Abstract: A wireless communication device in a wireless system may generate a High Efficiency Physical Layer Convergence Procedure (PLCP) Protocol Data Unit (HE PPDU) frame including (i) an Orthogonal Frequency Division Multiplexing (OFDM) symbol including padding bits and (ii) an extension having a non-zero signal strength, and transmit the HE PPDU frame. A High Efficiency signal (HE-SIG) field of the transmitted HE PPDU frame may include an indication for a duration of the extension to avoid ambiguity of the extension. A communication device in a wireless system may receive an HE PPDU frame including (i) an OFDM symbol including padding bits, and (ii) an extension having a non-zero signal strength, and transmit an Acknowledgement frame a predetermined inter-frame space after an end of the HE PPDU frame. An HE-SIG field of the received HE PPDU may include an indication for duration of the extension to avoid ambiguity of the extension.