Hi Bruce and others,
The main issue is latency. If we limit the channel coding to 40 msec frames
the number of information bits is too small to use iterative codes (like
LDPC or SCCC turbo). In this case we should stick with block codes - like
Golay or BCH. These can be decoded efficiency. BTW I don't think the Golay
code can be shortened to (say) rate 2/3. In general it is always best to
use longer codewords - Shannon shows that channel capacity is achieved with
infinite codeword length. Recent work has quantified the coding gain as a
function of codeword length. For example some of the short codes like
Hamming perform well for their length, but compared to longer codes, will
provide very little benefit. So Golay is a reasonable option for 40 msec
frames even though its coding gain is relatively poor at high BER. If we
envisage a few modes of operation - then LDPC over (say) 10 frames would be
a good option. There should be no patent issues with any of the codes
mentioned above and quite a lot of good open-source code is available.
Cheers, Bill
On 25 October 2012 02:14, Bruce <[email protected]> wrote:
>
> Golay and Hamming are easy to use for a fast way to get on the air, but
> when we set a standard for other hams to use it should be based on a
> capacity-approaching code. LDPC is available for us to use without
> patent issues today.
>
> Thanks
>
> Bruce
>
>
--
*Bill Cowley
from Gmail *
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