Spectrally and Energy Efficient Wireless Communications: Signal and System Design, Mathematical Modelling and Optimisation

This thesis explores engineering studies and designs aiming to meeting the requirements of enhancing capacity and energy efficiency for next generation communication networks. Challenges of spectrum scarcity and energy constraints are addressed and new technologies are proposed, analytically investigated and examined. The thesis commences by reviewing studies on spectrally and energy-efficient techniques, with a special focus on non-orthogonal multicarrier modulation, particularly spectrally efficient frequency division multiplexing (SEFDM). Rigorous theoretical and mathematical modelling studies of SEFDM are presented. Moreover, to address the potential application of SEFDM under the 5th generation new radio (5G NR) heterogeneous numerologies, simulation-based studies of SEFDM coexisting with orthogonal frequency division multiplexing (OFDM) are conducted. New signal formats and corresponding transceiver structure are designed, using a Hilbert transform filter pair for shaping pulses. Detailed modelling and numerical investigations show that the proposed signal doubles spectral efficiency without performance degradation, with studies of two signal formats; uncoded narrow-band internet of things (NB-IoT) signals and unframed turbo coded multi-carrier signals. The thesis also considers using constellation shaping techniques and SEFDM for capacity enhancement in 5G system. Probabilistic shaping for SEFDM is proposed and modelled to show both transmission energy reduction and bandwidth saving with advantageous flexibility for data rate adaptation. Expanding on constellation shaping to improve performance further, a comparative study of multidimensional modulation techniques is carried out. A four-dimensional signal, with better noise immunity is investigated, for which metaheuristic optimisation algorithms are studied, developed, and conducted to optimise bit-to-symbol mapping. Finally, a specially designed machine learning technique for signal and system design in physical layer communications is proposed, utilising the application of autoencoder-based end-to-end learning. Multidimensional signal modulation with multidimensional constellation shaping is proposed and optimised by using machine learning techniques, demonstrating significant improvement in spectral and energy efficiencies

New scheme for PAPR reduction in FBMC-OQAM systems based on combining TR and deep clipping techniques

Filter bank multi-carrier with offset quadrature amplitude modulation (FBMC-OQAM) system is a very efficient multicarrier modulation technique for 5G, but it suffers as all multicarriers designs from large peak-to-average power ratio (PAPR). Tone reservation (TR) is a method designed to solve this problem by reserving several subcarriers called tones in the frequency domain to generate a cancellation signal in the time domain to eliminate high peaks. In this paper, we suggest a serial combination of tone reservation (TR) method with an enhanced version of clipping called deep clipping (DC) method (TR&DC) to enhance the peaks (PAPR) mitigation in FBMC-OQAM signal model without significantly impacting the quality of transmission. Numerical results and analysis show that the new TR&DC approach allows better overall performance and offers remarkable gain in term of PAPR mitigation than the TR method, with similar BER performance to TR over additive white gaussian noise channel and Rapp HPA model

Coherent Phonons in Carbon Nanotubes and Graphene

We review recent studies of coherent phonons (CPs) corresponding to the radial breathing mode (RBM) and G-mode in single-wall carbon nanotubes (SWCNTs) and graphene. Because of the bandgap-diameter relationship, RBM-CPs cause bandgap oscillations in SWCNTs, modulating interband transitions at terahertz frequencies. Interband resonances enhance CP signals, allowing for chirality determination. Using pulse shaping, one can selectively excite speci!c-chirality SWCNTs within an ensemble. G-mode CPs exhibit temperature-dependent dephasing via interaction with RBM phonons. Our microscopic theory derives a driven oscillator equation with a density-dependent driving term, which correctly predicts CP trends within and between (2n+m) families. We also find that the diameter can initially increase or decrease. Finally, we theoretically study the radial breathing like mode in graphene nanoribbons. For excitation near the absorption edge, the driving term is much larger for zigzag nanoribbons. We also explain how the armchair nanoribbon width changes in response to laser excitation.Comment: 48 pages, 41 figure

Low-complexity iterative receiver algorithms for multiple-input multiple-output underwater wireless communications

This dissertation proposes three low-complexity iterative receiver algorithms for multiple-input multiple-output (MIMO) underwater acoustic (UWA) communications. First is a bidirectional soft-decision feedback Turbo equalizer (Bi-SDFE) which harvests the time-reverse diversity in severe multipath MIMO channels. The Bi-SDFE outperforms the original soft-decision feedback Turbo equalizer (SDFE) while keeping its total computational complexity similar to that of the SDFE. Second, this dissertation proposes an efficient direct adaptation Turbo equalizer for MIMO UWA communications. Benefiting from the usage of soft-decision reference symbols for parameter adaptation as well as the iterative processing inside the adaptive equalizer, the proposed algorithm is efficient in four aspects: robust performance in tough channels, high spectral efficiency with short training overhead, time efficient with fast convergence and low complexity in hardware implementation. Third, a frequency-domain soft-decision block iterative equalizer combined with iterative channel estimation is proposed for the uncoded single carrier MIMO systems with high data efficiency. All the three new algorithms are evaluated by data recorded in real world ocean experiment or pool experiment. Finally, this dissertation also compares several Turbo equalizers in single-input single-output (SISO) UWA channels. Experimental results show that the channel estimation based Turbo equalizers are robust in SISO underwater transmission under harsh channel conditions --Abstract, page iv

Universal-Filtered Multi-Carrier: A Waveform Candidate for 5G

The emerging Internet of Things will make the next generation 5G systems to support a broad range of diverse needs with greater efficiency requirements. The new class of services will need a higher data rates, to handle these demands, the lowest layer of the 5G systems must be flexible. Therefore, the waveform will have an important role in offering these new requirements. These waveforms should enable efficient multiple access to handle the requirements of the future wireless communication system. This means that the corresponding required waveforms should be able to handle as much different type of traffic as possible in the same band. In this paper we compare three candidate multicarrier waveforms for the air interface of 5G: the original cyclic prefix OFDM applied in the 4G systems today, the Filter Bank Multicarrier (FBMC) heavily discussed in previous papers, and Universal Filtered Multi-Carrier (UFMC) a new contender making its appearance recently. These new waveforms will be more robust against the time frequency synchronization problem, it has the potential for mixing different traffic specifications, and supports the scenarios of spectrum fragmentation, due to the improvement in the localization of spectrum. In the same time, they support all multiple input and multiple output (MIMO) scenarios and applications. The simulation results shown that there is a good difference in the time frequency efficiency for transmitting very small bursts where the response time is required (like car-to-car communications). Due to the cyclic prefix the FBMC and CP-OFDM suffer when transmitting short bursts, the UFMC outperforms CP-OFDM by 10% for any case and FBMC for the very short packets and it is similar to FBMC for long sequences. Other simulation results are shown, which demonstrate the potential of this waveform

High-performance wireless power and data transfer interface for implantable medical devices

D’importants progès ont été réalisés dans le développement des systèmes biomédicaux implantables grâce aux dernières avancées de la microélectronique et des technologies sans fil. Néanmoins, ces appareils restent difficiles à commercialier. Cette situation est due particulièrement à un manque de stratégies de design capable supporter les fonctionnalités exigées, aux limites de miniaturisation, ainsi qu’au manque d’interface sans fil à haut débit fiable et faible puissance capable de connecter les implants et les périphériques externes. Le nombre de sites de stimulation et/ou d’électrodes d’enregistrement retrouvés dans les dernières interfaces cerveau-ordinateur (IMC) ne cesse de croître afin d’augmenter la précision de contrôle, et d’améliorer notre compréhension des fonctions cérébrales. Ce nombre est appelé à atteindre un millier de site à court terme, ce qui exige des débits de données atteingnant facilement les 500 Mbps. Ceci étant dit, ces travaux visent à élaborer de nouvelles stratégies innovantes de conception de dispositifs biomédicaux implantables afin de repousser les limites mentionnées ci-dessus. On présente de nouvelles techniques faible puissance beaucoup plus performantes pour le transfert d’énergie et de données sans fil à haut débit ainsi que l’analyse et la réalisation de ces dernières grâce à des prototypes microélectroniques CMOS. Dans un premier temps, ces travaux exposent notre nouvelle structure multibobine inductive à résonance présentant une puissance sans fil distribuée uniformément pour alimenter des systèmes miniatures d’étude du cerveaux avec des models animaux en ilberté ainsi que des dispositifs médicaux implantbles sans fil qui se caractérisent par une capacité de positionnement libre. La structure propose un lien de résonance multibobines inductive, dont le résonateur principal est constitué d’une multitude de résonateurs identiques disposés dans une matrice de bobines carrées. Ces dernières sont connectées en parallèle afin de réaliser des surfaces de puissance (2D) ainsi qu’une chambre d’alimentation (3D). La chambre proposée utilise deux matrices de résonateurs de base, mises face à face et connectés en parallèle afin d’obtenir une distribution d’énergie uniforme en 3D. Chaque surface comprend neuf bobines superposées, connectées en parallèle et réailsées sur une carte de circuit imprimé deux couches FR4. La chambre dispose d’un mécanisme naturel de localisation de puissance qui facilite sa mise en oeuvre et son fonctionnement. En procédant ainsi, nous évitons la nécessité d’une détection active de l’emplacement de la charge et le contrôle d’alimentation. Notre approche permet à cette surface d’alimentation unique de fournir une efficacité de transfert de puissance (PTE) de 69% et une puissance délivrée à la charge (PDL) de 120 mW, pour une distance de séparation de 4 cm, tandis que le prototype de chambre complet fournit un PTE uniforme de 59% et un PDL de 100 mW en 3D, partout à l’intérieur de la chambre avec un volume de chambre de 27 × 27 × 16 cm3. Une étape critique avant d’utiliser un dispositif implantable chez les humains consiste à vérifier ses fonctionnalités sur des sujets animaux. Par conséquent, la chambre d’énergie sans fil conçue sera utilisée afin de caractériser les performances d’ une interface sans fil de transmisison de données dans un environnement réaliste in vivo avec positionement libre. Un émetteur-récepteur full-duplex (FDT) entièrement intégré qui se caractérise par sa faible puissance est conçu pour réaliser une interfaces bi-directionnelles (stimulation et enregistrement) avec des débits asymétriques: des taux de tramnsmission plus élevés sont nécessaires pour l’enregistrement électrophysiologique multicanal (signaux de liaison montante) alors que les taux moins élevés sont utilisés pour la stimulation (les signaux de liaison descendante). L’émetteur (TX) et le récepteur (RX) se partagent une seule antenne afin de réduire la taille de l’implant. L’émetteur utilise la radio ultra-large bande par impulsions (IR-UWB) basée sur l’approche edge combining et le RX utilise la bande ISM (Industrielle, Scientifique et Médicale) de fréquence central 2.4 GHz et la modulation on-off-keying (OOK). Une bonne isolation (> 20 dB) est obtenue entre le TX et le RX grâce à 1) la mise en forme les impulsions émises dans le spectre UWB non réglementée (3.1-7 GHz), et 2) le filtrage espace-efficace (évitant l’utilisation d’un circulateur ou d’un diplexeur) du spectre du lien de communication descendant directement au niveau de l’ amplificateur à faible bruit (LNA). L’émetteur UWB 3.1-7 GHz utilise un e modultion OOK ainsi qu’une modulation par déplacement de phase (BPSK) à seulement 10.8 pJ / bits. Le FDT proposé permet d’atteindre 500 Mbps de débit de données en lien montant et 100 Mbps de débit de données de lien descendant. Il est entièrement intégré dans un procédé TSMC CMOS 0.18 um standard et possède une taille totale de 0.8 mm2. La consommation totale d’énergie mesurée est de 10.4 mW (5 mW pour RX et 5.4 mW pour TX au taux de 500 Mbps).In recent years, there has been major progress on implantable biomedical systems that support most of the functionalities of wireless implantable devices. Nevertheless, these devices remain mostly restricted to be commercialized, in part due to weakness of a straightforward design to support the required functionalities, limitation on miniaturization, and lack of a reliable low-power high data rate interface between implants and external devices. This research provides novel strategies on the design of implantable biomedical devices that addresses these limitations by presenting analysis and techniques for wireless power transfer and efficient data transfer. The first part of this research includes our proposed novel resonance-based multicoil inductive power link structure with uniform power distribution to wirelessly power up smart animal research systems and implanted medical devices with high power efficiency and free positioning capability. The proposed structure consists of a multicoil resonance inductive link, which primary resonator array is made of several identical resonators enclosed in a scalable array of overlapping square coils that are connected in parallel and arranged in power surface (2D) and power chamber (3D) configurations. The proposed chamber uses two arrays of primary resonators, facing each other, and connected in parallel to achieve uniform power distribution in 3D. Each surface includes 9 overlapped coils connected in parallel and implemented into two layers of FR4 printed circuit board. The chamber features a natural power localization mechanism, which simplifies its implementation and eases its operation by avoiding the need for active detection of the load location and power control mechanisms. A single power surface based on the proposed approach can provide a power transfer efficiency (PTE) of 69% and a power delivered to the load (PDL) of 120 mW, for a separation distance of 4 cm, whereas the complete chamber prototype provides a uniform PTE of 59% and a PDL of 100 mW in 3D, everywhere inside the chamber with a chamber size of 27×27×16 cm3. The second part of this research includes our proposed novel, fully-integrated, low-power fullduplex transceiver (FDT) to support bi-directional neural interfacing applications (stimulating and recording) with asymmetric data rates: higher rates are required for recording (uplink signals) than stimulation (downlink signals). The transmitter (TX) and receiver (RX) share a single antenna to reduce implant size. The TX uses impulse radio ultra-wide band (IR-UWB) based on an edge combining approach, and the RX uses a novel 2.4-GHz on-off keying (OOK) receiver. Proper isolation (> 20 dB) between the TX and RX path is implemented 1) by shaping the transmitted pulses to fall within the unregulated UWB spectrum (3.1-7 GHz), and 2) by space-efficient filtering (avoiding a circulator or diplexer) of the downlink OOK spectrum in the RX low-noise amplifier (LNA). The UWB 3.1-7 GHz transmitter using OOK and binary phase shift keying (BPSK) modulations at only 10.8 pJ/bit. The proposed FDT provides dual band 500 Mbps TX uplink data rate and 100 Mbps RX downlink data rate. It is fully integrated on standard TSMC 0.18 nm CMOS within a total size of 0.8 mm2. The total power consumption measured 10.4 mW (5 mW for RX and 5.4 mW for TX at the rate of 500 Mbps)