140 lines
3.9 KiB
C++
140 lines
3.9 KiB
C++
/* -*- c++ -*- */
|
|
/*
|
|
* gr-satnogs: SatNOGS GNU Radio Out-Of-Tree Module
|
|
*
|
|
* Copyright (C) 2018, Libre Space Foundation <http://librespacefoundation.org/>
|
|
*
|
|
* 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 3 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, see <http://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
#ifdef HAVE_CONFIG_H
|
|
#include "config.h"
|
|
#endif
|
|
|
|
#include <gnuradio/io_signature.h>
|
|
#include "quad_demod_filter_ff_impl.h"
|
|
|
|
namespace gr {
|
|
namespace satnogs {
|
|
|
|
quad_demod_filter_ff::sptr
|
|
quad_demod_filter_ff::make(float gain, int window)
|
|
{
|
|
return gnuradio::get_initial_sptr
|
|
(new quad_demod_filter_ff_impl(gain, window));
|
|
}
|
|
|
|
/*
|
|
* The private constructor
|
|
*/
|
|
quad_demod_filter_ff_impl::quad_demod_filter_ff_impl (float gain,
|
|
int window) :
|
|
gr::sync_block ("quad_demod_filter_ff",
|
|
gr::io_signature::make (1, 1, sizeof(float)),
|
|
gr::io_signature::make (1, 1, sizeof(float))),
|
|
d_gain (gain),
|
|
d_norm (1.0f / window),
|
|
d_win (window),
|
|
d_sum (0.0f),
|
|
d_sum_sq (0.0f),
|
|
d_remaining (0)
|
|
{
|
|
if(window < 1) {
|
|
throw std::invalid_argument ("Window must be a positive");
|
|
}
|
|
set_history (window);
|
|
}
|
|
|
|
/*
|
|
* Our virtual destructor.
|
|
*/
|
|
quad_demod_filter_ff_impl::~quad_demod_filter_ff_impl()
|
|
{
|
|
}
|
|
|
|
/**
|
|
* Fast approximation of the inverse of the square root.
|
|
* Thank you OpenArena!
|
|
* @param number the number to be computed
|
|
* @return the inverse of the square root of the number
|
|
*/
|
|
static inline float
|
|
inv_sqrt (float number)
|
|
{
|
|
long i;
|
|
float x2, y;
|
|
const float threehalfs = 1.5f;
|
|
|
|
x2 = number * 0.5f;
|
|
y = number;
|
|
i = *(long *) &y;
|
|
i = 0x5f3759df - (i >> 1); /* what the fuck? */
|
|
y = *(float *) &i;
|
|
y = y * (threehalfs - (x2 * y * y));
|
|
return y;
|
|
}
|
|
|
|
int
|
|
quad_demod_filter_ff_impl::work (int noutput_items,
|
|
gr_vector_const_void_star &input_items,
|
|
gr_vector_void_star &output_items)
|
|
{
|
|
const float *in = (const float *) input_items[0];
|
|
float *out = (float *) output_items[0];
|
|
float m;
|
|
float m_sq;
|
|
float snr;
|
|
float in_old;
|
|
float in_new;
|
|
|
|
float diff;
|
|
for (int i = 0; i < noutput_items; i++) {
|
|
in_old = std::abs (in[i]);
|
|
in_new = std::abs (in[i + d_win - 1]);
|
|
d_sum -= in_old;
|
|
d_sum += in_new;
|
|
d_sum_sq -= (in_old * in_old);
|
|
d_sum_sq += (in_new * in_new);
|
|
|
|
m = (d_sum * d_norm);
|
|
m_sq = (d_sum_sq * d_norm);
|
|
snr = m * inv_sqrt (m_sq - m * m);
|
|
|
|
/*
|
|
* If the SNR is high enough start passing the data to the output.
|
|
* In order not to loose any samples due to the settling period, start
|
|
* from the buffered and let a window of samples to pass after the
|
|
* trigger is off
|
|
*/
|
|
if (snr > d_gain * 1.8) {
|
|
d_remaining = 2 * d_win;
|
|
}
|
|
|
|
if (d_remaining) {
|
|
out[i] = in[i];
|
|
d_remaining--;
|
|
}
|
|
else {
|
|
out[i] = 0.0f;
|
|
}
|
|
}
|
|
|
|
// Tell runtime system how many output items we produced.
|
|
return noutput_items;
|
|
}
|
|
|
|
} /* namespace satnogs */
|
|
} /* namespace gr */
|
|
|