sigproc: Always use 625 sample length bursts with 4 SPS
At 4 samples per symbol, we don't need to maintain the 156/157 sample
slot structure to account for the GSM 156.25 sample burst length.
Set the 4 SPS Laurent modulator to ignore the guard interval setting
and always output 625 sample sized bursts. The EDGE 8-PSK modulator
already has this behavior.
Signed-off-by: Tom Tsou <tom.tsou@ettus.com>
diff --git a/Transceiver52M/sigProcLib.cpp b/Transceiver52M/sigProcLib.cpp
index f846950..1a15e51 100644
--- a/Transceiver52M/sigProcLib.cpp
+++ b/Transceiver52M/sigProcLib.cpp
@@ -789,26 +789,26 @@
burst[i] = burst[i] * rot;
}
-static signalVector *modulateBurstLaurent(const BitVector &bits,
- int guard_len, int sps)
+/*
+ * Ignore the guard length argument in the GMSK modulator interface
+ * because it results in 624/628 sized bursts instead of the preferred
+ * burst length of 625. Only 4 SPS is supported.
+ */
+static signalVector *modulateBurstLaurent(const BitVector &bits)
{
- int burst_len;
+ int burst_len, sps = 4;
float phase;
signalVector *c0_pulse, *c1_pulse, *c0_burst;
signalVector *c1_burst, *c0_shaped, *c1_shaped;
signalVector::iterator c0_itr, c1_itr;
- /*
- * Apply before and after bits to reduce phase error at burst edges.
- * Make sure there is enough room in the burst to accomodate all bits.
- */
- if (guard_len < 4)
- guard_len = 4;
-
c0_pulse = GSMPulse4->c0;
c1_pulse = GSMPulse4->c1;
- burst_len = sps * (bits.size() + guard_len);
+ if (bits.size() > 156)
+ return NULL;
+
+ burst_len = 625;
c0_burst = new signalVector(burst_len, c0_pulse->size());
c0_burst->isReal(true);
@@ -1083,7 +1083,7 @@
if (emptyPulse)
return rotateBurst(wBurst, guardPeriodLength, sps);
else if (sps == 4)
- return modulateBurstLaurent(wBurst, guardPeriodLength, sps);
+ return modulateBurstLaurent(wBurst);
else
return modulateBurstBasic(wBurst, guardPeriodLength, sps);
}