Methods and system for establishing multiple starting points for sidelink transmissions

1. A method of wireless communication performed by a first user equipment (UE), the method comprising:

performing a channel access procedure to access a first physical sidelink shared channel (PSSCH) transmission resource of an unlicensed new radio spectrum including a first slot with a predetermined number of orthogonal frequency division multiplexing (OFDM) symbols starting at a slot boundary and a plurality of transmission starting points, an initial transmission starting point of the plurality of transmission starting points being at the slot boundary and other transmission starting points of the plurality of transmission starting points being at other OFDM symbols of the first slot,

reserving, via a control message, the first PSSCH transmission resource; and

transmitting first data to a second UE via the first PSSCH transmission resource using a portion less than all of the predetermined number of OFDM symbols of the first slot starting at a later transmission starting point of the first slot than one or more prior transmission starting points of the plurality of transmission starting points of the first slot when the performing the channel access procedure fails at each of the one or more prior transmission starting points,

the one or more prior transmission starting points including the initial transmission starting point.

2. The method of claim 1 , wherein the first data is a portion of a transport block configured for transmission, via the first PSSCH transmission resource, starting at the initial transmission starting point of the plurality of transmission starting points.

3. The method of claim 1 , wherein the control message is a sidelink control information (SCI), the method further comprising:

transmitting, to the second UE, the SCI to reserve one or more PSSCH transmission resources including the first PSSCH transmission resource.

4. The method of claim 3 , wherein:

the one or more PSSCH transmission resources include at least two PSSCH transmission resources; and

the SCI is configured to reserve the at least two PSSCH transmission resources for transmitting a same transport block.

5. The method of claim 4 , wherein the at least two PSSCH transmission resources include the first PSSCH transmission resource and a second PSSCH transmission resource, the method further comprising:

retransmitting, to the second UE, a transport block via the second PSSCH transmission resource without receiving a hybrid automatic request acknowledgment (HARQ ACK) from the second UE after transmitting the transport block to the second UE via the first PSSCH transmission resource.

6. The method of claim 3 , wherein:

the one or more PSSCH transmission resources include at least two PSSCH transmission resources; and

the SCI is configured to reserve the at least two PSSCH transmission resources for transmitting different transport blocks.

7. The method of claim 3 , further comprising:

transmitting, to the second UE, a scrambled DMRS sequence configured to include identifying information of the first UE when a number of bits of the SCI associated with the first data is no greater than a threshold number of bits.

8. The method of claim 3 , wherein the transmission of the first data occurs after the first UE receives an ACK from the second UE acknowledging receiving the transmitted SCI reserving the first PSSCH transmission resource.

9. The method of claim 3 , wherein:

the SCI is transmitted to the second UE with second data; and

the transmission of the first data occurs after the first UE receives an HARQ ACK from the second UE acknowledging receiving the second data.

10. The method of claim 1 , further comprising:

receiving, from a base station of a wireless communication network to which the first UE is connected, a configured grant (CG) configured to allocate the first PSSCH transmission resource to the first UE.

11. The method of claim 10 , further comprising:

transmitting, to the second UE, the control message to reserve the first PSSCH transmission resource for the first UE to transmit to the second UE a transport block that includes the first data.

12. The method of claim 1 , further comprising:

receiving, from the second UE, a second control message configured to poll the first UE to collect a transport block that includes the first data.

13. The method of claim 1 , wherein the control message is a medium access control (MAC)-control element (CE) or a proximity-based communication (Interface) 5 radio resource control (RRC) message.

14. The method of claim 1 , wherein the control message is a downlink control information (DCI), the method further comprising:

receiving, from a base station of a wireless communication network to which the first UE and the second UE are connected, the DCI to allocate the first PSSCH transmission resource for the first UE to transmit to the second UE a transport block that includes the first data.

15. The method of claim 14 , wherein an enhanced DCI coupled to the DCI is transmitted from the base station to the second UE to reserve the allocated first PSSCH transmission resource for the first UE to transmit to the second UE a transport block that includes the first data.

16. A first user equipment (UE), comprising:

a memory; and

a processor coupled to the memory, the processor configured to:

perform a channel access procedure to access a first physical sidelink shared channel (PSSCH) transmission resource of an unlicensed new radio spectrum including a first slot with a predetermined number of orthogonal frequency division multiplexing (OFDM) symbols starting at a slot boundary and a plurality of transmission starting points, an initial transmission starting point of the plurality of transmission starting points being at the slot boundary and other transmission starting points of the plurality of transmission starting points being at other OFDM symbols of the first slot,

reserve, via a control message, the first PSSCH transmission resource; and

transmit first data to a second UE via the first PSSCH transmission resource using a portion less than all of the predetermined number of OFDM symbols of the first slot starting at a later transmission starting point of the first slot than one or more prior transmission starting points of the plurality of transmission starting points of the first slot when the performing the channel access procedure fails at each of the one or more prior transmission starting points,

the one or more prior transmission starting points including the initial transmission starting point.

17. The first UE of claim 16 , wherein the control message is a sidelink control information (SCI), the first UE further comprising a transceiver configured to:

receive, from a third UE, the SCI to reserve the first PSSCH transmission resource for the first UE to transmit to the second UE a transport block that includes the first data.

18. The first UE of claim 16 , wherein the first PSSCH transmission resource is reserved for transmitting a first transport block including the first data, the processor further configured to:

monitor the first PSSCH transmission resource for a SCI for an indication of an upcoming transmission, by a third UE, of a second transport block via the first PSSCH transmission resource.

19. The first UE of claim 18 , wherein the processor is further configured to:

abort the transmission of the first data when the indication indicates that the second transport block has higher priority than the first transport block.

20. The first UE of claim 16 , wherein the processor is further configured to:

monitor a physical sidelink control channel (PSCCH) transmission resource of the unlicensed new radio spectrum for a demodulation reference signal (DMRS) for an indication of an upcoming transmission, by a third UE, of a second transport block via the first PSSCH transmission resource.

21. The first UE of claim 16 , wherein the processor is further configured to:

transmit, to the second UE, a scrambled DMRS sequence configured to include identifying information of the first UE.

22. The first UE of claim 16 , wherein a last transmission starting point of the plurality of transmission starting points immediately precedes a last DMRS symbol of the PSSCH transmission resource.

23. The first UE of claim 16 , wherein each transmission starting point of the plurality of transmission starting points immediately precedes a respective DMRS symbol of a plurality of DMRS symbols of the PSSCH transmission resource.

24. The first UE of claim 16 , wherein:

the channel access procedure includes:

a first channel access procedure for transmitting starting at the initial transmission starting point, the first channel access procedure associated with a random number within a contention window; and

a second channel access procedure for transmitting starting at the later transmission starting point, the second channel access procedure associated with a subsequent random number within the contention window; and

the processor is configured to perform the second channel access procedure after failure of the first channel access procedure to transmit starting at the initial transmission starting point.

25. The first UE of claim 16 , further comprising a transceiver configured to:

transmit, to the second UE and after the transmission of the first data, a SCI including information about the later transmission starting point.

26. The first UE of claim 16 , wherein:

the channel access procedure includes a first channel access procedure for transmitting starting at the initial transmission starting point and a second channel access procedure for transmitting the first data starting at the later transmission starting point; and

an energy detection threshold level of the first channel access procedure is lower than an energy detection threshold level of the second channel access procedure.

27. The first UE of claim 16 , wherein the processor is further configured to:

monitor the first PSSCH transmission resource for a SCI for an indication of an upcoming transmission of a second transport block over the first PSSCH transmission resource; and

abort the transmission of the first data based on the indication.

28. The first UE of claim 27 , wherein the indication indicates that the second transport block has higher priority than the first transport block and/or the SCI has an energy level exceeding a pre-determined energy detection threshold.

29. A non-transitory computer-readable medium (CRM) having program code recorded thereon, the program code comprising:

code for causing a first user equipment (UE) to perform a channel access procedure to access a physical sidelink shared channel (PSSCH) transmission resource of an unlicensed new radio spectrum including a first slot with a predetermined number of orthogonal frequency division multiplexing (OFDM) symbols starting at a slot boundary and a plurality of transmission starting points, an initial transmission starting point of the plurality of transmission starting points being at the slot boundary and other transmission starting points of the plurality of transmission starting points being at other OFDM symbols of the first slot,

code for causing the first UE to reserve, via a control message, the PSSCH transmission resource; and

code for causing the first UE to transmit data to a second UE via the PSSCH transmission resource using a portion less than all of the predetermined number of OFDM symbols of the first slot starting at a later transmission starting point of the first slot than one or more prior transmission starting points of the plurality of transmission starting points of the first slot when the performing the channel access procedure fails at each of the one or more prior transmission starting points,

the one or more prior transmission starting points including the initial transmission starting point.

30. A first user equipment (UE), comprising:

means for performing a channel access procedure to access a physical sidelink shared channel (PSSCH) transmission resource of an unlicensed new radio spectrum including a first slot with a predetermined number of orthogonal frequency division multiplexing (OFDM) symbols starting at a slot boundary and a plurality of transmission starting points, an initial transmission starting point of the plurality of transmission starting points being at the slot boundary and other transmission starting points of the plurality of transmission starting points being at other OFDM symbols of the first slot,

means for reserving, via a control message, the PSSCH transmission resource; and

means for transmitting data to a second UE via the PSSCH transmission resource using a portion less than all of the predetermined number of OFDM symbols of the first slot starting at a later transmission starting point of the first slot than one or more prior transmission starting points of the plurality of transmission starting points of the first slot when the performing the channel access procedure fails at each of the one or more prior transmission starting points,

the one or more prior transmission starting points including the initial transmission starting point.