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Efficiency

AX's prime directive is to increase airtime efficiency, i.e. use less airtime to move a given number of packets. Fortunately, octoScope's Pals measure airtime congestion. So by looking at the difference in congestion with OFDMA on and off, we can see if AX is following its directive. I'll be using bar plots of Airtime congestion measured by the Pal6 associated to the DUT to show what OFDMA brings to the party.

The downlink congestion plot shows the three ASUS routers, with the first bar in each pair the average OFDMA off congestion and the second the on. Although congestion is relatively low, hovering around 25% for all products, you see a slight increase in congestion when OFDMA is enabled for each product. Much like we saw with latency, however, you'd never notice this in real-world use.

ASUS airtime congestion - OFDMA effect - downlink

ASUS airtime congestion - OFDMA effect - downlink

I didn't include the Pal6 and two AC reference products on the plot above, because the Pal6 would have compressed the scale, making it difficult to see the subtle change in airtime congestion. So here are the products plotted separately. Looks like high latency and high congestion go together for the Pal6.

Reference product airtime congestion - OFDMA effect - downlink

Reference product airtime congestion - OFDMA effect - downlink

Here's the uplink congestion plot for the ASUS trio. Airtime use is more than double that of downlink. And, this time, enabling OFDMA ever-so-slightly lowers congestion. But you wouldn't notice it and it's just as likely just measurement variation.

ASUS airtime congestion - OFDMA effect - uplink

ASUS airtime congestion - OFDMA effect - uplink

Here's uplink congestion for the reference products. The IQrouter v3 and R7800 both have lower congestion in this direction. But look at the Pal6! Its almost 20% reduction in congestion is the most significant change I've seen in all these tests.

Reference product airtime congestion - OFDMA effect - downlink

Reference product airtime congestion - OFDMA effect - downlink

Now for the NETGEARs. Here's downlink...

NETGEAR airtime congestion - OFDMA effect - downlink

NETGEAR airtime congestion - OFDMA effect - downlink

...and uplink, below. We finally see a product stand out from the pack, the two-stream RAX15. It has both lower congestion than all the other products tested and the congestion is significantly reduced when OFDMA is enabled. In fact, all three NETGEAR routers show lower congestion when OFDMA is enabled. But the reduction for the RAX45 is pretty slight.

As we saw with the ASUS routers, the three NETGEARs' uplink congestion is more than twice their downlink. The RAX15 congestion increase with OFDMA is large enough to be real. But the changes in RAX120 and RAX45 congestion are likely within measurement accuracy.

NETGEAR airtime congestion - OFDMA effect - downlink

NETGEAR airtime congestion - OFDMA effect - downlink

 Conclusion: While there is some evidence that OFDMA affects airtime efficiency, the effect, when seen, is very slight.

Throughput

The story for total throughput improvement with OFDMA enabled isn't any rosier than for latency or congestion. OFDMA's desired effect here is higher aggregate throughput. But if there is any improvement seen in these tests, it's very slight; well within the +/- 5% that I use as a rule of thumb when dealing with any Wi-Fi measurements. I'm going to use bar charts of average throughput, since time plots aren't that helpful.

I'll use the same plotting method used for airtime congestion, with OFDMA off, then on, for each product. Here's ASUS downlink. Not much to see here.

ASUS average aggregate throughput - OFDMA effect - downlink

ASUS average aggregate throughput - OFDMA effect - downlink

And average dowlink throughput for the reference products. The Pal6's lower throughput with OFDMA off tracks with its higher latency we saw earlier.

Reference product average aggregate throughput - OFDMA effect - downlink

Reference product average aggregate throughput - OFDMA effect - downlink

And here's uplink. Aside from around 20 Mbps lower average throughput, there isn't much to see here, either.

Average aggregate throughput - OFDMA effect - uplink

Average aggregate throughput - OFDMA effect - uplink

Here's uplink for the references. No big OFDMA on/off difference here for the Pal6.

Reference product average aggregate throughput - OFDMA effect - uplink

Reference product average aggregate throughput - OFDMA effect - uplink

Moving on to the NETGEARs. Downlink...

NETGEAR average aggregate throughput - OFDMA effect - downlink

NETGEAR average aggregate throughput - OFDMA effect - downlink

...and uplink. The only significant change is the RAX15, going in the opposite of the desired direction. This appears to track with the big change in congestion observed earlier

NETGEAR average aggregate throughput - OFDMA effect - uplink

NETGEAR average aggregate throughput - OFDMA effect - uplink

Conclusion: OFDMA does nothing to improve aggregate throughput.

One last observation about throughput. Note that this benchmark uses four, 50 Mbps throughput streams, but none of the products achieve 200 Mbps total throughput. Experiments I've done show some of this is due to the mix of traffic priorities and some is due to limiting buffer length.

Closing Thoughts

It's been a long wait to have consumer router manufacturers enable OFDMA in their Wi-Fi 6 products. Along the way, I've tried various OFDMA test methods, some suggested by Broadcom, others by router manufacturers. My conclusion at this point is that OFDMA produces no discernable benefit for the average consumer.

It's possible that more devices and different traffic mixes will show latency, throughput and/or airtime congestion improvements. But the use cases are very specific and the improvements are not consistent enough to make OFDMA a reason to buy a Wi-Fi 6 router.

At this point, I'm going to set aside my OFDMA testing efforts and turn back to putting together a new Wi-Fi test suite so that I can get back to product testing. Sadly, OFDMA is yet another technology borrowed from the mobile/cellular world that doesn't deliver the goods in the Wi-Fi world, where the device, not the network, is the boss.

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