WO2022221976A1

WO2022221976A1 - Configuration of reconfigurable intelligent surfaces (ris) selection

Info

Publication number: WO2022221976A1
Application number: PCT/CN2021/088018
Authority: WO
Inventors: Alexandros MANOLAKOS; Yu Zhang; Hung Dinh LY; Ahmed Elshafie
Original assignee: Qualcomm Incorporated
Priority date: 2021-04-19
Filing date: 2021-04-19
Publication date: 2022-10-27

Abstract

Aspects of the disclosure relate to selecting a set of reconfigurable intelligent surfaces (RISs). The user equipment (UE) may be configured to receive a first reference signal via a direct channel and receive at least two second reference signals via the direct channel and at least two corresponding first channels that transit corresponding RISs. The UE may further measure the direct channel based on the first reference signal and measure the direct channel with the at least two first channels based on the at least two corresponding second reference signals. The UE may further receive a codebook for determining one or more second channels and determine the one or more second channels based on the codebook, the direct channel, and the at least two first channels. The UE may report channel information based on the one or more second channels. Other aspects, embodiments, and features are also claimed and described.

Description

CONFIGURATION OF RECONFIGURABLE INTELLIGENT SURFACES (RIS) SELECTION

TECHNICAL FIELD

The technology discussed below relates generally to wireless communication systems, and more particularly, to a controllable reflective surface (e.g., reconfigurable intelligent surface (RIS) ) .

INTRODUCTION

Recently, reconfigurable intelligent surface (RIS) technologies have been introduced to enhance system throughput and enlarge cell coverage with low hardware cost and low power consumption. As a relaying technology, an RIS may extend the coverage area of a cell by redirecting impinging signals on the RIS panel to given directions. As the demand for mobile broadband access continues to increase, research and development continue to advance wireless communication technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications with multiple RISs.

BRIEF SUMMARY OF SOME EXAMPLES

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

In various aspects, the disclosure generally relates to configuration of controllable reflective surfaces (e.g., reconfigurable intelligent surfaces (RISs) ) selection. In some scenarios, a user equipment (UE) may determine channel characteristics of channels without receiving corresponding reference signals based on other measured channels and a codebook determined by a base station. Thus, the base station may reduce the reference signal overhead using the codebook.

In some aspects of the disclosure, a scheduled entity (e.g., a UE) may receive a first reference signal via a direct channel and receive at least two second reference signals via at least two corresponding first channels. A first channel of the at least two first channels may include a direct channel component associated with the direct channel and a reflected channel component that is reflected on a controllable reflective surface. The scheduled entity may also receive a codebook for determining one or more second channels. The scheduled entity, then, may determine the one or more second channels based on the codebook and the direct channel and the at least two first channels. The scheduled entity may report channel information based on the one or more second channels.

In some aspects of the disclosure, a scheduling entity (e.g., a base station) may schedule a first reference signal via a direct channel. The scheduling entity may schedule at least two second reference signals via at least two corresponding first channels. A first channel of the at least two first channels may include a direct channel component associated with the direct channel and a reflected channel component that is reflected on a controllable reflective surface. The scheduling entity may also transmit a codebook for determining one or more second channels. The scheduling entity may receive channel information based on the one or more second channels. The scheduling entity, then, may transmit a set of one or more third reference signals based on the channel information.

These and other aspects of the technology discussed herein will become more fully understood upon a review of the detailed description, which follows. Other aspects, features, and embodiments will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary embodiments in conjunction with the accompanying figures. While the following description may discuss various advantages and features relative to certain embodiments and figures, all embodiments can include one or more of the advantageous features discussed herein. In other words, while this description may discuss one or more embodiments as having certain advantageous features, one or more of such features may also be used in accordance with the various embodiments discussed herein. In similar fashion, while this description may discuss exemplary embodiments as device, system, or method embodiments it should be understood that such exemplary embodiments can be implemented in various devices, systems, and methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a wireless communication system according to some embodiments.

FIG. 2 is a conceptual illustration of an example of a radio access network according to some embodiments.

FIG. 3 is a block diagram illustrating a wireless communication system supporting multiple-input multiple-output (MIMO) communication according to some embodiments.

FIG. 4 is a conceptual illustration of an example of reconfigurable intelligent surface (RIS) communication according to some embodiments.

FIG. 5 is a schematic illustration of exemplary channel estimation using an RIS according to some embodiments.

FIG. 6 is a conceptual illustration of an example of RIS subset selection configuration according to some embodiments.

FIG. 7 is a block diagram conceptually illustrating an example of a hardware implementation for a scheduling entity according to some embodiments.

FIG. 8 is a block diagram conceptually illustrating an example of a hardware implementation for a scheduled entity according to some embodiments.

FIG. 9 is a flow chart illustrating an exemplary process for RIS selection configuration according to some embodiments.

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, those skilled in the art will readily recognize that these concepts may be practiced without these specific details. In some instances, this description provides well known structures and components in block diagram form in order to avoid obscuring such concepts.

While this description describes aspects and embodiments 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, packaging arrangements. For example, embodiments and/or uses may come about via integrated chip embodiments and other non-module-component based devices (e.g., end-user devices, vehicles, communication devices, computing devices, industrial equipment, retail/purchasing devices, medical devices, 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 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 necessarily include additional components and features for implementation and practice of claimed and described embodiments. 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, end-user devices, etc. of varying sizes, shapes and constitution.

The disclosure that follows presents various concepts that may be implemented across a broad variety of telecommunication systems, network architectures, and communication standards. Referring now to FIG. 1, as an illustrative example without limitation, this schematic illustration shows various aspects of the present disclosure with reference to a wireless communication system 100. The wireless communication system 100 includes several interacting domains: a core network 102, a radio access network (RAN) 104, and a user equipment (UE) 106a. By virtue of the wireless communication system 100, the UE 106a may be enabled to carry out data communication with an external data network 110, such as (but not limited to) the Internet.

The RAN 104 may implement any suitable wireless communication technology or technologies to provide radio access to the UE 106a. As one example, the RAN 104 may operate according to 3 ^rd Generation Partnership Project (3GPP) New Radio (NR) specifications, often referred to as 5G. As another example, the RAN 104 may operate under a hybrid of 5G NR and Evolved Universal Terrestrial Radio Access Network (eUTRAN) standards, often referred to as LTE. The 3GPP refers to this hybrid RAN as a next-generation RAN, or NG-RAN. Of course, many other examples may be utilized within the scope of the present disclosure.

As illustrated, the RAN 104 includes a plurality of base stations 108. Broadly, a base station is a network element in a radio access network responsible for radio transmission and reception in one or more cells to or from a UE. In different technologies, standards, or contexts, those skilled in the art may variously refer to a base station as a base transceiver station (BTS) , a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS) , an extended service set (ESS) , an access point (AP) , a Node B (NB) , an eNode B (eNB) , a gNode B (gNB) , or some other suitable terminology.

The radio access network 104 supports wireless communication for multiple mobile apparatuses. Those skilled in the art may refer to a mobile apparatus as user equipment (UE) in 3GPP standards, but may also be refer to a mobile station (MS) , 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 (AT) , a mobile terminal, a wireless terminal, a remote terminal, a handset, a terminal, a user agent, a mobile client, a client, or some other suitable terminology. A UE may be an apparatus that provides access to network services. A UE may take on many forms and can include a range of devices.

Within the present document, a “mobile” apparatus (aka a UE) need not necessarily have a capability to move, and may be stationary. The term mobile apparatus or mobile device broadly refers to a diverse array of devices and technologies. UEs may include a number of hardware structural components sized, shaped, and arranged to help in communication; such components can include antennas, antenna arrays, RF chains, amplifiers, one or more processors, etc. electrically coupled to each other. For example, some non-limiting examples of a mobile apparatus include a mobile, a cellular (cell) phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal computer (PC) , a notebook, a netbook, a smartbook, a tablet, a personal digital assistant (PDA) , and a broad array of embedded systems, e.g., corresponding to an “Internet of things” (IoT) . A mobile apparatus may additionally be an automotive or other transportation vehicle, a remote sensor or actuator, a robot or robotics device, a satellite radio, a global positioning system (GPS) device, an object tracking device, a drone, a multi-copter, a quad-copter, a remote control device, a consumer and/or wearable device, such as eyewear, a wearable camera, a virtual reality device, a smart watch, a health or fitness tracker, a digital audio player (e.g., MP3 player) , a camera, a game console, etc. A mobile apparatus may additionally be a digital home or smart home device such as a home audio, video, and/or multimedia device, an appliance, a vending machine, intelligent lighting, a home security system, a smart meter, etc. A mobile apparatus may additionally be a smart energy device, a security device, a solar panel or solar array, a municipal infrastructure device controlling electric power (e.g., a smart grid) , lighting, water, etc.; an industrial automation and enterprise device; a logistics controller; agricultural equipment; military defense equipment, vehicles, aircraft, ships, and weaponry, etc. Still further, a mobile apparatus may provide for connected medicine or telemedicine support, e.g., health care at a distance. Telehealth devices may include telehealth monitoring devices and telehealth administration devices, whose communication may be given preferential treatment or prioritized access over other types of information, e.g., in terms of prioritized access for transport of critical service data, and/or relevant QoS for transport of critical service data.

Wireless communication between a RAN 104 and a UE 106a may be described as utilizing an air interface. Transmissions over the air interface from a base station (e.g., base station 108) to one or more UEs (e.g., UE 106a) may be referred to as downlink (DL) transmission. In accordance with certain aspects of the present disclosure, the term downlink may refer to a point-to-multipoint transmission originating at a scheduling entity (described further below; e.g., base station 108) . Another way to describe this scheme may be to use the term broadcast channel multiplexing. Transmissions from a UE (e.g., UE 106a) to a base station (e.g., base station 108) may be referred to as uplink (UL) transmissions. In accordance with further aspects of the present disclosure, the term uplink may refer to a point-to-point transmission originating at a scheduled entity (described further below; e.g., UE 106a) .

In some examples, access to the air interface may be scheduled, wherein a scheduling entity (e.g., a base station 108) allocates resources for communication among some or all devices and equipment within its service area or cell. Within the present disclosure, as discussed further below, the scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more scheduled entities. That is, for scheduled communication, UEs 106a, which may be scheduled entities, may utilize resources allocated by the scheduling entity 108.

Base stations 108 are not the only entities that may function as scheduling entities. That is, in some examples, a UE may function as a scheduling entity, scheduling resources for one or more scheduled entities (e.g., one or more other UEs) .

As illustrated in FIG. 1, a scheduling entity 108 may broadcast downlink traffic 112 to one or more scheduled entities 106a. Broadly, the scheduling entity 108 is a node or device responsible for scheduling traffic in a wireless communication network, including the downlink traffic 112 and, in some examples, uplink traffic 116 from one or more scheduled entities 106a to the scheduling entity 108. On the other hand, the scheduled entity 106a is a node or device that receives downlink control information 114, including but not limited to scheduling information (e.g., a grant) , synchronization or timing information, or other control information from another entity in the wireless communication network such as the scheduling entity 108.

In general, base stations 108 may include a backhaul interface for communication with a backhaul portion 120 of the wireless communication system. The backhaul 120 may provide a link between a base station 108 and the core network 102. Further, in some examples, a backhaul network may provide interconnection between the respective base stations 108. Various types of backhaul interfaces may be employed, such as a direct physical connection, a virtual network, or the like using any suitable transport network.

The core network 102 may be a part of the wireless communication system 100, and may be independent of the radio access technology used in the RAN 104. In some examples, the core network 102 may be configured according to 5G standards (e.g., 5GC) . In other examples, the core network 102 may be configured according to a 4G evolved packet core (EPC) , or any other suitable standard or configuration.

In some examples, scheduled entities such as a first scheduled entity 106a and a second scheduled entity 106b may utilize sidelink signals for direct D2D communication. Sidelink signals may include sidelink traffic 124 and sidelink control 122. Sidelink control information 122 may in some examples include a request signal, such as a request-to-send (RTS) , a source transmit signal (STS) , and/or a direction selection signal (DSS) . The request signal may provide for a scheduled entity 106a to request a duration of time to keep a sidelink channel available for a sidelink signal. Sidelink control information 122 may further include a response signal, such as a clear-to-send (CTS) and/or a destination receive signal (DRS) . The response signal may provide for the scheduled entity 106b to indicate the availability of the sidelink channel, e.g., for a requested duration of time. An exchange of request and response signals (e.g., handshake) may enable different scheduled entities 106b performing sidelink communications to negotiate the availability of the sidelink channel prior to communication of the sidelink traffic information 124.

FIG. 2 provides a schematic illustration of a RAN 200, by way of example and without limitation. In some examples, the RAN 200 may be the same as the RAN 104 described above and illustrated in FIG. 1. The geographic area covered by the RAN 200 may be divided into cellular regions (cells) that a user equipment (UE) can uniquely identify based on an identification broadcasted from one access point or base station. FIG. 2 illustrates

macrocells

202, 204, and 206, and a small cell 208, each of which may include one or more sectors (not shown) . A sector is a sub-area of a cell. All sectors within one cell are served by the same base station. A radio link within a sector can be identified by a single logical identification belonging to that sector. In a cell that is divided into sectors, the multiple sectors within a cell can be formed by groups of antennas with each antenna responsible for communication with UEs in a portion of the cell.

FIG. 2 shows two base stations 210 and 212 in

cells

202 and 204; and shows a third base station 214 controlling a remote radio head (RRH) 216 in cell 206. That is, a base station can have an integrated antenna or can be connected to an antenna or RRH by feeder cables. In the illustrated example, the

cells

202, 204, and 206 may be referred to as macrocells, as the

base stations

210, 212, and 214 support cells having a large size. Further, a base station 218 is shown in the small cell 208 (e.g., a microcell, picocell, femtocell, home base station, home Node B, home eNode B, etc. ) which may overlap with one or more macrocells. In this example, the cell 208 may be referred to as a small cell, as the base station 218 supports a cell having a relatively small size. Cell sizing can be done according to system design as well as component constraints.

The RAN 200 may include any number of wireless base stations and cells. Further, a RAN may include a relay node to extend the size or coverage area of a given cell. The

base stations

210, 212, 214, 218 provide wireless access points to a core network for any number of mobile apparatuses. In some examples, the

base stations

210, 212, 214, and/or 218 may be the same as the base station/scheduling entity 108 described above and illustrated in FIG. 1.

In FIG. 2, a reconfigurable intelligent surface (RIS) 252 may be deployed to extend the size or coverage area of a given cell. The RIS 252 may be within the cell 204 of the base station 212. The base station 212 may transmit signals to the RIS 252 through a forward link 251. Then, the RIS 252 may redirect the signals to a UE 254 or another RIS 256 through an access link 261 or 253. While the RIS 252 may access the UE 254 and another RIS 256, the UE 254 and another RIS 256 may not be within the cell 204 of the base station 212. The access link 253 between the base station 212 and the RIS 252 may be a forward link 253 between another RIS 256 and a different UE 258. Another RIS 256 may receive the signals from the RIS 252 through the forward link 253 and redirect the signals to a different UE 258 through the access link 257. Similarly, although another RIS 256 may access the UE 258, the base station 212 or the RIS 252 may not access the UE 258 because the UE 258 may not be within the coverage area that the base station 212 or the RIS 252 can serve. In some examples, the base station 212 may communicate with the UE 254 through more than one RIS, such as through RIS 252 and RIS 255. The base station 212 may transmit signals to

RISs

252 and 255 through

forward links

259 and 251, respectively. The

RISs

252 and 255 may redirect the signals to the UE 254 through access links 261 and 260. For example, based on measurements from the UE 254 of signals through each

RIS

252, 255, the base station 212 may determine and evaluate all possible channels, or a subset of all possible channels, through the

RISs

252, 255. In response to the evaluation, which involves linear resource overhead, the base station 212 may select one or both of the

RISs

252, 255 to communicate with the UE 254.

FIG. 2 further includes a quadcopter or drone 220, which may be configured to function as a base station. That is, in some examples, a cell may not necessarily be stationary, and the geographic area of the cell may move according to the location of a mobile base station such as the quadcopter 220.

Within the RAN 200, the cells may include UEs that may be in communication with one or more sectors of each cell. Further, each

base station

210, 212, 214, 218, and 220 may be configured to provide an access point to a core network 102 (see FIG. 1) for all the UEs in the respective cells. For example,

UEs

222 and 224 may be in communication with base station 210;

UEs

226 and 228 may be in communication with base station 212;

UEs

230 and 232 may be in communication with base station 214 by way of RRH 216; UE 234 may be in communication with base station 218; and UE 236 may be in communication with mobile base station 220. In some examples, the

UEs

222, 224, 226, 228, 230, 232, 234, 236, 238, 240, and/or 242 may be the same as the UE/scheduled entity 106 described above and illustrated in FIG. 1.

In some examples, a mobile network node (e.g., quadcopter 220) may be configured to function as a UE. For example, the quadcopter 220 may operate within cell 202 by communicating with base station 210.

In a further aspect of the RAN 200, sidelink signals may be used between UEs without necessarily relying on scheduling or control information from a base station. For example, two or more UEs (e.g., UEs 226 and 228) may communicate with each other using peer to peer (P2P) or sidelink signals 227 without relaying that communication through a base station (e.g., base station 212) . In a further example, UE 238 is illustrated communicating with

UEs

240 and 242. Here, the UE 238 may function as a scheduling entity or a primary sidelink device, and

UEs

240 and 242 may function as a scheduled entity or a non-primary (e.g., secondary) sidelink device. In still another example, a UE may function as a scheduling entity in a device-to-device (D2D) , peer-to-peer (P2P) , or vehicle-to-vehicle (V2V) network, and/or in a mesh network. In a mesh network example,

UEs

240 and 242 may optionally communicate directly with one another in addition to communicating with the scheduling entity 238. Thus, in a wireless communication system with scheduled access to time–frequency resources and having a cellular configuration, a P2P configuration, or a mesh configuration, a scheduling entity and one or more scheduled entities may communicate utilizing the scheduled resources.

In some aspects of the disclosure, the scheduling entity and/or scheduled entity may be configured with multiple antennas for beamforming and/or multiple-input multiple-output (MIMO) technology. FIG. 3 illustrates an example of a wireless communication system 300 with multiple antennas, supporting beamforming and/or MIMO. The use of such multiple antenna technology enables the wireless communication system to exploit the spatial domain to support spatial multiplexing, beamforming, and transmit diversity.

Beamforming generally refers to directional signal transmission or reception. For a beamformed transmission, a transmitting device may precode, or control the amplitude and phase of each antenna in an array of antennas to create a desired (e.g., directional) pattern of constructive and destructive interference in the wavefront. In a MIMO system, a transmitter 302 includes multiple transmit antennas 304 (e.g., N transmit antennas) and a receiver 306 includes multiple receive antennas 308 (e.g., M receive antennas) . Thus, there are N × M signal paths 310 from the transmit antennas 304 to the receive antennas 308. Each of the transmitter 302 and the receiver 306 may be implemented, for example, within a scheduling entity 108, a scheduled entity 106, or any other suitable wireless communication device.

In a MIMO system, spatial multiplexing may be used to transmit multiple different streams of data, also referred to as layers, simultaneously on the same time-frequency resource. In some examples, a transmitter 302 may send multiple data streams to a single receiver. In this way, a MIMO system takes advantage of capacity gains and/or increased data rates associated with using multiple antennas in rich scattering environments where channel variations can be tracked. Here, the receiver 306 may track these channel variations and provide corresponding feedback to the transmitter 302. In the simplest case, as shown in FIG. 3, a rank-2 (i.e., including 2 data streams) spatial multiplexing transmission on a 2x2 MIMO antenna configuration will transmit two data streams via two transmit antennas 304. The signal from each transmit antenna 304 reaches each receive antenna 308 along a different signal path 310. The receiver 306 may then reconstruct the data streams using the received signals from each receive antenna 308.

In some examples, a transmitter may send multiple data streams to multiple receivers. This is generally referred to as multi-user MIMO (MU-MIMO) . In this way, a MU-MIMO system exploits multipath signal propagation to increase the overall network capacity by increasing throughput and spectral efficiency, and reducing the required transmission energy. This is achieved by a transmitter 302 spatially precoding (i.e., multiplying the data streams with different weighting and phase shifting) each data stream (in some examples, based on known channel state information) and then transmitting each spatially precoded stream through multiple transmit antennas to the receiving devices using the same allocated time-frequency resources. A receiver (e.g., receiver 306) may transmit feedback including a quantized version of the channel so that the transmitter 302 can schedule the receivers with good channel separation. The spatially precoded data streams arrive at the receivers with different spatial signatures, which enables the receiver (s) (in some examples, in combination with known channel state information) to separate these streams from one another and recover the data streams destined for that receiver. In the other direction, multiple transmitters can each transmit a spatially precoded data stream to a single receiver, which enables the receiver to identify the source of each spatially precoded data stream.

The number of data streams or layers in a MIMO or MU-MIMO (generally referred to as MIMO) system corresponds to the rank of the transmission. In general, the rank of a MIMO system is limited by the number of transmit or receive

antennas

304 or 308, whichever is lower. In addition, the channel conditions at the receiver 306, as well as other considerations, such as the available resources at the transmitter 302, may also affect the transmission rank. For example, a base station in a RAN (e.g., transmitter 302) may assign a rank (and therefore, a number of data streams) for a DL transmission to a particular UE (e.g., receiver 306) based on a rank indicator (RI) the UE transmits to the base station. The UE may determine this RI based on the antenna configuration (e.g., the number of transmit and receive antennas) and a measured signal-to-interference-and-noise ratio (SINR) on each of the receive antennas. The RI may indicate, for example, the number of layers that the UE may support under the current channel conditions. The base station may use the RI along with resource information (e.g., the available resources and amount of data to be scheduled for the UE) to assign a DL transmission rank to the UE.

The transmitter 302 determines the precoding of the transmitted data stream or streams based, e.g., on known channel state information of the channel on which the transmitter 302 transmits the data stream (s) . For example, the transmitter 302 may transmit one or more suitable reference signals (e.g., a channel state information reference signal, or CSI-RS) that the receiver 306 may measure. The receiver 306 may then report measured channel quality information (CQI) back to the transmitter 302. This CQI generally reports the current communication channel quality, and in some examples, a requested transport block size (TBS) for future transmissions to the receiver. In some examples, the receiver 306 may further report a precoding matrix indicator (PMI) to the transmitter 302. This PMI generally reports the receiver’s 306 preferred precoding matrix for the transmitter 302 to use, and may be indexed to a predefined codebook. The transmitter 302 may then utilize this CQI/PMI to determine a suitable precoding matrix for transmissions to the receiver 306.

In Time Division Duplex (TDD) systems, the UL and DL may be reciprocal, in that each uses different time slots of the same frequency bandwidth. Therefore, in TDD systems, a transmitter 302 may assign a rank for DL MIMO transmissions based on an UL SINR measurement (e.g., based on a sounding reference signal (SRS) or other pilot signal transmitted from the receiver 306) . Based on the assigned rank, the transmitter 302 may then transmit a channel state information reference signal (CSI-RS) with separate sequences for each layer to provide for multi-layer channel estimation. From the CSI-RS, the receiver 306 may measure the channel quality across layers and resource blocks. The receiver 306 may then transmit a CSI report (including, e.g., CQI, RI, and PMI) to the transmitter 302 for use in updating the rank and assigning resources for future DL transmissions.

Controllable Reflective Surface (Reconfigurable Intelligent Surface)

In 5G NR, massive multiple-input multiple-output (MIMO) can play a role in increasing throughput. In some examples, active antenna units (AAUs) may achieve the benefits of massive MIMO with high beamforming gain. In the AAUs, each antenna port may have an individual radio frequency transceiver chain. However, due to their active electronic components, the AAUs may result in a significant increase in power consumption.

Therefore, in some other examples, to reduce power consumption and extend communication coverage at the same time, a controllable reflective surface 402 may be used. In some examples, the controllable reflective surface 402 may include a reconfigurable intelligent surface (RIS) 402, such as shown in FIG. 4, may be used. An RIS may also be referred to as an RIS panel, an intelligent reflecting surface (IRS) , a large intelligent surface (LIS) , or a software-controlled metasurface. The RIS panel 402, may be, for example, a surface of electromagnetic (EM) material, which can be reconfigurable or electronically controllable with integrated electronics. The RIS panel 402 may include a two-dimensional array of discrete antenna elements 403. An RIS controller 404 coupled to the RIS panel 402 may control the antenna elements 403 individually or on a group level to redirect an impinging signal 414 on the antenna elements 403 of the surface 402 to a given direction 408. In addition, the RIS controller 404 may control the RIS panel 402 to differently modify the properties of signals on different frequency ranges.

The RIS panel 402 may modify the properties of the signal 414 and redirect the signal 416 to a scheduled entity 408. In some examples, software may control and modify the properties, including absorption, reflection, refraction, and/or diffraction, of the surface of the RIS panel 402. Thus, the RIS panel 402 can change, e.g., the phase, amplitude, frequency, and polarization of the impinging signals 414 and redirect the impinging signals 414 to particular directions (e.g., towards the scheduled entity 408) . In some examples, a scheduling entity 401 may communicate with the RIS controller 404 to control the reflection direction and/or other properties of the RIS panel 402, and thus the properties of the impinging signals 414 reaching the surface of the RIS panel 402 through the RIS controller 404 coupled to the RIS panel 402. Further, since software in the RIS controller 404 may program and control the RIS panel 402, the RIS panel 402 can be adaptive, e.g., configurable and reconfigurable, after its deployment.

In addition, the RIS panel 402 may be a nearly passive device because the surface of the RIS panel 402 might not require any transmit radio-frequency (RF) chains to redirect impinging signals. Due to its relatively low power consumption and its software-defined surface, the RIS 402 might not require complex signal processing. However, it should be appreciated that the RIS panel 402 is not limited to a nearly passive device. In some examples, the RIS panel 402 may change the amplitude of an impinging signal and/or generate new radio waves based on the impinging signal.

Additionally, in some examples, the RIS 402 may operate in full-duplex mode. In some examples, the RIS 402 may support simultaneous two-way communications with frequency division duplex (FDD) and/or time division duplex (TDD) . In other examples, the RIS 402 may also operate in half-duplex FDD and/or half-duplex TDD.

FIG. 4 illustrates an example of the ability of an RIS 402 to expand communication coverage and create additional propagation paths. The scheduling entity 401 may support a coverage area 424 in which one or more scheduled entities (e.g., a scheduled entity 406) can communicate with the scheduling entity 401 based on a signal transmitted from the scheduling entity 401. The scheduling entity 401 may be a base station, a monitoring UE for sidelink, or any other suitable node that can transmit and receive a signal to other nodes. Here, each of the scheduled

entities

406 and 408 may be a user equipment (UE) , another RIS, or any other suitable node to communicate with the scheduling entity 401. In FIG. 4, the scheduled entity 406 is within the cell 424 and without any blockage 430 between the base station 401 and the scheduled entity 406. Accordingly, the scheduled entity 406 may directly communicate with the base station 401. However, some scheduled entities may not be capable of directly accessing the base station 401 because of a blockage that exists between the scheduled entities and the base station 401, or because the scheduled entities are not within the cell coverage area. For example, in the scenario illustrated in FIG. 4, the scheduled entity 408 may not be capable of directly accessing the base station 401 because a blockage 430 exists between the scheduled entity 408 and the base station 401, and because the scheduled entity 408 is not within the cell coverage area 424. Although the scheduled entity 408 is illustrated as both blocked by blockage 430 and outside of the cell coverage area 424, either cause may prevent the direct access of the base station 401 by the scheduled entity 408. For example, the scheduled entity 408 may be in the cell coverage area 424, but still may not be capable of directly accessing the base station 401 because the blockage 430 exists between the scheduled entity 408 and the base station 40. Alternatively, the blockage 430 may not be between the scheduled entity 408 and the base station 401, but the scheduled entity 408 still may not be capable of directly accessing the base station 401 because the scheduled entity 408 is outside the cell coverage area 424.

An RIS 402 as a relaying technology may extend the size and/or coverage area of the cell 424. The RIS 402 may be within the cell 424 of the base station 401, and may redirect signals from the base station 401 to nodes that are not within the coverage area of the cell 424 or are not able to access the base station 401 for any suitable reasons. In some examples, the base station 401 may not directly communicate with the scheduled entity 408 due to the blockage 430, the scheduled entity 408 being in an out-of-coverage location from the base station 401, or another reason preventing direct communication with the base station 401. However, the base station 401 may communicate with the scheduled entity 408 through the RIS 402. For example, the base station 401 may transmit a signal to the RIS panel 402. The RIS panel 402 may receive the signal from the base station 401 and redirect the signal to the scheduled entity 408 such that the RIS panel 402 shifts the phase and/or the properties of the signal and redirects the signal to the scheduled entity 408. In addition, the RIS panel 402 may transmit the signal 414 to other nodes at the same time. The base station 401 may also communicate with the RIS controller 404 to configure one or more of the antenna elements 403 of the RIS panel 402 to redirect a signal 414 from the base station 401 to the scheduled entity 408. It should be appreciated that the RIS 402 is not limited to use the communication between a base station 401 and a scheduled entity 408. In some examples, the RIS 402 may be in use for sidelink communication between a monitoring UE and a monitored UE. In addition, the communication through the RIS panel 402 may be bidirectional. The scheduled entity 408 may also transmit a signal to the base station 401 through the RIS panel 402. For example, the RIS panel 402 may receive the signal from the scheduled entity 408 and redirect the signal to the base station 401 such that the RIS panel 402 shifts the phase and/or the properties of the signal and redirects the signal to the base station 401.

An RIS controller 404 may control the RIS panel 402 for the redirection of a signal to a given direction. In some examples, the RIS controller 404 may be coupled to the RIS 402. The coupling may be physical such that the RIS controller 404 may be physically connected to the RIS 402. That is, a wire or cable may connect the RIS controller 404 to the RIS 402. In other examples, the RIS controller 404 may be attached to the RIS 402 as part of the RIS 402. However, it should be appreciated that the coupling between the RIS controller 404 and the RIS 402 may not be limited to material connections. For example, the connection may be a wireless-based connection via a radio frequency signal using the current state of the art.

In some examples, the RIS controller 404 may receive, from the scheduling entity 401, RIS control information to control or configure the RIS panel 402. Based on the RIS control information, the RIS controller 404 may configure the RIS panel 402 to change or modify impinging signals on the RIS panel 402 to be redirected to given directions or scheduled entities 408.

To facilitate operation of such an RIS and enable redirection of impinging signals as described above, the RIS may in some examples employ beamforming. As described above in relation to FIG. 3, beamforming may utilize precoding of communications via an antenna array, with the precoding being based on a timely estimate of the communication medium or channel. FIG. 5 illustrates a channel estimation example between a scheduling entity 502 (e.g., a base station 401 in FIG. 4) and a scheduled entity 504 (e.g., a UE 408 in FIG. 4) through an RIS 506. The channel estimation or channel state information (CSI) between the scheduling entity 502 and the RIS 506 and between the RIS 506 and the scheduled entity 504, as described herein, might improve communication performance in terms of bit error rate and beamforming. In some examples, the scheduling entity 504 may transmit controlling information to a RIS controller 508 to control the RIS 506 to direct beams impinging on the RIS 506 to the scheduled entity 504. The scheduling entity 502 may exploit channel properties to reduce overhead with higher estimating accuracy. In channel estimation of channels via the RIS 506, the signal overhead reduction may be possible through cascaded channel estimation. The scheduling entity 502 may sequentially estimate channel H ₁ between the base station 502 and the RIS 506 and channel H ₂ between the RIS 506 and the scheduled entity 504 in a cascaded manner. In cascaded channel estimation, the base station 502 may estimate channel H ₁ and channel H ₂ together. Channel H ₁ may be expressed as

Channel H ₂ may be expressed as

K1 and K2 may be the Rician factors of the channel.

and

may be the LOS channel or the Rician component of the channel.

and

are the multipath components. In some examples, channel estimation for channel H ₁ and channel H ₂ may be separable with its scaling or quantity. Further, channel H ₁ may be common to all scheduled entities 504. Thus, the overhead may be largely reduced by using such channel correlations among scheduled entities 504. Channel H ₁ may be quasi-static in a case where there is no major mobility of the scheduling entity 502 and the RIS 506. Thus, the line-of-sight (LOS) between the base station 502 and the RIS 506 is a considering factor to deploy the RIS 506. Here, the optimal RIS codebook may be expressed as: Φ ^HΦ=αI with a maximum value of α. The RIS codebook may have orthogonal columns, and α may be the norm of each column Thus, minimum variance estimation is possible for a single scheduled entity 504.

FIG. 6 is a conceptual illustration of an example of RIS subset selection configuration according to some aspects of this disclosure. As described above, the RIS technology has advantages in improving wireless channel capacity and quality due to its reconfigurable surface to redirect a signal to a given direction. Thus, the RIS deployment may improve communication networks in urban areas by removing blind spots and enhance the interconnection in various networks. As the number of RISs increases in an area, a UE 604 may have more than one communication channel with a base station 602. For example, in a case where the base station 602 may transmit a signal to the UE 604 through more than one

RIS

612, 614, 616, the UE 604 may have

communication channels

622, 624, 626, 628 with the base station 602. Each communication channel may have different channel quality and properties. Thus, the base station 602 may select one or more channels having given performance characteristics to enhance communication with the UE 604. In some examples, the base station 602 may select one or more channels having the highest receiver metric, e.g., spectral efficiency, signal to interference ratio (SINR) , reference signal received power (RSRP) , and/or channel quality information (CQI) . However, it should be appreciated that the performance characteristic is not limited to the listed examples. It may be any other suitable channel properties to enhance communication with the UE 604.

To select the one or more channels having given performance characteristics, the base station 602 may first transmit reference signals to the UE 604 with and/or without the more than one

RIS

612, 614, 616. In some examples, the base station 602 may transmit one constant and unidirectional beam including the reference signals. The reference signals may be time-division multiplexed signals having quasi co-located (QCL) relationship with the same spatial beam e.g., single synchronization signal block (SSB) and/or tracking reference signal (TRS) . However, the reference signals may be other types of reference signals, e.g., channel status information reference signal (CSI-RS) , physical downlink control channel (PDCCH) demodulation reference signal (DM-RS) , and/or physical downlink shared channel (PDSCH) DM-RS.

The UE 604 may receive the reference signals. Then, the UE 604 may perform sampling of the reference signals and store the reference signal samples for future use. The UE may measure the reference signals received through the more than one

RIS

612, 614, 616 and/or without any RIS and report channel information corresponding to a set of the channels of the reference signals. In some examples, the channel information may include a set of one or more channel indexes corresponding to the set of the channels. The set of one or more channels indexes may include an ordered sequence that ranks the set of channels according to one or more performance characteristics based on measurements of the channels. The measurements may include, but are not limited to, spectral efficiency, channel state information (CSI) , signal to interference ratio (SINR) , reference signal received power (RSRP) , and/or channel quality information (CQI) . In some examples, the channel information may indicate one or more of these measurements or performance characteristics of the channels. Based on the channel information reported by the UE 604, the base station 602 may determine one or more suitable channels among them for use in communicating with the UE 604.

As RISs linearly increase, the number of reference signals to evaluate and select channels or antenna ports may exponentially increase because the number of channels between the base station 602 and the UE 604 may exponentially increase. For example, if three (3) RISs (RIS 1, RIS 2, RIS 3) exist for communication between the base station 602 and the UE 604, the base station 602 might transmit eight (8) time-division multiplexed reference signals (2 ³) because eight (8) possible channels or antenna ports exist when each RIS is on or off. The possible channels are shown below in Table 1:

Similarly, if four (4) RISs exist between the base station 602 and the UE 604, the base station 602 might transmit sixteen (16) time-division multiplexed reference signals (2 ⁴) . If N RISs exist between the base station 602 and the UE 604, the base station 602 might transmit 2 ^N time-division multiplexed reference signals to determine one or more suitable channels among 2 ^N channels.

In some examples, the base station 602 may reduce the reference signal overhead using a codebook by replacing one or more natural channels (e.g., Channels 5–8 above) corresponding to reference signals with one or more second or virtual channels without corresponding reference signals. A natural channel may include one or more channels on which one or more corresponding reference signals are transmitted. The natural channel may include a direct channel between the base station 602 and the UE 604 without an

RIS

612, 614, 616 and/or one or more channels that are reflected on one or more RISs 612, 614, 616.

In some examples, the base station 602 may configure and transmit a codebook for configuring one or more second channels. The base station 602 may also schedule and transmit a reference signal via a direct channel 622 and at least two other reference signals via at least two corresponding

first channels

622, 624, 626, 628. The direct channel may include a channel between the base station 602 and the UE 604, which are not reflected on any

RIS

612, 614, 616. A first channel of the at least two

first channels

622, 624, 626, 628 may be a channel that includes a direct channel component and a reflected channel component, i.e., a path on which a reference signal transits (e.g., is reflected by) one

RIS

612, 614, 616 between the base station 602 and the UE 604. In some examples, the base station 602 may control RISs to turn off all RISs at a time and transmit a reference signal via the direct channel 622. Also, the base station 602 may control RISs to turn on each RIS at a respective time and turn off other RISs at the respective time. Thus, the base station 602 may transmit a reference signal via the direct channel component 622 and transmit the same reference signal via a reflected channel component that are reflected on the one RIS at a time to the UE 604. To transmit the reference signal via the direct channel 622 along with the same reference signal through each RIS at a time, the base station 602 may also transmit RIS control information to indicate when and which RIS is on and off. The reference signal may be a time-division multiplexed resource having quasi co-location (QCL) relationship with another reference signal on the same or a different channel. For example, a time-division multiplexed reference signal may include a CSI-RS resource which may have QCL relationship with SSB or another CSI-RS on the same channel or a different channel. Each CSI-RS resource may be a single antenna port corresponding to a channel. In some examples, the CSI-RS resource may belong to the same set of CSI-RS resources.

For example, if three (3) RISs are able to redirect signals from/to the base station 602 to/from the UE 604, the base station 602 may transmit to the UE 604 four (4) time-division multiplexed reference signals associated with the same spatial beam (e.g., single SSB, TRS, CSI-RS, PDSCH DMRS, and/or PDCCH DMRS) . The base station 602 may transmit reference signal 1 (622) directly to the UE 604 via direct channel h ₁ 622 without transiting any

RIS

612, 614, 616. The base station 602 may transmit reference signal 2 (622, 624) via first channel h ₁ 622, h ₂ 624 including direct channel component h ₁ 622 and directly to the UE 604 and reflected channel component h ₂ 624 that transits RIS 1 (612) and does not transit RIS 2 (614) or RIS 3 (616) . Thus, the base station 602 may transmit to the UE 604 reference signal 2 (622, 624) via first channel h ₁ + h ₂ (622+624) . The base station 602 may transmit reference signal 3 (622, 626) to the UE 604 via first channel having direct channel component h ₁ 622 and reflected channel component h ₃ 626 that transits RIS 2 (614) and does not transit RIS 1 (612) or RIS 3 (616) . Thus, the base station 602 may transmit to the UE 604 reference signal 3 (622, 626) via first channel h ₁ + h ₃ (622+626) . The base station 602 may transmit reference signal 4 (622, 628) to the UE 604 via first channel including direct channel component h ₁ 622 and reflected channel component h ₄ 628 that transits RIS 3 (616) and does not transit RIS 1 (612) or RIS 2 (614) . Thus, the base station 602 may transmit to the UE 604 reference signal 4 (622, 628) via first channel h ₁ + h ₄ (622+628) . In a similar way, if N RISs are able to redirect signals from/to the base station 602 to/from the UE 604, the base station 602 may transmit to the UE 604 N+1 time-division multiplexed reference signals. The base station 602 may transmit directly to the UE 604 via a direct channel one (1) reference signal that does not transit any RIS. In addition, the base station 602 may transmit N other reference signals, each at a respective time, via corresponding N first channels, that are reflected on corresponding RISs.

The UE 604 may receive reference signals via natural channels. For example, a natural channel may include a direct channel 622 that does not transit any

RIS

612, 614, 616. Another natural channel also may include a first channel having a direct channel component associated with the direct channel and a reflected channel component which is reflected on one

RIS

612, 614, or 616. One reference signal via the direct channel 622 may not transit any RIS. For other reference signals, the UE 604 may receive one reference signal via a first channel including direct channel component 622 and reflected

channel component

624, 626, 628 that is reflected on one RIS at a given time. The UE 604 may sample the reference signals and store the reference signal samples at memory. The UE 604, then, may determine channel information of the channels by measuring the reference signals on the channels. In some examples, the UE 604 may determine channel information of the direct channel 622 that does not transit any RIS by measuring the reference signal on the direct channel 622. In addition, the UE 604 may determine channel information of a combined or first channel of the direct channel component and a reflected channel component that transits a respective RIS at a time by measuring the reference signal on the combined channel. In some examples, the UE 604 may determine channel characteristics of a first channel that transits a respective RIS without the direct channel by subtracting the direct channel measurement from the combined channel measurement of the direct and first channels. In some examples, the channel information may include channel state information (CSI) , spectral efficiency, signal to interference ratio (SINR) , reference signal received power (RSRP) , and/or channel quality information (CQI) . It should be appreciated that the measurements are not limited to the listed examples. It could be any other suitable measurement for the base station 602 to determine one or more channels based on the measurements to improve communication quality and/or performance between the base station 602 and the UE 604.

For example, the UE 604 may determine channel information of direct channel h ₁ 622 by measuring reference signal 1. In addition, the UE 604 may determine channel information of channel h ₁ + h ₂ (622, 624) by measuring received reference signal 2 (622, 624) that transits RIS 1 (612) and does not transit RIS 2 (614) or RIS 3 (616) . The UE 604 may determine channel information of channel h ₁ + h ₃ (622, 626) by measuring received reference signal 3 (622, 626) that transits RIS 2 (614) and does not transit RIS 1 (612) or RIS 3 (616) . The UE 604 may determine channel information of channel h ₁ + h ₄ (622, 628) by measuring received reference signal 4 (622, 628) that transits RIS 3 (618) and does not transit RIS 1 (612) or RIS 2 (614) . Thus, the UE 604 may determine channel information of four (4) channels (e.g., h ₁ (622) , h ₁ + h ₂ (622, 624) , h ₁ + h ₃ (622, 626) , h ₁ +h ₄ (622, 628) ) . The base station 602 may not transmit other reference signals for the remaining channels or second channels (e.g., h ₁ + h ₂ + h ₃ (622, 624, 626) , h ₁ + h ₃ + h ₄ (622, 626, 628) , h ₁ + h ₂ + h ₄ (622, 624, 628) , h ₁ + h ₂ + h ₃ + h ₄ (622, 624, 626, 628) ) to determine channel information of the remaining channels. Thus, the base station 602 may reduce the overhead that would otherwise result from transmitting the other reference signals for the remaining or second channels.

Nonetheless, in some examples, the UE 604 may determine channel characteristics of the remaining or second channels (e.g., h ₁ + h ₂ + h ₃ (622, 624, 626) , h ₁ + h ₃ + h ₄ (622, 626, 628) , h ₁ + h ₂ + h ₄ (622, 624, 628) , h ₁ + h ₂ + h ₃ + h ₄ (622, 624, 626, 628) ) based on the codebook and the measured channels (e.g., h ₁ (622) , h ₁ + h ₂ (622, 624) , h ₁ + h ₃ (622, 626) , h ₁ + h ₄ (622, 628) ) . Here, a measured channel may include channel information of the channel by measuring a reference signal on the channel. Thus, the UE 604 may determine a second channel without transmitting a reference signal via the second channel. To determine the second channel, the base station 602 may first configure a codebook. The codebook may include one or more precoders corresponding to the one or more second channels applied on at least three channel elements corresponding to the direct channel and the at least two first channels. The codebook may be referred to as a codeword, vector, or a column matrix. The channel element may include channel characteristics or channel information of a natural channel (direct channel or first channel) . In some examples, the codebook may be a column matrix to derive a second channel from the measured channels. In other examples, the codebook may be one multiple-column matrix. The number of columns of the codebook may correspond to the number of second channels. The number of rows of the codebook may correspond to the number of measured channels (e.g., the direct channel and the at least two first channels) . The base station 602 may configure the codebook for the UE 604 to determine a second channel with linear combination of the codebook and the measured channels. The base station 602 may transmit the one-column codebooks corresponding to second channels or the one multiple-column codebook to the UE 604 in a separate message. For example, the base station 602 may transmit the codebook via an RRC message, a media access control (MAC) control element (CE) message, a downlink control information (DCI) message, a combination of the messages, or any other suitable message to transmit the codebook to the UE 604. The base station 602 may transmit the codebook before or after transmitting the reference signals to the UE 604.

In the aforementioned example, the base station 602 may determine four (4) codebooks for the UE 604 to determine four (4) second channels (e.g., h ₁ + h ₂ + h ₃ (622, 624, 626) , h ₁ + h ₃ + h ₄ (622, 626, 628) , h ₁ + h ₂ + h ₄ (622, 624, 628) , h ₁ + h ₂ + h ₃ + h ₄ (622, 624, 626, 628) ) based on the codebooks and the four (4) measured channels (h ₁ (622) , h ₁ + h ₂ (622, 624) , h ₁ + h ₃ (622, 626) , h ₁ + h ₄ (622, 628) ) . Second channel h ₁ + h ₂ + h ₃ (622, 624, 626) may be via RIS 1 and RIS 2. Second channel h ₁ + h ₃ + h ₄ (622, 626, 628) may be via RIS 2 and RIS 3. Second channel h ₁ + h ₂ + h ₄ (622, 624, 628) may be via RIS 1 and RIS 3. Second channel h ₁ + h ₂ + h ₃ + h ₄ (622, 624, 626, 628) may be via RISs 1–3. The base station 602 may not necessarily transmit reference signals for the four (4) second channels. Specifically, the base station may determine codebook 1

for the UE 604 to determine second channel 1 (h ₁ + h ₂ + h ₃ (622, 624, 626) ) by the linear combination of the four (4) measured channels and codebook 1:

The linear combination of the four (4) measured channels and codebook 2

may determine second channel 2 (h ₁ + h ₃ + h ₄ (622, 626, 628) ) :

The linear combination of the four (4) measured channels and codebook 3

may determine second channel 3 (h ₁ + h ₂ + h ₄ (622, 624, 628) ) :

The linear combination of the four (4) measured channels and codebook 4

may determine second channel 4 (h ₁ +h ₂ + h ₃ + h ₄ (622, 624, 626, 628) ) :

In other examples, the codebook may be one multiple-column matrix. For example, the base station 602 may configure one multiple-column codebook

with the four (4) codebooks described above (codebook 1–4) . The base station 602 may configure the codebook

for the UE 602 to determine the four (4) second channels (e.g., h ₁ + h ₂ + h ₃ (622, 624, 626) , h ₁ + h ₃ + h ₄ (622, 626, 628) , h ₁ + h ₂ + h ₄ (622, 624, 628) , h ₁ + h ₂ + h ₃ + h ₄ (622, 624, 626, 628) ) as follows:

Similarly, if N RISs exist, the base station 602 may transmits N + 1 reference signals to the UE 604. One reference signal may go directly to the UE 604 without transiting any RIS. Each of N reference signals may transit one RIS and at the same time go directly to the UE 604 via the direct channel. In some examples, the base station 602 may determine the codebook for the UE 604 to determine other channels or second channels (2 ^N-N-1) . The codebook may include 2 ^N-N-1 matrices with N + 1 rows or one matrix having 2 ^N-N-1 columns and N + 1 rows.

In some example, the base station 602 may further transmit channel restriction information to the UE 604. The channel restriction information may include that one or more of the RISs should be always on or off based on a previous codebook, the UE location, a temporary or permanent blockage on a channel between the base station 602 and the UE 604, and/or any other suitable factor to restrict the channel. For example, three (3) RISs 612, 614, 616 may be able to redirect signals from/to the base station 602 to/from the UE 604. Then, eight (8) possible channels may exist. If the base station 602 may transmit channel restriction information which indicate that RIS 1 (612) should be always on, the base station 602 may not transmit a reference signal on channels that do not transit RIS 1 (612) . Also, the UE 604 may not consider second channels that do not transit RIS 1 (612) . In other example, the base station 602 may configure a codebook considering the channel restriction information. For example, the codebook may not include a column that determines a second channel that does not transit RIS 1 (612) as follows:

Thus, if there is no channel restriction information, four (4) second channels exist. However, if channel restriction information exists, the number of possible second channels may decrease.

The UE 604 may receive the codebook and configure the one or more second channels by the linear combination of the measured channels corresponding to the reference signals and the codebook. Thus, the UE 604 may derive the second channels without additional reference signals based on the measured channels and the codebook. The UE 604 may determine channel information of the direct channel 622 that does not transit any RIS by measuring a reference signal on the direct channel 622. In addition, the UE 604 may determine channel information of a first channel that transits a respective RIS and does not transit any RIS at a time. Based on the measured channels and the codebook, the UE 604 may determine channel information or characteristics of the one or more second channels.

For the aforementioned example, the UE 604 may first measure the spectral efficiency, CSI, SINR, RSRP, and/or CQI of the natural channels with reference signals (M (h ₁ (622) ) , M (h ₁ + h ₂ (622+624) ) , M (h ₁ + h ₃ (622+626) ) , M (h ₁ + h ₄ (622+628) ) ) . Based on the linear combination of the measurements of the natural channels and the codebook, the UE 604 may determine channel characteristics (e.g., the spectral efficiency, CSI, SINR, RSRP, and/or CQI) of the second channels (M (h ₁ + h ₂ + h ₃ (622+624+626) ) , M (h ₁ + h ₃ + h ₄ (622+626+628) ) , M (h ₁ + h ₂ + h ₄ (622+624+628) ) , M (h ₁ + h ₂ + h ₃ + h ₄ (622+624+626+628) ) ) as follows:

The codebook may include one or more one-column matrices rather than a multi-column matrix. The UE may determine each second channel based on a respective one-column matrix of one or more one-column matrices. Thus, the UE 604 may determine channel characteristics of all eight (8) channels (M (h ₁) , M (h ₁ + h ₂) , M (h ₁ + h ₃) , M (h ₁ + h ₄) , M (h ₁ + h ₂ + h ₃) , M (h ₁ + h ₃ + h ₄) , M (h ₁ + h ₂ + h ₄) , M (h ₁ + h ₂ + h ₃ + h ₄) ) .

Based on the channel characteristics of all eight (8) channels, the UE 604 may report channel information. Thus, the UE 604 may report channel information based at least one the one or more second channels that are determined as described above. The channel information may correspond to a set of one or more channels selected from the group of: the natural and second channels. In some examples, the channel information may include a set of one or more channel indexes corresponding to the set of the one or more channels. In some examples, the set of one or more channel indexes may include an ordered sequence that ranks the set of one or more channels according to a given performance characteristic based on measurements of the direct channel and the at least two first channels and the determination of the second channels. The set of one or more channels may include one channel out of the one or more channels, all channels of the one or more channels, or a portion of the one or more channels. For example, the set of all eight (8) channels (M (h ₁) , M (h ₁ + h ₂) , M (h ₁ + h ₃) , M (h ₁ + h ₄) , M (h ₁ + h ₂ + h ₃) , M (h ₁ +h ₃ + h ₄) , M (h ₁ + h ₂ + h ₄) , M (h ₁ + h ₂ + h ₃ + h ₄) ) with three (3) RISs may have a list of at least a portion of the channels that meet a given performance. The list may include an ordered sequence that ranks the at least a portion of the channels based on measurements of the natural channels and the second channel determination. The measurements may include spectral efficiency, channel state information (CSI) , signal to interference ratio (SINR) , reference signal received power (RSRP) , and/or channel quality information (CQI) . However, it should be appreciated that the performance characteristic is not limited to the listed examples. It may be any other suitable channel properties to enhance communication with the UE 604. For example, the UE may determine channel information of the direct channel (h ₁) and the first channels (h ₁ + h ₂, h ₁ + h ₃, h ₁ + h ₄) , and determine channel information of the second channels (h ₁ + h ₂ + h ₃, h ₁ + h ₃ + h ₄, h ₁ + h ₂ +h ₄, h ₁ + h ₂ + h ₃ + h ₄) and may rank the channels as follows in table 2:

In some examples, the base station 602 may provide a criterion indicating that the RSRP of a channel meets a given threshold. In the example above, the threshold RSRP may be the RSRP of channel h ₁ (622) . Then, the US 604 may transmit a list including an ordered sequence (h ₁ + h ₂ + h ₃ (622+624+626) (Rank 1) , h ₁ + h ₂ (622+624) (Rank 2) , h ₁ + h ₂ + h ₄ (622+624+628) (Rank 3) , h ₁ (622) (Rank 4) ) that meets the threshold RSRP (h ₁ (622) ) . It should be appreciated that the given example is a mere example to report channel information to the base station 602. For example, the UE 604 may determine one or more channel groups. Each group may include at least one channel. In each group of the one or more channel groups, the UE 604 may determine channel indexes corresponding to the channels in each group. In some examples, the channel indexes in each group may include an ordered sequence that ranks the channels in each group according to a given performance channel characteristic. In some examples, the reporting may be in the uplink control information (UCI) or an RRC message. In other example, the reporting may be in an MSG3/MSGB in the random access procedure.

The base station 602 may receive the channel information corresponding to a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels. Based on the channel information, the base station 602 may configure which RIS is on. In the aforementioned examples, the base station 602 may receive a list including an ordered sequence based on the RSRPs of channels. In some examples, the base station 602 may select the best channel in terms of the RSRP, which is the second channel herein h ₁ + h ₂ + h ₃ (622+624+626) for communication between the base station 602 and the UE 604. The base station 602, then, may transmit RIS control information to turn on RIS 1 (612) and RIS 2 (614) and turn off RIS 3 (616) . It should be appreciated that the base station 602 may select a portion of the channels for the communication and configure corresponding RISs.

In some examples, the base station 602 may configure and transmit QCL information indicating a QCL relationship between a set of the one or more second channels and a set of the one or more channels. In some examples, the base station 602 may transmit the QCL information in the transmission configuration indicator (TCI) state information via an RRC message, a media access control (MAC) control element (CE) message, a downlink control information (DCI) message, a combination of the messages, or any other suitable message to transmit the QCL information to the UE 604. In some examples, the QCL information identifies a second channel of the one or more second channels as a source for another channel to estimate another channel. In some examples, the base station 602 may configure the QCL information of the second channel as a source based on the natural channels and codebook. For example, the source may include the natural channels and the codebook to indicate the second channel. In other examples, the source may include a link in the nzp-csi-rs-resourceid field of QCL-Info element. The link may map the second channel to the natural channels and the codebook to indicate the second channel.

In some examples, after selecting a channel based on the channel information, the base station 602 may control

RISs

612, 614, 616 for the selected channel. The base station 602 may also configure and transmit QCL information between the selected channel as a source and a new reference signal (e.g., PDSCH DMRS, CSI-RS, or PDCCH DMRS) as a target to be transmitted via the channel. The base station 602, then, may transmit the new reference signal via the selected channel. The UE 604 may receive the QCL information and estimate the new reference signal based on the QCL information. The QCL information may include a Doppler shift, Doppler spread, average delay, delay spread, power delay profile, and/or spatial receiver parameter of the selected channel as a source for the new reference signal. Based on the QCL information, the UE may estimate the channel properties (e.g., CSI, RSRP, SINO, PMI, CQI, or RI) of the new reference signal. The QCL information is not limited to the second channel and a new reference signal via the second channel. The QCL information may include any QCL relationship between the second channel as a source and any other reference signals via any other channels. For example, the QCL information may indicate that the second channel has a QCL relationship with another second channel. Then, the UE may estimate another second channel based on the QCL information.

In other examples, the QCL information may indicate a source channel for a second channel as a target to estimate the second channel. For example, the base station 602 may configure QCL information between a SSB as a source and a second channel of the one or more second channels as a target. Thus, the UE 604 may estimate the channel properties (e.g., channel state information, RSRP, SINO, PMI, CQI, or RI) of the second channel based on the QCL information with the source (e.g., the SSB) . It should be appreciated that the QCL relationship above is a mere example. In other examples, the QCL information may indicate that a reference signal (e.g., CSI-RS or TRS) as a source has a QCL relationship with the second channel. Then, the UE may estimate the channel properties (e.g., channel state information, RSRP, SINO, PMI, CQI, or RI) of the second channel with a PDCCH DMRS or a PDSCH DMRS based on the QCL information.

FIG. 7 is a block diagram illustrating an example of a hardware implementation for a scheduling entity 700 employing a processing system 714. For example, the scheduling entity 700 may include a base station or any other suitable node (e.g., a

scheduling entity

108, 210, 212, 216, 218, 240, 302, 401, 502, and 602) as illustrated in any one or more of FIGs 1–6

The scheduling entity 700 may include a processing system 714 having one or more processors 704. Examples of processors 704 include microprocessors, microcontrollers, digital signal processors (DSPs) , 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. In various examples, the scheduling entity 700 may be configured to perform any one or more of the functions described herein. That is, the processor 704, as utilized in a scheduling entity 700, may be configured (e.g., in coordination with the memory 705) to implement any one or more of the processes and procedures described below and illustrated in FIG. 9.

The processing system 714 may be implemented with a bus architecture, represented generally by the bus 702. The bus 702 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 714 and the overall design constraints. The bus 702 communicatively couples together various circuits including one or more processors (represented generally by the processor 704) , a memory 705, and computer-readable media (represented generally by the computer-readable medium 706) . The bus 702 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further. A bus interface 708 provides an interface between the bus 702 and a transceiver 710. The transceiver 710 provides a communication interface or means for communicating with various other apparatus over a transmission medium. Depending upon the nature of the apparatus, a user interface 712 (e.g., keypad, display, speaker, microphone, joystick) may also be provided. Of course, such a user interface 712 is optional, and some examples, such as a base station or an RIS, may omit it.

In some aspects of the disclosure, the processor 704 may include transceiving circuitry 740 configured (e.g., in coordination with the memory 705) for various functions, including, e.g., scheduling a first reference signal via a direct channel, scheduling at least two second reference signals via the direct channel and at least two corresponding first channels that are reflected on corresponding controllable reflective surfaces (e.g., RISs) , transmitting a codebook for determining one or more second channels, receiving channel information corresponding to a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels, and/or transmitting QCL information. For example, the transceiving circuitry 740 may be configured to implement one or more of the functions described below in relation to FIG. 9, including, e.g., blocks 932, 934, 936, and/or 942.

In some aspects of the disclosure, the processor 704 may also include codebook configuration circuitry 742 configured (e.g., in coordination with the memory 705) for various functions, including, e.g., configuring a codebook for determining one or more second channels. For example, the codebook configuration circuitry 742 may be configured to implement one or more of the functions described below in relation to FIG. 9, including, e.g., block 932.

In some aspect of the disclosure, the processor 704 may also include QCL determination circuitry 744 configured (e.g., in coordination with the memory 705) for various functions, including, e.g., determining quasi co-location (QCL) information indicating a QCL relationship between a set of the one or more second channels and a set of the one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels. For example, the QCL determination circuitry 744 may be configured to implement one or more of the functions described below in relation to FIG. 9, including, e.g., block 940.

In some aspect of the disclosure, the processor 704 may also include RIS configuration circuitry 746 configured (e.g., in coordination with the memory 705) for various functions, including, e.g., selecting one or more channels and configuring one or more RISs based on the selected one or more channels. For example, the RIS configuration circuit 746 may be configured to implement one or more of the functions described below in relation to FIG. 9, including, e.g., blocks 934 and/or 938.

The processor 704 is responsible for managing the bus 702 and general processing, including the execution of software stored on the computer-readable medium 706. The software, when executed by the processor 704, causes the processing system 714 to perform the various functions described below for any particular apparatus. The processor 704 may also use the computer-readable medium 706 and the memory 705 for storing data that the processor 704 manipulates when executing software.

One or more processors 704 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 modules, 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. The software may reside on a computer-readable medium 706. The computer-readable medium 706 may be a non-transitory computer-readable medium. A non-transitory computer-readable medium includes, by way of example, a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip) , an optical disk (e.g., a compact disc (CD) or a digital versatile disc (DVD) ) , a smart card, a flash memory device (e.g., a card, a stick, or a key drive) , a random access memory (RAM) , a read only memory (ROM) , a programmable ROM (PROM) , an erasable PROM (EPROM) , an electrically erasable PROM (EEPROM) , a register, a removable disk, and any other suitable medium for storing software and/or instructions that may be accessed and read by a computer. The computer-readable medium 706 may reside in the processing system 714, external to the processing system 714, or distributed across multiple entities including the processing system 714. The computer-readable medium 706 may be embodied in a computer program product. By way of example, a computer program product may include a computer-readable medium in packaging materials. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system.

In one or more examples, the computer-readable storage medium 706 may store computer-executable code that includes transceiving instructions 752 that configure a scheduling entity 700 for various functions, including, e.g., scheduling a first reference signal via a direct channel, scheduling at least two second reference signals via the direct channel and at least two corresponding first channels that are reflected on corresponding controllable reflective surfaces (e.g., RISs) , transmitting a codebook for determining one or more second channels, receiving channel information corresponding to a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels, and/or transmitting QCL information. For example, the transceiving instructions 752 may be configured to cause a scheduling entity 700 to implement one or more of the functions described below in relation to FIG. 9, including, e.g., blocks 932, 934, 936, and/or 942. The computer-readable storage medium 706 may further store computer-executable code that includes codebook configuration instructions 754 that configure a scheduling entity 700 for various functions, including, e.g., configuring a codebook for determining one or more second channels. The codebook configuration instructions 754 may be configured to cause a scheduling entity 700 to implement one or more of the functions described below in relation to FIG. 9, including, e.g., block 932. The computer-readable storage medium 706 may further store computer-executable code that includes QCL determination instructions 756 that configure a scheduling entity 700 for various functions, including, e.g., determining quasi co-location (QCL) information indicating a QCL relationship between a set of the one or more second channels and a set of the one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels. The QCL determination instructions 756 may be configured to cause a scheduling entity 700 to implement one or more of the functions described below in relation to FIG. 9, including, e.g., block 940. The computer-readable storage medium 706 may further store computer-executable code that includes RIS configuration instructions 758 that configure one or more scheduling entity 700 for various functions, including, e.g., selecting one or more channels and configuring one or more controllable reflective surfaces (e.g., RISs) based on the selected one or more channels. The RIS configuration instructions 758 may be configured to cause a scheduling entity 700 to implement one or more of the functions described below in relation to FIG. 9, including, e.g., block 938.

In one configuration, the apparatus 700 for wireless communication includes means for receiving a controller frequency capability indication, scheduling a first reference signal via a direct channel, scheduling at least two second reference signals via the direct channel and at least two corresponding first channels (a first channel including a direct channel component associated with the direct channel and a reflected channel component that is reflected on a controllable reflective surface (e.g., RIS) , transmitting a codebook for determining one or more second channels, receiving channel information corresponding to a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels, transmitting QCL information, configuring a codebook for determining one or more second channels, and/or determining quasi co-location (QCL) information indicating a QCL relationship between a set of the one or more second channels and a set of the one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels. In one aspect, the aforementioned means may be the processor (s) 704 shown in FIG. 7 configured to perform the functions recited by the aforementioned means. In another aspect, the aforementioned means may be a circuit or any apparatus configured to perform the functions recited by the aforementioned means.

Of course, in the above examples, the circuitry included in the processor 704 is merely provided as an example, and other means for carrying out the described functions may be included within various aspects of the present disclosure, including but not limited to the instructions stored in the computer-readable storage medium 706, or any other suitable apparatus or means described in any one of the FIGs. 1–6, and utilizing, for example, the processes and/or algorithms described herein in relation to FIG. 9.

FIG. 8 is a conceptual diagram illustrating an example of a hardware implementation for a scheduled entity 800 employing a processing system 814. For example, the scheduled entity 800 may be any suitable device (e.g., scheduled

entity

106a, 106b, 220, 222, 226, 228, 230, 232, 234, 236, 238, 240, 242, 254, 258, 306, 406, 408, 504, 508, and 604) as illustrated in any one or more of FIGs. 1–6.

The processing system 814 may be substantially the same as the processing system 714 illustrated in FIG. 7, and may include a bus interface 808, a bus 802, memory 805, a processor 804, and a computer-readable medium 806. In some examples, the scheduled entity 800 may optionally include a user interface 812. And in further examples, the scheduled entity 800 may include a transceiver 810, e.g., substantially similar to those described above in FIG. 7. The processor 804, as utilized in a scheduled entity 800, may be configured (e.g., in coordination with the memory 805) to implement any one or more of the processes described below and illustrated in FIG. 9.

In some aspects of the disclosure, the processor 804 may include transceiving circuitry 840 configured (e.g., in coordination with the memory 805) for various functions, including, for example, receiving a first reference signal via a direct channel, receiving at least two second reference signals via the direct channel and at least two corresponding first channels that are reflected on corresponding RISs, receiving a codebook for determining one or more second channels, reporting channel information corresponding to a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels, and/or receiving quasi co-location (QCL) information indicating a QCL relationship between a set of the one or more second channels and a set of the one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels. For example, the transceiving circuitry 840 may be configured to implement one or more of the functions described below in relation to FIG. 9, including, e.g., blocks 912, 914, 922, and/or 924.

In some aspects of the disclosure, the processor 804 may further include channel measurement circuit 842 configured (e.g., in coordination with the memory 805) for various functions, including, for example, measuring the direct channel based on the first reference signal, measuring the direct channel with the at least two first channels based on the at least two corresponding second reference signals, estimating the second channel based on the QCL information, and/or estimating the another channel based on the QCL information. For example, the channel measurement circuit 842 may be configured to implement one or more of the functions described below in relation to FIG. 9, including, e.g., blocks 916 and/or 924.

In some aspects of the disclosure, the processor 804 may further include channel determination circuit 844 configured (e.g., in coordination with the memory 1005) for various functions, including, for example, determining the one or more second channels, determining the one or more second channels, multiplying the codebook by the measured direct channel and the measured at least two first channels, and/or determining the set of one or more channel indexes comprising an ordered sequence that ranks the set of one or more channels according to a given performance characteristic based on measurements of the direct channel and the at least two first channels and the second channel determination. For example, the channel determination circuit 844 may be configured to implement one or more of the functions described below in relation to FIG. 9, including, e.g., blocks 918, and/or 920.

And further, the computer-readable storage medium 806 may store computer-executable code that includes transceiving instructions 852 that configure a scheduled entity 800 for various functions, including, e.g., receiving a first reference signal via a direct channel, receiving at least two second reference signals via the direct channel and at least two corresponding first channels that transit corresponding RISs, receiving a codebook for determining one or more second channels, reporting channel information corresponding to a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels, and/or receiving quasi co-location (QCL) information indicating a QCL relationship between a set of the one or more second channels and a set of the one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels. For example, the transceiving instructions 852 may be configured to cause a scheduled entity 800 to implement one or more of the functions described below in relation to FIG. 9, including, e.g., blocks 912, 914, 922, and/or 924.

The computer-readable storage medium 806 may also store computer-executable code that includes channel measurement instructions 854 that configure a scheduled entity 800 for various functions, including, e.g., measuring the direct channel based on the first reference signal, measuring the at least two first channels based on the at least two corresponding second reference signals, estimating the second channel based on the QCL information, and/or estimating the another channel based on the QCL information. For example, the channel measurement instructions 854 may be configured to cause a scheduled entity 800 to implement one or more of the functions described below in relation to FIG. 9, including, e.g., block 916 and/or 924.

The computer-readable storage medium 806 may also store computer-executable code that includes channel determination instructions 856 that configure a scheduled entity 800 for various functions, including, e.g., determining the one or more second channels, multiplying the codebook by the measured direct channel and the measured at least two first channels, and/or determining the set of one or more channel indexes comprises an ordered sequence that ranks the set of one or more channels according to a given performance characteristic based on measurements of the direct channel and the at least two first channels and the second channel determination. For example, the channel determination instruction 856 may be configured to cause a scheduled entity 800 to implement one or more of the functions described below in relation to FIG. 9, including, e.g., blocks 918 and/or 920.

In one configuration, the apparatus 900 for wireless communication includes means for receiving a first reference signal via a direct channel, receiving at least two second reference signals via the direct channel and at least two corresponding first channels that transit corresponding RISs, receiving a codebook for determining one or more second channels, reporting channel information corresponding to a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels, receiving quasi co-location (QCL) information indicating a QCL relationship between a set of the one or more second channels and a set of the one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels, measuring the direct channel based on the first reference signal, measuring the at least two first channels based on the at least two corresponding second reference signals, estimating the second channel based on the QCL information, and/or estimating the another channel based on the QCL information, determining the one or more second channels, determining the one or more second channels, multiplying the codebook by the measured direct channel and the measured at least two first channels, and/or determining the set of one or more channel indexes comprises an ordered sequence that ranks the set of one or more channels according to a given performance characteristic based on measurements of the direct channel and the at least two first channels and the second channel determination. In one aspect, the aforementioned means may be the processor (s) 804 shown in FIG. 8 configured to perform the functions recited by the aforementioned means. In another aspect, the aforementioned means may be a circuit or any apparatus configured to perform the functions recited by the aforementioned means.

Of course, in the above examples, the circuitry included in the processor 804 is merely provided as an example, and other means for carrying out the described functions may be included within various aspects of the present disclosure, including but not limited to the instructions stored in the computer-readable storage medium 806, or any other suitable apparatus or means described in any one of the FIGs. 1–6, and utilizing, for example, the processes and/or algorithms described herein in relation to FIG. 9.

FIG. 9 is a flow chart illustrating an exemplary process 900 for RIS selection configuration in accordance with some aspects of the present disclosure. As described below, a particular implementation may omit some or all illustrated features, and may not require some illustrated features to implement all embodiments. In some examples, the process may be carried out by a scheduled entity (e.g., a UE) 904 and a scheduling entity (e.g., a base station) 902. In some examples, the scheduled entity 800 in FIG. 8 (or another scheduled entity described herein) serves as the scheduled entity 904, and the scheduling entity 700 in FIG. 7 (or another scheduling entity described herein) serves as the scheduling entity 902. In some examples, the process may be carried out by any suitable apparatus or means for carrying out the functions or algorithm described below.

As the number of controllable reflective surfaces increases in an area, more possible communication channels (e.g., signal paths, or paths of wireless signal propagation) may exist between a scheduling entity 902 and a scheduled entity 904 via controllable reflective surfaces. In some examples, a channel may include an antenna port. Also, in some examples, the controllable reflective surface may include a RIS. It should be appreciated that the controllable reflective surface is not limited to the RIS. It may be any controllable surface to configure the surface to reflect a reference signal to a given direction (e.g., scheduled entity 904) . In the disclosure that follows, a natural channel refers to a channel that can be either a direct channel or a first (e.g., reflected) channel. Here, a direct channel may be a channel on which a reference signal does not transit any controllable reflective surface between the scheduling entity 902 and the scheduled entity 904 (e.g., a line-of-sight channel or path) . A first/reflected channel may be a channel that includes a direct channel component, and a reflected channel component, i.e., a path on which a reference signal transits (e.g., is reflected by) one controllable reflective surface between the scheduling entity 902 and the scheduled entity 904. Since each channel can have a different channel quality and performance, the scheduled entity 904 may estimate each natural channel using a corresponding reference signal from the scheduling entity 902.

According to an aspect of this disclosure, a wireless network may further utilize one or more other channels (e.g., a second channel, a configured channel, a virtual channel, a mixed channel, or a composite channel) for communication between a scheduling entity 902 and a scheduled entity 904. Here, a virtual channel may be based on a suitable combination of a plurality of natural channels. That is, a scheduling entity 902 may transmit a signal to a scheduled entity 904 via a plurality of natural channels (e.g., a direct channel and one or more first/reflected channels) , acting jointly or collectively as a virtual channel. However, because a potentially large set of such virtual channels might be available, channel characterization via a respective reference signal on each such virtual channel may result in significant signaling overhead. To reduce signal overhead due to transmission of a reference signal per channel, according to an aspect of the present disclosure, the scheduled entity 904 may estimate a virtual channel without a reference signal being transmitted on that virtual channel, using a codebook and channel estimates of a plurality of natural channels. A scheduling entity 902 may forgo transmission of a reference signal via a virtual channel.

At block 932, the scheduling entity 902 may configure and transmit a codebook for configuring one or more second channels (e.g., virtual channels) . The codebook may include one or more precoders corresponding to the one or more second channels applied on at least three channel elements corresponding to the direct channel and the at least two first channels. The codebook may be referred to as a codeword, vector, or a column matrix. The channel element may include channel characteristics or channel information of a natural channel (direct channel or first channel) . The codebook may include one or more one-column codebooks or one or more multiple-column matrices. The number of columns may indicate the number of second or configured channels, while the number of rows may indicate the number of natural channels. Here, the natural channels may include a direct channel and one or more channels. Each channel of the one or more channels may include a first channel having a direct channel component associated with the direct channel and a reflected channel component that transits one controllable reflective surface. The scheduling entity 902 may transmit the codebook via an RRC message, a media access control (MAC) control element (CE) message, a downlink control information (DCI) message, a combination of the messages, or any other suitable message to transmit the codebook to the scheduled entity 904. The scheduling entity 902 may transmit the codebook before or after transmitting the reference signals to the scheduled entity 904.

At block 934, the scheduling entity 902 may schedule and transmit reference signals to the scheduled entity 904 via different channels. The reference signals (e.g., SSB, TRS, CSI-RS, PDSCH DMRS, and/or PDCCH DMRS) may be time-division multiplexed reference signals that may be the same omnidirectional spatial beam with the same precoding. The scheduling entity 902 may transmit the reference signals via different channels by controlling controllable reflective surfaces. For example, the scheduling entity 902 may turn off all controllable reflective surfaces and transmit a first reference signal via a direct channel. Since the scheduling entity 902 turns off all controllable reflective surfaces, the first reference signal may travel directly to the scheduled entity without transiting any controllable reflective surface via the direct channel. The scheduling entity 902 may turn on one controllable reflective surface at a given time and transmit a second reference signal via a first channel including a direct channel component associated with the direct channel and a reflected channel component which is reflected on one RIS. Thus, the second reference signal may travel in two different channels: traveling directly to the UE without transiting any controllable reflective surface via the direct channel component and transiting one controllable reflective surface via the reflected channel component reflected on the one RIS at a given time. The scheduling entity 902 may transmit a first reference signal via the direct channel and at least two second reference signals via at least two corresponding first channels. A first channel of the at least two first channels may include a direct channel component associated with the direct channel and a reflected channel component that is reflected on a controllable reflective surfaces (e.g., RISs) . The scheduling entity 902 may not necessarily transmit reference signals on the remaining channels or second channels. A remaining or second channel may include at least two first channels without a reference signal at a given time. In addition, the scheduling entity 902 may additionally transmit restriction information to the scheduled entity 904. The channel restriction information may include that some of the controllable reflective surfaces should be always on or off based on a previous codebook, the UE location, a temporary or permanent blockage on a channel between the scheduling entity 902 and the scheduled entity 904, and/or any other suitable factor to restrict the channel.

At

blocks

912 and 914, the scheduled entity 904 may receive the codebook and reference signals, respectively. In particular, the scheduled entity 904 may receive the first reference signal via the direct channel and receive at least two reference signals via at least two corresponding first channels that include reflected channel components that are reflected on corresponding controllable reflective surfaces (e.g., RISs) . The scheduled entity 904 may sample the reference signals and store reference signal samples at memory.

At block 916, the scheduled entity 904 may determine channel information of the natural channels by measuring the reference signal samples. The scheduled entity 904 may determine channel information of the direct channel by measuring the first reference signal. The scheduled entity 904 may further determine channel information of the at least two first channels by measuring the at least two corresponding second reference signals. For example, if three (3) controllable reflective surfaces are able to communicate with the scheduled entity 902 and the scheduling entity 904, eight (2 ³) channels are possible for the communication. The scheduling entity 902 may transmit four (4) reference signals: a first reference signal via a direct channel and three second reference signals via three first channels that are reflected on corresponding controllable reflective surfaces. The scheduled entity 904 may receive the four (4) reference signals and determine channel information of four channels (one direct channel and three first channels (each first channel including one direct channel component and one reflected channel component reflected on one RIS) ) by measuring the four (4) reference signals. The scheduling entity may not necessarily transmit other reference signals for the remaining or second channels. In some examples, the measurements may include spectral efficiency, channel state information (CSI) , signal to interference ratio (SINR) , reference signal received power (RSRP) , and/or channel quality information (CQI) . It should be appreciated that the measurements are not limited to the listed examples. It could be any other suitable measurement for the scheduling entity 902 to determine one or more channels based on the measurements to improve communication quality and/or performance between the scheduling entity 902 and the scheduled entity 904.

At block 918, the scheduled entity may determine the one or more remaining or second (configured) channels without receiving corresponding reference signals based on the codebook and the natural channels. The determination of the one or more second channels may include determining second channels based on the codebook and measured channels (one direct channel and N first channels (each channel including one direct channel and one reflected channel reflected on one RIS) ) corresponding N reference signals that are reflected on corresponding N RISs. In some examples, determining the one or more second channels may be performed by multiplying the codebook by measurements of the measured channels. For the example mentioned above, the scheduled entity 904 may measure four reference signals on four natural channels (h ₁, h ₁ + h ₂, h ₁ + h ₃, h ₁ + h ₄) and determine channel information of the four natural channels (h ₁, h ₁ + h ₂, h ₁ + h ₃, h ₁ + h ₄) where h ₁ is a direct channel and h ₁ + h ₂, h ₁ + h ₃, h ₁ + h ₄ are first channels that include reflected channel components that are reflected on corresponding three (3) controllable reflective surfaces. The scheduled entity 904 may use the codebook

received in block 912 to determine the four (4) remaining or second channels (h ₁ + h ₂ + h ₃, h ₁ + h ₃ + h ₄, h ₁ + h ₂ + h ₄, h ₁ + h ₂ + h ₃ + h ₄) . The scheduled entity 904 may determine channel characteristics of the four (4) second channels by linear combination of the codebook and measurements of the four (4) natural channels as follows:

With the second channel determination, the scheduled entity may have all channel characteristics (measurements of the four (4) natural channels and the four (4) second channels) of all eight (8) channels between the scheduling entity 902 and the scheduled entity 904.

At block 920, based on the channel characteristics of the natural channels and second channels, the scheduled entity 904 may determine channel information corresponding to a set of one or more channels selected from the group of: the natural and second channels to the scheduling entity 902. The natural channel may include the direct channel and the at least two first channels. In some examples, the channel information may include a set of one or more channel indexes corresponding to the set of the one or more channels. In some examples, as described above, the set of one or more channel indexes may include an ordered sequence that ranks the set of one or more channels according to one or more performance characteristics based on the measured or determined channel characteristics of the natural channels and the second channels.

At block 922, the scheduled entity 904 may report the channel information to the scheduling entity 902. In some examples, the channel information may include one or more channel indexes, which include an ordered sequence that ranks the set of one or more channels according to a given performance characteristic. In other examples, the channel information may include one or more of the measured or determined channel characteristics of the natural channels and the second channels.

At block 936, the scheduling entity 902 may receive the channel information corresponding to a set of one or more channels from the scheduled entity 904. The one or more channels may include natural channels and one or more second channels.

At block 938, the scheduling entity 902 may select one or more channels based on the channel information. For example, the scheduling entity 902 may select the one or more channels having the best ranking or performance characteristics indicated by the received channel information. The scheduling entity 902 may also configure RISs based on the selected one or more channels. For example, the scheduling entity 902 may determine which controllable reflective surfaces are to be turned on or off to achieve the selected one or more channels and then send control signals to enable and/or disable the respective RISs accordingly.

At block 940, the scheduling entity 902 may determine QCL information indicating a QCL relationship between a set of the one or more second channels and a set of one or more channels (e.g., selected from the group of the direct channel, the at least two first channels, and the one or more second channels) . The set of the one or more channels may include all channels (natural and second channels) between the scheduling entity 902 and the scheduled entity 904. The set of the one or more channels may correspond to the set of the one or more second channels. In some examples, the QCL information may identify a source channel for a second channel of the one or more second channels to estimate the second channel. For example, the reference signal on the source channel may be a SSB. The QCL information may indicate that a second channel has a QCL relationship with the SSB. The QCL information may include a Doppler shift, Doppler spread, average delay, delay spread, power delay profile, and/or spatial receiver parameter of the SSB as a source channel for the second channel. In other examples, the QCL information identifies a second channel of the one or more second channels as a source channel for another channel. For example, the source channel may include the natural channels and the codebook to indicate the second channel. In some examples, the source channel may include a link in the nzp-csi-rs-resourceid field of QCL-Info element. The link may map the second channel to the natural channels and the codebook to indicate the second channel. The another channel identified as a target channel may include a new reference signal (e.g., PDSCH DMRS, CSI-RS, or PDCCH DMRS) on the second channel or any other natural or second channel.

At block 942, the scheduling entity 902 may transmit the QCL information and transmit one or more new reference signals via selected one or more channels. In some examples, the one or more new reference signals may be a target channel or a source channel in the QCL information.

At block 924, the scheduled entity 904 may receive the QCL information and estimate the target channel based on the QCL information. In some examples, the QCL information may indicate a second channel as a target channel. Then, based on the QCL information, the scheduled entity 904 may estimate the channel properties (e.g., channel state information, RSRP, SINO, PMI, CQI, or RI) of the (target) second channel. In other examples, the QCL information may indicate a second channel as a source channel. Then, based on the QCL information, the scheduled entity 904 may estimate the channel properties (e.g., CSI, RSRP, SINO, PMI, CQI, or RI) of a target channel based on the Doppler shift, Doppler spread, average delay, delay spread, power delay profile, and/or spatial receiver parameter of the second channel. The Doppler shift, Doppler spread, average delay, delay spread, power delay profile, and/or spatial receiver parameter may be derived from the measured natural channels and the codebook. Based on the channel estimation based on the QCL information, the scheduled entity 904 may transmit data on the target channel (e.., to the scheduling entity 902) .

Further Examples Having a Variety of Features:

Example 1: A method of wireless communication operable at a scheduled entity, the method comprising: receiving a first reference signal via a direct channel; receiving at least two second reference signals via at least two corresponding first channels, a first channel of the at least two first channels comprising a direct channel component associated with the direct channel and a reflected channel component that is reflected on a controllable reflective surface; receiving a codebook for determining one or more second channels; determining the one or more second channels based on the codebook and the direct channel and the at least two first channels; and reporting channel information based on the one or more second channels.

Example 2: The method of Example 1, wherein a controllable reflective surface of the controllable reflective surfaces comprises a reconfigurable intelligent surface (RIS) configured to reflect an incident signal into a reflected signal.

Example 3: The method of Example 1, further comprising: receiving quasi co-location (QCL) information indicating a QCL relationship between a set of the one or more second channels and a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels.

Example 4: The method of Example 3, wherein the QCL information identifies a source channel for a second channel of the one or more second channels, the method further comprising: estimating the second channel based on the QCL information.

Example 5: The method of Example 3, wherein the QCL information identifies a second channel of the one or more second channels as a source for another channel, the method further comprising: estimating the another channel based on the QCL information.

Example 6: The method of Example 1, wherein the codebook comprises one or more precoders corresponding to the one or more second channels applied on at least three channel elements corresponding to the direct channel and the at least two first channels.

Example 7: The method of Example 1, further comprising: measuring the first reference signal via the direct channel; and measuring the at least two second reference signals via at least two corresponding first channels.

Example 8: The method of Example 7, wherein the determining one or more second channels comprises multiplying the codebook by a measurement of the direct channel and measurements of the at least two first channels.

Example 9: The method of Example 7, wherein the channel information corresponds to a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels.

Example 10: The method of Example 9, wherein the channel information comprises a set of one or more channel indexes corresponding to the set of the one or more channels.

Example 11: The method of Example 10, wherein the set of one or more channel indexes comprises an ordered sequence that ranks the set of one or more channels according to a given performance characteristic based on the measured direct channel, the measured at least two first channels, and the determined one or more second channels.

Example 12: A non-transitory computer-readable medium storing computer-executable code, comprising code for causing a scheduled entity to: receive a first reference signal via a direct channel; receive at least two second reference signals via at least two corresponding first channels, a first channel of the at least two first channels comprising a direct channel component associated with the direct channel and a reflected channel component that is reflected on a controllable reflective surface; receive a codebook for determining one or more second channels; determine the one or more second channels based on the codebook and the direct channel and the at least two first channels; and report channel information based on the one or more second channels.

Example 13: The non-transitory computer-readable medium of Example 12, wherein the codebook comprises one or more precoders corresponding to the one or more second channels applied on at least three channel elements corresponding to the direct channel and the at least two first channels.

Example 14: The non-transitory computer-readable medium of Example 12, wherein the code is further configured to: measure the first reference signal via the direct channel; and measure the at least two second reference signals via the at least two corresponding first channels.

Example 15: The non-transitory computer-readable medium of Example 14, wherein the determining one or more second channels comprises multiplying the codebook by a measurement of the direct channel and measurements of the at least two first channels.

Example 16: The non-transitory computer-readable medium of Example 12, wherein the channel information corresponds to a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels.

Example 17: The non-transitory computer-readable medium of Example 16, wherein the channel information comprises a set of one or more channel indexes corresponding to the set of the one or more channels, and wherein the set of one or more channel indexes comprises an ordered sequence that ranks the set of one or more channels according to a given performance characteristic based on the measurement of the direct channel, the measurements of the at least two first channels, and the determined one or more second channels.

Example 18: A method of wireless communication operable at a scheduling entity, the method comprising: scheduling a first reference signal via a direct channel; scheduling at least two second reference signals via at least two corresponding first channels, a first channel of the at least two first channels comprising a direct channel component associated with the direct channel and a reflected channel component that is reflected on a controllable reflective surface; transmitting a codebook for determining one or more second channels; receiving channel information based on the one or more second channels; and transmitting a set of one or more third reference signals based on the channel information.

Example 19: The method of Example 18, wherein the codebook comprises one or more precoders corresponding to the one or more second channels applied on at least three channel elements corresponding to the direct channel and the at least two first channels.

Example 20: The method of Example 18, further comprising: transmitting quasi co-location (QCL) information indicating a QCL relationship between a set of the one or more second channels and a set of one or more channels selected from the group of: the direct channel, the at least two first channels with the direct channel, and the one or more second channels.

Example 21: The method of Example 20, wherein the QCL information identifies a source channel for a second channel of the one or more second channels for estimating the second channel.

Example 22: The method of Example 20, wherein the QCL information identifies a second channel of the one or more second channels as a source for another channel for estimating the another channel.

Example 23: The method of Example 18, wherein the channel information corresponds to a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels.

Example 24: The method of Example 23, wherein the channel information comprises a set of one or more channel indexes corresponding to the set of the one or more channels.

Example 25: The method of Example 24, wherein the set of one or more channel indexes comprises an ordered sequence that ranks the set of one or more channels according to a given performance characteristic based on a measurement of the direct channel, measurements of the direct channel with the at least two first channels and the determined one or more second channels.

Example 26: A non-transitory computer-readable medium storing computer-executable code, comprising code for causing a scheduling entity to: schedule a first reference signal via a direct channel; schedule at least two second reference signals via at least two corresponding first channels, a first channel of the at least two first channels comprising a direct channel component associated with the direct channel and a reflected channel component that is reflected on a controllable reflective surface; transmit a codebook for determining one or more second channels; receive channel information based on the one or more second channels; and transmit a set of one or more third reference signals based on the channel information.

Example 27: The non-transitory computer-readable medium of Example of 26, wherein the codebook comprises one or more precoders corresponding to the one or more second channels applied on at least three channel elements corresponding to the direct channel and the at least two first channels.

Example 28: The non-transitory computer-readable medium of Example of 26, wherein the channel information corresponds to a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels.

Example 29: The non-transitory computer-readable medium of Example of 28, wherein the channel information comprises a set of one or more channel indexes corresponding to the set of the one or more channels.

Example 30: The non-transitory computer-readable medium of Example of 29, wherein the set of one or more channel indexes comprises an ordered sequence that ranks the set of one or more channels according to a given performance characteristic based on a measurement of the direct channel, measurements of the direct channel with the at least two first channels and the determined one or more second channels.

This disclosure presents several aspects of a wireless communication network with reference to an exemplary implementation. As those skilled in the art will readily appreciate, various aspects described throughout this disclosure may be extended to other telecommunication systems, network architectures and communication standards.

By way of example, various aspects may be implemented within other systems defined by 3GPP, such as Long-Term Evolution (LTE) , the Evolved Packet System (EPS) , the Universal Mobile Telecommunication System (UMTS) , and/or the Global System for Mobile (GSM) . Various aspects may also be extended to systems defined by the 3rd Generation Partnership Project 2 (3GPP2) , such as CDMA2000 and/or Evolution-Data Optimized (EV-DO) . Other examples may be implemented within systems employing IEEE 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, Ultra-Wideband (UWB) , Bluetooth, and/or other suitable systems. The actual telecommunication standard, network architecture, and/or communication standard employed will depend on the specific application and the overall design constraints imposed on the system.

The present disclosure uses the word “exemplary” to mean “serving as an example, instance, or illustration. ” Any implementation or aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term “aspects” does not require that all aspects of the disclosure include the discussed feature, advantage or mode of operation. The present disclosure uses the term “coupled” to refer to a direct or indirect coupling between two objects. For example, if object A physically touches object B, and object B touches object C, then objects A and C may still be considered coupled to one another-even if they do not directly physically touch each other. For instance, a first object may be coupled to a second object even though the first object is never directly physically in contact with the second object. The present disclosure uses the terms “circuit” and “circuitry” broadly, to include both hardware implementations of electrical devices and conductors that, when connected and configured, enable the performance of the functions described in the present disclosure, without limitation as to the type of electronic circuits, as well as software implementations of information and instructions that, when executed by a processor, enable the performance of the functions described in the present disclosure.

One or more of the components, steps, features and/or functions illustrated in FIGs. 1–9 may be rearranged and/or combined into a single component, step, feature or function or embodied in several components, steps, or functions. Additional elements, components, steps, and/or functions may also be added without departing from novel features disclosed herein. The apparatus, devices, and/or components illustrated in FIGs. 1–9 may be configured to perform one or more of the methods, features, or steps described herein. The novel algorithms described herein may also be efficiently implemented in software and/or embedded in hardware.

It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein.

Applicant provides this description to enable any person skilled in the art to practice the various aspects described herein. Those skilled in the art will readily recognize various modifications to these aspects, and may apply the generic principles defined herein to other aspects. Applicant does not intend the claims to be limited to the aspects shown herein, but to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” Unless specifically stated otherwise, the present disclosure uses the term “some” to refer to one or more. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a; b; c; a and b; a and c; b and c; and a, b and 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.

Claims

A method of wireless communication operable at a scheduled entity, the method comprising:

receiving a first reference signal via a direct channel;

receiving at least two second reference signals via at least two corresponding first channels, a first channel of the at least two first channels comprising a direct channel component associated with the direct channel and a reflected channel component that is reflected on a controllable reflective surface;

receiving a codebook for determining one or more second channels;

determining the one or more second channels based on the codebook, the direct channel, and the at least two first channels; and

reporting channel information based on the one or more second channels.
The method of claim 1, wherein the controllable reflective surface comprises a reconfigurable intelligent surface (RIS) configured to reflect an incident signal into a reflected signal.
The method of claim 1, further comprising:

receiving quasi co-location (QCL) information indicating a QCL relationship between a set of the one or more second channels and a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels.
The method of claim 3, wherein the QCL information identifies a source channel for a second channel of the one or more second channels,

the method further comprising: estimating the second channel based on the QCL information.
The method of claim 3, wherein the QCL information identifies a second channel of the one or more second channels as a source for another channel,

the method further comprising: estimating the another channel based on the QCL information.
The method of claim 1, wherein the codebook comprises one or more precoders corresponding to the one or more second channels applied on at least three channel elements corresponding to the direct channel and the at least two first channels.
The method of claim 1, further comprising:

measuring the first reference signal via the direct channel; and

measuring the at least two second reference signals via at least two corresponding first channels.
The method of claim 7, wherein the determining one or more second channels comprises multiplying the codebook by a measurement of the direct channel and measurements of the at least two first channels.
The method of claim 7, wherein the channel information corresponds to a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels.
The method of claim 9, wherein the channel information comprises a set of one or more channel indexes corresponding to the set of the one or more channels.
The method of claim 10, wherein the set of one or more channel indexes comprises an ordered sequence that ranks the set of one or more channels according to a given performance characteristic based on the measurement of the direct channel, the measurements of the at least two first channels, and the determined one or more second channels.
A non-transitory computer-readable medium storing computer-executable code, comprising code for causing a scheduled entity to:

receive a first reference signal via a direct channel;

receive at least two second reference signals via at least two corresponding first channels, a first channel of the at least two first channels comprising a direct channel component associated with the direct channel and a reflected channel component that is reflected on a controllable reflective surface;

receive a codebook for determining one or more second channels;

determine the one or more second channels based on the codebook, the direct channel, and the at least two first channels; and

report channel information based on the one or more second channels.
The non-transitory computer-readable medium of claim 12, wherein the codebook comprises one or more precoders corresponding to the one or more second channels applied on at least three channel elements corresponding to the direct channel and the at least two first channels.
The non-transitory computer-readable medium of claim 12, wherein the code is further configured to:

measure the first reference signal via the direct channel; and

measure the at least two second reference signals via the at least two corresponding first channels.
The non-transitory computer-readable medium of claim 14, wherein the determining one or more second channels comprises multiplying the codebook by a measurement of the direct channel and measurements of the at least two first channels.
The non-transitory computer-readable medium of claim 12, wherein the channel information corresponds to a set of one or more channels selected from the group of:the direct channel, the at least two first channels, and the one or more second channels.
The non-transitory computer-readable medium of claim 16, wherein the channel information comprises a set of one or more channel indexes corresponding to the set of the one or more channels, and

wherein the set of one or more channel indexes comprises an ordered sequence that ranks the set of one or more channels according to a given performance characteristic based on the measurement of the direct channel, the measurements of the at least two first channels, and the determined one or more second channels.
A method of wireless communication operable at a scheduling entity, the method comprising:

scheduling a first reference signal via a direct channel;

scheduling at least two second reference signals via at least two corresponding first channels, a first channel of the at least two first channels comprising a direct channel component associated with the direct channel and a reflected channel component that is reflected on a controllable reflective surface;

transmitting a codebook for determining one or more second channels;

receiving channel information based on the one or more second channels; and

transmitting a set of one or more third reference signals based on the channel information.
The method of claim 18, wherein the codebook comprises one or more precoders corresponding to the one or more second channels applied on at least three channel elements corresponding to the direct channel and the at least two first channels.
The method of claim 18, further comprising:

transmitting quasi co-location (QCL) information indicating a QCL relationship between a set of the one or more second channels and a set of one or more channels selected from the group of: the direct channel, the at least two first channels with the direct channel, and the one or more second channels.
The method of claim 20, wherein the QCL information identifies a source channel for a second channel of the one or more second channels for estimating the second channel.
The method of claim 20, wherein the QCL information identifies a second channel of the one or more second channels as a source for another channel for estimating the another channel.
The method of claim 18, wherein the channel information corresponds to a set of one or more channels selected from the group of: the direct channel, the at least two first channels, and the one or more second channels.
The method of claim 23, wherein the channel information comprises a set of one or more channel indexes corresponding to the set of the one or more channels.
The method of claim 24, wherein the set of one or more channel indexes comprises an ordered sequence that ranks the set of one or more channels according to a given performance characteristic based on a measurement of the direct channel, measurements of the at least two first channels, and the determined one or more second channels.
A non-transitory computer-readable medium storing computer-executable code, comprising code for causing a scheduling entity to:

schedule a first reference signal via a direct channel;

schedule at least two second reference signals via at least two corresponding first channels, a first channel of the at least two first channels comprising a direct channel component associated with the direct channel and a reflected channel component that is reflected on a controllable reflective surface;

transmit a codebook for determining one or more second channels;

receive channel information based on the one or more second channels; and

transmit a set of one or more third reference signals based on the channel information.
The non-transitory computer-readable medium of claim of 26, wherein the codebook comprises one or more precoders corresponding to the one or more second channels applied on at least three channel elements corresponding to the direct channel and the at least two first channels.
The non-transitory computer-readable medium of claim of 26, wherein the channel information corresponds to a set of one or more channels selected from the group of:the direct channel, the at least two first channels, and the one or more second channels.
The non-transitory computer-readable medium of claim of 28, wherein the channel information comprises a set of one or more channel indexes corresponding to the set of the one or more channels.
The non-transitory computer-readable medium of claim of 29, wherein the set of one or more channel indexes comprises an ordered sequence that ranks the set of one or more channels according to a given performance characteristic based on a measurement of the direct channel, measurements of the at least two first channels and the determined one or more second channels.