1. MobiSteer: Using Steerable Beam Directional Antenna for Vehicular Network Access Samir R. Das Computer Science Department Stony Brook University Joint work with Vishnu Navda, Anand Prabhu Subramanian, Kannan Dhanasekaran, and Andreas Timm-Giel

2. Vehicle to Roadside Communication Problems: Poor link quality: 80% delivery ratio. Short connectivity duration: 13 sec avg. High handoff cost:1-2 sec. MIT CarTel Project [MobiCom06] WiFi client in car accessing WiFi APs in the neighborhood

3. Use Steerable Beam Directional Antenna Omni Directional Beam High transmit and receive gain with directional antenna translate to better SNR Beam steering

4. Effect of Beam Steering on Link Quality AP Link Quality

5. Problem – How to Beam Steer? AP Link Quality

6. Handoff to AP2 Problem – AP Selection AP1 AP3 AP2 Handoff to AP3 Associate with AP1 Scenario 1 AP1 AP3 AP2 Handoff to AP3 Associate with AP1 Scenario 2 Which AP to handoff? When to handoff ?

7. Optimal Beam Steering and AP Selection AP1 Goal: Maximize overall throughput. Both online and offline approaches possible. AP2 AP3 AP4

8. Offline Approach: Cached Mode Operation Scan and collect tuples during idle mode. <location, beam, channel, AP, SNR> RF Signature Database

9. Offline Approach: Cached Mode Operation Run optimal beam steering and AP selection algo during operational mode. Route from navigation system at every point on route RF Signature Database <location, beam, channel, AP, SNR>

10. Mobisteer Prototype Phocus Array Steerable Antenna system from Fidelity Comtech –8 Beams - 45° beam width/ 15dBi gain –Atheros 802.11b/g radio –250usec beam steering

11. Controlled Outdoor Experiments 5m Segments Mobisteer Omni Beam1 Number of packets at bit-rates Beam2 Beam3 Beam4 Beam5 Beam6 Beam7 Beam8

12. Controlled Outdoor Experiments Segments #of Packets at bit-rates Mobisteer Omni Beam1 Beam2 Beam3 Beam4 Beam5 Beam6 Beam7 Beam8

13. Overall Performance Improvement Experiments with APs under our control –2-4 times improvement in throughput. Experiments with neighborhood APs –More than 2 times increase in connectivity duration. –+15dB gain in SNR. [ACM MobiSys 2007 (best paper award)]

14. Drive-by Localization of Neighborhood APs Challenge: Handling reflections. Localization Error: 10-30m. Compare with Place Lab (error 13-40m in spite of elaborate RF fingerprinting). [Submitted for publication. Send email for a copy.]

15. Conclusions Directional antenna beam steering + moving vehicle = Potential for good performance + interesting applications.