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| CATHAL'S
CORNER |
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Cathal Mc Daid
January 2002 |
Bluetooth & 802.11b - Part 1
Although aimed at different markets and roles, there has long been
speculation about the effects 802.11b (also called Wi-Fi,
IEEE 802.11, Wireless LAN, ... ) and Bluetooth have on each other,
not just technical interference, but also whether they are in
competition with each other commercially. Often these are simplistic
press reports attempting to compare the two and seeking to decide a
winner. This article however explains the similarities and differences
between Bluetooth & 802.11b on a broad level and tries to show that
there is no serious competition between the two. In fact both have their
own advantages and disadvantages, and both technologies can complement
each other.
Note: in this article 802.11 refers to 802.11b
unless specified.
Wireless Technologies
One place where it is correct to assume Bluetooth
& 802.11b are the same is that they are both Wireless technologies.
i.e. their role is to allow the transmission of information between
devices by a radio link, technically speaking: using the atmosphere for
the transmission media. However this is something also shared by devices
such as cellular phones, walkie-talkies, satellite phones etc. However no
one would assume that walkie-talkies are in competition with satellite
phones! this is because there are several fundamental differences, such as
range, price, abilities, primary role, power consumption etc. One of the
most important, if not the most important is range, and this is one field
which is often used (combined with role) to differentiate between wireless
technologies. Common nomenclature is to import network (fixed connection)
definitions like WAN, LAN.
and append W (for wireless) to them. Also a less common term: PAN is used,
(Personal Area Network), and must also be appended with W.
This gives us a segmented view of wireless
technologies. WWAN technologies would include cellular phones such
as GSM, GPRS, CDMA etc.These are characterised by long range and high
power consumption. WLAN technologies would include 802.11, airport etc.
These are characterised by medium power, medium range.Finally WPAN
technologies would include Bluetooth, IrDA, HomeRF. Now we will examine
the 2 technologies in slightly more detail, and what marketplace they are
aimed for.
IEEE 802.11b : History, Technology and Role
Wireless LAN technologies (of which 802.11b is a
member) were originally designed to complement the existing
fixed-connection LANs, made up of wires, fibre optics etc. These media are
tried and tested, however they do require installation and maintenance
costs. Also some buildings present major problems in installing wire, such
as historic buildings or old buildings with asbestos components.
Increasing mobility of the worker due to projects and people that move
frequently and so this presents some problems for hardwired systems. In
1990, the IEEE 802 Executive Committee established the 802.11 Working
Group to create a wireless local area network (WLAN) standard. The
standard specified an operating frequency in the 2.4GHz ISM (Industrial,
Scientific, and Medical) band. Seven years later, the group approved IEEE
802.11 as the world's first WLAN standard with data rates of 1 and 2 Mbps.
Afterwards the committee began work on another 802.11 extension that would
satisfy future needs. Within 24 months, the working group approved two
higher rate physical layer extensions to 802.11. The two extensions were
designed to work with the existing 802.11 MAC layer (Medium Access
Control), with one being the IEEE 802.11a - 5.2GHz, and the other IEEE
802.11b - 2.4GHz. Recently 802.11g has been
announced, which operates at 2.4 GHz and uses OFDM. However in this
article the 802.11 type we are concerned with is 802.11b. The other 2
802.11 standards are less common that 802.11b, and so will not be
addressed.
The 802.11b protocol operates in the unlicensed
2.4GHz ISM band, using DSSS (direct-sequence spread-spectrum)
transmission. Data is transmitted on BPSK and QPSK constellations at
11Msps. Maximum data rate is about 11 Mbits/s with fallback rates of 5.5,
2 and 1 Mbits/s, depending on distance, noise and other factors. Range can
be up to 100m, but this too is dependent on the environment. In a protocol
view, 802.11b only modifies the bottom 2 layers of the 802 model, PHY
& MAC, (OSI layers 1:Physical & 2:DataLink). Any LAN application,
network operating system, or protocol, including TCP/IP and Novell
NetWare, will run on an 802.11-compliant WLAN as easily as they run over
Ethernet.
Thanks to 802.11b's high throughput, medium range
and medium power consumption, a number of application have been designed
and successfully implemented using 802.11b. Sales of network cards for
laptops and desktop computers and Wi-Fi access points are constantly
increasing. Together these allow the user to connect to wired LANs in
airports , shops, hotels, homes, businesses, even city parks. Once
connected the user can surf the net, send and receive email, typically the
same applications the user would attempt on a wired LAN. This shows the
success in using Wireless LAN to augment or even replace wired LANs.
However this all comes at a price: battery power.
Due to 802.11b's power demand to sustain high throughput and medium range,
only certain portable devices like laptops can supply this power for long
and still retain a reasonable batter life. Pagers, handhelds, mobiles etc
are not so lucky, they don't possess the energy to allow 802.11b to
operate for long periods without directly impacting on their own
performance. The price for 802.11b chipsets is also a (declining) factor.
To combat these WPAN technology such as Bluetooth is required.
Bluetooth: History, Technology and Role
Bluetooth is a standard for a small, cheap,
low-power radio chip to be plugged into computers, printers, mobile
phones, etc. A Bluetooth chip is designed to replace cables by taking the
information normally carried by the cable, and transmitting it to a
receiver Bluetooth chip, which will then give the information received to
the computer, phone, whatever. Bluetooth is a WPAN technology; it connects
personal devices within a small area. The Bluetooth specification was
originally conceived by Ericsson in 1998, before a number of other
companies stared to collaborate and launch the Bluetooth SIG (Special
Interest Group). Currently there are over 2500 members of this group. By
signing a zero cost agreement, companies can join the SIG and qualify for
a royalty-free licence to build products based on the Bluetooth
technology.
The Bluetooth protocol also operates in the
unlicensed 2.4GHz ISM band, but uses FHSS (frequency-hopping
spread-spectrum) transmission. Frequency hopping means the Bluetooth chip
transmits and receives on 79 different hop frequencies from 2402 to 2480
MHz, switching between one hop frequency to another in a pseudo-random
sequence, 1600 times a second. It uses GFSK modulation, maximum data rate
is around 721kbits/s and the maximum range is meant to be 10 meters,
although in a clean environment ranges up to 20-30 meters have been
reported. a complete Bluetooth protocol stack has been developed , as well
as imported layers as TCP/IP and OBEX, thus allowing greater
compatibility.
Even though Bluetooth has a much lower range and
throughput that 802.11, it's consequently significantly reduced power
consumption means it has the ability to be much more ubiquitous than
802.11. It can be placed in printers, keyboards, mice, to fulfil its
original role, to replace short-range cables. It can also be placed in
pagers, mobile phones, temperature sensors to allow information download,
monitoring and so on in areas equipped with a Bluetooth access point. Low
power and a projected stabilisation price of ~$5 gives it this potential.
Bluetooth vs. 802.11b ?
After reading the above, one would believe that life
is clear for both technologies. However its human nature to want to do
more with what you have. Directors, Sales managers, engineers, and even
the public would generally have one new technology that go for what they
see as a 'mishmash' of new acronyms in their new wireless device. Heated
debate, overly-optimistic claims and 'mine is better than yours mentality'
has lead to a confusing of the situation. During 2000 and the initial part
of 2001 Bluetooth was seen as the must-have technology, capable of being
everywhere to do a wide variety of roles, limited only by imagination.
Bluetooth profiles that allow access to wired networks and the fact most
companies developed chipsets and applications for both technologies lead
many to assume Bluetooth was trying to become a WLAN contender. However
the subsequent constant delays, public over-exposure, and the fact that
802.11 has had a greater market maturity has now lead to some questioning
the need for Bluetooth at all, and going the way of WAP.
This seems unlikely however. Companies have begun
again to realise that 802.11 and Bluetooth are designed for different
roles. Their is no point trying to force one technology to do what the
other is better suited to do. Bluetooth technology is designed for quick ,
seamless short range networks, and features better power consumption,
small protocol stack, robust data & voice transfer and cheap price.
These same features that make it so suited for WPAN give it a disadvantage
in WLAN terms, were it would be described as slow and limited. Likewise
802.11b is designed for infrequent mobility, IP-based data transmission,
medium range and high data rate make it an ideal choice for WLAN but a
poor choice for WPAN, being clumsy, expensive and power-hungry in WPAN
terms.
Indeed the IEEE and Bluetooth SIG have always tried
to make this distinction, pointing out that they are not in competition
for the same niche, but these points have often been overlooked by
over-ambitious engineers. Ironically, as an indication of the industry
groups position on the standards, the Bluetooth lower protocol layers
are set to become IEEE 802.15.1 , the industry standard WPAN solution!
Clearly no confusing of technology role is foreseen by the IEEE, they
foresee a need for both technologies. A recent raft of positive opinion
and announcements for Bluetooth may have indicated that the tide has
turned once again for Bluetooth. the fact.The fact that Bluetooth chip
sales has overtaken 802.11x chip sales[14]
and the recent declaration by Microsoft that Bluetooth support will be
included in their next release of Windows XP[13],
(together with the fact that 802.11 is already supported) means that
the industry has realised that both Bluetooth and 802.11 both have a role
to play, and indeed can complement each other . So now that we've decided
we need both technologies, can they work with each other?
Continued in part 2...
Part 2 of
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