwide frequency channels. However, it requires the coexistence with numerous concurrent technologies within this 2.4 GHz band, and an evolution of the MAC and networking protocols for utilizing LoRaWAN connectivity. In this paper, we make the first experimental comparison between LoRa sub-GHz and LoRa 2.4 GHz in both indoor and outdoor scenarios. We show that LoRa 2.4 GHz can have a communication range of more than 2 km outdoor, and it can achieve a packet delivery rate of at least 0.98 for a distance of up to 39 meters indoor with the presence of obstacles. We also make an extensive discussion on the researches challenges that need to be addressed in order to fully take advantage of this new technology.

Temporal Correlation Characteristics of Air-to-Ground Wireless Channel With UAV Wobble

Air-to-ground (A2G) communication based on Unmanned aerial vehicle (UAV) is an important part of the future communication system. In this paper, an A2G channel model with UAV three-dimensional (3D) wobbles (pitch, roll, and yaw) based on the geometry-based stochastic model (GBSM) is proposed. On this basis, the UAV’s internal vibration is modeled as a sinusoidal random process, and the UAV wobble caused by the atmospheric flow is modeled as the uniform distribution random process. We derive the channel temporal correlation function (CF) with UAV 3D wobbles, analyze the variation of the temporal CF with different carrier frequencies, and amplitudes of the wobble angles. It is found that, even if the UAV wobbles slightly, the channel temporal correlation will be significantly affected. Numerical results show that the channel CF will decrease rapidly with the increase of the amplitudes of wobble angles and the carrier frequency. Therefore, the coherence time of millimeter wave (mmWave) band is significantly less than that of sub-6 GHz band. The consistency of simulation results and measurement results in published papers ensures the availability of the proposed model. For the MUAVs scenario, when the distance between different UAVs is much greater than the wavelength, the A2G channels between different UAVs and user equipment (UE) on the ground are not correlated to each other, and the temporal auto-correlation function (ACF) of each UAV is the same as that of the SUAV scenario. This work contributes to the theoretical exploration and system design of A2G communication based on UAV.

Dual-sense slot-based CP MIMO antenna with polarization bandwidth reconfigurability

In this letter, a compact, planar circularly polarized (CP) sub-GHz slot-based multiple-input-multiple-output (MIMO) antenna with dual sense CP along with polarization bandwidth reconfigurability is presented. The pentagonal reactively loaded slot is fed by two folded tapered feedlines to achieve CP. The antenna offers left-hand-circular polarization (RHCP) with the as well as right hand circular polarization (LHCP). The antenna exhibit linearly polarization (LP) by exciting two ports simultaneously. Moreover, the antenna CP resonance can be reconfigured by varying the capacitance of the varactor diode. The antenna has a wide −10 dB operating frequency band from 578–929 MHz. while the axial ratio (AR) bandwidth ranges from 490–810 MHz. Moreover, the two elements MIMO are optimized and placed on compact dimensions 100 × 100 × 0.76 mm3 to realize pattern diversity. The antenna’s key characteristics are compact size, wide-band sub-GHz operation, dual sense CP, polarization bandwidth reconfigurability and good MIMO performance. Thus, it is a suitable candidate to be utilized in CubeSats applications in sub-GHz bands.

Highly Efficient GaN Doherty Power Amplifier for N78 Sub-6 GHz Band 5G Applications

In this paper, a high-efficiency GaN Doherty power amplifier (DPA) for 5G applications in the N78 sub-6 GHz band is introduced. The theoretical analysis of the matching networks for the peak and carrier transistors is presented, with a focus on the impact of unequal power splitting for both transistors and the recommendation of a post-harmonic suppression network. The proposed design features an unequal Wilkinson power divider at the input and a post-harmonic suppression network at the output, both of which are crucial for achieving high efficiency. The Doherty power amplifier comprises two GaN 10 W HEMTs, measured across the 3.3 GHz to 3.8 GHz band (the N78 band), and the results reveal significant improvements in gain, output power, drain efficiency, and power-added efficiency. Specifically, the proposed design achieved a power gain of over 12 dB and 42 dBm saturated output power. It also achieved a drain efficiency of 80% at saturation and a power-added efficiency of 75.2%. Furthermore, the proposed harmonic suppression network effectively attenuated the harmonics at the output of the amplifier from the second to the fourth order to more than −50 dB, thus enhancing the device’s linearity.

Local PAPR-Aware Precoding for Energy-Efficient Cell-Free Massive MIMO-OFDM Systems

Orthogonal frequency-division multiplexing (OFDM) based Cell-free massive multiple-input multiple-output (CF-mMIMO) is the most promising technology that, compared to cellular technology, provide uniformly better quality of service for users in sub-6GHz bands. To make OFDM based CF-mMIMO more cost-effective and power-efficient, the access points (APs) should be equipped with low-cost and low-quality transceiver hardware. However, transmitting OFDM signals with high peak-to-average power ratio (PAPR) via such hardware causes severe hardware impairments (HWI), damaging the system performance. In this paper, we present an energy-efficient downlink transmission scheme adequate to the emerging CF-mMIMO-OFDM technology. Specifically, we introduce a smart PAPR-aware precoding scheme, referred to as localPAPRfree, adequate for cell-free architecture. Interestingly, the proposed technique can be implemented in a distributed and scalable manner, demonstrating benefits of CF-mMIMO-OFDM. The PAPR-aware precoding scheme is formulated as a simple convex optimization problem solved via an efficient and steepest iterative algorithm. In addition, we present a theoretical study to analyze the downlink (DL) spectral-efficiency (SE) and energy-efficiency (EE) performance of CF-mMIMO-OFDM under power amplifier (PA) non-linearity, providing important insights into the practical impact of nonlinear PA. Numerical results show that the proposed localPAPRfree algorithm offers excellent PAPR reduction performance, guaranteeing high EE.

Multi-Band Full Duplex MAC Protocol (MB-FDMAC)

In this paper, we propose a multi-band medium access control (MAC) protocol for an infrastructure-based network with an access point (AP) that supports In-Band full-duplex (IBFD) and multiuser transmission to multi-band-enabled stations. The Multi-Band Full Duplex MAC (MB-FDMAC) protocol mainly uses the sub-6 GHz band for control-frame exchange, transmitted at the lowest rate per IEEE 802.11 standards, and uses the 60 GHz band, which has significantly higher instantaneous bandwidth, exclusively for data-frame exchange. We also propose a selection method that ensures fairness among uplink and downlink stations. Our result shows that MB-FDMAC effectively improves the spectral efficiency in the mmWave band by 324%, 234%, and 189% compared with state-of-the-art MAC protocols. In addition, MB-FDMAC significantly outperforms the combined throughput of sub-6 GHz and 60 GHz IBFD multiuser MIMO networks that operate independently by more than 85%. In addition, we study multiple network variables such as the number of stations in the network, the percentage of mmWave band stations, the size of the contention stage, and the selection method on MB-FDMAC by evaluating the change in the throughput, packet delay, and fairness among stations. Finally, we propose a method to improve the utilization of the high bandwidth of the mmWave band by incorporating time duplexing into MB-FDMAC, which we show can enhance the fairness by 12.5 % and significantly reduces packet delay by 80%.

On the devolvement of fractal antenna for IoT applications

A fractal patch antenna is designed and fabricated on FR4-epoxy substrate for Internet of Things (IoT) applications. Minkowski fractal has been used in the design of radiating element of antenna and slots are incorporated in the partial ground structure. The proposed antenna is miniaturized by 65% in terms of resonating frequency using Minkowski fractal. The proposed structure of antenna has an overall size of 60× 40 ×1.6 mm3. The antenna resonates at 1.223, 1.58, 2.69, and at 3.54 GHz. It exhibits an impedance bandwidth of 0.11 (1.16–1.27) GHz, 0.23 (1.47–1.70) GHz, and 4.5 (1.99–6.49) GHz. The proposed antenna has a peak gain of 3.4 dBi. The key benefits of the proposed antenna are: simple structure, improved performance characteristics, and its usefulness for applications such as Global Positioning System (GPS), Radar Altimeter, Public Safety Applications, and 5G communications in sub-6 GHz band. The simulated results of the proposed fractal antenna have been verified experimentally. The results are highly convincing.

Link-Level Simulator for 5G Localization

Channel-state-information-based localization in 5G networks has been a promising way to obtain highly accurate positions compared to previous communication networks. However, there is no unified and effective platform to support the research on 5G localization algorithms. This paper releases a link-level simulator for 5G localization, which can depict realistic physical behaviors of the 5G positioning signal transmission. Specifically, we first develop a simulation architecture considering more elaborate parameter configuration and physical-layer processing. The architecture supports the link modeling at sub-6GHz and millimeter-wave (mmWave) frequency bands. Subsequently, the critical physical-layer components that determine the localization performance are designed and integrated. In particular, a lightweight new-radio channel model and hardware impairment functions that significantly limit the parameter estimation accuracy are developed. Finally, we present three application cases to evaluate the simulator, i.e. two-dimensional mobile terminal localization, mmWave beam sweeping, and beamforming-based angle estimation. The numerical results in the application cases present the performance diversity of localization algorithms in various impairment conditions.

Gain enhancement of a monopole antenna using frequency selective surface for sub-6 GHz band applications

Gain enhancement of a monopole antenna using frequency selective surface for sub-6 GHz band applications

Dual-Band Aerial Networks for Priority-Based Traffic

Unmanned aerial vehicle networks suffer from lackluster performance due to line-of-sight issues as well as resource scarcity. Network slicing, multi-band transmission, and numerology show great potential in mitigating such limitations. In this work, we propose the use of the sub-6 GHz and mmWave bands, the latter of which requires careful consideration of line-of-sight, with numerology for aerial network slicing to provision time-critical services and broadband access. Accordingly, we formulate a user admission control policy to regulate band access after which we formulate a joint resource block and power allocation problem, a mixed-integer non-linear programming problem, to minimize the quality-of-service gap of the throughput-dependent broadband users as a best-effort service and meet the time-critical service requirements. We propose a low-complexity algorithm, PREDICT, to tackle the formulated problem and present extensive simulation results to validate the advantages of our scheme.

Spectrum Sharing of the 12 GHz Band with Two-Way Terrestrial 5G Mobile Services: Motivations, Challenges, and Research Road Map

Telecommunication industries and spectrum regulation authorities are increasingly interested in unlocking the 12 GHz band for two-way 5G terrestrial services. The 12 GHz band has a much larger bandwidth than the current sub-6 GHz band and better propagation characteristics than the millimeterwave (mmWave) band. Thus, the 12 GHz band offers great potential for improving the coverage and capacity of terrestrial 5G networks. However, interference issues between incumbent receivers and 5G radio links present a major challenge in the 12 GHz band. If one could exploit the dynamic contexts inherent to the 12 GHz band, one could reform spectrum sharing policy to create spectrum access opportunities for 5G mobile services. This article makes three contributions. First, it presents the characteristics and challenges of the 12 GHz band. Second, we explain the characteristics and requirements for spectrum sharing at a variety of levels to resolve those issues. Lastly, we present several research opportunities to enable harmonious coexistence of incumbent licensees and 5G networks within the 12 GHz band.

Performance Enhancement of Cooperative MIMO-NOMA Systems Over Sub-6 GHz and mmWave Bands

In this paper, two radio links with different frequency bands are considered for base stations (BS) serving users via decode-and-forward (DF) cooperative relays. Backhaul and access links are proposed with sub-6 GHz and millimeter wave (mmWave) bands, respectively. Non-orthogonal multiple access (NOMA) is employed in the backhaul link to simultaneously transmit a superposed signal in the power domain, using the same band. The superposed signals, containing two signals that differ in terms of power allocation factors (PAFs), are designed for two selected DF relays in the BS. The two relays are chosen from several relays to be serviced by the BS based on a pairing algorithm that depends on different users’ circumstances. The furthest DF relay detects the incoming NOMA signal directly, while the nearest one applies successive interference cancellation (SIC) before extracting its signal. Each DF relay forwards the detected signals toward their intended users over mmWave channels. Three performance metrics are utilized to evaluate the system’s performance: outage probability, achievable throughput, and bit error rate. Comparisons between two mmWave bands in the access link (28 and 73 GHz) are made to demonstrate the superiority of the 28 GHz band in terms of the three performance-related metrics.

A Patch Antenna with Enhanced Gain and Bandwidth for Sub-6 GHz and Sub-7 GHz 5G Wireless Applications

This paper presents a novel microstrip patch antenna design using slots and parasitic strips to operate at the n77 (3.3–4.2 GHz)/n78 (3.3–3.8 GHz) band of sub-6 GHz and n96 (5.9–7.1 GHz) band of sub-7 GHz under 5G New Radio. The proposed antenna is simulated and fabricated using an FR-4 substrate with a relative permittivity of 4.3 and copper of 0.035 mm thickness for the ground and radiating planes. A conventional patch antenna with a slot is also designed and fabricated for comparison. A comprehensive analysis of both designs is carried out to prove the superiority of the proposed antenna over conventional dual-band patch antennas. The proposed antenna achieves a wider bandwidth of 160 MHz at 3.45 GHz and 220 MHz at 5.9 GHz, with gains of 3.83 dBi and 0.576 dBi, respectively, compared to the conventional patch antenna with gains of 2.83 dBi and 0.1 dBi at the two frequencies. Parametric studies are conducted to investigate the effect of the parasitic strip’s width and length on antenna performance. The results of this study have significant implications for the deployment of high-gain compact patch antennas for sub-6 GHz and sub-7 GHz 5G wireless communications and demonstrate the potential of the proposed design to enhance performance and efficiency in these frequency bands.

NR5G-SAM: A SLAM Framework for Field Robot Applications Based on 5G New Radio.

Robot localization is a crucial task in robotic systems and is a pre-requisite for navigation. In outdoor environments, Global Navigation Satellite Systems (GNSS) have aided towards this direction, alongside laser and visual sensing. Despite their application in the field, GNSS suffers from limited availability in dense urban and rural environments. Light Detection and Ranging (LiDAR), inertial and visual methods are also prone to drift and can be susceptible to outliers due to environmental changes and illumination conditions. In this work, we propose a cellular Simultaneous Localization and Mapping (SLAM) framework based on 5G New Radio (NR) signals and inertial measurements for mobile robot localization with several gNodeB stations. The method outputs the pose of the robot along with a radio signal map based on the Received Signal Strength Indicator (RSSI) measurements for correction purposes. We then perform benchmarking against LiDAR-Inertial Odometry Smoothing and Mapping (LIO-SAM), a state-of-the-art LiDAR SLAM method, comparing performance via a simulator ground truth reference. Two experimental setups are presented and discussed using the sub-6 GHz and mmWave frequency bands for communication, while the transmission is based on down-link (DL) signals. Our results show that 5G positioning can be utilized for radio SLAM, providing increased robustness in outdoor environments and demonstrating its potential to assist in robot localization, as an additional absolute source of information when LiDAR methods fail and GNSS data is unreliable.

Radio wave propagation analysis with dominant path model using MIMO antenna element for vehicular base station application

AbstractA low-profile slant ±45° polarized antenna for a 4G/5G base station with a dominant path wave propagation model (DPM) is reported in this paper. For dual-polarization and wide impedance bandwidth, the two dipole radiators are crisscrossed and a square metallic ring is integrated with the dipole arms and screwed with the four shorting vias. The antenna operates in Band 40/41/42/43 with strong isolation and low ECC (Envelop Correlation Coefficient). Fabricated antenna results show that the predicted wideband antenna has 13.38% bandwidth in 4G, which is Band 40/41, and 29.33% bandwidth in 5G sub-6 GHz Band 42/43. The antenna has a consistent radiation pattern, a 40 dB XPD (Cross Pol Discrimination), and a beam width of 69.5° ±1.5° in the entire frequency band. Three base station sites were explored to deploy the radiation pattern of a dual-polarized antenna in the 3D EM (Electromagnetic Analysis) tool. To evaluate signal quality, strength, radio network planning, and wave propagation analysis by analyzing antenna performance in real-time scenarios with 64 and 256 QAM (Quadrature Amplitude Modulation) techniques. For the proposed four-stream MIMO (Multiple-Input-Multiple-Output) antenna arrangement at deployed cell sites for 4G/5G base station applications, the maximum downlink and uplink data rates are 3.826/2.8 Mbps and 1044/800 Mbps respectively.