IIT Bombay

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Skymobile Safe In-flight Mobile Telephony
Department of Electrical Engineering INDIAN
INSTITUTE OF TECHNOLOGY, BOMBAY Aditya Dua, Aman
Kansal, Arjunan R, Sumitra Ganesh, and Vivek
Raghunathan Mentor Prof. U B Desai
IIT Bombay
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The Need

• Air passengers need to stay connected on board
• Would like to both make and receive calls
• Call reception not supported by current
  technologies
• Would like to use their personal handsets
• Phone book, hotkeys etc.

IIT Bombay
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The Challenge

• Signals emitted by the mobile phone interfere
  with Air Traffic Control (ATC) signals,
  undermining the safety of the flight
• A mobile at such an altitude connects to
  multiple base stations simultaneously, clogging
  the resources of the ground network

IIT Bombay
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The Challenge

• FCC, Part 22, Subpart H,Cellular Radiotelephone
  Service Sec. 22.925
• Prohibition on airborne operation of cellular
  telephones.
• Cellular telephones installed in or carried
  aboard airplanes, balloons or any other type of
  aircraft must not be operated while such aircraft
  are airborne (not touching the ground). When any
  aircraft leaves the ground, all cellular
  telephones on board that aircraft must be turned
  off.

IIT Bombay
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Our Solution

• Allows air passengers to stay connected
• Use their personal handset and mobile number
• Does not require user initiation
• Does not interfere with ATC signals
• Bluetooth has FH and low power
• Does not clog multiple base stations

IIT Bombay
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Our Solution
IIT Bombay
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Innovation

• In-flight connectivity without endangering
  safety of flight
• Integration of various networks - PSTN, GSM,
  Bluetooth
• Seamless operation
• Use of ACL for voice

IIT Bombay
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Operation

• Automatic call forwarding set up
• Unconscious switchover from GSM to Bluetooth
• GSM emissions turned off
• Handset connected to Bluetooth gateway
• Voice calls now made/received over Bluetooth
• GSM settings restored while leaving the plane

IIT Bombay
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Operation
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System Architecture

• Hardware
• Users mobile unit (MU)
• Bluetooth Airplane gateway (BTAG)
• Ground switching center (GSC)
• Software
• GSM module
• PSTN module
• Bluetooth module

IIT Bombay
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Hardware
Mobile Unit
Bluetooth Link
GSCBTAG
IIT Bombay
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Hardware

• BTAG
• Interfaces to the air to ground link
• Connects incoming voice call to the appropriate
  handset
• GSC
• Handles voice calls over the ground to air link
• Interfaces to the phone network on land
• BTAG and GSC combined into one PC
• Air to ground link not used

IIT Bombay
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Software

• Bluetooth Module
• Automatic connection establishment, with
  authentication
• Voice communication (over ACL)
• Controls interaction among other modules

IIT Bombay
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Bluetooth Module

• Automatic Connection Establishment
• Periodic Inquiry by BTAG
• Pages devices which are handsets
• Sets up RFCOMM connection with handsets having
  Skymobile server

IIT Bombay
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Bluetooth Module

• Authentication
• Only authentic gateways should be able to issue
  GSM commands to handsets
• Only registered mobile handsets should be able
  to use the BTAG
• Assumed that keys purchased before check-in

IIT Bombay
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Bluetooth Module
Authentication
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Bluetooth Module

• Voice Communication
• Multiple threads for simultaneous playout,
  recording, transmission and reception

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GSM Module
Operation
Open Connection to COMM Port
Retrieve COMM port settings
Modify COMM port settings
Bluetooth Module
Event
Issue GSM Commands over COMM

Response
Receive Response from port
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PSTN Module

• Handles calls arriving at the landline
  forwarding numbers
• Microsoft Telephone API used
• Modem abstracted as a wave audio device
• 8kHz CCCIT ?-law, mono voice used

IIT Bombay
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PSTN Module

• Accepts incoming calls and establishes a
  connection on PSTN
• Indicates call arrival to BTAG
• Streams voice from BTAG over PSTN and vice versa
• Handles outgoing calls from in-flight mobile
  units

IIT Bombay
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Summary

• Safe in-flight connectivity provided
• Integration of diverse networks to achieve voice
  communication
• Future Work
• Replacing ACL with SCO
• Emulating other GSM services (WAP or I-Mode)

IIT Bombay