Method and apparatus of transmitting a spatial stream for MU-MIMO in a wireless local area network system

A receiving station for receiving a data packet in a wireless local area network, the receiving station comprising;

• a transceiver configured to transmit and receive radio signals;
• and
• a processor operably coupled to the transceiver and configured to:
• control the transceiver to receive a Very High Throughput (VHT) physical layer protocol data unit (PPDU) including a group identity (ID) field, a spatial stream (SS) field and a data field,
• wherein the group ID field and the SS field are included in a VHT signal (SIG) field of the VHT PPDU,
• wherein the SS field includes information on a total number of SSs used by the receiving station,
• wherein the group ID field has a length of M bits representing 2M different states, each of the 2M different states including information for either a single user-multiple input multiple output (SU-MIMO) scheme used for the VHT PPDU or a group ID for a group to which the receiving station belongs, and
• wherein only one state of the 2M different states is used for the VHT PPDU being received from an access point (AP) based on the SU-MIMO scheme;
• and
• decode the data field based on the at least one SS field.