Interference Mitigation and Localization Based on Time-Frequency Analysis for Navigation Satellite Systems

Interference Mitigation and Localization Based on Time-Frequency Analysis for Navigation Satellite SystemsNowadays, the operation of global navigation satellite systems (GNSS) is imperative across a multitude of applications worldwide. The increasing reliance on accurate positioning and timing information has made more serious than ever the consequences of possible service outages in the satellite navigation systems. Among others, interference is regarded as the primary threat to their operation. Due the recent proliferation of portable interferers, notably jammers, it has now become common for GNSS receivers to endure simultaneous attacks from multiple sources of interference, which are likely spatially distributed and transmit different modulations. To the best knowledge of the author, the present dissertation is the first publication to investigate the use of the S-transform (ST) to devise countermeasures to interference. The original contributions in this context are mainly: • the formulation of a complexity-scalable ST implementable in real time as a bank of filters; • a method for characterizing and localizing multiple in-car jammers through interference snapshots that are collected by separate receivers and analysed with a clever use of the ST; • a preliminary assessment of novel methods for mitigating generic interference at the receiver end by means the ST and more computationally efficient variants of the transform. Besides GNSSs, the countermeasures to interference proposed are equivalently applicable to protect any direct-sequence spread spectrum (DS-SS) communication

Treatise on Hearing: The Temporal Auditory Imaging Theory Inspired by Optics and Communication

A new theory of mammalian hearing is presented, which accounts for the auditory image in the midbrain (inferior colliculus) of objects in the acoustical environment of the listener. It is shown that the ear is a temporal imaging system that comprises three transformations of the envelope functions: cochlear group-delay dispersion, cochlear time lensing, and neural group-delay dispersion. These elements are analogous to the optical transformations in vision of diffraction between the object and the eye, spatial lensing by the lens, and second diffraction between the lens and the retina. Unlike the eye, it is established that the human auditory system is naturally defocused, so that coherent stimuli do not react to the defocus, whereas completely incoherent stimuli are impacted by it and may be blurred by design. It is argued that the auditory system can use this differential focusing to enhance or degrade the images of real-world acoustical objects that are partially coherent. The theory is founded on coherence and temporal imaging theories that were adopted from optics. In addition to the imaging transformations, the corresponding inverse-domain modulation transfer functions are derived and interpreted with consideration to the nonuniform neural sampling operation of the auditory nerve. These ideas are used to rigorously initiate the concepts of sharpness and blur in auditory imaging, auditory aberrations, and auditory depth of field. In parallel, ideas from communication theory are used to show that the organ of Corti functions as a multichannel phase-locked loop (PLL) that constitutes the point of entry for auditory phase locking and hence conserves the signal coherence. It provides an anchor for a dual coherent and noncoherent auditory detection in the auditory brain that culminates in auditory accommodation. Implications on hearing impairments are discussed as well.Comment: 603 pages, 131 figures, 13 tables, 1570 reference

RFI Mitigation for VLBI and Arrays - Water Megamasers in Active Galaxies

This thesis studies the central parsec in active galaxies via spectral line observations of OH and water megamasers and millimeter-wave interferometry. The aims are four-fold: 1) measure the mass of the supermassive black hole in active galactic nuclei (AGN) through circumnuclear water maser observations, 2) measure the Hubble constant through circumnuclear water maser observations, 3) mitigate the radio frequency interference that degrades spectral line observations, and 4) probe the innermost regions of AGN by expanding a mm-wavelength interferometer. The current paradigm conjectures that AGN contain a supermassive black hole The high spatial resolution of very long baseline radio interferometry (VLBI) allows to track AGN-launched jets over pc to kilo-pc scales outside an AGN. Within AGN, water megamaser emission mapped by VLBI is an excellent tracer of the sub-pc structure, in particular of the accretion disk. Its rotation curve, traced by water masers, allows an accurate SMBH mass measurement, important for constraining the empirical relation between black hole mass and stellar velocity dispersion in the galactic bulge – current evidence suggest that this MBH–sigma -relation is not universal, indicating differences in SMBH feeding, accretion history and AGN evolution. Disk masers further yield accurate distances to nearby maser galaxies by an almost purely geometric means. This allows measuring the current rate of expansion of the Universe, described by the Hubble constant, H0, an important cosmological parameter. To constrain DE models the key goal of the Megamaser Cosmology Project (MCP; Braatz, NRAO) is to measure H0 to at least 3% precision. Relatively few (~5%) active galaxies have been detected in water masers. In this thesis I carried out a water maser survey in nearby galaxies, some with AGN, some also detected in the dissociation product of water, the neutral hydroxyl radical (OH). Four new water masers were detected, including OH-detected galaxies, such as NGC 4261 famous for its dusty torus. The MCP project by J. Braatz et al. conducts 22 GHz VLBI and single-dish observations of disk maser galaxies. I analyzed the data of three quite different maser galaxies with putative AGN (NGC 23, UGC 3193 and IC 2560). The maser data for NGC 23 suggest either an association with a possibly truncated low-luminosity jet, or exceptionally luminous nuclear /extranuclear star formation masers. The AGN disk water masers in UGC 3193 reveal a large accretion disk with two rings suggestive of a disrupted disk around a low central SMBH mass of about 0.6+-0.2 x 10^6 Msun The disk masers in IC 2560 on the other hand indicate a SMBH mass of 5.4^+0.9_-0.6 x 10^6 Msun, and undermassive in the common MBH-sigma -relation, consistent the trend seen in other water maser galaxies. The IC 2560 disk masers also allowed the Hubble constant to be measured, resulting in an H0 of 67.7^+11.6_-8:9 km/s/Mpc. Combined with recent MCP results (UGC 3789, NGC 6264) this yields a new maser-based Hubble constant of 68.4+-5.3 km/s/Mpc (8%). Spectral lines observations are often degraded by man-made radio frequency interference (RFI). Thus I also discuss two techniques for mitigating RFI. The first was implemented in a popular VLBI software correlator. I evaluate the theoretical and practical performance, also in a VLBI search for 1.6 GHz OH in tori of Cygnus A and NGC 1068. I find the mitigation method to be effective but limited in practice due to the particular software correlator architecture. The second method improves over two existing approaches for antenna arrays, including focal plane arrays. While current instrumentation did not allow an immediate application, e.g., in the maser survey, I find that the method shows great potential for future observations in presence of RFI. Lastly, our recent work on expanding a global sub-millimeter VLBI array has enabled extreme angular resolution, suffcient to resolve the SMBH/disk system and the jet launching region. I present the first 230 GHz VLBI observation of the core region of blazar 3C 279. The work allows extreme-resolution observations of, e.g., Sgr A* and the SMBHs in M87 that will lead to a better understanding of SMBH spin, accretion, and jet launching

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion

Evolutionary genomics : statistical and computational methods

This open access book addresses the challenge of analyzing and understanding the evolutionary dynamics of complex biological systems at the genomic level, and elaborates on some promising strategies that would bring us closer to uncovering of the vital relationships between genotype and phenotype. After a few educational primers, the book continues with sections on sequence homology and alignment, phylogenetic methods to study genome evolution, methodologies for evaluating selective pressures on genomic sequences as well as genomic evolution in light of protein domain architecture and transposable elements, population genomics and other omics, and discussions of current bottlenecks in handling and analyzing genomic data. Written for the highly successful Methods in Molecular Biology series, chapters include the kind of detail and expert implementation advice that lead to the best results. Authoritative and comprehensive, Evolutionary Genomics: Statistical and Computational Methods, Second Edition aims to serve both novices in biology with strong statistics and computational skills, and molecular biologists with a good grasp of standard mathematical concepts, in moving this important field of study forward

Evolutionary Genomics

This open access book addresses the challenge of analyzing and understanding the evolutionary dynamics of complex biological systems at the genomic level, and elaborates on some promising strategies that would bring us closer to uncovering of the vital relationships between genotype and phenotype. After a few educational primers, the book continues with sections on sequence homology and alignment, phylogenetic methods to study genome evolution, methodologies for evaluating selective pressures on genomic sequences as well as genomic evolution in light of protein domain architecture and transposable elements, population genomics and other omics, and discussions of current bottlenecks in handling and analyzing genomic data. Written for the highly successful Methods in Molecular Biology series, chapters include the kind of detail and expert implementation advice that lead to the best results. Authoritative and comprehensive, Evolutionary Genomics: Statistical and Computational Methods, Second Edition aims to serve both novices in biology with strong statistics and computational skills, and molecular biologists with a good grasp of standard mathematical concepts, in moving this important field of study forward