/ Bluetooth

Bluetooth protocol cheat sheet

This is a very simplified summary of the bluetooth protocol. Useful for quick reference.

Physical layer:

Modes

There are 4 modes for Bluetooth. Mainly :

  • BR 1Mbps (Basic Rate) :
    • GFSK
    • Peak to average : 0dB
    • Can support saturation (since FSK can be received with saturation detectors).
  • EDR 2Mbps (pi/4 DQPSK)
    • DQPSK
  • EDR 3Mbps (pi/8 D8PSK)
    • Peak to average : ~3.5dB
  • LE 1Mbps:
    • GFSK
  • LE 2Mbps:
    • GFSK
  • LE Long-Range: Achieved by using strong FEC.

Channel Bandwitdh:

  • 1MHz channels (2402 to 2480 MHz):
    • BR (GFSK)
    • EDR (DQPSK, D8PSK)
  • 2MHz channels. Total of 40 2MHz channels.
    • LE

Time/frequency characteristics:

  • Bluetooth is a TDMA system. It has predetermined time when a packet will be sent.

  • There are 1600 slots per seconds (1 slot = 625us). A data packet can be either 1 slot or 5 slots.

  • Symbol rate is 1Msps (Mega symbol per seconds). Irrespective of the modulation rate. For example D8PSK has 3 bits per symbol.

  • Bluetooth hops over 78 frequencies.

  • Bandwitdh is 1MHz.

Link manager:

Connection:

  • Inquiry = Discovery.
    • Master finds other device with Inquiry.
  • Paging = Connection
    • Master then connects to device with Paging.
  • Piconet :
    • 1 Master
    • Up to 7 active slaves
    • Up to 255 parked devices

BT Addresses:

Each bluetooth address contains 48 bits.

  • NAP
    • 16 bits
  • UAP
    • 8 bits
  • LAP
    • 24 bits
  • NAP & UAP are assigned by IEEE
  • LAP is assigned by the manufacturer

Bluetooth Stack:

BTStack

Bluetooth Mesh:

A new feature is Bluetooth Mesh. It allows many-to-many device communication. It will allow up to 32767 Nodes in a single mesh.
Here is more details on the mesh specification.

References:
[1] : http://www.dziwior.org
[2] : Bluetooth Specification Core 5
[3] : Bluetooth Long Range
[4] : Bluetooth mesh