Single and Multi-Hop Vehicular Visible and Infrared Light Communications

Visible light communications (VLC) have been proposed as a complementary technology in vehicular networks due to its several merits including high security, high scalability than RF technology. Notably, the RF technology established for vehicular networks best known as the dedicated short-range communications, supports many applications but doubts still exist on the capability of this technology to meet the low latency (where not more than 20 ms is required for pre-crash sensing and cooperative collision mitigation) and high reliability requirements in intelligent transport systems (ITS), when considering issues such as network outages as well as security issues. Of interest is the wide increase in the use of light emitting diode (LED)-based vehicle and traffic lights, and cameras in vehicles (rear and dashcams), traffic and security cameras, hence opening more opportunities for the VLC technology as part of ITS. Remarkably, camera-based VLC (i.e., optical camera communications) offers even further capabilities such as vehicle localization, motion and scene detection and pattern recognition. However, the VLC system has few challenges that needs addressing for the practical implementation of this technology as part of ITS. Consequently, this thesis focuses on addressing the key challenges and proposing novel technical analytical and experimental solutions. Firstly, increasing the robustness to sunlight induced noise is one of the major challenges in vehicular VLC, hence this thesis proposes an infrared (IR) transmission, as the amount of solar irradiance is lesser in the IR band than in the visible band. Performance of the proposed scheme is validated through numerical simulations with realistic emulated sunlight noise from empirical measurement. Investigations on the effects of turbulence with aperture averaging and fog on vehicular VLC is also carried out via experiments. Secondly, increasing the communication range is another major challenge, consequently the feasibility of using different vehicle taillights (TLs) as the VLC transmitter are evaluated via simulations based on empirical measurements of the radiation characteristics and transmit powers of the TLs. Results obtained indicate that, only a very low link span of 89 m at the forward error correction (FEC) bit error rate (BER) limit of 3.8 × 10-3, compared to 4.5, 5.4, and 6.3 m for the BMW vehicle-based TL at data rates of 10, 6, and 2 Mbps are achieved under realistic sunlight conditions. While, to increase the communication distance of camera-based VLC links, reducing the spatial bandwidth of the camera in its out of focus regions is proposed, mathematically analysed, and experimentally demonstrated where up to a 400 m link span at a 100 % success reception rate is achieved at a data rate of 800 bps, which is the longest so far reported. Relay-assisted links are also investigated using amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes under the emulated sunlight noise. A mathematical and simulation-based system model is developed, where different transmitter/receiver geometries are considered and AF and DF schemes. Results obtained via simulations shows that the DF scheme is a suitable candidate for vehicular VLC connectivity under emulated sunlight noise, offering at the FEC BER limit of 3.8 × 10-3 up to 150 % increase in the link distance by the end of the 2nd hop. Proof of concept experimental demonstration of AF and DF schemes for vehicular VLC are also carried out showing that DF is the preferred option. Moreover, insights are provided into the impact of various system parameters on the relay-assisted links. Finally, increasing the mobility of the vehicular VLC system is another major challenge, hence analysis on the required angular field of view (AFOV) for vehicular links considering necessary geometry parameters is investigated. Mathematical expressions to determine the required AFOV based on key system parameters are also derived. Furthermore, the relevance of the choice of the receiver parameters for an enhanced AFOV is also analysed, consequently a means to mitigate the effects of beam spot offset induced power losses at the photodiode caused by the misalignment of the transmitter and imaging receiver is proposed

Development of advanced control strategies for Adaptive Optics systems

Atmospheric turbulence is a fast disturbance that requires high control frequency. At the same time, celestial objects are faint sources of light and thus WFSs often work in a low photon count regime. These two conditions require a trade-off between high closed-loop control frequency to improve the disturbance rejection performance, and large WFS exposure time to gather enough photons for the integrated signal to increase the Signal-to-Noise ratio (SNR), making the control a delicate yet fundamental aspect for AO systems. The AO plant and atmospheric turbulence were formalized as state-space linear time-invariant systems. The full AO system model is the ground upon which a model-based control can be designed. A Shack-Hartmann wavefront sensor was used to measure the horizontal atmospheric turbulence. The experimental measurements yielded to the Cn2 atmospheric structure parameter, which is key to describe the turbulence statistics, and the Zernike terms time-series. Experimental validation shows that the centroid extraction algorithm implemented on the Jetson GPU outperforms (i.e. is faster) than the CPU implementation on the same hardware. In fact, due to the construction of the Shack-Hartmann wavefront sensor, the intensity image captured from its camera is partitioned into several sub-images, each related to a point of the incoming wavefront. Such sub-images are independent each-other and can be computed concurrently. The AO model is exploited to automatically design an advanced linear-quadratic Gaussian controller with integral action. Experimental evidence shows that the system augmentation approach outperforms the simple integrator and the integrator filtered with the Kalman predictor, and that it requires less parameters to tune

Optical Communication

Optical communication is very much useful in telecommunication systems, data processing and networking. It consists of a transmitter that encodes a message into an optical signal, a channel that carries the signal to its desired destination, and a receiver that reproduces the message from the received optical signal. It presents up to date results on communication systems, along with the explanations of their relevance, from leading researchers in this field. The chapters cover general concepts of optical communication, components, systems, networks, signal processing and MIMO systems. In recent years, optical components and other enhanced signal processing functions are also considered in depth for optical communications systems. The researcher has also concentrated on optical devices, networking, signal processing, and MIMO systems and other enhanced functions for optical communication. This book is targeted at research, development and design engineers from the teams in manufacturing industry, academia and telecommunication industries

Modern Applications in Optics and Photonics: From Sensing and Analytics to Communication

Optics and photonics are among the key technologies of the 21st century, and offer potential for novel applications in areas such as sensing and spectroscopy, analytics, monitoring, biomedical imaging/diagnostics, and optical communication technology. The high degree of control over light fields, together with the capabilities of modern processing and integration technology, enables new optical measurement systems with enhanced functionality and sensitivity. They are attractive for a range of applications that were previously inaccessible. This Special Issue aims to provide an overview of some of the most advanced application areas in optics and photonics and indicate the broad potential for the future

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Control and Characterization of Line-Addressable Micromirror Arrays

This research involved the design and implementation of a complete line-addressable control system for a 32x32 electrostatic piston-actuated micromirror array device. Line addressing reduces the number of control lines from N2 to 2N making it possible to design larger arrays and arrays with smaller element sizes. The system utilizes the electromechanical bi-stability of individual elements to bold arbitrary bi-stable phase patterns. The control system applies pulse width modulated (PWM) signals to the rows and columns of the micromirror array. Three modes of operation were conceived and built into the system. The first was the traditional signal scheme which requires the array to be reset before a new pattern can be applied. The second is an original scheme that allows dynamic switching between bi-stable patterns. The third and final mode applies an effective voltage ramp across the device by operating above mechanical cutoff. Device characterization and control system testing were conducted on predesigned and prefabricated samples from two different foundry processes. Testing results showed that the control system was successfully integrated. However, bi-stable control of individual mirror elements was not successfully demonstrated on samples due to flaws in the device design. A more robust device design which corrects these flaws and increases operational yield is proposed

Advanced Trends in Wireless Communications

Physical limitations on wireless communication channels impose huge challenges to reliable communication. Bandwidth limitations, propagation loss, noise and interference make the wireless channel a narrow pipe that does not readily accommodate rapid flow of data. Thus, researches aim to design systems that are suitable to operate in such channels, in order to have high performance quality of service. Also, the mobility of the communication systems requires further investigations to reduce the complexity and the power consumption of the receiver. This book aims to provide highlights of the current research in the field of wireless communications. The subjects discussed are very valuable to communication researchers rather than researchers in the wireless related areas. The book chapters cover a wide range of wireless communication topics

Annual Review of Progress in Applied Computational Electromagnetics

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