MobiSteer: Using Steerable Beam Directional Antenna for Vehicular Network Access

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MobiSteer Using Steerable Beam Directional
Antenna for Vehicular Network Access

• Vishnu Navda, Anand Prabhu Subramanian, Kannon
  Dhanasekaran, Andreas Timm-Giel, Samir R. Das
• Originally Presented at MobiSys 07
• Reviewed by Lauren Cohen on 2/12/08

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Motivation

• Wireless communication between moving vehicles
  and roadside access points
• Three application types
• Traffic safety and information
• Mobile sensors
• Internet access for vehicle occupants
• Current connectivity is poor
• Access point inter-arrival time gtgt median
  connection time
• Link layer delivery rate 80

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Design Goals

• Directional antennas to increase gain and reduce
  interference
• Steerable to maintain best link quality over
  longest duration
• Optimize handoff between access points

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• Omnidirectional
• Directional

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Assumptions

• APs use omnidirectional antennas
• Vehicles access stationary network using one-hop
  links
• in other words, well be considering
  applications 2 (mobile sensors) and 3 (Internet
  access)

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MobiSteer Architecture Overview
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Hardware/Software Setup

• Multi-beam 2.4 GHz antenna
• One omnidirectional beam
• 16 45 directional beams
• Computer-controlled steering commands via serial
• Data on captured packets logged to RF signature
  database during idle times

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Operational Modes

• Cached
• Familiar territory
• RF signature database used to determine optimal
  steering and AP selection
• Databases can be downloaded from a server
• Online
• Previously untravelled routes
• Scans all beams/channels and determines best
  based in SNR value

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Data Collection

• Link quality of received frames stored in RF
  signature database
• Passive scanning
• Monitors each beam/channel for any frame
• Active probing
• Periodic probe requests sent
• Responses from APs recorded
• Allows quicker sampling

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Cached Mode Operation
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Optimal AP and Beam Selection

• Computes best AP and beam for every point in
  trajectory
• Segments of length ?
• RF signature database queried for SNR
• Still need to deal with handoff latency

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Optimal Handoff Algorithm

• Estimate speed of vehicle from RF signature
  database to calculate handoff latency between
  possible APs
• Use dynamic programming to select best APs to
  minimize latency between segments

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Experimental Scenarios

• Controlled scenarios
• Single AP in empty parking lot
• Multiple APs in apartment complex
• Typically two within hearing range
• All on same channel
• In situ scenario
• Existing APs along campus roadways
• Again all on same channel
• No actual data transferred

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Experimental Results

• Controlled scenario
• Data collected on of packets received and rate
  of transmission
• MobiSteer greatly increased both
• In situ scenario
• MobiSteer improved average SNR and distance from
  which each beam could be heard
• Alas, no actual data rate results

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Online Mode Operation
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Intricacies

• Constantly uses active probing
• Simple heuristic used to choose best AP/beam
  combination from probed data
• Only steering considered, as handoff and AP
  selection covered in other literature

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Experimental Results

• Used controlled scenario setup
• Again measured of packets received and data
  rate
• MobiSteer again improved both measurements over
  using an omnidirectional beam in online mode

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Conclusions

• MobiSteer provides good alternative to
  omnidirectional beams for vehicular networking by
  improving connectivity duration and data rate
• Cached mode is superior to online mode
• Future ideas
• Use for localization of roadside APs
• Interface with cellular modem networks for
  additional connectivity

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Questions

• What about communications between moving
  vehicles?
• Can this be used to improve cellular networks as
  well?
• How do we alleviate the overhead of active
  probing (since its necessary to build the RF
  signature database)?