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Ap Coverage

Posted on 2013-01-29
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Last Modified: 2013-02-23
Does anyone know how to determine coverage (feet) of an AP in free space.  The information I have currently is:

23dbm = transmit power
3 dbi = antenna gain
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Question by:simonphoenix10
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9 Comments
 
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Expert Comment

by:ArneLovius
ID: 38833674
in free space, you need to apply cube law

to calculate the range, you also need the receiving unit antenna gain and both units minimum signal level.
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by:Rick_O_Shay
ID: 38835344
The maximum distance is going to vary depending on the radio band and connection speed. Check the web for tables relating to wireless distance for details.
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by:ArneLovius
ID: 38835620
@Rick_O_Shay in free space as per the original question) , the frequency (band)  is irrelevant for RF propogation.
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by:Rick_O_Shay
ID: 38837287
But for the coverage of an AP in a real world situation the band and the speed the device connects at do matter.
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by:ArneLovius
ID: 38837476
I would agree, but the original question was for "free space"...
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Author Comment

by:simonphoenix10
ID: 38837499
Thanks, but really interested in general guidelines and not absolute math or is anyone aware of an online calculator
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Accepted Solution

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ArneLovius earned 500 total points
ID: 38837845
RF propagation at 2.4 and 5Ghz, is affected by much smaller objects than for GSM., it gets attenuated by some things, and bounces off others, this can create "interesting" interference patterns.

There is modeling software available for several vendors, this "hides" some of the mathematics (physics), however it is always worthwhile doing a site survey, as site drawings are never "complete", things like people changing from wooden desks to metal topped desks, desk dividers that change from being foam covered MDF, to sheet aluminium with or without holes, changing glass walls from clear single thickness, to reflective coated (very thin layer of aluminium) double glazed, changing ceiling tiles from punched metal, to fibreboard, etc etc

The other aspect is the antenna, dbi is measured relative to "i", an isotropic radiator, it has gain by reducing the directions that it works in, presuming that a vertical antenna is used, it would in simple terms, "flatten" the sphere of radiation of an isotropic radiator, so would have more gain sideways and less gain upwards or downwards.than an isotropic radiator.

I have put APs into some building where to combat the internal structures we needed an AP every ~30 feet (on very low power), others where one was needed for each conference room but only two to cover the rest of the floor, the quantity of users can also affect usable bandwidth.

tl:dr no simple calculator can be accurate
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by:Rick_O_Shay
ID: 38839278
Attached is a table from an AP manufacturer from before 802.11n and 80211.ac (because I couldn't find a newer version) with maximum distances. You'll want to look at the ones for "outside" as they are for free space.
max-dist-a-b-g.pdf
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by:ArneLovius
ID: 38839310
just love their use of the word "obstruction"...
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