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Wireless Service engineering

Bluetooth information sources

  • Books:
    • Morrow: Bluetooth: Operation and Use
    • Bray et al. : Bluetooth Application Developer's Guide

Bluetooth

  • Widely supported
    • Built-in on many PDA's, mobile phones and some laptops
    • Several embedded solutions exist
    • Adding the capability to the device
      • PCMCIA cards
      • CF cards
      • USB dongle
  • Current version of Bluetooth is 2.0 with Enhanced data rate (EDR) was released November 8, 2004
    • Most devices currently on market use version 1.2
    • 2.0 is backward compatible
    • Next version of Bluetooth will use UWB in the future on a physical layer?
  • Uses 2.4Ghz ISM band
    • 79 channels,
    • frequency hopping (1600hops/s)
  • Gross datarate 1Mbps
    • EDR triples this.
  • Different links for data and audio
    • SCO voice link
      • synchronous
      • CVSD voiide encoding
      • 64 kbps
  • ACL data link
    • asynchronous
    • max data rate
      • 433,9 kbps symmetric
      • 723/57 kbps asymmetric
    • Can be used also to audio.
  • Different power classes to support different needs
Power classOutput powerRange
Class 1100 mW100 meters
Class 22.5 mW10 meters
Class 31 mW1 meter
  • Topology
    • Star topology
    • One master up to 7 slaves
      • Initiator of connection is master
      • Role switch can be used to switch roles
      • Does not affect on application layer client-server roles
  • All devices have unique 48bit Bluetooth Device Address (BD ADDR)
    • all devices can be identified
    • BD ADDR can be rather easily forged
  • Access points
    • Omnidirectional RF
      • Class 1 or 2 radio
    • Class 1 devices have ethernet connection to bridge TCP/IP connections
    • Many models are running embedded linux
      • Possibility to add own applications and services.
    • Many brands to choose from
      • Low cost
    • Do it yourself with PC and Bluetooth dongle?
  • Specification is divided in two
    • Part 1 the core defines the Bluetooth interfaces and protocols
    • Part 2 consists of profiles
      • Profiles define what features has to be supported on certain types of applications
  • Full protocol stack from link to application layer.
  • HCI is the interface used to communicate with Bluetooth hardware
  • Newer BNEP protocol can be used instead of RFCOMM and PPP under IP
  • The way to use these protocols on different types of products is defined in profiles
  • On what layer you should start creating your application?
  • Profiles goal is to guarantee interoperability
    • Generic access profile has to be followed by all products
    • Service discovery application profile defines the service discovery process
    • Serial port defines the use of RFCOMM
  • Some New profiles
    • Extended service discovery to enhance the service discovery process
    • PAN profile for use of BNEP
    • SIM profile for use of SIM card
    • Remote Control Profile, video /audio profiles…

Connectivity with Bluetooth

  • The connection forming between two devices consist of 3 steps

1. Device discovery (Inquiry)

  • The initiator sends inquiry messages in order to find devices in it's proximity
  • Devices in discoverable mode reply with their BD ADDR
  • Inquiry in Bluetooth 1.1 takes 10.24 seconds and still might not find all devices on proximity (~90% success)
    • shorter time in inquiry adds unreliability
  • Enhanced inquiry in Bluetooth 1.2 requires maximum of 5 seconds and is almost 100% reliable
    • 10 seconds is often used for inquiry due the compatibility reasons
  • Interlaced inquiry scan in Bluetooth 1.2 speeds up the discovery process by 2x to a maximum of 2.5 seconds
    • Requires more power
    • Is not supported by all devices

2. Connecting devices (paging)

  • The initiator pages the device it wants to connect at (BD ADDR)
    • BD ADDR can be the one fetched by inquiry or provided by user or fetched from database
  • Takea average of 1.28 seconds and maximum of 2.56 seconds
  • Interlaced page scan of Bluetooth 1.2 halves the time
    • Requires more power
    • Is not supported by all devices

3. Service discovery

  • Service Discovery protocol is used to discover the capabilities of the device that the basic data connection is formed at.
  • More information at the service discovery lecture
  • Specification gives no roaming support
    • Access point vendors have some own roaming allowing solutions.
    • Create your own roaming system?
  • Want to create Bluetooth games?
Last modified: 2013/07/01 14:41