Herman Fernández

Path Loss Characterization for Vehicular Communications at 700 MHz and 5.9 GHz Under LOS and NLOS Conditions

In this letter, we present a path loss characterization of the vehicular-to-vehicular (V2V) propagation channel. We have assumed a path loss model suitable for vehicular ad hoc networks (VANETs) simulators. We have investigated the value of the model parameters, categorizing in line-of-sight (LOS) and non-LOS (NLOS) paths. The model parameters have been derived from extensive narrowband channel measurements at 700 MHz and 5.9 GHz. The measurements have been collected in typical expected V2V communications scenarios, i.e., urban, suburban, rural, and highway, for different road traffic densities, speeds, and driven conditions. The results reported here can be used to simulate and design the future vehicular networks.

Experimental UWB Propagation Channel Path Loss and Time-Dispersion Characterization in a Laboratory Environment

The knowledge of the propagation channel properties is an important issue for a successful design of ultrawideband (UWB) communication systems enabling high data rates in short-range applications. From an indoor measurement campaign carried out in a typical laboratory environment, this paper analyzes the path loss and time-dispersion properties of the UWB channel. Values of the path loss exponent are derived for the direct path and for a Rake receiver structure, examining the maximum multipath diversity gain when an all Rake (ARake) receiver is used. Also, the relationship between time-dispersion parameters and path loss is investigated. The UWB channel transfer function (CTF) was measured in the frequency domain over a channel bandwidth of 7.5 GHz in accordance with the UWB frequency range (3.1–10.6 GHz).

Propagation Aspects in Vehicular Networks

Traffic accidents have become an important health and social problem due to the enormous number of fatalities and injuries. The total number of deaths and injuries in the European Union (EU), United States of America (USA) and Japan has been steadily reduced over the last decade. This reduction is mainly attributed to the implementation of a set of road safety measures, such as seat-belt use, vehicle crash protection, traffic-calming interventions and traffic law enforcement. However, the number of accidents has remained uniform due to the increasing number of vehicles and total distance driven (Peden et al., 2004). In addition to passive vehicle safety systems, such as airbags, anti-lock braking system (ABS) and electronic stability control (ESP), new active safety systems have been introduced to improve vehicular safety. To this end, the last decade has witnessed the traffic management industry, engage and promote the integration of information and communications technology (wireless, computing and advanced sensor technologies) into both vehicles and the wider transport infrastructure. These proposals have led to the intelligent transportation system (ITS) concept. At present, different ITS applications have been introduced, such as variable message signs (VMS), located at strategic points (e.g., tunnels and merging highways) or spaced at given distances, to inform drivers about traffic and dangerous situations; automated toll collection systems for highways and parkings; and real-time traffic information broadcasted in the FM radio band. Besides this, onboard ITS applications have improved the assistance and protection mechanisms for drivers: navigation systems, rear and front parking radars, and cameras are extensively used in the vehicle. Vehicles now incorporate sophisticated computing systems, with several sensors interconnected. However, short-range sensors employed in emergency systems, such as forward collision warning and lane keeping assist, are insufficient, specially when these sensors need to extend their communication horizon in emergency cases due to the limitation of their operating range to line-of-sight (LOS) conditions (Vlacic et al., 2001). Therefore, there are safety applications for distance emergency situations, such as blind corners and traffic crossing, where large-range vehicular communication systems are required, e.g., operating rages of about 1000 meters, in both LOS and non-LOS (NLOS) conditions (Gallagher & Akatsuka, 2006). Wireless communications systems which can operate with these constraints are known as cooperative systems on the road. In the cooperative system concept, vehicles and infrastructure exchange safety messages to extend the distance horizon and provide more information in real time to drivers. Cooperative systems involve two

Analysis of Small-Scale Fading Distributions in Vehicle-to-Vehicle Communications

This work analyzes the characteristics of the small-scale fading distribution in vehicle-to-vehicle (V2V) channels. The analysis is based on a narrowband channel measurements campaign at 5.9 GHz designed specifically for that purpose. The measurements were carried out in highway and urban environments around the city of Valencia, Spain. The experimental distribution of the small-scale fading is compared to several analytical distributions traditionally used to model the fast fading in wireless communications, such as Rayleigh, Nakagami-, Weibull, Rice, and distributions. The parameters of the distributions are derived through statistical inference techniques and their goodness-of-fit is evaluated using the Kolmogorov-Smirnov (K-S) test. Our results show that the distribution exhibits a better fit compared to the other distributions, making its use interesting to model the small-scale fading in V2V channels.

Path loss characterization for vehicular-to-infrastructure communications at 700 MHz and 5.9 GHz in urban environments

In this work, we perform a path loss characterization of the vehicular-to-infrastructure (V2I) channel in an urban environment based on a log-distance path loss propagation model. The model parameters have been derived from channel measurements at 700 MHz and 5.9 GHz. The correlation between the path loss exponent and the height of the antenna used in the infrastructure side is investigated. The measurements have been collected in an urban area of Valencia, Spain, under real road traffic conditions.

Investigation of the path loss propagation for V2V communications in the opposite direction

In this work, we investigate the path loss propagation of the vehicular-to-vehicular (V2V) channel when the vehicles are driving in the opposite direction. The investigation is based on narrowband channel measurements at 700 MHz and 5.9 GHz carried out in different environments under real road traffic conditions, i.e., rural, highway, suburban and urban environments. The results show that there is a path loss offset between the forward and reverse directions, which is related to the environment. Also, we provide mean values of the path loss propagation exponent showing that are higher than the values derived when the vehicles are driving in the same direction. These results should be considered for a proper simulation and design of the future V2V communications systems.

Experimental frequency dispersion study of the vehicular-to-vehicular propagation channel

In this work, we perform an experimental study of the received envelope autocorrelation and the power spectrum density (PSD) of the vehicular-to-vehicular (V2V) propagation channel. The coherence time and Doppler spread have been derived from narrowband channel measurements at 5.9 GHz. The measurements have been collected in urban and highway environments under real road traffic conditions. The relationship of the coherence time and Doppler spread between the effective speed of the Tx and Rx is investigated. The values of the coherence time and Doppler spread reported here can be useful for protocols evaluation and future vehicular networks design.

On the applicability of ray-tracing propagation models to V2V-intersection environments

In this work, we analyze the applicability of a geometric-based stochastic (GBS) model based on ray-tracing techniques to vehicular-to-vehicular (V2V) intersections. The accuracy and usefulness of the proposed model is analyzed using simulated results and narrowband channel measurements at 5.9 GHz. The results show that these type of models can be a good choice to evaluate communications protocols and system performance of future vehicular networks.

Small-Scale Fading Analysis of the Vehicular-to-Vehicular Channel inside Tunnels

We present a small-scale fading analysis of the vehicular-to-vehicular (V2V) propagation channel at 5.9 GHz when both the transmitter (Tx) and the receiver (Rx) vehicles are inside a tunnel and are driving in the same direction. This analysis is based on channel measurements carried out at different tunnels under real road traffic conditions. The Rice distribution has been adopted to fit the empirical cumulative distribution function (CDF). A comparison of the factor values inside and outside the tunnels shows differences in the small-scale fading behavior, with the values derived from the measurements being lower inside the tunnels. Since there are so far few published results for these confined environments, the results obtained can be useful for the deployment of V2V communication systems inside tunnels.