Don't let wireless LAN transmission impairments ruin your day!

By Jim Geier, |  Networking

The implementation of a wireless LAN may seem easy at first. All you have to do is install a few access points, connect them to an Ethernet switch, and you're ready to go. Right?

Well, it's not always that easy. Unlike wired networks, seen and unseen obstacles can often impede wireless network transmissions. Common wireless LAN transmission impairments include path loss, multipath distortion, and RF interference. If you don't carefully assess the environment where the wireless LAN will operate, then those impairments will cause problems that are difficult to diagnosis and correct after installation.

Path loss, which is the attenuation that a signal undergoes because of the propagation distance between the radio and the access point, is present in all wireless LAN transmissions. In general, path loss varies directly with transmission distance and frequency. As a radio moves farther away from the access point, path loss will increase and cause the signal-to-noise ratio at the receiver to decrease to the point at which the radio is unable to distinguish the data signal from the noise. When that occurs, the radio is operating in a fringe area, the maximum distance from the access point. Of course, that limited range is why you'll often need multiple access points to cover a particular facility.

A problem with path loss is that it will become much more significant as you begin to deploy higher frequency, 5 GHz wireless LANs as specified by the IEEE 802.11a standard. That higher operating frequency will require you to implement a relatively large number of access points to cover the same area of a contemporary 2.4 GHz system.

RF interference is a bit more disruptive than path loss. Because of carrier-sensing medium access protocols, a wireless LAN station will not transmit when it senses other stations transmitting. If the interfering signal falls within the same frequency of the wireless LAN, then the interfering signal will appear legitimate and block the wireless LAN from transmitting. The interfering signal can also strike a packet in transit, resulting in errors, retransmissions, and corresponding delays -- not something that you want to happen.

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