OOK slicer, clock recovery classes.

firmware/baseband/ook.hpp

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+/*
+ * Copyright (C) 2016 Jared Boone, ShareBrained Technology, Inc.
+ *
+ * This file is part of PortaPack.
+ *
+ * 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 2, 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; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __OOK_HPP__
+#define __OOK_HPP__
+
+#include "phase_detector.hpp"
+#include "phase_accumulator.hpp"
+
+#include <cstdint>
+#include <complex>
+#include <algorithm>
+#include <cmath>
+
+class OOKSlicerMagSquaredInt {
+public:
+	using symbol_t = bool;
+
+	constexpr OOKSlicerMagSquaredInt(
+		const float samples_per_symbol
+	) : mag2_threshold_leak_factor {
+			static_cast<uint32_t>(
+				factor_sq(-1.0f / (8.0f * samples_per_symbol)) * float(1ULL << 32)
+			)
+		}
+	{
+	}
+
+	symbol_t operator()(const std::complex<int16_t> in) {
+		const uint32_t real2 = in.real() * in.real();
+		const uint32_t imag2 = in.imag() * in.imag();
+		const uint32_t mag2 = real2 + imag2;
+
+		const uint32_t mag2_attenuated = mag2 >> 3;	// Approximation of (-4.5dB)^2
+		mag2_threshold = (uint64_t(mag2_threshold) * uint64_t(mag2_threshold_leak_factor)) >> 32;
+		mag2_threshold = std::max(mag2_threshold, mag2_attenuated);
+		const bool symbol = (mag2 > mag2_threshold);
+		return symbol;
+	}
+
+private:
+	const uint32_t mag2_threshold_leak_factor;
+	uint32_t mag2_threshold = 0;
+
+	constexpr float factor_sq(float db) {
+		return std::pow(10.0f, db / (10.0f / 2));
+	}
+};
+
+class OOKClockRecovery {
+public:
+	constexpr OOKClockRecovery(
+		const float samples_per_symbol
+	) : symbol_phase_inc_nominal { static_cast<uint32_t>(std::round((1ULL << 32) / samples_per_symbol)) },
+		phase_detector { samples_per_symbol },
+		phase_accumulator { symbol_phase_inc_nominal }
+	{
+	}
+
+	template<typename SymbolHandler>
+	void operator()(const uint32_t slicer_history, SymbolHandler symbol_handler) {
+		if( phase_accumulator() ) {
+			const auto detector_result = phase_detector(slicer_history);
+			phase_accumulator.set_inc(symbol_phase_inc_nominal + detector_result.error * (symbol_phase_inc_nominal >> 3));
+			symbol_handler(detector_result.symbol);
+		}
+	}
+
+private:
+	const uint32_t symbol_phase_inc_nominal;
+	PhaseDetectorEarlyLateGate phase_detector;
+	PhaseAccumulator phase_accumulator;
+};
+
+#endif/*__OOK_HPP__*/

firmware/baseband/phase_accumulator.hpp

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+/*
+ * Copyright (C) 2016 Jared Boone, ShareBrained Technology, Inc.
+ *
+ * This file is part of PortaPack.
+ *
+ * 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 2, 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; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __PHASE_ACCUMULATOR_HPP__
+#define __PHASE_ACCUMULATOR_HPP__
+
+#include <cstdint>
+
+class PhaseAccumulator {
+public:
+	constexpr PhaseAccumulator(
+		const uint32_t phase_inc
+	) : phase_inc { phase_inc }
+	{
+	}
+
+	bool operator()() {
+		const auto last_phase = phase;
+		phase += phase_inc;
+		return (phase < last_phase);
+	}
+
+	void set_inc(const uint32_t new_phase_inc) {
+		phase_inc = new_phase_inc;
+	}
+
+private:
+	uint32_t phase { 0 };
+	uint32_t phase_inc;
+};
+
+#endif/*__PHASE_ACCUMULATOR_HPP__*/

firmware/baseband/phase_detector.hpp

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+/*
+ * Copyright (C) 2016 Jared Boone, ShareBrained Technology, Inc.
+ *
+ * This file is part of PortaPack.
+ *
+ * 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 2, 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; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef __PHASE_DETECTOR_HPP__
+#define __PHASE_DETECTOR_HPP__
+
+#include <cstdint>
+#include <cstddef>
+#include <cmath>
+
+class PhaseDetectorEarlyLateGate {
+public:
+	using history_t = uint32_t;
+
+	using symbol_t = bool;
+	using error_t = int;
+
+	struct result_t {
+		symbol_t symbol;
+		error_t error;
+	};
+
+	constexpr PhaseDetectorEarlyLateGate(
+		const float samples_per_symbol
+	) : late_mask { (1U << static_cast<size_t>(std::ceil(samples_per_symbol / 2))) - 1 },
+		early_mask { late_mask << static_cast<size_t>(std::floor(samples_per_symbol / 2)) },
+		sample_bit { static_cast<size_t>(std::floor(samples_per_symbol / 2)) }
+	{
+	}
+
+	result_t operator()(const history_t symbol_history) const {
+		// history = ...0111, early
+		// history = ...1110, late
+
+		const symbol_t symbol = (symbol_history >> sample_bit) & 1;
+		const int late_side = __builtin_popcount(symbol_history & late_mask);
+		const int early_side = __builtin_popcount(symbol_history & early_mask);
+		const int lateness = late_side - early_side;
+		const int direction = lateness; //std::min(std::max(lateness, -1), 1);
+		const error_t error = direction;
+		return { symbol, error };
+	}
+
+private:
+	const history_t late_mask;
+	const history_t early_mask;
+	const size_t sample_bit;
+};
+
+#endif/*__PHASE_DETECTOR_HPP__*/