Bluetooth
Presentation by
Dr. S. Radha, HOD/ ECE
SSN College of Engineering
Objective
The main objective of this session is to make
the students,
• Understand the Bluetooth which is a
wireless LAN technology, its architecture,
layers and frame formats.
BLUETOOTH
Bluetooth is a wireless LAN technology designed
to connect devices of different functions such as
telephones, notebooks, computers, cameras,
printers, coffee makers, and so on. A Bluetooth
LAN is an ad hoc network, which means that the
network is formed spontaneously.
Topics discussed in this section
Architecture
Bluetooth Layers
Baseband Layer
L2CAP
Bluetooth - Architecture
• Bluetooth defines two types of networks: piconet
and scatternet.
• Piconet
– Small net
– Can have up to eight stations
– One of the stations is called primary (master) and the
rest are secondaries (slave).
– One to one and one to many communication.
– Along with seven secondaries, additional eight
secondaries can be in the parked state.
Bluetooth - Architecture
• Scatternet
– Piconets are combined to form scatternets.
– A station can be a member of two piconets.
– A secondary station in one piconet can be a primary
in other piconet.
• Bluetooth devices
– built-in short range radio transmitter.
– Data rate is 1 Mbps.
– 2.4GHz bandwidth.
Piconet
Scatternet
Bluetooth - Layers
• Bluetooth uses several layers that do not exactly
match with those of the Internet model.
• Radio layer
– Roughly equivalent to the physical layer of the
Internet model.
– Range is limited to 10m and they are low power
devices.
• Band
– Uses 2.4GHz ISM band divided into 79 channels of
1MHz each.
Bluetooth - Layers
• FHSS
– Bluetooth uses the frequency hopping spread
spectrum method to avoid interference from other
networks.
– 1600 hops per second.
– A device uses a frequency for only 625 s.
• Modulation
– GFSK modulation
– GFSK uses a carrier frequency. Bit 1 is represented by
a deviation above the carrier and Bit 0 is represented
by a frequency below the carrier.
Bluetooth - Layers
• Modulation
– These frequencies are defined according to the
formula for each channel as,
fc = 2402 + n, n = 0,1,2………….78
• Baseband layer
– Roughly equivalent to the MAC sublayer in LANs.
– Access method is TDMA (using time slots).
– Length of the time slot is equal to the dwell time
(625s).
– During the time one frequency is used, a sender sends
a frame to the receiver.
Bluetooth layers
Bluetooth - Layers
• TDMA
– Bluetooth uses TDD-TDMA, which is a kind of half
duplex communication.
– Communication for each direction uses different
hops.
– If a piconet has a single secondary, TDMA operation
is simple.
– Time is divided into 625s slots.
– Primary communicate in even numbered slots and
secondary in odd numbered slots.
Single-secondary communication
Multiple-secondary communication
Bluetooth - Layers
• Physical links
– Two types of links can be created between primary
and secondary namely, SCO links and ACL links.
• SCO
– Synchronous connection oriented link.
– Used when avoiding latency is more important than
integrity
– Physical link is created between primary and
secondary by reserving specific slots at regular
intervals.
– No retransmission in case of packet damage.
– Used for real time audio
Bluetooth - Layers
• ACL
– Asynchronous connectionless link.
– Used when data integrity is more important than
delay.
– Retransmission takes place in case of corrupted
package.
– Maximum data rate is 721 kbps.
Bluetooth - Layers
• Frame format
– Three types : one-slot, three-slot and five-slot.
– A slot is 625 s. In that, 259 s is needed for hopping
and control mechanisms.
– Then one-slot frame lasts only for 366 s. With 1MHz
Bandwidth and 1 bit/Hz, the size of a one-slot frame
is 366 bits.
– Size of a three-slot frame is 1616 bits.
– Size of a five-slot frame is 2866 bits.
Bluetooth - Layers
• Access code
– 72 bit field, contains synchronization bits and the
identifier of the primary to distinguish the frame of
one piconet from another.
• Header
– Address : three bit subfield can define upto seven
secondaries. Bits 000 indicates broadcast.
– Type : defines the type of data coming from the upper
layers.
– F : 1 bit subfield for flow control. When set to 1, it
indicates that the device is unable to receive more
frames (buffer is full).
Bluetooth - Layers
• Header
– A : 1 bit subfield used for acknowledgement.
Bluetooth uses stop and wait ARQ.
– S : 1 bit subfield holds a sequence number.
– HEC : 8 bit header error correction is a checksum to
detect errors in each 18 bit header section.
– Payload : data from upper layers.
Frame format types
Bluetooth - Layers
• L2CAP
– Logical Link Control and Adaptation Protocol is
roughly equivalent to LLC sublayer in LANs.
– Used for data exchange on an ACL link.
– L2CAP frame contains a 16 bit length field which
defines the size of the data coming from the upper
layer, a channel ID field which defines a unique
identifier for the virtual channel created at this level
and the payload.
– The functions of L2CAP include multiplexing,
segmentation and reassembly, QoS and group
management.
L2CAP data packet format
Summary
• Bluetooth is a wireless LAN technology that
connects devices (called gadgets) in a small area.
• A Bluetooth network is called a piconet.
Multiple piconets form a scatternet.
• A Bluetooth network consists of one primary
and up to seven secondaries.
• Bluetooth layers are radio layer, baseband layer,
L2CAP layer and upper layers.
• Bluetooth used FHSS and GFSK modulation.
• Access method is TDD – TDMA.
• Phsyical links can be SCO or ACL links.