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Bluetooth (IEEE 802.15.1)
An Introduction


Prof. David Bernstein
James Madison University

Computer Science Department
bernstdh@jmu.edu

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Background
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  • Purpose:
    • Short-range, low-power, low-cost wireless communications
  • About the Name:
    • Named after King Harald Blatand of Denmark (who united the warring factions in what is now Norway, Sweden and Denmark)
Devices
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  • Class 1:
    • 100 milliwatts of power
    • Range of 100m
  • Class 2:
    • 2.5 milliwatts of power
    • Range of 10m
  • Class 3:
    • 1 milliwatt of power
    • Range of 1m
Power-Saving Modes
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  • Hold:
    • The device does not actively exchange data
  • Sniff:
    • The device periodically listens for messages
  • Park:
    • The device listens for messages and resynchronizes its clock but does not actively communicate
The Physical Layer
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  • Frequency:
    • 2.4GHz band
  • Spread Spectrum:
    • 79 1MHz channels
    • Frequency hopping spread spectrum (FHSS) in which each transmission lasts 625 microseconds
  • Modulation:
    • v1 uses Gaussian Frequency Shift Keying (GFSK) for a throughput of about 1 Mbit/s
    • v2 also uses Phase Shift Keying (PSK) for a throughput of about 3 Mbit/s
Networks
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  • Terminology:
    • Piconet - A group of (synchronized) communicating devices
    • A device that is involved in more than one piconet at the same time is said to be part of a scatternet
  • Roles:
    • 1 boss (the first device that initiates communication)
    • Up to 7 minions
  • Piconet Topology:
    • Star - for purposes of clock and hopping sequence synchronization (i.e., the boss's clock is used)
    • Completely Connected - for other purposes
Procedures
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  • Inquiry (a.k.a. Discovering):
    • An inquiring device is attemping to find other nearby devices
    • A discoverable device is available to be found and responds to inquiries
    • Uses a special physical channel
  • Paging (a.k.a. Connecting):
    • A paging (a.k.a. connecting) device initiates
    • A page scanning (a.k.a. connectable) device listens for pages
    • Uses a special physical channel
Types of Links
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  • Synchronous Connection Oriented (SCO):
    • Reserved time slots are set aside (between the boss and a particular minion)
  • Asynchronous Connectionless (ACL):
    • Can use any time slot (not being used for SCO links)
Frames in Bluetooth
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  • Access Code (68 or 72 bits):
    • A Channel Access Code (CAC) is used to identify a particular piconet
    • A Device Access Code (DAC) is used in signaling (e.g., paging)
    • An Inquiry Access Code (IAC) is used primarily to discover other Bluetooth devices
  • Header (54 bits):
    • 3-bit active member address (AM_ADDR)
    • PM_ADDR (used for park mode)
    • 4-bit type (ID, Null, Poll, FHS, DM1)
    • 1-bit flow control (i.e., stop or not)
    • 1-bit acknowledgment (ARQN)
    • 1-bit "sequence number" (SEQN) -- alternates between 0 and 1
    • 8-bit header error check (HEC)
    • Other stuff...
  • Payload (0-2745 bits)
Bluetooth Profiles
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  • Purpose:
    • Define the capabilities of Bluetooth products
  • Examples:
    • Generic Access Profile (discovery and link management for all Bluetooth devices)
    • Service Discovery Application Profile
    • Cordless Telephony Profile
    • Serial Port Profile
    • Headset Profile
    • Dial-Up Networking Profile
    • LAN Access Profile
    • General Object Exchange Profile (similar to OBEX)
There's Always More to Learn
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