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C-Nav Hardware Reference Guide
13
together with the advanced processing algorithms, which makes the exceptional accuracy of the
C-Nav Subscription Service 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 C-Nav-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 C-Nav precision GNSS receiver actually have two
receivers in a single package, a GNSS receiver and an L-Band communications receiver, both
designed by C-Nav for this system. The GNSS receiver tracks all the satellites in view and
makes pseudorange measurements to the GNSS satellites. Simultaneously, the L-Band
receiver receives the correction messages broadcast via the L-Band satellite. When the
corrections are applied to the GNSS measurements, a position measurement of unprecedented
real-time accuracy is produced.
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 back-up system.
All 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 back up 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.
The network is a fully automated self-monitoring system. To ensure overall system integrity, an
independent integrity monitor receiver, similar to a standard C-Nav user receiver, is installed at
every reference station to monitor service quality. Data from these integrity monitors is sent to
the two independent processing hubs in Torrance, California and Moline, Illinois. Through these
integrity monitors the network is continuously checked for overall SBAS positioning accuracy, L-
Band signal strength, data integrity and other essential operational parameters
C-NavC
2
Subscription Service
C-Nav now offers a second independent full constellation (GPS + GLONASS) GNSS correction
service called C-NavC
2
. C-NavC
2
features include GLONASS and GPS (GNSS) clock, as well
as orbit correctors (Galileo and COMPASS planned). It provides a fully independent suite of
clock and orbit correction algorithms, and fully independent servers in geographically separated
processing centers. Features also include a second independent global network of C-Nav dual
frequency GPS / GLONASS reference stations equipped with Sapphire© based technology, and
simultaneously broadcasts from two independent satellite networks (Net-1 and Net-2).