From a9c190b6bb4f0a84f65eb6be425f6981a3309aef Mon Sep 17 00:00:00 2001
From: Jared Boone <jboone@earfeast.com>
Date: Mon, 28 Sep 2015 10:57:56 -0700
Subject: [PATCH] Matched filter implementation.

Essentially a complex FIR filter that's more flexible than the ones already in the code base. Refactor?!
---
 firmware/baseband/matched_filter.hpp | 99 ++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 firmware/baseband/matched_filter.hpp

diff --git a/firmware/baseband/matched_filter.hpp b/firmware/baseband/matched_filter.hpp
new file mode 100644
index 000000000..694c46bfb
--- /dev/null
+++ b/firmware/baseband/matched_filter.hpp
@@ -0,0 +1,99 @@
+/*
+ * Copyright (C) 2015 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 __MATCHED_FILTER_H__
+#define __MATCHED_FILTER_H__
+
+#include <cstddef>
+
+#include <complex>
+#include <array>
+#include <vector>
+#include <memory>
+
+#include <algorithm>
+#include <numeric>
+
+namespace dsp {
+namespace matched_filter {
+
+class MatchedFilter {
+public:
+	using sample_t = std::complex<float>;
+	using tap_t = std::complex<float>;
+
+	using taps_t = std::vector<tap_t>;
+
+	template<size_t N>
+	MatchedFilter(
+		const std::array<tap_t, N>& taps,
+		size_t decimation_factor = 1
+	) : taps(taps.cbegin(), taps.cend()),
+		decimation_factor { decimation_factor }
+	{
+		samples.assign(taps.size(), 0.0f);
+	}
+
+	bool execute_once(
+		const sample_t input
+	) {
+		samples[samples.size() - decimation_factor + decimation_phase] = input;
+
+		advance_decimation_phase();
+		if( is_new_decimation_cycle() ) {
+			output = std::inner_product(samples.cbegin(), samples.cend(), taps.cbegin(), sample_t { 0.0f, 0.0f });
+			shift_by_decimation_factor();
+			return true;
+		} else {
+			return false;
+		}
+	}
+
+	sample_t get_output() const {
+		return output;
+	}
+
+private:
+	using samples_t = std::vector<sample_t>;
+
+	samples_t samples;
+	taps_t taps;
+	size_t decimation_factor { 1 };
+	size_t decimation_phase { 0 };
+	sample_t output;
+
+	void shift_by_decimation_factor() {
+		std::rotate(samples.begin(), samples.begin() + decimation_factor, samples.end());
+	}
+
+	void advance_decimation_phase() {
+		decimation_phase = (decimation_phase + 1) % decimation_factor;
+	}
+
+	bool is_new_decimation_cycle() {
+		return (decimation_phase == 0);
+	}
+};
+
+} /* namespace matched_filter */
+} /* namespace dsp */
+
+#endif/*__MATCHED_FILTER_H__*/