*Bluetooth is a wireless low power technology for short
range, point to point and point to multi point voice and
data transfer using radio transmission.
*It was developed at 1994 at Ericsson in Sweden.
*Originally it was build to eliminate the need for cable
connections between PDAs and notebook PCs. Later the
goals were to enable different devices through a commonly
accepted standard for wireless connectivity.
*It operates on 2.45 GHz radio signals and has an effective
range of 10 metres.
*Devices need not be pointing towards each other, as signals
It is mainly based on the IEEE 802.15 standard. Unlike other
wireless standards, the Bluetooth Core Specification provides
product developers both link layer and application layer
definitions, which support data and voice applications.
The IEEE 802.11communications standard defines the protocol
for two types of networks; Ad-hoc and client/server.
The Ad-hoc network is a simple network where
communications are established between multiple stations in a
given coverage area without the use of an access point or
server. The 802.11- standard specifies the etiquette that each
station must observe so that all units have fair access to the
Bluetooth technology operates in the unlicensed industrial,
scientific and medical (ISM) band at 2.4 to 2.485 GHz, using
a spread spectrum, frequency hopping, full-duplex signal at
a nominal rate of 1600 hops/sec. The 2.4 GHz ISM band is
available and unlicensed in most countries.
Bluetooth technology's adaptive frequency hopping (AFH)
capability was designed to reduce interference between
wireless technologies sharing the 2.4 GHz spectrum. This is
done by the technology detecting other devices in the
spectrum and avoiding the frequencies they are using. The
devices hop randomly between frequencies up to 1600 times
per second. So, if another device using a 2.4 GHz frequency,
then the interference lasts only for about 1/1600 of a second.
By then, the devices hop to another frequency.
Range is application specific and although a minimum range is
mandated by the Core Specification, there is not a limit and
manufacturers can tune their implementation to support the
use case they are enabling.
Range may vary depending on class of radio used in an
• Class 3 radios – have a range of up to 1 meter or 3 feet.
• Class 2 radios – most commonly found in mobile devices –
have a range of 10 meters or 33 feet.
• Class 1 radios – used primarily in industrial use cases – have a
range of 100 meters or 300 feet
Bluetooth technology is designed to have very low power
consumption. This is reinforced in the specification by
allowing radios to be powered down when inactive.
The Power consumption based on various Bluetooth classes
• Class 1: Max Power – 100mW
• Class 2: Max Power – 2.5mW
• Class 3: Max Power – 1mW
*The two main topologies are: Piconet
Topology and Scatternet Topology.
•A piconet consists of upto 8 BWT
•When piconet is established, one
device sets up frequency-hopping
pattern and other devices synchr-
-onize their signals to the same
•Each piconet has a different
•Scatternet consists of several piconetsconnected by
devices participating inmultiple piconet.
• There is a ‘BRIDGE’ connecting 2piconets which is also
a slave individual piconets.
Advantages of Scatternet :
•Multi-hop connections between devices indifferent
• Responsible for the modulation and demodulation of data
into RF signals.
• The radio layer describes the physical characteristics a
Bluetooth device’s receiver-transmitter component must
• Responsible for channel coding and decoding.
• Digitizes the signals received by the radio for passing up the
• Formats the data it receives from the Link Controller
(upper protocol) for transmission over the channel.
• Responsible for establishing and maintaining the links
between Bluetooth units.
*The Link Manager Protocol (LMP)
• Handles link setup, authentication, link configuration and
• Establishes all connections with the help of baseband protocol.
*Host Controller Interface
• The Host Controller Interface (HCI) defines uniform methods for
accessing and controlling the lower layers of the protocol stack
(baseband and the link manager).
*Logical Link Control and Adaptation Protocol (L2CAP)
• Responsible for:
Establishing connections across existing ACL ( Asynchronous
Connection-oriented) links or requesting an ACL link if one does not
• Allow many different applications to use a single ACL link through
• Repackaging the data packets it receives from the higher layers
into the form expected by the lower layers.
Defines procedures for-
• Discovering services of other devices.
• Determining the characteristics of those services.
*Telephony Control ProtocolSpecification (TCS) defines call
• Control signaling for establishing speech and data calls
between Bluetooth devices, providing them with telephony
*Object Exchange Protocol
• Is a specification for Object data exchange over IR(InfraRed
• Examples for using OBEX include exchanging business cards
and synchronizing calendar applications.
*Bluetooth Networks use a master/slave model to control when
and where devices can send data.
In this model, a single master can be connected upto
seven different slave devices. Any slave device can only be
connected to a single master device.
The master can send data
to any of its slaves and request
data from them. But, slaves are
only allowed to transmit to and
receive from their master. They
are not even allowed to talk to
other slaves in the same
* All the slaves synchronize their clocks and hopping
sequences to that of the master. A Time Division Duplex (TDD)
scheme is used where master and slave alternatively
*The OSI Physical (PHY) layer is represented by the radio and
-The Radio is responsible for transmitting and receiving the
analog sinal upto a specified range depending upon the radio
-The Baseband is responsible for channel coding and decoding
and low level timing control and management of the link within
the domain of a single packet transfer.
-The Link Controller (LC) is responsible for carrying out link
level operations in response to higher level commands from the
Link Manager (LM). The LC will manage the process of
establishing a link once commanded by LM and will maintain the
link once established.
The Bluetooth uses a Bluetooth socket to transfer data
The socket transfers the data serially, which means one byte
at a time.
*Now let us discuss about the Bluetooth packet structure that
are used for communication over ACL links. The packets are
broken down into their constituent parts such as access code,
packet header, payload header, and payload. Each packet type
has a different level of error correction and protection and
different size payloads.
*The Access code is used to detect the presence of a packet and
to address the packet to a specific device. The header packet
contains control information associated with the packet such
as the address of the Slave for which the packet is intended.
Finally, the payload contains the message information.
*The Bluetooth modulation scheme is GFSK (Gaussian Frequency
Shift Keying) with a symbol rate of 1Ms/s and modulation index
between 0.28~0.35. The Gaussian-shaped, binary FSK
modulation minimizes transceiver complexity. Using positive
frequency deviation a binary one is represented while a binary
zero is represented by a negative frequency deviation.
*During one time slot the data can change value every 1us, so
the transmit frequency oscillates back and forth around the
channel center frequency. The minimum deviation can never
be smaller than 115kHz. Maximum frequency deviation is
between 140 kHz and 175 kHz.
*3 Types of Hardware is required to complete
the conversion, they are:
This device is used to convert digital signal to analog
signal. In this case when binary data arrives as input
of this device, it takes them as digital signal and
converts it as analog signal using some conversion
protocol(eg: NRZ,RZ,quadrant etc.)
II.Base Band Generator:
In this stage the converted analog signal is amplified to
the acceptable amplitude for transmission.
In this process:
Consider a carrier wave (sine wave) of frequency fc and
amplitude A given by:
c(t) = A.sin(2πfct),.
Let m(t) represent the modulation waveform. For this
example we shall take the modulation to be simply a sine
wave of a frequency fm, a much lower frequency (such as
an audio frequency) than fc:
m(t) = M.cos(2πfmt + Φ)
where M is the amplitude of the modulation. We
shall insist that M<1 so that (1+m(t)) is always
positive. Amplitude modulation results when the
carrier c(t) is multiplied by the positive quantity
y(t)= [1 + m(t)].c(t)
= [1 + M.cos(2πfmt + Φ)].A.sin(2πfct)
*Now that the signal is amplified to an
acceptable range, the radio transmits the
analog signal to the receiver device. Hence
the format of the raw data conversion is
*The technology of Bluetooth centers around a 9mm x 9mm
microchip, which functions as a low cost and short range
radio link. Bluetooth Technology provide a 10 meter
personal bubble that support simultaneous transmission of
both voice and data for multiple devices. Up to 8 devices
can be connected in a piconet, and up to 10 piconets can
exist within the 10 meter bubble.
*In order to establish new connections the procedures
inquiry and paging are used.
• INQUIRY- If two Bluetooth devices know absolutely nothing
about each other, then one must run a query to try to
discover the other, and any device listening for such a
request will respond with its address, and possibly its name
and other information.
• PAGING- Now, both the devices know each other’s addresses which
was found in the enquiry step. Now, Paging is done which is the
process of forming a connection between two bluetooth devices.
• After the connection has been established a device can be in any of
the four nodes:
oActive mode: In this mode, the device is actually transmitting or
oSniff mode: This is a power saving mode where the device is
sleeping and is only listening for transmission.
oHold mode: In this mode, a device can sleep for a defined period
and then returns back to active mode.
oPark node: It is the deepest sleep mode. A device enters this mode
when its master asks it to, and again wakes up, on its master’s
In order to obtain qualification of a component or product,
the manufacturer may use a test house for two services:
oThe test house is contracted to make tests to a Bluetooth test
specification, and to produce a test report containing the
results of the tests.
oAn employee of the test house who is appointed by the
Bluetooth SIG as a Bluetooth Qualification Body(BQB) reviews
evidence submitted by the manufacturer in a Compliance
Folder (CF), and if satisfactory, the BQB submits the product to
the Bluetooth Qualification Administrator(BQA) for listing on
the Bluetooth Qualified Products List (BQPL).
The list that follows gives more details on the tests necessary
oRF tests are required to made once for each new PCB design.
oUSB, UART or BCSP variants need not be retested for RF as the
HCI does not affect the radio performance.
oThe Bluetooth Qualification Body(BQB) may require one or
more BB timing tests to be repeated for each new PCB design.
oBoth module manufacturers and end product users can use a
software component that is prequalified at Baseband(BB) and
oIf the new design includes the upper layer stack components
or Bluetooth profiles, these must also be qualified.
oSoftware components affecting profiles must also be qualified.
This could be done by developing and qualifying your own
profile software components, or by buying in prequalified
software components and integrating them into the end
*It is possible to directly modulate analog signals into a
radio without converting them into digital format. Then
why we do not go for this?
There are several reasons:
-Digital signals tend to be more robust in the noisy
-Encoding into a digital format means easy error detection
and error correction.
Ofcourse in the case of Bluetooth wireless
technology, the baseband is designed to handle only digital
signals, so transmitting analog signals is not even an option.
Bluetooth specification forces a low data rate, so the
codecs are required to compress the signal as well as
convert them to digital from analog.
*Bluetooth uses either a 64 kb/s log PCM format (A-law or m-
law) or a 64 kb/s CVSD(Continuous Variable Slope Delta
Modulation) for audio transmission.
In any wireless networking setup, security is a concern.
Devices can easily grab radio waves out of the air, so people
who send sensitive information over a wireless connection
need to take precautions to make sure those signals aren't
intercepted. Bluetooth technology is no different
Bluetooth offers several security modes, and device
manufacturers determine which mode to include in a
Bluetooth-enabled gadget. In almost all cases, Bluetooth
users can establish "trusted devices" that can exchange data
without asking permission.
When any other device tries to establish a connection to the
user's gadget, the user has to decide to allow it. Service-
level security and device-level security work together to
protect Bluetooth devices from unauthorized data
transmission. Security methods include authorization and
identification procedures that limit the use of Bluetooth
services to the registered user and require that users make
a conscious decision to open a file or accept a data