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   1 /* -*- c++ -*- */
   2 /*
   3  * Copyright 2006,2007,2008 Free Software Foundation, Inc.
   4  *
   5  * This file is part of GNU Radio
   6  *
   7  * GNU Radio 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  * GNU Radio 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 GNU Radio; 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 #ifdef HAVE_CONFIG_H
  24 #include "config.h"
  25 #endif
  26
  27 #include <gr_ofdm_frame_acquisition.h>
  28 #include <gr_io_signature.h>
  29 #include <gr_expj.h>
  30 #include <gr_math.h>
  31 #include <cstdio>
  32
  33 #define VERBOSE 0
  34 #define M_TWOPI (2*M_PI)
  35 #define MAX_NUM_SYMBOLS 1000
  36
  37 gr_ofdm_frame_acquisition_sptr
  38 gr_make_ofdm_frame_acquisition (unsigned int occupied_carriers, unsigned int fft_length,
  39                                 unsigned int cplen,
  40                                 const std::vector<gr_complex> &known_symbol,
  41                                 unsigned int max_fft_shift_len)
  42 {
  43   return gr_ofdm_frame_acquisition_sptr (new gr_ofdm_frame_acquisition (occupied_carriers, fft_length, cplen,
  44                                                                         known_symbol, max_fft_shift_len));
  45 }
  46
  47 gr_ofdm_frame_acquisition::gr_ofdm_frame_acquisition (unsigned occupied_carriers, unsigned int fft_length,
  48                                                       unsigned int cplen,
  49                                                       const std::vector<gr_complex> &known_symbol,
  50                                                       unsigned int max_fft_shift_len)
  51   : gr_block ("ofdm_frame_acquisition",
  52               gr_make_io_signature2 (2, 2, sizeof(gr_complex)*fft_length, sizeof(char)*fft_length),
  53               gr_make_io_signature2 (2, 2, sizeof(gr_complex)*occupied_carriers, sizeof(char))),
  54     d_occupied_carriers(occupied_carriers),
  55     d_fft_length(fft_length),
  56     d_cplen(cplen),
  57     d_freq_shift_len(max_fft_shift_len),
  58     d_known_symbol(known_symbol),
  59     d_coarse_freq(0),
  60     d_phase_count(0)
  61 {
  62   d_symbol_phase_diff.resize(d_fft_length);
  63   d_known_phase_diff.resize(d_occupied_carriers);
  64   d_hestimate.resize(d_occupied_carriers);
  65
  66   unsigned int i = 0, j = 0;
  67
  68   std::fill(d_known_phase_diff.begin(), d_known_phase_diff.end(), 0);
  69   for(i = 0; i < d_known_symbol.size()-2; i+=2) {
  70     d_known_phase_diff[i] = norm(d_known_symbol[i] - d_known_symbol[i+2]);
  71   }
  72
  73   d_phase_lut = new gr_complex[(2*d_freq_shift_len+1) * MAX_NUM_SYMBOLS];
  74   for(i = 0; i <= 2*d_freq_shift_len; i++) {
  75     for(j = 0; j < MAX_NUM_SYMBOLS; j++) {
  76       d_phase_lut[j + i*MAX_NUM_SYMBOLS] =  gr_expj(-M_TWOPI*d_cplen/d_fft_length*(i-d_freq_shift_len)*j);
  77     }
  78   }
  79 }
  80
  81 gr_ofdm_frame_acquisition::~gr_ofdm_frame_acquisition(void)
  82 {
  83   delete [] d_phase_lut;
  84 }
  85
  86 void
  87 gr_ofdm_frame_acquisition::forecast (int noutput_items, gr_vector_int &ninput_items_required)
  88 {
  89   unsigned ninputs = ninput_items_required.size ();
  90   for (unsigned i = 0; i < ninputs; i++)
  91     ninput_items_required[i] = 1;
  92 }
  93
  94 gr_complex
  95 gr_ofdm_frame_acquisition::coarse_freq_comp(int freq_delta, int symbol_count)
  96 {
  97   //  return gr_complex(cos(-M_TWOPI*freq_delta*d_cplen/d_fft_length*symbol_count),
  98   //        sin(-M_TWOPI*freq_delta*d_cplen/d_fft_length*symbol_count));
  99
 100   return gr_expj(-M_TWOPI*freq_delta*d_cplen/d_fft_length*symbol_count);
 101
 102   //return d_phase_lut[MAX_NUM_SYMBOLS * (d_freq_shift_len + freq_delta) + symbol_count];
 103 }
 104
 105 void
 106 gr_ofdm_frame_acquisition::correlate(const gr_complex *symbol, int zeros_on_left)
 107 {
 108   unsigned int i,j;
 109
 110   std::fill(d_symbol_phase_diff.begin(), d_symbol_phase_diff.end(), 0);
 111   for(i = 0; i < d_fft_length-2; i++) {
 112     d_symbol_phase_diff[i] = norm(symbol[i] - symbol[i+2]);
 113   }
 114
 115   // sweep through all possible/allowed frequency offsets and select the best
 116   int index = 0;
 117   float max = 0, sum=0;
 118   for(i =  zeros_on_left - d_freq_shift_len; i < zeros_on_left + d_freq_shift_len; i++) {
 119     sum = 0;
 120     for(j = 0; j < d_occupied_carriers; j++) {
 121       sum += (d_known_phase_diff[j] * d_symbol_phase_diff[i+j]);
 122     }
 123     if(sum > max) {
 124       max = sum;
 125       index = i;
 126     }
 127   }
 128
 129   // set the coarse frequency offset relative to the edge of the occupied tones
 130   d_coarse_freq = index - zeros_on_left;
 131 }
 132
 133 void
 134 gr_ofdm_frame_acquisition::calculate_equalizer(const gr_complex *symbol, int zeros_on_left)
 135 {
 136   unsigned int i=0;
 137
 138   // Set first tap of equalizer
 139   d_hestimate[0] = d_known_symbol[0] /
 140     (coarse_freq_comp(d_coarse_freq,1)*symbol[zeros_on_left+d_coarse_freq]);
 141
 142   // set every even tap based on known symbol
 143   // linearly interpolate between set carriers to set zero-filled carriers
 144   // FIXME: is this the best way to set this?
 145   for(i = 2; i < d_occupied_carriers; i+=2) {
 146     d_hestimate[i] = d_known_symbol[i] /
 147       (coarse_freq_comp(d_coarse_freq,1)*(symbol[i+zeros_on_left+d_coarse_freq]));
 148     d_hestimate[i-1] = (d_hestimate[i] + d_hestimate[i-2]) / gr_complex(2.0, 0.0);
 149   }
 150
 151   // with even number of carriers; last equalizer tap is wrong
 152   if(!(d_occupied_carriers & 1)) {
 153     d_hestimate[d_occupied_carriers-1] = d_hestimate[d_occupied_carriers-2];
 154   }
 155
 156   if(VERBOSE) {
 157     fprintf(stderr, "Equalizer setting:\n");
 158     for(i = 0; i < d_occupied_carriers; i++) {
 159       gr_complex sym = coarse_freq_comp(d_coarse_freq,1)*symbol[i+zeros_on_left+d_coarse_freq];
 160       gr_complex output = sym * d_hestimate[i];
 161       fprintf(stderr, "sym: %+.4f + j%+.4f  ks: %+.4f + j%+.4f  eq: %+.4f + j%+.4f  ==>  %+.4f + j%+.4f\n",
 162               sym .real(), sym.imag(),
 163               d_known_symbol[i].real(), d_known_symbol[i].imag(),
 164               d_hestimate[i].real(), d_hestimate[i].imag(),
 165               output.real(), output.imag());
 166     }
 167     fprintf(stderr, "\n");
 168   }
 169 }
 170
 171 int
 172 gr_ofdm_frame_acquisition::general_work(int noutput_items,
 173                                         gr_vector_int &ninput_items,
 174                                         gr_vector_const_void_star &input_items,
 175                                         gr_vector_void_star &output_items)
 176 {
 177   const gr_complex *symbol = (const gr_complex *)input_items[0];
 178   const char *signal_in = (const char *)input_items[1];
 179
 180   gr_complex *out = (gr_complex *) output_items[0];
 181   char *signal_out = (char *) output_items[1];
 182
 183   int unoccupied_carriers = d_fft_length - d_occupied_carriers;
 184   int zeros_on_left = (int)ceil(unoccupied_carriers/2.0);
 185
 186   if(signal_in[0]) {
 187     d_phase_count = 1;
 188     correlate(symbol, zeros_on_left);
 189     calculate_equalizer(symbol, zeros_on_left);
 190     signal_out[0] = 1;
 191   }
 192   else {
 193     signal_out[0] = 0;
 194   }
 195
 196   for(unsigned int i = 0; i < d_occupied_carriers; i++) {
 197     out[i] = d_hestimate[i]*coarse_freq_comp(d_coarse_freq,d_phase_count)
 198       *symbol[i+zeros_on_left+d_coarse_freq];
 199   }
 200
 201   d_phase_count++;
 202   if(d_phase_count == MAX_NUM_SYMBOLS) {
 203     d_phase_count = 1;
 204   }
 205
 206   consume_each(1);
 207   return 1;
 208 }