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ROME: Road Monitoring and Alert System through Geo-Cache
Bin Zan, Tingting Sun, Marco Gruteser, Yanyong Zhang
WINLAB, Rutgers University
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Road Monitoring in Mobile Sensor Networks
New road monitoring services are enabled by cars with sensing, communication, computing and storage capabilities.
System Assumption Location-based interests Data items are accessed through queries after they are generated.
camera
GPS
rotationsensor
accelerometer
vibrationsensor
cell phone
DSRC
Communication
Sensing
Positioning
Skid Resistance
Surface Distress
Road Roughness
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Data Collection Challenges in Mobile Networks
Centralized Bandwidth (Cellular) Cost (DSRC) Storage
Query-response Difficult to locate data
source afterwards
Local aggregation Data are stored around where they are generated by passing cars Short-ranged radios have larger bandwidth than cellular links
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Location Aggregation
Three local aggregations.
Aggregation content formatLocation Time Event Id Detector
(−92315:74000) 2:00PM 1 VD 3245
(−92316:73989) 2:30PM 2 SX 1443
(−92316:73989) 2:45PM 3 MK 3098
Duration
2 hours
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Geo-Cache Concept Anchor Location: Locations of interest, where sensed results
are aggregated.
Geo-Cache Aggregated information around
the Anchor Location. Geo-Cache Collection Protocol
Protocols to hand over information
through inter-vehicle communication
as nodes move away.
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Geo-Cache Collection Protocol
Broadcast Geo-Cache (Baseline) Periodically broadcasting Geo-Cache to those closer to the
anchor location, until time-to-live timer expires. High overhead
Relay Geo-Cache Acknowledgment Overhearing
Delayed Geo-Cache
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Relay Geo-Cache Relay Protocol
Acknowledgement
AB
C
ACK
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Relay Geo-Cache
AB
C
Relay Protocol Acknowledgement
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Relay Geo-Cache
AB
C
ACK
Handoff
Relay Protocol Acknowledgement
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Relay Geo-Cache
AB
C
Relay Protocol Overhearing
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Relay Geo-Cache
AB
C
Relay Protocol Overhearing
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Relay Geo-Cache
AB
C
Handoff
Relay Protocol Overhearing
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Delayed Geo-Cache (Boomerang) Relay protocol incurs high overhead when detection probability is
low Delayed protocol: cars keep their Geo-Cache locally, and later hand
off to an opposite collector
A
B
Detect
C
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Delayed Geo-Cache (Boomerang)
A
B
C
D
Relay protocol incurs high overhead when detection probability is low
Delayed protocol: cars keep their Geo-Cache locally, and later hand off to an opposite collector
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Delayed Geo-Cache (Boomerang)
A
B
D
C
Relay protocol incurs high overhead when detection probability is low
Delayed protocol: cars keep their Geo-Cache locally, and later hand off to an opposite collector
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Delayed Geo-Cache (Boomerang)
B
D
CGeo-Cache back to
Anchor LocationA
Relay protocol incurs high overhead when detection probability is low
Delayed protocol: cars keep their Geo-Cache locally, and later hand off to an opposite collector
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When Nobody is Around …
What if the handoff process cannot find a candidate (the current carrier is the only node in the area)? Infrastructure: cellular,
WiFi, road-side DSRC units, etc.
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Performance Evaluation Performance metrics
Communication Overhead Geo-Cache anchoring delay (the time between when the geo-cache is carried away
from the anchor and when it returns) NJTP Trace
Represents relatively sparse off-peak traffic from 6 to 8 AM, south NJ. Synthetic workload
70km two lane road. Cars’ arrival rate as Poisson distribution. Average speed: 30 m/s. Radio range: 100m for dense traffic and 250m for sparse traffic
NS2 802.11b as PHY and MAC Two-ray-ground propagation model
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Performance Evaluation
Broadcast Geo-Cache vs. Relay Geo-Cache.
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Performance Evaluation
Delayed (Boomerang) vs. Relay Geo-Cache.
Conclusion
New mobile sensing applications are being enabled Local aggregation through the Geo-Cache structure provides a
cost-effective method for mobile sensing Delayed Geo-Cache protocol can significantly reduce the
communication overhead while anchoring the Geo-Cache especially with lower detection probabilities.
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Questions & Answers
