Fernando Machado

Distributed Sensors Network Applied to the Rain Impairment Study on Radiocommunication Systems

The performance of millimetre wavelength wireless access network technologies are significantly impaired by rain effects. To evaluate the rain effects over a communication system, it is essential to know the temporal and spatial evolution of rainfall rate. For this reason it is necessary to develop an experimental network that provides sufficient data to study and establish means to prevent and compensate for the detrimental effects of rain. In this paper, an experimental rain gauge network is presented. This network comprises weather stations capable of measuring rainfall rate, temperature and humidity. The paper describes first the experimental network for automatic data acquisition as a system based in a distributed process. The design of the experimental network is explained in detail and finally the interest for millimetre wavelength applications is pointed out.

Hybrid Distributed Instrumentation Network for Integrating Meteorological Sensors Applied to Modeling RF Propagation Impairments

Rainfall rate is the main cause of fades in the frequency bands above 10 GHz. To optimize the planning of satellite and terrestrial radio communication systems operating on these frequency bands, it is essential to have a detailed knowledge of the temporal and spatial distributions of the rainfall rate. For this reason, it is necessary to develop experimental networks, which provide adequate data to study, prevent, and compensate the rain fade. In this paper, an experimental instrumentation network is presented. This network comprises weather stations that are capable of measuring rainfall rate, temperature, and humidity; a weather radar; and three radio links. This paper first introduces the rationale and the state of the art in meteorological sensors and describes the experimental network for automatic data acquisition as a distributed process system. The design of the experimental network is explained in detail. Finally, the interest in millimeter wavelength for broadband applications is outlined, and some research lines from the collected data are presented.

An enhanced Markov chain based model for the narrowband LMS channel in built-up areas

In this paper, a technique to derive the transition probabilities for a Markov chain model for the land mobile satellite (LMS) channel in built-up areas is presented. This technique contributes to improving empirically derived parameters in that it can account for elevation and street orientation effects as well as building density. Physical-statistical or ‘virtual city’ techniques are used to relate observed edification statistics to signal attenuation statistics. This methodology can also be applied to generating correlated time-series for simultaneous links to a constellation of satellites from the same mobile terminal. The proposed approach also allows the generation of enhanced time-series which take into account diffuse multipath and diffraction effects. Copyright

Combining meteorological radar and network of rain gauges data for space–time model development

SUMMARY Technological developments and the trend to go higher and higher in frequency give rise to the need for true space–time rain field models for testing the dynamics of fade countermeasures. There are many models that capture the spatial correlation of rain fields. Worth mentioning are those models based on cell ensembles. However, the rain rate fields created in this way need the introduction of the time variable to reproduce their dynamics. In this paper, we have concentrated on addressing the time domain effects while we have relied on existing spatial rain field models for creating initial fields, which are propagated (advected) according to proposed models and assumptions, some of which have been drawn from a combined use of a concurrent weather radar and a network of rain gauges. The dynamic modeling presented simulates the advection of a synthetically generated rain field according to dynamic, spatially correlated advection fields extracted from the analysis of weather radar images. Experimental data and model fits have been presented as well. Further ideas on how to improve the realism of the generated dynamic fields have also been presented. Furthermore, the limitations of radar data, especially those related to their limited time resolution, for the required space–time models have been pointed out. These can be overcome by using data from a network of rain gauges. However, it is important to be aware of the similarities and differences between these two sources. A comparative study of these two data sets has also been presented. Copyright r 2009 John Wiley & Sons, Ltd.

A very short distance dynamic diversity experiment

The objective of this experiment is to carry out a study of the rapid fading and enhancements (scintillations), simultaneously experienced by two Ka band receivers 9 metres apart. The signal source is, in this case, the beacon transmission at 20.7 GHz of the UF09 geosynchronous satellite from the US American Defence Department. The receivers are located at the UK Chilbolton Observatory in Hampshire. On-site digital signal processing permits display of the main investigated functions (time series, cross-correlation, power spectral densities, standard deviations, etc.). Fast data storage takes also place on-site, and on-line web control permits remote data monitoring, acquisition and presentation of results. Other data acquired included ground temperature and wind velocity. As regards results, analysis of the running cross-correlation indicates that for a non-negligible amount of time there is a significant negative correlation between the signals of both receivers, permitting to consider some form of dynamic diversity gain over few dBs. Often however, both signals are either hardly correlated (including the case of rain), or reasonably well correlated. This paper summarizes the installation of the receptor, the development of the data acquisition system and the preliminary results.

FPGA-Based Instrument for Satellite Beacon Monitoring on Propagation Experiments

This paper presents the design of an instrument for satellite beacon monitoring based on field programmable gate array (FPGA). The aim of this paper is to receive a beacon transmitted by a satellite in the Ka-band (18-21 GHz), process this signal, and obtain results for propagation studies (attenuation, fading, scintillation, etc.). The analog front-end performs the frequency down-conversion from the Ka-band RF beacon frequency to an intermediate frequency (IF) of 10.7 MHz. This IF signal is processed with the developed FPGA-based beacon detector to obtain the amplitude fluctuations of the received signal. The amplitude data is stored and later processed in a computer to obtain the experimental results (scintillation and rain attenuation measurements). This paper describes in detail the satellite beacon monitoring instrument structure, analyzes the receiver characteristics, and presents some operational test results.

Nowcasting of the Spatiotemporal Rain Field Evolution for Radio Propagation Studies

This paper presents a nowcasting method capable of short-term forecasting the spatiotemporal rain field evolution, based exclusively on the analysis of radar reflectivity data without any a priori assumption on its spatial structure. The method has been developed to be integrated into future foreseen propagation impairment mitigation techniques, which take advantage of the temporal and spatial variability of rain in order to improve significantly the capacity and performance of the next-generation radiocommunication networks, operating at frequencies above 10 GHz . The rain field database used for assessing the nowcasting method consisted of 746 radar images collected by the weather radar located at A Coruña (Northwest Spain) during 25 rain events. The proposed method is made up of three main parts: a procedure that estimates the rain field displacement between two consecutive weather radar images, an algorithm that makes predictions for the next rain field displacement, and an operation that shifts the rain field according to the forecast displacement. The forecast quality of the developed method has been assessed by means of six skill indices common in the literature. Results reveal that the nowcasting method achieves a reasonably good forecast skill.

On the spatial structure of rainfall rate: Merging radar and rain gauge data

This paper extends some first steps given in merging radar and rain gauge data for a better understanding of rainfall rate spatial structure. The study has been performed analyzing spatial correlation between sites within a densely meshed rain gauge network and also with their corresponding pixels in weather radar images.

Applied information system through the interoperability of data interfaces

The objective of the current work is the design and development of a data acquisition, processing and storage system for condition monitoring. This system is used by an application that uses mathematical models for predicting potential failures in the functioning of power electric transformers. Applying data warehouse techniques and virtual instruments, a measurement system was created in four working power transformers of 40 MVA. The application that handles the prediction models was provided with an abstraction of the sensors the authors have called virtual acquisition cards. The acquisition system was designed for being scalable and easily reconfigurable. The prediction application experimented a great reduction in system complexity and development time, being able to focus on the prediction algorithm exclusively

An experimental measuring instrument to characterize partial discharges by sensor fusion

The goal of this research work was the design and implementation of a measurement system that will be used for the partial discharge (PD) characterization in order to assess the condition of paper-oil (PO) insulation systems. In addition, the developed measuring instrument can be used to achieve a deeper understanding of the PD phenomena and their basis. This instrument integrates PD signals simultaneously measured using electric and ultrasonic sensors for making PD detection easier. The post-processing of the data captured from theses sensors allows a PD characterization based on the identification of the PD root cause and the localization of its source site. The performance of the proposed instrument was evaluated by sessions of controlled PD tests in the laboratory.