Slot Length Research Articles

LoRaWAN Scheduling: From Concept to Implementation

While the Internet of Things continues to grow, the LoRaWAN standard is generating special interest due to its open-source nature, ultralow-power consumption and long-range connectivity. Recent works have explored the challenges of implementing LoRaWAN, with scalability being considered one of the major bottlenecks imposed by its Aloha-based medium access control (MAC) layer. Despite much on-going research on LoRaWAN scheduling aimed at alleviating this concern, experimental approaches are rarely found in the literature. In this work, we describe the steps taken and the technical issues overcome to move from a low-overhead synchronization and scheduling concept to its real-world implementation on top of LoRaWAN Class A. Accordingly, an end-to-end architecture was designed and deployed on top of STM32L0 MCUs, which communicate with a central entity responsible for providing synchronization metrics and allocating transmission slots on demand. The clock drift of devices was measured in a temperature-controlled chamber, which served as a basis to define slot lengths in the network. As a result, an operational end-to-end system was implemented and evaluated for different setup scenarios, with 10-ms accuracy being achieved. Our experimental results show significant improvements in packet delivery ratios with respect to Aloha-based setups, especially under high network loads (up to 29% for SF12), thereby demonstrating the feasibility of the presented approach.

Multiple-input multiple-output antenna for dual-band applications with a novel radiating patch and enhanced feeding network

PurposeAn Elephant trunk shape (ETS) radiating element is used to achieve the two covering bands of multi-input multi-output (MIMO) antenna. These frequency bands can be controlled by the length of a slot embedded in ETS. The slot length in ETS plays a defining role in controlling the impedance bandwidth (IBW) of the MIMO antenna, and its diligent adjustment of it leads to cover the frequency range of Bluetooth and Wireless Local Area Network systems.Design/methodology/approachA new MIMO antenna is introduced in this paper in conjunction with an enhanced Wilkinson power divider feeding platform.FindingsThese frequency bands can be controlled by the length of a slot embedded in ETS. The slot length in ETS plays a defining role in controlling the IBW of the MIMO antenna, and its diligent adjustment leads to covering the frequency range of Bluetooth and WLAN systems.Originality/valueThe proposed MIMO antenna benefits from good isolation between ports for both frequency bands. The proposed MIMO antenna is constructed on FR4 substrate with a volume of 90 × 134 × 1.6 mm3.

Compact Multiport MIMO Antenna System for 5G IoT and Cellular Handheld Applications

A low-profile, compact, four-element, eight-port multiple-input--multiple-output and diversity antenna for 5G Internet of Things and cellular handheld applications is presented in this letter. This antenna structure contains four antenna elements, which are same in its configuration. The antenna ground dimensions are taken similar to a modern mobile handset, i.e., 60 mm × 120 mm. The four antenna elements are situated at four corners of antenna ground structure. Each antenna element has two feeding ports, thus making a total of eight-port antenna. A single antenna element has two feeding plates, which are placed perpendicular to one another so that they become cross polarized, thus exploiting polarization diversity, whereas spatial diversity also exists between different antenna elements. For reducing mutual coupling between different antenna ports, slots are cut in ground plane, including a small strip etched along the entire length of ground plane and rectangular slots cut in ground plane under every antenna element. The minimum bandwidth attained by all eight ports for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> < –10 dB is more than 1.4 GHz from 2.4 GHz to more than 3.8 GHz, which testify that it covers majority of frequency bands allocated for 5G sub-6 GHz spectrum. The isolation obtained between different ports has a minimum value of –13 dB, and the maximum value goes below –30 dB. For the covered frequency bands by this antenna structure, the correlation coefficient is found to be below 0.03, whereas the measured peak gain is in the range of 3.2--5 dB.

Flow-induced vibration suppression of elastic square cylinder using windward-suction-leeward-blowing approach

This article covers the application of the windward-suction-leeward-blowing concept in the reduction of flow-induced vibration of an elastically-mounted square-section cylinder in the active open-loop control framework. Certain slots with equal length are devised on the front and rear surfaces of the cylinder to perform flow suction and flow blowing. These slots have the same actuation velocity. To study the effectiveness of the present flow control approach, fluid-structure interaction simulations for both the lock-in (85 < Reynolds Number < 95) and galloping (Reynolds Number > 170) regions are conducted based on a finite volume code. According to the plots of maximum cylinder cross-flow displacement, planar orbital trajectories and snapshots of vorticity contours, the success of this control approach in complete suppression of vortex shedding and thus the flow-induced oscillations in both mentioned regions is shown. Also, increasing the actuation velocity and slot length improves the performance of windward-suction-leeward-blowing in flow control and vibration attenuation. The minimum actuation velocity required for attenuation of cylinder oscillations in the galloping zone is higher than that of the lock-in region. Moreover, with increasing actuation velocity and slot length, the shear layer is stretched, suppressing the vortex-shedding and changing the mode of wake structure from 2S (for lock-in region) and 2S+2P (for galloping zone) to a vortex-free symmetric wake. Also, the proposed control approach alters the orbital pattern diagrams of the cylinder that are in the form of figure-8-shaped plots and transfers them to a bounded region commensurate to the small transverse and in-line displacements of the cylinder.

DMP: Content Delivery With Dynamic Movement Pattern in Vehicular Networks

Vehicular ad-hoc networks (VANETs) have been widely studied in intelligent transportation. Content delivery is an important topic that attracts many researchers. Due to vehicles that may have intermittent connections and uncertain routes, it is difficult to select an appropriate node. In this paper, we analyze the movement pattern of vehicles from real taxis’ trajectories and propose a framework for delivery prediction, which aims to select appropriate nodes. First, we propose the framework which consists of a contact clique model, a social clique model, and a prediction model based on Markov chains, to characterize the movement pattern of vehicles. Second, we capture dynamic movement patterns by dividing the time requirement into equal length slots and construct clique sequences. Based on the fact that the sociality of nodes has strong temporal correlations, we utilize the prediction model to derive future cliques and evaluate two kinds of delivery performance in the future. Finally, we design a content delivery algorithm with dynamic movement pattern (DMP) to select the appropriate node. In our experiment, DMP performs better than that of other methods in terms of overhead, average hops. Also, as the number of nodes increases, our algorithm keeps small fluctuations in node sociality.

Compact open-ended SIW antenna based on CRLH-TL and U-shaped slots for Ku-band application

A compact open-ended substrate integrated waveguide (SIW) antenna based on composite right/left-handed transmission line (CRLH-TL) and unequal U-shaped slots for extended impedance bandwidth (IBW) and improved gain for Ku-band application is illustrated in this work. The proposed antenna comprises a CRLH-TL, which is composed of two inter-digital spiral-shaped capacitors placed on the top metal patch, which serves as series capacitor. Further, periodic metallic vias placed at the sidewalls, which act as shunt inductor for realizing the left-handed nature of CRLH-TL. To extend the antenna IBW performance, two unequal size U-shaped slots are placed at the middle of the antenna ground plane. By parametric analysis, these U-shaped slots lengths and widths are optimized to provide extended IBW ranging from 11.88 GHz to 14.05 GHz (16.74%). The antenna also offers a maximum gain of 6.1 dBi with bi-directional radiation performance, and radiation efficiency better than 96.1% is obtained throughout the complete antenna operating band. Hence the proposed SIW antenna is suitable for Ku-band applications.

A Novel UWB Monopole Antenna with Reconfigurable Band Notch Characteristics Based on PIN Diodes

Our design for a novel UWB monopole antenna structure with reconfigurable band notch characteristics based on PIN diodes is presented in this paper. The proposed antenna is comprised of a modified circular patch and a partial ground plane. The band-notch characteristics are achieved by etching a slot on the partial ground plane and inserting three PIN diodes into the slots for adjusting the operating antenna bands. The reconfigurability is achieved by adding three PIN diodes to obtain eight states with UWB, dual and triple operating bands which can be obtained by changing the PIN state from ON to OFF, and vice versa. The proposed design shows a simple biasing process to switch the frequency bands with insignificant gain variation and low radiation efficiency reduction. The reconfigurability of the frequency is accomplished by adjusting the effective slot length through modifying the PIN diodes states at the desired operating bands. The desired operating frequency bands can be obtained by switching the diodes. A systematic parametric study based on a numerical analysis is invoked to verify and refine the proposed performance. The proposed antenna is fabricated on FR-4 substrate with dimensions of 50×60×1 mm3. The proposed antenna performance was tested experimentally and compared to the simulated results from CSTMW based on FIT. Experimental results were in concordance with simulated results. We found that the proposed antenna design had simple geometry and it was easy to control the frequency bands to suit the applications of WiMAX and WiFi systems.

A Flexible Enhanced Throughput and Reduced Overhead (FETRO) MAC Protocol for ETSI SmartBAN

Smart body area networks (SmartBAN) is an emerging wireless body area networks (WBAN) standard proposed by the European Telecommunications Standards Institute (ETSI). This paper first examines the potential of SmartBAN medium access control (MAC) layer with scheduled access to support a myriad of WBAN applications, having diverse data rate requirements. Extra scheduled access slots can be allocated to high date rate sensor nodes for managing their data rate requirements. High data rate sensor nodes can also be re-assigned to use the available time slots of low data rate sensor nodes in Inter-Beacon Interval (IBI) by the central hub. But these two schemes incorporate different physical (PHY) and MAC layer overheads related to frame transmission, frame acknowledgement and slot re-assignment. This redundant overhead transmission results in high overhead energy consumption and reduced effective throughput. Therefore, an innovative and flexible enhanced throughput and reduced overhead (FETRO) MAC protocol for scheduled access is proposed in this article. In the proposed scheme, the sensor node data rate requirements are considered while assigning the scheduled access slot duration by allowing minimal changes in the base-line standard implementation. This infers the provision of scheduled access slots with variable slot durations within an IBI. We also evaluate the existing techniques of extra slot allocation and slot re-assignment in SmartBAN as well as the proposed FETRO MAC protocol with variable slot length. The proposed FETRO MAC scheme results in optimizing both the overall throughput and normalized overhead energy consumption per kilo bits per second (Kbps). Additionally, the impact of various WBAN channel models over these throughput management approaches is also investigated. The proposed FETRO MAC protocol with variable slot duration gives an average reduction of 65.5 and 59.16 percent, respectively, in the hub and nodes normalized overhead energy consumption per Kbps outcomes, as compared to the de-facto SmartBAN MAC scheduling strategies.

Transient Roebel Bar Force Calculation in Large Salient-Pole Synchronous Machines

The radial and tangential force components acting on each sub-conductor of a Roebel bar in a large generator lead to mechanical vibration of the stator bars in the slot. This double-frequency vibration results in additional mechanical stress on fixation materials in the slot and causes insulation deterioration and looseness of stator bars. Particularly during short circuits, the stator bars are subjected to immense radial forces. Understanding the origin of these vibrations and developing models to anticipate them is essential to increase the reliability and expected life time of large generators. This paper presents an analytical method for the estimation of Roebel bar forces during symmetrical and asymmetrical short circuits. For this purpose, an analytical calculation method is developed to estimate the transient three-phase currents during different short circuits. These currents induce tangential and radial flux density components along the slot width and length, respectively. An analytical approach is introduced to estimate these flux densities as a function of the slot length. Subsequently, an analytical method for calculating the Roebel bar forces considering three-dimensional transpositions is developed and verified with finite element calculations. Beyond the state of the art, the impact of the rotor field on the radial and tangential components of the stray fluxes are analytically estimated. The result is a comprehensive analytical tool for the estimation of Roebel bar forces during different short circuits in large generators.

Miniature tri‐polarized MIMO slit‐postwall step impedance resonator slot antenna array

A miniaturized tri-polarized MIMO slot antenna loaded with slit-postwall-slot step impedance resonator (SIR) is proposed. The SIR, which shortens the length of radiation slot for the miniature purpose, consist of two slit-slot lines with high impedance and a slit-postwall-slot line with low impedance, because the postwall can decrease the characteristic impedance of slit-slot line. Meanwhile, the slits can improve the polarization purity and isolation of the antenna array effectively. Compared with the conventional slot antenna array, the measured results of proposed antenna array shows that the cross-polarization ratio has improved 2 dB on H plane and 3 dB on E plane at 2.45 GHz, while the lengths of ground plane and slot are shortened 77.8% and 77%, respectively. Furthermore, the proposed antenna array operates at dual band and the isolation are −22 dB at 2.45 GHz and -27 dB at 4 GHz. The performance and structure of the proposed antenna array can be applied for the condition of high polarization purity and demanding volume.

Frequency Selective Surface With Quasi-Elliptic Bandpass Response Using Radiation Null of Patch Antenna

A novel design of bandpass frequency selective surface (FSS) with high selectivity is proposed based on the antenna-filter-antenna (AFA) concept. Traditional AFA-based FSSs improve filtering performance by adding the order of resonator or the coupling paths. On account of the reciprocity theorem, transmission zeros are here introduced by the antenna's radiation null. The proposed FSS consists of two patch antennas connected with one pin and a C-type slot on the ground. The aforementioned structure generates two controllable radiation nulls related to the lengths of slots without any extra circuits. Therefore, two transmission zeros at both edges of the passband can be controlled by adjusting the dimension of slots. A prototype is fabricated and measured. Numerical simulation and measured results are in good agreement, which demonstrates that the proposed AFA-based FSS exhibits a quasi-elliptic bandpass response and a low profile.

Numerical investigation of active flow control with co-flowing jet in a horizontal axis wind turbine

In this paper, a three-dimensional numerical simulation of the aerodynamic performance of a horizontal axis wind turbine (HAWT) whose blades are equipped with a new active flow control concept called Co-Flowing Jet (CFJ) is carried out. Numerical results show that the use of CFJ over the blade suction surface can effectively delay flow separation, thus improving the net torque and power output of HAWT. Besides, this increment in the net power produced by the turbine is considerably higher than the power consumed by the CFJ. Thus, the overall efficiency of the HAWT can be greatly increased. Furthermore, influences of different CFJ operating parameters including location of injection port, jet momentum coefficient and slot length on the performance enhancement of a HAWT are also systematically studied and the optimal combination of these parameters to obtain the best possible turbine efficiency throughout a range of different wind speeds has been identified.

THE SLOT LENGTH OF A FAMILY OF MATRICES

AbstractWe introduce the notion of the slot length of a family of matrices over an arbitrary field ${\mathbb {F}}$ . Using this definition it is shown that, if $n\ge 5$ and A and B are $n\times n$ complex matrices with A unicellular and the pair $\{A,B\}$ irreducible, the slot length s of $\{A,B\}$ satisfies $2\le s\le n-1$ , where both inequalities are sharp, for every n. It is conjectured that the slot length of any irreducible pair of $n\times n$ matrices, where $n\ge 5$ , is at most $n-1$ . The slot length of a family of rank-one complex matrices can be equal to n.

Design procedure for planar slotted waveguide antenna arrays with controllable sidelobe level ratio for high power microwave applications

SummaryThis article presents a complete design procedure for planar slotted waveguide antennas (SWA). For a desired sidelobe level ratio (SLR), the proposed method provides a pencil shape pattern with a narrow half power beamwidth, which makes the proposed system suitable for high power microwave applications. The proposed planar SWA is composed of only two layers, and uses longitudinal coupling slots rather than the conventional inclined coupling slots. For a desired SLR, the slots excitation in the radiating and feeder SWAs are calculated based on a specified distribution. Simplified closed‐form equations are then used to determine the slots nonuniform displacements, for both the radiating and feeder SWAs, without the need to use optimization algorithms. Using simplified equations, the slots lengths, widths, and their distribution along the length of the radiating and feeder SWAs can be found. The feeder dimensions and slots positions are deduced from the dimensions and total number of the radiating SWAs. An 8 × 8 planar SWA has been designed and tested to show the validity of the proposed method. The obtained measured and simulated results are in accordance with the design objectives.

High Figure of Merit Optical Buffering in Coupled-Slot Slab Photonic Crystal Waveguide with Ionic Liquid.

Slow light with adequate low group velocity and wide bandwidth with a flat band of the zero-dispersion area were investigated. High buffering capabilities were obtained in a silicon-polymer coupled-slot slab photonic crystal waveguide (SP-CS-SPCW) with infiltrating slots by ionic liquid. A figure of merit (FoM) around 0.663 with the lowest physical bit length of 4.6748 µm for each stored bit in the optical communication waveband was gained by appropriately modifying the square air slot length. Posteriorly, by filling the slots with ionic liquid, the was enhanced to be 4.2817 μm with the highest FoM of 0.72402 in wider transmission bandwidth and ultra-high bit rate in terabit range, which may become useful for the future 6G mobile communication network. Ionic liquids have had a noticeable effect in altering the optical properties of photonic crystals. A polymer was used for the future incorporation of an electro-optic effect in buffers to realize the dynamic controlling of optical properties. Ionic liquids enhanced the transmission rate through optical materials. Additionally, the delay time in the ns-range was achieved, providing longer delay and ultra-low group velocity, which is important for light-matter interaction in light amplifiers and nonlinear devices.

Investigation on the vibration characteristics of circular saw blade with different slots

Irregular vibration of circular saw blade caused by complex forces in the process of cutting harms the operators, product quality and the life of circular saw blade. In this paper, the modal analysis of circular saw blades with different slot length and four kinds of unequal slot length saw blades are carried out based on the finite element theory. The vibration characteristics of circular saw blades with different slot length is studied. The results show that the natural frequency and the maximum deformation increase with the increasing slot length. In the case of higher order after the 5th order, the phenomenon is even more obvious. The effects of slot length, slot depth and diamond segment on natural frequency are compared. The results show that slot length has the greatest effect on natural frequency. Circular saw blades of different structures with unequal slot length can be selected to avoid resonance during operation.

Investigation on impact absorbed energy index of drill pipe

Drill pipe is one of the most important tools for petroleum and natural gas drilling exploitation. The application of S135 drill pipe can significantly increase drilling depth, reduce drilling cost and improve drilling quality. Impact absorbed energy is the most important toughness index, which has a decisive influence on the service safety of drill pipe. The statistical results of 91 drill pipe failure cases show that the piercing is the main failure mode of S135 drill pipe, including oval-shaped piercing and slot piercing. The length of oval-shaped piercing hole is mainly distributed in 20–50 mm, and the impact absorbed energy of failed drill pipe is dispersed in 42–156 J. The length of slot piercing hole is mainly distributed in 60–90 mm, and impact absorbed energy of failed drill pipe is concentrated in 76–150 J. Analysis results show that there is certain correlation between the length of piercing hole and impact absorbed energy values of drill pipes. In this work, the impact absorbed energy index calculation formula of “leakage before fracture” failure mode for drill pipe is proposed. The results show that the impact absorbed energy value increases with the increasing of critical crack length, square of stress strength coefficient and strength level. The impact absorbed energy value of S135 drill pipe should be greater than 80 J to ensure the service safety.

A High Gain Elliptical Slot Antenna for Lower C-band and X-band Application

A novel design of printed CPW-fed planar elliptical slot antenna with transformed circular patch is presented here for dual-band application. The obtained impedance band finds application in lower C-band satellite communication and entire X-band with significant gain. Electromagnetic wave simulator HFSS® is used to simulate the structure and the study of parameter behaviour is carried out. The performance of the proposed antenna in terms of return loss, radiation pattern and gain are analysed. Furthermore, the same structure is designed and simulated with microstrip feed line. An imperial formula in terms of axial length and ellipticity ratio of the elliptical slot is formulated to find the lower edge frequency of impedance bandwidth.

PSPL: A Generalized Model to Convert Existing Neighbor Discovery Algorithms to Highly Efficient Asymmetric Ones for Heterogeneous IoT Devices

Neighbor discovery is a prerequisite procedure in communication among energy-limited Internet-of-Things (IoT) devices. Discovering neighbors should be achieved in an energy-efficient way. Communication between heterogeneous IoT devices is a common phenomenon for achieving extensive connections among IoT devices. Generally, existing asymmetric neighbor discovery methods are evolved from the symmetric methods and lack specialized designs for heterogeneous IoT devices which led to relatively poor energy-efficient performance. In this article, we use a generalized slot model using pure sending (PS) slot and pure listening (PL) slot, called PSPL, to convert existing neighbor discovery algorithms (symmetric and asymmetric) to highly energy-efficient asymmetric ones. The core idea of PSPL is that to achieve highly energy-efficient one-way discovery , PS slot and PL slot are only used in devices with smaller and larger energy budgets, respectively, and the length of PL slot is much larger than that of PS slot. In this way, the energy efficiency of asymmetric neighbor discovery can be substantially improved. After implementing one-way discovery , two-way discovery can be easily achieved with mutual assistance. Two examples of how to convert existing algorithms into highly efficient asymmetric ones are presented, the one is to convert Disco to Disco+PSPL and the other one is to convert Griassdi to Griassdi+PSPL. The theoretical analysis results indicate that with the same energy budget, Disco+PSPL and Griassdi+PSPL reduce the worst case latency bounds by up to 82.28% and 87.69%, respectively, compared with the best known asymmetric solutions. The simulation evaluation verifies the effectiveness of our designs.

Particle swarm optimization based metamaterial inspired circularly polarized patch antenna for S band applications

In this paper Particle Swarm Optimization technique (PSO) has been used to design a metamaterial inspired circularly polarised patch antenna with truncated corners and embedded square slots. The circular polarization has been achieved by trimming the corners of the square patch along one of its diagonal and square slots have been embedded along these truncated corners to improve the 3 dB axial ratio bandwidth of this proposed antenna. To achieve the maximum axial ratio bandwidth, the dimensions of this square slot have been optimized using PSO algorithm. Without any square slot, the axial ratio bandwidth of the patch antenna is 700 MHz. However, when square slots are embedded along the trimmed corners, with slot length w = 2.3 mm, axial ratio bandwidth of 1150 MHz is achieved. But, when PSO is applied to obtain the optimized dimension of this square slot so as to maximize this axial ratio bandwidth, the optimised w is determined to be 2.8 mm and the axial ratio bandwidth with this optimized slot length is determine to be 1600 MHz. Thus it is observed that by using the optimized value of w, obtained by using PSO technique, improvement in axial ratio bandwidth by 450 MHz is observed. To improve its gain, an array of splitted circular metamaterial rings is etched on the ground plane of this proposed patch antenna. The circularly polarised patch antenna with truncated corners resonates at 2.4 GHz with gain of 4.8 dBic and impedance bandwidth of 600 MHz. However, when square shaped slots of optimized length are embedded in the truncated corners and metamaterial substrate is loaded on the ground plane of this antenna, its gain reaches to 5.2 dBic. All simulations are done in an electronic simulator, HFSS.