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 <sheu...@gmail.com> > >> 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 >> > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio