Unsucking Wi-Fi - a quick and dirty guide for the neophyte wireless engineer

Recently, some of my colleagues have been coming to me for advice with wireless. There is a TON of information you need to know to get good at wireless networking, but there are also some quick tips that can get you quite far, quite fast. 

The intended audience is a technical person who's somewhat unfamiliar with wireless, or seeks to quickly learn a bit more. If you want an even more basic primer, check my previous article. 

This article doesn't particularly cover external Pt(M)P networking that may be used to cross a campus or run a WISP - it's focused on wireless supplying end clients (i.e. "traditional" in-building wireless coverage). 

It is not going to be the be all and end all of wireless (it's not several thousand pages long, for a start), and some things are context-specific, and guidelines are sometimes best broken, once you understand more; realise this is, at best, a primer to going off and doing (a lot) more reading (and careful experimentation!).

Read on...

Note: this post is a work in progress/living document, and it likely to get more work over time.
Last updated 28/10/2022.

First of all...

Does it really need to be on Wi-Fi? #WireAllTheThings

Some sage once put forward a simple statement: "Wire what you can; Wi-Fi (only) what you must" - in other words, if it doesn't need to be on the wireless, don't use wireless. 

Anything that is literally fixed in place (desktops, docking stations, AV equipment, etc) that needs network access should (MUST!) be wired, and if that equipment is missing an Ethernet port, it is not fit for purpose. Things without NICs that have USB can easily rectify that problem with a suitable USB device. Save scarce radio spectrum for applications where you CANNOT possibly fulfill a connectivity need any other way. A previous workplace enshrined these requirements in the network connection policy, and they helped enormously. Every device you take of the Wi-Fi saves room for one that can connect in no other way. 

Provide wired options wherever you can, and warmly encourage their use. If you're fancy, make sure you're using things like 802.1X and associated NAC to keep things nice and secure. 

Things not on wireless firstly (mostly) avoid any interference from anything else - they have "wire speed" service practically guaranteed. Furthermore, their actions don't typically tie up all the local network resources; a single wireless client can completely tie up an AP. In contrast, a modern wired network switch can handle pretty much every single port flat out, so long as there is enough uplink bandwidth. Wired (or even fibre) connections are particularly valuable for things that don't do well with latency, jitter or packet loss, or require very high bandwidth throughput (because of things like TCP congestion avoidance algorithms, bandwidth delay products, and of course, things that are grumpy about latency, jitter, out of order packets and packet loss, like VOIP or videoconferencing). Contrast the speeds you can get out of singlemode fibre with 5GHz wireless, and you'll rapidly see that shared spectrum radio is a horrible solution at scale. And the fibre is full duplex, unlike the radio.

Give me a picture of ALLLLLLL the things I need to think about

This other network blog has a diagram I've found quite useful in the past: 

https://wirednot.wordpress.com/2016/03/19/the-soon-to-be-famous-cocktail-napkin-wi-fi-big-picture/

By the author's admission, it's not 100% complete or accurate, but it is a good guideline to figuring out wireless issues top to bottom. Save a copy somewhere, or print out a couple of copies for you and colleagues. 

Cocktail parties everywhere, but not a drop to drink...

People often talk about many of the problems in wireless networking through the example of a (cocktail) party - there's so many conversations around you, you can't make out any conversations. As someone who really struggles with auditory discrimination against noise, I get this on a visceral level. 

Many wireless problems come down 3 "noise-related" problems:

1. Straight up noise (not wifi, just other RF emissions in the frequencies of interest); 
2. Co-Channel Interference (CCI - other wifi users on the same frequency and channel width); 
3. Adjacent Channel Interference (ACI - neighbouring wireless "channels" that overlap with yours).

As a first step, make sure you're not unreasonably suffering from ACI. This is a classic problem in 2.4 GHz wireless, where all too often, devices will settle on channels other than 1/6/11 - find them, and fix them if you can. 

Here's a basic example for the UK (image from Ofcom)

Keep a chart like this handy when you're trying to figure out what channels to assign where!
Obviously, use one for your country.
Click to enlarge.

There is little you can do about noise, ACI or CCI from networks or devices you cannot control - networks in shared or closely co-located spaces inherently mean you are not in control of everything, and the proliferation of things using wireless as a connection mechanism mean an increasingly hard-to-operate environment - bluetooth on everything, wireless printers and other IoT garbage devices, other uses of ISM bands, and so on. The only way to "win" that war is to be louder and closer to "your" devices - that is, having access points closer to the clients you're trying to connect to. Remember, radio waves follow an inverse square power law, so distance is king - be close! Read the High Density section later for more on that. 

It's time to have a look at the RF environment you're faced with. Hopefully, you have a vendor that supports some way of visualising the RF spectrum around the access points at least. (If you are at a properly equipped company, you should have more advanced equipment and software, like the stuff Ekahau sell). Even without the fancy stuff, you should get some indication of roughly what the RF environment "looks like" to your APs with any vendor that doesn't completely suck. Even the most basic will tell you what other SSIDs they can see on what channels - not a brilliant option compared to actual spectrum analysis, but better than just guessing channels. 

Check to see that:

• Your RRM (radio resource management) "auto" settings aren't being brain-dead. Earlier today, I saw 3 neighbouring APs using the same 2.4 and 5 GHz channels. Yes, from a major vendor. No, I was not impressed. Yes, the site was expressing that their Wi-Fi "sucked" around those APs. Things got markedly better when I told the system to use 40 instead of 80 MHz channels and to redo the RRM calculations. 
• You are using a "quiet" channel in that location - many vendors will either have a full time scanning radio (invaluable) or allow you to temporarily retask a wireless radio to do some basic spectrum analysis (at the cost of dropping clients) - these are VERY useful features. 
• That quiet channel doesn't overlap with others (so in 2.4GHz, there are only 3 valid channels in most countries - 1, 6 and 11 - any channels in use other than that are causing issues to the channels either side of that). There are good diagrams of this online. 
• In 5 GHz, that's slightly more complex, but the good news is there are more channels to choose from - but not if people use outlandishly wide bandwidths. Upcoming 6GHz will give us more spectrum - once we have client devices that can use it. 
• Valid channels change by country, and also over time, as regulators update national permitted uses, such as OFCOM relaxing the DFS rules for some of the 5GHz channels, or adding additional radio spectrum for WiFi (like 6GHz). 
• The bandwidth you use is appropriate. Using narrower bands (i.e. 20MHz instead of 40, 80 or 160 in 5GHz) means you can assign more unique "cells", which helps - completely clean channels are WiFi nirvana. Some authors have also claimed that narrower channels also help "punch through"or are somehow easier for radios deal with interference than wider ones, but I've always viewed this with some skepticism. Still worth a shot though, and aside from those claims, using spectrum more efficiently is usually a net gain! Be aware that more non-overlapping 20 Mhz APs is often better than fewer 40 or 80 wide channels (forget 160, it's unusable in the real world). Where client devices only support 20Mhz, the rest of the band is wasted (later standards do interesting things about this with things like MU-MIMO, or 802.11ax's RUs, where supported). 
• for 2.4, 40MHz wide is a travesty and should never be used. You only have 3 channels with 20MHz bandwidth; with 40Mhz, you're down to one (because the other overlaps no matter whether you use 1 or 6/11). 
• the trade-off, of course, is speed - more bandwidth = more data per second, so your throughput decreases as the bandwidth assigned goes down. However, you will generally see consistently better performance overall with more APs that don't overlap serving smaller numbers of clients per radio. 
• If you can, ABSOLUTELY make use of DFS channels, but be aware of "DFS hits" particularly if you are near to aviation users and/or weather radar stations. 
• Consider adjusting the TX power to a suitable (usually lower) limit
• Balance power between 2.4 and 5 GHz wireless (typically 2.4GHz lower TX power than 5GHz) to help encourage devices to use 5GHz. Consider where to disable 2.4 entirely on some APs in high density designs. 

Some other tragic things to check: 

• Get hold of nationally relevant permitted frequency bands for 2.4 and 5GHz Wi-Fi (this varies per country); make sure any details around indoor vs. outdoor and other permitted uses (i.e. fixed broadband access, etc) are suitably covered by your vendor - and your settings (it is your problem if your AP is doing something illegal in your jurisdiction, not the vendor's). 
• Remember: settings for interior vs exterior client APs may be different
• Remember: settings for wireless bridges (P2P or P2MP) may be different
• If you're messing with antennas, be aware of EIRP limits. 
• Vendors will often call these something like "regulatory domain" - find somewhere you can set a country, and do so! 
• Turn off wireless on things that don't need it - wireless printing features are a common fail here. Don't clutter those precious airwaves with junk. Most models will allow you to permanently disable the feature. This becomes increasingly common each year with IoT devices, most of which broadcast some kind of wireless network before they associate with yours (and some continue to do so). 
• Consider suggesting that the use of personal hotspots is against good practice (I've seen it cause chaos in shared accommodation). 
• Verify AP placement isn't brain dead (inside or behind a metal cupboard or similar obstruction), or hidden somewhere in a corner, or incorrectly mounted for the coverage pattern of that model (APs can be mounted in the wrong orientation or too high or low off the ground - RTFM!).  

You're holding it wrong

There was a time when you could literally hold a certain Apple device wrong and it would cause issues. This is still the case, and not just with that model. If large bodies of water (AKA people) are between their device and an AP, they WILL be blocking RF. If their device is in a metal drawer or at floor height, they may not find things work as expected. 

Cradled in hands, it's possible the very act of holding a device may block enough signal (particularly in a marginal coverage area) to render it unusable. 

Move around and see if it gets better!

Move your ass

The vagaries of RF propagation can mean moving may resolve a multitude of sins. Since the dawn of MIMO and antenna diversity, things like multipath and destructive interference have gotten less bad  (and spatial streams make multipath a good thing), but they still may cause issues in challenging environments. Always get a user reporting problems to go and reproduce their issue close to a "known good" AP - if possible, verify they are actually associated with that AP before they attempt to reproduce the issue. 

If a device has less than say -65dBm RSSI (i.e. a number higher than -65, like -80 or even worse), they're not going to have a good time if they expect high bandwidth, low latency and low loss. -65 dBm or closer to zero (like -50) is better; I don't consider a client getting worse than -65dBm adequately covered. 

This can also cover re-positioning APs, where they may be sub-optimally located to properly cover clients. In some cases, re-positioning an AP that's out of optimal positioning may be required. 

Obviously, if there are legit areas users need to be in that don't have coverage, that will only be solved by adding APs. 

Not all waves are equal

You should be aware that 5GHz is generally associated with better wireless (more or less entirely because there's way more spectrum available than at 2.4GHz), but you must also be aware that on the whole, 2.4 GHz frequencies are much better at going further than 5GHz frequencies, so changing power (TX) levels between 2.4 and 5 GHz radios can be helpful in most designs, as well as sometimes entirely disabling 2.4 GHz on some radios/APs.

6GHz is going to play an increasingly big role, where supported and available (and yeah, you'll need new APs and recent clients or new cards or dongles). 

Emerging alternatives to Wi-Fi like CBRS look really interesting (think basically "private LTE/5G"), and uses different spectrum (3.5-3.8GHz or so) - again if your clients can support it, but it may be ideal if you need to make a "it absolutely must work" wireless network in areas that are utterly swamped by competing wireless systems, like office buildings and shopping centres and the like. 

Eww! It's STICKY!

From time to time, you will come across wireless issues caused by "sticky clients". 

A common scenario is that devices stay associated with (are "sticky") with an AP they first pair with when a device enters a building or goes down a corridor - even when there are much better APs in locations the device ends up in shortly afterwards. 

Check to see if particular APs have a lot more connected devices than you might expect - take a look at things like APs near to entrance doors to buildings, in particular. 

One of the travesties of wireless is it is mostly controlled by the client devices themselves, NOT the wireless systems. (Cellular clients, on the other hand, are controlled by the network - look how much better that typically works!). This means that clients will often do things that are, if you have a better view of the network, rather silly. There are some hacks you can try to adjust this behaviour.

For example: 

• They'll stick to *that* AP far longer than you might expect, even if there is a "stronger" one in range.
• Careful layout of APs and TX strength adjustments can help control this. 
• Extensions such as 802.11 r/k/v may also help, but be cautious in deploying them around old client kit
• There may be vendor-specific hacks you can try
• There may be minimum client data rate (preferred) or minimum RSSI (sometimes problematic) settings you can use that make the AP de-associate a client outside of reasonable levels. 
• Minimum data rates are often very helpful; anything less than like 11 or 12 Mb/s is ridiculous, unless you have to support really legacy stuff. 
• higher than this may well be desirable in high density designs
• if you have to support really legacy stuff, your life sucks.
• They'll stick to *that* AP because it supports a more modern wireless standard, or has a fancier radio with more spatial streams
• It's generally best to stick to one make, model and generation of AP within a building
• Adjusting (reducing) TX strength settings may force earlier roaming as the signal will drop off faster (but you may need more APs to cover a given area)
• make sure the "best" APs are used in the most sensible locations
• They'll stick to *that* AP because it is using a wider channel width
• Use the same channel width throughout a building or campus. 
• Suggest users turn their device or wifi off and on again "when they get to their desk (or room)" - this can frequently force a client device to find an actually better AP. Not to mention this often helps poke slightly b0rked client devices and WiFi stacks. 
• There are more reasons, of course, most vendor-proprietary - but many of them aren't anything you can do anything about. 

You might find learning about the "green diamond" helps you understand some of this better. Try https://wlanprofessionals.com/greendiamond/

"That AP predates the founding of some countries!"

Ancient wireless systems should be gracefully retired, or inadvertently hit with a heavy, blunt object until they are replaced (I jest, property damage is bad, mkay?). 

If you're still using 802.11n or earlier access points, you have a very strong reason to motivate for modern APs, particularly if you have to support lots of users doing high bandwidth stuff.
Should you go for 802.11ax (or WiFi 6)?
Probably, but definitely don't get anything older than 802.11ac wave 2.
WiFi 6E is basically WiFi 6, with the addition of 6Ghz spectrum support - which will be great until everyone climbs on that frequency too (and of course if your client devices even support it). That's (as of the time of writing) the latest, greatest option.

With everyone having gotten used to videoconferencing as the "norm" for communication during the pandemic, everyone now does this, and it's an enormous strain on wireless. In very light usage scenarios (one or two users occasionally doing email and browsing non-video websites), old APs might still work, but you need to move them waaaaaay out to the edges of your coverage where they might remain "fit for purpose" - but on the whole, if it's that old, you want to get rid of it. 

High Density designs are what you should be providing, designing or otherwise advocating for. 

You may also find some older designs do things like having ALLLL the APs on the same channel (!) - this was quite popular with some vendors for "seamless" migrations between APs. This is horribly antiquated!

It is also hypothetically possible that an old, unsupported AP could become illegal if your local regulatory domain changes its mind about what is allowed (and you don't take action to prevent it doing the no longer allowed thing). This is one reason it's vital to make sure that country is set correctly on your devices, and where there are regulatory domain updates in firmware for your region/country, you apply them. And, quite aside from the performance and security issues at stake with EoL devices, give you yet another reason that you can't support things that the vendor themselves no longer support. 

RSSI - can you hear me? 

Remember, wireless is two way. 

There's what the AP sends and receives, and there's what the client sends and receives - both will be affected by the RF environment by various environmental factors with may not be equal in both directions, and device-specific issues around antenna diversity, gain, effectiveness, along with transmitted signal strength, and radio receiver sensitivity (and discrimination) and so on. 

Make sure you have a good handle on what both sides of the equation look like - you may need to go over there and literally take a look; having a "standard" device that is used to survey things can be quite useful in determining if a given location is "adequately" covered or not (-65dBm or better), but most basic mobile phones will have apps that will give you "good enough for government work" answers to signal strength in a particular area. 

Take a look at signal strength indicators if you can, and use that insight to help understand, diagnose and resolve issues related to signal strength. 

That's too busy!

The "busy-ness" of a given channel can have a very significant effect on how well wireless operates for the end users. 

If the airwaves are congested, inherently, you've got a wireless traffic jam - there isn't enough free space to get more data delivered. This can be from a mix of "your" wifi, as well as ACI and CCI from other neighbouring APs (yours or another network's), as well as any non-Wi-Fi "noise" that may affect things. 

Wireless is very much a victim of its own success. Getting clients to send or receive their data as quickly as possible is key - and, of course, if you simply have too many clients wanting too much data, the airwaves will be busier than ideal - so you need to spread them out (across more APs and different channels). 

This is where things like speed limits (shaping) can actually make things worse!

Or, you know, get some heavy users OFF wireless - provide wired "hot desks", identify heavy users and help them get wired up, and so on. 

There's a limit to the usable number of connected client devices per radio

Any decent vendor will give you an indication of the number of client devices that can (under idea conditions and certain performance envelope) connect to a single radio. This number is, on the whole, around 25. 

This will reduce where you have old clients, weakly connected clients, interference, and other negative influences, or particularly demanding (continuous high bandwidth) applications. 

 

If you have a LOT of devices associated with each radio, you need more radios - upgrade to a single AP that supports more clients [more radios, massive spatial streams and MU-MIMO or WiFi 6 OFDMA RUs, etc], or, better, add more APs with non-overlapping channels. When you need to cover VERY dense deployments, you'll need specialised design guides (like for stadium wireless, or in places like lecture venues). 

Putting more APs in, with a careful manual channel plan, narrower bandwidth and power adjusted WAY down (as well as making use of now useful radio attenuation by building materials) will allow you to re-use channels quite quickly. The density of APs needed to provide rock-solid coverage can be quite startling to the unprepared (the Meraki guide for some Cisco offices as an example is... interesting). At that stage, you're definitely into the "model in software, deploy, and verify with post-installation survey" territory. 

Eventually, just being associated takes up all the available capacity of an AP - so you might have 100 or whatever clients associated to an AP, but they can't do anything useful! As with many things, a pinch of salt when looking at "maximum" numbers is always useful. 

High Density Coverage / Design

How we use wireless, and what our users expect (nay, demand!) has massively changed in the past 20 years or so. When first designed, we were occasionally sending or receiving the odd 100kB or so email or webpage. I've see customers with wireless systems deployed literally 15+ years ago not getting the need to upgrade. Nowadays, we expect streams that may be tens of megabits per second to be flawlessly delivered to many devices - and most of us carry several of these around at any time. This is a HARD ask of wireless. 

Designs from that era attempted to cover areas in as few APs as possible - but what we mean by "cover" these days has changed rather a lot. 

If you're still dealing with wireless equipment or layouts from that bygone era, you're going to be well placed to think about redoing the wireless under the modern "high density" coverage paradigm. It's not literally "one AP per room" (some rooms also need several!), but that can (in some environments) not be a bad first stab approximation of the scale of the problem. Corridor WiFi is also the worst design. Most vendors have a high density design guide - reading that would be a good use of your time. 

In no particular order or endorsement some vendor guides: 

• Meraki
• Ruckus
• Ubiquiti

Other vendors exist - I've just happened to use those systems and read those guides, or former versions of them, in the past. 

Make sure you understand the needs your end users will have - what apps, devices and duty cycles are involved; how many per user; where those users are and so on. If you can afford it, there are wireless design tools that will let you model (and then validate, with a post-installation survey) a site design. Ekahau have some lovely tools here, but they (again) are not the only vendor.  

Don't Set It And Forget It

Many people assume that the vendors RRM (Radio Resource Management) is MUCH cleverer than it is. For simple sites and undemanding uses, it might be "good enough", but it will NEVER beat an intentional design and operational tweaks by someone who knows what they are doing. It can also have a bad day, and is constrained by decisions you take (AP placement, various settings around permitted channels, bandwidths and transmission power). 

If you're having problems, you've probably gone beyond what that RMM solution can offer you - use this guide, and further reading, to figure out what a better set of settings might be - usually, you can get quite far with manual adjustments to things like: 

• what channels an AP is using (and often, switching some 2.4GHz radios off completely)
• what channel width an AP is using (20 vs 40 vs 80 vs 160 MHz) - anyone using anything other than 20Mhz in 2.4GHz should be shot persuaded to stop.
• What TX strength is set - turning power down can often help a lot of things (if you have enough APs)
• Settings like minimum client data rate; disabling legacy protocols/rates
• vendor specific tweaks
• 802.11 r/k/v (and any further similar new fun toys as they come out)

Get a piece of paper out, sketch the site and AP locations, and come up with a manual channel plan, using information from your AP scanning to understand where particular frequencies may best be employed. 

In many cases, you'll need to walk around the site to truly get a "feel" for it. Ideally, do that with a suitable survey tool like an Ekahau sidekick, but you can get quite far with a laptop or smartphone and some free software and paying attention to signal strengths.

Talking of RMM and AI/ML, I hear good things about Juniper's Mist wireless system with the Marvis AI. I've not played with it myself. I once asked a company in a job interview "does it live up to the hype?" and they were pretty effusive in praise for it. They're (very) demanding wi-fi users, given what they do, so that's one to add to your list if you're evaluating vendors. 

Duplex? Not just for printers. 

One thing a lot of people forget about wireless is it is half duplex or "simplex". Something can either be transmitting OR receiving, not both at the same time. 

This further means that if ANY device associated with an AP is transmitting or receiving, no other device can validly do so in a given time period. 

Another related and particularly pernicious problem is that of a "hidden node", where for example two clients on opposite ends of the room to each other can't "hear" that the other is busy broadcasting, so it'll throw out signal, swamping the other node's transmission. This is more common where you have excessively "loud" APs that have TX set too high (and VERY common in outdoor PtMP wireless). There are knobs to help deal with this on many platforms. 

This set of challenges puts very significant performance penalties on wireless in general, and yet again underscores the need to get things off wireless when you can. 

Another thing to be aware of is that, therefore, single very slow clients drag down the entire network performance (a device connecting at 1Mb/s will take up a lot more "airtime" for and equal amount of data send or received vs. one at a more sane connection speed) - one reason minimum data rates can be really helpful in tweaking performance. In high density situations, you may find that setting some APs to permit somewhat crappy connections helps extend your coverage, and then having some others be really demanding about minimum speeds keeps the good citizens up and running quickly - but this is super site specific and requires careful consideration and iterative tweaking. 

OOOH, you think you're so Spatial!

Spatial Streams. 

What? 

You'll often see things on AP specs about "spatial streams". Or at least you'll have noticed specs like 2x2:2 or 8x8:8 - this refers to the available number of TX, RX antennas and the number of spatial streams they can handle. Without going into book length, antenna diversity plus multipath means you can effectively re-use some spectrum and multiplex signals for higher throughput. 

When you're assessing problematic wireless, pay attention to the spatial streams available on the APs in question - if you're needing to deal with very demanding clients or lots of them, they can make a real difference. If it's not obvious, "more is better" and a 2x2:2 is very basic. 

Hot Potato Wi-Fi

Get it out! GET IT OUT! 

The faster you can get data across the airwaves, the more things you can serve (all other things being equal). If you have a potential to do 300 Mb/s vs 100 Mb/s, you can serve roughly 3 times more client devices (under ideal conditions) under the 300 potential scenario. This is why you may want to use wider bandwidths, and why additional spatial streams are so very useful. You will need to balance the need for clients-per-radio against coverage requirements and channel planning to see whether or not you can use the higher bandwidth options or not. 

So Broadcast, Such Traffic. Wow. 

I've seen "internet background radiation" in the order of 4 megabits per second of garbage (BUM) cluttering up airwaves on large wireless LAN segments. Filter that nonsense! 

Get the right tool for the job

Get modern APs; turn off shitty all-in-one residential gateways. Mount them in the right place. Have decent backhaul and connectivity and supportive services. 

Things to Avoid

Meshing

Meshing sounds cool. It isn't. Use wires for backhaul; don't suck up precious spectrum on backhaul! YMMV in a home, of course, but professionally, get those APs wired in!

"wifi extenders" and "boosters"

Hopefully, you don't have customers that think these are helpful. They're not. Use additional APs that are wired back instead, because these devices either do mesh or halve your available bandwidth (because they have to retransmit everything you're sending through them - and if you have a chain of these things as repeaters, woe betide you). 

People

No, I'm not being a stereotypical sysadmin who would find everything works perfectly... until the users/customers turn up. People block wifi - make sure you avoid them by suitable AP placement - people height doesn't work very well - higher up tends to work better (so ceilings, usually, rather than walls, or heaven forbid, skirting height).  

Excessive SSIDs...

Most guides will tell you to use 3 or fewer SSIDs on any given AP. Where you need to hive different users off into different VLANs/subnets, use RADIUS assigned VLANs for this on a common SSID. That allows for a general 802.1X RADIUS SSID, a guest SSID and a 'terrible legacy device' SSID where you need one. 
see also: http://revolutionwifi.blogspot.com/p/ssid-overhead-calculator.html

....Buuuut don't necessarily rule out frequency banded SSIDs

It can be useful with some vendors and some clients to have different SSID names on 2.4 and 5 GHz wireless, so you can selectively connect to one or the other (i.e. Staff_2.4 or Staff_5.8) - because these are in different frequency bands, even though you have (say) 6 SSIDs, you only have 3 per rario. 

Don't break the law

• Make sure your system is set to the correct regulatory domain (country)
• Make sure you apply "indoor" settings to "indoor" APs, and "outdoor" settings to "outdoor" APs (these are frequently different)
• Don't exceed EIRPs by adding aftermarket antennas without understanding the consequences and requirements. 
  
  

Renegade!

If you work in environments were change control is done (you probably should) make sure any experimentation conforms to that (and, ideally, starts in a lab).  Don't be that guy that breaks the wireless when Janice from Accounting is running Payroll (of course, one might ask why Janice is even doing payroll over wireless...). :) 

If you are experimenting with settings, particularly if you're new to all this, I highly recommend you ONLY do it when you're in the building you're messing with so you can immediately check the results and also canvas other users in the building about resulting effects from any changes (for good or ill). Document things you change and results as you go along!

Be Nice To Your Neighbours

Although wireless is a classic tragedy of the commons, you should try to be nice to your neighbours (don't be a dick in how you place or configure your network) - and you may find that there is much mileage in politely engaging in dialogue with neighbouring network operators to establish a more equitable or functional overall wireless arrangement in an area. Establish or help to suggest useful rules of thumb around appropriate and equitable use of shared radio spectrum (you know, no-brainers like "use wires" and "use a sane channel plan" and "turn the radio down"). 

Where you have customers that do things like lease property, encourage them to provide (excellent) wireless services, with custom settings to isolate each customer into their own wireless network over common (shared) centrally managed infrastructure. It's MUCH worse when everyone in a building does their own thing. In some areas, it may even be plausible to have lease conditions to NOT run competing wireless networks (however that may be defined), although enforcement may be a challenge. 

Check the firmware

It is often worth trying newer firmware, particularly if the problem is with newer model APs, controllers or end user devices; there may be specific bug fixes. As always, upgrade based on release notes that suggest improvement to a known issue that gels with what you're seeing, or on the advice of the vendor through a support case (or due to a known security issue or critical feature upgrade). 

Don't forget that some versions will make things WORSE - like the vendor upgrade that caused ALL our APs (something like 1,000 of them) to toss all our clients off the system every 10-15 minutes for some random amount of time. Not great, and it took them more than 6 months to admit to and fix the regression (not to mention MANY late nights in maintenance windows repeatedly showing them how broken it was). 

What if it's not even the Wi-Fi?

Today, many users conflate the term "Wi-Fi" with "network connectivity" - heck, I've had tickets complaining about broken or missing "wifi cables" (yeah, I know), or calling any form of Internet connectivity "Wi-Fi". To be fair, in the age of pocket devices, wireless is all too often how things are accessed - and we need to just interpret what users say to what users are actually trying to report - as we always have, and always will. 

Don't forget to ascertain what the end user is trying to get done and blaming on "the Wi-Fi", when it might be something else (network-wide issues with DHCP or DNS; local switch misconfiguration; saturated uplinks; internet outage; service outage at some 3rd party application or service, incorrect credentials, misconfigured profile, etc). Similarly. "slowness" may not be something you can remediate if the remote resource is inherently slow, or has some limitation on the Internet path outside your control. The speed of light only travels so fast. 

Your average end user doesn't understand ANY of that.

Use your normal troubleshooting processes for EVERY problem. If all else fails, start at layer 1 and work up, end-to-end...!

If you've been given incomplete info, go back to the source and ask them to SHOW you the problem. 

And you'll be amazed how often removing and re-creating a wireless profile helps when the user is "absolutely sure" the settings are correct. Rebooting a device (ideally power-cycling) solves a good chunk more. ("Hello, IT; Have you tried turning it off and on again?") 

Some Things Are Just Broken

Occasionally, there is literally nothing you will be able to do. 

A specific client device may have a b0rked radio, driver or refuse to reconfigure their wireless settings or re-enter their credentials (yes, I've seen all of this), and there is NOTHING you can do to your wireless system. All you can do is point out the troubleshooting done, suggest alternatives (use a wire; try another device), or simply politely give up on that device / user. They may also have unreasonable expectations (such as workable wireless in areas that you don't actually cover, or particularly outlandish requirements in terms of numbers of devices associated and expected throughput). 

Sometimes, there may be site-specific factors you cannot fix or control - some incredibly noisy source of RF interference which you cannot get turned off, or get some spectrum enforcement agency (FCC, OFCOM, ICASA or so on) to deal with. You'll need to use wires (or even fibre) in such circumstances. Another common issue is where neighbouring networks overwhelm parts of yours (ACI and CCI) - or, embarrassingly, your own channel plan is self-defeating. 

You may have extensively documented the deficiencies in a wireless system and the organisation refuse to engage in an upgrade/refresh. You can't fix that. 

Document and CYA (Cover Your Ass)! 

Remember, application is key

No matter what you read here or elsewhere - if you absolutely have to support ancient devices (legacy things) that you cannot replace or wire up, then you may need to leave legacy protocols and data rates enabled, even if that drags down your whole network. 

You may find creating hyper-local hotspots for legacy gear useful (particularly where that legacy gear is static, as it tends to be) - dedicated APs next to the gear with the power turned right down. The rest of your wireless can then be tuned to modern settings. And of course, you may need serious conversations with management or customers around retiring and replacing legacy client devices - if you can prove legacy devices are making the Wi-Fi suck, they may be more willing to do something about it - but if it's a multi-million (insert currency) bit of OT gear, then they're also going to support you buying an additional AP just for that thing for your hyper-local hotspot concept instead (or buy that optional NIC for that kit you've been begging to get for years)!

The common (near) failure mode of Wi-Fi is "SLOW"

One parting thought - Wi-Fi is INCREDIBLY resilient. I sometimes think it would be better if it broke much earlier than it does. 

The main symptom of pretty broken wireless is "slowness" - i.e. low throughput. 

If wireless is slow, something is broken! 

Read more

If this has piqued your interest, there exist various books you could read. 

• You'll find a good basic to intermediate primer to be something like a CWNA book (I've owned a few copies of the 5th edition Sybex CWNA-107 study guide that have stood me in good stead) - more recent editions may now exist, so do check out the latest releases before you buy anything. The ISBN for that 5th edition is 978-1-119-42578-6.
• Google the problem; read some other blogs on this; read modern design and troubleshooting primers.