Le messager de l'époque capétienne nous est accessible par des sources variées. De ce fait apparaissent plusieurs figures de ce porteur invitant. D'abord, le porte-rouleaux qui assurait un geste indispensable à la cohésion des abbayes. Ensuite, le messager, thème récurrent des lettres médiévales, a déjà pour une part été étudié par ailleurs. Les sources doctrinales ont élaboré le stéréotype du bon messager. La documentation pragmatique montre, elle, qu'il existait une extrême variabilité dans le statut de la personne susceptible de servir, pour une durée elle-même variée, de messager et que, si tout le monde ne pouvait être un messager appointé par le roi, chacun pouvait un jour s'improviser messager en fonction des circonstances. Correspondant traditionnellement aux origines de la Poste en France, cette matière avait en fait intéressé depuis le XVIIe siècle. Son étude révèle, de plus, d'intimes problèmes inhérents à la condition de l'historien. / We can know the messenger on the capetian era by various sources. For this reason appear a few figures of this inviting holder. First, the scrolls holder who was in charge of an indispensable gesture for cohesion of abbeys. Then, the messenger, classical theme in medieval literature, has been before studied for a part. Doctrinal sources elaborated the stereotype of the good messenger. Pragmatic documents show that it existed a very great diversity in the status of the person that could serve, for a various period, as messenger and that if everybody could not be a salaried messenger of the king, everybody can one fine day be a messenger because of the circumstances. As always corresponding to origins of Post in France, this subject had in fact interested since the 17century. Furthermore, its study reveals intimate problems inherent in the historian's lot.

Harvesting energy became one of the most prominent research topics around the world, not only for research institutes and universities but also for technology companies as well. Mainly focused on internet of things (IoT) applications, harvesting energy is a crucial factor for reducing costs that come with the use of batteries and increasing the devices’ working time. Simultaneous lightwave information and power transfer is a technique that seeks to use wireless optical communication to achieve both fundamental objectives in modern communication systems. This work presents the main techniques that are used to achieve SLIPT, a novel circuit that improves the standard methods and applications employing this circuit.

Thesis (M.A.) - Carleton University, 2007. / Includes bibliographical references (p. 120-135). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 1996. / Includes bibliographical references (leaves 294-305).

This thesis first presents a new cooperative wireless communication network strategy that incorporates energy cooperation and data cooperation. The model establishment, design goal formulations, and algorithms for throughput maximization of the proposed protocol are presented and illustrated using a three-node network with two energy harvesting (EH) user nodes and a destination node. Transmission models are established from the performance analysis for a total of four scenarios. Based on the models, we seek to find optimal energy management strategies by jointly optimizing time allocation for each user, power allocations over these time intervals, and data throughputs at user nodes so as to maximize the sum-throughput or, alternatively, the minimum throughput of the two users in all scenarios. An accelerated Newton barrier algorithm and an alternative algorithm based on local quadratic approximation of the transmission models are developed to solve the aforementioned optimization problems. Then the thesis extends the cooperative strategy to multi-source wireless communication network, where N source users communicate with the destination via one relay that harvests energy from the RF signals transmitted by the sources through time-division multiple access (TDMA). We characterize the Energy-Throughput (E-T) tradeoff regions between the maximum achievable average throughput of the sources and the total amount of saved energy in three circumstances. For the case N=1, all harvested energy will be used to forward the message. For the case N>1, we compare two transmission strategies: one is common PS ratio strategy that the relay adopts the same PS ratio for all sources; the other is individual PS ratio strategy that each source uses an individual PS ratio. Numerical experiments under practical settings provide supportive evidences to our performance analysis. / Graduate

Wireless is everywhere. Smartphones, tablets, laptops, implantable medical devices, and many other wireless devices are massively taking part of our everyday activities. On average, an actively digital consumer has three devices. However, most of these wireless devices are small equipped with batteries that are often limited and need to be replaced or recharged. This fact limits the operating lifetime of wireless devices and presents a major challenge in wireless communication. To improve the perpetual energy operation of wireless communication systems, energy harvesting (EH) from the radio frequency (RF) signals is one promising solution to make the wireless communication systems self-sustaining. Since RF signals are known to transmit information, it is interesting to study when RF signals are simultaneously used to transmit information and scavenge energy, namely simultaneous wireless information and power transfer (SWIPT). In this thesis, we specifically aim to study the SWIPT in multiple-input multiple-output (MIMO) relay communication systems and in cognitive radio (CR) networks. First, we study the SWIPT in MIMO relay systems where the relay harvests the energy from the source and uses partially/fully the harvested energy to forward the signal to the destination. For both the amplify-and-forward (AF) and decode-and-forward (DF) relaying protocols, we consider the ideal scheme where both the energy and information transfer to the relay happen simultaneously, and the practical power splitting and time switching schemes. For each scheme, we aim to maximize the achievable end-to-end rate with a certain energy constraint at the relay. Furthermore, we consider the sum rate maximization problem for the multiuser MIMO DF relay broadcasting channels with multiple EH-enabled relays, and an enhanced low complex solution is proposed based on the block diagonalization method. Finally, we study the energy and data performance of the SWIPT in CR network where either the primary receiver (PR) or the secondary receiver (SR) is using the antenna switching (AS) technique. When the PR is an EH-enabled node, we illustrate the incentive of spectrum sharing in CR networks. When the SR is an EH-enabled node, we propose two thresholding-based selection schemes: the prioritizing data selection scheme and the prioritizing energy selection scheme.

Wireless communications has gone through tremendous growth in the past decades. There has been a shift in wireless network research from spectral efficiency and quality of service (QoS) constraints to energy efficiency and green communications to reduce power consumption. Green energy resources such as solar, wind, thermal and mechan- ical vibrations can be employed to increase the energy efficiency of energy-constrained networks such as wireless sensor networks. Converting the available energy in the sur- rounding area into electricity, energy harvesting (EH), has been the subject of recent research. EH from radio frequency (RF) signals can be utilized to prolong the lifetime of devices in energy-constrained systems. Wireless power transmission (WPT) for EH is a promising solution to provide a reliable source of energy for devices which are di cult to service due to mobility and/or hard to reach locations. The integration of relaying into conventional wireless networks is promising to increase the coverage area and reduce power consumption. However, the extra power consumed to relay signals may be a problem that can be mitigated by WPT. WPT has made it possible for relays to power themselves by capturing ambient energy wirelessly. The received signal at the relay can be utilized to both forward information and harvest energy. This dissertation focuses on practical energy harvesting schemes in wireless com- munication networks. Further, the broadcast nature of wireless systems makes wire- less transmissions more vulnerable to eavesdropping compared to wired signals. The goal of this work is to develop EH schemes that are capable of supplying sustainable energy to the relays and overcoming the secrecy hazards from potential eavesdroppers. Power splitting (PS) and time switching (TS) are studied in communication networks to prolong the lifetime of an energy-constrained relay. First, a dual hop system with an amplify and forward (AF) relay employing wireless information and power transfer (WIPT) via power splitting is studied. Optimal transmit antenna selection that max- imizes the end-to-end signal to noise ratio (SNR) at the destination is considered and the outage probability is derived. It is shown that the outage probability increases with the number of transmit antennas but this also increases the system complexity. Since the spectral efficiency with two-way relaying is higher than with one-way relaying, a two-way EH-based relay network with an eavesdropper is investigated. The secrecy capacity at the users is derived for two diversity combining cases at the eavesdropper, selection combining (SC) and maximal ratio combining (MRC). A friendly jammer is introduced to increase the secrecy capacity of the users by reducing the received signal to noise ratio at the eavesdropper since the signal of the jammer is considered as noise at the eavesdropper. The corresponding optimization problem is reformulated using the single condensation method (SCM) and geometric programming (GP) into a convex optimization problem. Then, GP is used to jointly optimize the power splitting factor of the relay and transmit powers of the two users and jammer to maximize the secrecy capacity of the system. Imperfect cancellation of the jamming signal at the relay is assumed. It is shown that increasing the power allocated to the jammer decreases the secrecy capacity at the users. However, when perfect jamming signal cancellation is assumed, increasing the power allocated to the jammer increases the secrecy capacity at the users. The secrecy capacity is also shown to be greater with a jammer than without a jammer. Channel state information uncertainty at the eavesdropper is also considered as an extra noise source. TS at the relay of a two-way EH-based relay network was also considered. GP is used to jointly optimize the time switching ratio of the relay and transmit powers of the two users and jammer to maximize the secrecy capacity of the system. It is shown that PS two-way relaying achieves a better secrecy capacity than TS two-way relaying. / Graduate

In practice, a communication system works with finite blocklength codes because of the delay constraints and the information-theoretic bounds which are proposed for finite blocklength systems can be exploited to determine the performance of a designed system. In this thesis, achievable rates for given average error probabilities are considered for finite blocklength systems. Although classical bounds can be used to upper bound the error probability, these bounds require the optimization of auxiliary variables. In this work, a bound which is called the dependence testing (DT) bound that is free of any auxiliary variables is exploited. The DT bound is evaluated by introducing a normal approximation to the information density. Simulations carried out both for the Gaussian and discrete input alphabets show the proposed approximation enables very good prediction of the achievable rates. The proposed approximation is also used to calculate the average error probability for block fading channels. Simulations performed for Rayleigh block fading channels demonstrate that the total blocklength of the system in addition to the number of fading blocks should be accounted for especially when the number of fading blocks is large. A power allocation problem in block fading channels when the channel state information is available to the transmitting side is investigated in the final part of this work. The DT bound is optimized for a given channel state vector by allocating different power levels to each fading block by exploiting short-term power allocation. A simple power allocation algorithm is proposed which comes out with very similar results compared with the analytically computed values.

This work deals with the issue of PLC with a focus on BPL technology (Broadbandover-power lines), which is explained in the theoretical part. The work describes in detailthe main components for PCB design with manufacturing and mounting process. Fur-thermore, the thesis provides instructions on how to establish communication betweenBPL modems and a description of individual functions. In conclusion, the procedureof measuring the noise intensity in the 230 V power line is described with the results.The output of the diploma thesis is the selection of components and the implementationof printed circuit boards for two BPL modems. These modems allow to measure SNR(signal to noise ratio) at physical speed.

L'analyse et l'optimisation au niveau de système sont indispensables pour la progression de performance des réseaux de communication. Ils sont nécessaires afin de faire fonctionner de façon optimale des réseaux actuels et de planifier des réseaux futurs. La modélisation et l'analyse au niveau de système des réseaux cellulaires ont été facilitées grâce à la maîtrise de l'outil mathématique de la géométrie stochastique et, plus précisément, la théorie des processus ponctuels spatiaux. Du point de vue de système, il a été empiriquement validé que les emplacements des stations cellulaires de base peuvent être considérés comme des points d'un processus ponctuel de Poisson homogène dont l'intensité coïncide avec le nombre moyen de stations par unité de surface. Dans ce contexte, des contributions de ce travail se trouvent dans le développement de nouvelles méthodologies analytiques pour l'analyse et l'optimisation des déploiements de réseaux cellulaires émergents.La première contribution consiste à introduire une approche pour évaluer la faisabilité de réseaux cellulaires multi-antennes, dans lesquels les dispositifs mobiles à faible énergie décodent les données et récupèrent l'énergie à partir d’un même signal reçu. Des outils de géométrie stochastique sont utilisés pour quantifier le taux d'information par rapport au compromis de puissance captée. Les conclusions montrent que les réseaux d'antennes à grande échelle et les déploiements ultra-denses de stations base sont tous les deux nécessaires pour capter une quantité d'énergie suffisamment élevée et fiable. En outre, la faisabilité de la diversité des récepteurs pour l'application aux réseaux cellulaires descendants est également étudiée. Diverses options basées sur la combinaison de sélection et la combinaison de taux maximal sont donc comparées. Notre analyse montre qu'aucun système n’est plus performant que les autres pour chaque configuration de système : les dispositifs à basse énergie doivent fonctionner de manière adaptative, en choisissant le schéma de diversité des récepteurs en fonction des exigences imposées.La deuxième contribution consiste à introduire une nouvelle approche pour la modélisation et l'optimisation de l'efficacité énergétique des réseaux cellulaires.Contrairement aux approches analytiques actuellement disponibles qui fournissent des expressions analytiques trop simples ou trop complexes de la probabilité de couverture et de l'efficacité spectrale des réseaux cellulaires, l'approche proposée est formulée par une solution de forme fermée qui se révèle en même temps simple et significative. Une nouvelle expression de l'efficacité énergétique du réseau cellulaire descendant est proposée à partir d’une nouvelle formule de l'efficacité spectrale. Cette expression est utilisée pour l’optimisation de la puissance d'émission et la densité des stations cellulaires de base. Il est prouvé mathématiquement que l'efficacité énergétique est une fonction uni-modale et strictement pseudo-concave de la puissance d'émission en fixant la densité des stations de base, et de la densité des stations de base en fixant la puissance d'émission. La puissance d'émission optimale et la densité des stations de base s'avèrent donc être la solution des équations non linéaires simples.La troisième contribution consiste à introduire une nouvelle approche pour analyser les performances des réseaux cellulaires hétérogènes équipés des sources d'énergie renouvelables, telles que les panneaux solaires. L'approche proposée permet de tenir compte de la distribution spatiale des stations de base en utilisant la théorie des processus ponctuels, ainsi que l'apparition aléatoire et la disponibilité de l'énergie en utilisant la théorie des chaînes de Markov. En utilisant l'approche proposée, l'efficacité énergétique des réseaux cellulaires peut être quantifiée et l'interaction entre la densité des stations de base et le taux d'énergie d'apparition peut être quantifiée et optimisée. / In communication networks, system-level analysis and optimization are useful when one is interested in optimizing the system performance across the entire network. System-level analysis and optimization, therefore, are relevant for optimally operating current networks, and for deploying and planning future networks. In the last few years, the system-level modeling and analysis of cellular networks have been facilitated by capitalizing on the mathematical tool of stochastic geometry and, more precisely, on the theory of spatial point processes. It has been empirically validated that, from the system-level standpoint, the locations of cellular base stations can be abstracted as points of a homogeneous Poisson point process whose intensity coincides with the average number of based stations per unit area.In this context, the contribution of the present Ph.D. thesis lies in developing new analytical methodologies for analyzing and optimizing emerging cellular network deployments. The present Ph.D. thesis, in particular, provides three main contributions to the analysis and optimization of energy-efficient cellular networks.The first contribution consists of introducing a tractable approach for assessing the feasibility of multiple-antenna cellular networks, where low-energy mobile devices decode data and harvest power from the same received signal. Tools from stochastic geometry are used to quantify the information rate vs. harvested power tradeoff. Our study unveils that large-scale antenna arrays and ultra-dense deployments of base stations are both necessary to harvest, with high reliability, a sufficiently high amount of power. Furthermore, the feasibility of receiver diversity for application to downlink cellular networks is investigated. Several options that are based on selection combining and maximum ratio combining are compared against each other. Our analysis shows that no scheme outperforms the others for every system setup. It suggests, on the other hand, that the low-energy devices need to operate in an adaptive fashion, by choosing the receiver diversity scheme as a function of the imposed requirements.The second contribution consists of introducing a new tractable approach for modeling and optimizing the energy efficiency of cellular networks. Unlike currently available analytical approaches that provide either simple but meaningless or meaningful but complex analytical expressions of the coverage probability and spectral efficiency of cellular networks, the proposed approach is conveniently formulated in a closed-form expression that is proved to be simple and meaningful at the same time. By relying on the new proposed formulation of the spectral efficiency, a new tractable closed-form expression of the energy efficiency of downlink cellular network is proposed, which is used for optimizing the transmit power and the density of cellular base stations. It is mathematically proved, in particular, that the energy efficiency is a unimodal and strictly pseudo-concave function in the transmit power, given the density of the base stations, and in the density of the base stations, given the transmit power. The optimal transmit power and density of base stations are proved to be the solution of simple non-linear equations.The third contribution consists of introducing a new tractable approach for analyzing the performance of multi-tier cellular networks equipped with renewable energy sources, such as solar panels. The proposed approach allows one to account for the spatial distribution of the base stations by using the theory of point processes, as well as for the random arrival and availability of energy by using Markov chain theory. By using the proposed approach, the energy efficiency of cellular networks can be quantified and the interplay between the density of base stations and energy arrival rate can be quantified and optimized.