460 lines
14 KiB
C
460 lines
14 KiB
C
/* Jolly's Version of PSK
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*
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* (C) 2020 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 <stdint.h>
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#include <unistd.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 "../libdebug/debug.h"
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#include "../libsample/sample.h"
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#include "psk.h"
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/* bits to phase change */
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double phase_change8[8] = {
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2.0 * M_PI * 1.0 / 8.0,
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2.0 * M_PI * 0.0 / 8.0,
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2.0 * M_PI * 2.0 / 8.0,
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2.0 * M_PI * 3.0 / 8.0,
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2.0 * M_PI * 6.0 / 8.0,
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2.0 * M_PI * 7.0 / 8.0,
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2.0 * M_PI * 5.0 / 8.0,
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2.0 * M_PI * 4.0 / 8.0,
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};
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/* phase change to bits */
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uint8_t phase2bits[8] = { 1, 0, 2, 3, 7, 6, 4, 5 };
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/* debug decoder */
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//#define DEBUG_DECODER
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/* use SIT original encoder */
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//#define SIT_ENCODER
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/* may be different for testing purpose */
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#define TX_CARRIER 1800.0
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#define RX_CARRIER 1800.0
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#ifdef SIT_ENCODER
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static int8_t symbols_int[8][30] = {
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{ 0xff, 0xfd, 0x00, 0x02, 0xfe, 0x02, 0x0d, 0x05, 0xf9, 0x05, 0x02, 0xd2, 0xc9, 0x23, 0x64, 0x23,
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0xc9, 0xd2, 0x02, 0x05, 0xf9, 0x05, 0x0d, 0x02, 0xfe, 0x02, 0x00, 0xfd, 0xff, 0x00 },
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{ 0xfe, 0xff, 0x03, 0x02, 0xff, 0x07, 0x0a, 0xfa, 0xf7, 0x03, 0xef, 0xd0, 0xfe, 0x56, 0x47, 0xdb,
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0xb4, 0xef, 0x14, 0x03, 0xff, 0x0e, 0x09, 0xfc, 0xfe, 0x01, 0xfd, 0xfd, 0x00, 0x00 },
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{ 0xff, 0x01, 0x04, 0x01, 0x01, 0x08, 0x00, 0xf2, 0xfa, 0x00, 0xe6, 0xea, 0x34, 0x57, 0x00, 0xa9,
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0xcc, 0x16, 0x1a, 0x00, 0x06, 0x0e, 0x00, 0xf8, 0xff, 0xff, 0xfc, 0xff, 0x01, 0x00 },
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{ 0x00, 0x03, 0x03, 0xff, 0x02, 0x04, 0xf7, 0xf2, 0x01, 0xfd, 0xec, 0x11, 0x4c, 0x25, 0xb9, 0xaa,
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0x02, 0x30, 0x11, 0xfd, 0x09, 0x06, 0xf6, 0xf9, 0x01, 0xfe, 0xfd, 0x01, 0x02, 0x00 },
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{ 0x01, 0x03, 0x00, 0xfe, 0x02, 0xfe, 0xf3, 0xfb, 0x07, 0xfb, 0xfe, 0x2e, 0x37, 0xdd, 0x9c, 0xdd,
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0x37, 0x2e, 0xfe, 0xfb, 0x07, 0xfb, 0xf3, 0xfe, 0x02, 0xfe, 0x00, 0x03, 0x01, 0x00 },
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{ 0x02, 0x01, 0xfd, 0xfe, 0x01, 0xf9, 0xf6, 0x06, 0x09, 0xfd, 0x11, 0x30, 0x02, 0xaa, 0xb9, 0x25,
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0x4c, 0x11, 0xec, 0xfd, 0x01, 0xf2, 0xf7, 0x04, 0x02, 0xff, 0x03, 0x03, 0x00, 0x00 },
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{ 0x01, 0xff, 0xfc, 0xff, 0xff, 0xf8, 0x00, 0x0e, 0x06, 0x00, 0x1a, 0x16, 0xcc, 0xa9, 0x00, 0x57,
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0x34, 0xea, 0xe6, 0x00, 0xfa, 0xf2, 0x00, 0x08, 0x01, 0x01, 0x04, 0x01, 0xff, 0x00 },
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{ 0x00, 0xfd, 0xfd, 0x01, 0xfe, 0xfc, 0x09, 0x0e, 0xff, 0x03, 0x14, 0xef, 0xb4, 0xdb, 0x47, 0x56,
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0xfe, 0xd0, 0xef, 0x03, 0xf7, 0xfa, 0x0a, 0x07, 0xff, 0x02, 0x03, 0xff, 0xfe, 0x00 },
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};
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static sample_t symbols[8][150];
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/* indexes are rotated by 45 degrees, because the phase change during one symbol is 360+45 degrees */
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static int bits2index[8] = { 2, 1, 3, 4, 7, 0, 6, 5 };
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#endif
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/* init psk */
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int psk_mod_init(psk_mod_t *psk, void *inst, int (*send_bit)(void *inst), int samplerate, double symbolrate)
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{
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double cutoff, transitionband;
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memset(psk, 0, sizeof(*psk));
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psk->send_bit = send_bit;
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psk->inst = inst;
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#ifdef SIT_ENCODER
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int i, j, s;
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sample_t spl;
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if (samplerate != 48000) {
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PDEBUG(DDSP, DEBUG_NOTICE, "Sampling rate for PSK encoder must be exactly 48000 Hz!\n");
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return -EINVAL;
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}
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if (symbolrate != 1600) {
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PDEBUG(DDSP, DEBUG_NOTICE, "Symbol rate for PSK encoder must be exactly 1600 Hz!\n");
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return -EINVAL;
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}
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cutoff = 3300.0;
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transitionband = 200;
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psk->lp[0] = fir_lowpass_init((double)samplerate, cutoff, transitionband);
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PDEBUG(DDSP, DEBUG_DEBUG, "Cut off frequency is at %.1f Hz and %.1f Hz.\n", TX_CARRIER + cutoff, TX_CARRIER - cutoff);
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/* interpolate symbol table from 9600 Hz to 48000 Hz */
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for (i = 0; i < 8; i++) {
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for (j = 0, s = 0; j < 30; j++) {
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spl = (double)symbols_int[i][j] / 128.0;
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symbols[i][s++] = spl;
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symbols[i][s++] = spl;
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symbols[i][s++] = spl;
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symbols[i][s++] = spl;
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symbols[i][s++] = spl;
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}
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}
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#else
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if (samplerate < 48000) {
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PDEBUG(DDSP, DEBUG_NOTICE, "Sampling rate for PSK encoder must be 48000 Hz minimum!\n");
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return -EINVAL;
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}
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/* fixme: make correct filter */
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cutoff = RX_CARRIER - 100;
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transitionband = 200;
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psk->lp[0] = fir_lowpass_init((double)samplerate, cutoff, transitionband);
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psk->lp[1] = fir_lowpass_init((double)samplerate, cutoff, transitionband);
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PDEBUG(DDSP, DEBUG_DEBUG, "Cut off frequency is at %.1f Hz and %.1f Hz.\n", TX_CARRIER + cutoff, TX_CARRIER - cutoff);
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psk->symbols_per_sample = symbolrate / (double)samplerate;
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PDEBUG(DDSP, DEBUG_DEBUG, "Symbol duration of %.4f symbols per sample @ %d.\n", psk->symbols_per_sample, samplerate);
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psk->carrier_phaseshift = 2.0 * M_PI * TX_CARRIER / (double)samplerate;
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PDEBUG(DDSP, DEBUG_DEBUG, "Carrier phase shift of %.4f per sample @ %d.\n", psk->carrier_phaseshift, samplerate);
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#endif
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return 0;
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}
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void psk_mod_exit(psk_mod_t *psk)
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{
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if (psk->lp[0]) {
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fir_exit(psk->lp[0]);
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psk->lp[0] = NULL;
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}
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if (psk->lp[1]) {
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fir_exit(psk->lp[1]);
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psk->lp[1] = NULL;
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}
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}
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void psk_mod(psk_mod_t *psk, sample_t *sample, int length)
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{
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uint8_t bits;
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int s;
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#ifdef SIT_ENCODER
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int index;
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for (s = 0; s < length; s++) {
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if (psk->spl_count == 0) {
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bits = (psk->send_bit(psk->inst) & 1) << 2;
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bits |= (psk->send_bit(psk->inst) & 1) << 1;
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bits |= (psk->send_bit(psk->inst) & 1);
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#ifdef DEBUG_DECODER
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static int nextbit = 0;
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if (++nextbit == 8)
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nextbit = 0;
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bits = nextbit;
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#endif
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index = psk->sym_list[psk->sym_count];
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psk->sym_count = (psk->sym_count + 1) % 5;
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psk->sym_list[psk->sym_count] = (index + bits2index[bits]) & 7;
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}
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sample[s] = symbols[psk->sym_list[psk->sym_count]][psk->spl_count];
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sample[s] += symbols[psk->sym_list[(psk->sym_count + 4) % 5]][30 + psk->spl_count];
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sample[s] += symbols[psk->sym_list[(psk->sym_count + 3) % 5]][60 + psk->spl_count];
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sample[s] += symbols[psk->sym_list[(psk->sym_count + 2) % 5]][90 + psk->spl_count];
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sample[s] += symbols[psk->sym_list[(psk->sym_count + 1) % 5]][120 + psk->spl_count];
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if (++psk->spl_count == 30)
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psk->spl_count = 0;
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}
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fir_process(psk->lp[0], sample, length);
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#else
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sample_t I[length], Q[length];
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/* count symbol and get new bits for next symbol */
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for (s = 0; s < length; s++) {
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psk->symbol_pos += psk->symbols_per_sample;
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if (psk->symbol_pos >= 1.0) {
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psk->symbol_pos -= 1.0;
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/* get tree bits */
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bits = (psk->send_bit(psk->inst) & 1) << 2;
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bits |= (psk->send_bit(psk->inst) & 1) << 1;
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bits |= (psk->send_bit(psk->inst) & 1);
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#ifdef DEBUG_DECODER
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static int nextbit = 0;
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if (++nextbit == 8)
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nextbit = 0;
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bits = nextbit;
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#endif
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/* change phase_shift */
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psk->phase_shift += phase_change8[bits];
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if (psk->phase_shift > M_PI)
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psk->phase_shift -= 2.0 * M_PI;
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}
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I[s] = cos(psk->phase_shift);
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Q[s] = sin(psk->phase_shift);
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}
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/* filter phase_shift to limit bandwidth */
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fir_process(psk->lp[0], I, length);
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fir_process(psk->lp[1], Q, length);
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/* modulate with carrier frequency */
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for (s = 0; s < length; s++) {
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/* compensate overshooting of filter */
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*sample++ = (I[s] * cos(psk->carrier_phase) - Q[s] * sin(psk->carrier_phase)) * 0.7;
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psk->carrier_phase += psk->carrier_phaseshift;
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if (psk->carrier_phase >= 2.0 * M_PI)
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psk->carrier_phase -= 2.0 * M_PI;
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}
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#endif
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}
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int psk_demod_init(psk_demod_t *psk, void *inst, void (*receive_bit)(void *inst, int bit), int samplerate, double symbolrate)
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{
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double cutoff, transitionband;
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if (samplerate < 48000) {
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PDEBUG(DDSP, DEBUG_NOTICE, "Sampling rate for PSK decoder must be 48000 Hz minimum!\n");
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return -EINVAL;
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}
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memset(psk, 0, sizeof(*psk));
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psk->receive_bit = receive_bit;
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psk->inst = inst;
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/* fixme: make correct filter */
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// cutoff = symbolrate / 2.0 * 1.5;
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cutoff = RX_CARRIER - 100;
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transitionband = 200;
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psk->lp[0] = fir_lowpass_init((double)samplerate, cutoff, transitionband);
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psk->lp[1] = fir_lowpass_init((double)samplerate, cutoff, transitionband);
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iir_lowpass_init(&psk->lp_error[0], 50.0, samplerate, 2);
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iir_lowpass_init(&psk->lp_error[1], 50.0, samplerate, 2);
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iir_bandpass_init(&psk->lp_clock, symbolrate, samplerate, 40);
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psk->sample_delay = (int)floor((double)samplerate / symbolrate * 0.25); /* percent of sine duration behind zero crossing */
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PDEBUG(DDSP, DEBUG_DEBUG, "Cut off frequency is at %.1f Hz and %.1f Hz.\n", RX_CARRIER + cutoff, RX_CARRIER - cutoff);
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psk->carrier_phaseshift = 2.0 * M_PI * -RX_CARRIER / (double)samplerate;
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PDEBUG(DDSP, DEBUG_DEBUG, "Carrier phase shift of %.4f per sample @ %d.\n", psk->carrier_phaseshift, samplerate);
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return 0;
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}
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void psk_demod_exit(psk_demod_t *psk)
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{
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if (psk->lp[0]) {
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fir_exit(psk->lp[0]);
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psk->lp[0] = NULL;
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}
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if (psk->lp[1]) {
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fir_exit(psk->lp[1]);
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psk->lp[1] = NULL;
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}
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}
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#ifdef DEBUG_DECODER
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static void debug_phase(double phase, double amplitude, double error, double amplitude2)
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{
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int x, y, xx = 100, yy = 50;
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char buffer[yy][xx + 1];
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double p;
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int i;
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if (amplitude > 1.0)
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amplitude = 1.0;
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if (amplitude < -0.0)
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amplitude = -0.0;
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if (amplitude2 > 0.5)
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amplitude2 = 0.5;
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if (amplitude2 < -0.5)
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amplitude2 = -0.5;
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amplitude2 += 0.5;
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/* clear (EOL) and fill spaces with border */
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memset(buffer, '\0', sizeof(buffer));
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memset(buffer[0], '#', xx);
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for (y = 1; y < yy - 1; y++) {
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memset(buffer[y], ' ', xx);
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buffer[y][0] = '|';
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buffer[y][xx - 1] = '|';
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}
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memset(buffer[yy - 1], '-', xx);
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buffer[0][0] = '+';
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buffer[0][xx - 1] = '+';
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buffer[yy - 1][0] = '+';
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buffer[yy - 1][xx - 1] = '+';
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/* plot target angles on buffer */
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for (i = 0, p = 0.0; i < 8; i++, p = p + M_PI / 4.0) {
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y = -(sin(p + error) * (double)yy / 1.1) + (double)yy;
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x = (cos(p + error) * (double)xx / 2.2) + (double)xx / 2.0;
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buffer[y >> 1][x] = '0' + i;
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}
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/* plot angle on buffer */
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y = -(amplitude * 1.1 * sin(phase) * (double)yy / 1.1) + (double)yy;
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x = (amplitude * 1.1 * cos(phase) * (double)xx / 2.2) + (double)xx / 2.0;
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if ((y & 1))
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buffer[y >> 1][x] = '.';
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else
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buffer[y >> 1][x] = '\'';
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/* plot amplitude on buffer */
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y = -(amplitude * (double)yy * 2.0 / 1.1) + (double)yy * 2.0 / 1.1;
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if ((y & 1))
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buffer[y >> 1][1] = '.';
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else
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buffer[y >> 1][1] = '\'';
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y = -(amplitude2 * (double)yy * 2.0 / 1.1) + (double)yy * 2.0 / 1.1;
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if ((y & 1))
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buffer[y >> 1][2] = '.';
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else
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buffer[y >> 1][2] = '\'';
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/* display on screen */
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for (y = 0; y < yy; y++)
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printf("%s\n", buffer[y]);
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}
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#endif
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void psk_demod(psk_demod_t *psk, sample_t *sample, int length)
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{
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sample_t I[length], Q[length], i;
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sample_t Ip[length], Qp[length];
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double phases[length];
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sample_t amplitudes[length], amplitudes2[length];
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double phaseshift, phase, phase_error, angle_error;
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uint16_t phase_error_int, offset;
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int s, ss;
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uint8_t sector, rotation, bits;
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/* demodulate phase from carrier */
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phaseshift = psk->carrier_phaseshift;
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phase = psk->carrier_phase;
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for (s = 0, ss = 0; s < length; s++) {
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phase += phaseshift;
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i = sample[ss++];
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if (phase < 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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I[s] = i * cos(phase);
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Q[s] = i * sin(phase);
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}
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psk->carrier_phase = phase;
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fir_process(psk->lp[0], I, length);
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fir_process(psk->lp[1], Q, length);
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/* get phase error */
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for (s = 0, ss = 0; s < length; s++) {
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phases[s] = atan2(Q[s], I[s]);
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amplitudes[s] = sqrt(Q[s] * Q[s] + I[s] * I[s]) * 2.0;
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amplitudes2[s] = amplitudes[s];
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Ip[s] = amplitudes[s] * cos(phases[s] * 8.0) * 2.0;
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Qp[s] = amplitudes[s] * sin(phases[s] * 8.0) * 2.0;
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}
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iir_process(&psk->lp_error[0], Ip, length);
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iir_process(&psk->lp_error[1], Qp, length);
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/* filter amplitude to get symbol clock */
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/* NOTE: the filter biases the amplitude, so that we have positive and negative peaks.
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positive peak is the sample point */
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iir_process(&psk->lp_clock, amplitudes2, length);
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for (s = 0; s < length; s++) {
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/* calculate change of phase error angle within one sample */
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phase_error_int = (int)floor(atan2(Qp[s], Ip[s]) / (2.0 * M_PI) * 65536.0);
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offset = phase_error_int - psk->last_phase_error;
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psk->last_phase_error = phase_error_int;
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/* apply change to current phase error value */
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psk->phase_error += (int16_t)offset;
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if (psk->phase_error >= 65536 * 8)
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psk->phase_error -= 65536 * 8;
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if (psk->phase_error < 0)
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psk->phase_error += 65536 * 8;
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phase_error = (double)psk->phase_error / 65536.0 * (2.0 * M_PI) / 8.0;
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/* if we have reached a zero crossing of the amplitude signal, wait for sample point */
|
|
if (psk->sample_timer && --psk->sample_timer == 0) {
|
|
/* sample point reached */
|
|
phase = fmod(phases[s] - phase_error + 4.0 * M_PI, 2.0 * M_PI);
|
|
if (phase < 2.0 * M_PI / 16.0 * 1.0)
|
|
sector = 0;
|
|
else if (phase < 2.0 * M_PI / 16.0 * 3.0)
|
|
sector = 1;
|
|
else if (phase < 2.0 * M_PI / 16.0 * 5.0)
|
|
sector = 2;
|
|
else if (phase < 2.0 * M_PI / 16.0 * 7.0)
|
|
sector = 3;
|
|
else if (phase < 2.0 * M_PI / 16.0 * 9.0)
|
|
sector = 4;
|
|
else if (phase < 2.0 * M_PI / 16.0 * 11.0)
|
|
sector = 5;
|
|
else if (phase < 2.0 * M_PI / 16.0 * 13.0)
|
|
sector = 6;
|
|
else if (phase < 2.0 * M_PI / 16.0 * 15.0)
|
|
sector = 7;
|
|
else
|
|
sector = 0;
|
|
angle_error = fmod(phase / 2.0 / M_PI * 8.0, 1.0);
|
|
if (angle_error > 0.5)
|
|
angle_error -= 1.0;
|
|
|
|
rotation = (sector - psk->last_sector) & 7; // might be negative, so we use AND!
|
|
bits = phase2bits[rotation];
|
|
#ifdef DEBUG_DECODER
|
|
printf("sector=%d last_sector=%d rotation=%d bits=%d angle_error=%.2f\n", sector, psk->last_sector, rotation, bits, angle_error);
|
|
#endif
|
|
psk->last_sector = sector;
|
|
/* report bits */
|
|
#ifndef DEBUG_DECODER
|
|
psk->receive_bit(psk->inst, bits >> 2);
|
|
psk->receive_bit(psk->inst, (bits >> 1) & 1);
|
|
psk->receive_bit(psk->inst, bits & 1);
|
|
#endif
|
|
}
|
|
if (psk->last_amplitude <= 0.0 && amplitudes2[s] > 0.0)
|
|
psk->sample_timer = psk->sample_delay;
|
|
psk->last_amplitude = amplitudes2[s];
|
|
|
|
#ifdef DEBUG_DECODER
|
|
static int when = 0;
|
|
if (++when > 10000) {
|
|
printf("\0337\033[H");
|
|
/* display amplitude between 0.0 and 1.0, aplitude2 between -0.5 and 0.5 */
|
|
debug_phase(phases[s], amplitudes[s], phase_error, amplitudes2[s]);
|
|
printf("phase2 = %.4f offset = %d, error = %d (error & 0xffff = %d)\n", phase_error, offset, psk->phase_error, psk->phase_error & 0xffff);
|
|
printf("\033[0;39m\0338"); fflush(stdout);
|
|
usleep(50000);
|
|
}
|
|
#endif
|
|
}
|
|
}
|
|
|