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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>
This commit is contained in:
Tom Tsou 2016-03-06 22:33:20 -08:00
parent af717b2d3c
commit 7fec3030d4
1 changed files with 35 additions and 22 deletions
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57
Transceiver52M/sigProcLib.cpp
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@ -1963,6 +1963,32 @@ static SoftVector *softSliceEdgeBurst(signalVector &burst)
return bits;
}
/*
* 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
@ -1972,17 +1998,11 @@ SoftVector *demodulateBurst(signalVector &rxBurst, int sps,
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 @@ SoftVector *demodEdgeBurst(signalVector &burst, int sps,
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);