Trying to catch OFDMA

These past few days have been pretty crazy. First of all I’ve attended my first WLPC (Wireless LAN Professionals Conference) ever, which was already an amazing experience. Then on the first conference evening I went to the Wi-Fi 6 party which François Vergès and Rowell Dionicio from the Clear To Send podcast were hosting, where some exciting stuff was happening. And after that I actually gave a TEN Talk at the conference about some of the results from the Wi-Fi 6 party, which I named the Wi-Fi 6 afterparty. The response was fantastic, which only amplified my sense of pride to be a part of this amazing community.

So let me detail these events and then I’ll talk about some of the things that are still quite unknown. At the Wi-Fi 6 party they used 802.11ax access points from several vendors and Wi-Fi 6 clients connecting to those AP’s. They also had loads of WLANPi’s for packet captures and iPerf servers, as well as several other tools. Their goal was to have the clients and access points use OFDMA signals, the exciting yet elusive new PHY from the 802.11ax standard, to communicate with each other and try to capture those frames and signals. In my presentation I’ve been able to give this game an appropriate name: Packetmon GOFDMA!

Earlier that day David Coleman had said that Broadcom has only very recently released firmware with OFDMA for their chipset and the AP vendors are just starting to release the OFDMA capable software for their products. That explained why we haven’t seen OFDMA signals and frames in the wild yet. So the hunt for OFDMA was on that evening, trying out several AP’s that might have the proper firmware. For a long time the results were negative, until we used a Mist AP43 access points. That’s when we started to see some interesting signals:

I was able to record these signals on my phone, as well as perform packet captures using Commview for Wi-Fi with my Intel AX200 adapter and record a spectrum graph using Ekahau Pro and the Sidekick. Back in my hotel room I created some screenshots and put them on Twitter:

The next day the conference floor was buzzing with the results from the Wi-Fi 6 party and since I had a video and some screenshots, people suggested I’d give a TEN Talk to present them. On the spur of the moment I agreed to do this, after which I felt quite honored, which was soon replaced by a sense of absolute terror. Did I just agree to give a last minute presentation before 100+ attendees at a conference which I was just visiting for the first time? Where was my brain while making this decision and what was it drinking?

Fortunately I was scheduled for the next day, which meant the panic would only need to last for 24 hours and I had a bit of time to prepare. Luckily I also had a great idea on how to do my presentation (see the logo above) and I was able to mask my fear with humor. When I eventually gave my presentation the response was overwhelming and I felt like I was doing the Wi-Fi 6 party justice. Ferney Munoz even called it his favorite presentation, which is one of the greatest compliments I’ve ever received.

But to be fair I still don’t know exactly what we’ve witnessed and recorded that evening. This is the first time we’re witnessing this PHY in the wild and we don’t fully comprehend what we’re dealing with yet. Gjermund Raaen has written a great blog about the frames he was able to capture in his own lab. You can download both our capture files here: His Jetson Nano even captured 802.11ax frames that Commview for WiFi didn’t, so apparently we need to be aware of limitations of our tools as well. But also the image of the 8 OFDMA “baby channels” doesn’t appear to relate to the captured OFDMA frames. We were using 4Wi-Fi 6 clients, which wouldn’t generate 8 resource units. This would rather generate 4 resource units and we those signal patterns would differ greatly from the pattern in the video.

So what is it exactly we’re seeing in the video? Is it OFDMA or not? And how is this generated? My current guess is this is Schrödinger’s cat meowing for attention.

In conclusion, my first WLPC experience has been rather surprising. It has far exceeded my expectations and even allowed me to speak in public for the very first time. A big thanks to Keith Parsons and Matthew Casteel for organizing this amazing event and I’m counting on returning next year. Hopefully we’ll finally be able to catch ’em all next time.