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ROME: Road Monitoring and Alert System through Geo-Cache

Bin Zan, Tingting Sun, Marco Gruteser, Yanyong ZhangWINLAB, 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

AB

Detect

C

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Delayed Geo-Cache (Boomerang)

AB

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)

AB

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