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sdrangel/modemm17/PhaseEstimator.h
2022-07-20 09:07:00 +02:00

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