BLUETOOTH AND ITS APPLICATION IN MOBILE PHONES
INTRODUCTION
Bluetooth is a short range wireless technology intended to replace the cables connecting
portable and/or fixed devices while maintaining high levels of security. Ericsson Mobile
Communication started this technology in 1994. This technology operates in the
unlicensed industrial, scientific and medical (ISM) band at 2.4 to 2.485 GHz using a
spread spectrum, frequency hopping full duplex signal at a nominal rate of 1600
hops/sec. Bluetooth enabled electronic devices connect and communicate wirelessly
through short-range adhoc networks known as piconets. The main draws of this
technology are its low cost, low power and robustness. Compared to other systems
operating in the same frequency band, Bluetooth radio typically hops faster and uses
shorter packets, which helps it to minimize unauthorized interruption or jamming of
telecommunication.. It also uses forward error correction (FEC) which limits the impact
of random noise on long-distance links. The ability to simultaneously handle both data
and voice transmissions is the fundamental strength of this technology, which gives a
variety of innovative solutions such as hands-free headset for voice calls, printing and fax
capabilities and synchronizing PDA (Personal Digital Assistance), laptop and mobile
phone applications.
VARIOUS TECHNICAL ASPECTS OF THIS TECHNOLOGY ARE GIVEN BELOW
OPERATING RANGE
Class 3 Radios
1 meter or 3 feet
Class 2 Radios
(For Mobile phones) 10 meters or 30 feet
Class 1 Radios
(For Industrial Use) 100 meters or 300 feet.
CORE SYSTEM
RF transceiver, baseband and protocol stack.
3 Core protocols

The logical link control and adaptation protocol (L2CAP) : Provides data services
to the high layer protocols with protocol multiplexing capability,segmantation and
reassembly operations and group abstractions.
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
Service discovery protocols (SDP) : Provides device information, services and the
characteristics of the services.

RFCOMM protocol : Provides transport capabilities for high level services that
use serial line as the transport mechanism.
BLUETOOTH CHANNELS

79 RF-Channels, on individual frequencies of 1 MHz apart.

Communication channels, consisting of a psuedo-random hopping sequence
through these 79 RF channels.

5 logic channels, used for control purposes.
PHYSICAL LINKS

SCO (Synchronous Connection – Oriented) –This link is point –to-point between
master and slave. Master maintains the link by using reserved time slots at regular
intervals. Packet retransmission is not allowed in this.

ACL (Asynchronous Connection-Less) - This provides packet-switched
connections between the master and all active slaves. Packet retransmissions are
usually applied to assure data integrity.
TRANSMISSION POWER LEVELS

A lower power level that covers the shorter personal area within a room

A higher power level that can cover a medium range, such as within a home.
OTHER RELEVANT INFORMATION
The 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

Up to 3 simultaneous synchronous voice channels

A channel, which simultaneously supports asynchronous data and synchronous
Or
voice.
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HOW NETWORKS ARE FORMED AND CONTROLLED?
The technology uses frequency hopping in time slots. All communication is done through
the master unit. There is no direct communication between the slave units. If the slave
units want to talk directly, they will form a new piconet, with one of them acting as
Master. They will be parked in the old net, unless they decide to quit the old net
altogether.
To establish a connection two procedures are used

Inquiry – This enables a unit to discover which units are in range and what their
device addresses and clocks are.

Paging- An actual connection can be established.
Ideally, only bluetooth device address is required to set up a connection. Knowledge
about the clock will accelerate the setup procedures. A unit that establishes a connection
will carry out a page procedure and will automatically become the master of the
connection. After the paging procedure, the master must poll the slave by sending POLL
or NULL packets to which the slaves will respond. LMP (Link Manager Protocol)
procedures that do not require any interaction between the Link Manager (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
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will send LMP_setup_complete. After this, the first packet on a logical channel different
from LMP can be transmitted.
Various states of bluetooth units

Standby mode: Initially all devices are in this mode. An unconnected unit
periodically ‘listens’ for messages every 1.28 seconds. A connection is made by a
page message, if the address is already known or by an inquiry message followed
by a subsequent page message if address is unknown.

Hold mode: In this mode only an internal timer is running. Data transfer restarts
instantly when units transition out of hold mode. It is used when connecting
several piconets or managing a low power device such as a temperature sensor.

Sniff mode: A slave device listens to the piconet at reduced rate, thus reducing its
duty cycle.

Park mode: A device is still synchronized to the piconet but does not participate in
the traffic.
BLUETOOTH’S SECURITY
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 adaption to reduce the range exactly to requirement, makes the
system extremely difficult to eavesdrop.
ERROR CORRECTION SCHEME
Bluetooth units often have to contend with electro-magnetically noisy environments.
Thus, the need for some kind of error-detection and -correction.3 error-correction
schemes defined for Bluetooth are :
1. 1/3 rate FEC (Forward Error Correction)
2. 2/3 rate FEC
3. ARQ unnumbered scheme (Automatic Repeat Request).
The purpose of the FEC scheme on the data payload is to reduce the number of retransmissions
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The ARQ-scheme is shown in the figure below. On two 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 (a NAK, depicted in red), which prompts
the other party to re-transmit that data block.
APPLICATION OF BLUETOOTH IS MOBILE PHONES
A Serendipity server and Bluetooth activated mobile phone interact using the Connected
Limited Device Configuration (CLDC) combined with the Mobile Information Device
Profile (MIDP).The CLDC and MIDP together make up the Java Runtime Environment
(JRE) for modern resources-constrained mobile information devices such as phones and
entry level PDAs.In mobile devices , the JRE must be embedded in ROM at
manufacturing time.
EXAMPLE:
The Serendipity server is located within the room where the meeting takes place. This
server acts as the master server within the Bluetooth piconet. The Serendipity server has a
predefined mobile phone profile stored in it.
The predefined profile contains values for settings such as ring tones, caller tunes,
message tones, message alerts, silent mode, vibrating mode, ringing mode, time/date
settings, alarm settings, ringing volume, and so on. For example, before entering a
meeting room, the user might want to change his mobile settings to silent and vibrating
mode, change the time and date to the GMT time zone, turn the alarm off, and establish
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that no message tones should be issued. The preconfigured mobile phone profile in the
Serendipity server contains all of this information.
At the start of a gathering, the Serendipity server is ready to register slave devices.
Whenever a meeting attendee enters the room with a Bluetooth-enabled mobile phone,
service discovery occurs and the device joins the piconet. After the piconet has been
formed, the Serendipity server inquires for device profile settings from each of the slave
devices. The server checks to see if each device profile matches with the predefined
profile it has stored. If this doesn't match, a profile change request is sent to that
particular user. The user has the option to either accept this profile change request or
deny it. When the user accepts the request, the server increases a weighted count against
the predefined profile. If the user denies this profile update request, the weighted count
against the user's device profile is increased. The Serendipity server determines the most
widely used device profile setting based on these weighted counts.
At regular intervals, the Serendipity server transmits the most widely used device profile
setting to those devices that have a profile setting different than the one most widely
used. The Serendipity server can sense the user's inclination to go with the profile settings
as directed by it, after looking at the history of rejection/acceptance of the previous
profile update requests. If the user has rejected any of the previous profile update
requests, it can exclude those users from the updates. This comes in handy: users can say
that they do not want to be bothered with profile change requests any more.
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TERMINOLOGY
Piconet: These networks allow one master device to interconnect with up to 7 active
slave devices[because a 3 bit MAC(Media Access Control) address is used] Up to 255
slave devices can be inactive or parked, which the master device can bring into active
status at any time.Piconets are established dynamically and automatically as bluetooth
enabled devices enter and leave radio proximity.
Master unit: 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
Slave units: All devices in a piconet that are not the master (up to 7 active units for each
master).
Mac address: A 3-bit Media Access Control address used to distinguish between units
participating in the piconet
Parked units: Devices in a piconet which are regularly synchronized but do not have
MAC addresses. The Master with a “beacon signal” wakes them up.
Sniff mode and hold mode: Devices that are synchronized to a piconet, and which have
temporarily entered power-saving modes in which device activity is lowered. They keep
their MAC-addresses.
Serendipity: Tool that lets two different devices within the range of bluetooth server
communicate with each other.
CLDC: Defines the base set of application programming interfaces and a virtual machine
for the resource-constrained devices like mobile phones, pagers and mainstream personal
digital assistants.
MIDP: Provides core application functions required by mobile applications -- including
user interface, network connectivity, local data storage, and application life cycle
management -- packaged as a standardized JRE and a set of Java technology APIs
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REFERENCES:
http://www.swedetrack.com/images/bluet00.htm
http://www-128.ibm.com/developerworks/library/wi-bluetooth/
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