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  • 1
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    Antenna Technology Shuttle Experiment (ATSE) (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Numerous space applications of the future will require mesh deployable antennas of 15 m in diameter or greater for frequencies up to 20 GHz. These applications include mobile communications satellites, orbiting very long baseline interferometry (VLBI) astrophysics missions, and Earth remote sensing missions. A Lockheed wrap rip antennas was used as the test article. The experiments covered a broad range of structural, control, and RF discipline objectives, which is fulfilled in total, would greatly reduce the risk of employing these antenna systems in future space applications. It was concluded that a flight experiment of a relatively large mesh deployable reflector is achievable with no major technological or cost drivers. The test articles and the instrumentation are all within the state of the art and in most cases rely on proven flight hardware. Every effort was made to design the experiments for low cost.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-Langley Research Center NASA(DOD Control)Structures Interaction Technology, 1986; p 779-807
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Differential encoding for multiple amplitude and phase shift keying systems (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Because of the symmetry in most two-dimensional signal constellations, ambiguities exist at the receiver as to the exact phase orientation of the received signal set. In PSK systems, this ambiguity is resolved by the use of differential encoding. This paper presents differential encoding techniques which can be used with a variety of symmetric signal sets to remove their phase ambiguity. While not proven to be optimum, the techniques do have low performance penalties relative to the uncoded performance. The key to reducing the performance penalty is to use the minimum amount of differential encoding necessary to resolve the ambiguity. Examples of encoding techniques for several common signal constellations are given, including their performance penalties.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications; COM-26; Mar. 197
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    An experiment to enable commercial mobile satellite service (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: A Mobile Satellite Experiment (MSAT-X) is described, based on a planned cooperative U.S./Canadian program. The experiment would establish network architecture, develop system and ground-segment technology, and define the technical characteristics needed to help structure the regulatory/institutional framework needed to enable a first-generation commercial satellite service. A satellite of this type would augment terrestrial systems, both cellular and noncellular, in the thin-route/rural areas of the country where service is either unavailable or inadequate. Applications range from wide-area radio/dispatch (e.g., oil exploration and interstate trucking) to extension of the public mobile telephone service. Market estimates are provided and experiment objectives and requirements are delineated. The requirements are being developed in close coordination with the Department of Communications (DOC) of Canada and with industry and potential-user organizations. The paper closes with a development plan and milestone chart.
    Keywords: COMMUNICATIONS AND RADAR
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    A decision-directed network for dual-polarization crosstalk cancellation (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Frequency reuse in the specific form of dual-polarized microwave communication systems has grown in importance in recent years as a practical means of radio spectrum conservation. Ideally the capacity of a given frequency allocation can be doubled through dual-polarization. However, hardware imperfections and propagation effects, particularly rain depolarization, prevent the achievement of this doubling without severe system performance degradation. A decision-directed cross-polarization correction network is presented whose operation depends on only simple base-band signal processing. No pilot tones or frequency offsets are required. The loop can work with any two-dimensional signal set for digital data transmission. The loop has been experimentally verified and provides a means of doubling the data capacity with little performance degradation.
    Keywords: COMMUNICATIONS AND RADAR
    Type: In: ICC ''79; International Conference on Communications; Jun 10, 1979 - Jun 14, 1979; Boston, MA
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    NASA's mobile satellite communications program; ground and space segment technologies (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: This paper describes the Mobile Satellite Communications Program of the United States National Aeronautics and Space Administration (NASA). The program's objectives are to facilitate the deployment of the first generation commercial mobile satellite by the private sector, and to technologically enable future generations by developing advanced and high risk ground and space segment technologies. These technologies are aimed at mitigating severe shortages of spectrum, orbital slot, and spacecraft EIRP which are expected to plague the high capacity mobile satellite systems of the future. After a brief introduction of the concept of mobile satellite systems and their expected evolution, this paper outlines the critical ground and space segment technologies. Next, the Mobile Satellite Experiment (MSAT-X) is described. MSAT-X is the framework through which NASA will develop advanced ground segment technologies. An approach is outlined for the development of conformal vehicle antennas, spectrum and power-efficient speech codecs, and modulation techniques for use in the non-linear faded channels and efficient multiple access schemes. Finally, the paper concludes with a description of the current and planned NASA activities aimed at developing complex large multibeam spacecraft antennas needed for future generation mobile satellite systems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IAF PAPER 84-84
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    The use of TWT amplifiers in M-ary amplitude and phase shift keying systems (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A great deal of research is presently being conducted to study modulation schemes in order to reduce the bandwidth of digital communications. These M-ary amplitude and phase shift keying (MAPSK) modulation systems place new requirements on TWT amplifiers in space applications in that the various signal sets usually include two or more discrete output power levels as well as discrete phases at each power level. This paper presents a variety of predistortion schemes to circumvent the TWT problems of AM distortion and AM-to-PM conversion in order to produce MAPSK signal sets. A feedback scheme is presented to correct for long-term phase and amplitude drifts in the transmitter. A complete transmitter is proposed using predistortion to produce the desired MAPSK signal set at very high data rates including the possible use of a feedback stabilization scheme.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Conference on Communications; Jun 16, 1975 - Jun 18, 1975; San Francisco, CA
    Format: text
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    NASA TECHNICAL REPORTS
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