Centimeter-Accurate GNSS Corrections and Integrity Information via ISO 26262 Certified Modules for Autonomous Driving Applications

Over the last decade the application of GNSS has changed w.r.t. business areas being covered. Especially the wide implementation of GNSS chips in mobile phones and lately the growing application of GNSS data and corrections in the area of autonomous driving has brought the GNSS technology to a far-reaching attention outside the sector of traditional GNSS users. Already in 2011, with the introduction of Trimble’s RTX technology Trimble has laid down the foundation for global GNSS correction data being transmitted in real-time “over the air” using L-Band transmission via geostationary satellites and alternatively, providing RTX corrections to Trimble customers using IP connections (NTRIP). To generate RTX corrections Trimble has build up a global network of GNSS receivers which are transmitting the observation data to Trimble network centers in which global (satellite clock and orbit corrections as well as global ionosphere corrections) and regional (ionospheric and tropospheric) GNSS correction data is computed. In order to fulfill the ISO 26262 requirements for the automotive business, Trimble has developed the Trimble Automotive RTX Client Library which is representing Trimble’s interface to access Trimble’s RTX corrections used by system integrators (Tier-1s or OEMs), hence enables positioning engines in Advanced Drivers-Assistance System (ADAS) devices to use decoded Trimble RTX corrections in the car. In addition Trimble has developed an integrity concept which led to the development of the Trimble RTX Post-Broadcast Integrity Module which is assessing RTX correction data including the transmission path as far as to the GNSS devices in the field. Both of the software modules have been developed according to ASPICE v3.1 and ISO 26262 safety requirements (part 2, 6, 8 and 9) and have been successfully ISO 26262 certified by TUV SUD already. Following the saying that there is “no safety without security” Trimble has introduced two-stage access control to its corrections by using AES 256-bit encryption and encoding the correction messages into Trimble’s proprietary CMRx format. In this paper, we present Trimble’s existing and already online approach to fulfil the safety requirements of automotive customers using the ISO 26262 certified Trimble Automotive RTX Client Library to decrypt and decode Trimble’s ultra-low bandwidth CMRx message format which includes Trimble GNSS RTX corrections as well as integrity information. Integrity and Alarm information is based on Trimble’s fully scalable GNSS infrastructure and added to the RTX data stream by ISO 26262 certified Trimble RTX Post-Broadcast Integrity Module.