Types of LANs:

Wireless LAN are generally categorized according to the transmission technique that is used, all current wireless LAN product fall into one of types. There are three types of LAN

• Infrared LANs
• Spread Spectrum LANs
• Narrowband microwave

Infrared LANs:

An individual cell of an IR LAN is limited to a single room, because infrared light does not penetrate opaque walls. Will see some of characteristics details of infrared LANs.

• Strength and weaknesses
• Transmission techniques

Strength and weaknesses:

The infrared has two advantages; the infrared communication can be more easily secured against snooping than microwave and separate infrared installation. The strength of infrared is that the equipment is relatively inexpensive and simple. Infrared data transmission typically uses intensity modulation, so that IR receivers need to detect only the amplitude of optical signals, whereas most microwave receivers must detect frequency.

Infrared LANs have some drawbacks; many indoor environments experience rather intense infrared background radiation, from sunlight and indoor lighting. This ambient radiation appears as noise in an infrared receiver, requiring the use of transmitters of higher power than would otherwise be required and also limiting the range.

Transmission Techniques:

There are three transmission techniques commonly used for IR data transmission. They are

• Directed-beam IR can be used to create point-to-point links.
• Omnidirectional configuration involves a single base station that is with in line of sight of all other station on the LAN.
• Diffused configuration the IR transmitters are focused and aimed at a point on a diffusely reflecting ceiling.

Spread Spectrum LANs:

This type of LAN makes use of spread spectrum transmission technology. In nearly all cases, these LANs operate in the ISM group so that no FCC licensing is required for their use in the US.

Configuration:

In this LANs topology can be either hub or peer-to-peer. I the hub topology, the hub is usually swelled on the maximum and connected to a moral fibre wired LAN to provide connectivity. A peer-to-peer topology is one in which there is no hub. AMAC algorithm such as CSMA is used to control access. This topology is appropriate for ad hoc LANs.

Transmission Issues:

The FCC has authorized two unlicensed application with in ISM band

• Which can operate at up to 1 watt in very low power system
• Which can operate at up to 0.5 watts, the FCC opened this band.

Narrowband microwave LANs:

These LANs operate microwave frequencies but some of these products operate at frequencies that require FCC licensing. It has two-band width they are

• Licensed Narrowband RF has the advantages is that guarantees interference-free communication.
• Unlicensed Narrowband RF can be used for narrowband transmission at lower power 0.5 watts or less.