RF Hell in Warehouse

Unanswered Question
Dec 12th, 2008

Hi guys, me again and now with one of those RF hells.

We are working on a Distribution Center of one of our clients. We are using two 4402 WLC with 19 Access Pont 1242, each with one 1728 antenna . The APs are installed at an height of 10 meters aproximately (almost at the ceiling). The problem here is that using the wireless cards from laptops, handhelds and IP phones (not cisco phones), the reception is rather erratical. BUT, using one laptop with a 350 Cisco card, the reception is way better.

Of course, our client won't be using Cisco cards, so we need to get a better coverage and reception in their handhelds and laptops.

We are using the B/G radios and most of the APs have a lowered power setting. I include a diagram with the position of the APs.

The warehouse is filled with a bunch of big (8 meters) metal shelves, with some robots and inventory products. So multipach should be a big issue (I imagine thats why we get the erratical behavior.. like PINGs with 2ms, 4ms, and then 130 ms and so on).

Also, I think the AP are placed too high, but then again, the shelves are also too high.

And in top of that, the client has some ad hoc networks (for their robots) in the same floor, running at channel 3. (We, of course, are using channel 1,6 and 11).

Any recommendation? I'd like to try everything before thinking about changing the position of the APs.

If you need more info, feel free to ask.

PS: Aggressive Load balancing not enabled.

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rob.huffman Fri, 12/12/2008 - 16:17

Hi Omar,

I'm pretty sure that you have already determined one of the major sources of these issues..."Mulitpath". A warehouse setup like this is a prime candidate for this type of problem. The Adhoc network isn't going to help either. The thing that may help more than anything is to add a second 1728 to each AP. These can then be set for Diversity Mode which is highly recommended to overcome Multipath issues. Have a look;

From this good doc;

Multipath and Diversity

http://www.cisco.com/en/US/tech/tk722/tk809/technologies_tech_note09186a008019f646.shtml

Hope this helps!

Rob

Jason Aarons Sun, 12/14/2008 - 07:53

How many APs per Square Foot do you have? I think your positioning with 10-25mW would work.

If you look in the WLC are the clients any version of CCX?

I agree with Rob about multipath and adding second antenna.

Have you used Cognio to check for inteference sources? Maybe adding a AP in Monitor Mode?

Any clues coming from logs or syslog from WLC? Like deauths or radius failures. You may need a Wireless sniffer to watch the control frames between clients and radios.

grzegorz.ciolek Sun, 12/14/2008 - 09:19

Hi,

I had similar issue. But mine client warehouse had 18 rows, length for 70 meters, where fork lifts drive with goods. Solution was simple 1250 with AIR-ANT2430V-R and AIR-ANT5140V-R. I changed antenna orientation.

In my opinion you should try lower your AP, change to 802.11a (this 3 on ad hoc will be pain) or as Rob said - add another antenna.

Cheers

Greg

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