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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Multicarrier Spread Spectrum Communications With Noncontiguous Subcarrier Bands for HF Skywave Links

Existing high-frequency (HF) radio platforms offer robust performance against the volatile HF propagation channel. However, the growing traffic across the band contests the reliability of these systems. While techniques to mitigate the effects of narrowband interference have been thoroughly explored, they are insufficient against wideband interference or when the transmission band is occupied by numerous scattered users. To improve reliability in these congested channel conditions, we propose a filter-bank based multicarrier spread-spectrum waveform with noncontiguous subcarrier bands. Using noncontiguous subcarrier bands enables the system to at once leverage the robustness of a wideband system while retaining the frequency agility of a narrowband system. In this study, we modify a filter-bank transmitter structure to accommodate noncontiguous subcarrier bands and consider several immediate impacts of this change, such as elevated peak-to-average-power ratios (PAPRs). A receiver architecture to process the noncontiguous spread-spectrum signal is also introduced, along with details regarding wideband channel estimation. Finally, we develop efficient transmitter and receiver structures to support practical system implementations. We conclude by comparing the performance of contiguous and noncontiguous systems through both simulation and over-the-air testing. The results show that the noncontiguous system remains robust in typical HF channels while significantly outperforming the contiguous system in congested spectral conditions.

(PAPR↗
NASA NTRS1991

New space research frequency band proposals in the 20- to 40.5-GHz range

Future space research communications systems may require spectra above 20 GHz. Frequency bands above 20 GHz are identified that are suitable for space research. The selection of the proper bands depends on consideration of interference with other radio services, adequate bandwidths, link performance, and technical requirements for practical implementation.

Bishop, D. F.↗
NASA NTRS2021

Simulation of Radio Frequency Power Received by a UAV Along Its Flight Path

A ray-tracing electromagnetic simulation using ALTAIR WinProp software was performed to calculate the 2.4 GHz power received by a UAV in flight, both from the intended controller transmitter and from a fictitious interference source of equal power located near the ground. The signal-to-interference ratio was then calculated. For the chosen example, the received power from the controller varied from -88.3 to -70.1 dBm, while the signal-to-interference ratio varied from -10.9 to +11.4 db. This work was done in support of the System-Wide Safety Project Technical Challenge 2 - Emerging Operations at NASA Langley, which is studying methods to avoid interference of UAV control and data relay signals.

Electromagnetic Simulation↗
NASA NTRS2005

Design and Performance Evaluation of a UWB Communication and Tracking System for Mini-AERCam

NASA Johnson Space Center (JSC) is developing a low-volume, low-mass, robotic free-flying camera known as Mini-AERCam (Autonomous Extra-vehicular Robotic Camera) to assist the International Space Station (ISS) operations. Mini-AERCam is designed to provide astronauts and ground control real-time video for camera views of ISS. The system will assist ISS crewmembers and ground personnel to monitor ongoing operations and perform visual inspections of exterior ISS components without requiring extravehicular activity (EAV). Mini-AERCam consists of a great number of subsystems. Many institutions and companies have been involved in the R&D for this project. A Mini-AERCam ground control system has been studied at Texas A&M University [3]. The path planning and control algorithms that direct the motions of Mini-AERCam have been developed through the joint effort of Carnegie Mellon University and the Texas Robotics and Automation Center [5]. NASA JSC has designed a layered control architecture that integrates all functions of Mini-AERCam [8]. The research described in this report is part of a larger effort focused on the communication and tracking subsystem that is designed to perform three major tasks: 1. To transmit commands from ISS to Mini-AERCam for control of robotic camera motions (downlink); 2. To transmit real-time video from Mini-AERCam to ISS for inspections (uplink); 3. To track the position of Mini-AERCam for precise motion control. The ISS propagation environment is unique due to the nature of the ISS structure and multiple RF interference sources [9]. The ISS is composed of various truss segments, solar panels, thermal radiator panels, and modules for laboratories and crew accommodations. A tracking system supplemental to GPS is desirable both to improve accuracy and to eliminate the structural blockage due to the close proximity of the ISS which could at times limit the number of GPS satellites accessible to the Mini-AERCam. Ideally, the tracking system will be a passive component of the communication system which will need to operate in a time-varying multipath environment created as the robot camera moves over the ISS structure. In addition, due to many interference sources located on the ISS, SSO, LEO satellites and ground-based transmitters, selecting a frequency for the ISS and Mini-AERCam link which will coexist with all interferers poses a major design challenge. To meet all of these challenges, ultrawideband (UWB) radio technology is being studied for use in the Mini-AERCam communication and tracking subsystem. The research described in this report is focused on design and evaluation of passive tracking system algorithms based on UWB radio transmissions from mini-AERCam.

Barton, Richard J.↗
NASA NTRS2010

Reducing Field Distortion in Magnetic Resonance Imaging

A concept for a magnetic resonance imaging (MRI) system that would utilize a relatively weak magnetic field provides for several design features that differ significantly from the corresponding features of conventional MRI systems. Notable among these features are a magnetic-field configuration that reduces (relative to the conventional configuration) distortion and blurring of the image, the use of a superconducting quantum interference device (SQUID) magnetometer as the detector, and an imaging procedure suited for the unconventional field configuration and sensor. In a typical application of MRI, a radio-frequency pulse is used to excite precession of the magnetic moments of protons in an applied magnetic field, and the decaying precession is detected for a short time following the pulse. The precession occurs at a resonance frequency proportional to the strengths of the magnetic field and the proton magnetic moment. The magnetic field is configured to vary with position in a known way; hence, by virtue of the aforesaid proportionality, the resonance frequency varies with position in a known way. In other words, position is encoded as resonance frequency. MRI using magnetic fields weaker than those of conventional MRI offers several advantages, including cheaper and smaller equipment, greater compatibility with metallic objects, and higher image quality because of low susceptibility distortion and enhanced spin-lattice-relaxation- time contrast. SQUID MRI is being developed into a practical MRI method for applied magnetic flux densities of the order of only 100 T

Eom, Byeong Ho↗
NASA NTRS2018

System to Perform Radio Frequency Interferometry Using Optical Fiber Sensing Signal Processing Techniques

Aspects of the present disclosure involve a system and method for performing radio frequency interferometry using optical fiber sensing. Optical fiber sensing is performed as a reference signal is defined and compared, in the optical domain, to incoming signals to obtain interference fringe patterns that can be used to decode phase shift offsets with respect to the designated reference signal. The phase shift offsets can be determined by first optically modulating the reference and incoming signals using a laser source as the carrier. In the optical domain, the reference and incoming signals are combined using an optical coupler and then converted back to the electrical domain for processing.

Ott, Melanie N.↗
NASA NTRS2006

RFID Transponders' Radio Frequency Emissions in Aircraft Communication and Navigation Radio Bands

Radiated emissions in aircraft communication and navigation bands are measured from several active radio frequency identification (RFID) tags. The individual tags are different in design and operations. They may also operate in different frequency bands. The process for measuring the emissions is discussed, and includes tag interrogation, reverberation chamber testing, and instrument settings selection. The measurement results are described and compared against aircraft emission limits. In addition, interference path loss for the cargo bays of passenger aircraft is measured. Cargo bay path loss is more appropriate for RFID tags than passenger cabin path loss. The path loss data are reported for several aircraft radio systems on a Boeing 747 and an Airbus A320.

Nguyen, Truong X.↗
NASA NTRS1984

Indirect Phase Height Measurements in Central and Eastern Europe for Monitoring D Region Plasma

Low-frequency propagation experiments for the investigation of the lower part of the ionospheric D region were at first used by BRACEWELL et al. (1951) in the early fifties. Among these was the method of indirect phase height measurements for continuous monitoring of the lower ionosphere. It is based upon field strength measurements of commercial radio transmitters in the frequency range between 50 and 200 kHz at distances from 500 to 1500 km. The field strength records show characteristic diurnal variations with maxima and minima, produced by interference between the ground wave and the ionospherically reflected sky wave, the phase difference between varies in correspondence to the diurnal variation of the reflection height. In order to check the validity of interpretations of indirect phase height data, comparisons were made with simultaneous rocket soundings. Results are summarized.

Cossart, G. V.↗
NASA NTRS1974

Surface electrical properties experiment. Part 2: Theory of radio-frequency interferometry in geophysical subsurface probing

The radiation fields due to a horizontal electric dipole laid on the surface of a stratified medium were calculated using a geometrical optics approximation, a modal approach, and direct numerical integration. The solutions were obtained from the reflection coefficient formulation and written in integral forms. The calculated interference patterns are compared in terms of the usefulness of the methods used to obtain them. Scattering effects are also discussed and all numerical results for anisotropic and isotropic cases are presented.

Kong, J. A.↗
NASA NTRS1975

An RF link analysis of MSBLS during ALT

An analysis of the microwave scanning beam landing system (MSBLS) ground station to orbiter radio frequency (RF) link was made to determine if the expected signal levels will be compatible with orbiter receiver capabilities. Of primary interest was whether or not loss of data will occur due to interference caused by the orbiter 101 nose boom which provides additional air data during the approach and landing test. The results of the analysis indicate that a small amount of data loss may occur due to the proximity of the MSBLS antennas and the nose boom. Tabulated data of antenna radiation patterns are given.

Speir, R. E.↗
NASA NTRS2009

Reducing Interference in ATC Voice Communication

Three methods have been proposed to be developed to enable reduction of the types of interference that often occur among voice-communication radio signals involved in air-traffic control (ATC). For historical reasons and for compatibility with some navigation systems, control towers and aircraft use amplitude modulation (AM) for voice communication. In the presence of two simultaneous AM transmissions in the same frequency channel, what is heard through a receiver includes not only the audio portions of both transmissions but also an audio heterodyne signal at the difference between the carrier frequencies of the transmissions (as a practical matter, the carrier frequencies almost always differ somewhat). The situation is further complicated by multiple heterodyne signals in the presence of more than two simultaneous transmissions. Even if one of the transmissions does not include AM because of a transmitter malfunction or because a transmitter was inadvertently turned on or left on, the heterodyne signal makes it difficult to understand the audio of the other transmission. The proposed methods would utilize digital signal processing to counteract this type of interference.

Battle, John O.↗
NASA NTRS2003

Investigations of Relatively Easy To Construct Antennas With Efficiency in Receiving Schumann Resonances: Preparations for a Miniaturized Reconfigurable ELF Receiver

Relatively little is known about the cavity between the Earth and the ionosphere, which opens opportunities for technological advances and unique ideas. One effective means to study this cavity is with extremely low frequency (ELF) antennas. Possible applications of these antennas are global weather prediction, earthquake prediction, planetary exploration, communication, wireless transmission of power, or even a free energy source. The superconducting quantum interference device SQUID) and the coil antenna are the two most acceptable receivers discovered for picking up ELF magnetic fields. Both antennas have the potential for size reduction, allowing them to be portable enough for access to space and even for personal ware. With improvements of these antennas and signal processing, insightful analysis of Schumann resonance (SR) can give the science community a band of radio frequency (RF) signals for improving life here on Earth and exploring beyond.

Farmer, Brian W.↗
NASA NTRS1995

Solar Probe Technology Challenges

A mission close to the sun is only possible if new spacecraft technologies can be developed and incorporated into a state-of-the-art spacecraft concept. The perihelion goal of 4 solar radii requires a shielded spacecraft that can tolerate the 3000 suns solar flux while maintaining the electronics components at room temperature. In addition, the shield surface should sublimate at a rate of less than 3 mg/s at perihelion. Many shield configuration designs have been studied and the most promising is a parabolic shape that functions as both a shield and a large high gain antenna. The shield material chosen for this design is a carbon-carbon material with highly emissive surface properties. A mission requirement for a high telecommunications power stems from the expected interference when attempting to transmit data through the solar corona. It is expected that the large carbon-carbon shield/antenna will have a large power gain even at high temperatures and will return adequate telemetry at the X-band radio frequency chosen for the Solar Probe mission. Other key technology needs include a non-nuclear power subsystem that can function in the extreme environments of the mission from Earth to Jupiter and onward to a 4 solar radii perihelion.

Solar↗
NASA NTRS1976

Effects of propagation phenomena and frequency allocation on the growth of satellite communications

The development of new allocations and new frequency and orbit sharing criteria for satellite communications below 10 GHz is discussed. These criteria are dependent on the outcome of current spectrum and orbit utilization and propagation studies addressing such problems as intersystem interference, satellite spacing, positioning, and repositioning, spillover of radio signals across geographic boundaries, and the adverse effects of propagation phenomena. These problems are discussed in relation to preparations for the 1979 General World Administrative Radio Conference.

Freibaum, J.↗
NASA NTRS1985

The Spectrum Orbit Utilization Program (SOUP) used for DBS plan analysis at RARC '83

This paper describes the history, functions, and usage of the program that was used to analyze the plans for direct broadcast satellite service developed in the course of the 1983 Regional Administrative Radio Conference for ITU Region 2. Given the requirements for direct broadcast service by the administrations, the conference delegates (1) developed the appropriate technical parameters; (2) made tentative assignments to the orbit locations, frequencies, and polarizations of space stations, (3) calculated the interferences and margins of such assignments through the use of the Spectrum Orbit Utilization Program (SOUP); and (4) iterated this procedure until an acceptable plan was found.

Davidson, J.↗