Consultative Committee For Space Data Systems - Specific Recommendations

Specific Recommendations

The CCSDS recommends for Spacecraft to Earth communications the

• avoidance of or the turning off of the 'randomizer', as the CCSDS currently recommends a randomizer similar to the BBC NICAM randomizer
• avoidance of transmission downlink waveforms with very poor Doppler performance, like FM
• avoidance of error correction systems with weaker performance than the Voyager Program code—a (7, 1/2) convolutional code concatenated with (255,223) Reed-Solomon code (typically with 3-bit quantization)
  • A rate 1/2, constraint length 7 convolutional code with Viterbi (maximum likelihood) decoding is already a standard for both NASA and ESA. It has been used in several missions and has demonstrated the expected coding gain.
• use of wavelet encoding of images using ICER or JPEG2000, as opposed to JPEG
• use of separate Packet and Frame sizes to increase error correction margin in the space channel
• avoidance of the False Sync Problem : Issue 1 of the Telemetry Channel Coding Blue Book (May 1984) made reference to a "False Sync" problem in footnote 5. As defined by the Recommendation at that time, the codeblock "attached sync marker" was included as a part of the Reed-Solomon data space. Various solutions were studied and it was finally decided to adopt the simplest technical solution: to remove the attached sync marker from the encoding process.