Adaptive sounding reference signal port configuration
Various aspects of the present disclosure generally relate to wireless communication. In some aspects, a user equipment (UE) may receive a sounding reference signal (SRS) configuration that indicates a maximum number of SRS ports and whether the UE is permitted to determine an actual number of SRS ports to be used for SRS transmission that is different from the maximum number of SRS ports. The UE may determine the actual number of SRS ports to be used for SRS transmission based at least in part on the SRS configuration. The UE may transmit one or more SRSs using the actual number of SRS ports. Numerous other aspects are provided.
1. A method of wireless communication performed by a user equipment (UE), comprising:
receiving a sounding reference signal (SRS) configuration that indicates a maximum number of SRS ports and indicates, based at least in part on a value of a bit in the SRS configuration, whether the UE is permitted to determine an actual number of SRS ports to be used for SRS transmission that is different from the maximum number of SRS ports;
determining the actual number of SRS ports to be used for SRS transmission based at least in part on the SRS configuration; and
transmitting one or more SRSs using the actual number of SRS ports that is different from the maximum number of SRS ports indicated in the SRS configuration.
2. The method of claim 1 , wherein the actual number of SRS ports is equal to a configured number of SRS ports for an SRS resource set, indicated in the SRS configuration, if the UE is not permitted to determine an actual number of SRS ports that is different from the maximum number of SRS ports.
3. The method of claim 1 , wherein the actual number of SRS ports is determined based at least in part on the maximum number of SRS ports and a rank indicator (RI) value determined by the UE.
4. The method of claim 3 , wherein the actual number of SRS ports is equal to a minimum value of the maximum number of SRS ports and the RI value.
5. The method of claim 3 , wherein the actual number of SRS ports is equal to a maximum value of the maximum number of SRS ports and the RI value.
6. The method of claim 1 , wherein the one or more SRSs are transmitted using a same transmit power for each of the actual number of ports.
7. The method of claim 1 , wherein SRS transmission is muted on one or more SRS ports if the actual number of SRS ports is less than the maximum number of SRS ports.
8. The method of claim 1 , wherein SRS transmission is repeated on one or more SRS ports if the actual number of SRS ports is equal to the maximum number of SRS ports.
9. The method of claim 1 , wherein a UE capability indicates that a number of transmit antennas of the UE is equal to a number of receive antennas of the UE, and wherein the maximum number of SRS ports is equal to the number of transmit antennas and is equal to the number of receive antennas.
10. The method of claim 1 , wherein the maximum number of SRS ports is indicated using a number of SRS ports parameter for an SRS resource.
11. The method of claim 10 , wherein the actual number of SRS ports is less than or equal to the number of SRS ports parameter for the SRS resource.
12. The method of claim 1 , wherein a UE capability indicates that a number of transmit antennas of the UE is less than a number of receive antennas of the UE, and wherein the UE is configured with a number of SRS resources, in an SRS resource set, that is equal to the maximum number of SRS ports.
13. The method of claim 12 , wherein different SRS resources, of the number of SRS resources, occur in different symbols of a same slot, and wherein the one or more SRSs are transmitted in the different SRS resources using different SRS ports.
14. The method of claim 12 , wherein different SRS resources, of the number of SRS resources, occur in different slots, and wherein the one or more SRSs are transmitted in the different SRS resources using different SRS ports.
15. The method of claim 1 , further comprising receiving an indication of whether to transmit a rank indicator (RI) report and selectively transmitting the RI report based at least in part on the indication.
16. The method of claim 15 , wherein the indication indicates that the RI report is to be transmitted when one or more SRS symbols overlap with one or more physical uplink control channel symbols, or that the RI report is not to be transmitted when SRS symbols do not overlap with physical uplink control channel symbols.
17. The method of claim 1 , wherein one or more muted SRS resources are used to transmit an uplink communication other than an SRS when the actual number of SRS ports is less than the maximum number of SRS ports and the UE is configured to transmit a rank indicator report.
18. A method of wireless communication performed by a network entity, comprising:
transmitting, to a user equipment (UE), a sounding reference signal (SRS) configuration that indicates a maximum number of SRS ports allowed for the UE and indicates, based at least in part on a value of a bit in the SRS configuration, that the UE is permitted to determine an actual number of SRS ports to be used for SRS transmission that is different from the maximum number of SRS ports;
determining, based at least in part on the SRS configuration, whether one or more SRS symbols overlap with one or more physical uplink control channel (PUCCH) symbols; and
transmitting, to the UE, an indication of whether to transmit a rank indicator (RI) report based at least in part on whether the one or more SRS symbols overlap with the one or more PUCCH symbols.
19. The method of claim 18 , further comprising determining an RI value based at least in part on the actual number of SRS ports used for SRS transmissions by the UE when the indication indicates not to transmit the RI report.
20. The method of claim 19 , wherein the RI value is equal to the actual number of SRS ports.
21. The method of claim 18 , wherein the indication indicates not to transmit the RI report based at least in part on a determination that the one or more SRS symbols and the one or more PUCCH symbols do not overlap.
22. The method of claim 18 , wherein the indication indicates to transmit the RI report based at least in part on a determination that the one or more SRS symbols and the one or more PUCCH symbols overlap.
23. The method of claim 18 , wherein the indication indicates not to transmit the RI report based at least in part on a determination that the one or more SRS symbols are configured on a first carrier and the one or more PUCCH symbols are configured on a second carrier.
24. The method of claim 18 , wherein the indication indicates not to transmit the RI report based at least in part on a determination that the one or more SRS symbols and the one or more PUCCH symbols occur on non-overlapping symbols of a same carrier.
25. The method of claim 18 , wherein the indication indicates to transmit the RI report based at least in part on a determination that the one or more SRS symbols and the one or more PUCCH symbols occur on overlapping symbols of a same carrier.
26. A user equipment (UE) for wireless communication, comprising:
one or more memories; and
one or more processors operatively coupled to the one or more memories, the one or more memories and the one or more processors configured to:
receive a sounding reference signal (SRS) configuration that indicates a maximum number of SRS ports and indicates, based at least in part on a value of a bit in the SRS configuration, whether the UE is permitted to determine an actual number of SRS ports to be used for SRS transmission that is different from the maximum number of SRS ports;
determine the actual number of SRS ports to be used for SRS transmission based at least in part on the SRS configuration; and
transmit one or more SRSs using the actual number of SRS ports that is different from the maximum number of SRS ports indicated in the SRS configuration.
27. The UE of claim 26 , wherein the actual number of SRS ports is equal to a configured number of SRS ports for an SRS resource set, indicated in the SRS configuration, if the UE is not permitted to determine an actual number of SRS ports that is different from the maximum number of SRS ports.
28. The UE of claim 26 , wherein the actual number of SRS ports is determined based at least in part on the maximum number of SRS ports and a rank indicator (RI) value determined by the UE.
29. The UE of claim 26 , wherein the one or more SRSs are transmitted using a same transmit power for each of the actual number of ports.
30. A network entity for wireless communication, comprising:
one or more memories; and
one or more processors operatively coupled to the one or more memories, the one or more memories and the one or more processors configured to:
transmit, to a user equipment (UE), a sounding reference signal (SRS) configuration that indicates a maximum number of SRS ports allowed for the UE and indicates, based at least in part on a value of a bit in the SRS configuration, that the UE is permitted to determine an actual number of SRS ports to be used for SRS transmission that is different from the maximum number of SRS ports;
determine, based at least in part on the SRS configuration, whether one or more SRS symbols overlap with one or more physical uplink control channel (PUCCH) symbols; and
transmit, to the UE, an indication of whether to transmit a rank indicator (RI) report based at least in part on whether the one or more SRS symbols overlap with the one or more PUCCH symbols.