Merriam-Webster defines a “silver bullet” as a magical weapon, one that instantly solves a long-standing problem. Well, it’s been about 30 years. Despite studies, analyses, tests, demonstrations and much hand-wringing, no silver bullet technology has been identified to back up the myriad GPS dependencies that now permeate U.S. critical infrastructure (CI).
<p>The President, members of Congress, Deputy Secretaries and the President’s National Space-Based PNT Advisory Board have all weighed in to insist that such a backup be put in place to preserve the operational continuity of domestic CI, all to no avail. As a participant in or observer of virtually all these efforts over the past 20 years, I am as familiar with and frustrated as anyone by the lack of progress or urgency.</p> <p>Now, the <a href="https://www.gpsworld.com/tag/fcc/" data-type="link" data-id="https://www.gpsworld.com/tag/fcc/"><strong>Federal Communications Commission (FCC)</strong></a> is the latest to join the fray in late March with a public hearing preceded by a <em>Notice of Inquiry (NOI) on Promoting the Development of PNT Technologies and Solutions</em>, as well as a separate but related <em>Notice of Proposed Rulemaking</em> on improving wireless E911 location accuracy. As with many of the preceding efforts, the NOI is comprehensive and seems all-inclusive regarding both technologies and governance, and it is timely, as it follows many recent press reports on both GPS and CI vulnerabilities. One can hope that its findings will be compelling and capable of implementation, though the sheer range of responses it invites in light of numerous recent industry initiatives for PNT services may only confuse the situation further.</p> <p>The NOI reflects the recent marketing of PNT services to the government by NextNav, the National Association of Broadcasters (NAB), various commercial SATCOM providers and others. NextNav proposes a commercial PNT service, potentially in conjunction with cellular communications providers, and the NAB proposes a Broadcast Positioning System (BPS) that would include PNT information with television signals using a proposed new broadcast standard. Both entities have separately petitioned the FCC for consideration of rulemaking changes to facilitate their planned solutions. However, their proposals highlight the confusion that can be created by commercial interests that do not take account of some fundamental differences between PNT and communications services. </p> <p>PNT services have unique requirements for coverage, availability, continuity, integrity and time management that differ from those for communications services, and which dictate how PNT services are provided and employed, particularly when nationwide service is required. This is not to say that the noted PNT initiatives involving market-focused communications providers should not be considered as viable complements to space-based GPS service. However, a viable backup to GPS must be able to provide service in rural and remote portions of the country, where commercial markets are lacking and robust commercial services are not available. </p> <p>There are significant differences among civil and military PNT service requirements. The Department of Defense (DOD) recognized the reality of this common variation in services, and in its <em>2019 Department of Defense PNT Enterprise Strategy</em> envisioned a multi-layered PNT architecture consisting of global, regional and local sources of PNT information to support U.S. and allied military systems worldwide. The global PNT layer is space-based and ubiquitous, with 3D position and precise time available worldwide. The regional PNT layer may be space-based or terrestrial with national or international coverage where PNT resiliency must be assured. The local layer may be space-based, terrestrial, and/or autonomous using manmade and natural PNT sources over a limited area based on source design and performance.</p> <p>In proposing to back up GPS use in domestic CI, both NextNav and the proposed BPS seem to be positioning themselves to serve as the regional layer for the entire country, though both are fundamentally focused on urban markets. NextNav proposes PNT services in urban areas using a network of beacons, potentially partnering with cell phone service providers to provide broader reach, primarily for timing. NextNav also offers a special precise vertical location service for first responders in select metro areas.</p> <p>The BPS proposal envisions mesh networks of television broadcast antennas, where one TV station is the lead for timing and provides a timing signal to other (follower) stations in a metro area. The PNT information (time, tower location) is contained in a small portion of each main TV broadcast message frame. In effect, it is a new instantiation of a technology demonstrated in 2008 by Naval Academy Midshipman David Taweel in collaboration with Johns Hopkins APL. Using time-managed TV transmissions in Washington and Baltimore, he designed and executed a closed-course UAV flight profile to demonstrate use of signals of opportunity (SOO) for navigation in the absence of GPS. In the same period, a company called Rosum briefly marketed similar PNT services using TV and other SOO transmissions. The technology was stymied by the lack of a nationwide broadcast standard for time-synchronized TV transmissions, which are essential to enable receivers to calculate PNT solutions. This is apparently still a problem today, as the NAB petition to the FCC requests that the latter mandate adoption by TV broadcasters of a new standard that will enable the BPS signal but will also require changes to TV sets and converter boxes. The end user market for a TV-based service is undefined, as is the willingness of station operators nationwide to accept a new standard.</p> <p>Both NextNav and BPS technologies have performed well within structured demonstrations conducted independently and by the government, and I don’t doubt their technical viability as local layer complements to GPS, particularly for timing. However, as complete backups to GPS positioning and timing services nationwide, issues of adding necessary infrastructure and coordinating precise time management among the range of broadcast system partners and cell network providers become cost prohibitive to serve remote and rural areas where relevant markets don’t exist. Also, TV towers, are sited to provide optimum reception of TV signals in their service areas but not to optimize geometric separation among them that is necessary for positioning services, particularly beyond the margins of metro areas. Finally, neither provider would be able to back up GPS in supporting national security and economic activities in the Alaskan Arctic region and over the northern ocean areas abutting the United States and Canada, where GPS may realistically be threatened in the face of growing competition from U.S. adversaries.</p> <p>In that context, and with respect to all the studies assessing GPS backups, NextNav stated in an FCC filing, “No one else has proposed a credible solution to the widely recognized and increasingly urgent problem that the United States has no wide-scale [terrestrial PNT] service to complement and back up GPS where the GPS signal is obstructed or when outages occur.” </p> <p>This is simply not correct, as government studies over years have identified enhanced Loran (eLoran) as the most viable and affordable backup to GPS, and eLoran remains the only terrestrial PNT service that can efficiently back up GPS nationwide, including the Alaskan Arctic and northern oceans. However, since 2015, and despite Congressional support, deliberate political resistance within OMB and resulting DOT/DHS inaction and attempts to shift responsibility to industry have allowed much of the legacy Loran infrastructure to degrade. Costs have risen, and the government is now considering selling the system off, losing access to the valuable sites where eLoran transmissions would be most useful to back up civil GPS use. At the same time, our adversaries in Russia, China and (reportedly) Iran, continue to build out eLoran networks of their own to back up their use of space-based PNT services.</p> <p>Unless our government accepts responsibility, there will be no PNT silver bullet for domestic CI. Experience shows that industry will not solve this problem alone.</p> <p><p>The post <a rel="nofollow" href="https://www.gpsworld.com/is-there-a-silver-bullet-for-resilient-pnt/">Is there a silver bullet for resilient PNT?</a> first appeared on <a rel="nofollow" href="https://www.gpsworld.com">GPS World</a>.</p></p>
