Systems and methods of transmitting a PPDU to or from a single user station (STA) in an MIMO transmission by using unequal MCSs. An access point (AP) allocates a plurality of spatial streams to the STA and assigned them into groups for the MIMO transmission. Multiple unequal MCSs are assigned to the different spatial stream groups. Correspondingly the STA ID is repeatedly specified in the user block fields of a SIG-B field of 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 block fields 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 grouped-based unequal MCSs scheme is used for the MIMO transmission.