WHAT IS BLUETOOTH?
Bluetooth is a method for data communication that uses short-range radio links to replace
cables between computers and their connected units. Many companies have been mulling over this
idea, but it was Ericsson Mobile Communication that finally (in 1994) started the project that was
named Bluetooth. In 1998, 5 industrial giants (ERICSSON, NOKIA, IBM, TOSHIBA, INTEL) joined
hands to create such a technology. Thus emerged the BLUETOOTH technology.
Fig: Bluetooth operation
Bluetooth wireless technology is a short-range radio technology. Bluetooth wireless
technology makes it possible to transmit signals over short distances between telephones, computers
and other devices and thereby simplify communication and synchronization between devices. It is a
global standard that:
• Eliminates wires and cables between both stationary and mobile devices
• Facilitates both data and voice communication
• Offers the possibility of ad-hoc networks and delivers the ultimate synchronicity
between all the devices.
The Bluetooth wireless technology comprises hardware, software and interoperability
requirements. Beyond unleashing devices by replacing cables, Bluetooth wireless technology provides
a universal bridge to existing data networks, a peripheral interface, and a mechanism to form small
private ad hoc groupings of connected devices away from fixed network infrastructures. Bluetooth
radio uses a fast acknowledgement and frequency-hopping scheme to make the link robust, even in
noisy radio environments.
WHY IT IS CALLED BLUETOOTH?
Harald Bluetooth was king of Denmark in the late 900s. He managed to unite Denmark and
part of Norway into a single kingdom & then introduced Christianity into Denmark. He left a large
monument, the Jelling rune stone, in memory of his parents. He was killed in 986 during a battle with
his son, Svend Forkbeard. Choosing this name for the standard indicates how important companies
from the Baltic region (nations including Denmark, Sweden, Norway and Finland) are to the
communications industry, even if it says little about the way the technology works.
Bluetooth is a standard developed by a group of electronics manufacturers that allow any sort
of electronic equipment -- from computers and cell phones to keyboards and headphones -- to make its
own connections, without wires, cables or any direct action from a user. Bluetooth is intended to be a
standard that works at two levels:
It provides agreement at the physical level -- Bluetooth is a radio frequency standard.
It also provides agreement at the next level up, where products have to agree on when bits are
sent, how many will be sent at a time and how the parties in a conversation can be sure that the
message received is the same as the message sent.
The companies belonging to the Bluetooth Special Interest Group, and there are more than 1,000 of
them, want to let Bluetooth's radio communications take the place of wires for connecting peripherals,
telephones and computers.
Photo courtesy Bluetooth SIG
fig: Bluetooth wireless PC card
OTHER WIRELESS CONNECTIONS
There are already a couple of ways to get around using wires. One is to carry information
between components via beams of light in the infrared spectrum. Infrared refers to light waves of a
lower frequency than human eyes can receive and interpret. Infrared is used in most television remote
control systems, and with a standard called IrDA (Infrared Data Association) it's used to connect some
computers with peripheral devices. For most of these computer and entertainment purposes, infrared is
used in a digital mode -- the signal is pulsed on and off very quickly to send data from one point to
Infrared communications are fairly reliable and don't cost very much to build into a device, but
there are a couple of drawbacks. First, infrared is a line of sight technology. For example, you have
to point the remote control at the television or DVD player to make things happen. The second
drawback is that infrared is almost always a one to one technology. You can send data between your
desktop computer and your laptop computer, but not your laptop computer and your PDA at the same
These two qualities of infrared are actually advantageous in some regards. Because infrared
transmitters and receivers have to be lined up with each other, interference between devices is
uncommon. The one-to-one nature of infrared communications is useful in that you can make sure a
message goes only to the intended recipient, even in a room full of infrared receivers.
The second alternative to wires, cable synchronizing, is a little more troublesome than
infrared .In synchronizing, you attach the PDA to your computer (usually with a cable), press a button
and make sure that the data on the PDA and the data on the computer match. It's a technique that
makes the PDA a valuable tool for many people, but synchronizing the PDA with the computer and
making sure you have the correct cable or cradle to connect the two can be a real hassle.
NEED FOR BLUETOOTH
As computerized implementations have grown and become increasingly more common in our
environment, there has also been a growing need for cables of varying kinds, to tie all these units
together and ensure communication between them. These cables, when they grow into a multitude, are
not only unsightly but also increasingly cumbersome to handle, both directly and (even more so)
indirectly. Thus bluetooth is the technology that owes the solution to this problem.
Fig: Cumbersome cable network
When any two devices need to talk to each other, they have to agree on a number of points
before the conversation can begin. The first point of agreement is physical:
Will they talk over wires, or through some form of wireless signals? If they use wires, how
many are required -- one, two, eight, 25? Once the physical attributes are decided, several more
Information can be sent 1 bit at a time in a scheme called serial communications, or in groups
of bits (usually 8 or 16 at a time) in a scheme called parallel communications. A desktop
computer uses both serial and parallel communications to talk to different devices: Modems,
mice and keyboards tend to talk through serial links, while printers tend to use parallel links.
All of the parties in an electronic discussion need to know what the bits mean and whether the
message they receive is the same message that was sent. In most cases, this means developing
a language of commands and responses known as a protocol. Some types of products have a
standard protocol used by virtually all companies so that the commands for one product will
tend to have the same effect on another. Modems fall into this category. Other product types
each speak their own language, which means that commands intended for one specific product
will seem gibberish if received by another. Printers are like this, with multiple standards like
PCL and PostScript.
Companies that manufacture computers, entertainment systems and other electronic devices
have realized that the incredible array of cables and connectors involved in their products makes it
difficult for even expert technicians to correctly set up a complete system on the first try. Setting up
computers and home entertainment systems becomes terrifically complicated when the person buying
the equipment has to learn and remember all the details to connect all the parts. In order to make home
electronics more user friendly, we need a better way for all the electronic parts of our modern life to
talk to each other. That's where Bluetooth comes in.
Bluetooth is intended to get around the problems that come with both infrared and cable
synchronizing systems. The hardware vendors, developed a specification for a very small radio module
to be built into computer, telephone and entertainment equipment. From the user's point of view, there
are three important features to Bluetooth:
Fig: Bluetooth enabled system
It's wireless. When you travel, you don't have to worry about keeping track of a briefcase full
of cables to attach all of your components, and you can design your office without wondering
where all the wires will go.
You don't have to think about it. Bluetooth doesn't require you to do anything special to
make it work. The devices find one another and strike up a conversation without any user input
AIM OF BLUETOOTH
The aim has been set quite high. It is to arrive at a specification for a technology that optimizes
the usage model of all mobile computing and communications devices, and providing:
Voice and data handling
The ability to establish ad-hoc connections
The ability to withstand interference from other sources in open band
Very small size, in order to accommodate integration into variety of devices
Negligible power consumption in comparison to other devices for similar use
An open interface standard
Competitively low cost of all units, as compared to their non-Bluetooth correspondents.
HOW COULD BLUETOOTH BE USED
What could be the practical use of Bluetooth? Well, it´s very much up to our imagination. But
the ambition is set high, indeed; practically all computerized equipment normally found in a modern
office (and home) which do not use a synchronous communications protocol could be adapted for use
Phones and pagers
LAN access devices
Desktop and handheld computers
Virtually any digital device can be part of the Bluetooth system. Bluetooth radio technology
can also provide a universal bridge to existing data networks, a peripheral interface, and a mechanism
to form small ad hoc groupings of connected devices, away from fixed network infrastructures.
1. A Bluetooth-mouse could be used at a further distance from a monitor, and while moving
about in the room.
2. A Bluetooth-keyboard could be used further away from the monitor. This would reduce
eyestrain for persons who are long-sighted. Increasing the distance would also reduce exposure
to electromagnetic radiation from the monitor.
Fig: Bluetooth in operation
3. A Bluetooth-keyboard could also be used to address more than one computer, in a dynamic,
switch less manner.
4. Use e-mail while your portable PC is still in the briefcase! When your portable PC receives an
e-mail, you'll get an alert on your mobile phone. You can also browse all incoming e-mails and
read those you select in the mobile phone's display.
5. A traveling businessman could ask his laptop computer to locate a suitable printer as soon as
he enters a hotel lobby, and send a printout to that printer when it has been found, and replied
in a positive manner.
6. Cable-less connection to printers and faxes.
7. Cable-less connection to digital cameras and video projectors.
8. Cordless connection from cell phone to hands free headset.
9. Dial-up networking and automatic e-mail.
10. Use cell phone as office cordless phone
FEATURES OF BLUETOOTH
The term Bluetooth refers to an open specification for a technology to enable short-range
wireless voice and data communications anywhere in the world. This simple and straightforward
description of the Bluetooth technology includes several points that are key to its understanding:
The Bluetooth Special Interest Group (SIG) has produced a specification for Bluetooth wireless
communication that is publicly available and royalty free. To help foster widespread acceptance of the
technology, a truly open specification has been a fundamental objective of the SIG since its formation.
There are many instances of short-range digital communication among computing and
communications devices; today much of that communication takes place over cables. These cables
connect to a multitude of devices using a wide variety of connectors with many combinations of
shapes, sizes and number of pins; this plethora of cables can become quite burdensome to users. With
Bluetooth technology, these devices can communicate without wires over a single air-interface, using
radio waves to transmit and receive data. Bluetooth wireless technology is specifically designed for
short-range (nominally 10 meters) communications; one result of this design is very low power
consumption, making the technology well suited for use with small, portable personal devices that
typically are powered by batteries.
Voice and data:
Traditional lines between computing and communications environments are continually
becoming less distinct. Voice is now commonly transmitted and stored in digital formats. Voice
appliances such as mobile telephones are also used for data applications such as information access or
browsing. Through voice recognition, computers can be controlled by voice, and through voice
synthesis, computers can produce audio output in addition to visual output. Some wireless
communication technologies are designed to carry only voice; others handle only data traffic.
Bluetooth wireless communication makes provisions for both voice and data, and thus it is an ideal
technology for unifying these worlds by enabling all sorts of devices to communicate using either or
both of these content types.
Anywhere in the world:
The telecommunications industry is highly regulated in many parts of the world. Telephone
systems, for example, must comply with many governmental restrictions, and telephony standards vary
Many forms of wireless communications are also regulated; radio frequency spectrum usage
often requires a license with strict transmission power obligations. However, some portions of the
available radio frequency spectrum may be used without license, and Bluetooth wireless
communications operate within a chosen frequency spectrum that is unlicensed throughout the world.
Thus devices that employ Bluetooth wireless communication can be used unmodified, no matter where
a person might be. The Bluetooth short-range wireless technology is ideally suited for replacing the
many cables that are associated with today's pervasive devices. The Bluetooth specification, (hereafter
referred to as the specification) explicitly defines a means for wireless transports to replace serial
cables, such as those used with modems, digital cameras and personal digital assistants; the technology
could also be used to replace other cables, such as those associated with computer peripherals
(including printers, scanners, keyboards, mice and others). Moreover, wireless connectivity among a
plethora of fixed and mobile devices can enable many other new and exciting usage scenarios beyond
simple cable replacement.
There are certain BLUETOOTH specifications.
It defines all layers of bluetooth protocol stack
A) Radio Front End(RF)
It is the lowest layer .Its specification defines the characteristics of the RF, frequency bands,
channel arrangements, and receiver sensitivity level.
Radio front (RF): Bluetooth operates in 2.24 GHZ ISM band. Europe and US allocate 83.5
MHz to this band but France, Spain and Japan allocate less. To accommodate these differences 79 RF
channels spread 1MHz are defined for Europe and US and 23 RF channels spread 1MHz are defined
for Spain, France and Japan. The radio hops through the full spectrum of 79 or 23 RF channels using
random hopping sequence. It has a hopping rate of 1600 bps, which prevents it from interference from
B) Logical Link Control And Adaptation Protocol (L2CAP)
L2CAP is the link layer of BLUETOOTH .The base band protocol is small for transporting
bigger data products to higher layers. Therefore the BLUETOOTH SIG defined L2CAP. The L2CAP
makes 2 assumptions, which significantly simplify the segmentation, and optimizes the L2CAP to
work in conjunction with the BASEBAND layer.
The different high layer protocols are differentiated by carrying them in different channels . L2CAP
channels are connection oriented because they require an explicit phase to establish the channel during
which both ends choose a local name and communicate it to the other end. Afterwards each packet
send over the channels contains a channel identifier which identifies the source as well as the protocol
which is being transported.
C) Service Discovery Protocol (SDP)
There must be a compatible set of protocols and applications on both devices to enable data
flow between them. Such setting may require adjustments to match the features and services provided
by the PEER BLUETOOTH device. SDP provides a standard way to a BLUETOOTH device to query
and discover services supported by the PEER BLUETOOTH device .The server maintains a list of
services provided by it. SDP query helps a client browse all the available records maintained at the
In addition the SDP specifications provide the standard way of describing service attributes.
These are represented as <identifier, value> pair. The developers of BLUETOOTH have the freedom
to define new sections of standard services or to create new ones. But since such services don’t require
any coordination with BLUETOOTH SIG numbering AUTHORITY, it is essential that two
independent services don’t conflict .To prevent such a clash there exist universally unique identifier
(UUID) which is generated at the time of services defined which are then included in the assigned
The client browses the list of available services and select from the list. There are 2 search
options supported by SDP which has 2 advantages over other IP based SDPs.
1. It is optimized to work with L2CAP.
2 Since most BLUETOOTH devices are non-IP devices they don’t support IP addressing
SDP provide the mechanism only for retrieving service information from other devices, but
invoking these services is outside its scope.
D) Link Manager Protocol (LMP)
Before two BLUETOOTH devices establish the L2CAP channel the link manager has to carry certain
base band specific actions which include PICONET, master slave role assignments and link
configuration .For these operations the link manager has to exchange LMP messages over the air link.
Security can also be configured using the LMP messages. The devices should authenticate
themselves before a voice or data transfer can take place. Also the transmitted data is in encrypted
form. This is possible when there exists a security association between the devices .The LMP uses a
shared secret key to verify the peer device’s authenticity. Only after the successful LMP handshake
further data exchange or voice communication takes place.
There is also a method called pairing defined by the base band specifications. This means
creating a security association using an out of band channel, which is then used as a seed to compute a
secure, shared secret key.
RFCOMM is layered on top of the L2CAP. As a ‘cable replacement’ protocol, RFCOMM
provides transport capabilities for high-level services (e.g. OBEX protocol) that use serial line as the
Fig: Bluetooth Chips
BLUETOOTH is unique in offering the front end RF processing integrated with the BASE BAND
MODULE .On chip integration lowers the cost of network interface ,and the small size makes it easy
to embed BLUETOOTH chips in devices such as cell phones etc. A BLUETOOTH chip can be
connected to its host processor using USB , UART, or PC interface cards . The Bluetooth technology
is quite complex. This is not so surprising, considering the task it has to handle. It is mainly based on
the IEEE 802.11 standard . Bluetooth uses the ad-hoc mode. This means that each station must
observe netiquette and give all other units fair access to the wireless media.
With today´s technology, the transmitter/receiver-part for Bluetooth´s requirements could be
made as small as a thumbnail (!!), and the antenna could be more or less hidden in the unit, much as it
is in mobile telephones. Thus, the connectors in corresponding older units would not be replaced by
something of similar dimensions; the transceiver would just disappear among other circuits.
One could say that there are 3 types of connections in Bluetooth, as shown:
Multi-slave (up to 7 ”slaves” on one master)
Fig: Connections in Bluetooth
A set of BLUETOOTH devices sharing a common channel is called a PICONET. It is a star
shaped configuration in which the device at the center is a MASTER and other acts as a SLAVE. Up to
7 slaves can be active and served simultaneously. To serve more then 7 slaves, they are switched to
LOW POWER MODE and then making other slaves to be active. When many group of devices are
needed to be active simultaneously each group can form a separate PICONET with their own
Piconet can also be called as a collection of devices connected via Bluetooth technology in an
ad hoc fashion. A piconet starts with two connected devices, such as a portable PC and a mobile
phone. The limit is set at 8 units in a piconet (that´s why the required address-space is limited to 3
bits). All Bluetooth devices are peer units and have identical implementations. However, when
establishing a piconet, one unit will act as a master for synchronization purposes, and the other unit(s)
will be slave(s) for the duration of the piconet connection.
This is a phenomena by which more than one PICONET communicate with each other .It is
formed by inter connecting multiple PICONETS. The connection is made by bridge nodes, which
participate in each PICONET on time-sharing basis. Hence by cycling through all member
PICONETS, the bridge node can send and receive packets in each PICONETS and also forward them
to other PICONETS. Bridge node can act as a slave in both PICONET or a MASTER in one and
SLAVE in other.
Scatter nets are two or more independent and non-synchronized Piconets that communicate with
each other. A slave as well as a master unit in one piconet can establish this connection by becoming a
slave in the other piconet. It will then relay communications between the piconets, if the need arises.
The device in a piconet whose clock and hopping sequence are used to synchronize all other
devices in the piconet. The master also numbers the communication channels.
Fig: Slave Units
All devices in a piconet that are not the master (up to 7 active units for each master).
INQUIRY & PAGING-
INQUIRY is a procedure used by BLUETOOTH for discovering other devices, whereas it uses
PAGING to establish connection with them. In order to establish new connections the procedures
inquiry and paging are used.
The inquiry procedure enables a unit to discover which units are in range, and what their
device addresses and clocks are. With the paging procedure, an actual connection can be established.
Only the Bluetooth device address is required to set up a connection. Knowledge about the clock will
accelerate the setup procedure. A unit that establishes a connection will carry out a page procedure and
will automatically become the master of the connection.
For the paging process, several paging schemes can be applied. There is one mandatory paging
scheme, which has to be supported by each Bluetooth device. This mandatory scheme is used when
units meet for the first time, and in case the paging process directly follows the inquiry process. Two
units, once connected using a mandatory paging/scanning scheme, may agree on an optional
THE CONNECTION ESTABLISMENT
Fig: Connection Establishment
After the paging procedure, the master must poll the slave by sending POLL or NULL packets,
to which the slave responds. LMP procedures that do not require any interactions between the LM and
the host at the paged unit’s side can then be carried out. When the paging device wishes to create a
connection involving layers above LM, it sends LMP_host_connection_req. When the other side
receives this message, the host is informed about the incoming connection. The remote device can
accept or reject the connection request by sending LMP_accepted or LMP_not_accepted.
When a device does not require any further link set-up procedures, it will send
LMP_setup_complete. The device will still respond to requests from the other device. When the other
device is also ready with link set-up, it will send LMP_setup_complete. After this, the first packet on a
logical channel different from LMP can then be transmitted.
CREATION OF A SCATTERNET
Fig: Creation of Scatternet
A Master or Slave can become Slave in another piconet by being paged by the Master in this
other piconet. This automatically means that any unit can create a new piconet by paging a unit that is
already a member of a piconet. Any unit participating in one piconet can page the Master or Slave in
another piconet. This could lead to a switch of roles between Master and Slave in this new connection.
Inter-piconet communications are established over the shared unit. Time multiplexing must be
used for that unit to switch between piconets. In case of ACL links, a unit can request to enter the
HOLD or PARK mode in the current piconet, during which time in may join another piconet by just
changing the channel parameters Units in the SNIFF mode may have sufficient time to visit another
piconet in between the sniff slots. If SCO links are established, other piconets can only be visited in
the non-reserved slots in-between.
2 types of physical links are defined:
SCO (Synchronous Connection-Oriented)
ACL (Asynchronous Connection-Less)
The SCO link is point-to-point between master and slave. The master maintains the link by
using reserved timeslots at regular intervals. Packet retransmissions are not allowed. ACL provides
packet-switched connections between the master and all active slaves. Packet retransmissions are
usually applied to assure data integrity.
WORKING OF BLUETOOTH
Fig: Frequency Hopping in time slots
Bluetooth uses frequency hopping in timeslots. Bluetooth has been designed to operate in noisy radio
frequency environments, and uses a fast acknowledgement and a frequency-hopping scheme to make
the communications link robust, communication-wise. Bluetooth radio modules avoid interference
from other signals by hopping to a new frequency after transmitting or receiving a packet. Compared
with other systems operating in the same frequency band, the Bluetooth radio typically hops faster and
uses shorter packets. This is because short packages and fast hopping limit the impact of microwave
ovens and other sources of disturbances. Use of Forward Error Correction (FEC) limits the impact
of random noise on long-distance links.
Two transmission power levels
The Bluetooth radio is built into a small microchip and operates in a globally available
frequency band ensuring communication compatibility worldwide. The Bluetooth specification has
two power levels defined;
a lower power level that covers the shorter personal area within a room, and
a higher power level that can cover a medium range, such as within a home.
Software controls and identity coding built into each microchip ensure that only those units preset
by their owners can communicate.
One thing that can be noted is that, although Bluetooth works in an ad-hoc fashion (and not
server-based) all communication is done vis-à-vis the Master unit. There is no direct communication
between slave units.
Nor is it intended for the Master to route messages between slave units. Rather, if slave units
find that they want to talk directly to each other, they would form a new piconet, with one of them
acting as Master. This does not mean that they have to leave the previous piconet. More likely, they
will be parked in the old net unless they decide to quit the old net altogether. This is not a big
decision for the slave units; reconfiguration in Bluetooth is dynamic and very fast.
The Bluetooth baseband protocol is a combination of circuit and packet switching. Time slots
can be reserved for synchronous packets. A frequency hop is done for each packet that is transmitted.
A packet nominally covers a single time slot, but can be extended to cover up to five slots.
Bluetooth can support;
an asynchronous data channel, or
up to 3 simultaneous synchronous voice channels, or
a channel which simultaneously supports asynchronous data and synchronous voice.
NETWORK FORMATION AND CONTROL
Fig: The Network
Bluetooth supports both point-to-point and point-to- multi-point connections. Several piconets
can be established and linked together ad hoc, where each piconet is identified by a different frequency
hopping sequence. All users participating on the same piconet are synchronized to this hopping
sequence. Before any connections in a piconet are created, all devices are in STANDBY mode. In this
mode, an unconnected unit periodically listens for messages every 1.28 seconds. Each time a device
wakes up, it listens on a set of 32 hop frequencies defined for that unit. The number of hop frequencies
varies in different geographic regions; 32 is the number for most countries.
The connection procedure for a non-existent piconet is initiated by any of the devices, which
then becomes master of the piconet thus created. A connection is made by a PAGE message being sent
if the address is already known, or by an INQUIRY message followed by a subsequent PAGE
message if the address is unknown.
The INQUIRY message is typically used for finding Bluetooth devices, including public
printers, fax machines and similar devices with an unknown address. The INQUIRY message is very
similar to the page message, but may require one additional train period to collect all the responses.
A power saving mode can be used for connected units in a piconet if no data needs to be
transmitted. The master unit can put slave units into HOLD mode, where only an internal timer is
running. Slave units can also demand to be put into HOLD mode. Data transfer restarts instantly when
units transition out of HOLD mode. The HOLD is used when connecting several piconets or managing
a low power device such as a temperature sensor. In the SNIFF mode, a slave device listens to the
piconet at reduced rate, thus reducing its duty cycle. The SNIFF interval is programmable and
depends on the application. In the PARK mode, a device is still synchronized to the piconet but does
not participate in the traffic. Parked devices have given up their MAC address and occasionally listen
to the traffic of the master to re-synchronize and check on broadcast messages.
BLUETOOTH OPERATIONAL STATES
The Connecting State is transitory, but the other three have no limit to their duration. The
sniffing corresponds to the Inquiry exchange, where the Master looks for a unit to which it does not
have the address. The search criteria in such a case would be certain attributes, such as looking for a
laser writer that can handle post-script or the like.
Fig: The operational states
LETTIN G MASTER AND SLAVE TRADE PLACES
In principle, the unit that creates the piconet becomes the Master. However, a Master-Slave
switch can take place when a Slave wants to become a Master. These 2 units then have to reverse their
TX and RX timing; a so-called TDD switch.
However, since the piconet parameters are derived from the device addresses and clock of the
Master, a Master-Slave switch involves a redefinition of the piconet as well; a piconet switch The
new piconet´s parameters are derived from the former Slave’s device address and clock.
As a consequence of this piconet switch, other slaves in the piconet, not involved in the switch,
have to be logically moved to the new piconet. This means changing their timing and their hopping
scheme. A rather complex procedure.
HOW TIMESLOTS ARE USED
Fig: Use of time slots
Transmission/reception takes place in timeslots that are only 625 microseconds in duration.
The Master uses even-numbered slots to address each slave in turn, and each addressed slave has the
opportunity to answer in the following odd-numbered timeslot. Or it can wait for it turns next time
In addition to this, some timeslots are used for broadcasts and as logical channels for
synchronization and other control signals. Thus, we get a rotating scheme, resembling the illustration
above. The slot numbering proceeds to a very high number; it takes about a day for the slot numbering
to start over again. The clock of the Master unit decides when these slots start and end, and the slaves
will thus need to be very closely synchronized to this clock.
ADVANTAGE OF FREQUENCY HOPPING
Bluetooth has been designed to operate in noisy radio frequency environments, and uses a fast
acknowledgement and frequency-hopping scheme to make the link robust, communication-wise.
Bluetooth radio modules avoid interference from other signals by hopping to a new frequency after
transmitting or receiving a packet.
Compared with other systems operating in the same frequency band, the Bluetooth radio
typically hops faster and uses shorter packets. This is because short packages and fast hopping limit
the impact of microwave ovens and other sources of disturbances. Use of Forward Error Correction
(FEC) limits the impact of random noise on long-distance links.
Whenever a connection (a piconet) is first established between 2 (or more) units, the Master-
unit establishes a frequency-hopping scheme, which is communicated to the other units. This
frequency selection scheme consists of two parts:
Selecting a sequence;
Mapping this sequence onto the hop frequencies.
Fig: Frequency Hopping
ADVANCEMENTS IN BLUETOOTH
Ratified as IEEE Standard 802.15.1-2002.
Many errors found in the 1.0B specifications were fixed.
Added support for non-encrypted channels.
Received Signal Strength Indicator (RSSI).
This version is backward-compatible with 1.1 and the major enhancements include the following:
Faster Connection and Discovery
Adaptive frequency-hopping spread spectrum (AFH), which improves resistance to radio
frequency interference by avoiding the use of crowded frequencies in the hopping sequence.
Higher transmission speeds in practice, up to 721 kbit/s, than in 1.1.
Extended Synchronous Connections (eSCO), which improve voice quality of audio links by
allowing retransmissions of corrupted packets, and may optionally increase audio latency to
provide better support for concurrent data transfer.
Host Controller Interface (HCI) support for three-wire UART.
Ratified as IEEE Standard 802.15.1-2005.
This version of the Bluetooth specification was released on November 10, 2004. It is backward-
compatible with the previous version 1.1. The main difference is the introduction of an Enhanced Data
Rate (EDR) for faster data transfer. The nominal rate of EDR is about 3 megabits per second, although
the practical data transfer rate is 2.1 megabits per second. The additional throughput is obtained by
using a different radio technology for transmission of the data. Standard, or Basic Rate, transmission
uses Gaussian Frequency Shift Keying (GFSK) modulation of the radio signal; EDR uses a
combination of GFSK and Phase Shift Keying (PSK) modulation.
According to the 2.0 specification, EDR provides the following benefits:
Three times faster transmission speed — up to 10 times (2.1 Mbit/s) in some cases.
Reduced complexity of multiple simultaneous connections due to additional bandwidth.
Lower power consumption through a reduced duty cycle.
The Bluetooth Special Interest Group (SIG) published the specification as Bluetooth 2.0 + EDR
which implies that EDR is an optional feature. Aside from EDR, there are other minor improvements
to the 2.0 specification, and products may claim compliance to Bluetooth 2.0 without supporting the
higher data rate. At least one commercial device, the HTC TyTN pocket PC phone, states Bluetooth
2.0 without EDR on its data sheet.
Bluetooth Core Specification Version 2.1 is fully backward-compatible with 1.1, and was adopted by
the Bluetooth SIG on July 26, 2007. This specification includes the following features:
Extended inquiry response: provides more information during the inquiry procedure to allow
better filtering of devices before connection. This information includes the name of the device,
a list of services the device supports, plus other information like the time of day and pairing
Sniff sub rating: reduces the power consumption when devices are in the sniff low-power
mode, especially on links with asymmetric data flows. Human interface devices (HID) are
expected to benefit the most, with mouse and keyboard devices increasing their battery life by
a factor of 3 to 10. It lets devices decide how long they will wait before sending keep alive
messages to one another. Previous Bluetooth implementations featured keep alive message
frequencies of up to several times per second. In contrast, the 2.1 specification allows pairs of
devices to negotiate this value between them to as infrequently as once every 5 or 10 seconds.
Encryption Pause Resume: enables an encryption key to be refreshed, enabling much
stronger encryption for connections that stay up for longer than 23.3 hours (one Bluetooth
Secure Simple Pairing: radically improves the pairing experience for Bluetooth devices, while
increasing the use and strength of security. It is expected that this feature will significantly
increase the use of Bluetooth.
Near Field Communication (NFC) cooperation: automatic creation of secure Bluetooth
connections when NFC radio interface is also available. This functionality is part of the Secure
Simple Pairing where NFC is one way of exchanging pairing information. For example, a
headset should be paired with a Bluetooth 2.1 phone including NFC just by bringing the two
devices close to each other (a few centimeters). Another example is automatic uploading of
photos from a mobile phone or camera to a digital picture frame just by bringing the phone or
camera close to the frame.
Future of Bluetooth
Broadcast Channel: enables Bluetooth information points. This will drive the adoption of
Bluetooth into mobile phones, and enable advertising models based around users pulling
information from the information points, and not based around the object push model that is
used in a limited way today.
Topology Management: enables the automatic configuration of the piconet topologies
especially in scatternet situations that are becoming more common today. This should all be
invisible to the users of the technology, while also making the technology just work.
Alternate MAC PHY: enables the use of alternative MAC and PHY's for transporting
Bluetooth profile data. The Bluetooth Radio will still be used for device discovery, initial
connection and profile configuration, however when lots of data needs to be sent, the high
speed alternate MAC PHY's will be used to transport the data. This means that the proven low
power connection models of Bluetooth are used when the system is idle, and the low power per
bit radios are used when lots of data needs to be sent.
QoS improvements: enable audio and video data to be transmitted at a higher quality,
especially when best effort traffic is being transmitted in the same piconet.
Security can mean two things in this context:
A) We want to be sure that transmitted data arrives in un-corrupted condition to the receiver.
B) We also want to feel that this data has not been eavesdropped by parties for whom it is not
Safer transmission of data
Are transmissions secure in a business and home environment? Yes, they are supposed to be
quite reliable. Bluetooth has built in sufficient encryption and authentication and is thus very secure in
any environment. In addition to this, a frequency-hopping scheme with 1600 hops/sec. is employed.
This is far quicker than any other competing system. This, together with an automatic output power
adaptation to reduce the range exactly to requirement, makes the system extremely difficult to
Bluetooth´s Error Correction Schemes
Bluetooth units often have to contend with electro-magnetically noisy environments. Thus, the
need for some kind of error-detection and correction. For error-detection, Bluetooth uses various
checksum-calculations. When errors are detected, there are 2 error-correction schemes defined for
1. FEC (Forward Error Correction)
2. ARQ unnumbered scheme (Automatic Repeat Request).
The purpose of the FEC scheme on the data payload is to reduce the number of re-transmissions.
However, in a reasonably error-free environment, FEC gives unnecessary overhead that reduces the
throughput. The ARQ-scheme is on 2 occasions; the transmitted data blocks get corrupted, which is
detected by the recipient. So the next time that recipient get a chance to communicate with that sender
(i.e. at the next appropriate timeslot), the recipient sends a Negative Acknowledgement NAK, which
prompts the other party to re-transmit that data block.
IS BLUETOOTH DANGEROUS?
Fig: Is Bluetooth Dangerous
It is a matter of concern for some people that the carrier waves used by Bluetooth´s
transmitters use the same frequency range as microwave Owens (Bluetooth uses 2.402 GHz to 2.480
GHz). What does it feel like to get in the path of such waves?
Actually, the transmitting power is far too weak to be noticeable for humans. Moreover, the
radiation is not concentrated in a beam, but dispersed more or less in all directions. When using a
wireless phone or a Bluetooth device, the body absorbs some of the emitted RF energy. The
penetration depth is about 1.5 cm at 2450 MHz (about 2.5 cm at 900 MHz), which means that the
absorption is very superficial.
BLUETOOTH’S GROWTH POTENTIAL
In the near future the wireless technique will be very important, in order for the e trading to
take off. This area is perfectly suited for Bluetooth, and Bluetooth will in all probability be the
dominating technique for wireless communication for handheld terminals. In the EU-countries,
handheld terminals are expected to have 75% of the market. USA lags somewhat behind when it
comes to wireless data communication and the use of handheld terminals. Apart from this; if prices can
be kept on a competitive level, we will soon very likely see a rapid switchover from wire-connected to
wireless appendages to new computers, both at the workplace and in the home. The mobility and
ability to dynamic reconfiguration on the go between units are attributes that will be widely
BLUETOOTH’S COMPETING TECHNOLOGIES
Is Bluetooth a Wireless LAN (WLAN)?
No, Bluetooth is not intended as a wireless extension of ordinary LANs. Both Bluetooth and
WLANs are based upon the IEEE 802.11-standard. But there are too many differences for these
systems to replace each others:
WLANs are essentially ordinary LAN-protocols modulated on carrier waves. Bluetooth is
more complex than that.
Bluetooth´s essence is dynamically configured units. That´s not how LANs work.
Bluetooth hops very fast (1600 hops/second) between frequencies, which does not allow for
long datablocks. A Bluetooth channel cannot handle as high data throughput as a WLAN.
Bluetooth relies on ad-hoc-connectivity. This does not square well with (predominantly)
Moreover, when a Bluetooth connection collides with a wireless LAN connection, either or
both connections can jam! Bluetooth may be a boon to mobile devices, but to wireless LANs, it's a
One of the 3 IrDa-standards that are used today is called ”IrDa-Data”, and this standard is
primarily meant for data transmission. But the main differences as compared to Bluetooth are:
IrDa is not omni directional, as is Bluetooth. The IrDa-beam has to be aimed at the receiving
IrDa must have a free line of sight.
IrDa is point-to-point; only 2 units at a time can communicate.
Fig: Infrared Technology
Bluetooth is simply the best!
Market predictions indicate that more then a BILLION devices was equipped by
BLUETOOTH devices by 2007, this number is significantly larger then the number of hosts connected
to INTERNET today. As people find innovative uses of technology of this technology new profiles
will be needed.
BLUETOOTH has caught the attention of the consumers because it will enable them to do
things which otherwise seem to be cumbersome today: synchronization data between CELL
PHONES,LAPTOPS and PDA’s using CELLPHONES as CORDLESS when at home. The challenge
is for vendors to meet this expectation.
The future of the BLUETOOTH depends much more on market forces rather then technical
issues .for e.g. Unless the initial adoption of BLUETOOTH is high it will be difficult to meet the low
Of the technical issues the most important is the security, proper safeguards are required to
prevent unauthorized leakage of information.
FREQUENTLY ASKED QUESTIONS
1. Who makes/owns Bluetooth?
The Bluetooth Special Interest Group (SIG) isn't a company per se - it's a community of
more than 2500 companies, including Nokia. Nokia designs and builds Bluetooth capability into its
products, but they are then tested and qualified by standards set by the SIG. When you buy a
product that uses Bluetooth technology, you're not buying it from a company or manufacturer
2. Why is it called Bluetooth?
Here's one for trivia buffs: In10th century Denmark, the Viking king Harald Blatand
(literally Bluetooth) united Norway and Denmark into a single kingdom. Apparently he got that
name from his penchant for blueberries.
3. How fast is data transferred?
The maximum rate is currently 2.1 Mbps. While this is already fast enough to complete most
data transfers within a few seconds, it's not the limit. Developers hope to double or triple the speed in
subsequent releases of Bluetooth technology.
4. Can I control more than one device at a time?
Yes. With Bluetooth you can have point-to-point communication between two device, or
point-to-multipoint communication, with a master and several slaves (when one device controls
another, it's called a master, and the devices it controls are slaves). In a Bluetooth network (a
very small local network sometimes called a piconet), one master can have up to seven slaves -
but keep in mind that the total transfer speed will be divided up between them because all traffic
goes through master device (think of the master as traffic control central)You could, for example,
be talking on the phone using a wireless headset and sending an image to your printer at the same
5. What's the difference between Bluetooth and Infrared?
The main difference is that Bluetooth operates using radio waves, and infrared uses very
fast pulses of light. With infrared, both devices' sensors must be in each other’s line of sight
(you've experienced this if you've ever tried to use your DVD remote control and there's someone
standing in the way). Bluetooth isn’t limited to this; it even works between walls.
Infrared also only works between two devices at a time.
6. What's the difference between Bluetooth and Wi-Fi?
Bluetooth and Wi-Fi are complementary technologies. While Wi-Fi is wireless Ethernet,
extending or replacing wired networks for dozens of computing devices, Bluetooth is designed to
replace cables between a few devices within a 10-meter range, providing data, voice, and audio
connections. Bluetooth is also ideal for battery-powered devices as it is low on power
1. www.wikipedia.com- Wikipedia, the online Encyclopedia
2. www.bluetooth.com – The official website of Bluetooth i.e Bluetooth SIG.
1. Introduction of Bluetooth Wireless Technology
BY- Jon Inouye
Staff Software Engineer
Mobile Platforms Group
2. Bluetooth Security
BY- Christian Gehrmann, Joakim Persson, Ben Smeets