From 1189019c30c1208c95868cb6998f6b7af25d2c45 Mon Sep 17 00:00:00 2001
From: Thomas Tsou <tom@tsou.cc>
Date: Wed, 16 Apr 2014 19:36:30 -0400
Subject: Transceiver52M: Add SCH detection capability

Use similar approach for detecting normal and RACH bursts, but apply a
sample shift after detection in order to gradually zero the measured
timing offset. SCH synchronization sequence and setup are added similar
to RACH detection with the main difference, aside being the SCH runs
full length of the burst. History is also added to accommodate full
length burst correlation.

Signed-off-by: Thomas Tsou <tom@tsou.cc>
---
 Transceiver52M/sigProcLib.cpp | 134 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 132 insertions(+), 2 deletions(-)

(limited to 'Transceiver52M/sigProcLib.cpp')

diff --git a/Transceiver52M/sigProcLib.cpp b/Transceiver52M/sigProcLib.cpp
index 54dd8fc..0db3a81 100644
--- a/Transceiver52M/sigProcLib.cpp
+++ b/Transceiver52M/sigProcLib.cpp
@@ -78,6 +78,7 @@ struct CorrelationSequence {
 
   signalVector *sequence;
   void         *buffer;
+  void         *history;
   float        toa;
   complex      gain;
 };
@@ -111,6 +112,7 @@ struct PulseSequence {
 
 CorrelationSequence *gMidambles[] = {NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL};
 CorrelationSequence *gRACHSequence = NULL;
+CorrelationSequence *gSCHSequence = NULL;
 PulseSequence *GSMPulse = NULL;
 PulseSequence *GSMPulse1 = NULL;
 
@@ -131,6 +133,7 @@ void sigProcLibDestroy()
   delete GMSKRotation1;
   delete GMSKReverseRotation1;
   delete gRACHSequence;
+  delete gSCHSequence;
   delete GSMPulse;
   delete GSMPulse1;
 
@@ -139,6 +142,7 @@ void sigProcLibDestroy()
   GMSKReverseRotationN = NULL;
   GMSKReverseRotation1 = NULL;
   gRACHSequence = NULL;
+  gSCHSequence = NULL;
   GSMPulse = NULL;
   GSMPulse1 = NULL;
 }
@@ -395,8 +399,10 @@ signalVector *convolve(const signalVector *x,
     break;
   case CUSTOM:
     if (start < h->size() - 1) {
-      head = h->size() - start;
-      append = true;
+      if (x->getStart() < h->size() - 1) {
+        head = h->size() - start;
+        append = true;
+      }
     }
     if (start + len > x->size()) {
       tail = start + len - x->size();
@@ -1274,6 +1280,69 @@ release:
   return status;
 }
 
+bool generateSCHSequence(int sps)
+{
+  bool status = true;
+  float toa;
+  complex *data = NULL;
+  signalVector *autocorr = NULL;
+  signalVector *seq0 = NULL, *seq1 = NULL, *_seq1 = NULL;
+
+  delete gSCHSequence;
+
+  seq0 = modulateBurst(gSCHSynchSequence, 0, sps, false);
+  if (!seq0)
+    return false;
+
+  seq1 = modulateBurst(gSCHSynchSequence, 0, sps, true);
+  if (!seq1) {
+    status = false;
+    goto release;
+  }
+
+  conjugateVector(*seq1);
+
+  /* For SSE alignment, reallocate the midamble sequence on 16-byte boundary */
+  data = (complex *) convolve_h_alloc(seq1->size());
+  _seq1 = new signalVector(data, 0, seq1->size());
+  _seq1->setAligned(true);
+  memcpy(_seq1->begin(), seq1->begin(), seq1->size() * sizeof(complex));
+
+  autocorr = convolve(seq0, _seq1, autocorr, NO_DELAY);
+  if (!autocorr) {
+    status = false;
+    goto release;
+  }
+
+  gSCHSequence = new CorrelationSequence;
+  gSCHSequence->sequence = _seq1;
+  gSCHSequence->buffer = data;
+  gSCHSequence->gain = peakDetect(*autocorr, &toa, NULL);
+  gSCHSequence->history = new complex[_seq1->size()];
+
+  /* For 1 sps only
+   *     (Half of correlation length - 1) + midpoint of pulse shaping filer
+   *     20.5 = (64 / 2 - 1) + 1.5
+   */
+  if (sps == 1)
+    gSCHSequence->toa = toa - 32.5;
+  else
+    gSCHSequence->toa = 0.0;
+
+release:
+  delete autocorr;
+  delete seq0;
+  delete seq1;
+
+  if (!status) {
+    delete _seq1;
+    free(data);
+    gSCHSequence = NULL;
+  }
+
+  return status;
+}
+
 static float computePeakRatio(signalVector *corr,
                               int sps, float toa, complex amp)
 {
@@ -1424,6 +1493,62 @@ int detectRACHBurst(signalVector &rxBurst,
   return 1;
 }
 
+int detectSCHBurst(signalVector &burst,
+		    float thresh,
+		    int sps,
+		    complex *amp,
+		    float *toa)
+{
+  int rc, start, target, head, tail, len;
+  float _toa;
+  complex _amp;
+  signalVector *corr, *_burst;
+  CorrelationSequence *sync;
+
+  if ((sps != 1) && (sps != 4))
+    return -1;
+
+  /* Search full length */
+  target = 3 + 39 + 64;
+  head = target - 1;
+  tail = 39 + 3 + 9;
+
+  start = (target - head) * sps - 1;
+  len = (head + tail) * sps;
+  sync = gSCHSequence;
+  corr = new signalVector(len);
+
+  _burst = new signalVector(burst, sync->sequence->size(), 5);
+
+  memcpy(_burst->begin() - sync->sequence->size(), sync->history,
+         sync->sequence->size() * sizeof(complex));
+
+  memcpy(sync->history, &burst.begin()[burst.size() - sync->sequence->size()],
+         sync->sequence->size() * sizeof(complex));
+
+  rc = detectBurst(*_burst, *corr, sync,
+                   thresh, sps, &_amp, &_toa, start, len);
+  delete corr;
+
+  if (rc < 0) {
+    return -1;
+  } else if (!rc) {
+    if (amp)
+      *amp = 0.0f;
+    if (toa)
+      *toa = 0.0f;
+    return 0;
+  }
+
+  /* Subtract forward search bits from delay */
+  if (toa)
+    *toa = _toa - head * sps;
+  if (amp)
+    *amp = _amp;
+
+  return 1;
+}
+
 /* 
  * Normal burst detection
  *
@@ -1717,6 +1842,11 @@ bool sigProcLibSetup(int sps)
     return false;
   }
 
+  if (!generateSCHSequence(1)) {
+    sigProcLibDestroy();
+    return false;
+  }
+
   generateDelayFilters();
 
   return true;
-- 
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