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MAX REVIEW

Cooperative Navigation in GPS

Denied Environments

19 April 2013

Control Automation Branch,Aerospace Systems DirectorateAir Force Research Laboratory

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Overview

Long-term Objective: Design control strategies such that a team of UAVs can navigate from one location to another in GPS denied environments.Why? “Further key emphasis must be placed on research to support increased freedom of operations in contested or denied environments…” (from TH)Approach: Teaming and cooperation

Information acquisition (main purpose) Reduced cost Improved robustness

Research: What information is needed? How to obtain it? Any optimality?

Our Expertise Portfolio: Cooperative control Stochastic control Optimal control Decentralized control

The basic idea is to have a team of UAVs maintain a desired rigid formation and rotate around some designated UAV (on top of a UGS) until one UAV in the team connects to a subsequent UGS.

UAV Autonomous Control in Denied Environments.

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Steps and Tasks

2-UAV navigation (a basic scenario) Navigation of two UAVs from one location to next Cooperative estimation Estimation of inter-UAV distances Structure estimation Estimation of the formation of the team Structure maneuver A match between the current formation and the desired formation Structure rotation Rotation of the formation CW or CCW Synthesis A closed-loop point of view

cost benefit

Note: We pay the price of “teaming and cooperation” to get “information”.

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Circumnavigation

• Objective: Develop control algorithms such that a UAV can orbit around some unknown static target at some desired distance.

: Target UAV: blue triangle : current distance from UAV

to Target at time : desired stable distance : actual stable distance : bearing angle: (constant) velocity of the UAV Circumnavigation is one fundamental research problem.

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UAV Dynamics & Control Algorithm

• UAV Dynamics

• Control Algorithm

• Range & Range Rate are needed for control algorithm– Assume a known, fixed velocity

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Algorithm Motivation

• Control Algorithm revisited

• The (desired) rate of change for– UAV heads toward tangent on

desired orbit

• Rate of change of given the UAV’s current heading

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Result

Note: A proof of the theorem can be found in a recent paper submitted to CDC13.

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Ongoing Research

• What if is unavailable?

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Challenges

• When using the linear filter, the challenges in the stability analysis are: Properties for the closed-loop system when the change rate of

is available do not necessarily hold Nonlinear system dynamics Limited information in the controller design due to the GPS

denied environments

Q1: Under what conditions the stability can be guaranteed if the change rate of is replaced by ?Q2: Any other options besides the linear filter?

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Additional Questions

• Consideration of uncertainties: Wind Measurement noises Latency Loss of package

• Other types of measurements: Heading (e.g., magnetometer) Bearing (e.g., VOR type of concept)

Note: Additional measurements can be useful in two ways Flexibility in the controller design Improved performance by information fusion techniques (e.g.,

Kalman Filtering)

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