sdr/pi4cxpsk: Add pi4-CxPSK raw primitives

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

1 files changed, 573 insertions, 0 deletions

diff --git a/src/sdr/pi4cxpsk.c b/src/sdr/pi4cxpsk.c
new file mode 100644
index 0000000..f8d887c
--- /dev/null
+++ b/src/sdr/pi4cxpsk.c
@@ -0,0 +1,573 @@
+/* GMR-1 SDR - pi4-CBPSK and pi4-CQPSK modulation support */
+/* See GMR-1 05.003 (ETSI TS 101 376-5-4 V1.2.1) - Section 5.1 & 5.2 */
+
+/* (C) 2011 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/sdr/cxvec.h>
+#include <osmocom/sdr/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[] = {
+	{ 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,
+};
+
+
+/*! \brief pi4-CQPSK symbols descriptions */
+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 modulation description */
+struct gmr1_pi4cxpsk_modulation gmr1_pi4cqpsk = {
+	.nbits = 2,
+	.syms = gmr1_pi4cqpsk_syms,
+};
+
+
+
+/*! \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
+ *  \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)
+{
+	struct osmo_cxvec _win, *win = &_win;
+	struct osmo_cxvec *corr, *corr_tmp;
+	int i, j, w;
+	float p_toa, p_pwr = 0.0f, p_idx;
+	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;
+
+		/* 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;
+		}
+
+		/* Find peak */
+		s_toa = osmo_cxvec_peak_energy_find(corr, 3, PEAK_EARLY_LATE, &s_peak);
+		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 */
+	*toa = p_toa;
+	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,csync=burst_type->sync[sync_id]; csync->pos>=0; i++,csync++)
+		{
+			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 += carg(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] = carg(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);
+	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, 1.0f / 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;
+}
+
+/*! }@ */