Acknowledgement feedback in unlicensed new radio
Methods, systems, and devices for wireless communications are described. A user equipment (UE) and a base station may communicate in an unlicensed spectrum (e.g., a shared radio frequency spectrum band). As such, the UE may determine a codebook size for transmitting hybrid access request (HARQ) acknowledgement (ACK) feedback with respect to the unlicensed spectrum. Accordingly, the UE may base the HARQ ACK codebook size on a number of HARQ processes with which the UE has been configured. Additionally or alternatively, the UE may base the HARQ ACK codebook size on a number and/or duration of downlink channel monitoring occasions indicated by the base station. In some cases, the UE may base the HARQ ACK codebook size on a combination of the techniques described herein.
1. A user equipment (UE), comprising:
one or more memories storing code; and
one or more processors coupled with the one or more memories and operable to execute the code to cause the UE to:
receive a feedback trigger for communication of hybrid automatic repeat request (HARQ) feedback, wherein a HARQ acknowledgement (ACK) codebook size associated with the HARQ feedback is based at least in part on a quantity of configured HARQ processes; and
communicate the HARQ feedback in accordance with the HARQ ACK codebook size in a shared radio frequency spectrum band, wherein the feedback trigger is included in a downlink control information (DCI) message that is separate from a downlink grant and an uplink grant.
2. The UE of claim 1 , wherein the one or more processors are further operable to execute the code to cause the UE to:
populate the HARQ feedback based at least in part on an ACK delay indication and receipt of a physical downlink shared channel (PDSCH).
3. The UE of claim 2 , wherein, to populate the HARQ feedback, the one or more processors are individually or collectively operable to execute the code to cause the UE to:
populate the HARQ feedback using decoding results when an ACK ready time for the PDSCH occurs prior to reception of the feedback trigger, wherein the ACK ready time is based on the ACK delay indication and the reception of the PDSCH.
4. The UE of claim 2 , wherein, to populate the HARQ feedback, the one or more processors are individually or collectively operable to execute the code to cause the UE to:
populate the HARQ feedback using default values when an ACK ready time for the PDSCH is greater than an ACK transmission time.
5. The UE of claim 2 , wherein, to populate the HARQ feedback with default values, the one or more processors are individually or collectively operable to execute the code to cause the UE to:
populate the HARQ feedback using an ACK value, a negative ACK (NACK) value, or a previous ACK/NACK value.
6. The UE of claim 1 , wherein the one or more processors are further operable to execute the code to cause the UE to:
determine the HARQ ACK codebook size based at least in part on a quantity of downlink channel monitoring occasions occurring within a reporting duration for the HARQ feedback.
7. The UE of claim 6 , wherein a control message received in downlink control information (DCI) indicates whether the quantity of downlink channel monitoring occasions comprises an ACK transmission time, whether the quantity of downlink channel monitoring occasions comprise different channel monitoring occasions, or a combination thereof.
8. The UE of claim 7 , wherein the ACK transmission time comprises a sum of data transmission time and an ACK delay value, the ACK delay value conveyed in the downlink grant corresponding to a current ACK transmission.
9. The UE of claim 7 , wherein the control message comprises an explicit indication received in the DCI.
10. The UE of claim 7 , wherein the control message comprises an implicit indication based at least in part on comparing a HARQ feedback parameter conveyed in the DCI with a parameter conveyed in radio resource control.
11. The UE of claim 7 , wherein receiving, during a transmission opportunity (TxOp) in which a downlink channel monitoring occasion is to occur and before the downlink channel monitoring occasion occurs, information from which the UE is able to determine a duration of the downlink channel monitoring occasion.
12. The UE of claim 7 , wherein the DCI includes an indication of the quantity of downlink channel monitoring occasions to include in determining the HARQ ACK codebook size.
13. The UE of claim 7 , wherein the DCI includes an indication of a set of downlink channel monitoring occasions to include in determining the HARQ ACK codebook size, and wherein the set of downlink channel monitoring occasions is one of a plurality of predefined sets of downlink channel monitoring occasions of the quantity of downlink channel monitoring occasions received via radio resource control (RRC) signaling.
14. The UE of claim 6 , wherein the HARQ ACK codebook size encompasses a quantity of transmission time intervals (TTIs) and at least some of the quantity of TTIs are non-contiguous, and wherein the quantity of TTIs encompassed by the HARQ ACK codebook size spans two different transmission opportunities (TxOps).
15. The UE of claim 6 , wherein the one or more processors are further operable to execute the code to cause the UE to:
determine the HARQ ACK codebook size based at least in part on a duration of the downlink channel monitoring occasions for a first set of HARQ feedback instances of the HARQ feedback; and
determine the HARQ ACK codebook size based at least in part on a number of configured HARQ processes for a second set of HARQ feedback instances of the HARQ feedback.
16. The UE of claim 15 , wherein the one or more processors are further operable to execute the code to cause the UE to:
receive a feedback trigger that indicates whether the HARQ ACK codebook size determination is to be based on the duration of at least one downlink channel monitoring occasion or on the number of configured HARQ processes.
17. The UE of claim 6 , wherein the quantity of the downlink channel monitoring occasions is identified based at least in part on a time location of the HARQ feedback.
18. The UE of claim 6 , wherein, to receive the feedback trigger, the one or more processors are operable to execute the code to cause the UE to:
receive a trigger for HARQ feedback in DCI for all of the quantity of configured HARQ processes or a subset of the quantity of configured HARQ processes for the UE via radio resource control (RRC) signaling, wherein the subset of the quantity of configured HARQ processes comprises a bitmap indication with each bit in the bitmap indication corresponds to one HARQ process or a group of HARQ processes.
19. A method for wireless communication at a user equipment (UE) in a shared radio frequency spectrum band, comprising:
receiving a feedback trigger for communication of hybrid automatic repeat request (HARQ) feedback, wherein a HARQ acknowledgement (ACK) codebook size associated with the HARQ feedback is based at least in part on a quantity of configured HARQ processes; and
communicating the HARQ feedback in accordance with the HARQ ACK codebook size, wherein the feedback trigger is included in a downlink control information (DCI) message that is separate from a downlink grant and an uplink grant.
20. A user equipment (UE) in a shared radio frequency spectrum band for wireless communication, comprising:
means for receiving a feedback trigger for communication of hybrid automatic repeat request (HARQ) feedback, wherein a HARQ acknowledgement (ACK) codebook size associated with the HARQ feedback is based at least in part on a quantity of configured HARQ processes; and
means for communicating the HARQ feedback in accordance with the HARQ ACK codebook size, wherein the feedback trigger is included in a downlink control information (DCI) message that is separate from a downlink grant and an uplink grant.