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WiFi Networks



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.Itís 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.




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 Western Europe, Japan, and is also used by AT&T Mobility (among other smaller carriers) in America.Verizon has also announced plans for service.


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 U.S., but Sprint just fired the CEO who championed the technology, so stay tuned.


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 Vancouver, PanAmSat will use WiMax to deliver what it claims to be the first-ever live video sent by satellite to a handheld device.

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 U.S.."Satellite-delivered WiMax technology is the future for handheld devices such as smartphones and laptops. WiMax will also enable the delivery of IPTV throughout the US, as well as being integrated into our satellite news gathering or SNG services."Bruce Haymes, PanAmSat.









About the Author:


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.






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