Making WiFi fast

Posted Nov 10, 2016 8:33 UTC (Thu) by Sesse (subscriber, #53779)
In reply to: Making WiFi fast by drag
Parent article: Making WiFi fast

They really don't. In empty space, they fade _exactly_ the same way (it's physics). And like I said in another comment, for most obstructions, they fade very similarly, too. The effects of “the band is seven times as wide” (really!) and “ambient noise tends to be about 3 dB lower on 5 GHz” drowns out these considerations in practice.

Making WiFi fast

Posted Nov 18, 2016 7:11 UTC (Fri) by Sertorius (guest, #47862) [Link] (1 responses)

If you're going to make comments like that, please make sure you actually *know* the physics. The relevant equation in this case, the Friis path loss equation, has a lambda squared on the top, or if you prefer f squared on the bottom. So yes, path loss is significantly lower at lower frequencies; this is the reason that satellites use the lower of a pair of frequencies to transmit (because they are power-constrained); likewise frequency-division duplex phones will use the lower frequency channel for the uplink (again, power-constrained). This is also the best-case scenario; usually the path loss exponent is higher than 2 due to multipath fading (due to reflections).

Here's a graph if you aren't convinced.

5 GHz is severely attenuated by relatively mild obstructions (such as gyprock/drywall or timber) that 2.4 penetrates very easily. If you have concrete or brick walls, you'll want an AP in every room.

The main benefits of 5 GHz are that you have a lot more non-overlapping channels, so it is easier to avoid interference - it is also good if you have a lot of users to support and want to have a LOT of short-range APs.

Making WiFi fast

Posted Nov 18, 2016 8:34 UTC (Fri) by zlynx (guest, #2285) [Link]

The 5GHz fade is also a great thing in apartment buildings. All of your neighbors have a WiFi router that they picked up somewhere and they managed to make it though the configuration wizard. So every single apartment is at 100% transmission power, all of the time. Having the walls cut that down (and having all of the extra channels) really helps.