FGI-OSNMA

FGI-OSNMA is a Galileo Open Service Navigation Message Authentication (OSNMA) implementation done with flexibility and integrability in mind. FGI-OSNMA can be used as a library in third-party applications, or alternatively, the command line utilities can be used for navigation message authentication and related functionalities.

Data

FGI-OSNMA (and OSNMA in general) functions by collecting nominal Galileo I/NAV pages that will be accumulated into sub-frames (15 nominal pages). The OSNMA material and the navigation messages are extracted from the sub-frames, and the OSNMA material is used to authenticate the navigation message.

Therefore, the raw navigation pages are required to perform the processing. At the moment these are available for example from Septentrio receiver (from the GALRawINAV blocks).

At the moment FGI-OSNMA only supports the Septentrio Binary Format (SBF), though the SBF can be read from either a file, network socket, or serial port.

Subscriber system

Occurring events, such as authentication attempts or other authentication related information, will be handled by executing callback function registered in the SubscriberSystem class. The user can register custom callbacks/subscribers by creating a class implementing the Subscriber class, and registering it in the datasink/subconfig.py file.

Usage

As a Python project, FGI-OSNMA is cross-platform. The project has been tested under Linux and Windows.

CLI

The command line interface (CLI) programs are located under app/. To get information on the arguments and options, use the -h or --help option with the given program.

The CLI programs included in the project are the following:

• osnma-cli: the command line interface, and the main way to use the project
• osnma-reporter: produce visualization and compute statistics related to the authentication events produced by the osnma-cli
• osnma-rinex-filter: remove unauthenticated navigation messages from RINEX3 navigation files. Uses the output of osnma-cli.

Library

The class responsible for the main authentication loop is the OsnmaEngine located in the osnma/engine.py file. The use of this class to handle the main authentication loop can be seen from app/osnma-cli.

The user can create custom subscribers, which can execute callback function when a subframe result with the authentication events arrives, or when other information is received. Examples of this can be seen from the datasink/subscribers.py file.

Changelog/TODOs

• 14.09.2023: Initial import.

• TODO:

  • Extend documentation
  • Resolve TODOs in the code
  • Add link to ION-GNSS+ 2023 publication
  • Add unit tests