Les systèmes de communication sans fil actuels évoluent vers un renforcement des réactivités des protocles de la gestion des ressources radio (RRM) et adaptation du lien radipe (FLA) afin d'optimiser conjointement les couches MAC et PHY. En parallèle, la technologie d'antenne multiples et turbo récepteurs avancés ont un grand potentiel pour augmenter l’efficacité spectrale dans les futurs systèmes de communication sans fil. Ces deux tendances, à savoir, l'optimisation inter couche et le traitement de turbo, nécessitent le développement de nouvelles abstractions de la couche PHY (aussi appelée méthode de prédiction de la performance) qui peuvent capturer les performances du récepteur itératif par itération pour permettre l'introduction en douceur de ces récepteurs avancés dans FLA et RRM.La thèse de doctorat revisite en détail l'architecture du turbo récepteur, plus particulièrement, la classe d'algorithme itératif effectuant la détection linéaire par minimisation d’erreur quadratique moyenne avec l'annulation d’interférence (LMMSE-IC). Ensuite, une méthode semi-analytique de prédiction de la performance est proposée pour analyser son l'évolution par la modélisation stochastique de chacun des composants. Intrinsèquement, la méthode de prédiction de la performance est subordonnée à la disposition de connaissance d’information d’état du canal au niveau du récepteur (CSIR), le type de codage de canal (code convolutif ou un code turbo), le nombre de mots de code ainsi que le type d’information probabilistic sur les bits codés réinjectée par le décodeur pour la reconstruction et l'annulation d'interférence à l'intérieur d’algorithme de LMMSE -IC itératif.Dans la deuxième partie, l’adaptation du lien en boucle fermée dans les systèmes MIMO codés basés sur les abstractions de la couche PHY proposées pour les récepteurs LMMSE -IC itératifs ont été abordés. Le schéma proposé d'adaptation de liaison repose sur un faible taux de rétroaction et exploite la sélection du précodeur spatiale (par exemple, la sélection d'antennes) et du schéma de modulation et de codage (MCS) de façon à maximiser le taux moyen soumis à une contrainte de taux d'erreur de bloc. Différents schémas de codage sont testés, tels qu’un codage parcourant tous les antennes où un codage par antenne. Les simulations montrent bien le gain important obtenu avec les turbo récepteurs comparée à celui d’un récepteur MMSE classique. / Current wireless communication systems evolve toward an enhanced reactivity of Radio Resource Management (RRM) and Fast Link Adaptation (FLA) protocols in order to jointly optimize the Media Access Control (MAC) and Physical (PHY) layers. In parallel, multiple antenna technology and advanced turbo receivers have a large potential to increase the spectral efficiency of future wireless communication system. These two trends, namely, cross layer optimization and turbo processing, call for the development of new PHY-layer abstractions (also called performance prediction method) that can capture the iterative receiver performance per iteration to enable the smooth introduction of such advanced receivers within FLA and RRM. The PhD thesis first revisits in detail the architecture of the turbo receiver, more particularly, the class of iterative Linear Minimum Mean-Square Error (soft) Interference Cancellation (LMMSE-IC) algorithms. Then, a semi-analytical performance prediction method is proposed to analyze its evolution through the stochastic modeling of each of the components. Intrinsically, the performance prediction method is conditional on the available Channel State Information at Receiver (CSIR), the type of channel coding (convolutional code or turbo code), the number of codewords and the type of Log Likelihood Ratios (LLR) on coded bits fed back from the decoder for interference reconstruction and cancellation inside the iterative LMMSE-IC algorithms. In the second part, closed-loop FLA in coded MIMO systems based on the proposed PHY-layer abstractions for iterative LMMSE-IC receiver have been tackled. The proposed link adaptation scheme relies on a low rate feedback and operates joint spatial precoder selection (e.g., antenna selection) and Modulation and Coding Scheme (MCS) selection so as to maximize the average rate subject to a target block error rate constraint. The cross antenna coding (the transmitter employs a Space-Time Bit-Interleaved Coded Modulation (STBICM) ) and per antenna coding (Each antenna employs an independent Bit-Interleaved Coded Modulation(BICM)) cases are both considered. The simulations clearly show the significant gain obtained with turbo receivers compared to that of a conventional MMSE receiver.

This thesis aims to abstract the physical layer (PHY) performance of current and upcoming technologies, so that, their suitability for various use cases and scenarios could be evaluated within an affordable time. For the said purpose, a new effective SINR mapping technique eEESM along with the dynamic optimization of the fitting parameter is proposed. The mapping accuracy of proposed eEESM techniques is analyzed and compared against the other state-of-the-art methods in the doubly selective channel. The results show that the proposed technique is more accurate and map closest to the reference packet error rate (PER) curves. Moreover, the mapping error of eEESM is the lowest for all considered MCSs. The justification for its better performance is the tighter symbol error rate (SER) approximation used to derive effective SINR and the proposed optimization approach. The main purpose of using PLA instead of full PHY simulations is to reduce simulation time. Therefore, a novel concept is presented to abstract PHY performance depending on the time and frequency selectivity of the channel. This further reduces the number of computations required to estimate performance using PLA. To demonstrate the gain in terms of simulation time, the computation complexity of PLA is compared against full PHY simulations. Results show that PLA is roughly 1000 to 1000000 times faster (depending on the abstracted fading conditions) compared to the PHY simulator. The effective SINR mapping approach is then further extended for future candidate multi-carrier techniques (i.e., OFDM, DFT-s-OFDM, GFDM, OTFS), which could be adopted by the upcoming technologies. For this purpose, the received SINR of symbols received through these multi-carrier techniques is derived. The resultant received SINR also considers the impact of ICI due to Doppler. Subsequently, the received SINR of symbols is mapped to effective SINR considering the selectivity of the channel. By comparing the effective SINR, OTFS outperforms other techniques. The reason for the better performance of OTFS is due to the spread of symbol energy over time and frequency, which results in higher effective SINR due to higher diversity. Furthermore, evaluation results show that the proposed PLA can accurately model the performance of these multi-carrier techniques under various fading conditions. Multi-connectivity is another enhancement being considered for future technologies, as an enabler for ultra-reliable communications under harsh channel conditions. Therefore, multi-connectivity communications are also studied in this thesis. Specifically, the frequency domain multi-connectivity networks are presented. To fully exploit frequency diversity under frequency selective channels, the subcarrier-based link combing scheme is proposed. The earlier derived received SINR is then extended for the state-of-the-art link combining schemes, i.e., SC, EGC, and MRC. The multi-connectivity gain in terms of the average received SINR is derived and compared for the above-mentioned combining schemes. To abstract the performance of multi-connectivity communications, the post-combined effective SINR mapping is proposed, where effective SINR represents the combined performance of connected links. The developed PLA performance is validated against the PHY simulations for the case of MRC. Results reveal that with the increase in multi-connectivity order, the RMSE error decreases due to the decrease in the variance of mapping SINRs. In the end, various applications of PLA are demonstrated. The developed multi-carrier PLAs are used to compare the performance of multi-carrier techniques under various fading conditions. Results depict that PER of multi-carrier techniques generally decreases with the increase in time or frequency selectivity, given that, the ideal channel estimation, ICI, and inter-symbol interference (ISI) cancellation is used. The multi-connectivity evaluation results depict that with the increase in channel selectivity higher diversity gain could be achieved. Besides, the proposed subcarrier-wise combining scheme achieves better performance compared to the traditional link combining approach. The next PLA application demonstrated is the performance comparison of V2X technologies, i.e., IEEE~802.11p, LTE-V2V, IEEE~802.11bd, and NR-V2X, in an Urban NLOS communications scenario. It is observed that 802.11bd outperforms other technologies in terms of PER and packet reception ratio (PRR). Its better performance is due to lower ICI compared to LTE-V2X and NR-V2X, and due to the use of LDPC codes compared to 802.11p. In contrast, NR-V2X outperforms other technologies in terms of data rates and packet inter-arrival time. The last PLA application shown is the link adaptation for single-link and multi-connectivity communications. In single-link communication, the performance of various PLA techniques is compared in terms of achieved data rates and outage probability against the case of perfect CQI. The CQI based on the proposed eEESM technique improves the data rates and reliability of the link, compared to other schemes. Further, in the case of multi-connectivity, the post-combined effective SINR mapping proposed in this thesis is used for link adaptation in terms of both MCS selection and adapting the number of links. The proposed scheme optimizes multi-connectivity data rates while using the lowest possible number of links required for the desired quality of service.

Le but de cette thèse est d'étudier la mise en œuvre de services de type Internet of Thing (IoT) ou Machine to Machine (M2M) par satellite. Ce type de système pose une double problématique: d'une part au niveau couche physique : les contraintes liées au terminal (limité en puissance, énergie, taille d'antenne), au canal (potentiellement avec masquage et multitrajet) et au segment spatial impliquent la mise en œuvre de différentes techniques (entrelacement, suppression d'interférents, ...) permettant d'assurer le bilan de liaison adéquat pour le service. D'autre part, le besoin d'offrir un accès à la ressource à un grand nombre de terminaux demandant un débit faible implique l'utilisation de techniques d'accès à contention optimisées, ainsi que la prise en compte au niveau accès des problématiques d'économie d'énergie. Cette couche accès doit également être en mesure de s'interfacer avec des architectures réseaux plus vastes. On peut citer par exemple les architectures Internet afin de supporter des services IP pour l'IoT, avec des notions de services intermittents, telles qu'on les retrouve dans les réseaux DTN, ou bien les architectures 4G/5G pour la mise en œuvre de services mobiles. Cette thèse va investiguer deux approches systèmes innovantes ainsi que différentes techniques aussi bien couche physique que couche accès (potentiellement couplée) permettant leur mise en œuvre. Le premier scénario système consiste à l'utilisation d'un terminal satellite relais très bas débit (contrairement au cas classique traité dans la littérature reposant sur des terminaux broadband), s'interfaçant avec des capteurs en technologie accès terrestres. Des techniques innovantes de gestion des ressources et d'économie d'énergie au travers d'une couche accès dédiée (non DVB) pourraient permettre de supporter le nombre très important de terminaux dans ce type de système. Le second scénario repose sur une communication directe avec des capteurs/objets via une constellation satellite. Cette approche pose le problème de l'efficacité de la forme d'onde pour des services extrêmement sporadique et de la fiabilisation de la communication. Il existe de nombreux travaux coté DLR sur ce type de forme d'onde avec notamment la définition de S-MIM. Néanmoins, cette solution semble complexe et de nombreuses optimisations pourraient être apportées. Coté accès, E-SSA (communication asynchrone à spectre étalé avec SIC) défini par l'ESA est également une piste de travail intéressante même si sa mise en œuvre au niveau système et sa complexité doivent être consolidées. / The aim of this thesis is to study the implementation of Internet-based services of Thing (IoT) and Machine to Machine (M2M) through a satellite link. This type of system have to deal with two issues: first the physical layer level: terminal related constraints (limited in power, energy, and antenna size), channel (potentially with masking and multipath) and the space segment involve the implementation of different techniques (interleaving, interference cancellation,) to ensure proper link budget allowing the communication. On the other hand , the need to provide access to the resource to a large number of terminals requiring low throughput involves the use of optimized contention access techniques , as well as taking into account the level of access issues energy saving. The access layer should also be able to interface with larger networks architectures. Internet architectures for example include supporting IP services for Iota, with sporadic services, such as the ones found in the DTN networks, or 4G architectures / 5G for the implementation of mobile services. This thesis will investigate two innovative approaches and different techniques as well as physical layer access layer (potentially coupled) to their implementation. The first scenario involves the use of a very low throughput satellite relay terminal (unlike in the conventional case found in the literature based on broadband terminals), interfacing with terrestrial access technology sensors. Innovative resource management and energy saving techniques through a dedicated access layer (not DVB) could absorb the large number of terminals in this type of architecture. The second scenario is based on direct communication with sensors / objects via satellite constellation. This approach raises the question of the efficiency of the waveform for extremely sporadic services and the reliability of communication. DLR works on this type of waveform including the definition of S -MIM. However, this solution seems to be complex and many optimizations can be made. From the access layer point of view, E -SSA (asynchronous spread spectrum communication with SIC) defined by the ESA is also interesting even if its implementation to the system and its complexity level should be consolidated.

Αντικείμενο της παρούσας διδακτορικής διατριβής είναι η μελέτη και ο σχεδιασμός καινοτόμων αλγορίθμων φυσικού επιπέδου σε ασύρματα συστήματα επικοινωνίας που χρησιμοποιούν διαμόρφωση με πολύπλεξη συχνότητας ορθογωνίων φερουσών (Orthogonal Frequency Division Multiplexing - OFDM). Η έρευνα επικεντρώθηκε σε δύο κατηγορίες προβλημάτων, στον σχεδιασμό αλγορίθμων προσαρμοστικής διαμόρφωσης καθώς και αλγορίθμων αντιμετώπισης ισχυρού θορύβου φάσης. Αναπτύχθηκαν αλγόριθμοι εκτίμησης φάσης με γραμμική πολυπλοκότητα, μέσω ενός καινούργιου εναλλακτικού μοντέλου περιγραφής του συστήματος. Το μοντέλο αυτό επιτρέπει την επέκταση των κλασικών αλγορίθμων εκτίμησης της κοινής φάσης με στόχο την εκτίμηση του συνολικού διανύσματος θορύβου φάσης. Επιπλέον, η τεχνική διαγώνιας φόρτωσης (diagonal-loading) προσαρμόστηκε κατάλληλα για τη βελτίωση σύγκλισης της προτεινόμενης λύσης. Τέλος, προτάθηκε και αξιολογήθηκε ένα συνολικό σύστημα OFDM όπου η εκτίμηση του καναλιού, της διαταραχής φάσης και των δεδομένων βασίζονται στο κριτήριο ελαχίστων τετραγώνων, διατηρώντας έτσι τη συνολική πολυπλοκότητα σε χαμηλά επίπεδα. Στο πλαίσιο του σχεδιασμού αλγορίθμων προσαρμοστικής διαμόρφωσης προτείνεται ένα γενικό μοντέλο περιγραφής απόδοσης συστήματος ικανό να περιγράψει τα αναπτυσσόμενα πρωτόκολλα μετάδοσης. Η πρόταση αυτή εντάσσεται στην οικογένεια των τεχνικών ισοδύναμης σηματοθορυβικής απεικόνισης (Εffective SNR Μapping - ESM). Χρησιμοποιώντας τις τεχνικές ESM και κατάλληλους περιορισμούς στην παραμετροποίηση των μεταβλητών μετάδοσης, αναπτύχθηκαν αλγόριθμοι προσαρμοστικής διαμόρφωσης χαμηλής πολυπλοκότητας που ικανοποιούν διαφορετικά κριτήρια βελτιστοποίησης. Επιπρόσθετα, προτείνεται ένα γενικό πλαίσιο για τον σχεδιασμό αλγορίθμων προσαρμοστικής διαμόρφωσης, χρησιμοποιώντας προσεγγιστικά μοντέλα απόδοσης. Ορίστηκαν οι κατάλληλες μετρικές για την ποσοτικοποίηση της σπατάλης ενέργειας που επιφέρει η χρήση προσεγγιστικών μοντέλων. Μελετήθηκε η επίδραση της καθυστέρησης ανατροφοδότησης πληροφορίας καναλιού στους αλγορίθμους και παρήχθησαν κατάλληλα μοντέλα περιγραφής απόδοσης που συμπεριλαμβάνουν το χρόνο καθυστέρησης. Το συνολικό αποτέλεσμα της εργασίας είναι αλγόριθμοι που καταφέρνουν υψηλή απόδοση συστήματος, με χαμηλή πολυπλοκότητα, κάτι το οποίο τους κάνει υλοποιήσιμους σε ρεαλιστικά συστήματα. / The objective of this thesis is to study and develop novel, low complexity physical layer algorithms for Orthogonal Frequency Division Multiplexing (OFDM) based communication systems. The study aims at two algorithmic categories, namely adaptive modulation and coding and compensation of severe phase noise (PHN) errors. A parameterized windowed least-squares (WLS) decision directed phase error estimator is proposed via proper (alternative) system modeling, applied to both channel estimation and data detection stage in OFDM systems. The window is optimized so as to minimize the post-compensation error variance (PCEV) of the residual phase, analytically computed for arbitrary PHN and frequency offset (FO) models. Closed-form expressions for near-optimal windows are derived for zero-mean FO, Wiener and first-order autoregressive PHN models, respectively. Furthermore, the diagonal-loading approach is properly employed, initially proposed for providing robustness to a general class of estimators in the presence of model mismatch, to enhance convergence of the iterative estimation scheme, in those high-SNR regions where the effect of data decision errors dominates performance. In the proposed OFDM scheme, channel, IFO estimation and data equalization are also based on the LS criterion, thus keeping the overall system complexity low. A generic performance description model is proposed and used for AMC algorithmic design, capable of describing most of current and under preparation communication protocols. This model proposition is incorporated to a larger family of performance modelling techniques named Effective SNR Mapping techniques (ESM). Using the ESM techniques and proper parameter adaptation constraints, a number of low-complexity AMC algorithms are developed under a chosen set of optimization scenarios. A framework for the design of AMC algorithms using approximate performance description models is proposed. Specific bounds are derived for quantifying the power loss when using approximate models. The effect of outdated channel state information is also studied by statistically characterizing the effective SNR at the receiver. This description allows parameter adaptation under mobility scenarios. The main value of this collective procedure is the development of low complexity- high performance algorithms, implementable on pragmatic OFDM systems.