RFWLAN 802.11ax Testing: Transmitter and Receiver Tests
Advertisement
This page describes WLAN 802.11ax testing, covering both transmitter and receiver tests as per the 802.11ax standard. It details 802.11ax tests for transmitter and receiver components, adhering to radio conformance specifications.
What is WLAN 802.11ax?
Introduction
IEEE has recently published a draft version of the 802.11ax standard, also known as Wi-Fi 6. The standard is expected to be ratified in 2019. It’s the successor to 802.11ac but operates in both the 2.4 GHz and 5 GHz bands.
Many new features have been added to this standard, including:
- 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 bandwidth (up to 160 MHz)
- BSS color
- Special packet format for outdoor applications
802.11ax Tests for 11ax Transmitter
Figure-1: Image Courtesy: Rohde & Schwarz
Figure 1 depicts a test setup used for testing the transmitter part of an 802.11ax device (i.e., an 11ax station). It showcases Rohde & Schwarz 802.11ax test equipment. The following table outlines 802.11ax tests for the 11ax transmitter component.
| Transmitter Specifications | Descriptions with limits |
|---|---|
| Transmit constellation error, EVM (Error Vector Magnitude) | -35 dB (For 1024QAM) |
| Unused tone error (for 11ax Stations) |  Subcarriers in close proximity to active RU26 subcarriers must lie 2 dB under the EVM limit. For distant subcarriers, the EVM requirement is reduced in 10dB steps down to -35 dB. The figure depicts the limit value for RU26. For other RU sizes, different limits and step widths are defined in the 802.11ax standard. |
| Transmit center frequency tolerance, i.e. Frequency offset & timing offset | In this test, initially, a trigger frame is sent to the DUT using R&S SGT 100A or any compliant generator equipment, and the DUT responds with an HE_TRIG frame towards the R&S FSW analyzer. The relative frequency error (Center frequency offset, tolerance +/- 350 Hz) of the response signal in the uplink, as well as the delay between the end of the trigger frame and the start of the response frame (timing accuracy, tolerance +/- 0.4 µs), are measured. |
| Transmit spectral mask | Verifies the 11ax STA (Station) output with respect to the spectrum mask, as specified in IEEE standard 802.11ax and shown in Figure-2 below. For 80+80 MHz non-contiguous spectrum mask, refer to the standard or radio conformance specifications. |
| Spectral flatness | It helps determine whether subcarriers have similar power and verifies that no individual subcarrier’s energy exceeds the specified limit. |
| 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
The following table lists 802.11ax tests for the 11ax receiver component.
| Receiver Specifications | Descriptions with limits |
|---|---|
| Sensitivity test | At low power (about -43dBm) at the receiver for the 1024QAM modulation test, only 10% of received packets should contain faulty bits. |
| Receiver Maximum input level tests | -30 dBm for 5 GHz/ 6 GHz bands-20 dBm for 2.4 GHz band. The receiver should demodulate at these levels with PER less than 10%. |
| Adjacent channel rejection | An adjacent channel is one that’s attached to the desired WLAN channel without any spacing in between. As specified in the IEEE 802.11ax standard. |
| Non-adjacent channel rejection | A non-adjacent channel is one that’s at some frequency spacing away from the desired WLAN channel. As specified in the IEEE 802.11ax standard. |
Other tests include:
- OTA (Over the air) testing: Wi-Fi equipment manufacturers require OTA tests in an anechoic chamber in accordance with the CTIA/WFA converged wireless group.
- EMC (Electro Magnetic Compatibility) tests
- Frame Error Rate or Packet Error Rate
Radio Conformance Test Equipment for 802.11ax Testing
Here is a list of radio conformance test equipment used for 802.11ax testing:
- 802.11ax test equipment should have EVM better than -35 dB with a margin of at least 10 dB. R&S spectrum and signal analyzers support EVM less than -53 dB. Hence, a measurement error of only 0.07 can be achieved with this 11ax equipment. 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, including OFDMA, MU-MIMO, 1024QAM constellation diagram with EVM, baseband IQ, and so on.
- Anritsu Corporation has launched the 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 a test solution for 802.11ax High-Efficiency (HE) devices.
Figure-2: Power spectrum mask as per 11ac/11ax
The figure shows one such 802.11ac transmitter test for power spectrum mask validation.
References
- IEEE 802.11ax draft standard
