1,176 research outputs found
Hybrid Free-Space Optical and Visible Light Communication Link
V souÄŤastnosti bezdrátovĂ© optickĂ© komunikace (optical wireless communication, OWC) zĂskávajà širokou pozornost jako vhodnĂ˝ doplnÄ›k ke komunikaÄŤnĂm pĹ™enosĹŻm v rádiovĂ©m pásmu. OWC nabĂzejĂ nÄ›kolik vĂ˝hod vÄŤetnÄ› vÄ›tšà šĂĹ™ky pĹ™enosovĂ©ho pásma, neregulovanĂ©ho frekvenÄŤnĂho pásma ÄŤi odolnosti vĹŻÄŤi elektromagnetickĂ©mu rušenĂ. Tato práce se zabĂ˝vá návrhem OWC systĂ©mĹŻ pro pĹ™ipojenĂ koncovĂ˝ch uĹľivatelĹŻ. Samotná realizace spojenĂ mĹŻĹľe bĂ˝t provedena za pomoci rĹŻznĂ˝ch variant bezdrátovĂ˝ch technologiĂ, napĹ™Ăklad pomocĂ OWC, kombinacĂ rĹŻznĂ˝ch OWC technologiĂ nebo hybridnĂm rádio-optickĂ˝m spojem. Za účelem propojenĂ tzv. poslednĂ mĂle je analyzován optickĂ˝ bezvláknovĂ˝ spoj (free space optics, FSO). Tato práce se dále zabĂ˝vá analĂ˝zou pĹ™enosovĂ˝ch vlastnostĂ celo-optickĂ©ho vĂce skokovĂ©ho spoje s dĹŻrazem na vliv atmosfĂ©rickĂ˝ch podmĂnek. V dnešnĂ dobÄ› mnoho uĹľivatelĹŻ trávĂ ÄŤas ve vnitĹ™nĂch prostorech kancelářà či doma, kde komunikace ve viditelnĂ©m spektru (visible light communication, VLC) poskytuje lepšà pĹ™enosovĂ© parametry pokrytĂ neĹľ Ăşzce smÄ›rovĂ© FSO. V rámci tĂ©to práce byla odvozena a experimentálnÄ› ověřena závislost pro bitovou chybovost pĹ™esmÄ›rovanĂ©ho (relaying) spoje ve VLC. Pro propojenĂ poskytovatele datavĂ˝ch sluĹľeb s koncovĂ˝m uĹľivatelem mĹŻĹľe bĂ˝t vĂ˝hodnĂ© zkombinovat vĂce pĹ™enosovĂ˝ch technologiĂ. Proto je navrĹľen a analyzovám systĂ©m pro pĹ™ekonánĂ 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
Visible Light Communications towards 5G
5G networks have to offer extremely high capacity for novel streaming applications. One of the most promising approaches is to embed large numbers of co-operating small cells into the macro-cell coverage area. Alternatively, optical wireless based technologies can be adopted as an alternative physical layer offering higher data rates. Visible light communications (VLC) is an emerging technology for future high capacity communication links (it has been accepted to 5GPP) in the visible range of the electromagnetic spectrum (~370–780 nm) utilizing light-emitting diodes (LEDs) simultaneously provide data transmission and room illumination. A major challenge in VLC is the LED modulation bandwidths, which are limited to a few MHz. However, myriad gigabit speed transmission links have already been demonstrated. Non line-of-sight (NLOS) optical wireless is resistant to blocking by people and obstacles and is capable of adapting its’ throughput according to the current channel state information. Concurrently, organic polymer LEDs (PLEDs) have become the focus of enormous attention for solid-state lighting applications due to their advantages over conventional white LEDs such as ultra-low costs, low heating temperature, mechanical flexibility and large photoactive areas when produced with wet processing methods. This paper discusses development of such VLC links with a view to implementing ubiquitous broadcasting networks featuring advanced modulation formats such as orthogonal frequency division multiplexing (OFDM) or carrier-less amplitude and phase modulation (CAP) in conjunction with equalization techniques. Finally, this paper will also summarize the results of the European project ICT COST IC1101 OPTICWISE (Optical Wireless Communications - An Emerging Technology) dealing VLC and OLEDs towards 5G networks
Nonlinearity and Noise Effects in Multi-level Signal Millimeter-Wave over Fiber Transmission using Single- and Dual-Wavelength Modulation
We transmit multilevel quadrature amplitude modulation (QAM) data-IEEE 802.16 schemes-at 20 MSps and an orthogonal frequency-division multiplexing (OFDM) 802.11 g signal (54 Mbps) with a 25 GHz millimeter-wave over fiber system, which employs a dual wavelength source, over 20 km of single mode fiber. Downlink data transmission is successfully demonstrated over both optical and wireless (up to 12 m) paths with good error vector magnitude. An analysis of two different schemes, in which data is applied to one (single) and both (dual) of the wavelengths of a dual wavelength source, is carried out. The system performance is analyzed through simulation and a good match with experimental results is obtained. The analysis investigates the impact of Mach-Zehnder modulator (MZM) and RF amplifier nonlinearity and various noise sources, such as laser relative intensity noise, amplified spontaneous emission, thermal, and shot noise. A comparison of single carrier QAM IEEE 802.16 and OFDM in terms of their sensitivity to the distortions from MZM and RF amplifier nonlinearity is also presented
On the Performance of Single- and Multi-carrier Modulation Schemes for Indoor Visible Light Communication Systems
In this paper, we investigate and compare the performance of single- and
multi-carrier modulation schemes for indoor visible light communication (VLC).
Particularly, the performances of single carrier frequency domain equalization
(SCFDE), orthogonal frequency division multiplexing (OFDM) and on-off keying
(OOK) with minimum mean square error equalization (MMSE) are analyzed in order
to mitigate the effect of multipath distortion of the indoor optical channel
where nonlinearity distortion of light emitting diode (LED) transfer function
is taken into account. Our results indicate that SCFDE system, in contrast to
OFDM system, does not suffer from high peak to average power ratio (PAPR) and
can outperform OFDM and OOK systems. We further investigate the impact of LED
bias point on the performance of OFDM systems and show that biasing LED with
the optimum value can significantly enhance the performance of the system.
Bit-interleaved coded modulation (BICM) is also considered for OFDM and SCFDE
systems to further compensate signal degradation due to inter-symbol
interference (ISI) and LED nonlinearity.Comment: 6 Pages, IEEE Globecom conference 201
A review of gallium nitride LEDs for multi-gigabit-per-second visible light data communications
The field of visible light communications (VLC) has gained significant interest over the last decade, in both fibre and free-space embodiments. In fibre systems, the availability of low cost plastic optical fibre (POF) that is compatible with visible data communications has been a key enabler. In free-space applications, the availability of hundreds of THz of the unregulated spectrum makes VLC attractive for wireless communications. This paper provides an overview of the recent developments in VLC systems based on gallium nitride (GaN) light-emitting diodes (LEDs), covering aspects from sources to systems. The state-of-the-art technology enabling bandwidth of GaN LEDs in the range of >400 MHz is explored. Furthermore, advances in key technologies, including advanced modulation, equalisation, and multiplexing that have enabled free-space VLC data rates beyond 10 Gb/s are also outlined
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