I constantly preach about “Knowing your airspace”. I honestly don’t think I can say it enough. Even if you have no control over what is out there at least knowing what it is, where it is, what frequencies it’s using, and what kind of volume of traffic there is gives you something to work with.

This applies to two of the major obstacles in Industrial WiFi, Non-WiFi based interference and (you guessed it) WiFi based interference.

Non-WiFi Based interference

Non-WiFi based interference is interference created by anything that is not specifically WiFi or other non-802.11 standard based wireless. One example of this could be a mechanical drive on a crane that creates Electro-Magnetic Interference (EMI) in the 900MHz frequency range. As seen in the image, it could make it more difficult for 900MHz radios to communicate by drastically raising the noise floor.

These kinds of interference are important to know about as they can inadvertently cause many problems. Just knowing about them can help you mitigate these issues by either eliminating the source or working around it. So, in the example above, if the drives are interfering with 900MHz transmissions, more than likely you will not be able to replace any drives. What you can do is use different wireless equipment and change radio frequencies. Maybe 5GHz would work better in this situation, perhaps even 2.4GHz if it’s not too crowded. If those frequencies were not feasible to use for whatever reason (like no clear line of sight) then maybe you can adjust the current radios to use the lower end of the 900MHz range.

Knowing about the problem gives you options!

WiFi Based Interference

By far the most common kind of interference is WiFi based interference. Basically, it’s just other WiFi networks broadcasting in the same airspace and the same frequencies that the local industrial/manufacturing facility is trying to use for its own purposes. 

Sometimes this interference can some from permanent, on-site contractors who have their own wireless infrastructure installed to support their engineers and other staff. This is usually easiest to mitigate through coordination with the contractors IT staff. Perhaps they would agree to use only 2.4GHz for their access points while corporate owned production facility uses 5GHz for theirs, or vice versa. Maybe each group could consent to use both frequencies but coordinate on who uses what channels to keep from stepping on one another.

The harder problems to solve are the ones that are not known (thanks Captain Obvious!). I have seen two common types of this problem in my travels:

• Wireless systems intentionally installed but not disclosed
• Transient wireless systems

Wait, you mean to tell me that there are companies that would install wireless access points, fire them up and then not tell me about them?

Yes, that is exactly what I am saying. To be honest, I see it quite a bit. I do a lot of work in the Pulp & Paper industries. This includes indoor/outdoor multi manufacturing environment assessments and deployments. It is common at these sites to see large plastic containers on fixed framed pallets containing all manner of chemicals. These containers are referred to as skids. Many of these chemical skid vendors use cellular devices for remote monitoring. Several of these vendors are notorious for using these devices and then blasting out their own WiFi off of each skid at full power and not telling the client that they are active. I often find several of these skids together all using the same frequency and channel.

I have been to some sites where outside vendors have come in to work on various systems and installed consumer grade WiFi routers. The scariest part is that they only change the SSID, leave the rest at default settings and then plug them into the OT network! So not only are they producing WiFi based interference, but they also risk back feeding services into the OT network like DHCP and DNS. Did these groups tell the facility management about these devices? In most of these cases they did not.

The other issue I run across is transient WiFi. So, what is transient WiFi anyway? It is a mobile 802.11 wireless network. It could be something as simple as a wireless hotspot from a cellular phone, or something more complex such as fleet management access points.

I run across fleet management access points at just about every site I go to. These are wireless access points with cellular uplinks that are installed on large trucks. The most common of these in my experience is PeopleNet. PeopleNet Fleet Manager is a commercial vehicle fleet management platform. From GPA location and safety controls to trip routing and other compliance features, it provides all manner of data from the vehicles that their devices are installed on. One of those other services it can provide is WiFi connectivity.

Honestly, I see their SSIDs EVERYWHERE I go. From Pulp & Paper, Specialty Chemical, and Oil & Gas to all manner of discreet and process manufacturing. It took me a while to figure out exactly what I was looking at. The SSIDs they use typically start with “PNet” which is then followed by a string of numbers. Something like:

• PNet6598496
• PNet6958743

It can be annoying during a survey to see a set of these and then comeback an hour later and they are either gone or are replaced by another set of them that are different from the first. But, at least knowing of their existence, what they are and how common they appear can help in wireless network design and planning.

It comes down to the fact that if you don’t know what’s going on in your airspace, you have zero chance of ever being able to really own it. So, take the time to have surveys done. Take the time to have some spectrum analysis done.

Get to know your airspace.

Own that shit.

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