Method and apparatus for non-codebook based uplink multiple-input and multiple-output

1. A method implemented by a user equipment (UE), the method comprising:

receiving an allocation of at least one sounding reference signal (SRS) resource in an uplink subframe from a transmission and reception point (TRP) for a first set of uplink transmission beams;

transmitting precoded SRSs in the at least one SRS resource to the TRP, wherein the precoded SRSs are precoded with UE-selected precoders and at least one rank; and

receiving an identification of one or more precoders for a second set of uplink transmission beams, wherein the second set of uplink transmission beams is selected from the first set of uplink transmission beams, and wherein the one or more precoders are based on the precoded SRSs.

2. The method of claim 1 , wherein the at least one SRS resource is a single SRS resource comprising a plurality of antenna ports corresponding to the second set of uplink transmission beams.

3. The method of claim 1 , wherein the at least one SRS resource comprises at least one SRS resource for each uplink transmission beam, and wherein the at least one SRS resource includes at least one antenna port.

4. The method of claim 1 , wherein the at least one SRS resource comprises a plurality of SRS resources for each uplink transmission beam, and wherein each SRS resource has at least one SRS antenna port.

5. The method of claim 1 , wherein transmitting the precoded SRSs comprises transmitting the precoded SRSs with a single UE-selected rank, and wherein the single UE-selected rank is determined by the UE over all selected uplink transmission beams.

6. The method of claim 1 , wherein transmitting the precoded SRSs comprises transmitting the precoded SRSs with a plurality of UE-selected ranks.

7. The method of claim 1 , wherein the first set of uplink transmission beams is selected from a third set of uplink transmission beams reported to the TRP by the UE.

8. The method of claim 1 , wherein a precoder and a rank for each uplink transmission beam are determined based on downlink channel estimation and channel reciprocity.

9. The method of claim 1 , further comprising receiving co-phasing between selected antenna ports from the TRP.

10. A method implemented by a transmission and reception point (TRP), the method comprising:

sending an allocation of at least one sounding reference signal (SRS) resource in a uplink subframe to a user equipment (UE) for a first set of uplink transmission beams;

receiving precoded SRSs sent in the at least one SRS resource, wherein the precoded SRSs are precoded with UE selected precoders and at least one rank; and

sending an identification of one or more precoders for a second set of uplink transmission beams to the UE, wherein the second set of uplink transmission beams is selected from the first set of uplink transmission beams, and wherein the one or more precoders for the second set of uplink transmission beams are based on the precoded SRSs.

11. The method of claim 10 , wherein the at least one SRS resource is a single SRS resource comprising a plurality of antenna ports corresponding to the second set of uplink transmission beams.

12. The method of claim 10 , wherein the at least one SRS resource comprises at least one SRS resource for each uplink transmission beam, and wherein the at least one SRS resource includes at least one antenna port.

13. The method of claim 10 , wherein the at least one SRS resource comprises a plurality of SRS resources for each uplink transmission beam, and wherein each SRS resource has at least one SRS antenna port.

14. The method of claim 10 , wherein receiving the SRSs comprises receiving the SRSs with a single UE-selected rank, and wherein the single UE-selected rank is determined by the UE over all selected UL transmission beams.

15. The method of claim 10 , wherein receiving the SRSs comprises receiving the SRSs with a plurality of UE-selected selected ranks.

16. The method of claim 10 , wherein the first set of uplink transmission beams is selected from a third set of uplink transmission beams reported to the TRP by the UE.

17. The method of claim 10 , wherein a precoder and a rank for each selected uplink transmission beam is based on downlink channel estimation and channel reciprocity.

18. The method of claim 10 , further comprising sending co-phasing between selected antenna ports from the TRP.

19. A user equipment (UE) comprising:

a processor; and

a non-transitory computer readable storage medium storing programming for execution by the processor, the programming including instructions to:

receive an allocation of at least one sounding reference signal (SRS) resource in an uplink subframe from a transmission and reception point (TRP) for a first set of uplink transmission beams;

transmit precoded SRSs in the at least one SRS resource to the TRP, wherein the precoded SRSs are precoded with UE-selected precoders and at least one rank; and

receive an identification of one or more precoders for a second set of uplink transmission beams, wherein the second set of uplink transmission beams is selected from the first set of uplink transmission beams, and wherein the one or more precoders are based on the precoded SRSs.

20. A transmission and reception point (TRP) comprising:

a processor; and

a non-transitory computer readable storage medium storing programming for execution by the processor, the programming including instructions to:

send an allocation of at least one sounding reference signal (SRS) resource in a uplink subframe to a user equipment (UE) for a first set of uplink transmission beams;

receive precoded SRSs sent in the at least one SRS resource, wherein the precoded SRSs are precoded with UE selected precoders and at least one rank; and

send an identification of one or more precoders for a second set of uplink transmission beams to the UE, wherein the second set of uplink transmission beams is selected from the first set of uplink transmission beams, and wherein the one or more precoders for the second set of uplink transmission beams are based on the precoded SRSs.

21. The method of claim 1 , further comprising transmitting data based on the one or more precoders.

22. The method of claim 10 , further comprising receiving data based on the one or more precoders.