Joint-Detection and Interference Cancellation Based Burst-by-Burst Adaptive CDMA Schemes

Spread adaptive quadrature amplitude modulated (AQAM) code-division multiple access (CDMA) is proposed as a powerful means of exploiting the time-variant channel capacity fluctuations of wireless channels. It is studied in comparison to variable spreading factor (VSF)-based techniques. These adaptive-rate transmission methods are compared in the context of joint detection and interference cancellation assisted adaptive CDMA (ACDMA) systems. More explicitly, we exploit the time-variant channel quality of mobile channels by switching either the modulation mode (AQAM) or the spreading factor (VSF) on a burst-by-burst basis. The most appropriate modulation mode or spreading factor is chosen based on the instantaneous channel quality estimated. The chosen modem mode or spreading factor is communicated to the remote communicator either through explicit signalling or extracted at the receiver using blind detection techniques. The multiuser joint detector (JD) and the successive interference cancellation (SIC) receiver are compared in the context of these adaptive schemes, with the conclusion that the JD outperformed the SIC receiver in the ACDMA schemes at the cost of increased complexity. Finally, the performance of the uncoded AQAM JD-CDMA scheme is also compared to that of adaptive trellis coded modulation (TCM) assisted AQAM JD-CDMA, which allows us to incorporate adaptive channel coding without any bandwidth expansion.We also show that in the particular scenario studied, adaptiveTCM outperformed adaptive turbo TCM since the system was designed for maintaining a low turbo-interleaver delay. Index Terms—Burst-by-burst adaptive code-division multiple access (CDMA), joint detection CDMA, parallel interference cancellation (PIC), successive interference cancellation (SIC), successive and parallel interference cancellation

Determination of real machine-tool settings and minimization of real surface deviation by computerized inspection

A numerical method is developed for the minimization of deviations of real tooth surfaces from the theoretical ones. The deviations are caused by errors of manufacturing, errors of installment of machine-tool settings and distortion of surfaces by heat-treatment. The deviations are determined by coordinate measurements of gear tooth surfaces. The minimization of deviations is based on the proper correction of initially applied machine-tool settings. The contents of accomplished research project cover the following topics: (1) Descriptions of the principle of coordinate measurements of gear tooth surfaces; (2) Deviation of theoretical tooth surfaces (with examples of surfaces of hypoid gears and references for spiral bevel gears); (3) Determination of the reference point and the grid; (4) Determination of the deviations of real tooth surfaces at the points of the grid; and (5) Determination of required corrections of machine-tool settings for minimization of deviations. The procedure for minimization of deviations is based on numerical solution of an overdetermined system of n linear equations in m unknowns (m much less than n ), where n is the number of points of measurements and m is the number of parameters of applied machine-tool settings to be corrected. The developed approach is illustrated with numerical examples

Effects of electrode surface roughness on motional heating of trapped ions

Electric field noise is a major source of motional heating in trapped ion quantum computation. While the influence of trap electrode geometries on electric field noise has been studied in patch potential and surface adsorbate models, only smooth surfaces are accounted for by current theory. The effects of roughness, a ubiquitous feature of surface electrodes, are poorly understood. We investigate its impact on electric field noise by deriving a rough-surface Green's function and evaluating its effects on adsorbate-surface binding energies. At cryogenic temperatures, heating rate contributions from adsorbates are predicted to exhibit an exponential sensitivity to local surface curvature, leading to either a large net enhancement or suppression over smooth surfaces. For typical experimental parameters, orders-of-magnitude variations in total heating rates can occur depending on the spatial distribution of absorbates. Through careful engineering of electrode surface profiles, our results suggests that heating rates can be tuned over orders of magnitudes.Comment: 12 pages, 5 figure

Instrumentation of a high-sensitivity microwave vector detection system for low-temperature applications

We present the design and the circuit details of a high-sensitivity microwave vector detection system, which is aiming for studying the low-dimensional electron system embedded in the slots of a coplanar waveguide at low temperatures. The coplanar waveguide sample is placed inside a phase-locked loop; the phase change of the sample may cause a corresponding change in the operation frequency, which can be measured precisely. We also employ a double-pulse modulation on the microwave signals, which comprises a fast pulse modulation for gated averaging and a slow pulse modulation for lock-in detection. In measurements on real samples at low temperatures, this system provides much better resolutions in both amplitude and phase than most of the conventional vector analyzers at power levels below -65 dBm.Comment: 7 pages, 11 figures, 1 table, lette

Computerized inspection of real surfaces and minimization of their deviations

A method is developed for the minimization of gear tooth surface deviations between theoretical and real surfaces for the improvement of precision of surface manufacture. Coordinate measurement machinery is used to determine a grid of surface coordinates. Theoretical calculations are made for the grid points. A least-square method is used to minimize the deviations between real and theoretical surfaces by altering the manufacturing machine-tool settings. An example is given for a hypoid gear

Significance and applications of Froude and Reynolds numbers as criteria for similitude

CER59HKL20.June 1959.Includes bibliographical references (pages 33-34)