Radio signal interference and degradation

An important challenge with WLANs is radio signal interference. In metropolitan area building-to-building designs, it is possible to have third-party interference from other companies using wireless technology . In this situation, network managers must ensure that different channels are utilized. Interference cannot always be detected until the link is actually implemented. Because the 802.11 standards use unlicensed spectrum, changing channels is the best way to avoid interference.

Many other devices such as portable phones, microwave ovens, wireless speakers, and security devices, also use these frequencies . The amount of mutual interference that will be experienced by these and planned networking devices is unclear. Interference between wireless speakers and other devices is common today. As this unlicensed band becomes more crowded, it is likely that other types of interference will appear. Physical objects and building structures also create various levels of interference.

Operation in unlicensed bands carries with it an inherently higher risk of interference, because the controls and protections of licensing are not available. In the United States, for example, the Federal Communications Commission (FCC) does not have any rule that specifically prohibits a new user from installing a new unlicensed-band radio link in an area and on a frequency that is already occupied. This may result in interference. There are two warnings to be aware of.

The first warning is, if someone installs a link that interferes with a wireless link, the interference is probably mutual. With point-to-point links that employ directional antennas, any signal source of a comparable power level that might cause interference would have to be physically aligned along the transmission path axis. In unlicensed bands, the potential for interference from another unlicensed user is becoming greater than for licensed bands. The difference is one of control. The license holders essentially own a licensed channel. They have a legal right to defend themselves against performance-robbing interference. Due to the popularity of WLANs, the use of unlicensed bands is increasing. Network administrators should be aware that there are other, licensed users who sometimes also operate in the unlicensed bands. The unlicensed bands are allocated on a shared basis. While there may be no requirement to obtain a license to operate a low-power data communications application using approved equipment, licensed users may be allowed to operate with significantly higher power.

The second warning is, it is possible for electromagnetic interference (EMI) to be generated by non-radio equipment operating in close proximity to the Cisco Aironet WLAN equipment. While it is theoretically possible for this interference to directly affect the reception and transmission of signals, it is more likely to affect the components of the transmitter. To minimize the possible effects of EMI, the best course of action is to isolate the radio equipment from potential sources of EMI. The equipment should be located away from such sources if possible, and a source of conditioned power to the WLAN equipment should be provided to help lessen the effects of EMI.

Lab Activity

Lab Exercise: Challenges of Wireless Regulations

The student will learn the future direction and technologies associated with wireless regulations.