GNSS assistance data is used to improve the time to the first fix (TTFF). In addition, it allows the GNSS device to achieve continuous position tracking with much weaker signal levels.
GNSS assistance data provides navigation models to the receiver, so that the initial search for satellites can be performed more accurately and satellite signals can be found faster.
Acquiring assistance data using HERE GNSS API completely removes the need to receive the navigation message from satellite and, therefore, improves the TTFF of the device, typically down to a few seconds.
In addition, the assistance data includes, for example, ionospheric data and real time information about the health of the satellites.
The format of GNSS assistance is described in Data Types / GNSS Assistance Data.