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

Performance study of air interface for broadband wireless packet access

Ph.DDOCTOR OF PHILOSOPH

Authentication and Message Integrity Verification without Secrets

Embedding network capabilities in a plethora of new devices and infrastructures--the Internet-of-Things, vehicular and aviation networks, the critical national infrastructure, industrial plants--are dramatically transforming the modern way of living. The rapid deployment pace of these emerging applications has brought unprecedented security challenges related to data confidentiality, user privacy, and critical infrastructure availability. A significant portion of these threats is attributed to the broadcast nature of the wireless medium, which exposes systems to easy-to-launch passive and active attacks. The slow security standards rollout combined with the ever-shrinking time-to-market, the device heterogeneity and the lack of user-friendly input interfaces (screen, keyboard, etc.) only exacerbate the security challenges. In this dissertation, we address the fundamental problem of trust establishment in the context of emerging network applications. We present techniques integrating physical layer properties with cryptographic primitives to guarantee message integrity and bootstrap initial trust without relying on any prior secrets. We present the ``helper'' security paradigm in which security is outsourced to one or more dedicated devices to allow for the scalable pairing of off-the-shelf heterogeneous devices. In addition, we present our work on message integrity verification of navigation information for aircrafts (speed, location, and heading) by exploiting the Doppler spread of the wireless channel. Finally, we develop a secure and fast voting technique for distributed networks which allows fast coordination of a group of devices without the overhead of messaging

Equalizador híbrido na banda das ondas milimétricas para sistemas GFDM

Wireless communication using very-large multiple-input multiple-output (MIMO) antennas has been regarded as one of the enabling technologies for the future mobile communication. It refers to the idea of equipping cellular base stations (BSs) with a very large number of antennas giving the possibility to focusing the transmitted signal energy into very short-range areas, which will provide huge improvements in the capacity, in addition to the spectral and energy efficiency. Concurrently, this demand for high data rates and capacity led to the necessity of exploiting the enormous amount of spectrum in the millimeter wave (mmWave) bands. However, the combination of millimeter-wave communications arrays with a massive number of antennas has the potential to dramatically enhance the features of wireless communication. This combination implies high cost and power consumption in the conventional full digital architecture, where each RF chain is dedicated to one antenna. The solution is the use of a hybrid architecture, where a small number of RF chains are connected to a large number of antennas through a network of phase shifters. On the other hand, another important factor that affect the transmission quality is the modulation technique, which plays an important role in the performance of the transmission process, for instance, GFDM is a flexible non-orthogonal multicarrier modulation concept, that introduces additional degrees of freedom when compared to other multicarrier techniques. This flexibility makes GFDM a promising solution for the future cellular generations, because it can achieve different requirements, such as higher spectrum efficiency, better control of out-of-band (OOB) emissions, as well as achieving low peak to average power ratio (PAPR). In this work, we present an analog-digital transmitter and receiver structures. Considering a GFDM modulation technique to be implemented in the digital part, while in the analog part, we propose a full connected hybrid multiuser linear equalizer, combined with low complexity hybrid precoder for wideband millimeter-wave massive MIMO systems. The hybrid equalizer is optimized by minimizing the mean square error between the hybrid approach and the full digital counterpart. The results show that the performance of the proposed hybrid scheme is very close to the full digital counterpart and the gap reduces as the number of RF chains increases.O uso de um número elevado de antenas, também designado por MIMO massivo, tem sido considerada uma das tecnologias mais promissoras para os futuros sistemas de comunicação sem fios. Esta tecnologia, refere-se à ideia de equipar as estações base (BSs) com um número muito grande de antenas, dando a possibilidade de focar a energia do sinal transmitido em áreas de alcance muito restritas, o que proporcionará grandes melhorias na capacidade, além das espectrais e eficiência energética. Simultaneamente, a exigência por taxas de dados elevadas e capacidade levou à necessidade de explorar uma enorme quantidade de espectro nas bandas de ondas milimétricas (mmWave). A combinação de comunicação na banda das ondas milimétricas com terminais equipados com um grande número de antenas tem o potencial de melhorar drasticamente os recursos da comunicação sem fios. Considerando no entanto uma arquitetura digital, usada em sistemas MIMO convencionais, em que cada cadeia de RF é dedicada a uma antena, implica um custo e um consumo de energia elevados. A solução é o uso de uma arquitetura híbrida, na qual um pequeno número de cadeias de RF é conectado a um grande número de antenas através de um conjunto de deslocadores de fase. Outro fator importante que afeta a qualidade da transmissão é a técnica de modulação usada, que desempenha um papel importante no desempenho do processo de transmissão. O GFDM é um conceito de modulação de portadora múltipla, não ortogonal e flexível, que introduz graus de liberdade adicionais, quando comparado a outras técnicas de portadora múltipla, como o OFDM. Essa flexibilidade faz do GFDM uma solução promissora para as futuras gerações celulares, pois pode atender a diferentes requisitos, como maior eficiência de espectro, melhor controle das emissões fora de banda (OOB), além de atingir baixo rácio de potência média / pico ( PAPR). Neste trabalho, é assumido uma arquitetura hibrida no transmissor e recetor. Considera-se uma técnica de modulação GFDM a ser implementada na parte digital, enquanto na parte analógica, é proposto um equalizador linear híbrido multiutilizador totalmente conectado, i.e., cada cadeia RF está ligada a todas as antenas, combinado com um pré-codificador híbrido, de baixa complexidade para sistemas MIMO massivo de banda larga. O equalizador híbrido é otimizado, minimizando o erro quadrático médio entre a abordagem híbrida e a contraparte totalmente digital. Os resultados mostram que o desempenho do esquema híbrido proposto está muito próximo do equivalente digital, à medida que o número de cadeias de RF aumenta.Mestrado em Engenharia Eletrónica e Telecomunicaçõe

Comparative study and performance evaluation of MC-CDMA and OFDM over AWGN and fading channels environment

Η απαίτηση για εφαρμογές υψηλής ταχύτητας μετάδοσης δεδομένων έχει αυξηθεί σημαντικά τα τελευταία χρόνια. Η πίεση των χρηστών σήμερα για ταχύτερες επικοινωνίες, ανεξαρτήτως κινητής ή σταθερής, χωρίς επιπλέον κόστος είναι μια πραγματικότητα. Για να πραγματοποιηθούν αυτές οι απαιτήσεις, προτάθηκε ένα νέο σχήμα που συνδυάζει ψηφιακή διαμόρφωση και πολλαπλές προσβάσεις, για την ακρίβεια η Πολλαπλή Πρόσβαση με διαίρεση Κώδικα Πολλαπλού Φέροντος (Multi-Carrier Code Division Multiple Access MC-CDMA). Η εφαρμογή του Γρήγορου Μετασχηματισμού Φουριέ (Fast Fourier Transform,FFT) που βασίζεται στο (Orthogonal Frequency Division Multiplexing, OFDM) χρησιμοποιεί τις περίπλοκες λειτουργίες βάσεως και αντικαθίσταται από κυματομορφές για να μειώσει το επίπεδο της παρεμβολής. Έχει βρεθεί ότι οι μετασχηματισμένες κυματομορφές (Wavelet Transform,W.T.) που βασίζονται στον Haar είναι ικανές να μειώσουν το ISI και το ICI, που προκαλούνται από απώλειες στην ορθογωνιότητα μεταξύ των φερόντων, κάτι που τις καθιστά απλούστερες για την εφαρμογή από του FFT. Επιπλέον κέρδος στην απόδοση μπορεί να επιτευχθεί αναζητώντας μια εναλλακτική λειτουργία ορθογωνικής βάσης και βρίσκοντας ένα καλύτερο μετασχηματισμό από του Φουριέ (Fourier) και τον μετασχηματισμό κυματομορφής (Wavelet Transform). Στην παρούσα εργασία, υπάρχουν τρία προτεινόμενα μοντέλα. Το 1ο, ( A proposed Model ‘1’ of OFDM based In-Place Wavelet Transform), το 2ο, A proposed Model ‘2’ based In-Place Wavelet Transform Algorithm and Phase Matrix (P.M) και το 3ο, A proposed Model ‘3’ of MC-CDMA Based on Multiwavelet Transform. Οι αποδόσεις τους συγκρίθηκαν με τα παραδοσιακά μοντέλα μονού χρήστη κάτω από διαφορετικά κανάλια (Κανάλι AWGN, επίπεδη διάλειψη και επιλεκτική διάλειψη).The demand for high data rate wireless multi-media applications has increased significantly in the past few years. The wireless user’s pressure towards faster communications, no matter whether mobile, nomadic, or fixed positioned, without extra cost is nowadays a reality. To fulfill these demands, a new scheme which combines wireless digital modulation and multiple accesses was proposed in the recent years, namely, Multicarrier-Code Division Multiple Access (MC-CDMA). The Fourier based OFDM uses the complex exponential bases functions and it is replaced by wavelets in order to reduce the level of interference. It is found that the Haar-based wavelets are capable of reducing the ISI and ICI, which are caused by the loss in orthogonality between the carriers. Further performance gains can be made by looking at alternative orthogonal basis functions and finding a better transform rather than Fourier and wavelet transform. In this thesis, there are three proposed models [Model ‘1’ (OFDM based on In-Place Wavelet Transform, Model ‘2’ (MC-CDMA based on IP-WT and Phase Matrix) and Model ‘3’ (MC-CDMA based on Multiwavelet Transform)] were created and then comparison their performances with the traditional models for single user system were compared under different channel characteristics (AWGN channel, flat fading and selective fading). The conclusion of my study as follows, the models (1) was achieved much lower bit error rates than traditional models based FFT. Therefore these models can be considered as an alternative to the conventional MC-CDMA based FFT. The main advantage of using In-Place wavelet transform in the proposed models that it does not require an additional array at each sweep such as in ordered Fast Haar wavelet transform, which makes it simpler for implementation than FFT. The model (2) gave a new algorithm based on In-Place wavelet transform with first level processing multiple by PM was proposed. The model (3) gave much lower bit error than other two models in additional to traditional models

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin

Multiple-Input Multiple-Output Detection Algorithms for Generalized Frequency Division Multiplexing

Since its invention, cellular communication has dramatically transformed personal lifes and the evolution of mobile networks is still ongoing. Evergrowing demand for higher data rates has driven development of 3G and 4G systems, but foreseen 5G requirements also address diverse characteristics such as low latency or massive connectivity. It is speculated that the 4G plain cyclic prefix (CP)-orthogonal frequency division multiplexing (OFDM) cannot sufficiently fulfill all requirements and hence alternative waveforms have been in-vestigated, where generalized frequency division multiplexing (GFDM) is one popular option. An important aspect for any modern wireless communication system is the application of multi-antenna, i.e. MIMO techiques, as MIMO can deliver gains in terms of capacity, reliability and connectivity. Due to its channel-independent orthogonality, CP-OFDM straightforwardly supports broadband MIMO techniques, as the resulting inter-antenna interference (IAI) can readily be resolved. In this regard, CP-OFDM is unique among multicarrier waveforms. Other waveforms suffer from additional inter-carrier interference (ICI), inter-symbol interference (ISI) or both. This possibly 3-dimensional interference renders an optimal MIMO detection much more complex. In this thesis, weinvestigate how GFDM can support an efficient multiple-input multiple-output (MIMO) operation given its 3-dimensional interference structure. To this end, we first connect the mathematical theory of time-frequency analysis (TFA) with multicarrier waveforms in general, leading to theoretical insights into GFDM. Second, we show that the detection problem can be seen as a detection problem on a large, banded linear model under Gaussian noise. Basing on this observation, we propose methods for applying both space-time code (STC) and spatial multiplexing techniques to GFDM. Subsequently, we propose methods to decode the transmitted signals and numerically and theoretically analyze their performance in terms of complexiy and achieved frame error rate (FER). After showing that GFDM modulation and linear demodulation is a direct application of Gabor expansion and transform, we apply results from TFA to explain singularities of the modulation matrix and derive low-complexity expressions for receiver filters. We derive two linear detection algorithms for STC encoded GFDM signals and we show that their performance is equal to OFDM. In the case of spatial multiplexing, we derive both non-iterative and iterative detection algorithms which base on successive interference cancellation (SIC) and minimum mean squared error (MMSE)-parallel interference cancellation (PIC) detection, respectively. By analyzing the error propagation of the SIC algorithm, we explain its significantly inferior performance compared to OFDM. Using feedback information from the channel decoder, we can eventually show that near-optimal GFDM detection can outperform an optimal OFDM detector by up to 3dB for high SNR regions. We conclude that GFDM, given the obtained results, is not a general-purpose replacement for CP-OFDM, due to higher complexity and varying performance. Instead, we can propose GFDM for scenarios with strong frequency-selectivity and stringent spectral and FER requirements

Recent Advances in Wireless Communications and Networks

This book focuses on the current hottest issues from the lowest layers to the upper layers of wireless communication networks and provides "real-time" research progress on these issues. The authors have made every effort to systematically organize the information on these topics to make it easily accessible to readers of any level. This book also maintains the balance between current research results and their theoretical support. In this book, a variety of novel techniques in wireless communications and networks are investigated. The authors attempt to present these topics in detail. Insightful and reader-friendly descriptions are presented to nourish readers of any level, from practicing and knowledgeable communication engineers to beginning or professional researchers. All interested readers can easily find noteworthy materials in much greater detail than in previous publications and in the references cited in these chapters