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