[Ground-station] responses to more comments on ka9q-radio

[Phil Karn]

On 4/27/18 07:52, Michelle Thompson wrote:
> OK, I think I understand what you're saying here.
> 
> Thank you for the clear demonstration of the value of RTP multicast.

That wasn't my original goal, but my thinking has evolved in that
direction. There are already a lot of SDR projects out there, so I
needed to find something new that hadn't really been tried yet, at least
not by hams. Multicast interconnection eventually emerged as that
"something". It also fits my old-school UNIX philosophy of building
small, self-contained building blocks that do just one thing and do it
really well, and which can be easily interconnected. I still don't like
monolithic GUI packages, and that's nearly all of the ham SDR programs
out there.

> I think it can be translated, almost literally, into GNU Radio blocks. I
> don't see anything quite like it as a block in GNU Radio right now. 

Almost. As I understand GNU Radio, the blocks are somewhat smaller than
my complete programs. My most complex program, radio, combines a complex
LO/mixer, complex filter/decimator, optional coherent carrier tracker,
demodulator and optional post-demodulation filtering. As I understand
GNU radio, each of these elements would probably be separate GNU radio
blocks, and the communication would likely dominate the processing for
many of them (e.g. complex mixing, which is only a few
instructions/sample and is best done inline). I have tried to
multithread things as much as possible but I have to be careful to not
go too far and increase the communication overhead. (Because threads run
in the same address space, most of this overhead is synchronization.)

> We spent some of yesterday working with codec2 blocks in the lab. I
> don't see Opus on the list of codecs in GNU Radio. I think it would be a
> great addition.

It should be. For a very good codec being promoted heavily by the IETF,
it should be more widespread by now.

David Rowe and I have been talking about Codec2 in RTP. He doesn't think
anybody has done it yet.

Phil