Transceiver52M: Setup dual Laurent pulse shaping filter
Provides substantially improved transmit phase error
performance when enabled. Requires use of 4 samples
per symbol, and is enabled by default when set.
Signed-off-by: Thomas Tsou <tom@tsou.cc>
diff --git a/Transceiver52M/sigProcLib.cpp b/Transceiver52M/sigProcLib.cpp
index 6650948..2350abb 100644
--- a/Transceiver52M/sigProcLib.cpp
+++ b/Transceiver52M/sigProcLib.cpp
@@ -77,20 +77,25 @@
* for SSE instructions.
*/
struct PulseSequence {
- PulseSequence() : gaussian(NULL), empty(NULL), buffer(NULL)
+ PulseSequence() : c0(NULL), c1(NULL), empty(NULL),
+ c0_buffer(NULL), c1_buffer(NULL)
{
}
~PulseSequence()
{
- delete gaussian;
+ delete c0;
+ delete c1;
delete empty;
- free(buffer);
+ free(c0_buffer);
+ free(c1_buffer);
}
- signalVector *gaussian;
+ signalVector *c0;
+ signalVector *c1;
signalVector *empty;
- void *buffer;
+ void *c0_buffer;
+ void *c1_buffer;
};
CorrelationSequence *gMidambles[] = {NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL};
@@ -409,10 +414,48 @@
return y;
}
+bool generateC1Pulse(int sps)
+{
+ int len;
+
+ switch (sps) {
+ case 4:
+ len = 8;
+ break;
+ default:
+ return false;
+ }
+
+ GSMPulse->c1_buffer = convolve_h_alloc(len);
+ GSMPulse->c1 = new signalVector((complex *)
+ GSMPulse->c1_buffer, 0, len);
+ GSMPulse->c1->isRealOnly(true);
+
+ /* Enable alignment for SSE usage */
+ GSMPulse->c1->setAligned(true);
+
+ signalVector::iterator xP = GSMPulse->c1->begin();
+
+ switch (sps) {
+ case 4:
+ /* BT = 0.30 */
+ *xP++ = 0.0;
+ *xP++ = 8.16373112e-03;
+ *xP++ = 2.84385729e-02;
+ *xP++ = 5.64158904e-02;
+ *xP++ = 7.05463553e-02;
+ *xP++ = 5.64158904e-02;
+ *xP++ = 2.84385729e-02;
+ *xP++ = 8.16373112e-03;
+ }
+
+ return true;
+}
+
void generateGSMPulse(int sps, int symbolLength)
{
int len;
- float arg, center;
+ float arg, avg, center;
delete GSMPulse;
@@ -438,15 +481,18 @@
len = 4;
}
- GSMPulse->buffer = convolve_h_alloc(len);
- GSMPulse->gaussian = new signalVector((complex *)
- GSMPulse->buffer, 0, len);
- GSMPulse->gaussian->setAligned(true);
- GSMPulse->gaussian->isRealOnly(true);
+ GSMPulse->c0_buffer = convolve_h_alloc(len);
+ GSMPulse->c0 = new signalVector((complex *)
+ GSMPulse->c0_buffer, 0, len);
+ GSMPulse->c0->isRealOnly(true);
- signalVector::iterator xP = GSMPulse->gaussian->begin();
+ /* Enable alingnment for SSE usage */
+ GSMPulse->c0->setAligned(true);
+
+ signalVector::iterator xP = GSMPulse->c0->begin();
if (sps == 4) {
+ *xP++ = 0.0;
*xP++ = 4.46348606e-03;
*xP++ = 2.84385729e-02;
*xP++ = 1.03184855e-01;
@@ -462,7 +508,7 @@
*xP++ = 1.03184855e-01;
*xP++ = 2.84385729e-02;
*xP++ = 4.46348606e-03;
- *xP++ = 0.0;
+ generateC1Pulse(sps);
} else {
center = (float) (len - 1.0) / 2.0;
@@ -472,12 +518,12 @@
*xP++ = 0.96 * exp(-1.1380 * arg * arg -
0.527 * arg * arg * arg * arg);
}
- }
- float avgAbsval = sqrtf(vectorNorm2(*GSMPulse->gaussian)/sps);
- xP = GSMPulse->gaussian->begin();
- for (int i = 0; i < len; i++)
- *xP++ /= avgAbsval;
+ avg = sqrtf(vectorNorm2(*GSMPulse->c0) / sps);
+ xP = GSMPulse->c0->begin();
+ for (int i = 0; i < len; i++)
+ *xP++ /= avg;
+ }
}
signalVector* frequencyShift(signalVector *y,
@@ -559,43 +605,160 @@
return true;
}
+static signalVector *rotateBurst(const BitVector &wBurst,
+ int guardPeriodLength, int sps)
+{
+ int burst_len;
+ signalVector *pulse, rotated, *shaped;
+ signalVector::iterator itr;
+
+ pulse = GSMPulse->empty;
+ burst_len = sps * (wBurst.size() + guardPeriodLength);
+ rotated = signalVector(burst_len);
+ itr = rotated.begin();
+
+ for (unsigned i = 0; i < wBurst.size(); i++) {
+ *itr = 2.0 * (wBurst[i] & 0x01) - 1.0;
+ itr += sps;
+ }
+
+ GMSKRotate(rotated);
+ rotated.isRealOnly(false);
+
+ /* Dummy filter operation */
+ shaped = convolve(&rotated, pulse, NULL, START_ONLY);
+ if (!shaped)
+ return NULL;
+
+ return shaped;
+}
+
+static signalVector *modulateBurstLaurent(const BitVector &bits,
+ int guard_len, int sps)
+{
+ int burst_len;
+ float phase;
+ signalVector *c0_pulse, *c1_pulse, c0_burst, 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 = signalVector(burst_len);
+ c0_burst.isRealOnly(true);
+ c0_itr = c0_burst.begin();
+
+ c1_burst = signalVector(burst_len);
+ c1_burst.isRealOnly(true);
+ c1_itr = c1_burst.begin();
+
+ /* Padded differential start bits */
+ *c0_itr = 2.0 * (0x00 & 0x01) - 1.0;
+ c0_itr += sps;
+
+ /* Main burst bits */
+ for (unsigned i = 0; i < bits.size(); i++) {
+ *c0_itr = 2.0 * (bits[i] & 0x01) - 1.0;
+ c0_itr += sps;
+ }
+
+ /* Padded differential end bits */
+ *c0_itr = 2.0 * (0x01 & 0x01) - 1.0;
+
+ /* Generate C0 phase coefficients */
+ GMSKRotate(c0_burst);
+ c0_burst.isRealOnly(false);
+
+ c0_itr = c0_burst.begin();
+ c0_itr += sps * 2;
+ c1_itr += sps * 2;
+
+ /* Start magic */
+ phase = 2.0 * ((0x01 & 0x01) ^ (0x01 & 0x01)) - 1.0;
+ *c1_itr = *c0_itr * Complex<float>(0, phase);
+ c0_itr += sps;
+ c1_itr += sps;
+
+ /* Generate C1 phase coefficients */
+ for (unsigned i = 2; i < bits.size(); i++) {
+ phase = 2.0 * ((bits[i - 1] & 0x01) ^ (bits[i - 2] & 0x01)) - 1.0;
+ *c1_itr = *c0_itr * Complex<float>(0, phase);
+
+ c0_itr += sps;
+ c1_itr += sps;
+ }
+
+ /* End magic */
+ int i = bits.size();
+ phase = 2.0 * ((bits[i-1] & 0x01) ^ (bits[i-2] & 0x01)) - 1.0;
+ *c1_itr = *c0_itr * Complex<float>(0, phase);
+
+ /* Primary (C0) and secondary (C1) pulse shaping */
+ c0_shaped = convolve(&c0_burst, c0_pulse, NULL, START_ONLY);
+ c1_shaped = convolve(&c1_burst, c1_pulse, NULL, START_ONLY);
+
+ /* Sum shaped outputs into C0 */
+ c0_itr = c0_shaped->begin();
+ c1_itr = c1_shaped->begin();
+ for (unsigned i = 0; i < c0_shaped->size(); i++ )
+ *c0_itr++ += *c1_itr++;
+
+ delete c1_shaped;
+
+ return c0_shaped;
+}
+
+static signalVector *modulateBurstBasic(const BitVector &bits,
+ int guard_len, int sps)
+{
+ int burst_len;
+ signalVector *pulse, burst, *shaped;
+ signalVector::iterator burst_itr;
+
+ pulse = GSMPulse->c0;
+ burst_len = sps * (bits.size() + guard_len);
+
+ burst = signalVector(burst_len);
+ burst.isRealOnly(true);
+ burst_itr = burst.begin();
+
+ /* Raw bits are not differentially encoded */
+ for (unsigned i = 0; i < bits.size(); i++) {
+ *burst_itr = 2.0 * (bits[i] & 0x01) - 1.0;
+ burst_itr += sps;
+ }
+
+ GMSKRotate(burst);
+ burst.isRealOnly(false);
+
+ /* Single Gaussian pulse approximation shaping */
+ shaped = convolve(&burst, pulse, NULL, START_ONLY);
+
+ return shaped;
+}
+
/* Assume input bits are not differentially encoded */
signalVector *modulateBurst(const BitVector &wBurst, int guardPeriodLength,
int sps, bool emptyPulse)
{
- int burstLen;
- signalVector *pulse, *shapedBurst, modBurst;
- signalVector::iterator modBurstItr;
-
if (emptyPulse)
- pulse = GSMPulse->empty;
+ return rotateBurst(wBurst, guardPeriodLength, sps);
+ else if (sps == 4)
+ return modulateBurstLaurent(wBurst, guardPeriodLength, sps);
else
- pulse = GSMPulse->gaussian;
-
- burstLen = sps * (wBurst.size() + guardPeriodLength);
- modBurst = signalVector(burstLen);
- modBurstItr = modBurst.begin();
-
- for (unsigned int i = 0; i < wBurst.size(); i++) {
- *modBurstItr = 2.0*(wBurst[i] & 0x01)-1.0;
- modBurstItr += sps;
- }
-
- // shift up pi/2
- // ignore starting phase, since spec allows for discontinuous phase
- GMSKRotate(modBurst);
-
- modBurst.isRealOnly(false);
-
- // filter w/ pulse shape
- shapedBurst = convolve(&modBurst, pulse, NULL, START_ONLY);
- if (!shapedBurst)
- return NULL;
-
- return shapedBurst;
+ return modulateBurstBasic(wBurst, guardPeriodLength, sps);
}
-float sinc(float x)
+float sinc(float x)
{
if ((x >= 0.01F) || (x <= -0.01F)) return (sinLookup(x)/x);
return 1.0F;
@@ -1040,6 +1203,10 @@
/* Normalize our channel gain */
*amp = *amp / sync->gain;
+ /* Compenate for residual rotation with dual Laurent pulse */
+ if (sps == 4)
+ *amp = *amp * complex(0.0, 1.0);
+
return 1;
}