Dynamic Traffic Load Research Articles

Adaptive congestion control for DSRC vehicle networks

Dedicated short range communications (DSRC) was proposed for collaborative safety applications (CSA) in vehicle communications. In this article we propose two adaptive congestion control schemes for DSRC-based CSA. A cross-layer design approach is used with congestion detection at the MAC layer and traffic rate control at the application layer. Simulation results show the effectiveness of the proposed rate control scheme for adapting to dynamic traffic loads.

Characteristic dynamic traffic load effects in bridges

When formulating an approach to assess bridge traffic loading with allowance for Vehicle-Bridge Interaction (VBI), a trade-off is necessary between the limited accuracy and computational demands of numerical models and the limited time periods for which experimental data is available. Numerical modelling can simulate sufficient numbers of loading scenarios to determine characteristic total load effects, including an allowance for VBI. However, simulating VBI for years of traffic is computationally expensive, often excessively so. Furthermore, there are a great many uncertainties associated with numerical models such as the road surface profile and the model parameter values (e.g., spring stiffnesses) for the heavy vehicle fleet. On site measurement of total load effect, including the influence of VBI, overcomes many of these uncertainties as measurements are the result of actual loading scenarios as they occur on the bridge. However, it is often impractical to monitor bridges for extended periods of time which raises questions about the accuracy of calculated characteristic load effects. Soft Load Testing, as opposed to Proof Load or Diagnostic Load Testing, is the direct measurement of load effects on bridges subject to random traffic. This paper considers the influence of measurement periods on the accuracy of soft load testing predictions of characteristic load effects, including VBI, for bridges with two lanes of opposing traffic. It concludes that, even for relatively short time periods, the estimates are reasonably accurate and tend to be conservative. Provided the data is representative, Soft Load Testing is shown to be a useful tool for calculating characteristic total load effect.

Cognitive networking of large scale wireless systems

We propose the concept of cognitive networking for large-scale wireless systems, which opportunistically utilises network resources including both spectrum bandwidth and radio availability. Both types of resources cannot be predetermined in large-scale wireless systems, due to various reasons such as interferences and dynamic traffic load. The proposed technology not only establishes dynamic wireless networks, but also provides for reliable network quality of services (QoS). The supporting network architecture, embedded wireless interconnect (EWI), is proposed to implement the cognitive networking concept and supply an effective application-programming interface for large-scale data management systems. Two example applications are presented, including wireless mesh networks for broadband wireless internet access and wireless sensor networks for target tracking. Major advantages of the technology are further discussed. We suggest that the performance of the proposed system would improve with larger network scale and the implementation complexity could be independent of the network scale.

Model for Integrating Home–Work Tour Scheduling with Time-Varying Network Congestion and Marginal Utility Profiles for Home and Work Activities

The existing literature on activity-based modeling emphasizes that individuals schedule their activities by keeping the whole-day activity pattern in mind. Several attempts have been made to integrate this with network congestion; however, for explicit explanation of travel behavior of individuals, further improvements are required. The proposed model is a combined model that addresses the scheduling of the home–work tour with time-varied network congestion in a fixed-point problem framework. Marginal utility profiles that represent individual time-of-day preferences and satiation effect of the activities are incorporated for the measurement of the utility of activity engagement along with the disutility of travel. Consideration of only time-of-day dependent marginal utility profiles of activities in the utility function does not appropriately integrate activities and travel within the tour. The proof is shown analytically and numerically. This finding contradicts earlier research into integration of morning and evening commutes with network congestion. Additionally, the results of two numerical experiments are presented. In the first experiment, an arbitrary dynamic tolling strategy is assumed, and then a detailed analysis is performed to show variation in the balance of trade-offs involved in the process. The second experiment assesses the sensitivity of the combined model through incorporation of different dynamic traffic loading models. Some meaningful observations are drawn from these experiments and are discussed with the identification of avenues for future research.

Bandwidth Reallocation for Bandwidth Asymmetry Wireless Networks Based on Distributed Multiservice Admission Control

This paper addresses when and how to adjust bandwidth allocation on uplink and downlink in a multi-service mobile wireless network under dynamic traffic load conditions. Our design objective is to improve system bandwidth utilization while satisfying call level QoS requirements of various call classes. We first develop a new threshold-based multi-service admission control scheme (DMS-AC) as the study base for bandwidth re-allocation. When the traffic load brought by some specific classes under dynamic traffic conditions in a system exceeds the control range of DMS-AC, the QoS of some call classes may not be guaranteed. In such a situation, bandwidth re-allocation process is activated and the admission control scheme will try to meet the QoS requirements under the adjusted bandwidth allocation. We explore the relationship between admission thresholds and bandwidth allocation by identifying certain constraints for verifying the feasibility of the adjusted bandwidth allocation. We conduct extensive simulation experiments to validate the effectiveness of the proposed bandwidth re-allocation scheme. Numerical results show that when traffic pattern with certain bandwidth asymmetry between uplink and downlink changes, the system can re-allocate the bandwidth on uplink and downlink adaptively and at the same time improve the system performance significantly.

Use of Slab Curvature and ProVAL to Identify the Cause of Premature Distresses

It has been argued that dynamic traffic loading due to the presence of a nonflat pavement shape may result in accelerated deterioration of the pavement because of higher stresses in the slab from restrained curling–warping movement. Slab curvature, though imperceptible to the naked eye, usually develops on the riding surfaces of the individual slab segments after construction. Select case studies on high- and low-altitude Bolivian concrete highways illustrate the magnitude of curvatures that are generated. The Butterworth high-pass and spectral density analysis tools in the ProVAL software are used to identify the pavement slab curvature in these projects. A mechanistic analysis is used to ascertain the causes of the observed longitudinal cracking. By resorting to a newly developed curvature index, the second-generation curvature index, the equivalent temperature gradient that corresponds to the fitted curvature was included in a finite element method analysis to determine stresses in the slabs. It is concluded that the curved shape of the slabs resulting from permanent curling–warping coupled with traffic loading is inducing excessive stresses and causing the observed cracking distress in one of the evaluated highways.

The dynamic response of the Berwick-upon-Tweed bypass bridge

The Al trunk road bridge over the River Tweed upstream from Berwick-upon-Tweed was monitored as part of the routine condition monitoring strategy. This paper presents details of the principal inspection report, traffic count, vehicle speed, and axle weight data derived from in situ induction loops and weigh-in-motion sensors, followed by data arising from the non-destructive testing of the bridge. The NDT used the random dynamic traffic loading to excite the bridge's natural frequency response, which was detected by accelerometers mounted under the deck. Modal analysis was then used to draw conclusions about the amplitudes, frequencies and modes of vibration of the bridge, especially with respect to the effect of the bearings and the expansion joints which were potentially problematic and as such, would be subject to rigorous inspection. Data presented here established a baseline case for future condition monitoring. The main theme of the research was to use modal analysis to determine the bridge's dynamic response.

A Fair Scheduling Algorithm for Multiple-Antenna Cellular Networks with Dynamic Traffic Load

Multiple-antenna wireless systems, also known as multiple-input multiple-output (MIMO) cellular networks, can improve the capacity and reliability of communications. To realize these advantages, a packet scheduler should effectively allocate radio resources to users in a fair way. The previously proposed MIMO schedulers have problems such as ignoring traffic arrival process or complexity. We propose a load adaptive multi-output fair queueing (LA-MO-FQ) scheduler, which is based on a fair queueing algorithm with mechanisms for rate selection, compensation of lagging users, and virtual time system. Since some of the scheduler's system parameters are sensitive to the traffic load, it dynamically adjusts them in a way with low complexity so the system performs better. Intensive simulation studies considering the mobility of users and the traffic arrival demonstrate the good performance of LA-MO-FQ. Furthermore, we also propose in this paper some formulae for the time and service fairness comparisons of MIMO schedulers and we use them for comparison with some famous existing schedulers.

Flexible Time-Triggered Sampling in Smart Sensor-Based Wireless Control Systems.

Wireless control systems (WCSs) often have to operate in dynamic environmentswhere the network traffic load may vary unpredictably over time. The sampling in sensors isconventionally time triggered with fixed periods. In this context, only worse-than-possiblequality of control (QoC) can be achieved when the network is underloaded, whileoverloaded conditions may significantly degrade the QoC, even causing system instability.This is particularly true when the bandwidth of the wireless network is limited and sharedby multiple control loops. To address these problems, a flexible time-triggered samplingscheme is presented in this work. Smart sensors are used to facilitate dynamic adjustment ofsampling periods, which enhances the flexibility and resource efficiency of the system basedon time-triggered sampling. Feedback control technology is exploited for adapting samplingperiods in a periodic manner. The deadline miss ratio in each control loop is maintainedat/around a desired level, regardless of workload variations. Simulation results show that theproposed sampling scheme is able to deal with dynamic and unpredictable variations innetwork traffic load. Compared to conventional time-triggered sampling, it leads to muchbetter QoC in WCSs operating in dynamic environments.

Optimal Resource Allocation and Adaptive Call Admission Control for Voice/Data Integrated Cellular Networks

Resource allocation and call admission control (CAC) are key management functions in future cellular networks, in order to provide multimedia applications to mobiles users with quality of service (QoS) guarantees and efficient resource utilization. In this paper, we propose and analyze a priority based resource sharing scheme for voice/data integrated cellular networks. The unique features of the proposed scheme are that 1) the maximum resource utilization can be achieved, since all the leftover capacity after serving the high priority voice traffic can be utilized by the data traffic; 2) a Markovian model for the proposed scheme is established, which takes account of the complex interaction of voice and data traffic sharing the total resources; 3) optimal CAC parameters for both voice and data calls are determined, from the perspective of minimizing resource requirement and maximizing new call admission rate, respectively; 4) load adaption and bandwidth allocation adjustment policies are proposed for adaptive CAC to cope with traffic load variations in a wireless mobile environment. Numerical results demonstrate that the proposed CAC scheme is able to simultaneously provide satisfactory QoS to both voice and data users and maintain a relatively high resource utilization in a dynamic traffic load environment. The recent measurement-based modeling shows that the Internet data file size follows a lognormal distribution, instead of the exponential distribution used in our analysis. We use computer simulations to demonstrate that the impact of the lognormal distribution can be compensated for by conservatively applying the Markovian analysis results.

Markov-Based OVSF Code Assignment Scheme and Call Admission Control for Wideband-CDMA Communication Systems

For the reason of the orthogonal characteristic of the Orthogonal Variable Spreading Factor (OVSF) code tree in Wideband CDMA (WCDMA) systems, code blocking increases as traffic load (i.e. Erlang load) or the required rate increases. This causes inefficient utilization of channelization codes. Hence, how to efficiently manage the resource of channelization codes of the OVSF code tree in WCDMA systems is an important issue and has been studied extensively. There are two aspects to achieve efficiency including code assignment and code reassignment. In the aspect of code assignment, an efficient code assignment scheme reduces code blocking probability significantly. In the aspect of code reassignment, code reassignment results in several drawbacks, such as large overhead of computation, high complexity of codes moving, and long call setup time for a new request call, etc. Therefore, in this paper we focus on the first aspect of how to efficiently assign the channelization codes. Additionally, most researches did not consider the analysis of tree state with dynamic traffic load and their analysis lack of systematic call admission control (CAC) mechanism. Therefore, in this paper, we first propose the Markov decision process (MDP) based analysis to assign channelization codes efficiently. Next, we extend the MDP-based approach as the call admission control mechanism to maximize the system revenue while reducing blocking probability. Furthermore, a bit string masking algorithm is proposed to reduce the time complexity of tree managing and searching for available channelization codes. Numerical results indicate that the proposed MDP approach yields the best fractional reward loss, code blocking reward loss, and code blocking ratio as compared to that of other schemes, including the random, left most, and crowded first schemes.

Downlink and uplink resource allocation in IEEE 802.11 wireless LANs

Wireless local area networks (WLANs) based on the IEEE 802.11 standard are becoming increasingly popular and widely deployed. It is likely that WLAN will become an important complementary technology for future cellular systems and will typically be used to provide hotspot coverage. In this paper, the complementary use of WLANs in conjunction with mobile cellular networks is studied. We identify the fairness problem between uplink and downlink traffic flows in the IEEE 802.11 distributed coordination function and then propose an easy solution that can be implemented at the access point (AP) in the MAC layer without modification of the standard for stations (STAs). This solution aims at providing a controllable resource-allocation method between uplink and downlink traffic flows and adapting the parameters according to the dynamic traffic load changes. The proposed solution also enhances the system utilization by reducing the probability of frame collision.

Randomized dynamic route maintenance for adaptive routing in multihop mobile ad hoc networks

Several approaches have been proposed for designing multihop routing protocols in mobile ad hoc networks (MANET). Many of them adopt a method, called flooding, to discover a routing path. Due to the time-varying nature of the route in MANET, the discovered route needs to be dynamically maintained for optimality in terms of traffic load, hop-distance, and resource usage. It is easy to see that flooding incurs significant overhead and hence is inappropriate for the dynamic route maintenance. In this paper we propose a randomized, dynamic route maintenance scheme for adaptive routing in MANET. The scheme makes use of a nomadic control packet (NCP) which travels through the network based on a random walk, and collects its stopovers as a traversal record. The NCP uses the traversal record to probabilistically provide the nodes with clue for routing path updates. From the clue, the nodes can find the routing path update information that is up-to-date and optimal (less-loaded and shorter), thereby adapting to the dynamic network topology and traffic load conditions. We present an analytical model for measuring the effectiveness of NCP in terms of its frequency of visits and probability of finding the clue from the NCP traversal record. The proposed randomized scheme serves as a routing protocol supporting layer and can be easily applied with minimum modifications to the existing on-demand routing protocols such as AODV and DSR. In our experimental study, we modified the AODV protocol to maintain routing paths using NCPs’ traversal record. Simulation results show that NCPs help the routing protocol to notably reduce average end-to-end packet delay with increased route optimality and better control on traffic congestion.

MAC protocol for resource allocation in hotspot microcell

An easy solution is proposed that can be implemented at the access point in the MAC layer without modification of the standard for stations. The solution aims at providing a controllable resource allocation method between uplink and downlink traffic flows and adapting the parameters according to the dynamic traffic load changes.

Intermediate-node initiated reservation (iir): a new signaling scheme for wavelength-routed networks

A problem of many distributed lightpath provisioning schemes is wavelength contention, which occurs when a connection request attempts to reserve a wavelength channel that is no longer available. This situation results from the lack of updated global link-state information at every node. In networks with highly dynamic traffic loads, wavelength contention may seriously degrade the network performance. To overcome this problem, we propose a new framework for distributed signaling and introduce a class of schemes referred to as intermediate-node initiated reservation. In the new scheme, reservations may be initiated at any set of nodes along the route; in contrast, reservations can only be initiated by the destination node in the classic destination initiated reservation (DIR) scheme. As a result, the possibility of having outdated information due to propagation delay is significantly lowered. Specifically, we consider two schemes within this framework, for networks with no wavelength conversion and for networks with sparse wavelength conversion, respectively. Theoretical and simulation results show that, compared with the classic DIR scheme, the new schemes can significantly improve the network blocking performance. The accuracy of the analytical models is also confirmed by extensive numerical simulations.

Design and implementation of wavelength-flexible network nodes

This paper analytically and experimentally examines node architectures for wavelength-routing networks, with emphasis on the degree of wavelength conversion provided. Wavelength flexibility simplifies network management and increases network capacity but requires large cross-connects and deployment of wavelength converters (WCs). A simple probabilistic model is used to upper-bound the number of WCs required at a network node, under dynamic traffic load. When provisioned in a shareable pool, with a fixed number of wavelength channels per fiber, the number of WCs required remains low as overall network capacity is scaled up. Motivated by this analysis, experiments demonstrate the feasibility of implementing wavelength-flexible network nodes using large microelectromechanical (MEMS)-based cross-connects and all-optical WCs. In one design, WCs were attached directly to cross-connect output ports, and in another, they were attached in a loop-back fashion to allow sharing. Error-free transmission at 10 Gb/s was demonstrated in both cases.

Analysis of a dynamically wavelength-routed optical burst switched network architecture

The concept of optical burst switching (OBS) aims to allow access to optical bandwidth in dense wavelength division multiplexed (DWDM) networks at fractions of the optical line rate to improve bandwidth utilization efficiency. This paper studies an alternative network architecture combining OBS with dynamic wavelength allocation under fast circuit switching to provide a scalable optical architecture with a guaranteed QoS in the presence of dynamic and bursty traffic loads. In the proposed architecture, all processing and buffering are concentrated at the network edge and bursts are routed over an optical transport core using dynamic wavelength assignment. It is assumed that there are no buffers or wavelength conversion in core nodes and that fast tuneable laser sources are used in the edge routers. This eliminates the forwarding bottleneck of electronic routers in DWDM networks for terabit-per-second throughput and guarantees forwarding with predefined delay at the edge and latency due only to propagation time in the core. The edge burst aggregation mechanisms are evaluated for a range of traffic statistics to identify their impact on the allowable burst lengths, required buffer size and achievable edge delays. Bandwidth utilization and wavelength reuse are introduced as new parameters characterizing the network performance in the case of dynamic wavelength allocation. Based on an analytical model, upper bounds for these parameters are derived to quantify the advantages of wavelength channel reuse, including the influence of the signaling round-trip time required for lightpath reservation. The results allow to quantify the operational gain achievable with fast wavelength switching compared to quasistatic wavelength-routed optical networks and can be applied to the design of future optical network architectures.

Performance analysis under dynamic loading of wavelength continuous and non‐continuous WDM networks with shortest‐path routing

AbstractThe performance of WDM networks using shortest path routing is studied under wavelength continuous (WC) and non‐continuous (NWC) constraints and dynamic traffic loading. Approximate analytical models are presented for the performance studies of such systems. Results of numerical calculations based on these models and simulations are given for different network topologies for the purposes of comparison. These analytical and simulation results are used to study the performance of these WDM networks under dynamic traffic loading. Copyright © 2001 John Wiley & Sons, Ltd.

Enhanced reserved polling multiaccess technique for multimedia personal communication systems

This article describes a multiaccess technique which allows the transport of multimedia information across global personal communication systems (PCS). Impressive growth in the application of wireless technologies to telecommunications has sparked active research on a new generation of mobile radio networks projected to handle heterogeneous traffic types. One of the key requirements of these advanced systems is the multiaccess protocol which must guarantee quality of service and provide efficient access to multirate broadband applications that combine voice, video and data communications. In addition, the protocol is required to operate with the demanding constraints imposed by moving users, dynamic traffic load variations and highly sensitive wireless links. To this end, a multiaccess scheme called “enhanced reserved polling” is proposed. The scheme is designed to execute many PCS-related functions including radio resource assignment, connection control and mobility management. It accommodates a diverse mixture of delay classes/message priorities and can also enhance the bandwidth sharing among different cells in the network.

Flexible transmission bandwidth management with effective channel reservation techniques for NGSO MSS networks

This paper describes efficient transmission bandwidth management based on flexible channel assignment and effective grade of service (GOS) control methods for nongeostationary orbit mobile satellite service (NGSO MSS) networks. Our basic approach for the flexible channel assignment is to use linear programming (FLEXCA-LP), and to apply the column generation technique for further reduction of the total bandwidth requirement. These methods efficiently assign channels, taking account of moving spot beam coverage and dynamic traffic load variation for large-scale networks. The GOS is investigated for the channel assignment by FLEXCA-LP to make the GOS of ongoing calls better than that of fresh calls as stipulated in ITU-T Recommendations. We propose a few effective means to improve the results of FLEXCA-LP by reducing the disruption possibility of ongoing calls. One is to add channels utilizing a hysteresis concept. The others are effective use of GOS control techniques for NGSO MSS networks. These techniques are evaluated by a simulation study to identify promising techniques. Under time-variant conditions, we show that a reliable channel assignment plan is generated first by FLEXCA-LP considering the traffic load of fresh calls only and then by GOS control techniques to improve handover failure and call disruption rates.