Wireless Access

Good morning community,

I am trying to adjust the power levels of a cluster of 8 IAPs (17 meters far each other approx.) to make the 5 GHz band more attractive to clients. Before making any change and with the default power levels settings which is Min "18" and Max "max" for both bands, Aruba Central showed some IAPs were 22 (2.4 GHz) and 23 (5GHz), and some 22 (2.4 GHz) and 20 (5GHz).

In addition to set the Band Steering Mode to "Prefer 5GHz" which is the default, now I have changed the power levels settings according to the RF and Roaming Optimization for Aruba 802.11ac Networks VRD, which says:

- A difference of not more than 6dbm should be maintained between minimum and maximum transmit power within each ARM profile.

- A difference of 6dbm should be maintained between 802.11a and 802.11g radios, so that both bands have equal coverage and clients do not switch to 802.11g radio due to stronger signal strength.

With this, I have configured for 2.4 GHz band Min "15" and Max "21" and for 5GHz band Min "21" and Max "27". After applying this change, Aruba Central shows some IAPs are 15 (2.4GHz) and 23 (5GHz), some 21 (2.4GHz) and 23 (5GHz), one 21 (2.4GHz) and 20 (5GHz) and one 18 (2.4GHz) and 20 (5GHz).

With this result, I see clients would not be steered to the 5GHz band, at least in terms of coverage since the 5GHz band is not 6 dB more than the 2.4GHz band and it would have less coverage.

What changes would you do?

Hi guys,

I have been tweaking the power levels and I have ended up with Mix "12" and Max "18" for 2.4GHz, and Mix "18" and Max "24" for 5GHz. With these settings the 5GHz power is around 5 dB higher than the 2.4GHz power in most of the IAPs, like 18 dBm for 2.4GHz and 23 dBm for 5GHz. With all these I think the design is more orientated to the 5GHz band as desired and clients would prefer such band. For those with hands-on experience on this, does these values make sense to you?

In most countries, the 5 GHz radio will only be allowed 200mW, which is 23 dBm [EIRP]. So that is why the APs will not go beyond 20-23 dBm (depending on the AP).

Also, operating the radio's at such high levels will create unbalance between the client transmit power and the AP transmit power, which is a bad thing in roaming, sticky clients, far away clients, hidden-node, etc.

From the 802.11ac VRD, I found this table in the WLAN Optimizations chapter:

Open Office:
 5 GHz: Min 12/Max 15 
 2.4 GHz: Min 6/Max 9
Walled Office or Classroom:
 5 GHz: Min 15/Max 18
 2.4 GHz: Min 6/Max 9

As you can see these values are much lower, still have the 6 dB between 2.4/5Ghz. Much has to do with a good RF planning, where we, in general, will not design that radios should go over 15 dBm of power to get proper coverage; in high-density power-levels should even be lower.

Hi Herman,

Good point, before following these recommendations I have seen at the beginning of the VRD that is intended for wireless LAN controllers:

This guide is intended for those who are willing to learn about the 802.11ac standards and understand the best practices in deploying a high-performing 802.11ac WLAN network by using wireless LAN controllers and Access Points (APs) from Aruba Networks, Inc.

My case is a cluster of Instant APs. Are these recommendations also applicable to Instant APs? I think they are but there is the Aruba Instant VRD, which also has some recommendations about power levels, but it is not as explicit as the 802.11ac VRD, since it doesn't differentiate between 2.4GHz and 5GHz band power levels. Please confirm if the power levels table of the 802.11ac VRD is also valid for Instant deployments.

Thanks for your interest on this.

Julián,

Yes, it will also apply for Aruba Instant, as it is more technology in general. If you have third party equipment, even then these guidelines for power-levels apply. In fact, it is generic WLAN engineering where you plan cell-sizes for good enough coverage, but low enough to prevent the co-channel interference; and keep in balance between the APs (approx equal sized) and AP-client (AP should not be much higher powered than client).

Herman

Hi Herman,

Ok, I guessed that. Indeed they are high power levels, I will lower them. Good explanation, many thanks for clarifying!