David W. Griffith

Modeling Smart Grid Applications with Co-Simulation

Our analysis of a complex Smart Grid control scheme uses simulation to model both the communication network and the power system. The control scheme uses a wireless communication network to activate distributed storage units in a segment of the electrical grid to compensate for temporary loss of power from a solar photovoltaic (PV) array. Our analytical model of the communication network provides a means to examine the effect of communication failures as a function of the radio frequency (RF) transmission power level. We use these results in an open source event-driven simulator to determine the impact on the electrical power system.

A New Call Admission Control Scheme for Heterogeneous Wireless Networks

Call Admission Control (CAC) between heterogeneous networks, such as an integrated 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) network and a Wireless Local Area Network (WLAN), plays an important role to utilize the system resources in a more efficient way. In this paper, we propose that the preference to the WLAN is determined based on the traffic load in the WLAN and the location of the cellular users. Our analysis relies on a previous study that divides the 3G cellular coverage area into zones based on the amount of resources that are required to support a connection to a mobile user. Using this model, we derive new call blocking and handoff failure probabilities as well as new call and handoff attempt failure probabilities. Through simulations, we investigate proper preference settings by changing the WLAN load in a 3 ring-based sector with a WLAN hotspot.

A Methodology to Evaluate Wireless Technologies for the Smart Grid

This paper presents a methodology for assessing the suitability of various wireless technologies for meeting the communication requirements of Smart Grid applications. It describes an approach for translating application requirements to link traffic characteristics, determining the transmission range or coverage area of a wireless technology, and modeling the link layer to obtain performance measures such as message reliability, delay, and throughput. To illustrate the use of this approach, we analyze the performance of three representative application use cases over an IEEE 802.11 link.

A probabilistic call admission control algorithm for WLAN in heterogeneous wireless environment

In an integrated WLAN and cellular network, if all mobile users whose connections originate in the cellular network migrate to the WLAN whenever they enter the double coverage area, the WLAN will be severely congested and its users will suffer from performance degradation. Therefore, we propose a Call Admission Control (CAC) algorithm that allows the WLAN to limit downward Vertical Handovers (VHOs) from the cellular network to reduce unnecessary VHO processing. Numerical and simulation results demonstrate that our CAC scheme reduces the unnecessary VHO processing while keeping the DVHO blocking rate within acceptable limits and maintaining reasonable throughput in the WLAN.

An integrated detection system against false data injection attacks in the Smart Grid

The Smart Grid is a new type of power grid that will use advanced communication network technologies to support more efficient energy transmission and distribution. The grid infrastructure was designed for reliability; but security, especially against cyber threats, is also a critical need. In particular, an adversary can inject false data to disrupt system operation. In this paper, we develop a false data detection system that integrates two techniques that are tailored to the different attack types that we consider. We adopt anomaly-based detection to detect strong attacks that feature the injection of large amounts of spurious measurement data in a very short time. We integrate the anomaly detection mechanism with a watermarking-based detection scheme that prevents more stealthy attacks that involve subtle manipulation of the measurement data. We conduct a theoretical analysis to derive the closed-form formulae for the performance metrics that allow us to investigate the effectiveness of our proposed detection techniques. Our experimental data show that our integrated detection system can accurately detect both strong and stealthy attacks. Copyright

Performance Metrics for IEEE 802.21 Media Independent Handover (MIH) Signaling

The IEEE 802.21 Media Independent Handover (MIH) working group is developing a set of mechanisms to facilitate migration of mobile users between access networks that use different link-layer technologies. Among these are mobility managers that create and process signaling messages to facilitate handovers. The MIH signaling architecture being developed in the Internet Engineering Task Force (IETF) allows any transport layer protocol to carry MIH messages. The IETF has considered using the unreliable but lightweight transport available with the User Datagram Protocol (UDP) as well as the reliable stream-oriented transport with congestion control offered by the Transmission Control Protocol (TCP). In this paper we develop mathematical models that result in expressions for the characteristic function of the time required to complete exchanges of an arbitrary number of MIH signaling messages between a mobile node (MN) and a remote mobility manager (MM). Our models also provide expressions for the average amount of overhead associated with MIH message exchanges due to retransmissions either by the MIH signaling entities or by the transport-layer protocol. In addition, we provide simulation results that confirm the results from the mathematical model and illustrate the effect of varying transport parameters such as the TCP maximum retransmission timeout.

Toward Integrating Distributed Energy Resources and Storage Devices in Smart Grid

The smart grid, as one of typical applications supported by Internet of Things, denoted as a re-engineering and a modernization of the traditional power grid, aims to provide reliable, secure, and efficient energy transmission and distribution to consumers. How to effectively integrate distributed (renewable) energy resources and storage devices to satisfy the energy service requirements of users, while minimizing the power generation and transmission cost, remains a highly pressing challenge in the smart grid. To address this challenge and assess the effectiveness of integrating distributed energy resources and storage devices, in this paper, we develop a theoretical framework to model and analyze three types of power grid systems: 1) the power grid with only bulk energy generators; 2) the power grid with distributed energy resources; and 3) the power grid with both distributed energy resources and storage devices. Based on the metrics of the power cumulative cost and the service reliability to users, we formally model and analyze the impact of integrating distributed energy resources and storage devices in the power grid. We also use the concept of network calculus, which has been traditionally used for carrying out traffic engineering in computer networks, to derive the bounds of both power supply and user demand to achieve a high service reliability to users. Through an extensive performance evaluation, our evaluation results show that integrating distributed energy resources conjointly with energy storage devices can reduce generation costs, smooth the curve of bulk power generation over time, reduce bulk power generation and power distribution losses, and provide a sustainable service reliability to users in the power grid.

Static vs. dynamic regenerator assignment in optical switches: models and cost trade-offs

Agile all optical switches (OXC) currently use an architecture in which regenerators and transceivers have preassigned fixed directionality. However, technology is evolving to enable new OXC architectures in which the directionality of regenerators and transceivers can be dynamically assigned on demand. In this paper, we quantify the performance and cost benefits of regenerators and transceivers with dynamically assignable directionality. We show that fewer regenerators and transceivers need to be used with the new architecture because of sharing of resources across all directionality combinations. This translates to significant cost savings for the new architecture, especially as the traffic load in the network increases.

A novel ring-based performance analysis for call admission control in wireless networks

In Orthogonal Frequency Division Multiplex (OFDM) wireless networks such as 3GPP LTE and IEEE 802.16 WiMAX, the scheduler should allocate more resources to users with lower channel quality, such as users near the edge of the Base Station (BS) coverage area who are attempting handovers. In conventional queue-based models, this feature has not been considered in Call Admission Control (CAC) so far. In this letter, we propose a new ring-based model of the BS coverage area to allow a more detailed and accurate analysis. We determine mobility-related parameters such as call dropping probability due to mobility, and validate our results using simulations.

Dynamic Deflection Routing with Virtual Wavelength Assignment in Optical Burst-Switched Networks

In optical burst-switched networks, one of the most significant issues is contention resolution. There have been several deflection routing techniques as contention resolution. While contention is resolved by traditional deflection routing, it cannot guarantee that the control packet will reserve all the wavelengths successfully to the destination on the alternate path, especially when traffic load in a network is high. Therefore, in this paper, we propose a Deflection Routing with Virtual Wavelength Assignment (DR-VWA) algorithm in order to provide a higher resource guarantee for loss-sensitive traffic bursts. The proposed DR-VWA scheme (1) dynamically decides the alternate path with the least traffic load and (2) allows high-priority bursts in terms of loss to be assigned available wavelengths over the path virtually. The proposed scheme is evaluated through simulation, and it is shown that significant improvement with regard to burst loss and wavelength conversion cost can be achieved.