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/*---------------------------------------------------------------------------*\
FILE........: modem_stats.c
AUTHOR......: David Rowe
DATE CREATED: June 2015
Common functions for returning demod stats from fdmdv and cohpsk modems.
\*---------------------------------------------------------------------------*/
/*
Copyright (C) 2015 David Rowe
All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License version 2.1, as
published by the Free Software Foundation. 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 Lesser General Public License
along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include "modem_stats.h"
#include <assert.h>
#include <math.h>
#include "codec2_fdmdv.h"
#include "kiss_fft.h"
void modem_stats_open(struct MODEM_STATS *f) {
int i;
/* zero out all the stats */
memset(f, 0, sizeof(struct MODEM_STATS));
/* init the FFT */
#ifndef __EMBEDDED__
for (i = 0; i < 2 * MODEM_STATS_NSPEC; i++) f->fft_buf[i] = 0.0;
f->fft_cfg = (void *)kiss_fft_alloc(2 * MODEM_STATS_NSPEC, 0, NULL, NULL);
assert(f->fft_cfg != NULL);
#endif
}
void modem_stats_close(struct MODEM_STATS *f) {
#ifndef __EMBEDDED__
KISS_FFT_FREE(f->fft_cfg);
#endif
}
/*---------------------------------------------------------------------------*\
FUNCTION....: modem_stats_get_rx_spectrum()
AUTHOR......: David Rowe
DATE CREATED: 9 June 2012
Returns the MODEM_STATS_NSPEC point magnitude spectrum of the rx signal in
dB. The spectral samples are scaled so that 0dB is the peak, a good
range for plotting is 0 to -40dB.
Note only the real part of the complex input signal is used at
present. A complex variable is used for input for compatibility
with the other rx signal processing.
Successive calls can be used to build up a waterfall or spectrogram
plot, by mapping the received levels to colours.
The time-frequency resolution of the spectrum can be adjusted by varying
MODEM_STATS_NSPEC. Note that a 2* MODEM_STATS_NSPEC size FFT is reqd to get
MODEM_STATS_NSPEC output points. MODEM_STATS_NSPEC must be a power of 2.
See octave/tget_spec.m for a demo real time spectral display using
Octave. This demo averages the output over time to get a smoother
display:
av = 0.9*av + 0.1*mag_dB
\*---------------------------------------------------------------------------*/
#ifndef __EMBEDDED__
void modem_stats_get_rx_spectrum(struct MODEM_STATS *f, float mag_spec_dB[],
COMP rx_fdm[], int nin) {
int i, j;
COMP fft_in[2 * MODEM_STATS_NSPEC];
COMP fft_out[2 * MODEM_STATS_NSPEC];
float full_scale_dB;
/* update buffer of input samples */
for (i = 0; i < 2 * MODEM_STATS_NSPEC - nin; i++)
f->fft_buf[i] = f->fft_buf[i + nin];
for (j = 0; j < nin; j++, i++) f->fft_buf[i] = rx_fdm[j].real;
assert(i == 2 * MODEM_STATS_NSPEC);
/* window and FFT */
for (i = 0; i < 2 * MODEM_STATS_NSPEC; i++) {
fft_in[i].real =
f->fft_buf[i] *
(0.5 - 0.5 * cosf((float)i * 2.0 * M_PI / (2 * MODEM_STATS_NSPEC)));
fft_in[i].imag = 0.0;
}
kiss_fft((kiss_fft_cfg)f->fft_cfg, (kiss_fft_cpx *)fft_in,
(kiss_fft_cpx *)fft_out);
/* FFT scales up a signal of level 1 FDMDV_NSPEC */
full_scale_dB = 20 * log10(MODEM_STATS_NSPEC * FDMDV_SCALE);
/* scale and convert to dB */
for (i = 0; i < MODEM_STATS_NSPEC; i++) {
mag_spec_dB[i] = 10.0 * log10f(fft_out[i].real * fft_out[i].real +
fft_out[i].imag * fft_out[i].imag + 1E-12);
mag_spec_dB[i] -= full_scale_dB;
}
}
#endif
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