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HOME REVIEWS CONTACT ABOUT March 14,
2009
WiFi Networks
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WiFi networks (802.11) are
being implemented by individuals
and organizations
of all sizes to improve productivity and decrease
costs.
There is a large bandwidth available (83.5 MHz), but even
so, the
2.4 GHz frequency band can sometimes become crowded
with
other 2.4 GHz devices like Bluetooth, microwave ovens, and
cordless
phones.
If there
is high network utilization, today's wireless LAN products
can
behave unpredictably. However, currently, most enterprise WiFi
networks
have relatively low utilization. In the
future, as wireless
LANs
assume a more central role, interference problems could
become
more critical.
American
Airlines is now equipping transcontinental 767s with
WiFi
access via Aircell, who is also doing something similar
with
Virgin Airlines. It’s perhaps a sign of
things to come.
Key Attributes
q High Data Rates
q 802.11b: 11 Mbps, uses direct sequence spread spectrum
(DSSS) modulation with Complementary Code Keying (CCK).
q 802.11g, 54 Mbps, uses orthogonal frequency-division
multiplexing (OFDM) modulation to increase the throughput.
q 802.11g systems operate in the same
2.4GHz spectrum as the 802.11b systems and is backward compatible with existing 802.11b
infrastructure. The term used to describe these devices is dual-band. Like
802.11b, 802.11g is limited to three non-overlapping channels.
q Reasonably priced.
q Weather Tolerant.
q Line of Sight is required for longer ranges (more than
1/4 mile).
q Maximum Wattage for the Transmitter (without FCC
licensing) is 1 Watt.
q Half-Duplex Protocol: the system receives or
transmits, but not simultaneously.
Access
points and wireless routers have an advantage over laptop and desktop cards
because they have a higher output power and therefore have the ability to send
a signal further then most laptop and desktop cards. When a higher-gain antenna
is installed on a desktop card the output power of that device is now increased
closer to the output level of the access point or wireless router therefore
equaling the two devices. In some cases, the antennas of both the access
point/wireless router and the desktop/laptop card may need to be replaced. This
is if the distance you are attempting to achieve is greater than the
capabilities of the access point/wireless router when using the antennas that
came with your card.
Wireless
network cards come in a couple of flavors, including a PCI card for
workstations and PC cards for laptops and other mobile devices. They can act in
a decentralized client-to-client mode, or in a centralized client-to-access
point mode. An access point is essentially a hub that gives wireless clients
the ability to attach to the wired LAN backbone. In a decentralized mode, the
wireless network card is configured to talk with other wireless network access
cards that are within its range. Decentralized client-to-client (also know as
peer-to-peer) WLANs are useful for small roaming workgroups that do not require
access to the LAN backbone or internet.
The use
of more than one access point in a given area is facilitated by the use of cell
structures, which are similar to what mobile phone providers use to maintain
your coverage area. One of the benefits to roaming mobile users is the ability
for one access point to automatically hand off communication to the next access
point in a roaming cell.
When
connecting two or more buildings it is best to first establish a wireless
bridge between the two points in the backbone. If you want to be wireless
within a building, once the building-to-building bridge is created, then
attempt to establish a wireless network within each building or location.
Desktops, laptops, and other client devices will not work reliably if the
access point/wireless router is not resident in the building where the access
point/wireless router is located.
Unobstructed
Line-Of-Sight
802.11b and
802.11g at 2.4GHz requires unobstructed visual Line-Of-Sight (LoS). There
should not be trees, terrain, or structures between your two (antenna) points.
Radio waves at this frequency will not penetrate metal, steel, concrete, stone,
etc. However, dry wall, sheet rock, and wood usually are not a problem.
Surrounding
the visual Line-Of-Sight is the "Fresnel zone". Any obstructions that
come into the Fresnel zone, although not obstructing the visual Line-Of-Sight,
may also slow down, hinder and affect your signal. The radio waves may deflect
off of those obstructions. This is called Near Line-Of-Sight. Although you may
see a slight signal with nLoS situations, your data transfer rate may decrease.
An obstruction that cuts across the visual Line-Of-Sight and prohibits an
optical visual between the two antennas in your bridge is considered
Non-Line-Of-Sight.
You may
find in your bridge application that the two antennas can visually see each
other through spaces and breaks in an obstructing tree or tree line.
Additionally, weather, RF interferences, and other site variables can have an
effect on your signal too.
Security
Extensible
Authentication Protocol, or EAP, is a universal authentication framework
frequently used in wireless networks and Point-to-Point connections. EAP can provide a secure authentication
mechanism between the client and NAS. EAP can support multiple authentication
mechanisms, such as token cards, smart cards, passwords, and public key encryption
authentication.
q 802.11i is WiFi (802.11g) with better security. Authentication mechanisms are automatically
changed frequently, preventing hackers from gaining access.
q 802.11n, this standard is still in the approval stage,
with final approval expected in 2009. It
uses multiple-input multiple-output (MIMO), a signal processing technique for
transmitting multiple data streams through multiple antennas. It offers five
times the throughput (300 Mbps) and up to twice the range compared to the
802.11g standard. Equipment meeting the
draft standard is already available, but there is no guarantee that networks
built under today's 802.11n draft standard will be software upgradeable to the
final ratified standard.
The Future: W-CDMA &
WiMax: WiFi on Steroids
Although
the WiMax boasts over 275 WiMax deployments throughout the world (mostly small
regional operators), the only place where WiMax has been a business success is
in Russia, where existing broadband infrastructure was very poor. In emerging
markets without extensive broadband infrastructure (DSL, cable), WiMax has an
advantage over W-CDMA. Many cell-phone
operators have invested in existing networks that naturally evolve into W-CDMA.
W-CDMA
(Wideband Code Division Multiple Access) is a type of 3G cellular network and
where much of the mobile broadband industry is heading if they aren't already
there. W-CDMA is the standard used in UMTS networks, which have been deployed
in much of
W-CDMA
is a European standard designed to support data transmission rates of 144 Kbps
for use in vehicles, 384 Kbps for pedestrian use and up to 2 Mbps for use
indoors.
WiMax
(Worldwide Interoperability for Microwave Access) will be similar to cellular
coverage, but with Wi-Fi's speed and lower cost. With players like Intel
leading the way to make sure WiMax chips are built into future laptops, there
is a lot of money riding on this technology.
·
(WiMax is) the
most important thing since the Internet itself." Intel
(the single largest investor in WiMax technology).
WiMax
technology will allow an operator to build a wireless network over a large area
(city) that will allow high-speed connections to the Internet. As with early cell phone coverage, rural
areas will be the last to receive service, but WiMax has a communication range
of up to 30 miles.
WiMax
supports peak data speeds of about 20 Mbps, but, as with most wireless technologies,
that bandwidth will be shared amongst users.
The average will see user data rates between 1 Mbps and 4 Mbps.
WiMax
will allow users to access the Internet with their laptops or PDAs anywhere in
a network. Sprint announced implementation in 19 major metropolitan markets in
the
One
problem has been that forecasts for WiFi subscriptions that were used to
justify the investment in WiMax have been overly optimistic. Between
15% to 30% of an area's population was expected to subscibe to WiMax,
but, so far, only 1% to 2% have subscribe so far according to Glenn Fleishman,
Wifinetnews.com.
WiFi
networks, including the newer technologies like WiMax, will continue to become
more prevalent in the future. There is the obvious: no dangling cables, but
also the performance is very good. The
main obstacle to the development of WiMax is not technical, it is a business
issue. The same companies which provide
DSL are the companies that need to be motivated to move on WiMax. Once a critical mass of not just a locale,
but of internet users worldwide, is on board, WiMax will probably be quickly
adopted in mass.
Satellite Delivered WiMax
A satellite communications company has called
satellite-delivered WiMax "the future for handheld devices." At a
WiMax Forum Plenary today and tomorrow in
PanAmSat predicts that PDA, cell phone, and laptop users to access the Internet
via satellite sourced WiMax. But also,
the technology will be a way to deliver TV throughout the
Brian Bradshaw is an InfoComm Certified Technical Specialist (CTS), Microsoft Certified Technology Specialist (MCTS), and CompTIA A+ Computer Technologist. Areas of expertise include Video, HDTV, Audio, Computation, SATCOM Systems, and Communications.
Website: http://bradshaw-vacuum-technology.com/
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