M17: add symbol deviation estimator

Signed-off-by: Silvano Seva <silseva@fastwebnet.it>

openrtx/include/protocols/M17/DevEstimator.hpp

@@ -0,0 +1,139 @@
+/***************************************************************************
+ *   Copyright (C) 2025 by Federico Amedeo Izzo IU2NUO,                    *
+ *                         Niccolò Izzo IU2KIN                             *
+ *                         Frederik Saraci IU2NRO                          *
+ *                         Silvano Seva IU2KWO                             *
+ *                                                                         *
+ *   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 3 of the License, 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; if not, see <http://www.gnu.org/licenses/>   *
+ ***************************************************************************/
+
+#ifndef DEV_ESTIMATOR_H
+#define DEV_ESTIMATOR_H
+
+#include <cstdint>
+
+/**
+ * Symbol deviation estimator.
+ * This module allows to estimate the outer symbol deviation of a baseband
+ * stream. The baseband samples used for the estimation should be takend at the
+ * ideal sampling point. To work properly, the estimator needs to be initialized
+ * with a reference outer symbol deviation.
+ */
+class DevEstimator
+{
+public:
+    /**
+     * Constructor
+     */
+    DevEstimator() : outerDev({0, 0}), offset(0), posAccum(0), negAccum(0),
+                     posCnt(0), negCnt(0)
+    {
+    }
+
+    /**
+     * Destructor
+     */
+    ~DevEstimator()
+    {
+    }
+
+    /**
+     * Initialize the estimator state.
+     * Calling this function clears the internal state.
+     *
+     * @param outerDev: initial value for outer symbol deviation
+     */
+    void init(const std::pair<int32_t, int32_t> &outerDev)
+    {
+        this->outerDev = outerDev;
+        offset = 0;
+        posAccum = 0;
+        negAccum = 0;
+        posCnt = 0;
+        negCnt = 0;
+    }
+
+    /**
+     * Process a new sample.
+     *
+     * @param sample: baseband sample.
+     */
+    void sample(int16_t value)
+    {
+        int32_t posThresh = (2 * outerDev.first) / 3;
+        int32_t negThresh = (2 * outerDev.second) / 3;
+
+        if (value > posThresh) {
+            posAccum += value;
+            posCnt += 1;
+        }
+
+        if (value < negThresh) {
+            posAccum += value;
+            posCnt += 1;
+        }
+    }
+
+    /**
+     * Update the estimation of outer symbol deviation and zero-offset and
+     * start a new acquisition cycle.
+     */
+    void update()
+    {
+        if ((posCnt == 0) || (negCnt == 0))
+            return;
+
+        int32_t max = posAccum / posCnt;
+        int32_t min = negAccum / negCnt;
+        offset = (max + min) / 2;
+        outerDev.first = max - offset;
+        outerDev.second = min - offset;
+        posAccum = 0;
+        negAccum = 0;
+        posCnt = 0;
+        negCnt = 0;
+    }
+
+    /**
+     * Get the estimated outer symbol deviation from the last update.
+     * The function returns a std::pair where the first element is the positive
+     * deviation and the second the negative one.
+     *
+     * @return outer deviation.
+     */
+    std::pair<int32_t, int32_t> outerDeviation()
+    {
+        return outerDev;
+    }
+
+    /**
+     * Get the estimated zero-offset from the last update.
+     *
+     * @return zero-offset.
+     */
+    int32_t zeroOffset()
+    {
+        return offset;
+    }
+
+private:
+    std::pair<int32_t, int32_t> outerDev;
+    int32_t offset;
+    int32_t posAccum;
+    int32_t negAccum;
+    uint32_t posCnt;
+    uint32_t negCnt;
+};
+
+#endif