WO2020061964A1

WO2020061964A1 - Apparatus, method and computer program on csi overhead reduction

Info

Publication number: WO2020061964A1
Application number: PCT/CN2018/108146
Authority: WO
Inventors: Hao Liu; Marco MASO; Xiaomao Mao; Rana Ahmed; William J. Hillery; Frederick Vook
Original assignee: Nokia Shanghai Bell Co., Ltd.; Nokia Solutions And Networks Oy; Nokia Technologies Oy
Priority date: 2018-09-27
Filing date: 2018-09-27
Publication date: 2020-04-02
Also published as: CN112840697A; CN112840697B

Abstract

There is provided an apparatus, said apparatus comprising means for: determining, at the apparatus, channel state information for a set of sub-bands within a multiple-input-multiple-output communications system; obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands; selecting a sub-set of sub-bands from the set of sub-bands; and providing to a network an indication of the selected sub-bands and related channel state information values.

Description

APPARATUS, METHOD AND COMPUTER PROGRAM ON CSI OVERHEAD REDUCTION

Field

The present application relates to a method, apparatus, system and computer program and in particular but not exclusively to channel state information (CSI) overhead reduction.

Background

A communication system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, base stations and/or other nodes by providing carriers between the various entities involved in the communications path. A communication system can be provided for example by means of a communication network and one or more compatible communication devices. The communication sessions may comprise, for example, communication of data for carrying communications such as voice, video, electronic mail (email) , text message, multimedia and/or content data and so on. Non-limiting examples of services provided comprise 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 communication system at least a part of a communication session between at least two stations occurs over a wireless link. Examples of wireless systems comprise public land mobile networks (PLMN) , satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN) . The wireless systems can typically be divided into cells, and are therefore often referred to as cellular systems.

A user can access the communication system by means of an appropriate communication device or terminal. A communication device of a user may be referred to as user equipment (UE) or user device. A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling access to a communication network or communications directly with other users. The communication device may access a carrier provided by a station, for example a base station of a cell, and transmit and/or receive communications on the carrier.

The 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. One example of a communications system is UTRAN (3G radio) . Other examples of communication systems are the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology and so-called 5G or New Radio (NR) networks. NR is being standardized by the 3rd Generation Partnership Project (3GPP) .

Summary

In a first aspect there is provided an apparatus, said apparatus comprising means for: determining, at the apparatus, channel state information for a set of sub-bands within a multiple-input-multiple-output communications system; obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands; selecting a sub-set of sub-bands from the set of sub-bands; and providing to a network an indication of the selected sub-bands and related channel state information values.

The means for obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands may be further for: determining a composite eigenvector matrix comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands, wherein the matrix structure is:

where an element of the composite eigenvector matrix V is v _i (j) , i = 1, …, N _p, j = 1, …, N _sb, N _p = 2L × N _ri, N _sb is a total number of sub-bands, and N _ri is a total number of layers and L is a total number of orthogonal beams per polarization used within the communications system.

The means for selecting a sub-set of sub-bands from the set of sub-bands may be further for: defining a discrete Fourier transform matrix, the discrete Fourier transform matrix with a dimension of N _sb × N _sb when the communications system employs an oversampling rate O = 1, or a dimension N _sb × (N _sb × O) when the communications system employs an oversampling rate O ＞ 1; selecting a set of vectors from the discrete Fourier transform matrix based on a selection criteria defined by

where f _j is the j-th column of the discrete Fourier transform matrix having N _sb × O candidate discrete Fourier transform vectors and V is the composite eigenvector matrix with the dimension of N _p × N _sb and λ _i is the index of an optimal discrete Fourier transform vector; and generating a discrete Fourier transformation matrix F formed by the selected set of vectors.

The means for providing to a network an indication of the selected sub-bands and related channel state information values may be further for generating a reduced overhead transformed matrix based on

with N _p × N _comp.

The means for providing to a network an indication of the selected sub-bands and related channel state information values may be further for signalling the reduced overhead transformed matrix using

The means for selecting a sub-set of sub-bands from the set of sub-bands may be further for: calculating a covariance matrix of the composite eigenvector matrix; performing eigen decomposition of the covariance matrix of the composite eigenvector matrix

and generating a transformation matrix Q comprising a first number N _comp of dominant eigenvectors of R _V.

with N _p × N _comp.

The means for providing to a network an indication of the selected sub-bands and related channel state information values may be further for signalling the reduced overhead transformed matrix by signalling an indication of the strongest coefficient for each dominant eigenvector in the transformation matrix Q using

bits and 3 bits for amplitude/phase coefficients other than the strongest coefficient in the transformation matrix Q.

The means for providing to a network an indication of the selected sub-bands and related channel state information values may be further for: selecting a sub-set of a set of reduced overhead transformed matrix coefficients based on determining a strongest one out of 2L coefficients for each layer in each selected sub-band; signalling the sub-set of reduced overhead transformed matrix coefficients according to a first scheme; signalling the remainder of the reduced overhead transformed matrix coefficients according to a further scheme.

The means for signalling the sub-set of reduced overhead transformed matrix coefficients according to a first scheme may be further for signalling the sub-set of reduced overhead transformed matrix coefficients as a wideband amplitude related reporting for the layer.

The means for signalling the sub-set of reduced overhead transformed matrix coefficients according to a first scheme may be further for signalling the sub-set of reduced overhead transformed matrix coefficients by: signalling a strongest one out of the sub-set of reduced overhead transformed matrix coefficients with

bits; and signalling the other of the sub-set of reduced overhead transformed matrix coefficients using (N _ri × N _comp-1) × (3 + 3) bits.

The means for signalling the remainder of the reduced overhead transformed matrix coefficients according to a second scheme may be further for considering non-zero wideband amplitudes related coefficients of the reduced overhead transformed matrix in each layer signalling a sub-band differential amplitude quantization using 1 bit and sub-band phase quantization using 3 bits.

The means for signalling the sub-set of reduced overhead transformed matrix coefficients according to a first scheme may be further for quantizing separately the sub-set of reduced overhead transformed matrix coefficients.

According to a second aspect there is provided a method comprising: determining, at an apparatus, channel state information for a set of sub-bands within a multiple-input-multiple-output communications system; obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands; selecting a sub-set of sub-bands from the set of sub-bands; and providing to a network an indication of the selected sub-bands and related channel state information values.

Obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands may further comprise: determining a composite eigenvector matrix comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands, wherein the matrix structure is:

Selecting a sub-set of sub-bands from the set of sub-bands may further comprise: defining a discrete Fourier transform matrix, the discrete Fourier transform matrix with a dimension of N _sb × N _sb when the communications system employs an oversampling rate O = 1, or a dimension N _sb × (N _sb × O) when the communications system employs an oversampling rate O ＞ 1; selecting a set of vectors from the discrete Fourier transform matrix based on a selection criteria defined by

Providing to a network an indication of the selected sub-bands and related channel state information values may further comprise generating a reduced overhead transformed matrix based on

with N _p × N _comp.

Providing to a network an indication of the selected sub-bands and related channel state information values may further comprise signalling the reduced overhead transformed matrix using

Selecting a sub-set of sub-bands from the set of sub-bands may further comprise: calculating a covariance matrix of the composite eigenvector matrix; performing eigen decomposition of the covariance matrix of the composite eigenvector matrix

with N _p × N _comp.

Providing to a network an indication of the selected sub-bands and related channel state information values may further comprise signalling the reduced overhead transformed matrix by signalling an indication of the strongest coefficient for each dominant eigenvector in the transformation matrix Q using

Providing to a network an indication of the selected sub-bands and related channel state information values may further comprise: selecting a sub-set of a set of reduced overhead transformed matrix coefficients based on determining a strongest one out of 2L coefficients for each layer in each selected sub-band; signalling the sub-set of reduced overhead transformed matrix coefficients according to a first scheme; signalling the remainder of the reduced overhead transformed matrix coefficients according to a further scheme.

Signalling the sub-set of reduced overhead transformed matrix coefficients according to a first scheme may further comprise signalling the sub-set of reduced overhead transformed matrix coefficients as a wideband amplitude related reporting for the layer.

Signalling the sub-set of reduced overhead transformed matrix coefficients according to a first scheme may further comprise signalling the sub-set of reduced overhead transformed matrix coefficients by: signalling a strongest one out of the sub-set of reduced overhead transformed matrix coefficients with

bits; and signalling the other of the sub-set of reduced overhead transformed matrix coefficients using (N _ri × N _comp-1) × (3+3) bits.

Signalling the remainder of the reduced overhead transformed matrix coefficients according to a second scheme may further comprise considering non-zero wideband amplitudes related coefficients of the reduced overhead transformed matrix in each layer signalling a sub-band differential amplitude quantization using 1 bit and sub-band phase quantization using 3 bits.

Signalling the sub-set of reduced overhead transformed matrix coefficients according to a first scheme may further comprise quantizing separately the sub-set of reduced overhead transformed matrix coefficients.

According to a third aspect there is provided an apparatus comprising at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: determine, at the apparatus, channel state information for a set of sub-bands within a multiple-input-multiple-output communications system; obtain a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands; select a sub-set of sub-bands from the set of sub-bands; and provide to a network an indication of the selected sub-bands and related channel state information values.

The apparatus caused to obtain a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands may further be caused to: determine a composite eigenvector matrix comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands, wherein the matrix structure is:

The apparatus caused to select a sub-set of sub-bands from the set of sub-bands may further be caused to: define a discrete Fourier transform matrix, the discrete Fourier transform matrix with a dimension of N _sb × N _sb when the communications system employs an oversampling rate O = 1, or a dimension N _sb × (N _sb × O) when the communications system employs an oversampling rate O ＞ 1; select a set of vectors from the discrete Fourier transform matrix based on a selection criteria defined by

where f _j is the j-th column of the discrete Fourier transform matrix having N _sb × O candidate discrete Fourier transform vectors and V is the composite eigenvector matrix with the dimension of N _p × N _sb and λ _i is the index of an optimal discrete Fourier transform vector; and generate a discrete Fourier transformation matrix F formed by the selected set of vectors.

The apparatus caused to provide to a network an indication of the selected sub-bands and related channel state information values may further be caused to generate a reduced overhead transformed matrix based on

with N _p × N _comp.

The apparatus caused to provide to a network an indication of the selected sub-bands and related channel state information values may further be caused to signal the reduced overhead transformed matrix using

The apparatus caused to select a sub-set of sub-bands from the set of sub-bands may further be caused to: calculate a covariance matrix of the composite eigenvector matrix; perform eigen decomposition of the covariance matrix of the composite eigenvector matrix

and generate a transformation matrix Q comprising a first number N _comp of dominant eigenvectors of R _V.

with N _p × N _comp.

The apparatus caused to provide to a network an indication of the selected sub-bands and related channel state information values may further be caused to signal the reduced overhead transformed matrix by signalling an indication of the strongest coefficient for each dominant eigenvector in the transformation matrix Q using

The apparatus caused to provide to a network an indication of the selected sub-bands and related channel state information values may further be caused to: select a sub-set of a set of reduced overhead transformed matrix coefficients based on determining a strongest one out of 2L coefficients for each layer in each selected sub-band; signal the sub-set of reduced overhead transformed matrix coefficients according to a first scheme; signal the remainder of the reduced overhead transformed matrix coefficients according to a further scheme.

The apparatus caused to signal the sub-set of reduced overhead transformed matrix coefficients according to a first scheme may further be caused to signal the sub-set of reduced overhead transformed matrix coefficients as a wideband amplitude related reporting for the layer.

The apparatus caused to signal the sub-set of reduced overhead transformed matrix coefficients according to a first scheme may further be caused to signal the sub-set of reduced overhead transformed matrix coefficients by: signalling a strongest one out of the sub-set of reduced overhead transformed matrix coefficients with

bits; and signalling the other of the sub-set of reduced overhead transformed matrix coefficients using (N _ri × N _comp -1) × (3 + 3) bits.

The apparatus caused to signal the remainder of the reduced overhead transformed matrix coefficients according to a second scheme may further be caused to consider non-zero wideband amplitudes related coefficients of the reduced overhead transformed matrix in each layer signalling a sub-band differential amplitude quantization using 1 bit and sub-band phase quantization using 3 bits.

The apparatus caused to signal the sub-set of reduced overhead transformed matrix coefficients according to a first scheme may further be caused to quantize separately the sub-set of reduced overhead transformed matrix coefficients.

According to a fourth aspect there is provided an apparatus comprising: means for determining, at the apparatus, channel state information for a set of sub-bands within a multiple-input-multiple-output communications system; means for obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands; means for selecting a sub-set of sub-bands from the set of sub-bands; and means for providing to a network an indication of the selected sub-bands and related channel state information values.

According to a fifth aspect there is provided a computer program comprising instructions [or a computer readable medium comprising program instructions] for causing an apparatus to perform at least the following: determining, at the apparatus, channel state information for a set of sub-bands within a multiple-input-multiple-output communications system; obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands; selecting a sub-set of sub-bands from the set of sub-bands; and providing to a network an indication of the selected sub-bands and related channel state information values.

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: determining, at the apparatus, channel state information for a set of sub-bands within a multiple-input-multiple-output communications system; obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands; selecting a sub-set of sub-bands from the set of sub-bands; and providing to a network an indication of the selected sub-bands and related channel state information values.

According to a seventh aspect there is provided an apparatus comprising: determining circuitry configured to determine channel state information for a set of sub-bands within a multiple-input-multiple-output communications system; obtaining circuitry configured to obtain a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands; selecting circuitry configured to select a sub-set of sub-bands from the set of sub-bands; and providing circuitry configured to provide to a network an indication of the selected sub-bands and related channel state information values.

According to an eighth aspect there is provided a computer readable medium comprising program instructions for causing an apparatus to perform at least the following: determining, at the apparatus, channel state information for a set of sub-bands within a multiple-input-multiple-output communications system; obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands; selecting a sub-set of sub-bands from the set of sub-bands; and providing to a network an indication of the selected sub-bands and related channel state information values.

The apparatus may be caused to perform providing a control message to the user equipment, the control message comprising an indication of the number of channel components on which the combined channel state information is based.

In a ninth 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 the third aspect or a method according to the fourth aspect.

In the above, many different embodiments have been described. It should be appreciated that further embodiments may be provided by the combination of any two or more of the embodiments described above.

Description of Figures

Embodiments will now be described, by way of example only, with reference to the accompanying Figures in which:

Figure 1 shows a schematic diagram of an example communication system comprising a base station and a plurality of communication devices;

Figure 2 shows a schematic diagram of an example mobile communication device;

Figure 3 shows a schematic diagram of an example control apparatus;

Figure 4 shows a flowchart of a first method according to an example embodiment; and

Figure 5 shows a flowchart of a further method according to an example embodiment.

Detailed description

Before explaining in detail the examples, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to Figures 1 to 3 to assist in understanding the technology underlying the described examples.

In a wireless communication system 100, such as that shown in figure 1, mobile communication devices or user equipment (UE) 102, 104, 105 are provided wireless access via at least one base station or similar wireless transmitting and/or receiving node or point. Base stations are typically controlled by at least one appropriate controller apparatus, so as to enable operation thereof and management of mobile communication devices in communication with the base stations. The controller apparatus may be located in a radio access network (e.g. wireless communication system 100) or in a core network (CN) (not shown) and may be implemented as one central apparatus or its functionality may be distributed over several apparatuses. The controller apparatus may be part of the base station and/or provided by a separate entity such as a Radio Network Controller. In Figure 1

control apparatus

108 and 109 are shown to control the respective macro

level base stations

106 and 107. The control apparatus of a base station can be interconnected with other control entities. The control apparatus is typically provided with memory capacity and at least one data processor. The control apparatus and functions may be distributed between a plurality of control units. In some systems, the control apparatus may additionally or alternatively be provided in a radio network controller.

In Figure 1

base stations

106 and 107 are shown as connected to a wider communications network 113 via gateway 112. A further gateway function may be provided to connect to another network.

The

smaller base stations

116, 118 and 120 may also be connected to the network 113, for example by a separate gateway function and/or via the controllers of the macro level stations. The

base stations

116, 118 and 120 may be pico or femto level base stations or the like. In the example,

stations

116 and 118 are connected via a gateway 111 whilst station 120 connects via the controller apparatus 108. In some embodiments, the smaller stations may not be provided.

Smaller base stations

116, 118 and 120 may be part of a second network, for example WLAN and may be WLAN APs.

The

communication devices

102, 104, 105 may access the communication system based on various access techniques, such as code division multiple access (CDMA) , or wideband CDMA (WCDMA) . Other non-limiting examples comprise time division multiple access (TDMA) , frequency division multiple access (FDMA) and various schemes thereof such as the interleaved frequency division multiple access (IFDMA) , single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA) , space division multiple access (SDMA) and so on.

An example of wireless communication systems are architectures standardized by the 3rd Generation Partnership Project (3GPP) . A latest 3GPP based development is often referred to as the long term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The various development stages of the 3GPP specifications are referred to as releases. More recent developments of the LTE are often referred to as LTE Advanced (LTE-A) . The LTE (LTE-A) employs a radio mobile architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and a core network known as the Evolved Packet Core (EPC) . Base stations of such systems are known as evolved or enhanced Node Bs (eNBs) and provide E-UTRAN features such as user plane Packet Data Convergence/Radio Link Control/Medium Access Control/Physical layer protocol (PDCP/RLC/MAC/PHY) and control plane Radio Resource Control (RRC) protocol terminations towards the communication devices. Other examples of radio access system comprise those provided by base stations of systems that are based on technologies such as wireless local area network (WLAN) and/or WiMax (Worldwide Interoperability for Microwave Access) . A base station can provide coverage for an entire cell or similar radio service area. Core network elements include Mobility Management Entity (MME) , Serving Gateway (S-GW) and Packet Gateway (P-GW) .

An example of a suitable communications system is the 5G or NR concept. Network architecture in NR may be similar to that of LTE-advanced. Base stations of NR systems may be known as next generation Node Bs (gNBs) . Changes to the network architecture may depend on the need to support various radio technologies and finer QoS support, and some on-demand requirements for e.g. QoS levels to support QoE of user point of view. Also network aware services and applications, and service and application aware networks may bring changes to the architecture. Those are related to Information Centric Network (ICN) and User-Centric Content Delivery Network (UC-CDN) approaches. NR may use multiple input -multiple output (MIMO) antennas, many more base stations or nodes than the LTE (aso-called small cell concept) , including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates.

Future networks may utilise network functions virtualization (NFV) which is a network architecture concept that proposes virtualizing network node functions into “building blocks” or entities that may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program codes using standard or general type servers instead of customized hardware. Cloud computing or data storage may also be utilized. In radio communications this may mean node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be non-existent.

An example 5G core network (CN) comprises functional entities. The CN is connected to a UE via the radio access network (RAN) . An UPF (User Plane Function) whose role is called PSA (PDU Session Anchor) may be responsible for forwarding frames back and forth between the DN (data network) and the tunnels established over the 5G towards the UE (s) exchanging traffic with the DN.

The UPF is controlled by an SMF (Session Management Function) that receives policies from a PCF (Policy Control Function) . The CN may also include an AMF (Access & Mobility Function) .

A possible mobile communication device will now be described in more detail with reference to Figure 2 showing a schematic, partially sectioned view of a communication device 200. 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 mobile device is typically provided with at least one data processing entity 201, at least one memory 202 and other possible components 203 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 204. The user may control the operation of the mobile device by means of a suitable user interface such as key pad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 208, a speaker and a microphone can be also provided. Furthermore, a mobile 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.

The mobile device 200 may receive signals over an air or radio interface 207 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 2 transceiver apparatus is designated schematically by block 206. The transceiver apparatus 206 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 mobile device.

Figure 3 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, eNB or gNB, a relay node or a core network node such as an MME or S-GW or P-GW, or a core network function such as AMF/SMF, or a server or host. The method may be implanted in a single control apparatus or across more than one control apparatus. 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 300 can be arranged to provide control on communications in the service area of the system. The control apparatus 300 comprises at least one memory 301, at least one

data processing unit

302, 303 and an input/output interface 304. 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.

The following may be applicable to channel state information feedback, and specifically Type II channel state information (CSI) for multiple input multiple output (MIMO) telecommunications systems and NR MIMO.

Type II CSI feedback codebook design has large feedback overhead due to separate quantization of beam combining coefficients in terms of amplitude and phase scaling for different beams, different polarizations, different layers and different sub-bands. Large feedback overhead limits the use of Type II CSI feedback.

The concepts as discussed herein aim to enhance feedback overhead reduction for Type II CSI, for example in 3GPP Rel. 15 and Rel. 16 NR MIMO systems, taking into account the tradeoff between performance and overhead.

In Rel-15 RAN1 meetings several frequency dependent overhead reduction solutions for Type II CSI enhancement have been discussed.

Some suggestions present a new codebook design (frequency selective precoding feedback: FSPF) for Type II CSI in order to reduce the payload size of sub-band reporting. The key idea of such codebook design is to apply linear combining of 2L beams which have different level of cyclic phase shift in frequency domain, and thus sub-band phase combining in the legacy linear combination (LC) codebook can be skipped. The proposed FSPF is an explicit CSI codebook design which exploits subcarrier or PRB level transformation.

A further proposal is one based on the observation that frequency correlation exists in the phases for each beam combination coefficient across multiple physical resource blocks (PRB) .

A third proposed approach was where the UE only reports phase information of partial sub-bands to reduce Type II CSI payload, and then gNB can recover phases of all sub-bands according to partial feedback. The partial sub-bands are selected in CSI report band based on a predefined comb pattern in which the comb size is 2.

The embodiments as discussed herein attempt to exploit frequency correlation among different sub-bands to compress and quantize sub-band beam combining coefficients in Type II CSI and to reduce the corresponding CSI feedback overhead.

With respect to Figure 4 is shown a first method for an example compressing and quantizing sub-band beam combining coefficients in Type II CSI according to some embodiments. In the following examples a number of bits for representing various coefficients/eigenvectors are provided. These numbers are examples only and it is understood that any suitable number of bits may be used to signal or represent the coefficients/eigenvectors.

The initial operation to compress and quantize sub-band beam combining coefficients in Type II CSI and to reduce the corresponding CSI feedback overhead is to construct a matrix V comprising of the dominant eigenvectors across all the sub-bands, after projecting the original channel matrix over orthogonal beams.

In other words, the embodiments as discussed herein are applicable assuming the original channel matrix is spatially compressed by means of a suitable beam selection matrix W ₁, as per legacy Type II CSI reporting in 3GPP Rel. 15.

The matrix V has size N _p × N _sb, where N _p = 2L × N _ri, N _sb is the number of sub-band, and N _ri is the feedback rank (i.e., number of layers) and L is the number of oversampled DFT beams per polarization.

The matrix structure is shown as follows, and its element v _i (j) , i = 1, …, N _p, j = 1, …, N _sb is actually a beam combining coefficient including amplitude and phase value for Type II CSI.

The operation of generating the matrix V comprising the dominant eigenvectors across all sub-bands after projecting the original channel matrix over orthogonal beams is shown in Figure 4 by step 401.

Having generated the matrix V the frequency or sub-band compression of the matrix can be performed in some embodiments by Discrete Fourier Transform (DFT) vector selection.

DFT vector selection is a sub-band compression approach in which a predefined DFT vector set is exploited to reduce frequency dimension from N _sb to N _comp.

As such a DFT matrix is defined with the dimension of N _sb × N _sb when oversampling rate O = 1, or alternatively N _sb × (N _sb × O) when oversampling rate O ＞ 1.

The defining of the DFT matrix is shown in Figure 4 by step 403.

Having defined the DFT matrix a set of suitable N _comp DFT vectors for the sub-band compression is selected from a DFT matrix by retaining only vectors which satisfy the following equation:

where f _j is the j-th column of DFT matrix having N _sb × O candidate DFT vectors and V is the composite eigenvector matrix with the dimension of N _p × N _sb and λ _i is the index of the optimal DFT vector. The DFT selection matrix F is thus formed by N _comp optimal DFT vectors, that is,

The selection of the DFT vectors from the DFT matrix is shown in Figure 4 by step 405.

Following the selection (in other words the sub-band compression) the matrix V is transformed into

of size N _p × N _comp.

The regeneration or transformation of the matrix

is shown in Figure 4 by step 407.

In such a manner the overhead reduction ratio may be calculated as

With respect to Figure 5 is shown a further method for compressing and quantizing sub-band beam combining coefficients in Type II CSI according to some embodiments. In these embodiments the matrix V comprising of the dominant eigenvectors across all the sub-bands, after projecting the original channel matrix over orthogonal beams is generated in a manner similar to that described above with respect to the earlier method.

As shown in Figure 5 the operation of generating the matrix V is shown by step 401.

However rather than DFT vector selection an eigen transformation is performed. Eigen transformation is an alternative to the above sub-band compression approach in which an orthogonal transformation Q is used to reduce the frequency dimension from N _sb to N _comp.

Having determined V, the covariance matrix of composite eigenvectors V is calculated with the dimension of N _sb × N _sb.

The operation of calculating the covariance matrix of composite eigenvectors V is shown in Figure 5 by step 503.

Having generated the covariance matrix of composite eigenvectors then perform eigen decomposition (ED)

The eigen decomposition of the covariance matrix is shown in Figure 5 by step 505.

A transformation matrix Q is then generated. The transformation matrix contains the first N _comp dominant eigenvectors of R _V, which are chosen from U

The generation of the transformation matrix is shown in Figure 5 by step 507.

From the transformation matrix Q and the matrix V a reduced overhead transformed matrix is generated by applying the transformation matrix to V matrix of composite eigenvectors V, and thus generate

of size N _p × N _comp.

The transforming of V is shown in Figure 5 by step 509.

The overhead reduction ratio in such embodiments is calculated about

The CSI feedback in some embodiments comprises several items, such as beam selection, sub-band compression and compressed matrix, etc.

In some embodiments the CSI feedback items for beam selection (in a manner similar to conventional Type II CSI) can be assuming per polarization antenna ports with (N1, N2) in the horizontal and vertical dimension, the corresponding oversampling rate (O ₁, O ₂) and the number of beams L:

a) Beam selection is signalled using

b) Wideband amplitude

1. Indication of the number of non-zero wideband amplitude for each layer:

2. Indication of the strongest coefficient out of 2L coefficients for each layer:

3. Wideband amplitude (each 3 bits) other than the strongest coefficient for each layer: (2L -1) × 3 bits

By implementing CSI feedback items for sub-band compression using DFT selection as described with respect to Figure 4 the DFT selection is signalled using

Furthermore implementing CSI feedback items for sub-band compression using Eigen transformation as described with respect to Figure 5 assuming transformation matrix Q having N _sb × N _comp coefficients in total then an indication of the strongest coefficient for each dominant eigenvector in matrix Q can be signalled using

bits and any coefficients (each 3 bits for amplitude/phase) other than the strongest ones in matrix Q can be signalled using (N _sb -1) × (3 + 3) × N _comp bits. These values for the number of bits representing the dominant and other eigenvectors are examples only and can be any suitable number of bits in other embodiments.

CSI feedback items for the compressed matrix are signalled according to some embodiments assuming a compressed matrix

having 2L × N _ri × N _comp coefficients in total for quantization after sub-band compression, and N non-zero wideband amplitudes for each layer and quantization of the strongest coefficients in matrix

Since channel vector per layer per selected DFT vector (for the DFT embodiments) or dominant eigenvector (for the Eigen decomposition embodiments) has no longer normalization after sub-band compression, all the strongest coefficients in matrix

in total N _ri × N _comp, should be quantized separately.

In such embodiments an indication of the strongest one out of 2L coefficients for each layer in each selected DFT vector (for the DFT embodiments) or dominant eigenvector (for Eigen decomposition embodiments) can reuse the wideband amplitude related reporting for the corresponding layer, hence it has no need to report again.

Furthermore in some embodiments the indication of the strongest one out of N _ri × N _comp strongest coefficients should be signalled with

bits and the other strongest coefficients signalled using (N _ri × N _comp -1) × (3 + 3) bits. The quantization of coefficients other than the strongest ones in matrix

only considering non-zero wideband amplitudes, which may total (N -1) × N _ri × N _comp, can be signalled in some embodiments in the following manner:

Sub-band differential amplitude quantization w/1 bit: (N -1) × N _ri × N _comp × 1 bits

Sub-band phase quantization w/3 bits: (N -1) × N _ri × N _comp × 3 bits

The specific number of bits representing the coefficients above are examples only and can be any suitable number of bits in other embodiments.

In some embodiments the Eigen transformation proposed sub-band compression scheme may produce only 4%loss of cell average SE, but 3%gain of cell edge SE compared with 3GPP Rel. 15 Type II CSI, while it may save up to 47%feedback overhead.

The DFT embodiments may produce less than 10%system performance loss as compared to 3GPP Rel. 15 Type II CSI, while providing significant overhead reduction capability, for example, up to 63%reduction over 3GPP Rel. 15 Type II CSI and 48%over the comb pattern reporting proposal.

The following details these payload statistic and performance comparisons.

Some configuration assumptions for a simulation to be analysed are:

- 9 sub-bands, rank 2

- (N1, N2) = (4, 4) , (O1, O2) = (4, 4) , beam number L = 4 for beam selection

- (WB amplitude, SB amplitude, SB phase) are quantized in (3, 1, 3) bits

- The number of non-zero WB amplitude is N in each layer for convenience of calculation and comparison with state of the art

- K= 2L for convenience of calculation

The detailed payload statistic for 3 kinds of CSI feedback of NR Type II CSI is given in the following table.

The system employing some embodiments as discussed above considers N _comp= 2 selected DFT vectors (for the DFT based embodiments) or dominant eigenvectors (for the eigen decomposition based embodiments) to perform sub-band compression, as per this invention, with oversampling rate O = 4 for the DFT based embodiments.

In such systems beam selection signalling requires the following:

Indication of beam selection:

and

Wideband amplitude:

Sub-band compression further requires the following:

DFT selection:

or

Eigen transformation:

Compressed matrix signalling requires

Quantization of the strongest coefficients:

and

Quantization of coefficients other than the strongest ones: (N -1) × N _ri × N _comp ×(1 + 3) = 16 × (N -1) bits.

In summary, the detailed payload statistic of the proposed sub-band compression CSI embodiments as discussed above is given in the following table.

The comparison of the payload of the 3 schemes as the number of non-zero wideband amplitude N changes are illustrated in the following table.

Additionally, the relative payload ratio of the proposed sub-band compression schemes, with respect to 3GPP Rel. 15 Type II CSI, is shown in the following table.

In the above table a positive (resp. negative) number means feedback overhead increase (reduction) .

Furthermore, we also note that the CSI schemes as discussed above have the same beam selection and wideband amplitude quantization design as 3GPP Rel. 15 Type II CSI, hence they have a common distribution of the number of non-zero wideband amplitude. The percentage of reported number of non-zero wideband amplitude coefficients over the overall reported numbers is thus shown in the following table

N	1	2	3	4	5	6	7	8
Percentage	0.1%	4.5%	4.5%	8.5%	13%	18%	23%	28%

According to the above tables, DFT selection based sub-band compression scheme embodiments have superior overhead reduction capability with respect to Type II CSI, except for the configuration N = 1 with only 0.1%probability.

Furthermore the ED based sub-band compression scheme can reduce CSI feedback overhead (e.g. up to 47%) as compared to 3GPP Rel. 15 Type II CSI in the majority of cases, except for N ≤ 3 with less than 10%probability.

For performance evaluation of the proposed sub-band compression CSI schemes, full buffer system level evaluations are carried out in LTE 3D UMa scenario, and MU-MIMO is considered in the user scheduling process with having maximum 2 layers per UE. The results are provided for 32 antenna ports with (N ₁, N ₂) = (4, 4) in the horizontal and vertical dimension, respectively. The relevant simulation parameters are given in the following table.

3GPP Rel. 15 Type II CSI is used as benchmarks. The simulation results are shown in the following table detailing a system level evaluation of different CSI schemes

As shown in the above table 9, ED based sub-band compression schemes as detailed in some embodiments have a simulated only 4%loss of cell average SE, but 3%gain of cell edge SE compared with 3GPP Rel. 15 Type II CSI, while it allows to achieve up to 47%feedback overhead reduction. In practice, DFT based sub-band compression schemes as detailed in some embodiments have less than 10%system performance loss compared with 3GPP Rel. 15 Type II CSI, while it has significant overhead reduction capability, for example, up to 63%reduction over 3GPP Rel. 15 Type II CSI.

The method may be implemented in a user equipment as described with reference to Figure 2 or a control apparatus as described with reference to Figure 3. An apparatus may comprise means for determining, at the apparatus, channel state information for a set of sub-bands within a multiple-input-multiple-output communications system The apparatus may further comprise means for obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands. Additionally the apparatus may comprise means for selecting a sub-set of sub-bands from the set of sub-bands. The apparatus may further comprise means for providing to a network an indication of the selected sub-bands and related channel state information values. In some embodiments the means for determining, the means for obtaining, the means for selecting and the means for providing are implemented by a single means.

It should be understood that the apparatuses may comprise or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and/or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities.

It is noted that whilst embodiments have been described in relation to type II CSI reporting systems, similar principles can be applied in relation to other networks and communication systems where explicit time domain CSI reporting is used. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

It is also noted herein that while the above describes example embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.

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.

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:

determining, at the apparatus, channel state information for a set of sub-bands within a multiple-input-multiple-output communications system;

obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands;

selecting a sub-set of sub-bands from the set of sub-bands; and

providing to a network an indication of the selected sub-bands and related channel state information values.
The apparatus according to claim 1, wherein the means for obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands is further for:

determining a composite eigenvector matrix comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands, wherein the matrix structure is:

where an element of the composite eigenvector matrix V is v _i (j) , i = 1, …, N _p, j =1, …, N _sb, N _p = 2L × N _ri, N _sb is a total number of sub-bands, and N _ri is a total number of layers and L is a total number of orthogonal beams per polarization used within the communications system.
The apparatus according to claim 2, wherein the means for selecting a sub-set of sub-bands from the set of sub-bands is further for:

defining a discrete Fourier transform matrix, the discrete Fourier transform matrix with a dimension of N _sb × N _sb when the communications system employs an oversampling rate O = 1, or a dimension N _sb × (N _sb × O) when the communications system employs an oversampling rate O ＞ 1;

selecting a set of vectors from the discrete Fourier transform matrix based on a selection criteria defined by
where f _j is the j-th column of the discrete Fourier transform matrix having N _sb × O candidate discrete Fourier transform vectors and V is the composite eigenvector matrix with the dimension of N _p × N _sb and λ _i is the index of an optimal discrete Fourier transform vector; and

generating a discrete Fourier transformation matrix F formed by the selected set of vectors.
The apparatus according to claim 3, wherein the means for providing to a network an indication of the selected sub-bands and related channel state information values is further for generating a reduced overhead transformed matrix based on
The apparatus according to claim 4, wherein means for providing to a network an indication of the selected sub-bands and related channel state information values is further for signalling the reduced overhead transformed matrix using
bits.
The apparatus according to claim 2, wherein the means for selecting a sub-set of sub-bands from the set of sub-bands is further for:

calculating a covariance matrix of the composite eigenvector matrix;

performing eigen decomposition of the covariance matrix of the composite eigenvector matrix
and

generating a transformation matrix Q comprising a first number N _comp of dominant eigenvectors of R _v.
The apparatus according to claim 6, wherein the means for providing to a network an indication of the selected sub-bands and related channel state information values is further for generating a reduced overhead transformed matrix based on
The apparatus according to claim 7, wherein means for providing to a network an indication of the selected sub-bands and related channel state information values is further for signalling the reduced overhead transformed matrix by signalling an indication of the strongest coefficient for each dominant eigenvector in the transformation matrix Q using
bits and 3 bits for amplitude/phase coefficients other than the strongest coefficient in the transformation matrix Q.
The apparatus as claimed in any claims dependent on claim 4 or 7, wherein the means for providing to a network an indication of the selected sub-bands and related channel state information values is further for:

selecting a sub-set of a set of reduced overhead transformed matrix coefficients based on determining a strongest one out of 2L coefficients for each layer in each selected sub-band;

signalling the sub-set of reduced overhead transformed matrix coefficients according to a first scheme;

signalling the remainder of the reduced overhead transformed matrix coefficients according to a further scheme.
The apparatus as claimed in claim 9 wherein the means for signalling the sub-set of reduced overhead transformed matrix coefficients according to a first scheme is further for signalling the sub-set of reduced overhead transformed matrix coefficients as a wideband amplitude related reporting for the layer.
The apparatus as claimed in claim 9 wherein the means for signalling the sub-set of reduced overhead transformed matrix coefficients according to a first scheme is further for signalling the sub-set of reduced overhead transformed matrix coefficients by:

signalling a strongest one out of the sub-set of reduced overhead transformed matrix coefficients with
bits; and

signalling the other of the sub-set of reduced overhead transformed matrix coefficients using (N _ri × N _comp -1) × (3 + 3) bits.
The apparatus as claimed in and of claims 9 and 11, wherein the means for signalling the remainder of the reduced overhead transformed matrix coefficients according to a second scheme is further for considering non-zero wideband amplitudes related coefficients of the reduced overhead transformed matrix in each layer signalling a sub-band differential amplitude quantization using 1 bit and sub-band phase quantization using 3 bits.
A method comprising:

determining, at an apparatus, channel state information for a set of sub-bands within a multiple-input-multiple-output communications system;

obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands;

selecting a sub-set of sub-bands from the set of sub-bands; and

providing to a network an indication of the selected sub-bands and related channel state information values.
The method according to claim 13, wherein obtaining a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands further comprises:

determining a composite eigenvector matrix comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands, wherein the matrix structure is:

where an element of the composite eigenvector matrix V is v _i (j) , i = 1, …, N _p, j =1, …, N _sb, N _p = 2L × N _ri, N _sb is a total number of sub-bands, and N _ri is a total number of layers and L is a total number of orthogonal beams per polarization used within the communications system.
An apparatus comprising at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to:

determine, at the apparatus, channel state information for a set of sub-bands within a multiple-input-multiple-output communications system;

obtain a set of the channel state information values comprising dominant eigenvectors across the set of sub-bands after projecting the channel state information over a suitable set of orthogonal beams for the set of sub-bands;

select a sub-set of sub-bands from the set of sub-bands; and

provide to a network an indication of the selected sub-bands and related channel state information values.