WO2023015509A1

WO2023015509A1 - Considerations on csi-rs configurations for interference in proximity to a reconfigurable intelligent surface

Info

Publication number: WO2023015509A1
Application number: PCT/CN2021/112169
Authority: WO
Inventors: Ahmed Elshafie; Yu Zhang; Hung Dinh LY; Saeid SAHRAEI
Original assignee: Qualcomm Incorporated
Priority date: 2021-08-12
Filing date: 2021-08-12
Publication date: 2023-02-16

Abstract

A UE receives a first RRC configuration associated with a reference signal, performs a measurement of the reference signal and receives information identifying at least one beam configuration selected by a first UE for a transmission from a first base station to the first UE via an RIS, transmits to at least one base station an indication of a null space based on the measurement of the reference signal and the at least one beam configuration selected by the first UE. In some aspects, the UE may be configured to receive a first RRC configuration associated with a reference signal, perform a measurement of the reference signal for multiple beam configurations associated with a transmission from a base station to the first UE via an RIS and transmit, to a second UE, an indication of at least one beam configuration based on the measurement.

Description

CONSIDERATIONS ON CSI-RS CONFIGURATIONS FOR INTERFERENCE IN PROXIMITY TO A RECONFIGURABLE INTELLIGENT SURFACE

TECHNICAL FIELD

The present disclosure relates generally to communication systems, and more particularly, to communications involving reconfigurable intelligent surfaces (RIS) .

INTRODUCTION

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources. Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is 5G New Radio (NR) . 5G NR is part of a continuous mobile broadband evolution promulgated by Third Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with Internet of Things (IoT) ) , and other requirements. 5G NR includes services associated with enhanced mobile broadband (eMBB) , massive machine type communications (mMTC) , and ultra-reliable low latency communications (URLLC) . Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE) standard. There exists a need for further improvements in 5G NR technology. These improvements may also be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

BRIEF SUMMARY

The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a second device at a second user equipment (UE) . The second device may be a processor and/or modem at the second UE or the second UE itself. The second UE may be configured to receive a first radio resource control (RRC) configuration associated with a reference signal. The second UE may further be configured to perform a measurement of the reference signal and receive information identifying at least one beam configuration selected by a first UE for a transmission from a first base station to the first UE via an RIS. The second UE may also be further be configured to transmit to at least one base station an indication of a null space based on the measurement of the reference signal and the at least one beam configuration selected by the first UE.

In another aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a first device at a first UE. The first device may be a processor and/or modem at the first UE or the first UE itself. The first UE may be configured to receive a first RRC configuration associated with a reference signal and perform a measurement of the reference signal for multiple beam configurations associated with a transmission from a base station to the first UE via an RIS. The first UE may also be configured to transmit, to a second UE, an indication of at least one beam configuration based on the measurement.

In another aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a first device at a base station. The first device may be a processor and/or modem at the base station or the base station itself. The base station may be configured to transmit, to the second UE a first RRC configuration associated with a reference signal. The base station may further be configured to receive an indication of a null space from the second UE based on measurement of the reference signal and at least one beam configuration selected by a first UE for transmission from a first base station to the first UE via a RIS.

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

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communications system and an access network.

FIG. 2A is a diagram illustrating an example of a first frame, in accordance with various aspects of the present disclosure.

FIG. 2B is a diagram illustrating an example of DL channels within a subframe, in accordance with various aspects of the present disclosure.

FIG. 2C is a diagram illustrating an example of a second frame, in accordance with various aspects of the present disclosure.

FIG. 2D is a diagram illustrating an example of UL channels within a subframe, in accordance with various aspects of the present disclosure.

FIG. 3 is a diagram illustrating an example of a base station and user equipment (UE) in an access network.

FIG. 4 is a set of diagrams illustrating examples in which a base station transmits beamformed communication to UEs using directional beams.

FIG. 5 illustrates an example in which the RIS includes multiple subsets of multiple RIS elements.

FIG. 6 is a set of diagrams illustrating examples in which a base station transmits beamformed communication to a UE using directional beams that increase interference at a second UE in a different cell or a same cell, respectively.

FIG. 7 is a call flow diagram illustrating a first and second UE served by a same base station mitigating interference at the second UE from transmissions to the first UE via an RIS.

FIG. 8 is a call flow diagram illustrating a first and second served by different base stations mitigating interference at the second UE from transmissions to the first UE from the first base station via an RIS.

FIG. 9 is a set of diagrams illustrating a set of beam training operations.

FIG. 10 is a diagram illustrating the transmission of a beam selection indication and the transmission a null space indication in a system of two base stations.

FIG. 11 is a flowchart of a method of wireless communication.

FIG. 12 is a flowchart of a method of wireless communication.

FIG. 13 is a flowchart of a method of wireless communication.

FIG. 14 is a flowchart of a method of wireless communication.

FIG. 15 is a flowchart of a method of wireless communication.

FIG. 16 is a flowchart of a method of wireless communication.

FIG. 17 is a diagram illustrating an example of a hardware implementation for an example apparatus.

FIG. 18 is a diagram illustrating an example of a hardware implementation for an example apparatus.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as “elements” ) . These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or any combination of elements may be implemented as a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs) , central processing units (CPUs) , application processors, digital signal processors (DSPs) , reduced instruction set computing (RISC) processors, systems on a chip (SoC) , baseband processors, field programmable gate arrays (FPGAs) , programmable logic devices (PLDs) , state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

Accordingly, in one or more example embodiments, the functions described may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise a random-access memory (RAM) , a read-only memory (ROM) , an electrically erasable programmable ROM (EEPROM) , optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of the types of computer-readable media, or any other medium that can be used to store computer executable code in the form of instructions or data structures that can be accessed by a computer.

While aspects and implementations are described in this application by illustration to some examples, those skilled in the art will understand that additional implementations and use cases may come about in many different arrangements and scenarios. Innovations described herein may be implemented across many differing platform types, devices, systems, shapes, sizes, and packaging arrangements. For example, implementations and/or uses may come about via integrated chip implementations and other non-module-component based devices (e.g., end-user devices, vehicles, communication devices, computing devices, industrial equipment, retail/purchasing devices, medical devices, artificial intelligence (AI) -enabled devices, etc. ) . While some examples may or may not be specifically directed to use cases or applications, a wide assortment of applicability of described innovations may occur. Implementations may range a spectrum from chip-level or modular components to non-modular, non-chip-level implementations and further to aggregate, distributed, or original equipment manufacturer (OEM) devices or systems incorporating one or more aspects of the described innovations. In some practical settings, devices incorporating described aspects and features may also include additional components and features for implementation and practice of claimed and described aspect. For example, transmission and reception of wireless signals necessarily includes a number of components for analog and digital purposes (e.g., hardware components including antenna, RF-chains, power amplifiers, modulators, buffer, processor (s) , interleaver, adders/summers, etc. ) . It is intended that innovations described herein may be practiced in a wide variety of devices, chip-level components, systems, distributed arrangements, aggregated or disaggregated components, end-user devices, etc. of varying sizes, shapes, and constitution.

FIG. 1 is a diagram illustrating an example of a wireless communications system and an access network 100. The wireless communications system (also referred to as a wireless wide area network (WWAN) ) includes base stations 102, UEs 104, an RIS 103, an Evolved Packet Core (EPC) 160, and another core network 190 (e.g., a 5G Core (5GC) ) . In some aspects, the RIS 103 may reflect beamformed communication between a base station and a UE to avoid a blockage 107 that blocks a directional beam between the base station 102 or 180 and the UE 104. The RIS 103 may be associated with a controller component 105. Discovery information, such as RIS capability information and/or position information for the RIS 103 may be transmitted by the controller component 105, e.g., via sidelink.

The base stations 102 may include macrocells (high power cellular base station) and/or small cells (low power cellular base station) . The macrocells include base stations. The small cells include femtocells, picocells, and microcells.

The base stations 102 configured for 4G LTE (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN) ) may interface with the EPC 160 through first backhaul links 132 (e.g., S1 interface) . The base stations 102 configured for 5G NR (collectively referred to as Next Generation RAN (NG-RAN) ) may interface with core network 190 through second backhaul links 184. In addition to other functions, the base stations 102 may perform one or more of the following functions: transfer of user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity) , inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS) , subscriber and equipment trace, RAN information management (RIM) , paging, positioning, and delivery of warning messages. The base stations 102 may communicate directly or indirectly (e.g., through the EPC 160 or core network 190) with each other over third backhaul links 134 (e.g., X2 interface) . The first backhaul links 132, the second backhaul links 184, and the third backhaul links 134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Each of the base stations 102 may provide communication coverage for a respective geographic coverage area 110. There may be overlapping geographic coverage areas 110. For example, the small cell 102′ may have a coverage area 110′ that overlaps the coverage area 110 of one or more macro base stations 102. A network that includes both small cell and macrocells may be known as a heterogeneous network. A heterogeneous network may also include Home Evolved Node Bs (eNBs) (HeNBs) , which may provide service to a restricted group known as a closed subscriber group (CSG) . The communication links 120 between the base stations 102 and the UEs 104 may include uplink (UL) (also referred to as reverse link) transmissions from a UE 104 to a base station 102 and/or downlink (DL) (also referred to as forward link) transmissions from a base station 102 to a UE 104. The communication links 120 may use multiple-input and multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The communication links may be through one or more carriers. The base stations 102 /UEs 104 may use spectrum up to YMHz (e.g., 5, 10, 15, 20, 100, 400, etc. MHz) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. The carriers may or may not be adjacent to each other. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or fewer carriers may be allocated for DL than for UL) . The component carriers may include a primary component carrier and one or more secondary component carriers. A primary component carrier may be referred to as a primary cell (PCell) and a secondary component carrier may be referred to as a secondary cell (SCell) .

Certain UEs 104 may communicate with each other using device-to-device (D2D) communication link 158. The D2D communication link 158 may use the DL/UL WWAN spectrum. The D2D communication link 158 may use one or more sidelink channels, such as a physical sidelink broadcast channel (PSBCH) , a physical sidelink discovery channel (PSDCH) , a physical sidelink shared channel (PSSCH) , and a physical sidelink control channel (PSCCH) . D2D communication may be through a variety of wireless D2D communications systems, such as for example, WiMedia, Bluetooth, ZigBee, Wi-Fi based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, LTE, or NR.

The wireless communications system may further include a Wi-Fi access point (AP) 150 in communication with Wi-Fi stations (STAs) 152 via communication links 154, e.g., in a 5 GHz unlicensed frequency spectrum or the like. When communicating in an unlicensed frequency spectrum, the STAs 152 /AP 150 may perform a clear channel assessment (CCA) prior to communicating in order to determine whether the channel is available.

The small cell 102′ may operate in a licensed and/or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell 102′ may employ NR and use the same unlicensed frequency spectrum (e.g., 5 GHz, or the like) as used by the Wi-Fi AP 150. The small cell 102′, employing NR in an unlicensed frequency spectrum, may boost coverage to and/or increase capacity of the access network.

The electromagnetic spectrum is often subdivided, based on frequency/wavelength, into various classes, bands, channels, etc. In 5G NR, two initial operating bands have been identified as frequency range designations FR1 (410 MHz -7.125 GHz) and FR2 (24.25 GHz -52.6 GHz) . Although a portion of FR1 is greater than 6 GHz, FR1 is often referred to (interchangeably) as a “sub-6 GHz” band in various documents and articles. A similar nomenclature issue sometimes occurs with regard to FR2, which is often referred to (interchangeably) as a “millimeter wave” band in documents and articles, despite being different from the extremely high frequency (EHF) band (30 GHz -300 GHz) which is identified by the International Telecommunications Union (ITU) as a “millimeter wave” band. The frequencies between FR1 and FR2 are often referred to as mid-band frequencies. Recent 5G NR studies have identified an operating band for these mid-band frequencies as frequency range designation FR3 (7.125 GHz -24.25 GHz) . Frequency bands falling within FR3 may inherit FR1 characteristics and/or FR2 characteristics, and thus may effectively extend features of FR1 and/or FR2 into mid-band frequencies. In addition, higher frequency bands are currently being explored to extend 5G NR operation beyond 52.6 GHz. For example, three higher operating bands have been identified as frequency range designations FR4a or FR4-1 (52.6 GHz -71 GHz) , FR4 (52.6 GHz -114.25 GHz) , and FR5 (114.25 GHz -300 GHz) . Each of these higher frequency bands falls within the EHF band.

With the above aspects in mind, unless specifically stated otherwise, it should be understood that the term “sub-6 GHz” or the like ifused herein may broadly represent frequencies that may be less than 6 GHz, may be within FR1, or may include mid-band frequencies. Further, unless specifically stated otherwise, it should be understood that the term “millimeter wave” or the like if used herein may broadly represent frequencies that may include mid-band frequencies, may be within FR2, FR4, FR4-a or FR4-1, and/or FR5, or may be within the EHF band.

A base station 102, whether a small cell 102′ or a large cell (e.g., macro base station) , may include and/or be referred to as an eNB, gNodeB (gNB) , or another type of base station. Some base stations, such as gNB 180 may operate in a traditional sub 6 GHz spectrum, in millimeter wave frequencies, and/or near millimeter wave frequencies in communication with the UE 104. When the gNB 180 operates in millimeter wave or near millimeter wave frequencies, the gNB 180 may be referred to as a millimeter wave base station. The millimeter wave base station 180 may utilize beamforming 182 with the UE 104 to compensate for the path loss and short range. The base station 180 and the UE 104 may each include a plurality of antennas, such as antenna elements, antenna panels, and/or antenna arrays to facilitate the beamforming.

The base station 180 may transmit a beamformed signal to the UE 104 in one or more transmit directions 182′. The UE 104 may receive the beamformed signal from the base station 180 in one or more receive directions 182". The UE 104 may also transmit a beamformed signal to the base station 180 in one or more transmit directions. The base station 180 may receive the beamformed signal from the UE 104 in one or more receive directions. The base station 180 /UE 104 may perform beam training to determine the best receive and transmit directions for each of the base station 180 /UE 104. The transmit and receive directions for the base station 180 may or may not be the same. The transmit and receive directions for the UE 104 may or may not be the same.

The EPC 160 may include a Mobility Management Entity (MME) 162, other MMEs 164, a Serving Gateway 166, a Multimedia Broadcast Multicast Service (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC) 170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be in communication with a Home Subscriber Server (HSS) 174. The MME 162 is the control node that processes the signaling between the UEs 104 and the EPC 160. Generally, the MME 162 provides bearer and connection management. All user Internet protocol (IP) packets are transferred through the Serving Gateway 166, which itself is connected to the PDN Gateway 172. The PDN Gateway 172 provides UE IP address allocation as well as other functions. The PDN Gateway 172 and the BM-SC 170 are connected to the IP Services 176. The IP Services 176 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS) , a PS Streaming Service, and/or other IP services. The BM-SC 170 may provide functions for MBMS user service provisioning and delivery. The BM-SC 170 may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a public land mobile network (PLMN) , and may be used to schedule MBMS transmissions. The MBMS Gateway 168 may be used to distribute MBMS traffic to the base stations 102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting eMBMS related charging information.

The core network 190 may include an Access and Mobility Management Function (AMF) 192, other AMFs 193, a Session Management Function (SMF) 194, and a User Plane Function (UPF) 195. The AMF 192 may be in communication with a Unified Data Management (UDM) 196. The AMF 192 is the control node that processes the signaling between the UEs 104 and the core network 190. Generally, the AMF 192 provides QoS flow and session management. All user Internet protocol (IP) packets are transferred through the UPF 195. The UPF 195 provides UE IP address allocation as well as other functions. The UPF 195 is connected to the IP Services 197. The IP Services 197 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS) , a Packet Switch (PS) Streaming (PSS) Service, and/or other IP services.

The base station may include and/or be referred to as a gNB, Node B, eNB, an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS) , an extended service set (ESS) , a transmit reception point (TRP) , or some other suitable terminology. The base station 102 provides an access point to the EPC 160 or core network 190 for a UE 104. Examples of UEs 104 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA) , a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player) , a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a large or small kitchen appliance, a healthcare device, an implant, a sensor/actuator, a display, or any other similar functioning device. Some of the UEs 104 may be referred to as IoT devices (e.g., parking meter, gas pump, toaster, vehicles, heart monitor, etc. ) . The UE 104 may also be referred to as a station, a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology. In some scenarios, the term UE may also apply to one or more companion devices such as in a device constellation arrangement. One or more of these devices may collectively access the network and/or individually access the network.

Referring again to FIG. 1, in certain aspects, the UE 104 may include a null space calculation component 198 that may be configured to receive a first RRC configuration associated with a reference signal, perform a measurement of the reference signal and receive information identifying at least one beam configuration selected by a first UE for a transmission from a first base station to the first UE via an RIS, transmit to at least one base station an indication of a null space based on the measurement of the reference signal and the at least one beam configuration selected by the first UE. The null space calculation component 198 may further be configured to receive a first RRC configuration associated with a reference signal, perform a measurement of the reference signal for multiple beam configurations associated with a transmission from a base station to the first UE via an RIS and transmit, to a second UE, an indication of at least one beam configuration based on the measurement. In certain aspects, the base station 180 may include an RIS training component 199 that may be configured to transmit, to the second UE a first RRC configuration associated with a reference signal and receive an indication of a null space from the second UE based on measurement of the reference signal and at least one beam configuration selected by a first UE for transmission from a first base station to the first UE via a RIS. Although the following description may be focused on 5G NR, the concepts described herein may be applicable to other similar areas, such as LTE, LTE-A, CDMA, GSM, and other wireless technologies.

FIG. 2A is a diagram 200 illustrating an example of a first subframe within a 5G NR frame structure. FIG. 2B is a diagram 230 illustrating an example of DL channels within a 5G NR subframe. FIG. 2C is a diagram 250 illustrating an example of a second subframe within a 5G NR frame structure. FIG. 2D is a diagram 280 illustrating an example of UL channels within a 5G NR subframe. The 5G NR frame structure may be frequency division duplexed (FDD) in which for a particular set of subcarriers (carrier system bandwidth) , subframes within the set of subcarriers are dedicated for either DL or UL, or may be time division duplexed (TDD) in which for a particular set of subcarriers (carrier system bandwidth) , subframes within the set of subcarriers are dedicated for both DL and UL. In the examples provided by FIGs. 2A, 2C, the 5G NR frame structure is assumed to be TDD, with subframe 4 being configured with slot format 28 (with mostly DL) , where D is DL, U is UL, and F is flexible for use between DL/UL, and subframe 3 being configured with slot format 1 (with all UL) . While

subframes

3, 4 are shown with slot formats 1, 28, respectively, any particular subframe may be configured with any of the various available slot formats 0-61. Slot formats 0, 1 are all DL, UL, respectively. Other slot formats 2-61 include a mix of DL, UL, and flexible symbols. UEs are configured with the slot format (dynamically through DL control information (DCI) , or semi-statically/statically through radio resource control (RRC) signaling) through a received slot format indicator (SFI) . Note that the description infra applies also to a 5G NR frame structure that is TDD.

FIGs. 2A-2D illustrate a frame structure, and the aspects of the present disclosure may be applicable to other wireless communication technologies, which may have a different frame structure and/or different channels. A frame (10 ms) may be divided into 10 equally sized subframes (1 ms) . Each subframe may include one or more time slots. Subframes may also include mini-slots, which may include 7, 4, or 2 symbols. Each slot may include 14 or 12 symbols, depending on whether the cyclic prefix (CP) is normal or extended. For normal CP, each slot may include 14 symbols, and for extended CP, each slot may include 12 symbols. The symbols on DL may be CP orthogonal frequency division multiplexing (OFDM) (CP-OFDM) symbols. The symbols on UL may be CP-OFDM symbols (for high throughput scenarios) or discrete Fourier transform (DFT) spread OFDM (DFT-s-OFDM) symbols (also referred to as single carrier frequency-division multiple access (SC-FDMA) symbols) (for power limited scenarios; limited to a single stream transmission) . The number of slots within a subframe is based on the CP and the numerology. The numerology defines the subcarrier spacing (SCS) and, effectively, the symbol length/duration, which is equal to 1/SCS.

For normal CP (14 symbols/slot) , different numerologies μ 0 to 4 allow for 1, 2, 4, 8, and 16 slots, respectively, per subframe. For extended CP, the numerology 2 allows for 4 slots per subframe. Accordingly, for normal CP and numerology μ, there are 14 symbols/slot and 2 ^μ slots/subframe. The subcarrier spacing may be equal to 2 ^μ * 15 kHz, where μ is the numerology 0 to 4. As such, the numerology μ=0 has a subcarrier spacing of 15 kHz and the numerology μ=4 has a subcarrier spacing of 240 kHz. The symbol length/duration is inversely related to the subcarrier spacing. FIGs. 2A-2D provide an example of normal CP with 14 symbols per slot and numerology μ=2 with 4 slots per subframe. The slot duration is 0.25 ms, the subcarrier spacing is 60 kHz, and the symbol duration is approximately 16.67 μs. Within a set of frames, there may be one or more different bandwidth parts (BWPs) (see FIG. 2B) that are frequency division multiplexed. Each BWP may have a particular numerology and CP (normal or extended) .

A resource grid may be used to represent the frame structure. Each time slot includes a resource block (RB) (also referred to as physical RBs (PRBs) ) that extends 12 consecutive subcarriers. The resource grid is divided into multiple resource elements (REs) . The number of bits carried by each RE depends on the modulation scheme.

As illustrated in FIG. 2A, some of the REs carry reference (pilot) signals (RS) for the UE. The RS may include demodulation RS (DM-RS) (indicated as R for one particular configuration, but other DM-RS configurations are possible) and channel state information reference signals (CSI-RS) for channel estimation at the UE. The RS may also include beam measurement RS (BRS) , beam refinement RS (BRRS) , and phase tracking RS (PT-RS) .

FIG. 2B illustrates an example of various DL channels within a subframe of a frame. The physical downlink control channel (PDCCH) carries DCI within one or more control channel elements (CCEs) (e.g., 1, 2, 4, 8, or 16 CCEs) , each CCE including six RE groups (REGs) , each REG including 12 consecutive REs in an OFDM symbol of an RB. A PDCCH within one BWP may be referred to as a control resource set (CORESET) . A UE is configured to monitor PDCCH candidates in a PDCCH search space (e.g., common search space, UE-specific search space) during PDCCH monitoring occasions on the CORESET, where the PDCCH candidates have different DCI formats and different aggregation levels. Additional BWPs may be located at greater and/or lower frequencies across the channel bandwidth. A primary synchronization signal (PSS) may be within symbol 2 of particular subframes of a frame. The PSS is used by a UE 104 to determine subframe/symbol timing and a physical layer identity. A secondary synchronization signal (SSS) may be within symbol 4 of particular subframes of a frame. The SSS is used by a UE to determine a physical layer cell identity group number and radio frame timing. Based on the physical layer identity and the physical layer cell identity group number, the UE can determine a physical cell identifier (PCI) . Based on the PCI, the UE can determine the locations of the DM-RS. The physical broadcast channel (PBCH) , which carries a master information block (MIB) , may be logically grouped with the PSS and SSS to form a synchronization signal (SS) /PBCH block (also referred to as SS block (SSB) ) . The MIB provides a number of RBs in the system bandwidth and a system frame number (SFN) . The physical downlink shared channel (PDSCH) carries user data, broadcast system information not transmitted through the PBCH such as system information blocks (SIBs) , and paging messages.

As illustrated in FIG. 2C, some of the REs carry DM-RS (indicated as R for one particular configuration, but other DM-RS configurations are possible) for channel estimation at the base station. The UE may transmit DM-RS for the physical uplink control channel (PUCCH) and DM-RS for the physical uplink shared channel (PUSCH) . The PUSCH DM-RS may be transmitted in the first one or two symbols of the PUSCH. The PUCCH DM-RS may be transmitted in different configurations depending on whether short or long PUCCHs are transmitted and depending on the particular PUCCH format used. The UE may transmit sounding reference signals (SRS) . The SRS may be transmitted in the last symbol of a subframe. The SRS may have a comb structure, and a UE may transmit SRS on one of the combs. The SRS may be used by a base station for channel quality estimation to enable frequency-dependent scheduling on the UL.

FIG. 2D illustrates an example of various UL channels within a subframe of a frame. The PUCCH may be located as indicated in one configuration. The PUCCH carries uplink control information (UCI) , such as scheduling requests, a channel quality indicator (CQI) , a precoding matrix indicator (PMI) , a rank indicator (RI) , and hybrid automatic repeat request (HARQ) acknowledgment (ACK) (HARQ-ACK) feedback (i.e., one or more HARQ ACK bits indicating one or more ACK and/or negative ACK (NACK) ) . The PUSCH carries data, and may additionally be used to carry a buffer status report (BSR) , a power headroom report (PHR) , and/or UCI.

FIG. 3 is a block diagram of a base station 310 in communication with a UE 350 in an access network. In the DL, IP packets from the EPC 160 may be provided to a controller/processor 375. In some aspects, the base station 310 may correspond to a base station 102 or 180, and the UE 350 may correspond to a UE 104. In such aspects, communication may be provided between the base station and the UE by an RIS 103. The communication may be intelligently reflected, e.g., by an RIS surface 393 of the RIS 103. Discovery information, such as RIS capability information and/or position information for the RIS 103 may be transmitted by the controller 391, e.g., via sidelink.

The controller/processor 375 implements layer 3 and layer 2 functionality. Layer 3 includes a radio resource control (RRC) layer, and layer 2 includes a service data adaptation protocol (SDAP) layer, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The controller/processor 375 provides RRC layer functionality associated with broadcasting of system information (e.g., MIB, SIBs) , RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release) , inter radio access technology (RAT) mobility, and measurement configuration for UE measurement reporting; PDCP layer functionality associated with header compression /decompression, security (ciphering, deciphering, integrity protection, integrity verification) , and handover support functions; RLC layer functionality associated with the transfer of upper layer packet data units (PDUs) , error correction through ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs) , re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs) , demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

The transmit (TX) processor 316 and the receive (RX) processor 370 implement layer 1 functionality associated with various signal processing functions. Layer 1, which includes a physical (PHY) layer, may include error detection on the transport channels, forward error correction (FEC) coding/decoding of the transport channels, interleaving, rate matching, mapping onto physical channels, modulation/demodulation of physical channels, and MIMO antenna processing. The TX processor 316 handles mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK) , quadrature phase-shift keying (QPSK) , M-phase-shift keying (M-PSK) , M-quadrature amplitude modulation (M-QAM) ) . The coded and modulated symbols may then be split into parallel streams. Each stream may then be mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator 374 may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE 350. Each spatial stream may then be provided to a different antenna 320 via a separate transmitter 318 TX. Each transmitter 318 TX may modulate a radio frequency (RF) carrier with a respective spatial stream for transmission.

At the UE 350, each receiver 354 RX receives a signal through its respective antenna 352. Each receiver 354 RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor 356. The TX processor 368 and the RX processor 356 implement layer 1 functionality associated with various signal processing functions. The RX processor 356 may perform spatial processing on the information to recover any spatial streams destined for the UE 350. If multiple spatial streams are destined for the UE 350, they may be combined by the RX processor 356 into a single OFDM symbol stream. The RX processor 356 then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT) . The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the base station 310. These soft decisions may be based on channel estimates computed by the channel estimator 358. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the base station 310 on the physical channel. The data and control signals are then provided to the controller/processor 359, which implements layer 3 and layer 2 functionality.

The controller/processor 359 can be associated with a memory 360 that stores program codes and data. The memory 360 may be referred to as a computer-readable medium. In the UL, the controller/processor 359 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the EPC 160. The controller/processor 359 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DL transmission by the base station 310, the controller/processor 359 provides RRC layer functionality associated with system information (e.g., MIB, SIBs) acquisition, RRC connections, and measurement reporting; PDCP layer functionality associated with header compression /decompression, and security (ciphering, deciphering, integrity protection, integrity verification) ; RLC layer functionality associated with the transfer of upper layer PDUs, error correction through ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

Channel estimates derived by a channel estimator 358 from a reference signal or feedback transmitted by the base station 310 may be used by the TX processor 368 to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor 368 may be provided to different antenna 352 via separate transmitters 354 TX. Each transmitter 354 TX may modulate an RF carrier with a respective spatial stream for transmission.

The UL transmission is processed at the base station 310 in a manner similar to that described in connection with the receiver function at the UE 350. Each receiver 318RX receives a signal through its respective antenna 320. Each receiver 318RX recovers information modulated onto an RF carrier and provides the information to a RX processor 370.

The controller/processor 375 can be associated with a memory 376 that stores program codes and data. The memory 376 may be referred to as a computer-readable medium. In the UL, the controller/processor 375 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover IP packets from the UE 350. IP packets from the controller/processor 375 may be provided to the EPC 160. The controller/processor 375 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

At least one of the TX processor 368, the RX processor 356, and the controller/processor 359 may be configured to perform aspects in connection with 198 of FIG. 1.

At least one of the TX processor 316, the RX processor 370, and the controller/processor 375 may be configured to perform aspects in connection with 198 of FIG. 1.

Massive MIMO may help to increase throughput in a wireless communication system. Beamforming gain may be achieved through the use of active antenna units. Individual RF chains may be used per antenna port. The use of active antenna units (AAU) may increase power consumption. A reconfiguration intelligent surface (RIS) may be employed to extend coverage, e.g., beamformed coverage, with reduced power consumption. The RIS may include a larger number of uniformly distributed electrically controllable elements. Each RIS element may have a reconfigurable electromagnetic characteristic, e.g., a reflection coefficient. Depending on the combination of configured states of the elements, the RIS may reflect and modify the incident radio waveform in a controlled manner, such as changing a reflected direction, changing a beam width, etc. The RIS may function as a near passive device, and the reflection direction may be controlled by the base station. The RIS may reflect an impinging wave in a direction indicated by the base station to a UE.

An RIS may be deployed in wireless communication systems, including cellular systems, such as LTE, NR, etc. An RIS may alter the channel realization in a controlled manner, which may improve channel diversity. The increased diversity may provide robustness to channel blocking/fading, which may be of particular importance for mmWave communication. Compared to a wireless relay or repeater systems, an RIS may be more cost and energy efficient.

A base station may control the RIS to extend beam coverage and/or to address blockages between the base station and the UE. FIG. 4 is a set of diagrams 410 and 420 illustrating examples in which a base station 402 transmits beamformed communication to UEs using

directional beams

412, 414, 432, and 434. Diagram 410 illustrates that a first UE 404a may be able to receive the direct transmission using the beam 414. However, diagram 410 illustrates a blockage 408 that blocks the beam 412 from reception at the second UE 404b. As illustrated in diagram 420, the base station 402 may transmit communication for the second UE 404b using a directional beam 432 (which may be referred to as the impinging beam) to the RIS 406 for reflection over a directional beam 436 to the UE 404b. The base station 402 may indicate the directional beam 436 to the RIS, and the RIS may reflect the impinging wave on beam 432 in the direction of the directional beam 436. The RIS may adjust the reflection of the impinging beam 432 based on a set of coefficients, Φ, indicating a set of configured states of the configurable elements 438 of the RIS 406.

FIG. 5 illustrates an example in which the RIS 506 includes multiple subsets 512 of multiple RIS elements 518. As illustrated, different subsets 512 of RIS elements 518 may serve different UEs 504. Accordingly, the different subsets 512 of multiple RIS elements 518 may be configured differently to adjust the reflected direction, the beam width, etc. of the impinging wave 508. The RIS elements 518 may be controlled by a controller 525 at the RIS 506 based on control information received by the base station 502. As described in connection with FIG. 4, the base station 502 may indicate a beam direction (e.g., any of 510a, 510b, 510c, 510d, 510e, or 510f) to the RIS for reflecting beamformed communication received as the impinging wave 508 to a particular UE 504 in a particular direction. The RIS may similarly be controlled by a UE for reflecting communication from the UE to a base station and/or to another UE.

In some aspects of wireless communication, UEs (e.g., cell edge UEs) may be limited by adjacent cell interference rather than thermal noise. Passive-MIMO using RIS may increase interference at the UEs (e.g., the cell edge UEs) via reflection of transmissions (e.g., beams) associated with other UEs in a same cell. In addition, intra-cell interference may also increase based on RIS reflection of transmissions from a different cell’s base station.

FIG. 6 is a set of diagrams 610 and 620 illustrating examples in which a base station 602a transmits beamformed communication to a UE 604a using

directional beams

614 and 624 that increase interference at a second UE 604b in a different cell or a same cell, respectively. Diagram 610 illustrates a first base station 602a transmitting a beamformed communication to UE 604a using directional beam 614. As illustrated, directional beam 614 may be reflected by configurable elements 618 of RIS 606 in a direction of reflected beam 616 (e.g., including

beam components

616a and 616b) . The reflected beam 616 (and specifically beam component 616b) may increase interference at a UE 604b served by a second base station 602b via directional beam 612.

Diagram 620 illustrates a first base station 602a transmitting a beamformed communication to UE 604a using directional beam 624. Diagram 620 also illustrates the first base station 602a transmitting a beamformed communication to UE 604b using directional beam 632. As illustrated, directional beam 624 may be reflected by configurable elements 618 of RIS 606 in a direction of reflected beam 636 (e.g., including

beam components

636a and 636b) . The reflected beam 636 (and specifically beam component 636b) may increase interference at the UE 604b. Accordingly, a method, a computer-readable medium, and an apparatus are provided to mitigate the increased interference at the second UE 604b (e.g., an interfered UE) in either of the situations depicted in diagrams 610 or 620. As will be discussed below, the method includes aspects related to CSI-RS for beam training the RIS to serve a first UE (e.g., a target UE such as UE604a) , quasi-colocation (QCL) information related to the CSI-RS and/or beam directions associated with beam training the RIS, and transmitting a null space associated with a second UE (e.g., an interfered UE such as UE 604b) and at least one beam configuration indicated by the first UE based on the RIS beam training.

For example, an interfered UE (e.g., UE 604b) may report null space information on certain resources while training RIS for serving a first UE (e.g., a target UE such as UE604a) . A first base station (e.g., base station 602a) serving the first UE may leverage the null space information to modify the precoder used to serve the first UE to reduce interference at the second UE. For example, the base station may linearly combine the channel precoder indicated by the first UE channel basis (i.e., the channel precoder indicated by the first UE) with the null space basis indicated by the second UE. Additional details are provided in FIGs. 7-18 below.

FIG. 7 is a call flow diagram 700 illustrating a first and second UE (e.g.,

UE

704a and 704b) served by a same base station (e.g., base station 702) mitigating interference at the second UE 704b from transmissions to the first UE via an RIS 706. The base station 702 may transmit, and each of the UE 704a, the UE 704b, and the RIS 706 may receive, a reference signal configuration for beam training 708. The reference signal configuration for beam training 708, in some aspects, may be an RRC configuration. The reference configuration may indicate a first number, L, of beams being trained and a second number, K, of channel state information (CSI) reference signal (CSI-RS) resources associated with each of the first number of beams. An example of beam training is provided in FIG. 9 below.

The reference signal configuration for beam training 708 may further include a set of RIS configurations (e.g., coefficients, Φ, associated with RIS elements, such as

configurable elements

438 or 618 of

RIS

406 or 606, respectively or RIS elements 518 of RIS 506) . In some aspects, the RIS configuration may be transparent (e.g., unknown) to the UEs and/or the base station, while in some aspects the RIS configuration is non-transparent (e.g., known) to the base station and/or the UEs. The second UE (e.g., UE 704b) , and in some aspects, the first UE (e.g., UE 704a) may receive QCL information relating to the reference signals associated with the RIS beam training (e.g., QCL information relating CSI-RS to a single-port RS such as SSB or a tracking reference signals (TRS) ) . The QCL information may indicate that the reference signal shares (e.g., with a particular SSB) a Doppler shift, Doppler spread, average delay, delay spread ( ‘QCL-TypeA’ ) , Doppler shift and Doppler spread ( ‘QCL-TypeB’ ) , a Doppler shift and average delay ( ‘QCL-TypeC’ ) , or a spatial reception/transmission parameter ( ‘QCL-TypeD’ ) . The QCL may be used to provide channel estimation information for the reference signal without doing an explicit channel estimation.

The base station 702 may transmit reference signals for RIS beam training 710 to UE 704a (and incidentally to UE 704b) via the RIS 706 during a period of time that may be referred to as a training duration. The UE 704a and the UE 704b may measure 712 the reference signals for RIS beam training 710. Although the measurement at 712 is shown separately than the transmission of the reference signals at 710, the UEs may perform the measurements at 712 during the training duration in which the reference signals are transmitted. The UE 704a may select 714, for transmissions from the base station 702, at least one beam configuration of the beam configurations associated with the measured reference signals. The selected at least one beam configuration of the beam configurations may be indicated by an index (or indexes) associated with the at least one beam configuration. Each index may indicate a beam configuration including a precoding matrix (associated with a beam direction and width) and/or an RIS configuration including a set of coefficients, Φ, associated with configurable elements of the RIS 706. The UE 704b may store 716 the measured characteristics of the reference signals for use in computing a null space (e.g., a set of vectors associated with eigenvectors with values below a threshold magnitude) associated with a selected at least one beam configuration.

The UE 704a may then transmit, and base station 702 and/or the UE 704b may receive, a beam selection indication 718 indicating the at least one selected beam configuration, e.g., at a time T0 following the training duration. The beam selection indication 718 may be transmitted to the UE 704b via a sidelink communication or may be transmitted to the base station 702 for the base station 702 to forward or otherwise transmit the beam selection indication 718 to the UE 704b. In some aspects, the RS configuration for RIS beam training 708 may include a configuration for a number of null space vectors (e.g., basis vectors for the null space) for the second UE 704b to report and/or indicate. The base station 702 may transmit, and UE 704b may receive, an updated null space vector indication configuration 720 to the number of null space vectors to report. In some aspects, the updated null space vector indication configuration 720 may be received via one of a medium access control (MAC) control element (CE) (MAC-CE) or a DCI.

After receiving the beam selection indication 718 indicating the selected at least one beam configuration, the UE 704b may use the stored measurements to identify 722 a null space (e.g., a set of precoding vectors, such as basis vectors, associated with eigenvalues having a magnitude below a threshold magnitude) associated with the indicated at least one beam configuration. For example, a selected beam configuration may be associated with a precoding matrix, P, and an RIS configuration including a set of coefficients, Φ, associated with configurable elements of the RIS 706. The precoding matrix and RIS configuration may define a precoding matrix P′ defined by the combination of P and Φ (e.g., P′ = (H _RIS, UE2Φ _RISG _RIS+H ₀) P, where H _RIS, UE2Φ _RISG _RIS represents a signal reflected from the RIS and H ₀ represents a directed channel) based on P′, the UE 704b may compute a set of precoding basis vectors associated with eigenvalues having a magnitude below a threshold magnitude.

The UE 704b may transmit, and base station 702 may receive, a null space indication 724 indicating a configured number of precoding vectors associated with the null space, e.g., at a time T1 following the receipt of the indication 718. Based on the received null space indication 724, the base station 702 may transmit a data transmission 726 to the UE 704a via the RIS 706. The data transmission 726 may be based on a precoding matrix consistent with the at least one beam configuration indicated in beam selection indication 718 and with the null space indicated in null space indication 724. For example, a precoding matrix associated with the at least one beam configuration indicated in beam selection indication 718 may be generated based on a set of basis vectors of the null space (e.g., a set of “Y” orthonormal basis vectors, where “Y” is number of indicated null space vectors (e.g., the dimension of the null space) ) . In some aspects, the maximum value that Y can have may be equal to the number of transmission antennas minus the number of reception antennas.

FIG. 8 is a call flow diagram 800 illustrating a first and second UE (e.g.,

UE

804a and 804b) served by different base stations (e.g., base station 802a and base station 802b, respectively) mitigating interference at the second UE 804b from transmissions to the first UE 804a from the first base station 802a via an RIS 806. The base station 802a may transmit, and each of the UE 804a, the second base station 802b, and the RIS 806 may receive, a reference signal configuration for beam training 808. The second base station 802b may receive the reference signal configuration for beam training 808 from the first base station 802a via an Xn or X2 interface. The second base station 802b may transmit, and UE 804b may receive, the reference signal configuration for beam training 808 (e.g., via a Uu interface) . The reference signal configuration for beam training 808, in some aspects, may be an RRC configuration. The reference configuration may indicate a first number, L, of beams being trained and a second number, K, of CSI-RS resources associated with each of the first number of beams. An example of beam training is provided in FIG. 9 below.

The reference signal configuration for beam training 808 may further include a set of RIS configurations (e.g., coefficients, Φ, associated with RIS elements, such as

configurable elements

438 or 618 of

RIS

406 or 606, respectively or RIS elements 518 of RIS 506) . In some aspects, the RIS configuration may be transparent (e.g., unknown) to the UEs and/or the base station (s) , while in some aspects the RIS configuration is non-transparent (e.g., known) to the base station (s) and/or the UEs. The second UE (e.g., UE 804b) , and in some aspects, the first UE (e.g., UE 804a) may receive QCL information relating to the reference signals associated with the RIS beam training (e.g., QCL information relating CSI-RS to a single-port RS such as SSB or a tracking reference signals (TRS) ) . The QCL information may indicate that the reference signal shares (e.g., with a particular SSB) a Doppler shift, Doppler spread, average delay, delay spread ( ‘QCL-TypeA’ ) , Doppler shift and Doppler spread ( ‘QCL-TypeB’ ) , a Doppler shift and average delay ( ‘QCL-TypeC’ ) , or a spatial reception/transmission parameter ( ‘QCL-TypeD’ ) . The QCL may be used to provide channel estimation information for the reference signal without doing an explicit channel estimation. Different types of QCL (e.g., QCL-TypeA, QCL-TypeB, etc. ) may be transmitted by (or received from) different base stations, e.g., base station 802a may transmit, and UE 804b may receive, QCL-TypeA, QCL-TypeB, or QCL-TypeC, while base station 802b may transmit, and UE 704b may receive, QCL-TypeD.

The base station 802a may transmit reference signals for RIS beam training 810 to UE 804a (and incidentally to UE 804b) via the RIS 806 during a period of time that may be referred to as a training duration. The UE 804a and the UE 804b may measure 812 the reference signals for RIS beam training 810. Although the measurement at 812 is shown separately than the transmission of the reference signals at 810, the UEs may perform the measurements at 812 during the training duration in which the reference signals are transmitted. The UE 804a may select 814, for transmissions from the base station 802a, at least one beam configuration of the beam configurations associated with the measured reference signals. The selected at least one beam configuration of the beam configurations may be indicated by an index (or indexes) associated with the at least one beam configuration. Each index may indicate a beam configuration including a precoding matrix (associated with a beam direction and width) and/or an RIS configuration including a set of coefficients, Φ (e.g., an N x N diagonal matrix) , associated with configurable elements (e.g., a set of N configurable resources) of the RIS 806. The UE 804b may store 816 the measured characteristics of the reference signals for use in computing a null space (e.g., a set of vectors associated with eigenvectors with values below a threshold magnitude) associated with a selected at least one beam configuration.

The UE 804a may then transmit, and base station 802a and/or the UE 804b may receive, a beam selection indication 818 indicating the at least one selected beam configuration, e.g., at a time T0 following the training duration. The beam selection indication 818 may be transmitted to the UE 804b via a sidelink communication. In some aspects, the beam selection indication 818 may be transmitted to the base station 802a for the base station 802a to communicate the beam selection indication 818 to the second base station 802b for the second base station 802b to transmit to the UE 804b. Accordingly, in some aspects, the base station 802b may transmit, and UE 804b may receive, a beam selection indication 818 or a beam selection indication based on beam selection indication 818. In some aspects, the RS configuration for RIS beam training 808 may include a configuration for a number of null space vectors (e.g., basis vectors for the null space) for the second UE 804b to report and/or indicate. As discussed in relation to FIG. 7, the second base station 802b (e.g., the base station serving the UE 804b) may transmit, and UE 804b may receive, an update to the number of null space vectors to report. In some aspects, the update may be received via one of a MAC-CE or a DCI.

After receiving the beam selection indication 818 indicating the selected at least one beam configuration, the UE 804b may use the stored measurements to identify 822 a null space (e.g., a set of precoding vectors, such as basis vectors, associated with eigenvalues having a magnitude below a threshold magnitude) associated with the indicated at least one beam configuration. For example, a selected beam configuration may be associated with a precoding matrix, P, and an RIS configuration including a set of coefficients, Φ, associated with configurable elements of the RIS 806. The precoding matrix and RIS configuration may define a precoding matrix P′ defined by the combination of P and Φ (e.g., P′ = (H _RIS, UE2Φ _RISG _RIS+H ₀) P, where H _RIS, UE2Φ _RISG _RIS represents a signal reflected from the RIS and H ₀ represents a directed channel) based on P′, the UE 804b may compute a set of precoding basis vectors (e.g., orthonormal vectors) associated with eigenvalues having a magnitude below a threshold magnitude.

The UE 804b may transmit, and base station 802b may receive, a null space indication 824 indicating a configured number of precoding vectors associated with the null space, e.g., at a time T1 following the receipt of the indication 818. The base station 802b may transmit, and base station 802a may receive, null space indication 825 based on the null space indication 824 received from the UE 804b, e.g., at a time T2 following the receipt of the indication 818 at the second base station 802b. Based on the received null space indication 825, the base station 802a may transmit a data transmission 826 to the UE 804a via the RIS 806. The data transmission 826 may be based on a precoding matrix consistent with the at least one beam configuration indicated in beam selection indication 818 and with the null space indicated in

null space indication

824 and 825. For example, a precoding matrix associated with the at least one beam configuration indicated in beam selection indication 818 may be generated based on a set of basis vectors of the null space (e.g., a set of “Y” orthonormal basis vectors, where “Y” is number of indicated null space vectors (e.g., the dimension of the null space) ) . In some aspects, the maximum value that Y can have may be equal to the number of transmission antennas minus the number of reception antennas.

FIG. 9 is a set of diagrams 900-930 illustrating a set of beam training operations. Diagram 900 illustrates a base station 902a serving UEs 904a and 904b via RIS 906. Diagram 900 illustrates that base station 902a (and a CSI-RS (or RIS training) configuration) may be associated with a set of transmission beams 914a-914d, the RIS 906 may be associated with reflection beams 916a-916e, and each UE (e.g., 904a and 904b) may be associated with a set of reception beams. FIG. 9 illustrates a small number of transmission, reflection, and reception beams for clarity, but some aspects may use larger numbers (e.g., tens, or hundreds, of transmission, reflection, and reception beams and/or transmission, reflection, and reception beam configurations) .

Diagram 900 illustrates that the base station 902a may transmit a CSI-RS via transmission beam 914a, that is reflected from the RIS 906 via reflection beam 916d (e.g., an RIS configuration Φ _d) and received at each of the UE 904a and the UE 904b via a

reception beam

924a and 934a, respectively. In some aspects, the base station may transmit the CSI-RS over multiple beams in a beam sweep pattern. RIS 906 may be utilized by base station 902a to circumvent blockage 908. The UE 904a and the UE 904b may measure a reference signal received power (RSRP) , a reference signal received quality (RSRQ) , a signal-to-interference and noise ratio (SINR) , etc. associated with the received reference signals (e.g., CSI-RS) . The UE 904a may use the measured reference signals (along with previously and/or subsequently measured reference signals) to select or identify a set of beam configurations (e.g., a configuration identifying each of a transmission beam, a reflection beam, and a reception beam) that maximize some characteristic (e.g., RSRP, RSRQ, SINR, etc. ) . The UE 904b may store the measurements of the reference signals (along with previously and/or subsequently measured reference signals) for use in calculating or identifying a null space after an indication of at least one beam configuration selected by the UE 904a.

Diagram 910 illustrates that the base station 902a may transmit a CSI-RS via a same transmission beam 914a, that is reflected from the RIS 906 via an updated reflection beam 916c (e.g., an RIS configuration Φ _c) and received at each of the UE 904a and the UE 904b via a

reception beam

924a and 934a, respectively. The UE 904a and the UE 904b may measure a RSRP, a RSRQ, a SINR, etc. associated with the received reference signals (e.g., CSI-RS) . The UE 904a may use the measured reference signals (along with previously and/or subsequently measured reference signals) to select or identify a set of beam configurations (e.g., a configuration identifying each of a transmission beam, a reflection beam, and a reception beam) that maximize some characteristic (e.g., RSRP, RSRQ, SINR, etc. ) . The UE 904b may store the measurements of the reference signals (along with previously and/or subsequently measured reference signals) for use in calculating or identifying a null space after an indication of at least one beam configuration selected by the UE 904a.

Diagram 920 illustrates that the base station 902a may transmit a series of CSI-RS via an updated (changed) transmission beam 914b, that are each reflected from the RIS 906 via one of a reflection beam 916a-916e (e.g., an RIS configuration Φ _a-Φ _e) and are received at each of the UE 904a and the UE 904b via a

reception beam

Diagram 930 illustrates that the base station 902a may transmit a series of CSI-RS via an updated (changed) transmission beam 914b, that are each reflected from the RIS 906 via one of a reflection beam 916a-916e (e.g., an RIS configuration Φ _a-Φ _e) and are received at each of the UE 904a and the UE 904b via an updated

reception beam

924b and 934b, respectively. The UE 904a and the UE 904b may measure a RSRP, a RSRQ, a SINR, etc. associated with the received reference signals (e.g., CSI-RS) . The UE 904a may use the measured reference signals (along with previously and/or subsequently measured reference signals) to select or identify a set of beam configurations (e.g., a configuration identifying each of a transmission beam, a reflection beam, and a reception beam) that maximize some characteristic (e.g., RSRP, RSRQ, SINR, etc. ) . The UE 904b may store the measurements of the reference signals (along with previously and/or subsequently measured reference signals) for use in calculating or identifying a null space after an indication of at least one beam configuration selected by the UE 904a.

In some aspects, the UE 904b may be served by a second base station (e.g., base station 602b of FIG. 6) as described in relation to FIGs. 6 and 8. The UE 904b, in some aspects, may measure the reference signals associated with the different transmit beam (e.g., beams 914a-914d) and reflection beam (e.g., beams 916a-916e) configurations as discussed in relation to diagrams 900-930 via a set of reception beams via which the UE 904b communicates with the second base station to measure the interference with the communication from the second base station. The UE 904b may store the measurements of the reference signals (along with previously and/or subsequently measured reference signals) for use in calculating or identifying a null space associated with the set of reception beams via which the UE 904b communicates with the second base station and an indicated at least one beam configuration selected by the UE 904a.

FIG. 10 is a diagram 1000 illustrating the transmission of a beam selection indication 1040 and the transmission a null space indication 1050 in a system of two

base stations

1002a and 1002b. Diagram 1000 illustrates that the UE 1004a may transmit, and UE 1004b may receive, beam selection indication 1040 (e.g., via a sidelink communication) . The UE 1004a may transmit, and base station 1002a may receive, beam selection indication 1040 (e.g., via an UL communication) via

directional beams

1024d, 1016d, and 1014b associated with the UE 1004a, the RIS 1006, and the base station 1002a, respectively. Beam selection indication 1040 may include a set of precoding matrix (P) indexes 1042 and a set of RIS coefficient (Φ) indexes 1044 associated with an effective precoding matrix P′ 1046 (e.g., P′ = (H _RIS, UE2Φ _RISG _RIS+H ₀) P) for a RIS 1006. Based on the beam selection indication 1040, the UE 1004b may calculate a null space including a set of null vectors (NV _i) 1052 (e.g., [NV ₁, ..., NV _j] , where j ≤ Y) . The UE 1004b may transmit, and base station 1002b may receive, null space indication 1050 to base station 1002b via transmission beam 1034e and reception beam 1012. Base station 1002b may transmit, and base station 1002a may receive, null space indication 1060 including a set of null vectors (NV _i) 1062 based on the null space indication 1050 received from UE 1004b.

FIG. 11 is a flowchart 1100 of a method of wireless communication. The method may be performed by a second UE (e.g., the

UE

104, 604b, 704b, 804b, 904b, 1004b; the apparatus 1702) . At 1102, the second UE may receive a first RRC configuration associated with a reference signal. For example, 1102 may be performed by RIS RS measurement component 1740. The UE, in some aspects, may receive the first RRC configuration from a second base station serving the second UE, where the first RRC configuration is a same RRC configuration transmitted to a first UE. The first RRC configuration may be received from a first base station serving the second UE, where the first RRC configuration is a same RRC configuration transmitted to the first UE, the first RRC configuration may be an RRC configuration used in beam training for the RIS.

In some aspects, the first RRC configuration of the reference signal is based on a QCL relationship with another reference signal from the first base station. For example, the UE may determine the QCL information of the CSI-RS using an SSB of the non-serving base station, e.g., without an explicit indication. The first RRC configuration of the reference signal, in some aspects, is based on a QCL relationship with another reference signal from a second base station. For example, the CSI-RS may be indicated by the serving base station to the UE based on one or more reference signals from the non-serving base station. The first RRC configuration indicates a first number of beams being trained and a second number of CSI-RS resources associated with each of the first number of beams. In some aspects, a first transmission beam of the first base station is associated with each of the second number of CSI-RS resources for a particular beam. The reference signal, in some aspects, may encoded with a precoder associated with a beam having a width above a threshold width. For example, referring to FIGs. 7 and 8, UE 704b and UE 804b may receive reference signal configuration for

RIS beam training

708 and 808, respectively.

At 1104, the UE may perform a measurement of the reference signal. In some aspects, performing, at 1104, the measurement may include measuring a plurality of transmissions of the reference signal over a plurality of beams based on the first RRC configuration and storing measurements of the plurality of transmissions of the reference signal. For example, referring to FIGs. 7-9, the

UE

704b, 804b, or 904b may measure 712 and 812 and

store

716 and 816 measurements of reference signals associated with different beam configurations as illustrated in diagram 900-930. For example, 1104 may be performed by RIS RS measurement component 1740.

The second UE may receive, at 1106, information identifying at least one beam configuration selected by a first UE for a transmission from a first base station to the first UE via an RIS. The information identifying at least one beam configuration selected by the first UE may be based on the first RRC configuration received at the first UE. In some aspects, the information identifying at least one beam configuration selected by the first UE may be received from the first UE via a sidelink or via a base station serving the second UE. As described in relation to FIGs. 7, 8, and 10, the

UE

704b, 804b, or 1004b may receive

beam selection indication

718, 818, or 1040 that may include a precoding matrix index 1042 and an RIS coefficient index 1044 that identifies at least one preferred beam configuration. For example, 1106 may be performed by null space computation component 1744.

Finally, at 1108, the second UE may transmit, to at least one base station, an indication of a null space based on the measurement of the reference signal and the received information identifying the at least one beam configuration selected by the first UE. The indication of the null space, in some aspects, may include a set of precoding vectors based on a stored set of the measurements associated with the at least one beam configuration indicated by the first UE. In some aspects, the null space corresponds to a set of precoding vectors associated with a set of eigenvalues with magnitudes below a threshold value. The set of precoding vectors may include a configured number of precoding vectors in the set of precoding vectors. The configured number, in some aspects may be updated via at least one of a MAC-CE or a DCI. For example, referring to FIGs. 7, 8, and 10, the

UE

704b, 804b, or 1004b may transmit a

null space indication

724, 824, or 1050 to the

base station

702, 802b, or 1002b. For example, 1108 may be performed by null space communication component 1746.

FIG. 12 is a flowchart 1200 of a method of wireless communication. The method may be performed by a second UE (e.g., the

UE

104, 604b, 704b, 804b, 904b, 1004b; the apparatus 1702) . At 1202, the second UE may receive a first RRC configuration associated with a reference signal. For example, 1202 may be performed by RIS RS measurement component 1740. The UE, in some aspects, may receive the first RRC configuration from a second base station serving the second UE, where the first RRC configuration is a same RRC configuration transmitted to a first UE. The first RRC configuration may be received from a first base station serving the second UE, where the first RRC configuration is a same RRC configuration transmitted to the first UE, the first RRC configuration may be an RRC configuration used in beam training for the RIS.

In some aspects, the first RRC configuration of the reference signal is based on a QCL relationship with another reference signal from the first base station. The first RRC configuration of the reference signal, in some aspects, is based on a QCL relationship with another reference signal from a second base station. The first RRC configuration indicates a first number of beams being trained and a second number of CSI-RS resources associated with each of the first number of beams. In some aspects, a first transmission beam of the first base station is associated with each of the second number of CSI-RS resources for a particular beam. The reference signal, in some aspects, may encoded with a precoder associated with a beam having a width above a threshold width. For example, referring to FIGs. 7 and 8, UE 704b and UE 804b may receive reference signal configuration for

RIS beam training

708 and 808, respectively.

At 1204, the UE may perform a measurement of the reference signal. In some aspects, performing, at 1204, the measurement may include measuring, at 1204A, multiple transmissions of the reference signal over multiple beams based on the first RRC configuration and storing, at 1204B measurements of the plurality of transmissions of the reference signal. For example, referring to FIGs. 7-9, the

UE

704b, 804b, or 904b may measure 712 and 812 and

store

716 and 816 measurements of reference signals associated with different beam configurations as illustrated in diagram 900-930. For example, 1204 may be performed by RIS RS measurement component 1740.

The second UE may receive, at 1206, receive information identifying at least one beam configuration selected by a first UE for a transmission from a first base station to the first UE via an RIS. The information identifying at least one beam configuration selected by the first UE may be based on the first RRC configuration received at the first UE. In some aspects, the information identifying at least one beam configuration selected by the first UE may be received from the first UE via a sidelink or via a base station serving the second UE. As described in relation to FIGs. 7, 8, and 10, the

UE

704b, 804b, or 1004b may receive

beam selection indication

718, 818, or 1040 that may include a precoding matrix index 1042, an RIS coefficient index 1044 that identifies at least one preferred beam configuration. For example, 1206 may be performed by null space computation component 1744.

At 1208, the second UE may receive an update of a configured number of precoding vectors via at least one of a MAC-CE or a DCI. The configured number of precoding vectors may be based on a number of transmission antennas and a number of reception antennas. For example, the configured number of precoding vectors may be a maximum number based on the number of transmission antennas and the number of reception antennas (e.g., number of transmission antennas minus the number of reception antennas) . For example, referring to FIG. 7, the UE 704b may receive updated null space vector indication configuration 720. For example, 1208 may be performed by null space computation component 1744.

At 1210, the second UE may identify (or calculate) a null space including a set of null vectors associated with eigenvectors having magnitudes less than a threshold magnitude. The set of null vectors may be calculated based on the stored, at 1204B, set of measurements associated with the at least one beam configuration indicated by the first UE. For example, referring to FIGs. 7 and 8, the

second UE

704b and 804b may use the stored measurements to identify 722 a null space (e.g., a set of precoding vectors, such as basis vectors, associated with eigenvalues having a magnitude below a threshold magnitude) associated with the indicated at least one beam configuration received at 1206. For example, 1210 may be performed by null space computation component 1744.

Finally, at 1212, the second UE may transmit, to at least one base station, an indication of the null space based on the measurement of the reference signal and the received information identifying the at least one beam configuration selected by the first UE. The indication of the null space, in some aspects, may include a set of precoding vectors based on a stored set of the measurements associated with the at least one beam configuration indicated by the first UE. In some aspects, the null space corresponds to a set of precoding vectors associated with a set of eigenvalues with magnitudes below a threshold value. The set of precoding vectors may include a configured number of precoding vectors in the set of precoding vectors. For example, referring to FIGs. 7, 8, and 10, the

UE

704b, 804b, or 1004b may transmit a

null space indication

724, 824, or 1050 to the

base station

702, 802b, or 1002b. For example, 1212 may be performed by null space communication component 1746.

FIG. 13 is a flowchart 1300 of a method of wireless communication. The method may be performed by a base station (e.g., the base station 102/180, 702, 802a, 802b, 902a, 1002a, or 1002b; the apparatus 1802) . At 1302, the base station may transmit, to a second UE a first RRC configuration associated with a reference signal. For example, 1302 may be performed by RIS RS configuration component 1840. In some aspects, the base station is a second base station serving the second UE and the second base station may receive the first RRC configuration from a first base station, where the first RRC configuration may be the same RRC configuration transmitted to the first UE by the first base station. The first RRC configuration may be an RRC configuration used in beam training for the RIS.

In some aspects, the first RRC configuration of the reference signal is based on a QCL relationship with another reference signal from the first base station. The first RRC configuration of the reference signal, in some aspects, is based on a QCL relationship with another reference signal from a second base station. The first RRC configuration indicates a first number of beams being trained and a second number of CSI-RS resources associated with each of the first number of beams. In some aspects, a first transmission beam of the first base station is associated with each of the second number of CSI-RS resources for a particular beam. The reference signal, in some aspects, may be encoded with a precoder associated with a beam having a width above a threshold width. For example, referring to FIGs. 7 and 8, the

base station

702 or 802b may transmit reference signal configuration for

RIS beam training

708 or 808, respectively, to

UE

704b or 804b.

At 1304, the base station may receive an indication of a null space from the second UE based on measurement of the reference signal and at least one beam configuration selected by a first UE for transmission from a first base station to the first UE via an RIS. The indication of the null space, in some aspects, may include a set of precoding vectors based on a stored set of the measurements associated with the at least one beam configuration indicated by the first UE. In some aspects, the null space corresponds to a set of precoding vectors associated with a set of eigenvalues with magnitudes below a threshold value. The set of precoding vectors may include a configured number of precoding vectors in the set of precoding vectors. For example, referring to FIGs. 7, 8, and 10, the

base station

702, 802b, and 1002b may receive a

null space indication

724, 824, or 1050 from the

UE

704b, 804b, or 1004b. For example, 1304 may be performed by null space transmission component 1846.

FIG. 14 is a flowchart 1400 of a method of wireless communication. The method may be performed by a first base station (e.g., the base station 102/180, 702, 802a, 902a, or 1002a; the apparatus 1802) . At 1402, the first base station may transmit, to a second UE a first RRC configuration associated with a reference signal. For example, 1402 may be performed by RIS RS configuration component 1840. The first RRC configuration may be an RRC configuration used in beam training for the RIS.

In some aspects, the first RRC configuration of the reference signal is based on a QCL relationship with another reference signal from the first base station. The first RRC configuration of the reference signal, in some aspects, is based on a QCL relationship with another reference signal from a second base station. The first RRC configuration indicates a first number of beams being trained and a second number of CSI-RS resources associated with each of the first number of beams. In some aspects, a first transmission beam of the first base station is associated with each of the second number of CSI-RS resources for a particular beam. For example, referring to FIGs. 7 and 8, the

base station

702 or 802a may transmit reference signal configuration for

RIS beam training

708 or 808, respectively, to

UE

704b or 804b.

At 1404, the first base station may encode the reference signal with a (wide-beam) precoder associated with a beam having a width above a threshold width. In some aspects, the wide beam may enable a second UE to calculate a null space associated with the wide-beam precoder. For example, referring to FIGs. 7-9, the

base station

702 or 802a may encode the reference signal for

RIS training

708 or 808, e.g., associated with transmit beams 914a-914d. For example, 1404 may be performed by RIS beam training component 1842.

At 1406, the first base station may transmit multiple transmissions of the reference signal over each of multiple beams including a CSI-RS in the second number of CSI-RS resources using a first beam. For example, referring to FIG. 9, the base station 902a, may transmit multiple transmissions of the reference signal associated with each transmission beam 914a-914d, where different transmission of the reference beam may be associated with different configurations of the reflection beam (e.g., one of 916a-916d) and the reception beam (e.g., one of 924a-924e) . For example, 1406 may be performed by RIS beam training component 1842.

At 1408, the first base station may transmit information identifying the at least one beam configuration selected by the first UE. The at least one beam configuration selected by the first UE may indicate a particular precoding matrix (P) and a set of RIS coefficients (Φ) . The indication may be made via indexes associated with different precoding matrixes and different sets of RIS coefficients. For example, referring to FIG. 7, the base station 702 may transmit beam selection indication 718 to UE 704b. For example, 1408 may be performed by RIS beam training component 1842.

At 1410, the first base station may update a configured number of precoding vectors via at least one of a MAC-CE or a DCI. The configured number of precoding vectors may be based on a number of transmission antennas and a number of reception antennas. For example, the configured number of precoding vectors may be a maximum number based on the number of transmission antennas and the number of reception antennas (e.g., number of transmission antennas minus the number of reception antennas) . For example, referring to FIG. 7, the first base station 702 may transmit updated null space vector indication configuration 720 to UE 704b. For example, 1410 may be performed by RIS beam training component 1842.

At 1412, the first base station may receive an indication of a null space from the second UE based on measurement of the reference signal and at least one beam configuration selected by a first UE for transmission from a first base station to the first UE via an RIS. The indication of the null space, in some aspects, may include a set of precoding vectors based on a stored set of the measurements associated with the at least one beam configuration indicated by the first UE. In some aspects, the null space corresponds to a set of precoding vectors associated with a set of eigenvalues with magnitudes below a threshold value. The set of precoding vectors may include a configured number of precoding vectors in the set of precoding vectors. For example, referring to FIGs. 7, 8, and 10, the

base station

702, 802a, and 1002a may receive a

null space indication

724, 825, or 1060 from the UE 704b, the base station 802b, or the base station 1002b. For example, 1412 may be performed by null space reception component 1844.

At 1414, the first base station may transmit data to the first UE via the RIS using a precoding matrix based on the indication of the null space. The precoding matrix, in some aspects is generated from the set of orthonormal basis vectors of the null space (e.g., the null vectors indicated in the null space indication) . For example, the

first base station

702 or 802a may transmit

data transmission

726 or 826 based on the null space. For example, 1414 may be performed by null space transmission component 1846.

FIG. 15 is a flowchart 1500 of a method of wireless communication. The method may be performed by a second base station (e.g., the base station 102/180, 802b, 902b, or 1002b; the apparatus 1802) . At 1502, the second base station may receive a first RRC configuration from the first base station. For example, 1502 may be performed by RIS RS configuration component 1840. For example, referring to FIG. 8, the base station 802b may receive reference signal configuration for RIS beam training 808 from a first base station 802a.

At 1504, the second base station may transmit, to a second UE a first RRC configuration associated with a reference signal. For example, 1504 may be performed by RIS RS configuration component 1840. The first RRC configuration may be an RRC configuration used in beam training for the RIS.

In some aspects, the first RRC configuration of the reference signal is based on a QCL relationship with another reference signal from the first base station. The first RRC configuration of the reference signal, in some aspects, is based on a QCL relationship with another reference signal from the second base station. The first RRC configuration indicates a first number of beams being trained and a second number of CSI-RS resources associated with each of the first number of beams. In some aspects, a first transmission beam of the first base station is associated with each of the second number of CSI-RS resources for a particular beam. For example, referring to FIG. 8, the base station 802b may transmit reference signal configuration for RIS beam training 808 to 804b.

At 1506, the second base station may transmit information identifying the at least one beam configuration selected by the first UE. The at least one beam configuration selected by the first UE may indicate a particular precoding matrix (P) and a set of RIS coefficients (Φ) . The indication may be made via indexes associated with different precoding matrixes and different sets of RIS coefficients. The For example, referring to FIG. 8, the base station 802b may transmit beam selection indication 818 to UE 804b. For example, 1506 may be performed by RIS beam training component 1842.

At 1508, the second base station may update a configured number of precoding vectors via at least one of a MAC-CE or a DCI. The configured number of precoding vectors may be based on a number of transmission antennas and a number of reception antennas. For example, the configured number of precoding vectors may be a maximum number based on the number of transmission antennas and the number of reception antennas (e.g., number of transmission antennas minus the number of reception antennas) . For example, referring to FIG. 8, the second base station 802b may transmit and updated null space vector indication configuration (similar to updated null space vector indication configuration 720) to UE 704b. For example, 1508 may be performed by RIS beam training component 1842.

At 1510, the second base station may receive an indication of a null space from the second UE based on measurement of the reference signal and at least one beam configuration selected by a first UE for transmission from a first base station to the first UE via an RIS. The indication of the null space, in some aspects, may include a set of precoding vectors based on a stored set of the measurements associated with the at least one beam configuration indicated by the first UE. In some aspects, the null space corresponds to a set of precoding vectors associated with a set of eigenvalues with magnitudes below a threshold value. The set of precoding vectors may include a configured number of precoding vectors in the set of precoding vectors. For example, referring to FIGs. 8 and 10, the

base station

802b and 1002b may receive a

null space indication

824, or 1050 from the UE 804b or the UE 1004b. For example, 1510 may be performed by null space reception component 1844.

At 1512, the second base station may transmit the indication of the null space to the first base station after receipt from the second UE. For example, referring to FIGs. 8 and 10, the

second base station

802b or 1002b may transmit

null space indication

825 or 1060 to the

first base station

802a or 1002a. For example, 1512 may be performed by null space transmission component 1846.

FIG. 16 is a flowchart 1600 of a method of wireless communication. The method may be performed by a first UE (e.g., the

UE

104, 604a, 704a, 804a, 904a, 1004a; the apparatus 1702) . At 1602, the first UE may receive a first RRC configuration associated with a reference signal. For example, 1602 may be performed by RIS RS measurement component 1740. The first RRC configuration may be received from a first base station serving the first UE, where the first RRC configuration is a same RRC configuration transmitted to a second UE, the first RRC configuration may be an RRC configuration used in beam training for the RIS.

In some aspects, the first RRC configuration of the reference signal is based on a QCL relationship with another reference signal from the first base station. The first RRC configuration indicates a first number of beams being trained and a second number of CSI-RS resources associated with each of the first number of beams. In some aspects, a first transmission beam of the first base station is associated with each of the second number of CSI-RS resources for a particular beam. The reference signal, in some aspects, may encoded with a precoder associated with a beam having a width above a threshold width. For example, referring to FIGs. 7 and 8, UE 704a and UE 804a may receive reference signal configuration for

RIS beam training

708 and 808, respectively.

At 1604, the first UE may perform a measurement of the reference signal. In some aspects, performing, at 1604, the measurement may include measuring a plurality of transmissions of the reference signal over a plurality of beams based on the first RRC configuration and determining at least one preferred beam configuration. For example, referring to FIGs. 7-9, the

UE

704a, 804a, or 904a may measure 712 and 812 and select 714 and 814, for transmissions from the

base station

702 or 802a, at least one beam configuration of the beam configurations associated with the measured reference signals (e.g., the measurements of reference signals associated with different beam configurations as illustrated in diagram 900-930) . For example, 1604 may be performed by RIS RS measurement component 1740 and configuration selection component 1742.

The first UE may transmit, at 1606, information identifying at least one beam configuration selected by the first UE for a transmission from a first base station to the first UE via an RIS to a second UE. The information identifying at least one beam configuration selected by the first UE may be based on the first RRC configuration received at the first UE. In some aspects, the information identifying at least one beam configuration selected by the first UE may be transmitted to the second UE via a sidelink (directly) or via a base station serving the second UE (indirectly) . As described in relation to FIGs. 7, 8, and 10, the

UE

704a, 804a, or 1004a may transmit

beam selection indication

718, 818, or 1040 that may include a precoding matrix index 1042 and an RIS coefficient index 1044 that identifies at least one preferred beam configuration. For example, 1606 may be performed by configuration selection component 1742.

Finally, at 1608, the first UE may receive, from the first base station, at least one transmission based on the at least one indicated beam configuration and a null space indication received at the first base station from a second UE. The indication of the null space, in some aspects, may include a set of precoding vectors based on a stored set of the measurements associated with the at least one beam configuration indicated by the first UE. In some aspects, the null space corresponds to a set of precoding vectors associated with a set of eigenvalues with magnitudes below a threshold value. The set of precoding vectors may include a configured number of precoding vectors in the set of precoding vectors. For example, referring to FIGs. 7 and 8, the

UE

704a or 804a may receive a

data transmission

726 or 826 based on the null vector from

base station

702 or 802a. For example, 1608 may be performed by null space communication component 1746.

FIG. 17 is a diagram 1700 illustrating an example of a hardware implementation for an apparatus 1702. The apparatus 1702 may be a UE, a component of a UE, or may implement UE functionality. In some aspects, the apparatusl702 may include a cellular baseband processor 1704 (also referred to as a modem) coupled to a cellular RF transceiver 1722. In some aspects, the apparatus 1702 may further include one or more subscriber identity modules (SIM) cards 1720, an application processor 1706 coupled to a secure digital (SD) card 1708 and a screen 1710, a Bluetooth module 1712, a wireless local area network (WLAN) module 1714, a Global Positioning System (GPS) module 1716, or a power supply 1718. The cellular baseband processor 1704 communicates through the cellular RF transceiver 1722 with the UE 104 and/or BS 102/180. The cellular baseband processor 1704 may include a computer-readable medium /memory. The computer-readable medium /memory may be non-transitory. The cellular baseband processor 1704 is responsible for general processing, including the execution of software stored on the computer-readable medium /memory. The software, when executed by the cellular baseband processor 1704, causes the cellular baseband processor 1704 to perform the various functions described supra. The computer-readable medium /memory may also be used for storing data that is manipulated by the cellular baseband processor 1704 when executing software. The cellular baseband processor 1704 further includes a reception component 1730, a communication manager 1732, and a transmission component 1734. The communication manager 1732 includes the one or more illustrated components. The components within the communication manager 1732 may be stored in the computer-readable medium /memory and/or configured as hardware within the cellular baseband processor 1704. The cellular baseband processor 1704 may be a component of the UE 350 and may include the memory 360 and/or at least one of the TX processor 368, the RX processor 356, and the controller/processor 359. In one configuration, the apparatus 1702 may be a modem chip and include just the baseband processor 1704, and in another configuration, the apparatus 1702 may be the entire UE (e.g., see 350 of FIG. 3) and include the additional modules of the apparatus 1702.

The communication manager 1732 includes an RIS RS measurement component 1740 that is configured to receive a first RRC configuration associated with a reference signal and perform a measurement of the reference signal, e.g., as described in connection with 1102, 1104, 1202, 1204, 1602, and 1604 of FIGs. 11, 12, and 16. The communication manager 1732 further includes a configuration selection component 1742 that receives input in the form of RS measurements from the component 1740 and is configured to select, for transmissions from a base station, at least one beam configuration of the beam configurations associated with the measured reference signals; and transmit, to a second UE, information identifying at least one beam configuration selected by the first UE for a transmission from a first base station to the first UE via an RIS, e.g., as described in connection with 1604 and 1606 of FIG. 16. The communication manager 1732 further includes a null space computation component 1744 that receives input in the form of a set of reference signal measurements from the component 1740 and at least one selected beam configuration from the component 1742 and is configured to receive information identifying at least one beam configuration selected by a first UE for a transmission from a first base station to the first UE via an RIS and identify (or calculate) a null space including a set of null vectors associated with eigenvectors having magnitudes less than a threshold magnitude, e.g., as described in connection with 1106, 1206, 1208, and 1210 of FIGs. 11 and 12. The communication manager 1732 further includes a null space communication component 1746 that receives input in the form of the identified null space (or null space vectors) from the component 1744 is configured to transmit, to at least one base station, an indication of a null space based on the measurement of the reference signal and the received information identifying the at least one beam configuration selected by the first UE; and to receive, from the first base station, at least one transmission based on the at least one indicated beam configuration and a null space indication received at the first base station from a second UE, e.g., as described in connection with 1108, 1212, and 1608 of FIGs. 11, 12, and 16.

The apparatus may include additional components that perform each of the blocks of the algorithm in the flowcharts of FIGs. 11, 12, and 16. As such, each block in the flowcharts of FIGs. 11, 12, and 16 may be performed by a component and the apparatus may include one or more of those components. The components may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof.

As shown, the apparatus 1702 may include a variety of components configured for various functions. In one configuration, the apparatus 1702, and in particular the cellular baseband processor 1704, includes means for receiving a first RRC configuration associated with a reference signal. The apparatus 1702, and in particular the cellular baseband processor 1704, may also include means for performing a measurement of the reference signal. The apparatus 1702, and in particular the cellular baseband processor 1704, may also include means for receiving information identifying at least one beam configuration selected by a first UE for a transmission from a first base station to the first UE via an RIS. The apparatus 1702, and in particular the cellular baseband processor 1704, may also include means for transmitting to at least one base station an indication of a null space based on the measurement of the reference signal and the at least one beam configuration selected by the first UE. The apparatus 1702, and in particular the cellular baseband processor 1704, may also include means for receiving each of the second number of CSI-RS resources associated with the first transmission beam via a first reception beam of the second UE. The apparatus 1702, and in particular the cellular baseband processor 1704, may also include means for measuring a plurality of transmissions of the reference signal over a plurality of beams based on the first RRC configuration. The apparatus 1702, and in particular the cellular baseband processor 1704, may also include means for storing measurements of the plurality of transmissions of the reference signal, wherein the indication of the null space comprises a set of precoding vectors based on a stored set of the measurements associated with the at least one beam configuration indicated by the first UE. The apparatus 1702, and in particular the cellular baseband processor 1704, may also include means for receiving an update of the configured number of precoding vectors via at least one of a MAC-CE or a DCI. The apparatus 1702, and in particular the cellular baseband processor 1704, may also include means for performing a measurement of the reference signal for multiple beam configurations associated with a transmission from a base station to the first UE via an RIS. The apparatus 1702, and in particular the cellular baseband processor 1704, may also include means for transmitting, to a second UE, an indication of at least one beam configuration based on the measurement. The means may be one or more of the components of the apparatus 1702 configured to perform the functions recited by the means. As described supra, the apparatus 1702 may include the TX Processor 368, the RX Processor 356, and the controller/processor 359. As such, in one configuration, the means may be the TX Processor 368, the RX Processor 356, and the controller/processor 359 configured to perform the functions recited by the means.

FIG. 18 is a diagram 1800 illustrating an example of a hardware implementation for an apparatus 1802. The apparatus 1802 may be a base station, a component of a base station, or may implement base station functionality. In some aspects, the apparatus 1702 may include a baseband unit 1804. The baseband unit 1804 may communicate through a cellular RF transceiver 1822 with the UE 104. The baseband unit 1804 may include a computer-readable medium /memory. The baseband unit 1804 is responsible for general processing, including the execution of software stored on the computer-readable medium /memory. The software, when executed by the baseband unit 1804, causes the baseband unit 1804 to perform the various functions described supra. The computer-readable medium /memory may also be used for storing data that is manipulated by the baseband unit 1804 when executing software. The baseband unit 1804 further includes a reception component 1830, a communication manager 1832, and a transmission component 1834. The communication manager 1832 includes the one or more illustrated components. The components within the communication manager 1832 may be stored in the computer-readable medium / memory and/or configured as hardware within the baseband unit 1804. The baseband unit 1804 may be a component of the base station 310 and may include the memory 376 and/or at least one of the TX processor 316, the RX processor 370, and the controller/processor 375.

The communication manager 1832 includes an RIS RS configuration component 1840 that may receive a first RRC configuration from a first base station and transmit, to a second UE a first RRC configuration associated with a reference signal, e.g., as described in connection with 1302, 1402, 1502, and 1504 of FIGs. 13, 14, and 15. The communication manager 1832 further includes an RIS beam training component 1842 that may encode the reference signal with a (wide-beam) precoder associated with a beam having a width above a threshold width, transmit information identifying the at least one beam configuration selected by the first UE, update a configured number of precoding vectors via at least one of a MAC-CE or a DCI, transmit information identifying the at least one beam configuration selected by the first UE, e.g., as described in connection with 1404, 1406, 1408, 1410, 1506, and 1508. The communication manager 1832 further includes a null space reception component 1844 that may receive an indication of a null space from the second UE based on measurement of the reference signal and at least one beam configuration selected by a first UE for transmission from a first base station to the first UE via an RIS, e.g., as described in connection with 1412 and 1510 of FIGs. 14 and 15. The communication manager 1832 further includes a null space transmission component 1846 that may receive an indication of a null space from the second UE based on measurement of the reference signal and at least one beam configuration selected by a first UE for transmission from a first base station to the first UE via an RIS, transmit the indication of the null space to the first base station after receipt from the second UE, transmit data to the first UE via the RIS using a precoding matrix based on the indication of the null space, e.g., as described in connection with 1304, 1414, and 1512 of FIGs. 13, 14, and 15.

The apparatus may include additional components that perform each of the blocks of the algorithm in the flowcharts of FIGs. 13-15. As such, each block in the flowcharts of FIGs. 13-15 may be performed by a component and the apparatus may include one or more of those components. The components may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof.

As shown, the apparatus 1802 may include a variety of components configured for various functions. In one configuration, the apparatus 1802, and in particular the baseband unit 1804, includes means for transmitting, to a second UE a first RRC configuration associated with a reference signal. The apparatus 1802, and in particular the baseband unit 1804, may also include means for receiving an indication of a null space from the second UE based on measurement of the reference signal and at least one beam configuration selected by a first UE for transmission from a first base station to the first UE via an RIS. The apparatus 1802, and in particular the baseband unit 1804, may also include means for transmitting information identifying the at least one beam configuration selected by the first UE for the transmission from the first base station to the first UE via the RIS. The apparatus 1802, and in particular the baseband unit 1804, may also include means for receiving the first RRC configuration from the first base station, the first RRC configuration being a same RRC configuration transmitted to the first UE by the first base station. The apparatus 1802, and in particular the baseband unit 1804, may also include means for transmitting the indication of the null space to the first base station after receipt from the second UE. The apparatus 1802, and in particular the baseband unit 1804, may also include means for transmitting data to the first UE via the RIS using a precoding matrix based on the indication of the null space. The apparatus 1802, and in particular the baseband unit 1804, may also include means for transmitting a CSI-RS in the second number of CSI-RS resources using a first beam in the first number of beams. The apparatus 1802, and in particular the baseband unit 1804, may also include means for transmitting a plurality of transmissions of the reference signal over each of a plurality of beams. The apparatus 1802, and in particular the baseband unit 1804, may also include means for encoding the reference signal with a precoder associated with a beam having a width above a threshold width. The apparatus 1802, and in particular the baseband unit 1804, may also include means for updating the configured number of precoding vectors via at least one of a MAC-CE or a DCI. The means may be one or more of the components of the apparatus 1802 configured to perform the functions recited by the means. As described supra, the apparatus 1802 may include the TX Processor 316, the RX Processor 370, and the controller/processor 375. As such, in one configuration, the means may be the TX Processor 316, the RX Processor 370, and the controller/processor 375 configured to perform the functions recited by the means.

Accordingly, a method, a computer-readable medium, and an apparatus are provided to mitigate the increased interference at a second UE (e.g., an interfered UE) in either of the situations depicted in diagrams 610 or 620 of FIG. 6 above. As will be discussed above, the method includes aspects related to CSI-RS for beam training the RIS to serve a first UE (e.g., a target UE) , QCL information related to the CSI-RS and/or beam directions associated with beam training the RIS, and transmitting a null space associated with a second UE (e.g., an interfered UE) and at least one beam configuration indicated by the first UE based on the RIS beam training.

For example, an interfered UE may report null space information on certain resources while training RIS for serving a first UE (e.g., a target UE) . A first base station serving the first UE may leverage the null space information to modify the precoder used to serve the first UE to reduce interference at the second UE. For example, the base station may linearly combine the channel precoder indicated by the first UE channel basis (i.e., the channel precoder indicated by the first UE) with the null space basis indicated by the second UE.

It is understood that the specific order or hierarchy of blocks in the processes /flowcharts disclosed is an illustration of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes /flowcharts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” Terms such as “if, ” “when, ” and “while” should be interpreted to mean “under the condition that” rather than imply an immediate temporal relationship or reaction. That is, these phrases, e.g., “when, ” do not imply an immediate action in response to or during the occurrence of an action, but simply imply that if a condition is met then an action will occur, but without requiring a specific or immediate time constraint for the action to occur. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration. ” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module, ” “mechanism, ” “element, ” “device, ” and the like may not be a substitute for the word “means. ” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for. ”

The following aspects are illustrative only and may be combined with other aspects or teachings described herein, without limitation.

Aspect 1 is an apparatus for wireless communication including at least one processor coupled to a memory and configured to receive a first RRC configuration associated with a reference signal, perform a measurement of the reference signal, receive information identifying at least one beam configuration selected by a first UE for a transmission from a first base station to the first UE via a RIS, and transmit to at least one base station an indication of a null space based on the measurement of the reference signal and the at least one beam configuration selected by the first UE..

Aspect 2 is the apparatus of aspect 1, where the first RRC configuration is received from a second base station serving the second UE, the first RRC configuration being a same RRC configuration transmitted to the first UE, and the at least one base station includes the second base station.

Aspect 3 is the apparatus of aspect 1, where the first RRC configuration is received from the first base station serving the second UE, the first RRC configuration being a same RRC configuration transmitted to the first UE, and the at least one base station includes the first base station.

Aspect 4 is the apparatus of any of aspects 1 to 3, where the first RRC configuration comprises an RRC configuration used in beam training for the RIS.

Aspect 5 is the apparatus of any of aspects 1 to 4, where the first RRC configuration of the reference signal is based on a QCL relationship with at least one of another reference signal from the first base station or another reference signal from a second base station.

Aspect 6 is the apparatus of any of aspects 1 to 5, where the first RRC configuration indicates a first number of beams being trained and a second number of CSI-RS resources associated with each of the first number of beams, and where a first transmission beam of the first base station is associated with each of the second number of CSI-RS resources for a particular beam.

Aspect 7 is the apparatus of aspect 6, the at least one processor further configured to receive each of the second number of CSI-RS resources associated with the particular beam via a first reception beam of the second UE.

Aspect 8 is the apparatus of any of

aspects

6 or 7, where a set of the second number of CSI-RS resources is associated with a particular beam at the RIS.

Aspect 9 is the apparatus of any of aspects 1 to 8, the at least one processor further configured to measure a plurality of transmissions of the reference signal over a plurality of beams based on the first RRC configuration, and store measurements of the plurality of transmissions of the reference signal, where the indication of the null space includes a set of precoding vectors based on a stored set of the measurements associated with the at least one beam configuration indicated by the first UE.

Aspect 10 is the apparatus of aspect 9, where the reference signal is encoded with a precoder associated with a beam having a width above a threshold width.

Aspect 11 is the apparatus of any of

aspects

1 or 10, where the null space corresponds to a set of precoding vectors associated with a set of eigenvalues with magnitudes below a threshold value.

Aspect 12 is the apparatus of aspect 11, where the set of precoding vectors includes a configured number of precoding vectors in the set of precoding vectors, the at least one processor further configured to receive an update of the configured number of precoding vectors via at least one of a MAC-CE or a DCI.

Aspect 13 is the apparatus of any of

aspects

1 or 12, further including a transceiver coupled to the at least one processor.

Aspect 14 is an apparatus for wireless communication including at least one processor coupled to a memory and configured to transmit, to a second UE a first RRC configuration associated with a reference signal, and receive an indication of a null space from the second UE based on measurement of the reference signal and at least one beam configuration selected by a first UE for transmission from a first base station to the first UE via a RIS.

Aspect 15 is the apparatus of aspect 14, the at least one processor further configured to transmit information identifying the at least one beam configuration selected by the first UE for the transmission from the first base station to the first UE via the RIS.

Aspect 16 is the apparatus of any of aspects 14 or 15, where the base station is a second base station serving the second UE, the at least one processor further configured to receive the first RRC configuration from the first base station, the first RRC configuration being a same RRC configuration transmitted to the first UE by the first base station, and transmit the indication of the null space to the first base station after receipt from the second UE.

Aspect 17 is the apparatus of any of aspects 14 or 15, where the base station is the first base station serving the second UE and the first RRC configuration including a same RRC configuration transmitted to the first UE by the first base station, the at least one processor further configured to transmit data to the first UE via the RIS using a precoding matrix based on the indication of the null space.

Aspect 18 is the apparatus of any of aspects 14 to 17, where the first RRC configuration includes an RRC configuration used in training the RIS.

Aspect 19 is the apparatus of aspect 18, where the first RRC configuration indicates a first number of beams being trained and a second number of CSI-RS resources associated with each of the first number of beams.

Aspect 20 is the apparatus of aspect 19, the at least one processor further configured to transmit a CSI-RS in the second number of CSI-RS resources using a first transmission.

Aspect 21 is the apparatus of any of aspects 19 or 20, where a set of the second number of CSI-RS resources is associated with a particular beam at the RIS.

Aspect 22 is the apparatus of any of aspects 14 to 21, the at least one processor further configured to transmit multiple transmissions of the reference signal over multiple beams.

Aspect 23 is the apparatus of aspect 19, the at least one processor further configured to encode the reference signal with a precoder associated with a beam having a width above a threshold width.

Aspect 24 is the apparatus of any of aspects 14 to 23, where the null space comprises a configured number of precoding vectors in a set of precoding vectors.

Aspect 25 is the apparatus of any of aspects 14 to 24, where the first RRC configuration of the reference signal is based on a QCL relationship with a reference signal from the first base station.

Aspect 26 is the apparatus of any of aspects 14 to 24, where the first RRC configuration of the reference signal is based on a QCL relationship with a reference signal from a different base station serving the first UE.

Aspect 27 is the apparatus of any of aspects 14 to 26, further including a transceiver coupled to the at least one processor.

Aspect 28 is an apparatus for wireless communication including at least one processor coupled to a memory and configured to receive a first RRC configuration associated with a reference signal, perform a measurement of the reference signal for multiple beam configurations associated with a transmission from a base station to the first UE via a RIS, and transmit, to a second UE, an indication of at least one beam configuration based on the measurement.

Aspect 29 is the apparatus of aspect 28, further including a transceiver coupled to the at least one processor.

Aspect 30 is a method of wireless communication for implementing any of aspects 1 to 29.

Aspect 31 is an apparatus for wireless communication including means for implementing any of aspects 1 to 29.

Aspect 32 is a computer-readable medium storing computer executable code, where the code when executed by a processor causes the processor to implement any of aspects 1 to 29.

Claims

An apparatus for wireless communication at a second user equipment (UE) , comprising:

a memory; and

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

receive a first radio resource control (RRC) configuration associated with a reference signal;

perform a measurement of the reference signal;

receive information identifying at least one beam configuration selected by a first UE for a transmission from a first base station to the first UE via a reconfigurable intelligent surface (RIS) ; and

transmit to at least one base station an indication of a null space based on the measurement of the reference signal and the at least one beam configuration selected by the first UE.
The apparatus of claim 1, wherein

the first RRC configuration is received from a second base station serving the second UE, the first RRC configuration being a same RRC configuration transmitted to the first UE, and

the at least one base station comprises the second base station.
The apparatus of claim 1, wherein

the first RRC configuration is received from the first base station serving the second UE, the first RRC configuration being a same RRC configuration transmitted to the first UE, and

the at least one base station comprises the first base station.
The apparatus of claim 1, wherein the first RRC configuration comprises an RRC configuration used in beam training for the RIS.
The apparatus of claim 1, wherein the first RRC configuration of the reference signal is based on a quasi-colocation (QCL) relationship with at least one of another reference signal from the first base station or another reference signal from a second base station.
The apparatus of claim 1, wherein the first RRC configuration indicates a first number of beams being trained and a second number of channel state information (CSI) reference signal (CSI-RS) resources associated with each of the first number of beams, and wherein a first transmission beam of the first base station is associated with each of the second number of CSI-RS resources for a particular beam.
The apparatus of claim 6, the at least one processor further configured to:

receive each of the second number of CSI-RS resources associated with the particular beam via a first reception beam of the second UE.
The apparatus of claim 6, wherein a set of the second number of CSI-RS resources is associated with the particular beam at the RIS.
The apparatus of claim 1, the at least one processor further configured to:

measure a plurality of transmissions of the reference signal over a plurality of beams based on the first RRC configuration; and

store measurements of the plurality of transmissions of the reference signal, wherein the indication of the null space comprises a set of precoding vectors based on a stored set of measurements associated with the at least one beam configuration indicated by the first UE.
The apparatus of claim 9, wherein the reference signal is encoded with a precoder associated with a beam having a width above a threshold width.
The apparatus of claim 1, wherein the null space corresponds to a set of precoding vectors associated with a set ofeigenvalues with magnitudes below a threshold value.
The apparatus of claim 11, wherein the set of precoding vectors comprises a configured number of precoding vectors in the set of precoding vectors, the at least one processor further configured to:

receive an update of the configured number ofprecoding vectors via at least one of a medium access control (MAC) control element (CE) (MAC-CE) or a downlink control element (DCI) .
The apparatus of claim 1, further comprising at least one antenna and a transceiver coupled to the at least one processor.
An apparatus for wireless communication at a base station, comprising:

a memory; and

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

transmit, to a second user equipment (UE) a first radio resource control (RRC) configuration associated with a reference signal; and

receive an indication of a null space from the second UE based on measurement of the reference signal and at least one beam configuration selected by a first UE for transmission from a first base station to the first UE via a reconfigurable intelligent surface (RIS) .
The apparatus of claim 14, the at least one processor further configured to:

transmit information identifying the at least one beam configuration selected by the first UE for the transmission from the first base station to the first UE via the RIS.
The apparatus of claim 14, wherein the base station is a second base station serving the second UE, the at least one processor further configured to:

receive the first RRC configuration from the first base station, the first RRC configuration being a same RRC configuration transmitted to the first UE by the first base station; and

transmit the indication of the null space to the first base station after receipt from the second UE.
The apparatus of claim 14, wherein the base station is the first base station serving the second UE and the first RRC configuration comprises a same RRC configuration transmitted to the first UE by the first base station, the at least one processor further configured to:

transmit data to the first UE via the RIS using a precoding matrix based on the indication of the null space.
The apparatus of claim 14, wherein the first RRC configuration comprises an RRC configuration used in training the RIS.
The apparatus of claim 18, wherein the first RRC configuration indicates a first number of beams being trained and a second number of channel state information (CSI) reference signal (CSI-RS) resources associated with each of the first number of beams.
The apparatus of claim 19, the at least one processor further configured to:

transmit a CSI-RS in the second number of CSI-RS resources using a first transmission.
The apparatus of claim 19, wherein a set of the second number of CSI-RS resources is associated with a particular beam at the RIS.
The apparatus of claim 14, the at least one processor further configured to:

transmit a plurality of transmissions of the reference signal over a plurality of beams.
The apparatus of claim 22, the at least one processor further configured to:

encode the reference signal with a precoder associated with a beam having a width above a threshold width.
The apparatus of claim 14, wherein the null space comprises a configured number of precoding vectors in a set ofprecoding vectors.
The apparatus of claim 14, wherein the first RRC configuration of the reference signal is based on a quasi-colocation (QCL) relationship with a corresponding reference signal from the first base station.
The apparatus of claim 14, wherein the first RRC configuration of the reference signal is based on a quasi-colocation (QCL) relationship with corresponding reference signal from a different base station serving the first UE.
The apparatus of claim 14, further comprising at least one antenna and a transceiver coupled to the at least one processor.
An apparatus for wireless communication at a first user equipment (UE) , comprising:

a memory; and

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

receive a first radio resource control (RRC) configuration associated with a reference signal;

perform a measurement of the reference signal for multiple beam configurations associated with a transmission from a base station to the first UE via a reconfigurable intelligent surface (RIS) ; and

transmit, to a second UE, an indication of at least one beam configuration based on the measurement.
The apparatus of claim 28, further comprising at least one antenna and a transceiver coupled to the at least one processor.
A method of wireless communication at a second user equipment (UE) comprising:

receiving a first radio resource control (RRC) configuration associated with a reference signal;

performing a measurement of the reference signal;

receiving information identifying at least one beam configuration selected by a first UE for a transmission from a first base station to the first UE via a reconfigurable intelligent surface (RIS) ; and

transmitting to at least one base station an indication of a null space based on the measurement of the reference signal and the at least one beam configuration selected by the first UE.