73 research outputs found
Empirical Evaluation of the Impact of Wind Turbines on DVB-T Reception Quality
[EN] This paper describes the results of two extensive measurement campaigns for evaluating the potential impact of scattered signals from wind turbines on terrestrial DTV reception quality in the UHF band. A detailed description of the different propagation channels encountered is provided. Furthermore, empirical threshold carrier-to-noise requirements for Quasi Error Free reception in the DVB-T system in the area of influence of a wind farm are presented, and the situations where a significant degradation can be found are identified and characterized.This work has been partially supported by the UPV/EHU GIC 07/110-IT-374-07, by the Basque Government under both the SAIOTEK program and the program for the training of the researcher staff (BFI08.230), by the Spanish Ministry of Science and Innovation under the project NG-RADIATE, TEC2009-14201, and by the Spanish Ministry of Industry, Tourism and Trade under the project ENGINES, TSI-020400-2010-188. ENGINES project is under the Celtic Initiative (Celtic Label CP7-005)
A Measurement-based Multipath Channel Model for Signal Propagation in Presence of Wind Farms in the UHF Band
[EN] Scattering signals on wind turbines may lead to
degradation problems on the communication systems provided
in the UHF band, such as terrestrial television broadcasting,
broadband wireless systems or public safety services. To date,
despite the continuous requests from the International Telecommunication
Union for studies on this field, no channel model has
been developed to characterize signal propagation under these
particular conditions. In response to this necessity, this paper
presents a complete Tapped Delay Line (TDL) channel model
to characterize multipath propagation in presence of a wind
farm, including novel scattering modeling and Doppler spectra
characterization. As proved later, this channel model, which
is based on both theoretical development and empirical data
obtained in the surroundings of a real wind farm, is adaptable
to the particular features of any case under study: wind turbine
dimensions, working frequency, and relative location of the wind
farm, transmitter and receivers.This work was supported in part by the European Union FP7 (grant agreement n 296164), by the Spanish Ministry of Economy and Competitiveness (project TEC2012-32370), and by the Basque Government (SAIOTEK program)
An Empirical Comparative Study of Prediction Methods for Estimating Multipath Due to Signal Scattering from Wind Turbines on Digital TV Services
[EN] Several authors have theoretically studied the
effect of wind turbines on the propagation of electromagnetic
waves in the UHF band. The International Telecommunication
Union also proposes a simplified model to evaluate the impact
caused to television reception by a wind turbine in the
Recommendation ITU-R BT.805. This paper presents an
empirical study of the above mentioned prediction methods for
estimating signal scattering from wind turbines in the UHF band,
comparing predicted values with empirical data obtained from a
DTV measurement campaign carried out in Spain. As signal
scattering is independent of the transmission standard or
modulation, the results are applicable to any broadcasting and
wireless communication signals in the UHF band that may be
affected by the multipath interference caused by a wind farm.This work was supported in part by the Basque Government under both the SAIOTEK program and the program for the training of the researcher staff (BFI08.230)
Empirical Doppler Characterization of Signals Scattered by Wind Turbines in the UHF Band under Near Field Condition
Time variability of the scattering signals from wind turbines may lead to degradation problems on the communication systems provided in the UHF band, especially under near field condition. In order to analyze the variability due to the rotation of the blades, this paper characterizes empirical Doppler spectra obtained from real samples of signals scattered by wind turbines with rotating blades under near field condition. A new Doppler spectrum model is proposed to fit the spectral characteristics of these signals, providing notable goodness of fit. Finally, the effect of this kind of time variability on the degradation of OFDM signals is studied
Corrección del modelo de propagación en redes de televisión digital terrestre en entornos urbanos
This article presents an ideal propagation model for the design of Digital Terrestrial Television (DTT) networks in Bogotá City. Here was developed, evaluated and compared three propagation models commonly used for the design of this type of networks; these are the methods Stanford University Interim (SUI), Xia-Bertoni and Okumura-Hata. Those were chosen because they allow to calculate the propagation losses over the UHF band and the cartographic information required to estimate the losses by diffraction is not high precision. Here, we found two of the selected models are close to the actual model in a range of 10-15 dB. So, all the models were adjusted and corrected by MATLAB in order to obtain an accurate estimate of signal propagation losses. The models were evaluated with statistical criteria of significance such as correlation coefficient, mean square error, standard deviation and so on [1]. As a result, both Okumura-Hata and Xia-Bertoni models were found to fit easily into the real model, however, the error of the Xia-Bertoni model is smaller compared to the Okumura model.Este artículo presenta un modelo de propagación idóneo para el diseño de redes Televisión Digital Terrestre (TDT) en la ciudad de Bogotá. En el desarrollo se encuentra la evaluación y comparación de tres modelos de propagación comúnmente usados para el diseño de este tipo de redes; estos son los métodos Stanford University Interim (SUI), Xia-Bertoni y Okumura-Hata, escogidos porque permiten calcular las pérdidas de propagación sobre la banda UHF y la información cartográfica que requieren para estimar las pérdidas por difracción no es de alta precisión. Aquí se determina que dos de los modelos escogidos son cercanos al modelo real en un rango de 10 – 15 dB. Dado esto, se ajustaron y se efectuó una corrección, por medio de Matlab, a los todos los modelos con el fin de obtener una acertada estimación de pérdidas en la propagación de la señal. Los modelos fueron evaluados con criterios estadísticos de significancia como lo son el coeficiente de correlación, error medio cuadrado, desviación estándar etc. [1] Como resultado se determinó que tanto el modelo Okumura-Hata como el Xia-Bertoni se ajustaban fácilmente al modelo real, sin embargo, el error del modelo Xia Bertoni es menor en comparación con Okumura
Modelo de canal para caracterizar la señal dispersada por un parque eólico en la banda UHF e influencia sobre la calidad de servicio de DVB-T
288 p. : il.[ES]La presencia de un parque eólico provoca una serie de efectos sobre las señales electromagnéticas que pueden dar lugar a una degradación de la calidad de los servicios de telecomunicaciones proporcionados en sus cercanías. En lo que respecta a la difusión de televisión, el efecto de un parque eólico en la difusión de televisión digital no había sido determinado hasta ahora.Por otra parte, la evaluación de la posible degradación de estos servicios se ha realizado tradicionalmente mediante modelos que caracterizan la señal dispersada por las aspas del aerogenerador. Estos modelos clásicos de dispersión no contemplan ni la contribución del mástil a la señal dispersada, ni la variabilidad temporal de la señal dispersada debida a la rotación de las palas, ni la influencia conjunta de un parque eólico compuesto por varias máquinas.En este contexto, se plantea el primero de los objetivos principales de esta tesis: la evaluación empírica de la degradación causada en la recepción de señales de televisión digital DVB-T debida a la presencia de un parque eólico. Del estudio realizado, basado en medidas de campo, se concluye que las condiciones de recepción más críticas se dan en la zona de backscattering, donde la propagación responde a las características de un canal multitrayecto discreto variante con el tiempo.El segundo objetivo principal de esta tesis se centra en la propuesta un nuevo modelo de canal para caracterizar la propagación multitrayecto típica en los alrededores de un parque eólico en esta banda. Este modelo de canal se adapta a las condiciones particulares de cada caso en estudio: posición relativa transmisor-turbina-receptor, dimensiones del aerogenerador, velocidad máxima de rotación de las aspas, características de los sistemas radiantes del transmisor y receptor, y frecuencia de trabajo.[EN]The presence of a wind farm causes several effects on the electromagnetic
signals that may degrade the quality of the telecommunication services provided
nearby.
In regard to television broadcasting, these effects are notable for the analogue
signal. However, a potential impact of a wind farm on digital television
broadcasting had not yet been assessed.
Apart from that, the evaluation of the potential degradation on these services
has been traditionally carried out by means of scattering models that only account
for the signal scattered by the blades of a wind turbine. These classic models do
not consider neither the mast contribution to the scattered signal nor the time
variability due to the blade rotation or the joint influence of a wind farm composed
of several turbines.
In this context, the first of the two main objectives of this thesis is the empirical
evaluation of the degradation caused to the DVB‐T digital television signals
reception due to the presence of a nearby wind farm. From this
measurement‐based study, it can be concluded that it is in the backscattering
region where the most critical reception conditions are encountered. In this zone,
the propagation channel can be characterized by a discrete time‐varying multipath
channel.
Therefore, in order to determine future possible degradations on the services
provided in the UHF band, the second main objective of this thesis focuses on
proposing a new channel model to characterize the multipath propagation typical
of the area surrounding a wind farm. This channel model is adaptable to the
particular features of each case under study: relative position transmitter‐wind
turbine‐receiver, wind turbine dimensions, maximum rotation rate, characteristics
of the transmitter and receiver radiating systems, and working frequency.
In this way, the results obtained in this research work give answer to the
studies requested by the International Telecommunications Union since the first
cases of impact were detected[EUS]Parke eolikoek hainbat efektu eragiten dute seinale elektromagnetikoetan eta,
ondorioz, zenbait kasutan, inguruan eskaintzen diren telekomunikazio zerbitzuek
kalitatearen degradazioa jasan dezakete.
Telebistari dagokionez, efektu hauek nabarmenak dira seinale analogikoaren
kasuan. Aitzitik, parke eolikoek telebista digitalean izan dezaketen eragina ez da
oraindik zehaztu.
Bestalde, oraindaino telebista zerbitzuek izandako inpaktuaren ebaluazioa
sakabanatze-ereduen bidez egin da. Sakabanatze-eredu klasiko hauek palek
sakabanatzen duten seinalea baino ez dute adierazten; eta horrenbestez, ez dute
kontuan hartzen dorreak sakabanatzen duen seinalea, ez besoen errotazio
mugimenduak eragindako denbora aldakortasuna, ezta hainbat aerosorgailuz
osatutako parkearen eragin bateratua ere.
Testuinguru honetan, ikerkuntza lan honen lehen helburu nagusia definitzen
da: parke eoliko batek DVB-T sisteman eragin dezakeen harrera-degradazioaren
ebaluazio enpirikoa egitea. Neurketetan oinarritutako analisi honetatik, harrerabaldintza
zailenak backsckattering delako eremuan gertatzen direla
ondorioztatzen da, non hedapenak Ibilbide anitzeko eredua jarraitzen duen. Eredu
honen portaera denborarekin aldakorra izango da palen errotazio mugimenduaren
ondorioz.
Horrez gain, UHF bandan igorritako zerbitzuetan gerta daitezkeen
degradazioak aurreikusi ahal izateko, tesiaren bigarren helburua zehazten da:
parke eoliko baten inguruan sortutako hedapen tipikoa deskribatzen duen kanal
eredu berria proposatzea. Kanal eredu hau aztergai dauden kasu guztien baldintza
partikularretara moldatzen da, eta kontuan hartzen du, besteak beste:
transmisore-turbina-hargailu arteko kokapen erlatiboa, aerosorgailuaren tamaina,
palen errotazio gehienezko abiadura, transmisore eta hargailuaren antenen
ezaugarriak, eta frekuentzia.
Tesi honetan lortutako emaitzei esker, lehenengo kasuak antzeman zirenetik
Telekomunikazioen Nazioarteko Batasunak proposatutako ikerketa eskariei
erantzuna ematen zaie.Tesis financiada con beca del Programa de Formación de Personal Investigador del Departamento de Educación, Universidades e Investigación (BFI08.230) del Gobierno Vasco.
Colaboración del Communications Research Centre (CRC) de Canadá a través del Dr. Yiyan Wu, Adivic Technology co., Abertis Telecom, Itelazpi y Eólicas de Euskadi (hoy Iberdrola Renovables
Solutions for New Terrestrial Broadcasting Systems Offering Simultaneously Stationary and Mobile Services
221 p.[EN]Since the first broadcasted TV signal was transmitted in the early decades of
the past century, the television broadcasting industry has experienced a series of
dramatic changes. Most recently, following the evolution from analogue to digital
systems, the digital dividend has become one of the main concerns of the
broadcasting industry. In fact, there are many international spectrum authorities
reclaiming part of the broadcasting spectrum to satisfy the growing demand of
other services, such as broadband wireless services, arguing that the TV services
are not very spectrum-efficient.
Apart from that, it must be taken into account that, even if up to now the
mobile broadcasting has not been considered a major requirement, this will
probably change in the near future. In fact, it is expected that the global mobile
data traffic will increase 11-fold between 2014 and 2018, and what is more, over
two thirds of the data traffic will be video stream by the end of that period.
Therefore, the capability to receive HD services anywhere with a mobile device is
going to be a mandatory requirement for any new generation broadcasting system.
The main objective of this work is to present several technical solutions that
answer to these challenges. In particular, the main questions to be solved are the
spectrum efficiency issue and the increasing user expectations of receiving high
quality mobile services. In other words, the main objective is to provide technical
solutions for an efficient and flexible usage of the terrestrial broadcasting spectrum
for both stationary and mobile services.
The first contributions of this scientific work are closely related to the study of
the mobile broadcast reception. Firstly, a comprehensive mathematical analysis of
the OFDM signal behaviour over time-varying channels is presented. In order to
maximize the channel capacity in mobile environments, channel estimation and
equalization are studied in depth. First, the most implemented equalization
solutions in time-varying scenarios are analyzed, and then, based on these existing
techniques, a new equalization algorithm is proposed for enhancing the receivers’
performance.
An alternative solution for improving the efficiency under mobile channel
conditions is treating the Inter Carrier Interference as another noise source.
Specifically, after analyzing the ICI impact and the existing solutions for reducing
the ICI penalty, a new approach based on the robustness of FEC codes is
presented. This new approach employs one dimensional algorithms at the receiver
and entrusts the ICI removing task to the robust forward error correction codes.
Finally, another major contribution of this work is the presentation of the
Layer Division Multiplexing (LDM) as a spectrum-efficient and flexible solution
for offering stationary and mobile services simultaneously. The comprehensive
theoretical study developed here verifies the improved spectrum efficiency,
whereas the included practical validation confirms the feasibility of the system and
presents it as a very promising multiplexing technique, which will surely be a strong
candidate for the next generation broadcasting services.[ES]Desde el comienzo de la transmisión de las primeras señales de televisión a
principios del siglo pasado, la radiodifusión digital ha evolucionado gracias a una
serie de cambios relevantes. Recientemente, como consecuencia directa de la
digitalización del servicio, el dividendo digital se ha convertido en uno de los
caballos de batalla de la industria de la radiodifusión. De hecho, no son pocos los
consorcios internacionales que abogan por asignar parte del espectro de
radiodifusión a otros servicios como, por ejemplo, la telefonía móvil, argumentado
la poca eficiencia espectral de la tecnología de radiodifusión actual.
Asimismo, se debe tener en cuenta que a pesar de que los servicios móviles no
se han considerado fundamentales en el pasado, esta tendencia probablemente
variará en el futuro cercano. De hecho, se espera que el tráfico derivado de
servicios móviles se multiplique por once entre los años 2014 y 2018; y lo que es
más importante, se pronostica que dos tercios del tráfico móvil sea video streaming
para finales de ese periodo. Por lo tanto, la posibilidad de ofrecer servicios de alta
definición en dispositivos móviles es un requisito fundamental para los sistemas de
radiodifusión de nueva generación.
El principal objetivo de este trabajo es presentar soluciones técnicas que den
respuesta a los retos planteados anteriormente. En particular, las principales
cuestiones a resolver son la ineficiencia espectral y el incremento de usuarios que
demandan mayor calidad en los contenidos para dispositivos móviles. En pocas
palabras, el principal objetivo de este trabajo se basa en ofrecer una solución más
eficiente y flexible para la transmisión simultánea de servicios fijos y móviles.
La primera contribución relevante de este trabajo está relacionada con la
recepción de la señal de televisión en movimiento. En primer lugar, se presenta un
completo análisis matemático del comportamiento de la señal OFDM en canales
variantes con el tiempo. A continuación, con la intención de maximizar la
capacidad del canal, se estudian en profundidad los algoritmos de estimación y
ecualización. Posteriormente, se analizan los algoritmos de ecualización más
implementados, y por último, basándose en estas técnicas, se propone un nuevo
algoritmo de ecualización para aumentar el rendimiento de los receptores en tales
condiciones.
Del mismo modo, se plantea un nuevo enfoque para mejorar la eficiencia de
los servicios móviles basado en tratar la interferencia entre portadoras como una
fuente de ruido. Concretamente, tras analizar el impacto del ICI en los receptores
actuales, se sugiere delegar el trabajo de corrección de dichas distorsiones en
códigos FEC muy robustos.
Finalmente, la última contribución importante de este trabajo es la
presentación de la tecnología LDM como una manera más eficiente y flexible para
la transmisión simultánea de servicios fijos y móviles. El análisis teórico presentado
confirma el incremento en la eficiencia espectral, mientras que el estudio práctico
valida la posible implementación del sistema y presenta la tecnología LDM c
ON THE LOCATION-AWARE COOPERATIVE SPECTRUM SENSING IN URBAN ENVIRONMENT
Spectrum sensing is a key enabling technology for cognitive radio networks (CRNs). The main objective of spectrum sensing is to provide more spectrum access opportunities to cognitive radio users without interfering with the operations of the licensed network. Spectrum sensing decisions can lead to erroneous sensing with low performance due to fading, shadowing and other interferences caused by either terrain inconsistency or dense urban structure. In order to improve spectrum sensing decisions, in this paper a cooperative spectrum sensing scheme is proposed. The propagation conditions such as the variance and intensity of terrain and urban structure between two points with respect to signal propagation are taken into consideration. We have also derived the optimum fusion rule which accounts for location reliability of secondary users (SUs). The analytical results show that the proposed scheme slightly outperforms the conventional cooperative spectrum sensing approaches
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Computation of near-field distribution around wind turbines
textIn this work, two approaches for computing the near-field distribution around wind turbines are proposed, including: (1) Huygens Principle and (2) the parabolic equation technique. In order to simplify the problem, the cylinder model is utilized to represent the wind turbines and transform the problem into a two-dimensional case. To make Huygens Principle computationally tractable, several approximations are made based on the problem geometry especially modelling the cylinder as a plate. The expression of the electromagnetic field radiated by the equivalent magnetic current can be analytically solved by the error function. To verify the results, FEKO is utilized to simulate the scattering of infinitely long cylinders using periodic boundary condition (PBC). In order to solve the problem of multiple cylinders, a modified method is derived. For more accurate results, the parabolic equation (PE) technique is utilized to solve this problem, which is usually utilized to solve wave propagation problems. In this case, wide-angle approximation is used to solve the parabolic equation, which can obtain accurate results in a region of up to 45 degrees. Although these two approaches are not full-wave simulation, the calculation time is significantly reduced and the error is acceptable. To further verify the computed results by the parabolic equation technique, two commercial transceivers from Time Domain Corporation are used to measure the field distribution behind a finite-length metal pole. The frequency-domain results are obtained from the measured time-domain results using the fast Fourier transform. It is shown that the computed results by the parabolic equation technique agree well with the measurement results.Electrical and Computer Engineerin
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