Franks comments are right on median and ROM in this case. I stayed up
to 4 AM and went to work at after having breakfast and a cup of coffee
and arrived by 9. It is showing.
The entire gist of my comments amount to nothing more than don't allow
"aliasing" of the spectral changes as your traverse the compressed power
spectrum to cause you to miss a peak that is ABOVE the detection threshold.
So, pardon me but, is this a pretty picture exercise or a real
detection problem? If it is a detection problem, then you might as
well just compress to the largest value in the bins to be pushed
together so you assure that your threshold is exceeded when it should
be. If it is a pretty picture problem, just prevent scalloping by any
old heuristic, just make it as fleet of calculation feet as possible and
throw in some pretty grassy stuff to make it look nice.
Bob
Marcus D. Leech wrote:
Bob McGwier wrote:
I suggest that the best algorithm for this would be the rank order
mean alternated with the max so long as you are going to insert
"heuristic grass". So it would be max, ROM, max, ROM, .....
Let [B1, B2, B3, B4, ... BN] be powers of five adjacent bins.
Put them in rank order
[R1, R2, R3, R4, ... RN]
If N is even, the rank order mean is (R_(N/2) + R_/(N/2 +1)*0.5.
If N is odd, the rank order mean is R_(N/2 +0.5)
But I still see a problem:
I suggest that in order to prevent "scalloping" of a swept tone across
this algorithm or any other like it, that some "bin" in the lossy
compression set of bins must ALWAYS be forced to take on the large of
the power spectrum otherwise your alternative min/max/min/max might
jump up and down as you sweep a tone through it. Or did I miss
something?
Bob
I love that phrase, Bob. "Heuristic grass".
I think that the real answer is to "play with it, and see what best
suits the application". Ranking the bin might end up being
expensive. I'd probably use qsort(), but I can't remember what its
computational complexity is. Just looked it up. Worst case
is O(N**2), and best-case is O(NlogN). For worst-case, that's rather
brutal at 4M bins (and even worse at my maximum of
16M bins).
This discussion has ended up being much more fascinating than I had
predicted. Keep it up everybody!
--
(Co)Author: DttSP, Quiktrak, PowerSDR, GnuRadio
Member: ARRL, AMSAT, AMSAT-DL, TAPR, Packrats,
NJQRP, QRP ARCI, QCWA, FRC.
"It is human nature to think wisely and act in
an absurd fashion.", Anatole France.
Twitter:rwmcgwier
Active: Facebook,Myspace,LinkedIn
_______________________________________________
Discuss-gnuradio mailing list
[email protected]
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
