Wireless Communication

Chapter: Network Concepts and Standards

Wireless Infrared

Contributed by J.M. Kahn

Free-space infrared links offer an economical, high-performance alternative to radio for many applications of short-range wireless communications. While the fact that infrared does not pass through walls limits the coverage that can be achieved by an infrared transmitter, it yields several key advantages. The same vast infrared bandwidth can be reused in different rooms without limit, so that infrared is unregulated worldwide. Infrared communications cannot be detected outside of enclosed spaces.


Figure: Non-directed wireless infrared LANs, showing use of wireless access to a backbone network, as well as an ad hoc network.

Traditionally, wireless infrared transmission links have been classified according to whether they employ directional or non-directional transmitters and receivers, and whether or not they rely upon the existence of an uninterrupted line-of-sight path between the transmitter and the receiver. Non-directed, non-line-of-sight, or diffuse infrared links behave much like radio links, and are used in several commercially available in-building wireless LANs.

Regulatory Considerations

Because the infrared bandwidth is unregulated, identical infrared systems can be operated worldwide. While the power emitted by an infrared transmitter is subject to regulation to prevent ocular hazards, regulations permit sufficient power levels to be radiated from non-point sources. Eye-safe infrared sources can employ LEDs, or can utilize high-efficiency, narrow-band laser diodes (LDs), whose output can be shaped to an arbitrary eye-safe angular distribution using a computer-generated hologram (CGH) as a diffuser.

Standardization

The Infrared Data Association (IrDA), a consortium of over 100 companies, has developed standards for directed, line-of-sight links over the past two years, e.g. for interconnection between notebook computer and a GSM phone. Bit rates are 115 kbit/s and higher.


Figure: Infrared hub allowing interconnection of IrDA-equipped devices in a multi-megabit-per-second wireless LAN.

Future Developments

Optical technology and communication techniques could enable the realization of a LAN that employs very high-bit-rate (up to 100 Mb/s) diffuse infrared links to access a wired backbone. Such a LAN would enable users to run communication-intensive applications, including real-time video, on portable computers.

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JPL's Wireless Communication Reference Website © Joseph Kahn (Author) and Jean-Paul M.G. Linnartz (Editor), 1993, 1995.

Joe Kahn authered an overview article for Proceedings of the IEEE, February 1997