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Maximum wifi bandwidth for Hap AC 2

Fri Jan 08, 2021 9:54 pm

I am making some experiments with Hap AC 2 wireless, and the 5 Ghz connection seems slow, the specs say:

Wireless 5 GHz Max data rate 867 Mbit/s
Wireless 5 GHz number of chains 2
Wireless 5 GHz standards 802.11a/n/ac

But under router wireless main menu, registration tab, I only see devices connected up to around 600 Mbps, but these devices can connect faster on other wifi.

- Don't I need to be able to connect at 867 Mbps ?
- And with 2 chains, does it mean that at least 2 devices should run at 867 Mbps at once ?

From what I can tell, it has around 600mbps bandwidth that gets shared between even 2 devices that connect at once, seems too slow :(
// looks like I am not smashing my router after all :) Thanks to Sob, anav, mkx, etc
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Re: Maximum wifi bandwidth for Hap AC 2  [SOLVED]

Sat Jan 09, 2021 2:02 pm

WiFi being TDMA half-duplex, every single device within certain area (defined by signal strength and reception sensitivity of AP) will share the bandwidth available. With 2x2 mimo (that's the number of chains) in 802.11ac theoretical maximum is 867Mbps. From that number it is necessary to substract AP broadcast overhead (e.g. SSID broadcasting) and in case of actual traffic overhead of bi-directional transfers (guard times between Tx and Rx). If there are multiple wireless clients, the overhead increases due to random access procedures and collisions between different clients trying to get radio access at the same time. And then bandwidth has to be divided between Tx and Rx. 2 chains are used by single client, only with 802.11ax multiple chains on AP can be divided between different clients - that's called MU MIMO (multi-user MIMO).
So in reality maximum practical throughput for usual TCP connections (e.g. HTTP) is around half of theoretical value. It can get lower if there are other access points operating on same channel, AP detects "alien" transmissions and doesn't allow transmissions of own clients.

And then the real life conditions drop the raw radio connection rate from maximum possible (you can see less-than-max values in registration table) due to non-ideal radio conditions. These include weak signal level (e.g. anything lower than around -60dBm), too strong signal (receiver sensitivity is too large, with most wifi chipsets that happens at signal higher than approx -35dBm to -40dBm) and external interference - mostly adjacent channel WiFi devices but also co-channel WiFi devices and non-wifi devices such as MW ovens, bluetooth devices, aviational and weather radars, etc.

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