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Galileo Open Service (OS)
|Title||Galileo Open Service (OS)|
|Year of Publication||2011|
The Galileo System will be an independent, global, European-controlled, satellite-based navigation system and will provide a number of guaranteed services to users equipped with Galileo-compatible receivers.
With positioning accurate to one metre, the freely accessible Galileo Open Service (OS) targets the mass market and is intended for motor vehicle navigation and location-based mobile telephone services. Free to the user, it provides positioning and synchronization information intended for high-volume satellite radio navigation applications. 
The Galileo Open Service (OS) provides positioning, velocity and timing information that can be accessed free of direct user charge. This service is suitable for mass-market applications, such as in-car navigation and hybridisation with mobile telephones. The Open Service is accessible to any user equipped with a receiver, with no authorisation required. While up to three separate signal frequencies are offered within the Open Service, cheap single-frequency receivers will be used for applications requiring only reduced accuracy. In general, Open Service applications will use a combination of Galileo and GPS signals, which will improve performance in severe environments such as urban areas. The Open Service could also be used by professionals who require high precision but not integrity, complementing this service with GNSS Augmentation techniques.
The timing service is synchronised with UTC when used with receivers in fixed locations. This timing service can be used for applications such as network synchronisation or scientific applications.
The Open Service does not offer integrity information, and the determination of the quality of the signals will be left entirely to the users. There will be no service guarantee or liability from the Galileo Operating Company on the Open Service.
Performance and features
The Galileo Open Service is accessible through the signals at L1, E5a and E5b, whether data or pilot. Several combinations are also possible, such as a dual frequency service based on using L1 and E5a (for best ionospheric error cancellation) or single frequency services (at L1, E5a, E5b or E5a and E5b together) in which case the ionospheric error is removed using a model, and even triple frequency services using all the signals together (L1, E5a and E5b), which can be exploited for very precise, centimetric applications. 
The performance objectives in terms of position accuracy and availability will be competitive with respect to existing GNSS and further planned evolutions. In addition, the Open Service will also be interoperable with other GNSS, in order to facilitate the provision of combined services. 
|Galileo Open Service (positioning & timing)|
|Single Frequency (SF)||Dual Frequency (DF)|
|Accuracy (95%)||Horizontal: 15 m||Horizontal: 4m|
|Vertical: 35 m||Vertical: 8m|
|Timing Accuracy wrt UTC/TAI||N/A||30 ns|
|Ionospheric Correction||Based on SF Model||Based on DF Measurements|
For more information about Open Service performances, see the article Galileo Performances.
The Open Service signals are separated in frequency to permit the correction of errors induced by ionospheric effects by differentiation of the ranging measurements made at each frequency. Each navigation frequency will include two ranging code signals (in-phase and quadrature). Data are added to one of the ranging codes while the other “pilot” ranging code is data-less for more precise and robust navigation measurements.
During the Initial Operational Capability (IOC) phase, the GALILEO open service, the search and rescue service and the PRS will be provided. At this stage, however, accuracy and availability will not have reached their optimum levels yet.
Edited by GMV, using information from ESA and European Union as indicated through the references.
- ^ a b Mid-term review of the European satellite radio navigation programmes
- ^ Galileo Services at ESA Galileo web page
- ^ a b Galileo Mission High Level Definition, v3, September 2002.
- ^ a b ESA Galileo web page
- ^ Galileo OS SIS ICD Issue 1 Revision 1 September 2010e
- ^ COMMUNICATION FROM THE COMMISSION TO THE EUROPEAN PARLIAMENT AND THE COUNCIL, State of progress of the Galileo programme (COM(2002) 518 final) (2002/C 248/02)