Traffic Load Increases Research Articles

Empirical approach for estimating the pavement transition probabilities used in non-homogenous Markov chains

An empirical approach is proposed to estimate the transition probabilities associated with non-homogenous Markov chains typically used in developing stochastic-based pavement performance prediction models. A reliable pavement performance prediction model is a key component of any advanced pavement management system. The proposed empirical approach is designed to account for two major factors that cause the transition probabilities (i.e. deterioration rates) to increase over time. The first major factor is the progressive increase in traffic loading as represented by the equivalent single axle load applications. The second major factor is the gradual decline in the pavement structural capacity which can be represented by an appropriate pavement strength indicator such as the structural number. The proposed empirical model can recursively estimate the non-homogenous transition probabilities for an analysis period of (n) transitions by simply multiplying the first-year (i.e. present) transition probabilities by two adjustment factors, namely the load and strength factors. Once the empirical model is calibrated, these two factors can capture the impact of traffic load increases and gradual pavement structural losses on the transition probabilities over time. The calibration process requires the estimation of the model two exponents to be obtained from the minimisation of sum of squared errors wherein the error is defined as the difference between the observed and predicted pavement distress ratings (DRs). The predicted DRs are mainly estimated based on the state probabilities, which are recursively derived from the non-homogenous Markov model. A sample empirical model is presented with results indicating its effectiveness in estimating the pavement non-homogenous transition probabilities.

Congestion transition in air traffic networks.

Air Transportation represents a very interesting example of a complex techno-social system whose importance has considerably grown in time and whose management requires a careful understanding of the subtle interplay between technological infrastructure and human behavior. Despite the competition with other transportation systems, a growth of air traffic is still foreseen in Europe for the next years. The increase of traffic load could bring the current Air Traffic Network above its capacity limits so that safety standards and performances might not be guaranteed anymore. Lacking the possibility of a direct investigation of this scenario, we resort to computer simulations in order to quantify the disruptive potential of an increase in traffic load. To this end we model the Air Transportation system as a complex dynamical network of flights controlled by humans who have to solve potentially dangerous conflicts by redirecting aircraft trajectories. The model is driven and validated through historical data of flight schedules in a European national airspace. While correctly reproducing actual statistics of the Air Transportation system, e.g., the distribution of delays, the model allows for theoretical predictions. Upon an increase of the traffic load injected in the system, the model predicts a transition from a phase in which all conflicts can be successfully resolved, to a phase in which many conflicts cannot be resolved anymore. We highlight how the current flight density of the Air Transportation system is well below the transition, provided that controllers make use of a special re-routing procedure. While the congestion transition displays a universal scaling behavior, its threshold depends on the conflict solving strategy adopted. Finally, the generality of the modeling scheme introduced makes it a flexible general tool to simulate and control Air Transportation systems in realistic and synthetic scenarios.

Designs, analyses, and optimizations for attribute-shuffling obfuscation to protect information from malicious cloud administrators

We developed an attribute-shuffling obfuscation for database applications in cloud environment and studied its potential in preventing information leaks to malicious administrators at cloud providers, who have unlimited and non-censored accesses to any local resources, possibly including the system security logs. The proposed obfuscation allows database management systems at cloud servers to perform fundamental query operations while cloud users' information is protected against leaks to malicious administrators. We studied the performance of the proposed obfuscation to find that the inflation of obfuscated tables at cloud servers and the increase in the network traffic load will be the major overhead. We developed algorithms that mitigate the inflation of obfuscated tables using 'α' parameter and the increase in the network traffic load using the query constructor. The former achieved a linear relation between the obfuscated table size and the degree of obfuscation how hard for malicious administrators to understand the meaning of users' information. The latter achieved that the network traffic load nearly converged to that of no obfuscation for busy systems. We conclude that the proposed attribute-shuffling obfuscation will be feasible and efficient for busy and large database systems, while it adapts to database systems with diverse configurations. Copyright © 2015 John Wiley & Sons, Ltd.

Impact of Irregularity and Loss of Punctuality on the Performance of Public Transportation System

Rapid growth and development had resulted into increase need of a mass transportation facility over the entire region for which different types of mass transit facilities are designed and provided. Such mass transportation facilities include GSRTC, AMTS, BRTS, CHARTEER BUSES, TRAINS, and TRAMS etc. The basic aim of such facilities is to provide safe, comfortable and timely services. But with rapid increase in traffic load and increase in the frequency of services provided, it had been observed that services are delayed or unable to maintenance a prescribed schedule. A study is conducted to quantify the causes and influence of such delays and irregularities in the services. Suggestions are made for appropriate improvement in services based on present study.

Influence of Anti-Rutting Agent on the Pavement Performance of Asphalt Mixture

With the increase of traffic volume and axle load, asphalt pavement rutting has become one of the major damage of highway. Adding anti-rutting agent in asphalt mixture is a kind of effective mean to prevent pavement rutting. In this paper, RA anti-rutting agent is selected as the admixture. Laboratory test is taken to study the pavement performance of asphalt mixture and analyze the influence of anti-rutting agent on the pavement performance of asphalt mixture.

Review of Energy Conservation Using Duty Cycling Schemes for IEEE 802.15.4 Wireless Sensor Network (WSN)

Energy conservation is one of the crucial issues in wireless sensor network (WSN). A significant solution to conserve energy is done by deploying duty cycle management mechanisms in the WSN applications. This paper reviews several duty cycle mechanisms in WSN such as Duty Cycle Learning Algorithm, adaptive media access control (MAC) protocol for efficient IEEE 802.15.4 (AMPE), distributed duty cycle management (DDCM), distributed duty cycle management low power broadcast (DDCM + LPB) and distributed beacon only period. These mechanisms change their parameters such as idle listening, packet accumulation and delay in the end device transmitting queue to improve the energy conservation in WSN. The performances of these different energy conservation mechanisms have been compared at the MAC layer of IEEE 802.15.4 standard. It is found that the DDCM + LPB has made approximately 100 % enhancement in terms of average energy efficiency as compared to the other mechanisms. DDCM + LPB has significant enhancements by adapting the duty cycle according to the network traffic load condition. Using this mechanism, the duty cycle is increased when the traffic load increases and vice versa. Its energy efficiency also outperforms the conventional DDCM by the average of 10 %.

Optimised relay selection for route discovery in reactive routing

On-demand routing protocols have the potential to provide scalable information delivery in large ad hoc networks. The novelty of these protocols is in their approach to route discovery, where a route is determined only when it is required by initiating a route discovery procedure. Much of the research in this area has focused on reducing the route discovery overhead when prior knowledge of the destination is available at the source or by routing through stable links. Hence, many of the protocols proposed to date still resort to flooding the network when prior knowledge about the destination is un-available. This paper proposes a novel routing protocol for ad hoc networks, called On-demand Tree-based Routing Protocol (OTRP). This protocol combines the idea of hop-by-hop routing (as used by AODV) with an efficient route discovery algorithm called Tree-based Optimised Flooding (TOF) to improve scalability of ad hoc networks when there is no prior knowledge about the destination. To achieve this in OTRP, route discovery overheads are minimised by selectively flooding the network through a limited set of nodes, referred to as branching nodes. The key factors governing the performance of OTRP are theoretically analysed and evaluated, including the number of branch nodes, location of branching nodes and number of Route REQuest (RREQ) retries. It was found that the performance of OTRP (evaluated using a variety of well-known metrics) improves as the number of branching nodes increases and the number of consumed RREQ retries is reduced. Additionally, theoretical analysis and simulation results shows that OTRP outperforms AODV, DYMO, and OLSR with reduced overheads as the number of nodes and traffic load increases.

Asynchronous Multi-Channel MAC Protocol for WSNs

To tackle control channel saturation and triple hidden terminal problems,this paper proposes RIM,a receiver-initiated multi-channel MAC protocol with duty cycling for WSNs.By adopting a receiver-initiated transmission scheme and probability-based random channel selection,RIM effectively alleviates,if not completely eliminates,control channel saturation and triple hidden terminal problems.In addition,RIM exploits a simple but reliable asynchronous broadcast scheme to solve the problem of broadcast data loss with reliable broadcast-intensive applications.More importantly,RIM is fully distributed with no requirements of time synchronization or multi-radio.Therefore,RIM is very easily implemented in resource-constrained sensor nodes.Via the theoretical analysis,the optimal duty cycle are obtained,respectively.The simulation and real testbed experimental results show that RIM achieves significant improvement in energy efficiency with increasing benefit when the number of channels and traffic loads increase,while maintaining higher throughput.Moreover,RIM exhibits a prominent ability to enhance its broadcast reliability.

Multiuser detectors for large CDMA random access systems over Rayleigh fading channels

AbstractIn this paper, large code division multiple access (CDMA) random access systems employing the decorrelator and minimum mean square error (MMSE) detectors are investigated over Rayleigh fading channels under the assumption that both the number of users and the spreading gain tend to infinity, but their ratio converges to a constant. The signal to interference ratio (SIR) is shown to converge almost surely to a constant and the bit‐error rate (BER) is expressed as a function of the traffic load, transmission probability, channel coefficient, and distribution of transmission power. Furthermore, the throughput, the spectrum efficiency, and the stability region are analyzed and simulated. For dominating systems, it is shown that the MMSE detector achieves much higher throughput and spectral efficiency than decorrelator detector. Besides, it is also disclosed that, when the signal to noise ratio (SNR) is larger than an optimum value, the spectrum efficiency increases as the ratio of bit energy to noise power spectrum density (Eb/N0) increases; however, when SNR is smaller than the optimum value, the spectrum efficiency decreases as Eb/N0 increases. For ordinary stable systems, it is demonstrated that their stability region gets narrower as the traffic load increases. Copyright © 2010 John Wiley & Sons, Ltd.

Safety Assessment of Existing Highway Bridges and Viaducts

The assessment of the structural safety of existing bridges and viaducts becomes increasingly important in many countries owing to an increase in traffic loads. Most existing standards, however, are developed for the design of new structures. For this reason, an assessment method for determining the actual safety level of highway bridges and viaducts has been developed. The method focuses on the determination of the effect of traffic actions and consists of a number of levels. The first level requires the least work from the engineer but is the most conservative. Each of the next levels is less conservative. Some levels require actual measurements at critical parts of the structure. This paper consists of two parts. The first part explains the basis of the safety assessment method and the second part shows the step-by-step application of the method to an existing highway bridge in The Netherlands.

단말 기반 IPTV 품질 측정을 위한 품질 관리 S/W 구현

IPTV 멀티캐스팅 서비스에서 증가되는 네트워크 트래픽 로드에 따른 화상 품질 측정과 화상 품질 변화에 대한 연구는 IPTV 서비스에 대한 관심이 현실화됨에 따라 필요하게 되었다. 본 연구에서는 네트워크 트래픽 로드에 따른 화상 품질의 효과가 주어지는 네트워크 성능 요소의 최적의 값을 파악하기 위하여, 테스트 베드 네트워크를 통하여 테스트 하는 S/W를 개발하였다. 그리고 테스트 환경을 학교 네트워크로 확장하여 실제 IPTV 서비스 환경과 비슷한 학교 네트워크에서 네트워크 트래픽 로드 증가에 따른 IPTV 멀티캐스팅 서비스의 화상 품질 변화를 측정하고자 하였다. The research of image quality estimation standard and the image quality change according to the network traffic load increase at IPTV multicasting service is necessary because the concern of IPTV(Internet Protocol TV) service become active recently. In the research, for finding out the threshold value of network performance elements giving the effect to the image quality according to the network traffic load, we developed S/W to operate the test bed network and make the test scenario through test bed network test and then we expand the test environment scope to the college network and try to measure the image quality change of IPTV multicasting service according to the network traffic load increase at the college network similar to the real IPTV service environment.

Performance analysis of traffic groomed optical network

In this paper we carry out the performance analysis of traffic groomed multilayer optical networks. It is seen that the number of wavelength channels required decreases as the wavelength grooming factor increases. We have evaluated blocking probability for different load and grooming factor. The performance of the network has been evaluated for different conditions; first for fixed number of links with grooming factor set to 3 and subsequently with increase in grooming factor up to 18 in steps. The load on each link is selected as 2, 5, 9, 12, 15 and 20 Erlangs and the blocking probability as function of number of optical channels has been evaluated. In this work the effect of number of wavelength channels, traffic load and grooming factor on network blocking probability has been studied. The investigation reveals that the blocking probability decreases with increase in wavelength channels. Similarly we found that the blocking probability increases with increase in traffic load which is quite evident. Further it is shown that when the grooming factor is increased to significant value (16), the number of wavelengths requirement (8) becomes relatively stable.

Construction of Optimal 2D Optical Codes Using (n,w,2,2) Optical Orthogonal Codes

Two-dimensional (2D) wavelength-time coding schemes have recently been studied for optical code-division multiple access. In this paper, we propose a new family of 2D codes, which use "synchronized" quadratic congruence sequences for wavelength hopping and (n, w, 2, 2) optical orthogonal codes for time spreading. The new 2D codes provide larger (asymptotically optimal) code cardinality than other 2D codes by relaxing the maximum cross-correlation function from one to two. Our study shows that the heavier code weight supported by our 2D codes results in better code performance than some of previously proposed 2D codes (of the maximum cross-correlation functions of one and two). The new codes potentially support more subscribers and heavier bursty asynchronous traffic with gradual performance degradation as traffic load increases.

The Study for the Image Quality Measurement in IPTV

The research of image quality estimation standard and the image quality change according to the network traffic load increase at IPTV multicasting service is necessary because the concern of IPTV(Internet Protocol TV) service become active recently. General quality indicators for imaging services should represent users' quality of experience. To do this, it should be represented the quality from the point of view of users. It should be developed the QoE measurements to represent the quality of users. Accordingly, we study an algorithm for how to be investigated QoE.

Probabilistic Assessment of Deteriorating Prestressed Concrete Box-Girder Bridges under Increased Vehicle Loads and Aggressive Environment

A probabilistic procedure for the assessment of the time-dependent reliability of existing prestressed concrete (PSC) box-girder bridges is presented. These bridges are subject to increased traffic loads and an aggressive environment, which result in structural deterioration such as cracking and corrosion. In this paper, a multiple-peak vehicle load model is proposed based on acquired traffic load data, which cannot be properly described by previous single-peak probability distributions. With the proposed vehicle load model, the maximal vehicle loads during the remaining life of bridges are obtained for evaluating the influence of the increase in traffic loads on bridge reliability. Time-dependent corrosion models are adopted to account for pitting corrosion because of chloride attack as well as uniform corrosion because of concrete carbonation. A degenerated shell element is used for accurate and efficient modeling of the PSC box-girder. Postcracking behaviors of reinforced concrete box-girders, simulated by using different crack models and elements, are compared with laboratory test results. To increase the efficiency of probabilistic analyses, an adaptive importance sampling method in conjunction with the truncated Latin hypercube sampling is used. Application of the proposed methodologies is demonstrated by a case study, in which the time-dependent reliabilities of a deteriorating PSC box-girder bridge are obtained.

Ground‐penetrating radar assessment of the medieval arch bridge of San Antón, Galicia, Spain

AbstractSeveral arched masonry bridges are listed historical monuments in Spain, which are valued tourist attractions or local landmarks. They are maintained by several organizations dedicated to the cultural heritage such as the International Council on Monuments and Sites (ICOMOS). Many of these important structures are the oldest constructions still in use within the transportation infrastructure and as a result of the increase in traffic loads and their age they have undergone some structural decay. Ground‐penetrating radar (GPR) has been shown to be valuable in evaluating the state of conservation of the San Antón medieval bridge in order to help preserve its historical character. This bridge was surveyed by using the 200, 250 and 500 MHz antennas. Interpretation and analysis of GPR reflection data were supported by finite‐difference time domain numerical modelling, based on the accurate external geometry obtained with three‐dimensional laser scanning methods. Results show that GPR mapping provides valuable information for detecting an internal structural element used for reinforcement as well as a possible interior hidden arch that remains from ancient times. This information is noteworthy for archaeologists and civil engineers as it can be used to make decisions about stability and for future strengthening measures. Copyright © 2010 John Wiley & Sons, Ltd.

Discrete-time modeling for performance analysis of real-time services in IEEE 802.16 networks

The IEEE 802.16 standard has been proposed to provide last-mile wireless broadband access, especially for real-time applications. Both unsolicited grant service (UGS) and real-time polling service (rtPS) are defined to support real-time data transmission. The most important parameters of UGS and rtPS are allocated bandwidth and number of request opportunities, respectively. The critical problems of real-time applications, including latency, packet loss, and bandwidth utilization, would be impacted by different parameters configurations of UGS and rtPS. Even though the discrete-time queueing systems could be more accurate and effect in modeling frame-based systems, discrete model is not widely applied due to its complicated analysis. It motivates us to utilize a discrete-time GI- D- c model and a GI- Geo-1 model to investigate the performance of UGS and rtPS, respectively. In both models, the arrival process and service process are both derived while accounting for the traffic load, data size, and number of request opportunities. Numerous experiments indicate that the simulation results agree well with the analysis results. The UGS performs stably in most circumstances. However, latency and transmission queue size degenerate as traffic load increases when the allocated bandwidth is less than the number of arrival PDUs. The latency of rtPS is higher than the latency of UGS due to the request/grant scheme, and decreases as the number of request opportunities increases. Moreover, the bandwidth utilization of UGS and request opportunity efficiency of rtPS are also analyzed under various traffic load and linearly increase as traffic load increases. The study provides a tool to analyze the impact of different parameter configurations and the tool can be easily applicable to other scheduling services.

Modeling of Adaptive Load Balancing with Hybrid F/CDMA and Sectorization Schemes in Mobile Communication Networks

In this paper, we investigate the load balancing problem in mobile communications by considering sectorization and a hybrid F/CDMA scheme (HFCS) jointly in the scenario of uneven traffic distributions. The problem is formulated as a combinatorial optimization model, subject to quality of service (QoS) requirements, and solved by the Lagrangean relaxation approach. In addition, Lagrangean multipliers are used to conduct sensitivity analysis. The model's objective is to minimize the weighted call blocking rate in terms of the distribution diversity. The model's performance is evaluated by the proposed HFCS, which is an adaptive scheme (AS). We compare the performance of AS with that of a non-adaptive (NA) scheme, which is a common power control method. Experiment results show that combining sectorization with the bandwidth segmentation scheme provides effective adaptive load balancing (ALB). The performance improvement achieved by the proposed adaptive scheme over the common power control scheme is as high as 68%. Moreover, under the scheme, the performance improves as the traffic load increases. Load balancing improves even further when AS is combined with the sectorization.

Developments in 3D surfacing seals FE modelling

A surfacing seal may not be considered a thin homogeneous bituminous layer and thus cannot be designed on the basis of material bulk properties. As a result, common design methodologies are of no value in seal design. Seals are thus designed on the basis of empirical methods or engineering judgement. The introduction of new tyre types, the increase in traffic loads and the introduction of new types of bitumen and modifiers ask for fundamental insight into seal behaviour. Hereto a 3D meso-mechanical FE model of a seal was developed. The model represents the seal as it is, i.e. aggregates sitting in a binder and partially worked into the base. Individual aggregates are loaded by forces that follow from a moving tyre. This paper shows that full insight into the stresses and strains that develop in the various relevant structural components of the seal is obtained. It is discussed how this insight may be used for seal design.

ILP formulations for non-simple p-cycle and p-trail design in WDM mesh networks

Conventional simple p-cycle (Preconfigured Protection Cycle) concept allows fast and capacity-efficient span protection in WDM mesh networks. Unlike simple p-cycle, non-simple p-cycle can traverse a node or span multiple times. The recently proposed p-trail (Pre-Cross-Connected Trail) concept further removes the cycle constraint by allowing arbitrary protection trails, leading to the most flexible and general design. Although non-simple p-cycles and p-trails are expected to be more capacity-efficient than simple p-cycles, it is still unclear how much capacity gain they can achieve compared with simple p-cycles. In this paper, we first point out some unique features of non-simple p-cycles and p-trails which are not fully explored in previous studies. This motivates us to formulate a new suite of ILPs (Integer Linear Programs) for optimal design of non-simple p-cycles and p-trails, based on which the achievable capacity gain over simple p-cycles can be investigated. Different from all the previous studies, the proposed ILPs are free of candidate cycle/trail enumeration, and can truly achieve an optimal design of non-simple p-cycles and p-trails. Our numerical results show that the capacity gain can be significant in some small-size networks with lightly-loaded traffic, but is generally trivial as the network size and the traffic load increase.