In 802.11ax communications, the trigger frame is used for multiple purposes. One of them is to allocate ressources for a specific multi-user OFDMA transmission. NI WLAN Toolkit could support trigger frame generation and analysis ，but no detail description about how to measure trigger frame in help documents. So i post the measurement steps here for your reference.
1. Open WLAN Analysis and click "Start" button to auto-measure the signal
2. Check the Frame Parameters in Analysis side as below, the frame parameters were wrong
3. Open the IQ Advanced Setting panel, set the OFDM Demod and OFDM Packet info as below.
4. Click "auto range" button to measure the correct waveform length.
5. Because the frame was trigger based type, you should set the Max Symbol Used as "-1".
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