SAM-M10Q - Integration manual
• The host downloads a copy of the latest data from the AssistNow Offline service and stores it
locally.
• Optionally it may also download a current set of almanac data from the AssistNow Online
service.
• The host wants to use the u-blox receiver.
• If necessary it uploads any almanac, position estimate and/or time estimate to the receiver.
• It scans through AssistNow Offline data looking for entries with a timestamp that most closely
matches the current (UTC) date and time.
• The host sends each such UBX-MGA-ANO message to the receiver.
Note that when data has been downloaded from the AssistNow Offline service with the (default)
resolution of one day, the means for selecting the closest matching timestamp is simply to look for
messages with the current (UTC) date.
2.12.4 AssistNow autonomous
The assistance scenarios covered by
AssistNow Online
and
AssistNow Offline
require an online
connection and a host that can use this connection to download aiding data and provide this to the
receiver when required.
The
AssistNow Autonomous
feature provides a functionality similar to
AssistNow Offline
without the
need for a host and a connection. Based on a broadcast ephemeris downloaded from the satellite
(or obtained by
AssistNow Online
), the receiver can autonomously (i.e. without any host interaction
or online connection) generate an accurate satellite orbit representation ("AssistNow Autonomous
data") that is usable for navigation much longer than the underlying broadcast ephemeris was
intended for. This makes downloading new ephemeris or aiding data for the first fix unnecessary for
subsequent startups of the receiver.
The
AssistNow Autonomous
feature is disabled by default. It can be enabled using the CFG-
ANA-USE_ANA configuration item.
2.12.4.1 Concept
The figure below illustrates the
AssistNow Autonomous
concept in a graphical way. Note that the
figure is a qualitative illustration and is not to scale.
• A broadcast ephemeris downloaded from the satellite is a precise representation of a part (for
GPS nominally four hours) of the satellite's true orbit (trajectory). It is not usable for positioning
beyond this validity period because it diverges dramatically from the true orbit afterwards.
• The
AssistNow Autonomous orbit
is an extension of one or more broadcast ephemerides. It
provides a long-term orbit for the satellite for several revolutions. Although this orbit is not
perfectly precise, it is a sufficiently accurate representation of the true orbit to be used for
navigation.
• The
AssistNow Autonomous data
is automatically and autonomously generated from
downloaded (or assisted) ephemerides. The data is stored automatically in the on-chip battery-
backed memory (BBR). Optionally, the data can be backed up on the host. The number of
satellites for which data can be stored depends on the receiver configuration and may change
during operation.
• If no broadcast ephemeris is available for navigation,
AssistNow Autonomous
automatically
generates the required parts of the orbits suitable for navigation from the stored data. The
data is also automatically kept current in order to minimize the calculation time once the
navigation engine needs orbits.
• The operation of the
AssistNow Autonomous
feature is transparent to the user and the
operation of the receiver. All calculations are done in the background and do not affect the
normal operation of the receiver.
UBX-22020019 - R01
2 Receiver functionality
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