Access points near each other a no no?

Jeff5
Conversationalist

Access points near each other a no no?

Our construction tech advisor wants to place MR56 access points, one serving each classroom, about 4 feet away from each other, separated by the classroom wall between the 2 classrooms.  Is that a good idea?  I thought prevailing idea was to place access as far away from each as practical to maximize their isolation and auto-power efficiency.

 

Thank you!

Jeff

5 REPLIES 5
ChrisLaird
Here to help

I think that depends on the materials of the walls and the density requirements within classrooms.  I also try to keep them "as far away as practical" as a rule, but in our classrooms, we haven't often found that to be very possible at a great distance. We have plenty of high-density classrooms and lecture halls with 2,3,4 APs all within 10-20 feet of each other. Most other classrooms are 1 AP per room, probably about 10-15 apart with walls in between. We've had it this way for about 3 years now and performance has been pretty solid. Our profiles keep them at 20 MHz channels, channels 149 and 153 are disabled to prevent interference with Airplay devices. In areas with drywall walls, we turn down transmit strength on 2.4ghz, but many of our buildings are much older and don't require that due to the contruction materials.

 

But, if it was new construction and I had the choice of placement, I'd expect omnidirectional APs to be placed in the center of each room. Having them hug the walls doesn't make sense to me.

Bossnine
Building a reputation

Having them hug the wall, even if the math works out, seems like it would introduce problems with far end clients potentially reaching for an AP not in their physical room. (which has happened to me in my environment).  That being the case, I try to center the AP in each classroom as I come across them.

GIdenJoe
Kind of a big deal

The main reason why you should have at least a few meters of space between your access points is the fact that even when the AP's are on a different channel the side lobes of the transmissions that are about 20 dB lower can still cause the AP to defer tranmission causing severe loss of airtime and efficiency.

PhilipDAth
Kind of a big deal

The 2.4Ghz wavelength is about 125mm (5Ghz is about 60mm).  In a perfect world, the antennas would be a multiple of the wavelength apart.  You would especially avoid 1/4 and 1/2 wavelengths (you'll notice those little stubby WiFi antennas tend to be 31mm or 62mm - 1/4 and 1/2 wavelengths long).

 

Once the antennas get more than a couple of wavelengths apart (244mm) they should have a negligible impact on each other.  Especially if they are operating on different channels.

 

So with a spacing of 1.22m (4ft) - you are fine (that happens to be almost exactly 10 wavelengths - your tech advisor might actually be a maths genius).

KarstenI
Kind of a big deal

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