For example, an Access Point (AP) may be configured to set Resource Unit (RU) allocation information in a Signal (SIG) field, the RU allocation information configured to indicate an RU allocation for a user; to set Unequal Modulation and Coding Scheme (MCS) (UEM) information for the user in the SIG field, the UEM information for the user configured to indicate an assignment of a plurality of MCSs to a plurality of frequency sub-channels in the RU allocation for the user, respectively; and to transmit a Downlink (DL) Physical layer (PHY) Protocol Data Unit (PPDU) including the SIG field and a data field for the user, wherein the data field for the user is configured according to the assignment of the plurality of MCSs to the plurality of frequency sub-channels in the RU allocation for the user.