Issues in a high density wireless network

[Majid Jalinousi]

Hi buddies,

We've deployed a wireless network with WLC 5508 and aireos 8.0.120 for a high density multi floor building.

but there are issues like below:

1. In spite of nearby APs hearing themselves really good, WLC choose same channels for them. Is channel utilization on the other channels so bad?

what is WLC criteria for choosing channels?

2. Decreasing power for shrinking cell size doesn't have any sensible effect to APs, but clients RSSI will be decrease. Is it because of wrong AP position? or because of the clients NICs?

3. our APs are 40 feet far from each other aproximately, which maximum power level assignment is recommended for this kind of networks?

4. I analyzed WLC configuration with WLCCA, there is an item showing RF health, for some APs this value is 0. what does it mean?

BR,

Majid Jalinousi

[Freerk Terpstra]

There are only three usable (non-overlapping) channels available for the 802.11b/g/n, so if you have a high density deployment there is not much choice for RRM. For 802.11a/n/ac it depends on the country you are in, but there are always more channels available comparing to 802.11b/g/n and the signals will reach less far due to the high frequency.

Based on the information in WLCCA and what you are saying I recommend you to do the following:
1. Conduct an post-deployment site survey in Ekahau
2. Based on the channel-overlap information you can determine which 802.11b/g/n radios can be disabled. You should aim for an maximum of 2 access-point radios on the same channel with a minimal signal strength of -85dBm. This should really lower the channel utilization.
3. Tune your data-rate settings so that clients will generally use an higher data-rate and (hopefully) roam quicker. It really depends on the clients you have to support, but for office spaces making 12Mbit/s the mandatory data-rate and disable all of the lower rates is a good starting point. This is also to minimal the channel utilization.
4. Conduct the post-deployment site survey again and repeat this process if needed.

It is nice that access-points are "dual-radio" by default, but for high density environments this is not something you want. The only thing that RRM can do is lower the power levels which does not help to lower the channel utilization and might even create coverage problems. Because you disable the "undeeded" radios, RRM will come with better power-levels fixing these coverage problems as well. Keep in mind that RRM is not a silver bullet and that manual override might still be needed based on the site survey information. That information is leading.

Directional antennas can be used as well to limit the channel utilization be making the cell more focused. It really depends on the building if this is needed or even required, but this should be determined in the pre-deployment survey/design phase and is not something we can do remotely.. :-)

Please rate useful posts... :-)

[Majid Jalinousi]

Hi Freerk,

when do you say "Based on the channel-overlap information you can determine which 802.11b/g/n radios can be disabled", what does it mean?

This means I should disable 802.11b or 802.11g or 802.11n technology. isn't so strictly?

would you please explain for me, how it can help to RRM decision?

Thanks in advance

[Freerk Terpstra]

Hi Majid,

Check out this link for an example about the channel-overlap output within Ekahau. Yes, based on this information from your site-survey you are probably going to disable the 802.11b/g/n radios.

Because you are currently having a lot of access-points in a small space they "hear" each other very loud. This information is used as input for the RRM process to decide how much power is being used. Because your access-points are slow close RRM will end up with very low power-levels and coverage holes might be created because of this.

Performing site surveys and tuning your RF based on it is not something you learn overnight and requires a lot of practice. Because of this I advice you to hire somebody with actually experience in this field. Buy Ekahau for your company as well but use that person/company to learn it yourself.

Please rate useful posts... :-)

[Majid Jalinousi]

Thanks a lot for your answer Freerk,

Our company has bought Ekahau premium pack and I know how to work with it somehow.
If it's possible I want you help me, because of some policy we can't use a outsource help.
If it doesn't bother you, I wanna describe whole the works we've been doing for getting better experience in our wireless network.
Our building is a multi-floor building and the floors are same neither in architectural design nor user density.
In some floors there are between 100 to 120 users connecting to the wireless network, in some other floors density is somehow moderate and in average 60 to 70 users connecting to wireless network.
Roaming is a normal thing in our building and there are lots of rough APs in whole building.
Because there were excessive load on some APs in the 2.4G band we were forced to increase our APs, after that for decreasing channel overlap we forced to decrease maximum power threshold to 11 dbm, but in spite of this power decreasing, some of the APs have still set their tx power level to 8, then there are some users complaining about RSSI weakness and when I see in the WLC trap log there are lots of "coverage hole detection warnings".

If I want to be honest, I don't understand why you recommend to disable 802.11 b/g/n on some APs. if I want to disable them, then what do I do with available excessive load in this frequency band?
what do you think about changing coverage hole settings to power up APs or increasing max power assignment again? Isn't there anyway to tune interference without powering off 802.11b/g/n radio? Then how can I handle the available users in 2.4 Ghz band?

I would very appreciate if you help me find best practice for our WLC settings.

Thanks in advance,

BR,
Majid Jalinousi.

[Freerk Terpstra]

It is really hard to do these kinds of tuning without having the survey data available, but I don't think you are allowed to share that data...

The reason I advice you to disable radios is that there are only three available channels for the 802.11b/g/n spectrum. So if you have four access-point relative nearby of each other two will be on the same channel. This means that they are going to share the available "channel capacity" without any benefits for the clients using that channel as well. Because you disable some radios RRM will see less neighbors and power up the radios. For high density networks it is not uncommon to disable 1/3 of the 802.11b/g/n radios. But again this depends on your survey data / design.

Other things you should look into are disabling the 802.11b data-rates and band steering / band-select features to trick clients to use the 802.11a/n/ac spectrum.

Please rate useful posts... :-)

[Majid Jalinousi]

Hi Freerk,

Thanks a lot for your care about solving the problem.

Unfortunately most of the clients have only 2.4Ghz-support NICs, then band select can't help a lot.

but about survey data, I did a survey in one of the floors and you can find result of channel overlap and spectrum utilization on the attachment.

Only APs containing "WLC-AP" are our APs and only APs begin with "WLC-AP2" are related to the floor I've done survey in it, other APs containing "WLC-AP" are belong to other floors and all the others are rouge APs.

I have some questions like below:

1. Why WLC channel assignment on some part of floor is not optimized? For example at the top part of attached images while utilization of channel 11 is more better, WLC has put most of the APs in channel 1. Is it OK? Isn't ridiculous to set channel of some APs manually to override WLC channel assignment?

2. Type of APs are 2602-E or 2702-E, and all the Antenna are omnis. should I reconsider about type of antenna and change them to directional antenna for future plans?

3. With this survey data would you suggest what can I do to get better experince? which APs do you suggest to turn down? if you need any more information I would be very appreciate to send it for you.

Thanks in advance for any kind of suggestion.

BR,

Majid