Search results for "correlated channel"

showing 3 items of 3 documents

Rateless Codes Performance Analysis in Correlated Channel Model for GEO Free Space Optics Downlinks

2012

Settore ING-INF/03 - TelecomunicazioniFree Space Optics (FSO) technologies for satellite communications offer several advantages: wide bandwidth high rate capability immunity to electromagnetic interference and small equipment size. Thus they are suitable for inter-satellite links deep space communications and also for high data rate ground-to-satellite/satellite-to-ground communications. Nevertheless FSO links suffer impairments that cause power signal degradation at the receiver. Scattering and absorption cause power signal attenuations predictable by suitable deterministic models. Optical turbulence causes random irradiance fluctuations which can generate signal fading events and can thereby only be predicted by statistical models. Attenuation and fading events can corrupt FSO links and so it would be recommended to add mitigation error codes on the communication link. FSO channel can be described as an erasure channel: fading events can cause erasure errors. We have identified in rateless codes (RCs) a suitable solution to be employed in FSO links. RCs do not need feedback and they add a redundant coding on the source data that allows the receiver to recover the whole payload despite erasure errors. We implemented two different of rateless codes: Luby Transform (LT) and Raptor. We analyzed their performances on a simulated turbulent GEO FSO downlink (1 Gbps - OOK modulation) at a 106 μm wavelength and for different values of zenith angles. Assuming a plane-wave propagation and employing Hufnagel-Valley we modeled the downlink using: 1) a temporal correlated channel model based on Gamma-Gamma probability distribution and 2) an irradiance covariance function that we converted on a time function using Taylor frozen eddies hypothesis. Our new channel model is able to simulate irradiance fluctuations at different turbulence conditions as it will be shown in the full paper. We will also report performance results of LT and Raptor codes at overhead range varying between 0 and 50% and for different values of source packets.Settore ING-INF/01 - Elettronica
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Rateless Codes Performance Tests On Terrestrial FSO Time-Correlated Channel Model

2012

Free Space Optics (FSO) links are affected by several impairments: optical turbulence, scattering, absorption, and pointing. In particular, atmospheric optical turbulence generates optical power fluctuations at the receiver that can degrade communications with fading events, especially, in high data rate links. A way to mitigate FSO link outages can be to add a coding to communications. Nevertheless, in order to study innovative solutions (software or hardware) and to improve the FSO link performance it needs accurate testing models. In this paper we describe an accurate time-correlated channel model able to predict random temporal fluctuations of optical signal irradiance caused by optical…

Physicsbusiness.industrySettore ING-INF/03 - Telecomunicazionicorrelated channelrateless code.Fountain codeOptical powerSettore ING-INF/02 - Campi ElettromagneticiOptical performance monitoringRaptorQ (RQ)Settore ING-INF/01 - ElettronicaSoftwareFree Space Optics (FSO)Luby Tranform (LT)Electronic engineeringFadingbusinessRaptor codeTransform codingAtmospheric opticsComputer Science::Information TheoryCoding (social sciences)Free-space optical communication
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Indoor free space optics link under the weak turbulence regime: Measurements and model validation

2015

In this study, the authors present the measurements performed on a free space optics (FSO) communications link using an indoor atmospheric chamber. In particular, the authors have generated several different optical turbulence conditions, demonstrating how even the weak turbulence regime can strongly affect the FSO link performance. The authors have carried out an in-depth analysis of the data collected during the measurements, and calculated the turbulence strength (i.e. scintillation index and Rytov variance) and the important performance metrics (i.e. the Q-factor and bit error rate) to evaluate the FSO link quality. Moreover, the authors have tested, for the first time, an appositely de…

Time seriesComputer scienceOptical linksIrradianceGamma gamma channel modelSettore ING-INF/01 - ElettronicaScintillation indexoptical turbulenceQuality (physics)TEORIA DE LA SEÑAL Y COMUNICACIONESStatistical physicsError statisticsElectrical and Electronic EngineeringComunicació i tecnologiaScintillationtime-correlated channel modelbusiness.industryTurbulenceSettore ING-INF/03 - TelecomunicazioniIndoor atmospheric chamberRytov varianceAtmospheric turbulenceExperimental dataQ-factorTurbulence strengthSettore ING-INF/02 - Campi ElettromagneticiÒpticaComputer Science ApplicationsBit error rateQ factorFree Space OpticBit error rateGamma-Gamma modelIndoor free space optics communications linkTelecommunicationsbusinessFree-space optical communicationindoor link
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