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A laptop's antenna receives signals from a Wi-Fi router in two ways:

  1. signal falling directly on the antenna from the router, say 1 m away
  2. signal coming from same router but bouncing off the walls and traveling some distance, say 10 m.

Therefore, at any point of time, the antenna receives multiple signals at the same frequency. How is the resulting interference taken care of?

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  • $\begingroup$ This is covered extensively in many radar textbooks. In the meantime, draw some diagrams and keep in mind the wavelength of a WiFi signal at 2 or 5 GHz. You only get "interference" if there's a significant phase shift. $\endgroup$ – Carl Witthoft Jul 6 '16 at 14:30
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Wifi uses Orthogonal frequency-division multiplexing (OFDM). OFDM is resilient to delay spreading which essentially is multipath RF signals or signal bouncing off walls per your question. Here is better explanation from PHY Basics: How OFDM Subcarriers Work.

An advantage of OFDM is that by using a reduced symbol rate of 250,000 symbols per second the negative effects of multipath distortion are reduced. Since each symbol occupies more time, there is more resilience to delay spread which is caused by multipath when signal reflections cause multiple copies of the same transmitted symbol to arrive at the receiver at slightly different times.

I suggest that you scan and read the references below for multipath and you will get will better reads to your question.

References:

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