/*
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* Copyright 2019 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.android.server.wifi;
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import android.annotation.NonNull;
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import com.android.server.wifi.WifiCandidates.Candidate;
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import com.android.server.wifi.WifiCandidates.ScoredCandidate;
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import com.android.server.wifi.WifiScoreCardProto.Event;
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import java.util.Collection;
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/**
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* A candidate scorer that uses the scorecard to influence the choice.
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*/
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final class ScoreCardBasedScorer implements WifiCandidates.CandidateScorer {
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/**
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* This should match WifiNetworkSelector.experimentIdFromIdentifier(getIdentifier())
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* when using the default ScoringParams.
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*/
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public static final int SCORE_CARD_BASED_SCORER_DEFAULT_EXPID = 42902385;
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private final ScoringParams mScoringParams;
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// config_wifi_framework_RSSI_SCORE_OFFSET
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public static final int RSSI_SCORE_OFFSET = 85;
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// config_wifi_framework_RSSI_SCORE_SLOPE
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public static final int RSSI_SCORE_SLOPE_IS_4 = 4;
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// config_wifi_framework_5GHz_preference_boost_factor
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public static final int BAND_5GHZ_AWARD_IS_40 = 40;
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// config_wifi_framework_SECURITY_AWARD
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public static final int SECURITY_AWARD_IS_80 = 80;
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// config_wifi_framework_LAST_SELECTION_AWARD
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public static final int LAST_SELECTION_AWARD_IS_480 = 480;
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// config_wifi_framework_current_network_boost
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public static final int CURRENT_NETWORK_BOOST_IS_16 = 16;
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// config_wifi_framework_SAME_BSSID_AWARD
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public static final int SAME_BSSID_AWARD_IS_24 = 24;
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// Only use scorecard id we have data from this many polls
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public static final int MIN_POLLS_FOR_SIGNIFICANCE = 30;
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// Maximum allowable adjustment of the cutoff rssi (dB)
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public static final int RSSI_RAIL = 5;
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ScoreCardBasedScorer(ScoringParams scoringParams) {
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mScoringParams = scoringParams;
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}
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@Override
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public String getIdentifier() {
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return "ScoreCardBasedScorer";
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}
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/**
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* Calculates an individual candidate's score.
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*/
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private ScoredCandidate scoreCandidate(Candidate candidate) {
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int rssiSaturationThreshold = mScoringParams.getGoodRssi(candidate.getFrequency());
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int rssi = Math.min(candidate.getScanRssi(), rssiSaturationThreshold);
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int cutoff = estimatedCutoff(candidate);
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int score = (rssi - cutoff) * RSSI_SCORE_SLOPE_IS_4;
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if (candidate.getFrequency() >= ScoringParams.MINIMUM_5GHZ_BAND_FREQUENCY_IN_MEGAHERTZ) {
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score += BAND_5GHZ_AWARD_IS_40;
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}
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score += (int) (candidate.getLastSelectionWeight() * LAST_SELECTION_AWARD_IS_480);
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if (candidate.isCurrentNetwork()) {
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score += CURRENT_NETWORK_BOOST_IS_16 + SAME_BSSID_AWARD_IS_24;
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}
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if (!candidate.isOpenNetwork()) {
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score += SECURITY_AWARD_IS_80;
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}
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// To simulate the old strict priority rule, subtract a penalty based on
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// which evaluator added the candidate.
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score -= 1000 * candidate.getEvaluatorId();
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return new ScoredCandidate(score, 10, candidate);
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}
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private int estimatedCutoff(Candidate candidate) {
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int cutoff = -RSSI_SCORE_OFFSET;
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int lowest = cutoff - RSSI_RAIL;
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int highest = cutoff + RSSI_RAIL;
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WifiScoreCardProto.Signal signal = candidate.getEventStatistics(Event.SIGNAL_POLL);
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if (signal == null) return cutoff;
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if (!signal.hasRssi()) return cutoff;
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if (signal.getRssi().getCount() > MIN_POLLS_FOR_SIGNIFICANCE) {
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double mean = signal.getRssi().getSum() / signal.getRssi().getCount();
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double mean_square = signal.getRssi().getSumOfSquares() / signal.getRssi().getCount();
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double variance = mean_square - mean * mean;
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double sigma = Math.sqrt(variance);
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double value = mean - 2.0 * sigma;
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cutoff = (int) Math.min(Math.max(value, lowest), highest);
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}
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return cutoff;
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}
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@Override
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public ScoredCandidate scoreCandidates(@NonNull Collection<Candidate> group) {
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ScoredCandidate choice = ScoredCandidate.NONE;
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for (Candidate candidate : group) {
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ScoredCandidate scoredCandidate = scoreCandidate(candidate);
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if (scoredCandidate.value > choice.value) {
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choice = scoredCandidate;
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}
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}
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// Here we just return the highest scored candidate; we could
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// compute a new score, if desired.
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return choice;
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}
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@Override
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public boolean userConnectChoiceOverrideWanted() {
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return true;
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}
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}
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