A method includes: A transmitter device generates a link adaptation physical layer protocol data unit LA PPDU, where a signal of the LAPPDU on some of resources is a null signal, and the resources include any one or more of the following: a time resource, a frequency resource, a space resource, a time-frequency resource, a time-space resource, a frequency-space resource, and a time-space-frequency resource; the transmitter device sends the LA PPDU to a receiver device; and the receiver device determines a link adaptation result based on the null signal of the LA PPDU on the some of the resources.