GNU Radio 3.6.2 C++ API
gr::filter::pfb_channelizer_ccf Class Reference

Polyphase filterbank channelizer with gr_complex input, gr_complex output and float taps. More...

#include <pfb_channelizer_ccf.h>

Inheritance diagram for gr::filter::pfb_channelizer_ccf:

Public Types

typedef boost::shared_ptr
< pfb_channelizer_ccf
sptr
- Public Types inherited from gr_block
enum  { WORK_CALLED_PRODUCE = -2, WORK_DONE = -1 }
 Magic return values from general_work. More...
enum  tag_propagation_policy_t { TPP_DONT = 0, TPP_ALL_TO_ALL = 1, TPP_ONE_TO_ONE = 2 }

Public Member Functions

virtual void set_taps (const std::vector< float > &taps)=0
virtual void print_taps ()=0
virtual std::vector
< std::vector< float > > 
taps () const =0
virtual void set_channel_map (const std::vector< int > &map)=0
virtual std::vector< int > channel_map () const =0
- Public Member Functions inherited from gr_block
virtual ~gr_block ()
unsigned history () const
void set_history (unsigned history)
bool fixed_rate () const
 Return true if this block has a fixed input to output rate.
virtual void forecast (int noutput_items, gr_vector_int &ninput_items_required)
 Estimate input requirements given output request.
virtual int general_work (int noutput_items, gr_vector_int &ninput_items, gr_vector_const_void_star &input_items, gr_vector_void_star &output_items)=0
 compute output items from input items
virtual bool start ()
 Called to enable drivers, etc for i/o devices.
virtual bool stop ()
 Called to disable drivers, etc for i/o devices.
void set_output_multiple (int multiple)
 Constrain the noutput_items argument passed to forecast and general_work.
int output_multiple () const
bool output_multiple_set () const
void set_alignment (int multiple)
 Constrains buffers to work on a set item alignment (for SIMD)
int alignment () const
void set_unaligned (int na)
int unaligned () const
void set_is_unaligned (bool u)
bool is_unaligned () const
void consume (int which_input, int how_many_items)
 Tell the scheduler how_many_items of input stream which_input were consumed.
void consume_each (int how_many_items)
 Tell the scheduler how_many_items were consumed on each input stream.
void produce (int which_output, int how_many_items)
 Tell the scheduler how_many_items were produced on output stream which_output.
void set_relative_rate (double relative_rate)
 Set the approximate output rate / input rate.
double relative_rate () const
 return the approximate output rate / input rate
virtual int fixed_rate_ninput_to_noutput (int ninput)
 Given ninput samples, return number of output samples that will be produced. N.B. this is only defined if fixed_rate returns true. Generally speaking, you don't need to override this.
virtual int fixed_rate_noutput_to_ninput (int noutput)
 Given noutput samples, return number of input samples required to produce noutput. N.B. this is only defined if fixed_rate returns true. Generally speaking, you don't need to override this.
uint64_t nitems_read (unsigned int which_input)
 Return the number of items read on input stream which_input.
uint64_t nitems_written (unsigned int which_output)
 Return the number of items written on output stream which_output.
tag_propagation_policy_t tag_propagation_policy ()
 Asks for the policy used by the scheduler to moved tags downstream.
void set_tag_propagation_policy (tag_propagation_policy_t p)
 Set the policy by the scheduler to determine how tags are moved downstream.
gr_block_detail_sptr detail () const
void set_detail (gr_block_detail_sptr detail)
- Public Member Functions inherited from gr_basic_block
virtual ~gr_basic_block ()
long unique_id () const
std::string name () const
gr_io_signature_sptr input_signature () const
gr_io_signature_sptr output_signature () const
gr_basic_block_sptr to_basic_block ()
virtual bool check_topology (int ninputs, int noutputs)
 Confirm that ninputs and noutputs is an acceptable combination.
template<typename T >
void set_msg_handler (T msg_handler)
 Set the callback that is fired when messages are available.
- Public Member Functions inherited from gr_msg_accepter
 gr_msg_accepter ()
 ~gr_msg_accepter ()
void post (pmt::pmt_t msg)
 send msg to msg_accepter
- Public Member Functions inherited from gruel::msg_accepter
 msg_accepter ()
virtual ~msg_accepter ()

Static Public Member Functions

static sptr make (unsigned int numchans, const std::vector< float > &taps, float oversample_rate)

Additional Inherited Members

- Protected Types inherited from gr_basic_block
enum  vcolor { WHITE, GREY, BLACK }
- Protected Member Functions inherited from gr_block
 gr_block (void)
 gr_block (const std::string &name, gr_io_signature_sptr input_signature, gr_io_signature_sptr output_signature)
void set_fixed_rate (bool fixed_rate)
void add_item_tag (unsigned int which_output, uint64_t abs_offset, const pmt::pmt_t &key, const pmt::pmt_t &value, const pmt::pmt_t &srcid=pmt::PMT_F)
 Adds a new tag onto the given output buffer.
void add_item_tag (unsigned int which_output, const gr_tag_t &tag)
 Adds a new tag onto the given output buffer.
void get_tags_in_range (std::vector< gr_tag_t > &v, unsigned int which_input, uint64_t abs_start, uint64_t abs_end)
 Given a [start,end), returns a vector of all tags in the range.
void get_tags_in_range (std::vector< gr_tag_t > &v, unsigned int which_input, uint64_t abs_start, uint64_t abs_end, const pmt::pmt_t &key)
 Given a [start,end), returns a vector of all tags in the range with a given key.
- Protected Attributes inherited from gr_basic_block
std::string d_name
gr_io_signature_sptr d_input_signature
gr_io_signature_sptr d_output_signature
long d_unique_id
vcolor d_color

Detailed Description

Polyphase filterbank channelizer with gr_complex input, gr_complex output and float taps.

This block takes in complex inputs and channelizes it to M channels of equal bandwidth. Each of the resulting channels is decimated to the new rate that is the input sampling rate fs divided by the number of channels, M.

The PFB channelizer code takes the taps generated above and builds a set of filters. The set contains M 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.

Each filter operates using the gr_fir filter classs of GNU Radio, which takes the input stream at i and performs the inner product calculation to i+(n-1) where n is the number of filter taps. To efficiently handle this in the GNU Radio structure, each filter input must come from its own input stream. So the channelizer must be provided with M streams where the input stream has been deinterleaved. This is most easily done using the gr_stream_to_streams block.

The output is then produced as a vector, where index i in the vector is the next sample from the ith channel. This is most easily handled by sending the output to a gr_vector_to_streams block to handle the conversion and passing M streams out.

The input and output formatting is done using a hier_block2 called pfb_channelizer_ccf. This can take in a single stream and outputs M streams based on the behavior described above.

The filter's taps should be based on the input sampling rate.

For example, using the GNU Radio's firdes utility to building filters, we build a low-pass filter with a sampling rate of fs, a 3-dB bandwidth of BW and a transition bandwidth of TB. We can also specify the out-of-band attenuation to use, ATT, and the filter window function (a Blackman-harris window in this case). The first input is the gain of the filter, which we specify here as unity.

<B><EM>self._taps = filter.firdes.low_pass_2(1, fs, BW, TB,
     attenuation_dB=ATT, window=filter.firdes.WIN_BLACKMAN_hARRIS)</EM></B>

The filter output can also be overs ampled. The over sampling rate is the ratio of the the actual output sampling rate to the normal output sampling rate. It must be rationally related to the number of channels as N/i for i in [1,N], which gives an outputsample rate of [fs/N, fs] where fs is the input sample rate and N is the number of channels.

For example, for 6 channels with fs = 6000 Hz, the normal rate is 6000/6 = 1000 Hz. Allowable oversampling rates are 6/6, 6/5, 6/4, 6/3, 6/2, and 6/1 where the output sample rate of a 6/1 oversample ratio is 6000 Hz, or 6 times the normal 1000 Hz. A rate of 6/5 = 1.2, so the output rate would be 1200 Hz.

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.

Member Typedef Documentation

Member Function Documentation

virtual std::vector<int> gr::filter::pfb_channelizer_ccf::channel_map ( ) const
pure virtual

Gets the current channel map.

static sptr gr::filter::pfb_channelizer_ccf::make ( unsigned int  numchans,
const std::vector< float > &  taps,
float  oversample_rate 
)
static

Build the polyphase filterbank decimator.

Parameters
numchans(unsigned integer) Specifies the number of channels M
taps(vector/list of floats) The prototype filter to populate the filterbank.
oversample_rate(float) The over sampling rate is the ratio of the the actual output sampling rate to the normal output sampling rate. It must be rationally related to the number of channels as N/i for i in [1,N], which gives an outputsample rate of [fs/N, fs] where fs is the input sample rate and N is the number of channels.

For example, for 6 channels with fs = 6000 Hz, the normal rateis 6000/6 = 1000 Hz. Allowable oversampling rates are 6/6, 6/5, 6/4, 6/3, 6/2, and 6/1 where the output sample rate of a 6/1 oversample ratio is 6000 Hz, or 6 times the normal 1000 Hz.

virtual void gr::filter::pfb_channelizer_ccf::print_taps ( )
pure virtual

Print all of the filterbank taps to screen.

virtual void gr::filter::pfb_channelizer_ccf::set_channel_map ( const std::vector< int > &  map)
pure virtual

Set the channel map. Channels are numbers as:

N/2+1 | ... | N-1 | 0 | 1 |  2 | ... | N/2

<----------------— 0 -----------------—> freq

So output stream 0 comes from channel 0, etc. Setting a new channel map allows the user to specify which channel in frequency he/she wants to got to which output stream.

The map should have the same number of elements as the number of output connections from the block. The minimum value of the map is 0 (for the 0th channel) and the maximum number is N-1 where N is the number of channels.

We specify M as the number of output connections made where M <= N, so only M out of N channels are driven to an output stream. The number of items in the channel map should be at least M long. If there are more channels specified, any value in the map over M-1 will be ignored. If the size of the map is less than M the behavior is unknown (we don't wish to check every entry into the work function).

This means that if the channelizer is splitting the signal up into N channels but only M channels are specified in the map (where M <= N), then M output streams must be connected and the map and the channel numbers used must be less than N-1. Output channel number can be reused, too. By default, the map is [0...M-1] with M = N.

virtual void gr::filter::pfb_channelizer_ccf::set_taps ( const std::vector< float > &  taps)
pure virtual

Resets the filterbank's filter taps with the new prototype filter

Parameters
taps(vector/list of floats) The prototype filter to populate the filterbank.
virtual std::vector<std::vector<float> > gr::filter::pfb_channelizer_ccf::taps ( ) const
pure virtual

Return a vector<vector<>> of the filterbank taps


The documentation for this class was generated from the following file: