1 /* 2 * Copyright (C) 2011 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.android.server.wifi; 18 19 import android.content.BroadcastReceiver; 20 import android.content.ContentResolver; 21 import android.content.Context; 22 import android.content.Intent; 23 import android.content.IntentFilter; 24 import android.database.ContentObserver; 25 import android.net.ConnectivityManager; 26 import android.net.LinkProperties; 27 import android.net.NetworkInfo; 28 import android.net.wifi.RssiPacketCountInfo; 29 import android.net.wifi.SupplicantState; 30 import android.net.wifi.WifiInfo; 31 import android.net.wifi.WifiManager; 32 import android.os.Message; 33 import android.os.Messenger; 34 import android.os.SystemClock; 35 import android.provider.Settings; 36 import android.util.LruCache; 37 38 import com.android.internal.util.AsyncChannel; 39 import com.android.internal.util.Protocol; 40 import com.android.internal.util.State; 41 import com.android.internal.util.StateMachine; 42 43 import java.io.FileDescriptor; 44 import java.io.PrintWriter; 45 import java.text.DecimalFormat; 46 47 /** 48 * WifiWatchdogStateMachine monitors the connection to a WiFi network. When WiFi 49 * connects at L2 layer, the beacons from access point reach the device and it 50 * can maintain a connection, but the application connectivity can be flaky (due 51 * to bigger packet size exchange). 52 * <p> 53 * We now monitor the quality of the last hop on WiFi using packet loss ratio as 54 * an indicator to decide if the link is good enough to switch to Wi-Fi as the 55 * uplink. 56 * <p> 57 * When WiFi is connected, the WiFi watchdog keeps sampling the RSSI and the 58 * instant packet loss, and record it as per-AP loss-to-rssi statistics. When 59 * the instant packet loss is higher than a threshold, the WiFi watchdog sends a 60 * poor link notification to avoid WiFi connection temporarily. 61 * <p> 62 * While WiFi is being avoided, the WiFi watchdog keep watching the RSSI to 63 * bring the WiFi connection back. Once the RSSI is high enough to achieve a 64 * lower packet loss, a good link detection is sent such that the WiFi 65 * connection become available again. 66 * <p> 67 * BSSID roaming has been taken into account. When user is moving across 68 * multiple APs, the WiFi watchdog will detect that and keep watching the 69 * currently connected AP. 70 * <p> 71 * Power impact should be minimal since much of the measurement relies on 72 * passive statistics already being tracked at the driver and the polling is 73 * done when screen is turned on and the RSSI is in a certain range. 74 * 75 * @hide 76 */ 77 public class WifiWatchdogStateMachine extends StateMachine { 78 79 private static final boolean DBG = false; 80 81 private static final int BASE = Protocol.BASE_WIFI_WATCHDOG; 82 83 /* Internal events */ 84 private static final int EVENT_WATCHDOG_TOGGLED = BASE + 1; 85 private static final int EVENT_NETWORK_STATE_CHANGE = BASE + 2; 86 private static final int EVENT_RSSI_CHANGE = BASE + 3; 87 private static final int EVENT_SUPPLICANT_STATE_CHANGE = BASE + 4; 88 private static final int EVENT_WIFI_RADIO_STATE_CHANGE = BASE + 5; 89 private static final int EVENT_WATCHDOG_SETTINGS_CHANGE = BASE + 6; 90 private static final int EVENT_BSSID_CHANGE = BASE + 7; 91 private static final int EVENT_SCREEN_ON = BASE + 8; 92 private static final int EVENT_SCREEN_OFF = BASE + 9; 93 94 /* Internal messages */ 95 private static final int CMD_RSSI_FETCH = BASE + 11; 96 97 /* Notifications from/to WifiStateMachine */ 98 static final int POOR_LINK_DETECTED = BASE + 21; 99 static final int GOOD_LINK_DETECTED = BASE + 22; 100 101 /* 102 * RSSI levels as used by notification icon 103 * Level 4 -55 <= RSSI 104 * Level 3 -66 <= RSSI < -55 105 * Level 2 -77 <= RSSI < -67 106 * Level 1 -88 <= RSSI < -78 107 * Level 0 RSSI < -88 108 */ 109 110 /** 111 * WiFi link statistics is monitored and recorded actively below this threshold. 112 * <p> 113 * Larger threshold is more adaptive but increases sampling cost. 114 */ 115 private static final int LINK_MONITOR_LEVEL_THRESHOLD = WifiManager.RSSI_LEVELS - 1; 116 117 /** 118 * Remember packet loss statistics of how many BSSIDs. 119 * <p> 120 * Larger size is usually better but requires more space. 121 */ 122 private static final int BSSID_STAT_CACHE_SIZE = 20; 123 124 /** 125 * RSSI range of a BSSID statistics. 126 * Within the range, (RSSI -> packet loss %) mappings are stored. 127 * <p> 128 * Larger range is usually better but requires more space. 129 */ 130 private static final int BSSID_STAT_RANGE_LOW_DBM = -105; 131 132 /** 133 * See {@link #BSSID_STAT_RANGE_LOW_DBM}. 134 */ 135 private static final int BSSID_STAT_RANGE_HIGH_DBM = -45; 136 137 /** 138 * How many consecutive empty data point to trigger a empty-cache detection. 139 * In this case, a preset/default loss value (function on RSSI) is used. 140 * <p> 141 * In normal uses, some RSSI values may never be seen due to channel randomness. 142 * However, the size of such empty RSSI chunk in normal use is generally 1~2. 143 */ 144 private static final int BSSID_STAT_EMPTY_COUNT = 3; 145 146 /** 147 * Sample interval for packet loss statistics, in msec. 148 * <p> 149 * Smaller interval is more accurate but increases sampling cost (battery consumption). 150 */ 151 private static final long LINK_SAMPLING_INTERVAL_MS = 1 * 1000; 152 153 /** 154 * Coefficients (alpha) for moving average for packet loss tracking. 155 * Must be within (0.0, 1.0). 156 * <p> 157 * Equivalent number of samples: N = 2 / alpha - 1 . 158 * We want the historic loss to base on more data points to be statistically reliable. 159 * We want the current instant loss to base on less data points to be responsive. 160 */ 161 private static final double EXP_COEFFICIENT_RECORD = 0.1; 162 163 /** 164 * See {@link #EXP_COEFFICIENT_RECORD}. 165 */ 166 private static final double EXP_COEFFICIENT_MONITOR = 0.5; 167 168 /** 169 * Thresholds for sending good/poor link notifications, in packet loss %. 170 * Good threshold must be smaller than poor threshold. 171 * Use smaller poor threshold to avoid WiFi more aggressively. 172 * Use smaller good threshold to bring back WiFi more conservatively. 173 * <p> 174 * When approaching the boundary, loss ratio jumps significantly within a few dBs. 175 * 50% loss threshold is a good balance between accuracy and reponsiveness. 176 * <=10% good threshold is a safe value to avoid jumping back to WiFi too easily. 177 */ 178 private static final double POOR_LINK_LOSS_THRESHOLD = 0.5; 179 180 /** 181 * See {@link #POOR_LINK_LOSS_THRESHOLD}. 182 */ 183 private static final double GOOD_LINK_LOSS_THRESHOLD = 0.1; 184 185 /** 186 * Number of samples to confirm before sending a poor link notification. 187 * Response time = confirm_count * sample_interval . 188 * <p> 189 * A smaller threshold improves response speed but may suffer from randomness. 190 * According to experiments, 3~5 are good values to achieve a balance. 191 * These parameters should be tuned along with {@link #LINK_SAMPLING_INTERVAL_MS}. 192 */ 193 private static final int POOR_LINK_SAMPLE_COUNT = 3; 194 195 /** 196 * Minimum volume (converted from pkt/sec) to detect a poor link, to avoid randomness. 197 * <p> 198 * According to experiments, 1pkt/sec is too sensitive but 3pkt/sec is slightly unresponsive. 199 */ 200 private static final double POOR_LINK_MIN_VOLUME = 2.0 * LINK_SAMPLING_INTERVAL_MS / 1000.0; 201 202 /** 203 * When a poor link is detected, we scan over this range (based on current 204 * poor link RSSI) for a target RSSI that satisfies a target packet loss. 205 * Refer to {@link #GOOD_LINK_TARGET}. 206 * <p> 207 * We want range_min not too small to avoid jumping back to WiFi too easily. 208 */ 209 private static final int GOOD_LINK_RSSI_RANGE_MIN = 3; 210 211 /** 212 * See {@link #GOOD_LINK_RSSI_RANGE_MIN}. 213 */ 214 private static final int GOOD_LINK_RSSI_RANGE_MAX = 20; 215 216 /** 217 * Adaptive good link target to avoid flapping. 218 * When a poor link is detected, a good link target is calculated as follows: 219 * <p> 220 * targetRSSI = min { rssi | loss(rssi) < GOOD_LINK_LOSS_THRESHOLD } + rssi_adj[i], 221 * where rssi is within the above GOOD_LINK_RSSI_RANGE. 222 * targetCount = sample_count[i] . 223 * <p> 224 * While WiFi is being avoided, we keep monitoring its signal strength. 225 * Good link notification is sent when we see current RSSI >= targetRSSI 226 * for targetCount consecutive times. 227 * <p> 228 * Index i is incremented each time after a poor link detection. 229 * Index i is decreased to at most k if the last poor link was at lease reduce_time[k] ago. 230 * <p> 231 * Intuitively, larger index i makes it more difficult to get back to WiFi, avoiding flapping. 232 * In experiments, (+9 dB / 30 counts) makes it quite difficult to achieve. 233 * Avoid using it unless flapping is really bad (say, last poor link is < 1 min ago). 234 */ 235 private static final GoodLinkTarget[] GOOD_LINK_TARGET = { 236 /* rssi_adj, sample_count, reduce_time */ 237 new GoodLinkTarget( 0, 3, 30 * 60000 ), 238 new GoodLinkTarget( 3, 5, 5 * 60000 ), 239 new GoodLinkTarget( 6, 10, 1 * 60000 ), 240 new GoodLinkTarget( 9, 30, 0 * 60000 ), 241 }; 242 243 /** 244 * The max time to avoid a BSSID, to prevent avoiding forever. 245 * If current RSSI is at least min_rssi[i], the max avoidance time is at most max_time[i] 246 * <p> 247 * It is unusual to experience high packet loss at high RSSI. Something unusual must be 248 * happening (e.g. strong interference). For higher signal strengths, we set the avoidance 249 * time to be low to allow for quick turn around from temporary interference. 250 * <p> 251 * See {@link BssidStatistics#poorLinkDetected}. 252 */ 253 private static final MaxAvoidTime[] MAX_AVOID_TIME = { 254 /* max_time, min_rssi */ 255 new MaxAvoidTime( 30 * 60000, -200 ), 256 new MaxAvoidTime( 5 * 60000, -70 ), 257 new MaxAvoidTime( 0 * 60000, -55 ), 258 }; 259 260 /* Framework related */ 261 private Context mContext; 262 private ContentResolver mContentResolver; 263 private WifiManager mWifiManager; 264 private IntentFilter mIntentFilter; 265 private BroadcastReceiver mBroadcastReceiver; 266 private AsyncChannel mWsmChannel = new AsyncChannel(); 267 private WifiInfo mWifiInfo; 268 private LinkProperties mLinkProperties; 269 270 /* System settingss related */ 271 private static boolean sWifiOnly = false; 272 private boolean mPoorNetworkDetectionEnabled; 273 274 /* Poor link detection related */ 275 private LruCache<String, BssidStatistics> mBssidCache = 276 new LruCache<String, BssidStatistics>(BSSID_STAT_CACHE_SIZE); 277 private int mRssiFetchToken = 0; 278 private int mCurrentSignalLevel; 279 private BssidStatistics mCurrentBssid; 280 private VolumeWeightedEMA mCurrentLoss; 281 private boolean mIsScreenOn = true; 282 private static double sPresetLoss[]; 283 284 /* WiFi watchdog state machine related */ 285 private DefaultState mDefaultState = new DefaultState(); 286 private WatchdogDisabledState mWatchdogDisabledState = new WatchdogDisabledState(); 287 private WatchdogEnabledState mWatchdogEnabledState = new WatchdogEnabledState(); 288 private NotConnectedState mNotConnectedState = new NotConnectedState(); 289 private VerifyingLinkState mVerifyingLinkState = new VerifyingLinkState(); 290 private ConnectedState mConnectedState = new ConnectedState(); 291 private OnlineWatchState mOnlineWatchState = new OnlineWatchState(); 292 private LinkMonitoringState mLinkMonitoringState = new LinkMonitoringState(); 293 private OnlineState mOnlineState = new OnlineState(); 294 295 /** 296 * STATE MAP 297 * Default 298 * / \ 299 * Disabled Enabled 300 * / \ \ 301 * NotConnected Verifying Connected 302 * /---------\ 303 * (all other states) 304 */ 305 private WifiWatchdogStateMachine(Context context, Messenger dstMessenger) { 306 super("WifiWatchdogStateMachine"); 307 mContext = context; 308 mContentResolver = context.getContentResolver(); 309 mWifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE); 310 311 mWsmChannel.connectSync(mContext, getHandler(), dstMessenger); 312 313 setupNetworkReceiver(); 314 315 // the content observer to listen needs a handler 316 registerForSettingsChanges(); 317 registerForWatchdogToggle(); 318 addState(mDefaultState); 319 addState(mWatchdogDisabledState, mDefaultState); 320 addState(mWatchdogEnabledState, mDefaultState); 321 addState(mNotConnectedState, mWatchdogEnabledState); 322 addState(mVerifyingLinkState, mWatchdogEnabledState); 323 addState(mConnectedState, mWatchdogEnabledState); 324 addState(mOnlineWatchState, mConnectedState); 325 addState(mLinkMonitoringState, mConnectedState); 326 addState(mOnlineState, mConnectedState); 327 328 if (isWatchdogEnabled()) { 329 setInitialState(mNotConnectedState); 330 } else { 331 setInitialState(mWatchdogDisabledState); 332 } 333 setLogRecSize(25); 334 setLogOnlyTransitions(true); 335 updateSettings(); 336 } 337 338 public static WifiWatchdogStateMachine makeWifiWatchdogStateMachine(Context context, Messenger dstMessenger) { 339 ContentResolver contentResolver = context.getContentResolver(); 340 341 ConnectivityManager cm = (ConnectivityManager) context.getSystemService( 342 Context.CONNECTIVITY_SERVICE); 343 sWifiOnly = (cm.isNetworkSupported(ConnectivityManager.TYPE_MOBILE) == false); 344 345 // Watchdog is always enabled. Poor network detection can be seperately turned on/off 346 // TODO: Remove this setting & clean up state machine since we always have 347 // watchdog in an enabled state 348 putSettingsGlobalBoolean(contentResolver, Settings.Global.WIFI_WATCHDOG_ON, true); 349 350 WifiWatchdogStateMachine wwsm = new WifiWatchdogStateMachine(context, dstMessenger); 351 wwsm.start(); 352 return wwsm; 353 } 354 355 private void setupNetworkReceiver() { 356 mBroadcastReceiver = new BroadcastReceiver() { 357 @Override 358 public void onReceive(Context context, Intent intent) { 359 String action = intent.getAction(); 360 if (action.equals(WifiManager.RSSI_CHANGED_ACTION)) { 361 obtainMessage(EVENT_RSSI_CHANGE, 362 intent.getIntExtra(WifiManager.EXTRA_NEW_RSSI, -200), 0).sendToTarget(); 363 } else if (action.equals(WifiManager.SUPPLICANT_STATE_CHANGED_ACTION)) { 364 sendMessage(EVENT_SUPPLICANT_STATE_CHANGE, intent); 365 } else if (action.equals(WifiManager.NETWORK_STATE_CHANGED_ACTION)) { 366 sendMessage(EVENT_NETWORK_STATE_CHANGE, intent); 367 } else if (action.equals(Intent.ACTION_SCREEN_ON)) { 368 sendMessage(EVENT_SCREEN_ON); 369 } else if (action.equals(Intent.ACTION_SCREEN_OFF)) { 370 sendMessage(EVENT_SCREEN_OFF); 371 } else if (action.equals(WifiManager.WIFI_STATE_CHANGED_ACTION)) { 372 sendMessage(EVENT_WIFI_RADIO_STATE_CHANGE,intent.getIntExtra( 373 WifiManager.EXTRA_WIFI_STATE, WifiManager.WIFI_STATE_UNKNOWN)); 374 } 375 } 376 }; 377 378 mIntentFilter = new IntentFilter(); 379 mIntentFilter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION); 380 mIntentFilter.addAction(WifiManager.WIFI_STATE_CHANGED_ACTION); 381 mIntentFilter.addAction(WifiManager.RSSI_CHANGED_ACTION); 382 mIntentFilter.addAction(WifiManager.SUPPLICANT_STATE_CHANGED_ACTION); 383 mIntentFilter.addAction(Intent.ACTION_SCREEN_ON); 384 mIntentFilter.addAction(Intent.ACTION_SCREEN_OFF); 385 mContext.registerReceiver(mBroadcastReceiver, mIntentFilter); 386 } 387 388 /** 389 * Observes the watchdog on/off setting, and takes action when changed. 390 */ 391 private void registerForWatchdogToggle() { 392 ContentObserver contentObserver = new ContentObserver(this.getHandler()) { 393 @Override 394 public void onChange(boolean selfChange) { 395 sendMessage(EVENT_WATCHDOG_TOGGLED); 396 } 397 }; 398 399 mContext.getContentResolver().registerContentObserver( 400 Settings.Global.getUriFor(Settings.Global.WIFI_WATCHDOG_ON), 401 false, contentObserver); 402 } 403 404 /** 405 * Observes watchdogs secure setting changes. 406 */ 407 private void registerForSettingsChanges() { 408 ContentObserver contentObserver = new ContentObserver(this.getHandler()) { 409 @Override 410 public void onChange(boolean selfChange) { 411 sendMessage(EVENT_WATCHDOG_SETTINGS_CHANGE); 412 } 413 }; 414 415 mContext.getContentResolver().registerContentObserver( 416 Settings.Global.getUriFor(Settings.Global.WIFI_WATCHDOG_POOR_NETWORK_TEST_ENABLED), 417 false, contentObserver); 418 } 419 420 public void dump(FileDescriptor fd, PrintWriter pw, String[] args) { 421 super.dump(fd, pw, args); 422 pw.println("mWifiInfo: [" + mWifiInfo + "]"); 423 pw.println("mLinkProperties: [" + mLinkProperties + "]"); 424 pw.println("mCurrentSignalLevel: [" + mCurrentSignalLevel + "]"); 425 pw.println("mPoorNetworkDetectionEnabled: [" + mPoorNetworkDetectionEnabled + "]"); 426 } 427 428 private boolean isWatchdogEnabled() { 429 boolean ret = getSettingsGlobalBoolean( 430 mContentResolver, Settings.Global.WIFI_WATCHDOG_ON, true); 431 if (DBG) logd("Watchdog enabled " + ret); 432 return ret; 433 } 434 435 private void updateSettings() { 436 if (DBG) logd("Updating secure settings"); 437 438 // Unconditionally disable poor network avoidance, since this mechanism is obsolete 439 mPoorNetworkDetectionEnabled = false; 440 } 441 442 /** 443 * Default state, guard for unhandled messages. 444 */ 445 class DefaultState extends State { 446 @Override 447 public void enter() { 448 if (DBG) logd(getName()); 449 } 450 451 @Override 452 public boolean processMessage(Message msg) { 453 switch (msg.what) { 454 case EVENT_WATCHDOG_SETTINGS_CHANGE: 455 updateSettings(); 456 if (DBG) logd("Updating wifi-watchdog secure settings"); 457 break; 458 case EVENT_RSSI_CHANGE: 459 mCurrentSignalLevel = calculateSignalLevel(msg.arg1); 460 break; 461 case EVENT_WIFI_RADIO_STATE_CHANGE: 462 case EVENT_NETWORK_STATE_CHANGE: 463 case EVENT_SUPPLICANT_STATE_CHANGE: 464 case EVENT_BSSID_CHANGE: 465 case CMD_RSSI_FETCH: 466 case WifiManager.RSSI_PKTCNT_FETCH_SUCCEEDED: 467 case WifiManager.RSSI_PKTCNT_FETCH_FAILED: 468 // ignore 469 break; 470 case EVENT_SCREEN_ON: 471 mIsScreenOn = true; 472 break; 473 case EVENT_SCREEN_OFF: 474 mIsScreenOn = false; 475 break; 476 default: 477 loge("Unhandled message " + msg + " in state " + getCurrentState().getName()); 478 break; 479 } 480 return HANDLED; 481 } 482 } 483 484 /** 485 * WiFi watchdog is disabled by the setting. 486 */ 487 class WatchdogDisabledState extends State { 488 @Override 489 public void enter() { 490 if (DBG) logd(getName()); 491 } 492 493 @Override 494 public boolean processMessage(Message msg) { 495 switch (msg.what) { 496 case EVENT_WATCHDOG_TOGGLED: 497 if (isWatchdogEnabled()) 498 transitionTo(mNotConnectedState); 499 return HANDLED; 500 case EVENT_NETWORK_STATE_CHANGE: 501 Intent intent = (Intent) msg.obj; 502 NetworkInfo networkInfo = (NetworkInfo) 503 intent.getParcelableExtra(WifiManager.EXTRA_NETWORK_INFO); 504 505 switch (networkInfo.getDetailedState()) { 506 case VERIFYING_POOR_LINK: 507 if (DBG) logd("Watchdog disabled, verify link"); 508 sendLinkStatusNotification(true); 509 break; 510 default: 511 break; 512 } 513 break; 514 } 515 return NOT_HANDLED; 516 } 517 } 518 519 /** 520 * WiFi watchdog is enabled by the setting. 521 */ 522 class WatchdogEnabledState extends State { 523 @Override 524 public void enter() { 525 if (DBG) logd(getName()); 526 } 527 528 @Override 529 public boolean processMessage(Message msg) { 530 Intent intent; 531 switch (msg.what) { 532 case EVENT_WATCHDOG_TOGGLED: 533 if (!isWatchdogEnabled()) 534 transitionTo(mWatchdogDisabledState); 535 break; 536 537 case EVENT_NETWORK_STATE_CHANGE: 538 intent = (Intent) msg.obj; 539 NetworkInfo networkInfo = 540 (NetworkInfo) intent.getParcelableExtra(WifiManager.EXTRA_NETWORK_INFO); 541 if (DBG) logd("Network state change " + networkInfo.getDetailedState()); 542 543 mWifiInfo = (WifiInfo) intent.getParcelableExtra(WifiManager.EXTRA_WIFI_INFO); 544 updateCurrentBssid(mWifiInfo != null ? mWifiInfo.getBSSID() : null); 545 546 switch (networkInfo.getDetailedState()) { 547 case VERIFYING_POOR_LINK: 548 mLinkProperties = (LinkProperties) intent.getParcelableExtra( 549 WifiManager.EXTRA_LINK_PROPERTIES); 550 if (mPoorNetworkDetectionEnabled) { 551 if (mWifiInfo == null || mCurrentBssid == null) { 552 loge("Ignore, wifiinfo " + mWifiInfo +" bssid " + mCurrentBssid); 553 sendLinkStatusNotification(true); 554 } else { 555 transitionTo(mVerifyingLinkState); 556 } 557 } else { 558 sendLinkStatusNotification(true); 559 } 560 break; 561 case CONNECTED: 562 transitionTo(mOnlineWatchState); 563 break; 564 default: 565 transitionTo(mNotConnectedState); 566 break; 567 } 568 break; 569 570 case EVENT_SUPPLICANT_STATE_CHANGE: 571 intent = (Intent) msg.obj; 572 SupplicantState supplicantState = (SupplicantState) intent.getParcelableExtra( 573 WifiManager.EXTRA_NEW_STATE); 574 if (supplicantState == SupplicantState.COMPLETED) { 575 mWifiInfo = mWifiManager.getConnectionInfo(); 576 updateCurrentBssid(mWifiInfo.getBSSID()); 577 } 578 break; 579 580 case EVENT_WIFI_RADIO_STATE_CHANGE: 581 if (msg.arg1 == WifiManager.WIFI_STATE_DISABLING) { 582 transitionTo(mNotConnectedState); 583 } 584 break; 585 586 default: 587 return NOT_HANDLED; 588 } 589 590 return HANDLED; 591 } 592 } 593 594 /** 595 * WiFi is disconnected. 596 */ 597 class NotConnectedState extends State { 598 @Override 599 public void enter() { 600 if (DBG) logd(getName()); 601 } 602 } 603 604 /** 605 * WiFi is connected, but waiting for good link detection message. 606 */ 607 class VerifyingLinkState extends State { 608 609 private int mSampleCount; 610 611 @Override 612 public void enter() { 613 if (DBG) logd(getName()); 614 mSampleCount = 0; 615 if (mCurrentBssid != null) mCurrentBssid.newLinkDetected(); 616 sendMessage(obtainMessage(CMD_RSSI_FETCH, ++mRssiFetchToken, 0)); 617 } 618 619 @Override 620 public boolean processMessage(Message msg) { 621 switch (msg.what) { 622 case EVENT_WATCHDOG_SETTINGS_CHANGE: 623 updateSettings(); 624 if (!mPoorNetworkDetectionEnabled) { 625 sendLinkStatusNotification(true); 626 } 627 break; 628 629 case EVENT_BSSID_CHANGE: 630 transitionTo(mVerifyingLinkState); 631 break; 632 633 case CMD_RSSI_FETCH: 634 if (msg.arg1 == mRssiFetchToken) { 635 mWsmChannel.sendMessage(WifiManager.RSSI_PKTCNT_FETCH); 636 sendMessageDelayed(obtainMessage(CMD_RSSI_FETCH, ++mRssiFetchToken, 0), 637 LINK_SAMPLING_INTERVAL_MS); 638 } 639 break; 640 641 case WifiManager.RSSI_PKTCNT_FETCH_SUCCEEDED: 642 if (mCurrentBssid == null || msg.obj == null) { 643 break; 644 } 645 RssiPacketCountInfo info = (RssiPacketCountInfo) msg.obj; 646 int rssi = info.rssi; 647 if (DBG) logd("Fetch RSSI succeed, rssi=" + rssi); 648 649 long time = mCurrentBssid.mBssidAvoidTimeMax - SystemClock.elapsedRealtime(); 650 if (time <= 0) { 651 // max avoidance time is met 652 if (DBG) logd("Max avoid time elapsed"); 653 sendLinkStatusNotification(true); 654 } else { 655 if (rssi >= mCurrentBssid.mGoodLinkTargetRssi) { 656 if (++mSampleCount >= mCurrentBssid.mGoodLinkTargetCount) { 657 // link is good again 658 if (DBG) logd("Good link detected, rssi=" + rssi); 659 mCurrentBssid.mBssidAvoidTimeMax = 0; 660 sendLinkStatusNotification(true); 661 } 662 } else { 663 mSampleCount = 0; 664 if (DBG) logd("Link is still poor, time left=" + time); 665 } 666 } 667 break; 668 669 case WifiManager.RSSI_PKTCNT_FETCH_FAILED: 670 if (DBG) logd("RSSI_FETCH_FAILED"); 671 break; 672 673 default: 674 return NOT_HANDLED; 675 } 676 return HANDLED; 677 } 678 } 679 680 /** 681 * WiFi is connected and link is verified. 682 */ 683 class ConnectedState extends State { 684 @Override 685 public void enter() { 686 if (DBG) logd(getName()); 687 } 688 689 @Override 690 public boolean processMessage(Message msg) { 691 switch (msg.what) { 692 case EVENT_WATCHDOG_SETTINGS_CHANGE: 693 updateSettings(); 694 if (mPoorNetworkDetectionEnabled) { 695 transitionTo(mOnlineWatchState); 696 } else { 697 transitionTo(mOnlineState); 698 } 699 return HANDLED; 700 } 701 return NOT_HANDLED; 702 } 703 } 704 705 /** 706 * RSSI is high enough and don't need link monitoring. 707 */ 708 class OnlineWatchState extends State { 709 @Override 710 public void enter() { 711 if (DBG) logd(getName()); 712 if (mPoorNetworkDetectionEnabled) { 713 // treat entry as an rssi change 714 handleRssiChange(); 715 } else { 716 transitionTo(mOnlineState); 717 } 718 } 719 720 private void handleRssiChange() { 721 if (mCurrentSignalLevel <= LINK_MONITOR_LEVEL_THRESHOLD && mCurrentBssid != null) { 722 transitionTo(mLinkMonitoringState); 723 } else { 724 // stay here 725 } 726 } 727 728 @Override 729 public boolean processMessage(Message msg) { 730 switch (msg.what) { 731 case EVENT_RSSI_CHANGE: 732 mCurrentSignalLevel = calculateSignalLevel(msg.arg1); 733 handleRssiChange(); 734 break; 735 default: 736 return NOT_HANDLED; 737 } 738 return HANDLED; 739 } 740 } 741 742 /** 743 * Keep sampling the link and monitor any poor link situation. 744 */ 745 class LinkMonitoringState extends State { 746 747 private int mSampleCount; 748 749 private int mLastRssi; 750 private int mLastTxGood; 751 private int mLastTxBad; 752 753 @Override 754 public void enter() { 755 if (DBG) logd(getName()); 756 mSampleCount = 0; 757 mCurrentLoss = new VolumeWeightedEMA(EXP_COEFFICIENT_MONITOR); 758 sendMessage(obtainMessage(CMD_RSSI_FETCH, ++mRssiFetchToken, 0)); 759 } 760 761 @Override 762 public boolean processMessage(Message msg) { 763 switch (msg.what) { 764 case EVENT_RSSI_CHANGE: 765 mCurrentSignalLevel = calculateSignalLevel(msg.arg1); 766 if (mCurrentSignalLevel <= LINK_MONITOR_LEVEL_THRESHOLD) { 767 // stay here; 768 } else { 769 // we don't need frequent RSSI monitoring any more 770 transitionTo(mOnlineWatchState); 771 } 772 break; 773 774 case EVENT_BSSID_CHANGE: 775 transitionTo(mLinkMonitoringState); 776 break; 777 778 case CMD_RSSI_FETCH: 779 if (!mIsScreenOn) { 780 transitionTo(mOnlineState); 781 } else if (msg.arg1 == mRssiFetchToken) { 782 mWsmChannel.sendMessage(WifiManager.RSSI_PKTCNT_FETCH); 783 sendMessageDelayed(obtainMessage(CMD_RSSI_FETCH, ++mRssiFetchToken, 0), 784 LINK_SAMPLING_INTERVAL_MS); 785 } 786 break; 787 788 case WifiManager.RSSI_PKTCNT_FETCH_SUCCEEDED: 789 if (mCurrentBssid == null) { 790 break; 791 } 792 RssiPacketCountInfo info = (RssiPacketCountInfo) msg.obj; 793 int rssi = info.rssi; 794 int mrssi = (mLastRssi + rssi) / 2; 795 int txbad = info.txbad; 796 int txgood = info.txgood; 797 if (DBG) logd("Fetch RSSI succeed, rssi=" + rssi + " mrssi=" + mrssi + " txbad=" 798 + txbad + " txgood=" + txgood); 799 800 // skip the first data point as we want incremental values 801 long now = SystemClock.elapsedRealtime(); 802 if (now - mCurrentBssid.mLastTimeSample < LINK_SAMPLING_INTERVAL_MS * 2) { 803 804 // update packet loss statistics 805 int dbad = txbad - mLastTxBad; 806 int dgood = txgood - mLastTxGood; 807 int dtotal = dbad + dgood; 808 809 if (dtotal > 0) { 810 // calculate packet loss in the last sampling interval 811 double loss = ((double) dbad) / ((double) dtotal); 812 813 mCurrentLoss.update(loss, dtotal); 814 815 if (DBG) { 816 DecimalFormat df = new DecimalFormat("#.##"); 817 logd("Incremental loss=" + dbad + "/" + dtotal + " Current loss=" 818 + df.format(mCurrentLoss.mValue * 100) + "% volume=" 819 + df.format(mCurrentLoss.mVolume)); 820 } 821 822 mCurrentBssid.updateLoss(mrssi, loss, dtotal); 823 824 // check for high packet loss and send poor link notification 825 if (mCurrentLoss.mValue > POOR_LINK_LOSS_THRESHOLD 826 && mCurrentLoss.mVolume > POOR_LINK_MIN_VOLUME) { 827 if (++mSampleCount >= POOR_LINK_SAMPLE_COUNT) 828 if (mCurrentBssid.poorLinkDetected(rssi)) { 829 sendLinkStatusNotification(false); 830 ++mRssiFetchToken; 831 } 832 } else { 833 mSampleCount = 0; 834 } 835 } 836 } 837 838 mCurrentBssid.mLastTimeSample = now; 839 mLastTxBad = txbad; 840 mLastTxGood = txgood; 841 mLastRssi = rssi; 842 break; 843 844 case WifiManager.RSSI_PKTCNT_FETCH_FAILED: 845 // can happen if we are waiting to get a disconnect notification 846 if (DBG) logd("RSSI_FETCH_FAILED"); 847 break; 848 849 default: 850 return NOT_HANDLED; 851 } 852 return HANDLED; 853 } 854 } 855 856 /** 857 * Child state of ConnectedState indicating that we are online and there is nothing to do. 858 */ 859 class OnlineState extends State { 860 @Override 861 public void enter() { 862 if (DBG) logd(getName()); 863 } 864 865 @Override 866 public boolean processMessage(Message msg) { 867 switch (msg.what) { 868 case EVENT_SCREEN_ON: 869 mIsScreenOn = true; 870 if (mPoorNetworkDetectionEnabled) 871 transitionTo(mOnlineWatchState); 872 break; 873 default: 874 return NOT_HANDLED; 875 } 876 return HANDLED; 877 } 878 } 879 880 private void updateCurrentBssid(String bssid) { 881 if (DBG) logd("Update current BSSID to " + (bssid != null ? bssid : "null")); 882 883 // if currently not connected, then set current BSSID to null 884 if (bssid == null) { 885 if (mCurrentBssid == null) return; 886 mCurrentBssid = null; 887 if (DBG) logd("BSSID changed"); 888 sendMessage(EVENT_BSSID_CHANGE); 889 return; 890 } 891 892 // if it is already the current BSSID, then done 893 if (mCurrentBssid != null && bssid.equals(mCurrentBssid.mBssid)) return; 894 895 // search for the new BSSID in the cache, add to cache if not found 896 mCurrentBssid = mBssidCache.get(bssid); 897 if (mCurrentBssid == null) { 898 mCurrentBssid = new BssidStatistics(bssid); 899 mBssidCache.put(bssid, mCurrentBssid); 900 } 901 902 // send BSSID change notification 903 if (DBG) logd("BSSID changed"); 904 sendMessage(EVENT_BSSID_CHANGE); 905 } 906 907 private int calculateSignalLevel(int rssi) { 908 int signalLevel = WifiManager.calculateSignalLevel(rssi, WifiManager.RSSI_LEVELS); 909 if (DBG) 910 logd("RSSI current: " + mCurrentSignalLevel + " new: " + rssi + ", " + signalLevel); 911 return signalLevel; 912 } 913 914 private void sendLinkStatusNotification(boolean isGood) { 915 if (DBG) logd("########################################"); 916 if (isGood) { 917 mWsmChannel.sendMessage(GOOD_LINK_DETECTED); 918 if (mCurrentBssid != null) { 919 mCurrentBssid.mLastTimeGood = SystemClock.elapsedRealtime(); 920 } 921 if (DBG) logd("Good link notification is sent"); 922 } else { 923 mWsmChannel.sendMessage(POOR_LINK_DETECTED); 924 if (mCurrentBssid != null) { 925 mCurrentBssid.mLastTimePoor = SystemClock.elapsedRealtime(); 926 } 927 logd("Poor link notification is sent"); 928 } 929 } 930 931 /** 932 * Convenience function for retrieving a single secure settings value as a 933 * boolean. Note that internally setting values are always stored as 934 * strings; this function converts the string to a boolean for you. The 935 * default value will be returned if the setting is not defined or not a 936 * valid boolean. 937 * 938 * @param cr The ContentResolver to access. 939 * @param name The name of the setting to retrieve. 940 * @param def Value to return if the setting is not defined. 941 * @return The setting's current value, or 'def' if it is not defined or not 942 * a valid boolean. 943 */ 944 private static boolean getSettingsGlobalBoolean(ContentResolver cr, String name, boolean def) { 945 return Settings.Global.getInt(cr, name, def ? 1 : 0) == 1; 946 } 947 948 /** 949 * Convenience function for updating a single settings value as an integer. 950 * This will either create a new entry in the table if the given name does 951 * not exist, or modify the value of the existing row with that name. Note 952 * that internally setting values are always stored as strings, so this 953 * function converts the given value to a string before storing it. 954 * 955 * @param cr The ContentResolver to access. 956 * @param name The name of the setting to modify. 957 * @param value The new value for the setting. 958 * @return true if the value was set, false on database errors 959 */ 960 private static boolean putSettingsGlobalBoolean(ContentResolver cr, String name, boolean value) { 961 return Settings.Global.putInt(cr, name, value ? 1 : 0); 962 } 963 964 /** 965 * Bundle of good link count parameters 966 */ 967 private static class GoodLinkTarget { 968 public final int RSSI_ADJ_DBM; 969 public final int SAMPLE_COUNT; 970 public final int REDUCE_TIME_MS; 971 public GoodLinkTarget(int adj, int count, int time) { 972 RSSI_ADJ_DBM = adj; 973 SAMPLE_COUNT = count; 974 REDUCE_TIME_MS = time; 975 } 976 } 977 978 /** 979 * Bundle of max avoidance time parameters 980 */ 981 private static class MaxAvoidTime { 982 public final int TIME_MS; 983 public final int MIN_RSSI_DBM; 984 public MaxAvoidTime(int time, int rssi) { 985 TIME_MS = time; 986 MIN_RSSI_DBM = rssi; 987 } 988 } 989 990 /** 991 * Volume-weighted Exponential Moving Average (V-EMA) 992 * - volume-weighted: each update has its own weight (number of packets) 993 * - exponential: O(1) time and O(1) space for both update and query 994 * - moving average: reflect most recent results and expire old ones 995 */ 996 private class VolumeWeightedEMA { 997 private double mValue; 998 private double mVolume; 999 private double mProduct; 1000 private final double mAlpha; 1001 1002 public VolumeWeightedEMA(double coefficient) { 1003 mValue = 0.0; 1004 mVolume = 0.0; 1005 mProduct = 0.0; 1006 mAlpha = coefficient; 1007 } 1008 1009 public void update(double newValue, int newVolume) { 1010 if (newVolume <= 0) return; 1011 // core update formulas 1012 double newProduct = newValue * newVolume; 1013 mProduct = mAlpha * newProduct + (1 - mAlpha) * mProduct; 1014 mVolume = mAlpha * newVolume + (1 - mAlpha) * mVolume; 1015 mValue = mProduct / mVolume; 1016 } 1017 } 1018 1019 /** 1020 * Record (RSSI -> pakce loss %) mappings of one BSSID 1021 */ 1022 private class BssidStatistics { 1023 1024 /* MAC address of this BSSID */ 1025 private final String mBssid; 1026 1027 /* RSSI -> packet loss % mappings */ 1028 private VolumeWeightedEMA[] mEntries; 1029 private int mRssiBase; 1030 private int mEntriesSize; 1031 1032 /* Target to send good link notification, set when poor link is detected */ 1033 private int mGoodLinkTargetRssi; 1034 private int mGoodLinkTargetCount; 1035 1036 /* Index of GOOD_LINK_TARGET array */ 1037 private int mGoodLinkTargetIndex; 1038 1039 /* Timestamps of some last events */ 1040 private long mLastTimeSample; 1041 private long mLastTimeGood; 1042 private long mLastTimePoor; 1043 1044 /* Max time to avoid this BSSID */ 1045 private long mBssidAvoidTimeMax; 1046 1047 /** 1048 * Constructor 1049 * 1050 * @param bssid is the address of this BSSID 1051 */ 1052 public BssidStatistics(String bssid) { 1053 this.mBssid = bssid; 1054 mRssiBase = BSSID_STAT_RANGE_LOW_DBM; 1055 mEntriesSize = BSSID_STAT_RANGE_HIGH_DBM - BSSID_STAT_RANGE_LOW_DBM + 1; 1056 mEntries = new VolumeWeightedEMA[mEntriesSize]; 1057 for (int i = 0; i < mEntriesSize; i++) 1058 mEntries[i] = new VolumeWeightedEMA(EXP_COEFFICIENT_RECORD); 1059 } 1060 1061 /** 1062 * Update this BSSID cache 1063 * 1064 * @param rssi is the RSSI 1065 * @param value is the new instant loss value at this RSSI 1066 * @param volume is the volume for this single update 1067 */ 1068 public void updateLoss(int rssi, double value, int volume) { 1069 if (volume <= 0) return; 1070 int index = rssi - mRssiBase; 1071 if (index < 0 || index >= mEntriesSize) return; 1072 mEntries[index].update(value, volume); 1073 if (DBG) { 1074 DecimalFormat df = new DecimalFormat("#.##"); 1075 logd("Cache updated: loss[" + rssi + "]=" + df.format(mEntries[index].mValue * 100) 1076 + "% volume=" + df.format(mEntries[index].mVolume)); 1077 } 1078 } 1079 1080 /** 1081 * Get preset loss if the cache has insufficient data, observed from experiments. 1082 * 1083 * @param rssi is the input RSSI 1084 * @return preset loss of the given RSSI 1085 */ 1086 public double presetLoss(int rssi) { 1087 if (rssi <= -90) return 1.0; 1088 if (rssi > 0) return 0.0; 1089 1090 if (sPresetLoss == null) { 1091 // pre-calculate all preset losses only once, then reuse them 1092 final int size = 90; 1093 sPresetLoss = new double[size]; 1094 for (int i = 0; i < size; i++) sPresetLoss[i] = 1.0 / Math.pow(90 - i, 1.5); 1095 } 1096 return sPresetLoss[-rssi]; 1097 } 1098 1099 /** 1100 * A poor link is detected, calculate a target RSSI to bring WiFi back. 1101 * 1102 * @param rssi is the current RSSI 1103 * @return true iff the current BSSID should be avoided 1104 */ 1105 public boolean poorLinkDetected(int rssi) { 1106 if (DBG) logd("Poor link detected, rssi=" + rssi); 1107 1108 long now = SystemClock.elapsedRealtime(); 1109 long lastGood = now - mLastTimeGood; 1110 long lastPoor = now - mLastTimePoor; 1111 1112 // reduce the difficulty of good link target if last avoidance was long time ago 1113 while (mGoodLinkTargetIndex > 0 1114 && lastPoor >= GOOD_LINK_TARGET[mGoodLinkTargetIndex - 1].REDUCE_TIME_MS) 1115 mGoodLinkTargetIndex--; 1116 mGoodLinkTargetCount = GOOD_LINK_TARGET[mGoodLinkTargetIndex].SAMPLE_COUNT; 1117 1118 // scan for a target RSSI at which the link is good 1119 int from = rssi + GOOD_LINK_RSSI_RANGE_MIN; 1120 int to = rssi + GOOD_LINK_RSSI_RANGE_MAX; 1121 mGoodLinkTargetRssi = findRssiTarget(from, to, GOOD_LINK_LOSS_THRESHOLD); 1122 mGoodLinkTargetRssi += GOOD_LINK_TARGET[mGoodLinkTargetIndex].RSSI_ADJ_DBM; 1123 if (mGoodLinkTargetIndex < GOOD_LINK_TARGET.length - 1) mGoodLinkTargetIndex++; 1124 1125 // calculate max avoidance time to prevent avoiding forever 1126 int p = 0, pmax = MAX_AVOID_TIME.length - 1; 1127 while (p < pmax && rssi >= MAX_AVOID_TIME[p + 1].MIN_RSSI_DBM) p++; 1128 long avoidMax = MAX_AVOID_TIME[p].TIME_MS; 1129 1130 // don't avoid if max avoidance time is 0 (RSSI is super high) 1131 if (avoidMax <= 0) return false; 1132 1133 // set max avoidance time, send poor link notification 1134 mBssidAvoidTimeMax = now + avoidMax; 1135 1136 if (DBG) logd("goodRssi=" + mGoodLinkTargetRssi + " goodCount=" + mGoodLinkTargetCount 1137 + " lastGood=" + lastGood + " lastPoor=" + lastPoor + " avoidMax=" + avoidMax); 1138 1139 return true; 1140 } 1141 1142 /** 1143 * A new BSSID is connected, recalculate target RSSI threshold 1144 */ 1145 public void newLinkDetected() { 1146 // if this BSSID is currently being avoided, the reuse those values 1147 if (mBssidAvoidTimeMax > 0) { 1148 if (DBG) logd("Previous avoidance still in effect, rssi=" + mGoodLinkTargetRssi 1149 + " count=" + mGoodLinkTargetCount); 1150 return; 1151 } 1152 1153 // calculate a new RSSI threshold for new link verifying 1154 int from = BSSID_STAT_RANGE_LOW_DBM; 1155 int to = BSSID_STAT_RANGE_HIGH_DBM; 1156 mGoodLinkTargetRssi = findRssiTarget(from, to, GOOD_LINK_LOSS_THRESHOLD); 1157 mGoodLinkTargetCount = 1; 1158 mBssidAvoidTimeMax = SystemClock.elapsedRealtime() + MAX_AVOID_TIME[0].TIME_MS; 1159 if (DBG) logd("New link verifying target set, rssi=" + mGoodLinkTargetRssi + " count=" 1160 + mGoodLinkTargetCount); 1161 } 1162 1163 /** 1164 * Return the first RSSI within the range where loss[rssi] < threshold 1165 * 1166 * @param from start scanning from this RSSI 1167 * @param to stop scanning at this RSSI 1168 * @param threshold target threshold for scanning 1169 * @return target RSSI 1170 */ 1171 public int findRssiTarget(int from, int to, double threshold) { 1172 from -= mRssiBase; 1173 to -= mRssiBase; 1174 int emptyCount = 0; 1175 int d = from < to ? 1 : -1; 1176 for (int i = from; i != to; i += d) 1177 // don't use a data point if it volume is too small (statistically unreliable) 1178 if (i >= 0 && i < mEntriesSize && mEntries[i].mVolume > 1.0) { 1179 emptyCount = 0; 1180 if (mEntries[i].mValue < threshold) { 1181 // scan target found 1182 int rssi = mRssiBase + i; 1183 if (DBG) { 1184 DecimalFormat df = new DecimalFormat("#.##"); 1185 logd("Scan target found: rssi=" + rssi + " threshold=" 1186 + df.format(threshold * 100) + "% value=" 1187 + df.format(mEntries[i].mValue * 100) + "% volume=" 1188 + df.format(mEntries[i].mVolume)); 1189 } 1190 return rssi; 1191 } 1192 } else if (++emptyCount >= BSSID_STAT_EMPTY_COUNT) { 1193 // cache has insufficient data around this RSSI, use preset loss instead 1194 int rssi = mRssiBase + i; 1195 double lossPreset = presetLoss(rssi); 1196 if (lossPreset < threshold) { 1197 if (DBG) { 1198 DecimalFormat df = new DecimalFormat("#.##"); 1199 logd("Scan target found: rssi=" + rssi + " threshold=" 1200 + df.format(threshold * 100) + "% value=" 1201 + df.format(lossPreset * 100) + "% volume=preset"); 1202 } 1203 return rssi; 1204 } 1205 } 1206 1207 return mRssiBase + to; 1208 } 1209 } 1210 } 1211
