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Research has shown that counting WiFi packets called probe requests (PRs) implicitly provides a proxy for the number of people in an area. In this paper, we discuss a crowd counting system involving WiFi sensors detecting PRs over the air, then extracting and anonymizing their media access control (MAC) addresses using a hash-based approach. This paper discusses an anonymization procedure and shows time-synchronization inaccuracies among sensors and hashing collision rates to be low enough to prevent anonymization from interfering with counting algorithms. In particular, we derive an approximation of the collision rate of uniformly distributed identifiers, with analytical error bounds. [ABSTRACT FROM AUTHOR]

The very high frequency data exchange system (VDES) is promising in promoting electronic navigation (E-navigation) and improving navigation safety. The multiple access control (MAC) protocol is crucial to the transmission performance of VDES. The self-organising time division multiple access (SOTDMA) protocol, as the only access mode given by current recommendations, leads to a high rate of transmission collisions in the traditional automatic identification system (AIS), especially with heavy traffic loads. This paper proposes a novel feedback based time division multiple access (FBTDMA) protocol to address the problems caused by SOTDMA, such that collision of transmissions can be avoided in information transmission among vessels. Simulation results demonstrate that the proposed FBTDMA outperforms the traditional SOTDMA in terms of channel utilisation and throughput, and significantly reduces the transmission collision rate. The study is expected to provide insights into VDES standardisation and E-navigation modernisation. [ABSTRACT FROM AUTHOR]

The presence of charges on droplets and aerosol particles can increase collisions among these objects, which would ultimately have effects on precipitation and cloud over. The traditional experiments on the effects of growth of charged droplet have deficiency in that the charge of droplet was not accurately controlled. In this paper, better control of equivalent charge on a single droplet was realized by changing the voltage applied on the stainless steel needle whose tip was used as the condensation nuclei of the droplet. The breakdown voltage at the tip of the stainless steel needle (radius 1 \mu \textm ) was 2000 V at the humidity of 98 ± 2% and temperature of 3 ± 1°C. Voltage of less than 700 V could not lead to corona discharge, which further guarantees the accurate control the charge of droplet. Increasing equivalent charge of the droplet not only increased the growth rate of the droplet, but also increased the eventual size of the droplet. The electric field of 1.9 \times 10^7 V/m at the edge of the droplet was found to be the threshold for the growth of charged droplet under this experimental condition. The calculation of collision rate coefficient between the charged droplet and aerosol particles suggests that the contribution of electric force to the growth of droplet was at least three orders of magnitude higher than that of thermophoretic and diffusophoretic forces when the charge of the droplet was greater than 1.43 \times 10^5e . [ABSTRACT FROM AUTHOR]

In this paper, we measure broadband terahertz spectra from a single 744-nm filament produced in tight, medium, and loose geometrical focusing conditions. Terahertz spectra are measured using interferometer coupled to a helium-cooled bolometer avoiding any cutoff frequencies. Based on THz spectrum maximum position and spectral width, we estimate electron-heavy particle (neutrals and ions) collision rate. Numerical simulations are performed using the state-of-the-art model of unidirectional femtosecond pulse propagation and convergence/divergence of optical radiation at large angles. [ABSTRACT FROM AUTHOR]

Research has shown that counting WiFi packets called probe requests (PRs) implicitly provides a proxy for the number of people in an area. In this paper, we discuss a crowd counting system involving WiFi sensors detecting PRs over the air, then extracting and anonymizing their media access control (MAC) addresses using a hash-based approach. This paper discusses an anonymization procedure and shows time-synchronization inaccuracies among sensors and hashing collision rates to be low enough to prevent anonymization from interfering with counting algorithms. In particular, we derive an approximation of the collision rate of uniformly distributed identifiers, with analytical error bounds.

The rapid growth of the Internet-of-things (IoT) in recent years has led to the development of new access technologies targeting low-power wide area networks (LPWANs). LPWAN is a promising solution for long-range and low-power IoT and machine-to-machine (M2M) communication applications. However, practical LPWAN deployments suffer from intense collisions due to uncoordinated transmissions, given the dense deployment of devices and wide coverage area. Therefore, this paper proposes a deep learning-based collision aware transmission priority scheduling technique (CA-PST) to mitigate high packet collision rate in ultra-dense wireless networks. The proposed CA-PST is applied to the low-range wide area network (LoRaWAN) platform where the LoRa gateway configures the nodes to a particular transmission protocol classes based on the predicted number of packet collisions. Aided by unsupervised learning clustering, the nodes located at higher transmission priority clusters will be allowed to communicate with the gateway using class C and therefore avoid packet collisions. Whereas nodes in lower transmission priority clusters communicate with the gateway using class A. Therefore, the CA-PST offers a fair trade-off between the packet delivery rate (PDR) and total energy consumption. Extensive simulation results show that using CA-PST can significantly improve the LPWAN reliability in terms of PDR in ultra-dense networks.

The networks nodes in IEEE 802.11 standard need a strategy to enhance the system performance. The network performance can be evaluated in view of Quality of Service (QoS) parameters, for example, delay, throughput, packet loss, jitter and collision which are strict prerequisites for multimedia applications. This paper exhibits an element component to modify the contention window (CW) and distributed inter frame space (DIFS) parameters to the IEEE 802.11 Medium Access Control (MAC) convention to improve QoS. The proposed plan is in light of the Collision Rate (CR), Collision Rate Variation (CRV) and packet loss rate for every bundle activity class to modify the CW and DIFS at runtime in single-hop networks. The simulation results demonstrate that the proposed plan upgrades the normal QoS for high priority traffic by 34% and 33.9% for the 5 and 10 connections, respectively. While the normal QoS for the low priority traffic is enhanced by 17.3% and 33.6% for the 5 and 10 connections, respectively. The outcomes demonstrate that, the proposed methodology support the QoS in wireless networks. [ABSTRACT FROM AUTHOR]

In Cognitive Radio (CR) networks, CR user has to detect the spectrum channel periodically to make sure that the channel is idle during data transmission frame in order to avoid the collisions to the primary users. Hence recent research has been focused on the interference avoidance problem. Quality of Service (QoS) requirement of CR user will affect the time of data transmission in each frame. In this paper, in order to solve the interference avoidance and spectrum utilization problems without cooperation among CR users, a new scheme to obtain the optimal duration of data transmission frame is proposed to maximize the spectrum utilization and guarantee the protection to the primary users. The main advantages of our proposed scheme include the followings: (1) QoS requirement of CR user is concerned; (2) p-persistent Media Access Control (MAC) random access is used to avoid the collisions among CR users; (3) CR network system capacity is considered. We develop a Markov chain of the primary spectrum channel states and an exponential distribution of the CR user's traffic model to analyze the performance of our proposed scheme. Computer simulation shows that there is an optimal data transmission time to maximize the spectrum utilization. However, the regulatory constraint of the collision rate to the primary users has to be satisfied at the expense of spectrum utilization. And also the tradeoff between the spectrum utilization and the capacity of the CR system is taken into account. [ABSTRACT FROM AUTHOR]

This paper evaluates the accuracy of three commonly used models that predict accidents on two-lane, rural, arterial highways. The retrospective evaluation compared model outputs with empirical collision results for a sample of highway sections in the Province of New Brunswick. The analysis determined historical accident rates, identified key predictive variables, and compared the observed results with estimates from each safety model. All three models were found to significantly overestimate accident frequencies on the highway sections under study. The model generally employed in New Brunswick, MicroBENCOST, was found to yield the highest errors in estimated collisions. These findings suggest that the benefits from accident reduction are generally overestimated on highway improvement projects analyzed with these accident prediction models. Cet article évalue la précision de trois modèles couramment utilisés pour la prédiction d'accidents sur les autoroutes à deux voies; rurales et les avenues. L’évaluation rétrospective à comparé les résultats des modèles aux résultats empirique de collision pour un échantillon de sections d'autoroutes dans la province du Nouveau-Brunswick. L’analyse a permis de déterminer le taux historique d'accidents, a identifié les principales variables prédictives et à comparé les résultats observés aux estimations de chaque modèle de sécurité. Il a été trouvé que les trois modèles sur-estiment significativement les fréquences d’accidents sur les sections d’autoroutes étudiées. Il a été trouvé que le modèle généralement employé au Nouveau-Brunswick, MicroBENCOST, produit les erreurs les plus élevées pour l’estimation des collisions. Ces résultats suggèrent que les avantages dûs à la réduction des accidents sont généralement sur-estimés dans les projets d'amélioration des routes analysés avec ces modèles de prédiction des accidents. [ABSTRACT FROM AUTHOR]

Particle-laden turbulent flows are ubiquitous in natural and engineering flows. The preferential concentration and pair-statistics of heavy particles at small and intermediate Stokes numbers are mainly related to the small-scale motions, which are missing in conventional large-eddy simulation (LES). Therefore, studies on the effects of subgrid scale (SGS) motions on particle-pair statistics are significant. This paper will study the effects of SGS motions on the collision-related statistics of a bidisperse system that involves two groups of particles at different Stokes numbers using a direct numerical simulation (DNS), filtered DNS (FDNS) and LES. Compared with a monodisperse system at a single Stokes number, the relative error of the collision rates in the bidisperse system is much smaller than that in the monodisperse one. For given filter widths and Stokes numbers, the relative errors between the FDNS and LES are much smaller than their relative errors to DNS, implying that the error caused by the filtering operation in LES plays a leading role in the overall error of the particle collision rate at Stokes numbers less than 3. A particle SGS model is, thus, necessary to consider the effect of SGS motions on bidisperse heavy particles. [ABSTRACT FROM AUTHOR]

Abstract: The paper deals with collisions resulting from the interaction between particles (droplets, bubbles) and turbulent eddies of the continuous fluid medium (gas or liquid). A statistical model is developed for predicting the collision rate. This model is valid for arbitrary values of the particle-to-fluid density, the particle inertia parameter, and the ratio between the particle size and the fluid turbulent lengthscale. [Copyright &y& Elsevier]

Abstract: The objective of the paper is to present a statistical model for predicting collision rates of inertial particles immersed in turbulent flow. This model is valid over the entire range of particle inertia (from the zero-inertia to the high-inertia limit) and accounts for two mechanisms influencing the collision rate, namely, the particle relative motion induced by turbulence and the accumulation effect that leads to an additional enhancement to the collision rate. The model is applicable to near-homogeneous two-phase turbulent flows with colliding or coalescing particles. [Copyright &y& Elsevier]

Interparticle collision is an important phenomenon in the mechanics of two-phase flow. Most past researches on this problem have been based on the analogy with kinetic theory of gases with few experimental validations of the results. While this paper presents the directly measured experimental data of collision rate in vertical two-phase flow. This research used a high-speed camera and Particle Tracking Velocimetry (PTV) algorithms to focus on the interparticle collisions, especially the collision rate, on a millisecond time scale and a millimeter space scale, which is the particle size (1.8 mm in diameter). The camera speed was normally 2000 frames per second with an exposure of 1/2000 s and a laser power of 25 W for particle velocity of less than 4m/s in the collision region and particle fractions of about 0.015. A manual count of the collision numbers was chosen as the most accurate method for the determination of the collision rate. The PTV algorithms were applied to calculate the particle number density and relative velocities. The correlation between the particle collision rate, the particle number density, the average relative velocity between particles and the measured granular temperature, was compared with commonly used relations based on kinetic theory. The results demonstrated that great differences exist between the theoretical and experimental results for these experimental conditions. The collision rate determined experimentally is much lower than the theoretical estimation based on kinetic theory. This means the theoretical correlations overestimate the collision rate in the gas-particle flows. This discrepancy may be attributed to the assumptions in the theoretical collision model and experimental error. [Copyright &y& Elsevier]

The continuing global expansion of electricity networks increases the risk of bird collisions with power lines. Several field studies have demonstrated that this risk can be reduced by marking lines with flight diverters. A before‐after control‐impact (BACI) design is currently the suggested approach for evaluating the effectiveness of these diverters and is generally assumed to give unbiased results.Using systematic flight survey data, we demonstrate that the assumptions underlying the BACI approach are frequently violated, leading to biased effectiveness estimates. We present an alternative field and statistical design in which the number of bird strike victims is directly related to bird flight intensity ("fusion design"), instead of estimating it indirectly using a control site. The presented design is validated based on simulations.We demonstrate that the presented method is unbiased and shows an approximately 3‐fold higher statistical power compared with BACI, even under ideal/unbiased data conditions, with similar field‐experimental effort. Moreover, this approach can provide a direct analysis of bird reactions/collisions, estimation of collision rates, and the possibility of conducting the required fieldwork within a single season.Our presented method can be used to standardize and improve future studies on diverter effectiveness, for example, by supporting the acquisition of a more detailed picture of species‐, diverter type‐, and habitat‐specific estimates. [ABSTRACT FROM AUTHOR]

Long-Range (LoRa) communication technology is considered as a promising connectivity solutions for Internet of Things (IoT) dense applications. In particular, LoRa has drawn the interest due to its low power consumption and wide area coverage. Despite the benefits of LoRaWAN protocol, it still suffers from excessive random and simultaneous transmissions due to the adoption of ALOHA protocol. Therefore, resulting in severe packet collision rate as the network scales up. This leads to continuous retransmission attempts, which in return increase the transmission delay and energy consumption. Thus, this paper proposes a dynamic transmission Priority Scheduling Technique (PST) based on the unsupervised learning clustering algorithm to reduce the packet collision rate and enhance the network's transmission delay and energy consumption. Particularly, the LoRa gateway classifies the nodes into different transmission priority clusters. While the dynamic PST allows the gateway to configure the transmission intervals for the nodes according to the transmission priorities of the corresponding clusters. This work allows scaling up the network density while maintaining low packet collision rate and significantly enhances the transmission delay & the energy consumption. Simulation results show that the proposed work outperforms the typical LoRaWAN and recent clustering & scheduling schemes. Therefore, the proposed work is well suited for dense applications in LoRaWAN.

Accumulation of pollution particles on outdoor insulators is the premise of pollution flashover accidents in power systems. In this paper, according to the actual operating polymer insulators, the wind velocity, the concentration of pollution particles, the diameter of pollution particles, and the hanging angle of insulator were considered to investigate the accumulation characteristic of pollution particles by using FLUENT software. The pressure nephogram of polymer insulator, the velocity vector of air flow field, movement trajectory of pollution particles, and collision rate were obtained. It is found that the pressure of the insulator surface on the windward side is bigger than that on the leeward side, and the pressure difference increases with increasing the wind velocity. As the increase in particle diameter, the collision rate between pollution particles and insulator surface shows the increasing tendency. When the diameter of pollution particles is small, the easier the particles follow the airflow to bypass the insulator surface without colliding with it. However, due to the influence of gravity force and inertia, the collision rate of pollution particles increases significantly with the increase in particle diameter. Under the strong wind velocity, the air swirls are generated on the leeward side of the insulator surface, causing the collision rate of the pollution particles increases slowly with the increase in the wind velocity. While the concentration of pollution particle increases, the collision number between insulator surface and pollution particles shows the increasing tendency at different wind velocity. When the particle diameter is in range of 1 to 8 μm, with increasing the hanging angle of “V”type insulator from 0° to 60°, the collision rate of pollution particles shows the increasing tendency. When the particle diameter is 9 to 50 μm, the collision rate of particles shows the increasing tendency when the insulator angle is lower than 30°, but shows the decreasing tendency from 30°to 60°. As the humidity increases, the water vapor in the air prevents the movement of pollution particles, resulting in a decrease in the collision rate. With increasing the pollution particles diameter, the influence of air humidity on the collision rate of pollution particles is gradually weakened.

The market penetration of intelligent vehicles is a long‐term process. In recent years, significant attention has been paid to the influence of technology market penetration rate (MPR) on efficiency at signalised intersections, but little attention has been given to such an influence on safety at non‐signalised intersections. In this study, the influence of the intersection collision warning (ICW) system MPR on safety at non‐signalised intersections is investigated. The authors built a Matlab‐based simulation platform where an ICW algorithm was implemented. The simulation was firstly conducted to verify their models. Then the simulation results of different MPRs were obtained and compared statistically. Collision probability, conflict index, and collision rate were analysed for safety evaluation. The overall results showed that vehicle safety at non‐signalised intersections improves with the increase of the ICW system MPR. Without considerations of inappropriateness and otherness of driver reaction to warnings, when the MPR is 20% and all vehicles are connected by vehicle‐to‐everything, the collision probability, conflict index, and collision rate can be reduced by around 20, 20, and 35%, respectively. The simulation method can establish a mapping relation between the ICW system MPRs and vehicle safety indices at non‐signalised intersections. [ABSTRACT FROM AUTHOR]

A frequency-hopping (FH) space-frequency (SF)-coded clustered orthogonal frequency division multiple access (OFDMA) system is considered. It is shown that SF coding reduces the number of collisions in OFDMA with FH provided that the subcarrier clusters are formed randomly at each hopping instant. Analytical expressions for the collision rate, which is defined as the expected number of collisions per symbol, are derived. Bit error rate (BER) computations via simulations in a frequency-selective fading channel corroborate the theoretical findings for SF-coded FH-OFDMA. [ABSTRACT FROM PUBLISHER]