wireless local area network
A wireless local area network (WLAN) is a data communications system implemented as an extension—or as an alternative— to a wired LAN. Using a variety of technologies including narrowband radio, spread spectrum, and infrared, wireless LANs transmit and receive data through the air, minimizing the need for wired connections.
Applications Wireless LANs have become popular in a number of vertical markets, including health care, retail, manufacturing, and warehousing. These industries have profited from the productivity gains of using handheld terminals and notebook computers to transmit real-time information to centralized hosts for processing. Wireless LANs allow users to go where wires cannot always go. Specific uses of wireless LANs include
Technologies There are several technologies to choose from when selecting a wireless LAN solution, each with advantages and limitations. Most wireless LANs use spread spectrum, a wideband radio frequency technique developed by the military for use in reliable, secure, mission-critical communications systems. To achieve these advantages, the signal is spread out over the available bandwidth and resembles background noise that is virtually immune from interception. There are two types of spread-spectrum radio: frequency hopping and direct sequence. Frequency-hopping spread spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern known only to the transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel. To an unintended receiver, FHSS appears to be short-duration impulse noise.
Standard Technology – Wireless 802.11 Technologies
802.11b
| Release Date | Op. Frequency | Data Rate (Typ) | Data Rate (Max) |
|---|---|---|---|
| 1999 | 2.4 GHz | 6.5 Mbps* | 11 Mbps* |
802.11b has a maximum raw data rate of 11 Mbps and uses the same CSMA/CA media access method defined in the original standard. Hence, chipsets and products were easily upgraded to support the 802.11b enhancements. The dramatic increase in throughput of 802.11b (compared to the original standard) along with substantial price reductions led to the rapid acceptance of 802.11b as the definitive wireless LAN technology.
802.11b cards can operate at 11 Mbps, but will scale back to 5.5, then 2, then 1 Mbps (also known as Adaptive Rate Selection), if signal quality becomes an issue. Since the lower data rates use less complex and more redundant methods of encoding the data, they are less susceptible to corruption due to interference and signal attenuation. 802.11g, which has data rates up to 54 Mbps is backwards-compatible with 802.11b.
802.11a
| Release Date | Op. Frequency | Data Rate (Typ) | Data Rate (Max) |
|---|---|---|---|
| 1999 | 5 GHz | 25 Mbps* | 54 Mbps* |
The 802.11a standard uses the same core protocol as the original standard, operates in 5 GHz band, and uses a 52-subcarrier orthogonal frequency-division multiplexing (OFDM) with a maximum raw data rate of 54 Mbps, which yields realistic net achievable throughput in the mid-20 Mbps. The data rate is reduced to 48, 36, 24, 18, 12, 9 then 6 Mbps if required. 802.11a has 12 non-overlapping channels, 8 dedicated to indoor and 4 to point to point. It is not interoperable with 802.11b/g, except if using equipment that implements both standards.
Since the 2.4 GHz band is heavily used, using the 5 GHz band gives 802.11a the advantage of less interference. However, this high carrier frequency also brings disadvantages. It restricts the use of 802.11a to almost line of sight, necessitating the use of more access points; it also means that 802.11a cannot penetrate as far as 802.11b/g since it is absorbed more readily, other things (such as power) being equal.
There are dual-band, or dual-mode or tri-mode cards that can automatically handle 802.11a and b, or a, b and g, as available. Similarly, there are mobile adapters and access points which can support all these standards simultaneously.
802.11g
| Release Date | Op. Frequency | Data Rate (Typ) | Data Rate (Max) |
|---|---|---|---|
| 2003 June | 2.4 GHz | 25 Mbps* | 54 Mbps* |
In June 2003, a third modulation standard was ratified: 802.11g. This flavour works in the 2.4 GHz band (like 802.11b) but operates at a maximum raw data rate of 54 Mbps, or about 24.7 Mbps net throughput like 802.11a. 802.11g hardware will work with 802.11b hardware. Details of making b and g work well together occupied much of the lingering technical process. In older networks, however, the presence of an 802.11b participant significantly reduces the speed of an 802.11g network. The modulation scheme used in 802.11g is orthogonal frequency-division multiplexing (OFDM) for the data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps.
The 802.11g standard swept the consumer world of early adopters starting in January 2003, well before ratification. The corporate users held back and Cisco and other big equipment makers waited until ratification. By summer 2003, announcements were flourishing. Most of the dual-band 802.11a/b products became dual-band/tri-mode, supporting a, b, and g in a single mobile adaptor card or access point. Despite its major acceptance, 802.11g suffers from the same interference as 802.11b in the already crowded 2.4 GHz range. Devices operating in this range include microwave ovens, Bluetooth devices, and cordless telephones.
802.11n
| Release Date | Op. Frequency | Data Rate (Typ) | Data Rate (Max) |
|---|---|---|---|
| Expected mid 2007 | 2.4 GHz | 200 Mbps* | 540 Mbps* |
In January 2004 research announced that it had formed a new 802.11 Task Group (TGn) to develop a new amendment to the 802.11 standard for wireless local-area networks. The real data throughput is estimated to reach a theoretical 540 Mbps (which may require an even higher raw data rate at the physical layer), and should be up to 100 times faster than 802.11b, and well over 10 times faster than 802.11a or 802.11g. It is projected that 802.11n will also offer a better operating distance than current networks.
802.11n builds upon previous 802.11 standards by adding MIMO (multiple-input multiple-output). MIMO uses multiple transmitter and receiver antennas to allow for increased data throughput through spatial multiplexing and increased range by exploiting the spatial diversity, perhaps through coding schemes like Alamouti coding.
On May 2, 2006, the research 802.11 Working Group voted not to forward Draft 1.0 of the proposed 802.11n standard for a sponsor ballot. Only 46.6% voted to accept the proposal. To proceed to the next step in the research process, a majority vote of 75% is required. This letter ballot also generated approximately 12000 comments — much more than anticipated.
According to the research 802.11 Working Group Project Timelines, the 802.11n standard is not due for final approval until July 2007.
Wireless Standards Comparison Table
| Wireless Standard | Release Date | Op. Frequency | Data Rate (Typ) | Data Rate (Max) |
|---|---|---|---|---|
| 802.11b | 1999 | 2.4 GHz | 6.5 Mbps* | 11 Mbps* |
| 802.11a | 1999 | 5 GHz | 25 Mbps* | 54 Mbps* |
| 802.11g | 2003 | 2.4 GHz | 25 Mbps* | 54 Mbps* |
| 802.11n | Expected mid 2007 | 2.4 GHz | 200 Mbps* | 540 Mbps* |
Good links for WLAN
Introduction to research 802.11
overview of wireless Local area network
802.11 vs Bluetooth comparison
research 802.11g block diagram
research 802.11 Wireless Local Area Networks
Linuxant Wireless LAN technology to the Linux
wireless LANs with interoperable Layer 2 standards-based software
Multimedia Networks Laboratory
Introduction to wireless networks, 802.11a, 802.11b, 802.11g
Radio theory and link planning for Wireless LAN
A wireless broadband community network
Links information on basic theory of WLANs
The Unofficial 802.11 Security Web Page WLAN security information standards
collection of whitepapers, articles and websites about Wireless / 802.11 Security
Updated news on 802.11a
Updated news 802.11b
Updated news 802.11g
Updated news 802.16
Updated news OFDM
Wireless Lockdown ; guides and help about 802.11 security
WLAN Forum
802.11a System Performance
research 802.11
research802.11a IP
802.11a
802.11g
Glossary of Wlan Terms
IP creation research802.11a
research 802.11a and 802.11g products
802.11a+b
Proxim Products on research 802.11
Wireless Networking research 802.11g
WLAN – Standards
ACL Wireless
research 802.11a Wireless LAN Data Brief
Wireless Knowledge Base
Troubleshooting WLAN Radio Designs Part 1
Troubleshooting WLAN Radio Designs Part 2
RF, Microwave, and Wireless Components
RF Simulation Improves 802.11a System Performance
Amateur and Community Wireless Local Area Networks (WLANs) using Open Spectrum Technology
Database of wireless (wifi) Internet hotspots in Toronto Ontario
Wi-Fi Alliance
A global, non-profit industry association of more than 200 member companies devoted to promoting the growth of wireless Local Area Networks (WLANs).
Wireless LAN resources for Linux
wireless LAN drivers web pages, wireless Linux software on the Internet, security software for your wireless LAN, public wireless Linux networks, wireless LAN hardware (surveys and reviews)
Wireless LAN Association
The Wireless Networking Industries information source – Find out how about wireless LAN fundamentals, proper wireless LAN design, and advanced wireless network security.
Wireless LAN Security
Contains links to 802.11 Security related websites, whitepapers, articles, presentations
Access the
Get research 802 website at: http://standards.research.org/getresearch802/
WLAN standards overview
802.11
The research developed the 802.11 standard for wireless local area networks
(WLANs). There are four specifications including 802.11, 802.11a, 802.11b, and
802.11g. Each 802.11 standard operates in a different GHz range and/or offers a
different speed. 802.11 applies to wireless LANs and provides 1 or 2 Mbps
transmission in the 2.4 GHz band using either frequency hopping spread spectrum
(FHSS) or direct sequence spread spectrum (DSSS).
802.11a
The 802.11a specification operates in the unlicensed 5GHz range and offers data
speeds up to 54Mbps. The 5GHz range is not yet crowded so it offers advantages
in speed over the 802.11b specification which uses the more crowded 2.4GHz
range (which can interfere with cordless phones, microwaves, etc.). However, the
range and speed of 802.11a are inversely related – which is why 802.11a was not
adopted as the WiFi standard. 802.11a uses a modulation scheme known as
orthogonal frequency-division multiplexing (OFDM) versus the FHSS or DSSS. Most
802.11a products are not compatible with 802.11b or 802.11g products (although
this is changing).
802.11b
The 802.11b standard operates in the 2.4GHz range and offers a data speeds up
to 11Mbps. 802.11b is the de facto standard for WiFi services because of its
availability and low price (although 802.11g will now quickly become the
standard). While slower than 802.11a, 802.11b is still as fast as 10BaseT
Ethernet service. 802.11b uses direct sequence spread spectrum (DSSS) and
complementary code keying (CCK) modulation. 802.11b was certified by the research
in 1999.
802.11g
802.11g was approved on June 11, 2003 and offers data speeds up to 54Mbps and
operates in the 2.4GHz and 5GHz range making it backward compatible with
802.11b. Even before the research approval, it was clear the 802.11g would become
the standard for WiFi services and leading manufacturers started to release
products in early 2003. 802.11g uses OFDM modulation but, for backward
compatibility with 802.11b, it also supports complementary code keying (CCK)
modulation.
Wireless LAN Technology
In 1999, the Institute of Electrical and Electronics Engineers (research) published standard 802.11, which
specified a group of technologies governing wireless Ethernet connectivity between client devices—such
as desktop computers, laptops, and personal digital assistants (PDAs)—and the wireless hubs connect-ed
to the physical network. Wireless LANs typically emulate the wired network’s traditional hub-spoke
configuration and comprise two primary components: a wireless network interface card (NIC) and an
access point (AP). The 802.11 standard represents a significant step in electronic-data infrastructure
evolution, which in the last ten years has proceeded from coax, token ring, and 10/100 BaseT Ethernet
cabling to wireless radio transmissions.
The best known and most widely used variation of the 802.11 wireless LAN standard is 802.11b.
Products conforming to the 802.11b standard are called “WiFi” (pronounced Y-Phi) for “wireless
fidelity,” so named by the Wireless Ethernet Compatibility Alliance (www.wi-fi.org). This alliance is an
independent organization that promotes interoperability between 802.11b-based devices.
Under ideal conditions, WiFi products can receive and transmit data at speeds up to 11 Megabits per
second (Mbps). However, in typical conditions, most WiFi devices operate at speeds between 1 and
5 Mbps.
Regarding security and 802.11b, transmission encryption—called Wired Equivalent Privacy (WEP)—
has been incorporated into WiFi products. The goal of WEP is to provide a level of privacy (via the use
of encryption) that is equivalent to wired LAN privacy, which is achieved via various physical security
mechanisms. However, encrypted messages can be intercepted and decrypted. As vendors introduce
new technologies and products, other security gaps are likely to be revealed. For more WEP security
information, visit the UC Berkeley ISAAC Web site (www.isaac.cs.berkeley.edu) or the research Web site
(www.research.org).
research and its member organizations are working to address many of these limitations and vulnerabilities.
Efforts include new wireless LAN standards to increase security, bandwidth, and range, as well as reduce
power consumption. For example, the 802.11a standard, scheduled for 2002 release, is expected to
support speeds up to 54 Mbps. Visit the research Web site for more information on upcoming wireless
LAN standards.
?Benefits of Wireless LANs
A traditionally wired 10/100 BaseT Ethernet LAN infrastructure for 100 people costs about US$15,000
and requires several days to install (see Figure 1). Enterprises that use such an arrangement also incur
additional costs and disruptions with every change to the physical office. (Expenses vary according to
the physical layout and the quality of the equipment used.) Conversely, wireless LANs are less expensive
and less intrusive to implement and maintain, as user needs change.
SIMPLIFIED IMPLEMENTATION AND MAINTENANCE
Wireless APs can be placed in the ceiling, where they can accommodate a virtually endless
variety of office configurations (see Figure 2). Wired LANs, in contrast, consume time and
resources to run cables from a network closet to user’s desktops and to difficult-to-service areas
such as conference room tables and common areas. With a wired LAN, each additional user or
modification to the floor plan necessitates adjustments to the cabling system.
EXTENDED REACH
Wireless LANs enable employees to access company resources from any location within an AP’s
transmission range. This flexibility and convenience can directly improve employee productivity.
INCREASED WORKER MOBILITY
The roaming benefits of wireless LANs extend across all industries and disciplines. The shop
foreman can manage logistics from the warehouse as easily as office-based employees move
about the building with their laptops or PDAs. And field sales employees can connect to public
wireless LANs in coffee shops and airport lounges.
REDUCED TOTAL COST OF OWNERSHIP AND OPERATION
The cumulative benefits of simplified implementation and maintenance, an extended LAN
reach, and the freedom to roam minimize expenses and improve organizational and employee
productivity. The result is reduced total cost of ownership and operation.