WLAN 802.11ax testing | 802.11ax test for 11ax transmitter, 11ax receiver

This page on WLAN 802.11ax testing describes 802.11ax tests for transmitter and receiver as per 802.11ax standard. It covers 802.11ax tests for 11ax transmitter and 11ax receiver parts as per radio conformance specifications.

What is WLAN 802.11ax ?

IEEE has recently published draft version of 802.11ax standard known as wifi-6. The standard is going to be ratified in 2019. It is successor to 802.11ac but operates in both 2.4 GHz and 5 GHz bands. There are many new features added in newly released standard such as OFDMA in both downlink and uplink, MU-MIMO with beamforming in the downlink, MU-MIMO in the uplink, 1024-QAM, increased guard and symbol duration, larger bandwith (upto 160 MHz), BSS color, special packet format for outdoor applications and so on.
Refer WLAN 802.11ax tutorial >>.

802.11ax tests for 11ax transmitter part

WLAN 802.11ax Transmitter test setup
Figure-1 : Image Courtesy : Rohde & Schwarz

The figure-1 depicts test setup used for testing transmitter part of 802.11ax device (i.e. 11ax station). It shows Rohde & Schwarz 802.11ax test equipments.

Following table mentions 802.11ax tests for 11ax transmitter part.

Transmitter Specifications Descriptions with limits
Transmit constellation error, EVM (Error Vector Magnitude) -35 dB (For 1024QAM)
Unused tone error (for 11ax Stations) Unused tone error
Subcarriers in close proximity to active RU26 subcarriers must lie 2 dB under EVM limit. For distant subcarriers, EVM requirement is reduced in 10dB steps down to -35 dB. THe figure depicts limit value for RU26. For other RU sizes, there is different limits and step widths defined in the 802.11ax standard.
Transmit center frequency tolerance, i.e. Frequency offset & timing offset In this test, Initially trigger frame is sent to DUT using R&S SGT 100A or any compliant generator equipment and DUT responds with HE_TRIG frame towards R&S FSW analyzer. Relative frequency error (Center frequency offset, tolerance +/- 350 Hz) of response signal in the uplink as well as delay between end of trigger frame and start of response frame (timing accuracy, tolerance +/- 0.4 µs) are measured.
Transmit spectral mask Verifies 11ax STA (Station) output with respect to spectrum mask, as specified in IEEE standard 802.11ax and shown in the figure-2 below. For 80+80 MHz non-contiguous spectrum mask, refer standard or radio conformance specifications.
Spectral flatness It helps in determining whether subcarriers have similar power and verifies that no individual subcarrier's energy exceeds specified limit. Refer spectral flatness testing >> for 802.11ax device.
Symbol clock frequency tolerance As specified in IEEE 802.11ax
Power control test As specified in IEEE 802.11ax

802.11ax tests for 11ax receiver part

Following table mentions 802.11ax tests for 11ax receiver part.

Receiver Specifications Descriptions with limits
Sensitivity test At low power (about -43dBm) at the receiver for 1024QAM modulation test, only 10% of received packets should contain faulty bits.
Refer receiver input sensitivity testing >> for 802.11ax device.
Receiver Maximum input level tests -30 dBm for 5 GHz/ 6 GHz bands
-20 dBm for 2.4 GHz band.
Receiver should demodulate at these levels with PER less than 10%.
Adjacent channel rejection Adjacent channel is the one which is attached to the desired WLAN channel without any spacing in between. As specified in the IEEE 802.11ax standard
Non-adjacent channel rejection Non-adjacent channel is the one which is at some frequency spacing away from the desired WLAN channel. As specified in the IEEE 802.11ax standard

The other tests include following.
• OTA (Over the air) testing : Wifi equipment manufacturers require OTA tests in anechoic chamber in accordance with CTIA/WFA converged wireless group.
• EMC (Electro Magnetic Compatibility) tests
• Frame Error Rate or Packet Error Rate

Radio conformance test equipments for 802.11ax testing

Following is the list of radio conformance test equipments used for 802.11ax testing.
➤802.11ax test equipments should have EVM better than -35 dB with margin of atleast 10 dB. R&S spectrum and signal analyzer support EVM less than -53 dB. Hence measurement error of only 0.07 can be achieved with this 11ax equipments. R&S VSG (Vector Signal Generator) also offers EVM as required by 11ax specifications.
➤Keysight technologies offers 802.11ax test solutions validating various 11ax features which include OFDMA, MU-MIMO, 1024QAM constellation diagram with EVM, baseband IQ and so on.
➤Anritsu Corporation has launched Universal Wireless Test Set (MT8870A) which offers 802.11ax transmitter and receiver testing.
➤zSignal 802.11ax Software from LitePoint Corporation.
➤NI (National Instruments) has introduced test solution for 802.11ax High-Efficiency (HE) devices.

WLAN 802.11ac RF PHY conformance tests

802.11ac spectral mask
Figure-2 : Power spectrum mask as per 11ac/11ax

Refer Article on 802.11ac RF/PHY conformance testing >> for more information. The figure shows one such 802.11ac transmitter test for power spectrum mask validation.

•  IEEE 802.11ax draft standard

RF and Baseband Measurement Links

WiFi 6 Resources as per IEEE 802.11ax

Useful Links to Legacy WLAN Standards

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