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[Discuss-gnuradio] CCSDS 27 implementation specifics

From: Hrishikesh Shelar
Subject: [Discuss-gnuradio] CCSDS 27 implementation specifics
Date: Fri, 7 Oct 2016 09:55:13 -0700

Hi all,

I was taking a closer look into the CCSDS 27 blocks and noticed that the polynomials may be wrong?

The viterbi.c code says NASA code which has the polynomials 0x6D and 0x4F. However CCSDS is ordered 0x4F followed by 0x6D with an inversion on the 0x6D output. I see that the butterfly cells are hard coded to the NASA code. Would the fix be to recompute those ACS metrics and recompile that block?

Also I think the viterbi algorithm as coded cannot perform node synchronization. When I created a flow graph feeding the CCSDS 27 Encoder into the CCSDS 27 Decoder adding a delay of 1 causes the output to fail (or be erroneous). Is this expected?


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