CCSDS Telecommand Sync and Channel Coding Specification using advanced Block Codes Ed Greenberg NASA/JPL Oct. 15,

Content Driving Command Requirements – Emergency Communications – Limited Throughput – High Rate Production Basic CLTU Definition Coding Performance CLTU delimiting Issues/Options Turnaround Ranging 2

Driving Command Requirements Emergency Communications – Poor Communications with limited access window Requirement is to perform at least as good as current capability – Short Hardware Commands 56 bit minimum – Limited sequence of Commands (< 5 commands required to stop tumbling) Valid Command delivery can be as low 70% – Very Low Undetected Errors Allowed Accepted Erred Commands limited to maximum of Limited Throughput Communications – Stable communications link with limited performance Command rejection rate should be less than Accepted Erred Commands limited to maximum of High Rate Production Communications – Stable Communications link with nominal performance Command rejection rate should be less than Accepted Erred Commands limited to maximum of

Basic CLTU Definition The CLTU has three sections: Start Sequence (ASM) – Delimit the start of the CLTU Start Sequence size is determined by operating symbol error rate – Used to resolve data ambiguity Frame – A series of fixed length code words that contain the frame CLTU Termination – An erred Code word or – Other Options Fixed Length Frames using fixed number of code words (1 or more) or Use frame length to determine number of code words in the CLTU – Requires CLTU to contain only a single frame or single segment » Allows decoder to extract frame length to determine required number of code words 4

Coding Performance Emergency Communications Code (E b /N o )Word Error RateUndetected Error Rate BCH (TED ) 7 db LDPC 64 Binary 2.8 db LDPC 64 Non-Binary 2.0 db10- 1 ?? LDPC 256 Binary 2.2 db Stable Communications Code(E b /N o )Word Error RateUndetected Word Error Rate BCH (TED/SEC) )>11.5/9.0 db10 -5 > /10 -8 LDPC 64 Binary5.3 db10- 5 >10- 9 LDPC 64 Non-Binary4.1 db10- 5 ?? LDPC 256 Binary3.5 db10- 5 > LDPC 256 Non-Binary2.7 db10- 5 ?? LDPC 1024 Binary2.0 db10-5> LDPC 256 Non-Binary0.8 db10- 1 ?? 5

CLTU delimiting Issues/Options An erred Code word – Requires an added uncorrectable code word for each CLTU Overhead dependent on size of TC Frame and required fill – e.g. An 8000 bit frame using a 512/256 code has [ 192 (fill) +256(cw) ] 5.3% overhead Other Options for identifying end of a CLTU – Fixed Length Frames using fixed number of code words May impose significant overhead for the TC protocol Can be used to support an AOS frame protocol without overhead – Use frame length field in frame primary header Extracting the Frame Length field in the first Code word to determine the number of code words needed to contain the frame – Requires CLTU to contain only a single frame or segment – Requires decoder to extract frame length to determine required number of code words rather than delimiting the CLTU using only decoding firmware. 6

Turnaround Ranging Software Radios are on the threshold of being incorporated into space missions, the technology associated with them supports the inclusion of onboard correlators needed for turnaround ranging resulting in: Improved Ranging performance Ability to substantially improve time correlation performance 7

Backup 8

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NASA/JPL Non-Binary LDPC Short Code Performance 10

Decibel Table 11

A simple comparison of code performance For an 8192 bit frame – Using 1024 LDPC code requires 8 code words and thus requires an added 0.2 db to provide a frame error rate of on provided table – Using 256 LDPC code requires 32 code words and thus requires an added 0.5 db to provide a frame error rate of on provided table. – Using 64 BCH code (TED mode) requires 146 code words and thus requires an added 1.7 db to provide a frame error rate of on provided table. The advantage of the 1024 over the 256 is about 1.3 db (about 35% improvement) The advantage of the 256 over the 64 BCH ( TED ) is about 9.75 db ( about 1000% improvement ) The advantage of the 256 over the 64 BCH ( SED ) is about 7 db ( about 500% improvement ) 12 Note: Frame Error rate is Code word Error rate times the number of code words/frame