Lorenzo Rubio

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.

Random access channel (RACH) parameters optimization in WCDMA systems

The random access procedure, defined by the 3rd Generation Partnership Project (3GPP), is based on a slotted Aloha approach with fast acquisition indication, that is carried out in uplink by the random access channel (RACH) and acquisition indicator channel (AICH) in the downlink. In this paper, the RACH performance in a single omni cell under shadowing and fast-fading conditions is analyzed. An optimization procedure is performed to obtain, according to random access delay and random access success ratio, optimal values for RACH radio parameters such as the power offset between consecutive preambles (/spl Delta//sub pp/) and the preamble target signal to interference ratio (SIR/sub t/). Furthermore, curves of preamble signal to interference ratio (SIR), measured at base station point, are presented.

Estimation of the Composite Fast Fading and Shadowing Distribution Using the Log-Moments in Wireless Communications

In this work, we propose a framework to obtain estimators from a variety of distributions used in composite fast fading and shadowing modeling with applications in wireless communications: the Suzuki (Rayleigh-lognormal), Nakagami-lognormal, K (Rayleigh-gamma), generalized-K (Nakagami-gamma) and α-μ (generalized gamma) distributions. These estimators are derived from the method of moments of these distributions in logarithmic units, usually known as log-moments. The goodness-of-fit of these estimators to experimental distributions has been checked from a measurement campaign carried out in an urban environment. Moreover a new method to separate fast fading and shadowing based on the Rathgeber procedure is proposed. The results conclude that the best-fitting distribution to the measurements is the Nakagami-lognormal. Also, the α-μ distribution provides an acceptable matching with the advantage of its simplicity.

Analytical Approach to Model the Fade Depth and the Fade Margin in UWB Channels

In this paper, the variations of the ultrawideband (UWB) channel power as a function of the channel bandwidth are investigated. An analytical approach to characterize the fade depth and the fade margin due to small-scale fading in indoor environments is proposed. The approach is based on the IEEE 802.15.4a ultrawideband channel model and the assumption that the channel power can be modeled by a Gamma distribution. This analytical approach is checked by comparison with results derived through Monte Carlo simulations. The results show that the fade depth and the fade margin are closely related to the channel bandwidth. This analytical approach can be used to design and implement UWB communications systems.

Generation of bivariate Nakagami-m fading envelopes with arbitrary not necessary identical fading parameters

In this paper, a generation procedure of two correlated Nakagami-m random variables for arbitrary fading parameters values (not necessary identical) is described. For the generation of two correlated Nakagami-m samples, the proposed method uses the generalized Rice distribution, which appears in the conditional distribution of two correlated Nakagami-m variables. This procedure can be applied to simulate diversity systems such as selection combiners, equal-gain combiners, and maximal-ratio combiners as well as multiple-input multiple-output (MIMO) receiver systems, in Nakagami-m channels. Copyright

The use of semi-deterministic propagation models for the prediction of the short-term fading statistics in mobile channels

In this paper, a semi-deterministic propagation model for the prediction of short-term fading statistics in urban mobile cellular systems is presented. The model is based on digital map information and is also used to predict coverage areas. The short-term fading is modelled by the Nakagami distribution, where the two parameters defining the distribution for a local area around the mobile position can be obtained from the available digital map information of the urban area. Computer simulation results and measurement campaigns are compared, showing that the best approximation to the probability density function of the short-term fading in mobile urban channels is a Nakagami distribution.

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.

Performance of dual selection combiners over correlated Nakagami-m fading with different fading parameters

This letter presents infinite series expressions for the outage probability, the probability density function, the average error probability for binary modulations, and the average signal-to-noise ratio of dual selection combiners over correlated fading with arbitrary fading parameters at each input of the combiner. The outage probability is calculated for both thermal noise and interference-limited scenarios. The results obtained for the outage probabilities specified for identical fading parameters at both branches of the combiner are contrasted with the results of other studies in the literature

The UWB-OFDM Channel Analysis in Frequency

In this paper, the ultra-wideband channel with orthogonal frequency division multiplexing (UWB-OFDM) is analyzed in the frequency domain. For UWB-OFDM channels with log-normal fading in the time domain, we show that the amplitude of each subcarrier can be approximated by a Nakagami-m random variable, where the fading parameter, the mean power and the correlation coefficient are expressed in terms of the following parameters: time arrival of the clusters, inter-arrival time of rays inside clusters, and power decay constants of rays and clusters.

On Simple Estimators of the α-μ Fading Distribution

In this letter, new estimators of the α-μ distribution are derived based on the skewness of the logarithmic α-μ distribution using the moments method. This distribution has been recently proposed to model the received field strength in nonlinear propagation mediums. Therefore, simple and computationally efficient estimators are required to infer the parameters of the received signal amplitude distribution in nonlinear wireless communication propagation channels. The performance of these new estimators is compared to that obtained with the estimators calculated with the moments method of the α-μ distribution by solving numerically transcendental equations. These estimators are easily evaluated with simple expressions.