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I was curious to know how wifi is made robust to interference.How there is almost no interference between wifi signals from two nearby routers?

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  • \$\begingroup\$ What makes you believe that there isn't any interference between various WiFi devices? Is there some specific thing you're interested in, or do you want a broader look? The topic is quite complex. \$\endgroup\$
    – AndrejaKo
    Oct 10, 2016 at 5:37
  • \$\begingroup\$ @AndrejaKo Actually I was more curious to know how the RF interference is handled.If nearby routers are operating at the same channel which is very probable to happen in office complexes,then how do they still deliver pretty optimum perofrmance? \$\endgroup\$ Oct 10, 2016 at 6:48
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    \$\begingroup\$ how do they still deliver pretty optimum performance? I know that a lot of people who live in apartment buildings with many Wifi access points would disagree strongly with you on that. Performance is affected. It still works but certainly not at full speed. \$\endgroup\$ Oct 10, 2016 at 6:54
  • \$\begingroup\$ As an Aussie, may I just say that by far the more difficult problem is: how does the WiFi signal avoid interfering with itself? The signal reflections of a normal environment plays havoc with the transmitter and receiver, such that it's a wonder that an isolated AP-to-client works as well as it does... Why does being an Aussie matter? It's an Australian invention! \$\endgroup\$ Oct 10, 2016 at 9:01
  • \$\begingroup\$ @John Burger, Re "ghosts in WiFi": IMO the answer is OFDM. The frequency channel is subdivided into a couple dozen subcarriers with a lower individual symbol rate, thus only impaired by reflections that are geometrically further away/apart. \$\endgroup\$
    – frr
    Oct 10, 2016 at 11:11

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It depends what you mean by interference.

If you mean data passing through router A 'appears' on router B's clients, then no, this doesn't happen. Each router <-> client link is encoded to label it so that it only gets delivered to the right destinations, even for unencrypted links.

If you mean that RF from router A degrades the signal to noise ratio (SNR) at router B, trashing the throughput, then yes, this is the big problem with closely physically located WiFi links. There are only 11 RF channels defined (around 2.4GHz), and they overlap, so there are only really 3 clean channels 1, 6, and 11. If you have multiple routers operating in the same channel, then numerous data packets will be corrupted and have to be resent.

Microwave ovens, bluetooth devices and cordless telephones also share the same spectrum, and create interference.

A case in point. I have an 'n' router and client, that should be capable of 150Mb/s. When operating on the same channel as three of my neighbours, it drops to 1Mb/s. Move channels and the data rate restriction becomes my LAN or WAN connections.

Use linSSID if you're on linux to have a look at your local WiFi environment.

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