Model-Based Systems Engineering Helps GPS Upgrade

As part of the effort to upgrade the nation’s GPS system from a fixed-signal structure to a flexible-signal structure, the Air Force Research Laboratory (AFRL) at Kirtland Air Force Base in Albuquerque, New Mexico, tasked three contractors to submit designs for a new and improved version of a critical piece of satellite hardware—the digital waveform generator.  

Faced with three designs that were significantly different in form as well as function—AFRL needed a thorough and unbiased understanding of each so that it could clearly perceive their relative strengths and weaknesses and choose one architecture to serve as the prototype for all future digital waveform generators. For help achieving this understanding, AFRL partnered with Booz Allen.  

Waveform generators play a critical role in how GPS works. They produce signals that GPS satellites broadcast to navigation receivers in vehicles, phones, missiles—anything that uses a GPS signal. The receivers, in turn, process multiple signals from several satellites to determine their own speed, location, and direction of travel. The phone in your pocket is likely using this process right now to continually confirm its whereabouts.

The three designs submitted to AFRL were for a more efficient and versatile waveform generator—dubbed the on-orbit reprogrammable digital waveform generator (ORDWG, pronounced ord-wig). Because it’s digitally reprogrammable, rather than hardwired like its predecessors, the ORDWG will allow for the creation of better performing, more adaptable GPS satellites.

The chosen designs—or an improved version thereof—would provide the blueprint for an entire generation of ORDWGs, so determining such specifications as their baseline capabilities and interfaces was critical. Thus, it was important that AFRL account for every detail in its evaluation.

The designs, however, were so physically and functionally disparate that meaningfully comparing them was tough. To overcome this and associated challenges, AFRL partnered with Booz Allen on an innovative, comprehensive evaluation process using model-based systems engineering.

As is standard, the contractors submitted detailed technical documents along with their designs—hundreds of pages, authored by dozens of engineers—that laid down the dimensions and function of every circuit and wire.

In a traditional approach to design evaluation, AFRL would interview the engineers to verify the intended meaning of their documentation. The process is tedious, typically taking months or even years to complete, and creating a library’s worth of additional files.

Wanting to move faster, Booz Allen took a different approach, one that centered on model-based systems engineering (MBSE). With MBSE, specification documents are electronically digested, generating a functional digital model of the equipment in question. One can then run queries and simulations on these digital models to compare specifications, verify their functionality, measure their performance, and rate how well they meet the project’s requirements.

By using MBSE to reverse engineer and test each of the three designs, Booz Allen provided AFRL with a clear visual picture of the designs, their differences, and their relative strengths.

Booz Allen’s thoroughly examinable digital models helped AFRL achieve the understanding it needed to nail down the standard specifications for all future ORDWGs. With its blueprint defined, the U.S. Air Force need not rely on a single vendor for ORDWG manufacture. Any contractor can build one as long as it conforms to the established standards.

This enables the Air Force to own the designs, seek competitive pricing, and otherwise maneuver more flexibly moving forward as it continues to upgrade and maintain the satellites from which all GPS services spring—be they for military, scientific, or recreational use.