Listen-before-talk schemes for directional communications
Methods, systems, and devices for wireless communications are described. In some systems, wireless devices operating in an unlicensed radio frequency spectrum band may perform directional listen-before-talk (LBT) procedures to gain access to a channel. In a beam-shrinking scheme for directional LBT, a wireless device may start an LBT procedure using a first beam (e.g., a wide beam). If the clear channel assessment (CCA) fails for the first beam (e.g., due to directional interference), the device may switch the LBT procedure to a second beam (e.g., a narrower beam). Depending on the direction of the interference source, the second beam may result in a successful LBT procedure. In a beam sweeping scheme for directional LBT, a wireless device may perform concurrent LBT over multiple narrow beams. If any beam of the set of beams detects frequent or continuous interference, the device may drop that beam from the concurrent LBT procedure.
1. A method for wireless communications, comprising:
performing a first directional clear channel assessment for a channel using a first beam having a first beam width;
detecting interference for the first beam on the channel based at least in part on the first directional clear channel assessment; and
performing a second directional clear channel assessment for the channel in response to detecting the interference for the first beam, wherein the second directional clear channel assessment is performed using a second beam that is contained within a directional range spanned by the first beam and has a second beam width that is narrower than the first beam width based at least in part on the detected interference for the first beam.
2. The method of claim 1 , further comprising:
detecting additional interference for the second beam on the channel based at least in part on the second directional clear channel assessment; and
performing a third directional clear channel assessment for the channel using a third beam with a third beam width based at least in part on the detected additional interference for the second beam, wherein the third beam width is narrower than the second beam width.
3. The method of claim 1 , wherein performing the first directional clear channel assessment comprises:
selecting a countdown value for the first beam from a range of countdown values, wherein a maximum countdown value of the range of countdown values corresponds to a contention window value for the first beam;
starting a counter from the selected countdown value for the first beam;
monitoring the channel using the first beam based at least in part on starting the counter; and
decreasing the counter by one for each transmission time interval that the channel is determined to be clear according to the monitoring the channel using the first beam, wherein the interference for the first beam is detected based at least in part on the monitoring the channel using the first beam.
4. The method of claim 3 , wherein the counter comprises a first counter value when the interference for the first beam is detected, and wherein performing the second directional clear channel assessment comprises:
continuing the counter from the first counter value;
monitoring the channel using the second beam based at least in part on continuing the counter; and
decreasing the counter by one for each transmission time interval that the channel is determined to be clear according to the monitoring of the channel using the second beam.
5. The method of claim 3 , wherein performing the second directional clear channel assessment comprises:
restarting the counter from the selected countdown value for the first beam or an updated countdown value for the second beam;
monitoring the channel using the second beam based at least in part on restarting the counter; and
decreasing the counter by one for each transmission time interval that the channel is determined to be clear according to the monitoring of the channel using the second beam.
6. The method of claim 3 , wherein the counter comprises a first counter value when the interference for the first beam is detected, and wherein performing the second directional clear channel assessment comprises:
modifying the first counter value based at least in part on a penalty value;
continuing the counter from the modified first counter value;
monitoring the channel using the second beam based at least in part on continuing the counter; and
decreasing the counter by one for each transmission time interval that the channel is determined to be clear according to the monitoring of the channel using the second beam.
7. The method of claim 3 , wherein a contention window value for the second beam is equal to the contention window value for the first beam.
8. The method of claim 3 , wherein performing the second directional clear channel assessment comprises:
determining an updated contention window value for the second beam that is different from the contention window value for the first beam.
9. The method of claim 3 , wherein a countdown value for the second beam is equal to the selected countdown value for the first beam.
10. The method of claim 3 , wherein performing the second directional clear channel assessment comprises:
selecting an updated countdown value for the second beam that is different from the selected countdown value for the first beam.
11. The method of claim 3 , wherein the countdown value for the first beam is selected from the range of countdown values based at least in part on a random number generation process.
12. The method of claim 3 , wherein a directional clear channel assessment passes if the counter reaches zero.
13. The method of claim 1 , further comprising:
detecting additional interference for the second beam on the channel based at least in part on the second directional clear channel assessment; and
performing a third directional clear channel assessment for the channel using the first beam based at least in part on the detected additional interference for the second beam.
14. The method of claim 1 , wherein the second directional clear channel assessment passes for the channel using the second beam, the method further comprising:
transmitting a signal over the channel using the second beam based at least in part on the second directional clear channel assessment passing.
15. The method of claim 14 , further comprising:
determining a channel occupancy time duration based at least in part on the second beam width of the second beam, wherein the signal is transmitted according to the channel occupancy time duration.
16. The method of claim 14 , further comprising:
receiving a negative acknowledgment message in response to the signal; and
re-transmitting the signal over the channel using a third beam based at least in part on the negative acknowledgment message, wherein the third beam is different from the second beam.
17. An apparatus for wireless communications, comprising:
a processor;
memory in electronic communication with the processor; and
instructions stored in the memory and executable by the processor to cause the apparatus to:
perform a first directional clear channel assessment for a channel using a first beam having a first beam width;
detect interference for the first beam on the channel based at least in part on the first directional clear channel assessment; and
perform a second directional clear channel assessment for the channel in response to detecting the interference for the first beam, the second directional clear channel assessment performed using a second beam that is contained within a directional range spanned by the first beam and has a second beam width that is narrower than the first beam width based at least in part on the detected interference for the first beam.
18. The apparatus of claim 17 , wherein the instructions to perform the first directional clear channel assessment are executable by the processor to cause the apparatus to:
select a countdown value for the first beam from a range of countdown values, wherein a maximum countdown value of the range of countdown values corresponds to a contention window value for the first beam;
start a counter from the selected countdown value for the first beam;
monitor the channel using the first beam based at least in part on starting the counter; and
decrease the counter by one for each transmission time interval that the channel is determined to be clear according to the monitoring the channel using the first beam, wherein the instructions to detect the interference for the first beam are executable by the processor to cause the apparatus to detect the interference for the first beam based at least in part on the monitoring of the channel using the first beam.
19. The apparatus of claim 18 , wherein when the counter comprises a first counter value when the interference for the first beam is detected, the instructions to perform the second directional clear channel assessment are executable by the processor to cause the apparatus to:
continue the counter from the first counter value;
monitor the channel using the second beam based at least in part on continuing the counter; and
decrease the counter by one for each transmission time interval that the channel is determined to be clear according to the monitoring of the channel using the second beam.
20. The apparatus of claim 18 , wherein the instructions to perform the second directional clear channel assessment are executable by the processor to cause the apparatus to:
restart the counter from the selected countdown value for the first beam or an updated countdown value for the second beam;
monitor the channel using the second beam based at least in part on restarting the counter; and
decrease the counter by one for each transmission time interval that the channel is determined to be clear according to the monitoring of the channel using the second beam.
21. The apparatus of claim 18 , wherein when the counter comprises a first counter value when the interference for the first beam is detected, the instructions to perform the second directional clear channel assessment are executable by the processor to cause the apparatus to:
modify the first counter value based at least in part on a penalty value;
continue the counter from the modified first counter value;
monitor the channel using the second beam based at least in part on continuing the counter; and
decrease the counter by one for each transmission time interval that the channel is determined to be clear according to the monitoring of the channel using the second beam.
22. The apparatus of claim 17 , wherein when the second directional clear channel assessment passes for the channel using the second beam, the instructions are further executable by the processor to cause the apparatus to:
transmit a signal over the channel using the second beam based at least in part on the second directional clear channel assessment passing.
23. The apparatus of claim 22 , wherein the instructions are further executable by the processor to cause the apparatus to:
determine a channel occupancy time duration based at least in part on the second beam width of the second beam, wherein the instructions to transmit the signal are executable by the processor to cause the apparatus to transmit the signal according to the channel occupancy time duration.
24. The method of claim 1 , further comprising:
performing, before performing the second directional clear channel assessment for the channel, a third directional clear channel assessment for the channel in response to detecting the interference for the first beam, wherein the third directional clear channel assessment is performed using a third beam that is at least partially outside the directional range spanned by the first beam.
25. The method of claim 1 , further comprising:
performing a third directional clear channel assessment for the channel in response to detecting interference for the second beam on the channel, wherein the third directional clear channel assessment is performed using a third beam that is at least partially outside the directional range spanned by the first beam.
26. The apparatus of claim 17 , wherein the instructions are further executable by the processor to cause the apparatus to:
perform, before performing the second directional clear channel assessment for the channel, a third directional clear channel assessment for the channel in response to detecting the interference for the first beam, the third directional clear channel assessment using a third beam that is at least partially outside the directional range spanned by the first beam.
27. The apparatus of claim 17 , wherein the instructions are further executable by the processor to cause the apparatus to:
perform a third directional clear channel assessment for the channel in response to detecting interference for the second beam on the channel, the third directional clear channel assessment using a third beam that is at least partially outside the directional range spanned by the first beam.