WO2021243632A1

WO2021243632A1 - Decoupled port selection and coefficients reporting

Info

Publication number: WO2021243632A1
Application number: PCT/CN2020/094291
Authority: WO
Inventors: Chenxi HAO; Yu Zhang; Lei Xiao; Hao Xu; Liangming WU
Original assignee: Qualcomm Incorporated
Priority date: 2020-06-04
Filing date: 2020-06-04
Publication date: 2021-12-09

Abstract

Certain aspects of the present disclosure provide a method for channel state information (CSI) reporting. The method comprising: measuring the first channel state information reference signals (CSI-RS) from a network entity; selecting a preferred subset of CSI-RS ports based on the first CSI-RS measurements and selection criteria; sending a first report indicating the preferred subset of CSI-RS ports. Aspects of the present disclosure may help provide efficient CSI reporting, in terms of reporting overhead, by decoupling port/basis selection and coefficient reporting.

Description

DECOUPLED PORT SELECTION AND COEFFICIENTS REPORTING

BACKGROUND

Field of the Disclosure

Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for channel state information (CSI) feedback reporting.

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.

In some examples, a wireless multiple-access communication system may include a number of base stations (BSs) , which are each capable of simultaneously supporting communication for multiple communication devices, otherwise known as user equipments (UEs) . In an LTE or LTE-Anetwork, a set of one or more base stations may define an eNodeB (eNB) . In other examples (e.g., in a next generation, a new radio (NR) , or 5G network) , a wireless multiple access communication system may include a number of distributed units (DUs) (e.g., edge units (EUs) , edge nodes (ENs) , radio heads (RHs) , smart radio heads (SRHs) , transmission reception points (TRPs) , etc. ) in communication with a number of central units (CUs) (e.g., central nodes (CNs) , access node controllers (ANCs) , etc. ) , where a set of one or more DUs, in communication with a CU, may define an access node (e.g., which may be referred to as a BS, 5G NB, next generation NodeB (gNB or gNodeB) , transmission reception point (TRP) , etc. ) . A BS or DU may communicate with a set of UEs on downlink channels (e.g., for transmissions from a BS or DU to a UE) and uplink channels (e.g., for transmissions from a UE to BS or DU) .

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. NR (e.g., new radio or 5G) 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 communications between access points and stations in a wireless network.

Certain aspects of the disclosure relate to a method for wireless communication by a user equipment (UE) . The method generally includes measuring first channel state information reference signals (CSI-RS) from a network entity selecting a preferred subset of CSI-RS ports based on the first CSI-RS measurements and selection criteria comprising at least one of: a power of summation or linear average, across a frequency domain, of the channel measurement or the channel on which a first CSI-RS port is conveyed, a power at a delay zero of a power-delay-profile, across the frequency domain, of the channel measurement or the channel on which the first CSI- RS port is conveyed, or a power of a shortened channel on which the first CSI-RS port is conveyed, and sending a first report indicating the preferred subset of CSI-RS ports.

Certain aspects of the disclosure relate to a method for wireless communication by a network entity. The method generally includes transmitting first channel state information reference signals (CSI-RS) to a user equipment (UE) and receiving a first report from the UE, indication a preferred subset of CSI-RS ports based on UE measurements of the first CSI-RS and selection criteria comprising at least one of: a power of summation or linear average, across a frequency domain, of the channel measurement or the channel on which a first CSI-RS port is conveyed, a power at a delay zero of a power-delay-profile, across the frequency domain, of the channel measurement or the channel on which the first CSI-RS port is conveyed, or a power of a shortened channel on which the first CSI-RS port is conveyed.

Aspects of the present disclosure also provide various apparatuses, means, and computer readable including instructions for performing the operations 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 showing examples for implementing a communication protocol stack in the example RAN architecture, in accordance with certain aspects of the present disclosure.

FIG. 3 is a block diagram conceptually illustrating a design of an example base station (BS) and user equipment (UE) , in accordance with certain aspects of the present disclosure.

FIG. 4 illustrates an example of a frame format for a telecommunication system, in accordance with certain aspects of the present disclosure.

FIG. 5 illustrates a conceptual example of precoder matrices, in accordance with certain aspects of the present disclosure.

FIG. 6 is a call flow diagram illustrating a first example of Type II CSI feedback.

FIG. 7 is a call flow diagram illustrating a second example of Type II CSI feedback.

FIGs. 8A and 8B illustrate example ports and layer to port mapping.

FIG. 9 illustrates example operations for wireless communication by a UE, in accordance with certain aspects of the present disclosure.

FIG. 10 illustrates example operations for wireless communication by a network entity, in accordance with certain aspects of the present disclosure.

FIG. 11 illustrates example timing for first and second CSI-RS, in accordance with certain 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 relate to wireless communications, and more particularly, to techniques for performing efficient CSI feedback reporting. In some cases, a UE may report a preferred set of CSI-RS ports selected based on first CSI-RS measurements and separately report linear combination coefficients based on second CSI-RS measurements.

The following description provides examples, 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.

The techniques described herein may be used for various wireless communication technologies, such as LTE, CDMA, TDMA, FDMA, OFDMA, SC-FDMA 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) .

New Radio (NR) is an emerging wireless communications technology under development in conjunction with the 5G Technology Forum (5GTF) . 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are 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) . The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies. For clarity, while aspects may be described herein using terminology commonly associated with 3G and/or 4G wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems, such as 5G and later, including NR technologies.

New radio (NR) access (e.g., 5G technology) 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.

Example Wireless Communications System

FIG. 1 illustrates an example wireless communication network 100 in which aspects of the present disclosure may be performed. For example, a UE 120 in the wireless communication network 100 may include a CSI reporting module configured to perform (or assist the UE 120 in performing) operations 900 described below with reference to FIG. 10. Similarly, a base station 120 (e.g., a gNB) may be configured to perform (or assist the base station 110 in performing) operations 900 described below with reference to FIG. 9 to process CSI reports received from a UE (performing operations 800 of FIG. 8) .

As illustrated in FIG. 1, the wireless communication network 100 may include a number of base stations (BSs) 110 and other network entities. A BS may be a station that communicates with user equipment (UE) . Each BS 110 may provide communication coverage for a particular geographic area. 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 next generation NodeB (gNB or gNodeB) , NR BS, 5G NB, access point (AP) , or transmission reception point (TRP) may be interchangeable. In some examples, a cell may not necessarily be stationary, and the geographic area of the cell may move according to the location of a mobile BS. In some examples, the base stations may be interconnected to one another and/or to one or more other base stations or network nodes (not shown) in wireless communication network 100 through various types of backhaul interfaces, such as a direct physical connection, a wireless connection, a virtual network, or the like using any suitable transport network.

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. In some cases, NR or 5G RAT networks may be deployed.

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. 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 (e.g., three) cells.

Wireless communication network 100 may also include relay stations. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., a BS or a UE) and sends a transmission of the data and/or other information to a downstream station (e.g., a UE or a BS) . A relay station may also be a UE that relays transmissions for other UEs. In the example shown in FIG. 1, a relay station 110r may communicate with the BS 110a and a UE 120r in order to facilitate communication between the BS 110a and the UE 120r. A relay station may also be referred to as a relay BS, a relay, etc.

Wireless communication network 100 may be a heterogeneous network that includes BSs of different types, e.g., macro BS, pico BS, femto BS, relays, etc. These different types of BSs may have different transmit power levels, different coverage areas, and different impact on interference in the wireless communication network 100. For example, macro BS may have a high transmit power level (e.g., 20 Watts) whereas pico BS, femto BS, and relays may have a lower transmit power level (e.g., 1 Watt) .

Wireless communication network 100 may support synchronous or asynchronous operation. For synchronous operation, the BSs may have similar frame timing, and transmissions from different BSs may be approximately aligned in time. For asynchronous operation, the BSs may have different frame timing, and transmissions from different BSs may not be aligned in time. The techniques described herein may be used for both synchronous and asynchronous operation.

A network controller 130 may couple to a set of BSs and provide coordination and control for these BSs. The network controller 130 may communicate with the BSs 110 via a backhaul. The BSs 110 may also communicate with one another (e.g., directly or indirectly) via wireless or wireline backhaul.

The UEs 120 (e.g., 120x, 120y, etc. ) may be dispersed throughout the wireless communication network 100, and each UE may be stationary or mobile. 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.

Certain wireless networks (e.g., LTE) utilize orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, etc. Each subcarrier may be modulated with data. In general, modulation symbols are 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 (K) may be dependent on the system bandwidth. For example, the spacing of the subcarriers may be 15 kHz and the minimum resource allocation (called a “resource block” (RB) ) may be 12 subcarriers (or 180 kHz) . Consequently, the nominal Fast Fourier Transfer (FFT) size may be equal to 128, 256, 512, 1024 or 2048 for system bandwidth of 1.25, 2.5, 5, 10, or 20 megahertz (MHz) , respectively. The system bandwidth may also be partitioned into sub-bands. For example, a sub-band may cover 1.08 MHz (i.e., 6 resource blocks) , and there may be 1, 2, 4, 8, or 16 sub-bands for system bandwidth of 1.25, 2.5, 5, 10 or 20 MHz, respectively.

Communication systems such as NR may utilize OFDM with a cyclic prefix (CP) on the uplink and downlink and include support for half-duplex operation using time division duplex (TDD) . Beamforming may be supported 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 4 streams per UE. Multi-layer transmissions with up to 4 streams per UE may be supported. Aggregation of multiple cells may be supported with up to 8 serving cells.

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 FIG. 1, a solid line with double arrows indicates desired transmissions between a UE and a serving BS, which is a BS designated to serve the UE on the downlink and/or uplink. A finely dashed line with double arrows indicates interfering transmissions between a UE and a BS.

FIG. 2 illustrates a diagram showing examples for implementing a communications protocol stack in a RAN (e.g., such as the RAN 100) , according to aspects of the present disclosure. The illustrated communications protocol stack 200 may be implemented by devices operating in a wireless communication system, such as a 5G NR system (e.g., the wireless communication network 100) . In various examples, the layers of the protocol stack 200 may be implemented as separate modules of software, portions of a processor or ASIC, portions of non-collocated devices connected by a communications link, or various combinations thereof. Collocated and non-collocated implementations may be used, for example, in a protocol stack for a network access device or a UE. As shown in FIG. 2, the system may support various services over one or more protocols. One or more protocol layers of the protocol stack 200 may be implemented by the AN and/or the UE.

As shown in FIG. 2, the protocol stack 200 is split in the AN (e.g., BS 110 in FIG. 1) . The RRC layer 205, PDCP layer 210, RLC layer 215, MAC layer 220, PHY layer 225, and RF layer 230 may be implemented by the AN. For example, the CU-CP may implement the RRC layer 205 and the PDCP layer 210. A DU may implement the RLC layer 215 and MAC layer 220. The AU/RRU may implement the PHY layer (s) 225 and the RF layer (s) 230. The PHY layers 225 may include a high PHY layer and a low PHY layer.

The UE may implement the entire protocol stack 200 (e.g., the RRC layer 205, the PDCP layer 210, the RLC layer 215, the MAC layer 220, the PHY layer (s) 225, and the RF layer (s) 230) .

FIG. 3 illustrates example components of BS 110 and UE 120 (as depicted in FIG. 1) , which may be used to implement aspects of the present disclosure. For example, antennas 352,

processors

366, 358, 364, and/or controller/processor 380 of the UE 120 may be configured (or used) to perform operations 800 of FIG. 8 and/or antennas 334,

processors

320, 330, 338, and/or controller/processor 340 of the BS 110 may be configured (or used) to perform operations 900 described below with reference to FIG. 9.

At the BS 110, a transmit processor 320 may receive data from a data source 312 and control information from a controller/processor 340. 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. The processor 320 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The processor 320 may also generate reference symbols, e.g., for the primary synchronization signal (PSS) , secondary synchronization signal (SSS) , and cell-specific reference signal (CRS) . A transmit (TX) multiple-input multiple-output (MIMO) processor 330 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) 332a through 332t. Each modulator 332 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 332a through 332t may be transmitted via the antennas 334a through 334t, respectively.

At the UE 120, the antennas 352a through 352r may receive the downlink signals from the base station 110 and may provide received signals to the demodulators (DEMODs) in transceivers 354a through 354r, respectively. Each demodulator 354 may condition (e.g., filter, amplify, down-convert, 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 356 may obtain received symbols from all the demodulators 354a through 354r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor 358 may process (e.g., demodulate, de-interleave, and decode) the detected symbols, provide decoded data for the UE 120 to a data sink 360, and provide decoded control information to a controller/processor 380.

In a MIMO system, a transmitter (e.g., BS 120) includes multiple transmit antennas 354a through 354r, and a receiver (e.g., UE 110) includes multiple receive antennas 352a through 352r. Thus, there are a plurality of signal paths 394 from the transmit antennas 354a through 354r to the receive antennas 352a through 352r. Each of the transmitter and the receiver may be implemented, for example, within a UE 110, a BS 120, or any other suitable wireless communication device.

The use of such multiple antenna technology enables the wireless communication system to exploit the spatial domain to support spatial multiplexing, beamforming, and transmit diversity. Spatial multiplexing may be used to transmit different streams of data, also referred to as layers, simultaneously on the same time-frequency resource. The data streams may be transmitted to a single UE to increase the data rate or to multiple UEs to increase the overall system capacity, the latter being referred to as multi-user MIMO (MU-MIMO) . This is achieved by spatially precoding each data stream (i.e., multiplying the data streams with different weighting and phase shifting) and then transmitting each spatially precoded stream through multiple transmit antennas on the downlink. The spatially precoded data streams arrive at the UE (s) with different spatial signatures, which enables each of the UE (s) to recover the one or more data streams destined for that UE. On the uplink, each UE transmits a spatially precoded data stream, which enables the base station to identify the source of each spatially precoded data stream.

The number of data streams or layers corresponds to the rank of the transmission. In general, the rank of the MIMO system is limited by the number of transmit or receive antennas, whichever is lower. In addition, the channel conditions at the UE, as well as other considerations, such as the available resources at the base station, may also affect the transmission rank. For example, the rank (and therefore, the number of transmission layers) assigned to a particular UE on the downlink may be determined based on the rank indicator (RI) transmitted from the UE to the base station. The RI may be determined based on the antenna configuration (e.g., the number of transmit and receive antennas) and a measured signal-to-interference-and-noise ratio (SINR) on each of the receive antennas. The RI may indicate, for example, the number of layers that may be supported under the current channel conditions. The base station may use the RI, along with resource information (e.g., the available resources and amount of data to be scheduled for the UE) , to assign a transmission rank to the UE.

On the uplink, at UE 120, a transmit processor 364 may receive and process data (e.g., for the physical uplink shared channel (PUSCH) ) from a data source 362 and control information (e.g., for the physical uplink control channel (PUCCH) from the controller/processor 380. The transmit processor 364 may also generate reference symbols for a reference signal (e.g., for the sounding reference signal (SRS) ) . The symbols from the transmit processor 364 may be precoded by a TX MIMO processor 366 if applicable, further processed by the demodulators in transceivers 354a through 354r (e.g., for SC-FDM, etc. ) , and transmitted to the base station 110. At the BS 110, the uplink signals from the UE 120 may be received by the antennas 334, processed by the modulators 332, detected by a MIMO detector 336 if applicable, and further processed by a receive processor 338 to obtain decoded data and control information sent by the UE 120. The receive processor 338 may provide the decoded data to a data sink 339 and the decoded control information to the controller/processor 340.

The controllers/

processors

340 and 380 may direct the operation at the BS 110 and the UE 120, respectively. The processor 340 and/or other processors and modules at the BS 110 may perform or direct the execution of processes for the techniques described herein. The

memories

342 and 382 may store data and program codes for BS 110 and UE 120, respectively. A scheduler 344 may schedule UEs for data transmission on the downlink and/or uplink.

FIG. 4 is a diagram showing an example of a frame format 400 for NR. The transmission timeline for each of the downlink and uplink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 ms) and may be partitioned into 10 subframes, each of 1 ms, with indices of 0 through 9. Each subframe may include a variable number of slots depending on the subcarrier spacing. Each slot may include a variable number of symbol periods (e.g., 7 or 14 symbols) depending on the subcarrier spacing. The symbol periods in each slot may be 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.

In NR, a synchronization signal (SS) block is transmitted. The SS block includes a PSS, a SSS, and a two symbol PBCH. The SS block can be transmitted in a fixed slot location, such as the symbols 0-3 as shown in FIG. 4. The PSS and SSS may be used by UEs for cell search and acquisition. The PSS may provide half-frame timing, the SS may provide the CP length and frame timing. The PSS and SSS may provide the cell identity. The PBCH carries some basic system information, such as downlink system bandwidth, timing information within radio frame, SS burst set periodicity, system frame number, etc. The SS blocks may be organized into SS bursts to support beam sweeping. Further system information such as, remaining minimum system information (RMSI) , system information blocks (SIBs) , other system information (OSI) can be transmitted on a physical downlink shared channel (PDSCH) in certain subframes. The SS block can be transmitted up to sixty-four times, for example, with up to sixty-four different beam directions for mmW. The up to sixty-four transmissions of the SS block are referred to as the SS burst set. SS blocks in an SS burst set are transmitted in the same frequency region, while SS blocks in different SS bursts sets can be transmitted at different frequency locations.

A UE may operate in various radio resource configurations, including a configuration associated with transmitting pilots using a dedicated set of resources (e.g., a radio resource control (RRC) dedicated state, etc. ) or a configuration associated with transmitting pilots using a common set of resources (e.g., an RRC common state, etc. ) . When operating in the RRC dedicated state, the UE may select a dedicated set of resources for transmitting a pilot signal to a network. When operating in the RRC common state, the UE may select a common set of resources for transmitting a pilot signal to the network. In either case, a pilot signal transmitted by the UE may be received by one or more network access devices, such as an AN, or a DU, or portions thereof. Each receiving network access device may be configured to receive and measure pilot signals transmitted on the common set of resources, and also receive and measure pilot signals transmitted on dedicated sets of resources allocated to the UEs for which the network access device is a member of a monitoring set of network access devices for the UE. One or more of the receiving network access devices, or a CU to which receiving network access device (s) transmit the measurements of the pilot signals, may use the measurements to identify serving cells for the UEs, or to initiate a change of serving cell for one or more of the UEs.

Example CSI Report Configuration

Channel state information (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 measured at the receiver, quantized, and fed back to the transmitter.

The time and frequency resources that can be used by the UE to report CSI are controlled by a base station (e.g., gNB) . CSI may include Channel Quality Indicator (CQI) , precoding matrix indicator (PMI) , CSI-RS resource indicator (CRI) , SS/PBCH Block Resource indicator (SSBRI) , layer indicator (LI) , rank indicator (RI) and/or L1- RSRP. However, as described below, additional or other information may be included in the report.

The base station may configure UEs for CSI reporting. For example, the BS configures the UE with a CSI report configuration or with multiple CSI report configurations. The CSI report configuration may be provided to the UE via higher layer signaling, such as radio resource control (RRC) signaling (e.g., CSI-ReportConfig) . The CSI report configuration may be associated with CSI-RS resources for channel measurement (CM) , interference measurement (IM) , or both. The CSI report configuration configures CSI-RS resources for measurement (e.g., CSI-ResourceConfig) . 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 the Type II codebook, 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. For the PMI of any type, there can be wideband (WB) PMI and/or subband (SB) PMI as configured.

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 on physical uplink control channel (PUCCH) may be triggered via RRC. Semi-persistent CSI reporting on physical uplink control channel (PUCCH) may be activated via 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 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 on which the triggered CSI-RS resources (associated with the CSI report configuration) is conveyed. 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.

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.

In certain systems, the UE can be configured via higher layer signaling (e.g., in the CSI report configuration) with one out of two possible subband sizes (e.g., reportFreqConfiguration contained in a CSI-ReportConfig) which indicates a frequency granularity of the CSI report, where a subband may be defined as

contiguous physical resource blocks (PRBs) and depends on the total number of PRBs in the bandwidth part. The UE may further receive an indication of the subbands for which the CSI feedback is requested. In some examples, a subband mask is configured for the requested subbands for CSI reporting. The UE computes precoders for each requested subband and finds the PMI that matches the computed precoder on each of the subbands.

Compressed CSI Feedback Coefficient Reporting

As discussed above, a user equipment (UE) may be configured for channel state information (CSI) reporting, for example, by receiving a CSI configuration message from the base station. 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. For example, the precoder matrix W _r for layer r includes the W ₁ matrix, reporting a subest of selected beams using spatial compression and the W _2, r matrix, reporting (for cross-polarization) the linear combination coefficients for the selected beams (2L) across the configured FD units:

where

where b _i is the selected beam, c _i is the set of linear combination coefficients (i.e., entries of W _2, r matrix) , L is the number of selected spatial beams, and N ₃ corresponds to the number of frequency units (e.g., subbands, resource blocks (RBs) , etc. ) . In certain configurations, L is RRC configured. The precoder is based on a linear combination of DFT beams. The Type II codebook may improve MU-MIMO performance. In some configurations considering there are two polarizations, the W _2, r matrix has size 2L X N ₃.

In certain systems (e.g., Rel-16 5G NR) , the UE may be configured to report FD compressed precoder feedback to reduce overhead of the CSI report. As shown in FIG. 5, 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 520 consists of the linear combination coefficients (amplitude and co-phasing) , where each element represents the coefficient of a tap for a beam. The

matrix 520 as shown is 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 520. 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 520 corresponds to a row of

matrix 530. In the example shown, both the

matrix 520 at layer 0 and the

matrix 550 at layer 1 are 2L X M.

The

matrix 530 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 530 at layer 0 and the

matrix 560 at layer 1 include M=4 FD basis (illustrated as shaded rows) 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.

Example Decoupled Port Selection and Coefficients Reporting

Some deployments (e.g., NR Release 16 and 17 systems) support enhancements to CSI based feedback that are designed to exploit directional (angle) and delay reciprocity (meaning the same or similar conditions may be assumed to be observed on the uplink and downlink) . FIGs. 6 and 7 illustrate examples of such CSI based feedback where a gNB obtains the following terms based on a combination of SRS measurements taken at the gNB and feedback from the UE:

b _i: spatial domain basis;

frequency domain basis; and

c _i, m: linear combination coefficients.

FIG. 6 is a call flow diagram illustrating an example of Type II port-selection CSI feedback (according to Release 16) . The UE transmits SRS that the gNB measures to determine a spatial domain basis (b _i) . Assuming spatial reciprocity, the gNB precodes CSI-RS via the spatial domain basis (b _i) , wherein each CSI-RS port may be precoded via a particular spatial domain basis. Based on measurements of the precoded CSI-RS, the UE determines preferred CSI-RS ports and reports them and also reports other terms (c _i, m and

) used to combine the preferred CSI-RS ports.

FIG. 7 is a call flow diagram illustrating another example of Type II CSI feedback (according to Release 17) . In this case, the gNB determines both (b _i) and

based on SRS measurements. Assuming both spatial and delay reciprocity, the gNB precodes CSI-RS via the spatial domain basis (b _i) and the frequency domain basis

wherein each CSI-RS port maybe precoded via a particular pair of a spatial domain basis and a frequency domain basis. Based on measurements of the precoded CSI-RS, the UE determines preferred CSI-RS ports and reports them and also reports c _i, m used to combine the preferred CSI-RS ports.

In scenarios where there is an ideal spatial and delay reciprocity in the uplink and downlink frequency band, such as time division duplexing (TDD) scenarios, the CSI reporting of FIG. 7 may have certain benefits. Examples of such benefits include lower reporting overhead, lower UE complexity, and higher performance due to finer resolution of frequency domain basis and higher performance due to better spatial and frequency bases (gNB can use bases other than DFT bases, e.g., SVD bases, to gain more performance benefit) .

For the frequency selective precoding shown in FIG. 7, on an FD unit (RB or subband) , the precoder of a CSI-RS port is formed by a pair of an SD basis (or spatial domain transmission filter) b _i and an FD basis (frequency domain transmission filter/weight) f _m. When generating a wideband (WB) CSI report, for a given port p, the UE observes:

on FD unit n;

based on which the UE calculates CSI. In this equation, H is the wireless channel between UE and gNB without precoding, where i (p) and m (p) denote the indices of the spatial and frequency bases applied on port p, respectively.

For each layer, the UE selects a subset of total ports, and reports a single coefficient per port across the frequency band. The PMI for a certain layer on any of the N ₃ FD units is given as:

where

is of size P×1 with only one “1” in row i _k, P is the total number of CSI-RS ports. The UE reports

and

or a subset of

wherein the unreported coefficients are set to 0, K ₀ is the maximum number of ports allowed to be selected for linear combination.

As illustrated in FIG. 8, in current standards, the CSI-RS port index in each resource starts from 3000. The UE calculates CQI assuming a virtual PDSCH:

and the actual precoder of the virtual PDSCH is given as:

CSI-RS port precoding may be less than ideal for various reasons. In certain conditions, such as frequency division duplexing, the UL and DL band are mismatched so that UL/DL reciprocity may be poor which may impact the accuracy of precoding. For example, the gNB may determine the SD/FD combination used to precode each CSI-RS port. However, the UL/DL reciprocity may be poor considering UL/DL band mismatch and Rx/Tx calibration errors and/or practical sounding errors.

In an effort to compensate the poor reciprocity, the gNB may have to emulate more CSI-RS ports (32 ports) for each UE. While the gNB may determine a dominant SD-FD combination based on UL channel, but it may be biased from the dominant SD-FD combination in the DL channel (that biases the CSI reporting from the UE) . While emulating more CSI-RS ports could give the UE more options to select the dominant ports (dominant SD-FD combination) , this comes at a cost in terms of resource consumption: increased RS overhead, as the precoded CSI-RS is UE-specific.

Aspects of the present disclosure may help address these issues, however, providing a two-stage CSI report framework in some cases, decoupling port/basis selection and coefficient reporting. In some cases, a UE may report a preferred set of CSI-RS ports selected based on first CSI-RS measurements and separately report linear combination coefficients based on second CSI-RS measurements.

FIG. 9 illustrates example operations 900 for wireless communication by a UE for CSI reporting, in accordance with certain aspects of the present disclosure. Operations 900 may be performed, for example, by a UE 120 of FIG. 1 or FIG. 3.

Operations 900 begin, at 902, by measuring first channel state information reference signals (CSI-RS) from a network entity. At 904, the UE selects a preferred subset of CSI-RS ports based on the first CSI-RS measurements and selection criteria. The selection criteria may comprise at least one of:

1. a power of summation across a frequency domain, of the channel measurement of a first CSI-RS port,

2. a power of linear average, across a frequency domain, of the channel measurement of a first CSI-RS port,

3. a power of summation across a frequency domain, of the channel on which a first CSI-RS port is conveyed,

4. a power of linear average, across a frequency domain, of the channel on which a first CSI-RS port is conveyed,

5. a power at a delay zero of a power-delay-profile of the channel on which the first CSI-RS port is conveyed,

6. a power at a delay zero of a power-delay-profile of the channel measurement of the first CSI-RS port, or

7. a power of a shortened channel on which the first CSI-RS port is conveyed.

At 906, the UE sends a first report indicating the preferred subset of CSI-RS ports.

FIG. 10 is a flow diagram illustrating example operations 1000 for wireless communication by a network entity (e.g., a base station, such as an eNB or gNB) , in accordance with certain aspects of the present disclosure. Operations 1000 may be performed, for example, by BS 110 of FIG. 1 or 3 to transmit CSI-RS to a UE 120 for CSI reporting (in accordance with operations 900 of FIG. 9) .

Operations 1000 begin, at 1002, by transmitting first channel state information reference signals (CSI-RS) to a user equipment (UE) . At 1004, the network entity receives a first report from the UE, indication a preferred subset of CSI-RS ports based on UE measurements of the first CSI-RS and selection criteria comprising at least one of: a power of summation or linear average, across a frequency domain, of the channel measurement or the channel on which a first CSI-RS port is conveyed, a power at a delay zero of a power-delay-profile, across the frequency domain, of the channel measurement or the channel on which the first CSI-RS port is conveyed, or a power of a shortened channel on which the first CSI-RS port is conveyed.

In some cases, using a two-stage CSI report framework, the UE may decouple port/basis selection and coefficient reporting. In a first stage, the UE may indicate a port selection or SD-FD basis selection in a first CSI report (CSI report 1) .

The preferred ports or SD-FD basis may be selected based on one or more specific criteria. For example, if the gNB transmits CSI-RS precoded by SD-FD basis (as shown in FIG. 7) , the UE may simply report the port-selection. If the gNB transmits CSI-RS precoded by an SD basis (and not FD basis) , the UE may report the FD basis for each SD basis (i.e., each CSI-RS port) . As yet another example, if the gNB transmits non-precoded CSI-RS, the UE may report a preferred SD basis and the FD bases for each SD basis.

In a first stage, the UE may indicate the PMI comprising port selection if CSI-RS is precoded by SD-FD basis, or comprising FD basis and the associated port-selection if the CSI-RS is precoded by SD basis, or comprising SD and FD bases if the CSI-RS is non-precoded. In some cases, the CSI-RS on which CSI report 2 is based may be different from the CSI-RS associated with CSI report 1. In this case, the CSI-RS associated with CSI report 2 may be precoded based on the port-selection and basis reporting (if applicable) , and the UE may indicate the PMI in stage 2 comprising at least linear combination coefficients used to combine the CSI-RS ports associated in stage 2.

In other cases, the CSI-RS for CSI report 2 may be same as the CSI-RS for CSI report 1. In such cases, the linear combination coefficients are applied to the ports reported in CSI report 1.

As shown in FIG. 11, in some cases, the periodicity of CSI report 1 may have a longer corresponding cycle than CSI report 2. This may be because port-selection and basis selection are more likely longer-term statistics.

In case different CSI-RS are used for CSI-RS 1 and CSI-RS 2, the CSI-RS 1 associated with CSI report 1 may be common to all UEs in the cell (or common to a group of UEs) , while the CSI-RS 2 associated with CSI report 2 may be UE-specific. In such cases, the number of ports in CSI-RS 2 may be smaller than the number of ports in CSI-RS 1 (For instance, in stage 1, there are 64 ports to be measured by all UEs. Then, each UE selects their preferred 8 ports. As the channel of different UEs may be different, the selected 8 ports may be different for different UEs, e.g., UE 1 selects port 1-8, UE 2 selects 9-16. In the second stage, the gNB may transmit 8 ports to UE1 using the same precoder as ports 1-8 in stage 1 and transmit 8 ports to UE2 using the same precoder as ports 9-16 in stage 1) and, as noted above, the periodicity CSI-RS 1 may have a longer cycle than CSI-RS 2.

If time domain measurement restriction is not configured for CSI 1, the UE is expected to measure and filter multiple CSI-RS 1 transmissions before a CSI reference resource to obtain long term statistics. If time domain measurement restriction is configured for CSI 1, the UE is expected to measure only the most recent CSI-RS 1 before the CSI reference resource. In this case, the gNB may change the precoder CSI-RS 1 in each transmission.

As noted above, the UE may select ports/bases based on various criteria. For CSI reporting, current systems (e.g., according to current standard specifications) typically only support single resource reporting and each resource has up to 32 ports. This limitation may be insufficient as the number of ports may be greater than 32 in stage 1 reporting if cell-specific (common to all UEs) CSI-RS is used.

For beam management (BM) reporting, current systems support a “cri-RSRP” based reporting, wherein the CSI report may indicate a CSI-RS resource set with up to 64 resources, and each resource has single port. UE is allowed to report up to 4 resources. This limitation, again, may be insufficient as the UE may need to select at least 8 ports. This may be insufficient with CSI-RSRP conventionally defined as “the linear average over the power contributions (in [W] ) of the resource elements of the antenna port (s) that carry CSI reference signals configured for RSRP measurements within the considered measurement frequency bandwidth in the configured CSI-RS occasions. ”

Mathematically, RSRP may be expressed as:

where

represents the channel estimate/CSI-RS port p on FD unit n (e.g., Res, or RBs) and N is the total number of FD units (e.g., REs) . Since two ports may be precoded with same SD basis but different FD bases, these two ports may have same RSRP, which is why the conventional RSRP criteria may be insufficient to differentiate the ports.

In some cases, port selection criteria may use a different criteria. For example, a UE may calculate and report CSI-RS port/resource-selection based on a criteria of “the power of summation or linear average, across frequency domain, of the channel measurement or the channel on which CSI-RS port is conveyed” or “the power at delay zero of its power-delay-profile” or “the power of shortened channel. ” Mathematically, this criteria may be expressed as

where

represents the channel estimate/CSI-RS port p on FD unit n (e.g., REs) and N is the total number of FD units (e.g., Res, or RBs) . This may be generally expressed as “the power of summation or linear average of the channel measurement or the channel on which CSI-RS port is conveyed across all the REs carrying the CSI-RS port” or “the power of summation or linear average of the channel measurement or the channel on which CSI-RS port is conveyed across all the reference REs. ” For each port, the reference RE may be the first subcarrier of each RB on the first symbol carrying the CSI-RS port.

In some cases, the UE may be signaled an indication of what quantity to report. For example, the UE may receive a new report quantity, such as:

CRI only;

CRI-PowerAverageChannel;

CRI-PowerDelayZero; or

CRI-PowerShortendChannel.

In other words, the UE may determine the criteria for port-selection based on the new report quantity indicated.

In some cases, the gNB may configure N resources each with a single port, and the UE selects and report P ports out of the N via CRI. The UE may select and report the ports, for example, via an N-bit bitmap or an

indication based on combination number.

As noted above, in case the gNB transmits CSI-RS precoded by SD basis, the UE may report selected CSI-RS ports and the FD basis associated with each selected port, based on certain criteria. For example, such criteria may be expressed as

1. a power of weighted summation across a frequency domain, of the channel measurement of a first CSI-RS port,

2. a power of weighted linear average, across a frequency domain, of the channel measurement of a first CSI-RS port,

3. a power of weighted summation across a frequency domain, of the channel on which a first CSI-RS port is conveyed, or

4. a power of weighted linear average, across a frequency domain, of the channel on which a first CSI-RS port is conveyed.

Mathematically, such criteria for selecting an FD basis for a port p may be written as:

where f _m (n) is the n-th entry of an FD basis f _m. Mathematically, the criteria for selecting a port may be expressed as:

where f _p (m) is the m-th selected basis for port p.

In some cases, the criteria may be expressed as “the power of summation or linear average, across frequency domain, of the channel on which a virtual CSI-RS port is conveyed. ” More specifically,

1. a power of summation across a frequency domain, of the channel on which a virtual CSI-RS port is conveyed, or

2. a power of linear average, across a frequency domain, of the channel on which a virtual CSI-RS port is conveyed.

In such cases, a virtual port on FD unit n may be generated by a CSI-RS port p and a corresponding entry of a FD basis

The channel on which a virtual CSI-RS port is conveyed may be represented as

Mathematically, the criteria for selecting an FD basis for a port p may be written as:

while the criteria for selecting a port is based on all the associated virtual ports may be expressed as:

In case the gNB transmits non-precoded CSI-RS, the UE may report SD basis and the FD basis associated with each reported SD basis. The SD and FD basis selection may be based on criteria expressed as “the power of summation or linear average, across frequency domain, of the channel on which a virtual CSI-RS port is conveyed. ” In such cases, a virtual port on FD unit n may be generated by all CSI-RS ports and a SD basis I, b _i and a corresponding entry of a FD basis

The channel on which a virtual CSI-RS port may be conveyed as:

Mathematically, the criteria for selecting an FD basis for a SD basis i may be written as:

Mathematically, the criteria for selecting a SD basis i may be based on all the associated virtual ports:

As described herein, aspects of the present disclosure may help provide efficient CSI reporting, in terms of reporting overhead, by decoupling port/basis selection and coefficient reporting.

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. For example, the various processor shown in FIG. 3 may be configured to perform operations 800 and 900 of FIGs. 8 and 9.

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 120 (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 (e.g., instructions for performing the operations described herein and illustrated in FIGs. 8 and 9) .

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 communications by a user equipment (UE) , comprising:

measuring first channel state information reference signals (CSI-RS) from a network entity;

selecting a preferred subset of CSI-RS ports based on the first CSI-RS measurements and selection criteria comprising at least one of: a power of summation across a frequency domain, of the channel measurement of a first CSI-RS port, a power of linear average, across a frequency domain, of the channel measurement of a first CSI-RS port, a power of summation across a frequency domain, of the channel on which a first CSI-RS port is conveyed, a power of linear average, across a frequency domain, of the channel on which a first CSI-RS port is conveyed, a power at a delay zero of a power-delay-profile of the channel on which the first CSI-RS port is conveyed, a power at a delay zero of a power-delay-profile of the channel measurement of the first CSI-RS port, or a power of a shortened channel on which the first CSI-RS port is conveyed; and

sending a first report indicating the preferred subset of CSI-RS ports.
The method of claim 1, further comprising:

generating linear combination coefficients based on second CSI-RS measurements; and

sending a second report indicating the linear combination coefficients.
The method of claim 2, wherein the second report is sent more frequently than the first report.
The method of claim 2, wherein:

the first CSI-RS is common to all UEs in a cell or to a group of UEs; and

the second CSI-RS is specific to the UE.
The method of claim 2, wherein the second CSI-RS is sent with a fewer number of ports than the first CSI-RS.
The method of claim 2, wherein the first CSI-RS is sent with a periodicity that has a longer cycle than the second CSI-RS.
The method of claim 1, wherein:

if a time domain measurement restriction is not configured for the first CSI-RS, the UE selects the preferred subset of CSI parameters based on measuring multiple transmissions of the first CSI-RS, prior to the CSI reference resource; or

if the time domain measurement restriction is configured for the first CSI-RS, the UE selects the preferred subset of CSI parameters based on measuring a most recent first CSI-RS transmission prior to the CSI reference resource.
The method of claim 1, further comprising receiving signaling indicating the selection criteria for selecting the preferred subset of ports.
The method of claim 1, wherein the UE indicates the preferred subset of ports via a bitmap or a multi-bit indication based on a combination number.
The method of claim 1, further comprising:

selecting a preferred frequency domain basis for each of the selected preferred CSI-RS ports; and

including an indication of the preferred frequency domain bases in the first report.
The method of claim 10, wherein the selection criteria for selecting the preferred subset of ports and preferred frequency domain bases comprises at least one of:

a power of weighted summation or weighted linear average, across a frequency domain, of a channel measurement or a channel on which a first CSI-RS port is conveyed, wherein the weighted summation or weighted linear average is based on a frequency domain basis associated with the first CSI-RS port; or

a power of summation or linear average, across a frequency domain, of the channel on which a virtual first CSI-RS port is conveyed, wherein a virtual port is formed by a CSI-RS port and a frequency basis associated with the CSI-RS port.
The method of claim 1, further comprising:

selecting preferred spatial domain bases and, for each preferred spatial domain basis, an associated frequency domain basis; and

including an indication of the preferred frequency domain bases in the first report.
The method of claim 12, wherein the selection criteria for selecting the preferred subset of CSI-RS ports and preferred spatial domain bases involves a power of summation or linear average, across a frequency domain, of a channel on which a virtual first CSI-RS port is conveyed, wherein the virtual CSI-RS port is formed by all the CSI-RS ports, a spatial domain basis, and a frequency domain basis.
A method for wireless communications by a network entity, comprising:

transmitting first channel state information reference signals (CSI-RS) to a user equipment (UE) ; and

receiving a first report from the UE, indication a preferred subset of CSI-RS ports based on UE measurements of the first CSI-RS and selection criteria comprising at least one of: a power of summation across a frequency domain, of the channel measurement of a first CSI-RS port, a power of linear average, across a frequency domain, of the channel measurement of a first CSI-RS port, a power of summation across a frequency domain, of the channel on which a first CSI-RS port is conveyed, a power of linear average, across a frequency domain, of the channel on which a first CSI-RS port is conveyed, a power at a delay zero of a power-delay-profile of the channel on which the first CSI-RS port is conveyed, a power at a delay zero of a power-delay-profile of the channel measurement of the first CSI-RS port, or a power of a shortened channel on which the first CSI-RS port is conveyed.
The method of claim 14, further comprising:

transmitting second CSI-RS; and

receiving a second report indicating linear combination coefficients based on UE measurements of second CSI-RS.
The method of claim 15, wherein the second report is sent more frequently than the first report.
The method of claim 15, wherein:

the first CSI-RS is common to all UEs in a cell or to a group of UEs; and

the second CSI-RS is specific to the UE.
The method of claim 15, wherein the second CSI-RS is sent with a fewer number of ports than the first CSI-RS.
The method of claim 15, wherein the first CSI-RS is sent with a periodicity that has a longer cycle than the second CSI-RS.
The method of claim 14, wherein:

if a time domain measurement restriction is not configured for the first CSI-RS, the UE selects the preferred subset of CSI parameters based on measuring multiple transmissions of the first CSI-RS, prior to the CSI reference resource; or

if the time domain measurement restriction is configured for the first CSI-RS, the UE selects the preferred subset of CSI parameters based on measuring a most recent first CSI-RS transmission prior to the CSI reference resource.
The method of claim 14, further comprising sending the UE an indication of the selection criteria for selecting the preferred subset of ports.
The method of claim 14, wherein the UE indicates the preferred subset of ports via a bitmap or a multi-bit indication based on a combination number.
The method of claim 14, wherein:

the first report includes an indication of a preferred frequency domain basis for each of the selected preferred CSI-RS ports.
The method of claim 23, wherein the selection criteria for selecting the preferred subset of ports and preferred frequency domain bases comprises at least one of:

a power of weighted summation or weighted linear average, across a frequency domain, of a channel measurement or a channel on which a first CSI-RS port is conveyed, wherein the weighted summation or weighted linear average is based on a frequency domain basis associated with the first CSI-RS port; or

a power of summation or linear average, across a frequency domain, of the channel on which a virtual first CSI-RS port is conveyed, wherein a virtual port is formed by a CSI-RS port and a frequency basis associated with the CSI-RS port.
The method of claim 14, wherein:

the first report includes an indication of an associated frequency domain bases, for each preferred spatial domain basis.
The method of claim 25, wherein the selection criteria for selecting the preferred subset of CSI-RS ports and preferred spatial domain bases involves a power of summation or linear average, across a frequency domain, of a channel on which a virtual first CSI-RS port is conveyed, wherein the virtual CSI-RS port is formed by all the CSI-RS ports, a spatial domain basis, and a frequency domain basis.