383 lines
8.9 KiB
C
383 lines
8.9 KiB
C
/* FM modulation processing
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*
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* (C) 2017 by Andreas Eversberg <jolly@eversberg.eu>
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* All Rights Reserved
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <string.h>
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#include <errno.h>
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#include <math.h>
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#include "../common/sample.h"
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#include "fm.h"
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//#define FAST_SINE
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/* init FM modulator */
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int fm_mod_init(fm_mod_t *mod, double samplerate, double offset, double amplitude)
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{
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int i;
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memset(mod, 0, sizeof(*mod));
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mod->samplerate = samplerate;
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mod->offset = offset;
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mod->amplitude = amplitude;
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mod->ramp_length = samplerate * 0.001;
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mod->ramp_tab = calloc(mod->ramp_length, sizeof(*mod->ramp_tab));
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if (!mod->ramp_tab) {
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fprintf(stderr, "No mem!\n");
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return -ENOMEM;
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}
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mod->state = MOD_STATE_OFF;
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/* generate ramp up with ramp_length */
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for (i = 0; i < mod->ramp_length; i++)
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mod->ramp_tab[i] = 0.5 - cos(M_PI * i / mod->ramp_length) / 2.0;
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#ifdef FAST_SINE
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mod->sin_tab = calloc(65536+16384, sizeof(*mod->sin_tab));
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if (!mod->sin_tab) {
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fprintf(stderr, "No mem!\n");
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fm_mod_exit(mod);
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return -ENOMEM;
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}
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/* generate sine and cosine */
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for (i = 0; i < 65536+16384; i++)
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mod->sin_tab[i] = sin(2.0 * M_PI * (double)i / 65536.0) * amplitude;
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#endif
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return 0;
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}
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void fm_mod_exit(fm_mod_t *mod)
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{
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if (mod->ramp_tab) {
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free(mod->ramp_tab);
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mod->ramp_tab = NULL;
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}
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if (mod->sin_tab) {
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free(mod->sin_tab);
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mod->sin_tab = NULL;
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}
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}
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/* do frequency modulation of samples and add them to existing baseband */
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void fm_modulate_complex(fm_mod_t *mod, sample_t *frequency, uint8_t *power, int length, float *baseband)
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{
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double dev, rate, phase, offset;
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int ramp, ramp_length;
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double *ramp_tab;
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#ifdef FAST_SINE
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double *sin_tab, *cos_tab;
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#else
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double amplitude;
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#endif
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rate = mod->samplerate;
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phase = mod->phase;
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offset = mod->offset;
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ramp = mod->ramp;
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ramp_length = mod->ramp_length;
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ramp_tab = mod->ramp_tab;
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#ifdef FAST_SINE
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sin_tab = mod->sin_tab;
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cos_tab = mod->sin_tab + 16384;
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#else
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amplitude = mod->amplitude;
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#endif
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again:
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switch (mod->state) {
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case MOD_STATE_ON:
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/* modulate */
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while (length) {
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/* is power is not set, ramp down */
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if (!(*power)) {
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mod->state = MOD_STATE_RAMP_DOWN;
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break;
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}
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/* deviation is defined by the frequency value and the offset */
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dev = offset + *frequency++;
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power++;
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length--;
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#ifdef FAST_SINE
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phase += 65536.0 * dev / rate;
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if (phase < 0.0)
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phase += 65536.0;
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else if (phase >= 65536.0)
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phase -= 65536.0;
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*baseband++ += cos_tab[(uint16_t)phase];
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*baseband++ += sin_tab[(uint16_t)phase];
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#else
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phase += 2.0 * M_PI * dev / rate;
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if (phase < 0.0)
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phase += 2.0 * M_PI;
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else if (phase >= 2.0 * M_PI)
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phase -= 2.0 * M_PI;
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*baseband++ += cos(phase) * amplitude;
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*baseband++ += sin(phase) * amplitude;
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#endif
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}
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break;
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case MOD_STATE_RAMP_DOWN:
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while (length) {
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/* if power is set, ramp up */
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if (*power) {
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mod->state = MOD_STATE_RAMP_UP;
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break;
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}
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if (ramp == 0) {
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mod->state = MOD_STATE_OFF;
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break;
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}
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dev = offset + *frequency++;
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power++;
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length--;
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#ifdef FAST_SINE
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phase += 65536.0 * dev / rate;
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if (phase < 0.0)
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phase += 65536.0;
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else if (phase >= 65536.0)
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phase -= 65536.0;
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*baseband++ += cos_tab[(uint16_t)phase] * ramp_tab[ramp];
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*baseband++ += sin_tab[(uint16_t)phase] * ramp_tab[ramp];
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#else
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phase += 2.0 * M_PI * dev / rate;
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if (phase < 0.0)
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phase += 2.0 * M_PI;
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else if (phase >= 2.0 * M_PI)
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phase -= 2.0 * M_PI;
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*baseband++ += cos(phase) * amplitude * ramp_tab[ramp];
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*baseband++ += sin(phase) * amplitude * ramp_tab[ramp];
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#endif
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ramp--;
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}
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break;
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case MOD_STATE_OFF:
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while (length) {
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/* if power is set, ramp up */
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if (*power) {
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mod->state = MOD_STATE_RAMP_UP;
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break;
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}
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frequency++;
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power++;
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length--;
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baseband += 2;
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}
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break;
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case MOD_STATE_RAMP_UP:
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while (length) {
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/* is power is not set, ramp down */
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if (!(*power)) {
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mod->state = MOD_STATE_RAMP_DOWN;
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break;
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}
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if (ramp == ramp_length - 1) {
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mod->state = MOD_STATE_ON;
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break;
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}
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/* deviation is defined by the frequency value and the offset */
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dev = offset + *frequency++;
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power++;
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length--;
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#ifdef FAST_SINE
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phase += 65536.0 * dev / rate;
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if (phase < 0.0)
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phase += 65536.0;
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else if (phase >= 65536.0)
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phase -= 65536.0;
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*baseband++ += cos_tab[(uint16_t)phase] * ramp_tab[ramp];
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*baseband++ += sin_tab[(uint16_t)phase] * ramp_tab[ramp];
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#else
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phase += 2.0 * M_PI * dev / rate;
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if (phase < 0.0)
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phase += 2.0 * M_PI;
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else if (phase >= 2.0 * M_PI)
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phase -= 2.0 * M_PI;
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*baseband++ += cos(phase) * amplitude * ramp_tab[ramp];
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*baseband++ += sin(phase) * amplitude * ramp_tab[ramp];
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#endif
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ramp++;
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}
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break;
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}
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if (length)
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goto again;
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mod->phase = phase;
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mod->ramp = ramp;
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}
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/* init FM demodulator */
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int fm_demod_init(fm_demod_t *demod, double samplerate, double offset, double bandwidth)
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{
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memset(demod, 0, sizeof(*demod));
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demod->samplerate = samplerate;
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#ifdef FAST_SINE
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demod->rot = 65536.0 * -offset / samplerate;
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#else
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demod->rot = 2 * M_PI * -offset / samplerate;
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#endif
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/* use fourth order (2 iter) filter, since it is as fast as second order (1 iter) filter */
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iir_lowpass_init(&demod->lp[0], bandwidth / 2.0, samplerate, 2);
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iir_lowpass_init(&demod->lp[1], bandwidth / 2.0, samplerate, 2);
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#ifdef FAST_SINE
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int i;
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demod->sin_tab = calloc(65536+16384, sizeof(*demod->sin_tab));
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if (!demod->sin_tab) {
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fprintf(stderr, "No mem!\n");
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return -ENOMEM;
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}
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/* generate sine and cosine */
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for (i = 0; i < 65536+16384; i++)
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demod->sin_tab[i] = sin(2.0 * M_PI * (double)i / 65536.0);
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#endif
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return 0;
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}
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void fm_demod_exit(fm_demod_t *demod)
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{
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if (demod->sin_tab) {
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free(demod->sin_tab);
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demod->sin_tab = NULL;
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}
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}
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/* do frequency demodulation of baseband and write them to samples */
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void fm_demodulate_complex(fm_demod_t *demod, sample_t *frequency, int length, float *baseband, sample_t *I, sample_t *Q)
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{
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double phase, rot, last_phase, dev, rate;
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double _sin, _cos;
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sample_t i, q;
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int s, ss;
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#ifdef FAST_SINE
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double *sin_tab, *cos_tab;
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#endif
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rate = demod->samplerate;
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phase = demod->phase;
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rot = demod->rot;
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#ifdef FAST_SINE
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sin_tab = demod->sin_tab;
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cos_tab = demod->sin_tab + 16384;
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#endif
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for (s = 0, ss = 0; s < length; s++) {
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phase += rot;
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i = baseband[ss++];
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q = baseband[ss++];
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#ifdef FAST_SINE
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if (phase < 0.0)
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phase += 65536.0;
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else if (phase >= 65536.0)
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phase -= 65536.0;
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_sin = sin_tab[(uint16_t)phase];
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_cos = cos_tab[(uint16_t)phase];
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#else
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if (phase < 0.0)
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phase += 2.0 * M_PI;
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else if (phase >= 2.0 * M_PI)
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phase -= 2.0 * M_PI;
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_sin = sin(phase);
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_cos = cos(phase);
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#endif
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I[s] = i * _cos - q * _sin;
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Q[s] = i * _sin + q * _cos;
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}
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demod->phase = phase;
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iir_process(&demod->lp[0], I, length);
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iir_process(&demod->lp[1], Q, length);
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last_phase = demod->last_phase;
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for (s = 0; s < length; s++) {
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phase = atan2(Q[s], I[s]);
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dev = (phase - last_phase) / 2 / M_PI;
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last_phase = phase;
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if (dev < -0.49)
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dev += 1.0;
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else if (dev > 0.49)
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dev -= 1.0;
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dev *= rate;
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frequency[s] = dev;
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}
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demod->last_phase = last_phase;
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}
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void fm_demodulate_real(fm_demod_t *demod, sample_t *frequency, int length, sample_t *baseband, sample_t *I, sample_t *Q)
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{
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double phase, rot, last_phase, dev, rate;
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double _sin, _cos;
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sample_t i;
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int s, ss;
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#ifdef FAST_SINE
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double *sin_tab, *cos_tab;
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#endif
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rate = demod->samplerate;
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phase = demod->phase;
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rot = demod->rot;
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#ifdef FAST_SINE
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sin_tab = demod->sin_tab;
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cos_tab = demod->sin_tab + 16384;
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#endif
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for (s = 0, ss = 0; s < length; s++) {
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phase += rot;
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i = baseband[ss++];
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#ifdef FAST_SINE
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if (phase < 0.0)
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phase += 65536.0;
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else if (phase >= 65536.0)
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phase -= 65536.0;
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_sin = sin_tab[(uint16_t)phase];
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_cos = cos_tab[(uint16_t)phase];
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#else
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if (phase < 0.0)
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phase += 2.0 * M_PI;
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else if (phase >= 2.0 * M_PI)
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phase -= 2.0 * M_PI;
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_sin = sin(phase);
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_cos = cos(phase);
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#endif
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I[s] = i * _cos;
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Q[s] = i * _sin;
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}
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demod->phase = phase;
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iir_process(&demod->lp[0], I, length);
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iir_process(&demod->lp[1], Q, length);
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last_phase = demod->last_phase;
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for (s = 0; s < length; s++) {
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phase = atan2(Q[s], I[s]);
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dev = (phase - last_phase) / 2 / M_PI;
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last_phase = phase;
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if (dev < -0.49)
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dev += 1.0;
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else if (dev > 0.49)
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dev -= 1.0;
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dev *= rate;
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frequency[s] = dev;
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}
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demod->last_phase = last_phase;
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}
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