Vicent M. Rodrigo-Peñarrocha

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.

Fading Evaluation in the 60GHz Band in Line-of-Sight Conditions

An exhaustive analysis of the small-scale fading amplitude in the 60 GHz band is addressed for line-of-sight conditions (LOS). From a measurement campaign carried out in a laboratory, we have estimated the distribution of the small-scale fading amplitude over a bandwidth of 9 GHz. From the measured data, we have estimated the parameters of the Rayleigh, Rice, Nakagami-m, Weibull, and - distributions for the small-scale amplitudes. The test of Kolmogorov-Smirnov (K-S) for each frequency bin is used to evaluate the performance of such statistical distributions. Moreover, the distributions of the main estimated parameters for such distributions are calculated and approximated for lognormal statistics in some cases. The matching of the above distributions to the experimental distribution has also been analyzed for the lower tail of the cumulative distribution function (CDF). These parameters offer information about the narrowband channel behavior that is useful for a better knowledge of the propagation characteristics at 60 GHz.

Low-Loss Circularly Polarized Periodic Leaky-Wave Antenna

This letter presents a periodic leaky-wave array antenna with circular polarization at millimeter-wave frequencies. The antenna is designed on the low-loss planar Goubau transmission line to maximize the radiation efficiency of the antenna. The unit cell of the array is formed by four dipoles located on both faces of the Goubau lines substrate. A prototype has been fabricated and measured. Experimental results show an impedance bandwidth above 15% for |S11| <; -10 dB and a 3-dB axial-ratio bandwidth of 7.6%. The radiation efficiency and maximum gain of the prototype are above 90% and 15.6 dBi, respectively, from 38 to 41 GHz. The maximum gain and the minimum axial ratio present the characteristic steering behavior of leaky-wave antennas.

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).

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.

Algorithm for currents reconstruction using the FFT iterative method and a lattice of the spectrum

The knowledge of the equivalent currents of an antenna could become one of the most important aspects during its design process. This information can be obtained by knowing the currents obtained from the radiated field of the antenna. As this is usually measured in the near field region, is necessary to obtain a relationship between near field and equivalent currents. Basically, the process described in a previous paper obtains the far field from the near field measurements and with this far field calculates the plane wave spectrum. If this process is followed the maximum resolution achievable is 1 lambda. The reason for such a poor resolution is the use of only the visible spectrum. However, we need this non-visible spectrum to achieve a better resolution. For this reason we propose in this paper the combination of two techniques to obtain the non-visible spectrum. These techniques are the fft iterative method and the second technique is using the lattice of the spectrum to improve results. The use of both increases considerably the resolution of the reconstruction

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.

On the Bivariate Nakagami-Lognormal Distribution and Its Correlation Properties

The bivariate Nakagami-lognormal distribution used to model the composite fast fading and shadowing has been examined exhaustively. In particular, we have derived the joint probability density function, the cross-moments, and the correlation coefficient in power terms. Also, two procedures to generate two correlated Nakagami-lognormal random variables are described. These procedures can be used to evaluate the robustness of the sample correlation coefficient distribution in both macro- and microdiversity scenarios. It is shown that the bias and the standard deviation of this sample correlation coefficient are substantially high for large shadowing standard deviations found in wireless communication measurements, even if the number of observations is considerable.

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.