SL876Q5-A
Product User Guide
1VV0301333 Rev. 2
Page 20 of 68
2017-06-27
The minimum cold start TTFF can be reduced from 30 seconds to just a few seconds by
implementing AGPS, which can provide Extended Ephemeris (EE) data by two methods -
1. Locally-generated: The receiver includes software to project the future positions of
the satellites. This data may be calculated out to 14 days or even longer, depending
on the resources available in the receiver, e.g. computation ability and memory.
2. Server-generated: A server calculates the future position projections and makes them
available to a receiver, typically over the internet. This data may be good for 30 days,
depending on available resources, e.g. communication links and storage.
Both CGEE and SGEE are available for GPS and GLONASS satellites.
Client-generated Extended Ephemeris (CGEE)
Extended ephemeris is computed in the receiver and then stored locally in the flash memory.
Whenever the module receives ephemeris data for a satellite, it checks if it has computed
CGEE for that satellite recently. If it has not, it computes EE for that satellite (for the next 3
days for GPS and 1 day for GLONASS) and stores it in flash memory. The next time the module
turns on and broadcast ephemeris is not available for a visible satellite, the stored CGEE data
is searched to see if it is still valid and can be used. If EE data is available for enough satellites,
the receiver can obtain a first fix in 10 to 15 seconds (typical) rather than the usual 35 seconds
without EE data. CGEE is enabled by default.
Server-generated Extended Ephemeris (SGEE)
Extended ephemeris is computed at the server and saved in a file which can then be
downloaded to the receiver’s flash memory. The server file contains 1, 3, 7, and 14, days of
ephemerides. To use SGEE data, a file must be transferred using NMEA or OSP commands.
Please contact Telit support for subscription details.
2-D Positioning
By default, the module will compute a 2-D solution if possible when performing initial
acquisition. In a 2-D solution, the receiver assumes a value for altitude and uses it to estimate
the horizontal position. Under warm and hot start conditions, the receiver uses the last known
value of altitude, which is a good assumption in most situations. However under cold start
conditions, the last position is unknown, and the receiver assumes a value of 0. In situations
where the true altitude is significantly higher than that, the horizontal position estimate will be
noticeably impacted. 2_D positioning is controlled by
OSP MID 136
.
Static Navigation
Static Navigation is an operating mode in which the receiver will freeze the position fix when
the speed falls below a set threshold (indicating that the receiver is stationary). The course is
also frozen, and the speed is reported as 0. The navigation solution is unfrozen when the
speed increases above a threshold or when the computed position exceeds a set distance
from the frozen position (indicating that the receiver is again in motion). These thresholds
cannot be changed by the user.
This feature is useful for applications in which very low dynamics are not expected, the classic
example being an automotive application.
Static Navigation is disabled by default, but can be enabled by
OSP MID 143
command.
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