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Transceiver52M: Setup dual sample rate transceiver

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This patch applies oversampling, when selected with 4 sps,
to the downlink only, while running the receiver with
minimal sampling at 1 sps. These split sample rates allow
us to run a highly accurate downlink signal with minimal
distortion, while keeping receive path channel filtering
on the FPGA.

Without this patch, we oversample the receive path and
require a steep receive filter to get similar adjacent
channel suppression as the FPGA halfband / CIC filter
combination, which comes with a high computational cost.

Signed-off-by: Thomas Tsou <tom@tsou.cc>

git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@6747 19bc5d8c-e614-43d4-8b26-e1612bc8e597
This commit is contained in:
Thomas Tsou
2013-10-17 06:19:05 +00:00
parent 8652b22386
commit 22bc28edc4
10 changed files with 229 additions and 162 deletions
Download Patch File Download Diff File Expand all files Collapse all files

203
Transceiver52M/sigProcLib.cpp
View File

@@ -42,9 +42,11 @@ static const float M_PI_F = (float)M_PI;
static const float M_2PI_F = (float)(2.0*M_PI);
static const float M_1_2PI_F = 1/M_2PI_F;
/** Static vectors that contain a precomputed +/- f_b/4 sinusoid */
signalVector *GMSKRotation = NULL;
signalVector *GMSKReverseRotation = NULL;
/* Precomputed rotation vectors */
static signalVector *GMSKRotationN = NULL;
static signalVector *GMSKReverseRotationN = NULL;
static signalVector *GMSKRotation1 = NULL;
static signalVector *GMSKReverseRotation1 = NULL;
/*
* RACH and midamble correlation waveforms. Store the buffer separately
@@ -65,7 +67,7 @@ struct CorrelationSequence {
signalVector *sequence;
void *buffer;
float TOA;
float toa;
complex gain;
};
@@ -99,6 +101,7 @@ struct PulseSequence {
CorrelationSequence *gMidambles[] = {NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL};
CorrelationSequence *gRACHSequence = NULL;
PulseSequence *GSMPulse = NULL;
PulseSequence *GSMPulse1 = NULL;
void sigProcLibDestroy()
{
@@ -107,15 +110,21 @@ void sigProcLibDestroy()
gMidambles[i] = NULL;
}
delete GMSKRotation;
delete GMSKReverseRotation;
delete GMSKRotationN;
delete GMSKReverseRotationN;
delete GMSKRotation1;
delete GMSKReverseRotation1;
delete gRACHSequence;
delete GSMPulse;
delete GSMPulse1;
GMSKRotation = NULL;
GMSKReverseRotation = NULL;
GMSKRotationN = NULL;
GMSKRotation1 = NULL;
GMSKReverseRotationN = NULL;
GMSKReverseRotation1 = NULL;
gRACHSequence = NULL;
GSMPulse = NULL;
GSMPulse1 = NULL;
}
// dB relative to 1.0.
@@ -248,38 +257,38 @@ void initTrigTables() {
void initGMSKRotationTables(int sps)
{
GMSKRotation = new signalVector(157 * sps);
GMSKReverseRotation = new signalVector(157 * sps);
signalVector::iterator rotPtr = GMSKRotation->begin();
signalVector::iterator revPtr = GMSKReverseRotation->begin();
GMSKRotationN = new signalVector(157 * sps);
GMSKReverseRotationN = new signalVector(157 * sps);
signalVector::iterator rotPtr = GMSKRotationN->begin();
signalVector::iterator revPtr = GMSKReverseRotationN->begin();
float phase = 0.0;
while (rotPtr != GMSKRotation->end()) {
while (rotPtr != GMSKRotationN->end()) {
*rotPtr++ = expjLookup(phase);
*revPtr++ = expjLookup(-phase);
phase += M_PI_F / 2.0F / (float) sps;
}
}
bool sigProcLibSetup(int sps)
{
if ((sps != 1) && (sps != 4))
return false;
initTrigTables();
initGMSKRotationTables(sps);
generateGSMPulse(sps, 2);
if (!generateRACHSequence(sps)) {
sigProcLibDestroy();
return false;
GMSKRotation1 = new signalVector(157);
GMSKReverseRotation1 = new signalVector(157);
rotPtr = GMSKRotation1->begin();
revPtr = GMSKReverseRotation1->begin();
phase = 0.0;
while (rotPtr != GMSKRotation1->end()) {
*rotPtr++ = expjLookup(phase);
*revPtr++ = expjLookup(-phase);
phase += M_PI_F / 2.0F;
}
return true;
}
void GMSKRotate(signalVector &x) {
signalVector::iterator xPtr = x.begin();
signalVector::iterator rotPtr = GMSKRotation->begin();
static void GMSKRotate(signalVector &x, int sps)
{
signalVector::iterator rotPtr, xPtr = x.begin();
if (sps == 1)
rotPtr = GMSKRotation1->begin();
else
rotPtr = GMSKRotationN->begin();
if (x.isRealOnly()) {
while (xPtr < x.end()) {
*xPtr = *rotPtr++ * (xPtr->real());
@@ -294,9 +303,15 @@ void GMSKRotate(signalVector &x) {
}
}
void GMSKReverseRotate(signalVector &x) {
signalVector::iterator xPtr= x.begin();
signalVector::iterator rotPtr = GMSKReverseRotation->begin();
static void GMSKReverseRotate(signalVector &x, int sps)
{
signalVector::iterator rotPtr, xPtr= x.begin();
if (sps == 1)
rotPtr = GMSKReverseRotation1->begin();
else
rotPtr = GMSKReverseRotationN->begin();
if (x.isRealOnly()) {
while (xPtr < x.end()) {
*xPtr = *rotPtr++ * (xPtr->real());
@@ -412,10 +427,13 @@ signalVector *convolve(const signalVector *x,
return y;
}
bool generateC1Pulse(int sps)
static bool generateC1Pulse(int sps, PulseSequence *pulse)
{
int len;
if (!pulse)
return false;
switch (sps) {
case 4:
len = 8;
@@ -424,20 +442,20 @@ bool generateC1Pulse(int sps)
return false;
}
GSMPulse->c1_buffer = convolve_h_alloc(len);
GSMPulse->c1 = new signalVector((complex *)
GSMPulse->c1_buffer, 0, len);
GSMPulse->c1->isRealOnly(true);
pulse->c1_buffer = convolve_h_alloc(len);
pulse->c1 = new signalVector((complex *)
pulse->c1_buffer, 0, len);
pulse->c1->isRealOnly(true);
/* Enable alignment for SSE usage */
GSMPulse->c1->setAligned(true);
pulse->c1->setAligned(true);
signalVector::iterator xP = GSMPulse->c1->begin();
signalVector::iterator xP = pulse->c1->begin();
switch (sps) {
case 4:
/* BT = 0.30 */
*xP++ = 0.0;
*xP++ = 0.0;
*xP++ = 8.16373112e-03;
*xP++ = 2.84385729e-02;
*xP++ = 5.64158904e-02;
@@ -450,18 +468,17 @@ bool generateC1Pulse(int sps)
return true;
}
void generateGSMPulse(int sps, int symbolLength)
static PulseSequence *generateGSMPulse(int sps, int symbolLength)
{
int len;
float arg, avg, center;
delete GSMPulse;
PulseSequence *pulse;
/* Store a single tap filter used for correlation sequence generation */
GSMPulse = new PulseSequence();
GSMPulse->empty = new signalVector(1);
GSMPulse->empty->isRealOnly(true);
*(GSMPulse->empty->begin()) = 1.0f;
pulse = new PulseSequence();
pulse->empty = new signalVector(1);
pulse->empty->isRealOnly(true);
*(pulse->empty->begin()) = 1.0f;
/*
* For 4 samples-per-symbol use a precomputed single pulse Laurent
@@ -479,15 +496,14 @@ void generateGSMPulse(int sps, int symbolLength)
len = 4;
}
GSMPulse->c0_buffer = convolve_h_alloc(len);
GSMPulse->c0 = new signalVector((complex *)
GSMPulse->c0_buffer, 0, len);
GSMPulse->c0->isRealOnly(true);
pulse->c0_buffer = convolve_h_alloc(len);
pulse->c0 = new signalVector((complex *) pulse->c0_buffer, 0, len);
pulse->c0->isRealOnly(true);
/* Enable alingnment for SSE usage */
GSMPulse->c0->setAligned(true);
pulse->c0->setAligned(true);
signalVector::iterator xP = GSMPulse->c0->begin();
signalVector::iterator xP = pulse->c0->begin();
if (sps == 4) {
*xP++ = 0.0;
@@ -506,7 +522,7 @@ void generateGSMPulse(int sps, int symbolLength)
*xP++ = 1.03184855e-01;
*xP++ = 2.84385729e-02;
*xP++ = 4.46348606e-03;
generateC1Pulse(sps);
generateC1Pulse(sps, pulse);
} else {
center = (float) (len - 1.0) / 2.0;
@@ -517,11 +533,13 @@ void generateGSMPulse(int sps, int symbolLength)
0.527 * arg * arg * arg * arg);
}
avg = sqrtf(vectorNorm2(*GSMPulse->c0) / sps);
xP = GSMPulse->c0->begin();
for (int i = 0; i < len; i++)
avg = sqrtf(vectorNorm2(*pulse->c0) / sps);
xP = pulse->c0->begin();
for (int i = 0; i < len; i++)
*xP++ /= avg;
}
return pulse;
}
signalVector* frequencyShift(signalVector *y,
@@ -610,7 +628,7 @@ static signalVector *rotateBurst(const BitVector &wBurst,
signalVector *pulse, rotated, *shaped;
signalVector::iterator itr;
pulse = GSMPulse->empty;
pulse = GSMPulse1->empty;
burst_len = sps * (wBurst.size() + guardPeriodLength);
rotated = signalVector(burst_len);
itr = rotated.begin();
@@ -620,7 +638,7 @@ static signalVector *rotateBurst(const BitVector &wBurst,
itr += sps;
}
GMSKRotate(rotated);
GMSKRotate(rotated, sps);
rotated.isRealOnly(false);
/* Dummy filter operation */
@@ -673,7 +691,7 @@ static signalVector *modulateBurstLaurent(const BitVector &bits,
*c0_itr = 2.0 * (0x01 & 0x01) - 1.0;
/* Generate C0 phase coefficients */
GMSKRotate(c0_burst);
GMSKRotate(c0_burst, sps);
c0_burst.isRealOnly(false);
c0_itr = c0_burst.begin();
@@ -722,7 +740,11 @@ static signalVector *modulateBurstBasic(const BitVector &bits,
signalVector *pulse, burst, *shaped;
signalVector::iterator burst_itr;
pulse = GSMPulse->c0;
if (sps == 1)
pulse = GSMPulse1->c0;
else
pulse = GSMPulse->c0;
burst_len = sps * (bits.size() + guard_len);
burst = signalVector(burst_len);
@@ -735,7 +757,7 @@ static signalVector *modulateBurstBasic(const BitVector &bits,
burst_itr += sps;
}
GMSKRotate(burst);
GMSKRotate(burst, sps);
burst.isRealOnly(false);
/* Single Gaussian pulse approximation shaping */
@@ -1018,6 +1040,7 @@ void offsetVector(signalVector &x,
bool generateMidamble(int sps, int tsc)
{
bool status = true;
float toa;
complex *data = NULL;
signalVector *autocorr = NULL, *midamble = NULL;
signalVector *midMidamble = NULL, *_midMidamble = NULL;
@@ -1065,7 +1088,16 @@ bool generateMidamble(int sps, int tsc)
gMidambles[tsc] = new CorrelationSequence;
gMidambles[tsc]->buffer = data;
gMidambles[tsc]->sequence = _midMidamble;
gMidambles[tsc]->gain = peakDetect(*autocorr,&gMidambles[tsc]->TOA, NULL);
gMidambles[tsc]->gain = peakDetect(*autocorr, &toa, NULL);
/* For 1 sps only
* (Half of correlation length - 1) + midpoint of pulse shape + remainder
* 13.5 = (16 / 2 - 1) + 1.5 + (26 - 10) / 2
*/
if (sps == 1)
gMidambles[tsc]->toa = toa - 13.5;
else
gMidambles[tsc]->toa = 0;
release:
delete autocorr;
@@ -1084,6 +1116,7 @@ release:
bool generateRACHSequence(int sps)
{
bool status = true;
float toa;
complex *data = NULL;
signalVector *autocorr = NULL;
signalVector *seq0 = NULL, *seq1 = NULL, *_seq1 = NULL;
@@ -1117,7 +1150,16 @@ bool generateRACHSequence(int sps)
gRACHSequence = new CorrelationSequence;
gRACHSequence->sequence = _seq1;
gRACHSequence->buffer = data;
gRACHSequence->gain = peakDetect(*autocorr,&gRACHSequence->TOA, NULL);
gRACHSequence->gain = peakDetect(*autocorr, &toa, NULL);
/* For 1 sps only
* (Half of correlation length - 1) + midpoint of pulse shaping filer
* 20.5 = (40 / 2 - 1) + 1.5
*/
if (sps == 1)
gRACHSequence->toa = toa - 20.5;
else
gRACHSequence->toa = 0.0;
release:
delete autocorr;
@@ -1222,6 +1264,9 @@ static int detectBurst(signalVector &burst,
if (sps == 4)
*amp = *amp * complex(0.0, 1.0);
/* Compensate for residuate time lag */
*toa = *toa - sync->toa;
return 1;
}
@@ -1365,7 +1410,7 @@ SoftVector *demodulateBurst(signalVector &rxBurst, int sps,
// shift up by a quarter of a frequency
// ignore starting phase, since spec allows for discontinuous phase
GMSKReverseRotate(*shapedBurst);
GMSKReverseRotate(*shapedBurst, sps);
// run through slicer
if (sps > 1) {
@@ -1508,8 +1553,8 @@ SoftVector *equalizeBurst(signalVector &rxBurst,
signalVector::iterator dPtr = postForward->begin();
signalVector::iterator dBackPtr;
signalVector::iterator rotPtr = GMSKRotation->begin();
signalVector::iterator revRotPtr = GMSKReverseRotation->begin();
signalVector::iterator rotPtr = GMSKRotationN->begin();
signalVector::iterator revRotPtr = GMSKReverseRotationN->begin();
signalVector *DFEoutput = new signalVector(postForward->size());
signalVector::iterator DFEItr = DFEoutput->begin();
@@ -1548,3 +1593,23 @@ SoftVector *equalizeBurst(signalVector &rxBurst,
return burstBits;
}
bool sigProcLibSetup(int sps)
{
if ((sps != 1) && (sps != 4))
return false;
initTrigTables();
initGMSKRotationTables(sps);
GSMPulse1 = generateGSMPulse(1, 2);
if (sps > 1)
GSMPulse = generateGSMPulse(sps, 2);
if (!generateRACHSequence(1)) {
sigProcLibDestroy();
return false;
}
return true;
}