Satellite communication system designers are continuously struggling to improve the channel capacity. A critical challenge results from the limited power available aboard the satellite.Because of this constraint, the onboard power amplifier must work with a small power supply which limits its maximum output power. To ensure a sufficient Signal-to-Noise power Ratio (SNR) on the receiver side, the power amplifier must work close to its saturation point. This is power efficient but unfortunately adds non-linear distortions to the communication channel. The latters are very penalizing for high order modulations.In the literature, several equalization algorithms have been proposed to cope with the resulting non-linear communication channel. The most popular solution consists in using baseband Volterra series in order to build non-linear equalization filters. On the other hand, the Recurrent Neural Networks (RNNs), which come from the artificial neural network field, are also interesting candidates to generate such non-linear filters. But they are difficult to implement in practice due to the high complexity of their training. To simplify this task, the Echo State Network (ESN) paradigm has been proposed. It has the advantage of offering performances similar to classical RNNs but with a reduced complexity.The purpose of this work is, first, to compare this solution to the state-of-the-art baseband Volterra filters. We show that the classical ESN is able to reach the same performances, evaluated in terms of Bit Error Rate (BER), and has similar complexity. Secondly, we propose a new design for the ESN which achieves a strong reduction in complexity while conserving a similar BER.To compensate for the channel, the literature proposes to adapt the coefficients of these equalizers with the help of a training sequence in order to recover the transmitted constellation points. We show that, in such a case, the usual symbol detection criterion, based on Euclidean distances, is no longer optimal. For this reason, we first propose a new detection criterion which meets the Maximum Likelihood (ML) criterion. Secondly, we propose a modification of the equalizers training reference points in order to improve their performances and make the detection based on Euclidean distances optimal again. This last solution can offer a significant reduction of the BER without increasing the equalization and detection complexity. Only the new training reference points must be evaluated.In this work, we also explore the field of analog equalizers as different papers showed that the ESN is an interesting candidate for this purpose. It is a promising approach to reduce the equalizer complexity as the digital implementation is very challenging and power-hungry, in particular for high bandwidth communications. We numerically demonstrate that a dedicated analog optoelectronic implementation of the ESN can reach the state-of-the-art performance of digital equalizers. In addition, we show that it can reduce the required resolution of the Analog-to-Digital Converters (ADCs).Finally, a hardware demonstration of the digital solutions is proposed. For this purpose, we build a physical layer test bench which depicts a non-linear communication between two radios. We show that if we drive the transmitter power amplifier close to its saturation point, we can improve the communication range if the non-linear distortions are compensated for at the receiver. The transmitter and the receiver are implemented with Software Defined Radios (SDRs). / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Yes / This is the twelfth workshop to be organised under the postgraduate programmes in electrical and electronic engineering (EEE). In total, thirty-four papers from forty-nine submissions have been selected for the Proceedings. The Proceedings comprises eleven themes, which reflect today's research agenda.

Includes supplemental material. / Disaster relief operations, such as the 2005 Tsunami and Hurricane Katrina, and wartime operations, such as Operation Enduring Freedom and Operation Iraqi Freedom, have identified the need for a standardized command and control system interoperable among Joint, Coalition, and Interagency entities. The Systems Engineering Analysis Cohort 9 (SEA-9) Rapid Response Command and Control (R2C2) integrated project team completed a systems engineering (SE) process to address the military’s command and control capability gap. During the process, the R2C2 team conducted mission analysis, generated requirements, developed and modeled architectures, and analyzed and compared current operational systems versus the team’s R2C2 system. The R2C2 system provided a reachback capability to the Regional Combatant Commander’s (RCC) headquarters, a local communications network for situational assessments, and Internet access for civilian counterparts participating in Humanitarian Assistance/Disaster Relief operations. Because the team designed the R2C2 system to be modular, analysis concluded that the R2C2 system was the preferred method to provide the RCC with the required flexibility and scalability to deliver a rapidly deployable command and control capability to perform the range of military operations.

[pt] Este trabalho está relacionado ao problema do uso eficiente da órbita de satélite geoestacionário. A utilização eficiente da órbita é obtida através de um algoritmo de otimização que permite escolher as posições orbitais para os diversos sistemas de modo a reduzir ao máximo o percentual do arco orbital utilizado. Sendo assim, desenvolvido um modelo matemático que considerou além de aspectos de interferência, detalhes da geometria envolvida no problema (posições orbitais dos satélites, posições das estações terrenas, apontamento de antenas, etc.). Este modelo foi utilizado na definição de um problema de otimização com restrição cuja função objetivo se baseia na parcela do arco orbital utilizado. Neste problema de otimização com restrição foram consideradas restrições de níveis máximos de interferência (de entrada única e agregada) além de restrições de arcos orbitais, impostas por aspecto de propagação. O algoritmo de otimização utilizado requer o cálculo do Vetor Gradiente e da Matriz Hessiana. Para evitar erros de origem numéricos essas quantidades foram calculadas utilizando expressões analíticas desenvolvidas neste trabalho. O método matemático foi aplicado a situações específicas conduzindo a resultados que mostraram um uso eficiente da órbita de satélites geoestacionários através de soluções onde a parcela utilizada do arco é minimizada. / [en] This work is related to the efficient use of the geostationary satellite orbit. It presents and describes an optimization model which chooses the best orbital position for each satellite so that the length used orbital arc is minimized. A mathematical model considering aspects such as interference, geometry details (orbital position of the systems, earth station position, boresight of the antenna, etc) is proposed. This model was used in the definition of a constrained optimization problem in which the cost function is the length of the used orbital arc. Constrained imposed by propagation aspects (minimum elevation angle) and by the maximum allowable interference levels (aggregate and single-entry) are considered. The optimization algorithm requires the evaluation of the Gradient vector and the Hessian matrix. To avoid numeric problems, analytic expressions of these quantities were derived. Results of the application of this model to specific situations involving real data were also described and conducted to solutions where the length of the orbit used was minimized

[pt] Com a crescente utilização de sistemas de acesso sem fio ponto-multiponto em banda larga, operando em freqüências cada vez mais elevadas, cresce também a necessidade do desenvolvimento de novos modelos, mais precisos e consistentes, para a previsão da atenuação por chuvas, principal efeito da propagação em freqüências superiores a 10 GHz. Este trabalho apresenta uma modelagem semi-empírica para a previsão do comportamento estatístico da atenuação por chuvas em enlaces rádio terrestres ponto-a- ponto e via satélite. Os modelos foram desenvolvidos com base em resultados de medições conjuntas de taxa de precipitação e atenuação por chuvas em diversas regiões do Brasil, realizadas no período de desenvolvimento deste trabalho, além de medidas de várias partes do mundo, disponíveis no banco de dados de propagação da União Internacional de Telecomunicações (UIT-R). Os modelos desenvolvidos permitem obter a distribuição cumulativa de probabilidades da atenuação por chuvas a partir da distribuição da taxa de precipitação medida ou estimada na região do enlace. Embora existam diversos modelos propostos na literatura para previsão da atenuação em enlaces terrestres ou em enlaces via satélite, duas características importantes não são encontradas, conjuntamente, na maioria deles: utilizar, como base para a previsão, a distribuição da taxa de precipitação em toda a faixa de percentagens de tempo de interesse, e não apenas em um ou dois pontos; e manter consistência entre os modelos para os casos terrestre e via satélite. Além não de atender a estes requisitos, os modelos propostos apresentam erros de previsão menores ou equivalentes aos dos principais modelos da literatura, quando testados contra os resultados disponíveis de medidas em enlaces reais. / [en] The development of new technologies for broadband wireless access, using increasingly higher frequencies, points to the necessity of more accurate methods for rain attenuation, that represents the most serious impairment for radio systems operating in frequencies above 10 GHz. This work presents semi-empirical models for the prediction of rain attenuation in terrestrial and satellite links. The models were developed using data obtained in concurrent measurements of rain attenuation and point rainfall rate in different regions of Brazil. Some of these measurements were performed as part of this work and some were already available from previous measurements campaigns. Data available in the UIT-R data banks of propagation measurements were also used, in order to develop global methods. The models that have been developed allow the prediction of the cumulative probability distribution of rain attenuation from the cumulative distribution of point rainfall rate in the region of the link. Although several methods with these purpose can be found in the technical literature, the ones developed in this work present some important features that are not found, as a whole, in any of those models: they use the full rainfall rate distribution over the entire range of time percentages of interest; the terrestrial and satellite models are consistent, that is, the elements used in the terrestrial prediction model are kept in the satellite prediction model that involves a mor complex geometry. Besides that, the models proposed show an excelent performance in terms of prediction error, when compared with measured data.

Le travail de recherche présenté dans cette thèse est basé sur l’étude du protocole de communication par satellite appelé « Enhanced Spread Spectrum Aloha » (E-SSA) et créé par l’Agence Spatiale Européenne (ESA) en 2009. Il s’agit d’une technique qui permet à un terminal d’envoyer des messages courts par satellite de manière totalement asynchrone. L’intérêt est de maximiser l’efficacité spectrale tout en gardant une complexité minimale du terminal grâce aux techniques d’étalement de spectre et d’annulation d’interférences (SIC). Alors qu’au départ le protocole E-SSA avait pour but d’apporter un support physique pour des applications destinées à des terminaux mobiles en bande S, les développements se sont récemment étendus à une gamme de terminaux fixes dans des bandes de fréquence différentes (C, Ku ou Ka). À partir de ces deux modèles d’utilisation de l’E-SSA, ce travail de recherche se concentre sur la mise en place de solutions techniques permettant d’augmenter significativement la capacité globale du système. Cela est possible à travers une optimisation des différents paramètres du protocole et la conception d’algorithmes de gestion des puissances des terminaux. / The work presented in this thesis focuses on the satellite communication protocol named “Enhanced Spread Spectrum Aloha” (E-SSA) and developed in 2009 by the European Space Agency (ESA). The E-SSA structure, based on fully asynchronous random access, perfectly copes with low-duty cycle bursty transmissions adapted to satellite messaging. High performance in terms of spectral efficiency is possible by exploiting iterative successive interference cancellation (SIC) while keeping minimal complexity at the terminal side. If the first exploitation of the protocol concerned mobile applications in S-band, it has been extended to fleets of fixed terminals in other frequency bandwidths (C, Ku or Ka). Starting from these two scenarios, this thesis proposes different innovations to further boost the E-SSA global system capacity. These technical solutions particularly include a fine optimization of protocol parameters and new power control algorithms.

Satellite communication (Satcom) services are used worldwide for voice, data, and video links due to various appealing features. Parabolic reflector antennas are typically used to serve a cost effective scheme for commercial applications. However, mount degradation, roof sag, and orbital decay motivate the need for beam steering. Limited scan range beam steering opens a third option for electronic beam steering with lower cost than full aperture phased arrays and higher tracking speed and accuracy than mechanical-only steering.Multiple high efficiency passive patch array feeds were designed, fabricated, and measured, including a 2x2 MSA array, a stacked shorted annular patch antenna, and an SIW-fed hexagonal array feed based on PTFE material, achieving performance comparable to a horn feed. For multiband dual polarization applications, passive MSA feed solutions are also provided. Multiple MSA array feeds with high isolation were designed for dual band dual polarization applications. More functionality can be realized with multi-layer PCB techniques for complex communication scenarios.Limited scan range electronic beam-steering with a parabolic reflector fed by an active array feed which only needs gain control was demonstrated experimentally, leading to a low cost and effective solution for active beam scanning. A cost-effective flat-panel phased array with limited scan range electronic beam-steering was proposed by tiling high efficiency 4x4 passive subarrays and performing beam scanning at the tile level. The sidelobe issue was also investigated to comply with the pattern mask requirement set by FCC.To enable better use of circularly polarized (CP) MSAs for electronically beam-formed antenna systems, the impact of mutual coupling on the performance of high-sensitivity dual-polarized receivers for satellite communications applications was analyzed. A new analysis method for intrinsically dual-CP MSAs based on an equivalent circuit model and Jones matrices was proposed and validated to overcome the port isolation challenge. The model provides accurate estimates of impedances and S-parameters, as well as field parameters such as axial ratio. The feasible region for XPI and impedance mismatch factor is found for dual CP antennas. The circuit model enables multiple useful applications. Effective decoupling and matching schemes was proposed and demonstrated, leading to a high isolation, good match, and wide AR bandwidth dual CP MSA for satellite communications.

The design of a low cost electronically steered array feed (ESAF) is implemented and tested. The ESAF demonstrated satellite tracking capabilities over four degrees. The system was compared to a commercial low-noise block downconverter (LNBF) and was able to receive the signal over a wider angle than the commercial system. Its signal-to-noise ratio (SNR) performance was poor, but a proof of concept for a low cost ESAF used for tracking is demonstrated. Two compact low profile dual circularly polarized (CP) reflector feed antenna designs are also analyzed. One of the designs is a passive antenna dipole array over an electromagnetic band gap (EBG) surface. It demonstrated high isolation between ports for orthogonal polarizations while also achieving quality dual CP performance. Simulations and measurements are shown for this antenna. The other antenna was a microstrip cross antenna. This antenna demonstrated high gain and quality CP but had a large side lobe and low isolation between ports. A global positioning system (GPS) denied multiple input multiple output (MIMO) radar for unmanned aerial vehicles (UAVs) is simulated and tested in a physical optics scattering model. This model is developed and tested by comparing simulated and analytical results. The radar uses channel matrices generated from the MIMO antenna system. The channel matrices are then used to generate correlation matrices. A matrix distance between actively received correlation matrices to stored correlation matrices is used to estimate the position of the UAV. Simulations demonstrate the ability of the radar algorithm to determine its position when flying along a previously mapped path.

yes / This is the eleventh workshop to be organised under the postgraduate programmes in electrical and electronic engineering (EEE). In total, thirty-five papers from sixty-seven submissions have been selected for the Proceedings. Over the past eleven years, the Research Seminar Series has provided a snapshot of the research agenda. In this, the 11th issue of the Workshop Proceedings, the importance of sustainable energy generation and the emerging influence of cloud computing, the growing number of applications of wireless sensors and the ubiquitous nature of the World Wide Web are in evidence. / None

L’optimisation des communications par satellite devient un enjeu crucial pour fournir un accèsInternet aux zones blanches et/ou défavorisées et pour supporter des réseaux à grande échelle.Dans ce contexte, l’utilisation des techniques d’accès aléatoires sur le lien retour permetd’améliorer les performances de ces systèmes. Cependant, les techniques d’accès aléatoireclassiques comme ‘Aloha’ et ‘Slotted Aloha’ ne sont pas optimales pour la transmission dedonnées sur le lien retour. En effet, ces techniques présentent un taux élevé de pertes depaquets suite aux collisions. Par conséquent, des études récentes ont proposé de nouvellesméthodes d’accès aléatoire pour résoudre les collisions entre les paquets et ainsi, améliorerles performances. En particulier, ces méthodes se basent sur la redondance de l’informationet l’annulation successive des interférences. Dans ces systèmes, l’estimation de canal sur le lien retour est un problème difficile en raison du haut niveau de collisions de paquets. Dans une première contribution dans cette thèse, nous décrivons une technique améliorée d’estimation de canal pour les paquets en collision. Par ailleurs, nous analysons l’impact des erreurs résiduelles d’estimation de canal sur la performance des annulations successives des interférences. Même si les résultats obtenus sont encore légèrement inférieurs au cas de connaissance parfaite du canal, on observe une amélioration significative des performances par rapport aux algorithmes d’estimation de canal existants. Une autre contribution de cette thèse présente une méthode appelée ‘Multi-Replica Decoding using Correlation based Localisation’ (MARSALA). Celle-ci est une nouvelle technique de décodage pour la méthode d’accès aléatoire synchrone ‘Contention Résolution diversité Slotted Aloha’ (CRDSA), qui est basée sur les principe de réplication de paquets et d’annulation successive des interférences. Comparée aux méthodes d’accès aléatoire traditionnelles, CRDSA permet d’améliorer considérablement les performances. Toutefois, le débit offert par CRDSA peut être limité à cause des fortes collisions de paquets. L’utilisation deMARSALA par le récepteur permet d’améliorer les résultats en appliquant des techniques de corrélation temporelles pour localiser et combiner les répliques d’un paquet donné. Cette procédure aboutit à des gains en termes de débit et de taux d’erreurs paquets. Néanmoins, le gain offert par MARSALAest fortement dépendant de la synchronisation en temps et en phase des répliques d’un mêmepaquet. Dans cette thèse, nous détaillons le fonctionnement de MARSALA afin de corriger ladésynchronisation en temps et en phase entre les répliques. De plus, nous évaluons l’impactde la combinaison imparfaite des répliques sur les performances, en fournissant un modèle analytique ainsi que des résultats de simulation. En outre, plusieurs schémas d’optimisationde MARSALA sont proposés tels que le principe du ‘MaximumRatio Combining’, ou la transmissiondes paquets à des puissances différentes. Utilisées conjointement, ces différentespropositions permettent d’obtenir une amélioration très significative des performances. Enfin,nous montrons qu’en choisissant la configuration optimale pour MARSALA, le gain deperformance est considérablement amélioré. / With the need to provide the Internet access to deprived areas and to cope with constantlyenlarging satellite networks, enhancing satellite communications becomes a crucial challenge.In this context, the use of Random Access (RA) techniques combined with dedicated accesson the satellite return link, can improve the system performance. However conventionalRA techniques like Aloha and Slotted Aloha suffer from a high packet loss rate caused bydestructive packet collisions. For this reason, those techniques are not well-suited for datatransmission in satellite communications. Therefore, researchers have been studying andproposing new RA techniques that can cope with packet collisions and decrease the packet lossratio. In particular, recent RA techniques involving information redundancy and successiveinterference cancellation, have shown some promising performance gains.With such methods that can function in high load regimes and resolve packets with high collisions,channel estimation is not an evident task. As a first contribution in this dissertation, wedescribe an improved channel estimation scheme for packets in collision in new RAmethodsin satellite communications. And we analyse the impact of residual channel estimation errorson the performance of interference cancellation. The results obtained show a performancedegradation compared to the perfect channel knowledge case, but provide a performanceenhancement compared to existing channel estimation algorithms. Another contribution of this thesis is presenting a method called Multi-Replica Decoding using Correlation based Localisation (MARSALA). MARSALA is a new decoding technique for a recent synchronous RAmethod called Contention Resolution Diversity Slotted Aloha (CRDSA). Based on packets replication and successive interference cancellation, CRDSA enables to significantly enhance the performance of legacy RA techniques. However, if CRDSA is unable to resolve additional packets due to high levels of collision, MARSALA is applied. At the receiver side, MARSALA takes advantage of correlation procedures to localise the replicas of a given packet, then combines the replicas in order to obtain a better Signal to Noise plus Interference Ratio. Nevertheless, the performance ofMARSALA is highly dependent on replicas synchronisation in timing and phase, otherwise replicas combination would not be constructive. In this dissertation, we describe an overall framework ofMARSALA including replicas timing and phase estimation and compensation, then channel estimation for theresulting signal. This dissertation also provides an analytical model for the performancedegradation of MARSALA due to imperfect replicas combination and channel estimation.In addition, several enhancement schemes forMARSALA are proposed likeMaximum RatioCombining, packets power unbalance, and various coding schemes. Finally, we show thatby choosing the optimal design configuration for MARSALA, the performance gain can besignificantly enhanced.