EDGE: Combine shared GMSK and 8-PSK demodulator sections
Timing recovery and single tap channel compensation are identical
in both GMSK and EDGE receivers. This is the section ahead of and
including the optional 4-1 downsampler. GMSK and EDGE specific
sections operate at 1 SPS.
Signed-off-by: Tom Tsou <tom.tsou@ettus.com>
diff --git a/Transceiver52M/sigProcLib.cpp b/Transceiver52M/sigProcLib.cpp
index cf2c257..f3fa4f0 100644
--- a/Transceiver52M/sigProcLib.cpp
+++ b/Transceiver52M/sigProcLib.cpp
@@ -1964,6 +1964,32 @@
}
/*
+ * Shared portion of GMSK and EDGE demodulators consisting of timing
+ * recovery and single tap channel correction. For 4 SPS (if activated),
+ * the output is downsampled prior to the 1 SPS modulation specific
+ * stages.
+ */
+static signalVector *demodCommon(signalVector &burst, int sps,
+ complex chan, float toa)
+{
+ signalVector *delay, *dec;
+
+ if ((sps != 1) && (sps != 4))
+ return NULL;
+
+ scaleVector(burst, (complex) 1.0 / chan);
+ delay = delayVector(&burst, NULL, -toa * (float) sps);
+
+ if (sps == 1)
+ return delay;
+
+ dec = downsampleBurst(*delay);
+
+ delete delay;
+ return dec;
+}
+
+/*
* Demodulate GSMK burst. Prior to symbol rotation, operate at
* 4 SPS (if activated) to minimize distortion through the fractional
* delay filters. Symbol rotation and after always operates at 1 SPS.
@@ -1972,17 +1998,11 @@
complex channel, float TOA)
{
SoftVector *bits;
- signalVector *delay, *dec;
+ signalVector *dec;
- scaleVector(rxBurst, ((complex) 1.0) / channel);
- delay = delayVector(&rxBurst, NULL, -TOA * (float) sps);
-
- if (sps == 4) {
- dec = downsampleBurst(*delay);
- delete delay;
- } else {
- dec = delay;
- }
+ dec = demodCommon(rxBurst, sps, channel, TOA);
+ if (!dec)
+ return NULL;
/* Shift up by a quarter of a frequency */
GMSKReverseRotate(*dec, 1);
@@ -2015,24 +2035,17 @@
complex chan, float toa)
{
SoftVector *bits;
- signalVector *delay, *dec, *rot, *eq;
+ signalVector *dec, *rot, *eq;
- if ((sps != 1) && (sps != 4))
+ dec = demodCommon(burst, sps, chan, toa);
+ if (!dec)
return NULL;
- scaleVector(burst, ((complex) 1.0) / chan);
- delay = delayVector(&burst, NULL, -toa * (float) sps);
-
- if (sps == 4) {
- dec = downsampleBurst(*delay);
- delete delay;
- } else {
- dec = delay;
- }
-
+ /* Equalize and derotate */
eq = convolve(dec, GSMPulse4->c0_inv, NULL, NO_DELAY);
rot = derotateEdgeBurst(*eq, 1);
+ /* Soft slice and normalize */
bits = softSliceEdgeBurst(*dec);
vectorSlicer(bits);