Systems and methods of transmitting a PPDU to or from a single user station (STA) in an OFDMA transmission by using multiple RUs. An access point (AP) allocates multiple RUs to an STA for an OFDMA transmission and correspondingly specifies the STA ID repeatedly in the user specific field of a SIG-B field in a downlink PPDU, or in the user information fields of a trigger frame. Alternatively, multiple AIDs of the STA can be specified in the user specific field or the user information fields instead of repeating the same STA ID. An indication may be inserted in the SIG-A field to indicate that the enhanced RU allocation scheme is used for the OFDMA transmission.