Vehicle-to-everything ultra-reliable/low-latency communications design

1. A method for wireless communication, comprising:

identifying a plurality of shortened transmission time intervals (TTIs) to be used for priority communications to or from a vehicle having a first traffic priority level, the plurality of shortened TTIs each having a duration that is less than that of other TTIs used in other communications to or from the vehicle having a second traffic priority level which is less than the first traffic priority level;

performing a listen-before-talk (LBT) procedure in order to reserve the plurality of shortened TTIs for the priority communications; and

further reserving via a request-to-send/clear-to-send (RTS/CTS) exchange, at least one instance of the plurality of shortened TTIs for the priority communications based at least in part on the LBT procedure, wherein the RTS/CTS exchange is performed for only a portion of the plurality of shortened TTIs, wherein shortened TTIs other than the portion are available for other communications having the second traffic priority level.

2. The method of claim 1 , wherein the further reserving comprises transmitting a request to reserve the at least one instance of the plurality of shortened TTIs for the priority communication.

3. The method of claim 1 , wherein performing the LBT procedure further comprises:

performing the LBT procedure using the other TTIs having the second traffic priority level.

4. The method of claim 1 , further comprising:

receiving, during the LBT procedure, an acknowledgement (ACK) message from one or more UEs to participate in the priority communications; and

performing the priority communications with the UEs from which ACK messages were received.

5. The method of claim 1 , wherein performing the LBT procedure comprises:

identifying a resource tree that comprises a plurality of nodes, each node of the resource tree associated with some or all of a set of available time-frequency resources that include the plurality of shortened TTIs; and

selecting the node of the resource tree based at least in part on the plurality of shortened TTIs.

6. The method of claim 1 , further comprising:

configuring one or more of a scheduling assignment (SA) message, or a medium access control (MAC) control element (CE), or a radio resource control (RRC) message to provide an indication in the LBT procedure reserving the plurality of shortened TTIs.

7. The method of claim 1 , further comprising:

performing the RTS/CTS exchange for only the portion of the plurality of shortened TTIs based at least in part on an absence of receiving a negative acknowledgment (NACK) in response to the priority communications.

8. The method of claim 1 , further comprising:

transmitting an RTS message during the at least one instance of the plurality of shortened TTIs, the RTS message indicating an identifier and a configuration for the priority communications; and

receiving a CTS message from one or more wireless devices participating in the priority communications, the CTS message indicating a sequence associating the CTS message with the RTS message.

9. The method of claim 1 , further comprising:

determining that the priority communications include periodic traffic satisfying a threshold, wherein performing the LBT procedure is based at least in part on the periodic traffic satisfying the threshold.

10. A method for wireless communication, comprising:

receiving, during a listen-before-talk (LBT) procedure, an indication reserving a plurality of shortened transmission time intervals (TTIs) to be used for priority communications to or from a vehicle having a first traffic priority level, the plurality of shortened TTIs each having a duration that is less than that of other TTIs used in other communications to or from the vehicle having a second traffic priority level which is less than the first traffic priority level;

transmitting, during the LBT procedure, an acknowledgement (ACK) message responsive to the indication; and

receiving, during at least one instance of the plurality of shortened TTIs, a request further reserving the at least one instance of the plurality of shortened TTIs for the priority communications based at least in part on the transmitted ACK message, the request being part of a request-to-send/clear-to-send (RTS/CTS) exchange that is performed for only a portion of the plurality of shortened TTIs, wherein shortened TTIs other than the portion are available for other communications having the second traffic priority level.

11. The method of claim 10 , wherein receiving the indication further comprises:

receiving the indication on the other TTIs having the second traffic priority level.

12. The method of claim 10 , wherein receiving the indication reserving the plurality of shortened TTIs comprises:

identifying a resource tree that comprises a plurality of nodes, each node of the resource tree associated with some or all of a set of available time-frequency resources including the plurality of shortened TTIs; and

selecting the node of the resource tree based at least in part on the plurality of shortened TTIs.

13. The method of claim 10 , further comprising:

decoding one or more of a scheduling assignment (SA) message, or a medium access control (MAC) control element (CE), or a radio resource control (RRC) message to identify the indication reserving the plurality of shortened TTIs.

14. The method of claim 10 , wherein the request is an RTS, and wherein the method further comprises: sending a CTS message in response to the RTS.

15. The method of claim 10 , further comprising:

receiving an RTS message during the at least one instance of the plurality of shortened TTIs, the RTS message indicating an identifier and a configuration for the priority communications; and

transmitting a CTS message for participating in the priority communications, the CTS message indicating a sequence associating the CTS message with the RTS message.

16. A method for wireless communication, comprising:

receiving, during a listen-before-talk (LBT) procedure, an indication reserving a plurality of shortened transmission time intervals (TTIs) to be used for priority communications to or from a vehicle having a first traffic priority level, the plurality of shortened TTIs each having a duration that is less than that of other TTIs used in other communications to or from the vehicle having a second traffic priority level which is less than the first traffic priority level;

determining that a request-to-send (RTS) message is not transmitted during a first symbol in at least one of the shortened TTIs; and

performing an LBT procedure on resources that overlap in time with the at least one shortened TTI to reserve a TTI that includes the overlapping resources and that is longer than the at least one shortened TTI for other communications having the second traffic priority.

17. The method of claim 16 , wherein receiving the indication further comprises:

determining, based at least in part on the indication, not to participate in the communications to or from the vehicle having the first traffic priority level; and

refraining from transmitting an acknowledgement message during the LBT procedure.

18. The method of claim 16 , wherein receiving the indication further comprises:

receiving the indication on the other TTIs having the second traffic priority level.

19. An apparatus for wireless communication, 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:

identify a plurality of shortened transmission time intervals (TTIs) to be used for priority communications to or from a vehicle having a first traffic priority level, the plurality of shortened TTIs each having a duration that is less than that of other TTIs used in other communications to or from the vehicle having a second traffic priority level which is less than the first traffic priority level;

perform a listen-before-talk (LBT) procedure in order to reserve the plurality of shortened TTIs for the priority communications; and

further reserving via a request-to-send/clear-to-send (RTS/CTS) exchange, at least one instance of the plurality of shortened TTIs for the priority communications, wherein the RTS/CTS exchange is performed for only a portion of the plurality of shortened TTIs, wherein shortened TTIs other than the portion are available for other communications having the second traffic priority level.

20. The apparatus of claim 19 , wherein the instructions to further reserve are executable by the processor to cause the apparatus to:

transmit a request to reserve the at least one instance of the plurality of shortened TTIs for the priority communication.

21. The apparatus of claim 19 , wherein the instructions to perform the LBT procedure further are executable by the processor to cause the apparatus to:

perform the LBT procedure using the other TTIs having the second traffic priority level.

22. The apparatus of claim 19 , wherein the instructions are further executable by the processor to cause the apparatus to:

receive, during the LBT procedure, an acknowledgement (ACK) message from one or more UEs to participate in the priority communications; and

perform the priority communications with the UEs from which ACK messages were received.

23. The apparatus of claim 19 , wherein the instructions to perform the LBT procedure are executable by the processor to cause the apparatus to:

identify a resource tree that comprises a plurality of nodes, each node of the resource tree associated with some or all of a set of available time-frequency resources that include the plurality of shortened TTIs; and

select the node of the resource tree based at least in part on the plurality of shortened TTIs.

24. The apparatus of claim 19 , wherein the instructions are further executable by the processor to cause the apparatus to:

configure one or more of a scheduling assignment (SA) message, or a medium access control (MAC) control element (CE), or a radio resource control (RRC) message to provide an indication in the LBT procedure reserving the plurality of shortened TTIs.

25. The apparatus of claim 19 , wherein the instructions are further executable by the processor to cause the apparatus to:

perform the RTS/CTS exchange for only the portion of the plurality of shortened TTIs based at least in part on an absence of receiving a negative acknowledgment (NACK) in response to the priority communications.

26. The apparatus of claim 19 , wherein the instructions are further executable by the processor to cause the apparatus to:

transmit an RTS message during the at least one instance of the plurality of shortened TTIs, the RTS message indicating an identifier and a configuration for the priority communications; and

receive a CTS message from one or more wireless devices participating in the priority communications, the CTS message indicating a sequence associating the CTS message with the RTS message.