BLUETOOTH
The
most popular technology in recent years would have to be Bluetooth. Bluetooth
is a type of wireless communication allowing you to connect to Internet,
phones, cars, and satellite without the vast array of cables holding you down.
Bluetooth is a
method for data communication that uses short-range
radio links to replace cables between computers and their connected
units. Bluetooth is a developing, worldwide, open, short-range radio
specification focused on communication between the Internet and Net devices,
plus it defines communication protocols between devices and computers.
Bluetooth is a wireless technology standard for exchanging
data over short distances (using
hort-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 telecom 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 17,000 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 SIGA
network of patents is required to implement the
technology and are licensed only for those qualifying devices.
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; 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 2.4 GHz short-range
radio frequency band. It usually performs 800 hops per second, with Adaptive Frequency-Hopping (AFH) enabled. Originally Gaussian frequency-shift keying (GFSK) modulation was the only
modulation scheme available; subsequently, since the introduction of Bluetooth
2.0+EDR, π/4-DQPSK and 8DPSK
modulation may also be used between compatible devices. Devices functioning
with GFSK are said to be operating in basic rate (BR) mode where an
instantaneous data rate of
Mbit/s is possible.
The term Enhanced Data Rate (EDR) is used to describe π/4-DPSK and 8DPSK
schemes, each giving 2 and 3 Mbit/s respectively. The combination of these
(BR and EDR) modes in Bluetooth radio technology is classified as a
"BR/EDR radio".
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 transmits will begin in even slots and the slave transmits
in odd slots.
Bluetooth
provides a secure way to connect and exchange information between devices such
as faxes, mobile phones,
telephones, laptops, personal computers, printers, Global Positioning System (GPS) receivers, digital cameras, and video game consoles. It was
principally designed as a low-bandwidth technology.
BLUETOOTH FREQUENCY
Bluetooth networking transmits data via low-power
radio waves. It communicates on a frequency of 2.45 gigahertz (actually between 2.402 GHz and 2.480 GHz, to be
exact). This frequency band has been set aside by international agreement for
the use of industrial, scientific and medical devices(ISM).A
number of devices that you may already use take advantage of this same radio-frequency band.
Baby monitors,
garage-door openers and the newest generation of cordless phones
all make use of frequencies in the ISM band. Making sure that Bluetooth and
these other devices don't interfere with one another has been a crucial part of
the design process.
One
of the ways Bluetooth devices avoid interfering with other systems is by sending
out very weak signals of about 1
milli watt. By comparison, the most powerful cell phones can transmit a signal
of 3 watts. The low power limits the range of a Bluetooth device to about 10 meters (32 feet), cutting the
chances of interference between your computer system and your portable
telephone or television. Even with the low power, Bluetooth doesn't require
line of sight between communicating devices. The walls in your house won't stop
a Bluetooth signal, making the standard useful for controlling several devices
in different rooms. Bluetooth can connect up to eight devices simultaneously. With all of those devices in the
same 10-meter (32-foot) radius, you might think they'd interfere with one
another, but it's unlikely. Bluetooth uses a technique called spread-spectrum frequency hopping that
makes it rare for more than one device to be transmitting on the same frequency
at the same time. In this technique, a device will use 79 individual, randomly
chosen frequencies within a designated range, changing from one to another on a
regular basis. In the case of Bluetooth, the transmitters change frequencies
1,600 times every second, meaning that more devices can make full use of a
limited slice of the radio spectrum. Since every
Bluetooth transmitter uses spread-spectrum transmitting automatically, it’s
unlikely that two transmitters will be on the same frequency at the same time.
This same technique minimizes the risk that portable phones or baby monitors
will disrupt Bluetooth devices, since any interference on a particular
frequency will last only a tiny fraction of a second.
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 scatter net, 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 behavior in scatter
nets.
Many
USB Bluetooth adapters or "dongles" are available, some of
which also include an IrDA adapter. 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.
APPLICATIONS
·
A
typical Bluetooth mobile phone headset. Wireless control of and
communication between a mobile phone and a hands freehead set. 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
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.
·
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 tele healthdevices.
·
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 location.
RANGE
The operating range depends on the device class
·
Class 3 radios – have a range of up to 1
meter or 3 feet
·
Class 2 radios – most commonly found in
mobile devices – have a range of 10 meters or 30 feet
·
Class 1 radios – used primarily in
industrial use cases – have a range of 100 meters or 300 feet
AT COMMAND
AUBTM-20 is a Bluetooth v1.2 module with SPP
profiles. The module is intended to be integrated into another HOST system
which requires Bluetooth functions. The HOST system could send commands to
AUBTM-20 through a UART. AUBTM-20 will parse the commands and execute proper
functions, e.g. set the maximum transmit power, change the name of the module.
And next the module can transmit the data receive from the uart with SPP
profiles.
The purpose of this document is to define the
protocol between the HOST system and AUBTM-13 through the UART connection. The
protocol heavily depends on the AT commands of 3GPP 27.007 and 27.005 GSM
recommendations. Most of the commands are the same with the GSM standard, with
several special commands defined by AUSTAR technology.
For the exchange of the commands and unsolicited
results codes, the format, syntax and procedures of 3GPP 27.007 [1] shall be
taken as reference. The following rules specifically apply for this protocol.
•
Only one command (or unsolicited result code) per command line needs to be
expected.
•
The HOST, by default, shall not echo the command characters.
•
The HOST shall always transmit result codes using verbose format.
•
The characters below shall be used for AT commands and result codes formatting:
<cr>
corresponds to the carriage return (0/13) as stated in [6]
<lf>
corresponds to the line feed (0/10) as stated in [6]
•
The format of an AT command from the HOST to the module shall be:
<cr><lf><AT
command><cr><lf>
•
The format of the OK code from the module to the HOST shall be:
<cr><lf>OK<cr><lf>
•
The format of the generic ERROR code from the module to the HOST shall be:
<cr><lf>ERROR<cr><lf>
•
The format of an unsolicited result code from the module to the HOST shall be:
<cr><lf><result
code><cr><lf>.
The purpose of this document is to define the
protocol between the HOST system and AUBTM-13 through the UART connection. The
protocol heavily depends on the AT commands of 3GPP 27.007 and 27.005 GSM
recommendations.
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