SE868Kx-Ax Family Product User Guide
1VV0301201 Rev. 5
Page 20 of 83
2021-07-15
Not Subject to NDA
Differential GPS (DGPS)
DGPS is a Ground-Based Augmentation System (GBAS) for reducing position errors by
applying corrections from a set of accurately-surveyed ground stations located over a
wide area. These reference stations measure the range to each satellite and compare it
to the known-good range. The differences can then be used to compute a set of
corrections which are transmitted, either by radio to a DGPS receiver or over the internet.
The DGPS receiver can then send them to the module 2nd serial port (RX2) using the
RTCM SC-104 Version 2.3 protocol message types 1, 2, 3, and 9.
These corrections can significantly improve the accuracy of the position reported to the
user.
The MT3333-based modules can accept either the RTCM SC-104 messages or SBAS
differential corrections via command $PMTK501.
Assisted GPS (AGPS)
Assisted GPS (or Aided GPS) is a method by which information from a source other than
broadcast GPS signals is used to improve (i.e. reduce) TTFF.
The necessary ephemeris data is calculated either by the receiver itself (locally-
generated ephemeris) or a server (server-generated ephemeris) and is then stored in the
module.
Please refer to Section 2.3 Product Variants for applicability.
4.6.1.
Locally generated AGPS - Embedded Assist System (EASY)
Proprietary algorithms within the module perform GPS ephemeris prediction locally from
stored broadcast ephemeris data (received from tracked satellites). The algorithms
predict orbital parameters for up to three days. The module must operate in Full Power
mode for at least 5 minutes to collect ephemeris data from visible satellites, or 12 hours
for the full constellation.
EASY is disabled if the fix rate is > 1 Hz.
EASY is on by default, but can be disabled by command PMTK869.
Please refer to Section 2.3 Product Variants for applicability.
4.6.2.
Server-generated AGPS - Extended Prediction Orbit (EPO)
(SE868-A and SE868K3-Ax only)
