Real-Time Experimental Demonstration of Multi-band CAP Modulation in a VLC System with Off-the-Shelf LEDs

We demonstrate, for the first time, m-CAP modulation using off-the-shelf LEDs in a VLC in real time experimental setup using field programmable gate arrays based in universal software radio peripherals (USRPs). We demonstrate transmission speeds up to ~30 Mb/s can be achieved, which supports high definition television streaming.Comment: 2 pages, 4 figures, IEEE INFOCOM Demonstration

Visible Light Communications: Simplified Co-Equalisation of Fast OFDM in a Multiple-Input Multiple-Output Configuration

In this paper we experimentally demonstrate, for the first time, a simplified co-equalisation for imaging multiple-input multiple-output based visible light communication systems. We show that in such systems, where all channels have similar magnitude responses, an equaliser trained on a single channel produces coefficients that may be used in the form of a look-up table to equalise the remaining channels without the need for explicit or bespoke training. The system demonstrated is based on the fast-orthogonal frequency division multiplexing based on pulse amplitude modulation scheme to improve the spectral efficiency, where a data rate of 80 Mb/s is achieved using four light-emitting diodes, each of a 4 MHz raw bandwidth. We show that the reported system performance closely matches that of the traditional and more computationally complex system in terms of bit-error rate

Duobinary Modulation for Visible Light Communications

The paper proposes and experimentally investigates the performance of the duobinary transmission technique for a highly bandlimited VLC system. By adding a controlled amount of inter-symbol interference (ISI) into the transmitted signals through the use of pulse shaping filters, data rate can be doubled within the same signal bandwidth. To gain full insight into duobinary signalling, the so-called modified binary scheme is also tested. Bit error rate (BER) performance of both systems is measured for a range of data rates and compared to BERs for ideal binary and traditional on-off keying non-return to zero (OOK-NRZ) formats, across the same physical link. We show the duobinary system can support higher bit rates and lower BER than OOK-NRZ while requiring half the bandwidth of the binary scheme

Non-Orthogonal Multi-band CAP for Highly Spectrally Efficient VLC Systems

In this work we propose and experimentally demonstrate a novel non-orthogonal multi-band carrier-less amplitude and phase (NM-CAP) scheme for bandlimited visible light communication systems in order to increase the spectral efficiency. We show that a bandwidth saving up to 30% can be achieved thus resulting in 44% improvement in the measured spectral efficiency with no further bit error rate performance degradation compared to the traditional m-CAP scheme. We also show that higher order systems can provide higher bandwidth compression than low order systems. Furthermore, with no additional functional blocks at the transmitter or the receiver the proposed scheme introduces no extra computational complexity.Comment: 6 pages, 5 figure

Investigation into Using Compensation for the Nonlinear Effects of the Output of LEDs in Visible Light Communication Systems

This paper investigate the effects of the nonlinear output power to the input current transfer function of a light emitting diode (LED) used as the transmitter in visible light communication systems, and proposes a compensation technique to mitigate the non-linearity. Using an off the shelf red, amber, blue, green (RAGB) LED the nonlinear transfer function is measured and then compensated for. The results show that, for the green LED, which has the highest degree of nonlinearity, an improvement in the received error vector magnitude (EVM)of almost 7 dB can be achieved. We also show that, the improvement in EVM over the uncompensated scheme decreases with increased LED linearity

Experimental Demonstration of Staggered CAP Modulation for Low Bandwidth Red-Emitting Polymer-LED based Visible Light Communications

In this paper we experimentally demonstrate, for the first time, staggered carrier-less amplitude and phase (sCAP) modulation for visible light communication systems based on polymer light-emitting diodes emitting at ~639 nm. The key advantage offered by sCAP in comparison to conventional multiband CAP is its full use of the available spectrum. In this work, we compare sCAP, which utilises four orthogonal filters to generate the signal, with a conventional 4-band multi-CAP system and on-off keying (OOK). We transmit each modulation format with equal energy and present a record un-coded transmission speed of ~6 Mb/s. This represents gains of 25% and 65% over the achievable rate using 4-CAP and OOK, respectively.Comment: 6 pages, 9 figures, IEEE ICC 2019 conferenc

A 40 Mb/s VLC System Reusing an Existing Large LED Panel in an Indoor Office Environment

With advances in solid-state lighting, visible light communication (VLC) has emerged as a promising technology to enhance existing light-emitting diode (LED)-based lighting infrastructure by adding data communication capabilities to the illumination functionality. The last decade has witnessed the evolution of the VLC concept through global standardisation and product launches. Deploying VLC systems typically requires replacing existing light sources with new luminaires that are equipped with data communication functionality. To save the investment, it is clearly desirable to make the most of the existing illumination systems. This paper investigates the feasibility of adding data communication functionality to the existing lighting infrastructure. We do this by designing an experimental system in an indoor environment based on an off-the-shelf LED panel typically used in office environments, with the dimensions of 60 × 60 cm2. With minor modifications, the VLC function is implemented, and all of the modules of the LED panel are fully reused. A data rate of 40 Mb/s is supported at a distance of up to 2 m while using the multi-band carrierless amplitude and phase (CAP) modulation. Two main limiting factors for achieving higher data rates are observed. The first factor is the limited bandwidth of the LED string inside the panel. The second is the flicker due to the residual ripple of the bias current that is generated by the panel’s driver. Flicker is introduced by the low-cost driver, which provides bias currents that fluctuate in the low frequency range (less than several kilohertz). This significantly reduces the transmitter’s modulation depth. Concurrently, the driver can also introduce an effect that is similar to baseline wander at the receiver if the flicker is not completely filtered out. We also proposed a solution based on digital signal processing (DSP) to mitigate the flicker issue at the receiver side and its effectiveness has been confirmed

Optoelectronic Modelling, Circuit Design and Modulation for Polymer-Light Emitting Diodes for Visible Light Communication Systems

This paper investigates the use of organic polymer light emitting diodes (PLEDs) for the use in visible light communications (VLC). We prepared blue and green emitting PLEDs using commercial light-emitting polymers, and then characterised the device emission (spectrum and power), and extracted their circuit parameters for their electrical equivalent model for driving with small signals. In addition, we characterised the bandwidth ( Bmod ) of the devices over a period of continuous driving (∼ 4 h) and found that for the blue PLEDs the Bmod decreased from an initial 750 kHz to a steady state of ∼250 kHz. The green-emitting devices were found to benefit from an extended Bmod of ∼1.5 MHz at the beginning of the test, which then stabilised to ∼850 kHz. Furthermore, with the addition of a first order RC filter we show that, the steady state Bmod of the blue PLED cane be increased by a factor of ∼3, thus allowing > 1 Mbps non-return to zero on-off keying (NRZ OOK) data transmission in a complete VLC system