Apparatus and method for optimizing an antenna response

Abstract

An apparatus comprises a plurality of antenna elements and a control unit for controlling the plurality of antenna elements to form a plurality of beams using set of beamforming weighting factors and to concurrently transit and receive on the plurality of beams, the plurality of beams including at least a transmit beam and a receive beam. The control unit is configured for using a self-interference information indicating a self-interference between a first number of transmit antenna elements of the plurality of antenna elements used for forming the transmit beam and a second number of receive antenna elements of the plurality of antenna elements used for forming the receive beam for determining at least one set of beamforming weighting factors to optimize an antenna response related to the transmit beam and the receive beam. The control unit is configured for using the set of beamforming weighting factors for beamforming and / or for generating a beamforming codebook related to the plurality of antenna elements.

Description

[0001]Apparatus and Method for Optimizing an Antenna Response Description The present invention relates to the field of wireless communication and, more particularly, to an apparatus optimizing an antenna response using self-interference information and to a corresponding method. The present invention further relates to a beamforming codebook with self-interference cancellation for monostatic integrated sensing and communication. In mobile communications, a sensing procedure may be used, for example, to transmit a wireless signal and to simultaneously or at least with a small temporal distance receive wireless signals. This may include but is not limited to receive reflections from the transmitted signal. Integrated sensing and communication (ISAC) is an active research area towards next- generation mobile networks. Its underlying goal is the use of the wireless communication infrastructure for sensing tasks by leveraging the properties of electromagnetic propagation, in the same fashion as radar operates. In doing so, information from the environment can be extracted from a received signal of interest by an existing wireless network without additional hardware or spectral resources. In the case of infrastructure-based ISAC, a separate radio unit dedicated to sensing reception (also called sniffer) has been proposed in [1]. One of the main challenges for ISAC is the problem of self-interference, that is, the direct coupling of the transmitted signal at the receiver. In particular, self-interference hinders so- called monostatic ISAC approaches, i.e. those where transmitter and transceiver are co- located, by yielding adverse effects such as receive-amplifier saturation, decreased dynamic range, or the masking of the signal of interest. The self-interference problematic is inherent to the combination of the communication and sensing tasks. On the one hand, pulse-radar sensing circumvents self-interference by confining the signal transmission to short time intervals, while continuous-wave radar techniques typically exploit frequency diversity. On the other hand, communication requirements such as the achievement of a surge in date throughput usually imposes an intensive use of resources both in time and frequency. EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX Bi-static sensing, i.e., with physically transmitter and receiver, has been proposed as a self- interference-free alternative to monostatic ISAC. Nevertheless, bi-static sensing introduces other issues such as time-synchronization errors and the lack of knowledge of the transmitted signal. Experimental ISAC systems often opt for an intermediate “quasi- monostatic” solution where transmitter and receiver are just moderately separated but physically connected. Either of these approaches require additional hardware and physical space that may not be available in some practical situations. Digital signal processing can be applied to remove the self-interference in the digital domain while preserving the signal of interest. Nevertheless, both amplifier saturation and dynamic- range reduction occur before the digitalization of the received signal and must be consequently addressed in the analog domain. For this, additional self-interference- cancellation analog circuitry has been proposed, although it has not been widely adopted so far. There is, thus, a need to enhance beamforming. An object of the present invention is to provide for an apparatus and for a method that allow to enhance beamforming. A recognition of the present invention is that the self-interference information obtainable between receiver antennas and transmit antennas may be incorporated already in a codebook used for beamforming, in corresponding information respectively such that by use of self-interference information for determining one or more sets of beamforming weighting factors to optimize an antenna response, it is possible to enhance beamforming and / or for generating a corresponding codebook. According to an embodiment, an apparatus is provided that comprises a plurality of antenna elements. A control unit of the apparatus controls the plurality of antenna elements to form a plurality of beams using sets of beamforming weighting factors and to concurrently transmit and receive on the plurality of beams, the plurality of beams including at least a transmit beam and a receiver beam. The control unit is configured for using a self- interference information indicating a self-interference between a first number of transmit antenna elements of the plurality of antenna elements used for forming the transmit beam and a second number of receive antenna elements of the plurality of antenna elements used for forming the receive beam for determining at least one set of beamforming weighting EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX factors to optimize an antenna response related to the transmit beam and the receive beam. The control unit is configured for using the set of beamforming weighting factors for beamforming and / or for generating a beamforming codebook related to the plurality of antenna elements. According to an embodiment, a method comprises controlling a plurality of antenna elements to form a plurality of beams using sets of beamforming weighting factors and to concurrently transmit and receive on the plurality of beams, the plurality of beams including at least a transmit beam and a receive beam. The method comprises using a self- interference information indicating a self-interference between a first number of transmit antenna elements of the plurality of antenna elements used for forming the transmit beam and a second number of receive antenna elements of the plurality of antenna elements used for forming the receive beam for determining at least one set of beamforming weighting factors to optimize an antenna response related to the transmit beam and the receive beam. The method is executed such that the beam formed weighting factors are used for beamforming and / or for generating a beamforming codebook related to the plurality of antenna elements. Further advantageous modifications of the present invention are defined in the dependent claims. Preferred embodiments of the present invention will now be described whilst making reference to the accompanying figures in which: Fig.1 shows a schematic block diagram of an apparatus according to an embodiment; Fig.2 shows a schematic block diagram of an apparatus according to an embodiment comprising a base band processing unit; Fig.3a shows a schematic polar diagram of beams formed with a known 5G beam codebook ; Fig. 3b shows a schematic polar diagram of transmit beams formed with a codebook obtained according to embodiments to cancel or attenuate the self-interference; EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX Fig.3c shows a self-interference attenuation obtained by beam codebooks in Fig.3a and Fig.3b in accordance with embodiments described herein; and Fig.4 shows a schematic flow chart of a method that may be used to determine beam factor weights according to an embodiment. Equal or equivalent elements or elements with equal or equivalent functionality are denoted in the following description by equal or equivalent reference numerals even if occurring in different figures. In the following description, a plurality of details is set forth to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well known structures and devices are shown in block diagram form rather than in detail in order to avoid obscuring embodiments of the present invention. In addition, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise. Fig.1 shows a schematic block diagram of an apparatus 10 according to an embodiment. Apparatus 10 comprises a plurality of antenna elements 12 that comprises transmit antenna elements 14 and receive antenna elements 16. The configuration of antenna element of a plurality of antenna elements 12 may be static or constant but may, as an alternative, be changed in a semi-static manner or dynamically. For example, one or more antenna elements may be used for transmission purposes as well as for receive purposes, may be used as a transmission antenna element at a first instance of time and may be used as a receive antenna element at a different second instance of time. The plurality of antenna elements 12 may comprise individual antennas or antenna elements or one or more antenna arrays. For example, a first antenna array may form at least a part of the transmission antenna elements 14 and a second antenna array may form at least a part of the receive antenna elements 16. The transmission antenna elements 14 and the receive antenna elements 16 may be spaced from one another but may also be arranged co-located or at an essentially same location, e.g. arranged with antenna elements close to each other or even in an interleaved arrangement or the like. For transmitting a transmission beam 18, at least a subset of the transmission antenna elements 14 may be used. For forming a receive beam 22, at least a subset of the receive EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX antenna elements may be used. That is, one or more antenna elements may remain unused when forming a transmit beam 18 and / or a receive beam 22. According to embodiments, apparatus 10 may be configured for simultaneously forming 2 or more, e.g. at least 3, at least 4, at least 6, at least 7, at least 8, at least 10 or even more transmit beams and / or to form a same or different number of at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10 or even more received beams. Apparatus 10 comprises a control unit 24 configured for controlling the plurality of antenna elements 12 to form a plurality of beams using sets of beamforming weighting factors and to concurrently transmit and receive on the plurality of beams. That is, the transmit beam 18 and the receive beam 22 may be formed concurrently, i.e., simultaneously and / or for a digital signal processing that is parallel in time. The plurality of beams formed by apparatus 10 includes at least transmit beam 18 and receive beam 22. When forming the transmit beam 18, e.g. for transmitting a signal, a self-interference 26 may interfere on the signal chain related to the receive beam 22. In other words, reception of a signal received with the receive beam 22 may be interfered by the signal transmitted with the transmission beam 18. The control unit 24 is configured for using a self-interference information 28 indicating the self-interference 26 between the transmit antenna elements 14 and the receive antenna elements 16. The control unit 24 is configured for determining at least one set of beamforming weighting factors 32 based on the self-interference information 28 to optimize an antenna response related to the transmit beam 18 and the receive beam 22, i.e. to determine the set of beamforming weighting factors 32 such that the performance of the currently formed transmit beam 18 and receive beam 22 is optimized. This may relate to using an optimization criterion and will be explained in detail below. The at least one set 32 may be used by control unit 24 for forming the transmit beam 18 and / or the receive beam 22 or, more generally, for beamforming but may, as an alternative or in addition, be used by control unit 24 to generate a beamforming codebook related to the plurality of antenna elements 12. The plurality of antenna elements 12 may comprise one or more antenna arrays and / or a plurality of antennas. This may be understood that apparatus 10 may perform a sort of calibration resulting in a codebook comprising the set EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX of beamforming weighting factors 32 that may be used by other apparatuses having a same or at least comparable structure of the plurality of antenna elements 12. In other words, the set of beamforming weighting factors 32 may be used for the same plurality of antenna elements 12 or a similar arrangement. By use of the set of beamforming weighting factors 32, the transmit beam 18 may be adapted for the receive beam 22 or vice versa. By obtaining sets of beamforming weighting factors for both the transmit beam 18 and the receive beam 22, both beams may be adapted with regard to one another. Further, by obtaining more than a single set of beamforming weighting factors for more than a single transmit beam and / or for more than a single receive beam, there may be provided a basis for selection to use one or more specific transmit beams and / or one or more specific receive beams from a plurality of available beams. To use the self-interference information 28 for obtaining the set(s) of beamforming weighting factors 32, the self-interference attenuation or self-interference cancellation may be included already at a stage where the beams are selected such that the generation of self- interference is reduced or even minimized already when transmitting signals. When compared to digital signal processing to remove the self-interference, this may be of advantage as the self-interference is prevented from being generated. When using the sets of beamforming weighting factors in the form of a codebook, by way of example only, the complexity of avoiding self-interference may be comparable or even the same as forming regular beams as the generation thereof may simply rely on using other weighting factors. This may avoid computational power to be spent on a later removal of the effects of interference. According to an embodiment, apparatus 10 is configured to sense a surrounding of the apparatus using a reflection of a radio signal, e.g., apparatus may transmit the radio signal with the transmit beam 18 which is directed into a first direction or beam direction, e.g., a direction along which the main lobe of the transmit beam 18 points. Apparatus 10 may direct the receive beam 22 into a second direction pointing towards a reflector, the reflector receiving from a surrounding of the apparatus 10 the reflection of the radio signal and directing the reflection of the radio signal towards apparatus 10. Based on a location and / or distance of the reflector and / or a distance between transmission antenna elements 14 and receive antenna elements 16, the first and second direction may be essentially equal or may be different from one another. EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX According to an embodiment, the control unit 24 is configured for determining a set of transmit beamforming weighting factors for the transmit beam 18 along a transmit beam direction and for determining a set of receive beamforming weighting factors for the receive beam 22 along a receive beam direction, e.g., first and second directions described above. The receive beam direction may correspond to the transmit beam direction which may relate to a same direction but may also incorporate a scenario relating to a triangulation based on a spacing between the transmit antenna elements 14 and the receive antenna elements 16 as well as a distance to the reflector. The cell–interference information 28 may relate to an interference between transmit beams formed concurrently with receive beams using the plurality of antenna elements 12. The control element 24 may be adapted to determine, for the plurality of beams, a corresponding plurality of sets of beam forming weighting factors. Beamforming and Multi-Input Multi-Output (MIMO) techniques have been part of the 3GPP specifications since the standardization of 4G communication. Here, the focus has been twofold: on the one hand, digital and hybrid beamforming architectures enable the transmission of multiple data layers and multiusers MIMO; on the other hand, analog beamforming improves signal transmission via beam focusing. For 5G NR, beamforming precoder codebooks have been specified to serve as a common knowledge between the network and the user for MIMO channel estimation and beam management. The codebook of the current specification is based on the Discrete-Fourier-Transform (DFT) [2]. For these DFT precoding matrices, all entries have equal magnitude and varying phase, which makes them suitable for all types of beamforming architectures including phase-arrays. Fig.2 shows a schematic block diagram of an apparatus 20 according to an embodiment that may be based on apparatus 10. Apparatus 20 comprises a base band processing unit 34 that may be connected to a conversion unit 36, e.g., a digital-analog-converter, DAC. An up-converter 38 may receive the output signal of conversion unit 36, e.g., at a baseband frequency and may modulates it to a higher frequency based on a signal from a signal source 42, e.g., for a radio transmission to provide an input for a power amplifier 44 that may be connected to a number of Mttransmit chains 46, each connected to an antenna element 48 of the plurality of transmission antenna elements 14. As described, with the plurality of transmission antenna elements 14 one or more beams 181, 182may be directed along different directions at a same time or during different time intervals. Transmit beam 181may be directed, intentionally or unintentionally to a target or reflector 52 to result in a EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX signal received with receive beam 22 by use of a plurality Mrof antenna elements of the receive antenna elements 16. Transmit beam 182may be directed so as to point towards a different communication device such as a user equipment 54 operated by user k. At least for the antenna elements used for forming a transmit beam and / or a receive beam, a cell-interference may be generated or provided from each of the Mtantenna elements of the transmit antenna elements 14 towards each of the receive antenna elements 16. By way of non-limiting example only, the number Mtis 4 and Mris 4. Antenna element 481of the transmit antenna elements 14 may interfere each of the antenna elements 485, 486, 487and 488of the Mrantenna elements 16. Similarly, each of the antenna elements 482, 483and 484may interfere each of the antenna elements 485.486, 487and 488. Apparatus 20 may comprise receiver chain 56, e.g., connected to the plurality of receive antenna elements 16 that may be connected to a combiner 58 providing an input combined with a second signal source 62 for a further conversion unit 64, e.g., an analog-to-digital converter, ADC. The control unit of apparatus 20 may be configured, for example, to control the respective TX beam former weights w and the RX beam former weights C that may be each considered as a vector to provide input for each of chain 46 and 56. In an environment of apparatus 20 there may be arranged an unprobed target 66, each, a reflector towards which at least during some instances off time no beam is formed, whilst as an alternative or in addition to transmit beam 181there may also be pointed a transmit beam toward target 66. The control unit 24 may be configured to control a maximum antenna power Patapplied to the plurality of transmit antennas 14 as well as controlling the receive chain 56, e.g., to avoid saturation of one or more elements when exceeding a maximum power for saturation Psat. Conversion units 36 and / or 46 may be operated in a static or in a dynamic range. As will be described later in more detail, hkmay describe a channel between device 20 and device 54. Whilst θq*relates to the direction towards target q*, i.e., reflector 52, θq’relates to a direction towards to reflector 66 may provide for an attenuation α referred to αq’. wherein Hris the channel matrix between the transmit antennas 14 and the receive antennas 16. It is noted that in accordance with the described embodiments, Hrmay account especially or only for the direction of departure / arrival of a signal. EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX Some embodiments rely on the assumption of a radiofrequency frontend equipped with ^^^^TXtransmit antennas and ^^^^RXreceive antennas and capable of phase control for each transmit and receive antenna port. According to the embodiment, the self-interference channel, ^^^^^^^^,is a ^^^^RX × ^^^^TX complex matrix that is assumed to be known for one or more frequencies^^^^ ∈ {^^^1^ ,^^^2^ , … ,^^^^^^^^}. The ^^^^^^^^ can be obtained through a calibration process, e.g., by signals such as pilot signals. Such a calibration process may be performed in the production / assembling stage and / or once or periodically after deployment (i.e., during off-times or valley hours).According to an embodiment, the ^^^^RX + ^^^^TX − 2 degrees of freedom can be exploited tosuppress self-interference at the frequencies of interest below a predefined ^^^^^^^^. By comparison, DFT beamforming applies a constant phase shift between adjacent antenna ports and the degrees of freedom reduce thus to 2.Each transmit beam ℓ = {1, … , ^^^^} is, for example, characterized by a central angle ^^^^ℓ, andits array response at ^^^^ℓfor the beamforming weights^^^^ can be computed as ^^^^ℓ^^^^^^^^TX(^^^^)with ^^^^^^^^TX(^^^^) the steering vector of antenna array which may be referred to, according to some embodiments, synonymously as antenna element), which is determined by the arraygeometry and number of elements ^^^^TX. Likewise, the beamforming weights ^^^^ℓ for ℓ ={1, … , beams are characterized by the same or a different ^^^^ℓ and the arrayresponse can be obtained via the receive steering array ^^^^^^^^RX(^^^^)as ^^^^ℓ^^^^^^^^^^^^RX(^^^^). The controlunit may maximize the array response magnitude at the pointing direction in order to preserve the pointing direction of each beam. As a result, the beamforming weights ^^^^ℓand^^^^ for ℓ = {1, … , be determined by the control unit and / or with a methodto an embodiment as: maximize(^^^^)^^^^ ^^^^((( … ℓ ^^^^,^^^^ =Note that the optimization of the control unit is with regard to the antenna response based on the form: EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX^^^^ℓ^^^^^^^^^^^^RX(^^^^ℓ)^^^^^^^^^^^^TX(^^^^ℓ)^^^^ℓ may be related to further, less and / or other boundary conditions. The solutions to these optimization problems produce beamforming weights for phased- arrays. In the case where tapering (e.g. individual gain control of every antenna port) ispossible, the last two constraint groups can be substituted by ∥ ^^^^ℓ ∥= 1 and ∥ ^^^^ℓ ∥= 1,respectively, and the SIC will typically improve. Fig.3 a-c has for this case and may hence show a respective example. The optimization problems can also be extended to account for low sidelobe-level design or RX amplification saturation. The optimization problems can be solved by splitting it into transmit-only and receive-only subproblems and applying semidefinite relaxation techniques.More specifically, one can write the semidefinite matrices ⋅ ^^^^^^^^ and ^^^^ ^^^^ ℓ ℓ = ^^^^ℓ ⋅ ^^^^ℓ .Furthermore, one can write the self-interference matrix as the matrix product ^^^^^^^^ = ^^^^^^^^,U ⋅^^^^ is the singular valuedecomposition of ^^^^^^^^. Embodiments base on the recognition that with these considerations, the problem can be split into two semi-definite aspects or programs or tasks, e.g., for the control unit 24, for transmission, tx, and reception, rx, namely: ((( In case optimization is required or desired only for one of both aspects, the transmit side or the receive side, embodiments relate to solving one of the semi-definite aspect, e.g., using the control unit 24. EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX The matrices ^^^^ℓand ^^^^ℓcan be obtained, e.g., using the control unit 24, with standard convex optimization solvers, from which ^^^^ℓand ^^^^ℓcan be extracted as the principal component, i.e., the principal eigenvector times the root of the principal eigenvalue. As described above, An apparatus may be adapted that the control unit is adapted to optimize the antenna response based on the form: ^^^^^^^^^^^ wherein wlis a beamforming weight for the transmit beam, clis a beamforming weight for a receive beam, , ^^^^^^^^RX(^^^^ℓ)is a steering vector of the antenna array related to a beam direction Θlof the receive beam, ^^^^^^^^TX(^^^^ℓ)is a steering vector of the antenna array related to a beam direction Θlof the transmit beam. Alternatively or in addition the control unit may determine the set of beamforming weighting factors that optimizes the antenna response of at least one beam formed with the antenna array to determine a set of beamforming weighting factors for the transmit beam and a set of beamforming weighting factors for a corresponding receive beam based on the determination rule: wherein Hfis the self-interference information, wherein wlis a set of beamforming weights for the transmit beam, clis a set of beamforming weights for the receive beam. Alternatively or in addition the control unit may determine the set of beamforming weighting factors that optimizes the antenna response of at least one beam formed with the antenna array based on determining a solution for an optimization problem that is based on the determination rule: ^^^^ℓ∈ℂ^^^^TX , ^^^^ℓ∈ℂ^^^^RX�^^^^ℓ^^^^^^^^^^^^RX(^^^^ℓ)^^^^^^^^^^^^TX(^^^^ℓ)^^^^ℓ�wherein wlis a weight for the transmit beam, clis a for the receive beam, ℂ^^^^TXis a space of complex valued vectors of dimension MTX, ℂ^^^^RXis a EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX space of complex valued vectors of dimension MRX, ^^^^^^^^RX(^^^^ℓ)is a steering vector of the antenna array related to a beam direction Θlof the receive beam, ^^^^^^^^TX(^^^^ℓ)is a steering vector of the antenna array related to a beam direction Θlof the At least a part of the determined solution may be provided to a different entity, e.g., using a respective interface in order to harmonize the codebooks used in at least a part of the wireless communication network, e.g., in a cell thereof. For example, the control unit is to solve the optimization problem under a, possibly first boundary condition that is based on: ^^^^ wherein f is a frequency wlis a beamforming weight for the transmit beam, clis a beamforming weight for the receive beam, εfis a predefined value of an error. Alternatively or in addition the control unit is to solve the optimization problem under a possibly second boundary condition that is based on: wherein MTXis a number of transmit antenna elements and clis a set of beamforming weighting factors for the receive beam. Alternatively or in addition, the control unit is to solve the optimization problem under a possibly third boundary condition that is based on: ∀^^^^ ∈ {1, … ,^^^^ ^RX}: [^^^^ ^^^ℓ^^^^ℓ ]^^^^,^^^^ = 1wherein MRXis a number of receive antenna elements and clis a beamforming weight for the receive beam. According to an embodiment, the control unit may be configured to determine the set of beamforming weighting factors that optimizes the antenna response of at least one beam EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX formed with the antenna array based on determining a solution for an optimization problem that is based on the determination rule: maximize^^^^^^^^^^^^�^^^^ℓ ^^^^^^^^RXℓ∈ℂ^^^^TX, ^^^^ℓ∈ℂ^^^^RX (^^^^ℓ)^^^^^^^^TX (^^^^ℓ)^^^^ℓ�  s. t.^^^^ ^^^^^^^^ �^^^^^^^^^^^^^^^^^^^^� ≤ ^^^^( wherein wlis a beamforming weight for the transmit beam, clis a beamforming weight for the receive beam, wherein MRXis a number of receive antenna elements and clis a beamforming weight for the receive beam; wherein MTXis a number of transmit antenna elements and clis a set of beamforming weighting factors for the receive beam; ℂ^^^^TXis a space of complex valued vectors of dimension MTX, ℂ^^^^RXis a space of complex valued vectors of dimension MRX, ^^^^^^^^RX(^^^^ℓ)is a steering vector of the antenna array related to a beam direction Θlof the receive beam, ^^^^^^^^TX(^^^^ℓ)is a steering vector of the antenna array related to a beam direction Θlof the transmit beam; wherein f is a frequency, εfis a predefined value of an error. Although the array response is described to relate to a set of frequencies and / or a plurality of beams, the optimization procedure may also be implemented for determining a single solution, that is, a single vector w and / or a single vector c, each referring to set of beamforming weights as incorporating multiple vector elements, each element forming a beamforming weight. The antenna response that is subject of the underlying embodiments may comprise a transmit antenna response associated with the transmit beam 18 and may comprise a receive antenna response associated with the receive beam 22. Advantageous embodiments refer to an apparatus such as apparatus 10 and / or 20 being at least a part of a user equipment, UE, or a base station. The set(s) of beam forming weighting factor may be used to generate a codebook for another apparatus and / or may be used by the apparatus for forming the beam(s). Fig.3a shows a schematic polar diagram of beams 18’0to 18’7formed with a known 5G beam codebook (DFT based) with a beam directivity measured in dBi. Fig. 3b shows a schematic polar diagram of transmit beams 180to 187formed with a codebook obtained EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX according to embodiments to cancel or attenuate the self-interference SI to have tapered beams. The beam directivity is given in dBi. The beam directivity in Figs. 3a-b is shown for transmit beams Tx only. For the results presented, an embodiment is considered with 12 antenna elements in transmit (Tx) and receive (Rx) uniform linear arrays, ULAs. The self-interference attenuation shown in Fig.3c includes the SI channel and the Tx / Rx array gains. Fig. 3c shows a comparison of self-interference attenuation given in dB for the example configuration presented in Fig.3a and Fig.3b underlying the above-described optimization procedure. It may be shown that for each beam a considerable increase in self-interference attenuation may be obtained. In other words, Fig.3c shows schematic results for a self-interference attenuation for both beam codebooks in Figs.3a and 3b. The left set of bars corresponds to the 5G codebook and the right one to the codebook according to embodiments. Fig.4 shows a schematic flow chart of a method that may be used to determine beam factor weights according to an embodiment. In a step 410 of method 400 there is executed controlling a plurality of antenna elements to form a plurality of beams using sets of beamforming weighting factors and to concurrently transmit and receive on the plurality of beams, the plurality of beams including at least a transmit beam and a receive beam. A step 420 comprises using a self-interference information indicating a self-interference between a first number of transmit antenna elements of the plurality of antenna elements used for forming a transmit beam and a second number of receive antenna elements of the plurality of antenna elements used for forming the receive beam for determining at least one set of beamforming weighting factors to optimize an antenna response related to the transmit beam and the receive beam. The method is implemented such that the set of beamforming weighting factors are used for beamforming and / or for generating a beamforming codebook related to the plurality of antenna elements. Such a codebook may be provided by a suitable wired or wireless interface, e.g., from a base station to UEs and / or vice versa or between UEs. Embodiments provide for a solution to obtain a beamforming codebook design for self- interference-cancelling beamforming. Self-interference cancellation, SIC, as provided by the embodiments described herein enables integrated sensing and communication ISAC in EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX a monostatic setup. An apparatus described herein may, thus, comprise transmit antennas 14 and receive antennas 16 in a co-located or integrated manner and / or may implement the antenna elements in a monostatic setup. Embodiments may be used for a multi-input, multi-output, MIMO, beamforming codebook, e.g., in connection with 4G and / or 5G that are based on the DFT, which itself offers only limited SIC. Embodiments suggest to use information on the (possibly wideband) self- interference MIMO channel to enable monostatic ISAC at the base station and / or the user equipment, UE. The self-interference information and / or optimization procedure or process may use an interface between the transmitter and receiver. Embodiments allow for an optimization procedure to obtain transmit and receive codebooks that provide a good self-interference cancellation as described above. Embodiments allow to obtain a method to enable monostatic sensing in infrastructure and / or terminals. Embodiments allow for an increase in dynamic range for ISAC and may also be used to eliminate the need for additional hardware and / or isolation distances between transmitter and receiver antennas. Embodiments provide for the advantageous situation to avoid a separate sniffer for the infrastructure-based case. Embodiments may be used in mobile communications, for example, the 3GPP RAN implementing sensing functionality. Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus. Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be performed using a digital storage medium, for example a floppy disk, a DVD, a CD, a ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, having electronically readable control signals EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX stored thereon, which cooperate (or are capable of cooperating) with a programmable computer system such that the respective method is performed. Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed. Generally, embodiments of the present invention can be implemented as a computer program product with a program code, the program code being operative for performing one of the methods when the computer program product runs on a computer. The program code may for example be stored on a machine readable carrier. Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine readable carrier. In other words, an embodiment of the inventive method is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer. A further embodiment of the inventive methods is, therefore, a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may for example be configured to be transferred via a data communication connection, for example via the Internet. A further embodiment comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein. A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein. EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX In some embodiments, a programmable logic device (for example a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods are preferably performed by any hardware apparatus. The above described embodiments are merely illustrative for the principles of the present invention. It is understood that modifications and variations of the arrangements and the details described herein will be apparent to others skilled in the art. It is the intent, therefore, to be limited only by the scope of the impending patent claims and not by the specific details presented by way of description and explanation of the embodiments herein. EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX References [1] T. Wild, A. Grudnitsky, S. Mandelli, M. Henninger, J. Guan, and F. Schaich, “6G Integrated Sensing and Communication: From Vision to Realization,” ArXiv Prepr. ArXiv230501978, 2023. [2] 3GPP, “NR; Physical layer procedures for data,” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network, 3GPP TS 38.214, Sep.2023. EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX

Claims

Claims 1. An apparatus (10, 20) comprising: a plurality of antenna elements (12, 14, 48, 481-8, 16); a control unit (24) for controlling the plurality of antenna elements to form a plurality of beams (18, 181, 182, 22) using sets of beamforming weighting factors (32) and to concurrently transmit and receive on the plurality of beams, the plurality of beams including at least a transmit beam (18, 181, 182) and a receive beam (22); wherein the control unit is configured for using a self-interference information (28) indicating a self-interference (26) between a first number of transmit antenna elements (14, 48, 481-4) of the plurality of antenna elements used for forming the transmit beam and a second number of receive antenna elements (16, 485-8) of the plurality of antenna elements used for forming the receive beam for determining at least one set of beamforming weighting factors to optimize an antenna response related to the transmit beam and the receive beam; wherein the control unit is configured for using the set of weighting factors for beamforming and / or for generating a beamforming codebook related to the plurality of antenna elements.

2. The apparatus (10, 20) of claim 1, wherein the apparatus is configured to sense a surrounding of the apparatus using a reflection of a radio signal, wherein the apparatus is configured to transmit the radio signal on the transmit beam (18, 181, 182) which is directed into a first direction, wherein the apparatus is configured to direct the receive beam (22) into a second direction, the second direction pointing towards a reflector, the reflector receiving from the surrounding the reflection of the radio signal and directing the reflection of the radio signal towards the apparatus, and wherein the first direction into which the transmit beam is directed is essentially equal or different from the second direction into which the receive beam is directed. EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX3. The apparatus (10, 20) of claim 1 or 2, wherein the control unit (24) is for determining a set of transmit beamforming weighting factors for the transmit beam (18, 181, 182) along a transmit beam direction; and determining a set of receive beamforming weighting factors for the receive beam (22) along a receive beam direction corresponding to the transmit beam direction.

4. The apparatus (10, 20) of one of previous claims, wherein the self-interference information (28) relates to interference between transmit beams (18, 181, 182) formed concurrently with receive beams (22) using the plurality of antenna elements (12, 14, 48, 481-8, 16).

5. The apparatus (10, 20) of one of previous claims, wherein the plurality of antenna elements (12, 14, 48, 481-8, 16) comprises an antenna array or a plurality of antennas.

6. The apparatus (10, 20) of one of previous claims, wherein the control unit (24) is adapted to determine, for the plurality of beams (18, 181, 182, 22), a correspondingplurality of sets of beamforming weighting factors (32) .

7. The apparatus (10, 20) of one of previous claims, wherein the antenna response comprises a transmit antenna response associated with the transmit beam (18, 181, 182); and comprises a receive antenna response associated with the receive beam (22).

8. The apparatus (10, 20) of one of previous claims, wherein the control unit (24) is adapted to optimize the antenna response based on the form: ^^^^ℓ^^^^^^^^^^^^RX(^^^^ℓ)^^^^^^^^^^^^TX(^^^^ℓ)^^^^ℓwherein wlis a beamforming weight for the (18, 181, 182), clis abeamforming weight for a receive beam (22), , a steering vector of the antenna array or plurality of antenna elements related to a beam direction Θlof the receive beam (22), ^^^^^^^^TX(^^^^ℓ)is a steering vector of the plurality of antenna elements related to a beam direction Θlof the transmit beam (18, 181, 182). EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX9. The apparatus (10, 20) of one of previous claims, wherein the control unit (24) is to determine the set of beamforming weighting factors (32) that optimizes the antenna response of at least one beam formed with the plurality of antenna elements to determine a set of beamforming weighting factors for the transmit beam (18, 181, 182) and a set of beamforming weighting factors for a corresponding receive beam (22) based on the determination rule: ^^^^ℓ^^^^^^^^^^^^^^^^ℓwherein Hfis the self-interference information (28), wherein wlis a set of beamforming weights for the transmit beam (18, 181, 182), clis a set of beamforming weights for the receive beam.

10. The apparatus (10, 20) of one of previous claims, wherein the control unit (24) is to determine the set of beamforming weighting factors (32) that optimizes the antenna response of at least one beam formed with the plurality of antenna elements based on determining a solution for an optimization problem that is based on the determination rule:wherein wlis a beamforming weight for the transmit beam (18, 181, 182), clis a beamforming weight for the receive beam (22), ℂ^^^^TXis a space of complex valued vectors of dimension MTX, ℂ^^^^RXis a space of complex valued vectors of dimension MRX, ^^^^^^^^RX(^^^^ℓ)is a steering vector of the plurality of antenna elements related to a beam direction Θlof the receive beam, ^^^^^^^^TX(^^^^ℓ)is a steering vector of the plurality of antenna elements related to a beam direction Θlof the transmit beam.

11. The apparatus (10, 20) of claim 10, wherein the control unit (24) is to solve the optimization problem under a boundary condition that is based on:∈, , … ℓ ≤EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCXwherein f is a frequency wlis a beamforming weight for the transmit beam (18, 181, 182), clis a beamforming weight for the receive beam (22), εfis a predefined value of an error.

12. The apparatus (10, 20) of claim 10 or 11, wherein the control unit (24) is to solve the optimization problem under a boundary condition that is based on: ^^^^ =wherein MTXis a number of transmit antenna elements (14, 48, 481-4) and clis a set of beamforming weighting factors for the receive beam (22).

13. The apparatus (10, 20) of one of claims 10 to 12, wherein the control unit (24) is to solve the optimization problem under a boundary condition that is based on: ^^^^wherein MRXis a number of receive antenna elements (16, 485-8) and clis a beamforming weight for the receive beam (22).

14. The apparatus (10, 20) of one of previous claims, wherein the control unit (24) is to determine the set of beamforming weighting factors (32) that optimizes the antenna response of at least one beam formed with the plurality of antenna elements based on determining a solution for an optimization problem that is based on the determination rule: �  s.(…RX ^^^^ ^^^^ℓ ^^^^,^^^^ =wherein wlis a beamforming weight for the transmit beam (18, 181, 182), clis a beamforming weight for the receive beam (22), wherein MRXis a number of receive antenna elements (16, 485-8) and clis a beamforming weight for the receive beam; wherein MTXis a number of transmit antenna elements (14, 48, 481-4) and clis a set of beamforming weighting factors for the receive beam; ℂ^^^^TXis a space of complex EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCXvalued vectors of dimension MTX, ℂ^^^^RXis a space of complex valued vectors of dimension MRX, ^^^^^^^^RX(^^^^ℓ)is a steering vector of the plurality of antenna elements related to a beam direction Θlof the receive beam, ^^^^^^^^TX(^^^^ℓ)is a steering vector of the plurality of antenna elements related to a beam direction Θlof the transmit beam; wherein f is a frequency, εfis a predefined value of an error.

15. The apparatus (10, 20) of one of previous claims, being at least a part of a user equipment, UE, or a base station.

16. The apparatus (10, 20) of one of previous claims, being adapted to provide the set of beamforming weights as a codebook for another apparatus.

17. A method (400) comprising: controlling (410) a plurality of antenna elements (12, 14, 48, 481-8, 16) to form a plurality of beams (18, 181, 182, 22) using sets of beamforming weighting factors (32) and to concurrently transmit and receive on the plurality of beams, the plurality of beams including at least a transmit beam (18, 181, 182) and a receive beam (22); using (420) a self-interference information (28) indicating a self-interference (26) between a first number of transmit antenna elements (14, 48, 481-4) of the plurality of antenna elements used for forming the transmit beam and a second number of receive antenna elements (16, 485-8) of the plurality of antenna elements used for forming the receive beam for determining at least one set of beamforming weighting factors (32) to optimize an antenna response related to the transmit beam and the receive beam; such that the set of weighting factors are used for beamforming and / or for generating a beamforming codebook related to the plurality of antenna elements.

18. A computer readable digital storage medium having stored thereon a computer program having a program code for performing, when running on a computer, a method (400) according to claim 17. EINREICHFASSUNG - FH2024P67032-draft application text_ver5.DOCX

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