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  • Other Sources  (350)
  • COMMUNICATIONS AND RADAR  (350)
  • 2000-2004
  • 1990-1994  (350)
  • 1990  (350)
  • 1
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    NASA's Advanced Tracking and Data Relay Satellite System for the years 2000 and beyond (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: An Advanced Tracking and Data Relay Satellite System (ATDRSS) reference architecture that embodies many of the system features and technological enhancements considered essential is presented and described. The architectural and user service features of the existing TDRSS are reviewed, and certain evolutionary features that will take place by the mid-1990s are discussed. NASAs projected user service requirements for the first decade at the next century, which are the principal drivers for the ATDRSS architecture, are described, including such aspects as the real-time data rates and the quantity of simultaneous services that must be supported. The discussion of the ATDRSS reference architecture covers rationale, technology considerations, and key features of the future ATDRSS user service. A status summary of the ATDRSS program is given.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE, Proceedings (ISSN 0018-9219); 78; 1141-115
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    NASA TECHNICAL REPORTS
  • 2
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    Advanced Communications Technology Satellite (ACTS) (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The benefits that will be offered by the NASA-sponsored communication spacecraft ACTS which is scheduled for launch in 1992 are described together with examples of demonstrations on proposed data, video, and voice applications supported by the advanced ACTS technologies. Compared to existing satellite service, the ACTS will provide lower cost, better service, greater convenience, and improved service reliability of telecommunications to customers around the world. In addition, the pioneering ACTS technology will provide many capabilities qualitatively different from those of current satellite systems, such as on-demand assignment, frequency reuse, and the flexible targeting of spot beams directly to the very-small-aperture terminals at customer premises.
    Keywords: COMMUNICATIONS AND RADAR
    Type: AIAA PAPER 90-0839 , AIAA International Communication Satellite Systems Conference and Exhibit; Mar 11, 1990 - Mar 15, 1990; Los Angeles, CA; United States
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    NASA TECHNICAL REPORTS
  • 3
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    US development and commercialization of a North American mobile satellite service (1990)
    In:  CASI
    Details
    Publication Date: 2019-08-14
    Description: U.S. policies promoting applications and commercialization of space technology for the 'benefit of mankind,' and emphasis on international competitiveness, formed the basis of NASA's Mobile Satellite (MSAT) R&D and user experiments program to develop a commercial U.S. Mobile Satellite Service. Exemplifying this philosophy, the MSAT program targets the reduction of technical, regulatory, market, and financial risks that inhibit commercialization. The program strategy includes industry and user involvement in developing and demonstrating advanced technologies, regulatory advocacy, and financial incentives to industry. Approximately two decades of NASA's satellite communications development and demonstrations have contributed to the emergence of a new multi-billion dollar industry for land, aeronautical, and maritime mobile communications via satellite. NASA's R&D efforts are now evolving from the development of 'enabling' ground technologies for VHF, UHF, and L-Band mobile terminals, to Ka-Band terminals offering additional mobility and user convenience.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL, California Inst. of Tech., Proceedings of the 2nd International Mobile Satellite Conference (IMSC 1990); p 431-437
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    NASA TECHNICAL REPORTS
  • 4
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    Performance of a modified feedback loop adaptive array with TVRO satellite signals (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: The performance of an experimental adaptive antenna array system is evaluated using television-receive-only (TVRO) satellite signals. The experimental system is a sidelobe canceler with two auxiliary channels. Modified feedback loops are used to enhance the suppression of weak interfering signals. The modified feedback loops use two spatially separate antennas, each with an individual amplifier for each auxiliary channel. Thus, the experimental system uses five antenna elements. Instead of using five separate antennas, a reflector antenna with multiple feeds is used to receive signals from various TVRO satellites. The details of the earth station are given. It is shown that the experimental system can null up to two signals originating from interfering TVRO satellites while receiving the signals from a desired TVRO satellite.
    Keywords: COMMUNICATIONS AND RADAR
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    NASA TECHNICAL REPORTS
  • 5
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    Performance evaluation of land mobile satellite system under vegetative shadowing using differential multiple TCM and QPSK (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: A comparative analysis by computer simulation of the land mobile satellite system (LMSS) is presented for the uncoded quadrature phase shift keying (QPSK), rate 2/3 8-PSK trellis coded modulation (TCM), and rate 4/6 multiplicity 2 8-PSK TCM schemes. An analytical model is used for simulating the fading channel. The simulation results show that under Rayleigh fades, the TCM designed for the fading channel is superior to uncoded QPSK and to the conventional TCM optimized for the additive white Gaussian noise (AWGN) channel. The performance of differentially detected TCM under AWGN and fading is examined based on the preliminary results. Results of the uncoded QPSK with fading channel modeled with the empirical fade data are given.
    Keywords: COMMUNICATIONS AND RADAR
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    NASA TECHNICAL REPORTS
  • 6
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    Frame synchronization for a channel with different data rates (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: In some communication links, different data rates are used at different times on the same channel and each is assigned a separate frame synchronization (sync) marker. The frame search is completed within a finite number of frame intervals once both phase-lock and bit-sync are achieved because the incoming data rate can change. The probability of failure to frame-lock, and an upper bound of probability of false frame-lock in a frame search mode are derived for a communication link with a 10 to the -5th bit error probability. The probability of failure to detect data-rate change and the probability of false detection of data-rate change in a frame-lock mode are discussed. In a frame-lock mode, the probability of failure to detect data-rate change and probability detection of data-rate change an equal to 4.96 x 10 to the -12th. A frame-lock device can be used for the Space Station Freedom Ku-band return link.
    Keywords: COMMUNICATIONS AND RADAR
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    NASA TECHNICAL REPORTS
  • 7
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    S-band multiple-access interference study for advanced tracking and data relay satellite systems (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: The results of a study on the effect of mutual interference among S-band multiple access (SMA) system users of advanced tracking and data relay satellite system (ATDRSS) are presented. In the ATDRSS era, the SMA system is required to support data rates ranging from 10 kb/s to 3 Mb/s. The system will consist of four advanced tracking and data relay satellites (ATDRS) each supporting up to five telemetry links. All users have 10 MHz bandwidth with their carrier frequency equal to 2.2875 GHz. A hybrid SDMA/CDMA scheme is used to mitigate the effect of the interference among system users. SMA system interference probability is evaluated with CLASS software. User link margin degradation due to mutual interference between two users is evaluated. System interference probability is evaluated for the projected 1996 mission model, a reference mission model, and a modified reference mission model.
    Keywords: COMMUNICATIONS AND RADAR
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    NASA TECHNICAL REPORTS
  • 8
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    Custom CMOS Reed Solomon coder for the Hubble Space Telescope (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: A VLSI coder is presented that can function either as an encoder or decoder for Reed-Solomon codes. VLSI is one approach to implementing high-performance Reed-Solomon decoders. There are three VLSI technologies that could be used: gate arrays, standard cells, and full custom. The first two approaches are relatively easy to implement, but are limited in both performance and density. Full-custom VLSI is used to achieve both circuit density and speed, and allows control of the amount of interconnect. Speed, which is a function of capacitance, which is a function of interconnect, is an important parameter in high-performance VLSI. A single 8.2 mm x 8.4 mm, 200,000 transistor CMOS chip implementation of the Reed-Solomon code required by the Hubble Space Telescope is reported. The chip features a 10-MHz sustained byte rate independent of error pattern. The 1.6-micron CMOS integrated circuit has complete decoder and encoder functions and uses a single data/system clock. Block lengths up to 255 bytes and shortened codes are supported with no external buffering. Erasure corrections and random error corrections are supported with programmable correction of up to 10 symbol errors. Correction time is independent of error pattern and the number of errors in the incoming message.
    Keywords: COMMUNICATIONS AND RADAR
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    NASA TECHNICAL REPORTS
  • 9
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    Coherent lightwave communications; Proceedings of the Meeting, Boston, MA, Sept. 7, 8, 1989 (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: Various papers on coherent lightwave communications are presented. Individual topics addressed include: overview of coherent light wave communications, frequency stabilization techniques for coherent lightwave systems, characterization of laser diode intensity noise at microwave frequencies with high sensitivity, FP and DFB semiconductor lasers with arbitrary external optical feedback, birefringence-controlled phase-shifter, polarization diversity and scrambling techniques for coherent systems, polarization control scheme for coherent optical systems, simulation of IF filtering effects on the performance of coherent optical receivers. Also discussed are: performance of optical DPSK receivers in the presence of optical channel noise, optical heterodyne communications with polarization modulation, coherent fiber optical subcarrier multiplexed system, engineered rack-mounted coherent transmission system, technology aspects of a coherent optical MAN, broadband exchange by coherent multicarrier switching, generalized temporal CDMA for optical communications. Overviews are given of recent progress at individual companies.
    Keywords: COMMUNICATIONS AND RADAR
    Type: SPIE-1175 , Coherent Lightwave Communications; Sept. 7-8, 1989; Boston, MA; United States
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    NASA TECHNICAL REPORTS
  • 10
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    A correlative investigation of the propagation of ULF wave power through the dayside magnetosphere (1990)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Three different ULF wave phenomena (azimuthally polarized Pc 3 pulsations, radially polarized Pc 4 pulsations, and solitary Pc 5 pulsations related to solar wind pressure pulses) were studied. The main problems covered are: (1) how do magnetospheric Pc 3-4 pulsations, which appear to originate in the solar wind, enter the magnetosphere, and how is this wave energy transported throughout the magnetosphere once it enters; (2) what is the ULF response of the outer dayside magnetosphere to solar wind pressure pulses; and (3) how do Pc 3-4 pulsations modulate ELF-VLF emissions in the dayside magnetosphere.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-187784 , NAS 1.26:187784
    Format: application/pdf
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