[Ground-station] Opulent Voice update

[Michelle Thompson]

Opulent Voice is an open source high bitrate digital voice (and data)
protocol. It's what we are using for our native digital uplink protocol for
ORI's transponder project. Opulent Voice is also looking pretty darn good
for terrestrial.

We're getting nice clear 16kbps OPUS audio out of the demodulator. There
are some issues to clear up (we're losing synchronization at the moment
about 10% of the time), but we expect to present a nice demo at DEFCON and
at the QSO Today Ham Expo.

We'll be using COBS protocol within Opulent Voice. If you're unfamiliar
with COBS, please read about it here:

https://en.wikipedia.org/wiki/Consistent_Overhead_Byte_Stuffing

Authentication and authorization is built in and optional. There is no
separate "packet mode". Things are designed to "just work" and get out of
your way whether or not you're sending voice or data.

Opulent Voice is designed to where you can use higher bitrate OPUS codecs
if you wish. This will most likely be a build option and not a run-time
option, but if a run-time option is something you want to work on, speak
up.

16kpbs was such an improvement over all other digital ham voice modes that
we stopped right there and started implementation work. However, even at
16kbps it's not "perfect". As soon as everything is working, it's going to
be a powerful experiment to run even higher bitrates and hear how nice it
sounds. One goal is to make this sort of change - going to a higher or
lower bitrate codec - as easy as possible. You can see some of that work in
the repository linked below. We've parameterized the code and added a way
to generate all the "numerology" for the protocol. When we say
"numerology", this is shorthand for all of the codec-rate-dependent values
that the implementation needs.

Originally based on Mobilinkd codebase that implements M17, the Opulent
Voice development implementation can be found here:

https://github.com/phase4ground/opv-cxx-demod

Initial demos will be on a HackRF/PortaPack on the 1.2 GHz ham bands.

Thank you to OpenRTX for help with troubleshooting the audio quality on the
PortaPack. In order to have a good demo, basic FM transmit from the
microphone needs to work. The audio quality is pretty bad (this was a
surprise) with the stock application, so we've been spending some time with
the Mayhem codebase, the microphone transmit app, and the driver for the
audio codec in order to get it sounding like it should. This needs to
happen before we publish an app for the PortaPack.

Synthesized audio from the HackRF/PortaPack sounds clear and wonderful.
It's just the microphone that is splattery and overdriven.

ORI's Slack channel can be found at https://phase4ground.slack.com/

The authentication and authorization work is in #aaaaa
Opulent Voice work is in #opulent-voice

Thank you to everyone supporting the work!

-Michelle Thompson
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