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Re: [HLL] CELP



Status: RO
Content-Length: 2091
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On Fri, 16 Jan 1998, Volker Ernst wrote:
> 
> Our HLB uses a 30MHz/32-bit risc-cpu. This gives us about 25 Mips, i expect.
> Standard-gsm needs about 10Mips (full-duplex), crypto needs about 5 Mips.
> Let's have 5 Mips for everything remaining - then we use about 20 Mips.
> So there is not much room left to complicate things...
> 
> It's not that we could not build an even more powerful HLB-hardware ;-)
> But this would make it much more complex/expensive and should be avoided !!!
> We would probably have to use 'real DSPs' again.

Today, I discussed the HLP with some experts in [digital] telephony, chip
design, crypto, and assorted other disciplines. I walked away from that
discussion with the feeling that there is no solution to the problem given
the current state of codecs and your design constraints.

We worked over several options on the HLL: higher bandwith, a better
compressing codec, sync protocol. Neither seems to provide a solution.

There are a few other options, but again they fail to meet at least one of
the design constraints. One idea that comes to mind is:

More MIPS
============
Pro: you can use a high-performance codec that requires well under
9600baud and still sounds great.
Con: can't be emulated in software on even a low end Pentium, though it
might be doable in hardware.

[Sidebar: they way fielded systems get around that problem is by using
ASIC's. MIPS aren't a problem if you can build an ASIC for the task. Which
is what the cellphone manufacturers are doing. BTW, has anybody tried to
find out if there are codec ASIC's you can buy for cheap]?

My conclusion:
You might want to look at faster CPU's.


BTW, you really should consider putting up a webpage with the FAQ, a list
of the design constraints, the current state of the discussion, and an HLL
archive. Several people I talked with asked for this. You are welcome to
use this server.

Have fun,

-- Lucky Green <shamrock@cypherpunks.to> PGP v5 encrypted email preferred.
   "Tonga? Where the hell is Tonga? They have Cypherpunks there?"