Link Duration Research Articles

Network awareness and dynamic routing: The ad hoc network case

For extremely dynamic networks, such as ad-hoc, the topology change awareness has a crucial impact on the routing performance and consequently many routing protocols adapt their processes to the state of the network, from some network awareness. While several works have already been done on routing adaptations, this paper is more focused on the network awareness topic and the choice of the best metrics for a given adaptation. More precisely, the paper considers the way to represent by means of metrics the node mobility, the link degradation or the graph topology. The notion of metrics is illustrated through two adaptations of two well known ad hoc routing protocols (DSR, OLSR). We evaluate the effect of different metric choices by considering several adaptation strategies to the topology change which are based on the awareness of both the node movement and the number of nodes. We analyze the adaptation strategies and evaluate the performance of the adaptation depending on the chosen metrics. It is shown that the performance of adaptation is strongly correlated to the metrics that are themselves correlated to the network size. A metric combination based on link duration and number of nodes is found to be a good way to represent the topology change.

Dynamics of Network Connectivity in Urban Vehicular Networks

Vehicular ad hoc networks (VANETs) have emerged as a serious and promising candidate for providing ubiquitous communications both in urban and highway scenarios. Consequently, nowadays it is widely believed that VANETs will be able to support both safety and non-safety applications. For both classes of applications, since a zero-infrastructure is the typical premise assumed, it is crucial to understand the dynamics of network connectivity when one operates without relying on any telecommunications infrastructure. Using the key metrics of interest (such as link duration, connection duration, and re-healing time) we provide a comprehensive framework for network connectivity of urban VANETs. Our study, in addition to extensive simulations based on a new Cellular Automata Model for mobility, also provides a comprehensive analytical framework. This analytical framework leads to closed form results which facilitate physical insight into the impact of key system parameters on network connectivity. The predictions of our analytical framework also shed light on which type of safety and non-safety applications can be supported by urban VANETs.

A Discussion on Developing Multihop Routing Metrics Sensitive to Node Mobility

This paper is focused on a discussion of parameters and heuristics that are expected to assist multihop routing in becoming more sensitive to node mobility. We provide a discussion concerning existing and a few proposed parameters. Moreover, the work also discusses two new heuristics based on the notion of link duration. The heuristics are compared based on a meaningful set of scenarios that attain different mobility aspects.

Reader Coverage Analysis for Multi-Carrier Passive UHF RFID Systems

Applications of passive radio frequency identification (RFID) systems have gained considerable attentions in recent years. Because a passive tag must obtain its operating power from a continuous wave transmitted from a reader in a conventional RFID system, reader coverage is limited. Thus, expanding reader coverage is a current goal in RFID research. In this work, passive tags are provided with additional operating power via continuous waves in multiple frequency bands. In an interrogation region, continuous wave emitters, which provide additional operating power to passive tags, are deployed according to the base station configuration in a cellular phone system. Because transmission power of continuous wave emitters must consider the reader command demodulation constraint and minimum operating power required by a tag, transmission power of continuous wave emitters must be chosen carefully. A method for analyzing reader coverage in multi-carrier passive UHF RFID systems is derived in this work. Assuming all tags are uniformly distributed in an interrogation region, the optimal continuous wave emitter transmission power that achieves the largest reader coverage can be analytically determined. Simulation results verify that continuous wave emitters with suitable transmission power expand reader coverage in a multi-carrier passive UHF RFID system. Additionally, adjusting reader power in the forward (reader-to-tag) link duration can loosen the reader command demodulation constraint and thereby further expand reader coverage.

Prediction-Based Topology Control and Routing in Cognitive Radio Mobile Ad Hoc Networks

Recent research activities on cognitive radio (CR) have mainly focussed on opportunistic spectrum access and spectrum utilization. However, CR technology will have a significant impact on upper layer performance in wireless networks, particularly in mobile ad hoc networks (MANETs). In this paper, we study topology control and routing issues in CR-MANETs and propose a distributed prediction-based cognitive topology control (PCTC) scheme to provision cognition capability to routing in CR-MANETs. PCTC is a middleware-like cross-layer module residing between CR module and routing. It uses cognitive link availability prediction, which is aware of the interference to primary users and user mobility, to predict the available duration of links. Based on the link prediction, PCTC captures the dynamic changes of the topology and constructs an efficient and reliable topology, which is aimed at mitigating rerouting frequency and improving end-to-end network performance such as throughput and delay. Simulation results are presented to show the effectiveness of the proposed scheme.

A Probabilistic Routing Protocol in VANET

The key attribute that distinguishes Vehicular Ad hoc Networks (VANET) from Mobile Ad hoc Networks (MANET) is scale. While MANET networks involve up to one hundred nodes and are short lived, being deployed in support of special-purpose operations, VANET networks involve millions of vehicles on thousands of kilometers of highways and city streets. Being mission-driven, MANET mobility is inherently limited by the application at hand. In most MANET applications, mobility occurs at low speed. By contrast, VANET networks involve vehicles that move at high speed, often well beyond what is reasonable or legally stipulated. Given the scale of its mobility and number of actors involved, the topology of VANET is changing constantly and, as a result, both individual links and routing paths are inherently unstable. Motivated by this latter truism, the authors propose a probability model for link duration based on realistic vehicular dynamics and radio propagation assumptions. The paper illustrates how the proposed model can be incorporated in a routing protocol, which results in paths that are easier to construct and maintain. Extensive simulation results confirm that this probabilistic routing protocol results in more easily maintainable paths.

Evaluation and design of beaconing in mobile wireless networks

One of the intrinsic problems of mobility in wireless networks is the discovery of mobile nodes. A widely used solution for this problem is to use different variations of beacons, such as hello packets. Although a poorly designed beaconing scheme may lead to unnecessary energy usage or poor throughput, a systematic approach to analyze and select beaconing parameters is not provided in the literature. Here, we propose a model to study the beaconing efficiency using some measures such as the link lifetime, the probability of link establishment, and the delay to discover a new neighbor. The model is general and does not adhere to any particular mobility model; the only input from the mobility is the distribution of physical link durations, which not only abstracts away the mobility details but also all effects that contribute to the link stability such as non-perfectly omni-directional antennas and the path loss exponents. Among our results, we prove that the periodic beaconing (which is widely used owing to its simplicity) is the best in terms of beacon hits; we compare one-way and two-way beaconing schemes and study beaconing energy optimization. Finally, the model is applied to three cases of ad hoc, delay-tolerant, and sensor networks, and a simple rule of thumb is proposed to efficiently adjust the beacon interval.

Contact time in random walk and random waypoint: Dichotomy in tail distribution

Contact time (or link duration) is a fundamental factor that affects performance in Mobile Ad Hoc Networks. Previous research on theoretical analysis of contact time distribution for random walk models (RW) assume that the contact events can be modeled as either consecutive random walks or direct traversals, which are two extreme cases of random walk, thus with two different conclusions. In this paper we conduct a comprehensive research on this topic in the hope of bridging the gap between the two extremes. The conclusions from the two extreme cases will result in a power-law or exponential tail in the contact time distribution, respectively. However, we show that the actual distribution will vary between the two extremes: a power-law-sub-exponential dichotomy, whose transition point depends on the average flight duration. Through simulation results we show that such conclusion also applies to random waypoint.

A Novel Cluster based Routing Algorithm for Hybrid Mobility Model in VANET

This paper proposes a new approach for cluster based routing algorithm for hybrid mobility model to regulating the vehicular traffic. Our approach uses a new hybrid mobility model combining randomwaypoint and group mobility model using static and dynamic sources and a novel cluster based routing algorithm. To transmit the real time updated information and maintain long link duration to improve the data delivery ratio, we propose Location based Multipath Flooding (LMF) algorithm, which is suitable for vehicles with variable mobility. The scenario and the network are modeled and investigated through extensive simulations using Ns2 simulator to study the performance in terms of cluster construction.

MOTOROLA: MObility TOlerable ROute seLection Algorithm in wireless networks

In wireless networks, routing algorithms need to be tolerable to network dynamics. Existing route selection mechanisms suffer from a lack of considerations of stability and its induced routing overhead. Stabilities on route selection, traffic engineering and transmission schedule are fundamental issues in achieving a mobility-tolerable wireless network. In this study, the authors propose a mobility-tolerable paradigm (named ‘MOTOROLA’) in building a stable route level coordination algorithm for dynamic routing and scheduling. In MOTOROLA, mobility-awareness modules explore the mobility parameters and the link duration time, purely by adaptive beacon messages. Transitory links are mitigated based on threshold value of link duration. The route level resource allocation algorithm is also tolerable to network topology changes and the rescheduling costs are minimised in time scale. Analytical and simulation results show that because of mobility-awareness ability and route stability, MOTOROLA could improve network efficiency by transitory links' mitigation and coordinative route restoration.

Group force mobility model and its obstacle avoidance capability

Many mobility models attempt to provide realistic simulation to many real world scenarios. However, existing mobility models, such as RPGM [X. Hong, M. Gerla, G. Pei, C. Chiang, A group mobility model for ad hoc wireless networks, in: Proceedings of ACM/IEEE MSWiM’99, Seattle, WA, August 1999, pp. 53–60] and others, fail to address many aspects. These limitations range from mobile node (MN) collision avoidance, obstacle avoidance, and the interaction of MNs within a group. Our research, the group force mobility model (GFMM) [S.A. Williams, D. Huang, A group force mobility model, Appeared at 9th Communications and Networking Simulation Symposium, April 2006], proposes a novel idea which introduces the concept of attraction and repulsion forces to address many of these limitations. Williams and Huang [A group force mobility model, Appeared at 9th Communications and Networking Simulation Symposium, April 2006] described some of the limitations and drawbacks that many models neglect. This model effectively simulates the interaction of MNs within a group, the interaction of groups to one another, the coherency of a group, and the avoidance of collision with groups, nodes, and obstacles. This paper provides an overview of GFMM and particularly illustrates the GFMM's ability to avoid collision with obstacles, which is a vital property to posses in order to provide a realistic simulaition. We compare our model with the commonly used RPGM model and provide statistical assessments based on connectivity metrics such as link changed, link duration, and relative speed. All will be detailed and explained in this paper.

Impact of Node Mobility on Link Duration in Multihop Mobile Networks

In this paper, we study the impact of node mobility on link duration in multihop mobile networks. In multihop mobile networks, each node is free to move, and each link is established between two nodes. A link between two nodes is established when one node enters the transmission range of the other node, and the link is broken when either node leaves the transmission range of the other. The time interval during which the link remains active is referred to as the link duration. We develop an analytical model for link duration in multihop mobile networks. We find that the link duration for two nodes is determined by the relative speed between the two nodes and the distance during which the link is connected, which are, in turn, determined by the angles between the two nodes' velocities and the angle of one node incident to the other node's transmission range, respectively. The analytical result is then extended to model multipoint links, which appear in existing group mobility models. The accuracy of our framework is validated by simulations based on existing mobility models. The results show that our model can accurately describe the link-duration distribution for point-to-point and multi-point links in multihop mobile networks, particularly when the transmission range of each node is relatively smaller than the entire network coverage.

Simulation in Emergent Computational Systems.

Simulation in Emergent Computational Systems.

Application of path duration study in multihop ad hoc networks

Some ad hoc protocols allow the discovery and/or storage of multiple routes to the same destination node. The selection of the path to utilize is commonly based on the criterion of the minimum number of hops. However, other strategies could be more appropriate to improve the network performance. In this sense, this paper proposes the criterion based on the estimation of the Mean Residual Path Lifetime. In order to compute this metric, a formal description of link duration in mobile ad hoc networks is presented. The model has been verified by means of simulations enclosing different mobility and transmission conditions. From the link duration model, an analytical expression for path duration and mean residual lifetime is then derived. Finally, the authors show that selected ad hoc routing paths live longer when the proposed criterion is employed.

A Stable Routing Protocol to Support ITS Services in VANET Networks

There are numerous research challenges that need to be addressed until a wide deployment of vehicular ad hoc networks (VANETs) becomes possible. One of the critical issues consists of the design of scalable routing algorithms that are robust to frequent path disruptions caused by vehicles' mobility. This paper argues the use of information on vehicles' movement information (e.g., position, direction, speed, and digital mapping of roads) to predict a possible link-breakage event prior to its occurrence. Vehicles are grouped according to their velocity vectors. This kind of grouping ensures that vehicles, belonging to the same group, are more likely to establish stable single and multihop paths as they are moving together. Setting up routes that involve only vehicles from the same group guarantees a high level of stable communication in VANETs. The scheme presented in this paper also reduces the overall traffic in highly mobile VANET networks. The frequency of flood requests is reduced by elongating the link duration of the selected paths. To prevent broadcast storms that may be intrigued during path discovery operation, another scheme is also introduced. The basic concept behind the proposed scheme is to broadcast only specific and well-defined packets, referred to as ldquobest packetsrdquo in this paper. The performance of the scheme is evaluated through computer simulations. Simulation results indicate the benefits of the proposed routing strategy in terms of increasing link duration, reducing the number of link-breakage events and increasing the end-to-end throughput.

Distribution of Path Durations in Mobile Ad Hoc Networks and Path Selection

We investigate the issue of path selection in multihop wireless networks with the goal of identifying a scheme that can select a path with the largest expected duration. To this end, we first study the distribution of path duration. We show that, under a set of mild conditions, when the hop count along a path is large, the distribution of path duration can be well approximated by an exponential distribution even when the distributions of link durations are dependent and heterogeneous. Second, we investigate the statistical relation between a path duration and the durations of the links along the path. We prove that the parameter of the exponential distribution, which determines the expected duration of the path, is related to the link durations only through their means and is given by the sum of the inverses of the expected link durations. Based on our analytical results, we propose a scheme that can be implemented with existing routing protocols and select the paths with the largest expected durations. We evaluate the performance of the proposed scheme using ns-2 simulation.

Wireless Mobile Ad Hoc Networks

Wireless mobile ad hoc networks (MANETs), due to their dynamic nature and due to the unreliability of the wireless medium, pose unique challenges that are significantly more complex than those that arise in traditional wired or even cellular wireless networks. MANETs must self organize into a multihop peer-to-peer network without centralized control and without the help of base stations. Their topologies are unpredictable due to mobility and due to fading, shadowing, and other wireless channel impairments. The number and distribution of active nodes in the network are constantly changing, thereby creating additional variability in the network connectivity. Power and energy constraints, interference, and the shared nature of the wireless medium require adaptive relaying mechanisms and channel access. In such a harsh environment, robustness and quality of service (QoS) are essential. MANETs usually consist of a heterogeneous mixture of nodes with a variety of traffic types and different QoS requirements. Scaling laws for these networks are not fully understood. Diverse tradeoff studies related to capacity, delay, bandwidth, and energy consumption are currently under intense investigation. This special issue, which adds onemore collection of contributions to the vibrant field of ad hoc networking, includes 6 papers that address some of these issues. The first paper by S. Xu et al. investigates the reliability of communications paths in mobile ad hoc networks. They demonstrate an analysis framework for some mobility metrics such as link persistence, link duration, link availability, link residual time, and so forth. The second paper by D. Noh and H. Shin introduces an efficient way to handle service advertisement and discovery in MANETs so as to avoid redundant flooding and to lower overhead. The third paper by M. D. Colagrosso investigates the use of machine learning to facilitate adaptive intelligent broadcasting protocols in MANETs. The forth paper by C. Comaniciu and H. V. Poor introduces a cross-layer design that increases energy efficiency in MANETs through joint optimization of transmit power and routing selection. The fifth paper by L. Qian et al. develops a joint power control and routing algorithm for CDMA in wireless ad hoc networks. The sixth and last paper by E. Perevelov et al. studies scaling laws for ad hoc networks taking into account the overhead in route discovery algorithm.

Profile-driven energy reduction in network-on-chips

Reducing energy consumption of a Network-on-Chip (NoC) is a critical design goal, especially for power-constrained embedded systems.In response, prior research has proposed several circuit/architectural level mechanisms to reduce NoC power consumption. This paper considers the problem from a different perspective and demonstrates that compiler analysis can be very helpful for enhancing the effectiveness of a hardware-based link power management mechanism by increasing the duration of communication links' idle periods. The proposed profile-based approach achieves its goal by maximizing the communication link reuse through compiler-directed, static message re-routing. That is, it clusters the required data communications into a small set of communication links at any given time, which increases the idle periods for the remaining communication links in the network. This helps hardware shut down more communication links and their corresponding buffers to reduce leakage power. The current experimental evaluation, with twelve data-intensive embedded applications, shows that the proposed profile-driven compiler approach reduces leakage energy by more than 35% (on average) as compared to a pure hardware-based link power management scheme.

Random direction or random waypoint? A comparison of mobility models for urban environments

AbstractThe Random Direction (RD) and the Random Waypoint (RWP) mobility models have been discussed extensively in the literature. The focus of this discussion was the stationary distribution of users and speeds of users. In this paper, we extend the investigation to street‐based variants of the two mobility models. We compare statistical properties including user distribution, sojourn times in hotspots and link durations in ad hoc networks. In order to motivate the use of street‐based mobility models, we also perform a comparison with the basic models. Finally, we present our approach to achieve identical user distributions in both street‐based models and investigate the remaining differences, which prove to be negligible for wireless network simulations. Copyright © 2007 John Wiley & Sons, Ltd.

Integrated Routing and Scheduling of Hazmat Trucks with Stops En Route

We consider an integrated routing and scheduling problem in hazardous materials transportation where accident rates, population exposure, and link durations on the network vary with time of day. We minimize risk (accident probability multiplied by exposure) subject to a constraint on the total duration of the trip. We allow for stopping at the nodes of the network. We consider four versions of this problem with increasingly more realistic constraints on driving and waiting periods, and propose pseudopolynomial dynamic programming algorithms for each version. We use a realistic example network to experiment with our algorithms and provide examples of the solutions they generate. The computational effort required for the algorithms is reasonable, making them good candidates for implementation in a decision-support system. Many of the routes generated by our models do not exhibit the circuitous behavior common in risk-minimizing routes. The en route stops allow us to take full advantage of the time-varying nature of accident probabilities and exposure and result in the generation of routes that are associated with much lower levels of risk than those where no waiting is allowed.