Wantanee Viriyasitavat

Self-organized traffic control

In this paper we propose and present preliminary results on the migration of traffic lights as roadside-based infrastructures to in-vehicle virtual signs supported only by vehicle- to-vehicle communications. We design a virtual traffic light protocol that can dynamically optimize the flow of traffic in road intersections without requiring any roadside infrastructure. Elected vehicles act as temporary road junction infrastructures and broadcast traffic light messages that are shown to drivers through in-vehicle displays. This approach renders signalized control of intersections truly ubiquitous, which significantly increases the overall traffic flow. We pro- vide compelling evidence that our proposal is a scalable and cost-effective solution to urban traffic control.

Modeling urban traffic: A cellular automata approach

In this article we introduce a new cellular automata approach to construct an urban traffic mobility model. Based on the developed model, characteristics of global traffic patterns in urban areas are studied. Our results show that different control mechanisms used at intersections such as cycle duration, green split, and coordination of traffic lights have a significant effect on intervehicle spacing distribution and traffic dynamics. These findings provide important insights into the network connectivity behavior of urban traffic, which are essential for designing appropriate routing protocols for vehicular ad hoc networks in urban scenarios.

Dynamics of Network Connectivity in Urban Vehicular Networks

Vehicular ad hoc networks (VANETs) have emerged as a serious and promising candidate for providing ubiquitous communications both in urban and highway scenarios. Consequently, nowadays it is widely believed that VANETs will be able to support both safety and non-safety applications. For both classes of applications, since a zero-infrastructure is the typical premise assumed, it is crucial to understand the dynamics of network connectivity when one operates without relying on any telecommunications infrastructure. Using the key metrics of interest (such as link duration, connection duration, and re-healing time) we provide a comprehensive framework for network connectivity of urban VANETs. Our study, in addition to extensive simulations based on a new Cellular Automata Model for mobility, also provides a comprehensive analytical framework. This analytical framework leads to closed form results which facilitate physical insight into the impact of key system parameters on network connectivity. The predictions of our analytical framework also shed light on which type of safety and non-safety applications can be supported by urban VANETs.

UV-CAST: An urban vehicular broadcast protocol

Several vehicular communication applications will involve multicast/broadcast communications where all vehicles in a certain region of interest are the intended recipients of particular messages. While there are several existing broadcast routing protocols for highway VANETs, very few solutions exist for urban VANETs in cities like New York City or Chicago. This paper attempts to fill this gap by proposing a new broadcast routing protocol, namely UV-CAST, that addresses both the broadcast storm and disconnected network problems in urban VANETs. Key challenges imposed by urban VANETs as well as new mechanisms needed for this new scenario are identified and presented. Performance of the proposed UV-CAST protocol is evaluated in terms of network reachability, received distance, and network overhead in ideal Manhattan Street scenarios as well as in real cities, such as Pittsburgh. The overall performance of UV-CAST is excellent.

UV-CAST: an urban vehicular broadcast protocol

Several vehicular communication applications will involve multicast/broadcast communications where all vehicles in a certain region of interest are the intended recipients of particular messages. While there are several existing broadcast routing protocols for highway VANETs, very few solutions exist for urban VANETs in cities like New York City or Chicago. This article attempts to fill this gap by proposing a new broadcast routing protocol, Urban Vehicular BroadCAST (UV-CAST), which addresses both the broadcast storm and disconnected network problems in urban VANETs. Key challenges imposed by urban VANETs as well as new mechanisms needed for meeting these challenges are identified and presented. Performance of the proposed UV-CAST protocol is evaluated in terms of network reachability, received distance, and network overhead in ideal Manhattan Street scenarios as well as in real cities, such as Pittsburgh. The overall performance of UV-CAST is excellent.

Network Connectivity of VANETs in Urban Areas

Modeling complicated vehicular traffic behavior and the associated network connectivity in urban areas has been a challenging task for the past several years. In this paper, we study how intersections and two-dimensional road topology affect the connectivity behavior of traffic in urban areas. To better understand this phenomenon, we investigate both static and dynamic aspects of network connectivity in urban areas and analyze several characteristics such as network connectivity, path redundancy, re-healing time, etc. Based on a comprehensive study, we make several key observations and provide insights into the behavior of network connectivity whereby critical routing problems are identified and suggestions are made for the key components of an appropriate routing protocol for different vehicular ad hoc network (VANET) applications in urban areas.

Cars as roadside units: a self-organizing network solution

Deploying roadside units, RSUs, for increasing the connectivity of vehicular ad hoc networks is deemed necessary for coping with the partial penetration of DSRC radios into the market in the initial stages of DSRC deployment. Several factors, including cost, complexity, existing systems, and lack of cooperation between government and private sectors, have impeded the deployment of RSUs. In this article, we propose to solve this formidable problem by using a biologically inspired self-organizing network approach whereby certain vehicles serve as RSUs. The proposed solution is based on designing local rules and the corresponding algorithms that implement them. Results show that the proposed approach can increase the message reachability and connectivity substantially.

Feasibility of In-car Wireless Sensor Networks: A Statistical Evaluation

Statistical characterization of in-car wireless communication channels has recently gained significance, mainly due to the possibility of deploying a wireless sensor network in the vehicle. In this paper, we report different aspects of a statistical analysis of four representative in- car wireless channels based on the received power data collected from a binary phase shift keying (BPSK) transmission experiment. It is shown that the communication channel between the base station and a sensor placed under the engine compartment is the worst in terms of stability, average fade duration, and fade proportion, while the channel between the base station and a sensor placed in the trunk and the channel between the base station and a sensor placed on the hood are the best. We also show that the 4 representative in-car wireless channels can satisfy the maximum packet delay requirement of less than 500 ms and the trunk channel and the in-the-engine-compartment channels can satisfy the requirement of up to 98% packet reception rate. These statistical characteristics of the in- car wireless channels provide important guidelines for the designer of an in-car sensor system.

Improving VANET protocols via network science

Developing routing protocols for Vehicular Ad Hoc Networks (VANETs) is a significant challenge in these large, self-organized and distributed networks. We address this challenge by studying VANETs from a network science perspective to develop solutions that act locally but influence the network performance globally. More specifically, we look at snapshots from highway and urban VANETs of different sizes and vehicle densities, and study parameters such as the node degree distribution, the clustering coefficient and the average shortest path length, in order to better understand the networks structure and compare it to structures commonly found in large real world networks such as small-world and scale-free networks. We then show how to use this information to improve existing VANET protocols. As an illustrative example, it is shown that, by adding new mechanisms that make use of this information, the overhead of the urban vehicular broadcasting (UV-CAST) protocol can be reduced substantially with no significant performance degradation.

Modeling vehicle-to-vehicle line of sight channels and its impact on application-layer performance

We analyze the properties of line of sight (LOS) channels in vehicle-to-vehicle (V2V) communication. We use V2V measurements performed in open space, suburban, and urban environments. By separating LOS from non-LOS data, we show that a two-ray ground reflection path loss model with effective reflection coefficient range fits the LOS channels better than the frequently used free space path loss model. Two-ray model is a better fit not only in open space, but also in suburban and urban environments. We investigate the impact of using the modified two-ray model on the application-level performance metrics: packet delivery rate, throughput, latency, and jitter. Our results show that considerable differences arise in application performance when using the modified two-ray and free space models.