u-blox 6

13.7.3.2 Changing ALP files
The server function periodically attempts to receive new ALP data from an upstream server, as the result of an
HTTP request or other means of file transfer.
In case a new file becomes available, the server shall indicate this to the Client. This is the function of the
fileId field.
The server should number ALP files it serves arbitrarily. The only requirement is that the fileId actually is
changed when a new file is being served, and that it does not change as long as the same file is being
changed.
If the client, as a result of a client request, receives a fileId different from the one in earlier requests' replies,
it will reinitialize the ALP engine and request data anew.
Further, if the client attempts to send data to the server, using the ALPSRV-CLI method, it indicates, which
fileId needs to be written. The server shall ignore that request in case the fileId numbers do not match.
13.7.3.3 Sample Code
u-blox makes available sample code, written in C language, showing a server implementation, serving ALP data
from its file system to a client. Please contact your nearest u-blox Field Application Engineer to receive a copy.
13.8 AssistNow Autonomous
This functionality is only supported by u-blox 6 Firmware 7.01 and above.
13.8.1 Introduction
The A-GPS 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 A-GPS without the need for a host and a
connection. Based on a broadcast ephemeris downloaded from the satellite (or obtained by A-GPS) 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 start-ups of the receiver.
The AssistNow Autonomous feature is disabled by default.
13.8.2 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 (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 a broadcast ephemeris. 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. Data for approximately twenty satellites is stored automatically in the on-chip battery
backup RAM. Optionally, data for the full constellation (32 satellites) can be stored in external flash memory
(if available) or on the host.
GPS.G6-SW-10018-A Public Release Page 38 of 201