Armando Rocha

Estimation of the Number of Clusters in Multipath Radio Channel Data Sets

This communication deals with the grouping of the multipath radio channel components. The estimation of the number of clusters that a given data set exhibits is an important step in channel modeling and parameterization. We present a performance assessment of several cluster validity indices using Monte Carlo simulations. Synthetic channels were generated by means of the extended Saleh-Valenzuela model and used as input to a clustering algorithm which outputs several solutions with different number of clusters. The cluster validity indices allow the selection of the best solution. Finally, an example is presented where the best performing indices were applied to an experimental data set.

Joint results of long-term earth-space propagation experiments at 20-GHz in Canada and Europe

Propagation effects such as rain or clouds attenuation cause deeper fades in the Ka-band than at lower frequencies. In this collaborative paper, the main results of four long-term Ka-band propagation campaigns are presented. The experiments are carried out in Ottawa, Canada; Aveiro, Portugal; Madrid, Spain; and Toulouse, France. Attenuation statistics are derived from satellite beacon data collected over 6 years at Aveiro, 5 years at Ottawa and Madrid and 2 years at Toulouse. Multi-year measurements allow the production of more stable statistics reflecting the long-term behavior of propagation phenomena and to investigate its year-to-year variability. The beacon signal data was monitored and collected on a continuous basis over the whole measurement period. After a brief introduction of the experiments, rain rate and excess attenuation results are discussed, first for a common measurement period and later for the whole database available. Seasonal attenuation statistics for Ottawa and Aveiro are compared. Finally, fade duration and fade slope statistics derived at three locations are presented and discussed.

Joint Statistics of Rain Attenuation at 20 GHz in Madrid and Aveiro

Rain attenuation is the most severe propagation impairment affecting radiowave signals in the Ka-band. The use of these frequencies for satellite communication systems is facilitated by the implementation of fade mitigation techniques (FMTs). Spatial correlation of rain rate and rain attenuation for distances of several hundred kilometers has been rarely characterized in experiments, however it is relevant for site diversity studies, with distances in this range, and for the design and operation of multibeam satellite systems with shared on-board radio resources. In this letter, experimental results regarding joint statistics of rain and rain attenuation are presented for Madrid, Spain, and Aveiro, Portugal, located 420 km apart. These results have been achieved from two years of simultaneous measurements of the Eutelsat HB-6 Ka-band beacon at 19.7 GHz. It is shown that high-attenuation events are independent, whereas there is some correlation for low-attenuation levels.

Software Tools for Teaching Wave Propagation in Transmission Lines [Education Corner]

This article describes a demonstrator comprising four software tools that was developed to assist the teaching of some fundamental concepts about wave propagation in transmission lines and that can also serve as a student virtual laboratory. The tools, developed in MATLAB, are easy to use and offer a new approach, which intends to explore the physical basis of transmission line theory, including the transmission line model as a ladder inductor-capacitor circuit, the concept of traveling waves and their interaction in the transmission line, the nature of transmission line input impedance, and impedance matching issues. The tools are made available online to be used, modified, or improved by the community.

A 5 GHz LNA for a radio-astronomy experiment

The paper describes the project, implementation and test of a C-band (5GHz) Low Noise Amplifier (LNA) using new low noise Pseudomorphic High Electron Mobility Transistors (pHEMTS) from Avago. The amplifier was developed to be used as a cost effective solution in a receiver chain for Galactic Emission Mapping (GEM-P) project in Portugal with the objective of finding affordable solutions not requiring strong cryogenic operation, as is the case of massive projects like the Square Kilometer Array (SKA), in Earth Sensing projects and other niches like microwave reflectometry. The particular application and amplifier requirements are first introduced. Several commercially available low noise devices were selected and the noise performance simulated. An ultra-low noise pHEMT was used for an implementation that achieved a Noise Figure of 0.6 dB with 13 dB gain at 5 GHz. The design, simulation and measured results of the prototype are presented and discussed.

Earth-satellite ice depolarization revisited: New data

Depolarization has not been seen as an important impairment for Ka band (and above) telecommunication systems due to increased rain attenuation with respect to Ku-band. The most important databases on crosspolar discrimination (XPD) at Ka-bands were collected during the Olympus campaign, mainly at several sites in Northern Europe.

Detailed Analysis of Directional Radio Channel Measurements

Physical models describe the radio channel by characterizing the multipath propagation. Also, measurements are frequently employed in the establishment of such models, or for tuning the existing ones. This paper presents a systematic analysis of double-directional radio channel data, obtained by combining two single-input multiple-output measurements (forward and reverse), each, containing the channel frequency responses at the locations of a virtual rectangular antenna array. The measurement setup uses a vector network analyzer, which, together with the adopted data processing, represents an affordable, but very consistent, alternative to more sophisticated equipment, given that, a physical analysis of the identified channel contributions provided sensible results. The study comprised three main steps: 1) the characterization of each single-directional channel by employing a high-resolution algorithm to obtain the parameters of a chosen number of multipath components (MPCs); 2) the classification of the obtained MPCs in a twofold way, first, by grouping MPCs using clustering tools, and, second, by classifying these clusters according to their type of interaction with the propagation scenario; and 3) the extraction of typical values for the number of clusters, the number of MPCs per cluster, rules for power decay, and statistical distributions for inter and intracluster delays and azimuths.

Results from a First Approach to a Point-Scatter Simulator for MIMO Radio Channel Modeling

This paper presents some results obtained from a first approach to a point-scatter simulator for multiple-input multiple-output (MIMO) radio channel modeling. Specifically, we present the comparison of capacity obtained using the point- scatter simulator with that obtained with the Kronecker model. Capacity results obtained from measured propagation data are also presented. Ideas to enhance the simulator, which include the development of a statistical-based generative channel model for MIMO systems, are discussed.

Scintillation Prediction Models Compared with One Year of Measurements in Aveiro, Portugal

The paper presents new scintillation statistical results measured at Ka-band in the Iberian peninsula, where data is relatively scarce. The receiver is installed at Aveiro (8degW, 40.5degN), Portugal, and is pointed to HotBird-6 satellite. The data was collected at a rate of 8 S/s during one full year. Results for cumulative distribution of scintillation amplitude (fades and enhancements), scintillation intensity and diurnal variation are presented. The performance of some well known models in the literature - ITU, Karasawa and van de Kamp - are evaluated against the experimental data.

Ka band Scintillation Results: Meteorological Dependencies and Modelling

The paper presents results of one year ka-band scintillation measurements at a new site, Aveiro, Portugal. A co-located meteorological station made available concurrent measurements of ambient temperature, relative humidity and wind velocity. The available has been investigated from the point of view of long term modeling, meteorological dependence of scintillation parameters and parameters distributions. Results on the long term correlation between scintillation intensity and wind speed, temperature and refractive index are presented. The most interesting are those concerning long term correlation in a day hour mean basis extended over all year. It seems that there is good correlation with some parameter pointing to turbulence mechanisms that are strongly hour dependent. One interesting aspect is also a hysteresis in the daily intensity and wind velocity that is discussed together with some possible explanations and further data analysis needs to access the reasons. Also some results of fades, enhancements and scintillation intensity distributions are presented. With those results was possible to verify that exists a small difference between fades and enhancements. (4 pages)