1,721,016 research outputs found
Effectiveness of multisite diversity schemes to support optical systems in scientific missions
Full text linkThis contribution investigates the effectiveness of optical communication links in enabling high-speed data transfer from deep-space (DS) probes directly to Earth ground stations. In particular, the propagation impairments induced by clouds are estimated by exploiting long-term radiosonde observation data collected in some European sites. The impact of different cloud types on optical links operating at 1.55 μm is first quantified in terms of total path attenuation, and afterward, the implementation of multisite diversity schemes is discussed to counteract the extremely high attenuation levels caused by clouds. Results show that a three-site diversity system with target availability of 90% allows reduction of the link margin to counteract cloud attenuation from at least 40 dB to ∼6 dB, which makes optical communications a viable option also for DS mission
Preliminary Assessment Of Site Diversity Schemes For Earth-Space Optical Links
No full textFree Space Optical (FSO) links enable high-speed data transfer from Earth Observation satellites or deep space (DS) probes directly to ground stations. The presence on-board of remote sensing instruments with ever increasing accuracy and resolution fuels the need for transmitting large amounts of data. This contribution investigates the impairments to optical beam propagation due to clouds by exploiting radiosonde observation (RAOBS) data collected in two European sites. Long-term yearly statistics of path attenuation are calculated by first distinguishing between different cloud types and, afterwards, by integrating their contribution to the total attenuation along each vertical profile of RAOBS data. Finally, the effectiveness of a site diversity scheme, simultaneously employing both FSO links, is assessed. Results indicate that a dual-site diversity FSO system with target availability of 10% would require approximately a 40-dB fade margin to counteract cloud attenuation
Statistical Assessment of New Methods to Optimize the Power Flux Distribution in TV-sat Broadcasting at 20 GHz
No full textIn this paper we present the results of a statistical performance assessment of a new advanced TV-sat system operating in the ka band. The on-board transmission system is based on the idea of reconfigurable antenna, i.e. the antenna directivity can be modified so as to irradiate more power to the regions affected by bad weather. The core is a power flux distribution optimizer based on the “derivative slicing” method, whose mathematical basis is described in the companion paper [1] presented at this Conference. Here, the above technique is assessed by verifying the system performance through a statistical analysis over six-months.
The simulations make use of a meteorological database provided by the European Centre for Medium-range Weather Forecasts (ECMWF). The constraints unavoidably posed by the usage of a physically realizable Beam-Forming Network (BFN) are taken into account as well. The results presented allow a preliminary assessment of the predicted advantage (in terms of availability) of an adaptive system over non-adaptive systems currently implemented, which are based on long-term climatological data. The BFN used to distribute the signal power across the service area (Europe) is constituted by a set of 8x8 multiport amplifiers, each driven by a Butler-Like Matrix (BLM), covering the area with 64 beams. The BFN excitation coefficients are refreshed every 3-6 hours, in accordance with the update rate of the input meteorological data. Our analysis shows that the number of users lost due to atmospheric effects is reduced by a factor of about 5 with respect to the case of a non-reconfigurable system fed by the same transmitted power. Morevoer, the theoretical reduction factor achievable by the "derivative slicing” method removing the system constraints (i.e. the BLM elements) would increase to 10
An Investigation of Rain Echoes Correlation Properties Through Measurements and Simulations
No full textAssessment of rain fade mitigation techniques for high throughput satellites by a time series synthesizer
No full textWe assess here the effectiveness of fade mitigation
techniques on the user link side of a TLC satellite system by a
simulation tool able to generate correlated time series of rain
attenuation in multiple sites. A preliminary analysis of two case
studies shows that on-board dynamic power allocation coupled
with ACM reduces the impact of heavy fades, permits a larger
exploitation of efficient MODCODs and equalizes the
performance of the user links. However, in the presence of
convective cells, co-channel interference can be dominant, hence
reducing the benefits of the above techniques
Prediction of Microwave Attenuation Across a Satellite Link From the ERA-Interim Global Atmospheric Database
No full textThe high time and space resolution of the ERAInterim
atmospheric database is exploited here to predict the
components of microwave attenuation across a satellite link
which can be, for instance, used in the design of advanced
satellite telecommunication systems based on adaptive technique
Effetti propagativi sul segnale radio ricevuto in ambito urbano: confronto fra tecniche di tracciamento dei raggi e metodi statistici
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