Tamer Nadeem

TrafficView: traffic data dissemination using car-to-car communication

Vehicles are part of peoples life in modern society, into which more and more high-tech devices are integrated, and a common platform for inter-vehicle communication is necessary to realize an intelligent transportation system supporting safe driving, dynamic route scheduling, emergency message dissemination, and traffic condition monitoring. TrafficView, which is a part of the e-Road project, defines a framework to disseminate and gather information about the vehicles on the road. With such a system, vehicles driver will be provided with road traffic information that helps driving in situations as foggy weather, or finding an optimal route in a trip several miles long. This paper describes the design and implementation of TrafficView and the different mechanisms used in the system.

A Comparative Study of Data Dissemination Models for VANETs

VANETs (vehicular ad hoc networks) are emerging as a new network environment for intelligent transportation systems. Many of the applications built for VANETs will depend on the data push communication model, where information is disseminated to a group of vehicles. In this paper, we present a formal model of data dissemination in VANETs and study how VANET characteristics, specifically the bidirectional mobility on well defined paths, affects the performance of data dissemination. We study the data push model in the context of TrafficView, a system we have implemented to disseminate information about the vehicles on the road. Traffic data could be disseminated using vehicles moving on the same direction, vehicles moving in the opposite direction, or vehicles moving in both directions. Our analysis as well as simulation results show that dissemination using only vehicles in the opposite direction increases the data dissemination performance significantly.

Location-Aware Services over Vehicular Ad-Hoc Networks using Car-to-Car Communication

Recent advances in wireless inter-vehicle communication systems enable the establishment of vehicular ad-hoc networks (VANET) and create significant opportunities for the deployment of a wide variety of applications and services to vehicles. In this work, we investigate the problem of developing services that can provide car drivers with time-sensitive information about traffic conditions and roadside facilities. We introduce the vehicular information transfer protocol (VITP), a location- aware, application-layer, communication protocol designed to support a distributed service infrastructure over vehicular ad- hoc networks. We describe the key design concepts of the VITP protocol and infrastructure. We provide an extensive simulation study of VITP performance on large-scale vehicular networks under realistic highway and city traffic conditions. Our results demonstrate the viability and effectiveness of VITP in providing location-aware services over VANETs.

VITP: an information transfer protocol for vehicular computing

Recent advances in wireless inter-vehicle communication systems enable the development of Vehicular Ad-Hoc Networks (VANET) and create significant opportunities for the deployment of a wide variety of vehicular applications and services. In this paper, we introduce the Vehicular Information Transfer Protocol (VITP), an application-layer communication protocol, which is designed to support the establishment of a distributed, ad-hoc service infrastructure over VANET. The VITP infrastructure can be used to provide location-based, traffic-oriented services to drivers, using information retrieved from vehicular sensors and taking advantage of on-board GPS navigation systems. In this paper, we present the key design concepts of the protocol and the infrastructure, the protocol specification, simple examples of protocol interactions that support driver inquiries, and a simulation study of VITP performance properties.

TrafficView: a scalable traffic monitoring system

Vehicles are part of peoples life in modern society, into which more and more high-tech devices are integrated, and a common platform for inter-vehicle communication is necessary to realize an intelligent transportation system supporting safe driving, dynamic route scheduling, emergency message dissemination, and traffic condition monitoring. TrafficView, which is a part of the e-Road project, defines a framework to disseminate and gather information about the vehicles on the road. Using such a system will provide a vehicle driver with road traffic information, which helps driving in situations such as foggy weather, or finding an optimal route in a trip several miles long. This paper describes the basic design of TrafficView and different algorithms used in the system.

Context-Aware Migratory Services in Ad Hoc Networks

Ad hoc networks can be used not only as data carriers for mobile devices but also as providers of a new class of services specific to ubiquitous computing environments. Building services in ad hoc networks, however, is challenging due to the rapidly changing operating contexts, which often lead to situations where a node hosting a certain service becomes unsuitable for hosting the service execution any longer. We propose a novel model of service provisioning in ad hoc networks based on the concept of context- aware migratory services. Unlike a regular service that executes always on the same node, a migratory service can migrate to different nodes in the network in order to accomplish its task. The migration is triggered by changes of the operating context, and it occurs transparently to the client application. We designed and implemented a framework for developing migratory services. We built TJam, a proof-of-concept migratory service that predicts traffic jams in a given region of a highway by using only car-to-car short-range wireless communication. The experimental results obtained over an ad hoc network of personal digital assistants (PDAs) show the effectiveness of our approach in the presence of frequent disconnections. We also present simulation results that demonstrate the benefits of migratory services in large-scale networks compared to a statically centralized approach.

CARS: Context-Aware Rate Selection for vehicular networks

Traffic querying, road sensing and mobile content delivery are emerging application domains for vehicular networks whose performance depends on the throughput these networks can sustain. Rate adaptation is one of the key mechanisms at the link layer that determine this performance. Rate adaptation in vehicular networks faces the following key challenges: (1) due to the rapid variations of the link quality caused by fading and mobility at vehicular speeds, the transmission rate must adapt fast in order to be effective, (2) during infrequent and bursty transmission, the rate adaptation scheme must be able to estimate the link quality with few or no packets transmitted in the estimation window, (3) the rate adaptation scheme must distinguish losses due to environment from those due to hidden-station induced collision. Our extensive outdoor experiments show that the existing rate adaptation schemes for 802.11 wireless networks under utilize the link capacity in vehicular environments. In this paper, we design, implement and evaluate CARS, a novel context-aware rate selection algorithm that makes use of context information (e.g. vehicle speed and distance from neighbor) to systematically address the above challenges, while maximizing the link throughput. Our experimental evaluation in real outdoor vehicular environments with different mobility scenarios shows that CARS adapts to changing link conditions at high vehicular speeds faster than existing rate-adaptation algorithms. Our scheme achieves significantly higher throughput, up to 79%, in all the tested scenarios, and is robust to packet loss due to collisions, improving the throughput by up to 256% in the presence of hidden stations.

TrafficView: a driver assistant device for traffic monitoring based on car-to-car communication

TrafficView is a device that can be embedded in the next generation of vehicles to provide drivers with a real-time view of the road traffic far beyond what they can physically see. Vehicles equipped with TrafficView devices disseminate traffic information using short-range wireless communication. The main benefits of disseminating traffic information in a vehicle-to-vehicle fashion are scalability and ease of deployment. The paper describes the TrafficView prototype and presents preliminary experimental results for this prototype.

Effect of Antenna Placement and Diversity on Vehicular Network Communications

In this paper we present empirical results from a study examining the effects of antenna diversity and placement on vehicle-to-vehicle link performance in vehicular ad hoc networks. The experiments use roof- and in-vehicle mounted omni-directional antennas and IEEE 802.11a radios operating in the 5 GHz band, which is of interest for planned inter-vehicular communication standards. Our main findings are two-fold. First, we show that radio reception performance is sensitive to antenna placement in the 5 Ghz band. Second, our results show that, surprisingly, a packet level selection diversity scheme using multiple antennas and radios, multi-radio packet selection (MRPS), improves performance not only in a fading channel but also in line-of-sight conditions. This is due to propagation being affected by car geometry, leading to the highly non-uniform antenna patterns. These patterns are very sensitive to the exact antenna position on the roof, for example at a transmit power of 40 mW the line-of-sight communication range varied between 50 and 250 m depending on the orientation of the cars. These findings have implications for vehicular MAC protocol design. Protocols may have to cope with an increased number of hidden nodes due to the directional antenna patterns. However, car makers can reduce these effects through careful antenna placement and diversity.

Understanding the limitations of transmit power control for indoor wlans

A wide range of transmit power control (TPC) algorithms have been proposed in recent literature to reduce interference and increase capacity in 802.11 wireless networks. However, few of them have made it to practice. In many cases this gap is attributed to lack of suitable hardware support in wireless cards to implement these algorithms. In particular, many research efforts have indicated that wireless card vendors need to support power control mechanisms in a fine-grained manner - both in the number of possible power levels and the time granularity at which the controls can be applied. In this paper we claim that even if fine-grained power control mechanisms were to be made available by wireless card vendors, algorithms would not be able to properly leverage such degrees of control in typical indoor environments. We prove this claim through rigorous empirical analysis and then build a tunable empirical model (Model-TPC) that can determine the granularity of power control that is actually useful. To illustrate the importance of our solution, we conclude by demonstrating the impact of choice of power control granularity on Internet applications where wireless clients interact with servers on the Internet. We observe that the number of feasible power was found to be between 2-4 for most indoor environments. We believe that the results from this study can serve as the right set of assumptions to build practically realizable TPC algorithms in the future.