CWS adjustment for NR systems operating on unlicensed spectrum

1. An apparatus for a base station, comprising one or more processors configured to cause the base station to:

select a first downlink (DL) burst transmitted by the base station for use in determining a contention window size (CWS) in response to determining that a timing of a last Hybrid Automatic Repeat Request (HARQ) opportunity designated for the first DL burst occurs prior to a beginning of a base station processing time for adjusting the CWS, wherein a second DL burst is not selected in response to determining that the timing of a last HARQ opportunity for the second DL burst occurs during or after a base station processing time for adjusting the CWS;

set a timer having a length of N; and

adjust the CWS based on HARQ feedback received prior to expiration of the timer with respect to the first DL burst.

2. The apparatus of claim 1 , wherein the one or more processors are configured to cause the base station to:

increase the CWS to a higher value when HARQ-acknowledge (ACK) feedback is not received prior to expiration of the timer.

3. The apparatus of claim 1 , wherein the one or more processors are configured to cause the base station to:

revert the CWS to a value used for transmission of the first DL burst in response to receiving HARQ-ACK feedback for a reference physical downlink shared channel (PDSCH) of the first DL burst after expiration of the timer.

4. The apparatus of claim 1 , wherein the one or more processors are configured to cause the base station to:

increase the CWS in response to receiving HARQ-non-acknowledgement (NACK) feedback for a reference PDSCH of the first DL burst after expiration of the timer.

5. The apparatus of claim 1 , wherein the one or more processors are configured to cause the base station to:

double the CWS in response to receiving HARQ-non-acknowledgement (NACK) feedback for a reference PDSCH of the first DL burst after expiration of the timer.

6. The apparatus of claim 1 , wherein the one or more processors are configured to cause the base station to:

draw a Previously Presented random back-off counter for an ongoing LBT procedure in response to adjusting the CWS during the ongoing LBT procedure.

7. The apparatus of claim 1 , wherein the one or more processors are configured to cause the base station to:

adjust the CWS based on HARQ feedback received from a single user equipment device (UE) belonging to a set of UEs to which the first DL burst was transmitted.

8. The apparatus of claim 1 , wherein the one or more processors are configured to cause the base station to:

in response to determining that a UE uses discontinuous transmission (DTX) to report HARQ feedback, when HARQ feedback is not received adjust the CWS in a same manner as when HARQ feedback is received.

9. The apparatus of claim 1 , wherein the one or more processors are configured to cause the base station to:

maintain the CWS at a current value when a new DL transmission is initiated while the timer has not elapsed and feedback for a previous DL burst has not been received.

10. A method, comprising, with a base station:

selecting a first downlink (DL) burst transmitted by the base station for use in determining a contention window size (CWS) in response to determining that a timing of a last Hybrid Automatic Repeat Request (HARQ) opportunity designated for the first DL burst occurs prior to a beginning of a base station processing time for adjusting the CWS, wherein a second DL burst is not selected in response to determining that the timing of a last HARQ opportunity for the second DL burst occurs during or after a base station processing time for adjusting the CWS;

setting a timer having a length of N; and

adjusting the CWS based on HARQ feedback received prior to expiration of the timer with respect to the first DL burst.

11. The method of claim 10 , comprising:

increasing the CWS to a higher value when HARQ-acknowledge (ACK) feedback is not received prior to expiration of the timer.

12. The method of claim 10 , comprising:

reverting the CWS to a value used for transmission of the first DL burst in response to receiving HARQ-ACK feedback for a reference physical downlink shared channel (PDSCH) of the first DL burst after expiration of the timer.

13. The method of claim 10 , comprising:

increasing the CWS in response to receiving HARQ-non-acknowledgement (NACK) feedback for a reference PDSCH of the first DL burst after expiration of the timer.

14. The method of claim 10 , comprising:

doubling the CWS in response to receiving HARQ-non-acknowledgement (NACK) feedback for a reference PDSCH of the first DL burst after expiration of the timer.

15. The method of claim 10 , comprising:

drawing a Previously Presented random back-off counter for an ongoing LBT procedure in response to adjusting the CWS during the ongoing LBT procedure.

16. The method of claim 10 , comprising:

adjusting the CWS based on HARQ feedback received from a single user equipment device (UE) belonging to a set of UEs to which the first DL burst was transmitted.

17. The method of claim 10 , comprising:

in response to determining that a UE uses discontinuous transmission (DTX) to report HARQ feedback, when HARQ feedback is not received adjusting the CWS in a same manner as when HARQ feedback is received.

18. The method of claim 10 , comprising:

decreasing the CWS to a lower value when HARQ-acknowledge (ACK) feedback is not received prior to expiration of the timer.

19. The method of claim 10 , further comprising:

maintaining the CWS at a current value when a new DL transmission is initiated while the timer has not elapsed and feedback for a previous DL burst has not been received.