A Space-Based Highly Accurate and Certified Time and Frequency Distribution Service for the Telecommunication Market: System Concept and Business Drivers
- Paper number
IAC-07-D1.1.08
- Author
Mr. Francesco Ratti, European Space Agency (ESA)/ESTEC, The Netherlands
- Coauthor
Mr. Domenico Giunta, European Space Agency (ESA)/ESTEC, The Netherlands
- Year
2007
- Abstract
One of the most critical requirements in telecommunication network is the synchronization and synthonization of the nodes of the network. A lack of synchronization can cause malfunctioning in audio-video services such as sound and vision out of sink, picture freezing, dropping of calls, etc. The deployment of Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) in the 1990s is driving the requirements for synchronization. Third generation (3G) mobile communication networks demand also increased level of synchronization. SDH networks employ a hierarchical structure of clocks for synchronization. Normally an atomic clock is used as a Primary Reference Clock (PRC) due to its superior performance in terms of accuracy and stability. The lower level clocks are Rubidium or Quartz oscillators which can be slaved to a GPS receiver. The generation of the time signal is in this case related to the reception of the signal from the space segment. GPS has proven to be invaluable as a navigation system; however it has not been designed with the main purpose of synchronization. GPS receivers at different nodes of the network receive signals from different satellites. The bias and the drift of the Rubidium clocks on board the satellites, although kept to a minimum by periodic upload of correction factors, can lead to the generation of different timescales locally at nodes of the network. The influence of the ionosphere and troposphere on the signal transmission and the error in the ephemeris determination has also an influence on the synchronization of the receiver. Furthermore telecommunication is considered a critical infrastructure in modern society and the use of a certified synchronization services is key to avoid single system point of failures. In the following paper the needs of the stakeholders in the telecommunication field are discussed and the main requirements for the system are gathered. A possible concept for synchronization service based on a space segment is then presented. The system concept is chosen among possible concepts that have been proposed in the literature. In particular it is proposed to realize the Time and Frequency Distribution Service (TFDS) using a dedicated payload on a GEO mission. The time payload is kept continuously synchronized to a Precise Time Facility (PTF) on ground. The service can be accessed by the user via TDMA or alternatively CDMA. The user is charged a fee for the service. The encryption of the signal allows a high level of security for the user. The signal in space is periodically audited to guarantee and certify its accuracy. The audits are performed by certified bodies. The main business case assumptions are then presented. The business analysis shows that the profitability is linked to the ability of the system to use low cost receiver, to take advantage of synergy with future GEO missions, to provide a reliable service with a high level of accuracy, integrity, availability and continuity of service, to be certified by a competent authority and to become a well-known and recognized time service to complement the TFDS offered by current and future GNSS.
- Abstract document
- Manuscript document
IAC-07-D1.1.08.pdf (🔒 authorized access only).
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