Modulation par déplacement de fréquence

La modulation par déplacement de fréquence (MDF), plus connue sous sa dénomination anglophone frequency-shift keying (FSK) est un mode de modulation de fréquence numérique dans lequel la fréquence du signal modulé varie entre des fréquences prédéterminées. Classification FSK cohérente et FSK non cohérente Généralement, la fréquence instantanée peut prendre deux valeurs discrètes appelées mark et space. Il s'agit d'une forme non-cohérente de FSK. Dans les formes cohérentes de FSK, il n'y a pas de discontinuité de phase dans le signal de sortie. C'est le cas du signal de l'exemple. Il est possible de réaliser une modulation FSK sans discontinuité de phase (ce qui permet d'améliorer le spectre du signal modulé) par une méthode appelée CPM (). Minimum-shift keying Minimum-shift keying La minimum frequency-shift keying ou minimum-shift keying (MSK) est une forme très efficace de modulation FSK en termes d'occupation de spectre. En MSK, la différence

Performance analysis of dual-hop fixed-gain AF relaying systems with OSTBC over Nakagami-m fading channels

Serife Seda Kucur

In this paper, we present outage probability and symbol error rate (SER) performance analyses of a dual-hop transmission using fixed-gain amplify-and-forward relaying in flat Nakagami-m fading channels. The system under consideration is equipped with multiple antennas at source and destination adopting orthogonal space-time block coding to provide transmit diversity and maximum ratio combining to provide receive diversity, respectively. For integer and half-integer m values, closed forms of exact outage probability and moment generating function (MGF) expressions are derived through cumulative distribution function (CDF) of the overall system signal-to-noise ratio. Closed-form exact SER expressions based on the overall CDF are obtained for binary phase shift keying, binary frequency shift keying and M-ary pulse amplitude modulation. Exact SER expressions based on the MGF method are also obtained for binary differential phase shift keying, M-ary phase shift keying and M-ary quadrature amplitude modulation. Moreover, the asymptotic diversity order analysis is performed through derivations of asymptotic outage probability and SER. Theoretical analyses are validated by Monte Carlo simulations showing perfect match between each other. (C) 2012 Elsevier GmbH. All rights reserved.

Elsevier Gmbh, Urban & Fischer Verlag2012

High resolution differential laser interferometry for the VLTI (Very Large Telescope Interferometer)

Olivier Boris Scherler

One method for locating extrasolar planets is to observe the lateral movement of a star in the sky caused by a planet in orbit around it. In order to detect this displacement, the angular position of the star has to be measured with high accuracy. This technique is called astrometry. The Very Large Telescope Interferometer (VLTI) is operated by the European Southern Observatory and located at the Paranal Observatory in Chile. The purpose of the PRIMA instrument (Phase Referenced Imaging and Micro-arcsecond Astrometry) of the VLTI is to perform high-resolution astrometric measurements and high-resolution imaging of faint stars using white light interferometry, by combining the light collected by two telescopes. In order to allow the detection of extrasolar planets, the astrometric measurement has to be performed with micro-arcsecond accuracy. In astrometric mode the PRIMA instrument observes two targets at the same time: the object of scientific interest, and a bright reference star. The angular position of the science object relative to the reference star is obtained by monitoring the differential optical path travelled by the light of each object in two separate white-light interferometers. The aim of this work was to develop a high-resolution laser metrology based on superheterodyne interferometry, with an accuracy of 5 nm over a differential optical path of 100 mm. Moreover the laser source had to be stabilised on an absolute frequency reference, in order to ensure the long-term stability and calibration required to achieve the target performance. Superheterodyne interferometry allowed the direct measurement of the differential optical path using two heterodyne interferometers working with two different frequency shifts. The differential phase measurement between the two interferometers was obtained by electronic mixing of the two heterodyne signals, leading to the differential optical path needed for the astrometric measurement

Institut de Microtechnique, Université de Neuchâtel2006

High resolution differential laser interferometry for the VLTI (Very Large Telescope Interferometer)

Olivier Boris Scherler

Institut de Microtechnique, Université de Neuchâtel2006

Modulation par déplacement de fréquence

Performance analysis of dual-hop fixed-gain AF relaying systems with OSTBC over Nakagami-m fading channels

High resolution differential laser interferometry for the VLTI (Very Large Telescope Interferometer)

Active control of moving sound source radiation - numerical modelling in the space-frequency and space-time doMayns

Performance analysis of dual-hop fixed-gain AF relaying systems with OSTBC over Nakagami-m fading channels

High resolution differential laser interferometry for the VLTI (Very Large Telescope Interferometer)

Active control of moving sound source radiation - numerical modelling in the space-frequency and space-time doMayns