Hi all,
I've seen on ON1ARF's page that his MSK code seems to be leaning toward the
possibility of use with codec2. I'd just like to put the feelers out to
find out if he/someone else is already working on an implementation using
codec2. I've had some ideas myself, but find it pointless me moving forward
with an implementation if someone else is already doing so. It'd just lead
to confusing competing standards. Ideally it'd be nice if there was a
single "open" standard along side the D-Star standard already in existence.
Not a fragmented number of implementations.
The other point of interest is, in order to implement on VHF/UHF I'd
suggest the use of FEC in a similar way to D-Star today. By my (maybe
shoddy) calculations. If we use 4800 MSK (as per D-Star) and 1200 of that
for data/control. We're left with 3600, again just like D-Star. The
difference being that the bitrate of the actual codec is a bit different. I
don't think this is a problem though.
I think the layout could be similar to D-star in fact. With 2500 bps, we
work on 50 bits per frame. If we group blocks of 24 bits, into 4 blocks
(again like D-star) we get 96 bits. Minus 24 for data. Leaves 72 (or 3
blocks of 24 bits).
This actually works quite well for FEC purposes. We have 2x23 bits (46
bits) creating 2x12 bits of corrected data (24 bits) using golay2312. Plus
one block of unprotected 24 bits (48 bits) and 2 remaining unprotected bits
left over. 50 bits total. That's a nice perfect matching for 72 bits in, 50
bits out (I like to think you guys were aiming for this with the perfect
block size/data rate for this outcome).
So, the information needed to go forward is, whether there are a particular
24 bits that carry more useful information (and thus should be more
protected) out of the 50? The core of the question is, what bits should we
be protecting most?
As for the MSK/C4FM argument. To me, it came down to the fact that there is
a software implementation of an MSK modem already. I think it would really
promote codec2 DV, if people could hook up their sound card into their
packet socket and "plug and play" so to speak with maybe a simple circuit
they can easily build. Sure hardware MSK modems could also be used. But the
home brew is where it matters. So I think MSK is a good start. Also since
we're using the same modem as D-star does. It'd make it fairly easy to make
a multimode system (using the USB dongle for decoding/encoding D-star as an
optional extra).
So, back to my original question really. Is someone else already working on
this?
Best regards,
Peter.
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