Wi-Fi design is a complex business. We have to take into account a lot of information to ensure the design is correct. In this second part of the Wi-Fi Design series, let's take a look at the Technical Requirements.
In designing Wi-Fi, we need to take into account what the customer wants to use their network for (the Business Requirements) and the environment into which we will deploy the network (the Technical Requirements).
In this blog, we'll take a look at the Technical Requirements and how these inform our Wi-Fi Design.
- Wi-Fi Design Business Requirements
- Wi-Fi Predictive Design: The starting point for all new designs
- Wi-Fi Pre-deployment Survey: Visit site with a battery powered AP to test the walls
- Wi-Fi Deployment Validation Survey: Once installed, test the design works as expected
- Wi-Fi Diagnostic Survey: Deep dive diagnostic survey to determine root cause issues
Wi-Fi Design: Background
Customers Technical Requirements are much more about how the environment looks and how we need to design to fit into that environment.
The Business Requirements detailed how the network was to be used - but the technical requirements are all about how you make the network deliver on the outcomes the customer wants - but in their unique environment.
This is no easy task - while many buildings have similar building fabrics, many also don’t - and there’s a wide variety of businesses that use Wi-Fi from warehouses, high density offices, Universities, external spaces and so on.
Let’s take a look through some of the key technical requirements.
Wi-Fi Design Physical Environment
You can never quite be sure of a building fabric until you test it onsite, during the pre-deployment survey.
We’ve seen building that on the plan looked like standard drywall.. but actually had 30cm thick brick (which, by the way, doubles the number of required APs!).
Some environments are more tricky than others. Warehouses are interesting - you can encounter a lot of steelwork, including girders, racking, moveable doors and other obstructions.
The basic rules still apply - if you install an AP behind a metal obstruction, it won’t work very well.
Back on the topic of warehouses, be careful for hanging metal light fittings and the giant fans they use (they might not be spinning when you attend site, but they will be at some point!).
In hospitals, (particularly if you’re working in a new build hospital), its a classic to hang the wayfinding signs after the APs are installed. These can be installed right in front of your AP and cause major issues.
Wi-Fi Design: Attenuation
Wall attenuation is a key concept in Wi-Fi Design. Quite possibly, this is the key item in design.
RF Designs always start with wall drawing and the correct wall attenuation makes a massive difference to how well the design will work in practice.
The difference in varying the wall attenuation will be to increase, or decrease the AP density.
This costs the customer too much money, or the design not working at all, so getting the attenuation correct matters.
Watch out for tinted glass:
Typically, glass has very little attenuation, but tinted glass is sometimes tinted with a metallic film, which we’ve seen to have an attenuation all the way up to that of a brick wall (we are in Australia, so maybe the tint if quite dark here!)
Wi-Fi Design: RF Spectrum
RF is something all Wi-Fi engineers needs to be intimately familiar with!
This is not only how signals propagate and attenuate, but also how they interact with each other. In Wi-Fi we are purposely designing for channel and AP overlap - it’s required to allow devices to roam.
Too much of this though and your network will be on its knees, with poor throughput, intermittent client disconnections and an all round poor - and unreliable - experience.
There’s quite a bit to the RF side of things that needs to be taken into account.
You can increase throughput on a wireless network by aggregating channels:
- This is akin to adding more lanes to a motorway - more lanes, means more traffic throughput
- However, you only have a limited number of channels to use, so bonding a lot of channels will reduce your overall channel separation - and increase channel overlap (or interference)
- The best option is to use channel bonding where you need it most - and have different groups deployed to vary where that it
You’ll also encounter a wide range of interferers - these can be “non Wi-Fi” or “rogue” access points. The image below shows the impact from a mobile phone hotspot!
Microwave ovens, 4G repeaters, proprietary patient monitors, Bluetooth and a wide range of other devices all interfere with Wi-Fi!
If you’re near to an airport (or marine area), you might have RADAR in the vicinity.
Your Wi-Fi install actually interferes with this and it is a regulation that you must be able to change channel if this is experienced.
This is automatic in the network - but can have a detrimental effect on clients.
- Wi-Fi and the problem with RADAR
- Increasing AP Density
- Wi-Fi Surveys (Overview to the various types of RF Surveys)
- Wi-Fi Phone Dropouts
Wi-Fi Design Technical Requirements: Summary
in this second part of the two part blog series (see Wi-Fi Design Business Requirements for the first one), we've taken a look at the environmental aspects that should be considered when designing Wi-Fi.
Along with understanding what customers want to achieve with their network, we need to take into account the environment - and environmental factors too.
Wi-Fi that works has to be designed and the process has a number of stages to get this correct.