EP4335086A1

EP4335086A1 - A wireless communication device and a method for reducing interference in a wireless communication

Info

Publication number: EP4335086A1
Application number: EP21766208.9A
Authority: EP
Inventors: Mohamed Kamoun; Ali MOKH; Ramin KHAYATZADEH; Abdelwaheb Ourir; Julien Derosny; Arnaud Tourin; Mathias Fink
Original assignee: Huawei Technologies Co Ltd; Centre National de la Recherche Scientifique CNRS; Ecole Superieure de Physique et Chimie Industrielles de Ville de Paris ESPCI
Current assignee: Huawei Technologies Co Ltd; Centre National de la Recherche Scientifique CNRS; Ecole Superieure de Physique et Chimie Industrielles de Ville de Paris ESPCI
Priority date: 2021-06-18
Filing date: 2021-06-18
Publication date: 2024-03-13
Also published as: CN117529900A; WO2022263874A1

Abstract

The present disclosure relates to a wireless communication device for a wireless communication with two or more second wireless communication devices. The wireless communication device is configured to, for a channel between the wireless communication device and a respective second wireless communication device, initialize, based on a respective channel impulse response of the channel, a respective precoder for precoding a signal intended for the respective second communication device; determine one or more respective interference peaks caused at the respective second wireless communication device and/or at one or more other second wireless communication devices by transmitting a respective signal intended for the respective second wireless communication device and precoded by the respective precoder; select an interference peak fulfilling a criterion among the determined one or more respective interference peaks; and update, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak.

Description

A WIRELESS COMMUNICATION DEVICE AND A METHOD FOR REDUCING INTERFERENCE IN A WIRELESS COMMUNICATION TECHNICAL FIELD

The present disclosure relates to a wireless communication device for a wireless communication with two or more second wireless communication devices. The present disclosure further relates to a method for reducing interference in a wireless communication between a wireless communication device and two or more second wireless communication devices. The present disclosure relates in particular to communication networks formed by such wireless communication devices relying on ultra-wideband (UWB) waveforms.

BACKGROUND

Time reversal precoding (also called conventional time reversal precoding) may be used as a competitive precoding strategy for communication networks such as networks relying on ultra- wideband (UWB) waveforms. Time reversal precoding allows shifting the processing complexity to the transmitter side and thus to address low-power and low-complexity nodes. Thanks to its focusing property, time reversal precoding allows designing multiple access schemes for massive UWB networks.

SUMMARY

The present disclosure and its embodiments are based on the following considerations made by the inventors: In a wireless communication between a wireless communication device and two or more second wireless communication devices, inter-symbol interference (ISI) and inter-user interference (IUI) may occur, which reduce, respectively, damage the performance, in case this is not managed at the receiver side. In particular, in case of time-reversal division multiple access (TRDMA), signals wirelessly received by the two or more second wireless communication devices may suffer from a significant level of ISI and IUI.

ISI may be understood as the occurrence of interference, in particular one or more interference peaks, at a second wireless communication device of the two or more second wireless communication devices, when the wireless communication device transmits a wireless signal intended for the second wireless communication device to the second wireless communication device. IUI may be understood as the occurrence of interference, in particular one or more interference peaks, at the second wireless communication device, when the wireless communication device transmits a wireless signal intended for another second wireless communication device of the two or more second wireless communication devices to the other second wireless communication device.

In view of the above, embodiments of the present disclosure aim to provide a wireless communication device for a wireless communication with two or more second wireless communication devices that allows reducing at least one of ISI and IUI. A further objective may be to provide a wireless communication device that allows precoding, in particular time reversal precoding, and reducing at least one of ISI and IUI.

These and other objectives are achieved by the embodiments of the disclosure as described in the enclosed independent claims. Advantageous implementations of the embodiments of the disclosure are further defined in the dependent claims.

A first aspect of the present disclosure provides a wireless communication device for a wireless communication with two or more second wireless communication devices. The wireless communication device is configured to, for a channel between the wireless communication device and a respective second wireless communication device of the two or more second wireless communication devices, initialize, based on a respective channel impulse response (CIR) of the channel, a respective precoder for precoding a signal intended for the respective second wireless communication device. Further, the wireless communication device is configured to determine, for the respective second wireless communication device of the two or more second wireless communication devices, one or more respective interference peaks caused at the respective second wireless communication device and/or at one or more other second wireless communication devices of the two or more second wireless communication devices by transmitting a respective signal intended for the respective second wireless communication device, wherein the respective signal is precoded by the respective precoder. Furthermore, the wireless communication device is configured to select an interference peak fulfilling a criterion among the determined one or more respective interference peaks. Moreover, the wireless communication device is configured to update, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak.

In this disclosure, the terms “wireless communication device” and “second wireless communication device” may be abbreviated by the terms “communication device” and “second communication device” respectively. The terms “signal” and “wireless signal” may be used as synonyms.

The wireless communication device according to the first aspect allows to reduce inter-symbol interference (ISI) and inter-user interference (IUI) by determining the one or more respective interference peaks caused at the respective second wireless communication device and/or at one or more other second wireless communication devices, selecting the interference peak fulfilling the criterion among the determined one or more interference peaks and updating the respective precoder. Since this reduction may be performed by the wireless communication device the two or more second wireless communication devices do not need to perform a post-processing of received wireless signals during a wireless communication with the wireless communication device for reducing ISI and IUI. Moreover, the wireless communication device does not need to actually transmit wireless signals to the respective second wireless communication device and receive feedback from the two or more second wireless communication devices for performing the aforementioned steps. Thus, the wireless communication device does not need to actually transmit wireless signals to the respective second wireless communication device and receive feedback from the two or more second wireless communication devices for reducing ISI and IUI. For the reasons mentioned above, the wireless communication device is advantageous.

In particular, the wireless communication device may comprise one or more antennas. The number of antennas of the wireless communication device may be equal to the number of second wireless communication devices. The wireless communication device may be a transmitter. The two or more second wireless communication devices may be two or more receivers.

Optionally, the wireless communication device is configured to receive, for the channel between the wireless communication device and the respective second wireless communication device of the two or more second wireless communication devices the CIR of the channel. The wireless communication device may be configured to transmit a wireless signal to the respective second wireless communication device and receive feedback from the respective second wireless communication device in response thereto. The feedback may comprise or correspond to information with regard to respectively information on the CIR of the channel. Alternatively, the feedback may be obtained after a transmission from the respective second wireless communication device to the wireless communication device when reciprocity of links is present (respectively when reciprocity of links is ensured). That is, according to an alternative, the wireless communication device may be configured to obtain (respectively receive) feedback from the respective second wireless communication device after a transmission from the respective second wireless communication device to the wireless communication device when reciprocity of links is present. In this alternative case, the wireless communication device does not transmit a wireless signal to the respective second wireless communication device for obtaining the feedback. Optionally, the wireless communication device may determine (in particular compute) based on the feedback (from the respective second wireless communication device) the CIR of the channel.

The wireless communication device may be configured to transmit one or more wireless signals intended for the respective second wireless communication device, wherein the wireless communication device may be configured to precode the one or more wireless signals using the respective precoder before the aforementioned transmission. This allows to focus the one or more wireless signals intended for the respective second wireless communication device to the respective second wireless communication device. With respect thereto, only first estimates of the channel may be used to compute the one or more focusing signals. This allows reducing the complexity of the second wireless communication devices. In particular, this allows reducing the complexity of the receiver side.

In particular, the wireless communication device may be configured to determine the one or more respective interference peaks without transmitting the respective signal intended for the respective second wireless communication device. In other words, the wireless communication device may be configured to determine the one or more respective interference peaks that would be caused at the respective second wireless communication device and/or at the one or more other second wireless communication devices of the two or more second wireless communication devices when the wireless communication device transmits the respective signal intended for the respective second wireless communication device to the respective second wireless communication device (wherein the respective signal is precoded by the respective precoder).

In an implementation form of the first aspect, the respective precoder is configured for time reversal precoding.

The time reversal precoding allows to shift the processing complexity from the two or more second wireless communication devices to the wireless communication device. That is, the time reversal precoding allows to shift the processing complexity from the receiver side to the transmitter side. As a result the wireless communication device may be configured to address low-power and low-complexity nodes. With other words, the wireless communication device may be configured to transmit a wireless signal to a low power and low-complexity node, such as a low-power and low-complexity second wireless communication device.

Moreover, by using time reversal precoding the complexity of computations performed by the wireless communication device is less compared to a technique with generalized zero forcing, which is a precoding technique based on the knowledge of the channel.

In an implementation form of the first aspect, the wireless communication device is configured to determine, for the respective second wireless communication device of the two or more second wireless communication devices, a respective interference peak caused at the respective second wireless communication device by transmitting the respective signal intended for the respective second wireless communication device, wherein the respective signal is precoded by the respective precoder. Further, the wireless communication device may be configured to select an interference peak fulfilling a criterion among the determined respective interference peak. Furthermore, the wireless communication device may be configured to update, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak.

In particular, the respective precoder is the same precoder that may generate the respective signal intended for the respective second wireless communication device and the respective interference peak (ISI interference peak). In particular, the respective precoder is the same precoder that may generate a desired main peak for data of the respective signal intended for the respective second wireless communication device and the respective interference peak (ISI interference peak).

Thus, the wireless communication device allows reducing ISI. Optional the criterion comprises being the maximum interference peak among the determined interference peak.

In particular, the wireless communication device may be configured to determine the respective interference peak without transmitting the respective signal intended for the respective second wireless communication device. In other words, the wireless communication device may be configured to determine the respective interference peak that would be caused at the respective second wireless communication device when the wireless communication device transmits the respective signal intended for the respective second wireless communication device to the respective second wireless communication device (wherein the respective signal is precoded by the respective precoder).

In an implementation form of the first aspect, the wireless communication device is configured to determine, for the respective second wireless communication device of the two or more second wireless communication devices, one or more respective interference peaks caused at the one or more other second wireless communication devices of the two or more second wireless communication devices by transmitting the respective signal intended for the respective second wireless communication device, wherein the respective signal is precoded by the respective precoder. Further, the wireless communication device may be configured to select an interference peak fulfilling a criterion among the determined one or more respective interference peaks. Furthermore, the wireless communication device may be configured to update, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak.

Thus, the wireless communication device allows reducing IUI. Optional the criterion comprises being the maximum interference peak among the determined one or more respective interference peaks.

In particular, the wireless communication device may be configured to determine the one or more respective interference peaks without transmitting the respective signal intended for the respective second wireless communication device. In other words, the wireless communication device may be configured to determine the one or more respective interference peaks that would be caused at the one or more other second wireless communication devices of the two or more second wireless communication devices when the wireless communication device transmits the respective signal intended for the respective second wireless communication device to the respective second wireless communication device (wherein the respective signal is precoded by the respective precoder).

In an implementation form of the first aspect, the wireless communication device is configured to update, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak, by: subtracting from the respective precoder the CIR of the channel between the wireless communication device and the second wireless communication device at which the selected interference peak is caused, wherein the CIR is shifted in time to a time step at which the selected interference peak occurs and weighted with a weighting factor depending on the level of the selected interference peak.

Thus, the wireless communication device allows reducing ISI or IUI by performing a computation for updating the respective precoder. The wireless communication device does not require to receive feedback from the two or more second wireless communication devices with regard to ISI and IUI.

In an implementation form of the first aspect, for the respective second wireless communication device of the two or more second wireless communication devices, the wireless communication device is configured to determine a respective first equivalent channel for the respective second wireless communication device by computing a convolution of the respective CIR of the respective channel between the wireless communication device and the respective second wireless communication device, and a conjugation of the respective precoder for the respective channel between the wireless communication device and the respective second wireless communication device. Further, the wireless communication device may be configured to compute a respective first difference between the respective first equivalent channel and a first target CIR. Furthermore, the wireless communication device may be configured to determine a maximum peak of the respective first difference as a respective interference peak caused at the respective second wireless communication device by transmitting the respective signal intended for the respective second wireless communication device. Thus, the wireless communication device allows reducing ISI by performing a computation for determining the respective interference peak caused at the respective second wireless communication device by transmitting the respective signal intended for the respective second wireless communication device. The wireless communication device does not need to actually transmit the respective signal intended for the respective second wireless communication device and does not need to receive feedback from the respective second wireless communication devices with regard to ISI.

In particular, the wireless communication device may be configured to determine the maximum peak of the respective first difference as the respective interference peak without transmitting the respective signal intended for the respective second wireless communication device. In other words, the wireless communication device may be configured to determine the maximum peak of the respective first difference as the respective interference peak that would be caused at the respective second wireless communication device when the wireless communication device transmits the respective signal intended for the respective second wireless communication device to the respective second wireless communication device (wherein the respective signal is precoded by the respective precoder).

In an implementation form of the first aspect, for the respective second wireless communication device of the two or more second wireless communication devices, the wireless communication device is configured to, for each other second wireless communication device of the one or more other second wireless communication devices, determine a respective second equivalent channel by computing a convolution of the respective CIR of the respective channel between the wireless communication device and the other second wireless communication device, and a conjugation of the respective precoder for the respective channel between the wireless communication device and the respective second wireless communication device. Further, the wireless communication device may be configured to compute a respective second difference between the respective second equivalent channel and a second target CIR. Furthermore, the wireless communication device may be configured to determine a maximum peak of the respective second difference as the respective interference peak caused at the other second wireless communication device of the one or more other second wireless communication devices by transmitting the signal intended for the respective second wireless communication device. Thus, the wireless communication device allows reducing IUI by performing a computation for determining the respective interference peak caused at the other second wireless communication device by transmitting the respective signal intended for the respective second wireless communication device. The wireless communication device does not need to actually transmit the respective signal intended for the respective second wireless communication device and does not need to receive feedback from the other second wireless communication devices with regard to IUI.

In particular, the wireless communication device may be configured to determine the maximum peak of the respective second difference as the respective interference peak without transmitting the respective signal intended for the respective second wireless communication device. In other words, the wireless communication device may be configured to determine the maximum peak of the respective second difference as the respective interference peak that would be caused at the other second wireless communication device of the one or more other second wireless communication devices when the wireless communication device transmits the respective signal intended for the respective second wireless communication device to the respective second wireless communication device (wherein the respective signal is precoded by the respective precoder).

In an implementation form of the first aspect, the first target CIR is equal to a Dirac delta function. The second target CIR may be equal to zero for all time steps.

In an implementation form of the first aspect, for the respective second wireless communication device of the two or more second wireless communication devices, the wireless communication device is configured to transmit to the respective second wireless communication device of the two or more second wireless communication devices the respective signal intended for the respective second wireless communication device. Further, the wireless communication device may be configured to obtain, as feedback information, from the respective second wireless communication device of the two or more second wireless communication devices the respective interference peak caused at the respective second wireless communication device by transmitting the respective signal intended for the respective second wireless communication device. Alternatively, the wireless communication device may be configured to obtain the feedback information after a transmission from the respective second wireless communication device to the wireless communication device when reciprocity of links is present. In an implementation form of the first aspect, for the respective second wireless communication device of the two or more second wireless communication devices, the wireless communication device is configured to transmit to the respective second wireless communication device of the two or more second wireless communication devices the respective signal intended for the respective second wireless communication device. Further, the wireless communication device may be configured to obtain, as feedback information, from each other second wireless communication device of the one or more other second wireless communication devices the respective interference peak caused at the other second wireless communication device by transmitting the respective signal intended for the respective second wireless communication device.

In an implementation form of the first aspect, the wireless communication device is configured to iteratively re-determine, for the respective second wireless communication device of the two or more second wireless communication devices, the one or more respective interference peaks caused at the respective second wireless communication device and/or at the one or more other second wireless communication devices by transmitting the respective signal intended for the respective second wireless communication, wherein the respective signal is precoded by the respective precoder.

In particular, the wireless communication device may be configured to perform one or more iterations. In each iteration the wireless communication device determines (respectively re determines), for the respective second wireless communication device of the two or more second wireless communication devices, one or more respective interference peaks caused at the respective second wireless communication device and/or at one or more other second wireless communication devices of the two or more second wireless communication devices by transmitting a respective signal intended for the respective second wireless communication device, wherein the respective signal is precoded by the respective precoder (which may have been updated in a previous iteration). Further, the wireless communication device may select an interference peak fulfilling a criterion among the determined one or more respective interference peak and the wireless communication device may update, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak. In other words, the wireless communication device may be configured to iteratively perform the aforementioned steps for reducing ISI and IUI. Thus, the above description of the operation respectively method steps performable by the wireless communication device are correspondingly valid for describing each iteration performable by the wireless communication device. This allows to achieve different reduction levels of ISI and IUI and different amount of computation steps performed by the wireless communication device which depend on the amount of iterations performed. The greater the number of iterations the greater the reduction of the ISI and IUI and the greater the amount of computations steps performed, and vice versa.

Thus, the wireless communication device is advantageous compared to a wireless communication device that uses an algorithm based on linear processing (involving in many cases matrix inversion) for reducing ISI and IUI. Namely, the number of iteration performed by the wireless communication device may be tuned (respectively adjusted) to the available processing capability. Moreover, the wireless communication device is advantageous compared to a wireless communication device that uses an algorithm based on an iterative procedure involving feedback from the two or more second wireless communication devices, for the reasons outlined already above. That is, there is no need of iterative feedback between the wireless communication device and the second wireless communication devices. For scenarios where a residual interference may be tolerated or the residual interference is less important than latency of the wireless communication, the wireless communication device allows a tuneable (respectively adjustable) compromise between performance, latency and power consumption.

In particular, the wireless communication device may be configured to iteratively re-determine the one or more respective interference peaks without transmitting the respective signal intended for the respective second wireless communication device. In other words, the wireless communication device may be configured to iteratively re-determine the one or more respective interference peaks that would be caused at the respective second wireless communication device and/or at the one or more other second wireless communication devices of the two or more second wireless communication devices when the wireless communication device transmits the respective signal intended for the respective second wireless communication device to the respective second wireless communication device (wherein the respective signal is precoded by the respective precoder). In an implementation form of the first aspect, the wireless communication device is configured to iteratively perform the re-determining step until the one or more respective interference peaks determined in the latest iteration are smaller than a threshold value, or until a threshold number of iterations is reached.

In particular, the wireless communication device may iteratively perform the above described steps for reducing ISI and IUI (i.e. the steps of the above described operation respectively method performable by the wireless communication device) until the one or more respective peaks determined in the latest iteration are smaller than a threshold value, or until a threshold number of iterations is reached. That is, the wireless communication device may perform the iterations until the one or more respective peaks determined in the latest iteration are smaller than a threshold value, or until a threshold number of iterations is reached.

In an implementation form of the first aspect, the threshold value is set by a target signal to noise and interference ratio for the wireless communication between the wireless communication device and the two or more second wireless communication devices.

In an implementation form of the first aspect, the wireless communication device is configured to normalize, after the updating step or after the last iteration of the re-determining step, the updated respective precoder.

The wireless communication device may comprise at least one antenna and may be configured to, for each channel between the at least one antenna and a respective second wireless communication device of the two or more second wireless communication devices, initialize, based on a respective channel impulse response (CIR) of the channel, a respective precoder for precoding a signal intended for the respective second wireless communication device. Further, the wireless communication device may be configured to determine, for each second wireless communication device of the two or more second wireless communication devices, one or more respective interference peaks caused at the second wireless communication device and/or at one or more other second wireless communication devices by transmitting a respective signal intended for the second wireless communication device from the at least one antenna, wherein the respective signal is precoded by the respective precoder. Furthermore, the wireless communication device may be configured to select an interference peak fulfilling a criterion among the determined interference peaks. Moreover, the wireless communication device may be configured to update, based on the selected interference peak, the precoder, which precodes the signal that causes the selected interference peak.

The wireless communication device may be configured to determine, for each second wireless communication device of the two or more second wireless communication devices, a respective interference peak caused at the second wireless communication device by transmitting the respective signal intended for the second wireless communication device from the at least one antenna, wherein the respective signal is precoded by the respective precoder. Further, the wireless communication device may be configured to select an interference peak fulfilling a criterion among the determined interference peaks. Furthermore, the wireless communication device may be configured to update, based on the selected interference peak, the precoder, which precodes the signal that causes the selected interference peak.

The wireless communication device may be configured to determine, for each second wireless communication device of the two or more second wireless communication devices, one or more respective interference peaks caused at the one or more other second wireless communication devices by transmitting the respective signal intended for the second wireless communication device from the at least one antenna, wherein the respective signal is precoded by the respective precoder. Further, the wireless communication device may be configured to select an interference peak fulfilling a criterion among the determined interference peaks. Furthermore, the wireless communication device may be configured to update, based on the selected interference peak, the precoder, which precodes the signal that causes the selected interference peak.

The wireless communication device may be configured to update, based on the selected interference peak, the precoder, which precodes the signal that causes the selected interference peak, by: subtracting from the precoder the CIR of the channel between the at least one antenna of the wireless communication device and the second wireless communication device, at which the selected interference peak is caused, wherein the CIR is shifted in time to a time step at which the selected interference peak occurs and weighted with a weighting factor depending on the level of the selected interference peak.

For each second wireless communication device of the two or more second wireless communication devices, the wireless communication device may be configured to determine a respective first equivalent channel for the second wireless communication device by computing a convolution of the respective CIR of the respective channel between the at least one antenna and the second wireless communication device, and a conjugation of the respective precoder for the respective channel between the at least one antenna and the second wireless communication device. Further, the wireless communication device may be configured to compute a respective first difference between the respective first equivalent channel and a first target CIR. Furthermore, the wireless communication device may be configured to determine a maximum peak of the respective first difference as the respective interference peak caused at the second wireless communication device by transmitting the signal intended for the second wireless communication device from the at least one antenna.

For each second wireless communication device of the two or more second wireless communication devices, the wireless communication device may be configured to, for each other second wireless communication device of the one or more other second wireless communication devices, determine a respective second equivalent channel by computing a convolution of the respective CIR of the respective channel between the at least one antenna and the other second wireless communication device, and a conjugation of the respective precoder for the respective channel between the at least one antenna and the second wireless communication device. Further, the wireless communication device may be configured to compute a respective second difference between the respective second equivalent channel and a second target CIR. Furthermore, the wireless communication device may be configured to determine a maximum peak of the respective second difference as the respective interference peak caused at the other second wireless communication device of the one or more other second wireless communication devices by transmitting the signal intended for the second wireless communication device from the at least one antenna.

For each second wireless communication device of the two or more second wireless communication devices, the wireless communication device may be configured to transmit to each second wireless communication device of the two or more second wireless communication devices the respective signal intended for the second wireless communication device from the at least one antenna. Further, the wireless communication device may be configured to obtain, as feedback information , from each second wireless communication device of the two or more second wireless communication devices the respective interference peak caused at the second wireless communication device by transmitting the respective signal intended for the second wireless communication device from the at least one antenna. Alternatively, the wireless communication device may be configured to obtain the feedback information after a transmission from each second wireless communication device of the two or more second wireless communication devices to the at least one antenna of the wireless communication device when reciprocity of links is present.

For each second wireless communication device of the two or more second wireless communication devices, the wireless communication device may be configured to transmit to each second wireless communication device of the two or more second wireless communication devices the respective signal intended for the second wireless communication device from the at least one antenna. Further, for each second wireless communication device of the two or more second wireless communication devices, the wireless communication device may be configured to obtain, as feedback information, from each other second wireless communication device of the one or more other second wireless communication devices the respective interference peak caused at the other second wireless communication device by transmitting the respective signal intended for the second wireless communication device from the at least one antenna.

The wireless communication device may be configured to iteratively re-determine, for each second wireless communication device of the two or more second wireless communication devices, the one or more interference peaks caused at the second wireless communication device and/or at the one or more other second wireless communication devices by transmitting a respective signal intended for the second wireless communication device from the at least one antenna, wherein the respective signal is precoded by the respective precoder.

In order to achieve the wireless communication device according to the first aspect of the present disclosure, some or all of the implementation forms and optional features of the first aspect, as described above, may be combined with each other.

A second aspect of the present disclosure provides a method for reducing interference in a wireless communication between a wireless communication device and two or more second wireless communication devices. The method comprises, for a channel between the wireless communication device and a respective second wireless communication device of the two or more second wireless communication devices, initializing, based on a respective channel impulse response (CIR) of the channel, a respective precoder for precoding a signal intended for the respective second wireless communication device. Further, the method comprises determining, for the respective second wireless communication device of the two or more second wireless communication devices, one or more respective interference peaks caused at the respective second wireless communication device and/or at one or more other second wireless communication devices of the two or more second wireless communication devices by transmitting a respective signal intended for the respective second wireless communication device, wherein the respective signal is precoded by the respective precoder. Furthermore, the method comprises selecting an interference peak fulfilling a criterion among the determined one or more respective interference peaks. Moreover, the method comprises updating, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak.

The method of the second aspect and its implementation forms and optional features achieve the same advantages as the wireless communication device of the first aspect and its respective implementation forms and respective optional features.

The wireless communication device may be the wireless communication device according to the first aspect or any of its implementation forms.

The implementation forms and optional features of the wireless communication device according to the first aspect are correspondingly valid for the method according to the second aspect.

In an implementation form of the second aspect, the method comprises determining, for the respective second wireless communication device of the two or more second wireless communication devices, a respective interference peak caused at the respective second wireless communication device by transmitting the respective signal intended for the respective second wireless communication device, wherein the respective signal is precoded by the respective precoder. Further, the method may comprise selecting an interference peak fulfilling a criterion among the determined respective interference peak. Furthermore, the method may comprise updating, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak. In an implementation form of the second aspect, the method comprises determining, for the respective second wireless communication device of the two or more second wireless communication devices, one or more respective interference peaks caused at the one or more other second wireless communication devices of the two or more second wireless communication devices by transmitting the respective signal intended for the respective second wireless communication device, wherein the respective signal is precoded by the respective precoder. Further, the method may comprise selecting an interference peak fulfilling a criterion among the determined one or more respective interference peaks. Furthermore, the method may comprise updating, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak.

In an implementation form of the second aspect, updating, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak, comprises: subtracting from the respective precoder the CIR of the channel between the wireless communication device and the second wireless communication device at which the selected interference peak is caused, wherein the CIR is shifted in time to a time step at which the selected interference peak occurs and weighted with a weighting factor depending on the level of the selected interference peak.

In an implementation form of the second aspect, for the respective second wireless communication device of the two or more second wireless communication devices, the method comprises determining a respective first equivalent channel for the respective second wireless communication device by computing a convolution of the respective CIR of the respective channel between the wireless communication device and the respective second wireless communication device, and a conjugation of the respective precoder for the respective channel between the wireless communication device and the respective second wireless communication device. Further, the method may comprise computing a respective first difference between the respective first equivalent channel and a first target CIR. Furthermore, the method may comprise determining a maximum peak of the respective first difference as a respective interference peak caused at the respective second wireless communication device by transmitting the respective signal intended for the respective second wireless communication device. In an implementation form of the second aspect, for the respective second wireless communication device of the two or more second wireless communication devices, the method may comprise, for each other second wireless communication device of the one or more other second wireless communication devices, determining a respective second equivalent channel by computing a convolution of the respective CIR of the respective channel between the wireless communication device and the other second wireless communication device, and a conjugation of the respective precoder for the respective channel between the wireless communication device and the respective second wireless communication device. Further, the method may comprise computing a respective second difference between the respective second equivalent channel and a second target CIR. Furthermore, the method may comprise determining a maximum peak of the respective second difference as the respective interference peak caused at the other second wireless communication device of the one or more other second wireless communication devices by transmitting the signal intended for the respective second wireless communication device.

In an implementation form of the second aspect, for the respective second wireless communication device of the two or more second wireless communication devices, the method comprises transmitting to the respective second wireless communication device of the two or more second wireless communication devices the respective signal intended for the respective second wireless communication device. Further, the method may comprise obtaining, as feedback information, from the respective second wireless communication device of the two or more second wireless communication devices the respective interference peak caused at the respective second wireless communication device by transmitting the respective signal intended for the respective second wireless communication device. In particular, the aforementioned method steps of transmitting and obtaining may be performed by the wireless communication device. According to an alternative, the method may comprise obtaining the feedback information after a transmission from the respective second wireless communication device to the wireless communication device when reciprocity of links is present. In particular, the aforementioned method step of obtaining may be performed by the wireless communication device.

In an implementation form of the second aspect, for the respective second wireless communication device of the two or more second wireless communication devices, the method may comprise transmitting to the respective second wireless communication device of the two or more second wireless communication devices the respective signal intended for the respective second wireless communication device. Further, the method may comprise obtaining, as feedback information, from each other second wireless communication device of the one or more other second wireless communication devices the respective interference peak caused at the other second wireless communication device by transmitting the respective signal intended for the respective second wireless communication device.

In an implementation form of the second aspect, the method comprises iteratively re determining, for the respective second wireless communication device of the two or more second wireless communication devices, the one or more respective interference peaks caused at the respective second wireless communication device and/or at the one or more other second wireless communication devices by transmitting the respective signal intended for the respective second wireless communication, wherein the respective signal is precoded by the respective precoder.

In particular, the method may comprise performing one or more iterations of the above described method steps. In each iteration the method comprises determining (respectively re determines), for the respective second wireless communication device of the two or more second wireless communication devices, one or more respective interference peaks caused at the respective second wireless communication device and/or at one or more other second wireless communication devices of the two or more second wireless communication devices by transmitting a respective signal intended for the respective second wireless communication device, wherein the respective signal is precoded by the respective precoder (which may have been updated in a previous iteration). Further, the method comprises selecting an interference peak fulfilling a criterion among the determined one or more respective interference peak and updating, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak.

In other words, the aforementioned steps for reducing ISI and IUI may be iteratively performed. Thus, the above description of the method steps are correspondingly valid for describing each iteration.

In an implementation form of the second aspect, the method comprises iteratively performing the re-determining step until the one or more respective interference peaks determined in the latest iteration are smaller than a threshold value, or until a threshold number of iterations is reached.

In particular, the above described method steps may be iteratively performed until the one or more respective peaks determined in the latest iteration are smaller than a threshold value, or until a threshold number of iterations is reached.

In an implementation form of the second aspect, the method comprises normalizing, after the updating step or after the last iteration of the re-determining step, the updated respective precoder.

The method may comprise, for each channel between at least one antenna of the wireless communication device and a respective second wireless communication device of the two or more second wireless communication devices, initializing, based on a respective channel impulse response (CIR) of the channel, a respective precoder for precoding a signal intended for the respective second wireless communication device. Further, the method may comprise determining, for each second wireless communication device of the two or more second wireless communication devices, one or more respective interference peaks caused at the second wireless communication device and/or at one or more other second wireless communication devices by transmitting a respective signal intended for the second wireless communication device from the at least one antenna, wherein the respective signal is precoded by the respective precoder. The method may comprise further steps of selecting an interference peak fulfilling a criterion among the determined interference peaks; and updating, based on the selected interference peak, the precoder, which precodes the signal that causes the selected interference peak.

The method may comprise determining, for each second wireless communication device of the two or more second wireless communication devices, a respective interference peak caused at the second wireless communication device by transmitting the respective signal intended for the second wireless communication device from the at least one antenna, wherein the respective signal is precoded by the respective precoder. The method may comprise the further steps of selecting an interference peak fulfilling a criterion among the determined interference peaks; and updating, based on the selected interference peak, the precoder, which precodes the signal that causes the selected interference peak. The method may comprise determining, for each second wireless communication device of the two or more second wireless communication devices, one or more respective interference peaks caused at the one or more other second wireless communication devices by transmitting the respective signal intended for the second wireless communication device from the at least one antenna, wherein the respective signal is precoded by the respective precoder. The method may comprise the further steps of selecting an interference peak fulfilling a criterion among the determined interference peaks; and updating, based on the selected interference peak, the precoder, which precodes the signal that causes the selected interference peak.

Updating, based on the selected interference peak, the precoder, which precodes the signal that causes the selected interference peak, may comprise: subtracting from the precoder the CIR of the channel between the at least one antenna of the wireless communication device and the second wireless communication device, at which the selected interference peak is caused, wherein the CIR is shifted in time to a time step at which the selected interference peak occurs and weighted with a weighting factor depending on the level of the selected interference peak.

For each second wireless communication device of the two or more second wireless communication devices, the method may comprise determining a respective first equivalent channel for the second wireless communication device by computing a convolution of the respective CIR of the respective channel between the at least one antenna and the second wireless communication device, and a conjugation of the respective precoder for the respective channel between the at least one antenna and the second wireless communication device. Further, the method may comprise computing a respective first difference between the respective first equivalent channel and a first target CIR. Furthermore, the method may comprise determining a maximum peak of the respective first difference as the respective interference peak caused at the second wireless communication device by transmitting the signal intended for the second wireless communication device from the at least one antenna. For each second wireless communication device of the two or more second wireless communication devices, the method may comprise, for each other second wireless communication device of the one or more other second wireless communication devices, determining a respective second equivalent channel by computing a convolution of the respective CIR of the respective channel between the at least one antenna and the other second wireless communication device, and a conjugation of the respective precoder for the respective channel between the at least one antenna and the second wireless communication device. Further, the method may comprise computing a respective second difference between the respective second equivalent channel and a second target CIR. Furthermore, the method may comprise determining a maximum peak of the respective second difference as the respective interference peak caused at the other second wireless communication device of the one or more other second wireless communication devices by transmitting the signal intended for the second wireless communication device from the at least one antenna.

For each second wireless communication device of the two or more second wireless communication devices, the method may comprise transmitting to each second wireless communication device of the two or more second wireless communication devices the respective signal intended for the second wireless communication device from the at least one antenna. Further, the method may comprise obtaining, as feedback information, from each second wireless communication device of the two or more second wireless communication devices the respective interference peak caused at the second wireless communication device by transmitting the respective signal intended for the second wireless communication device from the at least one antenna. According to an alternative, the method may comprise obtaining the feedback information after a transmission from each second wireless communication device of the two or more second wireless communication devices to the at least one antenna of the wireless communication device when reciprocity of links is present.

For each second wireless communication device of the two or more second wireless communication devices, the method may comprise transmitting to each second wireless communication device of the two or more second wireless communication devices the respective signal intended for the second wireless communication device from the at least one antenna. Further, the method may comprise obtaining, as feedback information, from each other second wireless communication device of the one or more other second wireless communication devices the respective interference peak caused at the other second wireless communication device by transmitting the respective signal intended for the second wireless communication device from the at least one antenna.

The method may comprise the further step of re-determining, for each second wireless communication device of the two or more second wireless communication devices, the one or more interference peaks caused at the second wireless communication device and/or at the one or more other second wireless communication devices by transmitting a respective signal intended for the second wireless communication device from the at least one antenna, wherein the respective signal is precoded by the respective precoder. The further steps may be iteratively performed. That is, the method may comprise iteratively performing the further steps.

The further steps may be iteratively performed until the interference peaks determined in the latest iteration are smaller than a threshold value. Alternatively, the further steps may be iteratively performed until a threshold number of iterations is reached.

The method may comprise normalizing, after the updating step or after the last iteration of the further steps, the one or more updated respective precoders.

In order to achieve the method according to the second aspect of the present disclosure, some or all of the implementation forms and optional features of the second aspect, as described above, may be combined with each other.

A third aspect of the present disclosure provides a computer-readable storage medium storing executable program code which, when executed by a computer, causes the method according to the second aspect or any of its implementation forms to be performed.

A fourth aspect of the present disclosure provides a non-transitory storage medium storing executable program code which, when executed by a processor, causes the method according to the second aspect or any of its implementation forms to be performed.

A fifth aspect of the present disclosure provides a computer program comprising program code for performing when implemented on a processor, a method according to the second aspect or any of its implementation forms.

A sixth aspect of the present disclosure provides a computer comprising a memory and a processor, which are configured to store and execute program code to perform the method according to the second aspect or any of its implementation forms. The computer-readable storage medium of the third aspect, the non-transitory storage medium of the fourth aspect, the computer program of the fifth aspect and the computer of the sixth aspect each achieve the same advantages as the method of the second aspect and its respective implementation forms and respective optional features.

It has to be noted that all steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which:

Figure 1 shows an example of a wireless communication device according to the first aspect of the present disclosure.

Figure 2 shows an example of a wireless communication device according to the first aspect of the present disclosure.

Figure 3 shows an example of a convolution performable by a wireless communication device according to the first aspect of the present disclosure.

Figure 4 shows an example of time reversal precoding based on a diagram showing two interference peaks.

Figure 5 shows an example of cancellation of an interference peak caused by inter-user interference (IUI) according to the present disclosure. Figure 6 shows an example of a method according to the second aspect of the present disclosure. The method shown in Figure 6 may be performed by an example of a wireless communication device according to the first aspect of the present disclosure.

Figure 7 shows an example of cancellation of an interference peak caused by inter symbol interference (ISI) according to the present disclosure.

In the following, corresponding elements are labelled by the same reference sign.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 shows an example of a wireless communication device according to the first aspect of the present disclosure. As shown in Figure 1, the wireless communication device 1 is configured to wirelessly communicate with N second wireless communication devices 2₁, .. . , 2_N; wherein N is a positive integer greater than or equal to two (N ≥ 2). That is, the wireless communication device 1 is configured to wirelessly communicate with two or more second wireless communication devices 2₁, ... , 2_N. Exemplarily, the channel CH₁₁ between the wireless communication device 1 and the second wireless communication device 2₁ and the respective channel impulse response (CIR) h₁₁ is shown. In addition, the channel CH_1N between the wireless communication device 1 and the N-th second wireless communication device 2_N and the respective CIR h_N1 is indicated. The wireless communication device 1 may be a transmitter TX. The second wireless communication devices 2₁ , ... , 2_N may be receivers RX₁ , ... , RX_N.

The wireless communication device 1 is configured to wirelessly transmit to any one of the second wireless communication devices 2₁, ..., 2_N a signal intended for the respective second wireless communication device. For example, the wireless communication device 1 may be configured to wirelessly transmit to the second wireless communication device 2₁ a signal intended for the second wireless communication device 2₁. For this, the wireless communication device 1 may precode the signal intended for the second wireless communication device 2₁ using a respective precoder. The respective precoder may be initialized based on the respective (CIR) h₁₁ of the channel CH₁₁ between the wireless communication device 1 and the second wireless communication device 2₁. The respective precoder may be configured for time reversal precoding. That is, the wireless communication device 1 may be configured for time reversal precoding.

When the wireless communication device 1 transmits the wireless signal intended for the second wireless communication device 2₁ an interference peak may be caused at the second wireless communication device 2₁. That is, inter-symbol interference (ISI) may occur. In addition an interference peak may be caused at the other one or more second wireless communication devices of the wireless communication devices 2₁, ..., 2_N, e.g. at the other second wireless communication device 2_N. That is, inter-user interference (IUI) may occur.

For reducing the ISI and the IUI, the wireless communication device 1 is configured to, for a channel (e.g. CH₁₁) between the wireless communication device 1 and a respective second wireless communication device (e.g. second wireless communication device 2_\) of the two or more second wireless communication devices 2₁, ..., 2_N, initialize, based on a respective CIR (e.g. h₁₁) of the channel (e.g. CH₁₁), a respective precoder for precoding a signal intended for the respective second wireless communication device (e.g. second wireless communication device 2₁). Further, the wireless communication device 1 is configured to determine, for the respective second wireless communication device (e.g. second wireless communication device 2₁) of the two or more second wireless communication devices 2₁, ..., 2_N, one or more respective interference peaks caused at the respective second wireless communication device (e.g. second wireless communication device 2i) and/or at one or more other second wireless communication devices (e.g. second wireless communication device 2_N) of the two or more second wireless communication devices 2₁, ..., 2_N by transmitting a respective signal intended for the respective second wireless communication device (e.g. second wireless communication device 2i), wherein the respective signal is precoded by the respective precoder. Furthermore, the wireless communication device 1 is configured to select an interference peak fulfilling a criterion among the determined one or more respective interference peaks. Moreover, the wireless communication device 1 is configured to update, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak. The wireless communication device 1 may comprise a communication circuitry and a processing circuitry which are configured to perform, conduct or initiate the various operations of the wireless communication device 1 described herein (not shown in Figure 1). The communication circuitry may comprise or correspond to at least one communication unit, in particular at least one communication module. The processing circuitry may comprise or correspond to at least one processing unit, in particular at least one processing module. The processing circuitry may be configured to control the communication circuitry, in particular the wireless communication performable by the communication circuitry. The communication circuitry may comprise hardware and/or the communication circuitry may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The hardware may comprise one or more antennas for wireless communication (as indicated in Figure 2 (A)). In particular, the hardware may comprise one or more antennas for wireless communication with the two or more second wireless communication devices 2₁ , ... , 2_N.

The processing circuitry may comprise hardware and/or the processing circuitry may be controlled by software. The hardware may comprise analog circuitry or digital circuitry, or both analog and digital circuitry. The digital circuitry may comprise or correspond to components such as one or more application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), and/or multi-purpose processors.

The wireless communication device 1 may further comprise memory circuitry (not shown in Figure 1), which stores one or more instruction(s) that can be executed by the processing circuitry and optionally the communication circuitry, in particular under control of the respective software. For instance, the memory circuitry may comprise a non-transitory storage medium storing executable software code which, when executed by the processing circuitry and optionally the communication unit, causes the various operations of the wireless communication device 1 to be performed.

In one embodiment, the processing circuitry of the wireless communication device 1 comprises one or more processors and a non-transitory memory connected to the one or more processors. The non-transitory memory may carry executable program code which, when executed by the one or more processors, causes the wireless communication device 1 to perform, conduct or initiate the operations or methods described herein.

For a detailed description of implementation forms of the wireless communication device 1, in particular on how the wireless communication device 1 may be configured for reducing ISI and IUI, reference is made to the above description with regard to the wireless communication device of the first aspect of the present disclosure as well as the following description with regard to Figures 2 to 7.

Figure 2 shows an example of a wireless communication device according to the first aspect of the present disclosure. The wireless communication device 1 of Figure 2 corresponds to the wireless communication device 1 of Figure 1. Therefore, the above description with regard to Figure 1 is correspondingly valid for the wireless communication device 1 of Figure 2. In the following mainly an additional feature is described.

The wireless communication device 1 may comprise M antennas, wherein M is a positive integer greater than or equal to one (M = 1). Figure 2A exemplarily shows the case, in which the wireless communication device 1 comprises two or more antennas TX₁, ..., TX_M. Thus, the wireless communication device 1 may comprise one or more antennas. In other words, the wireless communication device 1 may comprise at least one antenna.

Figure 2B shows the channel CH_mi between the m-th antenna 1_m of the wireless communication device 1 and the i-th second wireless communication device 2_i (m = 1 , ... , M and i = 1 , ... , N). The respective CIR is h_im. The annotation used in Figure 2 will be used in the following description.

That is, a scenario is exemplarily considered including one wireless communication device 1 with M antennas 1₁ , ... , 1_M indexed by m and N second wireless communication devices 2₁ , . . . , 2_N with single antenna each, that may be indexed by i and j.

The channel impulse response (CIR) between the m-th antenna 1_m of the wireless communication device 1 and the i-th second wireless communication device 2_i is denoted as h_im which may be a vector of size L. It is assumed that all channel impulse responses (CIRs) have the same length L. The coefficients of CIR im are denoted h_im[k] k = 1..L

The normalized version of a CIR is denoted Without loss of generality, it is assumed that the channel impulse response vectors are zero padded at the beginning and the end with an arbitrary number of zero coefficients. This padding is meant to ensure that shifted versions of the CIR, which are employed later for the processing, contain the same number of non-zero coefficients. For the m-th antenna l_m, the autocorrelation function between the respective CIR h_im of the i- th second wireless communication device 2_i and the respective CIR h_jm of the j-th second wireless communication device 2_j may be given by The multi-antenna correlation function between CIRs of the i-th second wireless communication device 2i and CIRs of the j-th second wireless communication device 2_j may be given by: It is assumed for any CIR that

The autocorrelation function R_ji of equation Eq (2) may be understood as the equivalent channel seen by the j-th second wireless communication device 2_j, when one or more signals intended for the i-th second wireless communication device 2_i are transmitted from the wireless communication device 1, wherein the one or more signals are precoded by the respective precoder (e.g. using time reversal precoding). In other words, the autocorrelation function R_ji of equation Eq (2) may be understood as the equivalent channel seen by the j-th second wireless communication device 2_j for data intended for the i-th second wireless communication device 2_i when using precoding, e.g. time reversal precoding.

The wireless communication device 1 may be configured to precode a signal intended for a respective second wireless communication device (using a respective precoder) for transmitting the signal to the respective second wireless communication device. In particular, the wireless communication device 1 may be configured to use time reversal precoding for this. For the following description, it is assumed that for a precoding time reversal precoding is used. That is, the respective precoder is configured for time reversal precoding. This is not limiting for the present disclosure and, thus, the following description is correspondingly valid in case of using a different precoding technique.

Time reversal precoding consists in precoding a transmitted signal with the normalized flipped conjugate of the channel impulse response (CIR) of the intended second wireless communication device (i.e. the CIR of the channel between the antenna of the wireless communication device 1 transmitting the signal and the intended second wireless communication device). For simplicity, it is assumed that only one data symbol denoted x is transmitted to an intended i-th second wireless communication device 2i. At time l the transmitted signal from the m-th antenna l_m of the wireless communication device 1 may be given by

In the above equation Eq (3), s_im [l] correspond to a time reversal precoded signal intended for the i-th second wireless communication device 2_i and to be transmitted from the m-th antenna 1_m of the wireless communication device 1. For each j-th second wireless communication device 2_j, the signal is received after convolution with the corresponding impulse response h_jm. The output of this convolution may be understood as the output of a sliding window correlation, as exemplarily indicated in Figure 3. The origin of time for the received signal is the time sample of a maximum of the correlation for the second wireless communication device of interest. Using this convention, the received signal for the j-th second wireless communication device 2_j at sample k may be given by

Figure 4 shows an example of time reversal precoding based on a diagram showing two interference peaks. Equation Eq (4) shows that time reversal precoding with the flipped conjugate of the channel induces a maximum of signal level at time 0. In order to focus energy on another time sample k, it is sufficient to use a flipped conjugate of a shifted version of the CIR of interest. Without loss of generality, it is assumed that the CIRs are padded with zeros (in the beginning and the end) to ensure that all shifted versions contain the whole set of non-zero coefficients of the CIR. Figure 4, shows a signal peak with initial time reversal (right side of diagram) and a signal peak with 5 time samples delay (left side of diagram). That is, the time reversal precoding with a shifted version of the CIR (shown on the left side of the diagram) may induce a peak at position p, wherein p is the size of the shift. As shown in Figure 4, the size of the shift p may be exemplarily 5 time samples.

Figure 5 shows an example of cancellation of an interference peak caused by inter-user interference (IUI) according to the present disclosure.

The wireless communication device 1 may be configured to cancel unwanted interference peaks in the desired signal (ISI) or interfering signals (IUI). In particular, time reversal precoding performable by the wireless communication device 1 may be used to cancel unwanted interference peaks in the desired signal (ISI) or interfering signals (IUI). For simplicity, a scenario is assumed with one wireless communication device 1 comprising one antenna 11 and two second wireless communication devices 2₀ and 2₁, which may represent two single antenna receivers (not shown in Figure 5). The following description is correspondingly valid for a different number of antennas of the wireless communication device 1 and/or a different number of second wireless communication devices. For describing the example of Figure 5, it is exemplarily assumed that the index of the N second wireless communication devices is between zero and N-1 (2_i, i = 0, ..., N-1), wherein N is exemplarily assumed to be two (N = 2). The following description is correspondingly valid when using a different index scheme, for example where the index of the N wireless communication devices is between one and N (2_i, wherein i = 1 , ... , N), wherein N is exemplarily assumed to be two (N = 2) for describing the example of Figure 5.

The diagram of Figure 5 (A) shows, using a solid line, a signal (signal level) SLO seen by a second wireless communication device 2₀ (may be called device of interest) and, using a dashed line, a signal (signal level) SL1 seen by the other second wireless communication device 2₁ (may be called victim device), when the wireless communication device 1 focuses on the device 2₀ of interest. That is, when the wireless communication device 1 wirelessly transmits a precoded signal (e.g. time reversal precoded) that is intended for the device 2₀ of interest. The channel impulse response (CIR) after time reversal precoding (i.e. the signal level SLO) seen by the device 2₀ of interest includes a main peak and several inter-symbol interference peaks. The signal SL1 seen by the victim device 2₁ when focusing on the device 2₀ of interest (i.e. when the wireless communication device 1 wirelessly transmits the precoded signal intended for the device 2₀ of interest) includes several non-negligible interference peaks (IUI peaks). It is possible to cancel individually one of these interference peaks as follows:

With the initial time reversal precoding intended for the device 2₀ of interest, the transmitted signal is modulated by the flipped conjugate of the CIR of the device 2₀ of interest. An example of the signal received by the device 2₀ of interest after conventional time reversal precoding focused to the device 2₀ of interest is shown by a solid line in the diagram of Figure 5 (A).

The victim device 2₁ receives an interfering signal y₁ whose level SL1 is represented in the diagram of Figure 5 (A) using a dashed line. To cancel the unwanted interference peak (peak to cancel) seen by the victim device 2i, the wireless communication device 1 may apply a time reversal precoding including the difference between the initial flipped conjugate channel of the device 2₀ of interest and a shifted version of a time reversal precoder intended for the victim device 2₁, but shifted to the desired peak to be cancelled. The signal s_0m (m = 1) intended for the device 2₀ of interest becomes: In the equation Eq (5), δ is the shift corresponding to the time position of the desired peak to be cancelled, α₀₁ is a weighting factor which accounts for the level of the peak to be cancelled and may be given by:

The normalized signal focused on the victim device 2₁ to cancel the unwanted interference peak (peak to cancel) is shown in the diagram of Figure 5 (C). The received signal after this peak cancellation received by the device 2₀ of interest is shown in the diagram of Figure 5 (B). The received signal after this peak cancellation received by the victim device 2₁ is shown in the diagram of figure 5 (D). As may be derived from Figure 5, the unwanted interference peak (peak to cancel) is cancelled for the victim device 2₁, wherein for the device 2₀ of interest the impact on the desired peak is minimal. The procedure described above may also apply for interference peaks included in the signal received by the device 2₀ of interest. In, this case, the signal intended for the device 2₀ of interest may be updated as follows:

Figure 6 shows an example of a method according to the second aspect of the present disclosure. The method shown in Figure 6 may be performed by an example of a wireless communication device according to the first aspect of the present disclosure.

The method of Figure 6 may be performed by the wireless communication devices 1 of Figures 1 and 2.

The first step S1 comprises, for each channel between a m-th antenna 1_m of the wireless communication device 1 and an i-th second wireless communication device 2_i, initializing, based on a respective channel impulse response (CIR) h_im[k] of the channel, a respective precoder p_im[k] for precoding a signal intended for the i-th second wireless communication device 2_i. That is, a signal to be transmitted from the m-th antenna l_m to the i-th second wireless communication device 2_i may be precoded by the respective precoder p_im[k]. The first step S1 in particular may comprise applying a conventional (respectively regular) time reversal precoding for each second wireless communication device. This precoding may induce inter- symbol interference (ISI) and inter-user (IUI) interference. The principle of the method (algorithm) of Figure 6 may be suppressing the highest interference peak (ISI or IUI) at each iteration, and updating the precoders accordingly. In particular, the principle of the method may be iteratively removing spurious contributions to a time reversal focusing, i.e. focusing using time reversal precoding. In the first step SI, the precoders p_i [k] may be initialized with a time reversal version of a respective CIR h_im[k].

The observed channel impulse responses (CIRs) may be given by the correlation function R_ji which correspond to the equivalent channels for useful signals (j = i) and interference signals (j ≠ i). In step S2, these CIRs may be compared to ideal ISI free and IUI free CIRs δ[k]δ_ji (may be called first target CIR used for reducing ISI and second target CIR used for reducing IUI).

According to one option of the disclosure, these CIRs may be compared to a smoothed version such as an exponential or Gaussian shape, e.g. exp or in a more general form 1 and p and g are predefined functions, and η₁ anη η₂ are predefined values.

Step S2 may comprise, for a respective second wireless communication device 2_i of the two or more second wireless communication devices 2₁,..., 2_N, determining a respective first equivalent channel (R_ji[k], j = i) for the respective second wireless communication device 2_i by computing a convolution of the respective CIR of the respective channel between the wireless communication device 1 and the respective second wireless communication device 2_i, and a conjugation of the respective precoder (p_im[k]) for the respective channel between the wireless communication device 1 and the respective second wireless communication device 2_i. Further, step S2 may comprise computing a respective first difference (Δ_ji[k], j = i) between the respective first equivalent channel (R_ji[k], j = i) and a first target CIR (D_ji[k], j = i). Furthermore, step S2 may comprise determining a maximum peak of the respective first difference (Δ_ji[k], j = i) as a respective interference peak caused at the respective second wireless communication 2_i device by transmitting the respective signal intended for the respective second wireless communication device 2_i (wherein the respective signal is precoded by the respective precoder

(p_im[k])). In addition or alternatively, step S2 may comprise, for the respective second wireless communication device 2_i of the two or more second wireless communication devices 2₁,..., 2N, determining, for each other second wireless communication device 2_j of the one or more other second wireless communication devices, a respective second equivalent channel (R_ji[k], j ≠ i) by computing a convolution of the respective CIR of the respective channel between the wireless communication device 1 and the other second wireless communication device 2_j, and a conjugation of the respective precoder (p_im[k]) for the respective channel between the wireless communication device 1 and the respective second wireless communication device 2_i. Further, the step S2 may comprise computing a respective second difference (Δ_j,[k], j ≠ i) between the respective second equivalent channel (R_ji[k], j ≠ i) and a second target CIR (D_ji[k], j ≠ i). Furthermore, step S2 may comprise determining a maximum peak of the respective second difference (Δ_ji[k], j ≠ i) as the respective interference peak caused at the other second wireless communication device 2_j of the one or more other second wireless communication devices by transmitting the signal intended for the respective second wireless communication device 2i (wherein the respective signal is precoded by the respective precoder (p_im[k])).

The step S2 may comprise or correspond to determining, for the respective second wireless communication device 2_i of the two or more second wireless communication devices 2₁, ..., 2N, one or more respective interference peaks caused at the respective second wireless communication device 2_i and/or at one or more other second wireless communication devices 2_j of the two or more second wireless communication devices 2₁, ..., 2_N by transmitting a respective signal intended for the respective second wireless communication device 2_i, wherein the respective signal is precoded by the respective precoder (p[_im[k]).

The highest ISI and IUI interference may be identified and calculated in step S3. The step S3 may comprise or correspond to selecting an interference peak fulfilling a criterion among the determined one or more respective interference peaks (which may be determined in step S2).

The corresponding interference peak, (i.e. the interference peak selected in step S3) may be cancelled in step S4. The step S4 may correspond to a highest interference peak cancellation. This may be done by performing an updating step. In particular, step S4 may comprise or correspond to updating, based on the selected interference peak (selected in step S3), the respective precoder, which precodes the respective signal that causes the selected interference peak. For further details on the updating, reference is made to the above description regarding updating performable by the wireless communication device of the first aspect and updating comprised by the method of the second aspect.

In step S5, a conditional stop check is performed. In this conditional stop, the presence of an interference peak exceeding the ideal ISI free and IUI free CIRs with more than a predefined value ε is checked. In particular, in step S5 it may be determined whether the interference peaks determined in the latest iteration are smaller than a threshold value. If this is not the case (“False”), a further iteration of the method of Figure 6 is performed (n = n+1). If this is the case (“True”), the iterations may be stopped and optionally step S6 may be performed. Alternatively, in step S5 it may be determined whether a threshold number of iterations is reached. If this is not the case (“False”), a further iteration of the method of Figure 6 is performed (n = n+1). If this is the case (“True”), the iterations may be stopped and optionally step S6 may be performed. Finally, in step S6, the precoders that are found may be normalized with respect to the allowed power. The number of iterations of the method of Figure 6 may be indicated by n, wherein an initial iteration is indicated by n equaling to zero (n = 0).

The above description of operation respectively method steps performable by the wireless communication device of the first aspect of the present disclosure and the above description of the method of the second aspect of the present disclosure may be correspondingly valid for the method of Figure 6.

A method according to the present disclosure for reducing interference in a wireless communication between a wireless communication device 1 with at least one antenna and two or more second wireless communication devices 2₁, ..., 2_N (Figure 6 showing an example of such a method) may comprise the following steps, outlined in the following using respective formulas. For the following, reference is made to the above description of Figures 1 to 5.

At first, for all second wireless communication devices 2₁, ..., 2_N a channel impulse response (CIR) h_im or their estimate may be determined, wherein 1 ≤ i < N, 1 ≤ m ≤ M, N corresponds to the number of second wireless communication devices (N ≥ 2) and M corresponds to the number of antennas of the wireless communication device 1 ( M ≥ 1). Further desired equivalent channels (i.e. target CIRs) may be determined. The desired equivalent channels (target CIRs) comprise data channels D_ii[k ] (respectively D_ji[k], j = i) and interfering channels D_ji [k] for j ≠ i. For performing iterations of the method a stop criterion may be selected, which is either a maximum number of iteration N_{iter rnax} or a maximum interference level ε. After completion of the method, a set of time-domain precoders may be provided as final output, one for each antenna 1₁, . . . , 1_M of the wireless communication device 1 : p ... p_M.

In detail, in an initial iteration of the method (cf. Figure 6, iteration n = 0), precoders for each second wireless communication device 2₁, ..., 2_N may be computed (cf. step SI of Figure 6): For the m-th antenna 1_m of the wireless communication device 1 and i-th second wireless communication device 2_i on time k the precoder may be given by

Next, equivalent channels after time reversal precoding R_ji [k] may be computed using equations Eq (1) and Eq (2):

Further, the difference between the computed equivalent channels and desired channels may be computed (cf. step S2 of Figure 6):

This may correspond to determining, for each second wireless communication device of the two or more second wireless communication devices 2₁, 2_N, one or more respective interference peaks caused at the second wireless communication device (ISI) and/or at one or more other second wireless communication devices (IUI) by transmitting a signal intended for the second wireless communication, wherein the signal is precoded by the respective precoder.

Furthermore, the highest amplitude difference may be computed (cf. step S3 of Figure 6): This may correspond to selecting an interference peak fulfilling a criterion among the determined one or more respective interference peaks. Pairs of second wireless communication devices i_{max max} and time sample k_max corresponding to this maximum may be output for the next step.

In each further iteration (iteration n > 0), pairs of second wireless communication devices i_maxj_max and time sample k_max corresponding to an interference peak to be cancelled may be used as inputs. The precoder of the second wireless communication device i_max may be updated as follows (cf. step S4 of Figure 6):

This may correspond to updating, based on the selected interference peak, the precoder, which precodes the signal that causes the selected interference peak. Further, new equivalent channels according to equations Eq (9) and Eq (10) may be computed. Next, the difference between equivalent channels and desired channels according to Eq (11) may be computed. Furthermore, the highest amplitude difference according to equation Eq (12) may be computed. The stop criterion may be computed (cf. step S5 of Figure 6):

Performing the iterations is stopped in case the stop criterion is true. Finally, all precoders p_jm may be normalized according to transmit power constraints (cf. step S6 of Figure 6):

A signal that may be transmitted by the wireless communication device 1 may be given by where x_i is the symbol data destined to (intended for) the i-th second wireless communication device 2_i. According to one option of the method, the update of precoders of each iteration may cancel only inter-user interference and update multiple-precoders simultaneously. In this case j_max is not a single index but a set of indices. In one option, the i_max is one second wireless communication device and j_max is the set of all other second wireless communication devices (users). In this case, the equations Eq (11) and Eq (12) may be replaced by respectively, where D_i [k ] is an objective CIR (target CIR) accounting only for total inter-user interference experienced by the i-th second wireless communication device 2_i.

The update of the precoders of each iteration may be given by:

According to another option of the method, the update of the precoders may deal only with inter-symbol interference. In this case, the equations Eq (11) and Eq (12) may be rewritten as: The update of the precoders for each iteration may be given by:

In one option of the method, the difference between the equivalent CIR seen by each second wireless communication device and the target CIR and the maximum of the amplitude of this difference may be computed at the receiver side. Only the time delay and the amplitude of this maximum may be sent back, as feedback, to the wireless communication device 1 for updating the precoders. Eq (11) and Eq (12) may be computed at the receiver side, and a predefined total or partial result may be sent back to the wireless communication device 1. An example of a partial result may be the maximum interference peak of each second wireless communication device, or the first two, three or any other number of interference peaks.

Optionally, it may also comprise or correspond to allowing only one or more second wireless communication devices of the second wireless communication devices 2₁, ..., 2_N to send feedback. The description of the method of the second aspect of the present disclosure is correspondingly valid for the method described above.

Figure 7 shows an example of cancellation of an interference peak caused by inter-symbol interference (ISI) according to the present disclosure. The diagram of Figure 7 (A) shows the channel impulse response (CIR) after the application of a precoder in an initial iteration, e.g. a conventional time reversal precoder. The diagram of Figure 7 (B) shows the difference between this CIR and the ideal desired CIR respectively target CIR (e.g. a dirac function). The diagram 7 (C) shows the CIR after one iteration cancelling the highest level peak seen in the diagram of Figure 7 (B).

A regularized zero forcing precoder may be written in the frequency domain as follows: where W(f) is the spatial precoder at the transmitter side (e.g. a wireless communication device) at frequency or sub-carrier /.

H is the concatenation of the channel impulse responses of all devices (respectively users) at the receiver side (e.g. second wireless communication devices) in frequency domain:

Further, α is a regularization factor. The comparison of the complexity between the regularized zero forcing precoder and the method performable by the wireless communication device of the present disclosure for reducing ISI and IUI (i.e. the method according to the second aspect of the present disclosure) is presented in the following:

Method according to the present disclosure: 2 M N L log(L) + Lf(MN+ n M)

Regularized zero forcing precoder: 2 M N L log(L) + Lf(MN + N³)

In the above complexity comparison, M corresponds to the number of antennas 1₁ . .., 1_M of the wireless communication device 1, N corresponds to the number of second wireless communication devices 2_\, ..., 2_N, L corresponds to the Fast Fourier Transform (FFT) size and n corresponds to the number of iterations performed.

Besides the above indicated complexity advantage of the method performable by the wireless communication device of the present disclosure compared to using a regularized zero forcing precoder, the method of the present disclosure allows to tune the complexity to a desired performance and the available computation resources while achieving the following features: The effect of ISI and the effect of IUI may be significantly reduced, as outlined above. The bit error rate (BER) may be reduced compared to using conventional time reversal precoding, especially when the symbol rate is large. An iterative feedback between the wireless communication device (transmitter side) and the second communication devices (receiver side) is not needed. Thus, a signal does not need to go forth and back between the transmitter side and receiver side multiple times, which requires relatively flat channels. Merely, a first channel estimation may be used to compute the focusing signal.

The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed subject matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

1. A wireless communication device (1) for a wireless communication with two or more second wireless communication devices (2₁, 2_N), wherein the wireless communication device is configured to: for a channel (CH₁₁) between the wireless communication device (1) and a respective second wireless communication device (2₁) of the two or more second wireless communication devices (2₁, 2_N), initialize (SI), based on a respective channel impulse response (h₁₁) CIR, of the channel (CH₁₁), a respective precoder for precoding a signal intended for the respective second wireless communication device (2₁); determine (S2), for the respective second wireless communication device (2₁) of the two or more second wireless communication devices (2₁ , 2_N), one or more respective interference peaks caused at the respective second wireless communication device (2₁) and/or at one or more other second wireless communication devices (2_N) of the two or more second wireless communication devices (2₁, 2_N) by transmitting a respective signal intended for the respective second wireless communication device (2₁), wherein the respective signal is precoded by the respective precoder; select (S3) an interference peak fulfilling a criterion among the determined one or more respective interference peaks; and update (S4), based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak.

2. The wireless communication device (1) according to claim 1, wherein the respective precoder is configured for time reversal precoding.

3. The wireless communication device (1) according to claim 1 or 2, wherein the wireless communication device (1) is configured to: transmit a wireless signal to the respective second wireless communication device (2₁) and receive feedback from the respective second wireless communication device (2₁) in response thereto, and determine, based on the feedback, the CIR (h₁₁₎ of the channel (CH₁₁); or obtain feedback from the respective second wireless communication device (2₁) after a transmission from the respective second wireless communication device (2₁) to the wireless communication device (1) when reciprocity of links is present and determine, based on the feedback, the CIR (h₁₁₎ of the channel (CH₁₁).

4. The wireless communication device (1) according to any one of the previous claims, wherein the wireless communication device (1) is configured to: determine, for the respective second wireless communication device (2₁) of the two or more second wireless communication devices (2₁, 2_N), a respective interference peak caused at the respective second wireless communication device (2₁) by transmitting the respective signal intended for the respective second wireless communication device (2i), wherein the respective signal is precoded by the respective precoder; select an interference peak fulfilling a criterion among the determined respective interference peak; and update, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak.

5. The wireless communication device (1) according to any one of the previous claims, wherein the wireless communication device (1) is configured to: determine, for the respective second wireless communication device (2₁) of the two or more second wireless communication devices (2₁, 2_N), one or more respective interference peaks caused at the one or more other second wireless communication devices (2_N) of the two or more second wireless communication devices (2₁, 2_N) by transmitting the respective signal intended for the respective second wireless communication device, wherein the respective signal is precoded by the respective precoder; select an interference peak fulfilling a criterion among the determined one or more respective interference peaks; and update, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak.

6. The wireless communication device (1) according to claim 4 or 5, wherein the wireless communication device (1) is configured to update, based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak, by: subtracting from the respective precoder the CIR of the channel between the wireless communication device (1) and the second wireless communication device at which the selected interference peak is caused, wherein the CIR is shifted in time to a time step at which the selected interference peak occurs and weighted with a weighting factor depending on the level of the selected interference peak.

7. The wireless communication device (1) according to any one of the previous claims, wherein, for the respective second wireless communication device (2₁) of the two or more second wireless communication devices (2₁, 2_N), the wireless communication device (1) is configured to: determine a respective first equivalent channel for the respective second wireless communication device (2₁) by computing a convolution of the respective CIR (h₁₁) of the respective channel (CH₁₁) between the wireless communication device (1) and the respective second wireless communication device (2₁), and a conjugation of the respective precoder for the respective channel (CH₁₁) between the wireless communication device (1) and the respective second wireless communication device (2₁); compute (S2) a respective first difference between the respective first equivalent channel and a first target CIR; and determine a maximum peak of the respective first difference as a respective interference peak caused at the respective second wireless communication device (2₁) by transmitting the respective signal intended for the respective second wireless communication device (2₁).

8. The wireless communication device (1) according to any one of the previous claims, wherein, for the respective second wireless communication device (2_\) of the two or more second wireless communication devices (2₁, 2_N), the wireless communication device (1) is configured to: for each other second wireless communication device (2_N) of the one or more other second wireless communication devices (2_N), determine a respective second equivalent channel by computing a convolution of the respective CIR (h _N1) of the respective channel (CH_1N) between the wireless communication device (1) and the other second wireless communication device (2_N), and a conjugation of the respective precoder for the respective channel (CH₁₁) between the wireless communication device (1) and the respective second wireless communication device (2₁) compute (S2) a respective second difference between the respective second equivalent channel and a second target CIR; and determine a maximum peak of the respective second difference as the respective interference peak caused at the other second wireless communication device (2_N) of the one or more other second wireless communication devices (2_N) by transmitting the signal intended for the respective second wireless communication device (2i).

9. The wireless communication device (1) according to claim 7 or 8, wherein the first target CIR is equal to a Dirac delta function, and the second target CIR is equal to zero for all time steps.

10. The wireless communication device (1) according to any one of the previous claims, wherein, for the respective second wireless communication device (2_\) of the two or more second wireless communication devices (2₁, 2_N), the wireless communication device (1) is configured to: transmit to the respective second wireless communication device (2₁) of the two or more second wireless communication devices (2₁, 2_N) the respective signal intended for the respective second wireless communication device (2₁); and obtain, as feedback information, from the respective second wireless communication device (2₁) of the two or more second wireless communication devices (2₁, 2_N) the respective interference peak caused at the respective second wireless communication device (2₁) by transmitting the respective signal intended for the respective second wireless communication device (2₁).

11. The wireless communication device (1) according to any one of the previous claims, wherein, for the respective second wireless communication device (2₁) of the two or more second wireless communication devices (2₁, 2_N), the wireless communication device (1) is configured to: transmit to the respective second wireless communication device (2₁) of the two or more second wireless communication devices (2₁, 2_N) the respective signal intended for the respective second wireless communication device (2₁); and obtain as feedback information from each other second wireless communication device of the one or more other second wireless communication devices (2_N) the respective interference peak caused at the other second wireless communication device by transmitting the respective signal intended for the respective second wireless communication device (2₁).

12. The wireless communication device (1) according to any one of the previous claims, wherein the wireless communication device (1) is configured to iteratively re-determine, for the respective second wireless communication device (2₁) of the two or more second wireless communication devices (2₁, 2_N), the one or more respective interference peaks caused at the respective second wireless communication device (2₁) and/or at the one or more other second wireless communication devices (2_N) by transmitting the respective signal intended for the respective second wireless communication (2₁), wherein the respective signal is precoded by the respective precoder.

13. The wireless communication device (1) according to claim 12, wherein the wireless communication device (1) is configured to iteratively perform the re-determining step until the one or more respective interference peaks determined in the latest iteration are smaller than a threshold value, or until a threshold number of iterations is reached.

14. The wireless communication device (1) according to claim 13, wherein the threshold value is set by a target signal to noise and interference ratio for the wireless communication between the wireless communication device (1) and the two or more second wireless communication devices (2₁, 2_N).

15. The wireless communication device (1) according to any one of the previous claims, wherein the wireless communication device (1) is configured to normalize (S6), after the updating step or after the last iteration of the re-determining step, the updated respective precoder.

16. A method for reducing interference in a wireless communication between a wireless communication device (1) and two or more second wireless communication devices (2₁, 2_N), wherein the method comprises: for a channel (CH₁₁) between the wireless communication device (1) and a respective second wireless communication device (2₁) of the two or more second wireless communication devices (2₁, 2_N), initializing (S1), based on a respective channel impulse response (h₁₁), CIR, of the channel (CH₁₁), a respective precoder for precoding a signal intended for the respective second wireless communication device (2₁); determining (S2), for the respective second wireless communication device (2₁) of the two or more second wireless communication devices (2i, 2N), one or more respective interference peaks caused at the respective second wireless communication device (2₁) and/or at one or more other second wireless communication devices (2_N) of the two or more second wireless communication devices (2₁, 2_N) by transmitting a respective signal intended for the respective second wireless communication device (2₁), wherein the respective signal is precoded by the respective precoder; selecting (S3) an interference peak fulfilling a criterion among the determined one or more respective interference peaks; and updating (S4), based on the selected interference peak, the respective precoder, which precodes the respective signal that causes the selected interference peak.

17. A computer-readable storage medium storing executable program code which, when executed by a computer, causes the method according to claim 16 to be performed.