# Forum

## What power for 2.4GHz versus 5GHz cell size

3 posts by 3 authors in: Forums > CWNA - Enterprise Wi-Fi Admin
Last Post: May 29, 2013:
• We all know 2.4GHz goes further than 5GHz.  What I'm wondering from some of you guys with experience in this, what dbm output power difference will make the cell size about the same?  For example if the AP is 19dbm on 5GHz, what power would you be at on 2.4GHz to get (approximately) the same cell size?

I realize there are many variables, I just would like a general number, thanks!!

• Daniel,
That's a great question!

One of the fundamental differences between communications operating at 2.4 and 5GHz is the achievable communication range between the AP and the station. Holding variables above constant 2.4 GHz frequency offer roughly double the range of those operating in the 5GHz band.

By increasing the power of a 5GHz system approximately 4 times can achieve ranges similar to 2.4GHz systems

• By Tom Carpenter - edited: May 29, 2013

Daniel, Xyro is right. roughly 4-5 times the signal strength is the ideal world value that can give similar coverage patterns to 2.4 GHz for your 5 GHz cells. This is due to the fact that 5 GHz signals attenuate in space at about 7 dB more than 2.4 GHz. For example, at a given distance, the same signal at the same strength in 2.4 GHz will be 7 dB stronger than that signal at 5 GHz. Of course, all of this is based on "free space", which we seldom have. In the real world, it's not as simple because you have varying materials through which and around which waves must pass, to which 2.4 and 5 GHz wave forms react differently. The best thing to do is test and prove the materials in the target building and then do a virtual site survey based on these measurements and then tweak as needed during implementation (assuming no overengineering).

BTW, here is a simple formula you can use to calculate free space path loss:

L(dB) = 20log(d) + 20log(f) - 27.55

Where d is the distance in meters and f is the frequency in megahertz (for example 2400 for 2.4 and 5200 for 5.2). You can plug it into Excel exactly like this:

=20*log(10) + 20*log(2400) - 27.55

And you will get the loss in dB. Change the 10 to the meters you desire. Change the 2400 to the frequency you desire and you can play with the numbers.

Frames Are Food,
Tom

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