Physical channel and resource determination for collision resolution inter-UE coordination signaling in NR V2X

1 . An apparatus for a first user equipment (UE), the apparatus comprising:

processing circuitry to configure the first UE to:

receive a first sidelink message from a second UE;

transmit, to the other second UE, a second sidelink message;

in response to transmission of the second sidelink message, receive, from the second UE, inter-UE coordination feedback containing a conflict indication that indicates a collision of the second sidelink message or with a future sidelink message from the first UE, the collision indicating simultaneous access of a channel using overlapping resources, the conflict indication being at least 1 bit, the conflict indication having a physical sidelink feedback channel (PSFCH) physical structure with a 1 physical resource block (PRB) frequency domain allocation and a 2 symbol time domain allocation, the PSFCH physical structure reused for both transmision of the conflict indication and transmission of sidelink Hybrid Automatic Repeat Request Acknowledgment (SL HARQ-ACK) feedback; and

in response to reception of the conflict indication, take action to resolve the collision; and

a memory configured to store the inter-UE coordination feedback.

2 . The apparatus of claim 1 , wherein:

the conflict indication is 1 bit, and

the conflict indication and the SL HARQ-ACK feedback co-exist in a same resource pool using the PSFCH physical structure.

3 . The apparatus of claim 1 , wherein:

the conflict indication is 2 bits encoded using different frequency shifts of a sequence mapped to 12 resource elements, and

the conflict indication and the SL HARQ-ACK feedback co-exist in a same resource pool using the PSFCH physical structure.

4 . The apparatus of claim 1 , wherein:

the conflict indication is 2 bits, and

the conflict indication has a frequency domain allocation size of at least 2 physical resource blocks (PRB).

5 . The apparatus of claim 1 , wherein slots for transmission of the conflict indication are configured as a full set or as a subset of slots for transmission of a PSFCH for the SL HARQ-ACK feedback in a sidelink resource pool.

6 . The apparatus of claim 1 , wherein frequency resources for transmission of the conflict indication are configured as a PRB pattern separate from resources of a PSFCH.

7 . The apparatus of claim 1 , wherein a starting symbol in a slot for the conflict indication is L_end+1 where L_end is a last symbol of a physical sidelink shared channel (PSSCH) in a slot.

8 . The apparatus of claim 1 , wherein the conflict indication is differentiated from a PSFCH using a base sequence for the conflict indication that is configured separately per resource pool from a PSFCH-based sequence.

9 . The apparatus of claim 1 , wherein the conflict indication is differentiated from a PSFCH using a cyclic shift for the conflict indication that is configured separately per resource pool from a PSFCH-based sequence.

10 . The apparatus of claim 1 , wherein the conflict indication is encoded using a Reed-Muller coding scheme for at most 11 bits and a Polar Coding scheme for greater than 11 bits.

11 . The apparatus of claim 10 , wherein a starting physical resource block (PRB) of the conflict indication is a function of at least one of:

a starting sub-channel of a physical sidelink control channel (PSCCH) of the second sidelink message,

a number of physical resource blocks (PRB) of a PSSCH allocation of the second sidelink message,

a source layer 1 (L1) identity,

a destination L1 identity, or

a sidelink control information (SCI) format 1 or SCI format 2 payload dedicated to resource determination of the conflict indication.

12 . The apparatus of claim 1 , wherein:

the conflict indication is at least two bits, and

each bit of the conflict indication is carried separately by a different PRB PSFCH channel such that the first UE receives a 1 PRB PSFCH channel in a first resource in response to one type of conflict being detected, and the 1 PRB PSFCH channel in the first resource and in a second resource in response to two types of conflict being detected.

13 . The apparatus of claim 1 , wherein at least one of:

HARQ feedback transmission or reception is prioritized over transmission or reception of the inter-UE coordination feedback,

the inter-UE coordination feedback is associated with sidelink transmission priority and the sidelink transmission priority is used to determine which of the inter-UE coordination feedback and HARQ feedback to prioritize,

transmission priority of the conflict indication is reduced in response to conflict detection on a retransmission of the conflict indication that is later than a first retransmission of the conflict indication,

transmission of the conflict indication is dependent on a congestion metric exceeding a congestion threshold, or

transmission of the conflict indication is dependent on whether an earlier conflict indication of a same conflict indication has already been transmitted.

14 . The apparatus of claim 1 , wherein the processing circuitry further configures the first UE to ignore the conflict indication in response to at least one of:

determination of successful delivery of the second sidelink message to intended receivers based on reception of an acknowledgment from the receivers,

a time for a next transmission is smaller than a time to make changes to the next transmission,

resources to be used for a predetermined set of retransmissions of the second sidelink message, or

the second UE meeting at least one predetermined criterion.

15 . The apparatus of claim 14 , wherein the at least one predetermined criterion is selected from at least one of: being below a minimum Reference Signal Received Power (RSRP), being below a minimum Reference Signal Received Quality (RSRQ), having a particular identity (ID), or being beyond a predetermined range from the first UE.

16 . An apparatus for a first user equipment (UE), the apparatus comprising:

processing circuitry configured to configure the first UE to:

transmit a first sidelink message to a second UE;

receive, from the second UE, a second sidelink message;

in response to reception of the second sidelink message, detect a collision with the second sidelink message or with a future sidelink message from the first UE, the collision indicating simultaneous access of a channel using overlapping resources;

determine whether to provide a conflict indication to the second UE;

in response to a determination to provide the conflict indication to the second UE, report, to the second UE, the conflict indication as inter-UE coordination feedback; and

at least one of:

determine whether to transmit, or reduce transmission priority of, the conflict indication dependent on whether the second sidelink message is a retransmission of an earlier sidelink transmission based on at least one of preconfiguration, whether a sidelink control information (SCI) format of the second sidelink message conveys a retransmission index, or a flag in the SCI format indicates that the conflict indication is allowed in response to the second sidelink message,

detect a congestion metric of a channel to be used to transmit the conflict indication and determine whether to transmit the conflict indication dependent on whether the congestion metric exceeds a congestion threshold, and

detect whether an earlier conflict indication has been previously transmitted that indicates a collision with a transport block used to transmit the second sidelink message; and

a memory configured to store the inter-UE coordination feedback.

17 . A non-transitory computer-readable storage medium that stores instructions for execution by one or more processors of a first user equipment (UE), the one or more processors to configure the first UE to, when the instructions are executed:

receive a first sidelink message from a second UE;

transmit, to the other second UE, a second sidelink message;

in response to transmission of the second sidelink message, receive, from the second UE, inter-UE coordination feedback containing a conflict indication that indicates a collision of the second sidelink message or with a future sidelink message from the first UE, the collision indicating simultaneous access of a channel using overlapping resources, the conflict indication being at least 1 bit, the conflict indication having a physical sidelink feedback channel (PSFCH) physical structure with a 1 physical resource block (PRB) frequency domain allocation and a 2 symbol time domain allocation, the PSFCH physical structure reused for both transmission of the conflict indication and transmission of sidelink Hybrid Automatic Repeat Request Acknowledgment (SL HARQ-ACK) feedback; and

in response to reception of the conflict indication, take action to resolve the collision.

18 . The non-transitory computer-readable storage medium of claim 17 , wherein the conflict indication is 2 bits encoded using different frequency shifts of a sequence mapped to 12 resource elements.