Cannot get 80MHz bandwith on 5G (RT-AC68U) [Solved]

[Rasmus Faber]

Hi,

I recently bought an RT-AC68U router, but I have been having trouble fully utilizing the AC-network.

With the automatic settings, I get a 20 MHz network on channel 36.

If I try to force the bandwidth to 80 MHz, it sometimes give me a 40 MHz network on 36+40 or 52+56, but also sometimes just give me a 20 MHz network on 36 or 110.

Overriding the control channel does not make any difference.

I am currently running Merlin 378.55 firmware with unlocked CFE, but I had the same problem on stock firmware (I only modded it to try to fix the bandwidth issue).

I have verified the small bandwidth with Inssider and I can see that I cannot get close to the expected performance with my Killer 1525 ac adapter (at best I get 300/300 using 802.11ac when I should be able to get up to 867/867).

There are no other 5GHz networks nearby.

Do anyone have any pointers to what I can look into to fix this? Some debug logging I can enable or some other way to set the bandwidth?

Cheers,
Rasmus.

 

[System Error Message]

The reason is that you do not have any 80Mhz capable device to use with it. When you connect a single stream wifi device it will use 20Mhz whereas 2 streams use 40Mhz. Most phones for example use single stream wireless AC. When you have a single stream device connecting to an access point with 3 streams the access point will lower its width to 20mhz and every device connected to it will also lower to 20mhz. If you want to use 80Mhz mode you must only use 3 stream wifi devices while for 40mhz only 2 stream wifi devices which is why there are wifi routers with 2x5Ghz radios so slow devices can use one channel while faster ones can use a different channel.

 

[Rasmus Faber]

The reason is that you do not have any 80Mhz capable device to use with it. When you connect a single stream wifi device it will use 20Mhz whereas 2 streams use 40Mhz. Most phones for example use single stream wireless AC. When you have a single stream device connecting to an access point with 3 streams the access point will lower its width to 20mhz and every device connected to it will also lower to 20mhz. If you want to use 80Mhz mode you must only use 3 stream wifi devices while for 40mhz only 2 stream wifi devices which is why there are wifi routers with 2x5Ghz radios so slow devices can use one channel while faster ones can use a different channel.

Okay, so my best option for now seems to be to use a different SSID for the 5 GHz ac network and only let my 2x2 ac devices connect to that (I do not have any clients that support 3 streams yet).

Seems like a strange design not to be able to let multiple stream devices use the full spectrum while 1 stream devices only use part of it, but I guess there is a good explanation of why that wouldn't work.

Thanks!

 

[thiggins]

Sorry, SysError, but your answer is incorrect. All 802.11ac devices support 80 MHz bandwidth mode in 5 GHz. That's what makes them 802.11ac

A single-stream 1x1 AC device is capable of a max link rate of 433 Mbps in 5 GHz, operating with a 80 MHz wide channel.

Check the MCS tables.

 

[System Error Message]

I guess AC is different. So this means that having a 1 stream device and a 3 stream device on the same AP will work together better? I wonder if you've tested this.

 

[Rasmus Faber]

So how about a 802.11n device connecting on the 5 GHz (I have that)? Could that make the router lower its bandwidth?

Or is it something else entirely, I should look into?

 

[thiggins]

I guess AC is different. So this means that having a 1 stream device and a 3 stream device on the same AP will work together better? I wonder if you've tested this.

How Well Do AC Routers Handle Mixed Networks?

No, AC isn't different. Same mechanism and behavior is found in N devices. N150 1x1 devices require 40 MHz bandwidth to link at 150 Mbps.

 

[thiggins]

So how about a 802.11n device connecting on the 5 GHz (I have that)? Could that make the router lower its bandwidth?

It would not change a client's link rate. When the two devices are operating simultaneously, the AC device's bandwidth will be limited by the N's because the N eats up more airtime. See article link above.

 

[Rasmus Faber]

Clearing the nvram and setting everything up again fixed the problem for me.

Thanks for helping out.