High Collision Probability Research Articles

Performance Improvement of Sub 1 GHz WLANs for Future IoT Environments

IEEE 802.11ah task group has developed a new wireless local area network (WLAN) technology, sub 1GHz (S1G) WLAN, for future Internet of Things (IoT) environments. Because of the superior propagation feature of S1G frequency band, S1G WLAN can provide very long transmission range, wild coverage, and support more than 8000 devices. In order to alleviate the high collision probability raised in the dense network environment, S1G WLAN adopts an restricted access window (RAW) mechanism. However, as the time slots of RAW are allocated without any consideration of traffic load of devices, the medium resource might be inefficiently used. In addition, devices belonging to a same group have to contend for channel, and thus severe collisions may occur in a large size group. In this paper, we propose a sequential transmission scheme, which provides an efficient way of source management in the S1G WLANs by considering the traffic loads and allocating channel access times of the devices. Through conducting mathematical analysis and performing simulations, we prove that our proposed protocol can enhance the performance of the S1G WLANs for the IoT environments.

Clean low-rank-coal purification technique combining cyclonic-static microbubble flotation column with collector emulsification

The flotation upgrading of low-rank-coal is more difficult to achieve than that of bituminous and/or anthracite coal, especially for micro-fine coal slime, because of developed porosity and a large number of oxygen surface functional groups and low collision probability between bubble and particle. In this paper, previous works on high-efficiency low-rank-coal flotation were reviewed first and a clean micro-fine low-rank-coal purification technique that innovatively combined a cyclonic-static microbubble flotation column with collector emulsification was proposed. The results show that a satisfactory separation performance for micro-fine low-rank-coal flotation can be obtained by using a cyclonic-static microbubble flotation column with collector emulsification. The collision probability between a coal particle and diesel increased because of the collector emulsification. The specific adsorption of the surfactant on the hydrophilic groups on the particle surface also increased the hydrophobicity. The improved micro-fine low-rank-coal flotation performance by cyclonic-static microbubble flotation column can be attributed to the high collision probability because of turbulent mineralization mechanism and micro-bubbles, and high attachment probability and low detachment probability because of the introduction of the hydrophobic attractive force due to the existence of the nanobubble. The outcome of this research provided a new insight into the flotation of low-rank-coal and other difficult-to-float coal.

PTMAC: A Prediction-Based TDMA MAC Protocol for Reducing Packet Collisions in VANET

With the rapid development of wireless communications, vehicular ad hoc networks (VANETs) have recently attracted great attention. Although IEEE 802.11p has been approved as the standard medium access control (MAC) protocol for vehicle-to-vehicle communications, its contention-based nature and inability to handle hidden-terminal problems may incur high packet collision probability under high-traffic-density situations. To overcome the shortcoming of IEEE 802.11p, time-division multiple-access (TDMA)-based protocols are proposed. However, packet collisions can still occur due to contention or multiple vehicles using the same slot while approaching each other, i.e., encounter collisions, particularly in two-way traffic roads. Some proposed remedying the encounter collisions for two-way traffic by partitioning a frame into two sets: one for the traffic in each direction. However, these proposed protocols are harder to adapt to the uneven traffic loads on both directions and cannot solve the problem of four-way intersections. In this paper, we propose a new TDMA protocol called prediction-based TDMA MAC (PTMAC) based on a novel way of predicting encounter collisions and effectively reducing the number of collisions. To the best of our knowledge, PTMAC is the first protocol that is designed for both two-way traffic and four-way intersections. It has shown that, based on this predictability, the encounter collisions can be greatly reduced in both two-way traffic and four-way intersections, regardless of the traffic loads on different road segments.

Melt volume flow rate and melt flow rate of kenaf fibre reinforced Floreon/magnesium hydroxide biocomposites.

A study of the melt volume flow rate (MVR) and the melt flow rate (MFR) of kenaf fibre (KF) reinforced Floreon (FLO) and magnesium hydroxide (MH) biocomposites under different temperatures (160–180 °C) and weight loadings (2.16, 5, 10 kg) is presented in this paper. FLO has the lowest values of MFR and MVR. The increment of the melt flow properties (MVR and MFR) has been found for KF or MH insertion due to the hydrolytic degradation of the polylactic acid in FLO. Deterioration of the entanglement density at high temperature, shear thinning and wall slip velocity were the possible causes for the higher melt flow properties. Increasing the KF loadings caused the higher melt flow properties while the higher MH contents created stronger bonding for higher macromolecular chain flow resistance, hence lower melt flow properties were recorded. However, the complicated melt flow behaviour of the KF reinforced FLO/MH biocomposites was found in this study. The high probability of KF–KF and KF–MH collisions was expected and there were more collisions for higher fibre and filler loading causing lower melt flow properties.

A study of a target identification method for an active debris removal system

In a preparatory study conducted prior to the development of an active space debris removal system, a method for selecting target debris based on information such as the cumulative collision probability, the operational condition of objects, and their sizes and launch dates was developed for use in the protection of four Korea Multi-Purpose Satellite constellation satellites. This method can be used to select candidate removal targets. Two-line element data are used to identify threatening objects with high cumulative collision probability. Using information in the Satellite Catalog database, objects smaller than a certain size or objects that are currently operational were excluded from the selection range. The results of an analysis of the cumulative collision probability, object size, object type, and primary mission information showed that the COSMOS 1328, COSMOS 1862, COSMOS 375, and COSMOS 1606 satellites were suitable targets for an active debris removal mission.

An Efficient Time Slot Acquisition on the Hybrid TDMA/CSMA Multichannel MAC in VANETs

The multichannel MACs increase the throughput and reduce the collision probability compared to the single-channel MACs. However, coordination of multiple nodes across multichannels is nontrivial. Recently, a multichannel MAC, called HER-MAC, uses both TDMA and CSMA schemes to improve reliability in broadcasting safety messages and efficiency in service channel utilization. Nevertheless, HER-MAC suffers a high collision probability for a large number of vehicle nodes. In this letter, we propose a hybrid TDMA/CSMA multichannel MAC protocol for VANETs that allows efficient broadcasting of messages and increases throughput on the control channel. Furthermore, our proposed MAC eliminates unnecessary control packet such as HELLO and SWITCH packets in HER-MAC. Analysis and simulation results show that the proposed MAC can provide faster time slot acquisition on the control channel than HER-MAC.

Mathematical model for ice wall interactions within a level set method

De-icing systems work periodically to remove ice formed on aircraft protected surfaces. They achieve this result by reducing adhesive shear strength between ice and surfaces. In the present work, an immersed boundary method will predict ice-shedding trajectories and collisions. At the starting-point of shedding trajectory calculations, when the ice-shed particle is still close to the wing surface, there is a high probability of collision with the surface. A linear spring collision model is presented assuming the interacting bodies are connected tangentially and normally by linear springs. The verification of the model is made by comparison with literature results and study of ice trajectories around a cylinder and an aerofoil.

A TDoA Localization Scheme for Underwater Sensor Networks with Use of Multilinear Chirp Signals

Due to the multipath, Doppler, and other effects, the node location signals have high probability of access collision in the underwater acoustic sensor networks (UW-ASNs), and therefore, it causes the signal lost and the access block; therefore, it constrains the networks performance. In this paper, we take the multilinear chirp (MLC) signals as the location signal to improve the anticollision ability. In order to increase the detection efficiency of MLC, we propose a fast efficient detection method called mixing change rate-fractional Fourier transform (MCR-FrFT). This method transforms the combined rates of MLC into symmetry triangle rates and then separates the multiuser signals based on the transformed rates by using FrFT. Theoretical derivation and simulation results show that the proposed method can detect the locations signals, estimate the time difference of arrival (TDoA), reduce the multiple access interference, and improve the location performance.

MIMO slotted ALOHA systems with collision resolution and truncated HARQ transmission and combining

In this paper, we investigate throughput and delay enhancement for two multi-user multiple-input multiple-output (MIMO) systems one with space-time block coding (STBC), the other with spatial multiplexing (SM) at the transmitter. Users operate using the slotted ALOHA (SA) protocol to access the wireless channel resulting in a high probability of collision. For both systems, we consider the uplink scenario, and we propose to recover the collided packets with spatial successive interference cancelation (SSIC) and a protocol for retransmission and combining of unsuccessfully received collided packets applying a truncated Hybrid Automatic Repeat reQuest (HARQ) scheme. For the first system, we propose to use channel realizations of collided packets as different signatures to separate them. Moreover, we propose a solution for the problem when the received powers are comparable. For this system, we note that the orthogonality of the STBC matrix allows the use of a simple linear processing step for the initialization of SSIC. For the SM multi-user system, the separation of collided packets is based on V-BLAST processing and SSIC. We also propose how to combine retransmitted packets. For both systems, we evaluate the block error rate, the throughput, and the delay. A comparison is done with the single-user case and with other receivers proposed in the literature.

An OFDMA-Based MAC Protocol for Next-Generation VANETs

Vehicular ad hoc networks (VANETs) enable higher safety, enhanced mobility management, and new infotainment services. Currently, the foreseen standard at the medium access control (MAC) layer for VANETs is IEEE 802.11p, which is based on carrier sense multiple access with collision avoidance (CSMA/CA). However, under heavy traffic conditions, CSMA/CA suffers from a high collision probability, particularly in the presence of hidden terminals. Furthermore, the adoption of the request-to-send/clear-to-send (RTS/CTS) mechanism is not effective when a high data rate is required. If high-throughput services are addressed, a new MAC protocol should, thus, be designed. To this aim, in this paper, we propose a new protocol, which is denoted as the orthogonal frequency-division multiple-access (OFDMA)-based MAC protocol for VANETs (OBV), and we compare it with other MAC protocols taken as benchmarks. To verify the feasibility and the performance of the proposed algorithm, we first propose an analytical model in a simplified scenario. Then, we develop exhaustive simulations in realistic scenarios, considering both urban and highway environments. Results show that OBV outperforms all reference protocols, even doubling their throughput under heavy-load network conditions.

SU‐F‐BRB‐05: Collision Avoidance Mapping Using Consumer 3D Camera

Purpose:To develop a fast and economical method of scanning a patient's full body contour for use in collision avoidance mapping without the use of ionizing radiation.Methods:Two consumer level 3D cameras used in electronic gaming were placed in a CT simulator room to scan a phantom patient set up in a high collision probability position. A registration pattern and computer vision algorithms were used to transform the scan into the appropriate coordinate systems. The cameras were then used to scan the surface of a gantry in the treatment vault. Each scan was converted into a polygon mesh for collision testing in a general purpose polygon interference algorithm. All clinically relevant transforms were applied to the gantry and patient support to create a map of all possible collisions. The map was then tested for accuracy by physically testing the collisions with the phantom in the vault.Results:The scanning fidelity of both the gantry and patient was sufficient to produce a collision prediction accuracy of 97.1% with 64620 geometry states tested in 11.5 s. The total scanning time including computation, transformation, and generation was 22.3 seconds.Conclusion:Our results demonstrate an economical system to generate collision avoidance maps. Future work includes testing the speed of the framework in real‐time collision avoidance scenarios.Research partially supported by a grant from Varian Medical Systems

A probabilistic model for hydrokinetic turbine collision risks: exploring impacts on fish.

A variety of hydrokinetic turbines are currently under development for power generation in rivers, tidal straits and ocean currents. Because some of these turbines are large, with rapidly moving rotor blades, the risk of collision with aquatic animals has been brought to attention. The behavior and fate of animals that approach such large hydrokinetic turbines have not yet been monitored at any detail. In this paper, we conduct a synthesis of the current knowledge and understanding of hydrokinetic turbine collision risks. The outcome is a generic fault tree based probabilistic model suitable for estimating population-level ecological risks. New video-based data on fish behavior in strong currents are provided and models describing fish avoidance behaviors are presented. The findings indicate low risk for small-sized fish. However, at large turbines (≥5 m), bigger fish seem to have high probability of collision, mostly because rotor detection and avoidance is difficult in low visibility. Risks can therefore be substantial for vulnerable populations of large-sized fish, which thrive in strong currents. The suggested collision risk model can be applied to different turbine designs and at a variety of locations as basis for case-specific risk assessments. The structure of the model facilitates successive model validation, refinement and application to other organism groups such as marine mammals.

Random Access Based Blind Relay Selection in Large-Scale Relay Networks

A random access based blind relay selection (RAB RS) scheme is proposed. Due to the size and the blind characteristic of the large-scale relay service networks, collecting the real-time status of the relays is a very difficult task. To address this problem, the proposed scheme enables the user to randomly select a relay through slotted ALOHA, without requiring any relay information. In addition, the high collision probability of the selection phase can be reduced by introducing an available relay region to adaptively decrease the number of the available relays. This geographical region consists of all the relays that satisfy the required rate of the user at the target outage probability. Compared with the upper bound that requires the complete relay information, the proposed RABRS scheme is implemented in a blind manner while maintaining almost optimal performance.

Performance analyses of minimising emergency message collisions and maximising network throughput in IEEE 802.11p VANET network

IEEE 802.11p is proposed as the VANET wireless media access control (MAC) interface for the transmissions of emergency messages in V2V and V2I Communications. However, in a high mobility vehicular adhoc network (VANET), quality of service (QoS) of both the emergency message (EM) and handoff transmissions suffer from high collision probability of the contention-based media access mechanism and high interference exhibiting near the cell-edge that encodes a low coding rate of the adaptive modulation and coding (AMC) scheme. Thus, this paper proposes an efficient MAC for IEEE 802.11p to solve above critical issues, in which the approach consists of three main mechanisms to dynamically determine contention window (CW) based on the sigmoid function. Numerical results demonstrate that the analysis results are close to the simulation results, and thus justify the correctness of the mathematical analytical model. In addition, the proposed approach outperforms the compared approaches (including the IEEE 802.11p std.) in EM transmission delay, collision probability, throughput and MAC frame dropping probability.

Energy Efficient and Reliable ARQ Scheme (E $$^2$$ 2 R-ACK) for Mission Critical M2M/IoT Services

Wireless sensor networks (WSNs) are the main infrastructure for machine to machine (M2M) and Internet of thing (IoT). Since various sophisticated M2M/IoT services have their own quality-of-service (QoS) requirements, reliable data transmission in WSNs is becoming more important. However, WSNs have strict constraints on resources due to the crowded wireless frequency, which results in high collision probability. Therefore a more efficient data delivering scheme that minimizes both the transmission delay and energy consumption is required. This paper proposes energy efficient and reliable data transmission ARQ scheme, called energy efficient and reliable ACK (E $$^2$$ R-ACK), to minimize transmission delay and energy consumption at the same time. The proposed scheme has three aspects of advantages compared to the legacy ARQ schemes such as ACK, NACK and implicit-ACK (I-ACK). It consumes smaller energy than ACK, has smaller transmission delay than NACK, and prevents the duplicated retransmission problem of I-ACK. In addition, resource considered reliability (RCR) is suggested to quantify the improvement of the proposed scheme, and mathematical analysis of the transmission delay and energy consumption are also presented. The simulation results show that the E $$^2$$ R-ACK scheme achieves high RCR by significantly reducing transmission delay and energy consumption.

Evaluation of a satellite constellation for active debris removal

This paper analyzes an example of a three-dimensional constellation of debris removal satellites and proposes an effective constellation using a delta-V analysis that discusses the advisability of rendezvousing satellites with space debris. Lambert׳s Equation was used to establish a means of analysis to construct a constellation of debris removal satellites, which has a limit of delta-V injection by evaluating the amount of space debris that can be rendezvoused by a certain number of removal satellite. Consequently, we determine a constellation of up to 38 removal satellites for debris removal, where the number of space debris rendezvoused by a single removal satellite is not more than 25, removing up to 584 pieces of debris total. Even if we prepare 38 removal satellites in their respective orbits, it is impossible to remove all of the space debris. Although many removal satellites, over 100 for example, can remove most of the space debris, this method is economically disproportionate. However, we can also see the removal satellites are distributed nearly evenly. Accordingly, we propose a practical two-stage strategy. The first stage is to implement emergent debris removal with the 38 removal satellites. When we find a very high probability of collision between a working satellite and space debris, one of the removal satellites in the constellation previously constructed in orbit initiates a maneuver of emergent debris removal. The second stage is a long-term space debris removal strategy to suppress the increase of space debris derived from collisions among the pieces of space debris. The constellation analyzed in this paper, which consists of the first 38 removal satellites, can remove half of the over 1000 dangerous space debris among others, and then the constellation increases the number of the following removal satellites in steps. At any rate, an adequate orbital configuration and constellation form is very important for both space debris removal and economic efficiency. Though the size of constellation of debris removal satellites would be small originally, such a constellation of satellites should be one of the initial constellations of removal satellites to ensure the safety of the future orbital environment.

Joint routing, channel allocation and power control for real‐life wireless sensor networks

AbstractThe energy consumption of wireless sensor networks (WSNs) is a critical issue, because replacement of their batteries can be difficult or even impossible. It is well known that the radio is the most energy demanding part of the node. Therefore, efficient communications are imperative to increase the network lifetime. However, many issues arise in practical WSNs implementations because of the uncertainty and dynamics of the environment and the complexity constraints of the nodes. Routing protocol for low‐power and lossy networks (RPL) is one of the most widely implemented routing strategies because it deals with many of these practical issues. Unfortunately, this protocol does not adapt the nodes' transmission power nor the nodes' transmission channel. Nowadays, commercial motes have multi‐power and multi‐channel capabilities, and these can be used to reduce the network consumption and avoid the high collision probability that may arise in convergecast networks. In this paper, we enhance RPL to obtain a joint routing, transmission power control and channel allocation solution for real‐life WSNs. Two different strategies (minimum aggregated power and maximum probability delivery ratio) are designed and implemented in a WSN testbed with commercial motes. They are compared with the original RPL and also with other standard routing protocols, such as the routing strategy adopted in ZigBee. The experimental results show that the network performance is improved both in terms of reliability and energy consumption. Copyright © 2014 John Wiley & Sons, Ltd.

H∞Guaranteed Cost Control for Networked Control Systems under Scheduling Policy Based on Predicted Error

Scheduling policy based on model prediction error is presented to reduce energy consumption and network conflicts at the actuator node, where the characters of networked control systems are considered, such as limited network bandwidth, limited node energy, and high collision probability. The object model is introduced to predict the state of system at the sensor node. And scheduling threshold is set at the controller node. Control signal is transmitted only if the absolute value of prediction error is larger than the threshold value. Furthermore, the model of networked control systems under scheduling policy based on predicted error is established by taking uncertain parameters and long time delay into consideration. The design method ofH∞guaranteed cost controller is presented by using the theory of Lyapunov and linear matrix inequality (LMI). Finally, simulations are included to demonstrate the theoretical results.

A Beacon-Based Collision-Free Channel Access Scheme for IEEE 802.11 WLANs

In IEEE 802.11 based WLAN standard, distributed coordination function is the fundamental medium access control (MAC) technique. It employs a CSMA/CA with random binary exponential backoff algorithm and provides contention-based distributed channel access for stations to share the wireless medium. However, performance of this mechanism drops dramatically due to random structure of the backoff process, high collision probability and frame errors. That is why development of an efficient MAC protocol, providing both high throughput for data traffic and quality of service (QoS) support for real-time applications, has become a major focus in WLAN research. In this paper, we propose an adaptive beacon-based collision-free MAC adaptation. The proposed scheme makes use of beacon frames sent periodically by access point, lets stations enter the collision-free state and reduces the number of idle slots regardless of the number of stations and their traffic load (saturated or unsaturated) on the medium. Simulation results indicate that the proposed scheme dramatically enhances the overall throughput and supports QoS by reducing the delay, delay variation and dropping probability of frames.

Diffusive behaviors of circle-swimming motors

Spherical catalytic micromotors fabricated as described in Wheat et al. [Langmuir 26, 13052 (2010)] show fuel concentration dependent translational and rotational velocity. The motors possess short-time and long-time diffusivities that scale with the translational and rotational velocity with respect to fuel concentration. The short-time diffusivities are two to three orders of magnitude larger than the diffusivity of a Brownian sphere of the same size, increase linearly with concentration, and scale as v(2)/2ω. The measured long-time diffusivities are five times lower than the short-time diffusivities, scale as v(2)/{2D(r)[1+(ω/D(r))(2)]}, and exhibit a maximum as a function of concentration. Maximums of effective diffusivity can be achieved when the rotational velocity has a higher order of dependence on the controlling parameter(s), for example fuel concentration, than the translational velocity. A maximum in diffusivity suggests that motors can be separated or concentrated using gradients in fuel concentration. The decrease of diffusivity with time suggests that motors will have a high collision probability in confined spaces and over short times; but will not disperse over relatively long distances and times. The combination of concentration dependent diffusive time scales and nonmonotonic diffusivity of circle-swimming motors suggests that we can expect complex particle responses in confined geometries and in spatially dependent fuel concentration gradients.