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Acquisition time in laser inter-satellite link under satellite vibrationsLee, K., Mai, Vuong, Kim, H. 11 August 2024 (has links)
Yes / Pointing, acquisition, and tracking (PAT) is a major technical challenge of laser inter-satellite links (ISLs). For the fast establishment of laser link and the maximization of communication time, it is of importance to minimize the acquisition time. Satellite vibrations affect the PAT procedure adversely, and thus serve to increase the acquisition time. In this paper, we investigate through theoretical analysis the average acquisition time of laser ISLs in the presence of satellite vibrations. The analytic expression about the time taken from the beginning of spiral scan to the acquisition of the scan beam is provided in the presence of the pointing errors caused by vibrations. We also derive the optimum beam divergence angle for the acquisition time. The analyses are validated by Monte-Carlo computer simulations and a proof-of-concept experiment. The results show that the acquisition time can be minimized by adjusting the beam divergence angle adaptively to the link conditions. / Grant-in-aid of Hanwha Systems
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Demographically weighted traffic flow models for adaptive routing in packet-switched non-geostationary satellite meshed networksMohorcic, M., Svigelj, A., Kandus, G., Hu, Yim Fun, Sheriff, Ray E. January 2003 (has links)
no / In this paper, a performance analysis of adaptive routing is presented for packet-switched inter-satellite link (ISL)networks, based on shortest path routing and two alternate link routing forwarding policies. The selected routing algorithm
and link-cost function are evaluated for a low earth orbit satellite system, using a demographically weighted traffic flow model. Two distinct traffic flow patterns are modelled: hot spot and regional. Performance analysis, in terms
of quality of service and quantity of service, is derived using specifically developed simulation software to model the ISL network, taking into account topology adaptive routing only, or topology and traffic adaptive routing.
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Étude et réalisation d’un nouveau système de référence spatio-temporel basé sur des liens inter-satellites dans une constellation GNSS / Study and realization of a new spatio-temporal reference system based on inter-satellite links in a GNSS constellationRichard, Edouard 27 January 2016 (has links)
L'exactitude délivrée par les systèmes de positionnement globaux par satellites (GNSS) est un facteur clé pour de nombreuses applications scientifiques telles que le positionnement de points géodésiques ou d’autres satellites, l'établissement de systèmes de référence spatio-temporels, la synchronisation d’horloges ou encore l'étude directe du lien pour sonder l’atmosphère. L'augmentation de la constellation GNSS avec des mesures de pseudo-distances entre les satellites est une option prometteuse pour améliorer l'exactitude du système. Plusieurs études présentent l'apport qualitatif de ces liens inter-satellites (ISL), mais ne permettent pas de mesurer efficacement l'impact quantitatif de cette technologie. Dans cette thèse, nous avons effectué une étude différentielle entre un système classique (possédant seulement des liens standards espace-sol) et un système augmenté avec des ISL. Les deux systèmes sont étudiés sous les mêmes hypothèses et à travers le même code de calcul. Celui-ci est composé de deux parties distinctes et autonomes : une simulation d’observables sous la forme de pseudo-temps de vol bruités, et une analyse qui délivre, après ajustement des paramètres, les bilans d’erreurs quantitatifs. La comparaison des bilans d'erreurs quantitatifs associés aux deux systèmes nous permet d’établir, pour une même application donnée, les différences de performance relatives entre les deux systèmes. Les résultats obtenus permettent de franchir un pas de plus vers la validation de l’apport des liens inter-satellites et sont à considérer pour les versions futures des systèmes de navigation par satellites. / The accuracy reached by the Global Navigation Satellite Systems (GNSS) is critically important for many scientific applications such as geodetic point or satellite positioning, space-time reference frame realization, clocks synchronization or the study of the links to probe the atmosphere. One option for improving the system accuracy is the use of inter-satellite pseudo-range measurements, so called inter-satellite links (ISL). Several studies have shown the qualitative interest of ISL but do not allow to efficiently measure the quantitative impact of this new technology on space-time positioning. In this thesis, we present a differential study between a standard system (with standard satellite-to-ground links only) and system augmented by ISL. The two systems are compared under the same hypothesis and simulated within the same software. The software is made of two distinct and independent parts : the simulation which generates the noisy pseudo-ranges, and an analysis which uses a non linear adjustment procedure in order to recover the initial parameters of the simulation and compute the quantitative error budgets. For a given application, the quantitative comparison between the error budgets of both systems allow us to highlight the relative merits of the two configurations. Our results are a further step in the characterization of the interest of ISL and should prove useful for the design of future satellite navigation system design.
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[en] PROPAGATION EFFECTS IN LOW EARTH ORBIT SATTELITE LINKS / [pt] MODELAMENTO DE EFEITOS DE PROPAGAÇÃO EM ENLACES SATÉLITE DE ÓRBITA BAIXAMARTA PUDWELL CHAVES DE ALMEIDA 02 December 2003 (has links)
[pt] O efeito da atenuação por chuvas em enlaces satélites que
operam em frequências acima de 10 GHz é decisivo no cálculo
de desempenho do sistema. A evolução da tecnologia dos
sistemas satélite e a necessidade de expansão dos serviços
de comunicações móveis pessoais levaram ao uso de sistemas
de comunicação com satélites de órbita baixa. Estes
sistemas são particularmente interessantes para o
oferecimento destes serviços por suas características de
pequeno atraso de propagação e uso de potência de
transmissão mais baixas que os sistemas geoestacionários.
Satélites em órbita baixas (LEO) operam em altitudes de
cerca de 1000km e possuem movimento em relação à estação
terrena. Esta característica de mobilidade traz novas
questões sobre o comportamento da atenuação por chuvas, em
particular a necessidade de um modelo de previsão de
atenuação para estes enlaces com ângulo de elevação
variante no tempo. Neste trabalho um modelo para a previsão
de atenuação em enlaces com ângulo de elevação fixo, mais
preciso do que os existentes na literatura técnica, foi
desenvolvido como primeiro passo para o tratamento do
problema de enlaces com ângulo de elevação variável. A
seguir foi feita uma simulação de medidas em enlaces LEO a
partir do banco de dados de medidas de atenuação em enlaces
fixos no Brasil, considerando um modelo de constelação de
satélites. Foi implementado um método geral que utiliza o
histograma dos ângulos de elevação do satélite como
ponderação da distribuição cumulativa de atenuação em cada
ângulo. O método foi testado contra os resultados obtidos
com simulações para a constelação Globalstar sendo obtida
muito boa concordância entre o modelo de predição
desenvolvido e a simulação. / [en] Rain attenuation is the most important propagation effect
to be taken into account in the performance calculation for
satellite systems operation at frequencies above 10 GHz.
The technological evolution of such systems and the
need for personal communication systems with global
coverage lead to the use of low earth orbit communication
systems, that not only have shorter propagation
delays but also allow the use of lower transmission power
than the traditional geostationary systems. Low earth orbit
(LEO) satellites have altitudes around 1.000 Km and are in
motion relatively to the earth stations. This mobility
requires a new approach to the problem of rain attenuation
prediction, particularly the need for a prediction model
that takes into account the elevation angle variability.
In this work, an improved rain attenuation prediction
method for the geostationary case has been developed as a
starting point for the analysis of the nongeostationary
case. Then, the rain attenuation in the a LEO system has
been simulated using measured data from fixed system
systems and the satellite constellation model. A general
method for slant path rain attenuation prediction
considering variable elevation angles is proposed. The
method uses the histogram of the elevation angles to weight
the distributions obtained for fixed elevation. The method
has been tested with simulations performed for the
Globalstar LEO system and a very good agreement was
obtained.
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