WO2021087844A1

WO2021087844A1 - Compressed csi feedback without full csi-rs presence

Info

Publication number: WO2021087844A1
Application number: PCT/CN2019/116177
Authority: WO
Inventors: Chenxi HAO; Yu Zhang; Hao Xu
Original assignee: Qualcomm Incorporated
Priority date: 2019-11-07
Filing date: 2019-11-07
Publication date: 2021-05-14

Abstract

Certain aspects of the present disclosure provide techniques for compressed channel state information (CSI) feedback for subbands with partial CSI reference signal (RS) presence. A method that may be performed by a user equipment (UE) includes receiving a configuration to report CSI feedback for one or more subbands. The CSI feedback including at least precoding matrix indicator (PMI) feedback and channel quality indicator (CQI) feedback. The configuration indicates a first subband size for the CQI feedback and an indication of PMI granularity. The method includes determining a second subband size for PMI feedback based on the first subband size and the PMI granularity and determining a density of CSI-RS present in a CQI or PMI subband. The method includes dropping or reporting at least the CSI feedback for the CQI or PMI subband based on the determined density.

Description

COMPRESSED CSI FEEDBACK WITHOUT FULL CSI-RS PRESENCE

BACKGROUND

Field of the Disclosure

Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for compressed channel state information (CSI) without full channel state information reference signal (CSI-RS) presence.

Description of Related Art

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, broadcasts, etc. These wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc. ) . Examples of such multiple-access systems include 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, LTE Advanced (LTE-A) systems, code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems, to name a few.

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. New radio (e.g., 5G NR) is an example of an emerging telecommunication standard. NR is a set of enhancements to the LTE mobile standard promulgated by 3GPP. NR is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDMA with a cyclic prefix (CP) on the downlink (DL) and on the uplink (UL) . To these ends, NR supports beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation.

However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in NR and LTE technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

SUMMARY

The systems, methods, and devices of the disclosure each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this disclosure as expressed by the claims which follow, some features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description” one will understand how the features of this disclosure provide advantages that include improved compressed channel state information (CSI) feedback without full CSI reference signal (CSI-RS) presence.

One innovative aspect of the subject matter described in this disclosure can be implemented in a method for wireless communication by a user equipment (UE) . The method generally includes receiving a configuration to report CSI feedback for one or more subbands. The CSI feedback including at least precoding matrix indicator (PMI) feedback and channel quality indicator (CQI) feedback. The configuration indicates a first subband size for the CQI feedback and an indication of PMI granularity. The method generally includes determining a second subband size for PMI feedback based on the first subband size and the PMI granularity. The method generally includes determining a density of CSI-RS present in a CQI or PMI subband. The method generally includes dropping or reporting at least the CSI feedback for the CQI or PMI subband based on the determined density.

One innovative aspect of the subject matter described in this disclosure can be implemented in a method for wireless communication by a base station (BS) . The method generally includes configuring a UE to report CSI feedback for one or more subbands. The CSI feedback includes at least PMI feedback and CQI feedback. The configuration indicates a first subband size for the CQI feedback and indicates a PMI granularity. The method generally includes determining a second subband size for PMI feedback based on the first subband size and the PMI granularity. The method generally includes transmitting CSI-RS to the UE in at least a portion of a CQI or PMI subband. The method generally includes receiving CSI feedback for the CQI or PMI subband based on the configuration and the at least a portion.

Aspects of the present disclosure provide means for, apparatus, processors, and computer-readable mediums for performing the methods described herein.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the appended drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects.

FIG. 1 is a block diagram conceptually illustrating an example telecommunications system, in accordance with certain aspects of the present disclosure.

FIG. 2 is a block diagram conceptually illustrating a design of an example a base station (BS) and user equipment (UE) , in accordance with certain aspects of the present disclosure.

FIG. 3 illustrates an example of a frame format for a new radio (NR) system, in accordance with certain aspects of the present disclosure.

FIG. 4A is an example of subbands configured for precoding matrix indicator (PMI) feedback smaller than a subband configured for channel quality indicator (CQI) feedback, in accordance with certain aspects of the disclosure.

FIG. 4B is an example of CSI reference signal (CSI-RS) presence for one full PMI subband of FIG. 4A, in accordance with certain aspects of the disclosure.

FIG. 4C is an example of CQI and PMI for the subbands in FIG. 4B, in accordance with aspects of the present disclosure.

FIG. 4D is an example of CSI-RS presence for no full PMI subbands of FIG. 4A, in accordance with certain aspects of the disclosure.

FIG. 4E is an example of CQI and PMI for the subbands in FIG. 4D, in accordance with aspects of the present disclosure.

FIG. 5A is an example of subbands configured for PMI feedback for a subband smaller than a subband configured for CQI feedback, but larger than half the CQI subband size, in accordance with certain aspects of the disclosure.

FIG. 5B is an example of CSI-RS presence for one full PMI subband of FIG. 5A, in accordance with certain aspects of the disclosure.

FIG. 5C is an example of CQI and PMI for the subbands in FIG. 5B, in accordance with aspects of the present disclosure.

FIG. 5D is an example of CSI-RS presence for no full PMI subbands of FIG. 5A, in accordance with certain aspects of the disclosure.

FIG. 5E is an example of CQI and PMI for the subbands in FIG. 5D, in accordance with aspects of the present disclosure.

FIG. 6A is an example of subbands configured for PMI feedback for a subband smaller than half a subband size configured for CQI feedback, in accordance with certain aspects of the disclosure.

FIG. 6B is an example of CSI-RS presence for one full PMI subband of FIG. 6A, in accordance with certain aspects of the disclosure.

FIG. 6C is an example of CQI and PMI for the subbands in FIG. 6B, in accordance with aspects of the present disclosure.

FIG. 6D is an example of CSI-RS presence for no full PMI subbands of FIG. 6A, in accordance with certain aspects of the disclosure.

FIG. 6E is an example of CQI and PMI for the subbands in FIG. 6D, in accordance with aspects of the present disclosure.

FIG. 7 is a flow diagram illustrating example operations for wireless communication by a UE, in accordance with certain aspects of the present disclosure.

FIG. 8 is a flow diagram illustrating example operations for wireless communication by a BS, in accordance with certain aspects of the present disclosure.

FIG. 9 illustrates a communications device that may include various components configured to perform operations for the techniques disclosed herein in accordance with aspects of the present disclosure.

FIG. 10 illustrates a communications device that may include various components configured to perform operations for the techniques disclosed herein in accordance with aspects of the present disclosure.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one aspect may be beneficially utilized on other aspects without specific recitation.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatus, methods, processing systems, and computer readable mediums for compressed channel state information (CSI) feedback without full CSI reference signal (CSI-RS) presence.

In some cases, a user equipment (UE) may be configured with a subband granularity for precoder matrix indicator (PMI) feedback for a subband that is smaller than a subband size configured for channel quality indicator (CQI) feedback. Therefore, in some cases, some PMI subbands may still have a full CSI-RS presence even when the CQI subband size does not have full CSI-RS presence.

Aspects of the disclosure provide for PMI and CQI reporting that may be used for compressed CSI feedback for different actual and configured subband sizes and in various scenarios when there is not full CSI-RS presence in the configured CQI subband.

The following description provides examples of compressed CSI feedback without full CSI-RS presence in communication systems, and is not limiting of the scope, applicability, or examples set forth in the claims. Changes may be made in the function and arrangement of elements discussed without departing from the scope of the disclosure. Various examples may omit, substitute, or add various procedures or components as appropriate. For instance, the methods described may be performed in an order different from that described, and various steps may be added, omitted, or combined. Also, features described with respect to some examples may be combined in some other examples. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to, or other than, the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration. ” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects.

In general, any number of wireless networks may be deployed in a given geographic area. Each wireless network may support a particular radio access technology (RAT) and may operate on one or more frequencies. A RAT may also be referred to as a radio technology, an air interface, etc. A frequency may also be referred to as a carrier, a subcarrier, a frequency channel, a tone, a subband, etc. Each frequency may support a single RAT in a given geographic area in order to avoid interference between wireless networks of different RATs.

The techniques described herein may be used for various wireless networks and radio technologies. While aspects may be described herein using terminology commonly associated with 3G, 4G, and/or new radio (e.g., 5G NR) wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems.

NR access may support various wireless communication services, such as enhanced mobile broadband (eMBB) targeting wide bandwidth (e.g., 80 MHz or beyond) , millimeter wave (mmW) targeting high carrier frequency (e.g., 25 GHz or beyond) , massive machine type communications MTC (mMTC) targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra-reliable low-latency communications (URLLC) . These services may include latency and reliability requirements. These services may also have different transmission time intervals (TTI) to meet respective quality of service (QoS) requirements. In addition, these services may co-exist in the same subframe. NR supports beamforming and beam direction may be dynamically configured. MIMO transmissions with precoding may also be supported. MIMO configurations in the DL may support up to 8 transmit antennas with multi-layer DL transmissions up to 8 streams and up to 2 streams per UE. Multi-layer transmissions with up to 2 streams per UE may be supported. Aggregation of multiple cells may be supported with up to 8 serving cells.

FIG. 1 illustrates an example wireless communication network 100 in which aspects of the present disclosure may be performed. For example, the wireless communication network 100 may be an NR system (e.g., a 5G NR network) . As shown in FIG. 1, the wireless communication network 100 may be in communication with a core network 132. The core network 132 may in communication with one or more base station (BSs) 110 and/or user equipment (UE) 120 in the wireless communication network 100 via one or more interfaces.

As illustrated in FIG. 1, the wireless communication network 100 may include a number of BSs 110a-z (each also individually referred to herein as BS 110 or collectively as BSs 110) and other network entities. A BS 110 may provide communication coverage for a particular geographic area, sometimes referred to as a “cell” , which may be stationary or may move according to the location of a mobile BS 110. In some examples, the BSs 110 may be interconnected to one another and/or to one or more other BSs or network nodes (not shown) in wireless communication network 100 through various types of backhaul interfaces (e.g., a direct physical connection, a wireless connection, a virtual network, or the like) using any suitable transport network. In the example shown in FIG. 1, the

BSs

110a, 110b and 110c may be macro BSs for the

macro cells

102a, 102b and 102c, respectively. The BS 110x may be a pico BS for a pico cell 102x. The BSs 110y and 110z may be femto BSs for the

femto cells

102y and 102z, respectively. A BS may support one or multiple cells. A network controller 130 may couple to a set of BSs 110 and provide coordination and control for these BSs 110. The network controller 130 may communicate with the BSs 110 via a backhaul.

The BSs 110 communicate with UEs 120a-y (each also individually referred to herein as UE 120 or collectively as UEs 120) in the wireless communication network 100. The UEs 120 (e.g., 120x, 120y, etc. ) may be dispersed throughout the wireless communication network 100, and each UE 120 may be stationary or mobile. Wireless communication network 100 may also include relay stations (e.g., relay station 110r) , also referred to as relays or the like, that receive a transmission of data and/or other information from an upstream station (e.g., a BS 110a or a UE 120r) and sends a transmission of the data and/or other information to a downstream station (e.g., a UE 120 or a BS 110) , or that relays transmissions between UEs 120, to facilitate communication between devices.

According to certain aspects, the BSs 110 and UEs 120 may be configured for compressed CSI feedback. As shown in FIG. 1, the BS 110a includes a CSI manager 112. The CSI manager 112 may be configured for CSI feedback without full CSI-RS presence, in accordance with aspects of the present disclosure. As shown in FIG. 1, the UE 120a includes a CSI manager 122. The CSI manager 122 may be configured for CSI feedback without full CSI-RS presence, in accordance with aspects of the present disclosure.

FIG. 2 illustrates example components of BS 110a and UE 120a (e.g., in the wireless communication network 100 of FIG. 1) , which may be used to implement aspects of the present disclosure.

At the BS 110a, a transmit processor 220 may receive data from a data source 212 and control information from a controller/processor 240. The control information may be for the physical broadcast channel (PBCH) , physical control format indicator channel (PCFICH) , physical hybrid ARQ indicator channel (PHICH) , physical downlink control channel (PDCCH) , group common PDCCH (GC PDCCH) , etc. The data may be for the physical downlink shared channel (PDSCH) , etc. A medium access control (MAC) -control element (MAC-CE) is a MAC layer communication structure that may be used for control command exchange between wireless nodes. For example, the BS 110a may transmit a MAC-CE to a UE 120a to put the UE 120a into a discontinuous reception (DRX) mode to reduce the UE’s power consumption. The MAC-CE may be carried in a shared channel such as a physical downlink shared channel (PDSCH) , a physical uplink shared channel (PUSCH) , or a physical sidelink shared channel (PSSCH) . A MAC-CE may also be used to communicate information that facilitates communication, such as information regarding buffer status and available power headroom.

The processor 220 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor 220 may also generate reference symbols, such as for the primary synchronization signal (PSS) , secondary synchronization signal (SSS) , and channel state information reference signal (CSI-RS) . A transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) 232a-232t. Each modulator 232 may process a respective output symbol stream (e.g., for OFDM, etc. ) to obtain an output sample stream. Each modulator may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from modulators 232a-232t may be transmitted via the antennas 234a-234t, respectively.

At the UE 120a, the antennas 252a-252r may receive the downlink signals from the BS 110a and may provide received signals to the demodulators (DEMODs) in transceivers 254a-254r, respectively. Each demodulator 254 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator may further process the input samples (e.g., for OFDM, etc. ) to obtain received symbols. A MIMO detector 256 may obtain received symbols from all the demodulators 254a-254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor 258 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE 120a to a data sink 260, and provide decoded control information to a controller/processor 280.

On the uplink, at UE 120a, a transmit processor 264 may receive and process data (e.g., for the physical uplink shared channel (PUSCH) ) from a data source 262 and control information (e.g., for the physical uplink control channel (PUCCH) from the controller/processor 280. The transmit processor 264 may also generate reference symbols for a reference signal (e.g., for the sounding reference signal (SRS) ) . The symbols from the transmit processor 264 may be precoded by a TX MIMO processor 266 if applicable, further processed by the modulators in transceivers 254a-254r (e.g., for SC-FDM, etc. ) , and transmitted to the BS 110a. At the BS 110a, the uplink signals from the UE 120a may be received by the antennas 234, processed by the modulators 232, detected by a MIMO detector 236 if applicable, and further processed by a receive processor 238 to obtain decoded data and control information sent by the UE 120a. The receive processor 238 may provide the decoded data to a data sink 239 and the decoded control information to the controller/processor 240.

The

memories

242 and 282 may store data and program codes for BS 110a and UE 120a, respectively. A scheduler 244 may schedule UEs for data transmission on the downlink and/or uplink.

The controller/processor 280 and/or other processors and modules at the UE 120a may perform or direct the execution of processes for the techniques described herein. For example, as shown in FIG. 2, the controller/processor 240 of the BS 110a has a CSI manager 241 that may be configured for compressed CSI reporting without full CSI-RS presence, according to aspects described herein. As shown in FIG. 2, the controller/processor 280 of the UE 120a has a CSI manager 241 that may be configured for compressed CSI reporting without full CSI-RS presence, according to aspects described herein. Although shown at the controller/processor, other components of the UE 120a and BS 110a may be used to perform the operations described herein.

NR may utilize orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP) on the uplink and/or downlink and/or single-carrier frequency division multiplexing (SC-FDM) on the uplink. NR may use half-duplex operation with time division duplexing (TDD) . OFDM and SC-FDM partition the system bandwidth into multiple orthogonal subcarriers, referred to as tones, bins, etc. Each subcarrier may be modulated with data. Modulation symbols may be sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers) may be dependent on the system bandwidth. NR may support a base subcarrier spacing (SCS) of 15 KHz and other SCS may be defined with respect to the base SCS, for example, 30 kHz, 60 kHz, 120 kHz, 240 kHz, etc. In NR, the minimum resource allocation (a “resource block” (RB) ) may be 12 consecutive subcarriers. The system bandwidth may also be partitioned into subbands. For example, a subband may cover multiple RBs.

In NR, a subframe is 1 ms, but the basic TTI is referred to as a slot. A subframe contains a variable number of slots (e.g., 1, 2, 4, 8, 16, …slots) depending on the subcarrier spacing. The symbol, slot lengths, and CP scale with the SCS. FIG. 3 is a diagram showing an example of a frame format 600 for NR. As shown in FIG. 3, the transmission timeline for each of the downlink and uplink are partitioned into units of radio frames. Each radio frame has a predetermined duration (e.g., 10 ms) and is partitioned into 10 subframes, each of 1 ms, with indices of 0 through 9. Each subframe includes a variable number of slots depending on the SCS, and each slot includes a variable number of symbol periods (e.g., 7 or 14 symbols) depending on the SCS. The symbol periods in each slot are assigned indices. A mini-slot, which may be referred to as a sub-slot structure, refers to a transmit time interval having a duration less than a slot (e.g., 2, 3, or 4 symbols) . Each symbol in a slot may indicate a link direction (e.g., DL, UL, or flexible) for data transmission and the link direction for each subframe may be dynamically switched. The link directions may be based on the slot format. Each slot may include DL/UL data as well as DL/UL control information.

As discussed above, aspects of the disclosure relate to channel state feedback with analog feedforward. Channel state feedback may include channel state information (CSI) feedback.

Example CSI Feedback Configuration

CSI may refer to channel properties of a communication link. The CSI may represent the combined effects of, for example, scattering, fading, and power decay with distance between a transmitter and receiver. Channel estimation using pilots, such as CSI reference signals (CSI-RS) , may be performed to determine these effects on the channel. CSI may be used to adapt transmissions based on the current channel conditions, which is useful for achieving reliable communication, in particular, with high data rates in multi-antenna systems. CSI is typically estimated at the receiver, quantized, and fed back to the transmitter.

A UE (e.g., such as a UE 120a) may be configured by a BS (e.g., such as a BS 110) for CSI reporting. The BS may configure the UE with a CSI reporting configuration or with multiple CSI report configurations. The BS may provide the CSI reporting configuration to the UE via higher layer signaling, such as radio resource control (RRC) signaling (e.g., via a CSI-ReportConfig information element (IE) ) .

Each CSI report configuration may be associated with a single downlink bandwidth part (BWP) . The CSI report setting configuration may define a CSI reporting band as a subset of subbands of the BWP. The associated DL BWP may indicated by a higher layer parameter (e.g., bwp-Id) in the CSI report configuration for channel measurement and contains parameter (s) for one CSI reporting band, such as codebook configuration, time-domain behavior, frequency granularity for CSI, measurement restriction configurations, and the CSI-related quantities to be reported by the UE. Each CSI resource setting may be located in the DL BWP identified by the higher layer parameter, and all CSI resource settings may be linked to a CSI report setting have the same DL BWP.

The CSI report configuration may configure the time and frequency resources used by the UE to report CSI. For example, the CSI report configuration may be associated with CSI-RS resources for channel measurement (CM) , interference measurement (IM) , or both. The CSI report configuration may configure CSI-RS resources for measurement (e.g., via a CSI-ResourceConfig IE) . The CSI-RS resources provide the UE with the configuration of CSI-RS ports, or CSI-RS port groups, mapped to time and frequency resources (e.g., resource elements (REs) ) . CSI-RS resources can be zero power (ZP) or non-zero power (NZP) resources. At least one NZP CSI-RS resource may be configured for CM. For interference measurement, it can be NZP CSI-RS or zero power CSI-RS, which is known as CSI-IM (note, if NZP CSI-RS, it is called NZP CSI-RS for interference measurement, if zero power, it is called CSI-IM)

The CSI report configuration may configure the UE for aperiodic, periodic, or semi-persistent CSI reporting. For periodic CSI, the UE may be configured with periodic CSI-RS resources. Periodic CSI and semi-persistent CSI report on physical uplink control channel (PUCCH) may be triggered via RRC or a medium access control (MAC) control element (CE) . For aperiodic and semi-persistent CSI on the physical uplink shared channel (PUSCH) , the BS may signal the UE a CSI report trigger indicating for the UE to send a CSI report for one or more CSI-RS resources, or configuring the CSI-RS report trigger state (e.g., CSI-AperiodicTriggerStateList and CSI-SemiPersistentOnPUSCH-TriggerStateList) . The CSI report trigger for aperiodic CSI and semi-persistent CSI on PUSCH may be provided via downlink control information (DCI) . The CSI-RS trigger may be signaling indicating to the UE that CSI-RS will be transmitted for the CSI-RS resource. The UE may report the CSI feedback based on the CSI report configuration and the CSI report trigger. For example, the UE may measure the channel associated with CSI for the triggered CSI-RS resources. Based on the measurements, the UE may select a preferred CSI-RS resource. The UE reports the CSI feedback for the selected CSI-RS resource.

The CSI report configuration can also configure the CSI parameters (sometimes referred to as quantities) to be reported. Codebooks may include Type I single panel, Type I multi-panel, and Type II single panel. Regardless which codebook is used, the CSI report may include at least the channel quality indicator (CQI) , precoding matrix indicator (PMI) , CSI-RS resource indicator (CRI) , and rank indicator (RI) . The structure of the PMI may vary based on the codebook. The CRI, RI, and CQI may be in a first part (Part I) and the PMI may be in a second part (Part II) of the CSI report.

For the Type I single panel codebook, the PMI may include a W1 matrix (e.g., subest of beams) and a W2 matrix (e.g., phase for cross polarization combination and beam selection) . For the Type I multi-panel codebook, compared to type I single panel codebook, the PMI further comprises a phase for cross panel combination. The BS may have a plurality of transmit (TX) beams. The UE can feed back to the BS an index of a preferred beam, or beams, of the candidate beams. For example, the UE may feed back the precoding vector w for the l-th layer:

, where b represents the oversampled beam (e.g., discrete Fourier transform (DFT) beam) , for both polarizations, and

is the co-phasing.

For the Type II codebook (e.g., which may be designed for single panel) , the PMI is a linear combination of beams; it has a subset of orthogonal beams to be used for linear combination and has per layer, per polarization, amplitude and phase for each beam. The preferred precoder for a layer can be a combination of beams and associated quantized coefficients, and the UE can feedback the selected beams and the coefficients to the BS.

The UE may report the CSI feedback based on the CSI report configuration and the CSI report trigger. For example, the UE may measure the channel associated with CSI for the triggered CSI-RS resources. Based on the measurements, the UE may select a preferred CSI-RS resource. The UE reports the CSI feedback for the selected CSI-RS resource. LI may be calculated conditioned on the reported CQI, PMI, RI and CRI; CQI may be calculated conditioned on the reported PMI, RI and CRI; PMI may be calculated conditioned on the reported RI and CRI; and RI may be calculated conditioned on the reported CRI.

Example SD Compressed CSI Feedback

In certain systems (e.g., Release 15 5G NR) , the UE may be configured to report at least a Type II precoder across configured frequency domain (FD) units. The UE may report wideband (WB) PMI and/or subband (SB) PMI as configured.

For a layer l, its precoder across N ₃ FD units (also referred to as PMI subbands) may be given by a size-N _t×N ₃ matrix W _l as follows:

W _l=W ₁×W _2, l,

where W ₁ and W _2, l are as described in the following table:

The two matrices can be written as:

where the SD bases are DFT based and the SD basis with index

and

is written as

and where the coefficient matrix may be written as

In some cases, a common (P1) value may apply to all

coefficients (or simply P1 coefficients) in one row. In such cases, given 2L rows in the matrix, the P1 value is row-specific and there might be 2L different values for these coefficients. The coefficients

and

are described as follows:

More precisely, the linear combination representation may be written as:

For linear combination of spatial beams B, the UE may report the linear combination coefficients

for each layer l and each subband i, according to the precoding vector w:

The precoder matrix W is based on the spatial domain (SD) compression of a matrix W ₁ matrix and the W ₂ matrix for reporting (for cross-polarization) the linear combination coefficients for the selected beams (2L) across the configured FD units.

For port selection in certain systems (e.g., Rel-15 NR port selection) , the BS (e.g., a gNB) may use a beam in

as the precoder for CSI-RS. The precoder for a layer on a subband is given by:

where

is a vector. In this case, the UE selects the CSI-RS ports, for example, instead of selecting the beam. Thus, using this codebook, if the (i ₁₁d + i) -th entry is equal to 1 and the rest are 0s, this means that the (i ₁₁d + i) -th port is selected. With this codebook, there are P ports, where the first half of the ports are for polarization 1 and the other half of the ports are for polarization 2, and the same L ports are applied to both polarization. The UE reports the preferred candidate L ports via i ₁₁, where the candidates are candidate L ports is 0... L-1, and candidate L ports d... d + L-1. The last candidate L ports is

In this case, the UE may be restricted to select L consecutive ports (e.g., port i ₁₁d, …i ₁₁d+L-1) and the maximum number ports may be 32, which may be insufficient and should accommodate FD basis.

Example SD and FD Compressed CSI Feedback

In certain systems (e.g., Rel-16 5G NR) , the UE may be configured to report frequency domain (FD) compressed precoder feedback to reduce overhead of the CSI report. With codebook operation with FD compression, for a layer l, its precoder across N ₃ FD units (e.g., PMI subbands) is given by a size-N _t×N ₃ matrix W _l as follows:

where W ₁,

and W _f are as follows:

The precoder matrix (W _2, i) for layer i with i=0, 1 may use an FD compression

matrix to compress the precoder matrix into

matrix size to 2L X M (where M is network configured and communicated in the CSI configuration message via RRC or DCI, and M < N ₃) given as:

where the precoder matrix W _i (not shown) has P = 2N ₁N ₂ rows (spatial domain, number of ports) and N ₃ columns (frequency-domain compression unit containing RBs or reporting sub-bands) , and where M bases are selected for each of layer 0 and layer 1 independently. The

matrix consists of the linear combination coefficients (amplitude and co-phasing) , where each element represents the coefficient of a tap for a beam. The

matrix may be defined by size 2L X M, where one row corresponds to one spatial beam in W ₁ (not shown) of size P X 2L (where L is network configured via RRC) , and one entry therein represents the coefficient of one tap for this spatial beam.

The UE may be configured to report (e.g., CSI report) a subset K ₀ < 2LM of the linear combination coefficients of the

matrix. For example, the UE may report K _NZ, i < K ₀ coefficients (where K _NZ, i corresponds to a maximum number of non-zero coefficients for layer-i with i=0 or 1, and K ₀ is network configured via RRC) illustrated as shaded squares (unreported coefficients are set to zero) . In some configurations, an entry in the

matrix corresponds to a row of

matrix. In the example shown, both the

matrix at layer 0 and the

matrix at layer 1 are 2L X M.

The

matrix is composed of the basis vectors (each row is a basis vector) used to perform compression in frequency domain. In the example shown, both the

matrix at layer 0 and the

matrix at layer 1 include M=4 FD basis from N ₃ candidate DFT basis. In some configurations, the UE may report a subset of selected basis of the

matrix via CSI report. The M bases specifically selected at layer 0 and layer 1. That is, the M bases selected at layer 0 can be same/partially-overlapped/non-overlapped with the M bases selected at layer 1.

The precoder may be written as:

As discussed above, the Type II CSI with FD compression may compress N ₃ subbands via M FD bases. The FD bases are selected/reported layer-specific. For each layer, the UE reports a subset of the total 2LM coefficients, where the coefficient selection may be layer specific, and the UE may use a size-2LM bitmap to indicate the selected non-zero coefficients (NZC) and report each the NZC after quantization. In some examples, the UE may report up to K ₀ coeffcients per layer, where K _NZ, l≤K ₀. In some examples, the UE may report up to 2K ₀ coefficients across all layers, where

Unreported are set to zeros.

The UE may report the CSI in uplink control information (UCI) . In some examples, the CSI is reported in a two-part UCI. In some examples, in the UCI part one the UE may transmit RI, CQI, the number of non-zero coefficients (NNZC) . In some examples, in the UCI part two the UE may transmit for the supported layers (e.g., layers 0 to RI-1) the SD beam selection, FD basis selection, coefficient selection, strongest coefficient indication (SCI) , and/or coefficient quantization. The SD beam selection may indicate the selected beams (e.g., the subset of 2L beams) .

Example Compressed CSI Feedback without Full CSI-RS Presence

In some cases, the user equipment (UE) is configured to provide channel state information (CSI) feedback for one or more frequency resources (e.g., subbands) . As discussed above, CSI feedback may include precoding matrix indicator (PMI) feedback and channel quality indicator (CQI) feedback. The CQI feedback may be computed based on the PMI.

In certain systems (e.g., Rel-16 5G NR) , the UE may be configured with finer granularity for the PMI subbands than for the CQI subbands. In this case, the PMI subbands may be smaller than the CQI subbands. For example:

PMI subband

where R may be a configurable parameter (e.g., R=1, 2, ... ) . Thus, there may be up to R PMI subbands in one CQI subband. For example, FIG. 4 is an example for R=2, where two

PMI

404, 406 for a subband 408 are in one CQI subband 402, in accordance with certain aspects of the disclosure. Thus, the subband CQI may be calculated using up to the R PMIs.

In some examples, the actual subband size may smaller than the configured subband size (e.g., for edge subbands) . In this case, the number of PMI used to calculate the CQI may be based on the actual subband size and the configured CQI subband size.

For example, when the actual subband size 508 is more than half of the configured CQI subband size 502, then two PMIs 504, 506 (e.g., for R=2) may be used to calculate the CQI as shown in FIG. 5A. For example, the PMI 504 may be a full PMI for the portion of the actual subband 508 corresponding to half of the configured CQI subband size) and the PMI 506 may be for the remaining portion of the actual subband 508. On the other hand, when the actual subband size 508 is equal to or smaller than half of the configured CQI subband size 502, then only one PMI 504 (e.g., for R=2) may be used to calculate the CQI as shown in FIG. 6A.

In certain systems (e.g., Release 15 systems) , the UE does not expect to be configured with a CQI subband which does not have full CSI-RS presence. Full CSI-RS may correspond to when actual CSI-RS density in the CQI subband is equal to or greater than the configured CSI-RS density. On the other hand, partial CSI-RS presence may refer to when the CSI-RS density in the CQI subband is less than the configured CSI-RS density. In some examples, the configured CSI-RS density may be 3 resource elements (REs) per port and/or per resource block (RB) , 1 RE per port and/or per RB, 0.5 RE per port and/or per every other RB, etc. Other densities may also be configured for the CSI-RS.

In other systems (e.g., Rel-16 systems) , a CQI subband may not have full CSI-RS presence. However, because the PMI subbands may be smaller than the CQI subbands, some PMI subbands may still have full CSI-RS presence even when the CQI subband does not have full CSI-RS presence (e.g., has only partial CSI-RS presence) .

Aspects of the disclosure provide for PMI and CQI reporting that may be used for compressed CSI feedback for subbands in various scenarios when there is partial CSI-RS presence in the configured CQI subband.

According to certain aspects, the PMI and CQI reporting may be based on whether the actual subband size is more or less than half of the CQI subband size. According to certain aspects, the PMI and CQI reporting may be further based on whether there is full CSI-RS presence in the PMIs.

According to certain aspects, the UE can determine the number of PMIs the CQI subband. For example, the UE may be configured with a first subband size for CQI feedback and with a granularity for PMI feedback. The UE can determine a second subband size for PMI feedback based on the first subband size for the CQI feedback and the configured PMI granularity. In some examples, the UE determines that a CQI subband is associated with one or more PMI subbands based on the configured subband size for CQI feedback, the second subband size for PMI feedback, an actual CQI subband size, and an actual PMI subband size. The UE can determine the actual CQI subband size and the actual PMI subband size based on a configured/indicated frequency resource allocation of a cell or a configured/indicated bandwidth part (BWP) .

According to aspects of the disclosure, the UE does not expect to be configured with a PMI subband without full CSI-RS presence, but may expect to be configured with a CQI subband without full CSI-RS presence.

In some examples, the UE does not expect to be configured with a subband with less than full CSI-RS presence. In other words, the BS may configure all the PMI and CQI subbands having full CSI-RS presence. For example, the BS may be restricted from such as a configuration (e.g., the BS may be configured to avoid configuring a subband for CSI with less than full CSI-RS presence. Thus, as will be described in more detail below with respects FIGs. 4A-4E, FIGs. 5-5E, and FIGs. 6A-E, when the UE is configured with a subband for reporting CSI, and the subband does not have full CSI-RS presence (e.g., and regardless whether any PMI have full CSI-RS presence) , the UE may treat this as an error case (e.g., the UE behavior may be undefined) . For the error case, the UE drop (e.g., not report) CQI, PMI, or both, for the subband. In some examples, the UE drops the entire CSI. In some examples, the UE may not update the CSI for the subband.

The FIGs. 4B-4E, provide examples for the CQI and PMI feedback in the example scenario of FIG. 4A, where the actual subband 408 size is equal to the configured CQI subband 402 size. Multiple PMI may be calculated (e.g., two PMI) for the actual subband 408, as shown in FIG. 4A.

For the example shown in FIG. 4A, FIG. 4B shows an example with the CSI-RS presence 410b that is less than full for the configured CQI subband size 402 and less than full for the actual subband 408 size, but has full presence for the PMI subband 404, and partial presence for the PMI subband 406. As shown in FIG. 4C, in this case, the CQI 412 may be calculated using the PMI 404 (PMI 1) that has full CSI-RS presence. The PMI 406 (PMI 2) may be dropped (e.g., not computed or reported) . Thus, when a PMI subband has full CSI-RS presence and another PMI subband does not have full CSI-RS presence, then the PMI subband with full CSI-RS presence is reported for the subband 408, PMI without full CSI-RS presence is not reported, and the CQI is calculated using the reported PMI with the frequency resource allocation of the PMI subband with full frequency resource. In some examples, the UE does not expect to be configured with the CQI or PMI subband with less than full CSI-RS presence. For example, the BS may be restricted from such as a configuration (e.g., the BS may be configured to avoid configuring a subband for CSI with less than full CSI-RS presence. In other words, the BS configures all the PMI and CQI subbands having full CSI-RS presence. In some examples, the UE treats this as an error and drops the CQI 412 and/or the PMI 404. In some examples, the UE drops the entire CSI. In some examples, the UE does not update CSI feedback for the subband 408.

For the example shown in FIG. 4A, FIG. 4D shows an example with the CSI-RS presence 410d that is less than full for the actual subband size 408 and the configured CQI subband 402 size, and that does not have full presence for the PMI subband 404 nor for the PMI subband 406. In some examples, the UE does not expect to be configured with a CQI or PMI subband with less than full CSI-RS presence. In other words, the BS may configure all the PMI and CQI subbands having full CSI-RS presence. For example, the BS may be restricted from such as a configuration (e.g., the BS may be configured to avoid configuring a subband for CSI with less than full CSI-RS presence. As shown in FIG. 4E, in this case, the UE may treat this an error case. For example, the CQI is dropped for the CQI subband 402 (e.g., the CQI is not computed or reported) and the PMI 404 (PMI 1) and 406 (PMI 2) may also be dropped (e.g., not computed or reported) for the subband 408, but may report CQI and PMI for other subbands. In some examples, the UE drops the entire CSI. In some examples, the UE does not update CSI feedback for the subband 408.

The FIGs. 5B-5E, provide examples for the CQI and PMI feedback in the example scenario of FIG. 5A, where the actual subband 508 size is smaller than the configured CQI subband 502 size, but larger than half of the CQI subband 502 size. When the actual subband size is greater than half of the configured CQI subband size, more than one PMI may be calculated (e.g., two PMI) , as shown in FIG. 5A.

For the example shown in FIG. 5A, FIG. 5B shows an example with the CSI-RS presence 510b that is less than full for the actual subband size 508 and for the configured CQI subband 502 size, but has full presence for the PMI subband 504, and partial presence for the PMI subband 506. As shown in FIG. 5C, in this case, the CQI 512 may be calculated using the PMI 504 (PMI 1) that has full CSI-RS presence. The PMI 506 (PMI 2) may be dropped (e.g., not computed or reported) . Thus, when the actual subband size is more than half of the configured CQI subband, and when a PMI subband has full CSI-RS presence and another PMI subband does not have full CSI-RS presence, then PMI for the subband 508 is reported for the PMI subband with full CSI-RS presence, PMI is not reported for the PMI subband without full CSI-RS presence, and the CQI is calculated using the reported PMI with the frequency resource allocation of the PMI subband with full frequency resource. In some examples, the UE does not expect to be configured with the CQI or PMI subband with less than full CSI-RS presence. In other words, the BS may configure all the PMI and CQI subbands having full CSI-RS presence. For example, the BS may be restricted from such as a configuration (e.g., the BS may be configured to avoid configuring the subband for CSI with less than full CSI-RS presence. In some examples, the UE treats this as an error and drops the CQI 512 and/or the PMI 504. In some examples, the UE drops the entire CSI. In some examples, the UE does not update CSI feedback for the subband 508.

For the example shown in FIG. 5A, FIG. 5D shows an example with the CSI-RS presence 510d that is less than full for the configured CQI subband 502 size and the actual subband size 508, and that does not have full presence for the PMI subband 504 nor for the PMI subband 506. In some examples, the UE does not expect to be configured with a CQI or PMI subband with less than full CSI-RS presence. In other words, the BS may configure all the PMI and CQI subbands having full CSI-RS presence. For example, the BS may be restricted from such as a configuration (e.g., the BS may be configured to avoid configuring a subband for CSI with less than full CSI-RS presence. As shown in FIG. 5E, in this case, the UE may treat this an error case. For example, the CQI is dropped for the CQI subband 502 (e.g., the CQI is not computed or reported) and the PMI 504 (PMI 1) and 506 (PMI 2) may also be dropped (e.g., not computed or reported) for the subband 508. In some examples, the UE drops the entire CSI. In some examples, the UE does not update CSI feedback for the subband 508.

The FIGs. 6B-6E, provide examples for the CQI and PMI feedback in the example scenario of FIG. 6A, where the actual subband 608 size is equal to or smaller than half the configured CQI subband 602 size. When the actual subband size is equal to smaller than half the configured CQI subband size, only one PMI may be calculated, as shown in FIG. 6A.

For the example shown in FIG. 6A, FIG. 6B shows an example with the CSI-RS presence 610b that is less than full for the configured CQI subband 602 size, but has full presence for the actual subband size 608 and the PMI subband 604. As shown in FIG. 6C, in this case, the CQI 612 may be calculated using the PMI 604 (PMI 1) that has full CSI-RS presence. Thus, when the actual subband is more than half of the configured CQI subband, and when the single PMI subband has full CSI-RS presence, then PMI for subband 608 is reported for the PMI subband with full CSI-RS presence, and the CQI is calculated using the reported PMI with the frequency resource allocation of the PMI subband. In some examples, the UE does not expect to be configured with the CQI or PMI subband with less than full CSI-RS presence. In other words, the BS may configure all the PMI and CQI subbands having full CSI-RS presence. For example, the BS may be restricted from such as a configuration (e.g., the BS may be configured to avoid configuring the subband for CSI with less than full CSI-RS presence. In some examples, the UE treats this as an error and drops the CQI 612 and/or the PMI 604. In some examples, the UE drops the entire CSI. In some examples, the UE does not update CSI feedback for the subband 608.

For the example shown in FIG. 6A, FIG. 6D shows an example with the CSI-RS presence 610c that is less than full for the configured CQI subband 602 size, and that also does not have full presence for the actual subband size 608 and does not have full presence for the single PMI subband 604. In some examples, the UE does not expect to be configured with a CQI or PMI subband with less than full CSI-RS presence. In other words, the BS may configure all the PMI and CQI subbands having full CSI-RS presence. For example, the BS may be restricted from such as a configuration (e.g., the BS may be configured to avoid configuring a subband for CSI with less than full CSI-RS presence. As shown in FIG. 6E, in this case, the UE may treat this an error case. For example, the CQI is dropped for the CQI subband 602 (e.g., the CQI is not computed or reported) and the PMI 604 (PMI 1) may also be dropped (e.g., not computed or reported) for subband 608. In some examples, the UE drops the entire CSI. In some examples, the UE does not update CSI feedback for the subband 608.

FIG. 7 is a flow diagram illustrating example operations 700 for wireless communication, in accordance with certain aspects of the present disclosure. The operations 700 may be performed, for example, by UE (e.g., such as the UE 120a in the wireless communication network 100) . The operations 700 may be complimentary operations by the UE to the operations 800 performed by the BS. Operations 700 may be implemented as software components that are executed and run on one or more processors (e.g., controller/processor 280 of FIG. 2) . Further, the transmission and reception of signals by the UE in operations 700 may be enabled, for example, by one or more antennas (e.g., antennas 252 of FIG. 2) . In certain aspects, the transmission and/or reception of signals by the UE may be implemented via a bus interface of one or more processors (e.g., controller/processor 280) obtaining and/or outputting signals.

The operations 700 may begin, at 705, by receiving a configuration to report CSI feedback for one or more subbands. The CSI feedback includes at least PMI feedback and CQI feedback. The configuration indicates a first subband size for the CQI feedback and an indication of PMI granularity;

At 710, the UE determines a second subband size for PMI feedback based on the first subband size and the PMI granularity.

At 715, the UE determines a density of CSI reference signals (CSI-RS) present in a CQI or PMI subband.

In some examples, the UE determines that a CQI subband is associated with one or more PMI subbands based on the first subband size for CQI feedback, the second subband size for PMI feedback, an actual CQI subband size, and an actual PMI subband size. The actual CQI subband size and the actual PMI subband size may be determined based on a frequency resource allocation of a cell or a BWP.

At 720, the UE drops or reports at least the CSI feedback for the CQI or PMI subband based on the determined density.

In some examples, the determined density of the CSI-RS present in a CQI subband is less than a configured CSI-RS density; the determined density of the CSI-RS present in a first PMI subband is equal to or larger than a configured CSI-RS density; and the determined density of the CSI-RS present in a second PMI subband is less than a configured CSI-RS density. In this case, the UE may calculate and report a first PMI for the first PMI subband and calculate and report the CQI for the subband using the first PMI with the frequency resource of the first PMI subband; the UE may calculate and report a first PMI for the first PMI subband, calculate and report a second PMI for the second PMI subband using the frequency resources of the CSI-RS, and calculate and report CQI for the subband using the first PMI with the frequency resource of the first PMI subband and the frequency resource of CSI-RS in the second PMI subband the UE may drop all the PMIs and CQI of the subband; the UE may drop the entire CSI feedback for all subbands; the UE may not update the CSI feedback; and/or the UE may treat it as an error case.

In some examples, the density of the CSI-RS present in a CQI subband is less than a configured CSI-RS density; and the density of the CSI-RS present in each of the first and second PMI subbands is less than a configured CSI-RS density. In this case, the UE may drop the all the PMIs and CQI of the subband; the UE may drop the entire CSI feedback for all subbands; the UE may not update the CSI feedback; and/or the UE may treat it as an error case.

FIG. 8 is a flow diagram illustrating example operations 800 for wireless communication, in accordance with certain aspects of the present disclosure. The operations 800 may be performed, for example, by a BS (e.g., such as the BS 110a in the wireless communication network 100) . The operations 800 may be complimentary operations by the BS to the operations 700 performed by the UE. Operations 800 may be implemented as software components that are executed and run on one or more processors (e.g., controller/processor 240 of FIG. 2) . Further, the transmission and reception of signals by the BS in operations 800 may be enabled, for example, by one or more antennas (e.g., antennas 234 of FIG. 2) . In certain aspects, the transmission and/or reception of signals by the BS may be implemented via a bus interface of one or more processors (e.g., controller/processor 240) obtaining and/or outputting signals.

The operations 800 may begin, at 805, by configuring a UE to report CSI feedback for one or more subbands. The CSI feedback including at least PMI feedback and CQI feedback. The configuration indicates a first subband size for the CQI feedback and indicates a PMI granularity. In some examples, configuring the UE to report CSI feedback for the one or more subbands comprises configuring a CSI report, wherein each CQI and PMI subband configured for the CSI report has full CSI-RS presence.

At 810, the BS determines a second subband size for PMI feedback based on the first subband size and the PMI granularity.

At 815, the BS transmits CSI reference signals (CSI-RS) to the UE in at least a portion of a CQI or PMI subband.

At 820, the BS receives CSI feedback for the CQI or PMI subband based on the configuration and the at least a portion.

In some examples, the BS determines that a CQI subband is associated with one or more PMI subbands based on the first subband size for CQI feedback, the second subband size for PMI feedback, an actual CQI subband size, and an actual PMI subband size. The BS determines the actual CQI subband size and the actual PMI subband size based on a frequency resource allocation of a cell or a BWP.

In some examples, the density of the CSI-RS transmitted in a CQI subband is less than a configured CSI-RS density; the density of the CSI-RS transmitted in a first PMI subband is equal to or larger than a configured CSI-RS density; and the density of the CSI-RS transmitted in a second PMI subband is less than a configured CSI-RS density. In this case, the BS receives a first PMI for the first PMI subband and CQI feedback for the subband calculated using the first PMI with the frequency resource of the first PMI subband; the BS receives a first PMI for the first PMI subband, receives a second PMI for the second PMI subband using the frequency resources of the CSI-RS, and receives a CQI for the subband using the first PMI with the frequency resource of the first PMI subband and the frequency resource of CSI-RS in the second PMI subband; the BS does not receive any PMI and CQI of the subband; the BS does not receive CSI feedback for all subbands; and/or the BS receives CSI feedback without update.

In some examples, the density of the CSI-RS transmitted in a CQI subband is less than a configured CSI-RS density; and the density of the CSI-RS transmitted in each of PMI subband is less than a configured CSI-RS density. In this case, the BS receives a PMI for the PMI subband using the frequency resources of the CSI-RS, and receives CQI for the subband using the PMI with the frequency resource of CSI-RS in the PMI subband; the BS receives CSI feedback without any PMI and CQI of the subband; the BS does not receive CSI feedback for all subbands; and/or the BS receives CSI feedback without update.

FIG. 9 illustrates a communications device 900 that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for the techniques disclosed herein, such as the operations illustrated in FIG. 7. The communications device 900 includes a processing system 902 coupled to a transceiver 908 (e.g., a transmitter and/or a receiver) . The transceiver 908 is configured to transmit and receive signals for the communications device 900 via an antenna 910, such as the various signals as described herein. The processing system 902 may be configured to perform processing functions for the communications device 900, including processing signals received and/or to be transmitted by the communications device 900.

The processing system 902 includes a processor 904 coupled to a computer-readable medium/memory 912 via a bus 906. In certain aspects, the computer-readable medium/memory 912 is configured to store instructions (e.g., computer-executable code) that when executed by the processor 904, cause the processor 904 to perform the operations illustrated in FIG. 7, or other operations for performing the various techniques discussed herein for compressed CSI feedback without full CSI-RS presence. In certain aspects, computer-readable medium/memory 912 stores code 914 for receiving a configuration to report CSI feedback including PMI and CQI feedback; code 916 for determining a subband size for the PMI feedback; code 918 for determining density of CSI-RS present in a CQI or PMI subband; and code 920 for reporting or dropping CSI feedback for the CQI and/or PMI subband based on the density, in accordance with aspects of the disclosure. In certain aspects, the processor 904 has circuitry configured to implement the code stored in the computer-readable medium/memory 912. The processor 904 includes circuitry 922 for receiving a configuration to report CSI feedback including PMI and CQI feedback; circuitry 924 for determining a subband size for the PMI feedback; circuitry 926 for determining density of CSI-RS present in a CQI or PMI subband; circuitry code 928 for reporting or dropping CSI feedback for the CQI and/or PMI subband based on the density, in accordance with aspects of the disclosure.

FIG. 10 illustrates a communications device 1000 that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for the techniques disclosed herein, such as the operations illustrated in FIG. 8. The communications device 1000 includes a processing system 1002 coupled to a transceiver 1008 (e.g., a transmitter and/or a receiver) . The transceiver 1008 is configured to transmit and receive signals for the communications device 1000 via an antenna 1010, such as the various signals as described herein. The processing system 1002 may be configured to perform processing functions for the communications device 1000, including processing signals received and/or to be transmitted by the communications device 1000.

The processing system 1002 includes a processor 1004 coupled to a computer-readable medium/memory 1012 via a bus 1006. In certain aspects, the computer-readable medium/memory 1012 is configured to store instructions (e.g., computer-executable code) that when executed by the processor 1004, cause the processor 904 to perform the operations illustrated in FIG. 8, or other operations for performing the various techniques discussed herein for compressed CSI feedback without full CSI-RS presence. In certain aspects, computer-readable medium/memory 1012 stores code 1014 for configuring a UE to report CSI including PMI and CQI feedback; code 1016 for determining a subband size for the PMI feedback; code 1018 for transmitting CSI-RS to the UE in at least a portion of a CQI or PMI subband; and code 1020 for receiving CSI feedback for the CQI and/or PMI subband based on the configuration and the CSI-RS, in accordance with aspects of the disclosure. In certain aspects, the processor 1004 has circuitry configured to implement the code stored in the computer-readable medium/memory 1012. The processor 1004 includes circuitry 1022 for configuring a UE to report CSI including PMI and CQI feedback; circuitry 1024 for determining a subband size for the PMI feedback; circuitry 1026 for transmitting CSI-RS to the UE in at least a portion of a CQI or PMI subband; and circuitry 1028 for receiving CSI feedback for the CQI and/or PMI subband based on the configuration and the CSI-RS, in accordance with aspects of the disclosure.

Example Aspects

In a first aspect, a method for wireless communication by a user equipment (UE) includes receiving a configuration to report channel state information (CSI) feedback for one or more subbands. The CSI feedback includes at least precoding matrix indicator (PMI) feedback and channel quality indicator (CQI) feedback. The configuration indicates a first subband size for the CQI feedback and an indication of PMI granularity. The UE determines a second subband size for PMI feedback based on the first subband size and the PMI granularity; determines a density of CSI reference signals (CSI-RS) present in a CQI or PMI subband; and drops or reports at least the CSI feedback for the CQI or PMI subband based on the determined density.

In a second aspect, in combination with the first aspect, the UE determines that a CQI subband is associated with one or more PMI subbands based on the first subband size for CQI feedback, the second subband size for PMI feedback, an actual CQI subband size, and an actual PMI subband size. The actual CQI subband size and the actual PMI subband size are determined based on a frequency resource allocation of a cell or a bandwidth part (BWP) .

In a third aspect, in combination with one or more of the first and second aspects, the determined density of the CSI-RS present in a CQI subband is less than a configured CSI-RS density; the determined density of the CSI-RS present in a first PMI subband is equal to or larger than a configured CSI-RS density; and the determined density of the CSI-RS present in a second PMI subband is less than a configured CSI-RS density.

In a fourth aspect, in combination with one or more of the first through third aspects, dropping or reporting at least the CSI feedback for the CQI or PMI subband based on the determination includes at least one of: calculating and reporting a first PMI for the first PMI subband, and calculating and reporting the CQI for the subband using the first PMI with the frequency resource of the first PMI subband; calculating and reporting a first PMI for the first PMI subband, calculating and reporting a second PMI for the second PMI subband using the frequency resources of the CSI-RS, and calculating and reporting CQI for the subband using the first PMI with the frequency resource of the first PMI subband and the frequency resource of CSI-RS in the second PMI subband; dropping all the PMIs and CQI of the subband; dropping the entire CSI feedback for all subbands; not updating the CSI feedback; or treating it as an error case.

In a fifth aspect, in combination with one or more of the first through fourth aspects, the determined density of the CSI-RS present in a CQI subband is less than a configured CSI-RS density; and the determined density of the CSI-RS present in each of PMI subband is less than a configured CSI-RS density.

In a sixth aspect, in combination with one or more of the first through fifth aspects, dropping or reporting at least the CSI feedback for the CQI or PMI subband based on the determination includes at least one of: calculating and reporting a PMI for the PMI subband using the frequency resources of the CSI-RS, and calculating and reporting CQI for the subband using the PMI with the frequency resource of CSI-RS in the PMI subband; dropping the all the PMIs and CQI of the subband; dropping the entire CSI feedback for all subbands; not updating the CSI feedback; or treating it as an error case.

In a seventh aspect, a method for wireless communication by a base station (BS) includes configuring a user equipment (UE) to report channel state information (CSI) feedback for one or more subbands. The CSI feedback includes at least precoding matrix indicator (PMI) feedback and channel quality indicator (CQI) feedback. The configuration indicates a first subband size for the CQI feedback and indicates a PMI granularity. The BS determines a second subband size for PMI feedback based on the first subband size and the PMI granularity; transmits CSI reference signals (CSI-RS) to the UE in at least a portion of a CQI or PMI subband; and receives CSI feedback for the CQI or PMI subband based on the configuration and the at least a portion.

In an eighth aspect, in combination with the seventh aspect, the BS determines that a CQI subband is associated with one or more PMI subbands based on the first subband size for CQI feedback, the second subband size for PMI feedback, an actual CQI subband size, and an actual PMI subband size. The actual CQI subband size and the actual PMI subband size are determined based on a frequency resource allocation of a cell or a bandwidth part (BWP) .

In a ninth aspect, in combination with one or more of the seventh and eighth aspects, the density of the CSI-RS transmitted in a CQI subband is less than a configured CSI-RS density; the density of the CSI-RS transmitted in a first PMI subband is equal to or larger than a configured CSI-RS density; and the density of the CSI-RS transmitted in a second PMI subband is less than a configured CSI-RS density.

In a tenth aspect, in combination with one or more of the seventh through ninth aspects, receiving CSI feedback includes at least one of: receiving a first PMI for the first PMI subband and CQI feedback for the subband calculated using the first PMI with the frequency resource of the first PMI subband; receiving a first PMI for the first PMI subband, receiving a second PMI for the second PMI subband using the frequency resources of the CSI-RS, and receiving a CQI for the subband using the first PMI with the frequency resource of the first PMI subband and the frequency resource of CSI-RS in the second PMI subband; receiving a CSI feedback without any PMI and CQI of the subband; not receiving CSI feedback for all subbands; or receiving a CSI feedback without update.

In an eleventh aspect, in combination with one or more of the seventh through tenth aspects, the density of the CSI-RS transmitted in a CQI subband is less than a configured CSI-RS density; and the density of the CSI-RS transmitted in each of PMI subband is less than a configured CSI-RS density.

In a twelfth aspect, in combination with one or more of the seventh through eleventh aspects, monitoring CSI feedback includes at least one of: receiving a PMI for the PMI subband using the frequency resources of the CSI-RS, and receiving CQI for the subband using the PMI with the frequency resource of CSI-RS in the PMI subband; receiving a CSI feedback without any PMI and CQI of the subband; not receiving CSI feedback for all subbands; or receiving CSI feedback without update.

In a thirteenth aspect, in combination with one or more of the seventh through twelfth aspects, configuring the UE to report CSI feedback for the one or more subbands comprises configuring a CSI report. The configuration includes at least one of: each CQI subband configured for the CSI report has full CSI-RS presence; each PMI subband configured for the CSI report has full CSI-RS presence; or a combination thereof.

The techniques described herein may be used for various wireless communication technologies, such as NR (e.g., 5G NR) , 3GPP Long Term Evolution (LTE) , LTE-Advanced (LTE-A) , code division multiple access (CDMA) , time division multiple access (TDMA) , frequency division multiple access (FDMA) , orthogonal frequency division multiple access (OFDMA) , single-carrier frequency division multiple access (SC-FDMA) , time division synchronous code division multiple access (TD-SCDMA) , and other networks. The terms “network” and “system” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA) , cdma2000, etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM) . An OFDMA network may implement a radio technology such as NR (e.g. 5G RA) , Evolved UTRA (E-UTRA) , Ultra Mobile Broadband (UMB) , IEEE 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, Flash-OFDMA, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS) . LTE and LTE-Aare releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP) . cdma2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2) . NR is an emerging wireless communications technology under development.

In 3GPP, the term “cell” can refer to a coverage area of a Node B (NB) and/or a NB subsystem serving this coverage area, depending on the context in which the term is used. In NR systems, the term “cell” and BS, next generation NodeB (gNB or gNodeB) , access point (AP) , distributed unit (DU) , carrier, or transmission reception point (TRP) may be used interchangeably. A BS may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cells. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscription. A femto cell may cover a relatively small geographic area (e.g., a home) and may allow restricted access by UEs having an association with the femto cell (e.g., UEs in a Closed Subscriber Group (CSG) , UEs for users in the home, etc. ) . A BS for a macro cell may be referred to as a macro BS. A BS for a pico cell may be referred to as a pico BS. A BS for a femto cell may be referred to as a femto BS or a home BS.

A UE may also be referred to as a mobile station, a terminal, an access terminal, a subscriber unit, a station, a Customer Premises Equipment (CPE) , a cellular phone, a smart phone, a personal digital assistant (PDA) , a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a tablet computer, a camera, a gaming device, a netbook, a smartbook, an ultrabook, an appliance, a medical device or medical equipment, a biometric sensor/device, a wearable device such as a smart watch, smart clothing, smart glasses, a smart wrist band, smart jewelry (e.g., a smart ring, a smart bracelet, etc. ) , an entertainment device (e.g., a music device, a video device, a satellite radio, etc. ) , a vehicular component or sensor, a smart meter/sensor, industrial manufacturing equipment, a global positioning system device, or any other suitable device that is configured to communicate via a wireless or wired medium. Some UEs may be considered machine-type communication (MTC) devices or evolved MTC (eMTC) devices. MTC and eMTC UEs include, for example, robots, drones, remote devices, sensors, meters, monitors, location tags, etc., that may communicate with a BS, another device (e.g., remote device) , or some other entity. A wireless node may provide, for example, connectivity for or to a network (e.g., a wide area network such as Internet or a cellular network) via a wired or wireless communication link. Some UEs may be considered Internet-of-Things (IoT) devices, which may be narrowband IoT (NB-IoT) devices.

In some examples, access to the air interface may be scheduled. A scheduling entity (e.g., a BS) allocates resources for communication among some or all devices and equipment within its service area or cell. The scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more subordinate entities. That is, for scheduled communication, subordinate entities utilize resources allocated by the scheduling entity. Base stations are not the only entities that may function as a scheduling entity. In some examples, a UE may function as a scheduling entity and may schedule resources for one or more subordinate entities (e.g., one or more other UEs) , and the other UEs may utilize the resources scheduled by the UE for wireless communication. In some examples, a UE may function as a scheduling entity in a peer-to-peer (P2P) network, and/or in a mesh network. In a mesh network example, UEs may communicate directly with one another in addition to communicating with a scheduling entity.

In some examples, two or more subordinate entities (e.g., UEs) may communicate with each other using sidelink signals. Real-world applications of such sidelink communications may include public safety, proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V) communications, Internet of Everything (IoE) communications, IoT communications, mission-critical mesh, and/or various other suitable applications. Generally, a sidelink signal may refer to a signal communicated from one subordinate entity (e.g., UE1) to another subordinate entity (e.g., UE2) without relaying that communication through the scheduling entity (e.g., UE or BS) , even though the scheduling entity may be utilized for scheduling and/or control purposes. In some examples, the sidelink signals may be communicated using a licensed spectrum (unlike wireless local area networks, which typically use an unlicensed spectrum) .

The methods disclosed herein comprise one or more steps or actions for achieving the methods. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims.

As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c) .

As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure) , ascertaining and the like. Also, “determining” may include receiving (e.g., receiving information) , accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” Unless specifically stated otherwise, the term “some” refers to one or more. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112 (f) unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for. ”

The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component (s) and/or module (s) , including, but not limited to a circuit, an application specific integrated circuit (ASIC) , or processor. Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function components with similar numbering.

The various illustrative logical blocks, modules and circuits described in connection with the present disclosure may be implemented or performed with 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 (PLD) , 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 commercially available 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, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

If implemented in hardware, an example hardware configuration may comprise a processing system in a wireless node. The processing system may be implemented with a bus architecture. The bus may include any number of interconnecting buses and bridges depending on the specific application of the processing system and the overall design constraints. The bus may link together various circuits including a processor, machine-readable media, and a bus interface. The bus interface may be used to connect a network adapter, among other things, to the processing system via the bus. The network adapter may be used to implement the signal processing functions of the PHY layer. In the case of a user terminal (see FIG. 1) , a user interface (e.g., keypad, display, mouse, joystick, etc. ) may also be connected to the bus. The bus may also link various other circuits such as timing sources, peripherals, voltage regulators, power management circuits, and the like, which are well known in the art, and therefore, will not be described any further. The processor may be implemented with one or more general-purpose and/or special-purpose processors. Examples include microprocessors, microcontrollers, DSP processors, and other circuitry that can execute software. Those skilled in the art will recognize how best to implement the described functionality for the processing system depending on the particular application and the overall design constraints imposed on the overall system.

If implemented in software, the functions may be stored or transmitted over as one or more instructions or code on a computer readable medium. Software shall be construed broadly to mean instructions, data, or any combination thereof, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. Computer-readable media include both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. The processor may be responsible for managing the bus and general processing, including the execution of software modules stored on the machine-readable storage media. A computer-readable storage medium may be coupled to a processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. By way of example, the machine-readable media may include a transmission line, a carrier wave modulated by data, and/or a computer readable storage medium with instructions stored thereon separate from the wireless node, all of which may be accessed by the processor through the bus interface. Alternatively, or in addition, the machine-readable media, or any portion thereof, may be integrated into the processor, such as the case may be with cache and/or general register files. Examples of machine-readable storage media may include, by way of example, RAM (Random Access Memory) , flash memory, ROM (Read Only Memory) , PROM (Programmable Read-Only Memory) , EPROM (Erasable Programmable Read-Only Memory) , EEPROM (Electrically Erasable Programmable Read-Only Memory) , registers, magnetic disks, optical disks, hard drives, or any other suitable storage medium, or any combination thereof. The machine-readable media may be embodied in a computer-program product.

A software module may comprise a single instruction, or many instructions, and may be distributed over several different code segments, among different programs, and across multiple storage media. The computer-readable media may comprise a number of software modules. The software modules include instructions that, when executed by an apparatus such as a processor, cause the processing system to perform various functions. The software modules may include a transmission module and a receiving module. Each software module may reside in a single storage device or be distributed across multiple storage devices. By way of example, a software module may be loaded into RAM from a hard drive when a triggering event occurs. During execution of the software module, the processor may load some of the instructions into cache to increase access speed. One or more cache lines may then be loaded into a general register file for execution by the processor. When referring to the functionality of a software module below, it will be understood that such functionality is implemented by the processor when executing instructions from that software module.

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 (IR) , 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 medium. Disk and disc, as used herein, include compact disc (CD) , laser disc, optical disc, digital versatile disc (DVD) , floppy disk, and

disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Thus, in some aspects computer-readable media may comprise non-transitory computer-readable media (e.g., tangible media) . In addition, for other aspects computer-readable media may comprise transitory computer-readable media (e.g., a signal) . Combinations of the above should also be included within the scope of computer-readable media.

Thus, certain aspects may comprise a computer program product for performing the operations presented herein. For example, such a computer program product may comprise a computer-readable medium having instructions stored (and/or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein, for example, instructions for performing the operations described herein and illustrated in FIG. 7 and/or FIG. 8.

Further, it should be appreciated that modules and/or other appropriate means for performing the methods and techniques described herein can be downloaded and/or otherwise obtained by a user terminal and/or base station as applicable. For example, such a device can be coupled to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, various methods described herein can be provided via storage means (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or floppy disk, etc. ) , such that a user terminal and/or base station can obtain the various methods upon coupling or providing the storage means to the device. Moreover, any other suitable technique for providing the methods and techniques described herein to a device can be utilized.

It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims.

Claims

A method for wireless communication by a user equipment (UE) comprising:

receiving a configuration to report channel state information (CSI) feedback for one or more subbands, the CSI feedback including at least precoding matrix indicator (PMI) feedback and channel quality indicator (CQI) feedback, wherein the configuration indicates a first subband size for the CQI feedback and an indication of PMI granularity;

determining a second subband size for PMI feedback based on the first subband size and the PMI granularity;

determining a density of CSI reference signals (CSI-RS) present in a CQI or PMI subband; and

dropping or reporting at least the CSI feedback for the CQI or PMI subband based on the determined density.
The method of claim 1, further comprising:

determining that a CQI subband is associated with one or more PMI subbands based on the first subband size for CQI feedback, the second subband size for PMI feedback, an actual CQI subband size, and an actual PMI subband size, wherein the actual CQI subband size and the actual PMI subband size are determined based on a frequency resource allocation of a cell or a bandwidth part (BWP) .
The method of claim 1, wherein:

the determined density of the CSI-RS present in a CQI subband is less than a configured CSI-RS density;

the determined density of the CSI-RS present in a first PMI subband is equal to or larger than a configured CSI-RS density; and

the determined density of the CSI-RS present in a second PMI subband is less than a configured CSI-RS density.
The method of claim 3, wherein dropping or reporting at least the CSI feedback for the CQI or PMI subband based on the determination comprises at least one of:

calculating and reporting a first PMI for the first PMI subband, and calculating and reporting the CQI for the subband using the first PMI with the frequency resource of the first PMI subband;

calculating and reporting a first PMI for the first PMI subband, calculating and reporting a second PMI for the second PMI subband using the frequency resources of the CSI-RS, and calculating and reporting CQI for the subband using the first PMI with the frequency resource of the first PMI subband and the frequency resource of CSI-RS in the second PMI subband;

dropping all the PMIs and CQI of the subband;

dropping the entire CSI feedback for all subbands;

not updating the CSI feedback; or

treating it as an error case.
The method of claim 1, wherein:

the determined density of the CSI-RS present in a CQI subband is less than a configured CSI-RS density; and

the determined density of the CSI-RS present in each of PMI subband is less than a configured CSI-RS density.
The method of claim 5, wherein dropping or reporting at least the CSI feedback for the CQI or PMI subband based on the determination comprises at least one of:

calculating and reporting a PMI for the PMI subband using the frequency resources of the CSI-RS, and calculating and reporting CQI for the subband using the PMI with the frequency resource of CSI-RS in the PMI subband;

dropping the all the PMIs and CQI of the subband;

dropping the entire CSI feedback for all subbands;

not updating the CSI feedback; or

treating it as an error case.
A method for wireless communication by a base station (BS) comprising:

configuring a user equipment (UE) to report channel state information (CSI) feedback for one or more subbands, the CSI feedback including at least precoding matrix indicator (PMI) feedback and channel quality indicator (CQI) feedback, wherein the configuration indicates a first subband size for the CQI feedback and indicates a PMI granularity;

determining a second subband size for PMI feedback based on the first subband size and the PMI granularity;

transmitting CSI reference signals (CSI-RS) to the UE in at least a portion of a CQI or PMI subband; and

receiving CSI feedback for the CQI or PMI subband based on the configuration and the at least a portion.
The method of claim 7, further comprising:

determining that a CQI subband is associated with one or more PMI subbands based on the first subband size for CQI feedback, the second subband size for PMI feedback, an actual CQI subband size, and an actual PMI subband size, wherein the actual CQI subband size and the actual PMI subband size are determined based on a frequency resource allocation of a cell or a bandwidth part (BWP) .
The method of claim 7, wherein:

the density of the CSI-RS transmitted in a CQI subband is less than a configured CSI-RS density;

the density of the CSI-RS transmitted in a first PMI subband is equal to or larger than a configured CSI-RS density; and

the density of the CSI-RS transmitted in a second PMI subband is less than a configured CSI-RS density.
The method of claim 9, wherein receiving CSI feedback comprises at least one of:

receiving a first PMI for the first PMI subband and CQI feedback for the subband calculated using the first PMI with the frequency resource of the first PMI subband;

receiving a first PMI for the first PMI subband, receiving a second PMI for the second PMI subband using the frequency resources of the CSI-RS, and receiving a CQI for the subband using the first PMI with the frequency resource of the first PMI subband and the frequency resource of CSI-RS in the second PMI subband;

receiving a CSI feedback without any PMI and CQI of the subband;

not receiving CSI feedback for all subbands; or

receiving a CSI feedback without update.
The method of claim 7, wherein:

the density of the CSI-RS transmitted in a CQI subband is less than a configured CSI-RS density; and

the density of the CSI-RS transmitted in each of PMI subband is less than a configured CSI-RS density.
The method of claim 11, wherein monitoring CSI feedback comprises at least one of:

receiving a PMI for the PMI subband using the frequency resources of the CSI-RS, and receiving CQI for the subband using the PMI with the frequency resource of CSI-RS in the PMI subband;

receiving a CSI feedback without any PMI and CQI of the subband;

not receiving CSI feedback for all subbands; or

receiving CSI feedback without update.
The method of claim 7, wherein configuring the UE to report CSI feedback for the one or more subbands comprises configuring a CSI report, wherein the configuration comprises at least one of:

each CQI subband configured for the CSI report has full CSI-RS presence;

each PMI subband configured for the CSI report has full CSI-RS presence; or

a combination thereof.
An apparatus for wireless communication, comprising:

a memory; and

at least one processor coupled with the memory and configured to:

receive a configuration to report channel state information (CSI) feedback for one or more subbands, the CSI feedback including at least precoding matrix indicator (PMI) feedback and channel quality indicator (CQI) feedback, wherein the configuration indicates a first subband size for the CQI feedback and an indication of PMI granularity;

determine a second subband size for PMI feedback based on the first subband size and the PMI granularity;

determine a density of CSI reference signals (CSI-RS) present in a CQI or PMI subband; and

drop or report at least the CSI feedback for the CQI or PMI subband based on the determined density.
An apparatus for wireless communication, comprising:

a memory; and

at least one processor coupled with the memory and configured to:

configure a user equipment (UE) to report channel state information (CSI) feedback for one or more subbands, the CSI feedback including at least precoding matrix indicator (PMI) feedback and channel quality indicator (CQI) feedback, wherein the configuration indicates a first subband size for the CQI feedback and indicates a PMI granularity;

determine a second subband size for PMI feedback based on the first subband size and the PMI granularity;

transmit CSI reference signals (CSI-RS) to the UE in at least a portion of a CQI or PMI subband; and

receive CSI feedback for the CQI or PMI subband based on the configuration and the at least a portion.
An apparatus for wireless communication, comprising:

means for receiving a configuration to report channel state information (CSI) feedback for one or more subbands, the CSI feedback including at least precoding matrix indicator (PMI) feedback and channel quality indicator (CQI) feedback, wherein the configuration indicates a first subband size for the CQI feedback and an indication of PMI granularity;

means for determining a second subband size for PMI feedback based on the first subband size and the PMI granularity;

means for determining a density of CSI reference signals (CSI-RS) present in a CQI or PMI subband; and

means for dropping or reporting at least the CSI feedback for the CQI or PMI subband based on the determined density.
An apparatus for wireless communication, comprising:

means for configuring a user equipment (UE) to report channel state information (CSI) feedback for one or more subbands, the CSI feedback including at least precoding matrix indicator (PMI) feedback and channel quality indicator (CQI) feedback, wherein the configuration indicates a first subband size for the CQI feedback and indicates a PMI granularity;

means for determining a second subband size for PMI feedback based on the first subband size and the PMI granularity;

means for transmitting CSI reference signals (CSI-RS) to the UE in at least a portion of a CQI or PMI subband; and

means for receiving CSI feedback for the CQI or PMI subband based on the configuration and the at least a portion.
A computer readable medium storing computer executable code thereon for wireless communication, comprising:

code for receiving a configuration to report channel state information (CSI) feedback for one or more subbands, the CSI feedback including at least precoding matrix indicator (PMI) feedback and channel quality indicator (CQI) feedback, wherein the configuration indicates a first subband size for the CQI feedback and an indication of PMI granularity;

code for determining a second subband size for PMI feedback based on the first subband size and the PMI granularity;

code for determining a density of CSI reference signals (CSI-RS) present in a CQI or PMI subband; and

code for dropping or reporting at least the CSI feedback for the CQI or PMI subband based on the determined density.
A computer readable medium storing computer executable code thereon for wireless communication, comprising:

code for configuring a user equipment (UE) to report channel state information (CSI) feedback for one or more subbands, the CSI feedback including at least precoding matrix indicator (PMI) feedback and channel quality indicator (CQI) feedback, wherein the configuration indicates a first subband size for the CQI feedback and indicates a PMI granularity;

code for determining a second subband size for PMI feedback based on the first subband size and the PMI granularity;

code for transmitting CSI reference signals (CSI-RS) to the UE in at least a portion of a CQI or PMI subband; and

code for receiving CSI feedback for the CQI or PMI subband based on the configuration and the at least a portion.