14.3 Satellite Radio Navigation Systems
261
Time synchronization accuracy for GALILEO signals will be 30 ns with a 95%
probability at any daily interval. The discrepancy between the GPS and GST time
scales is transmitted as a separate parameter, in the same way as it is done in
GLONASS.
The GALILEO ground control complex includes two independent loops:
• space vehicle control loop (ground control segment—GCS);
• ephemeris-time loop; ground mission segment (GMS).
The GCS control loop receives and processes telemetry from the GALILEO space
vehicle, controls the operation of the satellite subsystems, generates command information and transfers it to the satellite. The interface between the space segment and
the GCS control loop is through a network of tracking stations, receiving telemetry
and transmitting control commands (Telemetry Tracking and Command—TT&C)
in the S-band.
The GMS loop fulfills missions of collecting data from the global non-request
network of measuring stations (ground sensor stations—GSS), processing the
received information, generating and uploading of ephemeris-time information, as
well as information on the integrity on board the satellite through upload stations
(Uplink Station—ULS).
At the first stage of the GALILEO system deployment, the control center in
Oberpfaffenhofen (Germany) acts as the coordinating center for the GCS control
loop, and the control center in Fucino (Italy) acts as the GMS loop center. At the
stage of full operational readiness, all tasks of the ground control complex will be
coordinated by both centers in the hot standby mode. Thus, at the stage of normal
operation, the GALILEO ground control complex will include:
• system control center in Fucino (Italy) and Oberpfaffenhofen (Germany);
• data upload stations;
• global network of request-free measuring stations;
• stations for tracking, receiving telemetry and transmitting control commands;
• stations of the medium-orbit search and rescue system, receiving the distress
signal relayed by the satellite GALILEO.
In addition to the considered SRNS, it is necessary to mention the Chinese SRNS
BEIDOU, which is at the stage of the third stage of deployment and will soon provide
users with navigation information globally. The BEIDOU system will provide two
types of global and two types of regional services. Global services are services with
open and authorized access. Regional services are wide area differential correction
services and short message transmitting services.
The ground control complex BEIDOU is built according to the classical centralized scheme: a network of no-request measuring stations forms the readings of the
primary measurements of the navigation parameters of the radio signals of navigation
space vehicles and transmits them to the system control center, in which information
is generated that is uploaded on board the space vehicles via special-purpose ground
stations.
261
Time synchronization accuracy for GALILEO signals will be 30 ns with a 95%
probability at any daily interval. The discrepancy between the GPS and GST time
scales is transmitted as a separate parameter, in the same way as it is done in
GLONASS.
The GALILEO ground control complex includes two independent loops:
• space vehicle control loop (ground control segment—GCS);
• ephemeris-time loop; ground mission segment (GMS).
The GCS control loop receives and processes telemetry from the GALILEO space
vehicle, controls the operation of the satellite subsystems, generates command information and transfers it to the satellite. The interface between the space segment and
the GCS control loop is through a network of tracking stations, receiving telemetry
and transmitting control commands (Telemetry Tracking and Command—TT&C)
in the S-band.
The GMS loop fulfills missions of collecting data from the global non-request
network of measuring stations (ground sensor stations—GSS), processing the
received information, generating and uploading of ephemeris-time information, as
well as information on the integrity on board the satellite through upload stations
(Uplink Station—ULS).
At the first stage of the GALILEO system deployment, the control center in
Oberpfaffenhofen (Germany) acts as the coordinating center for the GCS control
loop, and the control center in Fucino (Italy) acts as the GMS loop center. At the
stage of full operational readiness, all tasks of the ground control complex will be
coordinated by both centers in the hot standby mode. Thus, at the stage of normal
operation, the GALILEO ground control complex will include:
• system control center in Fucino (Italy) and Oberpfaffenhofen (Germany);
• data upload stations;
• global network of request-free measuring stations;
• stations for tracking, receiving telemetry and transmitting control commands;
• stations of the medium-orbit search and rescue system, receiving the distress
signal relayed by the satellite GALILEO.
In addition to the considered SRNS, it is necessary to mention the Chinese SRNS
BEIDOU, which is at the stage of the third stage of deployment and will soon provide
users with navigation information globally. The BEIDOU system will provide two
types of global and two types of regional services. Global services are services with
open and authorized access. Regional services are wide area differential correction
services and short message transmitting services.
The ground control complex BEIDOU is built according to the classical centralized scheme: a network of no-request measuring stations forms the readings of the
primary measurements of the navigation parameters of the radio signals of navigation
space vehicles and transmits them to the system control center, in which information
is generated that is uploaded on board the space vehicles via special-purpose ground
stations.