moved gsm-receiver into directory - preparation to move to airprobe

1 files changed, 0 insertions, 853 deletions

diff --git a/src/lib/gsm_receiver_cf.cc b/src/lib/gsm_receiver_cf.cc
deleted file mode 100644
index 4742b33..0000000
--- a/src/lib/gsm_receiver_cf.cc
+++ /dev/null
@@ -1,853 +0,0 @@
-/* -*- c++ -*- */
-/*
- * @file
- * @author Piotr Krysik <pkrysik@stud.elka.pw.edu.pl>
- * @section LICENSE
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 3, or (at your option)
- * any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; see the file COPYING.  If not, write to
- * the Free Software Foundation, Inc., 51 Franklin Street,
- * Boston, MA 02110-1301, USA.
- */
-
-#ifdef HAVE_CONFIG_H
-#include "config.h"
-#endif
-
-#include <gr_io_signature.h>
-#include <gr_math.h>
-#include <math.h>
-#include <Assert.h>
-#include <boost/circular_buffer.hpp>
-#include <algorithm>
-#include <numeric>
-#include <gsm_receiver_cf.h>
-#include <viterbi_detector.h>
-#include <string.h>
-#include <sch.h>
-
-
-#include "RxBurst.h"
-#include "GSMCommon.h"
-
-#define SYNC_SEARCH_RANGE 30
-// #define TRAIN_SEARCH_RANGE 40
-//FIXME: decide to use this define or not
-
-//TODO: this shouldn't be here - remove it when gsm receiver's interface will be ready
-void decrypt(const unsigned char * burst_binary, byte * KC, float * decrypted_data, unsigned FN)
-{
-  byte AtoB[2*DATA_BITS];
-
-  keysetup(KC, FN);
-  runA51(AtoB);
-
-  for (int i = 0; i < 148; i++) {
-    decrypted_data[i] = burst_binary[i];
-  }
-
-  for (int i = 0; i < 57; i++) {
-    decrypted_data[i+3] = AtoB[i] ^ burst_binary[i+3];
-  }
-
-  for (int i = 0; i < 57; i++) {
-    decrypted_data[i+88] = AtoB[i+57] ^ burst_binary[i+88];
-  }
-}
-
-void gsm_receiver_cf::read_key(std::string key)
-{
-  int i;
-  int b;
-  for (i = 0;i < 8;i++) {
-    b = d_hex_to_int[(char)key[(i)*2]]*16 + d_hex_to_int[(char)key[i*2+1]];
-    d_KC[i] = (byte)b;
-  }
-}
-
-void gsm_receiver_cf::process_normal_burst(burst_counter burst_nr, const unsigned char * burst_binary)
-{
-//   static byte KC[] = {  0xAD, 0x6A, 0x3E, 0xC2, 0xB4, 0x42, 0xE4, 0x00 };
-//   static byte KC[] = {  0x2B, 0x08, 0x74, 0x9F, 0xDD, 0x0D, 0x9C, 0x00 };
-//   printf("%x", KC[0]);
-  float decrypted_data[148];
-  unsigned char * voice_frame;
-
-//   if (burst_nr.get_timeslot_nr() == 7) {
-  if (burst_nr.get_timeslot_nr() >= 1 && burst_nr.get_timeslot_nr() <= 7) {
-    decrypt(burst_binary, d_KC, decrypted_data, burst_nr.get_frame_nr_mod());
-
-    GSM::Time time(burst_nr.get_frame_nr(), burst_nr.get_timeslot_nr());
-    GSM::RxBurst rxbrst(decrypted_data, time);
-    switch (burst_nr.get_timeslot_nr()) {
-      case 1:
-        if ( d_tch_decoder1.processBurst( rxbrst ) == true) {
-          fwrite(d_tch_decoder1.get_voice_frame(), 1 , 33, d_gsm_file);
-        }
-        break;
-      case 2:
-        if ( d_tch_decoder2.processBurst( rxbrst ) == true) {
-          fwrite(d_tch_decoder2.get_voice_frame(), 1 , 33, d_gsm_file);
-        }
-        break;
-      case 3:
-        if ( d_tch_decoder3.processBurst( rxbrst ) == true) {
-          fwrite(d_tch_decoder3.get_voice_frame(), 1 , 33, d_gsm_file);
-        }
-        break;
-      case 4:
-        if ( d_tch_decoder4.processBurst( rxbrst ) == true) {
-          fwrite(d_tch_decoder4.get_voice_frame(), 1 , 33, d_gsm_file);
-        }
-        break;
-      case 5:
-        if ( d_tch_decoder5.processBurst( rxbrst ) == true) {
-          fwrite(d_tch_decoder5.get_voice_frame(), 1 , 33, d_gsm_file);
-        }
-        break;
-      case 6:
-        if ( d_tch_decoder6.processBurst( rxbrst ) == true) {
-          fwrite(d_tch_decoder6.get_voice_frame(), 1 , 33, d_gsm_file);
-        }
-        break;
-      case 7:
-        if ( d_tch_decoder7.processBurst( rxbrst ) == true) {
-          fwrite(d_tch_decoder7.get_voice_frame(), 1 , 33, d_gsm_file);
-        }
-        break;
-    }
-  }
-
-  if (burst_nr.get_timeslot_nr() == 0) {
-    GS_process(&d_gs_ctx, TIMESLOT0, 6, &burst_binary[3], burst_nr.get_frame_nr());
-  }
-}
-//TODO: this shouldn't be here also - the same reason
-void gsm_receiver_cf::configure_receiver()
-{
-  d_channel_conf.set_multiframe_type(TSC0, multiframe_51);
-
-  d_channel_conf.set_burst_types(TSC0, TEST_CCH_FRAMES, sizeof(TEST_CCH_FRAMES) / sizeof(unsigned), normal_burst);
-  d_channel_conf.set_burst_types(TSC0, FCCH_FRAMES, sizeof(FCCH_FRAMES) / sizeof(unsigned), fcch_burst);
-
-  d_channel_conf.set_multiframe_type(TIMESLOT1, multiframe_26);
-  d_channel_conf.set_burst_types(TIMESLOT1, TRAFFIC_CHANNEL_F, sizeof(TRAFFIC_CHANNEL_F) / sizeof(unsigned), dummy_or_normal);
-  d_channel_conf.set_multiframe_type(TIMESLOT2, multiframe_26);
-  d_channel_conf.set_burst_types(TIMESLOT2, TRAFFIC_CHANNEL_F, sizeof(TRAFFIC_CHANNEL_F) / sizeof(unsigned), dummy_or_normal);
-
-  d_channel_conf.set_multiframe_type(TIMESLOT3, multiframe_26);
-  d_channel_conf.set_burst_types(TIMESLOT3, TRAFFIC_CHANNEL_F, sizeof(TRAFFIC_CHANNEL_F) / sizeof(unsigned), dummy_or_normal);
-  d_channel_conf.set_multiframe_type(TIMESLOT4, multiframe_26);
-  d_channel_conf.set_burst_types(TIMESLOT4, TRAFFIC_CHANNEL_F, sizeof(TRAFFIC_CHANNEL_F) / sizeof(unsigned), dummy_or_normal);
-
-  d_channel_conf.set_multiframe_type(TIMESLOT5, multiframe_26);
-  d_channel_conf.set_burst_types(TIMESLOT5, TRAFFIC_CHANNEL_F, sizeof(TRAFFIC_CHANNEL_F) / sizeof(unsigned), dummy_or_normal);
-  d_channel_conf.set_multiframe_type(TIMESLOT6, multiframe_26);
-  d_channel_conf.set_burst_types(TIMESLOT6, TRAFFIC_CHANNEL_F, sizeof(TRAFFIC_CHANNEL_F) / sizeof(unsigned), dummy_or_normal);
-
-  d_channel_conf.set_multiframe_type(TIMESLOT7, multiframe_26);
-  d_channel_conf.set_burst_types(TIMESLOT7, TRAFFIC_CHANNEL_F, sizeof(TRAFFIC_CHANNEL_F) / sizeof(unsigned), dummy_or_normal);
-
-}
-
-
-typedef std::list<float> list_float;
-typedef std::vector<float> vector_float;
-
-typedef boost::circular_buffer<float> circular_buffer_float;
-
-gsm_receiver_cf_sptr
-gsm_make_receiver_cf(gr_feval_dd *tuner, gr_feval_dd *synchronizer, int osr, std::string key)
-{
-  return gsm_receiver_cf_sptr(new gsm_receiver_cf(tuner, synchronizer, osr, key));
-}
-
-static const int MIN_IN = 1; // mininum number of input streams
-static const int MAX_IN = 1; // maximum number of input streams
-static const int MIN_OUT = 0; // minimum number of output streams
-static const int MAX_OUT = 1; // maximum number of output streams
-
-/*
- * The private constructor
- */
-gsm_receiver_cf::gsm_receiver_cf(gr_feval_dd *tuner, gr_feval_dd *synchronizer, int osr, std::string key)
-    : gr_block("gsm_receiver",
-               gr_make_io_signature(MIN_IN, MAX_IN, sizeof(gr_complex)),
-               gr_make_io_signature(MIN_OUT, MAX_OUT, 142 * sizeof(float))),
-    d_OSR(osr),
-    d_chan_imp_length(CHAN_IMP_RESP_LENGTH),
-    d_tuner(tuner),
-    d_counter(0),
-    d_fcch_start_pos(0),
-    d_freq_offset(0),
-    d_state(first_fcch_search),
-    d_burst_nr(osr),
-    d_failed_sch(0),
-    d_tch_decoder1( GSM::gFACCH_TCHFMapping ),
-    d_tch_decoder2( GSM::gFACCH_TCHFMapping ),
-    d_tch_decoder3( GSM::gFACCH_TCHFMapping ),
-    d_tch_decoder4( GSM::gFACCH_TCHFMapping ),
-    d_tch_decoder5( GSM::gFACCH_TCHFMapping ),
-    d_tch_decoder6( GSM::gFACCH_TCHFMapping ),
-    d_tch_decoder7( GSM::gFACCH_TCHFMapping )
-{
-  int i;
-  gmsk_mapper(SYNC_BITS, N_SYNC_BITS, d_sch_training_seq, gr_complex(0.0, -1.0));
-  for (i = 0; i < TRAIN_SEQ_NUM; i++) {
-    gr_complex startpoint;
-    if (i == 6) {                           //this is nasty hack
-      startpoint = gr_complex(-1.0, 0.0);   //if I don't change it here all bits of normal bursts for BTSes with bcc=6 will have reversed values
-    } else {
-      startpoint = gr_complex(1.0, 0.0);    //I've checked this hack for bcc==0,1,2,3,4,6
-    }                                       //I don't know what about bcc==5 and 7 yet
-    //TODO:find source of this situation - this is purely mathematical problem I guess
-
-    gmsk_mapper(train_seq[i], N_TRAIN_BITS, d_norm_training_seq[i], startpoint);
-  }
-  d_gsm_file = fopen( "speech.gsm", "wb" );
-
-  d_hex_to_int['0'] = 0;
-  d_hex_to_int['4'] = 4;
-  d_hex_to_int['8'] =   8;
-  d_hex_to_int['c'] = 0xc;
-  d_hex_to_int['1'] = 1;
-  d_hex_to_int['5'] = 5;
-  d_hex_to_int['9'] =   9;
-  d_hex_to_int['d'] = 0xd;
-  d_hex_to_int['2'] = 2;
-  d_hex_to_int['6'] = 6;
-  d_hex_to_int['a'] = 0xa;
-  d_hex_to_int['e'] = 0xe;
-  d_hex_to_int['3'] = 3;
-  d_hex_to_int['7'] = 7;
-  d_hex_to_int['b'] = 0xb;
-  d_hex_to_int['f'] = 0xf;
-  read_key(key);
-  /* Initialize GSM Stack */
-  GS_new(&d_gs_ctx); //TODO: remove it! it's not a right place for a decoder
-}
-
-/*
- * Virtual destructor.
- */
-gsm_receiver_cf::~gsm_receiver_cf()
-{
-}
-
-void gsm_receiver_cf::forecast(int noutput_items, gr_vector_int &nitems_items_required)
-{
-  nitems_items_required[0] = noutput_items * floor((TS_BITS + 2 * GUARD_PERIOD) * d_OSR);
-}
-
-int
-gsm_receiver_cf::general_work(int noutput_items,
-                              gr_vector_int &nitems_items,
-                              gr_vector_const_void_star &input_items,
-                              gr_vector_void_star &output_items)
-{
-  const gr_complex *input = (const gr_complex *) input_items[0];
-  //float *out = (float *) output_items[0];
-  int produced_out = 0;  //how many output elements were produced - this isn't used yet
-  //probably the gsm receiver will be changed into sink so this variable won't be necessary
-
-  switch (d_state) {
-      //bootstrapping
-    case first_fcch_search:
-      if (find_fcch_burst(input, nitems_items[0])) { //find frequency correction burst in the input buffer
-        set_frequency(d_freq_offset);                //if fcch search is successful set frequency offset
-        //produced_out = 0;
-        d_state = next_fcch_search;
-      } else {
-        //produced_out = 0;
-        d_state = first_fcch_search;
-      }
-      break;
-
-    case next_fcch_search: {                         //this state is used because it takes some time (a bunch of buffered samples)
-        float prev_freq_offset = d_freq_offset;        //before previous set_frequqency cause change
-        if (find_fcch_burst(input, nitems_items[0])) {
-          if (abs(prev_freq_offset - d_freq_offset) > FCCH_MAX_FREQ_OFFSET) {
-            set_frequency(d_freq_offset);              //call set_frequncy only frequency offset change is greater than some value
-          }
-          //produced_out = 0;
-          d_state = sch_search;
-        } else {
-          //produced_out = 0;
-          d_state = next_fcch_search;
-        }
-        break;
-      }
-
-    case sch_search: {
-        vector_complex channel_imp_resp(CHAN_IMP_RESP_LENGTH*d_OSR);
-        int t1, t2, t3;
-        int burst_start = 0;
-        unsigned char output_binary[BURST_SIZE];
-
-        if (reach_sch_burst(nitems_items[0])) {                              //wait for a SCH burst
-          burst_start = get_sch_chan_imp_resp(input, &channel_imp_resp[0]); //get channel impulse response from it
-          detect_burst(input, &channel_imp_resp[0], burst_start, output_binary); //detect bits using MLSE detection
-          if (decode_sch(&output_binary[3], &t1, &t2, &t3, &d_ncc, &d_bcc) == 0) { //decode SCH burst
-            DCOUT("sch burst_start: " << burst_start);
-            DCOUT("bcc: " << d_bcc << " ncc: " << d_ncc << " t1: " << t1 << " t2: " << t2 << " t3: " << t3);
-            d_burst_nr.set(t1, t2, t3, 0);                                  //set counter of bursts value
-
-            //configure the receiver - tell him where to find which burst type
-            d_channel_conf.set_multiframe_type(TIMESLOT0, multiframe_51);  //in the timeslot nr.0 bursts changes according to t3 counter
-            configure_receiver();//TODO: this shouldn't be here - remove it when gsm receiver's interface will be ready
-            d_channel_conf.set_burst_types(TIMESLOT0, FCCH_FRAMES, sizeof(FCCH_FRAMES) / sizeof(unsigned), fcch_burst);  //tell where to find fcch bursts
-            d_channel_conf.set_burst_types(TIMESLOT0, SCH_FRAMES, sizeof(SCH_FRAMES) / sizeof(unsigned), sch_burst);     //sch bursts
-            d_channel_conf.set_burst_types(TIMESLOT0, BCCH_FRAMES, sizeof(BCCH_FRAMES) / sizeof(unsigned), normal_burst);//!and maybe normal bursts of the BCCH logical channel
-            d_burst_nr++;
-
-            consume_each(burst_start + BURST_SIZE * d_OSR);   //consume samples up to next guard period
-            d_state = synchronized;
-          } else {
-            d_state = next_fcch_search;                       //if there is error in the sch burst go back to fcch search phase
-          }
-        } else {
-          d_state = sch_search;
-        }
-        break;
-      }
-      //in this state receiver is synchronized and it processes bursts according to burst type for given burst number
-    case synchronized: {
-        vector_complex channel_imp_resp(CHAN_IMP_RESP_LENGTH*d_OSR);
-        int burst_start;
-        int offset = 0;
-        int to_consume = 0;
-        unsigned char output_binary[BURST_SIZE];
-
-        burst_type b_type = d_channel_conf.get_burst_type(d_burst_nr); //get burst type for given burst number
-
-        switch (b_type) {
-          case fcch_burst: {                                                                    //if it's FCCH  burst
-              const unsigned first_sample = ceil((GUARD_PERIOD + 2 * TAIL_BITS) * d_OSR) + 1;
-              const unsigned last_sample = first_sample + USEFUL_BITS * d_OSR - TAIL_BITS * d_OSR;
-              double freq_offset = compute_freq_offset(input, first_sample, last_sample);       //extract frequency offset from it
-
-              d_freq_offset_vals.push_front(freq_offset);
-
-              if (d_freq_offset_vals.size() >= 10) {
-                double sum = std::accumulate(d_freq_offset_vals.begin(), d_freq_offset_vals.end(), 0);
-                double mean_offset = sum / d_freq_offset_vals.size();                           //compute mean
-                d_freq_offset_vals.clear();
-                if (abs(mean_offset) > FCCH_MAX_FREQ_OFFSET) {
-                  d_freq_offset -= mean_offset;                                                 //and adjust frequency if it have changed beyond
-                  set_frequency(d_freq_offset);                                                 //some limit
-                  DCOUT("mean_offset: " << mean_offset);
-                  DCOUT("Adjusting frequency, new frequency offset: " << d_freq_offset << "\n");
-                }
-              }
-            }
-            break;
-          case sch_burst: {                                                                    //if it's SCH burst
-              int t1, t2, t3, d_ncc, d_bcc;
-              burst_start = get_sch_chan_imp_resp(input, &channel_imp_resp[0]);                //get channel impulse response
-              detect_burst(input, &channel_imp_resp[0], burst_start, output_binary);           //MLSE detection of bits
-              if (decode_sch(&output_binary[3], &t1, &t2, &t3, &d_ncc, &d_bcc) == 0) {         //and decode SCH data
-                // d_burst_nr.set(t1, t2, t3, 0);                                              //but only to check if burst_start value is correct
-                d_failed_sch = 0;
-                DCOUT("bcc: " << d_bcc << " ncc: " << d_ncc << " t1: " << t1 << " t2: " << t2 << " t3: " << t3);
-                offset =  burst_start - floor((GUARD_PERIOD) * d_OSR);                         //compute offset from burst_start - burst should start after a guard period
-                DCOUT(offset);
-                to_consume += offset;                                                          //adjust with offset number of samples to be consumed
-              } else {
-                d_failed_sch++;
-                if (d_failed_sch >= MAX_SCH_ERRORS) {
-//                   d_state = next_fcch_search;        //TODO: this isn't good, the receiver is going wild when it goes back to next_fcch_search from here
-//                   d_freq_offset_vals.clear();
-                  DCOUT("many sch decoding errors");
-                }
-              }
-            }
-            break;
-
-          case normal_burst:                                                                  //if it's normal burst
-            burst_start = get_norm_chan_imp_resp(input, &channel_imp_resp[0], d_bcc); //get channel impulse response for given training sequence number - d_bcc
-            detect_burst(input, &channel_imp_resp[0], burst_start, output_binary);            //MLSE detection of bits
-            process_normal_burst(d_burst_nr, output_binary); //TODO: this shouldn't be here - remove it when gsm receiver's interface will be ready
-            break;
-
-          case dummy_or_normal: {
-              burst_start = get_norm_chan_imp_resp(input, &channel_imp_resp[0], TS_DUMMY);
-              detect_burst(input, &channel_imp_resp[0], burst_start, output_binary);
-
-              std::vector<unsigned char> v(20);
-              std::vector<unsigned char>::iterator it;
-              it = std::set_difference(output_binary + TRAIN_POS, output_binary + TRAIN_POS + 16, &train_seq[TS_DUMMY][5], &train_seq[TS_DUMMY][21], v.begin());
-              int different_bits = (it - v.begin());
-
-              if (different_bits > 2) {
-                burst_start = get_norm_chan_imp_resp(input, &channel_imp_resp[0], d_bcc);
-                detect_burst(input, &channel_imp_resp[0], burst_start, output_binary);
-                if (!output_binary[0] && !output_binary[1] && !output_binary[2]) {
-                  process_normal_burst(d_burst_nr, output_binary); //TODO: this shouldn't be here - remove it when gsm receiver's interface will be ready
-                }
-              }
-            }
-          case rach_burst:
-            //implementation of this channel isn't possible in current gsm_receiver
-            //it would take some realtime processing, counter of samples from USRP to
-            //stay synchronized with this device and possibility to switch frequency from  uplink
-            //to C0 (where sch is) back and forth
-
-            break;
-          case dummy:                                                         //if it's dummy
-            burst_start = get_norm_chan_imp_resp(input, &channel_imp_resp[0], TS_DUMMY); //read dummy
-            detect_burst(input, &channel_imp_resp[0], burst_start, output_binary);   // but as far as I know it's pointless
-            break;
-          case empty:   //if it's empty burst
-            break;      //do nothing
-        }
-
-        d_burst_nr++;   //go to next burst
-
-        to_consume += TS_BITS * d_OSR + d_burst_nr.get_offset();  //consume samples of the burst up to next guard period
-        //and add offset which is introduced by
-        //0.25 fractional part of a guard period
-        //burst_number computes this offset
-        //but choice of this class to do this was random
-        consume_each(to_consume);
-      }
-      break;
-  }
-
-  return produced_out;
-}
-
-bool gsm_receiver_cf::find_fcch_burst(const gr_complex *input, const int nitems)
-{
-  circular_buffer_float phase_diff_buffer(FCCH_HITS_NEEDED * d_OSR); //circular buffer used to scan throug signal to find
-  //best match for FCCH burst
-  float phase_diff = 0;
-  gr_complex conjprod;
-  int start_pos = -1;
-  int hit_count = 0;
-  int miss_count = 0;
-  float min_phase_diff;
-  float max_phase_diff;
-  double best_sum = 0;
-  float lowest_max_min_diff = 99999;
-
-  int to_consume = 0;
-  int sample_number = 0;
-  bool end = false;
-  bool result = false;
-  circular_buffer_float::iterator buffer_iter;
-
-  /**@name Possible states of FCCH search algorithm*/
-  //@{
-  enum states {
-    init,               ///< initialize variables
-    search,             ///< search for positive samples
-    found_something,    ///< search for FCCH and the best position of it
-    fcch_found,         ///< when FCCH was found
-    search_fail         ///< when there is no FCCH in the input vector
-  } fcch_search_state;
-  //@}
-
-  fcch_search_state = init;
-
-  while (!end) {
-    switch (fcch_search_state) {
-
-      case init: //initialize variables
-        hit_count = 0;
-        miss_count = 0;
-        start_pos = -1;
-        lowest_max_min_diff = 99999;
-        phase_diff_buffer.clear();
-        fcch_search_state = search;
-
-        break;
-
-      case search: // search for positive samples
-        sample_number++;
-
-        if (sample_number > nitems - FCCH_HITS_NEEDED * d_OSR) { //if it isn't possible to find FCCH because
-          //there's too few samples left to look into,
-          to_consume = sample_number;                            //don't do anything with those samples which are left
-          //and consume only those which were checked
-          fcch_search_state = search_fail;
-        } else {
-          phase_diff = compute_phase_diff(input[sample_number], input[sample_number-1]);
-
-          if (phase_diff > 0) {                                 //if a positive phase difference was found
-            to_consume = sample_number;
-            fcch_search_state = found_something;                //switch to state in which searches for FCCH
-          } else {
-            fcch_search_state = search;
-          }
-        }
-
-        break;
-
-      case found_something: {// search for FCCH and the best position of it
-          if (phase_diff > 0) {
-            hit_count++;       //positive phase differencies increases hits_count
-          } else {
-            miss_count++;      //negative increases miss_count
-          }
-
-          if ((miss_count >= FCCH_MAX_MISSES * d_OSR) && (hit_count <= FCCH_HITS_NEEDED * d_OSR)) {
-            //if miss_count exceeds limit before hit_count
-            fcch_search_state = init;       //go to init
-            continue;
-          } else if (((miss_count >= FCCH_MAX_MISSES * d_OSR) && (hit_count > FCCH_HITS_NEEDED * d_OSR)) || (hit_count > 2 * FCCH_HITS_NEEDED * d_OSR)) {
-            //if hit_count and miss_count exceeds limit then FCCH was found
-            fcch_search_state = fcch_found;
-            continue;
-          } else if ((miss_count < FCCH_MAX_MISSES * d_OSR) && (hit_count > FCCH_HITS_NEEDED * d_OSR)) {
-            //find difference between minimal and maximal element in the buffer
-            //for FCCH this value should be low
-            //this part is searching for a region where this value is lowest
-            min_phase_diff = * (min_element(phase_diff_buffer.begin(), phase_diff_buffer.end()));
-            max_phase_diff = * (max_element(phase_diff_buffer.begin(), phase_diff_buffer.end()));
-
-            if (lowest_max_min_diff > max_phase_diff - min_phase_diff) {
-              lowest_max_min_diff = max_phase_diff - min_phase_diff;
-              start_pos = sample_number - FCCH_HITS_NEEDED * d_OSR - FCCH_MAX_MISSES * d_OSR; //store start pos
-              best_sum = 0;
-
-              for (buffer_iter = phase_diff_buffer.begin();
-                   buffer_iter != (phase_diff_buffer.end());
-                   buffer_iter++) {
-                best_sum += *buffer_iter - (M_PI / 2) / d_OSR;   //store best value of phase offset sum
-              }
-            }
-          }
-
-          sample_number++;
-
-          if (sample_number >= nitems) {    //if there's no single sample left to check
-            fcch_search_state = search_fail;//FCCH search failed
-            continue;
-          }
-
-          phase_diff = compute_phase_diff(input[sample_number], input[sample_number-1]);
-          phase_diff_buffer.push_back(phase_diff);
-          fcch_search_state = found_something;
-        }
-        break;
-
-      case fcch_found: {
-          DCOUT("fcch found on position: " << d_counter + start_pos);
-          to_consume = start_pos + FCCH_HITS_NEEDED * d_OSR + 1; //consume one FCCH burst
-
-          d_fcch_start_pos = d_counter + start_pos;
-
-          //compute frequency offset
-          double phase_offset = best_sum / FCCH_HITS_NEEDED;
-          double freq_offset = phase_offset * 1625000.0 / (12.0 * M_PI);
-          d_freq_offset -= freq_offset;
-          DCOUT("freq_offset: " << d_freq_offset);
-
-          end = true;
-          result = true;
-          break;
-        }
-
-      case search_fail:
-        end = true;
-        result = false;
-        break;
-    }
-  }
-
-  d_counter += to_consume;
-  consume_each(to_consume);
-
-  return result;
-}
-
-double gsm_receiver_cf::compute_freq_offset(const gr_complex * input, unsigned first_sample, unsigned last_sample)
-{
-  double phase_sum = 0;
-  unsigned ii;
-
-  for (ii = first_sample; ii < last_sample; ii++) {
-    double phase_diff = compute_phase_diff(input[ii], input[ii-1]) - (M_PI / 2) / d_OSR;
-    phase_sum += phase_diff;
-  }
-
-  double phase_offset = phase_sum / (last_sample - first_sample);
-  double freq_offset = phase_offset * 1625000.0 / (12.0 * M_PI);
-  return freq_offset;
-}
-
-void gsm_receiver_cf::set_frequency(double freq_offset)
-{
-  d_tuner->calleval(freq_offset);
-}
-
-inline float gsm_receiver_cf::compute_phase_diff(gr_complex val1, gr_complex val2)
-{
-  gr_complex conjprod = val1 * conj(val2);
-  return gr_fast_atan2f(imag(conjprod), real(conjprod));
-}
-
-bool gsm_receiver_cf::reach_sch_burst(const int nitems)
-{
-  //it just consumes samples to get near to a SCH burst
-  int to_consume = 0;
-  bool result = false;
-  unsigned sample_nr_near_sch_start = d_fcch_start_pos + (FRAME_BITS - SAFETY_MARGIN) * d_OSR;
-
-  //consume samples until d_counter will be equal to sample_nr_near_sch_start
-  if (d_counter < sample_nr_near_sch_start) {
-    if (d_counter + nitems >= sample_nr_near_sch_start) {
-      to_consume = sample_nr_near_sch_start - d_counter;
-    } else {
-      to_consume = nitems;
-    }
-    result = false;
-  } else {
-    to_consume = 0;
-    result = true;
-  }
-
-  d_counter += to_consume;
-  consume_each(to_consume);
-  return result;
-}
-
-int gsm_receiver_cf::get_sch_chan_imp_resp(const gr_complex *input, gr_complex * chan_imp_resp)
-{
-  vector_complex correlation_buffer;
-  vector_float power_buffer;
-  vector_float window_energy_buffer;
-
-  int strongest_window_nr;
-  int burst_start = 0;
-  int chan_imp_resp_center = 0;
-  float max_correlation = 0;
-  float energy = 0;
-
-  for (int ii = SYNC_POS * d_OSR; ii < (SYNC_POS + SYNC_SEARCH_RANGE) *d_OSR; ii++) {
-    gr_complex correlation = correlate_sequence(&d_sch_training_seq[5], N_SYNC_BITS - 10, &input[ii]);
-    correlation_buffer.push_back(correlation);
-    power_buffer.push_back(pow(abs(correlation), 2));
-  }
-
-  //compute window energies
-  vector_float::iterator iter = power_buffer.begin();
-  bool loop_end = false;
-  while (iter != power_buffer.end()) {
-    vector_float::iterator iter_ii = iter;
-    energy = 0;
-
-    for (int ii = 0; ii < (d_chan_imp_length) *d_OSR; ii++, iter_ii++) {
-      if (iter_ii == power_buffer.end()) {
-        loop_end = true;
-        break;
-      }
-      energy += (*iter_ii);
-    }
-    if (loop_end) {
-      break;
-    }
-    iter++;
-    window_energy_buffer.push_back(energy);
-  }
-
-  strongest_window_nr = max_element(window_energy_buffer.begin(), window_energy_buffer.end()) - window_energy_buffer.begin();
-//   d_channel_imp_resp.clear();
-
-  max_correlation = 0;
-  for (int ii = 0; ii < (d_chan_imp_length) *d_OSR; ii++) {
-    gr_complex correlation = correlation_buffer[strongest_window_nr + ii];
-    if (abs(correlation) > max_correlation) {
-      chan_imp_resp_center = ii;
-      max_correlation = abs(correlation);
-    }
-//     d_channel_imp_resp.push_back(correlation);
-    chan_imp_resp[ii] = correlation;
-  }
-
-  burst_start = strongest_window_nr + chan_imp_resp_center - 48 * d_OSR - 2 * d_OSR + 2 + SYNC_POS * d_OSR;
-  return burst_start;
-}
-
-void gsm_receiver_cf::detect_burst(const gr_complex * input, gr_complex * chan_imp_resp, int burst_start, unsigned char * output_binary)
-{
-  float output[BURST_SIZE];
-  gr_complex rhh_temp[CHAN_IMP_RESP_LENGTH*d_OSR];
-  gr_complex rhh[CHAN_IMP_RESP_LENGTH];
-  gr_complex filtered_burst[BURST_SIZE];
-  int start_state = 3;
-  unsigned int stop_states[2] = {4, 12};
-
-  autocorrelation(chan_imp_resp, rhh_temp, d_chan_imp_length*d_OSR);
-  for (int ii = 0; ii < (d_chan_imp_length); ii++) {
-    rhh[ii] = conj(rhh_temp[ii*d_OSR]);
-  }
-
-  mafi(&input[burst_start], BURST_SIZE, chan_imp_resp, d_chan_imp_length*d_OSR, filtered_burst);
-
-  viterbi_detector(filtered_burst, BURST_SIZE, rhh, start_state, stop_states, 2, output);
-
-  for (int i = 0; i < BURST_SIZE ; i++) {
-    output_binary[i] = (output[i] > 0);
-  }
-}
-
-//TODO consider placing this funtion in a separate class for signal processing
-void gsm_receiver_cf::gmsk_mapper(const unsigned char * input, int nitems, gr_complex * gmsk_output, gr_complex start_point)
-{
-  gr_complex j = gr_complex(0.0, 1.0);
-
-  int current_symbol;
-  int encoded_symbol;
-  int previous_symbol = 2 * input[0] - 1;
-  gmsk_output[0] = start_point;
-
-  for (int i = 1; i < nitems; i++) {
-    //change bits representation to NRZ
-    current_symbol = 2 * input[i] - 1;
-    //differentially encode
-    encoded_symbol = current_symbol * previous_symbol;
-    //and do gmsk mapping
-    gmsk_output[i] = j * gr_complex(encoded_symbol, 0.0) * gmsk_output[i-1];
-    previous_symbol = current_symbol;
-  }
-}
-
-//TODO consider use of some generalized function for correlation and placing it in a separate class  for signal processing
-gr_complex gsm_receiver_cf::correlate_sequence(const gr_complex * sequence, int length, const gr_complex * input)
-{
-  gr_complex result(0.0, 0.0);
-  int sample_number = 0;
-
-  for (int ii = 0; ii < length; ii++) {
-    sample_number = (ii * d_OSR) ;
-    result += sequence[ii] * conj(input[sample_number]);
-  }
-
-  result = result / gr_complex(length, 0);
-  return result;
-}
-
-//computes autocorrelation for positive arguments
-//TODO consider placing this funtion in a separate class for signal processing
-inline void gsm_receiver_cf::autocorrelation(const gr_complex * input, gr_complex * out, int nitems)
-{
-  int i, k;
-  for (k = nitems - 1; k >= 0; k--) {
-    out[k] = gr_complex(0, 0);
-    for (i = k; i < nitems; i++) {
-      out[k] += input[i] * conj(input[i-k]);
-    }
-  }
-}
-
-//TODO consider use of some generalized function for filtering and placing it in a separate class  for signal processing
-inline void gsm_receiver_cf::mafi(const gr_complex * input, int nitems, gr_complex * filter, int filter_length, gr_complex * output)
-{
-  int ii = 0, n, a;
-
-  for (n = 0; n < nitems; n++) {
-    a = n * d_OSR;
-    output[n] = 0;
-    ii = 0;
-
-    while (ii < filter_length) {
-      if ((a + ii) >= nitems*d_OSR)
-        break;
-      output[n] += input[a+ii] * filter[ii];
-      ii++;
-    }
-  }
-}
-
-//TODO: get_norm_chan_imp_resp is similar to get_sch_chan_imp_resp - consider joining this two functions
-//TODO: this is place where most errors are introduced and can be corrected by improvements to this fuction
-//especially computations of strongest_window_nr
-int gsm_receiver_cf::get_norm_chan_imp_resp(const gr_complex *input, gr_complex * chan_imp_resp, int bcc)
-{
-  vector_complex correlation_buffer;
-  vector_float power_buffer;
-  vector_float window_energy_buffer;
-
-  int strongest_window_nr;
-  int burst_start = 0;
-  int chan_imp_resp_center = 0;
-  float max_correlation = 0;
-  float energy = 0;
-
-  int search_center = (int)((TRAIN_POS + GUARD_PERIOD) * d_OSR);
-  int search_start_pos = search_center + 1;
-//   int search_start_pos = search_center -  d_chan_imp_length * d_OSR;
-  int search_stop_pos = search_center + d_chan_imp_length * d_OSR + 2 * d_OSR;
-
-  for (int ii = search_start_pos; ii < search_stop_pos; ii++) {
-    gr_complex correlation = correlate_sequence(&d_norm_training_seq[bcc][TRAIN_BEGINNING], N_TRAIN_BITS - 10, &input[ii]);
-
-    correlation_buffer.push_back(correlation);
-    power_buffer.push_back(pow(abs(correlation), 2));
-  }
-
-  //compute window energies
-  vector_float::iterator iter = power_buffer.begin();
-  bool loop_end = false;
-  while (iter != power_buffer.end()) {
-    vector_float::iterator iter_ii = iter;
-    energy = 0;
-
-    for (int ii = 0; ii < (d_chan_imp_length - 2)*d_OSR; ii++, iter_ii++) {
-//    for (int ii = 0; ii < (d_chan_imp_length)*d_OSR; ii++, iter_ii++) {
-      if (iter_ii == power_buffer.end()) {
-        loop_end = true;
-        break;
-      }
-      energy += (*iter_ii);
-    }
-    if (loop_end) {
-      break;
-    }
-    iter++;
-
-    window_energy_buffer.push_back(energy);
-  }
-  //!why doesn't this work
-  strongest_window_nr = max_element(window_energy_buffer.begin(), window_energy_buffer.end()) - window_energy_buffer.begin();
-  strongest_window_nr = 3; //! so I have to override it here
-
-  max_correlation = 0;
-  for (int ii = 0; ii < (d_chan_imp_length)*d_OSR; ii++) {
-    gr_complex correlation = correlation_buffer[strongest_window_nr + ii];
-    if (abs(correlation) > max_correlation) {
-      chan_imp_resp_center = ii;
-      max_correlation = abs(correlation);
-    }
-//     d_channel_imp_resp.push_back(correlation);
-    chan_imp_resp[ii] = correlation;
-  }
-  // We want to use the first sample of the impulseresponse, and the
-  // corresponding samples of the received signal.
-  // the variable sync_w should contain the beginning of the used part of
-  // training sequence, which is 3+57+1+6=67 bits into the burst. That is
-  // we have that sync_t16 equals first sample in bit number 67.
-
-  burst_start = search_start_pos + chan_imp_resp_center + strongest_window_nr - TRAIN_POS * d_OSR;
-
-  // GMSK modulator introduces ISI - each bit is expanded for 3*Tb
-  // and it's maximum value is in the last bit period, so burst starts
-  // 2*Tb earlier
-  burst_start -= 2 * d_OSR;
-  burst_start += 2;
-  //std::cout << " burst_start: " << burst_start << " center: " << ((float)(search_start_pos + strongest_window_nr + chan_imp_resp_center)) / d_OSR << " stronegest window nr: " <<  strongest_window_nr << "\n";
-
-  return burst_start;
-}
-