mirror of
https://github.com/f4exb/sdrangel.git
synced 2025-10-30 12:30:20 -04:00
51 lines
1.2 KiB
C++
51 lines
1.2 KiB
C++
// Copyright 2020 Mobilinkd LLC.
|
|
|
|
#pragma once
|
|
|
|
#include <array>
|
|
#include <algorithm>
|
|
#include <cassert>
|
|
|
|
namespace modemm17
|
|
{
|
|
|
|
/**
|
|
* Estimate the phase of a sample by estimating the
|
|
* tangent of the sample point. This is done by computing
|
|
* the magnitude difference of the previous and following
|
|
* samples. We do not correct for 0-crossing errors because
|
|
* these errors have not affected the performance of clock
|
|
* recovery.
|
|
*/
|
|
struct PhaseEstimator
|
|
{
|
|
using float_type = float;
|
|
using samples_t = std::array<float, 3>; // 3 samples in length
|
|
|
|
float_type dx_;
|
|
|
|
PhaseEstimator(float sample_rate, float symbol_rate)
|
|
: dx_(2.0 * symbol_rate / sample_rate)
|
|
{}
|
|
|
|
/**
|
|
* This performs a rolling estimate of the phase.
|
|
*
|
|
* @param samples are three samples centered around the current sample point
|
|
* (t-1, t, t+1).
|
|
*/
|
|
float_type operator()(const samples_t& samples)
|
|
{
|
|
assert(dx_ > 0.0);
|
|
|
|
float ratio = ((samples.at(2) - samples.at(0)) / 3.0) / dx_;
|
|
// Clamp +/-5.
|
|
ratio = std::min(float(5.0), ratio);
|
|
ratio = std::max(float(-5.0), ratio);
|
|
|
|
return ratio;
|
|
}
|
|
};
|
|
|
|
} // modemm17
|