Military Embedded Systems

Simplifying the integration of Assured PNT with CMOSS/SOSA-aligned solutions


May 10, 2021

Partially autonomous or unmanned trucks shown during a U.S. Army experiment on a Michigan highway. U.S. Army photo.

By Jason DeChiaro

From a design and engineering perspective, there are many moving parts to consider and combine in order to arrive at a position, navigation, and timing (PNT) truth. In addition, solutions must be easy to integrate into the available space on existing platforms, whether they are unmanned aerial systems (UASs) or other aircraft, ground-based operations, or systems at sea. They must provide reliable positioning information in GPS-degraded environments, where tall buildings, heavy foliage, and underground positions can affect signal quality, as well as in GPS-denied environments where adversaries have intervened to jam or compromise GPS signals.

Designing and developing an open standards-based deployable solution for assured position, navigation, and timing (A-PNT) that relies on information from multiple complementary sources, is not an easy task. In order to leverage today’s leading modular open systems approach standards, a desirable solution will be aligned with the U.S. Army’s C5ISR [Command, Control, Computers, Communications, Cyber, Intelligence, Surveillance, and Reconnaissance]/EW Modular Open Suite of Standards (CMOSS), The Open Group Sensor Open Systems Architecture (SOSA) Technical Standard, and the OpenVPX timing module. These solutions must be attained using the space-constrained 3U OpenVPX form factor preferred by CMOSS and SOSA.

Holistic A-PNT practices in action

A holistic approach to A-PNT is based on multiple complementary PNT technologies that leverage proven and trusted techniques to arrive at A-PNT truth and provide a trusted solution that will protect personnel and equipment in the field. Whether on tactical and combat vehicles, unmanned aerial systems (UASs), unmanned underwater vehicles (UUVs), or aircraft, proven hardware products with PNT capabilities can be upgraded to deliver higher performance and more sophisticated capabilities as technology evolves, ensuring warfighters always have access to the latest innovations to keep them safe and steps ahead of adversaries. Modules and systems designed in alignment with open standards such as the SOSA Technical Standard will simplify and reduce the cost of integration. The following is an overview of just a few of the technical challenges involved in developing effective and reliable A-PNT solutions.

Data processing

Data from all available PNT sources must be processed in a way that enables accurate positioning information to be provided to warfighters and systems when needed. Computing solutions must be able to process data that is received from a wide variety of sources, at different times, and in different formats. Complex data-processing algorithms are required to amalgamate and process all of this information in a way that accounts for varying and disparate temporal and spatial data. All of this processing must be completed extremely quickly so that people and systems always have access to accurate PNT information.

Data distribution

Once the data is processed, it must be made available to a variety of other systems and clients on the platform. The data may also need to be made available to systems on associated platforms in the field and at command centers. The main challenge here is that deployed platforms combine a variety of legacy and modern systems and clients with differing levels of sophistication, communications interfaces, and data processing requirements. Each system to which PNT information will be distributed – and more importantly, A-PNT information – must be considered.


A-PNT solutions must also be able to interoperate with existing legacy and modern systems on the deployed platform and must also anticipate future interoperability requirements. Hardware interoperability is challenging because it means A-PNT solutions must support the right combination of physical interfaces and pinouts to connect to legacy, modern, and future systems. Software interoperability is challenging because it means software must be easily updatable to support new capabilities and technologies as they emerge. In short, the entire A-PNT solution must be designed to interoperate with past, present, and future hardware and software.

Ease of use and flexibility

A-PNT solutions must provide PNT information to warfighters in a way that is fast and easy for them to access and understand, even while they are on the move or in dangerous situations. This is challenging because warfighters are already very familiar with GPS systems and how GPS information is provided. The transition to A-PNT information must be “invisible” so warfighters can continue to focus on mission tasks rather than struggle with unfamiliar controls and information formats. Developing A-PNT solutions that deliver an imperceptible level of change across all of the different systems involved is extremely difficult from every perspective – physical design, installation, integration, and usability.

Benefiting users and integrators

It’s a lot to ask of holistic A-PNT systems, addressing all of these challenges and requirements. With an A-PNT solution based on multiple complementary PNT information sources, warfighters have a far better ability to understand and respond to threats on the battlefield. They can quickly grasp the exact state of PNT signals, and then use this insight in a strategic way to conduct navigation warfare (NAVWAR), thereby enabling them to take defensive and offensive actions based on PNT information they trust to be accurate and uncompromised.

Knowing that GPS information is always at risk and that the information received may not be accurate adds considerable stress to already difficult situations. When war­fighters are working with trusted PNT information from complementary sources, they no longer have to worry about the risks associated with a single point of failure. With A-PNT information, warfighters have a higher level of trust in the information based on the knowledge that a range of defenses have been applied to protect against the possibility that inaccurate information will be provided.

A-PNT that is seamlessly integrated into the available space on the platform makes it easy for warfighters to transition from GPS to A-PNT information. Instead of having to think about the technology transition or learn new ways of operating, all actions related to location information are natural and intuitive for the warfighter.

Open standards-based A-PNT and radial clock module

An example of an open standards-based solution for A-PNT is the Curtiss-Wright’s VPX3-673 module. The 3U OpenVPX board is aligned with CMOSS, the SOSA Technical Standard, and the OpenVPX timing module standard. The variant module contains a GPS/GNSS receiver (M-CODE or SAASM), chip scale atomic clock (CSAC), and an onboard inertial measurement unit (IMU), all within a single slot. The module is intended for radial clock distribution applications and can provide a server for various low-power timing services. (Figure 1.)

[Figure 1 | The 3U OpenVPX board is aligned with CMOSS, the SOSA Technical Standard, and the OpenVPX timing module standard.]

The 10 degree of freedom IMU enables precise motion tracking in a denied or untrusted GPS environment. Support for an onboard GB-GRAM type II GPS with SAASM or M-CODE support is provided, including dedicated zeroize and keyfill functionality. An RS-232 port and RF 1 PPS input are provided for interfacing with an external RS-232 GPS sources.

Jason DeChiaro is a system architect at Curtiss-Wright. He received his electrical engineering degree, with distinction, from Worcester Polytechnic Institute. His responsibilities include supporting customers in architecting deployable VPX systems including CMOSS-/SOSA-compliant designs. Jason has over 15 years of engineering experience in the defense industry supporting the U.S. Air Force, U.S. Army, and U.S. Navy as well as the IC community. In addition to architecting VPX systems, Jason also supports customers’ assured position, navigation, and timing (A-PNT) requirements.

Curtiss-Wright Defense Solutions •

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