Sub-6 GHz Bands Research Articles

High‐conductivity graphene‐assembled film‐based bandpass filter for 5G applications

This article presents a compact 5G dual-wideband bandpass filter (DBPF) based on high-conductivity graphene assembled films (GAFs), which can meet the requirements of the sub-6 GHz bands, high integration and high information transmission rate for 5G wireless communication. The GAF DBPF consists of two folded open-loop stepped-impedance resonators with a compact size of 21.9 mm × 22.5 mm × 0.53 mm. The measured results show that the presented GAF DBPF has two passbands with 3 dB fractional bandwidths of 15.95% and 12.72% at center frequencies of 2.14 and 3.5 GHz, respectively. In addition, the filter exhibits an attenuation level greater than 20 dB up to 7.52 GHz.

Dual Band and Dual Diversity Four-Element MIMO Dipole for 5G Handsets.

The increasing popularity of using wireless devices to handle routine tasks has increased the demand for incorporating multiple-input-multiple-output (MIMO) technology to utilize limited bandwidth efficiently. The presence of comparatively large space at the base station (BS) makes it straightforward to exploit the MIMO technology’s useful properties. From a mobile handset point of view, and limited space at the mobile handset, complex procedures are required to increase the number of active antenna elements. In this paper, to address such type of issues, a four-element MIMO dual band, dual diversity, dipole antenna has been proposed for 5G-enabled handsets. The proposed antenna design relies on space diversity as well as pattern diversity to provide an acceptable MIMO performance. The proposed dipole antenna simultaneously operates at 3.6 and 4.7 sub-6 GHz bands. The usefulness of the proposed MIMO dipole antenna has been verified by comparing the simulated and measured results using a fabricated version of the proposed antenna. A specific absorption rate (SAR) analysis has been carried out using CST Voxel (a heterogeneous biological human head) model, which shows maximum SAR value for 10 g of head tissue is well below the permitted value of 2.0 W/kg. The total efficiency of each antenna element in this structure is −2.88, −3.12, −1.92 and −2.45 dB at 3.6 GHz, while at 4.7 GHz are −1.61, −2.19, −1.72 and −1.18 dB respectively. The isolation, envelope correlation coefficient (ECC) between the adjacent ports and the loss in capacity is below the standard margin, making the structure appropriate for MIMO applications. The effect of handgrip and the housing box on the total antenna efficiency is analyzed, and only 5% variation is observed, which results from careful placement of antenna elements.

Performance Analysis of Multi-Band Microwave and Millimeter-Wave Operation in 5G NR Systems

Blockage of millimeter-wave (mmWave) radio propagation paths in dense mobile scenarios requires advanced techniques to preserve session continuity in 5G New Radio (NR) systems. In this work, we employ the tools of stochastic geometry and queuing theory as well as rely on 3GPP cluster-based propagation modeling to formulate a mathematical framework, which captures session-level service dynamics of user equipment (UE) that supports multi-band operation. Accordingly, the sub-6 GHz NR base station (BS) is used to temporarily serve the sessions with strict throughput requirements that experience an outage at the mmWave NR BSs. We derive user- and system-centric key performance indicators, including new and ongoing session drop probabilities as well as radio resource utilization. Our numerical results confirm that the use of microwave BSs to serve mmWave sessions is only feasible in light traffic conditions. Particularly, the presence of throughput-hungry mmWave traffic increases the session drop probability at the sub-6 GHz band as well as decreases its utilization. Further, the support of sub-6 GHz radio may not improve the mmWave BS resource utilization, as many mmWave sessions are dropped during their service as a consequence of frequent blockage-induced outage situations.

Exploiting Beam Features for Spoofing Attack Detection in mmWave 60-GHz IEEE 802.11ad Networks

Spoofing attacks pose a serious threat to wireless communications. Exploiting physical-layer features to counter spoofing attacks is a promising solution. Although various physical-layer spoofing attack detection (PL-SAD) techniques have been proposed for conventional 802.11 networks in the sub-6GHz band, the study of PL-SAD for 802.11ad networks in 5G millimeter wave (mmWave) 60GHz band is largely open. In this paper, to achieve efficient PL-SAD in 5G networks, we propose a unique physical layer feature in IEEE 802.11ad networks, i.e., the signal-to-noise-ratio (SNR) trace obtained at the receiver in the sector level sweep (SLS) process. The SNR trace is readily extractable from the off-the-shelf device, and it is dependent on both transmitter location and intrinsic hardware impairment. Therefore, it can be used to achieve an efficient detection no matter the attacker is co-located with the legitimate transmitter or not. To achieve spoofing attack detection, we provide two methods based on different machine learning models. For the first method, the detection problem is formulated as a machine learning classification problem. To tackle the small sample learning and fast model construction challenges, we propose a novel neural network framework consisting of a backpropation network, a forward propagation network, and generative adversarial networks (GANs). Another method involves a Siamese network, in which the similarity between sample pairs from one device is used to achieve PL-SAD. It can tackle the training problem that the historical data cannot support the identification of the same device in a new communication session. We conduct experiments using off-the-shelf 802.11ad devices, Talon AD7200s and MG360, to evaluate the performance of the proposed PL-SAD schemes. Experimental results confirm the effectiveness of the proposed PL-SAD schemes, and the detection accuracy can reach 99% using small sample sizes under different scenarios.

Analytical Nonstationary 3D MIMO Channel Model for Vehicle-to-Vehicle Communication on Slope

Vehicle-to-vehicle communication plays a strong role in modern wireless communication systems, appropriate channel models are of great importance in future research, and propagation environment with slope is one special kind. In this study, a novel three-dimensional nonstationary multiple-input multiple-output channel model for the sub-6 GHz band is proposed. This model is a regular-shaped multicluster geometry-based analytical model, and it combines the line-of-sight component and multicluster scattering rays as the nonline-of-sight components. Each cluster of scatterers represents the influence of different moving vehicles on or near a slope, and scatterers are, respectively, distributed within two spheres around the transmitter and the receiver. In this model, it is considered that the azimuth and elevation angles of departure and arrival are jointly distributed and conform to the von Mises–Fisher distribution, which can easily control the range and concentration of the scatterers within spheres to mimic the real-world situation well. Moreover, the impulse response and the autocorrelation function of the corresponding channel is derived and proposed; then, the Doppler power spectrum density of the channel is simulated and analyzed. In addition, the nonstationary characteristics of the presented channel model are observed through simulations. Finally, the simulation results are compared with measurement data in order to validate the utility of the proposed model.

Sub-1 GHz Frequency Band Wireless Coexistence for the Internet of Things

Motivated by the explosion of the Internet of Things (IoT), we examined Sub-1 GHz (frequencies below 1 GHz) band wireless technologies that are essential to enable various IoT applications. IEEE 802.15.4g and IEEE 802.11ah are two wireless technologies developed for outdoor IoT applications such as smart utility, smart city and infrastructure monitoring for which both technologies operate in Sub-1 GHz Bands. Our coexistence simulation of IEEE 802.15.4g and IEEE 802.11ah using standard defined coexistence mechanisms shows serious interference problems due to fundamental protocol differences and channel access parameter differences. Accordingly, we proposed IEEE 802.19.3 Task Group formation to lead the IEEE 802.19.3 standard development of IEEE 802.15.4g and IEEE 802.11ah coexistence in the Sub-1 GHz band. In addition to our coexistence methods contributed to IEEE 802.19.3 standard, we propose a novel Active Carrier Sense based CSMA/CA mechanism for IEEE 802.15.4g to reduce CSMA/CA failure packet discard under interference from IEEE 802.11ah traffic and to keep interoperability with conventional IEEE 802.15.4g CSMA/CA mechanism. Our proposed coexistence techniques can improve fair spectrum sharing between IEEE 802.15.4g and IEEE 802.11ah networks for IoT applications.

A Decoupling Network for Resonant and Non-Resonant Sub-1 GHz MIMO Mobile Terminal Antennas With Improved Compactness and Efficiency

In this work, the design procedure of a new decoupling network for different antennas is presented for mobile terminals operating in the Sub-1 GHz band (from 0.698 to 0.96 GHz). To evaluate its applicability for different resonant and non-resonant antenna types, two antenna elements have been chosen to be decoupled using the proposed decoupling network: a printed inverted-F antenna and a capacitive coupling element antenna. Simulation and measurement results showed that the decoupling network offer promising improvements in terms of impedance matching, port isolation, envelope correlation coefficient (ECC), and total efficiency. In addition, the antennas are also investigated with the ergodic capacity, multiplexing efficiency, gain, and diversity gain (both calculated using maximal ratio combining technique). Due to the contribution of the decoupling network, the ECC of both types of multiple antennas are less than 0.3, with a 30 % improvement in total efficiency and an inter-element spacing miniaturization of 34 %.

Broadband Multimode Antenna for Sub-6 GHz Base Station Applications

In this paper, a novel dual-polarized multimode antenna is presented for sub-6 GHz base station applications. Two pairs of slotted patches act as the main radiator to excite two modes, and they are coupled with each other to bring the resonant frequency of the two modes together. Two baluns are orthogonally placed between the main radiator and the ground plane for impedance transforming and introducing a new mode at the lower frequency. The ends of the slotted patches are connected with a reversed T-shaped dipole to optimize the current path and introducing a new mode at the higher frequency. Measured results show that the prototype antenna can achieve a 15-dB impedance bandwidth of 2.30 ~ 3.96 GHz (53.1%) and an average gain of 9.67 ± 0.33 dBi in the operating band. The isolation is greater than 28.0 dB with a half-power beamwidth of around 64° among the operating frequency band. The proposed antenna can be a promising candidate for the fifthgeneration communication in the sub-6 GHz band.

Shielding Effectiveness of 5G Small-Cell Base Station Board-to-Board Connectors

5G small-cell base stations are featured by having massive electronics and signal processing hardware for the purpose of digital beamforming. This paper deals with important components within such 5G base stations which are the Board-to-Board (BtB) RF connectors that connect such electronic boards within the base station. It is attempted to introduce a simple and cost-effective simulation and measurement technique for determining shielding effectiveness (SE) in the near-field based on the IEC-61967-3 standard. A 16-channel BtB 5G system is investigated in the sub-6 GHz band as a real-scenario where the obtained results were proven to be highly accurate as compared to simulations.

4-Port MIMO Antenna Using Common Radiator on a Flexible Substrate for Sub-1GHz, Sub-6GHz 5G NR, and Wi-Fi 6 Applications

In this paper, an angular symmetric, common radiator coplanar waveguide (CPW) fed four-port multiple-input-multiple-output (MIMO) antenna is designed on a 0.129λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> L</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> RT Duroid ( ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> r</sub> = 3.0, tan δ = 0.001) substrate where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> L</sub> is the free space wavelength at the lowest operating frequency ( f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> L</sub> ) of 0.6 GHz. The antenna has a -6 dB impedance bandwidth from 0.6-1.09 GHz, 2.6-3.4 GHz and 4.2-7.0 GHz to cover the emerging wireless communication bands. At the same time, it also has a -10 dB impedance bandwidth extending from 0.7-1.01 GHz, 2.6-3.18 GHz, 5.3-6.06 GHz, and 6.7-6.94 GHz. Design steps to enhance the operating bandwidth and the isolation in the sub-1GHz bands are presented. The antenna has a reasonable realized gain at the simulated and measured frequencies. It exhibits the pattern diversity which is useful for the MIMO implementation. The envelope correlation coefficient (ECC), Mean effective gain (MEG), and the channel capacity of the antenna have been computed from the measured results. In spite of the small circuit size at f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> L</sub> , the ECC ≤ 0.50 over the entire band is observed. In addition to the existing communication applications, this antenna can find newer applications in the emerging 0.6-1.09 GHz band, sub-6GHz 5G near radio (NR), and Wi-Fi 6 communications.

5G Multi-Band Numerology-Based TDD RAN Slicing for Throughput and Latency Sensitive Services

This paper extensively examines the impact of the numerology schemes on a sliced TDD radio access network. The slices are multiplexed over both the sub-6 GHz and mmWave bands. The incorporation of numerology schemes into network slicing, the impact of which has yet to be explored, will be highly instrumental in realizing the future 5G and 6G networks. Thus, this work demonstrates the enhanced capabilities of sliced networks utilizing numerology. To that end, two optimization problems are formulated, one to maximize the downlink average spectral efficiency of a throughput-sensitive slice, and the other to minimize the uplink transmission power of the users of the latency-sensitive slice. This work optimizes key parameters such as duplex ratio, numerology scheme and optimally allocates power and bandwidth under numerology-enabled slicing. The comparative analyses highlight that for high-throughput applications, lower numerology schemes are significantly more spectrally efficient and can often achieve throughputs characteristic of higher schemes. On the other hand, the higher schemes are the best choice for the minimization of user transmission power and latency, which are crucial in energy-efficient communications and edge computing applications, respectively.

Geometrical Study of Millimeter-Wave Communication Area Covered by an Antenna Array

Because of the severe attenuation property, the communication area size of the millimeter-wave (mmWave) band is much smaller than that of the sub-6 GHz band, and the mmWave antennas must be placed at higher density, which means that a strong cost constraint is imposed on the system design. This paper aims to provide guidelines for the development of mmWave 28 GHz antenna devices by geometrically clarifying, via a numerical simulation, the number of antenna elements, the power supply, and the antenna installation conditions required for a 1000 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> coverage of the “nano-area”. The simulation results, assuming a simple line-of-sight situation with no blockages or reflectors, show that the coverage area over 1000 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> requires at least a power supply P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 1, 3, 4 and 8 dBm for 8 × 8-, 8 × 4-, 8 × 2-, and 8 × 1-element antenna arrays, respectively, for an antenna height H = 1.5 and 4.5 m and a received power sensitivity of -70 dBm. We conclude that these parameter results of the number of elements, the power supply, and the antenna height for “nano-area”coverage are important for the system design of mmWave antenna placement.

Experimental Exploration of Unlicensed Sub-GHz Massive MIMO for Massive Internet-of-Things

IoT networks are getting overcrowded following the vast increase in number of Internet-of-Things (IoT) devices and connections. Networks can be extended with more gateways, increasing the number of supported devices. However, as investigated in this work, massive MIMO has the potential to increase the number of simultaneous connections and moreover lower the energy expenditure of these devices. We present a study of the channel characteristics of massive MIMO in the narrowband unlicensed sub-GHz band. The goal is to support IoT applications with strict requirements in terms of number of devices, power consumption, and reliability. The assessment is based on experimental measurements using both a uniform linear and a rectangular array. Our study demonstrates and validates the advantages of deploying massive MIMO gateways to serve IoT nodes. While the results are general, here we specifically focus on static nodes. The array gain and channel hardening effect yield opportunities to lower the transmit power of IoT nodes while also increasing reliability. The exploration confirms that exploiting large arrays brings great opportunities to connect a massive number of IoT devices by separating the nodes in the spatial domain. In addition, we give an outlook on how static IoT nodes could be scheduled based on partial channel state information.

주파수 간섭의 이해, 분석 방법, Sub-GHz 주파수대역 적용 사례

Utilizing the frequency spectrum efficiently is critical to properly respond to increasing frequency demands owing to the rapid spread of wireless devices and the latest broadband technology trends. However, because all wireless devices emit radio waves into air, frequency interference with other wireless devices can be caused. If the use of these wireless devices is restricted owing to uncertain fears of such frequency interference, efficient utilization of the frequency spectrum becomes difficult. Therefore, it is crucial to quantitatively analyze frequency interference and establish a reasonable countermeasure against it. Therefore, this study shows that the frequency interference generated by wireless devices can be explained in terms of total interference power. However, practically, this approach is limited for various reasons. These shortcomings are discussed herein through an actual frequency allocation case considering frequency interference in the licensed and unlicensed bands of the sub-GHz band, in which several frequency interference issues are faced.

Triple Rectangular Notch UWB Antenna Using EBG and SRR

This paper investigates an ultra-wideband (UWB) antenna with a triple-rectangular notch band at 5G, WLAN, and Satellite downlink bands. The 5G and WLAN bands are notched by using a pair of electromagnetic bandgap (EBG) structures while the satellite downlink band is notched by using two split-ring resonators (SRRs). The EBG structure is a metallic conductor loaded on the backside of the radiator which is connected to the patch via a shorting pin. The SRRs consist of a pair of metallic rings etched on the backside of the feedline. The simulated and measured results show that the proposed antenna has an operational bandwidth from 3.1 - 11.8 GHz for |S11| <; -10 rejecting 5G sub-6 GHz (3.4 - 3.9 GHz), WLAN (5.15 - 5.825 GHz), and satellite downlink band (7.25 - 7.75 GHz) signals with high selectivity. The peak gain of the UWB antenna is 3.86 dBi but it sharply decreases up to -13 dBi at stop-bands. The antenna also has additional advantages of the overall compact size (20 x 26 x 1.52 mm3) with stable gain and radiation patterns at the pass-bands.

Simultaneous Nonlinear Self-Interference Cancellation and Signal of Interest Recovery Using Dual Input Deep Neural Network in New Radio Access Networks

An efficient method for simultaneous nonlinear self-interference (SI) cancellation and signal-of-interest (SOI) recovery is proposed and experimentally verified in a mmWave over fiber testbed, based on a specially designed dual-input deep neural network (DI-DNN). The mmWave band has been adopted in the U.S. to provide 5G wireless access services due to its wide-bandwidth, light-of-sight propagation, and inherent compatibility with small cell architecture. To further meet the uprising bandwidth-demanding services, the in-band full-duplex (IBFD) scheme is introduced to magnify the mmWave channel capacity for the 5G and beyond wireless communications. Fortunately, the mmWave band is more realistic to implement IBFD compared with the conventional sub-6GHz band, as it operates as a highly directional beam and shorter transmission distance resulting in a higher SOI to SI ratio. In our proposed solution, a DI-DNN is, for the first time, proposed and implemented to simultaneously realize the SI cancellation and the SOI recovery. Moreover, we firstly mitigate the nonlinearity arising from the transmitters of both the SI and SOI, as well as the nonlinear crosstalk from the SI to the SOI after detection by a nonlinear receiver. The demonstration of the DI-DNN joint with the experimental implementation in a mmWave over fiber system, promise spectral efficient, high-capacity signal transport in the 5G and beyond wireless communications.

Measurement and Simulation for Vehicle-to-Infrastructure Communications at 3.5 GHz for 5G

Intelligent Transportation System (ITS) is more and more crucial in the modern transportation field, such as the applications of autonomous vehicles, dynamic traffic light sequences, and automatic road enforcement. As the upcoming fifth-generation mobile network (5G) is entering the deployment phase, the idea of cellular vehicle-to-everything (C-V2X) is proposed. The same 5G networks, coming to mobile phones, will also allow vehicles to communicate wirelessly with each other. Hence, 3.5 GHz, as the main sub-6 GHz band licensed in 5G, is focused in our study. In this paper, a comprehensive study on the channel characteristics for vehicle-to-infrastructure (V2I) link at 3.5 GHz frequency band is conducted through channel measurements and ray-tracing (RT) simulations. Firstly, the channel parameters of the V2I link are characterized based on the measurements, including power delay profile (PDP), path loss, root-mean-square (RMS) delay spread, and coherence bandwidth. Then, the measurement-validated RT simulator is utilized to conduct the simulations in order to supplement other channel parameters, in terms of the Ricean K-factor, angular spreads, the cross-correlations of abovementioned parameters, and the autocorrelation of each parameter itself. This work is aimed at helping the researchers understand the channel characteristics of the V2I link at 3.5 GHz and support the link-level and system level design for future vehicular communications of 5G.

Design of a Broadband Radome-Enclosed Dual-Polarization Antenna Array Covering Sub-6 GHz Band with Differential Feeding

A differentially fed dual-polarized antenna with low cross-polarization is proposed for sub-6 GHz applications. The main patch is fed through two pairs of symmetrical ports, and annular-ring slits are etched around the feedings. The broadband 180° phase shifter provides a stable differential feeding structure, and a 1 mm thick radome with a parasitic patch printed on its inner surface is utilized to expand the impedance bandwidth. The impedance bandwidth of the proposed antenna ranges from 3.3 to 6.0 GHz, covering the entire sub-6 GHz band. The 4-element antenna array features low profile, wide bandwidth, low cross-polarization level, and stable gain over the entire operating band. The prototype of the antenna array is fabricated and measured, and the design is well validated by experimental results.

Channel Measurements and Modeling for 400–600-MHz Bands in Urban and Suburban Scenarios

Sub-1 GHz bands have been used for many years and now some of them will be reallocated for new applications, including the fifth generation (5G) wireless communication systems and beyond, Internet of Things (IoT), smart grid, etc. As the well-known path-loss (PL) models are mainly applicable in 2-6-GHz frequency range, a new channel measurement campaign is needed to study the propagation characteristics at sub-1 GHz bands. In this article, we conduct fixed-to-mobile wideband channel measurements at 400-600-MHz bands in urban and suburban scenarios using the time domain channel sounder. As the interference and noise signals are severe, the transmitted waveform is carefully designed to enlarge the system dynamic range. Meanwhile, ray tracing simulation is applied to construct the measurement environments and do the mutual verification with measurement results. The two-slope PL model and lognormal shadowing fading model are proposed for large-scale fading channel modeling. The root mean square (RMS) delay spread (DS), number of paths, and diffraction characteristics are also analyzed. The results will have great importance for the coming new applications at sub-1 GHz bands.

Optimal Selection of Heterogeneous Network Interfaces for High-Speed Rail Communications

Integrating millimeter Wave (mmWave) and long-term evolution (LTE) sub-6 GHz bands to provide wireless services for high-speed rails (HSRs) is a promising solution to balance the ever-rising service demand and operational cost. In this paper, we optimize the network interface selection of the mmWave and LTE interfaces for HSR communications, to minimize the operational cost while satisfying the service requests of passengers. The network interface selection problem is formulated as a finite-horizon discrete-time Markov decision process (MDP) problem. Based on the file requests and associated deadlines of a passenger and the train schedule, we solve the MDP problem ahead-of-time by using dynamic programming (DP) and achieve optimal interface selection for each waypoint along the railways. Further, by exploiting the subadditivity and superadditivity of the considered problem, we reveal that an optimal switch of interfaces is only triggered at the moment when the remaining undelivered data or the elapsed time reaches their specific thresholds. Based on the thresholds, the optimal interface selection can be directly achieved for every waypoint, hence eliminating the need for DP and substantially reducing the computational complexity. The proposed algorithms are evaluated with practical train schedules. Simulation results show that the proposed algorithms can substantially reduce the operational cost by 35% in our considered simulation setting, as compared to existing alternatives.