1 files changed, 124 insertions, 0 deletions
diff --git a/src/modem_stats.c b/src/modem_stats.c
new file mode 100644
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--- /dev/null
+++ b/src/modem_stats.c
@@ -0,0 +1,124 @@
+/*---------------------------------------------------------------------------*\
+
+  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 <assert.h>
+#include <math.h>
+#include "modem_stats.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