The EGNOS time offset to UTC

N. Suard (1) , Amale Kanj (1) , J. Delporte (1) , Pierre Uhrich (2, 3) , Philip Tuckey (2, 3) , P. Defraigne (4) , I. Sesia (5) , I. Signorile (5) , E. Armagou-Miret (6)

1 CNES - Centre National d'Études Spatiales [Toulouse]
2 SYRTE - Systèmes de Référence Temps Espace
3 Références micro-ondes et échelles de temps
4 ROB - Royal Observatory of Belgium = Observatoire Royal de Belgique
5 INRiM - Istituto Nazionale di Ricerca Metrologica
6 GSA - European GNSS Agency

EGNOS, the European SBAS is in principle known for its services augmenting GPS in the positioning domain as its Open Service for the accuracy (RD1) or its Safety of Life Service (RD2) for the integrity and a safe navigation. Nevertheless, an auxiliary timing service is also provided. The EGNOS Network time (ENT) is steered on GPS Time (GPST) in an accurate manner in order to be compliant with the SBAS requirements (below 50 ns - RD3). But EGNOS does not rely, as some other SBAS, on the GPS legal timing data to be synchronised to UTC and EGNOS is transmitting regularly such an offset for ENT-UTC by using a specific message type (MT#12). The content of this message is based on an independent physical realisation of UTC in Observatoire de Paris (OP, France) – called UTC(OP) – connected to a specific Ranging Integrity Monitoring Station (RIMS).The characteristics of ENT are defined in RD1. CNES has been awarded in 2015 by GSA of the Service Performance Member State Support (SPMS) grant. In this frame, CNES is leading a consortium of 8 state bodies from 7 countries. One part of this consortium activities is devoted to the time function monitoring, involving the italian Istituto Nazionale di Ricerca Metrologica (INRIM), the laboratory Systèmes de Références Temps- Espace (LNE-SYRTE) of Observatoire de Paris, the Royal Observatory of Belgium (ROB) and CNES. This paper details the time aspects of EGNOS and describes the connection of ENT to UTC(OP). EGNOS system time requirements are also reminded. The different methods used to assess the performance by the different SPMS partners are described and the obtained results are presented and commented. Secondly, the paper focuses on the GPS timing anomaly (RD4) that occurred on the 26th of January 2016, explaining what the GPS problem was in the transmitted data, and showing how the EGNOS time offset was not impacted by the event. On the other hand, there can be interruption in the transmission of ENT-UTC, as there is no hot redundancy for the RIMS at Paris and no link to another UTC local realisation. When a heavy maintenance occurs at the Observatoire de Paris in relation to the RIMS connections like at end of October 2015, the availability of the timing information ENT-UTC can’t be ensured by EGNOS. Based on these two considerations, some proposals are made to combine both sources of information (GPS and EGNOS) to synchronise the user clock to UTC in the more efficient manner for users being, at least, located in the EGNOS service area. A comparison of the GPS Time offset to UTC and of EGNOS Time offset to UTC is for this purpose also proposed.

Domaines: Astrophysique [astro-ph]

N. Suard, Amale Kanj, J. Delporte, Pierre Uhrich, Philip Tuckey, et al.. The EGNOS time offset to UTC. European Navigation Conference (ENC) on GNSS, 2016, Helsinki, Finland. ⟨hal-03743679⟩