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-rw-r--r--src/host/layer23/src/transceiver/gmsk.c289
1 files changed, 289 insertions, 0 deletions
diff --git a/src/host/layer23/src/transceiver/gmsk.c b/src/host/layer23/src/transceiver/gmsk.c
new file mode 100644
index 00000000..d21819fc
--- /dev/null
+++ b/src/host/layer23/src/transceiver/gmsk.c
@@ -0,0 +1,289 @@
+/*
+ * gmsk.c
+ *
+ * GMSK modulation support
+ *
+ * Copyright (C) 2013 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/>.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <osmocom/dsp/cxvec.h>
+#include <osmocom/dsp/cxvec_math.h>
+
+#include "gmsk.h"
+
+
+
+static struct osmo_cxvec *
+osmo_gmsk_generate_pulse(int sym_len, int sps);
+
+static int
+osmo_gmsk_generate_rotation_tables(int len, int sps,
+ struct osmo_cxvec **rot_fwd,
+ struct osmo_cxvec **rot_rev);
+
+
+/* ------------------------------------------------------------------------ */
+/* GMSK State */
+/* ------------------------------------------------------------------------ */
+
+struct osmo_gmsk_state *
+osmo_gmsk_init(int sps)
+{
+ struct osmo_gmsk_state *gs;
+
+ /* Base */
+ gs = calloc(1, sizeof(struct osmo_gmsk_state));
+ if (!gs)
+ return NULL;
+
+ gs->sps = sps;
+
+ /* GMSK pulse */
+ gs->pulse = osmo_gmsk_generate_pulse(2, sps);
+ if (!gs->pulse)
+ goto error;
+
+ /* Rotation fwd/rev */
+ osmo_gmsk_generate_rotation_tables(160, sps, &gs->rot_fwd, &gs->rot_rev);
+ if (!gs->rot_fwd || !gs->rot_rev)
+ goto error;
+
+ return gs;
+
+error:
+ osmo_gmsk_free(gs);
+ return NULL;
+}
+
+void
+osmo_gmsk_free(struct osmo_gmsk_state *gs)
+{
+ if (!gs)
+ return;
+
+ if (gs->pulse)
+ osmo_cxvec_free(gs->pulse);
+ if (gs->rot_fwd)
+ osmo_cxvec_free(gs->rot_fwd);
+ if (gs->rot_rev)
+ osmo_cxvec_free(gs->rot_rev);
+
+ free(gs);
+}
+
+
+/* ------------------------------------------------------------------------ */
+/* GMSK Modulation */
+/* ------------------------------------------------------------------------ */
+
+/* Generate a GMSK pulse shape.
+ * - sym_len: length of ISI
+ * - sps: samples per symbol
+ */
+static struct osmo_cxvec *
+osmo_gmsk_generate_pulse(int sym_len, int sps)
+{
+ struct osmo_cxvec *pulse;
+ int n = sps * sym_len + 1; /* length */
+ int c = (n-1)/2; /* center idx */
+ int i;
+ float avg;
+
+ pulse = osmo_cxvec_alloc(n);
+ if (!pulse)
+ return NULL;
+
+ pulse->len = n;
+ pulse->flags |= CXVEC_FLG_REAL_ONLY;
+
+ avg = 0.0f;
+
+ for (i=0; i<n; i++) {
+ float arg = (float)(i-c) / (float)sps;
+ float arg2 = arg * arg;
+ float v;
+ v = 0.96 * expf( -1.1380 * arg2 - 0.527 * arg2 * arg2); /* GSM pulse approx */
+ avg += v * v;
+ pulse->data[i] = v;
+ }
+
+ avg = sqrtf(avg);
+
+ for (i=0; i<n; i++)
+ pulse->data[i] /= avg;
+
+ return pulse;
+}
+
+static int
+osmo_gmsk_generate_rotation_tables(
+ int len, int sps,
+ struct osmo_cxvec **rot_fwd, struct osmo_cxvec **rot_rev)
+{
+ struct osmo_cxvec *rf, *rr;
+ float phase;
+ int i;
+
+ rf = osmo_cxvec_alloc(160 * sps);
+ rr = osmo_cxvec_alloc(160 * sps);
+
+ if (!rf || !rr)
+ return -1;
+
+ phase = 0.0f;
+
+ for (i=0; i<160*sps; i++) {
+ rf->data[i] = cexp( I * phase);
+ rr->data[i] = cexp(- I * phase);
+ phase += (M_PIf / 2.0f) / (float)sps;
+ }
+
+ rf->len = 160 * sps;
+ rr->len = 160 * sps;
+
+ *rot_fwd = rf;
+ *rot_rev = rr;
+
+ return 0;
+}
+
+void
+osmo_gmsk_rotate_fwd(const struct osmo_gmsk_state *gs, struct osmo_cxvec *v)
+{
+ int i;
+
+ if (v->flags & CXVEC_FLG_REAL_ONLY) {
+ for (i=0; i<v->len; i++)
+ v->data[i] = gs->rot_fwd->data[i] * crealf(v->data[i]);
+ } else {
+ for (i=0; i<v->len; i++)
+ v->data[i] = gs->rot_fwd->data[i] * v->data[i];
+ }
+
+ v->flags &= ~CXVEC_FLG_REAL_ONLY;
+}
+
+void
+osmo_gmsk_rotate_rev(const struct osmo_gmsk_state *gs, struct osmo_cxvec *v)
+{
+ int i;
+
+ if (v->flags & CXVEC_FLG_REAL_ONLY) {
+ for (i=0; i<v->len; i++)
+ v->data[i] = gs->rot_rev->data[i] * crealf(v->data[i]);
+ } else {
+ for (i=0; i<v->len; i++)
+ v->data[i] = gs->rot_rev->data[i] * v->data[i];
+ }
+
+ v->flags &= ~CXVEC_FLG_REAL_ONLY;
+}
+
+struct osmo_cxvec *
+osmo_gmsk_modulate_burst(const struct osmo_gmsk_state *gs,
+ const ubit_t *data, int data_len, int guard_len)
+{
+ struct osmo_cxvec *mod_burst, *shaped_burst;
+ int burst_size = gs->sps * (data_len + guard_len);
+ int i;
+
+ /* Alloc mod_burst */
+ mod_burst = osmo_cxvec_alloc(burst_size);
+ if (!mod_burst)
+ return NULL;
+
+ /* Fill mod_burst */
+ mod_burst->len = burst_size;
+ mod_burst->flags |= CXVEC_FLG_REAL_ONLY;
+
+ for (i=0; i<burst_size; i++)
+ mod_burst->data[i] = 0.0f;
+
+ for (i=0; i<data_len; i++)
+ mod_burst->data[i*gs->sps] = data[i] ? 1.0f : -1.0f;
+
+ /* Rotate up by pi/2 */
+ osmo_gmsk_rotate_fwd(gs, mod_burst);
+
+ /* Filter with pulse shape */
+ shaped_burst = osmo_cxvec_convolve(gs->pulse, mod_burst, CONV_NO_DELAY, NULL);
+
+ /* Release mod_burst */
+ osmo_cxvec_free(mod_burst);
+
+ return shaped_burst;
+}
+
+
+/* ------------------------------------------------------------------------ */
+/* GMSK training sequence */
+/* ------------------------------------------------------------------------ */
+
+struct osmo_gmsk_trainseq *
+osmo_gmsk_trainseq_generate(struct osmo_gmsk_state *gs, const ubit_t *train, int len)
+{
+ struct osmo_gmsk_trainseq *gts;
+ struct osmo_cxvec *autocorr = NULL;
+
+ gts = calloc(1, sizeof(struct osmo_gmsk_trainseq));
+ if (!gts)
+ return NULL;
+
+ gts->seq = osmo_gmsk_modulate_burst(gs, train, len, 0);
+ if (!gts->seq)
+ goto err;
+
+ printf("%d\n", gts->seq->len);
+
+ autocorr = osmo_cxvec_correlate(gts->seq, gts->seq, 1, NULL);
+ if (!autocorr)
+ goto err;
+
+ gts->toa = osmo_cxvec_peak_energy_find(autocorr, 5, PEAK_EARLY_LATE, &gts->gain);
+
+ printf("%d\n", autocorr->len);
+ gts->gain = autocorr->data[0];
+
+ osmo_cxvec_free(autocorr);
+
+ return gts;
+
+err:
+ if (gts) {
+ if (gts->seq)
+ osmo_cxvec_free(gts->seq);
+ free(gts);
+ }
+
+ if (autocorr)
+ osmo_cxvec_free(autocorr);
+
+ return NULL;
+}
+
+void
+osmo_gmsk_trainseq_free(struct osmo_gmsk_trainseq *gts)
+{
+ if (gts) {
+ osmo_cxvec_free(gts->seq);
+ free(gts);
+ }
+}
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