170,063 research outputs found
High-speed wireless infrared uplink scheme for airplane passengers' communications
No full textHybrid visible light communication/infrared communication (VLC/ IRC) systems are becoming the leading way for supplying highspeed Internet connectivity to airplane passengers. A robust IR uplink transmission scheme is presented for in-flight VLC/IRC systems which has the potential to support 10 Mbit/s transmission for each user in the cabin with uncoded bit error rate ≤10-6 under the assumption of line-of-sight communication scenario, also in the presence of misalignments between transmitter and receiver due to random movements of the passengers
Enabling on‐aircraft visible‐light communications in low‐light conditions
No full textVisible-light communications (VLCs) are emerging as a valid alternative to radio-frequency systems for the provision of Internet connectivity to aircraft passengers through the LED reading lamps. In this Letter, the authors investigate the minimum required level of emitted flux in order to support the communication with the users' terminals. A VLC system employing 1 lm of flux is able to achieve an average per-user capacity comparable with the one currently in use for 4G (6 bit/s/Hz) over an electrical bandwidth of 10 MHz, which is sufficient to support the latest multimedia services (40 Mb/s for Blu-ray video streaming)
Analysis of azimuthal variation of rain attenuation
No full textThe attenuation due to rain is the main source of impairments in satellite links operating above 10 GHz. In the design of systems based on Low Earth Orbit (LEO) satellites, the analysis of the rain attenuation must take into account both azimuth and elevation variations. It requires a deep knowledge on the nature of this dependence. As measurements at several elevation and azimuth angles are not available, it is necessary to use prediction models that aim at reproducing the rain profiles of each link. This paper presents an analysis of the azimuth dependence of rain attenuation according to the size of the azimuthal window where this attenuation occurs. It is shown that the azimuthal rain attenuation windows smaller than 180° are few at higher elevation but their probability increases exponentially with the decreasing of the elevation
On the Accuracy of Simplified Models for Water Vapor Attenuation Prediction at Ka band and Q band
No full textThe accuracy of the approximate prediction models included in recommendation ITU-R P.676 aimed at estimating the attenuation due to gases (water vapor and oxygen) from ground meteorological inputs is assessed. To this aim, the gaseous attenuation derived from a multi-channel radiometer installed at the experimental station of Spino d'Adda is used as reference. Two versions of the same recommendation are considered, defining different simplified expressions for the gaseous specific attenuation, but both taking advantage of the same equivalent height concept. Results, evaluated over a full year of data, indicate that the most recent model (version 11 of P.676) significantly underestimate the attenuation due to gases; on the contrary, the previous version of the recommendation turns out to be accurate enough to be used reliably in supporting the derivation of total tropospheric attenuation from the received beacon signal in electromagnetic wave propagation experiments, especially when no radiometric data are available at the site
Estimating the Spatial Cumulative Distribution of Rain from Precipitation Amounts
No full textThis contribution describes SPET (Spatial P(R) Estimation Technique), a methodology aimed at estimating the spatial rain rate complementary cumulative distribution function, PS(R), from Numerical Weather Prediction (NWP) rain precipitation data. SPET has been calibrated making use of a large database of rain maps derived from the S-band weather radar sited in Spino d'Adda, Italy, while its performance has been assessed against an independent data set derived from the NIMROD C-band radar network. Results indicate that SPET performance improves as both the observation area and reference time interval increase, which adds confidence to its use to estimate PS(R) starting from global rainfall data produced by meteorological re-analyses. SPET also proved to correctly predict the fractional rainy area, showing an RMS of the relative error that falls approximately between 15% and 20% for area and time interval values typical of NWP re-analysis data. As a final step, the proposed technique has been used to predict long-term rainfall statistics collected by rain gauges worldwide, receiving as input rainfall data extracted from 10 years of ERA40 products (ergodicity of the rain field). Very good performances have been obtained, only limited by the poor quality of the input data
Model to Scale Rain Attenuation Time Series With Link Elevation Angle for LEO Satellite Based Systems
No full textA model to scale time series of rain attenuation along an Earth-to-satellite path with variable elevation angle is proposed. Starting from the time series at the lowest elevation the algorithm scales up each sample to the elevation of interest while maintaining the space and time correlation of the rain process and by correctly reproducing the local long-term rain attenuation statistics. Because of these peculiarities, the model represents a key element for the development of attenuation time series synthesizers for LEO satellite-based applications, where the time decorrelation of the rain event during the quick spacecraft passage over the ground station (roughly 10 min) is quite limited. Moreover, the comparison with the simple geometric scaling (i.e., the cosecant law) carried out among the attenuation Complementary Cumulative Distribution Functions shows a definite improvement in the prediction accuracy, even more so when the elevation angle falls below 20°
Impact of Water Vapor Attenuation on Low Elevation SatCom Links
No full textThe water vapor absorption effect cannot be neglected in satellite communication (SatCom) systems operating at higher frequency bands (e.g. W band). It becomes even more significant when it comes to very low elevation angles, such as those characterizing GEO satellites with ground stations at high latitudes, or MEO/LEO satellites. This paper presents some preliminary results on the impact of water vapor attenuation AV at different elevation angles, as well as on scaling AV from zenithal pointing to low elevation angles. The results, obtained from an extensive set of large water vapor content maps, show that the customary cosecant scaling approach is accurate down to 5°. Finally, some preliminary results on the impact of AV on a link to a MEO satellite are also shown
Investigation of Rain Induced Depolarization by Means of a Physically Based Simulator
No full textA physically based simulator is applied in this work to investigate the depolarization induced by rain along Earth-space links, and specifically to shed light on the impact of different precipitation types (stratiform/convective) and of the axial ratio selected to model the drop oblateness. To this aim, we employ rain maps derived from an S-band weather radar as input to the simulator. Results indicate that the Cross Polar Discrimination (XPD) depends more on the drop axial ratio than on the type of precipitation event, and, more in general, they give a hint of the usefulness of the proposed simulator to isolate and investigate the contribution of the different atmospheric constituents to the overall XPD
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