SSB_HighSpeed_Modem/modem/liquid_if.c
Kurt Moraw f72c347e30 update
2020-11-01 01:21:52 +01:00

172 lines
5.2 KiB
C

/*
* High Speed modem to transfer data in a 2,7kHz SSB channel
* =========================================================
* Author: DJ0ABR
*
* (c) DJ0ABR
* www.dj0abr.de
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
* liquid_dsp_interface.c ... functions using liquid-dsp
*
* liquid-dsp must be previously installed by running ./liquid-dsp-install (under linux)
*
*/
#include "qo100modem.h"
void modulator(uint8_t sym_in);
void close_dsp();
// modem objects
modulation_scheme ms = LIQUID_MODEM_QPSK;
modem mod = NULL;
// NCOs for mixing baseband <-> 1500 Hz
#define FREQUENCY 1500
int type = LIQUID_NCO; // nco type
nco_crcf upnco = NULL;
// TX-Interpolator Filter Parameters
// 44100 input rate for 2205 Sym/s = 20
// change for other rates
firinterp_crcf TX_interpolator = NULL;
unsigned int k_SampPerSymb = 20; // 44100 / (4410/2)
unsigned int m_filterDelay_Symbols = 15; // not too short for good filter
float beta_excessBW = 0.3f; // filter excess bandwidth factor
float tau_FracSymbOffset = -0.2f; // fractional symbol offset
int init_dsp()
{
close_dsp();
printf("create DSP\n");
k_SampPerSymb = txinterpolfactor;
if(bitsPerSymbol == 2)
ms = LIQUID_MODEM_QPSK;
else
ms = LIQUID_MODEM_DPSK8;
// create modulator
mod = modem_create(ms);
// create NCO for upmixing to 1500 Hz
double RADIANS_PER_SAMPLE = ((2.0*M_PI*(double)FREQUENCY)/(float)caprate);
upnco = nco_crcf_create(LIQUID_NCO);
nco_crcf_set_phase(upnco, 0.0f);
nco_crcf_set_frequency(upnco, RADIANS_PER_SAMPLE);
// TX: Interpolator Filter
// compute delay
while (tau_FracSymbOffset < 0) tau_FracSymbOffset += 1.0f; // ensure positive tau
float g = k_SampPerSymb*tau_FracSymbOffset; // number of samples offset
int ds=floorf(g); // additional symbol delay
float dt = (g - (float)ds); // fractional sample offset
// force dt to be in [0.5,0.5]
if (dt > 0.5f)
{
dt -= 1.0f;
ds++;
}
// calculate filter coeffs
unsigned int h_len_NumFilterCoeefs = 2 * k_SampPerSymb * m_filterDelay_Symbols + 1;
float h[h_len_NumFilterCoeefs];
liquid_firdes_prototype( LIQUID_FIRFILT_RRC,
k_SampPerSymb,
m_filterDelay_Symbols,
beta_excessBW,
dt,
h);
// create the filter
TX_interpolator = firinterp_crcf_create(k_SampPerSymb,h,h_len_NumFilterCoeefs);
printf("DSP created\n");
return 1;
}
void close_dsp()
{
if(mod != NULL) modem_destroy(mod);
if(upnco != NULL) nco_crcf_destroy(upnco);
if(TX_interpolator != NULL) firinterp_crcf_destroy(TX_interpolator);
mod = NULL;
upnco = NULL;
TX_interpolator = NULL;
}
// d ... symbols to send
// len ... number of symbols in d
void sendToModulator(uint8_t *d, int len)
{
//printf("sendToModulator %d bytes\n",len);
int symanz = len * 8 / bitsPerSymbol;
uint8_t syms[symanz];
if(bitsPerSymbol == 2)
convertBytesToSyms_QPSK(d, syms, len);
else
convertBytesToSyms_8PSK(d, syms, len);
for(int i=0; i<symanz; i++)
{
// remove gray code
// this adds gray code, liquid adds it again which removes it
syms[i] ^= (syms[i]>>1);
modulator(syms[i]);
}
}
// call for every symbol
// modulates, filters and upmixes symbols and send it to soundcard
void modulator(uint8_t sym_in)
{
liquid_float_complex sample;
modem_modulate(mod, sym_in, &sample);
//printf("TX ================= sample: %f + i%f\n", sample.real, sample.imag);
// interpolate by k_SampPerSymb
liquid_float_complex y[k_SampPerSymb];
firinterp_crcf_execute(TX_interpolator, sample, y);
for(unsigned int i=0; i<k_SampPerSymb; i++)
{
// move sample to 1,5kHz carrier
nco_crcf_step(upnco);
float minus_sine = -nco_crcf_sin(upnco);
float cosinus = nco_crcf_cos(upnco);
float re = y[i].real * cosinus;
float im = y[i].imag * minus_sine;
float usb = re + im;
// value is -1 .. +1
// adapt speed to soundcard samplerate
int fs;
while(1)
{
fs = pb_fifo_freespace(0);
if(fs) break;
usleep(10000);
}
pb_write_fifo(usb * 0.2); // reduce volume and send to soundcard
}
}