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Infrared WLAN

The primary IEEE 802.11 standards in use today are 802.11a and 802.11b, which both use radio waves for transferring information wirelessly over a network. Few people realize, however, that the 802.11 standard also includes the 802.11 Infrared (IR) Physical Layer. 802.11 IR defines 1Mbps and 2Mbps operation by bouncing light off ceilings and walls to provide connectivity within a room or small office. This infrared version of the standard has been available since the initial release of the 802.11 standard in 1997.

The reason that 802.11 IR is unheard of is that there are no known vendors that sell products compliant with 802.11 IR. Some offer infrared-based wireless LANs that come close to the standard. For example Spectrix, once the chair of the 802.11 IR group, offers wireless LAN products that implement diffused optical technologies very similar to 802.11 IR.

There have not been any updates to the 802.11 IR standard in order to successfully compete with the higher performing 802.11a and 802.11b. With only 2Mbps data rates, most IT organizations opt for radio-based solutions instead. As a result, 802.11 is known primarily as a radio-based technology.

The primary difference between infrared and radio wireless LANs is the frequency of the transmitted signal. 802.11a and 802.11b operate in the 2.4 and 5GHz bands respectively, but infrared systems use frequencies in the terahertz range. This places infrared signals in the light region invisible to the human eye and beyond the control of the Federal Communications Commission (FCC).

Because of the extremely high frequency, infrared light is highly reflective, which makes it behave like an incandescent light bulb. Each client station (e.g., laptop or PC) is equipped with an infrared transducer that can both transmit and receive light signals. The transducer diffuses the light, which makes the signal available from anywhere within a typical room.

Infrared-based wireless LANs pulse a light on and off to represent the transmission of data bits with a carrier sensing mechanisms that are similar to what the 802.11 Medium Access Control (MAC) Layer provides. Stations take turns sending light signals addressed to another station that's capable of receiving the light.

Attributes Worth Considering

Before assuming that a radio-based solution is best for meeting wireless LAN requirements, think about the following attributes that infrared wireless LANs provide:

  • Higher security. Infrared light doesn't go through walls, so it's nearly impossible for an unauthorized person from outside the physical controlled area of the facility to eavesdrop on the system. This also makes denial of service attacks difficult to stage.
  • No radio frequency (RF) interference. Because infrared wireless LANs operate in the light frequency range, there is no possibility of either inward or outward interference with RF systems. In fact, an infrared wireless LAN can satisfy specific mobile applications (possibly ones requiring very high security) in the midst of a radio-based wireless LAN without any consideration of RF interference.
  • Limited range. Infrared light doesn't propagate through walls, which demands an access point in each room when providing coverage throughout a facility. This could make the system more expensive than deploying 802.11b access points that can each cover several rooms. The limitation of range to a single room, however, enables a higher concentration of access points, which can provide relatively high capacity despite the somewhat lower data rates provided by infrared access points.
  • Proprietary products. One of the biggest issues with infrared wireless LANs is the lack of conformance with standards. As a result the solutions are proprietary, meaning that the transducers and access points must be from the same vendor. This limits the use of infrared wireless LANs to scenarios where you have total management control over the client devices, which is not the case in public hotspots (e.g., airports and convention centers) and larger corporations.

Even though the traditional technology for wireless LANs is radio waves, at least ponder the idea of using infrared as an alternative. In almost all cases, the use of radio waves will prevail, but you may have a unique application that an infrared wireless LAN will satisfy the best.

Jim Geier provides independent consulting services to companies developing and deploying wireless network solutions. He is the author of the book, Wireless LANs and offers workshops on deploying wireless LANs.

Join Jim for discussions as he answers questions in the 802.11 Planet Forums.