HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert Ad-hoc network communication infrastructure for multi- robot systems in disaster scenarios IARP/EURON Workshop on Robotics for Risky Interventions and Environmental Surveillance January 7th-8th, Benicàssim

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 2 Ad-hoc network communication infrastructure for multi-robot systems in disaster scenarios Ulf Witkowski Mohamed El-Habbal Stefan Herbrechtsmeier Andry Tanoto Heinz Nixdorf Institute University of Paderborn Jacques Penders Lyuba Alboul Sheffield Hallam University Microsystems and Machine Vision Lab Veysel Gazi TOBB University of Economics and Technology, Dept. Electrical and Electronics Engineering Introduction: GUARDIANS’ scenario Objectives of the communication system Swarming and positioning Implementation – platform and features Results

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 3 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

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 4 Objectives of the communication infrastructure and 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)

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 5 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 to span the mobile ad-hoc network Supports service discovery (offering and accepting services)

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 6 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

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 7 Communication test platform HNI Minirobot System Processor PXA MHz SDRAM 64MB NOR Flash 64MB FPGA Spartan3E 1600k Wireless Communication ZigBee (UART) Bluetooth (UART) WLAN (USB-Adapter) Software Linux Kernel 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) 86 mm 93 mm 68 mm

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 8 Communication architecture Implementation of a mobile ad-hoc communication framework for the Linux operating system on the HNI-minirobot Communication Framework Service Discovery: manage, publish and subscribe of services (data) Data Exchange implement data communication Quality of Service (and Positioning) interact with application (swarming) to achieve stable networks Network Abstraction Layer One common of interface to different networks Development of a hardware module for integration into other systems (Khepera III and later on Robotnik system)

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 9 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 60 Spanning a (mesh of) nodes for a robust network Static nodes placement quasi static node (mobile robot, or dropped communication relay) Communication cell for mobile robots  hand over between cells if required

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 10 Swarming Swarming is used to (among others) distribute the robots to span a robust communication network Non communicative swarming Loosely coupled entities with local 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.

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 11 Static nodes placement Placement modes d1d2 Mode1 Mode2 Mode1 d2 d1

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 12 Static nodes placement Placement modes Mode1Mode2 Mode3 d1 d2

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 13 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 to the correct position to span a equi-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

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 14 Experiment 1 Signal quality measurements Path length: approx. 90 m, area with path (30m x 15m) Signal quality measurements for WLAN, Bluetooth, and ZigBee

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 15 Experiment 2 Positioning system Scenario: 4 mobile robots, 3 of these are ‘infrastructure’ robots with known positions, position of the 4 th robot has to be determined  all data is sent to local server, that display calculated and actual path of the 4 th robot

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 16 Experiment 3 LRF + communication Active laser sensor (ifm-efektor LRF, rotatable) Robot base with communication module Laser detector

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 17 Experiment 3 LRF + communication Mobile robot seeks to move to the desired position to complete the triangle It sends the request to the other static nodes Robot initiates wireless connection with the 2 static nodes using Bluetooth. After connection establishment, laser sensor on robot starts rotating and scanning for 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 to the robot, which stores the distance at that instant, and inverses its rotation to search for the other node. As the 2nd node is hit, same procedure occurs. Afterwards, using the necessary triangulation algorithm, the robot calculates the desired angle to rotate and the desired distance to move to reach its goal.

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 18 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

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 19 Thank you for your attention!

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 20 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

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 21 Positioning system Aim: Using of radio based communication system also for positioning  Signal strength: depends on the structure of the building, unknown signal fading, large errors (absorption map required)  Time of flight measurements between nodes  UWB: ideal candidate, but availability is bad  Chirp-ISM, technique used by Nanotron  used here Nanotron positioning and communication system 2.4 GHz nanoLOC Tranceiver Ranging capabilities  Symmetric Double Sided Two Way Ranging (SDS-TWR):  The round trip time of a signal between two robots is measured twice  The measurement is started once at each of both robots Accuracy: 1-2 m indoor

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 22 Experiment 3 LRF + communication 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

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 23 Experiment 3 LRF + communication

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 24 Experiment 3 Procedure Mobile robot seeks to move to the desired position to complete the equilateral triangle. It sends the request to the other 2 static nodes, which should guide him to the correct position. Robot initiates wireless connection with the 2 static nodes using Bluetooth. After connection establishment, Laser sensor on Robot starts rotating and scanning for the 2 static nodes. For each rotated step, it requests info from static nodes whether they 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 distance at that instant, and inverses its rotation to search for the other node. As the 2nd node is hit, same procedure occurs. Afterwards, using the necessary triangulation 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

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 25 Example for determining the position with Nanotron‘s nanoLOC RF Module R 1, R 2 and R 3 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 R 1 & T, R 2 & T and R 3 & T is measured with the Nanotron Transceiver The position of T can be calculated by solving a system of equations.

HEINZ NIXDORF INSTITUTE University of Paderborn System and Circuit Technology Prof. Dr.-Ing. Ulrich Rückert 26 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