WO2021247903A1

WO2021247903A1 - Wideband and subband precoder selection

Info

Publication number: WO2021247903A1
Application number: PCT/US2021/035756
Authority: WO
Inventors: Ahmed Elshafie; Alexandros MANOLAKOS; Muhammad Sayed Khairy Abdelghaffar; Hwan Joon Kwon
Original assignee: Qualcomm Incorporated
Priority date: 2020-06-04
Filing date: 2021-06-03
Publication date: 2021-12-09

Abstract

Methods, systems, and devices for wireless communication are described. In one aspect, a user equipment (UE) may select a wideband precoder to report to a base station based on channel state information reference signals (CSI-RSs). In this aspect, the UE may receive an indication of a subset of a set of beams on which to perform measurements, and the UE may perform the measurements on the subset of the set of beams. The UE may then report a wideband precoder corresponding to a preferred beam of the subset of the set of beams to a base station. In another aspect, a UE may select a subband precoder to report to a base station for each subband of a set of subbands based on a subset of a set of values of at least one subband parameter.

Description

WIDEBAND AND SUBBAND PRECODER SELECTION

CROSS REFERENCE

[0001] The present Application for Patent claims the benefit of Greece Provisional Patent Application No. 20200100314 by ELSHAFIE et al., entitled “WIDEBAND AND SUBBAND PRECODER SELECTION,” filed June 4, 2020, assigned to the assignee hereof, and expressly incorporated by reference herein.

FIELD OF TECHNOLOGY

[0002] The present disclosure relates to wireless communications and more specifically to wideband and subband precoder selection.

BACKGROUND

[0003] Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple- access systems include fourth generation (4G) systems such as Long Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, or LTE-A Pro systems, and fifth generation (5G) systems which may be referred to as New Radio (NR) systems. These systems may employ technologies such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), or discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S- OFDM).

[0004] A wireless multiple-access communications system may include a number of base stations or network access nodes, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as a user equipment (UE).

In some wireless communications systems, a UE may support communications with a base station using one or more beams. In such systems, a transmitting device may precode signals to be transmitted on a beam. Precoding may refer to a technique used to weight multiple streams (e.g., data streams) from a transmitting device and may limit the effects of a channel on the signals received at a receiving device. Improved techniques for selecting suitable precoders for precoding transmissions in a wireless communications system may be desirable.

SUMMARY

[0005] The described techniques relate to improved methods, systems, devices, and apparatuses that support wideband and subband precoder selection. In one aspect, a user equipment (UE) may select a wideband precoder to report to a base station based on channel state information (CSI) reference signals (CSI-RSs). In this aspect, the UE may receive CSI- RSs, and the UE may receive an indication of a subset of a set of beams on which to perform measurements. Thus, the UE may perform the measurements on the subset of the set of beams (e.g., rather than the full set of beams), and the UE may report a wideband precoder corresponding to a preferred (e.g., best) beam of the subset of the set of beams in channel state feedback (CSF) to a base station. In another aspect, a UE may select a subband precoder to report to a base station for each subband of a set of subbands based on a subset of a set of values of at least one subband parameter. Because the UE may perform less computations for wideband and subband precoder selection, the complexity at the UE may be minimized, and latency and power consumption at the UE may be reduced.

[0006] A method of wireless communication at a UE is described. The method may include receiving, from a base station, CSI-RSs, receiving, from the base station, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder, identifying the wideband precoder corresponding to a beam of the subset of the set of beams based on the CSI-RSs, and reporting, to the base station, the wideband precoder in CSF.

[0007] An apparatus for wireless communication at a UE is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to receive, from a base station, CSI-RSs, receive, from the base station, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder, identify the wideband precoder corresponding to a beam of the subset of the set of beams based on the CSI-RSs, and report, to the base station, the wideband precoder in CSF. [0008] Another apparatus for wireless communication at a UE is described. The apparatus may include means for receiving, from a base station, CSI-RSs, receiving, from the base station, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder, identifying the wideband precoder corresponding to a beam of the subset of the set of beams based on the CSI-RSs, and reporting, to the base station, the wideband precoder in CSF.

[0009] A non-transitory computer-readable medium storing code for wireless communication at a UE is described. The code may include instructions executable by a processor to receive, from a base station, CSI-RSs, receive, from the base station, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder, identify the wideband precoder corresponding to a beam of the subset of the set of beams based on the CSI-RSs, and report, to the base station, the wideband precoder in CSF.

[0010] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, to the base station, sounding reference signals (SRSs), where receiving the indication of the subset of the set of beams may be based on transmitting the SRSs. In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, receiving the indication of the subset of the set of beams may include operations, features, means, or instructions for receiving, from the base station, a first indication indicating one or more beams from which the UE may be to identify the wideband precoder, and receiving, from the base station, a second indication indicating neighboring beams to each of the one or more beams from which the UE may be to identify the wideband precoder.

[0011] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining the neighboring beams to each of the one or more beams based on the quantity of the neighboring beams. In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the second indication includes a radio resource control (RRC) message, a medium access control (MAC) control element (MAC-CE), or a downlink control information (DCI) message. In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the first indication includes a DCI message.

[0012] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the base station, an indication of one or more subband parameters for the UE to use to identify a subband precoder for each subband of a set of subbands, identifying the subband precoder for each subband of the set of subbands to report to the base station in CSF based on the one or more subband parameters, and reporting, to the base station, the subband precoder for each subband of the set of subbands in the CSF.

[0013] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the base station, an indication of a subset of a set of values of at least one subband parameter for the UE to use to identify a subband precoder for each subband of a set of subbands, identifying the subband precoder for each subband of the set of subbands to report to the base station in the CSF based on the subset of the set of values of the at least one subband parameter, and reporting, to the base station, the subband precoder for each subband of the set of subbands in the CSF.

[0014] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, receiving the indication of the subset of the set of values of the at least one subband parameter may include operations, features, means, or instructions for receiving, from the base station, a first indication indicating one or more values of the at least one subband parameter for the UE to use to identify the subband precoder for each subband of the set of subbands, and receiving, from the base station, a second indication indicating neighboring values to each of the one or more values for the UE to use to identify the subband precoder for each subband of the set of subbands.

[0015] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining the neighboring values to each of the one or more values based on the quantity of the neighboring values. Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the base station, a trigger to identify the subband precoder for each subband of the set of subbands based on the subset of the set of values of the at least one subband parameter. Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the base station, a trigger to identify the wideband precoder based on the subset of the set of beams. In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the indication of the subset of the set of beams may be received a threshold amount of time before reporting the CSF.

[0016] A method of wireless communication at a base station is described. The method may include transmitting, to a UE, CSI-RSs, transmitting, to the UE, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder, and receiving, from the UE, the wideband precoder corresponding to a beam of the subset of the set of beams based on transmitting the CSI-RSs and transmitting the indication of the subset of the set of beams.

[0017] An apparatus for wireless communication at a base station is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to transmit, to a UE, CSI-RSs, transmit, to the UE, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder, and receive, from the UE, the wideband precoder corresponding to a beam of the subset of the set of beams based on transmitting the CSI-RSs and transmitting the indication of the subset of the set of beams.

[0018] Another apparatus for wireless communication at a base station is described. The apparatus may include means for transmitting, to a UE, CSI-RSs, transmitting, to the UE, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder, and receiving, from the UE, the wideband precoder corresponding to a beam of the subset of the set of beams based on transmitting the CSI-RSs and transmitting the indication of the subset of the set of beams.

[0019] A non-transitory computer-readable medium storing code for wireless communication at a base station is described. The code may include instructions executable by a processor to transmit, to a UE, CSI-RSs, transmit, to the UE, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder, and receive, from the UE, the wideband precoder corresponding to a beam of the subset of the set of beams based on transmitting the CSI-RSs and transmitting the indication of the subset of the set of beams.

[0020] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the UE, SRSs, and selecting the subset of the set of beams from which the UE may be to identify the wideband precoder based on the SRSs. In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, transmitting the indication of the subset of the set of beams may include operations, features, means, or instructions for transmitting a first indication indicating one or more beams from which the UE may be to identify the wideband precoder, and transmitting a second indication indicating neighboring beams to each of the one or more beams from which the UE may be to identify the wideband precoder.

[0021] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the second indication indicates a quantity of the neighboring beams. In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the second indication includes an RRC message, a MAC-CE, or a DCI message. In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the first indication includes a DCI message. Some examples of the method, apparatuses, and non-transitory computer- readable medium described herein may further include operations, features, means, or instructions for transmitting, to the UE, an indication of one or more subband parameters for the UE to use to identify a subband precoder for each subband of a set of subbands, and receiving, from the UE, the subband precoder for each subband of the set of subbands in the CSF based on transmitting the indication of the one or more subband parameters.

[0022] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, to the UE, an indication of a subset of a set of values of at least one subband parameter for the UE to use to identify a subband precoder for each subband of a set of subbands, and receiving, from the UE, the subband precoder for each subband of the set of subbands in the CSF based on transmitting the indication of the subset of the set of values of the at least one subband parameter. [0023] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, transmitting the indication of the subset of the set of values of the at least one subband parameter may include operations, features, means, or instructions for transmitting, to the UE, a first indication indicating one or more values of the at least one subband parameter for the UE to use to identify the subband precoder for each subband of the set of subbands, and transmitting, to the UE, a second indication indicating neighboring values to each of the one or more values for the UE to use to identify the subband precoder for each subband of the set of subbands.

[0024] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the second indication indicates a quantity of the neighboring values. Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, to the UE, a trigger to identify the subband precoder for each subband of the set of subbands based on the subset of the set of values of the at least one subband parameter. Some examples of the method, apparatuses, and non-transitory computer- readable medium described herein may further include operations, features, means, or instructions for transmitting, to the UE, a trigger to identify the wideband precoder based on the subset of the set of beams. In some examples of the method, apparatuses, and non- transitory computer-readable medium described herein, the indication of the subset of the set of beams may be transmitted a threshold amount of time before receiving the CSF.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 illustrates an example of a wireless communications system that supports wideband and subband precoder selection in accordance with aspects of the present disclosure.

[0026] FIG. 2 illustrates an example of a process flow showing channel estimation using sounding reference signals (SRSs) in accordance with aspects of the present disclosure.

[0027] FIG. 3 illustrates an example of a process flow showing channel estimation using channel state information reference signals (CSI-RSs) in accordance with aspects of the present disclosure. [0028] FIG. 4 illustrates an example of a CSI timeline in accordance with aspects of the present disclosure.

[0029] FIG. 5 illustrates an example of a wireless communications system that supports wideband and subband precoder selection in accordance with aspects of the present disclosure.

[0030] FIG. 6 illustrates an example of a process flow that supports wideband and subband precoder selection in accordance with aspects of the present disclosure.

[0031] FIG. 7 illustrates an example of a process flow that supports wideband and subband precoder selection in accordance with aspects of the present disclosure.

[0032] FIGs. 8 and 9 show block diagrams of devices that support wideband and subband precoder selection in accordance with aspects of the present disclosure.

[0033] FIG. 10 shows a block diagram of a communications manager that supports wideband and subband precoder selection in accordance with aspects of the present disclosure.

[0034] FIG. 11 shows a diagram of a system including a device that supports wideband and subband precoder selection in accordance with aspects of the present disclosure.

[0035] FIGs. 12 and 13 show block diagrams of devices that support wideband and subband precoder selection in accordance with aspects of the present disclosure.

[0036] FIG. 14 shows a block diagram of a communications manager that supports wideband and subband precoder selection in accordance with aspects of the present disclosure.

[0037] FIG. 15 shows a diagram of a system including a device that supports wideband and subband precoder selection in accordance with aspects of the present disclosure.

[0038] FIGs. 16 and 17 show flowcharts illustrating methods that support wideband and subband precoder selection in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

[0039] In some wireless communications systems, a base station may use beamforming to transmit downlink signals to a user equipment (UE). In such systems, the base station may be capable of generating multiple beams for transmitting the downlink signals to the UE. Each beam may be associated with or may correspond to at least one precoder used for precoding signals transmitted on the beam. Precoding may refer to a technique used to weight multiple streams (e.g., data streams) from a transmitting device to limit the effects of a channel on the signals received at a receiving device. Further, precoding may depend on an estimation of a channel or other channel state information (CSI).

[0040] In some cases, a base station may transmit CSI reference signals (CSI-RSs) to a UE, and the UE may report channel state feedback (CSF) in a CSI report to the base station.

In particular, the UE may perform channel estimation measurements on each beam of a set of beams based on the CSI-RSs, and the UE may report a wideband precoder corresponding to a preferred beam of the set of beams. The UE may also perform channel estimation measurements on the CSI-RSs received on each sideband, and the UE may report a subband precoder to the base station for each subband. In some cases, however, if the UE is configured to compute channel estimation measurements on the full set of beams based on the CSI-RSs, the complexity of the computations may lead to high latency and power consumption at the UE, which may be detrimental to the UE.

[0041] As described herein, a wireless communications system may support efficient techniques for wideband and subband precoder selection. In one aspect, a UE may select a wideband precoder to report to a base station based on CSI-RSs. In this aspect, the UE may receive CSI-RSs, and the UE may receive an indication of a subset of a set of beams on which to perform measurements. Thus, the UE may perform the measurements on the subset of the set of beams (e.g., rather than the full set of beams), and the UE may report a wideband precoder corresponding to a preferred (e.g., best) beam of the subset of the set of beams in CSF to a base station. In another aspect, a UE may select a subband precoder to report to a base station for each subband of a set of subbands based on a subset of a set of values of at least one subband parameter. Because the UE may perform less computations for wideband and subband precoder selection, the complexity at the UE may be minimized, and latency and power consumption at the UE may be reduced.

[0042] Aspects of the disclosure introduced above are described below in the context of a wireless communications system. Examples of processes and signaling exchanges that support wideband and subband precoder selection are then described. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to wideband and subband precoder selection.

[0043] FIG. 1 illustrates an example of a wireless communications system 100 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The wireless communications system 100 may include one or more base stations 105, one or more UEs 115, and a core network 130. In some examples, the wireless communications system 100 may be a Long Term Evolution (LTE) network, an LTE- Advanced (LTE- A) network, an LTE-A Pro network, or a New Radio (NR) network. In some examples, the wireless communications system 100 may support enhanced broadband communications, ultra-reliable (e.g., mission critical) communications, low latency communications, communications with low-cost and low-complexity devices, or any combination thereof.

[0044] The base stations 105 may be dispersed throughout a geographic area to form the wireless communications system 100 and may be devices in different forms or having different capabilities. The base stations 105 and the UEs 115 may wirelessly communicate via one or more communication links 125. Each base station 105 may provide a coverage area 110 over which the UEs 115 and the base station 105 may establish one or more communication links 125. The coverage area 110 may be an example of a geographic area over which a base station 105 and a UE 115 may support the communication of signals according to one or more radio access technologies.

[0045] The UEs 115 may be dispersed throughout a coverage area 110 of the wireless communications system 100, and each UE 115 may be stationary, or mobile, or both at different times. The UEs 115 may be devices in different forms or having different capabilities. Some example UEs 115 are illustrated in FIG. 1. The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115, the base stations 105, or network equipment (e.g., core network nodes, relay devices, integrated access and backhaul (IAB) nodes, or other network equipment), as shown in FIG. 1.

[0046] The base stations 105 may communicate with the core network 130, or with one another, or both. For example, the base stations 105 may interface with the core network 130 through one or more backhaul links 120 (e.g., via an SI, N2, N3, or other interface). The base stations 105 may communicate with one another over the backhaul links 120 (e.g., via an X2, Xn, or other interface) either directly (e.g., directly between base stations 105), or indirectly (e.g., via core network 130), or both. In some examples, the backhaul links 120 may be or include one or more wireless links.

[0047] One or more of the base stations 105 described herein may include or may be referred to by a person having ordinary skill in the art as a base transceiver station, a radio base station, an access point, a radio transceiver, a NodeB, an eNodeB (eNB), a next- generation NodeB or a giga-NodeB (either of which may be referred to as a gNB), a Home NodeB, a Home eNodeB, or other suitable terminology.

[0048] A UE 115 may include or may be referred to as a mobile device, a wireless device, a remote device, a handheld device, or a subscriber device, or some other suitable terminology, where the “device” may also be referred to as a unit, a station, a terminal, or a client, among other examples. A UE 115 may also include or may be referred to as a personal electronic device such as a cellular phone, a personal digital assistant (PDA), a tablet computer, a laptop computer, or a personal computer. In some examples, a UE 115 may include or be referred to as a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, or a machine type communications (MTC) device, among other examples, which may be implemented in various objects such as appliances, or vehicles, meters, among other examples.

[0049] The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115 that may sometimes act as relays as well as the base stations 105 and the network equipment including macro eNBs or gNBs, small cell eNBs or gNBs, or relay base stations, among other examples, as shown in FIG. 1.

[0050] The UEs 115 and the base stations 105 may wirelessly communicate with one another via one or more communication links 125 over one or more carriers. The term “carrier” may refer to a set of radio frequency spectrum resources having a defined physical layer structure for supporting the communication links 125. For example, a carrier used for a communication link 125 may include a portion of a radio frequency spectrum band (e.g., a bandwidth part (BWP)) that is operated according to one or more physical layer channels for a given radio access technology (e.g., LTE, LTE-A, LTE-A Pro, NR). Each physical layer channel may carry acquisition signaling (e.g., synchronization signals, system information), control signaling that coordinates operation for the carrier, user data, or other signaling. The wireless communications system 100 may support communication with a UE 115 using carrier aggregation or multi-carrier operation. A UE 115 may be configured with multiple downlink component carriers and one or more uplink component carriers according to a carrier aggregation configuration. Carrier aggregation may be used with both frequency division duplexing (FDD) and time division duplexing (TDD) component carriers.

[0051] In some examples (e.g., in a carrier aggregation configuration), a carrier may also have acquisition signaling or control signaling that coordinates operations for other carriers.

A carrier may be associated with a frequency channel (e.g., an evolved universal mobile telecommunication system terrestrial radio access (E-UTRA) absolute radio frequency channel number (EARFCN)) and may be positioned according to a channel raster for discovery by the UEs 115. A carrier may be operated in a standalone mode where initial acquisition and connection may be conducted by the UEs 115 via the carrier, or the carrier may be operated in a non- standalone mode where a connection is anchored using a different carrier (e.g., of the same or a different radio access technology).

[0052] The communication links 125 shown in the wireless communications system 100 may include uplink transmissions from a UE 115 to a base station 105 (e.g., in a physical uplink shared channel (PUSCH) or a physical uplink control channel (PUCCH)), or downlink transmissions from a base station 105 to a UE 115 (e.g., in a physical downlink shared channel (PDSCH) or a physical downlink control channel (PDCCH)). Carriers may carry downlink or uplink communications (e.g., in an FDD mode) or may be configured to carry downlink and uplink communications (e.g., in a TDD mode).

[0053] A carrier may be associated with a particular bandwidth of the radio frequency spectrum, and in some examples the carrier bandwidth may be referred to as a “system bandwidth” of the carrier or the wireless communications system 100. For example, the carrier bandwidth may be one of a number of determined bandwidths for carriers of a particular radio access technology (e.g., 1.4, 3, 5, 10, 15, 20, 40, or 80 megahertz (MHz)). Devices of the wireless communications system 100 (e.g., the base stations 105, the UEs 115, or both) may have hardware configurations that support communications over a particular carrier bandwidth or may be configurable to support communications over one of a set of carrier bandwidths. In some examples, the wireless communications system 100 may include base stations 105 or UEs 115 that support simultaneous communications via carriers associated with multiple carrier bandwidths. In some examples, each served UE 115 may be configured for operating over portions (e.g., a sub-band, a BWP) or all of a carrier bandwidth.

[0054] Signal waveforms transmitted over a carrier may be made up of multiple subcarriers (e.g., using multi-carrier modulation (MCM) techniques such as orthogonal frequency division multiplexing (OFDM) or discrete Fourier transform (DFT) spread OFDM (DFT-S-OFDM)). In a system employing MCM techniques, a resource element may include one symbol period (e.g., a duration of one modulation symbol) and one subcarrier, where the symbol period and subcarrier spacing are inversely related. The number of bits carried by each resource element may depend on the modulation scheme (e.g., the order of the modulation scheme, the coding rate of the modulation scheme, or both). Thus, the more resource elements that a UE 115 receives and the higher the order of the modulation scheme, the higher the data rate may be for the UE 115. A wireless communications resource may refer to a combination of a radio frequency spectrum resource, a time resource, and a spatial resource (e.g., spatial layers or beams), and the use of multiple spatial layers may further increase the data rate or data integrity for communications with a UE 115.

[0055] The time intervals for the base stations 105 or the UEs 115 may be expressed in multiples of a basic time unit which may, for example, refer to a sampling period of T_s =

1 /{ f_{max '} Nf) seconds, where A/_ma may represent the maximum supported subcarrier spacing, and JV- may represent the maximum supported DFT size. Time intervals of a communications resource may be organized according to radio frames each having a specified duration (e.g., 10 milliseconds (ms)). Each radio frame may be identified by a system frame number (SFN) (e.g., ranging from 0 to 1023).

[0056] Each frame may include multiple consecutively numbered subframes or slots, and each subframe or slot may have the same duration. In some examples, a frame may be divided (e.g., in the time domain) into subframes, and each subframe may be further divided into a number of slots. Alternatively, each frame may include a variable number of slots, and the number of slots may depend on subcarrier spacing. Each slot may include a number of symbol periods (e.g., depending on the length of the cyclic prefix prepended to each symbol period). In some wireless communications systems 100, a slot may further be divided into multiple mini-slots containing one or more symbols. Excluding the cyclic prefix, each symbol period may contain one or more (e.g., Nf) sampling periods. The duration of a symbol period may depend on the subcarrier spacing or frequency band of operation.

[0057] A subframe, a slot, a mini-slot, or a symbol may be the smallest scheduling unit (e.g., in the time domain) of the wireless communications system 100 and may be referred to as a transmission time interval (TTI). In some examples, the TTI duration (e.g., the number of symbol periods in a TTI) may be variable. Additionally, or alternatively, the smallest scheduling unit of the wireless communications system 100 may be dynamically selected (e.g., in bursts of shortened TTIs (sTTIs)).

[0058] Physical channels may be multiplexed on a carrier according to various techniques. A physical control channel and a physical data channel may be multiplexed on a downlink carrier, for example, using one or more of time division multiplexing (TDM) techniques, frequency division multiplexing (FDM) techniques, or hybrid TDM-FDM techniques. A control region (e.g., a control resource set (CORESET)) for a physical control channel may be defined by a number of symbol periods and may extend across the system bandwidth or a subset of the system bandwidth of the carrier. One or more control regions (e.g., CORESETs) may be configured for a set of the UEs 115. For example, one or more of the UEs 115 may monitor or search control regions for control information according to one or more search space sets, and each search space set may include one or multiple control channel candidates in one or more aggregation levels arranged in a cascaded manner. An aggregation level for a control channel candidate may refer to a number of control channel resources (e.g., control channel elements (CCEs)) associated with encoded information for a control information format having a given payload size. Search space sets may include common search space sets configured for sending control information to multiple UEs 115 and UE-specific search space sets for sending control information to a specific UE 115.

[0059] In some examples, a base station 105 may be movable and therefore provide communication coverage for a moving geographic coverage area 110. In some examples, different geographic coverage areas 110 associated with different technologies may overlap, but the different geographic coverage areas 110 may be supported by the same base station 105. In other examples, the overlapping geographic coverage areas 110 associated with different technologies may be supported by different base stations 105. The wireless communications system 100 may include, for example, a heterogeneous network in which different types of the base stations 105 provide coverage for various geographic coverage areas 110 using the same or different radio access technologies.

[0060] The wireless communications system 100 may be configured to support ultra reliable communications or low-latency communications, or various combinations thereof. For example, the wireless communications system 100 may be configured to support ultra reliable low-latency communications (URLLC) or mission critical communications. The UEs 115 may be designed to support ultra-reliable, low-latency, or critical functions (e.g., mission critical functions). Ultra-reliable communications may include private communication or group communication and may be supported by one or more mission critical services such as mission critical push-to-talk (MCPTT), mission critical video (MCVideo), or mission critical data (MCData). Support for mission critical functions may include prioritization of services, and mission critical services may be used for public safety or general commercial applications. The terms ultra-reliable, low-latency, mission critical, and ultra-reliable low- latency may be used interchangeably herein.

[0061] In some examples, a UE 115 may also be able to communicate directly with other UEs 115 over a device-to-device (D2D) communication link 135 (e.g., using a peer-to-peer (P2P) or D2D protocol). One or more UEs 115 utilizing D2D communications may be within the geographic coverage area 110 of a base station 105. Other UEs 115 in such a group may be outside the geographic coverage area 110 of a base station 105 or be otherwise unable to receive transmissions from a base station 105. In some examples, groups of the UEs 115 communicating via D2D communications may utilize a one-to-many (1 :M) system in which each UE 115 transmits to every other UE 115 in the group. In some examples, a base station 105 facilitates the scheduling of resources for D2D communications. In other cases, D2D communications are carried out between the UEs 115 without the involvement of a base station 105.

[0062] The core network 130 may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. The core network 130 may be an evolved packet core (EPC) or 5G core (5GC), which may include at least one control plane entity that manages access and mobility (e.g., a mobility management entity (MME), an access and mobility management function (AMF)) and at least one user plane entity that routes packets or interconnects to external networks (e.g., a serving gateway (S-GW), a Packet Data Network (PDN) gateway (P-GW), or a user plane function (UPF)). The control plane entity may manage non-access stratum (NAS) functions such as mobility, authentication, and bearer management for the UEs 115 served by the base stations 105 associated with the core network 130. User IP packets may be transferred through the user plane entity, which may provide IP address allocation as well as other functions. The user plane entity may be connected to the network operators IP services 150. The operators IP services 150 may include access to the Internet, Intranet(s), an IP Multimedia Subsystem (IMS), or a Packet- Switched Streaming Service.

[0063] Some of the network devices, such as a base station 105, may include subcomponents such as an access network entity 140, which may be an example of an access node controller (ANC). Each access network entity 140 may communicate with the UEs 115 through one or more other access network transmission entities 145, which may be referred to as radio heads, smart radio heads, or transmission/reception points (TRPs). Each access network transmission entity 145 may include one or more antenna panels. In some configurations, various functions of each access network entity 140 or base station 105 may be distributed across various network devices (e.g., radio heads and ANCs) or consolidated into a single network device (e.g., a base station 105).

[0064] The wireless communications system 100 may operate using one or more frequency bands, typically in the range of 300 megahertz (MHz) to 300 gigahertz (GHz). Generally, the region from 300 MHz to 3 GHz is known as the ultra-high frequency (UHF) region or decimeter band because the wavelengths range from approximately one decimeter to one meter in length. The UHF waves may be blocked or redirected by buildings and environmental features, but the waves may penetrate structures sufficiently for a macro cell to provide service to the UEs 115 located indoors. The transmission of UHF waves may be associated with smaller antennas and shorter ranges (e.g., less than 100 kilometers) compared to transmission using the smaller frequencies and longer waves of the high frequency (HF) or very high frequency (VHF) portion of the spectrum below 300 MHz.

[0065] The wireless communications system 100 may also operate in a super high frequency (SHF) region using frequency bands from 3 GHz to 30 GHz, also known as the centimeter band, or in an extremely high frequency (EHF) region of the spectrum (e.g., from 30 GHz to 300 GHz), also known as the millimeter band. In some examples, the wireless communications system 100 may support millimeter wave (mmW) communications between the UEs 115 and the base stations 105, and EHF antennas of the respective devices may be smaller and more closely spaced than UHF antennas. In some examples, this may facilitate use of antenna arrays within a device. The propagation of EHF transmissions, however, may be subject to even greater atmospheric attenuation and shorter range than SHF or UHF transmissions. The techniques disclosed herein may be employed across transmissions that use one or more different frequency regions, and designated use of bands across these frequency regions may differ by country or regulating body.

[0066] The wireless communications system 100 may utilize both licensed and unlicensed radio frequency spectrum bands. For example, the wireless communications system 100 may employ License Assisted Access (LAA), LTE-Unlicensed (LTE-U) radio access technology, or NR technology in an unlicensed band such as the 5 GHz industrial, scientific, and medical (ISM) band. When operating in unlicensed radio frequency spectrum bands, devices such as the base stations 105 and the UEs 115 may employ carrier sensing for collision detection and avoidance. In some examples, operations in unlicensed bands may be based on a carrier aggregation configuration in conjunction with component carriers operating in a licensed band (e.g., LAA). Operations in unlicensed spectrum may include downlink transmissions, uplink transmissions, P2P transmissions, or D2D transmissions, among other examples.

[0067] A base station 105 or a UE 115 may be equipped with multiple antennas, which may be used to employ techniques such as transmit diversity, receive diversity, multiple-input multiple-output (MIMO) communications, or beamforming. The antennas of a base station 105 or a UE 115 may be located within one or more antenna arrays or antenna panels, which may support MIMO operations or transmit or receive beamforming. For example, one or more base station antennas or antenna arrays may be co-located at an antenna assembly, such as an antenna tower. In some examples, antennas or antenna arrays associated with a base station 105 may be located in diverse geographic locations. A base station 105 may have an antenna array with a number of rows and columns of antenna ports that the base station 105 may use to support beamforming of communications with a UE 115. Likewise, a UE 115 may have one or more antenna arrays that may support various MIMO or beamforming operations. Additionally, or alternatively, an antenna panel may support radio frequency beamforming for a signal transmitted via an antenna port. [0068] Beamforming, which may also be referred to as spatial filtering, directional transmission, or directional reception, is a signal processing technique that may be used at a transmitting device or a receiving device (e.g., a base station 105, a UE 115) to shape or steer an antenna beam (e.g., a transmit beam, a receive beam) along a spatial path between the transmitting device and the receiving device. Beamforming may be achieved by combining the signals communicated via antenna elements of an antenna array such that some signals propagating at particular orientations with respect to an antenna array experience constructive interference while others experience destructive interference. The adjustment of signals communicated via the antenna elements may include a transmitting device or a receiving device applying amplitude offsets, phase offsets, or both to signals carried via the antenna elements associated with the device. The adjustments associated with each of the antenna elements may be defined by a beamforming weight set associated with a particular orientation (e.g., with respect to the antenna array of the transmitting device or receiving device, or with respect to some other orientation).

[0069] A base station 105 or a UE 115 may use beam sweeping techniques as part of beam forming operations. For example, a base station 105 may use multiple antennas or antenna arrays (e.g., antenna panels) to conduct beamforming operations for directional communications with aUE 115. Some signals (e.g., synchronization signals, reference signals, beam selection signals, or other control signals) may be transmitted by a base station 105 multiple times in different directions. For example, the base station 105 may transmit a signal according to different beamforming weight sets associated with different directions of transmission. Transmissions in different beam directions may be used to identify (e.g., by a transmitting device, such as a base station 105, or by a receiving device, such as a UE 115) a beam direction for later transmission or reception by the base station 105.

[0070] Some signals, such as data signals associated with a particular receiving device, may be transmitted by a base station 105 in a single beam direction (e.g., a direction associated with the receiving device, such as a UE 115). In some examples, the beam direction associated with transmissions along a single beam direction may be determined based on a signal that was transmitted in one or more beam directions. For example, a UE 115 may receive one or more of the signals transmitted by the base station 105 in different directions and may report to the base station 105 an indication of the signal that the UE 115 received with a highest signal quality or an otherwise acceptable signal quality. [0071] In some examples, transmissions by a device (e.g., by a base station 105 or a UE 115) may be performed using multiple beam directions, and the device may use a combination of digital precoding or radio frequency beamforming to generate a combined beam for transmission (e.g., from a base station 105 to a UE 115). The UE 115 may report feedback that indicates precoding weights for one or more beam directions, and the feedback may correspond to a configured number of beams across a system bandwidth or one or more sub-bands. The base station 105 may transmit a reference signal (e.g., a cell-specific reference signal (CRS), a CSI-RS), which may be precoded or unprecoded. The UE 115 may provide feedback for beam selection, which may be a precoding matrix indicator (PMI) or codebook-based feedback (e.g., a multi-panel type codebook, a linear combination type codebook, a port selection type codebook). Although these techniques are described with reference to signals transmitted in one or more directions by a base station 105, a UE 115 may employ similar techniques for transmitting signals multiple times in different directions (e.g., for identifying a beam direction for subsequent transmission or reception by the UE 115) or for transmitting a signal in a single direction (e.g., for transmitting data to a receiving device).

[0072] A receiving device (e.g., a UE 115) may try multiple receive configurations (e.g., directional listening) when receiving various signals from the base station 105, such as synchronization signals, reference signals, beam selection signals, or other control signals. For example, a receiving device may try multiple receive directions by receiving via different antenna subarrays, by processing received signals according to different antenna subarrays, by receiving according to different receive beamforming weight sets (e.g., different directional listening weight sets) applied to signals received at multiple antenna elements of an antenna array, or by processing received signals according to different receive beamforming weight sets applied to signals received at multiple antenna elements of an antenna array, any of which may be referred to as “listening” according to different receive configurations or receive directions. In some examples, a receiving device may use a single receive configuration to receive along a single beam direction (e.g., when receiving a data signal). The single receive configuration may be aligned in a beam direction determined based on listening according to different receive configuration directions (e.g., a beam direction determined to have a highest signal strength, highest signal-to-noise ratio (SNR), or otherwise acceptable signal quality based on listening according to multiple beam directions). [0073] The wireless communications system 100 may be a packet-based network that operates according to a layered protocol stack. In the user plane, communications at the bearer or Packet Data Convergence Protocol (PDCP) layer may be IP -based. A Radio Link Control (RLC) layer may perform packet segmentation and reassembly to communicate over logical channels. A Medium Access Control (MAC) layer may perform priority handling and multiplexing of logical channels into transport channels. The MAC layer may also use error detection techniques, error correction techniques, or both to support retransmissions at the MAC layer to improve link efficiency. In the control plane, the Radio Resource Control (RRC) protocol layer may provide establishment, configuration, and maintenance of an RRC connection between a UE 115 and a base station 105 or a core network 130 supporting radio bearers for user plane data. At the physical layer, transport channels may be mapped to physical channels.

[0074] As mentioned above, a base station 105 in the wireless communications system 100 may use beamforming to transmit downlink signals to a UE 115. The base station 105 may be capable of generating multiple beams for transmitting the downlink signals to the UE 115. Each beam may be associated with or may correspond to at least one precoder used for precoding signals transmitted on the beam. Precoding may refer to a technique used to weight multiple streams (e.g., data streams) from a transmitting device to limit the effects of a channel on the signals received at a receiving device. In some cases, precoding may depend on an estimation of a channel or other CSI. In one example, to facilitate precoding, a base station 105 may transmit CSI-RSs to a UE 115, and the UE 115 may perform and report channel estimation measurements on the CSI-RSs to the base station 105. In another example, a UE 115 may transmit sounding reference signals (SRSs) to a base station 105, and the base station 105 may perform channel estimation measurements on the SRSs.

[0075] FIG. 2 illustrates an example of a process flow 200 showing channel estimation using SRSs in accordance with aspects of the present disclosure. The process flow 200 illustrates aspects of techniques performed by a UE 115-a, which may be an example of a UE 115 described with reference to FIG. 1. The process flow 200 also illustrates aspects of techniques performed by a base station 105-a, which may be an example of a base station 105 described with reference to FIG. 1. At 205, the UE 115-a may transmit SRSs to the base station 105-a. At 210, the base station 105-a may perform channel estimation based on the SRSs received from the UE 115-a. For example, the base station 105-a may perform measurements on the SRSs received from the UE 115-a. At 215, the base station 105-a may select a precoder to use for subsequent transmissions to the UE 115-a. At 220, the base station 105-a may transmit downlink data to the UE 115-a using the selected precoder.

[0076] FIG. 3 illustrates an example of a process flow 300 showing channel estimation using CSI-RSs in accordance with aspects of the present disclosure. The process flow 300 illustrates aspects of techniques performed by a UE 115-b, which may be an example of a UE 115 described with reference to FIG. 1. The process flow 300 also illustrates aspects of techniques performed by a base station 105-b, which may be an example of a base station 105 described with reference to FIG. 1. At 305, the base station 105-b may transmit CSI-RSs to the UE 115-b. At 310, the UE 115-b may perform channel estimation based on the CSI-RSs received from the base station 105-b. For example, the UE 115-b may perform measurements on the CSI-RSs received from the base station 105-b. At 315, the UE 115-b may transmit a CSI report to the base station 105-b. The CSI report may include a PMI, a rank indicator (RI), and a channel quality indicator (CQI). The PMI may indicate a wideband precoder and one or more subband precoders (e.g., a subband precoder for each subband of a set of subbands). At 320, the base station 105-b may select a precoder to use for subsequent transmissions to the UE 115-a based on the CSI report. At 325, the base station 105-b may transmit downlink data to the UE 115-b using the selected precoder.

[0077] In the example of FIG. 3, the CSI feedback in the CSI report from the UE 115-b may support all possible antenna configurations or a large group of antenna configurations. Further, the CSI report may include a dual stage codebook for some number of ports (e.g., four or more ports). The PMI codebook may assume a W = W₁W₂ precoder structure. W_x may correspond to long-term or wideband properties of the channel and may have the following format: W = where B is composed to L oversampled 2D DFT beams. W₂

may correspond to short-term or subband properties of the channel and may indicate a beam selection or cophasing of polarization. Thus, the search complexity of both W₁ and W₂ may be high, especially for a high number of ports and layers. As a result, the search for W_x and W₂ may use high power and a relaxed timing between receiving CSI-RSs and transmitting a CSI report (e.g., increased latency).

[0078] FIG. 4 illustrates an example of a CSI timeline 400 in accordance with aspects of the present disclosure. For CSF timeline evaluation, there may be three components. One component of the CSF timeline may include a time period420-a (Z) which may be defined as a time from a last symbol in a PDCCH 405 that schedules a PUCCH 415 with CSI feedback to a first uplink transmit symbol of the PUCCH. Another component of the CSF timeline may include a time period 420-b (Z’) which may be defined as a time from a last symbol of a CSI- RS transmission 410 to a first uplink transmit symbol of the PUCCH 415. Yet another component of the CSF timeline may include the time period KB which may be defined as a time from the last symbol in the PDCCH 405 to a time at which beam switching is performed (e.g., in mmW). As an example, for sub-6 communications, it may be appropriate for the Z and Z’ components to be satisfied. Alternatively, for mmW communications, it may be appropriate for the Z, Z’, and KB components to be satisfied. The values of Z and Z’ may be defined for multiple requirements as shown in the tables below, including a first requirement for a low latency case and a second requirement for a default (or normal) case (e.g., Z_x is for medium latency, Z₂ is for high latency, and Z₃ is for reference signal received power (RSRP)).

Table 1: CSI computation delay requirement 1

Table 2: CSI computation delay requirement 2

[0079] As can be seen in tables 1 and 2, the CSF timeline may be tight. As mentioned above, however, W_x and W₂ selection and reporting may use high complexity and power consumption at a UE 115, especially to enable faster and correct reporting. For example, complexity for W_x computation may be 0₁N₁0₂N₂ beam searches in the case of 32 ports (i.e., (O-_L * 0₂ ) * 16 = 16 * 16 = 256 beam searches, where 0-, = 0₂ = 4). The value of O may correspond to oversampling (e.g., four), and the value of N may correspond to a number of antennas (e.g., in a vertical array of antennas). Thus, it may be challenging for a UE 115 to efficiently report CSI feedback to a base station 105 (e.g., with W_x and W₂ selections) while satisfying a CSF timeline (e.g., limiting latency). The wireless communications system 100 may support efficient techniques for wideband and precoder selection to limit power consumption and latency at a UE 115 (e.g., to reduce UE complexity and satisfy a timeline). In one aspect, the UE 115 may search a subset of a set of beams instead of considering all possible beams for CSI feedback (e.g., to enable a faster timeline for the UE to compute a CSI report).

[0080] FIG. 5 illustrates an example of a wireless communications system 500 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The wireless communications system 500 includes abase station 105-c, which may be an example of a base station 105 described with reference to FIGs. 1-4. The wireless communications system 500 also includes a UE 115-c, which may be an example of a UE 115 described with reference to FIGs. 1-4. The base station 105-c may provide communication coverage for geographic coverage area 110-a, which may be an example of a geographic area 110 described with reference to FIG. 1. The base station 105-c may communicate with the UE 115-c on resources of a carrier 505. The wireless communications system 500 may implement aspects of the wireless communications system 100. For example, the wireless communications system 500 may support efficient techniques for wideband and subband precoder selection to limit power consumption and latency at the UE 115-c. [0081] The UE 115-c may transmit SRS to the base station 105-c in an uplink channel to allow the base station 105-c to perform channel estimation. For instance, the UE 115-c may sound the uplink channel through SRS with antenna switching usage that is targeted for downlink CSI acquisition in a reciprocal TDD system. Because the TDD system may be reciprocal, the channel conditions for uplink and downlink channels may be the same or similar. The base station 105-c may receive the SRSs and process the SRSs (e.g., the latest SRSs) and compute the best wideband beams that would provide the best performance to the UE 115-a (e.g., at the UE-side or from the perspective of the UE 115-a). In particular, the base station 105-c may perform measurements on a set of beams and select those beams of the set of beams whose measurements (e.g., RSRP, reference signal received quality (RSRQ), or signal-to-interference-plus-noise ratio (SINR)) satisfy a threshold. Additionally, or alternatively, the base station 105-c may select those beams of the set of beams with the best measurements (e.g., the top X beams with the highest measurements).

[0082] The base station 105-c may then transmit CSI-RSs to the UE 115-c. The base station 105-c may also transmit an indication of a subset of the set of beams to the UE 115-c that the UE 115-c may use to determine a wideband precoder to report to the base station 105-c. For example, the base station 105-c may indicate to the UE 115-c the best W1 beams and a number of neighboring beams (n₅) surrounding the best W1 beams for the UE 115-c to evaluate. The subset of the set of beams indicated to the UE 115-c may include the best W 1 beams and the number of neighboring beams surrounding the best W1 beams. The UE 115-c may then search the subset of the set of beams for the best W1 selection or the best selection of wideband beams based on the CSI-RSs received from the base station 105-c (e.g., estimate the channel across CSI-RS ports to identify a PMI, RI, or CQI). That is, the UE 115-c may perform measurements on the subset of the set of beams (e.g., based on the CSI-RSs) to identify a preferred (e.g., best) beam for the base station 105-c to use for downlink transmissions to the UE 115-c. As an example, the UE 115-c may search beam i indicated by the base station 105-c and neighboring beams around beam i (e.g., the UE 115-c may search beams with the following indices: ( i + n₅), where n_B e {—M, — (M — 1), . . . ,0,1,2, . . . , M.

[0083] Once the UE 115-c identifies the wideband precoder to report to the base station 105-c based on the subset of the set of beams, the UE 115-c may report the wideband precoder in the PUCCH 515. The UE 115-c may also transmit SRSs in the PUCCH to the base station 105-c. The base station 105-c may receive the indication of the wideband precoder and the SRSs in the PUCCH 515, and the base station 105 may identify a wideband precoder to use for transmitting a PDSCH to the UE 115-c based on one or more of the SRSs received before the CSI-RS 510, the wideband precoder indicated by the UE 115-c, and the SRSs received in the PUCCH 515 In particular, the base station 105-c may estimate a channel across SRS ports with the PMI, RI, and CQI received in the PUCCH 515 from the UE 115-c. The base station 105-c may then precode the PDSCH using the identified wideband precoder and transmit the precoded PDSCH 520 to the UE 115-c. Because the UE 115-c may avoid performing measurements on (e.g., evaluating) the full set of beams and may instead perform measurements on the subset of the set of beams, the complexity at the UE 115-c may be reduced. For example, the UE 115-c may search 2 M + 1 beams instead of 0₁N₁0₂N₂ beams.

[0084] In some cases, in addition to providing the subset of the set of beams to the UE 115-c to minimize the complexity of selecting and reporting a wideband precoder, the base station 105-c may provide subband parameters to the UE 115-c to minimize the complexity of selecting and reporting a subband precoder for each subband of a set of subbands. In one aspect, the base station 105-c may indicate one or more subband parameters to the UE 115-c for the UE 115-c to use to identify a subband precoder for each subband of a set of subbands. The one or more subband parameters may be a subset of a set of subband parameters, and the UE 115-c may avoid determining a subband precoder for a subband based on the full set of subband parameters. Instead, the UE 115-c may determine the subband precoder for the subband based on the subset of the set of subband parameters. In another aspect, the base station 150-c may indicate a subset of values of a set of values of a subband parameter to the UE 115-c for the UE 115-c to use to identify a subband precoder for each subband of a set of subbands. Thus, the UE 115-c may avoid determining a subband precoder for a subband based on the full set of values (e.g., all possible values) for the subband parameter. Instead, the UE 115-c may determine the subband precoder for the subband based on the subset of the set of values of the subband parameter.

[0085] FIG. 6 illustrates an example of a process flow 600 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The UE 115-d may transmit SRSs to the base station 105-d, and the base station 105-d may determine the best set of beams (e.g., a set of one or more beams). The base station 105-d may send an indication of the best set of beams to the UE 115-d (e.g., in DCI), where the best set of beams may correspond to a subset of a set of beams. The base station 105-d may then transmit CSI- RSs to the UE 115-d. The UE 115-d may receive the CSI-RSs (e.g., CSI-RS pilots) and may estimate a downlink channel on which the CSI-RSs are received. The UE 115-d may then perform W 1 selection to select a wideband precoder to report to the base station 105-d based on the subset of the set of beams (e.g., based on measurements or searches performed on the subset of the set of beams), and the UE 115-d may report the W1 selection to the base station 105-d.

[0086] The UE 115-d may also perform W2 selection based on phases sent by the base station 105-d. That is, the base station 105-d may indicate one or more phases to the UE 115-d, and the UE 115-d may select a subband precoder for each subband of a set of subbands (e.g., perform W2 selection) based on the one or more phases sent by the base station 105-d. The UE 115-d may also report the W2 selection to the base station 105-d. The base station 105-d may receive the W1 and W2 selection and compute the best joint W1W2 precoder based on the subset of the set of beams indicated to the UE 115-d, the report of the W1 and W2 selection from the UE 115-d, and the SRSs received from the UE 115-d (e.g., the SRSs received before and after indicating the subset of the set of beams). The base station 105-d may then precode a PDSCH using the joint W 1W2 precoder and may transmit the precoded PDSCH to the UE 115-d.

[0087] FIG. 7 illustrates an example of a process flow 700 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The UE 115-e may transmit SRSs to the base station 105-e, and the base station 105-e may determine the best set of beams (e.g., a set of one or more beams). The base station 105-e may send an indication of the best set of beams to the UE 115-e (e.g., in DCI), where the best set of beams may correspond to a subset of a set of beams. The base station 105-e may then transmit CSI- RSs to the UE 115-e. The UE 115-e may receive the CSI-RSs (e.g., CSI-RS pilots) and may estimate a downlink channel on which the CSI-RSs are received. The UE 115-e may then perform W 1 selection to select a wideband precoder to report to the base station 105-e based on the subset of the set of beams (e.g., based on measurements or searches performed on the subset of the set of beams), and the UE 115-e may report the W1 selection to the base station 105-e.

[0088] The UE 115-e may also perform W2 selection based on subband parameters sent by the base station 105-e. That is, the base station 105-e may indicate one or more subband parameters to the UE 115-e, and the UE 115-e may select a subband precoder for each subband of a set of subbands (e.g., perform W2 selection) based on the one or more phases sent by the base station 105-e. In some cases, the base station 105-e may also indicate a subset of a set of values of at least one subband parameter for the UE 115-e to use to identify a subband precoder for a subband. In such cases, the UE 115-e may perform W2 selection based on the subset of the set of values of the at least one subband parameter. The UE 115-e may then report the W2 selection to the base station 105-e. The base station 105-e may receive the W1 and W2 selection and compute the best joint W1W2 precoder based on the subset of the set of beams indicated to the UE 115-e, the report of the W1 and W2 selection from the UE 115-e, and the SRSs received from the UE 115-e (e.g., the SRSs received before and after indicating the subset of the set of beams). The base station 105-e may then precode a PDSCH using the joint W 1W2 precoder and may transmit the precoded PDSCH to the UE 115-e.

[0089] In the examples of FIGs. 6 and 7, the base station 105 may use multiple indications to indicate the subset of the set of beams to the UE 115 for the UE 115 to use to identify the wideband precoder. In particular, the base station 105 may transmit, to the UE 115, a first indication of one or more beams (e.g., the best wideband beams) and a second indication of a number of neighboring beams to the one or more beams. The base station 105 may transmit the first indication of the one or more beams (e.g., the indices of the one or more W1 and W2 beams) dynamically in DCI. And the base station 105 may transmit the second indication of the number of neighboring beam with respect to the one or more beams in RRC signaling, a MAC control element (MAC-CE), or DCI. Thus, the number of neighboring beams (e.g., denoted as the number of reduced beams) may be introduced at the CSI report level. Alternatively, the base station 105 may indicate the subset of the set of beams using a bitmap (e.g., in DCI or a MAC-CE). That is, the base station 105 may indicate a bitmap of the subset of the set of beams (e.g., W1 or W2 beams) to be considered at the UE 115 for reporting to the base station 105. Each bit in the bitmap may correspond to a beam in a set of beams, and a bit value of one in the bitmap may indicate that a corresponding beam is in the subset of the set of beams for the UE 115-d to use to identify the wideband precoder.

[0090] In the example of FIG. 7, the base station 105-e may also use multiple indications to indicate the subset of the set of values of at least one subband parameter to the UE 115-e for the UE 115-e to use to identify a subband precoder for a subband. The at least one subband parameter may be a phase, phase shift, scaling factor, etc. The base station 105-e may transmit, to the UE 115-e, a first indication of one or more values of the at least one subband parameter (e.g., the values that are most likely to result in the best subband precoder for a subband) and a second indication of a number of neighboring values to the one or more values. In some cases, the second indication of the number of neighboring values may be common for all subband parameters (e.g., the same number of neighboring values for multiple subband parameters). In other cases, the second indication of the number of neighboring values may be different for different subband parameters (e.g., different numbers of neighboring values for different subband parameters). In such cases, the base station 105-e may determine the number of neighboring values for a subband parameter based on CSI feedback (e.g., an NR CSI feedback type).

[0091] Thus, the base station 105-e may indicate to the UE 115-e the number of neighboring beams for W1 selection (e.g., denoted as the number of reduced beams) and the number of neighboring values for one or more values of a subband parameter (e.g., denoted as the number of reduced W2 parameters). That is, in addition to a W1 precoder or beam, the base station 105-e may send a W2 precoder to the UE 115-e. The UE 115-e may then use this information (e.g., the W1 and W2 precoders) to obtain more accurate precoders. If both W1 and W2 precoders are shared by the base station 105-e, the UE 115-e may search around provided parameters (e.g., subband parameters) to achieve the best precoders (e.g., corresponding to beams) among the values shared by the base station 105-e (e.g., among the W1 and W2 precoders shared by the base station 105-e). Then, the base station 105-e may identify the best precoders (e.g., joint W 1 and W2 precoders) to be used for PDSCH transmissions to the UE 115-e based on the information sent by the base station 105-e to the UE 115-e (e.g., the W1 and W2 precoders), based on computations performed by the UE 115-e to obtain W1 and W2 precoders that are reported to the base station 105-e, and based on SRSs received from the UE 115-e (e.g., newer SRSs received after transmitting CSI-RSs).

[0092] The example described with reference to FIG. 6 related to indicating a subset of a set of beams for a UE 115 to use to identify a wideband precoder may be referred to as a first mode of operation (e.g., mode 1). And the example described with reference to FIG. 7 related to indicating a subset of a set of beams for a UE 115 to use to identify a wideband precoder and indicating a subset of a set of values of at least one subband parameter for a UE 115 to use to identify a subband precoder for a subband may be referred to as a second mode of operation (e.g., mode 2). Thus, the base station 105 may indicate beam indices for the first and second modes of operation, and the base station 105 may indicate phases and subband parameters (e.g., values of the phases and subband parameters) for the second mode of operation. In the first mode of operation, a base station 105 may send W1 selection parameters which include a subset of potential wideband beams (e.g., one or more beams). In this mode of operation, a UE 115 may search around those beams for a W1 selection. The UE 115 may also search for a W2 selection (e.g., a subband precoder for a subband). In the second mode of operation, a base station 105 may send parameters for both W1 and W2 precoders. In this mode of operation, a UE 115 may search around a subset of W1 or wideband beams and a set of W2 parameters closely related to the W2 parameters sent by the base station 105.

[0093] In some cases, the techniques described herein may be configurable. For example, a base station 105 may transmit a trigger to a UE 115 for the UE 115 to perform measurements on a subset of a set of beams to identify a wideband precoder. Alternatively, a base station 105 may transmit a trigger to a UE 115 for the UE 115 to perform measurements on a full set of beams to identify a wideband precoder. Further, the mode of operation at a UE 115 may also be configurable. For example, a base station 105 may transmit a trigger for the UE 115 to operate in the first mode, where the UE 115 may identify a wideband precoder based on a subset of a set of beams. Alternatively, the base station 105 may transmit a trigger for the UE 115 to operate in the second mode, where the UE 115 may identify a wideband precoder based on a subset of a set of beams and identify a subband precoder for a subband based on a subset of a set of values of a subband parameter. In some examples, a base station 105 may also transmit a channel rank (e.g., number of layers) to a UE 115.

[0094] The techniques described herein may allow for a low power configuration at a UE 115, since the computations performed at the UE 115 may be minimized. Further, the UE 115 may support faster timelines (e.g., for CSF), and the UE 115 may be able to satisfy the requirements described with reference to FIG. 4. As mentioned above, a base station 105 may configure a UE 115 separately for each CSI report to either perform measurements on a full set of beams or a subset of the set of beams to identify a wideband precoder (e.g., such that the UE 115 may still be configured to perform measurements on the full set of beams to identify the wideband precoder for some CSI reports). Further, the base station 105 may transmit the indication of the subset of the set of beams to a UE 115 (e.g., in RRC, MAC-CE, or DCI signaling) a threshold amount of time before the UE 115 is scheduled to transmit a CSI report (e.g., at least X symbols before the UE 115 is to transmit the CSI report).

[0095] FIG. 8 shows a block diagram 800 of a device 805 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The device 805 may be an example of aspects of a UE 115 as described herein. The device 805 may include a receiver 810, a communications manager 815, and a transmitter 820. The device 805 may also include one or more processors, memory coupled with the one or more processors, and instructions stored in the memory that are executable by the one or more processors to enable the one or more processors to perform precoder management features discussed herein. Each of these components may be in communication with one another (e.g., via one or more buses).

[0096] The receiver 810 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to wideband and subband precoder selection, etc.). Information may be passed on to other components of the device 805. The receiver 810 may be an example of aspects of the transceiver 1120 described with reference to FIG. 11. The receiver 810 may utilize a single antenna or a set of antennas.

[0097] The communications manager 815 may receive, from a base station, CSI-RSs, receive, from the base station, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder, identify the wideband precoder corresponding to a beam of the subset of the set of beams based on the CSI-RSs, and report, to the base station, the wideband precoder in CSF. The communications manager 815 may be an example of aspects of the communications manager 1110 described herein. The communications manager 815 as described herein may be implemented to realize one or more potential improvements. At least one implementation may enable the communications manager 815 to support wideband and subband precoder selection. Because the UE may perform fewer computations for wideband and subband precoder selection as described herein, one or more processors of the device 805 may experience minimized complexity and reduced latency and power consumption.

[0098] The communications manager 815, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the communications manager 815, or its sub-components may be executed by a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field- programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure.

[0099] The communications manager 815, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the communications manager 815, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the communications manager 815, or its sub-components, may be combined with one or more other hardware components, including but not limited to an input/output (I/O) component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure.

[0100] The transmitter 820 may transmit signals generated by other components of the device 805. In some examples, the transmitter 820 may be collocated with a receiver 810 in a transceiver module. For example, the transmitter 820 may be an example of aspects of the transceiver 1120 described with reference to FIG. 11. The transmitter 820 may utilize a single antenna or a set of antennas.

[0101] FIG. 9 shows a block diagram 900 of a device 905 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The device 905 may be an example of aspects of a device 805, or a UE 115 as described herein. The device 905 may include a receiver 910, a communications manager 915, and a transmitter 940. The device 905 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses).

[0102] The receiver 910 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to wideband and subband precoder selection, etc.). Information may be passed on to other components of the device 905. The receiver 910 may be an example of aspects of the transceiver 1120 described with reference to FIG. 11. The receiver 910 may utilize a single antenna or a set of antennas.

[0103] The communications manager 915 may be an example of aspects of the communications manager 815 as described herein. The communications manager 915 may include a CSI-RS manager 920, a beam manager 925, a precoder manager 930, and a CSI report manager 935. The communications manager 915 may be an example of aspects of the communications manager 1110 described herein.

[0104] The CSI-RS manager 920 may receive, from a base station CSI-RSs. The beam manager 925 may receive, from the base station, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder. The precoder manager 930 may identify the wideband precoder corresponding to a beam of the subset of the set of beams based on the CSI-RSs. The CSI report manager 935 may report, to the base station, the wideband precoder in CSF.

[0105] The transmitter 940 may transmit signals generated by other components of the device 905. In some examples, the transmitter 940 may be collocated with a receiver 910 in a transceiver module. For example, the transmitter 940 may be an example of aspects of the transceiver 1120 described with reference to FIG. 11. The transmitter 940 may utilize a single antenna or a set of antennas.

[0106] In some cases, the CSI-RS manager 920, the precoder manager 930, and the CSI report manager 935 may each be or be at least a part of a processor (e.g., a transceiver processor, or a radio processor, or a transmitter processor, or a receiver processor). The processor may be coupled with memory and execute instructions stored in the memory that enable the processor to perform or facilitate the features of the CSI-RS manager 920, the precoder manager 930, and the CSI report manager 935 discussed herein. A transceiver processor may be collocated with or communicate with (e.g., direct the operations of) a radio (e.g., an NR radio, an LTE radio, a Wi-Fi radio) of the device, or both. A transmitter processor may be collocated with or communicate with (e.g., direct the operations of) a transmitter of the device, or both. A receiver processor may be collocated with or communicate with (e.g., direct the operations of) a receiver of the device, or both.

[0107] FIG. 10 shows a block diagram 1000 of a communications manager 1005 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The communications manager 1005 may be an example of aspects of a communications manager 815, a communications manager 915, or a communications manager 1110 described herein. The communications manager 1005 may include a CSI-RS manager 1010, a beam manager 1015, a precoder manager 1020, a CSI report manager 1025, a SRS manager 1030, and a subband parameter manager 1035. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses).

[0108] The CSI-RS manager 1010 may receive, from a base station, CSI-RSs. The beam manager 1015 may receive, from the base station, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder. In some examples, the beam manager 1015 may receive, from the base station, a first indication indicating one or more beams from which the UE is to identify the wideband precoder. In some examples, the beam manager 1015 may receive, from the base station, a second indication indicating neighboring beams to each of the one or more beams from which the UE is to identify the wideband precoder. In some examples, the beam manager 1015 may determine the neighboring beams to each of the one or more beams based on the quantity of the neighboring beams. In some cases, the second indication includes an RRC message, a MAC-CE, or a DCI message. In some cases, the first indication includes a DCI message. In some cases, the indication of the subset of the set of beams is received a threshold amount of time before reporting the CSF.

[0109] The precoder manager 1020 may identify the wideband precoder corresponding to a beam of the subset of the set of beams based on the CSI-RSs. In some examples, the precoder manager 1020 may identify the subband precoder for each subband of the set of subbands to report to the base station in the CSF based on the one or more subband parameters. In some examples, the precoder manager 1020 may identify the subband precoder for each subband of the set of subbands to report to the base station in the CSF based on the subset of the set of values of the at least one subband parameter. In some examples, the precoder manager 1020 may receive, from the base station, a trigger to identify the subband precoder for each subband of the set of subbands based on the subset of the set of values of the at least one subband parameter. In some examples, the precoder manager 1020 may receive, from the base station, a trigger to identify the wideband precoder based on the subset of the set of beams. [0110] The CSI report manager 1025 may report, to the base station, the wideband precoder in CSF. In some examples, the CSI report manager 1025 may report, to the base station, the subband precoder for each subband of the set of subbands in the CSF. The SRS manager 1030 may transmit, to the base station, SRSs, where receiving the indication of the subset of the set of beams is based on transmitting the SRSs. The subband parameter manager 1035 may receive, from the base station, an indication of one or more subband parameters for the UE to use to identify a subband precoder for each subband of a set of subbands. In some examples, the subband parameter manager 1035 may receive, from the base station, an indication of a subset of a set of values of at least one subband parameter for the UE to use to identify a subband precoder for each subband of a set of subbands.

[0111] In some examples, the subband parameter manager 1035 may receive, from the base station, a first indication indicating one or more values of the at least one subband parameter for the UE to use to identify the subband precoder for each subband of the set of subbands. In some examples, the subband parameter manager 1035 may receive, from the base station, a second indication indicating neighboring values to each of the one or more values for the UE to use to identify the subband precoder for each subband of the set of subbands. In some examples, the subband parameter manager 1035 may determine the neighboring values to each of the one or more values based on the quantity of the neighboring values.

[0112] In some cases, the CSI-RS manager 1010, the beam manager 1015, the precoder manager 1020, the CSI report manager 1025, the SRS manager 1030, and the subband parameter manager 1035 may each be or be at least a part of a processor (e.g., a transceiver processor, or a radio processor, or a transmitter processor, or a receiver processor). The processor may be coupled with memory and execute instructions stored in the memory that enable the processor to perform or facilitate the features of the CSI-RS manager 1010, the beam manager 1015, the precoder manager 1020, the CSI report manager 1025, the SRS manager 1030, and the subband parameter manager 1035 discussed herein.

[0113] FIG. 11 shows a diagram of a system 1100 including a device 1105 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The device 1105 may be an example of or include the components of device 805, device 905, or a UE 115 as described herein. The device 1105 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager 1110, an I/O controller 1115, a transceiver 1120, an antenna 1125, memory 1130, and a processor 1140. These components may be in electronic communication via one or more buses (e.g., bus 1145).

[0114] The communications manager 1110 may receive, from a base station, CSI-RSs, receive, from the base station, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder, identify the wideband precoder corresponding to a beam of the subset of the set of beams based on the CSI-RSs, and report, to the base station, the wideband precoder in CSF.

[0115] The I/O controller 1115 may manage input and output signals for the device 1105. The I/O controller 1115 may also manage peripherals not integrated into the device 1105. In some cases, the I/O controller 1115 may represent a physical connection or port to an external peripheral. In some cases, the I/O controller 1115 may utilize an operating system such as iOS®, ANDROID®, MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, or another known operating system. In other cases, the I/O controller 1115 may represent or interact with a modem, a keyboard, a mouse, a touchscreen, or a similar device. In some cases, the I/O controller 1115 may be implemented as part of a processor. In some cases, a user may interact with the device 1105 via the I/O controller 1115 or via hardware components controlled by the I/O controller 1115.

[0116] The transceiver 1120 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 1120 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1120 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas.

[0117] In some cases, the wireless device may include a single antenna 1125. However, in some cases the device may have more than one antenna 1125, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

[0118] The memory 1130 may include random-access memory (RAM) and read-only memory (ROM). The memory 1130 may store computer-readable, computer-executable code 1135 including instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory 1130 may contain, among other things, a basic input/output system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices.

[0119] The processor 1140 may include an intelligent hardware device, (e.g., a general- purpose processor, a DSP, a central processing unit (CPU), a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof). In some cases, the processor 1140 may be configured to operate a memory array using a memory controller. In other cases, a memory controller may be integrated into the processor 1140. The processor 1140 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1130) to cause the device 1105 to perform various functions (e.g., functions or tasks supporting wideband and subband precoder selection).

[0120] The code 1135 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 1135 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 1135 may not be directly executable by the processor 1140 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

[0121] FIG. 12 shows a block diagram 1200 of a device 1205 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The device 1205 may be an example of aspects of a base station 105 as described herein. The device 1205 may include a receiver 1210, a communications manager 1215, and a transmitter 1220. The device 1205 may also include one or more processors, memory coupled with the one or more processors, and instructions stored in the memory that are executable by the one or more processors to enable the one or more processors to perform precoder management features discussed herein. Each of these components may be in communication with one another (e.g., via one or more buses).

[0122] The receiver 1210 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to wideband and subband precoder selection, etc.). Information may be passed on to other components of the device 1205. The receiver 1210 may be an example of aspects of the transceiver 1520 described with reference to FIG. 15.

The receiver 1210 may utilize a single antenna or a set of antennas.

[0123] The communications manager 1215 may transmit, to a UE, CSI-RSs, transmit, to the UE, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder, and receive, from the UE, the wideband precoder corresponding to a beam of the subset of the set of beams based on transmitting the CSI-RSs and transmitting the indication of the subset of the set of beams. The communications manager 1215 may be an example of aspects of the communications manager 1510 described herein. The communications manager 1215 as described herein may be implemented to realize one or more potential improvements. At least one implementation may enable the communications manager 1215 to support wideband and subband precoder selection. Because the UE may perform fewer computations for wideband and subband precoder selection as described herein, one or more processors of the device 1205 may experience minimized complexity and reduced latency and power consumption.

[0124] The communications manager 1215, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the communications manager 1215, or its sub-components may be executed by a general-purpose processor, a DSP, an ASIC, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure.

[0125] The communications manager 1215, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the communications manager 1215, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the communications manager 1215, or its sub-components, may be combined with one or more other hardware components, including but not limited to an input/output (I/O) component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure. [0126] The transmitter 1220 may transmit signals generated by other components of the device 1205. In some examples, the transmitter 1220 may be collocated with a receiver 1210 in a transceiver module. For example, the transmitter 1220 may be an example of aspects of the transceiver 1520 described with reference to FIG. 15. The transmitter 1220 may utilize a single antenna or a set of antennas.

[0127] FIG. 13 shows a block diagram 1300 of a device 1305 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The device 1305 may be an example of aspects of a device 1205, or a base station 105 as described herein. The device 1305 may include a receiver 1310, a communications manager 1315, and a transmitter 1335. The device 1305 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses).

[0128] The receiver 1310 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to wideband and subband precoder selection, etc.). Information may be passed on to other components of the device 1305. The receiver 1310 may be an example of aspects of the transceiver 1520 described with reference to FIG. 15.

The receiver 1310 may utilize a single antenna or a set of antennas.

[0129] The communications manager 1315 may be an example of aspects of the communications manager 1215 as described herein. The communications manager 1315 may include a CSI-RS manager 1320, a beam manager 1325, and a precoder manager 1330. The communications manager 1315 may be an example of aspects of the communications manager 1510 described herein.

[0130] The CSI-RS manager 1320 may transmit, to a UE, CSI-RSs. The beam manager 1325 may transmit, to the UE, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder. The precoder manager 1330 may receive, from the UE, the wideband precoder corresponding to a beam of the subset of the set of beams based on transmitting the CSI-RSs and transmitting the indication of the subset of the set of beams.

[0131] The transmitter 1335 may transmit signals generated by other components of the device 1305. In some examples, the transmitter 1335 may be collocated with a receiver 1310 in a transceiver module. For example, the transmitter 1335 may be an example of aspects of the transceiver 1520 described with reference to FIG. 15. The transmitter 1335 may utilize a single antenna or a set of antennas.

[0132] In some cases, the CSI-RS manager 1320, the beam manager 1325, and the precoder manager 1330 may each be or be at least a part of a processor (e.g., a transceiver processor, or a radio processor, or a transmitter processor, or a receiver processor). The processor may be coupled with memory and execute instructions stored in the memory that enable the processor to perform or facilitate the features of the CSI-RS manager 1320, the beam manager 1325, and the precoder manager 1330 discussed herein. A transceiver processor may be collocated with or communicate with (e.g., direct the operations of) a radio (e.g., an NR radio, an LTE radio, a Wi-Fi radio) of the device, or both. A transmitter processor may be collocated with or communicate with (e.g., direct the operations of) a transmitter of the device, or both. A receiver processor may be collocated with or communicate with (e.g., direct the operations of) a receiver of the device, or both.

[0133] FIG. 14 shows a block diagram 1400 of a communications manager 1405 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The communications manager 1405 may be an example of aspects of a communications manager 1215, a communications manager 1315, or a communications manager 1510 described herein. The communications manager 1405 may include a CSI-RS manager 1410, a beam manager 1415, a precoder manager 1420, a SRS manager 1425, and a subband parameter manager 1430. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses).

[0134] The CSI-RS manager 1410 may transmit, to a UE, CSI-RSs. The beam manager 1415 may transmit, to the UE, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder. In some examples, the beam manager 1415 may select the subset of the set of beams from which the UE is to identify the wideband precoder based on the SRSs. In some examples, the beam manager 1415 may transmit a first indication indicating one or more beams from which the UE is to identify the wideband precoder. In some examples, the beam manager 1415 may transmit a second indication indicating neighboring beams to each of the one or more beams from which the UE is to identify the wideband precoder. In some cases, the second indication indicates a quantity of the neighboring beams. In some cases, the second indication includes an RRC message, a MAC- CE, or a DCI message. In some cases, the first indication includes a DCI message. In some cases, the indication of the subset of the set of beams is transmitted a threshold amount of time before receiving the CSF.

[0135] The precoder manager 1420 may receive, from the UE, the wideband precoder corresponding to a beam of the subset of the set of beams based on transmitting the CSI-RSs and transmitting the indication of the subset of the set of beams. In some examples, the precoder manager 1420 may receive, from the UE, the subband precoder for each subband of the set of subbands in the CSF based on transmitting the indication of the one or more subband parameters. In some examples, the precoder manager 1420 may receive, from the UE, the subband precoder for each subband of the set of subbands in the CSF based on transmitting the indication of the subset of the set of values of the at least one subband parameter. In some examples, the precoder manager 1420 may transmit, to the UE, a trigger to identify the subband precoder for each subband of the set of subbands based on the subset of the set of values of the at least one subband parameter. In some examples, the precoder manager 1420 may transmit, to the UE, a trigger to identify the wideband precoder based on the subset of the set of beams.

[0136] The SRS manager 1425 may receive, from the UE, SRSs. The subband parameter manager 1430 may transmit, to the UE, an indication of one or more subband parameters for the UE to use to identify a subband precoder for each subband of a set of subbands. In some examples, the subband parameter manager 1430 may transmit, to the UE, an indication of a subset of a set of values of at least one subband parameter for the UE to use to identify a subband precoder for each subband of a set of subbands. In some examples, the subband parameter manager 1430 may transmit, to the UE, a first indication indicating one or more values of the at least one subband parameter for the UE to use to identify the subband precoder for each subband of the set of subbands. In some examples, the subband parameter manager 1430 may transmit, to the UE, a second indication indicating neighboring values to each of the one or more values for the UE to use to identify the subband precoder for each subband of the set of subbands. In some cases, the second indication indicates a quantity of the neighboring values.

[0137] In some cases, the CSI-RS manager 1410, the beam manager 1415, the precoder manager 1420, the SRS manager 1425, and the subband parameter manager 1430 may each be or be at least a part of a processor (e.g., a transceiver processor, or a radio processor, or a transmitter processor, or a receiver processor). The processor may be coupled with memory and execute instructions stored in the memory that enable the processor to perform or facilitate the features of the CSI-RS manager 1410, the beam manager 1415, the precoder manager 1420, the SRS manager 1425, and the subband parameter manager 1430 discussed herein.

[0138] FIG. 15 shows a diagram of a system 1500 including a device 1505 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The device 1505 may be an example of or include the components of device 1205, device 1305, or a base station 105 as described herein. The device 1505 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager 1510, a network communications manager 1515, a transceiver 1520, an antenna 1525, memory 1530, a processor 1540, and an inter-station communications manager 1545. These components may be in electronic communication via one or more buses (e.g., bus 1550).

[0139] The communications manager 1510 may transmit, to a UE, CSI-RSs, transmit, to the UE, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder, and receive, from the UE, the wideband precoder corresponding to a beam of the subset of the set of beams based on transmitting the CSI-RSs and transmitting the indication of the subset of the set of beams.

[0140] The network communications manager 1515 may manage communications with the core network (e.g., via one or more wired backhaul links). For example, the network communications manager 1515 may manage the transfer of data communications for client devices, such as one or more UEs 115.

[0141] The transceiver 1520 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 1520 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1520 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas. [0142] In some cases, the wireless device may include a single antenna 1525. However, in some cases the device may have more than one antenna 1525, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

[0143] The memory 1530 may include RAM, ROM, or a combination thereof. The memory 1530 may store computer-readable code 1535 including instructions that, when executed by a processor (e.g., the processor 1540) cause the device to perform various functions described herein. In some cases, the memory 1530 may contain, among other things, a BIOS which may control basic hardware or software operation such as the interaction with peripheral components or devices.

[0144] The processor 1540 may include an intelligent hardware device, (e.g., a general- purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof). In some cases, the processor 1540 may be configured to operate a memory array using a memory controller. In some cases, a memory controller may be integrated into processor 1540. The processor 1540 may be configured to execute computer- readable instructions stored in a memory (e.g., the memory 1530) to cause the device 1505 to perform various functions (e.g., functions or tasks supporting wideband and subband precoder selection).

[0145] The inter-station communications manager 1545 may manage communications with other base station 105, and may include a controller or scheduler for controlling communications with UEs 115 in cooperation with other base stations 105. For example, the inter-station communications manager 1545 may coordinate scheduling for transmissions to UEs 115 for various interference mitigation techniques such as beamforming or joint transmission. In some examples, the inter-station communications manager 1545 may provide an X2 interface within an LTE/LTE-A wireless communication network technology to provide communication between base stations 105.

[0146] The code 1535 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 1535 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 1535 may not be directly executable by the processor 1540 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

[0147] FIG. 16 shows a flowchart illustrating a method 1600 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The operations of method 1600 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1600 may be performed by a communications manager as described with reference to FIGs. 8 through 11. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally, or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

[0148] At 1605, the UE may receive, from a base station, CSI-RSs. The operations of 1605 may be performed according to the methods described herein. In some examples, aspects of the operations of 1605 may be performed by a CSI-RS manager as described with reference to FIGs. 8 through 11.

[0149] At 1610, the UE may receive, from the base station, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder. The operations of 1610 may be performed according to the methods described herein. In some examples, aspects of the operations of 1610 may be performed by a beam manager as described with reference to FIGs. 8 through 11.

[0150] At 1615, the UE may identify the wideband precoder corresponding to a beam of the subset of the set of beams based on the CSI-RSs. The operations of 1615 may be performed according to the methods described herein. In some examples, aspects of the operations of 1615 may be performed by a precoder manager as described with reference to FIGs. 8 through 11.

[0151] At 1620, the UE may report, to the base station, the wideband precoder in CSF. The operations of 1620 may be performed according to the methods described herein. In some examples, aspects of the operations of 1620 may be performed by a C SI report manager as described with reference to FIGs. 8 through 11.

[0152] FIG. 17 shows a flowchart illustrating a method 1700 that supports wideband and subband precoder selection in accordance with aspects of the present disclosure. The operations of method 1700 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 1700 may be performed by a communications manager as described with reference to FIGs. 12 through 15. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described below. Additionally, or alternatively, a base station may perform aspects of the functions described below using special-purpose hardware.

[0153] At 1705, the base station may transmit, to a UE, CSI-RSs. The operations of 1705 may be performed according to the methods described herein. In some examples, aspects of the operations of 1705 may be performed by a CSI-RS manager as described with reference to FIGs. 12 through 15.

[0154] At 1710, the base station may transmit, to the UE, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder. The operations of 1710 may be performed according to the methods described herein. In some examples, aspects of the operations of 1710 may be performed by a beam manager as described with reference to FIGs. 12 through 15.

[0155] At 1715, the base station may receive, from the UE, the wideband precoder corresponding to a beam of the subset of the set of beams based on transmitting the CSI-RSs and transmitting the indication of the subset of the set of beams. The operations of 1715 may be performed according to the methods described herein. In some examples, aspects of the operations of 1715 may be performed by a precoder manager as described with reference to FIGs. 12 through 15.

[0156] The following provides an overview of aspects of the present disclosure:

[0157] Aspect 1 : A method for wireless communication at a UE, comprising: receiving, from a base station, CSI-RSs; receiving, from the base station, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder; identifying the wideband precoder corresponding to a beam of the subset of the set of beams based at least in part on the CSI-RSs; and reporting, to the base station, the wideband precoder in CSF. [0158] Aspect 2: The method of aspect 1, further comprising: transmitting, to the base station, SRSs, wherein receiving the indication of the subset of the set of beams is based at least in part on transmitting the SRSs.

[0159] Aspect 3: The method of any of aspects 1 through 2, wherein receiving the indication of the subset of the set of beams comprises: receiving, from the base station, a first indication indicating one or more beams from which the UE is to identify the wideband precoder; and receiving, from the base station, a second indication indicating neighboring beams to each of the one or more beams from which the UE is to identify the wideband precoder.

[0160] Aspect 4: The method of aspect 3, wherein the second indication indicates a quantity of the neighboring beams, the method further comprising: determining the neighboring beams to each of the one or more beams based at least in part on the quantity of the neighboring beams.

[0161] Aspect 5: The method of any of aspects 3 through 4, wherein the second indication comprises an RRC message, a MAC-CE, or a DCI message.

[0162] Aspect 6: The method of any of aspects 3 through 5, wherein the first indication comprises a DCI message.

[0163] Aspect 7: The method of any of aspects 1 through 6, further comprising: receiving, from the base station, an indication of one or more subband parameters for the UE to use to identify a subband precoder for each subband of a set of subbands; identifying the subband precoder for each subband of the set of subbands to report to the base station in the CSF based at least in part on the one or more subband parameters; and reporting, to the base station, the subband precoder for each subband of the set of subbands in the CSF.

[0164] Aspect 8: The method of any of aspects 1 through 7, further comprising: receiving, from the base station, an indication of a subset of a set of values of at least one subband parameter for the UE to use to identify a subband precoder for each subband of a set of subbands; identifying the subband precoder for each subband of the set of subbands to report to the base station in the CSF based at least in part on the subset of the set of values of the at least one subband parameter; and reporting, to the base station, the subband precoder for each subband of the set of subbands in the CSF. [0165] Aspect 9: The method of aspect 8, wherein receiving the indication of the subset of the set of values of the at least one subband parameter comprises: receiving, from the base station, a first indication indicating one or more values of the at least one subband parameter for the UE to use to identify the subband precoder for each subband of the set of subbands; and receiving, from the base station, a second indication indicating neighboring values to each of the one or more values for the UE to use to identify the subband precoder for each subband of the set of subbands.

[0166] Aspect 10: The method of aspect 9, wherein the second indication indicates a quantity of the neighboring values, the method further comprising: determining the neighboring values to each of the one or more values based at least in part on the quantity of the neighboring values.

[0167] Aspect 11 : The method of any of aspects 8 through 10, further comprising: receiving, from the base station, a trigger to identify the subband precoder for each subband of the set of subbands based at least in part on the subset of the set of values of the at least one subband parameter.

[0168] Aspect 12: The method of any of aspects 1 through 11, further comprising: receiving, from the base station, a trigger to identify the wideband precoder based at least in part on the subset of the set of beams.

[0169] Aspect 13: The method of any of aspects 1 through 12, wherein the indication of the subset of the set of beams is received a threshold amount of time before reporting the CSF.

[0170] Aspect 14: A method for wireless communication at a base station, comprising: transmitting, to a UE, CSI-RSs; transmitting, to the UE, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder; and receiving, from the UE, the wideband precoder corresponding to a beam of the subset of the set of beams based at least in part on transmitting the CSI-RSs and transmitting the indication of the subset of the set of beams.

[0171] Aspect 15: The method of aspect 14, further comprising: receiving, from the UE, SRSs; and selecting the subset of the set of beams from which the UE is to identify the wideband precoder based at least in part on the SRSs. [0172] Aspect 16: The method of any of aspects 14 through 15, wherein transmitting the indication of the subset of the set of beams comprises: transmitting a first indication indicating one or more beams from which the UE is to identify the wideband precoder; and transmitting a second indication indicating neighboring beams to each of the one or more beams from which the UE is to identify the wideband precoder.

[0173] Aspect 17: The method of aspect 16, wherein the second indication indicates a quantity of the neighboring beams.

[0174] Aspect 18: The method of any of aspects 16 through 17, wherein the second indication comprises an RRC message, a MAC-CE, or a DCI message.

[0175] Aspect 19: The method of any of aspects 16 through 18, wherein the first indication comprises a DCI message.

[0176] Aspect 20: The method of any of aspects 14 through 19, further comprising: transmitting, to the UE, an indication of one or more subband parameters for the UE to use to identify a subband precoder for each subband of a set of subbands; and receiving, from the UE, the subband precoder for each subband of the set of subbands in CSF based at least in part on transmitting the indication of the one or more subband parameters.

[0177] Aspect 21 : The method of any of aspects 14 through 20, further comprising: transmitting, to the UE, an indication of a subset of a set of values of at least one subband parameter for the UE to use to identify a subband precoder for each subband of a set of subbands; and receiving, from the UE, the subband precoder for each subband of the set of subbands in the CSF based at least in part on transmitting the indication of the subset of the set of values of the at least one subband parameter.

[0178] Aspect 22: The method of aspect 21, wherein transmitting the indication of the subset of the set of values of the at least one subband parameter comprises: transmitting, to the UE, a first indication indicating one or more values of the at least one subband parameter for the UE to use to identify the subband precoder for each subband of the set of subbands; and transmitting, to the UE, a second indication indicating neighboring values to each of the one or more values for the UE to use to identify the subband precoder for each subband of the set of subbands. [0179] Aspect 23 : The method of aspect 22, wherein the second indication indicates a quantity of the neighboring values.

[0180] Aspect 24: The method of any of aspects 21 through 23, further comprising: transmitting, to the UE, a trigger to identify the subband precoder for each subband of the set of subbands based at least in part on the subset of the set of values of the at least one subband parameter.

[0181] Aspect 25: The method of any of aspects 14 through 24, further comprising: transmitting, to the UE, a trigger to identify the wideband precoder based at least in part on the subset of the set of beams.

[0182] Aspect 26: The method of any of aspects 14 through 25, wherein the indication of the subset of the set of beams is transmitted a threshold amount of time before receiving the CSF.

[0183] Aspect 27: An apparatus for wireless communication at a UE, comprising a processor; memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to perform a method of any of aspects 1 through 13.

[0184] Aspect 28: An apparatus for wireless communication at a UE, comprising at least one means for performing a method of any of aspects 1 through 13.

[0185] Aspect 29: A non-transitory computer-readable medium storing code for wireless communication at a UE, the code comprising instructions executable by a processor to perform a method of any of aspects 1 through 13.

[0186] Aspect 30: An apparatus for wireless communication at a base station, comprising a processor; memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to perform a method of any of aspects 14 through 26.

[0187] Aspect 31 : An apparatus for wireless communication at a base station, comprising at least one means for performing a method of any of aspects 14 through 26. [0188] Aspect 32: A non-transitory computer-readable medium storing code for wireless communication at a base station, the code comprising instructions executable by a processor to perform a method of any of aspects 14 through 26.

[0189] It should be noted that the methods described herein describe possible implementations, and that the operations and the steps may be rearranged or otherwise modified and that other implementations are possible. Further, aspects from two or more of the methods may be combined.

[0190] Although aspects of an LTE, LTE-A, LTE-A Pro, or NR system may be described for purposes of example, and LTE, LTE-A, LTE-A Pro, or NR terminology may be used in much of the description, the techniques described herein are applicable beyond LTE, LTE-A, LTE-A Pro, or NR networks. For example, the described techniques may be applicable to various other wireless communications systems such as Ultra Mobile Broadband (UMB), Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, as well as other systems and radio technologies not explicitly mentioned herein.

[0191] Information and signals described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0192] The various illustrative blocks and components described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a DSP, an ASIC, a CPU, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration). [0193] The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described herein may be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations.

[0194] Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A non-transitory storage medium may be any available medium that may be accessed by a general-purpose or special purpose computer. By way of example, and not limitation, non-transitory computer-readable media may include RAM, ROM, electrically erasable programmable ROM (EEPROM), flash memory, compact disk (CD) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium that may be used to carry or store desired program code means in the form of instructions or data structures and that may be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of computer-readable medium. Disk and disc, as used herein, include CD, laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media.

[0195] As used herein, including in the claims, “or” as used in a list of items (e.g., a list of items prefaced by a phrase such as “at least one of’ or “one or more of’) indicates an inclusive list such that, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C). Also, as used herein, the phrase “based on” shall not be construed as a reference to a closed set of conditions. For example, an example step that is described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase “based on” shall be construed in the same manner as the phrase “based at least in part on.”

[0196] In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If just the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label, or other subsequent reference label.

[0197] The description set forth herein, in connection with the appended drawings, describes example configurations and does not represent all the examples that may be implemented or that are within the scope of the claims. The term “example” used herein means “serving as an example, instance, or illustration,” and not “preferred” or “advantageous over other examples.” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described examples.

[0198] The description herein is provided to enable a person having ordinary skill in the art to make or use the disclosure. Various modifications to the disclosure will be apparent to a person having ordinary skill in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein, but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.

Claims

CLAIMS What is claimed is:

1. A method for wireless communication at a user equipment (UE), comprising: receiving, from a base station, channel state information reference signals; receiving, from the base station, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder; identifying the wideband precoder corresponding to a beam of the subset of the set of beams based at least in part on the channel state information reference signals; and reporting, to the base station, the wideband precoder in channel state feedback.

2. The method of claim 1, further comprising: transmitting, to the base station, sounding reference signals, wherein receiving the indication of the subset of the set of beams is based at least in part on transmitting the sounding reference signals.

3. The method of claim 1, wherein receiving the indication of the subset of the set of beams comprises: receiving, from the base station, a first indication indicating one or more beams from which the UE is to identify the wideband precoder; and receiving, from the base station, a second indication indicating neighboring beams to each of the one or more beams from which the UE is to identify the wideband precoder.

4. The method of claim 3, wherein the second indication indicates a quantity of the neighboring beams, the method further comprising: determining the neighboring beams to each of the one or more beams based at least in part on the quantity of the neighboring beams.

5. The method of claim 3, wherein the second indication comprises a radio resource control (RRC) message, a medium access control (MAC) control element (MAC-CE), or a downlink control information (DCI) message.

6. The method of claim 3, wherein the first indication comprises a downlink control information (DCI) message.

7. The method of claim 1, further comprising: receiving, from the base station, an indication of one or more subband parameters for the UE to use to identify a subband precoder for each subband of a set of subbands; identifying the subband precoder for each subband of the set of subbands to report to the base station in the channel state feedback based at least in part on the one or more subband parameters; and reporting, to the base station, the subband precoder for each subband of the set of subbands in the channel state feedback.

8. The method of claim 1, further comprising: receiving, from the base station, an indication of a subset of a set of values of at least one subband parameter for the UE to use to identify a subband precoder for each subband of a set of subbands; identifying the subband precoder for each subband of the set of subbands to report to the base station in the channel state feedback based at least in part on the subset of the set of values of the at least one subband parameter; and reporting, to the base station, the subband precoder for each subband of the set of subbands in the channel state feedback.

9. The method of claim 8, wherein receiving the indication of the subset of the set of values of the at least one subband parameter comprises: receiving, from the base station, a first indication indicating one or more values of the at least one subband parameter for the UE to use to identify the subband precoder for each subband of the set of subbands; and receiving, from the base station, a second indication indicating neighboring values to each of the one or more values for the UE to use to identify the subband precoder for each subband of the set of subbands.

10. The method of claim 9, wherein the second indication indicates a quantity of the neighboring values, the method further comprising: determining the neighboring values to each of the one or more values based at least in part on the quantity of the neighboring values.

11. The method of claim 8, further comprising: receiving, from the base station, a trigger to identify the subband precoder for each subband of the set of subbands based at least in part on the subset of the set of values of the at least one subband parameter.

12. The method of claim 1, further comprising: receiving, from the base station, a trigger to identify the wideband precoder based at least in part on the subset of the set of beams.

13. The method of claim 1, wherein the indication of the subset of the set of beams is received a threshold amount of time before reporting the channel state feedback.

14. A method for wireless communication at a base station, comprising: transmitting, to a user equipment (UE), channel state information reference signals; transmitting, to the UE, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder; and receiving, from the UE, the wideband precoder corresponding to a beam of the subset of the set of beams based at least in part on transmitting the channel state information reference signals and transmitting the indication of the subset of the set of beams.

15. The method of claim 14, further comprising: receiving, from the UE, sounding reference signals; and selecting the subset of the set of beams from which the UE is to identify the wideband precoder based at least in part on the sounding reference signals.

16. The method of claim 14, wherein transmitting the indication of the subset of the set of beams comprises: transmitting a first indication indicating one or more beams from which the UE is to identify the wideband precoder; and transmitting a second indication indicating neighboring beams to each of the one or more beams from which the UE is to identify the wideband precoder.

17. The method of claim 16, wherein the second indication indicates a quantity of the neighboring beams.

18. The method of claim 16, wherein the second indication comprises a radio resource control (RRC) message, a medium access control (MAC) control element (MAC-CE), or a downlink control information (DCI) message.

19. The method of claim 16, wherein the first indication comprises a downlink control information (DCI) message.

20. The method of claim 14, further comprising: transmitting, to the UE, an indication of one or more subband parameters for the UE to use to identify a subband precoder for each subband of a set of subbands; and receiving, from the UE, the subband precoder for each subband of the set of subbands in channel state feedback based at least in part on transmitting the indication of the one or more subband parameters.

21. The method of claim 14, further comprising: transmitting, to the UE, an indication of a subset of a set of values of at least one subband parameter for the UE to use to identify a subband precoder for each subband of a set of subbands; and receiving, from the UE, the subband precoder for each subband of the set of subbands in the channel state feedback based at least in part on transmitting the indication of the subset of the set of values of the at least one subband parameter.

22. The method of claim 21, wherein transmitting the indication of the subset of the set of values of the at least one subband parameter comprises: transmitting, to the UE, a first indication indicating one or more values of the at least one subband parameter for the UE to use to identify the subband precoder for each subband of the set of subbands; and transmitting, to the UE, a second indication indicating neighboring values to each of the one or more values for the UE to use to identify the subband precoder for each subband of the set of subbands.

23. The method of claim 22, wherein the second indication indicates a quantity of the neighboring values.

24. The method of claim 21, further comprising: transmitting, to the UE, a trigger to identify the subband precoder for each subband of the set of subbands based at least in part on the subset of the set of values of the at least one subband parameter.

25. The method of claim 14, further comprising: transmitting, to the UE, a trigger to identify the wideband precoder based at least in part on the subset of the set of beams.

26. The method of claim 14, wherein the indication of the subset of the set of beams is transmitted a threshold amount of time before receiving the channel state feedback.

27. An apparatus for wireless communication at a user equipment (UE), comprising: a processor, memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to: receive, from a base station, channel state information reference signals; receive, from the base station, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder; identify the wideband precoder corresponding to a beam of the subset of the set of beams based at least in part on the channel state information reference signals; and report, to the base station, the wideband precoder in channel state feedback.

28. The apparatus of claim 27, wherein the instructions are further executable by the processor to cause the apparatus to: transmit, to the base station, sounding reference signals, wherein receiving the indication of the subset of the set of beams is based at least in part on transmitting the sounding reference signals.

29. An apparatus for wireless communication at a base station, comprising: a processor, memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to: transmit, to a user equipment (UE), channel state information reference signals; transmit, to the UE, an indication of a subset of a set of beams from which the UE is to identify a wideband precoder; and receive, from the UE, the wideband precoder corresponding to a beam of the subset of the set of beams based at least in part on transmitting the channel state information reference signals and transmitting the indication of the subset of the set of beams.

30. The apparatus of claim 29, wherein the instructions are further executable by the processor to cause the apparatus to: receive, from the UE, sounding reference signals; and select the subset of the set of beams from which the UE is to identify the wideband precoder based at least in part on the sounding reference signals.