Ac Standard Research Articles

Inter-laboratory Comparison between Particle and Bacterial Filtration Efficiencies of Medical Face Masks in the COVID-19 Context

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) transmission lead to the recommendation of mask wearing during the pandemic COVID-19. Bacterial filtration efficiency (BFE) measurements are used to measure the efficiency of medical face masks in preventing the spread of bioaerosols. Even though these measurements are simple, BFE testing still raise several scientific questions. This paper presents an inter-laboratory comparison between Bacterial Filtration Efficiency (BFE) and Particle Filtration Efficiency (PFE), in order to better understand and establish an overview of both ways for testing surgical masks. Filtration efficiency of six commercial surgical masks have been measured using such experimental methods, i.e., the BFE and the PFE using 3 µm particles initially developed for community face covering testing. The fractional filtration efficiencies have been measured and compared in order to explain the differences. Recommendations for improving associated EN14683:2019+AC standard are also proposed according to the results.

Development of Electrical Quantities Primary Standards

The developments of primary standards for electrical quantities that practically realize the electrical units such as ampere (A), volt (V), ohm (Ω), and farad (F) are introduced in this manuscript. These quantities are achieved in consistency with their definitions. According to the new definition of ampere, current can be realized directly such as single electron transport (SET) pump or indirectly using Ohm’s law. For the SET pump, developments are ongoing as trials to obtain higher current values with lower associated uncertainty to be suitable for metrological applications. With the discoveries of the Effects of Josephson and quantum Hall, it has become possible to consider quantum electrical standards that relate the volt and ohm units to h and e through the Josephson and the von Klitzing constants, respectively. The dc programmable Josephson standard was developed to overcome the problems of conventional standards such as stability and noise immunity with lower cost. Developments are continuing on ac Josephson standards to improve performance and increase output voltages and frequencies. For ac voltage measurements for voltages up to 1000 V, thermal voltage converters are introduced to extend the traceability for measuring the ac voltages in the frequency range from 10 Hz to 100 MHz where quantum-based ac standards still have limitations. Thermal current converters are used as the most accurate and precise standard for measurement of ac currents. The realization of ohm is done by the quantum Hall effect through a quantum Hall resistance (QHR) standard. Developments are occurring to make it simpler, more precise and accurate. The efforts that have been made to increase the values of the resistance quantum hall standard to disseminate its accuracy to other standard resistors to help in industry are also introduced. The farad is practically achieved by the calculable cross-capacitor. The calculable capacitor acts as the ac impedance primary standard because it can transfer the traceability to other impedances by using bridges such as the quadrature bridge. The development is occurring on its displacement sensing system to allow greater accuracy.

A QoS provisioning architecture of fiber wireless network based on XGPON and IEEE 802.11ac

Abstract The integration of the XGPON network with the 5G WLAN network is a suitable solution for next-generation high-speed access Internet service. We demonstrated the integration of two different standards via the QoS concept. Further, this work also presents a proper mapping scheme of QoS traffic between XG-PON and fifth-generation Wi-Fi standards known as IEEE 802.11ac. The analysis assessment compares the behavior of different IEEE 802.11ac standards with XGPON with-respect-to multimedia traffic in the FiWi network. To assess the performance of the FiWi network, the OMNET++ and INET framework are used to carrying out a comparative analysis in terms of upstream (US) delay and fairness index. The study concludes that the EDCA Wi-Fi module has better performance than the DCF Wi-Fi module with the integrated XGPON system for the FiWi access network.

High-performance wireless network based on IEEE 802.11 flexible architecture

Wireless networks have a key role in operational deployment, mobility, the flexibility of network organization and the variety of possible applications, in many cases being the only economically justified solution. Based on the above, for the deployment of wireless networks, the correct theoretical design of the wireless network is an important issue: the required number of devices, their characteristics, placement, energy characteristics of channels, distribution routes and coverage areas, etc. Correct theoretical analysis will ensure error-free construction of the network for the successful implementation of the tasks and will not lead to the need to attract additional material costs. One of the key tasks of wireless communication construction is a reliable assessment of the energy characteristics of a wireless communication channel. Modern global manufacturers of telecommunications equipment build both backbone equipment and equipment to cover WLAN (wireless local area networks) areas, based on IEEE 802.11 standards. One of the most modern standards of the IEEE 802.11 group is the IEEE 802.11ac standard, which is characterized by several improved technical characteristics compared to its predecessor IEEE 802.11n and older versions. That is why the task of evaluating the performance of modern wireless communication equipment based on IEEE 802.11ac standards and analyzing the evaluation of the energy characteristics of the communication channel to predict the parameters and performance characteristics of a point-to-point, point-to-multipoint or other wireless transmission systems within a certain wireless communication network. The following results of solving this problem are presented in this paper: – theoretical evaluation of the energy characteristics of the wireless communication channel. – laboratory studies of wireless communication equipment of the 802.11ac standard based on simulating a communication line using attenuators. – verification of the results of laboratory studies in field conditions based on the model for assessing the quality of communication in a wireless channel created based on the 802.11ac standard.

Comparative Analysis of User Exposure to the Electromagnetic Radiation Emitted by the Fourth and Fifth Generations of Wi-Fi Communication Devices.

A suitable metric to describe human exposure to microwaves emitted by wireless communication devices is still incomplete. By using both theoretical analysis and experimental validation (in controlled and real deployed networks), we analyze and compare the specificity of exposure due to data transmissions in different configurations of fourth and fifth generation wireless fidelity (Wi-Fi) standards in the proximity of a mobile device. Measurements made use of the capability of the amplitude probability density incorporated in a real-time spectrum analyzer, proving its agility of highlighting different user exposure profiles. The results are presented comparatively and indicate that, in Wi-Fi networks, the modulation and coding scheme (MCS) should be used together with the duty cycle for an improved exposure assessment. The present work introduces the emitted energy density per bit in describing the user’s exposure to Wi-Fi signals and proves its superiority in characterizing the true levels of exposure for the IEEE 802.11n and 802.11ac standards of communication.

Efficiency increase in the 802.11 Ac standard performance due to the influence of Airtime Fairness technology

The article considers one of the critical problems of wireless network performance, namely, monopolization of airtime by slow clients.The advantages of wireless Wi-Fi technology are considered. The main versions of Wi-Fi standards are analyzed. It is shown that a wide variety of Wi-Fi standards is aimed at improving network performance indicators, which is expressed in increasing the transmission speed, optimizing the use of frequency bands, increasing the efficiency of Wi-Fi in segments with high subscriber density, as well as in the possibility of multiple streaming of high definition video.The IEEE 802.11ac standard is analyzed. The choice of 802.11 ac technology is based on its availability and flexibility. It is indicated that the main problem point of this standard is the inconvenience of its performance under strong differentiation of client devices, which is reflected in a decrease in network bandwidth as a whole.The network performance using Airtime Fairness technology is analyzed. To solve the problem of monopolization of airtime by slow clients, the cyclic method of dividing airtime into given intervals has been used. The necessary equipment, hardware and initial conditions for the study are indicated. It is shown that the network efficiency is determined by the following productivity indicators: average packet productivity, average bandwidth and wireless channel utilization.It has been explained that with changes in system settings due to activation of Airtime Fairness technology algorithms, there is an increase in packet productivity and average bandwidth, as well as a decrease in the utilization rate of the wireless channel, which proves the presence of positive changes in the wireless network.

Testing and simulation of potential energy savings in renewing used split-type and window-type air-conditioners

In Saudi Arabia, air-conditioners ACs are responsible for 50% of electricity consumption due to hot weather conditions as well as the delay in implementing ACs standards. In this work, six used split-type and eight used window-type ACs that have ages from 3 to 32 years were tested according to American Society of Heating, Refrigerating and Air-Conditioning Engineers and Saudi Standard, Metrology and Quality Organization cooling test conditions and their performances were compared against new units that have 5.27 kW rated capacity. Test results show that coefficient of performance and cooling capacity of used split-type units compared to new one are 68% and 93%, respectively. For window-type, test results show that coefficient of performance and cooling capacity of used units compared to new one are 55% and 77%, respectively. The effect of replacing used compressor units with a new compressor was experimentally investigated. A model was developed using a commercially available software and was validated with experimental data. An economical map was developed to identify feasible ACs replacement regions. Practical application: Using standard methods this study experimentally quantifies energy savings when used split- and window-type units are replaced with new units. This will help HVAC and energy professionals develop recommendations regarding replacing existing units for a given power tariffs. Additionally, tests were conducted with replacing compressors in used air-conditioners, rather than replacing the entire unit, so as to assist in answering how much energy savings, CO2 and payback period can be achieved by simply replacing the compressors.

Sum Rate Optimization of Multi-Standard IEEE 802.11 WLANs

Aimed at providing high data rate in wireless local area networks (WLANs), the IEEE 802.11ac standard has been developed with key enhancements, including increasing the transmission rate and enlarging the packet payload length. The improvement in the sum rate performance, nevertheless, could become marginal or even disappear when nodes of legacy 802.11a/n standards coexist. It is, therefore, of paramount importance to study how to optimize the network sum rate of a multi-standard WLAN. In this paper, a multi-group model is proposed to analyze the data rate performance of a multi-standard WLAN where nodes with different standards have distinct transmission rates and packet payload lengths. It is shown that the packet payload length is a key system parameter that has a crucial impact on both the network sum rate and the ratio of node data rates. The enhancement proposed in the latest 802.11ac standard on enlarging the packet payload length can improve the data rate performance of its own nodes, but it may lead to the starvation of the legacy 802.11a/n nodes, and even impair the sum rate performance. To maximize the network sum rate with given target ratios of node data rates, the optimal packet payload lengths with or without joint tuning of the initial backoff window sizes are further obtained, which shed important light on the optimal network design of WLANs.

Decreased Pediatric Trauma Length of Stay and Improved Disposition With Implementation of Lewin's Change Model.

Although often cared for nonoperatively, trauma is a surgical disease managed by surgical services in a multidisciplinary manner. The American College of Surgeons Committee on Trauma (ACS COT) emphasizes this as part of the ACS COT verification process and expects nonsurgical service admission rate of less than 10%. In this project, we developed a collaborative care model captained by surgical services with medical service consultation to achieve this goal for optimal care of injured patients. The project was conducted at a freestanding pediatric trauma center undergoing verification as a Level 1 ACS COT pediatric trauma center. The trauma registry was utilized to obtain nonsurgical service admission rate from January 2011 to June 2015. Lewin's 3-Step Model was utilized to guide change. Adherence to the new ACS standards was continually tracked and fallouts were addressed on an individual basis. Overall compliance was reported routinely through trauma and hospital quality programs. Individual successes and accomplishments were recognized and reinforced. At the inception of the project, nonsurgical admission rate was 30%. Implementation of Lewin's 3-Step Model nonsurgical admission rate decreased to 3%, representing a reduction of 27%. In addition, a 21% reduction in hospital length of stay, 3.78-3 days, was demonstrated with no change in 30-day readmission rate. Lewin's change model facilitated culture change to achieve ACS COT standards and reduced nonsurgical admissions to less than 10%. Reduction in hospital length of stay supports an improvement in the efficiency of care when directed by the pediatric trauma surgery team.

Evaluation of Multi-Beam Massive MIMO Considering MAC Layer Using IEEE802.11ac and FDD-LTE

Massive multiple-input multiple-output (MIMO) transmission has attracted attention as a key technology for use in fifth-generation mobile communication systems. Multi-beam massive MIMO systems that apply beam selection in analog components and blind algorithms in digital components to eliminate the requirement for channel state information have been proposed as a method for reducing overhead. In this study, we developed an adaptive modulation scheme for implementing multi-beam massive MIMO and used computer simulation to compare it with digital and analog–digital hybrid beam-forming methods. The effectiveness of the proposed system was verified in a medium access control layer based on the IEEE802.11ac and frequency division duplex-LTE representative wireless communication standards.

Modeling and Performance Analysis of the Main MAC and PHY Features of the 802.11ac Standard: A-MPDU Aggregation vs Spatial Multiplexing

The Very High Throughput (VHT) supplied by the IEEE 802.11ac standard is the outcome of several amendments incorporated at its both Medium Access Control (MAC) and PHYsical (PHY) layers. In particular, the Aggregate-MAC Protocol Data Unit (A-MPDU) frame aggregation allows, at the MAC level, increasing the amount of data to be transmitted and the spatial multiplexing technique serves at the PHY level to accelerate the rate at which such data are forwarded. Therefore, the goals we are seeking to achieve in this paper are, on one hand, to demonstrate that A-MPDU aggregation and spatial multiplexing may, respectively, lead to a decrease in throughput and an increase in overhead, and on the other hand, to highlight that A-MPDU aggregation and spatial multiplexing have mutual needs that could mutually satisfy operational challenges. For this purpose, we model the 802.11ac station enabling A-MPDU aggregation and spatial multiplexing, and we compute the throughput and the overhead of the 802.11ac network. After that, we run Monte Carlo simulations for validating the accuracy of the mathematical model, and we calculate 95% confidence intervals to establish credibility to the simulation results.

An investigation of different Wi-Fi signal behaviours and their effects on indoor positioning accuracy

In recent years, in addition to 2.4 GHz Wi-Fi signals, 5 GHz signals have been introduced making it possible to transmit data at both IEEE 802.11n and 802.11ac standards. Therefore, researchers have increasingly focused on developing indoor positioning applications based on Wi-Fi dual band. This study was conducted in two stages. In the first stage, we investigated the behaviours of 2.4 and 5 GHz Wi-Fi signals by collecting received signal strength (RSS) values from access points and determined the relationship between RSS and distance for each signal frequency using a curve fitting technique. Furthermore, we comparatively analysed signal fluctuations and their effects on positioning accuracy. In the second part of the study, we compared the positioning accuracy of four algorithms; namely, bilateration, trilateration, weighted iterative non-linear least square and extended Kalman filter using 2.4 and 5 GHz Wi-Fi signals. The experimental results revealed that the 5 GHz signals were more stable and had better positioning accuracy than the 2.4 GHz signals. Concerning the positioning algorithms, bilateration had the best positioning accuracy at both frequencies.

A Flexible Geometric Mean Decomposition Processor for MIMO Communication Systems

This paper presents a geometric-mean-decomposition (GMD) processor for multiple-input multiple-output (MIMO) communication systems. The proposed GMD processor has a flexible architecture that supports channel matrices of arbitrary dimensions. A complex-valued bi-diagonalization is proposed at the preprocessing stage, which substantially reduces the overall hardware complexity. The proposed GMD processor naturally supports an economic channel state information (CSI) feedback mechanism, rendering it highly suitable for frequency-division-duplexing (FDD) systems. To illustrate the performance of the proposed architecture, we demonstrate an efficient implementation supporting 2 to 8 spatial streams in a 90-nm CMOS technology. The latency constraint of 16 μs specified in the 802.11ac standard is adopted for this hardware realization. The chip integrates 437.7 K gates in 1.830 × 1.829 mm 2 and dissipates 125.5 mW at 66.67 MHz from a 1 V supply. Compared with the existing GMD implementations, this work supports GMD for matrices of larger dimensions with comparable silicon area, despite the added spatial information feedback capability.

Performance Analysis of IEEE802.11ac DCF Enhancement for VHT with Frame Aggregation

<strong>IEEE 802.11ac standard has brought several significant improvements compared to its predecessor IEEE 802.11n. It managed to break the Gigabits barrier with a combination of both refining older techniques and presenting new ones. The new enhancements such as channel bonding, beamforming, frames aggregation and finer modulation allow Wireless Local Area Networks (WLAN) the use of Very High Throughput (VHT). The physical layer (PHY) data rates are in the range of Gbps in the 5 GHz band. But the variety of releases and options available for this standard has left many ambiguities regarding its real capabilities. The Medium Access Control layer (MAC) throughput is influenced by several factors, causing the MAC efficiency to decrease. In this paper we present a performance analysis in the VHT with frame aggregation for different access mechanisms, different channels and different modulation schemes.</strong>

A Systolic Array Based GTD Processor With a Parallel Algorithm

Generalized triangular decomposition (GTD) has been found to be useful in the field of signal processing, but the feasibility of the related hardware has not yet been established. This paper presents (for the first time) a GTD processor architecture with a parallel algorithm. The proposed parallel GTD algorithm achieves an increase in speed of up to 1.66 times, compared to the speed of its conventional sequential counterpart for an 8 ×8 matrix. For hardware implementation, the proposed reconfigurable architecture is capable of computing singular value decomposition (SVD), geometric mean decomposition (GMD), and GTD for matrix sizes from 1 ×1 to 8 ×8. The proposed GTD processor is composed of 16 processing cores in a heterogeneous systolic array. Computations are distributed over area-efficient coordinate rotation digital computers (CORDICs) to achieve a high throughput. To establish the validity of the concept, a GTD processor was designed and implemented. The latency constraint of 16 μs specified in the 802.11ac standard is adopted for the hardware realization. The proposed design achieves a maximum throughput of 83.3k matrices/s for an 8 ×8 matrix at 112.4 MHz. The estimated power and core area are 172.7 mW and 1.96 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively, based on standard 90 nm CMOS technology.

Pulse-Bias Electronics and Techniques for a Josephson Arbitrary Waveform Synthesizer

The Josephson arbitrary waveform synthesizer (JAWS) is a series array of thousands of superconducting Josephson junctions that are biased by current pulses such that the array produces voltage waveforms with quantum accuracy. Intrinsically accurate voltage waveforms synthesized with the quantized pulses from Josephson junctions were first demonstrated in 1996. Ten years later, a commercial ac standard was calibrated at an output root-mean-square (RMS) amplitude of 100 mV with the first practical superconducting digital-to-analog converter. Since then, many different bias techniques, pulse-drive electronics, and device technology have been developed and improved in order to achieve a maximum of 138 mV output RMS voltage per Josephson array. In this paper, we report new bias electronics and demonstrate two new pulse-bias techniques. The first technique has demonstrated 250 mV output RMS voltage per 6400-junction array and may enable a practical 1 V system with only four arrays. The second bias technique reduces inductance-related error signals at the signal frequency and should reduce systematic errors for waveforms with frequencies greater than 1 MHz.

Dynamic 20/40/60/80 MHz Channel Access for 80 MHz 802.11ac

This paper is to contribute a new dynamic channel access method for wireless local area networks. It allows a station accessing the 80 or 160 MHz channel to capture every idle non-primary 20 MHz channel along with the primary 20 MHz channel, whereas the number of channel configurations in which the station can transmit according to the 802.11ac standard is strictly limited. Simulation results shown in the paper prove the proposed access method to be superior to the method provided by the 802.11ac standard in terms of average network throughput. What is important for legacy reasons, the proposed method employs the conventional clear channel assessment function to determine which of the 20 MHz channels are idle and which are busy. The paper proposes a new receiver design that is able to reject the adjacent channel interference, arising as a result of the presence of the legacy 802.11a/n station signals inside the 80 or 160 MHz accessed channel.

IEEE 802.11ac sebagai Standar Pertama untuk Gigabit Wireless LAN

WLAN is a technology that currently has been used widely. This technology is considered as a data transferring media technology within the LAN/MAN. To ensure that WLAN technology can be used widely in the whole world, the IEEE has set a standard known as 802.11 to be an international standard for the WLAN technology. This standard was appeared in 1997, and has been revised and improved for several times. This improvement is done to anticipate the rapidly grown WLAN market as well as to keep this technology remains effective, efficient, and reliable at any time. At the beginning of 2014, the IEEE has set 802.11ac-2013 as a new standard for WLANs that operate below 6 GHz to achieve a data rate for up to 7 Gbps. The purpose of this article is to describe comprehensively the IEEE 802.11ac standard as a result of recent changes to the regulatory for WLAN technology which is known as the first standard issued by the IEEE for the gigabit WLANs. This article discusses the goals and objectives to be achieved by 802.11ac standard as well as the parts that have been enhanced significantly both in its PHY and MAC layers. This article will also contrast the differences between the 802.11ac standard and previous WLAN standards. Finally it will also explain the level of compatibility and interoperability of 802.11ac standards with some of previous WLAN standard. Keywords: IEEE, 802.11, 802.11ac, Gigabit WLAN

Optimal channel assignment with aggregation in multi-channel systems: A resilient approach to adjacent-channel interference

Channel assignment mechanisms in multi-channel wireless networks are often designed without accounting for adjacent-channel interference (ACI). To prevent such interference between different users in a network, guard-bands (GBs) are needed. Introducing GBs has significant impact on spectrum efficiency. In this paper, we present channel assignment mechanisms that aim at maximizing the spectrum efficiency. More specifically, these mechanisms attempt to minimize the amount of additional GB-related spectrum that is needed to accommodate a new link. Similar to the IEEE 802.11n and the upcoming IEEE 802.11ac standards, our assignment mechanisms support channel bonding, and more generally, channel aggregation. We first consider sequential assignment (i.e., one link at a time), and we formulate the optimal ACI-aware channel assignment that maximizes the spectrum efficiency as a subset-sum problem. An exact exponential-time dynamic programming (DP) algorithm, a polynomial-time greedy heuristic, and an ∊-approximation are presented and compared. Second, considering a set of links (batch assignment), we derive the optimal ACI-aware exponential-time assignment that maximizes the network’s spectrum efficiency. The optimal batch assignment is compared with the sequential assignment. Results reveal that our proposed algorithms achieve considerable improvement in spectrum efficiency compared to previously proposed schemes.

Empirical Performance Evaluation of Enhanced Throughput Schemes of IEEE802.11 Technology in Wireless Area Networks

The success in the growing wireless standards can be measured by the achievement of quality of service (QoS) specifications by the designers. The IEEE802.11 wireless standards are widely accepted as wireless technology for wireless LAN. Efforts have been made over the years by the task group to provide adequate number of QoS enhancement schemes for the increasing numbers of multimedia applications. This paper examines the empirical performances of ad hoc wireless networks deployed on IEEE802.11 standard variants. A survey to some of the QoS schemes incorporated in IEEE802.11 wireless PHY layers were carried out. Then the effects of this enhancement schemes in relation to data throughput and system capacity and reliability in the newest technology deployed on IEEE802.11ac standards was investigated using real time applications and simulation based approaches.