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Wireless Features

Got OFDMA?

While consumer router manufacturers are slowly slipping OFDMA into their products, most Wi-Fi 6 products still don't enable OFDMA. Of those that do, only a few products support both DL and UL OFDMA on either 5 GHz or both bands.

I check most frequently with ASUS and NETGEAR for updates on OFDMA support. I've given up checking with TP-Link. Every time I've asked, the reply has been they still don't support it on any of their Wi-Fi 6 products. D-Link is shipping only the DIR-X1560, which supports OFDMA DL+UL on 5 GHz only (2.4 GHz uses an 11n radio). Linksys has only its overpriced MX5/MX10 Velop AX Mesh system; I didn't ask them about OFDMA support.

The last check with ASUS about a month ago showed that all its AX routers supported 5 GHz DL, with support for 5 GHz UL and 2.4 GHz DL/UL marked as "Y - open in coming weeks". But a tip from Merlin over on SNBForums led me to picking up an RT-AX58U (aka RT-AX3000) via curbside pickup from my local Best Buy. A quick check of its GUI showed it does indeed offer, DL only, DL/UL and DL/UL+MU-MIMO OFDMA settings on both bands.

NETGEAR's list showed full OFDMA support (both bands, DL+UL) on its entry-level two-stream RAX15/20 and mid-market RAX45/50 routers. Among NETGEAR's early AX routers, the RAX80, still has no OFDMA support and its only Qualcomm-based router, the RAX120, supports DL only on both bands. For those who like buying expensive tri-band routers, at least the RAX200 has full OFDMA support. And both its Orbi and Nighthawk Wi-Fi 6 mesh systems have full OFDMA support. I bought an RAX15 and RAX45 (Costco exclusive) for testing and asked NETGEAR to send an RAX200. But due to Covid-19, they haven't been able to ship one and I'm not that flush with cash to part with the $488 Amazon is currently getting for it.

Best Case

While I was bringing up the equivalent of the Flent rtt_fair_var test on the octoScope testbed, an octoScope colleague shared some encouraging results he had gotten using a similar TCP/IP traffic plus ping test applied to octoScope's Pal6 partner device, configured as an AX AP. So I decided to experiment using the Pal6 configured as a four-stream AX AP. All the following plots were produced by importing the CSV test result file into octoScope's Expert Analysis tool.

The TCP/IP traffic settings for each of the four WinSTAPals that produced the following plots were:

  • 50 Mbps bit rate (iperf3 -b)
  • 256 byte buffer length (iperf3 -l)
  • DSCP = 192 (iperf3 --dscp)

The DSCP parameter sets the traffic priority level. If you search for information on DSCP, you'll find lots of different references that provide lots of different values to use as DSCP settings. For the octoScope system, 192 value equates to CS6 Voice priority for wireless QoS data frames. This was verified by packet inspection.

Note that when OFDMA was set to off on the Pal6, MU-MIMO (MU beamforming setting) was left enabled. The Pal6 has separate downlink and uplink OFDMA enables; both were enabled for the OFDMA on condition.

The first plot compares average OFDMA on/off latency for all four traffic pairs. There's obviously a significant improvement; ~48 to ~ 6 ms.

Pal6 AP - Average Latency CDF comparison - downlink

Pal6 AP - Average Latency CDF comparison - downlink

Uplink has lower latency with OFDMA off, but about the same as downlink latency with it on.

Pal6 AP - Average Latency CDF comparison - uplink

Pal6 AP - Average Latency CDF comparison - uplink

OFDMA also claims to increase aggregate throughput for multiple devices. The downlink throughput plot below appears to support that claim, too, but not at the start of the plot. This it-takes-time-to-settle behavior was seen during multiple runs.

Pal6 AP - Average aggregate throughput comparison - downlink

Pal6 AP - Average aggregate throughput comparison - downlink

Uplink throughput shows essentially no gain from OFDMA.

Pal6 AP - Average aggregate throughput comparison - uplink

Pal6 AP - Average aggregate throughput comparison - uplink

The basic tenet of 802.11ax is high efficiency; it's in the standard's name and is its prime directive. If AX delivers on its primary goal, airtime should be used more efficiently. Qualcomm chipsets report channel congestion and since Pal6 is based on Qualcomm's AX "Hawkeye 2.0" chipset, we have the plot below. Congestion is reduced by over 50% with OFDMA enabled!

Pal6 AP - Channel congestion comparison - downlink

Pal6 AP - Channel congestion comparison - downlink

Uplink also shows lower congestion with OFDMA enabled, but the gain is not as dramatic as downlink.

Pal6 AP - Channel congestion comparison - uplink

Pal6 AP - Channel congestion comparison - uplink

To me, these last two plots are the most important. Because even if latency isn't reduced and total throughput isn't increased, reduced channel congestion means less device contention, which should result in a better Wi-Fi experience for everyone using a channel.

So it looks like we finally have a benchmark that can show significant benefit (in most cases) from OFDMA!

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