Secure Satellite Communication Systems Design with Individual Secrecy Rate Constraints

In this paper, we study multibeam satellite secure communication through physical (PHY) layer security techniques, i.e., joint power control and beamforming. By first assuming that the Channel State Information (CSI) is available and the beamforming weights are fixed, a novel secure satellite system design is investigated to minimize the transmit power with individual secrecy rate constraints. An iterative algorithm is proposed to obtain an optimized power allocation strategy. Moreover, sub-optimal beamforming weights are obtained by completely eliminating the co-channel interference and nulling the eavesdroppers' signal simultaneously. In order to obtain jointly optimized power allocation and beamforming strategy in some practical cases, e.g., with certain estimation errors of the CSI, we further evaluate the impact of the eavesdropper's CSI on the secure multibeam satellite system design. The convergence of the iterative algorithm is proven under justifiable assumptions. The performance is evaluated by taking into account the impact of the number of antenna elements, number of beams, individual secrecy rate requirement, and CSI. The proposed novel secure multibeam satellite system design can achieve optimized power allocation to ensure the minimum individual secrecy rate requirement. The results show that the joint beamforming scheme is more favorable than fixed beamforming scheme, especially in the cases of a larger number of satellite antenna elements and higher secrecy rate requirement. Finally, we compare the results under the current satellite air-interface in DVB-S2 and the results under Gaussian inputs.Comment: 34 pages, 10 figures, 1 table, submitted to "Transactions on Information Forensics and Security

Modern optical astronomy: technology and impact of interferometry

The present `state of the art' and the path to future progress in high spatial resolution imaging interferometry is reviewed. The review begins with a treatment of the fundamentals of stellar optical interferometry, the origin, properties, optical effects of turbulence in the Earth's atmosphere, the passive methods that are applied on a single telescope to overcome atmospheric image degradation such as speckle interferometry, and various other techniques. These topics include differential speckle interferometry, speckle spectroscopy and polarimetry, phase diversity, wavefront shearing interferometry, phase-closure methods, dark speckle imaging, as well as the limitations imposed by the detectors on the performance of speckle imaging. A brief account is given of the technological innovation of adaptive-optics (AO) to compensate such atmospheric effects on the image in real time. A major advancement involves the transition from single-aperture to the dilute-aperture interferometry using multiple telescopes. Therefore, the review deals with recent developments involving ground-based, and space-based optical arrays. Emphasis is placed on the problems specific to delay-lines, beam recombination, polarization, dispersion, fringe-tracking, bootstrapping, coherencing and cophasing, and recovery of the visibility functions. The role of AO in enhancing visibilities is also discussed. The applications of interferometry, such as imaging, astrometry, and nulling are described. The mathematical intricacies of the various `post-detection' image-processing techniques are examined critically. The review concludes with a discussion of the astrophysical importance and the perspectives of interferometry.Comment: 65 pages LaTeX file including 23 figures. Reviews of Modern Physics, 2002, to appear in April issu

Dyson-Schwinger Equations: Density, Temperature and Continuum Strong QCD

Continuum strong QCD is the application of models and continuum quantum field theory to the study of phenomena in hadronic physics, which includes; e.g., the spectrum of QCD bound states and their interactions; and the transition to, and properties of, a quark gluon plasma. We provide a contemporary perspective, couched primarily in terms of the Dyson-Schwinger equations but also making comparisons with other approaches and models. Our discourse provides a practitioners' guide to features of the Dyson-Schwinger equations [such as confinement and dynamical chiral symmetry breaking] and canvasses phenomenological applications to light meson and baryon properties in cold, sparse QCD. These provide the foundation for an extension to hot, dense QCD, which is probed via the introduction of the intensive thermodynamic variables: chemical potential and temperature. We describe order parameters whose evolution signals deconfinement and chiral symmetry restoration, and chronicle their use in demarcating the quark gluon plasma phase boundary and characterising the plasma's properties. Hadron traits change in an equilibrated plasma. We exemplify this and discuss putative signals of the effects. Finally, since plasma formation is not an equilibrium process, we discuss recent developments in kinetic theory and its application to describing the evolution from a relativistic heavy ion collision to an equilibrated quark gluon plasma.Comment: 103 Pages, LaTeX, epsfig. To appear in Progress in Particle and Nuclear Physics, Vol. 4

Prevention of extreme roll motion through measurements of ship's motion responses

PhD ThesisExploring the operational links between a sea state and a ship’s heading and speed provides the opportunity to continuously monitor dynamic stability behaviour; and hence to avoid significant changes of stability in adverse weather. Significant changes of stability at sea can lead to dangerous transient situations and eventually stability failure. Despite its importance, the current intact stability (IS) criteria do not evaluate or consider the dynamics of the motion responses of a vessel in a wave environment. In this thesis, the full six degrees of freedom motion responses of two models have been tested in irregular waves under intact vessel conditions. The general modelling approach for a mathematical model was based on numerical simulations at different speeds, sea conditions and angle of heading relative to the waves. In the second model, a physical model was tested in a towing tank under similar simulated environmental conditions to that employed for the first model. The investigation was limited to the effects of encountered frequency components and the associated magnitude of energy of the ship’s motion responses. An analysis of heave, pitch and roll motion confirmed the vulnerability of the model to certain wave-excited frequency ranges. This particular range of frequency results in an adverse effect on the amplitude of the responses, and these were closely related to the natural mode frequencies and related coupling effects. It was confirmed that the roll motion maintains its highest oscillation amplitude at around the natural frequency in all sea conditions regardless of ship heading angles. It was also observed that spectral analysis of the heave and pitch responses revealed the wave peak frequency. Roll is magnified when the peak frequency of the waves approaches the natural roll frequency, therefore keeping them sufficiently apart avoids potentially large motion responses. It was concluded that peak frequency and associated magnitude are the two important inherent characteristics of motion responses. Detection of the most influential parameters of encountered waves through measurements of heave and pitch responses could be utilised to provide a method to limit the large motion of a ship at sea. The measurement of waves whilst a ship is underway is a major challenge, whereas ship motion, which is relatively easily measured, is a good indirect reflection of the encountered wave characteristics and which can be measured, stored and analysed using Prevention of extreme roll motion through measurements of ship’s motion responses iv on-board equipment. Motion responses are considered as continuous signals with a time-dependent spectral content, and signal processing is a suitable technique for detection, estimation and analysis of recorded time-varying signals. The method is fast enough to be considered as an on-board real-time monitoring of dynamic stability. Signal processing techniques are used in the detection and estimation of the influential parameters of a wave environment through the analysis of motion responses. The variables of the system were detected by spectral analysis of the heave and pitch motions. These variables are the peak wave frequencies and associated magnitudes which can cause a large roll motion when reasonably close to the ship’s natural roll frequency. The instantaneous frequency (IF) present in the signal is revealed through spectral analysis of short-time Fourier transforms (STFT) in less than a minute. The IF is a parameter of practical importance which can be used in real-time on-board decision making processes to enable the vessel to take actions in order to avoid large roll motions

Darwin -— an experimental astronomy mission to search for extrasolar planets

As a response to ESA call for mission concepts for its Cosmic Vision 2015–2025 plan, we propose a mission called Darwin. Its primary goal is the study of terrestrial extrasolar planets and the search for life on them. In this paper, we describe different characteristics of the instrument

Foreground simulations for the LOFAR - Epoch of Reionization Experiment

Future high redshift 21-cm experiments will suffer from a high degree of contamination, due both to astrophysical foregrounds and to non-astrophysical and instrumental effects. In order to reliably extract the cosmological signal from the observed data, it is essential to understand very well all data components and their influence on the extracted signal. Here we present simulated astrophysical foregrounds datacubes and discuss their possible statistical effects on the data. The foreground maps are produced assuming 5 deg x 5 deg windows that match those expected to be observed by the LOFAR Epoch-of-Reionization (EoR) key science project. We show that with the expected LOFAR-EoR sky and receiver noise levels, which amount to ~52 mK at 150 MHz after 300 hours of total observing time, a simple polynomial fit allows a statistical reconstruction of the signal. We also show that the polynomial fitting will work for maps with realistic yet idealised instrument response, i.e., a response that includes only a uniform uv coverage as a function of frequency and ignores many other uncertainties. Polarized galactic synchrotron maps that include internal polarization and a number of Faraday screens along the line of sight are also simulated. The importance of these stems from the fact that the LOFAR instrument, in common with all current interferometric EoR experiments has an instrumentally polarized response.Comment: 18 figures, 3 tables, accepted to be published in MNRA

The hunt for quasi-periodicities with wavelet and camera

Includes abstract. Includes bibliographical references (p. 357-379)