Application of advanced on-board processing concepts to future satellite communications systems: Bibliography

Abstracts are presented of a literature survey of reports concerning the application of signal processing concepts. Approximately 300 references are included

Exploração de Covert Channels de Rede sobre comunicações IEEE 802.15.4

The advancements in information and communication technology in the past decades have been converging into a new communication paradigm in which everything is expected to be interconnected with the heightened pervasiveness and ubiquity of the Internet of Things (IoT) paradigm. As these technologies mature, they are increasingly finding its way into more sensitive domains, such as Medical and Industrial IoT, in which safety and cyber-security are paramount. While the number of deployed IoT devices continues to increase annually, up to tens of billions of connected devices, IoT devices continue to present severe cyber-security vulnerabilities, which are worsened by challenges such as scalability, heterogeneity, and their often scarce computing capacity. Network covert channels are increasingly being used to support malware with stealthy behaviours, aiming at exfiltrating data or to orchestrate nodes of a botnet in a cloaked fashion. Nevertheless, the attention to this problem regarding underlying and pervasive IoT protocols such as the IEEE 802.15.4 has been scarce. Therefore, in this Thesis, we aim at analysing the performance and feasibility of such covertchannel implementations upon the IEEE 802.15.4 protocol to support the development of new mechanisms and add-ons that can effectively contribute to improve the current state of-art of IoT systems which rely on such, or similar underlying communication technologies.Os avanços nas tecnologias de informação e comunicação nas últimas décadas têm convergido num novo paradigma de comunicação, onde se espera que todos os intervenientes estejam interconectados pela ubiquidade do paradigma da Internet of Things (Internet das Coisas). Com a maturação destas tecnologias, elas têm-se vindo a infiltrar em domínios cada vez mais sensíveis, como nas aplicações médicas e industriais, onde a confiabilidade da informação e cyber-segurança são um fator crítico. Num contexto onde o número de dispositivos IoT continua a aumentar anualmente, já na ordem das dezenas de biliões de dispositivos interconectados, estes continuam, contudo, a apresentar severas vulnerabilidades no campo da cyber-segurança, sendo que os desafios como a escalabilidade, heterogeneidade e, na maioria das vezes, a sua baixa capacidade de processamento, tornam ainda mais complexa a sua resolução de forma permanente. Os covert channels de rede são cada vez mais um meio de suporte a malwares que apresentam comportamentos furtivos, almejando a extração de informação sensível ou a orquestração de nós de uma botnet de uma forma camuflada. Contudo, a atenção dada a este problema em protocolos de rede IoT abrangentes como o IEEE 802.15.4, tem sido escassa. Portanto, nesta tese, pretende-se elaborar uma análise da performance e da viabilidade da implementação de covert channels em modelos de rede onde figura o protocolo IEEE 802.15.4 de forma a suportar o desenvolvimento de novos mecanismos e complementos que podem efetivamente contribuir para melhorar a ciber-segurança de sistemas IoT que dependem do suporte destas tecnologias de comunicação

System design and validation of multi-band OFDM wireless communications with multiple antennas

[no abstract

Development of functional safety applications for Autec products. Study of protocols: CANopen, CANopen Safety, FSOE and ProfiSafe

This thesis has the principal goal of developing intrinsic safety applications in distributed real-time industrial systems, mainly based on fieldbuses and RTE networks. To achieve this important objective the first part of this elaborate provides an introduction of the principal protocols, such as CANopen Safety, Fail safe Over Ethercat (FSOE) and Profisafe, used for the safety relevant applications in the automation environment,analysing properties,story and the use of them by industry

Ultrafast exciton relaxation in quasi-one-dimensional perylene derivatives

This thesis deals with exciton relaxation processes in thin polycrystalline films and matrix-isolated molecules of the perylene derivatives PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride) and MePTCDI (N,N'-dimethylperylene-3,4,9,10-dicarboximide). Using femtosecond pump-probe spectroscopy, transient absorption spectra, excitonic relaxation in the lowest excited state subsequent to excitation, and exciton-exciton interaction and annihilation at high excitation densities have been addressed. Transient absorption spectroscopy in the range 1.2eV-2.6eV has been applied to thin polycrystalline films of PTCDA and MePTCDI and to solid solutions of PTCDA and MePTCDI molecules (monomers) in a SiO2 matrix. We are able to ascribe the respective signal contributions to ground state bleaching, stimulated emission, and excited state absorption. Both systems exhibit broad excited-state absorption features below 2.0eV, with dominant peaks between 1.8eV and 2.0eV. The monomer spectra can be consistently explained by the results of quantum-chemical calculations on single molecules, and the respective experimental polarization anisotropies for the two major transitions agree with the calculated polarizations. Dimer calculations allow to qualitatively understand the trends visible in the experimental results from monomers to thin films. The broad excited state absorption band between 1.8eV and 2.0eV allows to probe the population dynamics in the first excited state of thin films. We show that excitons created at the Gamma point relax towards the border of the Brillouin zone on a 100fs time scale in both systems. Excitonic relaxation is accelerated by increase of temperature and/or excitation density, which is attributed to stimulated phonon emission during relaxation in k-space. Lower and upper limits of the intraband relaxation time constants are 25fs (resolution limit) and 250fs (100fs) for PTCDA (MePTCDI). These values agree with the upper limit for the intraband relaxation time of 10ps, evaluated from time-resolved luminescence measurements. While the luminescence anisotropy is in full accordance with the predictions made by a luminescence anisotropy model being consistent with the exciton model of Davydov-split states, the pump-probe anisotropy calls for an explanation beyond the models presently available. At excitation densities 10^(19)cm^(-3), the major de-excitation mechanism for the relaxed excitons is exciton-exciton annihilation, resulting in a strongly reduced exciton life time. Three different models for the microscopic behavior have been tested: a diffusion-limited annihilation model in both three and one dimensions (with diffusion constant D as fit parameter) as well as a long-range single-step Förster-type annihilation model (with Förster radius RF as fit parameter). For PTCDA, the latter two, being structurally equivalent, allow to fit a set of multiexponential decay curves for multiple initial exciton densities with high precision. In contrast, the three-dimensional diffusion-limited model is clearly inferior. For all three models, we extract annihilation rates, diffusion constants and diffusion lengths (or Förster radii), for both room and liquid helium temperature. Temperature dependence and orders of magnitude of the obtained parameters D or RF correspond to the expectations. For MePTCDI, the 1D and the Förster model are in good agreement for a smaller interval of excitation densities. For a initial exciton densities higher than 5 x 10^(19)cm^(-3), the 3D model performs significantly better than the other two

Enhancing mobile services with DVB-S2X superframing

DVB-S2X is the cornerstone for satellite communication standards forming the state of the art of broadband satellite waveforms. In this paper, we propose new application scenarios and advanced techniques, including a reference design implementing superframing, predistortion, a robust synchronization chain, and a plug-and-play channel interleaver. We demonstrate by means of software simulations and hardware tests that the DVB-S2X can be a common technology enabler for land-mobile, aeronautical, and maritime satellite scenarios in addition to the more traditional VSAT scenario, even in very challenging conditions (eg, very low signal-to-noise ratio)

Personal area networks (PAN) : near-field intra-body communication

Thesis (M.S.)--Massachusetts Institute of Technology, Program in Media Arts & Sciences, 1995.Includes bibliographical references (leaves 80-81).by Thomas Guthrie Zimmerman.M.S

Distributed Topology Organization and Transmission Scheduling in Wireless Ad Hoc Networks

An ad hoc network is a set of nodes that spontaneously form a multi-hop all-wireless infrastructure without centralized administration. We study two fundamental issues arising in this setting: topology organization and transmission scheduling. In topology organization we consider a system where nodes need to coordinate their transmissions on a non-broadcast frequency hopping channel to discover each other. We devise a symmetric technique where two nodes use a randomized schedule to synchronize and connect in minimum time. This forms the basis for a topology construction protocol where a set of initially unsynchronized nodes are quickly grouped in multiple interconnected communication channels such that the resulting topology is connected subject to channel membership constraints imposed by the physical layer. In the transmission scheduling problem we consider Time Division Multiple Access (TDMA)the network operates with a schedule where at each slot transmissions can be scheduled without conflicts at the intended receivers. TDMA can provide deterministic allocations but typically relies on two restrictive assumptions: network-wide slot synchronization and global knowledge of network topology and traffic requirements. We first introduce an asynchronous TDMA communication model where slot reference for each link is provided locally by the clock of one of the node endpoints. We study the overhead introduced when nodes switch among multiple time references and propose algorithms for its minimization. We then introduce a distributed asynchronous TDMA protocol where nodes dynamically adjust the rates their adjacent links via local slot reassignments to reach a schedule that realizes a set of optimal link rates. We introduce fairness models for both links and multi-hop sessions sharing the network and devise convergent distributed algorithms for computing the optimal rates for each model. These rates are enforced by a distributed algorithm that decides the slots reassigned during each link rate adjustment. For tree topologies we introduce an algorithm that incrementally converges to the optimal schedule in finite time; for arbitrary topologies an efficient heuristic is proposed. Both topology organization and transmission scheduling protocols are implemented over Bluetooth, a technology enabling ad hoc networking applications. Through extensive simulations they demonstrate excellent performance in both static and dynamic scenarios

Data Aggregation and Cross-layer Design in WSNs

Over the past few years, advances in electrical engineering have allowed electronic devices to shrink in both size and cost. It has become possible to incorporate environmental sensors into a single device with a microprocessor and memory to interpret the data and wireless transceivers to communicate the data. These sensor nodes have become small and cheap enough that they can be distributed in very large numbers into the area to be monitored and can be considered disposable. Once deployed, these sensor nodes should be able to self-organize themselves into a usable network. These wireless sensor networks, or WSNs, differ from other ad hoc networks mainly in the way that they are used. For example, in ad hoc networks of personal computers, messages are addressed from one PC to another. If a message cannot be routed, the network has failed. In WSNs, data about the environment is requested by the data sink. If any or multiple sensor nodes can return an informative response to this request, the network has succeeded. A network that is viewed in terms of the data it can deliver as opposed to the individual devices that make it up has been termed a data-centric network [26]. The individual sensor nodes may fail to respond to a query, or even die, as long as the final result is valid. The network is only considered useless when no usable data can be delivered. In this thesis, we focus on two aspects. The first is data aggregation with accurate timing control. In order to maintain a certain degree of service quality and a reasonable system lifetime, energy needs to be optimized at every stage of system operation. Because wireless communication consumes a major amount of the limited battery power for these sensor nodes, we propose to limit the amount of data transmitted by combining redundant and complimentary data as much as possible in order to transmit smaller and fewer messages. By using mathematical models and computer simulations, we will show that our aggregation-focused protocol does, indeed, extend system lifetime. Our secondary focus is a study of cross-layer design. We argue that the extremely specialized use of WSNs should convince us not to adhere to the traditional OSI networking model. Through our experiments, we will show that significant energy savings are possible when a custom cross-layer communication model is used