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COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Experiments with Autonomous Mobile Radios for Wireless Tethering in.

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Presentation on theme: "COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Experiments with Autonomous Mobile Radios for Wireless Tethering in."— Presentation transcript:

1 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Experiments with Autonomous Mobile Radios for Wireless Tethering in Tunnels Kevin L. Moore, Manoja Weiss, John P. Steele, Ken Anderson, Jesse Hulbert, Christer Karlsson, Eric Larson, Chris Meehan, and Alejandro Weinstein Center for Robotics, Automation, and Distributed Intelligence Colorado School of Mines, 1500 Illinois St., Golden, CO, Unmanned Ground Systems XI Conference SPIE 2009 Security and Defense Symposium Orlando, Florida 08 April 2010

2 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Subterranean Environments Subways, mines, caves, underground buildings Limited entrances/exits, navigation Limited ventilation, communications Challenging emergency management environment 2 –Assume no infrastructure –Radio relays may be necessary at/near junctions –Rescue workers must carry their own comms

3 EXAMPLE: SAGO MINE EXPLOSION JANUARY 2, 2006 MSHA I.D. No INTERNATIONAL COAL GROUP SAGO MINE DRIFT OPENING 3

4 Sago Mine Layout Older Sealed Areas Recently Sealed Area Mine Entrance 2 Miles Travel Route Into Mine 2 Left Working Section 1 Left Working Section 1 Left crew mantrip found with lights on. Area Detailed Below 4

5 Acknowledgement: This work support by NIOSH under Grant #1R01OH

6 Reconfigurable topology to sustain information flow

7 Example: Autonomously Reconfigurable Systems Consider an underground mine Legend: Flows of people, material Flow of information Flows of air Fixed radio node Toxic gas Mobile radio node

8 Legend: Flows of people, material Flow of information Flows of air Fixed radio node Toxic gas Mobile radio node Add sensors and flows of people, material, and air

9 Legend: Flows of people, material Flow of information Flows of air Fixed radio node Toxic gas Mobile radio node Suppose a hazardous gas develops

10 Legend: Flows of people, material Flow of information Flows of air Fixed radio node Toxic gas Mobile radio node The system should autonomously-reconfigure to redirect flows of people, material, and air

11 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Another Motivation – DARPA’s LANDroids Program Our MineSENTRY program applies these ideas: - In a subterranean environment - Using realistically-sized robots Use what we call Autonomous Mobile Radios (AMRs)

12 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida MineSENTRY Motivations Scenario System Components Preliminary Results on Radio Propagation in the Mine Theoretical Approach –Consensus Variables –Tethering Example in RSS space Preliminary Experimental Results –Above-ground wireless tethering – 1 follower –Underground wireless tethering – 2 human-in-the-loop followers –Underground wireless tethering - 1 follower

13 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Scenario : 1) Accident Disrupts Communication and Blocks Access Sensor node VDSL node Phone cable Existing Sensor Network X Rubble Blocks Path and Communications X

14 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Scenario: 2) Deploy Robotic Wireless Nodes and Teleoperated Bobcat X X Bobcat Robotic ATV Radio Node

15 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida X X Scenario: 3) User Clears Rubble from Path Users tele-operate the Bobcat remotely over ad hoc network to clear rubble from path Robotic ATV Radio Nodes autonomously configure to form an ad hoc network

16 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida X Scenario: 4) Re-Establish Comms After rubble is clear, communication is autonomously re-established with sensor network via communication tether formed by Robotic ATV Radio Nodes and Bobcat

17 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida MineSENTRY Components Underground Sensor Network Teleoperated Bobcat Autonomous Radio Node (AMR) - Provides Communication Tether - Uses CSM-developed UGV Autopilot (briefed at SPIE DSS 2009) Operator Control Unit (OCU)‏ Mesh Radio System (Rajant Breadcrumb™)

18 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida MineSENTRY Motivations Scenario System Components Preliminary Results on Radio Propagation in the Mine Theoretical Approach –Consensus Variables –Tethering Example in RSS space Preliminary Experimental Results –Above-ground wireless tethering – 1 follower –Underground wireless tethering – 2 human-in-the-loop followers –Underground wireless tethering - 1 follower

19 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Radio Communication Challenges in Subterranean Environments VLF (<10kHz) –Good for through the earth communications ( ft) –Beacon, 2-way text, 1-way text MF (<3MHz) –> 1 mile range, accommodates curvature in tunnels –2-way voice and data VHF (100MHz) –Mostly Line Of Sight (LOS) –somewhat accommodates tunnel curvature –Leaky feeder cable: voice, data UHF (400MHz – 4GHz) –1500ft straight, mostly LOS –Wireless Mesh (2.4GHz, 5GHz) – commercial, low cost –High data rate: video, internet 19 Classic tradeoff between bandwidth and power consumption

20 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Evaluation: Wi-Fi Network Wireless signal strength is dependent on many parameters –Cross section of tunnel –Line of sight SNR vs. Dist is different for every environment

21 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Location of radio relative to wall makes a big difference Clay cave Stone cave Center excitationOff-axis excitation

22 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Path Loss Exponent n changes significantly when there is a turn 22 n changes with radius of curvature

23 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida RSS Between AMRs The RSS between two AMRs, based on our (and others) experimental measurements can be given in mW as: Losses in straight tunnel Losses due to a bend, about -3dB/m, for 40m then set to one Transmitted power

24 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida For a small section of the Edgar Mine Cumulative Path Loss From Start Bend 1 Bend 2

25 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida 1D Exploration in Long Tunnels Different propagation conditions exist in different segments of the mine AMRs should adjust spacing to adapt to these different propagation conditions Result is a 1D curvilinear path is made up of smaller sections with various propagation conditions 25

26 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Theoretical Approach Wireless 1-D tethering –Not in physical coordinates –Rather, in radio signal strength (RSS) space Goal is to maintain equal RSS between ARMs while the leader moves forward in the mine Approach uses consensus variable-like algorithm 26

27 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Consensus Variables Suppose we have N agents with a shared global consensus variable Each agent has a local value of the variable given as Each agent updates their local value based on the values of the agents that they can communicate with where are gains and defines the communication topology graph of the system of agents Key result from literature: If the graph has a spanning tree then for all i

28 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Example: Single Consensus Variable

29 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Consensus Variables Applied to Tethering in RSS Space Goal is for the AMRs to space themselves out between a mobile leader and a stationary base station, where the “spacing” objective is that each AMR is separated equally in terms radio signal strength (RSS). We use several extensions to the consensus variable ideas that we have developed over the last several years: –Forced consensus (consensus with a leader) –Higher-order (model-reference) consensus We further adapt the consensus idea so that the AMR velocity depends on the difference in RSS between itself and the AMR ahead and behind

30 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida First-Order Consensus in RSS Then, a consensus-like approach to motion control is suggested (using dB): Or, in terms of the expression for RSS in dB: This yields, for multiple vehicles in the same tunnel with no bends, the set of coupled equations:

31 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida First-Order Consensus in RSS This tracks nicely when trying to space out vehicles between a stationary lead vehicle and a stationary base station. Position RSS

32 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida First-Order Consensus in RSS However, it can be shown easily that this will not lead to tracking when the lead vehicle is moving. PositionRSS Bend 1

33 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Second-Order Consensus in RSS The remedy is to apply the internal model principle to develop a higher-order (2 nd ) consensus algorithm: It is an open question to study the stability and convergence properties of such a set of coupled algorithms However, simulations show that the idea works

34 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Second-Order Consensus in RSS Now all RSS values are the same Position RSS

35 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida MineSENTRY Motivations Scenario System Components Preliminary Results on Radio Propagation in the Mine Theoretical Approach –Consensus Variables –Tethering Example in RSS space Preliminary Experimental Results 1.Outdoor wireless tethering – 1 follower 2.Underground wireless tethering – 1 and 2 human-in-the-loop followers 3.Underground wireless tethering - 1 follower

36 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Vehicles Used: Autonomous Electric Mini-Baja Car

37 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Vehicles Used: Autonomous Ez-Go Golf Cart

38 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Generic Scenario Follower (Base Station) AMRLeader 1. START (RSS approx equal between AMR to Leader and AMR to Follower) Follower (Base Station) AMRLeader 2. LEADER MOVES (RSS less from AMR to Leader than AMR to Follower) Follower (Base Station) AMRLeader 3. AMR MOVES (RSS approx equal between AMR to leader and AMR to Follower) (might not be equally spaced in distance)

39 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Tethering Algorithm Implementation RSS signal updates are only updated in the commercial radio we were using every 6 seconds Significant variability in RSS when sitting still: +/- 5 dB Thus we implemented a variation on the consensus-based tethering scheme: –Initialize system –Wait 30 seconds –Compute estimated move distance (using RF propagation model) –Move –Wait 30 seconds –Repeat –Stop if within 5dB of target AMR control is two-part: –Velocity is controlled by the RSS tethering algorithm –Steering is controlled by a wall-following algorithm

40 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida 1 – Outdoor Experiment: Teleoperated Leader (Golf Cart), 1 AMR (Baja)

41 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Explanation: Human-in-the-loop experiments Replace the AMR with a human –Human carries radio –Human carries laptop talking to the radio –Laptop display tells human to move or stop Follower (Base Station) AMRLeader

42 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida 2a – Underground Experiment: One human-in-the-loop follower

43 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida 2b – Underground Experiment: Two human-in-the-loop followers AMR 2 AMR 3

44 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida 3a – Underground Experiment: One AMR follower

45 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida 3b – Underground Experiment: One AMR follower, leader moves Corresponding Video com/watch?v=1LhY AsaZTYw

46 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida Conclusions Presented ideas aimed at developing Autonomous Moble Radios applied to the problem of wireless tethering in underground environments –CONOPS –Characterization of RF environment in tunnels –Consensus variable algorithms to control AMR spacing Experiments demonstrated the feasibility of the ideas

47 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida The Joys of Field Work …!

48 COLORADO SCHOOL OF MINES SPIE Security and Defense 2009 – UGV XI, Orlando, Florida … in Colorado!


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