CSI Wireless SBX-3, Reference Manual

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SBX-3 Reference Manual
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1.4.3 Radiobeacon DGPS
Radiobeacons conforming to regional broadcast standards transmit a
limited selection of RTCM SC-104 messages, including message types
1, 2, 3, 5, 6, 7, 9, and 16.
•
A DGPS beacon will broadcast either Type 1 or Type 9 messages, both of
which contain similar information, including pseudorange corrections and
range rate corrections to each GPS satellite.
•
The Type 2 message contains delta differential corrections that are used
when the remote receiver is using a different satellite navigation message
than used by the base station.
•
The Type 3 message contains the position of the beacon reference station,
often accurate to within centimeters with respect to the WGS-84 reference
datum.
•
The Type 5 message contains GPS constellation health information used
for improving tracking performance of a GPS receiver
•
The Type 6 message contains null information, and is broadcast so that a
beacon receiver demodulating the data from the broadcast does not lose
lock when the beacon station has no new data to transmit.
•
The Type 7 message contains the radiobeacon almanac information
composed of location, frequency, service range, and health information of
sister stations for the currently tuned beacon.
•
The Type 16 message provides users with a 90 character text string that
may contain information regarding the status of the system, weather
warnings, etc.
Radiobeacon DGPS is often referred to as a local-area service, as the
data broadcast is appropriate for use within the coverage range of the
station. Corrections are specific to the beacon reference station, and
become less accurate with increasing distance from the reference
antenna. As a general rule, positioning accuracy will degrade by
approximately 1 m for every 150 km away from the beacon site.
1.4.4 Radiobeacon Coverage
Figure 1-1 shows the approximate radiobeacon coverage throughout
the world. In this figure, light shaded regions denote current coverage,
with beacon stations symbolized as white circles.