Atef Abdrabou

Probabilistic Delay Control and Road Side Unit Placement for Vehicular Ad Hoc Networks with Disrupted Connectivity

This paper studies the multihop packet delivery delay in a low density vehicular ad hoc network (VANET). We address a disrupted vehicle-to-infrastructure communication scenario, where an end-to-end path is unlikely to exist between a vehicle and the nearest road side unit (RSU). We present an analytical framework, which takes into account the randomness of vehicle data traffic and the statistical variation of the disrupted communication channel. Our framework employs the effective bandwidth theory and its dual, the effective capacity concept, in order to obtain the maximum distance between RSUs that stochastically limits the worst case packet delivery delay to a certain bound (i.e., allows only an arbitrarily small fraction of the packets received by the farthest vehicle from the RSU to exceed a required delay bound). Our study also investigates the effect of the vehicle density, transmission range, and speed difference between vehicles on the end-to-end packet delivery delay. Extensive simulation results validate our analytical framework.

Decentralized Economic Dispatch in Microgrids via Heterogeneous Wireless Networks

As essential building blocks of the future smart grid, microgrids can efficiently integrate various types of distributed generation (DG) units to supply the electric loads at the minimum cost based on the economic dispatch. In this paper, we introduce a decentralized economic dispatch approach such that the optimal decision on power generation is made by each DG unit locally without a central controller. The prerequisite power generation and load information for decision making is discovered by each DG unit via a multiagent coordination with guaranteed convergence. To avoid a slow convergence speed which potentially increases the generation cost because of the time-varying nature of DG output, we present a heterogeneous wireless network architecture for microgrids. Low-cost short-range wireless communication devices are used to establish an ad hoc network as a basic information exchange infrastructure, while auxiliary dual-mode devices with cellular communication capabilities are optionally activated to improve the convergence speed. Two multiagent coordination schemes are proposed for the single-stage and hierarchical operation modes, respectively. The optimal number of activated cellular communication devices is obtained based on the tradeoff between communication and generation costs. The performance of the proposed schemes is analyzed and evaluated based on real power generation and load data collected from the Waterloo Region in Canada. Numerical results indicate that our proposed schemes can better utilize the cellular communication links and achieve a desired tradeoff between the communication and generation costs as compared with the existing schemes.

A position-based QoS routing scheme for UWB mobile ad hoc networks

Ultra-wideband (UWB) wireless communication is a promising spread-spectrum technology that supports very high data rates and provides precise position information of mobile users. In this paper, we present a position-based quality-of-service (QoS) routing scheme for UWB mobile ad hoc networks. The scheme applies call admission control and temporary bandwidth reservation for discovered routes, taking into consideration the medium access control interactions. Via cross-layer design, it exploits UWB advantages at the network layer by using the position information in routing and bandwidth reservation and by supporting the multirate capability. Simulation results demonstrate that the proposed routing scheme is effective in end-to-end QoS support.

Statistical QoS routing for IEEE 802.11 multihop ad hoc networks

In this paper, we propose a model-based quality-of-service (QoS) routing scheme for IEEE 802.11 ad hoc networks. Unlike most of QoS routing schemes in the literature, the proposed scheme provides stochastic end-to-end delay guarantees, instead of average delay guarantees, to delay-sensitive bursty traffic sources. Via a cross-layer design approach, the scheme selects the routes based on a geographical on-demand ad hoc routing protocol and checks the availability of network resources by using traffic source and link-layer channel modeling, taking into consideration the IEEE 802.11 characteristics and node interactions. Our scheme extends the well developed effective bandwidth theory and its dual effective capacity concept to multihop IEEE 802.11 ad hoc networks. Extensive computer simulations demonstrate that the proposed scheme is effective in satisfying the end-to-end delay bound to a probabilistic limit.

Differentiated services for wireless mesh backbone

This article addresses the quality of service provisioning issues in the wireless mesh backbone for broadband wireless access. Differentiated services over the wireless mesh backbone is investigated in the avenues of QoS routing and MAC mechanisms. Challenges and open issues are identified, along with potential solutions and possible research directions.

Stochastic delay guarantees and statistical call admission control for IEEE 802.11 single-hop ad hoc networks

This paper presents a new approach to provide stochastic delay guarantees via fully distributed model-based call admission control for IEEE 802.11 single-hop ad hoc networks. We propose a novel stochastic link-layer channel model to characterize the variations of the channel service process in a non-saturated case using a Markov-modulated Poisson process (MMPP) model. We use the model to calculate the effective capacity of the IEEE 802.11 channel. The channel effective capacity concept is the dual of the effective bandwidth theory. Our approach offers a tool for distributed statistical resource allocation in ad hoc networks, which combines both efficient resource utilization and quality-of-service (QoS) provisioning to a certain probabilistic limit. Simulation results demonstrate that the MMPP link-layer model and the calculated effective capacity can be used effectively in allocating resources with stochastic delay guarantees.

Performance Evaluation of VeMAC Supporting Safety Applications in Vehicular Networks

Vehicular ad hoc networking (VANET) is an emerging paradigm that is expected to increase the public safety standards and enhance the safety level of drivers/passengers and pedestrians on roads through a variety of applications. We have recently proposed VeMAC, a medium access control protocol that supports a reliable one-hop broadcast service necessary for high priority safety applications in VANETs. This paper explains how the VeMAC protocol can deliver both periodic and event-driven safety messages in vehicular networks and presents a detailed delivery delay analysis, including queueing and service delays, for both types of safety messages. The probability mass function of the service delay is first derived; then, the D/G/1 and M/G/1 queueing systems are used to calculate the average queueing delay of the periodic and event-driven safety messages, respectively. In addition, a comparison between the VeMAC protocol and IEEE 802.11p standard is presented via extensive simulations using the network simulator ns-2 and the microscopic vehicle traffic simulator VISSIM. A real city scenario is considered and different performance metrics are evaluated, including the network goodput, protocol overhead, channel utilization, protocol fairness, probability of a transmission collision, and message delivery delay.

Cooperative Decentralized Resource Allocation in Heterogeneous Wireless Access Medium

In this paper, radio resource allocation in a heterogeneous wireless access medium is investigated. Mobile terminals (MTs) are equipped with multiple radio interfaces and are assumed to have multi-homing capabilities. A novel algorithm, namely prediction based resource allocation algorithm, is proposed for the resource allocation. Unlike the existing solutions in literature, the proposed algorithm does not require a central resource manager to perform the radio resource allocation. The MT plays an active role in the resource allocation operation by requesting a bandwidth share from each available network based on the available resources at the network, such that the total allocated bandwidth from different networks satisfies the MT service requirement. The proposed algorithm is suitable for implementation in a dynamic environment with call arrivals and departures, and relies on network cooperation to perform the decentralized radio resource allocation in an efficient manner. Simulation results are presented to investigate the performance tradeoffs of the proposed algorithm.

Energy Cost Models of Smartphones for Task Offloading to the Cloud

Task offloading from smartphones to the cloud is a promising strategy to enhance the computing capability of smartphones and prolong their battery life. However, task offloading introduces a communication cost for those devices. Therefore, the consideration of the communication cost is crucial for the effectiveness of task offloading. To make task offloading beneficial, one of the challenges is to estimate the energy consumed in communication activities of task offloading. Accurate energy estimation models will enable these devices to make the right decisions as to whether or not to perform task offloading, based on the energy cost of the communication activities. Simply put, if the offloading process consumes less energy than processing the task on the device itself, then the task is offloaded to the cloud. To design an energy-aware offloading strategy, we develop energy models of the WLAN, third-generation, and fourth-generation interfaces of smartphones. These models make smartphones capable of accurately estimating the energy cost of task offloading. We validate the models by conducting an extensive set of experiments on five smartphones from different vendors. The experimental results show that our estimation models accurately estimate the energy required to offload tasks.

A Wireless Communication Architecture for Smart Grid Distribution Networks

Electric power distribution networks in smart grids are envisaged to observe substantial modifications in order to suit the nature of nonradial power flow due to the wide spread of renewable energy resources (RERs) across the power grid. Most of the current supervisory control and data acquisition (SCADA) systems for power grids do not provide any monitoring to the low-voltage distribution networks where RERs (e.g., photovoltaic cells) may be connected. This paper proposes a multihop wireless network with a cellular frequency-reuse structure that can provide the communication infrastructure to the dense low-voltage distribution networks for active monitoring and control purposes. Moreover, this paper proposes an effective way of data dissemination across the introduced network architecture with prioritized data transfer using a position-based quality-of-service (QoS)-aware routing protocol. Furthermore, a load-balancing mechanism is proposed to account for data network overloading during the occurrence of abnormal events in the distribution network. In addition, this paper provides an analytical framework that can be used as a tool to estimate the capacity and coverage area of the proposed architecture mathematically. The analytical framework is validated by extensive computer simulations.