Spatial SRS sounding adaptation in LOS MIMO

1 . A method of wireless communication at a receiving device, comprising:

receiving a configuration of a persistent or semi-persistent sounding reference signal (SRS) resource set that configures a first number of SRS ports for a full spatial sounding mode;

transmitting a SRS on a partial sounding resource subset of the SRS resource set, the partial sounding resource subset corresponding to a partial sounding line of sight multiple-input-multiple-output (LSM) mode;

autonomously activating the partial sounding LSM mode in response to a measurement at the receiving device, wherein the measurement at the receiving device is an estimated line of sight percentage or an estimated spectral efficiency factor for the partial sounding LSM mode; and

sending an indication of the partial sounding LSM mode to a serving base station.

2 . The method of claim 1 , further comprising determining that partial sounding is to be used in response to receiving a downlink control information (DCI) or a media access control (MAC) control element (CE) that indicates an adaptation of a number of transmit antennas or receive antennas.

3 . The method of claim 1 , further comprising determining that partial sounding is to be used in response to receiving a DCI or a MAC-CE that indicates a change to the partial sounding LSM mode.

4 . The method of claim 1 , wherein the configuration of the persistent or semi-persistent SRS resource set indicates SRS ports to be skipped or deactivated in the partial sounding LSM mode.

5 . The method of claim 1 , further comprising returning to the full spatial sounding mode in response to expiration of a timer or detection of a performance degradation.

6 . The method of claim 5 , further comprising indicating the full spatial sounding mode or a performance metric associated with the performance degradation to the serving base station.

7 . The method of claim 6 , wherein the indication is a request to fall back to the full spatial sounding mode.

8 . The method of claim 1 , wherein the partial sounding resource subset corresponds to SRS ports for corner antennas of an antenna array of the receiving device.

9 . The method of claim 1 , wherein transmitting the SRS on the partial sounding resource subset comprises setting SRS ports that are in the SRS resource set but not in the partial sounding resource subset to zero power.

10 . The method of claim 1 , wherein transmitting the SRS on the partial sounding resource subset comprises repeating a transmission on a SRS port for the partial sounding resource subset on the resources of the SRS ports that are in the SRS resource set but not in the partial sounding resource subset.

11 . The method of claim 1 , wherein the partial sounding resource subset specifies a reduced periodicity for the SRS ports that are in the SRS resource set but not in the partial sounding resource subset.

12 . The method of claim 1 , wherein the partial sounding resource subset specifies reduced frequency domain resources or frequency domain hops for the SRS ports that are in the SRS resource set but not in the partial sounding resource subset.

13 . A method of wireless communication, comprising, at a base station:

transmitting a configuration of a persistent or semi-persistent sounding reference signal (SRS) resource set that configures a first number of SRS ports for a full spatial sounding mode for a first receiving device;

receiving a SRS on a partial sounding resource subset of the SRS resource set, the partial sounding resource subset corresponding to a partial sounding line of sight multiple-input-multiple-output (LSM) mode for the receiving device;

performing phase ramp interpolation for the partial sounding LSM mode to estimate a LSM channel between the base station and the first receiving device;

receiving an indication of the partial sounding LSM mode from the first receiving device; and

receiving an indication that the first receiving device has changed to the full spatial sounding mode or a performance metric measured by the first receiving device that indicates a change to the full spatial sounding mode.

14 . The method of claim 13 , further comprising transmitting a downlink control information (DCI) or media access control (MAC) control element (CE) that indicates an adaptation of a number of transmit antennas or receive antennas to the first receiving device for the partial sounding LSM mode.

15 . The method of claim 13 , further comprising transmitting a DCI or MAC-CE that indicates a change to the partial sounding LSM mode to the first receiving device.

16 . The method of claim 13 , wherein the configuration of the persistent or semi-persistent SRS resource set indicates SRS ports to be skipped or deactivated in the partial sounding LSM mode.

17 . The method of claim 13 , wherein the configuration of the persistent or semi-persistent SRS resource set identifies a second number of SRS ports for the LSM-partial sounding mode that is less than the first number of SRS ports.

18 . The method of claim 13 , wherein the partial sounding resource subset corresponds to SRS ports for corner antennas of an antenna array of the first receiving device.

19 . The method of claim 13 , wherein the partial sounding resource subset specifies a reduced periodicity for SRS ports for the SRS ports that are in the SRS resource set but not in the partial sounding resource subset.

20 . The method of claim 13 , wherein the partial sounding resource subset specifies reduced frequency domain resources or frequency domain hops for the SRS ports that are in the SRS resource set but not in the partial sounding resource subset.

21 . The method of claim 13 , further comprising assigning SRS resources that are in the SRS resource set but not in the partial sounding resource subset to a second receiving device while the first receiving device is in the partial sounding LSM mode.

22 . An apparatus for wireless communication at a receiving device, comprising:

a memory storing computer-executable instructions; and

at least one processor configured to execute the instructions to:

receive a configuration of a persistent or semi-persistent sounding reference signal (SRS) resource set that configures a first number of SRS ports for a full spatial sounding mode;

transmit a SRS on a partial sounding resource subset of the SRS resource set, the partial sounding resource subset corresponding to a partial sounding line of sight multiple-input-multiple-output (LSM) mode;

autonomously activate the partial sounding LSM mode in response to a measurement at the receiving device, wherein the measurement at the receiving device is an estimated line of sight percentage or an estimated spectral efficiency factor for the partial sounding LSM mode; and

send an indication of the partial sounding LSM mode to a serving base station.

23 . The apparatus of claim 22 , wherein the at least one processor is configured to determine that partial sounding is to be used in response to receiving a DCI or a MAC-CE that indicates a change to the partial sounding LSM mode.

24 . An apparatus for wireless communication at a base station, comprising:

a memory storing computer-executable instructions; and

at least one processor configured to execute the instructions to:

transmit a configuration of a persistent or semi-persistent sounding reference signal (SRS) resource set that configures a first number of SRS ports for a full spatial sounding mode for a first receiving device;

receive a SRS on a partial sounding resource subset of the SRS resource set, the partial sounding resource subset corresponding to a partial sounding line of sight multiple-input-multiple-output (LSM) mode for the receiving device; and

perform phase ramp interpolation for the partial sounding LSM mode to estimate a LSM channel between the base station and the first receiving device;

receive an indication of the partial sounding LSM mode from the first receiving device; and

receive an indication that the first receiving device has changed to the full spatial sounding mode or a performance metric measured by the first receiving device that indicates a change to the full spatial sounding mode.

25 . The apparatus of claim 24 , wherein the at least one processor is configured to assign SRS resources that are in the SRS resource set but not in the partial sounding resource subset to a second receiving device while the first receiving device is in the partial sounding LSM mode.

26 . The apparatus of claim 22 , wherein the at least one processor is configured to return to the full spatial sounding mode in response to expiration of a timer or detection of a performance degradation.

27 . The apparatus of claim 26 , wherein the at least one processor is configured to indicate the full spatial sounding mode or a performance metric associated with the performance degradation to the serving base station.

28 . The apparatus of claim 27 , wherein the indication is a request to fall back to the full spatial sounding mode.

29 . The apparatus of claim 24 , wherein the configuration of the persistent or semi-persistent SRS resource set identifies a second number of SRS ports for the LSM-partial sounding mode that is less than the first number of SRS ports.

30 . The apparatus of claim 24 , wherein the partial sounding resource subset corresponds to SRS ports for corner antennas of an antenna array of the first receiving device.