Single-carrier frequency domain equalization using subband decomposition for optical wireless communications

Optical wireless communication is intended to be applied into indoor and visual distance high-rate data transmission, which is complementary to radio frequency communications. There are specific problems and requirements in optical wireless communications compared with radio frequency communications. Single-carrier frequency domain equalization (SCFDE) is a transmission scheme which has been considered as an alternative of orthogonal frequency-division multiplexing (OFDM), because it has most of the advantages of OFDM and avoids the problems of OFDM. Subband decomposition is a multi-resolution signal analysis and synthesis method, using quadrature mirror filter (QMF) bank to convert time-domain signal to frequency-domain subbands. As a time-to-frequency transform, subband decomposition technique can be employed to frequency domain equalization. Compared with the commonly used discrete Fourier transform (DFT), subband transform is more flexible and efficient to compensate the fading of frequency-selective channels. This thesis includes the theories of SCFDE, subband decomposition, subband equalization, and optical wireless transmission scheme. Also, simulations are given to demonstrate the processing of signals and the implementation of equalizers. The results show that the transmitted signal can be effectively equalized to compensate the channel fading, and the transmission scheme is appropriate for optical wireless communications

System design and performance analysis of asymmetrically and symmetrically clipped optical (ASCO)-OFDM for IM/DD optical wireless communications

As the quantity of mobile communication devices, such as cellphones, tablets, and laptops, dramatically increase, the demand for high speed wireless service has been growing. Optical wireless communications (OWCs), which offer unlimited transmission bandwidth, have received a lot of attention and been studied in recent decades. They can be an effective alternative to radio frequency communications (RFCs) for indoor high speed data transmission. Intensity modulation direct detection (IM/DD) is a simple way to realize the transmission of optical wireless signals in an indoor environment. Information data streams are modulated into the intensity of optical carriers and transmitted by light emitting diodes (LEDs). At the receiver, the instantaneous power of optical signals can be directly detected by photodiodes. Multipath distortion, especially in an indoor environment, caused by reflection from walls or furniture, severely affects the transmission quality of optical signals. Orthogonal frequency division multiplexing (OFDM) is a promising modulation technique and has been widely used to combat inter-symbol-interference (ISI) resulting from multipath propagation in RFCs. So far, the technique of OFDM has also been successfully applied into IM/DD optical wireless systems. In this dissertation, the author focuses on the system design and performance analysis of a novel power-efficient scheme based on OFDM for IM/DD OWCs. This dissertation is divided into four main sections. In the first part, a novel power-efficient scheme, called asymmetrically and symmetrically clipped optical (ASCO)-OFDM, for intensity modulation direct detection (IM/DD) optical wireless systems is proposed. The average bit rate versus (vs.) normalized bandwidth and the optical power per bit of this novel scheme are expressed by a closed form, respectively. The symbol error rate (SER) performance is investigated when optical signals are transmitted in a flat fading channel. Simulation results show that this proposed scheme can achieve better performances in terms of both power efficiency and symbol error rate (SER) when the optical power of transmitted signals is limited. In the second part, an improved receiving technique is applied into the conventional receiver of ASCO-OFDM to improve the SER performance. This technique can explore and reuse some useful information hidden in the received signals. The detection procedure is described in detail and the improved SER performances are presented for different constellation cases. In the third part, the information rates of ADO-OFDM and ASCO-OFDM are obtained for an additive white Gaussian noise (AWGN) channel with an average transmitted optical power constraint. In the last part, this novel power efficient scheme, ASCO-OFDM, is extended into two-dimensional (2D) IM/DD optical wireless systems. The theoretical analysis and simulation results show that this technique not only achieves high average bit rate, but reduces the Peak-to-average power ratio (PAPR) as well

Advances in single carrier block modulation with frequency domain processing

International audienceThis special issue focuses on single carrier block modulation (SC-BM) with frequency domain processing. This class of modulation and multiple access schemes complements the orthogonal frequency division multiple access (OFDMA) and its variations. For example, LTE (the long term evolution of the 3GPP standard), and LTE-Advanced, employ OFDMA in the downlink (base stations to mobiles) and SC-FDMA, a version of SC-BM in the uplink (mobiles to base stations). The main reason for adapting the technology of SC-FDMA for uplink LTE is the fact that OFDMA has high "peak-to-average power ratio" (PAPR), which is a disadvantage for mobile devices that are limited by power availability. Besides its advantage of low PAPR, SC-BM technology has a similar performance/complexity to that of OFDMA, and simple frequency domain equalization methods for combating dispersive channels. There were 17 papers submitted to this special issue. All had merits, but the review process reduced the number of accepted papers to 9. The accepted papers cover a number of novel and advanced aspects of single carrier block modulation with frequency domain processing: near-optimal nonlinear and iterative equalization techniques; applications to CDMA, MIMO and ARQ; channel estimation; and application to free-space optical transmission. Following is a summary of the papers. In the paper "Iterative Successive Interference Cancellation for Quasi-Synchronous Block Spread CDMA Based on the Orders of the Times of Arrival", Wang, Bocus, and Coon [1] describe an interference cancellation scheme based on the times of arrival of the signals from different users, and they show that for practical channels this ordering criterion is equivalent to ordering with respect to decreasing average SINR. In "Complexity Reduced MLD Based on QR Decomposition in OFDM MIMO Multiplexing with Frequency Domain Spreading and Code Multiplexing", Nagatomi, Kawai, and Higuchi [2] propose a reduced-complexity maximum likelihood signal detection method for MIMO-OFDM systems with frequency-domain spreading and code multiplexing. They show how to exploit signal orthogonalization based on QR decomposition of the product of the channel and spreading code matrices in the frequency domain to obtain significant complexity reductions. In "Frequency-domain Block Signal detection with QRM-MLD for Training Sequence-aided Single-carrier Transmission", Yamamoto, Takeda and Adachi [3] propose replacement of the cyclic prefix with a known training sequence. The object is to improve BER performance of an equalization scheme which uses QR decomposition with M-algorithm detection, while keeping the number of surviving paths low for reduced complexity. The scheme is especially effective for 16QAM and 64QAM modulation. The paper "Joint Iterative Tx/Rx MMSE-FDE and ISI Cancellation for Single-carrier Hybrid ARQ with Chase Combining" by Takeda and Adachi [4] applies transmitter and receiver equalization and iterative intersymbol interference cancellation to a system with hybrid ARQ transmission, Chase combining and antenna diversity. The equalizer parameters at both transmitter and receiver are optimized for each retransmission. The paper "Novel Techniques of Single Carrier Frequency Domain Equalization for Optical Wireless Communications" by Acolaste, Bar-Ness, and Wilson [5] investigates the application of single-carrier frequency-domain equalization to diffuse optical wireless communications and demonstrates its advantages over OFDM in terms of reduced PAPR and improved error rate in the presence of LED nonlinearity. In the paper "Semi-Blind Channel Estimation for IFDMA in Case of Channels with Large Delay Spreads", Sohl and Klein [6] propose a subspace-based channel estimation algorithm which can cope with large delay spreads. In previous work on IFDMA, the number of channel taps that can be estimated was limited to the number of subcarriers per user. The subspace analysis in this paper relaxes this constraint and increases the number of taps that can be estimated. The paper "Channel Frequency response Estimation for MIMO with Systems with Frequency-Domain Equalization " by Yang, Shi, Chew, and Tjhung [7] suggests a training-based channel frequency response (CFR) estimation scheme which is hardware efficient when integrated with and SC-FDE and space time coding (STC) in MIMO Systems. An MSE analysis of this CFR estimation scheme is provided, which considered linear estimators based on both LS and minimum MSE criteria. Also with a given constraint which effectively limits the transmit power of the training signals, the paper investigates the optimal design of training signals under different a priori knowledge of the channel statistics. For the special case of 2 transmit antennas, it was demonstrated that CFR estimation could be implemented in adaptive manner. The paper by Dang, Ruder, Schober and Gerstacker [8], "MMSE Beamforming for SC-FDMA Transmission over MIMO ISI Channels", derives minimum mean squared error beamforming strategies for multi-antenna reception, as well as further modifications to reduce the transmitted peak to average power ratios. The paper by Nishino, Tanahashi, and Ochiai [9], "A Bit Labeling Design for Trellis-Shaped Single-Carrier PSK with PAPR Reduction", investigates application of trellis shaping to reduce the PAPR of band-limited single-carrier PSK signals. The authors demonstrate that the uncoded bit error rate and PAPR reduction capability of trellis shaping is highly dependent on bit labeling. They propose a bit labeling scheme for high-order PSK constellation that can efficiently reduce PAPR while achieving BER performance comparable to that of Gray labeling

High performance drive circuits for integrated microLED/CMOS arrays for visible light communication (VLC)

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

Advanced signal processing concepts for multi-dimensional communication systems

Die weit verbreitete Nutzung von mobilem Internet und intelligenten Anwendungen hat zu einem explosionsartigen Anstieg des mobilen Datenverkehrs geführt. Mit dem Aufstieg von intelligenten Häusern, intelligenten Gebäuden und intelligenten Städten wächst diese Nachfrage ständig, da zukünftige Kommunikationssysteme die Integration mehrerer Netzwerke erfordern, die verschiedene Sektoren, Domänen und Anwendungen bedienen, wie Multimedia, virtuelle oder erweiterte Realität, Machine-to-Machine (M2M) -Kommunikation / Internet of Things (IoT), Automobilanwendungen und vieles mehr. Daher werden die Kommunikationssysteme zukünftig nicht nur eine drahtlose Verbindung über Gbps bereitstellen müssen, sondern auch andere Anforderungen erfüllen müssen, wie z. B. eine niedrige Latenzzeit und eine massive Maschinentyp-Konnektivität, während die Dienstqualität sichergestellt wird. Ohne bedeutende technologische Fortschritte zur Erhöhung der Systemkapazität wird die bestehende Telekommunikationsinfrastruktur diese mehrdimensionalen Anforderungen nicht unterstützen können. Dies stellt eine wichtige Forderung nach geeigneten Wellenformen und Signalverarbeitungslösungen mit verbesserten spektralen Eigenschaften und erhöhter Flexibilität dar. Aus der Spektrumsperspektive werden zukünftige drahtlose Netzwerke erforderlich sein, um mehrere Funkbänder auszunutzen, wie zum Beispiel niedrigere Frequenzbänder (typischerweise mit Frequenzen unter 10 GHz), mm-Wellenbänder (einige hundert GHz höchstens) und THz-Bänder. Viele alternative Technologien wie Optical Wireless Communication (OWC), dynamische Funksysteme und zellulares Radar sollten ebenfalls untersucht werden, um ihr wahres Potenzial abzuschätzen. Insbesondere bietet OWC ein großes, aber noch nicht genutztes optisches Band im sichtbaren Spektrum, das Licht als Mittel zur Informationsübertragung nutzt. Daher können zukünftige Kommunikationssysteme als zusammengesetzte Hybridnetzwerke angesehen werden, die aus einer Anzahl von verschiedenen drahtlosen Netzwerken bestehen, die auf Funk und optischem Zugang basieren. Auf der anderen Seite ist es eine große Herausforderung, fortschrittliche Signalverarbeitungslösungen für mehrere Bereiche von Kommunikationssystemen zu entwickeln. Diese Arbeit trägt zu diesem Ziel bei, indem sie Methoden für die Suche nach effizienten algebraischen Lösungen für verschiedene Anwendungen der digitalen Mehrkanal-Signalverarbeitung demonstriert. Insbesondere tragen wir zu drei verschiedenen Anwendungsgebieten bei, d.h. Wellenformen, optischen drahtlosen Systemen und mehrdimensionaler Signalverarbeitung. Gegenwärtig ist das Cyclic Prefix Orthogonal Frequency Division Multiplexing (CP-OFDM) die weit verbreitete Multitragetechnik für die meisten Kommunikationssysteme. Um jedoch die CP-OFDM-Nachteile in Bezug auf eine schlechte spektrale Eingrenzung, Robustheit in hoch asynchronen Umgebungen und Unflexibilität der Parameterwahl zu überwinden, wurden viele alternative Wellenformen vorgeschlagen. Solche Mehrfachträgerwellenformen umfassen einen Filter bank Multicarrier (FBMC), ein Generalized Frequency Division Multiplexing (GFDM), einen Universal Filter Multicarrier (UFMC) und ein Unique Word Orthogonal Orthogonal Frequency Division Multiplexing (UW-OFDM). Diese neuen Luftschnittstellenschemata verwenden verschiedene Ansätze, um einige der inhärenten Mängel bei CP-OFDM zu überwinden. Einige dieser Wellenformen wurden gut untersucht, während andere sich noch in den Kinderschuhen befinden. Insbesondere die Integration von Multiple-Input-Multiple-Output (MIMO) -Konzepten mit UW-OFDM und UFMC befindet sich noch in einem frühen Forschungsstadium. Daher schlagen wir im ersten Teil dieser Arbeit neuartige lineare und sukzessive Interferenzunterdrückungstechniken für MIMO UW-OFDM-Systeme vor. Das Design dieser Techniken zielt darauf ab, Empfänger mit einer geringen Rechenkomplexität zu erhalten. Ein weiterer Schwerpunkt ist die Anwendbarkeit von Space-Time Block Codes (STBCs) auf UW-OFDM und UFMC-Wellenformen. Zu diesem Zweck stellen wir neue Techniken zusammen mit Detektionsverfahren vor. Wir vergleichen auch die Leistung dieser Wellenformen mit unseren vorgeschlagenen Techniken mit den anderen Wellenformen des Standes der Technik, die in der Literatur vorgeschlagen wurden. Wir zeigen, dass raumzeitblockierte UW-OFDM-Systeme mit den vorgeschlagenen Methoden nicht nur andere Wellenformen signifikant übertreffen, sondern auch zu Empfängern mit geringer Rechnerkomplexität führen. Der zweite Anwendungsbereich umfasst optische Systeme im sichtbaren Band (390-700 nm), die in Plastic Optical Fibers (POFs), Multimode-Fasern oder OWC-Systemen wie der Kommunikation über Visible Light Communication (VLC) verwendet werden können. VLC kann Lösungen für eine Reihe von Anwendungen anbieten, einschließlich drahtloser lokaler, persönlicher und Körperbereichsnetzwerke (WLAN, WPAN und WBANs), Innenlokalisierung und -navigation, Fahrzeugnetze, U-Bahn- und Unterwassernetze und bietet eine Reihe von Datenraten von wenigen Mbps zu 10 Gbps. VLC nutzt voll sichtbare Light Emitting Diodes (LEDs) für den doppelten Zweck der Beleuchtung und Datenkommunikation bei sehr hohen Geschwindigkeiten. Daher verwenden solche Systeme Intensitätsmodulation und Direct Detection (IM / DD), wodurch gefordert wird, dass das Sendesignal reellwertig und positiv sein sollte. Dies impliziert auch, dass die herkömmlichen Wellenformen, die für die Radio Frequency (RF) Kommunikation ausgelegt sind, nicht direkt verwendet werden können. Zum Beispiel muss eine hermetische Symmetrie auf das CP-OFDM angewendet werden, um ein reellwertiges Signal zu erhalten (oft als Discrete Multitone Transmission (DMT) bezeichnet), das im Gegenzug die Bandbreiteneffizienz verringert. Darüber hinaus begrenzt die LED / LED-Treiberkombination die elektrische Bandbreite. Alle diese Faktoren erfordern die Verwendung spektral effizienter Übertragungsverfahren zusammen mit robusten Entzerrungsschemata, um hohe Datenraten zu erzielen. Deshalb schlagen wir im zweiten Teil der Arbeit Übertragungsverfahren vor, die für solche optischen Systeme am besten geeignet sind. Insbesondere demonstrieren wir die Leistung der PAM-Blockübertragung mit Frequenzbereichsausgleich. Wir zeigen, dass dieses Schema nicht nur leistungsstärker ist, sondern auch alle modernen Verfahren wie CP-DMT-Schemata übertrifft. Wir schlagen auch neue UW-DMT-Schemata vor, die vom UW-OFDM-Konzept abgeleitet sind. Diese Schemata zeigen auch ein sehr überlegenes Bitfehlerverhältnis (BER) -Performance gegenüber den herkömmlichen CP-DMT-Schemata. Der dritte Anwendungsbereich konzentriert sich auf mehrdimensionale Signalverarbeitungstechniken. Bei der Verwendung von MIMO, STBCs, Mehrbenutzerverarbeitung und Mehrträgerwellenformen bei der drahtlosen Kommunikation ist das empfangene Signal mehrdimensional und kann eine multilineare Struktur aufweisen. In diesem Zusammenhang können Signalverarbeitungstechniken, die auf einem Tensor-Modell basieren, gleichzeitig von mehreren Formen von Diversität profitieren, um Mehrbenutzer-Signaltrennung / -entzerrung und Kanalschätzung durchzuführen. Dieser Vorteil ist eine direkte Konsequenz der Eigenschaft der wesentlichen Eindeutigkeit, die für matrixbasierte Ansätze nicht verfügbar ist. Tensor-Zerlegung wie die Higher Order Singular Value Decomposition (HOSVD) und die Canonical Polyadic Decomposition (CPD) werden weithin zur Durchführung dieser Aufgaben empfohlen. Die Leistung dieser Techniken wird oft mit zeitraubenden Monte-Carlo-Versuchen bewertet. Im letzten Teil der Arbeit führen wir eine Störungsanalyse erster Ordnung dieser Tensor-Zerlegungsmethoden durch. Insbesondere führen wir eine analytische Performanceanalyse des Semi-algebraischen Frameworks für approximative Canonical polyadic decompositions Simultaneous matrix diagonalizations (SECSI) durch. Das SECSI-Framework ist ein effizientes Werkzeug zur Berechnung der CPD eines rauscharmen Tensor mit niedrigem Rang. Darüber hinaus werden die erhaltenen analytischen Ausdrücke in Bezug auf die Momente zweiter Ordnung des Rauschens formuliert, so dass abgesehen von einem Mittelwert von Null keine Annahmen über die Rauschstatistik erforderlich sind. Wir zeigen, dass die abgeleiteten analytischen Ergebnisse eine ausgezeichnete Übereinstimmung mit den Monte-Carlo-Simulationen zeigen.The widespread use of mobile internet and smart applications has led to an explosive growth in mobile data traffic. With the rise of smart homes, smart buildings, and smart cities, this demand is ever growing since future communication systems will require the integration of multiple networks serving diverse sectors, domains and applications, such as multimedia, virtual or augmented reality, machine-to-machine (M2M) communication / the Internet of things (IoT), automotive applications, and many more. Therefore, in the future, the communication systems will not only be required to provide Gbps wireless connectivity but also fulfil other requirements such as low latency and massive machine type connectivity while ensuring the quality of service. Without significant technological advances to increase the system capacity, the existing telecommunications infrastructure will be unable to support these multi-dimensional requirements. This poses an important demand for suitable waveforms with improved spectral characteristics and signal processing solutions with an increased flexibility. Moreover, future wireless networks will be required to exploit several frequency bands, such as lower frequency bands (typically with frequencies below 10 GHz), mm-wave bands (few hundred GHz at the most), and THz bands. Many alternative technologies such as optical wireless communication (OWC), dynamic radio systems, and cellular radar should also be investigated to assess their true potential. Especially, OWC offers large but yet unexploited optical band in the visible spectrum that uses light as a means to carry information. Therefore, future communication systems can be seen as composite hybrid networks that consist of a number of different wireless networks based on radio and optical access. On the other hand, it poses a significant challenge to come up with advanced signal processing solutions in multiple areas of communication systems. This thesis contributes to this goal by demonstrating methods for finding efficient algebraic solutions to various applications of multi-channel digital signal processing. In particular, we contribute to three different scientific fields, i.e., waveforms, optical wireless systems, and multi-dimensional signal processing. Currently, cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) is the widely adopted multicarrier technique for most of the communication systems. However, to overcome the CP-OFDM demerits in terms of poor spectral containment, poor robustness in highly asynchronous environments, and inflexibility of parameter choice, and many alternative waveforms have been proposed. Such multicarrier waveforms include filter bank multicarrier (FBMC), generalized frequency division multiplexing (GFDM), universal filter multicarrier (UFMC), and unique word orthogonal frequency division multiplexing (UW-OFDM). These new air interface schemes take different approaches to overcome some of the inherent deficiencies in CP-OFDM. Some of these waveforms have been well investigated while others are still in its infancy. Specifically, the integration of multiple-input multiple-output (MIMO) concepts with UW-OFDM and UFMC is still at an early stage of research. Therefore, in the first part of this thesis, we propose novel linear and successive interference cancellation techniques for MIMO UW-OFDM systems. The design of these techniques is aimed to result in receivers with a low computational complexity. Another focus area is the applicability of space-time block codes (STBCs) to UW-OFDM and UFMC waveforms. For this purpose, we present novel techniques along with detection procedures. We also compare the performance of these waveforms with our proposed techniques to the other state-of-the-art waveforms that has been proposed in the literature. We demonstrate that space-time block coded UW-OFDM systems with the proposed methods not only outperform other waveforms significantly but also results in receivers with a low computational complexity. The second application area comprises of optical systems in the visible band (390-700 nm) that can be utilized in plastic optical fibers (POFs), multimode fibers or OWC systems such as visible light communication (VLC). VLC can provide solutions for a number of applications including wireless local, personal, and body area networks (WLAN, WPAN, and WBANs), indoor localization and navigation, vehicular networks, underground and underwater networks, offering a range of data rates from a few Mbps to 10 Gbps. VLC takes full advantage of visible light emitting diodes (LEDs) for the dual purpose of illumination and data communications at very high speeds. Because of the incoherent nature of the LED sources, such systems employ intensity modulation and direct detection (IM/DD), thus demanding that the transmit signal should be real-valued and positive. This also implies that the conventional waveforms designed for the radio frequency (RF) communication cannot be directly used. For example, a Hermitian symmetry has to be applied to the CP-OFDM spectrum to obtain a real-valued signal (often referred to as discrete multitone transmission (DMT)) that in return reduces the bandwidth efficiency. Moreover, the LED/LED driver combination limits the electrical bandwidth. All these factors require the use of spectrally efficient transmission schemes along with robust equalization schemes to achieve high data rates. Therefore, in the second part of the thesis, we propose transmission schemes that are best suited for such optical systems. Specifically, we demonstrate the performance of PAM block transmission with frequency domain equalization. We show that this scheme is not only more power efficient but also outperforms all of the state-of-the-art schemes such as CP-DMT schemes. We also propose novel UW-DMT schemes that are derived from the UW-OFDM concept. These schemes also show a much superior bit error ratio (BER) performance over the conventional CP-DMT schemes. The third application area focuses on multi-dimensional signal processing techniques. With the use of MIMO, STBCs, multi-user processing, and multicarrier waveforms in wireless communications, the received signal is multidimensional in nature and may exhibit a multilinear structure. In this context, signal processing techniques based on a tensor model can simultaneously benefit from multiple forms of diversity to perform multi-user signal separation/equalization and channel estimation. This advantage is a direct consequence of the essential uniqueness property that is not available for matrix based approaches. Tensor decompositions such as the higher order singular value decomposition (HOSVD) and the canonical polyadic decomposition (CPD) are widely recommended for performing these tasks. The performance of these techniques is often evaluated using time consuming Monte-Carlo trials. In the last part of the thesis, we perform a first-order perturbation analysis of the truncated HOSVD and the Semi-algebraic framework for approximate Canonical polyadic decompositions via Simultaneous matrix diagonalizations (SECSI). The SECSI framework is an efficient tool for the computation of the approximate CPD of a low-rank noise corrupted tensor. Especially, the SECSI framework shows a much improved performance and comparatively low-complexity as compared to the conventional algorithms such as alternative least squares (ALS). Moreover, it also facilitates the implementation on a parallel hardware architecture. The obtained analytical expressions for both algorithms are formulated in terms of the second-order moments of the noise, such that apart from a zero-mean, no assumptions on the noise statistics are required. We demonstrate that the derived analytical results exhibit an excellent match to the Monte-Carlo simulations

Spectrum and energy efficient digital modulation techniques for practical visible light communication systems

The growth in mobile data traffic is rapidly increasing in an unsustainable direction given the radio frequency (RF) spectrum limits. Visible light communication (VLC) offers a lucrative solution based on an alternative license-free frequency band that is safe to use and inexpensive to utilize. Improving the spectral and energy efficiency of intensity modulation and direct detection (IM/DD) systems is still an on-going challenge in VLC. The energy efficiency of inherently unipolar modulation techniques such as pulse-amplitude modulation discrete multitone modulation (PAM-DMT) and asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) degrades at high spectral efficiency. Two novel superposition modulation techniques are proposed in this thesis based on PAM-DMT and ACO-OFDM. In addition, a practical solution based on the computationally efficient augmented spectral efficiency discrete multi-tone (ASE-DMT) is proposed. The system performance of the proposed superposition modulation techniques offers significant electrical and optical power savings with up to 8 dB in the electrical signal-to-noise ratio (SNR) when compared with DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM). The theoretical bit error ratio (BER) performance bounds for all of the proposed modulation techniques are in agreement with the Monte-Carlo simulation results. The proposed superposition modulation techniques are promising candidates for spectrum and energy efficient IM/DD systems. Two experimental studies are presented for a VLC system based on DCO-OFDM with adaptive bit and energy loading. Micrometer-sized Gallium Nitride light emitting diode (m-LED) and light amplification by stimulated emission of radiation diode (LD) are used in these studies due to their high modulation bandwidth. Record data rates are achieved with a BER below the forward error correction (FEC) threshold at 7.91 Gb/s using the violet m-LED and at 15 Gb/s using the blue LD. These results highlight the potential of VLC systems in practical high speed communication solutions. An additional experimental study is demonstrated for the proposed superposition modulation techniques based on ASE-DMT. The experimentally achieved results confirm the theoretical and simulation based performance predictions of ASE-DMT. A significant gain of up to 17.33 dB in SNR is demonstrated at a low direct current (DC) bias. Finally, the perception that VLC systems cannot work under the presence of sunlight is addressed in this thesis. A complete framework is presented to evaluate the performance of VLC systems in the presence of solar irradiance at any given location and time. The effect of sunlight is investigated in terms of the degradations in SNR, data rate and BER. A reliable high speed communication system is achieved under the sunlight effect. An optical bandpass blue filter is shown to compensate for half of the reduced data rate in the presence of sunlight. This thesis demonstrates data rates above 1 Gb/s for a practical VLC link under strong solar illuminance measured at 50350 lux in clear weather conditions