Transceiver52M: Add dual channel diversity receiver option

This patch add support for dual channel diversity on the receive
path. This allows two antennas two shared antennas to be used for
each ARFCN handling channel in the receiver. This configuration
may improvde performance in multi-path fading environments,
however, noise andpotential interference levels are increased due
to the higher bandwidth used.

The receive path is oversampled by a factor of four for a rate
of 1.083333 Msps. If the receive paths are tuned within a
maximum channel spacing (currently set at 600 kHz), then both
ARFCN frequencies are processed by each channel of the receiver.
Otherwise, the frequency shifted diversity path is disabled and
standard non-diversity operation takes place.

Diversity processing is handled by selecting the path with the
higheset energy level and discarding the burst on the second
path. Selection occurs on a burst-by-burst basis.

Signed-off-by: Thomas Tsou <tom@tsou.cc>

1 files changed, 12 insertions, 12 deletions

diff --git a/Transceiver52M/radioInterface.cpp b/Transceiver52M/radioInterface.cpp
index 43fa3a3..ff9f493 100644
--- a/Transceiver52M/radioInterface.cpp
+++ b/Transceiver52M/radioInterface.cpp
@@ -34,10 +34,9 @@ extern "C" {
 #define NUMCHUNKS	4
 
 RadioInterface::RadioInterface(RadioDevice *wRadio,
-			       int wReceiveOffset,
-			       size_t sps, size_t chans,
-			       GSM::Time wStartTime)
-  : mRadio(wRadio), mSPSTx(sps), mSPSRx(1), mChans(chans),
+                               size_t sps, size_t chans, size_t diversity,
+                               int wReceiveOffset, GSM::Time wStartTime)
+  : mRadio(wRadio), mSPSTx(sps), mSPSRx(1), mChans(chans), mMIMO(diversity),
     sendCursor(0), recvCursor(0), underrun(false), overrun(false),
     receiveOffset(wReceiveOffset), mOn(false), powerScaling(1.0),
     loadTest(false)
@@ -52,11 +51,8 @@ RadioInterface::~RadioInterface(void)
 
 bool RadioInterface::init(int type)
 {
-  if (type != RadioDevice::NORMAL)
-    return false;
-
-  if (!mChans) {
-    LOG(ALERT) << "Invalid number of channels " << mChans;
+  if ((type != RadioDevice::NORMAL) || (mMIMO > 1) || !mChans) {
+    LOG(ALERT) << "Invalid configuration";
     return false;
   }
 
@@ -251,10 +247,14 @@ bool RadioInterface::driveReceiveRadio()
    */
   while (recvSz > burstSize) {
     for (size_t i = 0; i < mChans; i++) {
-      burst = new radioVector(rcvClock, burstSize, head);
+      burst = new radioVector(rcvClock, burstSize, head, mMIMO);
+
+      for (size_t n = 0; n < mMIMO; n++) {
+        unRadioifyVector((float *)
+                         (recvBuffer[mMIMO * i + n]->begin() + readSz),
+                         *burst->getVector(n));
+      }
 
-      unRadioifyVector((float *) (recvBuffer[i]->begin() + readSz),
-                       *burst->getVector());
 
       if (mReceiveFIFO[i].size() < 32)
         mReceiveFIFO[i].write(burst);