Search results for "fading"

showing 10 items of 155 documents

Throughput and energy efficiency comparison of one-hop, two-hop, virtual relay and cooperative retransmission schemes

2010

Two main types of approaches exist for implementing cooperative communications at the MAC layer: virtual-hop relay and cooperative retransmission. While the virtual-hop relay schemes employ relay nodes to forward packets when higher end-to-end throughput can be achieved compared with the direct transmission, the cooperative retransmission schemes use relays to retransmit data only after the direct transmission fails. However, the performance of the these different approaches has not been compared in the literature, especially when energy efficiency is considered. In order to find out the best transmission scheme, this paper evaluates and compares the performance of the one-hop direct transm…

Routing protocolbusiness.industryNetwork packetWireless networkComputer scienceRetransmissionDistributed computingComputerSystemsOrganization_COMPUTER-COMMUNICATIONNETWORKSThroughputData_CODINGANDINFORMATIONTHEORYlaw.inventionComputer Science::PerformanceRelaylawComputer Science::Networking and Internet ArchitectureFadingbusinessComputer Science::Information TheoryComputer networkEfficient energy use2010 European Wireless Conference (EW)
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Performance Analysis of M-DPSK Modulation over Fast-Hoyt Fading Channels under Non-Isotropic Scattering Conditions

2021

In this paper, we analyze the symbol error probability (SEP) performance of M-ary differential phase shift keying (M-DPSK) modulation schemes over frequency-flat fast-varying Hoyt multipath fading channels. Assuming general non-isotropic scattering conditions, we first derive a finite-range integral expression for the probability density function (PDF) of the phase difference between two non-isotropic Hoyt vectors perturbed by additive white Gaussian noise (AWGN). Based upon the theory of M-DPSK modulation and the obtained PDF formula, the SEP of M-DPSK and its corresponding asymptotic behavior in non-isotropic fast-Hoyt fading channels are derived. Specifically, a double semi-finite range …

ScatteringComputer scienceIsotropyMathematical analysisProbability density functionComputer Science::Performancesymbols.namesakeAdditive white Gaussian noiseModulation (music)Computer Science::Networking and Internet ArchitecturesymbolsFadingMultipath propagationComputer Science::Information TheoryRayleigh fading2021 IEEE 32nd Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC)
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An ergodic wideband MIMO channel simulator based on the geometrical T-junction scattering model for vehicle-to-vehicle communications

2010

In this paper, a wideband multiple-input multiple-output (MIMO) simulation model for vehicle-to-vehicle (V2V) channels in T-junction propagation environments is proposed. This simulation model takes the exact relationship between the angle-of-arrival (AOA) and the angle-of-departure (AOD) into account. In order to determine the parameters of the simulation model, the Riemann sum method (RSM) is applied. Furthermore, the statistical and ergodic properties of the simulation model are studied. Closed-form solutions are derived for the space-time-frequency cross-correlation function (STF-CCF), the two-dimensional (2D) spatial cross-correlation function (CCF), the temporal autocorrelation functi…

Scatteringbusiness.industryComputer scienceAutocorrelationMIMOFunction (mathematics)Correlation function (quantum field theory)TopologyAngle of arrivalFadingWidebandTelecommunicationsbusinessCommunication channelInternational Conference on Communications and Electronics 2010
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Fading mitigation coding techniques for space to ground free space optical communications

2014

In this manuscript, a Geostationary satellite-toground Free Space Optics (FSO) downlink channel model has been implemented, which is able to predict temporal irradiance fluctuations caused by scintillation at a wide range of turbulence conditions and for different values of the zenith angle. In order to mitigate fading events that occur in FSO communications, we have also tested the performance of three different families of Rateless Codes (Luby Transform, Raptor and RaptorQ) into our model and found that RaptorQ is the best candidate to mitigate errors in FSO links. Keywords— Optical Wireless Communications; Space-toGround FSO links, time-series, rateless codes; fading mitigation

ScintillationFading distributionGeographyOptical communicationGeostationary orbitElectronic engineeringFadingZenithOptical wireless communicationsFree-space optical communication2014 Euro Med Telco Conference (EMTC)
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On the First- and Second-Order Statistics of Selective Combining over Double Nakagami-m Fading Channels

2014

Second order statisticsElectronic engineeringFadingNakagami distributionAlgorithmMathematics2014 IEEE 80th Vehicular Technology Conference (VTC2014-Fall)
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I fenoli come nuovi materiali per la dosimetria EPR in campo misto neutroni-gamma

2014

Settore FIS/01 - Fisica SperimentaleSettore FIS/07 - Fisica Applicata(Beni Culturali Ambientali Biol.e Medicin)Dosimetria EPR NCT Gadolinio neutroni fading
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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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Fading mitigation coding techniques for space to ground free space optical communications

2014

Settore ING-INF/03 - TelecomunicazioniSpace-to-Ground FSO links time-series rateless codefading mitigationSettore ING-INF/02 - Campi ElettromagneticiOptical Wireless CommunicationSettore ING-INF/01 - Elettronica
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Performance of LoRa technology: link-level and cell-level performance

2020

Abstract LoRa is a chirp spread spectrum technology that is becoming very popular for low-power wide-area networks, with high-density devices. In this chapter, we study the capacity of LoRa in rejecting different interfering signals. First, we analyze LoRa modulation numerically demonstrating that channel captures appear easily and that collisions between packets modulated with different spreading factors (SFs) are not uncommon. We validate such findings in experiments based on commercial devices and software-defined radios. Second, we model the network capacity obtainable in a typical LoRa cell: we show that high SFs can be seriously influenced by inter-SF collisions and that fading has a …

Settore ING-INF/03 - Telecomunicazionibusiness.industryComputer scienceNetwork packetLoRa IoTspreading factorinterferencecapacityperformanceChirp spread spectrumCellular levelModulationDefault gatewayLink levelFadingbusinessCommunication channelComputer network
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Dissolvenze. Il corpo immaginario della fotografia

2020

Composto da fotografie appartenenti a tre progetti diversi – Lost in the K-Hole, Doppelgänger e Maelström – Human Surfaces è un diario visivo interpretativo che mette in luce, in modo originale, un’iconografia di varie e potenziali diversità individuali (l’alter ego, l’attore, il visionario) protagoniste di scene immaginarie ma non per questo meno obiettive. Di Donato si muove in un territorio non solo di osservazione ma di costruzione dell’immagine, a sancire che la fotografia, come tutte le forme visuali autoriali, è un’emanazione che contiene il suo artefice. Tessendo le fila delle sue visioni l’autore crea intersezioni, riconoscimenti, trasformazioni, vere e proprie descrizioni dense di…

Settore L-ART/06 - Cinema Fotografia E TelevisioneFotografia corpo ritratto dissolvenza apparizionePhotography body portrait fading apparition
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