Solved: AP with radio signal strength configurable

imiziqjaws1984 · ‎08-18-2011

Hi,

Is there any available cisco aironet model which enable administrator to configure the strength of the WiFi wireless radio signal? Example, we can tune to 10dB, 20dB, 30dB and yet maintaining the throughput (10 Mbps, 25 Mbps)

TQ

Matt Barber · ‎08-20-2011

Hi Imran,

This looks like an interesting research project. I've found some more information that might assist, as you wanted to use dB values and the AP will let you configure power in mW -

The unit dB measures the power of a signal as a function of its ratio to another standardized value. This abbreviation dB is often combined with other abbreviations in order to represent the values that are compared. Hence, dBm is the value which results from comparing dB with a standardized reference value of 1 mW.

The formula to calculate this dBm value from the given signal strength in mW is:

Power (in dB) = 10 * log10 (Signal/Reference)

This list defines the terms in the formula. log10 is logarithm base 10.

Signal is the power of the signal (for example, 50 mW).
Reference is the reference power (for example, 1 mW).

Example:If you want to calculate the power in dB of 50 mW signal strength, apply this formula:

Power (in dB) = 10 * log10 (50/1) = 10 * log10 (50) = 10 * 1.7 = 17 dBm

This formula results in a common rule that says:

For every increase of 3 dB (dBm here), it leads to a double increase in the current transmit power (mW). For every decrease of 3 dB, this reduces the transmit power to half its current value.
For every increase of 10 dB (dBm), it leads to a ten times increase in the current transmit power (mW). For every decrease of 10 dB, this reduces the transmit power to ten times its current value.
For every increase of 30 dB (dBm), it leads to a 1000 times increase in the current transmit power. For every decrease of 30 dB, this reduces the transmit power to 1000 times its current value.

This table provides approximate dBm to mW values:

I took this from the document "Cisco Aironet Access Point FAQ" for the 1200 AP series. The mW to dB comparison table above will apply to these APs. Please note if you change the antenna, different transmit power values and signal reach will obviously apply.

Doc ref: http://www.cisco.com/en/US/products/hw/wireless/ps430/products_qanda_item09186a008009483e.shtml#intro

Here's another page based on regulatory domains and power levels, including various antenna types and maximum power levels you can use:

http://www.cisco.com/en/US/docs/wireless/access_point/channels/ios/reference/guide/1300_chp.html

If you need a config example, I have access to a couple of APs so I can pull the config. It's literally just a couple of lines of config to change the TX power.

Let me know how it goes!

Hope that helps -
Matt

View solution in original post

Leo Laohoo · ‎08-18-2011

Except the 3500, all Cisco APs' radio strength can be configured.

I don't know WHY you want to do this though.

imiziqjaws1984 · ‎08-18-2011

actually, im doing a research which involve testing at a predefine dB. does this also applicable to linksys product?

Leo Laohoo · ‎08-18-2011

actually, im doing a research which involve testing at a predefine dB. does this also applicable to linksys product?

Ooops! I didn't realize you were talking about Linksys. I'm not sure. I thought you were talking about the enterprise-grade wireless AP like the 1040, 1140, 1250, 1260.

imiziqjaws1984 · ‎08-18-2011

Im talking about both actually. Linksys did reply me back saying none of their product supports that. Aironet 1260 with N network will do just what I need right? Seems like aironet below 1260 model only support up to G network

Leo Laohoo · ‎08-18-2011

Seems like aironet below 1260 model only support  up to G network

Only the 1130 will support 802.11a/b/g. The rest, 1040, 1140, 1250 and 1260, will support 802.11a/b/g/n.

All of the models I've mentioned will allow you to manually configure the radio strength. Again, I don't know why one wants to do this.

Do you mind elaborating what you are trying to achieve?

imiziqjaws1984 · ‎08-18-2011

Im actually doing a reserach on VoIP perfomance (MOS, Rfactor, etc) based on selected audio codec (G.729, iLBC,etc) compare to a predefined wifi network (10dB, 20dB, etc). End result will be which codec is suitable to use at different wifi network condition

Matt Barber · ‎08-20-2011

Hi Imran,

This looks like an interesting research project. I've found some more information that might assist, as you wanted to use dB values and the AP will let you configure power in mW -

The unit dB measures the power of a signal as a function of its ratio to another standardized value. This abbreviation dB is often combined with other abbreviations in order to represent the values that are compared. Hence, dBm is the value which results from comparing dB with a standardized reference value of 1 mW.

The formula to calculate this dBm value from the given signal strength in mW is:

Power (in dB) = 10 * log10 (Signal/Reference)

This list defines the terms in the formula. log10 is logarithm base 10.

Signal is the power of the signal (for example, 50 mW).
Reference is the reference power (for example, 1 mW).

Example:If you want to calculate the power in dB of 50 mW signal strength, apply this formula:

Power (in dB) = 10 * log10 (50/1) = 10 * log10 (50) = 10 * 1.7 = 17 dBm

This formula results in a common rule that says:

For every increase of 3 dB (dBm here), it leads to a double increase in the current transmit power (mW). For every decrease of 3 dB, this reduces the transmit power to half its current value.
For every increase of 10 dB (dBm), it leads to a ten times increase in the current transmit power (mW). For every decrease of 10 dB, this reduces the transmit power to ten times its current value.
For every increase of 30 dB (dBm), it leads to a 1000 times increase in the current transmit power. For every decrease of 30 dB, this reduces the transmit power to 1000 times its current value.

This table provides approximate dBm to mW values:

I took this from the document "Cisco Aironet Access Point FAQ" for the 1200 AP series. The mW to dB comparison table above will apply to these APs. Please note if you change the antenna, different transmit power values and signal reach will obviously apply.

Doc ref: http://www.cisco.com/en/US/products/hw/wireless/ps430/products_qanda_item09186a008009483e.shtml#intro

Here's another page based on regulatory domains and power levels, including various antenna types and maximum power levels you can use:

http://www.cisco.com/en/US/docs/wireless/access_point/channels/ios/reference/guide/1300_chp.html

If you need a config example, I have access to a couple of APs so I can pull the config. It's literally just a couple of lines of config to change the TX power.

Let me know how it goes!

Hope that helps -
Matt

imiziqjaws1984 · ‎08-21-2011

Hi Matt,

Thanks alot for the respond and information given. Actually, this is my first time handling cisco aironet APs . In regards towards the dB, I have some question here (do correct me if im wrong):

1. Regarding to the dB : For every increase of 3 dB (dBm here), it leads to a double increase in the current transmit power (mW). For every decrease of 3 dB, this reduces the transmit power to half its current value.

[Imran] Is my understanding correct that increase of dB will increase in current transmit power? Since transmit power is mention, do we configure mW in the APs rather than dB (assuming dB config is not available)?

2. After reading the 1200 AP series, will it work the same for 1040 series? Due to budget constrain, it is much easier to justify for 1040 series. In Malaysia, it makes big different (around addicitonal 100USD).

3. Given scenario below :

Data rate = 54 Mbps

dB/mW = variable based on the table given above.

Can I say that the AP is capable of maintaining the given data rate while we change the dB/mW? example : data rate at 54 Mbps but we test on low dB, let say 10dB. Yes I do understand that even we set data rate at 54Mbps but we will not archieve due to low dB. Main purpose is that we have the same data rate configure throughout the testing.

Thanks again for you time

Kayle Miller · ‎08-23-2011

1) Some devices you configure the transmit power in the dBm values typically -1 0 1 2 5 8 11 14 17 20, other devices will do it based on mw values typically 100mw, 50mw, 25mw, 12.5mw, 6mw, 3mw, 1.5mw, etc.

2) There are some differences in the transmit power depending on the model of 1200 you have but for research purposes you should be fine.

3) No the transmit power can change based on the modulation See the charts below these are for an AIR-LAP1242AG-A-K9

802.11a/n Radio

Configured Power: 17 dBm (level 1)
Active power levels by rate
     6.0 to 36.0 , 17 dBm
    48.0 to 48.0 , 16 dBm, changed due to regulatory maximum
    54.0 to 54.0 , 12 dBm, changed due to regulatory maximum
6.0-bf to 36.0-b, 17 dBm
48.0-b to 48.0-b, 16 dBm, changed due to regulatory maximum
54.0-b to 54.0-b, 12 dBm, changed due to regulatory maximum
     m0. to m4.   , 17 dBm
     m5. to m5.   , 15 dBm, changed due to regulatory maximum
     m6. to m6.   , 11 dBm, changed due to regulatory maximum
     m7. to m7.   , 10 dBm, changed due to regulatory maximum
     m8. to m12. , 17 dBm
    m13. to m13. , 15 dBm, changed due to regulatory maximum
    m14. to m14. , 11 dBm, changed due to regulatory maximum
    m15. to m15. , 10 dBm, changed due to regulatory maximum
   m0.-4 to m3.-4 , 17 dBm
   m4.-4 to m4.-4 , 16 dBm, changed due to regulatory maximum
   m5.-4 to m5.-4 , 14 dBm, changed due to regulatory maximum
   m6.-4 to m7.-4 , 10 dBm, changed due to regulatory maximum
   m8.-4 to m11.-4, 17 dBm
m12.-4 to m12.-4, 16 dBm, changed due to regulatory maximum
m13.-4 to m13.-4, 14 dBm, changed due to regulatory maximum
m14.-4 to m15.-4, 10 dBm, changed due to regulatory maximum
   6.0-d to 18.0-d, 17 dBm
24.0-d to 24.0-d, 16 dBm, changed due to regulatory maximum
36.0-d to 36.0-d, 15 dBm, changed due to regulatory maximum
48.0-d to 48.0-d, 14 dBm, changed due to regulatory maximum
54.0-d to 54.0-d, 10 dBm, changed due to regulatory maximum
OffChnl Power: 17, Rate 6.0

802.11b/g/n Radio

Configured Power: 20 dBm (level 1)
Active power levels by rate
     1.0 to 11.0 , 20 dBm
     6.0 to 48.0 , 17 dBm, changed due to regulatory maximum
    54.0 to 54.0 , 16 dBm, changed due to regulatory maximum
6.0-bf to 48.0-b, 17 dBm, changed due to regulatory maximum
54.0-b to 54.0-b, 16 dBm, changed due to regulatory maximum
     m0. to m5.   , 17 dBm, changed due to regulatory maximum
     m6. to m6.   , 16 dBm, changed due to regulatory maximum
     m7. to m7.   , 14 dBm, changed due to regulatory maximum
     m8. to m13. , 17 dBm, changed due to regulatory maximum
    m14. to m14. , 16 dBm, changed due to regulatory maximum
    m15. to m15. , 14 dBm, changed due to regulatory maximum
   m0.-4 to m4.-4 , 17 dBm, changed due to regulatory maximum
   m5.-4 to m6.-4 , 16 dBm, changed due to regulatory maximum
   m7.-4 to m7.-4 , 14 dBm, changed due to regulatory maximum
   m8.-4 to m12.-4, 17 dBm, changed due to regulatory maximum
m13.-4 to m14.-4, 16 dBm, changed due to regulatory maximum
m15.-4 to m15.-4, 14 dBm, changed due to regulatory maximum
   6.0-d to 18.0-d, 17 dBm, changed due to regulatory maximum
24.0-d to 36.0-d, 16 dBm, changed due to regulatory maximum
48.0-d to 48.0-d, 14 dBm, changed due to regulatory maximum
54.0-d to 54.0-d, 13 dBm, changed due to regulatory maximum
OffChnl Power: 20, Rate 1.0

Hope this helps

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imiziq1984 · ‎10-16-2012

Can anyone help me with this?

AP with radio signal strength configurable