The SCS shall encode the serial downlink telemetry stream as follows:
TELEMETRY RATE (kbps) ENCODING
23.4375 convolutional/bi-phase level
1125 convolutional
2250 convolutional
Where convolutional encoding is rate 1/2, constrain-length 7, with alternate symbol inversion as defined in the CCSDS standards and bi-phase L encoding is applied after the convolutional encoding for the lowest rate.
Convolutional encoding is used because of its simple implementation and large coding gain (about 5 dB at 10E-6 error rates). Also, the convolutional coding guarantees at least one transition every 14 bits, so the bit synchronizer on the ground will have enough transitions to maintain lock. The bi-phase L encoding is added to the lowest rate so that the lowest frequency components are well away from the S-band carrier.
Previous SMEX missions.
The coding will be tested throughout I&T, by all tests, since all tests require telemetry.
See bit synchronizer capabilities.
Revision: January 15, 1996