Artificial Neural Network Utilization for FSO Link Performance Estimation

This paper describes FSO link performance prediction based on available meteorological data using different Artificial Neural Network (ANN) approaches. Several types of ANNs were compared and their performance were evaluated. The paper introduces an ANN application utilizing real delayed data. This approach has been validated to be more precise than common feed-forward neural networks

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

Dispersion and Pulse Interferences Investigation for UWB Signal Propagation

The Ultra WideBand (UWB) technology utilizing nanosecond pulses has been one of the main phenomena in communications and radar applications for several years. This paper discusses the basic measurement techniques of impulse systems, particularly focusing on the dispersion and pulse interferences of the UWB propagation channel. Propagation aspects of two-ray approach are investigated in depth, using both measurements and simulations

Elliptic and Hyperbolic Dielectric Lens Antennas in mm-Waves

Dielectric lenses can substantially improve antenna parameters, especially the planarity of radiated waves and the antenna gain. The paper deals with their application in millimeter-wave band. The main goal concerns the introduction of characteristics and differences between the most commonly used types of dielectric lens antennas, i.e. elliptic and hyperbolic. Their particular features as well as behavior of radiating systems incorporating the lenses are investigated. Specific features of these lenses are discussed for both, near-field and farfield based on simulation and measurement results

Should Analogue Pre-Equalisers be Avoided in VLC Systems-

\ua9 2009-2012 IEEE.Visible light communication (VLC) systems are highly constrained by the limited 3-dB bandwidth of light-emitting diodes (LEDs). Analogue pre-equalisers have been proposed to extend the LED\u27s bandwidth at the cost of reduced signal-to-noise ratio (SNR). Compared with the pre-equaliser, the multi-carrier modulation with bit-loading can efficiently use the spectrum beyond the LED\u27s raw 3-dB bandwidth without incuring SNR penalties by employing multiple narrow quasi-flat sub-bands to eliminate the need for equalisation. In this work we show by means of theoretical and experimental investigation that VLC with multi-band carrierless amplitude and phase modulation with bit-loading can outperform VLC with analogue pre-equalisers

Filter-less WDM for visible light communications using colored pulse amplitude modulation

This paper demonstrates, for the first time, a new wavelength-division multiplexing (WDM) scheme for visible light communications using multi-level coloured pulse amplitude modulation (M-CPAM). Unlike traditional WDM, no optical bandpass filters are required and only a single optical detector is used. We show that, by transmitting n independent sets of weighted on-off keying non-return-to-zero data on separate wavelengths over a line-of-sight transmission path, the resultant additive symbols can be successfully demodulated. Hence, the data rates can be aggregated for a single user or divided into individual colours for multiple user access schemes. The system is empirically tested for M = 4 and 8 using an off-the-shelf red, green and blue (RGB) chip light emitting diode (LED). We demonstrate that for M = 4, using the R and B chips a bit error rate (BER) of ≤10-6 can be achieved for each wavelength at bit rates up to 10 Mbps, limited by the LEDs under test. For M = 8 using R, G and B a BER of ≤10-6 can be achieved for each wavelength at bit rates up to 5 Mbps

A Survey on Recent Advances in Organic Visible Light Communications

Visible light communication (VLC) employs light emitting diodes (LEDs) to provide illumination and data communications simultaneously. Organic LEDs (OLEDs) employing small molecules and long-chain polymers PLEDs, have been gaining attention within the VLC research community due to their inherent advantages such as flexible substrates and low-cost manufacturing. However, the carrier mobility of organic semiconductors is much slower than the devices composed of metal alloys, such as gallium nitride, thus leading to a restriction in the OLED modulation bandwidth. The manufacturing processes, materials and the photoactive size of the devices can affect the raw bandwidth of OLEDs. To increase the transmission speeds, novel approaches have been proposed including equalization techniques, signalling schemes and the optimum driver circuits. The paper provides a survey on the evolution of OLED-based VLC systems, and the respective challenges and recent progresses

Demonstration of a Hybrid FSO/VLC Link for the Last Mile and Last Meter Networks

OAPA In this paper, a hybrid free-space optical and visible light communication (FSO/VLC) system was experimentally demonstrated as a solution to overcome the last mile and last meter access networks bandwidth bottleneck. We evaluate the system performance of a multiband carrier-less amplitude and phase ($\textit{m}$-CAP) modulation scheme for a range of FSO/VLC link lengths and $\textit{m}$-CAP parameters (i.e., the roll-off factor of the filters and a number of subcarriers) in terms of the data rate $R_b$ (i.e., spectral efficiency). We show that for the configuration with a 1 m VLC link the \mbox{10-CAP} offers more than a 40% improvement in the measured $R_b$ compared to 2-CAP for the same bit error rate target. The $R_b$ penalty due to the extension of a VLC link span from 1 m to 3 m reaches to 12.6 Mb/s for the \mbox{10-\text{CAP}} scheme (i.e., $\sim$39% degradation in $R_b$). To fully cover all aspects of the hybrid FSO/VLC system, we also investigate the atmospheric turbulence effect on the 500 m FSO link where $R_b$ is decreased by 30% for the refractive index structure parameter $C_n^2$ of \mbox{2.4\times10^{\minus15} m^{\minus2/3}} compared to a clear channel condition

Visible light communications: multi-band super-Nyquist CAP modulation

In this paper, we experimentally demonstrate the performance of a non-orthogonal multi-band super-Nyquist carrier-less amplitude and phase (m-SCAP) modulation for visible light communications (VLC). We break the orthogonality between sub-bands in the frequency domain by compressing the spectrum, purposely overlapping them, and introducing inter-band interference (IBI). We demonstrate that our proposed system can tolerate IBI, and hence spectral efficiency can be increased without introducing additional complexity to the receiver. We show that m-SCAP can tolerate up to 30% and 20% compression for 4- and 16-level quadrature amplitude modulation, respectively, thus leading to an improvement in spectral efficiencies up to 40% and 25%, respectively, at the cost of bit error rate performance, which however remains below the 7% forward error correction limit. Moreover, the experimental results are supported by numerical simulations

Strategies for organic VLC: Effects of clipping on the performance of multi-band CAP modulation with polymer-based light-emitting diodes

We investigate, for the first time, the effect of signal clipping on multi-band carrier-less amplitude and phase (m-CAP) modulation in visible light communications based on PLEDs. We experimentally demonstrate a Q-factor improvement up to ~2.25 dB can be obtained with a clipping level of 50%