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Wyszukujesz frazę "free space" wg kryterium: Temat


Tytuł:
Free spaces
Autorzy:
Song, Jian
Tymchatyn, E.
Powiązania:
https://bibliotekanauki.pl/articles/1205112.pdf
Data publikacji:
2000
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
free space
hereditarily indecomposable continuum
polyhedron
Opis:
A space Y is called a free space if for each compactum X the set of maps with hereditarily indecomposable fibers is a dense $G_δ$-subset of C(X,Y), the space of all continuous functions of X to Y. Levin proved that the interval I and the real line ℝ are free. Krasinkiewicz independently proved that each n-dimensional manifold M (n ≥ 1) is free and the product of any space with a free space is free. He also raised a number of questions about the extent of the class of free spaces. In this paper we will answer most of those questions. We prove that each cone is free. We introduce the notion of a locally free space and prove that a locally free ANR is free. It follows that every polyhedron is free. Hence, 1-dimensional Peano continua, Menger manifolds and many hereditarily unicoherent continua are free. We also give examples that show some limits to the extent of the class of free spaces.
Źródło:
Fundamenta Mathematicae; 2000, 163, 3; 229-239
0016-2736
Pojawia się w:
Fundamenta Mathematicae
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Relay-assisted WDM-FSO System: A Better Solution for Communication under Rain and Haze Weather Conditions
Autorzy:
Dayal, N.
Singh, P.
Kaur, P.
Powiązania:
https://bibliotekanauki.pl/articles/958123.pdf
Data publikacji:
2017
Wydawca:
Instytut Łączności - Państwowy Instytut Badawczy
Tematy:
Free Space Optics
Wavelength Division Multiplexing
Opis:
Among various conventional wireless communication systems, Free Space Optics (FSO) may be distinguished as well, which provides a good level security, high data rates, an enormous bandwidth and negligible susceptibility to electromagnetic interference. The main problem arises with unfavorable weather conditions, which affect the system’s parameters and require an aversion to other paths. The weather conditions discussed are rain and haze. Elimination of their adverse effects is essential for establishing a better communication system. The routing path is a major issue, as its decreased parameters lead to the diversion of the transmitted signal or to its total loss. In this article, increased system path length and proficiency levels are demonstrated by using relays, which are assisted by Wavelength Division Multiplexing (WDM).
Źródło:
Journal of Telecommunications and Information Technology; 2017, 4; 54-59
1509-4553
1899-8852
Pojawia się w:
Journal of Telecommunications and Information Technology
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Performance probability distribution function for modeling visibility for free space optical link in Nigeria
Autorzy:
Ojo, Joseph Sunday
Olakunle Lawrence, Ojo
Ibitola, Gilbert Akin
Powiązania:
https://bibliotekanauki.pl/articles/1163564.pdf
Data publikacji:
2018
Wydawca:
Przedsiębiorstwo Wydawnictw Naukowych Darwin / Scientific Publishing House DARWIN
Tematy:
Free Space Optical
Nigeria
distribution functions
lognormal
visibility
Opis:
This paper attempt to assess the performance of the most appropriate distribution function for modeling atmospheric visibility over five selected locations (Akure, Enugu, Ikeja, Jos and Port-Harcourt) in Nigeria. The distribution functions are tested based on 5-year (2010-2014) visibility data obtained from Nigeria Meteorological Agency (NIMET). Five distribution functions are tested to determine most suitable one based on four different metric measures. The associated parameters of the most suitable fitted distribution are estimated and the trends in the characteristic of the visibility are deduced. The result shows that lognormal distribution present the best probability distribution function for modeling visibility over the selected locations. A typical result for one of the locations (Akure) show that the lognormal distribution has Root Mean Square Error (RMSE) of 0.0766 km, Mean Absolute Error (MAE) of 0.0095 km, Mean Absolute Percentage Error (MAPE) of 17.8 % and coefficient of determination (R2) of 0.87. When compared with other distribution functions, the same trend could be seen in other locations although with different values of RMSE, MAE, MAPE and R2. The location and the scale parameters for the total distribution varies seasonal-wise and are location depended. The overall result will be useful for predicting future visibility over the locations. It will also be a good tool for free space optical link design in Nigeria.
Źródło:
World Scientific News; 2018, 109; 211-234
2392-2192
Pojawia się w:
World Scientific News
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
An Overview of Free Space Optics with Quantum Cascade Lasers
Autorzy:
Mikołajczyk, J.
Powiązania:
https://bibliotekanauki.pl/articles/226628.pdf
Data publikacji:
2014
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
quantum cascade laser
free space optics
laser communications
Opis:
The article presents an overview of the work on quantum cascade lasers application in free space optical systems (Free Space Optics - FSO). There are discussed the main issues of the open-space laser communications and their practical construction. Comparative analyses of each FSO technology were performed. Brief description of quantum cascade (QC) lasers and some developments related to the use of these lasers in optical data link are also presented. In summary, the constructed models of FSO links with QC lasers are characterized.
Źródło:
International Journal of Electronics and Telecommunications; 2014, 60, 3; 259-264
2300-1933
Pojawia się w:
International Journal of Electronics and Telecommunications
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Compact QCL driver for free-space transmitter
Autorzy:
Mikołajczyk, J.
Garlińska, M.
Wesołowski, M.
Wojtas, J.
Bielecki, Z.
Powiązania:
https://bibliotekanauki.pl/articles/201659.pdf
Data publikacji:
2012
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
free space optics
laser communication
quantum cascade lasers
laser driver
Opis:
The paper presents investigations of a free space optical transmitter operating with quantum cascade lasers. The main goal of the research was to determine influence of lasers driver parameters on an optical data link performance. Using some commercial driving devices, the laser pulse limitations of power, repetition rate and time duration have been observed. In the paper, the preliminary results of the designed laser driver are described. The driver was developed at the Institute of Optoelectronics, MUT in cooperation with scientists from the Faculty Electrical Engineering, WUT. It is characterized by high current efficiency, high pulse repetition rate, and compact construction. Additionally, the driver also includes a controller of Peltier modules
Źródło:
Bulletin of the Polish Academy of Sciences. Technical Sciences; 2012, 60, 4; 763-768
0239-7528
Pojawia się w:
Bulletin of the Polish Academy of Sciences. Technical Sciences
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Measurements of shielding effectiveness of textile materials containing metal by the free-space transmission technique with data processing in the time domain
Autorzy:
Dvurechenskaya, N.
Bajurko, P. R.
Zieliński, R. J.
Yashchyshyn, Y.
Powiązania:
https://bibliotekanauki.pl/articles/221789.pdf
Data publikacji:
2013
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
textiles
shielding effectiveness
free-space transmission technique
time-domain gating
Opis:
The results of shielding effectiveness (SE) measurements of textile materials containing metal by the free-space transmission technique (FSTT) in the 1-26.5 GHz frequency range are presented in the paper. It is shown that experimental data processing using time-domain gating (TDG) makes it possible to effectively remove diffracted and reflected components from the desired signal. The comparison with the results obtained by other techniques, namely modified FSTT with TDG and coaxial line probe technique (ASTM D4935-99) is given. The comparison shows that the proposed technique gives more reasonable results while the measurement set-up is simpler in realization.
Źródło:
Metrology and Measurement Systems; 2013, 20, 2; 217-228
0860-8229
Pojawia się w:
Metrology and Measurement Systems
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Performance Analysis of WDM-FSO Link under Turbulence Channel
Autorzy:
Mazin, Ali A. Ali
Powiązania:
https://bibliotekanauki.pl/articles/1192036.pdf
Data publikacji:
2016
Wydawca:
Przedsiębiorstwo Wydawnictw Naukowych Darwin / Scientific Publishing House DARWIN
Tematy:
free space optics
BER
Atmospheric Turbulence
NRZ format
RZ technique
Opis:
In this paper, the performance analysis of FSO communication link in various atmospheric turbulence has been analysis for different bit rate using NRZ and RZ technique. The effect of turbulence on the link performance has been investigated by varying bit rate, turbulence strength and modulation format. FSO performance carried out for BER, Q. factor, received power under maximum link. Simulation results show that RZ format is best for strong turbulence. Where NRZ technique is used for low and medium turbulence.
Źródło:
World Scientific News; 2016, 50; 160-173
2392-2192
Pojawia się w:
World Scientific News
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Investigation of optical short pulse generation using intensity modulation for LiDAR and free-space communications
Autorzy:
Wang, Fei
Kang, Wen
Powiązania:
https://bibliotekanauki.pl/articles/1835768.pdf
Data publikacji:
2021
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
intensity modulator
optical pulse generator
pulsed LiDAR
free-space communication
Opis:
A simple optical pulse generation scheme for pulsed light detection and ranging (LiDAR) and free-space communications is proposed and experimentally and numerically demonstrated, in which continuous-wave light emitted by a distributed feedback-laser diode (DFB-LD) is modulated by a lithium-niobate Mach–Zehnder intensity modulator to generate optical short pulses, and an Er-doped fiber amplifier (EDFA) is used to boost transmitting light power. Possibilities of intensity modulators for high speed communications being used to generate optical short pulses for low speed pulsed LiDAR are investigated. The influences of bias voltage of intensity modulator and bit rate of modulation signal on the generated optical pulses are discussed. The pulse width obtained by using the return to zero signal with 33% duty cycle on bit rate of 2.5 and 5 Gbit/s is respectively 128.0 and 63.2 ps, and the corresponding nominal accuracy of pulsed LiDAR is respectively 19.2 and 9.5 mm, and low repetition frequency required by pulsed LiDAR is achieved by coding to high-speed modulation signal. The system performance for free-space communications and pulsed LiDAR is evaluated, respectively. We believe that the proposed scheme is suitable for the integrated system of pulsed LiDAR and free-space communications.
Źródło:
Optica Applicata; 2021, 51, 1; 97-107
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The kurtosis parameter of partially coherent controllable dark hollow beams in free space
Autorzy:
Li, J.
Wang, W W
Lai, Y
Powiązania:
https://bibliotekanauki.pl/articles/173815.pdf
Data publikacji:
2014
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
kurtosis parameter
partially coherent controllable dark hollow beams
free space
Opis:
Based on the extended Huygens–Fresnel principle and the definition of second-order moments of the Wigner distribution function, the analytical expression for the kurtosis parameter of partially coherent controllable dark hollow beams in free space is derived, and used to study the influence of beam parameters on the kurtosis parameter. It is shown that the kurtosis parameter increases with increasing the wavelength and the waist width, or decreasing the scaling factor, however, the effect of the beam order and the spatial correlation length on the kurtosis parameter depends on the propagation distance. The results can be interpreted physically.
Źródło:
Optica Applicata; 2014, 44, 4; 533-543
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Average capacity analysis of FSO system with Airy beam as carrier over exponentiated Weibull channels
Autorzy:
Li, Yi
Chu, Xingchun
Han, Zhongxiang
Tang, Hanling
Song, Xinkang
Powiązania:
https://bibliotekanauki.pl/articles/2202763.pdf
Data publikacji:
2023
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
Airy beam
free-space optical communication
channel capacity
exponentiated Weibull model
Opis:
Based on scintillation index of Airy beam and exponentiated Weibull channel model, analytical expressions of average channel capacity for free-space optical (FSO) communication links with Airy beam as signal carrier under weak atmospheric turbulence and on-off keying modulation scheme are derived. The average capacity at various propagation distances, transverse scale factors and exponential decay factors has been evaluated. And we compared the average capacity of FSO links with Airy beam and Gaussian beam as signal carrier. The results show that the average capacity of FSO links with Airy beam as carrier increases with the increase of mean signal-to-noise ratio and decreases uniformly with the increase of propagation distance. When the transverse scale factor of Airy beam is about 2 cm, a higher average capacity can be obtained. And the smaller the exponential decay factor of Airy beam, the larger the average capacity. Under the same source power or source width, the average capacity of FSO links with Airy beam as carrier is significantly higher than that of FSO links with Gaussian beam as carrier. The results of this research have some reference significance for the application of Airy beam in FSO communication system.
Źródło:
Optica Applicata; 2023, 53, 1; 35--48
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Optical Wireless Communications Operated at Long-Wave Infrared Radiation
Autorzy:
Mikolajczyk, Janusz
Szabra, Dariusz
Prokopiuk, Artur
Achtenberg, Krzysztof
Wojtas, Jacek
Bielecki, Zbigniew
Powiązania:
https://bibliotekanauki.pl/articles/226104.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
optical wireless communication
free space optics
quantum cascade lasers
optoelectronics
telecommunications
Opis:
This paper presents some construction analysis and test results of a Free Space Optics system operating at the wavelength of 9.35 μm. In the system, a quantum cascade laser and a photoreceiver with mercury cadmium telluride photodetectors were used. The main parameters of these elements were discussed taking into account a data link operation. It also provides to determine a data range for various weather conditions related to scattering and scintillation. The results of numerical analyses defined the properties of currently available FSO technologies working in the near infrared or in the short infrared range of spectrum versus the performances of the developed system. The operation of this system was verified in three different test environments. The obtained results may also contain important issues related to the practical application of any FSO system.
Źródło:
International Journal of Electronics and Telecommunications; 2020, 66, 2; 383-387
2300-1933
Pojawia się w:
International Journal of Electronics and Telecommunications
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Variable antennas positions solution to reduce pointing errors due to wind speed and temperature coupled effects during free space optical link using matrix Rician pointing error model
Autorzy:
Teuma Mbezi, Michel
Eke, Samuel
Som, Idelette Hermine Judith
Mouangue, Ruben Martin
Powiązania:
https://bibliotekanauki.pl/articles/27310098.pdf
Data publikacji:
2023
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
atmospheric turbulence
pointing error
free space optical transmission
Rician pointing error model
Opis:
Pointing errors (PE) during free space optical (FSO) transmission can be caused by laser beam wander due to thermal and wind dynamic instability. The aim of this work is to study the coupled effects of temperature and wind speed on PE using matrix Rician pointing error (MRPE) model; then show how variable antennas height can reduce PE due to wind speed and temperature coupled effects. To achieve this purposes, average PE expression was established using MRPE model. Then considering a Gaussian beam wave and Monin–Obukhov similarity functions for the structure parameters of temperature, explicit relationship was established between average PE, temperature and wind speed. It comes out of this study that under dynamic turbulence, one can appropriately modify temperature to reduce PE due to dynamic instability and reciprocally. Depending on turbulence large cells or frozen turbulence eddies distribution, PE can be reduced by appropriately modified antennas height or the distance between transmitter and receiver. That is why this work suggests to install variable or dynamic antennas (rather than fixed ones) which could intelligently modify its positions according to laser beam wander created by atmospheric turbulence.
Źródło:
Optica Applicata; 2023, 53, 3; 393--406
0078-5466
1899-7015
Pojawia się w:
Optica Applicata
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Indoor localization based on visible light communication and machine learning algorithms
Autorzy:
Ghonim, Alzahraa M.
Salama, Wessam M.
Khalaf, Ashraf A. M.
Shalaby, Hossam M. H.
Powiązania:
https://bibliotekanauki.pl/articles/2063908.pdf
Data publikacji:
2022
Wydawca:
Polska Akademia Nauk. Stowarzyszenie Elektryków Polskich
Tematy:
free-space optical communication
visible light communication
neural networks
random forests
machine learning
Opis:
An indoor localization system is proposed based on visible light communications, received signal strength, and machine learning algorithms. To acquire an accurate localization system, first, a dataset is collected. The dataset is then used with various machine learning algorithms for training purpose. Several evaluation metrics are used to estimate the robustness of the proposed system. Specifically, authors’ evaluation parameters are based on training time, testing time, classification accuracy, area under curve, F1-score, precision, recall, logloss, and specificity. It turned out that the proposed system is featured with high accuracy. The authors are able to achieve 99.5% for area under curve, 99.4% for classification accuracy, precision, F1, and recall. The logloss and precision are 4% and 99.7%, respectively. Moreover, root mean square error is used as an additional performance evaluation averaged to 0.136 cm.
Źródło:
Opto-Electronics Review; 2022, 30, 2; art. no. e140858
1230-3402
Pojawia się w:
Opto-Electronics Review
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
SAC-OCDMA over Hybrid FTTx Free Space Optical Communication Networks
Autorzy:
Sahbudin, R. K. Z.
Chun, T. T. K.
Anas, S. B. A.
Hitam, S.
Mokhtar, M.
Powiązania:
https://bibliotekanauki.pl/articles/308402.pdf
Data publikacji:
2015
Wydawca:
Instytut Łączności - Państwowy Instytut Badawczy
Tematy:
Hybrid FTTx free space optical
Khazani-Syed code
SAC-OCDMA
Spectral direct decoding
Opis:
This paper presents an investigation of Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) over hybrid Fiber-to-the-x (FTTx) Free Space Optical (FSO) link under different weather conditions. FTTx and FSO are the last mile technologies that complement each other in delivering secure and high speed communication to customers' residence or office. SAC-OCDMA is one of the potential multiplexing techniques that has become a research area of interest in optical communications and considered a promising technique for FTTx access networks. It is based on Khazani-Syed (KS) code with Spectral Direct Decoding (SDD) technique. All the components involved in the network were specied according to the available market product in order to simulate the actual environment as close as possible. The result shows that for bit error rate (BER) of 10‾9, the network is able to perform with 20 km Single Mode Fiber (SMF) spanning from the central office (CO) and 1.48 km FSO range with transmission rate of 1.25 Gb/s during heavy rain.
Źródło:
Journal of Telecommunications and Information Technology; 2015, 2; 52-58
1509-4553
1899-8852
Pojawia się w:
Journal of Telecommunications and Information Technology
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Analiza możliwości transmisji danych z wykorzystaniem laserów impulsowych
Analysis of possibility of data transmission with use of pulsed lasers
Autorzy:
Drozd, T.
Zygmunt, M.
Knysak, P.
Wojtanowski, J.
Powiązania:
https://bibliotekanauki.pl/articles/210004.pdf
Data publikacji:
2011
Wydawca:
Wojskowa Akademia Techniczna im. Jarosława Dąbrowskiego
Tematy:
transmisja danych
lasery impulsowe
łącze optoelektroniczne
data transmission
pulsed lasers
free space optics
Opis:
W systemach transmisji danych wykorzystywane są lasery o pracy ciągłej. W artykule przedstawiono koncepcje transmisji danych z wykorzystaniem laserów impulsowych. Jest to szczególnie istotne dla urządzeń, w których laser impulsowy już jest wbudowany i realizuje inne funkcje (np. dalmierz). Przedstawione zostały zalety oraz ograniczenia takiego sposobu kodowania. Dokonana została analiza szybkości transmisji danych wraz z przedstawieniem wpływu poszczególnych elementów kanału transmisyjnego na wynikową szybkość transmisji danych.
Pulsed lasers are used mainly in lidar systems, which generate laser pulses and detect and analyze reflected signals. In data transmission systems, continuous work lasers are used. It is also possible to use pulsed lasers in such systems. These features would be especially important for devices in which pulsed laser is already embedded and execute another function. This article shows data transmission system conception with the use of pulsed laser. Advantages and limits of this transmission method were described. Analysis of speed of data transmission was performed and influence of individual channel transmission elements on the data transmission speed was shown.
Źródło:
Biuletyn Wojskowej Akademii Technicznej; 2011, 60, 2; 63-73
1234-5865
Pojawia się w:
Biuletyn Wojskowej Akademii Technicznej
Dostawca treści:
Biblioteka Nauki
Artykuł

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