Methods, apparatus, and systems for a physical layer protocol data unit (PPDU) transmission are provided. In one aspect, a method includes: generating a physical layer protocol data unit (PPDU) including a signal extension (SE) field arranged after a last orthogonal frequency division multiplexing (OFDM) symbol of a plurality of OFDM symbols, the PPDU including indication information in a high efficiency signaling field (HE-SIG), the indication information being generated based on a symbol length of the SE field and configured to indicate whether a receive end needs to adjust a calculated quantity of the plurality of OFDM symbols, and sending the PPDU to the receive end.