[Commit-gnuradio] r7845 - gnuradio/branches/developers/trondeau/ofdmtiming/gnuradio-core/src/lib/general

[trondeau]

Author: trondeau
Date: 2008-02-26 13:08:16 -0700 (Tue, 26 Feb 2008)
New Revision: 7845

Modified:
   
gnuradio/branches/developers/trondeau/ofdmtiming/gnuradio-core/src/lib/general/gr_ofdm_frame_acquisition.cc
   
gnuradio/branches/developers/trondeau/ofdmtiming/gnuradio-core/src/lib/general/gr_ofdm_frame_acquisition.h
Log:
switching correlation decision since we know the preamble is here we just need 
to find the peak and not test if it meets some criteria.

Modified: 
gnuradio/branches/developers/trondeau/ofdmtiming/gnuradio-core/src/lib/general/gr_ofdm_frame_acquisition.cc
===================================================================
--- 
gnuradio/branches/developers/trondeau/ofdmtiming/gnuradio-core/src/lib/general/gr_ofdm_frame_acquisition.cc
 2008-02-26 20:05:35 UTC (rev 7844)
+++ 
gnuradio/branches/developers/trondeau/ofdmtiming/gnuradio-core/src/lib/general/gr_ofdm_frame_acquisition.cc
 2008-02-26 20:08:16 UTC (rev 7845)
@@ -101,63 +101,34 @@
   //return d_phase_lut[MAX_NUM_SYMBOLS * (d_freq_shift_len + freq_delta) + 
symbol_count];
 }
 
-bool
+void
 gr_ofdm_frame_acquisition::correlate(const gr_complex *symbol, int 
zeros_on_left)
 {
-  unsigned int i = 0;
-  int search_delta = 0;
-  bool found = false;
+  unsigned int i,j;
   
-  gr_complex h_sqrd = gr_complex(0.0,0.0);
-  float power = 0.0F;
-
   std::fill(d_symbol_phase_diff.begin(), d_symbol_phase_diff.end(), 0);
   for(i = 0; i < d_fft_length-2; i++) {
     d_symbol_phase_diff[i] = fabs(gr_fast_atan2f(symbol[i]) - 
gr_fast_atan2f(symbol[i+2]));
   }
 
-  
-  while(!found && ((unsigned)abs(search_delta) <= d_freq_shift_len)) {
-    h_sqrd = gr_complex(0.0,0.0);
-    power = 0.0F;
-    
-    //FIXME: power calculation doesn't really make sense 
-    for(i = 0; i < d_occupied_carriers; i++) {
-      h_sqrd += (d_known_phase_diff[i] * 
d_symbol_phase_diff[i+zeros_on_left+search_delta]);
-      power += d_known_phase_diff[i]*d_known_phase_diff[i];
+  // sweep through all possible/allowed frequency offsets and select the best
+  int index = 0;
+  float max = 0, sum=0;
+  for(i =  zeros_on_left - d_freq_shift_len; i < zeros_on_left + 
d_freq_shift_len; i++) {
+    sum = 0;
+    for(j = 0; j < d_occupied_carriers; j++) {
+      sum += (d_known_phase_diff[j] * d_symbol_phase_diff[i+j]);
     }
-    
-    if(VERBOSE) {
-      printf("bin %d\th_sqrd = ( %f, %f )\t power = %f\t real(h)/p = %f\t 
angle = %f\n",
-            search_delta, h_sqrd.real(), h_sqrd.imag(), power, 
h_sqrd.real()/power, arg(h_sqrd));
+    if(fabs(sum) > max) {
+      max = sum;
+      index = i;
     }
-
-    //FIXME: these threshold values are arbitrary
-    if((h_sqrd.real() > 0.80*power) && (h_sqrd.real() < 1.2*power)) {
-      found = true;
-      d_coarse_freq = search_delta;
-      d_phase_count = 1;
-     
-      //printf("bin %d\th_sqrd = ( %f, %f )\t power = %f\t real(h)/p = %f\t 
angle = %f\n",
-      //     search_delta, h_sqrd.real(), h_sqrd.imag(), power, 
h_sqrd.real()/power, arg(h_sqrd));
-
-      if(VERBOSE) {
-       printf("CORR: Found, bin %d\tdB\tcorr power fraction %f\n",
-              search_delta, h_sqrd.real()/power);
-      }
-      break;
-    }
-    else {
-      if(search_delta <= 0)
-       search_delta = (-search_delta) + 2;
-      else
-       search_delta = -search_delta;
-    }
   }
-  return found;
+  
+  // set the coarse frequency offset relative to the edge of the occupied tones
+  d_coarse_freq = index - zeros_on_left;
 }
 
-
 void
 gr_ofdm_frame_acquisition::calculate_equalizer(const gr_complex *symbol, int 
zeros_on_left)
 {

Modified: 
gnuradio/branches/developers/trondeau/ofdmtiming/gnuradio-core/src/lib/general/gr_ofdm_frame_acquisition.h
===================================================================
--- 
gnuradio/branches/developers/trondeau/ofdmtiming/gnuradio-core/src/lib/general/gr_ofdm_frame_acquisition.h
  2008-02-26 20:05:35 UTC (rev 7844)
+++ 
gnuradio/branches/developers/trondeau/ofdmtiming/gnuradio-core/src/lib/general/gr_ofdm_frame_acquisition.h
  2008-02-26 20:08:16 UTC (rev 7845)
@@ -81,7 +81,7 @@
   
  private:
   unsigned char slicer(gr_complex x);
-  bool correlate(const gr_complex *symbol, int zeros_on_left);
+  void correlate(const gr_complex *symbol, int zeros_on_left);
   void calculate_equalizer(const gr_complex *symbol, int zeros_on_left);
   gr_complex coarse_freq_comp(int freq_delta, int count);