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Wireless How To

Throughput vs. Attenuation Test Notes

Moving the DUT through an entire 360° while the IxChariot test is running removes any orientation bias from the test and eliminates the need to determine the "best" run out of multiple fixed-position tests. Because throughput typically varies during the test run, the averaged result tends to be lower. Rotation at lower signal levels, particularly in 5 GHz, frequently causes the connection to be dropped sooner than if the DUT were stationary.

The IxChariot plot below shows a typical test run. The first 30 seconds of the run include a throughput step-up that is caused by an IxChariot artifact and does not reflect true device performance. The first 30 seconds also provides time for DUT rate adaptation algorithms to settle. For both reasons, the test script excludes the first 30 seconds of data in the average value saved in the Charts database.

IxChariot Test Data detail

IxChariot Test Data detail

Maximum Wireless Throughput Test Configuration

The V8 process AC1900 test client was unable to test maximum throughput of 4x4 products. So we had to resort to using pairs of routers, which makes fair relative comparison impossible. We're addressing this in the new process by using the VeriWave system to test maximum throughput for all products.

We use an Ixia VeriWave WaveTest 20 three slot chassis loaded with RF46014 WaveBlade Wi-Fi, WBE1604 WaveBlade Ethernet and Management modules. This is the same configuration used for MU-MIMO testing.

The Wi-Fi blade acts as the Wi-Fi device (STA), supporting 802.11a/b/g/n/ac. It has four RF ports, and can emulate any STA from 802.11b 1 Mbps to 4x4 802.11ac MU-MIMO 1733 Mbps. The Wi-Fi blade can create up to 500 fully independent stateful clients.

The Management blade is the controller for the two instrumentation blades, allowing the chassis to sit on a LAN and be accessed via a web interface for simple management chores. The Ethernet blade is a quad-port Gigabit wire-speed traffic generator with full packet-capture capability. The VeriWave's 4x4 capability supports testing maximum throughput for 802.11a/b/g/n and ac standards including 256-QAM, i.e. (AC2350 / 2400, AC2600, AC5200).

The test setup is shown below. An octoScope quadAtten is used between the Veriwave Wi-Fi blade and octoScope chamber antennas. It is set to a 20 dB fixed attenuation to ensure signal levels don't exceed the Veriwave's maximum input level of -25 dBm.

Note we are using 40 MHz bandwidth mode for 2.4 GHz tests. 2.4 GHz testing also does not use 256-QAM because it is not part of the 802.11n standard. The Veriwave supports only HT MCS rates 0-31 for 802.11n testing. So maximum 2.4 GHz link rate used for 4x4 devices is 600 Mbps.

V9 configuration - Maximum wireless throughput

V9 configuration - Maximum wireless throughput

The router or AP under test is prepared as follows:

  • Check / update latest firmware
  • Reset router to defaults
  • Change settings:
    • LAN IP:
    • 2.4 GHz: Channel 6, Bandwidth: 40 MHz, Security: WPA2 / AES, Key: 11111111
    • 5 GHz: Channel 40, Bandwidth: Auto or 80 MHz, Security: WPA2 / AES, Key: 11111111

The VeriWave WaveBlade is configured to match these properties of the router / AP under test for each band:

  • Number of spatial streams: 1 - 4
  • Signal bandwidth: 20, 40, 80 MHz
  • VHT MCS Index: 0 - 9 for 5 GHz 802.11ac
  • HT MCS Index 0-31 for 2.4 GHz 802.11n
  • Short Guard interval

MIMO channel models (A-F) are not used; bypass mode is set. Example settings:

  • AC2600 5 GHz: 4 spatial streams, 80 MHz bandwidth, VHT MCS 9 (1733 Mbps PHY rate)
  • AC2600 2.4 GHz: 4 spatial streams, 40 MHz bandwidth, VHT MCS 31 (600 Mbps PHY rate)
  • AC1900 5 GHz: 3 spatial streams, 80 MHz bandwidth, HT MCS 9 (1300 Mbps PHY rate)
  • AC1900 2.4 GHz: 3 spatial streams, 40 MHz bandwidth, HT MCS 23 (450 Mbps PHY rate)
  • AC1750 5 GHz: 3 spatial streams, 80 MHz bandwidth, HT MCS 9 (1300 Mbps PHY rate)
  • AC1750 2.4 GHz: 3 spatial streams, 40 MHz bandwidth, HT MCS 23 (450 Mbps PHY rate)

20dB of fixed attenuation is set between router under test and the Veriwave.

Maximum Wireless Throughput Test Process

The following test process is run for 2.4 and 5 GHz, uplink and downlink:

  1. The Veriwave is configured to match the router / AP under test and associated. MCS rates are set to maximum for the router class.
  2. A TCP Goodput test with four simultaneous TCP/IP sessions is run for 30 seconds with MSS, Window and Frame size set so the Gigabit link is fully loaded.
  3. The MCS rate is lowered by 1 and the TCP Goodput test run again. If the throughput improves, the lower MCS rate is used. Otherwise, the maximum MCS rate is used.
  4. TCP Goodput is run with four simultaneous TCP/IP sessions for 60 seconds, repeated 10 times, with 5 second pause between test runs. The average of of all 10 runs is entered into the Charts database.

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