Dissertations / Theses on the topic 'HARQ'

ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada<br>A novel type-II hybrid automatic repeat request (HARQ) algorithm using adaptive modulations and bit-interleaved coded modulation (BICM) is presented. The algorithm uses different optimized puncturing patterns for different transmissions of the same data packet. The proposed approach exploits mapping diversity through BICM with iterative decoding. The modulation order is changed in each transmission to keep the number of symbols transmitted constant. We present new bit error rate and frame error rate analytical results for the proposed technique showing good agreement with simulation results. We compare the throughput performance of our proposed HARQ technique with a reference HARQ technique that uses different mapping arrangements but keeps the modulation order fixed. By using optimized puncturing patterns and adaptive modulations, our method provides significantly better throughput performance over the reference HARQ method in the whole signalto- noise ratio (SNR) range, and achieves a gain of 12 dB in the medium SNR region.

The performance and reliability of wireless communication links can be improved by employing multiple antennas at both ends, thereby creating multiple-input multiple-output (MIMO) channels. However, once multiple co-channel users are added to the system it can be difficult to provide as many receive antennas as transmit antennas, resulting in a so-called overloaded (rank-deficient) system. Under overloaded conditions, maximum likelihood (ML) detection works well, but its exponential complexity prohibits its use and suboptimal linear detectors perform poorly. In this thesis, new signal processing techniques for multi-user overloaded systems using hybrid automatic repeat request (HARQ) protocols are investigated. The HARQ retransmissions are used to form virtual receive antennas, which can efficiently transform an overloaded system into a critically loaded system (i.e. a system with an equal number of transmit and receive antennas). In the first part of the thesis, a multi-user non-cooperative overloaded system is considered. At first, it is demonstrated that the suboptimal linear minimum mean square error (MMSE) detector leads to significant performance degradation compared to an ML detector for such systems. To overcome this drawback, two multi-user transmission schemes are proposed that work well under overloaded conditions. The proposed schemes allow us to apply linear multi-user detection (MUD) algorithms without requiring additional antennas or hardware chains. Monte-Carlo simulations demonstrate that the proposed schemes can result in significant gains in terms of bit-error-rate (BER) and dropped packet performance. In the second part, the performance of multiple HARQ processes for a two-hop multi-source multi-relay decode-and-forward (DF) relaying network with no direct link are analyzed. Dealing with multiple HARQ processes at each relay, a retransmission scheme is proposed that utilizes virtual antennas to achieve increased receive diversity and improved throughput compared to traditional orthogonal (time division) retransmissions. A novel forwarding strategy at the relay(s) to destination link is proposed with the objective of further improving throughput. Finally, the end-to-end outage probability and throughput efficiency of the proposed retransmission and forwarding schemes are found analytically and confirmed with Monte-Carlo simulations.

Nous considérons dans cette thèse le problème de la transmission fiable de données par paquets en utilisant une transmission mono-porteuse sur des canaux sélectifs en fréquence à évanouissements. Notre objectif est de concevoir des couples émetteurs-récepteurs permettant d'améliorer les performances de la détection en l'absence d'information sur le canal à la transmission et ceci en exploitant la diversité temporelle disponible dans le cadre des protocoles de retransmission hybrides (HARQ). En analysant les performances du système de transmission avec un récepteur à maximum de vraisemblance, nous établissons un critère pertinent pour l'étude des performances du système basé sur les statistiques de la distance Euclidienne à la sortie du canal sélectif en fréquence. A partir de ce cadre théorique, nous proposons un nouveau schéma de diversité entre les différentes retransmissions, nommé précodage de phase, qui permet de combattre l'interférence entre symboles pour les canaux lentement variables dans le temps. Puis, à l'aide de nos outils d'analyse, nous revisitons un autre schéma de diversité qu'est la diversité d’entrelacement. En particulier, nous soulignons le double avantage offert par ce schéma, à savoir la diversité de modulation et la réduction de l'interférence entre symboles. Nous réalisons ensuite une étude comparative entre les deux schémas de diversité précédents sous traitement itératif ou non itératif au récepteur. Enfin, nous introduisons un nouveau protocole de retransmission adaptative pour les transmissions dîtes multi-couches afin de réduire l'interférence entre couches pour les canaux rapidement variant dans le temps utilisant des informations de retour limitées<br>In this thesis, we consider the problem of reliable data packets transmission using single-carrier signaling over frequency-selective fading channels. Our objective is to design enhanced transceivers with improved detection performance in the absence of channel state information at the transmitter by exploiting the available time-diversity in Chase combining Hybrid Automatic Repeat reQuest (HARQ) protocols. By analyzing the performance of the transmission scheme using an optimal maximum-likelihood receiver, we establish a suitable criterion for the study of system performance based on the statistics of the Euclidean distance at the output of a frequency-selective channel. From this theoretical framework, we propose a novel transmit-diversity scheme between subsequent HARQ transmissions, called phase-precoding, which allows the mitigation of intersymbol interference for slow time-varying channels. Then, with the help of our analytical tools, we revisit another transmit-diversity scheme which is the bit-interleaving diversity scheme. In particular, we emphasize the double advantage offered by this diversity scheme including the inherent modulation diversity in addition to the intersymbol interference reduction. Subsequently, we perform a comparative study between phase-precoding and bit-interleaving diversity schemes under iterative and non-iterative receiver structures. Finally, we introduce a new adaptive retransmission protocol for a multi-layer transmission scheme for the mitigation of inter-layers interference for rapidly time-varying channels using limited feedback information

Cette thèse traite le problème de l’allocation des ressources physiques dans les réseaux ad hoc mobiles en contexte multi-utilisateurs. Nous considérons qu’un noeud du réseau, appelé gestionnaire des ressources (GR) a pour tâche d’effectuer cette allocation de ressources, et que pour ce faire, les autres noeuds lui communiquent des informations relatives aux canaux de propagations de leurs liens de communications. Ce modèle de réseaux induit un délai entre le moment où les noeuds envoient leurs informations au GR et le moment où le GR leur envoie leur allocation de ressource, ce qui rend impossible l’utilisation d’informations de canal instantanées pour effectuer l’allocation. Ainsi, nous considérons que le GR ne dispose que d’informations statistiques relatives aux canaux des différents liens de communications. De plus, nous supposons que chaque lien utilise le mécanisme de l’ARQ Hybride (HARQ). Dans ce contexte, la thèse comporte deux objectifs principaux: i) Proposer des procédures d’estimation de la statistique du canal de propagation, et plus particulièrement du facteur K du canal de Rice avec et sans effet de masquage. ii) Proposer et étudier des algorithmes d’allocation de ressources basés sur les statistiques du canal et prenant en compte l’utilisation de l’HARQ ainsi que de schéma de modulation et de codage pratique. En particulier, on cherche à maximiser des grandeurs relatives à l’efficacité énergétique du système. Les ressources à allouer à chaque lien sont une énergie de transmission et une proportion de la bande de fréquence<br>This thesis addresses the Resource Allocation (RA) problem in multiuser mobile ad hoc networks. We assume that there is a node in the network, called the resource manager (RM), whose task is to allocate the resource and thus the other nodes send him there channel state information (CSI). This network model induces a delay between the time the nodes send the RM their CSI and the time the RM sends them their RA, which renders impossible the use of instantaneous CSI. Thus, we assume that only statistical CSI is available to perform the RA. Moreover, we assume that an Hybrid ARQ (HARQ) mechanism is used on all the links. In this context, the objective of the thesis is twofold: i) Propose procedures to estimate the statistical CSI, and more precisely to estimate the Rician K factor with and without shadowing. ii) Propose and analyse new RA algorithms using statistical CSI and taking into account the use of HARQ and practical modulation and coding schemes. We aim to maximize energy efficiency related metrics. The resource to allocate are per-link transmit energy and bandwidth proportion

Cette thèse traite le problème de l’allocation des ressources physiques dans les réseaux ad hoc mobiles en contexte multi-utilisateurs. Nous considérons qu’un noeud du réseau, appelé gestionnaire des ressources (GR) a pour tâche d’effectuer cette allocation de ressources, et que pour ce faire, les autres noeuds lui communiquent des informations relatives aux canaux de propagations de leurs liens de communications. Ce modèle de réseaux induit un délai entre le moment où les noeuds envoient leurs informations au GR et le moment où le GR leur envoie leur allocation de ressource, ce qui rend impossible l’utilisation d’informations de canal instantanées pour effectuer l’allocation. Ainsi, nous considérons que le GR ne dispose que d’informations statistiques relatives aux canaux des différents liens de communications. De plus, nous supposons que chaque lien utilise le mécanisme de l’ARQ Hybride (HARQ). Dans ce contexte, la thèse comporte deux objectifs principaux: i) Proposer des procédures d’estimation de la statistique du canal de propagation, et plus particulièrement du facteur K du canal de Rice avec et sans effet de masquage. ii) Proposer et étudier des algorithmes d’allocation de ressources basés sur les statistiques du canal et prenant en compte l’utilisation de l’HARQ ainsi que de schéma de modulation et de codage pratique. En particulier, on cherche à maximiser des grandeurs relatives à l’efficacité énergétique du système. Les ressources à allouer à chaque lien sont une énergie de transmission et une proportion de la bande de fréquence<br>This thesis addresses the Resource Allocation (RA) problem in multiuser mobile ad hoc networks. We assume that there is a node in the network, called the resource manager (RM), whose task is to allocate the resource and thus the other nodes send him there channel state information (CSI). This network model induces a delay between the time the nodes send the RM their CSI and the time the RM sends them their RA, which renders impossible the use of instantaneous CSI. Thus, we assume that only statistical CSI is available to perform the RA. Moreover, we assume that an Hybrid ARQ (HARQ) mechanism is used on all the links. In this context, the objective of the thesis is twofold: i) Propose procedures to estimate the statistical CSI, and more precisely to estimate the Rician K factor with and without shadowing. ii) Propose and analyse new RA algorithms using statistical CSI and taking into account the use of HARQ and practical modulation and coding schemes. We aim to maximize energy efficiency related metrics. The resource to allocate are per-link transmit energy and bandwidth proportion

Wireless technology is experiencing spectacular developments, due to the emergence of interactive and digital multimedia applications as well as rapid advances in the highly integrated systems. For the next-generation mobile communication systems, one can expect wireless connectivity between any devices at any time and anywhere with a range of multimedia contents. A key requirement in such systems is the availability of high-speed and robust communication links. Unfortunately, communications over wireless channels inherently suffer from a number of fundamental physical limitations, such as multipath fading, scarce radio spectrum, and limited battery power supply for mobile devices. Cooperative diversity (CD) technology is a promising solution for future wireless communication systems to achieve broader coverage and to mitigate wireless channels’ impairments without the need to use high power at the transmitter. In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version message to an intended destination node. The destination node combines the signal received from the relays, and takes into account the source’s original signal to decode the message. The CD communication systems exploit two fundamental features of the wireless medium: its broadcast nature and its ability to achieve diversity through independent channels. A variety of relaying protocols have been considered and utilized in cooperative wireless networks. Amplify and forward (AAF) and decode and forward (DAF) are two popular protocols, frequently used in the cooperative systems. In the AAF mode, the relay amplifies the received signal prior to retransmission. In the DAF mode, the relay fully decodes the received signal, re-encodes and forwards it to the destination. Due to the retransmission without decoding, AAF has the shortcoming that noise accumulated in the received signal is amplified at the transmission. DAF suffers from decoding errors that can lead to severe error propagation. To further enhance the quality of service (QoS) of CD communication systems, hybrid Automatic Repeat-reQuest (HARQ) protocols have been proposed. Thus, if the destination requires an ARQ retransmission, it could come from one of relays rather than the source node. This thesis proposes an improved HARQ scheme with an adaptive relaying protocol (ARP). Focusing on the HARQ as a central theme, we start by introducing the concept of ARP. Then we use it as the basis for designing three types of HARQ schemes, denoted by HARQ I-ARP, HARQ II-ARP and HARQ III-ARP. We describe the relaying protocols, (both AAF and DAF), and their operations, including channel access between the source and relay, the feedback scheme, and the combining methods at the receivers. To investigate the benefits of the proposed HARQ scheme, we analyze its frame error rate (FER) and throughput performance over a quasi-static fading channel. We can compare these with the reference methods, HARQ with AAF (HARQ-AAF) and HARQ with perfect distributed turbo codes (DTC), for which correct decoding is always assumed at the relay (HARQ-perfect DTC). It is shown that the proposed HARQ-ARP scheme can always performs better than the HARQ-AAF scheme. As the signal-to-noise ratio (SNR) of the channel between the source and relay increases, the performance of the proposed HARQ-ARP scheme approaches that of the HARQ-perfect DTC scheme.

Master of Philosophy<br>Wireless technology is experiencing spectacular developments, due to the emergence of interactive and digital multimedia applications as well as rapid advances in the highly integrated systems. For the next-generation mobile communication systems, one can expect wireless connectivity between any devices at any time and anywhere with a range of multimedia contents. A key requirement in such systems is the availability of high-speed and robust communication links. Unfortunately, communications over wireless channels inherently suffer from a number of fundamental physical limitations, such as multipath fading, scarce radio spectrum, and limited battery power supply for mobile devices. Cooperative diversity (CD) technology is a promising solution for future wireless communication systems to achieve broader coverage and to mitigate wireless channels’ impairments without the need to use high power at the transmitter. In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version message to an intended destination node. The destination node combines the signal received from the relays, and takes into account the source’s original signal to decode the message. The CD communication systems exploit two fundamental features of the wireless medium: its broadcast nature and its ability to achieve diversity through independent channels. A variety of relaying protocols have been considered and utilized in cooperative wireless networks. Amplify and forward (AAF) and decode and forward (DAF) are two popular protocols, frequently used in the cooperative systems. In the AAF mode, the relay amplifies the received signal prior to retransmission. In the DAF mode, the relay fully decodes the received signal, re-encodes and forwards it to the destination. Due to the retransmission without decoding, AAF has the shortcoming that noise accumulated in the received signal is amplified at the transmission. DAF suffers from decoding errors that can lead to severe error propagation. To further enhance the quality of service (QoS) of CD communication systems, hybrid Automatic Repeat-reQuest (HARQ) protocols have been proposed. Thus, if the destination requires an ARQ retransmission, it could come from one of relays rather than the source node. This thesis proposes an improved HARQ scheme with an adaptive relaying protocol (ARP). Focusing on the HARQ as a central theme, we start by introducing the concept of ARP. Then we use it as the basis for designing three types of HARQ schemes, denoted by HARQ I-ARP, HARQ II-ARP and HARQ III-ARP. We describe the relaying protocols, (both AAF and DAF), and their operations, including channel access between the source and relay, the feedback scheme, and the combining methods at the receivers. To investigate the benefits of the proposed HARQ scheme, we analyze its frame error rate (FER) and throughput performance over a quasi-static fading channel. We can compare these with the reference methods, HARQ with AAF (HARQ-AAF) and HARQ with perfect distributed turbo codes (DTC), for which correct decoding is always assumed at the relay (HARQ-perfect DTC). It is shown that the proposed HARQ-ARP scheme can always performs better than the HARQ-AAF scheme. As the signal-to-noise ratio (SNR) of the channel between the source and relay increases, the performance of the proposed HARQ-ARP scheme approaches that of the HARQ-perfect DTC scheme.

Orientador : Prof. Dr. Evelio Martín Garcia Fernández<br>Co-orientador : Prof. Dr. Richard Demo Souza<br>Dissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia Elétrica. Defesa: Curitiba, 20/04/2012<br>Inclui referências<br>Nesta dissertação é avaliado o uso de cooperação em uma rede cognitiva baseada em HARQ, onde a rede secundária aproveita as oportunidades originadas nas retransmissões do enlace primário. O objetivo principal é propor técnicas com o uso de comunicação cooperativa para conseguir uma transmissão da rede secundária com taxas maiores que as alcançadas na literatura, sem prejudicar significativamente o desempenho da rede primária. Na dissertação são feitas comparações em termos da vazão do sistema entre os protocolos de codificação. Além disso, avalia-se o efeito da linha de visada e do número de relays cooperando. As simulações demonstram que é possível o enlace secundário se comunicar com altas taxas mantendo uma mínima interferência no enlace primário com o uso de cooperação. Com os nós da rede secundária bem próximos entre si e do transmissor primário é possível obter taxas maiores que as alcançadas pela rede primária. Palavras chave: Comunicação cooperativa, redes cognitivas, HARQ, múltiplos relays, codificação por repetição, codificação paralela, Nakagami-m.<br>Abstract: This dissertation evaluates the use of cooperation in a cognitive network based on HARQ, where the secondary link exploits the retransmissions of the primary link. The main objective is to propose techniques with the use of cooperative communication to achieve a transmissions rates of the secondary link higher than those achieved in the literature, without significantly harming the performance of the primary network. Comparisons are made in terms of throughput between the coding protocols. The effect of line of sight and the number of cooperating relays is also evaluated. The simulations show that it is possible for the secondary link to communicate with high transmission rates while causing a minimum interference on the primary link with the use of cooperation. When the secondary link nodes are very close to each other and nearby the primary transmitter, it is possible to achieve higher rates than those achieved by the primary link. Key words: Cooperative communications, cognitive networks, HARQ, multiple relay, repetition coding, parallel coding, Nakagami-m.

Este trabalho estuda as potenciais melhorias na eficiência energética e vazão do método híbrido de requisição automática de retransmissão (Hybrid Automatic Retransmission Request, HARQ). A análise inclui as camadas física (PHY) e de acesso ao meio (MAC). É investigada a relação de compromisso gerada pelo HARQ, o qual demanda uma menor potência de transmissão para uma certa probabilidade de falha alvo ao custo de mais acessos ao canal. Uma vez que a competição para acesso ao canal na camada MAC é bastante custosa em termos de energia e atraso, os resultados mostram que a utilização do HARQ leva a uma grande melhoria de performance devido ao menor número de nós competidores – uma consequência da redução na potência de transmissão necessária. Contra-intuitivamente, esta análise leva à conclusão que retransmissões podem diminuir o atraso, melhorando a performance do sistema. Finalmente, são também investigados valores ótimos para o número de retransmissões permitidas, visando maximizar vazão ou/e eficiência energética.<br>This work studies the potential improvements in terms of energy efficiency and throughput of a hybrid automatic retransmission request (HARQ) mechanism. The analysis includes both the physical (PHY) and medium access (MAC) layers. We investigate the trade-off provided by HARQ, which demands reduced transmit power for a given target outage probability at the cost of more accesses to the channel. Since the competition for channel access at the MAC layer is very expensive in terms of energy and delay, our results show that HARQ leads to great performance improvements due to the decrease in the number of contending nodes – a consequence of the reduced required transmit power. Counter-intuitively, our analysis leads to the conclusion that retransmissions may decrease the delay, improving the system performance. Finally, we investigate the optimum values for the number of allowed retransmissions in order to maximize either the throughput or the energy efficiency.

The explosive growth of data traffic in wireless communication systems comes together with the urgent need to minimize its environmental and financial impact. Therefore, the main objective in the field of green radio communication is to improve the energy efficiency of wireless communication systems with respect to the future performance demands on the wireless communication infrastructure. In this context, recent research in cooperative and cognitive communication techniques attracts particular attention. While cognitive radio improves spectral efficiency by enhanced spectrum utilization, cooperative communication techniques achieve remarkable gains in spectral efficiency by enabling the terminals to share their resources. In particular, creating virtual multi-antenna arrays by antenna sharing enables exploitation of spatial diversity gains and multiplexing gains within a network of single antenna terminals. This technique is particularly attractive for mobile wireless networks, since power and space constraints often prohibit the integration of multiple antennas into mobile terminals. This work studies the performance of the hybrid automatic repeat-request (HARQ) dynamic decode-and-forward (DDF) protocol in the half-duplex relay channel. The reason behind exploration of the HARQ-DDF protocol is that it achieves the optimal performance in terms of the diversity-multiplexing tradeoff (DMT) and the diversity-multiplexing-delay tradeoff(DMDT). However, DMT and DMDT are evaluated as the signal-to-noise ratio (SNR) approaches infinity. In practice, key performance measures are the fixed-rate outage probability and delay-limited throughput achieved at the SNR expected during operation. To this end, it is common practice to give the performance of the DDF protocol as a function of the source-to-destination channel SNR (SD-SNR). In this dissertation the focus is to study the performance of the HARQ-DDF protocol measured as a function of the SNR as seen at the destination (D-SNR). This approach enables the performance comparison with the HARQ-SISO and the HARQ-MISO protocol from an energy efficiency perspective on the system level. Furthermore, a novel variant of the HARQ-MISO protocol, the hybrid repeat-with-diversity-request (HARDQ) MISO protocol, is introduced. Considering outage probability as measure of reliability, closed-form solutions and simulation results show that the HARDQ-MISO and the HARQ-DDF protocol outperform the HARQ-MISO protocol from an energy efficiency point of view. From a delay-limited throughput point of view the HARQ-MISO protocol is beneficial. It is demonstrated that code-rate assignment allows to achieve significant performance gains in terms of delay-limited throughput. Furthermore, reducing the decoding cost using code-rate assignment techniques comes together with only negligible performance loss.

Abstract. With the advent of new use-cases requiring high reliability and low-latency, transmission with finite blocklength becomes inevitable to reduce latency. In contrast to classical information-theoretic principles, the use of finite blocklength results in a non-negligible decoder error probability. Hybrid automatic repeat request (HARQ) procedures are used to improve the accuracy in decoding by exploiting time-diversity at the expense of increased latency. Thus, achieving high reliability and low-latency are Pareto-optimal, which calls for a trade-off between the two. Concurrently, non-orthogonal multiple access (NOMA) has gained widespread attention in research due to the ability to outperform its counterpart, orthogonal multiple access (OMA) in terms of spectral efficiency and user fairness. This thesis investigates the performance of a two-user downlink NOMA system using HARQ with chase combining (HARQ-CC) in finite blocklength unifying the three enablers. First, an analytical framework is developed by deriving closed-form approximations for the individual average block error rate (BLER) of the near and the far user. Based upon that, the performance of NOMA is discussed in comparison to OMA, which draws the conclusion that NOMA outperforms OMA in terms of user fairness. Further, asymptotic expressions for average BLER are derived, which are used to devise an algorithm to determine such minimum blocklength and power allocation coefficients for NOMA that satisfies reliability targets for the users. NOMA has a lower blocklength in high transmit signal-to-noise ratio (SNR) conditions, leading to lower latency than OMA when reliability requirements in terms of BLER for the two users are in the order of 10^(-5).

Dans le cadre des communications par satellite, les caractéristiques du lien rendent difficile la mis en œuvre des systèmes de télécommunications. Pour certaines applications, le problème principal est le délai de propagation. Un autre problème est la perte des données due aux caractéristiques du canal. Le but de cette thèse est de proposer un mécanisme qui assure la fiabilité de la communication tout en maximisant l’efficacité d’utilisation de la bande passante. Le protocole HARQ est reconnu pour sa capacité à atteindre le meilleur compromis fiabilité/débit. Cependant, ce mécanisme doit être optimisé pour pouvoir être utilisé sur un lien satellite. Dans un premier temps, nous proposons une méthode de fiabilisation basée sur l’HARQ statique, où le nombre de bits à envoyer à chaque transmission est fixé à l’avance. Cette méthode s’adresse aux services qui tolèrent un certain délai avant la réception du message. À partir de la distribution statistique du canal, elle définit la probabilité de décodage optimale à chaque transmission. Le nombre de bits à envoyer est calculé en fonction de ces probabilités et de la distribution d’information mutuelle du canal. Dans un deuxième temps, nous introduisons une version adaptative de la méthode précédente. Le récepteur calcule le nombre de bits à envoyer en fonction de l’état du canal pendant la transmission actuelle. Le nombre de bits calculé est renvoyé dans un acquittement vers l’émetteur. Finalement, nous présentons une structure de trame couche physique dans le cadre des mécanismes HARQ proposés et nous évaluons ses performances en faisant varier les paramètres du système. L’objectif est de trouver l’ordre de grandeur optimal des tailles de trames et des codes correcteurs d'erreurs à utiliser<br>As part of a satellite communications system, the characteristics of the communication links make it difficult to set up telecommunications systems. For certain applications, the main problem is the propagation delay. Another problem is the loss of data due to the characteristics of the channel. The aim of this thesis is to propose a mechanism that ensures the reliability of communication and maximize the utilization efficiency of the available bandwidth. HARQ protocol is known for its ability to achieve the best compromise reliability/ throughput.However, this mechanism must be optimized to be used on a satellite link. First, we propose a reliability method based on static HARQ, where the number to be sent is fixed previously. This method is specifically for services that tolerate some delay before the reception of the message. It consists in defining the probability of decoding at each transmission, using an optimization algorithm that we propose. The number of bits to be sent is calculated based on these probabilities and the distribution of the mutual information, assuming knowledge of the statistical distribution of the channel attenuation. Secondly, we introduce an adaptive version of the proposed method. This new approach calculates the number of bits to be sent by taking into account variations of the channel state during the communication. The receiver calculates the number of bits to be sent depending on the channel state during the current transmission. This calculated number is sent in an acknowledgement to the transmitter. Finally, we propose a frame structure for a physical layer that implements the proposed mechanisms and evaluate their performance by varying the system parameters. The aim is to find the optimal order of frame sizes and codes to be used

L’évolution majeur de l’UMTS, ces dernières années est le HSDPA (High Speed Downlink Packet Access) qui est basé sur la transmission en mode paquet. Il est conçu pour répondre au besoin en débit des utilisateurs dans la liaison descendante. Le HSDPA permet d’atteindre des débits qui peuvent dépasser 10 Mbits/s. Ceci est possible grâce à l’utilisation du principe de transmission multicodes en application conjointe avec de nouvelles technologies telles que la modulation et codage adaptatifs (MCA) ainsi que l’HARQ (Hybrid Automatic Repeat reQuest). Cette thèse porte sur la transmission de données pour le HSDPA en mode FDD, et l’étude des algorithmes HARQ. Pour augmenter le débit de transmission, la technique MCA adapte la modulation et le rendement de codage au fur et à mesure que les conditions du canal de propagation varient. L’utilisation des modulations d’ordre supérieur (16-QAM) dégrade les performances du récepteur Rake. En plus, avec ce dernier, le simulateur HSDPA demande un temps de calcul très long pour atteindre de bonnes performances. Ceci nous a motivé à introduire une méthode de simulation rapide qui fournit pratiquement les mêmes performances dans un temps de calcul plus réduit. Pour améliorer les performances du MCA avec le récepteur Rake, nous avons implémenté les techniques de retransmission HARQ. Selon l’implémentation et les performances, on distingue deux approches de retransmission : la première est basée sur l’algorithme de Chase où les retransmissions portent la même information que celle portée par la transmission originale, et la deuxième repose sur l’algorithme IR (Incremental Redundancy) dans lequel chaque retransmission transporte une redondance supplémentaire. L’analyse des performances a montré que l’HARQ apporte un gain considérable après seulement 2 transmissions. Cependant, avec les modulations d’ordre supérieur, cette technique peut atteindre ses limites lorsque le canal de transmission induit une interférence multitrajets sévère. Cette limitation nous a amené à introduire une méthode qui combine l’HARQ avec la suppression d’interférence multitrajets (MPIC). Pour améliorer cette technique nous avons proposé d’utiliser la technique de réarrangement de constellation qui apporte une diversité importante en changeant la constellation d’une transmission à l’autre. Nous avons constaté une nette amélioration des performances malgré la présence de trajets multiples<br>The major evolution of UMTS (Universal Mobile Telecommunications System) in recent years is the High Speed Downlink Packet Access (HSDPA) which provides data rates up to 10 Mbps. The implementation of HSDPA includes multicode transmission in joint application with Adaptive Modulation and Coding (AMC) as well as Hybrid Automatic Repeat reQuest (HARQ). This thesis deals with the implementation of the HSDPA simulator in FDD (FrequencyDivision Duplex) mode according to 3GPP technical specifications. It also aims to study the HARQ algorithms for HSDPA. The performance of AMC is significantly degraded when higher order modulation (16-QAM) is used in a multipath environnement. Moreover, the HSDPA simulator requires a very long time of computation to provide good performance in multipath channel. In order to solve this problem, we have introduced a simplified simulator which exploits the performance of HSDPA over gaussien channel as look-up tables to compute the block error rate in multipath channel. To make the AMC technique more powerful, we have implemented the HARQ technique. It combines ARQ methods with turbo coding. There are two fundamental approaches for HARQ : the first is Chase approach in which retransmissions are identical to the original transmission, the second approach is IR (Incremental Redundancy) in which the retransmissions carry additionnal redundancy. The performance analysis shows that a significant gain is offered by HARQ after only 2 transmissions. However this technique can exhibit an error floor when using higher order modulation in multipath environnement. As a solution to this limitation, we have employed HARQ technique combined with soft Multipath Interference Cancellation (MPIC). For enhancing this method, we have proposed to use the constellation rearrangement technique which provides additionnal diversity by changing the constellation from one transmission to other. With this techniques, very good performance is offered, and the error floor is mitigated or completely removed

Les demandes de haut débit, faible latence et grande fiabilité augmentent dans les nouvelles générations de systèmes de radiocommunications. Par conséquent, on propose de combiner la transmission non orthogonale avec les retransmissions HARQ afin de combattre les fluctuations de canal de transmission à haut débit. Dans la première partie de la thèse, on propose des protocoles de retransmissions HARQ avec l'aide d'un relai afin d'améliorer le débit et la fiabilité du système. Une version renforcée du protocole HARQ qui prend en compte le délai de retour est proposée dans la seconde partie de la thèse<br>HARQ has become an important research field in the wireless digital communications area during the last years. In this thesis, we improve the HARQ mechanisms in terms of throughput and/or latency which are the bottleneck of next generation wireless communication systems. More precisely, we improve the time-slotted HARQ systems by mimicking NOMA, which means using superposed packets in a single-user context. In the first part of the thesis, we propose HARQ protocols using the help of a relay to improve the transmission rate and reliability. An enhanced HARQ protocol adapted to delayed feedback is proposed in the second part. In this new multi-layer HARQ protocol, additional redundant packets are sent preemptively before receiving the acknowledgement, and in superposition to other HARQ processes

The cellular networks are evolving to meet the future requirements of data rate,coverage and capacity. The fourth generation mobile communication system, LTEhas been developed to meet these goals. LTE uses multiple antenna features andlarger bandwidths in order to accomplish this task. These features will furtherextend the requirements of data rate, coverage, latency and flexibility. LTE also utilizes the varying quality of the radio channel and the interferencefrom other transmitters by adapting the data rate to the instantaneous channelquality at all the time. This is typically referred to as Link Adaptation. Thelink adaptation fails from time to time due to the varying channel quality as wellas the interference from other transmitters. In order to counteract these failures,retransmission methods are employed. These methods detect the errors on thereceiver side and signals the transmitter for the retransmission of the erroneousdata. The efficiency of link adaptation increases if combined with a properly designedretransmission scheme at the expense of delays due to retransmissions. This master thesis focuses on the study of the retransmission schemes with fasterfeedback, resulting in a reduction in delay. The feedback is generated by makingan early estimate of the decoding outcome and sending it early to the transmitterresulting in faster retransmission. This is important in certain applications wherethe data transmission is intolerant to delays.The thesis work shows by system performance simulations that fast packet retransmission,precisely called Early HARQ Feedback, significantly affects the systemperformance together with the utilization of the link adaptation. The study alsoshows that the link adaptation, in certain scenarios, can be optimized to improvethe system performance. In that respect, it is also possible to increase the numberof retransmissions within the same resource utilization. That optimization is basicallycalled aggressive link adaptation. Consequently, Early HARQ Feedback incombination with aggressive link adaptation provides a large improvement in thedownlink performance of the studied cases.

Multiple Input Multiple Output (MIMO) systems use multiple transmit and receive antennas to achieve higher data rates by transmitting multiple independent data systems. Transmission errors can be reduced by using Hybrid Automatic Repeat request (HARQ) combining techniques with MIMO systems. In this thesis, the use of HARQ for MIMO multi-hop communication is studied. We propose two MIMO HARQ combining methods which are based on using pre-combiningonly and a joint pre and post combining techniques. In addition to conventional single-hop transmission, HARQ schemes for MIMO multi-hop relay systems are also investigated. A novel approach is proposed to deal with the parallel HARQ processes in MIMO relay scenario. An information theoretic throughput analysis is performed to evaluate the performance of the relay system by employing various transmission techniques for relay-destination link. Evaluation is carried out on the delay involved while employing the relay systems as compared to single hop systems. Simulation results show that the proposed system can enhance the overall throughput performance of MIMO single-hop and multi-hop relay systems. Considering the recent research interest in green radio and requirements of reduced energy consumption by the wireless networks, we evaluated the energy efficiency of existing and proposed MIMO HARQ techniques for sensor and cellular networks. The results show that the proposed scheme is more energy efficient compared to other schemes in single-hop as well as multi-hop scenarios.

Reliability of data transmission is a fundamental problem in wireless communications. Fading in wireless channels causes the signal strength to vary at the receiver and this results in loss of data packets. To improve the reliability, automatic repeat request (ARQ) schemes were introduced. However these ARQ schemes suffer from a reduction in the throughput. To address the throughput reduction, conventional ARQ schemes were combined with forward error correction (FEC) schemes to develop hybrid-ARQ (HARQ) schemes. For improving the reliability of data transmission, HARQ schemes are included in the present wireless standards like LTE, LTE-Advanced and WiMAX. Conventional HARQ systems use the same transmission power and the same number of channel uses in different ARQ rounds. However this is not optimal in terms of minimizing the average transmit power or the average energy spent for successful transmission of a data packet. We address this issue in the first part of the dissertation, where we consider optimal resource allocation in HARQ systems with a limit on the maximum number of allowed transmissions for a data packet. Specifically, we consider the problem of minimizing the packet drop probability (PDP) under an average transmit power constraint or equivalently minimizing the average transmit power under a fixed PDP constraint. We consider both incremental redundancy (IR)-based and Chase combining (CC)-based HARQ systems in our work. For an IR-HARQ system, for the special case of two allowed transmissions for each packet, we provide a solution for the optimal number of channel uses and the optimal power to be used in each ARQ round. For a CC-HARQ system, we solve the problem of optimal power allocation in i.i.d. Rayleigh fading channels as well as correlated Rayleigh fading channels. For the CC-HARQ case, we also provide a low complexity geometric programming (GP) solution using an approximation of the outage probability expression. HARQ systems conventionally use one bit acknowledgement (ACK)/negative ACK (NACK) feedback from the receiver to the transmitter. In the 3GPP-LTE systems, one method for sending these HARQ acknowledgement bits is to jointly code them with the other control signaling information using a specified Reed-Muller code consisting of 20 coded bits. Even though the resources used for sending this control signaling information can inherently provide a diversity gain, the Reed-Muller code with such a short block size is not good at extracting all of the available diversity. To address this issue, in the second part of this dissertation, we propose two new methods: i) based on complex-field coding (CFC), and ii) using repetition across frequency bands, to extract the inherent diversity available in the channel resources and improve the error protection for the HARQ acknowledgement bits along with the other control signaling information. In the second part of the dissertation, we also propose a new signal space diversity (SSD) scheme, which results in transmit signals having constant envelope (CE). The proposed CE-SSD scheme results in a better overall power efficiency due to the reduced back-off requirements on the radio frequency power amplifier. Moreover, the proposed CE-SSD technique can be useful for application scenarios involving transmission of small number of information bits, such as in the case of control signaling information transmission. In conventional HARQ systems, during the retransmission phase, the channel resources are exclusively used for the retransmitted data packet. This is not optimal in terms of efficient resource utilization. For efficient utilization of channel resources during the retransmissions, a superposition coding (SPC) based HARQ scheme was proposed in the literature. In an SPC based HARQ system, an erroneous packet is transmitted together with a new data packet by superposition in the Euclidean space. In the final part of this dissertation, we study performance of different bits-to-symbol mappings for such an SPC based HARQ system.

CAPES<br>Nessa dissertação de mestrado apresentamos um novo método HARQ para sistemas de comunicação cooperativa, denominado Retransmissão Parcial Codificada (RPC). Esse método é baseado na retransmissão de apenas uma fração da palavra código original por parte dos nós cooperativos, aplicando a essa fração um ganho de potência apropriado. Os resultados numéricos utilizando códigos LDPC e HARQ Tipo-I com Chase Combining mostram que o RPC supera os esquemas HARQ cooperativos tradicionais considerando os protocolos AAF e SDF. Além disso, mostramos que a vazão (throughput) do RPC, utilizando apenas um único relay, pode ser consideravelmente maior que a vazão de alguns métodos HARQ cooperativos que utilizam múltiplos relays.<br>In this master thesis we present a novel HARQ scheme for cooperative communication systems, called Coded Partial Retransmission (CPR). The method is based on the retransmission of only a fraction of the original codeword by the cooperating nodes, applying an appropriate power allocation. Numerical results using LDPC codes and Type-I HARQ with Chase Combining show that CPR outperforms regular cooperative HARQ techniques considering both AAF and SDF protocols. Additionally, we show that the CPR throughput, using a single relay, may be considerably larger than the throughput of some regular cooperative HARQ schemes using multiple relays.

Dans cette thèse, nous étudions plusieurs scénarios de communication pour les futurs réseaux sans fil. Plus particulièrement, cette thèse porte son attention sur comment la communication directe entre équipements mobiles (D2D) peut améliorer les performances des technologies existantes dans les systèmes sans fil. Le premier scénario étudié durant cette thèse est celui de la communication par multidiffusion d’un message commun entre un émetteur et plusieurs récepteurs. Il peut être illustré par le streaming vidéo, les messages d’alerte à destination de la police ou des pompiers ou des ambulanciers. Le second scénario étudié est celui d’une transmission à contraintes critiques en latence et en fiabilité. Ce dernier est illustré par son implication primordiale dans les futures technologies telles que les voitures connectées, avec pour but d’éviter des accidents, ou bien les machines connectées pour améliorer les services hospitaliers tels que la télé-chirurgie entre autres. Le dernier scénario étudié est celui de la localisation d’un groupe d’équipement dans un réseau densément peuplé tel qu’on peut trouver dans le contexte des objets connectés en masse. En général les objets communiquent entre eux à un niveau local et sont intéressés par des services communs et locaux. Plus concrètement, dans cette thèse, nous montrons les bienfaits de la communication D2D dans les trois scénarios précédents. Dans le cas du premier scénario de multidiffusion, contrairement à la tendance habituelle d’avoir un taux de transmission qui diminue en fonction du nombre d’équipements mobiles (en particulier, car l’équipement émetteur doit adapter sa transmission à l’équipement récepteur en plus mauvaise condition), en ajoutant la communication D2D, on observe que ce même taux de transmission augmente en fonction du nombre d’équipements mobiles présents. Dans le deuxième scénario où la communication est soumise à des contraintes de fiabilité et de latence exigeantes, nous déduisons une politique de retransmission optimale et proposons une autre politique semi-optimale qui est beaucoup moins gourmande en temps et qui a prouvé son optimalité dans plusieurs cas pratiques. Enfin dans le dernier scénario, nous proposons une méthode de localisation d’équipements mobile et l’étudions dans plusieurs environnements (avec et sans visibilité directe dans les cas intra-muros et extérieurs). L’identification de ces zones est ensuite utilisée pour créer de petites cellules virtuelles adaptatives aux situations changeantes et non prédictibles, dans le but de réduire les coûts liés aux infrastructures actuelles<br>This thesis studies D2D communication in realistic and challenging scenarios for future wireless systems. In particular, the thesis focuses on how may D2D communication help other technologies to enhance their performance. The first wireless scenario is the one of multicasting, used for example in video streaming or common alert message transmission for police, firefighters or ambulances. The second wireless scenario is the critical one of URLLC expected to be used to avoid cars crashes in the upcoming V2X context, and also when connecting machines together in environments like connected hospitals, airports, factories (industry 4.0), and last but not least in e-health context in order to enhance medical tele-surgery. The last wireless scenario is the one of UE group localization in the context of massive IoT, where devices are interacting with each other and are mostly confined in local groups, needing local services. In the multicast channel scenario, where a transmitter wishes to convey a common message to many receivers, it is known that the multicast rate decrease as the number of UEs increases. This vanishing behavior changes drastically when enabling the receivers to cooperate with each other via D2D. Indeed, the multicast rate increases with high probability when the number of receivers increases. This chapter also analyzes the outage rate of the proposed scheme in the same setting. Extensions regarding firstly resource utilization and secondly considering the use of HARQ are also analyzed. Next chapter addresses one of the major challenges for future networks, named URLLC. Specifically, the chapter studies the problem of HARQ with delayed feedback, where the transmitter is informed after some delay on whether or not his transmission was successful. The goal is to minimize the expected number of retransmissions subject to a reliability constraint within a delay budget. This problem is studied at two levels: (i) a single transmitter faced with a stochastic i.i.d. noisy environment and (ii) a group of transmitters whom shares a collision channel. Then the chapter that follows provides a cooperative UE mapping method that is highly accurate. Four different channel models are studied in this chapter: LOS and NLOS for indoor and outdoor environments. The results show significant improvement compared to already existing methods. Identifying the dense local areas in real time and informing the network allows the Base Station (BS) to increase the capacity through highly directive beams, and therefore, avoids the deployment cost of new infrastructure

Cette thèse porte sur l'établissement des expressions analytiques des performances des schémas Hybrid ARQ dans un contexte d'optimisation inter-couches. Le mécanisme Hybrid ARQ permet de tirer profit des propriétés de l'ARQ et des propriétés d'un FEC, selon la valeur du SNR. Par conséquent, la quantité de redondance transmise est automatiquement adaptée à la qualité du canal, en se basant sur l'acquittement de la transmission précédente. Sachant qu'aujourd'hui, tous les systèmes opèrent (ou sont sur le point d'opérer) sous le protocole IP, il est intéressant d'étudier leurs performances au niveau de la couche IP. Les métriques considérées sont le taux d'erreur paquet, l'efficacité, le délai et la gigue. Ces métriques sont utiles puisque les besoins en QoS dépendent d'une combinaison de celles-ci. Cependant, dans la littérature, les performances des schémas HARQ sont surtout analysées au niveau MAC. De plus, elles sont souvent évaluées au moyen de simulations. L'objectif est donc ici d'établir les expressions analytiques des quatre métriques de performances pour tout type de mé- canisme HARQ, aux niveaux MAC et IP, en prenant en compte des solutions existantes d'optimisation entre les couches MAC et IP. Il est ensuite prouvé que ces dérivations sont utiles pour construire des algorithmes dédiés à la gestion des ressources radio aussi bien qu'à la protection inégale des données.

Nous considérons dans cette thèse le problème de la transmission fiable de données par paquets en utilisant une transmission mono-porteuse sur des canaux sélectifs en fréquence à évanouissements. Notre objectif est de concevoir des couples émetteurs-récepteurs permettant d'améliorer les performances de la détection en l'absence d'information sur le canal à la transmission et ceci en exploitant la diversité temporelle disponible dans le cadre des protocoles de retransmission hybrides (HARQ). En analysant les performances du système de transmission avec un récepteur à maximum de vraisemblance, nous établissons un critère pertinent pour l'étude des performances du système basé sur les statistiques de la distance Euclidienne à la sortie du canal sélectif en fréquence. A partir de ce cadre théorique, nous proposons un nouveau schéma de diversité entre les différentes retransmissions, nommé précodage de phase, qui permet de combattre l'interférence entre symboles pour les canaux lentement variables dans le temps. Puis, à l'aide de nos outils d'analyse, nous revisitons un autre schéma de diversité qu'est la diversité d'entrelacement. En particulier, nous soulignons le double avantage offert par ce schéma, à savoir la diversité de modulation et la réduction de l'interférence entre symboles. Nous réalisons ensuite une étude comparative entre les deux schémas de diversité précédents sous traitement itératif ou non itératif au récepteur. Enfin, nous introduisons un nouveau protocole de retransmission adaptative pour les transmissions dîtes multi-couches afin de réduire l'interférence entre couches pour les canaux rapidement variant dans le temps utilisant des informations de retour limitées.

Os recentes padrões de sistemas de comunicação estão incluindo em suas normas mecanismos de retransmissão de pacotes. Este trabalho apresenta mecanismos de retransmissão de pacotes de formas simples e mais eficientes do que os mecanismos clássicos de retransmissão de pacotes. São apresentados esquemas de retransmissão de pacotes que utilizam retransmissões parciais e combinação por diversidade. Além disso, serão apresentadas análises teóricas para validar os resultados obtidos das simulações. Estas análises teóricas são obtidas através das análises de EXIT charts e da informação mútua. Os resultados e análises foram realizados em canais do tipo AWGN e com desvanecimento por blocos (Block-Fading). A complexidade computacional, facilidade de implementação e baixo consumo médio de energia por transmissão dos métodos propostos são alguns dos motivos pelos quais, tornam-se interessantes tanto para a área acadêmica quanto para a indústria.<br>Modern standards of communication systems are including in their standards retransmission mechanisms. This work presents mechanisms for retransmission of packets by simpler and more efficient than the classical mechanisms of packet retransmissions. The proposed schemes are presented that use packet retransmission with partial retransmission and diversity combining. In addition, theoretical analysis will be presented to validate the results of the simulations. These theoretical analysis are obtained through the analysis EXIT charts and mutual information. The results and analysis were performed on channels such as AWGN and Block-Fading. The computational complexity, ease implementation and low average energy consumption for transmission of the proposed methods are some of the reasons they become interesting both for academia and for industry.

Cette thèse porte sur l'établissement des expressions analytiques des performances des schémas Hybrid ARQ dans un contexte d'optimisation inter-couches. Le mécanisme Hybrid ARQ permet de tirer profit des propriétés de l'ARQ et des propriétés d'un FEC, selon la valeur du SNR. Par conséquent, la quantité de redondance transmise est automatiquement adaptée à la qualité du canal, en se basant sur l'acquittement de la transmission précédente. Sachant qu'aujourd'hui, tous les systèmes opèrent (ou sont sur le point d'opérer) sous le protocole IP, il est intéressant d'étudier leurs performances au niveau de la couche IP. Les métriques considérées sont le taux d'erreur paquet, l'efficacité, le délai et la gigue. Ces métriques sont utiles puisque les besoins en QoS dépendent d'une combinaison de celles-ci. Cependant, dans la littérature, les performances des schémas HARQ sont surtout analysées au niveau MAC. De plus, elles sont souvent évaluées au moyen de simulations. L'objectif est donc ici d'établir les expressions analytiques des quatre métriques de performances pour tout type de mécanisme HARQ, aux niveaux MAC et IP, en prenant en compte des solutions existantes d'optimisation entre les couches MAC et IP. Il est ensuite prouvé que ces dérivations sont utiles pour construire des algorithmes dédiés à la gestion des ressources radio aussi bien qu'à la protection inégale des données<br>This thesis deals with the performance closed-form derivations and the analysis of Hybrid ARQ retransmission schemes in a cross-layer context. Hybrid ARQ mechanism enables us to take benefit from the properties of both ARQ and FEC according to the SNR value. As a consequence, the total amount of transmitted redundancy is automatically adapted to the channel quality, based on the acknowledgment of the previous transmission. Actually, since all the systems operate or are going to operate under IP, it is of interest to evaluate their performance at the IP layer. The metrics considered here are the Packet Error Rate, the efficiency, the delay and the jitter. These four metrics are useful since the different QoS requirements depend on a combination of them. However, in the literature, the performance of HARQ based systems are mainly analyzed at the MAC level only. Furthermore, the analyses are often carried out by means of simulations. The goal is then here to derive the four performance metrics for any HARQ mechanism, at both MAC and IP level, by taking into account some existing optimizations between the IP and MAC layers. Our theoretical derivations are proven to be useful for building algorithms dedicated to radio resource management as well as to unequal data protection

Cette thèse porte sur l'allocation de ressources dans les réseaux mobiles ad hoc basés sur les protocoles ARQ Hybrides (HARQ), qui offrent une souplesse de déploiement rapide pour des communications à court terme dans le cadre d'applications militaires ou de futurs réseaux intelligents. L'OFDMA (Orthogonal Frequency Division Multiple Access) est considérée en particulier, en tant que solution prometteuse dans les standards de communication sans fil les plus récents. Bien qu'une coordination centralisée des communications soit rendue possible grâce à une organisation en clusters, il est toutefois difficile de remonter au coordinateur des informations fiables sur l'état du canal en vertu de la latence due à l'organisation de ce réseau. Ainsi les performances des liens seront renforcées par des mécanismes de retransmission HARQ, qui permettent de gérer les variations rapides du canal. L'objectif principal de cette thèse est l'allocation des ressources OFDMA dans les réseaux mobiles ad hoc basés sur les protocoles HARQ, en utilisant uniquement les statistiques à long terme du canal. Pour répondre à un besoin industriel, des schémas de modulation et de codage pratiques seront considérés en lieu et place des outils de capacité hérités de la théorie de l'information. En particulier, nous concevons et analysons de nouveaux algorithmes qui optimisent l'attribution de puissance, de largeur de bande, d'ordre de modulation et de rendement de codage, pour les mécanismes HARQ insérés dans le schéma multi-utilisateurs proposé. En raison de la présence de protocoles HARQ dans le réseau, une partie de la thèse est dédiée à l'étude des performances de l'HARQ que nous étendons à de nouveaux contextes.

Wireless Sensor Networks (WSN) are used in many applications, for example industrial applications, automatic control applications, monitoring applications, to name but a few. Although WSN can employ different standards in order to achieve short range wireless communication, the mainstream of the market is toadopt the low-power, low-rate IEEE 802.15.4 standard. However, this standard does not specify any block codes on the Physical layer (PHY) and the MAC sublayer. Reliability and energy efficiency are two important metrics used to evaluate the WSN performance. In order to enhance the reliability of the WSN performance, schemes such as Forward Error Correction (FEC) and HybridAutomatic Repeat-reQuest (HARQ) can be introduced on the PHY and MACsublayer when transmitting signals. However, this will reduce the energy efficiency of the WSN. In order to investigate what does affect the reliability and energy efficiency, this thesis has been conducted with the assistance of Matlab simulations, which simulate different transmission schemes proposed by the authors. Based on the simulations, both the reliability and energy efficiency can be evaluated and the results are illustrated for both metrics. The objective of this thesis is to determine a scheme that is able to meet these metric requirements.

Les demandes de haut débit, faible latence et grande fiabilité augmentent dans les nouvelles générations de systèmes de radiocommunications. Par conséquent, on propose de combiner la transmission non orthogonale avec les retransmissions HARQ afin de combattre les fluctuations de canal de transmission à haut débit. Dans la première partie de la thèse, on propose des protocoles de retransmissions HARQ avec l'aide d'un relai afin d'améliorer le débit et la fiabilité du système. Une version renforcée du protocole HARQ qui prend en compte le délai de retour est proposée dans la seconde partie de la thèse<br>HARQ has become an important research field in the wireless digital communications area during the last years. In this thesis, we improve the HARQ mechanisms in terms of throughput and/or latency which are the bottleneck of next generation wireless communication systems. More precisely, we improve the time-slotted HARQ systems by mimicking NOMA, which means using superposed packets in a single-user context. In the first part of the thesis, we propose HARQ protocols using the help of a relay to improve the transmission rate and reliability. An enhanced HARQ protocol adapted to delayed feedback is proposed in the second part. In this new multi-layer HARQ protocol, additional redundant packets are sent preemptively before receiving the acknowledgement, and in superposition to other HARQ processes

In these years we are experiencing an incredible explosion for mobile connectivity. Devices such as smart-phones, tablets and laptops are more and more data hungry, asking for faster and faster connections. In the meantime, many industry sectors are pushing mobile network operators to provide internet connectivity with different characteristics for a new set of machine-driven applications. Machine-to-machine (M2M) or machine type communications (MTC), is the new paradigm: lower latencies, lower energy consumption, less signalling, higher reliability, are only few of new requirements. MTC devices will become a massive presence in tomorrow mobile networks and finally the Internet of Things will become real in its entirety. Although still under constant update, the current 4G mobile networks have some limitations due to their intrinsic architecture. A newer disruptive mobile network generation is the only possible solution to satisfy the future demands for connectivity. While within the so-called 5G networks, many new technologies are under study, focusing on reaching higher point-to-point data-rates, one of the most important aspects of 5G is the support for MTC. In this thesis different aspects of M2M communications are taken into account. Inter-vehicular communications and the IEEE 802.11p protocol for vehicular ad-hoc networks are analysed. In particular the IEEE 802.11p shortcomings on channel response estimation and channel access are taken into consideration. The physical layer of the IEEE 802.11p protocol does not provide sufficient information to track the channel response; we propose a novel technique that exploits information provided by in-car sensors like GPS or speedometer to improve channel response tracking. Current protocols for vehicular direct communications considers the concurrent use of more than one radio channel at the same time, and leave to terminals the duty of choosing which channel to use. In this thesis we consider the most common channel occupancy detectors, derived by the cognitive radio theory, in a vehicular environment, and measure their performances in terms of probability of misdetection and detection delay. In the field of MTC, we present out implementation of an IETF IPv6-6LoWPAN protocol stack for resource-constrained devices. The stack provides the minimum requirements for these devices to support IPv6-based connectivity. The architecture is organized to decouple the stack from the data-link protocol and to seamlessly manage more than one radio access technology interface present in the device. Our tests show an increase in the final throughput respect to the other most known implementation, thanks to a memory usage optimization. Finally 5G networks and green communications are considered in this thesis. In particular we analyse HARQ protocols, largely used in modern wireless protocols, in terms of energy efficiency. We use the recent theory on channel coding in finite block-length regime by Polyanskiy-Poor-Verdù, the most appropriate in MTC scenarios, as starting point to find the analytic formula of the outage probability for HARQ protocols of Type-I and Type-II. We then propose a novel optimal allocation strategy for the transmitting power of the subsequent transmission attempts. Results show the outstanding performances in terms of energy saved that even the simplest combining techniques that such protocols use, could bring into play.<br>Negli ultimi anni si sta assistendo ad un’esplosione nella domanda di connettività in mobilità. Dispositivi quali smartphone, tablet e laptop offrono funzionalità e servizi sempre più basati sulla disponibilità di una connessione sempre attiva. Allo stesso modo, sempre più settori dell’industria premono gli operatori di rete mobile, chiedendo connettività per una nuova classe di dispositivi che rientrano nella categoria del Machine-Type-Communication. Coi termini Machine-Type-Communication (MTC) o Machine-2-Machine (M2M) si indica un paradigma con il quale si identificano una pletora di nuovi servizi di connettività in cui vincoli sulla latenza, disponibilità, affidabilità, consumo energetico della connessione sono più stringenti e meglio definiti. Le MTC diventeranno in un futuro prossimo una presenza massiva nelle reti cellulari, dando vita finalmente al mondo globalmente interconnesso descritto dal paradigma dell’Internet delle Cose. Sebbene in costante evoluzione e aggiornamento l’attuale generazione di rete mobile 4G ha alcune limitazioni intrinseche che rendono necessario un ulteriore salto generazionale ad una rete 5G di nuova concezione, come unica soluzione percorribile per soddisfare la crescente domanda di connettività. Nonostante in letteratura la maggior parte delle nuove soluzioni tecnologiche proposte hanno come obiettivo il raggiungimento di connessioni più veloci, uno degli aspetti più importanti del 5G e il pieno supporto alle MTC. In questa tesi vengono presi in esame alcuni aspetti delle comunicazioni M2M. In primo luogo si prendono in considerazione le reti veicolari, nello specifico si affrontano alcune criticita dell’attuale protocollo per reti wireless ad-hoc tra veicoli, il protocollo IEEE 802.11p, perciò che riguarda la stima del canale radio e il meccanismo di accesso al mezzo. Il livello fisico del protocollo non fornisce sufficienti risorse per permettere il tracking delle fluttuazioni del canale radio, qui proponiamo una tecnica innovativa che sfrutta informazioni aggiuntive provenienti da sensori e sistemi elettronici, di cui le moderne auto sono dotate, per migliorare il tracking del canale radio. Gli attuali protocolli per le reti veicolari prevedono l’uso concorrente di più canali radio, e lasciano totale libertà ai terminali sui metodi di scelta del canale radio da utilizzare. In questo lavoro, vengono presi in esame alcuni tra i più comuni rilevatori di occupazione del canale radio, mutuati dalla teoria del “cognitive radio”, e ne vengono analizzate le performance in termini di probabilità di mancata rilevazione e ritardo di rilevazione in ambiente veicolare. Nel campo delle MTC, presentiamo l’implementazione di uno stack protocollare IETF IPv6-6LoWPAN, realizzato per permettere a dispositivi low-cost con risorse limitate, di supportare comunicazioni su rete IPv6. L’architettura dello stack stata progettata allo scopo di disaccoppiare le funzionalità dello stack dal particolare protocollo data-link utilizzato, e di supportare dispositivi equipaggiati con più moduli per la comunicazione wireless. I test comparativi dimostrano un throughput maggiore rispetto all’implementazione più conosciuta del protocollo IPv6 per questi dispositivi. In conclusione, sono messi in relazione le reti 5G e il paradigma delle green communication. I protocolli di tipo Automatic Repeat reQuest (ARQ) ibrido, largamente usati nelle moderne reti cellulari, vengono analizzati in termini di efficienza energetica usando i recenti risultati di Polyanskiy-Poor-Verdù sulla capacità di canale in regime di parola di codice di lunghezza finita. Tale teoria affronta l’analisi della capacità di correzione dei codici di canale a fronte di una parola di codice di lunghezza finita, teoria che si concilia con la natura delle reti MTC. L’analisi propone inoltre, una tecnica di ottimizzazione della potenza trasmissiva nelle ritrasmissioni dei protocolli HARQ di tipo Type-I e Type-II. L’analisi mostra i risultati ottenuti in termini di probabilità di outage finale e di risparmio energetico ottenuto.

Les communications massives pour l’Internet des objets sont l'un des principaux services fournis par le réseau mobile de cinquième génération (5G). L’Internet des objets (IoT) représente un défi majeur pour les réseaux cellulaires car il se caractérise par un grand nombre d'objets connectés de faible complexité qui envoient de petits paquets de données. Ces objets connectés sont souvent alimentés par batterie, cette batterie devant fonctionner pendant de longues périodes sans avoir besoin d’être rechargée ou remplacée. Les réseaux cellulaires traditionnels, conçus pour les communications humaines, et pas assez économes en énergie, ne sont pas adaptés à ce type de service. Pour résoudre ce problème, dans cette thèse, nous étudions l'utilisation d’un équipement utilisateur de type smartphone comme relais pour transmettre les données de l’objet connecté à proximité. Ce mécanisme est appelé relayage D2D (Device-to-Device). Notre première étude a consisté à évaluer l'énergie consommée par l’objet connecté dans chaque phase du processus de communication lorsqu’il est localisé en bordure de cellule pour la technologie LTE-M. Ensuite, à l'aide d'un modèle simple, nous avons comparé la consommation d'énergie des modes de transmission cellulaire et D2D, et déterminé la localisation optimale du relais. Grâce à l'utilisation de la géométrie stochastique, nous avons ensuite analysé les performances d’une communication D2D utilisant les mécanismes de répétitions ARQ et CC-HARQ en termes de consommation d'énergie. Enfin, nous avons proposé un mécanisme de relayage D2D adapté aux applications IoT, en termes de complexité d’implémentation et de consommation d’énergie. Ce mécanisme utilise une approche de sélection de relais distribuée, qui priorise la sélection des relais bénéficiant des meilleures qualités de canal<br>Massive machine-type communication (mMTC) is one of the main services delivered by the 5G mobile network. mMTC represents a major challenge for 5G network since it is characterized by a large number of low complexity devices thats end small data packets. Moreover, mMTC devices are often battery-powered, and the battery is expected to operate for long periods without being recharged or replaced. Traditional cellular networks, which are designed for human communications, are not energy efficient for this type of service. To address this problem, in this thesis, we study the use of Device-to-Device(D2D) relaying as a complementary transmission. In this approach, the mMTC device can transmit its data using a nearby UE as a relay. First, we calculate the energy consumed in each phase of the communication process for a device located at the cell border that uses LTE-Mtechnology. Then, using a simple model, we compare the energy consumption of cellular and D2D transmission modes, and we determine the optimal relay location. Through the use of stochastic geometry, we analyze the performance of D2D communication with ARQ and CC-HARQ with regard to the transmission success probability, the average number of transmissions, and MTD energy consumption. Finally, we propose an energy-efficient D2D relaying mechanism suitable for mMTC applications thanks to its easy implementation. This mechanism uses a distributed relay selection approach, which prioritizes the selection of the user equipments (UEs) with the best channel qualities. Moreover, we present a tractable model to evaluate the performance of our mechanism

<p>New high quality mobile telecommunication services are offered everyday and the demand for higher data rates is continuously increasing. To maximize the uplink throughput in HSPA when transmission is propagated through a dispersive channel causing self-interference, equalizers are used. One interesting solution, where the equalizer and decoder exchange information in an iterative way, for improving the equalizer performance is Turbo equalization.</p><p>In this thesis a literature survey has been performed on Turbo equalization methods and a chosen method has been implemented for the uplink HSPA standard to evaluate the performance in heavily dispersive channels. The selected algorithm has been adapted for multiple receiving antennas, oversampled processing and HARQ retransmissions. The results derived from the computer based link simulations show that the implemented algorithm provide a gain of approximately 0.5 dB when performing up to 7 Turbo equalization iterations. Gains up to 1 dB have been obtained by disabling power control, not using retransmission combining and utilizing a single receiver antenna. The algorithm has also been evaluated considering alternative dispersive channels, Log-MAP decoding, different code rates, number of Turbo equalization iterations and number of Turbo decoding iterations.</p><p>The simulation results do not motivate a real implementation of the chosen algorithm considering the increased computational complexity and small gain achieved in a full featured receiver system. Further studies are needed before concluding the HSPA uplink Turbo equalization approach.</p>

The use of wireless technology in the process industry is becoming increasingly important to obtain fast deployment at low cost. However, poor channel quality often leads to retransmissions, which are governed by Automatic Repeat Request (ARQ) schemes. While ARQ is a simple and useful tool to alleviate packet errors, it has considerable disadvantages: retransmissions lead to an increase in energy expenditure and latency. The use of Forward Error Correction (FEC) however offers several advantages. We consider a Hybrid-ARQ-Adaptive-FEC scheme (HAF) based on BCH codes and Channel State Information. This scheme is evaluated on AWGN and fading channels. It is shown that HAF offers significantly improved performance both in terms of energy efficiency and latency, as compared to ARQ.

Abstract This thesis seeks to develop a robust semi-analytical performance prediction method for an advanced iterative receiver that processes spatially multiplexed signals that have propagated through frequency-selective receive correlated multiple-input multiple-output (MIMO) wireless communication channels. In a change of perspective, the proposed performance prediction methods are applied at the transmitter, which seeks to attain a target frame error rate (FER) either by adaptive power control or by adaptive modulation and coding (AMC). The performance prediction scheme utilises the statistical properties of the channel—namely noise variance, number of separable propagation paths and the eigenvalues of the receive correlation matrix—to predict the signal-to-interference-plus-noise ratio (SINR) at the output of a frequency domain soft interference cancellation minimum mean square error equaliser. The SINR distribution is used to derive the distribution of the variance of the log-likelihood ratios (LLRs) at the output of a soft symbol-to-bit demapper. Mutual information transfer charts establish a bijective relationship between the variance of the LLRs and mutual information. A 3rd Generation Partnership Project compliant turbo code is assumed. Since the decoder operates independently from the channel, its extrinsic information transfer (EXIT) charts can be simulated in advance. By utilising the approximate LLR variance distribution of the demapped equaliser output, it is possible to evaluate the probability of an intersection between an equaliser chart associated with a random channel realisation and a fixed decoder chart. This probability provides the FER. Since the proposed performance prediction method does not require any instantaneous channel state information, it can be applied at the transmitter side as a robust link adaptation scheme. In adaptive transmission power control, the modulation order and code rate are fixed. By iteratively adjusting transmission power, the transmitter attempts to find an equaliser output LLR variance distribution that reaches a specified target FER. In AMC, transmission power is fixed. The equaliser output's LLR variance distribution is determined by the modulation order, while the decoder chart's position is determined by the code rate. The transmitter iteratively adjusts the code rate and attempts to find a modulation order and code rate pairing that reaches the target FER. For vertically encoded spatially multiplexed systems, the adaptive transmission power control and AMC schemes are complemented by adaptive repeat redundancy and incremental redundancy hybrid automatic repeat request (HARQ) techniques, respectively<br>Tiivistelmä Työn tavoitteena on kehittää luotettava semianalyyttinen suorituskyvyn ennustusmenetelmä tehokkaalle iteratiiviselle vastaanottimelle, joka käsittelee taajuusselektiivisen, vastaanotinpäässä tilakorreloituneen moniantennikanavan kautta kulkeneita tilakanavoituja signaaleja. Toisessa vaiheessa esitettyjä ennustusmenetelmiä hyödynnetään mukauttamalla lähetystehoa tai modulaatioastetta ja koodisuhdetta (adaptive modulation and coding [AMC]), samalla säilyttäen tavoitteeksi asetetun kehysvirhesuhteen (frame error rate [FER]). Suorituskyvyn ennustusmenetelmä hyödyntää kanavan tilastollisia ominaisuuksia – kohinan varianssia, eroteltavien etenemispolkujen lukumäärää sekä vastaanottimen korrelaatiomatriisin ominaisarvoja – ennustaakseen signaali–kohina-plus-interferenssisuhteen (signal-to-interference-plus-noise ratio [SINR]) jakauman taajuustasossa toimivan, häiriötä poistavan pienimmän keskineliösumman kanavakorjaimen lähdössä. SINR-jakaumasta johdetaan pehmän symboleista biteiksi -muunnoksen jälkeisten logaritmisten bittitodennäköisyyksien suhdelukujen (log-likelihood ratio [LLR]) jakauma. Keskinäisinformaation siirroskartat perustuvat LLR:ien varianssin sekä keskinäisinformaation väliseen bijektiivisyyteen. Informaatio on kanavakoodattu 3rd Generation Partnership Project -standardin mukaisella turbokoodilla. Turbodekooderin toiminta on kanavasta riippumatonta, joten dekooderin lisäinformaation siirroskartat (extrinsic information transfer [EXIT] charts) voidaan simuloida itsenäisesti. Hyödyntämällä kanavakorjaimen lähdön pehmeiden bittipäätösten LLR:ien varianssin jakaumaa, on mahdollista arvioida millä todennäköisyydellä korjaimen satunnaisen kanavarealisaation siirroskartta leikkaa dekooderin siirroskartan. Tämä todennäköisyys voidaan tulkita kehysvirhesuhteeksi. Koska suorituskyvyn ennustusmenetelmä ei vaadi hetkellistä tietoa kanavan tilasta, sitä voidaan hyödyntää lähetyksen mukautuksessa. Mukautuvassa tehonsäädössä modulaatio ja koodisuhde eivät muutu. Lähetin pyrkii iteratiivisella tehonsäädöllä löytämään korjaimen lähdölle LLR-jakauman, joka tuottaa halutun kehysvirhesuhteen. Mukautuvassa modulaation ja koodisuhteen valinnassa lähetysteho säilyy vakiona. Modulaatioaste vaikuttaa korjaimen lähdön LLR-jakaumaan ja koodisuhde dekooderin siirroskartan muotoon. Iteratiivisesti koodisuhdetta säätämällä lähetin pyrkii löytämään modulaation ja koodisuhteen yhdistelmän, joka saavuttaa tavoitellun kehysvirhesuhteen. Vertikaalisesti tilakanavoiduissa järjestelmissä mukautuvaa tehonsäätöä täydennetään lähetystehoa mukauttavilla uudellenlähetyksillä, kun taas mukautuvaa modulaation ja koodisuhteen valintaa täydennetään puolestaan koodisuhdetta pienentävillä automattisilla uudelleenlähetyspyynnöillä (hybrid automatic repeat request [HARQ])

Dans cette thèse, les techniques de coopération ont été étudiées pour un canal multi-accès multi-relais composé d'au moins deux sources qui communiquent avec une seule destination à l'aide d'au moins deux nœuds de relayage en mode semi-duplex. Le multiplexage par répartition dans le temps est supposé. Tout d'abord, l’algorithme d’adaptation de lien est exécuté par l'ordonnanceur centralisé. Durant la première phase de transmission, les sources transmettent chacune à leur tour leur message respectif pendant des intervalles de temps consécutifs. Dans chaque intervalle de temps dans la deuxième phase, la destination planifie un nœud pour transmettre les redondances, mettant en œuvre un protocole coopératif d'Hybrid Automatic Repeat reQuest (HARQ), où les canaux de contrôle limités bidirectionnels sont disponibles depuis les sources et les relais vers la destination. Dans la première partie de la thèse, les stratégies de sélection des nœuds centralisé sont proposées pour la deuxième phase de transmission. Les décisions d’ordonnancement sont prises en fonction de la connaissance des ensembles de sources correctement décodées par chaque noeud et ayant comme objectif de maximiser l’efficacité spectrale moyenne. L'analyse de la probabilité de coupure de l'information ainsi que les simulations Monte-Carlo (MC) sont effectués afin de valider ces stratégies. Dans la seconde partie, un algorithme d’adaptation de lien lent est proposé afin de maximiser l’efficacité spectrale moyenne sous contrainte de vérification d'une qualité de service individuelle cible pour une famille donnée de schémas de modulation et de codage, réposant sur l'information sur la distribution des canaux signalée. Les débits des sources discrets sont déterminés en utilisant l’approche "Genie-Aided" suivie d’un algorithme itératif de correction de débit. Les simulations MC montrent que l’algorithme d’adaptation de lien proposé offre des performances proches de celles de la recherche exhaustive. Dans la troisième partie, les performances de protocole HARQ à redondance incrémentale (IR) avec codage mono et multi-utilisateur, ainsi que l'HARQ de type Chase Combining avec codage mono-utilisateur sont comparées. Les simulations MC montrent que l'IR-HARQ avec codage mono-utilisateur offre le meilleur compromis entre performance et complexité pour le scénario de petit nombre de sources. Un schéma de codage pratique est proposé et validé à l'aide de simulations MC<br>In this thesis, cooperation techniques have been studied for Multiple Access Multiple Relay Channel, consisted of at least two sources which communicate with a single destination with the help of at least two half-duplex relaying nodes. Time Division Multiplexing is assumed. First, the link adaptation algorithm is performed at the centralised scheduler. Sources transmit in turns in consecutive time slots during the first transmission phase. In each time slot of the second phase, the destination schedules a node to transmit redundancies, implementing a cooperative Hybrid Automatic Repeat reQuest (HARQ) protocol, where bidirectional limited control channels are available from sources and relays towards the destination. In the first part of the thesis, centralized node selection strategies are proposed for the second phase. The scheduling decisions are made based on the knowledge of the correctly decoded source sets of each node, with the goal to maximize the average spectral efficiency. An information outage analysis is conducted and Monte-Carlo (MC) simulations are performed to evaluate their performance. In the second part, a slow-link adaptation algorithm is proposed which aims at maximizing the average spectral efficiency under individual QoS targets for a given modulation and coding scheme family relying on the reported Channel Distribution Information of all channels. Discrete source rates are first determined using the "Genie-Aided" assumption, which is followed by an iterative rate correction algorithm. The resulting link adaptation algorithm yields performance close to the exhaustive search approach as demonstrated by MC simulations. In the third part, performances of Incremental Redundancy (IR) HARQ with Single and Multi User encoding, as well as the Chase Combining HARQ with Single User encoding are compared. MC simulations demonstrate that IR-HARQ with Single User encoding offers the best trade-off between performance and complexity for a small number of sources in our setting. Practical coding scheme is proposed and validated using MC simulations

Dans cette thèse, on s'est intéressé à l'étude des canaux de diffusion avec des contraintes de transmission pratiques. Tout d'abord, on a étudié l'impact de la contrainte pratique de l'utilisation d'un alphabet fini à l'entrée du canal de diffusion Gaussien avec deux utilisateurs. Deux modèles de canaux de diffusion sont considérés lorsqu'il y a, en plus d'un message commun pour les deux utilisateurs, (i) un message privé pour l'un des deux utilisateurs sans contrainte de sécurité (ii) un message confidentiel pour l'un des deux utilisateurs qui doit être totalement caché de l'autre utilisateur. On a présenté plusieurs stratégies de diffusion distinguées par leur complexité d'implémentation. Plus précisément, on a étudié les régions des débits atteignables en utilisant le partage de temps, la superposition de modulation et le codage par superposition. Pour la superposition de modulation et le cas général du codage par superposition, les régions des débits atteignables maximales sont obtenues en maximisant par rapport aux positions des symboles dans la constellation et la distribution de probabilité jointe. On a étudié le compromis entre la complexité d'implémentation des stratégies de transmission et leurs efficacités en termes de gains en débits atteignables. On a étudié aussi l'impact de la contrainte de sécurité sur la communication en comparant les débits atteignables avec et sans cette contrainte. Enfin, on a étudié les performances du système avec des schémas d'accusés de réception hybrides (HARQ) pour un canal à écoute à évanouissement par blocs lorsque l'émetteur n'a pas une information parfaite sur l'état instantané du canal mais connait seulement les statistiques. On a considéré un schéma adaptatif pour la communication sécurisée en utilisant des canaux de retour à niveaux multiples vers l'émetteur pour changer la longueur des sous mots de code à chaque retransmission afin que le débit utile secret soit maximisé sous des contraintes d'"outages".

L'augmentation de l'utilisation de l'Internet et des services de données motive l'évolution des réseaux cellulaires de troisième. Dans ce contexte, HSDPA (High Speed Downlink Packet Access) a été développé dans les releases 5 et 6 au sein de 3GPP pour poursuivre l'évolution du mode "paquet" de l'UMTS. Ce système utilise de nouvelles technologies telles que le Hybrid-ARQ (Automatic Repeat Request), la modulation adaptative et l'ordonnancement rapide (fast Scheduling) pour permettre de véhiculer des débits plus élevés sur l'interface radio et d'augmenter la capacité. Cette thèse se focalise sur l'analyse et la modélisation des interactions entre la couche MAC-hs de HSDPA et les autres couches (physique, transport). L'objectif est de trouver la configuration optimale de cette entité MAC-hs afin de réduire les interactions "négatives" entre-couches et optimiser les performances de HSDPA. Par conséquent, cette thèse fournit des études et des modélisations analytiques couvrant les aspects suivants: -Analyse et modélisation de l'impact du canal radio (shadowing, fast fading) sur les performances du système HSDPA dans le cas où plusieurs "schedulers" sont utilisés -Analyse et modélisation de l'effect des services "Circuit" de l'UMTS R99 sur les performances de HSDPA. -Modélisation de l'interaction entre le protocole TCP et l'entité MAC-hs. Une nouvelle stratégie d'ordonnancement est proposée afin d'améliorer les performances du système -Charactérisation de l'interaction entre MAc-hs et les services streaming. Une nouveau "scheduler" est proposé afin de garantir les contraintes sévères de QoS des services streaming sans trop perdre de capacité cellulaire.

A drastic increase in traffic of mobile broadband is seen in the past few years, which is further accelerated by the increase in usage of smart phones and its applications. The availability of good smart phones and better data connectivity are encouraging mobile users to use video services. This huge increase in usage will pose a lot of challenges to the wireless networks. The wireless network has to become content aware in order to offer enhanced quality of video service through efficient utilization of the wireless spectrum. This thesis focuses on improving the Quality of Experience (QoE) for video transmission over Long Term Evolution (LTE) networks by imparting the content awareness to the system and providing unequal error protection for critical video packets. Two different schemes for the improvement of video quality delivery over LTE networks are presented in this thesis. Using content awareness, the retransmission count of Hybrid Automatic Repeat reQuest (HARQ) are changed dynamically such that the most important video frame gets more number of retransmission attempts, which increases its success for delivery in-turn increasing the received video quality. Since Radio Link Control (RLC) is the link layer for radio interface, the second approach focuses on optimizing this layer for efficient video transmission. As part of this scheme, a new operation mode called Hybrid Mode (HM) for RLC is defined. This mode performs retransmission only for the critical video frames, leaving other frames to unacknowledged transmission. The simulation results of both proposed schemes provide significant improvement in achieving good video quality without affecting the system performance.

In the last decades, we have witnessed an explosion of wireless communications and networking, spurring a great interest in the research community. The design of wireless networks is challenged by the scarcity of resources, especially spectrum and energy. In this thesis, we explore the potential offered by two novel technologies to cope with spectrum and energy scarcity: Cognitive Radio (CR) and Energy Harvesting (EH). CR is a novel paradigm for improving the spectral efficiency in wireless networks, by enabling the coexistence of an incumbent legacy system and an opportunistic system with CR capability. We investigate a technique where the CR system exploits the temporal redundancy introduced by the Hybrid Automatic Retransmission reQuest (HARQ) protocol implemented by the legacy system to perform interference cancellation, thus enhancing its own throughput. Recently, EH has been proposed to cope with energy scarcity in Wireless Sensor Networks (WSNs). Devices with EH capability harvest energy from the environment, e.g., solar, wind, heat or piezo-electric, to power their circuitry and to perform data sensing, processing and communication tasks. Due to the random energy supply, how to best manage the available energy is an open research issue. In the second part of this thesis, we design control policies for EH devices, and investigate the impact of factors such as the finite battery storage, time-correlation in the EH process and battery degradation phenomena on the performance of such systems. We cast both paradigms in a stochastic optimization framework, and investigate techniques to cope with spectrum and energy scarcity by opportunistically leveraging interference and ambient energy, respectively, whose benefits are demonstrated both by theoretical analysis and numerically. As an additional topic, we investigate the issue of channel estimation in UltraWide-Band (UWB) systems. Due to the large transmission bandwidth, the channel has been typically modeled as sparse. However, some propagation phenomena, e.g., scattering from rough surfaces and frequency distortion, are better modeled by a diffuse channel. We propose a novel Hybrid Sparse/Diffuse (HSD) channel model which captures both components, and design channel estimators based on it.<br>Negli ultimi decenni, abbiamo assistito alla diffusione delle comunicazioni e reti wireless, suscitando un crescente interesse nella comunità scientifica. Tuttavia, la progettazione delle reti wireless è resa difficile dalla scarsità di risorse, in particolare, spettro ed energia. In questa tesi, si esplora il potenziale offerto da due nuove tecnologie nell’affrontare il problema della scarsità di spettro e di energia nelle future reti wireless: "Cognitive Radio" (CR) ed "Energy Harvesting" (EH). CR è un nuovo paradigma che consente di migliorare l’efficienza di utilizzo dello spettro nelle reti wireless, abilitando la coesistenza di un preesistente sistema titolare dello spettro, comunemente denominato Utente Primario, e un sistema opportunistico "intelligente", noto come Utente Secondario. In questa tesi, si sviluppa una tecnica per sfruttare, da parte di un utente secondario, la ridondanza temporale introdotta dal protocollo "Hybrid Automatic Retransmission reQuest" (HARQ) utilizzato da un Utente Primario, per eseguire tecniche di cancellazione di interferenza, consentendo così di migliorare il throuhgput secondario. Recentemente, EH è stato proposto per superare il problema della scarsità di energia nelle "Wireless Sensor Networks" (WSNs). I dispositivi con capacità di EH accumulano energia resa disponibile nell’ambiente circostante, come, per esempio, energia solare, eolica, termica o piezo-elettrica, per alimentare il dispositivo e per eseguire compiti di "data sensing", processamento e comunicazione. Dato che la disponibilità di energia è aleatoria e intermittente, il problema di come utilizzare al meglio l’energia disponibile è di grande interesse nella comunità scientifica. Nella seconda parte di questa tesi, si propongono politiche di controllo per dispositivi con capacità di EH, e si analizza l’impatto di vari fattori quali la capacità finita della batteria, la correlazione temporale nel processo di EH, la conoscenza imperfetta dello stato di carica della batteria e i fenomeni di degrado della batteria. Si studiano entrambi i paradigmi in un framework di ottimizzazione stocastica, e vengono proposte tecniche per far fronte alla scarsità di spettro ed energia sfruttando in modo opportunistico, rispettivamente, l’interferenza e l’energia ambientale. Si dimostrano i benefici delle tecniche proposte per mezzo sia di un’analisi teorica che per via numerica. Come argomento di ricerca aggiuntivo, nell’ultima parte di questa tesi, si studia il problema della stima di canale nei sistemi Ultra Wide-Band (UWB). Data la larga banda di trasmissione utilizzata in questi sistemi, il canale è stato tipicamente modellato come sparso. Tuttavia, alcuni fenomeni di propagazione come, per esempio, la dispersione dovuta a superfici scabrose e la distorsione in frequenza, sono modellabili in modo più accurato da un canale diffuso. Si propone un nuovo modello di canale denominato "Hybrid Sparse/Diffuse" (HSD) che cattura entrambe le componenti di canale, e si propongono stimatori di canale basati sul modello proposto.

L'objectif de cette thèse est de concevoir, implémenter et évaluer les algorithmes cross-layer pratiques. Nous nous concentrons sur la technologie LTE et les réseaux non coordonnés post-LTE où l'interférence est un enjeu majeur compte tenu des nouvelles tendances du trafic. L'objectif est d'allouer les ressources radio d'une manière efficace. Nous développons des modèles d'interférence mathématiques et informatiques qui nous permettent de comprendre le comportement de ces réseaux et nous appliquons une approche basée sur la théorie de l'information à différents scénarios d'interférence et caractéristiques du trafic. Nous avons essayé de s'approcher le plus possible de systèmes réels pour être en mesure de tester la faisabilité des techniques proposées. La thèse porte sur l'évaluation de la performance des scénarios d'interférence dans les réseaux 4G, en particulier celles qui découlent du déploiements de cellules de petite taille ("small cells"). Le travail dans cette thèse s'adresse également à l'analyse de l'allocation des ressources et la requête de répétition automatique hybride (HARQ) à redondance incrémentale pour les interférences sporadiques (de façon plus générale les canaux variables dans le temps) qui permet uniquement des informations partielles de l'état du canal à l'émetteur. Ce travail est ensuite appliquée à la conception d'ordonnanceur pour les stations de base LTE et inclut une analyse de performance pour les modems LTE réels<br>The aim of this thesis is to design, implement and evaluate practical cross-layer algorithms. We focus on LTE and post-LTE uncoordinated networks where interference is a key issue given the new traffic patterns. The goal is to allocate the radio resources in an efficient way. We develop mathematical and computational interference models that allow us to understand the behavior of such networks and we apply an information-theoretic approach to different interference scenarios and traffic characteristics. We have tried to remain as close as possible to practical systems to be able to test the feasibility of the proposed techniques. The thesis deals with performance evaluation of interference scenarios in 4G networks, in particular those arising from small-cell deployments. The work in this thesis also deals with analysis of resource-allocation and incremental-redundancy based hybrid automatic repeat request (HARQ) for bursty interference (or more general time-varying channels) which allows for only partial channel state information at the transmitter. The work is then applied to practical scheduler design for LTE base stations and includes performance analysis for real LTE modems

In the wireless channel, cooperative communications allow one or many relays to assist the communication between the source and the destination. The aim of this thesis is the development of tools for the analysis of cooperative systems, when HARQ techniques are employed to provide cross-layer error protection. The first chapter of the thesis gives background information on network coding in cooperative relay networks, and introduces the motivation for this work. The second chapter is devoted to the analysis of the energetic-fair performance evaluations of FEC, ARQ-STBC and HARQ schemes at the MAC and IP layers. New analytical framework is derived and applied to a point-to-point network scenario. This framework allows to make energetic fair comparisons between the schemes with and without retransmissions. We determine under which channel conditions the cross-layer error protection is energetically more efficient than the simple channel coding. In the third chapter of this thesis we study the cooperative deterministic protocols. The protocols that we consider differ based on the behaviour of the relay(s), source(s), and destination. We consider two major types of cooperative protocols: decode-and forward (DCF), and demodulate-and-forward (DMF). Each of these protocols in its turn is analysed with and without combining mechanisms at the destination. We derive the soft decoders at the destination side for each respective case, and compare the performances of these protocols at the MAC layer. The following quality of service metrics are evaluated: frame error rate, delay, efficiency, goodput. The analysis is done evaluating the steady-state, using finite state Markov chains and a combinatorial approach. The analysis, however, becomes very complex as the number of transmissions and/or nodes in the network increases. The fourth chapter introduces a class of probabilistic communication protocols, where the devices retransmit with a given probability. We prove the existence of an equivalent class of protocols, with the same performances as the deterministic class. Using proofs of concept it is shown that the probabilistic protocol class allows for tractable steady-state analysis, even for many nodes in the network. Based on this, we then derive the QoS metrics and evalute them also by simulations. The derived performance evaluation metrics are then optimized by constraining the frame error rate, and trying to find the most optimal transmissions number and code rates which maximize the goodput. It is furthermore shown, that the equivalent protocol has larger optimal region than the deterministic one.

The increasing penetration of mobile devices in everyday life is posing a broad range of research challenges to meet such a massive data demand. Mobile users seek connectivity "anywhere, at anytime". In addition, killer applications with multimedia contents, like video transmissions, require larger amounts of resources to cope with tight quality constraints. Spectrum scarcity and interference issues represent the key aspects of next generation wireless networks. Consequently, designing proper resource management solutions is critical. To this aim, we first propose a model to better assess the performance of Orthogonal Frequency-Division Multiple Access (OFDMA)-based simulated cellular networks. A link abstraction of the downlink data transmission can provide an accurate performance metric at a low computational cost. Our model combines Mutual Information-based multi-carrier compression metrics with Link-Level performance profiles, thus expressing the dependency of the transmitted data Block Error Rate (BLER) on the SINR values and on the modulation and coding scheme (MCS) being assigned. In addition, we aim at evaluating the impact of Jumboframes transmission in LTE networks, which are packets breaking the 1500-byte legacy value. A comparative evaluation is performed based on diverse network configuration criteria, thus highlighting specific limitations. In particular, we observed rapid buffer saturation under certain circumstances, due to the transmission of oversized packets with scarce radio resources. A novel cross-layer approach is proposed to prevent saturation, and thus tune the transmitted packet size with the instantaneous channel conditions, fed back through standard CQI-based procedures. Recent advances in wireless networking introduce the concept of resource sharing as one promising way to enhance the performance of radio communications. As the wireless spectrum is a scarce resource, and its usage is often found to be inefficient, it may be meaningful to design solutions where multiple operators join their efforts, so that wireless access takes place on shared, rather than proprietary to a single operator, frequency bands. In spite of the conceptual simplicity of this idea, the resulting mathematical analysis may be very complex, since it involves analytical representation of multiple wireless channels. Thus, we propose an evaluative tool for spectrum sharing techniques in OFDMA-based wireless networks, where multiple sharing policies can be easily integrated and, consequently, evaluated. On the other hand, relatively to contention-based broadband wireless access, we target an important issue in mobile ad hoc networks: the intrinsic inefficiency of the standard transmission control protocol (TCP), which presents degraded performance mainly due to mechanisms such as congestion control and avoidance. In fact, TCP was originally designed for wired networks, where packet losses indicate congestion. Conversely, channels in wireless networks might vary rapidly, thus most loss events are due to channel errors or link layer contention. We aim at designing a light-weight cross-layer framework which, differently from many other works in the literature, is based on the cognitive network paradigm. It includes an observation phase, i.e., a training set in which the network parameters are collected; a learning phase, in which the information to be used is extracted from the data; a planning phase, in which we define the strategies to trigger; an acting phase, which corresponds to dynamically applying such strategies during network simulations. The next generation mobile infrastructure frontier relies on the concept of heterogeneous networks. However, the existence of multiple types of access nodes poses new challenges such as more stringent interference constraints due to node densification and self-deployed access. Here, we propose methods that aim at extending femto cells coverage range by enabling idle User Equipments (UE) to serve as relays. This way, UEs otherwise connected to macro cells can be offloaded to femto cells through UE relays. A joint resource allocation and user association scheme based on the solutions of a convex optimization problem is proposed. Another challenging issue to be addressed in such scenarios is admission control, which is in charge of ensuring that, when a new resource reservation is accepted, previously connected users continue having their QoS guarantees honored. Thus, we consider different approaches to compute the aggregate projected capacity in OFDMA-based networks, and propose the E-Diophantine solution, whose mathematical foundation is provided along with the performance improvements to be expected, both in accuracy and computational terms.<br>L'esplosiva penetrazione di dispositivi mobili nella vita di tutti i giorni pone molteplici sfide nel campo della ricerca nelle comunicazioni 'senza fili', al fine di sostenere la crescente mole di dati generata dagli utenti cellulari, i quali richiedono connettività "in ogni momento, in ogni dove". Inoltre, le applicazioni più richieste, dotate di contenuti multimediali quali le trasmissioni video, richiedono l'utilizzo di molte risorse per sostenere stringenti vincoli di qualità. La limitatezza dello spettro, congiuntamente ai problemi legati all'interferenza, rappresentano i fattori chiave delle reti cellulari di nuova generazione. Conseguentemente, il design di tecniche per la gestione delle risorse risulta essere un aspetto particolarmente critico. A questo fine, proponiamo in primo luogo un modello per valutare le prestazioni simulate delle reti cellulari basate sulla tecnologia Orthogonal Frequency-Division Multiple Access (OFDMA). Un modello di astrazione del canale associato alla trasmissione in downlink di dati fornisce un'accurata metrica valutativa a basso costo computazionale. Il nostro modello combina metriche di compressione multi-portante basate sull'Informazione Mutua con profili prestazionali generati a livello di canale, esprimendo così la dipendenza del rate d'errore associato al blocco di dati trasmesso con i valori di SINR, e l'indice di codifica e modulazione (MCS) assegnato dall'allocatore di risorse. Inoltre, ci proponiamo di valutare l'impatto della trasmissione di Jumboframes in reti LTE, ovvero pacchetti la cui dimensione supera il massimo valore tradizionale di 1500 Bytes. Una valutazione comparativa viene eseguita relativamente a varie configurazioni di rete, in modo da mettere in luce specifiche limitazioni. In particolare, abbiamo potuto osservare una rapida saturazione del buffer di trasmissione legato alla trasmissione di maxi pacchetti attraverso link di bassa qualità. Abbiamo dunque proposto un'architettura di rete 'cross-layer' che ci permetta di prevenire tale esubero di risorse disponibili; si tratta di un approccio che rende possibile la regolazione della dimensione dei pacchetti a seconda della capacità istantanea del canale, nota attraverso procedure standard basate sulla conoscenza di predefinite sequenze pilota alle quali vengono associate valori di qualità (CQI). Nella ricerca applicata alle reti wireless è stato recentemente introdotto il concetto di condivisione delle risorse, visto come promettente approccio attraverso cui migliorare le prestazioni delle comunicazioni radio. Lo spettro radio è limitato, e il suo utilizzo risulta spesso inefficiente. Per questi motivi appare significativo proporre soluzioni nelle quali diversi operatori uniscano le proprie forze al fine di fornire accesso wireless a bande condivise piuttosto che proprietarie. Diversamente dalla semplicità concettuale di tale idea, l'analisi matematica che ne deriva può essere molto complessa. Per questo motivo proponiamo uno strumento atto a valutare le prestazioni delle tecniche di condivisone dello spettro nelle reti cellulari basate sulla tecnologia OFDMA, al cui interno è dunque possibile integrare, testare e valutare ogni politica di condivisione. D'altra parte, relativamente all'accesso a banda larga basato sulla contesa al mezzo, ci soffermiamo su un'importante problematica all'interno delle reti mobili ad hoc WiFi, ovvero l'intrinseca inefficienza del protocollo di trasporto universalmente riconosciuto come standard, il TCP. Quest'ultimo presenta ridotte prestazioni, principalmente legate alle politiche di controllo della congestione. Infatti il TCP è stato originariamente pensato per le reti cablate, dove le perdite di pacchetti indicano una congestione. Diversamente, gli eventi di perdita nelle reti wireless possono essere legati alle variazioni del canale radio, o alla contesa sul collegamento. Intendiamo dunque definire un'architettura 'cross-layer' sufficientemente snella e dinamica, basata sul paradigma delle reti cognitive. Questo framework include una fase di osservazione, i.e., un 'training set' all'interno del quale vengono collezionati svariati parametri di rete; una fase di apprendimento, in cui viene estratta l'informazione da utilizzare per il miglioramento delle prestazioni di rete; una fase di pianificazione, in cui vengono definite le strategie da utilizzare con le informazioni 'imparate'; infine, una fase di azione che rappresenta l'esecuzione 'online' di tali strategie all'interno della rete. La più recente frontiera per le infrastrutture di rete di prossima generazione si sviluppa intorno al concetto di reti eterogenee. Tuttavia, la presenza di una moltitudine di dispositivi diversi fra loro, in quanto a tecnologia e tecniche di accesso al mezzo, pone nuove sfide. Fra tutte, l'incremento dell'interferenza legato alla densificazione dei nodi e alla pianificazione autonoma. Proponiamo dunque un approccio atto a supportare il reindirizzamento del carico di rete dalle macro celle alle femto celle, attraverso una cooperazione fornita dagli utenti mobili in modalità 'idle', che operano a tutti gli effetti come nodi relay. In questo modo aumentiamo la probabilità che un utente connesso alla macro cella possa alternativamente connettersi ad una femto cella (procedura nota come offload). Abbiamo così definito un modello di ottimizzazione congiunto per l'allocazione delle risorse e la determinazione del collegamento stazione radio base - utente. Un ulteriore tema particolarmente importante riguarda il controllo per l'accettazione di nuovi utenti nel sistema. Tale modello deve garantire il mantenimento dei margini di qualità (QoS) associati ai nodi precedentemente connessi alla rete. A questo fine consideriamo diversi approcci per il calcolo della proiezione di capacità allocata in reti wireless basate sulla tecnologia OFDMA. Infine proponiamo la soluzione 'E-Diophantine' basata sulla teoria diofantina, di cui forniamo le basi matematiche, e mostriamo l'incremento delle prestazioni che ne risulta.

L'objectif de cette thèse est de concevoir, implémenter et évaluer les algorithmes cross-layer pratiques. Nous nous concentrons sur la technologie LTE et les réseaux non coordonnés post-LTE où l'interférence est un enjeu majeur compte tenu des nouvelles tendances du trafic. L'objectif est d'allouer les ressources radio d'une manière efficace. Nous développons des modèles d'interférence mathématiques et informatiques qui nous permettent de comprendre le comportement de ces réseaux et nous appliquons une approche basée sur la théorie de l'information à différents scénarios d'interférence et caractéristiques du trafic. Nous avons essayé de s'approcher le plus possible de systèmes réels pour être en mesure de tester la faisabilité des techniques proposées. La thèse porte sur l'évaluation de la performance des scénarios d'interférence dans les réseaux 4G, en particulier celles qui découlent du déploiements de cellules de petite taille ("small cells"). Le travail dans cette thèse s'adresse également à l'analyse de l'allocation des ressources et la requête de répétition automatique hybride (HARQ) à redondance incrémentale pour les interférences sporadiques (de façon plus générale les canaux variables dans le temps) qui permet uniquement des informations partielles de l'état du canal à l'émetteur. Ce travail est ensuite appliquée à la conception d'ordonnanceur pour les stations de base LTE et inclut une analyse de performance pour les modems LTE réels<br>The aim of this thesis is to design, implement and evaluate practical cross-layer algorithms. We focus on LTE and post-LTE uncoordinated networks where interference is a key issue given the new traffic patterns. The goal is to allocate the radio resources in an efficient way. We develop mathematical and computational interference models that allow us to understand the behavior of such networks and we apply an information-theoretic approach to different interference scenarios and traffic characteristics. We have tried to remain as close as possible to practical systems to be able to test the feasibility of the proposed techniques. The thesis deals with performance evaluation of interference scenarios in 4G networks, in particular those arising from small-cell deployments. The work in this thesis also deals with analysis of resource-allocation and incremental-redundancy based hybrid automatic repeat request (HARQ) for bursty interference (or more general time-varying channels) which allows for only partial channel state information at the transmitter. The work is then applied to practical scheduler design for LTE base stations and includes performance analysis for real LTE modems

L'accès à Internet par satellite permet de connecter des régions isolées de la terre ou des utilisateurs en mouvement, pour lesquels une solution terrestre peut s’avérer couteuse voire impossible. L’utilisation de constellations de satellite en orbite basse permet de transmettre avec des délais similaires à ceux des transmissions terrestres, permettant l’utilisation des protocoles de transport classiques comme TCP. L’utilisation d’un tel environnement engendre cependant des contraintes spécifiques à ce type de réseau, comme des délais de transmission variables et un important taux d’erreur, principalement lors de la traversée de l’atmosphère. Pour compenser ces forts taux de pertes, des mécanismes de fiabilisation doivent être introduit au niveau des couche basse. Ces mécanismes ont toutefois un impact négatif sur les performances des protocoles de transport, notamment TCP, limitant grandement le débit. Le but de cette thèse est de comprendre dans un premier temps les interactions entre les mécanismes de fiabilisation et les protocoles de transport, pour ensuite proposer des solutions permettant d’améliorer la qualité des transmissions<br>LEO satellite constellations allow to connect isolated or mobile users to the Internet, when terrestrial solutions are too expensive or impossible to deploy. Using such constellations allow to connect these areas with transmission delays close to terrestrial delays, and then to use the classic transport protocols such as TCP. However, this environment brings new impairments such as variable delays and important error rate between the satellite and the ground receiver. To counteract this high error rate, reliability schemes are introduced on the link between the satellite and the ground user. However, these schemes have a negative impact on the transport protocol (TCP), mitigating the throughput, and which has not been deeply studied yet. In this thesis, we first understand the impact of the reliability schemes on the transport layer, and then propose solutions to improve the efficiency of the transmissions

De nos jours, les communications mobiles sont caractérisées par une demande croissante de services basés sur Internet. Les services vidéo représentent une grande partie du trafic Internet aujourd'hui. Selon Cisco, 75% du trafic mondial de données mobiles sera constitué par données vidéo d'ici 2020. Cette demande toujours croissante a été le principal moteur du développement du réseau cellulaire numérique 4G, où les services numériques à commutation de paquet sont la principale brique de conception. En particulier, le système global doit assurer à la fois hauts et bas débit de transmission, et fournir des garanties de temps réel, par exemple dans le cas du streaming vidéo ou des jeux en ligne. Cela a motivé, dans la dernière décennie, un intérêt renouvelé dans la technologie d'accès radio. Le canal sans fil est affecté par divers phénomènes physiques, comme les Chemins multiples, le shadowing, l'évanouissement, l'interférence, etc. Dans les technologies les plus récentes, ces effets sont contrastés en utilisant le protocole ARQ (Automatic Repeat reQuest), qui consiste à retransmettre le même signal depuis la source. Le protocole ARQ est généralement combiné avec des codes de canal au niveau de la couche physique, qui est connu comme HARQ (Hybrid ARQ). Une autre technique pour améliorer la communication entre une source et une destination est la communication coopérative, où un relais est utilisé comme nœud intermédiaire. La communication coopérative et le HARQ, si appliquées individuellement, améliorent considérablement les performances du système de communication. Une question ouverte est de savoir si leur combinaison apporterait la somme des améliorations singulières, ou si ne serait que marginalement bénéfique. Dans la littérature on peut trouver de nombreuses études sur la combinaison de ces deux techniques, mais dans notre thèse, nous nous concentrons principalement sur cette interaction à niveau de la couche physique (PHY) et de la couche de contrôle d'accès (MAC). Nous utilisons des exemples de protocoles sur un réseau composé de trois noeuds (source, destination et relais). Pour l'analyse théorique nous nous concentrons sur les Chaînes de Markov à états finis (FSMC). Nous abordons le cas où le relais fonctionne en mode Decode-and-Forward (DCF), très commun dans la littérature, mais notre analyse se concentre de manière plus accentuée sur le cas où le relais fonctionne en mode Demodulate-and-Forward (DMF), en raison de sa simplicité d'implémentation et de son efficacité. Ce cas est beaucoup plus rarement abordé dans la littérature disponible, à cause de la complexité supérieure demandée par son analyse. Habituellement, l'interaction entre les deux techniques a été étudiée dans le cas de protocoles déterministes, mais dans notre analyse, nous nous concentrerons sur les protocoles déterministes et probabilistes. Jusqu'à présent, les protocoles probabilistes, où le noeud retransmetteur est choisi selon un modèle probabiliste, ont été principalement proposés pour des couches supérieures du système de communication. Au contraire, cette thèse étudie des protocoles probabilistes sur la couche PHY et sur la couche MAC, qui permet de mieux analyser et optimiser les performances. Le protocole probabiliste ne contient que deux paramètres, qui peut être optimisé pour de meilleures performances. Ces paramètres peuvent être calculés pour imiter le comportement d'un protocole déterministe donné, et ses performances optimisées ne peuvent que s'améliorer par rapport à celui-ci. De plus, les performances du protocole probabiliste est comparées aux résultats présent en littérature, et la comparaison montre que notre protocole fonctionne mieux. Enfin, la question de la sélection des relais est également abordée. Nous proposons un critère pour opérer le choix du relais à utiliser, en cas de plusieurs candidats. La performance obtenue par ce critère est comparée à celle obtenue avec les critères de référence dans la littérature<br>Nowadays, mobile communications are characterized by a fast-increasing demand for internet-based services (voice, video data). Video services constitutes a large fraction of the internet traffic today. According to a report by Cisco, 75% of the world's mobile data traffic will be video-based by 2020. This ever-increasing demand in delivering internet-based services, has been the main driver for the development of the 4G digital cellular network, where packet- switched services are the primary design target. In particular, the overall system needs to ensure high peak data rates to the user and low delay in the delivery of the content, in order to support real time applications such as video streaming and gaming. This has motivated, in the last decade, a renewed and raising interest and research in wireless radio access technology. Wireless channel suffers from various physical phenomena like path-loss, shadowing, fading, interference, etc. In the most recent technologies, these effects are contrasted using Automatic Repeat re-Quest (ARQ) protocol, which consist on the retransmission of the same signal from the same node. ARQ protocol is usually combined with channel codes at the physical layer, which is known as Hybrid Automatic Repeat re-Quest (HARQ) protocol. Another improvement for communications over wireless channels is achieved when Relays are used as intermediate nodes for helping the communication between a Source and a Destination, which is known as cooperative communication. Both techniques, cooperation and HARQ, if individually applied, significantly improve the performance of the communication system. One open question is whether their combination would bring the sum of the singular improvements, or be only marginally beneficial. In the literature we can find many studies for the combination of these two techniques, but in our thesis we focus mainly on this interaction at the level of the physical layer (PHY) and the medium access control layer (MAC). We use example protocols on a network of three nodes (Source, Destination and Relay). For the theoretical analysis of these systems we focus on Finite State Markov Chains (FSMC). We discuss the case where Relay works in Decode-and-Forward (DCF) mode, which is very common in the literature, but our analysis focuses more strongly on the case where the Relay works in Demodulate-and-Forward (DMF) mode, because of its simplicity of implementation and its efficiency. This case is much more rarely addressed in the available literature, because of the higher complexity required by its analysis. Usually, the interaction between the two techniques has been studied using deterministic protocols, but in our analysis we will focus on both, deterministic and probabilistic protocols. So far, probabilistic protocols, where the retransmitting node is chosen with a given probability, have been mainly proposed for higher layers of communication systems, but, in contrast, this thesis studies probabilistic protocols on the physical layer and MAC layer, which give more insight on the analysis and performance optimization. The probabilistic protocols contains very few parameters (only 2) that can be optimized for best performance. Note that these parameters can be computed to mimic the behavior of a given deterministic protocol, and the result of the probabilistic protocol after optimization can only improve over this one. Moreover, the performance of our optimized probabilistic protocol is checked against results of the literature, and the comparison shows that our protocol performs better. In the end, there is also discussed the issue of relay selection. In a scenario of several candidate Relays, we propose a criterion for choosing the best Relay. The performance obtained by this criterion is compared to that obtained with the reference criteria in the literature

Master’s thesis is focused on part of mobile network named LTE. Project is analyzes the LTE physical layer, which is divided into four basic parts: Physical channels and modulation, Multiplexing and channel coding, Physical layer procedures, Physical layer measurements. Every part is described by actual 3GPP standard [1]. To understand the problem is expected a reader basic knowledge of OFDM systems, which the LTE system uses. The next part of this master’s thesis is dedicated to mathematic model physical layer of system LTE, created by program Matlab. This model is designed to measure errors in data transmission.

In the recent years, there has been a rapid development in the field of fisheries especially with reference to aquaculture. India has vast fisheries resources with a total EEZ (Exclusive Economic Zone) of 2.02 million square kilometers and a coastline of 8047 kilometers. The total riverine length is above 29,000 square kilometers. The lentic water bodies include lakes, ponds, tanks, reservoirs, bheels, bans, jheels,etc,which are estimated to be nearly 1.29 lakh hectares in area. The rivers upon joining the sea form large areas of brackish water estuaries. The area suitable for brackishwater fish farming is around 2 million hectares. These form a tremendous resource for fisheries in the country. The marine environment produces around 2.6 million tonnes of fish, comprised of different variety of fishes, crustaceans and mollusks. The inland water resources produce around 2.3 million tonne of fish. Eventhough the current inland production lags behind the marine production there has been a tremendous increase in the annual growth rate primarily due to aquaculture.

Thesis (M.S.)--University of Tennessee Health Science Center, 2009.<br>Title from title page screen (viewed on August 11, 2009). Research advisor: Jegdish P. Babu, Ph.D. Document formatted into pages (ix, 32 p. : ill.). Vita. Abstract. Includes bibliographical references (p. 28-31).