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Bluetooth - General
Bluetooth - General
Bluetooth
is a proprietary open
wireless
technology standard for exchanging data over short distances (using
short-wavelength radio transmissions in the ISM band from
2400–2480 MHz) from fixed and mobile devices, creating personal area networks (PANs) with high
levels of security.
Created
by telecoms vendor Ericsson in 1994, it was originally conceived as a wireless
alternative to RS-232
data cables.
It
can connect several devices, overcoming problems of synchronization.
Bluetooth
is managed by the Bluetooth Special Interest Group,
which has more than 16,000 member companies in the areas of telecommunication,
computing, networking, and consumer electronics.
The
SIG oversees the development of the specification, manages the qualification
program, and protects the trademarks.
To
be marketed as a Bluetooth device, it must be qualified to standards
defined by the SIG.
Implementation
Bluetooth
uses a radio technology called frequency-hopping spread
spectrum, which chops up the data being sent and transmits chunks of it on
up to 79 bands- 1 MHz each.
1 MHz
each; centered from 2402 to 2480 MHz in the range 2,400–2,483.5 MHz allowing
for guard bands.
This
range is in the globally unlicensed Industrial, Scientific and Medical (ISM)
2.4 GHz short-range radio frequency band. It usually performs
800 hops per second, with AFH enabled.
Bluetooth
is a packet-based
protocol with a master-slave structure.
One
master may communicate with up to 7 slaves in a piconet; all
devices share the master's clock.
Packet
exchange is based on the basic clock, defined by the master, which ticks at
312.5 µs intervals.
Two
clock ticks make up a slot of 625 µs; two slots
make up a slot pair of 1250 µs. In the simple case of single-slot packets
the master transmits in even slots and receives in odd slots; the slave,
conversely, receives in even slots and transmits in odd slots.
Packets
may be 1, 3 or 5 slots long but in all cases the master transmit will begin in
even slots and the slave transmit in odd slots.
Bluetooth
provides a secure way to connect and exchange information between devices such
as
Global Positioning System (GPS)
receivers,
digital
cameras, and
Communication and connection
A
master Bluetooth device can communicate with a maximum of seven devices in a piconet (an
ad-hoc computer network using Bluetooth technology), though not all devices
reach this maximum.
The
devices can switch roles, by agreement, and the slave can become the master
(for example, a headset initiating a connection to a phone will necessarily
begin as master, as initiator of the connection; but may subsequently prefer to
be slave).
The
Bluetooth Core Specification provides for the connection of two or more
piconets to form a scatternet, in which certain devices simultaneously play
the master role in one piconet and the slave role in another.
At
any given time, data can be transferred between the master and one other device
(except for the little-used broadcast mode.
The
master chooses which slave device to address; typically, it switches rapidly
from one device to another in a round-robin fashion.
Since
it is the master that chooses which slave to address, whereas a slave is (in
theory) supposed to listen in each receive slot, being a master is a lighter
burden than being a slave. Being a master of seven slaves is possible; being a
slave of more than one master is difficult. The specification is vague as to
required behaviour in scatternets.
Older
(pre-2003) Bluetooth dongles, however, have limited capabilities, offering only
the Bluetooth Enumerator and a less-powerful Bluetooth Radio incarnation. Such
devices can link computers with Bluetooth with a distance of 100 meters, but
they do not offer as many services as modern adapters do.
Uses
Bluetooth is a standard wire-replacement
communications protocol primarily designed for low power consumption, with a
short range (power-class-dependent, but effective ranges vary in practice; see
table below) based on low-cost transceiver
microchips in each device.
Because the devices use a radio
(broadcast) communications system, they do not have to be in visual line of
sight of each other, however a quasi optical wireless path must be
viable.
Class
|
Maximum permitted power
|
Range
(m) |
|
(mW)
|
(dBm)
|
||
Class 1
|
100
|
20
|
~100]
|
Class 2
|
2.5
|
4
|
~10
|
Class 3
|
1
|
0
|
~5
|
The effective range varies due to propagation conditions, material coverage,
production sample variations, antenna configurations and battery conditions.
In most cases the effective range of
Class 2 devices is extended if they connect to a Class 1 transceiver,
compared to a pure Class 2 network. This is accomplished by the higher sensitivity
and transmission power of Class 1 devices.
Version
|
Data rate
|
Maximum application throughput
|
Version 1.2
|
1 Mbit/s
|
0.7 Mbit/s
|
Version 2.0 + EDR
|
3 Mbit/s
|
2.1 Mbit/s
|
Version 3.0 + HS
|
See Version
3.0+HS.
|
|
Version 4.0
|
See Version
4.0LE.
|
|
While the Bluetooth Core Specification
does mandate minimums for range, the range of the technology is application
specific and is not limited. Manufacturers may tune their implementations to
the range needed for individual use cases.
Bluetooth profiles
To use Bluetooth wireless technology, a
device has to be able to interpret certain Bluetooth profiles, which are
definitions of possible applications and specify general behaviors that
Bluetooth enabled devices use to communicate with other Bluetooth devices.
These profiles include settings to
parametrize and to control the communication from start. Adherence to profiles
saves the time for transmitting the parameters anew before the bi-directional
link becomes effective.
There are a wide range of Bluetooth
profiles that describe many different types of applications or use cases for
devices.
List of applications
A typical Bluetooth mobile phone headset.
·Wireless
control of and communication between a mobile
phone and a handsfree headset.
This was one of the earliest applications to become popular.
·Wireless
control of and communication between a mobile
phone and a Bluetooth compatible car stereo system
·Wireless
networking between PCs in a confined space and where little bandwidth is
required.
·Wireless
communication with PC input and output devices, the most common being the mouse,
keyboard and printer.
·Transfer
of files, contact details, calendar appointments, and reminders between devices
with OBEX.
·Replacement
of previous wired RS-232
serial communications in test equipment, GPS receivers, medical equipment, bar
code scanners, and traffic control devices.
·For
controls where infrared
was often used.
·For
low bandwidth applications where higher USB bandwidth is not
required and cable-free connection desired.
·Sending
small advertisements from Bluetooth-enabled advertising hoardings to other,
discoverable, Bluetooth devices.
·Wireless
bridge between two Industrial Ethernet (e.g., PROFINET)
networks.
·Three
seventh
and eighth generation
game
consoles, Nintendo's
WiFi and Sony's PlayStation
3, PSP Go
and PSVita, use
Bluetooth for their respective wireless controllers.
·Dial-up
internet access on personal computers or PDAs using a data-capable mobile phone
as a wireless modem.
·Short
range transmission of health sensor data from medical devices to mobile
phone, set-top box or dedicated telehealth
devices.
·Allowing
a DECT phone to ring
and answer calls on behalf of a nearby mobile phone
·Real-time
location systems (RTLS), are used to track and identify the location of objects
in real-time using “Nodes” or “tags” attached to, or embedded in the objects
tracked, and “Readers” that receive and process the wireless signals from these
tags to determine their locations
·Personal
security application on mobile phones for prevention of theft or loss of items.
The protected item has a Bluetooth marker (e.g. a tag) that is in constant
communication with the phone. If the connection is broken (the marker is out of
range of the phone) then an alarm is raised. This can also be used as a man overboard
alarm. A product using this technology has been available since 2009.
Bluetooth vs. Wi-Fi (IEEE 802.11)
Bluetooth and Wi-Fi (the brand name
for products using IEEE 802.11 standards) have some similar applications:
setting up networks, printing, or transferring files.
Wi-Fi is intended as a replacement for
cabling for general local area network access in work areas. This
category of applications is sometimes called wireless local area networks (WLAN).
Bluetooth was intended for portable
equipment and its applications. The category of applications is outlined as the
wireless personal area network (WPAN).
Wi-Fi is a wireless version of a common
wired Ethernet
network, and requires configuration to set up shared resources, transmit files,
and to set up audio links.
Wi-Fi uses the same radio frequencies as
Bluetooth, but with higher power, resulting in higher bit rates and better
range from the base station.
The nearest equivalents in Bluetooth are
the DUN profile, which allows devices to act as modem
interfaces, and the PAN profile, which allows for ad-hoc networking.
Devices
A Bluetooth USB dongle with a
100 m range. The MacBook Pro, shown, also has a built in Bluetooth
adaptor.
Bluetooth exists in many products, such
as the iPhone, iPad, iPod Touch,
Lego Mindstorms NXT, PlayStation
3, PSP Go,
telephones, the Nintendo Wii,
and some high definition headsets,
modems, and
watches.
The technology is useful when
transferring information between two or more devices that are near each other
in low-bandwidth situations. Bluetooth is commonly used to transfer sound data
with telephones or byte data with hand-held computers (transferring files).
Bluetooth protocols simplify the
discovery and setup of services between devices. Bluetooth devices can
advertise all of the services they provide. This makes using services easier
because more of the security, network address and permission configuration can
be automated than with many other network types.
Computer requirements
A personal
computer that does not have embedded Bluetooth can be used with a Bluetooth
adapter that will enable the PC to communicate with other Bluetooth devices (such
as mobile
phones, mice and keyboards).
While some desktop
computers and most recent laptops come with a built-in Bluetooth radio, others will
require an external one in the form of a dongle.
Unlike its predecessor, IrDA, which requires a separate adapter
for each device, Bluetooth allows multiple devices to communicate with a
computer over a single adapter.
Specifications and features
The Bluetooth
specification was developed as a cable replacement in 1994 by Jaap
Haartsen and Sven Mattisson, who were working for Ericsson in Lund, Sweden.
The specification is based on frequency-hopping spread
spectrum technology.
The specifications
were formalized by the Bluetooth Special Interest Group
(SIG). The SIG was formally announced on May 20, 1998. Today it has a
membership of over 16,000 companies worldwide. It was established by Ericsson, IBM, Intel, Toshiba and Nokia, and later
joined by many other companies.
All versions of the Bluetooth standards
are designed for downward compatibility. That lets the latest standard cover
all older versions.
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