SEARCH · Search NASA

Results for “error correction”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30

All sources NASA NTRS DOE OSTI

NASA NTRS1987

An algorithm to design finite field multipliers using a self-dual normal basis

Finite field multiplication is central in the implementation of some error-correcting coders. Massey and Omura have presented a revolutionary design for multiplication in a finite field. In their design, a normal base is utilized to represent the elements of the field. The concept of using a self-dual normal basis to design the Massey-Omura finite field multiplier is presented. Presented first is an algorithm to locate a self-dual normal basis for GF(2 sup m) for odd m. Then a method to construct the product function for designing the Massey-Omura multiplier is developed. It is shown that the construction of the product function base on a self-dual basis is simpler than that based on an arbitrary normal base.

Wang, C. C.↗

NASA NTRS1986

Design of a digital flexible mobile transceiver

A flexible, modular transceiver design for digital voice and data transmissions in the proposed Mobile Satellite Experimental (MSAT-X) System is presented. Major system design issues are addressed, including frequency stability control, modulation method, linear predictive coding vocoder algorithm, and error control technique. Detailed design aspects of the modular and flexible transceiver, including the core, RF/IF, modem, vocoder, forward error correction codec, and I/O modules, as well as the flexible interface, are also discussed.

Fang, R. J. F.↗

NASA NTRS1986

VLSI Reed Solomon decoder design

A Reed Solomon code is a highly efficient error correcting code that NASA will use in future space communication missions. A VLSI implementation of the decoder is presented that accepts data rates of 80 Mbits/second. A total of seven chips are needed and operate with the symbol clock being the system clock for the chip set. Approximately 1.65 billion Galois Field operations per second are achieved with this chip set.

Maki, Gary K.↗

NASA NTRS1987

Hydrostatic temperature calculations

Comparisons are made between hydrostatically computed temperatures and ambient temperatures associated with nine different data sources, including analyses, forecasts and conventional observations. Five-day averages and the day-to-day variations in the root-mean-square temperature differences are presented. Several different numerical and interpolation procedures are examined. Error correction and a constrained optimum procedure that minimizes ambient minus calculated hydrostatic temperature differences are introduced. Systematic differences between ambient and hydrostatic temperatures are found to be associated with the sinoptic situation. When compared with ambient temperatures, hydrostatic temperatures at 500 mb tend to be too warm at or in front of a trough and too cold behind the trough. In the vertical direction, for the eight-level configuration tested, the average hydrostatic temperatures are too cold at low levels (850, 700 mb) and too warm at upper levels, (300, 250 mb).

Raymond, William H.↗

NASA NTRS1988

Pitch-Learning Algorithm For Speech Encoders

Adaptive algorithm detects and corrects errors in sequence of estimates of pitch period of speech. Algorithm operates in conjunction with techniques used to estimate pitch period. Used in such parametric and hybrid speech coders as linear predictive coders and adaptive predictive coders.

Bhaskar, B. R. Udaya↗

NASA NTRS1988

Bandwidth and power efficient satellite TDMA demodulator and decoder

A proof-of-concept demodulator for TDMA applications requiring high total data rates composed of many low data rate users is proposed. High-spectrum efficiency is obtained via a bandwidth efficient combined modulation and coding system, and low TDMA overhead is obtained via a fast acquiring digital phase lock loop. The system employs a data rate of 200 Mb/s with a bit error rate of better than 5 x 10 to the -7th in the presence of adjacent channel interference 20 dB above the weakest user. The 8-PSK modulation combined with the rate 5/6 forward error correction coding results in a bandwidth efficiency of better than 2 bits/second per Hz.

Ames, Stephen A.↗

NASA NTRS1987

Single event upset (SEU) testing at JPL

It is believed that the increase in SEUs with more modern devices may have serious consequences for future space missions. The physics behind an SEU is discussed as well as SEU test philosophy and equipment, and testing results. It is concluded that the problem may be ameliorated by careful device selection and the use of redundancy or error correction.

Coss, James R.↗

NASA NTRS1987

Design of an MSAT-X mobile transceiver and related base and gateway stations

This paper summarizes the results of a design study of the mobile transceiver, base station, and gateway station for NASA's proposed Mobile Satellite Experiment (MSAT-X). Major ground segment system design issues such as frequency stability control, modulation method, linear predictive coding vocoder algorithm, and error control technique are addressed. The modular and flexible transceiver design is described in detail, including the core, RF/IF, modem, vocoder, forward error correction codec, amplitude-companded single sideband, and input/output modules, as well as the flexible interface. Designs for a three-carrier base station and a 10-carrier gateway station are also discussed, including the interface with the controllers and with the public-switched telephone networks at the gateway station. Functional specifications are given for the transceiver, the base station, and the gateway station.

Fang, Russell J. F.↗

NASA NTRS1989

Improved Algorithm For Finite-Field Normal-Basis Multipliers

Improved algorithm reduces complexity of calculations that must precede design of Massey-Omura finite-field normal-basis multipliers, used in error-correcting-code equipment and cryptographic devices. Algorithm represents an extension of development reported in "Algorithm To Design Finite-Field Normal-Basis Multipliers" (NPO-17109), NASA Tech Briefs, Vol. 12, No. 5, page 82.

Wang, C. C.↗

NASA NTRS1988

ACTS and OLYMPUS propagation experiments

The OLYMPUS and ACTS satellites both provide opportunities for 10 to 30 GHz propagation measurements. The spacecraft are sufficiently alike that OLYMPUS can be used to test some prototype ACTS equipment and experiments. Data are particularly needed on short term signal behavior and in support of uplink power control and adaptive forward error correction (FEC) techniques. The Virginia Tech Satellite Communications Group has proposed a set of OLYMPUS experiments including attenuation and fade rate measurements, data communications, uplink power control, rain scatter interference, and small-scale site diversity operation. A digital signal processing receiver for the OLYMPUS and ACTS beacon signals is being developed.

Bostian, Charles W.↗

NASA NTRS1989

Additional development of the XTRAN3S computer program

Additional developments and enhancements to the XTRAN3S computer program, a code for calculation of steady and unsteady aerodynamics, and associated aeroelastic solutions, for 3-D wings in the transonic flow regime are described. Algorithm improvements for the XTRAN3S program were provided including an implicit finite difference scheme to enhance the allowable time step and vectorization for improved computational efficiency. The code was modified to treat configurations with a fuselage, multiple stores/nacelles/pylons, and winglets. Computer program changes (updates) for error corrections and updates for version control are provided.

Borland, C. J.↗

NASA NTRS1989

A robust compression system for low bit rate telemetry: Test results with lunar data

A robust noiseless encoding scheme is presented for encoding the gamma ray spectroscopy data. The encoding algorithm is simple to implement and has minimal buffering requirements. The decoder contains error correcting capability in the form of a MAP receiver. While the MAP receiver adds some complexity, this is limited to the decoder. Nothing additional is needed at the encoder side for its functioning.

Sayood, Khalid↗

NASA NTRS1989

Phase-ambiguity resolution for QPSK modulation systems. Part 1: A review

Part 1 reviews the current phase-ambiguity resolution techniques for QPSK coherent modulation systems. Here, those known and published methods of resolving phase ambiguity for QPSK with and without Forward-Error-Correcting (FEC) are discussed. The necessary background is provided for a complete understanding of the second part where a new technique will be discussed. An appropriate technique to the Consultative Committee for Space Data Systems (CCSDS) is recommended for consideration in future standards on phase-ambiguity resolution for QPSK coherent modulation systems.

Nguyen, Tien Manh↗

NASA NTRS1988

dc-free coset codes

A class of block coset codes with disparity and run-length constraints are studied. They are particularly well suited for high-speed optical fiber links and similar channels, where dc-free pulse formats, channel error control, and low-complexity encoder-decoder implementations are required. The codes are derived by partitioning linear block codes. The encoder and decoder structures are the same as those of linear block codes with only slight modifications. A special class of dc-free coset block codes are derived from BCH codes with specified bounds on minimum distance, disparity, and run length. The codes have low disparity levels (a small running digital sum) and good error-correcting capabilities.

Deng, Robert H.↗

NASA NTRS1988

Flight software operation of the Hubble Space Telescope fine guidance sensor

The Hubble Space Telescope (HST) is to carry five major scientific instruments to collect imagery, spectrographic, and photometric astronomical data. The Pointing Control System is designed to achieve pointing accuracies and line of sight jitter levels an order of magnitude less than can be achieved with ground mounted telescopes. This paper describes the operation of the pointing control system flight software in targeting a celestial object in a science instrument aperture and in performing the coordinate transformations necessary for commanding the fine guidance sensor and determining the attitude-error corrections.

Rodden, J. J.↗

NASA NTRS1988

Gravity gradient measurements

It is shown that, for floated satellite gradiometers subject to very low levels of unmodeled forces and torques, dynamic estimation can dramatically reduce rotation correction errors. The filter structure is developed, and the value of factorization techniques is examined. Numerical examples are given for a few practical cases using plausible instrument ensembles. To achieve these early results, great simplifications have been made, and important error sources have been suppressed.

Sonnabend, D.↗

NASA NTRS1988

VLSI high speed packet processor

The Goddard Space Flight Center Mission Operations and Data Systems Directorate has developed a packet processor card utilizing semicustom very large scale integration (VLSI) devices, microprocessors, and programmable gate arrays to support the implementation of multichannel telemetry data capture systems. This card will receive synchronized error corrected telemetry transfer frames and output annotated application packets derived from this data. An adaptable format capability is provided by the programmability of three microprocessors while the throughput capability of the packet processor is achieved by a data pipeline consisting of two separate RAM systems controlled by specially designed semicustom VLSI logic.

Grebowsky, Gerald J.↗

NASA NTRS1990

Synchronization Technique For Reception Of Coded Data

Shortest sequence of bits likely to be filled with error bursts examined. Algorithm improves synchronization of frames of noisy binary-coded data signals after Viterbi decoding (recovery from "inner" convolutional code used in transmission channel) and before Reed-Solomon or other decoding (recovery from "outer" error-correcting block code). Based on comparisons of sequences of correct and erroneous Viterbi-decoded received bits with known marker sequence denoting beginning of frame of data. Does not require count of number of bits in received sequence disagreeing with corresponding bits in marker sequence.

Shahshahani, Mehrdad M.↗