Haniph A. Latchman

A novel MAC protocol with fast collision resolution for wireless LANs

Design of efficient medium access control (MAC) protocols with both high throughput performance and high-degree of fairness performance is a major focus in distributed contention-based MAC protocol research. In this paper, we propose a novel and efficient contention-based MAC protocol for wireless local area networks, namely, the fast collision resolution (FCR) algorithm. This algorithm is developed based on the following innovative ideas: to speed up the collision resolution, we actively redistribute the backoff timers for all active nodes; to reduce the average number of idle slots, we use smaller contention window sizes for nodes with successful packet transmissions and reduce the backoff timers exponentially fast when a fixed number of consecutive idle slots are detected. We show that the proposed FCR algorithm provides high throughput performance and low latency in wireless LANs. The extensive simulation studies show that the FCR algorithm could significantly improve the performance of the IEEE 802.11 MAC protocol if our efficient collision resolution algorithm is used and that the fairly scheduled FCR (FS-FCR) algorithm could simultaneously achieve high throughput performance and a high degree of fairness.

Frequency sweeping tests for stability independent of delay

In this paper we study the stability properties of linear time-invariant delay systems given in a state space form. We consider specifically the notion of asymptotic stability independent of delay. Systems with both commensurate and noncommensurate delays are investigated. We present for each class of systems a necessary and sufficient condition in terms of structured singular values, and further we demonstrate how these conditions may be extended to study stability independent of delay for uncertain systems. Our results consist of several frequency sweeping tests that can be systematically implemented and that should complement the previous work. >

HomePlug 1.0 powerline communication LANs—protocol description and performance results

Products implementing the HomePlug 1.0 standard allowing high-speed communication on low-voltage powerlines have recently started arriving on the U.S. market for home and office networking without the requirement for installing new wires. Effective use of the powerline bandwidth requires robust physical (PHY) and medium access control (MAC) protocols to mitigate the harsh conditions of the powerline channel as well as the capability to support prioritized multimedia traffic. This paper describes powerline communications and the HomePlug 1.0 protocol, based on orthogonal frequency division multiplexing (OFDM) and carrier sense multiple access with collision avoidance (CSMA/CA), along with its changes to allow prioritized channel access. It then presents performance results for the HomePlug 1.0 protocol using a simulation model, ideal laboratory measurements with actual HomePlug 1.0 devices and field tests in a residential building. Simulation and laboratory data rates were around 6 Mbps, and field tests gave rates from 1.6 to 5.3 Mbps at the application level. Copyright

Information technology enhanced learning in distance and conventional education

The rapid growth of the Internet and the media-rich extensions of the World Wide Web allow new developments in the way instructors transfer knowledge to their students. There is no doubt that nothing will replace synchronous learning through face to face interaction but it is sometimes not feasible for students to attend conventional classes due to distance or time constraints. This paper presents a model for using information technology to enhance the learning experience for conventional on-campus students, as well as for those students whose circumstances require that they be asynchronous in time or space. The approach described emphasizes a solution which allows students to attend the class in real time via the Internet, or to access asynchronously digitally stored video material with hyperlinks to online training resources at any time. The proposed solution permits interaction in real-time and asynchronously among students and between students and instructor, which is a key for effective learning. In addition, the instructor maintains a significant level of spontaneity in using multimedia material prepared in advance or using conventional chalkboard or hand written materials via traditional overhead projection. The paper describes the technical issues involved and the chosen solutions to provide enhanced live and archived classes. This paper provides some comments on the evaluation of the learning experience using this method of delivery for on-campus and distance education students. Finally the authors share their vision on future trends to improve the proposed learning environment and the need for an optimal balance between expositive teaching and active learning for both synchronous and asynchronous activities.

Design of MAC protocols with fast collision resolution for wireless local area networks

Development of efficient medium access control (MAC) protocols providing both high throughput performance for data traffic and good quality of service (QoS) support for real-time traffic is the current major focus in distributed contention-based MAC protocol research. In this paper, we propose an efficient contention resolution algorithm for wireless local area networks, namely, the fast collision resolution (FCR) algorithm. The MAC protocol with this new algorithm attempts to provide significantly higher throughput performance for data services than the IEEE 802.11 MAC algorithm and more advanced dynamic tuning backoff (DTB) algorithm. We demonstrate that this algorithm indeed resolves collisions faster and reduces the idle slots more effectively. To provide good fairness performance and to support good QoS for real-time traffic, we incorporate the self-clocked fair queueing algorithm and a priority scheme into the FCR algorithm and come up with the real-time FCR (RT-FCR) algorithm, and show that RT-FCR can simultaneously achieve high throughput and good fairness performance for nonreal-time traffic while maintaining satisfactory QoS support for real-time traffic.

Airborne traffic surveillance systems: video surveillance of highway traffic

Timely information about highway traffic conditions is very important for the Department of Transportation (DOT) and other relevant agencies. Such live information would be very important when traffic incidents or accidents occur. An aerial view is the best for traffic situations, particularly over highways. Unmanned aircraft equipped with video cameras and/or other sensors may be able to deliver the necessary information through video images with relatively low operational costs and risks to human life. ATSS (Airborne Traffic Surveillance System), a project funded by the Florida Department of Transportation, attempts to make this vision a reality. This paper describes how the University of Florida research team implemented a system for ATSS from the ground up, using unmanned aerial vehicles, digital video encoding, and transmission of data and multimedia video streams over FDOTs microwave IP networks.

A comparative performance study of wireless and power line networks

Local area networks based on the IEEE 802.11a/b wireless networking standards and emerging power line communication (PLC) standards are attractive for establishing networks with no new wires for in-home and business applications. This article presents a theoretical performance comparison of the 802.11 a/b and HomePlug 1.0 PLC protocols. The article also presents comprehensive comparative field test results addressing such issues as coverage, channel stability, and reliability as well as the associated implications on the capability of these technologies to provide QoS support for multimedia traffic in typical residential settings.

Channel Adaptation based on Cyclo-Stationary Noise Characteristics in PLC Systems

As power line communication (PLC) systems become more pervasive, there is increasing demand for new generations of PLC systems that enable bandwidth intensive applications like audio/video streaming and broadband access. To achieve the data rates necessary to support such applications within the current regulatory constraints, PLC systems should exploit the inherent characteristics of the power line channel that enable a more aggressive and optimized channel adaptation. One such characteristic is the cyclic variation of the noise power with the phase of the underlying AC line cycle. In this paper, we use extensive channel characterization measurements and analysis to investigate the performance enhancements that can be achieved by using a channel adaptation mechanism that exploits the cyclic variation in power line noise characteristics. The results show that a 30% improvement in physical layer (PHY) data rates can be obtained by continuously adapting to, and synchronizing communications with, the AC line cycle. Since continuous adaptation with respect to time is unduly complex for practical systems, we propose dividing the AC line cycle into multiple regions and adapting independently in each region. Results show that using a region size of 1-2 milliseconds provides optimal MAC throughput on most paths tested

Asymptotic stability independent of delays: simple necessary and sufficient conditions

Studies stability properties of linear time-invariant delay systems. The authors consider specifically the notion of asymptotic stability independent of delays. Systems with both commensurate and non-commensurate delays are investigated. The authors present for each case a necessary and sufficient condition, and further they demonstrate how these conditions may be extended readily to study asymptotic stability independent of delays for uncertain systems. These conditions can be readily checked, and they appear to be considerably simpler than results developed elsewhere previously.

Power line local area networking

he use of ubiquitous electrical wiring as a potential medium for communication signals has been suggested over past generations. Indeed, for some decades now, power line wires have been used for low-speed data communication, culminating in such standards and products as LonWorks, CEBus, and X-10, as well as many proprietary systems for the transmission of control and management signals. However, the power line has largely been dismissed as being too noisy and unpredictable to be useful as a practical high-speed communication channel. On the other hand, recent advances in communicat ion and modulation methodologies, as well as in adaptive digital signal processing and error detection and correction, have opened the way for the development of effective medium access control and physical layer protocols that support power line communications (PLC) networks operating at speeds comparable to those obtained from specially wired and more recent wireless local area networks. In mid-2001, an industrial standards organization called the HomePlug Powerline Alliance, originally founded by 13 companies including Cisco, Motorola, Intel, Panasonic, and Texas Instruments, announced the completion of the HomePlug 1.0 specification for a 10 Mbis class in-home power line networking technology based on orthogonal frequency-division multiplexing (OFDM). Products based on this industry standard are enjoying much positive attention in the market press from industry and product analysts based on performance and ease of use. It was clear at the January 2003 Consumer Electronics Show that HornePlug is now recognized as one of three attractive in-borne networking solutions, together with Ethernet and Wi-Fi (IEEE 802.11~). The HomePlug Powerline Alliance recently announced an effort to establish a 100 Mbis class in-home power line networking standard, called HomePlug AV, to provide distribution of data and multistream video and audio, including high-definition television (HDTV) throughout the home. Measurements and analysis of in-home power line channel capacity demonstrate that this goal is fe.asible. This new technology will be well positioned to revolutionize in-home entertainment networking by providing a simple, reliable, and cost-effective solution for consumer products such as personal video recorders, media centers, and flat panel televisions. In addition to developments associated with in-building PLC LANs, progress has also been made in the use of the powerline as an alternative to DSL and cable modems for broadband Internet access. The purpose of this feature topic in IEEE Communications Magazine is to highlight and document the significant progress in high-speed digital communication over power lines that is precipitating a new genre of wired local area and access networks requiring no new or specialized wiring. There are five articles in this series of articles. The article “Power Line Communications: State of the Art and Future Trends” by Niovi Pavlidou, Han Vink, Javad Yazdan, and Bahram Honary gives an overview on the history of PLC as well as a description of ongoing research, applications, regulatory activities, market perspectives, and