Explain functioning of Bluetooth baseband layer.

Mumbai University > Computer Engineering > Sem6 > Mobile Communication and Computing

Marks: 10M

Year: May 2015

2 Answers
  • Bluetooth is a universal radio interface operating in the ISM band.

  • It provides ad-hoc wireless connectivity between portable electronic devices located at a short range from each other.

  • The Bluetooth protocol stack contains various layers like radio layer, baseband layer, L2CAP layer etc. Let’s discuss the baseband layer in depth:

  • The following figure describes the components of a Bluetooth packet at baseband layer.

  • The baseband is the digital engine of a Bluetooth system. It is responsible for

    • constructing and decoding packets,
    • encoding and managing error correction,
    • encrypting and decrypting for secure communications,
    • calculating radio transmission frequency patterns,
    • maintaining synchronization,
    • controlling the radio,
    • All of the other low level details necessary to realize Bluetooth communications.

enter image description here

Access code:

  • This field is needed for timing synchronization and piconet identification
  • The access code is unique to a frequency hopping (FH) channel and also to a piconet.
  • It may also contain special codes during paging activity or during inquiry.
  • A station listens tp the access code of a packet it has just received and checks if the packet has been sent by a station belonging to the same piconet.
  • If not the, the rest of the packet is ignored.
  • An access code consist of

    • A 4-bit preamble.
    • 64- bit synchronization field.
    • 4-bit trailer (optional-used if a packet header is attached)

Packet header:

  • The header is a packet field which follows the access code field. Some of the fields it contains are :
AM address 3-bit Also called as Active Member address, it represents the active address of the slaves which are assigned temporarily in a piconet. It’s a 3-bit value
Type 4-bit It determines the type of packet. It is based on the type of connection (seen in Payload section) the applied coding rate, symmetry/asymmetry of connection.
Flow 1-bit Its meant to implement a flow control mechanism.
If flow=0 ; Asynchronous data → Stop flow of data
If flow=1 ; Synchronous data → Resume the flow
1-bit 1-bit ARQN stands for acknowledgement number and SEQN stands for sequence number. They are used for packet acknowledgement purposes.
HEC 8-bit The Header Error Check (HEC) is used to protect the packet header


  • Upto 343 bytes of payload data can be transferred via a single packet.

  • A basic requirement for Bluetooth was to provide both voice as well as data transmission facility.

  • Depending on the requirement (i.e. voice or data ) we classify the links into two which are:

  • Synchronous Connection Oriented (SCO):

    • Used for supporting symmetrical, point-to-point, and circuit-switched connection which are meant for voice transmissions.

    • They are realized by reserving two slots at fixed slots intervals for forward and reverse transmission.

  • Asynchronous Connection-less (ACL):

    • These links are used for bursty data transmissions

    • It supports packet switched, symmetrical and asymmetrical conditions.

Please log in to add an answer.