Differential channel estimation and probing associated with reconfigurable smart surfaces

Abstract

A wireless transmit / receive unit (WTRU) may receive configuration information associated with a reconfigurable smart surface (RIS). The configuration information may indicate a first set of RIS parameters associated with the first RIS configuration. The configuration information may indicate a second set of RIS parameters associated with a second RIS configuration. The WTRU may receive a first channel state information reference signal (CSI-RS) associated with the first set of RIS parameters. The WTRU may receive a second CSI-RS associated with a second set of RIS parameters. The WTRU may determine a differential CSI measurement associated with a base station (BS)-RIS-WTRU channel based on a first CSI-RS associated with the first set of RIS parameters and a second CSI-RS associated with the second set of RIS parameters. The WTRU may transmit a CSI report including the differential CSI measurement.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 433,076, filed on December 16, 2022, the disclosure of which is incorporated herein by reference in its entirety. Background Art

[0003] Mobile communication using wireless communication continues to evolve. The fifth generation can be referred to as 5G. The previous generation (legacy) mobile communication can be, for example, the fourth generation (4G) Long Term Evolution (LTE). Summary of the Invention

[0004] Systems, methods, and instrumentalities for channel estimation related to a Reconfigurable Intelligent Surface (RIS) are described herein. In an example, a Wireless Transmit / Receive Unit (WTRU) may receive configuration information associated with the RIS. The configuration information may indicate a first set of RIS parameters associated with a first RIS configuration. The configuration information may indicate a second set of RIS parameters associated with a second RIS configuration. The WTRU may receive a first Channel State Information - Reference Signal (CSI - RS) associated with the first set of RIS parameters. The WTRU may receive a second CSI - RS associated with the second set of RIS parameters. The WTRU may determine differential CSI measurements associated with the Base Station (BS) - RIS - WTRU channel based on the first CSI - RS associated with the first set of RIS parameters and the second CSI - RS associated with the second set of RIS parameters. The WTRU may transmit a CSI report including the differential CSI measurements.

[0005] In an example, the first RIS configuration may correspond to a first RIS state, and the second RIS configuration may correspond to a second RIS state. The first set of RIS parameters may represent the first RIS state. The second set of RIS parameters may represent the second RIS state. The RIS parameters may include phase shifts and / or amplification gains. For example, the first set of RIS parameters may include a first phase shift and a first amplification gain, and the second set of RIS parameters may include a second phase shift and a second amplification gain. The first phase shift and the second phase shift may be different, and the first amplification gain and the second amplification gain may be different. In some examples, the first set of RIS parameters may represent a first RIS state of a sub - surface of the RIS, and the second set of RIS parameters may represent a second RIS state of the sub - surface of the RIS.

[0006] In an example, the WTRU may determine a first channel measurement based on a first CSI-RS and a first set of RIS parameters. The WTRU may determine a second channel measurement based on a second CSI-RS and a second set of RIS parameters. The WTRU may determine a differential CSI measurement associated with the BS-RIS-WTRU channel based on the first channel measurement and the second channel measurement.

[0007] In an example, the WTRU may determine a first list of CSI-RS resource identifiers (IDs) and a second list of CSI-RS resource IDs based on received configuration information. The first list of CSI-RS resource IDs may be associated with a first RIS configuration. The second list of CSI-RS resource IDs may be associated with a second RIS configuration. The WTRU may determine a first set of CSI-RS resources based on the first list of CSI-RS resource IDs. The WTRU may use one or more CSI-RS resources from the first set of CSI-RS resources to receive the first CSI-RS. The WTRU may determine a second set of CSI-RS resources based on the second list of CSI-RS resource IDs. The WTRU may use one or more CSI-RS resources from the second set of CSI-RS resources to receive the second CSI-RS.

[0008] In an example, the WTRU may determine a rank indicator (RI) associated with the BS-RIS-WTRU channel, a precoding matrix indicator (PMI) associated with the BS-RIS-WTRU channel, and / or a channel quality indicator (CQI) associated with the BS-RIS-WTRU channel based on the differential CSI measurement. The WTRU may determine an RI associated with the BS-WTRU channel between the WTRU and the BS, a PMI associated with the BS-WTRU channel between the WTRU and the BS, and a CQI associated with the BS-WTRU channel between the WTRU and the BS. The WTRU may report the RI, PMI, and CQI associated with the BS-RIS-WTRU channel, and the RI, PMI, and CQI associated with the BS-WTRU channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1A is a system diagram illustrating an example communication system in which one or more disclosed embodiments may be implemented;

[0010] Figure 1B is a system diagram illustrating an example wireless transmit / receive unit (WTRU) that may be used in the Figure 1A illustrated communication system according to one embodiment;

[0011] Figure 1C is a system diagram illustrating an example that may be in Figure 1ASystem diagrams of an example radio access network (RAN) and an example core network (CN) used in the illustrated communication system;

[0012] Figure 1D is a system diagram illustrating another example RAN and another example CN that can be used in the Figure 1A illustrated communication system;

[0013] Figure 2 illustrates an example of a RIS-assisted system;

[0014] Figure 3 illustrates an example distribution of RIS elements into subsurfaces: Figure 3 A and Figure 3 B illustrate an example of a uniform distribution, while Figure 3 C illustrates an example of a non-uniform distribution.

[0015] Figure 4 illustrates an example of a RIS-assisted system in which the RIS is divided into S (e.g., S = 6) subsurfaces;

[0016] Figure 5 illustrates an example of differential channel estimation;

[0017] Figure 6 illustrates an example signaling diagram for differential channel estimation (e.g., RIS differential channel estimation);

[0018] Figure 7 illustrates an example signaling diagram for differential channel estimation (e.g., RIS differential channel estimation);

[0019] Figure 8 illustrates an example of CSI-RS resources having two resource sets of size M;

[0020] Figure 9 illustrates an example of CSI-RS resources having resource sets scattered in different time slots;

[0021] Figure 10 illustrates an example of CSI-RS resources that appear in multiple time slots;

[0022] Figure 11 illustrates an example of CSI-RS resources with M = 1; and

[0023] Figure 12 illustrates an example of (one or more) CSI-RS resources having (one or more) RIS states. Detailed Description

[0024] Figure 1AFIG. is a schematic diagram illustrating an example communication system 100 in which one or more of the disclosed embodiments may be implemented. The communication system 100 may be a multi-access system that provides content such as voice, data, video, messages, broadcasts, etc. to a plurality of wireless users. The communication system 100 may enable the plurality of wireless users to access this content by sharing system resources including wireless bandwidth. For example, the communication system 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 UWDFT-s OFDM), unique-word OFDM (UW-OFDM), resource block filtered OFDM, filter bank multicarrier (FBMC), etc.

[0025] As Figure 1A shown, the communication system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, RAN 104 / 113, CN 106 / 115, public switched telephone network (PSTN) 108, Internet 110, and other networks 112, but it should be understood 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, any one of the WTRUs 102a, 102b, 102c, 102d may be referred to as a "station" and / or "STA", may be configured to transmit and / or receive wireless signals, and may include a user equipment (UE), mobile station, fixed or mobile subscriber unit, subscription-based unit, pager, cellular phone, personal digital assistant (PDA), smartphone, laptop, netbook, personal computer, wireless sensor, hotspot or Mi-Fi device, Internet of Things (IoT) device, watch or other wearable device, head-mounted display (HMD), vehicle, drone, medical device and applications (e.g., remote surgery), industrial device and applications (e.g., robots and / or other wireless devices operating in an industrial and / or automation processing chain environment), consumer electronic devices, devices operating on commercial and / or industrial wireless networks, etc. Any one of the WTRUs 102a, 102b, 102c, and 102d may be interchangeably referred to as a WTRU.

[0026] The communication system 100 may also include base station 114a and / or base station 114b. Each of base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as CN 106 / 115, the Internet 110, and / or other networks 112. By way of example, base stations 114a, 114b may be base transceiver stations (BTSs), Node Bs, eNode Bs, home Node Bs, home eNode Bs, gNBs, NR Node Bs, site controllers, access points (APs), wireless routers, etc. Although base stations 114a, 114b are each depicted as a single element, it should be understood that base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0027] Base station 114a may be part of RAN 104 / 113, which may also include other base stations and / or network elements (not shown), such as base station controllers (BSCs), radio network controllers (RNCs), relay nodes, etc. Base station 114a and / or 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 cells (not shown). These frequencies may be in licensed spectrum, unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide coverage of wireless services to a particular geographic area, which may be relatively fixed or may change over time. The cell may also be divided into cell sectors. For example, the cell associated with base station 114a may be divided into three sectors. Thus, in one embodiment, base station 114a may include three transceivers, i.e., one transceiver for each sector of the cell. In one embodiment, base station 114a may employ multiple-input multiple-output (MIMO) technology and may use multiple transceivers for each sector of the cell. For example, beamforming may be used to transmit and / or receive signals in a desired spatial direction.

[0028] Base stations 114a, 114b may communicate with one or more of WTRUs 102a, 102b, 102c, 102d via air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, centimeter wave, millimeter wave, infrared (IR), ultraviolet (UV), visible light, etc.). Any suitable radio access technology (RAT) may be used to establish air interface 116.

[0029] More specifically, as described above, the communication system 100 can be a multi-access system and can employ one or more channel access schemes such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, etc. For example, the base stations 114a in the RAN 104 / 113 and the WTRUs 102a, 102b, 102c can implement radio technologies such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which can use Wideband CDMA (WCDMA) to establish the air interfaces 115 / 116 / 117. WCDMA can include communication protocols such as High-Speed Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA can include High-Speed Downlink (DL) Packet Access (HSDPA) and / or High-Speed UL Packet Access (HSUPA).

[0030] In one embodiment, the base stations 114a and the WTRUs 102a, 102b, 102c can implement radio technologies such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which can use Long-Term Evolution (LTE) and / or Advanced LTE (LTE-A) and / or Advanced LTE Pro (LTE-A Pro) to establish the air interface 116.

[0031] In one embodiment, the base stations 114a and the WTRUs 102a, 102b, 102c can implement radio technologies such as NR radio access, which can use New Radio (NR) to establish the air interface 116.

[0032] In an embodiment, the base stations 114a and the WTRUs 102a, 102b, 102c can implement multiple radio access technologies. For example, the base stations 114a and the WTRUs 102a, 102b, 102c can implement LTE radio access and NR radio access together, for example, using the Dual Connectivity (DC) principle. Thus, the air interfaces used by the WTRUs 102a, 102b, 102c can be characterized by multiple types of radio access technologies and / or transmissions to / from multiple types of base stations (e.g., eNB and gNB).

[0033] 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 so on.

[0034] For example, Figure 1A the base station 114b in may be a wireless router, a home Node B, a home eNodeB, or an access point, and may utilize any suitable RAT to facilitate wireless connectivity in a local area, such as a commercial establishment, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., for drones), a road, etc. 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 one 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 pico cell or a femto cell. As Figure 1A shown, the base station 114b may be directly connected to the Internet 110. Thus, the base station 114b may not need to access the Internet 110 via the CN 106 / 115.

[0035] The RAN 104 / 113 may communicate with the CN 106 / 115, and the CN 106 / 115 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 different Quality of Service (QoS) requirements, such as different throughput requirements, latency requirements, fault tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, etc. The CN 106 / 115 may provide call control, billing services, location-based services for mobile devices, prepaid calling, Internet connectivity, video distribution, etc. and / or perform advanced security functions, such as user authentication. Although in Figure 1AAlthough not shown in the figure, it should be understood that RAN 104 / 113 and / or CN 106 / 115 can communicate directly or indirectly with other RANs that use the same RAT as RAN 104 / 113 or a different RAT. For example, in addition to being connected to RAN 104 / 113 which may utilize NR radio technology, CN 106 / 115 can also communicate with another RAN (not shown) that uses GSM, UMTS, CDMA2000, WiMAX, E-UTRA, or WiFi radio technology.

[0036] CN 106 / 115 can also serve as a gateway for WTRU 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 can include a circuit-switched telephone network that provides plain old telephone service (POTS). The Internet 110 can include a global system of interconnected computer networks and devices that use common communication protocols such as the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and / or the Internet Protocol (IP) in the TCP / IP Internet protocol suite. The network 112 can include wired and / or wireless communication networks owned and / or operated by other service providers. For example, the network 112 can include another CN that is connected to one or more RANs, which can use the same RAT as RAN 104 / 113 or a different RAT.

[0037] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communication system 100 can include multi-mode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d can include multiple transceivers for communicating with different wireless networks via different wireless links). For example, Figure 1A the WTRU 102c shown in the figure can be configured to communicate with a base station 114a that can use cellular-based radio technology and communicate with a base station 114b that can use IEEE 802 radio technology.

[0038] Figure 1B is a system diagram illustrating an example WTRU 102. As Figure 1B shown, among other things, the WTRU 102 can particularly include a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, a non-removable memory 130, a removable memory 132, a power supply 134, a Global Positioning System (GPS) chipset 136, and / or other peripheral devices 138, etc. It should be understood that the WTRU 102 can include any sub-combination of the foregoing elements while remaining consistent with the embodiments.

[0039] The processor 118 can be a general-purpose processor, a dedicated processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) circuit, any other type of integrated circuit (IC), a state machine, etc. The processor 118 can perform signal encoding, data processing, power control, input / output processing, and / or any other functions that enable the WTRU 102 to operate in a wireless environment. The processor 118 can be coupled to a transceiver 120, and the transceiver 120 can be coupled to a transmit / receive element 122. Although Figure 1B the processor 118 and the transceiver 120 are depicted as separate components, it should be understood that the processor 118 and the transceiver 120 can be integrated together in an electronic package or chip.

[0040] The transmit / receive element 122 can be configured to transmit signals to or receive signals from a base station (e.g., base station 114a) over the air interface 116. For example, in one embodiment, the transmit / receive element 122 can be an antenna configured to transmit and / or receive RF signals. In one embodiment, the transmit / receive element 122 can be a transmitter / detector configured to transmit and / or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit / receive element 122 can be configured to transmit and / or receive both RF and optical signals. It should be understood that the transmit / receive element 122 can be configured to transmit and / or receive any combination of wireless signals.

[0041] Although the transmit / receive element 122 is depicted as a single element in Figure 1B the WTRU 102 can include any number of transmit / receive elements 122. More specifically, the WTRU 102 can employ MIMO technology. Thus, in one embodiment, the WTRU 102 can include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0042] The transceiver 120 can be configured to modulate the signals to be transmitted by the transmit / receive element 122 and demodulate the signals received by the transmit / receive element 122. As described above, the WTRU 102 can have multi-mode capabilities. Thus, for example, the transceiver 120 can include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as NR and IEEE802.11.

[0043] The processor 118 of the WTRU 102 may be coupled to a speaker / microphone 124, a keypad 126, and / or a display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or an organic light emitting diode (OLED) display unit), and may receive user input data therefrom. 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 (e.g., non-removable memory 130 and / or 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, etc. In other embodiments, the processor 118 may access information from and store data in a memory that is not physically located on the WTRU 102 (e.g., a server or a home computer (not shown)).

[0044] The processor 118 may receive power from a power source 134 and may be configured to distribute and / or control power to 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 cells (e.g., nickel cadmium (NiCd), nickel zinc (NiZn), nickel metal hydride (NiMH), lithium ion (Li-ion), etc.), a solar cell, a fuel cell, etc.

[0045] The processor 118 may also be coupled to a 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 instead of, information from the GPS chipset 136, the WTRU 102 may receive location information from a base station (e.g., base stations 114a, 114b) over the air interface 116, and / or may determine its location based on the timing of signals received from two or more nearby base stations. It should be understood that the WTRU 102 may obtain location information by any suitable location determination method while remaining consistent with the embodiments.

[0046] The processor 118 may be further coupled to other peripheral devices 138, which may include one or more software and / or hardware modules that provide additional features, functions, and / or wired or wireless connections. For example, the peripheral devices 138 may include an accelerometer, an electronic compass, a satellite transceiver, a digital camera (for photos and / or videos), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands-free headset, Modules, FM radio units, digital music players, media players, electronic game player modules, Internet browsers, virtual reality and / or augmented reality (VR / AR) devices, activity trackers, etc. The peripheral device 138 may include one or more sensors, which 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 geographical location sensor, an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, an attitude sensor, a biosensor, and / or a humidity sensor, etc.

[0047] The WTRU 102 may include a full-duplex radio for which the transmission and reception of some or all signals (e.g., signals associated with a particular subframe for UL (e.g., for transmission) and downlink (e.g., for reception)) may be concurrent and / or simultaneous. The full-duplex radio may include an interference management unit to reduce and / or substantially eliminate self-interference via hardware (e.g., a choke) or via signal processing by a processor (e.g., a separate processor (not shown) or via the processor 118). In one embodiment, the WTRU 102 may include a half-duplex radio for which the transmission and reception of some or all signals (e.g., signals associated with a particular subframe for UL (e.g., for transmission) or downlink (e.g., for reception)).

[0048] Figure 1C FIG. is a system diagram of the RAN 104 and the CN 106 according to an embodiment. As described above, the RAN 104 may communicate with the WTRU 102a, 102b, 102c over the air interface 116 using E-UTRA radio technology. The RAN 104 may also communicate with the CN 106.

[0049] The RAN 104 may include eNode-Bs 160a, 160b, 160c, but it should be understood that the RAN 104 may include any number of eNode-Bs while remaining consistent with the embodiment. The eNode-Bs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRU 102a, 102b, 102c over the air interface 116. In one embodiment, the eNode-Bs 160a, 160b, 160c may implement MIMO technology. Thus, for example, the eNode-B 160a may use multiple antennas to transmit wireless signals to and / or receive wireless signals from the WTRU 102a.

[0050] Each of eNode-Bs 160a, 160b, and 160c can be associated with a specific cell (not shown) and can be configured to handle radio resource management decisions, handover decisions, user scheduling in UL and / or DL, etc. As Figure 1C shown, eNode-Bs 160a, 160b, and 160c can communicate with each other over the X2 interface.

[0051] Figure 1C The CN 106 shown in can include a Mobility Management Entity (MME) 162, a Serving Gateway (SGW) 164, and a Packet Data Network (PDN) Gateway (or PGW) 166. Although each of the foregoing elements is described as part of the CN 106, it should be understood that any of these elements can be owned and / or operated by entities other than the CN operator.

[0052] The MME 162 can be connected to each eNode-B 160a, 160b, 160c in the RAN 104 via the S1 interface and can act as a control node. For example, the MME 162 can be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation / deactivation, selecting a specific serving gateway during the initial attachment of the WTRUs 102a, 102b, 102c, etc. The MME 162 can provide control plane functions for handover between the RAN 104 and other RANs (not shown) employing other radio technologies such as GSM and / or WCDMA.

[0053] The SGW 164 can be connected to each eNode B 160a, 160b, 160c in the RAN 104 via the S1 interface. The SGW 164 can generally route and forward user data packets to / from the WTRUs 102a, 102b, 102c. The SGW 164 can perform other functions such as anchoring the user plane during handover between eNode Bs, triggering paging when DL data is available for the WTRUs 102a, 102b, 102c, managing and storing the context of the WTRUs 102a, 102b, 102c, etc.

[0054] The SGW 164 can be connected to the PGW 166, which can provide the WTRUs 102a, 102b, 102c with access to a packet switched network such as the Internet 110 to facilitate communication between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0055] CN 106 may facilitate communication with other networks. For example, CN 106 may provide the WTRUs 102a, 102b, 102c with access to a circuit-switched network such as the PSTN 108 to facilitate communication between the WTRUs 102a, 102b, 102c and traditional landline communication devices. For example, CN 106 may include an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts as an interface between CN 106 and the PSTN 108, or may communicate therewith. Additionally, CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers.

[0056] Although the WTRU is described in Figures 1A - 1D as a wireless terminal, it is contemplated that in some representative embodiments, such a terminal may use (e.g., temporarily or permanently) a wired communication interface to the communication network.

[0057] In a representative embodiment, another network 112 may be a WLAN.

[0058] 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 access or interface with a distributed system (DS) or another type of wired / wireless network that transports traffic to and / or from the BSS. Traffic destined for an STA from outside the BSS may arrive at the AP and may be delivered to the STA. Traffic originating from an STA to a destination outside the BSS may be sent to the AP to be delivered to the corresponding destination. For example, traffic between STAs within the BSS may be sent through the AP, where the source STA may send the traffic to the AP and the AP may deliver the traffic to the destination STA. Traffic between STAs within the BSS may be considered and / or referred to as peer-to-peer traffic. Peer-to-peer traffic may be sent between the source and destination STAs (e.g., directly between them) using direct link setup (DLS). In some representative embodiments, DLS may use 802.11e DLS or 802.11z tunnel DLS (TDLS). A WLAN using an independent BSS (IBSS) mode may not have an AP, and STAs within the IBSS or using the IBSS (e.g., all STAs) may communicate directly with each other. The IBSS communication mode is sometimes referred to herein as the "ad hoc" communication mode.

[0059] When operating in 802.11ac infrastructure mode or a similar operating mode, the AP can transmit beacons on a fixed channel (e.g., the primary channel). The primary channel can be of a fixed width (e.g., a 20 MHz wide bandwidth) or a width dynamically set via signaling. The primary channel can be the operating channel of the BSS and can be used by the STA to establish a connection with the AP. In some representative embodiments, for example, in 802.11 systems, Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) can be implemented. For CSMA / CA, STAs including the AP (e.g., each STA) can sense the primary channel. If a particular STA senses / detects and / or determines that the primary channel is busy, that particular STA can back off. Only one STA (e.g., only one station) can transmit at any given time in a given BSS.

[0060] High Throughput (HT) STAs can communicate using 40 MHz wide channels, e.g., by combining the primary 20 MHz channel with an adjacent or non - adjacent 20 MHz channel to form a 40 MHz wide channel.

[0061] Very High Throughput (VHT) STAs can support channels that are 20 MHz, 40 MHz, 80 MHz, and / or 160 MHz wide. 40 MHz and / or 80 MHz channels can be formed by combining consecutive 20 MHz channels. A 160 MHz channel can be formed by combining eight consecutive 20 MHz channels or by combining two non - consecutive 80 MHz channels, which can be referred to as an 80 + 80 configuration. For the 80 + 80 configuration, after channel coding, the data can pass through a segment parser, which can divide the data into two streams. The Inverse Fast Fourier Transform (IFFT) processing and time - domain processing can be performed separately on each stream. These streams can be mapped to two 80 MHz channels, and the data can be transmitted by the transmitting STA. At the receiver of the receiving STA, the operation of the above 80 + 80 configuration can be reversed, and the combined data can be sent to the Media Access Control (MAC).

[0062] 802.11af and 802.11ah support operation modes below 1 GHz. The channel operation bandwidth and carrier in 802.11af and 802.11ah are reduced compared 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 can support metering type control / machine type communication, such as MTC devices in a macro coverage area. MTC devices can have certain capabilities, for example, limited capabilities, including supporting (e.g., only supporting) certain and / or limited bandwidths. MTC devices can include a battery with a battery life higher than a threshold (e.g., to maintain a very long battery life).

[0063] A WLAN system that can support multiple channels and channel bandwidths (e.g., 802.11n, 802.11ac, 802.11af, and 802.11ah) includes a channel that can be designated as a primary channel. The bandwidth of the primary channel can be equal to the maximum common operation bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel can be set and / or restricted by one STA among all STAs operating in the BSS that supports the minimum bandwidth operation mode. In an example of 802.11ah, for an STA that supports (e.g., only supports) the 1 MHz mode (e.g., an MTC type device), the primary channel can be 1 MHz wide, even if the AP and other STAs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16 MHz, and / or other channel bandwidth operation modes. Carrier sensing and / or network allocation vector (NAV) setting may depend on the state of the primary channel. If the primary channel is busy, for example, due to an STA (which only supports the 1 MHz operation mode) transmitting to the AP, all available frequency bands can be considered busy, even if most of the frequency bands remain idle and can be available.

[0064] In the United States, the available frequency band that 802.11ah can use is from 902 MHz to 928 MHz. In Korea, the available frequency band is from 917.5 MHz to 923.5 MHz. In Japan, the available frequency band is from 916.5 MHz to 927.5 MHz. The total available bandwidth for 802.11ah is 6 MHz to 26 MHz, depending on the country code.

[0065] Figure 1DFIG. illustrates a system diagram of RAN 113 and CN 115 according to one embodiment. As described above, RAN 113 may communicate with WTRUs 102a, 102b, 102c over air interface 116 using NR radio technology. RAN 113 may also communicate with CN 115.

[0066] RAN 113 may include gNBs 180a, 180b, 180c, but it should be understood that RAN113 may include any number of gNBs while remaining consistent with the embodiment. gNBs 180a, 180b, 180c may each include one or more transceivers for communicating with WTRUs 102a, 102b, 102c over air interface 116. In one embodiment, gNBs 180a, 180b, 180c may implement MIMO technology. For example, gNB 180a, 108b may utilize beamforming to transmit signals to and / or receive signals from gNBs 180a, 180b, 180c. Thus, for example, gNB 180a may use multiple antennas to transmit wireless signals to and / or receive wireless signals from WTRU 102a. In one embodiment, gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, gNB 180a may transmit multiple component carriers (not shown) to WTRU 102a. A subset of these component carriers may be on unlicensed spectrum while the remaining component carriers may be on licensed spectrum. In one embodiment, 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).

[0067] WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using transmissions associated with scalable numerology. For example, the OFDM symbol interval and / or the OFDM subcarrier interval may be different for different transmissions, different cells, and / or different portions of the radio transmission spectrum. WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using subframes or transmission time intervals (TTIs) of various or scalable lengths (e.g., including a variable number of OFDM symbols and / or of continuously variable absolute time).

[0068] gNBs 180a, 180b, 180c may be configured to communicate with WTRUs 102a, 102b, 102c in stand-alone configuration and / or non-stand-alone configuration. In stand-alone configuration, WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c without also accessing another RAN (e.g., such as eNode-Bs 160a, 160b, 160c). In stand-alone configuration, WTRUs 102a, 102b, 102c may utilize one or more of gNBs 180a, 180b, 180c as a mobility anchor. In stand-alone configuration, WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using signals in an unlicensed band. In non-stand-alone configuration, WTRUs 102a, 102b, 102c may communicate / connect with gNBs 180a, 180b, 180c while also communicating / connecting with another RAN such as eNode-Bs 160a, 160b, 160c. For example, WTRUs 102a, 102b, 102c may implement the DC principle to communicate with one or more of gNBs 180a, 180b, 180c and one or more of eNode-Bs 160a, 160b, 160c substantially simultaneously. In non-stand-alone configuration, eNode-Bs 160a, 160b, 160c may act as a mobility anchor for WTRUs 102a, 102b, 102c, and gNBs 180a, 180b, 180c may provide additional coverage and / or throughput for serving WTRUs 102a, 102b, 102c.

[0069] Each of gNBs 180a, 180b, 180c may be associated with a specific cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, user scheduling in UL and / or DL, network slice support, dual connectivity, interworking between NR and E-UTRA, routing user plane data to user plane functions (UPFs) 184a, 184b, routing control plane information to access and mobility management functions (AMFs) 182a, 182b, etc. As Figure 1D shown, gNBs 180a, 180b, 180c may communicate with each other over the Xn interface.

[0070] Figure 1DThe CN 115 shown 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 data networks (DN) 185a, 185b. Although each of the foregoing elements is depicted as part of the CN 115, it should be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0071] The AMF 182a, 182b may be connected to one or more gNBs 180a, 180b, 180c in the RAN 113 via the N2 interface and may act as a control node. For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRU 102a, 102b, 102c, supporting network slicing (e.g., handling different PDU sessions with different requirements), selecting a particular SMF 183a, 183b, managing the registration area, terminating NAS signaling, mobility management, and so on. The AMF 182a, 182b may use network slicing in order to customize the CN support for the WTRU 102a, 102b, 102c based on the type of service used by the WTRU 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 etc. The AMF 182 may provide control plane functions for handover between the RAN 113 and other RANs (not shown) employing other radio technologies (such as LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies such as WiFi).

[0072] The SMF 183a, 183b may be connected to the AMF 182a, 182b in the CN 115 via the N11 interface. The SMF 183a, 183b may also be connected to the UPF 184a, 184b in the CN 115 via the 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 addresses, managing PDU sessions, controlling policy enforcement and QoS, providing downlink data notifications, etc. The PDU session type may be IP-based, non-IP-based, Ethernet-based, and so on.

[0073] UPF 184a and 184b can be connected to one or more gNBs 180a, 180b, 180c in the RAN 113 via the N3 interface, which can provide the WTRUs 102a, 102b, 102c with access to a packet switched network (such as the Internet 110) to facilitate communication between the WTRUs 102a, 102b, 102c and IP-enabled devices. The UPFs 184, 184b can 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, etc.

[0074] The CN 115 can facilitate communication with other networks. For example, the CN 115 can include an IP gateway (such as an IP Multimedia Subsystem (IMS) server) that acts as an interface between the CN 115 and the PSTN 108, or can communicate therewith. In addition, the CN 115 can provide the WTRUs 102a, 102b, 102c with access to other networks 112, which can include other wired and / or wireless networks owned and / or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c can be connected to local data networks (DNs) 185a, 185b via the N3 interface to the UPFs 184a, 184b and the N6 interface between the UPFs 184a, 184b and the DNs 185a, 185b.

[0075] In view of Figures 1A - 1D and Figures 1A - 1D In view of the corresponding descriptions, one or more or all of the functions described herein with respect to one or more of the following can be performed by one or more emulation devices (not shown): WTRUs 102a-d, base stations 114a-b, eNode-Bs 160a-c, MME 162, SGW 164, PGW 166, gNBs 180a-c, AMFs 182a-b, UPFs 184a-b, SMFs 183a-b, DNs 185a-b, and / or any other device(s) described herein. The emulation device(s) can be one or more devices configured to emulate one or more or all of the functions described herein. For example, the emulation device(s) can be used to test other devices and / or simulate network and / or WTRU functions.

[0076] A simulation device can be designed to implement one or more tests of other devices in a laboratory environment and / or an operator network environment. For example, one or more simulation devices can perform 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 to test other devices within the communication network. One or more simulation devices can perform one or more or all functions while being temporarily implemented / deployed as part of a wired and / or wireless communication network. The simulation device can be directly coupled to another device for testing purposes and / or can perform tests using over-the-air wireless communication.

[0077] One or more simulation devices can perform one or more functions, including all functions, rather than being implemented / deployed as part of a wired and / or wireless communication network. For example, the simulation device can be used to test test scenarios in a laboratory and / or a non-deployed (e.g., test) wired and / or wireless communication network to implement testing of one or more components. One or more simulation devices can be test devices. The simulation device can transmit and / or receive data using direct RF coupling and / or wireless communication via an RF circuit (e.g., which can include one or more antennas).

[0078] Systems, methods, and tools associated with differential channel estimation and sounding of reconfigurable intelligent surfaces are described herein. Enhancements to a WTRU, RIS, and / or network device can be implemented. These enhancements can be associated with CSI acquisition, CSI-RS provision, RIS configuration, RIS control, CSI feedback or reporting, etc.

[0079] A wireless transmit / receive unit (WTRU) can include a processor.

[0080] The WTRU can receive an indication of a set of channel state information reference signal (CSI-RS) resources for a set of reconfigurable intelligent surface (RIS) states. The WTRU can receive one or more CSI-RS resources. The WTRU can measure and calculate a differential channel based on one or more of the indicated set of CSI-RS resources and the one or more CSI-RS resources. The WTRU can send a message to a device, and the message can include a differential channel report corresponding to the differential channel.

[0081] The WTRU can receive configuration information via RRC signaling that indicates one or more of a plurality of RIS-related parameters, a plurality of CSI-RS resources, and a plurality of RIS configuration parameters.

[0082] The WTRU can receive CSI report configuration information, where the differential channel report is at least partially generated based on the CSI report configuration information.

[0083] A device such as a RIS controller may include a processor. The device may report the capabilities of the device to a network. The device may apply a sub-surface configuration during multiple configured time instances. The device may receive a RIS state at the RIS element level. The device may apply the RIS state at the RIS element level during a configured time instance.

[0084] Systems, methods, and tools for channel estimation related to a reconfigurable intelligent surface (RIS) are described herein. In an example, a wireless transmit / receive unit (WTRU) may receive configuration information associated with the RIS. The configuration information may indicate a first set of RIS parameters associated with a first RIS configuration. The configuration information may indicate a second set of RIS parameters associated with a second RIS configuration. The WTRU may receive a first channel state information reference signal (CSI-RS) associated with the first set of RIS parameters. The WTRU may receive a second CSI-RS associated with the second set of RIS parameters. The WTRU may determine a differential CSI measurement associated with a base station (BS)-RIS-WTRU channel based on the first CSI-RS associated with the first set of RIS parameters and the second CSI-RS associated with the second set of RIS parameters. The WTRU may transmit a CSI report including the differential CSI measurement.

[0085] In an example, the first RIS configuration may correspond to a first RIS state, and the second RIS configuration may correspond to a second RIS state. The first set of RIS parameters may represent the first RIS state. The second set of RIS parameters may represent the second RIS state. The RIS parameters may include phase shifts and / or amplification gains. For example, the first set of RIS parameters may include a first phase shift and a first amplification gain, and the second set of RIS parameters may include a second phase shift and a second amplification gain. The first phase shift and the second phase shift may be different, and the first amplification gain and the second amplification gain may be different. In some examples, the first set of RIS parameters may represent a first RIS state of a sub-surface of the RIS, and the second set of RIS parameters may represent a second RIS state of the sub-surface of the RIS.

[0086] In an example, the WTRU may determine a first channel measurement based on the first CSI-RS and the first set of RIS parameters. The WTRU may determine a second channel measurement based on the second CSI-RS and the second set of RIS parameters. The WTRU may determine a differential CSI measurement associated with the BS-RIS-WTRU channel based on the first channel measurement and the second channel measurement.

[0087] In an example, a WTRU may determine a first list of CSI-RS resource identifiers (IDs) and a second list of CSI-RS resource IDs based on received configuration information. The first list of CSI-RS resource IDs may be associated with a first RIS configuration. The second list of CSI-RS resource IDs may be associated with a second RIS configuration. The WTRU may determine a first set of CSI-RS resources based on the first list of CSI-RS resource IDs. The WTRU may receive a first CSI-RS using one or more CSI-RS resources from the first set of CSI-RS resources. The WTRU may determine a second set of CSI-RS resources based on the second list of CSI-RS resource IDs. The WTRU may receive a second CSI-RS using one or more CSI-RS resources from the second set of CSI-RS resources.

[0088] In an example, a WTRU may determine a rank indicator (RI) associated with a BS-RIS-WTRU channel, a precoding matrix indicator (PMI) associated with the BS-RIS-WTRU channel, and / or a channel quality indicator (CQI) associated with the BS-RIS-WTRU channel based on differential CSI measurements. The WTRU may determine an RI associated with a BS-WTRU channel between the WTRU and the BS, a PMI associated with the BS-WTRU channel between the WTRU and the BS, and a CQI associated with the BS-WTRU channel between the WTRU and the BS. The WTRU may report the RI, PMI, and CQI associated with the BS-RIS-WTRU channel, and the RI, PMI, and CQI associated with the BS-WTRU channel.

[0089] CSI acquisition is a function in a wireless communication system that may be used to adapt transmission schemes, such as transmitter precoding. CSI acquisition may be based on CSI WTRU reporting, which is based on measurements of reference signals (e.g., CSI-RS). With reconfigurable intelligent surfaces (RISs) in the radio environment, CSI procedures (e.g., CSI acquisition procedures) may be extended to incorporate adaptation of the RIS state in the presence of a link (e.g., an additional link) between the WTRU-RIS and the BS-RIS.

[0090] The features of RIS differential CSI acquisition are discussed in one or more examples in this document. In one or more examples in this document, the features of differential channel estimation can be discussed, and (one or more) associated procedures can be developed. In one or more examples in this document, the enhancements associated with RIS CSI are discussed. In one or more examples in this document, CSI-RS transmission schemes (e.g., suitable CSI-RS transmission schemes for differential channel estimation) are discussed. (One or more) CSI report changes (e.g., CSI report enhancements) can be proposed for RIS-aided differential channels. The RIS-aided differential channel can be changed (e.g., enhanced) to facilitate link adaptation and state adaptation of RISs already deployed in a wireless communication system (e.g., while achieving enhanced communication performance).

[0091] A reconfigurable intelligent surface (RIS) can be included in a wireless network, e.g., due to its ability to configure the wireless propagation environment. The RIS can include a flat surface that includes a large number of sub-wavelength-sized scattering elements to form cells (e.g., also referred to as RIS elements in this document), whose responses can be changed (e.g., dynamically changed) with an electronic RIS controller to affect the electromagnetic characteristics (e.g., phase and / or amplitude) of the incident signal. For example, by appropriately optimizing the states of the RIS elements, the incident signal can be steered towards a desired receiver while improving communication performance, such as higher spectral efficiency, enhanced coverage, etc. In addition to providing an improved wireless communication environment, the RIS elements can also support one or more of the following applications: joint communication, sensing, and / or wireless power transfer. The RIS elements can support one or more of the following features: reflection, refraction, focusing, collimation, polarization, etc. The RIS can be classified as passive, semi-active, or active. A passive RIS can shift the phase of the incident signal and / or can include multiple passive elements. A semi-active RIS and / or an active RIS can provide phase shifts and / or amplification gains. A semi-active RIS can include multiple active elements (e.g., a hybrid of active and passive elements), while an active RIS can include active elements (e.g., all active elements or only active elements). An active RIS element can provide sensing capabilities (e.g., can be referred to as an autonomous RIS). Phase shifts or amplification gains can be applied on the RIS at the single element level and / or on groups of RIS elements (e.g., sub-surface level). The electromagnetic characteristics of individual or grouped RIS elements can be changed (e.g., dynamically changed) with an RIS controller. The RIS controller can be co-located with the RIS or located remotely from the RIS (e.g., at the BS).

[0092] A RIS can be a type of network node. RIS-assisted communication can involve three nodes (e.g., a BS, a WTRU, and a RIS node). A communication path (e.g., a channel) can be formed via the RIS, e.g., a BS-RIS-WTRU path called the RIS-assisted path along with a legacy BS-WTRU direct communication path. In RIS-assisted communication, there may be multiple paths between the BS and the WTRU, e.g., a path via the RIS (RIS-assisted path) and one or more paths that constitute the BS-WTRU direct path.

[0093] The total channel between the BS and the WTRU can be estimated (e.g., in some cases, it can be called cascaded RIS channel estimation) (e.g., including estimating the RIS-assisted BS-RIS-WTRU composite channel and the BS-WTRU channel of the direct path). Estimating the RIS-assisted BS-RIS-WTRU path can be called differential channel estimation. With the existence of different communication channel paths in RIS-assisted communication, different communication aspects (e.g., issues) including initial access, beamforming, control signaling, channel acquisition, and CSI reporting, etc., can be updated to enable the RIS-assisted communication path and support the introduction of RIS in the network. The features of cross-channel acquisition and CSI reporting for implementing differential channel estimation in a RIS-assisted communication scenario are disclosed in one or more examples herein.

[0094] The term RIS can represent the RIS itself, the RIS and the RIS controller, or the RIS controller (e.g., the RIS controller can be separate from the BS, collocated with the BS, or part of the BS). The BS can communicate with the RIS (e.g., it can be assumed that the BS can communicate with the RIS). The BS can communicate with the RIS (e.g., using the NR air interface to provide control information to the RIS). In one or more examples herein, the terms RIS cell and RIS element can be used interchangeably.

[0095] An example RIS system can include one or more RIS elements. An example RIS system can include multiple RIS elements of the RIS (e.g., multiple RIS elements of a single RIS). An example RIS system can include (e.g., one) RIS element of the RIS (e.g., of a single RIS). Various RIS systems can be described herein with respect to downlink (DL) implementations, but the same or similar systems (e.g., the same or similar models) can apply to uplink (UL) implementations.

[0096] For simplicity, a single-antenna WTRU and a narrowband system (e.g., a subcarrier of an OFDM system) can be used in the examples provided herein (e.g., including Figure 2The example systems in). Such a system (e.g., such a model) can be applied to a scenario with a multi-antenna WTRU, such as a WTRU that can combine multiple received signals into a single received signal based on receiver processing (e.g., using analog, digital, or hybrid beamforming or combination techniques). In one or more of these examples, such receiver processing can be included in a radio channel.

[0097] A RIS system (e.g., a RIS system model) can include one RIS element of the RIS (e.g., one of the M RIS elements of the RIS), as Figure 2 illustrated. Figure 2 The example RIS system in (e.g., the RIS system model) can include RIS elements, one or more TRPs, and one or more WTRUs. At least in such a scenario, the signal at the WTRU (e.g., the complex-valued scalar signal received at the equivalent baseband) y m The example of can be given by Equation 1,

[0098] y m =(b m a′ m φ m +d′)Ps + z (1).

[0099] where s can represent a complex-valued scalar symbol, such as a reference / pilot symbol (e.g., a known reference / pilot symbol), P can represent a complex-valued precoding vector of dimension N T ×1 (e.g., N T can be, for example, the number of transmit antennas at the network-side transmit-receive point (TRP)), d can represent the complex-valued channel between the TRP and the WTRU (e.g., not including the propagation path via the RIS of dimension 1×N T ), a' m can represent the complex-valued vector channel between the TRP and the RIS element of dimension 1×N T ), φ m can represent the complex-valued scalar RIS element factor of RIS element m, where m = 1,…,M, b m can represent the complex-valued scalar channel between the RIS element and the WTRU, and z can represent additive noise and / or interference.

[0100] In a passive RIS, the factor φ m can have a fixed magnitude, e.g., unit magnitude (|φ m | = 1). In an active or hybrid RIS, the magnitude can be variable and / or controllable. In some cases, e.g., for a passive RIS, the RIS element can be turned off (e.g., φ m = 0 or φm ≈ 0). The RIS element can be in a certain state at a certain time (φ m ), and can be assumed to be applicable to one or more (e.g., all) subcarriers within a certain bandwidth.

[0101] The terms reference signal (RS) and pilot can be used interchangeably herein. In OFDM, the RS / pilot can include multiple (e.g., known) reference / pilot symbols. The reference / pilot symbols can be mapped to different subcarriers and / or OFDM symbols.

[0102] For example, by including the TRP precoding P into the TRP to RIS channel, the Figure 2 example shown in can be simplified. The following equation 2 can be applicable to such a scenario:

[0103] y m =(b m a m φ m +d)s+z=(c m φ m +d)s+z (2).

[0104] where d = d'P can represent the complex-valued scalar effective direct TRP to RIS channel (e.g., including TRP precoding), a m =a’ m P can represent the complex-valued scalar channel between the TRP and the RIS element, c m =b m a m can represent the cascaded complex-valued scalar channel from the TRP to the m-th RIS element of the WTRU.

[0105] The RIS system (e.g., RIS system model) can include multiple RIS elements of the RIS (e.g., all M RIS elements of the RIS). Such a system can be established, for example, by including the signal corresponding to the RIS element (e.g., M RIS elements) of the RIS (c m φ m s) according to, for example, the following equation 3:

[0106] y = ((a⊙b)Φ + b)s + z = (cΦ + d)s + z (3).

[0107] where a can represent a complex-valued vector channel of dimension 1×M between the TRP and the RIS (e.g., M can be the number of RIS elements), b can represent a complex-valued vector channel between the RIS elements and the WTRU (e.g., a complex-valued vector channel of dimension 1×M), c = a⊙b can represent the element-wise (e.g., Hadamard) product of a and b, and Φ can represent a complex-valued vector of dimension M×1 containing M RIS element factors φ m The complex-valued vector of dimension M×1. Φ can correspond to the RIS state.

[0108] In an example (e.g., an example with a rectangular RIS), M x can represent the number of RIS elements in the first direction (e.g., horizontal), M y can represent the number of RIS elements in the second direction (e.g., vertical), and M can be equal to M x *M y .

[0109] The RIS element channels can be estimated. For example, to estimate the cascaded channel c and / or the direct channel d in Equation 3, the network device can transmit multiple pilot / reference symbols (e.g., multiple known pilot / reference symbols) s. Since the cascaded channel c can include M elements (e.g., the pilot symbols can be associated with the elements of the cascaded channel c), and the direct channel d can include one element (e.g., the pilot symbol can be associated with the element of the direct channel d), so M + 1 pilot / reference symbols can be used to estimate the channel (e.g., estimate the channel coefficients).

[0110] For simplicity of notation, the same pilot symbol s can be assumed in M + 1 instances herein, but the pilot symbols can be different in different instances (e.g., according to a certain complex-valued sequence as long as it is known to the WTRU). For example, the first pilot symbol can be used for the first instance, and the second pilot symbol can be used for the second instance. The first pilot symbol and the second pilot symbol can be different. Some (e.g., all) of the received pilot symbols can be combined, for example, according to Equation 4 below:

[0111] y = hΘs + z (4).

[0112] where y = [y0 … y M can represent M + 1 received pilot symbols, and h = [d c] can represent a 1×(M + 1) vector with one direct channel and M channels via the RIS. Θ can be equal to where Φ i can be an M×1 vector with RIS element factors during the i-th pilot symbol, and Θ can be a square matrix of dimension M×1. Θ can be referred to as the RIS estimation matrix. z = [z0 … zM can represent noise (e.g., received noise) and / or interference (e.g., received interference).

[0113] In an example (e.g., an example where Θ has full rank known to the WTRU), the channel can be estimated based on y, e.g., according to Equation 5 below. A method (e.g., a method based on minimum mean square error (MMSE)) can be used to estimate the channel,

[0114]

[0115] Different methods can be used to design Φ i . For example, in the on - off method described herein, during a pilot symbol (transmission) such as the first pilot symbol (transmission), the RIS elements (e.g., all RIS elements) can be turned off (e.g., Φ0 = 0 or Φ0≈0). This can result in a received pilot symbol such as in Equation 7.

[0116] For example, the direct channel d can be estimated by the WTRU. For example, during pilot symbols 1 to M (transmission), the RIS elements can be turned on one by one (e.g., where the other elements remain off). For example, the i - th RIS element can be turned on during the i - th pilot symbol (transmission). This can result in the received i - th pilot symbol such as in Equation 6,

[0117] y i =(c i φ i +d)s + z i where i = 1,…,M (6).

[0118] Φ i can be zero (e.g., all zeros), except that the i - th element Φ i can be equal to 1. For example, Φ i can be equal to where 1 is an M - dimensional row vector of all 1s, and I M is the identity matrix of dimension M. This example can assume that the RIS elements can be turned on in the order of the RIS element indices, but those skilled in the art will understand that the RIS elements can be turned on in other orders.

[0119] In an example, Φ i can be a vector with no elements equal to zero (e.g., multiple (e.g., all) RIS elements can be turned on during pilot symbol transmission). In an example, Θ can be a discrete Fourier transform (DFT) matrix. In an example, Θ can be a Hadamard matrix. At least in these examples, Θ -1 can be equal to Θ T , which can simplify the implementation.

[0120] The aggregated channel reflected by the RIS can be estimated (e.g., cascaded channel estimation). The channel in Equation 3 includes the direct channel d and the aggregated channel cΦ reflected by the RIS: (cΦ + d). In one or more examples herein, the terms “channel,” “path,” and “channel path” may be used interchangeably. The aggregated channel cΦ can be scalar since it includes the aggregation (sum) of the reflections of the RIS elements. The two components d and cΦ can be estimated based on two pilot symbols. During the first pilot symbol (transmission), using, for example, the received pilot symbol as in Equation 7, the RIS can be turned off,

[0121] y0 = ds + z0 (7).

[0122] The WTRU can estimate the direct channel d (e.g., using state-of-the-art channel estimation methods).

[0123] During the second pilot symbol (transmission), the RIS can be turned on, with a certain RIS state Φ, for example, as in Equation 8,

[0124] y1 = (cΦ + d)s + z1 = hs + z1 (8).

[0125] The WTRU can estimate h (e.g., using state-of-the-art channel estimation methods). The WTRU can estimate the aggregated channel cΦ reflected by the RIS based on these two pilot symbols.

[0126] In an example, the number of RIS elements on the RIS may be high. For example, in terms of overhead and signaling, channel estimation and / or CSI reporting for each RIS element may be costly. For example, by using differential channel estimation as described in one or more examples herein, the cost of channel estimation and / or CSI reporting can be reduced. For example, differential channel estimation as described in one or more examples herein can be performed (e.g., as opposed to performing channel estimation for each subsurface / RIS element and / or processing (e.g., aggregating) the channel estimation for each subsurface / RIS element).

[0127] For example, by introducing subsurface-based estimation and reporting, the cost for channel estimation and / or CSI reporting can be reduced. The RIS elements of the RIS can be distributed (e.g., grouped) into S subsurfaces, including, for example, S x horizontal elements in the subsurface and S yVertical elements. The distribution of RIS elements to the subsurfaces can be uniform (e.g., each subsurface has the same number of RIS elements) or non-uniform (e.g., different subsurfaces have different numbers of RIS elements). In the case of multi-panel RIS, (e.g., each) panel can be considered a subsurface, or (e.g., each) panel can be divided into multiple subsurfaces. The multi-panel RIS can include several panels, and a panel (e.g., each panel) can contain a set of cells or scattering elements (e.g., the set of cells or scattering elements can be jointly controlled within each panel to direct and manipulate electromagnetic waves). Figure 3 Figure A-3C illustrates an example of the distribution of RIS elements to the subsurfaces. Figure 3 A and Figure 3 Figure B illustrate examples of uniform distribution, while Figure 3 Figure C illustrates an example of non-uniform distribution. In cases where different RIS surfaces can be assigned to different users, the number of RIS elements or resources assigned to a user (e.g., a WTRU) can be increased or decreased (e.g., a non-uniform RIS distribution can be used). A WTRU requesting more resources can be assigned a subsurface with a larger dimension (e.g., with more RIS elements), while a subsurface with a smaller dimension (e.g., with fewer RIS elements) can be reserved for a WTRU with less stringent requests and / or requirements.

[0128] The number of pilots for CSI and / or channel acquisition can be M + 1 (e.g., in the case of element-by-element RIS aggregated channel estimation). In some examples, as the size of the RIS surface increases, the computational complexity of the estimation process increases significantly, making the channel estimation process inefficient and / or time-consuming. One or more examples herein (e.g., differential channel estimation and / or partitioning of RIS into subsurfaces) can reduce the computational complexity of the estimation process, even when the size of the RIS increases.

[0129] In an example, channel estimation can be performed by partitioning and / or grouping RIS elements into smaller groups (e.g., which can be referred to herein as subsurfaces) and performing channel estimation at the subsurface level. Such a subsurface can include a set of one or more RIS elements. The distribution of RIS elements to the subsurfaces can be uniform or non-uniform. In the case of multi-panel RIS, (e.g., each) panel can be considered a subsurface, or (e.g., each) panel can be further divided into multiple subsurfaces. Figure 4 Figure illustrates an example of a RIS-assisted system, in which the RIS is divided into S (e.g., S = 6) subsurfaces.

[0130] The RIS state can be configured at the subsurface level (e.g., the same RIS element factor φ mcan be applied to (e.g., all) RIS elements in the sub-surface. Channel estimation at the sub-surface level can be performed by sending (e.g., one) pilot through each sub-surface (e.g., instead of sending pilots through each RIS element). By introducing the sub-surface, the dimension of channel estimation can be reduced from M + 1 to S + 1 (e.g., in terms of pilot transmission and / or computation). The on-off method and / or on method described in one or more examples herein can be applied to the sub-surface (e.g., instead of applying to individual RIS elements), e.g., to reduce pilot overhead and / or channel estimation complexity.

[0131] In one or more examples herein (e.g., Figure 2 the example shown in), the RIS system (e.g., RIS model) described can be used to illustrate the (one or more) RIS operations based on the sub-surface (e.g., Figure 4 the (one or more) RIS operations). Assume Γ j represents a set of RIS element indices in the j-th sub-surface, where j = 1, …, S. The union of the sub-surfaces can include multiple (e.g., all) RIS element indices, e.g., ∪ j Γ j = {1, …, M}, and in some examples, the set of sub-surfaces can be disjoint. Assume γ j is an M×1 vector, with values of 1 on the rows given by the indices in Γ j and 0 elsewhere (e.g., for simplicity, the row indices can start from 1). The RIS elements in γ j can be selected corresponding to the j-th sub-surface.

[0132] Assume G = [γ1 … γ S is a sub-surface selection matrix of dimension M×S. Equation 3 (e.g., which can represent the system model) can be written as the following equation 9:

[0133] y = (cGΦ s + d)s + z = (c s Φ s + d)s + z (9),

[0134] where Φ s can represent a complex-valued vector of dimension S×1 including S sub-surface factors where the factor can be applied to the RIS elements in Γ j e.g., and the same RIS element factor can be applied to (e.g., each) element in the j-th sub-surface. c s= cG can represent a 1×S dimensional vector, which includes S (e.g., c s the j-th element of which can be equal to ).

[0135] In Equation 9, (c s Φ s + d) can have the same form as (cΦ + d) in Equation 3, except for the length of the vector, which can be S (e.g., representing the number of subsurfaces) in the former and M (e.g., representing the number of RIS elements) in the latter. Methods for channel estimation, CSI, etc. that can be applied to each RIS element operation can be applied to each subsurface operation, and vice versa.

[0136] For example, the descriptions in one or more examples herein regarding RIS channel estimation can be applied by changing the problem dimension by adding an s superscript. h = [d c s can be a 1×(S + 1) vector with a direct channel and S channels via RIS subsurfaces. where can be an S×1 vector with a RIS subsurface factor during the i-th pilot symbol. Θ can be a square matrix of dimension (S + 1)×(S + 1).

[0137] In one or more downlink transmissions (e.g., one or more downlink transmissions associated with NR), the BS / TRP can transmit CSI-RS for channel sounding. The WTRU can perform measurements (e.g., using CSI-RS) to estimate the quality of the channel based on reports received by the WTRU (e.g., implicitly and / or explicitly).

[0138] The first mode of DL CSI acquisition (e.g., associated with NR) can be based on the WTRU performing measurements on one or more CSI-RS and reporting the corresponding CSI. The second mode of DL CSI acquisition (e.g., associated with NR) can be based on the WTRU transmitting a sounding reference signal (SRS), e.g., including one or more of the following: antenna switching between antennas that can be used for DL reception, CSI measurements on the network side, and / or an assumption of UL / DL reciprocity (e.g., CSI estimated on the UL can be applied to the DL).

[0139] A WTRU may be configured to use CSI-RS resources to perform channel measurements and / or compute CSI, where the CSI-RS resources may include one or more ports (e.g., antenna ports). One or more CSI-RS resources may be grouped into CSI-RS resource sets. The WTRU may be configured to perform interference and / or noise measurements on the CSI-RS resources used for CSI. In an example, the CSI-RS resources may be non-zero power (NZP) CSI-RS resources, where the WTRU may assume that a certain RS is being transmitted. In some examples, the CSI-RS resources may be CSI-RS resources for interference measurement, where the WTRU may not assume that a certain RS is being transmitted. The CSI-RS resources and resource sets may be, for example, non-zero power (NZP) CSI-RS resources and resource sets or interference measurement (IM) CSI-RS resources or resource sets. For brevity, the terms (one or more) CSI-RS resources and (one or more) CSI-RS resource sets are used herein, which may refer to NZP and / or (one or more) IM CSI-RS resources and (one or more) resource sets.

[0140] The CSI-RS resources may be periodic, semi-persistent (e.g., it may be activated / deactivated), or aperiodic (e.g., it may be triggered). The WTRU may be configured with periodic, semi-persistent, or aperiodic CSI reporting. In an example, the periodic CSI reporting may be transmitted on the physical uplink control channel (PUCCH), while the aperiodic CSI reporting may be transmitted on the physical uplink shared channel (PUSCH). The semi-persistent CSI reporting may be configured to be transmitted on the PUCCH or on a semi-persistent PUSCH.

[0141] The CSI reporting may be based on channel measurements of a resource set (e.g., a CSI-RS resource set). Each channel measurement resource may be associated with an interference measurement resource and / or a non-zero power CSI-RS resource for interference measurement.

[0142] The WTRU may report CSI corresponding to one or more resources in the resource set used for channel measurement. If the resource set includes multiple resources, the WTRU may report a resource index, e.g., to identify the corresponding resources used. Such a resource index may include a CSI-RS resource indicator (CRI) or an SSB resource indicator (SSBRI).

[0143] In an example (e.g., if multi-port CSI-RS is used as a channel measurement resource), the WTRU may be configured to calculate one or more precoding matrix indicators (PMI), e.g., a broadband PMI and / or multiple sub-band PMIs. For example, the PMI may correspond to a precoding vector or matrix directly selected from a codebook. The PMI may include a combination (e.g., a linear combination) of multiple precoding vectors or matrices from the codebook.

[0144] The CSI report may include one or more channel quality indicators (CQI). If the CSI report includes a PMI, the CQI may correspond to a set of layers of the PMI. The CSI report may include a broadband CQI (e.g., if broadband physical downlink shared channel (PDSCH) transmission is performed). The CSI report may include sub-band CQIs (e.g., if sub-band PDSCH transmission is performed).

[0145] The WTRU may receive one or more CSI-RS resources (e.g., in a CSI-RS resource set), and may use the received CSI-RS resource set to obtain downlink CSI. The WTRU may perform measurements and report the obtained CSI based on the performed measurements (e.g., via PUCCH or PUSCH).

[0146] The RIS may be represented by one or more RIS parameters (e.g., one or more phase shifts and one or more amplification gains associated with the RIS state configured using the RIS configuration). If there is an RIS in the communication system, the RIS may introduce one or more phase shifts and one or more amplification gains into the impulse signal based on, e.g., a predefined / set RIS state configured by a control node (e.g., an RIS controller, a BS, a WTRU, etc.), and reflect the impulse signal, e.g., in one direction (e.g., the expected direction). The RIS may be composed of RIS cells (e.g., a large number of RIS cells), which may be capable of introducing one or more amplification gains and / or one or more phase shifts (e.g., individually or jointly as a group of RIS elements). During communication between the BS and the WTRU, multiple channel components may be used (e.g., the direct path between the BS and the WTRU and / or the RIS-assisted BS-RIS-WTRU path). To improve communication quality, both of these paths (e.g., BS-WTRU and / or BS-RIS-WTRU) may be optimized (e.g., individually or jointly), e.g., by utilizing the CSI report. In some examples, some reports (e.g., legacy reports) effectively measured on the path (e.g., all paths) may not be effective for optimizing the RIS-assisted BS-RIS-WTRU path and / or for utilizing the report feedback for these reports, and it may be difficult to infer the impact of the RIS-assisted BS-RIS-WTRU path.

[0147] RIS-assisted path channel estimation (e.g., differential channel) can be described in one or more examples herein, where the channel estimation can be performed by the BS and / or the WTRU. The differential channel can be utilized to optimize the BS-RIS-WTRU path by incorporating one or more of RIS-assisted link adaptation (e.g., to update system parameters such as precoder, modulation, etc.), RIS parameter adaptation (e.g., to update the RIS state, etc.), and so on. To achieve these communication gains through differential channel estimation, some CSI-RS transmissions and CSI reports can be changed (e.g., enhancements to legacy CSI-RS transmissions and CSI reports in NR) to incorporate the RIS-assisted BS-RIS-WTRU path. CSI-RS changes (e.g., CSI-RS enhancements in NR) can enable differential channel estimation. Changes to CSI reporting / feedback (e.g., enhancements in NR CSI reporting / feedback) can incorporate the impact of the differential channel in the communication system.

[0148] CSI estimation and reporting from the WTRU to the BS can be used by the BS for link adaptation, such as adjusting the BS transmission scheme from one or more of the following aspects: modulation and coding, multi-antenna precoding, or frequency domain resource allocation. The adjustment can be related to improving the received signal quality (e.g., precoding and frequency selective scheduling). The adjustment can be related to achieving a certain block error rate (e.g., modulation and coding scheme (MCS) selection). The estimated CSI and reporting can be utilized to update or adjust the RIS state. In an example, the adjustment of the RIS state can be similar to precoder selection and / or MCS selection (e.g., more similar to precoder selection compared to MCS selection). The adjustment of the RIS state can improve the received signal quality. Some CSI procedures may not support CSI-based adjustments for RIS-assisted communication. In one or more examples described herein, the impact of the RIS-assisted differential channel in the communication system can be incorporated by changing the CSI report (e.g., through enhancements in NR CSI reporting).

[0149] CSI-RS-based differential CSI acquisition can be changed (e.g., enhanced) to facilitate link adaptation and / or adaptation of the state of the RIS already deployed in the wireless communication system. One or more of the WTRU, the RIS, and the BS can be changed (e.g., enhanced). Based on the acquired differential channel estimation, the communication link performance can be improved. The WTRU can be configured with CSI-RS and / or RIS CSI (e.g., CSI-RS enhancements and / or RIS CSI enhancements).

[0150] A WTRU may measure one or more CSI-RSs and / or calculate a RIS differential channel. The WTRU may use the obtained differential RIS channel to calculate a CSI report (e.g., an enhanced CSI report), and may transmit the CSI report (e.g., to report CSI). Based on the CSI report (e.g., as feedback from the WTRU), the BS may configure / update a precoder and / or one or more RIS states, and indicate the one or more RIS states to the RIS.

[0151] Features associated with differential channel estimation may be described in one or more examples herein. In RIS-assisted communication (e.g., using direct (BS-WTRU) channel components and multipath fading components), in the case of one or more downlink communications, the WTRU may receive data along one or more paths (e.g., primarily along two paths) including a RIS-assisted path (BS-RIS-WTRU path) and a direct path (BS-WTRU path). In the case of one or more downlink transmissions, the differential channel may correspond to (e.g., may be) the effective RIS-assisted channel path gain (c) at the WTRU. Information about the differential channel (e.g., information obtained through differential channel estimation) may be beneficial for evaluating the effectiveness and performance of the RIS in communication. This information may be utilized to generate a report (e.g., an enhanced report) and link adaptation for the RIS-assisted path. Obtaining the differential channel coefficients may result in improved communication performance.

[0152] A RIS-assisted channel may be used in one or more examples herein (e.g., in some cases, it may be referred to as a RIS cascaded channel or a RIS reflected aggregation channel). The terms differential channel, cascaded channel, and aggregation channel may be used interchangeably in one or more examples as described herein, and they may refer to a RIS-assisted signal path (e.g., a BS-RIS-WTRU channel).

[0153] Features associated with differential channel estimation may be described in one or more examples herein. In one or more examples herein where differential channel estimation is described, the RIS may be considered to be turned on during pilot transmission (e.g., during all pilot transmissions). The RIS state may be set element-by-element, surface-by-surface, or for the state of the RIS (e.g., for a single state of the complete RIS) (e.g., according to setting a radio resource control (RRC) configuration as described in one or more examples herein). For example, the state of the RIS (e.g., a single state of the RIS) may be set in an orthogonal space that may be configured to belong to codewords from (e.g., different) orthogonal dictionaries (e.g., Hadamard matrix, DFT, etc.) during a set of pilot transmissions. The WTRU may be configured by the BS, and the BS may indicate the orthogonal dictionary selected for the RIS state and / or enable differential channel estimation at the WTRU side.

[0154] If the RIS state is set to Φ1 and the transmitter (e.g., the BS in the case of (one or more) downlink transmissions) transmits a pilot (e.g., a known pilot) s, the signal received at the WTRU may be given by Equation 10,

[0155] y1 = (cΦ1 + d)s + z1 (10).

[0156] If the RIS state is set to Φ2, the signal received at the WTRU may be given by Equation 11,

[0157] y2 = (cΦ2 + d)s + z2 (11).

[0158] The differential channel may be obtained by subtracting Equation 10 from Equation 11 as follows,

[0159] y2 - y1 = c(Φ2 - Φ1)s + (d - d)s - (z2 - z1)

[0160]

[0161] The estimated RIS-assisted channel may be given in Equation 12:

[0162]

[0163] The obtained differential channel gain may correspond to (e.g., may be) the resulting RIS-assisted channel path, which may be used for RIS-specific performance analysis and / or reporting.

[0164] In the case of sub-surface-based channel estimation (e.g., as described in one or more examples herein), where the complete RIS is divided into M sub-surfaces, at equal

[0165] Obtain the differential channel for the m-th sub-surface in Equation 113:

[0166]

[0167] where y i,m can represent the signal received at the WTRU, and the RIS state for the m-th sub-surface can be set to Φ for the i-th pilot transmission i,m . One sub-surface can be turned on at a given time, and / or the sub-surface states can be orthogonal to each other. The effective additive noise and interference component (z2 - z1) can be compensated for by using additive noise and interference cancellation.

[0168] The direct signal path can be calculated by the WTRU using differential channel knowledge and the received signal (e.g., implicitly calculated because the effect of the direct signal path may not be explicitly captured in some examples herein). In some examples (e.g., a special case of differential channel estimation as described in one or more examples herein), the direct signal path can be used to obtain the differential channel c. In this case, in one of the pilot transmissions (e.g., i = 1) among the pilot transmissions, the RIS can be turned off (Φ1 = 0), resulting in the received signal in Equation 14:

[0169] y1 = ds + z1 (14).

[0170] In one of the pilot transmissions (e.g., i = 2) among the pilot transmissions, the RIS state can be set to Φ2, and the received signal in Equation 15 can be given:

[0171] y2 = (cΦ2 + d)s + z2 (15),

[0172] The differential channel can be obtained as follows:

[0173] y2 - y1 = (cΦ2 + d)s - ds + z2 - z1

[0174] y2 - y1 = (cΦ2 + d)s - ds + z

[0175]

[0176] In some examples, if the WTRU does not know the existence of the RIS, the WTRU can measure the CSI for states 1 and 2 and report the CSI (e.g., as a legacy CSI report to the BS). Using the received report (e.g., the CSI report from the WTRU for two RIS states), the BS can calculate the differential CSI. The BS can calculate a channel quality indicator, e.g., to perform link adaptation and / or update the RIS state.

[0177] Figure 5 Example 500 (e.g., differential channel estimation example) is illustrated, in which one or more of the actions may be performed. For example, the WTRU may perform one or more of 510, 514, 516, or 518.

[0178] Example embodiments (e.g., using Figure 5 ) may include nodes performing RIS differential channel estimation using differential channel estimation as described in one or more of the examples herein. Network nodes (such as one or more base stations (e.g., gNB), one or more TRPs, one or more RISs, etc.) and / or one or more WTRUs, etc. may be included in the example system (e.g., a system for performing one or more of 502 - 518).

[0179] As Figure 5 shown, at 502, the example of 500 may be started. At 504, a node (e.g., a RIS node) may (e.g., also shown at 602 of Figure 6 ) indicate its capabilities (e.g., the node may report its capabilities, which may include one or more of the following: the number of RIS elements, the structure of the RIS (e.g., rectangular, circular, etc.), sub-surface or element-by-element configuration capabilities, the resolution of the RIS, etc.). In an example, the node may indicate its capabilities to the BS. The WTRU may be configured at 506 (e.g., also shown at 616 of Figure 6 ). In an example, the BS may configure the WTRU at 506 based on the capability information indicated by the node (e.g., using this RIS capability knowledge), e.g., in a manner related to RIS CSI enhancement (e.g., including one or more of legacy and / or RIS-assisted CSI reporting configurations, RIS state configurations, sub-surface or element-by-element RIS operation configurations, etc.). For example, the BS may send configuration information to the WTRU to configure the WTRU.

[0180] At 508, the BS may (e.g., also shown at one or more of 604 - 607 of Figure 6 ) configure the RIS with the required configuration and / or set the RIS state 1 (e.g., by sending RIS configuration information to the RIS controller: for example, the first RIS configuration may correspond to RIS state 1; the second RIS configuration may correspond to RIS state 2). At 510, the WTRU may (e.g., also shown at 618 of Figure 6 ) perform CSI acquisition with respect to the set RIS state 1. For example, the WTRU may receive a first CSI-RS associated with a first set of RIS parameters representing RIS state 1. The WTRU may determine a first channel measurement based on the first CSI-RS and / or the first set of RIS parameters.

[0181] As set by the BS, 508 and 510 can be repeated at 512 and 514 respectively using RIS state 2 (e.g., different RIS states). At 512, the BS can configure the RIS and / or set RIS state 2 with the desired configuration (e.g., also shown at one or more of Figure 6 604 and one or more of 608 - 610) (e.g., by sending RIS configuration information to the RIS controller). At 514, the WTRU can perform CSI acquisition regarding the set RIS state 2 (e.g., also shown at 619). For example, the WTRU can receive a second CSI-RS associated with a second set of RIS parameters representing RIS state 2. The WTRU can determine a second channel measurement based on the second CSI-RS and / or the second set of RIS parameters.

[0182] RIS state 1 and RIS state 2 can be selected from a predefined dictionary, and / or they can be the RIS states required in two different time slots.

[0183] At 516, the WTRU can perform differential channel estimation (e.g., as shown at Figure 6 630) by, for example, using the CSI acquired at 510 and 514. The WTRU can perform differential channel estimation by, for example, determining the difference between the measurements and CSI calculations for state 1 and the measurements and CSI calculations for state 2. The WTRU can perform differential channel estimation using, for example, Equation 12. In an example, the differential channel estimation can be determined by subtracting the measurements and CSI calculations for state 2 from the measurements and CSI calculations for state 1.

[0184] At 518, the WTRU can (e.g., also shown at Figure 6 620 and 622) report differential CSI measurements and / or legacy reports to the BS, for example. As described in one or more examples herein, the WTRU can determine one or more of a rank indicator (RI), a precoding matrix indicator (PMI), and a channel quality indicator (CQI) associated with the BS-RIS-WTRU channel based on the differential CSI measurements. The WTRU can determine the RI, PMI, and CQI associated with the BS-WTRU channel between the WTRU and the base station. The WTRU can report the RI, PMI, and CQI associated with the BS-RIS-WTRU channel, and the RI, PMI, and CQI associated with the BS-WTRU channel.

[0185] Figure 6Illustrated is an example signaling diagram for differential channel estimation (e.g., RIS differential channel estimation). For example, when using a sub-surface or element-by-element RIS configuration, or if the WTRU reports vary based on NR specifications (such as periodic, semi-persistent, aperiodic, etc.), additional signaling can be used in the scenario. In the example, one or more of 602 - 614 and / or one or more of 616 - 626 in Figure 6 can be omitted. As Figure 6 shown, at 602, RIS capability information can be sent from the RIS to the BS. At 604, the BS can send RIS configuration information to the RIS (e.g., RIS controller). At 606, the BS can set RIS state 1 for the RIS. At 607, the BS can send scheduling information to the RIS (e.g., scheduling information associated with RIS state 1). At 608, the BS can set RIS state 2 for the RIS. At 610, the BS can send scheduling information to the RIS (e.g., scheduling information associated with RIS state 2). 628 can include the RIS state during CSI-RS transmission. 628 can include one or more of 606 - 610. At 612, the BS can set a RIS state for the RIS (e.g., a RIS state the same as or different from RIS state 1 or RIS state 2). At 614, the BS can send RIS scheduling information (e.g., scheduling information associated with the RIS state set at 612). 632 can include the RIS state during other DL / UL transmissions. 632 can include 612 - 614.

[0186] As Figure 6 shown, at 616, the BS can send WTRU configuration information to the WTRU. At 618, the BS can send a first CSI / CSI-RS activation / trigger to the WTRU. At 619, the BS can send a second CSI / CSI-RS activation / trigger to the WTRU. The WTRU can send a differential CSI report at 622 and / or other CSI reports (e.g., legacy CSI reports) at 620. As described in one or more examples herein, 630 can be used for differential channel CSI acquisition and measurement. 630 can include 606 - 610 and 618 - 619. At 624, the WTRU can receive (one or more) DL transmissions. At 626, the WTRU can send (one or more) UL transmissions.

[0187] It can be illustrated in Figure 7 a case for an example method (e.g., Figure 5 the example shown and / or Figure 6A signaling diagram for a special case of the example shown, in which the RIS state is set to off in one of the pilot transmissions and then the RIS state is set to Φ1 in another pilot transmission. Figure 7 Illustrates an example signaling diagram for differential channel estimation (e.g., RIS differential channel estimation). In different examples, the order of the set RIS states and the RIS off state can be different.

[0188] As described in one or more examples herein, CSI-RS modification (e.g., enhancement) can be performed on differential channel estimation (e.g., to support differential channel estimation and / or implementation of differential channel estimation as described in one or more examples herein). CSI-RS can be used for one or more of beam management, mobility, time-frequency tracking, CSI acquisition, etc. The configuration and transmission possibilities of CSI-RS can cover various uses. One or more CSI-RS can be configured and / or transmitted in various ways, in which one or more CSI-RS can be used for one or more of beam management, mobility, time-frequency tracking, CSI acquisition, etc.

[0189] For example, CSI-RS can be used as a pilot for differential channel estimation (e.g., RIS differential channel estimation) and / or CSI acquisition. As described in one or more examples herein, 2M CSI-RS resources can be used, where M can be the number of subsurfaces (or in some cases RIS elements), and the factor (e.g., factor 2 here) corresponds to at least 2 RIS states for differential channel estimation.

[0190] The 2M CSI-RS resources can be included in a CSI-RS resource set. The 2M CSI-RS resources can be included in multiple CSI-RS resource sets. The CSI-RS resources can be single-port or multi-port (e.g., dual-port).

[0191] Figure 8 Illustrates an example of CSI-RS resources with two M-sized resource sets.

[0192] Figure 8The examples in [ ] can have (one or more) CSI-RS resources with the same subcarrier offset(s). In an example, different resources can have different offsets (e.g., different CSI-RS resources can have different subcarrier offsets). Different CSI-RS resources can have the same or different densities in terms of frequency, bandwidth, number of antenna ports, code division multiplexing (CDM) type, etc. The periodicity of the CSI-RS resources can be the same or different, and the slot offset can be the same or different. In some examples, CSI-RS resources may not overlap in time on (e.g., any) symbol, which can be used as a constraint.

[0193] Figure 9 FIG. illustrates an example of CSI-RS resources having a set of resources scattered in different time slots.

[0194] 2M CSI-RS resources can appear at similar (but not identical) times (e.g., in consecutive symbols, in the same time slot (see Figure 8 ), in consecutive time slots (see Figure 9 ), and / or distributed continuously over multiple time slots (see Figure 10 ), etc.), e.g., to enable timely and relevant CSI measurements and reporting.

[0195] Figure 10 FIG. illustrates an example of CSI-RS resources that appear in multiple time slots.

[0196] M CSI-RS resources in the CSI-RS resources (e.g., the first M CSI-RS resources) can correspond to channel estimates with RIS state 1 (e.g., each subsurface (or RIS element) channel estimate with RIS state 1), and another M CSI-RS resources in the CSI-RS resources can correspond to channel estimates with RIS state 2 (e.g., each subsurface (or RIS element) with RIS state 2). If the subsurface is the entire RIS, e.g., M = 1, differential channel estimation can be performed by utilizing two CSI-RS resources (e.g., each CSI-RS resource can correspond to a different RIS state, as shown in Figure 11 .

[0197] Figure 11 FIG. illustrates an example of CSI-RS resources with M = 1.

[0198] The WTRU can be notified of the association between CSI-RS resources and RIS states (e.g., which CSI-RS resources correspond to which RIS states). For example, when differential channel estimation is performed at the WTRU, the WTRU can be notified (e.g., the WTRU may need to know) which CSI-RS resources correspond to which RIS states. Examples of determining CSI-RS resources associated with RIS states in a CSI-RS resource set are described in one or more of the following. The CSI-RS resources in the CSI-RS resource set can be configured in a list (e.g., a list of CSI-RS resource IDs). The list (e.g., each list entry) can be associated with a corresponding RIS state (e.g., the first list entry can be used for RIS state 1 and the second list entry can be used for RIS state 2). The CSI-RS resources in the CSI-RS resource set can have different CSI-RS resource IDs. The RIS state can be associated with the CSI-RS resource ID based on a predefined equation (e.g., even CSI-RS resource IDs can correspond to RIS state 1 and odd CSI-RS resource IDs can correspond to RIS state 2, e.g., as Figure 11 illustrated). For example, the WTRU can determine a first list of CSI-RS resource IDs and a second list of CSI-RS resource IDs based on received configuration information. The first list can be associated with a first RIS configuration. The second list can be associated with a second RIS configuration. The WTRU can determine a first set of CSI-RS resources based on the first list of CSI-RS resource IDs. One or more CSI-RS resources in the first set can be used to receive a first CSI-RS. The WTRU can determine a second set of CSI-RS resources based on the second list of CSI-RS resource IDs. One or more CSI-RS resources in the second set can be used to receive a second CSI-RS.

[0199] One or more resource sets including M CSI-RS resources can be included (e.g., by their IDs) in a CSI-RS resource setting (e.g., included in the IE CSI-ResourceConfig). The CSI-RS resource setting can include, for example, a list of CSI-RS resource sets for differential channel measurement and / or estimation. The list can include a sequence of CSI-RS resource set IDs of the CSI-RS resource sets, which can be configured (e.g., configured elsewhere, e.g., preconfigured).

[0200] The WTRU may not know that there is a RIS in the network and may perform CSI measurements (e.g., using CSI-RS associated with different RIS states). In an example, when the WTRU does not know that there is a RIS in the network, the WTRU may measure CSI corresponding to two utilized RIS states (e.g., using CSI-RS associated with different RIS states) and / or report CSI corresponding to two utilized RIS states to the BS. Based on the received CSI (e.g., the CSI report received by the WTRU), the BS may perform differential channel estimation using an example shown in one or more of Figure 8 , Figure 9 , Figure 10 , Figure 11 and Figure 12 (e.g., using CSI-RS enhancements similar to an example shown in one or more of Figure 8 , Figure 9 , Figure 10 , Figure 11 and Figure 12 ). The WTRU may not know (e.g., may not need to know) the utilized RIS state. Figure 12 illustrates an example of (one or more) CSI-RS resources with (one or more) RIS states.

[0201] In one or more examples herein, changes to the CSI report (e.g., CSI report enhancements) are described. In some examples, during (one or more) downlink transmissions, the WTRU may perform measurements and / or CSI acquisition by utilizing received pilot / reference signals transmitted by the BS (e.g., gNB). Based on these measurements, in the case of transmissions in frequency division duplex (FDD), the WTRU may report the quality of the channel (e.g., explicitly or implicitly) by explicitly transmitting CSI (e.g., as channel coefficients) and / or implicitly in the form of a CSI report (e.g., RI, PMI, CQI, etc.). When the transmission occurs in time division duplex (TDD), the BS may utilize the reciprocity of the communication channel and obtain the channel estimate itself. The BS may use the CSI report and / or the channel estimate to adjust / update system parameters, including one or more of the type of precoder, modulation, code rate, etc.

[0202] In a RIS-assisted communication system, RIS-assisted CSI may be used to adjust / update RIS parameters, e.g., the RIS state at the BS and RIS-assisted path parameters (e.g., codebook and precoder selection for the BS-RIS-WTRU path). Changes to the CSI report (e.g., CSI report enhancements for a RIS-assisted system) may be used for differential channel estimation.

[0203] Changes to CSI reports (e.g., features associated with report enhancements for (one or more) differential channels) are described in one or more examples herein. In an example of a RIS-assisted differential channel, during (one or more) downlink transmissions, a WTRU may perform measurements (e.g., to obtain a differential channel and calculate a CSI report) based on received pilot / reference signals transmitted by a BS. The WTRU may calculate a CSI report for a RIS-assisted signal path (e.g., a conventional CSI report for a RIS-assisted differential signal path, which may include RI, PMI, CQI, etc.) to indicate the quality of the RIS-assisted signal path. The WTRU may convey the CSI report for the RIS-assisted signal path (e.g., a RIS-assisted CSI report) along with other CIS reports (e.g., a legacy CSI report including the impact of the RIS-assisted plus direct path). The WTRU may convey a CSI report for the RIS-assisted signal path (e.g., reporting only a differential CSI report), such as a differential PMI, a differential RI, etc. In an example, the differential CSI report may be determined or considered as the difference between the RIS-assisted path and the direct signal path (e.g., in indicators such as RI, PMI, and / or COI). The (one or more) differential CSI reports may be based on a weighted difference (e.g., a function thereof) between the PMI determined for the RIS-assisted path and the PMI determined for the direct path. The WTRU may indicate the differential CSI report with the same periodicity as the WTRU indicates (one or more) other CSI reports (e.g., a legacy CSI report), such as a periodicity configured by the network. The WTRU may indicate the differential CSI report with a periodicity different from the periodicity with which the WTRU indicates (one or more) other CSI reports (e.g., a legacy CSI report), such as a periodicity configured by the network. The WTRU may send the differential CSI report and (one or more) other CSI reports (e.g., a legacy CSI report) together. For example, the WTRU may send the (one or more) differential CSI reports and the (one or more) other CSI reports together by indicating an index associated with the (one or more) differential CSI reports and an index associated with the (one or more) other CSI reports (e.g., by indicating a unique index for each report representing the channel link to which the report may correspond), or by specifying the location of the (one or more) differential CSI reports in the report and the location of the (one or more) other CSI reports in the report (e.g., the first part of the report may represent the legacy report, and the second part of the report may be the differential report, etc.).

[0204] In an example, a WTRU may be configured (e.g., receive via RRC signaling) with configuration information that indicates one or more RIS-related parameters (e.g., (one or more) phase shifts and / or (one or more) amplification gains), (one or more) corresponding CSI-RS resources, and / or other RIS-related configuration parameters (e.g., the number of sub-surfaces or elements in the x and y directions of the RIS). The WTRU may be configured with a CSI reporting configuration that indicates one or more reporting parameters corresponding to the type of CSI report (e.g., legacy and / or differential), reporting periodicity, reporting function, etc. The WTRU may receive an indication of a set of CSI-RS resources for a set of RIS states (e.g., configuration information indicating the set of CSI-RS resources), where the set of CSI-RS resources is configured at, for example, the RIS by one or more of: a BS, a RIS controller, a WTRU in the network, a Radio Access Network Intelligent Controller (RIC), etc. The WTRU may receive (one or more) CSI-RS resources. For example, the WTRU may measure and calculate a differential channel using one or more of the examples described herein. For example, the WTRU may report (one or more) differential channel reports if the WTRU is configured to do so in the reporting configuration.

[0205] In an example, the RIS may report its capabilities to the network / RIS control node. The RIS may be configured with an element-by-element or sub-surface configuration. For example, during a time instance determined by configuration / activation / indication / trigger, the RIS may apply the sub-surface configuration. The RIS may receive RIS states at the RIS element level. For example, during a configured time instance determined by configuration / activation / indication / trigger, the RIS may apply the RIS states at the RIS element level.

[0206] Although the above features and elements are described in a particular combination, each feature or element may be used alone without the other features and elements of the preferred embodiment, or may be used in various combinations with or without other features and elements.

[0207] Although the embodiments described herein may consider 3GPP-specific protocols, it is to be understood that the embodiments described herein are not limited to this scenario and may be applicable to other wireless systems. For example, although the solutions described herein consider LTE, LTE-A, New Radio (NR), or 5G-specific protocols, it is to be understood that the solutions described herein are not limited to this scenario and are also applicable to other wireless systems.

[0208] The above process may be implemented in a computer program, software, and / or firmware incorporated in a computer-readable medium and executable by a computer and / or a processor. Examples of the computer-readable medium include, but are not limited to, electronic signals (transmitted via wired and / or wireless connections) and / or computer-readable storage media. Examples of the computer-readable storage media include, but are not limited to, read-only memory (ROM), random access memory (RAM), registers, cache memory, semiconductor storage devices, magnetic media (such as, but not limited to, internal hard disks and removable disks), magneto-optical media, and / or optical media (such as compact disc (CD)-ROM disks and / or digital versatile discs (DVDs)). A processor associated with the software may be used to implement a radio frequency transceiver used in a WTRU, a terminal, a base station, an RNC, and / or any host computer.

Claims

1. A wireless transmit / receive unit (WTRU) comprising: a processor configured to: receive configuration information associated with a reconfigurable intelligent surface (RIS), wherein the configuration information indicates a first set of RIS parameters associated with a first RIS configuration and a second set of RIS parameters associated with a second RIS configuration; receive a first channel state information reference signal (CSI-RS) associated with the first set of RIS parameters and a second CSI-RS associated with the second set of RIS parameters; determine a differential CSI measurement associated with a base station (BS)-RIS-WTRU channel based on the first CSI-RS associated with the first set of RIS parameters and the second CSI-RS associated with the second set of RIS parameters; and transmit a CSI report including the differential CSI measurement.

2. The WTRU according to claim 1, wherein, The first RIS configuration corresponds to a first RIS state, and the second RIS configuration corresponds to a second RIS state, and wherein the first set of RIS parameters represents the first RIS state, and the second set of RIS parameters represents the second RIS state.

3. The WTRU according to claim 2, wherein The first set of RIS parameters includes a first phase shift and a first amplification gain, and the second set of RIS parameters includes a second phase shift and a second amplification gain, wherein the first phase shift and the second phase shift are different, and the first amplification gain and the second amplification gain are different.

4. The WTRU according to claim 1, wherein The first set of RIS parameters represents a first RIS state of the sub-surface of the RIS, and the second set of RIS parameters represents a second RIS state of the sub-surface of the RIS.

5. The WTRU according to claim 1, wherein, The processor is further configured to: determine a first channel measurement based on the first CSI-RS and the first set of RIS parameters; determine a second channel measurement based on the second CSI-RS and the second set of RIS parameters; and determine a differential CSI measurement associated with the BS-RIS-WTRU channel based on the first channel measurement and the second channel measurement.

6. The WTRU according to claim 1, wherein, The processor is further configured to: determine a first list of CSI-RS resource identifiers (IDs) and a second list of CSI-RS resource IDs based on the received configuration information, wherein the first list is associated with the first RIS configuration, and the second list is associated with the second RIS configuration; determine a first set of CSI-RS resources based on the first list of CSI-RS resource IDs, wherein the first CSI-RS is received using one or more CSI-RS resources of the first set; and determine a second set of CSI-RS resources based on the second list of CSI-RS resource IDs, wherein the second CSI-RS is received using one or more CSI-RS resources of the second set.

7. The WTRU according to claim 1, wherein The processor is further configured to: determine a rank indicator (RI), a precoding matrix indicator (PMI), and a channel quality indicator (CQI) associated with the BS-RIS-WTRU channel based on the differential CSI measurement. Determine the RI, PMI, and CQI associated with the BS-WTRU channel between the WTRU and the base station; and Report the RI, PMI, and CQI associated with the BS-RIS-WTRU channel and the RI, PMI, and CQI associated with the BS-WTRU channel.

8. A method performed by a wireless transmit / receive unit (WTRU), comprising: Receiving configuration information associated with a reconfigurable intelligent surface (RIS), wherein the configuration information indicates a first set of RIS parameters associated with a first RIS configuration and a second set of RIS parameters associated with a second RIS configuration; Receiving a first channel state information reference signal (CSI-RS) associated with the first set of RIS parameters and a second CSI-RS associated with the second set of RIS parameters; Determining differential CSI measurements associated with a base station (BS)-RIS-WTRU channel based on the first CSI-RS associated with the first set of RIS parameters and the second CSI-RS associated with the second set of RIS parameters; and Transmitting a CSI report including the differential CSI measurements.

9. The method according to claim 8, wherein, The first RIS configuration corresponds to a first RIS state, and the second RIS configuration corresponds to a second RIS state, and wherein the first set of RIS parameters represents the first RIS state and the second set of RIS parameters represents the second RIS state.

10. The method according to claim 9, wherein, The first set of RIS parameters includes a first phase shift and a first amplification gain, and the second set of RIS parameters includes a second phase shift and a second amplification gain, wherein the first phase shift and the second phase shift are different, and the first amplification gain and the second amplification gain are different.

11. The method according to claim 8, wherein, The first set of RIS parameters represents a first RIS state of the sub-surface of the RIS, and the second set of RIS parameters represents a second RIS state of the sub-surface of the RIS.

12. The method according to claim 8, further comprising: Determining a first channel measurement based on the first CSI-RS and the first set of RIS parameters; Determining a second channel measurement based on the second CSI-RS and the second set of RIS parameters; And Determining differential CSI measurements associated with the BS-RIS-WTRU channel based on the first channel measurement and the second channel measurement.

13. The method according to claim 8, further comprising: Determining a first list of CSI-RS resource identifiers (IDs) and a second list of CSI-RS resource IDs based on the received configuration information, wherein the first list is associated with the first RIS configuration and the second list is associated with the second RIS configuration; Determining a first set of CSI-RS resources based on the first list of CSI-RS resource IDs, wherein the first CSI-RS is received using one or more CSI-RS resources of the first set; and Determine a second set of CSI-RS resources based on the second list of CSI-RS resource IDs, wherein one or more CSI-RS resources of the second set are used to receive the second CSI-RS.

14. The method according to claim 8, further comprising: Determine a rank indicator (RI), a precoding matrix indicator (PMI), and a channel quality indicator (CQI) associated with the BS-RIS-WTRU channel based on the differential CSI measurement; Determine the RI, PMI, and CQI associated with the BS-WTRU channel between the WTRU and the base station; and Report the RI, PMI, and CQI associated with the BS-RIS-WTRU channel, and the RI, PMI, and CQI associated with the BS-WTRU channel.

15. The method according to claim 8, wherein Receive the configuration information from the BS, and the BS-RIS-WTRU channel is a communication path for the BS and the WTRU via the RIS.

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