On Wed, Jan 5, 2011 at 4:14 AM, Jimmy Richardson<address@hidden> wrote:
Hi, Tom:
Please see my comments below.
Thanks
On 1/4/2011 11:44 PM, Tom Rondeau wrote:
On Mon, Jan 3, 2011 at 11:25 PM, Jimmy Richardson<address@hidden>
wrote:
Indeed. Very strange. My guess is that there is a misconception
somewhere in the code about sample rate. I can't quite see it in my
head, but I'm guessing that the channel spacing isn't exactly the
channel spacing you think it is.
You mean the oversample rate O = N/i is wrong? As far as I can see,
that's
the only number that could go wrong, since pfb_channelizer_ccf only takes
3
parameters, # of channels, taps and oversample rate, and it doesn't look
like the other two can be wrong.
I checked the calculation of O again, but couldn't find the problem. In
the
Matlab code, harris uses loops "for nn=1:28:5600-28" to do the
processing,
so it does seems a 28-to-1 downsampling in 40 channels.
No, not the oversample rate, just the sample rate. I'm thinking that
there is some misunderstanding somewhere about the actual sample rate
and the therefore the channel bandwidths such that the channels you
are pulling out are not covering the same frequencies that you think
they are.
Sorry, maybe I didn't get how the algorithm works, but it looks to me the
actual sample rate does not enter into the equation, except in the filter
generation part? If we use the same filter on both methods, then the actual
sample rate should not cause the difference?
No, the sample rate as a real number doesn't enter into the code, but
it does abstractly in where the signals exist, what the channel
bandwidths mean, etc. I'm not sure what else to say here, really, just
to think closely about the signals and the channelizer. Again, it
could be that there is a bug in the code that only worked for my
cases.
On the other hand, it could be a miscalculation in the
pfb_channelizer, although all of my tests with it came out fine.
Is the test cases included in the GNURadio source code? Also if I want to
understand the logic inside pfb_channelizer implementation, are there any
book or paper I should review besides harris' paper and book?
No, they aren't. It shouldn't be difficult to modify the example codes
that are there, though, to see what happens and make sure it makes
sense.
Tom