WO2023227596A1

WO2023227596A1 - Multi-device transmission using in-phase and quadrature components of signal

Info

Publication number: WO2023227596A1
Application number: PCT/EP2023/063780
Authority: WO
Inventors: Jose Flordelis; Fredrik RUSEK; Chaitanya TUMULA; Erik Bengtsson
Original assignee: Sony Group Corporation; Sony Europe B.V.
Priority date: 2022-05-27
Filing date: 2023-05-23
Publication date: 2023-11-30

Abstract

Various examples relate to a multi-device transmission, e.g., from a transmitter communication device to two receiver communication devices and via a coverage enhancing device, e.g., a repeater device. The multi-device transmission is implemented using an in-phase component and a quadrature component of a signal, the in-phase component being associated with a first one of the two receiver communication devices and the quadrature component being associated with a second one of the two receiver components.

Description

D E S C R I P T I O N

MULTI-DEVICE TRANSMISSION USING IN-PHASE AND QUADRATURE COMPONENTS OF SIGNAL

TECHNIAL FIELD

Various examples of the disclosure generally pertain to communication, via a coverage enhancing device, between a transmitter communication device and multiple receiver communication devices, as well as communication, via a coverage enhancing device, between multiple transmitter communication devices and a receiver communication device.

BACKGROUND

To increase a coverage area for wireless communication, it is envisioned to use coverage enhancing devices (CEDs), such as Network Controlled Repeaters (NCRs) or re-configura- ble relaying devices (RRD). One example of RRDs are re-configurable reflective devices, sometimes also referred to as reflecting large intelligent surfaces (LISs). See, e.g., Huang, C., Zap- pone, A., Alexandropoulos, G. C., Debbah, M., & Yuen, C. (2019). Reconfigurable intelligent surfaces for energy efficiency in wireless communication. IEEE Transactions on Wireless Communications, 18(8), 4157-4170.

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. Semi-passive can correspond to a scenario in which the antennas can impose a variable phase shift and typically provide no signal amplification.

In contrast, NCRs can amplify a signal at antenna elements of a respective array. An NCR can implement one of reflection for coverage enhancement, amplify-forward for coverage enhancement, or decode-forward for coverage enhancement. Each antenna element may impose an antenna-element-specific amplitude gain and phase shift (i.e., provide signal amplification and variable phase shift). Oftentimes, operation of an NCR may be restricted to analog domain; i.e., digital forward error correction may not be provided. An NCR may include multiple antenna arrays, e.g., one for receiving (RX array) and one for transmitting (TX array). There may be analog signal processing in the baseband in between receiving and transmitting.

For any CED, an input spatial direction (or simply, input direction) from which incident signals on a radio link are accepted by a CED and an output spatial direction (or simply, output direction) into which the incident signals are redirected by the CED can be re-configured by changing a phase relationship (and, where possible, amplitude relationship) between the antennas.

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 transmit the incident signals in an output spatial direction to the UE. The AN may transmit the signals using a beam directed to the CED.

Scenarios are possible where multiple UEs are served by the AN via a CED. See WO 2021 109 345 A1.

SUMMARY

There is a need for advanced techniques of communicating via a CED. Specifically, there is a need for techniques which facilitate communicating contemporaneously with multiple communication devices via a CED.

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

Various techniques disclosed herein facilitate communicating between a first communication device (CD) and multiple second CDs via a CED. This can be referred to as multi-device transmission (MDT). For instance, multiple UEs can be served by an AN via a CED. Uplink and/or downlink transmission of data is possible using MDT.

It would also be possible that a UE communicates with multiple ANs.

Using MDT, a transmitter CD (TX CD) can transmit a signal that includes multiple components. Then, at a CED, this signal can be decomposed into its different components and then the different components can be provided to different receiver CDs (RX CDs). Likewise, it is possible that multiple TX CDs transmit signals which are then merged into a single signal at a CED, wherein different components of the signal transmitted by the CED to the RX CD are associated with the different signals transmitted by the multiple TX CDs.

A method of operating a device - e.g., an access node such as a base station or a coverage enhancing device such as a repeater device - is disclosed. The device includes an array of multiple antenna elements to contemporaneously provide an in-phase component of a signal along a first output direction to a first communication device and a quadrature component of the signal along a second output direction to a second communication device. The method includes establishing a first internal signal and a second internal signal corresponding to the signal. The method also includes applying a 180° phase offset to the quadrature component of the second internal signal. The method further includes applying, at a first subset of the array, first phase shifts to the first internal signal when transmitting the first internal signal. The method further includes applying, at a second subset of the array, second phase shifts to the second internal signal when transmitting the second internal signal.

The 180° phase offset may not be applied to the in-phase component of the second signal. The 180° phase offset may not be applied to the first internal signal.

In some examples it would be possible that the first phase shifts are determined based on a normalized subtraction of a first beamforming vector and a second beamforming vector. Here, the first beamforming vector is associated with the first output direction, the second beamforming vector is associated with the second output direction. The second phase shifts can be determined based on a normalized sum of the first beamforming vector and the second beamforming vector.

A computer program or a computer-program product includes program code. The program code can be loaded and executed by at least one processor. The at least one processor, upon executing the program code performs a method of operating a device - e.g., an access node such as a base station or a coverage enhancing device such as a repeater device. The device includes an array of multiple antenna elements to contemporaneously provide an in- phase component of a signal along a first output direction to a first communication device and a quadrature component of the signal along a second output direction to a second communication device. The method includes establishing a first internal signal and a second internal signal corresponding to the signal. The method also includes applying a 180° phase offset to the quadrature component of the second internal signal. The method further includes applying, at a first subset of the array, first phase shifts to the first internal signal when transmitting the first internal signal. The method further includes applying, at a second subset of the array, second phase shifts to the second internal signal when transmitting the second internal signal.

A device - e.g., an access node such as a base station or a coverage enhancing device such as a repeater device - is disclosed. The device includes a processor, a memory, and an array of multiple antenna elements to contemporaneously provide an in-phase component of a signal along a first output direction to a first communication device and a quadrature component of the signal along a second output direction to a second communication device. The processor can load program code from the memory and execute the program code. Upon executing the program code, the processor is configured to establish a first internal signal and a second internal signal corresponding to the signal. The processor is further configured to apply a 180° phase offset to the quadrature component of the second internal signal. The processor is further configured to apply, at a first subset of the array, first phase shifts to the first internal signal when transmitting the first internal signal. The processor is further configured to apply, at a second subset of the array, second phase shifts to the second internal signal when transmitting the second internal signal.

A method of operating a repeater device is disclosed. The repeater device includes an array of multiple antenna elements. The method includes applying, at a first subset of the array, first phase shifts when receiving an incident signal, thereby obtaining a first internal signal. The method also includes applying, at a second subset of the array, second phase shifts when receiving the incident signal, thereby obtaining a second internal signal. The method further includes applying a 180° phase offset to a quadrature component of the second internal signal. The method further includes combining the first internal signal and the second internal signal, to thereby obtain an output signal. The output signal includes the first internal signal as in-phase component and further includes the second internal signal as quadrature component. The method further includes transmitting the output signal to a communication device.

The first phase shifts may, e.g., be determined based on a normalized subtraction of a first beamforming vector and a second beamforming vector, the first beamforming vector being associated with a first input direction associated with a first communication device, the second beamforming vector being associated with a second input direction associated with a second communication device; and the second phase shifts may be determined based on a normalized sum of the first beamforming vector and the second beamforming vector.

A computer program or a computer-program product includes program code. The program code can be loaded and executed by at least one processor. The at least one processor, upon executing the program code performs a method of operating a repeater device. The repeater device includes an array of multiple antenna elements. The method includes applying, at a first subset of the array, first phase shifts when receiving an incident signal, thereby obtaining a first internal signal. The method also includes applying, at a second subset of the array, second phase shifts when receiving the incident signal, thereby obtaining a second internal signal. The method further includes applying a 180° phase offset to a quadrature component of the second internal signal. The method further includes combining the first internal signal and the second internal signal, to thereby obtain an output signal. The output signal includes the first internal signal as in-phase component and further includes the second internal signal as quadrature component. The method further includes transmitting the output signal to a communication device.

A coverage enhancing device, e.g., a repeater device, in includes a processor, a memory, and an array of multiple antenna elements. The processor can load program code from the memory and execute the program code. Upon executing the program code, the processor is configured to apply, at a first subset of the array, first phase shifts when receiving an incident signal, thereby obtaining a first internal signal. The processor is further configured to apply, at a second subset of the array, second phase shifts when receiving the incident signal, thereby obtaining a second internal signal. The processor is further configured to apply a 180° phase offset to a quadrature component of the second internal signal. The processor is further configured to combine the first internal signal and the second internal signal, to thereby obtain an output signal. The output signal includes the first internal signal as in-phase component and further includes the second internal signal as quadrature component. The processor is further configured to transmit the output signal to a communication device.

A method of operating a communication device is disclosed. The method includes transmitting, towards a repeater device and using a transmit interface of the communication device, a signal including an in-phase component and a quadrature component. The in-phase component is for a first communication device served via the repeater device, the quadrature component is for a second communication device also served via the repeater device. The method also includes applying, when transmitting the signal, a phase correction to mitigate a phase offset. The phase offset is between a radio-frequency oscillator of the repeater device and a radio-frequency oscillator of the transmit interface. Alternatively or additionally the phase correction is to mitigate a frequency-dependent phase shift due to signal propagation between the communication device and the repeater device.

The communication device could be an access node, e.g., a base station of a cellular network.

The communication device could be a handset terminal, a laptop, a smartphone, etc.

A computer program or a computer-program product includes program code. The program code can be loaded and executed by at least one processor. The at least one processor, upon executing the program code performs a method of operating a communication device. The method includes transmitting, towards a repeater device and using a transmit interface of the communication device, a signal including an in-phase component and a quadrature component. The in-phase component is for a first communication device served via the repeater device, the quadrature component is for a second communication device also served via the repeater device. The method also includes applying, when transmitting the signal, a phase correction to mitigate a phase offset. The phase offset is between a radio-frequency oscillator of the repeater device and a radio-frequency oscillator of the transmit interface. Alternatively or additionally the phase correction is to mitigate a frequency-dependent phase shift due to signal propagation between the communication device and the repeater device.

A communication device includes a processor and a memory. The processor can load program code from the memory and execute the program code. Upon executing the program code, the processor is configured to transmit, towards a repeater device and using a transmit interface of the communication device, a signal including an in-phase component and a quadrature component. The in-phase component is for a first communication device served via the repeater device, the quadrature component is for a second communication device also served via the repeater device. The processor is further configured to apply, when transmitting the signal, a phase correction to mitigate a phase offset. The phase offset is between a radio-frequency oscillator of the repeater device and a radio-frequency oscillator of the transmit interface. Alternatively or additionally the phase correction is to mitigate a frequency-dependent phase shift due to signal propagation between the communication device and the repeater device.

A method of operating a first communication device is disclosed. The method includes receiving, from a repeater device and using a receive interface of the first communication device, one of an in-phase component or a quadrature-component of a signal transmitted to the repeater device by a communication device. The method further includes applying, to the signal, a phase correction to mitigate at least one of a phase offset between a radio-frequency oscillator of the repeater device and a radio-frequency oscillator of the transmit interface, or a frequency-dependent phase shift due to signal propagation between the repeater device and the first communication device.

A computer program or a computer-program product includes program code. The program code can be loaded and executed by at least one processor. The at least one processor, upon executing the program code performs a method of operating a first communication device. The method includes receiving, from a repeater device and using a receive interface of the first communication device, one of an in-phase component or a quadrature-component of a signal transmitted to the repeater device by a communication device. The method further includes applying, to the signal, a phase correction to mitigate at least one of a phase offset between a radio-frequency oscillator of the repeater device and a radio-frequency oscillator of the transmit interface, or a frequency-dependent phase shift due to signal propagation between the repeater device and the first communication device.

A first communication device includes a processor and a memory. The processor can load program code from the memory and execute the program code. The processor, upon executing the program code, is configured to receive, from a repeater device and using a receive interface of the first communication device, one of an in-phase component or a quadrature-component of a signal transmitted to the repeater device by a communication device. The method further includes applying, to the signal, a phase correction to mitigate at least one of a phase offset between a radio-frequency oscillator of the repeater device and a radio-frequency oscillator of the transmit interface, or a frequency-dependent phase shift due to signal propagation between the repeater device and the first communication device.

The first communication device could be a handset terminal, a laptop, a smartphone, etc.

The first communication device could be an access node, e.g., a base station of a cellular network.

A method of operating a communication device is disclosed. The method includes establishing synchronization between a radio-frequency oscillator of a repeater device and a radiofrequency oscillator of a transmit interface of the communication device. The method also includes transmitting, towards the repeater device, a signal comprising an in-phase component and a quadrature component, the in-phase component being for a first communication device served via the repeater device, the quadrature component being for a second communication device also served via the repeater device.

A computer program or a computer-program product includes program code. The program code can be loaded and executed by at least one processor. The at least one processor, upon executing the program code performs a method of operating a communication device is disclosed. The method includes establishing synchronization between a radio-frequency oscillator of a repeater device and a radio-frequency oscillator of a transmit interface of the communication device. The method also includes transmitting, towards the repeater device, a signal comprising an in-phase component and a quadrature component, the in-phase component being for a first communication device served via the repeater device, the quadrature component being for a second communication device also served via the repeater device.

A communication device includes a processor and a memory. The processor can load program code from the memory and execute the program code. The processor, upon executing the program code, is configured to establish synchronization between a radio-frequency oscillator of a repeater device and a radio-frequency oscillator of a transmit interface of the communication device. The processor is also configured to transmit, towards the repeater device, a signal comprising an in-phase component and a quadrature component, the in-phase component being for a first communication device served via the repeater device, the quadrature component being for a second communication device also served via the repeater device.

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 invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a communication system according to various examples.

FIG. 2 schematically illustrates the communication system of FIG. 1 in further detail.

FIG. 3 schematically illustrates a variant of the communication system of FIG. 1 and FIG. 2 according to various examples, wherein the communication system of FIG. 3 includes an NCR.

FIG. 4 schematically illustrates details of the NCR according to various examples. FIG. 5 is a flowchart of a method of operating an NCR or a transmitter communication device according to various examples.

FIG. 6 is a signal processing diagram illustrating signal processing at the NCR according to an example which corresponds to downlink MDT transmission.

FIG. 7 is a signaling processing diagram illustrating signal processing at a base station according to an example which corresponds to downlink MDT transmission.

FIG. 8 is a signal processing diagram illustrating signal processing at the NCR according to an example which corresponds to uplink DT transmission.

FIG. 9 schematically illustrates an RF-conjugator signal processing block employed for l/Q separation of an in-phase component and a quadrature component of a signal according to various examples.

FIG. 10 schematically illustrates a variant of the RF-conjugator signal processing block of FIG. 9 according to various examples.

FIG. 11 is a flowchart of a method of operating a transmitter communication device according to various examples.

FIG. 12 is a flowchart of a method associated with determining phase correction parameters for an MDT transmission employing l/Q separation according to various examples.

FIG. 13 is a flowchart of a method associated with determining phase correction parameters for an MDT transmission employing l/Q separation according to various examples.

FIG. 14 is a signaling diagram of an MDT transmission according to various examples.

FIG. 15 is a signaling diagram of an MDT transmission according to various examples.

FIG. 16 is a signaling diagram of an MDT transmission according to various examples.

FIG. 17 is a flowchart of a method of operating a receiver communication device according to various examples.

FIG. 18 is a flowchart of a method of operating a transmitter communication device according to various examples.

FIG. 19 is a flowchart of a method of operating a receiver communication device according to various examples. 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 CDs. A wireless communication system includes a TX CD and one or more RX CDs. Alternatively or additionally, the wireless communication system can include multiple TX CDs and a single RX CD. In some examples, the wireless communication system can be implemented by a wireless communication network, e.g., a radio-access network (RAN) of a 3GPP-specified cellular network (NW). In such a case, the TX CD can be implemented by an AN, in particular a base station (BS), of the RAN, and the one or more RX CDs can be implemented by terminals (also referred to as user equipment, UE). This corresponds to a downlink (DL) transmission. It would also be possible that the TX CD is implemented by a UE and the one or more RX CDs are implemented by one or more ANs and/or further UEs. Uplink (UL) and/or sidelink (SL) transmission is possible.

According to the disclosure, the wireless communication system may, in some scenarios, include a CED. The CED supports, e.g., UL and/or DL transmission or SL transmission.

In other scenarios, a CED is not required.

Various examples pertain to a CED being implemented by an NCR. While generally also other implementations of the CED are conceivable, e.g., as RRD, hereinafter, for sake of simplicity reference will be made to an implementation of the CED by an NCR. The communication system can employ MDT. In MDT, at the same time/frequency/spatial resources, a signal is communicated that includes multiple components associated with different CDs.

Multiple scenarios for MDT are summarized in TAB. 1 below.

TAB. 1: Different example scenarios of MDT. The MDT is operating based on a signal having multiple components. These components can be separated, e.g., at the NCR or an RX CD.

According to various examples, the MDT (cf. TAB. 1) is implemented using an in-phase component (l-component) and a quadrature component (Q-component) of a signal.

For instance, referring to TAB. 1 : example I, it would be possible that the l-component of the incident signal transmitted by the BS is transmitted to one of two different UEs while the Q- component of the incident signal transmitted by the BS is transmitted to the other one of the two UEs. I.e., the l-component and Q-component can then be transmitted, by the NCR, along different output spatial directions, targeting the different UEs.

Splitting up l/Q signal components into different directions provides an additional degree of freedom for multiplexing data streams, e.g., associated with the multiple RX CDs that are served via the NCR or TX CDs. For instance, two UEs located at same or different directions as seen from the NCR can share the same time-frequency-space resource, each UE getting an independent data stream. The shared spatial resource here is the BS TX beam. Spectrum utilization can be increased. Data throughput can be increased.

Next, details with respect to such l/Q separation are explained.

First, the signal model is discussed. The signal model is discussed for a DL transmission from a BS (TX CD) to two UEs (RX CDs); cf. TAB. 1 , example I. This is for exemplary purposes. The signal model could be likewise constructed for an UL transmission from two UEs (TX CDs) to a BS (RX CD); cf. TAB. 1 , example II. A signal model could also be constructed for TAB. 1 , example III, or any other example.

Seen in the complex baseband domain, the transfer function of an NCR serving two users (UE-1 , UE-2) can be described as

Kb* [s(«‘)b^s*'‘^sTWz'

Equation 1 where y_k is the gain of the signal sent towards UE k, k = 1,2; s(<z_fe) is the steering row-vector to UE k (k = 1,2 for UE-1 and UE-2, respectively) as seen from the NCR; s( ?) is the steering rowvector to the NCR as seen from the BS; x_A is a row-vector of phasors at the NCR representing the receive filter of the NCR (i.e., defining the RX beamformer, or more specifically RX antenna weights specifying amplitude and phase to be applied at each antenna element of the respective antenna array of the NCR used for reception); x_D is a row-vector of phasors at the NCR representing the transmit filter of the NCR (i.e., defining the TX beamformer, or more specifically the TX antenna weights specifying amplitude and phase to be applied at each antenna element of the respective antenna array of the NCR - as a general rule, different antenna arrays can be used for receiving and transmitting at the NCR); and z is signal transmitted by the BS in the DL having an l-component and a Q-component.

The proportionality symbol “oc” is used since some constants, e.g., path losses, are not explicitly considered (i.e. , such components are “absorbed” into the proportionality symbol).

In the following description, s(0_ol) G (?^NX1 and s(0_o2) G C^Nx denote steering vectors - as an example of beamforming vectors - corresponding to the two output directions, including the steering vector from the input direction to the NCR, where N denotes the number of elements of the respective antenna array (or subset thereof).

The beamforming vectors used herein are unit norm. x_A5^T(/?)z denotes the signal received at the NCR from the BS. One can select x_A (the RX beamformer at the BS) as x_A = s*(/?) (“*” denoting the complex conjugate) - this means that the RX beamformer accepts signals which are incident from the direction of the BS; this is reasonable for the assumption of the line-of-sight channel being strongest - which gives

Equation 2

Assume now that the antenna array of the NCR used for transmitting (TX array) is broken into two subsets for which it holds for each subset that

Equation 3 where the further sub-indexing (beyond Equation 2) refers to the two subsets of the NCR transmit array, and A is a real-valued number. For example, y₂,i represents the signal received by UE-2 from the first subset of the TX array, and so on.

The TX beamformers x_{D 1} and x_{D 2} (for the two subsets of the TX array) at the NCR can be chosen as

Equation 4 where x_{D 1/2} are vectors whose entries correspond to the antenna phase changes of the TX beamformers, absolute value 1. 1 and division should be interpreted as being elementwise, and “*” is complex conjugation. I.e., Equation 4 defines the spatial filter applied at the NCR to achieve MDT. Equation 4 describes an elementwise normalized subtraction (for _{D 1}) and sum (for x_{D 2}) of complex conjugates of the steering vectors.

The effect of the beamformer pair according to Equation 4 is to split an incoming signal into outgoing directions e₀₁, e_o2; other beamformer implementations may be possible.

At the NCR, respective first and second internal signals can be established, the first internal signal being transmitted using x_{D A}as TX beamformer (and at the second subset of the TX array); and the second internal signal being transmitted using x_{D 2} as TX beamformer (and at the first subset of the TX array). Both, the first and second internal signals are established based on a signal that is received from the BS, i.e., based on x_As^T(/?)z, cf. Equation 1, and then processed differently (in particular, using different TX beamformers at different subsets of the TX array). The signal received from the BS includes the l-component and the Q-component and these components are then separated using the appropriate TX beamformers and processing at the NCR, as explained below.

The effect of using such TX beamformers, according to Equation 4, at the two subsets of the TX array (for large arrays) is two-fold: (/) equally much energy is sent towards both UEs

(thereby, a strong signal can be expected at each UE), and (ii) a sign-change on the signal sent from the first subset of the TX array is obtained at UE-2. This sign-change will be instrumental later on but can for now be regarded as an arbitrary choice. Item (i) could be referred to as

“beam-splitting".

Next, the above equations are re-written with a real-valued exposition. Thus, inserting

Equation 4 into Equation 3, one obtains

Equation 5 where z = z_{ + jz_Q. This defines the l-component and the Q-component of the signal z that is received from the BS. The bottom two rows of each equation system represent signals received at UE-1 while the bottom two represent signals received at UE-2. It can be seen that both the I- component and the Q-component are received at both UEs.

Next, it is described how the NCR can process the signal so that only the l-component reaches UE-1 and only the Q-component reaches UE-2 (or vice versa). This can be referred to as l/Q separation.

First, a reference implementation of the l/Q separation is described. Provided that baseband signals at the NCR can be reached, one can accomplish l/Q separation - according to the reference implementation - in a conceptually simple way. This is possible - according to the reference implementation - by dividing the NCR array into two subsets, obtaining the baseband signals at each subset (first signal and second signal), nulling out l-component of the first signal and Q-component of the second signal, steering the remaining Q-component of the first signal to the UE-1 , and steering the remaining l-component of the second signal to the UE-2. The signal model for this reference implementation is given by (if there are M antennas at each subset), for the first subset:

Equation 6 and for the second subset:

Equation 7

The reference implementation according to Equation 6 and Equation 7 presented above requires both subsets of the RX array of the NCR to access the baseband signals. While this is generally possible, on the other hand, it requires certain hardware to be provisioned at the NCR which is not always desirable. Next, techniques will be disclosed which do not require multiple subsets of an RX array of the NCR to access the baseband signals. According to various examples, the complex baseband representation of an l/Q signal is conjugated, while still preserving the RF frequency. That is, if the input to such signal processing block is x_RF(t) = X](t) cos(6J_ct) — x_Q(t) sin( )_ct) then output should be x _F(t) ⁼ i(0 cos(<w_ct) + XQ( sin(to_ct).

Equation 8

One may call such signal processing block an “RF-conjugator”. A 180° phase offset is applied to the quadrature component of the processed signal. Practically, the signal processing of the RF-conjugator may be implemented as follows: first, demodulate x_RF(t) to baseband using two mixers and low-pass filters, then insert a “minus-sign”, and finally up-convert back to RF. Note that analog-to-digital conversion, digital-to-analog conversion, or any digital baseband processing is not needed.

One possible practical implementation of such RF-conjugator will be explained later on in connection with FIG. 9.

Next, starting from Equation 5, the RF-conjugator is applied to the second internal signal.

In other words, the 180° phase offset is applied by separating, in the analog domain, the l-com- ponent and the Q-component of the baseband representation of the second internal signal and then by inverting the amplitude of the Q-component. In an implementation, the RF-conjugator would be applied to the signal x_As^T(/?)z. With that, the right-hand-side of the bottom equation in

Equation 5 changes into

Equation 9

If the two internal signals (after processing the second internal signal in accordance with

Equation 9) are then combined, one obtains

Equation 10

The real-valued expression implies that the first two rows of the transfer matrix on the right-hand side of Equation 10 are received at UE-1 , while the bottom two rows of the right-hand side of Equation 10 are received at UE-2. Therefore, the received signal at UE-1 includes only the l-component of the transmitted signal (first column of the 4 x 2 matrix.), and the received signal at UE-2 contains only the Q-component of the transmitted signal (second column of the

4 x 2 matrix).

Therefore, l/Q separation (in conjunction with beam-splitting at an NCR) has been accomplished.

The l/Q separation relying on the 180° phase offset applied to the quadrature component can be compared against the l/Q separation in accordance with the reference implementation discussed above. From the right-hand sides of Equation 6 and Equation 7, it can be seen that the reference implementation achieves a beamforming gain of M². This can be compared to the l/Q separation expressed by Equation 10. The value A in Equation 10 can be shown to equate to A = 2M/n ® 0.6366M (also see Swedish patent application 2151540-8). But since the beamforming gain per UE is (2A)² , the for l/Q separation in accordance with Equation 10 a gain of (4M/TT)² « 1.6211M² is achieved. Comparing this to the baseline value M² according to the reference implementation of Equation 6 and Equation 7 reveals a 2.1 dB gain. Furthermore, l/Q separation in accordance with Equation 10 is simpler compared to the reference implementation, as it doesn’t require both subsets of the TX array to access the baseband signals (i.e., the first internal signal is not required to be down-converted to the baseband). Furthermore, only one of I or Q is required at each of the UEs for data transmissions (two RF chains, one for each of I and Q, are typically required for normal UE operation; here, however, only one RF would be required, at least when all the delays and impairments have been compensated for).

Above, l/Q separation has been described based on a signal model for TAB. 1 : example I. This example can be readily extended to scenarios according to TAB. 1 : examples II and III. This will also be shown hereinafter with reference to the Figures.

FIG. 1 schematically illustrates a communication system 100. The communication system 100 includes two CDs 101, 102 that are configured to communicate with each other via a radio link 112. In the example of FIG. 1 , the device 101 is implemented by a BS 101 and the CD 102 is implemented by a UE 102.

The UE 102 could be, e.g., a smartphone, a tablet PC, a smartwatch, a smart TV, a smart meter, to give just a few examples.

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 BS 101 of a cellular NW and a UE 102.

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.

While in the scenario of FIG. 1 only a single UE is shown, as a general rule, multiple UEs can be present in a respective communication system 100 and MDT transmission is possible, between the BS 101 and the multiple UEs.

FIG. 2 illustrates details with respect to the BS 101 . The BS 101 implements an access node of a communications network, e.g., a 3GPP-specified cellular network. The BS 101 includes control circuitry that is implemented by a processor 1011 and a non-volatile memory 1015. The processor 1011 can load program code that is stored in the memory 1015. The processor 1011 can then execute the program code. Executing the program code causes the processor to perform techniques as described herein, e.g.: transmitting and/or receiving (communicating) payload data on the data link 112 on the data carrier 111 , e.g., via an NCR (not shown in FIG. 2); employing MDT transmission to multiple UEs using l-component and Q-component of an internal signal; applying a phase correction to transmitted and/or received signals; merging two data streams (e.g., in digital domain) associated with two UEs when transmitting a signal, as l-component and Q-component; associating a first data stream associated with a first UE with an l-component of a transmitted or received signal and associating a second data stream associated with a second UE with a Q-component of the transmitted or received signal; etc.

FIG. 2 also illustrates details with respect to the UE 102. The UE 102 includes control circuitry that is implemented by a processor 1021 and a non-volatile memory 1025. The processor 1021 can load program code that is stored in the memory 1025. The processor can execute the program code. Executing the program code causes the processor to perform techniques as described herein, e.g.: transmitting and/or receiving (communicating) payload data on the data link 112 (cf. FIG. 1) on the data carrier 111, e.g., via an NCR (not shown in FIG. 2); applying a phase correction to transmitted and/or received signals; etc.

FIG. 2 also illustrates details with respect to communication between the BS 101 and the UE 102 on the data carrier 111. The BS 101 includes an interface 1012 that can access and control multiple antennas 1014. Likewise, the UE 102 includes an interface 1022 that can access and control multiple antennas 1024.

While the scenario of FIG. 2 illustrates the antennas 1014 being coupled to the BS 101, as a general rule, it would be possible to employ transmit-receive points (TRPs) that are spaced apart from the BS.

The interfaces 1012, 1022 can each include one or more TX chains and one or more RX chains. For instance, such RX chains can include low noise amplifiers, analogue to digital converters, mixers, etc. Analog and/or digital beamforming would be possible. Thereby, phase-coherent transmitting and/or receiving (communicating) can be implemented across the multiple antennas 1014, 1024. Multi-antenna techniques can be implemented.

By using a TX beam, the direction 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 1014, 1024. Thereby, a spatial data stream can be directed. The spatial 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-in- put 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 a variant of the communication system 100. FIG. 3 illustrates aspects with respect to communicating via an NCR 109. The NCR 109 is generally optional, e.g., cf. TAB. 1 : example III.

A UE 102 is served by the BS 101 via an NCR 109. Another UE 105 (that can be configured as the UE 102, cf. FIG. 1, FIG. 2) is also served by the BS 101 via the NCR 109. Different steering vectors at the NCR define TX and RX beams 671-672; only beam 671 is directed towards the UE 102. Beam 672 is directed towards the UE 105. Respective TX or RX beamformers are used at the NCR 109.

Also illustrated is a beam 679 of the NCR 109 that is directed towards the BS 101 and can be accessed by respective RX or TX beamformers (as explained above: _A = s*(/?))

Also illustrated in FIG. 3 is a control node 108 that can communicate with the NCR 109 on a control link 199. The control node 108 is generally optional. While the control node 108 is shown as a separate device, it would be possible that the control node 108 is implemented as a functionality of the BS 101 or one of the UEs 102, 105.

FIG. 4 illustrates aspects in connection with the NCR 109. The NCR 109 includes an array 690 of antenna elements 1094 each imposing a respective configurable antenna-element- specific phase shift when transmitting or receiving incident electromagnetic waves and optionally an antenna-element-specific amplification; this defines a respective spatial filter.

The array 690 may be flexibly structured into subarrays; FIG. 4 illustrates two subarray 691 , 692. Different beamformers may be applied at the antenna elements 1095 of the two subarrays 691 , 692. The formation of subarrays can be a logical partitioning of the antennas 1094 with respect to the selected beamformers; i.e., there may not be a structural manifestation of a subarray.

Typically, the NCR 109 includes multiple antenna arrays (albeit in FIG. 4 only a single array is illustrated), e.g., separate antenna arrays for TX and RX (TX array and RX array) The role of the multiple antenna arrays can be switched; e.g., one array may operate as TX array first and then as RX array, or vice versa.

Also illustrated is an RF/IF signal processing module 670. At the RF/IF signal processing module 670, the RF signals associated with each antenna element 1094 can be processed, e.g., up- and/or down-converted from/to the baseband, combined with each other, split up, phase shifts can be applied, amplification can be applied, etc.. The order of these signal processing steps can vary, depending on the implementation. It is possible that the signal processing is restricted to the analog domain.

The NCR 109 may not include an analog-to-digital converter for processing the received signals. Digital-domain forward-error correction may not be provided for.

The (re-)configuration of antenna elements 1094 defines respective TX or RX beamformers and accordingly the corresponding beams (cf. FIG. 3). The NCR 109 includes an antenna interface 1095 and a processor 1091 that can set respective antenna weights, i.e. , an- tenna-element-specific amplitude gains and phase shifts.

Further, there is a communication interface 1092 such that communication on a control link 199 can be established between the NCR 109 and a remote device, e.g., the BS 101 or the control node 108 (cf. FIG. 3).

The processor 1091 can load program code from a non-volatile memory 1093 and execute the program code. Executing the program code causes the processor to per-form techniques as described herein, e.g.: re-configuring each one of the antenna elements 1094 to activate one of multiple spatial filters, i.e., to activate a certain TX or RX beamformer; activate or deactivate baseband processing of an l-component and/or a Q-component of the received signal or signals; etc.

While FIG. 4 illustrates an NCR 109, as a general rule, similar techniques may be applied with other types of CEDs. For instance, the NCR can add up all the incident signals, after a suitable (first) phase-shift (RX beamforming), into a single signal, which is then amplified, and finally fanned-out to each of the output antennas with a suitable (second) phase shift (TX beamforming); on the other hand, for reflective intelligent surfaces (RIS) or reconfigurable relaying devices (RRD) there is no addition and ulterior fanning-out of the incident signals, but phase shifting (and possibly amplification) is applied at each of the antenna elements. For NCRs, the additional steps of down-conversion, phase reversal, and up-conversion can be conveniently done in one place: after the adder stage. For RISs/RRD, however, separate downconverters, phase inverters and up-converters would be needed at each cell (or at every second cell, since half of the cells leave the phase unchanged.)

Details with respect to the operation of the NCR 109 will be explained next in connection with FIG. 5.

FIG. 5 is a flowchart of a method according to various examples. For instance, FIG. 5 can be implemented by an NCR, e.g., an NCR such as the NCR 109. The NCR can support communication between a BS and two UEs. UL transmission and/or DL transmission can be supported. The NCR can support MDT transmission.

The various boxes of FIG. 5 are discussed in the context of the example scenarios illustrated in FIG. 6, FIG. 7, and FIG. 8.

Optional boxes are shown with dashed lines.

At optional box 6005, RX beamforming is applied. At box 6005, a signal transmitted by a TX CD is received. For instance, a signal transmitted by a BS can be received.

A dedicated RX array - different than a TX array - can be used for receiving RX beamforming.

Each antenna element of the RX array may be associated with a respective phase shifter to apply the RX beamforming. Each antenna element applies a certain phase shift. It would be possible to apply certain amplitude gains at each antenna element. It would also be possible to add a same amplitude gain to the signal of each antenna element or to a combination of them.

The RX beamformer is discussed above in connection with Equation 2. Box 6005 is also illustrated in the signal processing diagram of FIG. 6. Here, the incident signal 711 transmitted by the BS is received by the antenna elements of the RX array 695 and, at phase shifters 7010, individual phase shifts <5 are applied. The respective signal components are then added at summation element 7011 (e.g., implemented as part of RF/IF processing circuitry 670, cf. FIG. 4). The signal 720 then corresponds to the signal 711 transmitted by the BS (including noise and interference). The signal 720 is split-up into a first internal signal 721 and a second internal signal 722.

Referring again to FIG. 5: such splitting of the signal 720 into the internal signals 721, 722 corresponds to box 6010. Note that box 6005 is optional; in some scenarios (cf. FIG. 7; TAB. 1 : example III), it is possible to obtain the first and second internal signals 721 , 722 from respective digital representations using a digital-to-analog converter 7101. In yet another scenario (cf. FIG. 8; TAB. 1: example II), it is possible to obtain the first and second internal signals 721 , 722 from RX beamformers at two subarrays 691 , 692 of an antenna array 690. These RX beamformers select signals 731, 732 transmitted by the UEs 102, 105, respectively. Here, for RX beamforming the beamformers according to Equation 4 are used at the two subsets 691 , 692 of the array 690 (then acting as RX array 690).

Next, referring to FIG. 5, at box 6015, a 180° phase offset is applied to the Q-component of the second internal signal 722. See Equation 8. This is achieved using an RF-conjugator signal processing block 7013 (cf. FIG. 6, FIG. 7, FIG. 8).

Details with respect to an implementation of the RF-conjugator signal block 7013 (e.g., implemented as part of RF/IF processing circuitry 670, cf. FIG. 4) are described in connection with FIG. 9. The second internal signal 722 includes the l-component 791 and the Q-component 792. By using an RF oscillator 7501, a 90° phase shifter 7511, and two mixers 7505, 7510 in combination with low-pass filters 7521 , 7522, the baseband representations of the l-component 791 and the Q-component can be determined (Z_;, ZQ). At processing block 7530, the amplitude of the baseband representation of the Q-component 792 is inverted. Then, using blocks 7541, 7542, 7543, the internal signal is converted back to the RF from baseband and, due to block 7530, a 180° phase shift is obtained for the Q-component 792.

The RF-conjugator 7013 according to FIG. 9 can operate bidirectionally. This enables flexible use in scenarios according to FIG. 6 and FIG. 8 (cf. TAB. 1: example I and example II). For higher signal fidelity, an implementation of the RF-conjugator 7013 according to FIG. 10 is conceivable using directional switches 7501, 7502 and unidirectionally operating RF-conjugator the sub-blocks 7013-1, 7013-2. Each sub block 7013-1, 7013-2 can operate as explained in connection with FIG. 9.

Referring again to FIG. 5: at optional box 6020 the first and second internal signals can be combined, e.g., when implementing example II of TAB. 1 (cf. FIG. 7).

At box 6025, the two internal signals (when box 6020 is not implemented) or the resulting single signal (when box 6020 is implemented) are/is then transmitted. TX beamforming is used. For instance, referring to FIG. 6, the two internal signals 721 , 722 can be transmitted using the subarrays 691, 692 and the TX beamformers according to Equation 4 (cf. TAB. 1: example I). This also applies to FIG. 7 (cf. TAB. 1 : example III). In FIG. 8, the steering vector towards the BS can be used for the TX beamformer across the entire TX array.

The flowchart of FIG. 5 illustrated the operation behavior of an NCR, e.g., the NCR 109. Next, operation behavior of a TX CD is described in connection with FIG. 11 .

FIG. 11 is a flowchart of a method according to various examples. For instance, FIG. 11 can be implemented by a TX CD, e.g., a BS such as the BS 101 or a UE such as the UE 102 or the UE 105. An NCR can support communication between the TX CD(s) and the RX CD(s). FIG. 11 illustrates examples I and II of TAB. 1. For better readability, FIG. 11 will be explained in the context of TAB. 1 , example I (i.e., DL communication; TX CD is a BS), but is equally applicable to TAB. 1 , example II (UL communication; TX CD is a UE).

Optional boxes are shown with dashed lines.

At box 6105, synchronization between the BS and the NCR may be established.

To motivate this, the impact of synchronization or lack of synchronization between the RF oscillator 7501 of the NCR 109 and an RF oscillator at the BS 101 is discussed, exemplarily for the scenario of FIG. 6 (cf. TAB. 1 : example I). It is possible that the sin(o»_ct), cos(<y_ct) bases of the BS 101 may not be synchronized with the corresponding bases of the NCR 109. If this is the case, the signals yi(t), y₂(t) will generally not be the l-/and Q-components of z(t), as desired, but a mixture of the two.

Accordingly, in some examples it is possible that synchronization between the RF oscillators of the NCR 109 and the BS 101 is established, before the BS 101 transmits the signal 711. For instance, such synchronization could be established by communicating synchronization signals, e.g., on an auxiliary data link or on the carrier itself that later-on carries the signal 711. One synchronization of the RF oscillators at the NCR 109 and the BS 101 is obtained, mixing of the l-component and the Q-component is avoided.

It is not feasible, in all scenarios, that synchronization between the BS 101 and the NCR 109 is established. For instance, sometimes the NCR 109 may not have the capability to synchronize its RF oscillator with the RF oscillator of the BS 101 , e.g., due to hardware-limitations. As such, box 6105 is optional.

To mitigate such scenario when synchronization is not possible, box 6110 - communication of reference signals between the BS and the UEs - and, based on the reference signals (also referred to as pilots), respective channel sounding applying a phase correction at box 6115 can be executed. This is discussed hereinafter.

As a general rule, reference signals have a predetermined transmit shape known to the RX CD. This enables the RX CD to conclude on the impact of the channel (including the NCR), by comparing the received shape with the known transmit shaped.

When the phase correction is applied, it is possible to avoid mixing of the l-component and the Q-component by applying phase corrections at the BS 101 (box 6115) and the receiving UEs 102, 105.

The issue identified above is that the RF-conjugator 7013 would introduce a random phase offset due to, e.g., the local oscillator. These artifacts introduced by the phase offset due to the RF-conjugator 7013 at the NCR 109 not being synchronized with the RF oscillator at the

BS 101 can be modeled for the DL transmission (cf. TAB. 1 : example I; FIG. 6) by the system of equations

where 9 G [0,2TT) is the phase offset between the RF oscillator 7501 (cf. FIG. 9) of the RF-conju- gator 7013 at the NCR 109 and the RF oscillator used for RF modulation of the transmitted signal.

In the above model, the impairments of the RF-conjugator are modeled by a rotation cos(0) — sin(0)' ) = One way to address this impairment is to use more accurate compo- sin(0) cos(0) . nents at the NCR, limiting the range of the phase offset to small values, i.e., 0 ~ 0. Another way is to add some hardware for detection and compensation of said phase offset (i.e., establishing synchronization, as explained above). Both options, however, increase the cost of the NCR. Alternatively, one can let the BS and/or the UEs apply signal processing to compensate, or at least mitigate, the effects of the phase offset. This is described next.

The model in Equation 11 can be expanded to include such BS- and/or UE-side pro- cessing as follows:

Here, the matrix P₀ ^DL, whose form is to be determined, represents the signal processing done at the BS to compensate the phase offset 9 of the RF-conjugator, and the matrices P₁ ^DL, P₂ ^DL represent the UE-side counterparts. Moreover, propagation delays of the signals have also been included, where d₀, d_lt d₂ denote the distances between the NCR 109 and the BS 101 , and the two UEs 102, 105, respectively. The required processing to accomplish l/Q splitting (i.e. , phase correction), can be summarized as

Equation 13 where f is the frequency of the OFDM subcarrier. Note that since only one l/Q component is received by the UEs, the rotations R( at the UEs can be implemented as delays.

P°^Ldenotes the phase correction applied at the BS at box 6115 for DL transmission. This phase correction includes two components, i.e., the component /? \ -2nf — ) associated with the frequency-dependent phase shift due to signal propagation between the BS and the NCR (distance d₀); and the component 7? + ^associated with the phase offset between the RF oscillators at the BS and the NCR. When synchronization is established between the BS and the NCR, the phase offset 9 is 0 and the respective component is not required to be compensated.

Next, the UL scenario (FIG. 8; TAB. 1, example II) is discussed. The signal processing required at the BS and the UEs can be summarized by the equations

Equation 14

As will be appreciated from the above, the TX CD or CDs compensate impairments due to non-synchronous RF-conjugation, i.e., the phase offset 9, as well as frequency-dependent phase shifts exp ( -j2nf — ). This mitigates the undesirable effect of unwanted l/Q components infiltrate the RX CD or CDs.

To maximize the received power on the intended l/Q branch, the RX CD or CDs compensate the above two terms, see Equation 13 and Equation 14. The RX CD or CDs, however, cannot reject an undesired l/Q component.

To be able to apply the phase correction at box 6115, it is required to estimate and track the phase offset, 9, of the RF-conjugator. Further, estimates of the distances d₀, d₁, d₂ are required. These values can all be estimated either at the BS, or at the UEs. In many settings, the BS and the NCR are stationary, and so d₀ is fixed and can be estimated with great accuracy using positioning techniques available in the prior art (e.g., using multi-lateration, satellite-based, etc.).

Next, making reference to FIG. 11 , scenarios with respect to communicating the reference signals at box 6110 and inferring the phase correction for box 6115 are discussed.

In a first scenario, illustrated in the flowchart of FIG. 12, the first UE transmits reference signals h[0], h[l], ..., b[N - 1] over N subcarriers (i.e., multiple UL reference signals are communicated at multiple frequencies); box 6205. The transmitted modulation symbols can be real or complex.

Always-on reference signals may be transmitted. It would also be possible that these reference signals are transmitted on request, i.e., a respective request message may be received from the BS.

At box 6210, the BS receives r[0],r[l], ...,r[N - 1] via the NCR, where r[n] =

, are independ- ent additive white Gaussian noise samples. Ignoring the conjugate b[n]’s, this corresponds to two echoes of the original sequence 6[0], 6[1], ..., b[N - 1] at delays T⁺ = ^{DO +DL} and T~ = ^D°~^DL.

^CO ^co

From the received sequence r[0], r[l], ...,r[N - 1], the BS can produce, at box 6215, estimates d₀, d_r, of d₀, d_r, 9, respectively. This can be done with good accuracy when the delays r⁺, T~ are well separated, i.e., when — » — - — .

If there is a frequency offset between the NCR and the reference oscillator, then after an initial phase correction (initial execution of box 6115), the phase offset starts to build up and the adjustment procedure needs to be repeated regularly. I.e., box 6115 can be repeated from time to time.

Then, box 6220 corresponds to box 6205 with the second UE transmitting the reference signals; box 6225 corresponds to box 6210; and box 6230 corresponds to box 6230.

Next, for applying a phase correction at the UEs, the UEs are informed of the parameters such as d₀, d₁,d₂, 9. / first option would be executing box 6235; a second option would be executing box 6240.

At box 6235, the BS communicates the consolidated parameter estimates d_r, 9 and d₂, 9 (from boxes 6215, 6230) to the two UEs. A respective report message may be communicated.

At box 6240, the BS inserts DL Reference signals £ [0], b'[l], ..., b'[N' - 1], e.g., as demodulation reference signals (DMRS). The first UE may receive r'[0],r'[l], ...,r'[N - 1] via the NCR, where r'[n]

+ iv'[n]. The first UE can now produce suitable estimates of d_lt 9 for UL transmissions. This is also applicable for the second UE.

A second scenario for communicating the reference signals at box 6110 and inferring the phase correction at box 6115 is discussed in the flowchart of FIG. 13.

FIG. 13 generally corresponds to FIG. 12; however, the estimations of the phase correction components is implemented at the first and second UE, rather than at the BS as in FIG. 12. At box 6305, the BS transmits the reference signals £>[0], b [1], ..., b[N - 1] over N subcarriers (i.e., at different frequencies). The transmitted modulation symbols can be real or complex.

At box 6310, the first UE receives r_x [0], [1], ...,r\[N - 1] via the NCR, with r_t[n] =

produces estimates d_Qf d_lf 0 of d₀, d , 9, respectively, at box 6315.

At box 6320, the second UE receives r₂ [0], r₂ [1], -,r₂[N - 1] via the NCR, with r₂[n] =

produces estimates d_o,d_2l O of d₀, d₂, 0, respectively, at box 6325.

Then, relevant parameters for phase correction are fed back to the BS. This can be implemented using a report message (e.g., a Radio Resource Control, RRC, or Layer 1 or Layer 2 control message) at box 6330. Here, the first and second UEs communicate d₀, d_lr and d₀, d₂, 9, respectively, to the BS.

Alternatively, at box 6335, the first UE inserts pilots Z?'[0], / [l], ...,b’[N’ - 1], The BS receives r'[0],r'[l], ..., r'[N - 1] via the

w'[n]. The BS can now produce suitable estimates of d₀, 9 for DL transmissions. The second UE can alternatively, or additionally, send the reference signals (sometimes also referred to as pilots). The BS may signal the consolidated parameter estimates d_1; 9 and d₂, to UE1 and UE2, respectively (not shown in FIG. 13).

Summarizing, above and with reference to boxes 6105, 6110, and 6115, techniques of compensating for phase errors have been disclosed. The phase offset between the NCR and the TX CD 9 can be either reduced through synchronization or by measuring and pre-compensating.

Note that even in a case where synchronization between the NCR 109 and the BS 101 has been established (i.e., 9 = 0), the frequency-dependent phase offsets can be compensated at the one or more TX CDs and the one or more RX CDs, to account for the distances d₀, d , d₂.

In another scenario, it would be possible that the phase correction is applied depending on whether or not a trigger event is detected. For instance, the trigger event could include determining that the NCR is not capable of establishing the synchronization with the BS. Alternatively or additionally, the trigger event could include that two UEs are being served via one and the same NCR so that l/Q separation becomes an option.

In TDD operation any other variants for parameter estimation presented above can be used. However, in FDD operation frequency-dependent measurements are feasible, because for different carrier frequencies a»_{c UL} , <o_c>DL, different impairments 0_UL, 0_DL can be observed.

FIG. 14 is a signaling diagram illustrating communication between the various CDs 101, 102, 105; such communication being supported by the NCR 109.

The signaling diagram of FIG. 14 corresponds to a scenario in accordance with FIG. 12.

FIG. 14 generally corresponds to TAB. 1 : example I.

At 5005, the NCR 109 provides to the BS 101 a capability message 4005. For instance, a control link (cf. FIG. 4). The capability message 4005 can be indicative of the capability of the NCR 109 to support l/Q separation. Alternatively or additionally, the capability message 4005 can be indicative of the capability of the NCR 109 to establish synchronization with an RF oscillator with the BS 101. For instance, the capability message 4005 could be indicative of the NCR 109 including the RF-conjugator 7013 (cf. FIG. 9).

At 5010, the BS 101 transmits a configuration message 4010 to the NCR 109. The configuration message 4010 can be indicative of activation of the l/Q separation mode. Subsequently, the NCR 109 may activate the l/Q separation, e.g., by controlling the RF/IF processing block 670 accordingly (cf. FIG. 4) to perform the 180° phase offset of the Q-component of one of the two internal signals.

At 5015, the BS 101 transmits, to the UE 102, a configuration message 4015. For instance, this could be an RRC control message.

The configuration message 4015 can be indicative of a request to transmit UL reference signals 4020 at 5020. Alternatively, it would also be possible that always-on reference signals are transmitted at 5020; then, a dedicated request for transmission of the UL reference signals 4020 is not required.

It would be possible that the configuration message 4015 transmitted by the BS 101 at 5015 is indicative of activation of the l/Q separation mode. This can prompt the UE 102 to apply a phase correction when receiving signals for transmitting signals via the NCR 109.

The BS 101 receives, at 5020, multiple UL reference signals 4020 transmitted by the UE 102 at multiple frequencies. This corresponds to box 6110 of the method of FIG. 11; as well as to box 6210 of the method of FIG. 12.

At 5025, the configuration message 4015 is transmitted by the BS 101 to the UE 105; and at 5030, the UL reference signals 4020 are transmitted by the UE 105 to the BS 101 via the NCR 109. This corresponds to box 6110 of the method of FIG. 11 ; as well as box 6225 of the method of FIG. 12.

At 5035, configuration messages 4030 are transmitted by the BS 101 to the UE 102 as well as the UE 105 via the NCR 109. These configuration messages can be indicative of the parameters for applying a phase correction when receiving signals at the UE 102 or the UE 105, as well as when transmitting signals at the UEs 102 and 105 and while operating in the l/Q separation mode. A component can be indicated corresponding to the phase offset 9 between the RF oscillators at the NCR and the BS; and a further component corresponding to frequency-dependent phase shifts can be indicated. This corresponds to box 6235 of the method of FIG. 12.

Next, at 5040, the BS 101 transmits DL data to the UE 102 and further DL data to the UE 105. Both respective data streams are merged into a common signal 711 ; specifically, the I- component 791 of the signal 711 encodes the DL data associated with the UE 102; while the Q- component 792 of the signal 711 encodes the DL data associated with the UE 105. This reduces spectrum utilization if compared to a scenario where the data streams would be transmitted using separate signals at different time or frequency resources.

At the NCR 109, the l/Q separation is applied, as previously discussed in connection with FIG. 6. Thus, the l-component 791 is then provided to the UE 102; while the Q-component 792 is provided to the UE 105.

The BS 101 while transmitting, as well as the UE 102 and the UE 105 while receiving apply phase correction.

FIG. 15 is a signaling diagram illustrating communication between the various CDs 101, 102, 105. The communication is supported by the NCR 109.

The signaling diagram of FIG. 15 corresponds to a scenario in accordance with FIG. 13.

FIG. 15 generally corresponds to TAB. 1 : example I.

5105 corresponds to 5005; and 5110 corresponds to 5010.

At 5115, the BS 101 transmits the configuration message 4015. For instance, the configuration message 4015 can be indicative of a request for the UE 102 to attempt to receive DL reference signals 4021 transmitted at 5120. Other than that, the configuration message 4015 in the example of FIG. 15 corresponds to the configuration message 4015 in the example of FIG. 14.

At 5120, the BS 101 transmits multiple DL reference signals 4021 at multiple frequencies. This corresponds to box 6305 of the method of FIG. 13. The UE 102 receives those reference signals 4021 which corresponds to box 6310 of the method of FIG. 13. Based on this, the UE 102 can estimate the distances between the BS 101 and the NCR 109, as well as between the UE 102 and the NCR 109. The UE 102 can estimate the phase offset between the RF oscillator at the NCR 109 and the RF oscillator the BS 101.

At 5121 , the UE 102 provides, to the BS 101, a respective report message 4023 that is indicative of such parameters. This corresponds to box 6330 of the method of FIG. 13.

Then, 5125 corresponds to 5115 with respect to the UE 105; 5130 corresponds to 5120 with respect to the UE 105; and 5131 corresponds to 5121 with respect to the UE 105.

5135 corresponds to 5035. 5140 corresponds to 5040.

FIG. 14 and FIG. 15 correspond to a scenario in which DL data is transmitted (cf. TAB. 1 : example I). Similarly, it would be possible that a UL transmission employs the l/Q separation, as illustrated in FIG. 16. In FIG. 16, at 5240, the UE 102 transmits a signal that is then converted into the l-component 791 of the signal 711 subsequently transmitted by the NCR 109; and the UE 105 transmits a signal that converted into the Q-component 792 of the signal 711 that is then transmitted by the NCR 109 to the BS 101.

5240 may be preceded, e.g., by the signaling of FIG. 14 or by the signaling of FIG. 15.

FIG. 17 is a flowchart of a method according to various examples. For instance, FIG. 17 could be implemented by a receiver CD, e.g., a UE such as the UE 102 of the UE 105. For the sake of simplicity, it is now assumed for the purpose of the description of FIG. 17, that a BS transmits a signal including an l-component and a Q-component to an NCR and the NCR performs l/Q splitting and provides one respective signal to the UE executing the method of FIG. 17.

The method of FIG. 17 is interrelated to the method of FIG. 11.

At optional box 6705, UL reference signals and/or DL reference signals are communicated. Respective aspects have been discussed in connection with box 6110 of the method of FIG. 11 , as well as in connection with the reference signals 4020 and the reference signals 4021 in the signaling diagrams of FIG. 14 and FIG. 15.

It would be optionally possible that phase correction parameters are then obtained or established.

At box 6710, RX beamforming is applied when receiving, from the NCR, an in-phase component of a signal that is transmitted to the repeater device by the BS. Alternatively, the creditor component could be received. Box 6710 accordingly is interrelated to box 6120 of the method of FIG. 11 and corresponds to 5040 and 5140 of the signaling diagrams of FIG. 14 and FIG. 15.

At 6715, a phase correction is applied to the received signal. This has been discussed in connection with Equation 13.

Phase correction and communication of reference signals at box 6705 may not be required if synchronization can be established between the NCR and the BS.

FIG. 18 is a flowchart of a method according to various examples. For instance, FIG. 18 could be implemented by a TX CD, e.g., a UE such as the UE 102 or the UE 105. The method of FIG. 18 corresponds to the method of FIG. 17, however, pertains to a transmission of UL data.

Box 6805 corresponds to box 6705.

At box 6810, a phase correction is applied, see Eq. 14.

At box 6815, TX beamforming is applied to transmit a signal towards the NCR. This signal that is transmitted at box 6815 is received at the NCR and then included, as the l-compo- nent or the Q-component, in a further signal that is transmitted by the NCR to the BS. This corresponds to FIG. 16, box 5240.

Phase correction and communication of reference signals at box 6715 may not be required if synchronization can be established between the NCR and the BS. FIG. 19 is a flowchart of a method according to various examples. For instance, FIG. 19 could be implemented by a receiver CD such as the BS, e.g., the BS 101. The method of FIG. 19 is interrelated to the method of FIG. 18.

Box 6905 corresponds to box 6805 and to box 6705.

At box 6910, RX beamforming is implemented to receive a signal transmitted by an NCR. The signal includes and l-component, as well as a Q-component. The l-component is associated with a first UE while the Q-component is associated with a second UE.

At box 6915, a phase correction is applied, see Eq. 14.

At box 6920, the l-component and the Q-component are separated from each other, e.g., an analog domain or in digital domain.

Summarizing, techniques have been disclosed for splitting, via a CED, l/Q component of a signal to UEs at different directions from the CED, i.e., an l/Q- and beam-splitting method, without using analog-to-digital or digital-to-analog converters onboard the CED has been disclosed.

A technique for estimating, at the BS and/or UEs, parameters required to carry out the l/Q- and beam-splitting method, as well as related signaling have been disclosed.

Signaling, by a CED, that it is capable of performing the l/Q- and beam-splitting method has been disclosed. Additionally, the CED can be capable of adjusting phase offset impairments that arise during the operation. Additionally, signaling of the frequency for up- and down-conversion (for FDD operation, two of them) have been disclosed.

Although the invention 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 invention includes all such equivalents and modifications and is limited only by the scope of the appended claims.

Claims

C L A I M S

1. A method of operating a device (101 , 109) comprising an array (690) of multiple antenna elements (1094) to contemporaneously provide an in-phase component (791) of a signal (711 , 720) along a first output direction (671) to a first communication device (102) and a quadrature component (792) of the signal (711) along a second output direction (672) to a second communication device (105), wherein the method comprises:

- establishing (6010) a first internal signal (721) and a second internal signal (722) corresponding to the signal (711),

- applying (6015) a 180° phase offset (7530) to the quadrature component (792) of the second internal signal (722),

- applying, at a first subset (691) of the array (690), first phase shifts to the first internal signal (721) when transmitting the first internal signal (721), the first phase shifts being determined based on a normalized subtraction of a first beamforming vector and a second beamforming vector, the first beamforming vector being associated with the first output direction (671), the second beamforming vector being associated with the second output direction (672), and

- applying, at a second subset (692) of the array (690), second phase shifts to the second internal signal (722) when transmitting the second internal signal (722), the second phase shifts being determined based on a normalized sum of the first beamforming vector and the second beamforming vector.

2. The method of claim 1, wherein the device is a repeater device (109), wherein the method further comprises:

- receiving the signal (711) from a communication device (101).

3. The method of claim 1, wherein the device is a transmitter communication device (101), wherein the method further comprises:

- obtaining the signal from a digital-to-analog converter (7101) of the transmitter communication device (101).

4. The method of any one of the preceding claims, further comprising: wherein the 180° phase offset is applied by separating, in the analog domain, the in- phase component (791) and the quadrature component (792) of a baseband representation of the second internal signal (722) and by inverting an amplitude of the quadrature component (792).

5. A method of operating a repeater device (109) comprising an array (690) of multiple antenna elements (1094), the method comprising:

- applying (6005), at a first subset (691) of the array, first phase shifts when receiving an incident signal, thereby obtaining a first internal signal, the first phase shifts being determined based on a normalized subtraction of a first beamforming vector and a second beamforming vector, the first beamforming vector being associated with a first input direction associated with a first communication device, the second beamforming vector being associated with a second input direction associated with a second communication device, - applying (6005), at a second subset (692) of the array, second phase shifts when receiving the incident signal, thereby obtaining a second internal signal, the second phase shifts being determined based on a normalized sum of the first beamforming vector and the second beamforming vector,

- applying (6015) a 180° phase offset to a quadrature component of the second internal signal,

- combining (6020) the first internal signal and the second internal signal, to thereby obtain an output signal comprising the first internal signal as in-phase component and comprising the second internal signal as quadrature component, and

- transmitting (6025) the output signal to a communication device (101).

6. A method of operating a communication device (101), the method comprising:

- transmitting, towards a repeater device (109) and using a transmit interface of the communication device (101), a signal (711) comprising an in-phase component (791) and a quadrature component (792), the in-phase component (791) being for a first communication device (102) served via the repeater device (109), the quadrature component (792) being for a second communication device (105) also served via the repeater device (109), and

- applying, when transmitting the signal (711), a phase correction to mitigate at least one of a phase offset between a radio-frequency oscillator (7501) of the repeater device (109) and a radio-frequency oscillator of the transmit interface, or a frequency-dependent phase shift due to signal propagation between the communication device and the repeater device.

7. The method of claim 6, wherein the phase correction comprises a first component associated with a frequencydependent phase shift due to signal propagation between the communication device and the repeater device and a second component associated with the phase offset.

8. The method of claim 6 or 7, further comprising:

- communicating (5020, 5030, 5120, 5130, 6110, 6205, 6210, 6220, 6225, 6240, 6305, 6310, 6320, 6335), between the communication device (101) and each one of the first communication device (102) and the second communication device (105), multiple reference signals (4020, 4021) at multiple frequencies to determine the phase correction.

9. The method of claim 8, wherein the multiple reference signals comprise at least one of first reference signals (4020) communicated, via the repeater device (109), from the first and second communication devices (102, 105) to the communication device (101) or second reference signals (4021) communicated, via the repeater device (109), from the communication device (101) to the first and second communication devices (102, 105).

10. The method of claim 8 or 9, wherein the multiple reference signals are always-on reference signals.

11. The method of any one of claims 6 to 10, further comprising:

- detecting at least one trigger event, wherein the phase correction is selectively applied responsive to detecting the at least one trigger event.

12. The method of claim 11 , wherein the at least one trigger event comprises determining that the repeater device (109) is not capable of establishing a synchronization of the radio-frequency oscillator of the repeater device with the radio-frequency oscillator of the transmit interface.

13. The method of claim 11 or 12, wherein the at least one trigger event comprises detecting that the first communication device and the second communication device are both being served via the repeater device.

14. A method of operating a first communication device (102), the method comprising:

- receiving (6710), from a repeater device (109) and using a receive interface of the first communication device (102), one of an in-phase component (791) or a quadrature-component (792) of a signal (711) transmitted to the repeater device (109) by a communication device (101), and

- applying (6715), to the signal, a phase correction to mitigate at least one of a phase offset between a radio-frequency oscillator (7501) of the repeater device (109) and a radio-frequency oscillator of the transmit interface, or a frequency-dependent phase shift due to signal propagation between the repeater device (109) and the first communication device (102).

15. The method of claim 14, wherein the phase correction comprises a first component associated with a frequencydependent phase shift due to signal propagation between the repeater device and the first communication device and a second component associated with the phase offset.

16. A method of operating a communication device (101), the method comprising:

- establishing (6105) synchronization (7501) between a radio-frequency oscillator of a repeater device (109) and a radio-frequency oscillator of a transmit interface of the communication device (101), and

- transmitting, towards the repeater device (109), a signal (711) comprising an in-phase component (791) and a quadrature component (792), the in-phase component (791) being for a first communication device (102) served via the repeater device (109), the quadrature component (792) being for a second communication device (105) also served via the repeater device (109).