GNU Radio's GSM Package
receiver_impl.h
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1 /* -*- c++ -*- */
2 /*
3  * @file
4  * @author (C) 2009-2017 by Piotr Krysik <ptrkrysik@gmail.com>
5  * @section LICENSE
6  *
7  * Gr-gsm is free software; you can redistribute it and/or modify
8  * it under the terms of the GNU General Public License as published by
9  * the Free Software Foundation; either version 3, or (at your option)
10  * any later version.
11  *
12  * Gr-gsm is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15  * GNU General Public License for more details.
16  *
17  * You should have received a copy of the GNU General Public License
18  * along with gr-gsm; see the file COPYING. If not, write to
19  * the Free Software Foundation, Inc., 51 Franklin Street,
20  * Boston, MA 02110-1301, USA.
21  */
22 
23 #ifndef INCLUDED_GSM_RECEIVER_IMPL_H
24 #define INCLUDED_GSM_RECEIVER_IMPL_H
25 
27 #include <grgsm/gsmtap.h>
28 #include <gsm_constants.h>
29 #include <receiver_config.h>
30 #include <vector>
31 
32 namespace gr {
33  namespace gsm {
34  class receiver_impl : public receiver
35  {
36  private:
37  unsigned int d_c0_burst_start;
38  float d_c0_signal_dbm;
39 
40  /**@name Configuration of the receiver */
41  //@{
42  const int d_OSR; ///< oversampling ratio
43  bool d_process_uplink;
44  const int d_chan_imp_length; ///< channel impulse length
45  float d_signal_dbm;
46  std::vector<int> d_tseq_nums; ///< stores training sequence numbers for channels different than C0
47  std::vector<int> d_cell_allocation; ///< stores cell allocation - absolute rf channel numbers (ARFCNs) assigned to the given cell. The variable should at least contain C0 channel number.
48  //@}
49 
50  gr_complex d_sch_training_seq[N_SYNC_BITS]; ///<encoded training sequence of a SCH burst
51  gr_complex d_norm_training_seq[TRAIN_SEQ_NUM][N_TRAIN_BITS]; ///<encoded training sequences of a normal and dummy burst
52 
53  float d_last_time;
54 
55  /** Counts samples consumed by the receiver
56  *
57  * It is used in beetween find_fcch_burst and reach_sch_burst calls.
58  * My intention was to synchronize this counter with some internal sample
59  * counter of the USRP. Simple access to such USRP's counter isn't possible
60  * so this variable isn't used in the "synchronized" state of the receiver yet.
61  */
62  unsigned d_counter;
63 
64  /**@name Variables used to store result of the find_fcch_burst fuction */
65  //@{
66  bool d_freq_offset_tag_in_fcch; ///< frequency offset tag presence
67  unsigned d_fcch_start_pos; ///< position of the first sample of the fcch burst
68  float d_freq_offset_setting; ///< frequency offset set in frequency shifter located upstream
69  //@}
70  std::list<double> d_freq_offset_vals;
71 
72  /**@name Identifiers of the BTS extracted from the SCH burst */
73  //@{
74  int d_ncc; ///< network color code
75  int d_bcc; ///< base station color code
76  //@}
77 
78  /**@name Internal state of the gsm receiver */
79  //@{
80  enum states {
81  fcch_search, sch_search, // synchronization search part
82  synchronized // receiver is synchronized in this state
83  } d_state;
84  //@}
85 
86  /**@name Variables which make internal state in the "synchronized" state */
87  //@{
88  burst_counter d_burst_nr; ///< frame number and timeslot number
89  channel_configuration d_channel_conf; ///< mapping of burst_counter to burst_type
90  //@}
91 
92  unsigned d_failed_sch; ///< number of subsequent erroneous SCH bursts
93 
94  /** Function whis is used to search a FCCH burst and to compute frequency offset before
95  * "synchronized" state of the receiver
96  *
97  * @param input vector with input signal
98  * @param nitems number of samples in the input vector
99  * @return
100  */
101  bool find_fcch_burst(const gr_complex *input, const int nitems, double & computed_freq_offset);
102 
103  /** Computes frequency offset from FCCH burst samples
104  *
105  * @param[in] input vector with input samples
106  * @param[in] first_sample number of the first sample of the FCCH busrt
107  * @param[in] last_sample number of the last sample of the FCCH busrt
108  * @param[out] computed_freq_offset contains frequency offset estimate if FCCH burst was located
109  * @return true if frequency offset was faound
110  */
111  double compute_freq_offset(const gr_complex * input, unsigned first_sample, unsigned last_sample);
112  /** Computes angle between two complex numbers
113  *
114  * @param val1 first complex number
115  * @param val2 second complex number
116  * @return
117  */
118  inline float compute_phase_diff(gr_complex val1, gr_complex val2);
119 
120  /** Function whis is used to get near to SCH burst
121  *
122  * @param nitems number of samples in the gsm_receiver's buffer
123  * @return true if SCH burst is near, false otherwise
124  */
125  bool reach_sch_burst(const int nitems);
126 
127  /** Extracts channel impulse response from a SCH burst and computes first sample number of this burst
128  *
129  * @param input vector with input samples
130  * @param chan_imp_resp complex vector where channel impulse response will be stored
131  * @return number of first sample of the burst
132  */
133  int get_sch_chan_imp_resp(const gr_complex *input, gr_complex * chan_imp_resp);
134 
135  /** MLSE detection of a burst bits
136  *
137  * Detects bits of burst using viterbi algorithm.
138  * @param input vector with input samples
139  * @param chan_imp_resp vector with the channel impulse response
140  * @param burst_start number of the first sample of the burst
141  * @param output_binary vector with output bits
142  */
143  void detect_burst(const gr_complex * input, gr_complex * chan_imp_resp, int burst_start, unsigned char * output_binary);
144 
145  /** Encodes differentially input bits and maps them into MSK states
146  *
147  * @param input vector with input bits
148  * @param nitems number of samples in the "input" vector
149  * @param gmsk_output bits mapped into MSK states
150  * @param start_point first state
151  */
152  void gmsk_mapper(const unsigned char * input, int nitems, gr_complex * gmsk_output, gr_complex start_point);
153 
154  /** Correlates MSK mapped sequence with input signal
155  *
156  * @param sequence MKS mapped sequence
157  * @param length length of the sequence
158  * @param input_signal vector with input samples
159  * @return correlation value
160  */
161  gr_complex correlate_sequence(const gr_complex * sequence, int length, const gr_complex * input);
162 
163  /** Computes autocorrelation of input vector for positive arguments
164  *
165  * @param input vector with input samples
166  * @param out output vector
167  * @param nitems length of the input vector
168  */
169  inline void autocorrelation(const gr_complex * input, gr_complex * out, int nitems);
170 
171  /** Filters input signal through channel impulse response
172  *
173  * @param input vector with input samples
174  * @param nitems number of samples to pass through filter
175  * @param filter filter taps - channel impulse response
176  * @param filter_length nember of filter taps
177  * @param output vector with filtered samples
178  */
179  inline void mafi(const gr_complex * input, int nitems, gr_complex * filter, int filter_length, gr_complex * output);
180 
181  /** Extracts channel impulse response from a normal burst and computes first sample number of this burst
182  *
183  * @param input vector with input samples
184  * @param chan_imp_resp complex vector where channel impulse response will be stored
185  * @param search_range possible absolute offset of a channel impulse response start
186  * @param bcc base station color code - number of a training sequence
187  * @return first sample number of normal burst
188  */
189  int get_norm_chan_imp_resp(const gr_complex *input, gr_complex * chan_imp_resp, float *corr_max, int bcc);
190 
191  /**
192  * Sends burst through a C0 (for burst from C0 channel) or Cx (for other bursts) message port
193  *
194  * @param burst_nr - frame number of the burst
195  * @param burst_binary - content of the burst
196  * @b_type - type of the burst
197  */
198  void send_burst(burst_counter burst_nr, const unsigned char * burst_binary, uint8_t burst_type, unsigned int input_nr);
199 
200  /**
201  * Configures burst types in different channels
202  */
203  void configure_receiver();
204 
205  /* State machine handlers */
206  void fcch_search_handler(gr_complex *input, int noutput_items);
207  void sch_search_handler(gr_complex *input, int noutput_items);
208  void synchronized_handler(gr_complex *input,
209  gr_vector_const_void_star &input_items, int noutput_items);
210 
211  public:
212  receiver_impl(int osr, const std::vector<int> &cell_allocation, const std::vector<int> &tseq_nums, bool process_uplink);
213  ~receiver_impl();
214 
215  int work(int noutput_items, gr_vector_const_void_star &input_items, gr_vector_void_star &output_items);
216  virtual void set_cell_allocation(const std::vector<int> &cell_allocation);
217  virtual void set_tseq_nums(const std::vector<int> & tseq_nums);
218  virtual void reset();
219  };
220  } // namespace gsm
221 } // namespace gr
222 
223 #endif /* INCLUDED_GSM_RECEIVER_IMPL_H */
224 
Definition: receiver_config.h:131
virtual void set_cell_allocation(const std::vector< int > &cell_allocation)
virtual void reset()
int work(int noutput_items, gr_vector_const_void_star &input_items, gr_vector_void_star &output_items)
#define N_TRAIN_BITS
Definition: gsm_constants.h:36
#define TRAIN_SEQ_NUM
Definition: gsm_constants.h:92
burst_type
Definition: gsm_constants.h:62
Definition: constants.h:29
#define N_SYNC_BITS
Definition: gsm_constants.h:37
receiver_impl(int osr, const std::vector< int > &cell_allocation, const std::vector< int > &tseq_nums, bool process_uplink)
Definition: receiver_config.h:67
Definition: receiver_impl.h:34
virtual void set_tseq_nums(const std::vector< int > &tseq_nums)
<+description of block+>
Definition: receiver.h:40