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  • 1
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    Performance evaluation of a class of systematic, rate (M-1)/M, convolutional codes (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The implementation and performance evaluation are described for a class of rate (M-1)/M, systematic, convolutional codes being decoded with a simple majority logic decoder. The encoding logic appends one parity bit for each PCM telemetry word. It is shown that over the critical range of received PCM telemetry signal-to-noise ratios, this coding procedure produces a net coding gain of from 1.5 to 2.5 db relative to an equal power transmission of uncoded PCM telemetry. Being a low-redundancy systematic code, it is possible to process this data without convolutional decoding with a small rate loss penalty of about 0.5 db.
    Keywords: COMMUNICATIONS
    Type: NASA-TM-X-66085 , X-522-72-403
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Distributed reservation control protocols for random access broadcasting channels (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Attention is given to a communication network consisting of an arbitrary number of nodes which can communicate with each other via a time-division multiple access (TDMA) broadcast channel. The reported investigation is concerned with the development of efficient distributed multiple access protocols for traffic consisting primarily of single packet messages in a datagram mode of operation. The motivation for the design of the protocols came from the consideration of efficient multiple access utilization of moderate to high bandwidth (4-40 Mbit/s capacity) communication satellite channels used for the transmission of short (1000-10,000 bits) fixed length packets. Under these circumstances, the ratio of roundtrip propagation time to packet transmission time is between 100 to 10,000. It is shown how a TDMA channel can be adaptively shared by datagram traffic and constant bandwidth users such as in digital voice applications. The distributed reservation control protocols described are a hybrid between contention and reservation protocols.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: IEEE Transactions on Communications; COM-29; May 1981
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    A packet telemetry system employing ARQ error control (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A proposed packet telemetry system employing automatic retransmission request (ARQ) mode of error control is characterized. Limitations of the present multiplexing/demultiplexing approach are considered, and the use of the proposed system in near-earth satellites in the 1980s is suggested. Onboard processing and an adaptive multiplexing technique are described, as is an elastic buffer, required because the instantaneous data rate will be different from the telemetry transmission rate. The telemetry packets would be encoded into a powerful error-detection block code. A mechanism involving temporary buffering in a long shift register will permit retransmission request from the ground station for packets received in error. The ARQ mode of operation should ensure essentially error-free transmission at lower signal-to-noise ratios and at considerably higher transmission rates than are usually used.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: Data Management Symposium; Oct 18, 1977 - Oct 19, 1977; Huntsville, AL
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Sensor data autonomy (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: 'Smart' sensors onboard NASA space missions will require variable data output bandwidth as they respond to phenomena of interest. An Instrument Telemetry Packet (ITP) approach has been developed which encodes experimental instrument data into an autonomous data package, along with pertinent engineering parameters and ancillary data (time, position, attitude, etc.). New requirements for onboard concentration and buffering, as well as for end-to-end error control, arise from this approach. Emphasis is placed on packet protocols compatible with the data link standard ADCCP, to enable one set of ground support equipment to readily support instrument development, launch site checkout and mission operations phases.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: AIAA PAPER 78-1705 , American Institute of Aeronautics and Astronautics and NASA, Conference on ''Smart'' Sensors; Nov 14, 1978 - Nov 16, 1978; Hampton, VA
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Minimax decoding of cyclic block codes (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A minimax decoding algorithm utilizing soft bit detection of an (n,k) cyclic block code is described which will permit the correction of up to n-k bit errors interspersed at random locations throughout the block. The decoding solution consists of: (1) identifying the ordered soft bit set and, (2) finding the minimum order solution to the resulting syndrome equations where the nonzero error vector components are constrained to be a subset of the soft bit set. An efficient implementation of the decoding operation is described. In essence, this algorithm focuses the correction capability of the code on those bit positions which have the lowest a posteriori probabilities of correct detection.
    Keywords: COMMUNICATIONS AND RADAR
    Type: In: NTC ''77; National Telecommunications Conference; Dec 05, 1977 - Dec 07, 1977; Los Angeles, CA
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    A concept for a transparent data acquisition and distribution system for spaceflight applications (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The paper describes the Modular Data System concept of the NASA End-to-End Data System program. Data from a single instrument along with the necessary ancillary data will be assembled into self-contained packets and subsequently transmitted over various communications links (space telemetry channel, ground communications circuits, etc.) to the experimenter's facility in real time; reliable error control coding will be included in each link transmission to protect the integrity of the data packets. A major objective is to make the entire data acquisition and distribution process transparent to the experimenter in the sense that the output terminal of the distribution system will be physically, logically and electrically identical to that of the experiment output channel.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: ITC/USA/''78; Proceedings of the International Telemetering Conference; Nov 14, 1978 - Nov 16, 1978; Los Angeles, CA
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Telemetry packetization for improved mission operations (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The requirements for mission-operations data management will accelerate sharply when the Space Transportation System (i.e., Space Shuttle) becomes the primary vehicle for research from space. These demands can be satisfied most effectively by providing a higher-level source encoding function within the spaceborne vehicle. An Instrument Telemetry Packet (ITP) concept is described which represents an alternative to the conventional multiplexed telemetry frame approach for acquiring spaceborne instrument data. By providing excellent data-integrity protection at the source and a variable instrument bandwidth capability, this ITP concept represents a significant improvement over present data acquisition procedures. Realignments in the ground telemetry processing functions are described which are intended to take advantage of the ITP concept and to make the data management system more responsive to the scientific investigators.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: International Telemetering Conference; Sep 28, 1976 - Sep 30, 1976; Los Angeles, CA
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    OAO date transmission study Final report, Feb. 10 - Jul. 25, 1967 (1967)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Reduction of OAO spacecraft data handling equipment telemetry data
    Keywords: COMMUNICATIONS
    Type: NASA-CR-90109 , G-93
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Development of advanced digital techniques for data acquisition processing and communication Interim scientific report (1969)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Digital techniques for automatic evaluation of images and data compression algorithms
    Keywords: COMMUNICATIONS
    Type: NASA-CR-86158 , G-98IS
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    Quasi-optimal decoding of linear block codes using soft decision detection (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A simple but effective decoding procedure, applicable to any (n,k) linear block code with symbols from GF(q), is described. The technique involves a transformation of the parity check equations which focuses the code's correction power on the soft symbol set while still retaining the capability to correct one symbol error from outside this set. The soft symbol set is defined to be the n-k least reliably detected code symbol positions whose parity check row-spaces are linearly independent. The process generates a number of error vector screening candidates, each a solution to the parity check equations, and the maximum-likelihood candidate is accepted.
    Keywords: COMMUNICATIONS AND RADAR
    Type: ITC/USA/''78; Proceedings of the International Telemetering Conference; Nov 14, 1978 - Nov 16, 1978; Los Angeles, CA
    Format: text
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    NASA TECHNICAL REPORTS
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