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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Design and performance evaluation of a wideband FM spread-spectrum multiple-access system

The system described performs the tracking and communications functions of a tracking and data relay satellite system (TDRS). The spread-spectrum signal format is achieved through wide deviation FM by a sinusoidal subcarrier unique to each multiple-access user. A compound phase-locked loop tracks carrier and subcarrier and demodulates data and ranging signals. Design parameters of user and ground terminals for TDRS are given. Acquisition procedures are described. Performance analyses are presented including the effects of noise, RFI, multipath and other users.

Wachsman, R. H.↗
NASA NTRS1972

Bias and spread in extreme value theory measurements of probability of error

Extreme value theory is examined to explain the cause of the bias and spread in performance of communications systems characterized by low bit rates and high data reliability requirements, for cases in which underlying noise is Gaussian or perturbed Gaussian. Experimental verification is presented and procedures that minimize these effects are suggested. Even under these conditions, however, extreme value theory test results are not particularly more significant than bit error rate tests.

Smith, J. G.↗
NASA NTRS1971

Relationship between Fe /+/ ions and equatorial spread F.

Evaluation of observations from the retarding potential analyzer on Ogo 6 near the magnetic equator, demonstrating an intimate relationship between the presence of Fe(+) ions and irregularities in the total ion concentration. The ionospheric irregularities (or structure) are probably another manifestation of equatorial spread F, although this has not yet been verified. Nearly half the nighttime equatorial crossings below 700 km exhibit both Fe(+) and structure, but only 10% of the passes without Fe(+) have structure. Approximately one-third of the passes with Fe(+) are not structured, which indicates that Fe(+) may be a necessary but not sufficient condition for structure formation. The Atlantic region shows an extremely high and detailed correlation between Fe(+) ions and the irregularities.

Hanson, W. B.↗
NASA NTRS1971

Bias and spread in EVT performance tests.

Performance tests (error probability measurements) of communications systems characterized by low bit rates and high reliability requirements frequently utilize classical extreme value theory (EVT) to avoid the excessive test times encountered with bit error rate (BER) tests. If the underlying noise is Gaussian or perturbed Gaussian, the EVT error estimates have either excessive bias or excessive variance if an insufficient number of test samples is used. EVT is examined to explain the cause of this bias and spread. Experimental verification is made by testing a known Gaussian source, and procedures that minimize these effects are described. It seems apparent that even under the best of conditions the EVT test results are not particularly better than those of BER tests.

Smith, J. G.↗
NASA NTRS1972

A surface wave spread spectrum communication link.

This development has resulted in a fast lock-up, 8-MHz bandwidth, 8-KHz data rate, spread spectrum communication link breadboard that is implemented using surface wave devices as the primary signal generators and signal processing elements. It uses surface wave tapped delay lines (SWTDL's) in the transmitter to generate the signals and in the receiver to match filter detect them. The system also incorporates a re-entry delay line (circulating integrator) which increases the effective code length per data bit by eight-fold.

Fugit, B. R.↗