Telit Wireless Solutions SE873 Series, Руководство пользователя

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SE873 Family Product User Guide Product Features
1VV0301216
Rev.4
Page 19 of 69 2018-08-24
2. Server-generated (SGEE): 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 a few seconds rather than the usual 30+ 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 nav solution.
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 command MID 143 .
Velocity Dead-Reckoning
Velocity dead-reckoning is the use of the last known velocity to propagate the navigation solution
when there are insufficient measurements to calculate an updated solution. It serves to mitigate
the effects of blocked satellite signals by continuing to provide a position output.
Note : The
receiver outputs status information which indicates that a solution is being maintained using dead-
reckoning.
This feature is disabled by default but can be enabled using the Mode Control message MID 136 .
Valid timeout values are in a range from zero (which disables dead-reckoning) to two minutes.