Communication over fading dispersive channels
Performance prediction, and error analysis for digital signal transmission over fading dispersive channel
Richters, J. S.↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Performance parameters that characterize a differential-pressure transducer
Performance characteristics and error reduction methods for differential pressure transducer
Gettelman, C. C.↗
Communications systems research - Sequential decoding
Error probability and performance of Pioneer-type sequential decoding communications system with noisy oscillators
Source record↗
Strapdown inertial attitude-indication evaluations
Strapdown inertial attitude indication, describing static and dynamic tests, error propagation profiles, performance prediction, etc
Gilmore, J. P.↗
Improvements in deep-space tracking by use of third-order loops.
Third-order phase-locked receivers have not yet found wide application in deep-space communications systems because the second-order systems now used have performed adequately on past spacecraft missions. However, a survey of the doppler profiles for future missions shows that an unaided second-order loop may be unable to perform within reasonable error bounds. This article discusses the characteristics of a simple third-order extension to present second-order systems that not only extends doppler-tracking capability, but widens the pull-in range and decreases pull-in time as well.
Tausworth, R. C.↗
Optical constants of concentrated aqueous ammonium sulfate.
Using experimental data obtained from applying spectroscopy to a 39-wt-% aqueous ammonium sulfate solution, it is shown that, even though specific aerosol optical constants appear quite accurate, spectral variations may exist as functions of material composition or concentration or both. Prudent users of optical constant data must then include liberal data error estimates when performing calculations or in interpreting spectroscopic surveys of collected aerosol material.
Remsberg, E. E.↗
Error modeling of precision orientation sensors in a fixed base simulation
Models of noise and dynamic characteristics of gyro and autocollimator for very small signal levels are presented. Measurements were evaluated using spectral techniques for identifying noise from base motion. The experiment was constructed to measure the precession, due to relativistic effects, of an extremely precise earth-orbiting gyroscope. The design goal for nonrelativistic gyro drift is 0.001 arcsec per year. An analogous fixed base simulator was used in developing methods of instrument error modeling and performance evaluation applicable to the relativity experiment sensors and other precision pointing instruments. Analysis of autocollimator spectra uncovered the presence of a platform gimbal resonance. The source of resonance was isolated to gimbal bearing elastic restraint properties most apparent at very small levels of motion. A model of these properties which include both elastic and coulomb friction characteristics is discussed, and a describing function developed.
Klinger, D. L.↗
Active Suppression of Pogo on the Space Shuttle
The use of active pogo suppressors on the space shuttle was qualitatively investigated. Suppressor design concepts and the effectiveness of these designs in maintaining the stability of the shuttle vehicle were the primary concerns. Suppressor design concepts were developed by means of a series of parametric stability analyses. These two designs together with two designs provided by NASA were evaluated in detail for control effectiveness, performance relative to a passive suppression device, sensitivity of performance to feedback error, suppressor volume flow requirements, and suppressor development requirements. An active device at the high pressure oxidizer pump inlet was shown to provide a simple and effective design that is insensitive to error in the feedback signal. The sizing of an active suppressor was demonstrated to be dependent upon knowledge of the dynamic characteristics of the system.
Lock, M. H.↗
Intermodal transfer in temporal discrimination
This study determined if training for accuracy in temporal discrimination would transfer across sensory modalities. A fractionation method was used in which subjects bisected the durations of acoustic and visual signals at three standard intervals (6, 12, and 18 sec). Absolute error was the performance index. Half of the subjects were trained with acoustic stimuli and then tested in vision; the remainder were trained in vision and tested in audition. Similar negatively accelerated acquisition functions were noted for both modalities. Positive intermodal transfer, characterized by symmetry across modalities, was obtained at all standard durations. The results were considered to provide support for the notion that a common mechanism underlies temporal discriminations in different sensory systems.
Warm, J. S.↗
Wideband 1.064 micrometer detector evaluation
Several types of communications detectors for use in a 400 Mbps 1.064 micrometer laser communication system were evaluated and characterized. The communication system Bit Error Rate (BER) performance was measured, and test results for the best detector of each type are summarized. The complete BER curves are presented. The 400 Mbps 1.064 micrometer communication system receiver test bed is described. The best performance levels which can be achieved by focusing the signal to diffraction limited spots on the photosensitive area are cited.
Green, S. I.↗
Recovery of refractivity profiles and pressure and temperature distributions in the lower atmosphere from satellite-to-satellite radio occultation data
The feasibility of recovering parameters from one-way range rate between two earth orbiting spacecraft during occultation of the tracking signal by the earth's lower atmosphere. The tracking data is inverted by an integral transformation (Abel transform) to obtain a vertical refractivity profile above the point of closest approach of the ray connecting the satellites. Pressure and temperature distributions can be obtained from values of dry refractivity using the hydrostatic equation and perfect gas law. Two methods are investigated for recovering pressure and temperature parameters. Results show that recovery is much more sensitive to satellite velocity errors than to satellite position errors. An error analysis is performed. An example is given demonstrating recovery of parameters from radio occultation data obtained during satellite-to-satellite tracking of Nimbus 6 by the ATS 6 satellite.
Murray, C. W., Jr.↗
Procedures for dealing with certain types of noise and systematic errors common to many Hadamard transform optical systems
Sources of noise and error correcting procedures characteristic of Hadamard transform optical systems were investigated. Reduction of spectral noise due to noise spikes in the data, the effect of random errors, the relative performance of Fourier and Hadamard transform spectrometers operated under identical detector-noise-limited conditions, and systematic means for dealing with mask defects are among the topics discussed. The distortion in Hadamard transform optical instruments caused by moving Masks, incorrect mask alignment, missing measurements, and diffraction is analyzed and techniques for reducing or eliminating this distortion are described.
Harwit, M.↗
Application of square-root filtering for spacecraft attitude control
Suitable digital algorithms are developed and tested for providing on-board precision attitude estimation and pointing control for potential use in the Landsat-D spacecraft. These algorithms provide pointing accuracy of better than 0.01 deg. To obtain necessary precision with efficient software, a six state-variable square-root Kalman filter combines two star tracker measurements to update attitude estimates obtained from processing three gyro outputs. The validity of the estimation and control algorithms are established, and the sensitivity of their performance to various error sources and software parameters are investigated by detailed digital simulation. Spacecraft computer memory, cycle time, and accuracy requirements are estimated.
Sorensen, J. A.↗
Optimization of satellite altimeter and wave height measurements
Two techniques for simultaneously estimating altitude, ocean wave height, and signal-to-noise ratio from the GEOS-C satellite altimeter data are described. One technique was based on maximum likelihood estimation, MLE, and the other on minimum mean square error estimation, MMSE. Performance was determined by comparing the variance and bias of each technique with the variance and bias of the smoothed output from the Geos altimeter tracker. Ocean wave height tracking performance for the MLE and MMSE algorithms was measured by comparing the variance and bias of the wave height estimates with that of the expression for the return waveform obtained by a fit to the average output of the 16 waveform sampling gates.
Dooley, R. P.↗
Antenna evaluation study for the shuttle multispectral radar, phase 3
The principal objectives of Phase III were: (1) to continue simulations of the effects of excitation errors in the performance of a planar array antenna, (2) to apply this model specifically, to the SIR-A antenna, (3) to support measurements of the SIR-A antenna at JPL by quick-turnaround analyses of the SIR-A antenna under a variety of conditions encountered at the JPL West Mesa Antenna Range, and (4) to document fully all software developed for NASA Johnson Space Center (JSC) during Phases I, II, and III.
Coffey, E. L., III↗
Kinetic energy budgets in areas of intense convection
A kinetic energy budget analysis of the AVE-SESAME 1 period which coincided with the deadly Red River Valley tornado outbreak is presented. Horizontal flux convergence was found to be the major kinetic energy source to the region, while cross contour destruction was the major sink. Kinetic energy transformations were dominated by processes related to strong jet intrusion into the severe storm area. A kinetic energy budget of the AVE 6 period also is presented. The effects of inherent rawinsonde data errors on widely used basic kinematic parameters, including velocity divergence, vorticity advection, and kinematic vertical motion are described. In addition, an error analysis was performed in terms of the kinetic energy budget equation. Results obtained from downward integration of the continuity equation to obtain kinematic values of vertical motion are described. This alternate procedure shows promising results in severe storm situations.
Fuelberg, H. E.↗
The development of convective instability, wind shear, and vertical motion in relation to convection activity and synoptic systems in AVE 4
Data from the Fourth Atmospheric Variability Experiment were used to investigate conditions/factors responsible for the development (local time rate-of-change) of convective instability, wind shear, and vertical motion in areas with varying degrees of convective activity. AVE IV sounding data were taken at 3 or 6 h intervals during a 36 h period on 24-25 April 1975 over approximately the eastern half of the United States. An error analysis was performed for each variable studied.
Davis, J. G.↗
Joint map data/phase sequence estimation for trellis phase codes
A unified estimation procedure is formulated for the coherent detection of trellis phase codes, including partial response FM codes and multi-h codes. The unknown carrier phase is imbedded in the system state vector, and by simple augmentation of the decoder's state space, joint data and carrier estimation may be accomplished. The procedure is general to all trellis phase codes analyzed thus far. The effect of a static phase error on detection performance is also treated.
Wilson, S. G.↗