Implementation of the L5 SBAS MOPS

T. Walter, J. Blanch, P. Enge

Abstract:	Several L1 and L5 capable satellites are already on orbit and many more are expected to be launched in the upcoming years. The operators of the various Satellite Based Augmentation Systems (SBASs) are actively investigating incorporating new constellations and new signals. We have recently proposed new messages for broadcast on L5. These messages will be specified in Minimum Operational Performance Standards (MOPS) and are designed to allow SBASs to communicate corrections and integrity information to the aircraft. Specifically they allow the use of L1 and L5 in combination to achieve better performance than today’s use of L1-only. The proposed L5 messages were designed to make better use of the limited data bandwidth between the SBAS geostationary satellites and the aircraft. The new messages will require some changes in the ground monitoring behavior. In particular, we have proposed eliminating the fast correction message that was originally designed to mitigate selective availability. The fast correction messages are also often used to communicate alerts to the user when unexpected behavior is observed on the satellites. The SBAS ground monitors may need to alter their clock estimation strategies as well as how to broadcast satellite alerts. This paper examines the behavior of the satellite clocks and orbits and proposes optimized approaches to estimating and broadcasting these corrections. We also examine historical alerts and how they have been communicated to the avionics. We then show how these same events can be handled by the new messages. The determination of what messages need to be sent, and at what time, is an important and often challenging algorithm for SBAS. We demonstrate a fairly simple approach that maximizes throughput of the desired messages, but also allows for alert messages to be sent as needed without significantly penalizing performance. This paper also examines the parameters required to ensure that the integrity information is maintained over the lifetime of the message and determines the optimal values to strike a balance between preventing the need for alerts versus excessively raising confidence bounds. The analyses in this paper demonstrate that the proposed message structure works very well with observed and expected satellite performance. We further compare performance to the existing L1 MOPS structure and examine the relative merits of the two approaches. We will show that the new L5 approach improves both accuracy and availability while simplifying both the ground generation of the messages as well as their airborne application.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	814 - 824
Cite this article:	Walter, T., Blanch, J., Enge, P., "Implementation of the L5 SBAS MOPS," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 814-824.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In