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Pharos: A Testbed for Mobile Cyber-Physical Systems at Worcester Polytechnic Institute

The Pharos Testbed is designed to validate and evaluate mobile cyber-physical systems (MCPS) through a network of autonomously mobile devices that interact with embedded sensors and actuators. This initiative addresses the need for robust and reliable evaluation mechanisms for MCPS, facilitating heterogeneous and extensible experiments. Key challenges include creating a supporting software infrastructure for repeatable experiments, quantifying discrepancies between experimental and simulated results, and addressing hardware limitations that affect scalability.

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Pharos: A Testbed for Mobile Cyber-Physical Systems at Worcester Polytechnic Institute

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  1. Pharos: A Testbed for MobileCyber-Physical Systems Daniel Sarafconn CS 525 Cyber-Physical Systems September 12, 2012

  2. Problem/ Motivation • “Mobile cyber-physical systems (MCPS) are gaining importance as key enablers of emerging applications; this necessitates reliable, robust, and rapid validation and evaluation mechanisms for integrated communication, coordination, and control solutions.” Worcester Polytechnic Institute

  3. Challenges Undertaken • “Design steps for the Pharos Testbed to supportheterogeneity and extensibility in both hardwareand software to enable a wide variety of experimentswith mobile cyber-physical systems; • Creation of a supporting software infrastructurethat enables push-button repeatability, includingrepeatability of mobility patterns and communicationcapabilities to the extent possible; and • Understanding of and quantifying the similaritiesand differences between experimental results andsimulated ones with the purpose of replicating experiments” Worcester Polytechnic Institute

  4. The Pharos Testbed Worcester Polytechnic Institute

  5. The Pharos Testbed • a networked system of autonomously mobile devices that can coordinate with each other and with networks of embedded sensors and actuators • an autonomous mobile testbed for extensive validation and evaluation of mobile cyber-physical systems Worcester Polytechnic Institute

  6. Proteus Platform Worcester Polytechnic Institute

  7. Proteus Software Architecture Worcester Polytechnic Institute

  8. Characterizing Repeatability Worcester Polytechnic Institute

  9. Types of Path Divergence Worcester Polytechnic Institute

  10. Test Path • “Lollipop” motion script • Different Segment Lengths • Different Angles Worcester Polytechnic Institute

  11. Lonestar Test Runs • Repeatability Testing • Execute motion script 7 times • Constant speed of 1.5m/s Worcester Polytechnic Institute

  12. Absolute Divergence of Lonestar Worcester Polytechnic Institute

  13. Relative Divergence of Lonestar Worcester Polytechnic Institute

  14. Reflexive Divergence of Lonestar Worcester Polytechnic Institute

  15. Relative-Speed Divergence of Lonestar Worcester Polytechnic Institute

  16. Repeatability Across Multiple Nodes • Absolute Divergences • Lonestar1.34±0.08m • Shiner 2.49±0.18m • Wynkoop 1.20±0.06m Worcester Polytechnic Institute

  17. Instant-Simulation Replay of Experiments • Log files can be fed directly into a simulator to create “instant replays” of a test • Useful to visualize what occurred for debugging purposes Worcester Polytechnic Institute

  18. Divergence From Simulation Worcester Polytechnic Institute

  19. Divergence From Simulation • “Real-world connectivity between wireless nodes often varies, sometimes to a large degree, from simulated connectivity.” • Characterizethe difference between simulated connectivity among mobile nodes and the real-world connectivity of the nodes in the Pharos testbed. • “This variance in communication characteristics is one of the most compelling reasons to evaluate mobile cyber-physical system solutions using real-world experiments in addition to simulations.” Worcester Polytechnic Institute

  20. Real-World Connections vs. Simulated Connections Worcester Polytechnic Institute

  21. Comparing Effective Radio Ranges Worcester Polytechnic Institute

  22. Limitations and Lessons Learned Worcester Polytechnic Institute

  23. Limitations in Architecture • High node complexity leads to frequent device failures thus limiting the scale of experiments • Limited software flexibility─ the current software only supports one form of motion script based on GPS waypoints Worcester Polytechnic Institute

  24. Limitations in Hardware & Device Drivers • μC is highly sensitive to interrupt latencies • Excessive current draw during acceleration was tripping the safety shut-offs of the batteries • Atheros wireless chipset drivers were unreliable • The compass was highly sensitive to voltage fluctuations • The GPS sometimes had trouble locking on to satellites Worcester Polytechnic Institute

  25. Limitations of Experiments to Date • Did not start all node in the same exact position and orientation • Only tested a single motion script • Did not test speed vs. motion repeatability or wireless connectivity Worcester Polytechnic Institute

  26. Related Work Worcester Polytechnic Institute

  27. Related Work • Hydra- a wireless emulator that focuses on repeatability at a very fine level of granularity at the physical layer • MiNT- a miniaturized multi-hop wireless network testbed that connects live emulations with running simulations in real time • EXC Toolkit- focuses on the software components of a wireless multi-hop network Worcester Polytechnic Institute

  28. Acknowledgements Information and figures are from “Pharos: A Testbed for Mobile Cyber-Physical Systems” by: Chien-Liang Fok, AgostonPetz, Drew Stovall, Nicholas Paine, Christine Julien, and SriramVishwanath at The University of Texas Worcester Polytechnic Institute

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