Self- and cross-sector interference suppression

Abstract

Disclosed is an apparatus for transmission of data comprising multiple sector antennas associated with sectors, each sector antenna of the sector antennas comprising a reception array of antenna array elements and a transmission array of antenna array elements, the apparatus comprising means, for each sector, referred to as current sector, the means being configured for transmitting a subset of the data, associated with the current sector using a subcarrier comprising at least: mapping the subset of the data associated with the current sector to data symbols; and transforming each data symbol using at least one weight vector for obtaining a beamformed data symbol, and modulating the beamformed data symbol with the subcarrier; the means being configured for obtaining the weight vectors by iteratively adjusting the weight vectors to reduce a contribution of self-interference and cross-sector interference in signals of the apparatus.

Description

[0001] DESCRIPTION

[0002] SELF- AND CROSS-SECTOR INTERFERENCE SUPPRESSION

[0003] Technical Field

[0004] Various example embodiments relate to telecommunication systems, and more particularly to cross-sector interference suppression.

[0005] Background

[0006] New radio (NR) in 5G employs two primary duplexing methods: Time Division Duplexing (TDD) and Frequency Division Duplexing (FDD). In TDD, both downlink (DL) and uplink (UL) transmissions may use the same frequency channel, but they are separated by time. Conversely, FDD may utilize two distinct frequency channels, one for DL and another for UL, allowing for simultaneous transmissions. A variation known as halfduplex FDD also exists, which may use two frequency channels like FDD but separates DL and UL in time, not simultaneously. This approach may help avoid the costly duplexing filters.

[0007] Additionally, a duplexing scheme called sub-band non-overlapping full duplex or nonoverlapping sub-band full duplex or sub-band full duplex (SBFD), based on the TDD model, has been developed. Unlike traditional TDD, where transmission in a time slot may be either DL or UL, SBFD may allow for simultaneous DL and UL transmissions within the same time slot. SBFD may operate on a single frequency channel but utilize multiple frequency subchannels for UL and DL. The introduction of SBFD may aim to enhance network coverage and reduce latency. Improved coverage may be achieved as user equipments (UEs) have more opportunities for UL transmission, allowing them to allocate more energy by a larger UL duty cycle than TDD with a fixed UL / DL rhythm. Moreover, the frequent UL transmission opportunities contribute to reduced latency. Some aspects of the duplexing scheme SBFD have been described in the technical report TR 38.858 developed by the 3rd Generation Partnership Project (3GPP).

[0008] Summary

[0009] Example embodiments provide an apparatus for transmission of data in a wireless communication system, the apparatus comprising multiple sector antennas associated with sectors, each sector antenna of the sector antennas comprising a reception array of antenna array elements and a transmission array of antenna array elements, each sector antenna being configured for transmitting signals, using the transmission array, to devices within a sector of the sectors that is associated with the sector antenna and for receiving signals, using the reception array, from devices within the sector, the apparatus comprising means, for each sector, referred to as current sector, the means being configured for transmitting a subset of the data, associated with the current sector using a subcarrier comprising at least: mapping the subset of the data associated with the current sector to data symbols; and transforming each data symbol using at least one weight vector for obtaining a beamformed data symbol, and modulating the beamformed data symbol with the subcarrier; the means being configured for obtaining the weight vectors by iteratively adjusting the weight vectors to reduce a contribution of selfinterference and cross-sector interference in signals of the apparatus.

[0010] Example embodiments provide a method (referred to as transmission method) transmission of data in a wireless communication system using an apparatus, the apparatus comprising multiple sector antennas associated with sectors, each sector antenna of the sector antennas comprising a reception array of antenna array elements and a transmission array of antenna array elements, each sector antenna being configured for transmitting signals, using the transmission array, to devices within a sector of the sectors that is associated with the sector antenna and for receiving signals, using the reception array, from devices within the sector, the method comprising, for each sector, referred to as current sector, transmitting a subset of the data, associated with the current sector using a subcarrier, by at least: mapping the subset of the data associated with the current sector to data symbols; and transforming each data symbol using at least one weight vector for obtaining a beamformed data symbol, and modulating the beamformed data symbol with the subcarrier; wherein the weight vectors are obtained by iteratively adjusting the weight vectors to reduce a contribution of selfinterference and cross-sector interference in signals of the apparatus.

[0011] Example embodiments provide a computer program comprising instructions, that when executed by an apparatus, cause the apparatus to perform the transmission method.

[0012] Example embodiments provide a calibration method for an apparatus, the apparatus comprising multiple sector antennas, each sector antenna comprising a reception array of antenna array elements and a transmission array of antenna array elements, each sector antenna being configured for transmitting signals, using the transmission array, to devices within a sector and for receiving signals, using the reception array, from devices within the sector, each sector antenna of the sector antennas being comprised in or connected to a radio unit, each radio unit being configured to operate in a source mode of operation and a target mode of operation, wherein, if a radio unit is configured to operate in the target mode of operation, at least one other radio unit is configured to operate in the source mode of operation for a determination relating to cross-sector interference, each radio unit operating in the source mode of operation being referred to as source radio unit, each radio unit operating in the target mode of operation being referred to as target radio unit, the calibration method comprising: controlling each radio unit to operate in the target mode of operation such that the target radio unit receives from each source radio unit that is different from the target radio unit at least one calibration signal; using the received calibration signals for determining a channel feature of at least one channel between the sector antennas, the channel feature relating to cross-sector interference.

[0013] For example, calibration signals for determining one or more channel features of a plurality of channels may be received simultaneously. The plurality of channels may comprise, in addition to the at least one channel between the sector antennas, one or more further channels. The target radio unit may act simultaneously as source radio unit, transmit at least one calibration signal and receive it, too, and at least one of the one or more further channels may be between the transmission array and the reception array of the sector antenna associated with the target radio unit (i.e. relating to selfinterference). In this context, ‘associated with’ may mean e.g. ‘comprised in’ or ‘connected to’. The determined one or more channel features may comprise one channel feature per channel of the plurality of channels. In this case, a channel feature may either relate to cross-sector interference or to self-interference. Alternatively, or additionally, the determined one or more channel features may comprise a channel feature of more than one channel of the plurality of channels, wherein the channel feature is, for example, a channel matrix. The more than one channel may, for example, be the plurality of channels.

[0014] Example embodiments provide a radio unit being configured to perform and / or control the calibration method, wherein the radio unit is part of the apparatus. The radio unit may comprise transmitters and receivers for one sector antenna. Example embodiments provide a distributed unit being configured to be involved in and / or control the calibration method, wherein the distributed unit is part of the apparatus. The distributed radio unit may comprise at last one scheduler.

[0015] Example embodiments provide a method (referred to as pre-calibration method) for enabling cross-sector interference determination for an apparatus, the apparatus comprising multiple sector antennas, each sector antenna comprising a reception array of antenna array elements and a transmission array of antenna array elements, each sector antenna being configured for transmitting signals, using the transmission array, to devices within a sector and for receiving signals, using the reception array, from devices within the sector, each sector antenna of the sector antennas being comprised in or connected to a radio unit, each radio unit being configured to operate in a source mode of operation and a target mode of operation, wherein the apparatus is configured to operate at least one radio unit in the target mode of operation and, at the same time, at least one other radio unit in the source mode of operation, each radio unit operating in the source mode of operation being referred to as source radio unit, each radio unit operating in the target mode of operation being referred to as target radio unit, each radio unit having an interface for signaling inside the apparatus, the pre-calibration method comprising exchanging calibration related information over the interfaces, the calibration comprising measuring at least one coupling or channel feature between at least one antenna array element of a transmission array of a sector antenna and at least one antenna array element of a reception array of another sector antenna.

[0016] Brief Description of the Drawings

[0017] The accompanying figures are included to provide a further understanding of examples, and are incorporated in and constitute part of this specification. In the figures:

[0018] FIG.1 illustrates a part of an exemplifying radio access network;

[0019] FIG. 2 is a flowchart of a method for transmission of data in a wireless communication system using an apparatus;

[0020] FIG. 3A illustrates an apparatus for data transmission in accordance with an example of the present subject matter; FIG. 3B illustrates self- and cross-sector interference in signals of the apparatus of FIG. 3A;

[0021] FIG. 30 shows further components of the apparatus of FIG. 3A and illustrates a method of transmission of data symbols using the apparatus of FIG. 3A;

[0022] FIG. 4 illustrates an apparatus for providing beamformed data symbols in accordance with an example of the present subject matter;

[0023] FIG. 5 is a look up table (LUT) that is used for the digital predistortion according to an example of the present subject matter;

[0024] FIG. 6 shows a cumulative distribution function of error vector magnitude (EVM) of the quadrature phase-shift keying (QPSK) constellation with and without digital p re-distortion for a fixed combination of transmit (TX) beamforming vectors;

[0025] FIG. 7 is a flowchart of an iterative beam nulling algorithm in accordance with an example of the present subject matter;

[0026] FIG. 8 is a flowchart of a calibration method in accordance with an example of the present subject matter;

[0027] FIG. 9 depicts diagrams of interfaces between radio units and a distributed unit that enables to perform the calibration method in accordance with present subject matter;

[0028] FIG. 10 is a block diagram showing an example of an apparatus according to an example of the present subject matter;

[0029] FIG. 11 is a block diagram illustrating an addition of a compensation signal between low noise amplifier (LNA) stages in accordance with an example of the present subject matter.

[0030] Detailed Description

[0031] In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc., in order to provide a thorough understanding of the examples. However, it will be apparent to those skilled in the art that the disclosed subject matter may be practiced in other illustrative examples that depart from these specific details. In some instances, detailed descriptions of well-known devices and / or methods are omitted so as not to obscure the description with unnecessary detail.

[0032] The present subject matter may mitigate self-interference and cross-sector interference, which might be particularly beneficial for several reasons. In multisector antenna configurations where antenna arrays for different sectors are mounted close together, significant cross-sector interference can occur. Sometimes, this cross-sector interference might surpass the level of self-interference, especially in scenarios where self-interference has been reduced using methods like beam-nulling, analog interference cancellation or similar techniques.

[0033] The wireless communication system comprises nodes such as base stations, wherein each node may serve user equipments (UEs) located within the node’s geographical area of service. The wireless communication system may support one or more radio access technologies (RATs). A radio access technology of the radio access technologies may, for example, be evolved universal terrestrial radio access (E-LITRA, a.k.a. LTE), 5G new radio (NR), or a future 6G based system, but it is not limited to, as a person skilled in the art may apply the present subject matter to other wireless communication systems provided with necessary properties.

[0034] The cross-sector interference may also be referred to as co-site inter-sector interference. This indicates that the cross-sector interference may be an interference between different sectors at the same site (as opposed to between sectors of different sites). The site may be where the apparatus (e.g., a base station or a group of base stations or parts thereof), in particular the antennas, are deployed. Typical macro base station sites have three sectors. A cell may refer to a carrier in a sector. Hence there may be many cells per site.

[0035] The means of the apparatus may, for example, comprise at least one processor; and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, perform the transmission method. The antenna array element may refer to an element of an antenna array that may be individually electrically connected to a transmitter and / or a receiver. The antenna array element may comprise at least one dipole or at least one other radiating element. The antenna array element may comprise one or more antenna elements.

[0036] The means of the apparatus are configured, for the current sector, to transmit the subset of the data, associated with the current sector using the subcarrier, wherein the transmission of the subset of the data comprises operations of: mapping the subset of the data associated with the current sector to data symbols and transforming each data symbol using at least one weight vector for obtaining a beamformed data symbol, and modulating the beamformed data symbol with the subcarrier. The modulated beamformed data symbol may, for example, be transmitted using the transmission array of the sector antenna associated with the current sector. The data symbols, to which the subset of the data is mapped, may consist of one data symbol on the subcarrier for each symbol period.

[0037] The processing involving the operations of mapping and transforming may be performed sequentially per sector or concurrently for the sectors. The term “subset of the data” does not necessarily imply a strict subset. For example, the subset of the data may actually include all of the data or just a portion of the data.

[0038] The means are configured for obtaining the weight vectors by iteratively adjusting the weight vectors to reduce a contribution of cross-sector interference or self-interference and cross-sector interference in signals of the apparatus, wherein the signals may, for example, be signals received by the apparatus. For instance, the iterative adjustment may relate to signals prior to their transmission, while the cross-sector interference and maybe also self-interference is in signals received by the apparatus, and originating from signals that the apparatus itself has transmitted. The weight vector may have values (or weights). Before the iterative adjustment is performed, the weight vector may have initial values. After the iterative adjustment is performed, the obtained weight vector may have final values which may be different from the initial values. Adjusting the weight vector means that the values of the weight vector are adjusted. The weight vector used to transform the data symbol is the weight vector obtained by the iterative adjustment and thus has final values.

[0039] According to one example, the weight vectors may be obtained using a self-interference and cross-sector interference channel matrix representing channel properties of channels between the transmission arrays and the reception arrays. The channel refers to a propagation channel (as opposed to a frequency channel with a predefined frequency for data transmission over the frequency channel). For example, each matrix element of the self-interference and cross-sector interference channel matrix may characterize one channel. There is a multitude of channels: from each antenna array element of a transmission array to each antenna array element of a reception array.

[0040] According to one first beamforming example, each weight vector of the weight vectors represents a pre-distorted data symbol multiplied by a beamforming vector. Each weight vector of the weight vectors is associated with a data symbol and a sector of the sectors. Each weight vector of the weight vectors comprises weights associated respectively with the antenna array elements of the transmission array of the sector antenna associated with the sector associated with the weight vector. The transformation of the data symbol may be performed by replacing the data symbol with the weight vector that is associated with the current sector and the data symbol.

[0041] According to one example implementation of the first beamforming example, the number of antenna array elements in each transmission array is higher than the number of antenna array elements in each reception array. Alternatively, the number of antenna array elements in each transmission array is equal to the number of antenna array elements in each reception array.

[0042] According to one example implementation of the first beamforming example, the weight vectors associated with a set of data symbols to be transmitted simultaneously on one subcarrier are obtained concurrently. The set of data symbols may be transmitted simultaneously using the multiple sector antennas.

[0043] According to one second beamforming example, each weight vector of the weight vectors is associated with a sector of the sectors. Each weight vector of the weight vectors comprises weights associated respectively with the antenna array elements of the transmission array of the sector antenna associated with the sector associated with the weight vector. The transformation of the data symbol may be performed by weighting the data symbol with the weight vector that is associated with the current sector. For example, each weight vector of the weight vectors consists of weights associated respectively with the antenna array elements of the transmission array of the sector antenna associated with the sector associated with the weight vector.

[0044] For example, the weight vector may be primarily associated with a beam to a device or into some geographical area. Also, a data symbol may be associated with a beam to a device or for some geographical area. However, several data symbols may typically be transmitted using the same beam and thus the same weight vector.

[0045] According to one example implementation of the second beamforming example, the number of antenna array elements in each transmission array is higher than the number of antenna array elements in each reception array multiplied by the number of sector antennas of the apparatus. Alternatively, the number of antenna array elements in each transmission array is equal to the number of antenna array elements in each reception array multiplied by the number of sector antennas of the apparatus.

[0046] The term 'sector antenna' as used herein refers to a sector antenna of the apparatus according to the present subject matter unless explicitly defined otherwise. In some contexts, the term 'sector antenna' may be used interchangeably with the term 'sector' that is associated with the sector antenna.

[0047] According to one example implementation of the second beamforming example, the number of antenna array elements in each transmission array is at least the sum of the number of antenna array elements in all reception arrays of all sector antennas.

[0048] According to one example implementation of the second beamforming example, the weight vectors are iteratively obtained independently for each sector of the sectors.

[0049] According to one third beamforming example, the transformation of the data symbol comprises: weighting the data symbol with the weight vector that is associated with the data symbol, wherein the weight vector comprises weights associated with the antenna array elements, of the transmission arrays, respectively.

[0050] According to one example implementation of the third beamforming example, the beamforming of a data symbol for a device is not limited to the transmission array of the sector antenna associated with the sector in which the device is, but the beamforming may make use of transmission arrays of other sector antennas, too. This may mean that, conversely, each sector antenna is in this example not only configured for transmitting signals, using its transmission array, to devices within the sector that is associated with the sector antenna, but also to devices in other sectors. Hence if, on a subcarrier during a symbol period, different data symbols are to be transmitted to devices in different sectors, a superposition of the beamformed data symbols for these devices may be modulated and transmitted using the transmission arrays of all sector antennas. According to one example implementation of the third beamforming example, the subset of the data comprises the data. That is, the subset of the data includes all of the data. ‘All the data’ may refer to the data for all sectors or all sector antennas of the apparatus. The ‘subset of the data’ may refer to the data for transmission using the sector antenna associated with the current sector. In this example implementation of the third beamforming example, data symbols for devices in any sector of the sectors may be transmitted using all sector antennas, thus including the sector antenna associated with the current sector. This may mean that in this example, all the data is transmitted using the sector antenna associated with the current sector and hence included in the subset of the data.

[0051] According to one example implementation of the third beamforming example, for weighted data symbols to be transmitted simultaneously on one subcarrier, parts of the weighted data symbols may be added together. The addition may be performed before or after modulating the subcarrier with the beamformed data symbol associated with the current sector. The parts refer to the transmission array of the sector antenna associated with the current sector. For example, for each data symbol, there may be a weight vector for beamforming with vector elements for all antenna array elements of all sector antennas’ transmission arrays. The weight vector may be a concatenation of parts referring to different sector antennas wherein each part of the weight vector contains beamforming weights for the antenna array elements of one sector antenna’s transmission array. A part of a weighted data symbol may be a data symbol after weighting with just one part of the weight vector, resulting in a vector with the same length as the part of the weight vector. Such a part of a weighted data symbol may contain the beamformed data symbol for the sector antenna for which the part of the weight vector contains the beamforming weights. On the same subcarrier, different data symbols may be transmitted simultaneously, e.g. to devices within different sectors. Since each data symbol is transmitted by all sector antennas, the simultaneous transmission of different data symbols may require a linear superposition. For the current sector, this may be achieved by adding together the parts of weighted data symbols referring to its associated sector antenna.

[0052] According to one example implementation of the second or third beamforming example, an iteratively adjusted weight vector is used for a set of subcarriers for which, before the iterative adjustment, the weight vector was the same. The set of subcarriers with the same iteratively adjusted weight vector being used may be a subset of the set of all subcarriers having the same weight vector before the iterative adjustment (i.e. the same weight vector may be used for fewer subcarriers after the iterative adjustment than before it).

[0053] According to one example, for each set of data symbols of the data to be transmitted simultaneously on the subcarrier, the weight vectors of the set of data symbols may be obtained during data transmission and before transmission of the set of data symbols.

[0054] According to one example, wherein the iterative adjustment of the weight vectors is performed to reduce the contribution of self-interference and cross-sector interference in the signals of the apparatus, until a stopping criterion is satisfied. The stopping criterion comprises at least one of: a maximum number of iterations is reached, a maximum combined interference feature over the antenna array elements of the reception arrays is at or below a limit, a mean combined interference feature over the antenna array elements of the reception arrays is at or below a limit, a combined interference feature after receiver beamforming is at or below a limit, the weight vector deviates from an original corresponding vector by at least a limit, or a beamforming gain is reduced by at least a limit, wherein the interference feature is an interference power or a gain.

[0055] The interference related (power) gain may be calculated as the ratio between a transmitted symbol's power (e.g. I2+Q2in the constellation diagram, where I and Q represent the in-phase and quadrature components, respectively) and the interference power its transmission (using the iteratively adjusted weight vector) causes to an antenna array element of a reception array. Except for the first beamforming example, the ratio does not depend on the transmitted symbol, but on the iteratively adjusted weight vector (e.g., DL beamforming vector).

[0056] A maximum combined interference feature over the antenna array elements of the reception arrays may be the largest interference related (power) gain to any of the reception arrays' antenna array elements that the iteratively adjusted weight vector causes.

[0057] A mean combined interference feature over the antenna array elements of the reception arrays may be an average of the interference related (power) gains to the reception arrays' antenna array elements that the iteratively adjusted weight vector causes.

[0058] A combined interference feature after receiver beamforming may be the (power) ratio between a transmitted symbol's power (e.g. I2+Q2in the constellation diagram) and the interference power its transmission (using the iteratively adjusted weight vector) causes in an UL beam. This ratio depends on the UL beam's beamforming vector.

[0059] According to one example, the transmission arrays have the same number of antenna array elements, and the reception arrays have the same number of antenna array elements.

[0060] According to one example, the sector antennas are configured to transmit signals and receive signals in accordance with a sub-band non-overlapping full duplex (SBFD) technique. The present subject matter may at least reduce the blocking signal caused by transmission in one or two DL sub-bands and desensitizing the reception in an UL sub-band.

[0061] Beam nulling related methods may not only be suitable for SBFD, but e.g. also for similar use cases where the transmission from one sector antenna may desensitize the reception at another sector antenna. An example is full-duplex communication in an unpaired frequency band. Another example is integrated communication and sensing (also referred to as joint communication and sensing). There, the problem may be closer to full duplex than to SBFD: The reflections that shall be received for sensing are not only in the same operating band as the TX signal, but on the same frequency as the TX signal. All DL signals of the site can desensitize the receiver, hence separate reception arrays for sensing may be needed. (For TDD UL communication, the same antenna array elements as for the DL signal may be used to benefit from the reciprocity of the channel in TDD systems.) A high attenuation between each TX beam in the site and each antenna array element of a reception array may be desirable for sensing in order to keep the dynamic range requirements manageable in the RX paths for sensing. Hence TX beam nulling may be advantageous for this use case.

[0062] According to one example, the transmission method may be repeated for each subcarrier that is allocated for the transmission of the data by the apparatus. Even though the transmission method is repeated for each subcarrier, the weight vectors may optionally be iteratively adjusted rather for the set of subcarriers than for each subcarrier. Furthermore, the transmission method may skip unused subcarriers.

[0063] According to one example, the transmission method is automatically performed in response to receiving a request to transmit the data. According to one example, the weight vectors are obtained by the apparatus or by a system that is configured to communicate with the apparatus.

[0064] The present subject matter may provide the calibration method for efficiently estimating the channel feature(s). Transmitting signals to devices and receiving signals from devices may be interrupted (at least in one link direction) during or started only after performing the calibration method. Operating a radio unit in the target mode of operation may refer to receiving, by the radio unit, a calibration signal. Operating a radio unit in the source mode of operation may refer to transmitting by the radio unit a calibration signal.

[0065] The controlling operation, of the calibration method, of each radio unit to operate in the target mode of operation may be performed simultaneously so that all radio units are simultaneously in the target mode of operation or sequentially so that one radio unit is in the target mode of operation after the other. The channels between the sector antennas may be propagation channels. However, the channel feature may comprise properties of further elements. These need not be part of the sector antennas. Examples of further elements may be wiring, filters and amplifiers.

[0066] A channel feature may comprise a property or characteristic of a propagation channel, e.g. between an antenna array element of a transmission array or a TX beam or a TX stream and an antenna array element of a reception array or an RX beam or an RX stream.

[0067] According to one example, the determining of the channel feature is performed using calibration related information. The calibration related information comprises for each received calibration signal at least one of: what calibration signals are transmitted, at what output power the received calibration signal is transmitted, a time at which the received calibration signal is transmitted, from which sector antenna the received calibration signal is transmitted, or from which one or more antenna array elements the received calibration signal is transmitted.

[0068] According to one example, determining the channel feature comprises: determining a cross-correlation or a co-variance between each received calibration signal and respective reference signal, and using the determined one or more cross-correlations or one or more co-variances for determining the channel feature. The reference signal refers to a reference of what calibration signal has been transmitted. According to one example, a signal that is broadcasted or transmitted to at least one device may additionally be used as calibration signal. The signal may be broadcasted or transmitted to the at least one device for channel estimation.

[0069] According to one example, the channel feature comprises an impulse response, a transfer function, and / or a channel matrix. The elements of the channel matrix may be impulse responses or transfer functions.

[0070] According to one example, the target radio unit is configured to receive via the reception array of the sector antenna associated with the target radio unit at least one calibration signal from the transmission array of the sector antenna associated with the target radio unit for a determination of self-interference, wherein the channel feature further relates to self-interference for one or more channels between the reception array and the transmission array. In this and the following example, ‘associated with’ may mean e.g. ‘comprised in’ or ‘connected to’.

[0071] For example, when the target radio unit receives from each source radio unit that is different from the target radio unit at least one calibration signal, the target radio unit, acting simultaneously as source radio unit, may transmit at least one calibration signal and receive it, too. In this case, a channel feature of at least one channel between the sector antennas and at least one channel between the transmission array and the reception array of the sector antenna associated with the target radio unit may be determined using the received calibration signals. This channel feature relates to crosssector interference and self-interference.

[0072] According to one example, the calibration method is controlled by a part of the apparatus, the part being referred to as distributed unit. Additionally, or alternatively, the part may be involved in the calibration method. This part of the apparatus may act as a master for the apparatus’ performance of the calibration method. For example, the distributed unit is involved in and / or controls an execution of the calibration method.

[0073] According to one example, the calibration method or part of it is performed by a radio unit of the radio units.

[0074] According to one example, a calibration or a part of it is controlled by a radio unit of the radio units. One radio unit may be the source radio unit, another radio unit may be the target radio unit, and any of the apparatus’ radio units may act as a master for controlling a calibration or a part of it, wherein ‘calibration’ means ‘execution of the calibration method’.

[0075] According to one example, at least one of sectors, time periods, or one or more frequency ranges, are, during a calibration, exclusively allocated for performing the calibration method. For example, a part of the apparatus, referred to as distributed unit, may avoid scheduling DL and / or UL traffic at least in sectors, during time periods and in frequency range(s) that are used for the calibration method in the same or in any link direction.

[0076] According to one example of the pre-calibration method, the calibration related information comprises information related to calibration signals that are transmitted.

[0077] According to one example of the pre-calibration method, the information related to the calibration signals that are transmitted comprises information about at least one of:

[0078] - what calibration signals are transmitted,

[0079] - what power is applied to the calibration signals,

[0080] - when the calibration signals are transmitted,

[0081] - from which sector antenna(s) the calibration signals are transmitted,

[0082] - from which antenna array element(s) the calibration signals are transmitted.

[0083] The phrase ‘are transmitted’ may not just refer to the present tense, but also to the past or to the future, ‘calibration signals’ is meant as a general term, not limited to plural but including the case that there is only one calibration signal.

[0084] According to one example of the pre-calibration method, information related to the calibration signals that are transmitted is provided to at least one of: a source radio unit, a target radio unit, or a part of the apparatus, referred to as distributed unit.

[0085] Providing the information to the source radio unit may be relevant if a different radio unit (Rll) or a distributed unit controls or acts as a master of the calibration. The source radio unit may need the information for correctly generating the calibration signal.

[0086] Providing the information to the target radio unit may be relevant if a different radio unit or a distributed unit (DU) controls or acts as a master of the calibration. The target radio unit may need the information for performing the measurement that is needed for the calibration. If the DU is not the master of the calibration, it may benefit from knowing when, in what sector and / or on what frequency resources traffic should better not be scheduled to avoid that a RU discards scheduled data (for sending the calibration signal instead) or to reduce the interference during the calibration so that the measurements can be sufficiently accurate.

[0087] According to one example of the pre-calibration method, at least one of

[0088] - a source radio unit,

[0089] - a target radio unit,

[0090] - a part of the apparatus, referred to as distributed unit, provides information related to the calibration signals that are transmitted.

[0091] Provision of the information by a source radio unit may be relevant if a radio unit operating as a source radio unit controls or acts as master of a calibration.

[0092] Provision of the information by a target radio unit may be relevant if a radio unit operating as a target radio unit controls or acts as master of a calibration.

[0093] Provision of the information by a distributed unit may be relevant if a distributed unit controls or acts as master of a calibration.

[0094] According to one example of the pre-calibration method, the calibration related information comprises information related to received calibration signals.

[0095] According to one example of the pre-calibration method, the information related to the received calibration signals comprises measured calibration signals.

[0096] According to one example of the pre-calibration method, the information related to the received calibration signals comprises information derived from measured calibration signals.

[0097] For example, ‘measuring’ may not just refer to a sampling of a signal, but also to a determining based on signal samples. Also, more than one coupling or channel feature may be measured at a time, e.g. using orthogonal calibration signals.

[0098] According to one example of the pre-calibration method, the information derived from the measured calibration signals comprises at least one of: - a cross-correlation or co-variance between the measured calibration signal and a reference signal,

[0099] - an impulse response,

[0100] - a transfer function,

[0101] - a channel feature.

[0102] The reference signal may be the transmitted calibration signal. The transfer function may comprise gain and phase information. Gain and phase may be frequency dependent. For example, the measured calibration signal may have been transmitted in accordance with an allocated frequency band, wherein the gain and the phase are functions of the frequency within that frequency band.

[0103] According to one example of the pre-calibration method, at least one target radio unit provides information related to received calibration signals.

[0104] According to one example of the pre-calibration method, wherein at least one target radio unit provides information related to received calibration signals to at least one of

[0105] - a different radio unit,

[0106] - a part of the apparatus, referred to as distributed unit.

[0107] According to one example of the pre-calibration method, a part of the apparatus, referred to as distributed unit, controls or acts as master of the calibration using an interface to at least one of the radio units (RUs).

[0108] According to one example of the pre-calibration method, a part of the apparatus, referred to as distributed unit, may schedule DL and / or UL traffic only outside at least combinations of

[0109] - sectors,

[0110] - time periods and

[0111] - frequency range(s) that are used for the calibration in the same or in any link direction.

[0112] The link direction may indicate uplink or downlink. In this example, the same link direction means that during a calibration, the same scheduling as when there is no calibration ongoing is possible in the UL of a radio unit that does not operate in the target mode of operation and in the DL of a radio unit that does not operate in the source mode of operation. During the calibration, for accurate measurement results, traffic in any sector may only be scheduled outside the frequency range(s) that are used for the calibration. This may prevent interference from any sector.

[0113] During the calibration, for accurate measurement results, DL traffic may not be scheduled in any sector. This may prevent that blocking or interference from the site's own DL impairs the reception of calibration signals.

[0114] During the calibration, for accurate measurement results, DL traffic from a target radio unit may not be scheduled. This may prevent that blocking from the radio unit's own DL or self-interference impairs the reception of calibration signals.

[0115] During the calibration, for accurate measurement results, DL traffic from a target radio unit may only be scheduled outside the frequency range(s) that are used for the calibration. This may mitigate an impairment of the reception of calibration signals by self-interference.

[0116] If the frequency range(s) used for the calibration is / are limited to one or more DL subbands, the UL traffic in the UL sub-band may continue during the calibration because the devices' unwanted emissions in the DL sub-band(s) may hardly impair the reception of calibration signals.

[0117] FIG. 1 depicts examples of simplified system architectures only showing some elements and functional entities, all being logical units, whose implementation may differ from what is shown. The connections shown in FIG.1 are logical connections; the actual physical connections may be different. It is apparent to a person skilled in the art that the system typically comprises also other functions and structures than those shown in FIG.1.

[0118] The embodiments are not, however, restricted to the system given as an example but a person skilled in the art may apply the solution to other communication systems provided with necessary properties.

[0119] The example of FIG.1 shows a part of an exemplifying radio access network.

[0120] FIG.1 shows devices 110 and 112. The devices 110 and 112 may, for example, be user devices. The devices 110 and 112 are configured to be in a wireless connection on one or more communication channels with a node 114. The node 114 is further connected to a core network 120. In one example, the node 114 may be an access node (such as (e / g)NodeB) 114 providing or serving devices in a cell. In one example, the node 114 may be a non-3GPP access node. The physical link from a device to a (e / g)NodeB is called uplink or reverse link and the physical link from the (e / g)NodeB to the device is called downlink or forward link. It should be appreciated that (e / g)NodeBs or their functionalities may be implemented by using any node, host, server or access point etc. entity suitable for such a usage.

[0121] A communications system typically comprises more than one (e / g)NodeB in which case the (e / g)NodeBs may also be configured to communicate with one another over links, wired or wireless, designed for the purpose. These links may be used for signaling purposes. The (e / g)NodeB is a computing device configured to control the radio resources of the communication system it is coupled to. The (e / g)NodeB may also be referred to as a base station, an access point or any other type of interfacing device including a relay station capable of operating in a wireless environment. The (e / g)NodeB includes or is coupled to transceivers. From the transceivers of the (e / g)NodeB, a connection is provided to an antenna unit that establishes bi-directional radio links to devices. The antenna unit may comprise a plurality of antennas or antenna elements. The (e / g)NodeB is further connected to the core network 120 (CN or next generation core NGC). For example, the (e / g)NodeB may connect to an access and mobility management function (AMF) and user plane function (UPF) in the control plane and user plane, respectively. Depending on the system, the counterpart on the CN side can be a serving gateway (S-GW, routing and forwarding user data packets), packet data network gateway (P-GW), for providing connectivity of devices (UEs) to external packet data networks, or mobile management entity (MME), etc.

[0122] The device (also called user device, UE, user equipment, user terminal, terminal device, etc.) illustrates one type of an apparatus to which resources on the air interface are allocated and assigned, and thus any feature described herein with a device may be implemented with a corresponding apparatus, such as a relay node. An example of such a relay node is a layer 3 relay (self-backhauling relay) towards the base station.

[0123] The device typically refers to a device (e.g. a portable or non-portable computing device) that includes wireless mobile communication devices operating with or without a subscriber identification module (SIM), including, but not limited to, the following types of devices: a mobile station (mobile phone), smartphone, personal digital assistant (PDA), handset, device using a wireless modem (alarm or measurement device, etc.), laptop and / or touch screen computer, tablet, game console, notebook, and multimedia device. It should be appreciated that a device may also be a nearly exclusive uplink only device, of which an example is a camera or video camera loading images or video clips to a network. A device may also be a device having capability to operate in Internet of Things (loT) network which is a scenario in which objects are provided with the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction, e.g. to be used in smart power grids and connected vehicles. The device may also utilize cloud. In some applications, a device may comprise a user portable device with radio parts (such as a watch, earphones or eyeglasses) and the computation is carried out in the cloud. The device (or in some embodiments a layer 3 relay node) is configured to perform one or more of user equipment functionalities. The device may also be called a subscriber unit, mobile station, remote terminal, access terminal, user terminal or user equipment (UE) just to mention but a few names or apparatuses.

[0124] Various techniques described herein may also be applied to a cyber-physical system (CPS) (a system of collaborating computational elements controlling physical entities). CPS may enable the implementation and exploitation of massive amounts of interconnected ICT devices (sensors, actuators, processors microcontrollers, etc.) embedded in physical objects at different locations. Mobile cyber physical systems, in which the physical system in question has inherent mobility, are a subcategory of cyberphysical systems. Examples of mobile physical systems include mobile robotics and electronics transported by humans or animals.

[0125] Additionally, although the apparatuses have been depicted as single entities, different units, processors and / or memory units (not all shown in FIG. 1) may be implemented. 5G enables using multiple input - multiple output (MIMO) antennas, many more base stations or nodes than an existing LTE system (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and employing a variety of radio technologies depending on service needs, use cases and / or spectrum available. 5G mobile communications supports a wide range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications (such as (massive) machine-type communications (mMTC), including vehicular safety, different sensors and real-time control). 5G may have multiple radio interfaces, namely below 6GHz, cmWave and mmWave, and also being integrable with existing legacy radio access technologies, such as the LTE. In other words, 5G may support both inter-RAT operability (such as LTE-5G) and inter-RI operability (inter-radio interface operability, such as below 6GHz - cmWave, below 6GHz - cmWave - mmWave). One of the concepts used in 5G networks is network slicing in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility.

[0126] The current architecture in LTE networks is fully distributed in the radio and fully centralized in the core network. The low latency applications and services in 5G require to bring the content close to the radio which leads to local break out and multi-access edge computing (MEC). 5G enables analytics and knowledge generation to occur at the source of the data. This approach requires leveraging resources that may not be continuously connected to a network such as laptops, smartphones, tablets and sensors. MEC provides a distributed computing environment for application and service hosting. It also has the ability to store and process content in close proximity to cellular subscribers for faster response time. Edge computing covers a wide range of technologies such as wireless sensor networks, mobile data acquisition, mobile signature analysis, cooperative distributed peer-to-peer ad hoc networking and processing also classifiable as local cloud / fog computing and grid / mesh computing, dew computing, mobile edge computing, cloudlet, distributed data storage and retrieval, autonomic self-healing networks, remote cloud services, augmented and virtual reality, data caching, Internet of Things (massive connectivity and / or latency critical), critical communications (autonomous vehicles, traffic safety, real-time analytics, time-critical control, healthcare applications).

[0127] The communication system is also able to communicate with other networks, such as a public switched telephone network or the Internet as illustrated by the component referenced by reference numeral 122, or utilize services provided by them. The communication network may also be able to support the usage of cloud services, for example at least part of core network operations may be carried out as a cloud service (this is depicted in FIG.1 by “cloud” 124). The communication system may also comprise a central control entity, or a like, providing facilities for networks of different operators to cooperate for example in spectrum sharing.

[0128] The technology of Edge cloud may be brought into a radio access network (RAN) by utilizing network function virtualization (NVF) and software defined networking (SDN). Using the technology of edge cloud may mean access node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head or base station comprising radio parts. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. Application of cloudRAN architecture enables RAN real time functions being carried out at the RAN side (in a distributed unit, DU 114) and non-real time functions being carried out in a centralized manner (in a centralized unit, CU 118).

[0129] It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be nonexistent. Some other technology advancements probably to be used are Big Data and all-IP, which may change the way networks are being constructed and managed. 5G is being designed to support multiple hierarchies, where MEC servers can be placed between the core and the base station or gnodeB (gNB). It should be appreciated that MEC can be applied in 4G networks as well.

[0130] 5G may also utilize satellite communication to enhance or complement the coverage of 5G service, for example by providing backhauling. Possible use cases are providing service continuity for machine-to-machine (M2M) or Internet of Things (loT) devices or for passengers on board of vehicles, or ensuring service availability for critical communications, and future railway / maritime / aeronautical communications. Satellite communication may utilize geostationary earth orbit (GEO) satellite systems, but also low earth orbit (LEO) satellite systems, in particular mega-constellations (systems in which hundreds of (nano)satellites are deployed). Each satellite 116 in the megaconstellation may cover several satellite-enabled network entities that create on-ground cells. The on-ground cells may be created via an on-ground relay node 114 or by a gNB located on-ground or in a satellite.

[0131] It is understandable for a person skilled in the art that the depicted system is only an example of a part of a radio access system and in practice, the system may comprise a plurality of (e / g)NodeBs, the device may have an access to a plurality of radio cells and the system may comprise also other apparatuses, such as physical layer relay nodes or other network elements, etc. Additionally, in a geographical area of a radio communication system a plurality of different kinds of radio cells as well as a plurality of radio cells may be provided. Radio cells may be macro cells (or umbrella cells) which are large cells, usually having a diameter of up to tens of kilometers, or smaller cells such as micro-, femto- or picocells. The (e / g)NodeBs of FIG.1 may provide any kind of these cells. A cellular radio system may be implemented as a multilayer network including several kinds of cells. Typically, in multilayer networks, one access node provides one kind of a cell or cells, and thus a plurality of (e / g)NodeBs are required to provide such a network structure. For fulfilling the need for improving the deployment and performance of communication systems, the concept of “plug-and-play” (e / g)NodeBs has been introduced. Typically, a network which is able to use “plug-and-play” (e / g)NodeBs, includes, in addition to Home (e / g)NodeBs (H(e / g)nodeBs), a home node B gateway, or HNB-GW (not shown in FIG.1). A HNB Gateway (HNB-GW), which is typically installed within an operator’s network may aggregate traffic from a large number of HNBs back to a core network.

[0132] FIG. 2 is a flowchart of a method for transmission of data in a wireless communication system using an apparatus. The apparatus comprises multiple sector antennas associated with sectors. Each sector antenna of the sector antennas comprises a reception array of antenna array elements and a transmission array of antenna array elements. Each sector antenna is configured for transmitting signals, using the transmission array, to devices within a sector of the sectors that is associated with the sector antenna and for receiving signals, using the reception array, from devices within the sector.

[0133] The apparatus may, for example, be part of the node 114 of FIG. 1. The apparatus may, for example, comprise a number NSEsector antennas. The number of antenna array elements in the transmission array of one sector antenna may be referred to as NTXand the number of antenna array elements in the reception array of one sector antenna may be referred to as NRX. It is assumed that all sector antennas have the same number of antenna array elements.

[0134] Each sector antenna may be denoted or indexed by k, where k is a positive integer that varies between 1 and the number of sector antennas NSE(k = 1, ..., NSE). For simplification of the description, FIGs. 3A-4 provide example implementations of the apparatus with the number NSEof sector antennas equal to three (NSE= 3).

[0135] For each sector, referred to as current sector, a subset of the data, associated with the current sector may be transmitted in step 201 using a subcarrier. The transmission of the subset of the data may comprise a step 201A of mapping the subset of the data associated with the current sector to data symbols, a step 201 B of transforming each data symbol using at least one weight vector for obtaining a beamformed data symbol, and a step 201 C of modulating the beamformed data symbol with the subcarrier.

[0136] The weight vectors may be obtained in step 203 by iteratively adjusting the weight vectors to reduce a contribution of self-interference and cross-sector interference in signals of the apparatus. Step 203 may, for example, be performed before step 201 . FIG. 3A illustrates an apparatus 300 in accordance with an example of the present subject matter, wherein the apparatus 300 comprises three sector antennas 301 , 302 and 303 associated with three sectors respectively. Each sector antenna comprises an upper array of antenna array elements and a lower array of antenna array elements. Each antenna array element may be dual polarized. In SBFD slots, the three upper arrays may be configured for transmission and the three lower arrays may be configured for reception. In UL slots, the three lower arrays may be configured for reception, and in DL slots, the three upper arrays may be configured for transmission. These configurations may be reversed so that the upper arrays may be configured for reception and the lower arrays may be configured for transmission. If hardware capabilities allow, then in UL slots, all arrays may be configured for reception, and / or in DL slots, all arrays may be configured for transmission.

[0137] FIG. 3B illustrates self- and cross-sector interference in signals of the apparatus 300. Arrow 311 indicates a self-interference in the sector antenna 301 in which a signal transmitted by the TX upper array of the sector antenna 301 interferes with a signal received by receive (RX) lower array of the sector antenna 301. Arrows 312 and 313 indicate cross-sector interference. Arrow 312 indicates that a signal transmitted by the TX upper array of the sector antenna 302 interferes with a signal received by the RX lower array of the sector antenna 301. Arrow 313 indicates that a signal transmitted by the TX upper array of the sector antenna 303 interferes with a signal received by the RX lower array of the sector antenna 301. The plus sign 314 in FIG. 3B indicates a combined self- and cross-sector interference to the sector antenna 301 .

[0138] The self- and cross-sector interference e.g., as illustrated with reference to FIG. 3B, may be associated with a channel matrix. In particular, the self- and cross-sector interference channel may be represented by a channel matrix H e (CNSENTXXNSENRXgjVen by where NTXis the number of TX antenna array elements of one sector antenna and NRXis the number of RX antenna array elements of one sector antenna. The j-th row of the matrix H represents a channel from the j-th TX antenna array element to all RX antenna array elements of all NSEsector antennas. Correspondingly, i-th column represents a channel to i-th RX antenna array element from all TX antenna array elements of all NSEsector antennas. In the case of Orthogonal Frequency Division Multiplexing (OFDM) modulation, this matrix may represent the interference channel at a certain subcarrier. For example, it may be enough to estimate H every d-th subcarrier and use estimated (or interpolated) matrices for remaining subcarriers. The covariance, C e (CNSENTXXNSENTX,Of the channel matrix H may be defined as follows: C = H(H)H.

[0139] The present subject matter may provide a beamforming method to suppress combined self and cross-sector interference to each individual RX antenna array element of all NSEsector antennas. The beamforming method may, for example, be used for suppressing combined self and cross-sector interference in SBFD system. The beamforming method may convert a DL beamforming vector, which does not take into account combined self and cross-sector interference, into a modified beamforming vector that suppresses the combined self and cross-sector interference. The beamforming method may suppress combined self and cross-sector interference at each RX antenna array element to a no less than required level, not necessary nulling it. This approach may reduce the deviation of the modified beamforming vector from the original beamforming vector. The modification of the beamforming vector may comprise an iterative adjustment of the beamforming vector.

[0140] The beamforming method may include four different beam nulling schemes, named Scheme 1 , Scheme 2, Scheme 3 and Scheme 4. These schemes may differ in the computation of the modified beamforming vector. Scheme 1 , Scheme 2 and Scheme 3 are intended for on-the-fly computing, e.g. the modification of the beamforming vector is calculated just before use. Scheme 4 may calculate modified beamforming vectors beforehand and store them in the memory. The apparatus may read the required modified beamforming vectors from the memory. Because of the computational complexity, Scheme 4 is much better suited for a predefined, limited set of beamforming vectors (incl. grid of beams) than for eigen-beamforming, zero forcing, etc. In Scheme 1 , the computation may be dependent on own data symbols and on the data symbols and beamforming vectors of the neighbour sector antennas. In Scheme 2, the computation may be independent on data symbols and dependent on the beamforming vectors of the neighbour sector antennas. In Scheme 3, the computation may be independent on the data symbols and on the beamforming vectors of the neighbour sector antennas. In Scheme 4, the computation of a modified beamforming vector may only depend on the original beamforming vector and the channel matrix.

[0141] Scheme 1 may provide an example implementation of the first beamforming example.

[0142] Scheme 2 may provide an example implementation of the third beamforming example. Scheme 3 may provide an example implementation of the second beamforming example. In the following, the description of each of the schemes may be provided.

[0143] FIG. 3C shows further components of the apparatus 300 of FIG. 3A and illustrates a method of transmission of data symbols using the apparatus 300 of FIG. 3A. The apparatus 300 comprises a distributed unit (DU) and radio units (RU 1 , RU 2 and RU 3). The distributed unit and / or each radio unit may comprise a beamforming unit (e.g., as described with reference to FIG. 4) that may provide beamformed data symbols in accordance with the present subject matter.

[0144] FIG. 4 illustrates a beamforming unit 400 for providing beamformed data symbols in accordance with an example of the present subject matter. FIG. 4 shows beamformed data symbols in each sector antenna k, denoted by Ake CNTXX1, where k is a positive integer that represents the sector antenna and varies between 1 and the number of sector antennas NSE(k = 1, ... , NSE), and NTXis the number of TX antenna array elements in one sector antenna. A beamformed data symbol for a sector antenna k may be defined in Scheme 1 and Scheme 3 in accordance with the following equation:

[0145] Ak= skwk(1) where wke CNTXX1is the unmodified beamforming vector used in the sector antenna k, and ske S is the data symbol to be transmitted in the sector antenna k. In case of OFDM modulation, skis a data symbol to be transmitted at a certain subcarrier. S denotes a digital modulation constellation (e.g., quadrature amplitude modulation (QAM) or phase shift keying (PSK)).

[0146] Scheme 2 calculates beamformed data symbol Akas a sum of the NSEbeamformed data symbols according to the following equation:

[0147] Ak= Siwlk+ ••• + sNsEwNsEk, k = 1, ..., NSE(2) where wlkis a beamforming vector, used in the sector antenna k for the symbol sj (i.e. the symbol generated for DL transmission to a UE in the sector I on a single subcarrier).

[0148] Scheme 1

[0149] The iterative beam nulling algorithm may be described for Scheme 1 with reference to FIG. 4. The beamforming unit 400 comprises a pre-distortion unit 401 for performing digital pre-distortion (DPD) and a beam nulling unit 405 for implementing the iterative beam nulling algorithm. The digital pre-distortion aims to correct amplitude and phase distortion which may be caused by the beam nulling. The input of the pre-distortion unit 401 is NSEdata symbols sk. The output of the predistortion unit 401 is NSEpre-distorted data symbols ske Clxl. The DPD unit 401 performs pre-distortion by using a look up table (LUT) as shown in FIG. 5 or reverse behavioral model of the beam nulling. The pre-distortion may also depend on the unmodified beamforming vectors wk. For that, the pre-distortion unit 401 may also receive the unmodified beamforming vectors wkas indicated in FIG. 4.

[0150] Furthermore, Scheme 1 may concatenate beamformed pre-distorted data symbols in an array A e CNSENTXX1as follows: A = [A-L ANSE] , where each element of the array

[0151] A is a beamformed pre-distorted data symbol: Ak= skwk. Hence, the array of beamformed pre-distorted data symbols may be provided as follows: A =

[0152] Scheme 1 computes the modification of the array A using the beam nulling unit 405. The goal of this modification may be to reduce combined self- and cross-sector interference. The modification is computed using the iterative beam nulling algorithm. In particular, Scheme 1 computes A e CNSENTXXIUSjng the iterative beam nulling algorithm.

[0153] The input of the beam nulling unit 405 is the product of unmodified beamforming vectors wkand pre-distorted data symbols sk, composite self- and cross-sector interference channel matrix H e CNSENTXXNSENRXand a value L. L is a value for a stopping criterion of the iterative beam nulling algorithm. In Scheme 1 , the number of RX antenna array elements may be limited by the constraint NTX> NRXrequiring that the number of TX antenna array elements is higher than or equal to the number of RX antenna array elements.

[0154] An array Vmmay be used by the beam nulling algorithm and updated in every iteration of the beam nulling algorithm, where m = 0 ... Niter- 1 and Niteris the maximum number of iterations. At the first execution (i.e. , m = 0) of the beam nulling algorithm, the array Vomay be initialized with the array of beamformed pre-distorted data symbols A as follows: Vo= vini= A. And for each current iteration m -i- 1, the array Vm+1may be defined as follows: where || || denotes / 2-norm, and vtx= [Ai ••• ANSE]T. Akis defined in equation (1). ||vtx|| in the numerator of equation (3) may prevent that the modification changes the combined TX power in the site. Iterations continue until the maximum number of iterations Niteris reached or until another stopping criterion is satisfied. The stopping criterion may be the maximum combined interference power (from self- and cross-sector interference) at RX antenna array element. For that, a combined interference vector Iinte CNSENRXX1is calculated as follows: pnt=(H)Tvm+1(4)

[0155] Moreover, the maximum combined interference power is calculated as follows: where Ijntis i-th element of the combined interference vector Iint. Then the stopping criterion may be defined as follows: iint<iint

[0156] AZQ\ max —Amax where lj£ixis the target value of the maximum combined interference. The iterations may stop when this target value is reached. lj£ixmay be selected low enough to avoid blocking or saturation of the RX RF circuits.

[0157] Alternatively, the stopping criterion may be the mean combined interference power at the RX antenna array elements or combined interference power after RX beamforming. Each iteration may increase suppression and at the same time deviation of the modified beamforming vector from the original beamforming vector. Because of that, in some applications it may be beneficial to introduce another stopping criterion: the deviation level of the modified beamforming vector from the original beamforming vector. This deviation level can be measured directly, for example, by Euclidean distance, or indirectly, by, for example, a loss of the beamforming gain.

[0158] FIG. 5 is an example of LUT that is used by the pre-distortion unit 401 to implement the digital pre-distortion. Each row of this LUT has six cells with input parameters and three cells with output parameters. The first three cells contain the data symbols for the sectors 1-3 indexes (for illustrative purposes FIG. 5 shows symbol values instead of indexes). The next three cells contain beamforming vector indexes for the same sectors. The last three cells contain pre-distorted data symbols. The LUT implementation of the digital pre-distortion may particularly be advantageous for a low order of modulation and a codebook-based TX beamforming with relatively small number of codewords.

[0159] The digital pre-distortion as used in Scheme 1 may be advantageous for the following reasons. Data symbols skand TX beamforming vectors wkare the input parameters of the beam nulling. Modification of the same set of the beamforming vectors wk, k = 1, ... , NSEmay be different for different sets of the data symbols sk, k = 1, ..., NSE. However, the modification may cause amplitude and phase distortion of data symbol sk. This distortion depends on the data symbol itself, on the data symbols in other sectors and on the beamforming vectors in own and other sectors. In NR, LTE and similar systems, demodulation of data symbols may be assisted by pilot symbols (e.g., Demodulation Reference Signal (DMRS) or Cell-specific Reference Signal (CRS)). Using the pilot symbols, the receiver can estimate the amplitude and phase offset of the received data symbols. It is assumed that the amplitude and phase offset caused, for example, by the propagation channel, is independent of the transmitted data. However, the present receiver may not compensate for this distortion using existing solutions, based on pilot symbols. This is because the present method may cause different distortions for different combinations of data symbols. To solve that, the present subject matter introduces the pre-distortion unit preceding the beam nulling unit at the transmitter side. The input of the pre-distortion unit is NSEdata symbols sk. The pre-distortion unit converts those symbols into NSEpre-distorted symbols sk. When fed to the beam nulling unit, pre-distorted symbols skmay provide much lower EVM than non-pre-distorted symbols sk. Illustrative performance results for Scheme 1 are shown in FIG. 6. FIG. 6 shows a curve of EVM of the QPSK constellation with digital pre-distortion (labelled as “DPD”) and a curve of EVM of the QPSK constellation without digital pre-distortion (labelled as “no DPD”) for a fixed combination of TX beamforming vectors. Each curve may represent a cumulative distribution function (CDF).

[0160] Scheme 2

[0161] With Scheme 2, a concatenation of beamforming vectors wlkmay be defined as follows:W1= [wi,i •"WI,NSE]T. A modification of the concatenation wj may be performed by the iterative beam nulling algorithm, or by Scheme 4, where 1 refers to the index of the sector, where the UE, receiving beamformed symbol, is allocated. The modification may result in Wj which is a concatenation of the modified beamforming vectors Wlk: Wj = [W ••• WLNSE]T, where the modified beamforming vector Wlkis applied in the sector antenna k to the symbol sbThe above described digital pre-distortion is not used in Scheme 2. In Scheme 2, the number of RX antenna array elements is limited by constraint,

[0162] NTX> NRXrequiring that the number of TX antenna array elements is higher than or equal to the number of RX antenna array elements. The iterative beam nulling algorithm is performed once for each vector wbThe algorithm is performed according to the description, given for Scheme 1 , and by the block diagram in FIG. 7, but vector vTXis replaced by w(: vTX= w(. The output of the algorithm is vector W W[ = vk+1.

[0163] Equation (2) shows beamformed data symbols in the sector antenna k. Each data symbol sj in this equation can be beamformed to a different UE. Beamforming vector wj and Wj beamforms the same data symbol across all sector antennas to the same UE. In the case of the OFDM modulation, Akin equation (2) is beamformed data symbols in the sector antenna k at one subcarrier. Data symbols destined for the same UE may be located on multiple subcarriers. Then, provided that the UE's allocation has a sufficiently narrow bandwidth, the same beamforming vector wj can be applied to a number of subcarriers and, therefore, the same modified beamforming vector Wj can be applied to those subcarriers (not necessarily to all subcarriers allocated to one UE). The number of terms in equation (2) is equal to the number of simultaneously transmitted symbols in all sectors at one subcarrier. This number may differ from the number of sectors. Scheme 2 may have much lower computational complexity than Scheme 1 , however, this advantage may diminish as the number of simultaneously scheduled UEs increases.

[0164] Scheme 3

[0165] Scheme 3 calculates the beamformed data symbol Akaccording to equation (1). The modified beamforming vector Wkis calculated using the iterative beam nulling algorithm. In the computations, the channel covariance matrix is calculated from self- and crosssector interference channel matrix. The above described digital pre-distortion is not used in Scheme 3. In Scheme 3, the number of RX antenna array elements is limited by constraint NTX> NSENRX, requiring that the number of antenna array elements in each transmission array is higher than or equal to the number of antenna array elements in each reception array multiplied by the number of sector antennas. In Scheme 3, the modified beamforming vector Wke CNTXX1is calculated independently for each sector. Wkis obtained from wkby the iterative beam nulling algorithm. The iterative beam nulling algorithm is performed once for each sector. The algorithm is performed according to the description, given for Scheme 1 , and by the block diagram FIG. 7, but vector vTXis replaced by wk: vTX= wk. The output of the algorithm is vector Wk: Wk= Vm+1.

[0166] FIG. 7 is a flowchart of an iterative beam nulling algorithm in accordance with an example of the present subject matter. The iterative beam nulling algorithm may be used in Scheme 1 , Scheme 2 and Scheme 3. The iterative beam nulling algorithm may comprise an initialization phase 800A and iteration phase 800B. In initialization phase 800A, the covariance matrix may be provided in step 801. The iterator m may be set to zero in step 802 and the array Vmmay be initialized in step 803.

[0167] The iterator m may be incremented by one in step 804. In steps 805 and 806, the current value of the array Vm+1may be determined using its previous value Vm. In step 807, the combined interference vector Iintis calculated according to equation (4). In steps 808 and 809, the maximum combined interference power is calculated according to equation (5). It may be determined in step 810 whether the maximum number of iterations Niteris reached. If the maximum number of iterations Niteris reached, the array Vm+1may be provided in step 812 and the algorithm may end. If the maximum number of iterations Niteris not reached, it may be determined in step 811 whether the stopping criteria of equation (6) is fulfilled. If the stopping criteria is fulfilled, step 812 may be performed; otherwise, the next iteration may be performed.

[0168] For Scheme 2 and Scheme 3, the vector Iintof equation (4) may be a combined interference gain vector.

[0169] Scheme 4

[0170] Beam nulling for Scheme 4 may refer to digital beamforming. In the following, it is assumed that the beamforming in Scheme 4 uses, contrary to e.g. zero forcing or eigen- beamforming, a limited set of beamforming vectors. These beamforming vectors may be modified beforehand by a numerical optimization according to at least one of the following criteria a) to d). Before the optimization, the beamforming vectors may be frequency dependent, in particular for wide bandwidths, and after the optimization, they may be frequency dependent already for moderate or even small bandwidths, a) The beamforming vectors which usually refer to a single sector antenna may be extended to all sector antennas with active DL. This may make them quite long. The frequency dependency and the extension of the beamforming vectors to the other sector antennas can result in challenging memory requirements. The beamforming vectors' elements for other sector antennas may be initialized with zeros. However, the objective is that each signal can be transmitted using all sector antennas of the site (at least those with active DL) to improve the entire site's TX beam nulling, b) An equivalent isotropic radiated power (EIRP) reduction, e.g. of 0.5 dB or 1 dB, may be defined that the modified beamforming vectors shall have in the expected direction of the UE. Since the beamforming gains in the direction of the UE will typically be reduced by applying further design criteria (such as low self-interference and cross-sector interference) to the beamforming vectors, this DL EIRP reduction may be accepted, assuming that the base station output power cannot be increased. The larger the allowed EIRP reduction is, the better the TX beam nulling can be, but the larger the sidelobes may be. In SBFD slots, a part of the channel is dedicated to the UL. If, e.g., almost 20 MHz out of 100 MHz channel bandwidth are allocated to the UL, and if a homogeneous power spectral density (PSD) can be assumed, the EIRP could be reduced by 1 dB without a change of the received PSD at the UEs in the remaining almost 80 MHz. c) The output power limit of the TX paths may not be exceeded, d) In the expected direction of the UE, the level received by a UE may have at each subcarrier frequency (approximately) the same phase as with the original beamforming vector (i.e. the beamforming vector before the numerical optimization), but the received carrier power may be reduced according to the targeted EIRP reduction.

[0171] The highest power at any of the site's RX antenna array elements resulting from that beamforming vector, assuming equal input power at each subcarrier frequency, may be minimized. The purpose is to minimize the desensitization of the UL by blocking and / or interference from the DL. Instead of a minimization, there may be just a reduction (e.g. if an iterative calculation converges slowly).

[0172] In an example in which the apparatus has an additional mitigation method for selfinterference (in particular if the calibration measurements do not reflect this mitigation), instead of considering the highest power resulting from weight vectors at the site's RX antenna array elements, the effect of self-interference may be excluded

[0173] • in the minimization of the highest power at the site's RX antenna array elements resulting from a weight vector (which, except for Scheme 1 , may be a beamforming vector) or

[0174] • in the iterative adjustment.

[0175] In the following description of Scheme 4, it is assumed that the matrix H describes the complex-valued gain from each antenna array element of a transmission array in the site to each antenna array element of a reception array in the site. The matrix H depends on the frequency. Three sector antennas are considered. For simplicity, each sector antenna has a transmission array with only two antenna array elements and a reception array with only two antenna array elements. If TX and RX are active in all sector antennas, H is a 6x6 matrix. The coupling between transmission and reception arrays usually affects the reception, hence the elements of H should be small. The following equation shows the relationship between complex-valued TX voltages L / TX at the frequency of a subcarrier during a symbol period, (frequency dependent) complex valued gains for the respective subcarrier frequency and complex-valued RX voltages L / RX at the subcarrier frequency during the symbol period. However, there can be periods of time when no UL is scheduled in a sector, a.k.a. micro

[0176] Discontinuous Reception (pDRX). Then, the RX in the sector antenna(s) without UL traffic can be ignored during the corresponding periods of time because blocking may not matter. For example, during a symbol period, no UL is scheduled in the 3rdsector.

[0177] Then the optimization only needs to consider the received signals in the first sector antenna and in the second sector antenna:

[0178] An optimization for such a case will result in a further set of beamforming vectors. Since there are more elements for the optimization than RX antenna array elements where the power is minimized, the TX beam nulling's suppression is expected to increase. Similarly, there can be periods of time when no DL is scheduled in a sector, a.k.a. micro Discontinuous Transmission (pDTX). This is relevant for energy saving because then some components of the TX paths, including the power amplifiers (PAs), can be switched to a mode with low power consumption. Although the TX beam nulling can be expected to provide a lower suppression if not all TX antenna array elements of the site are used for TX beam nulling, it may be assumed that the reduced interference due to this sector antenna's TX inactivity compensates this disadvantage. For example, during a symbol period, no DL is scheduled in the 2ndsector. Then, the optimization can only include the

[0179] TX signals in the first sector antenna and in the third sector antenna:

[0180] An optimization for such a case will result in yet another set of beamforming vectors, but the beamforming vectors are shorter because they cover fewer TX paths.

[0181] In the case of three sectors, there are forty-nine possibilities that at least one sector is transmitting and that at least one sector is receiving. An optimization for each of these cases results in a huge increase of the number of needed beamforming vectors. A compromise may be to ignore the pDRX and to calculate the modified beamforming vectors only for the 7 cases in which at least one of the sectors is transmitting.

[0182] The reduction of the dimensions of the channel matrix may also be used

[0183] • for Scheme 1 if the number of active TX antenna array elements in the site equals at least the number of active RX antenna array elements in the site,

[0184] • for Scheme 2 in the case of pDRX but rather not in the case of pDTX, and

[0185] • for Scheme 3.

[0186] The inconvenience of generating different beamforming vector optimizations for these numerous cases, of beamforming vectors whose length gets multiplied by the number of sectors, of the EIRP reduction and of larger sidelobes may be avoided as follows. Compensation signals may be digitally generated, digital-to-analog converted and added before the LNA or, as shown in FIG. 11 , between

[0187] • a first part of LNA gain stages which, even in the presence of high input level, may virtually not distort, and a second part of LNA gain stages whose input level may be reduced by the compensation signal so that the dynamic range requirements for the second part of gain stages may be manageable.

[0188] The benefit may be limited because the compensation may assume perfect signal generation, i.e. it may neither consider the EVM due to crest factor reduction (CFR) nor residual linear and non-linear distortions in the analog part of the TX path that may remain despite equalizer filters and the predistortion for the PA.

[0189] An approach to calculate the compensation signal may be to derive it from the input streams for the DL. To this end, the matrix H may be assumed to be composed of horizontally concatenated matrices Hi to HNSE, each of which reflects the impact of the transmission array's antenna array elements of the respective sector antenna on all reception arrays' antenna array elements in the site for a subcarrier. In the example of 3 sectors, H = [Hi H2 H3]. In the example of 64 antenna array elements per transmission array and 64 antenna array elements per reception array, H is a 192x192 matrix, and each of Hi to H3 is a 192x64 matrix. In sector k, the beamforming vector may be Wk (column vector with 64 elements) and the data symbol may be Sk. Hence the crosstalk from the site's transmission arrays to the reception arrays on a subcarrier may be described by HrWrSi + H2 W2 S2 +H3 W3 S3 where Hk Wk are column vectors with 192 elements that only need to be calculated once for each combination of beamforming vector and subcarrier frequency. In the case that several streams are simultaneously active so that, in the same sector, further beamforming vectors apply concurrently, their contributions may be calculated, too, and added. The sum may be a vector with one element for each antenna array element of the site's reception arrays and refer to one subcarrier. For each antenna array element of the site's reception arrays, the sums for the subcarriers may be modulated and converted into analog signals similarly to the TX signals, but since the digital-to-analog converter (DAC) shown in FIG. 11 is not followed by a PA, no predistortion for a PA may be needed. Thus, for each antenna array element of the site's reception arrays, an analog compensation signal may be generated which, with an appropriate scaling and phase, may be added to the analog received signal. However, having a CFR only for the TX signals may be a disadvantage. A purpose of TX beam nulling may be reducing the blocking of the receivers by the signal in the DL sub- band(s). Peaks are particularly important because they may force the receivers' automatic gain control (AGC) to reduce the analog gain and thus to increase the noise figure. A calculation for a peak of 10 dB above average power in the TX signal that the CFR reduces to 7 dB above average power shows that without the beam nulling, there may be an amplitude proportional to 107 / 20=2.24. The compensation signal may subtract an amplitude proportional to 1010 / 20=3.16 because the compensation signal generation may not be aware of the CFR's action. Thus, too much may be subtracted, the difference may be 2.24-3.16=-0.92 which is only 7.7 dB lower than 2.24. This suggests that the maximum benefit may be limited below 10 dB.

[0190] To achieve a better suppression, the compensation signal may be calculated from the signals that the CFR provides to the predistortion for the PA. This may also have the advantage that the signal is already beamformed, i.e. the factors needed to determine the compensation signal may not depend on the beamforming vector, but may be fixed, allowing for any beamforming. However, at this point of the signal processing, the signal may be in the time domain. This means that the frequency dependency of H may have to be reflected by a filter. Hence at every sampling period, for each combination of TX antenna array element and RX antenna array element, a filtered version of the respective TX path's signal would have to be calculated. In the case of 3 sectors with 64 antenna array elements per transmission array and 64 antenna array elements per reception array in each of the sectors, there are 192- 192 of these combinations, hence the large number of 36864 concurrent filters may be needed. For each of the 192 RX antenna array elements, 192 filter outputs may have to be summed to determine the desired compensation signal.

[0191] FIG. 8 is a flowchart of a calibration method for an apparatus. The apparatus comprises multiple sector antennas. Each sector antenna comprises a reception array of antenna array elements and a transmission array of antenna array elements, each sector antenna being configured for transmitting signals, using the transmission array, to devices within a sector and for receiving signals, using the reception array, from devices within the sector. Each sector antenna of the sector antennas is comprised in or connected to a radio unit. Each radio unit is configured to operate in a source mode of operation and a target mode of operation. If a radio unit is configured to operate in the target mode of operation, for a determination relating to cross-sector interference, at least one other radio unit is configured to operate in the source mode of operation. Each radio unit that operates in the source mode of operation is referred to as source radio unit and each radio unit that operates in the target mode of operation is referred to as target radio unit. For example, the communication with the devices may be interrupted during the calibration measurement, preferably in both link directions, at least on frequencies occupied by the calibration signal. Each radio unit may be controlled in step 901 to operate in the target mode of operation such that the target radio unit receives from each source radio unit that is different from the target radio unit at least one calibration signal.

[0192] The received calibration signals may be used in step 903 for determining a channel feature of at least one channel between the sector antennas, the channel feature relating to cross-sector interference. The calibration signals used in step 903 for determining the channel feature may be the calibration signals which are received at the target radio unit(s) of step 901. For example, if two radio units Ru1 and Ru2 are provided, step 901 may result in two target radio units tRu1 and tRu2 and associated source radio units sRu2 and sRu1 (that is, Ru2=sRu2 for Ru1=tRu1 and Ru1=sRu1 for Ru2=tRu2), wherein sRu2 provides at least one calibration signal to tRu1 and - sequentially or concurrently - sRu1 provides at least one calibration signal to tRu2. This may result in multiple calibration signals which are received at tRu1 and tRu2. Concurrently may comprise simultaneously or quasi simultaneously.

[0193] Step 901 may be performed by a part of the apparatus such as a DU. This means that the part of the apparatus controls each radio unit to operate in the target mode of operation such that the target radio unit receives from each source radio unit at least one calibration signal. The received calibration signals or the results of the calibration performed using the received calibrations signals may be provided to the part of the apparatus so that the part of the apparatus may perform step 903.

[0194] FIG. 9 depicts diagrams 1000A through 1000E, each diagram illustrates an example of interfacing between radio units and a distributed unit that enables to perform the calibration method and the transmission method in accordance with present subject matter. In particular, each diagram shows an example of interfaces between RUs that allow for conveying signals that are needed for the calibration of the cross-sector TX beam nulling and potentially also for the cross-sector TX beam nulling itself. The interfaces are represented by arrows. In particular, three types of interfaces are represented by the three different arrows 1001 , 1002 and 1003.

[0195] The arrow 1001 represents an interface for conveying a first content consisting of TX data such as subcarrier-wise symbols or l / Q samples. The arrow 1002 represents an interface for conveying a second content consisting of cross-sector calibration data and control. The arrow 1003 represents an interface for conveying a combination of the first and second contents. The calibration may comprise the transmission of a calibration signal from one or more TX antenna array elements of the site and measuring the received signal at the RX antenna array elements. For example, the Rlls know the calibration signal. Thus, they may calculate transfer function and / or channel related information. Rlls that have measured the calibration signal that they have received from another Rll may provide the information to that Rll, preferably via the dashed 1003 or dotted 1002 links in the diagrams.

[0196] Where direct links are missing, the DU in diagram 1000A or the RU2 in diagrams 1000B- D may forward the information as needed. There may be a master for controlling the calibration, e.g. a DU or one of the RUs. The calibration may not be limited to measurements related to cross-sector interference but may include also self-interference related measurements. The control by the DU may have the advantage that the DU can, by neither scheduling DL nor UL during the transmission of the calibration signal, minimize the interference during the calibration and thus improve the calibration's accuracy. There may be a fixed rhythm that some base stations or base station sites use in a geographical area to reduce also mutual interference, in particular those using the same frequency range(s). In this case, different sites may use different, in particular uncorrelated calibration signals to minimize the mutual interference during the calibration. Instead of the DU, there may be a different, separate unit controlling the calibration which is linked to at least one RU.

[0197] The schemes Scheme 1 through Scheme 4 as described above may be implemented using interfaces as described with FIG. 9. In the schemes 1 , 2 and 4, all links between the DU and the RUs in the diagrams 1000A, 1000D and 1000E may convey the DL data for all sectors.

[0198] There may be a calibration across the sites' sectors. The calibration may comprise one or more measurements. A measurement may include at least two RUs wherein at least one RU receives and another RU transmits. A first RU may measure how it receives a calibration signal or a combination of calibration signals transmitted by a second RU, the second RU comprising or being connected to a different sector antenna than the first RU. The received calibration signal may refer to an antenna array element (in particular an antenna array element of a reception array), an RX stream or an RX beam. The transmitted calibration signal may refer to an antenna array element (in particular an antenna array element of a transmission array), a TX stream or a TX beam. Beam nulling may not be applied to calibration signals in order to measure at least one channel feature, or it may be applied to measure at least one residual received signal. The first RU may share information about the measured signal with the DU and / or the second RU via an interface. The shared information may comprise the measured signal or parameters derived from it, in particular parameters characterizing a (propagation) channel or a radio link from the second RU to the first RU. Examples of the parameters are channel taps or a transfer function which comprises gain and phase information. The gain and / or phase information may be frequency dependent. A measurement related to cross-sector interference may be combined with a measurement related to self-interference, i.e., there may be a joint measurement. The calibration may comprise measurements from each antenna array element of a transmission array, each TX beam or each TX stream to each antenna array element of a reception array, RX beam or RX stream of the other sectors and optionally also of the own sector (wherein ‘sector’ may refer to ‘sector antenna’). The measurement results may be combined in a channel matrix for the crosssector interference or for both cross-sector interference and self-interference.

[0199] During the calibration, there may be no transmission between the base stations of a site or even of a geographical area and the UEs served by the base stations. This may apply at least at a given point in time to the frequencies which the calibration signal occupies at that point in time. At the site or in a geographical area, there may be a fixed rhythm for the calibration. As far as - by a RU, at a site or in a geographical area - calibration signals are simultaneously transmitted by different TX beams, TX streams or antenna array elements, orthogonal calibration signals or calibration signals with a low crosscorrelation may be used. If OFDM symbols are used for the calibration, orthogonal calibration signals can be achieved by using different subcarriers in different calibrations signals (each subcarrier being used in at most one calibration signal).

[0200] There may be a unit which controls the calibration for the site, in particular a DU or one of the RUs. To this end, the DU may use at least one interface to the RUs, or the RU controlling the calibration may use at least one interface to the other RUs. Information about a calibration signal to be transmitted by at least one sector antenna may be provided via at least one interface to at least one RU of the site, and the respective at least one RU may use it. The information about the calibration signal to be transmitted may include the desired beamforming. The measurements obtained during the calibration may be used for TX beam nulling and / or RX beam nulling and / or for generating analog compensation signals. It is understood that one or more of the mentioned examples or embodiments may be combined as long as the combined examples or combined embodiments are not mutually exclusive. For example, the analog compensation scheme in FIG. 11 and the RX beam nulling may be combined with the calibration and corresponding interfaces. In another example, RX beam nulling for an entire site may be implemented according to the same principles. Its primary purpose may be to reduce the interference from the unwanted emissions from the site's transmission arrays into each UL stream. For RX beam nulling, instead of the DL beamforming vectors, the UL beamforming vectors may be modified. Instead of the reduction of the EIRP, the reduction of the equivalent isotropic sensitivity may be considered. RX beam nulling and TX beam nulling may be used concurrently.

[0201] In FIG. 10, a block circuit diagram illustrating a configuration of an apparatus 1070 is shown, which is configured to implement at least part of the present subject matter. It is to be noted that the apparatus 1070 shown in FIG. 10 may comprise several further elements or functions besides those described herein below, which are omitted herein for the sake of simplicity as they are not essential for the understanding. Furthermore, the apparatus may be also another device having a similar function, such as a chipset, a chip, a module etc., which can also be part of an apparatus or attached as a separate element to the apparatus 1070, or the like. The apparatus 1070 may comprise a processing function or processor 1071 , such as a central processing unit (CPU) or the like, which executes instructions given by programs or the like related to a flow control mechanism. The processor 1071 may comprise one or more processing portions dedicated to specific processing as described below, or the processing may be run in a single processor. Portions for executing such specific processing may be also provided as discrete elements or within one or more further processors or processing portions, such as in one physical processor like a CPU or in several physical entities, for example. Reference sign 1072 denotes transceiver or input / output (I / O) units (interfaces) connected to the processor 1071. The I / O units 1072 may be used for communicating with one or more other network elements, entities, terminals or the like. The I / O units 1072 may be a combined unit comprising communication equipment towards several network elements or may comprise a distributed structure with a plurality of different interfaces for different network elements. Reference sign 1073 denotes a memory usable, for example, for storing data and programs to be executed by the processor 1071 and / or as a working storage of the processor 1071. The processor 1071 is configured to execute processing related to the above described subject matter. In particular, the apparatus 1070 may be configured to perform the method as described in connection with FIG. 2, 7, or 8.

[0202] As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as an apparatus, method, computer program or computer program product. Accordingly, aspects of the present invention may take entirely the form of a hardware embodiment, take entirely the form of a software embodiment (including firmware, resident software, micro-code, etc.) or take the form of an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer executable code embodied thereon. A computer program comprises the computer executable code or "program instructions".

[0203] Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable storage medium. A ‘computer- readable storage medium’ as used herein encompasses any tangible storage medium which may store instructions which are executable by a processor of a computing device. The computer-readable storage medium may be referred to as a computer-readable non- transitory storage medium. The computer-readable storage medium may also be referred to as a tangible computer readable medium. In some embodiments, a computer- readable storage medium may also be able to store data which is able to be accessed by the processor of the computing device.

[0204] ‘Computer memory’ or ‘memory’ is an example of a computer-readable storage medium. Computer memory is any memory which is directly accessible to a processor. ‘Computer storage’ or ‘storage’ is a further example of a computer-readable storage medium. Computer storage is any non-volatile computer-readable storage medium. In some embodiments computer storage may also be computer memory or vice versa.

[0205] A ‘processor’ as used herein encompasses an electronic component which is able to execute a program or machine executable instruction or computer executable code. References to the computing device comprising “a processor” should be interpreted as possibly containing more than one processor or processing core. The processor may for instance be a multi-core processor. A processor may also refer to a collection of processors within a single computer system or distributed amongst multiple computer systems. The term computing device should also be interpreted to possibly refer to a collection or network of computing devices each comprising a processor or processors. The computer executable code may be executed by multiple processors that may be within the same computing device or which may even be distributed across multiple computing devices.

[0206] Computer executable code may comprise machine executable instructions or a program which causes a processor to perform an aspect of the present invention. Computer executable code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages and compiled into machine executable instructions. In some instances the computer executable code may be in the form of a high level language or in a pre-compiled form and be used in conjunction with an interpreter which generates the machine executable instructions on the fly.

[0207] Generally, the program instructions can be executed on one processor or on several processors. In the case of multiple processors, they can be distributed over several different entities. Each processor could execute a portion of the instructions intended for that entity. Thus, when referring to a system or process involving multiple entities, the computer program or program instructions are understood to be adapted to be executed by a processor associated or related to the respective entity.

Claims

CLAIMS1. An apparatus for transmission of data in a wireless communication system, the apparatus comprising multiple sector antennas associated with sectors, each sector antenna of the sector antennas comprising a reception array of antenna array elements and a transmission array of antenna array elements, each sector antenna being configured for transmitting signals, using the transmission array, to devices within a sector of the sectors that is associated with the sector antenna and for receiving signals, using the reception array, from devices within the sector, the apparatus comprising means, for each sector, referred to as current sector, the means being configured for transmitting a subset of the data, associated with the current sector using a subcarrier comprising at least: mapping the subset of the data associated with the current sector to data symbols; and transforming each data symbol using at least one weight vector for obtaining a beamformed data symbol, and modulating the beamformed data symbol with the subcarrier; the means being configured for obtaining the weight vectors by iteratively adjusting the weight vectors to reduce a contribution of self-interference and cross-sector interference in signals of the apparatus.

2. The apparatus of claim 1 , the means being configured for obtaining the weight vectors using a self-interference and cross-sector interference channel matrix representing channel properties of channels between the transmission arrays and the reception arrays.

3. The apparatus of any of the preceding claims, each weight vector of the weight vectors representing a pre-distorted data symbol multiplied by a beamforming vector, each weight vector of the weight vectors being associated with a data symbol and a sector of the sectors, each weight vector of the weight vectors comprising weights associated respectively with the antenna array elements of the transmission array of the sector antenna associated with the sector associated with the weight vector, the means being configured to perform the transformation of the data symbol by replacing the data symbol with the weight vector that is associated with the current sector and the data symbol.

4. The apparatus of claim 3, the number of antenna array elements in each transmission array being higher than or equal to the number of antenna array elements in each reception array.

5. The apparatus of claim 3 or 4, the weight vectors associated with a set of data symbols to be transmitted simultaneously on one subcarrier being obtained concurrently.

6. The apparatus of any of the preceding claims 1 to 2, each weight vector of the weight vectors being associated with a sector of the sectors, each weight vector of the weight vectors comprising weights associated respectively with the antenna array elements of the transmission array of the sector antenna associated with the sector associated with the weight vector, the means being configured to perform the transformation of the data symbol by weighting the data symbol with the weight vector that is associated with the current sector.

7. The apparatus of claim 6, the number of antenna array elements in each transmission array being higher than or equal to the number of antenna array elements in each reception array multiplied by the number of sector antennas.

8. The apparatus of claim 6 or 7, wherein the weight vectors are iteratively obtained independently for each sector of the sectors.

9. The apparatus of any of the preceding claims 1 to 2, the means being configured to perform the transformation of the data symbol comprising: weighting the data symbol with the weight vector that is associated with the data symbol, wherein the weight vector comprises weights associated with the antenna array elements, of the transmission arrays, respectively.

10. The apparatus of claim 9, wherein the subset of the data comprises the data.

11. The apparatus of claim 9 or 10, the means being configured, for weighted data symbols to be transmitted simultaneously on one subcarrier, to add together parts of the weighted data symbols, the parts referring to the transmission array of the sector antenna associated with the current sector.

12. The apparatus of any of the preceding claims 1 , 2 or 6 to 11 , an iteratively adjusted weight vector being used for a set of subcarriers for which, before the iterative adjustment, the weight vector was the same.

13. The apparatus of any of the preceding claims, for each set of data symbols of the data to be transmitted simultaneously on the subcarrier, the means being configured to obtain the weight vectors of the set of data symbols during data transmission and before transmission of the set of data symbols.

14. The apparatus of any of the preceding claims, the means being configured for iteratively adjusting the weight vectors to reduce the contribution of selfinterference and cross-sector interference in the signals of the apparatus, until a stopping criterion is satisfied, the stopping criterion comprising at least one of: a maximum number of iterations is reached; a maximum combined interference feature over the antenna array elements of the reception arrays is at or below a limit; a mean combined interference feature over the antenna array elements of the reception arrays is at or below a limit; a combined interference feature after receiver beamforming is at or below a limit; the weight vector deviates from an original corresponding vector by at least a limit; or a beamforming gain is reduced by at least a limit, wherein the interference feature is an interference power or a gain.

15. The apparatus of any of the preceding claims, the transmission arrays having the same number of antenna array elements, the reception arrays having the same number of antenna array elements.

16. The apparatus of any of the preceding claims, the sector antennas being configured to transmit signals and receive signals in accordance with a sub-band non-overlapping full duplex (SBFD) technique.

17. A method for transmission of data in a wireless communication system using an apparatus, the apparatus comprising multiple sector antennas associated with sectors, each sector antenna of the sector antennas comprising a reception array of antenna array elements and a transmission array of antenna array elements, each sector antenna being configured for transmitting signals, using the transmission array, to devices within a sector of the sectors that is associated with the sector antenna and for receiving signals, using the reception array, from devices within the sector, the method comprising,for each sector, referred to as current sector, transmitting a subset of the data, associated with the current sector using a subcarrier, by at least: mapping the subset of the data associated with the current sector to data symbols; and transforming each data symbol using at least one weight vector for obtaining a beamformed data symbol, and modulating the beamformed data symbol with the subcarrier; wherein the weight vectors are obtained by iteratively adjusting the weight vectors to reduce a contribution of self-interference and cross-sector interference in signals of the apparatus.

18. The method of claim 17, repeating the method for each subcarrier that is allocated for the transmission of the data by the apparatus.

19. The method of claim 17 or 18, being automatically performed in response to receiving a request to transmit the data.

20. The method of claim 17 or 18 or 19, wherein the weight vectors are obtained by the apparatus or by a system that is configured to communicate with the apparatus.

21. A computer program comprising instructions, that when executed by an apparatus, cause the apparatus to perform at least the method of claim 17.

22. A calibration method for an apparatus, the apparatus comprising multiple sector antennas, each sector antenna comprising a reception array of antenna array elements and a transmission array of antenna array elements, each sector antenna being configured for transmitting signals, using the transmission array, to devices within a sector and for receiving signals, using the reception array, from devices within the sector, each sector antenna of the sector antennas being comprised in or connected to a radio unit, each radio unit being configured to operate in a source mode of operation and a target mode of operation, wherein if a radio unit is configured to operate in the target mode of operation, for a determination relating to cross-sector interference, at least one other radio unit is configured to operate in the source mode of operation, each radio unit operating in the source mode of operation being referred to as source radio unit, each radio unit operating in the target mode of operation being referred to as target radio unit, the calibration method comprising:controlling each radio unit to operate in the target mode of operation such that the target radio unit receives from each source radio unit that is different from the target radio unit at least one calibration signal; using the received calibration signals for determining a channel feature of at least one channel between the sector antennas, the channel feature relating to cross-sector interference.

23. The calibration method of claim 22, wherein the determining of the channel feature is performed using calibration related information, wherein the calibration related information comprises for each received calibration signal at least one of: at what output power the received calibration signal is transmitted; a time at which the received calibration signal is transmitted; from which sector antenna the received calibration signal is transmitted; or from which one or more antenna array elements the received calibration signal is transmitted.

24. The calibration method of any of the preceding claims 22 to 23, wherein determining the channel feature comprises: determining a cross-correlation or a co-variance between each received calibration signal and respective reference signal, and using the determined one or more cross-correlations or one or more co-variances for determining the channel feature.

25. The calibration method of any of the preceding claims 22 to 24, the channel feature comprising an impulse response, a transfer function, and / or a channel matrix.

26. The calibration method of any of the preceding claims 22 to 25, wherein, for a determination of self-interference, the target radio unit is configured to receive via the reception array of the sector antenna associated with the target radio unit at least one calibration signal from the transmission array of the sector antenna associated with the target radio unit, wherein the channel feature further relates to self-interference for one or more channels between the reception array and the transmission array.

27. The calibration method of any of the preceding claims 22 to 26, a part of the apparatus being configured to be involved in and / or control the calibration method, the part being referred to as distributed unit.

28. The calibration method of any of the preceding claims 22 to 27, the calibration method being performed and / or controlled by a radio unit of the radio units.

29. The calibration method of any of the preceding claims 22 to 28, wherein at least one of- sectors,- time periods, or- one or more frequency ranges, are exclusively allocated for performing the calibration method.

30. A radio unit being configured to perform and / or control the method of claim 17 or the calibration method of claim 22 or the method of claim 32, wherein the radio unit is part of the apparatus.

31. A distributed unit being configured to be involved in and / or control the method of claim 17 or the calibration method of claim 22 or the method of claim 32, wherein the distributed unit is part of the apparatus.

32. A method for enabling cross-sector interference determination for an apparatus, the apparatus comprising multiple sector antennas, each sector antenna comprising a reception array of antenna array elements and a transmission array of antenna array elements, each sector antenna being configured for transmitting signals, using the transmission array, to devices within a sector and for receiving signals, using the reception array, from devices within the sector, each sector antenna of the sector antennas being comprised in or connected to a radio unit, each radio unit being configured to operate in a source mode of operation and a target mode of operation, wherein the apparatus is configured to operate at least one radio unit in the target mode of operation and, at the same time, at least one other radio unit in the source mode of operation, each radio unit having an interface for signaling inside the apparatus, the method comprising: exchanging calibration related information over the interfaces, the calibration comprising measuring at least one coupling or channel feature between at least one antenna array element of a transmission array of a sector antenna and at least one antenna array element of a reception array of another sector antenna.

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