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/*
* demod.c
*
* Demodulation routines for tranceiver
*
* 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 <stdint.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <osmocom/dsp/cxvec.h>
#include <osmocom/dsp/cxvec_math.h>
#include <l1ctl_proto.h>
#include "app.h"
#include "gmsk.h"
#include "gsm_ab.h"
int
gsm_ab_ind_process(struct app_state *as,
struct l1ctl_bts_burst_ab_ind *bi,
sbit_t *data, float *toa_p)
{
struct osmo_cxvec *burst = NULL;
sbit_t *bits = NULL;
float complex chan;
float toa;
int i, rv;
/* Load burst */
burst = osmo_cxvec_alloc(88);
burst->len = 88;
for (i=0; i<88; i++) {
float f[2];
f[0] = ((float)((char)bi->iq[(i<<1) ])) / 128.0f;
f[1] = ((float)((char)bi->iq[(i<<1)+1])) / 128.0f;
burst->data[i] = f[0] + f[1] * I;
}
/* Normalize burst */
osmo_cxvec_sig_normalize(burst, 1, 0.0f, burst);
/* Detect potential RACH */
rv = gsm_ab_detect(as->gs, as->train_ab, burst, 2.0f, &chan, &toa);
if (rv)
goto err;
/* Check for a significant peak */
if (cabsf(chan) < 0.5) {
rv = -EINVAL;
goto err;
}
printf("TOA : %f\n", toa);
printf("chan : (%f %f) => %f\n", crealf(chan), cimagf(chan), cabsf(chan));
/* Demodulate */
bits = gsm_ab_demodulate(as->gs, burst, chan, toa);
if (!bits) {
rv = -ENOMEM;
goto err;
}
/* Copy */
memset(data, 0x00, 148);
memcpy(data, bits, GSM_AB_BITS);
/* Print result */
for (i=0; i<GSM_AB_BITS; i++)
printf("%d", !!(bits[i] & 0x80));
printf("\n");
*toa_p = toa;
rv = 0;
/* Cleanup */
err:
free(bits);
osmo_cxvec_free(burst);
return rv;
}
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