Title: Maintaining a Linked Network Chain Utilizing Decentralized Mobility Control
1Maintaining a Linked Network Chain Utilizing
Decentralized Mobility Control
- AIAA GNC Conference Exhibit
- Aug. 21, 2006
- Cory Dixon and Eric W. Frew
2Long Range SensingChaining with Small UAs
- Operational Range determined by the limiting
value - Endurance / Fuel Range
- Communication Range
- Fuel range gtgt 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
3Chaining 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
4AUGNetAd Hoc UAV Ground Network
Disconnected Networks
UAV-UAV Chain
UAV Swarm
5Communications ControlA 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.
6References 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)
7Channel Capacity and Signal-to-Noise Ratio
Radio Environment
Throughput vs. Range
- 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
8UA Kinematic Model
- UAV Motion Unicycle Model
- 0 lt VMIN VO VMAX
- steering input u uMAX
9SNR Path Gradient
Motion of Vehicle (Discrete Sampling
Time) SNR Gradient Field (no localized
noise) Change in Measured SNR Path Gradient
gt
10Balancing 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 Ki
11SimulationTwo Static Nodes with Two Helper Nodes
12Extension to Multiple Nodes
Energy Optimal Placement
a 2
a gt 2
q
p
a gt 8
13Extremum Seeking Algorithms
- Time derivative of Cost Function
- Path Gradient
- Low-pass filtering generates control update
?
Objective Map J(pi)
14Extremum SeekingSimulation
15Research 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
16Conclusion Future Work
The SNR controllers presented provide a robust
control method that is capable of leashing
disconnected nodes in the presence of localized
noise disturbances.
- 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?
17http//RECUV.Colorado.edu
- Questions and Comments are Welcomed!
-
- Thanks for Coming
- Cory.Dixon_at_Colorado.edu
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20Communications ControlA Closed Loop System
- Wireless ad hoc communication performance and
vehicle mobility control form a closed loop
system.
Networked Control Systems (NCS) Distributed
Cooperative Control
Team
Team
Network
Network
Performance
Control
Performance
Control
MANETS Fault Tolerant Networks
Swarm Intelligence Formation Flying
Vehicle
Vehicle
Network
Topology
Mobility
Mobility
Topology
Data Ferrying Mobile Infostations
21Closing the C2 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
22Tracking a Communication Performance Metric
- Maintain communication link?
- Traditionally (position based)
- Range RangeMAX
- Communication performance motivated
- Throughput ThroughputMIN
- Communication Performance Field
- Can view performance as a continuous, measurable
field - Distribution of field does not need to be known a
priori
Performance Field
Position Based
- Chaining Objectives
- Throughput ThroughputMIN defines a
communication region - Maximizing sensor coverage reduces region to
outer bound