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osmo-trx/Transceiver52M/sigProcLib.cpp

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/*
* Copyright 2008, 2011 Free Software Foundation, Inc.
*
* SPDX-License-Identifier: AGPL-3.0+
*
* This software is distributed under the terms of the GNU Affero Public License.
* See the COPYING file in the main directory for details.
*
* This use of this software may be subject to additional restrictions.
* See the LEGAL file in the main directory for details.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "sigProcLib.h"
#include "GSMCommon.h"
#include "Logger.h"
#include "Resampler.h"
extern "C" {
#include <osmocom/core/panic.h>
#include "convolve.h"
#include "scale.h"
#include "mult.h"
}
using namespace GSM;
#define TABLESIZE 1024
#define DELAYFILTS 64
/* Clipping detection threshold */
#define CLIP_THRESH 30000.0f
/** Lookup tables for trigonometric approximation */
static float sincTable[TABLESIZE+1]; // add 1 element for wrap around
/** Constants */
static const float M_PI_F = (float)M_PI;
/* Precomputed rotation vectors */
static signalVector *GMSKRotation4 = NULL;
static signalVector *GMSKReverseRotation4 = NULL;
static signalVector *GMSKRotation1 = NULL;
static signalVector *GMSKReverseRotation1 = NULL;
/* Precomputed fractional delay filters */
static signalVector *delayFilters[DELAYFILTS];
static const Complex<float> psk8_table[8] = {
Complex<float>(-0.70710678, 0.70710678),
Complex<float>( 0.0, -1.0),
Complex<float>( 0.0, 1.0),
Complex<float>( 0.70710678, -0.70710678),
Complex<float>(-1.0, 0.0),
Complex<float>(-0.70710678, -0.70710678),
Complex<float>( 0.70710678, 0.70710678),
Complex<float>( 1.0, 0.0),
};
/* Downsampling filterbank - 4 SPS to 1 SPS */
#define DOWNSAMPLE_IN_LEN 624
#define DOWNSAMPLE_OUT_LEN 156
static Resampler *dnsampler = NULL;
/*
* RACH and midamble correlation waveforms. Store the buffer separately
* because we need to allocate it explicitly outside of the signal vector
* constructor. This is because C++ (prior to C++11) is unable to natively
* perform 16-byte memory alignment required by many SSE instructions.
*/
struct CorrelationSequence {
CorrelationSequence() : sequence(NULL), buffer(NULL), toa(0.0)
{
}
~CorrelationSequence()
{
delete sequence;
}
signalVector *sequence;
void *buffer;
float toa;
complex gain;
};
/*
* Gaussian and empty modulation pulses. Like the correlation sequences,
* store the runtime (Gaussian) buffer separately because of needed alignment
* for SSE instructions.
*/
struct PulseSequence {
PulseSequence() : c0(NULL), c1(NULL), c0_inv(NULL), empty(NULL)
{
}
~PulseSequence()
{
delete c0;
delete c1;
delete c0_inv;
delete empty;
}
signalVector *c0;
signalVector *c1;
signalVector *c0_inv;
signalVector *empty;
};
static CorrelationSequence *gMidambles[] = {NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL};
static CorrelationSequence *gEdgeMidambles[] = {NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL};
static CorrelationSequence *gRACHSequences[] = {NULL,NULL,NULL};
static PulseSequence *GSMPulse1 = NULL;
static PulseSequence *GSMPulse4 = NULL;
void sigProcLibDestroy()
{
for (int i = 0; i < 8; i++) {
delete gMidambles[i];
delete gEdgeMidambles[i];
gMidambles[i] = NULL;
gEdgeMidambles[i] = NULL;
}
for (int i = 0; i < DELAYFILTS; i++) {
delete delayFilters[i];
delayFilters[i] = NULL;
}
for (int i = 0; i < 3; i++) {
delete gRACHSequences[i];
gRACHSequences[i] = NULL;
}
delete GMSKRotation1;
delete GMSKReverseRotation1;
delete GMSKRotation4;
delete GMSKReverseRotation4;
delete GSMPulse1;
delete GSMPulse4;
delete dnsampler;
GMSKRotation1 = NULL;
GMSKRotation4 = NULL;
GMSKReverseRotation4 = NULL;
GMSKReverseRotation1 = NULL;
GSMPulse1 = NULL;
GSMPulse4 = NULL;
}
static float vectorNorm2(const signalVector &x)
{
signalVector::const_iterator xPtr = x.begin();
float Energy = 0.0;
for (;xPtr != x.end();xPtr++) {
Energy += xPtr->norm2();
}
return Energy;
}
/*
* Initialize 4 sps and 1 sps rotation tables
*/
static void initGMSKRotationTables()
{
size_t len1 = 157, len4 = 625;
GMSKRotation4 = new signalVector(len4);
GMSKReverseRotation4 = new signalVector(len4);
signalVector::iterator rotPtr = GMSKRotation4->begin();
signalVector::iterator revPtr = GMSKReverseRotation4->begin();
auto phase = 0.0;
while (rotPtr != GMSKRotation4->end()) {
*rotPtr++ = complex(cos(phase), sin(phase));
*revPtr++ = complex(cos(-phase), sin(-phase));
phase += M_PI / 2.0 / 4.0;
}
GMSKRotation1 = new signalVector(len1);
GMSKReverseRotation1 = new signalVector(len1);
rotPtr = GMSKRotation1->begin();
revPtr = GMSKReverseRotation1->begin();
phase = 0.0;
while (rotPtr != GMSKRotation1->end()) {
*rotPtr++ = complex(cos(phase), sin(phase));
*revPtr++ = complex(cos(-phase), sin(-phase));
phase += M_PI / 2.0;
}
}
static void GMSKRotate(signalVector &x, int sps)
{
#if HAVE_NEON
size_t len;
signalVector *a, *b, *out;
a = &x;
out = &x;
len = out->size();
if (len == 157)
len--;
if (sps == 1)
b = GMSKRotation1;
else
b = GMSKRotation4;
mul_complex((float *) out->begin(),
(float *) a->begin(),
(float *) b->begin(), len);
#else
signalVector::iterator rotPtr, xPtr = x.begin();
if (sps == 1)
rotPtr = GMSKRotation1->begin();
else
rotPtr = GMSKRotation4->begin();
if (x.isReal()) {
while (xPtr < x.end()) {
*xPtr = *rotPtr++ * (xPtr->real());
xPtr++;
}
}
else {
while (xPtr < x.end()) {
*xPtr = *rotPtr++ * (*xPtr);
xPtr++;
}
}
#endif
}
static bool GMSKReverseRotate(signalVector &x, int sps)
{
signalVector::iterator rotPtr, xPtr= x.begin();
if (sps == 1)
rotPtr = GMSKReverseRotation1->begin();
else if (sps == 4)
rotPtr = GMSKReverseRotation4->begin();
else
return false;
if (x.isReal()) {
while (xPtr < x.end()) {
*xPtr = *rotPtr++ * (xPtr->real());
xPtr++;
}
}
else {
while (xPtr < x.end()) {
*xPtr = *rotPtr++ * (*xPtr);
xPtr++;
}
}
return true;
}
/** Convolution type indicator */
enum ConvType {
START_ONLY,
NO_DELAY,
CUSTOM,
UNDEFINED,
};
static signalVector *convolve(const signalVector *x, const signalVector *h,
signalVector *y, ConvType spanType,
size_t start = 0, size_t len = 0)
{
int rc;
size_t head = 0, tail = 0;
bool alloc = false, append = false;
const signalVector *_x = NULL;
if (!x || !h)
return NULL;
switch (spanType) {
case START_ONLY:
start = 0;
head = h->size() - 1;
len = x->size();
if (x->getStart() < head)
append = true;
break;
case NO_DELAY:
start = h->size() / 2;
head = start;
tail = start;
len = x->size();
append = true;
break;
case CUSTOM:
if (start < h->size() - 1) {
head = h->size() - start;
append = true;
}
if (start + len > x->size()) {
tail = start + len - x->size();
append = true;
}
break;
default:
return NULL;
}
/*
* Error if the output vector is too small. Create the output vector
* if the pointer is NULL.
*/
if (y && (len > y->size()))
return NULL;
if (!y) {
y = new signalVector(len, convolve_h_alloc, free);
alloc = true;
}
/* Prepend or post-pend the input vector if the parameters require it */
if (append)
_x = new signalVector(*x, head, tail);
else
_x = x;
/*
* Four convolve types:
* 1. Complex-Real (aligned)
* 2. Complex-Complex (aligned)
* 3. Complex-Real (!aligned)
* 4. Complex-Complex (!aligned)
*/
if (h->isReal() && h->isAligned()) {
rc = convolve_real((float *) _x->begin(), _x->size(),
(float *) h->begin(), h->size(),
(float *) y->begin(), y->size(),
start, len);
} else if (!h->isReal() && h->isAligned()) {
rc = convolve_complex((float *) _x->begin(), _x->size(),
(float *) h->begin(), h->size(),
(float *) y->begin(), y->size(),
start, len);
} else if (h->isReal() && !h->isAligned()) {
rc = base_convolve_real((float *) _x->begin(), _x->size(),
(float *) h->begin(), h->size(),
(float *) y->begin(), y->size(),
start, len);
} else if (!h->isReal() && !h->isAligned()) {
rc = base_convolve_complex((float *) _x->begin(), _x->size(),
(float *) h->begin(), h->size(),
(float *) y->begin(), y->size(),
start, len);
} else {
rc = -1;
}
if (append)
delete _x;
if (rc < 0) {
if (alloc)
delete y;
return NULL;
}
return y;
}
/*
* Generate static EDGE linear equalizer. This equalizer is not adaptive.
* Filter taps are generated from the inverted 1 SPS impulse response of
* the EDGE pulse shape captured after the downsampling filter.
*/
static bool generateInvertC0Pulse(PulseSequence *pulse)
{
if (!pulse)
return false;
pulse->c0_inv = new signalVector((complex *) convolve_h_alloc(5), 0, 5, convolve_h_alloc, free);
pulse->c0_inv->isReal(true);
pulse->c0_inv->setAligned(false);
signalVector::iterator xP = pulse->c0_inv->begin();
*xP++ = 0.15884;
*xP++ = -0.43176;
*xP++ = 1.00000;
*xP++ = -0.42608;
*xP++ = 0.14882;
return true;
}
static bool generateC1Pulse(int sps, PulseSequence *pulse)
{
int len;
if (!pulse)
return false;
switch (sps) {
case 4:
len = 8;
break;
default:
return false;
}
pulse->c1 = new signalVector((complex *) convolve_h_alloc(len), 0, len, convolve_h_alloc, free);
pulse->c1->isReal(true);
/* Enable alignment for SSE usage */
pulse->c1->setAligned(true);
signalVector::iterator xP = pulse->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;
}
static PulseSequence *generateGSMPulse(int sps)
{
int len;
float arg, avg, center;
PulseSequence *pulse;
if ((sps != 1) && (sps != 4))
return NULL;
/* Store a single tap filter used for correlation sequence generation */
pulse = new PulseSequence();
pulse->empty = new signalVector(1);
pulse->empty->isReal(true);
*(pulse->empty->begin()) = 1.0f;
/*
* For 4 samples-per-symbol use a precomputed single pulse Laurent
* approximation. This should yields below 2 degrees of phase error at
* the modulator output. Use the existing pulse approximation for all
* other oversampling factors.
*/
switch (sps) {
case 4:
len = 16;
break;
case 1:
default:
len = 4;
}
pulse->c0 = new signalVector((complex *) convolve_h_alloc(len), 0, len, convolve_h_alloc, free);
pulse->c0->isReal(true);
/* Enable alingnment for SSE usage */
pulse->c0->setAligned(true);
signalVector::iterator xP = pulse->c0->begin();
if (sps == 4) {
*xP++ = 0.0;
*xP++ = 4.46348606e-03;
*xP++ = 2.84385729e-02;
*xP++ = 1.03184855e-01;
*xP++ = 2.56065552e-01;
*xP++ = 4.76375085e-01;
*xP++ = 7.05961177e-01;
*xP++ = 8.71291644e-01;
*xP++ = 9.29453645e-01;
*xP++ = 8.71291644e-01;
*xP++ = 7.05961177e-01;
*xP++ = 4.76375085e-01;
*xP++ = 2.56065552e-01;
*xP++ = 1.03184855e-01;
*xP++ = 2.84385729e-02;
*xP++ = 4.46348606e-03;
generateC1Pulse(sps, pulse);
} else {
center = (float) (len - 1.0) / 2.0;
/* GSM pulse approximation */
for (int i = 0; i < len; i++) {
arg = ((float) i - center) / (float) sps;
*xP++ = 0.96 * exp(-1.1380 * arg * arg -
0.527 * arg * arg * arg * arg);
}
avg = sqrtf(vectorNorm2(*pulse->c0) / sps);
xP = pulse->c0->begin();
for (int i = 0; i < len; i++)
*xP++ /= avg;
}
/*
* Current form of the EDGE equalization filter non-realizable at 4 SPS.
* Load the onto both 1 SPS and 4 SPS objects for convenience. Note that
* the EDGE demodulator downsamples to 1 SPS prior to equalization.
*/
generateInvertC0Pulse(pulse);
return pulse;
}
/* Convert -1..+1 soft bits to 0..1 soft bits */
void vectorSlicer(float *dest, const float *src, size_t len)
{
size_t i;
for (i = 0; i < len; i++) {
dest[i] = 0.5 * (src[i] + 1.0f);
if (dest[i] > 1.0)
dest[i] = 1.0;
else if (dest[i] < 0.0)
dest[i] = 0.0;
}
}
static signalVector *rotateBurst(const BitVector &wBurst,
int guardPeriodLength, int sps)
{
int burst_len;
signalVector *pulse, rotated;
signalVector::iterator itr;
pulse = GSMPulse1->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, sps);
rotated.isReal(false);
/* Dummy filter operation */
return convolve(&rotated, pulse, NULL, START_ONLY);
}
static void rotateBurst2(signalVector &burst, double phase)
{
Complex<float> rot = Complex<float>(cos(phase), sin(phase));
for (size_t i = 0; i < burst.size(); i++)
burst[i] = burst[i] * rot;
}
/*
* 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, sps = 4;
float phase;
signalVector *c0_pulse, *c1_pulse, *c0_shaped, *c1_shaped;
signalVector::iterator c0_itr, c1_itr;
c0_pulse = GSMPulse4->c0;
c1_pulse = GSMPulse4->c1;
if (bits.size() > 156)
return NULL;
burst_len = 625;
signalVector c0_burst(burst_len, c0_pulse->size());
c0_burst.isReal(true);
c0_itr = c0_burst.begin();
signalVector c1_burst(burst_len, c1_pulse->size());
c1_itr = c1_burst.begin();
/* Padded differential tail 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 tail bits */
*c0_itr = 2.0 * (0x00 & 0x01) - 1.0;
/* Generate C0 phase coefficients */
GMSKRotate(c0_burst, sps);
c0_burst.isReal(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 *rotateEdgeBurst(const signalVector &symbols, int sps)
{
signalVector *burst;
signalVector::iterator burst_itr;
burst = new signalVector(symbols.size() * sps);
burst_itr = burst->begin();
for (size_t i = 0; i < symbols.size(); i++) {
float phase = i * 3.0f * M_PI / 8.0f;
Complex<float> rot = Complex<float>(cos(phase), sin(phase));
*burst_itr = symbols[i] * rot;
burst_itr += sps;
}
return burst;
}
static signalVector *derotateEdgeBurst(const signalVector &symbols, int sps)
{
signalVector *burst;
signalVector::iterator burst_itr;
if (symbols.size() % sps)
return NULL;
burst = new signalVector(symbols.size() / sps);
burst_itr = burst->begin();
for (size_t i = 0; i < burst->size(); i++) {
float phase = (float) (i % 16) * 3.0f * M_PI / 8.0f;
Complex<float> rot = Complex<float>(cosf(phase), -sinf(phase));
*burst_itr = symbols[sps * i] * rot;
burst_itr++;
}
return burst;
}
static signalVector *mapEdgeSymbols(const BitVector &bits)
{
if (bits.size() % 3)
return NULL;
signalVector *symbols = new signalVector(bits.size() / 3);
for (size_t i = 0; i < symbols->size(); i++) {
unsigned index = (((unsigned) bits[3 * i + 0] & 0x01) << 0) |
(((unsigned) bits[3 * i + 1] & 0x01) << 1) |
(((unsigned) bits[3 * i + 2] & 0x01) << 2);
(*symbols)[i] = psk8_table[index];
}
return symbols;
}
/*
* EDGE 8-PSK rotate and pulse shape
*
* Delay the EDGE downlink bursts by one symbol in order to match GMSK pulse
* shaping group delay. The difference in group delay arises from the dual
* pulse filter combination of the GMSK Laurent representation whereas 8-PSK
* uses a single pulse linear filter.
*/
static signalVector *shapeEdgeBurst(const signalVector &symbols)
{
size_t nsyms, nsamps = 625, sps = 4;
signalVector::iterator burst_itr;
nsyms = symbols.size();
if (nsyms * sps > nsamps)
nsyms = 156;
signalVector burst(nsamps, GSMPulse4->c0->size());
/* Delay burst by 1 symbol */
burst_itr = burst.begin() + sps;
for (size_t i = 0; i < nsyms; i++) {
float phase = i * 3.0f * M_PI / 8.0f;
Complex<float> rot = Complex<float>(cos(phase), sin(phase));
*burst_itr = symbols[i] * rot;
burst_itr += sps;
}
/* Single Gaussian pulse approximation shaping */
return convolve(&burst, GSMPulse4->c0, NULL, START_ONLY);
}
/*
* Generate a random GSM normal burst.
*/
signalVector *genRandNormalBurst(int tsc, int sps, int tn)
{
if ((tsc < 0) || (tsc > 7) || (tn < 0) || (tn > 7))
return NULL;
if ((sps != 1) && (sps != 4))
return NULL;
int i = 0;
BitVector bits(148);
/* Tail bits */
for (; i < 3; i++)
bits[i] = 0;
/* Random bits */
for (; i < 60; i++)
bits[i] = rand() % 2;
/* Stealing bit */
bits[i++] = 0;
/* Training sequence */
for (int n = 0; i < 87; i++, n++)
bits[i] = gTrainingSequence[tsc][n];
/* Stealing bit */
bits[i++] = 0;
/* Random bits */
for (; i < 145; i++)
bits[i] = rand() % 2;
/* Tail bits */
for (; i < 148; i++)
bits[i] = 0;
int guard = 8 + !(tn % 4);
return modulateBurst(bits, guard, sps);
}
/*
* Generate a random GSM access burst.
*/
signalVector *genRandAccessBurst(int delay, int sps, int tn)
{
if ((tn < 0) || (tn > 7))
return NULL;
if ((sps != 1) && (sps != 4))
return NULL;
if (delay > 68)
return NULL;
int i = 0;
BitVector bits(88 + delay);
/* delay */
for (; i < delay; i++)
bits[i] = 0;
/* head and synch bits */
for (int n = 0; i < 49+delay; i++, n++)
bits[i] = gRACHBurst[n];
/* Random bits */
for (; i < 85+delay; i++)
bits[i] = rand() % 2;
/* Tail bits */
for (; i < 88+delay; i++)
bits[i] = 0;
int guard = 68-delay + !(tn % 4);
return modulateBurst(bits, guard, sps);
}
signalVector *generateEmptyBurst(int sps, int tn)
{
if ((tn < 0) || (tn > 7))
return NULL;
if (sps == 4)
return new signalVector(625);
else if (sps == 1)
return new signalVector(148 + 8 + !(tn % 4));
else
return NULL;
}
signalVector *generateDummyBurst(int sps, int tn)
{
if (((sps != 1) && (sps != 4)) || (tn < 0) || (tn > 7))
return NULL;
return modulateBurst(gDummyBurst, 8 + !(tn % 4), sps);
}
/*
* Generate a random 8-PSK EDGE burst. Only 4 SPS is supported with
* the returned burst being 625 samples in length.
*/
signalVector *generateEdgeBurst(int tsc)
{
int tail = 9 / 3;
int data = 174 / 3;
int train = 78 / 3;
if ((tsc < 0) || (tsc > 7))
return NULL;
signalVector burst(148);
const BitVector *midamble = &gEdgeTrainingSequence[tsc];
/* Tail */
int n, i = 0;
for (; i < tail; i++)
burst[i] = psk8_table[7];
/* Body */
for (; i < tail + data; i++)
burst[i] = psk8_table[rand() % 8];
/* TSC */
for (n = 0; i < tail + data + train; i++, n++) {
unsigned index = (((unsigned) (*midamble)[3 * n + 0] & 0x01) << 0) |
(((unsigned) (*midamble)[3 * n + 1] & 0x01) << 1) |
(((unsigned) (*midamble)[3 * n + 2] & 0x01) << 2);
burst[i] = psk8_table[index];
}
/* Body */
for (; i < tail + data + train + data; i++)
burst[i] = psk8_table[rand() % 8];
/* Tail */
for (; i < tail + data + train + data + tail; i++)
burst[i] = psk8_table[7];
return shapeEdgeBurst(burst);
}
/*
* Modulate 8-PSK burst. When empty pulse shaping (rotation only)
* is enabled, the output vector length will be bit sequence length
* times the SPS value. When pulse shaping is enabled, the output
* vector length is fixed at 625 samples (156.25 symbols at 4 SPS).
* Pulse shaped bit sequences that go beyond one burst are truncated.
* Pulse shaping at anything but 4 SPS is not supported.
*/
signalVector *modulateEdgeBurst(const BitVector &bits,
int sps, bool empty)
{
signalVector *shape, *burst;
if ((sps != 4) && !empty)
return NULL;
burst = mapEdgeSymbols(bits);
if (!burst)
return NULL;
if (empty)
shape = rotateEdgeBurst(*burst, sps);
else
shape = shapeEdgeBurst(*burst);
delete burst;
return shape;
}
static signalVector *modulateBurstBasic(const BitVector &bits,
int guard_len, int sps)
{
int burst_len;
signalVector *pulse;
signalVector::iterator burst_itr;
if (sps == 1)
pulse = GSMPulse1->c0;
else
pulse = GSMPulse4->c0;
burst_len = sps * (bits.size() + guard_len);
signalVector burst(burst_len, pulse->size());
burst.isReal(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, sps);
burst.isReal(false);
/* Single Gaussian pulse approximation shaping */
return convolve(&burst, pulse, NULL, START_ONLY);
}
/* Assume input bits are not differentially encoded */
signalVector *modulateBurst(const BitVector &wBurst, int guardPeriodLength,
int sps, bool emptyPulse)
{
if (emptyPulse)
return rotateBurst(wBurst, guardPeriodLength, sps);
else if (sps == 4)
return modulateBurstLaurent(wBurst);
else
return modulateBurstBasic(wBurst, guardPeriodLength, sps);
}
static void generateSincTable()
{
for (int i = 0; i < TABLESIZE; i++) {
auto x = (double) i / TABLESIZE * 8 * M_PI;
auto y = sin(x) / x;
sincTable[i] = std::isnan(y) ? 1.0 : y;
}
}
static float sinc(float x)
{
if (fabs(x) >= 8 * M_PI)
return 0.0;
int index = (int) floorf(fabs(x) / (8 * M_PI) * TABLESIZE);
return sincTable[index];
}
/*
* Create fractional delay filterbank with Blackman-harris windowed
* sinc function generator. The number of filters generated is specified
* by the DELAYFILTS value.
*/
static void generateDelayFilters()
{
int h_len = 20;
complex *data;
signalVector *h;
signalVector::iterator itr;
float k, sum;
float a0 = 0.35875;
float a1 = 0.48829;
float a2 = 0.14128;
float a3 = 0.01168;
for (int i = 0; i < DELAYFILTS; i++) {
data = (complex *) convolve_h_alloc(h_len);
h = new signalVector(data, 0, h_len, convolve_h_alloc, free);
h->setAligned(true);
h->isReal(true);
sum = 0.0;
itr = h->end();
for (int n = 0; n < h_len; n++) {
k = (float) n;
*--itr = (complex) sinc(M_PI_F *
(k - (float) h_len / 2.0 - (float) i / DELAYFILTS));
*itr *= a0 -
a1 * cos(2 * M_PI * n / (h_len - 1)) +
a2 * cos(4 * M_PI * n / (h_len - 1)) -
a3 * cos(6 * M_PI * n / (h_len - 1));
sum += itr->real();
}
itr = h->begin();
for (int n = 0; n < h_len; n++)
*itr++ /= sum;
delayFilters[i] = h;
}
}
signalVector *delayVector(const signalVector *in, signalVector *out, float delay)
{
int whole, index;
float frac;
signalVector *h, *shift, *fshift = NULL;
whole = floor(delay);
frac = delay - whole;
/* Sinc interpolated fractional shift (if allowable) */
if (fabs(frac) > 1e-2) {
index = floorf(frac * (float) DELAYFILTS);
h = delayFilters[index];
fshift = convolve(in, h, NULL, NO_DELAY);
if (!fshift)
return NULL;
}
if (!fshift)
shift = new signalVector(*in);
else
shift = fshift;
/* Integer sample shift */
if (whole < 0) {
whole = -whole;
signalVector::iterator wBurstItr = shift->begin();
signalVector::iterator shiftedItr = shift->begin() + whole;
while (shiftedItr < shift->end())
*wBurstItr++ = *shiftedItr++;
while (wBurstItr < shift->end())
*wBurstItr++ = 0.0;
} else if (whole >= 0) {
signalVector::iterator wBurstItr = shift->end() - 1;
signalVector::iterator shiftedItr = shift->end() - 1 - whole;
while (shiftedItr >= shift->begin())
*wBurstItr-- = *shiftedItr--;
while (wBurstItr >= shift->begin())
*wBurstItr-- = 0.0;
}
if (!out)
return shift;
out->clone(*shift);
delete shift;
return out;
}
static complex interpolatePoint(const signalVector &inSig, float ix)
{
int start = (int) (floor(ix) - 10);
if (start < 0) start = 0;
int end = (int) (floor(ix) + 11);
if ((unsigned) end > inSig.size()-1) end = inSig.size()-1;
complex pVal = 0.0;
if (!inSig.isReal()) {
for (int i = start; i < end; i++)
pVal += inSig[i] * sinc(M_PI_F*(i-ix));
}
else {
for (int i = start; i < end; i++)
pVal += inSig[i].real() * sinc(M_PI_F*(i-ix));
}
return pVal;
}
static complex fastPeakDetect(const signalVector &rxBurst, float *index)
{
float val, max = 0.0f;
complex amp;
int _index = -1;
for (size_t i = 0; i < rxBurst.size(); i++) {
val = rxBurst[i].norm2();
if (val > max) {
max = val;
_index = i;
amp = rxBurst[i];
}
}
if (index)
*index = (float) _index;
return amp;
}
static complex peakDetect(const signalVector &rxBurst,
float *peakIndex, float *avgPwr)
{
complex maxVal = 0.0;
float maxIndex = -1;
float sumPower = 0.0;
for (unsigned int i = 0; i < rxBurst.size(); i++) {
float samplePower = rxBurst[i].norm2();
if (samplePower > maxVal.real()) {
maxVal = samplePower;
maxIndex = i;
}
sumPower += samplePower;
}
// interpolate around the peak
// to save computation, we'll use early-late balancing
float earlyIndex = maxIndex-1;
float lateIndex = maxIndex+1;
float incr = 0.5;
while (incr > 1.0/1024.0) {
complex earlyP = interpolatePoint(rxBurst,earlyIndex);
complex lateP = interpolatePoint(rxBurst,lateIndex);
if (earlyP < lateP)
earlyIndex += incr;
else if (earlyP > lateP)
earlyIndex -= incr;
else break;
incr /= 2.0;
lateIndex = earlyIndex + 2.0;
}
maxIndex = earlyIndex + 1.0;
maxVal = interpolatePoint(rxBurst,maxIndex);
if (peakIndex!=NULL)
*peakIndex = maxIndex;
if (avgPwr!=NULL)
*avgPwr = (sumPower-maxVal.norm2()) / (rxBurst.size()-1);
return maxVal;
}
void scaleVector(signalVector &x,
complex scale)
{
#ifdef HAVE_NEON
int len = x.size();
scale_complex((float *) x.begin(),
(float *) x.begin(),
(float *) &scale, len);
#else
signalVector::iterator xP = x.begin();
signalVector::iterator xPEnd = x.end();
if (!x.isReal()) {
while (xP < xPEnd) {
*xP = *xP * scale;
xP++;
}
}
else {
while (xP < xPEnd) {
*xP = xP->real() * scale;
xP++;
}
}
#endif
}
/** in-place conjugation */
static void conjugateVector(signalVector &x)
{
if (x.isReal()) return;
signalVector::iterator xP = x.begin();
signalVector::iterator xPEnd = x.end();
while (xP < xPEnd) {
*xP = xP->conj();
xP++;
}
}
static bool generateMidamble(int sps, int tsc)
{
bool status = true;
float toa;
complex *data = NULL;
signalVector *autocorr = NULL, *midamble = NULL;
signalVector *midMidamble = NULL, *_midMidamble = NULL;
if ((tsc < 0) || (tsc > 7))
return false;
delete gMidambles[tsc];
/* Use middle 16 bits of each TSC. Correlation sequence is not pulse shaped */
midMidamble = modulateBurst(gTrainingSequence[tsc].segment(5,16), 0, sps, true);
if (!midMidamble)
return false;
/* Simulated receive sequence is pulse shaped */
midamble = modulateBurst(gTrainingSequence[tsc], 0, sps, false);
if (!midamble) {
status = false;
goto release;
}
// NOTE: Because ideal TSC 16-bit midamble is 66 symbols into burst,
// the ideal TSC has an + 180 degree phase shift,
// due to the pi/2 frequency shift, that
// needs to be accounted for.
// 26-midamble is 61 symbols into burst, has +90 degree phase shift.
scaleVector(*midMidamble, complex(-1.0, 0.0));
scaleVector(*midamble, complex(0.0, 1.0));
conjugateVector(*midMidamble);
/* For SSE alignment, reallocate the midamble sequence on 16-byte boundary */
data = (complex *) convolve_h_alloc(midMidamble->size());
_midMidamble = new signalVector(data, 0, midMidamble->size(), convolve_h_alloc, free);
_midMidamble->setAligned(true);
midMidamble->copyTo(*_midMidamble);
autocorr = convolve(midamble, _midMidamble, NULL, NO_DELAY);
if (!autocorr) {
status = false;
goto release;
}
gMidambles[tsc] = new CorrelationSequence;
gMidambles[tsc]->sequence = _midMidamble;
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;
delete midamble;
delete midMidamble;
if (!status) {
delete _midMidamble;
free(data);
gMidambles[tsc] = NULL;
}
return status;
}
static CorrelationSequence *generateEdgeMidamble(int tsc)
{
complex *data = NULL;
signalVector *midamble = NULL, *_midamble = NULL;
CorrelationSequence *seq;
if ((tsc < 0) || (tsc > 7))
return NULL;
/* Use middle 48 bits of each TSC. Correlation sequence is not pulse shaped */
const BitVector *bits = &gEdgeTrainingSequence[tsc];
midamble = modulateEdgeBurst(bits->segment(15, 48), 1, true);
if (!midamble)
return NULL;
conjugateVector(*midamble);
data = (complex *) convolve_h_alloc(midamble->size());
_midamble = new signalVector(data, 0, midamble->size(), convolve_h_alloc, free);
_midamble->setAligned(true);
midamble->copyTo(*_midamble);
/* Channel gain is an empirically measured value */
seq = new CorrelationSequence;
seq->sequence = _midamble;
seq->gain = Complex<float>(-19.6432, 19.5006) / 1.18;
seq->toa = 0;
delete midamble;
return seq;
}
static bool generateRACHSequence(CorrelationSequence **seq, const BitVector &bv, int sps)
{
bool status = true;
float toa;
complex *data = NULL;
signalVector *autocorr = NULL;
signalVector *seq0 = NULL, *seq1 = NULL, *_seq1 = NULL;
if (*seq != NULL)
delete *seq;
seq0 = modulateBurst(bv, 0, sps, false);
if (!seq0)
return false;
seq1 = modulateBurst(bv.segment(0, 40), 0, sps, true);
if (!seq1) {
status = false;
goto release;
}
conjugateVector(*seq1);
/* For SSE alignment, reallocate the midamble sequence on 16-byte boundary */
data = (complex *) convolve_h_alloc(seq1->size());
_seq1 = new signalVector(data, 0, seq1->size(), convolve_h_alloc, free);
_seq1->setAligned(true);
seq1->copyTo(*_seq1);
autocorr = convolve(seq0, _seq1, autocorr, NO_DELAY);
if (!autocorr) {
status = false;
goto release;
}
*seq = new CorrelationSequence;
(*seq)->sequence = _seq1;
(*seq)->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)
(*seq)->toa = toa - 20.5;
else
(*seq)->toa = 0.0;
release:
delete autocorr;
delete seq0;
delete seq1;
if (!status) {
delete _seq1;
free(data);
*seq = NULL;
}
return status;
}
/*
* Peak-to-average computation +/- range from peak in symbols
*/
#define COMPUTE_PEAK_MIN 2
#define COMPUTE_PEAK_MAX 5
/*
* Minimum number of values needed to compute peak-to-average
*/
#define COMPUTE_PEAK_CNT 5
static float computePeakRatio(signalVector *corr,
int sps, float toa, complex amp)
{
int num = 0;
complex *peak;
float rms, avg = 0.0;
/* Check for bogus results */
if ((toa < 0.0) || (toa > corr->size()))
return 0.0;
peak = corr->begin() + (int) rint(toa);
for (int i = COMPUTE_PEAK_MIN * sps; i <= COMPUTE_PEAK_MAX * sps; i++) {
if (peak - i >= corr->begin()) {
avg += (peak - i)->norm2();
num++;
}
if (peak + i < corr->end()) {
avg += (peak + i)->norm2();
num++;
}
}
if (num < COMPUTE_PEAK_CNT)
return 0.0;
rms = sqrtf(avg / (float) num) + 0.00001;
return (amp.abs()) / rms;
}
float energyDetect(const signalVector &rxBurst, unsigned windowLength)
{
signalVector::const_iterator windowItr = rxBurst.begin(); //+rxBurst.size()/2 - 5*windowLength/2;
float energy = 0.0;
if (windowLength == 0) return 0.0;
if (windowLength > rxBurst.size()) windowLength = rxBurst.size();
for (unsigned i = 0; i < windowLength; i++) {
energy += windowItr->norm2();
windowItr+=4;
}
return energy/windowLength;
}
static signalVector *downsampleBurst(const signalVector &burst)
{
signalVector in(DOWNSAMPLE_IN_LEN, dnsampler->len());
signalVector *out = new signalVector(DOWNSAMPLE_OUT_LEN);
burst.copyToSegment(in, 0, DOWNSAMPLE_IN_LEN);
if (dnsampler->rotate((float *) in.begin(), DOWNSAMPLE_IN_LEN,
(float *) out->begin(), DOWNSAMPLE_OUT_LEN) < 0) {
delete out;
out = NULL;
}
return out;
};
/*
* Computes C/I (Carrier-to-Interference ratio) in dB (deciBels).
* It is computed from the training sequence of each received burst,
* by comparing the "ideal" training sequence with the actual one.
*/
static float computeCI(const signalVector *burst, const CorrelationSequence *sync,
float toa, int start, const complex &xcorr)
{
const int N = sync->sequence->size();
float S, C;
/* Integer position where the sequence starts */
const int ps = start + 1 - N + (int)roundf(toa);
/* Estimate Signal power */
S = 0.0f;
for (int i=0, j=ps; i<(int)N; i++,j++)
S += (*burst)[j].norm2();
S /= N;
/* Esimate Carrier power */
C = xcorr.norm2() / ((N - 1) * sync->gain.abs());
/* Interference = Signal - Carrier, so C/I = C / (S - C) */
return 3.0103f * log2f(C / (S - C));
}
/*
* Detect a burst based on correlation and peak-to-average ratio
*
* For one sampler-per-symbol, perform fast peak detection (no interpolation)
* for initial gating. We do this because energy detection should be disabled.
* For higher oversampling values, we assume the energy detector is in place
* and we run full interpolating peak detection.
*/
static int detectBurst(const signalVector &burst,
signalVector &corr, const CorrelationSequence *sync,
float thresh, int sps, int start, int len,
struct estim_burst_params *ebp)
{
const signalVector *corr_in;
signalVector *dec = NULL;
complex xcorr;
int rc = 1;
switch (sps) {
case 1:
corr_in = &burst;
break;
case 4:
dec = downsampleBurst(burst);
/* Running at the downsampled rate at this point: */
corr_in = dec;
sps = 1;
break;
default:
osmo_panic("%s:%d SPS %d not supported! Only 1 or 4 supported", __FILE__, __LINE__, sps);
}
/* Correlate */
if (!convolve(corr_in, sync->sequence, &corr,
CUSTOM, start, len)) {
rc = -1;
goto del_ret;
}
/* Peak detection - place restrictions at correlation edges */
ebp->amp = fastPeakDetect(corr, &ebp->toa);
if ((ebp->toa < 3 * sps) || (ebp->toa > len - 3 * sps)) {
rc = 0;
goto del_ret;
}
/* Peak-to-average ratio */
if (computePeakRatio(&corr, sps, ebp->toa, ebp->amp) < thresh) {
rc = 0;
goto del_ret;
}
/* Refine TOA and correlation value */
xcorr = peakDetect(corr, &ebp->toa, NULL);
/* Compute C/I */
ebp->ci = computeCI(corr_in, sync, ebp->toa, start, xcorr);
/* Normalize our channel gain */
ebp->amp = xcorr / sync->gain;
/* Compensate for residuate time lag */
ebp->toa = ebp->toa - sync->toa;
del_ret:
delete dec;
return rc;
}
static float maxAmplitude(const signalVector &burst)
{
float max = 0.0;
for (size_t i = 0; i < burst.size(); i++) {
if (fabs(burst[i].real()) > max)
max = fabs(burst[i].real());
if (fabs(burst[i].imag()) > max)
max = fabs(burst[i].imag());
}
return max;
}
/*
* RACH/Normal burst detection with clipping detection
*
* Correlation window parameters:
* target: Tail bits + burst length
* head: Search symbols before target
* tail: Search symbols after target
*/
static int detectGeneralBurst(const signalVector &rxBurst, float thresh, int sps,
int target, int head, int tail,
CorrelationSequence *sync,
struct estim_burst_params *ebp)
{
int rc, start, len;
bool clipping = false;
if ((sps != 1) && (sps != 4))
return -SIGERR_UNSUPPORTED;
// Detect potential clipping
// We still may be able to demod the burst, so we'll give it a try
// and only report clipping if we can't demod.
float maxAmpl = maxAmplitude(rxBurst);
if (maxAmpl > CLIP_THRESH) {
LOG(INFO) << "max burst amplitude: " << maxAmpl << " is above the clipping threshold: " << CLIP_THRESH << std::endl;
clipping = true;
}
start = target - head - 1;
len = head + tail;
signalVector corr(len);
rc = detectBurst(rxBurst, corr, sync,
thresh, sps, start, len, ebp);
if (rc < 0) {
return -SIGERR_INTERNAL;
} else if (!rc) {
ebp->amp = 0.0f;
ebp->toa = 0.0f;
ebp->ci = 0.0f;
return clipping?-SIGERR_CLIP:SIGERR_NONE;
}
/* Subtract forward search bits from delay */
ebp->toa -= head;
return 1;
}
/*
* RACH burst detection
*
* Correlation window parameters:
* target: Tail bits + RACH length (reduced from 41 to a multiple of 4)
* head: Search 8 symbols before target
* tail: Search 8 symbols + maximum expected delay
*/
static int detectRACHBurst(const signalVector &burst, float threshold, int sps,
unsigned max_toa, bool ext, struct estim_burst_params *ebp)
{
int rc, target, head, tail;
int i, num_seq;
target = 8 + 40;
head = 8;
tail = 8 + max_toa;
num_seq = ext ? 3 : 1;
for (i = 0; i < num_seq; i++) {
rc = detectGeneralBurst(burst, threshold, sps, target, head, tail,
gRACHSequences[i], ebp);
if (rc > 0) {
ebp->tsc = i;
break;
}
}
return rc;
}
/*
* Normal burst detection
*
* Correlation window parameters:
* target: Tail + data + mid-midamble + 1/2 remaining midamblebits
* head: Search 6 symbols before target
* tail: Search 6 symbols + maximum expected delay
*/
static int analyzeTrafficBurst(const signalVector &burst, unsigned tsc, float threshold,
int sps, unsigned max_toa, struct estim_burst_params *ebp)
{
int rc, target, head, tail;
CorrelationSequence *sync;
if (tsc > 7)
return -SIGERR_UNSUPPORTED;
target = 3 + 58 + 16 + 5;
head = 6;
tail = 6 + max_toa;
sync = gMidambles[tsc];
ebp->tsc = tsc;
rc = detectGeneralBurst(burst, threshold, sps, target, head, tail, sync, ebp);
return rc;
}
static int detectEdgeBurst(const signalVector &burst, unsigned tsc, float threshold,
int sps, unsigned max_toa, struct estim_burst_params *ebp)
{
int rc, target, head, tail;
CorrelationSequence *sync;
if (tsc > 7)
return -SIGERR_UNSUPPORTED;
target = 3 + 58 + 16 + 5;
head = 6;
tail = 6 + max_toa;
sync = gEdgeMidambles[tsc];
ebp->tsc = tsc;
rc = detectGeneralBurst(burst, threshold, sps,
target, head, tail, sync, ebp);
return rc;
}
int detectAnyBurst(const signalVector &burst, unsigned tsc, float threshold,
int sps, CorrType type, unsigned max_toa,
struct estim_burst_params *ebp)
{
int rc = 0;
switch (type) {
case EDGE:
rc = detectEdgeBurst(burst, tsc, threshold, sps, max_toa, ebp);
if (rc > 0)
break;
else
type = TSC;
case TSC:
rc = analyzeTrafficBurst(burst, tsc, threshold, sps, max_toa, ebp);
break;
case EXT_RACH:
case RACH:
rc = detectRACHBurst(burst, threshold, sps, max_toa, type == EXT_RACH, ebp);
break;
default:
LOG(ERR) << "Invalid correlation type";
}
if (rc > 0)
return type;
return rc;
}
/*
* Soft 8-PSK decoding using Manhattan distance metric
*/
static SoftVector *softSliceEdgeBurst(signalVector &burst)
{
size_t nsyms = 148;
if (burst.size() < nsyms)
return NULL;
signalVector::iterator itr;
SoftVector *bits = new SoftVector(nsyms * 3);
/*
* Bits 0 and 1 - First and second bits of the symbol respectively
*/
rotateBurst2(burst, -M_PI / 8.0);
itr = burst.begin();
for (size_t i = 0; i < nsyms; i++) {
(*bits)[3 * i + 0] = -itr->imag();
(*bits)[3 * i + 1] = itr->real();
itr++;
}
/*
* Bit 2 - Collapse symbols into quadrant 0 (positive X and Y).
* Decision area is then simplified to X=Y axis. Rotate again to
* place decision boundary on X-axis.
*/
itr = burst.begin();
for (size_t i = 0; i < burst.size(); i++) {
burst[i] = Complex<float>(fabs(itr->real()), fabs(itr->imag()));
itr++;
}
rotateBurst2(burst, -M_PI / 4.0);
itr = burst.begin();
for (size_t i = 0; i < nsyms; i++) {
(*bits)[3 * i + 2] = -itr->imag();
itr++;
}
signalVector soft(bits->size());
for (size_t i = 0; i < bits->size(); i++)
soft[i] = (*bits)[i];
return bits;
}
/*
* Convert signalVector to SoftVector by taking real part of the signal.
*/
static SoftVector *signalToSoftVector(signalVector *dec)
{
SoftVector *bits = new SoftVector(dec->size());
SoftVector::iterator bit_itr = bits->begin();
signalVector::iterator burst_itr = dec->begin();
for (; burst_itr < dec->end(); burst_itr++)
*bit_itr++ = burst_itr->real();
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(const signalVector &burst, int sps,
const struct estim_burst_params *ebp)
{
signalVector *delay, *dec;
if ((sps != 1) && (sps != 4))
return NULL;
delay = delayVector(&burst, NULL, -ebp->toa * (float) sps);
scaleVector(*delay, (complex) 1.0 / ebp->amp);
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
* delay filters. Symbol rotation and after always operates at 1 SPS.
*/
static SoftVector *demodGmskBurst(const signalVector &rxBurst, int sps,
const struct estim_burst_params *ebp)
{
SoftVector *bits;
signalVector *dec;
dec = demodCommon(rxBurst, sps, ebp);
if (!dec)
return NULL;
/* Shift up by a quarter of a frequency */
GMSKReverseRotate(*dec, 1);
/* Take real part of the signal */
bits = signalToSoftVector(dec);
delete dec;
return bits;
}
static float computeEdgeCI(const signalVector *rot)
{
float err_pwr = 0.0f;
float step = 2.0f * M_PI_F / 8.0f;
for (size_t i = 8; i < rot->size() - 8; i++) {
/* Compute the ideal symbol */
complex sym = (*rot)[i];
float phase = step * roundf(sym.arg() / step);
complex ideal = complex(cos(phase), sin(phase));
/* Compute the error vector */
complex err = ideal - sym;
/* Accumulate power */
err_pwr += err.norm2();
}
return 3.0103f * log2f(1.0f * (rot->size() - 16) / err_pwr);
}
/*
* Demodulate an 8-PSK burst. Prior to symbol rotation, operate at
* 4 SPS (if activated) to minimize distortion through the fractional
* delay filters. Symbol rotation and after always operates at 1 SPS.
*
* Allow 1 SPS demodulation here, but note that other parts of the
* transceiver restrict EDGE operation to 4 SPS - 8-PSK distortion
* through the fractional delay filters at 1 SPS renders signal
* nearly unrecoverable.
*/
static SoftVector *demodEdgeBurst(const signalVector &burst, int sps,
struct estim_burst_params *ebp)
{
SoftVector *bits;
signalVector *dec, *rot, *eq;
dec = demodCommon(burst, sps, ebp);
if (!dec)
return NULL;
/* Equalize and derotate */
eq = convolve(dec, GSMPulse4->c0_inv, NULL, NO_DELAY);
rot = derotateEdgeBurst(*eq, 1);
ebp->ci = computeEdgeCI(rot);
/* Soft slice and normalize */
bits = softSliceEdgeBurst(*rot);
delete dec;
delete eq;
delete rot;
return bits;
}
SoftVector *demodAnyBurst(const signalVector &burst, CorrType type,
int sps, struct estim_burst_params *ebp)
{
if (type == EDGE)
return demodEdgeBurst(burst, sps, ebp);
else
return demodGmskBurst(burst, sps, ebp);
}
bool sigProcLibSetup()
{
generateSincTable();
initGMSKRotationTables();
GSMPulse1 = generateGSMPulse(1);
GSMPulse4 = generateGSMPulse(4);
generateRACHSequence(&gRACHSequences[0], gRACHSynchSequenceTS0, 1);
generateRACHSequence(&gRACHSequences[1], gRACHSynchSequenceTS1, 1);
generateRACHSequence(&gRACHSequences[2], gRACHSynchSequenceTS2, 1);
for (int tsc = 0; tsc < 8; tsc++) {
generateMidamble(1, tsc);
gEdgeMidambles[tsc] = generateEdgeMidamble(tsc);
}
generateDelayFilters();
dnsampler = new Resampler(1, 4);
if (!dnsampler->init()) {
LOG(ALERT) << "Rx resampler failed to initialize";
goto fail;
}
return true;
fail:
sigProcLibDestroy();
return false;
}
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