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osmo-gmr/src/sdr/pi4cxpsk.c

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/* GMR-1 SDR - pi4-CBPSK and pi4-CQPSK modulation support */
/* See GMR-1 05.004 (ETSI TS 101 376-5-4 V1.2.1) - Section 5.1 & 5.2 */
/* (C) 2011-2019 by Sylvain Munaut <tnt@246tNt.com>
* All Rights Reserved
*
* 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/>.
*/
/*! \addtogroup pi4cxpsk
* @{
*/
/*! \file sdr/pi4cxpsk.c
* \brief Osmocom GMR-1 pi4-CBPSK and pi4-CQPSK modulation support implementation
*/
#include <complex.h>
#include <math.h>
#include <errno.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <osmocom/core/bits.h>
#include <osmocom/dsp/cxvec.h>
#include <osmocom/dsp/cxvec_math.h>
#include <osmocom/gmr1/sdr/defs.h>
#include <osmocom/gmr1/sdr/pi4cxpsk.h>
/*
* Symbol notation
*
* idx data modulating
* bits phase
*
* pi4-CBPSK:
*
* 0 0 0 * pi/2 = 1+0j
* 1 1 2 * pi/2 = -1+0j
*
* pi4-CQPSK:
*
* 0 00 0 * pi/2 = 1+0j
* 1 01 1 * pi/2 = 0+1j
* 2 11 2 * pi/2 = -1+0j
* 3 10 3 * pi/2 = 0-1j
*
* - idx : Symbol number
* - data bits : The encoded data bits
* - modulating phase : Phase used during modulation (in adition to the pi/4
* continuous rotation)
*/
/*! \brief pi4-CBPSK symbols descriptions */
static struct gmr1_pi4cxpsk_symbol gmr1_pi4cbpsk_syms_bits[] = {
{ 0, {0}, 0*M_PIf/2, 1+0*I },
{ 1, {1}, 2*M_PIf/2, -1+0*I },
};
/*! \brief pi4-CBPSK modulation description */
struct gmr1_pi4cxpsk_modulation gmr1_pi4cbpsk = {
.nbits = 1,
.syms = gmr1_pi4cbpsk_syms_bits,
.bits = gmr1_pi4cbpsk_syms_bits,
};
/*! \brief pi4-CQPSK symbols descriptions in symbol order */
static struct gmr1_pi4cxpsk_symbol gmr1_pi4cqpsk_syms[] = {
{ 0, {0,0}, 0*M_PIf/2, 1+0*I },
{ 1, {0,1}, 1*M_PIf/2, 0+1*I },
{ 2, {1,1}, 2*M_PIf/2, -1+0*I },
{ 3, {1,0}, 3*M_PIf/2, 0-1*I },
};
/*! \brief pi4-CQPSK symbols descriptions in bits order */
static struct gmr1_pi4cxpsk_symbol gmr1_pi4cqpsk_bits[] = {
{ 0, {0,0}, 0*M_PIf/2, 1+0*I },
{ 1, {0,1}, 1*M_PIf/2, 0+1*I },
{ 3, {1,0}, 3*M_PIf/2, 0-1*I },
{ 2, {1,1}, 2*M_PIf/2, -1+0*I },
};
/*! \brief pi4-CQPSK modulation description */
struct gmr1_pi4cxpsk_modulation gmr1_pi4cqpsk = {
.nbits = 2,
.syms = gmr1_pi4cqpsk_syms,
.bits = gmr1_pi4cqpsk_bits,
};
/*! \brief Generate a reference signal for all sync sequences of a burst type
* \param[in] burst_type Burst format description
* \returns 0 for success. -ernno for errors
*
* The reference waveforms are stored inside the burst_type itself.
*/
static int
_gmr1_pi4cxpsk_sync_gen_ref(struct gmr1_pi4cxpsk_burst *burst_type)
{
int i, j;
/* Scan all possible training sequences */
for (i=0; (i < GMR1_MAX_SYNC) && (burst_type->sync[i] != NULL); i++)
{
struct gmr1_pi4cxpsk_sync *csync;
/* Scan all 'chunks' */
for (csync=burst_type->sync[i]; csync->pos>=0; csync++)
{
int is_real = 1;
/* Already done ? */
if (csync->_ref)
continue;
/* Allocate it */
csync->_ref = osmo_cxvec_alloc(csync->len);
if (!csync->_ref)
return -ENOMEM;
/* Fill it */
for (j=0; j<csync->len; j++) {
int s;
float complex mv;
s = csync->syms[j];
mv = burst_type->mod->syms[s].mod_val;
if (cimagf(mv) != 0.0f)
is_real = 0;
csync->_ref->data[j] = mv;
}
csync->_ref->len = csync->len;
if (is_real)
csync->_ref->flags |= CXVEC_FLG_REAL_ONLY;
}
}
return 0;
}
/*! \brief Find the sync sequence inside a burst
* \param[in] burst_type Burst format description
* \param[in] burst The input complex vector
* \param[in] sps Input sample per symbol (how much to decimate)
* \param[out] toa Pointer to estimated fractional TOA return variable
* \param[out] pwr Pointer to power return variable
* \returns >=0 index of found sync sequence. -errno for errors
*
* The burst input is expected to be longer than the burst. The extra amount
* of samples will be the search window.
*/
static int
_gmr1_pi4cxpsk_sync_find(struct gmr1_pi4cxpsk_burst *burst_type,
struct osmo_cxvec *burst, int sps,
float *toa, float *pwr)
{
struct osmo_cxvec _win, *win = &_win;
struct osmo_cxvec *corr, *corr_tmp;
int i, j, w;
float p_toa = 0.0f, p_pwr = 0.0f, p_idx = -1;
int rv;
/* Window size */
w = burst->len - (burst_type->len * sps) + 1;
/* Corr vectors */
corr = osmo_cxvec_alloc(w);
corr_tmp = osmo_cxvec_alloc(w);
if (!corr || !corr_tmp) {
rv = -ENOMEM;
goto err;
}
/* Scan all possible training sequences */
for (i=0; (i < GMR1_MAX_SYNC) && (burst_type->sync[i] != NULL); i++)
{
struct gmr1_pi4cxpsk_sync *csync;
float s_toa, s_pwr;
float complex s_peak;
int first = 1, tl = 0;
/* Correlate all 'chunks' */
for (csync=burst_type->sync[i]; csync->pos>=0; csync++)
{
int b, l;
/* Extract the window of data to correlate with */
b = csync->pos * sps;
l = (csync->len * sps) + w - 1;
osmo_cxvec_init_from_data(win, &burst->data[b], l);
/* Correlate */
osmo_cxvec_correlate(csync->_ref, win, sps, first ? corr : corr_tmp);
/* If not the first, then combine results */
if (!first)
for (j=0; j<w; j++)
corr->data[j] += corr_tmp->data[j];
first = 0;
/* Add length of this 'chunk' */
tl += csync->_ref->len;
}
/* Find peak */
s_toa = osmo_cxvec_peak_energy_find(corr, 3, PEAK_EARLY_LATE, &s_peak);
s_peak /= (float)tl;
s_pwr = osmo_normsqf(s_peak);
if (s_pwr > p_pwr) {
/* Record the new winner */
p_pwr = s_pwr;
p_toa = s_toa;
p_idx = i;
/* Debug winner */
DEBUG_SIGNAL("pi4cxpsk_corr", corr);
}
}
/* Return winner */
if (toa)
*toa = p_toa;
if (pwr)
*pwr = p_pwr;
rv = p_idx;
/* Clean up */
err:
osmo_cxvec_free(corr_tmp);
osmo_cxvec_free(corr);
return rv;
}
/*! \brief Perform final alignement (1 sps and proper length/alignement)
* \param[in] burst_type Burst format description
* \param[in] burst The input complex vector
* \param[in] sps Input sample per symbol (how much to decimate)
* \param[in] toa Estimated fractional TOA to align to
* \returns 0 for success. -errno for errors
*
* In the end, each complex inside the burst corresponds to a sample,
* aligned according to the burst description.
*/
static int
_gmr1_pi4cxpsk_align(struct gmr1_pi4cxpsk_burst *burst_type,
struct osmo_cxvec *burst, int sps, float toa)
{
int i, rv = 0;
if (sps >= 4) {
/* Easy case: we can just round everything and not use
* fractional TOA. At worse we have a +-1/8 symbol alignement
* error, which doesn't matter */
int d;
d = roundf(toa);
for (i=0; i<burst_type->len; i++)
burst->data[i] = burst->data[i*sps+d];
burst->len = burst_type->len;
} else {
/* Hard case: we need to interpolate every point */
struct osmo_cxvec *conv = NULL, *src = burst;
int ofs_int;
float ofs_frac;
ofs_int = roundf(toa);
ofs_frac = toa - ofs_int;
src = burst;
/* Fractional part (if reasonable) */
if (fabs(ofs_frac) > 0.1f) {
const int N = 21;
float complex _data[N];
struct osmo_cxvec _sinc_pulse, *sinc_pulse = &_sinc_pulse;
/* Build sinc pulse */
for (i=0; i<N; i++)
_data[i] = osmo_sinc(
M_PIf * ((float)(i - (N>>1)) + ofs_frac)
);
osmo_cxvec_init_from_data(sinc_pulse, _data, N);
sinc_pulse->flags |= CXVEC_FLG_REAL_ONLY;
/* Apply it */
conv = osmo_cxvec_convolve(sinc_pulse, burst, CONV_NO_DELAY, NULL);
src = conv;
}
/* Integer part */
for (i=0; i<burst_type->len; i++) {
int j = (i*sps) + ofs_int;
if (j < 0 || j >= src->len)
burst->data[i] = 0.0f;
else
burst->data[i] = src->data[j];
}
burst->len = burst_type->len;
/* Cleanup */
if (conv)
osmo_cxvec_free(conv);
}
DEBUG_SIGNAL("pi4cxpsk_align", burst);
return rv;
}
/*! \brief Estimate fine frequency error based on sync sequence chunks phase
* \param[in] burst_type Burst format description
* \param[in] burst The input complex vector (1 sample per symbol)
* \param[in] sync_id ID of the sync sequence to use
* \param[out] freq_error Pointer to the return frequency error variable (rad/sym)
* \returns 0 for success. -errno for errors
*
* The method needs several chunks to estimate the frequency error. If
* there is only one, 0.0f is returned.
*/
static int
_gmr1_pi4cxpsk_freq_err(struct gmr1_pi4cxpsk_burst *burst_type,
struct osmo_cxvec *burst, int sync_id,
float *freq_error)
{
struct gmr1_pi4cxpsk_sync *csync;
int n, i, j;
/* Count the chunks */
for (n=0,csync=burst_type->sync[sync_id]; csync->pos>=0; n++,csync++);
/* Do we have several ? */
if (n > 1)
{
float complex corr[n];
float pos[n], f;
/* Correlate all 'chunks' */
for (i=0; i<n; i++)
{
csync = &burst_type->sync[sync_id][i];
corr[i] = 0.0f;
pos[i] = (float)csync->pos + (float)csync->len / 2.0f;
for (j=0; j<csync->len; j++)
corr[i] +=
conjf(csync->_ref->data[j]) *
burst->data[csync->pos+j];
}
/* From the data points, extract a single value */
f = 0.0f;
for (i=1; i<n; i++)
f += cargf(corr[i] * conjf(corr[0])) / (pos[i] - pos[0]);
f /= n - 1;
*freq_error = f;
}
else
{
/* FIXME: How the hell to do this reliably ??? */
*freq_error = 0.0f;
}
return 0;
}
/*! \brief Compute the current phase of a burst (compared to a 0 reference)
* \param[in] burst_type Burst format description
* \param[in] burst The input complex vector (1 sample per symbol)
* \param[in] sync_id ID of the sync sequence to use
* \param[out] phasor Pointer to the return phase variable
* \returns 0 for success. -errno for errors
*/
static int
_gmr1_pi4cxpsk_phase(struct gmr1_pi4cxpsk_burst *burst_type,
struct osmo_cxvec *burst, int sync_id,
float complex *phasor)
{
struct gmr1_pi4cxpsk_sync *csync;
float complex corr = 0.0f;
int i;
/* Correlate all 'chunks' */
for (csync=burst_type->sync[sync_id]; csync->pos>=0; csync++)
for (i=0; i<csync->len; i++)
corr += conjf(csync->_ref->data[i]) *
burst->data[csync->pos+i];
*phasor = corr / cabsf(corr);
return 0;
}
/*! \brief Convert complex vector into soft symbols based on phase
* \param[in] burst_type Burst format description
* \param[in] burst The input complex vector
* \returns Newly malloc'd array of float of same legnth as burst
*
* Phase must have been aligned properly obviously
*/
static float *
_gmr1_pi4cxpsk_soft_symbols(struct gmr1_pi4cxpsk_burst *burst_type,
struct osmo_cxvec *burst)
{
float *ssyms;
float d;
int i;
ssyms = malloc(sizeof(float) * burst->len);
if (!ssyms)
return NULL;
d = (2.0f * M_PIf) / (1<<burst_type->mod->nbits);
for (i=0; i<burst->len; i++)
ssyms[i] = cargf(burst->data[i]) / d;
return ssyms;
}
/*! \brief Convert a soft symbols array into softbits
* \param[in] burst_type Burst format description
* \param[in] ssyms Soft symbols array
* \param[out] ebits Encoded soft bits return array
* \returns 0 for success. -errno for errors
*/
static int
_gmr1_pi4cxpsk_soft_bits(struct gmr1_pi4cxpsk_burst *burst_type,
float *ssyms, sbit_t *ebits)
{
struct gmr1_pi4cxpsk_modulation *mod = burst_type->mod;
struct gmr1_pi4cxpsk_data *dc;
int mask = (1<<mod->nbits) - 1;
int i,j,k;
k=0;
for (dc = burst_type->data; dc->pos>=0; dc++) {
for (i=dc->pos; i<dc->pos+dc->len; i++)
{
float sv, svr;
int sp, ss, d;
sv = ssyms[i];
svr = roundf(sv);
sp = (int)svr & mask;
ss = (svr > sv ? (sp-1) : (sp+1)) & mask;
d = roundf((2.0f * fabs(svr - sv)) * 64.0f);
for (j=0; j<mod->nbits; j++) {
uint8_t vp = mod->syms[sp].data[j];
uint8_t vs = mod->syms[ss].data[j];
sbit_t v = 127 - ((vp^vs) ? d : (d>>1));
ebits[k++] = vp ? -v : v;
}
}
}
return 0;
}
/*! \brief All-in-one pi4-CxPSK demodulation method
* \param[in] burst_type Burst format description
* \param[in] burst_in Complex signal of the burst
* \param[in] sps Oversampling used in the input complex signal
* \param[in] freq_shift Frequency shift to pre-apply to burst_in (rad/sym)
* \param[out] ebits Encoded soft bits return array
* \param[out] sync_id_p Pointer to sync sequence id return variable
* \param[out] toa_p Pointer to TOA return variable
* \param[out] freq_err_p Pointer to frequency error return variable (rad/sym)
* \returns 0 for success. -errno for errors
*
* burst_in is expected to be longer than necessary. Any extra length will be
* used as 'search window' to find proper alignement. Good practice is to have
* a few samples too much in front and a few samples after the expected TOA.
*/
int
gmr1_pi4cxpsk_demod(struct gmr1_pi4cxpsk_burst *burst_type,
struct osmo_cxvec *burst_in, int sps, float freq_shift,
sbit_t *ebits,
int *sync_id_p, float *toa_p, float *freq_err_p)
{
struct osmo_cxvec *burst = NULL;
float toa, fine_freq_error;
float complex phasor;
float *ssyms = NULL;
int sync_id;
int rv = 0;
/* Generate reference sync bursts */
rv = _gmr1_pi4cxpsk_sync_gen_ref(burst_type);
if (rv)
goto err;
/* Normalize the burst and counter rotate by pi/4 */
burst = osmo_cxvec_sig_normalize(burst_in, 1, (freq_shift - (M_PIf/4)) / sps, NULL);
if (!burst) {
rv = -ENOMEM;
goto err;
}
DEBUG_SIGNAL("pi4cxpsk_burst", burst);
/* Find the training sequence */
sync_id = _gmr1_pi4cxpsk_sync_find(burst_type, burst, sps, &toa, NULL);
if (sync_id < 0) {
rv = sync_id;
goto err;
}
if (sync_id_p)
*sync_id_p = sync_id;
if (toa_p)
*toa_p = toa;
/* Align and decimate the burst */
rv = _gmr1_pi4cxpsk_align(burst_type, burst, sps, toa);
if (rv)
goto err;
/* Use sync sequence to find fine freq error */
rv = _gmr1_pi4cxpsk_freq_err(burst_type, burst, sync_id, &fine_freq_error);
if (rv)
goto err;
if (freq_err_p)
*freq_err_p = fine_freq_error;
/* Compensate fine freq error (in-place) */
if (fine_freq_error != 0.0f)
osmo_cxvec_rotate(burst, -fine_freq_error, burst);
/* Find current phase using sync sequence */
_gmr1_pi4cxpsk_phase(burst_type, burst, sync_id, &phasor);
/* Align phase for detection */
osmo_cxvec_scale(burst, conjf(phasor), burst);
DEBUG_SIGNAL("pi4cxpsk_final", burst);
/* Convert phase to soft symbols */
ssyms = _gmr1_pi4cxpsk_soft_symbols(burst_type, burst);
if (!ssyms) {
rv = -ENOMEM;
goto err;
}
/* Convert to data bits */
rv = _gmr1_pi4cxpsk_soft_bits(burst_type, ssyms, ebits);
if (rv)
goto err;
/* Cleanup */
err:
free(ssyms);
osmo_cxvec_free(burst);
return rv;
}
/*! \brief Try to identify burst type by matching training sequences
* \param[in] burst_types Array of burst types to test (NULL terminated)
* \param[in] e_toa Expected time of arrival
* \param[in] burst_in Complex signal of the burst
* \param[in] sps Oversampling used in the input complex signal
* \param[in] freq_shift Frequency shift to pre-apply to burst_in (rad/sym)
* \param[out] bt_id_p Pointer to burst type ID return variable
* \param[out] sync_id_p Pointer to sync sequence id return variable
* \param[out] toa_p Pointer to TOA return variable
* \returns -errno for errors, 0 for success
*
* The various burst types must be compatible in length.
*/
int
gmr1_pi4cxpsk_detect(struct gmr1_pi4cxpsk_burst **burst_types, float e_toa,
struct osmo_cxvec *burst_in, int sps, float freq_shift,
int *bt_id_p, int *sync_id_p, float *toa_p)
{
struct gmr1_pi4cxpsk_burst *bt;
struct osmo_cxvec *burst = NULL;
int id, p_id=-1, p_sid=-1;
float p_toa=0.0f, p_pwr=0.0f;
int rv = 0;
/* Normalize the burst and counter rotate by pi/4 */
burst = osmo_cxvec_sig_normalize(burst_in, 1, (freq_shift - (M_PIf/4)) / sps, NULL);
if (!burst) {
rv = -ENOMEM;
goto err;
}
DEBUG_SIGNAL("pi4cxpsk_burst", burst);
/* Scan all burst types */
for (id=0; burst_types[id]; id++)
{
int sid;
float toa, pwr;
bt = burst_types[id];
/* Generate reference sync bursts */
rv = _gmr1_pi4cxpsk_sync_gen_ref(bt);
if (rv)
goto err;
/* Try this burst type */
sid = _gmr1_pi4cxpsk_sync_find(bt, burst, sps, &toa, &pwr);
if (sid < 0) {
rv = sid;
goto err;
}
/* If we have an expected, toa, we 'modulate' power */
if (e_toa >= 0.0f)
pwr /= fabs(e_toa - toa);
/* Check for better ? */
if (pwr > p_pwr) {
p_id = id;
p_sid = sid;
p_pwr = pwr;
p_toa = toa;
}
}
if (bt_id_p)
*bt_id_p = p_id;
if (sync_id_p)
*sync_id_p = p_sid;
if (toa_p)
*toa_p = p_toa;
/* Done */
err:
osmo_cxvec_free(burst);
return rv;
}
/*! \brief Estimates modulation order by comparing power of x^2 vs x^4
* \param[in] burst_in Complex signal of the burst
* \param[in] sps Oversampling used in the input complex signal
* \param[in] freq_shift Frequency shift to pre-apply to burst_in (rad/sym)
* \returns <0 for error. 2 for BPSK, 4 for QPSK.
*/
int
gmr1_pi4cxpsk_mod_order(struct osmo_cxvec *burst_in, int sps, float freq_shift)
{
struct osmo_cxvec *burst = NULL;
float complex sb = 0.0f, sq = 0.0f;
float pb, pq;
int rv, i;
/* Normalize the burst and counter rotate by pi/4 */
burst = osmo_cxvec_sig_normalize(burst_in, 1, (freq_shift - (M_PIf/4)) / sps, NULL);
if (!burst) {
rv = -ENOMEM;
goto err;
}
DEBUG_SIGNAL("pi4cxpsk_burst", burst);
/* Detect modulation order by estimating power of x^2 vs x^4 */
for (i=0; i<burst->len; i++) {
float complex v;
v = burst->data[i];
v = (v * v) / osmo_normsqf(v);
sb += v;
sq += v * v;
}
pb = osmo_normsqf(sb);
pq = osmo_normsqf(sq);
rv = pb < (pq / 2.0f) ? 4 : 2;
/* Done */
err:
osmo_cxvec_free(burst);
return rv;
}
/*! \brief Modulates (currently at 1 sps)
* \param[in] burst_type Burst format description
* \param[in] ebits Encoded hard bits to pack in the burst
* \param[in] sync_id The sequence id to use (0 if burst_type only has one)
* \param[out] burst_out Complex signal to fill with modulated symbols
* \returns 0 for success. -errno for errors
*
* burst_out is expected to be long enough to contains the resulting symbols
* see the burst_type structure for how long that is.
*/
int
gmr1_pi4cxpsk_mod(struct gmr1_pi4cxpsk_burst *burst_type,
ubit_t *ebits, int sync_id, struct osmo_cxvec *burst_out)
{
struct gmr1_pi4cxpsk_modulation *mod = burst_type->mod;
struct gmr1_pi4cxpsk_sync *sync;
struct gmr1_pi4cxpsk_data *data;
int rv, i, j, k;
/* Check the output vector is long enough */
if (burst_out->max_len < burst_type->len) {
rv = -ENOMEM;
goto err;
}
burst_out->len = burst_type->len;
/* Generate reference sync bursts */
rv = _gmr1_pi4cxpsk_sync_gen_ref(burst_type);
if (rv)
goto err;
/* Fill guard */
for (i=0; i<burst_type->guard_pre; i++)
burst_out->data[i] = 0.0f;
for (i=0; i<burst_type->guard_post; i++)
burst_out->data[burst_out->len - i - 1] = 0.0f;
/* Fill training sequence */
for (sync=burst_type->sync[sync_id]; sync->len; sync++)
{
for (i=0; i<sync->len; i++)
burst_out->data[sync->pos+i] = sync->_ref->data[i];
}
/* Fill ebits */
k = 0;
for (data=burst_type->data; data->len; data++)
{
for (i=0; i<data->len; i++)
{
int sym = 0;
for (j=0; j<mod->nbits; j++)
sym = (sym << 1) | ebits[k++];
burst_out->data[data->pos+i] = burst_type->mod->bits[sym].mod_val;
}
}
/* Apply the final pi/4 rotation */
osmo_cxvec_rotate(burst_out, M_PIf / 4.0f, burst_out);
rv = 0;
err:
return rv;
}
/*! @} */
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