Mate Boban

Impact of Vehicles as Obstacles in Vehicular Ad Hoc Networks

A thorough understanding of the communications channel between vehicles is essential for realistic modeling of Vehicular Ad Hoc Networks (VANETs) and the development of related technology and applications. The impact of vehicles as obstacles on vehicle-to-vehicle (V2V) communication has been largely neglected in VANET research, especially in simulations. Useful models accounting for vehicles as obstacles must satisfy a number of requirements, most notably accurate positioning, realistic mobility patterns, realistic propagation characteristics, and manageable complexity. We present a model that satisfies all of these requirements. Vehicles are modeled as physical obstacles affecting the V2V communication. The proposed model accounts for vehicles as three-dimensional obstacles and takes into account their impact on the LOS obstruction, received signal power, and the packet reception rate. We utilize two real world highway datasets collected via stereoscopic aerial photography to test our proposed model, and we confirm the importance of modeling the effects of obstructing vehicles through experimental measurements. Our results show considerable obstruction of LOS due to vehicles. By obstructing the LOS, vehicles induce significant attenuation and packet loss. The algorithm behind the proposed model allows for computationally efficient implementation in VANET simulators. It is also shown that by modeling the vehicles as obstacles, significant realism can be added to existing simulators with clear implications on the design of upper layer protocols.

Experimental study on the impact of vehicular obstructions in VANETs

Channel models for vehicular networks typically disregard the effect of vehicles as physical obstructions for the wireless signal. We aim to clarify the validity of this simplification by quantifying the impact of obstructions through a series of wireless experiments. Using two cars equipped with Dedicated Short Range Communications (DSRC) hardware designed for vehicular use, we perform experimental measurements in order to collect received signal power and packet delivery ratio information in a multitude of relevant scenarios: parking lot, highway, suburban and urban canyon. Upon separating the data into line of sight (LOS) and non-line of sight (NLOS) categories, our results show that obstructing vehicles cause significant impact on the channel quality. A single obstacle can cause a drop of over 20 dB in received signal strength when two cars communicate at a distance of 10 m. At longer distances, NLOS conditions affect the usable communication range, effectively halving the distance at which communication can be achieved with 90% chance of success. The presented results motivate the inclusion of vehicles in the radio propagation models used for VANET simulation in order to increase the level of realism.

Vehicular Communications: Survey and Challenges of Channel and Propagation Models

Vehicular communication is characterized by a dynamic environment, high mobility, and comparatively low antenna heights on the communicating entities (vehicles and roadside units). These characteristics make vehicular propagation and channel modeling particularly challenging. In this article, we classify and describe the most relevant vehicular propagation and channel models, with a particular focus on the usability of the models for the evaluation of protocols and applications. We first classify the models based on the propagation mechanisms they employ and their implementation approach. We also classify the models based on the channel properties they implement and pay special attention to the usability of the models, including the complexity of implementation, scalability, and the input requirements (e.g., geographical data input). We also discuss the less-explored aspects in vehicular channel modeling, including modeling specific environments (e.g., tunnels, overpasses, and parking lots) and types of communicating vehicles (e.g., scooters and public transportation vehicles). We conclude by identifying the underresearched aspects of vehicular propagation and channel modeling that require further modeling and measurement studies.

Geometry-Based Vehicle-to-Vehicle Channel Modeling for Large-Scale Simulation

Due to the dynamic nature of vehicular traffic and the road surroundings, vehicle-to-vehicle (V2V) propagation characteristics vary greatly on both small and large scale. Recent measurements have shown that both large static objects (e.g., buildings and foliage) and mobile objects (surrounding vehicles) have a profound impact on V2V communication. At the same time, system-level vehicular ad hoc network (VANET) simulators by and large employ simple statistical propagation models, which do not account for surrounding objects explicitly. We designed Geometry-based Efficient propagation Model for V2V communication (GEMV2), which uses outlines of vehicles, buildings, and foliage to distinguish the following three types of links: line of sight (LOS), non-LOS (NLOS) due to vehicles, and NLOS due to static objects. For each link, GEMV2 calculates the large-scale signal variations deterministically, whereas the small-scale signal variations are calculated stochastically based on the number and size of surrounding objects. We implement GEMV2 in MATLAB and show that it scales well by using it to simulate radio propagation for city-wide networks with tens of thousands of vehicles on commodity hardware. We make the source code of GEMV2 freely available. Finally, we validate GEMV2 against extensive measurements performed in urban, suburban, highway, and open-space environments.

Multiplayer games over Vehicular Ad Hoc Networks: A new application

In this paper we investigate the possibility of a new type of application, namely multiplayer games, in a Vehicular Ad Hoc Network (VANET) environment. First, we analyze the available empirical data on travel and traffic volume in the United States, and point out the most important challenges that have to be met in order to enable multiplayer games over VANET. We then propose a new paradigm of multiplayer games over VANET, one which utilizes the new, interactive and dynamic VANET environment, while adapting to its inherent constraints.

What is the Best Achievable QoS for Unicast Routing in VANETs

Significant efforts and studies were recently reported for enabling active safety, traffic management, and commercial applications in Vehicular Ad Hoc Networks (VANET), since these applications are the drivers of the recent surge in VANET research and development. However, very few research efforts considered analyzing the Quality of Service (QoS) metrics that will be available to these applications in VANET. Furthermore, although there are many proposed solutions for routing in VANET, it is still unclear as to what specific characteristics VANET routing protocols should possess, since none of the proposed solutions achieves optimum performance in both urban and highway, as well as sparse and dense environment. To shed light on these issues, in this paper we analyze some of the most important QoS metrics in VANET. Namely, we determine the upper performance bound for connection duration, packet delivery ratio, end-to-end delay, and jitter for unicast communication in typical highway and urban VANET environments. According to our results, delay and jitter in VANET would be adequate for most of the envisioned unicast-based applications, whereas the packet delivery ratio and connection duration might not meet the requirements for most unicast-based applications.

TVR—Tall Vehicle Relayingin Vehicular Networks

Vehicle-to-Vehicle (V2V) communication is a core technology for enabling safety and non-safety applications in next generation intelligent transportation systems. Due to relatively low heights of the antennas, V2V communication is often influenced by topographic features, man-made structures, and other vehicles located between the communicating vehicles. On highways, it was shown experimentally that vehicles can obstruct the line of sight (LOS) communication up to 50 percent of the time; furthermore, a single obstructing vehicle can reduce the power at the receiver by more than 20 dB. Based on both experimental measurements and simulations performed using a validated channel model, we show that the elevated position of antennas on tall vehicles improves communication performance. Tall vehicles can significantly increase the effective communication range, with an improvement of up to 50 percent in certain scenarios. Using these findings, we propose a new V2V relaying scheme called tall vehicle relaying (TVR) that takes advantage of better channel characteristics provided by tall vehicles. TVR distinguishes between tall and short vehicles and, where appropriate, chooses tall vehicles as next hop relays. We investigate TVRs system-level performance through a combination of link-level experiments and system-level simulations and show that it outperforms existing techniques.

Unicast communication in vehicular ad hoc networks: a reality check

We characterize the unicast performance available to applications in infrastructureless vehicular ad hoc networks (VANETs) in terms of connection duration, packet delivery ratio, end-to-end delay, and jitter in both highway and urban VANET environments. The results show the existence of several stringent QoS constraints for unicast applications in infrastructureless VANETs.

Exploiting the height of vehicles in vehicular communication

One of the most challenging research issues in vehicular ad hoc networks (VANETs) is how to efficiently relay messages between vehicles. We propose a heuristic that uses the physical dimensions of vehicles to help determine whether or not a vehicle is an appropriate next hop. We base the heuristic on the intuition that taller vehicles have an advantage over shorter ones because the former are less susceptible to shadowing from other vehicles. We implement a model that evaluates the efficacy of the proposed heuristic and we perform the experiments to validate the model. Based on both the experimental measurements and the simulations performed using the model, it is shown that tall vehicles consistently and significantly increase both the effective communication range and the message reachability. The effective communication range increased by more than 50%: from 290 meters when short vehicles are communicating to 450 meters in the case of tall vehicles. The results suggest that, when available, tall vehicles are significantly more likely to better relays than short vehicles. The proposed heuristic is not dependent on any specific routing technique and can be used to improve the performance of different classes of routing protocols.

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.