WO2023206556A1

WO2023206556A1 - Method and apparatus for csi feedback

Info

Publication number: WO2023206556A1
Application number: PCT/CN2022/090730
Authority: WO
Inventors: Hao Liu; Filippo Tosato; Tao Yang; Yan Zhao
Original assignee: Nokia Shanghai Bell Co., Ltd.; Nokia Solutions And Networks Oy; Nokia Technologies Oy
Priority date: 2022-04-29
Filing date: 2022-04-29
Publication date: 2023-11-02

Abstract

Embodiments of the present disclosure relate to CSI feedback. A terminal device obtains power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS for two or more transmission reception points, TRPs, wherein the two or more TRPs are configured to serve the terminal device; and transmits the power imbalance information to one or more of the two or more TRPs. The solution for CSI feedback as provided in the present disclosure can report power imbalance information.

Description

METHOD AND APPARATUS FOR CSI FEEDBACK

FIELD

Embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to a method, device, apparatus and computer readable storage medium for Channel State Information (CSI) feedback.

BACKGROUND

Multiple-Input Multiple-Out-put (MIMO) is one of the key technologies in New Radio (NR) systems and is successful in commercial deployment. In Rel-15/16/17, MIMO features were investigated and specified for both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) systems, of which major parts were for downlink MIMO operation. In Rel-18, it is important to identify and specify necessary enhancements for uplink MIMO, while necessary enhancements on downlink MIMO that facilitate the use of large antenna array.

For MIMO evolution, in Rel-15/16/17, Type-II codebooks are designed to achieve more accurate CSI for one transmission and reception point (TRP) . In Rel. 18, Type II codebooks are aimed at extending to multiple TRPs and supporting coherent joint transmission (CJT) scheme, in which a MIMO layer can be mapped to antennas of multiple TRPs.

SUMMARY

In general, example embodiments of the present disclosure provide a solution for CSI feedback.

In a first aspect, there is provided a terminal device. The terminal device comprises at least one processor; and at least one memory including computer program codes. The at least one memory and the computer program codes are configured to, with the at least one processor, cause the terminal device to: obtain power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS for two or more transmission reception points, TRPs, the two or more TRPs are configured to serve the terminal device; and transmit the power imbalance information to one or more of the two or more TRPs.

In a second aspect, there is provided a network device. The device comprises at least one processor; and at least one memory including computer program codes; wherein the at least one memory and the computer program codes are configured to, with the at least one processor, cause the network device to: receive, from a terminal device, power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS; and construct a precoding matrix at least based on the received power imbalance information.

In a third aspect, there is provided a method implemented at a terminal device. The method comprises obtaining power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS for two or more transmission reception points, TRPs, wherein the two or more TRPs are configured to serve the terminal device; and transmitting the power imbalance information to one or more of the two or more TRPs.

In a fourth aspect, there is provided a method implemented at a network device. The method comprises receiving, from a terminal device, power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS; and constructing a precoding matrix at least based on the received power imbalance information.

In a fifth aspect, there is provided an apparatus of terminal device comprising means for obtaining power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS for two or more transmission reception points, TRPs, wherein the two or more TRPs are configured to serve the terminal device; and means for transmitting the power imbalance information to one or more of the two or more TRPs.

In a sixth aspect, there is provided an apparatus of network device comprising means for receiving, from a terminal device, power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS; and means for constructing a precoding matrix at least based on the received power imbalance information.

In a seventh aspect, there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the method according to any one of the above third to fourth aspect.

It is to be understood that the summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Some example embodiments will now be described with reference to the accompanying drawings, where:

Fig. 1 illustrates an example communication network in which embodiments of the present disclosure may be implemented;

Fig. 2 illustrates a flowchart of a method 200 of CSI report enhancement at terminal device according to some embodiments of the present disclosure;

Fig. 3 illustrates an example of codebook structure 300 according to some embodiments of the present disclosure;

Fig. 4 illustrates an example of codebook structure 400 according to some embodiments of the present disclosure;

Fig. 5 illustrates a flowchart of a method 500 of CSI enhancement at network device according to some embodiments of the present disclosure;

Fig. 6 illustrates a process 600 for CSI feedback according to some embodiments of the present disclosure.

Fig. 7 illustrates a simplified block diagram of an apparatus that is suitable for implementing embodiments of the present disclosure; and

Fig. 8 illustrates a block diagram of an example computer readable medium in accordance with some embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

References in the present disclosure to “one embodiment, ” “an embodiment, ” “an example embodiment, ” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a” , “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” , “comprising” , “has” , “having” , “includes” and/or “including” , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof.

As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable) :

(i) a combination of analog and/or digital hardware circuit (s) with software/firmware and

(ii) any portions of hardware processor (s) with software (including digital signal processor (s) ) , software, and memory (ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) hardware circuit (s) and or processor (s) , such as a microprocessor (s) or a portion of a microprocessor (s) , that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

As used herein, the term “communication network” refers to a network following any suitable communication standards, such as Long Term Evolution (LTE) , LTE-Advanced (LTE-A) , Wideband Code Division Multiple Access (WCDMA) , High-Speed Packet Access (HSPA) , Narrow Band Internet of Things (NB-IoT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the third generation (3G) , the fourth generation (4G) , 4.5G, the future fifth generation (5G) communication protocols, and/or beyond. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP) or a transmission and reception point (TRP) , for example, a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a NR NB (also referred to as a gNB) , a Remote Radio Unit (RRU) , a radio header (RH) , a remote radio head (RRH) , an Integrated Access and Backhaul (IAB) node, a relay, a low power node such as a femto, a pico, and so forth, depending on the applied terminology and technology.

The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE) , a Subscriber Station (SS) , a Portable Subscriber Station, a Mobile Station (MS) , or an Access Terminal (AT) . The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA) , portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE) , laptop-mounted equipment (LME) , USB dongles, smart devices, wireless customer-premises equipment (CPE) , an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD) , a vehicle, a drone, a medical device and applications (e.g., remote surgery) , an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts) , a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like. In the following description, the terms “terminal device” , “communication device” , “terminal” , “user equipment” and “UE” may be used interchangeably.

As used herein, the term “resource” , “transmission resource” , “resource block” , “physical resource block” (PRB) , “uplink (UL) resource” or “downlink (DL) resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network device, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, a resource in a combination of more than one domain or any other resource enabling a communication, and the like. In the following, a resource in time domain (such as, a subframe) will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

As used herein, the term “TRP” refers to a transmit-receive point having an antenna array (with one or more antenna elements) at the network side located at a specific geographical location, which may be used for transmitting and receiving signals to/from the terminal device. In embodiment of the present disclosure, a TRP may refer to Macro Cell, micro cell, an RRH, a relay, a femto node, a pico node, etc. Although some embodiments of the present disclosure are described with reference to two TRPs for example, these embodiments are only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitations as to the scope of the present disclosure. It is to be understood that the present disclosure described herein can be implemented in various manners other than the ones described below.

As discussed above, Multiple-Input Multiple-Out-put (MIMO) is one of the key technologies in New Radio (NR) systems and is successful in commercial deployment. In Rel-15/16/17, MIMO features were investigated and specified for both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) systems, of which major parts were for downlink MIMO operation. In Rel-18, it is important to identify and specify necessary enhancements for uplink MIMO, while necessary enhancements on downlink MIMO that facilitate the use of large antenna array.

For MIMO evolution, in Rel-15/16/17, Type-II codebooks are designed to achieve more accurate CSI for one TRP. In Rel. 18, Type II codebooks are aimed at extending to multiple TRPs and supporting Coherent Joint Transmission (CJT) scheme, in which a MIMO layer can be mapped to antennas of multiple TRPs. Currently, how to accurately design and specify the channel information feedback among multiple TRPs is one of key challenges of Rel. 18 task.

According to embodiments of the present disclosure, there is provided a solution for Type II codebook enabling satisfactory Rel. 18 CJT application. In this solution, the wideband (WB) power imbalances associated with all the TRPs (except for the reference TRP) will be reported to the network by a terminal device. By this solution, the multi-TRP CSI feedback accuracy may be increased and the CJT throughput may be improved correspondingly.

Although functionalities described herein can be performed, in various example embodiments, in a fixed and/or a wireless network node may, in other example embodiments, functionalities may be implemented in user equipment (such as a cell phone or tablet computer or laptop computer or desktop computer or mobile IOT device or fixed IOT device) . This user equipment may, for example, be furnished with corresponding capabilities as described in connection with the fixed and/or the wireless network node (s) , as appropriate. The user equipment may be the user equipment and/or or a control device, such as a chipset or processor, configured to control the user equipment when installed therein. Examples of such functionalities include the bootstrapping server function and/or the home subscriber server, which may be implemented in the user equipment apparatus by providing the user equipment apparatus with software configured to cause the user equipment apparatus to perform from the point of view of these functions/nodes.

Principle and embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. However, it is to be noted that these embodiments are given to enable the skilled in the art to implement the solution as proposed herein and not intended to limit scope of the present application in any way.

Reference is first made to Fig. 1, which illustrates an example communication system 100 in which embodiments of the present disclosure may be implemented. As illustrated in Fig. 1, the system 100 includes two network devices, such as two

network devices

111 and 112. The

network devices

111 and 112 may have one respective group of antenna ports. So the

network devices

111 and 112 may be associated with or function as two respective TRPs, and thus can be also called as TRP 111 and TRP 112 in the present disclosure. The TRP 111 and TRP 112 have antenna ports belonging to the two respective CSI-RS port groups and may use coherent joint transmission, CJT, for downlink, DL, communication. In the CJT, joint beamforming is performed from all coordinated TRPs, and thus can be regarded as a distributed multiple-input multiple-output. (MIMO) system.

The system 100 also includes terminal devices, such as a terminal device 101. The terminal device 101 is capable of communicating with the TRP 111 and TRP 112. The terminal device 101 may receive CSI-RS resources information from the two TRPs. The terminal device 101 may determine precoding information/parameters for DL precoding by the at least two respective TRPs based on the one or more received CSI-RS resources. The terminal device 101 may further transmit CSI report to the one or more TRPs. The CSI report comprises precoding information.

In the solution of present disclosure, the precoding information further comprises power imbalances information reflecting power difference among different TRPs. Then the TRP 111 and/or TRP 112 can construct a precoding matrix at least based on the received power imbalance information.

In communication systems, “UL” refers to a communication link in a direction from a terminal device to a network device, and “DL” refers to a communication link in a direction from the network device to the terminal device.

It is to be understood that in Fig. 1, the number of network devices (TRPs) and terminal devices is only for the purpose of illustration without suggesting any limitations. The system 100 may include any suitable number of network devices (TRPs) and terminal devices adapted for implementing embodiments of the present disclosure.

Communications in the communication system 100 may be implemented according to any proper communication protocol (s) , comprising, but not limited to, cellular communication protocols of the third generation (3G) , the fourth generation (4G) and the fifth generation (5G) or beyond, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and/or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA) , Frequency Division Multiple Access (FDMA) , Time Division Multiple Access (TDMA) , Frequency Division Duplex (FDD) , Time Division Duplex (TDD) , Multiple-Input Multiple-Output (MIMO) , Orthogonal Frequency Division Multiple (OFDM) , Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and/or any other technologies currently known or to be developed in the future.

Reference is made to Fig. 2, which illustrates a method 200 of CSI enhancement at terminal device. In this method, a solution is provided to report power imbalances associated with all the TRPs (except for the reference TRP) by a terminal device. Hereinafter, the solution will be described with reference to CJT, but it is to be noted that it is only an example scenario and the present disclosure is not limited thereto.

At block 210, the terminal device obtains power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS for two or more transmission reception points, TRPs, the two or more TRPs are configured to serve the terminal device. The power imbalance information indicates the difference among the two or more TRPs to the terminal device.

In some embodiments, the power imbalance information is reflected within the information on selection of spatial-domain basis components of precoding information. Reference is made to Fig. 3, which illustrates an example of CJT codebook structure, for a generic layer. In this codebook, for example, the number of TRP is N _TRP=2 and the number of beams is L=4. In the codebook, three codebook components are considered which comprise Space Domain (SD) beam matrix W ₁, Frequency Domain (FD) component matrix W _f and combination coefficient matrix W ₂.

As illustrated in Fig. 3, matrix W ₁ is a block diagonal matrix for two polarizations with dimension of 2N _TRPN ₁N ₂×2L. N ₁ is antenna ports in azimuth and N ₂ is antenna ports in elevation, for each polarisation. And 2N ₁N ₂ are antenna ports in total per TRP. In matrix W ₁, each block containing for example, L=4 aggregated SD beams v _i. In this codebook, beams selected for two or more TPRs are aggregated within matrix W ₁.

As illustrated in Fig. 3, matrix W _f is common to all TRPs. Matrix W _f is composed of M=4 FD components, each with the size of N ₃. Alternatively, or additionally, W _f can be designed differently for TRPs. In some embodiments, the FD components may be designed in terms of the number of the frequency bands or the subbands.

As illustrated in Fig. 3, combination coefficients are constructed to matrix W ₂ with dimension of 2L×M by matrix W _f and W ₁.

When multiple TRPs, such as TRP 111 and TRP 112 in Fig. 1, jointly serve a terminal device, such as terminal device 101, by using CJT mode, power imbalance among different TRPs unavoidably exists due to different transport distance to the same terminal device. Such power imbalance has large impact on CSI quantization accuracy and CJT transmission throughput.

According to the above CJT codebook design shown in Fig. 3, FD components matrix W _f is related to multi-path delays instead of power imbalance. Combination coefficients of matrix W ₂ are used to linearly combine different pairs of spatial domain (SD) beam and FD component and to approximate aggregated eigenvectors from multiple TRPs for multiple layers and subbands.

However, according to Fig. 3, combination coefficients may have different weight effect on antenna ports of 2 polarizations, but are common to antenna ports of multiple TRPs, so matrix W ₂ feedback cannot solve power imbalance problem.

In some embodiments, to enhance CJT codebook and CSI report at terminal device, a method is provided for reporting wideband (WB) power imbalances and/or phase offsets associated with all the TRPs (except for a reference TRP) by a terminal device together with SD beams per TRP in matrix W ₁.

In some embodiments , the power imbalance information comprises: a reference TRP among the two or more TRPs in the two or more TRPs and a power imbalance factor each of the two or more TRPs except for the reference TRP.

The additional feedback issues may help to determine the optimal SD beam selection and permutation for each TRP (except for the reference TRP) and to achieve the most significant beamforming gains for the aggregated SD beams, so that multi-TRP CSI feedback accuracy can be increased and thus CJT throughput can be improved correspondingly.

As shown in Fig. 3, matrix W ₁ of Type II codebook is a block diagonal matrix and is composed of L aggregated SD beams common to 2 polarizations:

In some embodiments, the aggregated SD beams v _i, i=0, …, L-1, can be expressed as follows:

wherein

denotes the SD beam i for TRP x=0, …N _TRP-1;

denotes the permuted SD beam i for TRP x;

TRP 0 denotes a reference TRP among the two or more TRPs, x=0;

α _x denotes power imbalance factor of all TRPs except for the reference TRP, x=1, …N _TRP-1;

denotes phase offset of all TRPs except for the reference TRP, x=1, …N _TRP-1;

In some embodiments, the index of the reference TRP is quantized and reported as

bits.

In some embodiments, the power imbalance α _x is quantized uniformly or non-evenly over (0, 1) .

In some embodiments, the power imbalance α _x is common or different to all the aggregated beams.

In some embodiments, the phase offset is quantized uniformly over [0, 2π] .

In some embodiments, the phase offset is common or different to all the aggregated beams.

In some embodiments, the calculation and feedback process for power imbalance information and phase offsets is as below.

By means of such codebook, it is possible consider the power imbalance information in DL precoding.

In some embodiments, the power imbalance information may be determined based on power information (including for example, received power or channel amplitude statistic value from each TRP, etc. ) of the two or more TRPs measured from CSI-RS, resources associated with the two or more TRPs.

Taking the scenario of Fig. 1 as an example, wherein there are N _TRP=2 TRPs, such as TRP 111 and TRP 112, and they are coordinated to serve a terminal device, such as terminal device 101 in Fig. 1. From the CSI-RS measurement, WB dominant eigenvector

and

are determined, for example, are calculated and averaged over 2 polarizations and all frequency units (e.g., subcarriers or PRBs) for the 2 TRPs respectively. Each of the TPRs having the dimension of N ₁N ₂×1 in a single polarization. Channel matrices of the 2 TRPs are aggregated. WB dominant eigenvector

is calculated and averaged over 2 polarizations and all frequency units for the aggregated channel.

has the dimension of 2N ₁N ₂×1 per polarization, as below:

In above formula,

is an eigenvector component associated with TRP x, with dimension of N ₁N ₂×1.

Power imbalance of the 2 TRPs are denoted by the factors α ₁₁₁ and α ₁₁₂∈ (0, 1) , which may be calculated as follows:

wherein α ₁₁₁ and α ₁₁₂Satisfy (α ₁₁₁) ²+ (α ₁₁₂) ²=1 due to

For example, TRP 111 is set to the reference TRP, and the power α ₁₁₂ of TRP 112 is quantized according to

or

with uniform or non-even quantization granularity over (0, 1) .

In some embodiments, the terminal device is further configured to obtain phase offset information, wherein the phase offset information comprises a phase offset factor for each of the two or more TRPs except for the reference TRP.

In some embodiments, phase offset information are further reported to the network and the phase offset is determined based on phase information of the two or more TRPs measured from CSI-RS, resources associated with the two or more TRPs.

Also taking the scenario of Fig. 1 as an example, phase offset among these 2 TRPs is denoted by

for TRP 112 over TRP 111. The phase offset

may be calculated as follows:

Where the scalar

x=111, 112, is the correlation coefficient of vector

and

for TRP x,

is the amplitude of scalar

and θ _x is its phase. Thus, the phase offset between TRP 112 and TRP 111 may be determined as

and it can be quantized uniformally over [0, 2π] .

Therefore, the aggregated beam of matrix W ₁ as shown Fig. 3 may be denoted by

for SD beam i=0, …, L-1. When power imbalance and phase offset are considered, the aggregated beam may be updated as

The power imbalance and/or phase offset values may help to determine the optimal L SD beams for each TRP except for the reference TRP and then beam permutation operation to achieve the most significant beamforming gains for all the L aggregated beams.

In this solution, the other two codebook components of CJT Type II CSI, including FD components W _f, and combination coefficients W ₂, as shown in Fig. 3, may not be modified.

In some embodiments, such a codebook regarding power imbalance information for the CSI report can be configured by the network by for example a higher layer. signaling. In such a case, the terminal device 101 may receive a codebook configuration regarding power imbalance information for the CSI report.

Reference is made to Fig. 4, which illustrates an example of another CJT codebook structure for a generic layer. In this codebook, for example, the number of TRP N _TRP=2 and the number of beams is L=4. The code book comprises SD beam matrix W ₁, FD component matrix W _f and combination coefficient matrix W ₂.

As illustrated in Fig. 4, for example, matrix W ₁ is a matrix for two polarizations with dimension of 2N _TRPN ₁N ₂×2L. N ₁ is antenna ports in azimuth and N ₂ is antenna ports in elevation, for each polarisation. And 2N ₁N ₂ are antenna ports in total per TRP. In matrix W ₁, each block containing L=2 SD beams v _i.

As illustrated in Fig. 4, matrix W _f is common to all TRP and is composed of M=4 FD components, with the size of N ₃ each. Alternatively, or additionally, W _f can be designed differently for TRPs. In some embodiments, the FD components may be designed in terms of the number of the frequency bands or the subbands.

As illustrated in Fig. 4, combination coefficients are constructed to matrix W ₂ with dimension of 2L×M by matrix W _f and W ₁.

In this codebook, terminal device 101 selects L ₁₁₁=2 and L ₁₁₂=2 beams for TRP 111 and TRP 112, respectively, with L ₁₁₁+L ₁₁₂=L. The beams selected for the two TRPs are not combined in W ₁ to form a beam for the aggregated array. The combination is done by the coefficients in W ₂. In other words, beams selected for the two or more TPRs are combined within information on the combination coefficients of basis components.

When multiple TRPs, such as TRP 111 and TRP 112 in Fig. 1, jointly serve a terminal device, such as terminal device 101, by using CJT mode, power imbalance among different TRPs unavoidably exists due to different transport distance to the same terminal device, and it has large impact on CSI quantization accuracy and CJT transmission throughput.

According to the above CJT codebook design shown in Fig. 4, FD components matrix W _f is related to multi-path delays instead of power imbalance. Combination coefficients of matrix W ₂ are used to linearly combine different pairs of SD beam and FD component and to approximate aggregated eigenvectors from multiple TRPs.

In matrix W ₂, the coefficients might be different for antenna ports of different TRPs, and power imbalance may induce large variation of amplitude values and affect their quantization accuracy.

In some embodiments, a solution is provided to enhance Type II codebook for Rel. 18 CJT application. In this method, the power imbalance between TRPs is compensated in W ₂ by determining the reference amplitude of the strongest coefficient for each TRP. The strongest coefficient for each TRP is indicated by the strongest coefficient indicator (SCI) for each TRP. And the strongest coefficient for each TRP is scaled by a strongest coefficient of a reference TRP. The reference TRP has strongest coefficient among all TRPs.

In some embodiment of the present disclosure, the power imbalance information comprises: a strongest coefficient indicator, SCI, for each TRP of the two or more TRPs; and reference amplitude associated with different polarisations for each TRP of the two or more TRPs.

In some embodiments, for example, one TRP may be denoted by k. So the SCI of TRP k may be indicated by the position (e.g., polarization, beam) of the strongest coefficient in a sub matrix of size 2L _kM with log ₂ (2L _kM) bits. The sub matrix is for TRP k in matrix W ₂.

In some embodiments, the FD basis component of the strongest coefficient for the reference TRP can be assumed to be component 0 of the FD basis codebook. So the first column of matrix W ₂ has the strongest frequency components, the SCI of TRP k may be indicated only by the beam position with log ₂ (2L _k) bits.

In some embodiments, the SCI of the reference TRP indicates a position where the strongest coefficient of the reference TRP is located within a matrix of the combination coefficients of basis components. For example, if SCIs for TRPs excluding the reference TRP are reported, the SCI for the reference TRP may be reported separately. The SCI for the reference TRP may be indicated by log ₂ (2L) bits. The log ₂ (2L) bits indicate the polarisation and the beam and the index of the reference TRP where the strongest coefficient is located.

In some embodiments, the SCI of a reference TRP indicates an index of the reference TRP among the two or more TRPs. For example, if SCIs for all TRPs (including the reference TRP) are reported, the SCI for the reference TRP may be additionally indicated by an index among all TRPs. For example, the number of total TRPs can be denoted by N _TRP , the SCI of the reference TRP can be additionally indicated by an index with

bits among all TRPs.

In some embodiments, there are 2 polarisations for each TRP. One polarisation is stronger polarisation having the strongest coefficient of the TRP, and then another polarisation is weaker polarisation.

In some embodiments, the reference amplitude of each of the two or more TRPs for the weaker polarization may be reported. For example, the total number of TRPs is denoted byN _TRP. And N _TRP reference amplitudes are reported for the weaker polarisation of all TRPs.

In some embodiments, reference amplitude of each of the two or more TRPs except for the reference TRP for the stronger polarization may be reported. For example, the N _TRP-1 reference amplitudes are reported for the stronger polarisation of each TRP except the reference TRP.

In some embodiments, the reference amplitude, relative amplitude and phase of strongest coefficient of the reference TRP are not reported. And the relative amplitude of strongest coefficient of each of the other NTRP-1 TRPs is not reported.

In this method, the other two codebook components of CJT Type II CSI, including FD components W _f, and combination coefficients W ₁, as shown in Fig. 4, may not be modified.

In some embodiments, the terminal device may receive a codebook configuration regarding combination coefficients of basis component.

At block 220, the terminal device transmits the power imbalance information to one or more of the two or more TRPs. In some embodiments, the power imbalance information may be included in CSI report.

Reference is made to Fig. 5, which illustrates a method 500 of CJT codebook and CSI enhancement at network device.

At block 510, the network device such as a TRP may receive, from a terminal device, power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS

At block 520, additionally, the network device constructs a precoding matrix at least based on the received power imbalance information.

It is to be noted that, the codebook at the network side is similar to the codebook at the terminal device and the received CSI information regarding power imbalances or phase offset values are also similar to those reported by the terminal device. Therefore, details of the codebook and received parameter may refer to those descriptions with Fig. 1 to 4 and will be omitted herein.

Reference is now made to Fig. 6, which shows a process 600 for CSI feedback according to an embodiment of the present disclosure. For the purpose of discussion, the process 600 will be described with reference to Fig. 1. The process 600 may involve the terminal device 101 and the network device 111, network 112 as illustrated in Fig. 1. It would be appreciated that although the process 600 has been described in the communication system 100 of Fig. 1, this process may be likewise applied to other communication scenarios where different network devices are jointly deployed to provide respective serving cells. It would also be appreciated that although the CSI feedback of the terminal device 101 is discussed, a similar process can be applied for any other terminal devices.

In the process 600, the network device 111 transmits 601 CSI-RS information to terminal device 101and the network device 112 transmits 602 CSI-RS information to terminal device 101. The terminal device 101 obtains 603 obtain power imbalance information based on measurement of the CSI-RS. The power imbalance information indicates the difference among the two network devices to the terminal device 101. Then the terminal device 101 transmits 604/605 the power imbalance information to one or both of network device 111 and network device 112. The power imbalance information may be included in CSI report, but not limited thereto. The network device 111 receives the power imbalance information and constructs 606 a precoding matrix at least based on the received power imbalance information. The network device 112 may also receive the power imbalance information or obtain the information from the network device 111, and constructs 607 a precoding matrix at least based on the received power imbalance information.

In some embodiments, an apparatus capable of performing any of the method 200 (for example, the terminal device 101) may comprise means for performing the respective steps of the method 200. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some embodiments, the apparatus comprises means for means for obtaining power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS for two or more transmission reception points, TRPs, wherein the two or more TRPs are configured to serve the terminal device; and means for transmitting the power imbalance information to one or more of the two or more TRPs.

In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of the method 200. In some embodiments, the means comprises at least one processor; and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

In some embodiments, an apparatus capable of performing any of the method 500 (for example, the network device 111) may comprise means for performing the respective steps of the method 500. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. In some embodiments, the apparatus comprises: means for means for receiving, from a terminal device, power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS; and means for constructing a precoding matrix at least based on the received power imbalance information.

In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of the method 500. In some embodiments, the means comprises at least one processor; and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

FIG. 7 is a simplified block diagram of a device 700 that is suitable for implementing embodiments of the present disclosure. The device 700 may be provided to implement the communication device, for example the terminal device 101, the network device 111 and network device 112 as shown in Fig. 1. As shown, the device 700 includes one or more processors 710, one or more memories 740 coupled to the processor 710, and one or more transmitters and/or receivers (TX/RX) 740 coupled to the processor 710.

The TX/RX 740 is for bidirectional communications. The TX/RX 740 has at least one antenna to facilitate communication. The communication interface may represent any interface that is necessary for communication with other network elements.

The processor 710 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 700 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

The memory 720 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 724, an electrically programmable read only memory (EPROM) , a flash memory, a hard disk, a compact disc (CD) , a digital video disk (DVD) , and other magnetic storage and/or optical storage. Examples of the volatile memories include, but are not limited to, a random access memory (RAM) 722 and other volatile memories that will not last in the power-down duration.

A computer program 730 includes computer executable instructions that are executed by the associated processor 710. The program 730 may be stored in the ROM 720. The processor 710 may perform any suitable actions and processing by loading the program 730 into the RAM 722.

The embodiments of the present disclosure may be implemented by means of the program 730 so that the device 700 may perform any process of the disclosure as discussed with reference to FIGs. 2 to 6. The embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

In some embodiments, the program 730 may be tangibly contained in a computer readable medium which may be included in the device 700 (such as in the memory 720) or other storage devices that are accessible by the device 700. The device 700 may load the program 730 from the computer readable medium to the RAM 722 for execution. The computer readable medium may include any types of tangible non-volatile storage, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. Fig. 8 shows an example of the computer readable medium 800 in form of CD or DVD. The computer readable medium has the program 730 stored thereon.

Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the

method

200 and 500 as described above with reference to FIGs. 2-6. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

In the context of the present disclosure, the computer program codes or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in languages specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A terminal device, comprising:

at least one processor; and

at least one memory including computer program codes;

wherein the at least one memory and the computer program codes are configured to, with the at least one processor, cause the terminal device to:

obtain power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS for two or more transmission reception points, TRPs, wherein the two or more TRPs are configured to serve the terminal device; and

transmit the power imbalance information to one or more of the two or more TRPs.
The terminal device of claim 1, wherein the power imbalance information indicates the difference among the two or more TRPs to the terminal device.
The terminal device of claims 1 or 2, wherein the power imbalance information is reflected within the information on selection of spatial-domain basis components of precoding information.
The terminal device of any of claims 1 to 3, wherein the power imbalance information comprises:

a reference TRP among the two or more TRPs; and

a power imbalance factor for each of the two or more TRPs except for the reference TRP.
The terminal device of any of claims 1 to 4, wherein the terminal device is further configured to obtain phase offset information, wherein the phase offset information comprises a phase offset factor for each of the two or more TRPs except for the reference TRP.
The terminal device of any one of claims 1 to 5, wherein the terminal device is further configured to:

receive a codebook configuration regarding power imbalance information.
The terminal device of claims 1 or 2, wherein the power imbalance information is reflected within information on combination coefficients of basis components of precoding information.
The terminal device of claim 7, wherein the power imbalance information comprises:

a strongest coefficient indicator, SCI, for each TRP of the two or more TRPs; and

reference amplitude associated with different polarisations for each TRP of the two or more TRPs.
The terminal device of claims 7 or 8, wherein the power imbalance information comprises:

a SCI of a reference TRP among the two or more TRPs, wherein the reference TRP has strongest coefficient in combination coefficients of basis components for the two or more TRPs.
The terminal device of claim 9, wherein the SCI of the reference TRP indicates a position where the strongest coefficient of the reference TRP is located within a matrix of the combination coefficients of basis components; and

wherein the power imbalance information comprises: an SCI of each of the two or more TRPs except for the reference TRP, indicating a position where the strongest coefficient of the TRP is located within a submatrix of the combination coefficients of basis components for the TRP.
The terminal device of claim 9, wherein the SCI of a reference TRP indicates an index of the reference TRP among the two or more TRPs; and

wherein the power imbalance information comprises: an SCI of each of the two or more TRPs including the reference TRP, indicating a position where the strongest coefficient of the TRP is located within a submatrix of the combination coefficients of basis components for the TRP.
The terminal device of any one of claims 10 to 11, wherein the reference amplitude of each of the two or more TRPs is scaled by the strongest coefficient of the reference TRP.
The terminal device of any of claims 7 to 12, wherein the power imbalance information comprises one or both:

reference amplitude of each of the two or more TRPs for the weaker polarization; and

reference amplitude of each of the two or more TRPs except for the reference TRP for the stronger polarization.
The terminal device of any of claims 7 to 13, wherein the terminal device is further configured to:

receive a codebook configuration regarding combination coefficients of basis component.
A network device comprising, comprising:

at least one processor; and

at least one memory including computer program codes;

wherein the at least one memory and the computer program codes are configured to, with the at least one processor, cause the terminal device to:

receive, from a terminal device, power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS; and

construct a precoding matrix at least based on the received power imbalance information.
The network device of claim 15, wherein the power imbalance information indicated the difference among TRPs to the terminal device.
The network device of claims 15 or 16, wherein the power imbalance information is reflected within the information on selection of spatial-domain basis components of precoding information.
The network device of claims 15 or 16, wherein the power imbalance information is reflected within information on combination coefficients of basis components of precoding information.
A method at a terminal device comprising:

obtaining power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS for two or more transmission reception points, TRPs, wherein the two or more TRPs are configured to serve the terminal device; and

transmitting the power imbalance information to one or more of the two or more TRPs.
A method at a network device comprising:

receiving, from a terminal device, power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS; and

constructing a precoding matrix at least based on the received power imbalance information.
An apparatus of terminal device comprising:

means for obtaining power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS for two or more transmission reception points, TRPs, wherein the two or more TRPs are configured to serve the terminal device; and

means for transmitting the power imbalance information to one or more of the two or more TRPs.
An apparatus of network device comprising:

means for receiving, from a terminal device, power imbalance information based on measurement of downlink, DL, channel state information reference signal, CSI-RS; and

means for constructing a precoding matrix at least based on the received power imbalance information.
A non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the method of any of claims 19 to 20.