kopia lustrzana https://github.com/projecthorus/radiosonde_auto_rx
119 wiersze
3.6 KiB
C
119 wiersze
3.6 KiB
C
/*---------------------------------------------------------------------------*\
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FILE........: modem_stats.c
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AUTHOR......: David Rowe
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DATE CREATED: June 2015
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Common functions for returning demod stats from fdmdv and cohpsk modems.
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\*---------------------------------------------------------------------------*/
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/*
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Copyright (C) 2015 David Rowe
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All rights reserved.
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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 Lesser General Public License version 2.1, as
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published by the Free Software Foundation. This program is
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distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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License for more details.
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You should have received a copy of the GNU Lesser 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 <assert.h>
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#include <math.h>
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#include "modem_stats.h"
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#include "codec2_fdmdv.h"
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void modem_stats_open(struct MODEM_STATS *f)
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{
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int i;
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/* zero out all the stats */
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memset(f, 0, sizeof(struct MODEM_STATS));
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/* init the FFT */
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for(i=0; i<2*MODEM_STATS_NSPEC; i++)
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f->fft_buf[i] = 0.0;
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f->fft_cfg = kiss_fft_alloc (2*MODEM_STATS_NSPEC, 0, NULL, NULL);
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assert(f->fft_cfg != NULL);
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}
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void modem_stats_close(struct MODEM_STATS *f)
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{
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KISS_FFT_FREE(f->fft_cfg);
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}
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/*---------------------------------------------------------------------------*\
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FUNCTION....: modem_stats_get_rx_spectrum()
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AUTHOR......: David Rowe
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DATE CREATED: 9 June 2012
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Returns the MODEM_STATS_NSPEC point magnitude spectrum of the rx signal in
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dB. The spectral samples are scaled so that 0dB is the peak, a good
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range for plotting is 0 to -40dB.
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Note only the real part of the complex input signal is used at
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present. A complex variable is used for input for compatability
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with the other rx signal procesing.
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Successive calls can be used to build up a waterfall or spectrogram
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plot, by mapping the received levels to colours.
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The time-frequency resolution of the spectrum can be adjusted by varying
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MODEM_STATS_NSPEC. Note that a 2* MODEM_STATS_NSPEC size FFT is reqd to get
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MODEM_STATS_NSPEC output points. MODEM_STATS_NSPEC must be a power of 2.
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See octave/tget_spec.m for a demo real time spectral display using
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Octave. This demo averages the output over time to get a smoother
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display:
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av = 0.9*av + 0.1*mag_dB
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\*---------------------------------------------------------------------------*/
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void modem_stats_get_rx_spectrum(struct MODEM_STATS *f, float mag_spec_dB[], COMP rx_fdm[], int nin)
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{
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int i,j;
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COMP fft_in[2*MODEM_STATS_NSPEC];
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COMP fft_out[2*MODEM_STATS_NSPEC];
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float full_scale_dB;
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/* update buffer of input samples */
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for(i=0; i<2*MODEM_STATS_NSPEC-nin; i++)
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f->fft_buf[i] = f->fft_buf[i+nin];
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for(j=0; j<nin; j++,i++)
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f->fft_buf[i] = rx_fdm[j].real;
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assert(i == 2*MODEM_STATS_NSPEC);
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/* window and FFT */
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for(i=0; i<2*MODEM_STATS_NSPEC; i++) {
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fft_in[i].real = f->fft_buf[i] * (0.5 - 0.5*cosf((float)i*2.0*M_PI/(2*MODEM_STATS_NSPEC)));
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fft_in[i].imag = 0.0;
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}
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kiss_fft(f->fft_cfg, (kiss_fft_cpx *)fft_in, (kiss_fft_cpx *)fft_out);
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/* FFT scales up a signal of level 1 FDMDV_NSPEC */
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full_scale_dB = 20*log10(MODEM_STATS_NSPEC*FDMDV_SCALE);
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/* scale and convert to dB */
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for(i=0; i<MODEM_STATS_NSPEC; i++) {
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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);
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mag_spec_dB[i] -= full_scale_dB;
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}
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}
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