Uplink multiple-input multiple-output (MIMO) scheduling using beamformed reference signals
Aspects of the present disclosure provide methods and apparatus for selecting beamforming parameters for uplink transmissions based on an uplink reference signal. An example method generally includes identifying one or more parameters for beamformed transmission to a transmit receive point (TRP), transmitting a reference signal using beamforming in accordance with the identified parameters, and receiving, from the TRP in response to the reference signal, signaling for adjusting the one or more parameters for one or more subsequent beamformed transmissions.
1. A method for wireless communications by a wireless node, comprising:
identifying one or more parameters including a precoder matrix for beamformed uplink reference signal transmission to a transmit receive point (TRP);
transmitting an uplink reference signal, wherein the uplink reference signal is beamformed in accordance with the one or more parameters; and
receiving, from the TRP in response to the uplink reference signal, an uplink grant comprising an indication of the one or more parameters including the precoder matrix for use in one or more subsequent beamformed uplink transmissions.
2. The method of claim 1 , wherein the one or more parameters comprise at least one of a beam direction, a rank, or a modulation and coding scheme (MCS).
3. The method of claim 1 , wherein the one or more parameters comprise an adjustment relative to a beam direction of the beamformed uplink reference signal.
4. The method of claim 1 , wherein the identifying is based on information received from the TRP.
5. The method of claim 4 , wherein the information comprises an indication of a precoder matrix index.
6. The method of claim 4 , wherein the information comprises interference information estimated by the TRP.
7. The method of claim 4 , wherein the information is received via one of broadcast or groupcast signaling.
8. The method of claim 1 , wherein the identifying comprises selecting a beam for transmitting the uplink reference signal based on at least one of a channel condition or a TRP interference profile.
9. The method of claim 1 , wherein the identifying comprises selecting a beam direction for transmitting the uplink reference signal by cycling through a predefined codebook.
10. The method of claim 1 , wherein the identifying comprises selecting a beam direction for transmitting the uplink reference signal using cyclic delay diversity.
11. The method of claim 1 , wherein the uplink reference signal comprises one of a channel state information reference signal (CSI-RS) or a sounding reference signal (SRS).
12. The method of claim 1 , further comprising:
receiving, from the TRP, one of information about measured signal strength of the beamformed uplink reference signal or a change in measured signal strength of the beamformed uplink reference signal relative to a previously transmitted beamformed uplink reference signal; and
adjusting a direction of beam phase adjustment based, at least in part, on the information.
13. A method for wireless communications by a transmit receive point (TRP), comprising:
receiving, from a wireless node, a beamformed uplink reference signal;
determining, based on the beamformed uplink reference signal, a value of one or more parameters including a precoder matrix for the wireless node to use in one or more subsequent beamformed uplink transmissions; and
signaling, in an uplink grant, the value of the one or more parameters including the precoder matrix to the wireless node for use in beamforming one or more subsequent uplink transmissions.
14. The method of claim 13 , wherein the one or more parameters comprise at least one of a beam direction, a rank, or a modulation and coding scheme (MCS).
15. The method of claim 13 , wherein signaling the value of the one or more parameters for use in beamforming one or more subsequent uplink transmissions comprises signaling indication of an adjustment relative to a beam direction the wireless node used for the beamformed uplink reference signal.
16. The method of claim 13 , further comprising:
transmitting, to the wireless node, information identifying the one or more parameters for the beamformed uplink transmission.
17. The method of claim 16 , wherein the information comprises an indication of a precoder matrix index.
18. The method of claim 16 , wherein the information comprises interference estimation information estimated by the TRP.
19. The method of claim 16 , wherein the information is transmitted via one of broadcast or groupcast signaling.
20. The method of claim 13 , wherein determining the value of the one or more parameters comprises generating a down-selected set of beams for a group of wireless nodes based, at least in part, on mutual interference between wireless nodes in the group.
21. The method of claim 20 , further comprising:
selecting a modulation and coding scheme for the wireless node and one or more other wireless nodes based on the down-selected group of beams.
22. The method of claim 20 , further comprising:
receiving, from a neighbor TRP, information indicating that the wireless node is causing interference to the neighbor TRP; and
excluding the wireless node from the group of wireless nodes.
23. The method of claim 22 , wherein the information indicating that the wireless node is causing interference to the neighbor TRP is received via a backhaul link between the TRP and the neighbor TRP.
24. An apparatus for wireless communications, comprising:
a processor configured to:
identify one or more parameters including a precoder matrix for beamformed uplink reference signal transmission to a transmit receive point (TRP);
transmit an uplink reference signal, wherein the uplink reference signal is beamformed in accordance with the one or more parameters; and
receive, from the TRP in response to the uplink reference signal, an uplink grant comprising an indication of the one or more parameters including the precoder matrix for use in one or more subsequent beamformed uplink transmissions; and
a memory coupled to the processor.
25. The apparatus of claim 24 , wherein the identifying is based on information received from the TRP.
26. The apparatus of claim 24 , wherein the identifying comprises selecting a beam for transmitting the uplink reference signal based on at least one of a channel condition or a TRP interference profile.
27. The apparatus of claim 24 , wherein the identifying comprises selecting a beam direction for transmitting the uplink reference signal by cycling through a predefined codebook.
28. An apparatus for wireless communications, comprising:
a processor configured to:
receive, from a wireless node, a beamformed uplink reference signal;
determine, based on the beamformed uplink reference signal, a value of one or more parameters including a precoder matrix for the wireless node to use in one or more subsequent beamformed uplink transmissions; and
signal, in an uplink grant, the value of the one or more parameters including the precoder matrix to the wireless node for use in beamforming one or more subsequent uplink transmissions; and
a memory coupled to the processor.
29. The apparatus of claim 28 , wherein determining the value of the one or more parameters comprises generating a down-selected set of beams for a group of wireless nodes based, at least in part, on mutual interference between wireless nodes in the group.
30. The apparatus of claim 29 , wherein the processor is further configured to select a modulation and coding scheme for the wireless node and one or more other wireless nodes based on the down-selected group of beams.