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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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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Self-checking sequential circuit design using m-out-of-n codes

A technique for designing sequential circuits which are totally self-checking for single stuck at faults is presented. This technique uses m-out-of-n codes for state assignments and for output encoding. The next stage logic and the output logic are implemented such that any stuck-at-fault will either create a single bit error or unidirectional multibit error at the output. The technique has been applied to MCNC benchmark circuits and the overhead is estimated.

Busaba, F. Y.↗
NASA NTRS1988

A concatenated coded modulation scheme for error control

A concatenated coded modulation scheme for error control in data communications is presented. The scheme is achieved by concatenating a Reed-Solomon outer code and a bandwidth efficient block inner code for M-ary PSK modulation. Error performance of the scheme is analyzed for an AWGN channel. It is shown that extremely high reliability can be attained by using a simple M-ary PSK modulation inner code and relatively powerful Reed-Solomon outer code. Furthermore, if an inner code of high effective rate is used, the bandwidth expansion required by the scheme due to coding will be greatly reduced. The proposed scheme is particularly effective for high speed satellite communication for large file transfer where high reliability is required. Also presented is a simple method for constructing block codes for M-ary PSK modulation. Some short M-ary PSK codes with good minimum squared Euclidean distance are constructed. These codes have trellis structure and hence can be decoded with a soft decision Viterbi decoding algorithm.

Kasami, Tadao↗
NASA NTRS1988

A concatenated coded modulation scheme for error control

A concatenated coded modulation scheme for error control in data communications is presented. The scheme is achieved by concatenating a Reed-Solomon outer code and a bandwidth efficient block inner code for M-ary PSK modulation. Error performance of the scheme is analyzed for an AWGN channel. It is shown that extremely high reliability can be attained by using a simple M-ary PSK modulation inner code and a relatively powerful Reed-Solomon outer code. Furthermore, if an inner code of high effective rate is used, the bandwidth expansion required by the scheme due to coding will be greatly reduced. The proposed scheme is very effective for high speed satellite communications for large file transfer where high reliability is required. A simple method is also presented for constructing codes for M-ary PSK modulation. Some short M-ary PSK codes with good minimum squared Euclidean distance are constructed. These codes have trellis structure and hence can be decoded with a soft decision Viterbi decoding algorithm. Furthermore, some of these codes are phase invariant under multiples of 45 deg rotation.

Lin, Shu↗
NASA NTRS1988

A concatenated coded modulation scheme for error control (addition 2)

A concatenated coded modulation scheme for error control in data communications is described. The scheme is achieved by concatenating a Reed-Solomon outer code and a bandwidth efficient block inner code for M-ary PSK modulation. Error performance of the scheme is analyzed for an AWGN channel. It is shown that extremely high reliability can be attained by using a simple M-ary PSK modulation inner code and a relatively powerful Reed-Solomon outer code. Furthermore, if an inner code of high effective rate is used, the bandwidth expansion required by the scheme due to coding will be greatly reduced. The proposed scheme is particularly effective for high-speed satellite communications for large file transfer where high reliability is required. This paper also presents a simple method for constructing block codes for M-ary PSK modulation. Some short M-ary PSK codes with good minimum squared Euclidean distance are constructed. These codes have trellis structure and hence can be decoded with a soft-decision Viterbi decoding algorithm. Furthermore, some of these codes are phase invariant under multiples of 45 deg rotation.

Lin, Shu↗
NASA NTRS1990

A concatenated coded modulation scheme for error control

A concatenated coded modulation scheme for error control in data communications is presented. The scheme is achieved by concatenating a Reed-Solomon outer code and a bandwidth efficient block inner code for M-ary PSK modulation. Error performance of the scheme is analyzed for an AWGN channel. It is shown that extremely high reliability can be attained by using a simple M-ary PSK modulation inner code and relatively powerful Reed-Solomon outer code. Furthermore, if an inner code of high effective rate is used, the bandwidth expansion required by the scheme due to coding will be greatly reduced. The proposed scheme is particularly effective for high speed satellite communications for large file transfer where high reliability is required. Also presented is a simple method for constructing block codes for M-ary PSK modulation. Some short M-ary PSK codes with good minimum squared Euclidean distance are constructed. These codes have trellis structure and hence can be decoded with a soft-decision Viterbi decoding algorithm.

Kasami, Tadao↗
NASA NTRS1995

Probability Quantization for Multiplication-Free Binary Arithmetic Coding

A method has been developed to improve on Witten's binary arithmetic coding procedure of tracking a high value and a low value. The new method approximates the probability of the less probable symbol, which improves the worst-case coding efficiency.

coding binary arithmetic coding probability quanti↗
NASA NTRS1985

On the binary weight distribution of some Reed-Solomon codes

Consider an (n,k) linear code with symbols from GF(2 sup M). If each code symbol is represented by a m-tuple over GF(2) using certain basis for GF(2 sup M), a binary (nm,km) linear code is obtained. The weight distribution of a binary linear code obtained in this manner is investigated. Weight enumerators for binary linear codes obtained from Reed-Solomon codes over GF(2 sup M) generated by polynomials, (X-alpha), (X-l)(X-alpha), (X-alpha)(X-alpha squared) and (X-l)(X-alpha)(X-alpha squared) and their extended codes are presented, where alpha is a primitive element of GF(2 sup M). Binary codes derived from Reed-Solomon codes are often used for correcting multiple bursts of errors.

Lin, S.↗
NASA NTRS2004

Swift/BAT Calibration and Spectral Response

The Burst Alert Telescope (BAT) aboard NASA#s Swift Gamma-Ray Burst Explorer is a large coded aperture gamma-ray telescope consisting of a 2.4 m (8#) x 1.2 m (4#) coded aperture mask supported 1 meter above a 5200 square cm area detector plane containing 32,768 individual 4 mm x 4 mm x 2 mm CZT detectors. The BAT is now completely assembled and integrated with the Swift spacecraft in anticipation of an October 2004 launch. Extensive ground calibration measurements using a variety of radioactive sources have resulted in a moderately high fidelity model for the BAT spectral and photometric response. This paper describes these ground calibration measurements as well as related computer simulations used to study the efficiency and individual detector properties of the BAT detector array. The creation of a single spectral response model representative of the fully integrated BAT posed an interesting challenge and is at the heart of the public analysis tool #batdrmgen# which computes a response matrix for any given sky position within the BAT FOV. This paper will describe the batdrmgen response generator tool and conclude with a description of the on-orbit calibration plans as well as plans for the future improvements needed to produce the more detailed spectral response model that is required for the construction of an all-sky hard x-ray survey.

Parsons, A.↗
NASA NTRS1989

Generalized Multiple-Trellis-Coded Modulation

Generalized multiple-trellis-coded modulation technique combines multiple trellis coding (more than one channel symbol per trellis branch transmitted) with symmetrical M-ary phase-shift keying. Transmitter puts out k M-ary code symbols for every b input binary symbols. Throughout performances, b/k, of trellis-coded multiple-phase-shift-keying channels compared with computational cutoff rates, R0, of multiple-phase-shift keying. Performs better than conventional trellis-coded modulation technique, with no increase in complexity.

Divsalar, D.↗
NASA NTRS1971

Performance of convolution coding concatenated with MFSK modulation in a Gaussian channel

The improvement in db due to concatenation over conventional M-ary coding is studied to reduce the probability of a bit error and to increase the available bit rate for the same system parameters of error rate, transmitter power, and range. The results of calculations for orthogonal modulation with noncoherent detection and Q-level correlator quantization are presented. It is shown that the correlator outputs are quantized to one of the Q levels, and the receiver output is a vector consisting of a list of the M correlator quantum levels. The channel has Q(M) possible outputs and M possible inputs. Optimum output is approached by increasing fine quantization

Choudhury, A. K.↗
NASA NTRS1990

A hybrid M-algorithm/sequential decoder for convolutional and trellis codes

The Viterbi Algorithm (VA) is optimum in the sense of being maximum likelihood for decoding codes with a trellis structure. However, since the VA is in fact an exhaustive search of the code trellis, the complexity of the VA grows exponentially with the constraint length upsilon. This limits its application to codes with small values of upsilon and relatively modest coding gains. The M-Algorithm (MA) is a limited search scheme which carries forward M paths in the trellis, all of the same length. All successors of the M paths are extended at the next trellis depth, and all but the best M of these are dropped. Since a limited search convolutional decoder will flounder indefinitely if one of the paths in storage is not the correct one, the data are usually transmitted in blocks. It has been shown that the performance of the MA approaches the VA at high signal to noise ratios (SNR's) with an M which is far less than the 2 sup upsilon states in the full trellis. Thus the MA can be used with larger values of upsilon, making larger coding gains possible at high SNR's. However, it still requires a relatively large fixed computational effort to achieve good performance.

Wang, Fu-Quan↗
NASA NTRS1992

Nonlinear, nonbinary cyclic group codes

New cyclic group codes of length 2(exp m) - 1 over (m - j)-bit symbols are introduced. These codes can be systematically encoded and decoded algebraically. The code rates are very close to Reed-Solomon (RS) codes and are much better than Bose-Chaudhuri-Hocquenghem (BCH) codes (a former alternative). The binary (m - j)-tuples are identified with a subgroup of the binary m-tuples which represents the field GF(2 exp m). Encoding is systematic and involves a two-stage procedure consisting of the usual linear feedback register (using the division or check polynomial) and a small table lookup. For low rates, a second shift-register encoding operation may be invoked. Decoding uses the RS error-correcting procedures for the m-tuple codes for m = 4, 5, and 6.

Solomon, G.↗
NASA NTRS1991

First ultraviolet spectropolarimetry of hot supergiants

UV spectropolarimetric observations of the early-type supergiant stars P Cygni and Kappa Cassiopeiae obtained with the Wisconsin UV Photo-Polarimeter Experiment (WUPPE) are presented. Contrary to model predictions, the intrinsic polarization of P Cyg remains constant in the Balmer continuum except for a broad dip between 2600 and 3000 A. This decrease in polarization is discussed in terms of possible Fe line blanketing effects. The intrinsic position angle is essentially constant in the UV except for a rotation across the feature between 2600 and 3000 A. The intrinsic polarization of Kappa Cas is small; most of the observed polarization is interstellar in nature. The Serkowski curve extrapolated into the UV is found to fall consistently below the observed polarization. A slight rotation in position angle from optical to UV wavelengths is noted. Very good agreement is found between the mean continuum polarization obtained by WUPPE and the broadband UV polarization measurement obtained by Gehrels (1968).

Taylor, M.↗
NASA NTRS1991

Error control techniques for satellite and space communications

Research activities related to error control techniques for satellite and space communication are reported. Specific areas of research include: coding gains for bandwidth efficient codes, hardware implementation of a bandwidth efficient coding scheme for the Hubble Space Telescope, construction of long trellis codes for use with sequential decoding, performance analysis of multilevel trellis codes, and M-algorithm decoding of trellis codes. Each topic is discussed in a corresponding paper that appears in the appendices.

Costello, Daniel J., Jr.↗
NASA NTRS1994

(abstract) Communications in Space

This paper provides an overview of the results of the JPL/NASA unmanned exploration of all of the planets of the solar system (except Pluto) as well as the telecommunications capability which was developed to enable/support those missions. The telecommunications link improvements will be described to show increases in data rate capability resulting from addition of ground antenna aperture, transmitter power, coding techniques, lower noise receivers, etc. The paper will also describe (briefly), the current and future flight missions.

coding↗
NASA NTRS2009

Truncation Depth Rule-of-Thumb for Convolutional Codes

In this innovation, it is shown that a commonly used rule of thumb (that the truncation depth of a convolutional code should be five times the memory length, m, of the code) is accurate only for rate 1/2 codes. In fact, the truncation depth should be 2.5 m/(1 - r), where r is the code rate. The accuracy of this new rule is demonstrated by tabulating the distance properties of a large set of known codes. This new rule was derived by bounding the losses due to truncation as a function of the code rate. With regard to particular codes, a good indicator of the required truncation depth is the path length at which all paths that diverge from a particular path have accumulated the minimum distance of the code. It is shown that the new rule of thumb provides an accurate prediction of this depth for codes of varying rates.

Moision, Bruce↗
NASA NTRS1998

Progressive Failure And Life Prediction of Ceramic and Textile Composites

An engineering approach to predict the fatigue life and progressive failure of multilayered composite and textile laminates is presented. Analytical models which account for matrix cracking, statistical fiber failures and nonlinear stress-strain behavior have been developed for both composites and textiles. The analysis method is based on a combined micromechanics, fracture mechanics and failure statistics analysis. Experimentally derived empirical coefficients are used to account for the interface of fiber and matrix, fiber strength, and fiber-matrix stiffness reductions. Similar approaches were applied to textiles using Repeating Unit Cells. In composite fatigue analysis, Walker's equation is applied for matrix fatigue cracking and Heywood's formulation is used for fiber strength fatigue degradation. The analysis has been compared with experiment with good agreement. Comparisons were made with Graphite-Epoxy, C/SiC and Nicalon/CAS composite materials. For textile materials, comparisons were made with triaxial braided and plain weave materials under biaxial or uniaxial tension. Fatigue predictions were compared with test data obtained from plain weave C/SiC materials tested at AS&M. Computer codes were developed to perform the analysis. Composite Progressive Failure Analysis for Laminates is contained in the code CPFail. Micromechanics Analysis for Textile Composites is contained in the code MicroTex. Both codes were adapted to run as subroutines for the finite element code ABAQUS and CPFail-ABAQUS and MicroTex-ABAQUS. Graphic user interface (GUI) was developed to connect CPFail and MicroTex with ABAQUS.

Xue, David Y.↗