WO2022207320A1

WO2022207320A1 - Delays for improving communication via coverage enhancing devices

Info

Publication number: WO2022207320A1
Application number: PCT/EP2022/056799
Authority: WO
Inventors: Erik Bengtsson; Kun Zhao; Fredrik RUSEK; Jose Flordelis; Olof Zander
Original assignee: Sony Group Corporation; Sony Europe B.V.
Priority date: 2021-03-31
Filing date: 2022-03-16
Publication date: 2022-10-06

Abstract

According to a first aspect, examples provide a method of operating a first communication node (CN) wherein the first CN is configured for controlling a first coverage enhancing device (CED) and a second CED, wherein the first CED and the second CED are reconfigurable to provide multiple spatial filterings, each one of the multiple spatial filterings being associated with a respective input spatial direction from which incident signals on a radio channel are accepted and with a respective output spatial direction into which the incident signals are transmitted by the first CED and the second CED, respectively, wherein the first CED is configurable for applying a first delay to the incident signals; wherein the second CED is configurable for applying a second delay to the incident signals, wherein the method comprises providing, to the first CED, a message indicative of the first delay which is to be applied to the incident signals, providing, to the second CED, a message indicative of the second delay which is to be applied to the incident signals, wherein a difference between the first delay and the second delay is larger than a sampling period of the first CN and/or a sampling period of a second CN communicating with the first CN via the first CED and the second CED. Further examples, provide a method of operating a second CN, a method of operating a CED, a first CN, a second CN and a CED.

Description

Delays for improving communication via coverage enhancing devices TECHNICAL FIELD

Various examples generally relate to communicating between nodes using coverage enhancing devices.

BACKGROUND

In order to increase a coverage area for wireless communication, it is envisioned to use coverage enhancing devices (CED), particularly re-configurable relaying devices (RRD), more particularly, re-configurable reflective devices. Re-configurable reflective devices are sometimes also referred to as reflecting large intelligent surface (LIS). See, e.g., Sha Hu, Fredrik Rusek, and Ove Edfors. "Beyond massive MIMO: The potential of data transmission with large intelligent surfaces." IEEE Transactions on Signal Processing 66.10 (2018): 2746-2758.

An RRD can be implemented by an array of antennas that can reflect incident electromagnetic waves/signals. The array of antennas can be semi-passive. Semipassive can correspond to a scenario in which the antennas can impose a variable phase shift and typically provide no signal amplification. An input spatial direction from which incident signals on a radio channel are accepted and an output spatial direction into which the incident signals are reflected can be re-configured, by changing a phase relationship between the antennas. Radio channel may refer to a radio channel specified by the 3GPP standard. In particular, the radio channel may refer to a physical radio channel. The radio channel may offer several time/frequency-resources for communication between different communication nodes of a communication system.

An access node (AN) may transmit signals to a wireless communication device (UE) via a CED. The CED may receive the incident signals from an input spatial direction and emit the incident signals in an output spatial direction to the UE. The AN may transmit the signals using a beam directed to the CED. In some scenarios, several CEDs may be used in parallel to transmit the signals from the AN to the UE. For example, a signal may be transmitted from the AN to the UE via a first propagation path and a second propagation path, wherein the first propagation path involves a reception and transmission of the signal by a first CED, and wherein the second propagation path involves a reception and transmission of the signal by a second CED. In case of different propagation path lengths of the first propagation path and the second propagation path, the signal portions propagating via the first propagation path and the second propagation path may not necessarily interfere constructively and the improved coverage associated with the combined surfaces of the first CED and the second CED may not be obtained to the full extent. In particular, there may be at least some phase incoherence between the respective signal portions.

SUMMARY

Accordingly, there may be a need for further improving communication between nodes using coverage enhancing devices.

Said need is addressed with the subject matter of the independent claims. The dependent claims describe further advantageous examples.

According to a first aspect, examples provide a method of operating a first communication node (CN) wherein the first CN is configured for controlling a first coverage enhancing device (CED), wherein the first CED is reconfigurable to provide multiple spatial filterings, each one of the multiple spatial filterings being associated with a respective input spatial direction from which incident signals on a radio channel are accepted and with a respective output spatial direction into which the incident signals are transmitted by the first CED, wherein the first CED is configurable for applying a first delay to the incident signals. The first CN is also configured for controlling a second CED, wherein the second CED is reconfigurable to provide multiple spatial filterings, each one of the multiple spatial filterings being associated with a respective input spatial direction from which incident signals on the radio channel are accepted and with a respective output spatial direction into which the incident signals are transmitted by the second CED, wherein the second CED is configurable for applying a second delay to the incident signals. The method comprises providing, to the first CED, a message indicative of the first delay which is to be applied to the incident signals, providing, to the second CED, a message indicative of the second delay which is to be applied to the incident signals. A difference between the first delay and the second delay is larger than a sampling period of the first CN and/or a sampling period of a second CN communicating with the first CN via the first CED and the second CED.

According to a second aspect, examples provide a method of operating a second communication node (CN), wherein the second CN is configured for communicating with a first CN via a first coverage enhancing device (CED), wherein the first CED is reconfigurable to provide multiple spatial filterings, each one of the multiple spatial filterings being associated with a respective input spatial direction from which incident signals on a radio channel are accepted and with a respective output spatial direction into which the incident signals are transmitted by the first CED, wherein the first CED is configurable for applying a first delay to the incident signals. The second CN is also configured for communication with the first CN via a second CED, wherein the second CED is reconfigurable to provide multiple spatial filterings, each one of the multiple spatial filterings being associated with a respective input spatial direction from which incident signals on the radio channel are accepted and with a respective output spatial direction into which the incident signals are transmitted by the second CED, wherein the second CED is configurable for applying a second delay to the incident signals. The method comprises transmitting, to the first CN on the radio channel, a reference signal via a first propagation path and a second propagation path, wherein receiving the reference signal via the first propagation path comprises receiving, via the first CED, a first delayed component of the reference signal, wherein receiving the reference signal via the second propagation path comprises receiving, via the second CED, a second delayed component of the reference signal.

According to a third aspect, examples provide a method of operating a coverage enhancing device, wherein the CED is reconfigurable to provide multiple spatial filterings, each one of the multiple spatial filterings being associated with a respective input spatial direction from which incident signals on a radio channel are accepted and with a respective output spatial direction into which the incident signals are transmitted by the CED, wherein the CED is configurable for applying a first delay to the incident signals, wherein the method comprises obtaining, from a first communication node a message indicative of the first delay which is to be applied to the incident signals.

Further aspects provide a first communication node, a second communication node and a coverage enhancing device each comprising control circuitry configured for performing the respective aforementioned method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a communication system according to various examples. FIG. 2 schematically illustrates details of the communication system according to the example of FIG. 1 .

FIG. 3 schematically illustrates multiple downlink transmit beams used at a transmitter node of the communication system and further schematically illustrates a CED towards which one of the multiple transmit beams is directed according to various examples.

FIG. 4 schematically illustrates details with respect to a CED.

FIG. 5 schematically illustrates a scenario for using CEDs.

FIG. 6 schematically illustrates a scenario for using CEDs

FIG 7 illustrates examples of spectral efficiencies for communication via CEDs

FIG. 8 illustrates examples of spectral efficiencies for communication via CEDs

FIG. 9 illustrates signaling for communication via CEDs;

FIG. 10 illustrates signaling for communication via CEDs.

DETAILED DESCRIPTION

Some examples of the present disclosure generally provide for 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 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. A wireless communication system includes a transmitter node and one or more receiver nodes. 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 (3GPP)-specified cellular network (NW). In such case, the transmitter node can be implemented by an access node (AN), in particular a base station (BS), of the RAN, and the one or more receiver nodes can be implemented by terminals (also referred to as user equipment, UE). It would also be possible that the transmitter node is implemented by a UE and the one or more receiver nodes are implemented by a AN and/or further UEs. Hereinafter, for the sake of simplicity, various examples will be described with respect to an example implementation of the transmitter node by a AN and the one or more receiver node by UEs - 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.

Communication via CEDs

According to various examples, the transmitter node can communicate with at least one of the receiver nodes via one or more CEDs.

The CED may include an antenna array. The CEDs may include a meta-material surface. In examples, the CEDs may include a reflective antenna array (RAA). There are many schools-of-thought for how CEDs should be integrated into 3GPP- standardized RANs.

In an exemplary case, the NW operator has deployed the CEDs and is, therefore, in full control of the CED operations. The UEs, on the other hand, may not be aware of the presence of any CED, at least initially, i.e. , it is transparent to a UE whether it communicates directly with the AN or via the CEDs. The CEDs essentially function as a coverage-extender of the AN. The AN may have established control links with the CEDs.

According to another exemplary case, it might be a private user or some public entity that deploys the CEDs. Further, it may be that the UE, in this case, controls CED operations. The AN, on the other hand, may not be aware of the presence of any CED and, moreover, may not have control over it/them whatsoever. The UE may gain awareness of the presence of a CED by means of some short-range radio technology, such as Bluetooth, wherein Bluetooth may refer to a standard according to IEEE 802.15, or WiFi, wherein WiFi may refer to a standard according to IEEE 802.11 , by virtue of which it may establish the control link with the CED. It is also possible that the UE gains awareness of the presence of a CED using UWD (Ultra wideband) communication. Using UWB may offer better time resolution due to the wider bandwidth compared to other radio technologies. The two exemplary cases described above are summarized in TAB. 1 below.

TAB. 1 : Scenarios for CED integration into cellular NW hereinafter, techniques will be described which facilitate communication between a transmitter node - e.g., an AN - and one or more receiver nodes - e.g., one or more UEs - using a CED. FIG. 1 schematically illustrates a communication system 100. The communication system 100 includes two nodes 110, 120 that are configured to communicate with each other via a radio channel 150. In the example of FIG. 1 , the node 120 is implemented by an access node (AN) and the node 110 is implemented by a UE. The AN 120 can be part of a cellular NW (not shown in FIG.1 ).

As a general rule, the techniques described herein could be used for various types of communication systems, e.g., also for peer-to-peer communication, etc. For the sake of simplicity, however, hereinafter, various techniques will be described in the context of a communication system that is implemented by an AN 120 of a cellular NW and a UE 110.

As illustrated in FIG. 1 , there can be DL communication, as well as UL communication. Examples described herein particularly focus on the DL communication, but similar techniques may be applied to UL communication and/or sidelink communication. Input sweep and receive beam sweep may relate to DL communication and output sweep and transmit beam sweep may relate to UL communication.

FIG. 2 illustrates details with respect to the AN 220. The AN 220 includes control circuitry that is implemented by a processor 221 and a non-volatile memory 222. The processor 221 can load program code that is stored in the memory 222. The processor 221 can then execute the program code. Executing the program code causes the processor to perform techniques as described herein.

Moreover, FIG. 2 illustrates details with respect to the UE 210. The UE 210 includes control circuitry that is implemented by a processor 211 and a non-volatile memory 212. The processor 211 can load program code that is stored in the memory 212. The processor can execute the program code. Executing the program code causes the processor to perform techniques as described herein.

Further, FIG. 2 illustrates details with respect to communication between the AN 220 and the UE 210 on the radio channel 250. The AN 220 includes an interface 223 that can access and control multiple antennas 224. Likewise, the UE 210 includes an interface 213 that can access and control multiple antennas 214.

The UE 210 comprises a further interface 215 that can access and control at least one antenna 216 to transmit or receive a signal on an auxiliary radio channel different from the radio channel 250. Likewise, the AN 220 may comprise an additional interface 225 that can access and control at least one antenna 226 to transmit or receive a signal on the or a further auxiliary radio channel different from the radio channel. In general, the interface 225 may also be a wired interface. It may also be possible that the interface 225 is a wired or wireless optical interface. If wireless, the auxiliary radio channel may use in-band signaling or out-of-band signaling. The radio channel and the auxiliary radio channel may be offset in frequency. The auxiliary radio channel may be at least one of a Bluetooth radio channel, a WiFi channel, or an ultra-wideband radio channel. Methods for determining an angle of arrival may be provided by a communication protocol associated with the auxiliary radio channel. For example, methods for determining an angle of arrival may be provided by a Bluetooth radio channel.

While the scenario of FIG. 2 illustrates the antennas 224, 226 being coupled to the AN 220, as a general rule, it would be possible to employ transmit-receive points (TRPs) that are spaced apart from the AN 220.

The interfaces 213, 223 can each include one or more TX chains and one or more receiver chains. For instance, such RX 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 214, 224. Thereby, the AN 220 and the UE 210 can selectively transmit on multiple TX beams (beamforming), to thereby direct energy into distinct spatial directions.

By using a TX beam, the direction of the wavefront of signals transmitted by a transmitter of the communication system 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 214, 224. Energy may also be focused to a specific point (or small sphere) at a specific direction and a specific distance of the transmitter Thereby, a spatial data stream may be directed in multiple spatial directions and/or multiple specific points. 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.

As a general rule, alternatively or additionally to such TX beams, it is possible to employ receive (RX) beams. FIG. 3 illustrates DL TX beams 301-306 used by the AN 320. Here, the AN 320 activates the beams 301-306 on different resources (e.g., different time-frequency resources, and/or using orthogonal codes/precoding) such that the UE 310 can monitor for respective signals transmitted on the DL TX beams 301-306.

It is possible that the AN 320 transmits signals to the UE 310 via a CED 330. In the scenario of FIG. 3, the downlink transmit beam 304 is directed towards the CED 330. Thus, whenever the AN 320 transmits signals to the UE 310 using the downlink transmit beam 304 - e.g., a respective block of a burst transmission -, a spatial filter is provided by the CED 330. The spatial filter is associated with a respective spatial direction into which the incident signals are then selectively reflected by the CED 330. Details with respect to the CED 330 are illustrated in connection with FIG. 4.

FIG. 4 illustrates aspects in connection with the CED 430. The CED 430 includes a phased array of antennas 434 that impose a configurable phase shift when reflecting incident signals. This defines respective spatial filters that may be associated with spatial directions into which the incident signals are reflected. The antennas 434 can be passive or semi-passive elements. The CED 430 thus provides coverage extension by reflection of radio-frequency (RF) signals. A translation to the baseband may not be required. This is different to, e.g., decode-and-forward repeater or regenerate functionality. The antennas 434 may induce an amplitude shift by attenuation. In some examples, the antennas 434 may provide forward amplification with or without translation of signals transmitted on the radio channel to the base band. In some examples, the CEDs may be configurable to shift power from one polarization to the orthogonal polarization. The antennas 434 may amplify and forward the signals.

The CED 430 includes an antenna interface 433 which controls an array of antennas 434; a processor 431 can activate respective spatial filters one after another. The CED 430 further includes an interface 436 for receiving and/or transmitting signals on an auxiliary radio channel 460. There is a memory 432 and the processor 431 can load program code from the non-volatile memory and execute the program code. Executing the program code causes the processor to perform techniques as described herein.

FIG. 4 is only one example implementation of a CED. Other implementations are conceivable. For example, a meta-material surface not including distinct antenna elements may be used. The meta-material can have a configurable refraction index. To provide a re-configurable refraction index, the meta-material may be made of repetitive tunable structures that have extensions smaller than the wavelength of the incident RF signals.

Transmitting signals on a radio channel via two or more coverage enhancing devices (CEDs)

FIG. 5 illustrates an exemplary scenario B as described hereinbefore with reference to TAB. 1 . A UE 510 is to communicate with an AN 520 over a radio channel via a first propagation path 591 . The radio channel may be a 5G NR channel, in particular, a 5G NR channel in Frequency Range 2 or beyond. It is also conceivable that the radio channel is a 3GPP channel belonging to the frequency range from 7 to 24 GFIz. An obstacle 540 between the UE 510 and the AN 520 may impede a direct line-of-sight communication between the UE 510 and the AN 520 on the radio channel.

A CED 531 may be employed to provide a physical propagation path 591 for the communication over the radio channel. In some examples, the position and orientation of the CED 531 with respect to the AN 520 may be fixed and known to the CED 531 . As described hereinbefore, the CED 531 may be semi-passive and free of circuitry for encoding and decoding signals transmitted over the radio channel.

The CED 531 may provide multiple spatial filters, wherein each one of the multiple spatial filters is associated with a respective input spatial direction from which incident signals on a radio channel are accepted and with a respective output spatial direction into which the incident signals are reflected by the CED.

The CED 531 may perform an output sweep comprising changing the output spatial direction while using the given input spatial direction. In particular, the output sweep may be performed over signals transmitted by the AN 520. For example, the CED 531 can toggle through different output spatial directions by changing the phase relationships between the antenna elements.

The AN may send reference signals at certain times to the CED which emits the reference signals in different output spatial directions. During the beam sweep, the incident signals accepted by the CED are typically not emitted in an output spatial direction to the UE. In case the UE receives the reference signal, the reception properties determined by the UE may be used to re-configure the CED.

A further CED 532 may be employed to provide an additional (second) physical propagation path 592 for the communication over the radio channel. Both the first CED 531 and the second CED 532 may be controlled by the UE 510 via signaling 581 and 582, respectively.

In case of different propagation path lengths of the first propagation path and the second propagation path, the signal portions propagating via the first propagation path 591 and the second propagation path 592 may not necessarily interfere constructively and the improved coverage associated with the combined surfaces of the first CED 531 and the second CED 532 may not be obtained to the full extent. There may be at least some phase incoherence between the signal portions. FIG. 5 is an example of first communication node, CN, controlling the CEDs, wherein the first CN is receiving signals on the radio channel transmitted by a second communication node via the first propagation path and the second propagation path. In the example, the first CN is implemented by a UE and the second CN by an AN. However, it is also possible that the first CN is implemented by an AN and the second CN by a UE. In some scenarios, even both the first CN and the second CN may be implemented by UEs.

FIG. 6 illustrates an exemplary scenario A as described hereinbefore with reference to TAB. 1. An AN 610 is to communicate with a UE 620 over a radio channel via a first propagation path 691 . The radio channel may be a 5G NR channel, in particular, a 5G NR channel in Frequency Range 2 or beyond. It is also conceivable that the radio channel is a 3GPP channel belonging to the frequency range from 7 to 24 GHz. An obstacle 640 between the UE 620 and the AN 610 may impede a direct line-of-sight communication between the UE 620 and the AN 610 over the radio channel.

A first CED 631 may be employed to provide a physical propagation path 691 for the communication over the radio channel. In some examples, the position and orientation of the first CED 631 with respect to the AN 610 may be fixed and known to the first CED 631 . As described hereinbefore, the CED 631 may be semi-passive and free of circuitry for encoding and decoding signals transmitted over the radio channel.

The CED 631 may provide multiple spatial filters, wherein each one of the multiple spatial filters is associated with a respective input spatial direction from which incident signals on a radio channel are accepted and with a respective output spatial direction into which the incident signals are reflected by the first CED 631.

The CED 631 may perform an output sweep comprising changing the output spatial direction while using the given input spatial direction. In particular, the output sweep may be performed over signals transmitted by the AN 610. For example, the CED 631 can toggle through different output spatial directions by changing the phase relationships between the antenna elements.

The AN may send reference signals at certain times to the CED which emits the reference signals in different output spatial directions. During the beam sweep, the incident signals accepted by the CED are typically not emitted in an output spatial direction toward the UE. In case the UE receives the reference signal, the reception properties determined by the UE may be fed back to the AN and used to re-configure the CED.

A further CED 632 may be employed to provide an additional (second) physical propagation path 692 for the communication over the radio channel. Both the first CED 631 and the second CED 632 may be controlled by the AN 610 via signaling 681 and 682, respectively.

In case of different propagation path lengths of the first propagation path and the second propagation path, the signal portions propagating via the first propagation path 691 and the second propagation path 692 may not necessarily interfere constructively and the improved coverage associated with the combined surfaces of the first CED 631 and the second CED 632 may not be obtained to the full extent. There may be at least some phase incoherence between the signal portions. FIG. 6 is an example of first communication node, CN, controlling the CEDs, wherein the first CN is transmitting signals on the radio channel transmitted by a second communication node via the first propagation path and the second propagation path. In the example, the first CN is implemented by an AN and the second CN by a UE. However, it is also possible that the first CN is implemented by a UE and the second CN by an AN. In some scenarios, even both the first CN and the second CN may be implemented by UEs.

Applying delays to improve communication over two or more CEDs

In an exemplary scenario, without loss of generality, a single UE with a single antenna port is to receive a signal from an AN over a radio channel via CEDs.

In a given resource element (RE) of the radio channel, the data value x is to be communicated by the AN. The AN uses beamforming across its antennas and transmits the vector cx; the dimension of said vector equals the number of antennas at the AN. The radio channel between the AN and the n-th CED can be represented with the matrix G_n, which has dimensions that reflect the number of antennas at the AN (number of columns) and the CED (number of rows). Accordingly, the received signal at the n-th CED may be described by

The n-th CED may apply spatial filtering, wherein each spatial filtering is associated with a respective input spatial direction from which incident signals on a radio channel are accepted (i.e. , receive- beamforming) and with a respective output spatial direction into which the incident signals are transmitted by the CED (i.e., transmit- beamforming).

The spatial filterings may be represented as diagonal matrices, whose dimensions are commensurate with the number of antennas at the CEDs. Thus, the transmitted signal from the n-th CED may read

where diag(·) puts its argument along the main diagonal of an all-zero square matrix, and the p variables are row-vectors.

Assuming that the channel between the n-th CED to the UE’s antenna port (i.e., including the UE’s beamforming) as a row vector h_n, y at the UE becomes

Under ideal circumstances (line-of-sight (LOS) between the AN and the CEDs, no multipath reflections, and ideal beamforming at both AN and CEDs) the beamforming at the AN together with the receive-beamforming diag(p_{rx n})G_nc may be represented by

where b represents the overall path loss. Thus, y becomes y = h_n diag(p_{tx n})diag(p_{rx, n})G_ncx = h_n diag(p_{tx n} ) β1x = h_n p^T _{tx n} βx

Now, absorbing β into, e.g., h_n, removing the subscript “tx” from the transmit- beamforming, re-defining p as its complex conjugate, and taking a sum across all CEDs, leads to

In non-ideal circumstances, i.e. , non-ideal beamforming at the AN and non-ideal receive-beamforming at the CED, diag(p_{rx n})G_nc may be represented by

with some arbitrary vector e. Then, y becomes

Absorbing diag(e^T ) into h_n, i.e., re-defining h_n as h_n := h_n diag(e^T), removing the subscript “tx” from the transmit-beamforming, re-defining p as its complex conjugate, and take a sum across all CEDs, y may still be represented as y

Thus, h_n may not strictly represent the channel between the UE and the CEDs, but rather an equivalent channel between the UE and the CEDs, in the sense that with such interpretation, the AN can be omitted from the mathematical exposition.

Thus, without loss of generality, in the exemplary scenario, in which a single UE with a single antenna port is to receive a signal from an AN over a radio channel via N CEDs, in a given resource element (RE) of the radio channel, the value x may be received by the n-th CED from the AN and may be forwarded by the n-th CED to the UE.

The UE may then receive the following value y in the respective RE:

In the formula h_n is the (equivalent) channel vector between the n-th CED and the UE, p_n is a beamforming vector at the n-th CED, H means Hermitian transposition (conjugation and transposition), and w is a term relating to noise. The beamforming vector p_n describes the spatial filtering performed by the respective CED.

Coherent CED transmission may refer to a scenario with vectors p_n selected in such a way that the signal portions transmitted via the n CEDs interfere constructively at the UE. Using the expression

the requirement of constructive interference implies that all n CEDs should be configured to obtain

such that y becomes

The ensuing signal-to-noise ratio (SNR) then becomes proportional to

For a non-coherent CED transmission, on the other hand, y remains

with an SNR proportional to

This SNR may be several orders of magnitude smaller than the SNR for coherent transmission.

In practice, the channel vectors h_n between the CEDs and the UE are not known but can only be estimated. However, even in the absence of noise during channel estimation, the estimated channel vectors

will never coincide with the true channel vector h_n.

For example, it may prove to be difficult to perfectly synchronize reference oscillation clocks used for estimating the channel vectors. Hence, the estimated channel vectors

is a phase offset that originates from the phase offset of the reference clocks used during estimation of the channel vectors.

Thus, even if the beamforming vectors p_n are selected to obtain

the signal y at the UE will become

which may result in a SNR/performance similar to the SNR/performance in the case of non-coherent CED transmission performance.

Accordingly, there may be a need for improving transmission performance in networks using several CEDs.

In examples, the n-th CED may introduce a time delay of (n - 1)Δ, wherein the value of Δ is larger than a sampling period, in particular a multiple of the sampling period. The sampling period may be the inverse of the bandwidth used for transmission on the radio channel. More specifically, of OFDM the sampling period may correspond to 1/FC with the sub-carrier spacing F and the number of carriers . In other words, the sampling period may correspond to the minimum time a receiver of the transmission on the radio channel can resolve. Furthermore, the time delay (n - 1)Δ may fulfil the inequality (N - 1)Δ < T_cp, wherein T_cp may correspond to the duration of the cyclic prefix. Such a small time delay < T_cp may already allow for significantly improving transmission performance in networks using several CEDs. The received analog signal y(t) at the UE then becomes

wherein * is the convolution operator and

is an equivalent impulse response.

After suitable receiver processing to obtain a discrete-time model at inverse baud-rate sample-spacing at the UE, the signal becomes y = h * s + w with the equivalent impulse response h.

Assuming for clarity that Δ corresponds to exactly one sample spacing, it immediately follows that the equivalent impulse response may be written as follows:

The same result would also emerge for Δ not corresponding to exactly one sample spacing. The signal s(t) transmitted from the AN to the UE may be an OFDM signal and reference signal (RS) may be inserted into a single OFDM symbol in order to estimate h.

Summarizing, by introducing the delays, the channels between the CEDs and the UE are transformed into an inter-symbol interference channel. The duration of the so created impulse response is controlled to not exceed the duration of the cyclic prefix. By standard channel estimation, the impulse response can be found at the UE, and the taps of the impulse response correspond to the phase shifts at the CEDs that would need to be compensated to achieve coherent CED transmission.

In examples, the CEDs may use cyclic delay diversity (CDD) to introduce the delays mentioned hereinbefore. In other examples, the CEDs may also use true delay diversity

In examples, the UE may feed the values g_n exp(iθ_n) obtained by estimating h back to the CEDs. The CEDs may apply respective compensation phase shifts and remove the delay (n - 1)Δ From this point onwards, the CEDs may operate coherently.

In some examples, feedback from the UE to the CEDs may not be possible, for example, in pure broadcast situations. The delays (n - 1)Δ may nevertheless improve performance.

A first channel h_A emerging when the CEDs introduce delays

may be compared with a second channel h₀ emerging when there are no delays

The average capacity for the two channels may be roughly the same. However, the capacity for the first channel h_Δ may display less randomness (i.e. fading) than the capacity for the second channel h₀ as illustrated by the diagrams of Figs. 7 and 8 derived from numerical examples.

Fig. 7 illustrates a numerical example of the spectral efficiency SE in bits per Hertz of a radio channel between a first CN and a second CN over a number N of CEDs. In this simple example, the gain g_n per CED after application of the spatial filtering (i.e., beamforming) is set to unity for all CEDs g_n = g = 1. This may approximately correspond to a scenario of collocated CEDs. The noise variance of w is selected to be 0.1.

In the case of coherent CED transmission (curve 701), the capacity of the radio channel between the first CN and the second CN is deterministic since g_n = g = 1. However, for non-coherent CED transmission, the capacity of the radio channel between the first CN and the second CN is not deterministic. Thus, the spectral efficiency 702 for the ergodic rate, i.e. the mean spectral efficiency, and the spectral efficiency 703 for the 10%-outage rate are shown in Fig. 7. As can be seen, coherent CED transmission 701 grossly outperforms non-coherent CEDs transmission 702. Moreover, curve 703 shows that non-coherent CED transmission displays a rich randomness.

Fig. 8 additionally depicts the spectral efficiency 802 for the ergodic rate, i.e. the mean spectral efficiency, after applying the delays at the CEDs and the spectral efficiency 803 for the 10%-outage rate after applying the delays at the CEDs. It may be observed that the mean capacity does not improve with the delays, but that the capacity is significantly more deterministic.

Flence, nothing more than applying delays at the CEDs and then treating the resulting channel as an inter-symbol interference channel at the UE side may already result in performance gains.

Generally, the optimal delays may depend on the UE position. Control signaling, where a UE requests a CED to change the delay can be implemented. In examples, the CED may select a new delay from a list, or randomly select one.

Fig. 9 is a signaling diagram illustrating a method for communicating in a network comprising a first CN 510, a first CED 531 , a second CED 532, and a second CN 520, wherein optional signaling is indicated with dashed lines. As indicated above, the first CN 510 may be implemented by a UE and the second CN 520 by an AN or vice versa. The first CN 510 is configured for controlling the first CED 531 and the second CED 532. The first CED 531 and the second CED 532 are reconfigurable to provide multiple spatial filterings, each one of the multiple spatial filterings being associated with a respective input spatial direction from which incident signals on a radio channel are accepted and with a respective output spatial direction into which the incident signals are transmitted by the first CED 510 and the second CED 520, respectively. The first CED 531 is configurable for applying a first delay to the incident signals and the second CED 532 is configurable for applying a second delay to the incident signals.

Optionally, the first CN 510 may obtain, from the first CED 531 , a message 911 indicative of a capability of the first CED 531 to apply a first delay to incident signals. Likewise, the second CED 532 may provide, to the first CN 510, a message 912 indicative of a capability of the second CED 532 to apply a second delay to incident signals. The messages 911 , 912 may indicate whether the respective CED 531 , 532 is capable of applying a delay at all. In examples, the messages 911 , 912 may be indicative of which delays the respective CED 531 , 532 may apply. For example, the CED 531 may be capable of applying one of i different delays and the CED 532 may be capable of applying one of j different delays.

The first delay and/or the second delay may correspond to a rational multiple of a clock period of the radio channel. For example, the first CED 531 and/or the second CED 532 may be synchronized to the network. Synchronization to the network may correspond to the CEDs 531 , 532 being aware of a clock period of the radio channel.

Typically, the first CED 531 and the second CED 532 are positioned relatively close to each other (e.g. forming part of a larger group of CEDs working together) such that without an application of additional delays by the first CED 531 and the second CED 532, a difference in propagation time from signals transmitted by the second CN 520 via a first propagation path involving a reception and transmission by the first CED 531 and via a second propagation path involving a reception and transmission by the second CED 532 cannot be resolved by the first CN 510.

The first CN 510 provides, to the first CED 531 , a message 921 indicative of the first delay which is to be applied to the incident signals. Likewise, the second CED 532 obtains, from the first CN 510, a message 922 indicative of the second delay which is to be applied to the incident signals.

The difference between the first delay and the second delay is larger than a sampling period of the first CN 510. In examples, the difference may be an integer multiple of the sampling period of the first CN 510. In particular, the difference may be selected to avoid time alignment of signal components received by the first CN 510 via the first propagation path and the second propagation path. In OFDM systems, the sampling period may correspond to the symbol period divided by the number of sub-carriers in the waveform. The sampling period may commensurate with the inverse of the system bandwidth. Typically, the sampling period of the first CN 510 and the sampling period of the second CN 520 may be equal. In some examples, the sampling period of the first CN 510 and the sampling period of the second CN 520 may be different. For example, the first CN 510 may transmit signals using additional sub-carriers for, e.g., multi-cast, or a third CN, which the second CN 520 does not receive.

In examples, the providing of the messages 921 and 922 is triggered by an indication that a received relative signal power is below a predefined threshold. For example, the first CN 510 and the second CN 520 may have already established communication with each other on the radio channel. Then, the first CN 510 and the second CN 520 may determine that a received relative signal power decreases, for example, due to a change in a relative position of one of the first CN 510, the first CED 531 , the second CED 532, and the second CN 520. Accordingly, messages 921 and 922 may only be transmitted when required. Thus, resources for transmitting the messages 921 and 922 may be conserved for different purposes.

The second CN 520 may obtain, from the first CN 510, a message 930 triggering the second CN 520 to transmit a reference signal 940. In other examples, the second CN 520 may transmit reference signals 940 without a specific message 930. For example, reference signals 940 transmitted in regular intervals may be used for the optional methods described herein.

The first CN 510 may receive, from the second CN 520 on the radio channel, the reference signal 940 via a first propagation path 941 and a second propagation path 942. The receiving the reference signal 940 via the first propagation path 941 comprises receiving, via the first CED 531 , a first delayed component of the reference signal 940. Likewise, the receiving the reference signal 940 via the second propagation path 942 comprises receiving, via the second CED 532, a second delayed component of the reference signal 940.

The first delayed component and the second delayed component of the reference signal 940 will interfere at the first CED 510. The first CN 510 may determine a reception property of the reference signal 940. As explained above, the reception property of the reference signal may be used to determine at least one of a first phase shift induced by the first propagation path 941 and a second phase shift induced by the second propagation path 942. The reception property of the reference signal may be used to determine a phase difference between a first phase shift induced by the first propagation path 941 and a second phase shift induced by the second propagation path 942. The phase shifts may refer to the phase shifts induced in the propagation paths in absence of delays induced by the CEDs.

The first CN 510 may provide, to the first CED 531 , a message 951 for reconfiguring the first CED 531 to induce a first compensation phase shift for compensating for the first phase shift. Likewise, the second CED 532 may obtain, from the first CN 510, a message 952 for reconfiguring the second CED 532 to induce a second compensation phase shift for compensating for the second phase shift. In examples (not shown), the first CN 510 may provide, to the second CN 520, a message indicative of the reception property of the reference signal 940. The second CN 520 may then determine the phase shifts and/or compensation phase shifts and provide, to the first CN 510, a message indicative of the phase shifts and/or compensation phase shifts. If the first CN 510 determines the phase shifts and/or compensation phase shifts, less signaling may be required. Letting the second CN 520 determine the phase shifts and/or compensation phase shifts, may have the advantage that less computational resources have to be provided by the first CN 510. Thus, power consumption of the first CN 510 may be reduced. For example, the first CN 510 may be a mobile device being powered by a battery. A reduced power consumption may thus increase battery lifetime.

The first CN 510 may provide, to the first CED 531 , a message 961 for reconfiguring the first CED 531 to stop applying the first delay and, to the second CED 532, a message 962 for reconfiguring the first CED 532 to stop applying the second delay. In Fig. 9, separate messages 951 , 961 for indicating the first compensation phase shift and stopping the application of the first delay have been shown, instead a single message may be used. Likewise, the messages 952, 962 may be replaced by a single message.

Afterwards, the first CN 510 may perform receiving and/or transmitting payload data 970 from and/or to the second CN 520. Thus, receiving and/or transmitting payload data 970 from and/or to the second CN 520 may be performed with coherent CED transmission leading to an improved signal-to-noise ratio and/or an increased channel capacity.

In examples, the determination of the receiving of the reference signal 940, the providing of the messages 951 , 952, 961 , 962 and the related method steps may be omitted. Thus, receiving and/or transmitting payload data 970 may take place directly after the application of the first delay and the second delay. As explained above, said approach may, compared to an exchange of payload data without the application of delays, lead to a channel capacity between the first CN 510 and the second CN 520 displaying less randomness.

The signaling diagram has been used with respect to communication in a network comprising a first CED 531 and a second CED 532. However, as explained above the network may comprise more than two CEDs. Similar signaling may be used to improve communication between the first CN and the second CN via the more than two CEDs.

Fig. 10 is a signaling diagram illustrating a method for communicating in a network comprising a first CN 610, a first CED 631 , a second CED 632, and a second CN 620, wherein optional signaling is indicated with dashed lines. The first CN 610 is configured for controlling the first CED 631 and the second 632. In both Figs. 9 and 10, the reference signals are transmitted from right to left. In Fig. 10, in contrast to the signaling diagram of Fig. 9, the communication node controlling the CEDs, i.e., the first CN 610, may transmit the reference signal 1040 as explained more in detail below. The first CN 610 may be implemented by an AN and the second CN 620 may be implemented by a UE or vice versa. It may also be possible that both the first CN 610 and the second CN 620 are implemented as UEs.

The first CED 631 and the second CED 632 are reconfigurable to provide multiple spatial filterings, each one of the multiple spatial filterings being associated with a respective input spatial direction from which incident signals on a radio channel are accepted and with a respective output spatial direction into which the incident signals are transmitted by the first CED 610 and the second CED 620, respectively. The first CED 631 is configurable for applying a first delay to the incident signals and the second CED 632 is configurable for applying a second delay to the incident signals.

Optionally, the first CN 610 may obtain, from the first CED 631 , a message 1011 indicative of a capability of the first CED 610 to apply a first delay to incident signals. Likewise, the second CED 632 may provide, to the first CN 610, a message 1012 indicative of a capability of the second CED 632 to apply a second delay to incident signals. The messages 1011 , 1012 may indicate whether the respective CED 631 , 632 is capable of applying a delay at all. In examples, the messages 1011 , 1012 may be indicative which delays the respective CED 631 , 632 may apply. For example, the 631 may be capable of applying one of i different delays and the CED 632 may be capable of applying one of j different delays.

The first delay and/or the second delay may correspond to a rational multiple of a clock period of the radio channel. For example, the first CED 631 and/or the second CED 632 may be synchronized to the network. Synchronization to the network may correspond to the CEDs 631 ,632 being aware of a clock period of the radio channel. In most cases, the first CED 631 and the second CED 632 may be assumed to be collocated. Thus, without an application of additional delays by the first CED 631 and the second CED 632, a difference in propagation time from signals transmitted by the first CN 610 via a first propagation path involving a reception and transmission by the first CED 631 and via a second propagation path involving a reception and transmission by the second CED 632 cannot be resolved by the second CN 620.

The first CN 610 provides, to the first CED 631 , a message 1021 indicative of the first delay which is to be applied to the incident signals. Likewise, the second CED 632 obtains, from the first CN 610, a message 1022 indicative of the second delay which is to be applied to the incident signals.

The difference between the first delay and the second delay is larger than a sampling period of the second CN 620. For example, the difference may be an integer multiple of the sampling period of the second CN 620. In particular, the difference may be selected to avoid time alignment of signal components received by the second CN 620 via the first propagation path and the second propagation path. In OFDM systems, the sampling period may correspond to the symbol period divided by the number of sub carriers in the waveform. The sampling period may commensurate with the inverse of the system bandwidth. Typically, the sampling period of the first CN 610 and the sampling period of the second CN 620 may be equal. In some examples, the sampling period of the first CN 610 and the sampling period of the second CN 620 may be different.

Sometimes, the providing of the messages 1021 and 1022 may be triggered by an indication that a received signal power is below a predefined threshold. For example, the first CN 610 and the second CN 620 may have already established communication with each other on the radio channel. Then, the first CN 610 and the second CN 620 may determine that a received relative signal power decreases, for example, due to a change in a relative position of one of the first CN 610, the first CED 631 , the second CED 632, and the second CN 620. As messages 1021 and 1022 may only be transmitted when required, resources for transmitting the messages 1021 and 1022 may be conserved for different purposes.

The second CN 620 may obtain, from the first CN 610, a message 1030 triggering the second CN 620 to determine a reception property of a reference signal 1040. In other examples, the second CN 620 may determine reception properties of reference signals on a regular basis.

The second CN 620 may receive, from the first CN 610 on the radio channel, the reference signal 1040 via a first propagation path 1041 and a second propagation path 1042. The receiving the reference signal 1040 via the first propagation path 1041 comprises receiving, via the first CED 631 , a first delayed component of the reference signal 1040. Likewise, the receiving the reference signal 1040 via the second propagation path 1042 comprises receiving, via the second CED 632, a second delayed component of the reference signal 1040.

The first delayed component and the second delayed component of the reference signal 1040 will both be received by the second CED 620. The second CN 620 may determine a reception property of the reference signal 1040.

The second CN 620 may provide a message 1050 indicative of the reception property of the reference signal 1040 to the first CN 610. Using a method explained above, the first CN 610 may then determine at least one of a first phase shift induced by the first propagation path 1041 and a second phase shift induced by the second propagation path 1042. The reception property of the reference signal may be used to determine a phase difference between a first phase shift induced by the first propagation path 1041 and a second phase shift induced by the second propagation path 1042. The phase shifts may refer to the phase shifts induced in the propagation paths in absence of delays induced by the CEDs.

The first CN 610 may provide, to the first CED 631 , a message 1061 for reconfiguring the first CED 631 to induce a first compensation phase shift for compensating for the first phase shift. Likewise the second CED 632 may obtain, from the first CN 610, a message 1062 for reconfiguring the second CED 632 to induce a second compensation phase shift for compensating for the second phase shift.

In examples, the second CN 620 may determine the phase shifts and/or compensation phase shifts based on the reception property of the reference signal. In these examples, the message 1050 may then indicate to the first CN 610 the phase shifts and/or compensation phase shifts. Letting the second CN 620 determine the phase shifts and/or compensation phase shifts, may have the advantage that less computational resources have to be provided by the first CN 610. Thus, power consumption of the first CN 610 may be reduced. For example, the first CN 610 may be a mobile device being powered by a battery. A reduced power consumption may thus increase battery lifetime.

The first CN 610 may provide, to the first CED 631 , a message 1071 for reconfiguring the first CED 631 to stop applying the first delay and, to the second CED 632, a message 1072 for reconfiguring the second CED 632 to stop applying the second delay. In Fig. 10, separate messages 1061 , 1071 for indicating the first compensation phase shift and stopping the application of the first delay have been shown, instead a single message may be used. Likewise, the message 1062, 1072 may be replaced by a single message.

Finally, the first CN 610 may perform receiving and/or transmitting payload data 1080 from and/or to the second CN 620 via the first CED 631 and the second CED 632. Thus, receiving and/or transmitting payload data 1080 from and/or to the second CN 620 may be performed with coherent CED transmission leading to an improved signal- to-noise ratio and/or an increased channel capacity.

Alternatively, the determination of the receiving of the reference signal 1040, the providing of the messages 1050, 1061 , 1062, 1071 , 1072 and the related method steps may be omitted. Thus, receiving and/or transmitting payload data 1080 may take place directly after the application of the first delay and the second delay. As explained above, said approach may, compared to an exchange of payload data without the application of delays, lead to a channel capacity between the first CN 610 and the second CN 620 displaying less randomness.

Summarizing, examples have been presented, wherein CEDs apply a delay in scenarios in which the CEDs are not operating coherently in the beginning.

In examples, after applying the delays, a CN estimates the channel using a reference signal from a further CN via the CEDs and sends compensation phase shifts corresponding to each tap of the impulse response determined based on the reference signal to the respective CED. After that, the CEDs remove the delays and the CNs may exchange payload data using coherent CED transmission. One possible form of implementation is to implement the delays at the SRs using cyclic delay diversity (CDD) introduced at each CED.

Possible scheduling/configuration signals of the delays for multiple CEDs have been presented above. For further illustration, above, various scenarios have been described in which the spatial filter provided by the CED is associated with a respective spatial direction into which the incident signals are reflected. It is, as a general rule, possible, that the spatial filter is designed to provide a reflection into a single spatial direction or multiple spatial directions.

For further illustration, well above various scenarios have been described with an implementation of the CED using an antenna array, similar techniques may be readily applied to other kinds and types of surfaces having a re-configurable refractive index.

As explained, CEDs or LIS (large intelligent surface) reflectors are foreseen to be an essential part of mm-wave communication systems to combat large propagation loss and blocking.

Claims

1. A method of operating a first communication node, CN, wherein the first CN is configured for controlling a first coverage enhancing device, CED, and a second CED, wherein the first CED and the second CED are reconfigurable to provide multiple spatial filterings, each one of the multiple spatial filterings being associated with a respective input spatial direction from which incident signals on a radio channel are accepted and with a respective output spatial direction into which the incident signals are transmitted by the first CED and the second CED, respectively, wherein the first CED is configurable for applying a first delay to the incident signals; wherein the second CED is configurable for applying a second delay to the incident signals, wherein the method comprises: providing, to the first CED, a message indicative of the first delay which is to be applied to the incident signals, providing, to the second CED, a message indicative of the second delay which is to be applied to the incident signals, wherein a difference between the first delay and the second delay is larger than a sampling period of the first CN and/or a sampling period of a second CN communicating with the first CN via the first CED and the second CED.

2. The method of operating the first CN of claim 1 , wherein the method comprises, in response to an indication that a received relative signal power is below a predefined threshold, triggering the providing of the message indicative of the first delay and the message indicative of the second delay.

3. The method of operating the first CN of claim 1 or 2, wherein the method comprises receiving and/or transmitting payload data from and/or to the second CN on the radio channel.

4. The method of operating the first CN of claim 1 or 2, wherein the method comprises

- receiving, from a second CN on the radio channel, a reference signal via a first propagation path and a second propagation path, wherein receiving the reference signal via the first propagation path comprises receiving, via the first CED, a first delayed component of the reference signal, wherein receiving the reference signal via the second propagation path comprises receiving, via the second CED, a second delayed component of the reference signal,

- determining a reception property of the reference signal,

- determining, based on the reception property of the reference signal, at least one of a first phase shift induced by the first propagation path and a second phase shift induced by the second propagation path.

5. The method of operating the first CN of claim 4, wherein the method comprises providing, to the first CED, a message for reconfiguring the first CED to induce a first compensation phase shift for compensating the first phase shift.

6. The method of operating the first CN of claim 5, wherein the method comprises providing, to the second CED, a message for reconfiguring the second CED to induce a second compensating phase shift for compensating the second phase shift.

7. The method of operating the first CN of claim 5 or 6, wherein the method comprises providing, to the first CED, a message for reconfiguring the first CED to stop applying the first delay, providing, to the second CED, a message for reconfiguring the second CED to stop applying the second delay, receiving and/or transmitting payload data from and/or to the second CN on the radio channel.

8. The method of operating the first CN of any one of claims 1 to 7, wherein the method further comprises obtaining, from the first CED, a message (911 ) indicative of a capability of the first CED to apply a first delay to the incident signals.

9. The method of operating the first CN of claim 1 , wherein the method comprises

- transmitting, to the second CN on the radio channel, a reference signal via first propagation path and a second propagation path, wherein transmitting via the first propagation path comprises transmitting the reference signal, via the first CED, for applying the first delay, wherein transmitting via the second propagation path comprises transmitting the reference signal, via the second CED, for applying the second delay,

- obtaining, from the second CN, a message indicative of a reception property of the reference signal,

- determining, based on the message indicative of the reception property of the reference signal, a first phase shift induced by the first propagation path and a second phase shift induced by the second propagation path.

10. The method of operating the first CN of claim 9, wherein the method comprises providing, to the first CED, a message for reconfiguring the first CED to induce a first compensating phase shift for compensation the first phase shift.

11. The method of operating the first CN of claim 10, wherein the method comprises providing, to the second CED, a message for reconfiguring the second CED to induce a second compensating phase shift for compensation the second phase shift.

12. The method of operating the first CN of claim 10 or 11 , wherein the method comprises providing, to the first CED, a message for reconfiguring the first CED to stop applying the first delay; providing, to the second CED, a message for reconfiguring the second CED to stop applying the second delay; receiving and/or transmitting payload data from and/or to the second CN on the radio channel.

13. A method of operating a second communication node, CN, wherein the second CN is configured for communicating with a first CN via a first coverage enhancing device, CED, and a second CED, wherein the first CED and the second CED are reconfigurable to provide multiple spatial filterings, each one of the multiple spatial filterings being associated with a respective input spatial direction from which incident signals on a radio channel are accepted and with a respective output spatial direction into which the incident signals are transmitted by the first CED and the second CED, respectively, wherein the first CED is configurable for applying a first delay to the incident signals, and wherein the second CED is configurable for applying a second delay to the incident signals, wherein the method comprises

- transmitting, to the first CN on the radio channel, a reference signal via a first propagation path and a second propagation path, wherein receiving the reference signal via the first propagation path comprises receiving, via the first CED, a first delayed component of the reference signal, wherein receiving the reference signal via the second propagation path comprises receiving, via the second CED, a second delayed component of the reference signal,

14. A method of operating a second communication node, CN, wherein the second CN is configured for communicating with a first CN via a first coverage enhancing device, CED, and a second CED, wherein the first CED and the second CED are reconfigurable to provide multiple spatial filterings, each one of the multiple spatial filterings being associated with a respective input spatial direction from which incident signals on a radio channel are accepted and with a respective output spatial direction into which the incident signals are transmitted by the first CED and the second CED, respectively, wherein the first CED is configurable for applying a first delay to the incident signals, and wherein the second CED is configurable for applying a second delay to the incident signals, wherein the method comprises - receiving, from the first CN on the radio channel, a reference signal via a first propagation path and a second propagation path, wherein transmitting via the first propagation path comprises transmitting the reference signal, via the first CED, for applying the first delay, wherein transmitting via the second propagation path comprises transmitting the reference signal, via the second CED, for applying the second delay,

- providing, to the first CN, a message indicative of the reception property of the reference signal.

15. The method of any one of the preceding claims, wherein the first delay and the second delay correspond to a rational multiple of a clock period of the radio channel.

16. A method of operating a coverage enhancing device, CED, wherein the CED is reconfigurable to provide multiple spatial filterings, each one of the multiple spatial filterings being associated with a respective input spatial direction from which incident signals on a radio channel are accepted and with a respective output spatial direction into which the incident signals are transmitted by the CED, wherein the CED is configurable for applying a first delay to the incident signals, wherein the method comprises obtaining, from a first communication node, CN, a message indicative of the first delay which is to be applied to the incident signals.

17. The method of operating the CED of claim 16, wherein the method comprises providing, to the first CN, a message indicative of the capability of the first CED to apply the first delay.

18. A first communication node, CN, wherein the first CN comprises control circuitry configured for performing the method of any one of claims 1 to 12.

19. A second communication node, CN, wherein the second CN comprises control circuitry configured for performing the method of any one of claims 13 to 15.

20. A coverage enhancing device, CED, wherein the CED comprises control circuitry configured for performing the method of any one of claims 16 to 17.