Cooperative PNT in a Relative Reference Frame using Two Way Time and Range, Barometric Pressure and Inertial Measurements.
William Kirchner, Ramachandra Sattigeri, Vladislav Gavrilets, and James Doty, Collins Aerospace
Alternate Number 3
Absolute Positioning, Navigation and Timing (PNT), referenced to common Earth-fixed coordinate frames like WGS-84 and Universal Coordinated Time (UTC), is preferred on the battlefield as it allows multiple disparate platforms to coordinate their movement (vehicles, personnel, weapons, etc.) on a common reference frame. Developing a “cloud” in which these same platforms can operate without absolute PNT, but where precision relative state is known, enables some of the same operational behaviors. Maintaining a precise, 6DOF, relative navigation solution also enables absolute 6DOF PVAT (position, velocity, attitude and time) information to be distributed from a single platform that is advantaged (e.g. access to GPS). Typical solutions to networked navigation utilize Two Way Time and Range (TWTR) from multiple advantaged nodes (i.e. access to GPS) to distribute PNT to disadvantaged nodes (i.e. no/limited access to GPS). This approach can require three or more advantaged nodes to constrain the 6DOF PVAT solution of a disadvantaged node, which presents unique operational constraints. This work has focused on developing a purely relative formulation of the inertial navigation problem that uses an Extended Kalman Filter to blend inertial measurements, TWTR and barometric pressure measurements to estimate the relative 6DOF state (position and orientation) of each platform across a network or swarm of four or more platforms. This relative navigation solution allows the swarm to act like a single large distributed vehicle which enables the integration of navigation and surveillance sensors into one integrated solution that is bounded in 6DOF. Simulation results demonstrating the utility of this approach when using SWAP constrained sensors (IMU, Barometric Pressure and TWTR enabled radios) will be presented. The relative formulation and 6DOF relative state estimates address two relevant operational challenges. First, it allows distribution of PNT (6DOF) from a single advantaged node. Secondly, it provides a scalable approach to networked navigation that avoids practical challenges in avoiding unstable feedback loops when using observer-based estimation approaches to distribute PNT across a network.