Type II CSI Port Selection Codebook Enhancement with Partial Reciprocity

Abstract

A base station and wireless communication (UE) may perform type II CSI-RS port selection based at least on partial reciprocity between an uplink path and a downlink path between the base station and the UE. The base station may identify dominant signal paths between the base station and the UE, based on measurements performed during uplink transmissions, and may transmit, to the UE, corresponding information indicative of CSI measurement and reporting configuration that may include a single measurement resource or multiple measurement resources. Each measurement resource may include multiple-port CSI-RS ports. The UE may indicate, to the base station, selection of a measurement resource when multiple measurement resources are configured, and may also report layer independent or layer common selection of a subset of CSI-RS ports included in the indicated single measurement resource or multiple measurement resources. Further enhancements include frequency domain compression enhancement and dynamic codebook parameter reconfiguration.

Description

FIELD OF THE INVENTION

[0001] The present application relates to wireless communications, and more particularly toChannel State Information (CSI) port selection codebook enhancement during wireless cellularcommunications, e.g. during 5G-NR communications.DESCRIPTION OF THE RELATED ART

[0002] Wireless communication systems are rapidly growing in usage. In recent years, wirelessdevices such as smart phones and tablet computers have become increasingly sophisticated. Inaddition to supporting telephone calls, many mobile devices (e.g., user equipment devices orUEs) now provide access to the internet, email, text messaging, and navigation using the globalpositioning system (GPS), and are capable of operating sophisticated applications that utilizethese functionalities. Additionally, there exist numerous different wireless communicationtechnologies and standards. Some examples of wireless communication standards include GSM,UMTS (WCDMA, TDS-CDMA), LTE, LTE Advanced (LTE-A), HSPA, 3GPP2 CDMA2000(e.g., IxRTT, IxEV-DO, HRPD, eHRPD), LEEE 802.11 (WLAN or Wi-Fi), LEEE 802.16(WiMAX), BLUETOOTH, etc. A next telecommunications standards moving beyond thecurrent International Mobile Telecommunications-Advanced (IMT-Advanced) Standards iscalled Sth generation mobile networks or 5th generation wireless systems, referred to as 3GPPNR (otherwise known as 5G-NR for 5G New Radio, also simply referred to as NR). NR proposesa higher capacity for a higher density of mobile broadband users, also supporting device-to-device, ultra-reliable, and massive machine communications, as well as lower latency and lowerbattery consumption, than current LTE standards.

[0003] In general, wireless communication technologies, such as cellular communicationtechnologies, are substantially designed to provide mobile communication capabilities towireless devices. The ever increasing number of features and functionality introduced inwireless communication devices creates a continuous need for improvement in both wirelesscommunications and in wireless communication devices. In particular, it is important to ensurethe accuracy of transmitted and received signals. The UEs, which may be mobile telephones orsmart phones, portable gaming devices, communication systems / devices housed in or otherwisecarried by transportation vehicles (e.g. cars, buses, trains, trucks, motorcycles, etc.), laptops,wearable devices, PDAs, tablets, portable Internet devices, music players, data storage devices,or other handheld devices, etc. are generally powered by a portable power supply, e.g., a batteryand may have multiple radio interfaces that enable support of multiple radio access technologies(RATs) as defined by the various wireless communication standards (LTE, LTE-A, 5G-NR,Wi-Fi, BLUETOOTH, etc.). There are ongoing efforts to achieve efficient use of wirelesscommunication resources and thereby increase system and device operation efficiency.

[0004] Many wireless communication standards provide for the use of known signals (e.g., pilotor reference signals) for a variety of purposes, such as synchronization, measurements,equalization, control, etc. For example, in cellular wireless communications, reference signals(RS, for short) represent a special signal that exists only at the physical layer and is not used fordelivering any specific information but to deliver a reference point for the downlink power.When a wireless communication device or mobile device (UE) attempts to determine downlinkpower (e.g. the power of the signal from a base station, such as eNB for LTE and gNB for NR),it measures the power of the reference signal and uses it to determine the downlink cell power.The reference signal also assists the receiver in demodulating the received signals. Since thereference signals include data known to both the transmitter and the receiver, the receiver mayuse the reference signal to determine / identify various characteristics of the communicationchannel. This is commonly referred to as 'Channel Estimation', which is a critical part of manyhigh-end wireless communications such as LTE and 5G-NR communications. Known channelproperties of a communication link in wireless communications are referred to as channel stateinformation (CSI), which provides information indicative of the combined effects of, forexample, scattering, fading, and power decay with distance. The CSI makes it possible to adapttransmissions to current channel conditions, which is crucial for achieving reliablecommunications with high data rates in multi-antenna systems.

[0005] Oftentimes multi-antenna systems use precoding for improved communications.Precoding is an extension of beamforming to support multi-stream (or multi-layer)transmissions for multi-antenna wireless communications and is used to control the differencesin signal properties between the respective signals transmitted from multiple antennas bymodifying the signal transmitted from each antenna according to a precoding matrix. In onesense, precoding may be considered a process of cross coupling the signals before transmission(in closed loop operation) to equalize the demodulated performance of the layers. The precodingmatrix is generally selected from a codebook that defines multiple precoding matrix candidates,and a precoding matrix candidate is typically selected according to a desired performance level,based on any of a number of different factors, such as current system configuration,communication environment, and / or feedback information from the receiver, e.g. a mobiledevice (UE) receiving the transmitted signal(s).

[0006] The feedback information is used in selecting a precoding matrix candidate by definingthe same codebook at both the transmitter (which may be a base station) and the receiver (whichmay be a mobile device, or UE), and using the feedback information from the receiver as anindication of a preferred precoding matrix. In such cases the feedback information includeswhat is referred to as a precoding matrix index (PMI), which can be based on properties of thesignals received at the receiver. For example, the receiver may determine that a received signalhas relatively low signal-to-noise ratio (SNR), and may accordingly transmit a PMI that wouldreplace a current precoding matrix with a new precoding matrix to increase the signal-to-noiseratio (SNR).

[0007] The precoding matrices are based upon a specific set of assumed antenna configurations.These antenna configurations are specified by defining the number of rows and columns of crosspolar antenna elements. For example, a smaller antenna may have 1 row and 2 columns of crosspolar antenna elements, supporting a total of 4 transceivers. A larger antenna could have 4 rowsand 4 columns of cross polar antenna elements, supporting a total of 32 transceivers. The set ofantenna configurations does not restrict live network deployments from using otherconfigurations. The maximum antenna configuration can support a specified total number (e.g.32) of transceivers and is thus able to transmit the specified total number of CSI ReferenceSignals. An actual network deployment could use an active antenna with more transceivers, butfor the purposes of CSI reporting it could transmit CSI Reference Signals using up to thespecified total number of its transceivers.

[0008] Four solutions for PMI reporting have been defined thus far, Type I Single Panel, TypeI Multi Panel, Type LI Single Panel, and Type LI Port Selection. Generally, the Type LI solutionsfocus upon providing more detailed CST for the purposes of Multi-User MIMO. They supporta maximum rank of two (2) corresponding to a maximum of two (2) layers per UE. Themaximum number of layers per cell is likely to be higher to allow multiple UEs to use 2x2 MIMOsimultaneously while sharing a common Resource Block (RB) allocation. Type IT reports arebased upon selecting a set of beams and then specifying relative amplitudes and phases togenerate a weighted combination of beams for each layer of transmission. The Type II PortSelection solution relies upon the base station having some advance information to allowbeamforming of the CSI-RS transmissions. This advance information can originate from uplink(UL) measurements if channel reciprocity is available. Otherwise it can originate from beammanagement reports or it can use the wideband reports from a different PMI reporting solution(sometimes referred to as a "hybrid solution" when a combination of PMI reporting solutionsis used). For more efficient and streamlined reporting by the UE, it may be beneficial to takeadvantage of even partial reciprocity that may exist between UL and DL transmissions.

[0009] Other corresponding issues related to the prior art will become apparent to one skilledin the art after comparing such prior art with the disclosed embodiments as described herein.SUMMARY OF THE INVENTION

[0010] Embodiments are presented herein of, infer alia, of methods and procedures for supportin various devices, e.g. wireless communication devices, to use a Type II CSI port selectioncodebook with improved feedback taking advantage of partial reciprocity between uplink anddownlink transmissions, eg. during 5G-NR communications. Embodiments are furtherpresented herein for wireless communication systems containing wireless communicationdevices (UEs) and / or base stations and access points (APs) communicating with each otherwithin the wireless communication systems.

[0011] In the 3GPP Rel-15 specification, beamformed CSI-RS (channel state information -reference signal) exploits DL (downlink) and UL (uplink) channel reciprocity for Type IT PortSelection. A total number of "X" CSI-RS ports may be selected, specifically X / 2 ports forhorizontal polarization (HPol) and X / 2 ports for vertical polarization (VPol). A number "L" ofCSI-RS ports may be selected out of X / 2 CSI-RS port, with the first CSI-RS port selected everynumber "d" of ports. Then consecutive L ports may be selected with wraparound. The 3GPPRel-16 specification discloses the same port selection design as Rel-15, while adding certainfeatures. For example, when subband PMI (precoding matrix index) is configured, frequencydomain DFT matrix can be used to compress the linear combination coefficient. For Type LLport selection codebook, the gNB is assumed to precode the CSI-RS based on channelreciprocity. E.g., the DL channel may be estimated based on the UL channel. For FDD(frequency division duplex), exact channel reciprocity may not be present, especially when theduplexing distance is large. However, even for FDD, partial reciprocity may still exist. Forexample, the angle of arrival or departure may be similar between the DL and UL carrier, andthe channel delay profile may be similar between the DL and UL carrier. In some embodiments,the Type II CSI port selection codebook may be enhanced by exploiting partial channelreciprocity, facilitating layer independent CSI-RS port selection, layer common CSI-RS portselection, frequency domain compression enhancement, and / or dynamic codebook parameterreconfiguration.

[0012] Pursuant to the above, based on an uplink (UL) Sounding Reference Signal (SRS)transmitted by the UE to the base station (e.g. to a gNB), the base station may estimate the ULchannel and assume certain reciprocity of the channel to derive downlink (DL) channelproperties such as preferred beam(s). The base station may then transmit the CSI-RS precodewith the preferred beam(s). The CSI-RS may have multiple CSI-RS ports, and each port maybe transmitted from the base station using a different beam, i.e. each CSI-RS port maycorrespond to a different beam over which the CSI-RS port is transmitted. The UE may indicateto the base station the preferred CSI-RS port(s) via CSI reporting, e.g. indicate the preferredbeam in an implicit way.

[0013] In some embodiments, a UE may receive, from a base station, information indicative ofchannel state information (CSI) measurement and reporting configuration that may include asingle measurement resource or multiple measurement resources. Each measurement resourcemay include multiple-port CSI-RS ports. The UE may indicate the selection of a measurementresource to the base station when multiple measurement resources are configured, and mayreport to the base station selection of a subset of CSI-RS ports included in the indicated singlemeasurement resource or multiple measurement resources. The selection of the subset of CSI-RS ports may be performed independently for each layer of a multilayer transmission or it maybe performed in common for each layer of the multilayer transmission.

[0014] In some embodiments, a base station may identify dominant signal paths between thebase station and a device, based on channel estimates performed using uplink communicationsbetween the base station and the device. The base station may transmit preferred CSI-RS portscorresponding to the dominant signal paths to the device, with the CSI-RS ports transmittedover corresponding beams identified independently by the base station for each dominant signalpath of the dominant signal paths.

[0015] This Summary is intended to provide a brief overview of some of the subject matterdescribed in this document. Accordingly, it will be appreciated that the above-described featuresare merely examples and should not be construed to narrow the scope or spirit of the subjectmatter described herein in any way. Other features, aspects, and advantages of the subjectmatter described herein will become apparent from the following Detailed Description, Figures,and Claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 illustrates an exemplary (and simplified) wireless communication system,according to some embodiments;

[0017] Figure 2 illustrates an exemplary base station in communication with an exemplarywireless user equipment (UE) device, according to some embodiments;

[0018] Figure 3 illustrates an exemplary block diagram of a UE, according to someembodiments;

[0019] Figure 4 illustrates an exemplary block diagram of a base station, according to someembodiments;

[0020] Figure 5 shows an exemplary simplified block diagram illustrative of cellularcommunication circuitry, according to some embodiments;

[0021] Figure 6 shows an exemplary diagram illustrating a precoding structure associated withType II CSI reporting, according to prior art;

[0022] Figure 7 shows, an exemplary diagram illustrating the reporting structure used by theUE to report back to a base station, according to prior art;

[0023] Figure 8 shows an exemplary diagram illustrating a codebook structure with compressedcombination coefficients, for Type II CSI reporting;

[0024] Figure 9 shows an exemplary diagram illustrating layer independent CSI-RS portselection, according to some embodiments;

[0025] Figure 10 shows an exemplary diagram illustrating layer common CSI-RS port selection,according to some embodiments;

[0026] Figure 11 shows an exemplary diagram illustrating frequency domain compression forCSLRS port selection, according to some embodiments;

[0027] Figure 12 shows an exemplary diagram illustrating layer common CSI-RS port selectionusing completely free indication, according to some embodiments; and

[0028] Figure 13 shows an exemplary diagram illustrating antenna group selection for layercommon CSI-RS port selection, according to some embodiments.While features described herein are susceptible to various modifications and alternative forms,specific embodiments thereof are shown by way of example in the drawings and are hereindescribed in detail. It should be understood, however, that the drawings and detaileddescription thereto are not intended to be limiting to the particular form disclosed, but on thecontrary, the intention is to cover all modifications, equivalents and alternatives falling withinthe spirit and scope of the subject matter as defined by the appended claims.DETAILED DESCRIPTION OF THE EMBODIMENTSAcronyms

[0029] Various acronyms are used throughout the present application. Definitions of the mostprominently used acronyms that may appear throughout the present application are providedbelow:• AMR: Adaptive Multi-Rate• AP: Access Point• APN: Access Point Name• APR: Applications Processor• AS: Access Stratum• BS: Base Station• BSR: Buffer Size Report• BSSID: Basic Service Set Identifier• CBRS: Citizens Broadband Radio Service• CBSD: Citizens Broadband Radio Service Device• CBSR: Codebook Subset Restriction• CCA: Clear Channel Assessment• CMR: Change Mode Request• CS: Circuit Switched• CST: Channel State Information• DL: Downlink (from BS to UE)• DSDS: Dual SIM Dual Standby• DYN: Dynamic• EDCF: Enhanced Distributed Coordination Function• FDD: Frequency Division Duplexing• FO: First-Order state• FT: Frame Type• GAA: General Authorized Access• GPRS: General Packet Radio Service• GSM: Global System for Mobile Communication• GTP: GPRS Tunneling Protocol• IMS: Internet Protocol Multimedia Subsystem• IP: Internet Protocol• IR: Initialization and Refresh state• KPI; Key Performance Indicator• LAN: Local Area Network• LBT: Listen Before Talk• LQM: Link Quality Metric• LTE: Long Term Evolution• MIMO: Multiple-In Multiple-Out• MNO: Mobile Network Operator• MU: Multi-User• NAS: Non-Access Stratum• NB: Narrowband• OOS: Out of Sync• PAL: Priority Access Licensee• PDCP: Packet Data Convergence Protocol• PDN: Packet Data Network• PDU: Protocol Data Unit• PGW: PDN Gateway• PLMN: Public Land Mobile Network• PMI: Precoding Matrix Indicator• PSD: Power Spectral Density• PSS: Primary Synchronization Signal• PT: Payload Type• QBSS: Quality of Service Enhanced Basic Service Set• QI: Quality Indicator• RAN: Radio Access Network• RAT: Radio Access Technology• RF: Radio Frequency• ROHC: Robust Header Compression• RRC: Radio Resource Control• RS: Reference Signal• RTP: Real-time Transport Protocol• RTT: Round Trip Time• RX: Reception / Receive• SAS: Spectrum Allocation Server• SI: System Information• SID: System Identification Number• SIM: Subscriber Identity Module• SGW: Serving Gateway• SMB: Small / Medium Business• SRS: Sounding Reference Signal• SSS: Secondary Synchronization Signal• TBS: Transport Block Size• TCP: Transmission Control Protocol• TDD: Time Division Duplexing• TX: Transmission / Transmit• UE: User Equipment• UI: User Interface• UL: Uplink (from UE to BS)• UMTS: Universal Mobile Telecommunication System• USIM: UMTS Subscriber Identity Module• WB: Wideband• Wi-Fi: Wireless Local Area Network (WLAN) RAT based on the Institute of Electricaland Electronics Engineers' (TEEE) 802.11 standards• WLAN: Wireless LANTermsThe following is a glossary of terms that may appear in the present application:

[0030] Memory Medium - Any of various types of non-transitory memory devices or storagedevices. The term "memory medium" is intended to include an installation medium, e.g., a CD-ROM, floppy disks, or tape device; a computer system memory or random access memory suchas DRAM, DDR RAM, SRAM, EDO RAM, Rambus RAM, etc.; a non-volatile memory such asa Flash, magnetic media, e.g., a hard drive, or optical storage; registers, or other similar typesof memory elements, etc. The memory medium may comprise other types of memory as well orcombinations thereof. In addition, the memory medium may be located in a first computersystem in which the programs are executed, or may be located in a second different computersystem which connects to the first computer system over a network, such as the Internet. In thelatter instance, the second computer system may provide program instructions to the firstcomputer system for execution. The term "memory medium" may include two or more memorymediums which may reside in different locations, e.g., in different computer systems that areconnected over a network. The memory medium may store program instructions (e.g.,embodied as computer programs) that may be executed by one or more processors.

[0031] Carrier Medium - a memory medium as described above, as well as a physicaltransmission medium, such as a bus, network, and / or other physical transmission medium thatconveys signals such as electrical, electromagnetic, or digital signals.

[0032] Programmable Hardware Element - includes various hardware devices comprisingmultiple programmable function blocks connected via a programmable interconnect. Examplesinclude FPGAs (Field Programmable Gate Arrays), PLDs (Programmable Logic Devices),FPOAs (Field Programmable Object Arrays), and CPLDs (Complex PLDs). Theprogrammable function blocks may range from fine grained (combinatorial logic or look uptables) to coarse grained (arithmetic logic units or processor cores). A programmable hardwareelement may also be referred to as "reconfigurable logic".

[0033] Computer System (or Computer) - any of various types of computing or processingsystems, including a personal computer system (PC), mainframe computer system, workstation,network appliance, Internet appliance, personal digital assistant (PDA), television system, gridcomputing system, or other device or combinations of devices. In general, the term "computersystem" may be broadly defined to encompass any device (or combination of devices) having atleast one processor that executes instructions from a memory medium.

[0034] User Equipment (UE) (or "UE Device") - any of various types of computer systemsdevices which perform wireless communications. Also referred to as wireless communicationdevices, many of which may be mobile and / or portable. Examples of UE devices include mobiletelephones or smart phones (e.g., iPhone, Android-based phones) and tablet computerssuch as iPad, Samsung Galaxy, etc., gaming devices (e.g. Sony PlayStation, MicrosoftXBox*, etc.), portable gaming devices (e.g., Nintendo DS, PlayStation Portable, GameboyAdvance, iPod), laptops, wearable devices (e.g. Apple Watch, Google Glass), PDAs,portable Internet devices, music players, data storage devices, or other handheld devices, etc.Various other types of devices would fall into this category if they include Wi-Fi or both cellularand Wi-Fi communication capabilities and / or other wireless communication capabilities, forexample over short-range radio access technologies (SRATs) such as BLUETOOTH, etc. Ingeneral, the term "UE" or "UE device" may be broadly defined to encompass any electronic,computing, and / or telecommunications device (or combination of devices) which is capable ofwireless communication and may also be portable / mobile.

[0035] Wireless Device (or wireless communication device) - any of various types of computersystems devices which performs wireless communications using WLAN communications, SRATcommunications, Wi-Fi communications and the like. As used herein, the term "wirelessdevice" may refer to a UE device, as defined above, or to a stationary device, such as a stationarywireless client or a wireless base station. For example a wireless device may be any type ofwireless station of an 802.11 system, such as an access point (AP) or a client station (UE), or anytype of wireless station of a cellular communication system communicating according to acellular radio access technology (e.g. LTE, CDMA, GSM), such as a base station or a cellulartelephone, for example.

[0036] Communication Device - any of various types of computer systems or devices thatperform communications, where the communications can be wired or wireless. Acommunication device can be portable (or mobile) or may be stationary or fixed at a certainlocation. A wireless device is an example of a communication device. A UE is another exampleof a communication device.

[0037] Base Station (BS)- The term "Base Station" has the full breadth of its ordinary meaning,and at least includes a wireless communication station installed at a fixed location and used tocommunicate as part of a wireless telephone system or radio system.

[0038] Processor - refers to various elements (e.g. circuits) or combinations of elements that arecapable of performing a function in a device, e.g. in a user equipment device or in a cellularnetwork device. Processors may include, for example: general purpose processors andassociated memory, portions or circuits of individual processor cores, entire processor cores orprocessing circuit cores, processing circuit arrays or processor arrays, circuits such as ASICs(Application Specific Integrated Circuits), programmable hardware elements such as a fieldprogrammable gate array (FPGA), as well as any of various combinations of the above.

[0039] Channel - a medium used to convey information from a sender (transmitter) to areceiver. It should be noted that since characteristics of the term "channel" may differaccording to different wireless protocols, the term "channel" as used herein may be consideredas being used in a manner that is consistent with the standard of the type of device with referenceto which the term is used. In some standards, channel widths may be variable (e.g., dependingon device capability, band conditions, etc.). For example, LTE may support scalable channelbandwidths from 1.4 MHz to 20MHz. In contrast, WLAN channels may be 22MHz wide whileBluetooth channels may be 1 Mhz wide. Other protocols and standards may include differentdefinitions of channels. Furthermore, some standards may define and use multiple types ofchannels, e.g., different channels for uplink or downlink and / or different channels for differentuses such as data, control information, etc.

[0040] Band - The term "band" has the full breadth of its ordinary meaning, and at leastincludes a section of spectrum (e.g., radio frequency spectrum) in which channels are used orset aside for the same purpose. Furthermore, "frequency band" is used to denote any intervalin the frequency domain, delimited by a lower frequency and an upper frequency. The termmay refer to a radio band or an interval of some other spectrum. A radio communicationssignal may occupy a range of frequencies over which (or where) the signal is carried. Such afrequency range is also referred to as the bandwidth of the signal. Thus, bandwidth refers tothe difference between the upper frequency and lower frequency in a continuous band offrequencies. A frequency band may represent one communication channel or it may besubdivided into multiple communication channels. Allocation of radio frequency ranges todifferent uses is a major function of radio spectrum allocation.

[0041] Wi-Fi - The term "Wi-Fi" has the full breadth of its ordinary meaning, and at leastincludes a wireless communication network or RAT that is serviced by wireless LAN (WLAN)access points and which provides connectivity through these access points to the Internet. Mostmodern Wi-Fi networks (or WLAN networks) are based on TEEE 802.11 standards and aremarketed under the name "Wi-Fi". A Wi-Fi (WLAN) network is different from a cellularnetwork.

[0042] Automatically - refers to an action or operation performed by a computer system (e.g.,software executed by the computer system) or device (e.g., circuitry, programmable hardwareelements, ASICs, etc.), without user input directly specifying or performing the action oroperation. Thus the term "automatically" is in contrast to an operation being manuallyperformed or specified by the user, where the user provides input to directly perform theoperation. An automatic procedure may be initiated by input provided by the user, but thesubsequent actions that are performed "automatically" are not specified by the user, e.g., arenot performed "manually", where the user specifies each action to perform. For example, auser filling out an electronic form by selecting each field and providing input specifyinginformation (e.g., by typing information, selecting check boxes, radio selections, etc.) is fillingout the form manually, even though the computer system must update the form in response tothe user actions. The form may be automatically filled out by the computer system where thecomputer system (e.g., software executing on the computer system) analyzes the fields of theform and fills in the form without any user input specifying the answers to the fields. Asindicated above, the user may invoke the automatic filling of the form, but is not involved in theactual filling of the form (e.g., the user is not manually specifying answers to fields but ratherthey are being automatically completed). The present specification provides various examplesof operations being automatically performed in response to actions the user has taken.

[0043] Approximately - refers to a value that is almost correct or exact. For example,approximately may refer to a value that is within 1 to 10 percent of the exact (or desired) value.It should be noted, however, that the actual threshold value (or tolerance) may be applicationdependent. For example, in some embodiments, "approximately" may mean within 0.1% ofsome specified or desired value, while in various other embodiments, the threshold may be, forexample, 2%, 3%, 5%, and so forth, as desired or as required by the particular application.

[0044] Concurrent - refers to parallel execution or performance, where tasks, processes, orprograms are performed in an at least partially overlapping manner. For example, concurrencymay be implemented using "strong" or strict parallelism, where tasks are performed (at leastpartially) in parallel on respective computational elements, or using "weak parallelism", wherethe tasks are performed in an interleaved manner, e.g., by time multiplexing of executionthreads.

[0045] Station (STA) - The term "station" herein refers to any device that has the capability ofcommunicating wirelessly, e.g. by using the 802.11 protocol. A station may be a laptop, adesktop PC, PDA, access point or Wi-Fi phone or any type of device similar to a UE. An STAmay be fixed, mobile, portable or wearable. Generally in wireless networking terminology, astation (STA) broadly encompasses any device with wireless communication capabilities, andthe terms station (STA), wireless client (UE) and node (BS) are therefore often usedinterchangeably.

[0046] Configured to - Various components may be described as "configured to" perform atask or tasks. In such contexts, "configured to" is a broad recitation generally meaning "havingstructure that" performs the task or tasks during operation. As such, the component can beconfigured to perform the task even when the component is not currently performing that task(e.g., a set of electrical conductors may be configured to electrically connect a module to anothermodule, even when the two modules are not connected). In some contexts, "configured to" maybe a broad recitation of structure generally meaning "having circuitry that" performs the taskor tasks during operation. As such, the component can be configured to perform the task evenwhen the component is not currently on. In general, the circuitry that forms the structurecorresponding to "configured to" may include hardware circuits.

[0047] Transmission Scheduling - Refers to the scheduling of transmissions, such as wirelesstransmissions. In cellular radio communications, signal and data transmissions may beorganized according to designated time units of specific duration during which transmissionstake place. For example, in LTE, transmissions are divided into radio frames, each radio framebeing of equal (time) duration (e.g. each radio frame may be 10ms). A radio frame in LTE maybe further divided into ten subframes, each subframe being of equal duration, with thesubframes designated as the smallest (minimum) scheduling unit, or the designated time unitfor a transmission. Similarly, a smallest (or minimum) scheduling unit for 5G NR (or NR, forshort) transmissions is referred to as a slot. Accordingly, as used herein, the term "slot" is usedto reference a smallest (or minimum) scheduling time unit for the wireless communicationsbeing described for NR communications. However, as noted above, in different communicationprotocols such a scheduling time unit may be named differently, e.g. a "subframe" in LTE, etc.

[0048] Various components may be described as performing a task or tasks, for convenience inthe description. Such descriptions should be interpreted as including the phrase "configuredto." Reciting a component that is configured to perform one or more tasks is expressly intendednot to invoke 35 U.S.C. § 112, paragraph six, interpretation for that component.Figures 1 and 2- Exemplary Communication Systems

[0049] Figure 1 illustrates an exemplary (and simplified) wireless communication system,according to some embodiments. It is noted that the system of Figure 1 is merely one exampleof a possible system, and embodiments may be implemented in any of various systems, asdesired.

[0050] As shown, the exemplary wireless communication system includes a base stations 102Athrough 102N, also collectively referred to as base station(s) 102 or base station 102. As shownin Figure 1, base station 102A communicates over a transmission medium with one or more userdevices 106A, 106B, etc., through 106N. Each of the user devices may be referred to herein asa "user equipment" (UE) or UE device. Thus, the user devices 106A through 106N are referredto as UEs or UE devices, and are also collectively referred to of UE(s) 106 or UE 106. Variousones of the UE devices may use an enhanced Type IT CST port selection codebook based at leaston partial reciprocity, according to various embodiments disclosed herein.

[0051] The base station 102A may be a base transceiver station (BTS) or cell site, and mayinclude hardware that enables wireless communication with the UEs 106A through 106N. Thebase station 102A may also be equipped to communicate with a network 100, e.g., a core networkof a cellular service provider, a telecommunication network such as a public switched telephonenetwork (PSTN), and / or the Internet, neutral host or various CBRS (Citizens Broadband RadioService) deployments, among various possibilities. Thus, the base station 102A may facilitatecommunication between the user devices and / or between the user devices and the network 100.The communication area (or coverage area) of the base station may be referred to as a "cell."It should also be noted that "cell" may also refer to a logical identity for a given coverage areaat a given frequency. In general, any independent cellular wireless coverage area may bereferred to as a "cell". In such cases a base station may be situated at particular confluences ofthree cells. The base station, in this uniform topology, may serve three 120 degree beam widthareas referenced as cells. Also, in case of carrier aggregation, small cells, relays, etc. may eachrepresent a cell. Thus, in carrier aggregation in particular, there may be primary cells andsecondary cells which may service at least partially overlapping coverage areas but on differentrespective frequencies. For example, a base station may serve any number of cells, and cellsserved by a base station may or may not be collocated (e.g. remote radio heads). As also usedherein, from the perspective of UEs, a base station may sometimes be considered as representingthe network insofar as uplink and downlink communications of the UE are concerned. Thus, aUE communicating with one or more base stations in the network may also be interpreted asthe UE communicating with the network, and may further also be considered at least a part ofthe UE communicating on the network or over the network.

[0052] The base station(s) 102 and the user devices may be configured to communicate over thetransmission medium using any of various radio access technologies (RATs), also referred to aswireless communication technologies, or telecommunication standards, such as GSM, UMTS(WCDMA), LTE, LTE-Advanced (LTE-A), LAA / LTE-U, 5G-NR (NR, for short), 3GPP2CDMA2000 (e.g., IxRTT, 1xEV-DO, HRPD, eHRPD), Wi-Fi, WiMAX etc. Note that if the basestation 102A is implemented in the context of LTE, it may alternately be referred to as an'eNodeB' or 'eNB'. Note that if the base station 102A is implemented in the context of 5G NR, itmay alternately be referred to as 'gNodeB' or 'gNB'. In some embodiments, the base station102 may communicate with UEs that use an enhanced Type II CSI port selection codebookbased at least on partial reciprocity, as described herein. Depending on a given application orspecific considerations, for convenience some of the various different RATs may be functionallygrouped according to an overall defining characteristic. For example, all cellular RATs may becollectively considered as representative of a first (form / type of) RAT, while Wi-Ficommunications may be considered as representative of a second RAT. In other cases,individual cellular RATs may be considered individually as different RATs. For example, whendifferentiating between cellular communications and Wi-Fi communications, "first RAT" maycollectively refer to all cellular RATs under consideration, while "second RAT" may refer toW7-Fi. Similarly, when applicable, different forms of Wi-Fi communications (e.g. over 2.4 GHzvs. over 5 GHz) may be considered as corresponding to different RATs. Furthermore, cellularcommunications performed according to a given RAT (e.g, LTE or NR) may be differentiatedfrom each other on the basis of the frequency spectrum in which those communications areconducted. For example, LTE or NR communications may be performed over a primarylicensed spectrum as well as over a secondary spectrum such as an unlicensed spectrum.Overall, the use of various terms and expressions will always be clearly indicated with respectto and within the context of the various applications / embodiments under consideration.

[0053] As shown, the base station 102A may also be equipped to communicate with a network100 (e.g., a core network of a cellular service provider, a telecommunication network such as apublic switched telephone network (PSTN), and / or the Internet, among various possibilities).Thus, the base station 102A may facilitate communication between the user devices and / orbetween the user devices and the network 100. In particular, the cellular base station 102A mayprovide UEs 106 with various telecommunication capabilities, such as voice, SMS and / or dataservices.

[0054] Base station 102A and other similar base stations (such as base stations 102B...102N)operating according to the same or a different cellular communication standard may thus beprovided as a network of cells, which may provide continuous or nearly continuous overlappingservice to UEs 106A-106N and similar devices over a geographic area via one or more cellularcommunication standards.

[0055] Thus, while base station 102A may act as a "serving cell" for UEs 106A-106N asillustrated in Figure 1, each UE 106 may also be capable of receiving signals from (and possiblywithin communication range of) one or more other cells (which might be provided by basestations 102B-N and / or any other base stations), which may be referred to as "neighboringcells". Such cells may also be capable of facilitating communication between user devices and / orbetween user devices and the network 100. Such cells may include "macro" cells, "micro" cells,"pico" cells, and / or cells which provide any of various other granularities of service area size.For example, base stations 102A-B illustrated in Figure 1 might be macro cells, while basestation 102N might be a micro cell. Other configurations are also possible.

[0056] In some embodiments, base station 102A may be a next generation base station, e.g., a5G New Radio (5G NR) base station, or "gNB". In some embodiments, a gNB may be connectedto a legacy evolved packet core (EPC) network and / or to a NR core (NRC) network. In addition,a gNB cell may include one or more transmission and reception points (TRPs). In addition, aUE capable of operating according to 5G NR may be connected to one or more TRPs within oneor more gNBs.

[0057] As mentioned above, UE 106 may be capable of communicating using multiple wirelesscommunication standards. For example, a UE 106 might be configured to communicate usingany or all of a 3GPP cellular communication standard (such as LTE or NR) or a 3GPP2 cellularcommunication standard (such as a cellular communication standard in the CDMA2000 familyof cellular communication standards). Base station 102A and other similar base stationsoperating according to the same or a different cellular communication standard may thus beprovided as one or more networks of cells, which may provide continuous or nearly continuousoverlapping service to UE 106 and similar devices over a wide geographic area via one or morecellular communication standards.

[0058] The UE 106 might also or alternatively be configured to communicate using WLAN,BLUETOOTH, BLUETOOTH Low-Energy, one or more global navigational satellitesystems (GNSS, e.g., GPS or GLONASS), one and / or more mobile television broadcastingstandards (e.g., ATSC-M / H or DVB-H), etc. Other combinations of wireless communicationstandards (including more than two wireless communication standards) are also possible.Furthermore, the UE 106 may also communicate with Network 100, through one or more basestations or through other devices, stations, or any appliances not explicitly shown but consideredto be part of Network 100. UE 106 communicating with a network may therefore be interpretedas the UE 106 communicating with one or more network nodes considered to be a part of thenetwork and which may interact with the UE 106 to conduct communications with the UE 106and in some cases affect at least some of the communication parameters and / or use ofcommunication resources of the UE 106.

[0059] Furthermore, as also illustrated in Figure 1, at least some of the UEs, e.g. UEs 106D and106E may represent vehicles communicating with each other and with base station 102, e.g. viacellular communications such as 3GPP LTE and / or SG-NR communications, for example. Inaddition, UE 106F may represent a pedestrian who is communicating and / or interacting withthe vehicles represented by UEs 106D and 106E in a similar manner. Further aspects of vehiclescommunicating in network exemplified in Figure 1 will be discussed below, for example in thecontext of vehicle-to-everything (V2X) communication such as the communications specified by3GPP TS 22.185 V.14.3.0, among others.

[0060] Figure 2 illustrates an exemplary user equipment 106 (e.g., one of the devices 106Athrough 106N) in communication with the base station 102 and an access point 112, accordingto some embodiments. The UE 106 may be a device with both cellular communication capabilityand non-cellular communication capability (e.g., BLUETOOTH, Wi-Fi, and so forth) such asa mobile phone, a hand-held device, a computer or a tablet, or virtually any type of wirelessdevice. The UE 106 may include a processor that is configured to execute program instructionsstored in memory. The UE 106 may perform any of the method embodiments described hereinby executing such stored instructions. Alternatively, or in addition, the UE 106 may include aprogrammable hardware element such as an FPGA (field-programmable gate array) that isconfigured to perform any of the method embodiments described herein, or any portion of anyof the method embodiments described herein. The UE 106 may be configured to communicateusing any of multiple wireless communication protocols. For example, the UE 106 may beconfigured to communicate using two or more of CDMA2000, LTE, LTE-A, NR, WLAN, orGNSS. Other combinations of wireless communication standards are also possible.

[0061] The UE 106 may include one or more antennas for communicating using one or morewireless communication protocols according to one or more RAT standards. In someembodiments, the UE 106 may share one or more parts of a receive chain and / or transmit chainbetween multiple wireless communication standards. The shared radio may include a singleantenna, or may include multiple antennas (e.g., for MIMO) for performing wirelesscommunications. Alternatively, the UE 106 may include separate transmit and / or receive chains(e.g., including separate antennas and other radio components) for each wireless communicationprotocol with which it is configured to communicate. As another alternative, the UE 106 mayinclude one or more radios which are shared between multiple wireless communicationprotocols, and one or more radios which are used exclusively by a single wireless communicationprotocol. For example, the UE 106 may include a shared radio for communicating using eitherof LTE or CDMA2000 1xRTT or NR, and separate radios for communicating using each ofWi-Fi and BLUETOOTH. Other configurations are also possible.Figure 3 - Exemplary UE

[0062] Figure 3 illustrates a block diagram of an exemplary UE 106, according to someembodiments. As shown, the UE 106 may include a system on chip (SOC) 300, which mayinclude portions for various purposes. For example, as shown, the SOC 300 may includeprocessor(s) 302 which may execute program instructions for the UE 106 and display circuitry304 which may perform graphics processing and provide display signals to the display 360. Theprocessor(s) 302 may also be coupled to memory management unit (MMU) 340, which may beconfigured to receive addresses from the processor(s) 302 and translate those addresses tolocations in memory (e.g., memory 306, read only memory (ROM) 350, NAND flash memory310) and / or to other circuits or devices, such as the display circuitry 304, radio circuitry 330,connector I / F 320, and / or display 360. The MMU 340 may be configured to perform memoryprotection and page table translation or set up. In some embodiments, the MMU 340 may beincluded as a portion of the processor(s) 302.

[0063] As shown, the SOC 300 may be coupled to various other circuits of the UE 106. Forexample, the UE 106 may include various types of memory (e.g., including NAND flash 310), aconnector interface 320 (e.g., for coupling to the computer system), the display 360, and wirelesscommunication circuitry (e.g., for LTE, LTE-A, NR, CDMA2000, BLUETOOTH", Wi-Fi,GPS, etc.). The UE device 106 may include at least one antenna (e.g, 335a), and possibly multipleantennas (e.g. illustrated by antennas 335a and 335b), for performing wireless communicationwith base stations and / or other devices. Antennas 335a and 335b are shown by way of example,and UE device 106 may include fewer or more antennas. Overall, the one or more antennas arecollectively referred to as antenna(s) 335. For example, the UE device 106 may use antenna(s)335 to perform the wireless communication with the aid of radio circuitry 330. As noted above,the UE may be configured to communicate wirelessly using multiple wireless communicationstandards in some embodiments.

[0064] As further described herein, the UE 106 (and / or base station 102) may include hardwareand software components for implementing methods for at least UE 106 to use an enhancedType If CST port selection codebook based at least on partial reciprocity during wirelesscommunications, e.g. during 5G-NR communications, as further detailed herein. Theprocessor(s) 302 of the UE device 106 may be configured to implement part or all of the methodsdescribed herein, e.g., by executing program instructions stored on a memory medium (e.g., anon-transitory computer-readable memory medium). In other embodiments, processor(s) 302may be configured as a programmable hardware element, such as an FPGA (FieldProgrammable Gate Array), or as an ASIC (Application Specific Integrated Circuit).Furthermore, processor(s) 302 may be coupled to and / or may interoperate with othercomponents as shown in Figure 3, to use an enhanced Type II CSI port selection codebook basedat least on partial reciprocity during wireless communications, e.g. during 5G-NRcommunications, according to various embodiments disclosed herein. Processor(s) 302 may alsoimplement various other applications and / or end-user applications running on UE 106.

[0065] In some embodiments, radio circuitry 330 may include separate controllers dedicated tocontrolling communications for various respective RAT standards. For example, as shown inFigure 3, radio circuitry 330 may include a Wi-Fi controller 356, a cellular controller (e.g. LTEand / or NR controller) 352, and BLUETOOTH controller 354, and in at least someembodiments, one or more or all of these controllers may be implemented as respectiveintegrated circuits (ICs or chips, for short) in communication with each other and with SOC300 (and more specifically with processor(s) 302). For example, Wi-Fi controller 356 maycommunicate with cellular controller 352 over a cell-ISM link or WCI interface, and / orBLUETOOTH controller 354 may communicate with cellular controller 352 over a cell-ISMlink, etc. While three separate controllers are illustrated within radio circuitry 330, otherembodiments have fewer or more similar controllers for various different RATs that may beimplemented in UE device 106. For example, at least one exemplary block diagram illustrativeof some embodiments of cellular controller 352 is shown in Figure 5 as further described below.Figure 4 - Exemplary Base Station

[0066] Figure 4 illustrates a block diagram of an exemplary base station 102, according to someembodiments. It is noted that the base station of Figure 4 is merely one example of a possiblebase station. As shown, the base station 102 may include processor(s) 404 which may executeprogram instructions for the base station 102. The processor(s) 404 may also be coupled tomemory management unit (MMU) 440, which may be configured to receive addresses from theprocessor(s) 404 and translate those addresses to locations in memory (e.g., memory 460 andread only memory (ROM) 450) or to other circuits or devices.

[0067] The base station 102 may include at least one network port 470. The network port 470may be configured to couple to a telephone network and provide a plurality of devices, such asUE devices 106, access to the telephone network as described above in Figures 1 and 2. Thenetwork port 470 (or an additional network port) may also or alternatively be configured tocouple to a cellular network, e.g., a core network of a cellular service provider. The corenetwork may provide mobility related services and / or other services to a plurality of devices,such as UE devices 106. In some cases, the network port 470 may couple to a telephone networkvia the core network, and / or the core network may provide a telephone network (e.g., amongother UE devices serviced by the cellular service provider).

[0068] The base station 102 may include at least one antenna 434, and possibly multipleantennas. The at least one antenna 434 may be configured to operate as a wireless transceiverand may be further configured to communicate with UE devices 106 via radio 430, The antenna434 communicates with the radio 430 via communication chain 432. Communication chain 432may be a receive chain, a transmit chain or both. The radio 430 may be designed tocommunicate via various wireless telecommunication standards, including, but not limited to,LTE, LTE-A, 5G-NR (or NR for short), WCDMA, CDMA2000, etc. The processor(s) 404 of thebase station 102 may be configured to implement part or all of the methods described herein,e.g., by executing program instructions stored on a memory medium (e.g., a non-transitorycomputer-readable memory medium), for base station 102 to communicate with a UE devicethat may use an enhanced Type II CSI port selection codebook based at least on partialreciprocity during wireless communications, eg. during SG-NR communications.Alternatively, the processor(s) 404 may be configured as a programmable hardware element,such as an FPGA (Field Programmable Gate Array), or as an ASIC (Application SpecificIntegrated Circuit), or a combination thereof. In the case of certain RATs, for example Wi-Fi,base station 102 may be designed as an access point (AP), in which case network port 470 maybe implemented to provide access to a wide area network and / or local area network (s), e.g. itmay include at least one Ethernet port, and radio 430 may be designed to communicateaccording to the Wi-Fi standard. Base station 102 may operate according to the variousmethods and embodiments as disclosed herein for communicating with UE devices that use anenhanced Type II CSI port selection codebook based at least on partial reciprocity for enhancedchannel state information reporting during wireless communications, e.g. during 5G-NRcommunications, as disclosed herein.Figure 5 - Exemplary Cellular Communication Circuitry

[0069] Figure 5 illustrates an exemplary simplified block diagram illustrative of cellularcontroller 352, according to some embodiments. It is noted that the block diagram of the cellularcommunication circuitry of Figure 5 is only one example of a possible cellular communicationcircuit; other circuits, such as circuits including or coupled to sufficient antennas for differentRATs to perform uplink activities using separate antennas, or circuits including or coupled tofewer antennas, e.g., that may be shared among multiple RATs, are also possible. According tosome embodiments, cellular communication circuitry 352 may be included in a communicationdevice, such as communication device 106 described above. As noted above, communicationdevice 106 may be a user equipment (UE) device, a mobile device or mobile station, a wirelessdevice or wireless station, a desktop computer or computing device, a mobile computing device(e.g., a laptop, notebook, or portable computing device), a tablet and / or a combination ofdevices, among other devices.

[0070] The cellular communication circuitry 352 may couple (e.g., communicatively; directly orindirectly) to one or more antennas, such as antennas 335a-b and 336 as shown. In someembodiments, cellular communication circuitry 352 may include dedicated receive chains(including and / or coupled to (e.g., communicatively; directly or indirectly) dedicated processorsand / or radios) for multiple RATs (e.g., a first receive chain for LTE and a second receive chainfor 5G NR). For example, as shown in Figure 5, cellular communication circuitry 352 mayinclude a first modem 510 and a second modem 520. The first modem 510 may be configuredfor communications according to a first RAT, e.g., such as LTE or LTE-A, and the secondmodem 520 may be configured for communications according to a second RAT, e.g., such as 5GNR.

[0071] As shown, the first modem 510 may include one or more processors 512 and a memory516 in communication with processors 512. Modem 510 may be in communication with a radiofrequency (RF) front end 530. RF front end 530 may include circuitry for transmitting andreceiving radio signals. For example, RF front end 530 may include receive circuitry (RX) 532and transmit circuitry (TX) 534. In some embodiments, receive circuitry 532 may be incommunication with downlink (DL) front end 550, which may include circuitry for receivingradio signals via antenna 335a.

[0072] Similarly, the second modem 520 may include one or more processors 522 and a memory526 in communication with processors 522. Modem 520 may be in communication with an RFfront end 540. RF front end 540 may include circuitry for transmitting and receiving radiosignals. For example, RF front end 540 may include receive circuitry 542 and transmit circuitry544. In some embodiments, receive circuitry 542 may be in communication with DL front end560, which may include circuitry for receiving radio signals via antenna 335b.

[0073] In some embodiments, a switch 570 may couple transmit circuitry 534 to uplink (UL)front end 572. In addition, switch 570 may couple transmit circuitry 544 to UL front end 572.UL front end 572 may include circuitry for transmitting radio signals via antenna 336. Thus,when cellular communication circuitry 352 receives instructions to transmit according to thefirst RAT (e.g., as supported via the first modem 510), switch 570 may be switched to a firststate that allows the first modem 510 to transmit signals according to the first RAT (e.g., via atransmit chain that includes transmit circuitry 534 and UL front end 572). Similarly, whencellular communication circuitry 352 receives instructions to transmit according to the secondRAT (e.g., as supported via the second modem 520), switch 570 may be switched to a secondstate that allows the second modem 520 to transmit signals according to the second RAT (e.g.,via a transmit chain that includes transmit circuitry 544 and UL front end 572).

[0074] As described herein, the first modem 510 and / or the second modem 520 may includehardware and software components for implementing any of the various features andtechniques described herein. The processors 512, 522 may be configured to implement part orall of the features described herein, e.g., by executing program instructions stored on a memorymedium (e.g., a non-transitory computer-readable memory medium). Alternatively (or inaddition), processors 512, 522 may be configured as a programmable hardware element, suchas an FPGA (Field Programmable Gate Array), or as an ASIC (Application Specific IntegratedCircuit). Alternatively (or in addition) the processors 512, 522, in conjunction with one or moreof the other components 530, 532, 534, 540, 542, 544, 550, 570, 572, 335 and 336 may beconfigured to implement part or all of the features described herein.

[0075] In addition, as described herein, processors 512, 522 may include one or more processingelements. Thus, processors 512, 522 may include one or more integrated circuits (ICs) that areconfigured to perform the functions of processors 512, 522. In addition, each integrated circuitmay include circuitry (e.g., first circuitry, second circuitry, etc.) configured to perform thefunctions of processors 512, 522.

[0076] In some embodiments, the cellular communication circuitry 352 may include only onetransmit / receive chain. For example, the cellular communication circuitry 352 may not includethe modem 520, the RF front end 540, the DL front end 560, and / or the antenna 335b. As anotherexample, the cellular communication circuitry 352 may not include the modem 510, the RF frontend 530, the DL front end 550, and / or the antenna 335a. In some embodiments, the cellularcommunication circuitry 352 may also not include the switch 570, and the RF front end 530 orthe RF front end 540 may be in communication, e.g., directly, with the UL front end 572.Type I Channel State Information (CSD Reporting

[0077] In 3GPP new radio (NR, or 5G-NR) systems, two types of codebook, Type I codebookand Type II codebook, have been standardized for CSI feedback in support of advanced MIMOoperations. The two types of codebook are constructed from a two-dimensional (2D) discreteFourier transform (DFT) based grid of beams, enabling CSI feedback of beam selection and co-phase combining between two polarizations. Type II codebook based CSI feedback also reportsthe wideband and subband amplitude information of the selected beams, allowing for moreaccurate CSI to be obtained. This, in turn, provides improved precoded MIMO transmissionsover the network.

[0078] Figure 6 shows an exemplary diagram illustrating the precoding structure associatedwith Type Il CSL reporting, according to prior art. The CSI may be reported to the base station(gNB) to indicate which precoding is preferred by the UE. As mentioned above, there are twotypes of codebooks for CSI reporting, or, worded differently, two types of CSI reporting, TypeI and Type II. In Type IT reporting, the precoding matrix is reported for each PMT subband,and is represented by a linear combination of a set of a specified number (L) of DFT vectorsrepresenting each column. As illustrated in Figure 6, there may be a specified number (Ns)subbands, with a corresponding precoding matrix W for each subband. Each precoding matrixincludes two columns, w1 and w2, Each column corresponds to the precoding vector for onelayer. For each layer, the precoding vector may be further divided into two parts, a firstpolarization and second polarization. The L DFT vectors are common for all subbands and areused in subband-specific combinations. Specifically, each column vector is a weightedsummation of the specified number (L) of vectors. The weighting (or combination) coefficientsfor the combination / combined weight are indicated in Figure 6 by co, ci, and c2. As indicated inthe example of Figure 6, vo, v1, and +2 represent three DFT vectors. The UE reports to the gNB,which three DFT vectors are preferred.

[0079] Figure 7 shows an exemplary diagram illustrating the reporting structure used by theUE to report back to the base station (e.g. to the gNB), according to prior art. Each subbandhas its own corresponding set of combination coefficients, and eventually the UE needs to reportall the combination coefficients. When considering the reporting by the UE, the Type IToverhead is dominated by the subband combination coefficient. According to the informationshown in Figure 7, the total number of entries is 2L x Ns, there is one (1) bit for amplitude, andthere are three (3) bits for phase. In a worst case scenario, there may be 19 subbands, 32transmit (TX) ports, and a CSI payload size of more than 1000 bits.Enhanced Codebook for Channel State Information (CSI) Port Selection

[0080] As previously indicated, in the 3GPP Rel-15 specification, beamformed CSI-RS (channelstate information - reference signal) exploits DL (downlink) and UL (uplink) channelreciprocity for Type II Port Selection. A total number of "X" CSI-RS ports may be selected,specifically X / 2 ports for horizontal polarization (HPol) and X / 2 ports for vertical polarization(VPol). A number "L" of CSI-RS ports may be selected out of X / 2 CSI-RS port, with the firstCSI-RS port selected every number "d" of ports. Then consecutive L ports may be selected withwraparound. The 3GPP Rel-16 specification discloses the same port selection design as Rel-15,while adding certain features. For example, when subband PMI (precoding matrix index) isconfigured, frequency domain DFT matrix can be used to compress the linear combinationcoefficient. For Type Il port selection codebook, the gNB is assumed to precode the CSI-RSbased on channel reciprocity. E.g., the DL channel may be estimated based on the UL channel.For FDD (frequency division duplex), exact channel reciprocity may not be present, especiallywhen the duplexing distance is large.

[0081] As indicated above, the use of channel reciprocity helps simplify Type II CSI-RS portselection design. The UL and DL channel may exhibit very similar channel characteristics, thuschannel estimates performed for either UL or DL may be used for the complementary direction,(DL or UL). The base station, instead of merely transmitting the non-precoded CSI-RSs andquerying the UE to report what the preferred beamforming vector is, may perform portselection so it can beamform the CSI-RSs and query the UE to indicate which CSI-RSs the UEprefers. The UE is allowed to indicate 'L" CSI-RS ports, e.g. 2 or 4 ports. Only L consecutive"window" contains L ports may be indicated to keep signaling manageable. The indicationconsecutive CSI-RS ports. The starting point of the window may be flexible but subject toanother parameter "d" in that the starting points have to be separated by a number "d" of CSI-RS ports. "d" may itself configurable (e.g. 1, 2, 3, or 4). In the worst case, only every forth CSI-RS port may represent the starting point of the window. Once the starting point of the windowhas been indicated, the next L CSI-RS ports may be reported.

[0082] There are clear limitations of how CSI ports are reported. The enhancements in 3GPPRel-16 are quite limited, for example to compressing the linear combination coefficient of thefrequency domain DFT matrix, as indicated in Figure 8). As previously mentioned, theassumption pertaining to reciprocity is that the UL channel and DL channel may be similar,and only one direction (UL or DL) channel needs to be estimated, with the same estimation usedfor the other, complementary channel. For FDD, there may be a paired UL / DL carrier with aduplexing distance introduced to minimize the interference between UL and DL channels. Asa result, there may not be channel reciprocity between UL and DL, especially when theduplexing distance is large. However, despite this the channels may still not be completelyuncorrelated, and some reciprocity may be present. In other words, even for FDD partialreciprocity may exist. Two properties have been identified as being highly correlated betweenUL and DL, the angle of arrival or departure and channel delay profile. The former pertainsto the angle of signal reflection, the latter itself is related to the signal reflection insofar thatsimilarly reflected signals will experience similar delays. Potentially, even the delay powerprofile may be similar. Type II Port selection may be enhanced by accommodating this partialreciprocity for FDD designs. For example, compression may be made more efficient by usingknowledge of channel delay and power profile, especially from the perspective of the base station(e.g. gNB), which may configure compression that is simpler for the UE. Overall, Type I CSIport selection may be enhanced by exploiting partial channel reciprocity, facilitating layerindependent CSI-RS port selection, layer common CSI-RS port selection, frequency domaincompression enhancement, and / or dynamic codebook parameter reconfiguration.

[0083] For improved CSI-RS transmission and CSI feedback or reporting, in someembodiments, based on an UL SRS transmitted by the UE to the base station (e.g. to a gNB), thegNB may estimate the UL channel and assume certain reciprocity of the channel to derivedownlink (DL) channel properties, e.g. preferred beam(s). The base station may then transmitthe CSI-RS precode with the preferred beam(s). The CSI-RS may have multiple CSI-RS ports,and each port may be transmitted from the base station using a different beam, i.e. each CSI-RS port may correspond to a different beam using which the CSI-RS port is transmitted. TheUE may indicate to the base station the preferred CSI-RS port(s) via CSI reporting, e.g. indicatethe preferred beam in an implicit way.

[0084] The base station may configure multiple frequency and time resources for a CSI-RSresource. For example, a CSI-RS resource may span up to 4 OFDM symbols and may occupydifferent resource elements (REs) in the frequency domain. A CSI-RS resource may have up to32 ports, i.e., there may be patterns to create up to 32 ports within the same CSI-RS resource.The patterns may be orthogonal to each other to allow the UE to properly identify separateports, e.g. to separate each port. When the gNB transmits CSI-RS port(s), the gNB may transmitup to 32 CSI-RS ports, and each CSI-RS port may be transmitted with (or using) a differentbeam (precoder). In a sense when the gNB transmits a CSI-RS resource, the gNB may betransmitting up to 32 ports with each port potentially being separately beamformed. The UEmay separate different CSI-RS ports according to specified orthogonal patterns, enabling theUE to measure the quality of each CSI-RS port and determine which CSI-RS port(s) have therelative highest quality.It should be noted that a port, as used herein, is understood to be a logic concept as establish inthe 3GPP specification. Accordingly, each port is configured or associated with certain resourceallocations and certain patterns on how to transmit certain signals, for example how to transmitCSI-RSs. Resource(s) may be configured or allocated for a CSI-RS port, for example, the first2 REs for each 6 REs in the frequency domain (an RE is the unit of subcarrier or tone in OFDM,and consecutive 4 symbols in the time domain.) Then, the pattern and how to generate thesequence for that particular port may be defined. For example, particular orthogonal patternsmay be specified. Thus, transmission of a CSI-RS port may be interpreted as transmission of aCSI-RS according to a specific frequency domain and time domain resource configuration andorthogonal pattern. The UE may also have an indication of the same configuration of frequencyand time resources and orthogonal pattern, allowing the UE to extract the correspondingsignal(s) and measure the quality of each CSI-RS port. For example, for every 4 REs in thefrequency domain, a gNB may transmit CSI-RS port 0, on the first RE, transmit CSI-RS port 1on the second RE, transmit CSI-RS port 2 on the third RE, and transmit CSI-RS port 3, on thefourth RE. Each CSI-RS port may be transmitted with a different corresponding beam, i.e.with a different corresponding precoding. In short, "transmitting a CSI-RS port" may beinterpreted as transmitting a CSI-RS according to a specific resource configuration, which mayinclude frequency resources, time resources, and additional possible resource configuration(s),such as the use of orthogonal cover codes corresponding to an orthogonal pattern.Layer Independent CSI-RS Port Selection

[0085] Figure 9 shows an exemplary diagram illustrating layer independent CSI-RS portselection. Referring to Figure 9, the signal between a transmitter 908 and receiver 902 maytravel through three different signal paths. A line of sight signal path (920), and two reflectedsignal paths (922 and 924, respectively). The respective signals over the three signal paths mayreach the receiver at the same time or at different times. The reflectors (904 and 906) maytypically be the same for UL and DL (e.g. representing a stationary element / structure). Thebase station 908 may detect the three paths during UL, e.g. it may detect that the strongestsignals were received over paths 920, 922, and 924, and may also proceed to transmit (DL)across / along those same three paths. The angle(s) of the strongest beams may be assumed tobe the same for UL and DL. There may thus be three channel directions with multiple beams(CSI-RS ports) associated with each direction. CSI-RS 0 and CSI-RS 1 correspond to signalpath 922, CSI-RS 2 and CSI-RS 3 correspond to signal path 920, and CSI-RS 4 and CSI-RS 5correspond to signal path 924. In the example shown in Figure 9, the base station (e.g. gNB) 908may identify two separate (candidate) beams (CSI-RS ports) and may select a preferred one ofthe two beams.

[0086] Considering the spatial basis, the beam may be common for the layer. That is, whenreporting a multilayer (e.g. four-layer) transmission, every layer may share the same spatialbasis. For example, when CSI-RS 0 is selected for layer 0, it may also be applied to (or selectedfor) layers 1, 2, and 3. However when the direction of the signal path is clearly known, it maybe beneficial to indicate which specific CSI port(s) is(are) preferred independently of thelayer(s). For example, when the UE and gNB support 3-layer transmission, there may be adominant path, and path 922 may be selected by (for) layer 1, and path 924 may be selected forlayer 2. In brief, the CSI-RS port selection may be performed independently for each layer.

[0087] According to one proposal, for each layer, only one CSI-RS port may be selected. TheCSI-RS port may be indicated for one polarization, and the same index may be automaticallyused for the other polarization. The first number "X / 2" of CSI-RS ports may correspond to thehorizontal polarization (HPol) and the second number "X / 2" of CSI-RS ports may correspondto the vertical polarization (VPol). The CSI-RS port with the same relative index may beselected for HPol and VPol.

[0088] According to another proposal, for each layer and for each PMI subband, beforecompression, only one linear combination coefficient is needed. For the HPol, no coefficientmay be needed, e.g. it may be assumed to have a specific value. For the VPol, the phase andamplitude may be needed. In other words, two CSI-RS ports may be selected for each layer, afirst port for HPol and second port for VPol. Not only the port but also the phase compensationthat the gNB intends to use may be indicated to ensure multiple ports are combined coherentlyon the UE side.

[0089] According to yet another proposal, the CSI-RS port selected from among the X / 2 CSI-RS ports may be indicated according to multiple options, still in a layer independent manner.

[0090] According to a first option, the UE may freely indicate which port to choose. In theexample of Figure 9, there are six ports, and any one of those six ports may be indicated. Threebits are required to indicate one out 6 of possible ports. This represents the most flexible design,essentially a completely free indication where [log2(X / 2)] bits may be needed per layer.

[0091] According to a second option, the X / 2 CSI-RS ports may be divided in to e groups, eachgroup with d CSI-RS ports. For example, the six ports shown in Figure 9 are divided into threegroups where each group corresponds to one of the signal paths as indicated (and previouslynoted above). Beam refinement (final selection) may be made within each respective group,with the corresponding path identified in the UL. So the group may be indicated, and then thespecific beam within the group may be selected. That is, the preferred group and an offsetwithin that group may be indicated to identify the port. The offsets may be the same for alllayers, and only the groups may need to be independently indicated per layer. Tradeoff isbetween overhead (less flexibility with reduced overhead) and flexibility (increased flexibilitywith increased overhead). The offset within the group may be common among all the layers,indicated using [leg2(d)] bits. The index of which group is independently signaled per layer maybe indicated using [log2(e)] bits. For example, if el and e2 are signaled for layer 1 and 2,respectively, and d_c is for all layers, el*d + d_c CSI-RS port is selected for layer1, and e2*d +d_c CSI-RS port is selected for layer2. The group index may be jointly coded across differentlayers to save overhead, using [log2(CeRI)] bits where CeRI; is the number of possible RI selectionsof out of e, where RI is the number of layers.Layer Common CSI-RS Port Selection

[0092] Figure 10 shows an exemplary diagram illustrating layer common CSI-RS port selection.For sake of simplicity only two signal paths 1022 and 1024 are shown (the line of sight signalpath is not considered). Signal path 1022 is reflected off reflector 1004 between base station1008 and UE 1002, while signal path 1024 is reflected off reflector 1006 between base station1008 and UE 1002. In this case there are two groups of four possible ports each, respectivelycorresponding to the two different (reflected) signal paths 1022 and 1024. In this case the portselection may be common for each layer. A respective beam may be selected from each group,the first group including CSI-RS 0, CSI-RS 1, CSI-RS 2, and CSI-RS 3, and the second groupincluding CSI-RS 4, CST-RS 5, CSI-RS 6, and CSI-RS 7. For example, two CSI-RS ports maybe selected from the two groups, and the beam(s) may be used for any single layer. Every singlelayer may be transmitted using any of the selected beams or using a linear combination of theselected beams.

[0093] In some embodiments, non-consecutive ports may be selected. In the example shown inFigure 10, CSI-RS ports 1 and 5 may be selected. This provides flexibility for the UE to pairthe beams instead of being limited by the ordering of the ports, e.g. by the order in which theports are transmitted by the gNB. The CSI-RS port selection may be done jointly and may becommon for each layer. L out of X / 2 CSI-RS ports may be selected for HPol and VPol, and theCSI-RS ports with the same relative index may be selected for HPol and VPol.

[0094] The CSI-RS ports may be indicated according to multiple options.

[0095] According to a first option 1, the ports may be divided into groups, e.g. two groups maybe selected. Within the groups, one CSI-RS port may be selected, and an offset may also beindicated. In the example shown in Figure 10, the offset is 1, hence CSI-RS (port) 1 is selectedfrom the top group (corresponding to signal path 1022) and CSI-RS (port) 5 is selected from thebottom group (corresponding to signal path 1024). More generally, the number "X / 2" of CSI-RS ports may be divided into a number "e" of groups, each group with a number "d" of CSI-RS ports. The offset within the group may be common among all the layers, for example e = 2and d= 4. A number "L" out of "e" groups may be selected using. [log2(CeL)] bits. For eachselected group, one CSI-RS may be selected. The relative index with the CSI-RS group may bethe same, e.g. [log2(d)] for all groups, or it may be independent, e.g. [leg2(d)] for each group.

[0096] According to a second option, a completely free indication may be provided using[log2(CLX / 2 )] bits.

[0097] According to a third option, multiple ports may be reported within a group. Forexample, instead of reporting one port from a group (CSI-RS 1 in top group as in previousexample), multiple ports from the group may be reported. Thus, the X / 2 CSI-RS may be dividedinto a number "e" of groups, each group with a number "d" CSI-RS ports. The offset withinthe group may be common among all the layers, for example e = 2 and d =4. A subset of groupsmay be selected, with a total number "L" out of X / 2 CSI-RS ports selected. One, or more thanone CSI-RS port may be chosen for each group, and the number of CSI-RS ports selected pergroup may be limited to be the same.

[0098] According to a fourth option, a subset of groups may be selected, which may be one groupor more than one group. When a group is selected, all the CSI-RS ports within the group maybe selected.Frequency Domain Compression Enhancement

[0099] In 3GPP Rel-16, N3 refers to the number of subbands for PMI reporting. DFTcompression is used to compress frequency domain coefficients. Only a number "M" out of anumber "N3" of DFT bases are used. When N3 <= 19, M is chosen freely among N3 DFT bases.When N3 > 19, M is chosen within a 2M window. The location of the 2M window may be shiftedup to 2M around the DC component.

[00100] Figure 11 shows an exemplary diagram illustrating frequency domain compression forCSI-RS port selection, according to some embodiments. The number of rows in matrix 1100represent the spatial bases. For example, for L spatial bases there are 2L rows (L for eachpolarization). The number of columns represent the subband, for example up to 19 or 38subbands to be reported. The example illustrates an 8 x 19 matrix (1100). Every column forthis particular subband is a preferred linear combination among 8 spatial bases. The matrix isto be reported back to the gNB together with the spatial bases. The gNB then multiplies thematrix with the spatial bases to reconstruct the beam that the gNB will use for DL transmission.

[00101] One issue that may arise is the channel exhibiting a flat frequency characteristic. If thechannel has a much shorter time span, then it may be fairly flat in frequency. If there is nomultipath in the time domain then the channel delay profile may be very short and there maynot be much frequency selectivity, for example every single frequency domain may contain thesame / similar channels. _ If there are more multipaths in the time domain then there may bemore selectivity in the frequency domain.

[00102] Delay reciprocity may be leveraged by considering how many multipaths the ULchannel has and what the delay profile of the UL channel is. The delay profile may be verysimilar for UL and DL. The base station may be able to determine frequency selectivity on theDL based on the UL delay profile. DFT (of the matrix) from frequency domain to time domainallows for compression. In the example of Figure 11, only columns 1, 3, 4, and 6 correspond tofrequency bases with high energy (e.g. worth considering for transmissions), therefore the otherfrequency bases need not be considered. Thus, to provide further improvement, in someembodiments, the base station may not request information for the entire time domain. Oncethe base station has knowledge of the time domain pattern of the channel, it may help reduceoverhead by instructing the UE to report a subset of the frequency bases, which afterundergoing DFT represent different time domain taps.

[00103] In some embodiments, the base station may preconfigure the subset of DFT bases forcoefficient compression according to multiple options. That is, the base station may indicatewhich taps (each tap represented by a column in matrix 1150) it prefers.

[00104] According to a first option, the bases station may provide a bitmap to indicate the DFTbasis (or bases) that may be used for compression. For each enabled DFT basis, the base stationmay further configure the limitation on the amplitude that can be used. The same amplitudelimit may apply to all the spatial bases and layers. The amplitude limit may apply to theamplitude average over all spatial bases within the same layer and / or over all spatial basesacross all layers. Each coefficient may correspond to a spatial basis. The base station mayindicate in the bitmap whether the UE is to provide an indication corresponding to a given tap.The base station may provide an indication to the UE regarding restrictions for the given taps,such as energy restricted within certain threshold, for example. The bitmap may berepresentative of which taps are to be turned on and off. For "on", additional restrictions maybe indicated. E.g. the total energy corresponding to a given (selected / active) column may notexceed a specified threshold.

[00105] According to a second option, the base station may provide the window size for the DFTbasis (or bases), e.g. the maximum delay spread. The windows may have an initial offset withrespect to the DC component. The base station may further limit the basis selection within thewindow. Generally, once the base station has determined / obtained the delay profile of thechannel and how to select the column (select the frequency basis), it may assist the UE in furtherreducing overhead.Dynamic Codebook Parameter Reconfiguration

[00106] The codebook resolution and overhead depends on many factors for Type II CSIreporting. The configuration is mostly semi-statically configured in RRC per the current 3GPPRel-15 and Rel-16 standard. When the Sounding Reference Signal (SRS) can provide partialreciprocity, the parameter may be dynamically configured for further base CSI reportingenhancement. The SRS is a reference signal transmitted by the UE in the uplink direction andis used by the base station to estimate the uplink channel quality over a wider bandwidth. Thebase station may use this information for uplink frequency selective scheduling. When SRSprovides partial reciprocity based CSI report enhancement, dynamic configuration of theparameters may provide additional advantages. Thus, as opposed to configuring theparameters semi-statically via RRC, they may be dynamically configured in response toindication(s) received by the UE from the base station. For example, the base station maydetermine that the channel has become very directional and may instruct UE to report a reducednumber of spatial bases with respect to possible available spatial bases. The dynamicconfiguration may be achieved through MAC-CE or L1 DCI. The configured parameters mayinclude angle related parameters, e.g. the number of spatial bases selected. They may furtherinclude delay related parameters, e.g. the number of frequency bases selected, the number ofnon-zero coefficients, and / or the PMI oversampling factor (e.g. 1 or 2).Layer common CSI-RS Port Selection Examples

[00107] In some embodiments, downlink CSI may be derived from uplink transmissions, e.g.with SRS for FDD systems. For an FDD system, due to the duplex separation between DL andUL, many parameters for the propagation channels (DL and UL) can be consideredindependent, but some other parameters may be treated as correlated, for example angle ofdeparture and the delay profile at the base station (e.g. gNB), which may provide an opportunityfor the gNB to derive useful information concerning DL from the received UL signal, e.g. SRSor DMRS of PUSCH / PUCCH or PRACH or even UL channels such as PUSCH or PUCCH.Similar to the situation for TDD, due to various reasons, e.g. power consumption, form factor,etc., a UE may have more DL antennas than UL antennas, hence for a FDD system, besidesduplex separation, the imparity between DL and UL antenna numbers may lead to furtherobstacles in deriving DL CSI from UL transmission(s).

[00108] One feasible approach is for the gNB to derive the angle of departure and delay profilefrom UL observations over UL signals, e.g. identifying orthogonal DFT beams at the ULfrequency with significant power, then applying the necessary carrier frequency adjustment toorthogonal DFT beams at the DL frequency. It may also be possible for the gNB to implementa proprietary algorithm which may be applied to the UL observations to obtain the DLprecoding vectors for CSI-RS. Hence if a solution which does not depend on any specialstructure in the precoder for CSI-RS is available, then it may be applicable to broad scenarios.

[00109] In 3GPP Rel-15 and 3GPP Rel-16, for Type I port selection codebook design the portselection is through a number of neighboring CSI-RS ports, and is wideband. Considering theabove, and further considering that the overhead due to wideband signaling may present a lessserious issue than that due to subband signaling in CSI feedback, free antenna port selectionmay be used.

[00110] Instead of using i,; to select ports {i1,1 x d +0,i1,1 x d + 1,..., i1,1 x d - L - 1}and {PCSI-RS / 2 + i1,1 x d + 0,PCSI-RS / 2 + i1,1 x d + 1,..., PCSI-RS / 2 + i1,1 x d - L - 1},where d is the parameter configured by the gNB, and PCSI-RS is the number of CSI-RS portsconfigured for the port selection codebook, L ports from among PCSI-RS / 2 ports may bechosen, presumably for polarization 0. The selected port indices are given by{S0,0,S01,...,S0,L-1}, and S0,0 < S0,1 <...< S0,L-1, and the same port selection is applied topolarization 1 (presumably): {S1,0,S1,1,...,S1,L-1} = {PCSI-RS / 2 + S0,0,PCSI-RS / 2 +S0,1,...,PCSI-RS / 2 + S0,L-1}.

[00111] Depending on the precoders applied to the CSI-RS, the gNB may select differentnumbers of CSI-RS ports for different polarizations: e.g. three ports for the +45° polarization,and five ports for -45° polarization, hence ports may also be selected from among all CSI-RSports.

[00112] In some embodiments, port selection may freely be conducted over all PCSI-RS ports,e.g. 2L out of PCSI-RS ports may be selected. Combinatorial indexing (as also defined in 3GPPRel-15 and 3GPP Rel-16) may be used. Alternatively, a PCSI-RS bit bitmap or PCSI-RS / 2 bitbitmap can be used to indicate the selection of ports, eg. with PCSI-RS = 8,a 8 bit bitmap[00111001] signifies ports 2, 3, 4, 7 are selected, anda4 bit bitmap [01 01] signifies ports 1, 3, 5, 7 are selected.

[00113] It is also possible that due to difference in UL and DL channel propagation, the DLchannel information derived from the UL channel may not match the actual DL channelinformation. To tackle that, the gNB may choose to use one or more beam groups in theneighbor of the beam group derived from the UL channel, and precode all of them for the UEto test. In such a case the UE may feed back both the beam group index, and the port selectionwith the selected beam group. Assuming a beam group is mapped to Q CSI-RS ports, and therebeing G beam groups in total - e.g. the first Q CSI-RS ports for beam group 1, and the secondQCSI-RS ports for beam group 2 - the UE may feed back the beam group index (1 or 2 in theexample), and a bitmap for the selected ports in selected beam group. In Figure 13, two beamgroups (1302 and 1304) are shown, so G = 2,Q = 4. Within each beam group, there are Qbeams. If, for example, the UE selects the 1302 beam, the bitmap

[1001] may select beams 1 and4 from the 1302 beam group.

[00114] Referring again to Figure 10, the CSI-RS port selection may be done jointly and may becommon for each layer. A number "L" out of X / 2 CSI-RS ports may be selected for HPol andVPol. The CSI-RS ports with the same relative index may be selected for HPol and V-Pol. Thesignaling overhead may be [log2(CLX / 2)] bits. In the example shown in Figure 10, X=8, andselection of port 0 from the top group may be coupled with selection of port 5 from the bottomgroup, and selection of port 1 from the top group may be coupled with selection of port 6 fromthe bottom group.

[00115] Figure 12 shows an exemplary diagram illustrating layer common CSI-RS port selectionusing completely free indication. For sake of simplicity only two signal paths 1222 and 1224 areshown (the line of sight signal path is not considered). Signal path 1222 is reflected off reflector1204 between base station 1208 and UE 1202, while signal path 1224 is reflected off reflector1206 between base station 1208 and UE 1202. In this case there are two groups of four possibleports each, respectively corresponding to the two different (reflected) signal paths 1222 and1224, In this case the port selection may be common for each layer. A respective beam may beselected from each group, the first group including CSI-RS 0, CSI-RS 1, CSI-RS 2, and CSI-RS3, and the second group including CSI-RS 4, CSI-RS 5, CSI-RS 6, and CSI-RS 7. For example,two CSI-RS ports may be selected from the two groups, and the beam(s) may be used for anysingle layer. Every single layer may be transmitted using any of the selected beams or using alinear combination of the selected beams. In the example shown in Figure 12, CSI-RS 1 isselected from the top group, while CSI-RS 7 is selected from the bottom group, which suggeststhat selection of the CSI-RS ports is completely free, and the ports may be indicated to the UEusing [log2(CLX)] bits.

[00116] Antenna group selection may be combined with either approach described above.Figure 13 shows an exemplary diagram illustrating antenna group selection for layer commonCSI-RS port selection, as previously referenced above. In the example illustrated in Figure 13,X=32, X'°=8, e=4. The number "X" of CSI-RSs may be divided in to a number "e" of groups,each group with X' CSI-RS ports. One of the groups may be selected, with a total number "L"out of X' CSRS ports selected. One CSI-RS port or more than one CSI-RS port may be chosenfor each group. The number of CSI-RS ports selected per group may be determined accordingto either approach discussed above. If the gNB bases decisions on the observed beams (1304 -DL), then under certain conditions there may be a mismatch between UL and DL. As a safetymeasure, it is possible for the gNB to configure two beam groups. A first beam group (1302)and a second beam group (1304). UE may select a beam group, e.g. 1302, and may take thenecessary steps to select the ports. In the example in Figure 13, if X is the total number ofantenna ports, e is the number of beam groups, and X' is the number of CSI ports per beamgroup, then e=2 and X'=4.

[00117] It is well understood that the use of personally identifiable information should followprivacy policies and practices that are generally recognized as meeting or exceeding industry orgovernmental requirements for maintaining the privacy of users. In particular, personallyidentifiable information data should be managed and handled so as to minimize risks ofunintentional or unauthorized access or use, and the nature of authorized use should be clearlyindicated to users.

[00118] Embodiments of the present invention may be realized in any of various forms. Forexample, in some embodiments, the present invention may be realized as a computer-implemented method, a computer-readable memory medium, or a computer system. In otherembodiments, the present invention may be realized using one or more custom-designedhardware devices such as ASICs. In other embodiments, the present invention may be realizedusing one or more programmable hardware elements such as FPGAs.

[00119] In some embodiments, a non-transitory computer-readable memory medium (e.g., anon-transitory memory element) may be configured so that it stores program instructionsand / or data, where the program instructions, if executed by a computer system, cause thecomputer system to perform a method, e.g., any of a method embodiments described herein, or,any combination of the method embodiments described herein, or, any subset of any of themethod embodiments described herein, or, any combination of such subsets.

[00120] In some embodiments, a device (e.g., a UE) may be configured to include a processor (ora set of processors) and a memory medium (or memory element), where the memory mediumstores program instructions, where the processor is configured to read and execute the programinstructions from the memory medium, where the program instructions are executable toimplement any of the various method embodiments described herein (or, any combination ofthe method embodiments described herein, or, any subset of any of the method embodimentsdescribed herein, or, any combination of such subsets). The device may be realized in any ofvarious forms.

[00121] Although the embodiments above have been described in considerable detail, numerousvariations and modifications will become apparent to those skilled in the art once the abovedisclosure is fully appreciated. It is intended that the following claims be interpreted to embraceall such variations and modifications.

Claims

1. A method comprising: identifying, by a base station, dominant signal paths between the base station and a device, based on channel estimates performed using uplink communications between the base station and the device; and transmitting, by the base station to the device, channel state information reference signal (CSI-RS) ports corresponding to the dominant signal paths, wherein the CSI-RS ports are transmitted over corresponding beams identified independently by the base station for each dominant signal path of the dominant signal paths.

2. The method of claim 1, further comprising: indicating, by the device to the base station, selection of a subset of the CSI-RS ports, wherein the selection is either independent for each layer of a multilayer transmission or in common for each layer of the multilayer transmission.

3. The method of claim 2, wherein the selection is of a single respective CSI-RS port for each layer of the multilayer transmission.

4. The method of claim 3, wherein the single respective CSI-RS port is for a first polarization, and a same index corresponding to the single CSI-RS port is automatically used for a second polarization.

5. The method of claim 1, wherein the selection is of two respective CSI-RS ports for each layer of the multilayer transmission.

6. The method of claim 5, wherein a first of the two respective CSI-RS ports is for a first polarization and a second of the two respective CSI-RS ports is for a second polarization.

7. The method of claim 1, further comprising: identifying a respective plurality of candidate CSI-RS ports for each dominant signal path of the dominant signal paths; selecting respective preferred CSI-RS ports of the respective plurality of candidate CSI- RS ports for each dominant signal path; and transmitting the respective preferred CSI-RS ports as the CSI-RS ports to the device.

8. An apparatus comprising: a processor configured to cause a device to: receive channel state information reference signal (CSI-RS) ports corresponding to dominant signal paths between a base station and the device, wherein the dominant signal paths are identified based on channel estimates performed using uplink communications between the base station and the device, wherein the CSI-RS ports are transmitted over corresponding beams identified independently by the base station for each dominant signal path of the dominant signal paths.

9. The apparatus of claim 8, wherein the processor is configured to cause the device to: indicate to the base station, selection of a subset of the CSI-RS ports, wherein the selection is either independent for each layer of a multilayer transmission or in common for each layer of the multilayer transmission.

10. The apparatus of claim 9, wherein the selection is of a single respective CSI-RS port for each layer of the multilayer transmission.

11. The apparatus of claim 10, wherein the single respective CSI-RS port is for a first polarization and a same index corresponding to the single CSI-RS port is automatically used for a second polarization.

12. The apparatus of claim 8, wherein the selection is of two respective CSI-RS ports for each layer of the multilayer transmission.

13. The apparatus of claim 12, wherein a first of the two respective CSI-RS ports is for a first polarization and a second of the two respective CSI-RS ports is for a second polarization.

14. An apparatus comprising: a processor configured to cause a base station to: identify dominant signal paths between the base station and a device based on channel estimates performed using uplink communications between the base station and the device; and transmit, to the device, channel state information reference signal (CSI-RS) ports corresponding to the dominant signal paths, wherein the CSI-RS ports are transmitted over corresponding beams identified independently by the base station for each dominant signal path of the dominant signal paths.

15. The apparatus of claim 14, wherein the processor is configured to cause the base station to: receive, from the device, an indication of a selection of a subset of the CSI-RS ports, wherein the selection is either independent for each layer of a multilayer transmission or in common for each layer of the multilayer transmission.

16. The apparatus of claim 15, wherein the selection is of a single respective CSI-RS port for each layer of the multilayer transmission.

17. The apparatus of claim 16, wherein the single respective CSI-RS port is for a first polarization and a same index corresponding to the single CSI-RS port is automatically used for a second polarization.

18. The apparatus of claim 14, wherein the selection is of two respective CSI-RS ports for each layer of the multilayer transmission.

19. The apparatus of claim 18, wherein a first of the two respective CSI-RS ports is for a first polarization and a second of the two respective CSI-RS ports is for a second polarization.

20. The apparatus of claim 14, wherein the processor is configured to cause the base station to: identify a respective plurality of candidate CSI-RS ports for each dominant signal path of the dominant signal paths; select respective preferred CSI-RS ports of the respective plurality of candidate CSI-RS ports for each dominant signal path; and transmit the respective preferred CSI-RS ports as the CSI-RS ports to the device.