8,711 research outputs found
Study of the atmospheric turbulence in free space optical communications
Abstract-In this paper the effect of atmospheric turbulence on free space optical (FSO) communications is investigated experimentally by designing a turbulence simulation chamber. The distributions of bits â0 â and â1 â levels are measured with and without turbulence. The bit error rate (BER) is then obtained from the distributions. The temperature gradient within the channel is less than 6 °C resulting in turbulence of log irradiance variance of 0.002. The received average signal is measured and used to characterise the simulated turbulence strength. We then evaluated the BER with turbulence and found that from an error free link in the absence of turbulence, the BER increased significantly to about 10-4 due to the turbulence effect. I
Ethernet - a survey on its fields of application
During the last decades, Ethernet progressively became the most widely used local area networking (LAN) technology. Apart from LAN installations, Ethernet became also attractive for many other fields of application, ranging from industry to avionics, telecommunication, and multimedia. The expanded application of this technology is mainly due to its significant assets like reduced cost, backward-compatibility, flexibility, and expandability. However, this new trend raises some problems concerning the services of the protocol and the requirements for each application. Therefore, specific adaptations prove essential to integrate this communication technology in each field of application. Our primary objective is to show how Ethernet has been enhanced to comply with the specific requirements of several application fields, particularly in transport, embedded and multimedia contexts. The paper first describes the common Ethernet LAN technology and highlights its main features. It reviews the most important specific Ethernet versions with respect to each application fieldâs requirements. Finally, we compare these different fields of application and we particularly focus on the fundamental concepts and the quality of service capabilities of each proposal
Hybrid Free-Space Optical and Visible Light Communication Link
V souÄastnosti bezdrĂĄtovĂ© optickĂ© komunikace (optical wireless communication, OWC) zĂskĂĄvajĂ ĆĄirokou pozornost jako vhodnĂœ doplnÄk ke komunikaÄnĂm pĆenosĆŻm v rĂĄdiovĂ©m pĂĄsmu. OWC nabĂzejĂ nÄkolik vĂœhod vÄetnÄ vÄtĆĄĂ ĆĄĂĆky pĆenosovĂ©ho pĂĄsma, neregulovanĂ©ho frekvenÄnĂho pĂĄsma Äi odolnosti vĆŻÄi elektromagnetickĂ©mu ruĆĄenĂ. Tato prĂĄce se zabĂœvĂĄ nĂĄvrhem OWC systĂ©mĆŻ pro pĆipojenĂ koncovĂœch uĆŸivatelĆŻ. SamotnĂĄ realizace spojenĂ mĆŻĆŸe bĂœt provedena za pomoci rĆŻznĂœch variant bezdrĂĄtovĂœch technologiĂ, napĆĂklad pomocĂ OWC, kombinacĂ rĆŻznĂœch OWC technologiĂ nebo hybridnĂm rĂĄdio-optickĂœm spojem. Za ĂșÄelem propojenĂ tzv. poslednĂ mĂle je analyzovĂĄn optickĂœ bezvlĂĄknovĂœ spoj (free space optics, FSO). Tato prĂĄce se dĂĄle zabĂœvĂĄ analĂœzou pĆenosovĂœch vlastnostĂ celo-optickĂ©ho vĂce skokovĂ©ho spoje s dĆŻrazem na vliv atmosfĂ©rickĂœch podmĂnek. V dneĆĄnĂ dobÄ mnoho uĆŸivatelĆŻ trĂĄvĂ Äas ve vnitĆnĂch prostorech kancelĂĄĆĂ Äi doma, kde komunikace ve viditelnĂ©m spektru (visible light communication, VLC) poskytuje lepĆĄĂ pĆenosovĂ© parametry pokrytĂ neĆŸ Ășzce smÄrovĂ© FSO. V rĂĄmci tĂ©to prĂĄce byla odvozena a experimentĂĄlnÄ ovÄĆena zĂĄvislost pro bitovou chybovost pĆesmÄrovanĂ©ho (relaying) spoje ve VLC. Pro propojenĂ poskytovatele datavĂœch sluĆŸeb s koncovĂœm uĆŸivatelem mĆŻĆŸe bĂœt vĂœhodnĂ© zkombinovat vĂce pĆenosovĂœch technologiĂ. Proto je navrĆŸen a analyzovĂĄm systĂ©m pro pĆekonĂĄnĂ tzv. problĂ©mu poslednĂ mĂle a poslednĂho metru kombinujĂcĂ hybridnĂ FSO a VLC technologie.The field of optical wireless communications (OWC) has recently attracted significant attention as a complementary technology to radio frequency (RF). OWC systems offer several advantages including higher bandwidth, an unregulated spectrum, resistance to electromagnetic interference and a high order of reusability. The thesis focuses on the deployment and analyses of end-user interconnections using the OWC systems. Interconnection can be established by many wireless technologies, for instance, by a single OWC technology, a combination of OWC technologies, or by hybrid OWC/RF links. In order to establish last mile outdoor interconnection, a free-space optical (FSO) has to be investigated. In this thesis, the performance of all-optical multi-hop scenarios is analyzed under atmospheric conditions. However, nowadays, many end users spend much time in indoor environments where visible light communication (VLC) technology can provide better transmission parameters and, significantly, better coverage. An analytical description of bit error rate for relaying VLC schemes is derived and experimentally verified. Nonetheless, for the last mile, interconnection of a provider and end users (joint outdoor and indoor connection) can be advantageous when combining multiple technologies. Therefore, a hybrid FSO/VLC system is proposed and analyzed for the interconnection of the last mile and last meter bottleneck
Optically powered communication system with distributed amplifiers
An optically powered communication system with distributed amplification is demonstrated using either distributed parametric amplification (DPA) or distributed Raman amplification (DRA) within the dispersion-shifted fiber (DSF) and single-mode fiber (SMF). At the fiber output the residual pump after the distributed amplification is recycled to power the receiver component. Our scheme is also a potential candidate for the last mile transmission. Based on our scheme, 4 channels of 10 Gb/s WDM signals are used to obtain practical performance evaluation. In the presence of 10-dB gain for signals, the power penalties of-dB at the BER of are achieved for DPA in DSF, and as the comparing counterpart of DPA, counter-pumping DRA induce approximately the same level of power penalty in DSF and -dB in SMF. Co-pumping DRA are also tested in both kind of fibers. Finally, the energy-efficiency issue for different pumping schemes is analyzed. © 2006 IEEE.published_or_final_versio
On the Performance of Millimeter Wave-based RF-FSO Multi-hop and Mesh Networks
This paper studies the performance of multi-hop and mesh networks composed of
millimeter wave (MMW)-based radio frequency (RF) and free-space optical (FSO)
links. The results are obtained in cases with and without hybrid automatic
repeat request (HARQ). Taking the MMW characteristics of the RF links into
account, we derive closed-form expressions for the networks' outage probability
and ergodic achievable rates. We also evaluate the effect of various parameters
such as power amplifiers efficiency, number of antennas as well as different
coherence times of the RF and the FSO links on the system performance. Finally,
we determine the minimum number of the transmit antennas in the RF link such
that the same rate is supported in the RF- and the FSO-based hops. The results
show the efficiency of the RF-FSO setups in different conditions. Moreover,
HARQ can effectively improve the outage probability/energy efficiency, and
compensate for the effect of hardware impairments in RF-FSO networks. For
common parameter settings of the RF-FSO dual-hop networks, outage probability
of 10^{-4} and code rate of 3 nats-per-channel-use, the implementation of HARQ
with a maximum of 2 and 3 retransmissions reduces the required power, compared
to cases with open-loop communication, by 13 and 17 dB, respectively.Comment: Submitted to IEEE Transactions on Wireless Communication
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