Before we get to the results, let's review what is supposed to happen. The diagram below shows three SU (non MU-MIMO) STAs take three transmit airtime periods.
Three STAs - SU
For three MU STAs, only one time period is required, ideally tripling effective bandwidth use.
Three STAs - MU
Switching back to SU, increasing the STAs to four, just takes up more airtime. Each must wait its turn.
Four STAs - SU
For four MU STAs, only two time periods are needed. Since two other STAs get time in the second slot, the AP is challenged to provide even throughput distribution for all clients. This challenge resulted in much lower overall throughput than the 3 STA case as well see.
Four STAs - MU
I'll be showing an MU vs. SU throughput plot for each product tested. First up is the Linksys EA8500. It does pretty well, peaking at 730 Mbps for three devices. The fourth STA causes throughput to drop below the SU throughput line, which steadily declines as each STA is added. MU throughput then heads up and hits a lower peak at 7 STAs, then declines again.
Linksys EA8500 - MU vs. SU total throughput vs. STAs
The NETGEAR R7500v2 plot's overall shape is similar to the Linksys'. But its maximum three-client peak is only 653 Mbps. It also hits throughput equal to SU mode with 14 STAs and stays with the SU line. In contrast, the Linksys looks like it still hasn't settled down at the maximum 16 STAs tested.
NETGEAR R7500v2 - MU vs. SU total throughput vs. STAs
TP-LINK Archer C2600
Now we get to the interesting stuff. TP-LINK's MU-MIMO router shows the usual three client peak at 688 Mbps. But what's up with the SU line? Instead of starting around 340 Mbps like the Linksys and NETGEAR and slowly ramping down, it starts at 156 Mbps and ramps up. The more interesting result is at 12 STAs, where things basically stop working. The STAs still connect, they just aren't passing much traffic at all.
TP-LINK Archer C2600 - MU vs. SU total throughput vs. STAs
Amped Wireless RTA2600
Bringing up the rear is Amped's RTA2600. With SU STAs, it behaved like the Linksys and NETGEAR. But it obviously didn't handle the MU clients well at all, producing total throughput worse than SU for two to 14 STAs.
Amped Wireless RTA2600 - MU vs. SU total throughput vs. STAs
So let's put this all together. The composite plot below enables easier comparison of the four tested products, along with a handy average SU throughput line.
The Linksys EA8500, the first QCA-based MU router released in May and the most recently-released NETGEAR R7500v2 are the two best-behaved products in this test. Both produce similar maximum throughput with three STAs and manage to stay above the SU line (except for the four STA test) up to around 10 STAs.
The TP-LINK Archer C2600 starts out pretty good, but basically loses it at after 8 STAs and really loses it at 12 and above. Finally, the Amped Wireless RTA2600, is just a puzzle. Although it uses the same basic QCA design as the other three products, it obviously doesn't react very well to our test conditions.
All products - MU total throughput vs. STAs
The composite SU plot isn't as interesting, although it shows how closely three of the four routers behave.
All products - SU total throughput vs. STAs
To make sure a bad test run wasn't at fault for the Amped's poor results, two more full test passes were run for both MU and SU to produce the composite plot below. While there is run-to-run variation, the trend is pretty consistent.
Amped Wireless RTA2600 MU vs. SU repeatibility
There's one other bit of insight the VeriWave system can provide into what might be going on. By using its packet capture ability, wireless frames can be examined and data extracted to see how many STAs are actually using MU frames. Ideally, MU devices should be using MU frames all the time, especially under the ideal conditions of this test.
STAs with MU Frames
The plot above shows this was not the case. The Linksys EA8500 and NETGEAR R7500v2 were able to work with the highest number of MU STAs - 11. They also happened to be the most well-behaved. The fact that the TP-LINK Archer C2600 stops using MU frames after 8 STAs could be releated to its drop to essentially no throughput with 12 and higher STAs connected.
For most buyers of MU-MIMO routers, these results are academic. They have no MU devices, so aren't really affected one way or another. Since the hardware is essentially the same for all these products, the difference is in firmware, which can be fixed well before MU devices ever hit their antennas.
But the exercise shows how far some manufacturers have to go in understanding this very complex new technology. And the work they have ahead to design products using it that provide user experiences that justify the high prices being asked.
For me, this has been more of a tryout of the VeriWave system, which looks like it will be able to significantly expand SmallNetBuilder's wireless test capabilities. Look for lots more testing fun to come!