fix(dmr): recover handheld voice sync

DMRDecoder.pas

@@ -139,6 +139,8 @@ type
     FInverted: Boolean;
     FSyncCount: QWord;
     FLastSyncTick: QWord;
+    FLastSyncSample: QWord;
+    FMobileActiveBurst: Boolean;
 
     function PopSamples(var Buf: array of Single): Integer;
     procedure ProcessSample(S: Single);
@@ -170,6 +172,8 @@ implementation
 const
   DMR_SYNC_MASK = LongWord($00FFFFFF);
   DMR_SYNC_HOLD_MS = 500;
+  DMR_SYNC_MAX_ERRORS = 2;
+  DMR_SUPERFRAME_SAMPLES = DMR_INPUT_RATE * 360 div 1000;
 
   // One bit per DSD-FME sync character: '1'=0, '3'=1. These are the eight
   // ETSI DMR 48-bit sync patterns after collapsing each dibit to its sign.
@@ -332,6 +336,8 @@ begin
       FInverted := False;
       FSyncCount := 0;
       FLastSyncTick := 0;
+      FLastSyncSample := 0;
+      FMobileActiveBurst := True;
     finally
       FStatusLock.Leave;
     end;
@@ -426,6 +432,8 @@ var
   Pat: LongWord;
   Dibit: Byte;
   V: Double;
+  DeltaSamples, CycleOffset: QWord;
+  CandidateAllowed: Boolean;
 begin
   V := Symbol;
   if FInputInverted then V := -V;
@@ -466,11 +474,29 @@ begin
         FBestSyncPhase := Phase;
         FBestCandidateKind := SYNC_KIND[i];
       end;
-    end;
-    if FSyncShift[Phase] = Pat then
-    begin
-      NoteSync(Phase, SYNC_KIND[i], FInputInverted);
-      Exit;
+      // Real on-air sync commonly carries one or two sign errors. DSD-FME
+      // likewise uses a bounded sync tolerance; requiring an exact 24-symbol
+      // match lost almost every superframe in recorded handheld-radio IQ.
+      DeltaSamples := FSampleNo - FLastSyncSample;
+      CandidateAllowed := (FLastSyncSample = 0) or
+        (DeltaSamples > DMR_INPUT_RATE * 2) or
+        (SYNC_KIND[i] = FSyncKind);
+      // MS voice/data sync repeats every 360 ms. Cadence gating rejects
+      // chance <=2-bit matches inside AMBE payload while still accepting a
+      // superframe after one or more missed sync words.
+      if CandidateAllowed and (FLastSyncSample <> 0) and
+         (FSyncKind in [dskMSData, dskMSVoice]) and
+         (SYNC_KIND[i] = FSyncKind) and (DeltaSamples > 20) then
+      begin
+        CycleOffset := DeltaSamples mod DMR_SUPERFRAME_SAMPLES;
+        CandidateAllowed := (CycleOffset <= 20) or
+          (CycleOffset >= DMR_SUPERFRAME_SAMPLES - 20);
+      end;
+      if (Distance <= DMR_SYNC_MAX_ERRORS) and CandidateAllowed then
+      begin
+        NoteSync(Phase, SYNC_KIND[i], FInputInverted);
+        Exit;
+      end;
     end;
   end;
 end;
@@ -542,6 +568,8 @@ begin
     end;
   end;
   DecodeVoiceBurst;
+  if FSyncKind in [dskMSData, dskMSVoice] then
+    FMobileActiveBurst := not FMobileActiveBurst;
   Inc(FBurstCount);
   FCurrentBurstPos := 0;
 end;
@@ -558,6 +586,10 @@ begin
      (GetTickCount64 - FLastSyncTick > DMR_SYNC_HOLD_MS) then Exit;
   if not (FSyncKind in [dskBSVoice, dskMSVoice, dskDirectTS1Voice,
           dskDirectTS2Voice]) then Exit;
+  // Mobile simplex occupies one 30 ms half-slot and leaves the alternating
+  // half-slot idle. A 144-dibit continuous assembler sees both; only every
+  // other record contains the three AMBE frames.
+  if (FSyncKind = dskMSVoice) and not FMobileActiveBurst then Exit;
 
   if FSyncKind in [dskBSVoice] then
   begin
@@ -566,6 +598,7 @@ begin
   end
   else if FSyncKind = dskDirectTS2Voice then Slot := 1
   else Slot := 0;
+  if FSyncKind = dskMSVoice then FSelectedSlot := 0;
   NowTick := GetTickCount64;
   if (FSelectedSlot < 0) or
      ((Slot <> FSelectedSlot) and (FLastSelectedVoiceTick <> 0) and
@@ -608,7 +641,8 @@ begin
     // Adjacent timing hypotheses recognize the same physical burst within one
     // sample period. Keep the phase with the largest 24-symbol eye opening,
     // not merely the first phase that happened to match the sign pattern.
-    if (FLastSyncTick <> 0) and (NowTick - FLastSyncTick < 5) then
+    if (FLastSyncSample <> 0) and
+       (FSampleNo - FLastSyncSample <= DMR_SAMPLES_PER_SYM * 2) then
     begin
       if FMagSum[Phase] > FBestSyncQuality then
       begin
@@ -623,7 +657,9 @@ begin
     FInverted := Inverted;
     Inc(FSyncCount);
     FLastSyncTick := NowTick;
+    FLastSyncSample := FSampleNo;
     FBestSyncQuality := FMagSum[Phase];
+    if Kind in [dskMSData, dskMSVoice] then FMobileActiveBurst := True;
     StartBurstTracking(Phase);
   finally
     FStatusLock.Leave;