Wi-Fi 6 OFDMA Resource Unit Calculator

Beyond increased throughput for streaming, Wi-Fi 6 is also for handling multiple device talking simultaneousy. Think of traditional Wi-Fi as a one-lane road (every device must wait its turn). With OFDMA, that spectrum get broken up into smaller lanes and now an access point can talk to multiple user simultaneously.

Many people makes this mistake: they prioritize speed for their own laptop instead of freeing up bandwidth when everyone in the office log in. This enables you to think in terms of resource units, or RUs, which are slices that you can see on the calculator. Rather than thinking about throughput, you think about device density: How much do I need?

How to Share Wi-Fi Fairly

That begins with your choice of channel width, which tells you how many lanes there are. A smaller 20 MHz channel is going to have less room different than a bigger 80 MHz channel. But then you decide how you want to carve up that channel. Do you want to get as many users as possible per transmission window (smaller 26-tone RUs) or do you want to give each user a bigger piece (larger 242-tone RUs), even if it’s at the expense of serving fewer users? It’s a speed versus capacity tradeoff.

The latter is ideal for Internet of Things device that send small data packets; the former serve nine users in a single transmission window. Next, you enter how many actual customer you think will be connected. That’s the part where most people screw up with their plans. They believe that their access point can handles hundreds of devices, but Wi-Fi is a shared medium. Adding more users mean everyone gets a smaller slice of air time.

The tool models this by taking all available goodput and dividing it by the number of users. Then it factors in efficiency losses, guard intervals, and other extra costs. It tell you how much bandwidth each device gets. Compare that against your target traffic per user. If the former is less then the latter, your plan is overcrowded.

Note that the split between downlink and uplink is key: Most traffic goes one way, yet video conferencing and cloud backups pushes lots of data upstream these days. Spend too much time scheduling downlink and your voice handset or camera will experience lag. The calculator accounts for this split and automatically reduces available budget to match; i.e., you see how it will perform in both directions, realisticly.

The other key element is MCS (Modulation and Coding Scheme). The MCS tell how high your signal can go theoreticaly, but since real-world conditions rarely support those maximums, it’s better to use a conservative estimate for your planning. However, things don’t work like that in the real world. Clients with weaker antennas or those at edge of a cell will negotiate a lower MCS. A good planning strategy use a conservative estimate so there aren’t any surprises when the performance isn’t as advertised.

With this feature, you’re able to choose the MCS most of your clients are likely to adopt and thus your calculations of goodput reflect what’s going on in the field, rather than what makes marketing charts look pretty. The last component is airtime efficiency. A lot of Wi-Fi’s time is spent sending management frames, acknowledgements and handshakes instead of data. That’s wasted time, which is shown by the efficiency percent in the tool. Lower numbers mean more overhead are eating up your usable bandwidth.

Slide this around to get an idea of just how much room you have until your network starts to feel slow. With this in mind, OFDMA becomes less of a buzzword and more of an engineering reality: instead of wondering if your access points are up to the task, you know exactly what’s possible. You should of not need to max out all metrics, but rather achieve a balance that allows each user their share of airtime. That is why it pays off to calculate resource units before deploying anything. This helps you create a network that is efficient rather than just powerful, which makes it feel fast.