Wi-Fi preferred network offload (PNO) scans are low-powered Wi-Fi scans that
occur at regular intervals when a device is disconnected from Wi-Fi and the
screen is off. PNO scans are used to find and
connect to saved networks. These scans are scheduled by the framework using the
NL80211_CMD_START_SCHED_SCAN command. For more information, see
Optimizing power usage with device mobility information
On devices running Android 9 or lower, when the device is disconnected from Wi-Fi and the screen is off, PNO scans occur at 20 second intervals for the first three scans, then slow down to one scan every 60 seconds for all subsequent scans. PNO scanning stops when a saved network is found or the screen is turned on.
Android 10 introduces an optional API method named
WifiManager that increases the interval between
PNO scans based on the device's mobility state to reduce power consumption.
The possible mobility states are:
DEVICE_MOBILITY_STATE_UNKNOWN: Unknown mobility
DEVICE_MOBILITY_STATE_HIGH_MVMT: On a bike or in a motor vehicle
DEVICE_MOBILITY_STATE_LOW_MVMT: Walking or running
DEVICE_MOBILITY_STATE_STATIONARY: Not moving
If the device is stationary, the Android framework increases the interval between PNO scans from 60 seconds to 180 seconds to reduce power consumption. This optimization is made on the assumption that the device is unlikely to find any new networks in PNO scans when the device is not moving.
If the device is in any other mobility state or if the method isn't called, the device uses the default PNO scan behavior.
To implement this power-optimizing feature on a device running Android
10 or higher, derive the device mobility information
and call the
setDeviceMobilityState() method from a custom system app.