WIRELESS COMMUNICATION DEVICE AND METHOD EMPLOYING CHANNEL STATE INFORMATION COMPRESSION

Provided is an operating method of a wireless communication device, the method including receiving a channel state information reference signal (CSI-RS) from a base station, generating channel information by estimating a channel between the wireless communication device and the base station, based on the CSI-RS, and reporting the channel information to the base station, wherein the generating of the channel information includes generating first compressed data by compressing, in a spatial domain, channel characteristic information of a subband in which the CSI-RS is received, generating second compressed data by compressing the first compressed data in a frequency domain by using a first Discrete Fourier transform (DFT) function having a size corresponding to the number of subbands in which the CSI-RS is received in a bandwidth part (BWP) for communication with the base station, and generating the channel information, based on the second compressed data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application Nos. 10-2022-0133617, filed on Oct. 17, 2022, and 10-2023-0018042, filed on Feb. 10, 2023, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties.

TECHNICAL FIELD

This disclosure relates to an apparatus that compresses channel state information in a wireless communication system, and an operating method thereof.

DISCUSSION OF RELATED ART

Wireless communication devices compliant with recent Third Generation Partnership Project (3GPP) standards (e.g., Rel. 16) may perform communication with a base station using an Enhanced TypeII (eTypeII) codebook to reduce the overhead of channel state information (CSI) feedback. Through use of the eTypeII codebook, overhead reduction may be achieved by feeding back channel information utilizing correlation characteristics between space and frequency of CSI. To this end, the following process may be followed: 1) A base station transmits a channel state information-resource signal (CSI-RS) to a wireless communication device using an antenna port defined in the standard and a time/frequency resource element (RE). 2) The wireless communication device estimates a multiple-input multiple-output (MIMO) channel between the base station and the wireless communication device from the received CSI-RS signal, and then generates CSI to be reported to the base station. In the CSI generation process of step 2), the wireless communication device determines precoding (or beamforming) at the base station, and transmits corresponding channel information (e.g., a precoding matrix indicator (PMI)) in a compressed form according to the eTypeII codebook, in consideration of spatial domain/frequency domain characteristics of precoding at the base station.

The channel information compression process advantageously enables the wireless communication device to transmit channel information using fewer wireless communication resources (e.g., time/frequency RE). The spatial domain characteristic of the base station's precoding selects a basis having a dominant value among bases of a spatial domain in which values corresponding to antenna ports are re-expressed in an oversampling Discrete Fourier Transform (DFT) space. The frequency domain characteristic of the precoding at the base station selects a dominant basis among bases of the frequency domain in which values corresponding to the frequencies of the channel information are re-expressed in the DFT space. Only the precoding values for precoding at the base station re-expressed in the small-dimensional (DFT) space determined through the compression process of channel information for selecting space/frequency dimensions as bases of the selected space/frequency domain are reported to the base station.

Therefore, in the process of compressing channel information, compression of the space/frequency domain is performed in consideration of the space/frequency domain characteristics of precoding at the base station, a wireless communication device that minimizes loss of channel information in the compression process is desired.

SUMMARY

Embodiments of the inventive concept provide a terminal device that reduces overhead of channel state information (CSI) reporting and performs efficient CSI feedback through compression of channel information. The compression may be based on information on a subband in which a channel state information-resource signal (CSI-RS) is received in a wireless communication system when CSI-RS is transmitted in at least some of the subbands of an entire bandwidth part (BWP).

According to an aspect of the inventive concept, there is provided an operating method of a wireless communication device, the method including receiving a channel state information reference signal (CSI-RS) from a base station, generating channel information by estimating a channel between the wireless communication device and the base station based on the CSI-RS, and reporting the channel information to the base station, wherein the generating of the channel information includes generating first compressed data by compressing channel characteristic information, in a spatial domain, of a subband in which the CSI-RS is received, generating second compressed data by compressing the first compressed data in a frequency domain by using a first Discrete Fourier transform (DFT) function having a size corresponding to the number of subbands in which the CSI-RS is received in a bandwidth part (BWP) for communication with the base station, and generating the channel information based on the second compressed data.

According to another aspect of the inventive concept, there is provided an operating method of a wireless communication device, the method including receiving a CSI-RS from a base station, generating channel information by estimating a channel between the wireless communication device and the base station based on the CSI-RS, and reporting the channel information to the base station, wherein the generating of the channel information includes generating first compressed data by compressing channel characteristic information of a subband in which the CSI-RS is received in a spatial domain, generating second compressed data by compressing the first compressed data in a frequency domain using a first partial DFT function composed of a column domain corresponding to a subband constituting a BWP for communication with the base station and a row domain corresponding to a subband in which the CSI-RS is received, and generating the channel information based on the second compressed data.

According to another aspect of the inventive concept, there is provided an operating method of a wireless communication device, the method including receiving a CSI-RS from a base station, generating channel information by estimating a channel between the wireless communication device and the base station based on the CSI-RS, and reporting the channel information to the base station, wherein the generating of the channel information includes generating first compressed data by compressing channel characteristic information of a subband in which the CSI-RS is received in a spatial domain, performing pre-processing with respect to a subband in which the CSI-RS is not received among subbands of a BWP for communication with the base station, according to a preset method, generating second compressed data by compressing the pre-processed first compressed data in a frequency domain by using a DFT function having a size corresponding to the number of subbands constituting the BWP, and generating the channel information based on the second compressed data.

DETAILED DESCRIPTION OF EMBODIMENTS

For convenience of description, this description partially uses terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard or New Radio (NR) standard. However, the inventive concept is not limited by the above terms and names, and may be equally applied to systems conforming to other standards.

Herein, the word “index” may be understood to mean “index value” (as opposed to a list of values) as is customary in modern wireless communication standards.

Examples of an entity that communicates with a wireless communication device according to an embodiment and allocates communication network resources to the wireless communication device include a cell, a base station (BS), a NodeB (NB), an eNodB (eNB), a next generation radio access network (NG RAN), a radio access unit, a base station controller, a node on the network, and a gnodeB (gNB).

A wireless communication device is an entity that communicates with a base station or other wireless communication device, examples of which include a node, a user equipment (UE), a next generation UE (NG UE), a mobile station (MS), a mobile equipment (ME), a device, and a terminal.

Other examples of wireless communication devices may include at least one of smart phones, tablet personal computers (PCs), mobile phones, video phones, e-book readers, desktop PCs, laptop PCs, netbook computers, personal digital assistants (PDAs), portable multimedia players (PMPs), MP3 players, medical devices, cameras, and wearable devices. In addition, wireless communication devices may include at least one of televisions, digital video disk (DVD) players, audio devices, refrigerators, air conditioners, vacuum cleaners, ovens, microwave ovens, washing machines, air purifiers, set-top boxes, home automation control panels, security control panels, media boxes (e.g. Samsung HomeSync™, Apple TV™, and Google TV™), game consoles (e.g. Xbox™, and PlayStation™), electronic dictionaries, electronic keys, camcorders, and electronic photo frames. Further examples of wireless communication devices may include at least one of various medical devices (e.g., various portable medical measuring devices, such as blood glucose monitors, heart rate monitors, blood pressure monitors, or body temperature monitors, magnetic resonance angiography (MRA), magnetic resonance imaging (MRI), computed tomography (CT), imaging devices, or sonicator, etc.), a navigation device, a global navigation satellite system (GNSS), an event data recorder (EDR), a flight data recorder (FDR), an automotive infotainment device, marine electronic equipment (e.g. a marine navigation system, a gyrocompass, etc.), avionics, security equipment, a vehicle head unit, industrial or domestic robots, drones, an automated teller machine (ATM) at a financial institution, a point of sale (POS) at a store, and Internet of things (IoT) devices (e.g., light bulbs, various sensors, sprinkler devices, fire alarms, thermostats, street lights, toasters, exercise equipment, hot water tanks, heaters, boilers, etc.) Other examples may include various types of multi-media systems capable of performing communication functions.

FIG.1is a block diagram illustrating a wireless communication system according to an embodiment.

Referring toFIG.1, a wireless communication system10may include a base station200and a wireless communication device100. The wireless communication system10is shown as including only one base station200and one wireless communication device100, but this is merely an example for simplicity of explanation; the wireless communication system10may be implemented to include various numbers of base stations and wireless communication devices.

The base station200may be connected to the wireless communication device100through a radio channel to provide various communication services. The base station200may provide services through a shared channel for all user traffic, and perform scheduling by collecting status information such as the buffer status, available transmission power status, and channel status of the wireless communication device100. The wireless communication system10may support a beamforming technology using orthogonal frequency division multiplexing (OFDM) as a radio access technology. In addition, the wireless communication system10may support an adaptive modulation & coding (AMC) method for determining a modulation scheme and a channel coding rate according to the channel condition of the wireless communication device100.

The wireless communication system10may transmit and receive signals using a wide frequency band existing in a frequency band of 6 GHz or higher. For example, the wireless communication system10may achieve a high data transmission rate by using a millimeter wave band such as a 28 GHz band or a 60 GHz band. Now, since the millimeter wave band has a relatively large signal attenuation per distance, the wireless communication system10may support transmission and reception based on a directional beam generated using multiple antennas to secure coverage. The wireless communication system10may be a system supporting multiple input, multiple output (MIMO), and thus the base station200and the wireless communication device100may support beamforming technology. Beamforming technology may be classified into digital beamforming, analog beamforming, and hybrid beamforming. Hereinafter, the spirit of the present technology will be described in the wireless communication system based on an embodiment supporting the hybrid beamforming technology, but it will be fully understood that the present technology may be applied to other beamforming technologies.

As shown inFIG.1, the base station200may transmit a channel state information-reference signal (CSI-RS) to the wireless communication device100. The wireless communication device100may estimate a downlink channel using CSI-RS.

The wireless communication device100may utilize CSI compression technology (e.g., spatial domain/frequency domain compression technology) to accurately transmit channel state information to the base station using reduced uplink resources. As an example, the wireless communication device100may generate first compressed data through spatial domain compression based on a subband in which CSI-RS is received, and generate second compressed data by performing frequency domain compression using various Discrete Fourier Transform (DFT) functions on the first compressed data. The wireless communication device100may transmit channel information (e.g., CSI report) generated based on the second compressed data to the base station200.

The inventive concept involves a method for improving/maximizing compression performance of channel information by reporting channel information through a frequency domain compression technique based on various DFT functions, as will be detailed below.

FIG.2is a block diagram illustrating a block diagram of a wireless communication device100according to an example embodiment. The components may be part of a modem chip of the wireless communication device100.

The wireless communication device100may include a baseband processor110, a first RF integrated circuit (RFIC)120, first to ith antenna modules130_1to130_i(i=two or more), a second RFIC140, a plurality of antennas150, and a memory160.

The baseband processor110may control overall operations of the wireless communication device100. For example, the baseband processor110may include a channel quality measurement circuit112, a switching control circuit114, and a channel state information (CSI) compression circuit116.

The channel quality measurement circuit112, the switching control circuit114, and the CSI compression circuit116may be implemented as hardware or through use of software. Operations of the channel quality measurement circuit112, the switching control circuit114, and the CSI compression circuit116to be described below may be understood as operations of the baseband processor110.

When communicating with the base station200or other devices, to identify whether a channel of a primary component carrier among a plurality of component carriers is degraded, the channel quality measurement circuit112may measure the channel quality of the first to ith antenna modules130_1to130_i.

The channel quality measurement circuit112may measure conditions of a channel receiving a signal through each of the first to ith antenna modules130_1to130_i,and generate indicators indicating channel conditions for each of a plurality of component carriers corresponding to the first to ith antenna modules130_1to130_ibased on the measured channel conditions.

For example, the channel quality measurement circuit112may measure at least one of a rank indicator (RI), a channel quality indicator (CQI), a reference signal received power (RSRP), a reference signal received quality (RSRQ), a signal to Interference plus noise ratio (SINR), a received signal strength indicator (RSSI), a reference signal related correlation, and a variable gain index of received signals.

The switching control circuit114may control the connection between the first through ith antenna modules130_1through130_iand the first RFIC120based on the layer allocation information received to perform communication with the base station200device or other devices. The first RFIC120may include first to kth RF chains121_1to121_kcorresponding to RF resources. Each of the first to ith antenna modules (sets of antenna-associated circuitry)130_1to130_imay include first to mth antenna arrays130_11to130_1m.Each of the first to mth antenna arrays130_11to130_1mmay include first to nth RF front-ends131_11to131_1nand first to nth antennas132_11to132_1n.According to the layer assignment information received from the base station200device, the switching control circuit114may control the connection between the first to kth RF chains121_1to121_kand the first to mth antenna arrays130_11to130_1min the first to ith antenna modules130_1to130_i.

The switching control circuit114may control a connection between the selected antenna module and the first RFIC120based on the layer assignment information received from the base station200device. For example, the switching control circuit114may disconnect the selected antenna module from the first RFIC120based on the layer assignment information received from the base station200device, and perform an antenna module switching operation by controlling a connection between another antenna module and the first RFIC120.

For example, the first RFIC140may support communication in a millimeter wave band, and the second RFIC140may support communication in a frequency band lower than the millimeter wave band. The second RFIC140may be selectively connected to the plurality of antennas150.

The CSI compression circuit116may perform spatial domain compression and frequency domain compression based on the reference signal (e.g., CSI-RS) received from the base station200, and generate channel information for channel information reporting (e.g., cell specific reference (CSR)-resource signal (RS) reporting). The generated channel information may be stored in an uplink control information (UCI) bit sequence and reported to the base station200.

The memory160may store indicators of the first to ith antenna modules130_1to130_i.The memory160may store information required for connection control between the first RFIC140and the first to ith antenna modules130_1to130_i.In some embodiments, the channel quality measurement circuit112and the switching control circuit114may be implemented as software and stored in the memory160in code form. Switching history information may also be stored in the memory160.

For example, the memory160may be implemented with volatile memory such as static random access memory (SRAM). In some embodiments, memory160may be implemented as volatile memory, such as Dynamic Random Access Memory (DRAM), or a non-volatile memory, such as ROM, flash memory, Resistive Random Access Memory (ReRAM), or Magnetic Random Access Memory (MRAM).

FIG.3is a block diagram for explaining a certain implementation example of the first RFIC and the first antenna module ofFIG.2.

In detail, inFIG.3, as a first RFIC and a first antenna module of the wireless communication device100, the wireless communication device100ofFIG.2reports (or transmits) channel information compressed in the spatial domain/frequency domain by the CSI compression circuit116to the base station through the first RFIC120aand the first antenna module130_1a.

Referring toFIG.3, a first RFIC120aof the wireless communication device100ofFIG.1may include first to kth RF chains121_1ato121_kaand a switch interface122a.The implementation example of the first antenna module130_1adescribed inFIG.3may also be applied to the second to ith antenna modules130_2to130_iofFIG.2. For example, in the initial stage of access between the base station200and the wireless communication device100in a wireless communication system, connection between the first to kth RF chains121_1ato121_kaand the first antenna module130_1amay be controlled based on the layer assignment information set by the base station200.

For example, when the channel state of a major component carrier is deteriorated in a wireless communication system, the switch interface122amay control the connection between the first to kth RF chains121_1ato121_kaand the first antenna module130_1abased on the changed layer assignment information received from the base station200.

Each of the first to kth RF chains121_1ato121_kamay include an analog-to-digital converter ADC, a mixer MX, and a variable gain amplifier VGA. The variable gain amplifier VGA may amplify the received signal based on a variable gain, the mixer MX may frequency down-convert the amplified signal based on the frequency signal LO, and the analog-to-digital converter ADC may convert the converted signal into a digital signal. A digital signal output from the analog-to-digital converter ADC may be provided to the baseband processor110ofFIG.2.

The analog-to-digital converter ADC, the mixer MX, and the variable gain amplifier VGA form a path for a signal received by the wireless communication device100, and the first to kth RF chains121_1ato121_kaofFIG.3may further include components forming a path of a signal transmitted by the wireless communication device100. The switch interface122amay connect the first to kth RF chains121_1ato121_kaand the first antenna module130_1ain response to a switch control signal.

The first antenna module130_1amay include first to mth antenna arrays130_11ato130_1maand first to mth combiners133_1ato133_ma.The implementation example of the first antenna array130_11amay be applied to the second to mth antenna arrays130_12ato130_1ma.Each of the first to mth antenna arrays130_11ato130_1mamay include first to nth RF front-ends131_11ato131_1naand first to mth antennas132_11ato132_maconnected thereto. Each of the first to nth RF front-ends131_11ato131_1namay include a phase shifter PS and a low noise amplifier LNA. A plurality of reception beam patterns may be formed in the first antenna module130_1athrough phase adjustment of the plurality of phase shifters PS included in the first antenna module130_1a.The first to mth combiners133_1amay combine signals received from the connected first to mth antenna arrays130_11ato130_1maand output the summed signals to the first RFIC120a.

The implementation of the first RFIC120aand the first antenna module130_1aofFIG.3is merely an example embodiment, but is not limited thereto, and various implementations suitable for communication in the millimeter wave band will be applicable.

FIG.4is a block diagram of a channel state information compression circuit according to an example embodiment. The block diagram illustrates a spatial domain compression process and a frequency domain compression process of the baseband processor110(particularly, the CSI compression circuit116ofFIG.2).

As shown inFIG.4, the CSI compression circuit116may include a spatial domain (SD) compression block410, a frequency domain (FD) compression block420(including a non-zero coefficients (NZC) selection and quantization block427), and an uplink channel information (UCI) bit sequence generation block430.

Based on the received CSI-RS, the SD compression block410may perform spatial domain compression by utilizing a spatial codebook according to spatial domain characteristics of a subband in which the CSI-RS is received. For example, the SD compression block410may re-express values corresponding to the antenna ports of the base station in an oversampled Discrete Fourier Transform (DFT) space (interchangeably, “oversampling DFT space”), and then select an SD basis having a dominant value among candidate bases (e.g., column vectors).

The FD compression block420may include a DFT transform block421, an FD basis selection block426, the NZC selection and quantization block427, and a bypass path428. (Note that the bypass path428may be used when the ratio of the number of subbands constituting BWP, NSBBWP, to the number, NSBCSIRS, of subbands in which the CSI-RS is received, is an integer).

The DFT transform block421may include a first sub-transform block421, a second sub-transform block422, a third sub-transform block423, and a fourth sub-transform block424. When CSI-RS is received in some subbands of the entire BWP for communication between the base station and the wireless communication device, the DFT transform block421according to an embodiment may perform frequency domain compression using any one of the first sub-transform block421, the second sub-transform block422, the third sub-transform block423, or the fourth sub-transform block424. When the CSI-RS is received over the entire BWP, although not shown inFIG.4, frequency domain compression may be performed using a DFT function corresponding to the entire BWP size (e.g., a DFT function defined in 3GPP Rel. 16 or 17). In one embodiment, the matrix corresponding to the nth subband of the SD-compressed first compressed data is defined as Vn∈CL×Rank, and here, L may refer to the number of dimensions reduced by SD compression, and Rank may refer to the total number of layers for MIMO communication between the base station and the terminal.

In one embodiment, the input matrix VlCSIRSof the DFT transformation may be in the L×NSBCSIRSform of a matrix generated by extracting the 1st layer of each subband in which the CSI-RS is received from the SD-compressed first compressed data. VlCSIRSmay be expressed based on Equation 1.

In one embodiment, the first sub-transform block421may generate second compressed data by compressing the first compressed data in the frequency domain using a DFT function having a size corresponding to the number of subbands in which the CSI-RS is received. A detailed description of this will be described later with reference toFIGS.5to6B. The second sub-transform block422may generate second compressed data by compressing the first compressed data in the frequency domain using a DFT function oversampled by the number of subbands in which the CSI-RS is received. A detailed description of this will be described later with reference toFIGS.7to8E. The third sub-transform block423may generate second compressed data by compressing the first compressed data in the frequency domain using a partial DFT function of a form determined based on the number of subbands constituting the BWP and the number of subbands in which the CSI-RS is received. A detailed description of this will be described later with reference toFIGS.9to10D. The fourth sub-transform block424may perform pre-processing on the subbands to which the CSI-RS is not received among the subbands constituting the BWP, and generate second compressed data by compressing the preprocessed first compressed data in the frequency domain using the DFT function. A detailed description of this will be described later inFIGS.11to12G.

The FD basis selection block426may receive the second compressed data from the DFT transform block421and select a dominant basis of the second compressed data as the FD basis. Here, the FD basis may refer to an index of a column having a dominant value among the first compressed data re-expressed in the DFT space. For example, the FD basis selection block426may calculate the average values of the squares of components for each column of the second compressed data on which FD compression is performed, sort the average values according to size, and then select and output a preset number of FD basis (e.g., order in which the magnitude of the average value of the square of each column component is large).

The NZC selection and quantization block427may calculate the absolute values of the components included in the second compressed data in the form of ‘SD basis×FD basis’, sorts the absolute values according to size, and then select a preset number of NZCs (e.g., select an order with a large absolute value). The NZC selection and quantization block427may quantize the selected FD basis and NZC into a form that may be represented in a UCI bit sequence.

However, the UCI bit sequence generation block430may receive the quantized FD basis and NZC from the NZC selection and quantization block427and generate a UCI bit sequence for CSI reporting to the base station.

According to an embodiment, when CSI-RS of BWP is transmitted from a base station through some subbands, it is possible to provide a wireless communication device in which compression performance of channel information is maximized by efficiently performing frequency domain compression within a range in which channel information of a subband in which CSI-RS is transmitted is not damaged.

Through a process of compressing channel information in the frequency domain according to the technical idea of the inventive concept, it is possible to provide a wireless communication device capable of preventing deformation and contamination (or distortion) of CSI report contents due to interference between channels.

FIG.5is a flowchart illustrating a method of operating a wireless communication device according to an example embodiment.

In detail,FIG.5is a diagram for explaining an operation of performing CSI-RS dimension FD compression on channel characteristic information by the baseband processor110(e.g., the first sub-transform block422ofFIG.4) when the CSI-RS is received in some subbands of the entire BWP in the baseband processor110of the wireless communication device100ofFIG.2. Herein, the “CSI-RS dimension” may refer to a DFT space converted based on the number NSBCSIRSof some subbands (less than all the subbands of a BWP) in which the CSI-RS is received among the subbands of the BWP, and the “BWP dimension” may refer to a DFT space converted based on the number NSBBWPof subbands included in the BWP.

Referring toFIG.5, an operation of generating channel information by compressing channel characteristic information in the spatial domain and in the frequency domain may include operations S10, S20, S30, S40, S50, S60, and S70.

In operation S10, the baseband processor110may receive the CSI-RS from the base station. For example, the base station transmits the CSI-RS to the terminal using a predefined antenna port and a radio communication resource (e.g., a time/frequency resource element (RE)).

In operation S20, the baseband processor110may determine (or identify) whether or not the CSI-RS is received through “some subbands” of the BWP (less than all subbands of the BWP), or one or more subbands of interest designated by the base station (when the CSI-RS is transmitted in all the subbands of the BWP). Since the CSI-RS may be freely allocated within the BWP by the base station, the CSI-RS may be transmitted either in all subbands of the BWP, or only in some subbands in the BWP. Herein, when the CSI-RS is said to be received in “some subbands” within the BWP, this may encompass 1) the case in which the CSI-RS is received in less than all of the subbands within the BWP, and 2) the case in the CSI-RS is transmitted by the base station over the entire BWP, but the base station designates at least one subband of interest through CSI-reporting band information (e.g., bit sequence) and requests CSI-reporting only for the corresponding at least one subband.

The baseband processor110may perform operation S30when the CSI-RS is received through some subbands of the BWP. When the CSI-RS is received through all subbands of the BWP, or at least one subband of interest was designated as discussed above, in operation S40, the baseband processor110may generate channel information by estimating a channel based on the CSI-RS.

In operation S30, the baseband processor110may compress the channel characteristic information of the subband in which the CSI-RS is received in the spatial domain (hereinafter, referred to as SD compression) to generate first compressed data. For example, the baseband processor110re-expresses the spatial domain characteristics (e.g., values corresponding to antenna ports) of the subband in which the CSI-RS is received as an oversample Discrete Fourier Transform (DFT) space, and then selects the dominant SD basis among the SD bases. The baseband processor110may generate first compressed data composed of selected SD basis instead of basis constituting existing BWP. That is, the first compressed data may be configured in the form of a matrix having dimensions reduced by the selected SD basis compared to before compression.

In operation S50, the baseband processor110may generate second compressed data using a DFT function having a size corresponding to the number of subbands in which the CSI-RS is received. That is, the baseband processor110may generate second compressed data by compressing the first compressed data in a frequency domain using the DFT function (hereinafter, referred to as FD compression). For example, the baseband processor110may select an FD basis indicating an index of a column having a dominant value among second compressed data obtained by re-expressing the first compressed data in the DFT space. In addition, the baseband processor110may calculate absolute values of components included in the second compressed data (e.g., matrix form data) in the DFT transformation space, and select a preset number of NZCs according to the size of the absolute values. The baseband processor110may quantize channel information including the selected FD basis and NZC to display the channel information in the UCI bit sequence. A detailed description of this will be described later with reference toFIGS.6A and6B.

In operation S60, the baseband processor110may generate channel information based on the second compressed data. For example, the baseband processor110may generate a UCI bit sequence based on quantized channel information (e.g., information on the selected FD basis and NZC).

In operation S70, the baseband processor110may report channel information to the base station. The base station may determine a precoder for downlink data transmission by receiving a report of spatial domain/frequency domain compressed channel information of the wireless communication device. Additionally, in an embodiment according to the inventive concept, the base station may perform CSI-RS configuration and CSI configuration again based on the channel information report of the wireless communication device. The base station may know the amount of information of a corresponding channel based on the spatial domain/frequency domain compressed channel information report of the wireless communication device. The information amount of the channel may be determined based on the energy distribution of NZCs corresponding to the reported FD basis. For example, if the energy of NZCs is concentrated on some FD basis, the base station may control the wireless communication device to increase the compression rate of channel information to minimize the amount of overhead generated by CSI reporting.

Therefore, the wireless communication system according to an embodiment, by adjusting the size of the CSI-RS allocation area according to the amount of channel information by the base station so that there is an effect of increasing spectral efficiency by transmitting data only for a certain wireless communication resource. In addition, the wireless communication device according to the technical concept of the inventive concept may prevent deformation and distortion of CSI report content due to interference through a compression process in the frequency domain (FD).

FIGS.6A and6Bare diagrams for explaining an FD compression operation by a first sub-transform block according to example embodiments.

In detail,FIGS.6A and6Bshow diagrams for explaining an FD compression operation by the first sub-transform block422ofFIG.4.

FIG.6Ashows a case in which CSI-RS is received in some subbands within BWP as a first case in operation S20ofFIG.5, andFIG.6Bshows a case in which CSI-reporting band information (e.g., a bit sequence) is requested by the base station for CSI-reporting only for a subband of interest as a second case in operation S20ofFIG.5.

As noted above, the “CSI-RS dimension” may refer to a DFT space converted based on the number, NSBCSIRS, of some subbands in which the CSI-RS is received among BWPs, and the “BWP dimension” may refer to a DFT space converted based on the number, NSBBWP, of subbands included in the BWP.

InFIGS.6A and6B, the baseband processor110uses a DFT function set to correspond to the number of subbands in which the CSI-RS is received (e.g., a DFT function in the “CSI-RS dimension”, defined earlier) for the size (e.g., K-point) of the DFT transformation to generate second compressed data.

Referring toFIG.6A, in the first case, the BWP610for communication between the base station and the wireless communication device100includes the first subband SB1to the nth subband SBNSBBWPincluding subbands620in which the CSI-RS is received.

In one embodiment, in the first case, the baseband processor110(e.g., the CSI compression circuit116) compresses the first compressed data in the frequency domain (hereinafter, referred to as FD compression) to generate second compressed data {tilde over (V)}lCSIRS(at this time, FD compression may be performed for each layer in the first compressed data) using a DFT function DƒNSBCSIRS(e.g., a DFT function in the CSI-RS dimension) having a size corresponding to the number of subbands in which the CSI-RS is received. For example, the second compressed data {tilde over (V)}lCSIRSmay be calculated based on Equation 2.

Here, VlCSIRSis an input matrix of DFT transformation, which is determined based on Equation 1 inFIG.4, DƒNSBCSIRSmay refer to a NSBCSIRS-point DFT matrix of NSBCSIRS×NSBCSIRSsize, and NSBCSIRSmay refer to the number of subbands in which CSI-RS is received.

Referring toFIG.6B, in the second case, the BWP610includes the first subband SB1to the nth subband SBNSBBWPincluding the subband620in which the CSI-RS is received. For example, the base station may indicate the subband651of interest as ‘1’ (active), and transmit a bit sequence (e.g., CSI-reporting band information) in which the non-interest subband652is indicated as ‘0’ (inactive) to the wireless communication device100.

In the second case, when there is a non-interest subband among the subbands in which the CSI-RS is received, the baseband processor110(e.g., the CSI compression circuit116) may determine the DFT size for FD compression as ‘NSB_activeCSIRS=NSBCSIRS−NSB_inactiveCSIRS’. In this case, the baseband processor110may also generate the second compressed data {tilde over (V)}lCSIRS_activebased on Equation 3 below (at this time, FD compression may be performed for each layer in the first compressed data).

Here, VlCSIRS_activeis an input matrix of the DFT transform for the subbands of interest and is determined based on Equation 1 ofFIG.4, and DƒNSB_activeCSIRSmay refer to a DFT function (e.g., a CSI-RS dimension DFT function) set to a size corresponding to NSB_activeCSIRS.

After FD compression, the baseband processor110may calculate and sort the norm of each column of the second compressed data to determine (or select) an index of a column having a dominant value on an FD basis.

FIG.7is a flowchart illustrating a method of operating a wireless communication device according to an example embodiment.

In detail,FIG.7is a diagram for explaining an operation of performing FD compression by mapping to BWP-dimensional FD compression after performing CSI-RS dimension FD compression (e.g., applying oversampled DFT) by the baseband processor110(e.g., the second sub-transform block423ofFIG.4), an operation of performing FD compression by mapping to BWP-dimensional FD compression when the CSI-RS is received in some subbands of the entire BWP in the baseband processor110of the wireless communication device100ofFIG.2.

Referring toFIG.7, an operation of performing FD compression by mapping to a BWP dimension (defined earlier) after performing CSI-RS dimension FD compression may include operations S51, S53, and S55. It is reiterated here that herein, the CSI-RS dimension may refer to a DFT space converted based on the number NSBCSIRSof some subbands in which the CSI-RS is received among BWPs, and the BWP dimension may refer to a DFT space converted based on the number NSBBWPof subbands included in the BWP.

In operation S51, the baseband processor110may determine(or identify) whether the ratio Z of the number of subbands constituting BWP NSBBWPto the number of subbands NSBCSIRSin which the CSI-RS is received, is an integer. Here, Z may refer to ‘NSBBWP/NSBCSIRS’. For example, when the number of subbands constituting the BWP is ‘6’ and the number of subbands through which the CSI-RS is received is ‘2’, Z is ‘3’, which is an integer. For example, when the number of subbands constituting the BWP is ‘7’ and the number of subbands through which the CSI-RS is received is ‘2’, Z is ‘3.5’, which is not an integer.

In operation S53, the baseband processor110may generate second compressed data of the CSI-RS dimension by using an oversampled DFT function (interchangeably, “oversampling DFT function”) which it may generate. An oversampling factor may be ‘Z(NSBBWP/NSBCSIRS)’. For example, the baseband processor110may generate the oversampled DFT function (e.g., a CSI-RS dimension DFT function) by applying at least one of a rotation index or a position indication matrix of CSI-RS. The baseband processor110may generate second compressed data by compressing the first compressed data in the frequency domain using the oversampled DFT function. A detailed description of this will be described later with reference toFIGS.8A to8E.

In operation S55, the baseband processor110may generate channel information by mapping the second compressed data of the CSI-RS dimension to the BWP dimension.

After applying the oversampled DFT, the baseband processor110may select the FD basis and NZC based on the FD basis and NZC selection method described above inFIG.4.

The baseband processor110may map the FD basis selected in the CSI-RS dimension to the FD basis in the BWP dimension by multiplying the FD basis selected in the CSI-RS dimension by the ratio Z, or the baseband processor110may map the FD basis selected in the CSI-RS dimension to the FD basis in the BWP dimension by adding the rotation index to the value obtained by multiplying the FD basis selected in the CSI-RS dimension by the ratio Z.

The baseband processor110may perform phase compensation on the NZC selected in the CSI-RS dimension according to a preset method to map the NZC selected in the CSI-RS dimension to the NZC in the BWP dimension. A detailed description of this will be described later with reference toFIGS.8A to8E.

FIG.7has been described on the premise that FD compression in the CSI-RS dimension is performed based on the DFT function ofFIG.5, but is not limited thereto. For instance, the baseband processor110according to an embodiment may perform FD compression in the CSI-RS dimension using various types of DFT functions, and perform FD compression in which the result is mapped to the BWP dimension. In addition, the FD compression operation ofFIG.7may be applied as an independent embodiment in which the wireless communication device100maps channel characteristic information to FD compression of a high dimension (e.g., BWP dimension) after FD compression of a low dimension (e.g., CSI-RS dimension).

The baseband processor110according to an embodiment may replace FD compression of the BWP dimension with FD compression of the CSI-RS dimension. This has the effect of reducing the amount of overhead generated in the FD compression process and reducing energy consumption. In addition, the wireless communication device according to the technical concept of the inventive concept may prevent degradation and distortion of CSI report contents due to interference through a process of compressing channel information in the frequency domain.

FIGS.8A to8Eare diagrams for explaining an FD compression operation by a second sub-transform block according to example embodiments.

In detail,FIGS.8A to8Eare diagrams for explaining an FD compression operation by the second sub-transform block423ofFIG.4(e.g., an operation of mapping to FD compression in the BWP dimension after FD compression in the CSI-RS dimension).

As stated earlier, herein, the CSI-RS dimension may refer to a DFT space converted based on the number NSBCSIRSof some subbands in which the CSI-RS is received among BWPs, and the BWP dimension may refer to a DFT space converted based on the number NSBBWPof subbands included in the BWP. Also, herein, “Z” may be expressed as an integer as a ratio of the number NSBBWPof subbands included in the BWP to the number of subbands NSBCSIRSin which the CSI-RS is received.

FIG.8Aillustrates a wireless communication environment800for performing FD compression (e.g., illustrated inFIGS.8B to8E) by the second sub-transform block423ofFIG.4. For example, the wireless communication environment800includes a case in which CSI-RS is received in some consecutive subbands of BWP or a case in which the base station receives the CSI reporting band set as subbands of interest (e.g., a subband marked with ‘1’ in the bitmap of the channel information reporting band inFIG.8A) only for some consecutive subbands of the BWP.

Referring toFIG.8A, the wireless communication environment800ofFIGS.8B to8Eassumes that the BWP810for communication between the base station and the wireless communication device100includes subbands (e.g., 1st subband SB1to nth subband SBNSBBWP) and some subbands820through which CSI-RSs are received include NSBCSIRSsubbands (e.g., subband SBNstartCSIRSwhere CSI-RS reception starts to the subband SBNendCSIRSwhere CSI-RS reception ends). In this case, some subbands820through which the CSI-RS is received may be continuous subbands in the frequency domain.

Referring toFIGS.8B and8C, an example first oversample DFT block (interchangeably, “oversampling DFT block”)830in the BWP dimension and a second oversample DFT transform block840in the CSI-RS dimension are shown.

InFIG.8B, the first DFT input matrix VlBWP831of the first oversample DFT block830may represent a matrix of ‘L×NSBBWP’ size, and the area831where the CSI-RS is received in the first DFT input matrix VlBWP831may be represented by an ‘L×NSBCSIRS’ matrix.

The first oversample DFT block830may perform BWP-dimensional FD compression using the first DFT function DƒNSBBWP. Here, the first DFT function DƒNSBBWPmay refer to a partial DFT function of the BWP dimension.

The first DFT function DƒNSBBWPmay represent an ‘NSBCSIRS×NSBBWP’ size matrix (e.g., a partial DFT matrix). The area832corresponding to the subband in which the CSI-RS is received in the first DFT function DƒNSBBWPmay include DFT columns (e.g., 1st DFT column832-1, 2nd DFT column832-2, . . . , zth DFT column832-z) rotated according to a preset period. In this case, the number of rotated DFT columns may be determined based on the ratio Z of the number of subbands NSBBWPconstituting the BWP to the number NSBCSIRSof subbands in which the CSI-RS is received. After oversampling by the first oversample DFT block830, the FD basis and NZC may be selected according to the method described inFIG.4.

InFIG.8C, the second oversample DFT block840may perform BWP-level FD compression using the CSI-RS-level second oversampled DFT function

The second DFT input matrix VlCSIRS841of the second oversample DFT block840may be expressed as a matrix of ‘NSBCSIRS×NSBCSIRS’ size. The second DFT function

(e.g., the first oversampled DFT function842-1to the zth oversampled DFT function842-z) of the second oversample DFT block840may represent a matrix of ‘NSBCSIRS×NSBCSIRS’ size. For example, each of the first oversample DFT function842-1to the zth oversample DFT function842-zmay include an orthogonal matrix of a ‘NSBCSIRS×NSBCSIRS’ size.

The second oversample DFT block840may calculate a DFT transformation result {tilde over (V)}l,rCSIRSfor the second DFT input matrix VlCSIRS841based on Equation 4.

Here, Rris a matrix indicating the rotation index for each oversampled DFT function, and may be composed of a diagonal matrix of a ‘NSBCSIRS×NSBCSIRS’ size.

is a matrix indicating the reception start position of the CSI-RS and may be composed of a diagonal matrix of size ‘x’. For example, when

may divide the BWP-dimensional DFT function into Z orthogonal matrices of a ‘NSBCSIRS×NSBCSIRS’ size, this may refer to a rotation matrix for expressing each orthogonal matrix as DƒNSBCSIRSof a ‘NSBCSIRS×NSBCSIRS’ size.

The rotation index and FD basis selection block843may determine (or select) the rotation index and FD basis of the CSI-RS dimension after DFT transformation based on Equation 5.

The NSBBWP-point DFT mapping block845may map the rotation index and FD basis of the CSI-RS dimension to the BWP dimension based on Equation 6.

Here, Z refers to the ratio of the number nSBCWPof subbands constituting the BWP to the number NSBCSIRSof subbands through which the CSI-RS is received, and rlmay refer to a rotation index.

The NZC phase compensation block847may map the selected NZC of the CSI-RS dimension to the BWP dimension based on Equation 7.

When the ratio of the number NSBBWPof subbands constituting the BWP to the number NSBCSIRSof subbands in which the CSI-RS is received is an integer, the second compressed data output from the NSBBWP-point DFT mapping block845may skip a phase compensation process through a bypass path848(e.g., the bypass path848may be used when the ratio of the number NSBBWPof subbands constituting the BWP to the number NSBCSIRSof subbands in which the CSI-RS is received is an integer) and generate channel information.

When performing FD compression based on a DFT transform block (e.g., the second oversample DFT block840) according to an embodiment, in preparation for the DFT transform block (e.g., the first oversample DFT block830) according to the comparative embodiment, by performing low-dimensional FD compression, the efficiency of FD compression may be maximized by significantly reducing the overhead generated in the FD compression process.

Referring toFIG.8D, an embodiment of phase compensation according to the starting position of the CSI-RS of the second oversample DFT transform block840ofFIG.8Cis shown. InFIG.8D, configurations ofFIG.8D(e.g, configurations843,845,847,848,427) that overlap with the above-described drawings may be replaced by the description of the above-described drawings.

In detail, the first case853and the second case854may be included as an embodiment of the application time point of

for phase compensation according to the starting position of the CSI-RS.

The third oversample DFT block850in the first case853may perform BWP-dimensional FD compression using the CSI-RS-dimensional third DFT function RrDƒNSBCSIRS. Here, the third DFT function RrDƒNSBCSIRSmay refer to an oversampled DFT function.

The third DFT input matrix VlCSIRS851of the third oversample DFT block850may be expressed as a matrix of a ‘L×NSBCSIRS’ size. The third DFT function RrDƒNSBCSIRSof the third DFT transform block850(e.g., the first oversample DFT function R1DƒNSBCSIRS852-1to the zth oversample DFT function RZDƒNSBCSIRS) represents a matrix of a ‘NSBCSIRS×NSBCSIRS’ size. For example, each of the first oversample DFT function R1DƒNSBCSIRS852-1to the zth oversample DFT function RZDƒNSBCSIRS852-zmay include an orthogonal matrix of a ‘NSBCSIRS×NSBCSIRS’ size.

The third oversample DFT block850may calculate a DFT transformation result {tilde over (V)}lCSIRSfor the third DFT input matrix851based on Equation 8.

Here, Rris a matrix indicating the rotation index for each oversampled DFT function, and may be composed of a diagonal matrix of a ‘NSBCSIRS×NSBCSIRS’ size.

After the third oversample DFT block850, the rotation index and FD basis may be selected according to the manner described in the second oversample DFT block840ofFIG.8C, and the rotation index and FD basis of the CSI-RS dimension may be mapped to the BWP dimension.

The NZC phase compensation block855may apply

indicating a start position of a received subband of the CSI-RS to compensate for a phase used for mapping NZC of the CSI-RS dimension to the BWP dimension.

Based on the method described above inFIG.4, the NZC selection and quantization block selects a dominant NZC among NZCs mapped to the BWP dimension and performs quantization for generating channel information (e.g., a UCI bit sequence). Here, in the first case853, NZC may be selected based on the DFT result mapped to the BWP dimension by applying

before NZC selection and quantization.

The oversample DFT block860of the second case854is the same as the third oversample DFT block850, and the rotation index and FD basis selection blocks and the NSBBWP-point DFT mapping blocks may be the same as those of the first case853.

However, in the second case854, unlike the first case853, the application point of

may be applied after NZC selection and quantization. That is, in the second case854, by applying

after NZC selection and quantization, NZC may be selected based on the DFT result in the CSI-RS dimension and mapping may be performed in the BWP dimension.

The first case853and the second case854ofFIG.8Dhave different application times of

but the FD basis of the finally selected BWP dimension and NZC in each case may be the same.

FIG.8Eillustrates an embodiment of FD compression through DFT without considering the effect of oversampling when the ratio Z of the number NSBBWPof subbands constituting the BWP to the number NSBCSIRSof subbands in which the CSI-RS is received is not an integer. InFIG.8E, configurations ofFIG.8E(e.g, configurations845,848,426,427) that overlap with the above-described drawings may be replaced by the description of the above-described drawings.

The fourth oversample DFT block870may perform BWP-level FD compression using the CSI-RS-level DFT function

Here, the DFT function

may refer to a function that does not consider the effect of the oversampled DFT or uses only some of the oversampled DFTs (e.g., rlis regarded as 1).

The fourth DFT input matrix VlCSIRS871of the fourth oversample DFT block870may be expressed as a matrix of a ‘L×NSBCSIRS’ size.

The fourth oversample DFT block870may calculate a DFT transformation result {tilde over (V)}lCSIRSfor the fourth DFT input matrix VlCSIRS871based on Equation 9.

Here, Rris a matrix indicating the rotation index for each oversampled DFT function, and may be composed of a diagonal matrix of a ‘NSBCSIRS×NSBCSIRS’ size.

In one embodiment, when the ratio Z of the number NSBBWPof subbands constituting the BWP to the number NSBCSIRSof subbands in which the CSI-RS is received is not an integer, without considering the oversampled DFT effect, rlmay be regarded as 1 (e.g., the DFT function872ofFIG.8E). In this case, the FD basis in the CSI-RS dimension after DFT transformation is determined (or selected) by removing ‘Rrl’ from Equation 5 ofFIG.8C(i.e., not selecting a rotation index), the FD basis selected in the CSI-RS dimension may be mapped to the BWP dimension based on Equation 6 described above. In addition, the embodiment of phase compensation according to the starting position of the CSI-RS ofFIG.8Dis applicable to the embodiment ofFIG.8E.

FIG.9is a flowchart illustrating a method of operating a wireless communication device according to an example embodiment.

In detail,FIG.9is a diagram for explaining an operation of performing BWP-dimensional FD compression (e.g., partial DFT application) by the baseband processor110(e.g., the third sub-transform block424ofFIG.4) when the baseband processor110of the wireless communication device100ofFIG.2receives CSI-RS in some subbands of the entire BWP.

As defined earlier, herein, the CSI-RS dimension may refer to a DFT space converted based on the number of some subbands in which the CSI-RS is received among a BWP, and the BWP dimension may refer to a DFT space converted based on the number of subbands included in the BWP.

In operation S250, the baseband processor110may generate second compressed data using the partial DFT function.

For example, the baseband processor110compresses the SD-compressed first compressed data in the frequency domain using a partial DFT function (hereinafter, referred to as FD compression) to generate second compressed data. For example, the baseband processor110may select an FD basis indicating an index of a column having a dominant value among second compressed data obtained by re-expressing the first compressed data in the partial DFT space. In addition, the baseband processor110may calculate absolute values of components included in the second compressed data (e.g., matrix form data) in the DFT transformation space, and select a preset number of NZCs according to the size of the absolute values. The baseband processor110may quantize channel information including the selected FD basis and NZC to display the channel information in the UCI bit sequence. A detailed description of this will be described later with reference toFIGS.10A and10D.

In the wireless communication system according to an embodiment, the base station performs FD compression through partial DFT according to the amount of channel information and adjusts the size of the CSI-RS allocation area so that there is an effect of improving resource efficiency by transmitting data only for a certain wireless communication resource. In addition, the wireless communication device according to a technical concept of the inventive concept may prevent degradation and distortion of CSI report content due to interference through a compression process in the frequency domain (FD).

FIGS.10A to10Dare diagrams for explaining an FD compression operation by a third sub-transform block according to example embodiments.

In detail,FIGS.10A and10Dshow diagrams for explaining an FD compression operation by the third sub-transform block424of the baseband processor110ofFIG.4.

FIG.10Ashows a diagram for explaining the partial DFT function of operation S250ofFIG.9and the resulting DFT transformation result.

Referring toFIG.10A, the base station allocates NSBBWPsubbands to the BWP1001and allocates NSBCSIRSsubbands (or frequency resources) to the area1002(e.g., some sub-band areas of BWP1001) in which the CSI-RS is transmitted.

The baseband processor110may generate a partial DFT function DƒNSBBWP,NSBCSIRSfor FD compression based on the DFT basis of the position of the subband corresponding to the area where the CSI-RS is received from the NSBBWP-point DFT matrix (or DFT function). For example, the partial DFT function DƒNSBBWP,NSBCSIRSmay refer to a partial DFT matrix of a NSBCSIRS×NSBBWPsize.

The baseband processor110may calculate a partial DFT transformation result {tilde over (V)}lBWPfor the DFT input matrix VlCSIRSbased on Equation 10.

The baseband processor110may calculate an optimized partial DFT transformation result {tilde over (V)}lBWPbased on Equation 11 according to the sparsity characteristic of the partial DFT transformation result {tilde over (V)}lBWP.

Here, supp(a) may refer to a set of position indices of non-zero or significant coefficients of vector a. M may refer to a parameter required for FD basis selection. For example, the baseband processor110may derive a partial DFT transformation result {tilde over (V)}lBWPbased on Equation 11 through algorithms related to compressed sensing, sparse signal recovery, or sparse representation. Examples of related algorithms may include a basis pursuit (BP) algorithm related to convex relaxation, a basis pursuit with inequality constraints (BPIC) algorithm, a basis pursuit denoising (BPDN) algorithm, and the like. In addition, an orthogonal matching pursuit (OMP) algorithm related to greedy pursuit, a stagewise orthogonal matching pursuit (StOMP) algorithm, a regularized orthogonal matching pursuit (R-OMP) algorithm, a compressive sampling matching pursuit (CoSaMP) algorithm, an iterative hard thresholding (IHT) algorithm, a two-stage thresholding (TST) algorithm, a subspace pursuit (SP) algorithm, and the like may be used. Alternatively, a method of finding an optimized DFT result by substituting possible candidates from a brute force perspective may be utilized.

FIG.10Bshows a partial DFT transformation result {tilde over (V)}lBWPderived from Equation 11 ofFIG.10A.

Referring toFIG.10B, the baseband processor110performs FD compression based on a partial DFT function DƒNSBBWP,NSBCSIRS1022on a DFT input matrix VlCSIRS1021based on Equation 10 ofFIG.10to derive the partial DFT transformation result {tilde over (V)}lBWP1023. For example, when the DFT input matrix VlCSIRS1021is re-expressed as a partial DFT space, it may appear as a column vector (or column index)1024having a dominant value. The baseband processor110may determine (or select) the column vector (or column index)1024as an FD basis.

FIG.10Cshows a partial DFT function according to an embodiment when there is an ‘inactive’ subband in the CSI-RS reporting band received from the base station.

Referring toFIG.10C, the DFT input matrix VlCSIRS_active1031may be composed of a matrix of a ‘L×NSBCSIRS−NSB_inactiveCSIRS’ size, and the partial DFT function DƒNSBBWP,NSB_activeCSIRS1032may be composed of a DFT matrix of a ‘NSBCSIRS−NSB_inactiveCSIRS×NSBBWP’ size.

The baseband processor110may calculate a partial DFT transformation result {tilde over (V)}lBWPbased on Equation 12.

The baseband processor110may calculate an optimized partial DFT transformation result {tilde over (V)}lBWPthrough an optimization equation similar to Equation 11 ofFIG.10B.

FIG.10Dshows a partial DFT function according to another embodiment when there is an ‘inactive’ subband in the CSI-RS reporting band received from the base station.

If there is an ‘inactive’ subband in the CSI-RS reporting band received from the base station, the baseband processor110may pad the ‘inactive’ subband1043of the DFT input matrix VlCSIRS1041with a certain value (e.g., ‘0’), and derive an optimized DFT transformation result by re-expressing the padded result in a DFT space in a manner similar to that ofFIG.10B(e.g., Equation 11).

FIG.11is a flowchart illustrating a method of operating a wireless communication device according to an example embodiment.

In detail,FIG.11is a diagram for explaining an operation of performing BWP-dimensional FD compression (e.g., apply DFT after performing pre-processing) by the baseband processor110(e.g., the third sub-transform block425ofFIG.4) when the baseband processor110of the wireless communication device100ofFIG.2receives CSI-RS in some subbands of the entire BWP.

As stated earlier, the “CSI-RS dimension” may refer to a DFT space converted based on the number NSBCSIRSof some subbands in which the CSI-RS is received among BWPs, and the “BWP dimension” may refer to a DFT space converted based on the number of subbands NSBBWPincluded in the BWP.

Referring toFIG.11, the operation of performing FD compression by applying DFT after performing pre-processing may include operations S310, S320, S330, S340, S351, S352, S360, and S370. Here, operations S310to S340and operations S360to S370correspond to the operations S10, S20, S30, S40, S60, and S70ofFIG.4, respectively, and thus redundant descriptions may be replaced with those ofFIG.4.

In operation S351, the baseband processor110may perform pre-processing according to a preset method on the first compressed data. Here, the first compressed data may include a DFT input matrix VlBWPas a result of SD compression.

When CSI-RS is received in some subbands of the entire BWP, the baseband processor110may configure a BWP-dimensional DFT input matrix VlBWPby performing pre-processing on subbands in which CSI-RS are not received. For example, the pre-processing method may include a zero padding method, a zero interpolation method, a phase difference rotation method, a mirror copy method, a repeating method, and the like. A detailed description of this will be described later inFIGS.12A to12G.

For example, the baseband processor110may select an FD basis indicating an index of a column having a dominant value among the second compressed data re-expressing the first compressed data (e.g., the BWP-dimensional DFT input matrix VlBWP) in the DFT space. In addition, the baseband processor110may calculate absolute values of components included in the second compressed data (e.g., matrix form data) in the DFT transformation space, and select a preset number of NZCs according to the size of the absolute values. The baseband processor110may quantize channel information including the selected FD basis and NZC to display the channel information in the UCI bit sequence.

In operation S352, the baseband processor110may generate second compressed data by using a DFT function having a size corresponding to the number of subbands constituting the BWP. For example, the baseband processor110may perform BWP-dimensional FD compression by performing DFT transformation on the BWP-dimensional DFT input matrix VlBWPconfigured through the pre-processing operation of operation351.

A wireless communication device according to an embodiment performs pre-processing on a subband in which CSI-RS is not transmitted to configure a BWP-dimensional DFT input matrix VlBWP, so that while complying with FD compression-related standards (e.g., performing FD compression through BWP-dimensional DFT transformation) of communication standards (e.g., 3GPP Rel. 16 to 17), there is an effect of reducing the overhead generated in FD compression through the pre-processing process. In addition, the wireless communication device according to the technical concept of the inventive concept may prevent deformation and distortion of CSI report content due to interference through a compression process in the frequency domain (FD).

FIGS.12A to12Gare diagrams for explaining an FD compression operation by a fourth sub-transform block according to exemplary examples of the inventive concept.

In detail,FIGS.12A and12Gshow diagrams for explaining an FD compression operation by the fourth sub-transform block425of the baseband processor110ofFIG.4. InFIGS.12A and12G, a horizontal axis may represent a subband area in a frequency domain, and a vertical axis may represent a precoding vector of a subband.FIGS.12A and12Gassume that the CSI-RS is not allocated to a subband of a low frequency band for convenience of explanation, and the embodiments ofFIGS.12A and12Gare applicable even if the location of a subband to which CSI-RS is not allocated is changed.

FIG.12Ais a diagram for explaining the first pre-processing method and the second pre-processing method of operation S531ofFIG.11. InFIG.12A, it is assumed that a first area1201is a subband area to which CSI-RSs are not allocated, and a second area1202is a subband area to which CSI-RSs are allocated.

The first pre-processing method may include a linear interpolation method (e.g., zero interpolation method).

For example, the baseband processor110may set the precoding vector1203of the first subband of the first area1201to a zero vector, and configure a DFT input matrix ( ) by performing linear interpolation with the precoding vector1204of the first subband to which the CSI-RS of the second area1202is allocated. To this end, the DFT input matrix ( ) may be expressed by Equation 13.

and N1may refer to the number of precoding vectors of a subband to which a CSI-RS is not allocated, and n1may refer to an index of a subband to which a CSI-RS, which is 0≤n1<N1, is not allocated.

Although not shown inFIG.12A, the second pre-processing method may include a zero padding method.

The baseband processor110may configure a DFT input matrix VlBWPby padding the first area1201with a certain value (e.g., ‘0’). With this approach, the DFT input matrix VlBWPmay be expressed by Equation 14.

FIG.12Bis a diagram for explaining the third pre-processing method of operation S531ofFIG.11. InFIG.12B, it is assumed that a first area1211is a subband area to which CSI-RS is not allocated, and a second area1212is a subband area to which CSI-RS is allocated.

The third pre-processing method may include a linear interpolation method using phase difference rotation (e.g., phase difference rotation-based zero interpolation method).

For example, the baseband processor110may set the precoding vector1213of the first subband of the first area1211to a zero vector, and configure a DFT input matrix VlBWPby applying phase difference rotation after performing linear interpolation with the precoding vector1214of the first subband to which the CSI-RS of the second area1212is allocated. In this regard, the DFT input matrix VlBWPmay be expressed by Equation 15.

and N1refers to the number of precoding vectors of a subband to which a CSI-RS is not allocated, and n1refers to an index of a subband to which a CSI-RS, which is 0≤n1<N1, is not allocated. Rp(θ) may be defined based on Equation 16 as a phase difference rotation matrix, and Rp(θ)a may be defined based on Equation 17 as a vector increasing the phase difference between components of the a vector1214by θ.

In addition, the θ1, θ2, . . . , θN1−1values of Equation 15 are determined differently depending on the phase difference rotation method, the phase difference rotation method may include 1) a random phase difference rotation method (e.g., a method of randomly selecting a θ value), and 2) a phase difference cyclic shift method (e.g., a method of applying θN1−1=δ, θN1−2=2δ, θ1=(N1−1)δ). Note that the baseband processor110according to an embodiment is not limited thereto; various alternative phase difference rotation schemes may be applied.

FIG.12Cis a diagram for explaining a fourth pre-processing method in operation S531ofFIG.11. InFIG.12C, it is assumed that a first area1221is a subband area to which CSI-RS is not allocated, and a second area1222is a subband area to which CSI-RS is allocated.

The fourth pre-processing method may include a linear interpolation method to which an average is applied.

For example, the baseband processor110calculates an average vector {right arrow over (m)} of precoding vectors of the subbands of the first area1221and calculates the precoding vector of the first subband1223to which CSI-RS is not allocated. The baseband processor110may then configure a DFT input matrix {right arrow over (m)}6 by performing linear interpolation with the precoding vector of the first subband1224to which the CSI-RS of the second area1222is allocated. In this case, the DFT input matrix VlBWPmay be expressed by Equation 18, and although not shown, phase difference rotation may also be applied.

and N1may refer to the number of precoding vectors of a subband to which a CSI-RS is not allocated, and n1may refer to an index of a subband to which a CSI-RS, which is 0≤n1<N1, is not allocated. The average vector {right arrow over (m)} may be calculated based on Equation 19.

FIG.12Dis a diagram for explaining the fifth pre-processing method of operation S531ofFIG.11. InFIG.12D, it is assumed that a first area1231is a subband area to which CSI-RS is not allocated, and a second area1232is a subband area to which CSI-RS is allocated.

A fifth pre-processing method may include a minor copy method.

For example, the baseband processor110mirror-copys the precoding vector of the second area1232to the first area1231based on the first subband1234of the second area1232and configure the DFT input matrix VlBWP. At this time, the DFT input matrix VlBWPmay be expressed by Equation 20.

and N1may refer to the number of precoding vectors of a subband to which a CSI-RS is not allocated, and n and m may refer to an index of a subband to which a CSI-RS, which is 0≤n≤m<N1, is not allocated.

FIG.12Eis a diagram for explaining a sixth pre-processing method of operation S531ofFIG.11. InFIG.12E, it is assumed that a first area1241is a subband area to which CSI-RS is not allocated, and a second area1242is a subband area to which CSI-RS is allocated.

A sixth pre-processing method may include a repetition method.

For example, the baseband processor110may configure a DFT input matrix VlBWPby repeatedly applying the precoding vector of the second area1232to the first area1231. At this time, the DFT input matrix VlBWPmay be expressed by Equation 21.

and N1refers to the number of precoding vectors of a subband to which CSI-RS is not allocated, and n may be defined as 0≤n<NSBCSIRS.

FIG.12Fshows a diagram for explaining a seventh pre-processing method of operation S531ofFIG.11. InFIG.12F, it is assumed that a first area1251is a subband area to which CSI-RS is not allocated, and a second area1252is a subband area to which CSI-RS is allocated.

A seventh pre-processing method may include a repetition method.

For example, the baseband processor110may repeatedly apply the precoding vector of the second area1252to the first area1251, and configure a DFT input matrix VlBWPby padding a certain value (e.g., ‘0’) to the remaining subband area1253of the first area1251. At this time, the DFT input matrix VlBWPmay be expressed by Equation 22.

and N1refers to the number of precoding vectors of a subband to which CSI-RS is not allocated, and n may be defined as 0≤n<NSBCSIRS.

FIG.12Gshows a diagram for explaining an eighth pre-processing method of operation S531ofFIG.11. InFIG.12G, configurations ofFIG.12G(e.g, configurations848,410,426,427,430) that overlap with the above-described drawings may be replaced by the description of the above-described drawings.

InFIG.12G, it is assumed that a first area1261is a subband area to which CSI-RS is not allocated, and a second area1262is a subband area to which CSI-RS is allocated.

An eighth pre-processing method may include a wide band (WB) precoding method.

The baseband processor110may replace the matrix Vncorresponding to the channel characteristic information of the nth subband with a wide band matrix VWBafter SD compression. For example, when the DFT block1260of the baseband processor110compresses the matrix VlCSIRSof the 1st layer of CSI-RS area in the frequency domain, if the number of FD basis to effectively represent the frequency domain characteristics of the matrix (e.g., changes in the frequency aspect, etc.) is identified as insufficient, rather than compressing and transmitting the matrix VWB,lof the 1st layer of CSI-RS area, the matrix VlCSIRSof the 1st layer in a wide band perspective may be quantized and transmitted to the base station. Here, VWB,lmay include all CSI-RS channel information matrices in which the subband bitmap is ‘active’ or a matrix after SD compression is performed by base station precoding determined by the terminal.

For example, the DFT block1260of the baseband processor110may determine (or select) a representative channel among subbands to which the CSI-RS is allocated, and after copying the channel values of the representative channel to channel values of all subbands of the entire BWP, perform FD compression on subbands of the entire BWP.

FIG.13is a block diagram illustrating an electronic device according to an example embodiment.

The wireless communication device1300ofFIG.13may correspond to the wireless communication device100ofFIG.1.

Referring toFIG.13, the electronic device may include a memory1310, a processor unit1320, an input/output control unit1340, a display unit1350, an input device1360, and a communication processing unit1390. Here, a plurality of memories1310may exist. A brief discussion of each component is as follows.

The memory1310may include a program storage unit1311for storing a program for controlling the operation of the electronic device, and a data storage unit1312for storing data generated during program execution. The data storage unit1312may store data necessary for the operation of the application program1313and the CSI compression setting program1314. The program storage unit1311may include an application program1313and a CSI compression setting program1314. Here, the program included in the program storage unit1311may be expressed as an instruction set as a set of instructions.

The application program1313includes an application program operating in the electronic device. That is, the application program1313may include instructions of an application driven by the processor1322. According to example embodiments, when CSI-RSs are allocated only to some subbands in the entire BWP, the CSI compression configuration program1314may perform frequency domain compression using a DFT function (e.g., DFT function in CSI-RS dimension, partial DFT function, oversampled DFT function, etc.) based on channel characteristic information of a subband to which the CSI-RS is allocated.

The peripheral device interface1323may control the connection between the input/output peripheral device of the base station and the processor1322and the memory interface1321. The processor1322controls the base station to provide a corresponding service using at least one software program. In this case, the processor1322may execute at least one program stored in the memory1310to provide a service corresponding to the program.

The input/output control unit1340may provide an interface between an input/output device such as the display unit1350and the input device1360and the peripheral device interface1323. The display unit1350displays state information, input characters, moving pictures, and still pictures. For example, the display unit1350may display application program information driven by the processor1322.

The input device1360may provide input data generated by selection of the electronic device to the processor unit1320through the input/output control unit1340. In this case, the input device1360may include a keypad including at least one hardware button and a touch pad for sensing touch information. For example, the input device1360may provide touch information, such as a touch sensed through a touch pad, a touch movement, and a touch release, to the processor1322through the input/output controller1340. The electronic device may include a communication processing unit1390that performs communication functions for voice communication and data communication. The communication processing unit1390may include a plurality of antenna modules1392for supporting millimeter wave band communication according to example embodiments.