sigproc: Setup downlink bursts at 156.25 duration with 4 SPS
Instead of extending 156/157 symbol sized bursts to 624/628 when 4
samples-per-symbol are used, use a fixed size of 625 samples, or
625.25 us.
This is a breaking timing change.
diff --git a/Transceiver52M/sigProcLib.cpp b/Transceiver52M/sigProcLib.cpp
index 4355fce..4b2ccd2 100644
--- a/Transceiver52M/sigProcLib.cpp
+++ b/Transceiver52M/sigProcLib.cpp
@@ -44,6 +44,9 @@
/* Clipping detection threshold */
#define CLIP_THRESH 30000.0f
+/* GSM 4 sps burst length */
+#define GSM_BURST_LEN_4SPS 625
+
/** Lookup tables for trigonometric approximation */
float cosTable[TABLESIZE+1]; // add 1 element for wrap around
float sinTable[TABLESIZE+1];
@@ -697,27 +700,22 @@
return shaped;
}
-static signalVector *modulateBurstLaurent(const BitVector &bits,
- int guard_len, int sps)
+/*
+ * Laurent decomposition based GMSK modulator - 4 SPS only
+ */
+static signalVector *modulateBurstLaurent(const BitVector &bits)
{
- int burst_len;
+ const int burst_len = GSM_BURST_LEN_4SPS;
+ const int 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 = GSMPulse->c0;
c1_pulse = GSMPulse->c1;
- burst_len = sps * (bits.size() + guard_len);
-
c0_burst = new signalVector(burst_len, c0_pulse->size());
c0_burst->isReal(true);
c0_itr = c0_burst->begin();
@@ -826,7 +824,7 @@
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);
}