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

(1)

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 BASICS

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.

(2)

Photo courtesy Bluetooth SIGfig: 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 another.

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 time.

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

(3)

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:

(4)

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

questions arise:

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:

(5)

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.

It's inexpensive.

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 at all.

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:

Global usage

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

(6)

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.[1]

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 with Bluetooth.

Phones and pagers

Modems

LAN access devices

Headsets

Notebook computers

Desktop and handheld computers

Printers

Fax machines

Keyboards

Joysticks

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.

APPLICATION EXAMPLES:

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.

(7)

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:

(8)

Open specification:

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.

Short-range wireless:

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:

(9)

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 by country.

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.

BLUETOOTH SPECIFICATIONS

There are certain BLUETOOTH specifications.

Specifications:

It defines all layers of bluetooth protocol stack

(10)

Fig: 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 other sources.

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.

(11)

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 server.

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

numbered documents.

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)

(12)

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.

E) RFCOMM

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

transport mechanism.

Fig: Bluetooth Chips

(13)

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.

BLUETOOTH DEFINITIONS

One could say that there are 3 types of connections in Bluetooth, as shown:

Single-slave

Multi-slave (up to 7 ”slaves” on one master)

Scatternet

Fig: Connections in Bluetooth

(14)

PICONETS-

Fig: Piconets

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

MASTER nodes.

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.

SCATTERNETS-

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

(15)

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.

Fig: Scatternet

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.

MASTER UNITS

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.

(16)

SLAVE UNITS

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 paging/scanning scheme.

THE CONNECTION ESTABLISMENT

Fig: Connection Establishment

(17)

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

(18)

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

(19)

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.

Communication routes

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

(20)

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

(21)

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.

(22)

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.

(23)

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

around.

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

(24)

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

Bluetooth 1.1

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).

Bluetooth 1.2

This version is backward-compatible with 1.1 and the major enhancements include the following:

Faster Connection and Discovery

(25)

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.

Bluetooth 2.0

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.

(26)

Bluetooth 2.1

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 information.

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

day).

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

(27)

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.

BLUETOOTH’S SECURITY

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

intended.

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

(28)

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 eavesdrop.

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

Bluetooth:

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

(29)

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 appreciated.

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.

(30)

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)

server-based LANs.

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

bully!!

INFRARED TECHNOLOGY

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

antenna.

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!

CONCLUSION

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

(31)

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 cost objective.

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

called"Bluetooth."

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

(32)

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

time.

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

consumption.

(33)

REFERENCES

1. www.wikipedia.com- Wikipedia, the online Encyclopedia

2. www.bluetooth.com – The official website of Bluetooth i.e Bluetooth SIG.

3. www.howstuffworks.com

(34)

BIBLIOGRAPHY

1. Introduction of Bluetooth Wireless Technology

BY- Jon Inouye Staff Software Engineer Mobile Platforms Group Intel Corporation

2. Bluetooth Security

BY- Christian Gehrmann, Joakim Persson, Ben Smeets

(35)