De nouveaux usages des systèmes de communications sans fils, tels que les réseaux de capteurs ou les voitures autonomes, ont émergé au cours des dernières années. Ces usages sont fondamentalement différents des applications haut-débit actuelles des réseaux cellulaires. La future technologie mobile, la 5G New Radio, introduit donc le concept de numérologie du signal afin de pouvoir satisfaire aux besoin hétérogènes des multiples applications supportées. En effet en supportant différentes numérologies de signaux, l'allocation temps/fréquence des signaux devient plus flexible et le signal transmis peut être adapté en conséquence. Cependant, supporte simultanément différentes numérologies génère de l'interférence et donc distord les signaux. Les filtrages spatiaux, comme la formation de faisceaux, est envisagée en 5G pour limiter l'interférence générée mais pour les communications au-dessus de 6 GHz. Il n'y a cependant pas de solutions proposées pour mes communications en-dessous de 6 GHz. Dans ce travail, des techniques d'atténuation des lobes secondaires sont étudiées pour faciliter le multiplexage des services pour les communications sous 6 GHz. L’interférence entre-utilisateurs est alors contrôlée mais la bande est également mieux utilisée. Une solution innovante, combinant bancs de filtres et orthogonalité complexe, est proposée. L'orthogonalité complexe est garanti grâce à un précodage OFDM qui remplace le précodage OQAM communément utilisé. De plus, le système développé, le Block-Filtered OFDM, utilise un récepteur 5G classique ce qui garantit la retro-compatibilité avec les techniques déjà déployée. Le modèle du BF-OFDM est entièrement décrit et adapté aux normes des réseaux mobiles. De plus, de multiples méthodes de conception des filtres prototypes sont proposées afin de mieux répondre aux besoins des systèmes. La forme d'onde étudiée est également comparée avec les autres solutions de l'état de l'art sur des scénarios d'étude classiques mais également adaptés aux nouveaux enjeux des technologies sans fils. / New use cases for wireless communications recently emerged ranging from massive sensor networks to connected cars. These applications highly differ from typical signals supported by already deployed mobile technologies, which are mainly high data rate pipes. The forthcoming generation of mobile technology, 5G New Radio, introduces the concept of signal numerology so as to properly serve the requirements of the diverse applications it will support. Indeed by considering different numerologies, the time/frequency signal allocation is made more flexible which allows to shape the transmitted signal according to its needs. However, multiplexing signals with different numerologies generates interference and therefore signal distortion. Spatial filtering, such as beamforming, is envisioned for 5G above 6-GHz communications to limit inter-user interference. However, this issue still holds for sub-6 GHz systems where spatial filtering is not considered in 5G.In this work, we consider side lobe rejection techniques to ease service multiplexing in sub-6 GHz bands. Not only it provides inter-user interference mitigation but it also improves the bandwidth use efficiency in bands where frequency is a scarce resource. A novel solution, mixing filter-bank for confined spectrum and complex orthogonality for a straightforward re-use of known-how 4G/5G techniques, is proposed. The complex orthogonality is restored thanks to an OFDM precoding substituting the commonly used Offset-QAM signaling which limits the orthogonality to the real field. Moreover, the proposed solution, named Block-Filtered Orthogonal Frequency Division Multiplexing (BFOFDM), relies on a simple 5G receiver scheme which makes it backward compatible with already deployed technologies.The BF-OFDM system model is fully described and adapted to cellular standards. Besides, different prototype filter designs methods are proposed to either improve the intrinsic interference attenuation or to better confined the spectrum of the transmitted signal. Last but not least, the proposed waveform will be compared with state-of-the-art solutions for both typical and 5G oriented evaluation scenarios such as multi-service coexistence.

The growth of broadband Internet access has paved the way for the development of many new technologies. As the cost of implementing broadband access soars, the best alternative will be to use fixed wireless for these services. This thesis addresses the possibility of 3rd Generation (3G) mobile cellular wireless systems as the basis for fixed broadband wireless service. Two of the 3G technologies aimed at providing fixed broadband wireless access are Time Division Synchronous Code Division Multiple Access (TD-SCDMA) and Orthogonal Frequency Division Multiplexing (OFDM). This thesis aims to provide a preliminary study on using TD-SCDMA and OFDM for broadband wireless systems. Currently, there is not enough theory and information to establish the feasibility of using either of these technologies for broadband wireless access. First, the basic features and background on synchronous CDMA and OFDM are presented for the reader to better understand these technologies. Then, an example TD-SCDMA system is described, and some analytical and experimental results are presented. Finally, TD-SCDMA's technologies, along with this system's attributes, are compared analytically to that of Vector OFDM (VOFDM). / Master of Science

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

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The increasing demand for high data rate services necessitates the adoption of very wideband waveforms. In this case, the channel is frequency-selective, that is, a large number of resolvable multipaths are present in this environment and fading is not highly correlated across the band. Orthogonal frequency division multiplexing (OFDM) is well-known to be effective against multipath distortion. It is a multicarrier communication scheme, in which the bandwidth of the channel is divided into subcarriers and data symbols are modulated and transmitted on each subcarrier simultaneously. By inserting guard time that is longer than the delay spread of the channel, an OFDM system is able to mitigate intersymbol interference (ISI). Deploying an adaptive antenna array at the receiver can help separate the desired signal from interfering signals which originate from different spatial locations. This enhancement of signal integrity increases system capacity. In this research, we apply adaptive array algorithms to OFDM systems and study their performance in a multipath environment with the presence of interference. A novel adaptive beamforming algorithm based on the minimum mean-squared error (MMSE) criterion, which is referred to as frequency-domain beamforming, is proposed that exploits the characteristics of OFDM signals. The computational complexity of frequency-domain beamforming is also studied. Simulation results show employing an adaptive antenna array with an OFDM system significantly improves system performance when interference is present. Simulations also show that the computational complexity of the algorithm can be reduced by half without significant performance degradation. Adaptive array algorithms based on the maximum signal-to-noise ratio (MSNR) and the maximum signal-to-interference-plus-noise ratio (MSINR) criteria are also applied to adaptive vector OFDM systems (AV-OFDM). Simulation results show that the adaptive algorithm based on the MSNR criterion has superior performance in the multipath environment but performs worse than the one based on the MSINR criterion under the flat fading channel. / Master of Science

Yes / This paper presents the advantages of using a wideband spectrum adopting multi-carrier to improve targets localization within a simulated indoor environment using the Time of Arrival (TOA) technique. The study investigates the effect of using various spectrum bandwidths and a different number of carriers on localization accuracy. Also, the paper considers the influence of the transmitters’ positions in line-of-sight (LOS) and non-LOS propagation scenarios. It was found that the accuracy of the proposed method depends on the number of sub-carriers, the allocated bandwidth (BW), and the number of access points (AP). In the case of using large BW with a large number of subcarriers, the algorithm was effective to reduce localization errors compared to the conventional TOA technique. The performance degrades and becomes similar to the conventional TOA technique while using a small BW and a low number of subcarriers.

[pt] A presente tese se dedica ao estudo do sistema de comunicação sem fio MIMO-GFDM-IM. Este sistema, por apresentar atratividades como elevada eficiência espectral, eficiência energética e resiliência ao canal de propagação multipercurso, é de interesse para os futuros sistemas de comunicação. Antecedendo o estudo deste sistema, o modelo de sinais e sistemas para MIMO-GFDM é desenvolvido com base no modelo MIMOOFDM e estratégias de detecção para o sistema são propostas. Uma nova proposta para a detecção MIMO-GFDM, baseada em duas fases de filtragem, é apresentada, resultando em atrativa relação desempenho de detecção e complexidade computacional. O modelo de sistema apresentado é então estendido para incluir a modulação de índice como portadora de informação, resultando no sistema MIMO-GFDM-IM. Inicialmente considerando sistemas ponto-a-ponto, são avaliados diferentes propostas de detectores baseados no processamento da matriz de canal completa e também para os detectores de complexidade reduzida, sob a ótica de desempenho de detecção e complexidade computacional. Por fim, é considerado o sistema MIMO-GFDM-IM no uplink de um sistema multiusuário. / [en] This thesis is dedicated to the study of the MIMO-GFDM-IM wireless communication system. This system, due to its attractiveness such as high spectral efficiency, energy efficiency and resilience to the multipath propagation channel, is of interest for future communication systems. Preceding the study of this system, the model of signals and systems for MIMOGFDM is developed based on the MIMO-OFDM model and detection strategies for the system are proposed. A new proposal for MIMO-GFDM detection, based on two filtering phases, is presented, resulting in an attractive relation between detection performance and computational complexity. The presented system model is then extended to include index modulation as an information carrier, resulting in the MIMO-GFDM-IM system. Initially considering point-to-point systems, different proposals for detectors based on processing the complete channel matrix and also for detectors of reduced complexity are evaluated, from the perspective of detection performance and computational complexity. Finally, the MIMOGFDM-IM system is considered in the uplink of a multiuser system.

Les modulations multiporteuses apparaissent aujourd'hui comme une technologie éprouvée pour la transmission de données à haut-débits sur des canaux pouvant être très perturbés. L'OFDM (Orthogonal Frequency Division Multiplexing) a d'ailleurs été choisie dans plusieurs normes de télécommunications (ADSL, Wi-Max, IEEE 802.11a/g/n, LTE, DVB,...). Cependant un des inconvénients de ce type de modulation est la forte variation de la puissance instantanée à transmettre. Cette propriété rend ces modulations très sensibles aux non-linéarités des composants analogiques, en particulier celles de l'amplificateur de puissance à l'émission. Or l'amplificateur de puissance est un élément déterminant dans une chaîne de communication dans la mesure où il a une influence prépondérante sur le bilan global de la transmission en termes de puissance, de rendement et de distorsion. Plus l'on souhaite que l'impact de ses non linéarités soit faible et plus son rendement est faible, et inversement. Il est donc nécessaire d'effectuer un compromis linéarité/rendement.L'objectif de la thèse est d'éviter cette détérioration du rendement tout en conservant de bonnes performances de linéarité, de surcroit pour des signaux OFDM. Pour ce faire nous proposons d'utiliser conjointement des méthodes de linéarisation (prédistorsion numérique en bande de base) et d'amélioration du rendement (envelope tracking) de l'amplificateur de puissance ainsi qu'une méthode de réduction de la dynamique du signal (active constellation extension). La prédistorsion numérique classique échouant aux fortes puissances, nous proposons une méthode d'amélioration de cette technique à ces puissances. Nos résultats sont validés par des mesures sur un amplificateur de puissance 50W. Nous proposons également une association des méthodes permettant d'améliorer simultanément les performances en terme de linéarité hors bande et de rendement en minimisant les dégradations des performances de taux d'erreur binaire. / Multi-carrier modulations appear as a well-tried technology for high-speed data transmission on potentially disrupted channels. OFDM (Orthogonal Frequency Division Multiplexing) has been chosen for that matter in several telecommunication standards (ADSL, Wi-Max, IEEE 802.11a/g/n, LTE, DVB,...). However one of the drawbacks of this modulation type is its high variation of the instantaneous power to transmit. This property makes these modulations very sensitive to the non-linearities of analog components, especially those related to power amplifiers. Yet the power amplifiers are critical elements in the communication chain as they have a major influence on the global assessment in terms of power, efficiency and distortion. More we want its non linearity impact is weak, more its efficiency is weak too. It is therefore necessary to make a trade-off between linearity and efficiency.The purpose of the thesis is to avoid this efficiency damage keeping at the same time the good linearity performance, moreover for OFDM signals. In this way we propose to jointly use a linearization technique (the base band digital predistortion) and a technique of efficiency improvement (the envelope tracking) for the power amplifier, together with a technique of signal dynamic reduction (the active constellation extension). The classic predistortion failing for high powers, we propose an improvement of this technique for these powers. Our results are validated by measurements on a 50W power amplifier. We also propose an association of the techniques allowing an improvement of the performance in terms of out-of-band linearity and efficiency, with smallbit error rate damages.

[pt] Os sistemas de transmissão em bloco, permitem a transmissão de N símbolos de forma simultânea, seja em modulação de portadora única ou multiportadora. A recepção ótima, no sentido de máxima verossimilhança em canais com multipercursos apresenta um custo computacional elevado de AN, onde A é a ordem da constelação (A igual a 2 para BPSK). Para evitar este alto custo computacional é usual fazer a detecção símbolo a símbolo após a equalização. Nesta dissertação é proposto um receptor com detecção por grupos que apresenta uma complexidade intermediária entre o receptor ótimo e os receptores que utilizam detecção símbolo-a-símbolo em sistemas com transmissão em blocos. O tipo de estrutura idealizada agrupa as componentes do bloco equalizado em grupos e realiza detecção conjunta ótima dos símbolos em cada grupo. Com relação possíveis estratégias de agrupamento foram propostos três métodos, o primeiro método faz uma busca exaustiva pelo agrupamento ótimo e tem como consequência um custo computacional elevado para um número grande de símbolos por bloco. Na procura por algoritmos que evitem uma busca exaustiva pelo agrupamento ótimo, mas que resultem em bons ganhos de desempenho, e a sua aplicação em sistemas com um número elevado de símbolos por bloco, foram propostos dois métodos de agrupamento sub-ótimos e eficientes, cujos receptores apresentaram ganhos de desempenho apreciáveis quando comparados ao receptor convencional. / [en] Block transmission systems allow transmissions of N symbols simultaneously, with single carrier or multi-carrier modulation. Maximum likelihood optimal reception in multipath channels have a high computational cost of AN, where A is the constellation order (A iqual 2 for BPSK). To avoid this cost is usual to make symbol-by-symbol detection after equalization. In this work we propose a receiver with group detection that has a good tradeof between computation complexity and bit error rate performance. The idealized structure groups the components of the equalized block in sub-blocks and does optimal joint detection of the symbols in each sub-block. With relation to possible grouping strategies three methods were proposed. The first one searchs for an optimal grouping and has, as a consequence, a high computational cost for block with a large number of symbols. Sub-optimal efficient algorithms that avoid the exhaustive search for the optimal grouping but show good performance gains and feasible application in systems with large number of symbols per block were proposed. The resulted receivers achieved substantial performance gain in comparison with the conventional symbol-by-symbol receiver.