Interference on 2.4 GHz

[jmorphew]

We have a newer Meraki wireless deployment. The building is a 2-story office area attached to a large warehouse. Our 2.4 GHz wireless is not working reliably in the warehouse portion of the building, the 5 GHz wireless is working. I am already working with Meraki support and a local vendor, site surveys have been completed. So far neither has provided a solution. Here’s some additional information:

• We are using MR36 and MR44 access points throughout the entire building (warehouse and office)
• Our warehouse access points are mounted at 34 feet, a few feet below ceiling height
• Nearly all access points in our warehouse show 90% or higher utilization on 2.4 GHz
• The minimum power level of our access points in the warehouse was set 29/30 to address some deadspots and low coverage areas. We have been adjusting this setting, they are currently set to 20/30.
  • We adjusted minimum the power level back down to 6 for testing, but it only reduced our average utilization by 4.5%
• The 2.4 GHz connectivity issue is consistent across all SSIDs

There are problems throughout the warehouse, but to make this easier I will focus on one location. The attached image is our floorplan in this location. The red numbers are utilization, the blue numbers are 2.4 GHz channel. Here's some information about one specific location in our warehouse:

• A portion of our warehouse has racks that are 30 feet high and 8 feet across. The racks are filled with pallets containing cardboard, wood, metal, and plastic
  • The access points are 19 feet apart East/West (between racking aisles)
  • The access points are 84 feet apart North/South (down the same aisle)
• When a client is using 2.4 GHz and stands where the Green X is located, they have the following issues:
  • Slow internet (1 mbps or less on a 1 Gbps connection)
  • High latency (500-2,000 ms)
  • Dropped connections, no internet
• This client is closest to access point W-21 (green box)
• Access point W-21 is on channel 6
• The average channel Utilization for access point W-21 is 98% (jammed)
• There are hundreds of entries on the ‘Interfering APs’ list for this access point
  • The top 4 interfering BSSIDs belong to neighboring access points WH20, WH19, WH23, WH28 (red boxes)
  • These access points are also on channel 6

I believe our issues are caused by co-channel interference due to a high density of access points in our warehouse. I also believe the wrong model of access point was chosen for a warehouse deployment, driving higher density and more channel overlap. I would like help confirming this theory or help identifying any other potential causes. I would also love suggestions on how to resolve this issue.

 

 

 

[ww^]

Try disable some of the ap's 2.4 ghz radio

For example on w26 w28 and w30 and see if things get better in that area

Or Maybe disable all 2.4ghz if you dont need it

[jmorphew]

I planned on disabling 2.4 GHz on the warehouse, then re-enabling it for a few access points. But I read that Meraki has a hidden network for mesh that would be broadcasted regardless. So I wasn’t sure if this would be a valid test. I plan on powering down access points next time I have a downtime window, but it might be a few weeks. We might be able to get away without 2.4 GHz, but I would like to explore anyway to fix it before giving up.

[ww^]

If you dont use mesh then better turn mesh off. On network wide settings

[PaulMcG]

In any warehouse deployment we always go with external antennas, so in your case it would be a MR46E.

The location of the APs all in a row aren't helping either. A proper site survey will indicate where they should be, but I don't see the logic of having them placed as you've indicated.

Power settings aren't helping either. At a customer with a similar environment to what you describe, we have power settings of 9-14 for 2.4, and 10-17 for 5 and almost all the APs are running on the lower end of the scale.

[jmorphew]

Thanks, this aligns with my understanding as well.

[Ryan_Miles · Accepted solution]

The Warehouse RF profile you have instructs both radio bands to use all data rates and min power of 20dBm. That is likely a big part of the issue here. In a dense warehouse environment you'd want to raise the min bitrate and allow lower TX powers.

As others have mentioned internal antenna APs and AP placement might not be ideal here. Internal antenna APs at 30+ feet is generally not recommended. And I would tend to only see this end of row deployment is directional antennas were being used to shoot the signal down the row (like mounted on a wall pointing down the row).

[jmorphew]

Thanks, I'll ask them to try lowering power and increasing bitrate and let you know how it goes.

[joey.debra]

Usually your power levels should be no higher than 14 dBm on 5 GHz and 8 dBm on 2.4 GHz to kind of have the same coverage area.

Your ceiling height is a bit high so you could have made the case for directional antennas.

How many SSID's are you transmitting ( no more than 3 hopefully )?
How high is the minimum bitrate (12Mbps minimum I hope)

Did you check for any non WiFi interference using a spectrum analyser?

[jmorphew]

We are transmitting 5 SSIDs. Four are required, one was added to troubleshoot connectivity issues with the tablets on our forklifts. The warehouse profile has a min bit rate of 1 for 2.4 GHz and 6 for 5 GHz. I will ask the vendor if they used a spectrum analyzer, they were walking around with some device but I think it was just measuring signal strength.

[joey.debra]

Ok, it seems like best practices are not followed and you are able to fix alot of the airtime by channging these.
1) if you do not use any 802.11b devices in your network you should be safe to use 12 Mbps as a minimum bitrate, this will alleviate most of your airtime shortage. If you do still have 802.11b then try 11 Mbps. (risk: if you don't have enough coverage you might have more dead spots with higher bitrate but your survey should have taken care of this)
2) try getting more done with fewer SSID's. If you are segmenting onto VLANs using SSID's you're better off using iPSK on one or two SSID's. iPSK couples each pre shared key with it's own Meraki group policy which can set a custom VLAN and this all on one single SSID 😉

[jmorphew]

Thanks, I will try adjusting the bitrate and temporarily disabling the other SSIDs. Yes, we had deadspots before. That's why the vendor adjusted these settings.

[joey.debra]

Ok I hope that works for you without too many deadspots.
If it does improve and you have deadspots you might want to consider doing a validation survey by a professional. There might be an issue with how the current AP positioning has been done.

Btw: without any user traffic you can have high levels of management frame overhead with low minimum bitrates. The screenshot below is from wifi professionals showing the effect of 6Mbps minimum rate: It is even way worse in 1 Mbps but you need the excel sheet for that 😉

[joey.debra]

Oh I didn't realise I still have the original excel file.
Here are the calculations for 1Mbps as your situation was:

[jmorphew]

Thanks for this chart, to make sure I have this right. The 'number of APs on channel' column refers to the number of overlapping APs? And the overhead percentage is similar to Meraki's 'channel utilization'? So we have a bit rate of 1, 5 SSIDs, and many overlapping access points. Which basically makes it impossible to avoid interference.