• Josh Clanton - Principal Engineer, IS4S

GPS remains the gold standard for timing distribution and synchronization. Today’s GPS receivers are small and cheap making them a popular choice to embed in other technologies to provide precision time. GPS based technology is now used in many critical infrastructure sectors. While GPS receivers are generally incredibly accurate and reliable devices, GPS’s weak signal power and publicly known signal structure make it vulnerable to malicious interference and disruptions.

Integrated Solutions for Systems (IS4S) and Auburn University (AU), under the direction of DHS Science and Technology (S&T), are developing an open architecture integrity framework for protecting timing systems in critical infrastructure. An open source reference implementation is also being developed that can be integrated with existing timing systems to help detect these errors and disruptions to prevent them from propagating into connected systems. The package offers a baseline integration approach for use with existing systems and deeper integration methods for new timing servers/receivers as they are developed. The proposed system will be capable of detecting many known GPS attacks and providing an output signal that can alert operators to a potential issue or automatically switch to a backup system such as a holdover oscillator.

The baseline integration approach can leverage readily available observables and navigation solution data that are standard outputs on many receivers in use today. Simple model-based consistency checks can be deployed on this data to provided a basic level of GNSS signal integrity to the device. Deeper integration approaches could take advantage of signal processing or RF-front end data to perform integrity checks such as acuisition power level analysis and multi-peak search and removal. If networks of receivers are available, shared observable and solution data allow for multi-node assurance checks, such as a common angle-of-arrival check, to be performed adding a hardened layer of integrity across all devices on the network

The software library will be made available to manufacturers of PNT devices to integrate into existing and future products. However, it is also understood that many legacy devices are in need of enhanced integrity and assuredness. For that reason, IS4S is also developing a reference hardware platform that can be used as a “bolt-on” system that implements the integrity algorithms externally from the existing device. Both the software library and reference hardware system are being developed as reference implementations for DHS S&Ts Resilient PNT Conformance Framework, which aims to develop an integrated conformance framework for describing resilient PNT systems, with a focus on GNSS dependent timing devices within critical infrastructure.

The integrity algorithms are not limited to timing applications, but can provide additional layers of assuredness and resiliency to all GPS/GNSS-enabled PNT applications. Many of the assurance checks included in the library take advantage of other available measurements and known dynamics in the application(s) to further increase the algorithm’s effectiveness in detecting spoofing attacks.

This presentation will give an overview of the integrity architecture and how it can be integrated into existing PNT systems both as an embedded library and as a bolt-on hardware component. In addition, testing results of the algorithms from both field and laboratory experiements will be presented.

Acknowledgement:
This work was funded by the Department of Homeland Security, Science and Technology Directorate, contract # 70RSAT18CB0000020.

Authors:
Josh Clanton (josh.clanton@is4s.com) & David Hodo (david.hodo@is4s.com), IS4S
John David Sprunger (jss0027@auburn.edu) & Dr. Scott Martin (smm0008@auburn.edu), Auburn University