WO2020164119A1

WO2020164119A1 - Apparatus, method and computer program

Info

Publication number: WO2020164119A1
Application number: PCT/CN2019/075244
Authority: WO
Inventors: Hao Liu; Wolfgang Zirwas; Marco MASO
Original assignee: Nokia Shanghai Bell Co., Ltd.; Nokia Solutions And Networks Oy; Nokia Technologies Oy
Priority date: 2019-02-15
Filing date: 2019-02-15
Publication date: 2020-08-20
Also published as: CN113439396B; CN113439396A

Abstract

According to the disclosure there is provided an apparatus comprising means for performing: dividing channel state information into a first part and a second part, for a channel state information message to be sent from the apparatus; and in the first part, including information of a number of spatial beams of the apparatus, and information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the apparatus.

Description

APPARATUS, METHOD AND COMPUTER PROGRAM

Field

This disclosure relates to communications, and more particularly to an apparatus, method and computer program in a wireless communication system. More particularly the present invention relates to channel state information.

Background

A communication system can be seen as a facility that enables communication between two or more devices such as user terminals, machine-like terminals, base stations and/or other nodes by providing communication channels for carrying information between the communicating devices. A communication system can be provided for example by means of a communication network and one or more compatible communication devices. The communication may comprise, for example, communication of data for carrying data for voice, electronic mail (email) , text message, multimedia and/or content data communications and so on. Non-limiting examples of services provided include two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet.

In a wireless system at least a part of communications occurs over wireless interfaces. Examples of wireless systems include public land mobile networks (PLMN) , satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN) . A local area wireless networking technology allowing devices to connect to a data network is known by the tradename WiFi (or Wi-Fi) . WiFi is often used synonymously with WLAN. The wireless systems can be divided into cells, and are therefore often referred to as cellular systems. A base station provides at least one cell.

A user can access a communication system by means of an appropriate communication device or terminal capable of communicating with a base station. Hence nodes like base stations are often referred to as access points. A communication device of a user is often referred to as user equipment (UE) .

A communication system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. Communication protocols and/or parameters which shall be used for the connection are also typically defined. Non-limiting examples of standardised radio access technologies include GSM (Global System for Mobile) , EDGE (Enhanced Data for GSM Evolution) Radio Access Networks (GERAN) , Universal Terrestrial Radio Access Networks (UTRAN) and evolved UTRAN (E-UTRAN) . An example communication system architecture is the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The LTE is standardized by the third Generation Partnership Project (3GPP) . The LTE employs the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access and a further development thereof which is sometimes referred to as LTE Advanced (LTE-A) .

Since introduction of fourth generation (4G) services increasing interest has been paid to the next, or fifth generation (5G) standard. 5G may also be referred to as a New Radio (NR) network. Standardization of 5G or New Radio networks has been finalized in 3GPP release 15.

Statement of invention

According to a first aspect there is provided an apparatus comprising means for performing: dividing channel state information into a first part and a second part, for a channel state information message to be sent from the apparatus; and in the first part, including information of a number of spatial beams of the apparatus, and information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the apparatus.

According to an example the restricted frequency domain coefficient subset comprises a subset of a full frequency domain coefficient matrix for all spatial beams of the apparatus. According to some examples the restricted frequency domain coefficient subset is obtained by applying a bit-mask to the full frequency domain coefficient matrix.

According to an example the information of a number of spatial beams of the apparatus comprises a numerical quantity of spatial beams, L ₀, selected from 2L-1 spatial beams of the apparatus, where 2L is a total number of spatial beams of the apparatus.

According to an example the information of non-zero frequency domain coefficients comprises a ratio of non-zero coefficients, K ₁, to L _o＊ (M-1) or L _o＊M coefficients in the restricted frequency domain coefficient subset, where M represents a total number of frequency domain components per beam.

According to an example the ratio is represented by α ∈ (0, 1) , and where

or

According to an example α has a constant payload size.

According to an example the means are further configured to perform explicitly indicating a total payload size of the channel state information message, in the second part.

According to an example the means are further configured to perform reporting indices of the non-zero frequency domain coefficients of the restricted frequency domain coefficient subset in the second part, according to: combinatorial indexing with

bits where

or a bitmap with L ₀ (M-1) bits; or combinatorial indexing with

bits where

or a bitmap with L ₀M bits.

According to an example the means are further configured to divide wideband frequency domain coefficients in to a plurality of parameters to be reported in the second part, the wideband frequency domain coefficients being associated with a respective wideband frequency domain component and being non-zero frequency domain coefficients.

According to an example the plurality of parameters to be reported comprises: a strongest index of the wideband frequency domain coefficients, and quantizing the index as

bits, where 2L is a total number of spatial beams of the apparatus; indices of L ₀ spatial beams out of 2L-1 frequency domain coefficients, which are quantized jointly using combinatorial signaling with

bits, where L ₀ comprises a numerical quantity of spatial beams selected from 2L-1 spatial beams of the apparatus; and information of L ₀ frequency domain coefficients in terms of amplitude and phase, which is quantized as (q _a+q _p) × L ₀ bits, where q _a represents a bit length of amplitude and q _p represents a bit length of phase.

According to an example 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.

According to a second aspect there is provided an apparatus comprising: dividing circuitry for dividing channel state information into a first part and a second part, for a channel state information message to be sent from the apparatus; and including circuitry for, in the first part, including information of a number of spatial beams of the apparatus, and information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the apparatus.

According to a third aspect there is provided a method comprising: dividing channel state information into a first part and a second part, for a channel state information message to be sent from an apparatus; and in the first part, including information of a number of spatial beams of the apparatus, and information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the apparatus.

According to an example the ratio is represented by α ∈ (0, 1) , and where

or

According to an example α has a constant payload size.

According to an example the method comprises explicitly indicating a total payload size of the channel state information message, in the second part.

According to an example the method comprises reporting indices of the non-zero frequency domain coefficients of the restricted frequency domain coefficient subset in the second part, according to: combinatorial indexing with

bits where

or a bitmap with L ₀ (M-1) bits; or combinatorial indexing with

bits where

or a bitmap with L ₀M bits.

According to an example the method comprises dividing wideband frequency domain coefficients in to a plurality of parameters to be reported in the second part, the wideband frequency domain coefficients being associated with a respective wideband frequency domain component and being non-zero frequency domain coefficients.

bits, where 2L is a total number of spatial beams of the apparatus;

indices of L ₀ spatial beams out of 2L-1 frequency domain coefficients, which are quantized jointly using combinatorial signaling with

bits, where L ₀ comprises a numerical quantity of spatial beams selected from 2L-1 spatial beams of the apparatus; and information of L ₀ frequency domain coefficients in terms of amplitude and phase, which is quantized as (q _a + q _p) × L ₀ bits, where q _a represents a bit length of amplitude and q _p represents a bit length of phase.

According to a fourth aspect there is provided a computer program comprising instructions for causing an apparatus to perform at least the following: dividing channel state information into a first part and a second part, for a channel state information message to be sent from the apparatus; and in the first part, including information of a number of spatial beams of the apparatus, and information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the apparatus.

According to a fifth aspect there is provided a computer program comprising instructions stored thereon for performing at least the following: dividing channel state information into a first part and a second part, for a channel state information message to be sent from an apparatus; and in the first part, including information of a number of spatial beams of the apparatus, and information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the apparatus.

According to a sixth aspect there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the following: dividing channel state information into a first part and a second part, for a channel state information message to be sent from the apparatus; and in the first part, including information of a number of spatial beams of the apparatus, and information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the apparatus.

According to a seventh aspect there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: dividing channel state information into a first part and a second part, for a channel state information message to be sent from an apparatus; and in the first part, including information of a number of spatial beams of the apparatus, and information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the apparatus.

According to an eighth aspect there is provided an apparatus comprising means for performing: receiving a channel state information message from a user equipment, the channel state information message comprising a first part and a second part; and

determining information of a number of spatial beams of the user equipment from the first part of the message, and determining information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the user equipment from the first and second part of the message.

According to an example the restricted frequency domain coefficient subset comprises a subset of a full frequency domain coefficient matrix for all spatial beams of the user equipment. According to some examples the restricted frequency domain coefficient subset is obtained by applying a bit-mask to the full frequency domain coefficient matrix.

According to an example, the information of a number of spatial beams of the user equipment comprises a numerical quantity of spatial beams, L ₀, selected from 2L-1 spatial beams of the user equipment, where 2L is a total number of spatial beams of the user equipment.

According to an example, the information of non-zero frequency domain coefficients comprises a ratio of non-zero coefficients, K ₁, to L _o＊ (M-1) or L _o＊M coefficients in the restricted frequency domain coefficient subset, where M represents a total number of frequency domain components per beam.

According to an example the ratio is represented by α ∈ (0, 1) , and where

or

According to an example α has a constant payload size.

According to an example the means are further configured to perform determining a total payload size of the channel state information message, from an indication in the second part.

According to a ninth aspect there is provided an apparatus comprising: receiving circuitry for receiving a channel state information message from a user equipment, the channel state information message comprising a first part and a second part; and determining circuitry for determining information of a number of spatial beams of the user equipment from the first part of the message, and determining information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the user equipment from the first and second part of the message.

According to a tenth aspect there is provided a method comprising: receiving a channel state information message from a user equipment, the channel state information message comprising a first part and a second part; and determining information of a number of spatial beams of the user equipment from the first part of the message, and determining information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the user equipment from the first and second part of the message.

According to an example the ratio is represented by α ∈ (0, 1) , and where

or

According to an example α has a constant payload size.

According to an example the method comprises determining a total payload size of the channel state information message, from an indication in the second part.

According to an eleventh aspect there is provided a computer program comprising instructions for causing an apparatus to perform at least the following: receiving a channel state information message from a user equipment, the channel state information message comprising a first part and a second part; and determining information of a number of spatial beams of the user equipment from the first part of the message, and determining information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the user equipment from the first and second part of the message.

According to a twelfth aspect there is provided a computer program comprising instructions stored thereon for performing at least the following: receiving a channel state information message from a user equipment, the channel state information message comprising a first part and a second part; and determining information of a number of spatial beams of the user equipment from the first part of the message, and determining information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the user equipment from the first and second part of the message.

According to a thirteenth aspect there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the following: receiving a channel state information message from a user equipment, the channel state information message comprising a first part and a second part; and determining information of a number of spatial beams of the user equipment from the first part of the message, and determining information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the user equipment from the first and second part of the message.

According to a fourteenth aspect there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: receiving a channel state information message from a user equipment, the channel state information message comprising a first part and a second part; and determining information of a number of spatial beams of the user equipment from the first part of the message, and determining information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the user equipment from the first and second part of the message.

According to a fifteenth aspect there is provided an apparatus comprising means for performing: selecting a wideband frequency domain component from a set of frequency domain components; and including information of the selected wideband frequency domain component as at least part of channel state information to be reported.

According to an example the apparatus comprises means for selecting a sub-set of 2L-1 wideband frequency domain coefficients to be reported.

According to an example the means are further configured to divide frequency domain coefficients related to the selected wideband frequency domain component in to a plurality of parameters to be reported.

According to an example the plurality of parameters to be reported comprises: a strongest index of frequency domain coefficients of a plurality of spatial beams of the apparatus, a number of the plurality of spatial beams being 2L, and quantizing the index as

bits; an indication of a number of selected spatial beams, L ₀, out of 2L-1 frequency domain coefficients, which is quantized as

bits; indices of the L ₀ spatial beams out of 2L-1 frequency domain coefficients, which are quantized jointly using combinatorial signaling with

bits; information of L ₀ frequency domain coefficients in terms of amplitude and phase, which is quantized as (q _a + q _p) ×L ₀ bits, where q _a represents a bit length of amplitude and q _p represents a bit length of phase.

According to an example a payload of the channel state information to be reported comprises

bits.

bits; a bitmap of size 2L-1 to identify a power state of remaining 2L-1 frequency domain coefficients except for the frequency domain coefficient having the strongest index, and to implicitly indicate a number of non-zero spatial beams L ₀ out of 2L-1 frequency domain coefficients; information of L ₀ frequency domain coefficients in terms of amplitude and phase, which is quantized as (q _a + q _p) ×L ₀ bits, where q _a represents a bit length of amplitude and q _p represents a bit length of phase respectively.

bits.

According to an example the plurality of parameters to be reported comprises: a bitmap of size 2L, where 2L is a number of plurality of spatial beams of the apparatus, to identify a power state of frequency domain coefficients of the 2L spatial beams, and also to implicitly indicate a number of non-zero spatial beams L ₀ + 1, including a strongest frequency domain coefficient; a strongest index out of L ₀ + 1 frequency domain coefficients, which is quantized as

bits.

According to an example the means are further configured to perform reporting the parameters to a base station.

According to an example the means comprises at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the performance of the apparatus.

According to a sixteenth aspect there is provided an apparatus comprising: selecting circuitry for selecting a wideband frequency domain component from a set of frequency domain components; and including circuitry for including information of the selected wideband frequency domain component as at least part of channel state information to be reported.

According to a seventeenth aspect there is provided a method comprising: selecting a wideband frequency domain component from a set of frequency domain components; and including information of the selected wideband frequency domain component as at least part of channel state information to be reported.

According to an example the method comprises selecting a sub-set of 2L-1 wideband frequency domain coefficients to be reported.

According to an example the method comprises dividing frequency domain coefficients related to the selected wideband frequency domain component in to a plurality of parameters to be reported.

bits; information of L ₀ frequency domain coefficients in terms of amplitude and phase, which is quantized as (q _a + q _p) × L ₀ bits, where q _a represents a bit length of amplitude and q _p represents a bit length of phase.

bits.

According to an example the plurality of parameters to be reported comprises:

a strongest index of frequency domain coefficients of a plurality of spatial beams of the apparatus, a number of the plurality of spatial beams being 2L, and quantizing the index as

bits; a bitmap of size 2L-1 to identify a power state of remaining 2L-1 frequency domain coefficients except for the frequency domain coefficient having the strongest index, and to implicitly indicate a number of non-zero spatial beams L ₀ out of 2L-1 frequency domain coefficients; information of L ₀ frequency domain coefficients in terms of amplitude and phase, which is quantized as (q _a + q _p) × L ₀ bits, where q _a represents a bit length of amplitude and q _p represents a bit length of phase respectively.

bits.

According to an example the method comprises reporting the parameters to a base station.

According to an eighteenth aspect there is provided a computer program comprising instructions for causing an apparatus to perform at least the following: selecting a wideband frequency domain component from a set of frequency domain components; and including information of the selected wideband frequency domain component as at least part of channel state information to be reported.

According to a nineteenth aspect there is provided a computer program comprising instructions stored thereon for performing at least the following: selecting a wideband frequency domain component from a set of frequency domain components; and including information of the selected wideband frequency domain component as at least part of channel state information to be reported.

According to a twentieth aspect there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the following: selecting a wideband frequency domain component from a set of frequency domain components; and including information of the selected wideband frequency domain component as at least part of channel state information to be reported.

According to a twenty first aspect there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: selecting a wideband frequency domain component from a set of frequency domain components; and including information of the selected wideband frequency domain component as at least part of channel state information to be reported.

According to a twenty second aspect there is provided an apparatus comprising means for performing: reporting channel state information in a channel state information message, and including in the channel state information message all frequency domain coefficients of a strongest spatial beam of a plurality of spatial beams of the apparatus.

According to a twenty third aspect there is provided an apparatus comprising: reporting circuitry for reporting channel state information in a channel state information message, and including circuitry for including in the channel state information message all frequency domain coefficients of a strongest spatial beam of a plurality of spatial beams of the apparatus.

According to a twenty fourth aspect there is provided a method comprising: reporting channel state information in a channel state information message, and including in the channel state information message all frequency domain coefficients of a strongest spatial beam of a plurality of spatial beams of the apparatus.

According to a twenty fifth aspect there is provided a computer program comprising instructions for causing an apparatus to perform at least the following: reporting channel state information in a channel state information message, and including in the channel state information message all frequency domain coefficients of a strongest spatial beam of a plurality of spatial beams of the apparatus.

According to a twenty sixth aspect there is provided a computer program comprising instructions stored thereon for performing at least the following: reporting channel state information in a channel state information message, and including in the channel state information message all frequency domain coefficients of a strongest spatial beam of a plurality of spatial beams of an apparatus.

According to a twenty seventh aspect there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the following: reporting channel state information in a channel state information message, and including in the channel state information message all frequency domain coefficients of a strongest spatial beam of a plurality of spatial beams of the apparatus.

According to a twenty eighth aspect there is provided a provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: reporting channel state information in a channel state information message, and including in the channel state information message all frequency domain coefficients of a strongest spatial beam of a plurality of spatial beams of an apparatus.

According to a twenty ninth aspect there is provided an apparatus comprising means for performing: receiving a channel state information message, the channel state information message comprising information of a channel state information matrix comprising information of all frequency domain coefficients of a strongest spatial beam amongst a plurality of spatial beams of a user equipment; and reconstructing the channel state information matrix.

According to an example the means are further configured to perform reconstructing the channel state information matrix, W ₂, according to:

where

in the diagonal matrix is quantized in terms of its amplitude and phase, and W _f is a frequency compression matrix composed of M frequency domain components.

where

j= 1, …, M corresponding to the strongest spatial beam i in the diagonal matrix is quantized in terms of its amplitude and phase, and W _f is a frequency compression matrix composed of M frequency domain components, and wherein k comprises a coefficient with a maximum amplitude among coefficients

j = 1, …, M in the diagonal matrix.

According to a thirtieth aspect there is provided an apparatus comprising: receiving circuitry for receiving a channel state information message, the channel state information message comprising information of a channel state information matrix comprising information of all frequency domain coefficients of a strongest spatial beam amongst a plurality of spatial beams of a user equipment; and reconstructing circuitry for reconstructing the channel state information matrix.

According to a thirty first aspect there is provided a method comprising: receiving a channel state information message, the channel state information message comprising information of a channel state information matrix comprising information of all frequency domain coefficients of a strongest spatial beam amongst a plurality of spatial beams of a user equipment; and reconstructing the channel state information matrix.

According to an example, the method comprises reconstructing the channel state information matrix, W ₂, according to:

where

According to an example the method comprises reconstructing the channel state information matrix, W ₂, according to:

where

j = 1, …, M corresponding to the strongest spatial beam i in the diagonal matrix is quantized in terms of its amplitude and phase, and W _f is a frequency compression matrix composed of M frequency domain components, and wherein k comprises a coefficient with a maximum amplitude among coefficients

j = 1, …, M in the diagonal matrix.

According to a thirty second aspect there is provided computer program comprising instructions for causing an apparatus to perform at least the following: receiving a channel state information message, the channel state information message comprising information of a channel state information matrix comprising information of all frequency domain coefficients of a strongest spatial beam amongst a plurality of spatial beams of a user equipment; and reconstructing the channel state information matrix.

According to a thirty third aspect there is provided a computer program comprising instructions stored thereon for performing at least the following: receiving a channel state information message, the channel state information message comprising information of a channel state information matrix comprising information of all frequency domain coefficients of a strongest spatial beam amongst a plurality of spatial beams of a user equipment; and reconstructing the channel state information matrix.

According to a thirty fourth aspect there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the following: receiving a channel state information message, the channel state information message comprising information of a channel state information matrix comprising information of all frequency domain coefficients of a strongest spatial beam amongst a plurality of spatial beams of a user equipment; and reconstructing the channel state information matrix.

According to a thirty fifth aspect there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: receiving a channel state information message, the channel state information message comprising information of a channel state information matrix comprising information of all frequency domain coefficients of a strongest spatial beam amongst a plurality of spatial beams of a user equipment; and reconstructing the channel state information matrix.

Brief description of Figures

The invention will now be described in further detail, by way of example only, with reference to the following examples and accompanying drawings, in which:

Figure 1 is a diagram showing a proposal on subset selection for K ₀ frequency domain (FD) coefficients;

Figure 2 shows a comparison of CSI feedback of three proposals, compared to a traditional CSI scheme;

Figure 3 shows an example of a communication device;

Figure 4 shows an example of a control apparatus;

Figure 5 is a flow chart of a method according to an example;

Figure 6 is a flow chart of a method according to an example;

Figure 7 is a flow chart of a method according to an example;

Figure 8 is a flow chart of a method according to an example;

Figure 9 is a flow chart of a method according to an example.

Detailed description

Channel state information (CSI) refers to known channel properties of a communication link. Channel state information may comprise one or more of: channel quality indicator (CQI) ; precoding matrix indicator (PMI) ; precoding type indicator (PTI) ; rank indication (RI) . CSI may be measured at the UE side and then reported to the network. The network can then use the received channel state information to effectively control communications in the network.

As is known, a UE may communicate with the network using a plurality of beams. In some examples a total or maximum number of beams available to a UE is denoted 2L. For example if a UE has a maximum of eight beams available, then 2L =8. Each beam may be referred to as a spatial beam.

A codebook may be used by the UE for reporting CSI to the network. This means that the UE can report the CSI in a manner that will be understood by the network. “Type II” codebook design was introduced in Rel-15 NR due to its superior performance gains over Rel-14 LTE. However, the present inventors have identified that the current Type II CSI feedback design has a large feedback overhead, which limits the use of Type II CSI feedback.

In 3GPP TSG RAN WG1 Meeting #95, R1-1814131, there was agreement to select one of presented alternatives for basis subset selection scheme for each spatial layer. The “basis subset” may be considered a subset of a frequency domain beam or a frequency domain component. In particular, section 2.2 of this document discussed basis subset or linear combination (LC) coefficient for the 2L beams. This section of R1-1814131 states:

● Alt1A. Common selection for all the 2L beams, wherein M coefficients (FD components) are reported for each beam

○

where W _f comprises a matrix of a selected basis subset;

○

is composed of K = 2LM linear combination coefficients, where

provides the complex coefficients used for combining the M basis vectors

○ The value of M (applied to all 2L beams) is higher-layer configured and the M basis vectors are dynamically selected (hence reported with CSI)

● Alt1B. Common selection for all the 2L beams, but only a size K ₀ ＜ 2LM subset of coefficients are reported (not reported coefficients are treated as zero)

○

is composed of K = 2LM linear combination (LC) coefficients, but (K-K ₀) of its coefficients are zero

○ The value of M(applied to all 2L beams)is higher-layer configured and the M basis vectors are dynamically selected(hence reported with CSI)

○ For evaluation,companies should state their assumption on the selection of K ₀ LC coefficients(applied to all 2L beams) ,e.g.

■ The value of K ₀ is fixed or higher-layer configured, and the K ₀ LC coefficients are dynamically selected by the UE(hence reported with CSI) ,or

■ The K ₀ LC coefficients and its size are dynamically selected by the UE(hence reported with CSI)

● Alt2.Independent selection for all the 2L beams, wherein M _i coefficients are reported forthe i-th beam(i=0, 1, ..., 2L-1)

○ W _f = [W _f (0) , ..., W _f(2L-1) ] , where

i.e. M _i frequency-domain components (per beam) are selected

○

is composed of

linear combination coefficients

○ The value of K (applied to all 2L beams) is higher-layer configured

○ For evaluation, companies should state their assumption on size-M _i basis subset selection (applied to the i-th beam) , e.g. for i=0, 1, ..., 2L-1

■ The size-M _i subset and the value of M _i are dynamically selected by the UE (hence reported with CSI)

■ The size-M _i subset is dynamically selected by the UE (hence reported with CSI) , but the value of M _i is determined by a predefined rule in specification

■ The size-M _i subset is dynamically selected by the UE (hence reported with CSI) , but the value of M _i is higher-layer configured

○ The size-M _i subset can be chosen either from the fixed basis set or from a beam-common UE-selected intermediate subset of the fixed basis set

Assume Rel. 15 3-bit amplitude and Rel. 15 8PSK co-phasing for

quantization for evaluation purposes.

It may be considered that M defines the number of basis vectors, which are down-selected from N3 possible basis vectors. The basis vectors are chosen from a DFT (discrete Fourier transform) matrix.

The K ₀ coefficients are the complex weights for each basis vector. K means the total number of linear combination (LC) coefficients, while only K ₀ out of K LC coefficients will be reported.

An earlier Nokia proposal on subset selection of K ₀ frequency domain (FD) coefficients has been discussed in a presentation entitled “Type II overhead reduction: CC#2, Dec 2018” . A summary of this presentation is discussed below with respect to Figure 1, which shows a frequency domain coefficient matrix for CSI reporting.

The upper part of Figure 1 shows a table of FD components 0 to 12 (x-axis) , against 2L spatial beams 0 to 7 (y-axis) . 2L represents the number of beams (i.e. so there are 8 beams in this example, or in other words 2L=8) . The maximum number of FD components that could be reported per beam is 13 in this example (i.e. 0 to 12) . Of course, in practice not all FD components will be reported for each beam. Selected FD coefficients are represented in Figure 1 by the blacked-out squares. This is by way of example, and the selected coefficients may vary depending on the radio channel. The strongest spatial beam is represented by the hatched squares. That is in this example spatial beam 2 is the strongest spatial beam.

In terms of definitions, the FD “component “may be considered to mean the DFT vectors from matrix W _f in frequency domain (FD) with the number of M≤ N ₃, and “beam” means the DFT vectors in spatial domain with the number of 2L, while “coefficient” means FD linear combination coefficients in matrix

with a size of 2L＊M. Thus it may be considered that the FD coefficients in the column m of

are related to FD component m. So in Figure 1, it may be considered that each square or block represents a different FD coefficient, and each column vector is related to a different FD component, and each row vector is related to a different spatial beam. Thus it may be considered that each FD coefficient is related to a respective FD component.

As discussed in the earlier Nokia proposal:

· Basis subset selection for M FD components to be reported is as follows:

· Basis subset selection is common to all the 2L spatial beams.

· FD component ‘0’ (shown at column 102 in Figure 1) , or namely wideband (WB) component, is always included in the basis subset.

· The other M-1 FD components are dynamically reported with

bits, where N ₃ is the maximum number of FD components (in this case N ₃ = 13)

· Subset selection for K ₀ FD coefficients (not reported coefficients are treated as zero) is as follows:

· The strongest spatial beam is selected according to 2L coefficients of FD component ‘0’ , and indicated with

bits.

· All the M FD coefficients in the row vector corresponding to the strongest spatial beam are not reported as shown in Figure 1, and assumed 1 after column-wise normalization.

· 2L-1 coefficients of FD component ‘0’ are always reported except for strongest beam.

· The remaining K ₀-2L+1 FD coefficients are freely selected inside a reduced size table of size L ₀ × (M-1) , where L ₀ is the number of selected spatial beams. The reduced table size is shown in the lower part of Figure 1.

· Selection of spatial beams (rows) : only the L ₀ ≤ 2L -1 spatial beams with largest amplitudes in the WB component are selected

· L ₀ can be

· Fixed or RRC configured, such as L ₀ = 2L-1 or

etc.

· Dynamically configured (2/3 bits)

· K ₀ is RRC configured, and K ₁ is the actual number of nonzero reported coefficients

· If K ₁ = K ₀, K ₁ nonzero coefficients are selected according to combinatorial indexing with

bits

· If K ₁ ＜ K ₀, K ₁ nonzero coefficients are selected according to a bitmap with L ₀ (M-1) bits

Thus in the proposal of Figure 1, CSI can be reported by means of the reported FD components. The reduced table size for reporting is intended to reduce signaling overhead.

In the present disclosure, some CSI enhancements are considered based on the proposal of Figure 1. These enhancements include: (1) Feedback enhancement for FD component “0” (WB component) ; (2) Additional CSI item design for the 1 ^st CSI part; and (3) Feedback enhancement for the strongest spatial beam. For ease of explanation they are each discussed in turn below, though it will be understood that elements of each enhancement may be combined. Terminology and definitions which have been explained with respect to Figure 1 are applicable to the foregoing, unless explained otherwise.

1. Feedback enhancement for FD component “0”

In the existing proposal discussed with respect to Figure 1, the FD component “0” or wideband (WB) component of each spatial beam is always selected and included in the basis subset for reporting to the network.

Among 2L coefficients of FD component ‘0’ , the strongest spatial beam is selected and indicated with

bits, and then L ₀ spatial beams are determined out of the remaining 2L-1 FD coefficients in terms of the largest amplitudes to further constrain the whole CSI payload. The remaining 2L-1-L ₀ FD coefficients can be regarded as 0. The existing feedback of FD component ‘0’ contains the following three parameters in each layer:

a) The strongest index out of 2L FD coefficients, which is quantized as

bits

b) Indication of the number of selected spatial beams L ₀ out of 2L-1 FD coefficients, which is quantized as

bits

c) Feedback of 2L-1 FD coefficients in terms of amplitude and phase, which is quantized as (4 + 4) × (2L-1) bits, assuming 4 bits for each amplitude/phase

d) Therefore, the total payload is

bits.

In this disclosure, three alternatives of enhanced feedback of FD component ‘0’ are proposed to reduce its feedback overhead considering the selection of L ₀ spatial beams. According to examples, a sub-set of 2L-1 coefficients corresponding to WB FD component are selected and reported, instead of all of 2L-1 coefficients according to the earlier Nokia proposal of Figure 1.

For example, coefficient feedback corresponding to FD component ‘0’ can be divided into multiple parameters for each spatial layer in each of the three alternatives, which are discussed in turn below.

Alternative 1

The reported CSI information comprises:

a) The strongest index (i.e. beam with strongest power in WB FD component) out of 2L FD coefficients, which is quantized as

bits

b) Indication of the number of selected spatial beams L ₀ out of 2L -1 FD coefficients, which is quantized as

bits

c) Indices of the L ₀ spatial beams out of 2L -1 FD coefficients, which are quantized jointly using combinatorial signaling with

bits

d) Feedback of L ₀ FD coefficients in terms of amplitude and phase, which is quantized as (q _a + q _p) ×L ₀ bits, where q _a and q _p represents the bit length of amplitude and phase respectively, for example, q _a = 4 and q _p = 4.

e) Therefore, the total payload is

bits (where for example q _a = 4 and q _p = 4) .

Alternative 2

The reported information comprises:

a) The strongest index out of 2L FD coefficients, which is quantized as

bits

b) A bitmap of size 2L-1 to identify the power state (e.g.: zero or nonzero) of the remaining 2L-1 FD coefficients except for the strongest one, and also to implicitly show the number of nonzero spatial beam L ₀ out of 2L-1 FD coefficients

c) Feedback of L ₀ FD coefficients in terms of amplitude and phase, which is quantized as (q _a + q _p) ×L ₀ bits, where q _a and q _p represents the bit length of amplitude and phase respectively, for example, q _a = 4 and q _p = 4.

d) Therefore, the total payload is

bits (where for example q _a = 4 and q _p = 4) .

Alternative 3

The reported information comprises:

a) A bitmap of size 2L to identify the power state (e.g.: zero or nonzero) of the 2L FD coefficients, and also to implicitly show the number of nonzero spatial beam L ₀ + 1 including the strongest FD coefficients

b) The strongest index out of L ₀ + 1 FD coefficients, which is quantized as

bits

c) Feedback of L ₀ FD coefficients in terms of amplitude and phase, which is quantized as (q _a + q _p) × L ₀ bits, where q _a and q _p represents the bit length of amplitude and phase respectively, for example, q _a = 4 and q _p = 4.

d) Therefore, the total payload is

bits (where for example q _a = 4 and q _p = 4) .

Figure 2 shows a comparison of CSI feedback of the above three alternatives compared to a traditional CSI scheme (i.e. the traditional scheme of Figure 1) . The plot shows CSI payload bits (y axis) , against number of selected spatial beams L0 (x-axis) . The plot of Figure 2 assumes rank 1, L = 4 and 4-bit amplitude/phase quantization. According to Figure 2, the enhanced feedback alternatives of FD component ‘0’ (i.e. wideband component) has reduced CSI payload with decrease of selected beam number L ₀, while the existing feedback has constant or almost constant payload regardless of variation of L ₀. Therefore, the proposed feedback scheme can in most cases achieve lower feedback payload than the traditional feedback scheme, up to 70%reduction in some L ₀ cases. One exception is that when L ₀ = 2L -1, alternative 2 and alternative 3 have a slightly higher payload than the traditional scheme, while alternative 1 has the same payload as the traditional scheme.

2. Additional CSI item for the 1 ^st CSI part

In the existing proposal discussed with respect to Figure 1, in the subset selection of K ₀ FD coefficients, 2L-1 FD coefficients corresponding to FD component ‘0’ are always reported, and the remaining K ₀ -2L + 1 FD coefficients are freely selected inside a reduced size table of size L ₀ × (M -1) , where L ₀ is the number of selected spatial beams and M is the number of FD components. The practical CSI payload can be constant with K ₀ FD coefficients, or it can be variable with the actual number of nonzero reported coefficients. Where the CSI payload is variable, the CSI payload fluctuates in terms of selected beam number L ₀ assuming dynamic configuration and a bitmap with L ₀ (M-1) bits.

In Rel. 15 NR spec (Section 5.2.3 of 3GPP, Physical layer procedures for data, TS 38.214, v15.0.0, December 2017) , CSI is split into two parts. A first part has a fixed payload size. A payload size of Part 2 CSI is variable depending on the first CSI part. The number of selected spatial beams L ₀ is indicated with

bits, so it can be defined in the 1 ^st CSI part due to fixed payload size. However the bitmap with L ₀ (M-1) bits cannot be specified in the 1 ^st CSI part, since the bitmap has variable payload size depending on L ₀. But if the bitmap is defined in the 2 ^nd CSI part, the actual number of nonzero reported coefficients and the whole CSI payload in the 2 ^nd CSI part is relied on the bitmap in the 2 ^nd CSI part as well as the number of selected spatial beams L ₀ in the 1 ^st CSI part. In other words, the payload size of Part 2 CSI cannot be determined by the 1 ^st CSI part completely. Therefore, the existing feedback method is partially contradicted with the Rel. 15 two-part CSI report mechanism.

According to this disclosure, a new CSI item is introduced into the 1 ^st CSI part in addition to indication of the number of selected spatial beams L ₀. Supposing that CSI payload is variable with the actual number of nonzero reported coefficients K ₁ and the number of selected spatial beams L ₀ is dynamically configured. Since the reported nonzero coefficients are freely selected from the reduced size table of size L ₀ × (M-1) , the actual number of nonzero reported coefficients K ₁ should be specifically defined in the 1 ^st CSI part. If K ₁ is quantized as

its payload size is not stable due to variation of value L ₀. In this context, it is proposed to define that K ₁ = α × L ₀ × (M-1) , or

where α ∈ (0, 1) is the ratio of K ₁ nonzero coefficients among L ₀ × (M-1) coefficients. Since α has a constant payload size (2/3 bits) , it is suitable to be specified in the 1 ^st CSI part. Therefore, two parameters (L ₀ and α) may be defined in the 1 ^st CSI part to jointly determine a number of nonzero reported coefficients K ₁, and to explicitly indicate the payload size of the whole CSI reporting in the 2 ^nd CSI part. In addition, the indices of nonzero reported coefficients can be reported in Part 2 CSI according to combinatorial indexing with

bits where

or a bitmap with L ₀ (M-1) bits.

3. Feedback enhancement for the strongest spatial beam

In the existing proposal discussed with respect to Figure 1, it is assumed that linear combination matrix

is formed after spatial domain and frequency domain compression, and has a size of 2L × M (i.e. each beam can have up to M coefficients) as shown in equation (1) below. The 1 ^st column of matrix

is achieved according to FD component ‘0’ (wideband component) , and it is always reported. The strongest spatial beam is selected according to 2L coefficients in 1 ^st column vector of matrix

Suppose that beam i is selected since the coefficient

has the largest amplitude in the 1 ^st column vector. Accordingly, all the M FD coefficients in row i corresponding to the strongest spatial beam perform column-wise normalization respectively, as shown in the following matrix

shown in equation (2) below. The transformed matrix

has an all-one vector in row i. and all the M coefficients

j = 1, …, M corresponding to the strongest beam i in the original matrix

are not reported.

Now according to the present disclosure, it is proposed that all the M coefficients

j = 1, …, M corresponding to the strongest spatial beam i in the original matrix

still need to be reported for better CSI reconstruction in gNB side. For example, CSI matrix W ₂ should be reconstructed according to equation (3) below:

where

in the diagonal matrix is quantized in terms of its amplitude and phase, and W _f is a frequency compression matrix composed of M FD components.

Furthermore, coefficient k with a maximum amplitude among coefficients

j = 1, …, M in the diagonal matrix does not have to be reported considering further normalization. For example, M-1 coefficients

in the diagonal matrix will be quantized in terms of its amplitude/phase and reported except for coefficient k. In addition, the strongest index (k) out of M coefficients

j = 1, …, M will also be reported as

bits.

In summary, CSI matrix W ₂ should be reconstructed according to equation (4) below:

For performance evaluation of the proposed feedback enhancement, full buffer system level evaluations were carried out in a dense urban scenario. The relevant simulation parameters are given in Table 1 below.

Table 1: simulation assumptions for system level evaluation

Then the CSI enhancement scheme considering the above-described additional diagonal matrix has been evaluated and compared with the baseline (i.e. without additional diagonal matrix feedback) . Simulation results are shown in Table 2 below.

Table 2: System level evaluation of different CSI schemes

From this it can be understood that the proposed CSI enhancement scheme has significant performance gains compared with the baseline by considering additional diagonal matrix feedback, such as 76%～95%gains, while it only introduces very limited CSI payload for diagonal matrix feedback.

As discussed above, it will of course be understood that aspects of the three proposals discussed above can be combined. For example, according to some examples aspects of “2. Additional CSI item for the 1 ^st CSI part” may be combined with aspects of “1. Feedback enhancement for FD component “0” ” .

Where discussed herein, “non-zero” FD coefficients may be considered to mean coefficients having a non-zero amplitude. Where a coefficient is zero, there is no need for it to be reported including amplitude and phase information to reduce feedback overhead. According to this disclosure, in some examples there are first determined some non-zero FD coefficients out of all FD coefficients, and then only the non-zero coefficients are reported including amplitude and phase information. But it will be understood that in examples all the FD components still exist, regardless of how to determine zero or non-zero FD coefficients.

A possible wireless communication device will now be described in more detail with reference to Figure 3 showing a schematic, partially sectioned view of a communication device 300. Such a communication device is often referred to as user equipment (UE) or terminal. An appropriate mobile communication device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples comprise a mobile station (MS) or mobile device such as a mobile phone or what is known as a ’smart phone’ , a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle) , personal data assistant (PDA) or a tablet provided with wireless communication capabilities, or any combinations of these or the like. A mobile communication device may provide, for example, communication of data for carrying communications such as voice, electronic mail (email) , text message, multimedia and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services comprise two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. Users may also be provided broadcast or multicast data. Non-limiting examples of the content comprise downloads, television and radio programs, videos, advertisements, various alerts and other information.

A wireless communication device may be for example a mobile device, that is, a device not fixed to a particular location, or it may be a stationary device. The wireless device may need human interaction for communication, or may not need human interaction for communication. In the present teachings the terms UE or “user” are used to refer to any type of wireless communication device.

The wireless device 300 may receive signals over an air or radio interface 307 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 3 transceiver apparatus is designated schematically by block 306. The transceiver apparatus 306 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the wireless device.

A wireless device is typically provided with at least one data processing entity 301, at least one memory 302 and other possible components 303 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 304. The user may control the operation of the wireless device by means of a suitable user interface such as key pad 305, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 308, a speaker and a microphone can be also provided. Furthermore, a wireless communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto.

Figure 4 shows an example of a control apparatus for a communication system, for example to be coupled to and/or for controlling a station of an access system, such as a RAN node, e.g. a base station, gNB, a central unit of a cloud architecture or a node of a core network such as an MME or S-GW, a scheduling entity such as a spectrum management entity, or a server or host. The control apparatus may be integrated with or external to a node or module of a core network or RAN. In some embodiments, base stations comprise a separate control apparatus unit or module. In other embodiments, the control apparatus can be another network element such as a radio network controller or a spectrum controller. In some embodiments, each base station may have such a control apparatus as well as a control apparatus being provided in a radio network controller. The control apparatus 400 can be arranged to provide control on communications in the service area of the system. The control apparatus 400 comprises at least one memory 401, at least one

data processing unit

402, 403 and an input/output interface 404. Via the interface the control apparatus can be coupled to a receiver and a transmitter of the base station. The receiver and/or the transmitter may be implemented as a radio front end or a remote radio head. For example the control apparatus 400 or processor 401 can be configured to execute an appropriate software code to provide the control functions.

Figure 5 is a flow chart of a method according to an example. The flow chart of Figure 5 may be viewed from the perspective of an apparatus. The apparatus may for example be a user equipment.

At S1, the method comprises dividing channel state information into a first part and a second part, for a channel state information message to be sent from an apparatus.

At S2, the method comprises, in the first part, including information of a number of spatial beams of the apparatus, and information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the apparatus.

Figure 6 is a flow chart of a method according to an example. The flow chart of Figure 6 may be viewed from the perspective of an apparatus. The apparatus may for example be a base station or gNB.

At S1, the method comprises receiving a channel state information message from a user equipment, the channel state information message comprising a first part and a second part.

At S2, the method comprises determining information of a number of spatial beams of the user equipment from the first part of the message, and determining information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the user equipment from the first and second part of the message.

Figure 7 is a flow chart of a method according to an example. The flow chart of Figure 7 may be viewed from the perspective of an apparatus. The apparatus may for example be a user equipment.

At S1, the method comprises selecting a wideband frequency domain component from a set of frequency domain components.

At S2, the method comprises including information of the selected wideband frequency domain component as at least part of channel state information to be reported.

Figure 8 is a flow chart of a method according to an example. The flow chart of Figure 8 may be viewed from the perspective of an apparatus. The apparatus may for example be a user equipment.

At S1, the method comprises reporting channel state information in a channel state information message.

At S2, the method comprises including in the channel state information message all frequency domain coefficients of a strongest spatial beam of a plurality of spatial beams of the apparatus.

Figure 9 is a flow chart of a method according to an example. The flow chart of Figure 9 may be viewed from the perspective of an apparatus. The apparatus may for example be a base station or gNB.

At S1, the method comprises receiving a channel state information message, the channel state information message comprising information of a channel state information matrix comprising information of all frequency domain coefficients of a strongest spatial beam amongst a plurality of spatial beams of a user equipment.

At S2, the method comprises reconstructing the channel state information matrix.

In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of the invention 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, although the invention is not limited thereto. While various aspects of the invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods 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.

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.

The embodiments of this invention may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and/or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computer-executable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it.

Further in this regard it should be noted that any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD. The physical media is a non-transitory media.

The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) , application specific integrated circuits (ASIC) , FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting examples.

Embodiments of the inventions may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of this invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of this invention as defined in the appended claims. Indeed there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.

Claims

An apparatus comprising means for performing:

dividing channel state information into a first part and a second part, for a channel state information message to be sent from the apparatus; and

in the first part, including information of a number of spatial beams of the apparatus, and information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the apparatus.
An apparatus according to claim 1, wherein the information of a number of spatial beams of the apparatus comprises a numerical quantity of spatial beams, L ₀, selected from 2L-1 spatial beams of the apparatus, where 2L is a total number of spatial beams of the apparatus.
An apparatus according to claim 2, where the information of non-zero frequency domain coefficients comprises a ratio of non-zero coefficients, K ₁, to L _o ＊ (M-1) or L _o＊M coefficients in the restricted frequency domain coefficient subset, where M represents a total number of frequency domain components per beam.
An apparatus according to claim 3, wherein the ratio is represented by α ∈ (0, 1) , and where
or
An apparatus according to claim 4, where α has a constant payload size.
An apparatus according to any of claims 1 to 5, wherein the means are further configured to perform explicitly indicating a total payload size of the channel state information message, in the second part.
An apparatus according to claim 3, wherein the means are further configured to perform reporting indices of the non-zero frequency domain coefficients of the restricted frequency domain coefficient subset in the second part, according to: combinatorial indexing with
bits where
or a bitmap with L ₀ (M -1) bits; or combinatorial indexing with
bits where
or a bitmap with L ₀M bits.
An apparatus according to any of claims 1 to 7, wherein the means are further configured to divide wideband frequency domain coefficients in to a plurality of parameters to be reported in the second part, the wideband frequency domain coefficients being associated with a respective wideband frequency domain component and being non-zero frequency domain coefficients.
An apparatus according to claim 8, wherein the plurality of parameters to be reported comprises:

a strongest index of the wideband frequency domain coefficients, and quantizing the index as
bits, where 2L is a total number of spatial beams of the apparatus;

indices of L ₀ spatial beams out of 2L -1 frequency domain coefficients, which are quantized jointly using combinatorial signaling with
bits, where L ₀ comprises a numerical quantity of spatial beams selected from 2L-1 spatial beams of the apparatus; and

information of L ₀ frequency domain coefficients in terms of amplitude and phase, which is quantized as (q _a + q _p) × L ₀ bits, where q _a represents a bit length of amplitude and q _p represents a bit length of phase.
An apparatus according to any of claims 1 to 9, wherein 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.
A method comprising:

dividing channel state information into a first part and a second part, for a channel state information message to be sent from an apparatus; and

in the first part, including information of a number of spatial beams of the apparatus, and information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the apparatus.
A method according to claim 11, wherein the information of a number of spatial beams of the apparatus comprises a numerical quantity of spatial beams, L ₀, selected from 2L-1 spatial beams of the apparatus, where 2L is a total number of spatial beams of the apparatus.
A method according to claim 12, where the information of non-zero frequency domain coefficients comprises a ratio of non-zero coefficients, K ₁, to L _o ＊ (M-1) or L _o＊M coefficients in the restricted frequency domain coefficient subset, where M represents a total number of frequency domain components per beam.
A method according to claim 13, wherein the ratio is represented by α ∈ (0, 1) , and where
or
A method according to claim 14, where α has a constant payload size.
A method according to any of claims 11 to 15, comprising explicitly indicating a total payload size of the channel state information message, in the second part.
A method according to claim 13, wherein the method comprises reporting indices of the non-zero frequency domain coefficients of the restricted frequency domain coefficient subset in the second part, according to: combinatorial indexing with
bits where
or a bitmap with L ₀ (M-1) bits; or combinatorial indexing with
bits where
or a bitmap with L ₀M bits.
A method according to any of claims 11 to 17, wherein the method comprises dividing wideband frequency domain coefficients in to a plurality of parameters to be reported in the second part, the wideband frequency domain coefficients being associated with a respective wideband frequency domain component and being non-zero frequency domain coefficients.
A method according to claim 18, wherein the plurality of parameters to be reported comprises:

a strongest index of the wideband frequency domain coefficients, and quantizing the index as
bits, where 2L is a total number of spatial beams of the apparatus;

indices of L ₀ spatial beams out of 2L -1 frequency domain coefficients, which are quantized jointly using combinatorial signaling with
bits, where L ₀ comprises a numerical quantity of spatial beams selected from 2L-1 spatial beams of the apparatus; and

information of L ₀ frequency domain coefficients in terms of amplitude and phase, which is quantized as (q _a + q _p) ×L ₀ bits, where q _a represents a bit length of amplitude and q _p represents a bit length of phase.
A computer program comprising instructions for causing an apparatus to perform at least the following:

dividing channel state information into a first part and a second part, for a channel state information message to be sent from the apparatus; and

in the first part, including information of a number of spatial beams of the apparatus, and information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the apparatus.
An apparatus comprising means for performing:

receiving a channel state information message from a user equipment, the channel state information message comprising a first part and a second part; and

determining information of a number of spatial beams of the user equipment from the first part of the message, and determining information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the user equipment from the first and second part of the message.
An apparatus according to claim 21, wherein 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.
A method comprising:

receiving a channel state information message from a user equipment, the channel state information message comprising a first part and a second part; and

determining information of a number of spatial beams of the user equipment from the first part of the message, and determining information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the user equipment from the first and second part of the message.
A computer program comprising instructions for causing an apparatus to perform at least the following:

receiving a channel state information message from a user equipment, the channel state information message comprising a first part and a second part; and

determining information of a number of spatial beams of the user equipment from the first part of the message, and determining information of non-zero frequency domain coefficients in a restricted frequency domain coefficient subset of the user equipment from the first and second part of the message.