Re: Viterbi Synchronization

On Aug 30, 6:12 pm, "jeffsimp" <J...@xxxxxxxxxxx> wrote:
On Aug 30, 7:00 am, "jeffsimp" <J...@xxxxxxxxxxx> wrote:

The way I understand this concept is, when the Viterbi Decoder is
synchronized it should not have to normalize any of the branch metrics
therefore the normalization rate should be very low. The same is true
for
the BER. So I figured that I can just determine an appropriate
threshold
value and monitor when the BER and normalizations exceed the threshold
and
auto adjust my incoming data accordingly to ensure that I'm always
synchronized. Makes sense to me, but Altera says that these
parameters
are only good for estimating channel quality and not synchronizing.

Xilinx has a comparable Viterbi IP core that claims I can use BER and
normalizations for my purpose.

My experience has been that the Viterbi normalization rate has a
fairly broad distribution and is very dependent on the signal
environment, so a single threshold value is not adequate for
determining node sync under all conditions. If your signal environment
is well constrained however you may find that one value is OK. You may
also find that a more complex evaluation of the normalization rate
will work. I've used re-encode & compare measurements successfully in
a wide range of applications though and it's fairly easy to implement.

Eric

---------------------------------------------------------------
Thanks Eric,
My plan is to determine a BER threshold based on measured data. I use a
Bit Error Rate Test(BERT) machine that allows me to inject 'x' dB of noise
onto my encoded stream. My board is expected to perform in within 1 dB of
theoretical with Eb/No ranging from 12 dB down to 2 dB. I plan to
determine a threshold for BER and normalization based on taking an average
of these metrics over 'x' amount of clock cycles when I'm running at Eb/No
= 2dB. This should be my worst case scenario then I can compare it to
measured thresholds at different noise levels. Does this sound similar
to some of the approaches you have used in the past?

Jeff

Another idea to consider is the use of a saturating up/down counter
followed by a
threshold. This can be a useful way to detect a change in
distribution. The
increment and decrement values need not be the same.

John

.

Relevant Pages

  • Re: Viterbi Synchronization
    ... Bit Error Rate Testmachine that allows me to inject 'x' dB of noise ... theoretical with Eb/No ranging from 12 dB down to 2 dB. ... determine a threshold for BER and normalization based on taking an average ...
    (comp.dsp)
  • Re: Viterbi Synchronization
    ... synchronized it should not have to normalize any of the branch metrics ... therefore the normalization rate should be very low. ... I've used re-encode & compare measurements successfully in ... My plan is to determine a BER threshold based on measured data. ...
    (comp.dsp)