GNU Radio 3.6.5 C++ API

Polyphase filterbank bandpass decimator with gr_complex input, gr_complex output and float taps. More...
#include <pfb_decimator_ccf.h>
Public Types  
typedef boost::shared_ptr < pfb_decimator_ccf >  sptr 
Public Member Functions  
virtual void  set_taps (const std::vector< float > &taps)=0 
virtual std::vector < std::vector< float > >  taps () const =0 
virtual void  print_taps ()=0 
Static Public Member Functions  
static sptr  make (unsigned int decim, const std::vector< float > &taps, unsigned int channel) 
Polyphase filterbank bandpass decimator with gr_complex input, gr_complex output and float taps.
This block takes in a signal stream and performs interger down sampling (decimation) with a polyphase filterbank. The first input is the integer specifying how much to decimate by. The second input is a vector (Python list) of floatingpoint taps of the prototype filter. The third input specifies the channel to extract. By default, the zeroth channel is used, which is the baseband channel (first Nyquist zone).
The channel parameter specifies which channel to use since this class is capable of bandpass decimation. Given a complex input stream at a sampling rate of fs and a decimation rate of decim, the input frequency domain is split into decim channels that represent the Nyquist zones. Using the polyphase filterbank, we can select any one of these channels to decimate.
The output signal will be the basebanded and decimated signal from that channel. This concept is very similar to the PFB channelizer (see gr_pfb_channelizer_ccf) where only a single channel is extracted at a time.
The filter's taps should be based on the sampling rate before decimation.
For example, using the GNU Radio's firdes utility to building filters, we build a lowpass filter with a sampling rate of fs, a 3dB bandwidth of BW and a transition bandwidth of TB. We can also specify the outofband attenuation to use, ATT, and the filter window function (a Blackmanharris window in this case). The first input is the gain of the filter, which we specify here as unity.
self._taps = filter.firdes.low_pass_2(1, fs, BW, TB, attenuation_dB=ATT, window=filter.firdes.WIN_BLACKMAN_hARRIS)
The PFB decimator code takes the taps generated above and builds a set of filters. The set contains decim number of filters and each filter contains ceil(taps.size()/decim) number of taps. Each tap from the filter prototype is sequentially inserted into the next filter. When all of the input taps are used, the remaining filters in the filterbank are filled out with 0's to make sure each filter has the same number of taps.
The theory behind this block can be found in Chapter 6 of the following book.
f. harris, "Multirate Signal Processing for Communication Systems," Upper Saddle River, NJ: Prentice Hall, Inc. 2004.
static sptr gr::filter::pfb_decimator_ccf::make  (  unsigned int  decim, 
const std::vector< float > &  taps,  
unsigned int  channel  
)  [static] 
Build the polyphase filterbank decimator.
decim  (unsigned integer) Specifies the decimation rate to use 
taps  (vector/list of floats) The prototype filter to populate the filterbank. 
channel  (unsigned integer) Selects the channel to return [default=0]. 
virtual void gr::filter::pfb_decimator_ccf::print_taps  (  )  [pure virtual] 
Print all of the filterbank taps to screen.
Implemented in gr::filter::pfb_decimator_ccf_impl.
virtual void gr::filter::pfb_decimator_ccf::set_taps  (  const std::vector< float > &  taps  )  [pure virtual] 
Resets the filterbank's filter taps with the new prototype filter
taps  (vector/list of floats) The prototype filter to populate the filterbank. 
Implemented in gr::filter::pfb_decimator_ccf_impl.
virtual std::vector<std::vector<float> > gr::filter::pfb_decimator_ccf::taps  (  )  const [pure virtual] 
Return a vector<vector<>> of the filterbank taps
Implemented in gr::filter::pfb_decimator_ccf_impl.