On the PNT Integrity Score Model
Vinnie Benvenuto, The MITRE Corporation
Alternate Number 4
Approved for Public Release; Distribution Unlimited. Public Release Case Number 21-0192
This technical data deliverable was developed using contract funds under Basic Contract No. W56KGU-18-D-0004.
©2021 The MITRE Corporation.
This presentation introduces a model for defining and implementing the Positioning, Navigation, and Timing (PNT) Integrity Score concept originally introduced by the US Army Program Manager PM PNT. The model generates an Integrity Score, a mechanism used by a PNT system to quantify and report on the ability to deliver a PNT solution that uses only authentic signals. The Integrity Score is used by the hosting platform’s Command & Control/Situational Awareness (C2/SA) client application that provides situational awareness to the warfighter. Within the PNT system, a function referred to as the Integrity Score Engine computes and generates the Integrity Score using a prescribed set of rules. The rules are used to assign an Integrity Factor to each protection mechanism included in the PNT system. The Integrity Factor is a quantification of the ability of a unique protection mechanism to detect, avoid, reject, and replace invalid Global Positioning System / Global Navigation Satellite System (GPS/GNSS) signals. Protection mechanisms include anti-jam antenna systems, modernized anti-spoofing, and integrity monitors using Kalman filter-based fusion engines. Some PNT sources, such as inertial measurement units (IMUs), generate measurements with integrity. Accordingly, IMUs are assigned a high Integrity Factor. The Integrity Score Engine computes the Integrity Score by summing the Integrity Factors involved with the PNT computation. Algorithms in the C2/SA client application translate the reported Integrity Score into a trust metric used to convey the trustworthiness of the PNT solution to the warfighter.
In the proposed model, the Integrity Score is a numerical value ranging from 0 to 100, where a score of 100 indicates the PNT solution has the most integrity. The Integrity Score rendered by the model may vary dynamically based on the quantity and efficacy of the protections afforded the GPS measurements and solution, as well as the non-spectrum measurement sources. Should GPS be jammed off and non-spectrum sources invoked, we expect the reported Integrity Score to be relatively high (e.g., IS = 90) and constant.
The Integrity Score provides the warfighter with a consistent means of reporting and interpreting PNT integrity. The integrity mechanisms currently available are limited to the assurance status generated by the Modernized Anti-Spoofing per the Military GPS User Equipment (MGUE) Increment 1 Positioning, Velocity, and Timing (PVT) Assurance Model. This model offers a simple integrity scoring system consisting of two values; the PVT output is either usable or assured. This model is inadequate because a binary representation of integrity is not sufficient; integrity is best represented by a spectrum of values reflecting the range of integrity possible with multiple integrity protections contributing to a layered defense. Whereas the MGUE Increment 1 PVT model generates the usable and assured outputs, the Integrity Score output can reflect multiple degrees of integrity.
Designing the Integrity Score Engine involves defining the rule set for how the Integrity Score is computed and assigning an Integrity Factor to each available protection mechanism. In the proposed Integrity Score model, the initial assignment of Integrity Factors is based on engineering judgment; preferably, a PNT system vendor would use modeling and simulation combined with live sky test results to assign the Integrity Factor.
Ideally, the Integrity Score would be adopted as a common convention for PNT systems and users across the Department of Defense. Similar to positional accuracy Figure of Merit, two PNT systems from different vendors, implementing the same general class of protection mechanisms, would generate the same or similar Integrity Score when exposed to the same signal conditions. Achieving a common Integrity Score convention requires development of a common approach for assessing and scoring PNT protection effectiveness as well
This presentation introduces the Integrity Score concept, presents a use case for how the Integrity Score is used by the warfighter, explores factors that contribute to an effective Integrity Score approach, and describes a notional implementation of the Integrity Score model.
The audience for this presentation includes engineering staff responsible for implementing integrity reporting capability for combat platforms. This includes PNT system vendors, program office PNT subject matter experts, development teams planning and building C2/SA client applications, and Command level staff seeking to deliver PNT solutions that meet the requirement for reporting PNT integrity and trustworthiness to the warfighter.