Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “bit error”

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.

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

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Satellite ground-terminal user simulation

Realistic simulation of satellite communication systems and evaluation of satellite networking schemes require emulation of the systems's users. A laboratory model of a Ka-band satellite-switched time-division multiple-access (SS-TDMA) communication network, referred to as the System Integration, Test, and Evaluation (SITE) project, uses special bit-error-rate (BER) test sets to simulate the transmitting and receiving users of a communication network. The bit-error-rate test sets contain circuit boards that can be modified to create a variety of interfaces to satellite system ground terminals.

Shalkhauser, Mary Jo W.↗
NASA NTRS1987

A study of the effect of group delay distortion on an SMSK satellite communications channel

The effects of group delay distortion on an SMSK satellite communications channel have been investigated. Software and hardware simulations have been used to determine the effects of channel group delay variations with frequency on the bit error rate for a 220 Mbps SMSK channel. These simulations indicate that group delay distortions can significantly degrade the bit error rate performance. The severity of the degradation is dependent on the amount, type, and spectral location of the group delay distortion.

Kerczewski, Robert J.↗
NASA NTRS1989

Performance of concatenated codes using 8-bit and 10-bit Reed-Solomon codes

The performance improvement of concatenated coding systems using 10-bit instead of 8-bit Reed-Solomon codes is measured by simulation. Three inner convolutional codes are considered: (7,1/2), (15,1/4), and (15,1/6). It is shown that approximately 0.2 dB can be gained at a bit error rate of 10(-6). The loss due to nonideal interleaving is also evaluated. Performance comparisons at very low bit error rates may be relevant for systems using data compression.

Pollara, F.↗
NASA NTRS1988

Lateral charge transport from heavy-ion tracks in integrated circuit chips

A 256K DRAM has been used to study the lateral transport of charge (electron-hole pairs) induced by direct ionization from heavy-ion tracks in an IC. The qualitative charge transport has been simulated using a two-dimensional numerical code in cylindrical coordinates. The experimental bit-map data clearly show the manifestation of lateral charge transport in the creation of adjacent multiple-bit errors from a single heavy-ion track. The heavy-ion data further demonstrate the occurrence of multiple-bit errors from single ion tracks with sufficient stopping power. The qualitative numerical simulation results suggest that electric-field-funnel-aided (drift) collection accounts for single error generated by an ion passing through a charge-collecting junction, while multiple errors from a single ion track are due to lateral diffusion of ion-generated charge.

Zoutendyk, J. A.↗
NASA NTRSDate not supplied

NOR Flash Memory Scrubbing Application for Boot File Preservation of NASA’s Descent and Landing Computer (DLC)

Progress on NASA’s Safe and Precise Landing Integrated Capabilities Evolution (SPLICE)project continues, specifically with this development of the Descent and Landing Computer(DLC). One of the DLC’s primary contributions as a SPLICE technology is its implementationof algorithms and operation of sensors to autonomously guide a spacecraft in performing moreprecise and safer landings on celestial bodies such as the Moon and Mars. The second iterationof the DLC is known as the Engineering Test Unit (ETU) and one of its desired functionalitiesis the ability to preserve the fidelity of the system’s boot file through the use of memoryscrubbing. The ETU has two primary boards, one for housing a Multi-Processor System ona Chip (MPSoC) and the other for housing a Xilinx Kintex Ultrascale FPGA3. To emulate amemory scrubbing function implemented on the ETU’s FPGA board, the design and testingof a software application was performed on a Xilinx KCU105 FPGA evaluation board. Thememory scrubbing application had to meet certain key criteria such as (1) properly utilize withthe flash memory’s Serial Peripheral Interface (SPI) to read, write, and erase flash memoryproperly, (2) be able to detect arbitrarily large or small amounts of bit-errors, (3) be able tocorrect all detected errors, and (4) perform memory scrubbing indefinitely and autonomously.A prototype implementation was constructed and tested, demonstrating successful detectionand correction of bit errors in multiple configurations. In the form of burst errors or singularbit flips, and in amounts of errors ranging from one to fifteen (per 256 Bytes), the applicationwas successful in preserving memory fidelity.

Radiation tolerant↗
NASA NTRS1976

Convolutional code performance in the Rician fading channel

The performance of short constraint length convolutional codes in conjunction with binary phase-shift keyed (BPSK) modulation and Viterbi maximum likelihood decoding on the classical Rician fading channel is examined in detail. Primary interest is in the bit error probability performance as a function of E sub b/N sub 0 parameterized by the fading channel parameters. Fairly general upper bounds on bit error probability performance in the presence of fading are obtained and compared with simulation results in the two extremes of zero channel memory and infinite channel memory. The efficacy of simple block interleaving in combating the memory of the channel is thoroughly explored. Results include the effects of fading on tracking loop performance and the subsequent impact on overall coded system performance. The approach is analytical where possible; otherwise resort is made to digital computer simulation.

Modestino, J. W.↗
NASA NTRS1996

Data Transfer Efficiency Over Satellite Circuits Using a Multi-Socket Extension to the File Transfer Protocol (FTP)

In several experiments using NASA's Advanced Communications Technology Satellite (ACTS), investigators have reported disappointing throughput using the transmission control protocol/Internet protocol (TCP/IP) protocol suite over 1.536Mbit/sec (T1) satellite circuits. A detailed analysis of file transfer protocol (FTP) file transfers reveals that both the TCP window size and the TCP 'slow starter' algorithm contribute to the observed limits in throughput. In this paper we summarize the experimental and and theoretical analysis of the throughput limit imposed by TCP on the satellite circuit. We then discuss in detail the implementation of a multi-socket FTP, XFTP client and server. XFTP has been tested using the ACTS system. Finally, we discuss a preliminary set of tests on a link with non-zero bit error rates. XFTP shows promising performance under these conditions, suggesting the possibility that a multi-socket application may be less effected by bit errors than a single, large-window TCP connection.

Allman, Mark↗
DOE OSTI2026

A scalable superconducting nanowire memory array with row–column addressing

Scalable superconducting memory is required for the development of low-energy superconducting computers and fault-tolerant quantum computers. Conventional superconducting logic-based memory cells possess a large footprint that limits scaling; nanowire-based superconducting memory cells, although more compact, have high error rates, which hinders integration into large arrays. Here we report a 4 × 4 superconducting nanowire memory array that is designed for scalable row–column operations and has a functional density of 2.6 Mbit cm −2 . Each memory cell is based on a nanowire loop consisting of two temperature-dependent superconducting switches and a variable kinetic inductor. The arrays operate at 1.3 K, where we implement and characterize multiflux quanta state storage and destructive read-out. By optimizing the write- and read-pulse sequences, we minimize bit errors and maximize operating margins. We achieve a minimum bit error rate of 10 −5 . Here, we also use circuit-level simulations to understand the memory cell’s dynamics, performance limits and stability under varying pulse amplitudes.

Electrical and electronic engineering↗
NASA NTRS2001

EFQPSK Versus CERN: A Comparative Study

This report presents a comparative study on Enhanced Feher's Quadrature Phase Shift Keying (EFQPSK) and Constrained Envelope Root Nyquist (CERN) techniques. These two techniques have been developed in recent times to provide high spectral and power efficiencies under nonlinear amplifier environment. The purpose of this study is to gain insights into these techniques and to help system planners and designers with an appropriate set of guidelines for using these techniques. The comparative study presented in this report relies on effective simulation models and procedures. Therefore, a significant part of this report is devoted to understanding the mathematical and simulation models of the techniques and their set-up procedures. In particular, mathematical models of EFQPSK and CERN, effects of the sampling rate in discrete time signal representation, and modeling of nonlinear amplifiers and predistorters have been considered in detail. The results of this study show that both EFQPSK and CERN signals provide spectrally efficient communications compared to filtered conventional linear modulation techniques when a nonlinear power amplifier is used. However, there are important differences. The spectral efficiency of CERN signals, with a small amount of input backoff, is significantly better than that of EFQPSK signals if the nonlinear amplifier is an ideal clipper. However, to achieve such spectral efficiencies with a practical nonlinear amplifier, CERN processing requires a predistorter which effectively translates the amplifier's characteristics close to those of an ideal clipper. Thus, the spectral performance of CERN signals strongly depends on the predistorter. EFQPSK signals, on the other hand, do not need such predistorters since their spectra are almost unaffected by the nonlinear amplifier, Ibis report discusses several receiver structures for EFQPSK signals. It is observed that optimal receiver structures can be realized for both coded and uncoded EFQPSK signals with not too much increase in computational complexity. When a nonlinear amplifier is used, the bit error rate (BER) performance of the CERN signals with a matched filter receiver is found to be more than one decibel (dB) worse compared to the bit error performance of EFQPSK signals. Although channel coding is found to provide BER performance improvement for both EFQPSK and CERN signals, the performance of EFQPSK signals remains better than that of CERN. Optimal receiver structures for CERN signals with nonlinear equalization is left as a possible future work. Based on the numerical results, it is concluded that, in nonlinear channels, CERN processing leads towards better bandwidth efficiency with a compromise in power efficiency. Hence for bandwidth efficient communications needs, CERN is a good solution provided effective adaptive predistorters can be realized. On the other hand, EFQPSK signals provide a good power efficient solution with a compromise in band width efficiency.

Borah, Deva K.↗
NASA NTRS1988

Gaussian approximation versus nearly exact performance analysis of optical communication systems with PPM signaling and APD receivers

A 25-Mb/s direct-detection optical communication system that used Q = 4 PPM (pulse-position modulation) signaling was constructed and its performance measured under laboratory conditions. The system used a single-mode AlGaAs laser diode (lambda = 834 nm) and low-noise silicon avalanche photodiode (APD). A procedure for numerically computing system performance is given that uses the nearly exact Webb approximation of the true Conradi distribution for the APD output and does not require excessive amounts of computer time. Comparison revealed that modeling the APD ouptut as a Gaussian process under conditions of negligible background radiation and low (less than 10 to the -12 A) APD bulk leakage currents leads to substantial underestimates of optimal APD gain and overestimates of system bit error probability. Examples illustrate the breakdown of the Gaussian approximation in assessing system performance. The measured performance was in excellent agreement with that predicted by the computational procedure. The system achieved a bit error probability of 10 to the -6 at a received signal energy, corresponding to an average of 60 absorbed photons/bit and optimal APD gain of 700.

Davidson, Frederic M.↗
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 NTRS2001

Survey of Header Compression Techniques

This report provides a summary of several different header compression techniques. The different techniques included are: (1) Van Jacobson's header compression (RFC 1144); (2) SCPS (Space Communications Protocol Standards) header compression (SCPS-TP, SCPS-NP); (3) Robust header compression (ROHC); and (4) The header compression techniques in RFC2507 and RFC2508. The methodology for compression and error correction for these schemes are described in the remainder of this document. All of the header compression schemes support compression over simplex links, provided that the end receiver has some means of sending data back to the sender. However, if that return path does not exist, then neither Van Jacobson's nor SCPS can be used, since both rely on TCP (Transmission Control Protocol). In addition, under link conditions of low delay and low error, all of the schemes perform as expected. However, based on the methodology of the schemes, each scheme is likely to behave differently as conditions degrade. Van Jacobson's header compression relies heavily on the TCP retransmission timer and would suffer an increase in loss propagation should the link possess a high delay and/or bit error rate (BER). The SCPS header compression scheme protects against high delay environments by avoiding delta encoding between packets. Thus, loss propagation is avoided. However, SCPS is still affected by an increased BER (bit-error-rate) since the lack of delta encoding results in larger header sizes. Next, the schemes found in RFC2507 and RFC2508 perform well for non-TCP connections in poor conditions. RFC2507 performance with TCP connections is improved by various techniques over Van Jacobson's, but still suffers a performance hit with poor link properties. Also, RFC2507 offers the ability to send TCP data without delta encoding, similar to what SCPS offers. ROHC is similar to the previous two schemes, but adds additional CRCs (cyclic redundancy check) into headers and improves compression schemes which provide better tolerances in conditions with a high BER.

Ishac, Joseph↗
NASA NTRS1974

Threshold detection in an on-off binary communications channel with atmospheric scintillation

The optimum detection threshold in an on-off binary optical communications system operating in the presence of atmospheric turbulence was investigated assuming a poisson detection process and log normal scintillation. The dependence of the probability of bit error on log amplitude variance and received signal strength was analyzed and semi-emperical relationships to predict the optimum detection threshold derived. On the basis of this analysis a piecewise linear model for an adaptive threshold detection system is presented. Bit error probabilities for non-optimum threshold detection system were also investigated.

Webb, W. E.↗
NASA NTRS1975

Threshold detection in an on-off binary communications channel with atmospheric scintillation

The optimum detection threshold in an on-off binary optical communications system operating in the presence of atmospheric turbulence was investigated assuming a poisson detection process and log normal scintillation. The dependence of the probability of bit error on log amplitude variance and received signal strength was analyzed and semi-empirical relationships to predict the optimum detection threshold derived. On the basis of this analysis a piecewise linear model for an adaptive threshold detection system is presented. The bit error probabilities for nonoptimum threshold detection systems were also investigated.

Webb, W. E.↗
NASA NTRS1975

Threshold detection in an on-off binary communications channel with atmospheric scintillation

The optimum detection threshold in an on-off binary optical communications system operating in the presence of atmospheric turbulence has been investigated assuming a Poisson detection process and log normal scintillation. The dependence of the probability of bit error on log amplitude variance and received signal strength has been analyzed, and semi-empirical relationships to predict the optimum detection threshold have been derived. On the basis of this analysis, a piecewise-linear model for an adaptive threshold detection system is presented. The bit-error probabilities for nonoptimum threshold detection systems have also been investigated.

Webb, W. E.↗
NASA NTRS1973

VHF command system study

Solutions are provided to specific problems arising in the GSFC VHF-PSK and VHF-FSK Command Systems in support of establishment and maintenance of Data Systems Standards. Signal structures which incorporate transmission on the uplink of a clock along with the PSK or FSK data are considered. Strategies are developed for allocating power between the clock and data, and spectral analyses are performed. Bit error probability and other probabilities pertinent to correct transmission of command messages are calculated. Biphase PCM/PM and PCM/FM are considered as candidate modulation techniques on the telemetry downlink, with application to command verification. Comparative performance of PCM/PM and PSK systems is given special attention, including implementation considerations. Gain in bit error performance due to coding is also considered.

Gee, T. H.↗
NASA NTRS1990

Adaptive box filters for removal of random noise from digital images

Adaptive box-filtering algorithms to remove random bit errors and to smooth noisy data have been developed. For both procedures, the standard deviation of those pixels within a local box surrounding each pixel is used. A series of two or three filters with decreasing box sizes can be run to clean up extremely noisy images and to remove bit errors near sharp edges. The second filter, for noise smoothing, is similar to the 'sigma filter' of Lee (1983). The technique effectively reduces speckle in radar images without eliminating fine details.

Eliason, Eric M.↗
NASA NTRS2010

Reception of Multiple Telemetry Signals via One Dish Antenna

A microwave aeronautical-telemetry receiver system includes an antenna comprising a seven-element planar array of receiving feed horns centered at the focal point of a paraboloidal dish reflector that is nominally aimed at a single aircraft or at multiple aircraft flying in formation. Through digital processing of the signals received by the seven feed horns, the system implements a method of enhanced cancellation of interference, such that it becomes possible to receive telemetry signals in the same frequency channel simultaneously from either or both of two aircraft at slightly different angular positions within the field of view of the antenna, even in the presence of multipath propagation. The present system is an advanced version of the system described in Spatio- Temporal Equalizer for a Receiving-Antenna Feed Array NPO-43077, NASA Tech Briefs, Vol. 34, No. 2 (February 2010), page 32. To recapitulate: The radio-frequency telemetry signals received by the seven elements of the array are digitized, converted to complex baseband form, and sent to a spatio-temporal equalizer that consists mostly of a bank of seven adaptive finite-impulse-response (FIR) filters (one for each element in the array) plus a unit that sums the outputs of the filters. The combination of the spatial diversity of the feedhorn array and the temporal diversity of the filter bank affords better multipath suppression performance than is achievable by means of temporal equalization alone. The FIR filter bank adapts itself in real time to enable reception of telemetry at a low bit error rate, even in the presence of frequency-selective multipath propagation like that commonly found at flight-test ranges. The combination of the array and the filter bank makes it possible to constructively add multipath incoming signals to the corresponding directly arriving signals, thereby enabling reductions in telemetry bit-error rates.

Mukai, Ryan↗