No description available.

The COVID-19 global pandemic forced long lock-downs and physical distancing in different world regions. As a consequence, many jobs, services, and courses switched to online mode. This sudden turn of events created a dramatic increase in internet bandwidth demand, which has reached crisis point—even in developed countries—and widened the gap between those living in cities and far-flung regions. Installing new optical fibers to extend the capacity can be expensive. Radiofrequency (RF) is cur- rently the technology of choice to satisfy the bandwidth demand in under-connected regions, but is bandwidth-limited and strictly regulated. Connecting the unconnected via laser beams propagating in the atmosphere can be an efficient solution to provide fiber-like connectivity, while also being economically profitable. Free-space optics (FSO) is an unlicensed technology that uses infrared links to connect two communi- cating terminals. FSO systems can be running quickly compared to RF ones. FSO is also seen as a potential solution to provide high-speed connectivity between satellites and ground stations, and fly unmanned aerial vehicles (UAVs) and ground terminals. However, FSO is subject to various channel-related challenges, including atmospheric attenuation, turbulence, and pointing errors. In this thesis, we develop an FSO chan- nel simulation tool that considers the various effects that could potentially occur in terrestrial and vertical channels. We extend our study to cover structured light beams, which have been intensively considered in the last decade, as an extra degree of freedom for FSO. Finally, we consider realistic meteorological data from different regions in the Kingdom of Saudi Arabia to identify the best locations to deploy FSO systems.

The need for wireless connectivity is ever increasing while conventional radio frequency (RF) communications are limited by the amount of available spectrum. Visible light communications (VLC) are emerging as a promising complementary to the RF wireless, thanks to the enormous available bandwidth in the visible spectrum. Moreover, VLC integrates into the ubiquitous illumination infrastructures to satisfy the need for wireless connectivity indoors. Commercially available light-emitting diodes (LEDs) are low-cost, simple, and have a small modulation bandwidth. For the small modulation bandwidth, VLC systems must enjoy high spectral efficiency to achieve high-rate transmission. Additionally, VLC systems must have high power efficiency to help preserve the critical advantage of LEDs for illumination applications. Furthermore, since LED luminaires are constrained by cost, deployed VLC systems must be low-complexity. Indoor VLC channels are dispersive due to multipath propagation indoors and due to the limited bandwidth of the optoelectronics. However, time-domain equalization on such channels can be prohibitively expensive for long serials. These challenges motivate extensive research on optical orthogonal frequency division multiplexing (OFDM). Given those problems and challenges, this thesis introduces novel spectrum- and power-efficient optical OFDM modulation schemes to implement with low complexity in VLC systems. Firstly, absolute value layered asymmetrically clipped optical OFDM (ALACO-OFDM) is presented to achieve high spectral efficiency and high power efficiency with fewer layers, thus requiring low complexity. Compared to its counterparts, ALACO-OFDM can achieve higher spectral efficiency and information rate even with fewer layers. Antisymmetry-constructed clipped optical OFDM (AC-OFDM) is then introduced as a novel low-complexity modulation scheme. To enhance the spectral efficiency and retain low-complexity, layered AC-OFDM (LAC-OFDM) is introduced, consisting of several layers of AC-OFDM signals. LAC-OFDM is shown to be less complex compared to its state-of-the-art counterparts. Concerning a practical VLC dispersive channel, low-complexity layered ACO-OFDM (L-LACO) is introduced with simple equalization. Mathematically, L-LACO generates identical signals to the existing layered asymmetrically-clipped optical OFDM (LACO-OFDM); however, it requires only half arithmetic operations at both the transmitter and the receiver. For a practical bandlimited VLC dispersive channel, the previous optical OFDM modulation schemes will be no longer non-negative after interpolation with sinc(t) pulse. This thesis presents Kramers-Kronig (KK) optical OFDM (KKO-OFDM) to enhance the spectral efficiency and power efficiency for such bandlimited VLC channels. The KKO-OFDM transmit signal is constructed to be real-valued, non-negative, and strictly bandlimited. Numerical results show that KKO-OFDM outperforms DCO-OFDM and LACO-OFDM in bandlimited VLC channels in terms of optical power efficiency. / Thesis / Doctor of Philosophy (PhD) / Visible light communications (VLC) integrate into the ubiquitous light-emitting diode (LED) luminaires, providing lighting and communication simultaneously. Commercially available LEDs are low-cost, simple, and have a limited modulation bandwidth. These LEDs demand that VLC orthogonal frequency division multiplexing (OFDM) modulation schemes be spectrum- and power-efficient with low complexity. Concerning these challenges, this thesis presents a novel spectrum- and power-efficient VLC OFDM scheme with low complexity. Firstly, absolute value layered asymmetrically clipped optical OFDM (ALACO-OFDM) is presented to achieve high spectral and power efficiency while requiring fewer layers. Then layered antisymmetry-constructed clipped optical OFDM (LAC-OFDM) is introduced, which requires low complexity as compared to existing layered asymmetrically-clipped optical OFDM (LACO-OFDM). Given a VLC dispersive channel, low-complexity LACO-OFDM (L-LACO) is furthermore introduced with simple equalization but generates an identical signal to the existing LACO-OFDM. Finally, for a bandlimited VLC channel, Kramers-Kronig optical OFDM (KKO-OFDM) is presented to achieve high spectral and power efficiency. The ALACO-OFDM and LAC-OFDM work in flat VLC line-of-sight links while L-LACO in VLC dispersive links and KKO-OFDM in bandlimited VLC dispersive links with simple equalizer.

Optical wireless communications (OWC) has the potential to become a remedy for the shortage of the radio frequency (RF) spectrum. Especially in indoor environments, OWC could enable wireless home networking systems which offload data traffic from existing RF systems. In OWC, data is transmitted by modulating the intensity of light sources, typically incoherent light emitting diodes (LEDs). Thus, OWC systems employ intensity modulation (IM) and direct detection (DD) of the optical carrier. Since off-the-shelf LEDs have a limited modulation capability, the transmission bandwidth of practical OWC systems is restricted. Consequently, the available bandwidth has to be used efficiently. In this thesis, spectrally efficient optical wireless transmission techniques are evaluated. Firstly, multiple transmitter-receiver techniques are investigated. These multiple-input-multiple-output (MIMO) techniques provide high spectral efficiency, and therefore high data rates. Specifically, the MIMO techniques repetition coding (RC), spatial multiplexing (SMP) and spatial modulation (SM) are analysed for indoor OWC. The performance of these techniques is evaluated analytically and by means of computer simulations. It is shown that inducing power imbalance between the multiple optical transmitters can substantially improve the performance of optical MIMO techniques as the power imbalance improves the differentiability of the multiple channels. In addition, it is found that link blockage and the utilisation of transmitters having different optical wavelengths enhance channel differentiability as well. These methods enable the utilisation of optical MIMO techniques under conditions which typically disallow the application of MIMO schemes due to little differences between the multiple links. Secondly, a novel optical wireless transmitter concept is developed. This concept uses discrete power level stepping to generate intensity modulated optical signals, such as orthogonal frequency division multiplexing (OFDM) waveforms. The transmitter consists of several on-off-switchable LED groups which are individually controlled to emit scaled optical intensities. As a result, the digital-to-analogue conversion of the signals to be sent is done in the optical domain. This method enables the implementation of low-complex and power-efficient optical transmitter front-ends – the major shortcoming of conventional optical OFDM transmitters. Thirdly, a novel approach for wireless data transmission within an aircraft cabin is presented. The data is transferred by 2-dimensional visual code sequences. These sequences are displayed on the in-flight entertainment (IFE) screen and are captured by the built-in camera of a user device which acts as receiver. Transmission experiments within an aircraft cabin mock-up demonstrate the functionality of the implemented system under realistic conditions, such as ambient illumination and geometric configuration. Altogether, this thesis has analysed the potential of spectrally efficient optical wireless transmission techniques. It is shown that OWC systems can greatly benefit from these techniques.

Some pages are blank, but are kept to satisfy the page count of the thesis. / <p> Indoor optical wireless links can potentially achieve high bitrates because there is a wide and unregulated bandwidth in the optical spectrum. Moreover, optical wireless links can be implemented using simple and inexpensive devices. However, indoor optical wireless links have their own drawbacks such as limited power due to safety issues and incapability of passing thorough opaque objects, which limit their mobility, range and bandwidth and have prevented them from being used widely in commercial systems. Therefore, there has been much effort to find new configurations for indoor optical wireless links which are able to overcome these limitations. In this thesis, a novel configuration for indoor optical wireless communication, termed the dynamic spot diffusing (DSD) channel, is proposed. In the DSD system, the transmitter sends optical signals to a small moving area on the ceiling termed a spot. The receiver receives reflections of optical signal from the spot when spot is in field of view of the receiver. This configuration is shown to achieve high bitrates and provide a good deal of mobility for users inside the room. In this work, a theoretical model for the DSD channel is proposed and the DSD channel capacity is discussed and computed. Furthermore, the DSD system design is explained and design issues are discussed in order to approach capacity. Finally, using computer simulations, achievable rates inside a room are computed and shown to be close to calculated channel capacity.</p> / Thesis / Master of Applied Science (MASc)

The main objective of this thesis is to develop a communication system that can minimize the micro-machine size and power consumption and maximize the link range and the number of micro-machines that can communicate simultaneously with the base station. Several possible communication systems are compared, including RF communications and active and passive free space optical communications. A directed, half duplex LOS link using a Ferroelectric liquid crystal (FLC) or multiple quantum well (MQW) modulating retroreflector-base passive uplink is then examined in more detail. Two potential geometries are described. In a broad-beam system, light from a source is broadcast to all micro-machines within the field of view (FOV). However, simulations show that the performance is unacceptable for most applications. In a narrow-beam system, light is holographically steered to active micro-machines within the same FOV. Therefore, the link budget has been improved. For a BER not exceeding 10-9, the 850 nm LC narrowbeam system can support maximum range of 146 m at a data rate of 10kbits/s, and the 1525 nm MQW narrowbeam system can support a maximum range of 34 m at a data rate of 10Mbits/s, when the transmitted power in the diffracted beam of the positive first order is 0.5 mW. Experiments have been carried out to verify the model. These were initially carried out with MQW Modulating RetroReflector (MRR). Results were then be used to modify the characteristics of these components in the model. Available components and discrete electronics have been used to set up a simple retro-reflecting link. Experiments have been performed at a limited data rate of 1 kbits/s over a limited range of 1m due to creating a uniform interrogation beam spot, and the active area of the receiver of 1 mm diameter. An algorithm to find the MQW MRR within the FOV is designed and tested.

In this report, an optical wireless multiple-input multiple-output communication system employing intensity-modulation direct-detection is considered. The performance of direct current offset space-time block codes (DC-STBC) is studied in terms of pairwise error probability (PEP). It is shown that among the class of DC-STBCs, the worst case PEP corresponding to the minimum distance between two codewords is minimized by repetition coding (RC), under both electrical and optical individual power constraints. It follows that among all DC-STBCs, RC is optimal in terms of worst-case PEP for static channels and also for varying channels under any turbulence statistics. This result agrees with previously published numerical results showing the superiority of RC in such systems. It also agrees with previously published analytic results on this topic under log-normal turbulence and further extends it to arbitrary turbulence statistics. This shows the redundancy of the time-dimension of the DCSTBC in this system. This result is further extended to sum power constraints with static and turbulent channels, where it is also shown that the time dimension is redundant, and the optimal DC-STBC has a spatial beamforming structure. Numerical results are provided to demonstrate the difference in performance for systems with different numbers of receiving apertures and different throughput.

Adaptive and smart systems are growing in popularity as we shift toward personalization as a culture. With progressive demands on energy efficiency, it is increasingly important to focus on the utilization of energy in a novel way. This thesis investigates a microelectromechanical system (MEMS) mirror with the express intent to provide flexibility in solid state lighting (SSL). By coupling the micromirror to an optical source, the reflected light may be reshaped and directed so as to optimize the overall illumination profile. In addition, the light may be redirected in order to provide improved signal strength in visible light communications (VLC) with negligible impact on energy demands. With flexibility and full analog control in mind, the design of a fully integrated tip-tilt-piston micromirror with an additional variable focus degree of freedom is outlined. Electrothermal actuators are used to both steer the light and tune the focal length. A detailed discussion of the underlying physics behind composite beams and thermal actuators is addressed. This leads directly into an overview of the two main mirror components, namely the segmented mirror and the deflection actuators. An in-depth characterization of the dynamics of the mirror is discussed including the linearity of the thermal response. Frequency domain analysis of such a system provides insight into tunable mechanical properties such as the resonant frequency and quality factor. The degenerate resonant modes can be separated significantly. It is shown that the frequency response may be tuned by straining specific actuators and that it follows a predictable pattern. As a result, the system can be scanned at increasingly large angles. In other words, coupled mechanical modes allow variable damping and amplification. A means to determine the level of coupling is examined and the mode shape variations are tracked as a function of the tuning parameters. Finally, the applications of such a device are explored and tested. Such applications include reliable signal-to-noise ratio (SNR) enhancements in VLC of 30 dB and color tunable steerable lights using laser diodes. A brief discussion of the implications of dynamic illumination and tunable systems is juxtaposed with an explanation behind the integration of an electrothermal micromirror and an all digital driver.

Indoor positioning is an enabling technology primed to impact the indoor application space as Global Navigation Satellite Systems (GNSS) did for the outdoor space. Amongst the competing positioning technologies are methods of different mediums: light, radio frequency and ultra-wideband, ultrasonic, and imaging; methods of different modalities: received signal strength, angle-of-arrival, time-of-flight; and methods of different mathematics: trilateration, triangulation, machine learning, and signal processing. Light-based positioning compared to other positioning schemes exploits fixed-location directional luminaires placed regularly throughout a space as anchor points -- there is an efficiency argument for multi-purpose lighting and a cost-share argument for infrastructure-based positioning. Similar to the satellite infrastructure with GNSS, with anchor points and models for light propagation and construction, position is estimated based on received signals at active photodiode-equipped target devices. Received signal strength, a common first order attribute, alone is not noise resilient enough for centimeter-level 3D positioning. Methods using angle diversity produce better results particularly in 3D but with more complex hardware. For this dissertation, we exploit angle diversity and modulated optical sources in light-based positioning systems to estimate position to centimeter-level accuracy in 3D. We propose, analyze, and contribute two novel positioning schemes that use these concepts. One of the proposed schemes is a new hybrid 3D indoor positioning technique, Ray-Surface Positioning (RSP), which incorporates a narrow field-of-view (FOV) optical source (Ray) with wide diffuse optical sources (Surfaces) to position active devices in 3D. The second scheme, a Zone-based Positioning Service (ZPS), is a positioning scheme and architecture that incorporates an angle diverse narrow FOV optical source at the positioned device. This unique design decision allows the active device to position itself directly with respect to photovoltaic anchor points but also to position other devices in its FOV called transitive positioning. Along with these contributions, we also investigate several other related topics. Concisely, as part of the dissertation, we contribute (a) review of the state-of-the-art, (b) analysis for steering Lambertian sources, (c) method of creating angle diversity from a narrow FOV optical source, (d) novel positioning approaches in (1) RSP and (2) ZPS, (e) proof of concept prototypes for (1) RSP and (2) ZPS, and (f) architectures for indoor positioning applications.

Traffic from wireless and mobile devices is predicted to increase 10-fold between 2014 and 2019, surpassing wired data traffic by 2016. Given the expected radio frequency (RF) capacity crunch, this growing wireless demand will have to be met using a variety of new technologies exploiting other parts of the electromagnetic spectrum. Promising research areas include the Millimetre Band as well as Optical Wireless Communications (OWC). Millimetre Band demonstrations have accomplished ultrafast multi-Gigabit links, making use of state-of-the-art fibre transmission systems. However, complex opto-electronic (OE) interfaces are required to convert the optical carrier into Millimetre wireless signals. To avoid these interfaces, an all-optical transparent network is proposed here, spanning over both the fibre and OWC domains, in order to deliver ultrahigh data rates to mobile end-users in indoor environments. This is supported by the recent deployment of fibre-to-the-home (FTTH) networks creating the potential for Terabit aggregate connections at the user's doorstep. Therefore, infrared fibre-wireless-fibre (FWF) links are studied to support data rates over 100 Gb/s in nomadic applications. The link coverage is achieved via narrow beam beamsteering over a wide field-of-view (FOV) using suitable localization and tracking techniques. The proposed model is inherently bidirectional and transparent, i.e. independent of the data rate and modulation format. In this thesis, the potential for ultrafast wide coverage OWCs using SMF-based transceivers and coherent transmission is demonstrated. A record data rate of 418 Gb/s and 209 Gb/s with a wide FOV of &theta;_FOV=±30° and &theta;_FOV=±20°, respectively, is shown at a free space range of 3 m. To the best of our knowledge, this is the fastest demonstration of an indoor wireless link that offers practical room-scale coverage. The automated alignment of this FWF link is also demonstrated with the design and implementation a mm-accurate localization and tracking system. Finally, architectures for point-to-multipoint communications are explored in order to adapt the system to multiple users.