Power level of Access point

[kentislander]

I am currently running WCS 7.0.164 and 1130 series access point firmware 7.0.98.0.

I am getting lot of complains from students that their laptops are not getting 5 bars signals.   They are getting at least 1 or 2 bars with being disconnect frequency.

Problem is that the nearest 2 access points are showing TX power level 2.   For the testing purpose, I increase tx power level to 8 on both access points and the laptop show 5 bars signals.

The layout of dorm is 3  (2 bedrooms / 2 persons per bedroom plus bathroom and living room) suites per wings.The walls are concrete.

I was told that using custom setting for TX level power is not recommend.

What are the solution to this problem?    Use custom setting or what?

[Kayle Miller · Accepted solution]

Allen,

     Your description of the problem makes no sense especially considering that a power level of 8 is lower than power level 2.

If you do a 'show ap config 802.11a '

It will show you this

Tx Power
      Num Of Supported Power Levels ............. 5
      Tx Power Level 1 .......................... 11 dBm
      Tx Power Level 2 .......................... 8 dBm
      Tx Power Level 3 .......................... 5 dBm
      Tx Power Level 4 .......................... 2 dBm
      Tx Power Level 5 .......................... -1 dBm
      Tx Power Configuration .................... AUTOMATIC
      Current Tx Power Level .................... 5

If you do a 'show ap config 802.11b '

It will show you this

Tx Power
      Num Of Supported Power Levels ............. 8
      Tx Power Level 1 .......................... 20 dBm
      Tx Power Level 2 .......................... 17 dBm
      Tx Power Level 3 .......................... 14 dBm
      Tx Power Level 4 .......................... 11 dBm
      Tx Power Level 5 .......................... 8 dBm
      Tx Power Level 6 .......................... 5 dBm
      Tx Power Level 7 .......................... 2 dBm
      Tx Power Level 8 .......................... -1 dBm
      Tx Power Configuration .................... AUTOMATIC
      Current Tx Power Level .................... 8

So based on that the fact that you said Power Level 8 gives you a stronger signal is suspicious to say the least.

Hope this helps... Please rate useful posts.

Thanks,

Kayle

[kentislander]

Yes  -  you are right ---  I was looking at wrong map.   Setting power level to 1 on ap cause laptop to get 5 bar signals.  2 Neighbor access points between a room show tx power level at 6.  Both access points are within 50 feet of each other.

Do I need to increase power level manually or let controller do the work?

Is there a way for me to get log of reason why laptop get disconnected?  It seem that iMac users get disconnect more often than windows laptop.

[Kayle Miller · Accepted solution]

Allen,

     I would first check the transmit power threshold you have configured on the controllers, using the 2 commands shown here, there is a good possibility that because of the distance between the AP (especially with out knowing if there is anything between the AP's) that they are seeing each other so strong that they have to turn the power way down as a result. This could be tweaked some using the Tx-power-threshold settting. This is common and proper behavior.  See the commands below and some sample output.

show advanced 802.11a txpower

Automatic Transmit Power Assignment
  Transmit Power Assignment Mode................. AUTO
  Transmit Power Update Interval................. 600 seconds
  Transmit Power Threshold....................... -70 dBm
  Transmit Power Neighbor Count.................. 3 APs
  Min Transmit Power............................. -100 dBm
  Max Transmit Power............................. 100 dBm
  Transmit Power Update Contribution............. SNI..
  Transmit Power Assignment Leader............... wlc-2 (x.x.x.x)

show advanced 802.11b txpower

Automatic Transmit Power Assignment
  Transmit Power Assignment Mode................. AUTO
  Transmit Power Update Interval................. 600 seconds
  Transmit Power Threshold....................... -70 dBm
  Transmit Power Neighbor Count.................. 3 APs
  Min Transmit Power............................. -100 dBm
  Max Transmit Power............................. 100 dBm
  Transmit Power Update Contribution............. SNI..
  Transmit Power Assignment Leader............... wlc-2 (x.x.x.x)

default now is -70dbm which means that the ap's will turn down their power until their neighbors hear them at a -70 signal.. You may need to change this to -65dbm but be aware that this could cause more co-channel interference depending on where the next ap on the same channel is, this setting is also global.  The other option you have in the newer code is the set a minimum and maximum that the RRM system will allow, here you see they are set at -100 & 100 respectively. You could try setting the minimum to say 12.5 dbm which is like power level 1 or 3 depending on the radio, band, channel, modulation, etc.

Lastly keep in mind that it could also be a client side power issue, since the communication to the AP has to be a two-way communication; which means if your client has a maximum transmit power of say 25mw or 14dbm, then having the AP push out 50mw or 17dbm of signal is useless since in many cases the AP can reach the client device but the client device won't be able to talk back.

Hope this helps.  Please rate useful posts.

Thanks,

Kayle

[George Stefanick · Accepted solution]

Also keep in mind. Depending on the channel you select  in 802.11A ALSO changes the TX power...

I posted this on my site ...

http://www.my80211.com/home/2009/10/30/what-you-need-to-know-about-tx-power-and-80211a-5ghz-on-a-ci.html

Power, power power.... One of the MOST important design factors is selecting the proper radio TX power when designing any wireless network. You must consider your lowest common denominator and adjust your power equally between your client and AP for optimal design.

But did you know when you select different UNII channels in the 5 GHz band you are also changing the TX power of your AP on a Cisco WLC? When selecting power on a cisco ap in the WLC you are presented with the power levels 1,2,3,4,5 etc. Most folks are aware on the 2.4 GHz side power levels.

1 = 20 dBm / 100mW
2 = 17 dBm / 50mW
3 = 14 dBm / 25 mW
4 = 11 dBm / 12.5 mW

But did you know depending on the UNII band you select the power levels are different on the 802.11a 5GHz radio.

UNII 1                                                 UNII 2 / 3

1 = 11 dBm / 12.5 mW                          1 = 17 dBm / 50mW
2 = 8 dBm / 6.25 mW                            2 = 14 dBm / 25 mW
3 = 5 dBm / 3 mW                                3 = 11 dBm / 12.5 mW
4 = 2 dBm / 1.5 mW                              4 = 8 dBm / 6.25 dBm

[Bruno Dinis]

I've checked my configured thresholds and they are a bit different than yours. Please help me understand what's the difference, specially in the Min/Max Transmit Power. That could be the solution for my problem:

I've got a library with 600 devices, and 12x Cisco3702 connected to a 2960X gigabit, and 50 users max per AP. The SNR are ok and I don't have much interferences.. But the connections are slow.. download/upload 20mbps..

show advanced 802.11a txpower

(wlc1) >show advanced 802.11a txpower

Local Automatic Transmit Power Assignment
 Transmit Power Assignment Mode................. AUTO
 Transmit Power Update Interval................. 600 seconds
 Transmit Power Threshold....................... -70 dBm
 Transmit Power Neighbor Count.................. 3 APs
 Min Transmit Power............................. -10 dBm
 Max Transmit Power............................. 30 dBm
 Update Contribution
 Noise........................................ Enable
 Interference................................. Enable
 Load......................................... Disable
 Device Aware................................. Disable
 Transmit Power Assignment Leader............... wlc2 (10.2.0.69) (::)
 TPC Mode....................................... 
 TPCv2 Target RSSI.............................. -67 dBm
 TPCv2 VoWLAN Guide RSSI........................ -67.0 dBm
 TPCv2 SOP...................................... -85.0 dBm
 TPCv2 Default Client Ant Gain.................. 0.0 dBi
 TPCv2 Path Loss Decay Factor................... 3.6
 TPCv2 Search Intensity......................... 5 Iterations

Leader Automatic Transmit Power Assignment
 Transmit Power Assignment Mode................. AUTO
 Transmit Power Update Interval................. 600 seconds
 Transmit Power Threshold....................... -70 dBm
 Min Transmit Power............................. -10 dBm
 Max Transmit Power............................. 30 dBm

show advanced 802.11b txpower

(wlc1) >show advanced 802.11b txpower

Local Automatic Transmit Power Assignment
  Transmit Power Assignment Mode................. AUTO
  Transmit Power Update Interval................. 600 seconds
  Transmit Power Threshold....................... -70 dBm
  Transmit Power Neighbor Count.................. 3 APs
  Min Transmit Power............................. 13 dBm
  Max Transmit Power............................. 30 dBm
  Update Contribution
    Noise........................................ Enable
    Interference................................. Enable
    Load......................................... Disable
    Device Aware................................. Disable
  Transmit Power Assignment Leader............... wlc2 (10.2.0.69) (::)
  TPC Mode....................................... 
  TPCv2 Target RSSI.............................. -67 dBm
  TPCv2 VoWLAN Guide RSSI........................ -67.0 dBm
  TPCv2 SOP...................................... -85.0 dBm
  TPCv2 Default Client Ant Gain..................   0.0 dBi
  TPCv2 Path Loss Decay Factor...................   3.6
  TPCv2 Search Intensity......................... 5 Iterations

Leader Automatic Transmit Power Assignment
  Transmit Power Assignment Mode................. AUTO
  Transmit Power Update Interval................. 600 seconds
  Transmit Power Threshold....................... -70 dBm
  Min Transmit Power............................. 13 dBm
  Max Transmit Power............................. 30 dBm

[Kayle Miller]

Bruno,

the Min/Max Transmit Power is a setting that can be configured on the controller to limit or define the transmit power range. From the GUI on the WLC goto the Wireless Tab, then from the left hand menu expand the 802.11a/n/ac (or 802.11b/g/n), once expanded look under RRM and click on TPC this will take you to the Transmit Power Control Settings page.

on this page you will see the options to set the minimum power level and maximum power level. These values should match what you saw in the CLI, if they don't then that may mean you are using RF Profiles, in which case under the Wireless Tab on the left side you should see an Option of RF Profiles if you click on that it will give you a list of RF Profiles there are (6) by default Low Density, Typical Density, High Density (there will be one for 802.11b/g/n & one for 802.11a/n/ac) You can then click on the RF Profile and Click the RRM Tab to see the same info that is under the Global TPC tab.

Now specifically in your case the 5GHz radios which can serve up 802.11a/n/ac/ac2 are configured to use the full range of power meaning the Auto-RRM system has the option to turn the 5GHz radios down to a really low transmit power which could potentially shrink their coverage area; but it also has the ability to make them full power. Keeping that in mind on the 2.4GHz band which serves 802.11b/g/n the Auto-RRM system is configured to limit the minimum transmit power to 13 dBm which means the system can make the AP's go to full power but if it desires to turn down the radios it must stop at 13 dBm (depending on the AP means Tx Power Level 4).

So in a dense environment the settings on the 2.4GHz side will keep AP power much higher than it may need to be; the inverse of that is it maybe allowing the 5GHz to go to low. One thing you can look at is if you goto the Wireless Tab on the GUI then from the left menu Under Access Points> Radios> Click on 802.11a/n/ac you should see a list of your AP's, look under the Power Level Column and see what value is listed (1 thru 8 also an * means it's using RRM and not statically set) ideally most deployments you want a Power level of 3 or 4 (30 to 50 ft between AP's) unless it's really dense in which case maybe 5-7 (Less than 30 ft between AP's). You can look at the 802.11b/g/n Values in the same way.

Also in your case definite check the Data Rates.

Hope this helps and answers your questions.

[wyfy-2015]

Hi,

if rrm set auto and if we could  see lot of access point power level is 1 ,does it mean we have coverage hole ?

"

look under the Power Level Column and see what value is listed (1 thru 8 also an * means it's using RRM and not statically set) ideally most deployments you want a Power level of 3 or 4 (30 to 50 ft between AP's) unless it's really dense in which case maybe 5-7 (Less than 30 ft between AP's)

"

Maximum Power level available is 5  in wlc 5760 

Can you clarify the below part 

"

So in a dense environment the settings on the 2.4GHz side will keep AP power much higher than it may need to be; the inverse of that is it maybe allowing the 5GHz to go to low." 

Thanks a lot 

[Kayle Miller]

Just to clarify in regards to the Power Levels a TX Power of 1 is the highest transmit power as George has indicated below this message so 5 would be a lower setting.

The power levels available 1 thru 8 (or 1 thru 5, or variations) are dependent on the specific Access Point, Country Code, and Channel in use again as referenced in George's great comment below, it is not a limit of the controller itself.

Now to clarify my statement from above 

"So in a dense environment the settings on the 2.4GHz side will keep AP power much higher than it may need to be; the inverse of that is it maybe allowing the 5GHz to go to low." 

In a very dense deployment the 2.4GHz signal will propagate a lot farther thru the air and objects than the 5GHz signal does, so when you have access points that are 20ft - 40ft apart the 2.4GHz signal that the access points hear from each other will tend to be strong than the 5GHz signal and as such if Default RRM is used where it is set to Auto-TX Power then the WLC will turn the power on the access points down until the access points hear their neighbors at a value of -70 dBm (although some code revisions this is set at -67 dBm) as specified in the default RRM profile. 

Now lets say that everything is default it may turn the access point power level down to say Tx Power Level 5 which for a normal 3600 (on 2.4GHz) is 8dBm or 6.25 mW; but if you notice the screenshot provided above shows that the Auto-TX Power has a minimum value set of 13 dBm; which means that the WLC can only turn those access points down to TX Power Level 2 (although it may allow a 3 which is 14 dBm; but most likely not). This is why I stated that the values set could enable the WLC to keep the TX Power higher on the 2.4GHz than it needed to be.

Hope this helps clarify this for you.

[George Stefanick]

Old post live on :). 

The 3700/3800 changes a good bit of what  posted 5-6 years ago. TX power is much hotter for example. 

+5 Kayle 

[black_vamp]

To clarify the, the transmit power threshold (-70 dBm) means that each AP will lower its transmit power until it hears each AP at a minimum of -70?

To give a little quick background, I'm currently preparing and submitting a default configuration for all remote sites, medical clinics and am trying to determine best power setting(ugh) for both 2.4 and 5ghz...in case anyone has any suggestions.

[ptmorgan]

Just came across this thread.

This is a really old thread, but it is great stuff.

I did a blog post on this stuff, and it shows some new really useful commands:

https://nc-expert.com/tips-tricks/wlc-ap-power-settings/