Adaptive Coding - Examples

Examples

Adaptive image coding is currently being used by the Cassini-Huygens craft to relay images from Saturn. Only about 5% of the images show any visual signs of damage. As the spacecraft has an error correcting Flash drive and long timeframes between image taking events, damaged images like this can be resent. It is assumed that the number of damaged, but unrecoverable images from the Cassini mission is about 0.01% or less.


Cassini Lossless Compression

  • Both converted (8-bit) and unconverted (12-bit) data can be losslessly compressed. The Cassini hardware data compressor uses a modified Huffman encoding scheme as part of its adaptive compressor.
  • Each compressed image can be reconstructed on the ground with no loss to the information content of the image, provided the image entropy does not exceed the threshold where 2:1 compression is reached.
  • Due to camera problems and the need to reduce file size, there is a slight modification to the image coding scheme so that each compressed line is effectively bandwidth limited on the number of bits available to encode it.


Consultative Committee for Space Data Systems
Data compression
  • Images
    • ICER
    • JPEG
    • JPEG 2000
    • 122.0.B1
  • Data
    • Adaptive Entropy Coder
Error Correction
Current
Binary Golay code
Concatenated codes
Turbo codes
Proposed
LDPC codes
Telemetry command uplink
  • Command Loss Timer Reset
  • Proximity-1 Space Link Protocol
Telemetry downlink
  • Spacecraft Monitoring & Control
  • Beacon mode service
Telemetry general
  • Space Communications Protocol Specifications (SCPS): Performance Enhancing Proxy
Telemetry modulation systems
Current
BPSK
QPSK
OQPSK
Proposed
GMSK
Frequencies
  • X band
  • S band
  • Ku band
  • Ka band
  • K band
Networking, interoperability and monitoring
  • Service-oriented architecture (Message Abstraction Layer)

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