GNU Radio Manual and C++ API Reference  3.7.9.2
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cc_decoder.h
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1 /* -*- c++ -*- */
2 /*
3  * Copyright 2013-2014 Free Software Foundation, Inc.
4  *
5  * This file is part of GNU Radio
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7  * GNU Radio is free software; you can redistribute it and/or modify
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14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15  * GNU General Public License for more details.
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22 
23 #ifndef INCLUDED_FEC_CC_DECODER_H
24 #define INCLUDED_FEC_CC_DECODER_H
25 
26 #include <gnuradio/fec/api.h>
28 #include <gnuradio/fec/cc_common.h>
29 #include <map>
30 #include <string>
31 
32 namespace gr {
33  namespace fec {
34  namespace code {
35 
36  typedef void(*conv_kernel)(unsigned char *Y, unsigned char *X,
37  unsigned char *syms, unsigned char *dec,
38  unsigned int framebits, unsigned int excess,
39  unsigned char *Branchtab);
40 
41  /*!
42  * \brief Convolutional Code Decoding class.
43  * \ingroup error_coding_blk
44  *
45  * \details
46  * This class performs convolutional decoding via the Viterbi
47  * algorithm. While it is set up to take variable values for K,
48  * rate, and the polynomials, currently, the block is only
49  * capable of handling the following settings:
50  *
51  * \li K = 7
52  * \li rate = 1/2 (given as 2 to the constructor)
53  * \li polynomials = [109, 79]
54  *
55  * This is the well-known convolutional part of the Voyager code
56  * implemented in the CCSDS encoder.
57  *
58  * The intent of having this FECAPI code classes fully
59  * parameterizable is to eventually allow it to take on generic
60  * settings, much like the cc_encoder class where the CCSDS
61  * settings would be a highly-optimized version of this.
62  *
63  * The decoder is set up with a number of bits per frame in the
64  * constructor. When not being used in a tagged stream mode,
65  * this encoder will only process frames of the length provided
66  * here. If used in a tagged stream block, this setting becomes
67  * the maximum allowable frame size that the block may process.
68  *
69  * The \p mode is a cc_mode_t that specifies how the convolutional
70  * encoder will behave and under what conditions.
71  *
72  * \li 'CC_STREAMING': mode expects an uninterrupted flow of
73  * samples into the encoder, and the output stream is
74  * continually encoded. This mode is the only mode for this
75  * decoder that has a history requirement because it requires
76  * rate*(K-1) bits more to finish the decoding properly. This
77  * mode does not work with any deployments that do not allow
78  * history.
79  *
80  * \li 'CC_TERMINATED': is a mode designed for packet-based
81  * systems. This mode adds rate*(k-1) bits to the output as a
82  * way to help flush the decoder.
83  *
84  * \li 'CC_TAILBITING': is another packet-based method. Instead of
85  * adding bits onto the end of the packet, this mode will
86  * continue the code between the payloads of packets by
87  * pre-initializing the state of the new packet based on the
88  * state of the last packet for (k-1) bits.
89  *
90  * \li 'CC_TRUNCATED': a truncated code always resets the registers
91  * to the \p start_state between frames.
92  *
93  * A common convolutional encoder uses K=7, Rate=1/2,
94  * Polynomials=[109, 79]. This is the Voyager code from NASA:
95  * \li 109: b(1101101) --> 1 + x + x^3 + x^4 + x^6
96  * \li 79: b(1001111) --> 1 + x^3 + x^4 + x^5 + x^6
97  */
98  class FEC_API cc_decoder : virtual public generic_decoder
99  {
100  public:
101 
102  /*!
103  * Build a convolutional code decoding FEC API object.
104  *
105  * \param frame_size Number of bits per frame. If using in the
106  * tagged stream style, this is the maximum allowable
107  * number of bits per frame.
108  * \param k Constraint length (K) of the encoder.
109  * \param rate Inverse of the coder's rate
110  * (rate=2 means 2 output bits per 1 input).
111  * \param polys Vector of polynomials as integers.
112  * \param start_state Initialization state of the shift register.
113  * \param end_state Ending state of the shift register.
114  * \param mode cc_mode_t mode of the encoding.
115  * \param padded true if the encoded frame is padded
116  * to the nearest byte.
117  */
118  static generic_decoder::sptr make
119  (int frame_size, int k,
120  int rate, std::vector<int> polys,
121  int start_state=0, int end_state=-1,
122  cc_mode_t mode=CC_STREAMING,
123  bool padded=false);
124 
125  /*!
126  * Sets the uncoded frame size to \p frame_size. If \p
127  * frame_size is greater than the value given to the
128  * constructor, the frame size will be capped by that initial
129  * value and this function will return false. Otherwise, it
130  * returns true.
131  */
132  virtual bool set_frame_size(unsigned int frame_size) = 0;
133 
134  /*!
135  * Returns the coding rate of this encoder.
136  */
137  virtual double rate() = 0;
138  };
139 
140  } /* namespace code */
141  } /* namespace fec */
142 } /* namespace gr */
143 
144 #endif /* INCLUDED_FEC_CC_DECODER_H */
Convolutional Code Decoding class.
Definition: cc_decoder.h:98
Parent class for FECAPI objects.
Definition: generic_decoder.h:60
enum _cc_mode_t cc_mode_t
void(* conv_kernel)(unsigned char *Y, unsigned char *X, unsigned char *syms, unsigned char *dec, unsigned int framebits, unsigned int excess, unsigned char *Branchtab)
Definition: cc_decoder.h:36
Include this header to use the message passing features.
Definition: logger.h:131
#define FEC_API
Definition: gr-fec/include/gnuradio/fec/api.h:30
boost::shared_ptr< generic_decoder > sptr
Definition: generic_decoder.h:75
Definition: cc_common.h:27