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

Source: arXiv

ABSTRACT The vehicle-to-vehicle (V2V) propagation channel has significant implications
on the design and performance of novel communication protocols for vehicular ad
hoc networks (VANETs). Extensive research efforts have been made to develop V2V
channel models to be implemented in advanced VANET system simulators for
performance evaluation. 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 measurements performed in urban and highway
scenarios. The measurement data is separated into three categories,
line-of-sight (LOS), obstructed line-of-sight (OLOS) by vehicles, and non
line-of-sight (NLOS) by buildings, with the help of video information, recorded
during the measurements. It is observed that vehicles obstructing the LOS
induce an additional attenuation of about 10 dB in the received signal power.
We use a Markov chain based state transition diagram to model the transitions
between the LOS, OLOS and NLOS states. Further, sample state transition
intensities based on the measurements and simulated traffic are presented. An
approach to incorporate the LOS/OLOS model into existing VANET simulators is
also provided. Finally, system level VANET simulation results are presented,
which show the difference between the LOS/OLOS model and a channel model based
on Nakagami-m fading.

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    ABSTRACT: We perform an extensive study of cooperative awareness in vehicular communication based on periodic message exchange. We start by analyzing measurements collected on four test sites across Europe. To measure cooperative awareness, we use three metrics: 1) neighborhood awareness ratio; 2) ratio of neighbors above range; and 3) packet delivery rate. Using the collected data, we define a simple model for calculating neighborhood awareness given packet delivery ratio for a given environment. Finally, we perform realistic, large-scale simulations to explore the achievable performance of cooperative awareness under realistic transmit power and transmit rate constraints. Our measurements and simulation results show that: i) above a certain threshold, there is little benefit in increasing cooperative message rate to improve the awareness; higher transmit power and fewer messages transmissions are a better approach, since message delivery is dominated by shadowing. ii) the efficacy of cooperative awareness varies greatly in different environments on both large scale (e.g., 90% awareness is achievable up to 200 m in urban and over 500 m in highway) and small scale (e.g., vehicles in nearby streets can have significantly different awareness); iii) V2V and V2I communication have distinct awareness and interference patterns; iv) each location has a distinct transmit power that achieves high awareness; and v) achieving high awareness levels results in increased interference; therefore, a balance needs to be found between awareness and interference, depending on the specific context. We hope our results will serve as a starting point for designing more effective periodic message exchange services for cooperative awareness.

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May 30, 2014