An extended rate PHY transmission — the OFDM preamble and data of Clause 17, followed by a signal extension.
Reading a capture
Every field before the data is identical to a non-HT PPDU's. Put the two rows side by side on the comparison page and the only difference is the bar at the end, which is the entire point of having both.
Subfields
DATA field — SERVICE, the PSDU, tail and pad bits, modulated at the rate the SIGNAL field named.
Signal Extension — Six microseconds of nothing after the data, so that receivers in the same band have time to finish.