WO2025108559A1

WO2025108559A1 - Devices and methods for beam alignment for wireless communication

Info

Publication number: WO2025108559A1
Application number: PCT/EP2023/083031
Authority: WO
Inventors: Damiano BADINI; Malte Schellmann
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2023-11-24
Filing date: 2023-11-24
Publication date: 2025-05-30
Anticipated expiration: 2026-05-24

Abstract

A base station (110) for communication with a user equipment, UE, (130) via a range extension device (120), such as a reflecting intelligent surface, RIS. The base station (110) is configured to transmit a plurality of pilot signal subcarriers in the direction of the range extension device (120) for being reflected or retransmitted by the range extension device (120) towards the UE (130). The range extension device (120) comprises an antenna array with a plurality of antenna elements, wherein the plurality of antenna element is subdivided into a plurality of sub-groups (121a-d) and wherein at least two sub-groups (121a-d) of the plurality of antenna elements are configured to reflect or retransmit the plurality of pilot signal subcarriers with a different frequency shift. A frequency spacing between adjacent pilot signal subcarriers of the plurality of pilot signal subcarriers is larger than the largest frequency shift induced by the at least two sub-groups (121a-d) of the plurality of antenna elements of the range extension device (120). Moreover, a corresponding range extension device (120) and a corresponding UE (130) is disclosed.

Description

DEVICES AND METHODS FOR BEAM ALIGNMENT FOR WIRELESS COMMUNICATION

TECHNICAL FIELD

The present disclosure relates to wireless communication. More specifically, the present disclosure relates to devices and methods for beam alignment for wireless communication between a base station and a user equipment, UE, making use of a communication range extension device, such as a Reconfigurable Intelligent Surface, RIS, or a Network Controlled Repeater, NCR.

BACKGROUND

Reconfigurable Intelligent Surfaces, RISs, or a Network Controlled Repeaters, NCRs, have the potential to extend the communication range in a wireless network. An RIS, for instance, is usually a planar array consisting of a large number of (nearly) passive, low-cost and low-energy consuming reflecting antenna elements with reconfigurable parameters. Each of these antenna elements is configured to reflect an impinging radio wave with an individually configurable phase shift, which results in the formation of a reflection beam, the direction of which can be actively controlled by choosing the phase shifts for the reflecting antenna elements accordingly.

RISs can be implemented in different sizes, but in order to achieve a broader coverage and more complex signal manipulation, large RISs are generally preferred. Despite providing a lot of performance gain, large surfaces have the disadvantage of requiring complex beam pointing procedures, that are either time consuming or they rely on information from external systems.

Conventional beam alignment (also referred to beam pointing) procedures comprise exhaustive search, hierarchical search or position-based techniques. Recently, the concept of space-time modulated antenna arrays has enabled more advanced techniques, such as the one described in US11570629, which discloses a beam alignment technique wherein the RIS is configured to reflect the various frequencies composing the incident signal in different directions.

SUMMARY

It is an objective of the present disclosure to provide improved devices and methods for beam alignment for wireless communication between a base station and a user equipment, UE, making use of a communication range extension device, such as a Reconfigurable Intelligent Surface, RIS, or a Network Controlled Repeater, NCR.

The foregoing and other objectives are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect, a base station for communication with a user equipment, UE, via a range extension device is provided. The range extension device may be, for instance, a Reconfigurable Intelligent Surface, RIS, device or a Network Controlled Repeater, NCR, device.

The base station is configured to transmit a plurality of pilot signal subcarriers in the direction of the range extension device for being reflected or retransmitted by the range extension device towards the UE. The range extension device comprises an antenna array with a plurality of antenna elements, wherein the plurality of antenna elements is subdivided into a plurality of sub-groups, i.e. sub-arrays and wherein at least two sub-groups of the plurality of antenna elements are configured to reflect or retransmit the plurality of pilot signal subcarriers towards the UE with a different frequency shift. The frequency spacing between adjacent pilot signal subcarriers of the plurality of pilot signal subcarriers is larger than the largest frequency shift induced by the at least two sub-groups of the plurality of antenna elements of the range extension device. Thus, by means of the plurality of pilot signal subcarriers generated by the base station according to the first aspect and the way in which these are reflected by the plurality of sub-groups of the plurality of antenna elements of the range extension device towards the UE the time for aligning the beam from the range extension device towards the UE may be reduced substantially. In particular, the resulting time saving compared with an exhaustive beam search is proportional to the number of sub-arrays obtained from the plurality of antenna elements in the antenna array.

Differently from hierarchical search techniques, implementation forms and embodiments disclosed herein are not affected by beam gain drop during the procedure.

Differently from position-based techniques, implementation forms and embodiments disclosed herein do not need to rely on an external system (i.e. GNSS) to align the beams. Differently from techniques based on space-time modulated antenna arrays (as the one described in US11570629), according to implementation forms and embodiments disclosed herein each sub-array is modulated in time but not in space. This allows for a significant reduction in the number of quantization bits required for the reconfigurable parameters, enabling simpler hardware implementations., Furthermore, implementation forms and embodiments disclosed herein do not generate multiple high-gain beams for different frequency bands and, thus, simplify interference management.

In a further possible implementation form, the base station is configured to transmit configuration information representative of a configuration of the antenna array of the range extension device to the UE.

In a further possible implementation form, the configuration information comprises information about at least one of the following:

- the number of the sub-groups of the plurality of antenna elements,

- a spatial arrangement of the sub-groups of the plurality of antenna elements,

- the frequency shift induced by each of the sub-groups of the plurality of antenna elements,

- a codebook of a plurality of codebooks, wherein each codebook defines a plurality of phase vectors to be tested by the UE when combining the received pilot signal subcarriers.

The plurality of codebooks may be predefined to support different numbers and/or spatial arrangements of the sub-groups of the plurality of antenna elements.

In a further possible implementation form, the base station is configured to obtain the configuration information representative of the configuration of the antenna array of the range extension device from the range extension device.

In a further possible implementation form, the base station is configured to receive feedback information in response to the pilot signal from the UE, wherein the feedback information is representative of a preferred direction of the reflection or retransmission from the range extension device to the UE.

In a further possible implementation form, the base station is configured to forward the feedback information to the range extension device.

According to a second aspect a method for operating a base station for communication with a user equipment, UE, via a range extension device is provided. The method comprises the steps of: transmitting a plurality of pilot signal subcarriers in the direction of the range extension device for being reflected or retransmitted by the range extension device towards the UE, wherein the range extension device comprises an antenna array with a plurality of antenna elements, wherein the plurality of antenna elements is subdivided into a plurality of sub-groups, i.e. subarrays and wherein at least two sub-groups of the plurality of antenna elements are configured to reflect or retransmit the plurality of pilot signal subcarriers towards the UE with a different frequency shift; wherein a frequency spacing between adjacent pilot signal subcarriers of the plurality of pilot signal subcarriers is larger than the largest frequency shift induced by the at least two subgroups of the plurality of antenna elements of the range extension device.

The method according to the second aspect can be performed by the base station according to the first aspect. Thus, further features of the method according to the second aspect result directly from the functionality of the base station according to the first aspect as well as its different implementation forms described above and below.

According to a third aspect, a communication range extension device for relaying communication from a base station to a user equipment, UE, is provided. The range extension device comprises an antenna array with a plurality of antenna elements, wherein the plurality of antenna elements is subdivided into a plurality of sub-groups, i.e. sub-arrays for reflecting or retransmitting a plurality of pilot signal subcarriers from the base station towards the UE, wherein at least two sub-groups of the plurality of antenna elements are configured to reflect or retransmit the plurality of pilot signal subcarriers towards the UE with a different frequency shift. Thus, by means of the plurality of pilot signal subcarriers received from the base station and the way in which these are reflected by the plurality of sub-groups of the plurality of antenna elements of the range extension device according to the third aspect towards the UE the time for aligning the beam from the range extension device towards the UE may be reduced substantially.

In a further possible implementation form, a frequency spacing between adjacent pilot signal subcarriers of the plurality of pilot signal subcarriers is larger than the largest frequency shift induced by the at least two sub-groups of the plurality of antenna elements.

In a further possible implementation form, the antenna elements of the at least two sub-groups are configured to vary a phase with different speeds for reflecting or retransmitting the plurality of pilot signal subcarriers towards the UE with a different frequency shift. In a further possible implementation form, the range extension device is configured to provide configuration information to the base station and/or the UE, wherein configuration information is representative of a configuration of the antenna array of the range extension device.

In a further possible implementation form, the configuration information comprises information about the number of the sub-groups of the plurality of antenna elements, a spatial arrangement of the sub-groups of the plurality of antenna elements, and/or the frequency shift induced by each of the sub-groups of the plurality of antenna elements.

In a further possible implementation form, the range extension device is a reconfigurable intelligent surface, RIS, device configured to reflect the plurality of pilot signal subcarriers towards the UE, or a networked-controlled repeater, NCR, device configured to retransmit the plurality of pilot signal subcarriers towards the UE.

According to a fourth aspect a method for operating a communication range extension device for relaying communication from a base station to a user equipment, UE, is provided. The method according to the fourth aspect comprises the step of reflecting or retransmitting a plurality of pilot signal subcarriers from the base station towards the UE by a plurality of subgroups of a plurality of antenna elements of an antenna array of the range extension device, wherein at least two sub-groups of the plurality of antenna elements are configured to reflect or retransmit the plurality of pilot signal subcarriers towards the UE with a different frequency shift.

The method according to the fourth aspect can be performed by the range extension device according to the third aspect. Thus, further features of the method according to the fourth aspect result directly from the functionality of the range extension device according to the third aspect as well as its different implementation forms described above and below.

According to a fifth aspect a user equipment, UE, for communication with a base station via a range extension device is provided. The UE according to the fifth aspect is configured to receive a plurality of pilot signal subcarriers from the base station reflected or retransmitted by the range extension device, wherein the range extension device comprises an antenna array with a plurality of antenna elements, wherein the plurality of antenna elements is subdivided into a plurality of sub-groups, i.e. sub-arrays for reflecting or retransmitting the plurality of pilot signal subcarriers from the base station towards the UE, wherein at least two sub-groups of the plurality of antenna elements are configured to reflect or retransmit the plurality of pilot signal subcarriers towards the UE with a different frequency shift. Moreover, the UE according to the fifth aspect is configured to determine, based on the received plurality of pilot signal subcarriers, a preferred direction of the reflection or retransmission from the range extension device to the UE. Thus, by means of the plurality of pilot signal subcarriers from the base station and the way in which these are reflected by the plurality of sub-groups of the plurality of antenna elements of the range extension device towards the UE according to the fifth aspect the time for aligning the beam from the range extension device towards the UE may be reduced substantially.

In a further possible implementation form, the UE is configured to determine the preferred direction of the reflection or retransmission from the range extension device to the UE by determining a set, in particular a vector of phase factors to be used by the UE for the constructive combination of the received pilot signal subcarriers reflected or retransmitted with different frequency shifts by the at least two sub-groups of the plurality of antenna elements.

In a further possible implementation form, the UE is configured to receive configuration information from the base station or the range extension device, wherein the configuration information is representative of a configuration of the antenna array of the range extension device and wherein the UE is configured to determine, based on the received plurality of pilot signal subcarriers and the configuration information, the preferred direction of the reflection or retransmission from the range extension device to the UE.

In a further possible implementation form, the UE is configured to provide feedback information, such as a codebook index, to the base station and/or the range extension device, wherein the feedback information is representative of the preferred direction of the reflection or retransmission from the range extension device to the UE.

In a further possible implementation form, the UE is configured to provide the feedback information to the base station in a different frequency band than the one used for the plurality of pilot signal subcarriers.

In a further possible implementation form, the UE is configured to provide the feedback information to the base station by sending a feedback information signal via the range extension device to the base station, wherein the feedback information signal comprises the plurality of pilot signal subcarriers received from the range extension device and wherein the plurality of pilot signal subcarriers are modulated by a set of phase factors for the received pilot signal subcarriers, resulting in a constructive interference superposition after being reflected or retransmitted with different frequency shifts by the at least two sub-groups of the plurality of antenna elements. The feedback information is carried by the feedback information signal without affecting its modulation by a set of phase factors resulting in a constructive interference superposition after being reflected or retransmitted with different frequency shifts by the at least two sub-groups of the plurality of antenna elements.

According to a sixth aspect a method for operating a user equipment, UE, for communication with a base station via a range extension device is provided. The method according to the sixth aspect comprises the steps of: receiving a plurality of pilot signal subcarriers from the base station reflected or retransmitted by the range extension device, wherein the range extension device comprises an antenna array with a plurality of antenna elements, wherein the plurality of antenna elements is subdivided into a plurality of sub-groups, i.e. sub-arrays for reflecting or retransmitting the plurality of pilot signal subcarriers from the base station towards the UE, wherein at least two sub-groups of the plurality of antenna elements are configured to reflect or retransmit the plurality of pilot signal subcarriers towards the UE with a different frequency shift; and determining, based on the received plurality of pilot signal subcarriers, a preferred direction of the reflection or retransmission from the range extension device to the UE.

The method according to the sixth aspect can be performed by the UE according to the fifth aspect. Thus, further features of the method according to the sixth aspect result directly from the functionality of the UE according to the fifth aspect as well as its different implementation forms described above and below.

According to a seventh aspect, a computer program product is provided, comprising a computer-readable storage medium for storing program code which causes a computer or a processor to perform the method according to the second aspect, the method according to the fourth aspect, or the method according to the sixth aspect, when the program code is executed by the computer or the processor.

Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which:

Fig. 1a shows a schematic diagram illustrating a communication system including a base station according to an embodiment, a range extension device according to an embodiment in the form of a reconfigurable intelligent surface and a user equipment according to an embodiment;

Fig. 1b shows a diagram illustrating a determination of an optimal beam by a user equipment according to an embodiment for the exemplary scenario of figure 1a;

Fig. 2 shows a schematic diagram illustrating the communication system of figure 1a, wherein the user equipment according to an embodiment provides feedback to the base station according to an embodiment;

Fig. 3a shows a schematic diagram illustrating the communication system of figure 1 , wherein the user equipment according to a further embodiment provides feedback to the base station according to a further embodiment;

Fig. 3b shows a schematic diagram illustrating further aspects of the user equipment for providing the feedback, as illustrated in figure 3b;

Figs. 4a, 4b show schematic diagrams illustrating a range extension device according to an embodiment in the form of a reconfigurable intelligent surface and a network-controlled repeater, respectively;

Fig. 5 shows a signalling diagram illustrating interactions for beam alignment between a base station according to an embodiment, a range extension device according to an embodiment, and a user equipment according to an embodiment;

Fig. 6a shows a range extension device according to an exemplary embodiment in the form of a reconfigurable intelligent surface, with a linear array of antenna elements;

Fig. 6b shows different radiation patterns for the reconfigurable intelligent surface of figure 6a; Fig. 6c shows the results of an FFT analysis performed by the user equipment according to an embodiment for performing beam alignment;

Fig. 7 shows a flow diagram illustrating a method of operating a base station according to an embodiment;

Fig. 8 shows a flow diagram illustrating a method of operating a range extension device according to an embodiment; and

Fig. 9 shows a flow diagram illustrating a method of operating a user equipment according to an embodiment.

In the following, identical reference signs refer to identical or at least functionally equivalent features.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise.

Figure 1a shows a schematic diagram illustrating a communication system 100 including a base station 110 according to an embodiment, a communication range extension device 120 according to an embodiment and a user equipment, UE, 130 according to an embodiment. In an embodiment, the base station 110 is configured to provide communication services, in particular network access for the UE 130 (also referred to as mobile terminal 130) and may be a base station or access point of a 3GPP network, such as a 5G or 6G network, or of an IEEE 802.11 Wi-Fi network.

As will be described in more detail below, the communication range extension device 130 may be implemented as a Reconfigurable Intelligent Surface, RIS, 130 or a Network Controlled Repeater, NCR, 130 for reflecting or retransmitting the beamed communication between the base station 110 and the UE 130. To this end, the range extension device 130 comprises an antenna array with a plurality of antenna elements 121 (indicated in figures 4a, 4b and 6a). Each of these antenna elements 121 is configured to reflect or retransmit an impinging radio wave with an individually configurable phase shift, which results in the formation of a reflection or retransmission beam, whose direction can be actively controlled by choosing the phase shifts for the plurality of antenna elements 121. In an embodiment, the range extension device 130 may comprise a controller 125 controlled by the base station 110 (or a further radio access network entity).

As illustrated in figure 1a, for implementing one or more of the features described in the following the base station 110 may comprise processing circuitry 111 , e.g. one or more processors 111 and a transceiver 113. The processing circuitry 111 may be implemented in hardware and/or software. The hardware may comprise digital circuitry, or both analog and digital circuitry. Digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs), or one or more general-purpose processors. Moreover, the base station 110 may comprise a memory 115 configured to store executable program code which, when executed by the processing circuitry 111 , causes the base station 110 to perform the functions and operations described herein.

Likewise, for implementing one or more of the features described in the following the UE 130 (as well as the range extension device 120 although not shown in figure 1a) may comprise processing circuitry 131 , e.g. one or more processors 131 and a transceiver 133. The processing circuitry 131 may be implemented in hardware and/or software. The hardware may comprise digital circuitry, or both analog and digital circuitry. Digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs), or one or more general-purpose processors. Moreover, the UE 130 (as well as the range extension device 120) may comprise a memory 135 configured to store executable program code which, when executed by the processing circuitry 131 , causes the UE 130 to perform the functions and operations described herein.

As will be described in more detail in the following, the base station 120 is configured to transmit a plurality of pilot signal subcarriers (for instance, as part of a pilot signal) in the direction of the range extension device 120 for being reflected or retransmitted by the range extension device 120 towards the UE 130. For the sake of clarity only a single pilot signal subcarrier at a single subcarrier frequency is illustrated in figure 1a. As illustrated in figure 1a, the plurality of antenna elements 121 of the range extension device 120 is subdivided into a plurality of sub-groups 121a-d, i.e. sub-arrays 121a-d, which, by way of example, comprises four sub-groups 121a-d in the illustrative embodiment shown in figure 1a. At least two, preferably all of the sub-groups 121a-d of the plurality of antenna elements 121 are configured to reflect or retransmit the plurality of pilot signal subcarriers towards the UE 130 with different frequency shifts. For instance, in the illustrative embodiment shown in figure 1a, the subgroups 121a, 121b, 121c, and 121 d are configured to reflect or retransmit the plurality of pilot signal subcarriers towards the UE 130 with a zero-frequency shift, a frequency shift of Af, a frequency shift of 2Af, and a frequency shift of 3Af, respectively. In an embodiment, these different frequency shifts by the different sub-groups 121a-d of the plurality of antenna elements 121 may be achieved by varying a phase (more specifically a phase change) induced by the plurality of antenna elements 121 of the different sub-groups 121a-d with different speeds. In other words, the antenna array of the range extension device 120 is sub-divided into a plurality of sub-groups or sub-panels 121a-d, where every sub-panel 121a-d of the range extension device 120 may generate a beamformed reflection signal with a different frequency shift Af for the channel probing. As already mentioned above, the frequency shift may be realized by introducing a time modulation on the antenna elements of each sub-panel 121a-d. In an embodiment, Af may be as small as the subcarrier spacing.

For allowing the UE 130 to still resolve the plurality of different frequency shifts induced by the different sub-groups 121a-d of the plurality of antenna elements 121 of the range extension device 120 the base station 110 is configured to transmit the plurality of pilot signal subcarriers towards the range extension device 120 such that the frequency spacing between adjacent pilot signal subcarriers of the plurality of pilot signal subcarriers is larger than the largest frequency shift induced by the different sub-groups 121a-d of the plurality of antenna elements 121 of the range extension device 120. For instance, for the illustrative embodiment shown in figure 1a, the largest frequency shift of 3Af is induced by the sub-group 121 d of the plurality of antenna elements 121 so that the frequency spacing between adjacent pilot signal subcarriers of the plurality of pilot signal subcarriers emitted by the base station 110 is larger than 3Af, for instance, 4Af. Thus, according to embodiments disclosed herein, the base station 110 is configured to transmit a properly designed set of pilots, in which there is a number of empty subcarriers depending on the largest frequency induced by one of the sub-panels 121 a-d of the range extension device 120.

Figure 1 b shows a diagram illustrating how the UE 130 according to an embodiment may determine a desired beam alignment or preferred beam direction from the range extension device towards the UE 130, based on the received plurality of pilot signal subcarriers, which have been shifted in frequency due to the different frequency shifts caused by the different sub-groups 121 a-d of the plurality of antenna elements 121 of the range extension device 120. More specifically, the UE 130 is configured to determine the preferred direction of the reflection or retransmission of the plurality of pilot signal subcarriers (with the different induced frequency shifts) by the range extension device 120 to the UE 130 by determining a set, in particular a vector of phase factors for the received pilot signal subcarriers resulting in a constructive superposition, i.e. combination of the reflected or retransmitted signals. Thus, for the illustrative embodiment shown in figures 1a and 1 b, the UE 130 is configured to determine the four phases o. i. 02. and 03 (which may be generally complex numbers and which may be represented as a vector), which lead to the largest signal strength of the plurality of superposed pilot signal subcarriers.

Thus, as will be appreciated, the beams reflected by the plurality of sub-panels 121 a-d of the range extension device 120 are observed on a plurality of adjacent subcarriers in the signal received by the UE 130, and the UE 130 may test multiple phase combining patterns, i.e. multiple phase vectors (e.g. from a pre-defined codebook) for combining the signals on the plurality adjacent subcarriers to find the one creating the maximum peak after combining, as described in the context of figure 1b above. The gain in terms of beam alignment overhead reduction may be proportional to the number of sub-panels 121 a-d of the range extension device 120. The number of sub-panels 121a-d, in which the antenna array of the range extension device 120 may be divided and the way the plurality of sub-panels 121 a-d are structured within the antenna array define the size and structure of a codebook of phase patterns, which may be used by the UE 130 and the base station 110 according to an embodiment for reducing the signalling overhead. These parameters (as well as the codebooks) may be pre-defined (i.e. standardized), and may be limited to a certain number of supported configurations (similar to the 3GPP TS 38.214 for 5G CSI-RS procedure).

As will be described in the following in the context of figures 2 and 3a, 3b, the set of phases o , i , 02 . and 0₃ corresponding to the preferred beam direction or other feedback information representative thereof may be fed back from the UE 130 to the base station 110 and/or the range extension device 120 according to two main embodiments. In an embodiment, the feedback information may be a phase pattern identifier indicative of a phase pattern or phase vector in a codebook of phase patterns available at the UE 130 and the base station 110.

According to a first main embodiment illustrated in figure 2, the UE 130 is configured to provide the feedback information to the base station 110 (and/or the range extension device 120) in a different frequency band than the one used for the plurality of pilot signal subcarriers. For instance, in an embodiment the UE 130 is configured to transmit the feedback information over a control channel in a lower frequency band. If, for instance, the range extension device 120 is meant to improve FR2 propagation, the feedback frequency can be FR1 , as indicated in figure 2.

According to a second main embodiment illustrated in figures 3a and 3b, the UE 130 is configured to provide the feedback information to the base station 110 (and/or the range extension device 120) by sending a feedback information signal via the range extension device 120 to the base station 110, wherein the feedback information signal comprises the plurality of pilot signal subcarriers received from the range extension device 120 and wherein the plurality of pilot signal subcarriers are modulated by the UE 130 with the set of phase factors 0_O, <p₁, <p₂, and 0₃ resulting in the constructive superposition at the UE 130. Thus, by exploiting channel reciprocity, according to the second main embodiment, it is possible to provide feedback to the base station 110 without relying on another frequency band (provided, for instance, by an external system). More specifically, according to the second main embodiment, the UE 130 transmits a multi-tone signal resembling the one that it received during the sounding phase (illustrated in figures 1a,b). As already mentioned above, the different frequencies are modulated with the selected phase pattern found during the sounding phase, while the range extension device 120 is configured to apply the inverse frequency shift, i.e. -A/, at the different sub-panels 120a-d. With this configuration, the adjacent subcarriers signals will collapse during this reporting slot to a single subcarrier that is reflected to the base station 110, yielding the signal to be received with high beamforming gain at high SNR. Since multiple frequency blocks (each one including four subcarriers, equal to the number of subarrays) of a plurality of subcarriers may be used for the feedback signal, the feedback information may be encoded (without affecting the modulation yielding the constructive combination at the base station 110) by adding a common phase term to all subcarriers in the frequency block in order to apply a differential phase modulation over consecutive frequency blocks with a high modulation and coding scheme (MCS).

Figures 4a, 4b show schematic diagrams illustrating two more detailed embodiments of the range extension device 120 in the form of a RIS 120 (figure 4a) and an NCR 120 (figure 4b), respectively. In the embodiments shown schematically in figures 4a and 4b the RIS 120 or NCR 120 comprises, by way of example, two sub-groups or sub-arrays 121a, b of the plurality of antenna elements 121 , wherein the sub-group 121a induces a zero frequency shift, while the sub-group 121b induces a frequency shift of Af = f_x. For both embodiments, each antenna element 121 comprises or is connected with a phase adjusting element 122 for adjusting the phase of the signal reflected or retransmitted by the respective antenna element 121 , in the way already described above. In the embodiment shown in figure 4b, the range extension device 120 in the form of the NCR 120 may further comprise a receive antenna 123 and a plurality of amplifiers 123, 126.

Figure 5 shows a signalling diagram illustrating interactions for beam alignment between the base station 110 according to an embodiment, the range extension device 120, e.g. RIS 120 or NCR 120, according to an embodiment, and the UE 130 according to an embodiment.

In step 501 of figure 5, the range extension device 120, e.g. RIS 120 or NCR 120, communicates to the base station 110 configuration representative of its hardware capabilities, in particular its antenna array with the plurality of antenna elements, such as the number of antenna elements and/or the size of the antenna array.

In steps 503a, b of figure 5, the base station determines a division of the plurality of antenna elements 121 of the antenna array of the range extension device 120 into a plurality of subarrays 121a-d of antenna elements 121 and the related configuration of codebooks and pilot signals. The configuration of the pilots may define the frequency shift and other parameters necessary for the UE 130 to decode the pilots (for instance the kind of pilot sequence that is used). The codebook type allows to identify the phase vectors that the UE 130 has to test on the received pilots. This configuration information is transmitted to the range extension device 120 and in particular to the UE 130. In step 505 of figure 5 the base station 110 transmits a channel probing signal, i.e. pilot signal with a plurality of pilot signal subcarriers towards the range extension device 120 such that the frequency spacing between adjacent pilot signal subcarriers of the plurality of pilot signal subcarriers is larger than the largest frequency shift induced by the different sub-groups 121a- d of the plurality of antenna elements 121 of the range extension device 120, as already described above. In the signal reflected or retransmitted by the range extension device 120 towards the UE in step 507 of figure 5, the original number of subcarriers transmitted by the base station 110 is increased by a factor equal to the number of sub-groups 121a-d of the plurality of antenna elements 121 of the range extension device 120.

In order to minimize the probability of collision with other UEs covered by the same sub-panel’s beam, the feedback from the UE 130 may be transmitted in steps 509, 511 of figure 5 after waiting for a Random Collision Avoidance (CA) Backoff. As already described above, the feedback information provided by the UE may include a codebook ID indicative of the optimal phase pattern associated with the preferred beam direction (but it may also carry other ancillary information, additional redundancy or a further layer of CA).

Once the base station 110 has received the feedback information from the UE 130 (in an embodiment via the range extension device 120), the base station may configure in step 513 of figure 5 to use the preferred beam from the codebook set on the range extension device 120.

Figure 6a shows a further exemplary embodiment of the range extension device 120 in the form of a RIS 120 with a linear array of antenna elements 121 , by way of example, 40 elements divided into 8 sub-groups 120a-h (i.e. 5 antenna elements in each sub-group). The far-field radiation pattern of the exemplary RIS 120 shown in figure 6a can be computed as:

wherein E(e, <p) is the far-field radiation pattern of the single element of the RIS 120, N is the number of antenna elements (40 in this case), a_n is the complex weight associated to the n-th RIS element and d is the inter-element distance normalized by the wavelength. For the sake of simplicity, it may be assumed that E(e, <p) = 1 and the RIS gain may be computed as l/(^o< o)l² when a_n = e^{j2nd n sm e}<> ^cos < >₀ y following this approach the maximum gain is equal to the number of elements N, which corresponds to 16dB. Similarly, by considering only a subset of 5 elements, the maximum gain of a single virtual sub-group 121a-h may be computed to be equal to 7dB.

If all the 8 virtual sub-groups 121a-h of the RIS 120 of figure 6a are pointing in the same direction (0_O, < >₀), the resulting gain measured at the receiving UE 130, assumed to be in direction (6₀, <p₀), is random and may often be lower than the maximum single sub-panel gain (7dB), as in the example shown in figure 6b, where the UE 130 is assumed to be in the direction 0_O = 0°, <p₀ = 10° . More specifically, figure 6b shows exemplary radiation patterns of the illustrative RIS 120 of figure 6a. As can be taken from figure 6b, in the direction of the UE 130 (vertical dashed line), the gain of a single sub-panel configured to generate the radiation pattern depicted with the curve “b” is larger than that of all sub-panels sharing the same configuration (curve “c”).

During the sounding phase, the UE 130 receives the subcarrier signals with Single-Sub-Panel gain (maximum 7dB). Instead of estimating the channel for each sub-carrier, the UE 130 just needs to test a codebook of combination phase coefficients, thus creating a compound pointing beam from the K sub-panel beams received on the adjacent subcarriers (i.e. , curve “b” in figure 6b), until it finds the one yielding the highest beam pointing gain (i.e., curve “a” in figure 6b).

In an embodiment, the UE 130 may be configured to use an FFT codebook. The output of the FFT codebook of size 8 is shown in figure 6c for the illustrative range extension device 120 of figure 6a. The number of entries of the FFT codebook is equal to the number of sub-groups (K=8), and their linear arrangement determines the fact a 1 D FFT is computed instead of a 2D FFT (which would be the case for a planar arrangement of the panels).

For the exemplary embodiment shown in figures 6a-c the feedback information provided by the UE may be based on the solution of: arg

Once the index of the best phase combining pattern from the codebook is found, the feedback signal to convey this information to the base station 110 may be designed considering a certain number of system parameters, as shown in the following example. Assuming operating frequency within FR2 (i.e. sub-carrier spacing 120kHz) and operating bandwidth 400MHz, the total number of subcarriers may be about 3300. The number of symbols N_sym available for the feedback according to the second main embodiment described above is equal to N_sc/N_subpaneis ® 400. Depending on the modulation order, the number of bits may be N_bit = N_sym (binary modulation) or N_bit > N_sym. In the following binary modulation is assumed for the sake of simplicity.

The number of bits necessary for the feedback of the phase combining pattern ID is l°g2(^Nsubpaneis) = 3 « N_bit. Using the bits that are left (actually most of them), it is possible to: transmit other information, such as UE identifier, channel quality indicator, and the like; increase the reliability of the signaling link by introducing redundancy (e.g. channel coding); implement a Collision Avoidance (CA) mechanism, where one out of the N_bit/ l°g2(^Nsubpaneis) = 133 available feedback resources (or a certain subset of them) is randomly selected for transmission by the UE 130; and/or feedback multiple beams (not just the one providing the highest combination gain) and the optimal weights to combine them coherently. Using this information, it is possible to synthesize Type II codebooks, as defined in 3GPP TS 38.214.

Figure 7 shows a flow diagram illustrating a method 700 of operating the base station 110 according to an embodiment. The method 700 comprises the step 701 of transmitting by the base station 110 a plurality of pilot signal subcarriers in the direction of the range extension device 120 for being reflected or retransmitted by the range extension device 120 towards the UE 130. As already described above, the range extension device 120 comprises an antenna array with a plurality of antenna elements 121 , wherein the plurality of antenna elements 121 is subdivided into a plurality of sub-groups 121a-h and wherein at least two sub-groups 121a- h of the plurality of antenna elements 121 are configured to reflect or retransmit the plurality of pilot signal subcarriers with a different frequency shift. As further already described above, the frequency spacing between adjacent pilot signal subcarriers of the plurality of pilot signal subcarriers is larger than the largest frequency shift induced by the at least two sub-groups 121a-h of the plurality of antenna elements 121 of the range extension device 120.

The method 700 can be performed by the base station 110 according to an embodiment. Thus, further features of the method 700 result directly from the functionality of the base station 110 as well as the different embodiments thereof described above and below. Figure 8 shows a flow diagram illustrating a method 800 of operating a range extension device 120, for instance, a RIS 120 or a NCR 120, according to an embodiment. The method 800 comprises a step 801 of reflecting or retransmitting a plurality of pilot signal subcarriers from the base station 110 towards the UE 130 by the plurality of sub-groups 121 a-h of the plurality of antenna elements 121 of the antenna array of the range extension device 120. As already described above, at least two sub-groups 121 a-h of the plurality of antenna elements 121 are configured to reflect or retransmit the plurality of pilot signal subcarriers with a different frequency shift.

The method 800 can be performed by the range extension device 120, in particular RIS 120 or NCR 120, according to an embodiment. Thus, further features of the method 800 result directly from the functionality of the range extension device 120 as well as the different embodiments thereof described above and below.

Figure 9 shows a flow diagram illustrating a method 900 of operating a UE 130 according to an embodiment. The method 900 comprises a step 901 of receiving a plurality of pilot signal subcarriers from the base station 110 reflected or retransmitted by the range extension device 120. As already described above, the range extension device 120 comprises an antenna array with a plurality of antenna elements 121 , wherein the plurality of antenna elements 121 is subdivided into the plurality of sub-groups 121 a-h for reflecting or retransmitting the plurality of pilot signal subcarriers from the base station 110 towards the UE 130, wherein at least two sub-groups 121 a-h of the plurality of antenna elements 121 are configured to reflect or retransmit the plurality of pilot signal subcarriers with a different frequency shift. Moreover, the method 900 comprises a step 903 of determining, based on the received plurality of pilot signal subcarriers, a preferred direction of the reflection or retransmission from the range extension device 120 to the UE 130.

As will be appreciated, in comparison to exhaustive search techniques, embodiments disclosed herein allow for a more rapid preferred beam determination, wherein the time saved is proportional to the number of sub-panels 121 a-h chosen for the range extension device 120. In comparison to hierarchical search techniques, embodiments disclosed herein do not suffer from a gain drop during the procedure. In comparison to position-based techniques, embodiments disclosed herein do not need to rely on external systems, such as GPS for providing positional information. In comparison to the beam alignment technique based on a RIS prism effect, as disclosed in US11570629, embodiments disclosed herein allow for an easier implementation, as embodiments disclosed herein make use of a simple frequency shift instead of relying on the RIS prism effect. Moreover, the multiple beams generated by the prism effect of the RIS disclosed in US11570629 may increase the interference level in the system and complicate frequency re-use. When embodiments disclosed herein are applied to electrically small surfaces (common in low frequency range), every antenna element of the range extension device 120 may be mapped to a sub-panel, so that the optimal beam configuration may be extracted with the transmission of only one OFDM symbol.

The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments of the present disclosure (rather than necessarily individual "units" in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described embodiment of an apparatus is merely exemplary. For example, the unit division is merely a logical function division and may be another division in an actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.

In addition, functional units in the embodiments of the disclosure may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units may be integrated into one unit.

Claims

1. A base station (110) for communication with a user equipment, UE, (130) via a range extension device (120), wherein the base station (110) is configured to: transmit a plurality of pilot signal subcarriers in the direction of the range extension device

(120) for being reflected or retransmitted by the range extension device (120) towards the UE (130), wherein the range extension device (120) comprises an antenna array with a plurality of antenna elements (121), wherein the plurality of antenna elements (121) is subdivided into a plurality of sub-groups (121a-h) and wherein at least two sub-groups (121a-h) of the plurality of antenna elements (121) are configured to reflect or retransmit the plurality of pilot signal subcarriers with a different frequency shift; wherein a frequency spacing between adjacent pilot signal subcarriers of the plurality of pilot signal subcarriers is larger than the largest frequency shift induced by the at least two sub-groups (121a-h) of the plurality of antenna elements (121) of the range extension device (120).

2. The base station (110) of claim 1 , wherein the base station (110) is configured to transmit configuration information representative of a configuration of the antenna array of the range extension device (120) to the UE (130).

3. The base station (110) of claim 2, wherein the configuration information comprises information about at least one of the following:

- the number of the sub-groups (121a-h) of the plurality of antenna elements (121),

- a spatial arrangement of the sub-groups (121a-h) of the plurality of antenna elements

(121),

- the frequency shift induced by each of the sub-groups (121a-h) of the plurality of antenna elements (121),

- a codebook of a plurality of codebooks, wherein each codebook defines a plurality of phase vectors to be tested by the UE when combining the received plurality of pilot signal subcarriers.

4. The base station (110) of claim 2 or 3, wherein the base station (110) is configured to obtain the configuration information representative of the configuration of the antenna array of the range extension device (120) from the range extension device (120).

5. The base station (110) of any one of the preceding claims, wherein the base station (110) is configured to receive feedback information in response to the pilot signal from the UE (130), wherein the feedback information is representative of a preferred direction of the reflection or retransmission from the range extension device (120) to the UE (130).

6. The base station (110) of claim 5, wherein the base station (110) is configured to forward the feedback information to the range extension device (120).

7. A method (700) for operating a base station (110) for communication with a user equipment, UE, (130) via a range extension device (120), wherein the method (700) comprises: transmitting (701) a plurality of pilot signal subcarriers in the direction of the range extension device (120) for being reflected or retransmitted by the range extension device (120) towards the UE (130), wherein the range extension device (120) comprises an antenna array with a plurality of antenna elements (121), wherein the plurality of antenna elements (121) is subdivided into a plurality of sub-groups (121a-h) and wherein at least two sub-groups (121a-h) of the plurality of antenna elements (121) are configured to reflect or retransmit the plurality of pilot signal subcarriers with a different frequency shift; wherein a frequency spacing between adjacent pilot signal subcarriers of the plurality of pilot signal subcarriers is larger than the largest frequency shift induced by the at least two sub-groups (121a-h) of the plurality of antenna elements (121) of the range extension device (120).

8. A range extension device (120) for relaying communication from a base station (110) to a user equipment, UE, (110), wherein the range extension device (120) comprises: an antenna array with a plurality of antenna elements (121), wherein the plurality of antenna elements (121) is subdivided into a plurality of sub-groups (121a-h) for reflecting or retransmitting a plurality of pilot signal subcarriers from the base station (110) towards the UE (130), wherein at least two sub-groups (121-ah) of the plurality of antenna elements (121) are configured to reflect or retransmit the plurality of pilot signal subcarriers with a different frequency shift.

9. The range extension device (120) of claim 8, wherein a frequency spacing between adjacent pilot signal subcarriers of the plurality of pilot signal subcarriers is larger than the largest frequency shift induced by the at least two sub-groups of the plurality of antenna elements (121).

10. The range extension device (120) of claim 8 or 9, wherein the antenna elements (121) of the at least two sub-groups (121a-h) are configured to vary a phase with different speeds for reflecting or retransmitting the plurality of pilot signal subcarriers with a different frequency shift.

11. The range extension device (120) of any one of claims 8 to 10, wherein the range extension device (120) is configured to provide configuration information to the base station (110) and/or the UE (130), wherein configuration information is representative of a configuration of the antenna array of the range extension device (120).

12. The range extension device (120) of claim 11 , wherein the configuration information comprises information about the number of the sub-groups (121a-h) of the plurality of antenna elements (121), a spatial arrangement of the sub-groups (121a-h) of the plurality of antenna elements (121), and/or the frequency shift induced by each of the sub-groups (121a-h) of the plurality of antenna elements (121).

13. The range extension device (120) of any one of claims 8 to 12, wherein the range extension device (120) is a reconfigurable intelligent surface, RIS, device (120) configured to reflect the plurality of pilot signal subcarriers towards the UE (130), or a networked-controlled repeater, NCR, device (120) configured to retransmit the plurality of pilot signal subcarriers towards the UE (130).

14. A method (800) for operating a range extension device (120) for relaying communication from a base station (110) to a user equipment, UE, (130), wherein the method (800) comprises: reflecting or retransmitting (801) a plurality of pilot signal subcarriers from the base station (110) towards the UE (130) by a plurality of sub-groups (121a-h) of a plurality of antenna elements (121) of an antenna array of the range extension device (120), wherein at least two sub-groups (121a-h) of the plurality of antenna elements (121) are configured to reflect or retransmit the plurality of pilot signal subcarriers with a different frequency shift.

15. A user equipment, UE, (130) for communication with a base station (110) via a range extension device (120), wherein the UE (130) is configured to: receive a plurality of pilot signal subcarriers from the base station (110) reflected or retransmitted by the range extension device (120), wherein the range extension device (120) comprises an antenna array with a plurality of antenna elements (121), wherein the plurality of antenna elements (121) is subdivided into a plurality of sub-groups (121a- h) for reflecting or retransmitting the plurality of pilot signal subcarriers from the base station (110) towards the UE (130), wherein at least two sub-groups (121a-h) of the plurality of antenna elements (121) are configured to reflect or retransmit the plurality of pilot signal subcarriers with a different frequency shift; and determine, based on the received plurality of pilot signal subcarriers, a preferred direction of the reflection or retransmission from the range extension device (120) to the UE (130).

16. The UE (130) of claim 15, wherein the UE (130) is configured to determine the preferred direction of the reflection or retransmission from the range extension device (120) to the UE (130) by determining a set of phase factors to be used by the UE for a constructive combination of the received pilot signal subcarriers reflected or retransmitted with different frequency shifts by the at least two sub-groups (121a-h) of the plurality of antenna elements (121).

17. The UE (130) of claim 15 or 16, wherein the UE (130) is configured to receive configuration information from the base station (110) or the range extension device (120), wherein the configuration information is representative of a configuration of the antenna array of the range extension device (120) and wherein the UE (130) is configured to determine, based on the received plurality of pilot signal subcarriers and the configuration information, the preferred direction of the reflection or retransmission from the range extension device (120) to the UE (130).

18. The UE (130) of claim 17, wherein the configuration information comprises information about the number of the sub-groups (121a-h) of the plurality of antenna elements (121), a spatial arrangement of the sub-groups (121a-h) of the plurality of antenna elements (121), and/or the frequency shift induced by each of the sub-groups (121a-h) of the plurality of antenna elements (121).

19. The UE (130) of any one of claims 15 to 18, wherein the UE (130) is configured to provide feedback information to the base station (110) and/or the range extension device (120), wherein the feedback information is representative of the preferred direction of the reflection or retransmission from the range extension device (120) to the UE (130).

20. The UE (130) of claim 19, wherein the UE (130) is configured to provide the feedback information to the base station (110) in a different frequency band than the one used for the plurality of pilot signal subcarriers.

21. The UE (130) of claim 19, wherein the UE (130) is configured to provide the feedback information to the base station (110) by sending a feedback information signal via the range extension device (120) to the base station (110), wherein the feedback information signal comprises the plurality of pilot signal subcarriers received from the range extension device (120) and wherein the plurality of pilot signal subcarriers are modulated by a set of phase factors for the received pilot signal subcarriers, resulting in a constructive superposition after being reflected or retransmitted with different frequency shifts by the at least two sub-groups (121a-h) of the plurality of antenna elements (121).

22. A method (900) for operating a user equipment, UE, (130) for communication with a base station (110) via a range extension device (120), wherein the method (900) comprises: receiving (901) a plurality of pilot signal subcarriers from the base station (110) reflected or retransmitted by the range extension device (120), wherein the range extension device (120) comprises an antenna array with a plurality of antenna elements (121), wherein the plurality of antenna elements (121) is subdivided into a plurality of sub-groups (121a- h) for reflecting or retransmitting the plurality of pilot signal subcarriers from the base station (110) towards the UE (130), wherein at least two sub-groups (121a-h) of the plurality of antenna elements (121) are configured to reflect or retransmit the plurality of pilot signal subcarriers with a different frequency shift; and determining (903), based on the received plurality of pilot signal subcarriers, a preferred direction of the reflection or retransmission from the range extension device (120) to the UE (130).