NavCom SF-3050 Rev.I - Manual (Page 149)

SF-3050 GNSS Product User Guide – Rev I
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multi-frequency pseudorange and carrier phase measurements back to the processing
centers together with the data messages, which all GPS satellites broadcast.
At the processing centers, NavCom's proprietary differential processing techniques are
used to generate real-time precise orbits and clock correction data for each satellite in the
GPS constellation. This proprietary Wide Area DGPS (WADGPS) algorithm is optimized
for a multi-frequency system such as StarFire, in which multi-frequency ionospheric
measurements are available at both the reference receivers and the user receivers. It is
the use of multi-frequency receivers at both the reference stations and the user
equipment, together with the advanced processing algorithms, which makes the
exceptional accuracy of the StarFire system possible.
Creating the corrections is just the first part. From our two processing centers, the
differential corrections are then sent to the Land Earth Station (LES) for uplink to L-Band
communications satellites. The uplink sites for the network are equipped with NavCom-
built modulation equipment, which interfaces with the satellite system transmitter and
uplinks the correction data stream to the satellite that broadcasts it over the coverage
area. Each L-Band satellite covers more than a third of the earth.
Users equipped with a StarFire precision GPS receiver actually have two receivers in a
single package, a GPS receiver and an L-Band communications receiver, both designed
by NavCom for this system. The GPS receiver tracks all the satellites in view and makes
pseudorange measurements to the GPS satellites. Simultaneously, the L-Band receiver
receives the correction messages broadcast via the L-Band satellite. When the
corrections are applied to the GPS measurements, a position measurement of
unprecedented real-time accuracy is produced.
The StarFire network ground reference frame transitioned from the ITRF-2005 to the
ITRF-2008 system on January 21, 2014 at 0900 hours UTC. The back-up systems
provide fully redundant transition as of January 27, 2014 at 00:00 hours UTC. For
information on this transition, please consult the Troubleshooting Guide StarFire GPS
Transition to ITRF2008 Ground Reference Network located on the NavCom website.
Reliability
The entire system meets or exceeds a target availability of 99.99%. To achieve this,
every part of the infrastructure has a built-in backup system.
All of the reference stations are built with duplicate receivers, processors, and
communication interfaces, which switch automatically or in response to a remote control
signal from the processing centers. The data links from the reference stations use the
Internet as the primary data link and are backed up by dedicated communications lines,
but in fact the network is sufficiently dense that the reference stations effectively act as
backup for each other. If one or several fail, the net effect on the correction accuracy is
not impaired.
There are two continuously running processing centers, each receiving all of the
reference site inputs and each with redundant communications links to the uplink LES.
The LESs are equipped with two complete and continuously operating sets of uplink
equipment arbitrated by an automatic fail over switch. Finally, a comprehensive team of
support engineers maintains round the clock monitoring and control of the system.