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