GNU Radio 3.6.5.1 C++ API
pfb_channelizer_ccf.h
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22 
23 
24 #ifndef INCLUDED_FILTER_PFB_CHANNELIZER_CCF_H
25 #define INCLUDED_FILTER_PFB_CHANNELIZER_CCF_H
26 
27 #include <filter/api.h>
28 #include <gr_block.h>
29 
30 namespace gr {
31  namespace filter {
32 
33  /*!
34  * \brief Polyphase filterbank channelizer with
35  * gr_complex input, gr_complex output and float taps
36  * \ingroup channelizers_blk
37  *
38  * \details
39  * This block takes in complex inputs and channelizes it to <EM>M</EM>
40  * channels of equal bandwidth. Each of the resulting channels is
41  * decimated to the new rate that is the input sampling rate
42  * <EM>fs</EM> divided by the number of channels, <EM>M</EM>.
43  *
44  * The PFB channelizer code takes the taps generated above and builds
45  * a set of filters. The set contains <EM>M</EM> number of filters
46  * and each filter contains ceil(taps.size()/decim) number of taps.
47  * Each tap from the filter prototype is sequentially inserted into
48  * the next filter. When all of the input taps are used, the remaining
49  * filters in the filterbank are filled out with 0's to make sure each
50  * filter has the same number of taps.
51  *
52  * Each filter operates using the gr_fir filter classs of GNU Radio,
53  * which takes the input stream at <EM>i</EM> and performs the inner
54  * product calculation to <EM>i+(n-1)</EM> where <EM>n</EM> is the
55  * number of filter taps. To efficiently handle this in the GNU Radio
56  * structure, each filter input must come from its own input
57  * stream. So the channelizer must be provided with <EM>M</EM> streams
58  * where the input stream has been deinterleaved. This is most easily
59  * done using the gr_stream_to_streams block.
60  *
61  * The output is then produced as a vector, where index <EM>i</EM> in
62  * the vector is the next sample from the <EM>i</EM>th channel. This
63  * is most easily handled by sending the output to a
64  * gr_vector_to_streams block to handle the conversion and passing
65  * <EM>M</EM> streams out.
66  *
67  * The input and output formatting is done using a hier_block2 called
68  * pfb_channelizer_ccf. This can take in a single stream and outputs
69  * <EM>M</EM> streams based on the behavior described above.
70  *
71  * The filter's taps should be based on the input sampling rate.
72  *
73  * For example, using the GNU Radio's firdes utility to building
74  * filters, we build a low-pass filter with a sampling rate of
75  * <EM>fs</EM>, a 3-dB bandwidth of <EM>BW</EM> and a transition
76  * bandwidth of <EM>TB</EM>. We can also specify the out-of-band
77  * attenuation to use, <EM>ATT</EM>, and the filter window
78  * function (a Blackman-harris window in this case). The first input
79  * is the gain of the filter, which we specify here as unity.
80  *
81  * <B><EM>self._taps = filter.firdes.low_pass_2(1, fs, BW, TB,
82  * attenuation_dB=ATT, window=filter.firdes.WIN_BLACKMAN_hARRIS)</EM></B>
83  *
84  * The filter output can also be overs ampled. The over sampling rate
85  * is the ratio of the the actual output sampling rate to the normal
86  * output sampling rate. It must be rationally related to the number
87  * of channels as N/i for i in [1,N], which gives an outputsample rate
88  * of [fs/N, fs] where fs is the input sample rate and N is the number
89  * of channels.
90  *
91  * For example, for 6 channels with fs = 6000 Hz, the normal rate is
92  * 6000/6 = 1000 Hz. Allowable oversampling rates are 6/6, 6/5, 6/4,
93  * 6/3, 6/2, and 6/1 where the output sample rate of a 6/1 oversample
94  * ratio is 6000 Hz, or 6 times the normal 1000 Hz. A rate of 6/5 = 1.2,
95  * so the output rate would be 1200 Hz.
96  *
97  * The theory behind this block can be found in Chapter 6 of
98  * the following book.
99  *
100  * <B><EM>f. harris, "Multirate Signal Processing for Communication
101  * Systems," Upper Saddle River, NJ: Prentice Hall, Inc. 2004.</EM></B>
102  *
103  */
104 
105  class FILTER_API pfb_channelizer_ccf : virtual public gr_block
106  {
107  public:
108  // gr::filter::pfb_channelizer_ccf::sptr
110 
111  /*!
112  * Build the polyphase filterbank decimator.
113  * \param numchans (unsigned integer) Specifies the number of
114  * channels <EM>M</EM>
115  * \param taps (vector/list of floats) The prototype filter to
116  * populate the filterbank.
117  * \param oversample_rate (float) The over sampling rate is the
118  * ratio of the the actual output
119  * sampling rate to the normal
120  * output sampling rate. It must
121  * be rationally related to the
122  * number of channels as N/i for
123  * i in [1,N], which gives an
124  * outputsample rate of [fs/N,
125  * fs] where fs is the input
126  * sample rate and N is the
127  * number of channels.
128  *
129  * For example, for 6 channels
130  * with fs = 6000 Hz, the normal
131  * rateis 6000/6 = 1000
132  * Hz. Allowable oversampling
133  * rates are 6/6, 6/5, 6/4, 6/3,
134  * 6/2, and 6/1 where the output
135  * sample rate of a 6/1
136  * oversample ratio is 6000 Hz,
137  * or 6 times the normal 1000 Hz.
138  */
139  static sptr make(unsigned int numchans,
140  const std::vector<float> &taps,
141  float oversample_rate);
142 
143  /*!
144  * Resets the filterbank's filter taps with the new prototype filter
145  * \param taps (vector/list of floats) The prototype filter to populate the filterbank.
146  */
147  virtual void set_taps(const std::vector<float> &taps) = 0;
148 
149  /*!
150  * Print all of the filterbank taps to screen.
151  */
152  virtual void print_taps() = 0;
153 
154  /*!
155  * Return a vector<vector<>> of the filterbank taps
156  */
157  virtual std::vector<std::vector<float> > taps() const = 0;
158 
159  /*!
160  * Set the channel map. Channels are numbers as:
161  *
162  * N/2+1 | ... | N-1 | 0 | 1 | 2 | ... | N/2
163  * <------------------- 0 -------------------->
164  * freq
165  *
166  * So output stream 0 comes from channel 0, etc. Setting a new
167  * channel map allows the user to specify which channel in frequency
168  * he/she wants to got to which output stream.
169  *
170  * The map should have the same number of elements as the number
171  * of output connections from the block. The minimum value of
172  * the map is 0 (for the 0th channel) and the maximum number is
173  * N-1 where N is the number of channels.
174  *
175  * We specify M as the number of output connections made where M
176  * <= N, so only M out of N channels are driven to an output
177  * stream. The number of items in the channel map should be at
178  * least M long. If there are more channels specified, any value
179  * in the map over M-1 will be ignored. If the size of the map
180  * is less than M the behavior is unknown (we don't wish to
181  * check every entry into the work function).
182  *
183  * This means that if the channelizer is splitting the signal up
184  * into N channels but only M channels are specified in the map
185  * (where M <= N), then M output streams must be connected and
186  * the map and the channel numbers used must be less than
187  * N-1. Output channel number can be reused, too. By default,
188  * the map is [0...M-1] with M = N.
189  */
190  virtual void set_channel_map(const std::vector<int> &map) = 0;
191 
192  /*!
193  * Gets the current channel map.
194  */
195  virtual std::vector<int> channel_map() const = 0;
196  };
197 
198  } /* namespace filter */
199 } /* namespace gr */
200 
201 #endif /* INCLUDED_FILTER_PFB_CHANNELIZER_CCF_H */