Adaptive bootstrap signal separators for BPSK/QAM-modulated wireless CDMA systems in a multipath environment

CDMA is an attractive multiple-access scheme, because of its potential capacity increase and its anti-multipath fading capability. For satisfactory performance, however, the effect of the near-far problem has to be resolved. This problem can be combated by using power-control, which, however, results in an overall reduction in communication ranges, and thus in a loss of capacity. Among other methods for mitigating the near-far problem is the use of decorrelating receivers, both of fixed type, which directly utilizes the cross-correlation of the users codes, and of adaptive type, which uses recursive algorithms that leads to signal decorrelation. Not to lessen the importance of other adaptive algorithms, the current research concentrates on what was termed in the literature bootstrap algorithm . Although the emphasis will be on applying the adaptive bootstrap decorrelator, the fixed type will be used primarily to provide comparison. Also used for comparison are both blind adaptive and training sequence based MMSE. Most of the literature on multiuser detection has been assuming BPSK. However, a need for transferring wideband data demands using modulation schemes with high bits/cycle, such as QAM. Therefore, modification of the receiver is considered, so that QAM-modulation can be applied efficiently, using the complex signal approach of this modulation. For the asynchronous channel, vast amounts of research have been devoted to using one-shot matched filter banks followed by conventional decorrelators which implement the inverse of some (partial) correlation matrix. In this work, an adaptive bootstrap version is presented, which is suitable for the one-shot structure shown previously to be more robust to errors in delay estimation. It has also been noted that such a correlation matrix can, depending on the channel characteristics, become ill-conditioned or even singular. Therefore, another matched filtering structure, followed by what is called a multishot conventional (fixed type) decorrelator, has been previously suggested to mitigate this singularity problem. However, the fixed type of the multishot decorrelator is expected to have similar non-robustness to errors in delay estimation as was previously shown for the one-shot. Therefore, the adaptive multishot bootstrap decorrelator is presented and evaluated. Also, by adding an adaptive canceler, an extension to the above matched filter-decorrelator combination, will be proposed and evaluated. A multipath time-variant fading environment will be used in some of these performance evaluations. Finally, when handling multipath channels, the question is raised whether path combining should be done before or after the signals are decorrelated. For the asynchronous case, a one-shot extension of the bootstrap algorithm is presented, which is capable of decorrelating the signals from resolved paths of different users, to facilitate the decorrelate before combining case

Clustering Via Supervised Support Vector Machines

An SVM-based clustering algorithm is introduced that clusters data with no a priori knowledge of input classes. The algorithm initializes by first running a binary SVM classifier against a data set with each vector in the set randomly labeled. Once this initialization step is complete, the SVM confidence parameters for classification on each of the training instances can be accessed. The lowest confidence data (e.g., the worst of the mislabeled data) then has its labels switched to the other class label. The SVM is then re-run on the data set (with partly re-labeled data). The repetition of the above process improves the separability until there is no misclassification. Variations on this type of clustering approach are shown

Clustering Via Supervised Support Vector Machines

An SVM-based clustering algorithm is introduced that clusters data with no a priori knowledge of input classes. The algorithm initializes by first running a binary SVM classifier against a data set with each vector in the set randomly labeled. Once this initialization step is complete, the SVM confidence parameters for classification on each of the training instances can be accessed. The lowest confidence data (e.g., the worst of the mislabeled data) then has its labels switched to the other class label. The SVM is then re-run on the data set (with partly re-labeled data). The repetition of the above process improves the separability until there is no misclassification. Variations on this type of clustering approach are shown

Adaptation and Control State Detection Techniques for Brain-Computer Interfaces

Ph.DDOCTOR OF PHILOSOPH

The three-dimensional topology of magnetic fields in and around sunspots

The most prominent features on the surface of the solar disc are the sunspots, which have been studied since their detection in the 17th century. Despite this years and centuries of scientific investigations, surprisingly many facets of sunspots are not well understood. In this thesis, the properties of a sunspots' penumbra are derived from the observed spectra by means of an inversion, a forward modeling technique. A method for the construction of a 3-dimensional model of the field topology from the inversion results is presented. It offers the possibility to build a toy-model of the spot. This allows to investigate the relationships between the geometry and other properties of the sunspot like flow velocities, intensity, temperature, or field strength. The application of the procedure to time series of observations will allow to study the temporal evolution of the geometry and the other properties, to determine the physical processes happening and their respective drivers. A second part of the thesis is devoted to the analysis of isolated field concentrations in the surroundings of the sunspot. These isolated magnetic elements are assumed to be the elementary building blocks of the solar surface magnetism. In the turbulent surroundings of the solar atmosphere, only relatively strong concentrations with a field strength above 1 kG are assumed to be stable at all ...thesi

Space time coding in MIMO systems

Multiple-input multiple-output (MIMO) antenna technology is promising for high-speed wireless communications without increasing the transmission band- width. Space time coding (STC) is a scheme that employs multiple antennas to increase transmission rate or to improve transmission quality. STC is used widely in mobile cellular networks, wireless local area networks (WLAN) and wireless metropolitan area networks (WMAN). However, there are still many unsolved or partially solved issues in STC. In this thesis, I propose a new STC design from cyclic design. I then propose a systematic method to design quasi-orthogonal space time block codes (QOSTBC) for an arbitrary number of transmit antennas, and derive the optimal constellation rotation angles to achieve full diversity. I also propose an analytical method to derive the exact error probabilities of orthogonal space time block codes (OSTBC). In order to improve the error performance, I introduce an adaptive power allocation scheme for OSTBC. Combining STC with continuous phase modulation (CPM) is an attractive solution for mobile commu- nications for which power is limited. Thus, I apply OSTBC to binary CPM with modulation index h = 0.5, and develop a simplified receiver for such scheme. Finally, I present a decoding method to reduce the complexity of QOSTBC without degrading its error performance

High-power few-cycle pulse generation towards the gigawatt frontier

The advent of precision spectroscopic techniques has brought about diverse opportunities in extending our understanding of fundamental physics and bio-medical sciences. This is especially true when harnessing radiation in the exotic extreme ultra-violet (XUV) and mid-infrared (IR) regions of the electromagnetic spectrum. While the former covers a multitude of atomic and molecular electronic transitions, the latter contains fundamental vibrational and rotational modes of numerous biologically-relevant molecules. Regardless of spectral range, many of the novel spectroscopic methodologies rely on the availability of broadband, waveform-controlled radiation with high brightness. The lack of suitable laser gain media in the aforementioned wavelength ranges means such radiation is conventionally generated by nonlinearly converting high-power, femtosecond laser pulses in the near-IR spectral range, such as those generated by thin-disk oscillators. However, those pulses generally have durations in the hundreds of femtoseconds — too long for the desired high peak-power and broad spectral coverage for effective nonlinear frequency conversion. Their electric waveform also varies randomly from pulse to pulse, hindering their applications to, among others, frequency-comb spectroscopy. This thesis describes the experimental development of various techniques to further compress the pulse duration, and the active stabilization of the output waveform in high-power thin-disk oscillators. It is shown that dispersion-controlled Herriott-type multipass-cells constitute an efficient means to broaden the spectral bandwidth of laser pulses with, in contrast to many other techniques, practically no degradation to the spatial beam quality. It presents the first time Herriott-cells operating in the net-negative dispersion regime have been used for spectral broadening with thin-disk oscillators. The demonstration yielded the highest broadening factor obtained from any multipass-cell broadening scheme using a single nonlinear bulk medium. Spectral broadening in the positive dispersion regime is also described. Two Herriott-cells in tandem facilitated the generation of 15.6 fs pulses with an unprecedented peak power of 463 MW — a record for a system driven directly by a laser oscillator with no amplification stages. Further compression of this dual-stage output was achieved by introducing the distributed quasi-waveguide approach. This technique enables the independent tailoring of nonlinearity and dispersion, which is essential for pulse compression towards few-optical-cycle durations. With a pulse duration of 10.8 fs and a peak and average power of 0.64 GW and 101 W, respectively, this marks the dawn of a new class of gigawatt-scale amplifier-free thin-disk laser system. The few-cycle laser pulses are shown to drive, via intra-pulse difference-frequency generation, the formation of broadband, waveform-stable mid-IR radiation with an exceptionally short cut-off wavelength. The achieved spectral extension down to 3.6 µm (at -30 dB level), at an average output power of 7.6 mW, opens up new perspectives for extending field-resolved spectroscopy to the biologically important amide functional groups. To actively stabilize the near-IR driver laser waveform — crucial for deriving from it a frequency comb in the XUV region — a novel, power-scalable concept for controlling the carrier-envelope-offset (CEO) frequency of Kerr-lens mode-locked oscillators was developed. It yielded CEO-frequency-stable pulses with sub-90 mrad in-loop phase noise at an unprecedented average output power of 105 W. The envisioned combination of waveform control with the presented nonlinear pulse compression techniques will pave the way for a new generation of compact, low-noise frequency combs with high photon-flux in the XUV spectral range. The various advancements presented in this thesis not only mark a substantial development of the respective techniques themselves, but also represent a significant contribution to the coming-of-age of high-precision laser-based spectrometers for scientific and medical applications.Das Aufkommen hochpräziser Spektroskopiemethoden, insbesondere im extremen Ultraviolett (XUV) und im mittleren Infrarot, hat eine Vielzahl von Möglichkeiten eröffnet, unser Verständnis physikalischer und biomedizinischer Zusammenhänge grundlegend zu erweitern. Dabei deckt der XUV-Bereich eine große Anzahl elektronischer Übergänge in Atomen und Molekülen ab, während das mittlere Infrarot zahlreiche fundamentale Schwingungs- und Rotationsmoden verschiedenster biologisch relevanter Moleküle enthält. Unabhängig vom Spektralbereich sind viele dieser neuartigen Spektroskopieverfahren gleichermaßen auf die Verfügbarkeit von breitbandiger Strahlung mit einem kontrollierten Feldverlauf und einer hohen Brillanz angewiesen. Da es in den oben genannten Wellenlängenbereichen keine geeigneten Laserverstärkungsmedien gibt, wird derartige Strahlung üblicherweise durch die nichtlineare Frequenzkonversion von hochintensiven Femtosekunden-Laserimpulsen im Spektralbereich des nahen Infrarot erzeugt, wie sie beispielsweise von Dünnscheibenoszillatoren generiert werden. Diese Impulse haben jedoch im Allgemeinen eine Dauer von Hunderten von Femtosekunden — zu lang, um die gewünschte hohe Spitzenleistung und breite spektrale Abdeckung für eine effektive nichtlineare Frequenzumwandlung bereitstellen zu können. Außerdem variiert ihre elektrische Wellenform von Impuls zu Impuls nach dem Zufallsprinzip, was ihre Anwendung für beispielsweise die Frequenzkammspektroskopie behindert. Diese Arbeit beschreibt experimentelle Entwicklungen von Methoden zur weiteren Komprimierung der Impulsdauer sowie zur aktiven Stabilisierung des elektrischen Feldverlaufs von hochintensiven Dünnscheibenoszillatoren. Es wird gezeigt, dass dispersionskontrollierte Herriott-Multipasszellen ein effizientes Mittel zur Erweiterung der spektralen Bandbreite von Laserpulsen darstellen, wobei im Gegensatz zu vielen anderen Techniken nahezu keine Verschlechterung der räumlichen Strahlqualität auftritt. Erstmalig wurde die durch einen Dünnscheibenlaser getriebene spektrale Verbreiterung in einer Herriott-Zelle im negativen Dispersionsregime durchgeführt. Die spektrale Verbreiterung erreichte dabei höhere Verbreiterungsfaktoren, als sie jemals zuvor mit einem auf Multipass-Zellen basierenden Verbreiterungsschema mit einem einzigen nichtlinearen Medium erzielt wurden. Darüber hinaus wurde auch die spektrale Verbreiterung im positiven Dispersionsregime untersucht. Das Hintereinanderschalten zweier Herriott-Zellen ermöglichte die Erzeugung von 15.6 fs kurzen Impulsen mit einer zuvor unerreichten Spitzenleistung von 463 MW — ein Rekord für ein System, das ohne weitere Verstärkerstufen direkt von einem Laseroszillator getrieben wird. Die weitere zeitliche Kompression am Ausgang dieses zweistufigen Systems wurde mit dem Ansatz eines verteilten Quasi-Wellenleiters gelöst. Diese Technik ermöglicht die unabhängige Anpassung von Nichtlinearität und Dispersion, was für die Impulskompression in Richtung einer Dauer von wenigen optischen Zyklen unerlässlich ist. Mit einer Impulsdauer von lediglich 10.8 fs bei einer Spitzen- und Durchschnittsleistung von 0.64 GW und 101 W markieren die erzeugten Laserimpulse den Beginn einer neuen Ära von verstärkerfreien Dünnscheibenlasersystemen im Gigawattbereich. Des Weiteren wurden die beschriebenen Laserimpulse dafür genutzt, um mittels Differenzfrequenzerzeugung breitbandige und phasenstarre Strahlung im mittleren Infrarot zu erzeugen. Letztere zeichnet sich insbesondere durch ihre außergewöhnlich niedrige Grenzwellenlänge aus. Die erreichte spektrale Ausdehnung auf 3.6 µm (auf - 30 dB-Niveau) mit einer mittleren Ausgangsleistung von 7.6 mW eröffnet neue Perspektiven für die feldaufgelöste Spektroskopie von biologisch relevanten funktionellen Amidgruppen. Um die Wellenform des nahinfraroten Lasers aktiv zu stabilisieren — unabdingbar für die Ableitung eines Frequenzkamms im XUV-Spektralbereich — wurde ein neuartiges und leistungsskalierbares Konzept entwickelt. Dieses erlaubt, die Träger-Einhüllenden-Frequenz von Kerr-Linsen-modengekoppelten Oszillatoren zu kontrollieren und zu stabilisieren. Das dabei erreichte Phasenrauschen lässt sich auf weniger als 90 mrad bei einer beispiellosen Durchschnittsleistung von 105 W beziffern. Die mögliche Kombination einer Feldverlaufstabilisierung mit den zuvor vorgestellten nichtlinearen Pulskompressionstechniken ebnet den Weg für die Entwicklung einer neuen Generation kompakter oszillatorbasierter Frequenzkämme mit hohem Photonenfluss im XUV-Spektralbereich. Die zahlreichen in dieser Dissertation vorgestellten Entwicklungen beschränken sich nicht nur auf einen Fortschritt der jeweiligen Techniken selbst, sondern liefern auch einen wichtigen Beitrag für die zukünftige Entwicklung hochpräziser laserbasierter Spektrometer für wissenschaftliche und medizinische Anwendungen

Engineering Dynamics and Life Sciences

From Preface: This is the fourteenth time when the conference “Dynamical Systems: Theory and Applications” gathers a numerous group of outstanding scientists and engineers, who deal with widely understood problems of theoretical and applied dynamics. Organization of the conference would not have been possible without a great effort of the staff of the Department of Automation, Biomechanics and Mechatronics. The patronage over the conference has been taken by the Committee of Mechanics of the Polish Academy of Sciences and Ministry of Science and Higher Education of Poland. It is a great pleasure that our invitation has been accepted by recording in the history of our conference number of people, including good colleagues and friends as well as a large group of researchers and scientists, who decided to participate in the conference for the first time. With proud and satisfaction we welcomed over 180 persons from 31 countries all over the world. They decided to share the results of their research and many years experiences in a discipline of dynamical systems by submitting many very interesting papers. This year, the DSTA Conference Proceedings were split into three volumes entitled “Dynamical Systems” with respective subtitles: Vibration, Control and Stability of Dynamical Systems; Mathematical and Numerical Aspects of Dynamical System Analysis and Engineering Dynamics and Life Sciences. Additionally, there will be also published two volumes of Springer Proceedings in Mathematics and Statistics entitled “Dynamical Systems in Theoretical Perspective” and “Dynamical Systems in Applications”

The Telecommunications and Data Acquisition Report

Reports on developments in programs managed by JPL's Office of Telecommunications and Data Acquisition (TDA) are provided. In space communications, radio navigation, radio science, and ground-based radio and radar astronomy, it reports on activities of the Deep Space Network (DSN) in planning, supporting research and technology, implementation, and operations. Also included are standards activity at JPL for space data and information systems and reimbursable DSN work performed for other agencies through NASA