EP4659368A1 - Methods for full-duplex operation-based separated channel estimation and sounding for reconfigurable intelligent surfaces - Google Patents

Abstract

A method for full duplex operation based separated channel estimation is provided. A wireless transmit/receive unit (WTRU) may receive configuration information from a base station (BS) that includes one or more of a channel state information (CSI) report configuration, a reconfigurable intelligent surface (RIS)-related parameter, one or more CSI reference signals (CSI-RS) resources, and/or a number of sub-surfaces. The WTRU may measure a RIS-WTRU channel associated with the received configuration information. The WTRU may send a differential CSI report including first CSI associated with a RIS-aided channel to the base station. The WTRU may receive a BS-RIS CSI report from the base station. The WTRU may send a separated CSI report to the base station. The separated CSI report may include second CSI associated with the RIS-WTRU channel and third CSI associated with the BS-RIS channel. The WTRU may communicate with the base station using the RIS-aided channel.

Description

METHODS FOR FULL-DUPLEX OPERATION-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. 63/443,133 filed February 3, 2023, which is incorporated herein by reference in its entirety. FIELD [0002] Example embodiments are generally directed to the fields of communications, software and/or encoding, including, for example, to methods, architectures, apparatuses, and/or systems related to separated channel estimation and sounding for reconfigurable intelligent surfaces. BACKGROUND [0003] Reconfigurable intelligent surface (RIS) may be a promising technology of future wireless network due to its capability of configuring the wireless propagation environment. RIS may be a planar surface comprising a large number of sub-wavelength sized scattering elements to form unit-cells (also called RIS elements herein), whose response may be tuned to dynamically alter the electromagnetic properties (e.g., phase and amplitude) of the impinging signal with an electronic RIS controller. Thus, by properly optimizing the state of RIS elements, the impinging signal may be directed towards the desired receiver while improving communication performance, e.g., higher spectral efficiency, enhanced coverage, etc. Along with providing an improved wireless communication environment, RIS may support applications such as joint communication and sensing and wireless power transfer. RIS elements may support one or many features such as reflection, refraction, focusing, collimation, polarization etc. RIS may be classified as passive, semi-active or active RIS. Passive RIS shifts (e.g., only shifts) the phase of the impinging signals and comprises one or more (e.g., all) the passive elements while the semi-active and active RIS may offer both phase shift and amplification gains and may respectively comprises one or more active elements. Active elements may also provide sensing capabilities. The phase shifts or amplification gains may be applied at the RIS on an individual element level 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 dynamically altered with the help of RIS controller. The RIS controller may be co- located with RIS or located remotely for example at the network or base station (BS). [0004] As RIS may be considered a new type of network node, the RIS aided communication may be assumed to have three nodes namely the BS, the wireless transmit / receive unit (WTRU) and the RIS nodes. Thus, there exist a new communication path via the RIS i.e., BS-RIS-WTRU path namely referred as the RIS-aided path along with the legacy BS-WTRU direct communication path. Similar to the legacy multi-path transmission, in a 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. Further in the RIS-aided path, there are two separate channel components; the first communication channel component may be considered as the one between the BS and RIS i.e., BS-RIS channel while, the second channel component may be between RIS and the WTRU, i.e., RIS-WTRU channel. Estimating the two separate channel components i.e., BS-RIS and RIS-WTRU, individually, may be referred to as separated RIS channel estimation. Whereas, when the overall channel between the BS and WTRU may be 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. Further, the case of estimating (e.g., only estimating) the RIS-aided BS-RIS-WTRU path may be referred as differential channel estimation. In the presence of different communication channel paths in RIS-aided communication, different communication problems including initial access, beamforming, control signaling, channel acquisition and channel state information (CSI) reports etc., need to be updated to enable the RIS-aided communication path and support the introduction of RIS in the network. In this disclosure, we discuss the ideas across channel acquisition and CSI reporting to enable separated channel estimation in the RIS- aided communication scenario. [0005] Herein, the term RIS may denote the RIS itself, the RIS and RIS controller, or the RIS controller. The BS may communicate with the RIS, e.g., using the new radio (NR) air interface, in order to provide RIS with control information. Furthermore, the terms RIS unit-cells and RIS elements may be used interchangeably. SUMMARY [0006] CSI acquisition may be an important function in wireless communication systems that may be used to adapt the transmission scheme, such as transmitter precoding. The CSI acquisition may be often based on the WTRU-reporting of CSI that may be based on measurement of reference signals, e.g., CSI reference signal (CSI-RS). With the introduction of a reconfigurable intelligent surface (RIS) in the radio environment, the CSI procedure needs to be extended to incorporate the adaptation of the RIS state in the presence of additional links between WTRU-RIS and BS-RIS. [0007] In some example embodiments, a method for RIS separated CSI acquisition may be defined. For RIS-aided separated channel acquisition, a method may be provided to put into context the proposed separated channel estimation, along with CSI-RS enhancements. CSI report enhancements may be provided for RIS-aided separated channels that are enhanced to facilitate link adaptation and adaptation of the state of an RIS that has been deployed in a wireless communication system. [0008] In some example embodiments, a method of network operation may be defined having one or more of the following may be provided: a WTRU is configured with RRC indicating one or more RIS-related parameters, corresponding CSI-RS resource(s) and other RIS-related configuration parameters; a WTRU configured with CSI report configuration indicating one or more reporting parameters corresponding to the type of CSI report, report periodicity, reporting functions etc.; a WTRU receiving the CSI-RS for a set of RIS states that were configured at the RIS by the BS / RIS controller / WTRUs in the network / RAN intelligent controller (RIC) / etc.; a WTRU receives CSI-RS resource(s); a WTRU measures and computes the differential channel; a WTRU reporting the differential channel reports based on report configuration; a WTRU determining the separate BS-RIS and RIS-WTRU channels; and a WTRU reporting separated channel CSI report(s) based on the report configuration. [0009] In some example embodiments, a method of network operation may be defined having one or more of the following: an RIS may report its capability to the network / RIS controlling node; an RIS may be configured with an element-wise or sub-surface configuration; an RIS may apply sub-surface configuration during time instances determined by configuration / activation / indication / triggering; an RIS may receive a RIS-element level RIS state; and an RIS may apply RIS-element level RIS state during configured time instances determined by configuration / activation / indication / triggering. [0010] In some example embodiments, a method for full duplex operation based separated channel estimation within a network is provided. The method may include transmitting of CSI-RS and acquiring a RIS channel via the CSI-RS directed towards RIS. First RIS channel estimates are sent to the WTRU, and RIS-aided differential channel estimates are determined based on the first RIS channel estimates so as to estimate a RIS-WTRU channel. In embodiments, the CSI-RS may include a first set of CSI-RS resources having RIS state configured to reflect back to a transmitting node within the network. Further, a second set of CSI-RS resources may be used by the WTRU to estimate a differential RIS-aided channel. In embodiments, the frequency of determining estimates of the RIS-WTRU channel may be configured to be different than the frequency of acquiring the RIS channel. [0011] In some example embodiments, a method for full duplex operation based separated channel estimation is provided. A WTRU may receive configuration information from a base station (BS). The configuration information may include one or more of a channel state information (CSI) report configuration, a reconfigurable intelligent surface (RIS)-related parameter, one or more CSI reference signals (CSI-RS) resources, and/or a number of sub-surfaces. The WTRU may measure a RIS-WTRU channel associated with the received configuration information. The WTRU may send a differential CSI report to the base station. The differential CSI report may include first CSI associated with a BS-RIS-WTRU path. The WTRU may receive a BS-RIS CSI report from the base station. The WTRU may send a separated CSI report to the base station. The separated CSI report may include second CSI associated with the RIS-WTRU channel and third CSI associated with the BS-RIS channel. The WTRU may communicate uplink information or downlink information with the base station using the BS-RIS-WTRU path. BRIEF DESCRIPTION OF THE DRAWINGS [0012] FIG. 1A is a system diagram illustrating an example communications system in which one or more disclosed embodiments may be implemented. [0013] 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. [0014] 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. [0015] 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. [0016] FIG.2 is a diagram illustrating an example RIS-aided system. [0017] FIG.3 are diagrams illustrating example distributions of RIS elements within sub- surfaces. [0018] FIG.4 is a diagram illustrating an example RIS-aided system with an RIS having sub-surfaces. [0019] FIG. 5 is a diagram illustrating an example system model representing an RIS separated channel for MIMO transceivers in a RIS-aided downlink communication. [0020] FIG.6 is a flow chart illustrating an example high-level procedure for RIS separated channel acquisition. [0021] FIG. 7 is a signaling diagram illustrating an example RIS separated channel estimation. [0022] FIG.8 is a flow chart illustrating an example WTRU procedure for RIS separated channel estimation. [0023] FIG. 9 is a flow chart illustrating an example RIS procedure for RIS separated channel estimation. [0024] FIG.10 is a diagram illustrating an example system model for separated channel estimation with a full-duplex base station. [0025] FIG.11 is a diagram illustrating an example system model for separated channel estimation with a full-duplex WTRU. [0026] FIG. 12 is a flow chart illustrating an example procedure performed by a base station for separated channel acquisition using full-duplex operation. [0027] FIG.13 is a diagram illustrating an example full-duplex operation-based separated channel estimation. [0028] FIG.14 is a diagram illustrating example CSI-RS resources for full-duplex mode separated channel estimation with partial CSI estimated and utilized in a current resource block. [0029] FIG.15 is a diagram illustrating example CSI-RS resources for full-duplex mode separated channel estimation with partial CSI estimated with pre-configured frequency and utilized in between. [0030] FIG.16 is a diagram illustrating example CSI-RS resources for full-duplex mode separated channel estimation with partial CSI estimated in parts based on pre-defined configuration and utilized after complete or partial estimation. DETAILED DESCRIPTION [0031] 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. [0032] 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. [0033] 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. [0034] 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. [0035] 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). [0036] 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). [0037] 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). [0038] 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 NR. [0039] 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). [0040] 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, CDMA2000 1X, 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. [0041] 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. [0042] 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. [0043] 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 include another CN connected to one or more RANs, which may employ the same RAT as the RAN 104 / 113 or a different RAT. [0044] 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. [0045] 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. [0046] 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. [0047] 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. [0048] 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. [0049] 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. [0050] 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). [0051] 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. [0052] 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. [0053] 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. [0054] 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 139 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)). [0055] 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. [0056] 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. [0057] 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. [0058] 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. [0059] 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. [0060] 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 may be available for the WTRUs 102a, 102b, 102c, managing and storing contexts of the WTRUs 102a, 102b, 102c, and the like. [0061] 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. [0062] 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. [0063] Although the WTRU may be 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. [0064] In representative embodiments, the other network 112 may be a WLAN. 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. [0065] 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. [0066] 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. [0067] 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). [0068] 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). [0069] 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. [0070] 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. [0071] 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. [0072] 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). [0073] 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). [0074] 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. [0075] 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. [0076] 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. [0077] 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. [0078] 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. [0079] 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. [0080] 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. [0081] In view of FIGS.1A-1D, and the corresponding description of FIGS.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-ab, 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. [0082] 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. [0083] 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. [0084] An embodiment for a system model including one RIS element is presented. Secondly, an embodiment of a system model including one or more (e.g., all) RIS elements of a single RIS is presented. Downlink (DL) models are discussed here, but the same or similar models may be applicable to the uplink (UL). [0085] For simplicity, consider a single-antenna WTRU and a narrowband system, e.g., a subcarrier of an OFDM system. Such a model may also cover the case with a multi- antenna WTRU that combines multiple received signals into a single received signal by using receiver processing, e.g., analog, digital or hybrid beamforming or combining techniques. In this case, the receiver processing may be included in the radio channel. [0086] An illustration of an embodiment of an RIS-aided system is shown in FIG.2 and is considered to be an equivalent baseband received complex-valued scalar signal ^^_^ at the WTRU is given by Equation 1: ^^_^ ൌ ^ ^^_^ ^^^ᇱ ^_^ ^^_^ ^ ^^^ᇱ^ ^^ ^^ ^ ^^ (1) e.g., a known reference (pilot) symbol. P is the complex-valued precoding vector of dimension ^^_் ൈ 1, where ^^_் is the number of transmit antennas, e.g., at a network-side transmission and reception point (TRP). ^^′ is the complex-valued channel between the TRP and the UE, excluding propagation paths via the RIS, of dimension 1 ൈ ^^_். ^^^ᇱ ^ is the complex-valued vector channel between the TRP and the RIS element, of dimension 1 ൈ ^^_். ^^_^ is the complex-valued scalar RIS element factor of RIS element m, with m=1, …, M. In a passive RIS, the factor may have a fixed amplitude, e.g., a unit amplitude (^| ^^_^ ^| ൌ 1). In an active or hybrid RIS, the amplitude may be variable In some cases, e.g., even for a passive RIS, a RIS element may be turned off, i.e., ^^_^ ൌ 0 or ^^_^ ^ 0. A RIS element may be in a certain state ( ^^_^) at a be applicable to one or more (e.g., all) within a certain bandwidth. ^^_^ is the complex-valued scalar channel between the RIS element and the UE. z is the additive noise and interference. [0087] The terms reference signal (RS) and pilot are used interchangeably herein. In OFDM, an RS/pilot may comprise multiple (known) reference/pilot symbols mapped to different sub-carriers and OFDM symbols. [0088] The model may be further simplified by including the TRP precoding P into the TRP-to-RIS channel, as given by Equation 2: ^_{^^ ൌ} ^{^} _{^^^ ^^^ ^^^ ^ ^^} ^{^} _{^^ ^ ^^ ൌ} ^{^} _{^^^ ^^^ ^ ^^} ^{^} _{^^ ^ ^^ (2)} ൌ direct TRP-to-RIS channel (including TRP precoding). ^^_^ ൌ ^^^ᇱ ^ ^^ is the complex-valued scalar channel between the TRP and the RIS ൌ is the cascaded complex-valued scalar channel, TRP to m:th RIS element to WTRU. [0089] A model including one or more (e.g., all) RIS elements can be obtained by adding the signals corresponding to one or more (e.g., all) M RIS elements of the RIS ( ^^_^ ^^_^ ^^) as in Equation 1: ^^ ൌ ^^ ^^ ^ ^^^ ^^ ^ ^^^ ^^ ^ ^^ ൌ ^ ^^ ^^ ^ ^^^ ^^ ^ ^^ (3) the TRP and the RIS, of dimension 1 ൈ ^^, where M is the number of RIS elements. ^^{^ is the complex-valued vector channel between the RIS element and the UE, also} 1 _{ൈ ^^.} ^^ ൌ ^^ ^ ^^ is the element-wise (Hadamard) product of a and b. complex-valued vector of dimension ^^ ൈ 1 containing the M RIS element factors ^^_^. ^^ may correspond to the RIS state. [0090] In the case RIS, let M_x denote the number of RIS elements in a first direction, e.g., horizontal, and M_y denote the number of RIS elements in a second direction, e.g., vertical, for instance such that M=M_x*M_y.. [0091] In some example embodiments, a CSI acquisition in RIS-aided communication systems may include an estimation of RIS aided channels. To estimate the cascaded channel c as well as the direct channel d in Equation 3, the network may transmit a number of known pilot (reference) symbols s. Since c has M elements and d has one element, M+1 pilots may be needed to estimate the channel coefficients. [0092] In some example embodiments, the same pilot symbol s in the M+1 occasions may be assumed, but it may also be different in different occasions, as long as it’s known by the WTRU. [0093] The received pilot symbols may be combined as in Equation 4: ^^ ൌ ^^ ^^ ^^ ^ ^^ (4) _{ൌ M+1 received pilot symbols.} ^ ^^ ^ 1^ vector with the direct channel and the M channels via ^_{^ ൌ ^} ^{1 ⋯ 1} ⋯ _{where ^^^ is the ^^ ൈ 1 vector with the RIS element factors} pilot symbol. Note that ^^ is a square matrix with dimension ൈ ^_{^ ൌ ^} ^{^^} _^ ^{⋯ ^^} _{ெ^ is received noise and interference vector.} [0094] With a ^^ with full rank and known to the WTRU, the channels may be estimated based on ^^, or using another method such as the minimum mean square error (MMSE), e.g., as 5: ^^{^} _{^ ൌ} ^{భ ି^} ೞ _{^^ ^^ (5)} to design ^^_^ are described below. [0096] In the on-off method, one or more (e.g., all) the RIS elements are turned off (e.g., ^^_^ ൌ ^^ or ^^_^ ^ ^^) during the first pilot symbol, resulting in a received symbol for example as in Equation 7, below. [0097] Thereby, the direct channel d may be estimated by the WTRU. During pilot symbols 1 to M, the RIS elements may be turned on one-by-one, with other elements still turned off. This results in a received i:th pilot symbol for example as in Equation 6: ^_{^^ ൌ} ^{^} _{^^^ ^^^ ^ ^^} ^{^} _{^^ ^ ^^^ with ^^ ൌ 1, … , ^^ (6)} all zero, except the i:th element ^^_^ ൌ 1. In other words, ^^_^ ൌ ^ ^{^^} where ^^ is an all-ones M-dimensional row vector and ^^_ெ is the identity matrix of dimension M. Even though this presentation assumes that the RIS elements are turned on in the order of RIS element index, the elements may be turned on in any order in general. [0099] In other methods, the ^^_^ are vectors without elements equal to zero, meaning that all RIS elements are turned on during the pilot symbol transmissions. In one example, ^^ may be a DFT matrix. In another example, ^^ may be a Hadamard matrix. In these examples ^^^{ି^} ൌ ^^^், which simplifies implementation. [0100] In some example embodiments, an estimation of RIS-reflected aggregate channel may include a cascaded channel estimation. The channel in Equation 1 includes the direct path d and the RIS-reflected aggregate channel ^^ ^^, i.e., ^ ^^ ^^ ^ ^^^. Note that the aggregate channel ^^ ^^ may be scalar since it comprises 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 instance as in Equation 7: ^^_^ ൌ ^^ ^^ ^ ^^_^ (7) [0101] The WTRU may estimate d, e.g., using a channel estimation method. During a second pilot symbol, the RIS may be turned on, with a certain RIS state Φ, e.g., as in Equation 8: ^^_^ ൌ ^ ^^ ^^ ^ ^^^ ^^ ^ ^^_^ ൌ ℎ ^^ ^ ^^_^ (8) [0102] The WTRU may estimate h, e.g., using channel estimation method. The WTRU may also estimate the RIS-reflected aggregate channel ^^ ^^ based on the two pilots. [0103] In some example embodiments, the number of RIS elements may be relatively high. Channel estimation procedure and CSI reporting per RIS element may be too costly in terms of overhead and signaling. For example, instead of performing these procedures based on per RIS element, the overall problem may be reduced by introducing the sub- surface based estimation and reporting. The total number of RIS elements can be distributed into S sub-surfaces having S_x, S_y horizontal and vertical elements in a sub- surface. The distribution of the number of elements in the sub-surfaces can be uniform or non-uniform. In the case of multi-panel RIS, each panel may be considered as a sub- surface, or each panel may further be divided into multiple sub-surfaces. An example embodiment of the RIS element distribution into sub-surfaces may be seen in FIG.3. For instance, FIG. 3 depicts an embodiment of the distribution of RIS elements into sub- surfaces, where uniform distribution may be observed in the example of FIG.3(a) and (b) and RIS elements are non-uniformly distributed in the example of FIG.3(c). In the case where different RIS surfaces are allocated to different users, then based on the WTRU’s demand the number or RIS resources may be increased or decreased wherein the non- uniform RIS distribution may be used. Thus, the WTRU requires a greater number of resources and the bigger-dimensional sub-surface may be allocated whereas a smaller- dimensional sub-surface may be reserved for the WTRU with less-stringent requirement. [0104] In some example embodiments, the number of pilots needed for the CSI and channel acquisition in the case of elementwise RIS aggregate channel estimation may be M+1. With the increasing size of RIS surface, the computational complexity of the overall process may increase tremendously. As such, the process of making channel estimation may be inefficient and time-consuming. Another potential method of doing the channel estimation may be performed by dividing / grouping the total number of RIS elements into smaller groups called sub-surfaces and then the channel estimation may be performed at each sub-surface level. A sub-surface may be a set of RIS elements. The distribution of the number of elements in the sub-surfaces may be uniform or non-uniform. In the case of multi-panel RIS, each panel may be considered as one sub-surface, or each panel may further be divided into multiple sub-surfaces. An embodiment of the RIS being partitioned into six sub-surfaces (S=6) is shown in FIG.4. [0105] In some example embodiments, a RIS state may be configured at the sub-surface level, which may mean that the same RIS element factor may be applied to the RIS elements in a sub-surface. Sub-surface level channel estimation may be done by sending one pilot per sub-surface, rather than per RIS element. Further, by introducing the sub- surfaces, the dimension of the channel estimation problem may be reduced from M+1 to S+1 in terms of pilot transmissions and computation. The on-off method and on-method described above, such as related to Equations 4 and 5, may be applied to sub-surfaces, instead of on individual RIS elements, with decreased pilot overhead and channel estimation complexity. [0106] The system model described above may be used here to describe an embodiment of an RIS operation based on sub-surfaces. Let Γ_^ denote the set of RIS element indices in the j:th sub-surface, with j=1, …, S. The union of sub-surfaces may typically include one or more (e.g., all) RIS element indices, i.e., ⋃_^ Γ_^ ൌ ^{^}1, … , ^^^{^}, and the sub-surface sets may typically be disjoint. Further, let ^^_^ ^^ with ones on the rows given by the indices in Γ, ^ and starts at 1 for convenience. In other ^^_^ selects RIS elements corresponding to the j:th sub- _{surface. Still further, let ൌ} ^{^ ⋯ ^^} _ௌ ^{^} _{be a sub-surface selection matrix of dimension} ^^ ൈ ^^. The system may now be written as follows, as Equation 9: ^^ ൌ ^ ^^ ^^ ^^^{^} ^ ^^^ ൌ ^^ ^ ^^ (9) ൈ 1 containing the S sub-surface factors ^^_^ ^{^}, where the factor ^^_^ ^{^} may be applied to the RIS elements in Γ_^, i.e., ^^_^ ൌ ^^_^ ^{^} ∀ In other same RIS element factor ^^_^ ^{^} is j:th sub- ൌ 1 ൈ ^^ dimensional vector containing S per RIS-reflected aggregate channels. In other words, the j:th element of ^^^{^} equals ^∑ _^ೕ ^^_^ . [0107] In some example embodiments, the term ^ ^^^{^} ^^^{^} ^ ^^^ in the same form as ^ ^^ ^^ ^ ^^^ in Equation 3, except the length of the vectors, which is S in the former (i.e., the number of sub-surfaces) and M in the latter (i.e., the number of RIS elements). Therefore, any methods for channel estimation, CSI etc., applicable to per RIS elements operation may be applicable also to per sub-surface operation, and vice versa. [0108] In some embodiments, as an example, the RIS channel estimation may be directly applicable by just changing the problem dimension by adding the s superscript: ^^ ൌ ^{^} ^^ ^^^{^^} is a 1 ൈ ^ ^^ ^ 1^ vector with the direct channel and the S channels via the RIS sub-surfaces. ^_{^ ൌ ^} ^{1 1 ⋯ 1} w_{here ^^^} ^{^} _{is the ^^ ൈ 1 vector with the RIS sub-surface} i:th symbol. (Note that ^^ is a square matrix with dimension ^ ^^ ^ 1^ ൈ ^ ^^ ^ 1^.) [0109] In some example embodiments, differential channel estimation may be utilized, for example, in an RIS-aided communication, in case of downlink communication, the WTRU receives data mainly along two-paths which includes the RIS-aided path (BS-RIS-WTRU path) and direct path (BS-WTRU path), which may include direct (BS-WTRU) channel component and other multi-path fading components. The differential channel may be the effective RIS-aided channel path gain (c) at the WTRU in case of downlink transmission. The knowledge of the differential channel may benefit in evaluating the effect and performance of RIS in the communication. This knowledge may be utilized in generating enhanced reports and link adaptation for the RIS-aided path. As such, obtaining differential channel coefficients may result in improved communication performance. [0110] The RIS-aided channel may also be referred to as RIS cascaded channel or RIS- reflected aggregate channel. In this disclosure, the terms differential channel / cascaded channel / aggregate channel may be interchangeably used and they refer to the RIS- aided channel path. [0111] One method of differential channel estimation may consider that RIS surface may be turned on during one or more (e.g., all) pilot transmissions. The RIS state could be set element-wise, sub-surface wise or a single state for complete RIS as per the set RRC configuration. For example, a single state of RIS may be set in an orthogonal space which may be configured to belong to the codewords from different orthogonal dictionaries (e.g., Hadamard matrix, DFT etc.), during a set of pilot transmissions and the WTRU may be configured by the BS, indicating the selected orthogonal dictionary for the RIS state, enabling differential channel estimation at the WTRU end. [0112] Considering, when the RIS state may be set to ^^_^ and a known pilot s may be transmitted by the transmitter (say BS in case of downlink transmission), then the received signal at the WTRU may be given by Equation 10: _{^^^ ൌ} ^{^} _{^^ ^^^ ^ ^^} ^{^} _{^^ ^ ^^^ (10)} [0113] Similarly, in some example embodiments, when the RIS state is set to ^^ _^^, the received signal may be given by Equation 2: _{^^ଶ ൌ} ^{^} _{^^ ^^ଶ ^ ^^} ^{^} _{^^ ^ ^^ଶ (11)} [0114] The differential channel may be obtained by subtracting Equation 10 and Equation 11 as follows: ^^_ଶ െ ^^_^ ൌ ^^^ ^^_ଶ െ ^^_^^ ^^ ^ ^ ^^ െ ^^^ ^^ െ ^ ^^_ଶ െ ^^_^^ _^^| ^{|^} _{^^ଶ െ ^^^} ^{^|} _| ^{^^} _ൌ ^{^} ^ _{^ ^^ଶ െ ^^^^} ^{^} _{^^ଶ െ ^^^} ^{^ ^^} _{+ z} ^{^} _{^^ ^^ െ ^^ ^^} ^{^ ^^} as follows by Equation 3: _{ൌ ^||^ ^^మି ^^భ^|| ^^ െ െ} the resultant RIS-aided channel path analysis and reporting. [0117] In some example embodiments, such as sub-surface based channel estimation, as discussed herein above, and wherein the complete RIS may be distributed into ^^ sub- surfaces, the differential channel for ^^-th sub-surface is obtained as Equation 12(a): ^^^ ൌ ^{^} ^ ^^ െ ^^ ^ ൫ ^{ି^} ^ _{^ ଶ,^ ^,^} ^^_ଶ,^ െ ^^_^,^൯ (12a) the RIS state for ^^-th sub-surface may [0118] example embodiments, it may be assumed that either one (e.g., only one) sub-surface may be turned-on at a given time or the sub-surface state are mutually orthogonal to each other. The effective additive noise and interference component ^ ^^_ଶ െ ^^_^^ may be compensated by using an additive noise and/or an interference cancellation. [0119] In some example embodiments, the effect of the direct channel path may be not explicitly captured. However, the direct channel path may be calculated implicitly by the WTRU utilizing the differential channel knowledge and the received signal. A special case of the presented differential method may be considered wherein the direct channel path may be exploited to obtain the differential channel ^^. In such a case, consider in one of the pilot transmissions (say ^^ ൌ 1), RIS may be turned off ( ^^ _^^ ൌ 0), and the resulting in the received signal as, ^^_^ ൌ ^^ ^^ ^ ^^_^ and in another transmission (say ^^ state may be set to ^^ _^^, then received signal may be given by, ^^_ଶ ൌ ^ ^^ ^^_ଶ ^ ^^^ ^^ ^ ^^_ଶ [0120] The differential channel ^^_ଶ െ ^^_^ ൌ ^ ^^ ^^_ଶ ^ ^^^ ^^ െ ^^ ^^ ^ ^^_ଶ െ ^^_{^ ^} ^{^} _{^ ൌ} ^{1 ^} _{^^ െ ^^} ^{^} _^ ^{ି^} ^_{^ ଶ ^ ^ଶ} [0121] In another example, if a the presence of RIS, a WTRU may measure the CSI for both states e.g., as legacy CSI reports to the BS. Utilizing the received reports from the WTRU for 2 RIS states, BS may compute the differential CSI. Furthermore, BS may compute the channel quality indicators to perform the link adaptation and update the RIS state. [0122] In some example embodiments, the downlink transmission in 5G NR the BS/TRP transmits the CSI-RS that are used for the channel sounding. With the help of the CSI- RS, WTRU may perform the measurements to estimate the quality of the channel based on the received reports (either implicitly or explicitly) by the WTRU. [0123] The first mode of DL CSI acquisition in NR may be based on the WTRU performing measurements on one or more CSI-RS and reporting corresponding CSI. A second mode of DL CSI acquisition in NR may be based on the WTRU transmission of sounding reference signal (SRS), potentially including antenna switching between antennas that may be used for DL reception, CSI measurement at the network side, and the assumption of UL/DL reciprocity, i.e., that CSI estimated on the UL may be applicable to the DL. [0124] A WTRU may be configured to perform channel measurement and compute a CSI for a CSI-RS resource, which may comprise one or more ports (antenna ports). One or more CSI-RS resources may be grouped into CSI-RS resource sets. A WTRU may also be configured to perform interference and/or noise measurement on a CSI-RS resource for a CSI. The CSI-RS resource may be a non-zero power (NZP) CSI-RS resource, in which the WTRU may assume a certain RS being transmitted. The CSI-RS resource may be a CSI-RS resource for interference measurement, in which the WTRU might not assume a certain RS being transmitted. In NR, CSI-RS resource 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 and CSI-RS resource sets are used herein, which may refer to either NZP and/or IM CSI-RS resources and resource sets. [0125] A CSI-RS resource may be periodic, semi-persistent, which needs to be activated / deactivated, or aperiodic, which needs to be triggered. A WTRU may receive one or more 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, through physical UL control channel (PUCCH) or physical ULK shared channel (PUSCH). [0126] In some example embodiments, when a RIS may be present in the communication system, RIS may introduce the phase shifts and amplification gains to the impinging signal based on the predefined / set RIS state, as configured by a controlling node e.g., RIS controller, BS, WTRU, etc., and reflect the impinging signal, e.g., in the desired direction. In practice, RIS may be assumed to be composed of large number of RIS unit- cells which are 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 i.e., direct path between the BS and WTRU and RIS aided BS-RIS-WTRU path. To achieve improved communication quality, both these paths i.e., BS-WTRU and BS-RIS-WTRU, needs to be optimized e.g., by utilizing the CSI reports. However, legacy reports measured effectively over one or more (e.g., all) the paths may not be efficient to optimize the RIS-aided BS-RIS-WTRU path. Furthermore, utilizing the legacy reporting feedback, it may be difficult to infer the effect of the RIS-aided path specifically. In this disclosure, methods for RIS-aided path channel estimation (differential channel) are proposed, wherein the channel estimation may be performed either by the BS or WTRU. The differential channel could 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. The differential / cascaded channel for the RIS-aided BS- RIS-WTRU path may be an aggregate effect of one or more of (e.g., all) the RIS elements and have dimensionality dependent on the number of antenna elements at the BS and WTRU. However, with the presence of large number of the RIS elements, the channel for individual paths i.e., between BS-RIS and RIS-WTRU will have higher dimensionality as compared to the cascaded / differential RIS-aided channel i.e., BS-RIS-WTRU path. In this disclosure, the individual channels between BS-RIS and RIS-WTRU paths are referred as separated channels. The high dimensional channels obtained from the separated channel estimation may be exploited to achieve enhanced communication performance as compared to utilizing a (e.g., only a) differential (BS-RIS-WTRU) channel. Estimating separated channels may be important for achieving reliable solutions with improved throughput. Furthermore, in certain applications when RIS may be static and either of the BS or WTRU may be static as well, the gains from one of the channels among 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 performed) for the time-varying channel path, and the computational complexity may be decreased as compared to estimating both separated channel paths. As RIS may be assumed to be mostly passive node and may be not capable of baseband processing, the channel estimation may not be performed at an RIS node. Further, obtaining the separated channel estimates may be challenging in the case of passive RIS. In this disclosure, the channel estimation methods for separated RIS channels have been proposed wherein, the estimation may either be done at the BS or at the WTRU. Further, the CSI reports in the current NR include the reporting of rank indicator (RI), precoder matrix indicator (PMI), channel quality indicator (CQI), etc. These conventional reports may be insufficient to capture the effect of the RIS state. [0127] 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 instance in terms of modulation and coding, but also multi-antenna precoding, and frequency domain resource allocation. Some adjustments may pertain to improving the received signal quality, for example precoding and frequency-selective scheduling. Other adjustments may pertain to achieving a certain block error rate, e.g., modulation and coding scheme (MCS) selection. The estimated CSI and reporting may also be utilized to update or adjust RIS state. The adjustment of the RIS state may be more similar to precoder selection than to MCS selection, i.e., it may improve the received signal quality. However, existing CSI procedures may not support CSI based adjustments for RIS-aided communication. As such, enhancements in the NR CSI-reports may be possible so as to incorporate the effect of RIS-aided separated channels in the communication system. [0128] In some example embodiments, in RIS-aided communication, there may be a RIS separated channel estimation. For example, independent channel gains between BS- RIS and RIS-WTRU may be referred to as separated channels, whereas the cascaded channel may be referred to as BS-RIS-WTRU channel gains. In cascaded channels, the dimensionality of the RIS may be lost in the estimated channel as the resultant channel gain depends on (e.g., only on) the gNB and WTRU antenna elements (N_T x N_R). The granular knowledge of channel gain over each RIS element may provide better estimates, and may result in enhanced communication performance. Furthermore, this loss would be crucial with the increasing dimension of the RIS surface. The separated channels estimation may overcome this loss and may capture this information resulting in high resolution channel estimates between BS-RIS and RIS-WTRU paths. The passive nature of RIS prohibits performing channel estimation at the RIS node, making separated channel estimation challenging problem for the terminal nodes (gNB or WTRU); the responsible nodes for separated channel estimation task. [0129] Multiple embodiments for separated channel estimation are presented below. At first, a high-level procedure for separated channel estimation is presented. It may be followed by decomposition based separated channel estimation methods, as discussed thereafter, wherein the multiple estimation solutions are discussed along with the CSI-RS enhancements. Further, CSI reporting enhancements for separated channel estimation are discussed. [0130] In some example embodiments, a system model for separated channel components in a RIS-aided communication may be discussed may be considered. Consider a RIS-aided MIMO downlink communication as shown in FIG.5, where a BS transmits a pilot / reference signal to the WTRU and WTRU performs the channel estimation. Following the system model as discussed in above let the channel between the BS and RIS be A of dimension ^ ^^_ோூௌ ^^ ^^_்^ and the channel between RIS and the WTRU be ^^ of dimension ^{^}1 ^^ ^^_ோூௌ ^{^}. The composite channel between BS-RIS-WTRU may be given by ^^^ᇱ ൌ ^^ ^^ ^^, wherein ^^ is an ^^-dimensional complex valued diagonal matrix representing RIS state. P is the complex-valued precoding vector of dimension ^^_் ൈ 1 e.g., at a network-side BS. Thus, the received signal at the WTRU is obtained as Equation 13: ^^ ൌ ^ ^^ ^ ^^^ ^^ ^ ^^ (13) 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 may be given by ^^ ൌ ^^ ^^ ^^ ^^ ൌ ^^ ^^ ^^ ൌ ^^ ^^^ᇱ ^^ ൌ ^^ ^^ , such that ^^ ൌ ^^ ^^ ^^ ^^^ ^^^, ^^^ᇱ ൌ ^^ ^^ ^^ ^^^ ^^^ and, ^^ ^^ ^^ and of ൈ [0131] From the received signal ^^ in Equation 13, the differential channel ^^ may be estimated at first (for example by using Equation 12) to obtain the BS-RIS-WTRU channel gain, which may further be processed to obtain the separated channels utilizing any of the methods as discussed below. [0132] FIG. 6 illustrates an example high-level process for RIS separated channel acquisition and RIS reporting, according to one embodiment. The system may contain one or more TRPs, one or more base stations, e.g., gNB, one or more RISs, and one or more users. The procedures followed for the high level process at the gNB, WTRU, and RIS are discussed herein. Different procedures illustrated in FIG.6 are discussed further below. In the example of FIG.6, the process may start at 601 and, at 602, RIS reports its capability to the BS. This may be followed by the BS configuring RIS at 603. Based on the capability reporting from the RIS, BS configures the WTRU as shown at 604. At 605, WTRU performs CSI measurements to compute the RIS differential CSI acquisition and reports RIS CSI at 606. Following this, WTRU performs separated RIS channel acquisition by decomposing the RIS differential channel, as shown at 607. WTRU reports RIS separated CSI reports at 608. Based on the CSI reports from the WTRU, BS may modify and/or update the system parameters including precoding, modulation, set RIS state etc. At 609, RIS may utilize set and/or updated RIS state during UL/DL transmissions. [0133] FIG. 7 illustrates an example signaling diagram, according to one embodiment. Note that additional signaling may be used in various examples. Furthermore, some signaling shown in FIG. 7 may be omitted in various examples. As illustrated in the example of FIG.7, RIS capability may be signaled to the BS. The BS may configure the WTRU, for example, by sending configuration information to the WTRU. The BS may also configure the RIS. This may be followed by RIS CSI measurement, which may involve the BS transmitting CSI-RS. In the case of semi-persistent or aperiodic CSI-RS, corresponding activation or triggering signaling may be needed. Also, 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 may be called RIS state scheduling in FIG.7. The BS may configure the RIS in one state (set RIS state or for that instance the RIS may be turned off indicating the first RIS state as illustrated FIG.7). The BS may indicate the CSI-RS to WTRU while triggering and/or setting the RIS into another RIS state (e.g., state 1 in the example of FIG.7). Based on the RIS CSI measurement and computation, the WTRU may report the legacy CSI and/or differential RIS CSI to the BS. Based on the RIS CSI report, the network may perform RIS parameter update or change in 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. The WTRU may perform the separated CSI acquisition and send the separated CSI reports to the BS. This may be followed by DL and UL transmissions, e.g., the physical DL shared channel (PDSCH) and/or PUSCH. [0134] In some example embodiments, RIS capability reporting may be desirable. 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, for example, the number of RIS elements (e.g., M), the RIS design / architecture (e.g., rectangular, single array, circular, fluid, etc.), the range and/or resolution of RIS element amplifications and phase shifts, a range may for example comprise a minimum and/or maximum value, e.g., for RIS element amplification, and a resolution may for example comprise a step size between supported ^{values, e.g., within a range. For example, a phase shift resolution of ^^} _{ൗ 16} ^{may be} supported for an RIS. A resolution / range capability may also list the supported values. In addition, sub-surface and parameter interpolation capability may be supported, along with the type of the RIS i.e., passive, semi-active, active, etc., including possibly different type for transmitting versus receiving. An RIS with active elements may report the number of active elements and their properties e.g., their position on RIS surface, associated RF chains, etc. Further, an RIS may also report on the function support which may be provided by the active elements, i.e., channel estimation, signal decoding, etc. [0135] A RIS capability may comprise a set of parameters related to such aspects that may differ between RISs. A RIS class may comprise one or more capabilities. A RIS may connect to the network and report its capabilities and/or class (e.g., class 1, class 2, etc.) to the network, e.g., as shown at 602 in FIG.6. The capabilities / class may be signaled using an RRC message. [0136] A RIS may be configured by the network, e.g., by a BS or gNB, as illustrated at 603 in FIG.6. The configuration may be an RRC configuration. The configuration may be communicated to the RIS in a manner similar to how a WTRU may be configured, e.g., using RRC signaling. In another case, where RIS state may be set by the RIS controller, the BS may communicate the RRC configuration to the RIS controller, which may further set and/or update the RIS state. [0137] The configuration parameters may include, among others, (i) a sub-surface or elementwise RIS configuration, for example number of sub-surfaces (e.g. S), number of RIS elements per sub-surface, etc.; (ii) a time-domain configuration, which may indicate time instances when a RIS configuration may be to be used, for example time-domain behavior such as periodic or semi-persistent, etc., periodicity, time offset, etc.; (iii) a configuration of the range(s) and/or resolution(s) for RIS element and/or sub-surface factors (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; (iv) one or more RIS states and/or RIS state IDs that may be associated with one or more sub-surface configurations. [0138] In the presence of active RIS elements, or active element configuration, the configuration parameters may include one or more of: the configuration may set the RIS function support e.g., channel estimation, signal decoding etc., using active RIS elements, active elements to be utilized for a specific task, configuration which may include the RIS active element state, amplification gains, etc., RIS CSI resource configuration indicating the resource id., periodicity etc., and RIS configuration trigger for transmission and reception of the CSI resources using active elements. The trigger may be initialized similar to the legacy NR which may include periodic, semi-persistent or aperiodic setting etc. [0139] In some example embodiments, the active element configuration may not be configured in some cases, for example when an RIS surface is operating in passive mode even in presence of active elements, etc. When active elements are not configured, RIS active elements may be configured similar to passive RIS elements configuration. [0140] The network or base station (BS) may configure a WTRU with parameters associated with RIS CSI enhancements, e.g., as shown at 604 in FIG.6, for example one or more of the following: a WTRU configuration, e.g., including one or more of the parameters of the RIS as discussed with respect to procedure 603 and may be detailed as below; information about a sub-surface configuration may be useful for a WTRU for various RIS CSI parameter computations; and information about active RIS element configuration may be useful for a WTRU for CSI acquisition task. For instance, in case of RIS separated channel estimation, WTRU may use the active element position on RIS surface to compute and extrapolate the channel gains. In addition, a legacy CSI reporting configuration, e.g., including CQI reporting, may be provided. Further provided may be an enhanced CSI reporting configuration, for example including one or more RIS parameters, updated one or more link adaptation parameters, a legacy CSI resource configuration, separate report configuration to indicate the periodicity (e.g., periodic, semi- persistent, and/or aperiodic) of the CSI reports for each BS-RIS and RIS-WTRU separated channels. Configuration may also include the specific RIS-aided CSI reports e.g., CQI, PMI, RIS-QI, etc., for each of the separated channels, or enhanced RIS CSI resource configuration for decomposition based separated channel estimation. [0141] In some example embodiments, WTRU differential channel estimation and reporting may be included. Based on WTRU configuration, the WTRU receives RSs, performs measurements, and computes CSI which may include complete CSI, as discussed above, and/or differential CSI, as also discussed, and, e.g. referred to in procedure 605 of FIG.6. [0142] Based on its configuration, the WTRU reports 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. procedure 608 in FIG. 6) may also include differential channel specific indicators, such as differential PMI, differential RI, etc., 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 some cases, a CSI report may include (e.g., include only) RIS parameters. In other cases, RIS parameters and legacy CSI parameters, such as CQI, PMI, RI, etc., may be included in the same report. [0143] In some example embodiments, WTRU separated channel estimation may be included. Based on its configuration, WTRU may perform the separated channel measurements utilizing the RSs received from BS and/or from RIS active elements and compute separated channel estimates, e.g., at 607 in FIG 6. [0144] For example, the WTRU may estimate RIS-WTRU path channel gains based on the CSI-RS resource received from RIS active elements. For separated channel estimation performed using RSs from BS, WTRU may utilize decomposition techniques. Further, a WTRU may perform separated channel estimation utilizing the partial CSI from the BS. [0145] In some example embodiments, WTRU separated CSI reporting may be included. Based on its configuration, the WTRU may include the separated CSI indicators in the CSI report to the network. e.g., as in procedure 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. Based on the set configuration by the BS, the WTRU may report separated channel with different periodicity and/or frequency. For example, the WTRU may report the BS-RIS CSI reports with a higher frequency as compared to the frequency at which WTRU reports the RIS- WTRU CSI. To ensure an association between two separated channel reports, the following may be performed at the WTRU/BS: [0146] WTRU may associate a unique report id with both the separated CSI reports (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. [0147] The association may also be provided from the base station, e.g., as part of a CSI measurement and reporting configuration. For example, two CSI reporting configurations may be linked by RRC configuration. Alternatively, two separate CSI reports may be configured in a CSI reporting configuration. [0148] WTRU may include the unique report id in one part of the separated channel report for example, WTRU may include the associated report id for BS-RIS channel report in RIS-WTRU channel report, which may then be utilized by the network to identify the respective reports. [0149] In some example embodiments, RIS operation during DL/UL channel/signal transmission may be included. The network may indicate and/or configure to the RIS to use a set RIS state during subsequent DL/UL transmissions, for example by configuring, indicating, triggering, and/or 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 physical DL control channel (DCCH), PDSCH, CSI-RS/TRS, and/or positioning reference signal (PRS), etc., and UL transmissions may include PUCCH, PUSCH, SRS, etc. Since DL/UL transmissions may be dynamic, the use of a certain RIS state may need to be dynamically indicated, e.g., as shown at 609 in FIG 6. [0150] FIG.8 illustrates an example of a WTRU process for separated channel estimation, according to one embodiment. FIG.8 may follow the high-level procedure illustrated in the example of FIG.6. In the example of FIG.8, the process begins at 801 and, at 802, the WTRU is configured, which includes configurations for RIS CSI. This may be followed by the WTRU performing measurements and/or computation of RIS CSI and/or differential channel CSI, e.g., as in step 803, and the WTRU may report RIS CSI and/or differential CSI reports inc., differential PMI etc., to report the quality of the RIS-aided path as depicted in step 804. This may be followed by a legacy CSI measurement in step 805 and reporting in step 806, e.g., incl. 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, in step 807, the WTRU may perform measurements and RIS separated channel estimation e.g., by decomposing the acquired differential channel estimates (discussed further herein), etc. The WTRU may report the separated channel reports as given in step 808 (and discussed herein). This may be followed by DL reception and UL transmission, e.g., PDSCH and/or PUSCH, depicted in step 809. [0151] An example embodiment of a RIS process for RIS separated channel estimation is shown in FIG.9. As illustrated in the example of FIG.9, the process may start at 901 and, at 902, a RIS may report its capability to a BS or gNB. At 903, the RIS is configured, e.g., the RIS may receive configuration information from the BS or gNB. If the RIS does not have active elements for RSI separated CSI, as shown at 904, the RIS may apply passive elements RIS configuration during CSI-RS for RIS CSI and, at 905, the RIS may use passive RIS elements configuration during RIS CSI-RS for RIS CSI acquisition. If the RIS has active elements for RIS separated CSI, as shown at 906, the RIS may apply active elements RIS configuration during CSI-RS for RIS CSI and, at 907, the RIS may use active RIS elements configuration during RIS CSI-RS for separated RIS CSI acquisition. At 908, the RIS uses RIS configuration during DL and/or UL transmissions. [0152] Full-duplex operation-based estimation may be provided, according to an embodiment. In full-duplex mode of operation, a communicating node (e.g., such as BS/TRP or WTRU) may simultaneously transmit and receive signals during a communication. The full-duplex mode can be achieved in two or more ways. For example, the full-duplex mode may be achieved when a node operates in two different frequencies simultaneously for transmitting and receiving the signal. This can be considered to be similar to the FDD mode of operation and hence, channel reciprocity may not apply. The full-duplex mode may be achieved when a node operates on the same frequency simultaneously for transmitting and receiving a signal, e.g., in-band full- duplex mode of operation. Channel reciprocity may be preserved in full-duplex mode. Full-duplex capability may be utilized by any node (e.g., BS/TRP or WTRU) to perform the separated CSI acquisition when communicating via RIS. For example, consider that the BS is operating in full-duplex mode as shown in FIG.10, then the BS may transmit reference signals for CSI acquisition e.g., CSI-RS etc., directed towards a RIS. The BS may intend to receive the transmitted reference signals back at the BS itself. The BS may configure one or more RIS states. For example, the BS may configure one or more RIS states such that a phase-shift at each RIS element is set to reflect the reference signal back to the BS. [0153] A received signal at the BS may be given by: ^^ ൌ ^^ _^^ ^^ ^^ _^^ ^^ ^ ^^_ௌூ ^^ ^ ^^ Where, - x is the reference signal transmitted by the BS/TRP, - ^^ _^^ is the forward channel vector between BS and RIS of dimension (1 x ^^_ோூௌ), - ^^ _^^ is the reverse channel vector between RIS and BS of dimension ( ^^_ோூௌ ^^ 1), - ^^ _{^^ ^^} is the self-interference at the BS, and - n is the additive gaussian noise or interference from other multiple paths. [0154] When the self-interference component can be compensated by any self- interference mitigating technique and additive noise may be processed using noise suppression filters, the received signal can be given by Equation 14: ^^ ^ ^^ _^^ ^^ ^^ _^^ ^^ (14) operation wherein the channel reciprocity applies, the as the reciprocal of the forward channel ^^ _^^. Hence the received signal can then be given as ^^ ^ ^^ _^^ ^^ ^^ _^^ ^{^^} ^^ [0156] This can be rewritten as ^^ ^ ^ ^^ ⊙ ^ ^{^^} ^_^ ^ _^^ ^ ^^ ^^ ^^ _^^ and ^^ _^^ in in-band mode of operation may be as [0158] Let ^^ _^^ ൌ ^ ^^_௧^ ^^_௧ଶ … ^^_௧ெ^, where the i-th element of the channel vector ^^ _^^ is such that ^^_௧^ ^^^ ^^_௧^^ and ^^_^ ൌ ^^ ^^^ ^^_௧^^. The Hadamard product ^ ^^ _^^ ⊙ ^^ _^^ ith element ^^_௧^ ൌ ^^^ଶ ^ _^ 15, the ^^ _^^ can ^^{^} _{^ ൌ} ^{௬ ^^ ^^} ^_{^ (16)} ^^_^ for all ^^ ∊ ^1, 2, … , ^^^ in Equation 16 may then be calculated by solving a set of ^^ two variable quadratic equations for each element of the RIS which can then be reconstructed into the channels ^^ _^^ and ^^ _^^. [0160] In case of FDD, the estimates of ^^ _^^ and ^^ _^^ may be determined by formulating Equation 14 as an optimization problem e.g., least square solution, maximum likelihood solution, etc., wherein the channel gains may be obtained directly or iteratively. [0161] Once the BS-RIS channel ^ ^^ _^^^ is obtained utilizing any process in full-duplex mode (e.g., quadratic equation solution using Equation 16, least square solution, etc.), the channel between RIS-WTRU ^ ^^^ may be obtained by one or more of the following. [0162] A WTRU may first estimate the differential channel ^^. The WTRU may report the estimated channel either explicitly or implicitly back to the BS. The BS may then estimate the RIS-WTRU channel ^^ by utilizing ^^ ൌ ^^ ^ ^^, where ^^ ൌ ^^ _^^. [0163] The BS may implicitly or the BS-RIS channel ^^ _^^ estimates to the WTRU. The WTRU may then channel ^^ _^^ estimates along with the differential channel ^^ to estimate the RIS-WTRU channel ^^. [0164] In some examples, the BS may be capable of full-duplex operation and channel acquisition may be performed by the BS. A similar procedure may be performed by the WTRU node in a system where the WTRU is capable of full-duplex operation and can transmit the reference signal for CSI acquisition at the RIS node. [0165] FIG.11 depicts an example RIS-aided system for separated channel estimation with a full-duplex WTRU. In the WTRU-initiated full-duplex operation, either the BS can configure the RIS state in BS/network controlled RIS or the WTRU may configure the RIS state in WTRU-controlled RIS, to set the RIS state that can reflect the signal back to the WTRU. The WTRU may follow similar estimation procedure as the BS to obtain the estimates of the forward ^^ _^^ and reverse ^^ _^^ channels between the RIS and WTRU. The WTRU may then estimate the channel ^^ between the BS and RIS from the estimated differential channel ^^ and ^^ _^^ utilizing a procedure similar to an exemplary procedure provided for the BS. [0166] In some examples, the BS and the WTRU may both be operational in full-duplex mode. When both the BS and the WTRU are operating in full-duplex mode, both the BS and WTRU may acquire their individual link (e.g., channel) with respect to RIS e.g., the BS may acquire a BS-RIS channel while the WTRU acquires a RIS-WTRU channel. Then, one of the nodes (e.g., the WTRU) may either explicitly or implicitly communicate the acquired channel information with the other node (e.g., the BS in this case). The other node may determine the complete separated channel (e.g., BS-RIS-WTRU), for example, for optimizing and/or updating one or more system parameters. [0167] A similar method may apply when a node is operational in a sub-band mode of operation and is capable of full-duplex operation for a sub-band or a set of sub-bands. The solutions described herein may be applied to sub-band-based full duplex operations, either fully overlapping, partially overlapping, or non-overlapping among sub-bands. [0168] FIG.12 depicts an example process for separated channel estimation by the BS utilizing the full-duplex operation, according to one embodiment. An example system may include one or more TRPs, one or more base stations e.g., gNB, one or more RISs, one or more users, and/or one or more supporting nodes (e.g., anchor nodes/beacon nodes, active elements at RIS, etc.), which may be configured for channel acquisition, for example, in an RIS-aided communication. [0169] As illustrated in the example of FIG. 12, the process may start at 1201 and, at 1202, a RIS may report capability to the BS. For example, the RIS may send capability information to the BS. At 1203, the BS may configure the RIS with a first RIS state (e.g., RIS state 1), for example, to acquire a BS-RIS channel. For example, the BS may send first configuration information to the RIS that indicates the first RIS state. At 1204, the BS may measure the BS-RIS channel (e.g., the BS may perform BS-RIS channel measurements). For example, the BS may determine BS-RIS CSI using full-duplex mode. The BS may configure the RIS state such that the RIS reflects back the received signal from the BS, back to the BS. Based on knowledge of the transmitted signal and the signal received from the RIS, while the RIS state was set (e.g., in state 1), the BS may acquire BS-RIS CSI. At 1205, the BS may configure the RIS with a second RIS state (e.g., RIS state 2), for example, to acquire a BS-RIS-WTRU channel. For example, the BS may send second configuration information to the RIS that indicates the second RIS state. At 1206, the BS may configure the WTRU. For example, the BS may send the set configuration information to the WTRU. At 1207, the WTRU may measure the RIS-WTRU channel (e.g., the WTRU may perform RIS-WTRU channel measurements). For example, the WTRU may determine RIS CSI and/or perform an RIS differential channel computation, utilizing which WTRU may acquire the RIS-WTRU channel. At 1208, the WTRU may report the RIS CSI to the BS. At 1209, the BS and/or the WTRU may perform separated channel computation using acquired BS-RIS, RIS-WTRU, and/or BS-RIS- WTRU channels. At 1210, the WTRU may report RIS separated CSI reports to the BS. The BS may update the configured RIS state. At 1211, the RIS may use the set and/or updated RIS state during DL and/or UL transmission(s). [0170] FIG. 13 depicts an example signaling diagram for full-duplex operation-based separated channel estimation, according to one embodiment. As shown in FIG. 13, a RIS may send RIS capability information to a BS. The BS may send WTRU configuration information to a WTRU. The BS may send RIS configuration information to the RIS. The BS may trigger the WTRU to perform a differential channel CSI acquisition and measurement. For example, the BS may send a CSI/CSI-RS activation trigger to the WTRU. The WTRU may perform the differential channel CSI acquisition and measurement in response to receipt of the CSI/CSI-RS activation trigger. The BS may schedule (e.g., update) the RIS state (e.g., RIS off state, RIS state 1, etc.) during CSI-RS transmission(s). The WTRU may send a legacy CSI (e.g., a legacy CSI report) and/or a differential CSI (e.g., a differential CSI report) to the BS. The BS may send BS-RIS CSI to the WTRU. The WTRU may perform a separated channel CSI acquisition. For example, the WTRU may acquire a BS-RIS-WTRU channel based on the RIS-WTRU CSI and/or the BS-RIS CSI. The WTRU may send separated CSI (e.g., a separated CSI report) to the BS. The BS may schedule (e.g., update) the RIS state for other DL and/or UL transmission(s). For example, the BS may schedule the RIS state for DL/UL transmission(s) based on the separated CSI received from the WTRU. The BS may send a DL transmission to the WTRU using the BS-RIS-WTRU channel. The WTRU may send an UL transmission to the BS using the BS-RIS-WTRU channel. [0171] Additional signaling may be used in various scenarios, for example when sub- surface based or element-wise RIS configuration may be used or when the WTRU reporting may be varied based on NR specifications such as periodic, semi-persistent, aperiodic etc. Furthermore, some signaling shown in FIG.13 may be omitted in various examples. [0172] CSI-RS enhancements may be provided for full-duplex operation-based separated channel estimation. In the full-duplex operation-based separated channel estimation, the CSI-RS resources utilized as pilots for channel estimation may belong to the same resource block, or may be repeated in separate slots, and/or may be split across multiple slots. [0173] FIG.14 depicts example CSI-RS resource for full-duplex mode separated channel estimation with partial CSI estimated and utilized in a current resource block. Partial CSI- RS resources may be sent by one of the nodes (e.g., the BS). The first set of ^^ CSI-RS resources (where ^^ may represent the sub-surfaces, RIS elements, or the whole RIS surface), forming a resource set, may be directed towards a RIS, with RIS state configured to reflect back the signal to the transmitting node. The transmitting node (e.g., the BS) may estimate the partial channel between the transmitting node and the RIS using the first set of M CSI-RS resources. The receiving node (e.g., the WTRU) may estimate a differential RIS-aided channel using the next ^^ CSI-RS resources. The WTRU may acquire the remaining separated channel using the differential channel and the partial channel. [0174] FIG.15 depicts example CSI-RS resource for full-duplex mode separated channel estimation with partial CSI estimated with pre-configured frequency and utilized in between. The frequency of estimating the partial channel utilizing the full-duplex mode may be configured (e.g., by the network). The frequency for estimating the partial channel may be different from the frequency of acquiring the differential RIS-aided channel, as shown in FIG. 15. The CSI-RS resource set for acquiring the partial channel may be communicated at preset intervals (e.g., at a first periodicity). One or more CSI-RS resource sets for differential channel estimation may be communicated in between the CSI-RS resource sets for acquiring the partial channel with a second periodicity. CSI-RS resource sets for differential channel estimation may be communicated in between the CSI-RS resource sets for acquiring the partial channel when one of the separated channel paths does not change as frequently as the other channel path e.g. in case when BS and RIS nodes are mostly static, while the WTRU is mobile and frequently moving. [0175] FIG. 16 depicts example CSI-RS resources for full-duplex mode separated channel estimation with partial CSI estimated in parts based on pre-defined configuration and utilized after complete or partial estimation. CSI-RS resources, to minimize the latency for partial channel acquisition, of one of the separated channel paths may be split into multiple smaller CSI-RS resource sets. For example, as shown in FIG.16, the full- duplex operation-based partial CSI acquisition may be split into ^^ ^ ^^ size resource sets which may be communicated at a predetermined frequency. In between the resources for the full-duplex operation-based partial CSI acquisition, the RIS-aided channel CSI-RS resource sets may be transmitted. In case when BS is in full-duplex mode, the BS may acquire partial channel in union of, i.e., by combining, all smaller k CSI-RS resource sets which may then be explicitly or implicitly communicated to the UE after every kth resource set or after the partial channel is fully acquired. [0176] A WTRU may identify the communicated CSI-RS resource with the same sub- carrier offset(s) as indicated in CSI-RS resource configuration. In examples, different resources may have different offsets. Different CSI-RS resources may have the same or different density in frequency, bandwidth, number of antenna ports, code-division multiplexing (CDM) type, etc. The periodicity of the CSI-RS resources may be the same or different, as well as the slot offset. The CSI-RS resources may be associated with one or more constraints. For example, a constraint may be that the CSI-RS resources do not overlap in time on any symbol. [0177] The CSI-RS resources in a CSI-RS resource set for RIS-aided channel estimation may be configured in a list e.g., a list of CSI-RS resource IDs. These resource IDs may be associated with a partial CSI ID as communicated e.g., by the BS to the WTRU. The WTRU may utilize this association to identify the corresponding partial CSI for the estimated RIS-aided channel. [0178] The one or more resource set(s) including the M CSI-RS resources may be included (e.g., by their IDs) in a CSI-RS resource setting (e.g., in the IE CSI- ResourceConfig). A CSI-RS resource setting may include a list of CSI-RS resource sets, e.g., for partial and/or RIS-aided channel measurement. The list of CSI-RS resource sets may comprise a sequence of CSI-RS resource set IDs of the CSI-RS resource sets, which may be configured elsewhere. [0179] CSI report enhancements may be provided for full-duplex mode separated channel estimation. During downlink transmission, a WTRU may perform measurements and CSI acquisition by utilizing the received pilot/reference signals transmitted by a BS. Based on these measurements, in case of transmissions in FDD, the WTRU may report (e.g., either explicitly or implicitly) the quality of channel by either explicitly transmitting the CSI, e.g., as channel coefficients, or implicitly, in the form of the CSI reports e.g., RI, PMI, CQI etc. Whereas, when transmissions occur in TDD, the BS may exploit the reciprocity of the communication channel and obtain the channel estimates itself. The BS may use the CSI reports and/or channel estimates to adjust/update the system parameters such as type pf precoder, modulation, code rate etc. In the RIS-aided communication system, along with the conventional system parameters, RIS-aided CSI may be exploited to adjust/update the RIS parameters e.g., RIS state and RIS-aided path parameters at the BS, e.g., codebook and precoder selection for BS-RIS-WTRU path. In this section, the CSI report enhancements for RIS-aided system are discussed for differential and separated channels. [0180] Reporting enhancements may be provided for separated channels. In case of separated channel, two or more communication links may be used, e.g., a BS-RIS link and a RIS-WTRU link. The WTRU may perform measurements based on the received pilots from BS in case of downlink transmission and to acquire these separated channels. The WTRU may generate independent CSI reports or joint CSI reports and communicate it to the BS, for example, to indicate the quality of these separated channels. RIS separated channel reporting may include one or more of the following. [0181] The WTRU may indicate individual reports each for BS-RIS and RIS-WTRU channels. The independent reports may contain a same set of indicators or a different set of indicators. For example, the WTRU may report PMI for the BS-RIS channel and the WTRU may report PMI, RI, and CQI for the RIS-WTRU channel. These parameters may be configured by the BS indicating the performance indicators required in each report based on the scenario and/or application. [0182] The independent report parameters may be configured by the BS at same or different periodicity. In examples, the WTRU may communicate RIS-WTRU channel reports more frequently than BS-RIS channel reports. [0183] The WTRU may send the preferred set of periodicities for reporting CSI respective to individual separated channels (e.g., BS-RIS channels and/or RIS-UE channels) and/or for joint CSI. For example, the WTRU may request a greater periodicity for the WTRU- RIS channel as compared to the BS-RIS channel. In examples, the WTRU may send a request for on demand CSI reporting for the RIS separated channels. [0184] In case of independent reporting, the WTRU may be configured to communicate the CSI reports for one (e.g., only one) of the separated channels. For example, the WTRU may report (e.g., only report) RIS-WTRU channel reports and may not report BS- RIS CSI reports. [0185] In case of joint CSI reports for both the separated channels, the WTRU may indicate the performance indicators as a set (e.g., [PMI for BS-RIS, PMI for RIS-UE]). The index, presence, and/or order for each channel report may be configured in the WTRU report configuration by the BS. [0186] Instead of explicitly reporting the CSI performance indicators for separated channels, the WTRU may report the CSI performance indicators as a function of indicators e.g., instead on communicating the PMI for BS-RIS and PMI for RIS-WTRU, WTRU may communicate PMI for BS-RIS and PMI for RIS-WTRU as a function for example, a linear function, compression algorithms, etc. The function may be configured from a predefined set of functions by the BS in the report configuration. This can achieve the reduced overhead for CSI reporting. One exemplary solution how the BS can identify the PMI using linear equation shown in Equation 17. [0187] Consider that the maximum index achievable in PMI’s is p. Then, the following linear function represented by Equation 17 can be utilized by the WTRU for reporting the combined PMI. _^^ ^{^} _{^^, ^^} ^{^} _{ൌ V ൌ ^ ^^ ^ 1^ ^^ ^ ^^, (17)} where, ^^ indicates the PMI for BS-RIS path and ^^ represents the PMI for RIS-WTRU path. The value for ^^ can then be obtained as ^^ ^^ ^^ ^^ ^^^ ^{^} ^_ା^ ^ and the value of ^^ can then be computed as ^^ ^^ ^^ ^^ ^{^} െ ^^^ ^ ^^ ^ 1^^. [0188] The (e.g., only communicate) the separated CSI reports. The WTRU may communicate separated CSI reports and 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. The BS may select the CSI report to be reported by the WTRU based on the WTRU capabilities (e.g., if the WTRU is capable to perform separated channel estimation), application (e.g. eMBB, URLLC), and scenario (e.g. mobile WTRU with static BS and RIS nodes). [0189] A WTRU may be configured with RRC indicating 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., such as legacy and/or differential and/or separated), report periodicity, reporting functions etc. The WTRU may receive the CSI-RS for a set of RIS states that were configured at the RIS by the BS, a RIS controller, one or more WTRUs in the network, a RIC, etc. The WTRU may receive CSI-RS resource(s). The WTRU may measure and/or calculate the differential channel. The WTRU may report (e.g., send to the BS) the differential channel reports, for example, if configured in the CSI report configuration. The WTRU may calculate the separate BS- RIS and RIS-WTRU channels. The WTRU may report (e.g., send to the BS) separated channel CSI report(s), for example, if configured in the CSI report configuration. [0190] A RIS may report its capability to the network, BS, and/or RIS controlling node. The RIS may be configured with an element-wise or sub-surface configuration. The RIS may apply a sub-surface configuration during time instances determined by configuration, activation, indication, and/or triggering. The RIS may receive a RIS-element level RIS state. The RIS may apply the RIS-element level RIS state during configured time instances determined by configuration, activation, indication, and/or triggering. [0191] In some example embodiments, a method for full duplex operation based separated channel estimation within a network is provided. The method may include the transmitting of CSI-RS and acquiring a RIS channel via the CSI-RS directed towards RIS. First RIS channel estimates are sent to a the WTRU, and RIS-aided differential channel estimates are determined based on the first RIS channel estimates so as to estimate a RIS-WTRU channel. In some example embodiments, the CSI-RS may include a first set of CSI-RS resources having RIS state configured to reflect back to a transmitting node within the network. Further, a second set of CSI-RS resources may be used by the WTRU to estimate a differential RIS-aided channel. In some example embodiments, the frequency of determining estimates of the RIS-WTRU channel may be configured to be different that the frequency of acquiring the RIS channel. [0192] Some example embodiments may be directed to a process, which may be implemented by a WTRU, such as WTRU 102 discussed above. In an embodiment, the method may include receiving, from a network or BS, configuration information for RIS- based CSI acquisition (or measurement or estimation) and reporting. For example, the CSI measurement and reporting may be in full-duplex mode of operation. According to some example embodiments, the configuration information may indicate a type of CSI reporting and/or a set of RIS states. For instance, in one embodiment, the type of CSI reporting may be indicated as being separated CSI acquisition and reporting. In further example embodiments, the type of CSI reporting may additionally or alternatively include or may be indicated as differential CSI reporting and/or legacy CSI reporting. [0193] In an embodiment, the method may include receiving CSI-RS associated with the set of RIS states, and determining, based on the CSI-RS associated with the set of RIS states, separated BS-RIS channel and RIS-WTRU channel estimation in full-duplex mode. Based on the separated BS-RIS channel and RIS-WTRU channel estimation, the method may include sending at least one separated CSI report. For example, the at least one separated CSI report may include an independent CSI report indicating one of (1) CSI parameters associated with the BS-RIS channel estimation or (2) CSI parameters associated with the RIS-WTRU channel estimation, or the at least one CSI report may include a joint CSI report indicating (1) the CSI parameters associated with the BS-RIS channel estimation and (2) the CSI parameters associated with the RIS-WTRU channel estimation. [0194] In an embodiment, the method may include receiving CSI-RS resources. [0195] In an embodiment, the configuration information may further indicate any of: one or more reporting parameters corresponding to the type of CSI report, a CSI reporting function and/or CSI reporting periodicity. [0196] In an embodiment, the method may include sending any of a legacy CSI report and/or differential CSI report. For example, if the configuration information indicates that the type of CSI reporting is legacy CSI reporting, then the method may include sending a legacy CSI report. Similarly, if the configuration information indicates that the type of CSI reporting is differential CSI reporting, then the method may include sending a differential CSI report. [0197] In an embodiment, the independent CSI report indicating CSI parameters associated with the BS-RIS channel estimation may be sent at a first frequency and the independent CSI report indicating CSI parameters associated with the RIS-WTRU channel estimation may be sent at a second frequency. [0198] In an embodiment, the method may include sending an uplink transmission to the BS, e.g., using the BS-RIS-WTRU channel, and/or receiving a downlink transmission from the BS using the BS-RIS-WTRU channel. [0199] In an embodiment, the at least one separated CSI report may be sent in any of uplink control information (UCI) and/or a medium access control (MAC) control element (CE). [0200] In an embodiment, on condition that the at least one separated CSI report includes an independent CSI report, the method may comprise including, in the separated CSI report, a unique report identifier (ID) associated with both the CSI parameters associated with the BS-RIS channel estimation and the CSI parameters associated with the RIS- WTRU channel estimation. The unique report ID can therefore be used to associate the BS-RIS channel estimation with the RIS-WTRU channel estimation. [0201] In an embodiment, the configuration information may further indicate RIS-related configuration parameters comprising a number of RIS sub-surfaces and/or RIS elements in the x- and y-direction. [0202] In an embodiment, e.g., if the configuration information indicates that the type of CSI report is a differential CSI report, the method may include measuring a differential channel and sending a differential channel report indicating the measurement of the differential channel. [0203] Some example embodiments may be directed to a process, which may be implemented by a network element, such as a RIS. In an embodiment, the method may include the RIS reporting its capability to the network and/or a RIS controlling node. In an embodiment, the method may include receiving configuration information including an element-wise or sub-surface configuration. In an embodiment, the method may include applying sub-surface configuration during time instances determined by configuration, activation, indication, and/or triggering. In an embodiment, the method may include receiving a RIS-element level RIS state and applying the RIS-element level RIS state during configured time instances determined by configuration, activation, indication, and/or triggering. [0204] As used herein, the 3GPP standards terms and information elements described and used in this document are to be interpreted consistent with their meaning as commonly used in industry. For example, terms may further be interpreted consistently with their meaning in the following document, which is herein incorporated by reference: Marcu, Ioana & Pirnog, Ionut & Florea, Carmen & Dragulinescu, Ana. (2020). Delta-Sigma Modulation for Noise Cancellation in 5G-Compliant Network. Wireless Personal Communications.126.10.1007/s11277-020-07327-w. However, the terms and concepts disclosed herein include terms and concepts not disclosed or described in those documents, and thus the concepts and terms herein are not meant to be solely limited to how such terms are used in the existing standards. Rather, the standards and documents are referenced to the extent necessary in order to provide reference for understanding the background of terms used herein. [0205] The processes and instrumentalities described herein may apply in any combination, may apply to other wireless technologies, and for other services. A WTRU may refer to an identity of the physical device, or to the user's identity such as subscription related identities, e.g., MSISDN, SIP URI, etc. WTRU may refer to application based identities, e.g., user names that may be used per application. [0206] 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 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, WTRU, terminal, base station, RNC, and/or any host computer. [0207] 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. [0208] 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. [0209] 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. [0210] 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. [0211] 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. [0212] 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. [0213] 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. [0214] 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." [0215] 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. [0216] 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. [0217] 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. [0218] 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. [0219] 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.). [0220] 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. [0221] 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. [0222] 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. [0223] 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". [0224] 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. [0225] 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. [0226] 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" so intended. [0227] Although various have been described in terms of communication systems, it is contemplated that the systems may be implemented in software on microprocessors/general purpose computers (not shown). In certain embodiments, one or more of the functions of the various components may be implemented in software that controls a general-purpose computer. [0228] In addition, although some example embodiments are illustrated and described herein, the invention is not intended to just be limited to the details shown. Rather, various modifications and variations may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit or scope invention. REFERENCES [0229] The following references may have been referred to hereinabove, each of which is incorporated herein by reference in its entirety: Marcu, Ioana & Pirnog, Ionut & Florea, Carmen & Dragulinescu, Ana. (2020). Delta-Sigma Modulation for Noise Cancellation in 5G-Compliant Network. Wireless Personal Communications.126.10.1007/s11277-020- 07327-w.

Claims

What is Claimed is: 1. A wireless transmit/receive unit (WTRU), comprising: circuitry, including any of a processor, memory and transceiver, the circuitry configured to: receive, from a base station (BS), configuration information for reconfigurable intelligent surface (RIS)-based channel state information (CSI) acquisition and reporting in full-duplex mode, wherein the configuration information indicates (i) that a type of the CSI acquisition and reporting is separated CSI acquisition and reporting and (ii) a set of RIS states; receive channel state information-reference signal (CSI-RS) associated with the set of RIS states; determine, based on the CSI-RS associated with the set of RIS states, separated BS-RIS channel and RIS-WTRU channel estimation in full-duplex mode; and based on the separated BS-RIS channel and RIS-WTRU channel estimation, send at least one separated CSI report, wherein the at least one separated CSI report comprises one of: an independent CSI report indicating one of (1) CSI parameters associated with the BS-RIS channel estimation or (2) CSI parameters associated with the RIS- WTRU channel estimation, or a joint CSI report indicating (1) the CSI parameters associated with the BS- RIS channel estimation and (2) the CSI parameters associated with the RIS- WTRU channel estimation.

2. The WTRU of claim 1, wherein the configuration information further indicates any of: one or more reporting parameters corresponding to the type of CSI report, a CSI reporting function and/or CSI reporting periodicity.

3. The WTRU of claims 1 or 2, wherein the circuitry is configured to send any of a legacy CSI report and/or differential CSI report.

4. The WTRU of any of claims 1-3, wherein the independent CSI report indicating CSI parameters associated with the BS-RIS channel estimation is sent at a first frequency and the independent CSI report indicating CSI parameters associated with the RIS- WTRU channel estimation is sent at a second frequency.

5. The WTRU of any of claims 1-4, wherein the circuitry is configured to send an uplink transmission to the BS using the BS-RIS-WTRU channel or receive a downlink transmission from the BS using the BS-RIS-WTRU channel.

6. The WTRU of any of claims 1-5, wherein the at least one separated CSI report is sent in any of uplink control information (UCI) and a medium access control (MAC) control element (CE).

7. The WTRU of any of claims 1-6, wherein, on condition that the at least one separated CSI report comprises an independent CSI report, the circuitry is configured to include, in the separated CSI report, a unique report identifier associated with both (1) the CSI parameters associated with the BS-RIS channel estimation and (2) the CSI parameters associated with the RIS-WTRU channel estimation, to associate the BS- RIS channel estimation with the RIS-WTRU channel estimation.

8. The WTRU of any of claims 1-7, wherein the configuration information further indicates RIS-related configuration parameters comprising any of: a number of RIS sub- surfaces and/or RIS elements in the x- and y-direction.

9. The WTRU of any of claims 1-8, wherein the circuitry is configured to: measure a differential channel; and on condition that the configuration information indicates that the type of CSI report is a differential CSI report, send a differential channel report indicating the measurement of the differential channel.

10. A method, implemented by a wireless transmit/receive unit (WTRU), the method comprising: receiving, from a base station (BS), configuration information for reconfigurable intelligent surface (RIS)-based channel state information (CSI) acquisition and reporting in full-duplex mode, wherein the configuration information indicates (i) that a type of the CSI acquisition and reporting is separated CSI acquisition and reporting and (ii) a set of RIS states; receiving channel state information-reference signal (CSI-RS) associated with the set of RIS states; determining, based on the CSI-RS associated with the set of RIS states, separated BS-RIS channel and RIS-WTRU channel estimation in full-duplex mode; and based on the separated BS-RIS channel and RIS-WTRU channel estimation, sending at least one separated CSI report, wherein the at least one separated CSI report comprises one of: an independent CSI report indicating one of (1) CSI parameters associated with the BS-RIS channel estimation or (2) CSI parameters associated with the RIS- WTRU channel estimation, or a joint CSI report indicating (1) the CSI parameters associated with the BS- RIS channel estimation and (2) the CSI parameters associated with the RIS- WTRU channel estimation.

11. The method of claim 10, wherein the configuration information further indicates any of: one or more reporting parameters corresponding to the type of CSI report, a CSI reporting function and/or CSI reporting periodicity.

12. The method of claims 10 or 11, comprising sending any of a legacy CSI report and/or differential CSI report.

13. The method of any of claims 10-12, wherein the independent CSI report indicating CSI parameters associated with the BS-RIS channel estimation is sent at a first frequency and the independent CSI report indicating CSI parameters associated with the RIS- WTRU channel estimation is sent at a second frequency.

14. The method of any of claims 10-13, comprising sending an uplink transmission to the BS using the BS-RIS-WTRU channel or receiving a downlink transmission from the BS using the BS-RIS-WTRU channel.

15. The method of any of claims 10-14, wherein the at least one separated CSI report is sent in any of uplink control information (UCI) and a medium access control (MAC) control element (CE).

16. The method of any of claims 10-15, wherein, on condition that the at least one separated CSI report comprises an independent CSI report, the method comprises including, in the separated CSI report, a unique report identifier associated with both (1) the CSI parameters associated with the BS-RIS channel estimation and (2) the CSI parameters associated with the RIS-WTRU channel estimation, to associate the BS- RIS channel estimation with the RIS-WTRU channel estimation.

17. The method of any of claims 10-16, wherein the configuration information further indicates RIS-related configuration parameters comprising any of: a number of RIS sub-surfaces and/or RIS elements in the x- and y-direction.

18. The method of any of claims 10-17, comprising: measuring a differential channel; and on condition that the configuration information indicates that the type of CSI report is a differential CSI report, sending a differential channel report indicating the measurement of the differential channel.