Hi Damindra,
basically, you'll have to parameterize the PFB channelizer with a
prototype filter – imagine you had just one channel centered at 0 Hz in
your input band, and design a low-pass filter that would select that.
To illustrate: You've got something like
^S
----- | -----
/ \ | / \
/ \ | / \
/ \|/ \
------------+----------->
0 f
so, channel 0 and 1 centered at - and +f_sample/4, respectively.
Imagine some shifted your signal so that channel 0 was exactly at 0 Hz
(that's especially easy to imagine and to implement; that's a frequency
shift by multiplication with exp(j*2pi * (f_sample/4)/f_sample *
n)=exp(j*2pi /4 *n)=exp(j*pi/2*n)=1, j, -1, -j, 1, j, …)
^ S
- - --|-- - -
. / | \ ,
. / | \ ,
./ | \,
------------+----------->
0 f
You should be able to design a LPF to select that channel alone.
Now, using that filter, the PFB channelizer calculates a filterbank that
is essentially nothing more than the even and the odd taps of that
filter, applied each to half of the input signal, and then, with a 2-FFT
(yeah, that's kind of a boring FFT) transformed back into being elements
of a sensible signal. That's basically two filters for the cost of one +
one FFT.
Cheers,
Marcus
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