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Bluetooth

Introduction

  • PAN technology
  • Widely supported
    • PDAs, mobile phones, notebooks, picture frames etc
    • Used in embedded solutions
      • Keyboards, mice, head sets, printer, etc
  • Adding capability
    • PCMCIA cards, CF cards, USB dongle

Bluetooth 4.0

  • Specification June 2010
    • Core Specification Addendum 2, december 2011
    • First supporting mobile phone late 2011
  • Bluetooth classic protocols
  • Bluetooth highspeed protocols (from bluetooth v3.0 + HS)
    • Based on wi-fi on lower layers
  • Bluetooth low energy protocols (BLE) (formerly known as WiBree and Bluetooth Ultra Low Power (ULP))
    • Own protocol stack
      • Lacks backward compatibility
    • For sensor networking
    • Coin cell battery for years!
    • Bluetooth smart branding
      • Bluetooth smart for sensors
      • Blueooth smart ready for readers/hosts

Introduction ...

  • Uses 2.4 GHz ISM band
  • 79 channels
  • Frequency hopping (1600 hops/s)
  • Gross data rate is 1 Mbps
  • EDR triples this
  • Different links for data & audio
  • SCO voice link
    • Synchronous
    • CVSD encoding
    • 64 kbps
  • ACL data link
    • Max data rates
      • 433,9 kbps symmetric
      • 723/57 kbps asymmetric
  • Also useable with audio

Classes

  • Different power classes for different needs
Power Class Output power Range
Class 1 100 mW 100 meters
Class 2 2.5 mW 10 meters
Class 3 1 mW ~1 meter

Topology

  • Star topology
    • 1 Master connects 7 slaves
    • Master initiates the connection
    • Role switch used to switch roles
    • Does not affect application layer client-server roles
  • All devices have “unique” 48bit Bluetooth Device Address (BDADDR)
  • All devices can be identified
  • BDADDR easily forged

Access points

  • Omni-directional RF
    • Class 1 & 2 radio
    • Class 1 devices have ethernet connection to brigde TCP/IP connections
  • Many models run embedded Linux
    • Posibility to add own applications & services
  • Many brands to choose from
    • Low cost
  • Do it yourself - PC & Bluetooth dongle?

Specification

  1. Core definitions of the Bluetooth interfaces & protocols
    • Radio, LMP, HCI, L2CAP, SDP, etc
  2. Profiles
    • Profiles defines what feature have to be supported on certain application types
    • GAP, SDAP, CTP, FTP, SP, FP

  • HCI
    • Interface used to communicate with Bluetooth hardware
  • BNEP
    • Newer protocol useable instead of RFCOMM & PPP under IP
  • How to use these protocols on different product types are defined in profiles
  • On what layer should you start your application development?

Profiles

  • Aim to guarantee inter-operability
    • Generic Access Profile - followed by all products
    • Service discovery (SD) application profile defines the SD process
    • Serial port defines use of RFCOMM
  • Some new profiles
    • Extended SD to enhance the SD process
    • PAN profile for use of BNEP
    • SIM profile for use of SIM card
    • Remote control profile, video/audio profile, …

Bluetooth connectivity

  • Connection forming consist of 3 steps
    1. Device discovery (Inquiry)
    2. Connecting devices (Paging)
    3. Service discovery

Inquiry

  • Initiator sends inquiry messages in order to find devices in it's proximity
  • Devices in discoverable modes reply with their BDADDR
  • Inquiry in v1.1 takes ~10.24 seconds with ~90% success rate
    • Shorter inquiry time add unreliabilty
  • Enhanced inquiry in v1.2 takes max of 5 seconds with 100% success rate
    • 10 seconds inquiry often used for compatibiliy reasons
  • Interlaced inquiry scan in v1.2 speeds up discovery x2 to a max of 2.5 seconds
    • Requires more power
    • Not supported by all devices

Paging

  • Initiator pages device it intends to connect at BDADDR
    • BDADDR could be fetched at inquiry, user input or database retrieved
  • Takes ~1.28 seconds & maximum of 2.56 seconds
  • Interlaced page scan in v1.2 halves the time
    • Requires more power
    • Not supported by all devices

Service discovery

  • To discover capabilities of device that basic data connection is formed at
    • More details in service discovery demo lecture
  • Specification lacks roaming support - WiP
    • Vendors have own solutions for enabling roaming
    • Create your own roaming system
  • Bluetooth games?
Last modified: 2014/05/14 11:06