How Bluetooth Works

When you use computers, entertainment systems or telephones,
the various pieces and parts of the systems make up
a community of electronic devices. These devices communicate
with each other using a variety of wires, cables, radio
signals and infrared light beams, and an even greater variety
of connectors, plugs and protocols.


There are lots of different ways that electronic devices can
connect to one another. For example:

* Component cables.
* Electrical wires.
* Ethernet cables.
* WiFi.
* Infrared signals.

The art of connecting things is becoming more and more
complex every day. In this article, we will look at a method
of connecting devices, called Bluetooth, that can streamline
the process. A Bluetooth connection is wireless and
automatic, and it has a number of interesting features that
can simplify our daily lives.

The Problem

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
questions arise:

* How much data will be sent at a time? For instance,
serial ports send data 1 bit at a time, whil­e parallel ports
send several bits at once.

* How will they speak to each other? 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. This means developing a set of commands and
responses known as a protocol.

Bluetooth offers a solution to the problem.

How Bluetooth Creates a Connection

Bluetooth takes small-area networking to the next level by
removing the need for user intervention and keeping
transmission power extremely low to save battery power.
Picture this: You're on your Bluetooth-enabled cell phone,
standing outside the door to your house. You tell the person
on the other end of the line to call you back in five minutes
so you can get in the house and put your stuff away. As soon
as you walk in the house, the map you received on your cell
phone from your car's Bluetooth-enabled GPS system is
automatically sent to your Bluetooth-enabled computer,
because your cell phone picked up a Bluetooth signal from
your PC and automatically sent the data you designated for
transfer. Five minutes later, when your friend calls you
back, your Bluetooth-enabled home phone rings instead of your
cell phone. The person called the same number, but your home
phone picked up the Bluetooth signal from your cell phone and
automatically re-routed the call because it realized you were
home. And each transmission signal to and from your cell
phone consumes just 1 milliwatt of power, so your cell phone
charge is virtually unaffected by all of this activity.

Bluetooth is essentially a networking standard that works at
two levels:

* It provides agreement at the physical level. Bluetooth
is a radio-frequency standard.

* It provides agreement at the protocol level, 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 big draws of Bluetooth are that it is wireless,
inexpensive and automatic. There are other ways to get around
using wires, including infrared communication. Infrared (IR)
refers to light waves of a lower frequency than human eyes
can receive and interpret. Infrared is used in most
television remote control systems. 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. (See How Remote Controls Work to learn more about
infrared communication.)

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.

Bluetooth is intended to get around the problems that come
with infrared systems. The older Bluetooth 1.0 standard has
a maximum transfer speed of 1 megabit per second (Mbps),
while Bluetooth 2.0 can manage up to 3 Mbps. Bluetooth 2.0 is
backward-compatible with 1.0 devices.