ABERDEEN PROVING GROUND, Md. (April 4, 2017) - The Assured Positioning, Navigation and Timing program, or A-PNT, is advancing technologies to aid GPS when its signal becomes degraded or denied, but executing developmental testing on these capabilities is not always logistically or financially feasible.
The U.S. Army Materiel Command’s Communications-Electronics Research, Development and Engineering Center, or CERDEC, is augmenting live testing with modeling and simulation, or M&S, technologies that can better measure how effective PNT technologies perform in the context of the warfighter’s mission.
“For decades, GPS has revolutionized PNT capabilities for Soldiers, but its susceptibility to interference has generated a need for complementary sources of PNT,” said Gina Guiducci, chief of the CERDEC Command Power and Integration Directorate, or CP&ID, PNT Performance Analysis branch. “Our extensive experience developing GPS-aiding technologies coupled with our M&S expertise across multiple tools is allowing us to accurately and efficiently evaluate PNT technologies.”
CERDEC’s M&S solutions help engineers plan the locations and attributes of pseudolites -- a word blend of pseudo and satellite -- and jammers affecting the signal. These pseudolites, include satellite-like transmitters that function similarly to GPS, but their transmitters reside in platforms such as a vehicle or low flying aircraft versus in space.
“Pseudolites’ close proximity to the ground allows Soldiers to obtain position information in environments that GPS ordinarily struggles to reach, including forests, valleys and canyons, or even partially within city buildings,” said John Del Colliano, CERDEC CP&ID PNT Integrated Systems branch chief. “For the same reason, pseudolites are also harder for the enemy to jam versus the GPS signal.”
To test pseudolites in a simulated environment, engineers must account for the differences between the signal strength in the GPS constellation and the pseudolites.
“Pseudolites do not benefit from the GPS satellites’ good Dilution of Precision, or DOP, which determines the accuracy of the positional measurements,” said Anni Woolley, CERDEC PNT M&S lead. “One achieves good DOP when the satellites are evenly spread apart in the sky as with GPS; set close together as with terrestrial-based Pseudolites, the DOP can be poor.
To account for these attributes, CERDEC engineers have developed the Pseudolite Planning Tool, or PLPT, to model GPS, pseudolites, receivers and jammers. PLPT is a front-end app that is powered by CERDEC’s Integrated GPS Navigation Model, or CIGNM, which is an in-house M&S modeling tool that performs the “number crunching” brains behind the system to calculate PNT coverage and DOP quality.
Analysts plot an area of interest on the digital map and “place” various pseudolites within the area of interest, such as mounted on a pole or on an Unmanned Aerial Vehicle. The analyst then inputs a Soldier’s projected path across the terrain, and runs calculations to determine if the Soldier would have obtained sufficient PNT while traversing this path, as long as the pseudolite is functioning correctly.
“The CIGNM covers all components of the GPS infrastructure, such as transmitters, receivers, terrain modeling and RF propagation,” said Bill Sudnikovich, CERDEC PNT engineer. “CIGNM provides an extensible simulation capability that integrates all of these components to investigate and analyze the performance characteristics of each piece of equipment and the system as a whole.”
M&S allows engineers to plug in many “what if” scenarios to calculate the coverage and produce the desired test environment to better understand the possible outcome, Woolley said.
CERDEC recently created another simulated test environment to help measure the effects of a jamming signal aimed at a warhead equipped with a precision guided kit. By using CIGNM, engineers modeled the trajectory to accurately measure the jammer strength at several points along the missile’s trajectory.
“Our engineer made assumptions based on the warhead’s speed of how it would react when it reached the jamming signal, and CIGNM provided mathematical results to confirm his assumptions,” Woolley said.
CERDEC's PNT M&S support is not limited to test teams; the Office of the Assistant Secretary of Defense for Research & Engineering, or OASD(R&E) OASD/R&E, established the PNT M&S Collaborative Initiative, with the primary purpose of informing senior leadership on how best to invest in M&S technologies.
The initiative kicked off in FY17, with plans to first identify what models currently exist, and it will proceed with two, one-year pilots.
“The focus of the tri-service initiative is to ensure we establish collaborative efforts to investigate complementary PNT technologies,” Sudnikovich said. “Our goal is to interface PNT M&S with higher-level simulations and war-gaming scenarios to determine its impacts on mission effectiveness.”
CERDEC PNT M&S team is currently working with CERDEC’s Space and Terrestrial Communications Directorate, or S&TCD, to produce system of system M&S analysis to access vulnerability. Many systems in the field are using PNT data; this analysis aims to answer what the first, second and third order of effects are when PNT is degraded or unavailable.
“That is where we want to help all the S&T programs,” Guiducci said. “We are analysts; we can answer the hard questions. If we implement M&S before these organizations fully invest in a technology, we can predict likely successes that allow them to make informed decisions.”
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