METHODS, APPARATUSES AND SYSTEMS FOR SUPPORTING MULTI-USER TRANSMISSIONS IN A WIRELESS LOCAL AREA NETWORK (WLAN) SYSTEM

1 . A wireless transmit/receive unit (WTRU) comprising:

a receiver configured to receive a frame;

at least one processor configured to decode the received frame and determine whether the received frame is a null data packet (NDP) multi-user (MU) media access control (MAC) physical layer convergence protocol (PLCP) protocol data unit (PPDU) (NDP MU MAC PPDU) based on meeting an NDP condition, wherein the NDP MU MAC PPDU is related to an MU transmission and includes a PLCP header which includes an NDP signal (SIG) field having MU simultaneous transmission control information configured to control simultaneous transmissions of multiple users,

wherein, based on the received frame meeting the NDP condition, the at least one processor is further configured to process the NDP SIG field and generate a response based on the NDP SIG field and the MU simultaneous transmission control information; and

a transmitter configured to transmit the response simultaneously with at least one other user.

2 . The WTRU of claim 1 , wherein the at least one processor determines a length of the received frame and determines that the received frame meets the NDP condition if the length of the received frame is less than a threshold.

3 . The WTRU of claim 1 , wherein the at least one processor determines whether an NDP indicator is set in the NDP SIG field and determines that the received frame meets the NDP condition if the NDP indicator is set.

4 . The WTRU of claim 1 , wherein the NDP SIG field indicates a NDP MAC frame type of the NDP MU MAC PPDU, and the at least one processor is further configured to determine the NDP MAC frame type from the NDP SIG field and generate the response based on the determined NDP MAC frame type.

5 . The WTRU of claim 4 , wherein the NDP MAC frame type is one of a MU-request-to-send (RTS) frame, an MU-Poll frame or an MU uplink schedule frame.

6 . The WTRU of claim 1 , wherein the NDP SIG field includes an access point (AP) address and a group identifier (ID), and the at least one processor is further configured to determine whether the WTRU is an intended recipient of the NDP MU MAC PPDU based on the AP address and the group ID, and

on a condition that the WTRU is an intended recipient of the NDP MU MAC PPDU, the at least one processor is configured to generate the response.

7 . The WTRU of claim 6 , wherein the NDP SIG field includes duration information, and

on a condition that the WTRU is not an intended recipient of the MU transmission, the at least one processor is configured to defer preparing the response and set a network allocation vector (NAV) based on the duration information.

8 . The WTRU of claim 1 , wherein the NDP SIG field includes an access point (AP) address, and the at least one processor is further configured to determine whether the WTRU is associated with an AP based on the AP address, and

on a condition that the WTRU associated with the AP, the at least one processor is configured to generate the response.

9 . The WTRU of claim 1 , wherein the NDP SIG field includes an NDP SIG-A field and an NDP SIG-B field, wherein the NDP SIG-A field includes common control information that corresponds to a plurality of WTRUs and the NDP SIG-B field includes user and resource dedicated information.

10 . (canceled).

11 . The WTRU of claim 9 , wherein the NDP SIG-A field includes an access point (AP) address and the NDP SIG-B field includes a STA identity (ID), and

the at least on processor is further configured to determine whether the WTRU is associated with an AP based on the AP address, to determine whether the WTRU is an intended recipient of the MU transmission based on the STA ID, and to generate the response based on whether the WTRU is associated with the AP and based on whether the WTRU is the intended recipient of the MU transmission.

12 . A method for use by a wireless transmit/receive unit (WTRU), the method comprising:

receiving, by the WTRU, a frame;

decoding, by the WTRU, the received frame and determining whether the received frame is a null data packet (NDP) multi-user (MU) media access control (MAC) physical layer convergence protocol (PLCP) protocol data unit (PPDU) (NDP MU MAC PPDU) based on the received frame meeting an NDP condition, wherein the NDP MU MAC PPDU is related to an MU transmission and includes a PLCP header which includes an NDP signal (SIG) field having MU simultaneous transmission control information configured to control simultaneous transmissions of multiple users;

processing, by the WTRU, based on the received frame meeting the NDP condition, the NDP SIG field;

generating, by the WTRU, a response based on the NDP SIG field and the MU simultaneous transmission control information; and

transmitting, by the WTRU, the response simultaneously with at least one other user.

13 . The method of claim 12 , further comprising:

determining, by the WTRU, a length of the received frame and determining that the received frame meets the NDP condition if the length of the received frame is less than a threshold.

14 . The method of claim 12 , further comprising:

determining, by the WTRU, whether an NDP indicator is set in the NDP SIG field and determining that the received frame meets the NDP condition if the NDP indicator is set.

15 . The method of claim 12 , wherein the NDP SIG field indicates a NDP MAC frame type of the NDP MU MAC PPDU, and the method further comprises:

determining, by the WTRU, the NDP MAC frame type from the NDP SIG field and generating the response based on the determined NDP MAC frame type.

16 . (canceled)

17 . The method of claim 12 , wherein the NDP SIG field includes an access point (AP) address and a group identifier (ID), and the method further comprises:

determining, by the WTRU, whether the WTRU is an intended recipient of the NDP MU MAC PPDU based on the AP address and the group ID; and

preparing, by the WTRU, the response on a condition that the WTRU is an intended recipient of the NDP MU MAC PPDU.

18 . The method of claim 17 , wherein the NDP SIG field includes duration information, and the method further comprises:

on a condition that the WTRU is not an intended recipient of the MU transmission, deferring, by the WTRU, preparation of the response and setting a network allocation vector (NAV) based on the duration information.

19 . The method of claim 12 , wherein the NDP SIG field includes an access point (AP) address, and the method further comprises:

determining, by the WTRU, whether the WTRU is associated with an AP based on the AP address, and

on a condition that the WTRU associated with the AP, generating, by the WTRU, the response.

20 . (canceled)

21 . (canceled)

22 . The method of claim 20 , wherein the NDP SIG field includes an NDP SIG-A field and an NDP SIG-B field, wherein the NDP SIG-A field includes common control information that corresponds to a plurality of WTRUs and the NDP SIG-B field includes user and resource dedicated information, and

wherein the NDP SIG-A field includes an access point (AP) address and the NDP SIG-B field includes a STA identity (ID), and the method further comprises:

determining, by the WTRU, whether the WTRU is associated with an AP based on the AP address;

determining, by the WTRU, whether the WTRU is an intended recipient of the MU transmission based on the STA ID; and

preparing, by the WTRU, the response based on whether the WTRU is associated with the AP and based on whether the WTRU is the intended recipient of the MU transmission.

23 - 26 . (canceled)

27 . The WTRU of claim 1 , wherein the MU simultaneous transmission control information includes orthogonal frequency-division multiple access (OFDMA) control information for configuring simultaneous uplink data transmissions of multiple users.

28 . The method of claim 12 , wherein the MU simultaneous transmission control information includes orthogonal frequency-division multiple access (OFDMA) control information for configuring simultaneous uplink data transmissions of multiple users.

29 . (canceled)