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At least 289 records · Page 16

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NASA NTRS1998

Comparison of MPEG digital video with super VHS tape for diagnostic echocardiographic readings

BACKGROUND: Digital recording of echocardiographic studies is on the clinical horizon. However, full digital capture of complete echocardiographic studies in traditional video format is impractical, given current storage capacity and network bandwidth. To overcome these constraints, we evaluated the diagnostic image quality of digital video by using MPEG (Motion Picture Experts Group) compression. METHODS AND RESULTS: Fifty-eight complete, consecutive studies were recorded simultaneously with the use of MPEG-1 and sVHS videotape. Each matched MPEG and sVHS study pair was reviewed by two from a total of six readers, and findings were recorded with the use of a detailed, computerized reporting tool. Intrareader and interreader discrepancies were characterized as major or minor and analyzed in total and for specific subgroups of findings (left and right ventricular parameters, valvular insufficiency, and left ventricular regional wall motion). Intrareader discrepancies were reviewed by a consensus panel for agreement with either MPEG or sVHS findings. There was an exact concordance between MPEG and sVHS readings in 83% of findings. The majority of discrepancies were minor, with major discrepancies in only 2.7% of findings. There was no difference in the rate of consensus panel agreement with MPEG or sVHS for instances of intrareader discrepancy, either in total or for any subgroup of findings. Interreader discrepancy rates were nearly identical for both MPEG and sVHS. CONCLUSIONS: MPEG-1 digital video is equivalent to sVHS videotape for diagnostic echocardiography. MPEG increases the range of practical options for digital echocardiography and offers, for the first time, the advantages of digital recording in a familiar video format.

Non-NASA Center↗

NASA NTRS2005

Digital Audio Radio Broadcast Systems Laboratory Testing Nearly Complete

Radio history continues to be made at the NASA Lewis Research Center with the completion of phase one of the digital audio radio (DAR) testing conducted by the Consumer Electronics Group of the Electronic Industries Association. This satellite, satellite/terrestrial, and terrestrial digital technology will open up new audio broadcasting opportunities both domestically and worldwide. It will significantly improve the current quality of amplitude-modulated/frequency-modulated (AM/FM) radio with a new digitally modulated radio signal and will introduce true compact-disc-quality (CD-quality) sound for the first time. Lewis is hosting the laboratory testing of seven proposed digital audio radio systems and modes. Two of the proposed systems operate in two modes each, making a total of nine systems being tested. The nine systems are divided into the following types of transmission: in-band on-channel (IBOC), in-band adjacent-channel (IBAC), and new bands. The laboratory testing was conducted by the Consumer Electronics Group of the Electronic Industries Association. Subjective assessments of the audio recordings for each of the nine systems was conducted by the Communications Research Center in Ottawa, Canada, under contract to the Electronic Industries Association. The Communications Research Center has the only CCIR-qualified (Consultative Committee for International Radio) audio testing facility in North America. The main goals of the U.S. testing process are to (1) provide technical data to the Federal Communication Commission (FCC) so that it can establish a standard for digital audio receivers and transmitters and (2) provide the receiver and transmitter industries with the proper standards upon which to build their equipment. In addition, the data will be forwarded to the International Telecommunications Union to help in the establishment of international standards for digital audio receivers and transmitters, thus allowing U.S. manufacturers to compete in the world market.

Source record↗

NASA NTRS1999

Bandwidth Efficient Wireless Digital Modem Developed

NASA Lewis Research Center has developed a digital approach for broadcasting highfidelity audio (nearly compact disk (CD) quality sound) in the commercial frequencymodulated (FM) broadcast band. This digital approach provides a means of achieving high data transmission rates with low hardware complexity--including low mass, size, and power consumption. Lewis has completed the design and prototype development of a bandwidth-efficient digital modem (modulator and demodulator) that uses a spectrally efficient modulation scheme: 16-ary rectangular quadrature amplitude modulation, or 16- ary QAM. The digital implementation is based strictly on inexpensive, commercial off-theshelf digital signal processing (DSP) hardware to perform up and down conversions and pulse shaping. The digital modem transmits data at rates up to 76 kilobits per second (kbps), which is almost 3 times faster than standard 28.8-kbps telephone modems. In addition, the modem offers improved power and spectral performance, flexible operation, and low-cost implementation.

Kifle, Muli↗

NASA NTRS2002

Digital Distortion Caused by Traveling- Wave-Tube Amplifiers Simulated

Future NASA missions demand increased data rates in satellite communications for near real-time transmission of large volumes of remote data. Increased data rates necessitate higher order digital modulation schemes and larger system bandwidth, which place stricter requirements on the allowable distortion caused by the high-power amplifier, or the traveling-wave-tube amplifier (TWTA). In particular, intersymbol interference caused by the TWTA becomes a major consideration for accurate data detection at the receiver. Experimentally investigating the effects of the physical TWTA on intersymbol interference would be prohibitively expensive, as it would require manufacturing numerous amplifiers in addition to acquiring the required digital hardware. Thus, an accurate computational model is essential to predict the effects of the TWTA on system-level performance when a communication system is being designed with adequate digital integrity for high data rates. A fully three-dimensional, time-dependent, TWT interaction model has been developed using the electromagnetic particle-in-cell code MAFIA (Solution of Maxwell's equations by the Finite-Integration-Algorithm). It comprehensively takes into account the effects of frequency-dependent AM (amplitude modulation)/AM and AM/PM (phase modulation) conversion, gain and phase ripple due to reflections, drive-induced oscillations, harmonic generation, intermodulation products, and backward waves. This physics-based TWT model can be used to give a direct description of the effects of the nonlinear TWT on the operational signal as a function of the physical device. Users can define arbitrary excitation functions so that higher order modulated digital signals can be used as input and that computations can directly correlate intersymbol interference with TWT parameters. Standard practice involves using communication-system-level software packages, such as SPW, to predict if adequate signal detection will be achieved. These models use a nonlinear, black-box model to represent the TWTA. The models vary in complexity, but most make several assumptions regarding the operation of the high-power amplifier. When the MAFIA TWT interaction model was used, these assumptions were found to be in significant error. In addition, digital signal performance, including intersymbol interference, was compared using direct data input into the MAFIA model and using the system-level analysis tool SPW for several higher order modulation schemes. Results show significant differences in predicted degradation between SPW and MAFIA simulations, demonstrating the significance of the TWTA approximations made in the SPW model on digital signal performance. For example, a comparison of the SPW and MAFIA output constellation diagrams for a 16-ary quadrature amplitude modulation (16-QAM) signal (data shown only for second and fourth quadrants) is shown. The upper-bound degradation was calculated from the corresponding eye diagrams. In comparison to SPW simulations, the MAFIA data resulted in a 3.6-dB larger degradation.

Kory, Carol L.↗

NASA NTRS2002

622-Mbps Orthogonal Frequency Division Multiplexing (OFDM) Digital Modem Implemented

Future generation space communications systems feature significantly higher data rates and relatively smaller frequency spectrum allocations than systems currently deployed. This requires the application of bandwidth- and power-efficient signal transmission techniques. There are a number of approaches to implementing such techniques, including analog, digital, mixed-signal, single-channel, or multichannel systems. In general, the digital implementations offer more advantages; however, a fully digital implementation is very difficult because of the very high clock speeds required. Multichannel techniques are used to reduce the sampling rate. One such technique, multicarrier modulation, divides the data into a number of low-rate channels that are stacked in frequency. Orthogonal frequency division multiplexing (OFDM), a form of multicarrier modulation, is being proposed for numerous systems, including mobile wireless and digital subscriber link communication systems. In response to this challenge, NASA Glenn Research Center's Communication Technology Division has developed an OFDM digital modem (modulator and demodulator) with an aggregate information throughput of 622 Mbps. The basic OFDM waveform is constructed by dividing an incoming data stream into four channels, each using either 16- ary quadrature amplitude modulation (16-QAM) or 8-phase shift keying (8-PSK). An efficient implementation for an OFDM architecture is being achieved using the combination of a discrete Fourier transform (DFT) at the transmitter to digitally stack the individual carriers, inverse DFT at the receiver to perform the frequency translations, and a polyphase filter to facilitate the pulse shaping.

Kifle, Muli↗

NASA NTRS2008

Digital Receiver Phase Meter

The software of a commercially available digital radio receiver has been modified to make the receiver function as a two-channel low-noise phase meter. This phase meter is a prototype in the continuing development of a phase meter for a system in which radiofrequency (RF) signals in the two channels would be outputs of a spaceborne heterodyne laser interferometer for detecting gravitational waves. The frequencies of the signals could include a common Doppler-shift component of as much as 15 MHz. The phase meter is required to measure the relative phases of the signals in the two channels at a sampling rate of 10 Hz at a root power spectral density <5 microcycle/(Hz)1/2 and to be capable of determining the power spectral density of the phase difference over the frequency range from 1 mHz to 1 Hz. Such a phase meter could also be used on Earth to perform similar measurements in laser metrology of moving bodies. To illustrate part of the principle of operation of the phase meter, the figure includes a simplified block diagram of a basic singlechannel digital receiver. The input RF signal is first fed to the input terminal of an analog-to-digital converter (ADC). To prevent aliasing errors in the ADC, the sampling rate must be at least twice the input signal frequency. The sampling rate of the ADC is governed by a sampling clock, which also drives a digital local oscillator (DLO), which is a direct digital frequency synthesizer. The DLO produces samples of sine and cosine signals at a programmed tuning frequency. The sine and cosine samples are mixed with (that is, multiplied by) the samples from the ADC, then low-pass filtered to obtain in-phase (I) and quadrature (Q) signal components. A digital signal processor (DSP) computes the ratio between the Q and I components, computes the phase of the RF signal (relative to that of the DLO signal) as the arctangent of this ratio, and then averages successive such phase values over a time interval specified by the user.

Marcin, Martin↗

NASA NTRS2009

Analysis of the Measurement and Modeling of a Digital Inverter Based on a Ferroelectric Transistor

The use of ferroelectric materials for digital memory devices is widely researched and implemented, but ferroelectric devices also possess unique characteristics that make them have interesting and useful properties in digital circuits. Because ferroelectric transistors possess the properties of hysteresis and nonlinearity, a digital inverter containing a FeFET has very different characteristics than one with a traditional FET. This paper characterizes the properties of the measurement and modeling of a FeFET based digital inverter. The circuit was set up using discrete FeFETs. The purpose of this circuit was not to produce a practical integrated circuit that could be inserted directly into existing digital circuits, but to explore the properties and characteristics of such a device and to look at possible future uses. Input and output characteristics are presented, as well as timing measurements. Comparisons are made between the ferroelectric device and the properties of a standard digital inverter. Potential benefits and possible uses of such a device are presented.

MacLeod, Todd C.↗

NASA NTRS2004

Comparison of Two Digital Stethoscopes with the Traditional Stethoscope Used on International Space Station

A traditional stethoscope is currently flown on the International Space Station (ISS). The background noise on the ISS is much higher than a normal exam room, and the literature shows that traditional stethoscopes are unable to function effectively in high noise environments. Digital stethoscopes provide amplification which improves the audibility in a quiet environment. This study is designed to determine if digital stethoscopes offer any advantage over traditional stethoscopes in being able to identify normal and abnormal sounds in the ISS noise environment. Methods: An ISS noise simulation facility was created to reproduce ISS noise profiles by modifying pink noise with a software-based graphic equalizer. The files were played in a continuous loop on a computer, amplified through a high-end stereo system and adjusted using a sound level meter. Nine caregiver analogues were given the same auscultation lesson received by astronauts. They began testing by becoming familiar with normal and abnormal sounds on a Student Auscultation Manikin . They then used two digital stethoscopes and a traditional stethoscope identical to the one flown on the ISS to auscultate the manikin sounds in the noise facility. They identified the sounds on a questionnaire and picked which of the three stethoscopes they preferred. Results: Evaluators displayed equivalent accuracy in sound identification when using either the 3M model 4000 digital stethoscope or traditional stethoscope. However, the 3M was preferred 2 to 1 by the evaluators, primarily because of additional amplification of the sounds. Discussion: Although our results show that the current ISS stethoscope and the "best-of-breed" digital stethoscope provide essentially the same auscultation utility, the latter has the advantage of recording and transmitting sounds to a remote physician. Since the astronaut caregivers are non-physiCians, this capability may be worth the additional expense and effort needed to certify the digital stethoscope for flight.

Rasbury, Jack↗

NASA NTRS2010

The Digital Data Acquisition System for the Russian VLBI Network of New Generation

The system consists of several identical channels of 1024 MHz bandwidth each. In each channel, the RF band is frequency-translated to the intermediate frequency range 1 - 2 GHz. Each channel consists of two parts: the digitizer and Mark 5C recorder. The digitizer is placed on the antenna close to the corresponding Low-Noise Amplifier output and consists of the analog frequency converter, ADC, and a device for digital processing of the signals using FPGA. In the digitizer the subdigitization on frequency of 2048 MHz is used. For producing narrow-band channels and to interface with existing data acquisition systems, the polyphase filtering with FPGA can be used. Digital signals are re-quantized to 2-bits in the FPGA and are transferred to an input of Mark 5C through a fiber line. The breadboard model of the digitizer is being tested, and the data acquisition system is being designed.

Fedotov, Leonid↗

NASA NTRS2006

Digital Front End for Wide-Band VLBI Science Receiver

An upgrade to the very-long-baseline-interferometry (VLBI) science receiver (VSR) a radio receiver used in NASA's Deep Space Network (DSN) is currently being implemented. The current VSR samples standard DSN intermediate- frequency (IF) signals at 256 MHz and after digital down-conversion records data from up to four 16-MHz baseband channels. Currently, IF signals are limited to the 265-to-375-MHz range, and recording rates are limited to less than 80 Mbps. The new digital front end, denoted the Wideband VSR, provides improvements to enable the receiver to process wider bandwidth signals and accommodate more data channels for recording. The Wideband VSR utilizes state-of-the-art commercial analog-to-digital converter and field-programmable gate array (FPGA) integrated circuits, and fiber-optic connections in a custom architecture. It accepts IF signals from 100 to 600 MHz, sampling the signal at 1.28 GHz. The sample data are sent to a digital processing module, using a fiber-optic link for isolation. The digital processing module includes boards designed around an Advanced Telecom Computing Architecture (ATCA) industry-standard backplane. Digital signal processing implemented in FPGAs down-convert the data signals in up to 16 baseband channels with programmable bandwidths from 1 kHz to 16 MHz. Baseband samples are transmitted to a computer via multiple Ethernet connections allowing recording to disk at rates of up to 1 Gbps.

Jongeling, Andre↗

NASA NTRS2011

Digital Interface Board to Control Phase and Amplitude of Four Channels

An increasing number of parts are designed with digital control interfaces, including phase shifters and variable attenuators. When designing an antenna array in which each antenna has independent amplitude and phase control, the number of digital control lines that must be set simultaneously can grow very large. Use of a parallel interface would require separate line drivers, more parts, and thus additional failure points. A convenient form of control where single-phase shifters or attenuators could be set or the whole set could be programmed with an update rate of 100 Hz is needed to solve this problem. A digital interface board with a field-programmable gate array (FPGA) can simultaneously control an essentially arbitrary number of digital control lines with a serial command interface requiring only three wires. A small set of short, high-level commands provides a simple programming interface for an external controller. Parity bits are used to validate the control commands. Output timing is controlled within the FPGA to allow for rapid update rates of the phase shifters and attenuators. This technology has been used to set and monitor eight 5-bit control signals via a serial UART (universal asynchronous receiver/transmitter) interface. The digital interface board controls the phase and amplitude of the signals for each element in the array. A host computer running Agilent VEE sends commands via serial UART connection to a Xilinx VirtexII FPGA. The commands are decoded, and either outputs are set or telemetry data is sent back to the host computer describing the status and the current phase and amplitude settings. This technology is an integral part of a closed-loop system in which the angle of arrival of an X-band uplink signal is detected and the appropriate phase shifts are applied to the Ka-band downlink signal to electronically steer the array back in the direction of the uplink signal. It will also be used in the non-beam-steering case to compensate for phase shift variations through power amplifiers. The digital interface board can be used to set four 5-bit phase shifters and four 5-bit attenuators and monitor their current settings. Additionally, it is useful outside of the closed-loop system for beamsteering alone. When the VEE program is started, it prompts the user to initialize variables (to zero) or skip initialization. After that, the program enters into a continuous loop waiting for the telemetry period to elapse or a button to be pushed. A telemetry request is sent when the telemetry period is elapsed (every five seconds). Pushing one of the set or reset buttons will send the appropriate command. When a command is sent, the interface status is returned, and the user will be notified by a pop-up window if any error has occurred. The program runs until the End Program button is depressed.

Smith, Amy E.↗

NASA NTRS2012

Digital Architecture for a Trace Gas Sensor Platform

A digital architecture has been implemented for a trace gas sensor platform, as a companion to standard analog control electronics, which accommodates optical absorption whose fractional absorbance equivalent would result in excess error if assumed to be linear. In cases where the absorption (1-transmission) is not equivalent to the fractional absorbance within a few percent error, it is necessary to accommodate the actual measured absorption while reporting the measured concentration of a target analyte with reasonable accuracy. This requires incorporation of programmable intelligence into the sensor platform so that flexible interpretation of the acquired data may be accomplished. Several different digital component architectures were tested and implemented. Commercial off-the-shelf digital electronics including data acquisition cards (DAQs), complex programmable logic devices (CPLDs), field-programmable gate arrays (FPGAs), and microcontrollers have been used to achieve the desired outcome. The most completely integrated architecture achieved during the project used the CPLD along with a microcontroller. The CPLD provides the initial digital demodulation of the raw sensor signal, and then communicates over a parallel communications interface with a microcontroller. The microcontroller analyzes the digital signal from the CPLD, and applies a non-linear correction obtained through extensive data analysis at the various relevant EVA operating pressures. The microcontroller then presents the quantitatively accurate carbon dioxide partial pressure regardless of optical density. This technique could extend the linear dynamic range of typical absorption spectrometers, particularly those whose low end noise equivalent absorbance is below one-part-in-100,000. In the EVA application, it allows introduction of a path-length-enhancing architecture whose optical interference effects are well understood and quantified without sacrificing the dynamic range that allows quantitative detection at the higher carbon dioxide partial pressures. The digital components are compact and allow reasonably complete integration with separately developed analog control electronics without sacrificing size, mass, or power draw.

Gonzales, Paula↗

NASA NTRS2014

All-Digital Baseband 65nm PLL/FPLL Clock Multiplier using 10-cell Library

PLLs for clock generation are essential for modern circuits, to generate specialized frequencies for many interfaces and high frequencies for chip internal operation. These circuits depend on analog circuits and careful tailoring for each new process, and making them fault tolerant is an incompletely solved problem. Until now, all digital PLLs have been restricted to sampled data DSP techniques and not available for the highest frequency baseband applications. This paper presents the design and preliminary evaluation of an all-digital baseband technique built entirely with an easily portable 10-cell digital library. The library is also described, as it aids in research and low volume design porting to new processes. The advantages of the digital approach are the wide variety of techniques available to give varying degrees of fault tolerance, and the simplicity of porting the design to new processes, even to exotic processes that may not have analog capability. The only tuning parameter is digital gate delay. An all-digital approach presents unique problems and standard analog loop stability design criteria cannot be directly used. Because of the quantization of frequency, there is effectively infinite gain for very small loop error feedback. The numerically controlled oscillator (NCO) based on a tapped delay line cannot be reliably updated while a pulse is active in the delay line, and ordinarily does not have enough frequency resolution for a low-jitter output.

Shuler, Robert L., Jr.↗

NASA NTRS2014

ALL-Digital Baseband 65nm PLL/FPLL Clock Multiplier Using 10-Cell Library

Schuler, Robert L., Jr.↗

NASA NTRS2015

Data Services Upgrade: Perfecting the ISIS-I Topside Digital Ionogram Database

The ionospheric topside sounders of the International Satellites for Ionospheric Studies (ISIS) program were designed as analog systems. More than 16,000 of the original telemetry tapes from three satellites were used to produce topside digital ionograms, via an analog-to-digital (A/D) conversion process, suitable for modern analysis techniques. Unfortunately, many of the resulting digital topside ionogram files could not be auto-processed to produce topside Ne(h) profiles because of problems encountered during the A/D process. Software has been written to resolve these problems and here we report on (1) the first application of this software to a significant portion of the ISIS-1 digital topside-ionogram database, (2) software improvements motivated by this activity, (3) N(sub e)(h) profiles automatically produced from these corrected ISIS-1 digital ionogram files, and (4) the availability via the Virtual Wave Observatory (VWO) of the corrected ISIS-1 digital topside ionogram files for research. We will also demonstrate the use of these N(sub e)(h) profiles for making refinements in the International Reference Ionosphere (IRI) and in the determination of transition heights from Oxygen ion to Hydrogen ion.

topside ionosphere↗

NASA NTRS2018

Digital Proxy Simulation of Robotic Hardware

A computer-implemented method, computer program product, and computing system is provided for a digital proxy simulation of robotic hardware. In an implementation, a method may include creating a digital proxy simulation for a robotic hardware wherein the digital simulation and the robotic hardware may share a network interface. a user may be provided with an option to switch between the robotic hardware and the digital proxy simulation. The switch may be executed, upon receiving a user selection, between the robotic hardware and the digital proxy simulation, wherein executing the switch includes transferring input and output signals between the digital proxy simulation and the robotic hardware.

Bacon, James A.↗

NASA NTRS2019

NASA Aeronautics: Knowledge Management and Digital Transformation in Partnership

Knowledge management and digital transformation share common ground. Both maintain an interest in driving mission success, maximizing information access, and leveraging digital technologies to enhance efficiency and effectiveness. As NASA's Aeronautics Research Mission Directorate explores emerging digital capabilities, we are applying KM principles to strengthen our approach. Bringing digital transformation to knowledge management practices also helps us to reinvent antiquated processes and take advantage of new opportunities. This session identifies areas of complementarity between knowledge management and digital transformation, highlights ways KM practitioners can contribute to digital transformation activities in any organization, and provides some examples from NASA Aeronautics' experience in both.

Smith, Tiffany L.↗

NASA NTRS1993

The Trustworthy Digital Camera: Restoring Credibility to the Photographic Image

The increasing sophistication of computers has made digital manipulation of photographic images incredibly easy to perform and, as time goes on, increasingly difficult to detect. The proposed device is a new type of digital camera whose output can be certified as being unretouched, and can restore the credibility that the photographic image once enjoyed. The Trustworthy Digital Camera employs public key encryption techniques at the system level, and produces an encrypted digital signature and a standard-format digital image file each time a picture is taken. Although digitally retouching or altering these image files would still be possible, doing so will cause a mismatch with the verifying signature, proving that the image is not an untouched original...

Friedman, Gary L.↗