MobiSteer: Using Steerable Beam Directional Antenna

for Vehicular Network Access

Samir R. DasComputer Science Department

Stony Brook University

Joint work with Vishnu Navda, Anand Prabhu Subramanian, Kannan Dhanasekaran, and Andreas Timm-Giel

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

Use Steerable Beam Directional Antenna

Omni Directional Beam

High transmit and receive gain withdirectional antenna translate to better SNR

Beam steering

Problem – How to Beam Steer?

AP

Link Quality

Optimal Beam Steering and AP Selection

AP1

• Goal: Maximize overall throughput. • Both online and offline approaches possible.

AP2AP3

AP4

Offline Approach: Cached Mode Operation

• Scan and collect tuples during idle mode.

<location, beam, channel, AP, SNR>

RF Signature Database

Offline Approach: Cached Mode Operation

• Run optimal beam steering and AP selection algo during operational mode.

Route from navigation system

<beam, AP>at every point on route

RF Signature Database

<location, beam, channel, AP, SNR>

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

Controlled Outdoor Experiments

5m Segments

Mobisteer

Omni

Beam1

Nu

mb

er

of

pa

cke

ts a

t b

it-r

ate

s

Beam2

Beam3

Beam4

Beam5

Beam6

Beam7

Beam8

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)]

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.]

Conclusions

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