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cAP ac /wAP ac: recommended TX power?

Sat Nov 10, 2018 3:22 pm


looking at cAP a or wAP ac devices the Antenna gain dBi for 2.4 GHz / 5.0 GHz is 2 / 2.5
If you have a lot of smartphones connected it doesn´t make sense to have the TX power setting set to maximum value, as they are not able to respond with high power. So, what is your recommendation for TX power for 2.4 and 5.0 GHz?
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Re: cAP ac /wAP ac: recommended TX power?

Sat Nov 10, 2018 4:21 pm

What is working for me is 9 dBm for 2.4 GHz and 15 dBm for 5 GHz. Some 2.4 radios are also disabled. Your milage may vary.
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Re: cAP ac /wAP ac: recommended TX power?

Sat Nov 10, 2018 6:52 pm

There certainly are reasons for lowering AP's Tx power, most notable being reduction of interference to adjacent APs and their clients. However in OP's case this is not the best solution IMHO. If the problem are clients with low Tx power, then the solution is to reject associations from clients with too weak signal. Those clients will be baffled as they will sense SSID but won't be able to connect and they might complain.

One has to keep in mind that WiFi can have assymetric speeds in UL vs. DL. High APs Tx power enables good DL rates through utilization of higher MCS' that need better signal-to-noise ratio at receiver and higher Tx power helps here. If same client has low power transmitter, then UL will suffer due to reverting to lower MCS for UL. At the same time keep in mind that use of higher MCS not only helps particular client to achieve higher datarates (which that client might or might not need), but also reduces air time needed to transfer data for one client thus freeing air for other clients. Or same client in the opposite direction since WiFi is TDD technology.
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Re: cAP ac /wAP ac: recommended TX power?

Mon Nov 12, 2018 2:06 pm

It is much more safer to use the method I described that modifying the tx power directly. You risk damaging the wireless adapter if you accidentally adjust the tx power beyond the capacity of the card. Whereas, modifying the antenna gain allow the ROS to automatically adjust the tx power to ensure that the EIRP stays within legal limits without the risk of damaging the card.
Antenna gain is actually used for decreasing total power output when running frequency-mode=regulatory domain.
Wireless chip will adjust power so tx-power output + antenna gain sum does not go out of regulatory domain limits.

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