Is there anything worse than wires? If you've ever hooked
up a computer and half a dozen peripherals (add-ons), a digital television and
a DVD player, or run your own telephone extensions through the house, you'll
know just what a pain all those cables can be. Wouldn't it be nice if there
were a way of bringing electronic gadgets together so they could share whatever
signals they need without any wires at all? Enter Bluetooth! It's a simple way
for cellphones, printers, PCs, digital cameras, and other gadgets to link
together over relatively short distances using wireless (radio wave)
technology. The curious name comes from Harald Bluetooth, a Danish king who
united the Scandinavians in the 10th century. Will Bluetooth unite the
electronic world the same way? Let's take a closer look!
Tangled of messy wire cables under computer desk.
We're all use to wireless communication by now, even if
we don't always realize it. Radio receivers and television sets pick up
programs beamed in radio waves hundreds (possibly even thousands) of km/miles
through the air. Cordless telephones use similar technologies to carry calls
from a handset to a base station somewhere in your home. If you use Wi-Fi (wireless
Internet), your computer sends and receives a steady stream of Internet data to
and from a router that's probably wired directly to the Net. All these
technologies involve sending information back and forth not along copper cables
but in radio waves buzzing invisibly through the air.
Bluetooth is a similar radio-wave technology, but it's
mainly designed for communicating over short distances less than about 10m or
30ft. Typically, you might use it to download photos from a digital camera to a
PC, to hook up a wireless mouse to a laptop, to link a hands-free headset to
your cellphone so you can talk and drive safely at the same time, and so on.
Electronic gadgets that work this way have built-in radio antennas
(transmitters and receivers) so they can simultaneously send and receive
wireless signals to other Bluetooth gadgets. Older gadgets can be converted to
work with Bluetooth using plug-in adapters (in the form of USB sticks, PCMCIA
laptop cards, and so on). The power of the transmitter governs the range over
which a Bluetooth device can operate and, generally, devices are said to fall
into one of three classes: class 1 are the most powerful and can operate up to
100m (330ft), class 2 (the most common kind) operate up to 10m (33ft), and
class 3 are the least powerful and don't go much beyond 1m (3.3ft).
Two nearby Bluetooth devices exchange a pairing request.
Bluetooth sends and receives radio waves in a band of 79
different frequencies (channels) centered on 2.45 GHz, set apart from radio,
television, and cellphones, and reserved for use by industrial, scientific, and
medical gadgets. Don't worry: you're not going to interfere with someone's
life-support machine by using Bluetooth in your home, because the low power of
your transmitters won't carry your signals that far! Bluetooth's short-range
transmitters are one of its biggest plus points. They use virtually no power
and, because they don't travel far, are theoretically more secure than wireless
networks that operate over longer ranges, such as Wi-Fi. (In practice, there
are some security concerns.)
Bluetooth devices automatically detect and connect to one
another and up to eight of them can communicate at any one time. They don't
interfere with one another because each pair of devices uses a different one of
the 79 available channels. If two devices want to talk, they pick a channel
randomly and, if that's already taken, randomly switch to one of the others (a
technique known as spread-spectrum frequency hopping). To minimize the risks of
interference from other electrical appliances (and also to improve security),
pairs of devices constantly shift the frequency they're using—thousands of
times a second.
When a group of two or more Bluetooth devices are sharing
information together, they form a kind of ad-hoc, mini computer network called
a piconet. Other devices can join or leave an existing piconet at any time. One
device (known as the master) acts as the overall controller of the network,
while the others (known as slaves) obey its instructions. Two or more separate
piconets can also join up and share information forming what's called a
scatternet.
What is spread spectrum?
A torpedo fires from the deck of a warship
Suppose you're talking to a friend on a walkie-talkie or
with a CB (citizen's band) radio, but there are other people using the same
frequency and your conversation keeps getting interrupted. What can you do?
Most experienced radio users know the answer: you both change to a different
frequency (band) and resume your conversation there. And you can keep on
switching band until you find a place where you can happily talk without
interruption. In theory, you could use the same technique for covert
communication: if you were talking over the radio and someone was
eavesdropping, you could give a code-word to your friend and hastily switch to
another, pre-arranged frequency band where the eavesdropper wouldn't find you
(although they'd most likely still pick up your signal sooner or later).
Radios are clever electronic gadgets, so why can't they
do this neat trick for themselves? Why can't they simply switch to another
frequency automatically to prevent interference and eavesdropping? This is the
basic idea behind a technique called spread-spectrum frequency hopping, where
signals are rapidly and randomly switched across a wide range of different
frequencies to improve the security and reliability of wireless communication.
Numerous inventors contributed to the invention of
spread-spectrum, including electricity pioneer Nikola Tesla (1856–1943) and US
actress Hedy Lamarr (1913–2000), who, with the help of George Antheil,
developed a practical system for the US military during World War II. While
modern spread-spectrum systems are electronically controlled, Lamarr's, which
is illustrated below, was based on the mechanical, punched paper-tape technology
originally used in player pianos. The sender and receiver each had identical
machines with precisely synchronized electric motors that slowly pulled lengths
of paper tape through them. The two tapes were punched with matching patterns
of holes indicating which of 88 different radio frequencies the sender and
receiver should use to communicate with each other at any particular time. As
the tape chugged through the machines, communication switched from one
frequency to another, in tandem, in a way that was completely unpredictable to
outside observers. Since the radio transmissions were often extremely brief
signals for steering torpedoes, it was quite likely that an enemy wouldn't pick
them up at all or know what they meant even if they did.
Is Bluetooth secure?
Wireless is always less secure than wired communication.
Remember how old spy films used to show secret agents tapping into telephone
wires to overhear people's conversations? Cracking wired communication is
relatively difficult. Eavesdropping on wireless is obviously much easier
because information is zapping back and forth through the open air. All you
have to do is be in range of a wireless transmitter to pick up its signals.
Wireless Internet networks are encrypted (use scrambled communications) to get
around this problem.
How secure is Bluetooth? Like Wi-Fi, communications are
encrypted too and there are numerous other security features. You can restrict
certain devices so they can talk only to certain other, trusted devices—for
example, allowing your cellphone to be operated only by your Bluetooth
hands-free headset and no-one else's. This is called device-level security. You
can also restrict the things that different Bluetooth gadgets can do with other
devices using what's called service-level security.
Criminals get more sophisticated all the time; you've
probably heard about bluebugging (people taking over your Bluetooth device
without your knowledge), bluejacking (where people send messages to other
people's devices, often for advertising purposes), and bluesnarfing (downloading
information from someone else's device using a Bluetooth connection) and
doubtless there are more ways of hacking into Bluetooth networks still to come.
Generally, though, providing you take reasonable and sensible precautions if
you use Bluetooth devices in public places, security shouldn't worry you too
much.
People often get confused by Bluetooth and Wi-Fi because,
at first sight, they seem to do similar things. In fact, they're very
different. Bluetooth is mainly used for linking computers and electronic
devices in an ad-hoc way over very short distances, often for only brief or
occasional communication using relatively small amounts of data. It's
relatively secure, uses little power, connects automatically, and in theory
presents little or no health risk. Wi-Fi is designed to shuttle much larger
amounts of data between computers and the Internet, often over much greater
distances. It can involve more elaborate security and it generally uses much
higher power, so arguably presents a slightly greater health risk if used for
long periods. Bluetooth and Wi-Fi are complementary technologies, not rivals,
and you can easily use both together to make your electronic gadgets work more
conveniently for you!
Bluetooth has often been quite tricky to use: like any
wireless technology, it's another battery drainer for mobile devices; you can
often step out of range, making communication erratic or impossible; and even
getting two Bluetooth devices to talk to one another in the first place isn't
always as simple as it should be. The world of mobile devices is changing as we
move toward the so-called Internet of Things (where all kinds of everyday
objects become net-connected)—and Bluetooth has to keep evolving to keep up.
Recognizing the need to connect an increasing range of devices, more quickly,
and more securely, Bluetooth's developers are regularly coming up with improved
versions. First, there was Bluetooth BR/EDR (Basic Rate/Enhanced Data Rate, technically
Bluetooth Version 2.1), offering simpler connectivity between devices and
better security. Next came Bluetooth Highspeed (Bluetooth Version 3.0), which
offered faster communication and lower power consumption. More recently, we've
had Bluetooth Smart or Bluetooth Low Energy (technically referred to as
Bluetooth Version 4.0+). As these names suggest, this version is better at
connecting a wider range of simpler devices, uses much less power, and is much
easier to integrate into mobile (iOS and Android) applications.
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