Methods for near-field detection and beam optimization including reconfigurable intelligent surfaces

Abstract

A method of beam correlation measurements may be implemented by a wireless transmit / receive unit (WTRU). The WTRU may be configured to receive a beam correlation measurements configuration information message that may comprise resource sets for beam correlation measurements. Each resource set may comprise reference signals that correspond to a beam. The WTRU may be configured to receive a beam correlation reporting configuration information message. The WTRU may be configured to determine to start beam correlation measurements based on an event. The WTRU may be configured to perform beam correlation measurements on the reference signals based on the received beam correlation measurements configuration information message. The reference signals may be grouped in the resources sets for beam correlation measurements. The WTRU may be configured to send a beam correlation measurements report based on a triggering condition. The WTRU may be configured to stop the beam correlation measurements.

Description

METHODS FOR NEAR-FIELD DETECTION AND BEAM OPTIMIZATION INCLUDING RECONFIGURABLE INTELLIGENT SURFACESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 512,321, filed July 7, 2023, the contents of which are incorporated herein by reference.BACKGROUND

[0002] The use of Reconfigurable Intelligent Surfaces (RISs) to boost signal coverage and performance has gained interest in response to their ability to tailor the radio frequency (RF) characteristics of reflected signals. A RIS is a device that comprises multiple unit cells that can manipulate (e.g. reflect, refract, and / or absorb) electromagnetic waves impinging on it. They may be envisioned to be used in wireless systems to partially control the properties of radio environments. Since RISs typically comprise large number of antenna elements, they can be used to form very narrow beams thus leading to reinforced coverage. RISs may be passive (e.g. with unit cells applying only pure phase shifts), active (e.g. involving additional amplification at the unit cells), hybrid active-passive (e.g. having a few active elements with the ability to reflect and amplify incident signals), or active (e.g. with all unit cells having active elements).SUMMARY

[0003] A method of beam correlation measurements may be implemented by a wireless transmit / receive unit (WTRU). The WTRU may be configured to receive a beam correlation measurements configuration information message. The beam correlation measurements configuration information message may comprise resource sets for beam correlation measurements. Each resource set may comprise reference signals that correspond to a beam. The WTRU may be configured to receive a beam correlation reporting configuration information message. The WTRU may be configured to determine to start beam correlation measurements based on an event. The WTRU may be configured to perform beam correlation measurements on the reference signals based on the received beam correlation measurements configuration information message. The reference signals may be grouped in the resources sets for beam correlation measurements. The WTRU may be configured to send a beam correlation measurements report based on a triggering condition. The WTRU may be configured to stop the beam correlation measurements. The beam correlation measurements may be stopped on a condition that at least one of the following is satisfied: a reference signal for beam correlation measurements is no longer detected; the WTRU was requested by a network entity to start beam correlation measurements and reports are of aperiodic type or of semi-persistent type and are de-activated; the WTRU receives a request to stop the beam correlation measurements; or beam correlation measurement triggering conditions are no longer satisfied. The beam correlation measurements configuration information message may further comprise: a number of repetitions N to average measurements with a configured gap between repetitions and one or more threshold values for triggering beam correlation measurements. The beamcorrelation measurements configuration information message and the beam correlation reporting configuration information message may be a same message. The event to start beam correlation measurements may comprise: detection of a transmission pattern of the reference signals; a received network request; or a triggering condition for beam correlation measurements. The triggering condition for beam correlation measurements may comprise: a reference signal received power (RSRP) below an RSRP minimum threshold value, a physical downlink control channel (PDCCH) hypothetical block error rate (BLER) above a BLER maximum threshold value, a detection of a change in a state of a gNB transmitted beam, a detection of a change in physical displacement greater than a threshold value, detection of a change in signal strength greater than a threshold value, or detection of a value of a beam correlation metric larger than a threshold value. The WTRU may be configured to send a request for a network entity to transmit the reference signals and receive a confirmation information to measure the reference signals. The beam correlation measurements report may comprise: a beam correlation width lx given by a beam index difference for a X% correlation relative to a maximum; K compressed or uncompressed correlation values for all possible beam index differences; a quantized version of measured correlation metrics; an indication corresponding to a pre-defined state of a gNB transmitted beam; a signal to noise ratio (SNR); a rank; a reference signal received power (RSRP) value; or an index representing a WTRU receiver spatial beam used for the measurements. The beam correlation measurements may comprise a sum of products of two channel transfer functions of the reference signals, wherein one of the channel transfer functions in each of the products of two channel transfer functions is first conjugated by reversing a sign of its imaginary component prior to performing beam correlation measurements. The WTRU may be configured to detect the reference signals and obtain channel transfer functions.BRIEF DESCRIPTION OF THE DRAWINGS

[0004] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings, wherein like reference numerals in the figures indicate like elements, and wherein:

[0005] FIG. 1A is a system diagram illustrating an example communications system in which one or more disclosed embodiments may be implemented;

[0006] FIG. 1 B is a system diagram illustrating an example wireless transmit / receive unit (WTRU) that may be used within the communications system illustrated in FIG. 1A according to an embodiment;

[0007] FIG. 1C is a system diagram illustrating an example radio access network (RAN) and an example core network (CN) that may be used within the communications system illustrated in FIG. 1A according to an embodiment;

[0008] FIG. 1 D is a system diagram illustrating a further example RAN and a further example CN that may be used within the communications system illustrated in FIG. 1A according to an embodiment;

[0009] FIG. 2 shows an example schematic comparison of the impact of spherical and planar wavefronts on the spatial resolution of beams having different angle of departures (AoDs);

[0010] FIG. 3 shows an example scenario comprising a TRP and a RIS;

[0011] FIG. 4 shows an example MIMO clustered channel model;

[0012] FIG. 5 shows an example of measurements for computation of the correlation function across several CSI-RS resource sets corresponding to beams transmitted by the base station with different AoDs;

[0013] FIG. 6 shows an example of a schematic illustration of K CSI-RS resource sets that are frequency- staggered and repeated N times for beam correlation measurements;

[0014] FIG. 7 shows an example of a schematic illustration of K CSI-RS resource sets that are time- multiplexed and repeated N times for beam correlation measurements;

[0015] FIG. 8 shows an example arrangement of time-frequency resources where K CSI-RS resource sets each comprising L frequency resources are frequency-multiplexed and repeated N times for beam correlation measurements;

[0016] FIG. 9 shows as example of the beam correlation width for a correlation value above 10% of the maximum;

[0017] FIG. 10 shows an example of beam obstruction caused by an obstacle at the RIS backhaul link that increases beam correlation at the WTRU side;

[0018] FIG. 11 shows an example coordinate system for an array response vector;

[0019] FIG. 12 shows an example of a beamformed backhaul beam resembling a LOS path that gets ideally reflected towards the WTRU;

[0020] FIG. 13 shows an example of sudden deflection of the access beam caused by a change in the backhaul beam;

[0021] FIG. 14 shows an example of the change in the DL beamforming vectors needed after a DL beam change in the backhaul;

[0022] FIG. 15 shows an example method for WTRU measurements of beam correlation;

[0023] FIG. 16 shows an example method for WTRU reporting of beam correlation measurements;

[0024] FIG. 17 shows an example method for WTRU measurements of beam correlation and reporting of beam correlation measurements;

[0025] FIG. 18 shows an example method for enhanced RIS management of the RIS backhaul beam by a RIS capable of performing backhaul beam angular measurements;

[0026] FIG. 19 shows an example method for enhanced RIS management of the RIS backhaul beam by a RIS not capable of performing backhaul beam angular measurements;

[0027] FIG. 20 shows an example method for enhanced TRP management of the RIS backhaul beam; and

[0028] FIG. 21 shows an example method for WTRU measurements of beam correlation and reporting of beam correlation measurements.DETAILED DESCRIPTION

[0029] FIG. 1A is a diagram illustrating an example communications system 100 in which one or more disclosed embodiments may be implemented. The communications system 100 may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system 100 may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems 100 may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), singlecarrier FDMA (SC-FDMA), zero-tail unique-word discrete Fourier transform Spread OFDM (ZT-UW-DFT-S- OFDM), unique word OFDM (UW-OFDM), resource block-filtered OFDM, filter bank multicarrier (FBMC), and the like.

[0030] As shown in FIG. 1A, the communications system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) 104, a core network (ON) 106, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d, any of which may be referred to as a station (STA), may be configured to transmit and / or receive wireless signals and may include a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi device, an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like. Any of the WTRUs 102a, 102b, 102c and 102d may be interchangeably referred to as a UE.

[0031] The communications systems 100 may also include a base station 114a and / or a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the CN 106, the Internet 110, and / or the other networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a NodeB, an eNode B (eNB), a Home Node B, a Home eNode B, a next generation NodeB, such as a gNode B (gNB), a new radio (NR) NodeB, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0032] The base station 114a may be part of the RAN 104, which may also include other base stations and / or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, and the like. The base station 114a and / or the base station 114b may be configured to transmit and / or receive wireless signals on one or more carrier frequencies, which may be referred to as a cell (not shown). These frequencies may be in licensed spectrum, unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide coverage for a wireless service to a specific geographical area that may be relatively fixed or that may change over time. The cell may further be divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, i.e., one for each sector of the cell. In an embodiment, the base station 114a may employ multiple-input multiple output (MIMO) technology and may utilize multiple transceivers for each sector of the cell. For example, beamforming may be used to transmit and / or receive signals in desired spatial directions.

[0033] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0034] More specifically, as noted above, the communications system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station 114a in the RAN 104 and the WTRUs 102a, 102b, 102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 116 using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink (DL) Packet Access (HSDPA) and / or High-Speed Uplink (UL) Packet Access (HSUPA).

[0035] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and / or LTE-Advanced (LTE-A) and / or LTE-Advanced Pro (LTE-A Pro).

[0036] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR Radio Access , which may establish the air interface 116 using NR.

[0037] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement multiple radio access technologies. For example, the base station 114a and the WTRUs 102a, 102b, 102c may implement LTE radio access and NR radio access together, for instance using dual connectivity (DC) principles. Thus, the air interface utilized by WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and / or transmissions sent to / from multiple types of base stations (e.g., an eNB and a gNB).

[0038] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies such as IEEE 802.11 (i.e., Wireless Fidelity (WiFi), IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like.

[0039] The base station 114b in FIG. 1A may be a wireless router, Home Node B, Home eNode B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., for use by drones), a roadway, and the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In an embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR etc.) to establish a picocell or femtocell. As shown in FIG. 1A, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114b may not be required to access the Internet 110 via the CN 106.

[0040] The RAN 104 may be in communication with the CN 106, which may be any type of network configured to provide voice, data, applications, and / or voice over internet protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have varying quality of service (QoS) requirements, such as differing throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, and the like. The CN 106 may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and / or perform high-level security functions, such as user authentication. Although not shown in FIG. 1A, it will be appreciated that the RAN 104 and / or the CN 106 may be in direct or indirect communication with other RANs that employ the same RAT as the RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104, which may be utilizing a NR radio technology, the CN 106 may also be in communication with another RAN (not shown) employing a GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology.

[0041] The CN 106 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or the other networks 112. The PSTN 108 may include circuit-switched telephone networks that provide plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and / or the internet protocol (IP) in the TCP / IP internet protocol suite. The networks 112 may include wired and / or wireless communications networks owned and / or operated by other service providers. For example, the networks 112 may include another CN connected to one or more RANs, which may employ the same RAT as the RAN 104 or a different RAT.

[0042] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links). For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with the base station 114a, which may employ a cellularbased radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0043] FIG. 1B is a system diagram illustrating an example WTRU 102. As shown in FIG. 1 B, the WTRU 102 may include a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, non-removable memory 130, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and / or other peripherals 138, among others. It will be appreciated that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment.

[0044] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), any other type of integrated circuit (IC), a state machine, and the like. The processor 118 may perform signal coding, data processing, power control, input / output processing, and / or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit / receive element 122. While FIG. 1B depicts the processor 118 and the transceiver 120 as separate components, it will be appreciated that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0045] The transmit / receive element 122 may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, the transmit / receive element 122 may be an antenna configured to transmit and / or receive RF signals. In an embodiment, the transmit / receive element 122 may be an emitter / detector configured to transmit and / or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit / receive element 122 may be configured to transmit and / or receive both RF and light signals. It will be appreciated that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0046] Although the transmit / receive element 122 is depicted in FIG. 1 B as a single element, the WTRU 102 may include any number of transmit / receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0047] The transceiver 120 may be configured to modulate the signals that are to be transmitted by the transmit / receive element 122 and to demodulate the signals that are received by the transmit / receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may includemultiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as NR and IEEE 802.11 , for example.

[0048] The processor 118 of the WTRU 102 may be coupled to, and may receive user input data from, the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. In addition, the processor 118 may access information from, and store data in, any type of suitable memory, such as the non-removable memory 130 and / or the removable memory 132. The non-removable memory 130 may include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from, and store data in, memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown).

[0049] The processor 118 may receive power from the power source 134, and may be configured to distribute and / or control the power to the other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li- ion), etc.), solar cells, fuel cells, and the like.

[0050] The processor 118 may also be coupled to the GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or in lieu of, the information from the GPS chipset 136, the WTRU 102 may receive location information over the air interface 116 from a base station (e.g., base stations 114a, 114b) and / or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment.

[0051] The processor 118 may further be coupled to other peripherals 138, which may include one or more software and / or hardware modules that provide additional features, functionality and / or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs and / or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, a Virtual Reality and / or Augmented Reality (VR / AR) device, an activity tracker, and the like. The peripherals 138 may include one or more sensors. The sensors may be one or more of a gyroscope, an accelerometer, a hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor; a geolocation sensor, an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, a humidity sensor and the like.

[0052] The WTRU 102 may include a full duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for both the UL (e.g., for transmission) and DL (e.g., for reception) may be concurrent and / or simultaneous. The full duplex radio may include an interference management unit to reduce and or substantially eliminate self-interference via either hardware (e.g., a choke) or signal processing via a processor (e.g., a separate processor (not shown) or via processor 118). In an embodiment, the WTRU 102 may include a half-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for either the UL (e.g., for transmission) or the DL (e.g., for reception)).

[0053] FIG. 1C is a system diagram illustrating the RAN 104 and the CN 106 according to an embodiment. As noted above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the CN 106.

[0054] The RAN 104 may include eNode-Bs 160a, 160b, 160c, though it will be appreciated that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the eNode-Bs 160a, 160b, 160c may implement MIMO technology. Thus, the eNode-B 160a, for example, may use multiple antennas to transmit wireless signals to, and / or receive wireless signals from, the WTRU 102a.

[0055] Each of the eNode-Bs 160a, 160b, 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, and the like. As shown in FIG. 10, the eNode-Bs 160a, 160b, 160c may communicate with one another over an X2 interface.

[0056] The CN 106 shown in FIG. 1C may include a mobility management entity (MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN) gateway (PGW) 166. While the foregoing elements are depicted as part of the CN 106, it will be appreciated that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0057] The MME 162 may be connected to each of the eNode-Bs 162a, 162b, 162c in the RAN 104 via an S1 interface and may serve as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation / deactivation, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c, and the like. The MME 162 may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM and / or WCDMA.

[0058] The SGW 164 may be connected to each of the eNode Bs 160a, 160b, 160c in the RAN 104 via the S1 interface. The SGW 164 may generally route and forward user data packets to / from the WTRUs 102a, 102b, 102c. The SGW 164 may perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when DL data is available for the WTRUs 102a, 102b, 102c, managing and storing contexts of the WTRUs 102a, 102b, 102c, and the like.

[0059] The SGW 164 may be connected to the PGW 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0060] The CN 106 may facilitate communications with other networks. For example, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. For example, the CN 106 may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to the other networks 112, which may include other wired and / or wireless networks that are owned and / or operated by other service providers.

[0061] Although the WTRU is described in FIGS. 1A-1 D as a wireless terminal, it is contemplated that in certain representative embodiments that such a terminal may use (e.g., temporarily or permanently) wired communication interfaces with the communication network.

[0062] In representative embodiments, the other network 112 may be a WLAN.

[0063] A WLAN in Infrastructure Basic Service Set (BSS) mode may have an Access Point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP may have access or an interface to a Distribution System (DS) or another type of wired / wireless network that carries traffic in to and / or out of the BSS. Traffic to STAs that originates from outside the BSS may arrive through the AP and may be delivered to the STAs. Traffic originating from STAs to destinations outside the BSS may be sent to the AP to be delivered to respective destinations. Traffic between STAs within the BSS may be sent through the AP, for example, where the source STA may send traffic to the AP and the AP may deliver the traffic to the destination STA. The traffic between STAs within a BSS may be considered and / or referred to as peer-to-peer traffic. The peer-to- peer traffic may be sent between (e.g., directly between) the source and destination STAs with a direct link setup (DLS). In certain representative embodiments, the DLS may use an 802.11e DLS or an 802.11z tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may not have an AP, and the STAs (e.g., all of the STAs) within or using the IBSS may communicate directly with each other. The IBSS mode of communication may sometimes be referred to herein as an “ad-hoc” mode of communication.

[0064] When using the 802.11ac infrastructure mode of operation or a similar mode of operations, the AP may transmit a beacon on a fixed channel, such as a primary channel. The primary channel may be a fixed width (e.g., 20 MHz wide bandwidth) or a dynamically set width. The primary channel may be the operating channel of the BSS and may be used by the STAs to establish a connection with the AP. In certain representative embodiments, Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) may be implemented, for example in 802.11 systems. For CSMA / CA, the STAs (e.g., every STA), including the AP, may sense the primary channel. If the primary channel is sensed / detected and / or determined to be busy by a particular STA, the particular STA may back off. One STA (e.g., only one station) may transmit at any given time in a given BSS.

[0065] High Throughput (HT) STAs may use a 40 MHz wide channel for communication, for example, via a combination of the primary 20 MHz channel with an adjacent or nonadjacent 20 MHz channel to form a 40 MHz wide channel.

[0066] Very High Throughput (VHT) STAs may support 20MHz, 40 MHz, 80 MHz, and / or 160 MHz wide channels. The 40 MHz, and / or 80 MHz, channels may be formed by combining contiguous 20 MHz channels. A 160 MHz channel may be formed by combining 8 contiguous 20 MHz channels, or by combining two noncontiguous 80 MHz channels, which may be referred to as an 80+80 configuration. For the 80+80 configuration, the data, after channel encoding, may be passed through a segment parser that may divide the data into two streams. Inverse Fast Fourier Transform (IFFT) processing, and time domain processing, may be done on each stream separately. The streams may be mapped on to the two 80 MHz channels, and the data may be transmitted by a transmitting STA. At the receiver of the receiving STA, the above described operation for the 80+80 configuration may be reversed, and the combined data may be sent to the Medium Access Control (MAC).

[0067] Sub 1 GHz modes of operation are supported by 802.11 af and 802.11ah. The channel operating bandwidths, and carriers, are reduced in 802.11af and 802.11ah relative to those used in 802.11n, and 802.11ac. 802.11af supports 5 MHz, 10 MHz, and 20 MHz bandwidths in the TV White Space (TVWS) spectrum, and 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum. According to a representative embodiment, 802.11ah may support Meter Type Control / Machine- Type Communications (MTC), such as MTC devices in a macro coverage area. MTC devices may have certain capabilities, for example, limited capabilities including support for (e.g., only support for) certain and / or limited bandwidths. The MTC devices may include a battery with a battery life above a threshold (e.g., to maintain a very long battery life).

[0068] WLAN systems, which may support multiple channels, and channel bandwidths, such as 802.11 n, 802.11ac, 802.11af, and 802.11ah, include a channel which may be designated as the primary channel. The primary channel may have a bandwidth equal to the largest common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be set and / or limited by a STA, from among all STAs in operating in a BSS, which supports the smallest bandwidth operating mode. In the example of 802.11ah, the primary channel may be 1 MHz wide for STAs (e.g., MTC type devices) that support (e.g., only support) a 1 MHz mode, even if the AP, and other STAs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16 MHz, and / or other channel bandwidth operating modes. Carrier sensing and / or Network Allocation Vector (NAV) settings may depend on the status of the primary channel. If the primary channel is busy, for example, due to a STA (which supports only a 1 MHz operating mode) transmitting to the AP, all available frequency bands may be considered busy even though a majority of the available frequency bands remains idle.

[0069] In the United States, the available frequency bands, which may be used by 802.11 ah, are from 902 MHz to 928 MHz. In Korea, the available frequency bands are from 917.5 MHz to 923.5 MHz. In Japan, theavailable frequency bands are from 916.5 MHz to 927.5 MHz. The total bandwidth available for 802.11 ah is 6 MHz to 26 MHz depending on the country code.

[0070] FIG. 1D is a system diagram illustrating the RAN 104 and the CN 106 according to an embodiment. As noted above, the RAN 104 may employ an NR radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the CN 106.

[0071] The RAN 104 may include gNBs 180a, 180b, 180c, though it will be appreciated that the RAN 104 may include any number of gNBs while remaining consistent with an embodiment. The gNBs 180a, 180b, 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the gNBs 180a, 180b, 180c may implement MIMO technology. For example, gNBs 180a, 108b may utilize beamforming to transmit signals to and / or receive signals from the gNBs 180a, 180b, 180c. Thus, the gNB 180a, for example, may use multiple antennas to transmit wireless signals to, and / or receive wireless signals from, the WTRU 102a. In an embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, the gNB 180a may transmit multiple component carriers to the WTRU 102a (not shown). A subset of these component carriers may be on unlicensed spectrum while the remaining component carriers may be on licensed spectrum. In an embodiment, the gNBs 180a, 180b, 180c may implement Coordinated Multi-Point (CoMP) technology. For example, WTRU 102a may receive coordinated transmissions from gNB 180a and gNB 180b (and / or gNB 180c).

[0072] The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using transmissions associated with a scalable numerology. For example, the OFDM symbol spacing and / or OFDM subcarrier spacing may vary for different transmissions, different cells, and / or different portions of the wireless transmission spectrum. The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using subframe or transmission time intervals (TTIs) of various or scalable lengths (e.g., containing a varying number of OFDM symbols and / or lasting varying lengths of absolute time).

[0073] The gNBs 180a, 180b, 180c may be configured to communicate with the WTRUs 102a, 102b, 102c in a standalone configuration and / or a non-standalone configuration. In the standalone configuration, WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c without also accessing other RANs (e.g., such as eNode-Bs 160a, 160b, 160c). In the standalone configuration, WTRUs 102a, 102b, 102c may utilize one or more of gNBs 180a, 180b, 180c as a mobility anchor point. In the standalone configuration, WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using signals in an unlicensed band. In a non-standalone configuration WTRUs 102a, 102b, 102c may communicate with / connect to gNBs 180a, 180b, 180c while also communicating with / connecting to another RAN such as eNode-Bs 160a, 160b, 160c. For example, WTRUs 102a, 102b, 102c may implement DC principles to communicate with one or more gNBs 180a, 180b, 180c and one or more eNode-Bs 160a, 160b, 160c substantially simultaneously. In the non- standalone configuration, eNode-Bs 160a, 160b, 160c may serve as a mobility anchor for WTRUs 102a, 102b, 102c and gNBs 180a, 180b, 180c may provide additional coverage and / or throughput for servicing WTRUs 102a, 102b, 102c.

[0074] Each of the gNBs 180a, 180b, 180c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, support of network slicing, DC, interworking between NR and E-UTRA, routing of user plane data towards User Plane Function (UPF) 184a, 184b, routing of control plane information towards Access and Mobility Management Function (AMF) 182a, 182b and the like. As shown in FIG. 1 D, the gNBs 180a, 180b, 180c may communicate with one another over an Xn interface.

[0075] The CN 106 shown in FIG. 1 D may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one Session Management Function (SMF) 183a, 183b, and possibly a Data Network (DN) 185a, 185b. While the foregoing elements are depicted as part of the CN 106, it will be appreciated that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0076] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 via an N2 interface and may serve as a control node. For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, support for network slicing (e.g., handling of different protocol data unit (PDU) sessions with different requirements), selecting a particular SMF 183a, 183b, management of the registration area, termination of non-access stratum (NAS) signaling, mobility management, and the like. Network slicing may be used by the AMF 182a, 182b in order to customize CN support for WTRUs 102a, 102b, 102c based on the types of services being utilized WTRUs 102a, 102b, 102c. For example, different network slices may be established for different use cases such as services relying on ultra-reliable low latency (URLLC) access, services relying on enhanced massive mobile broadband (eMBB) access, services for MTC access, and the like. The AMF 182a, 182b may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies such as WiFi.

[0077] The SMF 183a, 183b may be connected to an AMF 182a, 182b in the CN 106 via an N11 interface. The SMF 183a, 183b may also be connected to a UPF 184a, 184b in the CN 106 via an N4 interface. The SMF 183a, 183b may select and control the UPF 184a, 184b and configure the routing of traffic through the UPF 184a, 184b. The SMF 183a, 183b may perform other functions, such as managing and allocating UE IP address, managing PDU sessions, controlling policy enforcement and QoS, providing DL data notifications, and the like. A PDU session type may be IP-based, non-IP based, Ethernet-based, and the like.

[0078] The UPF 184a, 184b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 via an N3 interface, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The UPF 184, 184b may perform other functions, such as routing and forwarding packets, enforcing user plane policies, supporting multi-homed PDU sessions, handling user plane QoS, buffering DL packets, providing mobility anchoring, and the like.

[0079] The CN 106 may facilitate communications with other networks. For example, the CN 106 may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that servesas an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to the other networks 112, which may include other wired and / or wireless networks that are owned and / or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c may be connected to a local DN 185a, 185b through the UPF 184a, 184b via the N3 interface to the UPF 184a, 184b and an N6 interface between the UPF 184a, 184b and the DN 185a, 185b.

[0080] In view of FIGs. 1A-1 D, and the corresponding description of FIGs. 1A-1 D, one or more, or all, of the functions described herein with regard to one or more of: WTRU 102a-d, Base Station 114a-b, eNode-B 160a-c, MME 162, SGW 164, PGW 166, gNB 180a-c, AMF 182a-b, UPF 184a-b, SMF 183a-b, DN 185a-b, and / or any other device(s) described herein, may be performed by one or more emulation devices (not shown). The emulation devices may be one or more devices configured to emulate one or more, or all, of the functions described herein. For example, the emulation devices may be used to test other devices and / or to simulate network and / or WTRU functions.

[0081] The emulation devices may be designed to implement one or more tests of other devices in a lab environment and / or in an operator network environment. For example, the one or more emulation devices may perform the one or more, or all, functions while being fully or partially implemented and / or deployed as part of a wired and / or wireless communication network in order to test other devices within the communication network. The one or more emulation devices may perform the one or more, or all, functions while being temporarily implemented / deployed as part of a wired and / or wireless communication network. The emulation device may be directly coupled to another device for purposes of testing and / or performing testing using over-the-air wireless communications.

[0082] The one or more emulation devices may perform the one or more, including all, functions while not being implemented / deployed as part of a wired and / or wireless communication network. For example, the emulation devices may be utilized in a testing scenario in a testing laboratory and / or a non-deployed (e.g., testing) wired and / or wireless communication network in order to implement testing of one or more components. The one or more emulation devices may be test equipment. Direct RF coupling and / or wireless communications via RF circuitry (e.g., which may include one or more antennas) may be used by the emulation devices to transmit and / or receive data.

[0083] RISs of reflective type may be equipped with a reflective surface comprising multiple unit cells made of meta-materials whose electromagnetic properties may be changed to steer the reflected beams. In some cases, the unit cells may apply elementary phase shifts to an arriving wave as commanded by a RIS control unit. When a plane wave impinges on the RIS with a given angle of arrival (AoA), the angle of departure (AoD) of the reflected wave may generally depend on the AoA and the relative phases applied on the unit cells, which altogether constitute a RIS beamforming vector. By adjusting those phases, the reflected wave may be steered to the desired direction thus improving coverage and / or capacity performance for the WTRU being serviced in the uplink (UL) and the downlink (DL).

[0084] There is some similarity between RISs and Network-Controlled Repeaters (NCR) as far as the signaling framework is concerned. NCRs are in-band radio frequency (RF) repeaters for extension of network coverage in Frequency Range 1 (FR1) or Frequency Range 2 (FR2) bands. NCR specifications consider singlehop stationary repeaters that are transparent to WTRUs and perform amplify-and-forwarding of UL / DL signals. While some NCRs are able to do separate beamforming at the receive and transmit sides, including amplification, some RISs of reflective type may have a single beamforming matrix comprising phase shifts without amplification. In such cases, the RIS backhaul and access links are interrelated, and not independent as in the NCR case, with regards to beam management.

[0085] Channel State Information (CSI) may refer to a set of quantities that a WTRU may measure and report to the network as an indication of the channel state. CSI may be measured by the network and / or the WTRU to obtain the UL and DL channel states respectively, which may be equal when channel reciprocity conditions hold (e.g. in TDD systems).

[0086] DL CSI may be measured by a WTRU with the aid of a set of CSI-RS signals or a set of SS / PBCH blocks. An SS / PBCH block (SSB) may carry a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS), a Physical Broadcast Channel (PBCH), and / or a PBCH Demodulation Reference Signals (DMRS).

[0087] UL CSI may be measured by the network with the aid of a sounding reference signal (SRS). CSI reporting may be configured by the network to perform CSI measurements on different quantities (e.g. reference signal received power (RSRP), channel quality information (CQI), precoding matrix indicator (PMI), or rank indicator (Rl)).

[0088] In terms of CSI reporting, there are solutions to identify and further request the channel state information corresponding to two sets of beams: one containing beams that are reflected by a RIS, and the other containing beams that directly reach the WTRU.

[0089] A transmit antenna may comprise multiple point sources that emit polarized spherical waves. The reactive near-field zone of the antenna usually vanishes very close to it and is usually neglected. The radiative near-field and the far-field zones follow and are separated by the Fraunhofer (or Rayleigh) distance dF= 2D2 / A (£> is the maximum length of the antenna), where the phase difference between a wave impinging at the center and the corner of an aperture is at most n / 8.

[0090] In the far-field, a wave has an amplitude that is constant over the receive antenna, and a phase that only depends on the incident angle. In the Fresnel region 1.2D < d < dF, amplitude variations at the receive (Rx) antenna may also be neglected, but not phase variations. Because of this, the ratio of antenna gains at the Fresnel and far-field regions is always < 1, and approaches unity for d > dF.

[0091] The Fraunhofer distance of a planar square antenna array with Ntelements is dFA= NtdF. Below the Fraunhofer distance, phase variations are significant across the Rx antenna and do not solely depend on the incidence angle. As the phases are not perfectly coherent anymore at the direction of maximum radiation,a reduction in the antenna gain occurs and an increase in the main lobe’s beamwidth. Beams in the near field can only be focused on a spatial region called Depth of Field (DoF), or Depth of Focus, around the focal point, which is finite below dFAand motivates the appearance of beam de-focusing, or blurring effects. Beams in the far field (i.e., beyond dFA) are always focused and their DoF extends to infinity.

[0092] A lower boundary for the near-field region in antenna arrays, analogous to the lower boundary of the Fresnel region, is called the Bjbrnson distance, dB=Amplitude variations across the Rx antenna can be considered negligible, but phases cannot, in the range dB< d < dFA. dBis usually rather small, hence most of the near-field region may be characterized by negligible amplitude variations and non-negligible phase variations when measured across the array’s antenna diagonal.

[0093] Figure 2 shows a schematic comparison of the impact of spherical and planar wave fronts (upper figures) on the spatial resolution of beams having different AoDs (bottom figures). Near-field effects in practice means poorer spatial resolution of the beams, and poorer ability to resolve different AoAs or AoDs. This is shown in figure 2 where beams having different AoDs present a poorer angular resolvability in the near field compared to the far field. Although independent of the presence of RIS, near-field effects may be more significant with RIS because the near-field condition is more restricted in this case, as given by < rl+rl2D2 / X, where and r2are respectively the BS-RIS and RIS-WTRU distances. Moreover, defocusing of the beam that impinges on a RIS may hinder the ability of the RIS elements to steer the wave towards the WTRU, and hence its effectiveness to improve coverage.

[0094] In summary, the spatial region dB< d < dFAin antenna arrays determines the range where amplitude variations can be considered negligible, but phase variations can be significant, when measured across the diagonal of a Rx antenna.

[0095] Contrary to NCRs, the backhaul and access links may not be independent in RISs of reflective type but may be interrelated via the RIS beamforming vector. If standard procedures for beam management are followed by the WTRU in the presence of RIS, WTRU mobility events may trigger beam changes in the access to adequately track its movement. Similarly, any signal obstruction in the backhaul may trigger a beam change between the transmit-receive point (TRP) and the RIS. As a result of the interrelation between both links, changes in the access beam may impact the backhaul beam and vice versa.

[0096] Computation of Fraunhofer distances is only an indicative measure of near-field effects and the actual impact on MIMO / RIS systems cannot easily be foreseen in advance because it depends on the exact geometries and phase relationships between the component waves. As a result, the amount of beam blurring or defocusing effects that is expected is strongly dependent on the geometry and cannot be predicted by the sole computation of Fraunhofer distances. Even in far-field cases, blurring of the beams may appear despite selecting the best available beam when there is significant obstruction at, for example the RIS backhaul link, because diffuse reflection and diffuse scattering may lead to similar degradation in the resulting spatial resolution.

[0097] In addition, RIS-aided communications may be hindered by two broad classes of impairments: beam blurring caused by near field effects or partial obstruction of the backhaul beam, and unexpected beam deflections caused by variations in the backhaul link.

[0098] The ability of RISs to focus energy towards the WTRU may depend on its beam focusing capabilities. In case that no near-field effects are present and the backhaul is free from obstructions, the reflected beam may exhibit good beam focusing characteristics because of the RIS beamforming gain. However, when spherical wave phenomena are significant, or the beam is partially obstructed by obstacles, beam blurring effects may appear that reduce the RIS effectiveness to improve coverage. Blurring effects lead to poor spatial resolution and as a result beams cannot be well resolved in space even if they point towards different directions.

[0099] The RIS backhaul link usually has a longer channel coherence time than the access link when both the base station and the RIS are in WTRU static positions. However, changes may occur when, for example an obstacle in the backhaul appears that drops the signal quality, therefore triggering a beam change as a result. After the backhaul beam is changed, connection to the WTRU might be compromised if the unexpected beam deflection at the access is not compensated by a corresponding update in the RIS beamforming vector.

[0100] In addition, there are applications that require the receiver to be essentially free from multipath component (MPC), for example, those relying on Reference Signal Time Difference (RSTD) measurements, or AoA estimation, for positioning. For example, even if the access link of a RIS is essentially unobstructed, it cannot be ensured that the receiver is free from MPC if multiple incident signals impinge on the RIS and are eventually reflected towards the receiver (or towards an obstacle and from there to the receiver) at different AoAs, which lead to different AoDs after reflection. The combined TRP-WTRU channel suffers from the so- called “multiplicative fading effect” whereby the frequency-domain transfer function may be described as the product of the transfer functions of the TRP-RIS and RIS-WTRU links, leading to the appearance of MPC at delays that are combinations of the delays at the TRP-RIS and RIS-WTRU links.

[0101] Optimizations for beam management are therefore desirable to detect beam blurring effects and improve robustness against channel variations in the backhaul link of a RIS-aided communication scenario.

[0102] Without loss of generality, it will be assumed that communication is established between one or multiple WTRUs and one or multiple base stations.

[0103] In some cases, connection is performed with the help of one or more RISs of reflective type that provide means for connecting WTRUs to the network, but in other cases this may not be required. When one or more RISs are present, there may be other entities communicating with the WTRU via the RIS, such as, for example, another WTRU through a sidelink interface, and the proposed procedures also apply to scenarios other than one or multiple BSs and one or multiple WTRUs connected by RISs.

[0104] In some embodiments, it will be assumed that the direct links between TRPs and WTRUs may be significantly obstructed by obstacles that impair the connection and coverage may be reinforced with RISs. RISs are in this case controlled by one or multiple RIS control units, either integrated at the RIS or located inanother entity (e.g., the TRP or the WTRU), that take care of providing the control information needed to steer the beams in the desired directions. RISs are assumed to be equipped with some active antenna elements to communicate with the network and exchange control information via a control link, for example for beam selection or initial access, among others. These active antenna elements may be a subset, or all, of the antenna elements in the RIS unit cells, or separate from the RIS unit cells.

[0105] Herein, a “UE” and a “WTRU” may be used interchangeably. A “TRP” may be used interchangeably with “gNB”. A “backhaul link” may be used to refer to a link established between a TRP and a RIS to forward data. An “access link” may be used to refer to a link established between a RIS and a WTRU to deliver data. A “control link” may be used to refer to a link established between a TRP and a RIS for control purposes. A “beam” may be used to refer to a transmission or reception of any physical channel or reference signal according to at least one spatial domain filter. “RIS beams” are beams transmitted or received by a TRP and reflected by a RIS. “Non-RIS beams” are beams transmitted or received by a TRP that are not reflected by a RIS. SS block, SS burst, SSB, SS / PBCH block, SSS, PBCH, and PBCH DM-RS may be used interchangeably to refer to any RS used for synchronization and initial access by a WTRU. “RS” and “CSI-RS” may be used interchangeably to refer to one or more reference signals aimed for channel measurement and reporting including but not limited to CSI-RS or SSB.

[0106] Figure 3 shows an example scenario comprising a TRP and a RIS for improved coverage. A cellular scenario is considered where a TRP establishes wireless connections with one or multiple WTRUs. In some embodiments, the links between the TRP and the one or multiple WTRUs may be significantly obstructed and connection is reinforced by using a RIS that provides a direct path to the WTRUs, as shown in figure 3. However, in other embodiments the presence of RIS may be optional.

[0107] The TRP may comprise Nttransmit-receive antennas in a Massive Multiple Input - Multiple Output (M-MIMO) configuration. The RIS may have M unit cells. Without loss of generality, WTRUs may be equipped with a single receive antenna. Embodiments described hereinafter may be generalized to more than one WTRU receive antenna by exploiting receive diversity techniques.

[0108] Descriptions hereinafter are applicable to any signal waveform susceptible of frequency-domain analysis by means of DFTs. For simplicity, an orthogonal frequency division multiplexing (OFDM)-like waveform such as cyclic prefix (CP)-OFDM or discrete fourier transform spread (DFT-s)-OFDM will be used in the descriptions comprising discrete samples in the time or frequency domain.

[0109] The embodiments may provide a capability for the WTRU to detect the appearance of beam blurring effects caused by either near field or beam obstruction phenomena. They also may provide a capability for the network to apply enhanced beamforming so as to enhance the beam focusing capabilities of the RIS, protect the WTRU against eventual beam changes in the backhaul, and improve the reliability of positioning methods based on observed time difference of arrival (OTDOA) or AoA estimation.

[0110] In an embodiment, a WTRU may detect beam blurring effects that may impair the spatial resolution and degrade the characteristics of a beam.

[0111] For clustered MIMO channel in the far-field zone, wave amplitudes and phases may be considered constant over the receive antenna and only directions may matter. Neglecting Doppler effects, the MIMO channel response matrix h[fc] e £Nr*Ntat the k-th subcarrier considering Q clusters, Lqpaths per cluster, Nttransmit antennas, and Nrreceive antennas, can be written: h[fc] =CW(0, cr2) are circularly symmetric complex normal variables, nL qis the discrete delay of the / -th path at the q-th cluster, NFFTis the number of subcarriers, and ateare £Nrxlarerespectively the transmit and receive array response matrices at the departure angle<pdq) and incidence angleThe array response vector contains the relative phases at the antenna elements with respect to a reference point, 1 where r, is the position vector of the / -th antenna and u is aunitary vector along the specified direction.

[0112] Figure 4 shows an example MIMO clustered channel model. Considering two beams pointing at directions that differ by a certain angle it is reasonable to assume that, above some angle e, the scatterers illuminated by one beam may be considered physically independent from those illuminated by the other beam (i.e., do not correspond to a same object). This is particularly reasonable when the Tx-Rx distances are higher than the macroscopic sizes of the surrounding scatterers. When that happens, their respective clusters may be considered uncorrelated, similar to the WSSUS (wide-sense stationary with uncorrelated scattering) assumption that holds in most typical RF channels. This means that the scatterers’ amplitudes satisfy= 0, where IE{-} stands for the expectation operator, and the delays are in general different, nl q*ni' q' ’ f°r anytwodusters q q' and any pair of rays .

[0113] In summary, considering two beams in the far field pointing at directions that differ by an angle e, the scatterers illuminated by each of the beams have complex amplitudes that may be considered uncorrelated, and path delays that are generally different, above a certain value of e.

[0114] For the near-field, in the region the amplitudes aL qand delays nL qmay retainthe same expressions while the array response vectors may account for the varying phases across the receive antennas. Therefore, the clustered MIMO channel may reuse the above expressions after generalizing the array response vectors at, arto a more general expression at= [e7<P1, ... , e7 <p"t] , whose phases not only depend on the directions but also on the position. Hence: h[fc] =

[0115] No amplitude variations are included in the near-field array response vector because amplitude variations across the Rx antennas are negligible in the Fresnel zone dB< d < dFAof an array. In conclusion,equation (1) for the channel transfer function remains valid if the array response vectors ar, ataccount for the varying phases that depend on the wavefront directions and the location of the Rx antenna elements.

[0116] Regarding a beam’s correlation matrix and function, consider the channel responses of two beams denoted as hco)and h^,

[0117] A beam correlation matrixNtmay be defined as a matrix containing cross-correlation terms between the Tx-Rx pairwise channel components of each of the beams: (4)where ® denotes the Kronecker product and IE{-} is the expectation operator. Given that different channel realizations will yield different frequency response functions, the expectation may be well approximated by a sum over the NFFTsubcarriers in the frequency domain, provided that the system bandwidth (BW) is much higher than the channel’s coherence BW so that the sum extends over all possible channel responses:

[0118] Statistical accuracy may be improved by extending the summation over more than one OFDM symbol. However, for simplicity we keep the calculation over a single symbol and further extend the conclusions to several symbols.

[0119] In far-field, if the beam angle separation e is such that the scatterers seen by the two beams are

[0120] The last term approaches zero for nl qnti qiwith a sufficient number of subcarriers, because it involves the sum of multiple complex roots of unity that are symmetric around the origin in the complex plane.

[0121] As a result, uncorrelated clusters with independent path delays will tend to produce negligible beam correlation values above a certain angle e. e may be approximately given by the angle that yields zero or minimum overlap between the beams.

[0122] The channel’s frequency selectivity is modelled by the last term, which ideally vanishes when there is a sufficient number of uncorrelated scatterers and the sum extends over a sufficiently high number ofsubcarriers for statistical accuracy. Even when scatterers are not physically independent, but part of, for example a larger object, the different path lengths of each beam will lead to different linear progressive phase terms that tend to cancel out when multiplying the exponentials over many subcarriers.

[0123] When Tx and Rx are in line of sight (LOS) with no apparent multipath, the array response vector will be small at and above an angle that produces minimal Tx beam response along the Tx-Rx path, hence yielding a negligible correlation. In that case there is no need to extend the summation over a wide bandwidth.

[0124] In near-field, beams lose their focusing ability out of their focal point, their observed beamwidth increases, and the overlap between beams also increases. Eventually, some of the individual paths (Z, q) from the first beam may overlap with paths (Z', q') from the second beam. Let us denote by J as the set of paths from both beams that do not overlap, and therefore illuminate uncorrelated scatterers. Let J' be the set of overlapping paths from both beams that eventually illuminate common scatterers. Then,R =

[0125] No matter how small J' is, correlation is higher than in the far-field case because of the nonvanishing terms introduced by the overlapping paths, whether in LOS or non-line of sight (NLOS) conditions. This fact may be exploited to infer the presence of spherical wavefront effects.

[0126] Correlation may be better computed by accumulating N OFDM symbols if the channel’s coherence time is much higher than the duration of N symbol periods. Extending the computation to K beams labelled by their indices Z = 0, ... , K - 1, and assuming single-antenna channel matrices, we may denote the channel response of the / -th beam at symbol n and subcarrier k by HL[n, k] . A beam correlation function R [Z] e <C may thus be obtained as a function of the beam index difference Z = 0, ... , K - 1, by averaging across all possible symbols, subcarriers, and beam pairs:

[0127] The beam correlation function will exhibit a wider set of non-null values in the near-field compared to the far-field.

[0128] The beam correlation function may detect the appearance of near-field effects by measuring the X% correlation width representing the beam index difference that yields an average correlation above X% of the maximum.

[0129] In an embodiment, a WTRU may estimate, measure, and / or determine one or more channel properties related with the appearance of beam blurring effects. For this purpose, the WTRU may receive several channels or signals to perform measurements in order to detect unusually high cross-correlation values between beams that are transmitted with different AoDs, that may be indicative of beam blurring effects. More specifically, the WTRU may receive several measurement resource sets, such as, for example, CSI-RS resource sets, each corresponding to a different beam that is transmitted by a TRP with a certain AoD and comprising a set of time-frequency resources. The resource sets are repeated a multiplicity of times to facilitate averaging by the WTRU so as to mitigate some noise and frequency-selective fading phenomena.

[0130] Figure 5 shows an example of measurements for computation of the correlation function across several CSI-RS resource sets corresponding to beams transmitted by a TRP (e.g. base station) with different AoDs. In figure 5, a procedure for measuring beam correlation showing an exemplary RIS that reflects signals towards the WTRU is shown. However, the procedure may equally be performed without any RIS. A WTRU configured to measure beam correlation may receive a set of beams, each with different AoDs, and first obtains the full channel transfer functions H n, fc] (in amplitude and phase) for symbol n, subcarrier k and resource set I , with I = 1, ... , K . Restricting the summation to the L subcarriers allocated for the measurement resource sets, then the WTRU computes the beam cross-correlation function given by the expression:

[0131] Correlation cannot be computed with just the amplitudes of the channel responses, or the RSRP values, and the full transfer functions need to be estimated in amplitude and phase.

[0132] Correlation is a function of the index difference i between the beams, thus expressing the amount of correlation between any two pair of beams with an index difference given by i. The result is averaged over the L frequency resources and N symbols that comprise a resource set, and across the ( / < - i) beams with an index difference i. For simplicity, it is assumed in the above expression that H n, fc] refer to consecutive time-frequency resources n = 1, ... , N and k = 1,but the expressions may be equally applicable to any other time-frequency arrangements involving non-adjacent resources according to the configuration.

[0133] Figure 6 shows an example of a schematic illustration of K CSI-RS resource sets that are frequency- staggered and repeated N times for beam correlation measurements. A computation may be performed by allocating RS resources in a frequency-staggered fashion, so that the summation is performed over a widefrequency region that is much larger than the highest channel’s coherence BW in NLOS. Each CSI-RS resource set corresponds to a different beam and comprises one or more single-port CSI-RS resources for measurements. Frequency-staggered allocation of CSI-RS resource sets requires that all beams are transmitted by the TRP at the same time, which may be accomplished, for example with the aid of digital beamforming techniques at the TRP side. The exact time and frequency resources may be indicated in the configuration (e.g., via RRC signalling through CSI-ReportConfig IE) involving, for example a certain comb shift and comb size per resource set, start RE, number of RBs, number of repetitions, and gap between repetitions (given in number of symbols or slots). CSI-RS resources may also be specified to be contiguous in time and / or frequency, for example with a comb size equal to one.

[0134] Figure 7 shows an example of a schematic illustration of K CSI-RS resource sets that are time- multiplexed and repeated N times for beam correlation measurements. RS resources may be multiplexed in the time domain provided that the overall duration of the KN symbol periods is much shorter than the channel’s coherence time. Time multiplexing of different beams may be characteristic of, for example, analog or hybrid beamforming techniques at the TRP side with the possibility to control one spatial beam at a time. The exact time and frequency resources may have a certain comb shift and be spaced a certain number of symbols, or be contiguous in time and / or frequency, as given by the configuration.

[0135] Figure 8 shows an example arrangement of time-frequency resources where K CSI-RS resource sets each comprising L frequency resources are frequency-multiplexed and repeated N times for beam correlation measurements. Frequency multiplexing of CSI-RS resource sets requires that all beams are transmitted by the TRP at the same time, which may be accomplished, for example, with the aid of digital beamforming techniques at the TRP side.

[0136] Measurements of beam correlation are intended to be reported to the base station upon fulfilment of certain triggering conditions, for example, a certain RSRP below a threshold, or a PDCCH hypothetical block error rate (BLER) above a threshold. In some cases, beam correlation values may be reported as a function of the beam index difference i, for example, as a set of K values that are properly quantized, compressed and / or encoded in a measurement report. As the absolute values are the ones with most importance for these measurements, phases can be disregarded and only amplitudes may need to be quantized. In other cases, beam correlation may be reported as the beam correlation width, for example, the beam index difference Ixfor which the correlation is above X% of the maximum, for example 10%, as shown in figure 9. This may save reporting bandwidth if only the width is needed to assess beam blurring effects.

[0137] If there is beam obstruction that is caused by, for example, a scatterer along the path of a serving beam, as shown in figure 10, the received signal will experience higher correlation between beams that reach the WTRU after being reflected / scattered by the obstacle despite having different AoDs, because they see a very similar propagation environment. As a result, lx will be larger than with no obstruction and this measurement may be used to assess the appearance of beam obstruction phenomena.

[0138] Advanced TRP beamforming may be performed on the signals in the RIS backhaul which may improve the beam focusing capabilities of the RIS.

[0139] For simplicity and without loss of generality, it will be assumed that TRP and RIS are at fixed positions and comprise uniform planar arrays (UPA) as in the scenario of figure 3. Any other array geometries are also valid and may equally be considered in the descriptions below by changing the corresponding array response vectors for transmission or reception.

[0140] Only the signal reflected by the RIS will be considered in the analyses below. Other signals that are not reflected by the RIS may also reach the WTRU, for example when the channel rank is higher than one and several streams are spatially multiplexed upon transmission. In that case, their contributions may be added to the expressions below without changing the main ideas described herein.

[0141] The DL channel matrix between the TRP and the RIS may be considered semistatic and its elements stable over long timescales. A matrix element expresses the input-output relationship between the n-th TRP transmit antenna and the m-th RIS receive antenna. The DL channel matrix between the RIS and the WTRU however may exhibit fast variations caused by small-scalefading phenomena motivated by the moving WTRU and / or surrounding moving objects. A matrix elementm expresses the input-output relationship between the m-th RIS transmit antenna and the WTRU receive antenna. Antenna elements are ordered column by column, starting from the origin.

[0142] In an embodiment, an array response vector a(0, <p) corresponding to a UPA may be defined on transmission or reception along the zenith and azimuth angles 0 andrespectively, as shown in figure 11 , aswhere ® is the Kronecker product and ay(0, <p), az(0) are the array response vectors, for example of the uniform linear arrays (ULA) that form the UPA along the y and z dimensions, with dimensions Nyand Nz, and inter-antenna spacing dyand dzrespectively, defined as

[0143] The magnitude of the array response vector represents the beamforming gain that would be attained in a given spatial direction (0, <p) when far-field conditions are met. In near-field conditions, the array response vector may have a different expression that generally depends on the distance to the transmitter.

[0144] An enhanced beamforming strategy is described that makes the backhaul channel resemble a direct-path LOS link along a given spatial direction to improve the beam focusing capabilities on the DL.

[0145] DL beamforming at the RIS can be described by a DL beamforming vectorthat comprises M complex phasors of the form o be applied on the M unit cells. may beknown by the RIS, and selection may be based on, for example, feedback signaling from the WTRU according to any suitable beam management procedure. The beamforming vector may also be dynamically updated by the RIS as the WTRU moves. The TRP may not be aware of the actual beamforming vector in use but it may command the RIS to select the preferred beam towards the user, for example, among a set of predefined RIS beams set by the implementation, through the control link.

[0146] In some cases, phasors may contain additional amplitude terms, e.g., , withe IR, to provide a given tapering response and thus reduce the sidelobe levels. The corresponding beamforming vector comprising only phase shifts with unit amplitude will be denoted by

[0147] Note that wDLhas a norm given by \wDL| = M.

[0148] The combined TRP-RIS-WTRU DL channel matrix in the frequency domain, HDLe CC'V-V1, may be written, including the effect of the RIS beamforming vector, as:H G(WQh),(15) where denotes point-wise multiplication of the elements o

[0149] The RIS-WTRU DL channel described by hDLmay be generally expressed as a summation of L paths of the type:is the / -th path gain of the DL reflected path, are respectively the / -th zenith andazimuth angles of departure of the / -th DL reflected path,is the delay of the / -th DL reflected path, and |S(pe arrayreSpOnsevector of the RIS. Although not explicitly denoted, aRIS:DLmay also depend on the RIS-WTRU distance if the WTRU is in the near field of the RIS.

[0150] The aim of RIS is to reinforce the signal in the line-of-sight direction towards the WTRU. If the number of RIS antenna elements M is large enough and the WTRU has beamforming capabilities, the RIS- WTRU channel may comprise essentially one direct path contribution. Then we can write L = 1 and, after dropping the subindices / ,

[0151] The combined channel of equation (15) becomes:

[0152] Assuming that a DL complex modulated symbol s e <C is beamformed by the TRP to yield a vector for transmission towards the RIS. HDLrepresents the combined channel experienced by thebeamformed signal when arriving at the WTRU, so the received signal y e <C can be written as

[0153] The presence of signal obstruction or near-field effects in GDLmay reduce the focusing capabilities of the RIS, leading to beam blurring effects. The best possible focusing of the energy towards the WTRU may be achieved when it resembles a pure LOS path at direction( , p ) with a delay rr'DLand whose amplitude is reinforced by a gain M , in the form . This is shown in figure 12. Thebeamformed signal s may therefore be constructed such that it counteracts the combined effect of the backhaul channel GDL, the RIS beamforming vector wDL(with no amplitude gain), and the array response vector aRis,DL (fy.DL, (pr.DL^ j0yjgijacombined gain of M:

[0154] where AHdenotes the Hermitian transpose of matrix A, and A+is the Moore-Penrose pseudoinverse matrix satisfying, among other conditions,AA+A = A,A+AA+= A+.

[0155] A solution expressed in terms of the pseudo-inverse matrix represents the least-squares best fit to a system of linear equations that may lack a solution, or may have multiple solutions, written as: Ax = b. The vector x = A+b is the one that best approaches the solution to the I inear system while having minimum norm.

[0156] The vector on the right-hand side of eq. (20) has a direct physical interpretation. In connected mode, the RIS beamforming vector wDLmay be constructed such that, given a DL incident wave with array response vector aRls(dl'DL, <pl,DL >), where dl'DL, <pl'DLare respectively the zenith and azimuth angles of arrival of the DL incident wave impinging on the RIS, detection at the WTRU has an ideal beamforming gain equal to M:where ( )* denotes the conjugate operator. Thus, equation (20) may be re-written

[0157] The beamformed DL signal is therefore constructed such that, when arriving at the RIS, is equal to the RIS array response vector along the spatial direction that maximizes WTRU detection after reflection at theRIS. Equality cannot be ensured by the pseudo-inverse operation, yielding only the solution that best approaches the ideal one with the least possible power.

[0158] If near-field effects are significant, attaining the full RIS beamforming gain (or close to it) may only be feasible in a certain range of RIS- WTRU distances where aRIS'DLis close to a maximum, because the depth of focus of beamforming is not infinite in that case but limited to a certain region beyond which reestimation o may be required at a new RIS-WTRU distance.

[0159] Equation (22) is valid for a single frequency but may be generalized to a multi-carrier system with K subcarriers in the form:where the subindex k denotes the k-th subcarrier of the corresponding vector or matrix element. The array response vector aRIS:DLdoes not generally have any frequency dependency unless phase shifters are replaced with, for example, true time delays, which is not common in RIS.

[0160] The beamforming operation in equation (23) yields a signal vector that best approaches an ideally pre-compensated channel between the TRP and the RIS. It requires knowledge of the TRP-RIS DL channel matrix GDL, the direction of arrival of the incident wavewith respect to the RIS orientation, the number of antennas of the RIS M, and the inter-antenna distances , according to equations (10)to (12). As the TRP-RIS link is semi-static, channel estimation may remain valid for a long time and hence not incur large overhead on average, despite comprising many matrix elements.

[0161] An exact solution may not be guaranteed as it depends on the backhaul channel properties, and the equality in equation (23) may be understood as the solution that best approaches the ideal one with the least possible power. In general, an ideal solution may be found when N equals M and the backhaul channel matrix is not ill-conditioned (i.e., the dispersion between the highest and smallest eigenvalues of the channel is not very large). If the channel is ill-conditioned, a solution may be found by having N values higher than M. Whether lacking an exact solution or because of implementation constraints, some residual multipath may remain after beamforming as a result. In some cases, a regularized version of the pseudo-inverse matrix may be used to deal with cases where GDLis ill-conditioned, for example, from the impact of noisy observations.

[0162] No attempt is done to pre-compensate the combined channel from the TRP to the WTRU. The reason is that the more dynamic RIS-WTRU channel may be better handled by beam management procedures, such as for example, based on a Transmission Configuration Indication (TCI) framework, without the complexity of having to estimate a highly varying channel for enhanced beamforming. In this way, the RIS-WTRU access link may be separately managed based on dynamic beam selection and subsequent update of the RIS beamforming vector as the user moves, while the more stable TRP-RIS link may undergo enhanced beamforming based on less frequent backhaul changes without impacting the instantaneous RIS beamforming vector.

[0163] Moreover, beamforming the combined channel may destroy the timing relationships between the DL signals received from TRPs (or their progressive phases in the frequency domain), as required in some applications such as for example, positioning based on RSTD measurements. As an example, if DL beamforming is applied to ideally pre-compensate the combined TRP-WTRU channel and remove multipath, the time of arrival (ToA) information needed by some positioning techniques may disappear from the received signals thus making RSTD measurements no longer viable. By only beamforming the backhaul link, RSTD measurements between signals received from different RISs may still be performed to derive the WTRU position.

[0164] Similar to the DL case, let us assume an UL complex modulated symbol transmitted by the WTRU and reflected by the RIS.

[0165] The combined WTRU-RIS-TRP UL channel matrixmay now be written aswhere is the UL channel matrix between the TRP and the RIS the UL channelmatrix between the RIS and the WTRU including any transmit beamforming or spatial precoding operationapplied by the WTRU, and wULe <ClxMis the UL beamforming vectors with complex elements^ L As in DL, we will use the beamforming vector comprising only phase shifts with unit amplitude, with When there is beam correspondence, the UL and DLbeamforming vectors may be equal.

[0166] The UL channel, assuming that only a direct path contribution is successfully reflected towards the TRP, may be written aswhere ( denotes the zenith and azimuth angles of arrival of the UL incident paths the array response vector of the RIS, and rl'ULis the delay of the UL incident path. Notice that, by definition,

[0167] After reflection, the UL path may be reflected by the beamforming vector and affected by an amplitude ar'ULand delay rr'UL, yielding a combined channel response,

[0168] Let us assume that a UL complex modulated symbol s e <C is reflected by the RIS and received by the TRP. The received signal y e <C at the TRP may be affected by a receive beamforming vecto such that

[0169] Combining equations (27) and (26),

[0170] The goal is to compensate the effect of the backhaul channel and yield a combined gain M after RIS reflection. Hence:

[0171] From the RIS operation we can also write, analogously to the DL case,where (dr'UL, (pr'UL) denotes the zenith and azimuth angles of departure of the UL reflected path. By combining (30) and (29), we can obtain the beamforming vector,t= aRIS,UL^gr,UL(pr,UL>)^GUL>)+y(31)

[0172] Equation (31) is the UL counterpart of eq. (22). In a multi-carrier system with K subcarriers,which is the UL counterpart of equation (23). It requires knowledge of the TRP-RIS UL channel matrix GUL, the angle of departure of the reflected wave with respect to the RIS orientation, the number of unit cells M, and the inter-antenna distanceyaccording to equations (10) to (12). As the TRP- RIS link is semi-static, channel estimation may remain valid for a long time period and hence not incur large overhead on average, despite comprising a large number of matrix elements.

[0173] The equality in equation (32) may be understood as the solution that best approaches the ideal one with the least possible power. Some residual multipath may remain after beamforming. In some cases, a regularized version of the pseudo-inverse matrix may be used to deal with cases where GULis ill-conditioned, for example from the impact of noisy observations.

[0174] In an embodiment of RIS-TRP exchange of the beams’ angular information methods are described to exchange the backhaul beam’s DL AoA / UL AoD between the TRP and a RIS, to protect the WTRU against eventual beam changes in the access induced by any changes in the backhaul beam because of, for example, unexpected obstruction or changes in the environment.

[0175] In this embodiment, a RIS is assumed to have established a connection with the TRP via the backhaul and control links for basic control information exchange, for example, authentication, capabilities, and configuration of the RIS reflective surface. In addition, it will be assumed that the RIS is capable to perform basic angle measurements on the signals received / transmitted in the backhaul, for example, AoD and AoA measurements, with the aid of a subset, or all, of the unit cells used for reflection, for example, those aimed totransmit and receive control link information, or separate from the RIS unit cells. These unit cells may be connected to one or several transceiver chains that can process digitized samples for angle estimation.

[0176] Once the RIS successfully camps in a cell, a suitable beam pair may be established in the backhaul, for example, by means of beam management (BM) techniques. In many cases (e.g. in 5G NR) the spatial characteristics of the DL and UL beams are not known by devices, and only suitable identifiers and quasicolocation relationships are needed, as based on, for example, TCI states in NR.

[0177] BM is also capable of further refining the beam overtime in response to changes in the environment, for example, by triggering a beam change, as shown in figure 13. When that happens, unless the RIS is made aware of the actual amount of beam deflection at the backhaul for, for example, updating the RIS beamforming vector, the WTRU may lose the connection and a beam failure recovery procedure may be triggered.

[0178] To avoid this, spatial information of the incident beam’s DL AoA, or the reflected beam’s UL AoD, may be shared between the TRP and RIS for fast re-calculation of the beamforming vector after any beam change in the backhaul. The RIS beamforming vectors wDLand wULmay be then updated based on the AoA / AoD and the RIS orientation. An example of this for the DL is shown in figure 14 considering that a certain value of wDLis used that is based on a difference X between the backhaul AoA and the access AoD. Any variation Y in the backhaul AoA (as triggered by BM) may be compensated with a corresponding change in the beamforming vector accordingly to a function of the angular variation (X - y), so that the access beam remains unchanged in the absence of WTRU mobility.

[0179] The actual DL AoA / UL AoD may be estimated by the RIS or reported by the TRP, according to at least one of the following possibilities. DL AoA / UL AoD estimation may be performed at the RIS upon request from the TRP. DL AoA / UL AoD measurements may be used by the RIS for updating the beamforming vectors. A DL AoA / UL AoD request may be made by the TRP via higher layer message, for example, RRC signaling, DCI signaling, or MAC control element (CE). The measured DL AoA / UL AoD may be represented as indexes to a codebook of pre-defined beam orientations known to the RIS and the TRP, or as quantized values of their respective azimuth and elevation angles. The value of DL AoA may be the same as the UL AoD if beam correspondence holds, otherwise they may be different. DL AoA / UL AoD measurements may be reported by the RIS via, for example, a physical uplink shared channel (PUSCH) or a physical uplink control channel (PUCCH). DL AoA / UL AoD measurements may be reported as part of, for example, the CSI reports sent to the TRP according to the measured quantities “DL AoA” and “UL AoD”, per as configuration via RRC signaling, for example, through CSI-ReportConfig IE. Additionally, the DL AoA / UL AoD may be requested by the RIS, for example, when it does not have angle estimation capabilities. The request may be made by the RIS via, for example, an RRC configuration message, uplink control indicator (UCI) signaling, or MAC CE. The TRP may quantize and transmit the DL AoA / UL AoD via a higher layer message, for example, an RRC configuration message, DCI signaling, or MAC CE.

[0180] The physical characteristics of the RIS may be exposed to the network as an initial capabilities message upon initial connection establishment, comprising, for example, at least one of the following. The message may comprise RIS orientation, expressed in one of the following forms: azimuth and elevation angles of a vector normal to its surface with respect to a known coordinate system, expressed in absolute angular units; a set of Euler angles, or a set of nautical angles (heading, elevation and bank), or a set of rotations around the principal axes (yaw, pitch and roll), with respect to a fixed coordinate system pointing in a given direction, such as for example, the north magnetic pole, or any other; and an index in a codebook of pre-defined beam orientations. The message may comprise a number of antennas in the H and V directions. The message may comprise inter-antenna spacing, for example, expressed as an absolute distance or relative to the wavelength in the H and V directions. This information may be needed by the TRP to derive, for example, the array response vector of equations (22), (23) and (31), (32).

[0181] In a first embodiment, a WTRU may detect beam blurring effects by measuring beam correlation effects over a configured set of resources. In a second embodiment, a WTRU may report beam correlation effects to the network. The first and second embodiment may be combined. In a third embodiment, a RIS may exchange the angles of arrival and departure of the backhaul beams with the network to improve beam resilience. In a fourth embodiment, a TRP may detect beam blurring effects at the WTRU and exchange the angles of arrival and departure of the backhaul beams with the RIS to improve beam resilience.

[0182] Considering the first and second embodiments, a WTRU may receive two or more reference signal configurations. The configured reference signals may be from a same or different reference signal sets. The configured reference signals may be periodic, aperiodic, or semi-persistent. A WTRU may be triggered to perform measurements on the configured resources. The measurements event may follow a transmission pattern of the configured reference signals. A WTRU may be configured with at least one measurement metric, for example, a (cross-beam) correlation, SNR, or rank. A WTRU may be configured with one or more threshold values.

[0183] A WTRU may perform a first and a second measurement based on the first and second configured reference signals, respectively. For example, a WTRU may perform separate channel estimations on the configured reference signals. Using the first and the second measurements, the WTRU may perform a third measurement. The third measurement may be in a form of one or more (cross-beam) correlation measurements performed based on measurements from the previous steps.

[0184] In an example, based on the performed measurements, the WTRU may report one or more of the measured metric, for example, a first SNR, a second SNR, a correlation metric, an / or rank. In another example, a WTRU may compare the third measurement against at least one or more of configured thresholds. Based on the comparison, a WTRU may report one or more of the following: a quantized version of the measured correlation metric, an indication corresponding to a pre-defined state of the gNB transmitted beam (e.g. whetherthe received beam is focused or blurred), together with an index representing the WTRU receiver spatial beam used for the measurements.

[0185] In an example, a WTRU may report or request for a grant or resources to report, based on one or more of the following: if it detects a change in the state of the gNB transmitted beam; if it detects a significant physical displacement based on its positioning information (e.g., when a movement larger than a configured threshold is detected); if it detects a significant change in signal strength (e.g. when a signal strength drop or boost larger than a configured threshold is detected).

[0186] In an embodiment, beam correlation measurements may be performed to detect and report the appearance of beam blurring effects.

[0187] A WTRU may send a capabilities information message to the network. The capabilities information message may be sent, for example, upon initial connection establishment. The capabilities information message may include at least one of the following: WTRU support of beam correlation measurement and reporting, (e.g. in the form of a bit indicator); and a maximum number of one or more of the measurement resource sets K, symbols N, and resources per resource set L, that the WTRU supports.

[0188] The configuration for receiving suitable channels or signals (e.g. reference signals) aimed to perform beam correlation measurements may be based on one or more of the following.

[0189] The WTRU may be configured to perform (cross-beam) correlation measurements via RRC signaling, for example, through an indication in, for example, a CSI-ReportConfig information element (IE). An indication to measure beam correlation may be provided via configuration of the CSI reporting parameters, for example, a reporting quantity of the type “BeamCorrelation”.

[0190] The WTRU may be configured via RRC signaling to measure beam correlation, for example, with the help of measurement resources following a certain time-frequency configuration. Measurement resources may be grouped into one or more measurement resource sets, specified by at least one of the following parameters: number of measurement resource sets K starting RE per resource set; number of RBs per resource set; symbol and slot number per resource set; comb size and comb offset per resource set. Measurement resources may be periodic, aperiodic or semi-persistent. Measurement resource sets may be repeated a number of times N with a configured gap between repetitions (e.g., expressed as a number of symbols or slots) to average measurements.

[0191] The WTRU may be configured with threshold values for triggering beam correlation measurements, including at least one of the following: threshold value RSRPmin for the minimum RSRP, which may be expressed as, for example, an absolute value in dBm or an index to a pre-defined table of RSRP values; threshold value BLERmax for the maximum PDCCH hypothetical BLER, which may be expressed as, for example, an integer percentage or an index to a pre-defined table of BLER values; threshold for detection of a significant WTRU movement; threshold for detection of a significant drop or boost of signal strength.

[0192] The WTRU may be configured, receive an indication, or determine to measure beam correlation on one or more measurement resources comprising several measurement resource sets according to the configured reference signal patterns.

[0193] In an example, the WTRU may receive a network request and a set of periodic, semi-persistent (activated and deactivated via, for example, a MAC CE), or triggered aperiodic (signaled, for example, via a DCI) RS to initiate measurements. The one or more DL signals may be at least one of the following: CSI-RS (e.g., for one or more of tracking, BM, and CSI) or SSB.

[0194] CSI-RS signals have the advantage that they may have finer spatial granularity to capture near-field effects compared to SSB, but also involve additional resource consumption.

[0195] In an example, based on the configuration, the WTRU may determine whether to start beam correlation measurements based on triggering conditions and, if satisfied, may send a request to the network to transmit a RS for beam correlation measurement, for example, CSI-RS or SSB, and may perform measurements.

[0196] Figure 15 shows an example method 1500 for WTRU measurement of beam correlation. The WTRU may send a capabilities information message to the network 1505. The capabilities information message may be sent, for example, upon initial connection establishment. The capabilities information message may indicate that the WTRU supports beam correlation measurements and may indicate measurement information, for example, a maximum number of resources, a maximum number of symbols, and / or a maximum number of resource sets for measurement. The network may be a network entity, for example, a gNB.

[0197] The WTRU may be configured (e.g. receive a beam correlation measurements configuration information message) to perform beam correlation measurements 1510. The WTRU may receive the beam correlation measurements configuration information from the gNB. The WTRU may receive the beam correlation measurements configuration information via, for example, RRC signaling The WTRU may receive an indication in the a CSI-ReportConfig IE. The WTRU may be configured with at least one of the following: (a) two or more measurement resources, grouped into a same or different measurement resource sets, or reference signal sets, each specified by at least one of starting RE, number of RBs, symbol and slot number, comb size, or comb offset; (b) number of repetitions N to average measurements with a configured gap between repetitions given in, for example, number of symbols or slots; and (c) one or more threshold values for triggering beam correlation measurements, for example, a threshold RSRPmin for the minimum RSRP value, a threshold BLERmax for the maximum PDCCH hypothetical BLER value, a threshold for detection of a significant WTRU movement, or a threshold for detection of a significant change in signal strength. Configured measurement resources may be periodic, aperiodic or semi-persistent.

[0198] The WTRU may determine whether to start beam correlation measurements 1515. The WTRU may determine whether to start beam correlation measurements based on at least one of the following. The WTRU may determine whether to start beam correlation measurements based on detection of a transmission patternof the configured reference signals for beam correlation measurements (e.g., CSI-RS or SSB), for example, via blind detection of an expected transmission pattern of the reference signals in time and frequency. The WTRU may determine whether to start beam correlation measurements based on a network request. The network request may be received for example, via RRC signaling, a DCI (WTRU-specific and / or group DCI), or a MAC CE. The network request may be received from the gNB. The WTRU may detect reference signals for beam correlation measurements, for example, CSI-RS or SSB, at the same time instant or after a specified or pre-determined number of symbols, or slots, or time duration. The WTRU may determine whether to start beam correlation measurements based on fulfilment of one or more triggering conditions for beam correlation measurements. A triggering condition may be an RSRP below an RSRP minimum (RSRPmin), and / or a PDCCH hypothetical BLER above a BLER maximum (BLERmax), as measured from any a-priori known reference signal, for example, a CSI-RS, a DM-RS, or an SSB. A triggering condition may be a detection of a change in the state of the gNB transmitted beam (e.g., blurred or focused). A triggering condition may be a detection of a significant physical displacement based on its positioning information, for example, when a movement larger than a configured threshold value is detected. A triggering condition may be a detection of a significant change in signal strength, for example, when a signal strength drop or boost larger than a configured threshold value is detected. If the triggering conditions are satisfied, the WTRU may send a request (e.g. request message) to the network for transmitting a measurement RS, for beam correlation measurements (e.g. CSI-RS or SSB). The WTRU may send the request for example, via UCI signaling or a MAC CE. The WTRU may receive a confirmation (e.g. confirmation message) from the network. The confirmation may be received via for example RRC signaling, a DCI, or a MAC CE. If the WTRU receives a confirmation from the network, the WTRU may detect a measurement RS at that time instant or after a specified or pre-determined number of symbols, or slots, or time duration.

[0199] In response to determining to start beam correlation measurements, the WTRU may detect measurement resources (e.g. RS) 1520. The WTRU may detect the measurement RS at that time instant or after a specified or pre-determined number of symbols, or slots, or time duration.

[0200] The WTRU may obtain the channel transfer functions at the specified resources 1525. The WTRU may obtain the channel transfer functions at the specified resources by, for example, removing the known amplitudes and phases at the measurement resources.

[0201] The WTRU may perform (e.g. calculate or determine) beam correlation measurements 1530. The WTRU may perform beam correlation measurements on the reference signals based on the received beam correlation measurements configuration information message. The reference signals may be grouped in the resources sets for beam correlation measurements. The WTRU may perform beam correlation measurements, for example, by computing or determining the value of the beam correlation as given by equation (9), SNR, RSRP, or rank. The beam correlation measurements may comprise a sum of products of two channel transfer functions of the reference signals. One of the channel transfer functions in each of the products of two channeltransfer functions may be first conjugated by reversing the sign of its imaginary component prior to performing beam correlation measurements.

[0202] The WTRU may send a report comprising beam correlation measurements 1535. The report may comprise or include one or more of the following: a beam correlation width lx given by a beam index difference for a X% correlation relative to a maximum; K correlation values for all possible beam index differences, with or without compression by a specified compression algorithm; a quantized version of the measured correlation metrics; an indication corresponding to a pre-defined state of a gNB transmitted beam, for example, whether the received beam is focused or blurred; a SNR, a rank and / or RSRP values, for example, averaged across the measurement resource sets for beam correlation; and an index representing the WTRU receiver spatial beam used for the measurements. In an example, in a system comprising up to K beam pairs, wherein each beam pair represents a couple of beams characterized by a beam index difference given by the absolute difference between the indexes of the beams, the beam correlation function yields up to K different correlation values. The K values may then be reported in compressed or uncompressed form, or a beam correlation width lx may be reported equal to the beam index difference below which the correlation function is above X%.

[0203] The WTRU may stop (e.g. determine to stop) beam correlation measurements and / or reporting 1540. The WTRU may stop beam correlation measurements on a condition that at least one of the following is fulfilled or satisfied. Otherwise the WTRU may repeat obtaining channel transfer functions 1525 and performing beam correlation measurements 1530. The WTRU may stop measurements if reference signals for beam correlation measurements are no longer detected. The WTRU may stop measurements if the WTRU was requested by the network to start measurements and reports are of aperiodic type, or of semi-persistent type and are de-activated by, for example, a MAC CE. The WTRU may stop measurements if the WTRU receives a request to stop measurements, via, for example, RRC signaling, a DCI, or a MAC CE. The WTRU may stop measurements if the triggering conditions are no longer satisfied.

[0204] Configuration for reporting of beam correlation measurements may be based on one or more of the following: value X% for computation of the beam correlation width lx, specified as an integer less than 100, or an index to a pre-defined table of values; periodicity in the case of semi-persistent or periodic reports, given, for example, in a number of symbols, slots, or time duration; one or more threshold values for triggering beam correlation reporting, for example, a threshold RSRPmin for the minimum RSRP value, a threshold BLERmax for the maximum PDCCH hypothetical BLER value, a threshold for detection of a significant WTRU movement, a threshold for detection of a significant change in signal strength, and / or a threshold for the maximum beam correlation width value above which reports may be triggered by the WTRU.

[0205] A WTRU may be configured, indicated, or determined to report beam correlation as obtained or determined from the measurement resource sets. The WTRU may perform beam correlation reporting, as shown in figure 16, after exchanging WTRU capabilities information with the network and receiving aconfiguration on the beam correlation measurements and reports, including triggering conditions for measurements.

[0206] Figure 16 shows an example method 1600 for WTRU reporting of beam correlation measurements aimed to inform the network about the presence of beam blurring effects at the WTRU side.

[0207] The WTRU may send a capabilities information message to the network 1605. The capabilities information message may be sent, for example, upon initial connection establishment. The capabilities information message may indicate that the WTRU supports beam correlation reports and a maximum number of, for example, resources, symbols, and / or resource sets for measurement. The network may be a network entity, for example, a gNB.

[0208] The WTRU may be configured (e.g. receive a beam correlation measurements configuration information message) to perform beam correlation measurements 1610. The WTRU may receive the beam correlation measurements configuration information message from the gNB. The WTRU may receive the beam correlation measurements configuration information message via, for example, RRC signaling. The WTRU may receive an indication in a CSI-ReportConfig IE. The WTRU may be configured with at least one of: the two or more measurement resources, number of repetitions N to average measurements, and triggering conditions for measurements (e.g., RSRP below a threshold value, PDCCH hypothetical BLER above a threshold value, physical displacement above a threshold value, or change in signal strength above a threshold value).

[0209] The WTRU may be configured (e.g. receive a beam correlation reporting configuration information message) to report beam correlation information 1615. A report may be periodic, aperiodic or semi-persistent. The configuration may include at least one of: Value of X%, e.g., an integer below 100 or an index to a predefined table of values; Periodicity of semi-persistent or periodic reports, given, e.g., in a number of symbols, slots, or time duration; one or more threshold values for triggering beam correlation reporting, e.g., a threshold RSRPmin for the minimum RSRP value, a threshold BLERmax for the maximum PDCCH hypothetical BLER value, a threshold value for detection of a significant WTRU movement, a threshold value for detection of a significant change in signal strength, and / or a threshold value for the maximum beam correlation value.

[0210] The beam correlation measurements configuration information message and the beam correlation reporting configuration information message may be a same message or a different message.

[0211] The WTRU may perform beam correlation measurements 1620. The WTRU may perform beam correlation measurements on the reference signals based on the received beam correlation measurements configuration information message. The reference signals may be grouped in the resources sets for beam correlation measurements. For example, the WTRU may perform beam correlation measurements based on the beam correlation function as given by equation (9), RSRP, SNR, or rank The WTRU may send or request to send, to the gNB, beam correlation measurements as part of a report based on the triggering conditions for reporting. The beam correlation measurements may be on the configured reference signals which may be grouped in the resources sets for beam correlation measurements. The beam correlation measurements maycomprise a sum of products of two channel transfer functions of the reference signals. One of the channel transfer functions in each of the products of two channel transfer functions may be first conjugated by reversing the sign of its imaginary component prior to performing beam correlation measurements.

[0212] Triggering conditions for reporting may include: RSRP below RSRPmin, and / or PDCCH hypothetical BLER above BLERmax, as measured from any a-priori known reference signal, for example, CSI-RS, DM-RS, or SSB; Detection of a change in the state of the gNB transmitted beam; Detection of a significant physical displacement based on its positioning information, for example, when a movement larger than a configured threshold value is detected; Detection of a significant change in signal strength, for example, when a signal strength drop, or boost, larger than a configured threshold value is detected; and Detection of a value of a beam correlation metric, for example, a beam correlation function as in equation (9), larger than a configured threshold value.

[0213] Beam correlation measurements may be included as part of a report containing channel state information, for example, a CSI report, or in a separate report.

[0214] The WTRU may send, or request to send, the beam correlations measurement report 1625. The WTRU may send the report via, for example, a PUCCH or a PUSCH channel in a periodic, semi-persistent or aperiodic form according to the configuration. The report may comprise or include one or more of the following: a beam correlation width lx given by a beam index difference for a X% correlation relative to a maximum; K correlation values for all possible beam index differences, with or without compression by a specified compression algorithm; a quantized version of the measured correlation metrics; an indication corresponding to a pre-defined state of a gNB transmitted beam, for example, whether the received beam is focused or blurred; a SNR, a rank and / or RSRP values, for example, averaged across the measurement resource sets for beam correlation; and an index representing the WTRU receiver spatial beam used for the measurements. In an example, in a system comprising up to K beam pairs, wherein each beam pair represents a couple of beams characterized by a beam index difference given by the absolute difference between the indexes of the beams, the beam correlation function yields up to K different correlation values. The K values may then be reported in compressed or uncompressed form, or a beam correlation width lx may be reported equal to the beam index difference below which the correlation function is above X%.

[0215] The WTRU may stop (e.g. determine to stop) beam correlation measurements and / or reporting 1630. The WTRU may stop reporting if at least one of the following is fulfilled or satisfied, otherwise the WTRU may repeat the above procedures (e.g. perform beam correlation measurements and send a report). The WTRU may stop reporting if reference signals for beam correlation measurements are no longer detected. If the WTRU was requested by the network to start beam correlation measurements, the WTRU may stop reporting if reports are of an aperiodic type or if reports are of a semi-persistent type and are de-activated by the network via, for example, a MAC CE. The WTRU may stop reporting if the WTRU receives a network request to stop reporting. , The WTRU may receive the network request to stop reporting via, for example, RRCsignaling, a DCI, ora MAC CE. TheWTRU may stop reporting if triggering conditions for reporting are no longer satisfied.

[0216] FIG. 17 shows an example method 1700 for WTRU measurements of beam correlation and reporting of beam correlation measurements.

[0217] The WTRU may send a capabilities information message to the network 1705. The capabilities information message may be sent, for example, upon initial connection establishment. The capabilities information message may indicate that the WTRU supports beam correlation measurements and may indicate measurement information, for example, a maximum number of resources, a maximum number of symbols, and / or a maximum number of resource sets for measurement. The network may be a network entity, for example, a gNB.

[0218] The WTRU may be configured (e.g. receive a beam correlation measurements configuration information message) to perform beam correlation measurements 1710. The WTRU may receive the beam correlation measurements configuration information from the gNB. The WTRU may receive the beam correlation measurements configuration information via, for example, RRC signaling The WTRU may receive an indication in the a CSI-ReportConfig IE. The WTRU may be configured with at least one of the following: (a) two or more measurement resources, grouped into a same or different measurement resource sets, or reference signal sets, each specified by at least one of starting RE, number of RBs, symbol and slot number, comb size, or comb offset; (b) a number of repetitions N to average measurements with a configured gap between repetitions given in, for example, number of symbols or slots; and (c) one or more threshold values for triggering beam correlation measurements, for example, a threshold RSRPmin for the minimum RSRP value, a threshold BLERmax for the maximum PDCCH hypothetical BLER value, a threshold for detection of a significant WTRU movement, or a threshold for detection of a significant change in signal strength. Configured measurement resources may be periodic, aperiodic or semi-persistent. Each resource set may comprise reference signals that correspond to a beam.

[0219] The WTRU may be configured (e.g. receive a beam correlation reporting configuration information message) to report beam correlation information 1715. A report may be periodic, aperiodic or semi-persistent. The configuration for reporting beam correlation measurements may include at least one of: Value of X% for computation of the beam correlation width lx, e.g., an integer below 100 or an index to a pre-defined table of values; Periodicity of semi-persistent or periodic reports, given, e.g., in a number of symbols, slots, or time duration; one or more threshold values for triggering beam correlation reporting, e.g., a threshold RSRPmin for the minimum RSRP value, a threshold BLERmax for the maximum PDCCH hypothetical BLER value, a threshold value for detection of a significant WTRU movement, a threshold value for detection of a significant change in signal strength, and / or a threshold value for the maximum beam correlation width value above which reports may be triggered by the WTRU.

[0220] The beam correlation measurements configuration information message and the beam correlation reporting configuration information message may be a same message or a different message.

[0221] The WTRU may determine whether to start beam correlation measurements 1720. The WTRU may determine whether to start beam correlation measurements based on at least one of the following. The WTRU may determine whether to start beam correlation measurements based on detection of a transmission pattern of the configured reference signals for beam correlation measurements (e.g., CSI-RS or SSB), for example, via blind detection of an expected transmission pattern of the reference signals in time and frequency. The WTRU may determine whether to start beam correlation measurements based on a network request. The network request may be received for example, via RRC signaling, a DCI (WTRU-specific and / or group DCI), or a MAC CE. The network request may be received from the gNB. The WTRU may detect reference signals for beam correlation measurements, for example, CSI-RS or SSB, at the same time instant or after a specified or pre-determined number of symbols, or slots, or time duration. The WTRU may determine whether to start beam correlation measurements based on fulfilment of one or more triggering conditions for beam correlation measurements. A triggering condition may be an RSRP below an RSRP minimum (RSRPmin), and / or a PDCCH hypothetical BLER above a BLER maximum (BLERmax), as measured from any a-priori known reference signal, for example, a CSI-RS, a DM-RS, or an SSB. A triggering condition may be a detection of a change in the state of the gNB transmitted beam (e.g., blurred or focused). A triggering condition may be a detection of a significant physical displacement based on its positioning information, for example, when a movement larger than a configured threshold value is detected. A triggering condition may be a detection of a significant change in signal strength, for example, when a signal strength drop or boost larger than a configured threshold value is detected. If the triggering conditions are satisfied, the WTRU may send a request (e.g. request message) to the network for transmitting a measurement RS, for beam correlation measurements (e.g. CSI-RS or SSB). The WTRU may send the request for example, via UCI signaling or a MAC CE. The WTRU may receive a confirmation (e.g. confirmation message) from the network. The confirmation may be received via for example RRC signaling, a DCI, or a MAC CE. If the WTRU receives a confirmation from the network, the WTRU may detect a measurement RS at that time instant or after a specified or pre-determined number of symbols, or slots, or time duration.

[0222] In response to determining to start beam correlation measurements, the WTRU may detect measurement resources (e.g. RS) 1725. The WTRU may detect the measurement RS at that time instant or after a specified or pre-determined number of symbols, or slots, or time duration.

[0223] The WTRU may obtain the channel transfer functions at the specified resources (i.e. the received beam correlation measurements configuration information )1730. The WTRU may obtain the channel transfer functions at the specified resources by, for example, removing the known amplitudes and phases at the measurement resources.

[0224] The WTRU may perform (e.g. calculate or determine) beam correlation measurements 1735. The WTRU may perform beam correlation measurements on the reference signals based on the received beam correlation measurements configuration information message. The reference signals may be grouped in the resources sets for beam correlation measurements. The WTRU may perform beam correlation measurements, for example, by computing or determining the value of the beam correlation as given by equation (9), SNR, RSRP, or rank. The beam correlation measurements may be on the configured reference signals which may be grouped in the resources sets for beam correlation measurements. The beam correlation measurements may comprise a sum of products of two channel transfer functions of the reference signals. One of the channel transfer functions in each of the products of two channel transfer functions may be first conjugated by reversing the sign of its imaginary component prior to performing beam correlation measurements.

[0225] The WTRU may send a report comprising beam correlation measurements 1740. The WTRU may send or request to send, to the gNB, beam correlation measurements as part of a report based on the triggering conditions for reporting. The WTRU may send the report via, for example, a PUCCH or a PUSCH channel in a periodic, semi-persistent or aperiodic form according to the beam correlation reporting configuration information message.

[0226] Triggering conditions for reporting may include: RSRP below RSRPmin, and / or PDCCH hypothetical BLER above BLERmax, as measured from any a-priori known reference signal, for example, CSI-RS, DM-RS, or SSB; Detection of a change in the state of the gNB transmitted beam; Detection of a significant physical displacement based on its positioning information, for example, when a movement larger than a configured threshold value is detected; Detection of a significant change in signal strength, for example, when a signal strength drop, or boost, larger than a configured threshold value is detected; and Detection of a value of a beam correlation metric, for example, a beam correlation function as in equation (9), larger than a configured threshold value.

[0227] The report may comprise or include one or more of the following: a beam correlation width / xgiven by a beam index difference for a X% correlation relative to a maximum; K correlation values for all possible beam index differences, with or without compression by a specified compression algorithm; a quantized version of the measured correlation metrics; an indication corresponding to a pre-defined state of a gNB transmitted beam, for example, whether the received beam is focused or blurred; a SNR, a rank and / or RSRP values, for example, averaged across the measurement resource sets for beam correlation; and an index representing the WTRU receiver spatial beam used for the measurements. In an example, in a system comprising up to K beam pairs, wherein each beam pair represents a couple of beams characterized by a beam index difference given by the absolute difference between the indexes of the beams, the beam correlation function yields up to K different correlation values. The K values may then be reported in compressed or uncompressed form, or a beam correlation width lx may be reported equal to the beam index difference below which the correlation function is above X%.

[0228] Beam correlation measurements may be included as part of a report containing channel state information, for example, a CSI report, or in a separate report.

[0229] The WTRU may stop (e.g. determine to stop) beam correlation measurements and / or reporting 1745. The WTRU may stop beam correlation measurements on a condition that at least one of the following is fulfilled or satisfied. Otherwise the WTRU may repeat obtaining channel transfer functions 1730 and performing beam correlation measurements 1735. The WTRU may stop measurements if reference signals for beam correlation measurements are no longer detected. If the WTRU was requested by the network to start beam correlation measurements, the WTRU may stop reporting if reports are of an aperiodic type or if reports are of a semi-persistent type and are de-activated by the network via, for example, a MAC CE. The WTRU may stop measurements if the WTRU receives a request to stop measurements or reporting. The WTRU may receive the request to stop measurements or reporting via, for example, RRC signaling, a DCI, or a MAC CE. The WTRU may stop measurements if the triggering conditions are no longer satisfied.

[0230] Enhanced RIS management of backhaul beams includes methods and procedures to improve beam management by the RIS based on exchanging the angles of arrival (AoA) and departure (AoD) of the backhaul beams with the network for higher beam resilience.

[0231] A RIS capable of performing backhaul measurements of DL AoA / UL AoD may be camped in a cell served by a TRP.

[0232] The RIS may send a capabilities information message to the network via a control link, for example, through RRC signaling upon initial connection establishment. The capabilities information message may comprise the RIS physical characteristics, the RIS support of backhaul measurements of DL AoA / UL AoD, and / or an indication of beam correspondence.

[0233] RIS physical characteristics may comprise RIS orientation, number of antennas, and / or interantenna distance. RIS orientation may be given at least in one of the following possibilities: azimuth and elevation angles of a vector normal to the RIS surface with respect to a known coordinate system, expressed in absolute angular units; a set of Euler angles, or nautical angles (heading, elevation and bank), or rotations around the principal axes (yaw, pitch and roll), with respect to a fixed coordinate system pointing in a given direction, for example, the north magnetic pole, or any other; and an index in a codebook of pre-defined beam orientations. A number of antennas may be given in the H and V directions. Inter-antenna distances in the H and V directions may be expressed as, for example, absolute distances or relative to the wavelength. Wavelength A may be obtained, for example, by means of the formula A=c / f, where c is the speed of light, and f is the carrier frequency or the central frequency of the operating band that the RIS is optimized for. Support of backhaul measurements of DL AoA / UL AoD by the RIS may be indicated in, for example, a bit field for the UL and the DL. An indication of whether beam correspondence holds for the RIS may indicate whether the physical characteristics of the UL beams can be derived from the DL beams and vice versa.

[0234] RIS capabilities may be reported to the TRP, for example, via a PUCCH or a PUSCH channel.

[0235] Measurements may be performed by a subset, or all, of the RIS unit cells having reception capabilities, or with the aid of a specific RIS receiving structure. If beam correspondence holds, measurements performed on the DL beams may also apply to the UL beams, otherwise separate measurements may be required for DL AoA and UL AoD.

[0236] Figure 18 shows an example method 1800 for enhanced RIS management of the RIS backhaul beam by a RIS capable of performing backhaul beam angular measurements. The RIS is capable of performing backhaul angular measurements that is forwarding signals between a TRP and a WTRU or set of WTRUs. The RIS may perform enhanced beam management at the backhaul link aimed to exchange the beams’ angles of arrival and departure with the network.

[0237] The RIS may send a capabilities information message to the network 1805. The capabilities information message may be sent, for example, via RRC signaling upon initial RIS connection establishment. The capabilities information message may indicate one or more of the following. The RIS may indicate RIS physical characteristics, comprising at least one of: RIS orientation (e.g., azimuth and elevation of a vector normal to the RIS surface, a set of angles, and / or an index in a codebook of pre-defined beam orientations); a number of antennas in the H and V directions; inter-antenna distances in the H and V directions, e.g., expressed as absolute distances, or relative to the wavelength at the carrier frequency or the central frequency of the operating band that the RIS is optimized for. The RIS may indicate support of backhaul angular measurements of the beams’ angles of arrival and departure, for example, as a bit field for the UL AoD and the DL AoA. Measurements may be performed on any RS sharing the same angular characteristics as the data channels, for example, CSI-RS, SSB, or DM-RS. The RIS may send an indication of whether RIS beam correspondence holds (i.e. whether the physical characteristics of the UL beams can be derived from the DL beams and vice versa).

[0238] The RIS may select the most suitable beams for the RIS backhaul in the UL and the DL 1810. For example, the RIS may select the most suitable beams for the RIS backhaul by beam management techniques selecting the beam with highest RSRP.

[0239] The RIS may measure the backhaul DL AoA / UL AoD and a quality metric Q1 1815. Measurements may be performed on any RS sharing the same angular characteristics as the data channels, for example, CSI- RS, SSB, or DM-RS. Q1 may be expressed as, for example, a signal to noise ratio, or a mean squared error of the DL AoA / UL AoD measurements.

[0240] The RIS may make a determination of a comparison between a quality metric (Q1 ) and a threshold value (T1) 1820. The RIS may request a TRP backhaul DL AoA / UL AoD to the network 1825 based on the determination of the comparison. The WTRU may determine whether Q1 is below or above threshold value T 1 , for example, after expiration of a timer, an elapsed time period, or a counter reaching a given value, Q1 may be an SNR or a mean squared error of detection. An insufficient quality may be expressed as Q1 < T1 where Q1 is an SNR and T1 is a minimum signal to noise ratio value. An insufficient quality may be expressed as Q1> T 1 where Q1 is mean squared error of detection and T1 is a maximum mean squared error value. Therefore, depending on an implementation or application, the quality metric may be triggered by a value above or below a threshold value T 1. The requests may be sent via, for example, UCI or a MAC CE. The request may be sent upon initial registration, to gather information about all the TRP beams, or incrementally during the connection, to inquire for a specific beam or set of beams. The response may be received, for example, via RRC signaling, a DCI, or a MAC CE. Angles may be expressed, for example, as azimuth and elevation angles of a vector normal to the TRP surface, Euler angles, nautical angles, a set of rotations, and / or an index in a codebook of pre-defined beam orientations.

[0241] If the TRP requests the backhaul beams’ AoA and AoD 1830 (e.g. if the RIS receives a request from the TRP), the RIS may report the measured DL AoA / UL AoD and Q1 1835. The TRP request may be received in a higher layer configuration message, for example, RRC signaling, DCI signaling, or a MAC CE. The measured DL AoA / UL AoD and Q1 may be reported via a data channel (e.g. PUSCH) ora control channel (e.g. PUCCH).

[0242] The RIS may update the beamforming vectors wDLand wULfrom the measured, or received, backhaul beams’ angular characteristics and the RIS orientation.

[0243] Figure 19 shows an example method 1900 for enhanced RIS management of the RIS backhaul beam by an RIS not capable of performing DL AoA / UL AoD measurements. The RIS is assumed to camp in a cell.

[0244] The RIS may send a capabilities information message to the network 1905. The RIS may send a capabilities information message on the control link, for example, through RRC signaling upon initial connection establishment. The capabilities information message may comprise one or more of the RIS physical characteristics (e.g., RIS orientation, number of antennas, or inter-antenna distances), the lack of support of RIS backhaul measurements of DL AoA / UL AoD, an indication of beam correspondence, and whether beam correspondence holds. RIS capabilities may be reported to the TRP, for example, via a PUCCH or PUSCH channel.

[0245] The RIS may perform enhanced beam management at the backhaul link, that does not involve AoA / AoD measurement or reporting.

[0246] The RIS may select the beam pair (UL / DL) (e.g. most suitable) that best serves the backhaul, for example, via beam management 1910.

[0247] If there is a change of the backhaul beam 1915, the RIS may request TRP backhaul DL AoA / UL AoD from the network 1920. The request may be sent via, for example, UCI or a MAC CE. The request may be sent upon initial registration, to gather information about all the TRP beams, or incrementally throughout the connection, to inquire for a specific beam or set of beams; The response may be received, for example, via RRC signaling, a DCI, or a MAC CE. Angles may be expressed, for example, as azimuth and elevation anglesof a vector normal to the TRP surface, Euler angles, nautical angles, a set of rotations, and / or an index in a codebook of pre-defined beam orientations.

[0248] The RIS may update the beamforming vectors wDLand wULfrom the backhaul beams’ angular characteristics received by the TRP and the RIS orientation.

[0249] In an embodiment, enhanced TRP management of RIS backhaul beams includes method and procedures to improve beam management by the TRP based on detection of beam blurring effects and exchanging the angles of arrival and departure of the backhaul beams with the RIS for better link resilience.

[0250] A TRP serving one or multiple WTRUs is aided by one or multiple RISs to reinforce the connection.

[0251] The TRP may receive a capabilities information message from the RIS via a control link, for example, through RRC signaling upon initial connection establishment, comprising, for example, the RIS physical characteristics, the support of RIS measurements on the backhaul beam’s DL AoA / UL AoD, and an indication on beam correspondence. RIS capabilities may be received by the TRP via, for example, PUCCH or PUSCH channels.

[0252] Figure 20 shows an example method 2000 for enhanced TRP management of the RIS backhaul beam. The TRP may perform the method for enhanced beam management at the backhaul link based on detection of beam blurring effects and exchange of angles of arrival and departure with the RIS.

[0253] The TRP may receive a capabilities information message from the RIS 2005. The capabilities information message may be received, for example, via RRC signaling upon initial RIS connection establishment. The capabilities information message may be received via a control link. The capabilities information message may indicate one or more of the RIS physical characteristics (e.g., RIS orientation, number of antennas, and / or inter-antenna distances), support of backhaul angular measurements, and whether beam correspondence holds. The TRP may receive the capabilities information message via, for example, a PUCCH or a PUSCH.

[0254] The TRP may select the beam between the TRP and RIS that best serves (e.g. most suitable for) the RIS backhaul, for example, via beam management techniques 2010.

[0255] If the TRP receives a request from the RIS to provide a TRP backhaul DL AoA / UL AoD indication 2015, the TRP may send the TRP backhaul beams’ DL AoA / UL AoD to the RIS 2020. The TRP may send the TRP backhaul beams’ DL AoA / UL AoD via, for example, RRC signaling, a DCI, or a MAC CE. The request may be received via, for example, RRC signaling, UCI, or a MAC CE. The TRP backhaul DL AoA / UL AoD may be expressed, for example, as azimuth and elevation angles of a vector normal to its surface, or as Euler angles, nautical angles, a set of rotations, or an index in a codebook of pre-defined beam orientations

[0256] The TRP may configure the WTRU to measure and report beam correlation on specified measurement resources for beam correlation, either upon network request or upon fulfilment of triggering conditions 2025. Measurement resources may be grouped into several measurement resource sets eachspecified by, for example, its starting RE, number of RBs, slot and symbol number, comb size, and / or comb offset. A network request may be sent to the WTRU to explicitly start measurements via, for example, RRC signaling, a DCI (WTRU-specific and / or group DCI), or a MAC CE. Triggering conditions may be configured for the WTRU to start measurements based on, for example, RSRP below a threshold or PDCCH hypothetical BLER above a threshold.

[0257] If the TRP receives a report from the WTRU comprising beam correlation measurements 2030, if beam correlation measurements exceed a given beam correlation threshold value 2035, the TRP may send a request to the RIS to report backhaul DL AoA / UL AoD measurements 2040. The TRP may send the request to the RIS via, for example, RRC configuration information, DCI signaling, or a MAC CE. A beam correlation threshold may be, for example, a maximum beam correlation width, or maximum values of the correlation of some, or all, of the beam index differences. The TRP may receive RIS backhaul DL AoA / UL AoD measurements 2045. The TRP may receive RIS backhaul AoA or AoD via, for example, a PUCCH or a PUSCH channel.

[0258] The TRP may leverage the RIS backhaul DL AoA / UL AoD to mitigate the detected beam blurring effects (caused by, for example, near-field or beam obstruction phenomena), by methods of, for example, enhanced beamforming on the backhaul that may improve the beam focusing capabilities of the RIS.

[0259] Similarly, the TRP may aid the RIS in updating its beamforming vectors by sharing a TRP backhaul DL AoA / UL AoD indication if requested by the RIS.

[0260] FIG. 21 shows an example method 2100 for WTRU measurements of beam correlation and reporting of beam correlation measurements.

[0261] The WTRU may be configured (e.g. receive a beam correlation measurements configuration information message) to perform beam correlation measurements 2105. The beam correlation measurements configuration information message may comprise resource sets for beam correlation measurements. Each resource set may comprise reference signals that correspond to a beam. The WTRU may receive the beam correlation measurements configuration information from the gNB. The WTRU may receive the beam correlation measurements configuration information via, for example, RRC signaling The WTRU may receive an indication in the a CSI-ReportConfig IE. The WTRU may be configured with at least one of the following: (a) two or more measurement resources, grouped into a same or different measurement resource sets, or reference signal sets, each specified by at least one of starting RE, number of RBs, symbol and slot number, comb size, or comb offset; (b) a number of repetitions N to average measurements with a configured gap between repetitions given in, for example, number of symbols or slots; and (c) one or more threshold values for triggering beam correlation measurements, for example, a threshold RSRPmin for the minimum RSRP value, a threshold BLERmax for the maximum PDCCH hypothetical BLER value, a threshold for detection of a significant WTRU movement, or a threshold for detection of a significant change in signal strength. Configuredmeasurement resources may be periodic, aperiodic or semi-persistent. Each resource set may comprise reference signals that correspond to a beam.

[0262] The WTRU may receive the beam correlation measurements configuration information in response to sending a capabilities information message to the gNB. The capabilities information message may be sent, for example, upon initial connection establishment. The capabilities information message may indicate that the WTRU supports beam correlation measurements and may indicate measurement information, for example, a maximum number of resources, a maximum number of symbols, and / or a maximum number of resource sets for measurement.

[0263] The WTRU may be configured (e.g. receive a beam correlation reporting configuration information message) to report beam correlation information 2110. A report may be periodic, aperiodic or semi-persistent. The configuration for reporting beam correlation measurements may include at least one of: Value of X% for computation of the beam correlation width lx, e.g., an integer below 100 or an index to a pre-defined table of values; Periodicity of semi-persistent or periodic reports, given, e.g., in a number of symbols, slots, or time duration; one or more threshold values for triggering beam correlation reporting, e.g., a threshold RSRPmin for the minimum RSRP value, a threshold BLERmax for the maximum PDCCH hypothetical BLER value, a threshold value for detection of a significant WTRU movement, a threshold value for detection of a significant change in signal strength, and / or a threshold value for the maximum beam correlation width value above which reports may be triggered by the WTRU.

[0264] The beam correlation measurements configuration information message and the beam correlation reporting configuration information message may be a same message or a different message.

[0265] The WTRU may determine whether to start beam correlation measurements 2115. The WTRU may determine whether to start beam correlation measurements based on at least one of the following. The WTRU may determine whether to start beam correlation measurements based on detection of a transmission pattern of the configured reference signals for beam correlation measurements (e.g., CSI-RS or SSB), for example, via blind detection of an expected transmission pattern of the reference signals in time and frequency. The WTRU may determine whether to start beam correlation measurements based on a network request. The network request may be received for example, via RRC signaling, a DCI (WTRU-specific and / or group DCI), or a MAC CE. The network request may be received from the gNB. The WTRU may detect reference signals for beam correlation measurements, for example, CSI-RS or SSB, at the same time instant or after a specified or pre-determined number of symbols, or slots, or time duration. The WTRU may determine whether to start beam correlation measurements based on fulfilment of one or more triggering conditions for beam correlation measurements. A triggering condition may be an RSRP below an RSRP minimum (RSRPmin), and / or a PDCCH hypothetical BLER above a BLER maximum (BLERmax), as measured from any a-priori known reference signal, for example, a CSI-RS, a DM-RS, or an SSB. A triggering condition may be a detection of a change in the state of the gNB transmitted beam (e.g., blurred or focused). A triggering condition may be adetection of a significant physical displacement based on its positioning information, for example, when a movement larger than a configured threshold value is detected. A triggering condition may be a detection of a significant change in signal strength, for example, when a signal strength drop or boost larger than a configured threshold value is detected. If the triggering conditions are satisfied, the WTRU may send a request (e.g. request message) to the network for transmitting a measurement RS, for beam correlation measurements (e.g. CSI-RS or SSB). The WTRU may send the request for example, via UCI signaling or a MAC CE. The WTRU may receive a confirmation (e.g. confirmation message) from the network. The confirmation may be received via for example RRC signaling, a DCI, or a MAC CE. If the WTRU receives a confirmation from the network, the WTRU may detect a measurement RS at that time instant or after a specified or pre-determined number of symbols, or slots, or time duration.

[0266] The WTRU may detect measurement resources (e.g. RS). The WTRU may detect measurement resources in response to determining to start beam correlation measurements, The WTRU may detect the measurement RS at that time instant or after a specified or pre-determined number of symbols, or slots, or time duration. The WTRU may obtain the channel transfer functions at the specified resources (i.e. the received beam correlation measurements configuration information ). The WTRU may obtain the channel transfer functions at the specified resources by, for example, removing the known amplitudes and phases at the measurement resources.

[0267] The WTRU may perform (e.g. calculate or determine) beam correlation measurements 2120. The WTRU may perform beam correlation measurements on the reference signals based on the received beam correlation measurements configuration information message. The reference signals may be grouped in the resources sets for beam correlation measurements. The WTRU may perform beam correlation measurements, for example, by computing or determining the value of the beam correlation as given by equation (9), SNR, RSRP, or rank. The beam correlation measurements may be on the configured reference signals which may be grouped in the resources sets for beam correlation measurements. The beam correlation measurements may comprise a sum of products of two channel transfer functions of the reference signals. One of the channel transfer functions in each of the products of two channel transfer functions may be first conjugated by reversing the sign of its imaginary component prior to performing beam correlation measurements.

[0268] The WTRU may send a report comprising beam correlation measurements 2125. The WTRU may send or request to send, to the gNB, beam correlation measurements as part of a report based on the triggering conditions for reporting. The WTRU may send the report via, for example, a PUCCH or a PUSCH channel in a periodic, semi-persistent or aperiodic form according to the beam correlation reporting configuration information message.

[0269] Triggering conditions for reporting may include: RSRP below RSRPmin, and / or PDCCH hypothetical BLER above BLERmax, as measured from any a-priori known reference signal, for example, CSI-RS, DM-RS, or SSB; Detection of a change in the state of the gNB transmitted beam; Detection of a significant physicaldisplacement based on its positioning information, for example, when a movement larger than a configured threshold value is detected; Detection of a significant change in signal strength, for example, when a signal strength drop, or boost, larger than a configured threshold value is detected; and Detection of a value of a beam correlation metric, for example, a beam correlation function as in equation (9), larger than a configured threshold value.

[0270] The report may comprise or include one or more of the following: a beam correlation width / xgiven by a beam index difference for a X% correlation relative to a maximum; K correlation values for all possible beam index differences, with or without compression by a specified compression algorithm; a quantized version of the measured correlation metrics; an indication corresponding to a pre-defined state of a gNB transmitted beam, for example, whether the received beam is focused or blurred; a SNR, a rank and / or RSRP values, for example, averaged across the measurement resource sets for beam correlation; and an index representing the WTRU receiver spatial beam used for the measurements. In an example, in a system comprising up to K beam pairs, wherein each beam pair represents a couple of beams characterized by a beam index difference given by the absolute difference between the indexes of the beams, the beam correlation function yields up to K different correlation values. The K values may then be reported in compressed or uncompressed form, or a beam correlation width lx may be reported equal to the beam index difference below which the correlation function is above X%.

[0271] Beam correlation measurements may be included as part of a report containing channel state information, for example, a CSI report, or in a separate report.

[0272] The WTRU may stop (e.g. determine to stop) beam correlation measurements and / or reporting 2130. The WTRU may stop beam correlation measurements on a condition that at least one of the following is fulfilled or satisfied. The WTRU may stop measurements if reference signals for beam correlation measurements are no longer detected. If the WTRU was requested by the network to start beam correlation measurements, the WTRU may stop reporting if reports are of an aperiodic type or if reports are of a semi- persistent type and are de-activated by the network via, for example, a MAC CE. The WTRU may stop measurements if the WTRU receives a request to stop measurements or reporting. The WTRU may receive the request to stop measurements or reporting via, for example, RRC signaling, a DCI, or a MAC CE. The WTRU may stop measurements if the triggering conditions are no longer satisfied.

[0273] Although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer.

Claims

CLAIMSWhat is Claimed:

1. A method of beam correlation measurements, implemented by a wireless transmit / receive unit (WTRU), the method comprising: receiving a beam correlation measurements configuration information message, wherein the beam correlation measurements configuration information message comprises resource sets for beam correlation measurements, wherein each resource set comprises reference signals that correspond to a beam; receiving a beam correlation reporting configuration information message; determining to start beam correlation measurements based on an event; performing beam correlation measurements on the reference signals based on the received beam correlation measurements configuration information message, wherein the reference signals are grouped in the resources sets for beam correlation measurements; and sending a beam correlation measurements report based on a triggering condition.

2. The method of claim 1 , further comprising: stopping the beam correlation measurements, wherein the beam correlation measurements are stopped on a condition that at least one of the following is satisfied: a reference signal for beam correlation measurements is no longer detected; the WTRU was requested by a network entity to start beam correlation measurements and reports are of aperiodic type or of semi-persistent type and are de-activated; the WTRU receives a request to stop the beam correlation measurements; or beam correlation measurement triggering conditions are no longer satisfied.

3. The method of claim 1 , wherein the beam correlation measurements configuration information message further comprises: a number of repetitions N to average measurements with a configured gap between repetitions and one or more threshold values for triggering beam correlation measurements.

4. The method of claim 1 , wherein the beam correlation measurements configuration information message and the beam correlation reporting configuration information message are a same message.

5. The method of claim 1 , wherein the event to start beam correlation measurements comprises: detection of a transmission pattern of the reference signals; a received network request; or a triggering condition for beam correlation measurements.

6. The method of claim 5, wherein the triggering condition for beam correlation measurements comprises:a reference signal received power (RSRP) below an RSRP minimum threshold value, a physical downlink control channel (PDCCH) hypothetical block error rate (BLER) above a BLER maximum threshold value, a detection of a change in a state of a gNB transmitted beam, a detection of a change in physical displacement greater than a threshold value, detection of a change in signal strength greater than a threshold value, or detection of a value of a beam correlation metric larger than a threshold value.

7. The method of claim 1 , further comprising: sending a request for a network entity to transmit the reference signals; and receiving a confirmation information to measure the reference signals.

8. The method of claim 1 , wherein the beam correlation measurements report comprises: a beam correlation width lx given by a beam index difference for a X% correlation relative to a maximum; K compressed or uncompressed correlation values for all possible beam index differences; a quantized version of measured correlation metrics; an indication corresponding to a pre-defined state of a gNB transmitted beam; a signal to noise ratio (SNR); a rank; a reference signal received power (RSRP) value; or an index representing a WTRU receiver spatial beam used for the measurements.

9. The method of claim 1, wherein the beam correlation measurements comprise a sum of products of two channel transfer functions of the reference signals, wherein one of the channel transfer functions in each of the products of two channel transfer functions is first conjugated by reversing a sign of its imaginary component prior to performing beam correlation measurements.

10. The method of claim 1 , further comprising: detecting the reference signals; and obtaining channel transfer functions.

11. A wireless transmit / receive unit (WTRU), configured for beam correlation measurements the WTRU comprising: a receiver; a processor; and a transmitter, wherein: the receiver is configured to receive a beam correlation measurements configuration information message, wherein the beam correlation measurements configuration information message comprises resource sets for beam correlation measurements, wherein each resource set comprises reference signals that correspond to a beam;the receiver is further configured to receive a beam correlation reporting configuration information message; the processor is configured to determine to start beam correlation measurements based on an event; the processor is further configured to perform beam correlation measurements on the reference signals based on the received beam correlation measurements configuration information message, wherein the reference signals are grouped in the resources sets for beam correlation measurements; and the transmitter is configured to send a beam correlation measurements report based on a triggering condition.

12. The WTRU of claim 11 , wherein, the processor is further configured to stop the beam correlation measurements, wherein the beam correlation measurements are stopped on a condition that at least one of the following is satisfied: a reference signal for beam correlation measurements is no longer detected; the WTRU was requested by a network entity to start beam correlation measurements and reports are of aperiodic type or of semi-persistent type and are de-activated; the WTRU receives a request to stop the beam correlation measurements; or beam correlation measurement triggering conditions are no longer satisfied.

13. The WTRU of claim 11, wherein the beam correlation measurements configuration information message further comprises: a number of repetitions N to average measurements with a configured gap between repetitions and one or more threshold values for triggering beam correlation measurements.

14. The WTRU of claim 11, wherein the beam correlation measurements configuration information message and the beam correlation reporting configuration information message are a same message.

15. The WTRU of claim 11 , wherein the event to start beam correlation measurements comprises: detection of a transmission pattern of the reference signals; a received network request; or a triggering condition for beam correlation measurements.

16. The WTRU of claim 15, wherein the triggering condition for beam correlation measurements comprises: a reference signal received power (RSRP) below an RSRP minimum threshold value, a physical downlink control channel (PDCCH) hypothetical block error rate (BLER) above a BLER maximum threshold value, a detection of a change in a state of a gNB transmitted beam, a detection of a change in physical displacement greater than a threshold value, detection of a change in signal strength greater than a threshold value, or detection of a value of a beam correlation metric larger than a threshold value.

17. The WTRU of claim 11 , wherein:the transmitter is further configured to send a request for a network entity to transmit the reference signals; and the receiver is further configured to receive a confirmation information to measure the reference signals.

18. The WTRU of claim 11 , wherein the beam correlation measurements report comprises: a beam correlation width lx given by a beam index difference for a X% correlation relative to a maximum; K compressed or uncompressed correlation values for all possible beam index differences; a quantized version of measured correlation metrics; an indication corresponding to a pre-defined state of a gNB transmitted beam; a signal to noise ratio (SNR); a rank; a reference signal received power (RSRP) value; or an index representing a WTRU receiver spatial beam used for the measurements.

19. The WTRU of claim 11 , wherein the beam correlation measurements comprise a sum of products of two channel transfer functions of the reference signals, wherein one of the channel transfer functions in each of the products of two channel transfer functions is first conjugated by reversing a sign of its imaginary component prior to performing beam correlation measurements.

20. The WTRU of claim 11 , wherein: the processor is further configured to detect the reference signals and obtain channel transfer functions.

Images