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
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.
