Performances Monitoring and Analysis for KASS

The Korea Augmentation Satellite System (KASS) is the future SBAS of the Republic of Korea. It is developed by the Korea Aerospace research Institute (KARI) for the government of the Republic of Korea, and Thales Alenia Space is the industry prime contractor of this development. The function of the KASS is to decompose all possible range error sources and to distribute corrections and/or alerts to its users by means of geostationary satellites. The KASS Processing Station (KPS) is the component of KASS in charge of computing the orbit, clock and ionosphere correction and alert information (below ‘Navigation Overlay Frame’, NOF) using data from a set of reference stations. The KPS is composed of two independent elements: the Processing Set (PS) and the Check Set (CS). The first element is responsible of computing the complete navigation context for the GNSS constellation (orbits and clock) and the ionosphere model, then to prepare and send the NOF to be broadcast to the users. The second element acts as a super user by applying the NOF to the GPS messages checking that this is consistent with an independent set of measurement to control and insure the integrity. The KPS-PS component plays a key role in the KASS performance achievement where the APV-1 service level is required. To feed the KPS, the KASS has specific KASS Reference Station (KRS) located on the Rep. of Korea land masses. Compared to other SBAS, this leads to a very concentrated station network. This particularity makes a specific algorithm adaptation of the KPS-PS necessary, as compared to the EGNOS solution, to provide the desired APV-1 performance. These adaptations regard both orbit determination and all the more ionosphere corrections due to the very low number of Ionosphere Grid Points (IPG) that need be modeled and monitored. To cope with these KASS specificities, Thales Alenia Space has designed, developed and qualified a new complete real time navigation algorithm chain that provides MOPS-compliant NOF messages. The ionosphere model is different from the EGNOS one that favors a local analysis counter to a global approach as the TRIN model [2] used in EGNOS. This new algorithm chain provides the specified APV-1 performance, particularly in the case of strong ionosphere activity, with a very good level of integrity margin. This paper presents the overall KASS system architecture as well as the results obtained using this new algorithm chain under different ionosphere contexts. The APV-1 service availability level is presented and the maximum of safety index on each monitored IGP and satellite is discussed.