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RF signals can reflect (bounce) off of metal obstructions they encounter - for example, doors, ducts, or support beams. Any given radio may receive both the primary signal and one or more reflections of that same signal - this phenomenon is referred to as multipath. Strong reflected signals cause interference by adding or subtracting to primary signal amplitude. Reflections can also leave gaps in RF coverage by canceling out (nulling) the primary signal.
One way to defeat multipath interference is to simply relocate a wireless device and its antenna to avoid obvious obstructions. If relocation proves insufficient, antenna diversity can be used to combat multipath. In this case, an access point with multiple antennas can continuously sample incoming signals, choosing the input source (antenna and receiver) with the best signal, then using the chosen antenna for the next transmission.
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