Taimoor Abbas

A Measurement Based Shadow Fading Model for Vehicle-to-Vehicle Network Simulations

The Vehicle-to-Vehicle (V2V) propagation channel has significant implications on the design and performance of novel communication protocols for Vehicular Ad Hoc Networks (VANET). Extensive research efforts have been made to develop and implement V2V channel models for advanced VANET system simulators. The impact of shadowing caused by other vehicles has, however, largely been neglected in most of the models, as well as in the system simulations. In this paper we present a simple shadow fading model targeting system simulations based on real world measurements performed in urban and highway scenarios. Video information from the measurements is used to separate the line-of-sight (LOS) condition from the obstructed line-of-sight (OLOS) by vehicles and non line-of-sight (NLOS) by buildings. It is observed that the vehicles obstructing LOS induce an additional attenuation of about

Radio Channel Measurements at Street Intersections for Vehicle-to-Vehicle Safety Applications

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Directional Analysis of Vehicle-to-Vehicle Propagation Channels

\,dB in the received signal power. We use a Markov chain based state transition diagram to model transitions from LOS to obstructed LOS and present an example of state transition intensities for a real traffic mobility model. We also provide a simple recipe, how to incorporate our shadow fading model in VANET network simulators. (Less)

Simulation and Measurement-Based Vehicle-to-Vehicle Channel Characterization: Accuracy and Constraint Analysis

This paper presents the results of an empirical study of wireless propagation channels for vehicle-to-vehicle communications in street intersections, a scenario especially important for collision avoidance applications. The results are derived from a channel measurement campaign performed at 5.6 GHz in four different types of urban intersections. We present results on typical power delay profiles, pathloss and delay spreads and discuss important propagation mechanisms. By comparing the results of the different intersections, we find that absence of line-of-sight is problematic for system coverage, especially when there are few other significant scattering objects in and around the intersection. Roadside buildings can create important propagation paths that account for a considerable part of the total received power.

Comparison of Ray Tracing and Channel-Sounder Measurements for Vehicular Communications

This paper presents a double directional analysis of vehicle-to-vehicle channel measurements conducted in three different traffic scenarios. Using a high- resolution algorithm, we derive channel parameters like Angle-of-Arrival (AOA), Angleof- Departure (AOD), propagation delay and Doppler shift and identify underlying propagation mechanisms by combining these estimates with maps of the measurement sites. The results show that first-order reflections from a small number of interacting objects can account for a large part of the received signal in the absence of line-of-sight (LOS). This effect is especially pronounced in the two traffic scenarios where the road is not lined with buildings. We also found that the direction spread is low (and conversely that the antenna correlation is high) in such scenarios, which suggests that beam forming rather than diversity-based methods should be used if multiple antenna elements are available. The situation is reversed, however, in the third scenario, a narrow urban intersection, where a larger number of higher-order reflections is found to result in a higher direction spread.

Radio Channel Properties for Vehicular Communication: Merging Lanes Versus Urban Intersections

In this paper, a deterministic channel model for vehicle-to-vehicle (V2V) communication is compared against channel measurement results collected during a V2V channel measurement campaign using a channel sounder. Channel metrics such as channel gain, delay and Doppler spreads, eigenvalue (EV) distribution, and antenna correlations are derived from the ray-tracing (RT) simulations as well as from the measurement data obtained from two different measurements in an urban four-way intersection. The channel metrics are compared separately for line-of-sight (LOS) and non-LOS (NLOS) situations. Most power contributions arise from the LOS component (if present) as well as from multipaths with single bounce reflections. Measurement and simulation results of the received power show a very good agreement in the presence of LOS, as most of the received power is carried by the LOS component. In NLOS, the difference is large because the ray-tracer is unable to capture some of the channel characteristics due to the underlying limitations of our ray-based propagation model. Despite the limitations, the model is suitable to characterize some, but not all, of the channel properties in a sufficient manner. We find that the diffuse scattering and multibounced nonspecular reflections must be considered for an accurate prediction of the channel in such a rich scattering environment.

Validation of a non-line-of-sight path-loss model for V2V communications at street intersections

This paper presents the results of an accuracy assessment of a deterministic channel model for vehicle-to-vehicle (V2V) communications. Channel simulations obtained from the ray-tracing model developed by TU Braunschweig are compared to data gathered during the DRIVEWAY V2V channel measurement campaign at 5.6 GHz in the city of Lund in summer 2009. The analysis focuses on PDP and channel gains in an urban four-way intersection scenario. Despite some implementation-based limitations of the ray-tracing model, a very good agreement between simulation and measurement results is achieved. Most relevant power contributions arising from multiple-bounce specular reflections as well as from single-bounce non-specular reflections are captured by the deterministic model. We also discuss the question to what extent roadside obstacles like traffic signs, parked cars or lamp posts have to be considered when characterizing the V2V channel.

Measurement-Based Analysis: The Effect of Complementary Antennas and Diversity on Vehicle-to-Vehicle Communication

Vehicle-to-vehicle (V2V) communication is a challenging but fast-growing technology. It has the potential to enhance road safety by helping the driver to avoid collisions during basic maneuvers such as crossing street intersections, changing lanes, merging on a highway, and driving safely in blind turns. The significance of V2V safety applications increases further where the visual line-of-sight (LOS) is unavailable because of buildings, roadside sound berms, or small hills at an intersection point of two or more roads intersecting at a certain angle, e.g., merging lanes, the entrance or exit ramps on a highway, or four-way street intersections. The reliability of V2V safety applications, which use IEEE 802.11p [1] as the underlying communication technology, highly depends on the quality of the communication link, which relies on the properties of the propagation channel. Therefore, understanding the properties of the propagation channel becomes extremely important.

Line-of-Sight Obstruction Analysis for Vehicle-to-Vehicle Network Simulations in a Two-Lane Highway Scenario

In this paper a non-line-of-sight (NLOS) path-loss and fading model developed for vehicle-to-vehicle (V2V) communication at 5.9 GHz is validated with independent and realistic measurement data. The reference NLOS model is claimed to be flexible and of low complexity, and incorporates specific geometric aspects in a closed-form expression. We validated the accuracy of the model with the help of realistic channel measurements performed in selected street intersections in the city of Lund and Malmö, Sweden. The model fits well, with a few exceptions, to the measurements. Those are in turn made in different intersections having variable geometries and scattering environments. It is found that the model can be made more general if an intersection dependent parameter, that depends on the property and number of available scatterers in that particular intersection, is included in the model.

Statistical Modeling and Estimation of Censored Pathloss Data

In vehicle-to-vehicle (V2V) communication systems, the antennas are prone to shadowing, and the antenna gain is dissimilar even for same antenna elements if mounted at different positions on the car. This letter investigates the impact of antenna placement based on channel measurements performed with four omnidirectional antennas mounted on the roof, bumper, windscreen, and left-side mirror of the transmitter and receiver cars. Results suggest to use antennas with complementary characteristics, e.g., antennas on each side, mounted on the roof and bumper, to exploit diversity and decrease the effect of shadowing.