The number of ways to wirelessly connect an increasing number of
formerly wired devices is becoming confusing. Wi-Fi, 802.11a, 802.11b,
802.11g, GPRS, IrDA and Bluetooth are just some of the terms now being
used to describe different types of wireless connectivity.
This article explains the differences between the main types of
wireless connectivity, and explains how Bluetooth can be useful for you.
Different Types of Connectivity Compared
To start off the
discussion, here is a table to show the major differences between the
main types of wireless connectivity and traditional networking.
| Type | Speed | Range | Comments |
| IrDA | 9.6kb - 115kb (- 4Mb) | < 6ft | Infra-red. The two devices must have their IR ports facing each other. For simple data exchange. Uses very little power. |
| Wi-Fi | 1Mb - 54Mb | see below | Wi-Fi
refers to any of the three 802.11 types of wireless service below, and
to future new subcategories yet to be released. Acts like a regular
wired network in most respects. Either built in or available as add-on
cards or adapters for desktop computers. |
| 802.11a | 1 - 54Mb | 50ft - 150ft | Not commonly used, uses different frequency than 802.11b/g. |
| 802.11b | 1 - 11Mb | 100ft - 300ft | Most common version at present. |
| 802.11g | 1 - 54Mb | 120ft - 350ft | The latest version, backwardly compatible with 802.11b. |
| Bluetooth | 120kb - 723kb | 30ft - 300ft | Class
3 devices (eg in most personal computing type devices) have a short
30ft range, high powered Class 1 devices have the longer range. Either
built in or available as add-on cards. |
| GPRS | < 115kb | wherever suitable cellphone coverage | Data
service used by GSM cellphones and by some add-on cards for laptops
and pda's. Speed typically about 30kb depending on how many users are
sharing the service on each cell at any given time. A 2.5G service. |
| 2.5G | variously up to about 128kb | wherever suitable cellphone coverage | Various
compromise new types of 'always on' data service for cell phones that
are better than nothing but not nearly as good as the 3G service that
all cell phone companies are hoping to introduce when funding and
technology allows. |
| 3G | 2Mb stationary, 384kb moving with good signal, 144kb moving fast/poor signal | wherever suitable cellphone coverage | A
largely futuristic technology not much deployed (yet) in the US which
promises amazingly fast data transfer. Sprint PCS Vision and AT&T
EDGE (100-130kb) are the closest things to 3G in the US at present. |
| Modem | < 56kb | not wireless | The 'old fashioned' way to dial up from a computer to the internet. |
| DSL/Cable | 100kb - 1.5Mb | not wireless | Not wireless.'Broadband' connections to the internet. |
| LAN | 10Mb - 100Mb | not wireless | Not wireless. Common type of cabled network in most offices. |
So What is Bluetooth?
Bluetooth is a very
simple type of wireless networking that can allow up to eight devices
to be connected together in a mini-network.
It is very short range in operation, and so is considered to be for
'personal' networking. With a range typically under 30ft, this allows
enough distance to perhaps communicate across your office, but not any
further. This short range is also its major security feature - anyone
wishing to eavesdrop on your Bluetooth communications would not only
need special equipment but would also need to be quite close to you.
It is a moderately slow type of networking, but it can transfer data sufficiently fast enough for most typical applications.
Bluetooth is hoped to be a very low cost type of networking, and, as it
becomes more widespread, the cost of adding Bluetooth to devices
should drop down to perhaps no more than an extra $5-10 on the selling
price.
Bluetooth is designed to be compatible across a range of very different
operating systems and devices, including things that you would not
normally think of as being 'computer' type items - for example, some
types of headset. Bluetooth networking can enable the headset to
connect with other devices such as your phone, your MP3 player, your
computer, or your PDA.
A Bluetooth enabled headset would mean that you can leave your
cellphone in your pocket or briefcase, but still receive incoming phone
calls. If your cellphone supports voice recognition for dialing out,
you can even place calls as well as receive them, while never needing
to reach for your phone. The safety benefits of this, if you're
driving, are obvious.
It is probably better from a health point of view to have a very low
powered headset close to your head than it is to have a phone that might
be generating 100 or even 300 times as much radio energy close to your
head.
Bluetooth can also help different devices to communicate with each
other. For example, you might have a phone, a PDA, and a computer. If
all three devices have Bluetooth capabilities, then (with the
appropriate software on each device) you can probably share contact
information between all three devices quickly and conveniently. And you
can look up a phone number on your PDA (or laptop) and then place a
call direct from the laptop or PDA, without needing to touch your
cellphone.
Bluetooth is not a magical solution giving universal connectivity
between devices. Each device also needs to have the appropriate software
as well as the basic Bluetooth communication capability, and so
sometimes the promise and theory of what could be possible is not fully
matched by the reality.
For best compatibility, devices should support the Bluetooth 1.1
standard. A new standard - 1.2, was formalized in early November 2003
and this will quickly become the dominant standard.
Bluetooth has been slow to become accepted in the market, but now is
starting to become increasingly prevalent. Prices are falling and
increasing numbers of devices are offering Bluetooth connectivity. Over
one million Bluetooth devices are now being sold every week (although
mainly outside the US).
Bluetooth Range
Most Bluetooth devices are described as 'Class
2'. These are very low power (typically 1 milliwatt - 1/1000th of a
watt) and have a range of about 10 m (33 ft).
Some devices - for example, some plug in 'dongles' that can be added to
to laptop computers - are Class 1. These have range comparable to
that of Wi-Fi, ie, 100 m or 330 ft.
With Bluetooth, short range is actually a benefit, because it reduces
the chance of interference between your Bluetooth devices and those
belonging to other people nearby.
Devices that Use Bluetooth
A limited, but growing number of
devices use Bluetooth at present. Devices that are starting to have
Bluetooth connectivity built in include:
- Digital cameras and camcorders
- Printers
- Scanners
- Cell Phones
- PDAs
- Laptops
- Keyboards and Mice
- Headsets
- In-car handsfree kits
- GPS navigation receivers
- Home appliances (microwaves, washers, driers, refrigerators)
In addition, add on Bluetooth adapters are available for computers (eg with a USB interface) and for PDAs (eg SD cards).
Bluetooth connections
Bluetooth is a high-speed, low-power
microwave wireless link technology, designed to connect phones,
laptops, PDAs and other portable equipment together with little or no
work by the user. Unlike infra-red, Bluetooth does not require
line-of-sight positioning of connected units. The technology uses
modifications of existing wireless LAN techniques but is most notable
for its small size and low cost. The current prototype circuits are
contained on a circuit board 0.9cm square, with a much smaller single
chip version in development. The cost of the device is expected to fall
very fast, from $20 initially to $5 in a year or two. It is envisioned
that Bluetooth will be included within equipment rather than being an
optional extra. When one Bluetooth product comes within range of
another, (this can be set to between 10cm and 100m) they automatically
exchange address and capability details. They can then establish a 1
megabit/s link (up to 2 Mbps in the second generation of the
technology) with security and error correction, to use as required. The
protocols will handle both voice and data, with a very flexible
network topography.
This technology achieves its goal by embedding tiny, inexpensive,
short-range transceivers into the electronic devices that are available
today. The radio operates on the globally-available unlicensed radio
band, 2.45 GHz (meaning there will be no hindrance for international
travelers using Bluetooth-enabled equipment.), and supports data speeds
of up to 721 Kbps, as well as three voice channels. The bluetooth
modules can be either built into electronic devices or used as an
adaptor. For instance in a PC they can be built in as a PC card or
externally attached via the USB port.
Each device has a unique 48-bit address from the IEEE 802 standard.
Connections can be point-to-point or multipoint. The maximum range is 10
meters but can be extended to 100 meters by increasing the power.
Bluetooth devices are protected from radio interference by changing
their frequencies arbitrarily upto a maximum of 1600 times a second, a
technique known as frequency hopping. They also use three different but
complimentary error correction schemes. Built-in encryption and
verification is provided.
Moreover, Bluetooth devices won't drain precious battery life. The
Bluetooth specification targets power consumption of the device from a
"hold" mode consuming 30 micro amps to the active transmitting range of
8-30 milliamps (or less than 1/10th of a watt). The radio chip
consumers only 0.3mA in standby mode, which is less than 3 % of the
power used by a standard mobile phone. The chips also have excellent
power-saving features, as they will automatically shift to a low-power
mode as soon as traffic volume lessens or stops.
But beyond untethering devices by replacing the cables, Bluetooth radio
technology provides a universal bridge to existing data networks, a
peripheral interface, and a mechanism to form small private ad hoc
groupings of connected devices away from fixed network infrastructures.
Designed to operate in a noisy radio frequency environment, the
Bluetooth radio uses a fast acknowledgment and frequency hopping scheme
to make the link robust. Bluetooth radio modules avoid interference
from other signals by hopping to a new frequency after transmitting or
receiving a packet. Compared with other systems operating in the same
frequency band, the Bluetooth radio typically hops faster and uses
shorter packets. This makes the Bluetooth radio more robust than other
systems. Short packages and fast hopping also limit the impact of
domestic and professional microwave ovens. Use of Forward Error
Correction (FEC) limits the impact of random noise on long-distance
links. The encoding is optimized for an uncoordinated environment.
Bluetooth guarantees security at the bit level. Authentication is
controlled by the user by using a 128 bit key. Radio signals can be
coded with 8 bits or anything upto 128 bits. The Bluetooth radio
transmissions will conform to the safety standards required by the
countries where the technology will be used with respect to the affects
of radio transmissions on the human body. Emissions from Bluetooth
enabled devices will be no greater than emissions from industry-standard
cordless phones. The Bluetooth module will not interfere or cause harm
to public or private telecommunications network.
The Bluetooth baseband protocol is a combination of circuit and packet
switching. Slots can be reserved for synchronous packets. Each packet
is transmitted in a different hop frequency. A packet nominally covers a
single slot, but can be extended to cover up to five slots. Bluetooth
can support an asynchronous data channel, up to three simultaneous
synchronous voice channels, or a channel, which simultaneously supports
asynchronous data and synchronous voice. It is thus possible to
transfer the date asynchronously whilst at the same time talking
synchronously at the same time. Each voice channel supports 64 kb/s
synchronous (voice) link. The asynchronous channel can support an
asymmetric link of maximally 721 kb/s in either direction while
permitting 57.6 kb/s in the return direction, or a 432.6 kb/s symmetric
link.
Bluetooth Operation Modes
An interesting aspect of the
technology is the instant formation of networks once the bluetooth
devices come in range to each other. A piconet is a collection of
devices connected via Bluetooth technology in an ad hoc fashion. A
Piconet can be a simple connection between two devices or more than two
devices. Multiple independent and non-synchronized piconets can form a
scatternet. Any of the devices in a piconet can also be a member of
another by means of time multiplexing. i.e a device can be a part of
more than one piconet by suitably sharing the time. The Bluetooth system
supports both point-to-point and point-to-multi-point connections.
When a device is connected to another device it is a point to point
connection. If it is connected to more that one (upto 7 ) it is a point
to multipoint connection. Several piconets can be established and
linked together ad hoc, where each piconet is identified by a different
frequency hopping sequence. All users participating on the same
piconet are synchronized to this hopping sequence. If a device is
connected to more than one piconet it communicates in each piconet
using a different hopping sequence. A piconet starts with two connected
devices, such as a portable PC and cellular phone, and may grow to
eight connected devices. All Bluetooth devices are peer units and have
identical implementations. However, when establishing a piconet, one
unit will act as a master and the other(s) as slave(s) for the duration
of the piconet connection. In a piconet there is a master unit whose
clock and hopping sequence are used to synchronize all other devices in
the piconet. All the other devices in a piconet that are not the
master are slave units. A 3-bit MAC address is used to distinguish
between units participating in the piconet. Devices synchronized to a
piconet can enter power-saving modes called Sniff and hold mode, in
which device activity is lowered. Also there can be parked units which
are synchronized but do not have a MAC addresses. These parked units
have a 8 bit address, therefore there can be a maximum of 256 parked
devices.
Voice channels use either a 64 kbps log PCM or the Continuous Variable
Slope Delta Modulation (CVSD) voice coding scheme, and never retransmit
voice packets. The voice quality on the line interface should be better
than or equal to the 64 kbps log PCM. The CVSD method was chosen for
its robustness in handling dropped and damaged voice samples. Rising
interference levels are experienced as increased background noise: even
at bit error rates up 4%, the CVSD coded voice is quite audible.
Bluetooth and the Internet
Bluetooth can be used to connect
between a device that has internet connectivity and another device that
does not, for example, you might use Bluetooth to connect from your
PDA to your laptop, and then your laptop might use Wi-Fi to connect to a
Wi-Fi router and from there you would be connected to the internet.
Sometimes when buying a PDA you may find yourself with an apparent
'either//or' choice - either buy a device with Bluetooth; or a device
with Wi-Fi capability. In such a case, it would seem at first glance
that if you want to connect to the internet - especially while traveling
out of your office, Wi-Fi would be a better choice.
However, this is not quite such a clear choice. Wi-Fi 'hotspots' are
few and far between. A much better approach might be to get Bluetooth on
your PDA and also on your cellphone and use Bluetooth to connect to
your cellphone and then connect through your cellphone and out to the
internet from there. I use T-Mobile's GPRS service - they offer
unlimited connect time and unlimited bandwidth usage for only $20/month
extra on top of my regular cellphone service (and GPRS connection time
does not count against my monthly minutes - it truly is unlimited for
only $20/month).
In my opinion, this is the perfect solution. GPRS coverage is much more
widespread than Wi-Fi coverage, and while it is not fast, it is
adequate for simple mail sending/receiving, instant messaging, and
occasional web browsing such as you're likely to do on a PDA. Although I
also have Wi-Fi in my laptop, these days I never use it, and indeed if
I'm sitting in a Starbucks with my laptop, I'll be connecting to the
internet not through the Wi-Fi in Starbucks, but via Bluetooth and my
cellphone's GPRS!
Which is better - Bluetooth or Wi-Fi
Wi-Fi is primarily used as
an alternate to traditional cable based networks. It has a longer range
than Bluetooth, and supports faster data transfer speeds, and so it
might seem better than Bluetooth.
But, in reality, Bluetooth and Wi-Fi have different purposes. Bluetooth
is intended for limited data transfer between many different types of
devices, Wi-Fi is more focussed on faster data transfer between
computers on a network.
One of the distinctive elements of Bluetooth is that is uses very much
less power than Wi-Fi. Class 2 devices (such as are in PDAs, phones,
headsets, etc) transmit a very low power signal (1 mW) and only
transmit intermittently when in standby mode, saving even more power.
Wi-Fi, on the other hand, consumes a great deal of power, and so for any
type of portable battery operated device, Bluetooth will allow for
substantially more battery life than would Wi-Fi.
If you're simply wanting to swap data between different devices in your
office and elsewhere on a casual and occasional basis, then - assuming
that the software and Bluetooth hardware is available - Bluetooth is
probably a better choice for you. If you need more range, and higher
bandwidth; perhaps if you want to connect computers into your office
LAN, then Wi-Fi is a better choice for you.
Bluejacking
Bluejacking is a moderately harmless 'fun' type
trick that some people have discovered. It involves sending messages
from your Bluetooth device to other people close to you with Bluetooth
devices, and surprising the recipient in the process.
The easiest way to Bluejack is to create a new phonebook contact, with
the message you want to send in the name field. Then, in a busy place
with lots of people (so that there is a chance that someone might have a
Bluetooth enabled phone or PDA), choose the option to send your new
contact via Bluetooth. Your phone or PDA will then search for all
Bluetooth devices in range, and present you with a list. Choose
whichever device you wish from the list and send it. The recipient will
get a message asking if they wish to accept your contact, and showing
the text you entered as the contact's name (eg something like 'Bad
weather today isn't it' or whatever else you wish to say).
If you're planning to enjoy Bluejacking (or Toothing, below) you'll
probably want to get your eye in to guessing how far away 10 m/33 ft is
so as to know how many people and devices might be within range.
Toothing
Harmless Bluejacking didn't take long to evolve into a
more goal oriented social activity, now known as 'toothing', whereby
people communicate to other Bluetooth equipped people around them,
trying to arrange casual and immediate trysts.
Summary
Bluetooth promises to be a low cost, convenient, and
simple way of enabling your various computer devices to talk to each
other and to their peripherals. The reality has yet to match the
promise, but Bluetooth is becoming more widespread and functional every
day. Bluetooth is almost certainly in your future.
Bluetooth is not a competitor to Wi-Fi. It offers different functionality for different purposes.
