ashtech DG14, Reference Manual

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62 DG14 and DG16 Board & Sensor Reference Manual
The DG16 validate all received differential corrections including the
checksum and parity validation checks included in the RTCM and SBAS
specifications, and uses only the valid correction data in the navigation
solution.
When in DGPS operation and using RTCM corrections, the DG16 supports
the Type 2 message for IODE changes.
A differential navigation solution is only computed when there is a sufficient
number of matched sets of satellite parameters and corrections. The DG16
will never calculate a partial differential solution. It there are enough corrected
satellites to compute a position even though not all tracked satellites have
corrections, the navigation solution disregards uncorrected measurement
data and/or unused corrections and includes only corrected measurement
data in the computation. When a navigation solution is computed using the
least-squares algorithm, the measurement data and corrections data for a
given satellite must both be available for the particular epoch. Satellites with
propagated measurement data and valid corrections data are included in a
differential navigation solution generated with the Kalman filter. Regardless of
the navigation algorithm, the number of satellites required to produce a valid
solution depends on the position mode: at least four satellites for a 3D
solution, and at least three satellites for a 2D solution.
The DG16 conducts validity tests on incoming RTCM messages before
incorporating them into the navigation solution.
Setting Up a Differential Remote Station
You must have the Differential remote option [U] installed on your receiver.
Figure 4.1 displays a typical DGPS remote station configuration