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What are the limiting factors that prevent access through WiFi to achieve the highest speed the radio link can provide?

Assuming, there is only 1 device (the wireless one) on the network, it's sitting right in front of the router.

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it's sitting right in front of the router. I'm taking it a bit literally, but having experienced it, place the device at least 4-5 feet from the router. This sounds counter-intuitive but an overly strong signal can swamp the receiver circuits in either the device or the router, causing degraded signal reception. – Fiasco Labs Dec 8 '11 at 22:01
up vote 6 down vote accepted

Cable broadband Internet connections in some countries go up to 100 Mbps.

802.11n WiFi is capable of 600 Mbps.

But your particular WiFi router might not provide that speed. Older WiFi devices might operate at 54 Mbps or lower.

In both cases, you won't see 100 Mbps of data because some proportion is consumed in low-level packet overheads and background chatter between devices.

There can be interference on one or more bands from other nearby WiFi devices (your neighbour), from non-WiFi devices that use the same frequencies and from poorly shielded appliances.

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You also have to remember that "600mbps" and "54mbps" etc... are in 1 direction. So the actual throughput is more like 300mbps duplex (up & down) and 27mbps... (you can't transmit & receive at the same time) Most wifi links will never reach full throughput outside of a lab environment. Interference will be the largest factor that will reduce bandwidth... as well as cheap hardware (being a close-second) where the internal CPU can't keep up with the flow of traffic or poorly designed antennas... etc... – TheCompWiz Dec 8 '11 at 16:28
If you live in a densely populated area (and see a lot of available APs, it's always a good idea to move the access point's channel from 6 (the default on every device I've seen). – Tim Coker Dec 8 '11 at 18:58

Make sure your channel is not used by another WiFi network, since this reduces the signal to noise ratio and limits traffic. You can check channels with an WiFi-Analyzer smart phone app for Android.

Also make sure both: router and wifi adapter support the same standard e.g. 802.11n.

And last but not least, if you use an unstable driver for your adapter you might also not end up with maximal speed.

If you plug in your adapter via USB, make sure USB 2.0 or higher is used.

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Also, if you are using 2.4GHz, there are a lot of other devices that share the same radio waves.

It can cause the Wi-Fi to resend packets when it gets congested.

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