GNU Radio 3.6.3 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  * \class pfb_channelizer_ccf
35  *
36  * \brief Polyphase filterbank channelizer with
37  * gr_complex input, gr_complex output and float taps
38  *
39  * \ingroup filter_blk
40  * \ingroup pfb_blk
41  *
42  * This block takes in complex inputs and channelizes it to <EM>M</EM>
43  * channels of equal bandwidth. Each of the resulting channels is
44  * decimated to the new rate that is the input sampling rate
45  * <EM>fs</EM> divided by the number of channels, <EM>M</EM>.
46  *
47  * The PFB channelizer code takes the taps generated above and builds
48  * a set of filters. The set contains <EM>M</EM> number of filters
49  * and each filter contains ceil(taps.size()/decim) number of taps.
50  * Each tap from the filter prototype is sequentially inserted into
51  * the next filter. When all of the input taps are used, the remaining
52  * filters in the filterbank are filled out with 0's to make sure each
53  * filter has the same number of taps.
54  *
55  * Each filter operates using the gr_fir filter classs of GNU Radio,
56  * which takes the input stream at <EM>i</EM> and performs the inner
57  * product calculation to <EM>i+(n-1)</EM> where <EM>n</EM> is the
58  * number of filter taps. To efficiently handle this in the GNU Radio
59  * structure, each filter input must come from its own input
60  * stream. So the channelizer must be provided with <EM>M</EM> streams
61  * where the input stream has been deinterleaved. This is most easily
62  * done using the gr_stream_to_streams block.
63  *
64  * The output is then produced as a vector, where index <EM>i</EM> in
65  * the vector is the next sample from the <EM>i</EM>th channel. This
66  * is most easily handled by sending the output to a
67  * gr_vector_to_streams block to handle the conversion and passing
68  * <EM>M</EM> streams out.
69  *
70  * The input and output formatting is done using a hier_block2 called
71  * pfb_channelizer_ccf. This can take in a single stream and outputs
72  * <EM>M</EM> streams based on the behavior described above.
73  *
74  * The filter's taps should be based on the input sampling rate.
75  *
76  * For example, using the GNU Radio's firdes utility to building
77  * filters, we build a low-pass filter with a sampling rate of
78  * <EM>fs</EM>, a 3-dB bandwidth of <EM>BW</EM> and a transition
79  * bandwidth of <EM>TB</EM>. We can also specify the out-of-band
80  * attenuation to use, <EM>ATT</EM>, and the filter window
81  * function (a Blackman-harris window in this case). The first input
82  * is the gain of the filter, which we specify here as unity.
83  *
84  * <B><EM>self._taps = filter.firdes.low_pass_2(1, fs, BW, TB,
85  * attenuation_dB=ATT, window=filter.firdes.WIN_BLACKMAN_hARRIS)</EM></B>
86  *
87  * The filter output can also be overs ampled. The over sampling rate
88  * is the ratio of the the actual output sampling rate to the normal
89  * output sampling rate. It must be rationally related to the number
90  * of channels as N/i for i in [1,N], which gives an outputsample rate
91  * of [fs/N, fs] where fs is the input sample rate and N is the number
92  * of channels.
93  *
94  * For example, for 6 channels with fs = 6000 Hz, the normal rate is
95  * 6000/6 = 1000 Hz. Allowable oversampling rates are 6/6, 6/5, 6/4,
96  * 6/3, 6/2, and 6/1 where the output sample rate of a 6/1 oversample
97  * ratio is 6000 Hz, or 6 times the normal 1000 Hz. A rate of 6/5 = 1.2,
98  * so the output rate would be 1200 Hz.
99  *
100  * The theory behind this block can be found in Chapter 6 of
101  * the following book.
102  *
103  * <B><EM>f. harris, "Multirate Signal Processing for Communication
104  * Systems," Upper Saddle River, NJ: Prentice Hall, Inc. 2004.</EM></B>
105  *
106  */
107 
108  class FILTER_API pfb_channelizer_ccf : virtual public gr_block
109  {
110  public:
111  // gr::filter::pfb_channelizer_ccf::sptr
113 
114  /*!
115  * Build the polyphase filterbank decimator.
116  * \param numchans (unsigned integer) Specifies the number of
117  * channels <EM>M</EM>
118  * \param taps (vector/list of floats) The prototype filter to
119  * populate the filterbank.
120  * \param oversample_rate (float) The over sampling rate is the
121  * ratio of the the actual output
122  * sampling rate to the normal
123  * output sampling rate. It must
124  * be rationally related to the
125  * number of channels as N/i for
126  * i in [1,N], which gives an
127  * outputsample rate of [fs/N,
128  * fs] where fs is the input
129  * sample rate and N is the
130  * number of channels.
131  *
132  * For example, for 6 channels
133  * with fs = 6000 Hz, the normal
134  * rateis 6000/6 = 1000
135  * Hz. Allowable oversampling
136  * rates are 6/6, 6/5, 6/4, 6/3,
137  * 6/2, and 6/1 where the output
138  * sample rate of a 6/1
139  * oversample ratio is 6000 Hz,
140  * or 6 times the normal 1000 Hz.
141  */
142  static sptr make(unsigned int numchans,
143  const std::vector<float> &taps,
144  float oversample_rate);
145 
146  /*!
147  * Resets the filterbank's filter taps with the new prototype filter
148  * \param taps (vector/list of floats) The prototype filter to populate the filterbank.
149  */
150  virtual void set_taps(const std::vector<float> &taps) = 0;
151 
152  /*!
153  * Print all of the filterbank taps to screen.
154  */
155  virtual void print_taps() = 0;
156 
157  /*!
158  * Return a vector<vector<>> of the filterbank taps
159  */
160  virtual std::vector<std::vector<float> > taps() const = 0;
161 
162  /*!
163  * Set the channel map. Channels are numbers as:
164  *
165  * N/2+1 | ... | N-1 | 0 | 1 | 2 | ... | N/2
166  * <------------------- 0 -------------------->
167  * freq
168  *
169  * So output stream 0 comes from channel 0, etc. Setting a new
170  * channel map allows the user to specify which channel in frequency
171  * he/she wants to got to which output stream.
172  *
173  * The map should have the same number of elements as the number
174  * of output connections from the block. The minimum value of
175  * the map is 0 (for the 0th channel) and the maximum number is
176  * N-1 where N is the number of channels.
177  *
178  * We specify M as the number of output connections made where M
179  * <= N, so only M out of N channels are driven to an output
180  * stream. The number of items in the channel map should be at
181  * least M long. If there are more channels specified, any value
182  * in the map over M-1 will be ignored. If the size of the map
183  * is less than M the behavior is unknown (we don't wish to
184  * check every entry into the work function).
185  *
186  * This means that if the channelizer is splitting the signal up
187  * into N channels but only M channels are specified in the map
188  * (where M <= N), then M output streams must be connected and
189  * the map and the channel numbers used must be less than
190  * N-1. Output channel number can be reused, too. By default,
191  * the map is [0...M-1] with M = N.
192  */
193  virtual void set_channel_map(const std::vector<int> &map) = 0;
194 
195  /*!
196  * Gets the current channel map.
197  */
198  virtual std::vector<int> channel_map() const = 0;
199  };
200 
201  } /* namespace filter */
202 } /* namespace gr */
203 
204 #endif /* INCLUDED_FILTER_PFB_CHANNELIZER_CCF_H */