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Some help with figuring out where to place access points

Posted on 2014-02-26
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Last Modified: 2014-02-26
We are trying to install wireless devices (Unifi UAR-LR) around a church which is an OLD stone and cinderblock building.  We are up to 5 devices which on its own likely means nothing without the size of the building. But the 6th looks like it should go in an adjacent room to a room we just put number 5.  A cinderblock and sheetrock wall is between these 2 rooms. From the weakness of the signal from one room to the other, we are thinking there is foil backed insulation between the sheet rock and cinderblocks.

Regardless of that, in general, how do you determine how many APs you use and where you put them? Simple trial and error?

We use the insider app on a phone to see how the signal strength looks. What level do you consider acceptable before you need another access point?

Standing directly under an UAR-LR, we get a signal of about -40 to -45 or so. Is that full strength?

I realize that depending on the walls and floors, wifi signals may not travel very far. Does anyone have any rules of thumb? If APs are going to be in each meeting room, do you bother with LR or higher power devices?
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Craig Beck earned 500 total points
ID: 39888479
In general terms - to accurately perform a survey you should drop an AP somewhere, then walk around measuring the signal at different places on a map.  Record the measurements, then pick a place where the signal was adequate at the edge of the coverage area and do it again... and so on.  There is professional software such as Airmagnet or Ekahau, or there is free heatmapper software which will help (from Ekahau).

It depends on what type of deployment you want though (standard data, voice-capable, etc.) to determine what kind of signal overlap and strength you need.  For example, for a standard data-ready deployment the recommendation is around 20% overlap with -75dBm signal at the desired data-rates and a SNR of at least 20dB, whereas for voice-ready deployments the requirement is 20-25% overlap minimum with a signal of -67dBm and SNR of at least 25dB.
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by:BeGentleWithMe-INeedHelp
ID: 39888498
Craig - thanks.

so is it reasonable to expect with thick walls, in some cases, that the wifi signal is not getting through the wall?

-75? I thought that was way too low. I would look at things with insider (any opinion on that app?) and then run http://speedof.me.  The normal speeds were 10 down, 2 up.  

at -75 type of numbers, I was getting 2 down?

what brand do you use?
I was realizing in insider, it has a page for 5 GHz channels and nothing was there using UAP-LRs?  To get in that band, I need 802.11 n access points, right?
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by:Craig Beck
Craig Beck earned 500 total points
ID: 39888537
so is it reasonable to expect with thick walls, in some cases, that the wifi signal is not getting through the wall?
Yes, absolutely, especially with 5GHz which propagates a shorter distance than 2.4GHz also.

-75? I thought that was way too low. I would look at things with insider (any opinion on that app?) and then run http://speedof.me.  The normal speeds were 10 down, 2 up.
The absolute cut-off is around -91dBm.  If you have a signal of -75dBm as long as the SNR is 20dB or more (so noise is around -95dBm or less) you should be fine and you should be able to achieve the data-rate you are connected at.  It's worth noting that faster data-rates require better signal strength, so for example you might only get a 54Mbps link at -60dBm, whereas you could get a 6Mbps link at -80dBm (again, just an example).

So,
at -75 type of numbers, I was getting 2 down?
...that could be a good transfer rate based on a 18Mbps data-rate.

I mainly use Cisco (I work for a Cisco Gold Partner) but I have lots of experience with many others such as Ubiquiti.

I was realizing in insider, it has a page for 5 GHz channels and nothing was there using UAP-LRs?  To get in that band, I need 802.11 n access points, right?
Nearly right.  It's a common mis-conception that 802.11n is 5GHz.  Actually 5GHz is 802.11a.  People simply associate 5GHz with faster speeds and automatically think that 802.11n is therefore 5GHz.  So to use 5GHz you need an access point which uses 802.11a.

802.11n is an enhancement of the radio (either 2.4GHz or 5GHz) and to put it simply allows for multiple transmitters/receivers to be used at the same time.  This is what gives the throughput increase.
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Author Comment

by:BeGentleWithMe-INeedHelp
ID: 39889632
thanks!
some other questions if you want to take a shot at them:

http://www.experts-exchange.com/Hardware/Networking_Hardware/Wireless/Q_28375313.html
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