Method and apparatus for multi-user concurrent random access for wireless local area networks (WLANs)

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

a receiver and a processor, the receiver and the processor being configured to detect a trigger frame for uplink (UL) multi-user (MU) transmission, the trigger frame including an assignment of resource units (RUs) for random access in upcoming UL MU physical layer protocol data units (PPDUs) and an indication that the trigger frame is one of a plurality of trigger frames in a cascading sequence of trigger frames in an MU transmission opportunity (TxOP); and

a transmitter, the processor and transmitter being configured to select one of the RUs in the assignment of RUs for a random access transmission and send the random access transmission on the selected one of the RUs.

2. The WTRU of claim 1 , wherein the receiver is further configured to receive an acknowledgement for the random access transmission, the acknowledgement being aggregated with one of the plurality of trigger frames in the sequence.

3. The WTRU of claim 1 , wherein the processor is further configured to enter a sleep state in response to a last trigger indication in at least one trigger frame of the plurality of trigger frames in the sequence.

4. The WTRU of claim 1 , wherein the trigger frame includes a field that polls for a traffic buffer status of the WTRU.

5. The WTRU of claim 1 , wherein the assignment of RUs for random access in the upcoming UL OFDMA transmission is for an integer number, M, of RUs, and the processor and the transmitter are configured to select the one of the RUs in the assignment of RUs for the random access transmission by:

generating a random backoff index, R, from a range of integer values between zero and a defined maximum value,

on a condition that R>M, holding the random access transmission and re-setting the value of R to R=R−M, and

using the re-set value of R to compete for the next MU random access opportunity in the TxOP.

6. The WTRU of claim 5 , wherein the processor and the transmitter are further configured to select the one of the RUs in the assignment of RUs for the random transmission by transmitting on an Rth RU of the RUs included in the assignment of RUs for random access on a condition that R≤M.

7. The WTRU of claim 1 , wherein the trigger frame includes a common information field that carries information to set a high efficiency (HE)-SIG-A field in the upcoming UL MU PPDU.

8. A method, implemented in a wireless transmit/receive unit (WTRU), the method comprising:

detecting a trigger frame for uplink (UL) multi-user (MU) transmission, the trigger frame including an assignment of resource units (RUs) for random access in upcoming UL MU physical layer protocol data units (PPDUs) and an indication that the trigger frame is one of a plurality of trigger frames in a cascading sequence of trigger frames in an MU transmission opportunity (TxOP);

selecting one of the RUs in the assignment of RUs for a random access transmission; and

sending the random access transmission on the selected one of the RUs.

9. The method of claim 8 , further comprising receiving an acknowledgement for the random access transmission, the acknowledgement being aggregated with one of the plurality of trigger frames in the sequence.

10. The method of claim 8 , further comprising entering a sleep state in response to a last trigger indication in at least one trigger frame of the plurality of trigger frames in the sequence.

11. The method of claim 8 , wherein the trigger frame includes a field that polls for a traffic buffer status of the WTRU.

12. The method of claim 8 , wherein the assignment of RUs for random access in the upcoming UL OFDMA transmission is for an integer number, M, of RUs, and the selecting one of the RUs in the assignment of RUs for a random access transmission comprises:

generating a random backoff index, R, from a range of integer values between zero and a defined maximum value,

on a condition that R>M, holding the random access transmission and re-setting the value of R to R=R−M, and

using the re-set value of R to compete for the next MU random access opportunity in the TxOP.

13. The method of claim 12 , further comprising transmitting on an Rth RU of the RUs included in the assignment of RUs for random access on a condition that R≤M.

14. The method of claim 8 , wherein the trigger frame includes a common information field that carries information to set a high efficiency (HE)-SIG-A field in the upcoming UL MU PPDU.

15. An access point (AP) comprising:

a processor and a transmitter, the processor and the transmitter being configured to generate and transmit a trigger frame for uplink (UL) multi-user (MU) transmission to a plurality of stations (STAs), the trigger frame including an assignment of resource units (RUs) for random access in upcoming UL trigger-based physical layer protocol data units (PPDUs) and an indication that the trigger frame is one of a plurality of trigger frames in a cascading sequence of trigger frames in an MU transmission opportunity (TxOP); and

a receiver, the receiver and the processor being configured to receive the UL trigger-based PPDUs, the received trigger-based PPDUs including at least one frame from at least one of the plurality of STAs on one of the assigned RUs,

wherein the transmitter and the processor are further configured to transmit an acknowledgement for the at least one frame, the acknowledgement being aggregated with one of the plurality of trigger frames in the sequence.

16. The AP of claim 15 , wherein at least one frame of the plurality of trigger frames in the sequence includes a last trigger indication that triggers STAs to enter a sleep state.

17. The AP of claim 15 , wherein the trigger frame includes a field that polls for a traffic buffer status of STAs.

18. The AP of claim 15 , wherein the trigger frame includes a common information field that carries information to set a high efficiency (HE)-SIG-A field in the UL MU PPDU.