Robert Murawski

Comprehensive Real-Time Simulation of the Smart Grid

This paper presents a real-time simulation platform for smart grid applications. The developed platform is capable of simulating complex smart grid models with large numbers of high-speed switching devices at real time. Furthermore, an integrated approach is adopted to combine real-time simulations of communication systems and electric power systems together, which provides an effective approach to examine communication and distributed control related issues in smart grids. With the flexibility in representing a wide range of communication network configurations, the developed platform can also be used to evaluate reconfiguration strategies of communication networks in smart grids. A case study is demonstrated based on this platform. Simulation results validate the capability of the platform and also show the importance of the proposed comprehensive approach for the study of smart grids.

SAMAC: A Cross-Layer Communication Protocol for Sensor Networks with Sectored Antennas

Wireless sensor networks have been used to gather data and information in many diverse application settings. The capacity of such networks remains a fundamental obstacle toward the adaptation of sensor network systems for advanced applications that require higher data rates and throughput. In this paper, we explore potential benefits of integrating directional antennas into wireless sensor networks. While the usage of directional antennas has been investigated in the past for ad hoc networks, their usage in sensor networks bring both opportunities as well as challenges. In this paper, Sectored-Antenna Medium Access Control (SAMAC), an integrated cross-layer protocol that provides the communication mechanisms for sensor network to fully utilize sectored antennas, is introduced. Simulation studies show that SAMAC delivers high energy efficiency and predictable delay performance with graceful degradation in performance with increased load.

SAND: Sectored-Antenna Neighbor Discovery Protocol for Wireless Networks

Directional antennas offer many potential advantages for wireless networks such as increased network capacity, extended transmission range and reduced energy consumption. Exploiting these advantages, however, requires new protocols and mechanisms at various communication layers to intelligently control the directional antenna system. With directional antennas, many trivial mechanisms, such as neighbor discovery, become more challenging since communicating parties must agree on where and when to point their directional beams to enable communication. In this paper, we propose a fully directional neighbor discovery protocol called Sectored-Antenna Neighbor Discovery (SAND) protocol. SAND is designed for sectored-antennas, a low-cost and simple realization of directional antennas, that utilize multiple limited beamwidth antennas. Unlike many proposed directional neighbor discovery protocols, SAND depends neither on omnidirectional antennas nor on time synchronization. In addition, SAND performs neighbor discovery in a serialized fashion allowing individual nodes to discover all potential neighbors within a predetermined time. Moreover, SAND guarantees the discovery of the best sector combination on both communication ends allowing more robust and higher reliability links. Finally, SAND gathers the neighborhood information in a centralized location, if needed, to be used by centralized networking protocols. The effectiveness of SAND has been assessed via simulation studies and real hardware implementation.

Neighbor discovery in wireless networks with sectored antennas

Abstract Directional antennas offer many potential advantages for wireless networks such as increased network capacity, extended transmission range and reduced energy consumption. Exploiting these advantages requires new protocols and mechanisms at various communication layers to intelligently control the directional antenna system. With directional antennas, many trivial mechanisms, such as neighbor discovery, become challenging since communicating parties must agree on where and when to point their directional beams to communicate. In this paper, we propose a fully directional neighbor discovery protocol called Sectored-Antenna Neighbor Discovery (SAND) protocol. SAND is designed for sectored-antennas, a low-cost and simple realization of directional antennas, that utilize multiple limited beamwidth antennas. Unlike many proposed directional neighbor discovery protocols, SAND depends neither on omnidirectional antennas nor on time synchronization. SAND performs neighbor discovery in a serialized fashion allowing individual nodes to discover all potential neighbors within a predetermined time. SAND guarantees the discovery of the best sector combination at both ends of a link, resulting in more robust and higher quality links between nodes. Finally, SAND reliably gathers the neighborhood information in a centralized location, if needed, to be used by centralized networking protocols. The effectiveness of SAND has been assessed via simulation studies and real hardware implementation.

Adaptive Channel Hopping for Interference Robust Wireless Sensor Networks

In this work, an Adaptive Channel Hopping (ACH) mechanism for sensor networks is proposed to avoid interference from other sources and narrow-band jamming. Under unfavorable channel conditions, ACH lets sensors switch to a new operating channel. ACH reduces the channel scanning and selection latency by ordering available channels using link quality indicator measurements and weights. The proposed ACH scheme is evaluated through simulations and a hardware implementation, which suggest low latency and high channel selection quality even in very adverse conditions.

PHEVs charging stations, communications, and control simulation in real time

This paper introduces a platform for real time simulation and its contribution towards smart grid related research, with focus on Plug-in Hybrid Electric Vehicles (PHEV) charging stations. The current system is able to simulate in real time key elements of a smart grid such as: high speed power electronics, distributed energy resources (DER), and communication networks. A description of the platform for real time simulation is presented along with the integration of communication emulation; achieved through OPNETs System in the Loop (SITL) package. In addition, an introduction to Networked Control Systems (NCS) is presented and a case study of PHEV charging stations which displays the latest results accomplished with the current setup.

Real time simulation for the study on smart grid

This paper introduces the latest real time simulation technologies and their applications to the smart grid related studies. A real time simulation platform now built at the Ohio State University is described in detail. With the help of this platform, distributed real time simulation of complex power system integrated with high switching speed power electronics components, renewable energy resources, and communication networks can be fulfilled. Two case studies are performed to illustrate the platform. The first realizes intentional islanding and seamless transition of the smart grid during a power grid failure; the other integrates communication network and power network simulation together to explore communication and distributed control issues in the smart grid.

Utilizing dynamic spectrum leasing for cognitive radios in 802.11-based wireless networks ☆

Abstract Dynamic spectrum access (DSA) is proposed to deal with the growing shortage of available leased spectrum for wireless communication. We investigate a subset of DSA referred to as dynamic spectrum leasing (DSL). At its core, DSL allows spectrum lease holders and cognitive radios to cooperate in an effort to leverage spatial diversity to improve channel utilization for both parties. In this research, cognitive radios offer their services as an intermediate relay node in an effort to improve throughput of primary users utilizing a 802.11-based channel access mechanism. In return, the cognitive radio ‘piggy-backs’ some of its own data while acting as a relay. In this paper, a simple coordination scheme is introduced that allows a network of Secondary Users to coordinate with a primary user network’s access point. This scheme does not require any modification to the primary users’ 802.11-based protocol stack as our protocol is implemented only at the access point and the Secondary Users. Analytical insights into the overhead required for this coordination and the optimization of the overhead are presented. It is shown that, given sufficient relay channel conditions, forwarding packets through a secondary relay channel can be beneficial to both parties in terms of saturation throughput.

Capacity achieving distributed scheduling with finite buffers

In this paper, we propose a distributed cross-layer scheduling algorithm for wireless networks with single-hop transmissions that can guarantee finite buffer sizes and meet minimum utility requirements. The algorithm can achieve a utility arbitrarily close to the optimal value with a tradeoff in the buffer sizes. The finite buffer property is not only important from an implementation perspective, but, along with the algorithm, also yields superior delay performance. In addition, another extended algorithm is provided to help construct the upper bounds of per-flow average packet delays. A novel structure of Lyapunov function is employed to prove the utility optimality of the algorithm with the introduction of novel virtual queue structures. Unlike traditional back-pressure-based optimal algorithms, our proposed algorithm does not need centralized computation and achieves fully local implementation without global message passing. Compared to other recent throughput/utility-optimal CSMA distributed algorithms, we illustrate through rigorous numerical and implementation results that our proposed algorithm achieves far better delay performance for comparable throughput/utility levels.

Performance of Highly Mobile Cognitive Radio Networks with Directional Antennas

Cognitive radio systems allow secondary users to operate on underutilized licensed spectrum. When considering highly congested communication channels, however, opportunities for channel access based on time or frequency division can be limited for secondary user networks. In this research, we consider leveraging enhanced spatial diversity through directional steerable antennas to allow secondary user channel access in parallel with licensed spectrum users. Furthermore, we consider effects of mobility on directional secondary user networks and introduce a mechanism for maintaining point-to-point directional communication links in the presence of mobility. We study the trade-offs between spatial diversity and coordination overhead to motivate the use of directional antennas, even in highly mobile cognitive radio networks.