WO2022032424A1

WO2022032424A1 - Procedures for port-selection codebook with frequency selective precoded reference signals

Info

Publication number: WO2022032424A1
Application number: PCT/CN2020/108103
Authority: WO
Inventors: Chenxi HAO; Yu Zhang; Lei Xiao; Wei XI; Liangming WU; Hao Xu
Original assignee: Qualcomm Incorporated
Priority date: 2020-08-10
Filing date: 2020-08-10
Publication date: 2022-02-17

Abstract

Methods, systems, and devices for wireless communications are described. A user equipment (UE) may receive a set of reference signal ports from a base station, may perform measurements based on the reference signal ports, may generate a report from the measurements using a strongest detected tap aggregating a subset or all the reference signal ports, and may transmit the report to the base station based on the measurements. In some cases, the report may indicate a channel on which the reference signal ports are conveyed, where the channel is based on the measurements performed using the strongest detected tap. Additionally or alternatively, the report may indicate a precoder based on the measurements performed using the strongest detected tap. Additionally or alternatively, the report may include a port-selection indication that indicates a subset of the reference signal ports based on the measurements performed using the strongest detected tap.

Description

PROCEDURES FOR PORT-SELECTION CODEBOOK WITH FREQUENCY SELECTIVE PRECODED REFERENCE SIGNALS

FIELD OF TECHNOLOGY

The following relates to wireless communications, including procedures for port-selection codebook with frequency selective precoded reference signals.

BACKGROUND

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 frequency division multiple access (OFDMA) , or discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM) . A wireless multiple-access communications system may include one or more base stations or one or more network access nodes, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE) .

In multiple-in multiple-out (MIMO) measurements, information may be obtained based on one or more reference signals. For example, the one or more reference signals may include cell-specific reference signals (CRSs) , user-specific demodulation reference signals (UE-DMRSs) , channel state information reference signals (CSI-RSs) , etc. In some cases, the UE may transmit reports based on measurements of the one or more reference signals across different ports with which the UE receives and measures the one or more reference signals. However, the different ports may experience different signal strengths for different instances of time at which the one or more reference signals are received at the UE and for different beams used for transmitting and receiving the one or more reference signals, thereby impacting the measurements of the one or more reference signals.

SUMMARY

The described techniques relate to improved methods, systems, devices, and apparatuses that support procedures for port-selection codebook with frequency selective precoded reference signals. Generally, the described techniques provide for a user equipment (UE) to report channel state information (CSI) feedback based on a CSI generated from CSI measurements performed on CSI reference signal (RS) reports using a strongest detected tap aggregating a subset or all CSI-RS ports of a set of CSI-RS ports. For example, the UE may receive a set of CSI-RS ports from a base station, may perform CSI measurements based on the CSI-RS ports, may generate CSI from the CSI measurements using the strongest detected tap aggregating all the CSI-RS ports, and may transmit a CSI report to the base station based on the generated CSI. In some cases, the CSI report may indicate a channel on which the CSI-RS ports are conveyed, where the channel is based on the CSI measurements performed using the strongest detected tap. Additionally or alternatively, the CSI report may indicate a precoder (e.g., a precoding matrix indicator (PMI) ) based on the CSI measurements performed using the strongest detected tap. Additionally or alternatively, the CSI report may include a port-selection indication that indicates a subset of the CSI-RS ports based on the CSI measurements performed using the strongest detected tap.

A method of wireless communications at a UE is described. The method may include receiving, from a base station, a set of CSI-RS ports, performing a CSI measurement based on the set of CSI-RS ports, generating a CSI based on the CSI measurement, where the CSI is associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports, and transmitting, to the base station, a CSI report based on the CSI measurement.

An apparatus for wireless communications 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, a set of CSI-RS ports, perform a CSI measurement based on the set of CSI-RS ports, generate a CSI based on the CSI measurement, where the CSI is associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports, and transmit, to the base station, a CSI report based on the CSI measurement.

Another apparatus for wireless communications at a UE is described. The apparatus may include means for receiving, from a base station, a set of CSI-RS ports, performing a CSI measurement based on the set of CSI-RS ports, generating a CSI based on the CSI measurement, where the CSI is associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports, and transmitting, to the base station, a CSI report based on the CSI measurement.

A non-transitory computer-readable medium storing code for wireless communications at a UE is described. The code may include instructions executable by a processor to receive, from a base station, a set of CSI-RS ports, perform a CSI measurement based on the set of CSI-RS ports, generate a CSI based on the CSI measurement, where the CSI is associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports, and transmit, to the base station, a CSI report based on the CSI measurement.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a CSI report configuration, and determining CSI reporting associated with the strongest detected tap aggregating the subset or all of the set of CSI-RS ports based on the CSI report configuration.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a CSI request triggering the CSI report, and transmitting the CSI report indicating the CSI measurement that may be associated with the strongest detected tap aggregating the subset or all of the set of CSI-RS ports based on the triggering.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, transmitting the CSI report may include operations, features, means, or instructions for transmitting, to the base station, the CSI report that indicates a channel on which the set of CSI-RS ports may be conveyed, the channel based on measurements measured using the strongest detected tap across a subset of ports of the set of CSI-RS ports or across all ports of the set of CSI-RS ports.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining that the channel may be a linear combination of the subset of ports associated with the strongest detected tap, and transmitting in the CSI report an indication of the subset of ports based at least on part on a measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining that the channel may be a linear combination of all of the set of CSI-RS ports associated with the strongest detected tap, and transmitting in the CSI report an indication of linear combination coefficients.

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, an indication of a number of antennas used for receiving a signal on a reference signal resource corresponding to the set of CSI-RS ports, and transmitting in the CSI report a channel measurement from the strongest detected tap of each receive antenna of the number of antennas.

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, an indication of a location of the strongest detected tap or an indication of a location of the strongest detected tap for each receive antenna of the number of antennas.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, transmitting the CSI report may include operations, features, means, or instructions for transmitting, to the base station, a PMI based on the CSI measurement measured using the strongest detected tap across a subset of ports of the set of CSI-RS ports or across all ports of the set of CSI-RS ports.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the PMI may include operations, features, means, or instructions for transmitting in the CSI report an indication of the subset of ports based on measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the PMI may include operations, features, means, or instructions for transmitting in the CSI report an indication of linear combination coefficients.

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, a rank indicator (RI) indicating a number of layers used to receive a signal on a reference signal resource corresponding to the set of CSI-RS ports, and transmitting in the CSI report the PMI as a linear combination of the subset of ports for each layer.

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, a channel quality indicator (CQI) based on the PMI, an RI, or a combination thereof.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, transmitting the CSI report may include operations, features, means, or instructions for transmitting, to the base station, a port selection indication that indicates a subset of ports of the set of CSI-RS ports based on a measurement measured using the strongest detected tap across the subset of ports of the set of CSI-RS ports or all ports of the set of CSI-RS ports.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for selecting the subset of ports from the set of CSI-RS ports based on an energy level measurement of a reference signal resource at the strongest detected tap using the subset of ports.

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, multiple reference signal resources, each reference signal resource of the multiple reference signal resources including a single CSI-RS port.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for selecting a subset of ports of the set of CSI-RS ports or resources across the multiple reference signal resources, and transmitting, to the base station, an indication of the subset of ports or resources via a CSI-RS indicator (CRI) .

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the CRI may include a bitmap with a length corresponding to a number of ports in the set of CSI-RS ports, an indicator based on the number of ports in the set of CSI-RS ports and a second number of ports in the subset of ports, or a combination thereof.

A method of wireless communications at a base station is described. The method may include transmitting, to a UE, a set of CSI-RS ports and receiving, from the UE, a CSI report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports.

An apparatus for wireless communications 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, a set of CSI-RS ports and receive, from the UE, a CSI report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports.

Another apparatus for wireless communications at a base station is described. The apparatus may include means for transmitting, to a UE, a set of CSI-RS ports and receiving, from the UE, a CSI report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports.

A non-transitory computer-readable medium storing code for wireless communications at a base station is described. The code may include instructions executable by a processor to transmit, to a UE, a set of CSI-RS ports and receive, from the UE, a CSI report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting a CSI report configuration, where the CSI report may be based on the CSI report configuration.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting a CSI request triggering the CSI report, and receiving the CSI report indicating the CSI measurement that may be associated with the strongest detected tap aggregating the subset or all of the set of CSI-RS ports based on the triggering.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, receiving the CSI report may include operations, features, means, or instructions for receiving the CSI report that indicates a channel on which the set of CSI-RS ports may be conveyed, the channel based on measurements measured using the strongest detected tap across a subset of ports of the set of CSI-RS ports or across all ports of the set of CSI-RS ports.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, receiving the CSI report may include operations, features, means, or instructions for receiving the CSI report that reports an indication of the subset of ports based at least on part on a measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving an indication of a number of antennas used for receiving a signal on a reference signal resource corresponding to the set of CSI-RS ports, and receiving the CSI report that reports a channel measurement from the strongest detected tap of each receive antenna of the number of antennas.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving an indication of a location of the strongest detected tap or an indication of a location of the strongest detected tap for each receive antenna of the number of antennas.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, receiving the CSI report may include operations, features, means, or instructions for receiving the CSI report that reports an indication of linear combination coefficients.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, receiving the CSI report may include operations, features, means, or instructions for receiving a PMI based on the CSI measurement measured using the strongest detected tap across a subset of ports of the set of CSI-RS ports or across all ports of the set of CSI-RS ports.

In some examples, the PMI may include a linear combination of the subset of ports associated with the strongest detected tap, and some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving the CSI report that reports an indication of the subset of ports based on measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.

In some examples, the PMI may include a linear combination of all of the set of CSI-RS ports associated with the strongest detected tap, and some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving an indication of linear combination coefficients.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving an RI indicating a number of layers used to receive a signal on a reference signal resource corresponding to the set of CSI-RS ports, and receiving the CSI report that reports the PMI as a linear combination of the subset of ports for each layer.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a CQI based on the PMI, an RI, or a combination thereof.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, receiving the CSI report may include operations, features, means, or instructions for receiving a port selection indication that indicates a subset of ports of the set of CSI-RS ports based on a measurement measured using the strongest detected tap across the subset of ports of the set of CSI-RS ports or all ports of the set of CSI-RS ports.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting multiple reference signal resources, each reference signal resource of the multiple reference signal resources including a single CSI-RS port.

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, a CRI indicating a subset of ports or resources across the multiple reference signal resources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a system for wireless communications that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure.

FIG. 2 illustrates an example of a wireless communications system that supports procedures for a port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure.

FIGs. 3 and 4 illustrate examples of channel state information (CSI) calculations in accordance with aspects of the present disclosure.

FIGs. 5A and 5B illustrate examples of CSI reporting configurations in accordance with aspects of the present disclosure.

FIG. 6 illustrates an example of a process flow that supports procedures for a port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure.

FIGs. 7 and 8 show block diagrams of devices that support procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure.

FIG. 9 shows a block diagram of a communications manager that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure.

FIG. 10 shows a diagram of a system including a device that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure.

FIGs. 11 and 12 show block diagrams of devices that support procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure.

FIG. 13 shows a block diagram of a communications manager that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure.

FIG. 14 shows a diagram of a system including a device that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure.

FIGs. 15 through 21 show flowcharts illustrating methods that support procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

Obtaining channel state information (CSI) at a base station may be important to the performance for different types of communication operations, such as multiple-in-multiple-out (MIMO) performance. In some cases, the base station may obtain CSI in various ways. For example, a user equipment (UE) may transmit a sounding reference signal (SRS) to the base station, and the base station may determine the CSI (e.g., measure the channel) based on measuring the SRS (e.g., assuming reciprocity between uplink and downlink channels) . Additionally or alternatively, the base station may obtain the CSI based on CSI reporting. With CSI reporting, the base station may transmit a CSI reference signal (RS) to the UE, and the UE may measure CSI via the CSI-RS and may report the CSI via predefined codebooks (e.g., Type I, Type II, Type II port-selection, enhanced Type (eType) II, eType II port-selection, etc. ) to the base station.

In some cases, the base station may obtain the CSI using the SRS measurement based on a good first order reciprocity for a channel between the base station and the UE (e.g., for a time division duplexing (TDD) system, first order reciprocity may mean a similar instantaneous channel in uplink and downlink) . Additionally or alternatively, if there is a poor reciprocity, the base station may use the CSI reporting to obtain the CSI. In a frequency division duplexing (FDD) system, while a first order reciprocity may not exist, a second order reciprocity may still exist. In some cases, the second order reciprocity may include a reciprocity for angle and delay characteristics. The base station may exploit this angle/delay reciprocity to transmit a precoded CSI-RS, and the UE may report CSI based on measuring the precoded CSI-RS. By exploiting the angle/delay reciprocity for CSI reporting, different advantages may be realized, such as low UE complexity, low reporting overhead, and better base station flexibility in selecting CSI-RS precoders in spatial domain and frequency domain based on the angle and delay reciprocity.

Without exploiting the angle and delay reciprocity for CSI-RS precoding, the base station may transmit (e.g., based on an eType II codebook) a non-precoded CSI-RS (e.g., P=32 ports) , where each port is transmitted via a single transmit antenna. Additionally, the UE may be triggered to report an eType II CSI. In eType II CSI, the UE may report a precoding matrix indicator (PMI) which indicates precoder for each layer. The precoder for each layer across N3 subbands may be given by:

with a size P*N3, where b _i is a spatial domain basis with size P*1,

is a frequency domain basis with size N3*1, and c _i, m is a coefficient used to combine 2L spatial domain bases and N3 FD bases. This codebook structure may be used for a CSI reporting payload reduction. Without compression of payload, the UE may report P*N3 coefficients for each layer. With the structure of eType II, the spatial domain basis may compress the spatial domain dimension from P to 2L by exploiting spatial domain correlation, the frequency domain basis may compress the frequency dimension from N3 to M by exploiting frequency domain correlation, and, in the remaining 2L*M dimension, a number of non-zero coefficients may be small, so that the total number of CSI payload is decreased. The UE may report indexes of b, report indexes of f (e.g., from predefined set) , and report c with quantization.

Since the second order reciprocity exists in an FDD system, the base station may determine proper spatial bases and frequency domain compression bases, and the UE may report the linear combination coefficients. For example, for a CSI-RS port precoded via spatial domain and frequency domain bases, on a frequency domain unit (e.g., a resource block (RB) , subband, etc. ) , the precoder of a CSI-RS port may be formed by a pair of spatial domain basis (or spatial domain transmission filter) and a frequency domain basis (e.g., frequency domain transmission filter/weight) . The precoder of a CSI-RS port p, on a frequency domain unit n, may be written as:

where b _i (p) is the spatial domain basis applied on port p and

is an n-th entry of the frequency domain basis applied on port p.

For the port p and on a frequency domain unit n, for the UE to calculate the CSI, the UE may observe:

where H is a wireless channel between a UE and the network without precoding. For each layer, the UE may select a subset of total ports and report a single coefficient per port across the frequency band. For example, the PMI for a certain layer on any of the N3 frequency domain units may be described by the expression:

where

is of size P x 1 with one “1” in row i _k, and P is the total number of CSI-RS ports.

In this case, the consequence of precoding via frequency domain bases may include shifting a significant tap of a spatial domain basis (e.g., spatial beam) to a first tap. For instance, if the base station identifies two spatial domain bases (e.g., spatial beams) , and each basis is associated with two significant taps (e.g., a tap may correspond to a frequency domain basis) , the base station may formulate four (4) ports. A first port may be associated with a first spatial domain basis and a first frequency domain basis associated with the first spatial domain basis, and the base station may physically shift the tap associated with the first frequency domain basis and first spatial domain basis to the first tap of a first CSI-RS port. A second port may be associated with the first spatial domain basis and a second frequency domain basis associated with the first spatial domain basis and the base station may physically shift the tap associated with the second frequency domain basis and the first spatial domain basis to the first tap of a second CSI-RS port. A third port may be associated with a second spatial domain basis and the first frequency domain basis associated with the second spatial domain basis, and the base station may physically shift the tap associated with the first frequency domain basis and second spatial domain basis to the first tap of a third CSI-RS port. A fourth port may be associated with the second spatial domain basis and the second frequency domain basis associated with the second spatial domain basis, and the base station may physically shift the tap associated with the second frequency domain basis and the second spatial domain basis to the first tap of a fourth CSI-RS port.

Then, the UE may calculate CSI associated with the first tap of each CSI-RS port. For example, the UE may calculate the CSI using the first tap (e.g., tap 0) for each port, where taps may represent different time instances that different beams carrying the CSI-RS are received at the UE with different powers and phases based on different paths the beams take to reach the UE. For example, a same beam or different beams may reach the UE carrying the CSI-RS via different paths, such that the UE receives the CSI-RS with different powers and phases for that same beam or different beams according to the different taps, and the UE may receive multiple beams carrying the CSI-RSs with each beam including different taps. However, in some implementations, due to receiver timing misalignment/offset, the channel measured by the base station for uplink may be a cyclic shift of the channel measured by the UE for downlink. In this case, although the base station may precode the CSI-RS based on the spatial domain and frequency domain bases calculated from the uplink channel and the significant taps of the uplink channels may align at the first tap, these significant taps may not appear at the first tap in the downlink.

As described herein, a UE may find a strongest detected tap for receiving a CSI-RS resource with a set of ports and to use that strongest detected tap to calculate the CSI aggregating all ports or a subset of all ports. In some implementations, the UE may report the CSI in an explicit report of measurements for the channel measured from the strongest detected tap aggregating all ports or the subset of all ports. Accordingly, the UE may report channel coefficients for a selected subset of ports, where the explicit report is a linear combination of the selected ports (e.g., a subset of ports or all ports) using the reported channel coefficients. The UE may also report a location of the strongest detected tap. Additionally or alternatively, the UE may report the CSI using implicit CSI feedback via a report of a precoder (e.g., precoding matrix indicator (PMI) ) used to measure and calculate the CSI from the strongest detected tap aggregating all ports or the subset of all ports. Accordingly, the UE may report linear combination coefficients for a selected subset of ports, where the subset of ports is selected per layer, and the report of the precoder may include a linear combination of the selected ports (e.g., a subset of ports or all ports) using corresponding linear combination coefficients. Additionally or alternatively, the UE may report a port selection based on measurements from the strongest detected tap aggregating all ports or the subset of all ports. In some implementations, the base station may configure multiple CSI-RS resources each with a single port, and the UE may select and report a subset of the multiple CSI-RS resources and corresponding ports via a CSI-RS indicator (CRI) .

Aspects of the disclosure are initially described in the context of wireless communications systems. Additionally, aspects of the disclosure are illustrated through an additional wireless communications system, CSI calculations, CSI reporting configurations, and a process flow. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to procedures for port-selection codebook with frequency selective precoded reference signals.

FIG. 1 illustrates an example of a wireless communications system 100 that supports procedures for port-selection codebook with frequency selective precoded reference signals 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.

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.

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.

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 S1, 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.

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.

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.

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.

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.

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) .

The communication links 125 shown in the wireless communications system 100 may include uplink transmissions from a UE 115 to a base station 105, or downlink transmissions from a base station 105 to a UE 115. 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) .

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.

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 spread OFDM (DFT-S-OFDM) ) . In a system employing MCM techniques, a resource element may consist of 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.

One or more numerologies for a carrier may be supported, where a numerology may include a subcarrier spacing (Δ? ) and a cyclic prefix. A carrier may be divided into one or more BWPs having the same or different numerologies. In some examples, a UE 115 may be configured with multiple BWPs. In some examples, a single BWP for a carrier may be active at a given time and communications for the UE 115 may be restricted to one or more active BWPs.

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/ (Δf _max·N _f) seconds, where Δf _max may represent the maximum supported subcarrier spacing, and N _f may represent the maximum supported discrete Fourier transform (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) .

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., N _f) sampling periods. The duration of a symbol period may depend on the subcarrier spacing or frequency band of operation.

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) ) .

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.

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.

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.

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.

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 network operators IP services 150 may include access to the Internet, Intranet (s) , an IP Multimedia Subsystem (IMS) , or a Packet-Switched Streaming Service.

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) .

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.

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.

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 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 a port.

The base stations 105 or the UEs 115 may use MIMO communications to exploit multipath signal propagation and increase the spectral efficiency by transmitting or receiving multiple signals via different spatial layers. Such techniques may be referred to as spatial multiplexing. The multiple signals may, for example, be transmitted by the transmitting device via different antennas or different combinations of antennas. Likewise, the multiple signals may be received by the receiving device via different antennas or different combinations of antennas. Each of the multiple signals may be referred to as a separate spatial stream and may carry bits associated with the same data stream (e.g., the same codeword) or different data streams (e.g., different codewords) . Different spatial layers may be associated with different ports used for channel measurement and reporting. MIMO techniques include single-user MIMO (SU-MIMO) , where multiple spatial layers are transmitted to the same receiving device, and multiple-user MIMO (MU-MIMO) , where multiple spatial layers are transmitted to multiple devices.

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) .

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 a UE 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.

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.

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) .

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) .

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.

The UEs 115 and the base stations 105 may support retransmissions of data to increase the likelihood that data is received successfully. Hybrid automatic repeat request (HARQ) feedback is one technique for increasing the likelihood that data is received correctly over a communication link 125. HARQ may include a combination of error detection (e.g., using a cyclic redundancy check (CRC) ) , forward error correction (FEC) , and retransmission (e.g., automatic repeat request (ARQ) ) . HARQ may improve throughput at the MAC layer in poor radio conditions (e.g., low signal-to-noise conditions) . In some examples, a device may support same-slot HARQ feedback, where the device may provide HARQ feedback in a specific slot for data received in a previous symbol in the slot. In other cases, the device may provide HARQ feedback in a subsequent slot, or according to some other time interval.

In some cases, a base station 105 and a UE 115 may use one or more reference signals to determine a quality or state of a channel for enhancing communications between the base station 105 and the UE 115. For example, the reference signals may include cell-specific reference signals (CRSs) , user-specific demodulation reference signals (UE-DMRSs) , CSI-RSs, etc. The base station 105 may transmit the one or more reference signals to the UE 115, and the UE 115 may then perform measurements on the reference signals to generate a report to transmit back to the base station 105. Additionally or alternatively, the UE 115 may transmit reference signals to the base station 105, and the base station 105 may perform measurements on the reference signals to determine information for communications with the UE 115. Based on the report transmitted by the UE 115 or on the measurements performed by the base station 105, the base station 105 may identify information and characteristics of the channel to then be able to adjust parameters for subsequent communications (e.g., based on measurements of the reference signals performed by the UE 115 or by the base station 105 and how the measurements compare to expected values for the reference signals) . In some cases, the reference signals and reports of measurements for the reference signals may enable the base station 105 to determine additional information concerning the UE 115 (e.g., such as a location of the UE 115, how to mitigate interference for the UE 115, etc. ) .

In particular, CSI-RS transmission may include a three step process. In a first step, a UE 115 may transmit an uplink sounding reference signal (SRS) to a base station 105. In a second step, the base station 105 may precode, based on a measurement of the SRS, a wideband CSI-RS signal for transmission over a set of beams via a set of ports. For example, the CSI-RS signal may be precoded with a discrete Fourier transform or Eigen beams. In a third step, the UE 115 may measure the CSI-RS signal on the set of ports, may calculate a precoding matrix indicator (PMI) , a channel quality indicator (CQI) , or both, and may report CSI feedback to indicate a port selection codebook to the base station 105. In some cases, precoding of the CSI-RS may occur in the spatial domain, in the frequency domain, or in both. Additionally, precoding of the CSI-RS may involve generating a signal using a spatial domain basis for precoding in the spatial domain, using a frequency domain basis for precoding in the frequency domain, and using a set of precoding coefficients that depend on current channel conditions.

As described previously, obtaining CSI at a base station 105 may be important for MIMO performance. In some cases, the base station 105 may obtain the CSI based on CSI reporting. With CSI reporting, the base station may transmit a CSI-RS to a UE 115, and the UE 115 may measure CSI via the CSI-RS and may report the CSI via predefined codebooks (e.g., Type I, Type II, Type II port-selection, enhanced Type (eType) II, eType II port-selection, etc. ) to the base station 105.

Based on a second order reciprocity (e.g., in an FDD system) , the base station 105 may determine proper spatial bases and frequency domain compression bases, and the UE 115 may report linear combination coefficients. For example, for a CSI-RS port precoded via spatial domain and frequency domain bases, on a frequency domain unit (e.g., a resource block (RB) , subband, etc. ) , the precoder of a CSI-RS port may be formed by a pair of spatial domain basis (or spatial domain transmission filter) and a frequency domain basis (e.g., frequency domain transmission filter/weight) . The precoder of a CSI-RS port p, on a frequency domain unit n, may be written as:

where b _i (p) is the spatial domain basis applied on port p and

is an n-th entry of the frequency domain basis applied on port p.

For the port p and on a frequency domain unit n, for the UE 115 to calculate the CSI, the UE may observe:

where H is a wireless channel between a UE and the network without precoding. For each layer, the UE 115 may select a subset of total ports and report a single coefficient per port across the frequency band. For example, the PMI for a certain layer on any of the N3 frequency domain units may be described by the expression:

where

In this case, the consequence of precoding via frequency domain bases may include shifting a significant tap of a spatial domain basis (e.g., spatial beam) to a first tap. For instance, if the base station 105 identifies two spatial domain bases (e.g., spatial beams) , and each basis is associated with two significant taps (e.g., a tap may correspond to a frequency domain basis) , the base station may formulate four (4) ports. A first port may be associated with a first spatial domain basis and a first frequency domain basis associated with the first spatial domain basis, and the base station may physically shift the tap associated with the first frequency domain basis and first spatial domain basis to the first tap of a first CSI-RS port. A second port may be associated with the first spatial domain basis and a second frequency domain basis associated with the first spatial domain basis and the base station may physically shift the tap associated with the second frequency domain basis and the first spatial domain basis to the first tap of a second CSI-RS port. A third port may be associated with a second spatial domain basis and the first frequency domain basis associated with the second spatial domain basis, and the base station may physically shift the tap associated with the first frequency domain basis and second spatial domain basis to the first tap of a third CSI-RS port. A fourth port may be associated with the second spatial domain basis and the second frequency domain basis associated with the second spatial domain basis, and the base station 105 may physically shift the tap associated with the second frequency domain basis and the second spatial domain basis to the first tap of a fourth CSI-RS port.

Then, the UE 115 may calculate CSI associated with the first tap of each CSI-RS port. That is, the UE 115 may calculate the CSI using the first tap (e.g., tap 0) for each port. Taps may represent different time instances that different beams carrying the CSI-RS are received at the UE 115 with different powers and phases based on different paths the beams take to reach the UE. For example, a same beam or different beams may reach the UE 115 carrying the CSI-RS via different paths, such that the UE 115 receives the CSI-RS with different powers and phases for that same beam or different beams according to the different taps, and the UE 115 may receive multiple beams carrying the CSI-RSs with each beam including different taps. However, in some implementations, due to receiver timing misalignment/offset, the channel measured by the base station for uplink may be a cyclic shift of the channel measured by the UE 115 for downlink. In this case, although the base station 105 may precode the CSI-RS based on the spatial domain and frequency domain bases calculated from the uplink channel and the significant taps of the uplink channels may align at the first tap, these significant taps may not appear at the first tap in the downlink.

Wireless communications system 100 may support efficient techniques for a UE 115 to select a tap from multiple ports for receiving and measuring CSI-RSs transmitted by a base station 105, where the tap is selected based on being a tap with a strongest detected measurement for the CSI-RSs across the multiple ports or a subset of ports. Subsequently, the UE 115 may then transmit channel feedback to the base station 105 based on the CSI-RSs measured across multiple ports using the selected tap. In some implementations, the UE 115 may transmit the channel feedback indicating explicit channel state feedback (e.g., H or H*W1) based on the selected tap. Additionally or alternatively, the UE 115 may transmit the channel feedback indicating implicit channel state feedback (e.g., W or W2) based on the selected tap. In some implementations, the UE 115 may transmit the channel feedback indicating a port selection based on the selected tap, where the UE 115 selects the ports based on a measurement using the selected tap.

FIG. 2 illustrates an example of a wireless communications system 200 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. In some examples, wireless communications system 200 may implement aspects of wireless communications system 100. For example, wireless communications system 200 may include a base station 105-a and a UE 115-a, which may represent examples of corresponding base stations 105 and UEs 115, respectively, as described with reference to FIG. 1.

The described techniques may include channel state feedback (CSF) for a reciprocity channel in a radio access technology (e.g., NR, NR MIMO, etc. ) . In some examples, UE 115-a may transmit an uplink SRS to base station 105-a. Additionally, base station 105-a may precode CSI-RS ports based on a measurement of the SRS to transmit one or more CSI-RSs 215. The multiple CSI-RS ports may include logical ports that are distinguished by reference signal sequences. In some examples, the CSI-RSs 215 may provide channel estimation for up to eight (8) layers (e.g., ports) . Additionally, the CSI-RSs 215 may be precoded with discrete Fourier transform (DFT) or Eigen beams. In some examples, base station 105-a may transmit, to UE 115-a, a reference signal (e.g., CSI-RSs 215) that is frequency domain precoded in accordance with at least a portion of a frequency domain basis vector via a set of ports and physically transmitted via beams. Subsequently, UE 115-a may measure the CSI-RS ports and may calculate channel quality indicator (CQI) , or precoding matrix index (PMI) , or rank indication (RI) , or any combination thereof, based on measuring the CSI-RS ports. In some examples, the UE may report a port selection codebook to the base station (e.g., port selection codebook feedback) , a CSI-RS indicator (CRI) , or additional information (e.g., CQI, PMI, RI, etc. ) based on measuring the CSI-RS ports. In some examples, the feedback may include or be based on type II CSI.

In some examples, base station 105-a may precode a spatial domain basis vector or a frequency domain basis vector, or both. In some examples, a CSI-RS port on N ₃ frequency domain units may be precoded with a determined spatial domain basis b _i and a determined frequency domain basis

For example, base station 105-a may perform a frequency selective precoding of the CSI-RS ports to transmit the CSI-RSs 215 based on the following table. In some cases, on a frequency domain (FD) unit (e.g., an RB, a subband, etc. ) , base station 105-a may form a precoder of a CSI-RS port by a pair of a spatial domain basis or a spatial domain transmission filter (e.g., b _i) and a frequency domain basis or a frequency domain transmission filter or weight (e.g., f _m or

) . The following table is an example of the various values of the spatial domain vector and frequency domain vector for respective ports (e.g., Port 0, Port 1, etc. ) and FD units (e.g., FD unit 0, FD unit 1, etc., such as resource blocks) :

In some cases, UE 115-a may transmit channel state feedback report 230 to indicate a CSI report to base station 105-a based on measuring the CSI-RSs 215from the precoded CSI-RS ports. For example, for a port p, UE 115-a may observe:

on a frequency domain unit n base on which UE 115-acalculates CSI. H may represent the wireless channel between UE 115-a and base station 105-a without precoding. For each layer, UE 115-a may select a subset of total ports and may report a single coefficient (c _i, m or c _k) per port across the frequency band. The PMI for a certain layer on any of the N ₃ frequency domain units may be given by:

where

represents a size P×1 with one “1” in row i _k; and P represents a total number of CSI-RS ports. In some examples, UE 115-a may report

and

or a subset of

where unreported values of

and c _k may be set to ‘0. ’ That is, UE 115-a may measure what it observes and may calculate coefficients (e.g., c) to combine those (subset) ports.

Additionally, a layer-to-port mapping may be generated. For example, UE 115-a may calculate a CQI assuming a virtual downlink shared channel (e.g., a physical downlink shared channel (PDSCH) ) . As an example, the calculated CQI (y) may be given by:

where x represents the data with rank v as indicated by the rank indicator (RI) . In some examples, a precoder of the virtual downlink shared channel may be given by:

In some cases, base station 105-a may configure a CSI report configuration and a CSI-RS resource configuration to UE 115-a. The CSI-RS resource configuration may include a type of CSI-RS, a resource mapping, a CDM type, density, etc. The CSI report configuration may include a type of CSI report (e.g., for UE 115-a to transmit channel state feedback report 230) , codebook configuration, etc. In some cases, an association may be present between CSI-RS resource and CSI report. Specifically, each CSI report may be linked to up to three (3) CSI-RS resource configurations. If each CSI report is linked to a single CSI-RS resource configuration, the CSI-RS resource configuration may include a non-zero power (NZP) CSI-RS configuration for channel measurement. If each CSI report is linked to two (2) CSI-RS resource configurations, one CSI-RS resource configuration may include the NZP CSI-RS configuration for channel measurement, and the second CSI-RS resource configuration may include an interference measurement CSI-RS resource configuration (e.g., a NZP-CSI-RS resource for interference measurement or a CSI interference measurement (IM) resource for interference measurement, such as a zero-power resource) . If each CSI report is linked to three (3) CSI-RS resource configurations, one CSI-RS resource configuration may include a channel measurement resource (CMR) , the second CSI-RS resource configuration may include an NZP IM resource (IMR) , and the third CSI-RS resource configuration may include a CSI-IM.

For example, base station 105-a may transmit the CSI report configuration and the CSI-RS resource configuration via RRC and may transmit an activation for the CSI report configuration and the CSI-RS resource configuration via RRC, a MAC CE, DCI, or a combination thereof (e.g., depending on a type of CSI-RS) . If configured to provide periodic reports, UE 115-a may start reporting CSI feedback after receiving an RRC configuration configuring channel state feedback report 230 (e.g., CSI report) . For semi-persistent reporting, UE 115-a may start reporting CSI feedback after receiving a MAC CE activating UE 115-a to report the CSI feedback. Accordingly, once activated, UE 115-a may continue to transmit semi-periodic CSI feedbacks (e.g., multiple channel state feedback reports 230) according to a periodic schedule until a second MAC CE is received that deactivates the reporting. For aperiodic reporting, UE 115-a may report the CSI feedback after receiving a DCI from base station 105-a requesting channel state feedback report 230, where channel state feedback report 230 is transmitted a single time (e.g., resulting in no need for a deactivation) .

Based on the CSI-RS configuration, UE 115-a may perform a reference signal monitoring 220 using the CSI-RS ports to measure CSI across the ports to then report the CSI feedback. In some cases, when measuring the CSI-RSs 215, UE 115-a may calculate CSI using a first tap (e.g., tap 0) for each port of the CSI-RS ports (e.g., a set of ports) as described previously (e.g., based on base station 105-a shifting the significant taps) and may transmit channel state feedback report 230 indicating the calculated CSI for base station 105-a. As described herein, taps may represent different time instances that CSI-RSs 215 are received at UE 115-a with different powers and phases based on different paths the CSI-RSs 215 take to reach UE 115-a. For example, CSI-RSs 215 may reach the UE 115 via different paths, such that UE 115-a receives the CSI-RSs 215 with different powers and phases according to the different taps, and UE 115-a may receive multiple CSI-RSs 215 including different taps. However, in some implementations, due to receiver timing misalignment/offset, the channel measured by base station 105-a for uplink may be a cyclic shift of the channel measured by UE 115-a for downlink. In this case, although base station 105-a may precode the CSI-RS based on the spatial domain and frequency domain bases calculated from the uplink channel and the significant taps of the uplink channels may align at the first tap, these significant taps may not appear at the first tap in the downlink.

In some cases, base station 105-a may transmit the CSI-RS ports (e.g., via the CSI-RS configuration) for UE 115-a to receive and measure the CSI-RSs 215 on different spatial domain bases (e.g., precoders, digital beams, digital precoders, spatial beams, etc. ) based on different taps (e.g., a first port corresponds to a first tap for a first spatial domain basis, a second port corresponds to a second tap for the first spatial domain basis, a third port corresponds to the second tap for a second spatial domain basis, and a fourth port corresponds to a third tap for the second spatial domain basis) . That is, base station 105-a may signal a CSI report configuration, and this configuration may indicate a codebook type. For this codebook type, UE 115-a may perform this procedure to calculate CSI. In some cases, the CSI-RS port precoding may be transparent to UE 115-a, where UE 115-a measures signals received on the CSI-RS ports and calculates CSI per the CSI report configuration. Subsequently, UE 115-a may receive the CSI-RSs 215. UE 115-a may be triggered or configured with a CSI report associated with these CSI-RS, and UE 115-a may calculate and report the CSI accordingly. However, as described previously, the first tap (e.g., tap 0) may not correspond to a ‘best’ tap for UE 115-a (e.g., a tap with the highest power level) to use when receiving and measuring the CSI-RSs 215 on the different CSI-RS ports.

Based on techniques described herein, UE 115-a may determine a CSI calculation using a selected tap 225 from a set of taps for CSI-RS ports. For example, UE 115-a may receive a CSI-RS resource (e.g., resources used to transmit the CSI-RSs 215) with a set of CSI-RS ports and may calculate (e.g., generate) CSI using selected tap 225 (e.g., a strongest detected tap) aggregating a subset or all the CSI-RS ports. UE 115-a may find a strongest detected tap (e.g., selected tap 225) based on seeing different power levels for each tap for each port and use the strongest detected tap to compute CSI. As shown in FIG. 2 (e.g., and described further with reference to FIG. 4) , base station 105-a may transmit four (4) CSI-RS ports that UE 115-a is to use to perform CSI measurements of CSI-RS resources, where the CSI-RS ports include a port 0 (e.g., a first port) , a port 1 (e.g., a second port) , a port 2 (e.g., a third port) , and a port 3 (e.g., a fourth port) .

Port 0 may be associated with a first spatial domain basis and a first frequency domain basis associated with the first spatial domain basis, and base station 105-a may physically shift the tap associated with the first frequency domain basis and first spatial domain basis to the first tap of a first CSI-RS port. Port 1 may be associated with the first spatial domain basis and a second frequency domain basis associated with the first spatial domain basis, and base station 105-a may physically shift the tap associated with the second frequency domain basis and the first spatial domain basis to the first tap of a second CSI-RS port. Port 2 may be associated with a second spatial domain basis and the first frequency domain basis associated with the second spatial domain basis, and base station 105-a may physically shift the tap associated with the first frequency domain basis and second spatial domain basis to the first tap of a third CSI-RS port. Port 3 may be associated with the second spatial domain basis and the second frequency domain basis associated with the second spatial domain basis, and base station 105-a may physically shift the tap associated with the second frequency domain basis and the second spatial domain basis to the first tap of a fourth CSI-RS port. Accordingly, UE 115-a may select a tap 1 (e.g., a second tap) for selected tap 225 based on signal strengths of the CSI-RSs 215 being strongest across each port at tap 1. While four (4) ports are shown in the example of FIG. 2, it is to be understood that the described techniques may be extended to a different number of ports. For example, base station 105-a may determine a spatial domain basis and a frequency domain basis for each port of a set of ports (e.g., 16 ports, 32 ports, etc. ) , and UE 115-a may determine a strongest detected tap across the set of ports using the described techniques.

In some implementations, UE 115-a may determine the strongest detected tap aggregating a subset or all ports based on:

where

may represent a channel estimate for a CSI-RS port p on an FD unit n (e.g., resource elements, resource blocks, subbands, etc. ) ; N may represent a total number of FD units; and f _m (n) may represent an n-th entry of an FD basis f _m associated with a tap m (e.g., selected tap 225, tap 1, etc. ) . UE 115-a may receive one or more CSI-RSs 215, and UE 115-a may determine the strongest detected tap aggregating a subset or all ports based on:

where

may represent a channel estimate for CSI-RS port p on FD unit n at a receive antenna r. For example, UE 115-a may generate a signal measurement (e.g., CSI measurement, measurement of CSI-RSs 215, etc. ) for each tap of a set of available taps for all of the ports and may select a strongest detected tap from the set of available taps based on the signal measurements.

Subsequently, based on reference signal monitoring 220 and calculating the CSI using selected tap 225 aggregating a subset or all ports, UE 115-a may then transmit channel state feedback report 230. For example, in a first implementation, UE 115-a may transmit explicit CSI feedback in channel state feedback report 230, where the explicit CSI feedback includes an explicit report of a channel measured (e.g., based on measurements of the CSI-RSs 215) from the strongest detected tap (e.g., selected tap 225) aggregating a subset or all ports. In some cases, UE 115-a may select up to K0 ports per receiver (e.g., per a receive antenna) and up to 2*K0 ports across all receivers. Subsequently, UE 115-a may report channel coefficients (e.g., c _i, m) for the selected ports (e.g., channel coefficients for unreported ports are set to ‘0’ ) when transmitting channel state feedback report 230. Additionally, UE 115-a may report an indication of a number of receivers used to receive the CSI-RSs 215 and calculate the CSI.

In some cases, the explicit report of the channel measured may be a linear combination of the selected ports using the corresponding reported channel coefficients, and UE 115-a may report the CSI as the linear combination of the selected ports based on measurements using the strongest detected tap with an indication of the selected ports. Additionally or alternatively, the channel measured may be a linear combination of all ports of the CSI-RS ports, and UE 115-a may report the linear combination coefficients (e.g., no indication of a port-selection) . Additionally, UE 115-a may also report the location of the strongest detected tap (e.g., selected tap 225) when transmitting the explicit CSI feedback in channel state feedback report 230.

When transmitting the explicit CSI feedback and denoting the strongest detected tap aggregating a subset or all ports by m ^* as described previously, for the K0 selected ports of a receiver r, UE 115-a may report

in channel state feedback report 230. For example, UE 115-a may select the K0 ports as strongest K0 coefficients at tap m ^* for the receiver r. Moreover, the strongest tap m ^* may be different at each receive antenna. In other words, UE 115-a may find a specific strongest tap m ^* for each particular receive antenna, e.g., the strongest tap for a first receive antenna is the first tap (e.g., tap 0) , the strongest tap for a second receive antenna is the second tap (e.g., tap 1) , etc. Additionally, the 2*K0 ports may be selected as strongest 2*K0 coefficients at corresponding tap m ^* across all receivers. At an FD unit n, the reported channel may include a P×N _r matrix, where the (p, r) -th entry of the matrix is:

if m ^* is reported by UE 115-a (e.g., unreported entries in the matrix may be set to ‘0’ Additionally, ) . If m ^* is not reported by UE 115-a, the (p, r) -th entry of the matrix may be linear combination coefficient c _r, p for a CSI-RS port p and receiver r.

In a second implementation, when transmitting channel state feedback report 230, UE 115-a may transmit implicit CSI feedback, where the implicit CSI feedback includes CSI indicated by a report of a precoder (e.g., PMI) measured and calculated from the strongest detected tap aggregating a subset or all ports. Similar to the explicit CSI feedback, UE 115-a may select up to K0 ports but per layer and up to 2*K0 ports across all layers. Subsequently, UE 115-a may then report linear combination coefficients c for the selected ports with the implicit CSI feedback (e.g., linear combination coefficients for unreported ports are set to ‘0’ ) . Additionally, UE 115-a may report an RI indicating a number of layers (e.g., a rank) when transmitting channel state feedback report 230 indicating the implicit CSI feedback. The precoder reported with the implicit CSI feedback may be a linear combination of the selected ports using the corresponding reported linear combination coefficients, where UE 115-a reports the CSI as the linear combination of the selected ports based on measurements using the strongest detected tap with an indication of the selected ports. Moreover, the strongest tap m ^* may be different for each layer. In other words, UE 115-a may find a specific strongest tap m ^* for each particular layer, e.g., the strongest tap for a layer 1 is the first tap (e.g., tap 0) , the strongest tap for a layer 2 is the second tap (e.g., tap 1) , etc.. In some cases, the strongest tap m ^* may be common for all layers. Additionally or alternatively, the precoder measured may be a linear combination of all ports of the CSI-RS ports, and UE 115-a may report the linear combination coefficients (e.g., no indication of a port-selection) . In some cases, UE 115-a may also report CQI based on the rank and the precoder and the CSI-RS ports.

When transmitting the implicit CSI feedback, UE 115-a may denote the strongest detected tap aggregating a subset or all ports by m ^* as described previously and may denote the channel measured from tap m ^* as

where

is a P×N _r matrix whose (r, p) -th entry is:

Subsequently, UE 115-a may calculate a singular value decomposition (SVD) of

based on:

Accordingly, rank may be determined using the columns of V; the K0 coefficient per layer may be selected as a strongest K0 coefficient in each column of V; and the 2*K0 coefficients across all layers may be selected as a strongest 2*K0 coefficient across column 1 to an RI of V. For any FD unit n, UE 115-a may report a PMI (e.g., in the implicit CSI feedback) for a layer l given by

(e.g., as a quantization of the l-th column of V) , where

includes a size P×1 with one “1” in row i _k, l representing a port selection; K′ _0, l is a total number of reported coefficients c for layer l; and c _k, l is a coefficient for layer l after quantizing the entries of V.

In a third implementation, UE 115-a may transmit CSI feedback via port-selection information in channel state feedback report 230, were the CSI feedback includes a report of port-selection based on measurements from a set of CSI-RS ports from the strongest detected tap (e.g., selected tap 225) aggregating a subset or all ports. For example, UE 115-a may select up to M ports across all ports based on an energy measured from the strongest detected tap aggregating a subset or all ports. Subsequently, UE 115-a may then report the port selection in channel state feedback report 230. In some cases, base station 105-a may configure N resources each with a single port (e.g., resulting in N total ports) , and UE 115-a may select and report P ports out of the N ports via a CRI. For example, UE 115-a may report the selected P ports via an N-bit bitmap or an

-bit indication based on a combination number of the selected P ports and the total N ports.

For the port-selection report, UE 115-a may denote the strongest detected tap aggregating a subset or all ports by m ^* as described previously, and, for a port p, UE 115-amay order the measured energy at tap m ^* based on:

Accordingly, UE 115-a may report the top M ports with largest measurements when transmitting channel state feedback report 230 to indicate the port-selection. If there are multiple receivers, the measurement may include aggregating measurements from a subset or all receivers based on:

In some cases, for MIMO operations, a received signal at UE 115-a may be denoted as:

y=H*W*x+n

where y represents a Nr*1 vector with Nr representing a number of receive antennas used for the received signal; H represents the channel that the signal is received on with a size of Nr*Nt with Nt representing a number of transmit antennas used for transmitting the signal; and W represents the precoder/beamformer with size Nt*R with R representing a rank used for the received signal (e.g., a number of layers used to transmit the signal) ; x represents the data included in the received signal with a size R*1; and n represents additive noise with a size Nr*1. W may affect or indicate performance of communications between UE 115-a and base station 105-a, such that base station 105-a may determine W to better communicate with UE 115-a, but W may be calculated based on H. Additionally, W may be represented by W=W1*W2, where base station 105-a may know W1 based on second order statistics (e.g., angle/delay information) , but W2 may be unknown. In some cases, base station 105-a may determine H based on CSI feedback (e.g., channel state feedback report 230) or by measuring SRSs transmitted by UE 115-a. Additionally or alternatively, base station 105-amay form CSI-RS ports based on W1 and may determine W2 based on the CSI feedback transmitted by UE 115-a using the formed CSI-RS ports.

Based on the implementations described herein, base station 105-a may determine H (e.g., W2) or based on channel state feedback report 230 transmitted by UE 115-a. For example, for the explicit CSI feedback, UE 115-a may transmit H (e.g., or H*W1) directly to base station 105-a based on the strongest detected tap (e.g., selected tap 225) . Additionally or alternatively, for the implicit CSI feedback, UE 115-a may measure H to calculate W (e.g., or measure H*W1 to calculate W2) and may report W (e.g., or W2) to base station 105-a, where W (e.g., or W2) is calculated using the strongest detected tap (e.g., selected tap 225) . For the port-selection feedback report, base station 105-a may transmit H*W1 via multiple ports, where each column of W1 is a port, and UE 115-a may select ports based on the strongest detected tap (e.g., selected tap 225) , where the port-selection feedback report indicates these selected ports according to the strongest detected tap. In some cases, base station 105-a may indicate which type of CSI feedback for UE 115-a to report (e.g., via a CSI-RS configuration, such as indicated via RRC) , or UE 115-a may determine which type of CSI feedback to transmit to base station 105-a.

After receiving channel state feedback report 230, base station 105-a may determine transmission parameters for subsequent communications (e.g., up to network implementation) with UE 115-a based on the CSI feedback included in channel state feedback report 230 (e.g., explicit CSI feedback, implicit CSI feedback, port-selection report, etc. ) . For example, base station 105-a may transmit a downlink shared channel (e.g., a PDSCH) to UE 115-a that is precoded based on the CSI feedback included in channel state feedback report 230.

FIG. 3 illustrates an example of a CSI calculation 300 in accordance with aspects of the present disclosure. In some examples, CSI calculation 300 may implement aspects of wireless communications system 100. For example, a UE 115 may use CSI calculation 300 to determine CSI feedback for CSI-RSs transmitted by a base station 105. Additionally, the base station 105 may transmit the CSI-RSs according to one or more spatial domain bases 305 (e.g., precoders, digital beams, digital precoders, spatial beams, etc. ) and frequency domain bases.

In some cases, the base station 105 may exploit angle and delay reciprocity to form frequency-selective precoding when transmitting signals (e.g., CSI-RSs) to the UE 115 using the spatial domain bases 305. For example, the base station 105 may observe a PDP of each spatial domain basis 305 and may pick significant taps. For instance, as shown in FIG. 3, the base station 105 may pick up two spatial domain bases 305-a and 305-b and up two frequency domain bases associated with two significant taps per spatial domain bases, such as a first tap (e.g., tap 0) and a second tap (e.g., tap 1) for spatial domain basis 305-a and the second tap (e.g., tap 1) and a third tap (e.g., tap 2) for spatial domain basis 305-b. By exploiting the angle and delay reciprocity, the base station 105 may align significant taps for each port at the first tap (e.g., tap 0) . For example, the base station 105 may transmit a first port (e.g., Port 0) that uses a frequency domain basis corresponding to the first tap (e.g., tap 0) of first spatial domain basis 305-a and may transmit a second port (e.g., Port 1) that uses a frequency domain basis corresponding to the second tap (e.g., tap 1) of first spatial domain basis 305-a, where the second tap of first spatial domain basis 305-a is shifted to tap 0 for the second port. Additionally, for second spatial domain basis 305-b, the base station 105 may transmit a third port (e.g., Port 2) that uses a frequency domain basis corresponding to the second tap (e.g., tap 1) of second spatial domain basis 305-b, where the second tap of second spatial domain basis 305-b is shifted to the first tap for the third port, and may transmit a fourth port (e.g., Port 3) that uses a frequency domain basis corresponding to the third tap (e.g., tap 2) of second spatial domain basis 305-b, where the third tap of second spatial domain basis 305-b is shifted to the first tap for the fourth port.

Subsequently, the UE 115 may calculate CSI using the first tap (e.g., tap 0) of each port. In some cases, if there is not a receiving timing offset between the base station 105 and the UE 115, the UE 115 may see all significant taps at the first tap. In some examples, the UE 115 may determine the first tap is a strongest detected tap according to the equations for m ^* as described with reference to FIG. 2. Additionally or alternatively, the UE 115 may determine the first tap is the strongest detected tap based in part on a sum of PDPs across the ports for the first tap being larger than a sum of the PDPs across the ports for any of the other taps. Based on the sum of the PDPs for the first tap being larger than sums of PDPs for the remaining taps, the UE 115 may determine the first tap as the strongest detected tap and not the other taps (e.g., the second tap, the third tap, etc. ) as a strongest detected tap. The UE 115 may then perform measurements on signals received according to the first tap for each port (e.g., based on the significant taps being shifted to the first tap by the base station 105 for each port) and may transmit a CSI report to the base station 105 based on the measurements. If there is no receiving misalignment/timing offset, the base station 105 and the UE 115 may cut a CP 310 at a same point (e.g., cut CP 310 entirely) , and the UE 115 may see a strongest tap at tap 0 (e.g., first tap) for an OFDM symbol 315 with the precoded CSI-RSs, which the base station 105 may expect the UE 115 to see. However, as described herein, due to receiver timing misalignment/offset, the channel measured by the base station 105 for uplink may be a cyclic shift of the channel measured by the UE 115 for downlink. In this case, although the base station 105 may precode the CSI-RS based on the spatial domain and frequency domain bases calculated from the uplink channel and the significant taps of the uplink channels may align at the first tap, these significant taps may not appear at the first tap in the downlink.

FIG. 4 illustrates an example of a CSI calculation 400 in accordance with aspects of the present disclosure. In some examples, CSI calculation 400 may implement aspects of wireless communications system 100. For example, a UE 115 may use CSI calculation 400 to determine CSI feedback for CSI-RSs transmitted by a base station 105. Additionally, the base station 105 may transmit the CSI-RSs according to one or more spatial domain bases 405 (e.g., precoders, digital beams, digital precoders, spatial beams, etc. ) .

Similar to FIG. 3, the base station 105 may pick up two spatial domain bases 405-a and 405-b and up two frequency domain bases associated with two significant taps per spatial domain bases, such as a first tap (e.g., tap 0) and a second tap (e.g., tap 1) for spatial domain basis 405-a and the second tap (e.g., tap 1) and a third tap (e.g., tap 2) for spatial domain basis 405-b.

The base station 105 may also transmit different ports based on the spatial domain bases 405 and the different taps for each spatial domain basis 405. In some cases, there may be a receiving timing offset between the base station 105 and the UE 115, and thus the receiving timing offset shifts a first tap (e.g., tap 0) seen by the base station 105 to a second tap (e.g., tap 1) when receiving at the UE 115. As described previously with reference to FIG. 3, if there is no receiving misalignment/timing offset, the base station 105 and the UE 115 may cut a CP at the same point (e.g., cut CP entirely) . Then the UE 115 may see strongest tap at tap 0 (e.g., first tap) as the base station 105 expects the UE 115 to see. However, with a receiver misalignment/timing offset (e.g., timing offset shifts) , a difference may occur on where the base station 105 and the UE 115 cut a CP 410 for an OFDM symbol 415 with the precoded CSI-RSs, were this difference may lead to a strongest tap seen by the UE 115 being shifted to a place other than tap 0.

By exploiting angle and delay reciprocity, the base station 105 may align significant taps for each port at the first tap (e.g., tap 0) . For example, the base station 105 may transmit a first port (e.g., Port 0) that uses a frequency domain basis corresponding to the first tap (e.g., tap 0) of first spatial domain basis 405-a and may transmit a second port (e.g., Port 1) that uses a frequency domain basis corresponding to the second tap (e.g., tap 1) of first spatial domain basis 405-a. Additionally, for second spatial domain basis 405-b, the base station 105 may transmit a third port (e.g., Port 2) that uses a frequency domain basis corresponding to the second tap (e.g., tap 1) of second spatial domain basis 405-b and may transmit a fourth port (e.g., Port 3) that uses a frequency domain basis corresponding to the third tap (e.g., tap 2) of second spatial domain basis 305-b. However, compared to the case where there is no misalignment as described with reference to FIG. 3, a PDP for each port observed by the UE 115 may be shifted by a corresponding offset (e.g., timing offset shifts) .

Accordingly, with the receiving timing offset, the UE 115 may see all significant taps at the second tap (e.g., tap 1) , and the UE 115 may not compute CSI using the first tap (e.g., tap 0) due to misalignment. The UE 115 may then perform measurements on signals received according to the second tap for each port (e.g., based on the significant taps being shifted to the first tap by the base station 105 for each port) and may transmit a CSI report to the base station 105 based on the measurements. That is, rather than using the first tap to measure and report CSI, the UE 115 may identify a strongest detected tap (e.g., tap 1) and then may report CSI feedback as described with reference to FIG. 2 (e.g., explicit CSI feedback, implicit CSI feedback, port-selection feedback, etc. ) using the strongest detected tap across all ports or a subset of ports (e.g., CSI-RS ports) .

FIGs. 5A and 5B illustrate examples of

CSI reporting procedures

500 and 501 in accordance with aspects of the present disclosure. In some examples,

CSI reporting procedures

500 and 501 may implement aspects of wireless communications system 100. CSI reporting procedure 500 may include a base station 105-b and a UE 115-b, which may represent examples of corresponding base stations 105 and UEs 115, respectively, as described with reference to FIGs. 1-4. Additionally, CSI reporting procedure 501 may include a base station 105-c and a UE 115-c, which may represent examples of corresponding base stations 105 and UEs 115, respectively, as described with reference to FIGs. 1-5A.

For CSI reporting procedure 500 (e.g., an enhanced port-selection type II CSI) , base station 105-b may precode CSI-RSs via b _i, and UE 115-b may report port-selection v _i, FD bases

and linear combination coefficients c _i, m. For each layer, the reported PMI across N3 subbands is written as

where v _i contains a single non-zero value, i.e., 1, indicating the corresponding port is selected. The reported port-selection v _i, FD bases

and linear combination coefficients c _i, m may be different for different layers. For example, at 505, UE 115-b may transmit one or more SRSs to base station 105-b. Base station 105-b may measure the SRS (s) to determine b _i. Subsequently, at 510, base station 105-b may transmit precoded CSI-RSs to UE 115-a, where the CSI-RSs are precoded based on spatial reciprocity. UE 115-b may then measure the CSI-RSs on received ports to calculate CSI for a channel for communication between base station 105-b and UE 115-b. At 515, UE 115-b may transmit CSI reporting to base station 105-b, where the CSI reporting includes c _i, m and

and port-selection.

For CSI reporting procedure 501 (e.g., a further enhanced port-selection type II CSI) , base station 105-c may precode CSI-RSs via b _i and

and UE 115-c may report port- selection v _i, and linear combination coefficients c _i, m. For each layer, the reported PMI may be written as

where v _i contains a single non-zero value, i.e., 1, indicating the corresponding port is selected. The reported port-selection v _i, and linear combination coefficients c _i, m may be different for different layers.. For example, at 520, UE 115-c may transmit one or more SRSs to base station 105-c. Base station 105-c may measure the SRS (s) to determine b _i and

Subsequently, at 525, base station 105-c may transmit precoded CSI-RSs to UE 115-a, where the CSI-RSs are precoded based on spatial reciprocity (e.g., according to b _i) and delay reciprocity (e.g., according to

) . UE 115-c may then measure the CSI-RSs on received ports to calculate CSI for a channel for communications between base station 105-c and UE 115-c. At 530, UE 115-b may transmit CSI reporting to base station 105-b, where the CSI reporting includes c _i, m and port-selection.

In some cases, CSI reporting procedure 501 may be mainly used for a FDD system or a TDD system with mismatched uplink and downlink bands. Additionally, CSI reporting procedure 501 may have a lower overhead than CSI reporting procedure 500, may include lower UE complexity than CSI reporting procedure 500, and may have higher performance than CSI reporting procedure 500 due to finer resolution of frequency domain basis (e.g., precoding the CSI-RSs based on

) . In some implementations, the described techniques for using a strongest detected tap for reporting CSI feedback (e.g., explicit CSI feedback, implicit CSI feedback, port-selection feedback, etc. ) may be based on using CSI reporting procedure 501 but may also be extended to techniques using CSI reporting procedure 500.

FIG. 6 illustrates an example of a process flow 600 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. In some examples, process flow 600 may implement aspects of

wireless communications systems

100 and 200. For example, process flow 600 may include a base station 105-d and a UE 115-d, which may represent examples of corresponding base stations 105 and UEs 115, respectively, as described with reference to FIGs. 1-5.

In the following description of the process flow 600, the operations between UE 115-d and base station 105-d may be transmitted in a different order than the exemplary order shown, or the operations performed by UE 115-d and base station 105-d may be performed in different orders or at different times. Certain operations may also be left out of the process flow 600, or other operations may be added to the process flow 600. It is to be understood that while UE 115-d and base station 105-d are shown performing a number of the operations of process flow 600, any wireless device may perform the operations shown.

At 605, UE 115-d may receive a CSI report configuration. For example, as described with reference to FIG. 2, the CSI report configuration may include a type of CSI-RS, a set of CSI-RS ports (e.g., including a spatial domain basis and a frequency domain basis that the CSI-RS ports are precoded with) , resource configurations for the CSI-RSs, a periodicity for reporting CSI feedback (e.g., periodically, semi-periodically, aperiodically, etc. ) , additional configuration information, or a combination thereof to enable UE 115-d to transmit a CSI report. In some cases, UE 115-d may receive the CSI report configuration via RRC signaling.

At 610, UE 115-d may transmit an SRS to base station 105-d. In some cases, base station 105-d may use the SRS to then transmit CSI-RS ports and resources to UE 115-d with precoding determined based on the SRS.

At 615, UE 115-d may receive a CSI request triggering the CSI report. For example, as described with reference to FIG. 2, the CSI request may include an activation for the CSI-RS configuration and for UE 115-d to transmit the CSI report. In some cases, UE 115-d may receive the CSI request via RRC signaling (e.g., for periodic CSI reporting) , a MAC CE (e.g., for semi-periodic CSI reporting) , DCI (e.g., for aperiodic CSI reporting) , or a combination thereof.

At 620, UE 115-d may receive, from base station 105-d, a set of CSI-RS ports. In some cases, the set of CSI-RS ports may be indicated via the CSI report configuration. For example, base station 105-d may transmit the CSI-RS ports (e.g., via the CSI-RS configuration) for UE 115-d to receive and measure CSI-RSs (e.g., reference signals) on one or more spatial domain bases (e.g., precoders, digital beams, digital precoders, spatial beams, etc. ) based on different taps.

At 625, UE 115-d may receive, from base station 105-d, multiple reference signal resources, each reference signal resource of the multiple reference signal resources corresponding to a single CSI-RS port. For example, as described with reference to FIG. 2, base station 105-d may configure N reference signal resources each with a single CSI-RS port (e.g., resulting in N total CSI-RS ports) .

At 630, UE 115-d may perform a CSI measurement based on the set of CSI-RS ports. For example, as described with reference to FIGs. 2-4, UE 115-d may determine a CSI calculation using taps for CSI-RS ports transmitted by base station 105-d. In some cases, the CSI measurement may include signal measurements for CSI-RSs received on the set of CSI-RS ports, such as received power measurements, received quality measurements, phase measurements, etc.

At 635, UE 115-d may generate a CSI based on the CSI measurement, where the CSI is associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports. For example, UE 115-d may calculate CSI using a reference signal (e.g., CSI-RS) received on a subset or all of the CSI-RS ports of the strongest detected tap. In some cases, UE 115-d may determine CSI reporting associated with the strongest detected tap aggregating a subset or all of the set of CSI-RS ports based on the CSI report configuration received at 605.

At 640, UE 115-d may transmit, to base station 105-d, a CSI report based on the CSI measurement. For example, UE 115-d may transmit the CSI report indicating the CSI measurement that is associated with the strongest detected tap aggregating a subset or all of the set of CSI-RS ports based on receiving the triggering at 615.

In some implementations, UE 115-d may transmit, to base station 105-d, the CSI report that indicates a channel (e.g., explicit CSI feedback as described with reference to FIG. 2) on which the set of CSI-RS ports is conveyed, where the channel is based on measurements measured using the strongest detected tap across a subset of ports of the set of CSI-RS ports or across all ports of the set of CSI-RS ports. For example, UE 115-d may determine that the channel is a linear combination of the subset of ports associated with the strongest detected tap and may transmit, in the CSI report, an indication of the subset of ports based on a measurement on the strongest detected tap using the subset of ports and an indication of linear combination coefficients. Additionally or alternatively, the channel may be a linear combination of all ports of the set of CSI-RS ports, and UE 115-d may report the linear combination coefficients (e.g., no indication of a port-selection) . In some cases, UE 115-d may transmit, to base station 105-d, an indication of a number of antennas used for receiving a signal on a reference signal resource corresponding to the set of CSI-RS ports and may transmit, in the CSI report, a channel measurement from the strongest detected tap of each receive antenna of the number of antennas. Additionally, UE 115-d may transmit, to base station 105-d, an indication of a location of the strongest detected tap or an indication of a location of the strongest detected tap for each receive antenna of the number of antennas.

In some implementations, UE 115-d may transmit, to base station 105-d, a PMI (e.g., a precoder) based on the CSI measurement measured using the strongest detected tap across a subset of ports of the set of CSI-RS ports or across all ports of the set of CSI-RS ports (e.g., implicit CSI feedback as described with reference to FIG. 2) . In some cases, the PMI may include a linear combination of a subset of ports of the set of CSI-RS ports associated with the strongest detected tap, and UE 115-d may transmit, in the CSI report, an indication of the subset of ports based on measurement on the strongest detected tap using the subset of ports and an indication of linear combination coefficients. Additionally or alternatively, the PMI may be a linear combination of all ports of the set of CSI-RS ports, and UE 115-d may report the linear combination coefficients (e.g., no indication of a port-selection) . Additionally, UE 115-d may transmit, to base station 105-d, an RI indicating a number of layers used to receive a signal on a reference signal resource corresponding to the set of CSI-RS ports and may transmit, in the CSI report, the PMI as a linear combination of the subset of ports for each layer. In some cases, UE 115-d may transmit, to base station 105-d, a CQI based on the PMI, an RI, or a combination thereof.

In some implementations, UE 115-d may transmit, to base station 105-d, a port selection indication (e.g., port-selection feedback as described with reference to FIG. 2) that indicates a subset of ports of the set of CSI-RS ports based on a measurement measured using the strongest detected tap across the subset of ports of the set of CSI-RS ports or all ports of the set of CSI-RS ports. In some cases, UE 115-d may select the subset of ports from the set of CSI-RS ports based on an energy level measurement of a reference signal resource at the strongest detected tap using the subset of ports. Additionally or alternatively, UE 115-d may select a subset of ports of the set of CSI-RS ports or resources across the multiple reference signal resources received at 625 and may transmit, to base station 105-d, an indication of the subset of ports or resources via a CRI. For example, the CRI may include a bitmap with a length corresponding to a number of ports in the set of CSI-RS ports, an indicator based on the number of ports in the set of CSI-RS ports and a second number of ports in the subset of ports, or a combination thereof.

FIG. 7 shows a block diagram 700 of a device 705 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The device 705 may be an example of aspects of a UE 115 as described herein. The device 705 may include a receiver 710, a communications manager 715, and a transmitter 720. The device 705 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 710 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 procedures for port-selection codebook with frequency selective precoded reference signals, etc. ) . Information may be passed on to other components of the device 705. The receiver 710 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The receiver 710 may utilize a single antenna or a set of antennas.

The communications manager 715 may receive, from a base station, a set of CSI-RS ports. In some cases, the communications manager 715 may perform a CSI measurement based on the set of CSI-RS ports. Additionally, the communications manager 715 may generate a CSI based on the CSI measurement, where the CSI is associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports. Subsequently, the communications manager 715 may transmit, to the base station, a CSI report based on the CSI measurement. The communications manager 715 may be an example of aspects of the communications manager 1010 described herein.

The communications manager 715, 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 715, 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.

The communications manager 715, 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 715, 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 715, 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.

In some examples, the communications manager 715 may be implemented as an integrated circuit or chipset for a mobile device modem, and the receiver 710 and transmitter 720 may be implemented as analog components (e.g., amplifiers, filters, antennas) coupled with the mobile device modem to enable wireless transmission and reception over one or more bands.

The communications manager 715 as described herein may be implemented to realize one or more potential advantages. One implementation may allow the device 705 to more accurately report CSI feedback for CSI-RSs received across different ports, on different spatial domain bases (e.g., precoders, digital beams, digital precoders, spatial beams, etc. ) , according to different taps, or a combination thereof. For example, the device 705 may use a strongest detected tap to measure CSI-RS ports rather than defaulting to a same tap regardless of signal power for the CSI-RS ports. Accordingly, the device 705 may report more accurate measurements of the CSI, which may result in more efficient subsequent communications with additional devices (e.g., a base station 105) , thereby also improving battery or power consumption of the device 705 by improving chances that subsequent communications are successfully communicated using the more accurate measurements and decreasing chances of processing and transmitting or receiving retransmissions.

The transmitter 720 may transmit signals generated by other components of the device 705. In some examples, the transmitter 720 may be collocated with a receiver 710 in a transceiver module. For example, the transmitter 720 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The transmitter 720 may utilize a single antenna or a set of antennas.

FIG. 8 shows a block diagram 800 of a device 805 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The device 805 may be an example of aspects of a device 705, or a UE 115 as described herein. The device 805 may include a receiver 810, a communications manager 815, and a transmitter 840. The device 805 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

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 procedures for port-selection codebook with frequency selective precoded reference signals, 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 1020 described with reference to FIG. 10. The receiver 810 may utilize a single antenna or a set of antennas.

The communications manager 815 may be an example of aspects of the communications manager 715 as described herein. The communications manager 815 may include a CSI-RS port component 820, a CSI measurement component 825, a CSI generation component 830, and a CSI report component 835. The communications manager 815 may be an example of aspects of the communications manager 1010 described herein.

The CSI-RS port component 820 may receive, from a base station, a set of CSI-RS ports.

The CSI measurement component 825 may perform a CSI measurement based on the set of CSI-RS ports.

The CSI generation component 830 may generate a CSI based on the CSI measurement, where the CSI is associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports.

The CSI report component 835 may transmit, to the base station, a CSI report based on the CSI measurement.

Based on performing a CSI measurement associated with a strongest detected tap as described herein, a processor of the UE 115 (e.g., controlling the receiver 810, the transmitter 840, or the transceiver 1020 as described with reference to FIG. 10) may more accurately measure CSI across a set of ports to then provide the CSI measurements to a network entity (e.g., a base station 105) for adjusting or configuring subsequent communications. Accordingly, the processor of the UE 115 may decrease signaling overhead that may arise from transmitting multiple CSI reports to enable the network device to determine appropriate adjustments or configurations. Additionally or alternatively, the signaling overhead may be decreased from scenarios where the network device determines a set of parameters to use for subsequent communications that are based on CSI measurements from a different tap than a strongest detected tap, thereby resulting in less than optimal parameters which may increase chances of retransmissions.

The transmitter 840 may transmit signals generated by other components of the device 805. In some examples, the transmitter 840 may be collocated with a receiver 810 in a transceiver module. For example, the transmitter 840 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The transmitter 840 may utilize a single antenna or a set of antennas.

FIG. 9 shows a block diagram 900 of a communications manager 905 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The communications manager 905 may be an example of aspects of a communications manager 715, a communications manager 815, or a communications manager 1010 described herein. The communications manager 905 may include a CSI-RS port component 910, a CSI measurement component 915, a CSI generation component 920, a CSI report component 925, a CSI report configuration component 930, a CSI report activation component 935, a channel indication component 940, a precoder indication component 945, and a port selection indication component 950. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses) .

The CSI-RS port component 910 may receive, from a base station, a set of CSI-RS ports.

The CSI measurement component 915 may perform a CSI measurement based on the set of CSI-RS ports.

The CSI generation component 920 may generate a CSI based on the CSI measurement, where the CSI is associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports.

The CSI report component 925 may transmit, to the base station, a CSI report based on the CSI measurement.

The CSI report configuration component 930 may receive a CSI report configuration. In some examples, the CSI report configuration component 930 may determine CSI reporting associated with the strongest detected tap aggregating the subset or all of the set of CSI-RS ports based on the CSI report configuration.

The CSI report activation component 935 may receive a CSI request triggering the CSI report. In some examples, the CSI report activation component 935 may transmit the CSI report indicating the CSI measurement that is associated with the strongest detected tap aggregating the subset or all of the set of CSI-RS ports based on the triggering.

The channel indication component 940 may transmit, to the base station, the CSI report that indicates a channel on which the set of CSI-RS ports is conveyed, the channel based on measurements measured using the strongest detected tap across a subset of ports of the set of CSI-RS ports or across all ports of the set of CSI-RS ports. In some examples, the channel indication component 940 may determine that the channel is a linear combination of the subset of ports associated with the strongest detected tap and may transmit in the CSI report an indication of the subset of ports based at least on part on a measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients. Additionally or alternatively, the channel indication component 940 may determine that the channel is a linear combination of all of the set of CSI-RS ports associated with the strongest detected tap and may transmit in the CSI report an indication of linear combination coefficients.

Additionally, the channel indication component 940 may transmit, to the base station, an indication of a number of antennas used for receiving a signal on a reference signal resource corresponding to the set of CSI-RS ports. In some examples, the channel indication component 940 may transmit in the CSI report a channel measurement from the strongest detected tap of each receive antenna of the number of antennas. Additionally, the channel indication component 940 may transmit, to the base station, an indication of a location of the strongest detected tap or an indication of a location of the strongest detected tap for each receive antenna of the number of antennas.

The precoder indication component 945 may transmit, to the base station, a PMI based on the CSI measurement measured using the strongest detected tap across a subset of ports of the set of CSI-RS ports or across all ports of the set of CSI-RS ports. In some examples, the PMI may include a linear combination of the subset of ports of the set of CSI-RS ports associated with the strongest detected tap, and the precoder indication component 945 may transmit in the CSI report an indication of the subset of ports based on measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients. Additionally or alternatively, the PMI may be a linear combination of all of the set of CSI-RS ports associated with the strongest detected tap, and the precoder indication component 945 may transmit in the CSI report an indication of linear combination coefficients.

Additionally, the precoder indication component 945 may transmit, to the base station, a RI indicating a number of layers used to receive a signal on a reference signal resource corresponding to the set of CSI-RS ports. In some examples, the precoder indication component 945 may transmit in the CSI report the PMI as a linear combination of the subset of ports for each layer. Additionally, the precoder indication component 945 may transmit, to the base station, a CQI based on the PMI, a RI, or a combination thereof.

The port selection indication component 950 may transmit, to the base station, a port selection indication that indicates a subset of ports of the set of CSI-RS ports based on a measurement measured using the strongest detected tap across the subset of ports of the set of CSI-RS ports or all ports of the set of CSI-RS ports. In some examples, the port selection indication component 950 may select the subset of ports from the set of CSI-RS ports based on an energy level measurement of a reference signal resource at the strongest detected tap using the subset of ports. Additionally or alternatively, the port selection indication component 950 may receive, from the base station, multiple reference signal resources, each reference signal resource of the multiple reference signal resources including a single CSI-RS port. Accordingly, the port selection indication component 950 may select a subset of ports of the set of CSI-RS ports or resources across the multiple reference signal resources and may transmit, to the base station, an indication of the subset of ports or resources via a CRI. In some cases, the CRI may include a bitmap with a length corresponding to a number of ports in the set of CSI-RS ports, an indicator based on the number of ports in the set of CSI-RS ports and a second number of ports in the subset of ports, or a combination thereof.

FIG. 10 shows a diagram of a system 1000 including a device 1005 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The device 1005 may be an example of or include the components of device 705, device 805, or a UE 115 as described herein. The device 1005 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager 1010, an I/O controller 1015, a transceiver 1020, an antenna 1025, memory 1030, and a processor 1040. These components may be in electronic communication via one or more buses (e.g., bus 1045) .

The communications manager 1010 may receive, from a base station, a set of CSI-RS ports. In some implementations, the communications manager 1010 may perform a CSI measurement based on the set of CSI-RS ports. Additionally, the communications manager 1010 may generate a CSI based on the CSI measurement, where the CSI is associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports. Subsequently, the communications manager 1010 may transmit, to the base station, a CSI report based on the CSI measurement.

The I/O controller 1015 may manage input and output signals for the device 1005. The I/O controller 1015 may also manage peripherals not integrated into the device 1005. In some cases, the I/O controller 1015 may represent a physical connection or port to an external peripheral. In some cases, the I/O controller 1015 may utilize an operating system such as

or another known operating system. In other cases, the I/O controller 1015 may represent or interact with a modem, a keyboard, a mouse, a touchscreen, or a similar device. In some cases, the I/O controller 1015 may be implemented as part of a processor. In some cases, a user may interact with the device 1005 via the I/O controller 1015 or via hardware components controlled by the I/O controller 1015.

The transceiver 1020 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 1020 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1020 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.

In some cases, the wireless device may include a single antenna 1025. However, in some cases the device may have more than one antenna 1025, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory 1030 may include random-access memory (RAM) and read-only memory (ROM) . The memory 1030 may store computer-readable, computer-executable code 1035 including instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory 1030 may contain, among other things, a basic I/O system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The processor 1040 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 1040 may be configured to operate a memory array using a memory controller. In other cases, a memory controller may be integrated into the processor 1040. The processor 1040 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1030) to cause the device 1005 to perform various functions (e.g., functions or tasks supporting procedures for port-selection codebook with frequency selective precoded reference signals) .

The code 1035 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 1035 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 1035 may not be directly executable by the processor 1040 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

FIG. 11 shows a block diagram 1100 of a device 1105 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The device 1105 may be an example of aspects of a base station 105 as described herein. The device 1105 may include a receiver 1110, a communications manager 1115, and a transmitter 1120. The device 1105 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 1110 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 procedures for port-selection codebook with frequency selective precoded reference signals, etc. ) . Information may be passed on to other components of the device 1105. The receiver 1110 may be an example of aspects of the transceiver 1420 described with reference to FIG. 14. The receiver 1110 may utilize a single antenna or a set of antennas.

The communications manager 1115 may transmit, to a UE, a set of CSI-RS ports. Additionally, the communications manager 1115 may receive, from the UE, a CSI report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports. The communications manager 1115 may be an example of aspects of the communications manager 1410 described herein.

The communications manager 1115, 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 1115, 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.

The communications manager 1115, 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 1115, 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 1115, or its sub-components, may be combined with one or more other hardware components, including but not limited to an 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.

The transmitter 1120 may transmit signals generated by other components of the device 1105. In some examples, the transmitter 1120 may be collocated with a receiver 1110 in a transceiver module. For example, the transmitter 1120 may be an example of aspects of the transceiver 1420 described with reference to FIG. 14. The transmitter 1120 may utilize a single antenna or a set of antennas.

FIG. 12 shows a block diagram 1200 of a device 1205 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The device 1205 may be an example of aspects of a device 1105, or a base station 105 as described herein. The device 1205 may include a receiver 1210, a communications manager 1215, and a transmitter 1230. The device 1205 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

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 procedures for port-selection codebook with frequency selective precoded reference signals, 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 1420 described with reference to FIG. 14. The receiver 1210 may utilize a single antenna or a set of antennas.

The communications manager 1215 may be an example of aspects of the communications manager 1115 as described herein. The communications manager 1215 may include a CSI-RS component 1220 and a CSI measurement report component 1225. The communications manager 1215 may be an example of aspects of the communications manager 1410 described herein.

The CSI-RS component 1220 may transmit, to a UE, a set of CSI-RS ports.

The CSI measurement report component 1225 may receive, from the UE, a CSI report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports.

The transmitter 1230 may transmit signals generated by other components of the device 1205. In some examples, the transmitter 1230 may be collocated with a receiver 1210 in a transceiver module. For example, the transmitter 1230 may be an example of aspects of the transceiver 1420 described with reference to FIG. 14. The transmitter 1230 may utilize a single antenna or a set of antennas.

FIG. 13 shows a block diagram 1300 of a communications manager 1305 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The communications manager 1305 may be an example of aspects of a communications manager 1115, a communications manager 1215, or a communications manager 1410 described herein. The communications manager 1305 may include a CSI-RS component 1310, a CSI measurement report component 1315, a CSI configuration component 1320, a CSI request component 1325, a channel measurement component 1330, a precoder measurement component 1335, and a port selection measurement component 1340. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses) .

The CSI-RS component 1310 may transmit, to a UE, a set of CSI-RS ports.

The CSI measurement report component 1315 may receive, from the UE, a CSI report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports.

The CSI configuration component 1320 may transmit a CSI report configuration, where the CSI report is based on the CSI report configuration.

The CSI request component 1325 may transmit a CSI request triggering the CSI report. In some examples, the CSI request component 1325 may receive the CSI report indicating the CSI measurement that is associated with the strongest detected tap aggregating the subset or all of the set of CSI-RS ports based on the triggering.

The channel measurement component 1330 may receive the CSI report that indicates a channel on which the set of CSI-RS ports is conveyed, the channel based on measurements measured using the strongest detected tap across a subset of ports of the set of CSI-RS ports or across all ports of the set of CSI-RS ports. In some examples, the channel measurement component 1330 may receive the CSI report that reports an indication of the subset of ports based at least on part on a measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients. Additionally or alternatively, the channel measurement component 1330 may receive the CSI report that reports an indication of linear combination coefficients.

Additionally, the channel measurement component 1330 may receive an indication of a number of antennas used for receiving a signal on a reference signal resource corresponding to the set of CSI-RS ports. In some examples, the channel measurement component 1330 may receive the CSI report that reports a channel measurement from the strongest detected tap of each receive antenna of the number of antennas. Additionally, the channel measurement component 1330 may receive an indication of a location of the strongest detected tap or an indication of a location of the strongest detected tap for each receive antenna of the number of antennas.

The precoder measurement component 1335 may receive a PMI based on the CSI measurement measured using the strongest detected tap across a subset of ports of the set of CSI-RS ports or across all ports of the set of CSI-RS ports. In some examples, the PMI may include a linear combination of the subset of ports associated with the strongest detected tap, and the precoder measurement component 1335 may receive the CSI report that reports an indication of the subset of ports based on measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients. Additionally or alternatively, the PMI may include a linear combination of all of the set of CSI-RS ports associated with the strongest detected tap, and the precoder measurement component 1335 may receive an indication of linear combination coefficients.

Additionally, the precoder measurement component 1335 may receive a RI indicating a number of layers used to receive a signal on a reference signal resource corresponding to the set of CSI-RS ports. In some examples, the precoder measurement component 1335 may receive the CSI report that reports the PMI as a linear combination of the subset of ports for each layer. Additionally, the precoder measurement component 1335 may receive a CQI based on the PMI, a RI, or a combination thereof.

The port selection measurement component 1340 may receive a port selection indication that indicates a subset of ports of the set of CSI-RS ports based on a measurement measured using the strongest detected tap across the subset of ports of the set of CSI-RS ports or all ports of the set of CSI-RS ports. Additionally or alternatively, the port selection measurement component 1340 may transmit multiple reference signal resources, each reference signal resource of the multiple reference signal resources including a single CSI-RS port. Accordingly, the port selection measurement component 1340 may receive, from the UE, a CRI indicating a subset of ports or resources across the multiple reference signal resources. In some cases, the CRI may include a bitmap with a length corresponding to a number of ports in the set of CSI-RS ports, an indicator based on the number of ports in the set of CSI-RS ports and a second number of ports in the subset of ports, or a combination thereof.

FIG. 14 shows a diagram of a system 1400 including a device 1405 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The device 1405 may be an example of or include the components of device 1105, device 1205, or a base station 105 as described herein. The device 1405 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager 1410, a network communications manager 1415, a transceiver 1420, an antenna 1425, memory 1430, a processor 1440, and an inter-station communications manager 1445. These components may be in electronic communication via one or more buses (e.g., bus 1450) .

The communications manager 1410 may transmit, to a UE, a set of CSI-RS ports. Additionally, the communications manager 1410 may receive, from the UE, a CSI report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports.

The network communications manager 1415 may manage communications with the core network (e.g., via one or more wired backhaul links) . For example, the network communications manager 1415 may manage the transfer of data communications for client devices, such as one or more UEs 115.

The transceiver 1420 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 1420 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1420 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.

In some cases, the wireless device may include a single antenna 1425. However, in some cases the device may have more than one antenna 1425, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory 1430 may include RAM, ROM, or a combination thereof. The memory 1430 may store computer-readable code 1435 including instructions that, when executed by a processor (e.g., the processor 1440) cause the device to perform various functions described herein. In some cases, the memory 1430 may contain, among other things, a BIOS which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The processor 1440 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 1440 may be configured to operate a memory array using a memory controller. In some cases, a memory controller may be integrated into processor 1440. The processor 1440 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1430) to cause the device 1405 to perform various functions (e.g., functions or tasks supporting procedures for port-selection codebook with frequency selective precoded reference signals) .

The inter-station communications manager 1445 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 1445 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 1445 may provide an X2 interface within an LTE/LTE-A wireless communication network technology to provide communication between base stations 105.

The code 1435 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 1435 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 1435 may not be directly executable by the processor 1440 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

FIG. 15 shows a flowchart illustrating a method 1500 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The operations of method 1500 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1500 may be performed by a communications manager as described with reference to FIGs. 7 through 10. 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.

At 1505, the UE may receive, from a base station, a set of CSI-RS ports. The operations of 1505 may be performed according to the methods described herein. In some examples, aspects of the operations of 1505 may be performed by a CSI-RS port component as described with reference to FIGs. 7 through 10.

At 1510, the UE may perform a CSI measurement based on the set of CSI-RS ports. The operations of 1510 may be performed according to the methods described herein. In some examples, aspects of the operations of 1510 may be performed by a CSI measurement component as described with reference to FIGs. 7 through 10.

At 1515, the UE may generate a CSI based on the CSI measurement, where the CSI is associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports. The operations of 1515 may be performed according to the methods described herein. In some examples, aspects of the operations of 1515 may be performed by a CSI generation component as described with reference to FIGs. 7 through 10.

At 1520, the UE may transmit, to the base station, a CSI report based on the CSI measurement. The operations of 1520 may be performed according to the methods described herein. In some examples, aspects of the operations of 1520 may be performed by a CSI report component as described with reference to FIGs. 7 through 10.

FIG. 16 shows a flowchart illustrating a method 1600 that supports procedures for port-selection codebook with frequency selective precoded reference signals 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. 7 through 10. 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.

At 1605, the UE may receive, from a base station, a set of CSI-RS ports. 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 port component as described with reference to FIGs. 7 through 10.

At 1610, the UE may perform a CSI measurement based on the set of CSI-RS ports. 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 CSI measurement component as described with reference to FIGs. 7 through 10.

At 1615, the UE may generate a CSI based on the CSI measurement, where the CSI is associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports. 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 CSI generation component as described with reference to FIGs. 7 through 10.

At 1620, the UE may transmit, to the base station, a CSI report based on the CSI measurement. 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 CSI report component as described with reference to FIGs. 7 through 10.

At 1625, the UE may transmit, to the base station, the CSI report that indicates a channel on which the set of CSI-RS ports is conveyed, the channel based on measurements measured using the strongest detected tap across a subset of ports of the set of CSI-RS ports or across all ports of the set of CSI-RS ports. The operations of 1625 may be performed according to the methods described herein. In some examples, aspects of the operations of 1625 may be performed by a channel indication component as described with reference to FIGs. 7 through 10.

FIG. 17 shows a flowchart illustrating a method 1700 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The operations of method 1700 may be implemented by a UE 115 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. 7 through 10. 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.

At 1705, the UE may receive, from a base station, a set of CSI-RS ports. 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 port component as described with reference to FIGs. 7 through 10.

At 1710, the UE may perform a CSI measurement based on the set of CSI-RS ports. 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 CSI measurement component as described with reference to FIGs. 7 through 10.

At 1715, the UE may generate a CSI based on the CSI measurement, where the CSI is associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports. 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 CSI generation component as described with reference to FIGs. 7 through 10.

At 1720, the UE may transmit, to the base station, a CSI report based on the CSI measurement. The operations of 1720 may be performed according to the methods described herein. In some examples, aspects of the operations of 1720 may be performed by a CSI report component as described with reference to FIGs. 7 through 10.

At 1725, the UE may transmit, to the base station, a PMI based on the CSI measurement measured using the strongest detected tap across a subset of ports of the set of CSI-RS ports or across all ports of the set of CSI-RS ports. The operations of 1725 may be performed according to the methods described herein. In some examples, aspects of the operations of 1725 may be performed by a precoder indication component as described with reference to FIGs. 7 through 10.

FIG. 18 shows a flowchart illustrating a method 1800 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The operations of method 1800 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1800 may be performed by a communications manager as described with reference to FIGs. 7 through 10. 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.

At 1805, the UE may receive, from a base station, a set of CSI-RS ports. The operations of 1805 may be performed according to the methods described herein. In some examples, aspects of the operations of 1805 may be performed by a CSI-RS port component as described with reference to FIGs. 7 through 10.

At 1810, the UE may perform a CSI measurement based on the set of CSI-RS ports. The operations of 1810 may be performed according to the methods described herein. In some examples, aspects of the operations of 1810 may be performed by a CSI measurement component as described with reference to FIGs. 7 through 10.

At 1815, the UE may generate a CSI based on the CSI measurement, where the CSI is associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports. The operations of 1815 may be performed according to the methods described herein. In some examples, aspects of the operations of 1815 may be performed by a CSI generation component as described with reference to FIGs. 7 through 10.

At 1820, the UE may transmit, to the base station, a CSI report based on the CSI measurement. The operations of 1820 may be performed according to the methods described herein. In some examples, aspects of the operations of 1820 may be performed by a CSI report component as described with reference to FIGs. 7 through 10.

At 1825, the UE may transmit, to the base station, a port selection indication that indicates a subset of ports of the set of CSI-RS ports based on a measurement measured using the strongest detected tap across the subset of ports of the set of CSI-RS ports or all ports of the set of CSI-RS ports. The operations of 1825 may be performed according to the methods described herein. In some examples, aspects of the operations of 1825 may be performed by a port selection indication component as described with reference to FIGs. 7 through 10.

FIG. 19 shows a flowchart illustrating a method 1900 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The operations of method 1900 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 1900 may be performed by a communications manager as described with reference to FIGs. 11 through 14. 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.

At 1905, the base station may transmit, to a UE, a set of CSI-RS ports. The operations of 1905 may be performed according to the methods described herein. In some examples, aspects of the operations of 1905 may be performed by a CSI-RS component as described with reference to FIGs. 11 through 14.

At 1910, the base station may receive, from the UE, a CSI report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports. The operations of 1910 may be performed according to the methods described herein. In some examples, aspects of the operations of 1910 may be performed by a CSI measurement report component as described with reference to FIGs. 11 through 14.

FIG. 20 shows a flowchart illustrating a method 2000 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The operations of method 2000 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 2000 may be performed by a communications manager as described with reference to FIGs. 11 through 14. 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.

At 2005, the base station may transmit a CSI report configuration, where a CSI report is based on the CSI report configuration. The operations of 2005 may be performed according to the methods described herein. In some examples, aspects of the operations of 2005 may be performed by a CSI configuration component as described with reference to FIGs. 11 through 14.

At 2010, the base station may transmit, to a UE, a set of CSI-RS ports. The operations of 2010 may be performed according to the methods described herein. In some examples, aspects of the operations of 2010 may be performed by a CSI-RS component as described with reference to FIGs. 11 through 14.

At 2015, the base station may receive, from the UE, the CSI report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports. The operations of 2015 may be performed according to the methods described herein. In some examples, aspects of the operations of 2015 may be performed by a CSI measurement report component as described with reference to FIGs. 11 through 14.

FIG. 21 shows a flowchart illustrating a method 2100 that supports procedures for port-selection codebook with frequency selective precoded reference signals in accordance with aspects of the present disclosure. The operations of method 2100 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 2100 may be performed by a communications manager as described with reference to FIGs. 11 through 14. 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.

At 2105, the base station may transmit a CSI request triggering a CSI report. The operations of 2105 may be performed according to the methods described herein. In some examples, aspects of the operations of 2105 may be performed by a CSI request component as described with reference to FIGs. 11 through 14.

At 2110, the base station may transmit, to a UE, a set of CSI-RS ports. The operations of 2110 may be performed according to the methods described herein. In some examples, aspects of the operations of 2110 may be performed by a CSI-RS component as described with reference to FIGs. 11 through 14.

At 2115, the base station may receive, from the UE, the CSI report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the set of CSI-RS ports. The operations of 2115 may be performed according to the methods described herein. In some examples, aspects of the operations of 2115 may be performed by a CSI measurement report component as described with reference to FIGs. 11 through 14.

At 2120, the base station may receive the CSI report indicating the CSI measurement that is associated with the strongest detected tap aggregating the subset or all of the set of CSI-RS ports based on the triggering. The operations of 2120 may be performed according to the methods described herein. In some examples, aspects of the operations of 2120 may be performed by a CSI request component as described with reference to FIGs. 11 through 14.

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.

The following provides an overview of embodiments of the present invention:

Embodiment 1: A method for wireless communications at a user equipment (UE) , comprising: receiving, from a base station, a plurality of channel state information reference signal (CSI-RS) ports; performing a channel state information (CSI) measurement based at least in part on the plurality of CSI-RS ports, generating a CSI based at least in part on the CSI measurement, wherein the CSI is associated with a strongest detected tap aggregating a subset or all of the plurality of CSI-RS ports; and transmitting, to the base station, a CSI report based at least in part on the CSI.

Embodiment 2: The method of embodiment 1, further comprising: receiving a CSI report configuration; and determining CSI reporting associated with the strongest detected tap aggregating the subset or all of the plurality of CSI-RS ports based on the CSI report configuration.

Embodiment 3: The method of any one of embodiments 1 through 2, further comprising: receiving a CSI request triggering the CSI report; and transmitting the CSI report indicating the CSI measurement that is associated with the strongest detected tap aggregating the subset or all of the plurality of CSI-RS ports based on the triggering.

Embodiment 4: The method of any one of embodiments 1 through 3, wherein transmitting the CSI report comprises: transmitting, to the base station, the CSI report that indicates a channel on which the plurality of CSI-RS ports are conveyed, the channel based at least in part on measurements measured using the strongest detected tap across a subset of ports of the plurality of CSI-RS ports or across all ports of the plurality of CSI-RS ports.

Embodiment 5: The method of embodiment 4, further comprising: determining that the channel is a linear combination of the subset of ports associated with the strongest detected tap; and transmitting in the CSI report an indication of the subset of ports based at least on part on a measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.

Embodiment 6: The method of embodiment 4, further comprising: determining that the channel is a linear combination of all of the plurality of CSI-RS ports associated with the strongest detected tap; and transmitting in the CSI report an indication of linear combination coefficients.

Embodiment 7: The method of any one of embodiments 5 through 6, further comprising: transmitting, to the base station, an indication of a number of antennas used for receiving a signal on a reference signal resource corresponding to the plurality of CSI-RS ports; and transmitting in the CSI report a channel measurement from the strongest detected tap of each receive antenna of the number of antennas.

Embodiment 8: The method of embodiment 7, further comprising: transmitting, to the base station, an indication of a location of the strongest detected tap or an indication of a location of the strongest detected tap for each receive antenna of the number of antennas.

Embodiment 9: The method of any one of embodiments 1 through 3, wherein transmitting the CSI report comprises: transmitting, to the base station, a precoding matrix indicator based at least in part on the CSI measurement measured using the strongest detected tap across a subset of ports of the plurality of CSI-RS ports or across all ports of the plurality of CSI-RS ports.

Embodiment 10: The method of embodiment 9, wherein the precoding matrix indicator comprises a linear combination of the subset of ports of the plurality of CSI-RS ports associated with the strongest detected tap, the method further comprising: transmitting in the CSI report an indication of the subset of ports based at least in part on measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.

Embodiment 11: The method of embodiment 9, wherein the precoding matrix indicator comprises a linear combination of all of the plurality of CSI-RS ports associated with the strongest detected tap, the method further comprising: transmitting in the CSI report an indication of linear combination coefficients.

Embodiment 12: The method of any one of embodiments 9 through 11, further comprising: transmitting, to the base station, a rank indicator indicating a number of layers used to receive a signal on a reference signal resource corresponding to the plurality of CSI-RS ports; and transmitting in the CSI report the precoding matrix indicator as a linear combination of the subset of ports for each layer.

Embodiment 13: The method of any one of embodiments 9 through 12, further comprising: transmitting, to the base station, a channel quality indicator based at least in part on the precoding matrix indicator, a rank indicator, or a combination thereof.

Embodiment 14: The method of any one of embodiments 1 through 3, wherein transmitting the CSI report comprises: transmitting, to the base station, a port selection indication that indicates a subset of ports of the plurality of CSI-RS ports based at least in part on a measurement measured using the strongest detected tap across the subset of ports of the plurality of CSI-RS ports or all ports of the plurality of CSI-RS ports.

Embodiment 15: The method of embodiment 14, further comprising: selecting the subset of ports from the plurality of CSI-RS ports based at least in part on an energy level measurement of a reference signal resource at the strongest detected tap using the subset of ports.

Embodiment 16: The method of any one of embodiments 1 through 3, further comprising: receiving, from the base station, multiple reference signal resources, each reference signal resource of the multiple reference signal resources comprising a single CSI-RS port.

Embodiment 17: The method of embodiment 16, further comprising: selecting a subset of ports of the plurality of CSI-RS ports or resources across the multiple reference signal resources; and transmitting, to the base station, an indication of the subset of ports or resources via a CSI-RS indicator.

Embodiment 18: The method of embodiment 17, wherein the CSI-RS indicator comprises a bitmap with a length corresponding to a number of ports in the plurality of CSI-RS ports, an indicator based at least in part on the number of ports in the plurality of CSI-RS ports and a second number of ports in the subset of ports, or a combination thereof.

Embodiment 19: A method for wireless communications at a base station, comprising: transmitting, to a user equipment (UE) , a plurality of channel state information reference signal (CSI-RS) ports; receiving, from the UE, a channel state information (CSI) report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the plurality of CSI-RS ports.

Embodiment 20: The method of embodiment 19, further comprising: transmitting a CSI report configuration, wherein the CSI report is based on the CSI report configuration.

Embodiment 21: The method of any one of embodiments 19 through 20, further comprising: transmitting a CSI request triggering the CSI report; and receiving the CSI report indicating the CSI measurement that is associated with the strongest detected tap aggregating the subset or all of the plurality of CSI-RS ports based on the triggering.

Embodiment 22: The method of any one of embodiments 19 through 21, wherein receiving the CSI report comprises: receiving the CSI report that indicates a channel on which the plurality of CSI-RS ports are conveyed, the channel based at least in part on measurements measured using the strongest detected tap across a subset of ports of the plurality of CSI-RS ports or across all ports of the plurality of CSI-RS ports.

Embodiment 23: The method of embodiment 22, wherein receiving the CSI report comprises: receiving the CSI report that reports an indication of the subset of ports based at least on part on a measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.

Embodiment 24: The method of embodiment 22, wherein receiving the CSI report comprises: receiving the CSI report that reports an indication of linear combination coefficients.

Embodiment 25: The method of any one of embodiments 23 through 24, further comprising: receiving an indication of a number of antennas used for receiving a signal on a reference signal resource corresponding to the plurality of CSI-RS ports; and receiving the CSI report that reports a channel measurement from the strongest detected tap of each receive antenna of the number of antennas.

Embodiment 26: The method of embodiment 25, further comprising: receiving an indication of a location of the strongest detected tap or an indication of a location of the strongest detected tap for each receive antenna of the number of antennas.

Embodiment 27: The method of any one of embodiments 19 through 21, wherein receiving the CSI report comprises: receiving a precoding matrix indicator based at least in part on the CSI measurement measured using the strongest detected tap across a subset of ports of the plurality of CSI-RS ports or across all ports of the plurality of CSI-RS ports.

Embodiment 28: The method of embodiment 27, wherein the precoding matrix indicator comprises a linear combination of the subset of ports associated with the strongest detected tap, the method further comprising: receiving the CSI report that reports an indication of the subset of ports based at least in part on measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.

Embodiment 29: The method of embodiment 27, wherein the precoding matrix indicator comprises a linear combination of all of the plurality of CSI-RS ports associated with the strongest detected tap, the method further comprising: receiving an indication of linear combination coefficients.

Embodiment 30: The method of any one of embodiments 27 through 29, further comprising: receiving a rank indicator indicating a number of layers used to receive a signal on a reference signal resource corresponding to the plurality of CSI-RS ports; and receiving the CSI report that reports the precoding matrix indicator as a linear combination of the subset of ports for each layer.

Embodiment 31: The method of any one of embodiments 27 through 30, further comprising: receiving a channel quality indicator based at least in part on the precoding matrix indicator, a rank indicator, or a combination thereof.

Embodiment 32: The method of any one of embodiments 19 through 21, wherein receiving the CSI report comprises: receiving a port selection indication that indicates a subset of ports of the plurality of CSI-RS ports based at least in part on a measurement measured using the strongest detected tap across the subset of ports of the plurality of CSI-RS ports or all ports of the plurality of CSI-RS ports.

Embodiment 33: The method of any one of embodiments 19 through 21, further comprising: transmitting multiple reference signal resources, each reference signal resource of the multiple reference signal resources comprising a single CSI-RS port.

Embodiment 34: The method of embodiment 33, further comprising: receiving, from the UE, a CSI-RS indicator indicating a subset of ports or resources across the multiple reference signal resources.

Embodiment 35: The method of embodiment 34, wherein the CSI-RS indicator comprises a bitmap with a length corresponding to a number of ports in the plurality of CSI-RS ports, an indicator based at least in part on the number of ports in the plurality of CSI-RS ports and a second number of ports in the subset of ports, or a combination thereof

Embodiment 36: An apparatus for wireless communications at a user equipment (UE) comprising at least one means for performing a method of any one of embodiments 1 through 18.

Embodiment 37: An apparatus for wireless communications at a user equipment (UE) comprising a processor and memory coupled to the processor, the processor and memory configured to perform a method of any one of embodiments 1 through 18.

Embodiment 38: A non-transitory computer-readable medium storing code for wireless communications at a user equipment (UE) , the code comprising instructions executable by a processor to perform a method of any one of embodiments 1 through 18.

Embodiment 39: An apparatus for wireless communications at a base station comprising at least one means for performing a method of any one of embodiments 19 through 35.

Embodiment 40: An apparatus for wireless communications at a base station comprising a processor and memory coupled to the processor, the processor and memory configured to perform a method of any one of embodiments 19 through 35.

Embodiment 41: A non-transitory computer-readable medium storing code for wireless communications at a base station, the code comprising instructions executable by a processor to perform a method of any one of embodiments 19 through 35.

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.

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.

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) .

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.

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.

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. ”

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.

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.

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

A method for wireless communications at a user equipment (UE) , comprising:

receiving, from a base station, a plurality of CSI-RS ports;

performing a channel state information (CSI) measurement based at least in part on the plurality of CSI-RS ports;

generating a CSI based at least in part on the CSI measurement, wherein the CSI is associated with a strongest detected tap aggregating a subset or all of the plurality of CSI-RS ports; and

transmitting, to the base station, a CSI report based at least in part on the CSI.
The method of claim 1, further comprising:

receiving a CSI report configuration; and

determining CSI reporting associated with the strongest detected tap aggregating the subset or all of the plurality of CSI-RS ports based on the CSI report configuration.
The method of claims 1 or 2, further comprising:

receiving a CSI request triggering the CSI report; and

transmitting the CSI report indicating the CSI measurement that is associated with the strongest detected tap aggregating the subset or all of the plurality of CSI-RS ports based on the triggering.
The method of any one of claims 1 to 3, wherein transmitting the CSI report comprises:

transmitting, to the base station, the CSI report that indicates a channel on which the plurality of CSI-RS ports is conveyed, the channel based at least in part on measurements measured using the strongest detected tap across a subset of ports of the plurality of CSI-RS ports or across all ports of the plurality of CSI-RS ports.
The method of claim 4, further comprising:

determining that the channel is a linear combination of the subset of ports associated with the strongest detected tap; and

transmitting in the CSI report an indication of the subset of ports based at least on part on a measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.
The method of claim 4, further comprising:

determining that the channel is a linear combination of all of the plurality of CSI-RS ports associated with the strongest detected tap; and

transmitting in the CSI report an indication of linear combination coefficients.
The method of any one of claims 5 or 6, further comprising:

transmitting, to the base station, an indication of a number of antennas used for receiving a signal on a reference signal resource corresponding to the plurality of CSI-RS ports; and

transmitting in the CSI report a channel measurement from the strongest detected tap of each receive antenna of the number of antennas.
The method of claim 7, further comprising:

transmitting, to the base station, an indication of a location of the strongest detected tap or an indication of a location of the strongest detected tap for each receive antenna of the number of antennas.
The method of any one of claims 1 to 3, wherein transmitting the CSI report comprises:

transmitting, to the base station, a precoding matrix indicator based at least in part on the CSI measurement measured using the strongest detected tap across a subset of ports of the plurality of CSI-RS ports or across all ports of the plurality of CSI-RS ports.
The method of claim 9, wherein the precoding matrix indicator comprises a linear combination of the subset of ports of the plurality of CSI-RS ports associated with the strongest detected tap, the method further comprising:

transmitting in the CSI report an indication of the subset of ports based at least in part on measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.
The method of claim 9, wherein the precoding matrix indicator comprises a linear combination of all of the plurality of CSI-RS ports associated with the strongest detected tap, the method further comprising:

transmitting in the CSI report an indication of linear combination coefficients.
The method of any one of claims 9 to 11, further comprising:

transmitting, to the base station, a rank indicator indicating a number of layers used to receive a signal on a reference signal resource corresponding to the plurality of CSI-RS ports; and

transmitting in the CSI report the precoding matrix indicator as a linear combination of the subset of ports for each layer.
The method of any one of claims 9 to 12, further comprising:

transmitting, to the base station, a channel quality indicator based at least in part on the precoding matrix indicator, a rank indicator, or a combination thereof.
The method of any one of claims 1 to 3, wherein transmitting the CSI report comprises:

transmitting, to the base station, a port selection indication that indicates a subset of ports of the plurality of CSI-RS ports based at least in part on a measurement measured using the strongest detected tap across the subset of ports of the plurality of CSI-RS ports or all ports of the plurality of CSI-RS ports.
The method of claim 14, further comprising:

selecting the subset of ports from the plurality of CSI-RS ports based at least in part on an energy level measurement of a reference signal resource at the strongest detected tap using the subset of ports.
The method of any one of claims 1 to 3, further comprising:

receiving, from the base station, multiple reference signal resources, each reference signal resource of the multiple reference signal resources comprising a single CSI-RS port.
The method of claim 16, further comprising:

selecting a subset of ports of the plurality of CSI-RS ports or resources across the multiple reference signal resources; and

transmitting, to the base station, an indication of the subset of ports or resources via a CSI-RS indicator.
The method of claim 17, wherein the CSI-RS indicator comprises a bitmap with a length corresponding to a number of ports in the plurality of CSI-RS ports, an indicator based at least in part on the number of ports in the plurality of CSI-RS ports and a second number of ports in the subset of ports, or a combination thereof.
A method for wireless communications at a base station, comprising:

transmitting, to a user equipment (UE) , a plurality of CSI-RS ports; and

receiving, from the UE, a channel state information (CSI) report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the plurality of CSI-RS ports.
The method of claim 19, further comprising:

transmitting a CSI report configuration, wherein the CSI report is based on the CSI report configuration.
The method of any one of claims 19 or 20, further comprising:

transmitting a CSI request triggering the CSI report; and

receiving the CSI report indicating the CSI measurement that is associated with the strongest detected tap aggregating the subset or all of the plurality of CSI-RS ports based on the triggering.
The method of any one of claims 19 to 21, wherein receiving the CSI report comprises:

receiving the CSI report that indicates a channel on which the plurality of CSI-RS ports is conveyed, the channel based at least in part on measurements measured using the strongest detected tap across a subset of ports of the plurality of CSI-RS ports or across all ports of the plurality of CSI-RS ports.
The method of claim 22, wherein receiving the CSI report comprises:

receiving the CSI report that reports an indication of the subset of ports based at least on part on a measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.
The method of claim 22, wherein receiving the CSI report comprises:

receiving the CSI report that reports an indication of linear combination coefficients.
The method of any one of claims 23 or 24, further comprising:

receiving an indication of a number of antennas used for receiving a signal on a reference signal resource corresponding to the plurality of CSI-RS ports; and

receiving the CSI report that reports a channel measurement from the strongest detected tap of each receive antenna of the number of antennas.
The method of claim 25, further comprising:

receiving an indication of a location of the strongest detected tap or an indication of a location of the strongest detected tap for each receive antenna of the number of antennas.
The method of any one of claims 19 to 21, wherein receiving the CSI report comprises:

receiving a precoding matrix indicator based at least in part on the CSI measurement measured using the strongest detected tap across a subset of ports of the plurality of CSI-RS ports or across all ports of the plurality of CSI-RS ports.
The method of claim 27, wherein the precoding matrix indicator comprises a linear combination of the subset of ports associated with the strongest detected tap, the method further comprising:

receiving the CSI report that reports an indication of the subset of ports based at least in part on measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.
The method of claim 27, wherein the precoding matrix indicator comprises a linear combination of all of the plurality of CSI-RS ports associated with the strongest detected tap, the method further comprising:

receiving an indication of linear combination coefficients.
The method of any one of claims 27 to 29, further comprising:

receiving a rank indicator indicating a number of layers used to receive a signal on a reference signal resource corresponding to the plurality of CSI-RS ports; and

receiving the CSI report that reports the precoding matrix indicator as a linear combination of the subset of ports for each layer.
The method of any one of claims 27 to 30, further comprising:

receiving a channel quality indicator based at least in part on the precoding matrix indicator, a rank indicator, or a combination thereof.
The method of any one of claims 19 to 21, wherein receiving the CSI report comprises:

receiving a port selection indication that indicates a subset of ports of the plurality of CSI-RS ports based at least in part on a measurement measured using the strongest detected tap across the subset of ports of the plurality of CSI-RS ports or all ports of the plurality of CSI-RS ports.
The method of any one of claims 19 to 21, further comprising:

transmitting multiple reference signal resources, each reference signal resource of the multiple reference signal resources comprising a single CSI-RS port.
The method of claim 33, further comprising:

receiving, from the UE, a CSI-RS indicator indicating a subset of ports or resources across the multiple reference signal resources.
The method of claim 34, wherein the CSI-RS indicator comprises a bitmap with a length corresponding to a number of ports in the plurality of CSI-RS ports, an indicator based at least in part on the number of ports in the plurality of CSI-RS ports and a second number of ports in the subset of ports, or a combination thereof.
An apparatus for wireless communications 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, a plurality of CSI-RS ports;

perform a channel state information (CSI) measurement based at least in part on the plurality of CSI-RS ports;

generate a CSI based at least in part on the CSI measurement, wherein the CSI is associated with a strongest detected tap aggregating a subset or all of the plurality of CSI-RS ports; and

transmit, to the base station, a CSI report based at least in part on the CSI.
The apparatus of claim 36, wherein the instructions are further executable by the processor to cause the apparatus to:

receive a CSI report configuration; and

determine CSI reporting associated with the strongest detected tap aggregating the subset or all of the plurality of CSI-RS ports based on the CSI report configuration.
The apparatus of any one of claims 36 or 37, wherein the instructions are further executable by the processor to cause the apparatus to:

receive a CSI request triggering the CSI report; and

transmit the CSI report indicating the CSI measurement that is associated with the strongest detected tap aggregating the subset or all of the plurality of CSI-RS ports based on the triggering.
The apparatus of any one of claims 36 to 38, wherein the instructions to transmit the CSI report are executable by the processor to cause the apparatus to:

transmit, to the base station, the CSI report that indicates a channel on which the plurality of CSI-RS ports is conveyed, the channel based at least in part on measurements measured using the strongest detected tap across a subset of ports of the plurality of CSI-RS ports or across all ports of the plurality of CSI-RS ports.
The apparatus of claim 39, wherein the instructions are further executable by the processor to cause the apparatus to:

determine that the channel is a linear combination of the subset of ports associated with the strongest detected tap; and

transmit in the CSI report an indication of the subset of ports based at least on part on a measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.
The apparatus of claim 39, wherein the instructions are further executable by the processor to cause the apparatus to:

determine that the channel is a linear combination of all of the plurality of CSI-RS ports associated with the strongest detected tap; and

transmit in the CSI report an indication of linear combination coefficients.
The apparatus of any one of claims 40 or 41, wherein the instructions are further executable by the processor to cause the apparatus to:

transmit, to the base station, an indication of a number of antennas used for receiving a signal on a reference signal resource corresponding to the plurality of CSI-RS ports; and

transmit in the CSI report a channel measurement from the strongest detected tap of each receive antenna of the number of antennas.
The apparatus of claim 42, wherein the instructions are further executable by the processor to cause the apparatus to:

transmit, to the base station, an indication of a location of the strongest detected tap or an indication of a location of the strongest detected tap for each receive antenna of the number of antennas.
The apparatus of any one of claims 36 to 38, wherein the instructions to transmit the CSI report are executable by the processor to cause the apparatus to:

transmit, to the base station, a precoding matrix indicator based at least in part on the CSI measurement measured using the strongest detected tap across a subset of ports of the plurality of CSI-RS ports or across all ports of the plurality of CSI-RS ports.
The apparatus of claim 44, wherein the precoding matrix indicator comprises a linear combination of the subset of ports of the plurality of CSI-RS ports associated with the strongest detected tap, and the instructions are further executable by the processor to cause the apparatus to:

transmit in the CSI report an indication of the subset of ports based at least in part on measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.
The apparatus of claim 44, wherein the precoding matrix indicator comprises a linear combination of all of the plurality of CSI-RS ports associated with the strongest detected tap, and the instructions are further executable by the processor to cause the apparatus to:

transmit in the CSI report an indication of linear combination coefficients.
The apparatus of any one of claims 44 to 46, wherein the instructions are further executable by the processor to cause the apparatus to:

transmit, to the base station, a rank indicator indicating a number of layers used to receive a signal on a reference signal resource corresponding to the plurality of CSI-RS ports; and

transmit in the CSI report the precoding matrix indicator as a linear combination of the subset of ports for each layer.
The apparatus of any one of claims 44 to 46, wherein the instructions are further executable by the processor to cause the apparatus to:

transmit, to the base station, a channel quality indicator based at least in part on the precoding matrix indicator, a rank indicator, or a combination thereof.
The apparatus of any one of claims 36 to 38, wherein the instructions to transmit the CSI report are executable by the processor to cause the apparatus to:

transmit, to the base station, a port selection indication that indicates a subset of ports of the plurality of CSI-RS ports based at least in part on a measurement measured using the strongest detected tap across the subset of ports of the plurality of CSI-RS ports or all ports of the plurality of CSI-RS ports.
The apparatus of claim 49, wherein the instructions are further executable by the processor to cause the apparatus to:

select the subset of ports from the plurality of CSI-RS ports based at least in part on an energy level measurement of a reference signal resource at the strongest detected tap using the subset of ports.
The apparatus of any one of claims 36 to 38, wherein the instructions are further executable by the processor to cause the apparatus to:

receive, from the base station, multiple reference signal resources, each reference signal resource of the multiple reference signal resources comprising a single CSI-RS port.
The apparatus of claim 51, wherein the instructions are further executable by the processor to cause the apparatus to:

select a subset of ports of the plurality of CSI-RS ports or resources across the multiple reference signal resources; and

transmit, to the base station, an indication of the subset of ports or resources via a CSI-RS indicator.
The apparatus of claim 52, wherein the CSI-RS indicator comprises a bitmap with a length corresponding to a number of ports in the plurality of CSI-RS ports, an indicator based at least in part on the number of ports in the plurality of CSI-RS ports and a second number of ports in the subset of ports, or a combination thereof.
An apparatus for wireless communications 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) , a plurality of CSI-RS ports; and

receive, from the UE, a channel state information (CSI) report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the plurality of CSI-RS ports.
The apparatus of claim 54, wherein the instructions are further executable by the processor to cause the apparatus to:

transmit a CSI report configuration, wherein the CSI report is based on the CSI report configuration.
The apparatus of any one of claims 54 or 55, wherein the instructions are further executable by the processor to cause the apparatus to:

transmit a CSI request triggering the CSI report; and

receive the CSI report indicating the CSI measurement that is associated with the strongest detected tap aggregating the subset or all of the plurality of CSI-RS ports based on the triggering.
The apparatus of any one of claims 54 to 56, wherein the instructions to receive the CSI report are executable by the processor to cause the apparatus to:

receive the CSI report that indicates a channel on which the plurality of CSI-RS ports is conveyed, the channel based at least in part on measurements measured using the strongest detected tap across a subset of ports of the plurality of CSI-RS ports or across all ports of the plurality of CSI-RS ports.
The apparatus of claim 57, wherein the instructions to receive the CSI report are executable by the processor to cause the apparatus to:

receive the CSI report that reports an indication of the subset of ports based at least on part on a measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.
The apparatus of claim 57, wherein the instructions to receive the CSI report are executable by the processor to cause the apparatus to:

receive the CSI report that reports an indication of linear combination coefficients.
The apparatus of any one of claims 58 or 59, wherein the instructions are further executable by the processor to cause the apparatus to:

receive an indication of a number of antennas used for receiving a signal on a reference signal resource corresponding to the plurality of CSI-RS ports; and

receive the CSI report that reports a channel measurement from the strongest detected tap of each receive antenna of the number of antennas.
The apparatus of claim 60, wherein the instructions are further executable by the processor to cause the apparatus to:

receive an indication of a location of the strongest detected tap or an indication of a location of the strongest detected tap for each receive antenna of the number of antennas.
The apparatus of any one of claims 54 to 56, wherein the instructions to receive the CSI report are executable by the processor to cause the apparatus to:

receive a precoding matrix indicator based at least in part on the CSI measurement measured using the strongest detected tap across a subset of ports of the plurality of CSI-RS ports or across all ports of the plurality of CSI-RS ports.
The apparatus of claim 62, wherein the precoding matrix indicator comprises a linear combination of the subset of ports associated with the strongest detected tap, and the instructions are further executable by the processor to cause the apparatus to:

receive the CSI report that reports an indication of the subset of ports based at least in part on measurement on the strongest detected tap using the subset of ports, and an indication of linear combination coefficients.
The apparatus of claim 62, wherein the precoding matrix indicator comprises a linear combination of all of the plurality of CSI-RS ports associated with the strongest detected tap, and the instructions are further executable by the processor to cause the apparatus to:

receive an indication of linear combination coefficients.
The apparatus of any one of claims 62 to 64, wherein the instructions are further executable by the processor to cause the apparatus to:

receive a rank indicator indicating a number of layers used to receive a signal on a reference signal resource corresponding to the plurality of CSI-RS ports; and

receive the CSI report that reports the precoding matrix indicator as a linear combination of the subset of ports for each layer.
The apparatus of any one of claims 62 to 65, wherein the instructions are further executable by the processor to cause the apparatus to:

receive a channel quality indicator based at least in part on the precoding matrix indicator, a rank indicator, or a combination thereof.
The apparatus of any one of claims 54 to 56, wherein the instructions to receive the CSI report are executable by the processor to cause the apparatus to:

receive a port selection indication that indicates a subset of ports of the plurality of CSI-RS ports based at least in part on a measurement measured using the strongest detected tap across the subset of ports of the plurality of CSI-RS ports or all ports of the plurality of CSI-RS ports.
The apparatus of any one of claims 54 to 56, wherein the instructions are further executable by the processor to cause the apparatus to:

transmit multiple reference signal resources, each reference signal resource of the multiple reference signal resources comprising a single CSI-RS port.
The apparatus of claim 68, wherein the instructions are further executable by the processor to cause the apparatus to:

receive, from the UE, a CSI-RS indicator indicating a subset of ports or resources across the multiple reference signal resources.
The apparatus of claim 69, wherein the CSI-RS indicator comprises a bitmap with a length corresponding to a number of ports in the plurality of CSI-RS ports, an indicator based at least in part on the number of ports in the plurality of CSI-RS ports and a second number of ports in the subset of ports, or a combination thereof.
An apparatus for wireless communications at a user equipment (UE) , comprising:

means for receiving, from a base station, a plurality of CSI-RS ports;

means for performing a channel state information (CSI) measurement based at least in part on the plurality of CSI-RS ports;

means for generating a CSI based at least in part on the CSI measurement, wherein the CSI is associated with a strongest detected tap aggregating a subset or all of the plurality of CSI-RS ports; and

means for transmitting, to the base station, a CSI report based at least in part on the CSI.
An apparatus for wireless communications at a base station, comprising:

means for transmitting, to a user equipment (UE) , a plurality of CSI-RS ports; and

means for receiving, from the UE, a channel state information (CSI) report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the plurality of CSI-RS ports.
A non-transitory computer-readable medium storing code for wireless communications at a user equipment (UE) , the code comprising instructions executable by a processor to:

receive, from a base station, a plurality of CSI-RS ports;

perform a channel state information (CSI) measurement based at least in part on the plurality of CSI-RS ports;

generate a CSI based at least in part on the CSI measurement, wherein the CSI is associated with a strongest detected tap aggregating a subset or all of the plurality of CSI-RS ports; and

transmit, to the base station, a CSI report based at least in part on the CSI.
A non-transitory computer-readable medium storing code for wireless communications at a base station, the code comprising instructions executable by a processor to:

transmit, to a user equipment (UE) , a plurality of CSI-RS ports; and

receive, from the UE, a channel state information (CSI) report indicating a CSI measurement associated with a strongest detected tap aggregating a subset or all of the plurality of CSI-RS ports.