This paper presents an experimental investigation of a screen-to-camera-based communication (S2C) system. The study examines the performance of the smartphone transmitter (Tx) screen in terms of power received, beam profile, and Lambertian order as well as evaluates the impact of different transmission conditions such as distance, tilt, and rotation angles. The results demonstrate that for the line of sight (LOS) link, the Tx has an average Lambertian order of 3.5 and a transmission accuracy of over 100%. Overall, the study demonstrates the potential of optical camera communication technology for the development of efficient and reliable S2C systems.

This paper addresses the effects of blocking and shadowing due to peoples’ movement on the performance of visible light positioning system based on received signal strength. We consider both line-of-sight and non-line-of-sight paths and using a non-sequential ray-tracing model, the channel is characterised with and without blocking and shadowing. A linear least square with a polynomial regression model is proposed for the position estimation. We show that, the VLP accuracy degrade by ~90 and ~67% due to blocking and shadowing, respectively. Besides, at a confidence interval of 90%, the positioning error ε p of 1.47 m is recorded with human blockage as compared with 0.15 m for the non-blocking cases while shadowing introduces ε p of 0.82 m compared with 0.27 m for the non-blocking case.

Visible light communications (VLC) are currently being exploited as a potential alternative to radio frequency (RF) communications, which have been the most widely used wireless access technology so far. The need to find possible alternatives to RF communications is highlighted by the exponential increase in mobile/fixed wireless devices and the decrease in available bandwidth in regulated RF bands. Alternatively, the visible band has hundreds of Terahertz (400-790 THz) of unlicensed spectrum available for wireless communications, which can be used complementary to RF networks. Furthermore, electromagnetic waves at these wavelengths do not penetrate opaque objects, making communications secure as the signal cannot be intercepted by anyone outside the room where the optical wireless communication is taking place. Another advantage of optical waves compared to radio signals is their immunity to electromagnetic interference. This feature allows communications to be carried out in places where very sensitive electronic equipment is operated, namely in hospitals and airplanes. Furthermore, most of the current lighting infrastructure already considers light-emitting diodes (LEDs) as the main light source, and in some applications, the use of laser diodes (LDs) is beginning to appear, such as in car headlights. Therefore, with a marginal additional cost, it is possible to integrate this system into the current illumination infrastructure, providing high-speed secure wireless communications, taking advantage of the fact that light does not pass through walls. This PhD thesis focuses on achieving multi-Gigabit per second (Gbit/s) VLC transmissions, specifically targeting next-generation wireless communication systems. By employing advanced digital signal processing techniques, particularly entropy loading, this research successfully reaches unprecedented bit rates in RGB-VLC systems that utilize diffused light illumination. In this thesis, bit rates ranging from 26 to 46 Gbit/s were achieved over free-space distances of 50 cm to 200 cm using RGB laser diodes. In addition to enhancing data transmission rates, the study meticulously evaluates the quality of light generated by the experimental setup, assessing its performance in various practical scenarios, mainly indoor environments. During this thesis, the joint optimization of correlated color temperature and bit rate of the VLC system was demonstrated, achieving bit rates around 30 Gbit/s. Moreover, the research includes the development of a robust structural interface designed to seamlessly connect a fiber optic network to VLC access points, optimizing both data transmission and overall system efficiency.

The concept of the Internet of Things (IoT) is the Internet connectivity of everyday objects, relying on low-cost, low-power, and small form factor devices. Current IoT technology is based on the radio-frequency spectrum, however with the increasing number of devices the channel is becoming crowded. Visible light communications (VLC) has been proposed as a complementary technology of IoT scenarios, having the advantage of reusing the spectrum within few meters due to the highly directive radiation pattern. In this thesis, VLC is used with a hybrid digital and analog architecture using m-CAP is used for addressing the multiple user access in such scenarios.

This paper addresses and implements a Direct Sequence Spread Spectrum (DSSS) transceiver for Visible Light Communication (VLC) systems based on FPGA. A transceiver was implemented including a transmitter capable of driving an array of light emitting diodes (LED) and a Pseudo-Noise (PN) matched decorrelator. The receiver architecture uses a discrete FIR correlator for data synchronization and acquisition. In this paper, a novel and simple PN code with a 10 bit sequence length is developed. This code offers a similar performance to the popular Barker code; however, it has a simple design. The used FPGA resources are presented along with a performance analysis. © 2011 IEEE.

This paper discusses system design considerations concerning the use of visible light communication (VLC) concepts in road traffic control systems. A simple traffic set-up model has been analyzed in order to optimize various important design parameters. This optimization is based on the gain variation over 100m transmission range. This approach will help to specify the needed gain for the receiver in the complete set-up in order to further increase the coverage area. It will also allow important simplifications at the front-end design level. © 2009 IEEE.

This paper discusses the implementation of a light emitting diode based visible light communication system, for intelligent transportation in road safety applications. The signal processing of both, transmitter and receiver are realized in a field programmable gate array using two Spartan-3E development kits. The implemented modulation scheme is based on direct sequence spread spectrum techniques. The performance of the overall system is evaluated and results are presented. It is found that the system is well suited for traffic broadcast at low data rate and medium range. The simulation results also show that spread spectrum modulation techniques mitigate the effect of noise produced by ambient artificial light sources. © 2011 IEEE.

Light emitting diodes (LEDs) used in visible light communications (VLC) have a limited optical power-current linear range, which could be a problem in multi-level and multicarrier frequency modulation schemes. Orthogonal frequency division multiplexing (OFDM) as a popular scheme in VLC suffers from nonlinear distortion due to the high peak to average power ratio (PAPR). In this paper, we present a novel single carrier optical frequency division multiplexing signaling scheme for VLC, where the symmetrical characteristics of single carrier frequency division multiple access is investigated in order to reduce PAPR. Simulation results show that PAPR reduced by 10 dB compared to the traditional asymmetrically clipped optical OFDM. We show that the bit-error-rate performance of the proposed scheme is enhanced compared to ACO-OFDM when the limited dynamic range of digital to analog converter and LED is considered.

In optical camera communication (OCC) systems leverage on the use of commercial off-the-shelf image sensors to perceive the spatial and temporal variation of light intensity to enable data transmission. However, the transmission data rate is mainly limited by the exposure time and the frame rate of the camera. In addition, the camera’s sampling will introduce intersymbol interference (ISI), which will degrade the system performance. In this paper, an artificial neural network (ANN)-based equaliser with the adaptive algorithm is employed for the first time in the field of OCC to mitigate ISI and therefore increase the data rate. Unlike other communication systems, training of the ANN network in OCC is done only once in a lifetime for a range of different exposure time and the network can be stored with a look-up table. The proposed system is theoretically investigated and experimentally evaluated. The results record the highest bit rate for OCC using a single LED source and the Manchester line code (MLC) non-return to zero (NRZ) encoded signal. It also demonstrates 2 to 9 times improved bandwidth depending on the exposure times where the system’s bit error rate is below the forward error correction limit.

Future IoT systems will require progressively smaller sizes, cost, complexity and power consumption. This paper proposes a new architecture using a hybrid m-CAP/QAM system with the goal to provide such features to future VLC based IoT devices. The proposed system architecture uses a ceiling LED light fixture implementing an m-CAP digital modulator, connected to several IoT devices, implemented by analog de modulators. The simulated performance presents an increase on BER when compared to a digital m-CAP receiver, between 1 and 2 dB. Nevertheless, considering IoT scenarios, having low cost/size/power devices can surpass the performance penalty.