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Multiple STA

The last test I'm showing is the Multiple STAs Performance Test (6.4.1) It's is similar to the Airtime Fairness test in that it uses mixed traffic from devices. This time, however, three sets of equal capability STAs (2x2 n for 2.4 GHz 2.2 ac for 5 GHz), are set at different "distances" from the DUT. This test also differs from the Airtime Fairness test in that each set of three STAs are actually virtual STAs.

The "distances" are defined as:

  • 10 dB of additional path loss in both bands for "short" distance
  • 38 dB of additional path loss in 2.4 GHz and 32 dB in 5 GHz for "medium" distance
  • 48 dB of additional path loss in 2.4 GHz and 42 dB in 5 GHz for "long" distance

Multiple STA Performance test

Multiple STA Performance test

Unlimited TCP traffic is run to all three "short" distance STAs in downlink, then uplink. Then the "medium" distance STA trio is associated and down and uplink tests run again. Finally the "long" distance STAs are connected and the tests run again. Total throughput in each direction is calculated for each test run and compared to the limits in the table below. Note that each group of STAs remains associated as others are added.

Test limits are shown in the Table 23 graphic below.

Multiple STA Performance test limits

Multiple STA Performance test limits

The 2.4 GHz part of this test was a challenge for the two-stream LAPAC1200. Section 5.2.2 of TR-398 allows DUT and STAs to be separated by a specific distance (for large-chamber or open-air testing), or by path loss for small(er) chamber testing. The usual default distance is 2 meters, which equals 46 dB of path loss in 2.4 GHz and 53 dB for 5 GHz. The requirements for this test add the "distance" path losses shown above to these starting values.

The other factor to be considered is the maximum input level of - 30 dBm for the octoScope Pals. With the Revision 10 test setup, I found I needed to add 10 dB of attenuation for 2.4 GHz tests to avoid overloading the octoScope Pal when testing four-stream devices. To keep a level playing field, that means that all devices are tested with that additional attenuation.

The Broadband Forum testbed has somewhat lower path loss, so I've found I need to increase the added attenuation to between 15 and 20 dB so that four-stream APs don't overload the Pal.

But when I used 20 dB to set the "default distance" for 2.4 GHz, this pushed levels for the "medium" and "long" distance STAs down to the point where vSTAs would disassociate during the test.

The upshot of all this is that the Linksys' results in Table 5 were obtained using 10 dB of starting attenuation vs. 20 dB for the two four-stream NETGEAR products. I don't intend for this to be the case once my test implementation is done. But it's been a useful exercise to show the challenge TR-398 users will have trying to compare results among the wide range of test setups allowed.

Table 5 shows 2.4 GHz results. All three products did pretty well, with only the R7800 having one failure.

  Linksys LAPAC1200 NETGEAR R7800 NETGEAR RAX80
Downlink Throughput (Mbps) Short Pass [109.6] Fail [59.9] Pass [120.2]
Short+Medium Pass [85.4] Pass [115.3] Pass [118.7]
Short+Medium+Long Pass [73.9] Pass [87.9] Pass [112.5]
Uplink Throughput (Mbps) Short Pass [81.5] Pass [109.7] Pass [105.6]
Short+Medium Pass [69.5] Pass [113] Pass [73.3]
Short+Medium+Long Pass [53.3] Pass [94.9] Pass [71.2]
Table 5: Multiple STA Performance - 2.4 GHz

To get some insight into the 2.4 GHz downlink results, let's go to the histogram plots. I removed the legend to increase the bar size for easier viewing. Linksys LAPAC1200, NETGEAR R7800 and NETGEAR RAX80 are plotted left to right. Each product includes short, medium and long distance throughput for three vSTAs. For the following plots, the test limit is compared against the sum of all nine test results for each product.

The plot below is for the 2.4 GHz downlink Short+Medium+Long test. It shows that there is more than one way to exceed the 50 Mbps bar for this test.

Multiple STA Test - 2.4 GHz downlink - short+medium+long test

Multiple STA Test - 2.4 GHz downlink - short+medium+long test

Table 6 contains the 5 GHz test summary. The Linksys AP fails the most tests, so we'll look into that more closely in a bit.

  Linksys LAPAC1200 NETGEAR R7800 NETGEAR RAX80
Downlink Throughput (Mbps) Short Fail [456.6] Pass [692.3] Pass [624.9]
Short+Medium Fail [329.4] Pass [660.4] Pass [496.8]
Short+Medium+Long Fail [265.7] Pass [562.9] Fail [281.5]
Uplink Throughput (Mbps) Short Fail [448.9] Pass [678.8] Pass [618.1]
Short+Medium Fail [322.4] Pass [599.9] Pass [576.3]
Short+Medium+Long Pass [336.5] Pass [506.7] Fail [511.8]
Table 6: Multiple STA Performance - 5 GHz

5 GHz downlink Short+Medium+Long test results are again shown. Both the Linksys and NETGEAR RAX80 fail to achieve the 300 Mbps minimum total throughput required to pass this test, while the NETGEAR R7800 easily exceeds it.

Multiple STA Test - 5 GHz downlink - short+medium+long test

Multiple STA Test - 5 GHz downlink - short+medium+long test

Looking again at the Linksys, here's what the short+medium downlink results look like.

Multiple STA Test - 5 GHz downlink - short+medium test

Multiple STA Test - 5 GHz downlink - short+medium test

Finally, just the short test results. That third vSTA wasn't doing very well.

Multiple STA Test - 5 GHz downlink - short+medium test

Multiple STA Test - 5 GHz downlink - short+medium test

Closing Thoughts

TR-398 is by no means a comprehensive Wi-Fi Performance test suite. But that fact that it exists at all is a major accomplishment for the Wi-Fi industry. So kudos to the Broadband Forum for taking this on and seeing it through to release.

Now that a standard exists, I'll be incorporating some of its tests into an upcoming SmallNetBuilder Wireless Test process. But my quest for a good way to tell whether a $600 Wi-Fi 6 (draft 11ax) router really delivers more value than a $200 top-of-line Wi-Fi 5 (11ac) router continues.

 

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