commit 78d1fc9a13f84b273facb2f22a291c3d2e6ebd33
author Alexander Chemeris <Alexander.Chemeris@gmail.com> Sat Mar 19 21:16:22 2016 +0300
committer Tom Tsou <tom.tsou@ettus.com> Wed Apr 20 13:45:00 2016 -0700
tree 04889e88b9281c0a9ce658e7d454e3f96bfe6f98
parent a8cf2086165480597251c2af240e0f44c47097f8

transceiver: Properly handle MAXDLY.

Previously MAXDLY value was applied to Normal Bursts, which was nice
when working with sloppy test equipment like CMD57, but useless for
real world usage. At the same time documentation and de facto usage
of MAXDLY in OsmoBTS and OpenBTS assumed that it actually applies to
Access Bursts (RACH). So this patch changes osmo-rx behavior to apply
MAXDLY to RACH bursts and introduces a new command MAXDLYNB for the
old behavior.

Transceiver52M/Transceiver.cpp

diff --git a/Transceiver52M/Transceiver.cpp b/Transceiver52M/Transceiver.cpp
index a1c6f1b..1f59f78 100644
--- a/Transceiver52M/Transceiver.cpp
+++ b/Transceiver52M/Transceiver.cpp
@@ -119,7 +119,8 @@
     mTransmitLatency(wTransmitLatency), mRadioInterface(wRadioInterface),
     rssiOffset(wRssiOffset),
     mSPSTx(tx_sps), mSPSRx(rx_sps), mChans(chans), mOn(false),
-    mTxFreq(0.0), mRxFreq(0.0), mTSC(0), mMaxExpectedDelay(0), mWriteBurstToDiskMask(0)
+    mTxFreq(0.0), mRxFreq(0.0), mTSC(0), mMaxExpectedDelayAB(0), mMaxExpectedDelayNB(0),
+    mWriteBurstToDiskMask(0)
 {
   txFullScale = mRadioInterface->fullScaleInputValue();
   rxFullScale = mRadioInterface->fullScaleOutputValue();
@@ -535,18 +536,19 @@
   switch (type) {
   case EDGE:
     rc = detectEdgeBurst(burst, mTSC, threshold, mSPSRx,
-                         amp, toa, mMaxExpectedDelay);
+                         amp, toa, mMaxExpectedDelayNB);
     if (rc > 0)
       break;
     else
       type = TSC;
   case TSC:
     rc = analyzeTrafficBurst(burst, mTSC, threshold, mSPSRx,
-                             amp, toa, mMaxExpectedDelay);
+                             amp, toa, mMaxExpectedDelayNB);
     break;
   case RACH:
     threshold = 6.0;
-    rc = detectRACHBurst(burst, threshold, mSPSRx, amp, toa);
+    rc = detectRACHBurst(burst, threshold, mSPSRx, amp, toa,
+                         mMaxExpectedDelayAB);
     break;
   default:
     LOG(ERR) << "Invalid correlation type";
@@ -753,9 +755,16 @@
     //set expected maximum time-of-arrival
     int maxDelay;
     sscanf(buffer,"%3s %s %d",cmdcheck,command,&maxDelay);
-    mMaxExpectedDelay = maxDelay; // 1 GSM symbol is approx. 1 km
+    mMaxExpectedDelayAB = maxDelay; // 1 GSM symbol is approx. 1 km
     sprintf(response,"RSP SETMAXDLY 0 %d",maxDelay);
   }
+  else if (strcmp(command,"SETMAXDLYNB")==0) {
+    //set expected maximum time-of-arrival
+    int maxDelay;
+    sscanf(buffer,"%3s %s %d",cmdcheck,command,&maxDelay);
+    mMaxExpectedDelayNB = maxDelay; // 1 GSM symbol is approx. 1 km
+    sprintf(response,"RSP SETMAXDLYNB 0 %d",maxDelay);
+  }
   else if (strcmp(command,"SETRXGAIN")==0) {
     //set expected maximum time-of-arrival
     int newGain;

Transceiver52M/Transceiver.h

diff --git a/Transceiver52M/Transceiver.h b/Transceiver52M/Transceiver.h
index 79b487a..472adbe 100644
--- a/Transceiver52M/Transceiver.h
+++ b/Transceiver52M/Transceiver.h
@@ -227,7 +227,8 @@
   double mTxFreq;                      ///< the transmit frequency
   double mRxFreq;                      ///< the receive frequency
   unsigned mTSC;                       ///< the midamble sequence code
-  unsigned mMaxExpectedDelay;          ///< maximum expected time-of-arrival offset in GSM symbols
+  unsigned mMaxExpectedDelayAB;        ///< maximum expected time-of-arrival offset in GSM symbols for Access Bursts (RACH)
+  unsigned mMaxExpectedDelayNB;        ///< maximum expected time-of-arrival offset in GSM symbols for Normal Bursts
   unsigned mWriteBurstToDiskMask;      ///< debug: bitmask to indicate which timeslots to dump to disk
 
   std::vector<TransceiverState> mStates;

Transceiver52M/sigProcLib.cpp

diff --git a/Transceiver52M/sigProcLib.cpp b/Transceiver52M/sigProcLib.cpp
index f3fa4f0..9674aa8 100644
--- a/Transceiver52M/sigProcLib.cpp
+++ b/Transceiver52M/sigProcLib.cpp
@@ -1816,21 +1816,22 @@
  *
  * Correlation window parameters:
  *   target: Tail bits + RACH length (reduced from 41 to a multiple of 4)
- *   head: Search 4 symbols before target 
- *   tail: Search 10 symbols after target
+ *   head: Search 4 symbols before target
+ *   tail: Search 4 symbols + maximum expected delay
  */
 int detectRACHBurst(signalVector &rxBurst,
             float thresh,
             int sps,
             complex &amp,
-            float &toa)
+            float &toa,
+            unsigned maxTOA)
 {
   int rc, target, head, tail;
   CorrelationSequence *sync;
 
   target = 8 + 40;
   head = 4;
-  tail = 10;
+  tail = 4 + maxTOA;
   sync = gRACHSequence;
 
   rc = detectGeneralBurst(rxBurst, thresh, sps, amp, toa,

Transceiver52M/sigProcLib.h

diff --git a/Transceiver52M/sigProcLib.h b/Transceiver52M/sigProcLib.h
index 870eb1a..93251b5 100644
--- a/Transceiver52M/sigProcLib.h
+++ b/Transceiver52M/sigProcLib.h
@@ -192,13 +192,15 @@
         @param sps The number of samples per GSM symbol.
         @param amplitude The estimated amplitude of received RACH burst.
         @param TOA The estimate time-of-arrival of received RACH burst.
+        @param maxTOA The maximum expected time-of-arrival
         @return positive if threshold value is reached, negative on error, zero otherwise
 */
 int detectRACHBurst(signalVector &rxBurst,
                     float detectThreshold,
                     int sps,
                     complex &amplitude,
-                    float &TOA);
+                    float &TOA,
+                    unsigned maxTOA);
 
 /**
         Normal burst correlator, detector, channel estimator.