Sirs,
I have not delved into your software, and being old and retired I may not
do so. From the superficial descriptions of FT8 I have found, your group
seems to know very well what they are doing.
https://users.ece.cmu.edu/~koopman/roses/dsn04/koopman04_crc_poly_embedded.pdf
Here is a link to a paper on CRCs that you should consider for future
design work. The paper gives the best CRC of a given length for a data
block of a given length. You can potentially have equal or better
corruption detection with a smaller CRC, Examine table 3 carefully. I
believe you could use an 8 bit CRC (0x97) for data blocks of up to length
119 bits and achieve a hamming distance of 4, which is equal to or better
than the performance achievable with the optimal 12 bit CRC at data block
lengths above 53 bits in length.
It may be too late to impact FT8, but the principles outlined in the paper
can save you a few bits in future development.
As a general caution, be aware that previous published "standard" and
"good" CRCs, may not be the best even at long block lengths.
If you were already aware of this paper, please forgive me for wasting your
time.
Is there a more detailed description of the various modes available to
members of this list? I am a new ham, but did waveform design and optimal
detection for many years until I retired last May. I may be able to help
in some manner.
73,
Don Goldston, AE0AG
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