This question appears in Mumbai University > Mobile Communication and Computing subject

Marks: 10 M

Year: May 2015

• 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

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

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

1. A 4-bit preamble.
2. 64- bit synchronization field.
3. 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 | | ARQN | 1-bit | ARQN stands for,acknowledgement number and SEQN stands for sequence number. They are used for,packet acknowledgement purposes. | | SEQN | 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 |

Payload:

• 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:

1. Synchronous Connection Oriented (SCO):
2. Used for supporting symmetrical, point-to-point, and circuit-switched connection which are meant for voice transmissions.

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

4. Asynchronous Connection-less (ACL):

5. These links are used for bursty data transmissions
6. It supports packet switched, symmetrical and asymmetrical conditions.