• GPS might be interfered with globally
• Multiple, diverse PNT sources, modular open system needed for receivers
• Civil use hampering military efforts to leverage GPS for military advantage
• DoD PNT efforts to be increasingly classified, not shared with civil users

In August of this year the United States Department of Defense (DoD) publicly released a version of its “Strategy for the Department of Defense Positioning, Navigation, and Timing (PNT) Enterprise” with the tagline “Ensuring a U.S. Military PNT Advantage.”

Calling PNT “foundational,” the strategy observes that the U.S. military has over the years structured its weapons systems and business processes around GPS PNT. This has created a tremendous dependence and associated vulnerability.

Added to this threat is the realization that “At the same time, it is increasingly clear… GPS will be targeted and will not always be available in contested military operating areas, or perhaps globally.”

Multiple diverse sources of PNT

One of the primary ways DoD will deal with is this is to access multiple diverse sources of PNT. These will be in a multi-layered architecture of global, regional and local services.

The strategy envisions GPS, paired with military-grade receivers, as the primary global layer source. It recognizes that allied GNSS will be available, but observes that DoD has not done any accuracy and integrity assessments to determine their usefulness. And, since “…all are vulnerable to the same interference and jamming effects” as GPS, “…other sources of PNT information with different characteristics are necessary.”

The regional layer is defined by systems that service large areas such as a few countries or even continents. Recognizing that regional sources can be in space, the strategy discusses two low-frequency ground-based systems with characteristics much different from satellites — enhanced Loran (eLoran) and spatial, temporal and orientation information in contested environments (STOIC).

“Their high power and low frequency enable regional/nationwide coverage, spectrally separate from GPS services, accessible in buildings and under water, and transmitted from dispersed terrestrial locations. Each can be considered as a possible complement to GPS, depending upon operational circumstances and requirements.”

Short-range radio frequency systems, clock, inertial, sensory and hybrid PNT services integrated with wireless networks are all cited as possible contributors to the local layer of DoD’s PNT architecture.

Modular, open-systems approach

Receivers that employ a modular, open-systems approach that can ingest and integrate the various sources of PNT information are needed to take advantage of this multi-source, multi-layer strategy. And integration of the various sources must be seamless and invisible to the user, unless they decide otherwise.

“The employment of multiple PNT sources should not require user awareness or intervention to switch among alternatives during mission execution unless the user elects that option.”

A critical need for implementing this approach, according to the strategy, is the establishment of PNT input/output standards. The document notes that candidate standards have been developed, and it is vital to finalize and approve the standards and bring them into operational service as soon as possible.

Other provisions

The strategy includes a number of other provisions regarding internal DoD processes, the complicated governance process for PNT within the department, and some complex graphics that may be of interest to the larger PNT community.

It also sends several messages about the department’s desires, intent and concerns in the world of PNT that are worth noting.

NAVWAR. The department’s main defensive capability during navigation warfare will be the use of its layered architecture of PNT information and modular, open-systems integration. For offensive operations, it cautions warfighters to not shoot themselves in the foot. PNT is so vital to a wide variety of allied systems, it warns, that denying it to hostiles could do as much damage to friendly forces.

PNT dominience/superiority. At at time when there are more of China’s brand new BeiDou satellites in the skies of many cities, and China is negotiating with Russia for closer BeiDou/GLONASS integration, the strategy calls for the U.S. DoD to achieve PNT dominance. To date, U.S. PNT leadership has been a big contributor to the nation’s political and military leadership in the world. The strategy seeks to continue this.

Accelerate M-code receivers. The need to get more M-code GPS receivers into the hands of warfighters is mentioned several times. GPS III satellites have been transmitting M-coded signals that are much more resilient to jamming and spoofing than civil signals since late 2018. These are useless, though, without properly equipped receivers in the field.

Future support to Civil PNT. The strategy also seems to…