Saturday, April 16, 2011

CUWN power levels and the 5GHz channels in the U-NII band

This is something that I have found to be confusing.  The UNII bands in the 5GHz range have different power limits.  They are as follows:
  • U-NII Low (U-NII-1): 5.15-5.25 GHz.  Power limited to 50mW
  • U-NII Mid (U-NII-2): 5.25-5.35 GHz.  Power level limited to 250 mW.  Subject to Dynamic Frequency Selection (DFS, or radar avoidance)
  • U-NII Extended 5.47-5.725 GHz.  Power limited to 250mW.  Subject to Dynamic Frequency Selection (DFS, or radar avoidance)
  • U-NII Upper (U-NII-3): 5.725 to 5.825 GHz. Power limited to 1 watt.
If you are a WLAN Engineer like me and you happen to use WCS, your power settings will be displayed as a number, 1 - 8, not in a dBm value.  The value of 1 is the highest power, and the value of 2 is 3dB lower than the value of 1, value of 3 is 3dB lower than the value of 2, and so forth.  Each 3dB is half the power of the the previous value.  Since the cell size is halved every 6 dB, an AP with a power level of 1 should have a cell twice the size of an AP with a power level of 3.

What if you have have a dozen APs all with a power level of 1 set via RRM?  If the AP's channels are dispersed throughout the U-NII low, mid, extended and upper bands, then theoretically the max outputs could be anywhere between 50mW to 1 Watt.

I would love a table or chart that displays the power settings and dBm values for all the model numbers under the CUWN product line.  Heck, if I ever have the time, maybe I will write it up and post it for y'all to reference.
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2 comments:

  1. Keith ParsonsApril 17, 2011 at 7:49 AM

    Tim,

    Halving the power Twice (-6dB) does NOT necessarily half the size of your cell. That's what the math says... but not always what happens in the real world with walls, corners, etc.

    What? Cisco hasn't published your power to dBm chart?

    Well then you ought to make one up to share.

    Thanks for the post.

    Keith

    ReplyDelete
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    CUWN power levels and the 5GHz channels in the U-NII band
    This is something that I have found to be confusing. The UNII bands in the 5GHz range have different power limits. They are as follows:
    U-NII Low (U-NII-1): 5.15-5.25 GHz. Power limited to 50mW
    U-NII Mid (U-NII-2): 5.25-5.35 GHz. Power level limited to 250 mW. Subject to Dynamic Frequency Selection (DFS, or radar avoidance)
    U-NII Extended 5.47-5.725 GHz. Power limited to 250mW. Subject to Dynamic Frequency Selection (DFS, or radar avoidance)
    U-NII Upper (U-NII-3): 5.725 to 5.825 GHz. Power limited to 1 watt.

    ReplyDelete

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