The document discusses topology control and mobility strategies for unmanned aerial vehicle (UAV) ad-hoc networks. It provides an overview of target application scenarios for UAV swarms and the motivation for maintaining connectivity in highly mobile UAV networks. Approaches for topology control from the related fields of boids flocking, potential fields, and virtual springs are reviewed. The document proposes a new approach that modifies the potential field method to consider both wireless signal strength and distance between UAVs to determine attractive and repulsive forces for topology control.

1. Joint ERCIM eMobility and
MobiSense Workshop
Topology Control and Mobility Strategy for
UAV Ad-hoc Networks
Zhongliang Zhao and Torsten Braun
Universität Bern, Switzerland
braun@iam.unibe.ch, cds.unibe.ch

2. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
Overview
> Target Application Scenarios
> UAV Swarms
> Motivation
> Related Work
— Boids Flocking
— Potential Field
— Virtual Springs
— Comparison of Approaches
> Topology Control for UAV Ad-hoc Networks
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3. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
Target Application Scenarios
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4. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
UAV Swarms
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5. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
UAV Platform
> mikokopter.de
> 4 brushless motors, controlled by 4 controllers
> FlightControl
> NaviControl
> MK3Mag (3-axis compass)
> GPS module
> 3 gyroscopes
> 3-axis acceleration sensor
> Pressure/height sensor
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6. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
Motivation I
> UAVs equipped with wireless mesh nodes form highly mobile
ad-hoc network (MANET)
> Connectivity required for live monitoring in areas of interest or
other real-time applications
> Example applications
— Security
— Agricultural/environmental
sensing
— Streaming of sports events
— Disaster recovery
— Communications relaying
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7. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
Motivation II
> Maintaining connectivity in highly mobile MANETS is
challenging.
> Needed: MANET topology control mechanism based on
swarm control schemes for UAV groups
> Challenges
— Application dependent parameters (speed, direction, density)
of UAV swarm
— Dynamic wireless channel characteristics
— Connectivity versus coverage needed by application
— Resource-constrained UAVs
– Mesh nodes with limited processing and communication facilities
(bandwidth, transmission range)
– Batteries are usually sufficient for a few 10 minutes.
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8. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
Related Work
Approaches from distributed agent-based formation control
> Boids flocking
> Potential field
> Virtual Springs
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9. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
Boids Flocking
Superposition of
> Separation
— Collision avoidance
> Alignment
— of speed and directions
> Cohesion
— Attraction to centroid between neighbours to stay close to them
results in formation building with a common heading and avoiding collisions
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10. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
Potential Field
> Techniques developed in
distributed robotics control
> Attractive and rejective virtual
potential fields to/from
goals/objects
> Rejective forces between
objects decrease with
increasing distance
> Attractive forces between
objects increase with increasing
distance.
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11. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
Virtual Springs
> Each object, e.g., UAV, forms virtual connection with each
neighbour object.
> Resulting forces should be 0 in equilibrium.
> Force in each dimension to an object is
— L: Length of spring to neighbour object i
— K: constant of spring to neighbour object i
— D: distance to neighbour object i
— Xi, Yi, Zi: position of neighbour object i
— Xi, Yi, Zi: position of object.
> Completely distributed processing, but neighbour knowledge
required.
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12. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
Comparison of Approaches
Mechanism Pros and Cons Applications
Boids Flocking Cons: mostly for Connectivity
computer animation
Virtual Spring Cons: only distance is Coverage
utilized, not accurate
Potential Field Pros: Both distance and Coverage and
RSSI are used connectivity
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13. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
Topology Control for UAV Ad-hoc Networks
> Consideration of wireless channel characteristics,
e.g. RSSI measured by wireless receivers,
in addition to location information obtained by GPS
> Proposed Approach
— Elect swarm leaders that indicate swarm direction and speed
— Distributed control of relative movements within UAV swarm
– Define lower / upper bounds for target distance and RSSI
– Modify potential field approach by considering RSSI values and GPS
data, e.g.,
– Rejective forces for collision avoidance: increasing force for
decreasing distance and for increasing RSSI between 2 UAVs
– Attractive forces for maintaining connectivity: increasing force for
increasing distance and for decreasing RSSI between 2 UAVs
– Weighting of RSSI and distance to calculate rejective and attractive
forces
– Use GPS data as backup for lacking channel information or lost
connectivity
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14. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
Rejective/Attractive Forces
F
distance
(RSS)
between
objects
minimum distance / optimum distance / maximum distance
maximum RSS / optimum RSS / minimum RSS
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15. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
Outlook
> Design and Implementation of
— MANET topology control mechanism
— Opportunistic multi-channel routing protocol
— Applications, e.g., multi-hop relaying, agricultural monitoring
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16. Torsten Braun: Topology Control and Mobility Strategy for UAV Ad-hoc Networks: A Survey
Thanks for your attention !
> braun@iam.unibe.ch
> cds.unibe.ch
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