added first draft of a wifi quality analyzer

sensors/radio/WiFiQualityAnalyzer.h

@@ -0,0 +1,106 @@
+#ifndef WIFIQUALITYANALYZER_H
+#define WIFIQUALITYANALYZER_H
+
+#include "WiFiMeasurements.h"
+#include <unordered_set>
+
+class WiFiQualityAnalyzer {
+
+private:
+
+	int historySize = 3;
+	std::vector<WiFiMeasurements> history;
+	float quality = 0;
+
+public:
+
+	/** attach the current measurement and infer the quality */
+	void add(const WiFiMeasurements& mes) {
+
+		// update the history
+		history.push_back(mes);
+		while(history.size() > historySize) {
+			history.erase(history.begin());
+		}
+
+		// recalculate
+		update();
+
+	}
+
+	/** get a quality score for the WiFi */
+	float getQuality() const {
+		return quality;
+	}
+
+private:
+
+	/** re-calculate the current quality */
+	void update() {
+
+		const float qCnt = getQualityByCount();
+		const float qAvgdB = getQualityByAvgDB();
+
+		quality = qAvgdB;
+
+	}
+
+	/** score [0:1] based on the average sig-strength. the higher the better */
+	float getQualityByAvgDB() const {
+
+		// stats
+		float sum = 0;
+		float sum2 = 0;
+		float cnt = 0;
+
+		for (const WiFiMeasurements& mes : history) {
+			for (const WiFiMeasurement& m : mes.entries) {
+				const float rssi = m.getRSSI();
+				sum += rssi;
+				sum2 += rssi*rssi;
+				++cnt;
+			}
+		}
+
+		// average sig strength
+		const float avg = sum/cnt;
+		const float avg2 = sum2/cnt;
+		const float stdDev = std::sqrt(avg2 - avg*avg);
+
+		// avg rssi score
+		const float minRSSI = -90;
+		const float maxRSSI = -65;
+		float score1 = (avg-minRSSI) / (maxRSSI-minRSSI);	// min = 0; max = 1
+		if (score1 > 1) {score1 = 1;}
+		if (score1 < 0) {score1 = 0;}
+		//const float score1 = 1.0 - std::exp(-0.07 * (avg-minRSSI));
+
+		// std dev score
+		const float score2 = 1.0 - std::exp(-1.0 * stdDev);
+
+		return score1 * score2;
+
+	}
+
+	/** quality score [0:1] according to the number of seen APs */
+	float getQualityByCount() const {
+
+		// distinct macs
+		std::unordered_set<MACAddress> macs;
+		for (const WiFiMeasurements& mes : history) {
+			for (const WiFiMeasurement& m : mes.entries) {
+				macs.insert(m.getAP().getMAC());
+			}
+		}
+
+		// number of distinct macs
+		const int cnt = macs.size();
+
+		// see function plot. function between [0.0:1.0] has 0.5 around 7 seen APs
+		return 1.0 - std::exp(-0.1 * cnt);
+
+	}
+
+};
+
+#endif // WIFIQUALITYANALYZER_H