Establishment of a UE to UE relay link

1. A method for wireless communications by a first user equipment (UE), comprising:

receiving a relay link beam sweep configuration from a base station for establishing a relay link with a second UE, wherein the relay link beam sweep configuration indicates a transmit beam sweep opportunity for the first UE, a receive beam sweep opportunity for the first UE, or both;

performing a relay link beam sweep procedure with the second UE using a plurality of beams based at least in part on the relay link beam sweep configuration, wherein the relay link beam sweep procedure is performed during the transmit beam sweep opportunity, the receive beam sweep opportunity, or both;

selecting a first beam pair based at least in part on the relay link beam sweep procedure; and

establishing a relay link with the second UE using the first beam pair.

2. The method of claim 1 , wherein receiving the relay link beam sweep configuration comprises:

receiving the relay link beam sweep configuration that indicates a transmit beam sweep opportunity parameter for the first UE, wherein the relay link beam sweep procedure is performed within a first transmit beam sweep opportunity corresponding to the transmit beam sweep opportunity parameter.

3. The method of claim 2 , wherein performing the relay link beam sweep procedure comprises:

transmitting a reference signal using a first subset of a plurality of beams in the first transmit beam sweep opportunity and a second subset of the plurality of beams in a second transmit beam sweep opportunity corresponding to the transmit beam sweep opportunity parameter.

4. The method of claim 1 , wherein receiving the relay link beam sweep configuration comprises:

receiving the relay link beam sweep configuration that indicates a receive beam sweep opportunity parameter for the first UE, wherein the relay link beam sweep procedure is performed within a first receive beam sweep opportunity corresponding to the receive beam sweep opportunity parameter.

5. The method of claim 4 , wherein performing the relay link beam sweep procedure comprises:

monitoring for a reference signal transmitted by the second UE using a first subset of the plurality of beams in the first receive beam sweep opportunity and a second subset of the plurality of beams in a second receive beam sweep opportunity corresponding to the receive beam sweep opportunity parameter.

6. The method of claim 1 , wherein establishing the relay link with the second UE comprises:

transmitting a random access channel message to the second UE using a transmission beam of the first beam pair at the first UE; and

receiving a random access channel response from the second UE using a receive beam of the first beam pair at the first UE.

7. The method of claim 1 , wherein performing the relay link beam sweep procedure comprises:

generating a measurement for each beam pair of a plurality of beam pairs based at least in part on cycling through the plurality of beam pairs.

8. The method of claim 7 , further comprising:

selecting the first beam pair based at least in part on the measurements.

9. The method of claim 7 , further comprising:

transmitting, to the base station, a measurement report comprising one or more of the measurements, wherein the relay link is established based at least in part on receiving an instruction from the base station to establish the relay link using the first beam pair.

10. The method of claim 1 , wherein performing the relay link beam sweep procedure comprises:

transmitting or monitoring for a reference signal generated based at least in part on a synchronization signal sequence.

11. The method of claim 1 , wherein performing the relay link beam sweep procedure comprises:

receiving a reference signal;

decoding a synchronization signal sequence from the reference signal; and

determining a timing offset based at least in part on the synchronization signal sequence, wherein the relay link is established based at least in part on the timing offset.

12. The method of claim 1 , wherein establishing the relay link with the second UE comprises:

transmitting a random access request to the second UE in a random access opportunity; and

receiving a random access response from the second UE based at least in part on the random access request.

13. The method of claim 1 , wherein establishing the relay link with the second UE comprises:

receiving a random access request from the second UE in a first random access opportunity or a second random access opportunity that occurs after the first random access opportunity; and

transmitting a random access response to the first UE based at least in part on the random access request.

14. The method of claim 1 , further comprising:

transmitting an identifier of the second UE, beam pair information of the first beam pair, or both, to the base station.

15. The method of claim 1 , wherein receiving the relay link beam sweep configuration comprises:

receiving the relay link beam sweep configuration that indicates a periodic resource in which to perform the relay link beam sweep procedure.

16. The method of claim 15 , wherein the periodic resource is a configured synchronization signal block resource or differs from the configured synchronization signal block resource.

17. The method of claim 15 , wherein receiving the relay link beam sweep configuration comprises:

receiving the relay link beam sweep configuration that indicates that a first plurality of UEs including the first UE to perform a transmit beam sweep procedure in a first instance of the periodic resource and a second plurality of UEs including the second UE to perform a receive beam sweep procedure in the first instance of the periodic resource.

18. The method of claim 15 , wherein receiving the relay link beam sweep configuration comprises:

receiving the relay link beam sweep configuration that indicates that a first plurality of UEs including the first UE to perform a receive beam sweep procedure in a first instance of the periodic resource and a second plurality of UEs including the second UE to perform a transmit beam sweep procedure in the first instance of the periodic resource.

19. The method of claim 1 , further comprising:

determining to perform the relay link beam sweep procedure based at least in part on at least one parameter.

20. The method of claim 19 , wherein the at least one parameter is one or more of a network identifier, a cell identifier, a radio network temporary identifier, a temporary mobile subscriber identity, a temporary identifier, or any combination thereof.

21. The method of claim 1 , further comprising:

detecting each beam pair of a plurality of beam pairs does not satisfy a threshold based at least in part on performing the relay link beam sweep procedure; and

repeating the relay link beam sweep procedure to identify the first beam pair.

22. The method of claim 21 , further comprising:

waiting for a random backoff time period prior to repeat the relay link beam sweep procedure.

23. The method of claim 1 , further comprising:

transmitting data to the second UE via the relay link for forwarding to the base station.

24. The method of claim 1 , further comprising:

receiving data from the base station via the second UE and the relay link.

25. A method for wireless communications by a base station, comprising:

transmitting a relay link beam sweep configuration to a first user equipment (UE) and a second UE, wherein the relay link beam sweep configuration indicates a transmit beam sweep opportunity for the first UE, a receive beam sweep opportunity for the first UE, or both; and

receiving an indication of a relay link established between the first UE and the second UE based at least in part on the relay link beam sweep configuration.

26. The method of claim 25 , wherein transmitting the relay link beam sweep configuration comprises:

transmitting the relay link beam sweep configuration that indicates a beam sweep opportunity parameter for indicating at least one opportunity to perform a relay link beam sweep procedure.

27. The method of claim 25 , wherein transmitting the relay link beam sweep configuration comprises:

transmitting the relay link beam sweep configuration that indicates a periodic resource in which to perform a relay link beam sweep procedure.

28. The method of claim 27 , wherein transmitting the relay link beam sweep configuration comprises:

transmitting the relay link beam sweep configuration that indicates that a first plurality of UEs including the first UE is to perform a first of a transmit beam sweep procedure or a receive beam sweep procedure in a first instance of the periodic resource and a second plurality of UEs including the second UE is to perform a second of the transmit beam sweep procedure or the receive beam sweep procedure in the first instance of the periodic resource.

29. An apparatus for wireless communications by a first user equipment (UE), 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:

receive a relay link beam sweep configuration from a base station for establishing a relay link with a second UE, wherein the relay link beam sweep configuration indicates a transmit beam sweep opportunity for the first UE, a receive beam sweep opportunity for the first UE, or both;

perform a relay link beam sweep procedure with the second UE using a plurality of beams based at least in part on the relay link beam sweep configuration, wherein the relay link beam sweep procedure is performed during the transmit beam sweep opportunity, the receive beam sweep opportunity, or both;

select a first beam pair based at least in part on the relay link beam sweep procedure; and

establish a relay link with the second UE using the first beam pair.

30. An apparatus for wireless communications by a base station, 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:

transmit a relay link beam sweep configuration to a first user equipment (UE) and a second UE, wherein the relay link beam sweep configuration indicates a transmit beam sweep opportunity for the first UE, a receive beam sweep opportunity for the first UE, or both; and

receive an indication of a relay link established between the first UE and the second UE based at least in part on the relay link beam sweep configuration.