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Re: [Discuss-gnuradio] USRP2 Halfband filter coefficients help
From: |
Jeff Brower |
Subject: |
Re: [Discuss-gnuradio] USRP2 Halfband filter coefficients help |
Date: |
Wed, 11 Nov 2009 10:02:27 -0600 (CST) |
User-agent: |
SquirrelMail/1.4.2-1 |
Ilkyoung Kwoun-
> Thank you for your advice. Actually I am aware of basic characteristics of
> half band filter. It is very well explained in Rick Ryon's "Understanding
> Digital Signal Processing (2nd Ed.)" (
> http://www.amazon.com/Understanding-Digital-Signal-Processing-2nd/dp/0131089897/ref=sr_1_1?ie=UTF8&s=books&qid=1257900094&sr=8-1
> )
>
> The thing I do not have any clue is the 'inner' and 'outer' coefficient
> things in FIR filter. I guess this is something related to the practical
> implementation issue rather than the fundamental concept. I did a simple
> googling yesterday and found a paper. (
> http://ce.et.tudelft.nl/publicationfiles/1090_509_shahbahrami_prorisc2005.pdf)
> I hope I can find a way to get started. :-)
Here is a Hypersignal log-magnitude plot showing the frequency response of the
two halfband filters (31-tap in blue,
7-tap in red):
http://www.signalogic.com/images/gnu_radio_halfband_filters.jpg
In the plots I used an arbitrary sampling rate of 25 MHz -- don't know what
you're using. Note that both filters have
an approx -6 dB point at Fs/4 as would be expected due to halfband symmetry
properties.
As for "inner and outer" mention in the Verilog code, I might guess that refers
to 2 multiplies needed when filtering
a complex signal. As for why there are two (2) filters, one is used for higher
rate up/down conversions and the other
for lower rate. Firas' documentation has some information on this... also here
is Q&A exchange between Firas and Matt
that might help you out:
http://old.nabble.com/Some-USRP2-Questions-td20729711.html
-Jeff
> 2009/11/10 Sebastiaan Heunis <address@hidden>
>
>> Hi
>>
>> I think Brian is just referring to the fact that you can see that the
>> HBFs are implemented as symmetric FIR filters (the coefficients). A
>> HBF is just a special filter that is designed so that the cutoff
>> frequency will always be at fs/2, so if you filter with it and
>> decimate by 2 afterwards (which is why you would use an HBF), you
>> don't get aliasing. Also, the decimation in the CIC filters can be
>> set to a wide range of values, so the HBF will always have to cut at
>> fs/2 regardless of the decimation in the CIC. From what I've read,
>> Goodman and Carey came up with them so you can probably look for some
>> papers if you're interested.
>>
>> Sebastiaan
>>
>> --
>> Sebastiaan Heunis
>> Radar Remote Sensing Group, University of Cape Town, South Africa
>> Tel: +27 72 950 9370
>>
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>
- [Discuss-gnuradio] USRP2 Halfband filter coefficients help, ILKYOUNG KWOUN, 2009/11/09
- Re: [Discuss-gnuradio] USRP2 Halfband filter coefficients help, Brian Padalino, 2009/11/09
- Re: [Discuss-gnuradio] USRP2 Halfband filter coefficients help, ILKYOUNG KWOUN, 2009/11/09
- Re: [Discuss-gnuradio] USRP2 Halfband filter coefficients help, Sebastiaan Heunis, 2009/11/10
- Re: [Discuss-gnuradio] USRP2 Halfband filter coefficients help, ILKYOUNG KWOUN, 2009/11/10
- Re: [Discuss-gnuradio] USRP2 Halfband filter coefficients help,
Jeff Brower <=
- Re: [Discuss-gnuradio] USRP2 Halfband filter coefficients help, Sebastiaan Heunis, 2009/11/11
- Re: [Discuss-gnuradio] USRP2 Halfband filter coefficients help, Matt Ettus, 2009/11/11
- Re: [Discuss-gnuradio] USRP2 Halfband filter coefficients help, ILKYOUNG KWOUN, 2009/11/11