GALILEO - Understanding GPS: Principles and Applications - page 591

Table 10.12 summarizes control drivers for integrity determination and dissem-
ination.
The navigation and integrity data sets, which are included in the navigation
data message, are multiplexed and uplinked via the ULS network for dissemination
to users through selected satellites. The uplink of integrity data requires real-time
connectivity with the selected satellites for integrity dissemination.
The function of the ULS network is:

• To upload updated navigation data every 100 minutes (corresponding to the
worst-case clock prediction validity time);
• To uplink to a subconstellation of satellites for the dissemination of integrity
data in real time.

For this purpose, some nine stations fitted with five to six antennas 1 will be
deployed worldwide in order to fulfill the global dissemination of integrity signals.
The mission ULS are 3m antennas transmitting spread-spectrum signals in the
C-band, without downlink implementation.

10.6 GALILEO SAR Architecture

GALILEO will contribute to the international SAR architecture and its associated
provided services. It is planned to provide a SAR payload on each GALILEO satel-
lite, which will be backward compatible with the present COSPAS/SARSAT system
and provide a rich set of additional capabilities. The GALILEO Ground Segment
will interface with Rescue Coordination Centers (RCCs) to allow for the dissemina-
tion of feedback messages to distress-emitting beacons. This architecture will fulfill

Table 10.12 Design Drivers for the Integrity System

Design Driver Value

TTA 5.2 seconds

Integrity determination
• Sampling frequency

1 second

• SISA

85 cm

• SISMA

0.7m (nominal GSS network);
1.3m (one GSS failure)

Integrity dissemination
• Integrity flag update rate

1 Hz

• Integrity user masking angle

10º

• Minimum number of SVs in view
broadcasting integrity data (diversity)

2 (user requirement)

• Uplink station masking angle

5º

1. The total number of ULS antennas is a function of the subconstellation broadcasting integrity data: in the

case of a 15-satellite subconstellation, three to four antennas per ULS site are considered sufficient. The
quoted number of five to six is related to all satellites broadcasting integrity data.