improved sync for hanging on in fades and small big in logging data in fdmdv_demod

git-svn-id: https://svn.code.sf.net/p/freetel/code@1165 01035d8c-6547-0410-b346-abe4f91aad63

diff --git a/codec2-dev/src/fdmdv.c b/codec2-dev/src/fdmdv.c
index d80a034eb96f35f9b97e4d10e400afa7a5e7fef9..9453b87d835afd2e00ad8a30ac737540c8ab470c 100644 (file)
--- a/codec2-dev/src/fdmdv.c
+++ b/codec2-dev/src/fdmdv.c
@@ -1123,11 +1123,21 @@ void CODEC2_WIN32SUPPORT fdmdv_put_test_bits(struct FDMDV *f, int *sync,
   tracking algorithm.  If we lose sync we switch back to coarse mode
   for fast re-acquisition of large frequency offsets.
 
+  The sync state is also useful for higher layers to determine when
+  there is valid FDMDV data for decoding.  We want to reliably and
+  quickly get into sync, stay in sync even on fading channels, and
+  fall out of sync quickly if tx stops or it's a false sync.
+
+  In multipath fading channels the BPSK sync carrier may be pushed
+  down in the noise, despite other carriers being at full strength.
+  We want to avoid loss of sync in these cases.
+
 \*---------------------------------------------------------------------------*/
 
 int freq_state(int sync_bit, int *state)
 {
     int next_state, coarse_fine;
+    int bad_sync = 0;
 
     /* acquire state, look for 6 symbol 010101 sequence from sync bit */
 
@@ -1162,27 +1172,40 @@ int freq_state(int sync_bit, int *state)
            next_state = 0;
        break;
     case 5:
-       if (sync_bit == 1)
+       if (sync_bit == 1) {
            next_state = 6;
+            bad_sync = 0;
+        }
        else 
            next_state = 0;
        break;
        
        /* states 6 and above are track mode, make sure we keep
-          getting 0101 sync bit sequence */
+          getting 0101 sync bit sequence. bad_sync allows us to track
+          through a few bad symbols when BPSK pilot is temporarilly
+          faded out, avoiding a costly re-sync when valid data still
+          exists on other carriers */
 
     case 6:
+        next_state = 7;
        if (sync_bit == 0)
-           next_state = 7;
-       else 
-           next_state = 0;
+            bad_sync = 0;
+       else {
+            bad_sync++;
+            if (bad_sync > 2)
+                next_state = 0;
+        }
 
        break;
     case 7:
+        next_state = 6;
        if (sync_bit == 1)
-           next_state = 6;
-       else 
-           next_state = 0;
+           bad_sync = 0;
+        else {
+            bad_sync++;
+            if (bad_sync > 2)
+                next_state = 0;
+        }
        break;
     }
 

diff --git a/codec2-dev/src/fdmdv_demod.c b/codec2-dev/src/fdmdv_demod.c
index a1f1dd39c3747cb6821e78241cda47c6f1b25c52..391843f17a84f8c54bb12acf973ae84d272ad51a 100644 (file)
--- a/codec2-dev/src/fdmdv_demod.c
+++ b/codec2-dev/src/fdmdv_demod.c
@@ -66,7 +66,7 @@ int main(int argc, char *argv[])
     int           f;
     FILE         *foct = NULL;
     struct FDMDV_STATS stats;
-    float        *rx_fdm_log;
+    COMP         *rx_fdm_log;
     int           rx_fdm_log_col_index;
     COMP          rx_symbols_log[FDMDV_NSYM][MAX_FRAMES];
     int           coarse_fine_log[MAX_FRAMES];
@@ -100,7 +100,7 @@ int main(int argc, char *argv[])
 
     /* malloc some of the bigger variables to prevent out of stack problems */
 
-    rx_fdm_log = (float*)malloc(sizeof(float)*FDMDV_MAX_SAMPLES_PER_FRAME*MAX_FRAMES);
+    rx_fdm_log = (COMP*)malloc(sizeof(COMP)*FDMDV_MAX_SAMPLES_PER_FRAME*MAX_FRAMES);
     assert(rx_fdm_log != NULL);
     rx_spec_log = (float*)malloc(sizeof(float)*FDMDV_NSPEC*MAX_FRAMES);
     assert(rx_spec_log != NULL);
@@ -128,7 +128,7 @@ int main(int argc, char *argv[])
 
            /* log modem states for later dumping to Octave log file */
 
-           memcpy(&rx_fdm_log[rx_fdm_log_col_index], rx_fdm, sizeof(float)*nin_prev);
+           memcpy(&rx_fdm_log[rx_fdm_log_col_index], rx_fdm, sizeof(COMP)*nin_prev);
            rx_fdm_log_col_index += nin_prev;
 
            for(c=0; c<FDMDV_NSYM; c++)
@@ -207,7 +207,7 @@ int main(int argc, char *argv[])
                        argv[3], strerror(errno));
                exit(1);
            }
-           octave_save_float(foct, "rx_fdm_log_c", rx_fdm_log, 1, rx_fdm_log_col_index, FDMDV_MAX_SAMPLES_PER_FRAME);  
+           octave_save_complex(foct, "rx_fdm_log_c", rx_fdm_log, 1, rx_fdm_log_col_index, FDMDV_MAX_SAMPLES_PER_FRAME);  
            octave_save_complex(foct, "rx_symbols_log_c", (COMP*)rx_symbols_log, FDMDV_NSYM, f, MAX_FRAMES);  
            octave_save_float(foct, "foff_log_c", foff_log, 1, f, MAX_FRAMES);  
            octave_save_float(foct, "rx_timing_log_c", rx_timing_log, 1, f, MAX_FRAMES);