Polarization-diversity telemetry receivers.
Polarization-diversity telemetry receivers for combining FM/FM penetrometer data, noting signal fading
TELEMETRY↗
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Results for “SIGNAL FADING”
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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Studies of auditory information processing emphasizing the application of signal detectability theory to the auditory sensory responses Semiannual report, 1 Dec. 1965 - 31 May 1966 and eighth quarterly status report, 1 Mar. - 31 May 1966
Free response to auditory signal detection, signal fading rate on energy band detector for electric ear model, and brightness adaptation research projects
HUMAN REACTION↗
Response of an FM discriminator to a digital FM signal in randomly fading channels.
Error rate from FSK binary signal detection calculated using FM discriminator for FM signal with nonselective fading in Gaussian noise
Nelson, E. A.↗
Performance of convolutional codes on fading channels typical of planetary entry missions
The performance of convolutional codes in fading channels typical of the planetary entry channel is examined in detail. The signal fading is due primarily to turbulent atmospheric scattering of the RF signal transmitted from an entry probe through a planetary atmosphere. Short constraint length convolutional codes are considered in conjunction with binary phase-shift keyed modulation and Viterbi maximum likelihood decoding, and for longer constraint length codes sequential decoding utilizing both the Fano and Zigangirov-Jelinek (ZJ) algorithms are considered. Careful consideration is given to the modeling of the channel in terms of a few meaningful parameters which can be correlated closely with theoretical propagation studies. For short constraint length codes the bit error probability performance was investigated as a function of E sub b/N sub o parameterized by the fading channel parameters. For longer constraint length codes the effect was examined of the fading channel parameters on the computational requirements of both the Fano and ZJ algorithms. The effects of simple block interleaving in combatting the memory of the channel is explored, using the analytic approach or digital computer simulation.
Modestino, J. W.↗
Fade durations in satellite-path mobile radio propagation
Fades on satellite to land mobile radio links are caused by several factors, the most important of which are multipath propagation and vegetative shadowing. Designers of vehicular satellite communications systems require information about the statistics of fade durations in order to overcome or compensate for the fades. Except for a few limiting cases, only the mean fade duration can be determined analytically, and all other statistics must be obtained experimentally or via simulation. This report describes and presents results from a computer program developed at Virginia Tech to simulate satellite path propagation of a mobile station in a rural area. It generates rapidly-fading and slowly-fading signals by separate processes that yield correct cumulative signal distributions and then combines these to simulate the overall signal. This is then analyzed to yield the statistics of fade duration.
Schmier, Robert G.↗
Effects of multipath fading on low data-rate space communications.
Studies have shown that there is a severe signal fading at the turbulent atmosphere of a distant planet such as Venus. The data may be lost during deep fade. It is the objective of this paper to examine the effects of multipath fading on the performance of the noncoherent coded system which is used for the low data-rate space communications especially with the small probes. An exact error probability of the wideband noncoherent MFSK receiver is derived from using the 'Rician' channel model. While the error performance of the receiver is worse than that of the ideal MFSK receiver, as expected, it is interesting to note that the performance degradation due to the multipath fading diminishes as the product of bit duration and IF filter bandwidth becomes large.
Chen, C. H.↗
Evidence of Chiral Fermion Edge Modes through Geometric Engineering of Thermal Hall Effect in 𝛼−RuCl 3
The experimental observation of half-integer-quantized thermal Hall conductivity in the Kitaev candidate material α-RuCl 3 has served as a signature of non-Abelian anyons through an associated chiral Majorana edge mode. However, both the reproducibility of the quantized thermal Hall conductivity and the fundamental nature of the associated heat carriers, whether bosonic or fermionic, are subjects of ongoing and vigorous debate. In a recent theoretical work, it was proposed that varying the sample geometry through creating constrictions can distinguish between different origins of the thermal Hall effect in magnetic insulators. Here, in this study, we provide experimental evidence of chiral fermion edge modes by comparing the thermal Hall effect of a geometrically constricted α-RuCl 3 sample with that of an unconstricted sample. In contrast to the unconstricted crystals where the thermal Hall signal fades below 5 K, the constricted crystals display a significant thermal Hall signal that remains measurable even at 2 K. This sharp difference agrees well with the theoretical prediction and provides compelling evidence for the contribution of chiral fermion edge modes to the thermal Hall effect in α-RuCl 3 . More broadly, this work confirms that the geometry dependence of the thermal Hall effect can help identify chiral spin liquids in candidate materials like α-RuCl 3 and paves the way for the experimental realization of thermal anyon interferometry.
Zhang, Heda [Oak Ridge National Laboratory (ORNL),↗
Compilation and Analysis of 20- and 30-GHz Rain Fade Events at the ACTS NASA Ground Station: Statistics and Model Assessment
Since the beginning of the operational phase of the NASA Research Center's Advanced Communication Technology Satellite (ACTS), signal-fade measurements have been recorded at the NASA Ground Station located in Cleveland, Ohio, with the use of the 20- and 30-GHz beacon signals. Compilations of the daily data have been statistically analyzed on a monthly and yearly basis. Such analyses have yielded relevant parameters as (1) cumulative monthly and yearly probability distributions of signal attenuation by rain, (2) attenuation duration versus attenuation threshold probabilities, and (3) rate-of-fade probabilities. Not only are such data needed for a realistic data base to support the design and performance analysis of future satellite systems, but they are necessary to assess predictions made with the ACTS Rain Attenuation Prediction Model.
Manning, Robert M.↗
Sensing propagation events and fade statistics at C-band for two over-water, line-of-sight propagation paths over a one year period
We examine signal fading statistics over a year period corresponding to two over-water, line-of-site, propagation links in the mid-Atlantic coast of the US. These links are comprised of a transmitter on a tower at Parramore Island, VA operating at 4.7 GHz sending simultaneous cw signals to two receiver systems located on a lighthouse and a lookout tower on Assateague Beach, VA at distances of 44 and 39 km, respectively. The receiving sites are separated by approximately 5 km. Cumulative fade distributions corresponding to yearly, monthly, and diurnal time scales were derived. Fade duration statistics correspond to sustained attenuation events were also derived. These events, which were arbitrarily defined as having fades relative to free space powers in excess of 20 dB for durations of two hours or more, are believed to be generally due to subrefraction. Analysis of synoptic weather conditions and nearby rawindsonde data during two sustained deep fading periods showed atmospheric conditions consistent with extreme subrefraction, where the refractivity-height profile had a positive lapse rate. The efficacy of employing the links as indicators of real time conditions of atmospheric propagation was also demonstrated by a telephone call-up procedure which enabled displays of time series of the fading at remote locations to be generated.
Goldhirsh, Julius↗
Systems implications of L-band fade data statistics for LEO mobile systems
This paper examines and analyzes research data on the role of foliage attenuation in signal fading between a satellite transmitter and a terrestrial vehicle-mounted receiver. The frequency band of measurement, called L-Band, includes the region 1610.0 to 1626.5 MHz. Data from tests involving various combinations of foliage and vehicle movement conditions clearly show evidence of fast fading (in excess of 0.5 dB per millisecond) and fade depths as great or greater than 16 dB. As a result, the design of a communications link power control that provides the level of accuracy necessary for power sensitive systems could be significantly impacted. Specific examples of this include the communications links that employ Code Division Multiple Access (CDMA) as a modulation technique.
Devieux, Carrie L.↗
Discriminator response to an FM signal in a fading channel.
Discriminator threshold and SNR above threshold response when demodulating FM signal undergoing selective fading
SIGNAL TO NOISE RATIO↗
Standards-Based Wireless Sensor Networking Protocols for Spaceflight Applications
Wireless sensor networks (WSNs) have the capacity to revolutionize data gathering in both spaceflight and terrestrial applications. WSNs provide a huge advantage over traditional, wired instrumentation since they do not require wiring trunks to connect sensors to a central hub. This allows for easy sensor installation in hard to reach locations, easy expansion of the number of sensors or sensing modalities, and reduction in both system cost and weight. While this technology offers unprecedented flexibility and adaptability, implementing it in practice is not without its difficulties. Any practical WSN deployment must contend with a number of difficulties in its radio frequency (RF) environment. Multi-path reflections can distort signals, limit data rates, and cause signal fades that prevent nodes from having clear access to channels, especially in a closed environment such as a spacecraft. Other RF signal sources, such as wireless internet, voice, and data systems may contend with the sensor nodes for bandwidth. Finally, RF noise from electrical systems and periodic scattering from moving objects such as crew members will all combine to give an incredibly unpredictable, time-varying communication environment.
Barton, Richard J.↗
The error probability of a wide-band FSK receiver in the presence of multipath fading.
Calculations are made for the probability of error of a wide-band FSK receiver of the type used in space telemetry when multipath reflections off the planetary surface cause signal fading. The error probability is found for both low and high fading bandwidths and for small or large reflected path delays.
Chadwick, H. D.↗
An improvement in SAR image interpretability provided by post-correlation signal processing
A presentation on the basis of subjective analysis of computer-generated SAR imagery depicts the improvement in interpretability obtained by post-correlation signal processing. A parametric study was conducted to determine the improvement in interpretability obtained by the application of signal weighting functions on the post-processed returns. The results suggest that a marked improvement in interpretability results from symmetrizing the exponential distribution of the fading signal. Preliminary analysis indicates that signal weighting improves the contrast ratio between the mean value of adjacent homogeneous regions in a SAR scene.
Matthews, N. D.↗
Field Measurements of Sonic Boom Penetration Into the Ocean
Six sonic booms, generated by F-4 aircraft under steady fight at a range of altitudes (610-6100 m) and Mach numbers (1.07-1.26), were measured just above the air/sea interface, and at five depths in the water column. The measurements were made with a vertical hydrophone array suspended from a small spar buoy at the sea surface, and telemetered to a nearby research vessel. The sonic boom pressure amplitude decays exponentially with depth, and the signal fades into the ambient noise field by 30-50 in, depending on the strength of the boom at the sea surface. Low-frequency components of the boom waveform penetrate significantly deeper than high frequencies. Frequencies greater than 20 Hz are difficult to observe at depths greater than about 10 m. Underwater sonic boom pressure measurements exhibit excellent agreement with predictions from analytical theory, despite the assumption of a flat air/sea interface. Significant scattering of the sonic boom signal by the rough ocean surface is not detected. Real ocean conditions appear to exert a negligible effect on the penetration of sonic booms into the ocean unless steady vehicle speeds exceed Mach 3, when the boom incidence angle is sufficient to cause scattering on realistic open ocean surfaces.
Sohn, R. A.↗
Theoretical and experimental comparison of an ultra-high-speed laser data transmission system
The performance of a digital optical data transmission system is specified by the probability that the system erroneously decides a signal has or has not been transmitted. Two factors which induce signal fading and thereby decrease system performance are atmospheric scintillation and transmitter pointing inaccuracy. A channel simulator was developed that is capable of producing the effects of both atmospheric scintillation and the transmitter pointing problem for a neodymium-yag optical data transmission systems. Comparison of data taken from the modulated intensity of a beam having been transmitted through the channel simulator with experimental data from GEOS-B argon laser transmission through the atmosphere to a low earth-orbiting satellite indicates that the modulated signal intensity is log-normal to the degree of measured atmospheric scintillation.
Tycz, M.↗
Fade measurements at L-band and UHF in mountainous terrain for land mobile satellite systems
Fading results related to land mobile satellite communications at L-band (1502 MHz) and UHF (870 MHz) are described. These results were derived from an experiment performed in a series of canyon passes in the Boulder, Colorado region of the US. The experimental configuration involved a helicopter as the source platform, which maintained a relatively fixed geometry with a mobile van containing the receiver and data-acquisition system. An unobstructed line of sight between the radiating sources and the receiving van was, for the most part, also maintained. In this configuration, the dominant mechanism causing signal fading (or enhancement) is a result of multipath. The resulting fade distributions demonstrated that at the 1 percent and 5 percent levels, 5.5- and 2.6-dB fades were on the average exceeded at L-band and 4.8- and 2.4-dB at UHF, respectively, for a path elevation angle of 45 deg. The canyon results as compared with previous roadside-tree-shadowing results demonstrate that the deciding factor dictating fade margin for future land mobile satellite systems is tree shadowing rather than fades caused by multipath.
Vogel, Wolfhard J.↗
Dynamic rain fade compensation techniques for the advanced communications technology satellite
The dynamic and composite nature of propagation impairments that are incurred on earth-space communications links at frequencies in and above the 30/20 GHz Ka band necessitate the use of dynamic statistical identification and prediction processing of the fading signal in order to optimally estimate and predict the levels of each of the deleterious attenuation components. Such requirements are being met in NASA's Advanced Communications Technology Satellite (ACTS) project by the implementation of optimal processing schemes derived through the use of the ACTS Rain Attenuation Prediction Model and nonlinear Markov filtering theory. The ACTS Rain Attenuation Prediction Model discerns climatological variations on the order of 0.5 deg in latitude and longitude in the continental U.S. The time-dependent portion of the model gives precise availability predictions for the 'spot beam' links of ACTS. However, the structure of the dynamic portion of the model, which yields performance parameters such as fade duration probabilities, is isomorphic to the state-variable approach of stochastic control theory and is amenable to the design of such statistical fade processing schemes which can be made specific to the particular climatological location at which they are employed.
Manning, Robert M.↗