Bluetooth LE scan parameters tell a Bluetooth module how to execute Bluetooth LE scanning and affect scanning speed and power consumption during receiving Bluetooth LE advertisements. These parameters are scan interval, scan window, and scanning mode.
As you know, there is no way to change the scan parameters when your application uses the standard Microsoft Bluetooth API. However, the Bluetooth Framework provides the unique feature that allows you to specify the Bluetooth LE scan parameters when your application uses the standard Microsoft Bluetooth driver or the BLED112 USB Bluetooth dongle.
This very short article describes each scan parameter, what it means, and how it affects the BLE scanning. You can test each Bluetooth LE scan parameter setting by running the Bluetooth Framework Beacons demo application.
Windows 11 24H2
Microsoft has updated its internal systems, so the usual method for setting scan parameters in older Windows versions no longer works on Windows 11 24H2. Fortunately, the Bluetooth Framework provides a solution, allowing you to adjust scan parameters even on the latest Windows 11 update.
Scan Parameters
Scan Interval
In BLE terminology, the scan interval is the duration of time between two consecutive times that the scanner wakes up to receive the advertising messages. This parameter is defined in units of 0.625 ms and has a range between 4 and 16384. By default, it is set to 189, which is equivalent to 118.125 ms.
Scan Window
The scan window parameter defines how long to scan at each interval. This parameter is defined in units of 0.625 ms and has a range between 4 and 16384. By default, it is set to 29, which is equivalent to 18.125 ms. The scan window parameter must be equal to or smaller than the scan interval.
Scanning Mode
The scanning mode defines how a BLE receiver collects information about advertising Bluetooth LE devices. There are two scanning modes: active and passive.
In the active scanning, the radio will request more information once an advertisement is received by sending the scan request, and the advertiser will answer with information like friendly name and supported profiles using scan response.
In the passive scanning, the BLE radio just listens to other devices advertisements. When one of these advertisements is detected, the radio reports the discovered device and all the advertisement packets. The advertisement contains information like discoverability and connectability modes, TX power level, MAC address of the device, and additional application data.