THE SAME

TECHNICAL FIELD

The present disclosure relates generally to the field of wireless communications, and particularly to a wireless signal reflector and a method for performing wireless communications by using the wireless signal reflector.

BACKGROUND

During recent years, a new direction has emerged in the field of wireless communications, which is related to a programmable radio environment or Smart Radio Environment (SRE). The SRE implies the ability to control a transmission environment through one or more special wireless signal reflectors referred to as, e.g., Intelligent Reflecting Surfaces (IRSs), Reconfigurable Intelligent Surfaces (RISs), and Large Intelligent Surfaces (LISs). The research already started in this direction is expected to achieve basic parameters of wireless network operation, such as a data rate, throughput, latency, energy consumption, reliability, etc., up to levels sufficient for dealing with future 6G wireless networks in which peak data rates should reach 1 Tbit/s.

Although there are many works dedicated to the IRS-related direction, comparatively little attention is paid to the interaction of an IRS with network objects, such as a user equipment (UE) and a network node (e.g., an access point, base station, evolved Node B (eNodeB), Next Generation Node B (gNB), etc.). It is possible to split the IRS operation into two separate phases: an initialization (or reconfiguration) phase and a normal operation phase. During the initialization phase, an IRS control system estimates information about a transmission environment and reconfigures an IRS state according to the obtained estimation. Since the transmission environment characteristics change over time, the IRS control system should periodically update the IRS state. This may be done during the reconfiguration phase. Most of recent research works draw the main attention to the normal operation phase of the IRS. Thus, the existing IRS-control systems do not provide flexibility for the deployment of IRS-assisted wireless networks. SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure.

It is an objective of the present disclosure to provide a technical solution that improves communications between a wireless signal reflector (e.g., an IRS) and network objects (e.g., a network node, a UE), which are in direct visibility with the wireless signal reflector.

One or more of the objectives above is achieved by the features of the independent claims in the appended claims. Further embodiments and examples are apparent from the dependent claims, the detailed description and the accompanying drawings.

According to a first aspect, a wireless signal reflector is provided. The wireless signal reflector comprises a plurality of reflecting elements, a first sensing element and a second sensing element that are adjacent to each other, and a control unit. The reflecting elements are configured to reflect a wireless signal from a source network object towards a target network object. Each of the reflecting elements has controllable reflective properties, and the reflected wireless signal has a directivity pattern. The first sensing element is configured to receive the wireless signal and generate a first sensing signal based on the wireless signal. The second sensing element is configured to receive the wireless signal and generate a second sensing signal based on the wireless signal. The control unit is configured to determine a direction of arrival of the wireless signal based on the first sensing signal and the second sensing signal. The control unit is further configured to use the determined direction of arrival of the wireless signal to control the reflective properties of one or more reflecting elements of the plurality of reflecting elements such that they provide the directivity pattern of the reflected wireless signal. Thus, the wireless signal reflector according to the first aspect may find appropriate configuration for its reflecting elements on its own, even without any help of the target network object. Given this, the wireless signal reflector according to the first aspect may operate in dynamically changing transmission environments, which is viable for cases when it is impossible to estimate the location of the target network object in advance.

In one embodiment of the first aspect, the control unit is configured to determine the direction of arrival of the wireless signal by performing phase-difference measurements on the first sensing signal and the second sensing signal. By using the phase-difference measurements, it is possible to properly determine the direction of arrival of the wireless signal from the source network object. In one embodiment of the first aspect, the first sensing element and the second sensing element comprise patch antennas. The patch antennas may be mounted next to each other on the same flat surface as the reflecting elements, thereby making the wireless signal reflector according to the first aspect more compact. Moreover, by using the adjacent patch antennas, it is possible to increase the accuracy of determining the direction of arrival of the wireless signal from the source network object and, therefore, the efficiency of controlling the reflective properties of the reflecting elements.

In one embodiment of the first aspect, the control unit is configured to control the reflective properties of the one or more reflecting elements by generating and sending an individual control signal to each of the one or more reflecting elements. The possibility of using digital and analog control signals may increase the flexibility-in-use of the wireless signal reflector according to the first aspect. Moreover, by using individual control signals, it is possible to control the reflecting elements more efficiently.

In one embodiment of the first aspect, the wireless signal reflector further comprises a probing element configured to emit a reference signal towards the target network object. In this embodiment, the first sensing element and the second sensing element are further configured to receive the reference signal reflected from the target network object and generate a third sensing signal and a fourth second sensing signal, respectively. In turn, the control unit is further configured to: determine a distance to the target network object based on one of the third sensing signal and the fourth sensing signal; determine a direction of arrival of the reference signal based on the third sensing signal and the fourth sensing signal; and based on the determined distance to the target network object, the determined direction of arrival of the wireless signal, and the determined direction of arrival of the reference signal, control the reflective properties of the one or more reflecting elements to provide the directivity pattern of the reflected wireless signal.

By using the determined distance to the target network object and the determined direction of arrival of the reference signal in addition to the determined direction of arrival of the wireless signal, it is possible to control the reflective properties of the reflecting elements more efficiently.

In one embodiment of the first aspect, the control unit is configured to determine the distance to the target network object by performing at least one of round-trip time measurements and amplitude measurements on one of the third sensing signal and the fourth sensing signal. By using these measurements, it is possible to properly determine the distance to the target network object. Moreover, the possibility of choosing among the round-trip time measurements, the amplitude measurements, and their combination may increase the flexibility-in-use of the wireless signal reflector according to the first aspect.

In one embodiment of the first aspect, the control unit is configured to determine the direction of arrival of the reference signal by performing phase-difference measurements on the third sensing signal and the fourth sensing signal. By using the phase-difference measurements, it is possible to properly determine the direction of arrival of the reference signal from the target network object.

In one embodiment of the first aspect, the control unit comprises a power meter configured to perform the amplitude measurements, and a mixer and a low-pass filter which are configured to perform the phase-difference measurements. This configuration of the control unit is easy to implement and at the same time provides the acceptable accuracy of the amplitude measurements and the phase-difference measurements.

In one embodiment of the first aspect, the probing element, the first sensing element, and the second sensing element are arranged in at least two transceiving patch antennas. By using the same patch antennas as both the probing and sensing elements, it is possible to increase the compactness of the wireless signal reflector according to the first aspect.

In one embodiment of the first aspect, the reflector has a planar layered structure comprising an upper layer and a lower layer. The upper layer comprises the plurality of reflecting elements, the probing element, the first sensing element, and the second sensing element, and the lower layer comprises the control unit. By so doing, it is possible to implement the wireless signal reflector as an IRS.

In one embodiment of the first aspect, the probing element is configured to emit the reference signal with a wavelength selected based on a spacing between the first sensing element and the second sensing element. With such a wavelength, it is possible to increase the accuracy of determining the direction of arrival of the reference signal from the target network object.

In one embodiment of the first aspect, the wireless signal reflector further comprises an amplifier configured to amplify each of the third sensing signal and the fourth sensing signal to a predefined signal level. This may increase the accuracy of determining the distance to the target network object.

In one embodiment of the first aspect, the probing element is configured to emit the reference signal as a predefined signal sequence or a defined coded signal. This may make the wireless signal reflector according to the first aspect more flexible in use, as well as may increase the accuracy of determining the distance to the target network object and the direction of arrival of the reference signal from the target network node.

According to a second aspect, a method for performing wireless communications is provided. The method comprises the step of reflecting, by a wireless signal reflector, a wireless signal from a source network object towards a target network object. The wireless signal reflector comprises a plurality of reflecting elements, a first sensing element and a second sensing element adjacent to each other, and a control unit. Each of the reflecting elements has controllable reflective properties, and the reflected wireless signal has a directivity pattern. The step of reflecting comprises: receiving the wireless signal by the first sensing element and the second sensing elements; based on the wireless signal, generating a first sensing signal and a second sensing signal by the first sensing element and the second sensing element, respectively; determining, by the control unit, a direction of arrival of the wireless signal based on the first sensing signal and the second sensing signal; and based on the determined direction of arrival of the wireless signal, controlling, by the control unit, the reflective properties of one or more reflecting elements of the plurality of reflecting elements to provide the directivity pattern of the reflected wireless signal.

By so doing, it is possible to transmit wireless signals even if the source and target network objects are not in each other's field of view, as well as to avoid communication loss between the source and target network objects.

In one embodiment of the second aspect, each of the source network object and the target network object comprises one of a UE, a network node, and another wireless signal reflector. This may allow one to transmit wireless signals between different network objects, thereby making the method according to the second aspect more flexible in use.

Other features and advantages of the present disclosure will be apparent upon reading the following detailed description and reviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is explained below with reference to the accompanying drawings in which:

FIG. 1 schematically shows an IRS in accordance with the prior art; FIG. 2 schematically shows a discretized IRS in accordance with the prior art;

FIG. 3 schematically shows one possible operational principle of each meta-atom of the IRS shown in FIG. 2;

FIG. 4 shows a schematic block diagram of a wireless signal reflector in accordance with one exemplary embodiment;

FIG. 5 shows the wireless signal reflector implemented as a planar layered structure in accordance with one exemplary embodiment;

FIG. 6 shows a schematic isometric view of an upper layer of the planar layered structure shown in FIG. 5; FIG. 7 shows a schematic circuit of a control unit of the wireless signal reflector in accordance with one exemplary embodiment;

FIG. 8 explains how to implement a Direction of Arrival (DoA) estimation algorithm;

FIG. 9 shows a flowchart of a method for performing wireless communications in accordance with one exemplary embodiment; FIG. 10 shows a schematic diagram of an IRS-assisted wireless communication network in accordance with one exemplary embodiment;

FIG. 11 shows a schematic diagram of a multi-IRS-assisted wireless communication network in accordance with one exemplary embodiment;

FIG. 12 shows an estimated angle of arrival (AoA) of a wireless signal as a function of a spacing between adjacent sensing elements of the wireless signal reflector implemented as an IRS;

FIG. 13 schematically shows how a receiver (RX) representing a target network node may be located or oriented relative to an IRS like the wireless signal reflector shown in FIG. 5; and

FIG. 14 shows an error rate of the estimated AoA as a function of an angle of departure of the wireless signal relative to the RX.

DETAILED DESCRIPTION

Various embodiments of the present disclosure are further described in more detail with reference to the accompanying drawings. However, the present disclosure may be embodied in many other forms and should not be construed as limited to any certain structure or function discussed in the following description. In contrast, these embodiments are provided to make the description of the present disclosure detailed and complete.

According to the detailed description, it will be apparent to the ones skilled in the art that the scope of the present disclosure encompasses any embodiment thereof, which is disclosed herein, irrespective of whether this embodiment is implemented independently or in concert with any other embodiment of the present disclosure. For example, the apparatus and method disclosed herein may be implemented in practice by using any numbers of the embodiments provided herein. Furthermore, it should be understood that any embodiment of the present disclosure may be implemented using one or more of the features presented in the appended claims.

The word “exemplary” is used herein in the meaning of “used as an illustration”. Unless otherwise stated, any embodiment described herein as “exemplary” should not be construed as preferable or having an advantage over other embodiments.

According to the embodiments disclosed herein, a wireless signal reflector may refer to a device configured to reflect or forward a wireless signal coming from a source network object to a target network object, without having to perform any processing of the wireless signal. For example, the wireless signal reflector may be implemented as an IRS, RIS, LIS, etc. However, it should be noted that the present disclosure is not limited to these certain wireless signal reflectors, and any other types of the wireless signal reflector are possible as long as they allow implementing the aspects disclosed herein. In particular, it is important that such a wireless signal reflector could have controllable reflective properties.

As used in the embodiments disclosed herein, a network object may refer to a device configured to participate in wireless communications in a wireless communication network. For example, such a network object may be implemented as a user equipment (UE), a network node, or a wireless signal reflector.

The UE may refer to a mobile device, a mobile station, a terminal, a subscriber unit, a mobile phone, a cellular phone, a smart phone, a cordless phone, a personal digital assistant (PDA), a wireless communication device, a desktop computer, a laptop computer, a tablet computer, a gaming device, a netbook, a smartbook, an ultrabook, a medical device or medical equipment, a biometric sensor, a wearable device (for example, a smart watch, smart glasses, a smart wrist band, etc.), an entertainment device (for example, an audio player, a video player, etc.), a vehicular component or sensor, a smart meter/sensor, an unmanned vehicle (e.g., an industrial robot, a quadcopter, etc.), industrial manufacturing equipment, a global positioning system (GPS) device, an Internet-of-Things (loT) device, an Industrial loT (lloT) device, a machine-type communication (MTC) device, a group of Massive loT (MloT) or Massive MTC (mMTC) devices/sensors, or any other suitable device configured to support wireless communications. In some embodiments, the UE may refer to at least two collocated and inter- connected UEs thus defined.

The network node may relate to a fixed point of communication for the UE in a particular wireless communication network. The network node may be implemented as a Radio Access Network (RAN) node referred to as a base transceiver station (BTS) in terms of the 2G communication technology, a NodeB in terms of the 3G communication technology, an evolved NodeB (eNodeB) in terms of the 4G communication technology, and a gNB in terms of the 5G New Radio (NR) communication technology. The RAN node may serve different cells, such as a macrocell, a microcell, a picocell, a femtocell, and/or other types of cells. The macrocell may cover a relatively large geographic area (for example, at least several kilometers in radius). The microcell may cover a geographic area less than two kilometers in radius, for example. The picocell may cover a relatively small geographic area, such, for example, as offices, shopping malls, train stations, stock exchanges, etc. The femtocell may cover an even smaller geographic area (for example, a home). Correspondingly, the RAN node serving the macrocell may be referred to as a macro node, the RAN node serving the microcell may be referred to as a micro node, and so on.

FIG. 1 schematically shows an IRS 100 in accordance with the prior art. The IRS 100 is shown to reflect an electromagnetic field 102 of a wireless signal coming, for example, from a network node towards a UE. The IRS is implemented as a substrate of small thickness (usually much less than a wavelength of the wireless signal), which may change its reflective properties such that a phase distribution of the reflected electromagnetic field 102 will change properly (as schematically shown by a big gradient-filled arrow in FIG. 1). As shown in FIG. 1, the phase distribution changes from -π to +π. There are two fundamentally different approaches to implementing such an IRS. The first approach consists in using reconfigurable or “smart” metamaterials, such as smart glass. The second approach implies a “discretization” of the whole surface of the substrate into small reflecting elements which may be referred to as “meta-atoms”.

FIG. 2 schematically shows a discretized IRS 200 in accordance with the prior art. In other words, the IRS 200 is implemented by using the above-mentioned second approach. As shown in FIG. 2, an electromagnetic field 202 of an incoming wireless signal is reflected by multiple meta-atoms 204 constituting the IRS 200. Each meta-atom 204 has controllable reflective properties (e.g., a controllable phase). The meta-atoms 204 may be implemented as printed circuit board (PCB) antennas, also referred to as patch antennas. FIG. 3 schematically shows one possible operational principle of each meta-atom 204 of the IRS 200. As exemplarily shown in FIG. 3, the IRS 200 comprises a substrate 300, three meta- atoms 204 provided on the substrate 300, as well as two control or switch elements 302 provided between the meta-atoms 204. The switch elements 302 may be implemented as varactors, pin diodes, etc. The electromagnetic field 202 incident on the middle meta-atom 204 induces a current 304. At the same time, there are currents 306 and 308 induced by the lateral meta-atoms 204 in the middle meta-atom 204 via the switch elements 302. The induced currents 304, 306, and 308 cause the incident electromagnetic field 202 of the wireless signal to reflect in a direction 310 at a certain reflection angle Q. It should be noted that the direction 310 may be changed by properly adjusting the induced currents 306 and 308 via the switch elements 302.

However, the existing control systems for IRSs, like the IRS 100 and the IRS 200, are mostly based on the so-called centralized architecture, according to which a central control unit responsible for controlling IRS states (i.e. reflective properties) of all available IRSs and control units included in the IRSs themselves are connected by wires. Therefore, the centralized architecture does not provide enough flexibility for the deployment of IRS-assisted wireless communications networks. In other words, the existing IRSs need to receive wired control signals from the central control unit in order to be able to configure themselves during operation depending on changing network conditions (e.g., changing directions of arrival of wireless signals).

The exemplary embodiments disclosed herein provide a technical solution that allows mitigating or even eliminating the above-sounded drawbacks peculiar to the prior art. In particular, the technical solution disclosed herein involves using at least two adjacent sensing elements in a wireless signal reflector to determine a direction of arrival of a wireless signal coming from a source network object to a target network object via the wireless signal reflector. The determined direction of arrival of the wireless signal is then used to properly control reflective properties of reflecting elements in the wireless signal reflector. To increase the efficiency of controlling the reflective properties, the wireless signal reflector may be further provided with at least one probing element configured to probe the target network object with a reference signal. With this configuration, the wireless signal reflector may control the reflective properties of the reflecting elements on its own (i.e. without having to communicate with a remote central control unit). Given this, the wireless signal reflector may operate in dynamically changing transmission environments.

FIG. 4 shows a schematic block diagram of a wireless signal reflector 400 in accordance with one exemplary embodiment. The wireless signal reflector 400 may be considered as an intermediate on the propagation path of a wireless signal from a source network object to a target network object. The wireless signal reflector 400 may be especially used when the source and target network objects are not in each other’s field of view. As shown in FIG. 4, the wireless signal reflector 400 comprises multiple reflecting elements 402-1 , 402-2, 402-3, ..., 402-n, two sensing elements 404-1 , 404-2, and a control unit 406. The reflecting elements 402-1 , 402-2, 402-3, ..., 402-n and the sensing elements 404-1 , 404-2 are assumed to be arranged on the same surface of the wireless signal reflector 400. Moreover, the sensing elements 404-1 , 404-2 should be arranged next to each other to provide proper measurements, as will be discussed later. The reflecting elements 402-1 , 402-2, 402-3,..., 402-n may be made of any suitable metamaterials (e.g., smart glass), the reflective properties of which are altered by applying control signals thereto. The control signals may be represented by analog or digital control signal. The sensing elements 404-1 , 404-2 may be implemented as patch antennas or any other antennas which may be mounted on the same surface. It should be noted that the number, arrangement and interconnection of the constructive elements constituting the wireless signal reflector 400, which are shown in FIG. 4, are not intended to be any limitation of the present disclosure, but merely used to provide a general idea of how the constructive elements may be implemented within the wireless signal reflector 400. For example, the control unit 406 may be implemented as multiple control subunits each used for controlling one of the reflecting elements 402-1 , 402-2, 402-3,..., 402- n, and/or the number of the sensing elements 404-1 , 404-2 may be more than two, depending on particular applications.

The operational principle of the wireless signal reflector 400 is as follows. Assume that a wireless signal is transmitted from a network node to a UE via the wireless signal reflector 400. Each of the sensing elements 404-1, 404-2 receives the wireless signal and generates a sensing signal in response to the received wireless signal. The sensing signals are fed to the control unit 406 which uses them to determine a direction of arrival of the wireless signal. Said determination may be done by performing phase-difference measurements on the sensing signals. Further, the control unit 406 controls the reflective properties of the reflecting elements

402-1 , 402-2, 402-3,..., 402-n based on the determined direction of arrival of the wireless signal, so that the reflecting elements 402-1 , 402-2, 402-3, ..., 402-n reflect the wireless signal (i.e. its electromagnetic field) with a required directivity pattern.

As also shown in FIG. 4, the wireless signal reflector 400 comprises one probing element 408. The probing element 408 is an optional constructive element of the wireless signal reflector 400, which may be used to improve the efficiency and quality of controlling the reflective properties of the reflecting elements. In particular, the control unit 406 may instruct the probing element 408 to probe the target network object with a reference signal, for example, configured as a predefined signal sequence or a predefined coded signal. The reference signal emitted by the probing element 408 is reflected by the target network object and then received by the sensing elements 404-1 , 404-2. In response to the received reference signal, each of the sensing elements 404-1 , 404-2 generates an additional sensing signal. The additional sensing signals are then fed to the control unit 406 which uses one of the sensing signals to determine a distance to the target network object and uses both the sensing signals to determine a direction of arrival of the reflected reference signal. For example, the distance to the target network object may be determined by performing round-trip time measurements and/or amplitude measurements on one of the additional sensing signals, while the direction of arrival of the reference signal may be determined similar to the determination of the direction of arrival of the wireless signal, i.e. by performing the phase-difference measurements on both the additional sensing signals. The control unit 406 may then use the determined distance to the target network object and the determined direction of arrival of the reference signal in addition to the determined direction of arrival of the wireless signal in order to properly control the reflective properties of the reflecting elements 402-1, 402-2, 402-3, ..., 402-n, i.e. to provide the required directivity pattern of the reflected wireless signal. It should be noted that there may be mbre than one probing element 408 simultaneously probing the target network object with multiple reference signals, or the wireless signal reflector 400 may be free of the probing element 408 at all (in such case, the reflective properties will be controlled based on the determined direction of arrival of the wireless signal only).

In one embodiment with the probing element(s) 408, the probing element(s) 408 and the sensing elements 404-1, 404-2 may be combined into two or more transceiving patch antennas. By so doing, it is possible to increase the compactness of the wireless signal reflector 400.

In one embodiment, the probing element(s) 408 may be configured to emit the reference signal(s) with a wavelength selected based on a spacing between the sensing elements 404- 1 , 404-2. By selecting the wavelength of the reference signal(s) in this manner, it is possible to increase the accuracy of determining the directions of arrival of the reference signal and the wireless signal. Moreover, when the spacing between the sensing elements 404-1 , 404-2 is less than the wavelength of the reference signal(s), it is possible to use only one of the additional sensing signals in the round-trip time measurements and/or amplitude measurements which are aimed at determining the distance to the target network object.

FIG. 5 shows the wireless signal reflector 400 implemented as a planar layered structure 500 in accordance with one exemplary embodiment. As can be seen, the planar layered structure 500 is a discretized IRS comprising an upper layer 502 which comprises the reflecting elements 402-1 , 402-2, 402-3, ..., 402-n in the form of meta-atoms, and four combined sensing/probing elements arranged next to each other in the center of the upper layer 502. It should be apparent to those skilled in the art that the sensing and probing elements may be separated from each other, if required and depending on particular applications. The planar layered structure 500 further comprises a substrate 504 serving as a support for the upper layer 502, a lower layer 506 comprising the control unit 406, and a shielding layer 508 separating the substrate 504 and the lower layer 506 to avoid the impact of electromagnetic interference on the control unit 406.

FIG. 6 shows a schematic isometric view of the upper layer 502 of the planar layered structure 500 in accordance with one exemplary embodiment. In this embodiment, the upper layer 502 comprises a greater number of the probing/sensing elements. More specifically, the probing/sensing elements are shown to be arranged in four 2-by-2 configurations 600 among the meta-atoms to precisely detect the directions of arrival of the wireless signal and the reference signal and the distance to the target network object.

FIG. 7 shows a schematic circuit of the control unit 406 of the wireless signal reflector 400 in accordance with one exemplary embodiment. As shown in FIG. 7, the control unit 406 comprises low-noise amplifiers (LNAs), an analog mixer, a low-pass filter (LPF), an RF power (PWR) sensor, and analog-to-digital converters (ADCs). The probing/sensing elements are assumed to be implemented as four adjacent patch antennas (schematically shown as grey- filled boxes) in the 2-by-2 configuration 600. The patch antennas are connected to the control unit 406 which is shown in FIG. 7 in a simplified form — only for one of the several pairs of the patch antennas. In case of dual polarizations of the wireless signal or the reference signal, the patch antennas may have two ports, one port per polarization. This would give 8 antenna ports in total, 8 LNAs and some other components per probing/sensing element. The idea of the circuit shown in FIG. 7 is to obtain both amplitudes and phase differences with reasonable sensitivity and, at the same time, circuit simplicity. The LNAs are used to achieve the sensitivity. The sensing signal generated by each of the two adjacent patch antennas in response to receiving the wireless signal or the reflected reference signal is amplified by the LNAs to a level that is suitable for analog signal processing. Then, it is split into two parts: one part is fed to the RF PWR sensor for the amplitude measurements, while another part goes to the mixer for the phase-difference measurement. The measured amplitude may be used to obtain a coarse estimation of the distance to the target network object relative to the adjacent patch antennas. The phase shift between the sensing signals generated by the two adjacent patch antennas allows measuring the direction of arrival (DoA) of the wireless signal towards the source network object or the DoA of the reference signal toward the target network object. The circuit of the control unit 406 shown in FIG. 7 allows such DoA measurement in both coordinates (elevation and azimuth) and for both polarizations.

To estimate the DoA of the wireless signal or the reference signal, it is necessary to measure a wavevector k of an incident electromagnetic wave (i.e. the wireless signal or the reference signal). Assume that the wireless signal reflector 400 is implemented as an IRS like the one shown in FIG. 5, with its center being placed on the phase center of the patch antennas, as schematically shown in FIG. 8. Then, let E ₁₁ (t) = a • cos (ω t + φ) and E ₁₂ (t) = a • cos (ω t - k _x d _x + φ), where E ₁₁ (t) and E ₁₂ (t) are the components of the electromagnetic wave (i.e. the sensing signals) obtained by the two adjacent patch antennas, a is the amplitude of each of the components E ₁₁ (t) and E ₁₂ (t), is the wavevector of the incident electromagnetic wave, d _x = λ/2 is the distance between the two adjacent patch antennas along an X axis and φ is some initial phase. First, it is required to compute the product of these two sensing signals (with one analog mixer):

If the resulting signal passes through the LPF, then one should only consider a ² cos (k _x d _x ):

Next, the computation of the product of E ₁₂ and delayed E ₁₁ (with another analog mixer) results in the following:

By using one more LPF, it is possible to obtain a ² sin(k _x d _x ). After that, two ADCs are used to digitize a ² cos(k _x d _x ) and a ² sin(k _x d _x ) in order to compute tan(k _x d _x ) and, therefore, k _x by using some Lookup Tables. The component k _y may be computed in the same manner as the component k _x , while the component k _z may be computed as follows:

FIG. 9 shows a flowchart of a method 900 for performing wireless communications in accordance with one exemplary embodiment. More specifically, the method 900 comprises reflecting a wireless signal from a source network object (e.g., a UE or network node) towards a target network object (e.g., another UE or network node) using a wireless signal reflector that may be implemented as the wireless signal reflector 400. In other words, the method 900 involves using the wireless signal reflector comprising a plurality of reflecting elements (like the reflecting elements 402-1, 402-2, 402-3, ..., 402-n), a first sensing element and a second sensing element adjacent to each other (like the sensing elements 404-1 , 404-2), and a control unit (like the control unit 406). Each of the reflecting elements is intended to have controllable reflective properties, so that the wireless signal is reflected with a required directivity pattern. To properly perform this reflection, the method 900 is performed as follows. Each of the first and second sensing elements receives the wireless signal in a step S902 and uses the wireless signal to generate a sensing signal in step S904. It should be again noted that the number of the sensing elements and, consequently, the sensing signals may vary depending on particular applications. The method 900 further proceeds to a step S906, in which the control unit determines a direction of arrival of the wireless signal based on the two sensing signals. Further, the method 900 goes on to a step S908, in which the control unit uses the determined direction of arrival of the wireless signal to control the reflective properties of one or more of the reflecting elements to provide the required directivity pattern of the reflected wireless signal.

FIG. 10 shows a schematic diagram of an IRS-assisted wireless communication network 1000 in accordance with one exemplary embodiment. The network 1000 is intended to operate in accordance with the method 900. As shown in FIG. 10, the network 1000 comprises a source network object 1002 represented by a network node (e.g., an access point), a target network object 1004 represented by a UE (e.g., a laptop), and the wireless signal reflector 400 implemented as a digitized IRS like the one shown in FIG. 5. As also can be seen from FIG. 10, the UE 1004 is "hidden” from the network node 1002 behind a wall. Given this, the use of the wireless signal reflector 400 is especially recommended to provide a proper quality of communications between the network node 1002 and the UE 1004. More specifically, the wireless signal reflector 400 reflects a wireless signal coming from the network node 1002 towards the UE 1004 with a required directivity pattern, which is achieved as explained earlier. The IRS-assisted wireless communication network may be implemented as part of a larger wireless network such as IEEE 802.11 (for indoor applications) or even as part of a cellular mobile communications, such as 5G NR. It should be noted that the wireless signal reflector, particularly implemented as an IRS, may be added to wireless communication networks without having to significantly change the upper layers of the Open Systems Interconnection model (OSI) model (only the physical layer requires minor changes).

FIG. 11 shows a schematic diagram of a multi-IRS-assisted wireless communication network 1100 in accordance with one exemplary embodiment. Similar to the network 1000, the network 1100 also operates in accordance with the method 900. As shown in FIG. 11 , the network 1100 comprises a transmitter (Tx) 1102 serving as a source network object (e.g., a transmitter of one network node or UE), a receiver (Rx) 1104 serving as a target network object (e.g., a receiver of another network node or UE), and two wireless signal reflectors 400 each implemented as an IRS, like the one shown in FIG. 5. A wireless signal transmitted by the transmitter 1102 to the receiver 1104 is successively reflected by each of the IRSs 400 with required directivity patterns, which are achieved as explained earlier.

It should be also noted that the IRS-assisted wireless communication networks, like the ones shown in FIGs. 10 and 11 , have the following advantages over non-IRS-assisted wireless communication networks:

• probing element(s) of one IRS and sensing element(s) of another IRS may exchange signals to measure their DoA, thereby allowing one to determine the locations of the IRSs;

• the round-trip time (RTT) and/or amplitude (e.g., received signal strength indicator (RSSI)) of reference signals may be measured between two IRSs and between a transmitter or receiver and one of the IRSs in order to calculate the distances therebetween (see “d1”, “d2”, and “d3” in FIG. 11);

• multiple IRSs may be used to track the location of the transmitter and the receiver;

• multiple IRSs may allow one to identify the locations of transmitter/receiver pairs during a handshake;

• the sensing elements may identify the transmitter and measure its location during preamble transmission time, as well as configure themselves before actual data transmission begins (this procedure may be utilized for multiple IRSs, and a packet preamble might be expanded to allow for more IRSs in a route).

To show the potential of the wireless signal reflector 400 and the proposed DoA estimation algorithm, two numerical tests were conducted, with the first test being aimed at studying the accuracy of an angle of arrival (AoA) of a wireless signal and the second test being aimed at studying how accurate the AoA estimation is when a target network node is in different positions. It should be noted that the AoA-DoA relationship is defined by tuning phases on the meta-atoms of the IRS like the one shown in FIG. 5. The results of the first numerical test are shown in FIG. 12, while the results of the second numerical test are shown in FIGs. 13 and 14.

More specifically, FIG. 12 shows an estimated AoA as a function of a spacing between the adjacent sensing elements of the wireless signal reflector 400 implemented as an IRS. More specifically, the accuracy of AoA estimation was studied for the spacing between the sensing elements ranging from 0.05 to 0.5 of the wavelength of the wireless signal. As follows from FIG. 12, the accuracy decreases as the spacing between the adjacent sensing elements increases. It also follows that the error rate of the estimated AoA is on the order of 0.001%, which is very small.

FIG. 13 schematically shows how a receiver (RX) representing the target network node may be located or oriented relative to an IRS like the one shown in FIG. 5. In FIG. 13, possible different positions of the RX are shown as empty circles, while the position of the IRS is shown as an empty rectangular.

FIG. 14 shows the error rate of the estimated AoA as a function of an angle of departure of the wireless signal relative to the RX. In other words, FIG. 14 shows how the estimated AoA depends on the different positions of the RX. As follows from FIG. 14, the error rate increases as the distance between the RX and the IRS (designated as “wall” in FIG. 14, meaning that the IRS is arranged on the wall) decreases because the assumption that all sensing elements of the IRS receive the same power becomes less accurate. For the same reason, the error rate increases as the angle of departure decreases. It should be noted that the error rate is 0 at the angle of departure equal to 90 degrees (from the IRS plane) because the above- mentioned assumption on the same power is satisfied.

Although the exemplary embodiments of the present disclosure are described herein, it should be noted that any various changes and modifications could be made in the embodiments of the present disclosure, without departing from the scope of legal protection which is defined by the appended claims. In the appended claims, the word “comprising” does not exclude other elements or operations, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.