EP4659367A1 - Decomposition-based separated channel estimation and sounding for reconfigurable intelligent surfaces - Google Patents

Abstract

A wireless transmit/receive unit (WTRU) may receive configuration information that indicates a channel state information (CSI) resource and information associated with separate reporting for a base station (BS)-reconfigurable intelligent surface (RIS) channel and a RIS-WTRU channel. The WTRU may measure a BS-RIS-WTRU channel using the indicated CSI resource and determine separated CSI for the BS-RIS channel and the RIS-WTRU channel based on the measurement for the BS-RIS-WTRU channel. The WTRU may then send the separated CSI for the BS-RIS channel and the RIS-WTRU channel. The measurement for a BS-RIS-WTRU channel may include a differential CSI measurement, and the separated CSI may be determined based on the differential CSI measurement. The differential CSI measurement may be performed by varying RIS states.

Description

DECOMPOSITION-BASED SEPARATED CHANNEL ESTIMATION AND SOUNDING FOR RECONFIGURABLE INTELLIGENT SURFACES CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional Patent Application No. 63/443,183 filed 03- February-2023 which is incorporated herein by reference in its entirety. BACKGROUND [0002] Mobile communications using wireless communication continue to evolve. A fifth generation may be referred to as 5G. A previous (legacy) generation of mobile communication may be, for example, fourth generation (4G) long term evolution (LTE). SUMMARY [0003] Described herein are systems, methods, and instrumentalities associated with separated channel estimates related to a reconfigurable intelligent surface (RIS). The separated channel estimates may be achieved using decomposition. [0004] In examples, a system may include a wireless transmit/receive unit (WTRU), an RIS, and a base station (BS). The WTRU may receive configuration information that indicates a channel state information (CSI) resource and information for separate reporting for a BS- RIS channel and a RIS-WTRU channel. The WTRU may measure a BS-RIS-WTRU channel using the indicated CSI resource and determine separated CSI for the BS-RIS channel and the RIS-WTRU channel based on the measurement for the BS- RIS-WTRU channel. The WTRU may then send the separated CSI for the BS-RIS channel and the RIS- WTRU channel. The measurement for a BS-RIS-WTRU channel may include a differential CSI measurement, and the separated CSI may be determined based on the differential CSI measurement. The differential CSI measurement may be performed by varying RIS states. [0005] The information for separate reporting for a BS-RIS channel and a RIS-WTRU channel may include different reporting periodicities for the BS-RIS channel and the RIS-WTRU channel, and the separated CSI for the BS-RIS channel and the RIS-WTRU channel may be sent using the different reporting periodicities. [0006] The configuration information may indicate information associated with a decomposition of the measurement for the BS-RIS-WTRU channel. For example, the configuration information may include an indication indicating decomposition-based measurement(s) is to be performed (e.g., the measurement herein is to be decomposed). One or more decomposition techniques may be used herein. The WTRU may determine the separated CSI for the BS-RIS channel and the RIS-WTRU channel by decomposing the measurement for the BS-RIS-WTRU channel based on the information associated with the decomposition. The WTRU may send the separated CSI. In some examples, the WTRU may iteratively perform a CSI measurement and/or a decomposition of the CSI measurement using one or more CSI instances. [0007] The performance for the communication links among the WTRU, the RIS, and/or network devices may be improved based on the separated channel estimates. BRIEF DESCRIPTION OF THE DRAWINGS [0008] FIG.1A is a system diagram illustrating an example communications system in which one or more disclosed embodiments may be implemented; [0009] FIG.1B is a system diagram illustrating an example wireless transmit/receive unit (WTRU) that may be used within the communications system illustrated in FIG.1A according to an embodiment; [0010] FIG.1C is a system diagram illustrating an example radio access network (RAN) and an example core network (CN) that may be used within the communications system illustrated in FIG.1A according to an embodiment; [0011] FIG.1D is a system diagram illustrating a further example RAN and a further example CN that may be used within the communications system illustrated in FIG.1A according to an embodiment; [0012] FIG.2 illustrates an example of an RIS-aided system; [0013] FIG.3 illustrates an example distribution of RIS elements into sub-surfaces; [0014] FIG.4 Illustrates an example of partitioning an RIS into six sub-surfaces; [0015] FIG.5 illustrates an example of a system model representing RIS separated channels for MIMO transceivers in an RIS-aided downlink communication; [0016] FIG.6 illustrates an example of RIS separated channel acquisition; [0017] FIG.7 illustrates an example of a signaling diagram for RIS separated channel estimation; [0018] FIG.8 illustrates an example WTRU procedure for separated channel estimation; [0019] FIG.9 Illustrates an example of RIS procedure for separated channel estimation; [0020] FIG.10 illustrates an example for a one-shot decomposition; [0021] FIG.11 illustrates an example signaling diagram for a one-shot decomposition; [0022] FIG.12 including 12(a) and 12(b) illustrates an example for iterative/multi-instance decomposition-based separated channel estimation; [0023] FIG.13 illustrates an example signaling diagram for a multi-instance decomposition-based approach; [0024] FIG.14 illustrates an example of CSI-RS configuration (e.g., enhancement) for iterative/multi- instance separated channel estimation using decomposition. [0025] FIG.15 is a flow chart of a method according to an embodiment. DETAILED DESCRIPTION [0026] FIG.1A is a diagram illustrating an example communications system 100 in which one or more disclosed embodiments may be implemented. The communications system 100 may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system 100 may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems 100 may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), zero-tail unique-word DFT-Spread OFDM (ZT UW DTS-s OFDM), unique word OFDM (UW-OFDM), resource block-filtered OFDM, filter bank multicarrier (FBMC), and the like. [0027] As shown in FIG.1A, the communications system 100 may include wireless transmit/receive units (WTRUs) 102a, 102b, 102c, 102d, a RAN 104/113, a CN 106/115, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and/or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d, any of which may be referred to as a “station” and/or a “STA”, may be configured to transmit and/or receive wireless signals and may include a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi device, an Internet of Things (IoT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like. Any of the WTRUs 102a, 102b, 102c and 102d may be interchangeably referred to as a WTRU. [0028] The communications systems 100 may also include a base station 114a and/or a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the CN 106/115, the Internet 110, and/or the other networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a gNB, a NR NodeB, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and/or network elements. [0029] The base station 114a may be part of the RAN 104/113, which may also include other base stations and/or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a and/or the base station 114b may be configured to transmit and/or receive wireless signals on one or more carrier frequencies, which may be referred to as a cell (not shown). These frequencies may be in licensed spectrum, unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide coverage for a wireless service to a specific geographical area that may be relatively fixed or that may change over time. The cell may further be divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, i.e., one for each sector of the cell. In an embodiment, the base station 114a may employ multiple-input multiple output (MIMO) technology and may utilize multiple transceivers for each sector of the cell. For example, beamforming may be used to transmit and/or receive signals in desired spatial directions. [0030] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT). [0031] More specifically, as noted above, the communications system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station 114a in the RAN 104/113 and the WTRUs 102a, 102b, 102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 115/116/117 using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink (DL) Packet Access (HSDPA) and/or High-Speed UL Packet Access (HSUPA). [0032] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A) and/or LTE-Advanced Pro (LTE-A Pro). [0033] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR Radio Access , which may establish the air interface 116 using New Radio (NR). [0034] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement multiple radio access technologies. For example, the base station 114a and the WTRUs 102a, 102b, 102c may implement LTE radio access and NR radio access together, for instance using dual connectivity (DC) principles. Thus, the air interface utilized by WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and/or transmissions sent to/from multiple types of base stations (e.g., a eNB and a gNB). [0035] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies such as IEEE 802.11 (i.e., Wireless Fidelity (WiFi), IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA20001X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like. [0036] The base station 114b in FIG.1A may be a wireless router, Home Node B, Home eNode B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., for use by drones), a roadway, and the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In an embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR etc.) to establish a picocell or femtocell. As shown in FIG.1A, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114b may not be required to access the Internet 110 via the CN 106/115. [0037] The RAN 104/113 may be in communication with the CN 106/115, which may be any type of network configured to provide voice, data, applications, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have varying quality of service (QoS) requirements, such as differing throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, and the like. The CN 106/115 may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication. Although not shown in FIG.1A, it will be appreciated that the RAN 104/113 and/or the CN 106/115 may be in direct or indirect communication with other RANs that employ the same RAT as the RAN 104/113 or a different RAT. For example, in addition to being connected to the RAN 104/113, which may be utilizing a NR radio technology, the CN 106/115 may also be in communication with another RAN (not shown) employing a GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology. [0038] The CN 106/115 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and/or the other networks 112. The PSTN 108 may include circuit- switched telephone networks that provide plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and/or the internet protocol (IP) in the TCP/IP internet protocol suite. The networks 112 may include wired and/or wireless communications networks owned and/or operated by other service providers. For example, the networks 112 may Inother CN connected to one or more RANs, which may employ the same RAT as the RAN 104/113 or a different RAT. [0039] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links). For example, the WTRU 102c shown in FIG.1A may be configured to communicate with the base station 114a, which may employ a cellular-based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology. [0040] FIG.1B is a system diagram illustrating an example WTRU 102. As shown in FIG.1B, the WTRU 102 may include a processor 118, a transceiver 120, a transmit/receive element 122, a speaker/microphone 124, a keypad 126, a display/touchpad 128, non-removable memory 130, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and/or other peripherals 138, among others. It will be appreciated that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment. [0041] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor 118 may perform signal coding, data processing, power control, input/output processing, and/or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit/receive element 122. While FIG.1B depicts the processor 118 and the transceiver 120 as separate components, it will be appreciated that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip. [0042] The transmit/receive element 122 may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, the transmit/receive element 122 may be an antenna configured to transmit and/or receive RF signals. In an embodiment, the transmit/receive element 122 may be an emitter/detector configured to transmit and/or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit/receive element 122 may be configured to transmit and/or receive both RF and light signals. It will be appreciated that the transmit/receive element 122 may be configured to transmit and/or receive any combination of wireless signals. [0043] Although the transmit/receive element 122 is depicted in FIG.1B as a single element, the WTRU 102 may include any number of transmit/receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit/receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116. [0044] The transceiver 120 may be configured to modulate the signals that are to be transmitted by the transmit/receive element 122 and to demodulate the signals that are received by the transmit/receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as NR and IEEE 802.11, for example. [0045] The processor 118 of the WTRU 102 may be coupled to, and may receive user input data from, the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128 (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128. In addition, the processor 118 may access information from, and store data in, any type of suitable memory, such as the non-removable memory 130 and/or the removable memory 132. The non-removable memory 130 may include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from, and store data in, memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown). [0046] The processor 118 may receive power from the power source 134, and may be configured to distribute and/or control the power to the other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and the like. [0047] The processor 118 may also be coupled to the GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or in lieu of, the information from the GPS chipset 136, the WTRU 102 may receive location information over the air interface 116 from a base station (e.g., base stations 114a, 114b) and/or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by way of any suitable location- determination method while remaining consistent with an embodiment. [0048] The processor 118 may further be coupled to other peripherals 138, which may include one or more software and/or hardware modules that provide additional features, functionality and/or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs and/or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, a Virtual Reality and/or Augmented Reality (VR/AR) device, an activity tracker, and the like. The peripherals 138 may include one or more sensors, the sensors may be one or more of a gyroscope, an accelerometer, a hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor; a geolocation sensor; an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, and/or a humidity sensor. [0049] The WTRU 102 may include a full duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for both the UL (e.g., for transmission) and downlink (e.g., for reception) may be concurrent and/or simultaneous. The full duplex radio may include an interference management unit to reduce and or substantially eliminate self-interference via either hardware (e.g., a choke) or signal processing via a processor (e.g., a separate processor (not shown) or via processor 118). In an embodiment, the WRTU 102 may include a half-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for either the UL (e.g., for transmission) or the downlink (e.g., for reception)). [0050] FIG.1C is a system diagram illustrating the RAN 104 and the CN 106 according to an embodiment. As noted above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the CN 106. [0051] The RAN 104 may include eNode-Bs 160a, 160b, 160c, though it will be appreciated that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the eNode-Bs 160a, 160b, 160c may implement MIMO technology. Thus, the eNode-B 160a, for example, may use multiple antennas to transmit wireless signals to, and/or receive wireless signals from, the WTRU 102a. [0052] Each of the eNode-Bs 160a, 160b, 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and/or DL, and the like. As shown in FIG.1C, the eNode-Bs 160a, 160b, 160c may communicate with one another over an X2 interface. [0053] The CN 106 shown in FIG.1C may include a mobility management entity (MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN) gateway (or PGW) 166. While each of the foregoing elements are depicted as part of the CN 106, it will be appreciated that any of these elements may be owned and/or operated by an entity other than the CN operator. [0054] The MME 162 may be connected to each of the eNode-Bs 162a, 162b, 162c in the RAN 104 via an S1 interface and may serve as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation/deactivation, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c, and the like. The MME 162 may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM and/or WCDMA. [0055] The SGW 164 may be connected to each of the eNode Bs 160a, 160b, 160c in the RAN 104 via the S1 interface. The SGW 164 may generally route and forward user data packets to/from the WTRUs 102a, 102b, 102c. The SGW 164 may perform other functions, such as anchoring user planes during inter- eNode B handovers, triggering paging when DL data is available for the WTRUs 102a, 102b, 102c, managing and storing contexts of the WTRUs 102a, 102b, 102c, and the like. [0056] The SGW 164 may be connected to the PGW 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. [0057] The CN 106 may facilitate communications with other networks. For example, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. For example, the CN 106 may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to the other networks 112, which may include other wired and/or wireless networks that are owned and/or operated by other service providers. [0058] Although the WTRU is described in FIGS.1A-1D as a wireless terminal, it is contemplated that in certain representative embodiments that such a terminal may use (e.g., temporarily or permanently) wired communication interfaces with the communication network. [0059] In representative embodiments, the other network 112 may be a WLAN. [0060] A WLAN in Infrastructure Basic Service Set (BSS) mode may have an Access Point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP may have an access or an interface to a Distribution System (DS) or another type of wired/wireless network that carries traffic in to and/or out of the BSS. Traffic to STAs that originates from outside the BSS may arrive through the AP and may be delivered to the STAs. Traffic originating from STAs to destinations outside the BSS may be sent to the AP to be delivered to respective destinations. Traffic between STAs within the BSS may be sent through the AP, for example, where the source STA may send traffic to the AP and the AP may deliver the traffic to the destination STA. The traffic between STAs within a BSS may be considered and/or referred to as peer-to- peer traffic. The peer-to-peer traffic may be sent between (e.g., directly between) the source and destination STAs with a direct link setup (DLS). In certain representative embodiments, the DLS may use an 802.11e DLS or an 802.11z tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may not have an AP, and the STAs (e.g., all of the STAs) within or using the IBSS may communicate directly with each other. The IBSS mode of communication may sometimes be referred to herein as an “ad- hoc” mode of communication. [0061] When using the 802.11ac infrastructure mode of operation or a similar mode of operations, the AP may transmit a beacon on a fixed channel, such as a primary channel. The primary channel may be a fixed width (e.g., 20 MHz wide bandwidth) or a dynamically set width via signaling. The primary channel may be the operating channel of the BSS and may be used by the STAs to establish a connection with the AP. In certain representative embodiments, Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) may be implemented, for example in in 802.11 systems. For CSMA/CA, the STAs (e.g., every STA), including the AP, may sense the primary channel. If the primary channel is sensed/detected and/or determined to be busy by a particular STA, the particular STA may back off. One STA (e.g., only one station) may transmit at any given time in a given BSS. [0062] High Throughput (HT) STAs may use a 40 MHz wide channel for communication, for example, via a combination of the primary 20 MHz channel with an adjacent or nonadjacent 20 MHz channel to form a 40 MHz wide channel. [0063] Very High Throughput (VHT) STAs may support 20MHz, 40 MHz, 80 MHz, and/or 160 MHz wide channels. The 40 MHz, and/or 80 MHz, channels may be formed by combining contiguous 20 MHz channels. A 160 MHz channel may be formed by combining 8 contiguous 20 MHz channels, or by combining two non-contiguous 80 MHz channels, which may be referred to as an 80+80 configuration. For the 80+80 configuration, the data, after channel encoding, may be passed through a segment parser that may divide the data into two streams. Inverse Fast Fourier Transform (IFFT) processing, and time domain processing, may be done on each stream separately. The streams may be mapped on to the two 80 MHz channels, and the data may be transmitted by a transmitting STA. At the receiver of the receiving STA, the above described operation for the 80+80 configuration may be reversed, and the combined data may be sent to the Medium Access Control (MAC). [0064] Sub 1 GHz modes of operation are supported by 802.11af and 802.11ah. The channel operating bandwidths, and carriers, are reduced in 802.11af and 802.11ah relative to those used in 802.11n, and 802.11ac.802.11af supports 5 MHz, 10 MHz and 20 MHz bandwidths in the TV White Space (TVWS) spectrum, and 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non- TVWS spectrum. According to a representative embodiment, 802.11ah may support Meter Type Control/Machine-Type Communications, such as MTC devices in a macro coverage area. MTC devices may have certain capabilities, for example, limited capabilities including support for (e.g., only support for) certain and/or limited bandwidths. The MTC devices may include a battery with a battery life above a threshold (e.g., to maintain a very long battery life). [0065] WLAN systems, which may support multiple channels, and channel bandwidths, such as 802.11n, 802.11ac, 802.11af, and 802.11ah, include a channel which may be designated as the primary channel. The primary channel may have a bandwidth equal to the largest common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be set and/or limited by a STA, from among all STAs in operating in a BSS, which supports the smallest bandwidth operating mode. In the example of 802.11ah, the primary channel may be 1 MHz wide for STAs (e.g., MTC type devices) that support (e.g., only support) a 1 MHz mode, even if the AP, and other STAs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16 MHz, and/or other channel bandwidth operating modes. Carrier sensing and/or Network Allocation Vector (NAV) settings may depend on the status of the primary channel. If the primary channel is busy, for example, due to a STA (which supports only a 1 MHz operating mode), transmitting to the AP, the entire available frequency bands may be considered busy even though a majority of the frequency bands remains idle and may be available. [0066] In the United States, the available frequency bands, which may be used by 802.11ah, are from 902 MHz to 928 MHz. In Korea, the available frequency bands are from 917.5 MHz to 923.5 MHz. In Japan, the available frequency bands are from 916.5 MHz to 927.5 MHz. The total bandwidth available for 802.11ah is 6 MHz to 26 MHz depending on the country code. [0067] FIG.1D is a system diagram illustrating the RAN 113 and the CN 115 according to an embodiment. As noted above, the RAN 113 may employ an NR radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 113 may also be in communication with the CN 115. [0068] The RAN 113 may include gNBs 180a, 180b, 180c, though it will be appreciated that the RAN 113 may include any number of gNBs while remaining consistent with an embodiment. The gNBs 180a, 180b, 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the gNBs 180a, 180b, 180c may implement MIMO technology. For example, gNBs 180a, 108b may utilize beamforming to transmit signals to and/or receive signals from the gNBs 180a, 180b, 180c. Thus, the gNB 180a, for example, may use multiple antennas to transmit wireless signals to, and/or receive wireless signals from, the WTRU 102a. In an embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, the gNB 180a may transmit multiple component carriers to the WTRU 102a (not shown). A subset of these component carriers may be on unlicensed spectrum while the remaining component carriers may be on licensed spectrum. In an embodiment, the gNBs 180a, 180b, 180c may implement Coordinated Multi-Point (CoMP) technology. For example, WTRU 102a may receive coordinated transmissions from gNB 180a and gNB 180b (and/or gNB 180c). [0069] The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using transmissions associated with a scalable numerology. For example, the OFDM symbol spacing and/or OFDM subcarrier spacing may vary for different transmissions, different cells, and/or different portions of the wireless transmission spectrum. The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using subframe or transmission time intervals (TTIs) of various or scalable lengths (e.g., containing varying number of OFDM symbols and/or lasting varying lengths of absolute time). [0070] The gNBs 180a, 180b, 180c may be configured to communicate with the WTRUs 102a, 102b, 102c in a standalone configuration and/or a non-standalone configuration. In the standalone configuration, WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c without also accessing other RANs (e.g., such as eNode-Bs 160a, 160b, 160c). In the standalone configuration, WTRUs 102a, 102b, 102c may utilize one or more of gNBs 180a, 180b, 180c as a mobility anchor point. In the standalone configuration, WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using signals in an unlicensed band. In a non-standalone configuration WTRUs 102a, 102b, 102c may communicate with/connect to gNBs 180a, 180b, 180c while also communicating with/connecting to another RAN such as eNode-Bs 160a, 160b, 160c. For example, WTRUs 102a, 102b, 102c may implement DC principles to communicate with one or more gNBs 180a, 180b, 180c and one or more eNode-Bs 160a, 160b, 160c substantially simultaneously. In the non-standalone configuration, eNode-Bs 160a, 160b, 160c may serve as a mobility anchor for WTRUs 102a, 102b, 102c and gNBs 180a, 180b, 180c may provide additional coverage and/or throughput for servicing WTRUs 102a, 102b, 102c. [0071] Each of the gNBs 180a, 180b, 180c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and/or DL, support of network slicing, dual connectivity, interworking between NR and E-UTRA, routing of user plane data towards User Plane Function (UPF) 184a, 184b, routing of control plane information towards Access and Mobility Management Function (AMF) 182a, 182b and the like. As shown in FIG.1D, the gNBs 180a, 180b, 180c may communicate with one another over an Xn interface. [0072] The CN 115 shown in FIG.1D may include at least one AMF 182a, 182b, at least one UPF 184a,184b, at least one Session Management Function (SMF) 183a, 183b, and possibly a Data Network (DN) 185a, 185b. While each of the foregoing elements are depicted as part of the CN 115, it will be appreciated that any of these elements may be owned and/or operated by an entity other than the CN operator. [0073] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 113 via an N2 interface and may serve as a control node. For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, support for network slicing (e.g., handling of different PDU sessions with different requirements), selecting a particular SMF 183a, 183b, management of the registration area, termination of NAS signaling, mobility management, and the like. Network slicing may be used by the AMF 182a, 182b in order to customize CN support for WTRUs 102a, 102b, 102c based on the types of services being utilized WTRUs 102a, 102b, 102c. For example, different network slices may be established for different use cases such as services relying on ultra-reliable low latency (URLLC) access, services relying on enhanced massive mobile broadband (eMBB) access, services for machine type communication (MTC) access, and/or the like. The AMF 162 may provide a control plane function for switching between the RAN 113 and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and/or non-3GPP access technologies such as WiFi. [0074] The SMF 183a, 183b may be connected to an AMF 182a, 182b in the CN 115 via an N11 interface. The SMF 183a, 183b may also be connected to a UPF 184a, 184b in the CN 115 via an N4 interface. The SMF 183a, 183b may select and control the UPF 184a, 184b and configure the routing of traffic through the UPF 184a, 184b. The SMF 183a, 183b may perform other functions, such as managing and allocating WTRU IP address, managing PDU sessions, controlling policy enforcement and QoS, providing downlink data notifications, and the like. A PDU session type may be IP-based, non-IP based, Ethernet-based, and the like. [0075] The UPF 184a, 184b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 113 via an N3 interface, which may provide the WTRUs 102a, 102b, 102c with access to packet- switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The UPF 184, 184b may perform other functions, such as routing and forwarding packets, enforcing user plane policies, supporting multi-homed PDU sessions, handling user plane QoS, buffering downlink packets, providing mobility anchoring, and the like. [0076] The CN 115 may facilitate communications with other networks. For example, the CN 115 may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN 115 and the PSTN 108. In addition, the CN 115 may provide the WTRUs 102a, 102b, 102c with access to the other networks 112, which may include other wired and/or wireless networks that are owned and/or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c may be connected to a local Data Network (DN) 185a, 185b through the UPF 184a, 184b via the N3 interface to the UPF 184a, 184b and an N6 interface between the UPF 184a, 184b and the DN 185a, 185b. [0077] In view of Figures 1A-1D, and the corresponding description of Figures 1A-1D, one or more, or all, of the functions described herein with regard to one or more of: WTRU 102a-d, Base Station 114a-b, eNode-B 160a-c, MME 162, SGW 164, PGW 166, gNB 180a-c, AMF 182a-b, UPF 184a-b, SMF 183a-b, DN 185a-b, and/or any other device(s) described herein, may be performed by one or more emulation devices (not shown). The emulation devices may be one or more devices configured to emulate one or more, or all, of the functions described herein. For example, the emulation devices may be used to test other devices and/or to simulate network and/or WTRU functions. [0078] The emulation devices may be designed to implement one or more tests of other devices in a lab environment and/or in an operator network environment. For example, the one or more emulation devices may perform the one or more, or all, functions while being fully or partially implemented and/or deployed as part of a wired and/or wireless communication network in order to test other devices within the communication network. The one or more emulation devices may perform the one or more, or all, functions while being temporarily implemented/deployed as part of a wired and/or wireless communication network. The emulation device may be directly coupled to another device for purposes of testing and/or may performing testing using over-the-air wireless communications. [0079] The one or more emulation devices may perform the one or more, including all, functions while not being implemented/deployed as part of a wired and/or wireless communication network. For example, the emulation devices may be utilized in a testing scenario in a testing laboratory and/or a non-deployed (e.g., testing) wired and/or wireless communication network in order to implement testing of one or more components. The one or more emulation devices may be test equipment. Direct RF coupling and/or wireless communications via RF circuitry (e.g., which may include one or more antennas) may be used by the emulation devices to transmit and/or receive data. [0080] CSI acquisition is a function in wireless communication systems that may be used to adapt the transmission scheme, such as transmitter precoding. The CSI acquisition may be based on the WTRU- reporting of CSI that is based on measurement of reference signals, e.g., CSI-RS. With a reconfigurable intelligent surface (RIS) in the radio environment, the CSI procedure may be extended to incorporate the adaptation of the RIS state in the presence of links (e.g., additional links) between WTRU-RIS and BS-RIS. [0081] In one or more examples herein, separated CSI acquisition(s) based on CSI-RS(s) may be enhanced to facilitate a link adaptation and/or the adaptation of a state of an RIS that has been deployed in a wireless communication system. The enhancements may involve WTRU(s), the RIS, and a base station. The performance for the communication links among the WTRU, the RIS, and/or network devices may be improved based on the separated channel estimates. In examples, a WTRU may be configured with CSI- RS(s) and/or RIS CSI. The WTRU may measure the CSI-RS(s) and/or compute an RIS differential channel. The WTRU may compute separated RIS channels. The WTRU may compute enhanced CSI reports, for example, using acquired differential and/or separated RIS channels and reports. Based on the CSI reports as feedback from the WTRU, the BS may configure/update system parameters (e.g., a precoder, modulation etc.) and an RIS state and/or indicate RIS state to the RIS. [0082] RIS-aided separated CSI acquisition may be described in one or more examples herein. For the RIS-aided separated channel acquisition, an example (e.g., a high-level procedure) may be described, to put the separated channel estimation approaches in context. Suitable CSI-RS enhancements may be used. CSI report enhancements may be proposed for RIS-aided differential channels. The RIS-aided differential channels may be enhanced to facilitate link adaptation and adaptation of the state of a reconfigurable intelligent surface (RIS) that has been deployed in a wireless communication system (e.g., while achieving enhanced communication performance). [0083] Separated channel reporting may be achieved by decomposing RIS-aided differential channel estimation (BS-RIS-WTRU), for example, to reduce CSI reporting overhead while maintaining the granularity of separate channels. For example, the BS-RIS path may need less frequent reporting than the RIS-WTRU path, which may save resources. In examples, a WTRU may receive configuration information associated with a reconfigurable intelligent surface (RIS), perform RIS-aided differential CSI measurement for the BS-RIS-WTRU channel using the configuration information, decompose the RIS-aided differential CSI measurement to be used for reporting separate RIS-WTRU path and BS-RIS path, and report the decomposed CSI measurement. The WTRU may send separate but linked CSI reports (e.g., each report comprising RIS parameters associated with the RIS-WTRU path and/or the BS-RIS path). The decomposition may be based on the configuration information. The RIS-aided differential CSI measurement may be based on varying RIS states. Single or multiple instances of RIS-aided CSI may be used to obtain individual RIS channels. A WTRU may iteratively improve/adapt estimated separated channels over multiple acquired RIS-aided CSI obtained over multi-instances of CSI-RS. A WTRU may estimate and/or update the separated channels after receiving a burst of differential channel instances (e.g., as opposed to doing so at every instance). CSI-RS(s) may be enhanced (e.g., adjusting the number and configuration of CSI-RSs for two RIS states). The WTRU may iteratively perform measurement(s) and decomposition(s) using one or more CSI instances. [0084] Separated channels may be estimated by utilizing differential channel/ RIS-aided channel and decomposing it into individual channel components. In a one-shot approach, a WTRU may utilize an instance (e.g., a single instance) of acquired RIS-aided CSI and decompose it to estimate the separated BS-RIS and RIS-WTRU channels. The WTRU may distinguish RIS-aided differential path and direct path based on set CSI-RS resource configuration indicating different CSI-RS resource IDs, density, periodicity, resources etc. In a multi-instance approach, a WTRU may utilize an iterative approach using single/multiple instances of RIS-aided CSI to obtain individual RIS channels. A WTRU may estimate RIS-aided channel and then utilize an iterative process using the same instance of acquired CSI to estimate separated channels. A WTRU may iteratively improve/adapt on estimated separated channels over multiple acquired RIS-aided CSI obtained over multi-instances of CSI-RS. A WTRU may estimate and/or update the separated channels after receiving a burst of differential channel instances (e.g., in contrast to at every instance). CSI-RS enhancements associated with the approaches herein may be used. The approaches herein may differ in performance, complexity and CSI-RS overhead and/or may be adapted based on specific target application(s). [0085] Reconfigurable intelligent surface (RIS) may be included in a wireless network, for example, due to its capability of configuring a wireless propagation environment. An RIS may include a planar surface comprising a large number of sub-wavelength sized scattering elements to form unit-cells (e.g., also referred to as RIS elements herein), whose response may alter (e.g., dynamically alter) the electromagnetic properties (e.g., phase and/or amplitude) of an impinging signal with an electronic RIS controller. For example, by properly optimizing the state of RIS elements, an impinging signal may be directed towards a desired receiver while improving communication performance, e.g., higher spectral efficiency, enhanced coverage, etc. Along with providing an improved wireless communication environment, RIS elements may support applications such as joint communication, sensing, and/or wireless power transfer. RIS elements may support features such as reflection, refraction, focusing, collimation, polarization, etc. An RIS may be classified as passive, semi-active, or active. A passive RIS may shift the phase of an impinging signals and may include multiple passive elements. A semi-active and/or active RIS may offer phase shift and/or amplification gains. A semi-active RIS may include a number of active elements (e.g., a mixture of active and passive elements), while an active RIS may include all active elements (e.g., only active elements). Active RIS elements may provide sensing capabilities (e.g., may be referred to as autonomous RIS). The phase shifts or amplification gains may be applied at the RIS on an individual element level and/or on the group of RIS elements (also known as sub-surface level). The electromagnetic properties of individual or group of RIS elements may be altered (e.g., dynamically altered) with an RIS controller. The RIS controller may be co-located with the RIS or located remotely, for example, at the BS. [0086] An RIS may be a type of network node. RIS aided communication may have three nodes (e.g., the BS, WTRU and RIS nodes). A communication path may exist via the RIS, e.g., BS-RIS-WTRU path referred as the RIS-aided path along with the legacy BS-WTRU direct communication path. In an RIS-aided communication, there may be multiple paths between the BS and the WTRU, e.g., a path via the RIS (RIS- aided path) and one or more paths contributing the BS-WTRU direct path. In the RIS-aided path, there may be multiple (e.g., two) separate channel components; the first communication channel component may be considered as the one between the BS and RIS (e.g., a BS-RIS channel). The second channel component may be between RIS and the WTRU (e.g., an RIS-WTRU channel). Estimating the two separate channel components (e.g., the BS-RIS channel and the RIS-WTRU channel), individually, may be referred to as separated RIS channel estimation. When the overall channel between the BS and WTRU is estimated that includes estimating the RIS-aided BS-RIS-WTRU composite channel, and the direct path’s BS-WTRU channel, it may be referred as cascaded RIS channel estimation. Estimating the RIS-aided BS-RIS-WTRU channel or path (e.g., only the RIS-aided BS-RIS-WTRU channel or path) may be referred to as differential channel estimation. With the presence of different communication channel paths in RIS-aided communication, different communication aspects (e.g., problems) including initial access, beamforming, control signaling, channel acquisition and CSI reports etc., may be updated to enable the RIS-aided communication path and support the introduction of an RIS in the network. Features across channel acquisition and CSI reporting to enable separated channel estimation in the RIS-aided communication scenario may be disclosed herein. [0087] The term RIS may denote the RIS itself, the RIS and RIS controller, or the RIS controller. It may be assumed that the BS can communicate with the RIS, e.g., using the NR air interface, in order to provide RIS with control information. Furthermore, the terms RIS unit-cells and RIS elements may be used interchangeably in this disclosure. [0088] An example RIS system may include at least one RIS element. An example RIS system may include multiple RIS elements of an RIS (e.g., of a single RIS). An RIS system may be described herein with respect to a downlink (DL) implementation, but the same or a similar model may be applicable to an uplink (UL) implementation. [0089] For simplicity, a single-antenna WTRU and a narrowband system (e.g., a subcarrier of an OFDM system) may be used in the examples provided herein. The examples may apply to cases with a multi- antenna WTRU such as a WTRU that may combine multiple received signals into a single received signal based on receiver processing (e.g., using analog, digital, or hybrid beamforming or combining techniques). In examples, such receiver processing may be included in a radio channel. [0090] An RIS system (e.g., an RIS system model) may include one RIS element of an RIS 200 (e.g., one of M RIS elements of the RIS), as illustrated in FIG.2. In at least this scenario, an example of an equivalent baseband received complex-valued scalar signal ^^_^ at a WTRU may be given by Equation 1 below. [0091] wherein s may represent a as a symbol, P may represent a complex-valued precoding vector of dimension NT×1 (e.g., NT may be the number of transmit antennas, for example, at a network-side transmission reception point (TRP) 201), ^^′ may represent a complex-valued channel between the TRP and the WTRU 202 (e.g., excluding propagation paths via an RIS of dimension’1× N_T), a’_m may represent a complex-valued vector channel between the TRP and the RIS element of dimension 1× N_T , ^^_^ may represent a complex-valued scalar RIS element factor of RIS element m, with m=1, …, M, bm may represent a complex-valued scalar channel between the RIS element and the WTRU, and z may represent additive noise and/or interference. [0092] In a passive RIS, factor ^^_^ may have a fixed amplitude, e.g., a unit amplitude (^| ^^_^ ^| ൌ 1). In an active or hybrid RIS, the amplitude may be variable and/or controllable. In some cases, e.g., for a passive RIS, an RIS element may be turned off (e.g., An RIS element may be in a certain state ( ^^_^) at a time and may be assumed to be applicable to one or more (e.g., all) sub-carriers within a certain bandwidth. [0093] The terms reference signal (RS) and pilot may be used interchangeably herein. In OFDM, an RS/pilot may include multiple (e.g., known) reference/pilot symbols. The reference/pilot symbols may be mapped to different sub-carriers and/or OFDM symbols. [0094] The example shown in FIG.2 may be simplified, for example, by including TRP precoding P into the TRP-to-RIS channel. Equation 2 below may be applicable in such a scenario: [0095] wherein d=d’P may represent a complex valued scalar effective direct TRP-to-RIS channel (e.g., including TRP precoding), a_m=a’_mP may represent a complex-valued scalar channel between the TRP and the RIS element, cm=bmam may represent a cascaded complex-valued scalar channel from the TRP to an m:th RIS element to the WTRU. [0096] An RIS system (e.g., an RIS system model) may include multiple RIS elements of an RIS (e.g., all M RIS elements of the RIS). Such a system may be established, for example, by including signals corresponding to the RIS elements (e.g., M RIS elements) of the RIS ( ^^_^ ^^_^ ^^ ) in the system, e.g., according to Equation 3 below: ^^ ൌ ^^ ^^ ^ ^^^ ^^ ^ ^^^ ^^ ^ ^^ ൌ ^ ^^ ^^ ^ ^^^ ^^ ^ ^^ (3) [0097] wherein a may represent a complex-valued vector channel between the TRP and the RIS, of dimension 1×M (e.g., M may be the number of RIS elements), b may represent a complex-valued vector channel between an RIS element and the WTRU (e.g., of dimension 1×M), c=a ^b may represent an element-wise (e.g., Hadamard) product of a and b, and Φ may represent a complex-valued vector of dimension M×1 containing the M RIS element factors ^^_^. Φ may correspond to an RIS state. [0098] In examples (e.g., with rectangular RIS), M_x may denote the number of RIS elements in a first direction (e.g., horizontal), My may denote the number of RIS elements in a second direction (e.g., vertical), and M may be equal to M_x*M_y. [0099] RIS element channels may be estimated. For example, to estimate the cascaded channel c and/or the direct channel ^^ in Equation 3, a network device may transmit a number of known pilot (reference) symbols s. Since c may include M elements and d may include one element, M+1 pilots may be used to estimate the channel coefficients. [0100] For simplicity of notation, the same pilot symbol s is assumed herein in M+1 occasions, but the pilot symbols may be different in different occasions (e.g., according to a certain complex-value sequence, as long as it is known by a WTRU). Received pilot symbols may be combined, e.g., in accordance with Equation 4 below: ^^ ൌ ^^ ^^ ^^ ^ ^^ (4) _{[0101] wherein ^^ ൌ ^} ^{^^} _^ ^{⋯ ^^} _{ெ^ may represent the M+1 received pilot symbols and ^^ ൌ ^ ^^ ^^^ may} represent a 1×(M+1) vector with a direct channel and M channels via the RIS. Θ may be equal to w_{here Φi may be an M×1 vector with RIS element factors during the i:th pilot symbol,} and Θ may be a square matrix with a dimension of ^^ ൈ 1. ^^ may be called an RIS estimation matrix. ^^ ൌ _^ ^{^^} _^ ^{⋯ ^^} _{ெ^ may represent a received noise and/or interference.} [0102] In examples (e.g., with Θ having a full rank known to the WTRU), the channels may be estimated based on ^^, e.g., in accordance with Equation 5 below. The channels may be estimated using a method such as one based on minimum mean square errors (MMSE). [0103] ^^ _^^ may be designed using different approaches. For example, in the on-off method described herein, RIS elements (e.g., all RIS elements) may be turned off (e.g., ^^_^ ൌ ^^ ^^ ^^ ^^_^ ^ ^^) during a pilot symbol such as a first pilot symbol. This may result in a received symbol such as in Equation 7. [0104] The direct channel d may be estimated by the WTRU. For example, during pilot symbols 1 to M, RIS elements may be turned on one-by-one (e.g., with other elements still turned off). This may result in a received i:th pilot symbol, for example, as in Equation 6. (6) [0105] may be zero (e.g., all zero), except that the i:th element may be equal to1. For example, ^^_^ may be equal to wherein 1 is an all-ones M-dimensional row vector and ^^_ெ is the identity matrix of dimension M. This presentation may assume that the RIS elements may be turned on in the order of RIS element indices, but those skilled in the art will understand that the elements may be turned on in other orders. [0106] In examples, ^^_^ may be vectors without elements equal to zero. This may mean that multiple (e.g., all) RIS elements may be turned on during pilot symbol transmissions. In examples, Θ may be a DFT matrix. In examples, Θ may be a Hadamard matrix. In at least these examples, ^^^{ି^} may be equal to ^^^் which may simplify implementation. [0107] An RIS-reflected aggregate channel may be estimated (e.g., cascaded channel estimation). The channel in Equation 3 includes the direct path d and the RIS-reflected aggregate channel ^^ ^^, e.g.., ^{^} ^^ ^^ ^ ^^^{^}. The aggregate channel ^^ ^^ may be scalar since it includes the aggregate (sum) of the RIS element reflections. The two components d and ^^ ^^ may be estimated based on two pilot symbols. During a first pilot, the RIS may be turned off, with a received pilot symbol, for example, as in Equation 7. ^^_^ ൌ ^^ ^^ ^ ^^_^ (7) [0108] The WTRU may estimate d, e.g., using a state-of-the-art channel estimation method. During a second pilot symbol, the RIS is turned on, with a certain RIS state ^^, e.g., as in Equation 8. ^^ _^^ ൌ ^{^} ^^ ^^ ^ ^^^{^} ^^ ^ ^^ _^^ ൌ ^^ ^^ ^ ^^ _^^ (8) [0109] The WTRU may estimate h, e.g., using a state-of-the-art channel estimation method. The WTRU may estimate the RIS-reflected aggregate channel ^^ ^^ based on the two pilots. [0110] Operation of sub-surfaces may be described herein. [0111] In examples, the number of RIS elements on an RIS may be high. Channel estimation and/or CSI reporting per RIS element may be costly, e.g., in terms of overheads and signaling. The cost may be reduced, for example, by introducing sub-surface-based estimation and reporting. The RIS elements may be distributed (e.g., grouped) into S sub-surfaces including, e.g., Sx horizontal elements and Sy vertical elements in a sub-surface. The distribution of the RIS elements into the sub-surfaces may be uniform (e.g., same number of RIS elements per sub-surface) or non-uniform (e.g., different numbers of RIS elements for different sub-surfaces). In the case of multi-panel RIS, a (e.g., each) panel may be considered a sub- surface, or a (e.g., each) panel may be divided into multiple sub-surfaces. FIGs.3A-3C illustrate examples of RIS element distribution into sub-surfaces. FIG.3A and FIG.3B illustrate examples of uniform distribution while FIG.3C illustrates an example of non-uniform distribution. In case where different RIS surfaces may be allocated to different users, the number of RIS elements or resources allocated to a user (e.g., a WTRU) may be increased or decreased (e.g., non-uniform RIS distribution may be used). A WTRU requiring more resources may be allocated a sub-surface with a bigger dimension (e.g., having more RIS elements) whereas a sub-surface with a smaller dimension (e.g., having fewer RIS elements) may be reserved for a WTRU with a less-stringent request. [0112] A system model of a sub-surface operation may be provided herein. [0113] The number of pilots for CSI and/or channel acquisition may be M+1 (e.g., in the case of elementwise RIS aggregated channel estimation). With increased RIS surface size, the computational complexity of the estimation process may increase tremendously, making the process of channel estimation inefficient and/or time-consuming. In examples, channel estimation may be performed by dividing and/or grouping RIS elements into smaller groups (e.g., which may be referred to herein as sub- surfaces) and performing the channel estimation at a sub-surface level. Such a sub-surface may include a set of one or more RIS elements. The distribution of RIS elements into sub-surfaces may be uniform or non-uniform. In the case of multi-panel RIS, a (e.g., each) panel may be considered a sub-surface, or a (e.g., each) panel may be further divided into multiple sub-surfaces. FIG.4. Illustrates an example of partitioning an RIS into six sub-surfaces (e.g., S=6). [0114] An RIS state may be configured at a sub-surface level (e.g., the same RIS element factor may be applied to the RIS elements in a sub-surface). Sub-surface level channel estimation may be performed by sending a (e.g., one) pilot per sub-surface (e.g., rather than a pilot per RIS element). By introducing the sub-surfaces, the dimension of the channel estimation problem may be reduced from M+1 to S+1 (e.g., in terms of pilot transmissions and/or computation). The on-off method and/or the on method described herein may be applied to sub-surfaces (e.g., instead of to individual RIS elements), for example, to reduce pilot overheads and/or channel estimation complexity. [0115] An RIS system described herein may be used to illustrate RIS operation based on sub-surfaces. Let Γ_^ denote a set of RIS element indices in the j:th sub-surface, with j=1, …, S. The union of sub-surfaces may include multiple (e.g., all) RIS element indices, e.g., ⋃_^ Γ_^ ൌ ^{^}1, … , ^^^{^}, and the sub-surface sets may be disjoint. Let ^^_^ be an M×1 vector with ones on the rows given by the indices in Γ_^, and zeroes elsewhere (e.g., the row indexing may start at 1 for convenience). The RIS elements in ^^_^ may be selected corresponding to the j:th sub-surface. _{[0116] Let ^^ ൌ ^} ^{^^} _^ ^{⋯ ^^} _{ௌ^ be a sub-surface selection matrix of dimension M×S. Equation 3 (e.g.,} which may represent a system model) may be written as Equation 9 below: ^_{^ ൌ} ^{^} _{^^ ^^ ^^} ^{^} _{^ ^^} ^{^} _{^^ ^ ^^ ൌ} ^{^} _^^ ^{^} _^^ ^{^} _{^ ^^} ^{^} _{^^ ^ ^^ (9)} wherein ^^^{^} may represent a complex-valued vector of dimension S×1 including the S sub-surface factors ^^_^ ^{^}, where factor ^^_^ ^{^} may be applied to the RIS elements in Γ_^, e.g., ^^_^ ൌ ^^_^ ^{^} ∀ ^^ ∈ Γ_^, and the same RIS element factor ^^_^ ^{^} may be applied to an (e.g., each) element in the j:th sub-Surface. ^^^{^} ൌ ^^ ^^ may represent a 1×S dimensional vector including S per sub-surface RIS-reflected aggregate channels (e.g., the j:th element of ^^^{^} may equal _[0117] ^{^} _^^ ^{^} _^^ ^{^} _{^ ^^} ^{^} _{in Equation 9 may have the same form as} ^{^} _{^^ ^^ ^ ^^} ^{^} _{in Equation 3, except for the} length of the vectors, which may be S in the former (e.g., representing the number of sub-surfaces) and M in the latter (e.g., representing the number of RIS elements). A method for channel estimation, CSI, etc. that may be applicable to per RIS element operation may be applicable to per sub-surface operation, and vice versa. [0118] For example, the description herein on RIS channel estimation may be applicable by changing the problem dimension by adding the s superscript. ^^ ൌ ^ ^^ ^^^{^}^ may be a 1 ൈ ^ ^^ ^ 1^ vector with the _{direct channel and the S channels via the RIS sub-Surfaces. ^^ ൌ where ^^^} ^{^} _may be the ^^ ൈ 1 vector with the RIS sub-surface factors during the i:th pilot symbol. ^^ may be a square matrix with dimension ^ ^^ ^ 1^ ൈ ^ ^^ ^ 1^. [0119] Differential CSI acquisition based on CSI-RS may be enhanced to facilitate link adaptation and adaptation of the state of a reconfigurable intelligent surface (RIS) that has been deployed in a wireless communication system. The WTRU, RIS, and base station may be enhanced. The communication link performance may be improved based on the acquired differential channel estimates. A WTRU may be configured with CSI-RS and RIS CSI. [0120] A WTRU may measure CSI-RS and compute an RIS differential channel. A WTRU may compute enhanced CSI reports using acquired differential RIS channels and reports. Based on the CSI reports as feedback from the WTRU, a base station (BS) may configure/update a precoder and RIS state and indicate the RIS state to the RIS. [0121] Features described herein may be associated with differential channel estimation. In an RIS- aided communication, in the case of downlink communication, the WTRU may receive data along (e.g., mainly along) two-paths that include the RIS-aided path (BS-RIS-WTRU path) and direct path (BS-WTRU path), which may include direct (BS-WTRU) channel component and multi-path fading components. The differential channel may be the effective RIS-aided channel path gain ( ^^) at the WTRU in the case of downlink transmission. Knowledge of a differential channel may benefit in evaluating the effect and performance of an RIS in the communication. The knowledge may be utilized in generating enhanced reports and link adaptation for the RIS-aided path. Obtaining differential channel coefficients may result in improved communication performance. [0122] The RIS-aided channel may be referred to as an RIS cascaded channel or an RIS-reflected aggregate channel. The terms differential channel, cascaded channel, and aggregate channel may be interchangeably used herein, and they may refer to the RIS-aided channel path. [0123] Features described herein may be associated with differential channel estimation. In differential channel estimation examples, it may be considered that an RIS surface is turned on during the pilot transmissions (e.g., all the pilot transmissions). The RIS state may be set elementwise, sub-surface wise, or a single state for a complete RIS as per the set radio resource control (RRC) configuration (see herein). For example, a single state of an RIS may be set in an orthogonal space which may be configured to belong to the codewords from (e.g., different) orthogonal dictionaries (e.g., Hadamard matrix, DFT etc.) during a set of pilot transmissions. The WTRU may be configured by the BS, and the BS may indicate the selected orthogonal dictionary for the RIS state and enable differential channel estimation at the WTRU end. [0124] If the RIS state is set to and a known pilot ^^ is transmitted by the transmitter (e.g., a BS in a case of downlink transmission), the received signal at the WTRU may be given by Equation 10. ^^_^ ൌ ^{^} ^^ ^^_^ ^ ^^^{^} ^^ ^ ^^_^ (10) [0125] If the RIS state is set to ^^ _^^, the received signal may be given by Equation 11. ^^_ଶ ൌ ^ ^^ ^^_ଶ ^ ^^^ ^^ ^ ^^_ଶ (11) [0126] The differential channel may be obtained by subtracting Equation 10 and Equation 11 as follows, ^_{^ଶ െ ^^^ ൌ ^^} ^{^} _{^^ଶ െ ^^^} ^{^} _{^^ ^ ^ ^^ െ ^^^ ^^ െ ^ ^^ଶ െ ^^^^} [0127] The estimated RIS-aided channel may be given in Equation 12: (12) [0128] The obtained differential channel gains ^^^ may be the resultant RIS-aided channel path that can be utilized (e.g., may be further utilized) for RIS specific performance analysis and reporting. [0129] In a case of sub-surface based channel estimation (e.g., as referred to herein), wherein the complete RIS is distributed into ^^ sub-surfaces, the differential channel for ^^-th sub-surface may be obtained in Equation 13: wherein, ^^_^,^ is the received signal at the WTRU, and the RIS state for ^^-th sub-surface is set to ^^_^,^ for ^^-th pilot transmission. One sub-surface may be turned-on at a given time, and/or the sub-surface state may be mutually orthogonal to each other. The effective additive noise and interference component ^ ^^_ଶ െ ^^_^^ may be compensated by using additive noise and interference cancellation methods. [0130] The effect of the direct channel path may not be explicitly captured under a presented example. The direct channel path may be calculated (e.g., calculated implicitly) by the WTRU utilizing the differential channel knowledge and the received signal. A case of the presented differential method may be considered wherein the direct channel path is exploited to obtain the differential channel ^^. In such a case, in one of the pilot transmissions (e.g., ^^ ൌ 1), RIS may be turned off ( ^^ _^^ ൌ 0), resulting in the received signal in Equation 14: ^^_^ ൌ ^^ ^^ ^ ^^_^ (14) [0131] In one of the pilot transmissions (e.g., ^^ ൌ 2), the RIS state may be set to ^^ _^^, and the received signal may be given in Equation 15: ^^_ଶ ൌ ^ ^^ ^^_ଶ ^ ^^^ ^^ ^ ^^_ଶ (15) The differential channel may be obtained, for example, as follows: ^_{^ଶ െ ^^^ ൌ} ^{^} _{^^ ^^ଶ ^ ^^} ^{^} _{^^ െ ^^ ^^ ^ ^^ଶ െ ^^^} ^^_ଶ െ ^^_^ ൌ ^ ^^ ^^_ଶ ^ ^^^ ^^ െ ^^ ^^ ^ ^^ [0132] In an example, if a WTRU is unaware of the presence of an RIS, a WTRU may measure the CSI for states 1 and 2 and report the CSI, e.g., as a legacy CSI reports to the BS. Utilizing the received reports from the WTRU for the RIS states (e.g., the two RIS states), the BS may compute the differential CSI. The BS may compute the channel quality indicators to perform the link adaptation and update the RIS state. [0133] In downlink transmission (e.g., associated with NR), the BS/TRP may transmit the CSI-RS that is used for the channel sounding. The WTRU may (e.g., with the CSI-RS) perform the measurements to estimate the quality of the channel based on the received reports (e.g., either implicitly and/or explicitly) by the WTRU. [0134] A first mode of DL CSI acquisition (e.g., associated with NR) may be based on a WTRU performing measurements on one or more CSI-RS and reporting corresponding CSI. A second mode of DL CSI acquisition (e.g., associated with NR) may be based on a WTRU transmitting a sounding reference signal (SRS), e.g., including antenna switching between antennas that may be used for DL reception, CSI measurement at the network side, and/or the assumption of UL/DL reciprocity (e.g., CSI estimated on the UL may be applicable to the DL). [0135] A WTRU may be configured to perform channel measurement and/or compute CSI using a CSI- RS resource, which may include one or multiple ports (e.g., antenna ports). One or multiple CSI-RS resources may be grouped into a CSI-RS resource set. A WTRU may be configured to perform interference and/or noise measurement on a CSI-RS resource for a CSI. A CSI-RS resource may be a non-zero power (NZP) CSI-RS resource, in which a WTRU may assume a certain RS being transmitted. A CSI-RS resource may be a CSI-RS resource for interference measurement, in which a WTRU may not assume a certain RS being transmitted. CSI-RS resources and resource sets may be, for example, non-zero power (NZP) CSI-RS resources and resource sets or interference measurement (IM) CSI-RS resources or resource sets. For brevity, the terms CSI-RS resource(s) and CSI-RS resource set(s) are used herein, which may refer to either NZP and/or IM CSI-RS resource(s) and resource set(s). [0136] A CSI-RS resource may be periodic, semi-persistent (e.g., which may be activated/deactivated), or aperiodic (e.g., which may be triggered). A WTRU may be configured with periodic, semi-persistent, or aperiodic CSI reporting. Periodic CSI reports may be transmitted on the PUCCH, while aperiodic CSI reports may be transmitted on the PUSCH. Semi-persistent CSI reports may be configured to be transmitted on the PUCCH or on a semi-persistent PUSCH. [0137] A CSI report may be based on channel measurements on a resource set, e.g., a CSI-RS resource set. A (e.g., each) channel measurement resource may be associated with an interference measurement resource and/or a non-zero power CSI-RS resource for interference measurement. [0138] A WTRU may report CSI corresponding to one or more resources in a resource set for channel measurement. If the resource set includes multiple resources, the WTRU may report a resource index, for example, to identify the corresponding resource used. Such a resource index may include a CSI-RS resource indicator (CRI) or an SSB resource indicator (SSBRI). [0139] In examples (e.g., if a multi-port CSI-RS is used as a channel measurement resource), a WTRU may be configured to compute one or more precoding matrix indicators (PMI), e.g., a wideband PMI and/or a number of sub-band PMIs. A PMI may, for instance, correspond to a precoding vector or matrix selected directly from a codebook. A PMI may include a combination (e.g., linear combination) of multiple precoding vectors or matrices from a codebook. [0140] A CSI report may include one or more channel quality indicators (CQI). If the CSI report includes a PMI, the CQI may correspond to a set of layers of the PMI. A CSI report may include a wideband CQI (e.g., if wideband PDSCH transmission is performed). A CSI report may include sub-band CQI (e.g., if sub- band PDSCH transmission is performed). [0141] A WTRU may receive one or multiple CSI-RS resources and may acquire the downlink CSI using the received CSI-RS resource set. The WTRU may perform measurements and report the acquired CSI based on the performed measurements (e.g., through PUCCH or PUSCH). [0142] If an RIS is present in the communication system, the RIS may introduce the phase shifts and amplification gains to the impinging signal based on the predefined/set RIS state, e.g., as configured by a controlling node (e.g., RIS controller, BS, WTRU, etc.), and reflect the impinging signal, for example in a direction, e.g., an intended direction). An RIS may be composed of RIS unit-cells (e.g., a large number of RIS unit-cells), which may be capable of (individually or jointly as a set of RIS elements) introducing the amplification gain/phase-shifts (or both). During the communication between the BS and WTRU, multiple channel components may exist (e.g., a direct path between the BS and WTRU and/or an RIS aided BS- RIS-WTRU path). To achieve improved communication quality, both these paths (e.g., BS-WTRU and/or BS-RIS-WTRU) may need to be optimized, e.g., by utilizing the CSI reports. Legacy reports measured (e.g., measured effectively) over the paths (e.g., all the paths) may not be efficient to optimize the RIS- aided BS-RIS-WTRU path. Utilizing the legacy reporting feedback, it may be difficult to infer the effect of the RIS-aided path. Methods for RIS-aided path channel estimation (e.g., differential channel) may be disclosed herein, wherein the channel estimation may be performed by the BS and/or WTRU. The differential channel may be utilized to optimize the BS-RIS-WTRU path through incorporating RIS-aided link adaptation (e.g., to update system parameters, such as precoder, modulation, etc.), RIS parameter adaptation (e.g., to update RIS state etc.), etc. [0143] A differential/cascaded channel for the RIS-aided BS-RIS-WTRU path may include an aggregate effect of some or all the RIS elements (e.g., as discussed in one or more examples herein related to a system model including all RIS elements) and have a dimensionality dependent on the number of antenna elements at the BS and WTRU. In some examples, with the presence of a large number of the RIS elements, the channel for individual paths (e.g., between BS-RIS and RIS-WTRU) may have a higher dimensionality as compared to the cascaded/differential RIS-aided channel (e.g., the BS-RIS-WTRU path). In one or more examples herein, the individual channels between BS-RIS and RIS-WTRU paths may be referred as separated channels. The high dimensional channels obtained from the separated channel estimation may be used to achieve an enhanced communication performance (e.g., as compared to utilizing only differential (BS-RIS-WTRU) channel). In examples, estimating separated channels may be used for achieving reliable solutions with an improved throughput. In certain applications when an RIS is static and either of the BS or WTRU is static as well, the gains from one of the channels among the BS-RIS and RIS-WTRU may remain constant while the other channel may be time-varying. In such cases, the separated channel estimation may be performed (e.g., only be performed) for the time-varying channel path, for example, to decrease the computational complexity as compared to estimating both separated channel paths. In some examples, as RIS may be assumed to be mostly passive node and may not be capable of baseband processing, the channel estimation may not be performed at an RIS node. Obtaining the separated channel estimates may be highly challenging in the case of passive RIS. In one or more examples herein, the channel estimation approaches for separated RIS channels are described, where the estimation can either be done at the BS or at the WTRU. The CSI reports may include the reporting of RI, PMI, CQI, etc. and more information used to capture the effect of the RIS state. [0144] The CSI estimation and reporting by the WTRU to the BS may be used by the BS for link adaptation, such as adjusting the BS transmission scheme, for example, in terms of one or more of: modulation and coding, multi-antenna precoding, or frequency domain resource allocation. Adjustments may pertain to improving the received signal quality, for example, precoding and frequency-selective scheduling. Adjustments may pertain to achieving a certain block error rate, e.g., modulation and coding scheme (MCS) selection. The estimated CSI and reporting may be utilized to update or adjust an RIS state. The adjustment of the RIS state may be more similar to precoder selection than MCS selection, e.g., the adjustment of the RIS state may improve the received signal quality. CSI procedures may not support CSI- based adjustments for RIS-aided communication. Enhancements in the NR CSI-reports may be disclosed herein, e.g., to incorporate the effect of an RIS-aided separated channels in the communication system. [0145] An RIS separated channel estimation may be performed in one or more examples herein. [0146] In one or more examples for a RIS-aided communication herein, independent channel gains between BS-RIS and RIS-WTRU may be referred as separated channels, whereas a cascaded channel is referred to as BS-RIS-WTRU channel gain(s). In some examples, the dimensionality of the RIS for cascaded channel(s) may be lost in an estimated channel (e.g., as the resultant channel gain depends only on base station antenna elements (e.g., gNB antenna elements) and WTRU antenna elements ( ^^_் ^^ ^^_ோ)). The granular knowledge of channel gain(s) over an (e.g., each) RIS element may provide better channel estimate(s), hence in examples, resulting in an enhanced communication performance. In some examples, the loss of the dimensionality in the cascaded channel(s) may become more pronounced (e.g., as a crucial factor) with increasing the dimension of an RIS. Separated channels estimation(s) can overcome the loss and/or capture information related to the loss, in some examples, resulting in high resolution channel estimate(s) between BS-RIS and RIS-WTRU paths. The passive nature of RIS may prohibit performing channel estimation(s) (e.g., a channel estimation at an RIS node), in some examples, making separated channel estimations challenging for the terminal nodes (e.g., a gNB or WTRU) or for the nodes responsible for separated channel estimation tasks. In one or more examples herein, multiple approaches for separated channel estimation are presented. An approach (e.g., a high-level procedure) for separated channel estimations is presented in one or more examples herein. Decomposition-based separated channel estimation approaches are discussed in one or more examples herein, where multiple estimation solutions may be discussed along with CSI-RS enhancements. CSI reporting enhancements for separated channel estimations are discussed in one or more examples herein. [0147] A system model for separated channel estimations may be provided herein. [0148] A system model for separated channel estimates or separate channel components may be used in an RIS-aided communication. FIG.5 illustrates an example of a system model representing RIS separated channels for MIMO transceivers in an RIS-aided downlink communication. A BS may transmit a pilot/reference signal to a WTRU, and the WTRU may perform the channel estimation in an RIS-aided MIMO downlink communication as shown in FIG.5. Using the system model as discussed in one or more examples herein (e.g., FIG.2), the channel between the BS and RIS may be ^^ of dimension ^ ^^_ோூௌ ^^ ^^_்^ and the channel between RIS and the WTRU may be ^^ of dimension ^{^}1 ^^ ^^_ோூௌ ^{^}. The composite channel between BS-RIS-WTRU may be provided in ^^^ᇱ ൌ ^^ ^^ ^^, wherein ^^ is an ^^-dimensional complex valued diagonal matrix representing an RIS state. P is the complex-valued precoding vector of dimension ^^_் ൈ 1 (e.g., at a network-side BS). [0149] The received signal at the WTRU may be obtained, for example, as in Equation 16. ^^ ൌ ^ ^^ ^ ^^^ ^^ ^ ^^ (16) [0150] Where ^^ is the additive noise component at the receiver node, ^^ ൌ ^^′ ^^ is the complex valued scalar effective direct BS-to-RIS channel (including BS precoding), ^^ ൌ ^^^ᇱ ^^ is the complex valued composite RIS-aided channel including BS precoding which can be given by ^^ ൌ ^^ ^^ ^^ ^^ ൌ ^^ ^^ ^^ ൌ ^^ ^^^ᇱ ^^ ൌ ^^ ^^ , such that ^^ ൌ ^^ ^^ ^^ ^^^ ^^^, ^^^ᇱ ൌ ^^ ^^ ^^ ^^^{^} ^^^{^} and, ^^ ൌ ^^ ^^ is the effective precoded channel gain between the BS and RIS of dimension ^^_ோூௌ ൈ 1. [0151] From the received signal ^^ in Equation 16, the differential channel ^^ may be estimated at first (e.g., by using Equation 12) to obtain the BS-RIS-WTRU channel gain, which can further be processed to obtain the separated channels utilizing one or more examples herein. [0152] An example approach (e.g., a high-level procedure) may be provided herein. [0153] FIG.6 illustrates an example of RIS separated channel acquisition and RIS reporting. A system that operates according to FIG.6 may include one or multiple TRPs, one or multiple base stations (e.g., gNB), one or multiple RISs, and one or multiple users. In one or more examples herein, a gNB, a WTRU, and an RIS may operate according to FIG.6.601-609 of FIG.6 are described in one or more examples herein. The example of FIG.6 starts at 601. At 602, an RIS may report its capability to a BS as discussed in one or more examples herein related to RIS capability reporting. At 603 (e.g., following 602), the BS may configure RIS as discussed in one or more examples herein related to BS configuration of RIS. Based on the capability reporting from the RIS, the BS may configure the WTRU at 604 as discussed in one or more examples herein related to BS configuration of WTRU. At 605, the WTRU may perform CSI measurements to compute the RIS differential CSI acquisition and, at 606, report as discussed in one or more examples herein related to WTRU differential channel estimation and/or reporting. At 607 (e.g., following 606), the WTRU may perform separated RIS channel acquisition by decomposing the RIS differential channel as discussed in one or more examples herein related to WTRU separated channel estimation. At 608, the WTRU may report RIS separated CSI reports as discussed in one or more examples herein related to WTRU separated CSI reporting. Based on the CSI reports from the WTRU, the BS may modify or update one or more system parameters including precoding, modulation, RIS state setting etc. At 609, the RIS may utilize set/ updated RIS state during UL/DL transmissions as discussed in one or more examples herein related to RIS operation during DL/UL channel/signal transmission. [0154] FIG.7 illustrates an example of a signaling diagram for RIS separated channel estimation. Additional signaling may be used in various examples, and some signaling in FIG.7 may be omitted in various examples. First, in 701, RIS capability is signaled to the BS (7001), e.g., as discussed in one or more examples herein related to RIS capability reporting. This is followed by the BS configuring the WTRU (7002) in 702, e.g., as discussed one or more examples herein related to the BS configuration of a WTRU. In 703 the BS configures the RIS (7000), e.g., as discussed in one or more examples herein related to BS configuration of RIS. This is followed by RIS CSI measurement, as discussed in one or more examples herein related to WTRU differential channel estimation and/or reporting, which may involve the BS transmitting CSI-RS in 704. In the case of semi-persistent or aperiodic CSI-RS, corresponding activation or triggering signaling may be used. The BS may indicate to the RIS to use a particular RIS state during some times, e.g., to use a specific set of RIS phase shifts or to use a sub-surface level RIS state during the symbols during which CSI-RS for RIS CSI are transmitted. This is referred as RIS state scheduling in FIG. 7. The BS may configure the RIS in a state (e.g., set RIS state or for that instance the RIS may be turned off indicating the first RIS state as illustrated FIG.7, 705), following which the BS may indicate in 706 the CSI-RS to WTRU while triggering/setting in 707 the RIS into another RIS state (e.g., shown as RIS state 1 in FIG.7). Following the RIS CSI measurement and/or computation, the WTRU may report CSI (e.g., the legacy CSI and/or differential RIS CSI) to the BS in 708, as discussed in one or more examples herein related to WTRU differential channel estimation and/or reporting. Based on the RIS CSI report, the network may perform an RIS parameter update or change in an RIS configuration (e.g., changing sub-surface level to element level configuration, change in RIS element resolution etc.). In the case of semi-persistent or aperiodic CSI-RS or CSI reporting, corresponding activation or triggering signaling may be used. Following this, the WTRU may perform the separated CSI acquisition and/or send the separated CSI reports to the BS, as discussed in one or more examples herein related to WTRU separated channel estimation and WTRU separated CSI reporting, respectively. This may be followed by DL and UL transmissions 709, e.g., PDSCH and/or PUSCH. [0155] RIS capability reporting may be performed herein. [0156] Different kinds or classes of RISs may be supported in a network. For example, RISs in a network may differ, for example, in terms of one or more of the following: the number of RIS elements (e.g., M); an RIS design/architecture (e.g., rectangular, single array, circular, fluid, etc.); the range and/or resolution of RIS element amplification(s) and phase shift(s) (e.g., a range may comprise a minimum and/or maximum value, e.g., for RIS element amplification; a resolution may comprise a step size between ^{supported values, e.g., within a range, and for example, a phase shift resolution of may be supported} for an exemplary RIS. A resolution/range capability may list the supported values); sub-surface and parameter interpolation capability(ies); type(s) of the RIS (e.g., passive, semi-active, active, etc., including possibly different type(s) for transmitting versus receiving). An RIS with active elements may report the number of active elements and the properties of the active elements (e.g., their position(s) on an RIS (surface), associated RF chains, etc). An RIS may report on the function support which can be provided by active element(s) (e.g., channel estimation, signal decoding, etc.). [0157] A RIS capability may comprise a set of parameters related to one or more aspects that may differ among RISs. A RIS class may comprise one or more capabilities. A RIS may connect to the network and/or report its capabilities and/or class (e.g., class 1, class 2, etc.) to the network, (e.g., as in 602 in FIG.6). In some examples, the capabilities/class may be signaled (e.g., using an RRC message). In some examples, a different interface may be used for a communication between an RIS and a BS. [0158] A BS may configure an RIS in one or more examples herein. [0159] A RIS may be configured by the network, e.g., by a BS or gNB, as illustrated in 603 in FIG.6. The configuration may be an RRC configuration. The configuration may be communicated to the RIS in a manner, for example, similar to how a WTRU is configured (e.g., using RRC signaling). In some examples where RIS state(s) is set by an RIS controller, the BS may communicate the RRC configuration to the RIS controller, which may further set/ update the RIS state(s). [0160] The configuration parameters may include one or more of the following: a sub-surface or elementwise RIS configuration, for example, the number of sub-surfaces (e.g., S), the number of RIS elements per sub-surface, etc.; a time-domain configuration, which may indicate time instance(s) when a RIS configuration is to be used, for example, a time-domain behavior (e.g., periodic or semi-persistent, etc.; periodicity, time offset, etc.); a configuration of the range(s) and/or resolution(s) for RIS element and/or sub-surface factors (e.g., amplification/phase-shifts), e.g., in the form of one or more codebooks, or one or more numbers of bits (e.g., the number of bits used to cover the range of phase shifts); one or more RIS states and/or RIS state IDs that may be associated with one or more sub-surface configurations; in the case of the presence of active RIS elements, active element configuration. [0161] Active element configuration may include one or more of the following: information about the RIS function support that may be set based on the configuration (e.g., channel estimation, signal decoding etc.) using active RIS elements; active element ID(s) to be utilized for a specific task; configuration information including one or more of an RIS active element state, amplification gains, etc.; RIS CSI resource configuration indicating the resource ID, periodicity etc.; an RIS configuration trigger for the transmission and/or reception of the CSI resources using active elements. The trigger may be initialized (e.g., similar to the legacy NR) such as periodic, semi-persistent or aperiodic setting etc. [0162] Active element configuration may not be configured in some cases, for example, when an RIS surface is operating in a passive mode (e.g., even in presence of active elements). When active elements are not configured, RIS active elements may be configured based on a configuration for passive RIS element (e.g., being similar to the passive RIS element configuration). In examples, when an RIS includes some of the active elements that are associated with the RF chains capable of baseband processing (e.g., instead of including only passive RIS elements), the RIS may perform tasks such as channel estimation, decoding etc. [0163] A BS may configure WTRU(s). [0164] The network (e.g., a BS) may configure WTRU(s) with parameters related to RIS CSI features (e.g., enhancement features), for example, as illustrated at 604 in FIG.6, using one or more of the following: a WTRU configuration (e.g., including one or more of the parameters of the RIS as discussed at 603 of FIG.6 and can be detailed in one or more examples herein, for example, information about a sub- surface configuration may be useful for a WTRU for various RIS CSI parameter computations, and information about an active RIS element configuration may be useful for a WTRU for CSI acquisition task. For instance, in the case of RIS separated channel estimation, the WTRU may use the active element position(s) on an RIS (surface) to compute and extrapolate channel gains); a CSI reporting configuration (e.g., a legacy CSI reporting configuration), for example, including CQI reporting; an enhanced CSI reporting configuration, for example, including one or more RIS parameters, one or more updated link adaptation parameters, e.g., as described in one or more examples herein related to reporting enhancements for separated channels herein; a CSI resource configuration (e.g., a legacy CSI resource configuration); separate report configuration(s) to indicate the periodicity (e.g., periodic, semi-persistent, aperiodic) of the CSI reports for BS-RIS and RIS-WTRU separated channels (e.g., each BS-RIS and RIS- WTRU separated channel) (e.g., the configuration may indicate the specific RIS-aided CSI reports (e.g., CQI, PMI, RIS-QI, etc.), for a separate channel (e.g., each of the separated channels)); an enhanced RIS CSI resource configuration e.g., as discussed in one or more examples herein related to decomposition- based separated channel estimation. [0165] A WTRU may perform differential channel estimation and/or reporting. [0166] Based on a WTRU configuration, a WTRU may receive RSs, perform measurements, and/or compute CSI which may include complete CSI (e.g., as described in or more examples herein related to CSI acquisition in RIS-aided communication systems) and/or differential CSI (e.g., as described in or more examples herein related to differential channel estimation), e.g., at 605 in FIG.6. [0167] Based on its configuration, the WTRU may report the CSI to the network, e.g., in one or more PUCCH transmissions, or in one or more PUSCH transmissions. RIS parameters in the CSI report (e.g., as 608 in FIG.6) may include differential channel specific indicators, such as differential PMI, differential RI, etc., for example, along with other RIS indicators. The RIS CSI may be included in an UL control information (UCI) or in a MAC control element (CE). In examples, RIS parameters and other CSI parameters (e.g., legacy CSI parameters, such as CQI, PMI, RI, etc.) may be included in the same report. In some examples, a CSI report may include RIS parameters (e.g., only RIS parameters). [0168] A WTRU may perform separated channel estimation. [0169] Based on its configuration, a WTRU may perform separated channel measurements utilizing the RSs received from a BS and/or from RIS active element(s) and/or compute separated channel estimates (e.g., in 607 in FIG.6). [0170] For example, the WTRU may estimate RIS-WTRU path channel gains based on the CSI-RS resource(s) received from RIS active elements. For separated channel estimation performed using RSs from a BS, the WTRU may utilize decomposition techniques as discussed in one or more examples herein related to decomposition-based separated channel estimation. In some examples, the WTRU may perform separated channel estimation utilizing partial CSI from the BS. [0171] A WTRU may carry out separated CSI reporting. [0172] Based on its configuration, a WTRU may include separated CSI indicators (e.g., separated RIS CSI indicators) in a CSI report to the network (e.g., as at 608 in FIG.6). The separated RIS CSI may be included in UL control information (UCI) or in a MAC control element (CE). The CSI report may include one or more RIS separated CSI parameters as discussed in one or more examples herein related to reporting enhancements for separated channels. Based on a configuration set by the BS, the WTRU may report separated channel(s) with different periodicity/ frequency. For example, the WTRU may report the BS-RIS CSI with a higher frequency as compared to the frequency at which the WTRU reports the RIS-WTRU CSI. One or more the following may be performed at the WTRU and/or BS (e.g., to ensure an association between two separated channel reports): a WTRU may associate a unique report ID with both of the separated CSI reports (e.g., for BS-RIS channel and RIS-WTRU channel), which may then be referenced by the BS to identify the associated channel links based on the set report configuration; the association may be provided from the BS, e.g., as part of a CSI measurement and/or reporting configuration (e.g., two CSI reporting configurations may be linked by RRC configuration; two separate CSI reports may be configured in a CSI reporting configuration); a WTRU may include the unique report ID in one part of the separated channel report, and, for example, a WTRU may include the associated report ID for the BS-RIS channel report in the RIS-WTRU channel report, which may then be utilized by the network to identify the respective reports. [0173] For differential and separated RIS CSI acquisition, the estimation and reporting features may be combined or may be executed separately. [0174] An RIS operation may be performed during a DL/UL channel/signal transmission. [0175] The network may indicate to/configure the RIS to use a set RIS state during DL/UL transmissions (e.g., subsequent DL/UL transmissions), for example, by configuring/indicating/triggering/activating a time- domain configuration for the RIS state that overlaps in time with one or more of the DL/UL transmissions. DL transmissions may include one or more of PDCCH, PDSCH, CSI-RS, tracking RS (TRS), positioning RS (PRS) etc. UL transmissions may include one or more of PUCCH, PUSCH, sounding RS etc. The use of a certain RIS state may be dynamically indicated (e.g., as at 609 in FIG.6), for example, since DL/UL transmissions may be dynamic. [0176] An example WTRU procedure for separated channel estimation (e.g., a high-level WTRU procedure for RIS separated channel estimation) is shown in FIG.8. [0177] One or more of the blocks in FIG.8 may follow the example in FIG.6. Some of the blocks in FIG. 8 may be omitted based on the capability. For example, a WTRU may report one of the differential CSI or separated CSI or both, based on the WTRU capability. [0178] The example in FIG.8 starts at 801. At 802, a WTRU is configured e.g., as discussed in one or more examples herein related to the BS configuration of a WTRU which includes configurations for RIS CSI. This is followed by the WTRU measurements and computation of RIS CSI and/or differential channel CSI at 803, e.g., as discussed in one or more examples herein related to WTRU differential channel estimation and/or reporting. The WTRU may report RIS CSI and/or differential CSI reports including differential PMI etc., to report the quality of the RIS-aided path at 804. This may be followed by a CSI measurement (e.g., a legacy CSI measurement) at 805 and reporting at 806, e.g., including CQI, PMI etc. In the case of semi-persistent or aperiodic CSI-RS or CSI reporting, corresponding activation or triggering signaling may be used. Following this, at 807, the WTRU may perform measurements and RIS separated channel estimation e.g., by decomposing the acquired differential channel estimates (e.g., as discussed in one or more examples herein related to decomposition-based separated channel estimation). The WTRU may report the separated channel reports at 808, for example, as discussed in one or more examples herein related to CSI report enhancements. This may be followed by DL reception and UL transmission, e.g., PDSCH and/or PUSCH, at 809. [0179] An example RIS procedure for separated channel estimation (e.g., a high-level RIS procedure for RIS separated channel estimation) is shown in FIG.9. One or more of the blocks in FIG.9 may follow the example in FIG.6. In examples, an RIS may be configured based on the capability reporting to the BS. Once the RIS is configured, the RIS may apply the passive RIS configuration, for example, if there are no active elements in the RIS surface or active elements are not indicated to be set as active elements. The RIS may use the passive RIS configuration for an RIS CSI acquisition and for DL/UL transmission. If the RIS surface consists of active elements that can be utilized and the RIS configuration setting includes active RIS elements, the RIS may apply the active RIS configuration during CSI-RS for RIS CSI acquisition. The RIS may use active RIS elements for RIS CSI-RS for separated RIS CSI acquisition and for DL/UL transmissions. [0180] Separated channel estimation may be decomposition-based. [0181] Separated channels can be estimated by utilizing the estimated differential channel and decomposing it into independent channel components using one or more techniques like eigen decomposition, sparse signal processing etc. A one-shot approach may be used where, for example, decomposed separated channels are obtained utilizing a single instance of the differential channel, or an iterative approach may be used where, for example, the decomposed separated channels are obtained iteratively over multiple differential channel instances. A difference between the one-shot and iterative approach may include the utilization of the number of pilots required for separated channel estimation versus the estimation accuracy of the estimated channels. Both types of approaches including CSI-RS enhancements that support these approaches are discussed in one or more examples herein, and the example procedure are discussed in one or more examples herein. [0182] A one-shot approach may include one or more features (e.g., enhancement features). In an example one-shot approach, CSI-RS resource(s) may be communicated to a WTRU to acquire a single instance of an RIS-aided channel. For example, a WTRU may receive a resource (e.g., only a single CSI- RS resource) if a complete RIS is considered as one sub-surface or it may require M CSI-RS resources (e.g., where M may be the number of sub-surfaces or the number of elements) to be transmitted and measured at the WTRU. Based on the received CSI-RS (e.g., the single instance of received CSI-RS), the WTRU may acquire an RIS-aided path and perform the decomposition into separate RIS channels. [0183] In a one-shot approach, a WTRU may firstly acquire the RIS-aided CSI (e.g., for the BS-RIS- WTRU path) based on the received reference signals e.g., CSI-RS(s) transmitted by a BS in case of a downlink transmission. As an example, consider using CSI-RS(s) as the pilot for RIS channel estimation and CSI acquisition, M CSI-RS resources may be used to acquire RIS-aided CSI (e.g., for the BS-RIS- WTRU path), where M is the number of sub-surfaces (or RIS elements in some cases). In examples, the M CSI-RS resources may be included in a CSI-RS resource set. The M CSI-RS resources may be included in multiple CSI-RS resource sets. The CSI-RS resources may be single-port or multi-port (e.g., dual-port). A WTRU may first acquire the RIS-aided channel using M CSI-RS resources and then decompose the RIS- aided channel to estimate the separated BS-RIS and RIS-WTRU channels in a single instance. The WTRU can perform this estimation in a single instance by using decomposition techniques such as eigen- decomposition, singular value decomposition (SVD)-based decomposition, etc. [0184] For example, consider a similar system model as discussed in one or more examples herein related to a system model for separated channel estimation as shown in FIG.5. From Equation 16,, the BS-RIS-WTRU channel is given by Equation 17. ^^ ൌ ^^ ^^’ (17) [0185] Considering the SVD on the RIS-aided channel ^^, it can be given as Equation 18. ^^ ൌ ^^ ^^ ^^ ^{^^} (18) [0186] Comparing Equation 17 and Equation 18, it may be considered that ^^ ൌ ^^ ^^ and ^^’ ൌ ^^ ^{^^}. To estimate the separated channels, the following pair of equations may be used. ^^ ^^ ^{^^} ൌ ^^ ^^ ^^ ^{^^} ^^ ^^ ^{^^} ^^^ு ൌ ^^ ^^ ^{^^} ^^^ு [0187] And ^^ ^{^^} ^^ ൌ ^^ ^^ ^{^^} ^^^ு ^^ ^^ ^^ ^{^^} ൌ ^^ ^^ ^{^^} ^^ ^{^^} [0188] Performing Eigen decomposition of each of ^^ ^^ ^{^^} and ^^ ^{^^} ^^, ^^, ^^, and ^^ can be obtained, which can effectively result in separated channels as ^^ ൌ ^^ ^^ and ^^’ ൌ ^^ ^{^^}. [0189] Through this approach, separated channels can be estimated (e.g., directly) by knowing/acquiring an instance (e.g., only one instance) of the RIS-aided channel. In some examples, this type of estimation approach may reduce the CSI-RS resource overhead, similar to the differential channel acquisition approach. [0190] FIG.10 illustrates an example for a one-shot decomposition. The example in FIG.10 may illustrate an RIS separated channel acquisition and/or RIS reporting using a one-shot decomposition-based approach. The exemplary procedure may contain one or multiple TRPs, one or multiple base stations e.g., gNB, one or multiple RISs, and one or multiple users, which may be configured for a channel acquisition task in an RIS- aided communication.1001-1005 of FIG.10 may be described in FIG.6, corresponding to 601-605 in FIG. 6, respectively. At 1006, based on the acquired RIS-aided channel, the WTRU may decompose the RIS- aided channel using one or more decomposition techniques herein and/or estimate the separated BS-RIS and RIS-WTRU channel components. The WTRU may then report the separated RIS CSI reports (e.g., as described in one or more examples herein related to reporting enhancements for separated channels) along with other RIS-aided channel (e.g., differential channel reports and/or legacy reports) as illustrated, at 1007. [0191] FIG.11 illustrates an example signaling diagram for a one-shot decomposition. Additional signaling may be used in various scenarios, for example, when sub-surface based or elementwise RIS configuration may be used or when the WTRU reporting may be varied based on NR specifications such as periodic, semi- persistent, aperiodic etc. Some signaling in FIG.11 may be omitted in various examples. [0192] An iterative/ multi-instance decomposition approach may include one or more features (e.g., enhancements). [0193] Separated channels may be estimated iteratively or over multiple RIS-aided channel acquisition instances. While considering using CSI-RS as the pilot for RIS channel estimation, a set of multiple resources (e.g., N representing the number of iterations required) consisting of M CSI-RS resources may be used to acquire RIS-aided CSI (e.g., for the BS-RIS-WTRU path), where M is the number of sub-surfaces (or RIS elements in some cases). For example, this may be followed in but not limited to one or more examples herein. [0194] There may be an iterative method, where, for example, in downlink CSI acquisition, a WTRU may estimate RIS-aided channel r and then utilize an iterative process using the same instance of acquired CSI of r to estimate separated channels. As an example, the channel estimation may be structured as an iterative optimization problem wherein both the separated channels are obtained iteratively while minimizing the difference between the estimated differential channel and differential channel computed from separated channel components. Let the estimated RIS-aided channel be ^^ such that ^^ ൌ ^^ ^^ ^^ , the separated ^{channel can be estimated by solving the minimization problem as below:} [0195] There may be an iterative method where, for example, in downlink CSI acquisition, a WTRU may iteratively improve/adapt on estimated separated channels over multiple acquired RIS-aided CSI obtained over multi-instances of CSI-RS. As an example, the separated channels may be estimated by considering a respective channel component (e.g., each channel component) as a random variable and then adjusting the components with an (e.g., each) acquired instance of differential channel. One of the techniques that may be utilized to achieve this is, for example, using a gradient descent approach. An initial estimation of separated channels ^^ _^^, ^^ _^^ may be performed e.g., using a one-shot method, then at the later instances, the estimates may be improved/adjusted iteratively using a gradient which can be calculated as in Equation 19 and/or Equation 20. [0197] where ^^ ^^ ൌ ^{^^௬^} ^_{^ ^^} [0198] A WTRU may estimate and/or update the separated channels, for example, after a burst of differential channel instances ^^, for example, in contrast to at every instance. In that case, Equation 19 and Equation 20 may be updated as Equation 21 and Equation 22, respectively. ^^ _^^ ൌ ^^ _{^^ି ^^} ^ ^^ ^^, (21) [0201] The periodicity of estimating and/or updating the separated channels may be configured at the WTRU. In examples, this estimation periodicity may be the same as the RIS separated CSI reporting periodicity as configured by the network. The WTRU may utilize some or all of the received signals between two periodic instances (e.g., (k+1 to 2k)) to obtain the gradients Δ ^^,Δ ^^, which may then be utilized to update the separated channel estimates at the set instance. The gradients may for example be calculated as below: ∑^{ଶ^} Δ _{^^ ൌ} ^{1 ^^ ^ୀ^ା^ ^^ ^} ^_{^ ^^ ^^} [0202] and, [0203] In examples (e.g., as a direct approach), in a downlink CSI acquisition, a WTRU may first acquire multiple instances of RIS-aided CSI and then utilize the acquired channels to estimate the separated channels. For example, the WTRU may acquire the separated channels by using the statistical knowledge gained over the multiple instances. Based on the previously acquired statistical knowledge and/or measurements, the WTRU may indicate/request for more instances of CSI-RS for preforming a number of iterations of acquiring the separated channels. The differential channel (e.g., as given in Equation 3) may be restructured to form a set of linear equations with unknown separated channel components as variables. These equations may be solved by first acquiring the required number of differential channel instances as the number of variables and then be solved, for example, using stochastic approaches, to obtain the separated channel components. [0204] FIG.12 illustrates an example for iterative/multi-instance decomposition-based separated channel estimation. The example in FIG.12 illustrates RIS separated channel acquisition and RIS reporting using iterative/multi-instance decomposition-based approach(es). The example in FIG. 12 may include one or multiple TRPs, one or multiple base stations e.g., gNB, one or multiple RISs, and one or multiple users, which may be configured for channel acquisition task(s) in an RIS-aided communication.1201-1206 of FIG.12(a) and/or (b) may be described in FIG.10, corresponding to 1000-1006 in FIG.10, respectively. At 1207, based on the approach used, the WTRU may decide or may be indicated by the BS, whether to further perform measurements to acquire RIS-aided CSI before computing the final separated channels. This may further be decided, for example, in the scenario where separated channels estimation is a secondary task but is important enough for improving a channel quality. In this scenario, the WTRU may compute RIS-aided channels to further acquire separated channels. In some examples, an RIS state may remain the same while the decision for requiring more iterations has been made or is being made. In such case, when more iterations or more instances are used, 1204 to 1206 in FIG.12(a) may be repeated, as illustrated in FIG.12(a). In some examples, it is possible that the RIS state is varied between iterations or instances. If this happens, BS (or the RIS controlling unit) may signal the updated RIS state to the WTRU, utilizing which the WTRU may acquire the RIS aided channel in that iteration/ instance. To enable this, when more iterations are used, steps 1205 to 1206 of FIG.12(b) may be repeated, as illustrated in FIG.12(b). For the examples shown in FIG. 12(a) or (b), if no further iterations or instances are required, the WTRU may then report the separated CSI reports (e.g., along with other RIS-aided channel and/or legacy reports) as configured by the network, as illustrated at 1208 for FIG.12(a) or (b), respectively. [0205] FIG. 13 illustrates an example signaling diagram for a multi-instance decomposition-based approach. Additional signaling may be used in various scenarios, for example, when a sub-surface based or elementwise RIS configuration may be used or when the WTRU reporting may be varied based on NR specifications such as periodic, semi-persistent, aperiodic etc. Some signaling in FIG.13 may be omitted in various examples. [0206] A number of CSI-RS resources may be used to perform the channel estimation (e.g., N number of CSI-RS resources), for example, to achieve the separated channel estimation using iterative/multi-instance decomposition-based separated channel estimation. FIG.14 illustrates an example of CSI-RS configuration (e.g., enhancement) for iterative/multi-instance separated channel estimation using decomposition. These CSI-RS resource sets (e.g., with N resources per set) may be transmitted in the same slot as shown in FIG. 14, where, each resource set is considered to be the size of number of CSI-RS resources required. In some examples, the required CSI-RS resource sets may be spread across multiple slots that may be consecutive or at preconfigured positions, or the same CSI-RS resource set that periodic or is with multiple repetitions in an aperiodic manner (e.g., as NR aperiodic (AP) CSI-RS). [0207] Features described herein may be associated with CSI report enhancements. In examples, during downlink transmission, a WTRU may perform measurements and CSI acquisition by utilizing the received pilot/reference signals transmitted by the gNB. Based on these measurements, in a case of transmissions in frequency-division duplexing (FDD), the WTRU may report (e.g., explicitly or implicitly) the quality of a channel by explicitly transmitting the CSI, e.g., as channel coefficients, and/or implicitly, in the form of the CSI reports, e.g., RI, PMI, CQI etc. When transmissions occur in time-division duplexing (TDD), the gnB may exploit the reciprocity of the communication channel and obtain the channel estimates itself. The gNB may use the CSI reports and/or channel estimates to adjust/update the system parameters, such as a type of precoder, modulation, code rate etc. In the RIS-aided communication system, an RIS-aided CSI may be exploited to adjust/update the RIS parameters, e.g., an RIS state and RIS-aided path parameters at a gNB (e.g., codebook and precoder selection for BS-RIS-WTRU path). The CSI report enhancements for RIS-aided system are disclosed herein for separated channels. [0208] Reporting separated channels may be carried out using one or more of the following (e.g., enhancements). [0209] In a case of separated channels, two communication links may be used (e.g., a channel via a BS- RIS path and a channel via a RIS-WTRU path). A WTRU may perform measurements based on the received pilots from a BS in a case of a downlink transmission, for example, to acquire these separated channels. The WTRU may generate independent CSI reports and/or joint CSI reports and communicate the reports to the BS, for example, to indicate the quality of these separated channels. To enable the RIS separated channel reporting, one or more of the following may be used. [0210] A WTRU may send (or indicate) individual or independent reports (e.g., each for a BS-RIS channel and a RIS-WTRU channel). The independent reports may contain the same set of parameters (e.g., indicators) or different sets of parameters. For example, the WTRU may report PMI for the BS-RIS channel, whereas it may report PMI, RI, and CQI for the RIS-WTRU channel. A BS may configure the parameters to be reported in one or more of the reports herein based on the scenario or application (e.g., based on different performance requirements for different applications). [0211] The BS may configure the parameters (e.g., the independent report parameters) to be reported at the same or different periodicities. In examples, the WTRU may send the RIS-WTRU channel report(s) more frequently than the BS-RIS channel report(s). [0212] The WTRU may send or indicate the preferred set of periodicities for reporting CSI respective to individual separated channels (e.g., BS-RIS channel(s) and/or RIS-WTRU channel(s)) and/or for a joint CSI report. For example, the WTRU may request a greater periodicity for reporting a WTRU-RIS channel as compared to reporting for a BS-RIS channel. In some examples, the WTRU may send a request for on- demand CSI reporting for the RIS separated channels. [0213] In a case of independent reporting, the WTRU may be configured to send CSI report(s) for one (e.g., only one) of the separated channels. For example, the WTRU may send CSI report(s) for a RIS- WTRU channel and may not send CSI report(s) for a BS-RIS channel. [0214] In a case of joint CSI report(s) for both of the separated channels, the WTRU may indicate parameters (e.g., performance indicators) as a set (e.g., PMI for a BS-RIS channel, PMI for a RIS-WTRU channel). The index, presence and/or order for a report (e.g., each channel report) may be configured in a report configuration (e.g., a WTRU report configuration) by the BS. In some examples, a WTRU may report the parameters (e.g., CSI performance indicators) as a function of indicators, for example, instead of explicitly reporting the CSI performance indicators for separated channels. In examples, a WTRU may communicate PMI for a BS-RIS channel and PMI for an RIS-WTRU channel as a function for example a linear function, compression algorithms, etc., for example, instead of communicating the PMI for the BS- RIS channel and PMI for the RIS-WTRU channel. The function may be configured from a predefined set of functions by the BS, for example, in the report configuration. The overhead for CSI reporting may be reduced. An example on how the BS can identify the PMI using a linear equation is as below: [0215] Consider that the maximum index achievable in PMI p. Then, the following linear function can be utilized by the WTRU for reporting the combined or joint PMI. ^^^ ^^, ^^^ ൌ V ൌ ^ ^^ ^ 1^ ^^ ^ ^^, [0216] where, ^^ indicates the PMI for a BS-RIS path/channel and ^^ represents the PMI for an RIS- WTRU path/channel. The value for ^^ can then be obtained as and the value of ^^ can then be computed [0217] A WTRU may send (e.g., only send) the separated CSI reports, or it may send separated CSI reports with other information (e.g., legacy and/or differential RIS-aided CSI reports). The report required to be reported by the WTRU may be configured by the BS through RRC message(s), for example, based on one or more of the following: the WTRU capabilities (e.g., if the WTRU is capable of performing separated channel estimation), application(s) (e.g., enhanced Mobile Broadband (eMBB), Ultra Reliable Low Latency Communications (URLLC)), and scenario(s) (e.g., a mobile WTRU with static BS and RIS nodes). In some examples, codebooks (e.g., codebook(s) that captures the RIS related parameters such as resolution of each RIS element, or at a sub-surface level, directivity etc.) that enable RIS-aided communication may be used. [0218] In examples, a WTRU may be configured with, e.g., receive via RRC signaling, configuration information that indicates one or more RIS-related parameters, corresponding CSI-RS resource(s), and/or other RIS-related configuration parameters, such as the number of sub-surfaces or elements in the x- and y-direction. The WTRU may be configured with a CSI report configuration indicating one or more reporting parameters corresponding to the type of CSI report (e.g., legacy and/or differential and/or separated), report periodicity, reporting functions, etc. The WTRU may receive an indication of (e.g., configuration information indicating) of a set of CSI-RS resources for a set of RIS states, e.g., that were configured at the RIS by the BS/RIS controller/ WTRUs in the network/RIC, etc. The WTRU may receive CSI-RS resource(s). The WTRU may measure and compute the differential channel. The WTRU may report the differential channel report(s), e.g., if the WTRU is configured to do so in a report configuration. The WTRU may compute the separate BS-RIS and RIS-WTRU channels. The WTRU may report separated channel CSI report(s) if configured in the report configuration. [0219] In examples, an RIS may report its capability to the network/ RIS controlling node. The RIS may be configured with an elementwise or sub-surface configuration. The RIS may apply a sub-surface configuration during time instances determined by configuration/activation/indication/triggering. The RIS may receive an RIS-element level RIS state. The RIS may apply an RIS-element level RIS state during configured time instances determined by configuration/activation/indication/triggering. [0220] FIG.15 is a flow chart of a method 1500, implemented by a WTRU, according to an embodiment. In 1501, the method may comprise receiving, from the network, configuration information that indicates a channel state information (CSI) resource and information associated with separate reporting for a base station -reconfigurable intelligent surface (BS-RIS) channel and a RIS-WTRU channel; In 1502, the method may comprise measuring a BS-RIS-WTRU channel using the indicated CSI resource; In 1503, the method may comprise determining separated CSI for the BS-RIS channel and the RIS-WTRU channel based on the measurement of the BS-RIS-WTRU channel; and In 1504, the method may comprise transmitting the separated CSI for the BS-RIS channel and the RIS- WTRU channel to the network. [0221] According to an embodiment of the method, the method may comprise, when measuring the BS- RIS-WTRU channel using the indicated CSI resource, performing a differential CSI measurement by varying RIS states, and determining the separated CSI for the BS-RIS channel and the RIS-WTRU channel based on the differential CSI measurement. [0222] According to an embodiment of the method, the configuration information may comprise different reporting periodicities for the BS-RIS channel and the RIS-WTRU channel, and the method may comprise transmitting the separated CSI for the BS-RIS channel and the RIS-WTRU channel to the network using the different reporting periodicities. [0223] According to an embodiment, the configuration information may comprise information associated with a decomposition of the measurement for the BS-RIS-WTRU channel, and the method may comprise determining the separated CSI for the BS-RIS channel and the RIS-WTRU channel by decomposing the measurement of the BS-RIS-WTRU channel based on the information associated with the decomposition. [0224] According to an embodiment, the method may comprise iteratively performing, using one or more CSI instances, a CSI measurement and a decomposition of the CSI measurement. [0225] There is also disclosed a WTRU in a network, the WTRU comprising at least one processor. The at least one processor may be configured to: receive, from the network, configuration information that indicates a channel state information (CSI) resource and information associated with separate reporting for a base station -reconfigurable intelligent surface (BS-RIS) channel and a RIS-WTRU channel; measure a BS-RIS-WTRU channel using the indicated CSI resource; determine separated CSI for the BS-RIS channel and the RIS-WTRU channel based on the measurement of the BS-RIS-WTRU channel; and transmit the separated CSI for the BS-RIS channel and the RIS-WTRU channel to the network. [0226] According to an embodiment, the at least one processor may be configured to perform, when measuring the BS-RIS-WTRU channel using the indicated CSI resource, a differential CSI measurement by varying RIS states, and to determine the separated CSI for the BS-RIS channel and the RIS-WTRU channel based on the differential CSI measurement. [0227] According to an embodiment, the configuration information may comprise different reporting periodicities for the BS-RIS channel and the RIS-WTRU channel, and wherein the at least one processor is configured to transmit the separated CSI for the BS-RIS channel and the RIS-WTRU channel to the network using the different reporting periodicities. [0228] According to an embodiment, the configuration information comprises information associated with a decomposition of the measurement for the BS-RIS-WTRU channel, and wherein the at least one processor is configured to determine the separated CSI for the BS-RIS channel and the RIS-WTRU channel by decomposition of the measurement of the BS-RIS-WTRU channel based on the information associated with the decomposition. [0229] According to an embodiment, the at least one processor is further configured to, using one or more CSI instances, iteratively perform a CSI measurement and a decomposition of the CSI measurement. [0230] Although features and elements described above are described in particular combinations, each feature or element may be used alone without the other features and elements of the preferred embodiments, or in various combinations with or without other features and elements. [0231] Although the implementations described herein may consider 3GPP specific protocols, it is understood that the implementations described herein are not restricted to this scenario and may be applicable to other wireless systems. For example, although the solutions described herein consider LTE, LTE-A, New Radio (NR) or 5G specific protocols, it is understood that the solutions described herein are not restricted to this scenario and are applicable to other wireless systems as well. [0232] The processes described above may be implemented in a computer program, software, and/or firmware incorporated in a computer-readable medium for execution by a computer and/or processor. Examples of computer-readable media include, but are not limited to, electronic signals (transmitted over wired and/or wireless connections) and/or computer-readable storage media. Examples of computer- readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as, but not limited to, internal hard disks and removable disks, magneto-optical media, and/or optical media such as compact disc (CD)-ROM disks, and/or digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, terminal, base station, RNC, and/or any host computer. [0233] Although features and elements are provided above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations may be made without departing from its spirit and scope, as will be apparent to those skilled in the art. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly provided as such. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods or systems. [0234] In some example embodiments described herein, (e.g., configuration) information may be described as received by a WTRU from the network, for example, through system information or via any kind of protocol message. Although not explicitly mentioned throughout embodiments described herein, the same (e.g., configuration) information may be pre-configured in the WTRU (e.g., via any kind of pre- configuration methods such as e.g., via factory settings), such that this (e.g., configuration) information may be used by the WTRU without being received from the network. [0235] Any characteristic, variant or embodiment described for a method is compatible with an apparatus device comprising means for processing the disclosed method, such as with a device comprising a processor configured to process the disclosed method, a computer program product comprising program code instructions and a non-transitory computer-readable storage medium storing program instructions. [0236] The foregoing embodiments are discussed, for simplicity, with regard to the terminology and structure of infrared capable devices, i.e., infrared emitters and receivers. However, the embodiments discussed are not limited to these systems but may be applied to other systems that use other forms of electromagnetic waves or non-electromagnetic waves such as acoustic waves. [0237] It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used herein, the term "video" or the term "imagery" may mean any of a snapshot, single image and/or multiple images displayed over a time basis. As another example, when referred to herein, the terms "user equipment" and its abbreviation "UE", the term "remote" and/or the terms "head mounted display" or its abbreviation "HMD" may mean or include (i) a wireless transmit and/or receive unit (WTRU); (ii) any of a number of embodiments of a WTRU; (iii) a wireless-capable and/or wired-capable (e.g., tetherable) device configured with, inter alia, some or all structures and functionality of a WTRU; (iii) a wireless-capable and/or wired-capable device configured with less than all structures and functionality of a WTRU; or (iv) the like. Details of an example WTRU, which may be representative of any WTRU recited herein, are provided herein with respect to FIGs.1A-1D. As another example, various disclosed embodiments herein supra and infra are described as utilizing a head mounted display. Those skilled in the art will recognize that a device other than the head mounted display may be utilized and some or all of the disclosure and various disclosed embodiments can be modified accordingly without undue experimentation. Examples of such other device may include a drone or other device configured to stream information for providing the adapted reality experience. [0238] In addition, the methods provided herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer. [0239] Variations of the method, apparatus and system provided above are possible without departing from the scope of the invention. In view of the wide variety of embodiments that can be applied, it should be understood that the illustrated embodiments are examples only, and should not be taken as limiting the scope of the following claims. For instance, the embodiments provided herein include handheld devices, which may include or be utilized with any appropriate voltage source, such as a battery and the like, providing any appropriate voltage. [0240] Moreover, in the embodiments provided above, processing platforms, computing systems, controllers, and other devices that include processors are noted. These devices may include at least one Central Processing Unit ("CPU") and memory. In accordance with the practices of persons skilled in the art of computer programming, reference to acts and symbolic representations of operations or instructions may be performed by the various CPUs and memories. Such acts and operations or instructions may be referred to as being "executed," "computer executed" or "CPU executed." [0241] One of ordinary skill in the art will appreciate that the acts and symbolically represented operations or instructions include the manipulation of electrical signals by the CPU. An electrical system represents data bits that can cause a resulting transformation or reduction of the electrical signals and the maintenance of data bits at memory locations in a memory system to thereby reconfigure or otherwise alter the CPU's operation, as well as other processing of signals. The memory locations where data bits are maintained are physical locations that have particular electrical, magnetic, optical, or organic properties corresponding to or representative of the data bits. It should be understood that the embodiments are not limited to the above-mentioned platforms or CPUs and that other platforms and CPUs may support the provided methods. [0242] The data bits may also be maintained on a computer readable medium including magnetic disks, optical disks, and any other volatile (e.g., Random Access Memory (RAM)) or non-volatile (e.g., Read-Only Memory (ROM)) mass storage system readable by the CPU. The computer readable medium may include cooperating or interconnected computer readable medium, which exist exclusively on the processing system or are distributed among multiple interconnected processing systems that may be local or remote to the processing system. It should be understood that the embodiments are not limited to the above- mentioned memories and that other platforms and memories may support the provided methods. [0243] In an illustrative embodiment, any of the operations, processes, etc. described herein may be implemented as computer-readable instructions stored on a computer-readable medium. The computer- readable instructions may be executed by a processor of a mobile unit, a network element, and/or any other computing device. [0244] There is little distinction left between hardware and software implementations of aspects of systems. The use of hardware or software is generally (but not always, in that in certain contexts the choice between hardware and software may become significant) a design choice representing cost versus efficiency tradeoffs. There may be various vehicles by which processes and/or systems and/or other technologies described herein may be effected (e.g., hardware, software, and/or firmware), and the preferred vehicle may vary with the context in which the processes and/or systems and/or other technologies are deployed. For example, if an implementer determines that speed and accuracy are paramount, the implementer may opt for a mainly hardware and/or firmware vehicle. If flexibility is paramount, the implementer may opt for a mainly software implementation. Alternatively, the implementer may opt for some combination of hardware, software, and/or firmware. [0245] The foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams, flowcharts, and/or examples. Insofar as such block diagrams, flowcharts, and/or examples include one or more functions and/or operations, it will be understood by those within the art that each function and/or operation within such block diagrams, flowcharts, or examples may be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In an embodiment, several portions of the subject matter described herein may be implemented via Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), and/or other integrated formats. However, those skilled in the art will recognize that some aspects of the embodiments disclosed herein, in whole or in part, may be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and or firmware would be well within the skill of one of skill in the art in light of this disclosure. In addition, those skilled in the art will appreciate that the mechanisms of the subject matter described herein may be distributed as a program product in a variety of forms, and that an illustrative embodiment of the subject matter described herein applies regardless of the particular type of signal bearing medium used to actually carry out the distribution. Examples of a signal bearing medium include, but are not limited to, the following: a recordable type medium such as a floppy disk, a hard disk drive, a CD, a DVD, a digital tape, a computer memory, etc., and a transmission type medium such as a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link, etc.). [0246] Those skilled in the art will recognize that it is common within the art to describe devices and/or processes in the fashion set forth herein, and thereafter use engineering practices to integrate such described devices and/or processes into data processing systems. That is, at least a portion of the devices and/or processes described herein may be integrated into a data processing system via a reasonable amount of experimentation. Those having skill in the art will recognize that a typical data processing system may generally include one or more of a system unit housing, a video display device, a memory such as volatile and non-volatile memory, processors such as microprocessors and digital signal processors, computational entities such as operating systems, drivers, graphical user interfaces, and applications programs, one or more interaction devices, such as a touch pad or screen, and/or control systems including feedback loops and control motors (e.g., feedback for sensing position and/or velocity, control motors for moving and/or adjusting components and/or quantities). A typical data processing system may be implemented utilizing any suitable commercially available components, such as those typically found in data computing/communication and/or network computing/communication systems. [0247] The herein described subject matter sometimes illustrates different components included within, or connected with, different other components. It is to be understood that such depicted architectures are merely examples, and that in fact many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality may be achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated may also be viewed as being "operably connected", or "operably coupled", to each other to achieve the desired functionality, and any two components capable of being so associated may also be viewed as being "operably couplable" to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components. [0248] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. [0249] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, where only one item is intended, the term "single" or similar language may be used. As an aid to understanding, the following appended claims and/or the descriptions herein may include usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim including such introduced claim recitation to embodiments including only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should be interpreted to mean "at least one" or "one or more"). The same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B." Further, the terms "any of" followed by a listing of a plurality of items and/or a plurality of categories of items, as used herein, are intended to include "any of," "any combination of," "any multiple of," and/or "any combination of multiples of" the items and/or the categories of items, individually or in conjunction with other items and/or other categories of items. Moreover, as used herein, the term "set" is intended to include any number of items, including zero. Additionally, as used herein, the term "number" is intended to include any number, including zero. And the term "multiple", as used herein, is intended to be synonymous with "a plurality". [0250] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group. [0251] As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein may be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as "up to," "at least," "greater than," "less than," and the like includes the number recited and refers to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth. [0252] Moreover, the claims should not be read as limited to the provided order or elements unless stated to that effect. In addition, use of the terms "means for" in any claim is intended to invoke 35 U.S.C. §112, ¶ 6 or means-plus-function claim format, and any claim without the terms "means for" is not so intended.

Claims

CLAIMS What is Claimed: 1. A wireless transmit/receive unit (WTRU) in a network, comprising at least one processor configured to: receive, from the network, configuration information that indicates a channel state information (CSI) resource and information associated with separate reporting for a base station -reconfigurable intelligent surface (BS-RIS) channel and a RIS-WTRU channel; measure a BS-RIS-WTRU channel using the indicated CSI resource; determine separated CSI for the BS-RIS channel and the RIS-WTRU channel based on the measurement of the BS-RIS-WTRU channel; and transmit the separated CSI for the BS-RIS channel and the RIS-WTRU channel to the network. 2. The WTRU of claim 1, wherein the at least one processor is configured to perform, when measuring the BS-RIS-WTRU channel using the indicated CSI resource, a differential CSI measurement by varying RIS states, and to determine the separated CSI for the BS-RIS channel and the RIS-WTRU channel based on the differential CSI measurement. 3. The WTRU of claim 1, wherein the configuration information comprises different reporting periodicities for the BS-RIS channel and the RIS-WTRU channel, and wherein the at least one processor is configured to transmit the separated CSI for the BS-RIS channel and the RIS-WTRU channel to the network using the different reporting periodicities. 4. The WTRU of claim 1, wherein the configuration information comprises information associated with a decomposition of the measurement for the BS-RIS-WTRU channel, and wherein the at least one processor is configured to determine the separated CSI for the BS-RIS channel and the RIS-WTRU channel by decomposition of the measurement of the BS-RIS-WTRU channel based on the information associated with the decomposition. 5. The WTRU of claim 1, wherein the at least one processor is further configured to, using one or more CSI instances, iteratively perform a CSI measurement and a decomposition of the CSI measurement. 6. A method, implemented by wireless transmit/receive unit (WTRU) in a network, the method comprising: receiving, from the network, configuration information that indicates a channel state information (CSI) resource and information associated with separate reporting for a base station -reconfigurable intelligent surface (BS-RIS) channel and a RIS-WTRU channel; measuring a BS-RIS-WTRU channel using the indicated CSI resource; determining separated CSI for the BS-RIS channel and the RIS-WTRU channel based on the measurement of the BS-RIS-WTRU channel; and transmitting the separated CSI for the BS-RIS channel and the RIS-WTRU channel to the network. 7. The method of claim 6, wherein the method comprises, when measuring the BS-RIS-WTRU channel using the indicated CSI resource, performing a differential CSI measurement by varying RIS states, and determining the separated CSI for the BS-RIS channel and the RIS-WTRU channel based on the differential CSI measurement. 8. The method of claim 6, wherein the configuration information comprises different reporting periodicities for the BS-RIS channel and the RIS-WTRU channel, and wherein the method comprises transmitting the separated CSI for the BS-RIS channel and the RIS-WTRU channel to the network using the different reporting periodicities. 9. The method of claim 6, wherein the configuration information comprises information associated with a decomposition of the measurement for the BS-RIS-WTRU channel, and the method comprises determining the separated CSI for the BS-RIS channel and the RIS-WTRU channel by decomposing the measurement of the BS-RIS-WTRU channel based on the information associated with the decomposition. 10. The method of claim 6, wherein the method comprises, iteratively performing, using one or more CSI instances, a CSI measurement and a decomposition of the CSI measurement.