What is Baseband?

The Baseband is the layer that controls the radio. The frequency

hop sequences are provided by this layer. Baseband also takes care

of lower level encryption for secure links. The packet handling

over the wireless link is the responsibility of Baseband.

Two types of links can be established:

SCO: Synchronous Connection Oriented. These links are meant

for synchronous data typically voice.

ACL: Asynchronous Connection less. These links may be used for data transfer applications, which do not require a synchronous link.

The Baseband provides the functionalities required for devices

to synchronize their clocks and establish connections. Inquiry

procedures for discovering the addresses of devices in proximity are

also provided. Error correction for packets is provided depending on

the type of packet. Various packet types are specified for some

common applications, differing in their data capacity and error

correction overheads. Five different channel types are provided for

control information, link management information, user synchronous

data, user asynchronous data and isosynchronous data. Data whitening

is also carried out at this layer. The functions required for generating

encryption keys and link keys are defined. A more detailed description

of some of the baseband operations related to connection

establishment is provided in the next section: Establishing a

connection in Bluetooth.