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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Performance of convolutionally encoded noncoherent MFSK modem in fading channels

The performance of a convolutionally encoded noncoherent multiple-frequency shift-keyed (MFSK) modem utilizing Viterbi maximum-likelihood decoding and operating on a fading channel is described. Both the lognormal and classical Rician fading channels are considered for both slow and time-varying channel conditions. Primary interest is in the resulting bit error rate as a function of the ratio between the energy per transmitted information bit and noise spectral density, parameterized by both the fading channel and code parameters. Fairly general upper bounds on bit error probability are provided and compared with simulation results in the two extremes of zero and infinite channel memory. The efficacy of simple block interleaving in combatting channel memory effects are thoroughly explored. Both quantized and unquantized receiver outputs are considered.

Modestino, J. W.↗
NASA NTRS1979

Efficient digital encoding scheme

Modified NRZ (non-return-to-zero) code immunizes record and playback systems against dc drift and bit slippage. In order to maximize bit packing density improved code called J-NRZ gives 100 percent NRZ efficiently and solves DC drift problem by adding check bits in specified format when long string is encountered. Remainder of data stream is encoded in NRZ format.

Obrien, D. E., III↗
NASA NTRS1977

Performance of DPSK with convolutional encoding on time-varying fading channels

The bit error probability performance of a differentially-coherent phase-shift keyed (DPSK) modem with convolutional encoding and Viterbi decoding on time-varying fading channels is examined. Both the Rician and the lognormal channels are considered. Bit error probability upper bounds on fully-interleaved (zero-memory) fading channels are derived and substantiated by computer simulation. It is shown that the resulting coded system performance is a relatively insensitive function of the choice of channel model provided that the channel parameters are related according to the correspondence developed as part of this paper. Finally, a comparison of DPSK with a number of other modulation strategies is provided.

Mui, S. Y.↗
NASA NTRS1979

Binary-to-Manchester encoders

Two circuit system converts 16-bit-word binary encoded data to 24-bit Manchester II code to allow easy interface of flight simulators with aircraft communications equipment.

St. Cyr, R. H., III↗
NASA NTRS1979

Improved reader for magnetically-encoded ID cards

Hybrid demodulator in electronic card reader for magnetically encoded identification cards, accommodates variations in insertion speeds, yet is simpler and less expensive than equivalent all-digital circuits.

Wu, T. T.↗
NASA NTRS1978

Voice encoding for the Space Shuttle using adaptive delta modulation

The paper describes the SONG and modified ABATE adaptive delta modulation algorithms for voice encoding. Waveforms of the response of the delta modulators to channel errors are given, and performance data which show the relationship between channel errors and word intelligibility are provided. An analytic derivation yielding a comparison between PCM and adaptive delta modulation with respect to channel errors is given. The Space Shuttle is employing the modified-ABATE device because it can tolerate a high error rate and operates at a relatively low sampling rate.

Schilling, D. L.↗
NASA NTRS1979

The effect of interference on delta modulation encoded video signals

An adaptive delta modulator which encodes composite color video signals was shown to provide a good response when operating at 16 Mb/s and near-commercial quality at 23Mb/s. The ADM was relatively immune to channel errors. The system design is discussed and circuit diagrams are included.

Schilling, D. L.↗
NASA NTRS1982

Spatial, High-Accuracy, Positioning-Encoding Sensor (SHAPES) for large space system control applications

The Spatial, High-Accuracy, Position-Encoding Sensor is a controls sensor suitable for the determination of the static shape and vibrational motion of large space structures and similar systems and for the determination of position and velocity in rendezvous and docking. It uses a combination of electro-optical techniques to measure the three-dimensional coordinates distributed over the structure at reading rates high compared to the rates at which the coordinates are changing. The technical approach is that of measuring the distance to and the direction of points on the structure from a single sensor head. Many points can be measured simultaneously from a single head without significantly increasing the complexity of the system.

Mclauchlan, J. M.↗
NASA NTRS1981

Entropy encoding applied to a video DM bit stream

This paper investigates bandwidth compression of delta modulated video signals using a variety of novel techniques. The video signal is encoded at 16 MHz with an adaptive delta modulator (ADM) using the Song video mode algorithm. One method of achieving bandwidth compression is through the detection and reduction of steady state patterns in the DM bit stream. Further reduction is obtained by deleting the horizontal and vertical drive information. Finally, a modified ADM algorithm is introduced to increase the frequency of steady state patterns. When the modified ADM is combined with entropy coding a 30-50% data compression can be realized.

Barba, J.↗
NASA NTRS1982

The VLSI design of a single chip Reed-Solomon encoder

A design for a single chip implementation of a Reed-Solomon encoder is presented. The architecture that leads to this single VLSI chip design makes use of a bit serial finite field multiplication algorithm.

Truong, T. K.↗
NASA NTRS1983

Evaluation of GOES encoder lamps

Aging characteristics and life expectancies of flight quality, tungsten filament, encoder lamps are similar to those of 'commercial' grade gas filled lamps of similar construction, filament material and filament temperature. The aging and final failure by filament burnout are caused by single crystal growth over large portions of the filament with the concomitant development of facets and notches resulting in reduction of cross section and mechanical weakening of the filament. The life expectancy of presently produced lamps is about one year at their nominal operating voltage of five volts dc. At 4.5 volts, it is about two years. These life times are considerably shorter, and the degradation rates of lamp current and light flux are considerably higher, than were observed in the laboratory and in orbit on lamps of the same type manufactured more than a decade ago. It is speculated that the filaments of these earlier lamps contained a crystallization retarding dopant, possibly thorium oxide. To obtain the desired life expectancy of or = to four years in present lamps, operating voltages of or = to four volts dc would be required.

Viehmann, W.↗
NASA NTRS1985

Reed-Solomon Encoder

Report presents mathematical principles of Berlekamp bit serial multiplier algorithm and its application to design of very-large-scale integrated (VLSI) encoders for Reed-Solomon error-correcting codes. Structure made readily on single chip of negatively doped channel metal oxide semiconductor.

Troung, T. K.↗
NASA NTRS1985

Design Primer for Reed-Solomon Encoders

Design and operation of Reed-Solomon (RS) encoders discussed in document prepared as instruction manual for computer designers and others in dataprocessing field. Conventional and Berlekamp architectures compared. Engineers who equip computer memory chips with burst-error and dropout detection and correction find report especially useful.

Perlman, M.↗
NASA NTRS1985

Encoding Scheme Reduces Hardware Requirements

Shift register time-shared in proposed error-correcting code for tape-storage systems. Error-correcting code logic for blocks of 256-bit data words implemented by 14-stage-time-shared shift register, two 4,096bit RAM's and logic gates. Encoding and decoding logic implement generator polynomial that defines error-correcting code, and error correction based on algorithm also implemented by logic.

Sasnowitz, H.↗
NASA NTRS1986

Obtaining One-Degree Accuracy With Shaft Encoders

Circuit converts output of 1-pulse-per-revolution shaft encoder to precise 360-pulses-per-revolution output. Circuit allows shaft angular position to be measured with 1-degree accuracy. With simple modifications, circuit provides higher or lower resolution from single- or multiple-pulse-perrevolution sources. Circuit used to synchronize aircraft beacon transponder-based plan-position indicator (PPI) display to remote host interrogator search antenna. Constructed using standard, commercially available components.

Franke, J. M.↗
NASA NTRS1986

Single-Chip VLSI Reed-Solomon Encoder

Reed-Solomon (RS) encoder based on Berlekamp bit-serial multiplier algorithm. RS code standard, based on code words of 255 8-bit symbols, of which 223 symbols convey information and remaining 32 are check symbols. This code enables correction of up to 16 erroneous information symbols per word. Berlekamp algorithm based on code-generating polynomial with 32 roots that occur in reciprocal pairs. Choice of algorithm permits compact design.

Truong, T. K.↗
NASA NTRS1985

Electroacoustical imaging technique for encoding incoherent radiance fields as Gabor elementary signals

A technique is presented for directly encoding incoherent radiance fields as Gabor elementary signals. This technique uses an electro-acoustic sensor to modulate the electronic charges induced by the incident radiance field with the electric fields generated by Gaussian modulated sinusoidal acoustic waves. The resultant signal carries the amplitude and phase information required for localizing spatial frequencies of the radiance field. These localized spatial frequency representations provide a link between the either geometric or Fourier transform representations currently used in computer vision and pattern recognition.

Fales, C. L.↗