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| <title>Bluetooth Low Energy</title> |
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| |
| <p> |
| Bluetooth Low Energy (BLE), available in Android 4.3 and later, creates |
| short connections between devices to transfer bursts of data. BLE |
| remains in sleep mode when not connected. This lets BLE provide lower |
| bandwidth and reduced power consumption compared to Classic Bluetooth. |
| It is ideal for applications such as a heart-rate monitor or a wireless |
| keyboard. To use BLE, devices need to have a chipset that supports BLE. |
| </p> |
| |
| <h2 id="implementation">Implementation</h2> |
| |
| <p> |
| All current BLE application profiles are based on the |
| <a href="https://www.bluetooth.com/specifications/gatt">Generic |
| Attribute Profile</a> (GATT). When an Android device interacts with a |
| BLE device, the device that sends information is the server and the |
| device that receives information is the client. Android includes |
| <a href="https://developer.android.com/guide/topics/connectivity/bluetooth-le.html"> |
| developer APIs for BLE</a>, including APIs for interactions between |
| GATT servers and GATT clients. To fully leverage the BLE APIs, |
| implement the |
| <a href="/devices/bluetooth/hci_requirements.html"> |
| Android Bluetooth HCI Requirements</a>. |
| </p> |
| |
| <h2 id="device-modes">Device modes</h2> |
| |
| <p> |
| When using BLE, an Android device can act as a peripheral device, a |
| central device, or both. Peripheral mode lets devices send |
| advertisement packets. Central mode lets devices scan for |
| advertisements. An Android device acting as both a peripheral and |
| central device can communicate with other BLE peripheral devices while |
| sending advertisements in peripheral mode. Devices supporting |
| Bluetooth 4.1 and earlier can only use BLE in central mode. Older |
| device chipsets may not support BLE peripheral mode. |
| </p> |
| |
| <h2 id="ble-scanning">BLE scanning</h2> |
| |
| <p> |
| An Android device can target and scan for specific Bluetooth devices |
| more efficiently when using BLE. BLE APIs let app developers create |
| filters for finding devices with less involvement from the host |
| controller. |
| </p> |
| |
| <aside class="caution"> |
| <strong>Caution:</strong> BLE scanning needs location permissions as BLE |
| scanning identifies objects that could be used for geolocation. Turning |
| off Location services will turn off Bluetooth scanning. |
| </aside> |
| |
| <h3 id="location-scanning">Location scanning</h3> |
| |
| <p> |
| A device's location services can use Bluetooth to detect Bluetooth |
| beacons and provide a more accurate location. This is how users |
| enable the feature: |
| </p> |
| |
| <ol> |
| <li>Go to <strong>Settings</strong> > <strong> Security & |
| Location</strong> > <strong>Location</strong>.</li> |
| <li>Check that the Location <strong>On</strong>/<strong>Off</strong> |
| toggle is in the <strong>On</strong> position.</li> |
| <li>Go to <strong>Mode</strong>.</li> |
| <li>Select either <strong>High accuracy</strong> or <strong>Battery |
| saving</strong> mode.</li> |
| </ol> |
| |
| <p> |
| Individual apps need location permissions to use BLE scanning, even |
| if they are scanning only to find devices to connect to. If the user |
| disables location scanning, or does not give an app location |
| permissions, then the app will not receive any BLE scanning results. |
| </p> |
| |
| <p> |
| Users can disable system-level Bluetooth background scanning by |
| going to <strong>Settings</strong> > <strong>Security & |
| Location</strong> > <strong>Location</strong> > <strong> |
| Scanning</strong> and disabling the toggle for <strong>Bluetooth |
| scanning</strong>. This does not affect BLE scanning for location or |
| local devices. |
| </p> |
| |
| <h3 id="filtering-scan-results">Filtering scan results</h3> |
| |
| <p> |
| Android 6.0 and later includes BLE scanning and filter-matching on |
| the Bluetooth controller. A device can filter scan results and |
| report <strong>found</strong> and <strong>lost</strong> events |
| related to BLE devices to the application processor (AP). Filtering |
| also works for batch scans, which helps save power as BLE scanning is |
| offloaded to the firmware. Batch scans reduce how often the AP wakes |
| up due to BLE scanning for devices or beacons. |
| </p> |
| |
| <p> |
| The <code>OnFound</code>/<code>OnLost</code> feature is implemented |
| in the Bluetooth controller and then tested to confirm that BLE |
| devices are not missed in scans. This provides power savings, and it |
| can also provide the following benefits: |
| </p> |
| |
| <ul> |
| <li>For an <code>OnFound</code> event, the main AP wakes up upon the |
| discovery of a specific device.</li> |
| <li>For an <code>OnLost</code> event, the AP wakes up when a |
| specific device cannot be found.</li> |
| <li>Framework apps get fewer unwanted notifications when a nearby device is in range.</li> |
| <li>Continuous scans enable framework apps to be notified when a device is out of range.</li> |
| </ul> |
| |
| <p> |
| A scan filter can be based on the discovery of a device's |
| advertisements (the <code>OnFound</code> event). The Java layer can |
| specify parameters such as first discovery (or a specified number of |
| advertisements since first discovery). Implement BLE filtering using |
| the <a href="/devices/bluetooth/hci_requirements#advertisement-packet-content-filter"> |
| Advertising Packet Content Filter HCI command</a>. |
| </p> |
| </body> |
| </html> |
