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Session D5: Navigating in Challenged Environments (e.g., Urban, Indoor and Sub-Surface Navigation)

Assured PNT with a Cell Phone IMU and Carrier Phase RF Measurements for GNSS Denied Environments
William T. Faulkner, Robert B. Alwood, Daniel T. Goff, Randall A. Lavoy, and William P. Lounsbury, ENSCO, Inc.
Location: Shoreline (Floor 1)
Date/Time: Wednesday, Jul. 11, 9:15 a.m.

Precision tracking of position and attitude in the absence of GNSS requires fusion of multiple complementary sensors for Assured Positioning Navigation and Timing (A-PNT). An approach is presented here to achieve high rate, high accuracy, six degrees of freedom (6-DOF) tracking using a single stationary base station to track one or more mobile rovers. This tracking method, originally developed for demanding indoor relative tracking applications, can be generalized for other GNSS denied applications. This tracking approach utilizes measurements of distance, distance rate, and Phase Difference of Arrival (PDoA) on multiple apertures to constrain the 3-D relative position of rovers from the single base station. Further fusion with a cell phone IMU on the rover yields full 6-DOF tracking capability. This capability enables accurate tracking of high dynamic motion in challenging environments using low cost, low SWAP-C components with minimal infrastructure.
To demonstrate this 6-DOF precision tracking approach, ENSCO has designed, built, and tested a prototype tracking system utilizing two-way Radio Frequency (RF) sensing fused with a Commercial Off-The-Shelf (COTS) cell phone IMU. This prototype hardware and signal processing, utilizing an Extended Kalman Filter (EKF), have been used to successfully demonstrate relative frame 6-DOF tracking of a handheld sensor system from a base station.
The prototype 6-DOF tracking system has two components: a base station and a rover. The base station is a multi-channel TCR-D with a four-antenna array. The mobile rover system utilizes a cell phone class IMU and a Timing, Communications, and Ranging Device (TCR-D) RF sensor. The 6-DOF tracking system fuses the high rate, high precision RF measurements of distance, distance rate, and PDoA between multiple antenna apertures with inertial data. Like classic IMU/GNSS fusion, the IMU/TCR fusion utilizes the complementary strengths of the sensors to provide robust relative position and attitude estimation without GNSS. The TCR also provides wireless time synchronization between the base station and rover. This enables robust, real-time synchronization of data acquired on remote platforms to nanosecond level.
The prototype system, utilizing existing 5.8GHz TCR-D Software Defined Radios (SDRs), has achieved cm per axis positioning errors and degree per axis orientation errors in typical indoor environments. Ongoing and future work includes testing in Warfighter relevant, GNSS denied scenarios to demonstrate performance for additional applications.



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