Apparatus, system, method, and computer program product for a reconfigurable intelligent surface

Abstract

According to one aspect, a device (204) is provided for performing the following operations. The device (204) maintains, in at least one memory (208), information regarding a reference incident direction and reference configuration information, the reference configuration information defining, for the reference incident direction, a plurality of configurations of a plurality of tunable load impedance circuits of a tunable reflection array (210) of a reconfigurable intelligent surface or a sub-panel thereof. The device (204) measures an incident direction in which an electromagnetic wave is received by the reconfigurable intelligent surface (201). The device (204) calculates corrected configuration information based on the reference incident direction, the measured incident direction, and the reference configuration information, the corrected configuration information defining a plurality of corrected configurations for the measured incident direction. Finally, the device (204) configures the plurality of tunable load impedance circuits according to the corrected configuration.

Description

Technical Field

[0001] Various example embodiments relate to wireless communication. Background Art

[0002] A reconfigurable intelligent surface (RIS) is an artificially designed reflective surface that includes an array of reflective elements (typically on the order of 10,000 elements) whose reflective properties (i.e., at least the reflection phase) are adjustable, and thus multiple different reflected beams can be achieved. The RIS has been widely studied in the literature as a means of low-cost coverage extension and providing additional degrees of freedom in controlling the propagation environment. Compared to repeaters / relays, the RIS provides a cheaper and less complex solution, while simplifying installation and deployment due to the design flexibility. Compared to integrated access and backhaul (IAB) relays and densification-type solutions, the RIS is also expected to be easier in terms of installation permits and zoning issues. The RIS has also been shown to provide a significant signal-to-noise ratio (SNR) improvement in non-line-of-sight (NLOS) scenarios. Therefore, using the RIS in the millimeter wave (mmWave) band may be particularly beneficial because the mmWave band has high path loss and poor scattering, and thus traditionally has to rely on line-of-sight (LOS) links rather than NLOS links. This helps to limit the signal coverage in these bands.

[0003] Although various solutions for configuring reconfigurable intelligent surfaces have been proposed, there is still a need for a solution that is computationally undemanding and simple in terms of implementation and deployment. Summary of the Invention

[0004] According to one aspect, the subject matter of the independent claims is provided. Embodiments are defined in the dependent claims. The scope of protection sought for the various embodiments is defined by the independent claims.

[0005] Embodiments and features described in this specification that are not within the scope of the independent claims (if any) will be construed as examples that contribute to the understanding of the various embodiments. Brief Description of the Drawings

[0006] Hereinafter, example embodiments will be described in more detail with reference to the drawings, in which

[0007] Figure 1 an illustrated wireless communication system is shown;

[0008] Figure 2A and Figure 2B a reconfigurable intelligent surface according to an embodiment and an adjustable reflection array of the reconfigurable intelligent surface are shown, respectively;

[0009] Figure 3A and Figure 3BTwo alternative implementations of the tunable reflection array of the reconfigurable intelligent surface are shown respectively; and

[0010] Figures 4 to 6 、 Figure 7A 、 Figure 7B 、 Figure 7C 、 Figure 7D and Figure 8 show an exemplary process according to an embodiment. Detailed implementation

[0011] In the following, a wireless access architecture based on Long-Term Evolution Advanced (LTE-advanced, LTE-A) or New Radio (NR, 5G) will be used as an example of an access architecture to which embodiments can be applied to describe different exemplary embodiments. However, the embodiments are not limited to such an architecture. By appropriately adjusting parameters and processes, these embodiments can also be applied to other types of communication networks with appropriate means. Some examples of other options for applicable systems are Universal Mobile Telecommunications System (UMTS) Radio Access Network (UTRAN or E-UTRAN), Long-Term Evolution (LTE, the same as E-UTRA), Wireless Local Area Network (WLAN or WiFi), Worldwide Interoperability for Microwave Access (WiMAX), Personal Communication Service (PCS), Wideband Code Division Multiple Access (WCDMA), systems using Ultra-Wideband (UWB) technology, sensor networks, Mobile Ad Hoc Networks (MANETs), and Internet Protocol Multimedia Subsystem (IMS) or any combination thereof.

[0012] As used in this application, the term "circuit" may refer to one or more or all of the following: (a) only a hardware circuit implementation, such as only an implementation in analog and / or digital circuits, and (b) a combination of a hardware circuit and software (and / or firmware), such as (if applicable): (i) a combination of (multiple) analog and / or digital hardware circuits and software / firmware, and (ii) (multiple) hardware processors and any part of the software, including (multiple) digital signal processors, software, and (multiple) memories that work together to enable a device (such as a terminal device or an access node) to perform various functions, and (c) (multiple) hardware circuits and (multiple) processors, such as a microprocessor or a part of a microprocessor, which require software (such as firmware) to operate, but when software is not required to operate, the software may not exist. The definition of "circuit" applies to all uses of this term in this application, including any claims. As a further example used in this application, the term "circuit" also only covers an implementation of a hardware circuit or a processor (or multiple processors) or a part of a hardware circuit or a part of a processor and its (or their) accompanying software and / or firmware.

[0013] Figure 1 An example of a simplified system architecture is described, showing only some of the elements and functional entities, all of which are logical units and whose implementation may differ from that shown. Figure 1 The connections shown in [figure] are logical connections; the actual physical connections may be different. It will be apparent to those skilled in the art that the system generally also includes Figure 1 other functions and structures than those shown.

[0014] However, the embodiments are not limited to the system given as an example, but those skilled in the art can apply the solution to other communication systems having the necessary characteristics.

[0015] Figure 1 The example of [figure] shows a part of the radio access network illustrated.

[0016] Figure 1 Devices 100 and 102 are shown. Devices 100 and 102 can be, for example, user equipment. Devices 100 and 102 are configured to make a wireless connection with node 104 over one or more communication channels. Node 104 is also connected to the core network 110. In one example, node 104 can be an access node, such as an (e / g)NodeB that provides or serves devices in a cell. In one example, node 104 can be a non-3GPP access node. The physical link from the device to the (e / g)NodeB is referred to as the uplink or reverse link, while the physical link from the (e / g)NodeB to the device is referred to as the downlink or forward link. It should be understood that the (e / g)NodeB or its functions can be implemented by using any entity such as a node, host, server, or access point suitable for such use.

[0017] A communication system typically includes more than one (e / g)NodeB. In this case, the (e / g)NodeBs can also be configured to communicate with each other via wired or wireless links designed for this purpose. These links can be used for signaling purposes. An (e / g)NodeB is a computing device configured to control the radio resources of the communication system to which it is coupled. A NodeB can also be referred to as a base station, an access point, or any other type of interface device, including a relay station capable of operating in a wireless environment. An (e / g)NodeB includes a transceiver or is coupled to a transceiver. A connection is provided from the transceiver of the (e / g)NodeB to an antenna unit that establishes a bi-directional radio link with the device. The antenna unit can include multiple antennas or antenna elements. The (e / g)NodeB is further connected to a core network 110 (CN or Next Generation Core NGC). Depending on the system, the counterpart on the CN side can be a Serving Gateway (S-GW, routing and forwarding user data packets), a Packet Data Network Gateway (P-GW) for providing a connection of a User Equipment (UE) to an external packet data network, or a Mobility Management Entity (MME), etc.

[0018] A device (also referred to as a user equipment, UE, user terminal, terminal device, etc.) represents a type of apparatus in which resources on an air interface are allocated and assigned, and thus any feature described herein regarding the device can be implemented with a corresponding apparatus such as a relay node. An example of such a relay node is a Layer 3 relay (self-backhaul relay) towards a base station.

[0019] The device generally refers to a device (such as a portable or non-portable computing device) that operates with or without a subscriber identity module (SIM), including but not limited to the following types of devices: mobile stations (mobile phones), smartphones, personal digital assistants (PDAs), cellular phones, devices using wireless modems (such as alarm or measurement devices), laptop computers and / or touchscreen computers, tablet computers, game consoles, notebook computers, and multimedia devices. It should be understood that the device can also be an almost exclusively uplink-only device, an example of which is a camera or video camera that loads images or video clips onto a network. The device can also be a device capable of operating in an Internet of Things (IoT) network, which is a scenario that provides objects with the ability to transmit data over a network without human-to-human or human-to-computer interaction. For example, for smart grids and connected vehicles. The device can also use the cloud. In some applications, the device can include a user-portable device with a radio part (such as a watch, headphones, glasses), and the computing is performed in the cloud. The device (or a layer 3 relay node in some embodiments) is configured to perform one or more user equipment functions. The device can also be referred to as a user unit, mobile station, remote terminal, access terminal, user terminal, or user equipment (UE), to name just a few.

[0020] The various techniques described herein can also be applied to cyber-physical systems (CPS) (systems of collaborative computing elements that control physical entities). CPS can implement and utilize a large number of interconnected ICT devices (sensors, actuators, processors, microcontrollers, etc.) embedded in physical objects at different locations. Mobile cyber-physical systems are a subcategory of cyber-physical systems, where the physical systems under discussion have inherent mobility. Examples of mobile physical systems include mobile robots and sub-devices transported by humans or animals.

[0021] In addition, although these devices are described as single entities, different units, processors, and / or memory units can also be implemented (not all as Figure 1 shown).

[0022] 5G is capable of using multiple-input multiple-output (MIMO) antennas, far more base stations or nodes than LTE (the so-called small cell concept), including macro sites operating in cooperation with smaller sites, and adopting various radio technologies depending on service requirements, usage, and / or available spectrum. 5G mobile communications support a wide range of use cases and related applications, including video streaming, augmented reality, different ways of data sharing, and various forms of machine type applications (such as (massive) machine-type communication (mMTC)), including vehicle safety, different sensors, and real-time control. 5G is expected to have multiple radio interfaces, namely below 6 GHz, centimeter wave (cmWave), and millimeter wave, and can also be integrated with existing legacy radio access technologies such as LTE. At least in the early stage, the integration with LTE can be realized as a system where LTE provides macro coverage, and 5G radio interface access is through aggregation from small cells to LTE. In other words, 5G plans to support both inter-RAT (such as LTE-5G) and inter-RI (inter-radio interface, such as centimeter wave below 6 GHz, millimeter wave of centimeter wave below 6 GHz) operability. One of the concepts considered to be used in 5G networks is network slicing, where multiple independent and dedicated virtual sub-networks (network instances) can be created in the same infrastructure to run services with different requirements for latency, reliability, throughput, and mobility.

[0023] The current architecture in LTE networks is fully distributed in the radio and fully centralized in the core network. Low-latency applications and services in 5G require content to be close to the radio, which has led to local breakout and multi-access edge computing (MEC). 5G enables analysis and knowledge generation to occur at the data source. This approach requires leveraging resources that may not be continuously connected to the network, such as laptops, smartphones, tablets, and sensors. MEC provides a distributed computing environment for application and service hosting. To speed up response times, it is also capable of storing and processing content near cellular users. Edge computing encompasses a wide range of technologies, such as wireless sensor networks, mobile data collection, mobile signature analysis, collaborative distributed peer-to-peer ad hoc networks, and processing can also be classified as local cloud / fog computing and grid / mesh computing, dew computing, mobile edge computing, cloudlet servers, distributed data storage and retrieval, self-healing autonomous networks, remote cloud services, augmented and virtual reality, data caching, Internet of Things (massive connection and / or latency-critical), critical communications (autonomous vehicles, traffic safety, real-time analysis, time-critical control, healthcare applications).

[0024] The communication system is also capable of communicating with other networks, such as the public switched telephone network or the Internet 112, or of utilizing the services provided by them. The communication network may also be capable of supporting the use of cloud services. For example, at least a part of the core network operation may be performed as a cloud service (which is depicted by the "cloud" 114 in Figure 1 ). The communication system may also include a central control entity or the like, which provides facilities for cooperation in, for example, spectrum sharing for the networks of different operators.

[0025] Edge cloud technology can be introduced into the radio access network (RAN) by leveraging network virtualization functions (NVF) and software defined networks (SDN). The use of edge cloud technology may mean that access node operations are performed at least partly in a server, host or node, which is operatively coupled to a remote radio head or base station including radio components. It is also possible that the node operations are distributed among multiple servers, nodes or hosts. The application of the cloudRAN architecture enables the execution of RAN real-time functions on the RAN side (in the distributed unit DU 104), and the execution of non-real-time functions in a centralized manner (in the centralized unit CU 108).

[0026] It should also be understood that the labor distribution between core network operations and base station operations may be different from that of LTE, or may not even exist. Some other technological advancements that may be used are Big Data and all-IP, which may change the way the network is built and managed. The 5G (or New Radio, NR) network is designed to support multiple hierarchies, where MEC servers can be placed between the core and the base station or node B (gNB). It should be understood that MEC can also be applied to 4G networks.

[0027] 5G can also utilize satellite communication to enhance or supplement the coverage of 5G services, for example, by providing backhaul. Possible use cases are to provide service continuity for machine-to-machine (M2M) or Internet of Things (IoT) devices or in-vehicle passengers, or to ensure service availability for critical communications and future railway / maritime / aviation communications. Satellite communication can utilize not only geostationary orbit (GEO) satellite systems but also low Earth orbit (LEO) satellite systems, especially mega constellations (systems with hundreds of (nano) satellites deployed). Each satellite 106 in the mega constellation can cover several satellite-enabled network entities that create a ground cell. The ground cell can be created by a ground relay node 104 or a gNB located on the ground or in a satellite.

[0028] It is obvious to those skilled in the art that the described system is merely an example of a part of a radio access system, and in practice, the system may include multiple (e / g)NodeBs, the device may have access to multiple radio cells, and the system may also include other devices, such as physical layer relay nodes or other network elements, etc. At least one of the (e / g)NodeBs may be a home (e / g)NodeB. Alternatively, in the geographical area of a radio communication system, multiple different types of radio cells and multiple radio cells may be provided. The radio cells may be macro cells (or umbrella cells) of large cells, usually having a diameter of up to dozens of kilometers, or smaller cells, such as micro cells, femto cells or pico cells. Figure 1 The (e / g)NodeBs can provide any of these types of cells. A cellular radio system can be implemented as a multi-layer network including several types of cells. Generally, in a multi-layer network, one access node provides one or more types of cells, and thus multiple (e / g)NodeBs are required to provide such a network structure.

[0029] To meet the need to improve the deployment and performance of communication systems, the concept of "plug-and-play" (e / g)NodeBs has been introduced. Generally, a network capable of using "plug-and-play" (e / g)NodeBs, in addition to home (e / g)NodeBs (H(e / g)NodeBs), also includes a home node B gateway or HNB-GW ( Figure 1 (not shown in the figure). The HNB gateway (HNB-GW), which is usually installed within the operator's network, can aggregate traffic from a large number of HNBs back to the core network.

[0030] The 6G network is expected to adopt flexible decentralized and / or distributed computing systems and architectures, as well as ubiquitous computing, based on mobile edge computing, artificial intelligence, short packet communication, and blockchain technology, to achieve local spectrum licensing, spectrum sharing, infrastructure sharing, and intelligent automation management. The key functions of 6G will include intelligent interconnection management and control functions, programmability, integrated sensing and communication, reduced energy footprint, trustworthy infrastructure, scalability, and affordability. In addition to this, 6G also targets new use cases, including integrating positioning and sensing functions into the system definition to unify the user experience in the physical and digital worlds.

[0031] As described above, a reconfigurable intelligent surface (RIS) is an artificially designed reflective surface that includes an array of reflective elements, and the reflection characteristics of the array of reflective elements (i.e., at least the reflected phase, and optionally also the gain) are adjustable, so that multiple different reflected beams can be achieved. To achieve significant gain using RIS, the number of reflective elements can be on the order of tens of thousands. The phase shift introduced by each reflective element can be tuned by the processing unit of the RIS.

[0032] Reconfigurable intelligent surfaces (RISs) have been widely studied in the literature as a means for low-cost coverage extension and providing additional degrees of freedom in controlling propagation environments. Compared with repeaters / relays, RISs offer a cheaper and less complex solution, while simplifying installation and deployment due to design flexibility. Compared with integrated access and backhaul (IAB) relay and densification-type solutions, RISs are also expected to be easier in terms of installation permits and zoning issues. RISs have also been shown to provide significant signal-to-noise ratio (SNR) improvements in non-line-of-sight (NLOS) scenarios. Therefore, using RISs in the millimeter-wave band, which suffers from high path loss and poor scattering and thus traditionally (i.e., when not using RISs) has to rely mainly on line-of-sight (LOS) links rather than NLOS links, can be particularly beneficial. Having to rely mainly or entirely on LOS links may often result in receivers being in blind spots due to signal blockage, especially in urban environments, thus limiting the signal coverage. More modest benefits can be obtained at lower frequencies (i.e., at frequencies below 10 GHz).

[0033] Significant gains have been demonstrated by using an RIS with a sufficient number of reconfigurable reflecting elements to direct the desired reflections of signals to NLOS users. For example, a practical RIS can use a 95×95 reflection array for a 1-square-meter panel at 28 GHz, where the reflecting elements are half-wavelength patch elements with Nyquist spacing. Such a large number of individual reflecting elements requires solving highly complex optimization problems to appropriately adjust the loads on the elements according to the location / channel state information (CSI) of the target terminal device.

[0034] Therefore, the problem of how to dynamically and effectively configure reconfigurable intelligent surfaces in an optimal way in a given situation still remains. A common approach to RIS optimization is to tune the M load elements of the RIS panel based on the instantaneous cascaded channel between the transmitter (Tx), RIS, and receiver (Rx) to maximize the reflections from the RIS for users. Therefore, it is desirable to obtain accurate and frequent CSI, which is an expensive overhead and also increases the complexity of the RIS optimization problem. For RIS optimization, finding a closed-form solution has been shown to be difficult. To overcome these problems, for example, using artificial intelligence (such as deep reinforcement learning) to solve the RIS optimization problem in real time has been proposed. However, due to the high computational requirements of such a solution, using artificial intelligence for RIS optimization requires providing a high-rate control channel between the RIS and edge artificial intelligence analysis or implementing complex and expensive processing units on the RIS. Both of these solutions raise serious concerns about the feasibility of RIS deployment.

[0035] Since the operation of a RIS is based on reflecting the incident electromagnetic signals received from a radio transmitter or transceiver (e.g., from an access node), the incident direction plays a crucial role in the design, implementation, and deployment of the RIS. If the configuration of the RIS does not change, a change in the incident direction will result in a change in the beam shape and / or direction. The incident direction may change, for example, due to:

[0036] - The need to switch between different transmitters, e.g., in the case of a multi-transmit / receive point (multi-TRP) access node,

[0037] - The use of mobile radio transmitters, e.g., device-to-device (D2D) and vehicle-to-vehicle (V2V) communications, and

[0038] - Slight changes in the orientation of a large-sized RIS caused by the environment, e.g., wind, rain, and other weather phenomena.

[0039] When the incident angle changes suddenly, the RIS should be reconfigured without delay to account for this change so as to maintain the same beam shape and direction. Given that there are typically a large number of individual reflecting elements in a RIS, the problem of how to perform such reconfiguration is far from trivial.

[0040] The embodiments to be discussed below seek to provide solutions that overcome or at least mitigate at least some of the problems associated with the above RIS optimization. That is, the embodiments provide a beam grid (GoB)-based solution for RIS optimization, where a set of reflecting beams (also referred to as transmission beams) are pre-configured to the RIS and deployed in a manner similar to a GoB-based (millimeter-wave) phased array access. This not only significantly reduces the manufacturing cost of the RIS but also makes the installation and deployment of the RIS simpler with less overhead. The proposed solution is capable of seamlessly integrating the RIS into existing cellular networks, such as Figure 1 the cellular network discussed in

[0041] Figure 2A shows a schematic diagram of a (reflective) reconfigurable intelligent surface (RIS) 201 (also referred to as an intelligent reflecting surface, IRS) according to an embodiment, while Figure 2B shows a more detailed view of the tunable reflecting array 210 of the RIS 201. Hereinafter, Figure 2A and Figure 2B are discussed in parallel. The RIS 201 can be deployed between one of the terminal devices 100, 102 and the access node 104 in Figure 1

[0042] Refer to Figure 2A and Figure 2B ​, RIS201 includes a tunable reflectarray 210 (also referred to as an electrically tunable reflectarray or reflectarray), which includes a plurality of reflective (or equivalently reflective) elements 211, element 212, element 213, and a plurality of tunable load impedance circuits 221 to tunable load impedance circuit 223, which are electrically connected (directly) to the plurality of reflective elements 211 to reflective element 213 to affect the phase of the electromagnetic wave reflected by the plurality of reflective elements 211 to 213. In other words, the phase of the reflected electromagnetic wave generated by a given reflective element 211 to 213 can be tuned via the corresponding tunable load impedance circuit 221 to tunable load impedance circuit 223. Due to the constructive and destructive interference between the electromagnetic waves generated by the plurality of reflective elements 211, reflective element 212, reflective element 213, different reflective (or equivalently transmissive) beams can be generated by adjusting the configuration of the plurality of tunable load impedance circuits 221 to tunable load impedance circuit 223. The shape and / or direction of the reflected beam 251 can be adjusted in this way.

[0043] RIS201 (or specifically, the tunable reflectarray 210) can be configured to operate at radio frequencies or, in practice, within its determined sub-range. Here and hereinafter, according to the general definition, radio frequencies can be defined as the frequency range from 3 kHz to 300 GHz.

[0044] The specific configuration of the plurality of tunable load impedance circuits 221 to tunable load impedance circuit 223 for fabricating a specific reflected beam can be specific to a specific incident direction (or equivalently, the incident beam direction). In other words, if the incident direction of the electromagnetic wave impinging on RIS201 changes, the direction of the reflected beam 251 may also change (unless the configuration of the plurality of tunable load impedance circuits 221 to tunable load impedance circuit 223 is adjusted to cope with this change). The reason for this behavior is that the phase of the incident electric field at the position of a given reflective element 211 to 213 depends not only on the position of the given reflective element 211 to 213 but also on the incident direction. The phase of the electric field at the positions of the plurality of reflective elements is defined as nα in Figure 2B where α is a determined phase shift value that depends on, for example, element spacing, frequency, and angle of incidence. n has an integer value from 0 to N - 1, which depends on the specific reflective element (N is the number of reflective elements along one direction). In particular, the incident direction has an impact on the relative phase between the plurality of reflective elements 211 to 213. Therefore, knowing the incident direction is crucial for the correct operation of RIS 201.

[0045] The multiple reflecting elements 211 to 213 can have the same geometry and dimensions. The multiple reflecting elements 211 to 213 can be at least partially made of metal or alloy (or other conductive materials). The multiple reflecting elements 211 to 213 can be resonant elements. In particular, the multiple reflecting elements 211 to 213 can be resonant elements configured to operate (i.e., resonate) at one or more operating frequencies of the RIS 201. In other embodiments, the multiple reflecting elements 211 to 213 can be electrically small antennas, i.e., antennas whose dimensions are at least less than (preferably much less than) half of the wavelength or a quarter of the wavelength.

[0046] As Figure 2A shown, the multiple reflecting elements 211 to 213 can be, for example, patch (antenna) elements, where the patch can have, for example, the shape of a square, rectangle, circle, ellipsoid, (regular) polygon, (circular) ring, annular sector, or disk sector. In some embodiments, the multiple reflecting elements 211 to 213 can be printed circuit board (PCB)-based antenna elements other than patch antenna elements.

[0047] The tunable reflecting array 210 including the multiple reflecting elements 211 to 213 can be a uniform array, which means that the multiple reflecting elements 211 to 213 can be equally spaced apart. Also as Figure 2A shown, the tunable reflecting array 210 can be a two-dimensional array, or more specifically, a two-dimensional uniform array. In other embodiments, the tunable reflecting array 210 can be a one-dimensional array, or more specifically, a one-dimensional uniform array, that is, the multiple reflecting elements 211 to 213 can be arranged along a line.

[0048] In some embodiments, the number of the multiple reflecting elements 211 to 213 in the tunable reflecting array 210 can be greater than or equal to 100. In other embodiments, the number of the multiple reflecting elements 211 to 213 in the tunable reflecting array 210 can be greater than or equal to 1000, or greater than or equal to 5000, or greater than or equal to 10000.

[0049] In some embodiments, adjacent reflecting elements among the multiple reflecting elements 211 to 213 can be arranged to be within the near-field range of each other at one or more operating frequencies of the RIS 201. The near-field range can be defined as zero to one wavelength at a given operating frequency.

[0050] Multiple tunable load impedance circuits 221 to 223 can be used to tune the load impedance of multiple reflecting elements 211 to 213 (i.e., the load impedance seen or experienced by multiple reflecting elements 211 to 213). According to antenna theory, a change in the load impedance of a radiating element will cause a change in the phase of the radiated electromagnetic wave. Each reflected beam implemented by the RIS 201 can be identified by a load impedance matrix, which includes the load impedance information of multiple tunable load impedance circuits 221 to 223. In other words, the load impedance matrix can include the values of the load impedance of each of the multiple tunable load impedance circuits 221 to 223, or be composed of the values of the load impedance of each of the multiple tunable load impedance circuits 221 to 223. The multiple tunable load impedance circuits 221 to 223 can be the same circuit (although the tuning between elements may be different, of course).

[0051] Some examples of the multiple tunable load impedance circuits 221 to 223 can include:

[0052] · Tunable (grounded) capacitors or other tunable (grounded) capacitive or reactive circuits, ● Tunable digital or analog filters, and

[0053] · A combination of an untunable (grounded) parasitic load impedance circuit and a conduction / cutoff switch electrically connected to the untunable (grounded) parasitic load impedance circuit.

[0054] In some embodiments, the multiple tunable load impedance circuits 221 to 223 can at least include corresponding multiple tunable phase shift elements for implementing the tuning of the multiple tunable load impedance circuits 221 to 223. Therefore, the multiple tunable load impedance circuits 221 to 223 can be used to tune the load impedance of multiple reflecting elements 211 to 213 (i.e., the load impedance seen or experienced by multiple reflecting elements 211 to 213) at least by adjusting the phase shift induced by the multiple tunable phase shift elements.

[0055] The multiple tunable phase shift elements included in the multiple tunable load impedance circuits 221 to 223 can be the same elements (although the tuning between them may be significantly different at any given time). The multiple tunable phase shift elements can be (dedicated) tunable phase shifters or any other elements capable of inducing an electrically tunable phase shift. Specifically, the multiple tunable phase shift elements can be tunable n-bit phase shifters, where n can be any positive integer (i.e., 1, 2, 3, etc.).

[0056] In an embodiment, the plurality of tunable phase shift elements included in the plurality of tunable load impedance circuits 221 to 223 can be 1-bit phase shifters that effectively act as on / off switches for connecting the plurality of reflection elements 211 to 213 to a parasitic (impedance load) circuit or a plurality of corresponding parasitic (impedance load) circuits. This simplified RIS design can provide a total of 2 M different reflection patterns, where M is the number of the plurality of tunable phase shift elements or is equal to the number of the plurality of reflection elements 211, reflection element 212, and reflection element 213.

[0057] In some embodiments, all or at least some of the plurality of tunable impedance load circuits 221 to 223 can be active circuits that are capable of tuning not only the phase of the reflected electromagnetic wave but also the gain applied to the reflected electromagnetic wave (i.e., tuning the amplitude of the reflected electromagnetic wave). In such an embodiment, each of the all or at least some of the plurality of tunable impedance load circuits 221 to 223 can include at least one tunable active circuit element, such as a programmable gain amplifier or a tunable reflection amplifier.

[0058] To be able to configure the plurality of tunable impedance load circuits 221 to 223 (i.e., to be able to tune the phase and optionally the amplitude of the electromagnetic wave reflected by the plurality of reflection elements 211 to 213), the RIS 201 includes a device 204 (or, generally, one or more devices). The device 201 can also be referred to as a computing device, a processing device, or a processing unit. According to an embodiment (which will be discussed in detail below), the device 204 can be specifically configured to at least adjust the configuration (i.e., tuning) of the plurality of tunable impedance load circuits 221 to 223 of the tunable reflection array 210. The device 204 (via its interface 207) is at least electrically connected to the tunable reflection array 210 (or specifically at least connected to the plurality of tunable impedance load circuits 221 to 223 to be able to tune).

[0059] The device 204 includes a processor 206, an interface 207, and a memory 208. The memory 208 includes at least one database 210 and software 209 (i.e., one or more algorithms). The processor 206 can be the central processing unit (CPU) of the RIS 201. In some embodiments, one or more control circuits, such as one or more processors, can be provided in the device 204 instead of the single processor 206.

[0060] According to some embodiments, the apparatus 204 may include one or more control circuits, such as at least one processor 206, and at least one memory 208, which includes one or more algorithms, such as computer program code (software) 209, wherein at least one memory 208 and the computer program code (software) 209 are configured to, together with at least one processor 206, cause the apparatus 201 to perform any of the example functions of the apparatus 204 described below (in conjunction with Figures 4 to 6 , Figure 7A , Figure 7B and Figure 8 ). It is also possible to use a specific integrated circuit, such as an ASIC (Application-Specific Integrated Circuit), a field-programmable gate array (FPGA), or other components and devices for implementing the functions according to different embodiments.

[0061] The memory 208 of the apparatus 204 can be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory, and removable memory.

[0062] The interface 207 of the apparatus 204 may include, for example, one or more communication interfaces, which include hardware and / or software for implementing a communication connection according to one or more communication protocols. Specifically, one or more interfaces 207 may include at least one interface providing a connection to the tunable reflectarray 210 to enable tuning. One or more communication interfaces 207 may include well-known standard components controlled by a corresponding control unit, such as amplifiers, filters, frequency converters, (de)modulators, and encoder / decoder circuits, as well as one or more antennas. One or more communication interfaces 207 may also include a user interface.

[0063] In some embodiments, the interface 207 may include a radio receiver or transceiver or provide a connection to an external radio receiver or transceiver. In either case, the radio receiver or transceiver may be configured to receive at least one or more control signals from one or more access nodes via a control channel. The radio receiver or transceiver may include at least one (dedicated) antenna for receiving (and possibly transmitting). Multiple different types of control signals may be defined, as will be described in conjunction with Figure 7A , Figure 7B , Figure 7C and Figure 7DAs described in detail. Alternatively, the radio receiver or transceiver can be configured to receive (and possibly transmit) using the tunable reflectarray 210. In the latter case, the radio receiver or transceiver can be assumed to be electrically connected to the tunable reflectarray 210. In some embodiments, such an electrical connection can be provided via a switch for switching between receive (and transmit) operations and reflection operations.

[0064] In some embodiments, a system including a reconfigurable intelligent surface 201 is provided, the system including a radio receiver or transceiver for receiving one or more control signals via a control channel (as described above), and an access node configured to transmit one or more control signals to the reconfigurable intelligent surface via the control channel (e.g., Figure 1 the access node 104 in Figure 7A , Figure 7B , Figure 7C and Figure 7D ). One or more control signals can include at least one control signal of at least one type of control signal discussed in conjunction with Figure 7A . Specifically, the access node can include at least one processor and at least one memory, the at least one memory for storing instructions to be executed by the processor, wherein the at least one memory and the instructions are configured to, together with the at least one processor, cause the access node to transmit at least one or more control signals to the reconfigurable intelligent surface via the control channel. In certain cases, the access node is also capable of receiving signals from the reconfigurable intelligent surface 201 via the control channel (e.g., see block 702 of Figure 7A discussed below).

[0065] In some embodiments, the device 204 can also include one or more user input devices (e.g., a control panel or a touch screen) for enabling a user to control the operation of the device 204 (via the device 204) and / or a display ( Figure 1 not shown in

[0066] ). One or more user input devices can be specifically electrically connected to the device 204). Figure 2A and 2B ).

[0067] First, how to use the IRS for beamforming is studied. Initially, it is assumed that the IRS knows the position of the radio transmitter (or transceiver), i.e., the elevation angle and azimuth angle (θ t , φ t)The defined reference incident direction. The tunable reflectarray is assumed to be a rectangular array of size R×C, where R and C are positive integers indicating the number of elements arranged along the y - direction and z - direction respectively. The objective is to use beamforming (or excitation) coefficients a rc to achieve uniform angular coverage in a predefined sector, where the sub - indicators r and c are array parameters that together indicate the specific reflecting element of the tunable reflectarray to which the beamforming coefficients are to be applied (r has integer values from 1 to R and c has integer values from 1 to C). Thus, the desired beam pattern can be expressed as,

[0068] For θ l ≤θ≤θ u ; φ l ≤φ≤φ u , E sθ (θ, φ)=c′ (1)

[0069] For other values of θ and φ, E sθ (θ, φ)=0 (2)

[0070] where E sθ (θ, φ) is the scattered electric field or the reflected electric field, θ and φ are the elevation angle and azimuth angle of the electromagnetic wave radiation (i.e., scattering or reflection), θ l and θ u are the lower and upper limits of the elevation angle respectively, φ l and φ u are the lower and upper limits of the azimuth angle respectively, and c′ is a constant. It should be emphasized that this is just an example of the desired beam shape, that is, for different definitions of E sθ (θ, φ), a similar methodology described below can be used.

[0071] We consider the normalized scattered field defined in (1) and (2) in order to eliminate the dependence on the radial distance ρ, i.e., For small patches (l, h << λ / 4 with patch length l and height h) and a large number of elements, the RIS beam pattern is mainly determined by the array factor (AF). Thus, we assume that for a given sector range (θ l , θ u ) and (φ l , φ u ), the variation of the element pattern (i.e., the radiation pattern of individual reflecting elements in the tunable reflectarray) can be neglected. In other words, E Pp，θ (θ, φ)≈c″, where c″ is for θ l ≤θ≤θ u ; φ l ≤φ≤φ uSome constants. Therefore, the purpose of beamforming can be simplified to (a constant normalized to one),

[0072] For θ l ≤ θ ≤ θ u ; φ l ≤ φ ≤ φ u , AF(θ, φ) = 1 (3)

[0073] For other values of θ and φ, AF(θ, φ) = 0 (4)

[0074] We assume that the beamforming coefficient a rc is separable in two orthogonal dimensions Y and Z, that is, we assume that any beamforming coefficient a rc can be written as a rc = a r · a c , where a r and a c are the r - oriented and c - oriented (or equivalently y - oriented and z - oriented) components of the beamforming coefficient, respectively. Then, the array factor AF in (3) and (4) can be expressed as

[0075]

[0076] where k is the wave number (or propagation constant), c L and c U are the lower and upper limits of the array parameter c, respectively, r L and r U are the upper and lower limits of the array parameter r, respectively, d y is the distance between the (phase) center points of adjacent reflecting elements along the y - direction, d z is the distance between the (phase) center points of adjacent reflecting elements along the z - direction, e is the Euler's number, and j is the imaginary unit.

[0077] To simplify the following analysis, we also define two auxiliary parameters ξ y and ξ z as

[0078]

[0079] Based on (5) to (7), we observe that AF(ξ y , ξ z ) = AF(ξ y )AF(ξ z ), where and are two separable one - dimensional discrete - time Fourier transform (DTFT) pairs. For (θ l , θ u ) and (φl For a given range of φ u ), let ξ y，l and ξ y，u correspond to the lower and upper bounds of ξ calculated from (6). A similar (i.e., analogous) definition also applies to ξ y defined in (7), ξ z，l , ξ z，u and ξ z . We can express the inverse transformation as

[0080]

[0081] The integral in (8) can be simplified to obtain the following closed form:

[0082] For c ∈ [c L , c U ,

[0083]

[0084] For r ∈ [r L , r U ,

[0085]

[0086] where is the normalization factor, and the total beamforming coefficient is a rc = a r · a c . The partial one-dimensional array factor AF(ξ y ) and AF(ξ z ) can be simply calculated as AF(ξ y ) = DTFT(a c ) and AF(ξ z ) = DTFT(a r ). Then the total approximate array factor is AF a (θ, φ) = AF(ξ y )AF(ξ z ).

[0087] From (1) to (10), the differences between beamforming using RIS and using active phased arrays can be clearly observed. That is, in an IRS, the excitation of the radiating elements (i.e., antenna elements) is the external incident electromagnetic field, as opposed to a set of excitation signals received from a radio transmitter or transceiver electrically connected to an active phased array. Additionally, unlike the case of phased arrays, this excitation is generally not the same for all radiating elements (unless the incident direction is exactly orthogonal to the RIS plane). Since the excitation varies with each radiating element, it can also be observed from (1) to (10) that the expected beamforming (or equal weight) coefficients are functions not only of the desired angular coverage but also of the angle of arrival (or equivalent incident direction) and the element spacing.

[0088] Figure 3A and Figure 3B illustrates two alternative implementations 301, implementation 321 of a tunable reflectarray of RIS. The RIS under discussion can be deployed between Figure 1 one of the terminal devices 100, terminal device 102 and the access node 104. Either of the tunable reflectarrays 301, 321 can be used together with Figure 2A and Figure 2B the RIS201.

[0089] Figure 3A illustrates a tunable reflectarray 301 similar to Figure 2A and Figure 2B shown, provided here only for comparison. The tunable reflectarray 301 includes a single reflective panel used to implement a single beam at a time.

[0090] Figure 3B illustrates the tunable reflectarray 321, which includes a plurality of reflective sub - panels 322 to 325, and the plurality of reflective sub - panels 322 to 325 are used to implement a corresponding plurality of beams 332 to 335 at a given time. Specifically, Figure 3B illustrates an exemplary tunable reflectarray 321 having four reflective sub - panels 322 to 325 (although other numbers of reflective sub - panels can be employed in other embodiments). Each of the plurality of reflective sub - panels 322 to 325 can be independently controlled by the device (i.e., computing device) of the RIS by changing the configuration (i.e., tuning) of the tunable impedance load circuit of the reflective elements electrically connected to the sub - panel. Each of the plurality of (different) beams 332 to 335 generated by the plurality of sub - panels 322 to 325 can be used, for example, to serve different terminal devices. Combining Figure 2A and Figure 2BAny feature of the described tunable reflectarray 210 (corresponding to a single reflecting panel) can (with appropriate modification) apply to each individual reflecting sub-panel 322 to 325 of the tunable reflectarray 321.

[0091] In some embodiments, the RIS can be configured to dynamically switch from Figure 3A single-panel operation of Figure 3B to multi-panel operation of

[0092] Figure 4 and vice versa. For example, when scheduling all resources for a single end device, the switch from multi-panel operation to single-panel operation can be triggered. This switch can be remotely controlled by the access node using a control channel. Figure 4 The process of Figure 2A can be performed by the apparatus of the RIS (e.g., a computing device), such as Figure 2A the apparatus 204 of Figure 2B The RIS and its components can be defined as described in any of the embodiments discussed in connection with Figure 3A and Figure 3B any one of Figure 4 The process of

[0093] can equally apply to the downlink direction (i.e., the case of receiving electromagnetic waves from the access node and reflecting them to the end device) and the uplink direction (i.e., the case of receiving electromagnetic waves from the end device and reflecting them to the access node). It should be noted that the uplink channel and the downlink channel formed via the RIS experience reciprocal channel gains without the need to adjust the load impedance to shift the signal direction.

[0093] Referring to Figure 4 , at block 401, the apparatus, in at least one memory, maintains information about a reference incident direction and reference configuration information, the reference configuration information defining multiple configurations of the multiple tunable load impedance circuits of the tunable reflectarray of the RIS for achieving multiple different reflected beams upon reception from the reference incident direction. In other words, each configuration of the multiple tunable load impedance circuits of the tunable reflectarray of the RIS corresponds to a single reflected beam specific to reception from the reference incident direction. The reference incident direction can be related to reception from a particular radio transmitter or transceiver.

[0094] In some alternative embodiments, the reference configuration information can define multiple configurations of the multiple tunable load impedance circuits of the sub-panels of the tunable reflectarray of the reconfigurable intelligent surface for achieving multiple different reflected beams upon reception from the reference incident direction. In other words, the reference configuration information can relate to a particular sub-panel of the tunable reflectarray of the RIS rather than to the entire tunable reflectarray.

[0095] The reference incident direction can be defined using the elevation angle and the azimuth angle (θ t and φ t respectively) or using one of the elevation angle and the direction angle (in the case of a one-dimensional tunable reflectarray). The elevation angle can here be defined as the angle relative to the plane of the tunable reflectarray of the RIS (depending on the definition, corresponding to 0° or 90° elevation angle of that plane). The reference incident direction can be specifically defined as assuming reception via the center point or a sub-panel thereof of the tunable reflectarray. The reference incident direction can correspond to the latest information on the position of the radio transmitter relative to the RIS.

[0096] Each of the multiple configurations maintained in the at least one memory can include an impedance load matrix. The multiple elements of each impedance load matrix can respectively define the load impedances that can be implemented by the multiple tunable impedance load circuits. The size of each impedance load matrix among the multiple impedance load matrices is equal to the size of the tunable reflectarray (i.e., the size in terms of the number of elements). In other words, if the tunable reflectarray is an R×C array (where R and C are positive integers), then each of the multiple load matrices has a size of R×C or C×R.

[0097] In addition, the apparatus can maintain multiple beam codebooks in the at least one memory. The multiple beam codebooks can define multiple sets of beamforming coefficients of the tunable reflectarray. The multiple sets of beamforming coefficients at least define the phases (and possibly gains) that can be induced by the multiple tunable load impedance circuits for realizing multiple reflected different beams. In other words, each beam codebook defines the phase (optionally also the gain) associated with the electromagnetic wave reflected (re-radiated) by the multiple reflecting elements of the tunable reflectarray for realizing a specific reflected beam among the multiple different reflected beams. For example, complex numbers can be used to define the phase values and optionally the gain values. A single complex number can be used to provide information on the phase and the gain (the phase corresponding to the phase or polar angle of the complex number and the gain corresponding to the magnitude of the complex number). The multiple beam codebooks can be defined as matrices. The size of each beam codebook among the multiple beam codebooks can be equal to the size of the tunable reflectarray (i.e., the size in terms of the number of elements). In other words, if the tunable reflectarray is an R×C array (where R and C are positive integers), then each of the multiple beam codebooks has a size of R×C or C×R.

[0098] Each beam codebook can be associated with a corresponding load impedance matrix. A given beam codebook can be derived based on the corresponding load impedance matrix and vice versa. Thus, in some embodiments, only one of the two can be maintained in the at least one memory.

[0099] At block 402, the apparatus configures a plurality of tunable load impedance circuits according to a configuration defined in the configuration information. In other words, the apparatus tunes the plurality of tunable load impedance circuits in order to achieve a specific reflected beam (assuming reception occurs from a reference incident direction).

[0100] At block 403, the apparatus measures the incident direction at which the electromagnetic wave is received by the RIS. The incident direction can be measured using, for example, radio-based methods such as using positioning techniques or methods employing geometric calculations based on camera or laser-based measurements.

[0101] More specifically, the angle of incidence can be measured, for example, using one of the following methods.

[0102] According to a first exemplary method, one of the RIS or the access node (or other radio transmitter or transceiver for transmission via the RIS) transmits a predefined reference signal, while the other of the RIS and the access node receives the predefined reference signal via a tunable reflection array (in the case of the RIS) or a separate antenna array (in either case), and subsequently performs an angle-of-arrival (AoA) estimation technique based on the received predefined reference signal. For example, the AoA estimation can be performed by measuring the time difference of arrival (TDoA) between a plurality of tunable reflection elements of the tunable reflection array or between a plurality of sub-antenna elements of the antenna array. The angle of incidence (i.e., AoA) can be determined based on the TDoA.

[0103] According to a second exemplary method, an optical direction-of-arrival technique can be used to estimate the angle of incidence. In this case, one of the RIS and the access node (or other radio transmitter or transceiver for transmission via the RIS) can be equipped with at least one laser, and the other is equipped with an optical sensor array. One of the RIS and the access node (or other radio transmitter or transceiver for transmission via the RIS) can emit one or more laser pulses using at least one laser, while the other of the RIS and the access node can measure the one or more laser pulses using the optical sensor array. Based on these measurements, the TDoA can be estimated. Furthermore, the AoA can be estimated based on the TDoA.

[0104] Ideally, the measured incident direction will correspond to the reference incident direction. However, this may not always be the case, as already described. For example, the radio transmitter (or transceiver) targeting the RIS can be a commonly used mobile radio transmitter, such as in D2D and V2V communications, or the orientation of the RIS may have changed, for example, due to weather conditions.

[0105] Similar to the reference incident direction, the measured incident direction can be represented using the elevation angle and the azimuth angle (θ′ t and φ′t ) or is defined using one of the elevation angle and the azimuth angle (in the case of a one-dimensional tunable reflectarray). The measured incident direction can be specifically defined as being received via the center point or a sub-panel of the tunable reflectarray.

[0106] At block 404, the apparatus calculates corrected configuration information based on the reference incident direction, the measured incident direction, and the reference configuration information, the corrected configuration information defining a plurality of corrected configurations of the plurality of tunable load impedance circuits for achieving a plurality of different reflection beams upon reception from the measured incident direction.

[0107] At block 405, the apparatus (re)configures the plurality of tunable load impedance circuits according to the corrected configurations defined in the corrected configuration information. In other words, the apparatus adjusts the current tuning of the plurality of tunable load impedance circuits so as to achieve a specific reflection beam assuming reception from the measured incident direction.

[0108] In some embodiments, block 402 may be omitted. In other words, the apparatus may initially not configure the plurality of tunable load impedance circuits according to any configuration defined in the configuration information. If block 402 is omitted, then block 405 may correspond to configuring (rather than reconfiguring) the plurality of tunable load impedance circuits according to the corrected configurations defined in the corrected configuration information.

[0109] In combination with Figure 4 The operations described may correspond to operations for a particular time slot t. A particular radio transmitter or transceiver (such as an access node or a terminal device) may be scheduled to use the RIS in that particular time slot t. In the next time slot, the operations in blocks 401 to 405 may be repeated, although the radio transmitter or transceiver scheduled to use the RIS may be different and thus the reference incident direction may also be different from before. Generally, the apparatus may maintain in the at least one memory the reference incident direction and the reference configuration information (and / or a set of beam codebooks) for one or more radio transmitters or transceivers.

[0110] In embodiments where the plurality of tunable load impedance circuits are the tunable load impedance circuits of a sub-panel of the RIS, the apparatus may repeat the steps described in blocks 401 to 405 for one or more additional sub-panels of the RIS. One or more additional sub-panels of the RIS may be associated with a reference incident direction that is different from or the same as that of the sub-panel.

[0111] Figure 5 Another process according to an embodiment is shown for correcting an initial configuration of a tunable reflectarray of a RIS based on a detected change in the incident direction of an electromagnetic wave. Figure 5 The process may be performed by an apparatus (such as a computing device) of the RIS, such asFigure 2A Device 204. The RIS and its components can be defined as described in any of the embodiments discussed in conjunction with Figure 2A , Figure 2B , Figure 3A and Figure 3B .

[0112] Figure 5 The process of Figure 4 largely corresponds to the process of Figure 4 . Therefore, unless otherwise explicitly stated, any features and / or definitions discussed in conjunction with Figure 5 can (with appropriate modifications) be applied to the process of Figure 5 . Specifically, the initial blocks 501 to 503 of the process of Figure 4 can exactly correspond to blocks 401 to 403 of

[0113] and are therefore not discussed for the sake of brevity.

[0114] After measuring the incident direction of the electromagnetic wave in block 503, in block 504, the device determines whether the measured incident direction is different from the reference incident direction (maintained in at least one memory in block 501) to at least the extent defined by one or more predefined criteria. For example, one or more predefined criteria can define a first threshold for the difference between the elevation angles of the measured incident direction and the reference incident direction and / or a second threshold for the difference between the azimuth angles of the measured incident direction and the reference incident direction, and one or more predefined criteria can define a combined threshold for the parameter quantifying the difference between the measured incident direction and the reference incident direction (e.g., depending on the azimuth and elevation angles defined for the measured incident direction and the reference incident direction). Figure 4 described above in conjunction with block 404 of

[0115] In response to the measured incident direction in block 504 being different from the reference incident direction to at least the extent defined by one or more predefined criteria, the device calculates corrected configuration information in block 505 based on the reference incident direction, the measured incident azimuth, and the reference configuration information, similar to

[0116] At block 506, the device stores the measured incident direction and the corrected configuration information in at least one memory. Specifically, the measured incident direction and the corrected configuration information may be defined in the at least one memory as a new reference incident direction and a new reference configuration information. Thus, when the process of blocks 503 to 507 is repeated, the previously measured incident direction serves as the new reference incident direction, and the corrected configuration information is used as the reference configuration information.

[0117] At block 507, the device (re)configures the plurality of tunable load impedance circuits according to the corrected configuration information, similar to that described above in connection with Figure 4 block 405.

[0118] In some embodiments, only one of the features discussed in connection with blocks 504 and 506 may be implemented.

[0119] Figure 6 Another process according to an embodiment is shown for correcting an initial configuration of a tunable reflectarray of a RIS based on a change in the incident direction of a detected electromagnetic wave. Figure 6 The process may be performed by a device (such as a computing device) of the RIS, such as Figure 2A device 204. The RIS and its elements may be defined as described in any of the embodiments discussed in connection with Figure 2A , Figure 2B , Figure 3A and Figure 3B any one of.

[0120] Figure 6 Shows Figure 4 a more detailed implementation of the process. Thus, any of the features discussed above in connection with Figure 4 may be applied here (with appropriate modifications). In some embodiments, Figure 6 the more detailed implementation may be combined with one or more additional functions discussed in connection with Figure 5 (i.e., the functions discussed in connection with Figure 5 blocks 503 and / or 505).

[0121] Referring to Figure 6 , in block 601, the device maintains information about a reference incident direction and reference configuration information in at least one memory, similar to Figure 4The frame 401 defines multiple configurations (e.g., load impedance matrix) of the tunable load impedance circuits of the RIS's tunable reflectarray for achieving multiple different reflection beams when receiving from the reference incident direction, with reference to the configuration information. Additionally, as also mentioned above, it is assumed here that the device also maintains multiple beam codebooks in at least one memory, and the multiple beam codebooks define multiple sets of beamforming coefficients for the tunable reflectarray. The multiple beam codebooks can be defined as matrices having sizes defined by the number of reflection elements in the tunable reflectarray.

[0122] The actions related to Figure 6 frame 602 and frame 603 can be performed as described in connection with Figure 4 frame 402 and frame 403. Similar to what is described in connection with Figure 4 , frame 602 can be omitted in some embodiments.

[0123] At frame 604, the device calculates a correction matrix based on the reference incident direction and the measured incident direction. Here, the correction matrix defines multiple correction coefficients (as defined in the multiple beam codebooks) for the multiple sets of beamforming coefficients. Each element of the correction matrix represents the correction coefficient for a given beamforming coefficient associated with the corresponding tunable impedance load circuit. An example of the specific mathematical formula of the correction matrix will be discussed later.

[0124] Hereinafter, the equations for calculating the correction matrix are derived. Based on the reference incident direction and the measured incident direction (defined as θ and φ using elevation angle and azimuth angle respectively), the difference terms Δξ y and Δξ z for the y - direction and z - direction can be written as:

[0125]

[0126] Here, the symbols can be defined as described above in connection with (1) to (10). Additionally, the beamforming coefficients a c and a r defined for the r - array direction and c - array direction can be defined as follows:

[0127]

[0128] Based on (13) and (14), the (total) corrected beamforming coefficient a′ rc can be written as

[0129]

[0130] Finally, the element ω rc of the correction matrix Ω of size R×C can be defined based on (15) as

[0131]

[0132] Thus, at block 604, the device can calculate the calibration matrix according to (16). Specifically, for each combination of r = 1, 2, ..., R and c = 1, 2, ..., C, the device can calculate a value for ω according to (16) to obtain the complete calibration matrix Ω. rc to obtain the complete calibration matrix Ω.

[0133] At block 605, the device calculates the calibrated configurations of the plurality of tunable load impedance circuits based on the plurality of beam codebooks and the calibration matrix.

[0134] Specifically, calculating the calibrated configurations of the plurality of tunable load impedance circuits based on the plurality of beam codebooks and the calibrated load impedance matrix at block 605 can include the following two steps. First, calculate the plurality of calibrated beam codebooks by performing element-wise multiplication between the plurality of beam codebooks defined as a matrix and the calibration matrix. In other words, the device performs the following calculation: where A is a beam codebook matrix of size R×C, Ω is a calibration matrix of size R×C, A′ is a calibrated beam codebook matrix of size R×C and is an element-wise product operator. Second, at block 605, the device calculates the calibrated configurations of the plurality of tunable load impedance circuits based on the plurality of calibrated beam codebooks. In other words, the device determines how the plurality of tunable load impedance circuits should be configured in order to achieve the phase shifts (and possibly gains) as defined in the plurality of calibrated beam codebooks.

[0135] At block 607, similar to the device described in connection with block 405 Figure 4 the device (re)configures the plurality of tunable load impedance circuits according to the calibrated configurations defined in the calibrated configuration information. In other words, the device adjusts the current tuning of the plurality of tunable load impedance circuits in order to achieve a specific reflected beam assuming reception from the measured incident direction.

[0136] As indicated by the arrow connecting block 607 back to block 603, the measurement of the incident direction (block 603), the calculation of the calibration matrix (block 604), the calibration of the beam codebook (block 605), the calibration of the configuration information (block 606), and the reconfiguration of the plurality of tunable load impedance circuits (block 607) can be repeated periodically or regularly and / or in response to a specific trigger, such as in response to receiving a command from an access node via a control channel. For example, such a command can be received if the access node or the terminal device (or other transmission entity) scheduled to use the RIS for transmission changes (and thus it is expected that the current reference incident direction is no longer applicable or up-to-date).

[0137] In some embodiments, at Figure 4 box 403 of Figure 5 box 503 of Figure 6 or box 603 of Figure 6 the incident direction measured may, in a more general sense, correspond to an effective or combined angle of incidence defined based on multiple incident directions, where the multiple incident directions may respectively correspond to multiple multipath components of a wireless channel. The multiple multipath components may include a line-of-sight component and / or one or more non-line-of-sight components. In such a case, when measuring the (effective or combined) incident direction and calculating the correction matrix (as described in box 604 of Figure 6 ), the incident direction of each multipath component may be considered. Knowledge of the incident direction in such a multipath channel setup and knowledge of the path gain of each path may be equivalent to channel state information (CSI). Thus, instead of multiple path gains and path angles corresponding to multiple incident directions, an estimated form and / or a quantized form of the CSI may be provided to the device. Typical channel estimation techniques in wireless communication may be used to measure the CSI, for example, the least squares (LS) method or the minimum mean square error (MMSE). The device may then determine the correction matrix to be used by using a predefined look-up table and / or function that maps each CSI to a corresponding correction matrix.

[0138] As described above, in some embodiments, the RIS may include a radio receiver or transceiver, or provide a connection to an external radio receiver or transceiver, for being able to receive (and possibly transmit) control signaling from one or more access nodes via a control channel. This operation may be similar to the operation of an integrated access and backhaul mobile terminal (IAB-MT) entity. Figure 7A , Figure 7B , Figure 7C and 7D respectively illustrate four processes, involving receiving such control signaling for authentication and synchronization, configuration of the RIS, reflection beam selection, and reference incident direction selection (or equivalent or incident beam selection or TRP selection). Figure 7A , Figure 7B , Figure 7C and Figure 7D Any process of Figure 2A may be performed by a device of the RIS (such as a computing device), such as the device 204 of Figure 2A . The RIS and its elements may be defined as described in any of the embodiments discussed in conjunction with Figure 2A , Figure 2B , Figure 3A and Figure 3B . The device receives / transmits signals on the control channel via a radio receiver or transceiver, as described in conjunction with Figure 7A , Figure 7B , Figure 7C andFigure 7D As described, it can be performed using at least one (dedicated) antenna of a radio receiver or transceiver or via a tunable reflectarray of the RIS (which is assumed to be electrically connected to the radio receiver or transceiver in these embodiments).

[0139] Since the RIS is configured to receive and decode control signaling from one or more access nodes, the RIS may also need to be authenticated in the network. From the perspective of the devices included in the RIS, the authentication can be performed as Figure 7A shown here. Here, it is assumed that the RIS includes or is electrically connected to a radio transceiver.

[0140] In Figure 7A , at block 701, the device first receives an authentication request from an access node via a radio transceiver on a control channel. Thereafter, at block 702, the device transmits an authentication response to the access node via the radio transceiver on the control channel. The authentication response can specifically include the international mobile subscriber identity (IMSI) of the RIS or other such mobile station identities of the RIS.

[0141] Thereafter, at block 703, the device can perform synchronization with the access node. Specifically, the device can receive one or more network synchronization signals via the radio transceiver on the control channel to synchronize the RIS clock to the beam switching time slots defined by the network.

[0142] Figure 7B The process of Figures 4 to 6 can be performed before any process of Figure 4 because it is related to the information maintained in at least one memory of the RIS in block 401 of Figure 5 block 501 of Figure 6 or block 601 of Figure 4 . That is, at block 711, the device receives (and decodes) information about the reference incident direction and associated reference configuration information for the RIS from the access node via a radio receiver or transceiver on the control channel. The reference configuration information can be defined as described in block 401 of

[0143] Figure 7C . The information about the reference incident angle and the associated reference configuration information can be obtained by the access node, for example, using an angle-of-arrival estimation method during the transmission of a channel estimation pilot signal. Thereafter, at block 712, the device stores the reference incident direction and the reference configuration information into at least one memory. Figure 7B The process of Figure 7CIn [the figure], the device receives (and decodes) reflection beam selection configuration information from an access node (or specifically, a serving access node) on a control channel via a radio receiver or transceiver in block 721. The reflection beam selection configuration information is used to configure a plurality of tunable load impedance circuits according to a specific configuration defined in the configuration information (maintained in at least one memory). The specific configuration corresponds to a specific reflection beam implemented by the RIS. In other words, the access node can command the device to change the configuration of the RIS to match the configuration specified in the reflection beam selection configuration information. In block 722, the device configures the plurality of tunable load impedance circuits of the RIS according to the reflection beam selection configuration information so as to implement the specific reflection beam.

[0144] Reference Figure 7D , in block 731, it is initially assumed that the device maintains information about a plurality of reference incident directions and a set of reference configuration information specified by the plurality of reference incident directions in at least one memory. The set of reference configuration information specified by the plurality of reference incident directions is for a plurality of tunable impedance circuits of a tunable reflection array of the RIS (or its sub-panel). In other words, the device can maintain in at least one memory the combination of a single reference incident direction for a plurality of reference incident directions Figure 4 of any information described in block 401. The plurality of reference incident directions may be associated with a corresponding plurality of radio transmitters (or transceivers) or more specifically with an access node. Therefore, the device is configured here to reflect electromagnetic waves received from a plurality of different access nodes, where the electromagnetic waves received from any of the plurality of different access nodes can be reflected to a plurality of different radio receivers (or transceivers) using a plurality of different reflection beams.

[0145] In some embodiments, the information described in conjunction with block 731 (or a part thereof) may have been previously received from an access node on a control channel via a radio receiver or transceiver. This may correspond to repeating Figure 7B the process multiple times for a plurality of different reference incident directions. The information may have been obtained by the access node, for example, using an angle-of-arrival estimation method during the transmission of a channel estimation pilot signal. Additionally or alternatively, the information (or a part thereof) may have been stored during the installation or deployment of the RIS.

[0146] At block 732, the device receives (and decodes) incident direction selection configuration information on a control channel from an access node (or specifically, a serving access node) via a radio receiver or transceiver. The incident direction selection configuration information is used to configure multiple tunable load impedance circuits to adopt a set of reference configuration information specified by a particular reference incident direction maintained in at least one memory. The incident direction selection configuration information may equivalently be referred to as incident beam selection configuration information or source access node configuration information. The incident direction selection configuration information includes at least information about a particular reference incident direction. The particular reference incident direction may correspond to a particular currently active access node (or other radio transmitter), i.e., the access node (or other radio transmitter) currently connected to the RIS.

[0147] At block 733, the device configures the multiple tunable load impedance circuits of the RIS according to the incident direction selection configuration information so as to be able to receive and reflect electromagnetic waves from a particular reference incident direction (or from a particular access node assumed to be located in the particular reference incident direction).

[0148] A particular configuration for the multiple tunable load impedance circuits may be selected from the set of reference configuration information specified by the reference incident direction, e.g., according to the process described in conjunction with Figure 7C the process described.

[0149] For Figure 7D an example use case of the process is a multi-TRP deployment with dynamic point selection. For example, in an indoor factory, depending on which TRP is selected for transmission, the RIS may be associated with a new reference incident direction.

[0150] In some embodiments, message 721, message 732 may be combined into a single message. Once such a combined message is received from the access node on the control channel, the configuration processes of block 722, block 733 may be performed one after another or in parallel. In other words, the reflected beam selection and the reference incident direction selection may be performed substantially simultaneously.

[0151] In some alternative embodiments, message 721, message 732 or a combination thereof may define a schedule that defines a periodic or regular switching between a determined reference incident direction and / or different individual reflected beams defined by different reference incident directions, similar to that described in conjunction with Figure 8 the process described below. Then, the device may configure the multiple tunable load impedance circuits according to the schedule.

[0152] Although Figure 7A , Figure 7B , Figure 7C and Figure 7Dshows a process of a RIS for communicating with an access node that is performed by a device, but it should be understood that corresponding processes can also be provided for the access node side. In other words, the access node can

[0153] ● Transmit an authentication request to the RIS on a control channel and subsequently receive an authentication response from the RIS on the control channel,

[0154] · Transmit information about a reference incident direction and associated reference configuration information for the RIS to the RIS on a control channel,

[0155] ● Transmit reflection beam selection information to the RIS on a control channel, and / or ● Transmit reference incident direction selection information to the RIS on a control channel.

[0156] In the case of a simpler RIS according to an embodiment without a radio receiver or transceiver (and thus unable to use a control channel to receive control data from an access node), the functions described in conjunction with Figure 7A and Figure 7B can be performed by connecting a computer (using a wired or wireless link) to the RIS during the installation or deployment of the RIS. It should be noted that synchronization may also be useful for such a simpler RIS as it enables, for example, periodic switching between reflection beam patterns synchronized with the network.

[0157] As described above, in some embodiments, the RIS may not include a radio receiver or transceiver and does not provide a connection to an external radio receiver or transceiver, and dynamic reflection beam selection as described in conjunction with Figure 7C and dynamic (reference) incident direction (or incident beam or TRP) selection as described in conjunction with Figure 7D are not possible. Figure 8 Alternative processes are provided to enable such a simpler RIS to use different reflection beams corresponding to one or more different reference incident directions configured for it without accessing the access node via a control channel. Figure 8 The process of Figure 2A can be performed by a device (e.g., a computing device) of the RIS, such as Figure 2A 、 Figure 2B 、 Figure 3A and Figure 3B The RIS and its elements can be defined as described in any of the embodiments discussed in conjunction with any one of

[0158] Refer to Figure 8, at block 801, the apparatus initially maintains in at least one memory information regarding one or more reference incident directions and a set of reference configuration information specified by one or more associated reference incident directions, the set of reference configuration information specified by one or more associated reference incident directions defining a plurality of configurations of the tunable load impedance circuits of the tunable reflection array of the RIS for achieving a plurality of different reflected beams upon reception occurring from any one of the one or more reference incident directions. Block 801 may exactly correspond to Figure 4 block 401.

[0159] In addition, at block 802, the apparatus maintains in at least one memory reflected beam and / or reference incident direction scheduling configuration information, the reference incident direction scheduling configuration information defining a periodic or regular scheduling of different reflected beams, with configurations of the plurality of tunable load impedance circuits defined for different reflected beams in the configuration information. The scheduled reflected beams may be associated with the one or more reference incident directions (i.e., in some cases, beam scheduling may involve reflected beams related to multiple different reference incident directions). For example, during installation or deployment of the RIS, the reflected beam scheduling and / or reference incident direction configuration information may have been stored in at least one memory.

[0160] At block 803, the apparatus configures the plurality of tunable load impedance circuits according to the beam scheduling and / or reference incident direction configuration information. In other words, the reflected beams of the RIS are switched according to a predefined schedule defined by the beam scheduling configuration information. The configuration at block 803 may be executed continuously in parallel with any process in Figures 4 to 6 . For a simple example, in the case of two TRP settings (i.e., configuring the RIS to adopt two different reference incident directions), a first set of reflected beams associated with a first reference incident angle may be scanned first, and then a second set of reflected beams associated with a second reference incident angle may be scanned.

[0161] The above-described blocks, related functions, and information exchanges through Figures 4 to 6 , Figure 7A , Figure 7B , Figure 7C , Figure 7D and Figure 8 do not have an absolute chronological order, and some of them may be executed simultaneously or in an order different from the given order. Other functions may also be executed between or within them, and other information may be sent and / or received, and / or other mapping rules may be applied. Some of the blocks or parts of blocks or one or more pieces of information in the blocks may also be omitted or replaced by corresponding blocks or parts of blocks or one or more pieces of information.

[0162] In an embodiment, at least one processor, a memory, and computer program code form a processing component or include one or more portions of computer program code for performing one or more operations in accordance with any one of the embodiments of Figure 2A , Figure 2B , Figure 3A , Figure 3B , Figures 4 to 6 , Figure 7A , Figure 7B , Figure 7C , Figure 7D and Figure 8 or one or more operations of its operation.

[0163] In one embodiment, in combination with Figure 2A , Figure 2B , Figure 3A , Figure 3B , Figures 4 to 6 , Figure 7A , Figure 7B , Figure 7C , Figure 7D and Figure 8 at least some of the processes described can be performed by a device including corresponding components for performing at least some of the described processes. Some example devices for performing the processes can include at least one of the following: a detector, a processor (including dual-core and multi-core processors), a digital signal processor, a controller, a receiver, a transmitter, an encoder, a decoder, a memory, a RAM, a ROM, software, firmware, a display, a user interface, a display circuit, a user interface circuit, user interface software, display software, a circuit, an antenna, an antenna circuit, and a circuit, a memory, and computer program code form a processing device, or include one or more portions of computer program code for performing one or more operations in accordance with any one of the embodiments of Figure 2A , Figure 2B , Figure 3A , Figure 3B , Figures 4 to 6 , Figure 7A , Figure 7B , Figure 7C , Figure 7D and Figure 8 or one or more operations of its operation.

[0164] According to one aspect, there is provided a device (e.g., a computing device) that includes components for performing the following operations:

[0165] Maintain, in at least one memory, information regarding a reference incident direction and reference configuration information, the reference configuration information defining multiple configurations of a plurality of tunable load impedance circuits of a tunable reflection array of a reconfigurable intelligent surface or a sub-panel thereof for achieving a plurality of different reflected beams upon reception from the reference incident direction;

[0166] Measure the incident direction of electromagnetic waves received by the reconfigurable intelligent surface;

[0167] Calculate corrected configuration information based on a reference incident direction, the measured incident direction, and reference configuration information, the corrected configuration information defining a plurality of corrected configurations of a plurality of tunable load impedance circuits for achieving a plurality of different reflected beams upon reception from the measured incident direction; and

[0168] Configure the plurality of tunable load impedance circuits according to the corrected configurations defined in the corrected configuration information.

[0169] The techniques and methods described herein can be implemented by various components. For example, these techniques can be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or combinations thereof. For a hardware implementation, the (multiple) devices of an embodiment can be implemented in one or more of the following: application specific integrated circuit (ASIC), digital signal processor (DSP), digital signal processing device (DSPD), programmable logic device (PLD), field programmable gate array (FPGA), processor, controller, microcontroller, microprocessor, other electronic units designed to perform the functions described herein, or combinations thereof. For firmware or software, it can be implemented by a module (procedure, function, etc.) of at least one chipset that performs the functions described herein. The software code can be stored in a memory unit and executed by a processor. The memory unit can be implemented within the processor or outside the processor. In the latter case, it can be communicatively coupled to the processor by various components known in the art. In addition, the components of the systems described herein can be rearranged and / or supplemented by additional components to facilitate the implementation of the various aspects described thereof, etc., and they are not limited to the exact configurations set forth in the given drawings, as will be understood by those skilled in the art.

[0170] The described embodiments can also be executed in the form of a computer program or a computer process defined by a part thereof. In combination with Figure 2A 、 Figure 2B 、 Figure 3A 、 Figure 3B 、 Figures 4 to 6 、 Figure 7A 、 Figure 7B 、 Figure 7C 、 Figure 7D and Figure 8Embodiments of the described method can be carried out by executing at least a portion of a computer program that includes corresponding instructions. The computer program can be provided as a computer-readable medium including program instructions stored thereon, or as a non-transitory computer-readable medium including program instructions stored thereon, or in some intermediate form, and it can be stored in some carrier, which can be any entity or device capable of carrying the program. For example, the computer program can be stored on a computer program distribution medium readable by a computer or a processor. For example, the computer program medium can be, for example but not limited to, a recording medium, a computer memory, a read-only memory, an electrical carrier signal, a telecommunication signal, and a software distribution package. The computer program medium can be a non-transitory medium. The code for the software for carrying out the illustrated and described embodiments is entirely within the scope of those of ordinary skill in the art.

[0171] A computer program stored in a computer-readable storage medium, the program including software code for performing the following steps:

[0172] In at least one memory, maintain information about a reference incident direction and reference configuration information, the reference configuration information defining multiple configurations of multiple tunable load impedance circuits of a tunable reflection array of a reconfigurable intelligent surface or a sub-panel thereof for achieving multiple different reflection beams when receiving from the reference incident direction;

[0173] Measure the incident direction of an electromagnetic wave received by the reconfigurable intelligent surface;

[0174] Based on the reference incident direction, the measured incident direction, and the reference configuration information, calculate corrected configuration information, the corrected configuration information defining multiple corrected configurations of multiple tunable load impedance circuits for achieving multiple different reflection beams when receiving from the measured incident direction; and

[0175] Configure multiple tunable load impedance circuits according to the corrected configurations defined in the corrected configuration information.

[0176] A computer-readable storage medium having a computer program, wherein the computer program is executable by a processor to cause the processor to perform the following method:

[0177] In at least one memory, maintain information about a reference incident direction and reference configuration information, the reference configuration information defining multiple configurations of multiple tunable load impedance circuits of a tunable reflection array of a reconfigurable intelligent surface or a sub-panel thereof for achieving multiple different reflection beams when receiving from the reference incident direction;

[0178] Measure the incident direction of an electromagnetic wave received by the reconfigurable intelligent surface;

[0179] Calculate corrected configuration information based on a reference incident direction, a measured incident direction, and reference configuration information, the corrected configuration information defining corrected configurations of a plurality of tunable load impedance circuits for achieving a plurality of different reflected beams upon reception from the measured incident direction; and

[0180] Configure the plurality of tunable load impedance circuits according to the corrected configuration defined in the corrected configuration information.

[0181] A computer program product embodied on a computer-readable distribution medium, the computer program product including program instructions that, when loaded into a device, execute a method that includes:

[0182] Maintain, in at least one memory, information regarding a reference incident direction and reference configuration information, the reference configuration information defining a plurality of configurations of a tunable reflection array of a reconfigurable intelligent surface or a sub-panel thereof for achieving a plurality of different reflected beams upon reception from the reference incident direction;

[0183] Measure an incident direction of electromagnetic waves received by the reconfigurable intelligent surface;

[0184] Calculate corrected configuration information based on the reference incident direction, the measured incident direction, and the reference configuration information, the corrected configuration information defining corrected configurations of a plurality of tunable load impedance circuits for achieving a plurality of different reflected beams upon reception from the measured incident direction; and

[0185] Configure the plurality of tunable load impedance circuits according to the corrected configuration defined in the corrected configuration information.

[0186] Although the present invention has been described above with reference to embodiments according to the drawings, it is obvious that the present invention is not limited thereto, but can be modified in various ways within the scope of the appended claims. Accordingly, all words and expressions should be interpreted broadly, and they are intended to illustrate rather than limit the embodiments. It is obvious to those skilled in the art that, with the progress of technology, the inventive concept can be implemented in various ways. In addition, it is clear to those skilled in the art that the described embodiments can, but do not require to, be combined with other embodiments in various ways.

Claims

1. An apparatus for a reconfigurable intelligent surface, comprising: at least one processor, and at least one memory for storing instructions to be executed by the at least one processor, wherein the at least one memory and the instructions are configured to cause the apparatus, together with the at least one processor, to at least perform: maintain, in the at least one memory, information about a reference incident direction and reference configuration information, the reference configuration information defining a plurality of configurations of a plurality of tunable load impedance circuits of a tunable reflection array of the reconfigurable intelligent surface or a sub-panel thereof, the plurality of configurations being for achieving a plurality of different reflection beams when reception occurs from the reference incident direction; maintain, in the at least one memory, a plurality of beam codebooks, the plurality of beam codebooks defining a plurality of sets of beamforming coefficients for the tunable reflection array, wherein the plurality of sets of beamforming coefficients at least define phases for achieving the plurality of different reflection beams that can be induced by the plurality of tunable load impedance circuits; measure an incident direction at which an electromagnetic wave is received by the reconfigurable intelligent surface; calculate corrected configuration information based on the reference incident direction, the measured incident direction, and the reference configuration information, the corrected configuration information defining a plurality of corrected configurations of the plurality of tunable load impedance circuits for achieving the plurality of different reflection beams when reception occurs from the measured incident direction, the calculation being by calculating a correction matrix based on the reference incident direction and the measured incident direction, and by calculating the plurality of corrected configurations of the plurality of tunable load impedance circuits based on the plurality of beam codebooks and the correction matrix, wherein the correction matrix defines a plurality of correction coefficients for the plurality of sets of beamforming coefficients; and configure the plurality of tunable load impedance circuits according to the corrected configurations defined in the corrected configuration information.

2. The apparatus according to claim 1, wherein the plurality of tunable load impedance circuits are tunable load impedance circuits of the sub-panel of the reconfigurable intelligent surface, and the at least one memory and the instructions are configured to cause the apparatus, together with the at least one processor, to at least repeat, for one or more additional sub-panels of the reconfigurable intelligent surface, the maintaining of the information about the reference incident direction and the reference configuration information, the maintaining of the plurality of beam codebooks, the measuring of the incident direction at which the electromagnetic wave is received by the reconfigurable intelligent surface, the calculating of the corrected configuration information, and the configuring of the plurality of tunable load impedance circuits, the one or more additional sub-panels being associated with a reference incident direction that is different from or the same as that of the sub-panel.

3. The apparatus according to claim 1 or 2, wherein the at least one memory and the instructions are configured to cause the apparatus, together with the at least one processor, to perform: Store the measured incident direction and the corrected configuration information in the at least one memory, wherein in the at least one memory, the measured incident direction and the corrected configuration information are defined as a new reference incident direction and a new reference configuration information.

4. The apparatus according to claim 1 or 2, wherein the at least one memory and the instructions are configured to, together with at least one processor, cause the apparatus to perform before the measurement: Configure the plurality of tunable load impedance circuits according to the configuration defined in the configuration information.

5. The apparatus according to claim 4, wherein the at least one memory and the instructions are configured to, together with the at least one processor, cause the apparatus to perform: Before the calculation of the corrected configuration information, determine whether the measured incident direction is different from the reference incident direction at least to an extent defined by one or more predefined criteria; and In response to the measured incident direction being different from the reference incident direction based on the one or more predefined criteria, perform the calculation of the corrected configuration information and the configuration of the plurality of tunable load impedance circuits according to the corrected configuration.

6. The apparatus according to claim 1 or 2, wherein the at least one memory and the instructions are configured to, together with the at least one processor, cause the apparatus to perform: Tune the plurality of tunable load impedance circuits at least by adjusting the phase shift induced by a plurality of tunable phase shift elements included in the plurality of tunable load impedance circuits.

7. The apparatus according to claim 1 or 2, wherein the plurality of corrected configurations of the plurality of tunable load impedance circuits are calculated based on the plurality of beam codebooks and the corrected load impedance matrix comprises: Calculate a plurality of corrected beam codebooks by performing element-wise multiplication between the plurality of beam codebooks defined as a matrix and the correction matrix; and Calculate the plurality of corrected configurations of the plurality of tunable load impedance circuits based on the plurality of corrected beam codebooks.

8. The apparatus according to claim 1 or 2, wherein at least some of the plurality of tunable impedance load circuits are active circuits, and correspondingly, at least some of the plurality of sets of beamforming coefficients define both the phase and the gain that can be induced by the at least some of the plurality of tunable impedance load circuits.

9. The apparatus according to claim 1 or 2, wherein the at least one memory and the instructions are configured to, together with the at least one processor, cause the apparatus to perform before the maintenance: Receive information about the reference incident direction and the reference configuration information from an access node on a control channel via a radio receiver or transceiver; and Store the reference incident direction and the reference configuration information in the at least one memory.

10. The apparatus according to claim 1 or 2, wherein the at least one memory and the instructions are configured to, together with the at least one processor, cause the apparatus to perform: In the at least one memory, beam scheduling configuration information is maintained, the beam scheduling configuration information defining a periodic or regular scheduling of different reflection beams, and configurations of the plurality of tunable load impedance circuits being defined in the configuration information for the different reflection beams; and Configure the plurality of tunable load impedance circuits according to the beam scheduling configuration information.

11. The apparatus according to claim 1 or 2, wherein the at least one memory and the instructions are configured to, together with the at least one processor, cause the apparatus to perform: Receive, via a radio receiver or transceiver, on a control channel, reflection beam selection configuration information from an access node, the reflection beam selection configuration information for configuring the plurality of tunable load impedance circuits according to a specific configuration defined in the configuration information and corresponding to a specific reflection beam; and Configure the plurality of tunable load impedance circuits according to the reflection beam selection configuration information so as to implement the specific reflection beam.

12. The apparatus according to claim 1 or 2, wherein the at least one memory and the instructions are configured to, together with the at least one processor, cause the apparatus to perform: In the at least one memory, maintain information on a plurality of reference incident directions and a set of reference configuration information specified by the plurality of reference incident directions, the set of reference configuration information specified by the plurality of reference incident directions defining a plurality of configurations of the plurality of tunable load impedance circuits for implementing a plurality of different reflection beams when reception occurs from the plurality of reference incident directions, wherein the plurality of reference incident directions includes the reference incident direction; Receive, via a radio receiver or transceiver, on a control channel, from an access node, reference incident direction selection configuration information for configuring the plurality of tunable load impedance circuits to use the set of reference configuration information specified by a specific reference incident direction; And Configure the plurality of tunable load impedance circuits according to the reference incident direction selection configuration information.

13. A reconfigurable intelligent surface, Comprising: A tunable reflection array including a plurality of reflection elements and a plurality of tunable load impedance circuits, the plurality of tunable load impedance circuits being electrically connected to the plurality of reflection elements for affecting the phase of electromagnetic waves reflected by the plurality of reflection elements; And An apparatus for configuring the plurality of tunable load impedance circuits, the apparatus including: At least one processor, and At least one memory for storing instructions to be executed by the processor, wherein the at least one memory and the instructions are configured to, together with the at least one processor, cause the apparatus to at least perform: In the at least one memory, maintain information on a reference incident direction and reference configuration information, the reference configuration information defining a plurality of configurations of the plurality of tunable load impedance circuits of the tunable reflection array of the reconfigurable intelligent surface or a sub-panel thereof for implementing a plurality of different reflection beams when reception occurs from the reference incident direction; In the at least one memory, a plurality of beam codebooks are maintained, the plurality of beam codebooks defining multiple sets of beamforming coefficients for the tunable reflectarray, wherein the multiple sets of beamforming coefficients at least define phases for implementing the multiple different reflected beams that can be induced by the plurality of tunable load impedance circuits; Measure the incident direction of the electromagnetic wave received by the reconfigurable intelligent surface; Calculate corrected configuration information based on the reference incident direction, the measured incident direction, and the reference configuration information, the corrected configuration information defining multiple corrected configurations of the plurality of tunable load impedance circuits for implementing the multiple different reflected beams when receiving occurs from the measured incident direction, the calculation being by calculating a correction matrix based on the reference incident direction and the measured incident direction, and by calculating the multiple corrected configurations of the plurality of tunable load impedance circuits based on the plurality of beam codebooks and the correction matrix, wherein the correction matrix defines multiple correction coefficients for the multiple sets of beamforming coefficients; and Configure the plurality of tunable load impedance circuits according to the corrected configurations defined in the corrected configuration information.

14. The reconfigurable intelligent surface according to claim 13, further comprising: A radio receiver or transceiver for receiving one or more control signals from one or more access nodes via a control channel.

15. A system for a reconfigurable intelligent surface, comprising: A reconfigurable intelligent surface and an access node, The reconfigurable intelligent surface includes a tunable reflectarray, a radio receiver or transceiver for receiving one or more control signals from one or more access nodes via a control channel, and a device, wherein the tunable reflectarray includes a plurality of reflective elements and a plurality of tunable load impedance circuits, the plurality of tunable load impedance circuits being electrically connected to the plurality of reflective elements for influencing the phase of the electromagnetic wave reflected by the plurality of reflective elements; and wherein the device includes at least one processor and at least one memory for storing instructions to be executed by the processor, wherein the at least one memory and the instructions are configured to cause the device to at least perform with the at least one processor: In the at least one memory, maintain information about a reference incident direction and reference configuration information, the reference configuration information defining multiple configurations of the plurality of tunable load impedance circuits of the tunable reflectarray of the reconfigurable intelligent surface or its sub-panel for implementing multiple different reflected beams when receiving occurs from the reference incident direction; In the at least one memory, maintain a plurality of beam codebooks, the plurality of beam codebooks defining multiple sets of beamforming coefficients for the tunable reflectarray, wherein the multiple sets of beamforming coefficients at least define phases for implementing the multiple different reflected beams that can be induced by the plurality of tunable load impedance circuits; Measure the incident direction of the electromagnetic wave received by the reconfigurable intelligent surface; Calculating corrected configuration information based on the reference incident direction, the measured incident direction, and the reference configuration information, where the corrected configuration information defines multiple corrected configurations of the multiple tunable load impedance circuits for achieving the multiple different reflection beams when receiving from the measured incident direction, and the calculation is by calculating a correction matrix based on the reference incident direction and the measured incident direction, and by calculating the multiple corrected configurations of the multiple tunable load impedance circuits based on the multiple beam codebooks and the correction matrix, where the correction matrix defines multiple correction coefficients for the multiple sets of beamforming coefficients; and Configuring the multiple tunable load impedance circuits according to the corrected configurations defined in the corrected configuration information; The access node includes at least one processor and at least one memory for storing instructions to be executed by the processor, where the at least one memory and the instructions are configured to cause the access node to transmit one or more control signals to the reconfigurable intelligent surface at least via a control channel.

16. A method for a reconfigurable intelligent surface, comprising: Maintaining, in at least one memory, information about a reference incident direction and reference configuration information, where the reference configuration information defines multiple configurations of multiple tunable load impedance circuits of a tunable reflection array of the reconfigurable intelligent surface or its sub-panel for achieving multiple different reflection beams when receiving from the reference incident direction; Maintaining, in the at least one memory, multiple beam codebooks that define multiple sets of beamforming coefficients for the tunable reflection array, where the multiple sets of beamforming coefficients at least define the phases that can be induced by the multiple tunable load impedance circuits for achieving the multiple different reflection beams; Measuring the incident direction of an electromagnetic wave received by the reconfigurable intelligent surface; Calculating corrected configuration information based on the reference incident direction, the measured incident direction, and the reference configuration information, where the corrected configuration information defines multiple corrected configurations of the multiple tunable load impedance circuits for achieving the multiple different reflection beams when receiving from the measured incident direction, and the calculation is by calculating a correction matrix based on the reference incident direction and the measured incident direction, and by calculating the multiple corrected configurations of the multiple tunable load impedance circuits based on the multiple beam codebooks and the correction matrix, where the correction matrix defines multiple correction coefficients for the multiple sets of beamforming coefficients; and Configuring the multiple tunable load impedance circuits according to the corrected configurations defined in the corrected configuration information.

17. A computer program product embodied on a non-transitory computer-readable medium, comprising program instructions that, when run, are adapted to execute: Maintain, in at least one memory, information regarding a reference incident direction and reference configuration information, the reference configuration information defining multiple configurations of a plurality of tunable load impedance circuits of a tunable reflection array of a reconfigurable intelligent surface or a sub-panel thereof for achieving multiple different reflection beams when reception occurs from the reference incident direction; Maintain, in the at least one memory, a plurality of beam codebooks, the plurality of beam codebooks defining multiple sets of beamforming coefficients for the tunable reflection array, wherein the multiple sets of beamforming coefficients at least define phases for achieving the multiple different reflection beams that can be induced by the plurality of tunable load impedance circuits; Measure an incident direction at which electromagnetic waves are received by the reconfigurable intelligent surface; Calculate corrected configuration information based on the reference incident direction, the measured incident direction, and the reference configuration information, the corrected configuration information defining multiple corrected configurations of the plurality of tunable load impedance circuits for achieving the multiple different reflection beams when reception occurs from the measured incident direction, the calculation being performed by calculating a correction matrix based on the reference incident direction and the measured incident direction, and by calculating the multiple corrected configurations of the plurality of tunable load impedance circuits based on the plurality of beam codebooks and the correction matrix, wherein the correction matrix defines multiple correction coefficients for the multiple sets of beamforming coefficients; And Configure the plurality of tunable load impedance circuits according to the corrected configurations defined in the corrected configuration information.

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