ad-hoc network communication infrastructure for multi- robot systems in disaster scenarios

HEINZ NIXDORF INSTITUTE

University of PaderbornSystem and Circuit Technology

Prof. Dr.-Ing. Ulrich Rückert

Ad-hoc network communication infrastructure for multi-

robot systems indisaster scenarios

Ad-hoc network communication infrastructure for multi-

robot systems indisaster scenarios

IARP/EURON Workshop on Robotics for Risky Interventions and Environmental Surveillance

January 7th-8th, 2008 - Benicàssim

HEINZ NIXDORF INSTITUTEUniversity of Paderborn

System and Circuit TechnologyProf. Dr.-Ing. Ulrich Rückert

2

Ad-hoc network communication infrastructurefor multi-robot systems in disaster scenarios

Ulf Witkowski Mohamed El-Habbal

Stefan HerbrechtsmeierAndry Tanoto

Heinz Nixdorf InstituteUniversity of Paderborn

Jacques PendersLyuba Alboul

Sheffield Hallam UniversityMicrosystems and

Machine Vision Lab

Veysel Gazi

TOBB University ofEconomics and

Technology, Dept. Electrical and Electronics

Engineering

• Introduction: GUARDIANS’ scenario

• Objectives of the communication system

• Swarming and positioning

• Implementation – platform and features

• Results



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Introduction

Disaster Scenario: Burning large warehouse

Building with huge dimensions (>100m)

May be (partly) filled with black smoke

Technical infrastructure destroyed

Only local Communication between

firefighters (exchange of commands)

Orientation of firefighters by applying ropes with nodes indicating direction to exit

Team of robots assisting firefighters by (excerpt)

Searching and inspection of the building

Providing communication infrastructure (between firefighters, to operator,

between robots and humans, robot-robot communication)

Providing position and orientation data

Guiding firefighters to the exit



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Objectives of the communication infrastructureand networking

1. Robust ad-hoc communication system for

• Communication between• Humans (HSM – HSM, and HSM - operator) • Humans and robots (HSM commands/asks robots)• Robots (for cooperation)

• to facilitate• Primary communication• Service discovery• Positioning• Navigational aid for fire fighters and robots

• by• Combining three (and more) communication technologies

(WLAN, Bluetooth, ZigBee, Chirp-ISM, UWB)• Plus all necessary layers of ISO/OSI model

(including ad-hoc-networking, service discovery, and positioning)• Single antenna, multiple antennas, antenna arrays + MAC-Layer)



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Objectives of the communication infrastructure

Communication system provides and uses position data

Useful data for the firefighters

Eases maintenance of the communication network

Enables position based / cell based service discovery

Supports map building (data for operator)

Supports placement of nodes tospan the mobile ad-hoc network

Supports service discovery(offering and accepting services)

[2]



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Communication technologies

Existing radio based communication technologies

WLAN:•Max. number of nodes: not specified•Range: 100m (300m), data rate: 54 Mbit/s•Power consumption: high

Bluetooth:•Piconet: 8 nodes, Scatternet: Network of Piconets•Range: 100m, data rate: 2.1 Mbit/s•Power consumption: low•Cell forming by adapted frequency hopping

ZigBee:•Up to 255 nodes•Range: 75m, data rate: 250 kbit/s•Power consumption: very low

UWB: Excellent for positioning BUT bad availability

Nanoloc: Two way ranging in ISM band by using chirp signals•Accuracy of distance measurements: 1-2 m



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Communication test platformHNI Minirobot

System• Processor PXA270 520MHz• SDRAM 64MB• NOR Flash 64MB• FPGA Spartan3E 1600k

Wireless Communication• ZigBee (UART)• Bluetooth (UART)• WLAN (USB-Adapter)

Software• Linux Kernel 2.6.23• Device Manager (udev)• GNU C Library (Glibc) 2.5• Complete Linux environment (Debian like)• Automated build and packet system (OpenEmbedded)

This robot together with Khepera III is used for experiments transfer to large robot (Robotnik)

processorMarvellPXA270

I2C

USB

Powering

sensors /µC /(motors)

GPIO

AC97

Cam

extensions / ext. HW /WLAN

SDRAM

CPLD(Config)

Flash

Proz.-Bus

UART

camera

Bluetooth /ZigBee /debug

GPIO /extensions

SD-/MMC-Memory

static hardware reconfigurable hardware

FPGASpartan 3E

1600Displ. touchscreen

86 mm93 mm

68 mm



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Communication architecture

• Implementation of a mobile ad-hoc communicationframework for the Linux operating systemon the HNI-minirobot

Communication Framework

• Service Discovery: manage, publish andsubscribe of services (data)

• Data Exchange implement data communication

• Quality of Service (and Positioning) interact withapplication (swarming) to achieve stable networks

Network Abstraction Layer

• One common of interface to different networks

• Development of a hardware module for integration intoother systems (Khepera III and later on Robotnik system)

BluetoothBluetoothNetwork(WLAN, Bluetooth, ZigBee, Nanotron, ...)

Communication Framework

ServiceDiscovery

DataExchange

Quality of Service

Application / Services

Network Abstraction LayerNetwork Abstraction LayerNetwork Abstraction Layer



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where L depends on :• Maximum radio range supported by the communication standard used• Maximum detection range supported by the distance sensor

(Radar, ultrasonic, LRF or LIDAR, Radio ToF)

Mesh of equilateral triangles (advantageous area coverage)

L

L

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Spanning a (mesh of) nodesfor a robust network Static nodes placement

quasi static node(mobile robot, ordroppedcommunication relay)

Communication cell for mobile robots hand over between cells if required



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Swarming

Swarming is used to (among others) distribute the robots to span a robustcommunication network

Non communicative swarming•Loosely coupled entities withlocal interaction•Used as fall back if communication fails

Communicative swarming•as standard control mode for robots and the team•distribution of robots in a triangular grid

for supporting •Various cooperative behaviors (e.g. navigation, search/exploration,sensing, area coverage, gradient following, formation control, localization)

by•Heuristic/ad-hoc, artificial potential functions,gradient based, probabilistic, game theory, etc.



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Static nodes placement

Placement modes

d1 d2

Mode1

Mode2

Mode1

d2

d1



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Static nodes placement

Placement modes

Mode1 Mode2

Mode3d1d2



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Experiments - Overview

Hybrid solution for node control/placement:

(1)Distance control <-> signal quality(2)Distance measurements (3)Laser range finder (LRF) and comm.

Aim: Place the third of three robots tothe correct position to span aequi-lateral triangle (part of the robot distribution scheme)

Experiments:

(1)Signal quality measurements vs. distance (+obstacles)WLAN, Bluetooth, ZigBee

(2)Radio based distance measurements(Several point to point measurements and calculation of robot’s psosition)

(3)Angle measurements with LRF supported by communication(‘Third’ robot measures its angle to fixed robots by using LRF that can be rotated)

L

L

60



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Experiment 1Signal quality measurements

Path length: approx. 90 m, area with path (30m x 15m)

0

10

20

30

40

50

60

70

80

90

100

1 15 29 43 57 71 85 99 113 127 141 155 169 183 197 211 225

Time [s]

Link Quality [%]

Signal Level [%]

Signal quality measurements forWLAN, Bluetooth, and ZigBee



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Experiment 2Positioning system

Scenario: 4 mobile robots, 3 of these are‘infrastructure’ robots with known positions,

position of the 4th robot has to bedetermined all data is sent tolocal server, that display calculatedand actual path of the 4th robot



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Experiment 3LRF + communication

60

Static node 1

Static node 2

Mobile Robot

Required position

Active laser sensor(ifm-efektor LRF,rotatable)

Ro

bo

t b

ase

wit

hco

mm

un

icat

ion

mo

du

le

Laser detector



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• Mobile robot seeks to move to the desiredposition to complete the triangle

• It sends the request to the other static nodes

• Robot initiates wireless connection withthe 2 static nodes using Bluetooth.

• After connection establishment, lasersensor on robot starts rotating and scanningfor the 2 static nodes. Robot gets feedback if nodes are hit by the laser beam

• As the 1st node is hit, it sends a reply tothe robot, which stores the distanceat that instant, and inverses its rotationto search for the other node.

• As the 2nd node is hit, same procedure occurs. Afterwards, using the necessarytriangulation algorithm, the robot calculates the desired angle to rotate and the desired distance to move to reach its goal.



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Conclusion and Outlook

• Ad-hoc communication network to support firefighters

• Distribution of robots to span the network

(infrastructure robots and mobile nodes)

• Hardware platform combing WLAN, Bluetooth, ZigBee, and

Chirp-ISM

• Experiments for node placement

• Accuracy analysis vs. requirements

• Communication protocol



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http://www.shu.ac.uk/mmvl/research/guardians/

Thank you for your attention!Thank you for your attention!

Ulf Witkowski Mohamed El-Habbal

Stefan HerbrechtsmeierAndry Tanoto

Heinz Nixdorf InstituteUniversity of Paderborn

Jacques PendersLyuba Alboul

Sheffield Hallam UniversityMicrosystems and

Machine Vision Lab

Veysel Gazi

TOBB University ofEconomics and

Technology, Dept. Electrical and Electronics

Engineering



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Minimizing interference

FCC and ETSI radio rules for Bluetooth• v1.0 and v1.1: Hopping channels: 78 (full spectrum) Hopping rate: 1600 hops/s• v2.0: Hopping channels: 15 (AFH) Hopping rate: 1600 hops/s

- By using Bluetooth v2.0, spectrum can be divided into 5 channel groups- 4 groups for intra-cell, and 1 group for inter-cell communication (static nodes)- A cell that requires more traffic can request the use of more channel groups from adjacent cells if they are free to use.

1 2

3 4

1 2

3 4



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Used Hardware

• Laser sensor : ifm-efektor LRF

• Laser detectors : near visible Red photo-transistors

• Communication devices : Mitsumi Bluetooth chips class-1

• Processing Board :FPGA Virtex-E board with ADC



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60

Static node 1

Static node 2

Mobile Robot

Required position



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Experiment 3

Procedure

• Mobile robot seeks to move to the desired position to complete the equilateraltriangle.

• It sends the request to the other 2 static nodes, which should guide him to thecorrect position.

• Robot initiates wireless connection with the 2 static nodes using Bluetooth.

• After connection establishment, Laser sensor on Robot starts rotating and scanningfor the 2 static nodes. For each rotated step, it requests info from static nodes whetherthey are hit by the Laser beam or not.

• As the 1st node is hit, it sends a positive reply to the Robot, which stores the distanceat that instant, and inverses its rotation to search for the other node.

• As the 2nd node is hit, same procedure occurs. Afterwards, using the necessarytriangulation algorithm, the Robot calculates the desired angle to rotate and the desired distance to move to reach its goal.In our demo, the Laser sensor just rotates with the desired angle and points at its goal.

• Laser detectors : near visible Red photo-transistors

• Communication devices : Mitsumi Bluetooth chips class-1

• Processing Board :FPGA Virtex-E board with ADC



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Example for determining the position withNanotron‘s nanoLOC RF Module

• R1, R2 and R3 are the robots

• with known coordinates• (infrastructure robots)

• They drive to their position from• a common start point and• get their coordinates by• odometry

• T is the robot which position• has to be calculated

• The distance between R1 & T,

• R2 & T and R3 & T is measured

• with the Nanotron Transceiver

• The position of T can be• calculated by solving a system• of equations.•



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Atmel ATmega128L implementation

• Apart from a package switching process displayed in the following picture, a driver for• controlling the nanoLOC transceiver is running on the Atmel of the DK – boards• This driver is written by nanotron and contains some time critical passages for• ranging and it provides the ranging capabilities

• The package switching process forwards communication packages in both direction and• filters ranging package from the PDA processor to start a ranging process

ad-hoc network communication infrastructure for multi- robot systems in disaster scenarios

Documents

communication systemswarming

communication technologieswlan

data rate

robots hsm

position datauseful

mobile ad

robust ad

hsm operator humans