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  • 1
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    Hybrid coding systems study (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The state of efficiency improvement available with high speed decoders presently in operation or under development is summarized. The required ratio of bit-energy-to-noise-density is given in each case for bit error probabilities.
    Keywords: COMPUTERS
    Type: NASA-CR-114486
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Study of information transfer optimization for communication satellites (1973)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The results are presented of a study of source coding, modulation/channel coding, and systems techniques for application to teleconferencing over high data rate digital communication satellite links. Simultaneous transmission of video, voice, data, and/or graphics is possible in various teleconferencing modes and one-way, two-way, and broadcast modes are considered. A satellite channel model including filters, limiter, a TWT, detectors, and an optimized equalizer is treated in detail. A complete analysis is presented for one set of system assumptions which exclude nonlinear gain and phase distortion in the TWT. Modulation, demodulation, and channel coding are considered, based on an additive white Gaussian noise channel model which is an idealization of an equalized channel. Source coding with emphasis on video data compression is reviewed, and the experimental facility utilized to test promising techniques is fully described.
    Keywords: SPACE VEHICLES
    Type: NASA-CR-114561
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Carrier tracking, bit synchronization, and coding for S-band communications links (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: This paper presents the results of a study of the performance of Viterbi-decoded convolutional codes in the presence of nonideal carrier tracking and bit synchronization. A constraint length 7, rate 1/3 convolutional code and parameters suitable for the space shuttle coded communications links are used. Mathematical models are developed and theoretical and simulation results are obtained to determine the tracking and acquisition performance of the system. It is shown that the combined energy-to-noise degradation due to nonideal carrier tracking and bit synchronization over that required for the ideal tracking case can be held to less than 1.5 dB and that combined carrier tracking and bit timing can be acquired in only a few seconds for the parameters and operating ranges of the space shuttle coded communications links.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: International Telemetering Conference; Oct 15, 1974 - Oct 17, 1974; Los Angeles, CA
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Concatenation of convolutional and block codes Final report (1971)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Comparison of concatenated and sequential decoding systems and convolutional code structural properties
    Keywords: COMPUTERS
    Type: NASA-CR-114358
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Coded spread spectrum digital transmission system design study (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Results are presented of a comprehensive study of the performance of Viterbi-decoded convolutional codes in the presence of nonideal carrier tracking and bit synchronization. A constraint length 7, rate 1/3 convolutional code and parameters suitable for the space shuttle coded communications links are used. Mathematical models are developed and theoretical and simulation results are obtained to determine the tracking and acquisition performance of the system. Pseudorandom sequence spread spectrum techniques are also considered to minimize potential degradation caused by multipath.
    Keywords: COMMUNICATIONS
    Type: NASA-CR-134310
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Further results on optimal decoding of convolutional codes (1969)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Algorithm for optimal decoding of convolutional codes confirmed using error probability upper bound
    Keywords: COMPUTERS
    Type: ; ACE(
    Format: text
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  • 7
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    Hybrid and concatenated coding applications. (1972)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Results of a study to evaluate the performance and implementation complexity of a concatenated and a hybrid coding system for moderate-speed deep-space applications. It is shown that with a total complexity of less than three times that of the basic Viterbi decoder, concatenated coding improves a constraint length 8 rate 1/3 Viterbi decoding system by 1.1 and 2.6 dB at bit error probabilities of 0.0001 and one hundred millionth, respectively. With a somewhat greater total complexity, the hybrid coding system is shown to obtain a 0.9-dB computational performance improvement over the basic rate 1/3 sequential decoding system. Although substantial, these complexities are much less than those required to achieve the same performances with more complex Viterbi or sequential decoder systems.
    Keywords: COMMUNICATIONS
    Type: International Telemetering Conference; Oct 10, 1972 - Oct 12, 1972; Los Angeles, CA
    Format: text
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    NASA TECHNICAL REPORTS
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