WO2022073663A1

WO2022073663A1 - Method, apparatus, and computer program

Info

Publication number: WO2022073663A1
Application number: PCT/EP2021/068026
Authority: WO
Inventors: Rana Ahmed Salem; Marco MASO
Original assignee: Nokia Technologies Oy
Priority date: 2020-10-06
Filing date: 2021-06-30
Publication date: 2022-04-14

Abstract

An apparatus comprising means for: identifying, for a matrix associated with a downlink channel state information signalling feedback, at least one row of the matrix which is characterized by an odd symmetry of its elements; and generating a channel state information uplink message for the downlink channel state information signalling feedback, the channel state information uplink message exploiting the odd symmetry of the elements of the identified at least one row of the matrix such that there is a performance improvement, wherein the means for generating the channel state information uplink message for downlink channel state information signalling feedback is for modifying a quantized version of the matrix associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows.

Description

METHOD, APPARATUS, AND COMPUTER PROGRAM

FIELD

The present application relates to a method, apparatus, system and computer program and in particular but not exclusively to establishing a connection between two access nodes in a communication network.

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). Some wireless systems can 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

According to an aspect, there is provided an apparatus comprising means for: identifying, for a matrix associated with a downlink channel state information signalling feedback, at least one row of the matrix which is characterized by an odd symmetry of its elements; and generating a channel state information uplink message for the downlink channel state information signalling feedback, the channel state information uplink message exploiting the odd symmetry of the elements of the identified at least one row of the matrix such that there is a performance improvement, wherein the means for generating the channel state information uplink message for downlink channel state information signalling feedback is for modifying a quantized version of the matrix associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows.

The means may be further for: determining a coefficient for each element in each column of the matrix associated with the downlink channel state information signalling feedback from a transformation of downlink channel state information measured over two or more sub-bands for one of a plurality of spatial beams, wherein an index of each column of the matrix associated with the downlink channel state information signalling feedback is an index of a frequency domain vector used to transform the downlink channel state information measured over two or more sub-bands for the plurality of spatial beams; and determining the quantized version associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows by selecting a plurality of elements from the matrix associated with the downlink channel state information signalling feedback matrix and assigning to these elements new values taken from a defined set of values, wherein each element of the matrix associated with the downlink channel state information signalling feedback is a frequency domain coefficient, and each frequency domain coefficient in the row of the matrix which is characterized by an odd symmetry of its elements is a complex conjugate of another frequency domain coefficient in the same row.

The means for determining a coefficient for each element in each column of the matrix associated with the downlink channel state information signalling feedback from a transformation of downlink channel state information measured over two or more sub-bands for one of a plurality of spatial beams may be for: calculating a coefficient for each element in at least one column of the matrix associated with the downlink channel state information signalling feedback from a transformation of downlink channel state information measured over two or more sub-bands for one of a plurality of spatial beams; calculating a complex- conjugate of the coefficient for each element in at least one column of the matrix; and assigning the complex-conjugate of the coefficient for each element in at least one column of the matrix as coefficients for a further column based on the odd symmetry of the elements of its rows.

The means for modifying a quantized version of the linear combination subband matrix based on the odd symmetric group of frequency domain coefficients may be for: identifying any mirror coefficients associated with selected coefficients within the quantized version of the matrix; and removing the identified mirror components from the quantized version of the matrix.

The means for modifying a quantized version of the linear combination subband matrix based on the odd symmetric group of frequency domain coefficients may be for: identifying any mirror coefficients associated with selected coefficients within the quantized version of the matrix; and substituting from the quantized version of the matrix at least one further coefficient with a complex conjugate of the identified mirror coefficients.

The means for substituting from the quantized version of the matrix at least one further coefficient with the complex conjugate of the identified mirror coefficients may be for: identifying the at least one further coefficient as the next strongest coefficient; and modifying an identification message for indicating positions of reported coefficients from within the matrix to include a position of the next strongest coefficient.

The means may be further for single-phase normalising the matrix.

The means for single-phase normalising the matrix may be for single-phase normalising based on beam coefficients from a beam with the largest energy.

The means may be further for generating a precoding matrix indicator channel state flag based on the modified quantized version of the matrix to indicate a modification of the quantized version of the matrix within the channel state information uplink message for the downlink channel state information signalling feedback, wherein the precoding matrix indicator channel state flag may be configured to control a processing of the modified quantized version of the matrix.

The means may be further for controlling the transmission of the channel state information uplink message for the downlink channel state information signalling feedback.

According to a second aspect there is provided an apparatus comprising means for: receiving a channel state information uplink message for downlink channel state information signalling feedback, the channel state information uplink message comprising a modified quantized matrix associated with a downlink channel state information signalling feedback wherein the modified quantized matrix having been generated by exploiting an odd symmetry of elements of at least one row of the matrix; and processing the modified quantized matrix such that there is a performance improvement, the processing further for obtaining a further version of the matrix based on the odd symmetry of the elements of the at least one row of the matrix. Each element of the modified quantized matrix associated with the downlink channel state information signalling feedback may be a frequency domain coefficient.

The means for processing the modified quantized matrix may be for: identifying any mirror coefficients associated with selected coefficients within the modified quantized matrix which are missing; and adding to the modified quantized matrix any identified mirror coefficients based on a complex conjugate of the selected coefficients.

The means for receiving the channel state information uplink message for downlink channel state information signalling feedback may be for: identifying any mirror coefficients associated with selected coefficients within the modified quantized matrix; and further modifying the quantized matrix by adding to the modified quantized matrix any identified mirror coefficients based on the complex conjugate of the selected coefficients.

The means may be further for receiving a precoding matrix indicator channel state flag based on the modified quantized version of the matrix to indicate the modification of the quantized version of the matrix within the received channel state information uplink message, wherein the means for processing the modified quantized matrix such that there is a performance improvement, the processing further for obtaining a further version of the matrix based on the odd symmetry of the elements of the at least one row of the matrix is further for processing the modified quantized matrix controlled by the precoding matrix indicator channel state flag.

According to a third aspect there is provided a method comprising: identifying, for a matrix associated with a downlink channel state information signalling feedback, at least one row of the matrix which is characterized by an odd symmetry of its elements; and generating a channel state information uplink message for the downlink channel state information signalling feedback, the channel state information uplink message exploiting the odd symmetry of the elements of the identified at least one row of the matrix such that there is a performance improvement, wherein generating the channel state information uplink message for downlink channel state information signalling feedback comprises modifying a quantized version of the matrix associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows.

The method may further comprise: determining a coefficient for each element in each column of the matrix associated with the downlink channel state information signalling feedback from a transformation of downlink channel state information measured over two or more sub-bands for one of a plurality of spatial beams, wherein an index of each column of the matrix associated with the downlink channel state information signalling feedback is an index of a frequency domain vector used to transform the downlink channel state information measured over two or more sub-bands for the plurality of spatial beams; and determining the quantized version associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows by selecting a plurality of elements from the matrix associated with the downlink channel state information signalling feedback matrix and assigning to these elements new values taken from a defined set of values, wherein each element of the matrix associated with the downlink channel state information signalling feedback is a frequency domain coefficient, and each frequency domain coefficient in the row of the matrix which is characterized by an odd symmetry of its elements is a complex conjugate of another frequency domain coefficient in the same row.

Determining a coefficient for each element in each column of the matrix associated with the downlink channel state information signalling feedback from a transformation of downlink channel state information measured over two or more sub-bands for one of a plurality of spatial beams may comprise: calculating a coefficient for each element in at least one column of the matrix associated with the downlink channel state information signalling feedback from a transformation of downlink channel state information measured over two or more sub-bands for one of a plurality of spatial beams; calculating a complex-conjugate of the coefficient for each element in at least one column of the matrix; and assigning the complex- conjugate of the coefficient for each element in at least one column of the matrix as coefficients for a further column based on the odd symmetry of the elements of its rows.

Modifying a quantized version of the linear combination subband matrix based on the odd symmetric group of frequency domain coefficients may comprise: identifying any mirror coefficients associated with selected coefficients within the quantized version of the matrix; and removing the identified mirror components from the quantized version of the matrix.

Modifying a quantized version of the linear combination subband matrix based on the odd symmetric group of frequency domain coefficients may comprise: identifying any mirror coefficients associated with selected coefficients within the quantized version of the matrix; and substituting from the quantized version of the matrix at least one further coefficient with a complex conjugate of the identified mirror coefficients.

Substituting from the quantized version of the matrix at least one further coefficient with the complex conjugate of the identified mirror coefficients may comprise: identifying the at least one further coefficient as the next strongest coefficient; and modifying an identification message for indicating positions of reported coefficients from within the matrix to include a position of the next strongest coefficient.

The method may further comprise single-phase normalising the matrix.

Single-phase normalising the matrix may comprise single-phase normalising based on beam coefficients from a beam with the largest energy.

The method may further comprise generating a precoding matrix indicator channel state flag based on the modified quantized version of the matrix to indicate a modification of the quantized version of the matrix within the channel state information uplink message for the downlink channel state information signalling feedback, wherein the precoding matrix indicator channel state flag may control a processing of the modified quantized version of the matrix.

The method may further comprise controlling the transmission of the channel state information uplink message for the downlink channel state information signalling feedback.

According to a fourth aspect there is provided a method comprising: receiving a channel state information uplink message for downlink channel state information signalling feedback, the channel state information uplink message comprising a modified quantized matrix associated with a downlink channel state information signalling feedback wherein the modified quantized matrix having been generated by exploiting an odd symmetry of elements of at least one row of the matrix; and processing the modified quantized matrix such that there is a performance improvement, the processing further for obtaining a further version of the matrix based on the odd symmetry of the elements of the at least one row of the matrix.

Each element of the modified quantized matrix associated with the downlink channel state information signalling feedback may be a frequency domain coefficient.

Processing the modified quantized matrix may comprise: identifying any mirror coefficients associated with selected coefficients within the modified quantized matrix which are missing; and adding to the modified quantized matrix any identified mirror coefficients based on a complex conjugate of the selected coefficients.

Receiving the channel state information uplink message for downlink channel state information signalling feedback may comprise: identifying any mirror coefficients associated with selected coefficients within the modified quantized matrix; and further modifying the quantized matrix by adding to the modified quantized matrix any identified mirror coefficients based on the complex conjugate of the selected coefficients.

The method may further comprise receiving a precoding matrix indicator channel state flag based on the modified quantized version of the matrix to indicate the modification of the quantized version of the matrix within the received channel state information uplink message, wherein processing the modified quantized matrix such that there is a performance improvement, the processing further for obtaining a further version of the matrix based on the odd symmetry of the elements of the at least one row of the matrix may comprise processing the modified quantized matrix controlled by the precoding matrix indicator channel state flag.

According to a fifth 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 computer program code configured to, with the at least one processor, cause the apparatus at least to: identify, for a matrix associated with a downlink channel state information signalling feedback, at least one row of the matrix which is characterized by an odd symmetry of its elements; and generate a channel state information uplink message for the downlink channel state information signalling feedback, the channel state information uplink message exploiting the odd symmetry of the elements of the identified at least one row of the matrix such that there is a performance improvement, wherein the apparatus caused to generate the channel state information uplink message for downlink channel state information signalling feedback is caused to modify a quantized version of the matrix associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows.

The apparatus may be further caused to: determine a coefficient for each element in each column of the matrix associated with the downlink channel state information signalling feedback from a transformation of downlink channel state information measured over two or more sub-bands for one of a plurality of spatial beams, wherein an index of each column of the matrix associated with the downlink channel state information signalling feedback is an index of a frequency domain vector used to transform the downlink channel state information measured over two or more sub-bands for the plurality of spatial beams; and determine the quantized version associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows by selecting a plurality of elements from the matrix associated with the downlink channel state information signalling feedback matrix and assigning to these elements new values taken from a defined set of values, wherein each element of the matrix associated with the downlink channel state information signalling feedback is a frequency domain coefficient, and each frequency domain coefficient in the row of the matrix which is characterized by an odd symmetry of its elements is a complex conjugate of another frequency domain coefficient in the same row.

The apparatus caused to determine a coefficient for each element in each column of the matrix associated with the downlink channel state information signalling feedback from a transformation of downlink channel state information measured over two or more sub-bands for one of a plurality of spatial beams may be caused to: calculate a coefficient for each element in at least one column of the matrix associated with the downlink channel state information signalling feedback from a transformation of downlink channel state information measured over two or more sub-bands for one of a plurality of spatial beams; calculate a complex-conjugate of the coefficient for each element in at least one column of the matrix; and assign the complex-conjugate of the coefficient for each element in at least one column of the matrix as coefficients for a further column based on the odd symmetry of the elements of its rows.

The apparatus caused to modify a quantized version of the linear combination subband matrix based on the odd symmetric group of frequency domain coefficients may be caused to: identify any mirror coefficients associated with selected coefficients within the quantized version of the matrix; and remove the identified mirror components from the quantized version of the matrix. The apparatus caused to modify a quantized version of the linear combination subband matrix based on the odd symmetric group of frequency domain coefficients may be caused to: identify any mirror coefficients associated with selected coefficients within the quantized version of the matrix; and substitute from the quantized version of the matrix at least one further coefficient with a complex conjugate of the identified mirror coefficients.

The apparatus caused to substitute from the quantized version of the matrix at least one further coefficient with the complex conjugate of the identified mirror coefficients may be caused to: identify the at least one further coefficient as the next strongest coefficient; and modify an identification message for indicating positions of reported coefficients from within the matrix to include a position of the next strongest coefficient.

The apparatus may be further caused to single-phase normalise the matrix.

The apparatus caused to single-phase normalise the matrix may be caused to single- phase normalise the matrix based on beam coefficients from a beam with the largest energy.

The apparatus may be further caused to generate a precoding matrix indicator channel state flag based on the modified quantized version of the matrix to indicate a modification of the quantized version of the matrix within the channel state information uplink message for the downlink channel state information signalling feedback, wherein the precoding matrix indicator channel state flag may be configured to control a processing of the modified quantized version of the matrix.

The apparatus may be further caused to control the transmission of the channel state information uplink message for the downlink channel state information signalling feedback.

According to a sixth 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 computer program code configured to, with the at least one processor, cause the apparatus at least to: receive a channel state information uplink message for downlink channel state information signalling feedback, the channel state information uplink message comprising a modified quantized matrix associated with a downlink channel state information signalling feedback wherein the modified quantized matrix having been generated by exploiting an odd symmetry of elements of at least one row of the matrix; and process the modified quantized matrix such that there is a performance improvement, the apparatus caused to process the modified quantized matrix further caused to obtain a further version of the matrix based on the odd symmetry of the elements of the at least one row of the matrix.

The apparatus caused to process the modified quantized matrix may be caused to: identify any mirror coefficients associated with selected coefficients within the modified quantized matrix which are missing; and add to the modified quantized matrix any identified mirror coefficients based on a complex conjugate of the selected coefficients.

The apparatus caused to receive the channel state information uplink message for downlink channel state information signalling feedback may be caused to: identify any mirror coefficients associated with selected coefficients within the modified quantized matrix; and further modify the quantized matrix by adding to the modified quantized matrix any identified mirror coefficients based on the complex conjugate of the selected coefficients.

The apparatus may be further caused to receive a precoding matrix indicator channel state flag based on the modified quantized version of the matrix to indicate the modification of the quantized version of the matrix within the received channel state information uplink message, wherein the apparatus caused to process the modified quantized matrix such that there is a performance improvement, the processing further for obtaining a further version of the matrix based on the odd symmetry of the elements of the at least one row of the matrix may be further caused to process the modified quantized matrix controlled by the precoding matrix indicator channel state flag.

According to a seventh aspect, there is provided an apparatus comprising: means for identifying, for a matrix associated with a downlink channel state information signalling feedback, at least one row of the matrix which is characterized by an odd symmetry of its elements; and means for generating a channel state information uplink message for the downlink channel state information signalling feedback, the channel state information uplink message exploiting the odd symmetry of the elements of the identified at least one row of the matrix such that there is a performance improvement, wherein the means for generating the channel state information uplink message for downlink channel state information signalling feedback is for modifying a quantized version of the matrix associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows.

According to an eighth aspect there is provided an apparatus comprising: means for receiving a channel state information uplink message for downlink channel state information signalling feedback, the channel state information uplink message comprising a modified quantized matrix associated with a downlink channel state information signalling feedback wherein the modified quantized matrix having been generated by exploiting an odd symmetry of elements of at least one row of the matrix; and means for processing the modified quantized matrix such that there is a performance improvement, the means for processing further for obtaining a further version of the matrix based on the odd symmetry of the elements of the at least one row of the matrix.

According to a ninth 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: identify, for a matrix associated with a downlink channel state information signalling feedback, at least one row of the matrix which is characterized by an odd symmetry of its elements; and generate a channel state information uplink message for the downlink channel state information signalling feedback, the channel state information uplink message exploiting the odd symmetry of the elements of the identified at least one row of the matrix such that there is a performance improvement, wherein the apparatus caused to generate the channel state information uplink message for downlink channel state information signalling feedback is caused to modify a quantized version of the matrix associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows.

According to a tenth 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: receive a channel state information uplink message for downlink channel state information signalling feedback, the channel state information uplink message comprising a modified quantized matrix associated with a downlink channel state information signalling feedback wherein the modified quantized matrix having been generated by exploiting an odd symmetry of elements of at least one row of the matrix; and process the modified quantized matrix such that there is a performance improvement, the apparatus caused to process the modified quantized matrix further caused to obtain a further version of the matrix based on the odd symmetry of the elements of the at least one row of the matrix.

According to an eleventh aspect there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the following: identify, for a matrix associated with a downlink channel state information signalling feedback, at least one row of the matrix which is characterized by an odd symmetry of its elements; and generate a channel state information uplink message for the downlink channel state information signalling feedback, the channel state information uplink message exploiting the odd symmetry of the elements of the identified at least one row of the matrix such that there is a performance improvement, wherein the apparatus caused to generate the channel state information uplink message for downlink channel state information signalling feedback is caused to modify a quantized version of the matrix associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows.

According to a twelfth aspect there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the following: receive a channel state information uplink message for downlink channel state information signalling feedback, the channel state information uplink message comprising a modified quantized matrix associated with a downlink channel state information signalling feedback wherein the modified quantized matrix having been generated by exploiting an odd symmetry of elements of at least one row of the matrix; and process the modified quantized matrix such that there is a performance improvement, the apparatus caused to process the modified quantized matrix further caused to obtain a further version of the matrix based on the odd symmetry of the elements of the at least one row of the matrix.

According to a thirteenth aspect there is provided an apparatus comprising: identifying circuitry configured to identify, for a matrix associated with a downlink channel state information signalling feedback, at least one row of the matrix which is characterized by an odd symmetry of its elements; and generating circuitry configured to generate a channel state information uplink message for the downlink channel state information signalling feedback, the channel state information uplink message exploiting the odd symmetry of the elements of the identified at least one row of the matrix such that there is a performance improvement, wherein the generating circuitry configured to generate the channel state information uplink message for downlink channel state information signalling feedback is configured to modify a quantized version of the matrix associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows.

According to a fourteenth aspect there is provided an apparatus comprising: receiving circuitry configured to receive a channel state information uplink message for downlink channel state information signalling feedback, the channel state information uplink message comprising a modified quantized matrix associated with a downlink channel state information signalling feedback wherein the modified quantized matrix having been generated by exploiting an odd symmetry of elements of at least one row of the matrix; and processing circuitry configured to process the modified quantized matrix such that there is a performance improvement, the processing circuitry configured to process the modified quantized matrix further configured to obtain a further version of the matrix based on the odd symmetry of the elements of the at least one row of the matrix.

According to a fifteenth aspect there is provided a computer readable medium comprising program instructions for causing an apparatus to perform at least the following: identify, for a matrix associated with a downlink channel state information signalling feedback, at least one row of the matrix which is characterized by an odd symmetry of its elements; and generate a channel state information uplink message for the downlink channel state information signalling feedback, the channel state information uplink message exploiting the odd symmetry of the elements of the identified at least one row of the matrix such that there is a performance improvement, wherein the apparatus caused to generate the channel state information uplink message for downlink channel state information signalling feedback is caused to modify a quantized version of the matrix associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows.

According to a sixteenth aspect there is provided a computer readable medium comprising program instructions for causing an apparatus to perform at least the following: receive a channel state information uplink message for downlink channel state information signalling feedback, the channel state information uplink message comprising a modified quantized matrix associated with a downlink channel state information signalling feedback wherein the modified quantized matrix having been generated by exploiting an odd symmetry of elements of at least one row of the matrix; and process the modified quantized matrix such that there is a performance improvement, the apparatus caused to process the modified quantized matrix further caused to obtain a further version of the matrix based on the odd symmetry of the elements of the at least one row of the matrix.

According to an aspect, there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the method according to any of the preceding aspects.

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 representation of a network system according to some example embodiments;

Figure 2 shows a representation of a control apparatus according to some example embodiments;

Figure 3 shows a representation of an apparatus according to some example embodiments;

Figure 4 shows an example method for signalling feedback from a user equipment to an access point;

Figures 5 to 7 show example method for signalling feedback from a user equipment to an access point according to some embodiments;

Figure 8 shows a graph of odd symmetry associated with amplitude values of frequency components of a beam within a linear combination subband matrix; and

Figure 9 shows signalling or overhead bits in signalling feedback based on employing some embodiments. DETAILED DESCRIPTION

In the following certain embodiments are explained with reference to mobile communication devices capable of communication via a wireless cellular system and mobile communication systems serving such mobile communication devices. Before explaining in detail the exemplifying embodiments, certain general principles of a wireless communication system, access systems thereof, and mobile communication devices are briefly explained with reference to Figures 1 , 2 and 3 to assist in understanding the technology underlying the described examples.

Figure 1 shows a schematic representation of a 5G system (5GS). The 5GS may be comprised by a terminal or user equipment (UE), a 5G radio access network (5GRAN) or next generation radio access network (NG-RAN), a 5G core network (5GC), one or more application function (AF) and one or more data networks (DN).

The 5G-RAN may comprise one or more gNodeB (gNB) or one or more gNodeB (gNB) distributed unit functions connected to one or more gNodeB (gNB) centralized unit functions.

The 5GC may comprise the following entities: Network Slice Selection Function (NSSF); Network Exposure Function; Network Repository Function (NRF); Policy Control Function (PCF); Unified Data Management (UDM); Application Function (AF); Authentication Server Function (AUSF); an Access and Mobility Management Function (AMF); and Session Management Function (SMF).

Figure 2 illustrates an example of a control apparatus 200 for controlling a function of the 5GRAN or the 5GC as illustrated on Figure 1. The control apparatus may comprise at least one random access memory (RAM) 211a, at least on read only memory (ROM) 211b, at least one processor 212, 213 and an input/output interface 214. The at least one processor 212, 213 may be coupled to the RAM 211a and the ROM 211 b. The at least one processor 212, 213 may be configured to execute an appropriate software code 215. The software code 215 may for example allow to perform one or more steps to perform one or more of the present aspects. The software code 215 may be stored in the ROM 211b. The control apparatus 200 may be interconnected with another control apparatus 200 controlling another function of the 5GRAN or the 5GC. In some embodiments, each function of the 5GRAN or the 5GC comprises a control apparatus 200. In alternative embodiments, two or more functions of the 5GRAN or the 5GC may share a control apparatus.

Figure 3 illustrates an example of a terminal 300, such as the terminal or UE illustrated on Figure 1. The terminal 300 may be provided by any device capable of sending and receiving radio signals. Non-limiting examples comprise a user equipment, 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), a personal data assistant (PDA) or a tablet provided with wireless communication capabilities, a machine-type communications (MTC) device, an Internet of things (loT) type communication device or any combinations of these or the like. The terminal 300 may provide, for example, communication of data for carrying communications. The communications may be one or more of voice, electronic mail (email), text message, multimedia, data, machine data and so on.

The terminal 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 mobile device.

The terminal 300 may be provided with at least one processor 301 , at least one memory ROM 302a, at least one RAM 302b 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 at least one processor 301 is coupled to the RAM 311a and the ROM 311b. The at least one processor 301 may be configured to execute an appropriate software code 308. The software code 308 may for example allow to perform one or more of the present aspects. The software code 308 may be stored in the ROM 311b.

The processor, 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 device may optionally have a user interface such as key pad 305, touch sensitive screen or pad, combinations thereof or the like. Optionally one or more of a display, a speaker and a microphone may be provided depending on the type of the device.

In frequency division duplex systems (FDD), due to the absence of channel reciprocity, downlink (DL) channel state information (CSI) feedback from UE to gNB is often the only available option for the latter to acquire sufficient information to increase the efficiency of DL transmissions. For this reason, both 3GPP LTE and NR specify a comprehensive framework by means of which the UE can be configured to feedback CSI reports which consist of one or more of the following CSI quantities:

1- CQI: channel quality indicator, wideband or per sub-band.

2- PM I: precoding matrix indicator(s)

3- CRI: CSI-RS resource indicator

4- Rl: rank indicator

5- 11 : PM I wide band indication

6- SSBRI: SSB resource Indicator

7- L1-RSRP: reference signal received power 8- L1-SINR: reference signal measured signal to noise plus interference ratio

9- LI: strongest layer indicator

Using the PMI, the gNB can build the DL precoder. In practice, precoder matrix indicator (PMI) makes use of a specified set of codebooks to signal to gNB the precoder chosen by UE. The PMI realization and structure depends on the configured codebook type. The codebooks are defined separately for each transmission rank.

In general, precoder codebooks are expressed using a specific formulation which may provide numerical values directly (e.g., for small number of antenna ports), or formulas that depend on the parameters regulating codebook resolution (e.g., for large number of antenna ports).

In known systems (such as 3GPP NR Rel-15), there exists two codebooks for a single panel UE (in other ways there are two ways to build the PM I) based on non-beamformed Channel State Information Reference Signal (CSI-RS): NR type I PMI and NR type II PMI, mainly designed for single user - multiple input multiple output (SU-MIMO) and multiple user - multiple input multiple output (MU-MIMO) respectively.

In 3GPP Rel-15, NR type II CSI may be used as an eigenvector approximation scheme used for PMI feedback, defined up to rank=2 transmission. This limitation is mostly due the large feedback overhead that would result from a higher rank PMI feedback. Indeed, in its most general instance, the feedback overhead of NR type II would scale linearly with the rank of the PMI feedback, if the legacy framework were simply extended. This requires a significant increase of the necessary uplink resources to perform the feedback. Despite this limitation, legacy Type II codebook can achieve significant performance enhancement, e.g., more than 30%, over LTE at the cost of higher feedback overhead.

The final weighing vector at the gNB is a weighted linear combination of L orthogonal beams per polarization as

For polarization r and layer is written as

Where the first term is the long term 2D DFT beam, the second term the wideband beam power scaling factor, the third term is the per-subband beam power scaling factor and the fourth term the beam combining coefficient.

In order to build the following steps may be implemented

1 . Building the matrix W₁ : choose L orthogonal vectors/beams per polarization r from a set of oversampled O₁O₂N₁N₂ DFT beams, where N₁ and N₂ are the number of antenna ports in horizontal and vertical domains. O₁ and O₂ are the oversampling factors in two dimensions, respectively. W₁ has thus size 2N₁N₂ x 2L.This collection of vectors can be used to express the precoder chosen by UE, by means of suitable weighted linear combinations. A typical implementation would likely use such vectors to approximate the eigenvectors of the channel covariance matrix. In practice, this operation achieves a compression in the spatial domain (SD). The resulting 2L beams are thus often referred to as SD components.

2. Building the linear combination (LC) subband matrix W₂: for every subband, calculate the coefficients to be used for the weighed linear combination of the columns of W₁ yielding the aforementioned approximation of the I strongest eigenvectors of the channel covariance matrix. The resulting matrix has size 2L x N₃, where N₃ is the number of subbands.

3. Quantization of linear combining coefficients: the correlation between the coefficients of the different W₂ matrices across all the subbands is exploited to achieve a reduction of the overall number of coefficients to feed back by means of a differential wideband+subband guantization.

In Rel-16 in order to reduce feedback overhead an enhanced NR type II PMI feedback was proposed. The main cause of the overhead was recognized to be the guantized W₂ coefficients per subband, as per step 3 above.

The enhancement of type II PMI feedback was based on exploiting the freguency correlation among the per subband coefficients across different W₂ matrices. A freguency domain compression scheme is thus applied on subband matrix W₂, by means of which W₂ is approximated as . The precoder for each layer W is then defined as

where is a 2L x M matrix of linear combining coefficients (LCC), W_f is an N₃ x M freguency-domain (FD) compression matrix, alternatively referred to as FD basis subset, M is the number of vectors used to compress W₂, often referred to as FD components, and N₃ is the number of subbands. The columns in W_f are drawn from a DFT codebook, i.e., a DFT compression/operation is applied on W₂ prior to LCC guantization.

Note that M < N₃ , hence the number of guantized coefficients in W₂ is smaller than the number of guantized coefficients in W₂ (Rel-15 counterpart), which enables the UL overhead reduction in Rel-16 as compared to Rel-15. The overhead caused by the additional W_f feedback in Rel-16 is in fact rather limited: only the indices of the codebook vectors in the selected FD basis subset of the DFT codebook are fed back by UE. Furthermore, owing to the sparse nature of , only a subset of the elements inside are quantized and fed back to

the gNB. The locations of the K₀ selected elements are signaled to the gNB via a bit-map for each layer.

Rel-16 NR type II CSI can provide a significant gain over Rel-15 type II CSI. However, each column inside W₂ may correspond to the dominant eigenvector of a certain layer of one subband of the channel frequency response (CFR). Also W₂ is of size 2L x N₃ for one layer, where the rows are associated to the spatial beams and the columns span the frequency subbands. Now, since eigenvectors of a channel covariance matrix are unique up to a phase factor, it is evident that different phase variations across columns of W₂ do not affect the accuracy of the eigenvector representation. On the other hand, different phase variations may indeed impact the accuracy of the reconstruction of W₂ at the gNB, once the quantized version of is received by the latter and the approximation is made. More precisely,

phase discontinuities or, alternatively, large phase variations across the columns of a matrix, e.g., W₂, may induce large energy spread across the columns of its DFT-transformed version, e.g., . In other words, the LCC matrix would not be sufficiently sparse prior to LCC

selection and quantization, and the approximation at the gNB would be less

accurate.

The conventional solution to this problem is to apply an appropriate phase pre- normalization on the columns of W₂, prior to DFT-compression. Such phase pre-normalization can be performed in several ways, which can be classified in two major categories:

Single phase pre-normalization: Normalize W₂ with respect to phase values of the elements of one of its rows, e.g., the one with largest energy (the strongest beam). In this case, each column of W₂ is multiplied by a complex phase so that the row whose phase values across elements are used for normalization has null phase after the normalization.

Multi-phase pre-normalization: Normalize every column of W₂ with respect to a previous column in order for the phase difference between two adjacent columns or, alternatively, subbands, to satisfy a certain criterion, e.g., minimum phase difference.

Comparison of two instances of the two approaches above shows that single phase pre-normalization methods can have a better performance. However, the actual choice of phase pre-normalization is left up to the UE implementation, hence performance in actual systems may vary depending on implementation choice.

With respect to Figure 4 is shown an example operation of the UE and gNB in implementing PMI based CSI report feedback.

Thus for example first the UE 400 is configured to observe the channel frequency response (CFR) H from the channel state information - reference signal (CSI-RS) as shown in Figure 4 by step 401. Having obtained H the UE 400 is then configured to obtain the matrix W₁ and the linear combination (LC) subband matrix W₂ are determined as discussed above and shown in Figure 4 by step 403.

Then phase pre-normalisation is performed on the linear combination (LC) subband matrix W₂ as shown in Figure 4 by step 405.

The FD compression matrix W_f is then generated as shown in Figure 4 by step 407.

Having determined the FD compression matrix W_f then the compressed linear combination (LC) subband matrix W₂ is generated as as shown in Figure

4 by step 409. A set of LCC taken from is then selected for reporting (prior to or after quantization of the coefficients itself, depending on the considered implementation). Subsequently, a sequence of M x N3 bits is generated, wherein each bit of the sequence conveys the information on whether the corresponding LCC in

is selected for reporting or not, such that if the sequence is defined as a matrix then the bit in row / and column j is set to 1 only if the LCC in row / and column j of is selected for reporting, and 0 otherwise. We

define the sequence as bitmap and will use this term to refer to it henceforth.

The feedback message comprising the matrix W₁, the selected LCC for reporting taken from the compressed subband matrix

, the bitmap indicating the position of the reported LCC and the FD compression matrix W_f is then generated as shown in Figure 4 by step 409.

The feedback message is then transmitted to the gNB 402 as shown in Figure 4 by the arrow 413.

The gNB 402 having received the feedback message is configured to generate a PMI parameter based on the matrix W₁, the compressed linear combination (LC) subband matrix obtained using the reported compressed LCC and the bitmap, and the FD compression matrix W_f, for example by building the PMI matrix as shown

in Figure 4 by step 415.

The concept as discussed herein in further detail by the embodiments hereafter describe a new UE and gNB behaviour related to how the columns in W_f are chosen and how the bitmap indicating the position of the reported LCC to gNB is handled. In other words, in the following embodiments a method is disclosed in which the UE and the gNB implement a specific instance of the PMI feedback mechanism which allows either to reduce UL overhead while keeping PMI accuracy reconstruction at gNB constant or to increase PMI accuracy reconstruction, while keeping the UL overhead constant.

More specifically the following embodiments describe a very low complexity method which can reduce the uplink (UL) overhead from feeding back the selected LCC from ,

when the single-phase pre-normalization method is implemented. In some embodiments the overhead reduction can be achieved directly. For example, the resulting PMI feedback requires a lower number of bits for the same PMI representation accuracy. In some embodiments the overhead reduction can be achieved indirectly. For example, the resulting PMI feedback has a higher PMI representation accuracy for a similar number of bits as the known methods.

It can be observed that whenever a single-phase pre-normalization method is applied, the row of W₂ whose phase values across columns are used to normalize the columns themselves carries only real valued elements after the normalization. As a result, the DFT- transformed version of such row will always have an odd symmetry around the DC component, i.e. , the one corresponding to FD component 0, as it is the DFT of a real valued signal.

Hence, the real valued row in W₂ will be transformed into a row with odd symmetry in . This means that it can be fully represented by only half of its coefficients, without incurring information loss. In the embodiments as described in further detail hereafter the other half of the coefficients can be referred to as mirror coefficients.

In the following description the notation used so far is modified such that

represents the element in the Z-th row and m-th column of

, associated to the x-th DFT codebook vector, with I ϵ [0,2L - 1], m ϵ [0, M - 1] and x ϵ [0, /V₃ - 1], This highlights the association between the m-th column of W_f and the x-th DFT codebook vector.

If we define the index of the strongest beam in W₂ as l_max. The odd symmetry of the so-obtained N₃ DFT-transformed elements is such that if both the x-th and (/V₃ - x)-th elements are included in , then it is possible to define the following:

for any k ϵ [0, M - 1] and k # m.

Furthermore, if for example N₃ = 13 for simplicity (without impacting the generality of the concept as discussed by the embodiments) it is possible to describe the example embodiments, which differ for the way they achieve the UL overhead reduction.

In some embodiments where an frequency domain (FD) component and its mirror are selected in W_f and in the bitmap by the UE, i.e., both the x-th and ( N₃ - x)-th DFT codebook vectors are included in the FD basis subset, then the UL overhead can be directly reduced as follows:

Firstly if both are selected for quantization and feedback, then UE

can drop the latter, i.e., the mirror coefficient, and gNB can add it back upon reception as complex conjugate of For instance, if both the 1^st and 12^th DFT codebook vectors are

included and both and are selected for quantization, then UE does not report

and gNB adds it back as

Secondly if an FD component and its mirror are selected in W_f and in the bitmap by the UE, i.e., both the x-th and (/V₃ - x)-th DFT codebook vectors are included in the FD basis subset, then the PM I accuracy can be increased for the same overhead as follows where if both and are selected for quantization and feedback, then the UE can drop

the latter, i.e., the mirror coefficient, and add the next largest coefficient from the rest of the matrix. The bitmap indicating the position of the reported LCCs is modified accordingly. Thereby, the overhead will be the same but the gNB can extrapolate more coefficients from at no further UL overhead cost.

Thirdly if the mirror LCC of a reported LCC is not present in

, i.e., it is neither reported nor selected in the bitmap, and/or the mirror DFT codebook vector index of a reported DFT codebook vector index is not included in W_f , then PM I accuracy can be increased without increasing UL overhead by including the DFT codebook vector x (e.g., 1) in W_f , whereas DFT codebook vector N₃ - x (e.g., 12) is not included. Upon PMI feedback reception, gNB can add another column to W_f and , corresponding to DFT codebook vector N₃ - x, which has a

non-zero coefficient in the row corresponding to its strongest beam. In practice, upon PMI feedback reception, gNB can add as many LCCs to the row of corresponding to its

strongest beam as the number of non-zero LCCs reported by UE in the row itself. Additionally, gNB can be configured to add, following PMI feedback reception, as many columns to W_f as the number of added LCCs from the above, corresponding to all the mirror counterparts of the FD components whose LCCs in the row of corresponding to its strongest beam have been

reported.

In such embodiments there is a positive impact on the PMI accuracy with no additional UL overhead.

As mentioned earlier, a phase pre-normalization operation can be performed on W₂ prior to FD compression. In some embodiments when single phase pre-normalization is implemented, the phase of each element of the reference row is used to normalize the phase of the column in which each element of the reference is.

Although any choice in this sense could be made, in some embodiments the row corresponding to the strongest beam is selected as the reference row. This choice has a significant advantage in that evaluations performed during Rel-16 specification work have found that the strongest coefficient of , whose row index is explicitly indicated to gNB via the so-called strongest coefficient indicator (SCI), is always found in the row of carrying the DFT of the row of W₂ corresponding to the strongest measured beam. Thus, gNB is informed of which row of W₂ has been used for the single-phase pre-normalization by means of the SCI.

In the following examples the strongest beam is taken as the reference row. However, it would be understood that the following methods may be applied to any suitable reference selection.

The structure of the linear combination (LC) subband matrix W₂ in some embodiments is defined as:

and the approximation , is

In some embodiments after single phase pre-normalisation, the complex coefficient of

1 element on row I and column n₃ can be written as:

Where l_max indicates the row index of the strongest beam, as previously defined.

The expression as shown above shows that the elements on the strongest row inside

W₂ will be all real valued, as previously discussed. As a result, the DFT transform of the strongest row of W₂, prior to FD component selection (i.e., prior to

determination) have an odd symmetry around the DC component.

An example of the mapping between FD component indices and corresponding mirror FD component indices for /V₃ = 13 is given by the table below

Furthermore, this is shown in the example shown in Figure 8 which illustrates the odd symmetry within the amplitude plot.

The embodiments discussed in detail herein exploit the odd symmetry depending on the realization of both W_f and bitmap. The elements in

are a subset of all the DFT- transformed elements of W₂. In other words, the choice of which DFT codebook vector indices to feedback to the gNB determines the FD components to be included in

, i.e., which columns of DFT-transformed coefficients are retained for the subsequent LCC selection and quantization. This choice also affects the realization the bitmap indicating the position of the selected LCCs for the feedback, it also being a function of the realization of W_f.

In some embodiments the odd symmetry is exploited by directly lowering the overhead of the feedback required. An example method implementing this direct lowering of the overhead of the feedback is shown with respect to Figure 5. As discussed above, the direct approach attempts to use the knowledge of the odd symmetry by dropping mirror components. In other words where an FD component and its mirror are selected in W_f and in the bitmap, i.e., both the x-th and ( N₃ - x)-th DFT codebook vectors are included in the FD basis subset, then the UL overhead can be directly reduced as follows: a. If both are selected for quantization and feedback, then

UE can drop the latter, i.e., the mirror coefficient, and gNB can add it back upon reception as complex conjugate of . For instance, if both the 1^st and 12^th

DFT codebook vectors are included and both are selected

for quantization, then UE does not report and gNB adds it back as

b. UE can choose to skip computation of mirror coefficients to save UE complexity. This can be used at the UE in the step before coefficient selection, i.e. before building the bitmap. In this case, it is a pure UE implementation step. Thus, for example first the UE 400 is configured to observe the channel frequency response (CFR) H from the channel state information - reference signal (CSI-RS) as shown in Figure 5 by step 501.

Having obtained H, the UE 400 is then configured to obtain the matrix W₁ and the linear combination (LC) subband matrix W₂, determined as discussed above and shown in Figure 5 by step 503.

Then phase pre-normalisation is performed on the linear combination (LC) subband matrix W₂ as shown in Figure 5 by step 505.

The FD compression matrix W_f is then generated as shown in Figure 5 by step 507.

5 by step 509.

Then, on the strongest beam row l_max in , drop all or any selected mirror

components, or as shown in Figure 5 by step 511. The bitmap

indicating the position of the reported LCCs is modified accordingly, i.e., bits corresponding to dropped mirror coefficients are set to 0.

The feedback message comprising the matrix

the compressed linear combination (LC) subband matrix

(without the mirror components), the modified bitmap indicating the position of the reported LCCs, and the FD compression matrix W_f is then generated as shown in Figure 5 by step 513.

The feedback message is then transmitted to the gNB 402 as shown in Figure 5 by the arrow 515.

The gNB 402 having received the feedback message is then configured to regenerate (or fill in) the missing parts of l_max in , for example by setting ^as shown

in Figure 5 by step 517.

Having regenerated then the gNB 402 is configured to generate a PMI parameter

based on the matrix

the regenerated compressed linear combination (LC) subband matrix , the bitmap included in the received feedback, and the FD compression matrix W_f, for example by building the PMI matrix as shown in Figure 5 by

step 519.

Although in the example above the dropped/added LCC/FD component is the one with the largest column index, the converse operation could be performed without affecting the validity of the description. In other words, in some embodiments the dropped/added LCC/FD component is the one with the smallest column index. The advantages of such embodiments are an uplink (UL) overhead reduction. Furthermore, as indicated, there is the possibility of reducing complexity in that at the calculation of certain components of at the UE side (and complex conjugate operation for some coefficients of at gNB) is not required.

An example of the outcome produced by the embodiment as discussed above is shown in Figure 9 which shows for L=2,4, where the distribution of different measured UL overhead values is depicted, and where the nominal UL overhead for known approaches are 190 and 95 bits, respectively. The average overhead saving shown is ~5 bits in both cases which, is certainly non-negligible. Furthermore, the overhead reduction is per UE, per layer, per report and for one Tx/Rx Point (TRP). This saving thus should be scaled by all the relevant parameters in a real implementation to fully assess the merit of the embodiment discussed herein (e.g., in terms of kbps saving over the PUSCH). For instance, a Rel-16 UE can be configured with up to 4 layers.

Moreover, this signaling overhead saving can be achieved with no additional cost in terms of complexity or overhead.

In some embodiments the odd symmetry is exploited by indirectly lowering the overhead of the feedback required. An indirect lowering of the overhead approach attempts to provide a PMI accuracy increase for the same UL overhead.

In these embodiments where an FD component and its mirror are selected in W_f and in the bitmap, i.e. , both the x-th and ( N₃ - x)-th DFT codebook vectors are included in the FD basis subset, then the PMI accuracy can be increased for the same overhead by determining whether both are selected for quantization and feedback. When both are

selected, the UE can be configured to drop the mirror coefficient and add the next largest coefficient from the rest of the matrix. The bitmap indicating the position of the reported

LCCs is modified accordingly, i.e., bits corresponding to dropped mirror coefficients are set to 0 whereas bits corresponding to added coefficients are set to 1.

Thereby, the overhead will be the same but the gNB can extrapolate more coefficients from at no further UL overhead cost.

An example of such a method is shown with respect to Figure 6.

Thus, for example first the UE 400 is configured to observe the channel frequency response (CFR) H from the channel state information - reference signal (CSI-RS) as shown in Figure 6 by step 601 .

Having obtained H, the UE 400 is then configured to obtain the matrix W₁ and the linear combination (LC) subband matrix W₂, determined as discussed above and shown in Figure 6 by step 603. Then phase pre-normalisation is performed on the linear combination (LC) subband matrix W₂ as shown in Figure 6 by step 605.

The FD compression matrix W_f is then generated as shown in Figure 6 by step 607.

Having determined the FD compression matrix W_f then the compressed linear combination (LC) subband matrix W₂ is generated as , as shown in Figure

6 by step 609.

Then, on the strongest beam row l_max in , drop all or any selected mirror

components, or wwhheerree and replace in the next strongest coefficient in ,

and modify the bitmap indicating the position of the reported LCCs accordingly as shown in Figure 6 by step 611.

The feedback message comprising the matrix W₁, the modified compressed linear combination (LC) subband matrix (without the mirror components but with the additional

components), the modified bitmap indicating the position of the reported LCCs, and the FD compression matrix W_f is then generated as shown in Figure 6 by step 613.

The feedback message is then transmitted to the gNB 402 as shown in Figure 6 by the arrow 615.

The gNB 402 having received the feedback message is then configured to regenerate

(or fill in) the missing parts of l_max in , for example by as shown in

Figure 6 by step 617.

Having regenerated , the gNB 402 is configured to generate a PMI parameter based

on the matrix W₁, the regenerated (and with additional components) compressed linear combination (LC) subband matrix , the bitmap included in the received feedback, and the

FD compression matrix W_f , for example by building the PMI matrix

as shown in Figure 6 by step 619.

In such embodiments, although the number of signaling bits are not reduced as in the earlier embodiments described above, the quality of the feedback with respect to the number of signaling bits is increased. This produces the indirect result of requiring fewer bits to achieve a desired quality feedback.

In some embodiments the odd symmetry is exploited by indirectly lowering the overhead of the feedback required in a further manner.

In such embodiments where the mirror LCC of a reported LCC is not present in

, i.e. , it is neither reported nor selected in the bitmap, and/or the mirror DFT codebook vector index of a reported DFT codebook vector index is not included in W_f , then the PMI accuracy can be increased without increasing UL overhead. In such embodiments the DFT codebook vector x (e.g., 1) is included in W_f , whereas the DFT codebook vector N₃ - x (e.g., 12) is not included. In these embodiments, upon PM I feedback reception, the gNB can be configured to add another column to W_f and

, corresponding to the DFT codebook vector N₃ - x, which has a non-zero coefficient in the row corresponding to its strongest beam.

This can in some embodiments be implemented by the gNB being configured to add: a) as many LCCs to the row of corresponding to its strongest beam as the

number of non-zero LCCs reported by UE in the row itself. b) As many columns to W_f as the number of added LCCs in a), corresponding to all the mirror counterparts of the FD components whose LCCs in the row of corresponding to its strongest beam have been reported.

An example of such embodiments is shown with respect to Figure 7 wherein first the UE 400 is configured to observe the channel frequency response (CFR) H from the channel state information - reference signal (CSI-RS) as shown in Figure 7 by step 701 .

Having obtained H, the UE 400 is then configured to obtain the matrix W_± and the linear combination (LC) subband matrix W₂, determined as discussed above and shown in Figure 7 by step 703.

Then phase pre-normalisation is performed on the linear combination (LC) subband matrix W₂ as shown in Figure 7 by step 705.

The FD compression matrix W_f is then generated as shown in Figure 7 by step 707.

Having determined the FD compression matrix W_f then the compressed linear combination (LC) subband matrix W₂ is generated as shown in Figure 7 by

step 709.

The feedback message comprising the matrix W_{l t} the modified compressed linear combination (LC) subband matrix

(without the mirror components but with the additional components), bitmap indicating the position of the reported LCCs in , and the FD

compression matrix W_f is then generated as shown in Figure 7 by step 711.

The feedback message is then transmitted to the gNB 402 as shown in Figure 7 by the arrow 713.

The gNB 402 having received the feedback message is then configured to detect an absence of mirror FD coefficients in W_f and bitmap for one or more as shown in

Figure 7 by step 715.

Based on the detection the gNB 402 can then be configured to add other column(s) inside W_f and which are non-zero at strongest beam row on l_max. The column values

may be determined as as shown in Figure 7 by step 717. The bitmap

included in the received feedback is also modified accordingly, i.e., by setting to 1 the bits corresponding to the added mirror coefficients. Having generated , the gNB 402 is configured to generate a PMI parameter based

on the matrix W₁ the regenerated (and with additional components) compressed linear combination (LC) subband matrix

, the bitmap included in the received feedback modified as described above, and the FD compression matrix W_f , for example by building the PMI matrix

as shown in Figure 7 by step 719.

In some embodiments the apparatus, such as the UE, is configured to generate a precoding matrix indicator channel state flag. The channel state flag can be based on the modified quantized version of the matrix and may be used to indicate that there has been a modification of the quantized version of the matrix within the channel state information uplink message. This flag can be received, for example by the gNB, and the flag be used to configure a processing of the received modified quantized version of the matrix. For example the flag may be used to indicate which of the methods employed to modify the quantized version of the matrix and thus enable the apparatus to efficiently ‘decode’ the modified quantized version of the matrix.

In such embodiments the PMI accuracy is improved with no additional UL overhead.

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 some embodiments have been described in relation to 5G networks, similar principles can be applied in relation to other networks and communication systems. 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 circuitry, software, logic or any combination thereof. Some aspects of the disclosure 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 disclosure is not limited thereto. While various aspects of the disclosure 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 disclosure 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 disclosure 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 scope of protection sought for various embodiments of the disclosure is set out by the independent claims. The embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the disclosure.

The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of this disclosure. 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 disclosure 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

1 . An apparatus comprising means for: identifying, for a matrix associated with a downlink channel state information signalling feedback, at least one row of the matrix which is characterized by an odd symmetry of its elements; generating a channel state information uplink message for the downlink channel state information signalling feedback, the channel state information uplink message exploiting the odd symmetry of the elements of the identified at least one row of the matrix such that there is a performance improvement, wherein the means for generating the channel state information uplink message for downlink channel state information signalling feedback is for modifying a quantized version of the matrix associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows; and generating a precoding matrix indicator channel state flag based on the modified quantized version of the matrix to indicate a modification of the quantized version of the matrix within the channel state information uplink message for the downlink channel state information signalling feedback, wherein the precoding matrix indicator channel state flag is configured to control a processing of the modified quantized version of the matrix.

2. The apparatus of claim 1 , wherein the means is further for: determining a coefficient for each element in each column of the matrix associated with the downlink channel state information signalling feedback from a transformation of downlink channel state information measured over two or more sub-bands for one of a plurality of spatial beams, wherein an index of each column of the matrix associated with the downlink channel state information signalling feedback is an index of a frequency domain vector used to transform the downlink channel state information measured over two or more sub-bands for the plurality of spatial beams; and determining the quantized version associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows by selecting a plurality of elements from the matrix associated with the downlink channel state information signalling feedback matrix and assigning to these elements new values taken from a defined set of values, wherein each element of the matrix associated with the downlink channel state information signalling feedback is a frequency domain coefficient, and each frequency domain coefficient in the row of the matrix which is characterized by an odd symmetry of its elements is a complex conjugate of another frequency domain coefficient in the same row.

3. The apparatus as claimed in claim 2, wherein the means for determining a coefficient for each element in each column of the matrix associated with the downlink channel state information signalling feedback from a transformation of downlink channel state information measured over two or more sub-bands for one of a plurality of spatial beams is for: calculating a coefficient for each element in at least one column of the matrix associated with the downlink channel state information signalling feedback from a transformation of downlink channel state information measured over two or more sub-bands for one of a plurality of spatial beams; calculating a complex-conjugate of the coefficient for each element in at least one column of the matrix; and assigning the complex-conjugate of the coefficient for each element in at least one column of the matrix as coefficients for a further column based on the odd symmetry of the elements of its rows.

4. The apparatus as claimed in any of claims 1 to 3, wherein the means for modifying a quantized version of the linear combination subband matrix based on the odd symmetric group of frequency domain coefficients is for: identifying any mirror coefficients associated with selected coefficients within the quantized version of the matrix; and removing the identified mirror components from the quantized version of the matrix.

5. The apparatus as claimed in any of claims 1 or 2, wherein the means for modifying a quantized version of the linear combination subband matrix based on the odd symmetric group of frequency domain coefficients is for: identifying any mirror coefficients associated with selected coefficients within the quantized version of the matrix; and substituting from the quantized version of the matrix at least one further coefficient with a complex conjugate of the identified mirror coefficients.

6. The apparatus as claimed in claim 5, wherein the means for substituting from the quantized version of the matrix at least one further coefficient with the complex conjugate of the identified mirror coefficients is for: identifying the at least one further coefficient as the next strongest coefficient; and modifying an identification message for indicating positions of reported coefficients from within the matrix to include a position of the next strongest coefficient.

7. The apparatus as claimed in any of claims 1 to 6, wherein the means is further for single-phase normalising the matrix.

8. The apparatus as claimed in claim 7, wherein the means for single-phase normalising the matrix is for single-phase normalising based on beam coefficients from a beam with the largest energy.

9. The apparatus as claimed in any of claims 1 to 8, wherein the means is further for controlling the transmission of the channel state information uplink message for the downlink channel state information signalling feedback.

10. An apparatus comprising means for: receiving a channel state information uplink message for downlink channel state information signalling feedback, the channel state information uplink message comprising a modified quantized matrix associated with a downlink channel state information signalling feedback wherein the modified quantized matrix having been generated by exploiting an odd symmetry of elements of at least one row of the matrix; receiving a precoding matrix indicator channel state flag based on the modified quantized version of the matrix to indicate the modification of the quantized version of the matrix within the received channel state information uplink message; and processing the modified quantized matrix controlled by the precoding matrix indicator channel state flag such that there is a performance improvement, the processing further for obtaining a further version of the matrix based on the odd symmetry of the elements of the at least one row of the matrix.

11. The apparatus as claimed in claim 10, wherein each element of the modified quantized matrix associated with the downlink channel state information signalling feedback is a frequency domain coefficient.

12. The apparatus as claimed in any of claims 10 or 11 , wherein the means for processing the modified quantized matrix is for: identifying any mirror coefficients associated with selected coefficients within the modified quantized matrix which are missing; and adding to the modified quantized matrix any identified mirror coefficients based on a complex conjugate of the selected coefficients.

13. The apparatus as claimed in claim 11 , wherein the means for receiving the channel state information uplink message for downlink channel state information signalling feedback is for: identifying any mirror coefficients associated with selected coefficients within the modified quantized matrix; and further modifying the quantized matrix by adding to the modified quantized matrix any identified mirror coefficients based on the complex conjugate of the selected coefficients.

14. A method comprising: identifying, for a matrix associated with a downlink channel state information signalling feedback, at least one row of the matrix which is characterized by an odd symmetry of its elements; generating a channel state information uplink message for the downlink channel state information signalling feedback, the channel state information uplink message exploiting the odd symmetry of the elements of the identified at least one row of the matrix such that there is a performance improvement, wherein generating the channel state information uplink message for downlink channel state information signalling feedback comprises modifying a quantized version of the matrix associated with the downlink channel state information signalling feedback matrix based on the odd symmetry of the elements of its rows and generating a precoding matrix indicator channel state flag based on the modified quantized version of the matrix to indicate a modification of the quantized version of the matrix within the channel state information uplink message for the downlink channel state information signalling feedback, wherein the precoding matrix indicator channel state flag is configured to control a processing of the modified quantized version of the matrix.

15. A method comprising: receiving a channel state information uplink message for downlink channel state information signalling feedback, the channel state information uplink message comprising a modified quantized matrix associated with a downlink channel state information signalling feedback wherein the modified quantized matrix having been generated by exploiting an odd symmetry of elements of at least one row of the matrix; receiving a precoding matrix indicator channel state flag based on the modified quantized version of the matrix to indicate the modification of the quantized version of the matrix within the received channel state information uplink message; and processing the modified quantized matrix controlled by the precoding matrix indicator channel state flag such that there is a performance improvement, the processing further for obtaining a further version of the matrix based on the odd symmetry of the elements of the at least one row of the matrix.