A method for identifying active resource units in a high-efficiency wireless system includes quantizing phase angles of samples received in a high-efficiency short training field of a transmission, performing a transform operation on quantized phase angle samples to derive transmitted power, comparing transmitted power of an individual resource unit as determined from transformed quantized phase angle samples to transmitted power of other resource units as determined from transformed quantized phase angle samples, and identifying, as active, resource units whose transmitted power, as determined from transformed quantized phase angle samples, bears a first predetermined relationship to transmitted power of the other resource units. Transmitted power of a resource unit may be compared to the total transmitted power of all resource units, or to the transmitted power of one of the other resource units whose transmitted power is a maximum transmitted power of all resource units. A receiver may implement the method.