Global Positioning System Reference
In-Depth Information
This section focuses on GALILEO services: these services will be provided
worldwide and independently from other satellite navigation systems by using only
the signals broadcast by the GALILEO satellite constellation. Five reference services
are defined: open service (OS), safety of life (SOL), commercial service, public regu-
lated service (PRS), and the support for a search and rescue (SAR) service. Table
10.1 highlights the anticipated performances for these services derived from the
GALILEO Mission High Level Definition [1].
10.2.1 Open Service (OS)
The OS will provide positioning, velocity, and timing information that can be
accessed free of direct charge. This service is suitable for mass-market applications,
such as in-car navigation. This service is also particularly suitable with integration in
Table 10.1
Performance for the GALILEO Services
GALILEO
Global Services
Commercial
Service
OS
SOL Service
PRS
Coverage
Global
Global
Global
Global
15m or 24m H-35m V
(single frequency)
4m H-8m V
(dual frequency)
Positioning accuracy
(Horizontal, 2
dRMS, 95%)
(Vertical, 95%)
4m H-8m V
(dual frequency)
15m or 24m H-35m V
(single frequency)
6.5m H-12m V
(dual frequency)
Timing
accuracy (95%)
30 ns
30 ns
30 ns
30 ns
Integrity 1
Alert limit
Time to alert
Integrity risk
None
None
12m H-20m V
6 seconds
3.5
20m H-35m V
10 seconds
3.5
10 −7 /150 seconds
10 −7 /150 seconds
×
×
Continuity risk 2
1
×
10 −5 /15 seconds
1
×
10 −5 /15 seconds
Service availability 3
99.5%
99.5%
99.5%
99.5%
Controlled access of
ranging codes and
navigation data
message
Access control
Free open access
Controlled access
of ranging codes
and navigation
data message
Authentication of
integrity information
in the navigation data
message
Certification and
service guarantees
None
Guarantee of
service possible
Build for certification
and guarantee of
service
Build for certification
and guarantee of
service
Single frequency accuracy depends on the frequency used: 15-m horizontal accuracy when using the L1 signal or 24m when using the other fre-
quencies (E5a, E5b, E6).
1. Integrity is defined by the following parameters:
Alert limit: the maximum allowable error in the user position solution before an alarm is to be raised within the specific time to alert;
Time to alert: the time from when an alarm condition occurs until when the alarm is received at the user level (including the time to detect
the alarm condition);
Integrity risk: the probability, during any continuous period of operation, that the computed vertical or horizontal positioning error
exceeds the corresponding alert limit and the user is not informed within the specified time to alert (note that the value reported in the
table includes the user contribution of 1.5
10 −7 /150 seconds).
2. Continuity risk is the probability that the specified performances (accuracy and integrity) are supported by the system over the time interval
applicable and within the coverage area, given that they are supported at the beginning of the operation and that they are predicted to be sup-
ported all along the operation duration (note that the value reported in the table includes the user contribution of 0.2
×
10 −5 /15 seconds).
3. Service availability represents the percentage of time averaged over the design lifetime (20 years) when the service is within the specified per-
formance (accuracy, integrity, and continuity) for any point within the service volume. It is derived from the availability of each operational
configuration (nominal, without failures, or nonnominal, with one or more failures), weighted by its probability of occurrence, averaged over
the design lifetime.
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