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A Quagmire of Wireless LAN Standards
By Bhavish Sood

There are many competing WLAN standards, each with its own advantages, limitations and support groups. Get under the hood with a through understanding of various WLAN standards

Wireless LANs are the hot new enterprise technology that everyone is talking about and considering implementing in varying degrees for vertical markets like medical, education, and manufacturing. Although the data communications market is bringing out innovations at a break neck speed it is also sending confusing signals to the consumers who are not sure which standard will attract more products. Lets take a look at some of the Wireless LAN standards and the technologies, which power them.

Under the hood
Before delving straight into the details of Wireless LAN standards lets take a look at technologies that makes it possible for a wireless LAN to operate:

1. Radio Frequency Systems: Radio Frequency is used for applications where communications are over longer distances and terminals are not seen by each other. The Radio Frequency signals travel through walls and communicate where there is no direct path between the terminals. In order to operate in the license free portion of the spectrum called the ISM band (Industrial, Scientific and Medical), the radio system must use a modulation technique called Spread Spectrum (SS). In this mode a radio is required to distribute the signal across the entire spectrum and cannot remain stable on a single frequency. This is done so that no single user can dominate the band and collectively that all users look like noise. The fact that such signals appear to be noise in the band means that they are difficult to find and to jam.

2. Infrared Systems: Infrared systems are rarely used in commercial wireless LANs. Infrared systems use very high frequencies, just below visible light in the electromagnetic spectrum, to carry data. Like light, infrared cannot penetrate opaque objects; it is either directed or diffuse technology. Inexpensive directed systems provide very limited range (3 ft) and typically are used for personal area networks but occasionally are used in specific wireless LAN applications. High performance directed infrared is impractical for mobile users and is therefore used only to implement fixed sub-networks. The application where infrared comes into use is as a docking function and in applications where the power available is extremely limited, such as a pager or PDA.

3. Spread Spectrum Implementation: Most wireless LAN systems use spread-spectrum technology; a wideband radio frequency technique developed by the military for use in reliable, secure, mission-critical communications systems. Spread-spectrum is designed to trade off bandwidth efficiency for reliability, integrity, and security. There are two methods of Spread Spectrum modulation used to comply with the regulations for use in the ISM band: Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS).

  • Frequency Hopping Spread Spectrum (FHSS): Frequency-hopping spread-spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern known to both 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.
  • Direct Sequence Spread Spectrum (DSSS): DSSS takes a signal at a given frequency and spreads it across a band of frequencies where the center frequency is the original signal. The spreading algorithm, which is the key to the relationship of the spread range of frequencies, changes with time in a pseudo random sequence that appears to make the spread signal a random noise source. The strength of this system is that when the ratio between the original signal bandwidth and the spread signal bandwidth is very large, the system offers great immunity to interference. For instance if a 1 Kbps signal is spread across 1 GHz of spectrum, the spreading ratio is one million times or 60 dB. This is the type of system developed for strategic military communications systems as it is very difficult to find and even more difficult to jam.

Wireless LAN Standards
Standards are absolutely critical for both the consumer interest as well as product manufacturers. The Wireless standards market however is plagued by a plethora of standards promoted either by Industry consortiums or by interest groups like IEEE, which recently brought out IEEE 802.11a, which operates at speeds of up to 54Mbps, allowing wireless LANs to accommodate heavier, multimedia-rich traffic loads.

1. IEEE 802.11: In the year 1990 the IEEE 802 standards groups for networking setup a specific group to develop a wireless LAN standard similar to the Ethernet standard. On June 26, 1997, the IEEE 802.11 Wireless LAN Standard Committee approved the IEEE 802.11 specification; a major milestone in the wireless arena for it now provides a solid specification for the vendors to target, both for systems products and components. This standard specifies a 2.4 GHz operating frequency with data rates of 1 and 2 Mbps. The IEEE has since published two supplements to this 802.11 standard: 802.11a (40 Mbps in the 5.8 GHz band), and 802.11b, (11 Mbps in the 2.4 GHz band).

2. HiperLAN2: The HiperLAN2 technology takes advantage of the latest developments in radio technology, MAC protocol for high efficiency and quality of service (QoS), radio resource management, power savings and plug-and-play. HiperLAN2 operates in the dedicated spectrum in the 5 GHz band. It provides connections, which can be assigned a specific QoS over the air between the terminal and the base station. Whilst moving, HiperLAN2 automatically performs handover to the nearest base station (called access point). H2 also has strong security support including both authentication and encryption and has a built-in facility for automatic

frequency allocation, removing the need for manual frequency planning. The standard has tremendous benefits since it offers high-speed wireless connectivity with up to 54 Mbps and seamless connectivity with corporate LAN, 3G cellular systems, mobility and QoS for future applications such as multimedia, voice over Internet protocol (VoIP) and real-time video. By design HiperLAN2 supports time critical services as well as asynchronous data. Thus packetized voice and video—and the QoS needed to deliver them properly—have been included. This also extends to the defined interfaces on the wired side; HiperLAN2 is compatible with ATM, 3G and 1394 networks as well as IP networks. HiperLAN2 includes transmit power control and dynamic frequency selection in the DLC/RLC layer, which should provide greater spectrum efficiency and lower interference probability with other systems operating on 5GHz. While providing high-bandwidth connectivity ensures interoperability with 3G cellular systems, HiperLAN2 is also complementary to other wireless technologies such as Bluetooth.

3. Bluetooth: Bluetooth is a short-range radio technology that allows voice and data connections to be made up to 10 meters (about 30 feet). The range can be extended to 100 meters with an amplifier. The first generation of the technology delivers performance up to 1Mbps. Subsequent versions may deliver anywhere from 2 Mbps to 12 Mbps of throughput. Spanning telecommunications, personal computing, and networking, Bluetooth frees users from having to wrestle with numerous cords and enables a host of new conveniences.

4. HomeRF: IrDA: Infrared Data Association (IrDA) standard provides a cordless, point-to-point cable replacement technology operating from 0 to 1 meter at 9600 bps to 4 Mbps. Although Bluetooth enables movement and greater distance between devices than IrDA, IrDA will still be useful for some functions such as quick e-business card exchange and faster data transfer.

Complexity Keeps Growing
Signal interference, cost and standards obstacles, and on top of this, everyone has a competing technology, from Bluetooth, Home RF, and phone line networking, to Sun's Jini, Universal Plug and Play, and Apple's FireWire. This pace of innovation and company promoted consortiums and standards are as usual creating hindrance in both their adoption and use. HiperLAN a standard currently being drafted by companies like Tenovis (Bosch), Dell, Ericsson, Nokia, Telia, Texas Instruments is fast gaining popularity and 802.11 a is already threatening the Bluetooth popularity, its clear that no one clear standard will see the light of the day and standards will be geographically concentrated, at least for now.

Bhavish Sood can be reached at bhavishsood@netscape.net

 

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