A trigger-based uplink transmission — one of several sent simultaneously on different resource units.
Reading a capture
The only PPDU here whose parameters were chosen by someone else. Rate, bandwidth, duration, transmit power and resource unit all came from the Trigger frame; this station chose none of them, which is what lets its transmission line up with several others to the microsecond.
Subfields
HE-SIG-A — Two symbols of common parameters. Its Format bit is zero, which is what marks this as trigger-based rather than single-user.
HE-STF — Short training, at twice the length of the single-user field.
HE-LTF — Long training fields for channel estimation.
Data field — The PSDU, padded to exactly the duration the Trigger frame demanded.