From 9e2f8c7743ac05cdb09fcfc26633ca8acda64e34 Mon Sep 17 00:00:00 2001
From: Vladimir <i@vladimir.cc>
Date: Tue, 14 Jul 2026 19:56:36 +0300
Subject: [PATCH] fix(dmr): choose timing phase by sync variance

---
 DMRDecoder.pas | 56 +++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 46 insertions(+), 10 deletions(-)

diff --git a/DMRDecoder.pas b/DMRDecoder.pas
index 7899426..3d8dc19 100644
--- a/DMRDecoder.pas
+++ b/DMRDecoder.pas
@@ -158,7 +158,7 @@ type
     procedure LoseSync;
     function Digitize(Phase: Integer; Symbol: Double): Byte;
     function SliceSymbol(Symbol, OuterLevel: Double): Byte;
-    function SyncEyeOpening(Phase: Integer): Double;
+    function SyncPhaseQuality(Phase: Integer): Double;
     procedure CalibrateSyncLevels(Phase: Integer);
     procedure StartBurstTracking(Phase: Integer);
     procedure CompleteBurst;
@@ -627,13 +627,49 @@ begin
   end;
 end;
 
-function TDMRDecoder.SyncEyeOpening(Phase: Integer): Double;
+function TDMRDecoder.SyncPhaseQuality(Phase: Integer): Double;
 var
-  i: Integer;
+  i, P, PositiveCount, NegativeCount: Integer;
+  V, PositiveMean, NegativeMean, ErrorSum, Scale: Double;
 begin
-  Result := 1.0e300;
+  PositiveMean := 0;
+  NegativeMean := 0;
+  PositiveCount := 0;
+  NegativeCount := 0;
+  P := (FHistoryPos[Phase] + DMR_SYNC_END_DIBIT + 1 - 24) mod
+       (DMR_SYNC_END_DIBIT + 1);
   for i := 0 to 23 do
-    Result := Min(Result, FMagHistory[Phase, i]);
+  begin
+    V := FSymbolHistory[Phase, P];
+    if V >= 0 then
+    begin
+      PositiveMean := PositiveMean + V;
+      Inc(PositiveCount);
+    end
+    else
+    begin
+      NegativeMean := NegativeMean - V;
+      Inc(NegativeCount);
+    end;
+    P := (P + 1) mod (DMR_SYNC_END_DIBIT + 1);
+  end;
+  if (PositiveCount = 0) or (NegativeCount = 0) then Exit(-1.0e300);
+  PositiveMean := PositiveMean / PositiveCount;
+  NegativeMean := NegativeMean / NegativeCount;
+  ErrorSum := 0;
+  P := (FHistoryPos[Phase] + DMR_SYNC_END_DIBIT + 1 - 24) mod
+       (DMR_SYNC_END_DIBIT + 1);
+  for i := 0 to 23 do
+  begin
+    V := FSymbolHistory[Phase, P];
+    if V >= 0 then ErrorSum := ErrorSum + Sqr(V - PositiveMean)
+    else ErrorSum := ErrorSum + Sqr((-V) - NegativeMean);
+    P := (P + 1) mod (DMR_SYNC_END_DIBIT + 1);
+  end;
+  Scale := Sqr(0.5 * (PositiveMean + NegativeMean));
+  if Scale <= 1.0e-18 then Exit(-1.0e300);
+  // Higher is better: zero denotes perfectly compact outer-level clusters.
+  Result := -ErrorSum / (24.0 * Scale);
 end;
 
 procedure TDMRDecoder.CalibrateSyncLevels(Phase: Integer);
@@ -789,14 +825,14 @@ begin
   FStatusLock.Enter;
   try
     // 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.
+    // sample period. Keep the phase whose known positive/negative sync levels
+    // form the tightest clusters, not merely the first sign-pattern match.
     if (FLastSyncSample <> 0) and
        (FSampleNo - FLastSyncSample <= DMR_SAMPLES_PER_SYM * 2) then
     begin
-      if SyncEyeOpening(Phase) > FBestSyncQuality then
+      if SyncPhaseQuality(Phase) > FBestSyncQuality then
       begin
-        FBestSyncQuality := SyncEyeOpening(Phase);
+        FBestSyncQuality := SyncPhaseQuality(Phase);
         FSyncKind := Kind;
         FInverted := Inverted;
         CalibrateSyncLevels(Phase);
@@ -809,7 +845,7 @@ begin
     Inc(FSyncCount);
     FLastSyncTick := NowTick;
     FLastSyncSample := FSampleNo;
-    FBestSyncQuality := SyncEyeOpening(Phase);
+    FBestSyncQuality := SyncPhaseQuality(Phase);
     CalibrateSyncLevels(Phase);
     if Kind in [dskMSData, dskMSVoice] then FMobileActiveBurst := True;
     StartBurstTracking(Phase);