Radio Frequency Interference (RFI) involves the presence of unwanted interfering RF signals that disrupt the original data signals from wireless devices. RFI in a wireless network may lead to adverse effects, such as intermittent connectivity loss, poor throughput, and low data rates.. There are different types of RFI that can occur in a wireless network environment, and these must be taken into consideration before implementing wireless networks. RFI types include narrowband RFI, all-band RFI, and RFI due to adverse weather conditions.
Narrowband RFINarrowband signals, depending on the frequency and signal strength, can intermittently interrupt or even disrupt RF signals from a spreadspectrum device, such as a wireless bridge. The best way to overcome narrowband RFI is by identifying the source of the RF signal. You can identify the source of the RF signal using Spectrum analyzers.
Spectrum analyzers are devices that can be used to identify and measure the strength of interfering RF signals. Once the source has been identified, you can either remove the source so that there is no RFI, or shield it properly. Because narrowband signals do not disrupt original data RF signals (from a wireless bridge) across the entire RF band, you can also choose an alternate channel for the bridge where there is no narrowband RF interference. For example, if one channel, say channel 11, is disrupted with unwanted RF signals, you can configure the wireless bridge to use another channel, say channel 3, where there is no narrowband RFI.
All-band RFIAs the name suggests, all-band interference involves any unwanted RF signal that interferes with the data RF signal across the entire RF band. All-band RFI can be defined as the interference covering the whole spectrum used by the radio. The entire RF band does not point to the ISM band alone. The RF band covers any band of frequencies that the wireless bridges are using.
A possible source of all-band interference that can be found commonly is a microwave oven. When all-band interference is present, the best possible solution is to use a different technology, such as moving from 802.11b to 802.11a (which uses the 5Ghz band). Also, the whole spectrum used by the radio is 83.5 MHz in FHSS (the whole ISM band), while for DSSS it is only 20 MHz (one of the sub-bands). The chances of having an interference covering a range of 20 MHz are greater than the chances of having the interference covering 83.5 MHz. If changing technologies is not possible, try to find and eliminate the source of the all-band interference. This is difficult, however, because you have to analyze the entire spectrum to track the source of the interference.
RFI Due to Adverse Weather ConditionsSeverely adverse weather conditions, such as extreme wind, fog, or smog can affect the performance of wireless bridges, and lead to intermittent connectivity issues. In these situations, a radome can be used to protect an antenna from the environmental effects. Antennas that do not have radome protection are vulnerable to environmental effects, and can cause degradation to the performance of the bridges. A common problem that can occur if the radome is not used is the one due to rain; the raindrops may accumulate on the antenna and affect its performance. Radomes also protect an antenna from falling objects, such as ice falling from an overhead tree.
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