Littérature scientifique sur le sujet « Broadband Doppler effect »
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Articles de revues sur le sujet "Broadband Doppler effect"
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Albuquerque, Daniel F., José M. N. Vieira, Sérgio I. Lopes, Carlos A. C. Bastos et Paulo J. S. G. Ferreira. « Indoor acoustic simulator for ultrasonic broadband signals with Doppler effect ». Applied Acoustics 97 (octobre 2015) : 140–51. http://dx.doi.org/10.1016/j.apacoust.2015.04.010.
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Zhou, Y., J. Wang et M. Sawahashi. « Downlink Transmission of Broadband OFCDM Systems—Part II : Effect of Doppler Shift ». IEEE Transactions on Communications 54, no 6 (juin 2006) : 1097–108. http://dx.doi.org/10.1109/tcomm.2006.876872.
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Tian, Haopeng, et Benshuai Lyu. « Prediction of broadband noise from rotating blade elements with serrated trailing edges ». Physics of Fluids 34, no 8 (août 2022) : 085109. http://dx.doi.org/10.1063/5.0094423.
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This paper conducts a theoretical investigation into the prediction of broadband trailing-edge noise for rotating serrated blades. Lyu's semi-analytical noise prediction model for isolated flat plates is extended to rotating blades using Schlinker and Amiet's approach and applied to three test applications including a wind turbine, a cooling fan, and an open propeller. The model is validated by comparing the straight edge results with that presented in the work of Sinayoko et al., which shows an excellent agreement. The noise spectra obtained using different-order approximations show that the second-order solution yields a converged result. It is found that trailing-edge serrations can lead to noise reduction in the intermediate- and high-frequency ranges at an observer angle of 45° at low Mach numbers but may lead to noise increase in the intermediate-frequency range at high Mach numbers. The results show that the directivity patterns change due to the use of trailing-edge serrations and the directivity peaks are observed at high frequencies. A detailed analysis on the effects of rotation shows that for low-Mach number applications, the Doppler effect is weak and the peaky directivity pattern is mainly affected by the nonuniform directivity of an isolated flat plate at high frequencies. However, for high-Mach number applications, the Doppler effect is significant and also contributes to the final directivity pattern of rotating blades.
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Khokhlova, Tatiana D., Minho Song, Randall P. Williams, Joo Ha Hwang, Yak-Nam Wang et Oleg A. Sapozhnikov. « Passive and active Doppler methods and metrics to quantify inertial cavitation induced by pulsed focused ultrasound ». Journal of the Acoustical Society of America 152, no 4 (octobre 2022) : A215. http://dx.doi.org/10.1121/10.0016055.
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Inertial cavitation induced by pulses of nonlinearly distorted focused ultrasound (FUS) at moderate intensity can result in mild mechanical disruption of tissue, short of its complete mechanical disintegration—histotripsy. This effect can be used to enhance diffusion of subsequently systemically administered drugs or biologics. Previously, single-element passive cavitation detection (PCD) of broadband noise emissions was successfully used to quantify tissue disruption and enhancement in drug concentration. This metric, however, has limitations: minimal spatial resolution and challenges with calibration when used at large depths in acoustically variable tissue. To address this, we developed a combination of passive and active Doppler-based methods that relied on relative, rather than absolute signal metrics. Specifically, destructive cavitation behaviors were previously linked to substantial motion of the bubbles during the FUS pulse due to acoustic radiation force and shock scattering. This was reflected in the backscattered FUS harmonics as Doppler shift and measurable from PCD. The bubbles were observed to dissolve within milliseconds following each FUS pulse, thus their distribution could be visualized as an area of rapid change via fast plane wave Doppler ensemble following the FUS pulse. The Doppler power distribution was spatially correlated with the area of tissue disruption in the in vivo experiments. [Work supported by NIH R01CA154451, R01EB025187, and R01EB23910.]
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Bonnefous, O., et P. Pesqué. « Time Domain Formulation of Pulse-Doppler Ultrasound and Blood Velocity Estimation by Cross Correlation ». Ultrasonic Imaging 8, no 2 (avril 1986) : 73–85. http://dx.doi.org/10.1177/016173468600800201.
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The Doppler effect is usually described as a frequency shift of the backscattered signals from moving targets with respect to the frequency transmitted. Recently, real-time blood flow imaging has become possible thanks to the development of a new velocity estimator based on phase-shift measurements of successive echoes. However, this method suffers from the well-known limitations of pulse-Doppler instruments. A new formulation is presented which describes the pulse-Doppler effect on the successive echoes from a cloud of moving targets as a progressive translation in time due to the displacement of the scatterers between two excitations. This approach allows us to generate efficiently computer-simulated data in order to evaluate accurately the various processing techniques. Furthermore, it leads to a novel class of velocity estimators in the time domain which measure the time shifts which are proportional to the local blood velocity. Among them, the cross correlation of the received rf signals turns out to be well suited. A local cross-correlation function is first calculated from a consecutive pair of range-gated echoes and the time shift is then determined by searching for the time position with the maximum correlation. The time-correlation technique is shown to provide accurate velocity profiles with broadband transducers. Moreover, the classical velocity limitation of pulse-Doppler is overcome because there is no ambiguity in measuring a time shift instead of a phase shift. These major advantages should make quantitative flow mapping possible and more reliable.
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Zhuravleva, L. M., M. A. Nilov, V. L. Loshkarev et V. V. Levshunov. « Evaluation of the Impact of Doppler Effect on Quality of HSR Radiocommunications ». World of Transport and Transportation 18, no 4 (5 janvier 2021) : 54–71. http://dx.doi.org/10.30932/1992-3252-2020-18-54-71.
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The article proposes a methodology for evaluating radio signal distortions caused by Doppler effect (DE; also, Doppler shift) under the conditions of highspeed train traffic (HSR, high-speed rail). The objective of the work is to develop criteria for assessing quality of radiocommunications with moving objects in HSR environment. For this, a technique is proposed for calculating the probability of an error arising from Doppler effect. A rationale for relevance of the topic is that radiocommunications are used on railways for controlling train traffic and ensuring safety and achieving required quality of radio signals is a major challenge. Quality assessment is especially important for organization of broadband communication channels with locomotive drivers using mobile networks. To solve this problem, a model for assessing quality of radiocommunication influenced by DE is considered. Distortions of signals in a radio channel due to DE are proposed to be estimated using the reduced dispersion of the total error, which consists of two components: dynamic and interference. Calculations of the total reduced signal error and the error probability for speeds above 100 km/h are described. Estimates of the effect of DE on a coherent receiver, in which errors may occur due to changes in duration of radio pulses, are suggested. Effectiveness of the receiver’s automatic frequency control (AFC) system is analysed as a means of challenging DE. For this, the concept of an instantaneous spectrum of parasitic frequency modulation due to DE was introduced and quality of radio communication was calculated using the reduced dispersion of the total error. The efficiency of using AFC has been proven after comparing the evaluations of reception quality with and without AFC in the form of the ratio of error probabilities. The features of the use of mobile communications on railways under the conditions of DE are formulated.
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Orta, Adil Han, Mathias Kersemans et Koen Van Den Abeele. « On the Identification of Orthotropic Elastic Stiffness Using 3D Guided Wavefield Data ». Sensors 22, no 14 (15 juillet 2022) : 5314. http://dx.doi.org/10.3390/s22145314.
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Scanning laser Doppler vibrometry is a widely adopted method to measure the full-field out-of-plane vibrational response of materials in view of detecting defects or estimating stiffness parameters. Recent technological developments have led to performant 3D scanning laser Doppler vibrometers, which give access to both out-of-plane and in-plane vibrational velocity components. In the present study, the effect of using (i) the in-plane component; (ii) the out-of-plane component; and (iii) both the in-plane and out-of-plane components of the recorded vibration velocity on the inverse determination of the stiffness parameters is studied. Input data were gathered from a series of numerical simulations using a finite element model (COMSOL), as well as from broadband experimental measurements by means of a 3D infrared scanning laser Doppler vibrometer. Various materials were studied, including carbon epoxy composite and wood materials. The full-field vibrational velocity response is converted to the frequency-wavenumber domain by means of Fourier transform, from which complex wavenumbers are extracted using the matrix pencil decomposition method. To infer the orthotropic elastic stiffness tensor, an inversion procedure is developed by coupling the semi-analytical finite element (SAFE) as a forward method to the particle swarm optimizer. It is shown that accounting for the in-plane velocity component leads to a more accurate and robust determination of the orthotropic elastic stiffness parameters.
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Fedorenko, A. K., A. V. Bespalova, O. K. Cheremnykh et E. I. Kryuchkov. « A dominant acoustic-gravity mode in the polar thermosphere ». Annales Geophysicae 33, no 1 (27 janvier 2015) : 101–8. http://dx.doi.org/10.5194/angeo-33-101-2015.
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Abstract. The article presents a summary of the main findings of the systematic study of acoustic-gravity waves (AGWs) in the polar thermosphere. This study was based on the in situ measurements made by the Dynamics Explorer 2 (DE2) spacecraft late in its mission when it descended low enough (250–400 km). It was found out that AGWs in the polar thermosphere are observed within a narrow frequency band close to the Brunt–Väisälä frequency and with horizontal wavelengths about 500–600 km. The broadband spectrum of travelling ionospheric disturbance (TID) frequencies observed by radars is caused by the Doppler effect. The AGW amplitudes do not depend on the altitude, but grow almost linearly with the wind velocity. They propagate towards the wind.
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Hou, Jiacheng, et Zhongquan Charlie Zheng. « Simulation of near-ground signals from a flying source on UAV over a building structure ». Journal of the Acoustical Society of America 151, no 4 (avril 2022) : A36. http://dx.doi.org/10.1121/10.0010577.
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Acoustic signals near the ground generated by a moving source on a fly-by UAV are simulated around a house. The simulation is carried out using a time-domain acoustics solver that can simulate acoustic propagations with the specified moving source, ground properties, and building geometries. The source on a UAV is approximated by a broadband source moving at a constant speed. The long-range three-dimensional computation is developed with a ground as a rigid or porous medium and a residential house with realistic geometries. Time histories and histograms of the near-ground sensors at different locations around the house are analyzed with their different behaviors due to Doppler shift, ground effect, and acoustic interference from the house structures. Comparisons will be made with literature results and available measured data.
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Prokopovich, V. V., et A. V. Shafranyuk. « Model of Signal Mark Detection in a Passive Sonar System ». IOP Conference Series : Materials Science and Engineering 1215, no 1 (1 janvier 2022) : 012009. http://dx.doi.org/10.1088/1757-899x/1215/1/012009.
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Abstract Modeling of broadband and narrowband signal mark detection is widely used for sonar and radar systems. In this work, the problem is considered in relation to hydroacoustics. The paper describes the formation of a stream of correctly detected and false signal marks and calculation of estimates of their parameters, taking into account the antenna characteristics as well as the processing parameters of the system being simulated. Also considered are the realistic distribution of false signal marks by heading angles and the influence of the Doppler effect on the estimation of the mark parameters. The resulting model can be used in simulation systems, in the formation of a stream of detected signal marks, and the development of tracking algorithms. The model can be also used for predictive calculations that determine the probability of detecting signal sources and their characteristics
Thèses sur le sujet "Broadband Doppler effect"
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Josso, Nicolas. « Caractérisation des milieux sous-marins en utilisant des sources mobiles d'opportunité ». Phd thesis, Grenoble INPG, 2010. https://theses.hal.science/tel-00546875.
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Les contraintes de rapidité et de discrétion imposées à un système moderne de caractérisation du milieu océanique ont conduit au développement de la tomographie passive, définie comme un moyen discret et rapide d'estimation des paramètres d'un canal acoustique. Ce concept fait appel aux signaux existants dans le milieu et transmis par des sources d'opportunité. Les signaux d'opportunité sont inconnus à la réception mais contiennent des informations relatives aux paramètres physiques du canal défini entre la source et le récepteur. Le travail de recherche présenté dans ce mémoire est d´edié à la caractérisation des milieux sous-marins en utilisant des signaux bioacoustiques d'opportunité (sifflements à modulation fréquentielle). La méconnaissance du signal transmis, de la position et de la vitesse de la source acoustique d'opportunité rendent la tomographie passive difficile à mettre en oeuvre. La propagation dans l'environnement océanique et le mouvement inconnu de la source transforment conjointement les signaux d'opportunité enregistrés. Dans un premier temps, nous présentons de nouvelles méthodes d'estimation simultanée des paramètres environnementaux et des déformations engendrées par le mouvement dans le plan d'ambiguïté large-bande, dans un contexte d'émissions actives (le signal transmis est supposé connu). Ces méthodes, permettant de compenser les effets du mouvement dans les scénarios d'´emissions actives, sont appliquées et validées sur différents jeux de données simulées et réelles enregistrées en mer. Puis nous nous intéressons à la tomographie océanique acoustique passive sur un unique hydrophone. Dans ce contexte, le signal transmis, la position et la vitesse de la source sont entièrement inconnus. A partir des estimateurs développés pour les scénarios d'émissions actives, nous présentons une nouvelle méthodologie permettant d'estimer les paramètres environnementaux en utilisant des vocalises de mammifères marins enregistrées sur un unique hydrophone. Les informations extraites sur les signaux naturels d'opportunité sont ensuite utilisées pour estimer la position puis le vecteur vitesse de la source d'opportunité. Ces méthodes sont appliquées et validées sur différents jeux de données simulées et réelles enregistrées en merQuickness, secrecy and loudness constraints imposed by modern oceanic characterization led to passive tomography which is defined as a quick, secretive and quiet mean of estimating underwater propagation canals. This concept uses signals naturally existing in the medium and transmitted by opportunity sources. Opportunity signals are unknown at the receiver but they also carry information about canal physical properties. This research work is dedicated to underwater environments characterization using opportunity bioacoustic signals (dolphin whistles). Opportunity signals are simultaneously transformed by underwater propagation and the unknown motion effects. Firstly, we propose new methods for estimating simultaneously environmental parameters and transformations created by motion effects. These parameters are estimated in the broadband ambiguity plane for active tomography (the emitted signal is known) with unknown motion in the system. This work, allowing to compensate for motion effect in active scenarios, is validated on different simulated and real data. Then, we apply our signal processing methods to passive underwater tomography, using a single hydrophone. In this context, both the transmitted signal, source position and source speed are completely unknown. From the theory we developed for active tomography, we derive new methods allowing the estimation of impulse response using underwater mammals vocalization recorded on a single hydrophone. Information extracted on opportunity signals is then used for source position and speed estimation. These methods are applied and validated on different simulated and real data from at sea experiments
Actes de conférences sur le sujet "Broadband Doppler effect"
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Ruyten, Wilhelmus R. « Rabi structures in a Doppler broadened gas ? » Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1988. http://dx.doi.org/10.1364/oam.1988.my6.
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The problem of a two-level atom interacting with modulated or multifrequency fields has been the subject of much work in magnetic resonance experiments. More recently, experiments dealing with optical interactions have been reported.1,2 Unlike the former, these have been performed in beam experiments to eliminate the effect of Doppler broadening. Here we calculate that Rabi structures, in particular, multiphoton resonances, should be observable even in a gas cell and/or for a broadband source. However, this is true only for fluorescence and absorption at the modulation frequency or harmonics thereof. By contrast, the time-averaged fluorescence, which is the quantity usually studied, becomes structureless on integration over the Doppler profile. The result, which is not consistent with a rate equation analysis, can be qualitatively understood from the resonance behavior of the system. In particular, earlier studies on generalized Bloch-Siegert shifts are extended to harmonic components of the interaction.
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Rahimian, Nariman, et Abolfazl Falahati. « New Analytical Method to Investigate the Effect of Normalized Doppler rate on the Capacity of MIMO channels Using Karhunen-Loeve Expansion ». Dans The 2nd International Conference on Wireless Broadband and Ultra Wideband Communications (AusWireless 2007). IEEE, 2007. http://dx.doi.org/10.1109/auswireless.2007.49.
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Hughes, Christopher E., Gary G. Podboy, Richard P. Woodward et Robert J. Jeracki. « The Effect of Bypass Nozzle Exit Area on Fan Aerodynamic Performance and Noise in a Model Turbofan Simulator ». Dans ASME Turbo Expo 2005 : Power for Land, Sea, and Air. ASMEDC, 2005. http://dx.doi.org/10.1115/gt2005-68573.
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The design of effective new technologies to reduce aircraft propulsion noise is dependent on identifying and understanding the noise sources and noise generation mechanisms in the modern turbofan engine, as well as determining their contribution to the overall aircraft noise signature. Therefore, a comprehensive aeroacoustic wind tunnel test program was conducted as part of the NASA Quiet Aircraft Technology program called the Fan Broadband Source Diagnostic Test. The test was performed in the anechoic NASA Glenn 9- by 15-Foot Low Speed Wind Tunnel using a 1/5 scale model turbofan simulator that representative of a current generation, medium pressure ratio high bypass turbofan engine. The investigation was focused on the simulated bypass section of the turbofan engine. The technical objectives of the test were not only to identify the noise sources within the model and determine their noise level, but also to investigate several component design technologies by evaluating their impact on the aerodynamic and acoustic performance as well as conducting detailed flow diagnostics within the research model to help in understanding the physics of the flowfield. This report will present details of the results obtained for one aspect of the test that investigated the effect of the bypass nozzle exit area on the bypass stage performance, specifically the fan and outlet guide vanes, or stators. The aerodynamic performance, farfield acoustics, and Laser Doppler Velocimeter measurements obtained for the fan and four different fixed-area bypass nozzles. The nozzles represented fixed engine operating lines encompassing the operating envelope of the turbofan engine from near stall to cruise, with a total change in area from the smallest to the largest nozzle of 12.9%. One nozzle exit area was selected as a baseline reference, and its area was 2% larger than the smallest nozzle and 10.9% smaller than the largest nozzle. The results will show that there are significant changes in aerodynamic performance and farfield acoustics as the nozzle area is increased. As the fan exit nozzle area was increased, the weight flow through the fan model increased between 7% and 9%, the fan and stage pressure dropped between 8% and 10%, and the adiabatic efficiencies increased between 2% and 3% — the magnitude of the change dependent on the fan speed. Results from force balance measurements made of fan and outlet guide vane thrust will show that as the nozzle exit area is increased the combined thrust of the fan and outlet guide vanes together also increases, between 2% and 3.5%. In terms of farfield acoustics, the overall sound power level produced by the fan model dropped between 1 and 3.5 dB as the nozzle exit area was increased, with the larger decrease in noise occurring near approach conditions and the smaller decrease near takeoff condition. Both fan tone and broadband levels are discussed. The amount of area the fan exit nozzle can be opened was limited, as the largest of the four nozzle designs encountered performance problems at full power takeoff conditions, at which point its performance was actually worse both in terms of lower aerodynamic performance and higher noise levels compared to the baseline nozzle. Finally, flow diagnostic results in the form of fan swirl angle survey data and Laser Doppler Velocimeter mean velocity and turbulence measurements obtained downstream of the fan within the wake will show that the noise of the fan module decreases as a result of lower swirl angles and lower turbulence levels within the wake as the fan exit nozzle area increases.
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Marconi, Jacopo, Gabriele Cazzulani, Massimo Ruzzene et Francesco Braghin. « A Physical Interpretation for Broken Reciprocity in Spatiotemporal Modulated Periodic Rods ». Dans ASME 2017 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/smasis2017-3877.
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Periodic systems have long been known for their peculiar characteristics in wave propagation and have been studied in many fields over the last century, going from electro-magnetics and optics to elastic structures, which drew an increasing interest in structural and mechanical engineering for vibration suppression and control spanning over broadband frequency ranges. Recently, on the stream of other studies conducted in different fields, spatiotemporal modulated elastic structures have been studied, showing promising results for wave control in that one-way propagation in the so called directional-bands can be achieved, constituting what may be called a mechanical diode. Despite of the fact that mathematical methods for the analysis of such structures have already been developed, often physics behind them is difficult to grasp. In this work, a simplified interpretation of the undergoing phenomena is thus given relating wave propagation in the mean to its physical characteristics as well as to modulation parameters. Exploiting Doppler effect and passive equivalent structures, it is shown that the broken reciprocity is due to the fact that opposite travelling waves effectively see two different periodic structures. To this aim the rod case is analysed for low modulation speeds and low modulation amplitudes; finally, in the light of the previous analysis, an explanation for First Brillouin Zone’s asymmetry is given.
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Aguado, Marina, Oscar Onandi, Eduardo Jacob, Christian Pinedo, Purificacion Saiz et Marivi Higuero. « WiMAX Role on CBTC Systems ». Dans ASME/IEEE 2007 Joint Rail Conference and Internal Combustion Engine Division Spring Technical Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/jrc/ice2007-40103.
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The recent progresses in mobile telecommunications technologies have allowed railway telecommunications technology to go a step forward, and, in the same way, the railway control systems. In this sense, while the mobile telecommunications technology evolved from the first generation of analogue mobile communication systems to what is known today as B3G (Beyond 3G), the same occurred with the telecommunication systems used in railways, from those based on analogue telecommunications, to the most recent ones based on 2G such as GSM-R or TETRA. Till recently, there was a technological gap regarding high mobility environments, high transmission rate and high interactivity (low latency). However, new emerging telecommunications technologies have shortened this gap significantly. This way, the train control systems will be affected by the availability of telecommunications technologies capable of offering earth-train broadband communications in real time. This article presents a telecommunications network architecture based on WiMAX (Worldwide Interoperability for Microwave Access) mobile technology (IEEE 802.16e) that fulfils the telecommunications needs in the railway environment. The WiMAX mobile technology most relevant features are: transmission rates up to 30Mbps at 15 km distance; mobility support up to 200km/h; QoS, security, low latency, fast, scalable and cost effective deployment, mainly compared to GSM-R deployment. In the mobile node design of this network telecommunications architecture, the multipath fading effect, and the Doppler effect, present in high speed mobility scenarios, have been taken into account. An improvement in the handoff between BSs, through a neighbouring and predictive mobility algorithm, is included. The architecture proposed supports the functional and system requirements identified in the UIC Project EIRENE (European Integrated Railway Radio Enhanced Network), and demanded to GSM-R technology. Measures on a real testbed and a model developed with the discrete event simulation tool, Opnet, have been employed in this work.
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Lee, Byung-Seub, Sim-Suk Lee, Min-Su Shin et Ho-Jin Lee. « New OFDM Schemes Robust to Doppler and Par Effects for Broadband Mobile Internet Services via Satellite Transponder ». Dans 25th AIAA International Communications Satellite Systems Conference (organized by APSCC). Reston, Virigina : American Institute of Aeronautics and Astronautics, 2007. http://dx.doi.org/10.2514/6.2007-3243.
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