Fast Decoder for Overloaded Uniquely Decodable Synchronous CDMA

We consider the problem of designing a fast decoder for antipodal uniquely decodable (errorless) code sets for overloaded synchronous code-division multiple access (CDMA) systems where the number of signals K_{max}^a is the largest known for the given code length L. The proposed decoder is designed in a such a way that the users can uniquely recover the information bits with a very simple decoder, which uses only a few comparisons. Compared to maximum-likelihood (ML) decoder, which has a high computational complexity for even moderate code length, the proposed decoder has a much lower computational complexity. Simulation results in terms of bit error rate (BER) demonstrate that the performance of the proposed decoder only has a 1-2 dB degradation at BER of 10^{-3} when compared to ML

Measuring aberrations in lithographic projection systems with phase wheel targets

A significant factor in the degradation of nanolithographic image fidelity is optical wavefront aberration. Aerial image sensitivity to aberrations is currently much greater than in earlier lithographic technologies, a consequence of increased resolution requirements. Optical wavefront tolerances are dictated by the dimensional tolerances of features printed, which require lens designs with a high degree of aberration correction. In order to increase lithographic resolution, lens numerical aperture (NA) must continue to increase and imaging wavelength must decrease. Not only do aberration magnitudes scale inversely with wavelength, but high-order aberrations increase at a rate proportional to NA2 or greater, as do aberrations across the image field. Achieving lithographic-quality diffraction limited performance from an optical system, where the relatively low image contrast is further reduced by aberrations, requires the development of highly accurate in situ aberration measurement. In this work, phase wheel targets are used to generate an optical image, which can then be used to both describe and monitor aberrations in lithographic projection systems. The use of lithographic images is critical in this approach, since it ensures that optical system measurements are obtained during the system\u27s standard operation. A mathematical framework is developed that translates image errors into the Zernike polynomial representation, commonly used in the description of optical aberrations. The wavefront is decomposed into a set of orthogonal basis functions, and coefficients for the set are estimated from image-based measurements. A solution is deduced from multiple image measurements by using a combination of different image sets. Correlations between aberrations and phase wheel image characteristics are modeled based on physical simulation and statistical analysis. The approach uses a well-developed rigorous simulation tool to model significant aspects of lithography processes to assess how aberrations affect the final image. The aberration impact on resulting image shapes is then examined and approximations identified so the aberration computation can be made into a fast compact model form. Wavefront reconstruction examples are presented together with corresponding numerical results. The detailed analysis is given along with empirical measurements and a discussion of measurement capabilities. Finally, the impact of systematic errors in exposure tool parameters is measureable from empirical data and can be removed in the calibration stage of wavefront analysis

Tectono-thermal history modeling and reservoir simulation study of the Nenana basin, central Alaska: implications for regional tectonics and geologic carbon sequestration

Thesis (Ph.D.) University of Alaska Fairbanks, 2017Central Interior Alaska is an active tectonic deformation zone highlighted by the complex interactions of active strike-slip fault systems with thrust faults and folds of the Alaska Range fold-and-thrust belt. This region includes the Nenana basin and the adjacent Tanana basin, both of which have significant Tertiary coal-bearing formations and are also promising areas (particularly the Nenana basin) with respect to hydrocarbon exploration and geologic carbon sequestration. I investigate the modern-day crustal architecture of the Nenana and Tanana basins using seismic reflection, aeromagnetic and gravity anomaly data and demonstrate that the basement of both basins shows strong crustal heterogeneity. The Nenana basin is a deep (up to 8 km), narrow transtensional pull-apart basin that is deforming along the left-lateral Minto Flats fault zone. The Tanana basin has a fundamentally different geometry and is a relatively shallow (up to 2 km) asymmetrical foreland basin with its southern, deeper side controlled by the northern foothills of the central Alaska Range. NE-trending strike-slip faults within the Tanana basin are interpreted as a zone of clockwise crustal block rotation. Seismic refection data, well data, fracture data and apatite fission track data further constrain the tectonic evolution and thermal history of the Nenana basin. The Nenana basin experienced four distinct tectonic phases since Late Paleocene time. The basin initiated as a narrow half-graben structure in Late Paleocene with accumulation of greater than 6000 feet of sediments. The basin was then uplifted, resulting in the removal of up to 5000 feet of Late Paleocene sediments in Eocene to Oligocene time. During Middle to Late Miocene time, left lateral strike-slip faulting was superimposed on the existing half-graben system. Transtensional deformation of the basin began in the Pliocene. At present, Miocene and older strata are exposed to temperatures > 60°C in the deeper parts of the Nenana basin. Coals have significant capacity for sequestering anthropogenic CO₂ emissions and offer the benefit of enhanced coal bed methane production that can offset the costs associated with the sequestration processes. In order to do a preliminary assessment of the CO₂ sequestration and coal bed methane production potential of the Nenana basin, I used available surface and subsurface data to build and simulate a reservoir model of subbituminous Healy Creek Formation coals. The petroleum exploration data were also used to estimate the state of subsurface stresses that are critical in modeling the orientation, distribution and flow behavior of natural coal fractures in the basin. The effect of uncertainties within major coal parameters on the total CO₂ sequestration and coal bed methane capacity estimates were evaluated through a series of sensitivity analyses, experimental design methods and fluid flow simulations. Results suggest that the mature, unmineable Healy Creek Formation coals of the Nenana basin can sequester up to 0.41 TCF of CO₂ while producing up to 0.36 TCF of CH₄ at the end of 44-year forecast. However, these volumes are estimates and they are also sensitive to the well type, pattern and cap rock lithology. I used a similar workflow to evaluate the state of in situ stress in the northeastern North Slope province of Alaska. The results show two distinct stress regimes across the northeastern North Slope. The eastern Barrow Arch exhibits both strike-slip and normal stress regimes. Along the northeastern Brooks Range thrust front, an active thrust-fault regime is present at depths up to 6000 ft but changes to a strike-slip stress regime at depths greater than 6000 ft.1. Introduction and Statement of Problem -- 2. Crustal structure of the Nenana basin and Tanana basin, central Alaska: constraints from integration of gravity, magnetic and seismic reflection data -- 3. Cenozoic tectonic and thermal history of the Nenana basin, central Interior Alaska: new constraints from seismic reflection data, fracture history and apatite fission-track analyses -- 4. In situ stress variations associated with regional changes in tectonic setting, Northeastern Brooks Range and eastern North Slope of Alaska -- 5. A preliminary study of the carbon sequestration and enhanced coal bed methane production potential of subbituminous to high-volatile bituminous coals of the Healy Creek Formation, Nenana Basin, Interior Alaska -- 6. Conclusions -- 7. Appendix