Tag: PNT architecture

China leads world with plan for ‘comprehensive’ PNT

Speaking at the annual Stanford Positioning, Navigation, and Timing (PNT) Symposium, a Chinese representative described how her nation is building the world’s first resilient and robust, and, in her words, “comprehensive” PNT architecture.

Xiaochun Lu presents at Stanford PNT Symposium on Oct. 30, 2019. (Photo: Stanford University)

Xiaochun Lu of China’s National Timing Service Center described a multi-source PNT system that will be “more ubiquitous, more integrated, more intelligent.”

Centered around continually upgraded BeiDou GNSS at medium earth orbit (MEO), it will incorporate a wide variety of other PNT sources. These will include a PNT constellation at low earth orbit (LEO), Loran-C, inertial sensors, and systems like quantum navigation that have yet to be developed.

A new PNT constellation at LEO was mentioned several times in the presentation according to Rich Lee, CEO of iPosi, who attended the symposium. Lee has advocated the benefits of LEO PNT and suggested the U.S. should pursue such a system to augment GPS.

Research has shown that received signals from PNT constellations at LEO will be stronger and more difficult to disrupt than those from MEO. When combined with MEO PNT signals, they will also enable much more precise positioning.

In discussions after her presentation, Lu indicated that China has an application pending at the ITU for 120 LEO PNT satellites flying at 700 km.

Also noteworthy was inclusion in the architecture of China’s existing Loran-C terrestrial PNT system. China has operated this system for decades and regularly coordinates its integrated use with Russian and South Korean systems as part of the Far East Radio Navigation Service (FERNS).

Xiaochun Lu discusses China’s Comprehensive PNT Plan with Rich Lee of iPosi and Logan Scott of Logan Scott Consulting at 2019 Stanford PNT Symposium. (Photo: Stanford University)

The United States terminated Loran-C service in 2010 over the objection of its national PNT advisory board. Europe’s Loran system was taken off the air at the end of 2015. This was despite the United Kingdom’s implementation of a more accurate and automated eLoran version at the beginning of that year.

Today the United States is in the process of establishing a terrestrial backup system for GPS timing that could be expanded to include positioning and navigation services.

Europe has acknowledged that GNSS alone is insufficient for critical and safety of life applications. Officials are examining what that means in terms of systems required.

China”s announcement at Stanford is the first for a plan to build a comprehensive national PNT architecture.

Graphic: Xiaochun Lu, China National Timing Center

Both Europe and the United States have published radionavigation plans, though these tend to be more descriptions of current systems than forward looking and actionable plans.

The United States published a “National Positioning, Navigation, and Timing Architecture Study” in 2008. Little action was ever taken to implement its recommendations. A graphic from this document was included in Lu’s Stanford presentation indicating that the U.S. study may have helped inspire and motivate China’s plan.

Xiaochun Lu presents at Stanford PNT Symposium on Oct. 30, 2019. (Photo: Stanford University)

In August 2019, the U.S. Department of Defense publicly released its PNT strategy. It is similar in many ways to the Chinese plan described by Lu, calling for the use of multiple and diverse sources of PNT. As part of this, Army Futures Command is working with the University of Texas to leverage for PNT thousands of yet-to-be-built communications satellites planned to be deployed at LEO.

U.S. military PNT efforts, though, are unlikely to help protect the American populace. The defense department strategy says that civil use of GPS has hindered the ability to leverage it for military purposes. Future U.S. military PNT systems will be “increasingly classified” and therefore not available for civil use.

November 15, 2019
US Department of Defense PNT strategy: ‘GPS is not enough’
- 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, 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 show the department is distancing itself from support of future civil PNT endeavors. While GPS has been an incredible economic engine and boon to civil users, this has not always been in DoD’s best interests.

“It must also be recognized that in this context growing civil dependence on GPS services for critical infrastructure and public use will continue to constrain the ability of the DoD to maintain a military PNT advantage from GPS.”

It goes on to warn that future DoD PNT systems and efforts will not follow the same path to civil-military use as was taken by GPS.

“DOD must take steps to ensure the civil agencies are aware of and are sensitive to the dual-use implications inherent in GPS and other PNT Enterprise applications. From this point forward, many of the specific PNT capabilities and combinations of PNT capabilities employed by the DoD for military purposes will increasingly be classified.”

The way ahead for the 99%

It is clear that the Department of Defense, through the very capable leadership of its CIO, Dana Deasy, has a clear idea of where it is with PNT, its critical challenges, and how to overcome them.

This does not appear to be the case for those in the federal government charged with safeguarding the interests of civil users. With responsibilities fragmented across a host of departments and agencies, efforts on behalf of the public at large are barely visible compared to those the Defense Department is taking to protect itself.

According to officials, this may change. They report that leadership of civil PNT within the executive branch is under review with an eye to making it more efficient and effective.

Perhaps it will result in a PNT strategy for the 99% of GPS users who are not connected with the Defense establishment, making them safer and more secure as well.

“Strategy for the Department of Defense Positioning, Navigation, and Timing (PNT) Enterprise” is available online.
October 4, 2019
DOT gets cracking on a new PNT concept

Congress mandated movement in December 2017.

U.S. National PNT Architecture from a 2007 Department of Transportation report, updated in 2017. (Graphic: U.S. Department of Transportation)

The U.S. Department of Transportation (DOT) says it will implement a terrestrial timing system to complement and back up GPS signals, and plans to demonstrate the new system “toward the end of the calendar year.”

The demo is anticipated to include a range of technologies, including among others local positioning systems such as Locata and NextNav, wide-area coverage by eLoran, and — though the parameters of DOT’s mandate specified terrestrial backup — space-based signals furnished by Satelles.

The statement came in response to an inquiry in March from the House of Representatives’ Transportation and Infrastructure Committee concerning progress on a GPS Backup Technology Demonstration that was mandated in December 2017. Although funds were appropriated for the project, committee chair Peter DeFazio of Oregon saw little to no evidence of work being done, and so required a status report.

DOT issued a Request for Information (RFI) on May 3, with a due date of June 3. The RFI asked for “readiness-level six” technologies (bearing demonstrated results in a relevant environment) “capable of providing backup positioning, navigation, and/or timing services to critical infrastructure in the event of a temporary disruption to GPS.

“This demonstration effort also is expected to encompass technologies capable of providing complementary PNT functions to GPS by either expanding PNT capabilities, including cross checks, or extending them to GPS or Global Navigation Satellite System (GNSS)-denied or degraded user environments.”

The DOT said it is “interested in leveraging PNT service technology initiatives.” Possibly, the agency intends to contract for a service rather than build a new system.

Congress first required DOT to establish an operational terrestrial timing system to back up GPS signals, then expanded that definition to include positioning and navigation services.

Systems or services, or combinations thereof, must now provide all three functions.

June 7, 2019