Methods and apparatuses for dynamic antenna array reconfiguration and signaling in millimeter wave bands

1. A method of wireless communication, comprising:

detecting, at a user equipment (UE), an antenna array change condition;

transmitting, from the UE, a request for beam training for an antenna array configuration of a subset of active antennas in response to the detecting the antenna array change condition, wherein the request lbr beam training includes a request to change an active antenna array configuration of the UE to a requested antenna array configuration;

receiving, from a base station, an indication of an antenna array configuration for the UE, wherein the indication of the antenna array configuration for the UE indicates the requested antenna array configuration and a number of reference signals to use for beam training with the requested antenna array configuration;

configuring an antenna array of the UE based on the requested antenna array configuration to activate a reconfigured active antenna array configuration;

training the reconfigured active antenna array configuration based on the number of reference signals, wherein the number of reference signals is a number of contiguous channel state information reference signals; and

transmitting a set of reference signal received powers (RSRPs) and associated beam indices to the base station.

2. The method of claim 1 , wherein the antenna array change condition is based on an angular spread of dominant and sub-dominant clusters in a channel between the base station and the UE.

3. The method of claim 1 , wherein the antenna array change condition is based on a power consideration of the UE.

4. The method of claim 1 , wherein the antenna array change condition is based on a thermal consideration or the UE.

5. The method of claim 1 , wherein the antenna array change condition is based on support for additional radio-frequency chains utilizing a hybrid beamforming architecture.

6. The method of claim 1 , wherein the request for beam training for the antenna array configuration includes an indication of beam weights to use with the requested antenna array configuration.

7. The method of claim 6 , wherein the indication of beam weights is a pointer to an analog beam forming codebook index.

8. A method of wireless communication, comprising:

receiving, at a base station from a user equipment (UE), a request for beam training for a requested antenna array configuration of a subset of active antennas;

determining whether to grant or deny the requested antenna array configuration;

transmitting, from the base station, an indication of an antenna array configuration for the UE, wherein the indication of the antenna array configuration for the UE indicates the requested antenna array configuration and a number of reference signals to use for beam training with the requested antenna array configuration; and

transmitting the number of reference signals to use for beam training as a set of contiguous channel state information reference signals (CSI-RS).

9. The method of claim 8 , wherein the request for beam training indicates support for additional radio-frequency chains utilizing a hybrid beamforming architecture.

10. The method of claim 8 , wherein the request for beam training includes an indication abeam weights to use with the requested antenna array configuration.

11. The method of claim 10 , wherein the indication of beam weights is a pointer to an analog beamforming codebook index.

12. The method of claim 8 , further comprising:

receiving a set of reference signal received powers (RSRPs) and associated beam indices from the UE; and

selecting a beam from the associated beam indices for transmissions to the UE.

13. An apparatus for wireless communication, comprising:

a memory; and

one or more processors coupled to the memory and individually combination, configured to:

detect, at a user equipment (UE), an antenna array change condition;

transmit, from the UE, a request for beam training for an antenna array configuration of a subset of active antennas in response to the detecting the antenna array change condition, wherein the request for beam training includes a request to change an active antenna array configuration of the UE to a requested antenna array configuration;

receive, from a base station, an indication of an antenna array configuration for the UE, wherein the indication of the antenna array configuration for the UE indicates the requested antenna array configuration and a number of reference signals to use for beam training with the requested antenna array configuration;

configure an antenna array of the UE based on the requested antenna array configuration to activate a reconfigured active antenna array configuration;

train the reconfigured active antenna array configuration based on the number of reference signals, wherein the number of reference signals is a number of contiguous channel state information reference signals; and

transmit a set of reference signal received powers (RSRPs) and associated beam indices to the base station.

14. The apparatus of claim 13 , wherein the antenna array change condition is based on an angular spread of dominant and sub-dominant clusters in a channel between the base station and the UE.

15. The apparatus of claim 13 , wherein the antenna array change condition is based on a power consideration of the UE.

16. The apparatus of claim 13 , wherein the antenna array change condition is based on a thermal consideration of the UE.

17. The apparatus of claim 13 , wherein the antenna array change condition is based on support for additional radio-frequency chains utilizing a hybrid beamforming architecture.

18. The apparatus of claim 13 , wherein the request for beam training for the antenna array configuration includes an indication of beam weights to use with the requested antenna array configuration.

19. The apparatus of claim 18 , wherein the indication of beam weighs is a pointer to an analog beamforming codebook index.

20. An apparatus for wireless communication, comprising:

a memory; and

one or more processors coupled to the memory and individually or in combination, configured to:

receive, at a base station from a user equipment (UE), a request for beam training for a requested antenna array configuration of a subset of active antennas;

determine whether to grant or deny the requested antenna array configuration of the UE;

transmit, from the base station, an indication of an antenna array configuration for the UE, wherein the indication of the antenna array configuration for the UE indicates the requested antenna array configuration and a number of reference signals to use for beam training with the requested antenna array configuration; and

transmit the number of reference signals to use for beam training as a set of contiguous channel state information reference signals (CSI-RS).

21. The apparatus of claim 20 , wherein the request for beam training indicates support for additional radio-frequency chains utilizing a hybrid beamforming architecture.

22. The apparatus of claim 20 , wherein the request for beam training includes an indication of beam weights to use with the requested antenna array configuration.

23. The apparatus of claim 22 , wherein the indication of beam weights is a pointer to an analog beamforming codebook index.

24. The apparatus of claim 20 , wherein the one or more processors, individually or in combination, are configured to:

receive a set of reference signal received powers (RSRPs) and associated beam indices from the UE; and

select a beam from the associated beam indices for transmissions to the UE.