High-quality Channel Research Articles

Fully Textile Dual-Band Logo Antenna for IoT Wearable Devices.

In recent years, the interest in the Internet of Things (IoT) has been growing because this technology bridges the gap between the physical and virtual world, by connecting different objects and people through communication networks, in order to improve the quality of life. New IoT wearable devices require new types of antennas with unique shapes, made on unconventional substrates, which can be unobtrusively integrated into clothes and accessories. In this paper, we propose a fully textile dual-band logo antenna integrated with a reflector for application in IoT wearable devices. The proposed antenna’s radiating elements have been shaped to mimic the logo of South-West University “Neofit Rilski” for an unobtrusive integration in accessories. A reflector has been mounted on the opposite side of the textile substrate to reduce the radiation from the wearable antenna and improve its robustness against the loading effect from nearby objects. Two antenna prototypes were fabricated and tested in free space as well as on three different objects (human body, notebook, and laptop). Moreover, in the two frequency ranges of interest a radiation efficiency of 25–38% and 62–90% was achieved. Moreover, due to the reflector, the maximum local specific-absorption rate, which averaged over 10 g mass in the human-body phantom, was found to be equal to 0.5182 W/kg at 2.4 GHz and 0.16379 W/kg at 5.47 GHz. Additionally, the results from the performed measurement-campaign collecting received the signal-strength indicator and packet loss for an off-body scenario in real-world use, demonstrating that the backpack-integrated antenna prototype can form high-quality off-body communication channels.

КОМУНІКАТИВНА ВЗАЄМОДІЯ ВИКЛАДАЧА І КУРСАНТА В ПРОЦЕСІ ФОРМУВАННЯ КУЛЬТУРИ ПРОФЕСІЙНОГО МОВЛЕННЯ У ЗАКЛАДІ ЛЬОТНОЇ ВИЩОЇ ОСВІТИ

The article reveals the peculiarities of the dialogical form of communication in the process of foreign language training in the institution of higher flight education. This article notes that a direct realization of professional communication of the air traffic controller in the workplace is performed via radio exchange. Civil aviation radio communication is an act of speech interaction, the exchange of professional information between the aircraft crew and ground control services and/or other aircraft, carried out through high-quality communication channels. The content of such communication is determined by the real circumstances in the ATC area, which are expressed in graphic and audiovisual form on the screens of instruments and consoles. The article also mentions that in the organization of the educational process, in particular, today and in the training of future air traffic controllers, as a way to exchange these messages often use one-way communication. Thus, the informational side of learning is preferred and procedurally underestimated is the fact that students quickly assimilate ready-made knowledge and the inability to independently acquire and use it. Such a monologue hinders the individualization of learning, taking into account the personal beginnings of the student and his self-realization, it does not correspond to the communicative component of modern life. The article also pays attention to the fact that radio exchange presupposes the presence of two parties - participants in radio exchange, which are the crew commander on the air side, and on the ground side - the controllers of interacting air traffic control points. The relations between the communicating participants are determined by the established rules of radio exchange. Among the two communicators, the representative of the control service is the main one, because it is he who transmits instructions on board the aircraft and monitors the movement of the aircraft; yes, communicators have their own functions in dialogue.

Doubling the mobility of InAs/InGaAs selective area grown nanowires

Selective area growth (SAG) of nanowires and networks promise a route toward scalable electronics, photonics, and quantum devices based on III-V semiconductor materials. The potential of high-mobility SAG nanowires however is not yet fully realised, since interfacial roughness, misfit dislocations at the nanowire/substrate interface and nonuniform composition due to material intermixing all scatter electrons. Here, we explore SAG of highly lattice-mismatched InAs nanowires on insulating GaAs(001) substrates and address these key challenges. Atomically smooth nanowire/substrate interfaces are achieved with the use of atomic hydrogen (a-H) as an alternative to conventional thermal annealing for the native oxide removal. The problem of high lattice mismatch is addressed through an ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ buffer layer introduced between the InAs transport channel and the GaAs substrate. The Ga-In material intermixing observed in both the buffer layer and the channel is inhibited via careful tuning of the growth temperature. Performing scanning transmission electron microscopy and x-ray diffraction analysis along with low-temperature transport measurements we show that optimized In-rich buffer layers promote high-quality InAs transport channels with the field-effect electron mobility over 10 000 ${\mathrm{cm}}^{2}$ ${\mathrm{V}}^{\ensuremath{-}1}$ ${\mathrm{s}}^{\ensuremath{-}1}$. This is twice as high as for nonoptimized samples and among the highest reported for InAs selective area grown nanostructures.

ChannelGAN: Deep Learning-Based Channel Modeling and Generating

The increasing complexity on channel modeling and the cost on collecting plenty of high-quality wireless channel data have become the main bottlenecks of developing deep learning (DL) based wireless communications. In this letter, a DL-based channel modeling and generating approach namely ChannelGAN is proposed. Specifically, the ChannelGAN is designed on a small set of 3rd generation partnerships project (3GPP) link-level multiple-input multiple-output (MIMO) channel. Moreover, two evaluation mechanisms including i) power comparison from the perspective of delay and antenna domain and ii) cross validation are implemented where the power comparison proves the consistency between the modeled fake channel and real channel, and the cross validation verifies the effectiveness and availability of the generated fake channel for supporting related DL-based channel state information (CSI) feedback.

Tunable Spin Injection in High-Quality Graphene with One-Dimensional Contacts.

Spintronics involves the development of low-dimensional electronic systems with potential use in quantum-based computation. In graphene, there has been significant progress in improving spin transport characteristics by encapsulation and reducing impurities, but the influence of standard two-dimensional (2D) tunnel contacts, via pinholes and doping of the graphene channel, remains difficult to eliminate. Here, we report the observation of spin injection and tunable spin signal in fully encapsulated graphene, enabled by van der Waals heterostructures with one-dimensional (1D) contacts. This architecture prevents significant doping from the contacts, enabling high-quality graphene channels, currently with mobilities up to 130 000 cm2 V–1 s–1 and spin diffusion lengths approaching 20 μm. The nanoscale-wide 1D contacts allow spin injection both at room and at low temperature, with the latter exhibiting efficiency comparable with 2D tunnel contacts. At low temperature, the spin signals can be enhanced by as much as an order of magnitude by electrostatic gating, adding new functionality.

DAHP–TOPSIS-Based Channel Decision Model for Co-Operative CR-Enabled Internet on Vehicle (CR-IoV)

The Internet of Vehicles (IoV) is an important idea in developing intelligent transportation systems and self-driving cars. Vehicles with various wireless networking options can communicate both inside and outside the vehicles. IoVs with cognitive radio (CR) enable communication between vehicles in a variety of communication scenarios, increasing the rate of data transfer and bandwidth. The use of CR can meet the future need for quicker data transport between vehicles and infrastructure (V2I). Vehicles with CR capabilities on VANET have a different appearance than regular VANET vehicles. This paper aims to develop effective spectrum management for CR-equipped automobiles. An improved channel decision model has been proposed with proven outcomes to boost the pace of transmission, eliminate end-to-end delays, and minimize the number of handoffs. Many high-bandwidth channels will be used in the near future to communicate large-sized multimedia content between vehicles and roadside units (RSU) for both entertainment and safety purposes. Co-operative sensing promotes energy-constrained CR vehicles for sensing a wide spectrum, resulting in high-quality communication channels for requesting vehicles. Our research on the CR-VANET focuses on channel decision instead of spectrum sensing and it differs from previous studies. We used the DAHP–TOPSIS model under multi-criteria decision analysis (MCDA), a sub-domain of operations research, to boost profits, i.e., transmission rate with less computing time. We constructed a test-bed in MATLAB and carried out several analyses to demonstrate that the suggested model performs better than other parallel MCDA models because there has been a limited amount of research work conducted with CR-VANET

Enhancement of InSe Field-Effect-Transistor Performance against Degradation of InSe Film in Air Environment.

The degradation of InSe film and its impact on field effect transistors are investigated. After the exposure to atmospheric environment, 2D InSe flakes produce irreversible degradation that cannot be stopped by the passivation layer of h-BN, causing a rapid decrease for InSe FETs performance, which is attributed to the large number of traps formed by the oxidation of 2D InSe and adsorption to impurities. The residual photoresist in lithography can cause unwanted doping to the material and reduce the performance of the device. To avoid contamination, a high-performance InSe FET is achieved by a using hard shadow mask instead of the lithography process. The high-quality channel surface is manifested by the hysteresis of the transfer characteristic curve. The hysteresis of InSe FET is less than 0.1 V at Vd of 0.2, 0.5, and 1 V. And a high on/off ratio of 1.25 × 108 is achieved, as well relative high Ion of 1.98 × 10−4 A and low SS of 70.4 mV/dec at Vd = 1 V are obtained, demonstrating the potential for InSe high-performance logic device.

Foreword: Journal of the Finnish Economic Association 1/2020

We are very happy to provide the very first issue of the Journal of the Finnish Economic Association (JFEA). JFEA is a new peer-reviewed international journal published biannually by the Finnish Economic Association and it replaces the Finnish Economic Papers. The objective of JFEA is to provide a high-quality and fast peer-reviewed publication channel for applied economic papers, and facilitate communication of topical research results to the research community and policymakers.

Multi-User Scheduling for 6G V2X Ultra-Massive MIMO System.

6G vehicle-to-everything (V2X) communication will be combined with vehicle automatic driving technology and play an important role in automatic driving. However, in 6G V2X systems, vehicle users have the characteristics of high-speed movement. Therefore, how to provide stable and reliable wireless link quality and improve channel gain has become a problem that must be solved. To solve this problem, a new multi-user scheduling algorithm based on block diagonalization (BD) precoding for 6G ultra-massive multiple-input multiple-output (MIMO) systems is proposed in this paper. The algorithm takes advantage of the sensitive nature of BD precoding to channel correlation, uses the Pearson coefficient after matrix vectorization to measure the channel correlation between users, defines the scheduling factor to measure the channel quality according to the user noise enhancement factor, and jointly considers the influence of the correlation between user channels and channel quality, ensuring the selection of high-quality channels while minimizing channel correlation. Simulation results show that compared with the multi-user scheduling algorithm based on subspace correlation, condition number, and geometric angle, the proposed algorithm can obtain higher user channel gain, effectively reduce the system bit error rate, and can be applied to 6G V2X communication.

Time-resolved investigation of plasmon mode along interface channels in integer and fractional quantum Hall regimes

The authors investigate here the fundamental charge dynamics of interface quantum Hall (QH) channels, formed at the interface of two QH regions, by using a time-resolved scheme. The measured plasmon mode is delayed and broadened due to the influence of charge puddles formed around the channel. The transport behavior can be understood with a distributed circuit model, which reveals the importance of gate-puddle capacitive coupling on plasmon dissipation. By reducing the puddle capacitance, a high-quality fractional interface channel can be realized.

Improved ISR for IEEE 802.11ah Nonlinearity Compensation via Adjustable Constellation Borders

Iterative subcarrier regularization (ISR) has been recently proposed as a receiver-side remedy for orthogonal frequency division multiplexing (OFDM) nonlinearity. It allows the power amplifier of OFDM transmitters to operate at a lower input back-off for more efficient uplinks. However, the compensation ability cannot align with increasing channel quality, because the standard quadrature amplitude modulation (QAM) used in ISR may eliminate compensation due to erroneous decisions. To solve this issue, an improved version of ISR was proposed to flexibly adjust the constellation borders of QAM and numerically optimize it based on IEEE 802.11ah (hereinafter referred to as 802.11ah) specifications. Simulations show that the proposed scheme not only improves the converged bit error rate of ISR but also accelerates its own convergence, especially in a high channel quality, thereby achieving better power efficiency for Internet of Things clients without additional computational complexity.

Numerical simulation of borehole wall remodel during gas drainage

Gas drainage bearing coal and rock mass can be simplified as isotropic homogeneous body with gas saturation. Numerical method was used to study the influence of borehole wall remodel-size, remodel-length and negative pressure on gas drainage effect which based on gas diffusion and seepage equation of pore fracture system and governing equation of coal and rock mass degeneration. The results showed that borehole wall remodel can maintain the support of coal skeleton in borehole and prevent blocking the gas flow channel, gas pressure drop in remodelled section is more obvious than that in the non-remodelled section, the longer the remodelled length of borehole wall the more smooth the gas flow channel between borehole and coal body around borehole, with the increase of negative pressure, the decrease range of gas pressure at the same depth increases, but the difference is small under different negative pressure. On the premise of preventing borehole creep instability, borehole wall remodel can provide high-quality gas flow channel for coal seam gas drainage, maintain the continuous influence of negative pressure on coal body along borehole depth to extend the life cycle of gas drainage and is not sensitive to borehole wall remodel size and negative pressure.

Gate-tunable photodetector and ambipolar transistor implemented using a graphene/MoSe2 barristor

Next-generation electronic and optoelectronic devices require a high-quality channel layer. Graphene is a good candidate because of its high carrier mobility and unique ambipolar transport characteristics. However, the on/off ratio and photoresponsivity of graphene are typically low. Transition metal dichalcogenides (e.g., MoSe2) are semiconductors with high photoresponsivity but lower mobility than that of graphene. Here, we propose a graphene/MoSe2 barristor with a high-k ion-gel gate dielectric. It shows a high on/off ratio (3.3 × 104) and ambipolar behavior that is controlled by an external bias. The barristor exhibits very high external quantum efficiency (EQE, 66.3%) and photoresponsivity (285.0 mA/W). We demonstrate that an electric field applied to the gate electrode substantially modulates the photocurrent of the barristor, resulting in a high gate tuning ratio (1.50 μA/V). Therefore, this barristor shows potential for use as an ambipolar transistor with a high on/off ratio and a gate-tunable photodetector with a high EQE and responsivity.

Superfast Growth Dynamics of High-Quality Silicon Nanowires on Polymer Films via Self-Selected Laser-Droplet-Heating

Growing high quality silicon nanowires (SiNWs) at elevated temperature on cooler polymer films seems to be contradictive but highly desirable for building high performance flexible and wearable electronics. In this work, we demonstrate a superfast (vnw > 3.5 μm·s-1) growth of high quality SiNWs on polymer/glass substrates, powered by self-selected laser at 808 nm heating of indium catalyst droplets that absorb amorphous Si layer to produce SiNWs. Because of the tiny heat capacity of the nanodroplets, the SiNW growth can be quickly heated up and frozen via rapid laser ON/OFF switching, enabling a deterministic diameter modulation in the ultralong SiNWs. Finally, prototype field effect transistors are also fabricated upon the laser-droplet-heating grown SiNWs with a high Ion/Ioff ratio of >104 and reasonable subthreshold swing of 386 mV·dec-1, opening a generic new route to integrate high-quality NW channels directly upon large area and lightweight polymer substrates for developing high-performance flexible electronics.

Wearable Magnetoinductive Waveguide for Low-Loss Wireless Body Area Networks

A novel approach of wearable magnetoinductive waveguide (MIW) is introduced for wireless body area network (WBAN) communications that brings forward significant advances over state-of-the-art. The MIW consists of series of electrically small resonant loops worn upon the human body to support magnetoinductive waves (MI waves) for low-loss/low-power WBANs. Compared to previous approaches, the proposed MIW exhibits 63 dB lower loss, translating conventional power levels of mW down to μW or nW. In this work, we introduce the operating principle of MIW WBAN through underlying theory and dispersion diagrams. The proof-of-concept numerical and experimental results are reported for frequency bands centered around 40.4 and 80.7 MHz for a cylindrical human limb and are found to be in excellent agreement. Design guidelines are extensively discussed to accommodate several possible scenarios (frequency selection, gap between the loops, number of loops, and loop radius) along with practical considerations including loop tilts, anatomical limbs, limb movements, unequal loop gaps, and loop failure. Specific absorption rate (SAR) calculations confirm that this technology is highly safe for human use. A bit error rate (BER) analysis further demonstrates that the MIW can form a high-quality communication channel for WBAN. Overall, the reported approach unveils a new possibility of low-loss and seamless WBANs.

Randomized Approximate Channel Estimator in Massive-MIMO Communication

Massive MIMO is considered as one key enabling technology in 5G communications. Although the high-quality channel state information (CSI) estimation is essential to improve the energy/spectrum efficiency of massive MIMO systems, the optimal MMSE estimator unfortunately creates one major challenge, due to its formidable computation complexity. In this letter, we propose a rank-restrained low-complexity MMSE channel estimator for massive MIMO communications, leveraging a novel concept of randomized low-rank approximation. To accomplish this, we first design a two-stage pilot training scheme. Rather than directly estimating the large channel matrix as usual, we then acquire two low-dimensional subsets of it, which respectively gives the row and column sampling version of unknown channel matrix. Finally, we reconstruct the complete channel matrix via such two estimated low-dimensional sketches, by exploiting the low-rank structure of channel. As demonstrated, our scheme significantly reduces the time complexity as well as the energy consumption in CSI acquisition, which yet attains the near-optimal estimation accuracy. It thus provides great promises to the practical deployment of massive MIMO communications.

High Performance and Efficiency Resonant Photo-Effect-Transistor by Near-Field Nano-Strip-Controlled Organic Light Emitting Diode Gate.

Phototriggered devices have attracted attention due to their exceptional characteristics, advanced multifunctionalities and unprecedented applications in optoelectronic systems. Here, we report a pioneer structural device, a resonant photoeffect-transistor (RPET) with a functionalized nanowire (NW) charge transport channel, modulated by a near-field nanostrip organic light emitting diode (OLED) and controlled by a gate bias to realize exceptional photoelectric properties. The RPET presents high-quality nanowire channel characteristics due to tunable optical cavities manifesting strong standing wave resonance under controlled light emission. To enhance performance, methodical analyses were carried out to determine the effects of the structural design, electric field distribution and charge carrier generation on photoresponsivity when light traverses a single or multiple nanoslit masks. The developed RPET yields stable photocurrents in the 105 range and generates current on/off ratios upward of 106 under the influence of intense electromagnetic distribution, effectively lending itself to promising opportunities in fully integrated optoelectronic devices.

Natural fractures in the Triassic tight sandstones of the Dongpu Depression, Bohai Bay Basin, eastern China: The key to production

Natural fractures are identified as high-quality storage space and seepage channels for the Triassic tight sandstone reservoirs in the Dongpu Depression, playing an important role in tight sandstone oil production. We have evaluated natural fracture growth at different scales using outcrops, cores, thin sections, and imaging logs and analyzed the correlation between fractures and crude oil production capacity with production data. Results show that natural fractures primarily are distributed in fine sandstones and siltstones, which mostly are shear fractures of near east–west and northeast–southwest strikes. The natural fractures of near east–west strikes generally are parallel to the present-day maximum horizontal principal stress with the biggest apertures and the highest permeability, which are the main seepage channels, next being the fractures of northeast–southwest strike. The natural fractures of near east–west strikes also are the most important contributors to the crude oil production in the Triassic tight sandstones of the Dongpu Depression. The intensity, permeability, and direction of natural fractures govern the crude oil productivity in the per-unit sandstone thickness.

A Local Channel Blacklisting Method Using Adaptive Channel-Quality Estimation in TSCH-Based Wireless Sensor Networks

Owing to the development of the Internet of Things (IoT) paradigm, the energy consumption of devices and the reliability of communication have become important issues. Enhanced TSCH technology introduces a technique to select high-quality channels by using energy detection in the TSCH protocol to improve the reliability of communication in a dynamic environment where interference changes. However, it is difficult to apply ETSCH technology to a multi-hop network because the node that performs energy detection consumes more energy than the node that does not. In this article, we propose an adaptive channel-quality estimation (ACE), which flexibly adjusts the duty cycle of energy detection according to whether interference dynamically changes or not. ACEs are generally applicable regardless of the degree of change of interference, which improves energy efficiency. Also, we present ACE-blacklisting based TSCH (ACEBTSCH) that uses ACE and local channel blacklisting to blacklist the wireless channel based on energy detection in a multi-hop network. Experimental results show that ACEB-TSCH has a performance improvement of 15.94% over TSCH and 8.59% over PDR-blacklisting based TSCH.

Atomic Layer Deposition Process-Enabled Carrier Mobility Boosting in Field-Effect Transistors through a Nanoscale ZnO/IGO Heterojunction.

Low-temperature (≤400 °C), stackable oxide semiconductors are promising as an upper transistor ingredient for monolithic three-dimensional integration. The atomic layer deposition (ALD) route provides a low-defect, high-quality semiconducting oxide channel layer and enables accurate controllability of the chemical composition and physical thickness as well as excellent step coverage on nanoscale trench structures. Here, we report a high-mobility heterojunction transistor in a ternary indium gallium zinc oxide system using the ALD technique. The heterojunction channel structure consists of a 10 nm thick indium gallium oxide (IGO) layer as an effective transporting layer and a 3 nm thick, wide band gap ZnO layer. The formation of a two-dimensional electron gas was suggested by controlling the band gap of the IGO quantum well through In/Ga ratio tailoring and reducing the physical thickness of the ZnO film. A field-effect transistor (FET) with a ZnO/In0.83Ga0.17O1.5 heterojunction channel exhibited the highest field-effect mobility of 63.2 ± 0.26 cm2/V s, a low subthreshold gate swing of 0.26 ± 0.03 V/dec, a threshold voltage of -0.84 ± 0.85 V, and an ION/OFF ratio of 9 × 108. This surpasses the performance (carrier mobility of ∼41.7 ± 1.43 cm2/V s) of an FET with a single In0.83Ga0.17O1.5 channel. Furthermore, the gate bias stressing test results indicate that FETs with a ZnO/In1-xGaxO1.5 (x = 0.25 and 0.17) heterojunction channel are much more stable than those with a single In1-xGaxO1.5 (x = 0.35, 0.25, and 0.17) channel. Relevant discussion is given in detail on the basis of chemical characterization and technological computer-aided design simulation.