High Traffic Conditions Research Articles

Enhanced Relay Selection and Scheduling for Better Load Balancing in Multi-Hop Networks

Relaying technology is likely to bring real progress to the next generation cellular networks due to its capability of boosting the system capacity and coverage. However, despite recent advances in relay deployment, some challenging problems still remain such as radio resource allocation and relay selection. The authors investigate both relay selection and scheduling strategy in order to improve the system radio capacity as well as the network load balancing. They propose a new path selection scheme based on the radio channel quality and the relay station load criteria. Performance analysis showed that the authors approach outperforms the existing path selection algorithms in terms of outage probability and global throughput in the system, especially in high traffic conditions. It is revealed that most of the cell edge users which would be rejected when applying common selection scheme, can now have access to a selected relay station and achieve a high end-to-end throughput. A new scheduling strategy is proposed in the second part of this paper, on the basis of a dynamic subframe partitioning. Simulation results show that the outage probability is reduced and more balanced resource allocation is provided. Simulation results showed that some relay stations which were not able to offer any service with the fixed subframe partitioning, can achieve a high data rate with the authors proposed dynamic scheduling strategy.

Impacts of freeway traffic conditions on in-vehicle exposure to ultrafine particulate matter

There is evidence of adverse health impacts from human exposure to traffic-related ultrafine particulate matter pollution. As more commuters are spending a significant portion of their daily routine inside vehicles, it is increasingly relevant to study exposure levels to harmful pollutants inside the vehicle microenvironment. This study is one of the first research efforts to combine detailed freeway traffic data (at 20 s intervals) and in-vehicle ultrafine particulate (UFP) exposure data under varying vehicle ventilation conditions. Results show that due to negative correlation between traffic speed and density, traffic states have a small but significant impact on in-vehicle UFP concentrations, highest in high traffic flow-high speed conditions or in high traffic density-low speed conditions. Vehicle cabin barrier effects are the primary determinant of in-vehicle exposure concentrations, providing 15% protection with the windows down, 47% protection with the windows up and the vent open, and 83–90% protection with the windows up and the vent closed (more with the air conditioning on). Unique results from this study include the dominance of ventilation over traffic effects on UFP and the non-linear relationships between traffic variables and UFP concentrations. The results of this research have important implications for exposure modeling and potential exposure mitigation strategies.

Building Web services middleware with predictable execution times

Predictability of execution has seldom been considered important in the design of Web services middleware. However, with the paradigm shift brought by cloud computing and with offerings of Platforms and Infrastructure as services, execution level predictability is mandating an increased importance. Existing Web services middleware are optimised for throughput with unconditional acceptance of requests and execution in a best-effort manner. While achieving perceived levels of throughput, they also result in highly unpredictable execution times. This paper presents a generic set of guidelines, algorithms and software engineering techniques that enable service execution to complete within a given deadline. The proposed algorithms accept requests for execution based on their laxity and executes them to meet requested deadlines. An introduced admission control mechanism results in a large range of laxities, enabling more requests to be scheduled together by phasing out their execution. Specialised development libraries and operating systems empower them with increased control over execution. Two widely used Web services middleware products were enhanced using these techniques. The two systems are compared with their unmodified versions to measure the predictability gain achieved. Empirical evidence confirms that the enhancements made enable these systems to achieve more than 90% of the deadlines under any type of traffic, while the unmodified versions achieve less than 10% of the deadlines in high traffic conditions. Predictability of execution achieved through these techniques, would open up new application areas such as industrial control systems, avionics, robotics and financial trading systems to the use of Web services as a middleware platform.

Optimal Flows On Road Networks In Emergency Cases

In this paper, we present a technique to redistribute car flows, described by a fluid dynamic model, on a portion of the Caltanissetta city, in Italy, when critical situations, such as car accidents, occur. Using a decentralized approach, a cost functional, that describes the asymptotic average velocity of emergency vehicles, is maximized with respect to distribution coefficients at simple junctions with two incoming roads and two outgoing ones. Then, in order to manage critical situations in high traffic conditions, local optimal coefficients at each node of the network are used. The overall traffic evolution is studied via simulations, that confirm the goodness of the optimization results. It is also proved that optimal coefficients allow a fast transit of emergency vehicles on assigned routes on the network.

Development of the Reconfigurable Data Acquisition Vehicle for Bio-Energy Crop Sensing and Management

In this article, the development of the Reconfigurable Data Acquisition Vehicle (R-DAV) that has a high performance as a wheeled mobile robot is presented. The R-DAV is designed to monitor and manage the growing status of bio-energy crops, and the vehicle will be used for image collection, density measurements, and chemical applications. A theoretical model has been proposed to optimize the configuration. The 4-Wheel-Drive-4-Wheel-Steering (4WD4WS) locomotion was proposed as the essential base for high traffic conditions and maneuverability, and a prototype model was fabricated for this scenario. The chassis was uniquely reconfigured in two ways: (1) by adjusting the clearance and (2) by changing the wheel gauge. The reconfiguration of the clearance was necessary to operate the vehicle over a range of heights of bio-energy crops at different growing stages in the Miscanthus (Miscanthus is a genus of about 15 species of perennial grasses native to subtropical and tropical regions of Africa and southern Asia). The adjustable wheel gauge layout was designed to follow variable inter-row tracks in the Miscanthus field. Furthermore, a triangle-shaped guard was specifically considered to minimize the crop damage when the vehicle enters into the field.

MIMO-Assisted MPR-Aware MAC Design for Asynchronous WLANs

The use of multiple-packet reception (MPR) in wireless networks is known to improve throughput especially in high-traffic conditions. The lack of synchronization among the nodes in random access systems introduces significant challenges toward the adoption of MPR in the PHY and the MAC design for systems using MPR. In this paper, we propose an asynchronous MPR method for the PHY and also design a compatible random access MAC for wireless local area networks (WLANs). Relying on space-time coding techniques, our MPR method detects multiple asynchronous packets while providing diversity and low bit error rates at the PHY layer. Extending the design of IEEE 802.11, our MPR MAC design encourages simultaneous packet transmissions and handles multiple packet receptions. Simulation results show that the throughput of a WLAN significantly improves in many scenarios of operation using our proposed PHY/MAC MPR framework.

Elemental contamination in urban parks of Rawalpindi/Islamabad—a source identification and pollution level assessment study

The soil quality of urban parks is of vital importance as the children playing in the parks get themselves easily contaminated. A study was conducted to assess the level of elemental pollution caused by constant urbanization and industrialization, in various parks of Islamabad and Rawalpindi. The soil samples, collected from 14 urban parks of Islamabad and Rawalpindi areas, were analysed for their elemental concentrations. In each sample, 32 elements were quantified using semi-absolute k (0)-instrumental neutron activation analysis and flame atomic absorption spectrophotometry. The quality of analysis was assured by analysing the International Atomic Energy Agency (IAEA) reference material IAEA-S7 (soil). The pollution level was assessed by enrichment factor, pollution load index and our suggested indicator called "average toxic element concentration". The elemental concentrations measured in the parks of two cities were compared by t test. Four sources of different elements in the soils were identified by employing principal component analysis and cluster analysis. The results of multivariate techniques grouped all parks into four classes. The use of enrichment factor indicated the presence of Ni at slightly higher level in all parks while the pollution load index revealed that the parks of Rawalpindi were relatively more polluted as compared to that of Islamabad. The hot spot areas of elemental concentration were closely related to high traffic conditions.

Seamless handover supported by parallel polling and dynamic multicast group in connected WLAN micro-cells system

WLAN (Wireless Local Area Network) has been seen to be one of the promising access technologies that adapts to 4G cellular network systems in providing very high speed connection with QoS guarantee through the polling function. However, when the handover happens, the contention-based medium access mechanism which is mainly used in WLAN is invoked and introduces unbounded transmission delay due to idle time periods and retransmission because of collision during the handover. If this technique is expanded to use in a microcellular network such as connected WLAN micro-cells, contention-based mechanism, therefore, should not be used to handle the MT’s handover, especially for vehicular users who change access point every few seconds. To overcome these difficulties in handover, we introduce parallel polling scheme in dynamic LMC (Logical Macro Cell) which can reduce delays much and remove packet loss rate. LMC is a virtual single macro cell which is built on a multicast group of adjacent micro-cells. In the same LMC, polling signals are sent from every BS (base station) to give MT (mobile terminal) permission to access one of these BSs. Instead of wasting much time to contend for resources of a new BS during handover, the MT answers the polling as an acknowledgment to connect to that new BS. The polling response is controlled to multicast to all BSs of the same LMC via the core network to synchronize for the next polling cycle. LMC is controlled to dynamically change when the MT comes in a new BS to make polling signals be continuous in a new LMC. Through analytical and simulation results, we show that the parallel polling scheme can achieve no handover latency, no packet loss and maintain mobile users’ throughput stably in the high traffic load condition though it causes overhead on the neighboring cells in both of wired and wireless sections. At speeds of up to70 m/s, the MT can still maintain its stable connection. OMNeT++ simulator with INET project is used to evaluate our proposal.

Energy-Efficiency Analysis of a Distributed Queuing Medium Access Control Protocol for Biomedical Wireless Sensor Networks in Saturation Conditions

The aging population and the high quality of life expectations in our society lead to the need of more efficient and affordable healthcare solutions. For this reason, this paper aims for the optimization of Medium Access Control (MAC) protocols for biomedical wireless sensor networks or wireless Body Sensor Networks (BSNs). The hereby presented schemes always have in mind the efficient management of channel resources and the overall minimization of sensors’ energy consumption in order to prolong sensors’ battery life. The fact that the IEEE 802.15.4 MAC does not fully satisfy BSN requirements highlights the need for the design of new scalable MAC solutions, which guarantee low-power consumption to the maximum number of body sensors in high density areas (i.e., in saturation conditions). In order to emphasize IEEE 802.15.4 MAC limitations, this article presents a detailed overview of this de facto standard for Wireless Sensor Networks (WSNs), which serves as a link for the introduction and initial description of our here proposed Distributed Queuing (DQ) MAC protocol for BSN scenarios. Within this framework, an extensive DQ MAC energy-consumption analysis in saturation conditions is presented to be able to evaluate its performance in relation to IEEE 802.5.4 MAC in highly dense BSNs. The obtained results show that the proposed scheme outperforms IEEE 802.15.4 MAC in average energy consumption per information bit, thus providing a better overall performance that scales appropriately to BSNs under high traffic conditions. These benefits are obtained by eliminating back-off periods and collisions in data packet transmissions, while minimizing the control overhead.

Assessing the accuracy and reliability of freeway traffic monitoring stations using GPS probe vehicle speed data

Freeway performance measures are extracted from Traffic Monitoring Stations (TMS) which gather traffic volume and speed data. Reported freeway speeds are usually aggregated over periods of 20 or 30-second or 1, 5, or 15-minute by traffic agencies. This paper examines the accuracy and reliability of reported TMS detector speeds. The study compares speeds collected by GPS-equipped probe vehicles with aggregated detector speeds. The paper evaluates how various aggregation intervals impact accuracy and reliability of TMS detector speeds and determines the optimal aggregation interval. Results indicate that shorter aggregation intervals are appropriate for high variability traffic conditions during peak periods.

Energy efficient wireless Internet access with cooperative cellular networks

In this paper we study the energy-aware cooperative management of the cellular access networks of the operators that offer service over the same area. In particular, we evaluate the amount of energy that can be saved by using all networks in high traffic conditions, but progressively switching off networks during the periods when traffic decreases, and eventually becomes so low that the desired quality of service can be obtained with just one network. When a network is switched off, its customers are allowed to roam over those networks that remain powered on. Several alternatives are studied, as regards the traffic profile, the switch-off pattern, the energy cost model, and the roaming policy. Numerical results indicate that a huge amount of energy can be saved with an energy-aware cooperative management of the networks, and suggest that, to reduce energy consumption, and thus the cost to operate the networks, new cooperative attitudes of the operators should be encouraged with appropriate incentives, or even enforced by regulation authorities.

Excessively Wet Subgrade Improvement with 100% Industry By-Products for Heavy Traffic Pavement – I. Solidification and Compaction Characteristics of Treated Soil

Deformation of excessively wet subgrade is often problematic during pavements construction as well as under regular vehicular traffic loads. In order to create a sturdy and stable platform for heavy traffic pavement, a “green materials” based entirely on industry byproduct of combination fly ash (FA) with carbide lime (CL) and flue gas desulfurization gypsum (FGDG) was proposed in this study. In order to investigate the effectiveness and improvement of engineering properties, solidification test and compaction test were carried out in laboratory, and Dynamic Cone Penetrometer (DCP) was conducted at the construction site. Investigation results showed significant improvement in drying rate, workability, and mechanical behavior. The addition of FA/CL/FDG stabilizer increases the solids content by “bulking” and reduces the free moisture through hydration reactions. The addition of FA/CL/FGDG leads to an increase of approximately 18% in the maximum allowable moisture content, which would largely facilitate the compaction of the excessively wet soils. Post construction evaluation using DCP indicates the stabilized soil can be utilized under high volume traffic condition.

An arterial signal optimization model for intersections experiencing queue spillback and lane blockage

This paper presents an arterial signal optimization model that features its effectiveness on: (1) explicitly modeling physical queue evolution on arterial links by lane-group to account for shared-lane traffic interactions; and (2) capturing the dynamic interactions of spillback queues among lane groups and between neighboring intersections due to high demand, geometric constraints, or signal settings. Depending on the detected traffic patterns, one can select the control objective to be either minimizing the total travel time or maximizing the total throughput over the target area. The solution procedures developed with the Genetic Algorithm (GA) have been tested with an example arterial of four intersections under different demand scenarios. Extensive experimental analyses in comparison with results from TRANSYT-7F (version 8) reveal that the proposed model and solution method are quite promising for use in design of arterial signals, especially under congested, high demand traffic conditions.

Energy efficient management of two cellular access networks

In this paper we evaluate the energy saving that can be achieved with the energy-aware cooperative management of the cellular access networks of two operators offering service over the same area. We evaluate the amount of energy that can be saved by using both networks in high traffic conditions, but switching off one of the two during the periods when traffic is so low that the desired quality of service can be obtained with just one network. When one of the two networks is off, its customers are allowed to roam over the one that is on. Several alternatives are studied, as regards the switch-off pattern: the one that balances the switch-off frequencies, the one that balances roaming costs, the one that balances energy savings, and the one that maximizes the amount of saved energy. Our results indicate that a huge amount of energy can be saved, and suggest that, to reduce energy consumption, new cooperative attitudes of the operators should be encouraged with appropriate incentives, or even enforced by regulation authorities.

In-home power line communication media access control protocol based on collision resolution

Most existing media access control (MAC) protocols in power line communication (PLC) networks just discard the colliding data packets when collision occurs. The collision deteriorates throughput and delay performance of system under high traffic conditions. This article presents a novel media access scheme with fast collision resolution for in-home power line networks. It works by first recognizing the colliding stations through detecting the inserted unique ID sequence ahead of data packets, then the source nodes retransmitting their packets immediately after the collision slot. The proposed protocol maintains the benefits of ALOHA systems. It needs no scheduling overhead and is suitable for bursty sources, such as multimedia data packets. Computer simulations have demonstrated that this approach can achieve high throughput due to its ability of resolving collisions.

Performance Analysis of TCP with Delayed Acknowledgments in Multi-hop Ad-hoc Networks

The acknowledgment strategy has great potential to increase TCP throughput when it runs over 802.11 MAC protocol. In particular, TCP acknowledgments (ACK) carry out an extensive number of medium accesses as they compete in the same route as data packets for media. In this paper, we first propose a dynamic TCP-MAC interaction strategy which tries to reduce the number of induced ACKs by monitoring the channel condition. To this end, the total collision probability collected along the path from sender to receiver in MAC layer has been used to properly set the number of delayed ACKs (DA) in TCP. Based on the estimated collision probability, TCP sender dynamically adjusts itself to the channel condition by delaying less ACKs in high traffic conditions and more ACKs in low traffic conditions. The simulation results show a throughput improvement up to 15% over the existing method called Dynamic Adaptive Acknowledgment (TCP-DAA) and much more over the regular TCP in different scenarios dealing with a dynamic loss rate. In addition, we show that our proposed strategy does not always benefit from a fixed delay policy along with a fixed congestion window size. In fact, the optimal number of delayed ACKs is based on the path length of a TCP connection and a large delay window may solely improve TCP throughput in short ranges with less number of flows. However, in a longer path congestion window limit provides more throughput gain.

Synchronized Signal Control Model for Maximizing Progression along an Arterial

For the most part, optimal signal timing is the most effective and economical method for mitigating traffic congestion in urban areas. In this study, a new mixed integer nonlinear programming model is proposed to develop an optimal arterial-based progression algorithm. The proposed algorithm is designed to optimize the bandwidths for contiguous signals along a signalized arterial. The traffic conditions for examining the proposed algorithm are extracted from moderate to high saturated traffic conditions. The main objective of the proposed algorithm is to allow traffic to traverse through the maximum number of downstream intersections without a stop. According to measures of effectiveness ( MOEs ) acquired by TSIS-CORSIM 6, the signal timing generated by the proposed model yields lower stops (%) when compared with the signal timing optimized and generated by Synchro. In addition, the proposed model yields lower network-wide average delays (sec/veh) and higher average travel speeds (km/h) under moderate to ...

Multivariate analysis of trace element concentrations in atmospheric deposition in the Yangtze River Delta, East China

The Yangtze River Delta (YRD), one of the fastest developing regions in China, was investigated for its trace element concentrations. Forty-three samples of atmospheric deposition were analyzed for their concentrations of thirteen elements, As, Cd, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Se, S and Zn. The results show that, in comparison with Chinese soil, the atmospheric deposition in the YRD generally has elevated trace element concentrations, except for Fe and Mn. The current atmospheric deposition of Cd, Cr, Cu, Pb and Zn in the YRD is significantly higher than the results from previous studies in other regions around the world. Four main sources of the trace elements were identified using statistical techniques including descriptive, correlation, and multivariate analyses, such as principal component analysis (PCA) and cluster analysis (CA). The four sources and associated cluster elements are: (1) road traffic emissions contributing As, Hg, Cu, Cd, Mo, S and Zn; (2) pyrometallurgical processes associated with Cr and Ni; (3) resuspension of soil particles contributing Fe and Mn; (4) coal combustion associated with Pb and Se. The four major sources were further verified by enrichment factor (EF) calculation and spatial analysis. Spatial distributions of four factor scores and EFs of elements show that high scores and EFs of trace metals (As, Hg, Cu, Cd, Mo, S and Zn) are mostly concentrated in the sites with high traffic conditions, and high scores of Fe and Mn are found at rural sites associated with high impact of soil particles resuspension, while Cr and Ni are higher in the area with long history of alloy machining.

“Soil Pollution Hazardous to Environment”: A case study on the chemical composition and correlation to automobile traffic of the roadside soil of Jeddah city, Saudi Arabia

Soil samples from different roads in Jeddah city were collected and analyzed for their elemental composition. The effects of traffic conditions were critically investigated to reflect the effect of the heavy and light traffic on the soil composition. Samples were analyzed for K, As, Co, Cr, Ni, Pb, Sb, V, and Zn. The results revealed great dependence of lead and zinc contents on traffic conditions. The lead content lies in the range 0.3–104.8 ± 0.003 mg/kg for the samples of high traffic conditions and 0.3 ± 0.0 mg/kg being for the sample with no traffic activity, whereas 104.8 ± 0.003 mg/kg was for the one of the most used highways area in Jeddah city. Zinc level lies in the range 56.59 ± 0.003–456.93 ± 0.06 mg/kg which is quite close to lead pattern. The high zinc concentration was found along the main turn roads. The high zinc content in tested soil samples may come from traffic sources, especially vehicle tires. Concentrations of other elements showed little dependence on traffic conditions.

Polling-Based High-Bit-Rate Packet Transfer in a Microcellular Network to Allow Fast Terminals

A microcellular network will be a good candidate for the future broadband mobile network. It is expected to support high-bit-rate connection for many fast mobile users if the handover is processed fast enough to lessen its impact on QoS requirements. One of the promising techniques is believed to use for the wireless interface in such a microcellular network is the WLAN (Wireless LAN) technique due to its very high wireless channel rate. However, the less capability of mobility support of this technique must be improved to be able to expand its utilization for the microcellular environment. The reason of its less support mobility is large handover latency delay caused by contention-based handover to the new BS (base station) and delay of re-forwarding data from the old to new BS. This paper presents a proposal of multi-polling and dynamic LMC (Logical Macro Cell) to reduce mentioned above delays. Polling frame for an MT (Mobile Terminal) is sent from every BS belonging to the same LMC — a virtual single macro cell that is a multicast group of several adjacent micro-cells in which an MT is communicating. Instead of contending for the medium of a new BS during handover, the MT responds to the polling sent from that new BS to enable the transition. Because only one BS of the LMC receives the polling ACK (acknowledgement) directly from the MT, this ACK frame has to be multicast to all BSs of the same LMC through the terrestrial network to continue sending the next polling cycle at each BS. Moreover, when an MT hands over to a new cell, its current LMC is switched over to a newly corresponding LMC to prevent the future contending for a new LMC. By this way, an MT can do handover between micro-cells of an LMC smoothly because the redundant resource is reserved for it at neighboring cells, no need to contend with others. Our simulation results using the OMNeT++ simulator illustrate the performance achievements of the multi-polling and dynamic LMC scheme in eliminating handover latency, packet loss and keeping mobile users' throughput stable in the high traffic load condition though it causes somewhat overhead on the neighboring cells.