Performance analysis of modified asymmetrically-clipped optical orthogonal frequency-division multiplexing systems

A modification to the Asymmetrically-Clipped Optical Orthogonal Frequency-Division Multiplexing (ACO-OFDM) technique is proposed through unipolar encoding. A performance analysis of the Bit Error Rate (BER) is developed and Monte Carlo simulations are carried out to verify the analysis. Results are compared to that of the corresponding ACO-OFDM system under the same bit energy and transmission rate; an improvement of 1 dB is obtained at a BER of 10-4. In addition, the performance of the proposed system in the presence of atmospheric turbulence is investigated using single-input multiple-output (SIMO) configuration and its performance under that environment is compared to that of ACO-OFDM. Energy improvements of 4 dB and 2.2 dB are obtained at a BER of 10-4 for SIMO systems of 1 and 2 photodetectors at the receiver for the case of strong turbulence, respectively

A novel unipolar transmission scheme for visible light communication

This paper proposes a novel unipolar transceiver for visible light communication (VLC) by using orthogonal waveforms. The main advantage of our proposed scheme over most of the existing unipolar schemes in the literature is that the polarity of the real-valued orthogonal frequency division multiplexing (OFDM) sample determines the pulse shape of the continuous-time signal and thus, the unipolar conversion is performed directly in the analog instead of the digital domain. Therefore, our proposed scheme does not require any direct current (DC) biasing or clipping as it is the case with existing schemes in the literature. The bit error rate (BER) performance of our proposed scheme is analytically derived and its accuracy is verified by using Matlab simulations. Simulation results also substantiate the potential performance gains of our proposed scheme against the state-of-the-art OFDM-based systems in VLC; it indicates that the absence of DC shift and clipping in our scheme supports more reliable communication and outperforms the asymmetrically clipped optical-OFDM (ACO-OFDM), DC optical-OFDM (DCO-OFDM) and unipolar-OFDM (U-OFDM) schemes. For instance, our scheme outperforms ACO-OFDM by at least 3 dB (in terms of signal to noise ratio) at a target BER of 10 −4 , when considering the same spectral efficiency for both schemes

Comparison of Visible Light Commuý

Tato bakalářská práce se věnuje optickému přenosu dat ve volném prostoru, tzv. VLC (visible light communication). Práce je rozdělena na dvě části. V první části se věnuji teoretickému úvodu do celé problematiky a ve druhé části se věnuji rozboru měření a naměřených hodnot. V teoretické části jsou popsány základní vztahy mezi jasem, svítivostí, intenzitou a účinností zdrojů světla. Mezi nejčastěji využívané zdroje světla u VLC se využívají LED a OLED pro jejich rychlou odezvu mezi stavy zapnuto a vypnuto (on-off keying) a nízkou pořizovací cenu. Modulací světla, která je popsána v následující kapitole, dosáhneme násobně vyššího využití potenciálu přenosu dat, nežli metodou zapnutí a vypnutí diody. Posledním velmi důležitým prvkem celého přenosu je nepochybně přijímač. Ten rozdělujeme podle způsobu detekce signálu na detekci pomocí kamery, nebo fotodiody. Na závěr jsou zde popsány standardy vyvinuté IEEE (Institute of Electrical and Electronics Engineers). První měření využívalo k detekci signálu kameru. Je to ukázkový příklad využití metody rolling shutter. Maximální bitový přenos byl naměřen 6 kbit / s. Datový přenos je omezen kvalitou kamery, ale přenos byl bezchybný. Druhé měření využívalo fotodiodu. Jednalo se o přenos 70 MHz s metodou modulace on/off keying (OOK).The bachelor thesis deals with optical data transmission in free space, so-called VLC (visible light communication). The thesis has two parts. In the first part, I deal with a theoretical introduction to the overall problem. In the second part, I deal with the analysis of measurements and measured values. The theoretical part describes the basics relationships between brightness, luminosity, intensity, and efciency of light sources. Among the most commonly used light sources in VLC are LEDs, and OLEDs, widely used for their short response between on and off states (on-off keying). By modulating the light, which I am describing in the following chapter, we achieve a much higher utilization of the data transmission potential than just by a method of only switching the diode on and off The last element and also very important of the whole transmission is undoubtedly the receiver. We divide it according to the method of signal detection into detection by a camera or photodiode. The thesis ends with the standard description developed by the Institute of Electrical and Electronics Engineers (IEEE). The first measurement used a camera to detect the signal. By this method, we provided a example of using the rolling shutter. We measure a maximum bitrate at 6 kbit / s. The response time limits only the camera quality, but the transmission was errorless. The second measurement used a photodiode. It was a 70 MHz transmission with the on off keying (OOK) modulation method