8/22/20061 Maintaining a Linked Network Chain Utilizing Decentralized Mobility Control AIAA GNC Conference & Exhibit Aug. 21, 2006 Cory Dixon and Eric W. Frew

8/22/20062 Long Range Sensing: Chaining with Small UAs Operational Range determined by the limiting value Endurance / Fuel Range Communication Range Fuel range >> communication range for single UA Limited size for antenna and electronics Limited available power Team of UAs Can utilize ad hoc communication network Extends communication range using relay nodes Adds robustness to aircraft loss

8/22/20063 Chaining Problem for Mobile Vehicles Radio Chaining: maintaining a communication link along a chain of vehicles using only locally measured communication performance metrics. Chaining Objectives Maintain communication along a chain of vehicles Increase operational range of the UAV team by using a chain of airborne relays Maximize UAV spacing to minimize the number of required UAV relays Maximize link throughput Chaining Applications Long-range sensing and communication Increasing search area for Search & Rescue missions Provide communication to disconnected networks

8/22/20064 AUGNet: Ad Hoc UAV Ground Network Disconnected Networks UAV-UAV Chain UAV Swarm

8/22/20065 Communications & Control: A Closed Loop System Wireless ad hoc network communication performance and vehicle mobility control form a closed loop system. Integrate communication performance into control architecture and use mobility control to maintain/improve communication performance. Network Performance Team Control Network Topology Vehicle Mobility Network Performance Team Control Topology Vehicle Mobility

8/22/20066 References & Related Work Communication as Control Primitive Controlled mobility to Improve Network Performance (Goldenberg et al., 2004) (Dixon and Frew, 2005) – “Leashing of an Unmanned Aircraft to a Radio Source” Connectivity & Limited Range Communications (Beard and McLain, 2003) (Spanos & Murray, 2004) Vehicle Control in a Sampled Environment Cooperative Level Set Tracking (Boundary Tracking) (Hsieh et al., 2004), (Marthaler & Bertozzi, 2003) Cooperative Gradient Climbing (Bachmayer et al., 2002), (Ogren et al., 2004) Adaptive Sampling Utilizing Vehicle Motion (Fiorelli et al., 2003) Path (Route) Tracking for Nonholonomic Vehicles Optimal Control of Bounded-Curvature Vehicles (Soures et al., 2000) (Balluchi et al., 2005)

8/22/20067 Channel Capacity and Signal-to-Noise Ratio Shannon Channel Capacity Radio Propagation Environment Received power is directional and link dependent Interference is dependent upon the location of the UAV Exponential power decay and fast fading (noisy channel) Communication Range Radio Environment Throughput vs. Range

8/22/20068 UA Kinematic Model UAV Motion – Unicycle Model 0 < V MIN ≤ V O ≤ V MAX steering input: |u| ≤ u MAX

8/22/20069 Motion of Vehicle (Discrete Sampling Time) SNR Gradient Field (no localized noise) Change in Measured SNR Path Gradient SNR Path Gradient * = =>

8/22/ Balancing SNR Link Gradients Re-cast Control Problem Control motion of an orbit center point (i.e. point mass) Autopilot system tracks orbit point Gradient Estimates for Each Link Feedback Force Move the point mass by generating forces based on link gradient. Scaling Parameter K i

8/22/ Simulation: Two Static Nodes with Two Helper Nodes

8/22/ Extension to Multiple Nodes p a = 2 a > 2 a => ∞ q Energy Optimal Placement

8/22/ Extremum Seeking Algorithms Time derivative of Cost Function Path Gradient Low-pass filtering generates control update  Objective Map: J(p i )

8/22/ Extremum Seeking: Simulation

8/22/ Research Questions & Algorithm Improvements Stability & Sensitivity Simulations have shown the controller to be stable, but a formal proof is still required Wireless communication channels are noisy (fast fading) and will require the SNR signal to be smoothed Effects of node mobility Estimation of SNR (performance) field Estimate the field to improve gradient estimation Radio source localization, and noise source detection and localization Initialization and Node Task Assignment When to introduce a relay node? In what position of the chain should it fill? Additional Control Parameters to Consider GPS position to improve tracking of highly mobile nodes Link importance and communication requirements Real-time vs. delay tolerant data Bandwidth requirement and node utility

4/27/0516 Conclusion & Future Work SNR as Control Input Does not require any additional communication Is extensible from one node to many nodes Finds the energy optimal location regardless of environment Provides a robust measure of link quality and bandwidth Simulation Results Show that the SNR, sampled at 1 Hz with GPS, can be used to leash a single aircraft to two mobile nodes. To obtain a leashed chain with multiple aircraft requires additional information to be shared, such as position, to aid in proper chain ordering Future work Experimental testing utilizing AUGNet platform, i.e. Ares UAV and MNR radios. Adapt ES algorithms and methods to provide research base Next Talk – Phase Transitions for Controlled Mobility When should a relay node be introduced into the chain to maintain a communication throughput requirement? The SNR controllers presented provide a robust control method that is capable of leashing disconnected nodes in the presence of localized noise disturbances.

8/22/ Questions and Comments are Welcomed! Thanks for Coming

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8/22/ Communications & Control: A Closed Loop System Wireless ad hoc communication performance and vehicle mobility control form a closed loop system. MANETS Fault Tolerant Networks Swarm Intelligence Formation Flying Data Ferrying Mobile Infostations Networked Control Systems (NCS) Distributed Cooperative Control Network Performance Team Control Network Topology Vehicle Mobility Network Performance Team Control Topology Vehicle Mobility

8/22/ Closing the C 2 Loop on SNR Communication Performance as a Control Primitive Integrate communication performance into control architecture Exploit mobility control to maintain/improve communication performance Closed Loop UAV Steering Controller Assume vehicle has low-level autopilot system controlling altitude and airspeed Use the SNR of each neighbor link to form the feedback signal Generate bounded steering commands for use by an autopilot

8/22/ Tracking a Communication Performance Metric Maintain communication link? Traditionally (position based): Range ≤ Range MAX Communication performance motivated: Throughput ≥ Throughput MIN Communication Performance Field Can view performance as a continuous, measurable field Distribution of field does not need to be known a priori Performance FieldPosition Based Chaining Objectives Throughput ≥ Throughput MIN defines a communication region Maximizing sensor coverage reduces region to outer bound