WO2018059691A1

WO2018059691A1 - A full-duplex wireless beamforming apparatus with self-interference cancellation and method

Info

Publication number: WO2018059691A1
Application number: PCT/EP2016/073257
Authority: WO
Inventors: Georgios ALEXANDROPOULOS; Melissa DUARTE GELVEZ
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2016-09-29
Filing date: 2016-09-29
Publication date: 2018-04-05

Abstract

This invention relates to a full-duplex wireless communication apparatus (300) configured to receive a radio-frequency receive signal and to transmit a radio-frequency transmit signal over a communication channel. The apparatus (300) comprises: at least one beamforming unit (304, 306, 307, 309) configured to apply beamforming to the radio-frequency receive signal, the corresponding base-band receive signal, the radio-frequency transmit signal or the corresponding base-band transmit signal on the basis of at least one fixed beamforming parameter of the beamforming unit (304, 306, 307, 309) and on the basis of at least one adjustable beamforming parameter of the beamforming unit (304, 306, 307, 309); an analog cancellation unit (312) configured to cancel a self-interference signal caused by the radio-frequency transmit signal over a self-interference channel, wherein the analog cancellation unit (312) is configured to cancel the self-interference signal using the radio-frequency transmit signal or the corresponding base-band transmit signal on the basis of at least one fixed parameter of the analog cancellation unit (312) and on the basis of at least one adjustable parameter of the analog cancellation unit (312); and a control unit (311) configured to determine the at least one adjustable parameter of the analog cancellation unit (312) and/or the at least one adjustable beamforming parameter of the beamforming unit (304, 306, 307, 309) on the basis of the at least one fixed parameter of the analog cancellation unit (312) and/or the at least one fixed parameter of the beamforming unit (304, 306, 307, 309) and an estimate of at least one of the communication channels and the self-interference channel.

Description

A FULL-DUPLEX WIRELESS BEAMFORMING APPARATUS WITH SELF-INTERFERENCE CANCELLATION AND METHOD

TECHNICAL FIELD

In general, the present invention relates to wireless communications. More specifically, the present invention relates to a full-duplex wireless communication apparatus and method.

BACKGROUND ln-band full-duplex, also known as full-duplex (FD), is a candidate technology for next generation wireless systems because of the potential gains in spectral efficiency that can be achieved through simultaneous uplink (UL) and downlink (DL) communication within the entire frequency band. As a full-duplex radio can transmit and receive at the same time and the same frequency resource unit, it can double the spectral efficiency achieved by a half- duplex radio, as shown in Figure 1 . Current wireless systems exploit Multiple-Input Multiple-Output antenna (MIMO)

communications, where increasing the number of antennas can increase spatial degrees of freedom (DoF), hence providing higher spectral efficiency. MIMO wireless communications with very large antenna arrays will play a major role in 5G network deployments, since very large antenna arrays have the potential of offering either many spatial DoF or high beamforming (BF) gains. Two possible large antenna array systems in 5G are so-called massive MIMO and mmWave. In massive MIMO, base stations are equipped with large antenna arrays creating multiple very directive beams that are intended to serve multiple users; massive MIMO may also be deployed in mmWave frequency bands. In mmWave, transmission and reception with very large antenna arrays (e.g., phased arrays, hybrid analog/digital (A/D) BF) are expected to be deployed in order to provide high-directional beams against the severe path loss. Phased arrays and BF is a current work item of the ETSI Group in mmWave Transmission (mWT ISG): currently, for point-to-point, in the future, for point-to-multipoint applications. Full-duplex mmWave communication is an objective of this group. Full-duplex mmWave is also included in ITU-R recommendations for V-band (57- 64 and 64-66 GHz) communication. Combining full-duplex with mmWave and with massive MIMO can provide further spectral efficiency gains. Thus, enabling full-duplex MIMO technology, for small to large antenna array systems, is of high interest in order to achieve the demanding requirements of next generation wireless communications, especially that for higher data rate.

An FD radio suffers from self-interference, which is the signal transmitted by the full-duplex radio transmitter (TX) that leaks to the full-duplex radio receiver (RX), as shown in Figure 2. At the RX of the full-duplex radio, the power of the self-interference signal can be many times stronger than the power of the signal of interest. Consequently, the self-interference can severely degrade the reception of the signal of interest (which is transmitted from another radio) and thus self-interference mitigation (SIM) is required at the FD radio in order to maximize the spectral efficiency gain of the MIMO FD operation. As the number of antennas increases, mitigating the self-interference becomes more challenging, since more antennas result in more self-interference components.

In light of the above, there is a need for an improved full-duplex wireless communication apparatus and method addressing, in particular, the self-interference problem that affects FD MIMO radios.

SUMMARY It is an object of the invention to provide an improved full-duplex wireless communication apparatus and method addressing, in particular, the self-interference problem that affects FD MIMO radios.

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

According to a first aspect the invention relates to a full-duplex wireless communication apparatus configured to receive a radio-frequency receive signal and to transmit a radio- frequency transmit signal over a communication channel. The apparatus comprises: at least one beamforming unit configured to apply beamforming to the radio-frequency receive signal, the corresponding base-band receive signal, the radio-frequency transmit signal or the corresponding base-band transmit signal on the basis of at least one fixed beamforming parameter associated with the hardware capabilities of the beamforming unit and on the basis of at least one adjustable beamforming parameter of the beamforming unit; an analog cancellation unit configured to cancel a self-interference signal caused by the radio- frequency transmit signal over a self-interference channel, wherein the analog cancellation unit is configured to cancel the self-interference signal using the radio-frequency transmit signal or the corresponding base-band transmit signal on the basis of at least one fixed parameter associated with the hardware capabilities of the analog cancellation unit and on the basis of at least one adjustable parameter of the analog cancellation unit; and a control unit configured to determine the at least one adjustable parameter of the analog cancellation unit and/or the at least one adjustable beamforming parameter of the beamforming unit on the basis of the at least one fixed parameter of the analog cancellation unit and/or the at least one fixed parameter of the beamforming unit and an estimate of at least one of the communication channels and the self-interference channel. Thus, an improved full-duplex wireless communication apparatus is provided addressing, in particular, the self-interference problem that affects FD Ml MO radios. The improved full- duplex wireless communication apparatus provides a joint design of the analog and/or digital (A/D) beamforming (BF) and the analog self-interference cancellation including a novel optimization framework for the joint design of BF (precoding (at TX) and/or combining (at RX)) and analog self-interference cancellation, where the optimization framework takes into account the analog canceller architecture. This joint design allows guaranteeing QoS to the signals of interest (both the outgoing and incoming), optimizing the use of hardware (HW) resources used for analog cancellation and, thus, reducing HW requirements, as well as optimizing the use of spatial DoF for both BF and SIM.

In an implementation form the at least one beamforming unit can include at least one beamforming unit for digital beamforming (or base-band beamforming) and/or at least one beamforming unit for analog beamforming (or radio-frequency beamforming). The at least one fixed beamforming parameter of the beamforming unit could be, for instance, the number of receive antennas of the apparatus, the number of transmit antennas of the apparatus, the number of radio-frequency processing chains of the apparatus, the number and resolution of phase shifters of the apparatus, the number and resolution of amplifiers of the apparatus and the like. In a first possible implementation form of the apparatus according to the first aspect as such, the control unit is configured to determine the at least one adjustable parameter of the analog cancellation unit and/or the at least one adjustable beamforming parameter of the

beamforming unit by optimizing a performance measure associated with one or more receive signals of interest and/or one or more transmit signals of interest.

In a second possible implementation form of the apparatus according to the first aspect as such, the control unit is configured to determine the at least one adjustable parameter of the analog cancellation unit and/or the at least one adjustable beamforming parameter of the beamforming unit by optimizing a performance measure associated with a receive signal of interest and/or a transmit signal of interest under the constraint that a residual self- interference signal is smaller than a predefined energy threshold. In a third possible implementation form of the apparatus according to the second

implementation form of the first aspect, the analog-cancellation unit is configured to provide the residual self-interference signal or the beamforming unit is configured to provide the residual self-interference signal. In a fourth possible implementation form of the apparatus according to the second or third implementation form of the first aspect, the control unit is configured to determine the at least one adjustable parameter of the analog cancellation unit and/or the at least one adjustable beamforming parameter of the beamforming unit by optimizing a performance measure associated with a receive signal of interest and/or a transmit signal of interest under the constraint that a residual self-interference signal is smaller than a predefined energy threshold and the further constraint that a further residual self-interference signal is smaller than a further predefined energy threshold. In an implementation form, the further residual self-interference signal is based on the residual self-interference signal. In an implementation form, the further predefined energy threshold is smaller than the predefined energy threshold. In an implementation form, the further predefined energy threshold is zero.

In a fifth possible implementation form of the apparatus according to the fourth

implementation form of the first aspect, the analog cancellation unit is configured to provide the residual self-interference signal and the beamforming unit is configured to provide the further residual self-interference signal.

In a sixth possible implementation form of the apparatus according to the first aspect as such or any one of the first to fifth implementation form thereof, the performance measure is based on a signal-to-noise ratio (SNR), a throughput, a signal-to-interference-plus-noise ratio (SINR), an outage probability and/or an energy consumption of the apparatus.

In a seventh possible implementation form of the apparatus according to the first aspect as such or any one of the first to sixth implementation form thereof, the analog cancellation unit comprises at least one tap, i.e. at least one analog delay-phase shifter-attenuation line, and the at least one fixed parameter of the analog cancellation unit defines the number of taps of the analog cancellation unit. In an eighth possible implementation form of the apparatus according to the first aspect as such or any one of the first to seventh implementation form thereof, the analog cancellation unit comprises at least one auxiliary transmitter and the at least one fixed parameter of the analog cancellation unit defines the number of auxiliary transmitters of the analog

cancellation unit.

In an implementation form, the at least one auxiliary transmitter of the analog cancellation unit is configured to generate a radio-frequency signal, which is used for analog cancellation, but not transmitted over the air. In an implementation form, the input of the at least one auxiliary transmitter is a base-band signal.

In a ninth possible implementation form of the apparatus according to the first aspect as such or any one of the first to eighth implementation form thereof, the beamforming unit comprises at least one analog phase shifter and/or at least one analog delay and the at least one fixed beamforming parameter of the beamforming unit defines the number of analog phase shifters and/or the number of analog delays of the beamforming unit.

In a tenth possible implementation form of the apparatus according to the first aspect as such or any one of the first to ninth implementation form thereof, the full-duplex wireless communication apparatus further comprises a digital cancellation unit.

In an eleventh possible implementation form of the apparatus according to the first aspect as such or any one of the first to tenth implementation form thereof, the analog cancellation unit comprises at least one multiplexer for signal routing and the at least one fixed parameter of the analog cancellation unit defines the number of multiplexers of the analog cancellation unit.

In a twelfth possible implementation form of the apparatus according to the eleventh implementation form of the first aspect, the analog cancellation unit comprises at least one tap, i.e. at least one analog delay-phase shifter-attenuation line, and the at least one fixed parameter of the analog cancellation unit comprises a further fixed parameter defining the number of taps of the analog cancellation unit, wherein the apparatus further comprises a memory unit for storing combinations of configurations of the multiplexers and the values or settings of the taps of the analog cancellation unit.

In a thirteenth possible implementation form of the apparatus according to the eleventh implementation form of the first aspect, the analog cancellation unit comprises at least one auxiliary transmitter and the at least one fixed parameter of the analog cancellation unit comprises a further parameter defining the number of auxiliary transmitters of the analog cancellation unit, wherein the apparatus further comprises a memory unit for storing combinations of configurations of the multiplexers and the settings of the auxiliary

transmitters of the analog cancellation unit.

In a fourteenth possible implementation form of the apparatus according to the first aspect as such or any one of the first to thirteenth implementation form thereof, the control unit is further configured to adjust the at least one adjustable parameter of the analog cancellation unit and/or the at least one adjustable beamforming parameter of the beamforming unit responsive to a change of the communication channels and/or the self-interference channel.

According to a second aspect the invention relates to a method of operating a full-duplex wireless communication apparatus configured to receive a radio-frequency receive signal and to transmit a radio-frequency transmit signal over a communication channel, the apparatus comprising a beamforming unit, an analog cancellation unit and a control unit. The method comprises the steps of: applying beamforming by the beamforming unit to the radio- frequency receive signal, a corresponding base-band receive signal, the radio-frequency transmit signal or a corresponding base-band transmit signal on the basis of at least one fixed beamforming parameter associated with the hardware capabilities of the beamforming unit and at least one adjustable beamforming parameter of the beamforming unit; cancelling by the analog cancellation unit a self-interference signal caused by the radio-frequency transmit signal over a self-interference channel using the radio-frequency transmit signal or the corresponding base-band transmit signal on the basis of at least one fixed parameter associated with the hardware capabilities of the analog cancellation unit and on the basis of at least one adjustable parameter of the analog cancellation unit; and determining by the control unit the at least one adjustable parameter of the analog cancellation unit and/or the at least one adjustable beamforming parameter of the beamforming unit on the basis of the at least one fixed parameter of the analog cancellation unit and/or the at least one fixed beamforming parameter of the beamforming unit and an estimate of at least one of the communication channels and the self-interference channel.

The method according to the second aspect of the invention can be performed by the full- duplex wireless communication apparatus according to the first aspect of the invention. Further features and implementation forms of the method according to the second aspect of the invention result directly from the functionality of the full-duplex wireless communication apparatus according to the first aspect of the invention and its different implementation forms. According to a third aspect, the invention relates to a computer program comprising program code for performing the method of the second aspect when executed on a computer.

Implementation forms of the invention can be implemented in hardware and/or software.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the invention will be described with respect to the following figures, wherein:

Fig. 1 shows a schematic diagram illustrating the main principle of a full duplex radio;

Fig. 2 shows a schematic diagram illustrating the problem of self-interference occurring in a full duplex MIMO radio;

Fig. 3 shows a schematic diagram of a full-duplex wireless communication apparatus according to an embodiment;

Fig. 4 shows a schematic diagram illustrating processing steps implemented in a full-duplex wireless communication apparatus according to an embodiment;

Fig. 5 shows a schematic diagram of the full-duplex wireless communication apparatus according to an embodiment of figure 3, including control signals exchanged between the units thereof;

Fig. 6 shows a schematic diagram of the full-duplex wireless communication apparatus according to an embodiment of figure 3, including an illustration of signals at different processing steps; Fig. 7 shows a schematic diagram illustrating different aspects of embodiments of the invention;

Fig. 8 shows a schematic diagram of a full-duplex wireless communication apparatus according to an embodiment including a multiplexed N-tap analog cancellation unit and a digital BF unit; Fig. 9 shows a schematic diagram of a full-duplex wireless communication apparatus according to an embodiment including a multiplexed analog cancellation unit with N AUX TX RF chains and a digital beamforming unit; Fig. 10 shows a schematic diagram of a full-duplex wireless communication apparatus according to an embodiment including a multiplexed analog cancellation unit and a hybrid A D digital beamforming unit;

Fig. 1 1 shows a schematic diagram of a full-duplex wireless communication apparatus according to an embodiment including a multiplexed analog cancellation unit with N AUX TX chains and a hybrid A D digital beamforming unit;

Fig. 12 shows a schematic diagram of a full-duplex wireless communication apparatus according to an embodiment;

Fig. 13 shows a schematic diagram of a full-duplex wireless communication apparatus according to an embodiment including a multiplexed N-tap analog cancellation unit and a digital BF unit; Fig. 14 shows a schematic diagram of a full-duplex wireless communication apparatus according to an embodiment including a multiplexed analog cancellation unit with N AUX TX RF chains and a digital beamforming unit;

Fig. 15 shows a schematic diagram of a full-duplex wireless communication apparatus according to an embodiment including a multiplexed N-tap analog cancellation unit and a hybrid A/D digital beamforming unit;

Fig. 16 shows a schematic diagram of a full-duplex wireless communication apparatus according to an embodiment including a multiplexed analog cancellation unit with N AUX TX chains and a hybrid A/D digital beamforming unit;

Fig. 17 shows a schematic diagram of a full-duplex wireless communication apparatus according to an embodiment; and Fig. 18 shows a schematic diagram of a method of operating a full-duplex wireless communication apparatus according to an embodiment. In the figures, identical reference signs will be used for identical or functionally equivalent features.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, reference is made to the accompanying drawings, which form part of the disclosure, and in which are shown, by way of illustration, specific aspects in which the present invention may be placed. It will be appreciated that the invention may be placed in other aspects and that structural or logical changes may be made without departing from the scope of the invention. The following detailed description, therefore, is not to be taken in a limiting sense, as the scope of the invention is defined by the appended claims.

For instance, it will be appreciated that a disclosure in connection with a described method will generally also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if a specific method step is described, a corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures.

Moreover, in the following detailed description as well as in the claims, embodiments with functional blocks or processing units are described, which are connected with each other or exchange signals. It will be appreciated that the invention also covers embodiments which include additional functional blocks or processing units that are arranged between the functional blocks or processing units of the embodiments described below. Finally, it is understood that the features of the various exemplary aspects described herein may be combined with each other, unless specifically noted otherwise.

Figure 3 shows a schematic diagram of a full-duplex wireless communication apparatus 300 according to an embodiment. In the embodiment shown in figure 3 the apparatus 300 comprises a set of transmit antennas 302 for emitting a RF transmit signal as well as a set of receive antennas 303 for receiving a RF receive signal. Thus, the apparatus 300 is implemented in form of a FD Ml MO transceiver 300.

The communication apparatus 300 shown in Figure 3 comprises several beamforming units for analog and/or digital beamforming, namely the analog beamforming units 306 and 309 and the digital beamforming units 304 and 307. In the embodiment shown in figure 3, these analog and digital beamforming units are implemented in the form of a TX BB processing unit 304, a TX Analog processing unit 306, a RX BB processing unit 307 and a RX Analog processing unit 309. In an embodiment, the TX BB processing unit 304, the TX Analog processing unit 306, the RX BB processing unit 307 and/or the RX Analog processing unit 309 can be configured to provide additional functions besides analog or digital beamforming, such as amplification, encoding or decoding and the like. As will be described in more detail further below, other embodiments of the communication apparatus can comprise only analog beamforming units 306 and 309 or only digital beamforming units 304 and 307.

In the embodiment shown in figure 3 the analog beamforming unit 309 is configured to apply beamforming to the RF receive signal provided by the set of RF receive antennas 303, the digital beamforming unit 307 is configured to apply beamforming to the corresponding baseband receive signal, the analog beamforming unit 306 is configured to apply beamforming to the RF transmit signal to be transmitted by the set of transmit antennas 302 and the digital beamforming unit 304 is configured to apply beamforming to the corresponding base-band transmit signal. According to the preset invention, at least one of these beamforming units 304, 306, 307, 309 is configured to apply beamforming on the basis of at least one fixed beamforming parameter of beamforming units 304, 306, 307, 309, where the fixed beamforming parameter is associated with the hardware capabilities of the communication apparatus 300 (e.g. number of receive antennas of the apparatus 300, the number of transmit antennas of the apparatus 300, the number of radio-frequency processing chains of the apparatus 300, the number and resolution of phase shifters of the apparatus 300, the number and resolution of amplifiers of the apparatus 300 and the like) and on the basis of at least one adjustable beamforming parameter of the beamforming units 304, 306, 307, 309. As will be described in more detail further below, the at least one fixed beamforming parameter associated with the hardware capabilities of the beamforming units could be, for instance, the number of RF receive antennas 303, the number of RF transmit antennas 302, the number of radio-frequency processing chains 305, 306 of the apparatus 300 and the like.

The communication apparatus 300 further comprises an analog cancellation unit (herein also referred to as analog canceller) 312. The analog cancellation unit 312 is configured to cancel a self-interference signal caused by a RF transmit signal over a self-interference channel, wherein the analog cancellation unit 312 is configured to cancel the self-interference signal using the RF transmit signal or the corresponding base-band transmit signal on the basis of at least one fixed parameter associated with the hardware capabilities of the analog cancellation unit 312 and on the basis of at least one adjustable parameter of the analog cancellation unit 312, as will be described in more detail further below.

The communication apparatus 300 further comprises a control unit 31 1 , which in figure 3 is referred to as the BDC module 31 1 , wherein BDC stands for beamforming-driven canceller. The control unit or BDC module 31 1 is configured to determine the at least one adjustable parameter of the analog cancellation unit 312 and/or the at least one adjustable beamforming parameter of the beamforming units 304, 306, 307, 309 on the basis of the at least one fixed parameter of the analog cancellation unit and/or the at least one fixed beamforming parameter of the beamforming unit 304, 306, 307, 309 and an estimate of at least one of the communication channels and the self-interference channel.

In the embodiment shown in figure 3, the communication apparatus 300 further comprises a digital canceller 310 as well as a plurality of transmit RF chains 305 for upconverting the base-band transmit signal(s) to the RF transmit signal(s) and a plurality of receive RF chains 308 for downconverting the RF receive signal(s) to the base-band receive signal(s). Digital cancellation (as employed, for example, in FD SISO systems) generally requires that the TX processing shares waveform data to the RX BB processing, since digital cancellation is typically done via self-interference regeneration followed by subtraction. In contrast, digital BF for SIM does not require knowledge of the TX waveform or samples. The digital BF for SIM only requires knowledge of the involved channels. In general, digital cancellation is the last stage of cancellation. Hence, in a FD MIMO context, digital cancellation can be used after the digital BF stage (to reduce any residual self-interference that remains after the digital BF stage). Other embodiments of the communication apparatus 300 do not have a digital canceller.

The block diagram in Figure 4 illustrates the general procedure implemented in the communication apparatus 300 according to embodiments of the present invention. In a first stage 401 , channel estimates for the outgoing signal channel (e.g. DL channel) and/or incoming signal channel (e.g. UL channel) and/or self-interference channel are obtained via channel estimation procedures (e.g. conventional channel estimation via training signals or blind channel estimation techniques). Using the channel estimates, and using also knowledge of the hardware architecture of the analog canceller 312, the BDC module 31 1 can proceed in a second stage 402 to perform a joint design of the adjustable parameters of the beamforming units 304, 306, 307, 309 and the analog canceller 312. In an embodiment, this joint design targets the optimization of a performance or QoS measure (e.g. a signal-to- noise ratio (SNR), a throughput, a signal-to-interference-plus-noise ratio (SINR), an outage probability and/or an energy consumption) for all the signals of interest. The adjustable beamforming and analog canceller parameters computed by the BDC module 31 1 are then fed in a third stage 403 to the involved units (either software or HW) in charge of performing the BF, i.e. the beamforming units 304, 306, 307 and/or 309, and analog cancellation processing, i.e. the analog canceller 312. At this stage 404, the full-duplex communication apparatus 300 can communicate in FD mode. If the communication channels (either incoming and/or outgoing and/or self-interference) change, then the communication apparatus 300 may re-initiate a channel estimation procedure. If new channel estimates are available, then the BDC module 31 1 can perform a new joint design of the adjustable parameters of the beamforming units 304, 306, 307, 309 and the analog canceller 312 and refresh the respective parameters of the units responsible for realizing the BF and analog cancellation processing.

In an embodiment, the BDC module 31 1 is configured to determine the following quantities:

denotes complex-valued BB precoding matrix including the transmit linear

processing of the

data streams from the TX BB unit that are fed as inputs to the TX RF chains at the TX of node k. denotes complex-valued RF precoding matrix including the outputs from

the TX RF chains that are fed as inputs to the TX antenna elements of the TX at node k. denotes complex-valued BB combining matrix including the receive linear

processing resulting to the estimation of the

data streams; this matrix gets inputs from the RX RF chains and its outputs are fed to the RX BB unit. denotes complex-valued RF combining matrix including the outputs from

the RX antenna elements that are fed as inputs to the RX RF chains of the RX at node k.

Figure 5 shows a block diagram of the communication apparatus 300 according to an embodiment, where it is explicitly indicated which outputs of the BDC module 31 1 are fed to which processing blocks of the communication apparatus 300. Herein k denotes the FD- enabled communication apparatus node k. In this embodiment, the joint BF and analog canceller design performed by the BDC module 31 1 is computed based on the knowledge of the outgoing channel (e.g. DL channel if node k is a base station and transmits to node

m), and/or incoming channel (e.g. U L channel if node k is a base station and receives

from node n), and/or self-interference channel and also taking into account the

hardware architecture of the analog canceller 312, i.e. the fixed parameters associated with the hardware capabilities of the analog canceller 312. Herein, denotes the channel from

node k to a node m (or a group of nodes labeled as m),

denotes the channel to node k from a node n (or a group of nodes labeled as n), and

denotes the self-interference channel at node k. The BF and analog canceller signals designed by the BDC module 31 1 shape the transmitted and received signals at different stages of the FD communication link, as shown in Figure 6, which will be described in more detail further below. In particular, the following signals are present:

• The received signal at node m (or group of nodes labeled as m) can be

represented as

wherein is the complex-valued vector of information data streams transmitted

from the TX of node k and denotes the total number of information data streams

transmitted from node k. The signal goes through the TX BB processing unit 304 including

digital beamforming, which applies the digital TX BF matrix The digital signal is then

converted to the analog domain and up converted to the carrier frequency, this happens at the TX RF chains 305. The analog signal goes through the TX analog processing unit 306 including analog beamforming, which applies the analog TX BF matrix

The framework implemented in embodiments of the invention is flexible regarding the design and use of TX BF matrices. For instance, it is possible to design both matrices and

or to consider that one or both matrices equals the identity matrix or any other fixed

value. The signal is the A/D processed outgoing signal of interest.

• The received signal at node k, y_k, is the sum of the incoming signal of interest and the received self-interference (this self-interference is a function of

the TX digital precoding the TX analog precoding the self-

interference channel and the signal Signals and are given

by

where the noise in the receiver path has been modeled as an additive noise term nk and where s is the

complex-valued vector of information data streams transmitted from node (or nodes) n and is the total number of information data streams transmitted from

node (or nodes) is the BF used by node (or nodes) n.

The received signal y_k undergoes the RX analog processing in the analog beamforming unit 309. Here, the received signal is modified by the RX BF matrix and the output of the analog RX processing unit 309 can be represented as

The signal is the effective self-interference which includes the

processing effects of TX A/D precoding respectively) and RX analog

combining

· Analog cancellation applied by the analog canceller 312 consists in adding a

cancellation signal to the received signal This addition is performed in the

analog domain, typically before the RX RF chains. The cancellation signal is equal to

where C_k is the analog cancellation matrix at node k. Matrix C_k has complex valued elements, wherein the dimensions of this matrix depend on the architecture of the analog canceller 312. The received signal after analog cancellation is equal to

The BDC module 31 1 is capable to adapt to cases, where the analog canceller 312 does not apply any analog cancellation. In this case, the optimization procedure performed by the BDC module 31 1 would simply assume

From equations (5) and (7) one obtains that the residual self-interference after analog cancellation is equal to

The RX RF chains 308 downconvert the received signal from RF to BB and

also convert from analog to digital domain. In the digital BB domain, the received signal goes through the digital RX BF unit 307. The received signal at node k after the digital BF 307 is equal to

The framework implemented in embodiments of the invention is flexible regarding the design and use of RX BF matrices. For instance, in an embodiment it is possible to design both matrices and or to consider that one or both matrices equals the identity matrix or

any other fixed value. From equations (5), (7) and (9) one obtains that the residual self-interference after the digital BF unit 307 is equal to

As shown in the block diagrams in figures 5 and 6 and as already described above, the FD communication apparatus 300 also includes a digital canceller 31 1 , as there is a difference between digital cancellation, as performed by the digital canceller 31 1 , and digital BF, as performed by the digital beamforming units 307, 304.

As already described above, in an embodiment the BDC module 31 1 is configured to determine the at least one adjustable parameter of the analog canceller 312 and/or the at least one adjustable beamforming parameter of the beamforming units 304, 306, 307, 309 by optimizing a performance measure associated with a receive signal of interest and/or a transmit signal of interest, while guaranteeing that the self-interference is maintained below a certain level.

Thus, in an embodiment the BDC module 311 can optimize a performance measure associated with a receive signal of interest and/or a transmit signal of interest under the constraint that a residual self-interference signal is smaller than a predefined energy threshold.

In a further embodiment, the BDC module 311 can be configured to perform the optimization on the basis of two energy threshold constraints for the residual self-interference and

This optimization procedure can be written as

where represents a function of the involved inputs (it could be, for example, the SNR or throughput or SINR or outage probability or energy consumption) and the maximization seeks to find the adjustable parameters for the beamforming units 304, 306, 307, 309 and the analog canceller 312. In an embodiment, the optimization procedure implemented in the BDC module 31 1 has the following inputs:

• Capabilities of the analog canceller 312 (e.g. number of taps, number of AUX TX RF chains).

· Channel estimates and BF values during estimation phase.

Herein denotes the energy of the residual self-interference at node k, after applying

analog cancellation and/or all BF stages that precede analog cancellation. Specifically,

is the energy of the signal represented by given in equation (8). The energy threshold

indicates the maximum acceptable level of residual self-interference energy in the

analog domain. Thus, the constraint in equation (11 ) is a constraint on the

energy of the residual self-interference after analog cancellation. Herein

denotes the energy of the residual self-interference at node k after digital BF. Specifically

is the energy of signal

given in equation (10). The energy threshold indicates the maximum acceptable level of residual self-interference energy after digital

BF. Thus, the constraint E in equation (11 ) is a constraint on the energy of the

residual self-interference after digital BF. For embodiments with a digital canceller 311 , the energy threshold A_(S1D) can be chosen by taking into account that there is a later digital cancellation stage and accounting for the cancellation capabilities of this digital cancellation stage 31 1. For example, if the digital canceller 311 can achieve 20 dB of self-interference cancellation then the energy threshold A_(S1D) can be set to 20 dB above the noise floor. This means that 20dB of SIM are left as a task to the digital canceller 311. In embodiments of the communication apparatus 300 without a digital canceller 311 the energy threshold A_(S1D) can be set, for example, equal or below the noise floor, wherein the term noise floor is used to denote the energy of the noise term

When solving the optimization problem in equation (1 1 ), it is also possible to have only one of the constraints active, as already described above. For example, if the main constraint is the energy of the residual after digital BF, then the optimization problem can be written with only this constraint as follows

The solution of the optimization procedure defined by equation (1 1 ) or (12) yields the BF matrices the control signals

and and the SIM parameters

and tap values or AUX TX RF chain settings). Figure 7 provides a schematic illustration of several aspects implemented in a FD wireless communication apparatus according to an embodiment, such as the communication apparatus 300 described above.

Embodiments of the invention are based on an analog canceller architecture, where inputs and/or outputs of the analog canceller 312 are routed via multiplexers to/from the processing units of the analog canceller 312. The following detailed embodiments illustrate some of the possible implementations of the analog canceller 312.

A first embodiment of the communication apparatus 300 with a possible implementation of the analog canceller 312 is shown in figure 8. In this embodiment, N analog canceller taps are applied, via multiplexers, between the TX and RX RF chains. Herein the term "tap" denotes a delay-phase shifter-attenuation line. The flexible signal routing that is enabled by the multiplexers allows the use of reduced number of taps for analog cancellation. The total number of taps N (N≥ 0) of the analog canceller 312 is flexible and can be chosen offline as a function of size constrains, cost per tap, or other constraint(s) on analog canceller hardware. The BDC module 311 is capable of optimizing the BF parameters and tap parameters for any number of taps N. Tap values and multiplexers' configuration are computed in an optimized way by the BDC module 31 1 which can take into account the TX BF and RX BF matrices and QoS of signals of interests (outgoing and incoming signals of interest).

For the tap hardware, adjustable phase shifters can be implemented with an RF digital phase shifter, adjustable attenuators can be implemented with an RF digital step attenuator, and adjustable delays can be implemented using optical techniques for reconfigurable true time delay. Another possibility for the tap HW is fixed delay and variable attenuator. The BDC module 31 1 will adapt its optimization to the specific tap HW.

In the embodiment shown in Figure 8, there are no analog beamforming units 306 and 309, hence the number of RF chains is equal to the number of antennas and

In this embodiment, the BDC module 311 jointly optimizes the digital BF

and the analog canceller 312 as follows (same as equation 11 and

repeated below for convenience of readability)

When the QoS requirements are the SNRs of the desired incoming signal

and the desired outgoing signal s_k, an adequate objective function for designing and could be

The constraint on the residual self-interference after analog cancellation is

and the constraint on the residual self-interference after digital BF

One way to solve the optimization problem in equation (14) is through alternating

optimization.

For this embodiment including chains

chains 3 and N analog canceller taps:

•

matrix that specifies the tap values and the multiplexers'

configuration of the analog canceller 312.

To satisfy the constraint of N taps for the analog canceller 312, the matrix must

have at most N non-zero entries.

The value of N can take values

N 0 and can be, for example, less than the number of TX RF chains and/or less than the number of RX RF chains

As a further simplification for online processing, the combinations of tap values and multiplexer configurations for different TX and RX BF can be computed offline and kept on a dedicated memory unit (e.g., a look-up table) of the FD communication apparatus 300.

During online operation tap values and multiplexers' configuration are chosen accordingly to the adjustable BF parameters, which depend on the QoS for the incoming and outgoing signals of interest and on the constraints on residual energy after SI M.

A second embodiment of the communication apparatus 300 with a possible implementation of the analog canceller 312 is shown in Figure 9. In this embodiment, N AUX TX RF chains are connected via multiplexers to the RX RF chains. This flexible signal routing that is enabled by the multiplexers allows the use of reduced number of AUX TX RF chains for analog cancellation. The total number of AUX TX RF chains N (N≥ 0) of the analog canceller 312 is flexible and can be chosen offline as a function of size constrains, cost per AUX TX RF chain, or other constraint(s) on analog canceller hardware. The BDC module 31 1 is capable of optimizing the BF and AUX TX RF chain parameters for any number of AUX TX RF chains N. Inputs to the AUX TX RF chains and multiplexers' configuration are computed in an optimized way by the BDC module 31 1 , which takes into account the TX BF and RX BF matrices and QoS of signals of interests, as already described above in great detail.

In the embodiment shown in figure 9, there is no analog BF, hence the number of RF chains is equal to the number of antennas In this embodiment,

the BDC module 31 1 is configured to jointly optimize the digital BF

and the analog canceller 312 following the same procedure described in equations (13), (14), (15) and (16). For this embodiment including chains and N AUX TX RF

chains:

• matrix that specifies the inputs to the AUX TX RF chains and

the multiplexers' configuration.

• To satisfy the constraint of N AUX TX RF chains, the matrix C_k must have at least rows.

• The value of N can take values

and can be, for example, less than the

number of TX RF chains and/or less than the number of RX RF chains

As a further simplification for online processing, the combinations of inputs to the AUX TX RF chains and multiplexers' configuration for different TX and RX BF can be computed offline and kept on a dedicated memory unit (e.g., a look-up table) of the FD communication apparatus 300. During online operation tap values and multiplexers' configuration are chosen accordingly to the BF; the BF depends on the QoS for the incoming and outgoing signals of interest and on the constraints on residual energy after SIM. A third embodiment of the communication apparatus 300 with a possible implementation of the analog canceller 312 is shown in figure 10. In this embodiment, N analog canceller taps are applied, via multiplexers, between the TX and RX RF chains. As in the first embodiment shown in figure 8, the term "tap" is used to denote a delay-phase shifter-attenuation line. The flexible signal routing that is enabled by the multiplexers allows the use of reduced number of taps for analog cancellation. The total number of taps N (N≥ 0) of the analog canceller 312 is flexible and can be chosen offline as a function of size constrains, cost per tap, or other constraint(s) on analog canceller hardware. The BDC module 311 is capable of optimizing the BF and tap parameters for any number of taps N. Tap values and multiplexers' configuration are computed in an optimized way by the BDC module 311 which takes into account the hybrid A/D TX BF, hybrid A/D RX BF and QoS of signals of interests.

In this embodiment, the BDC module 311 jointly optimizes the hybrid A/D BF

and the analog canceller, as in equation (13).

When the performance measure or QoS requirements are based on the SNRs of the desired incoming signal s_n and the desired outgoing signal s_k , an adequate objective function for designing and could be

The constraint on the residual self-interference after analog cancellation is

and the constraint on the residual self-interference after digital BF is

One way to solve the optimization problem in equation (17) is through alternating

optimization. For this embodiment of RX RF chains and N analog canceller

taps:

• matrix that specifies the tap values and the multiplexers'

routing configuration.

• To satisfy the constraint of N taps for the analog canceller 312, the matrix C_k must have at most N non-zero entries. • The value of N can take values N >0 and can be, for example, less than the number of TX RF chains ) and/or less than the number of RX RF chains (N <

As a further simplification for online processing, the combinations of tap values and multiplexer configurations for different TX and RX BF can be computed offline and kept on a dedicated memory unit (e.g., a look-up table) of the FD communication apparatus 300. During online operation tap values and multiplexers' configuration are chosen accordingly to the BF; the BF depends on the QoS for the incoming and outgoing signals of interest and on the constraints on residual energy after SIM.

A fourth embodiment of the communication apparatus 300 with a possible implementation of the analog canceller 312 is shown in figure 1 1 . In this embodiment, N AUX TX RF chains are connected, via multiplexers, to the RX RF chains. This flexible signal routing that is enabled by the multiplexers allows the use of reduced number of AUX TX RF chains for analog cancellation. The total number of AUX TX RF chains N (N≥ 0) of the analog canceller 312 is flexible and can be chosen offline as a function of size constrains, cost per AUX TX RF chain, or other constraint(s) on analog canceller hardware. The BDC module 31 1 is capable of optimizing the BF and AUX TX RF chain parameters for any number of AUX TX RF chains N. Inputs to the AUX TX RF chains and multiplexers' configuration are computed in an optimized way by the BDC module 31 1 , which takes into account the hybrid A/D TX BF, hybrid A/D RX BF, and QoS of signals of interests, as already described above.

In the embodiment shown in figure 1 1 , the BDC module 31 1 jointly optimizes the hybrid A/D BF and the analog canceller 312, as in equation (13) and

following the same procedure described in equations (17), (18) and (19).

For this embodiment of F chains, chains and N analog canceller

taps:

• matrix that specifies the inputs to the AUX TX RF chains and

the multiplexers' configuration.

• To satisfy the constraint of N AUX TX RF taps for the analog canceller, the matrix C_k must have at least rows.

• The value of N can take values N >0 and can be, for example, less than the number of TX RF chains and/or less than the number of RX RF chains (N <

As a further simplification for online processing, the combinations of inputs to the AUX TX RF chains and multiplexers' configuration for different TX and RX BF can be computed offline and kept on a dedicated memory unit (e.g., a look-up table) of the FD communication apparatus 300. During online operation tap values and multiplexers' configuration are chosen accordingly to the BF; the BF depends on the QoS for the incoming and outgoing signals of interest and on the constraints on residual energy after SIM.

The embodiments of the FD communication apparatus 300 shown in the previous figures and described above comprises a set of RF transmit antennas 302 and a separate set of RF receive antennas 303. In the following, further embodiments of the communication apparatus 300 will be described using transmission and reception over the same antenna(s).

Application to this case is straightforward, since the channel matrix representation described above is also valid for this scenario: the leakage due to same TX/RX antenna can be modeled as an entry in the channel matrix H^. The general block diagram for a full-duplex node that uses each antenna for transmission and reception is shown in figure 12. In this embodiment, at least one circulator 1213a, 1213n is used to route the transmitted and received signals at the antenna from the transmitter and to the receiver processing paths respectively. Any duplexer can be used as an alternative to the circulator.

The embodiments of the communication apparatus 300 shown in figures 8, 9, 10 and 1 1 can thus be extended to the scenario of same TX/RX antenna. The corresponding modified embodiments of the communication apparatus 300 are shown in figures 13, 14, 15 and 16, respectively. The optimization performed by the BDC module 31 1 is the same as in the embodiments shown in figures 8, 9, 10 and 1 1 , respectively. This is because all of the above matrix representations hold for the case of same TX/RX antenna as well.

Figure 17 shows a further embodiment of the FD communication apparatus 300, where some antenna elements 302 are only transmitting (TX), other antenna elements 303 only receiving (RX) and other antenna elements 1213a, 1213n are both transmitting and receiving (TX/RX). The analog canceller 312 and BDC module 312 described for the embodiments shown in figures 8, 9, 10 and 1 1 also apply to this embodiment of mixed antennas. Figure 18 shows a schematic diagram of a method 1800 of operating the full-duplex wireless communication apparatus 300 configured to receive a radio-frequency receive signal and to transmit a radio-frequency transmit signal over a communication channel. The method 1800 comprises the following steps: applying 1801 beamforming by the beamforming unit 304, 306, 307, 309 to the radio-frequency receive signal, the corresponding base-band receive signal, the radio-frequency transmit signal or the corresponding base-band transmit signal on the basis of at least one fixed beamforming parameter associated with the hardware capabilities of the beamforming unit 304, 306, 307, 309 and on the basis of at least one adjustable beamforming parameter of the beamforming unit 304, 306, 307, 309; cancelling 1803 by the analog cancellation unit 312 a self-interference signal caused by the radio- frequency transmit signal over a self-interference channel using the radio-frequency transmit signal or the corresponding base-band transmit signal on the basis of at least one fixed parameter associated with the hardware capabilities of the analog cancellation unit 312 and on the basis of at least one adjustable parameter of the analog cancellation unit 312; and determining 1805 by the control unit 31 1 the at least one adjustable parameter of the analog cancellation unit 312 and/or the at least one adjustable beamforming parameter of the beamforming unit 304, 306, 307, 309 on the basis of the at least one fixed parameter of the analog cancellation unit 312 and/or the at least one fixed beamforming parameter of the beamforming unit 304, 306, 307, 309 and an estimate of at least one of the communication channel and the self-interference channel.

While a particular feature or aspect of the disclosure may have been disclosed with respect to only one of several implementations or embodiments, such feature or aspect may be combined with one or more other features or aspects of the other implementations or embodiments as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "include", "have", "with", or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprise". Also, the terms "exemplary", "for example" and "e.g." are merely meant as an example, rather than the best or optimal. The terms "coupled" and "connected", along with derivatives may have been used. It should be understood that these terms may have been used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other. Although specific aspects have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent

implementations may be substituted for the specific aspects shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific aspects discussed herein.

Although the elements in the following claims are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

Many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teachings. Of course, those skilled in the art readily recognize that there are numerous applications of the invention beyond those described herein. While the present invention has been described with reference to one or more particular embodiments, those skilled in the art recognize that many changes may be made thereto without departing from the scope of the present invention. It is therefore to be understood that within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described herein.

Claims

1 . A full-duplex wireless communication apparatus (300) configured to receive a radio- frequency receive signal and to transmit a radio-frequency transmit signal over a

communication channel, the apparatus (300) comprising: at least one beamforming unit (304, 306, 307, 309) configured to apply beamforming to the radio-frequency receive signal, the corresponding base-band receive signal, the radio- frequency transmit signal or the corresponding base-band transmit signal on the basis of at least one fixed beamforming parameter of the beamforming unit (304, 306, 307, 309) and on the basis of at least one adjustable beamforming parameter of the beamforming unit (304, 306, 307, 309); an analog cancellation unit (312) configured to cancel a self-interference signal caused by the radio-frequency transmit signal over a self-interference channel, wherein the analog cancellation unit (312) is configured to cancel the self-interference signal using the radio- frequency transmit signal or the corresponding base-band transmit signal on the basis of at least one fixed parameter of the analog cancellation unit (312) and on the basis of at least one adjustable parameter of the analog cancellation unit (312); and a control unit (31 1 ) configured to determine the at least one adjustable parameter of the analog cancellation unit (312) and/or the at least one adjustable beamforming parameter of the beamforming unit (304, 306, 307, 309) on the basis of the at least one fixed parameter of the analog cancellation unit (312) and/or the at least one fixed parameter of the beamforming unit (304, 306, 307, 309) and an estimate of at least one of the communication channels and the self-interference channel.

2. The full-duplex wireless communication apparatus (300) of claim 1 , wherein the control unit (31 1 ) is configured to determine the at least one adjustable parameter of the analog cancellation unit (312) and/or the at least one adjustable beamforming parameter of the beamforming unit (304, 306, 307, 309) by optimizing a performance measure associated with a receive signal of interest and/or a transmit signal of interest.

3. The full-duplex wireless communication apparatus (300) of claim 1 or 2, wherein the control unit (31 1 ) is configured to determine the at least one adjustable parameter of the analog cancellation unit (312) and/or the at least one adjustable beamforming parameter of the beamforming unit (304, 306, 307, 309) by optimizing a performance measure associated with a receive signal of interest and/or a transmit signal of interest under the constraint that a residual self-interference signal is smaller than an energy threshold.

4. The full-duplex wireless communication apparatus (300) of claim 3, wherein the analog-cancellation unit (312) is configured to provide the residual self-interference signal or wherein the beamforming unit (304, 306, 307, 309) is configured to provide the residual self- interference signal.

5. The full-duplex wireless communication apparatus (300) of claim 3 or 4, wherein the control unit (31 1 ) is configured to determine the at least one adjustable parameter of the analog cancellation unit (312) and/or the at least one adjustable beamforming parameter of the beamforming unit (304, 306, 307, 309) by optimizing a performance measure associated with a receive signal of interest and/or a transmit signal of interest under the constraint that a residual self-interference signal is smaller than an energy threshold and the further constraint that a further residual self-interference signal is smaller than a further energy threshold.

6. The full-duplex wireless communication apparatus (300) of claim 5, wherein the analog cancellation unit (312) is configured to provide the residual self-interference signal and wherein the beamforming unit (304, 306, 307, 309) is configured to provide the further residual self-interference signal.

7. The full-duplex wireless communication apparatus (300) of any one of claims 2 to 6, wherein the performance measure is based on a signal-to-noise ratio, a throughput, a signal- to-interference-plus-noise ratio, an outage probability and/or an energy consumption.

8. The full-duplex wireless communication apparatus (300) of any one of the preceding claims, wherein the analog cancellation unit (312) comprises at least one tap and wherein the at least one fixed parameter of the analog cancellation unit (312) defines the number of taps of the analog cancellation unit (312).

9. The full-duplex wireless communication apparatus (300) of any one of the preceding claims, wherein the analog cancellation unit (312) comprises at least one auxiliary transmitter and wherein the at least one fixed parameter of the analog cancellation unit (312) defines the number of auxiliary transmitters of the analog cancellation unit (312).

10. The full-duplex wireless communication apparatus (300) of any one of the preceding claims, wherein the beamforming unit (306, 309) comprises at least one analog phase shifter and/or analog delays and wherein the at least one fixed parameter of the beamforming unit (306, 309) defines the number of analog phase shifters and/or analog delays of the beamforming unit (306, 309).

1 1 . The full-duplex wireless communication apparatus (300) of any one of the preceding claims, wherein the full-duplex wireless communication apparatus (300) further comprises a digital cancellation unit (310).

12. The full-duplex wireless communication apparatus (300) of any one of the preceding claims, wherein the analog cancellation unit (312) comprises at least one multiplexer for signal routing and wherein the at least one fixed parameter of the analog cancellation unit (312) defines the number of multiplexers of the analog cancellation unit (312).

13. The full-duplex wireless communication apparatus (300) of claim 12, wherein the analog cancellation unit (312) comprises at least one tap and wherein the at least one fixed parameter of the analog cancellation unit (312) comprises a further parameter defining the number of taps of the analog cancellation unit (312), wherein the full-duplex wireless communication apparatus (300) further comprises a memory unit for storing combinations of configurations of the multiplexers and the values of the taps of the analog cancellation unit (312).

14. The full-duplex wireless communication apparatus (300) of claim 12, wherein the analog cancellation unit (312) comprises at least one auxiliary transmitter and wherein the at least one fixed parameter of the analog cancellation unit (312) comprises a further parameter defining the number of auxiliary transmitters of the analog cancellation unit (312), wherein the full-duplex wireless communication apparatus (300) further comprises a memory unit for storing combinations of configurations of the multiplexers and the settings of the auxiliary transmitters of the analog cancellation unit (312).

15. The full-duplex wireless communication apparatus (300) of any one of the preceding claims, wherein the control unit (31 1 ) is further configured to adjust the at least one adjustable parameter of the analog cancellation unit (312) and/or the at least one adjustable beamforming parameter of the beamforming unit (304, 306, 307, 309) responsive to a change of the communication channel and/or the self-interference channel.

16. A method (1800) of operating a full-duplex wireless communication apparatus (300) configured to receive a radio-frequency receive signal and to transmit a radio-frequency transmit signal over a communication channel, the apparatus (300) comprising a beamforming unit (304, 306, 307, 309), an analog cancellation unit (312) and a control unit (31 1 ), wherein the method (1800) comprises: applying (1801 ) beamforming by the beamforming unit (304, 306, 307, 309) to the radio- frequency receive signal, the corresponding base-band receive signal, the radio-frequency transmit signal or the corresponding base-band transmit signal on the basis of at least one fixed beamforming parameter of the beamforming unit (304, 306, 307, 309) and at least one adjustable beamforming parameter of the beamforming unit (304, 306, 307, 309); cancelling (1803) by the analog cancellation unit (312) a self-interference signal caused by the radio-frequency transmit signal over a self-interference channel using the radio-frequency transmit signal or the corresponding base-band transmit signal on the basis of at least one fixed parameter of the analog cancellation unit (312) and on the basis of at least one adjustable parameter of the analog cancellation unit (312); and determining (1805) by the control unit (31 1 ) the at least one adjustable parameter of the analog cancellation unit (312) and/or the at least one adjustable beamforming parameter of the beamforming unit (304, 306, 307, 309) on the basis of the at least one fixed parameter of the analog cancellation unit (312) and/or the at least one fixed beamforming parameter of the beamforming unit (304, 306, 307, 309) and an estimate of at least one of the communication channel and the self-interference channel.

17. A computer program comprising program code for performing the method (1800) of claim 16 when executed on a computer.