Wireless PAN Technologies
Wireless PAN technologies utilize both radio frequencies and
infrared light, depending on the application.
802.15
The IEEE 802.15 standards working group focuses on the
development of standards for wireless PANs and coordinates with other standards,
such as 802.11 wireless LANs.
The 802.15 standards working group contains the following
elements:
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802.15.1— This working group,
Task Group 1, defines a wireless PAN standard based on Bluetooth v1.1
specifications, which uses frequency hopping spread spectrum (FHSS) and operates
at up to 1 Mbps. The 802.15 group published 802.11.1 in June of 2002, and it is
meant to serve as a resource for developers of Bluetooth devices.
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802.15.2— The group
responsible for this standard, Task Group 2, is defining recommended practices
to facilitate the coexistence of 802.15 and 802.11 networks. An issue is that
both networks operate in the same 2.4 GHz frequency band, making coordination
between operations necessary. The group is quantifying the interference and
proposing methods to counter the interference.
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802.15.3— This is Task Group
3, which is drafting a new standard for higher-rate wireless PANs. Data rates
include 11, 22, 33, 44, and 55 Mbps. Combined with these higher data rates,
quality of service (QoS) mechanisms make this standard good for satisfying needs
for multimedia applications. This group is also focusing on lower cost and power
requirements. A draft of the 802.15.3 standard is now available for purchase.
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802.15.4— This group, Task
Group 4, is investigating the definition of a standard with low data rates that
leads to extremely low-power consumption for small devices where it's not
practical to change batteries within months or years. For example, sensors,
smart badges, and home automation systems are candidates for this technology.
Data rates include 20, 40, and 250 kbps. A draft of the 802.15.4 standard is now
available for purchase.
Bluetooth
The introduction of Bluetooth in 1998 was the result of several
companies, including Ericsson, IBM, Intel, Nokia, and Toshiba, working together
to create a solution for wireless access among computing devices. Bluetooth,
which is a specification and not a standard, is ideal for small devices with
short-range, low-power, and inexpensive radio links. This makes Bluetooth a good
solution for connecting small devices within range of a person in a small
working area. That's why the 802.15 chose Bluetooth as the basis of the 802.15.1
standard.
Basic Features
The Bluetooth Special Interest Group (SIG) published the
initial version of the specification in mid-1999. There have been updates since
then, but the technical attributes are essentially the same. Bluetooth
transceivers operate at up to 1 Mbps data rate in the 2.4GHz band, using FHSS
technology. It constantly hops over the entire spectrum at a rate of 1,600 hops
per second, which is much faster than the 802.11 version of frequency hopping.
Low-power Bluetooth devices have a range of 30 feet. High-power
Bluetooth devices, however, can reach distances of around 300 feet. The
high-power mode, though, is rare.
Bluetooth modules have relatively small form factors. Typical
measurements are 10.2 x 14 x 1.6 millimeters, which is small enough to fit in a
variety of user devices.
Bluetooth enables automatic connection among Bluetooth devices
that fall within range of each other, but a user has the ability to accept and
disallow connections with specific users. Users, however, should always be aware
of whether their Bluetooth connection is enabled. To ensure security, disable
the Bluetooth connection. Encryption is also part of the specification.
Could Bluetooth Replace Wireless LANs?
Bluetooth has characteristics similar to wireless LANs. Through
the use of the high-power version of Bluetooth, manufacturers can develop
Bluetooth access points and routers with a similar range as 802.11 networks. The
current Bluetooth products, however, are mostly low power and focus on wireless
PAN functions. In addition, it would be difficult for any Bluetooth wireless LAN
products to gain a strong foothold in the market because 802.11 products already
have widespread adoption.
The place where Bluetooth falls behind 802.11 is performance
and range. 802.11 components can reach data rates of up to 54 Mbps, while
Bluetooth lags way behind at around 1 Mbps. This might be good enough for most
cable replacement applications— such as an interface between headphones and a
PDA— but higher performance is necessary when surfing the web through a
broadband connection or participating on a corporate network. Also, the range of
802.11 is typically 300 feet inside offices, which is much greater than
Bluetooth. Bluetooth would require many access points to fully cover larger
areas.
As a result, it's highly unlikely that Bluetooth products will
win over 802.11. This is certainly apparent because electronics stores primarily
sell 802.11 (Wi-Fi) solutions for wireless LAN applications, not Bluetooth.
Could Wireless LANs Replace Bluetooth?
It's possible that 802.11 wireless LANs could have a big impact
on the sale of Bluetooth devices, mostly because 802.11 meets or exceeds nearly
all of the characteristics of Bluetooth. Because widespread adoption of
Bluetooth is still lacking, there's time for 802.11 vendors to get their foot in
the door with manufacturers needing support for wireless PANs.
Some modifications would need to be made, however. The size of
802.11 components needs to be smaller, but that is becoming more of a reality as
semiconductor companies strive for miniaturization of their 802.11 chipsets.
These smaller components require less power, making them more competitive for
devices, such as mobile phones, that have smaller batteries. With the 802.15
group defining standards for wireless PANs based on Bluetooth— and the 802.11
group focusing on wireless LANs— it's likely that both Bluetooth and 802.11 will
continue to coexist and complement each other.
Minimizing Bluetooth Interference
As more wireless products become available, you need to
carefully manage potential frequency interference. Tests have shown significant
interference between Bluetooth and other systems operating in the 2.4 GHz band,
such as 802.11 wireless LANs. A critical problem is that Bluetooth and 802.11b
neither understand each other nor follow the same rules. A Bluetooth radio might
haphazardly begin transmitting data while an 802.11 station is sending a frame.
This results in a collision, which forces the 802.11 station to retransmit the
frame. This lack of coordination is the basis for radio frequency (RF)
interference between Bluetooth and 802.11.
Because of the potential for collisions, 802.11 and Bluetooth
networks suffer from lower performance. An 802.11 station automatically lowers
its data rate and retransmits a frame when collisions occur. Consequently, the
802.11 protocol introduces delays in the presence of Bluetooth interference.
The full impact of RF interference depends on the utilization
and proximity of Bluetooth devices. Interference occurs only when both Bluetooth
and 802.11b devices transmit at the same time. Users might have Bluetooth
devices in their PDAs or laptops, but no interference will exist if their
applications are not using the Bluetooth radio to send data.
Some Bluetooth applications, such as printing from a laptop or
synchronizing a PDA to a desktop, utilize the radio for a short period of time.
In this case, the Bluetooth devices are not active long enough to noticeably
degrade the performance of an 802.11 network. For example, a user might
synchronize her PDA to her desktop when arriving at work in the morning. Other
than that, their Bluetooth radio might be inactive and not cause interference
the rest of the day.
The biggest impact is when a company implements a large-scale
Bluetooth network, such as one that enables mobility for doctors and nurses
using PDAs throughout a hospital. If the Bluetooth network is widespread and
under moderate-to-high levels of utilization, the Bluetooth system will probably
offer a substantial number of collisions with an 802.11 network residing in the
same area. In this case, Bluetooth and 802.11 would have difficulties
coexisting, and performance would likely suffer.
In addition to utilization, the proximity of the Bluetooth
devices to 802.11 radio NICs and access points has a tremendous affect on the
degree of interference. The transmit power of Bluetooth devices is generally
lower than 802.11 wireless LANs. Therefore, an 802.11 station must be relatively
close (within 10 feet or so) of a transmitting Bluetooth device before
significant interference can occur.
A typical application fitting this scenario is a laptop user
utilizing Bluetooth to support connections to a PDA and printer and 802.11 to
access the Internet and corporate servers. The potential for interference in
this situation is enormous, especially when the user is operating within outer
limits of the coverage area of the 802.11 network. Figure 4-7 illustrates this situation. The signal from the
Bluetooth device will likely drown out the weaker 802.11 signal because of the
distance of the access point.
Here are some tips on how to avoid interference from Bluetooth
devices:
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Manage the use of RF devices—
One way to reduce the potential for interference is to regulate the types of RF
devices within your home or office. In other words, establish your own private
regulatory body for managing unlicensed RF devices. The extreme measure would be
to completely ban the use of Bluetooth; however, that is not practical or even
possible in all cases. For example, you can't feasibly prohibit the use of
Bluetooth in public areas of large offices. For private applications, you could
set company policies to limit the use of Bluetooth to specific applications,
such as synchronizing PDAs to desktops.
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Ensure adequate 802.11
coverage— Strong, healthy 802.11 signals throughout the coverage areas
reduce the impact of the Bluetooth signals. If wireless LAN transmissions become
too weak, the interfering Bluetooth signals will be more troublesome. Perform a
thorough RF site survey, and determine the appropriate location for access
points.
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Move to the 5 GHz band— If
none of the preceding steps solve the problem, consider using a 5 GHz wireless
LAN such as 802.11a. You can completely avoid RF interference in this band— at
least for the foreseeable future.
IrDA
Bluetooth's primary competitor is Infrared Data Association (IrDA), which has been
defining and publishing since 1993. The IrDA has a charter to create an
interoperable, low-cost, low-power, serial data communications standard for
short-range applications. IrDA has been around for much longer than Bluetooth.
In fact, many laptops and cell phones have been coming equipped with an IrDA
interface for years.
Basic Features
The basis for IrDA is infrared light, which doesn't go through
walls and other obstacles. This strictly limits the range of IrDA devices to
within an obstacle-free room. This makes IrDA useful only for point-to-point
applications, such as synchronizing PDAs to PCs. An advantage of IrDA, however,
is that there's no worry about RF interference.
The IrDA data standard, which is best for devices such as an
MP3 player needing to stream information, offers up to 4 Mbps data rates. This
version of the standard has up to 3 feet (1 meter range), but low-power versions
significantly conserve battery power and reduce operation to approximately 8
inches (20 centimeters).
To effectively support wireless computer peripherals, such as a
keyboard or mouse, the IrDA control version of the standard reduces data rates
to 75 kbps. In addition, the host computer can communicate with up to eight
peripherals simultaneously.
note
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For more information regarding the IrDA specification and
related products, refer to http://www.irda.org. |
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