Too many AP's in close proximity?

[sfeldmann]

A vendor has just completed a site survey, and throughout the design, there will be 5 AP's (350's with 2dBi omni's) within 50' of each other in a X pattern. I am concerned that too many will lead to poor performance, as the channels will certainly overlap. There will be different channels used, but due to the massive numbers involved, you can't get far enough away befor you will have to reuse a non-overlapping channel. The environment is Hospital In-Patient wings.

The main concern is that there will be in-air collisions(or signal detected by the other AP's) causing the AP's to wait their stand-off period befor transmitting.

Am I wrong?

Is there any good documentation that discusses overlapping AP's and what to avoid?

Any other opinions/comments are appreciated.

Thanks.

[shaun.oliver]

The purpose of a site survey is to determine the AP placement with the best coverage and without frequency overlap.

If the vendor has done a good site survey, there's a good chance each channel does not overlap enough to cause interference. Channel selection and AP placement can be difficult, but usually there is an optimial solution.

If in doubt, ask for a floor plan-based site survey document, showing cell coverage and overlap.

[blue.modal]

As a point of reference, we never approach a Site Survey with range as the first factor. We always consider capacity first (number of users per AP) and make the coverage area for each AP the right size and shape to maximize reliability and minimize noise.

The fact that the design uses five APs with 2.2dBi antennas would make me suspect that your consultant may be new to wireless.

If you have 75 or fewer users, you may be better off with three APs, but I could not give you a firm answer without at least a floor plan.

Matthew Wheeler

Chief Wireless Architect

www.BlueModal.com

[cwehner]

The 350 series APs are very resistent to same channel overlap. I've had 2 APs within 10 feet of each other using the same channel without a problem in a lab environment.

I wouldn't worry about the interference. However, 5 APs for a single area could be overkill depending on what type of throughput is required.

[Cintifacts]

My friend has a 3com 8000 Series and is the Parent AP in our network. I have a Cisco 350 Series and am a repeater of his signal. I can only maintain my signal and authentication w/ his AP for a moment of minutes. We think there is another AP in the area that is giving us interference. Any suggestions for this?

The error message tells me that the MAC address of this AP is not authenticated, though it is in my approved or "allowed" list.

Thank you,

David Z. Kil

kil.5@nd.edu

[pelms]

dont forget that power levels can be altered on clients and Access Points thereby reducing areas of coverage and avoiding excessive cell overlap

[dchia78]

Hi,

In the cisco aironet 1200 product specs, the range for 11b is 40m@11mbps. How about 11a?

[dchia78]

sorry, wrong post. Do not reply.

[Steve Dussault]

Did you ever find any documention on overlapping AP cells?

[Scott Fella]

I have played around with 4 350's using the same channel...... I have no problems at all. I don't implement that way, but just wanted to see for myself. I am no RF engineer, but are there any link to what you can get away with?

Like suggested, you can lower the output to prevent too much overlap. The number of users and applications that will be on this WLAN will decide if 5 is too many. On some of my installs, I have had to limit the number of users to 15 per AP just because of bandwidth issues. The problem with hospitals.... old ones especially are like bomb shelters. They might of planned for 5 just to cover all areas without having any dead spots. After the install, play around with applications and doing a continuous ping to see if you drop or if you see any problems.