WO2025202061A1

WO2025202061A1 - Methods and apparatuses for configuring a phase shift at a coverage enhancement device

Info

Publication number: WO2025202061A1
Application number: PCT/EP2025/057795
Authority: WO
Inventors: Erik Bengtsson; Fredrik RUSEK; Jose Flordelis; Olof Zander
Original assignee: Sony Europe Bv; Sony Group Corp
Current assignee: Sony Europe Bv; Sony Group Corp
Priority date: 2024-03-27
Filing date: 2025-03-21
Publication date: 2025-10-02
Anticipated expiration: 2026-09-27

Abstract

A first network node (106) communicates with a second network node (104) over a first communication channel (108) and a second communication channel (114). The first communication channel (108) is from the first network node (106) to the second network node (104) at least partially via a coverage enhancement device (102). The second communication channel (114) is from the second network node (104) to the first network node (106) at least partially via the coverage enhancement device (102). At least two different phase shifts for the first communication channel (108) are sequentially configured (608) at the coverage enhancement device (102). For each of the at least two different phase shifts corresponding channel characteristics of the first communication channel (108) are obtained (610, 612, 712). For each of the at least two different phase shifts, a corresponding reciprocity of the first communication channel (108) and the second communication channel (114) is evaluated (614, 714) based on the obtained channel characteristics and a target phase shift is determined (618 based on the evaluated reciprocities.

Description

METHODS AND APPARATUSES FOR CONFIGURING A PHASE SHIFT AT A COVERAGE ENHANCEMENT DEVICE

Technical Field

Various examples generally relate to methods and devices in a wireless communication systems including a coverage enhancement device.

Coverage enhancement devices (CED), including Reflective Intelligent Surfaces (RIS) and Network Controlled Repeaters (NCR), can be deployed in wireless communication systems to improve signal coverage and enhance overall network performance. These devices are particularly beneficial in scenarios where conventional methods like adding more base stations or increasing transmission power are not feasible or cost-effective.

In the context of the Third Generation Partnership Project (3GPP), coverage enhancement devices refer to technologies or solutions aimed at extending the coverage area of cellular networks or improving signal quality in areas with poor coverage, i.e. improving capacity. This can include various techniques and technologies, with Reflective Intelligent Surfaces (RIS) being one of them. Reflective Intelligent Surfaces are one type of CED that operates by intelligently reflecting and manipulating radio frequency signals. By adjusting the phase and amplitude of the reflected signals, RIS can optimize signal strength and quality at desired locations within the coverage area. Network Controlled Repeaters (NCRs) are another type of CED which may be used in wireless communication networks, particularly in scenarios where signal coverage needs to be extended or improved in areas with poor signal strength. NCRs are essentially repeater units that are remotely controlled and managed by the network operator. Unlike traditional repeaters, which operate autonomously and simply amplify and retransmit signals, NCRs can be dynamically configured and optimized based on network conditions and demand. Furthermore, NCRs may be spatially selective, i.e., they can accept signals from certain direction and retransmit them in another direction, as opposed to traditional repeaters, which are typically omnidirectional. Unlike repeaters, RIS and NCR can address the spatial dimension through beamforming.

Multiple Input Multiple Output (MIMO) technology may also enhance wireless communication systems by exploiting spatial diversity to improve data throughput, spectral efficiency, and overall system performance. In the context of cellular networks, the 3rd Generation Partnership Project has standardized MIMO techniques to enhance the performance of various wireless standards, including GSM, UMTS, LTE, and 5G. 3GPP MIMO utilizes multiple antennas at both the transmitter and receiver ends of the communication link to transmit and receive multiple spatial streams simultaneously. This allows for increased data rates, improved link reliability, and enhanced coverage.

One advancement within 3GPP MIMO is Time Division Duplexing (TDD) MIMO. TDD is a duplexing technique where the same frequency band is used for both uplink and downlink transmissions, with the time slots dynamically allocated between the two directions. This is in contrast to Frequency Division Duplex (FDD) MIMO. TDD MIMO leverages the asymmetric traffic patterns typically observed in cellular networks, allowing for flexible allocation of resources between uplink and downlink transmissions based on the varying demands of users. In TDD MIMO systems, antennas at the base station and user equipment are utilized to transmit and receive data within the same frequency band. By exploiting the spatial dimension, TDD MIMO enhances spectral efficiency and increases the capacity of wireless communication systems. Spatial Multiplexing in TDD MIMO enables the simultaneous transmission of multiple data streams over the same frequency band by exploiting the spatial dimension. This results in higher data rates and increased spectral efficiency. Different transmission paths may be established, e.g. between a base station and a wireless device.

MIMO communication systems and other communication systems using transmit diversity techniques may include CEDs, e.g. for improving coverage or transmission capacity.

TDD MIMO systems may rely on channel reciprocity to obtain channel state information (CSI). When a CED is introduced into the channel, the uplink (UL) and downlink (DL) channels may be different, so channel reciprocity may no longer be guaranteed. Summary

Accordingly, there is a need of improved techniques for communicating via CEDs, in particular in transmit diversity environments like MIMO.

This need is met by the features of the independent claims. The features of the dependent claims define examples.

According to an example, a method for use in a first network node is provided. The first network node may be for example a base station, for example a gNodeB (gNB) of a 3GPP communication network. The first network node communicates with a second network node over a first communication channel and a second communication channel. The second network node may be for example a wireless device (WD) for example a user equipment (UE) or terminal device (TD). However, in other scenarios, the first network node may be a wireless device and the second network node may be a base station. In yet further scenarios, the first network node as well as the second network node may be both wireless devices, for example terminal devices in a side link communication. The first communication channel is from the first network node to the second network node at least partially via a coverage enhancement device. For example, the first communication channel may be a downlink channel. The second communication channel is from the second network node to the first network node at least partially via the coverage enhancement device. The second communication channel may be an uplink communication channel.

According to the method, at least two different phase shifts for the first communication channel are configured sequentially at the coverage enhancement device. A first configuration of the phase shift may be a default configuration at the coverage enhancement device, and configuring a second phase shift may include transmitting the second phase shift from the first network node to the coverage enhancement device. In some examples, for each configuration of a corresponding phase shift, a corresponding transmission of the phase shift is performed from the first network node to the coverage enhancement device. In some examples, a set of phase shifts to be subsequently configured at the coverage enhancement device may be transmitted in a single message from the first network node to the coverage enhancement device, for example in conjunction with a timing schedule of when to apply which phase shift. The method further comprises obtaining corresponding channel characteristics of the first communication channel for each of the at least two different phase shifts. The channel characteristics may include, for example, a reference signal received power (RSRP) or any kind of performance information, for example, quality indicators, signal power, signal-to-noise ratio. Based on the obtained channel characteristics, a corresponding reciprocity of the first communication channel and the second communication channel is evaluated for each of the at least two different phase shifts. Based on the evaluated reciprocities, a target phase shift to be configured at the coverage enhancement device for the first communication channel is determined.

Generally, messages for configuring a phase shift at the coverage enhancement device may be communicated, for example, via an in-band control channel from the first network node to the coverage enhancement device. In some examples, messages for configuring a phase shift at the coverage enhancement device may be communicated via a network management system to which the first network node and the coverage enhancement device are connected.

Once a target phase shift has been determined, it may be configured at the coverage enhancement device for further communication with the second network node, for example by the first network node.

It should be noted that the target phase shift can be configured at the coverage enhancement device for the first communication channel while maintaining the same phase shift for the second communication channel. In other words, the configuration of the phase shift for the first communication channel may not affect the configuration of the phase shift for the second communication channel, i.e., the phase shift configurations for the first and second communication channels may be performed independently of each other. This may also apply to the sequential configuration of the at least two different phase shifts for the first communication channel. During the sequential configuration of the at least two different phase shifts for the first communication channel at the coverage enhancement device, a same phase shift for the second communication channel is maintained, i.e., the phase shift for the second communication channel is not influenced by the configuration of the phase shift for the first communication channel.

The phase shifts for the first and second communication channels may be configured as absolute values, for example, indicating the corresponding phase shift in degrees or radians of a phase angle, or as a time delay. In further examples, a phase shift for the first communication channel may be configured as a difference, i.e., as an offset, to the current phase shift for the second communication channel. Since the phase shift for the second communication channel is typically not varied during the application of the plurality of different phase shifts for the first communication channel, the phase shifts for the first communication channel may be applied as different offsets to the phase shift for the second communication channel, thereby automatically taking into account the configuration in the opposite direction for which reciprocity is being attempted.

In summary, according to at least some disclosed scenarios, in the downlink (first communication channel), a plurality of different phase shifts are tried or tested at the coverage enhancement device, and for each of these different phase shifts, the second network node, for example, the wireless device, provides channel characteristics as feedback. The different phase shifts may be selected randomly or from a predefined set of phase shifts such that a predefined range of phase shifts is tested. A best or most appropriate phase shift can be selected based on the channel characteristics and can be used for the downlink channel for further communication with the second network node. Note that the uplink (second communication channel) is not varied while trying different phase shifts in the downlink.

Note that the CED hardware may be responsible for non-reciprocity. For example, the CED hardware may be frequency selective. Therefore, the techniques described here may be applied to a sub-band. The sub-band may or may not be the entire bandwidth, e.g., of a certain base station. The techniques can be applied to all sub-bands in parallel. Examples sub-bands would be bandwidth parts or certain frequency layers.

According to various examples, determining the target phase shift may comprise selecting one of the at least two different phase shifts as the target phase shift based on the obtained channel characteristics. The channel characteristics indicating the best channel reciprocity may be determined and the associated phase shift may be selected as the target phase shift. In further examples, determining the target phase shift may comprise fitting the obtained channel characteristics to a cosine function. The fitting may be such that the argument of the cosine function is the phase and the value of the cosine function is the channel characteristics. Link performance, such as RSRP, may have a cosine dependency on phase offset. A few measurements may be sufficient to define an appropriate cosine function and estimate the optimum phase, which may be found at a maximum of the cosine function. The optimal phase can be used to determine the target phase shift.

According to various examples, the first communication channel includes at least one communication path through the coverage enhancement device and at least one further communication path not through the coverage enhancement device. The at least one further communication path (sometimes also referred to as layer) may be a line of sight (LOS) path. However, the at least one further communication path may be a reflected or redirected path or may comprise a plurality of paths, some of which may be LOS paths and some of which may not be LOS paths. The same may or may not be true for the second communication channel. In other words, the communication between the first network node and the second network node may be a diversity transmission, for example a TDD MIMO transmission. In particular, in a TDD transmission, reciprocity can be advantageously exploited.

For example, the first and second communication channels may have opposite directions. For example, the first communication channel may be an uplink communication channel and the second communication channel may be a downlink communication channel. Each of these communication channels is affected by the physical propagation channel over the air and by hardware used to access/observe the physical channel. The CED forms part of the hardware. Each channel may be constituted by two parts, a communication path through the CED and a further communication path not through the CED, e.g., a LOS path. Reciprocity may be achieved when the two communication paths differ, in uplink and downlink, by the same phase; in other words, i.e., the sum phase for the first and second communication channels are the same. For example, reciprocity may be achieved when the signal to noise ratio (SNR) is the same in uplink and downlink communication channels (under the assumption the same transmit power is used).

The method described above provides a simple and efficient technique for achieving reciprocity for the communication paths via the CED, in particular in a TDD MIMO communication.

The method may further comprise participating in a channel sounding procedure to obtain the corresponding channel characteristics of the first communication channel. A transmit precoding for the channel sounding procedure may be configured at the first network node based on a reference signal received from the second network node over the second communication channel. Obtaining, for each of the at least two different phase shifts, corresponding channel characteristics of the first communication channel may include the following.

The first network node may transmit, over the first communication channel, a signal using the transmit preceding when the CED is configured with the corresponding phase shift.

In other words, for each phase shift configured at the CED, a corresponding signal is transmitted from the first network node to the second network node using the transmit precoding. Since the phase shift at the CED is varied, each signal (as received by the second network node) may be affected differently by the different channel conditions due to the different phase shifts at the CED. Accordingly, the reported channel characteristics will vary.

In some examples, the first network node may receive, from the second network node and for each transmitted signal, at least one corresponding channel measurement report indicating corresponding channel characteristics.

In some examples, the first network node may receive, after transmitting at least two of the signals, a channel measurement report indicative of a given one of the at least two signals selected at the second network node. The indicated given signal may be the signal for which the best channel characteristics were determined at the second network node, such that the first network node can derive the corresponding optimal phase shift for the CED from the indicated given signal. In some examples, after transmitting at least two of the signals, the first network node may receive a channel measurement report indicating corresponding channel characteristics for each of the at least two signals. Thus, the channel measurement report may provide aggregated or collected corresponding channel characteristics for multiple signal transmissions. The first network node may then determine the best or most appropriate phase shift from these channel characteristics.

Generally, the signal may comprise for example a Demodulation Reference Signal (DMRS) or a Channel State Information Reference Signal (CSI-RS).

According to various examples, the first network node may determine the transmit precoding based on a conjugate transpose of a channel matrix derived from the received reference signal.

To enable the channel sounding procedure, the first network node may transmit a resource configuration message to the second network node. The resource configuration message may indicate resources to be used by the second network node to transmit the reference signal. Generally, a gain at the CED in the first communication channel may be the same as or configured to be the same as in the second communication channel. To achieve reciprocity, such a configuration may be advantageous and/or appropriate in most cases and may simplify the method by avoiding additional variables.

According to a further example, a method is provided for use in a second network node. The second network node may be a wireless device of the communication network, such as a user equipment or a terminal device. The second network node communicates with a first network node via a first communication channel and a second communication channel. The first communication channel is from the first network node to the second network node at least partially through a CED. The second communication channel is from the second network node to the first network node at least partially through the CED. In other words, the first communication channel and a second communication channel use the same propagation channel. The first network node sequentially configures at least two different phase shifts for the first communication channel at the CED. The method comprises providing corresponding channel characteristics of the first communication channel for each of the at least two different phase shifts. The provided channel characteristics may be used to determine, at the first network node, a target phase shift to be configured at the CED for further communication with the second network node.

In various examples, the channel characteristics include a Reference Signal Received Power (RSRP) as determined by the second network node.

In various examples, the method further comprises participating in a channel sounding procedure to provide the corresponding channel characteristics of the first communication channel. A reference signal is transmitted over the second communication channel. The reference signal may be used at the first network node for configuring a transmit preceding for the channel sounding procedure based on the reference signal.

Furthermore, when participating in the channel sounding procedure, a signal transmitted by the first network node using the transmit precoding may be received over the first communication channel. The signal may comprise a Demodulation Reference Signal (DM RS) or a Channel State Information Reference Signal (CSI-RS). Any other type of reference signal may be used. The first communication channel is at least partially via the CED which is configured with the corresponding phase shift. As such, the signal transmitted by the first network node is affected by the corresponding phase shift at the CED.

In various examples, for each received signal, at least one corresponding channel measurement report indicating the corresponding channel characteristics may be transmitted to the first network node.

In further examples, after receiving at least two of the signals, a channel measurement report is transmitted to the first network node. The channel measurement report may be a given signal of the at least two signals that is selected at the second network node, e.g., the signal associated with the presumed best channel characteristics or the signal for which a best channel reciprocity is presumed to be achievable. For participating in the channel sounding procedure, the second network node may receive a resource configuration message from the first network node. The resource configuration message may indicate resources to be used by the second network node to transmit the reference signal.

According to a further example, a method for use in a CED is provided. The CED is configured to forward a first signal of a first communication channel from a first network node to a second network node with a configurable first phase shift and to forward a second signal of a second communication channel from the second network node to the first network node with a configurable second phase shift. According to the method, a phase shift is received and the received phase shift is configured as the first phase shift for the first communication channel.

The received phase shift may be indicative of a difference between a phase shift to be configured for the first communication channel and the second phase shift. For example, the received phase shift may indicate a desired offset between the first phase shift and the current second phase shift. Thus, in a scenario where the first communication channel relates to a downlink path and the second communication channel relates to an uplink path via the CED, the value for the phase shift for the downlink path may be configured as an offset to the value for the phase shift for the uplink path.

Generally, configuring the received phase shift as the first phase shift for the first communication channel may not change the second phase shift. In other words, the first phase shift and the second phase shift may be configured independently, i.e. , corresponding transmit chains and receive chains may be separately configurable in the CED.

A further example relates to a further method for use in a CED. The CED is configured to forward a first signal of a first communication channel from a first network node to a second network node with at least one of a configurable first phase shift and a configurable first gain. The CED may also be configured to forward a second signal of a second communication channel from the second network node to the first network node with at least one of a configurable second phase shift and a configurable second gain. The method comprises transmitting a message to at least one of the first network node and the second network node. The message indicates a capability of the CED to configure the first phase shift and/or the first gain independently of the second phase shift and/or the second gain.

A first network node is provided. The first network node is configured to communicate with a second network node over a first communication channel and a second communication channel. The first communication channel is from the first network node to the second network node at least partially via a CED. The second communication channel is from the second network node to the first network node at least partially via the CED. The first network node comprises a processor configured to sequentially configure, at the CED, at least two different phase shifts for the first communication channel, and to obtain, for each of the at least two different phase shifts, corresponding channel characteristics of the first communication channel. The processor is further configured to evaluate, for each of the at least two different phase shifts, a corresponding reciprocity of the first communication channel and the second communication channel based on the obtained channel characteristics, and to determine a target phase shift based on the evaluated reciprocities. The processor may be further configured to perform the above described method steps performed by the first network node.

A second network node is provided. The second network node is configured to communicate with a first network node over a first communication channel and a second communication channel. The first communication channel is from the first network node to the second network node at least partially via a CED. The second communication channel is from the second network node to the first network node at least partially via the CED. The first network node sequentially configures at least two different phase shifts for the first communication channel at the CED. The second network node comprises a processor configured to provide corresponding channel characteristics of the first communication channel for each of the at least two different phase shifts. The provided channel characteristics may be configured to be used at the first network node to determine a target phase shift to be configured at the CED for further communication with the second network node.

The processor may further be configured to perform the above-described method steps performed by the second network node.

A CED is provided. The CED is configured to forward a first signal of a first communication channel from a first network node to a second network node with a configurable first phase shift, and to forward a second signal of a second communication channel from the second network node to the first network node with a configurable second phase shift. The CED comprising a processor configured to receive a phase shift, and to configure the received phase shift as the first phase shift for the first communication channel.

The processor may be further configured to perform the above described method steps performed by the CED.

A CED is provided. The CED is configured to forward a first signal of a first communication channel from a first network node to a second network node with a configurable first phase shift and/or a configurable first gain, and to forward a second signal of a second communication channel from the second network node to the first network node with a configurable second phase shift and/or a configurable second gain. The CED comprising a processor configured to transmit a message to at least one of the first and second network nodes. The message is indicative of a capability of the CED of configuring the first phase shift and/or the first gain independent of the second phase shift and/or the second gain.

It is to be understood that the features mentioned above and those yet to be explained below may be used not only in the respective combinations indicated, but also in other combinations or in isolation without departing from the scope of the disclosure.

Brief description of the drawings

FIG. 1 schematically shows a communication system including a base station, a wireless device, and a CED according to various examples.

FIG. 2 schematically illustrates communication between a base station and a wireless device via a CED according to various examples.

FIG. 3 schematically shows a base station according to various examples.

FIG. 4 schematically shows a wireless device according to various examples.

FIG. 5 schematically shows a CED according to various examples. FIG. 6 is a flowchart of a method for use in a base station according to various examples.

FIG. 7 is a flowchart of a further method for use in a base station according to various examples.

FIG. 8 is a flowchart of a method for use in a wireless device according to various examples.

FIG. 9 is a method for use in a CED according to various examples. Detailed Description

Some examples of the present disclosure generally provide a plurality of circuits or other electrical devices. All references to the circuits and other electrical devices and the functionality provided by each are not intended to be limited to encompassing only what is illustrated and described herein. While particular labels may be assigned to the various circuits or other electrical devices disclosed, such labels are not intended to limit the scope of operation for the circuits and the other electrical devices. Such circuits and other electrical devices may be combined with each other and/or separated in any manner based on the particular type of electrical implementation that is desired. It is recognized that any circuit or other electrical device disclosed herein may include any number of microcontrollers, a central processing unit (CPU), a graphics processor unit (GPU), integrated circuits, memory devices (e.g., FLASH, random access memory (RAM), read only memory (ROM), electrically programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), or other suitable variants thereof), and software, which co-act with one another to perform operation(s) disclosed herein. In addition, any one or more of the electrical devices may be configured to execute a program code that is embodied in a non-transitory computer readable medium programmed to perform any number of the functions as disclosed.

In the following, examples of the disclosure will be described in detail with reference to the accompanying drawings. It is to be understood that the following description of examples is not to be taken in a limiting sense. The scope of the disclosure is not intended to be limited by the examples described hereinafter or by the drawings, which are taken to be illustrative only.

The drawings are to be regarded as being schematic representations and elements illustrated in the drawings are not necessarily shown to scale. Rather, the various elements are represented such that their function and general purpose become apparent to a person skilled in the art. Any connection or coupling between functional blocks, devices, components, or other physical or functional units shown in the drawings or described herein may also be implemented by an indirect connection or coupling. A coupling between components may also be established over a wireless connection. Functional blocks may be implemented in hardware, firmware, software, or a combination thereof.

Techniques are described that facilitate wireless communication between nodes, in particular nodes of a wireless mobile communication network system. A wireless communication system includes a transmitter node and one or more receiver nodes. The nodes communicate on a data carrier. In some examples, the wireless communication system can be implemented by a wireless communication network, e.g., a radio-access network (RAN) of a Third Generation Partnership Project-specified cellular network (NW). In such case, the transmitter node can be implemented by an access node such as a base station (BS) of the RAN, e.g. a gNB, and the one or more receiver nodes can be implemented by wireless communication devices (also referred to as wireless device, WD, user equipment, UE, or terminal device, TD). The wireless communication devices may comprise mobile devices, for example mobile phones, smart phones, notebooks, tablet-PCs and Internet of Things (loT) devices. It would also be possible that the transmitter node is implemented by a WD and the one or more receiver nodes are implemented by a BS and/or further WDs. Hereinafter, for the sake of simplicity, various examples will be described with respect to an example implementation of the transmitter node by a BS and the one or more receiver nodes by WDs - i.e., to downlink (DL) communication; but the respective techniques can be applied to other scenarios, e.g., uplink (UL) communication and/or sidelink communication.

According to various examples, it is possible to use multi-antenna techniques. Multiantenna techniques are sometimes used to enhance reliability and/or throughput of wireless communication. Here, the transmitter node and the receiver node may both include multiple antennas that can be operated in a phase-coherent manner. Thereby, a signal can be transmitted redundantly (diversity multi-antenna mode) along multiple spatial data streams or multiple signals can be transmitted on multiple spatial data streams (spatial multiplexing multiantenna operational mode). It is possible to use beamforming: here, spatial data streams can be defined by focusing the transmission energy for transmitting (transmit beam, TX beam) and/or the receive sensitivity for receiving (receive beam, RX beam) to a particular spatial direction.

Configuring a multi-antenna operational mode may include characterizing a communication channel between the nodes. The communication channel may relate to an uplink channel or a downlink channel. The communication channel may include several communication paths. The several communication path may have different spatial propagation paths although they belong to the same communication channel. For example, a communication channel may include a communication path along a line of sight (LOS) between the nodes, and a further communication path propagating between the nodes via a forwarding device, for example a reflecting surface or a CED. The techniques described herein may be applied to an uplink channel as well as a downlink channel and therefore, the general term "communication channel" is used. For distinguishing communication channels in different directions, a channel from a first node to a second node may be referred to as "first communication channel", and a communication channel from the second node to the first node may be referred to as "second communication channel".

Generally, a communication channel may be characterized by channel sounding. For example, a communication between a BS (for example Next Generation NodeB, gNB) and a WD may utilize Channel State Information Reference Signals (CSI-RS).

The gNB may configure CSI-RS resources, including the frequency, time, and antenna ports used for transmitting CSI-RS, based on the network's requirements and the current operating conditions. The gNB may transmits CSI-RS on the configured resources. These signals are received by the WD, providing information about the current channel conditions between the gNB and the WD. For example, upon receiving the CSI-RS, the WD may measure the channel state information by analyzing the received signal quality, including factors such as signal strength, signal-to-noise ratio, and interference levels.

The WD may generate CSI reports based on the measured channel state information. These reports may typically include feedback related to channel quality indicators (CQI), rank indicators (Rl), and precoding matrix indicators (PMI), providing insights into the suitability of different transmission schemes for the current channel conditions. The WD may send the generated CSI reports back to the gNB using dedicated feedback channels or piggybacking the feedback onto uplink data transmissions.

The gNB receives these reports and utilizes the feedback to optimize various aspects of the communication link, such as adjusting beamforming parameters, selecting appropriate modulation and coding schemes, and allocating resources. Based on the received CSI feedback, the gNB may dynamically adapt its transmission parameters to maximize spectral efficiency, throughput, and overall system performance.

In a Time Division Duplexing (TDD) system, reciprocity allows for the exploitation of uplink channel knowledge for downlink transmission. This means that the channel from the WD to the gNB is approximately the same as the channel from the gNB to the WD, assuming the same frequency resources are used for both uplink and downlink transmissions.

In more detail, in the context of 3GPP TDD systems, channel reciprocity refers to the principle that the uplink and downlink channels experience similar propagation characteristics. This means that the wireless channel's behavior is symmetric for both the downlink transmission from the gNB to the WD and the uplink transmission from the WD to the gNB.

In TDD systems, the same frequency band may be used for both uplink and downlink transmissions, with the separation achieved by time division. Channel reciprocity suggests that the characteristics of the channel (such as fading, attenuation, and interference) are similar in both directions. When the gNB transmits signals to the WD (downlink), the signals experience certain propagation effects like fading and multipath interference. The same effects are experienced when the WD transmits signals to the gNB (uplink). Channel reciprocity implies that the effects observed in one direction are comparable to those observed in the other. Channel reciprocity may simplify the implementation of advanced antenna techniques like beamforming and Multiple Input Multiple Output (MIMO). These techniques rely on the knowledge of the channel state information (CSI) to optimize signal transmission and reception. With channel reciprocity, the CSI measured in one direction can be directly applied to the other direction without needing separate measurements.

A transmit precoder may be determined by the gNB based on received a Sounding Reference Signal (SRS) in a TDD system, leveraging reciprocity and conjugate operations. The WD may transmit SRS to the gNB. The gNB receives the SRS and estimates the uplink channel characteristics based on this received signal. This estimation may include parameters like channel amplitude, phase, and delay spread.

Based on the channel reciprocity assumption, the uplink and downlink channels are similar when using the same frequency resources. Therefore, the channel estimation obtained from the received SRS in the uplink can be used as an approximation for the downlink channel. A corresponding precoder for the downlink may be determined. For example, the gNB may apply the conjugate transpose of the uplink channel matrix (derived from SRS) to calculate the downlink precoding matrix. The calculated precoding matrix may then be used to precode the downlink data symbols before transmission from the gNB to the WD. By applying this preceding matrix, the gNB optimizes the transmitted signal based on the estimated downlink channel characteristics, aiming to maximize the received signal quality at the WD.

It is to note that there may be small differences between the uplink and downlink channels due to factors like hardware imperfections or propagation environment changes, particularly when the communication channel includes multiple communication paths between the gNB and the WD. For each communication path a corresponding reciprocity may be required.

Channel reciprocity may be measured using various techniques, primarily involving the estimation of the channel state information (CSI) in both the uplink and downlink directions. In a pilot-based estimation, known pilot symbols are inserted into the transmitted signal, and their received versions are used to estimate the channel response. By comparing the channel estimates obtained from the uplink pilots (WD to gNB) with those from the downlink pilots (gNB to WD), the reciprocity of the channel can be evaluated. Any significant discrepancies between the uplink and downlink channel estimates may indicate non-reciprocal effects in the system. By comparing RSRP measurements obtained from uplink and downlink transmissions, channel reciprocity may be assessed. Consistent RSRP values in both directions suggest channel reciprocity, while significant differences may indicate non-reciprocal effects.

Quantifying reciprocity may be based on different techniques. For example, the characteristics of the channel response obtained from uplink and downlink transmissions may be compared. This comparison may involve analyzing parameters such as amplitude, phase, delay spread, coherence bandwidth, and Doppler spread. A high degree of similarity between the channel responses in both directions suggests strong reciprocity. In some examples, channel correlation may measure the similarity between the uplink and downlink channels over time and frequency. High correlation coefficients indicate strong reciprocity, while lower coefficients suggest discrepancies between the channels. In some examples, reciprocity may also be evaluated by comparing the effective antenna gains in both uplink and downlink directions. Any differences in gain patterns or antenna performance may indicate non-reciprocal effects in the system. Also, in systems utilizing beamforming techniques, the beamforming performance in both uplink and downlink directions may be compared. Consistent beamforming gains and beam shapes indicate good reciprocity.

According to various examples, the transmitter node can communicate with at least one of the receiver nodes via a CED (CED). CEDs are devices or systems deployed to improve coverage in specific areas or to improve transmission capacity, by enabling diversity transmission. They may include various types and configurations, such as type-1 , type-2, or type-3 CEDs, each designed for different scenarios or requirements.

Type-1 CEDs may be designed to enhance coverage by reflecting, amplifying or repeating existing signals. They may consist of amplifiers or repeaters strategically placed to boost signal strength or redirect signals in areas with weak coverage. They may be implemented as a reconfigurable intelligent surface (RIS) with a single antenna array, where each antenna element reflects the signal with a configurable phase shift. Type-1 CEDs may be inherently reciprocal if their configuration is the same during UL and DL.

Type-2 CEDs may focus on improving coverage through the use of distributed antenna systems (DAS). These systems may consist of multiple antennas distributed throughout a coverage area and connected to a central hub or base station. A Type-2 CED may use separate antenna arrays towards the BS and WD, such as a traditional network controlled repeater (NCR). In this case, both array configurations (i.e., beams) must be the same during UL and DL. In addition, a Type-2 CED may need to be configured for UL and DL traffic in the appropriate time slots. In practice, reciprocity is not maintained because UL and DL use different paths within the CED. Each of these paths may have a different associated phase shift and gain/insertion loss, which may have an additional time and/or temperature dependency that can degrade reciprocity and must be addressed.

Type-3 CEDs are designed to extend coverage in areas with difficult propagation conditions, such as rural or remote areas. They typically use advanced techniques such as beamforming or relay nodes to extend coverage and improve signal quality. Type-3 CED implementations can use separate UL and DL arrays. With different arrays for UL and DL, not only phase and gain, but also the geometric distance between the arrays (assuming beam correspondence between UL and DL beams) will affect reciprocity when the CED operates in the near field. Therefore, the reciprocity may also depend on the position of the network nodes involved.

A CED may be used for improving coverage, i.e. enlarging the spatial area for serving WDs, or for improving channel richness, i.e., enlarging transmission capacity for a WD which may already be located within range of the BS. In general, a CED can amplify the signal. If the gain is different in the UL and DL, and possibly configurable by the network, the associated phase will typically change for different gain settings. A different gain in UL and DL is assumed to be more relevant if a CED is used to improve coverage and less relevant to improve channel richness. However, if the UL-DL gains are different, then the system is typically designed to have no UL/DL reciprocity.

FIG. 1 shows an exemplary scenario of a communications network 100 including a CED 102 used for improving channel richness. As shown in Fig. 1, the communications network 100 includes a wireless device (WD) 104, a base station (e.g. a gNB) 106, and the CED 102. The CED 102 is deployed to improve the transmission capacity between the gNB 106 and the WD 104. A downlink channel 108 (solid arrows) from the gNB 106 to the WD 104 comprises a direct downlink path 110 from the gNB 106 to the WD 104, and an indirect downlink path 112 from the gNB 106 to the WD 104 via the CED 102. An uplink channel 114 (dashed arrows) from the WD 104 to the gNB 106 comprises a direct uplink path 116 from the WD 104 to the gNB 106, and an indirect uplink path 118 from the WD 104 to the gNB 106 via the CED 102.

Assuming that the gain for the uplink path 118 and the downlink path 112 is essentially the same at the CED 102, the task is to compensate for the phase difference between the UL and DL transmission paths via the CED.

In this context, the phase shift introduced by the CED may depend on the phase response of the elements of the CED contributing to the signal forwarding. In general, the phase shift introduced by the CED to a forwarded signal can be defined as the joint phase shift of all the elements involved, i.e. the average phase shift of the forwarded signal.

Generally, the phase shift introduced by each CED element can be represented as:

<l)=2TTfT where is the phase shift introduced by the CED element, f is the frequency of the signal, T is the time delay introduced by the CED element. By controlling the time delay T introduced by each element, the phase shift can be adjusted accordingly. This enables precise control over the reflected signal's phase, allowing optimization of the wireless communication path.

One approach may be to directly measure the UL and DL communication channels independently and identify the CED transmission path (i.e., a tap) in the channel impulse responses (CIRs) and estimate the phase shift in each direction UL and DL, or the phase difference between the UL phase shift and the DL phase shift. This approach may involve the following. First, the phase may need to be measured accurately. To measure the phase accurately, the resolution may need to be high, which requires a lot of resources in the time or frequency domain. Second, the tap associated with the CED in the CIR must be identified, which requires additional resources. Finally, since it is an absolute measurement approach, it requires that both the WD and the gNB are fully characterized, i.e. the difference between the phases in the transmit and receive chains is known at both ends. In general, for reciprocitybased DL communication, only the gNB needs to be characterized, and only the phase difference between the transmit and receive chains needs to be known, not the absolute phases of the respective transmit and receive chains.

In connection with FIG. 2, a further approach is described. To achieve channel reciprocity, reciprocity may be desired on any communication path of the communication channel, in particular reciprocity on the communication path over the CED. In principle, reciprocity is evaluated for a set of applied phase configurations on either the uplink or the downlink path of the CED, and the best one is selected or evaluated.

This may require the CED 102 to be able to configure the phase shift in the uplink path 118 independently of the phase shift in the downlink path 112. Therefore, in step 202, the gNB 106 may query the CED 102 as to whether it is capable of configuring the uplink phase shift independently of the downlink phase shift. In step 204, the CED 102 may confirm that it is capable of independent uplink and downlink phase shift configurations. Based on this confirmation, the following steps may be performed.

In step 206, the gNB 106 may transmit a resource configuration indicating resources to be used by the WD 104 for transmitting sounding reference signals (SRS) for analyzing the uplink channel 114. In step 208, the WD 104 may transmit SRS using the configured resources. The gNB 106 receives the SRS and determines a downlink precoding in step 210. To determine the downlink precoding, the gNB 106 may assume channel reciprocity. Based on the received SRS, the gNB 106 may estimate channel characteristics of the uplink channel 114. The downlink precoding may be calculated as the conjugate of the estimated channel characteristics for each of the antennas of the gNB 106. Next, various phase shifts for the downlink path 112 are tried at the CED 102 and the resulting characteristics of the downlink path 112 are collected (e.g.., measured) and evaluated. To give some examples: The various phase shifts may be selected at random, starting with a phase shift substantially equal to the phase shift of the uplink path 118 at the CED 102 or with a phase shift of zero. The various subsequent phase shifts may be selected in small steps of a few degrees in both directions, e.g., +/-1 °, +1-2°, or +/-5°. The different subsequent phase shifts may be selected based on an evaluation of the already collected characteristics of the downlink path 112 for previously tried phase shifts. At least two different phase shifts are tried.

More specifically, in step 212, the gNB 106 configures a phase shift to be tried for the downlink path 112 at the CED 102. In step 214, the gNB transmits a downlink signal, such as a reference signal, e.g., CSI-RS or DMRS, over the downlink channel 108 with the CED 102 configured with the corresponding phase shift to be tried. Consequently, with each different configuration of the phase shift at the CED 102, the characteristics of the entire downlink channel 108 vary as the downlink path 112 is given a different phase shift via the CED 102. The WD 104 receives the downlink signal and determines characteristics of the downlink channel 108, such as a reference signal received power, RSRP, in step 226.

The WD 104 may respond to each received downlink signal in step 216 and report the determined characteristics, such as the RSRP. However, in some examples, the WD 104 may collect the determined characteristics for a plurality of received downlink signals and may report the determined characteristics aggregated to the gNB 106 in step 218. In further examples, the WD 104 may collect the determined characteristics for a plurality of received downlink signals and may report in step 218 for which downlink signal the best characteristics were determined, for example the strongest CSI-RS or DMRS was received.

In addition, the WD 104 may transmit further SRS to the gNB 106 at any time, as in the case of the SRS in step 208. These further SRS may be used by the gNB to (continuously) update its precoding for transmitting the downlink signal in step 214.

For the next phase shift to be tried for the downlink path 112, the method is repeated starting with step 212 above.

After transmitting a plurality of messages in corresponding steps 214 with correspondingly different phase shifts to be tested, the gNB 106 has finally obtained corresponding channel characteristics of the downlink channel 108 for each phase shift to be tested. Based on these channel characteristics, the gNB 106 can determine a best or most appropriate configuration for the downlink path 112 at the CED 102 in step 224. This best or most appropriate configuration is also referred to herein as the target phase shift.

For example, the gNB 106 may take as the target phase shift the phase shift associated with the downlink message that was reported by the WD 104 in step 218 as the downlink message for which the best characteristics were determined. In some examples, the gNB 106 may analyze the characteristics received from the WD 104 in step 216 or step 218 for each of the transmitted downlink messages and take the configuration as the target phase shift associated with the best characteristics.

It has been found that generally the link performance, for example expressed in RSRP, may have a cosine dependency on the phase shift. Therefore, in a further example, the gNB 106 may use the obtained channel characteristics and associated phase shifts for fitting a cosine function. Channel characteristics for two different phase shifts may be sufficient, according to the Nyquist sampling theorem. However, channel characteristics for more than two different phase shifts may be utilized for fitting the cosine function. Based on the cosine function, a phase of the maximum or peak of the cosine function may be determined and used as the target phase shift.

In step 220, the gNB 106 configures the determined target phase shift for the downlink path 112 at the CED 102. For example, the gNB 106 may transmit a corresponding message via the downlink channel 108 as an in-band information to the CED 102. In further examples, the gNB 106 may transmit a corresponding message to the CED 102 using a further communication channel. In some examples, the gNB 106 may transmit a corresponding message to the CED 102 via a management network.

With the configuration of the target phase at the CED 102 for the downlink path 112, reciprocity-based operation may be achieved. In particular, reciprocity-based operation of the downlink path 112 and the uplink path 118 may be achieved.

In step 222, the gNB 106 and the WD 104 may communicate via the uplink communication channel 114 and the downlink communication channel 108 at least partially via the CED 102, i.e., the downlink channel 108 includes the downlink path 112 via the CED 102 and the direct downlink path 110, and the uplink channel 114 includes the uplink path 118 via the CED 102 and the direct uplink path 116.

Reciprocity-based operation assumes that the propagation channel is the same for the uplink and the downlink. Typically, this assumption is only valid for a period of time called the channel coherence time. Therefore, the method described above, including the uplink channel sounding, the determination of the downlink precoding, and the determination and configuration of the target phase for the CED 104, may need to be performed within the coherence time. The coherence time may depend on the mobility of the CED 104 and the environmental conditions. In addition, temperature drift associated with the circuitry of the CED 102, may require that the method described above be repeated. Depending on the type of CED, network node positions may also affect reciprocity when changed.

FIG. 3 illustrates details with respect to the gNB 106. The gNB 106 implements an access node, e.g. a base station, to a communications network, e.g., a 3GPP-specified cellular network. The gNB 106 includes control circuitry that is implemented by a processor 302 and a non-volatile memory 304. The processor 302 can load program code that is stored in the memory 304. The processor 302 can then execute the program code. Executing the program code causes the processor 302 to perform techniques as described herein, e.g.: participating in a data transmission between the gNB 106 and the WD 104 via transmission channels 108,114 including direct paths 110, 116 and paths 112, 118 via the CED 102 as well as configuring a phase shift at the CED 102. Details on the techniques performed by the processor 302 will be described in connection with FIGs. 6 and 7.

The gNB 106 includes an interface 306 that can access and control multiple antennas 308. The interface 306 can include one or more transmit chains and one or more received chains. For instance, such receive chains can include low noise amplifiers, analogue to digital converters, mixers, etc. Analogue and/or digital beamforming would be possible. Thereby, phase-coherent transmitting and/or receiving (communicating) can be implemented across the multiple antennas 308. Multi-antenna techniques can be implemented.

By using a transmit beam, the direction of signals transmitted is controlled. Energy is focused into a respective direction or even multiple directions by phase-coherent superposition of the individual signals originating from each antenna 308. Thereby, a data stream can be directed. The data streams transmitted on multiple beams can be independent, resulting in spatial multiplexing multi-antenna transmission; or dependent on each other, e.g., redundant, resulting in diversity multi-input multi-output (MIMO) transmission. The downlink transmission paths 110, 112 may be formed. Alternatively or additionally to such transmit beams, it is possible to employ receive beams. These receive beams can be selective to receive signals from a specific direction. Corresponding reception sensitivity for the uplink paths 116, 118 may be formed.

FIG. 4 illustrates details with respect to the WD 104. The WD 104 implements a terminal node, e.g. a user equipment, in a communications network, e.g., a 3GPP-specified cellular network. The WD 104 includes control circuitry that is implemented by a processor 402 and a non-volatile memory 404. The processor 402 can load program code that is stored in the memory 404. The processor 402 can then execute the program code. Executing the program code causes the processor 402 to perform techniques as described herein, e.g.: participating in a data transmission between the gNB 106 and the WD 104 via transmission channels 108,114 including direct paths 110, 116 and paths 112, 118 via the CED 102. Details on the techniques performed by the processor 402 will be described in connection with FIG. 8.

The WD 104 includes an interface 406 that can access and control one or multiple antennas 408. The interface 406 can include one or more transmit chains and one or more received chains. For instance, such receive chains can include low noise amplifiers, analogue to digital converters, mixers, etc. Analogue and/or digital beamforming would be possible. Thereby, phase-coherent transmitting and/or receiving (communicating) can be implemented across the multiple antennas 408. Multi-antenna techniques can be implemented. However, in various examples, the WD 104 and may have single antenna 408 only and may not be capable of implementing multi-antenna techniques.

FIG. 5 illustrates aspects in connection with the CED 102. The CED 102 includes an array of antenna elements 508 each imposing a respective configurable phase shift when reflecting or re-transmitting or amplifying or attenuating incident signals. The array of antenna elements 508 may form a reflective surface. Typically, antennas can impose gradually varying phase shifts.

The CED 102 includes control circuitry that is implemented by a processor 502 and a memory 504. The processor 502 can load program code from the memory 504 and execute the program code. Upon loading and executing the program code, the processor 502 can (reconfigure the antenna elements 508 to implement a respective phase shift, via a respective control interface 506. There may also be provided a control interface 508 via which the processor 502 can communicate on a control link 510. Control messages or capability messages or other information can be exchanged between a node controlling the CED 102 and the CED 102. For instance, the control link 510 could be implemented using Bluetooth or Wi-Fi technology providing communication to a control layer of the cellular network. The node controlling the CED 102 may be the gNB 106. Control information for controlling the CED 102 may be provided as in-band information in signals received by the antenna elements 508.

The antenna elements 508 may be located spatially distributed. The antenna elements 108 may be configured to receive a radio signal of a transmission path incident in a specific direction and to transmit or reflect the radio signal in another specific direction, thereby amplifying, attenuating or phase shifting the signal. A phase shift may be configured individually for each antenna element 508 or for groups of antenna elements 508. Particularly, a phase shift of antenna elements 508 assigned to one transmission path, for example the transmission path 112, may be configurable independent from a phase shift of antenna elements assigned to another transmission path, for example the transmission path 118. Details on the techniques performed by the processor 502 will be described in connection with FIG. 9.

FIG. 6 shows method steps 602 to 620 of a method 600 for use in the gNB 106. As illustrated in FIG. 1 , the gNB 106 communicates with the WD 104 over a downlink communication channel 108 and an uplink communication channel 114. The downlink communication channel 108 has at least two downlink communication paths, the direct downlink communication path 110 and the indirect downlink communication path 112 via the CED 102. The uplink communication channel 114 has at least two uplink communication paths, the direct uplink communication path 116 and the indirect uplink path 118 via the CED 102. Each of the uplink and downlink communication channels may have further communication paths. In some examples, also the direct uplink and downlink communication paths may be indirect uplink and downlink communication paths, for example reflected at a building or forwarded by another CED.

In step 602, the gNB 106 may configure SRS resources at the WD 104, e.g. by transmitting an SRS resource configuration message to the WD 104. In response, the WD 104 may transmit SRS to the gNB 106 via the uplink communication channel 114 to sound the uplink communication channel 114. The gNB 106 receives the SRS in step 604. based on the received SRS, the gNB 106 may configure or adjust the phase shift of the uplink communication path 118 at the CED 102, for example to optimize SRS signal strength. Furthermore, based on a feedback from the gNB 106 indicating the signal strength of the SRS as received at the gNB 106, the WD 104 may change an uplink precoding at the WD 104 to achieve coherent reception via the uplink communication paths 116, 118.

Further, based on the received SRS, the gNB 106 may determine and configure in step 606 a transmit precoding used by the gNB 106 for transmitting signals over the downlink communication channel 108. The transmit precoding may be determined based on a conjugate transpose of a channel matrix derived from the received SRS. Transmit chains for the antennas 308 may be configured in the interface 306 accordingly.

Starting with step 608, a plurality of different phase shifts for the downlink communication path 112 are sequentially configured and tested at the CED 102. As a first phase shift for the downlink communication path 112, a default phase shift already configured at the CED 102 may be used. The default phase shift may have been configured at the CED when configuring the phase shift of the uplink communication path 118 or may be a default value, for example zero, automatically set at the CED 102 when establishing a transmission path. A second phase shift and further phase shifts to be tested may be configured at the CED 102 by transmitting corresponding configuration messages, for example from the gNB 106 to the CED 102.

For each configuration of the phase shift at the CED 102, corresponding channel characteristics of the downlink communication channel 108 may be obtained. For example, for each configuration of the phase shift at the CED 102, a reference signal may be transmitted in step 610 via the downlink communication channel 108. The reference signal may comprise for example a CSI-RS or DMRS. The WD 104 receives the reference signal and determines channel characteristics, for example a received signal strength, and notifies the channel characteristics to the gNB 106, for example by transmitting a RSRP message. The gNB 106 receives in step 612 for each transmitted reference signal the corresponding channel characteristics. Based on the channel characteristics, the gNB 106 may evaluate in step 614 channel reciprocity, in particular reciprocity of the downlink path 112 and the uplink path 118 via the CED 102. The evaluated reciprocity is assigned to the phase shift that was configured at the CED 102 when transmitting the corresponding reference signal.

In step 616 the gNB 106 decides whether further phase shifts are to be tested at the CED 102. For example, a number or set of phase shifts that should be tested may be predefined in the network. In some examples, a number or set of phase shifts to be tested may be predefined for a specific CED. In some examples, the gNB 106 may consider the already evaluated reciprocities, and may determine whether further phase shifts are needed to be tested or whether already sufficient or required reciprocity is achieved. If further phase shifts should be tested, the method continues in step 608, where a further phase shift is configured at the CED 102. For changing the phase shift at the CED 102, the gNB may transmit a corresponding configuration request to the CED 102, for example via a management network or by using in-band communication, i.e. the configuration change may be communicated with the signaling in the downlink communication path 112.

It is to be noted that the phase shift configuration for the downlink communication path 112 does not affect the phase shift of the uplink communication path 118, i.e. the downlink phase shift is configured independently from the uplink phase shift at the CED 102. Generally, the phase shift at the CED 102 for a specific direction, for example the downlink phase shift or the uplink phase shift, may be considered as the joint phase shift from all involved antenna elements 508 and corresponding components of the interface 506, i.e. the involved receive and transmit chains. As a result, the phase shift at the CED 102 for a specific direction may be considered as the average phase shift of the conveyed signal.

Configuring the phase shift for a specific direction, in particular the downlink transmission path 112, at the CED 102 may include an absolute value for the phase shift, for example a value of degrees of a phase angle or a value of a corresponding time delay, or may be indicated by an enumerated value indicating degrees of a phase angle or a time delay. In further examples the phase shift for the downlink transmission path may be configured as the relative phase shift with respect to the phase shift for the uplink transmission path at the CED 102. However, it is to be noticed that configuring the phase shift for the downlink transmission path does not affect the phase shift for the uplink transmission path.

After all the required phase shifts have been configured and tested at the CED 102, and the corresponding reciprocities have been evaluated, the gNB 106 may determine in step 618 a resulting best phase shift which is referred to as a target phase shift. In step 620, the target phase shift is configured at the CED 102. Configuring the target phase shift may be performed in the same way as configuring the tested phase shifts described above in step 608.

The target phase shift may be determined by selecting one of the phase shifts from the plurality of phase shifts that were configured in step 608 based on the associated reciprocities. For example the phase shift with the best associated reciprocity may be selected as the target phase shift. For example, it is assumed that in step 606 a transmit precoding is determined and the CED 102 is configured to get a flat or nearly flat frequency response on the uplink transmission channel 114 including the uplink transmission path 118 via the CED 102. When testing the plurality of phase shifts in steps 608 to 616, the downlink channel characteristics are measured and reciprocity determined, for example whether the signal strengths indicate a same flat frequency response. Thus, the phase shift for the downlink path 112 is adjusted so as to "flatten" the frequency response of the downlink channel 108.

Furthermore, the target phase shift may be determined based on the link performance, i.e. the RSRP, received as the channel characteristics. The link performance has an cosine dependency on the phase offset. Two or more measurements determined upon different phase shift configurations at the CED may be fitted to a cosine function and the optimal phase shift may be determined from a maximum value of the cosine function.

The gNB 106 and the WD 104 may then communicate via the downlink communication channel 108 and the uplink communication channel 114 including the uplink and downlink transmission paths 118, 112 via the CED 102.

The above-described method 600 may be repeated from time to time, for example after expiry of the coherence time, or the method 600 may be performed continuously to ensure high quality transmission between the gNB 106 and the WD 104. By including the transmission paths 112, 118 via the CED 102 in addition to the transmission paths 110, 116, transmission capacity between the gNB 106 and WD 104 may be enhanced.

FIG. 7 shows a further method 700 for use in the gNB 106. The method 700 comprises the method steps 602 to 610, 618 and 620 which are essentially the same as the corresponding method steps of method 600. The method 700 includes furthermore method steps 712 to 716.

As in method 600, it is assumed that the gNB 106 communicates with the WD 104 over the downlink communication channel 108 and an uplink communication channel 114.

In step 602, the gNB 106 may configure SRS resources at the WD 104, and, in response, the WD 104 may transmit SRS to the gNB 106 via the uplink communication channel 114 to sound the uplink communication channel 114. The gNB 106 receives the SRS in step 604 and configures or adjusts the phase shift of the uplink communication path 118 at the CED 102 based on the received SRS. Further, based on the received SRS, the gNB 106 may determine and configure in step 606 a transmit precoding used by the gNB 106 for transmitting signals over the downlink communication channel 108. Starting with step 608, a plurality of phase shifts for the downlink communication path 112 are sequentially configured and tested at the CED 102 as described above in connection with FIG. 6. However, instead of obtaining for each configuration of the phase shift at the CED 102, corresponding channel characteristics of the downlink communication channel 108 immediately, the WD 104 may collect the determined the channel characteristics for each configuration of the phase shift at the CED 102. For each configuration of the phase shift at the CED 102, a reference signal may be transmitted in step 610 via the downlink communication channel 108. The WD 104 receives the reference signals and determines and stores channel characteristics, for example a received signal strength, for each received reference signal.

In step 716 the gNB 106 decides whether further phase shifts are to be tested at the CED 102. For example, a number or set of phase shifts may be predefined in the network that should be tested. In some examples, a number or set of phase shifts to be tested may be predefined for a specific CED. If further phase shifts should be tested, the method continues in step 608, where a further phase shift is configured at the CED 102. When all the required phase shifts have been configured at the CED 102 and tested, the method 700 is continued in step 712.

In step 712, the gNB 106 may receive the aggregated channel characteristics from the WD 104. For example, the WD 104 may indicate a list of all channel characteristics measured for the set of tested phase shifts, or the WD 104 may indicate the best channel characteristics and the corresponding reference signal with which these best channel characteristics were achieved.

For example, based on the list of channel characteristics, the gNB 106 may evaluate in step 714 corresponding channel reciprocities, in particular reciprocity of the downlink path 112 and the uplink path 118 via the CED 102.

The gNB 106 may determine in step 618 a phase shift assigned to the best reciprocity or best channel characteristics as a target phase shift. In step 620, the target phase shift is configured at the CED 102.

FIG. 8 shows method steps 802 to 808 of a method 800 for use in the WD 104. As illustrated in FIG. 1 , the gNB 106 communicates with the WD 104 over a downlink communication channel 108 and an uplink communication channel 114. The downlink communication channel 108 has at least two downlink communication paths, the direct downlink communication path 110 and the indirect downlink communication path 112 via the CED 102. The uplink communication channel 114 has at least two uplink communication paths, the direct uplink communication path 116 and the indirect uplink path 118 via the CED 102. Each of the uplink and downlink communication channels 108, 114 may have further communication paths. In some examples, also the direct uplink and downlink communication paths may be indirect uplink and downlink communication paths, for example reflected at a building or forwarded via another CED. The WD 104 may participate in a channel sounding procedure. In step 802, the WD 104 receives an SRS resource configuration, for example from the gNB 106. I.e. , the WD 104 is configured with SRS resources. In some examples, the SRS resources may be preconfigured in the network or obtained from another network node. In step 804, the WD 104 transmits SRS for sounding the uplink channel 114. Based on this uplink channel sounding, the gNB 106 may configure its downlink precoding and may configure a phase shift for the uplink transmission path 118 at the C ED 102.

Beginning at step 806, the WD 104 receives a plurality of reference signals from the gNB 106. Each of the plurality of reference signals is transmitted with the CED being configured with a different phase shift for the downlink transmission path 108, while the phase shift for the uplink transmission path 118 is not modified. The reference signals may include a CSI-RS or DMRS. For each received reference signal, the WD 104 determines corresponding channel characteristics. The channel characteristics may include a RSRP. The WD 104 may transmit the corresponding channel characteristics immediately for each received reference signal to the gNB 106 in step 808. In some examples, the WD 104 stores/collects the channel characteristics and transmits the stored/collected channel characteristics in a single message to the gNB 106.

FIG. 9 shows method steps 902 to 908 of a method 900 for use in the CED 102. The CED 102 may be used in a scenario as illustrated in FIG. 1. The gNB 106 communicates with the WD 104 over a downlink communication channel 108 and an uplink communication channel 114. The downlink communication channel 108 has at least two downlink communication paths, the direct downlink communication path 110 and the indirect downlink communication path 112 via the CED 102. The uplink communication channel 114 has at least two uplink communication paths, the direct uplink communication path 116 and the indirect uplink path 118 via the CED 102.

In step 902, the gNB 106 may request a capability of the CED 102 regarding phase shift configuration and/or gain configuration. In response, the CED 102 may transmit in step 904 its corresponding capabilities. For example, the CED may indicate in a corresponding message that it is capable of configuring the phase shift for the uplink transmission path 118 independently from the phase shift of the downlink transmission path 112. Furthermore, the CED may indicate that it is capable of configuring the gain for the uplink transmission path 118 independently from the gain of the downlink transmission path 112. The CED 102 may indicate further details, for example a gain or attenuation range that can be configured for the uplink transmission path 118 and the downlink transmission path 112 as well as the phase shift ranges for the uplink transmission path 118 and the downlink transmission path 112. The phase shift may be configurable as an absolute phase shift value for each transmission path 112, 118, e.g. in degrees of a phase angle or as a time delay. The phase shift may be configurable as a relative value between the phase shift for the transmission path 112 and the phase shift for the transmission path 118, i.e. as a phase offset between the phase shift for the transmission path 112 and the phase shift for the transmission path 118, e.g. in degrees of a phase angle or as a time delay. In step 906, the CED 102 may receive a phase shift for the uplink transmission path 118 or for the downlink transmission path 112. Furthermore, the CED may receive a gain configuration for the uplink transmission path 118 or for the downlink transmission path 112. For example, the CED 102 may receive a corresponding message via the downlink channel 108 as an in-band information from the gNB 106, for example in a control channel. In further examples, the CED 102 may receive a corresponding message via a further communication channel to the gNB 106. In some examples, the CED 102 may receive a corresponding message via a management network from the gNB 106.

The CED 102 configures the received phase shift and/or gain separately for each transmission path 112, 118 in step 908. For example, the transmit chains and the receive chains in the interface 506 of the CED 102 may be configured accordingly. For example, an antenna element of the plurality of antenna elements 508 may be involved with reception of the downlink transmission path 112 from the gNB 106 and may also be involved with the transmission of the uplink transmission path 118 to the gNB 106. In the transmit chain and the received chain assigned to this antenna element, a phase shift for the transmit chain, i.e. for the uplink transmission path 118 to the gNB 106, is configured separately from a phase shift for the received chain, i.e. for the downlink transmission path 112 from the gNB 106.

In summary, in the CED, the phase shift for the uplink transmission path 118 can be configured independently of the phase shift of the downlink transmission path 112, i.e., a phase shift can be applied to only one transmission direction, such as transmissions associated with the downlink, while the phase shift of transmissions associated with the other transmission direction, such as transmissions associated with the uplink, remains unchanged.

Accordingly, at least the following EXAMPLES have been described above:

EXAMPLE 1. A method for use in a first network node, the first network node (106) communicating with a second network node (104) over a first communication channel (108) and a second communication channel (114), the first communication channel (108) being from the first network node (106) to the second network node (104) at least partially via a coverage enhancement device (102), the second communication channel (114) being from the second network node (104) to the first network node (106) at least partially via the coverage enhancement device (102), the method (600, 700) comprising: sequentially configuring (608), at the coverage enhancement device (102), at least two different phase shifts for the first communication channel (108), obtaining (610, 612, 712), for each of the at least two different phase shifts, corresponding channel characteristics of the first communication channel (108), evaluating (614, 714), for each of the at least two different phase shifts, a corresponding reciprocity of the first communication channel (108) and the second communication channel (114) based on the obtained channel characteristics, and determining (618) a target phase shift based on the evaluated reciprocities.

EXAMPLE 2. The method of EXAMPLE 1 , further comprising: configuring (620), at the coverage enhancement device (102), the target phase shift for further communication with the second network node (104), wherein the target phase shift is configured at the coverage enhancement device (102) for the first communication channel (108) while maintaining a same phase shift for the second communication channel (114).

EXAMPLE 3. The method of any one of the preceding EXAMPLES, wherein, while sequentially configuring, at the coverage enhancement device (102), the at least two different phase shifts for the first communication channel (108), maintaining, at the coverage enhancement device (102), a same phase shift for the second communication channel (114).

EXAMPLE 4. The method of any one of the preceding EXAMPLES, wherein the first communication channel (108) includes at least one communication path (112) via the coverage enhancement device (102) and at least one further communication path (110) not via the coverage enhancement device (102).

EXAMPLE 5. The method of any one of the preceding EXAMPLES, wherein the method further comprises: participating in a channel sounding procedure to obtain the corresponding channel characteristics of the first communication channel (108), and configuring (606), at the first network node (106), a transmit precoding for the channel sounding procedure based on a reference signal received from the second network node (104) over the second communication channel (114).

EXAMPLE 6. The method of EXAMPLE 5, wherein said participating in the channel sounding procedure comprises: transmitting (610), over the first communication channel (108), a signal using the transmit precoding upon the coverage enhancement device (102) being configured with the corresponding phase shift.

EXAMPLE 7. The method of any one of the preceding EXAMPLES, further comprising:

- setting each of the at least two phase shifts based on a difference of a corresponding phase shift of the at least two phase shifts and a further phase shift configured at the coverage enhancement device (102) for the second communication channel (114).

EXAMPLE 8. The method of any one of the preceding EXAMPLES, wherein determining (618) the target phase shift comprises: selecting one of the at least two different phase shifts as the target phase shift based on the obtained channel characteristics.

EXAMPLE 9. A method for use in a second network node (104), the second network node (104) communicating with a first network node (106) over a first communication channel (108) and a second communication channel (114), the first communication channel (108) being from the first network node (106) to the second network node (104) at least partially via a coverage enhancement device (102), the second communication channel (114) being from the second network node (104) to the first network node (106) at least partially via the coverage enhancement device (102), wherein the first network node (106) sequentially configures, at the coverage enhancement device (102), at least two different phase shifts for the first communication channel (108), the method comprising: providing (808), for each of the at least two different phase shifts, corresponding channel characteristics of the first communication channel (108), the provided channel characteristics being for determining, at the first network node (106), a target phase shift to be configured at the coverage enhancement device (102) for further communication with the second network node (104).

EXAMPLE 10. The method of EXAMPLE 9, wherein the method further comprises: participating in a channel sounding procedure to provide the corresponding channel characteristics of the first communication channel (108), and transmitting (804) a reference signal over the second communication channel (114), the reference signal being for configuring, at the first network node (106), a transmit precoding for the channel sounding procedure based on the reference signal, wherein said participating in the channel sounding procedure comprises: receiving (806), over the first communication channel (108), a signal transmitted by the first network node (106) using the transmit precoding upon the coverage enhancement device (102) being configured with the corresponding phase shift, transmitting (808), to the first network node (106) and for each received signal, at least one corresponding channel measurement report indicative of the corresponding channel characteristics, and after receiving at least two of the signals, transmitting (808) a channel measurement report indicating a given signal of the at least two signals that is selected at the second network node (104).

Although the disclosure has been shown and described with respect to certain preferred embodiments, equivalents and modifications will occur to others skilled in the art upon the reading and understanding of the specification. The present disclosure includes all such equivalents and modifications and is limited only by the scope of the appended claims.

Claims

1. A method for use in a first network node, the first network node (106) communicating with a second network node (104) over a first communication channel (108) and a second communication channel (114), the first communication channel (108) being from the first network node (106) to the second network node (104) at least partially via a coverage enhancement device (102), the second communication channel (114) being from the second network node (104) to the first network node (106) at least partially via the coverage enhancement device (102), the method (600, 700) comprising: sequentially configuring (608), at the coverage enhancement device (102), at least two different phase shifts for the first communication channel (108), obtaining (610, 612, 712), for each of the at least two different phase shifts, corresponding channel characteristics of the first communication channel (108), evaluating (614, 714), for each of the at least two different phase shifts, a corresponding reciprocity of the first communication channel (108) and the second communication channel (114) based on the obtained channel characteristics, and determining (618) a target phase shift based on the evaluated reciprocities.

2. The method of claim 1, further comprising: configuring (620), at the coverage enhancement device (102), the target phase shift for further communication with the second network node (104).

3. The method of claim 2, wherein the target phase shift is configured at the coverage enhancement device (102) for the first communication channel (108) while maintaining a same phase shift for the second communication channel (114).

4. The method of any one of the preceding claims, wherein, while sequentially configuring, at the coverage enhancement device (102), the at least two different phase shifts for the first communication channel (108), maintaining, at the coverage enhancement device (102), a same phase shift for the second communication channel (114).

5. The method of any one of the preceding claims, wherein the first communication channel (108) includes at least one communication path (112) via the coverage enhancement device (102) and at least one further communication path (110) not via the coverage enhancement device (102).

6. The method of any one of the preceding claims, wherein the method further comprises: participating in a channel sounding procedure to obtain the corresponding channel characteristics of the first communication channel (108), and configuring (606), at the first network node (106), a transmit precoding for the channel sounding procedure based on a reference signal received from the second network node (104) over the second communication channel (114).

7. The method of claim 6, wherein said participating in the channel sounding procedure comprises: transmitting (610), over the first communication channel (108), a signal using the transmit precoding upon the coverage enhancement device (102) being configured with the corresponding phase shift.

8. The method of claim 7, wherein said participating in the channel sounding procedure further comprises: receiving (612), from the second network node (104) and for each transmitted signal, at least one corresponding channel measurement report indicative of the corresponding channel characteristics.

9. The method of claim 7 or claim 8, wherein said participating in the channel sounding procedure further comprises: after transmitting at least two of the signals, receiving (712) a channel measurement report indicating a given signal of the at least two signals that is selected at the second network node (104).

10. The method of any one of claims 7-9, wherein the signal comprises at least one of a Demodulation Reference Signal and a Channel State Information Reference Signal.

11. The method of any one of claims 6-10, wherein configuring (606) the transmit precoding comprises: determining (606) the transmit precoding based on a conjugate transpose of a channel matrix derived from the received reference signal.

12. The method of claim 11 , further comprising: transmitting (602) a resource configuration message to the second network node (104), the resource configuration message being indicative of resources to be used by the second network node (104) for transmitting the reference signal.

13. The method of any one of the preceding claims, further comprising:

14. The method of any one of the preceding claims, wherein a gain at the coverage enhancement device (102) in the first communication channel (108) is the same as in the second communication channel (114).

15. The method of any one of the preceding claims, wherein the channel characteristics include a Reference Signal Received Power.

16. The method of any one of the preceding claims, wherein determining (618) the target phase shift comprises: selecting one of the at least two different phase shifts as the target phase shift based on the obtained channel characteristics.

17. The method of any one of the preceding claims, wherein determining (618) the target phase shift comprises: fitting the obtained channel characteristics to a cosine function, and determining the target phase shift based on the cosine function.

18. A method for use in a second network node (104), the second network node (104) communicating with a first network node (106) over a first communication channel (108) and a second communication channel (114), the first communication channel (108) being from the first network node (106) to the second network node (104) at least partially via a coverage enhancement device (102), the second communication channel (114) being from the second network node (104) to the first network node (106) at least partially via the coverage enhancement device (102), wherein the first network node (106) sequentially configures, at the coverage enhancement device (102), at least two different phase shifts for the first communication channel (108), the method comprising: providing (808), for each of the at least two different phase shifts, corresponding channel characteristics of the first communication channel (108), the provided channel characteristics being for determining, at the first network node (106), a target phase shift to be configured at the coverage enhancement device (102) for further communication with the second network node (104).

19. The method of claim 18, wherein the method further comprises: participating in a channel sounding procedure to provide the corresponding channel characteristics of the first communication channel (108), and transmitting (804) a reference signal over the second communication channel (114), the reference signal being for configuring, at the first network node (106), a transmit precoding for the channel sounding procedure based on the reference signal.

20. The method of claim 19, wherein said participating in the channel sounding procedure comprises: receiving (806), over the first communication channel (108), a signal transmitted by the first network node (106) using the transmit precoding upon the coverage enhancement device (102) being configured with the corresponding phase shift.

21. The method of claim 20, wherein said participating in the channel sounding procedure further comprises: transmitting (808), to the first network node (106) and for each received signal, at least one corresponding channel measurement report indicative of the corresponding channel characteristics.

22. The method of claim 20 or claim 21, wherein said participating in the channel sounding procedure further comprises: after receiving at least two of the signals, transmitting (808) a channel measurement report indicating a given signal of the at least two signals that is selected at the second network node (104).

23. The method of any one of claims 20-22, wherein the signal comprises at least one of a Demodulation Reference Signal and a Channel State Information Reference Signal.

24. The method of any one of claims 19-23, further comprising: receiving (802) a resource configuration message from the first network node (106), the resource configuration message being indicative of resources to be used by the second network node (104) for transmitting the reference signal.

25. The method of any one of claims 18-24, wherein the channel characteristics include a Reference Signal Received Power.

26. A method for use in a coverage enhancement device (102), wherein the coverage enhancement device (102) is configured to forward a first signal of a first communication channel (108) from a first network node (106) to a second network node (104) with a configurable first phase shift and to forward a second signal of a second communication channel (114) from the second network node (104) to the first network node (106) with a configurable second phase shift, wherein the method comprises: receiving (906) a phase shift, and configuring (908) the received phase shift as the first phase shift for the first communication channel (108).

27. The method of claim 26, wherein the received phase shift is indicative of a difference between a phase shift to be configured for the first communication channel (108) and the second phase shift.

28. The method or claim 26 or claim 27, wherein configuring the received phase shift as the first phase shift for the first communication channel (108) does not change the second phase shift.

29. A method for use in a coverage enhancement device (102), wherein the coverage enhancement device (102) is configured to forward a first signal of a first communication channel (108) from a first network node (106) to a second network node (104) with a configurable first phase shift and/or a configurable first gain, and to forward a second signal of a second communication channel (114) from the second network node (104) to the first network node (106) with a configurable second phase shift and/or a configurable second gain, wherein the method comprises: transmitting (904) a message to at least one of the first and second network nodes (104), the message being indicative of a capability of the coverage enhancement device (102) of configuring the first phase shift and/or the first gain independent of the second phase shift and/or the second gain.

30. A first network node (106), the first network node (106) communicating with a second network node (104) over a first communication channel (108) and a second communication channel (114), the first communication channel (108) being from the first network node (106) to the second network node (104) at least partially via a coverage enhancement device (102), the second communication channel (114) being from the second network node (104) to the first network node (106) at least partially via the coverage enhancement device (102), the first network node (106) comprising a processor (302) configured to: sequentially configure (608), at the coverage enhancement device (102), at least two different phase shifts for the first communication channel (108), obtain (610, 612, 712), for each of the at least two different phase shifts, corresponding channel characteristics of the first communication channel (108), evaluate (614, 714), for each of the at least two different phase shifts, a corresponding reciprocity of the first communication channel (108) and the second communication channel (114) based on the obtained channel characteristics, and determine (618) a target phase shift based on the evaluated reciprocities.

31. The first network node (106) of claim 30, wherein the processor (302) is further configured to perform the method of any one of claims 1-17.

32. A second network node (104), the second network node (104) communicating with a first network node (106) over a first communication channel (108) and a second communication channel (114), the first communication channel (108) being from the first network node (106) to the second network node (104) at least partially via a coverage enhancement device (102), the second communication channel (114) being from the second network node (104) to the first network node (106) at least partially via the coverage enhancement device (102), wherein the first network node (106) sequentially configures, at the coverage enhancement device (102), at least two different phase shifts for the first communication channel (108), the second network node (104) comprising a processor (402) configured to: provide (808), for each of the at least two different phase shifts, corresponding channel characteristics of the first communication channel (108), the provided channel characteristics being for determining, at the first network node (106), a target phase shift to be configured at the coverage enhancement device (102) for further communication with the second network node (104).

33. The first network node (106) of claim 32, wherein the processor (402) is further configured to perform the method of any one of claims 18-25.

34. A coverage enhancement device (102), wherein the coverage enhancement device (102) is configured to forward a first signal of a first communication channel (108) from a first network node (106) to a second network node (104) with a configurable first phase shift and to forward a second signal of a second communication channel (114) from the second network node (104) to the first network node (106) with a configurable second phase shift, the coverage enhancement device (102) comprising a processor (502) configured to: receive (906) a phase shift, and configure (908) the received phase shift as the first phase shift for the first communication channel (108).

35. The coverage enhancement device (102) of claim 34, wherein the processor (502) is further configured to perform the method of any one of claims 26-28.

36. A coverage enhancement device (102), wherein the coverage enhancement device (102) is configured to forward a first signal of a first communication channel (108) from a first network node (106) to a second network node (104) with a configurable first phase shift and/or a configurable first gain, and to forward a second signal of a second communication channel (114) from the second network node (104) to the first network node (106) with a configurable second phase shift and/or a configurable second gain, the coverage enhancement device (102) comprising a processor (502) configured to: transmit (904) a message to at least one of the first and second network nodes (104), the message being indicative of a capability of the coverage enhancement device (102) of configuring the first phase shift and/or the first gain independent of the second phase shift and/or the second gain.