WAP371 - Transmit power?

Didier_DN · ‎08-29-2015

Hi!

Recently I had to setup some good Wi-Fi coverage in a large flat located in a very old building, that is to say with huge brick walls (some are 70 cm / 2 feets thick with some iron structure inside ...). Long story short as I knew multiple antennas would be required, I decided to setup a small cluster of 3 WAP371 located at strategic places in the flat.

I've been tinkering with the settings for a while and finally found a reasonably good setup for most of the devices. I'm just facing one issue I can't solve, thus I'm kindly asking you some advice.

By default, no surprise, the 5 GHz signal is much more attenuated by the thick walls, so usually the signal from the 2.4 GHz radio is stronger, meaning that most of the devices will quickly switch to this network, in spite of the fact its throughput is not good at all. Indeed here in France (and I guess it's the same everywhere), the 2.4 GHz band is crowded and I can detect 30+ networks from my couch (broadband modems from the neighbours ...), meaning that whatever the settings, the speed is usually pretty bad. On the contrary, there is only one other 5 GHz network in the vicinity and on this band I can achieve very good performance (something like 400 mbps - perfect at home).

The easy solution I imagined was to lower the transmit power of my 2.4 GHz radios so their signal is on a rough par with the 5 GHz signal, but whatever the setting I applied (50%, 25% and even 12%), the signal strength doesn't seem to decrease. The documentation says that depending on the country and the channels in use, the change in power can be lower than expected, but in my case it seems this transmit power setting doesn't make any difference at all.

I've enabled the Channel Management feature on the cluster, so is it possible it also manages the power of the APs? Or am I doing something else wrong?

Thanks for your advice,

Didier

Eric Moyers · ‎08-31-2015

Hello

What size is the flat that you have these set up in?

Could you provide a scan of the wireless area showing the interference, that is found in the area?

There are several free programs available for laptop and smartphones that can help with that. One that I have used several times is Wi-Fi Analytics from ampedwireless.com.

How far apart would you say the WAP's are from each other?

Usually lowering the transmit power will just shorten the distance of the signal. I dont think it will make the signal any weaker. But I honestly have not measured that for confirmation.

However, it sounds like the main issue is the over reach of the surrounding signals and weakening your signals will not effect the signal quality.

No enabling the Channel Management feature will not affect the signal power, but in a crowded wireless environment it can make your ability to connect worse. The reason for that is that Channel Management will periodically monitor your channels and if the channel you are currently on is crowed it will change channels. What happens when it does this is that all connections will drop during the move to a new channel and reestablish, if the profile is saved in in the wireless client.

The bad thing with this is that in a crowed wireless environment the WAP cold potentially be searching for new a better channel and wireless client never connect.

The best thing for a crowded environment is to statically assign a channel. We just need to find the right place for yours. I can help with that with looking at your wireless scans.

Your other option is to call in and open a case with one of our engineers. Then they can help you walk through this process. If you do that, let me know the case number and I will be glad to assist them as well.

Eric Moyers
.:|:.:|:. CISCO | Cisco Presales Technical Support | Wireless Subject Matter Expert

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Didier_DN · ‎08-31-2015

Hi Eric!

Thanks for your help!

I've not surveyed the site yet (thought it would be easier to setup a working network, actually) but if I don't spot a solution then I will. The flat is 150 m2 large, L-shaped, and the huge wall create 3 areas so I basically installed 3 antennas where it was possible to bring cat 6 cable.

Basically, everything is fine as long as the clients are using the 5 GHz band. But the 2.4 GHz band is so crowded that it's not usable. Therefore my goal is to make sure all 5 GHz-enabled clients will use this band, but lowering the power of the 2.4 network doesn't seem to be the solution (and the few legacy devices are having difficulties to join it).

I think I'll try with band steer, it might be an acceptable solution here. The documentation says it's not recommended in case some time-sensitive voice or video apps are used: would you please be a bit more specific? What are the risks? Will it impact roaming between APs?

Cheers,

Didier