Restricted TWT operations for multi-link devices

1. A non-access point (AP) multi-link device (MLD) comprising:

a plurality of stations (STAs) that each comprise a transceiver configured to transmit and receive signals in target wake time (TWT) operation on multi-link operation (MLO) links between the STAs and corresponding APs of an AP MLD, respectively; and

a processor operably coupled to the transceivers, the processor configured to:

negotiate a broadcast TWT schedule over a first link between a first STA and a first AP of the AP MLD, wherein the broadcast TWT schedule is for a shared TWT session including a group of the links;

after the broadcast TWT schedule is successfully negotiated, apply the broadcast TWT schedule to the group of links;

negotiate a restricted TWT schedule with the AP MLD over at least one link of the group of links; and

after the restricted TWT schedule is successfully negotiated, establish the restricted TWT schedule on one or more links of the at least one link, such that the one or more links are members of the restricted TWT schedule.

2. The non-AP MLD of claim 1 , wherein:

the transceivers are further configured to transmit to or receive from the AP MLD on the at least one link of the group of links, via a corresponding at least one STA of the STAs, a broadcast TWT parameter set corresponding to the broadcast TWT schedule, and

the broadcast TWT parameter set indicates that the broadcast TWT schedule is the restricted TWT schedule.

3. The non-AP MLD of claim 2 , wherein a broadcast TWT recommendation subfield of a request type field of the broadcast TWT parameter set is set to a value in a range of 4 through 7 to indicate that the broadcast TWT schedule is the restricted TWT schedule.

4. The non-AP MLD of claim 2 , wherein a request type field of the broadcast TWT parameter set or a broadcast TWT info field of the broadcast TWT parameter set include an indication that the restricted TWT schedule is also an aligned schedule.

5. The non-AP MLD of claim 1 , wherein:

the processor is further configured to negotiate the restricted TWT schedule with the AP MLD for a desired link that is the same as or different from the at least one link over which the restricted TWT schedule is negotiated, and

each traffic identifier (TID) for which the restricted TWT schedule is negotiated is mapped to the desired link through TID-to-link mapping.

6. The non-AP MLD of claim 1 , wherein:

first and second links of the group of links form a non-simultaneous transmit/receive (NSTR) pair,

the first link has the restricted TWT schedule established, and

transmission of frames on the second link is terminated before a restricted TWT service period (SP) begins on the first link.

7. The non-AP MLD of claim 1 , wherein:

first and second links of the group of links form a non-simultaneous transmit/receive (NSTR) pair,

the first link has the restricted TWT schedule established, and

based on transmission of a downlink (DL) physical layer protocol data unit (PPDU) on the first link ending, transmission of a DL PPDU on the second link is truncated such that an end time of the DL PPDU on the second link is aligned with an end time of the DL PPDU on the first link, or

transmission of frames on the second link is elongated or padded, such that the end time of the DL PPDU on the second link is aligned with the end time of the DL PPDU on the first link.

8. An access point (AP) multi-link device (MLD) comprising:

a plurality of APs that each comprise a transceiver configured to transmit and receive signals in target wake time (TWT) operation on multi-link operation (MLO) links between the APs and corresponding stations (STAs) of a non-AP MLD, respectively; and

a processor operably coupled to the transceivers, the processor configured to:

negotiate a broadcast TWT schedule over a first link between a first AP and a first STA of the non-AP MLD, wherein the broadcast TWT schedule is for a shared TWT session including a group of the links;

after the broadcast TWT schedule is successfully negotiated, apply the broadcast TWT schedule to the group of links;

negotiate a restricted TWT schedule with the non-AP MLD over at least one link of the group of links; and

after the restricted TWT schedule is successfully negotiated, establish the restricted TWT schedule on one or more links of the at least one link, such that the one or more links are members of the restricted TWT schedule.

9. The AP MLD of claim 8 , wherein:

the transceivers are further configured to transmit to or receive from the non-AP MLD on the at least one link of the group of links, via a corresponding at least one AP of the APs, a broadcast TWT parameter set corresponding to the broadcast TWT schedule, and

the broadcast TWT parameter set indicates that the broadcast TWT schedule is the restricted TWT schedule.

10. The AP MLD of claim 9 , wherein a broadcast TWT recommendation subfield of a request type field of the broadcast TWT parameter set is set to a value in a range of 4 through 7 to indicate that the broadcast TWT schedule is the restricted TWT schedule.

11. The AP MLD of claim 9 , wherein a request type field of the broadcast TWT parameter set or a broadcast TWT info field of the broadcast TWT parameter set include an indication that the restricted TWT schedule is also an aligned schedule.

12. The AP MLD of claim 8 , wherein:

the processor is further configured to negotiate the restricted TWT schedule with the non-AP MLD for a desired link that is the same as or different from the at least one link over which the restricted TWT schedule is negotiated, and

each traffic identifier (TID) for which the restricted TWT schedule is negotiated is mapped to the desired link through TID-to-link mapping.

13. The AP MLD of claim 8 , wherein:

first and second links of the group of links form a non-simultaneous transmit/receive (NSTR) pair,

the first link has the restricted TWT schedule established, and

transmission of frames on the second link is terminated before a restricted TWT service period (SP) begins on the first link.

14. The AP MLD of claim 8 , wherein:

first and second links of the group of links form a non-simultaneous transmit/receive (NSTR) pair,

the first link has the restricted TWT schedule established, and

based on transmission of a DL PPDU on the first link ending, transmission of a DL PPDU on the second link is truncated such that an end time of the DL PPDU on the second link is aligned with an end time of the DL PPDU on the first link, or

transmission of frames on the second link is elongated or padded, such that the end time of the DL PPDU on the second link is aligned with the end time of the DL PPDU on the first link.

15. A method for facilitating broadcast target wake time (TWT) operation by a non-access point (AP) multi-link device (MLD), the method comprising:

negotiating a broadcast TWT schedule over a first link between a first STA and a first AP of the AP MLD, wherein the broadcast TWT schedule is for a shared TWT session including a group of the links;

after the broadcast TWT schedule is successfully negotiated, applying the broadcast TWT schedule to the group of links;

negotiating a restricted TWT schedule with the AP MLD over at least one link of the group of links; and

after the restricted TWT schedule is successfully negotiated, establishing the restricted TWT schedule on one or more links of the at least one link, such that the one or more links are members of the restricted TWT schedule.

16. The method of claim 15 , further comprising receiving a broadcast TWT parameter set corresponding to the broadcast TWT schedule,

wherein the broadcast TWT parameter set indicates that the broadcast TWT schedule is the restricted TWT schedule.

17. The method of claim 16 , wherein a broadcast TWT recommendation subfield of a request type field of the broadcast TWT parameter set is set to a value in a range of 4 through 7 to indicate that the broadcast TWT schedule is the restricted TWT schedule.

18. The method of claim 16 , wherein a request type field of the broadcast TWT parameter set or a broadcast TWT info field of the broadcast TWT parameter set include an indication that the restricted TWT schedule is also an aligned schedule.

19. The method of claim 15 , further comprising:

negotiating the restricted TWT schedule with the AP MLD for a desired link that is the same as or different from the at least one link over which the restricted TWT schedule is negotiated,

wherein each traffic identifier (TID) for which the restricted TWT schedule is negotiated is mapped to the desired link through TID-to-link mapping.

20. The method of claim 15 , wherein:

first and second links of the group of links form a non-simultaneous transmit/receive (NSTR) pair,

the first link has the restricted TWT schedule established, and

transmission of frames on the second link is terminated before a restricted TWT service period (SP) begins on the first link.