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.