Wireless communication is a form of communication that has been around for over hundreds of years and is the fastest growing segment of the communication industry. Today, wireless communication has become an essential part of almost everyone’s daily life, and the number of users has increased exponentially over the last decade with the introduction of the internet, mobile devices and smart phones. Radio Frequency (RF) transmission is arguably the most popular method of communication and is available worldwide. With the rapid progress in technology and the increase of number of users, the limited RF spectrum is becoming more congested which led to numerous research efforts to find an alternative that can help to alleviate the pending problem. One of the proposed solutions is Visible Light Communication (VLC), which uses visible Light Emitting Diode (LED) for data transmission. In this thesis, three integrated microLED/Complementary Metal Oxide Semiconductor (CMOS) Integrated Circuits (ICs) are presented with the main aim of increasing the data rate of transmission. The first microLED/CMOS IC presented here is the Generation V microLED/CMOS driver which represents the continuation of the earlier work in the HYPIX project, which aimed to develop a microLED/CMOS driver to optically pump an organic polymer laser. A 40x10 pixelarray of Generation V microLED/CMOS driver was thus designed, primarily for optical pumping polymer lasing purposes, but has also demonstrated the ability to perform communication transmission using an On-Off Keying (OOK) modulation scheme. The driver consumes up to 330mA current and produces approximately 12mW of optical power from a single pixel, which is about 3 times higher than its predecessor. The second microLED/CMOS IC is the microLED/CMOS Current Feedback (CCFBK) driver which was designed to facilitate Orthogonal Frequency Division Multiplexing (OFDM) modulation. OFDM is one of the modulation schemes, adopted from the RF domain, that was proposed to be implemented in VLC in order to increase the data transmission rate. To the best of the author’s knowledge, the microLED/CCFBK driver is the first CMOS driver for microLED that was designed to perform analogue modulation for VLC purposes. The driver is characterised and shows the ability to produce up to 3.5mW of optical power with a data transmission rate of up to 486Mbit/s. The microLED/CMOS Optical Feedback (COFBK) driver is the third microLED/CMOS IC presented in this thesis. The driver looks to improve on the performance of the microLED/CCFBK driver. OFDM transmission requires high linearity to ensure low Bit Error Rate (BER) transmission. However, the optical power output of an LED is not, in general, linear with the input voltage signal. The microLED/COFBK driver looks to increase the linearity of the optical power output by integrating a microLED and a photodiode in a single pixel to create a feedback loop. Once again, to the best of the author’s knowledge, the microLED/COFBK driver is the first CMOS driver for microLED which integrates both optical source and sensor in a single pixel to help linearise the optical power output for communication purposes; in this case, VLC. For a similar range of optical power, the microLED/COFBK driver shows a reduction about 5.3% in the degree of non-linearity compared to the microLED/CCFBK driver and produces lower Total Harmonic Distortion (THD). The microLED/COFBK driver showed the potential to increase the data rate by a factor of four over that of microLED/CCFBK driver. The analogue modulated microLED/CMOS ICs described here are the first-generation drivers that have demonstrated the possibilities to increase the data rate using OFDM. A number of possible design improvements have been identified which will enhance future performance and integration with the standard VLC system.

Indiana University-Purdue University Indianapolis (IUPUI) / Recently witnessed a great popularity of unobtrusive Visible Light Communication (VLC) using screen-camera channels. They overcomes the inherent drawbacks of traditional approaches based on coded images like bar codes. One popular unobtrusive method is the utilizing of alpha channel or color channels to encode bits into the pixel translucency or color intensity changes with over-the-shelf smart devices. Specifically, Uber-in-light proves to be an successful model encoding data into the color intensity changes that only requires over-the-shelf devices. However, Uber-in-light only exploit Multi Frequency Shift Keying (MFSK), which limits the overall throughput of the system since each data segment is only 3-digit long. Motivated by some previous works like Inframe++ or Uber-in-light, in this thesis, we proposes a new VLC model encoding data into color intensity changes on red and blue channels of video frames. Multi-Phase-Shift-Keying (MPSK) along with MFSK are used to match 4-digit and 5-digit long data segments to specific transmission frequencies and phases. To ensure the transmission accuracy, a modified correlation-based demodulation method and two learning-based methods using SVM and Random Forest are also developed.

The Internet-of-Things (IoT) infrastructure is made of uniquely identifiable wireless-enabled smart devices that use the Internet to communicate with each other as well as people, on a large scale. These IoT devices require power to operate, and to communicate with other smart devices. The optical bands have the capacity to provide power and wireless communication to the IoT devices. Simultaneous lightwave information and power transmission (SLIPT) is a technology through which information and optical power are received simultaneously by the receiver. SLIPT is made possible by solar cell-based SLIPT receivers. In this thesis, for the first time, the trade-off between the achievable data rate and the harvested power in solar cell-based SLIPT systems is quantified and analysed. It is known that the amount of power harvested using a solar cell is dependent on its operating voltage. By utilizing a realistic electrical model of the solar cells, an expression for the bandwidth and a lower bound on the data rate of a solar cell receiver as function of the operating voltage is derived. Using the dependency of rate and power on the operating voltage, the rate-power trade-off in solar cell based SLIPT receivers are studied in this thesis. This work proposes a novel solar cell based SLIPT receiver that includes a DC-DC boost converter, which allows control over the operating voltage of the solar cell. Finally, this thesis proposes an optimization problem to compute the optimum operating voltage for a SLIPT system located indoor where a desired trade-off between the data rate and harvested power can be attained based on the battery state of charge. / Thesis / Master of Applied Science (MASc)

The amount of wireless data traffic has been increasing exponentially. This results in the shortage of radio frequency (RF) spectrum. In order to alleviate the looming spectrum crisis, visible light communication (VLC) has emerged as a supplement to RF techniques. VLC uses light emitting diodes (LEDs) for transmission and employs photodiodes (PDs) for detection. With the advancement of the LED technology, LEDs can now fulfil two functions at the same time: illumination and high-speed wireless communication. In a typical indoor scenario, each single light fixture can act as an access point (AP), and multiple light fixtures in a room can form a cellular wireless network. We refer to this type of networks as ‘optical attocell network’. This thesis focuses on interference mitigation in optical attocell networks. Firstly, the downlink inter-cell interference (ICI) model in optical attocell networks is investigated. The conventional ray-tracing channel model for non-line-of-sight (NLOS) path is studied. Although this model is accurate, it leads to time-consuming computer simulations. In order to reduce the computational complexity, a simplified channel model is proposed to accurately characterise NLOS ICI in optical attocell networks. Using the simplified model, the received signal-to-interference-plus-noise ratio (SINR) distribution in optical attocell networks can be derived in closed-form. This signifies that no Monte Carlo simulation is required to evaluate the user performance in optical attocell networks. Then, with the knowledge of simplified channel model, interference mitigation techniques using angle diversity receivers (ADRs) are investigated in optical attocell networks. An ADR typically consists of multiple PDs with different orientations. By using proper signal combining schemes, ICI in optical attocell networks can be significantly mitigated. Also, a novel double-source cell configuration is proposed. This configuration can further mitigate ICI in optical attocell networks in conjunction with ADRs. Moreover, an analytical framework is proposed to evaluate the user performance in optical attocell networks with ADRs. Finally, optical space division multiple access (SDMA) using angle diversity transmitters is proposed and investigated in optical attocell networks. Optical SDMA can exploit the available bandwidth resource in spatial dimension and mitigate ICI in optical attocell networks. Compared with optical time division multiple access (TDMA), optical SDMA can significantly improve the throughput of optical attocell networks. This improvement scales with the number of LED elements on each angle diversity transmitter. In addition, the upper bound and the lower bound of optical SDMA performance are derived analytically. These bounds can precisely evaluate the performance of optical SDMA systems. Furthermore, optical SDMA is shown to be robust against user position errors, and this makes optical SDMA suitable for practical implementations.

Visible light communication (VLC) systems take advantage of ubiquitous light-emitting diodes (LED) and leverage existing illumination infrastructure to provide broadband optical communication links. Multiple-input multiple-output (MIMO) VLC systems are among the well studied topics in VLC research. However, most traditional MIMO VLC systems require accurate alignment and have to adjust to different magnifications at various link distances. Consequently, the alignment and calibration modules increase the complexity of the receiver structures. A pixelated MIMO VLC system is introduced in this thesis, which transmits a series of time-varying coded images that can be received and decoded by commercial digital cameras. Using a convex lens placed in front of the transmitter at its focal length, the system exploits the Bokeh effect to obtain fixed-scale images at all link distances. Compared with traditional pixelated MIMO VLC systems, which send information directly in space, this spatial-angular mapping system sends information in different angles instead. In contrast to the complex receiver structures in traditional setups, the proposed system can capture fixed-scale images with a simple receiver requiring no re-focusing as the camera moves. The channel model of the system is measured and modeled and a rateless code is applied to track the truncation of receive images for various link ranges and angular offsets. A proof-of-concept optical communication system is implemented with an LCD display and a high speed CMOS camera. Performance of the system is measured and analysed. The experimental system can achieve a throughput of approximately 10 bit per frame over 90 cm. This fixed-scale pixelated MIMO wireless optical communication system provides a less expensive option for short-range indoor broadcasting optical links and inter-vehicle communications due to its mobility, stability and simpler receiver structure compared to traditional designs in different working conditions. / Thesis / Master of Applied Science (MASc)

There is a trend to move the frequency band for wireless transmission to ever higher frequencies in the radio frequency (RF) spectrum to fulfil the exponentially increasing demand in wireless communication capacity. Research work has gone into improving the spectral efficiency of wireless communication system to use the scarce and expensive resources in the most efficient way. However, to make wireless communication future-proof, it is essential to explore ways to transmit wirelessly outside the traditional RF spectrum. The visible light (VL) spectrum bandwidth is 1000 times wider than the entire 300 GHz RF spectrum and is, therefore, a viable alternative. Visible light communication (VLC) enables existing lighting infrastructures to provide not only illumination but also wireless communication. In conjunction with the concept of cell densification, a networked VLC system, light fidelity attocell (LAC) network, has been proposed to offer wide coverage and high speed wireless data transmission. In this study, many issues related to the downlink system in LAC networks have been investigated. When analysing the downlink performance of LAC networks, a large number of random channel samples are required for the empirical calculation of some system metrics, such as the signal-to-interference-plus-noise ratio (SINR). However, using state-of-the-art approaches to calculate the non-line-of-sight (NLoS) channel component leads to significant computational complexity and prolonged computation time. An analytical method has been presented in this thesis to efficiently calculate the NLoS channel impulse response (CIR) in VLC systems. The results show that the proposed method offers significant reduction in computation time compared to the state-of-the-art approaches. A comprehensive performance evaluation of the downlink system of LAC networks is carried out in this thesis. Based on the research results in the literature in the field of optical wireless communication (OWC), a system level framework for the downlink system in LAC networks is developed. By using this framework, the downlink performance subject to a large number of parameters is evaluated. Additionally, the effect of varying network size, cell deployment and key system parameters are investigated. The calculation of downlink SINR statistics, cell data rate and outage probability are considered and analysed. The results show that the downlink performance of LAC networks is promising in terms of achievable data rate per unit area compared to other state-of-the-art RF small-cell networks. It is found that co-channel interference (CCI) is a major source of signal impairment in the downlink of LAC network. In order to mitigate the influence of CCI on signal distortion in LAC networks, widely used interference mitigation techniques for RF cellular systems are borrowed and extensively investigated. In this study, fractional frequency reuse (FFR) is adapted to the downlink of LAC networks. The SINR statistics and the spectral efficiency in LAC downlink system with FFR schemes are evaluated. Results show that the FFR technique can greatly improve the performance of cell edge users and as well the overall spectral efficiency. Further performance improvements can be achieved by incorporating angular diversity transmitters (ADTs) with FFR and coordinated multi-point joint transmission (JT) techniques.

White LEDs (Light Emitting Diodes) in Visible Light Communication (VLC) is an emerging technology that is being researched so it can eventually be used for common communications systems. LEDs have a number of advantages, one of which is long life expectancy. However, like many emerging technologies, VLC has many technical issues that need to be addressed. We proposed an optical indoor wireless communication system that used white LEDs like plug-in devices. We developed a practical implementation of VLC and demonstrated it experimentally. In particular we focused on designing a prototype of VLC that can be used without having to make major changes to the present infrastructure with two types of protocol — namely RS-232 and USB — for data transmission.

To date, group-III-nitride has undergone continuous improvements to provide a broader range of industrial applications, such as solid-state lighting (SSL), visible light communications (VLC), and light projection. Recently, VLC has attained substantial attention in the field of wireless communication because it offers ~ 370 THz of bandwidth of unregulated visible spectrum, which makes it a critical factor in the evolution of the 5G networks and beyond. GaN-based light-emitting diode (LED) and laser diode (LD) have become increasingly appealing in energy-sufficient SSL replacing conventional light sources. However, III- nitride LEDs suffer from efficiency-droop in their external quantum efficiency associated with high current densities, and their modulation bandwidth is limited to 10 ~ 100 MHz. Although LDs have shown gigabit-modulation bandwidth, unfavorable artifacts, such as speckles are observed, which may raise a concern about eye safety. This dissertation is devoted to the fabrication and electrical and optical characterization of a new class of III-nitride light-emitter known as superluminescent diode (SLD). SLD works in an amplified spontaneous emission (ASE) regime, and it combines several advantages from both LD and LED, such as droop-free, speckle-free, low-spatial coherence, broader emission, high-optical power, and directional beam. Here, SLDs were fabricated by a focused ion beam by tilting the front facet of the waveguide to suppress the lasing mode. They showed a high-power of 474 mW on c-plane GaN-substrate with a large spectral bandwidth of 6.5 nm at an optical power of 105 mW. To generate SLD- based white light, a YAG-phosphor-plate was integrated, and a CRI of 85.1 and CCT of 3392 K were measured. For the VLC link, SLD showed record high-data rates of 1.45 Gbps and 3.4 Gbps by OOK and DMT modulation schemes, respectively. Additionally, a widely single- and dual-wavelength tunability were designed using SLD-based external cavity (SLD-EC) configuration for a tunable blue laser source. These results underscore the practicality of c-plane SLDs in realizing high-power, high data rate, speckle-free, and droop-free SSL-VLC apparatus. Additionally, the SLD-EC configuration allows a wide range of applications, including biomedical applications, optical communication, and high-resolution spectroscopy.

Programmable self-assembly has been widely studied because of its capability to create ordered patterns from a group of multiple disordered agents without an external controller. To achieve this, assembly units must exhibit different characteristics: they need to be small, to have the ability to latch and unlatch, and low-power consumption. In addition, they need to be easily programmable and able to communicate with each other. This thesis presents an experimental robotic platform for programmable self-assembly. In this work, we build in the Usbot modular robotic cubes making use of their advantages and simplicity as its passive magnetic latching mechanism, and we endow them with communication capabilities. The system allows only local communication between the modules, specifically with the most recent linked neighbor cube. The transmission of the relevant cube data is performed by a pair of LED and ambient light sensors in a binary format. The different experiments demonstrate and compare distributed programmable self-assembly using various algorithms from the literature as Singleton and Lynchpin.

Radio frequency (RF) spectrum congestion motivates the search for alternative communication techniques to complement radio systems. Visible light communications (VLC) is an emerging technology that exploits the recent and ever-growing increase in the usage of energy-efficient light emitting diodes (LEDs) to imperceptibly modulate the optical power output of LEDs to enable communication and augment RF networks. Orthogonal frequency-divison multiplexing (OFDM) has been proposed as a modulation scheme for VLC due to its high spectral efficiency, ease of channel estimation and equalization, resistance to inter-symbol interference (ISI) and frequency-selective fading, efficient implementation using the Fast Fourier Transform (FFT), and compatibility with RF and power-line communication (PLC) standards that use OFDM. One of the major drawbacks of conventional OFDM techniques is the high peak-to-average power ratio (PAPR) of OFDM signals. The peaks of the OFDM signals are clipped due to the limited dynamic range of the LED, which translates the high PAPR of the OFDM signal into non-linear distortion (NLD). This signal distortion causes bit-error rate (BER) performance degradation, especially at high optical signal-to-noise ratios (SNRs) typical of indoor VLC scenarios. In this thesis, a new family of modulation techniques, termed spatial optical OFDM (SO-OFDM), is proposed with the aim of reducing the PAPR of conventional DC-biased optical OFDM (DCO-OFDM) by making use of the large number of LEDs typically available in indoor lighting settings. Each LED group signal is a narrowband signal consisting of a small number of subcarriers, and thus has a smaller PAPR than the original OFDM signal. Firstly, SO-OFDM is introduced and its two key concepts of frequency-to-space mapping and spatial summing are explained. Frequency-to-space mapping is achieved by allocating a subset of OFDM subcarriers to each LED. Each LED group signal is a narrowband signal consisting of a small number of subcarriers, and thus has a smaller PAPR than the original OFDM signal. Several design variations of the subcarrier assignment to LEDs are introduced and are shown through simulations, to reduce PAPR, and NLD noise due to clipping, and improve the BER performance at high SNRs as compared to DCO-OFDM. In addition, luminous efficacy is identified as an important lighting design parameter that is impacted by modulation. Relative luminous efficacy is defined as the ratio of the luminous efficacy of a modulated LED to that of an LED driven by a DC signal, and is introduced as a metric to assess the impact of modulation on LED lighting. Relative luminous efficacy links communication parameters such as signal variance to lighting design requirements. Secondly, a low-complexity amplify-and-forward (AF) scheme is proposed for an integrated power-line communication/visible-light communication (PLC/VLC) where SO-OFDM is used for the VLC link. Frequency translation of the incoming PLC signal is used to increase the usable bandwidth of the LED. The use of both frequency translation and SO-OFDM leads to capacity gains over DCO-OFDM in the high SNR regime. Finally, a low-complexity variant of SO-OFDM, termed square-wave SO-OFDM (SW-SO-OFDM), is proposed. Square-wave SO-OFDM uses square-wave carriers instead of sinusoidal waves to modulate a single OFDM subcarrier signal per LED. By using square-wave carriers, SW-SO-OFDM eliminates the need for digital-to-analog converters (DACs), digital predistortion (DPD), and the FFT operation. Squarewave SO-OFDM is also shown, through simulations, to achieve BER performance gains over SO-OFDM and DCO-OFDM. In addition, an experimental demonstration of SW-SO-OFDM with 64 QAM modulation on subcarriers is described. / Thesis / Doctor of Philosophy (PhD) / Visible-light communications (VLC) is an emerging technology that exploits the increasingly widespread use of light-emitting diodes (LEDs) for indoor lighting, and modulates the optical power output of the LED for data transmission. Among the various modulation techniques that have been proposed for VLC, orthogonal frequency-division multiplexing (OFDM) offers high data rates, resistance to channel impairments, and simple channel estimation and equalization. However, OFDM signals suffer from a high peak-to-average power ratio (PAPR) which degrades the efficiency of the power amplifier in the transmitter and hinders the communication performance. In this thesis, a new multiple-LED modulation technique, termed spatial optical OFDM (SO-OFDM), is proposed to reduce the PAPR. Using a frequency-to-space mapping, SO-OFDM divides the wideband high-PAPR OFDM signal into multiple narrowband low-PAPR signals and assigns each signal to a group of LEDs. Spatial summing of the transmitted signals occurs at the receiver allowing for the use of a conventional OFDM receiver. Several variations of SO-OFDM are introduced and are shown, using simulations, to reduce the PAPR, combat non-linear distortion (NLD), and improve the bit-error rate (BER) performance at high signal-to-noise ratios (SNRs), typical of VLC systems. Spatial optical OFDM is also applied to a practical scenario where its PAPR reduction capability is used to improve the overall capacity of a proposed system that integrates power-line communication (PLC) and VLC. A low-complexity variant of SO-OFDM, that uses square-wave carriers and simplifies the transmitter design by eliminating the need for digital predistortion (DPD) and digital-to-analog converters (DACs) is also proposed, and tested experimentally.