mirror of
https://github.com/f4exb/sdrangel.git
synced 2024-12-25 04:03:30 -05:00
79 lines
2.0 KiB
C++
79 lines
2.0 KiB
C++
// Copyright 2021 Mobilinkd LLC.
|
|
|
|
#pragma once
|
|
|
|
#include "SlidingDFT.h"
|
|
|
|
#include <array>
|
|
#include <complex>
|
|
#include <cstddef>
|
|
|
|
namespace modemm17 {
|
|
|
|
/**
|
|
* Data carrier detection using the difference of two DFTs, one in-band and
|
|
* one out-of-band. The first frequency is the in-band frequency and the
|
|
* second one is the out-of-band Frequency. The second frequency must be
|
|
* within the normal passband of the receiver, but beyond the normal roll-off
|
|
* frequency of the data carrier.
|
|
*
|
|
* This version uses the NSlidingDFT implementation to reduce the memory
|
|
* footprint.
|
|
*
|
|
* As an example, the cut-off for 4.8k symbol/sec 4-FSK is 2400Hz, so 3000Hz
|
|
* is a reasonable out-of-band frequency to use.
|
|
*
|
|
* Note: the input to this DCD must be unfiltered (raw) baseband input.
|
|
*/
|
|
template <size_t SampleRate, size_t Accuracy = 1000>
|
|
struct DataCarrierDetect
|
|
{
|
|
NSlidingDFT<SampleRate, SampleRate / Accuracy, 2> dft_;
|
|
float ltrigger_;
|
|
float htrigger_;
|
|
float level_1 = 0.0;
|
|
float level_2 = 0.0;
|
|
float level_ = 0.0;
|
|
bool triggered_ = false;
|
|
|
|
DataCarrierDetect(
|
|
size_t freq1,
|
|
size_t freq2,
|
|
float ltrigger = 2.0,
|
|
float htrigger = 5.0
|
|
) :
|
|
dft_({freq1, freq2}),
|
|
ltrigger_(ltrigger),
|
|
htrigger_(htrigger)
|
|
{
|
|
}
|
|
|
|
/**
|
|
* Accept unfiltered baseband input and output a decision on whether
|
|
* a carrier has been detected after every @tparam BlockSize inputs.
|
|
*/
|
|
void operator()(float sample)
|
|
{
|
|
auto result = dft_(sample);
|
|
level_1 += std::norm(result[0]);
|
|
level_2 += std::norm(result[1]);
|
|
}
|
|
|
|
/**
|
|
* Update the data carrier detection level.
|
|
*/
|
|
void update()
|
|
{
|
|
level_ = level_ * 0.8 + 0.2 * (level_1 / level_2);
|
|
level_1 = 0.0;
|
|
level_2 = 0.0;
|
|
triggered_ = triggered_ ? level_ > ltrigger_ : level_ > htrigger_;
|
|
}
|
|
|
|
|
|
float level() const { return level_; }
|
|
bool dcd() const { return triggered_; }
|
|
};
|
|
|
|
} // modemm17
|