System performance criteria in CDMA networks using gold codes

First, we have presented the autocorrelation and crosscorrelation properties for periodic and aperiodic binary sequences. The generation of binary sequences using shift registers with feedback was reviewed. We have also included correlation properties for the Gold codes. Next, we discussed Gold code generation for the balanced and unbalanced Gold codes. Thirdly, we investigated the number of simultaneous users in a CDMA system using Gold codes for the worst case and the average case of mutual interference. Finally, we simulated the probability of interference exceeding a threshold value, and the average crosscorrelation value caused by interference in a CDMA network which is using a Gold code. We compared probability and average crosscorrelation values simulated with theoretical bounds calculated. Here the simulation programs are done in C computer language

Efficient Radio Resource Allocation Schemes and Code Optimizations for High Speed Downlink Packet Access Transmission

An important enhancement on the Wideband Code Division Multiple Access (WCDMA) air interface of the 3G mobile communications, High Speed Downlink Packet Access (HSDPA) standard has been launched to realize higher spectral utilization efficiency. It introduces the features of multicode CDMA transmission and Adaptive Modulation and Coding (AMC) technique, which makes radio resource allocation feasible and essential. This thesis studies channel-aware resource allocation schemes, coupled with fast power adjustment and spreading code optimization techniques, for the HSDPA standard operating over frequency selective channel. A two-group resource allocation scheme is developed in order to achieve a promising balance between performance enhancement and time efficiency. It only requires calculating two parameters to specify the allocations of discrete bit rates and transmitted symbol energies in all channels. The thesis develops the calculation methods of the two parameters for interference-free and interference-present channels, respectively. For the interference-present channels, the performance of two-group allocation can be further enhanced by applying a clustering-based channel removal scheme. In order to make the two-group approach more time-efficient, reduction in matrix inversions in optimum energy calculation is then discussed. When the Minimum Mean Square Error (MMSE) equalizer is applied, optimum energy allocation can be calculated by iterating a set of eigenvalues and eigenvectors. By using the MMSE Successive Interference Cancellation (SIC) receiver, the optimum energies are calculated recursively combined with an optimum channel ordering scheme for enhancement in both system performance and time efficiency. This thesis then studies the signature optimization methods with multipath channel and examines their system performances when combined with different resource allocation methods. Two multipath-aware signature optimization methods are developed by applying iterative optimization techniques, for the system using MMSE equalizer and MMSE precoder respectively. A PAM system using complex signature sequences is also examined for improving resource utilization efficiency, where two receiving schemes are proposed to fully take advantage of PAM features. In addition by applying a short chip sampling window, a Singular Value Decomposition (SVD) based interference-free signature design method is presented

Signatures of correlations and interactions in the optical spectra of localized excitons in carbon nanotubes

Kohlenstoffnanoröhren sind Nanostrukturen, deren Form einer einatomigen Lage Graphit, aufgerollt zu einem Hohlzylinder, entspricht. Die Ladungsträger in halbleitenden Kohlenstoffnanoröhren bilden stark gebundene Elektron-Loch-Paare (Exzitonen), die Photolumineszenz vom Rand des sichtbaren Spektrums bis in das Telekom-Band emittieren. Häufig sind Exzitonen in Kohlenstoffnanoröhren lokalisiert, z. B. an künstlichen Kristalldefekten. Ihre physikalischen Eigenschaften werden dann durch die Gesetze der Quantenmechanik bestimmt, was sie in Verbindung mit ihrer variablen Wellenlänge zu vielversprechenden Kandidaten für Anwendungen in der Quanteninformationsverarbeitung macht. Lokalisierte Exzitonen sind starken Wechselwirkungen mit ihrer Umgebung ausgesetzt, die einen Einblick in ihre physikalischen Eigenschaften erlauben. Die vorliegende Dissertation erarbeitet ein tieferes Verständnis dieser Wechselwirkungen, das auch hilfreich für technische Anwendungen ist. Dafür wurden sowohl schwach gebundene Exzitonen in flachen Potentialmulden als auch an künstlichen Defekten lokalisierte Exzitonen untersucht. Kohlenstoffnanoröhren werden häufig mit Tensidmolekülen ummantelt, die eine chemische Aufbereitung erlauben. Die spektrale Linienform von schwach lokalisierten Exzitonen in Kohlenstoffnanoröhren mit Tensidhülle ist oft auffallend asymmetrisch. In dieser Arbeit wurde ein quantenmechanisches Modell entwickelt, um die Holstein-Wechselwirkung zwischen dem Dipolmoment des lokalisierten Exzitons und Molekülschwingungen des Tensids zu beschreiben. Charakteristika der relevanten Molekülschwingungen wurden anhand von Dichtefunktionaltheorie berechnet und Photolumineszenzspektren durch die Kombination mit dem Modell simuliert. Simulation und Messdaten stimmten über einen weiten Bereich von Probentemperaturen und Anregungslaserleistungen hervorragend überein. In kovalent funktionalisierten Kohlenstoffnanoröhren sind Exzitonen an künstlichen Kristalldefekten stark lokalisiert. Zwar ist die Photolumineszenz dieser Zustände ungewöhnlich intensiv, aber zwischen einzelnen Kohlenstoffnanoröhren variieren die Spektren erheblich. Magnetophotolumineszenzmessungen zeigten, dass diese Unterschiede, anders als für freie Exzitonen, nicht durch dunkle Zerfallskanäle erklärbar sind. Durch Photonenkorrelationsspektroskopie wurden zwei Arten von Emittern mit starken bzw. schwachen Korrelationen zwischen den beiden Ladungszuständen der lokalisierten Exzitonen identifiziert. Dieses Resultat ergab Niveauschemata zur Beschreibung der exzitonischen Besetzungsdichte und zeigte, dass häufig mehrere Defektstellen in unmittelbarer Nachbarschaft auftreten und durch Coulomb-Abstoßung miteinander korreliert sind. Die Ergebnisse dieser Arbeit identifizierten dipolare und elektrostatische Wechselwirkungen als bedeutende Kopplungsmechanismen lokalisierter Exzitonen in Kohlenstoffnanoröhren. Dies bietet eine Orientierung für das Design künftiger Techniken zur Funktionalisierung und Tensidumhüllung von Kohlenstoffnanoröhren, um deren nächste Generation von Anwendungen in der Photonik zu verbessern.Carbon nanotubes are a one-dimensional allotrope of carbon that can be imagined as a single-atomic layer of graphite rolled up to a hollow cylinder. The charge carriers in semiconducting carbon nanotubes form strongly bound electron-hole pairs (excitons) that support photoluminescence emission ranging from the edge of the visible spectrum into the telecom band. Frequently, the excitons are localized, e. g. at intentional defect sites, and their photophysical properties are then dominated by the laws of quantum mechanics. Along with their wavelength tunability, this feature makes localized excitons in carbon nanotubes promising candidates for quantum information processing applications. Localized excitons in carbon nanotubes are subject to strong interactions with their environment that provide insights into their fundamental physical properties. This thesis is aimed at providing a deeper understanding of these couplings that is also beneficial for the improvement of carbon nanotube technologies. Both weakly confined excitons in shallow potential minima and excitons localized intentionally at covalent defect sites were studied. Carbon nanotubes are frequently wrapped with surfactant molecules that enable wet-chemical purification processes. The photoluminescence lineshapes of weakly localized excitons in surfactant-wrapped carbon nanotubes often feature a peculiar asymmetry. In this work, a quantum-mechanical model was developed that describes the Holstein-like interaction between the dipole moment of localized excitons and molecular vibrations of the surfactant. Photoluminescence spectra were simulated by combining this model with the characteristics of the relevant molecular vibrations that were calculated by means of density functional theory. An excellent agreement between the simulations and the data was obtained over a broad range of sample temperatures and excitation laser irradiances. Covalently functionalized carbon nanotubes host strongly localized excitons confined at intentional lattice defects. While photoluminescence emission from these states is exceptionally bright, the spectral response shows significant variations on the level of individual carbon nanotubes. Magneto-photoluminescence experiments established that in contrast to diffusive excitons these variations cannot be attributed to the presence of nonradiative decay channels. Photon correlation measurements identified two classes of emitters with strongly and weakly pronounced correlations between the two possible charge states of the localized excitons. This finding guided the formulation of level schemes describing the exciton population dynamics and revealed the frequent presence of multiple proximal defect sites that are correlated by repulsive Coulomb interactions. Both studies in this work identified dipolar and electrostatic interactions as important coupling mechanisms of localized excitons in carbon nanotubes. These results provide guidance in the design of future carbon nanotube functionalization techniques and surfactant wrappings to improve the next generation of carbon nanotube-based photonics applications

State-of-the-Art and Comparative Review of Adaptive Sampling Methods for Kriging

Metamodels aim to approximate characteristics of functions or systems from the knowledge extracted on only a finite number of samples. In recent years kriging has emerged as a widely applied metamodeling technique for resource-intensive computational experiments. However its prediction quality is highly dependent on the size and distribution of the given training points. Hence, in order to build proficient kriging models with as few samples as possible adaptive sampling strategies have gained considerable attention. These techniques aim to find pertinent points in an iterative manner based on information extracted from the current metamodel. A review of adaptive schemes for kriging proposed in the literature is presented in this article. The objective is to provide the reader with an overview of the main principles of adaptive techniques, and insightful details to pertinently employ available tools depending on the application at hand. In this context commonly applied strategies are compared with regards to their characteristics and approximation capabilities. In light of these experiments, it is found that the success of a scheme depends on the features of a specific problem and the goal of the analysis. In order to facilitate the entry into adaptive sampling a guide is provided. All experiments described herein are replicable using a provided open source toolbox. © 2020, The Author(s)

Temporal Correlatability of Digital Thermal Infrared Scanner Data

General Engineerin

Informed source extraction from a mixture of sources exploiting second order temporal structure

Extracting a specific signal from among man

Investigation of code reconfigurable fibre Bragg gratings for Optical Code Division Multiple Access (OCDMA) and Optical Packet Switching (OPS) Networks

This thesis documents my work in the telecommunication system laboratory at the Optoelectronics Research Centre, towards the implementation of code reconfigurable OCDMA and all-optical packet switching nodes based on fibre Bragg grating (FBG) technology. My research work involves characterizing the performance of various gratings, specifically high reflectivity, short chip duration, long code sequences, multiple phase level and tunable superstructured fiber Bragg gratings (SSFBGs), by using the recently proposed Frequency-Resolved Optical Gating technique based on Electro-Absorption Modulator (EAM-FROG). This technology can obtain the complex code profile along the grating, making it a powerful method to understand the thermally-induced code-reconfigurable grating. Efforts have been made to improve the grating design to achieve better system performance. Three different types of FBGs optical encoder/decoder, e.g. conventional discrete phaseshift SSFBGs, code-reconfigurable gratings, and novel continuous phase-shift SSFBGs, have been investigated comparatively, as well as their performance in various optical coding/decoding systems. This thesis also discusses the possibility of reducing multiple access interference (MAI) using a Two-Photon Absorption (TPA) process. The advanced grating devices enable the improvement of system performance. A dynamically reconfigurable optical packet processing system and a 16-channel reconfigurable OCDMA/DWDM system with 50GHz DWDM intervals has been demonstrated.These results highlight the feasibility of FBG-based optical coding/decoding techniques, with improved system flexibility and sustainability

Eddy current automatic flaw detection system for heat exchanger tubes in steam generators

In this dissertation we present an automatic flaw detection system for heat exchanger tubes in steam generators. The system utilizes two well-known techniques, wavelets and fuzzy logic, to automatically detect the flaws in tubing data. The analysis of eddy current inspection data is a difficult task which requires intensive labor by experienced human analysts. To aid the analysts, an accurate and consistent automatic data analysis package was developed. The software development is divided into three parts: data preprocessing, wavelet analysis, and a fuzzy inference system. The data preprocessing procedure is used to set up a signal analysis standard for different data and also to remove the variations due to lift-off and other geometrical effects. The wavelet technique is used to reduce noise and identify possible flaw indications. Due to multiresolution and the unique time-frequency localization properties of the wavelet transform, the flaw signals have specific characteristics in the wavelet domain. We fully utilize those characteristics to distinguish flaw indications from noise. To further evaluate the flaw candidates and reduce false calls, we invoked fuzzy logic to discriminate between true positives and false positives. A template matching technique and fuzzy inference system were developed. The template matching technique uses signals from artificial flaws as templates to match with possible flaw signals and execute a normalized complex crosscorrelation. Through this process, we obtain both phase and shape information which are placed into a fuzzy inference system for final decision making. A rigorous test of the system using actual inspection data was undertaken. Results from tests indicate that the new techniques show a great deal of promise for automatic flaw detection. Investigating the novel techniques and integrating them into a system are the major contribution of this work

Tracking and data relay satellite system configuration and tradeoff study. Volume 4: TDRS system operation and control and telecommunications service system, part 1

Major study areas treated in this volume are: 1) operations and control and 2) the telecommunication service system. The TDRS orbit selection, orbital deployment, ground station visibility, sequence of events from launch to final orbit position, and TDRS control center functions required for stationkeeping, repositioning, attitude control, and antenna pointing are briefly treated as part of the operations and control section. The last topic of this section concerns the operations required for efficiently providing the TDRSS user telecommunication services. The discussion treats functions of the GSFC control and data processing facility, ground station, and TDRS control center. The second major portion of this volume deals with the Telecommunication Service System (TSS) which consists of the ground station, TDRS communication equipment and the user transceiver. A summary of the requirements and objectives for the telecommunication services and a brief summary of the TSS capabilities is followed by communication system analysis, signal design, and equipment design. Finally, descriptions of the three TSS elements are presented

Neural Processes Underlying the Flexible Control and Learning of Attentional Selection

In every-day life we are usually surrounded by a plethora of stimuli, of which only some may be relevant to us at a given moment in time. The dynamic interaction between internal factors, such as our previous experience and current goals, and external factors, such as salient sensory stimulation, determine where, how and what we attend to in our environment. This dissertation investigated some of the neural mechanisms that underlie successful goal-directed behavior in two conditions 1. when attention was actively cued to a target stimulus, and 2. when the attentional target had to be actively and repeatedly learned, in macaque monkeys and in humans. In Chapter 2, I investigated inter-areal spiketrain correlations in neuron pairs across the fronto-cingulate cortex when macaque monkeys are cued to shift their attention to one of two target stimuli. I found that neuron pairs in anterior cingulate cortex (ACC) and dorsal prefrontal cortex (PFC) with similar spatial preferences correlate their spiketrains at the time when attention needs to be actively shifted, suggesting that the flexible interaction between these two areas may support successful covert attention shifts. In Chapter 3, I show that when the attentional target stimulus needs to be repeatedly learned and is defined by only one of several stimulus features, neurons in macaque frontal and striatal regions encode prediction error signals that carry specific information about the stimulus feature that was selected in the preceding choice. These signals may be involved in identifying those synapses that require updating to allow flexible adjustments in goal-directed behavior. In Chapter 4, I found that when humans must repeatedly learn the identity of an attentional target, a human event-related potential over visual cortex that is thought to index attentional target selection, selectively decreases after successful learning, in particular for the distracting stimulus, and selectively increases for the target stimulus following negative feedback during learning. Overall, this dissertation provides novel insights into some of the complex neural mechanisms that support flexible control and learning of attention across brain regions of the human and non-human primate brain