Sensor network s for traffic monitoring

1. Sensor networks for traffic monitoring Pravin Varaiya et al

2. Outline • Challenge • Sensor networks for traffic applications • Pedamacs MAC protocol • Signal processing

3. Challenge • Accuracy and low delay • Biggest cost is deployment and maintenance-lifetime (power consumption) will determine economic feasibility

4. Sensor networks for traffic < 100 m • Nodes generate data, report to access point • At intersection, vehicle detection must be reported in 0.1 s; also 30-sec periodic data • Nodes are power- and energy-limited; access points are not Access point Sensor node Intersection Freeway

5. Current traffic monitoring technology • Loop detectors is the standard; loops last 10 years • Closing lane to cut loops in freeway pavement is very disruptive • Alternatives today are microwave radar, video cameras • Installed cost is $600-$1000 per detector (lane) per year • Can sensor networks compete?

6. < 100 m Intersection Sensor networks with two special characteristics • One distinguished node , Access Point or AP;sensornodes or SNperiodically (eg. 30 s) generate data for transmission to access point • SNs are power- and energy-limited but AP is not: Consequently TransmissionAP  SN is one-hop Transmission SN  AP is multi-hop • Two conditions satisfied in traffic applications Freeway

7. Pedamacs networks: Access point discovers network topology; nodes discover next hop Access point computes and broadcasts transmission schedule to all nodes (TDMA data) During data phase, node sleeps if it is not scheduled to listen or to transmit Random access networks: Access point and nodes discover next hop Nodes randomly transmit and constantly listen for incoming packets Refinements proposed to reduce node ‘listening’ time Pedamacs vs random access networks

8. Comparison of random access and Pedamacs networks • Comparison via TOSSIM, a TinyOS simulator • Need to select critical parameters for comparison • Backoff-listening random access scheme • Back-off window, listening window • Transmission range • Nodes randomly distributed inside unit circle

9. Power consumption in PEDAMACS vs random access • 50 kbps; one packet every 30 sec; vertical scale is log10 • Listening in random access uses 1000X more power, and receiving uses 10X power than in Pedamacs

10. Lifetime of PEDAMACS vs random access network • Two AA batteries: 2200 mA at 3 V • Pedamacs network lasts 600 days, need 5X improvement • Random access network lasts 10 days-unsuited for traffic control

11. Pedamacs vs random access delay • Random access delay excessive for traffic application

12. Detecting vehicles Experiments Spatial and temporal resolution Speed Vehicle classification

13. Data Set 1: motes in middle of lane 1 [Mic] 3 [MagXY] 2 [Mic] 4 [MagXY]

14. Ford15_x0_1.dat Wind disturbance

15. Ford27_x0_1_track_at_end.dat Noise from truck

16. Magnetic signature for classification Ford15_x0_1.dat ford27_x0_1_track_at_end.dat

17. Ford25_x0_2.dat

18. Ford_acc_x0_1.dat Vehicle accelerating going over the mote

19. ford_stopB4mote1_1sec_acc_x0_1_otherCars.dat From another car Car stopped before mote 1,3

20. Summary • Sensor networks offer a promising alternative • Acoustic signal is corrupted by noise--more filtering and processing needed for robust detection • Magnetic signal depends on orientation • Work needed to implement TDMA protocol • Signal processing for speed, vehicle classification • Deployment, reliability