RT-Link: A Time-Synchronized Link Protocol Anthony Rowe, Rahul Mangharam, Raj Rajkumar C Carnegie Mellon University i M ll U i it
What is RT-Link? • RT-Link is a scalable energy efficient multi-hop link protocol for: – Industrial Control – Surveillance S ill – Inventory Tracking • Provides Bounded Latency, Energy Efficient and Deterministic Operation Efficient and Deterministic Operation – Achieved through global time synchronization 2
3 NIOSH Research Coal Mine
Overview • Hardware Assisted Global Time Synchronization • RT-Link TDMA Protocol • Energy Benefits of TDMA 4
CMU FireFly Sensor Node Hardware Time Sync CC2420 Radio Atmega128L Processor Temperature FLASH Expansion Port Expansion Port Light Acceleration Audio PIR Motion 5
Global Time Synchronization Beacon y Power Grid Antenna AM Transmitter Carrier Current Nodes Adapter 6
FireFly v2.0 y Expansion Port Chipcon cc2420 802.15.4 Radio Programming Atmega 1281 Port 8K RAM 128K ROM 128K ROM Mini-SD slot (RDS, carrier current, atomic clock modules) 7
FireFly Synchronization Hardware 8
Current CSMA based approaches • Low-Power Listen Carrier Sense Multiple Access (LPL CSMA) (LPL-CSMA) schemes h Check for Data Radio RX Radio TX Radio TX Extended TX Preamble • Tradeoff: Check Faster or Listen Longer 9
LPL-CSMA Multiple Sampling Intervals ms) k Interval (m (yrs) 60 min 40 min 40 min Life ( mal Check 30 min 20 min Optim Radio Check Interval (ms) Data Sampling Interval (min) Radio Check Interval Radio RX Radio TX 10 Data Sampling Interval
TDMA-Based Approach (RT-Link) Time-Sync Cycle y y Frame (32 per TDMA Cycle) AM Sync Pulse Scheduled Slots Contention Slots 32 Slots Per Frame 11
RT-Link Graph Coloring • Color Topology Graph to Avoid Collisions • Each Color represents a TDMA slot Each Color represents a TDMA slot TX a a RX Gateway a a f f f f TX TX c c b RX b b e e d TX c RX TDMA Frame 12
In-Band Time Synchronization y m Gateway a a f c c b b e e d d Header Header Packet Body Packet Body Time Slot Application Data Overhearing Node Now Knows Time Overhearing Node Now Knows Time Offset Within Cycle… 13 Starting Time of Overheard Packet
Lifetime Given Periodic Sampling s) ifetime (yrs Li Optimal Optimal LPL-CSMA RT-Link Hardware RT-Link Software S Sample Interval (min) l I t l ( i ) 14
Lifetime vs Neighboring Degree 15
16 Logical Topology Pruning
NIOSH Research Coal Mine In-Band Time In-Band Time Synchronization Global Time Global Time Sync Pulse “Leaky Feeder” 17
Conclusion • Hardware-based Time Synchronization is a robust and scalable option b t d l bl ti • Global Time Synchronization is economical Global Time Synchronization is economical and convenient for indoor and outdoor deployments p y • RT-Link achieves practical lifetimes of 2 years p y 18
19 Questions?
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