[Ground-station] uplink convolutional encoder review

[Michelle Thompson]

When we forked the M17 codebase to start work on a digital voice/data
uplink, we inherited a set of decisions.

Some of those have turned out to be good for a higher bitrate voice/data
channel, and some of those have not.

The next big review for our uplink will be looking at the 1/2 rate
constraint length 5 free distance 7 code that we inherited.

It's equivalent to a code that shows up over and over again in 3GPP, that
has a different polynomial.

The convolutional encoder in LTE is a higher performance code with a
shorter frame length (10 mS vs. our 40 mS).

So, we're wondering if we're leaving a lot of performance on the table here.

Since we want this uplink to work in space for HEO/GEO, every dB of code
gain counts.

This next week we'll be looking at this more closely, so please join the
zoom calls if you're able. I'll do all I can to explain what we find and
what we're concerned about.

-Michelle Thompson
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