Patent Description:
The present invention relates to a wireless access system, and more specifically, a method for performing downlink hybrid beamforming, with a minimum scheduling unit related to beamforming in a broadband wireless access system set as a subcarrier group unit, and a device supporting the same.

In order to meet the demand for wireless data traffic soring since the 4th generation (<NUM>) communication system came to the market, there are ongoing efforts to develop enhanced 5th generation (<NUM>) communication systems or pre-<NUM> communication systems. For the reasons, the <NUM> communication system or pre-<NUM> communication system is called the beyond <NUM> network communication system or post LTE system.

For higher data transmit rates, <NUM> communication systems are considered to be implemented on ultra-high frequency bands (mmWave), such as, e.g., <NUM>. To mitigate pathloss on the ultra-high frequency band and increase the reach of radio waves, the following techniques are taken into account for the <NUM> communication system: beamforming, massive multi-input multi-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large scale antenna.

Also being developed are various technologies for the <NUM> communication system to have an enhanced network, such as evolved or advanced small cell, cloud radio access network (cloud RAN), ultra-dense network, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-point (CoMP), and interference cancellation.

There are also other various schemes under development for the <NUM> system including, e.g., hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC), which are advanced coding modulation (ACM) schemes, and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA), which are advanced access schemes.

Beamforming may be used in different communication systems to improve signal to noise ratio (SNR) and/or signal to interference noise ratio (SINR) or to improve a given communication link.

There may be a number of different ways to implement beamforming, but may be largely characterized by three different types. For example, there is analog (or radio frequency (RF)) beamforming, digital (or baseband) beamforming, and hybrid beamforming that uses both analog beamforming and digital beamforming to form a beam.

In the general MIMO environment, there are assumed to be up to eight transmit/receive antennas. However, as evolving to massive MIMO, the number of antennas may increase to a few tens or hundreds or more. Massive antenna technology is a major core technology for <NUM> systems and <NUM> systems, which are currently under discussion for standardization, and is a technology that increases spectral efficiency through spatial separation through multiple antennas. In LTE, the standard for supporting <NUM> and <NUM> antennas in the standard for full dimension multiple input multiple out (FD-MIMO) has been completed in Rel-<NUM>, and furthermore, the standard for supporting, e.g., <NUM> and <NUM> antennas is in progress in Rel-<NUM> LTE.

In the <NUM> standard, digital (or baseband) beamforming and analog beamforming are core technologies of the standard, and increasing the number of antennas is an essential consideration to overcome pathloss, such as free space loss in mm-Wave. Thus, it is a critical issue to efficiently calculate and implement a beamforming precoder according to an increase in the number of antennas supported in the modern communication system.

Since the millimeter-band channel may suffer from significant path attenuation, cell coverage may be reduced and the link quality may be deteriorated, whereas the millimeter-band signal wavelength is as short as several millimeters, so many antennas may be placed in a small space. Therefore, it is possible to compensate for the problems of coverage reduction and link quality degradation by creating an antenna array of multiple antennas and using directional beams at the transmit/receive ends via the antenna array. Therefore, beamforming technology is of significance in mm-Wave mobile communication systems.

The core issue with beamforming implementation is how to identify an appropriate beamforming matrix for each station, and there are open loop methods and closed loop methods. In the closed loop methods, the network generates an adequate beamforming matrix based on a specific report from the terminal. To that end, the network transmits a specific pilot signal, called CSI-RS, and the terminal evaluates the quality of the received signal based on the received CSI-RS and reports the result to the network. <NPL>; Author: <NPL> discloses in the context of beam management that the network needs to communicate CSI-RS configurations to UEs. A CSI-RS configuration may be UE-specific or UE-group-specific. In a hierarchical beam training process, a group of CSI-RS resources may be configured for a group of UEs while a second group of CSI-RS resources may then be configured for specific UEs within a UE group.

In <CIT> it is recognized herein that current LTE reference signals may be inadequate for future cellular (e.g., New Radio) systems. Configurable reference signals are described herein. The configurable reference signals can support mixed numerologies and different reference signal (RS) functions. Further, reference signals can be configured so as to support beam sweeping and beamforming training.

According to various embodiments, there are proposed an efficient precoder structure appropriate for a scheduler using the identified characteristics of the broadband massive antennas and a precoding scheme necessary therefor.

According to various embodiments, the base station and the terminal configures the minimum scheduling unit as the subcarrier group, and the base station applies beamforming per subcarrier group, and the terminal performs channel estimation and data decoding per subcarrier group.

According to various embodiments, when the base station and the terminal configure the minimum scheduling unit as the subcarrier group, the maximum transmission bandwidth of the subcarrier is reduced as compared with the maximum transmission bandwidth of the resource block so that influence by frequency selectivity fading is reduced, and thus, the performance of the base station and terminal may be improved.

According to various embodiments, the base station may apply a hybrid beamforming structure including a digital precoder (baseband precoder) configured to have a serial structure of a null precoder and a stream parallelizing precoder, thereby minimizing multi-user interference and maximizing the transmission rate per user and hence maximizing the total data transmission rate.

According to various embodiments, a method for performing downlink beamforming by a base station in a wireless access system comprises receiving information related to a channel state from a terminal, identifying channel state information estimated on a per-subcarrier group basis, based on the channel state-related information, obtaining analog beamforming information and digital beamforming information based on the channel state information, performing hybrid beamforming, which is a combination of analog beamforming and digital beamforming, on a per-subcarrier group basis, based on the analog beamforming information and the digital beamforming information, and transmitting subcarrier group information corresponding to the subcarrier group, wherein the subcarrier group includes a number of subcarriers less than or equal to a number of a plurality of subcarriers included in one resource block.

According to various embodiments, a method performed by a terminal in a wireless access system comprises receiving subcarrier group information corresponding to a subcarrier group unit to which beamforming is applied by a base station, from the base station, identifying the subcarrier group information, and performing channel estimation and decoding based on the identified subcarrier group information, wherein the subcarrier group includes a number of subcarriers less than or equal to a number of a plurality of subcarriers included in one resource block.

According to various embodiments, a base station configured to perform downlink beamforming in a wireless access system comprises a transceiver configured to transmit/receive a wireless signal, and a processor, wherein the processor is configured to control the transceiver to receive information related to a channel state from a terminal, identify channel state information estimated on a per-sub carrier group basis, based on the channel state-related information, obtain analog beamforming information and digital beamforming information based on the channel state information, perform hybrid beamforming, which is a combination of analog beamforming and digital beamforming, on a per-sub carrier group basis, based on the analog beamforming information and the digital beamforming information, and control the transceiver to transmit sub carrier group information corresponding to the sub carrier group, wherein the subcarrier group includes a number of subcarriers less than or equal to a number of a plurality of subcarriers included in one resource block.

According to various embodiments, a terminal in a wireless access system comprises a transceiver configured to transmit/receive a wireless signal and a processor, wherein the processor is configured to control the transceiver to receive subcarrier group information corresponding to a subcarrier group unit to which beamforming has is by a base station, from the base station, identify the subcarrier group information, and perform channel estimation and decoding based on the identified subcarrier group information, wherein the subcarrier group includes a number of subcarriers less than or equal to a number of a plurality of subcarriers included in one resource block.

According to various embodiments, the base station and the terminal may configure the minimum scheduling unit as the subcarrier group, and the base station may apply beamforming per subcarrier group, and the terminal may perform channel estimation and data decoding per subcarrier group.

Various changes may be made to the present invention, and the present invention may come with a diversity of embodiments. Some embodiments of the present invention are shown and described in connection with the drawings. However, it should be appreciated that the present disclosure is not limited to the embodiments.

The terms "first" and "second" may be used to describe various components, but the components should not be limited by the terms. The terms are used only to distinguish one component from another.

The terms as used herein are provided merely to describe some embodiments thereof, but not to limit the present disclosure. It will be further understood that the terms "comprise" and/or "have," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Hereinafter, various embodiments are described below with reference to the accompanying drawings and, in describing embodiments in connection with the drawings, the same reference denotations are used to refer to the same or similar components, and no duplicate description is presented.

Hereinafter, preferred embodiments of the present invention are described in detail with reference to the accompanying drawings. The following detailed description taken in conjunction with the accompanying drawings is intended for describing example embodiments of the disclosure, but not for representing a sole embodiment of the disclosure. The detailed description below includes specific details to convey a thorough understanding of the disclosure. However, it will be easily appreciated by one of ordinary skill in the art that embodiments of the disclosure may be practiced even without such details.

In some cases, to avoid ambiguity in concept, known structures or devices may be omitted or be shown in block diagrams while focusing on core features of each structure and device.

Embodiments of the disclosure are described focusing primarily on the relationship in data transmission and reception between the terminal and the base station. In the disclosure, "base station" means a network terminal node to directly communicate with a terminal.

In the disclosure, a particular operation described to be performed by a base station may be performed by an upper node of the base station in some cases. In other words, in a network constituted of multiple network nodes including the base station, various operations performed to communicate with a terminal may be performed by the base station or other network nodes than the base station. "Base station (BS)" may be interchangeably used with the term "fixed station," "Node B," "eNode B (eNB)," or "access point (AP). " "Relay" may be interchangeably used with "relay node (RN)" or "relay station (RS).

"Terminal" may be interchangeably used with the term "UE (User Equipment)," "MS (Mobile Station)," "MSS (Mobile Subscriber Station)," "SS (Subscriber Station)," "AMS (Advanced Mobile Station)," "WT (Wireless terminal)," "MTC (Machine-Type Communication) device," "M2M (Machine-to-Machine) device," or "D2D (Device-to-Device) device.

In the disclosure, each different piece of information sent using multi-antenna technology is defined as a 'transmit stream' or simply as a 'stream. ' Such 'stream' may be denoted a 'layer.

The terminology used herein is provided for a better understanding of the disclosure.

The bold upper and lower casing letters, respectively, denote a matrix and a vector. ()T and ()H denotes transposing and conjugate-transposing a matrix.

Spatial multiplexing means multi-layer transmission. If the transmitter and receiver each has a plurality of antennas, it is possible to avoid interference between different layers depending on proper signal processing in the transmitter and receiver. Thus, in the case of spatial multiplexing, the channel may be seen as a channel that has a plurality of inputs by the plurality of antennas of the transmitter, and has a plurality of outputs by the plurality of antennas of the receiver.

<FIG> is a view illustrating a base station and a terminal for performing downlink hybrid beamforming in a wireless access system supporting a massive multi-input-multi-output (MIMO) system according to various embodiments.

The massive multi-input-multi-output (MIMO) system regards the case where the base station <NUM> and the terminal <NUM> each use a plurality of antennas and theoretically has increased channel transmission capacity as compared with when only either the base station or terminal uses a plurality of antennas.

That is, since the increase in channel transmission capacity is proportional to the number of antennas, the transmission rate and the frequency efficiency may be improved.

For example, in the case where the base station <NUM> has NT transmission antennas and the terminal <NUM> has Nr reception antennas as shown in <FIG>, if the maximum transmission rate when one antenna is used is Ro, the transmission rate when multiple antennas are used may be theoretically increased up to the product of the maximum transmission rate Ro and a rate increase rate Ri as shown in Equation <NUM> below. Here, Ri is the smaller of NT and NR.

According to various embodiments, in the massive MIMO environment, instead of selectively applying only one of analog beamforming and digital beamforming, a base station structure in which hybrid beamforming, which is a fusion of analog beamforming and digital beamforming, is applied, may be provided, thereby reducing the implementational complexity of the base station and obtaining the maximum beamforming gain using massive MIMO.

Referring to <FIG>, according to various embodiments, a radio frequency (RF) chain <NUM> is a processing block in which a single digital signal is converted into an analog signal and is a structure inevitably generated as the hybrid beamforming structure adopts the scheme of connecting RF chains by bundling several antennas since the cost is increased when each antenna has an RF chain when the base station uses massive antennas.

Referring to <FIG>, Nt means the number of the antennas of the transmission base station, Nr means the reception antenna of each terminal, NRF means the total number of the RF chains, <MAT> means the number of the independent antennas provided in each RF chain and has the relationship of <MAT>.

According to various embodiments, Ns indicates the number of transmission data streams, and Ns is equal to or smaller than Nt, and Ns signals may be spatially multiplexed and transmitted via Nt transmission antennas.

According to various embodiments, k is the number of the terminals spatially multipleaccessed, and Ns,k is the number of transmit streams in the kth terminal.

According to various embodiments, k is the subcarrier index according to various embodiments, and Ns,k is the number of transmit streams at subcarrier index k.

For example, subcarrier index k has a value from <NUM> to NFFT -<NUM>. In this case, NFFT is the maximum fast Fourier transform (FFT) supported by the system, and the total number of subcarriers may be limited to be within the FFT size.

In the disclosure, kth terminal, subcarrier index k, or kth user all may be used to have the same meaning.

According to various embodiments, since the maximum information transmittable is NT, the transmission information may be represented as a vector as shown in Equation <NUM>.

In the beamforming structure shown in <FIG>, for the input signal sk, the reception signal model yk in the kth terminal or subcarrier index k may be expressed as shown in Equation <NUM>.

For example, Hk means a channel information matrix <NUM> in the kth terminal or subcarrier index k having a size of Nr × Nt.

For example, yk means the reception signal vector of the kth terminal having a size of Nr × <NUM> or the reception signal vector at subcarrier index k, and sk means the transmission signal vector of the kth terminal having a size of Ns × <NUM> or the transmission signal vector at subcarrier index k. sl is the transmission signal vector having a size of <MAT> and nk is the noise vector of the kth terminal having a size of Nr × <NUM>.

According to the hybrid beamforming structure of the base station <NUM> shown in <FIG>, a baseband digital signal to which a digital beamforming scheme first using a digital (or baseband) precoder VBB <NUM> has been applied is converted into an RF band analog signal via the RF chain <NUM>, and an analog beamforming scheme secondly using an analog precoder VRF <NUM> is applied to the analog signal.

The digital beamforming shown in <FIG> may apply an independent beamforming scheme per user, with the same time-frequency resources. Analog beamforming is limited by the need for a common beamforming scheme being applied to users with the same time-frequency resources.

According to the hybrid beamforming structure shown in <FIG>, the digital beamforming scheme is free in beamforming for multiple users/streams whereas the analog beamforming scheme performs beamforming by the same weight vector/matrix for the whole transmission band and thus has difficulty in independent beamforming per user or per stream.

For example, the digital (or baseband) precoder VBB,k means the precoding matrix (weight matrix) for digital beamforming in the kth terminal or subcarrier index k having a size of <MAT>, and the analog precoder VRF means the precoding matrix (weight matrix) for analog beamforming in all the subcarriers having a size of <MAT>.

For example, in Equation <NUM>, VRFVBB,k means the precoding matrix for hybrid beamforming in the kth terminal having a size of Nt×Ns,k and subcarrier index k, and VRFVBB,l means the precoding matrix of the interfering terminal at subcarrier index k or the kth terminal having a size of Nt × Ns,l.

In the hybrid beamforming structure shown in <FIG>, to restore, in the reception datayk, the transmission data sk in the model as shown in Equation <NUM>, the inverse matrix of the channel information matrix Hk is needed. However, there may be some matrix whose inverse matrix does not exist, and calculation of an inverse matrix may be not simple. Thus, the channel information matrix H may be represented as H=UΛVH using singular value decomposition (SVD).

For example, as the precoding matrix for hybrid beamforming of the base station <NUM>, the matrix V is used and, if the matrix UH is applied in the terminal, the overall channel becomes such a matrix as H'=Λ. Since H' is the diagonal matrix having a size of Ns×Ns having the largest Ns eigen value diagonal elements of , no interference exists between the spatially multiplexed in the terminal <NUM>.

Further, since U and V both have orthogonal columns, the transmit power, as well as the noise level of the decoder, does not vary spatially under the assumption of white noise.

In the hybrid beamforming structure shown in <FIG>, a scheme for optimization to increase the channel capacity in a single user may be found using Equation <NUM> below in such a model as Equation <NUM>.

For example, Vopt is the precoding matrix for hybrid beamforming when the maximum channel capacity is provided and may be the right singular matrix of the singular value decomposition (SVD) of the channel matrix H. That is, in H=UΛVH Vopt = V.

Accordingly, from Equation <NUM>, VRb may become Equation <NUM>.

According to various embodiments, the analog beamforming precoder VRF needs to be implemented in hardware and may thus be implemented as a low-freedom, simple phase shift.

For example, the analog beamforming precoder VRF may be obtained as one precoder among limited analog beamforming precoders that may be represented as phase shift, and the digital precoder VBB may be obtained based on Equation <NUM> and, from this, an algorithm to find an appropriate analog beamforming precoder VRF may be applied so that the precoding matrix, VRF VBB for hybrid beamforming when it has the maximum channel capacity according to Equation <NUM> may be obtained.

As described above, in the method for obtaining the precoding matrixes VRF and VBB for hybrid beamforming when the base station has the maximum channel capacity, the base station needs to first derive the optimized Vopt from Hk and own it and, as shown in Equation <NUM>, is limited in that it is not a solution for maximally addressing the sum transmission rate in the channel model considering multiple users.

<FIG> is a view illustrating a base station for performing hybrid beamforming using a digital precoder including a null precoder in a wireless access system supporting a massive MIMO system according to various embodiments.

In a wireless access system supporting massive MIMO system, the maximum total data transmission rate that may be obtained when the source coding and channel coding schemes are used may be defined as sum channel capacity.

According to various embodiments, the precoding matrix for hybrid beamforming may be obtained based on the approach of the maximum channel capacity. For example, as an approach of the maximum channel capacity, the Shannon-Hartley theorem may be used.

As shown in <FIG>, according to various embodiments, in the hybrid beamforming structure, independent digital beamforming may apply per user or per stream, and the kth user's digital precoder (baseband precoder) VBB,k may include the cascade of <MAT> and transmit layer parallelizing precoder <MAT>.

In the disclosure, the cascade structure of <MAT> and stream parallelizing precoder <MAT> is defined as a cascade precoder.

As shown in <FIG>, according to various embodiments, if the structure of the kth user's digital precoder (baseband precoder) VBB,k is reconfigured as the structure of the cascade precoder of <MAT> and transmit layer parallelizing precoder <MAT>, that is, <MAT>, Equation <NUM> may be expanded to Equation <NUM>.

For example, sk is the transmission signal vector at subcarrier index k or the transmission signal vector of the kth terminal having a size of Ns X1, Ns,k is the number of transmit streams at subcarrier index k or the kth terminal, NtRF is the number of independent antennas provided per RF chain, and Nt is the number of transmission base station antennas.

Meanwhile, according to various embodiments, the total data transmission rate Rk of each user is as shown in Equation <NUM>.

In Equation <NUM>, the channel information matrix <MAT> for the kth user considering the influence of the analog precoder VRF may be obtained based on information regarding the channel information matrix Hk for the kth user and information regarding the analog precoder VRF for all the users and may be represented as <MAT>, <MAT> means, and E{·} means the averaging operator.

Under the assumption that the reception noise is the white Gaussian noise (WGN), Equation <NUM> is expanded to Equation <NUM> at the high signal-to-noise ratio (SNR).

According to various embodiments, the kth user's digital precoder <MAT> may be configured so that <MAT> is minimized, and <MAT> is maximized, and Rk in Equation <NUM> may be maximized.

For example, the 1st user's null precoder <MAT> directly affecting <MAT> may be configured to, along with <MAT>, form the null space, minimizing the influence from multi-user interference.

According to various embodiments, the kth user's null precoder <MAT> may be used to minimize the influence form multi-user interference, and the kth user's null precoder <MAT> may be obtained based on the channel information matrix <MAT> considering the influence of the analog precoder VRF.

According to various embodiments, the kth user's transmit layer parallelizing precoder <MAT> may be obtained based on the effective channel information matrix Heff,k ( <MAT>) considering influence from the kth user's null precoder Vknull.

For example, the kth user's transmit layer parallelizing precoder <MAT> may be configured to allocate power per stream while meeting the power constraints by parallelizing the effective channel information matrix Heff,k.

An embodiment for obtaining the digital precoder VBB,k by obtaining the null precoder <MAT> based on the channel information matrix <MAT> considering the influence form the analog precoder VRF and obtaining the transmit layer parallelizing precoder <MAT> based on the effective channel information matrix Heff,k considering the influence from the kth user's null precoder <MAT> is described below with reference to <FIG>.

According to various embodiments, the hybrid beamforming structure includes the digital precoder (baseband precoder) VBB,k configured as a cascade structure which is a serial structure of the null precoder <MAT> and the stream parallelizing precoder <MAT>, thereby minimizing multi-user interference and maximizing the transmission rate for each user. Thus, the total data transmission rate may be maximized.

<FIG> and <FIG> are concept views illustrating various examples of a subcarrier group corresponding to a minimum scheduling unit to which beamforming is applied in a wireless access system supporting broadband according to various embodiments.

In <NUM>/LTE systems, the minimum frequency resource unit that may be allocated to each terminal is the resource block (RB) corresponding to <NUM>, and the minimum time resource unit is a transmission time interval (TTI) of <NUM>.

One downlink slot may include seven OFDM symbols in the frequency domain, and one resource block may include <NUM> subcarriers, but they are not limited thereto.

In <NUM>/LTE systems, each element on the resource grid is denoted as a resource element (RE), and one resource block includes 12x7 resource elements.

The number of resource blocks in the downlink slot depends upon the downlink transmission bandwidth. The structure of uplink slot may be identical to the structure of downlink slot.

According to various embodiments, the base station may apply beamforming based on the minimum scheduling unit, and the terminal may feed-back feedback information based on the minimum scheduling unit and perform channel estimation and decoding.

For example, channel estimation may be performed in the units of resource block which is the minimum scheduling unit allowed in the <NUM>/LTE standard and be performed in the units of bundling allowed in the standard.

For example, since the channel estimation unit in beamforming (BF) is the unit in which the same precoding is used upon channel estimation, it may become the minimum filtering unit in which noise reduction may be performed upon channel estimation.

For example, the larger filtering size is, the larger noise reduction effect may be obtained. Thus, the minimum scheduling unit for beamforming may be a critical unit for determining filtering.

Meanwhile, the larger filtering size may has a trade-off relationship in that it is effective in noise reduction but the beamforming gain is reduced in frequency selective fading.

According to various embodiments, the minimum scheduling unit may have a size of a bundle of resource blocks RB in the <NUM>/LTE system and, in the <NUM>/new radio (NR), it may be the unit of beamforming (BF) granularity.

As described above, in the <NUM>/LTE system, the minimum scheduling unit is one resource block unit.

For example, since in the <NUM>/LTE system, one resource block includes <NUM> subcarriers in the frequency domain and the subcarrier spacing (Δf) supports <NUM>, the maximum transmission bandwidth of one resource block, which is the minimum scheduling unit in the <NUM>/LTE system, is <NUM>.

Meanwhile, in the <NUM>/NR system, the subcarrier spacing supports at least one or more of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>, and thus, as the maximum transmission bandwidth of one resource block, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> may be supported.

Thus, when the minimum scheduling unit is one resource block in the <NUM>/NR system, the maximum transmission bandwidth of one resource block is equal to or larger than the maximum transmission bandwidth, <NUM>, of one resource block which is the minimum scheduling unit of the <NUM>/LTE system.

For example, if the maximum subcarrier spacing, <NUM>, when applying the broadband beamforming, such as mmWave, is applied, the size of one resource block which is the minimum scheduling unit may correspond to a <NUM> band.

In this case, if broadband beamforming is applied, with one resource block unit whose maximum transmission bandwidth is <NUM> set as the beamforming granularity unit, the beamforming gain may be reduced by the influence of frequency selectivity fading since mmWave has very sensitive scattering characteristics due to ultra-high frequency properties.

According to various embodiments, the minimum scheduling unit in the base station and terminal performing beamforming may be set as a subcarrier group having a frequency bandwidth identical to or smaller than the frequency bandwidth of one resource block.

For example, the subcarrier group which is the minimum scheduling unit may include the same or smaller number of subcarriers as/than <NUM> subcarriers included in one resource block.

According to various embodiments, the type of the subcarrier group may be varied depending on the number of subcarriers included in the subcarrier group.

For example, as shown in <FIG>, the types of the subcarrier group may include a first subcarrier group (SCG type <NUM>) <NUM> including <NUM> subcarriers included in one resource block, a second subcarrier group (SCG type <NUM>) <NUM> including six subcarriers, a third subcarrier group (SCG type <NUM>) <NUM> including four subcarriers, and a fourth subcarrier group (SCG type <NUM>) <NUM> including three subcarriers.

For example, as shown in <FIG>, one resource block may include one first subcarrier group <NUM>-<NUM>, two second subcarrier groups <NUM>-<NUM> and <NUM>-<NUM>, three third subcarrier groups <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, or four fourth subcarrier groups <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>.

For example, as shown in <FIG>, when the first subcarrier group (SCG type <NUM>) <NUM> includes <NUM> subcarriers having a subcarrier spacing of <NUM>, the maximum transmission bandwidth of the subcarrier group may be f<NUM>=<NUM>.

Further, as shown in <FIG>, when the fourth subcarrier group (SCG type <NUM>) <NUM> includes three subcarriers having a subcarrier spacing of <NUM>, the maximum transmission bandwidth of the subcarrier group is identical to the maximum transmission bandwidth, <NUM>, of the first subcarrier group.

Meanwhile, since the subcarrier spacing and the symbol duration have an inverse relation, the subcarrier spacing, <NUM>, of the fourth subcarrier group is four times the subcarrier spacing, <NUM>, of the first subcarrier group as shown in <FIG>, the symbol duration of the first subcarrier group becomes four times the symbol duration of the fourth subcarrier group.

According to various embodiments, since the base station may apply beamforming on a per-subcarrier group basis, beamforming may be applied, with a different beamforming weight vector applied per subcarrier group.

Further, according to various embodiments, the terminal may obtain feedback information based on the reference signal received on downlink from the base station and feed back the feedback information on a per-subcarrier group basis.

For example, the feedback information may include channel state information about the downlink.

In other words, according to various embodiments, when the base station and the terminal configure the minimum scheduling unit as the subcarrier group, the maximum transmission bandwidth of the subcarrier is reduced as compared with the maximum transmission bandwidth of the resource block so that influence by frequency selectivity fading is reduced, and thus, the performance of the base station and terminal may be improved.

<FIG> is a view illustrating information transmitted/received between a base station and a terminal in a wireless access system supporting a massive MIMO system according to various embodiments.

As shown in <FIG>, the base station may transmit subcarrier group information to the terminal via downlink, and the terminal may transmit channel state-related information to the base station via uplink.

According to various embodiments, the channel state-related information may include feedback information (e.g., channel state information (CSI) transmitted from the terminal in response to the reference signal (e.g., the channel state information reference signal (CSI-RS)) transmitted to the terminal or the reference signal (e.g., the sounding reference signal (SRS)) transmitted from the terminal via downlink.

For example, the channel state information may include at least one or more of the precoding matrix index (PMI), rank indicator (RI), and channel quality indicator (CQI).

For example, the RI denotes the rank information about the channel and means the number of signal streams (or layers) received by the terminal via the same frequency time resource.

For example, the PMI is the value reflecting the spatial properties of the channel and denotes the precoding index of the base station, favored by the terminal with respect to the metric, such as the signal to interference plus noise ratio (SINR).

In other words, the PMI is information about the precoding matrix used for transmission from the transmission end. The precoding matrix fed back from the reception end is determined considering the number of the layers indicated by the RI.

For example, the CQI is a value indicating the strength of channel and means the reception SINR that may be obtained when the base station uses PMI. The terminal reports, to the base station, the CQI index which indicates a specific combination in a set constituted of combinations of predetermined modulation schemes and coding rates.

For example, the feedback information may be fed back on a per-subcarrier group basis.

In this case, a terminal having a wide subcarrier spacing may perform feedback on a per-subcarrier group basis in the same quantity of feedback information as when a terminal having a small subcarrier spacing feeds back information on a per-resource block basis. In other words, although information is fed back on a per-subcarrier group basis, beamforming with higher granularity may be implemented without an increase in the amount of feedback information.

According to various embodiments, the base station may identify the channel state information about the downlink estimated on a per-subcarrier group basis based on the channel state-related information transmitted from the terminal via uplink.

According to various embodiments, the channel state information about the downlink estimated on a per-subcarrier group basis as identified by the base station may be differently obtained according to the duplex scheme, such as time division duplex (TDD) and frequency division duplex (FDD).

TDD system means a scheme in which the downlink and uplink use the same frequency band and are distinguished from each other by time. Accordingly, if the coherence time of radio channel is larger, that is, when the Doppler effect is small, the downlink and uplink may be assumed to have the same radio channel characteristics. This may be referred to as reciprocity.

According to various embodiments, using the reciprocity in the TDD system, the base station may obtain the channel state information about the downlink using channel state-related information (e.g., reference signal (RS)) transmitted from the terminal.

For example, the base station may perform channel estimation on a per-subcarrier group basis, based on the sounding reference signal (SRS) transmitted from the terminal via uplink and may obtain the channel state information about the downlink estimated on a per-subcarrier group basis.

FDD system refers to a system that uses different frequencies for downlink and uplink. Thus, the base station is unable to use the channel state information estimated using the reference signals (RS) of terminals transmitted via uplink, upon downlink transmission.

According to various embodiments, since the FDD system is unable to use the characteristics of channel reciprocity like the TDD system, the base station needs to transmit a reference signal (e.g., CSI-RS) and receive a feedback of channel state information obtained based on the reference signal from the terminal, so as to obtain the channel state information about the downlink.

For example, in the FDD system, the base station may transmit a reference signal (e.g., CSI-RS) to the terminal, and the terminal may obtain channel state information (e.g., CSI) about the downlink based on the reference signal received from the base station and feed back the downlink channel state information to the base station on a per-subcarrier group basis.

In this case, the base station may identify the channel state information about the downlink estimated on a per-subcarrier group basis based on the channel state information fed back from the terminal.

According to various embodiments, the base station may calculate the beamforming vector for each subcarrier group, based on the channel state information estimated on a per-subcarrier group basis, as identified, and transmit a beamforming-applied signal to the terminal via downlink, on a per-subcarrier group basis.

According to various embodiments, the beamforming vector means a vector constituted of the weights applied to antennas. For example, the base station may perform beamforming using the received PMI or may perform beamforming using a different PMI without being restricted to the PMI transmitted from the terminal.

According to various embodiments, the subcarrier group, as the minimum scheduling unit, may be configured in the base station, on a per-channel estimation basis and on a per-beamforming basis, and may be configured in the terminal on a per-feedback unit, on a per-channel estimation basis, or on a per-data decoding basis.

According to various embodiments, the base station may apply beamforming per subcarrier group based on the channel state information estimated on a per-subcarrier group basis and transmit the subcarrier group information, which is the minimum scheduling unit of beamforming, to the terminal.

For example, as shown in <FIG>, the base station may transmit the subcarrier group information, which is the minimum scheduling unit of beamforming, to the terminal.

According to various embodiments, the subcarrier group information may be transmitted from the base station to the terminal via downlink control information.

For example, the subcarrier group information may be transmitted from the base station to the terminal via the downlink control information (DCI) including information for controlling (scheduling) the resources of all physical layers in both directions of uplink or downlink.

According to various embodiments, the subcarrier group information may include information regarding the subcarrier group which is the minimum scheduling unit to which beamforming has been applied in the base station.

For example, the subcarrier group information may include indication information indicating the type of the subcarrier group.

For example, the type of the subcarrier group may be varied depending on the number of subcarriers included in the subcarrier group.

For example, as shown in <FIG>, there may be four types of subcarrier groups, and the indication information indicating the type of subcarrier group may be configured with two bits.

For example, the first subcarrier group (SCG type <NUM>) may be indicated with a bit stream of <NUM>, the second subcarrier group (SCG type <NUM>) may be indicated with a bit stream of <NUM>, the third subcarrier group (SCG type <NUM>) may be indicated with a bit stream of <NUM>, and the fourth subcarrier group (SCG type <NUM>) may be indicated with a bit stream of <NUM>.

According to various embodiments, the terminal may identify information about the subcarrier group unit to which beamforming has been applied in the base station, based on the subcarrier group information received from the base station.

According to various embodiments, the terminal may estimate the channel on a per-subcarrier group basis, as identified based on the subcarrier group information received from the base station and perform data decoding.

<FIG> is a flowchart illustrating an example of transmitting/receiving information between a base station and a terminal in a wireless access system supporting a massive MIMO system according to various embodiments.

In operation <NUM>, the base station may receive information related to the channel state from the terminal.

According to various embodiments, the channel state-related information may include a reference signal transmitted from the terminal on an uplink or feedback information transmitted from the terminal on the uplink, in response to a reference signal transmitted to the terminal on a downlink.

For example, the reference signal transmitted from the terminal may include a sounding reference signal (SRS).

For example, the feedback information may include channel state information (CSI) estimated on a per-subcarrier group basis, based on the channel state information reference signal (CSI-RS) received by the terminal from the base station and be fed back from the terminal to the base station on a per-subcarrier group basis.

In operation <NUM>, the base station may identify channel state information estimated on a per-sub carrier group basis, based on the channel state-related information.

For example, the base station may perform channel estimation on a per-subcarrier group basis in operation <NUM>, based on the sounding reference signal (SRS) transmitted from the terminal via uplink in operation <NUM> and may obtain and identify the channel state information about the downlink estimated on a per-subcarrier group basis.

For example, the base station may identify the channel state information about the downlink estimated on a per-subcarrier group basis based on the channel state information fed back from the terminal in operation <NUM>.

In operation <NUM>, the base station may obtain analog beamforming information and digital beamforming information based on the channel state information.

According to various embodiments, the base station may perform hybrid beamforming which is a fusion of analog beamforming and digital beamforming structures.

According to various embodiments, the analog beamforming information may include information about a precoding matrix (weight matrix) for analog beamforming.

According to various embodiments, the analog beamforming information may be set to differ per stream or per user or the same analog beamforming information may be set for all the users or all the subcarriers.

For example, when the same analog beamforming information is configured for all the users or all the subcarriers, the precoding matrix (weight matrix) for analog beamforming in all the users or all the subcarriers is the analog precoder VRF having a size of <MAT>.

For example, when different analog beamforming information is configured per user or per stream, the precoding matrix (weight matrix) for analog beamforming in the kth terminal or subcarrier index k may be changed to the kth user's analog precoder VRF,k, and VRF,k may be obtained according to the baseband algorithm to obtain a scheduler or digital beamforming information. This is described below in further detail with reference to <FIG>.

According to various embodiments, the digital beamforming information may include information about a precoding matrix (weight matrix) for digital beamforming.

According to various embodiments, different digital beamforming information may be configured per user or per stream.

For example, the precoding matrix (weight matrix) for digital beamforming in the kth terminal or subcarrier index k is the kth user's digital precoder VBB,k having a size of <MAT> and the digital precoder may differ per user or per stream.

According to various embodiments, the hybrid beamforming structure may include the analog precoder VRF and digital precoder (baseband precoder) VBB,k and, as shown in <FIG>, the digital precoder VBB,k may be configured as a cascade of the null precoder <MAT> and transmit layer parallelizing precoder <MAT>.

According to various embodiments, the kth user's digital beamforming information may be obtained based on information about the kth user's null precoder <MAT> and information about the kth user's transmit layer parallelizing precoder <MAT> and may be represented as <MAT>.

For example, according to various embodiments, the base station may obtain the information about the null precoder <MAT> based on the analog beamforming information and the channel information identified in operation <NUM> and, based on the obtained information about the null precoder <MAT>, then obtain the information about the transmit layer parallelizing precoder Vpk, thereby obtaining the information about the digital precoder VBB,k.

According to various embodiments, the information about the null precoder may be obtained based on the analog beamforming information and the channel information.

For example, the information about the kth user's null precoder may include information about the nulling matrix used to minimize the influence from multi-user interference except for the kth user to rectify/separate the kth user's transmission signals at the reception end.

For example, the nulling matrix in the kth terminal or subcarrier index k is the kth user's null precoder <MAT>.

For example, the kth user's null precoder <MAT> may be obtained based on the channel information matrix H̃ considering the influence of the analog precoder VRF.

For example, the kth user's null precoder <MAT> may be obtained using the nullspace(. ) after excluding the kth user's <MAT> considering the analog precoder VRF of the channel information matrix H̃ considering the influence from VRF.

According to various embodiments, the kth user's null precoder <MAT> may be obtained using the scheme of using a codebook or a scheme via singular value interpretation.

According to various embodiments, the information about the transmit layer parallelizing precoder may be obtained based on, the information about the null precoder, the analog beamforming information and the channel information.

For example, the information about the kth user's transmit layer parallelizing precoder <MAT> may include information about the precoding matrix necessary to easily implement the transmit power allocation of the transmit stream to meet the criterion to transmit the transmit power, with it adjusted to specific power.

For example, the kth user's transmit layer parallelizing precoder <MAT> may be obtained based on the effective channel information matrix Heff,k considering influence from the kth user's null precoder <MAT>.

For example, the effective channel information matrix Heff,k may be obtained based on the channel matrix Hk for the kth user, the analog precoder VRF for all the users, and the kth user's null precoder <MAT>, and may be represented as <MAT>.

For example, the information about the transmit layer parallelizing precoder <MAT> may be obtained based on the effective channel information matrix Heff,k, using at least one or more of zero forcing (ZF), minimum mean squared error (MMSE), and right singular precoding (RSP).

According to various embodiments, the kth user's digital precoder <MAT> may be configured to allocate power per stream while meeting the power constraints by parallelizing the effective channel information matrix Heff,k. This is described below in further detail with reference to <FIG>.

In operation <NUM>, the base station may perform hybrid beamforming, which is a combination of analog beamforming and digital beamforming, on a per-sub carrier group basis, based on the analog beamforming information and the digital beamforming information.

According to various embodiments, the hybrid beamforming information may include information about the precoding matrix for hybrid beamforming in the kth terminal or subcarrier index k.

For example, the precoding matrix for hybrid beamforming in the kth terminal or subcarrier index k may be obtained based on the analog precoder VRF and the digital precoder VBB,k obtained in operation <NUM>.

For example, according to various embodiments, the hybrid beamforming structure includes the digital precoder (baseband precoder) VBB,k configured as a cascade precoder structure of the null precoder <MAT> and the transmit layer parallelizing precoder <MAT>, and the precoding matrix for hybrid beamforming may be represented as <MAT>.

According to various embodiments, the hybrid beamforming structure includes a null precoder and a transmit layer parallelizing precoder obtained based on the null precoder, thereby minimizing multi-user interference and maximizing the transmission rate for each user. Thus, the total data transmission rate may be maximized.

According to various embodiments, the base station may apply hybrid beamforming on a per-subcarrier group basis, including the same or smaller number of subcarriers as/than the number of the plurality of subcarriers included in one resource block.

Thus, according to various embodiments, when the minimum scheduling unit is configured as the subcarrier group in the base station, the maximum transmission bandwidth of the subcarrier is reduced as compared with the maximum transmission bandwidth of the resource block so that influence by frequency selectivity fading is reduced, and thus, the beamforming performance of the base station may be improved.

In operation <NUM>, the base station may transmit subcarrier group information corresponding to the subcarrier group to the terminal.

For example, the subcarrier group information may include indication information indicating the type of the subcarrier group which is the minimum scheduling unit to which beamforming has been applied in the base station and may be transmitted from the base station to the terminal via downlink control information.

Further, the type of the subcarrier group may be varied depending on the number of subcarriers included in the subcarrier group, and the indication information indicating the type of the subcarrier group may be configured based on a bit stream.

Although not shown in the drawings, the base station may transmit hybrid beamforming-applied downlink data on a per-subcarrier group basis in operation <NUM>.

In operation <NUM>, the terminal may perform channel estimation and decoding based on the subcarrier group information received from the base station.

According to various embodiments, the terminal may estimate the channel on a per-subcarrier group basis, as identified based on the subcarrier group information received from the base station and perform data decoding. This is described below in further detail with reference to <FIG> and <FIG>.

<FIG> is a flowchart illustrating an example of obtaining digital beamforming information by a base station according to various embodiments.

According to various embodiments, since digital beamforming enables application of an independent beamforming scheme per user or per stream, with the same time-frequency resources, the digital beamforming information may differ per user or per stream, and the digital precoder may differ per user or per stream.

According to various embodiments, the kth user's digital beamforming information means the kth user'ssystolic pressure and diastolic pressure VBB,k which is the precoding matrix (weight matrix) for digital beamforming in subcarrier index k or the kth terminal having a size of <MAT>.

As shown in <FIG>, according to various embodiments, when the structure of the kth user's digital precoder (baseband precoder) VBB,k included in the hybrid beamforming structure is configured as a cascade precoder structure in which the null precoder <MAT> and the stream parallelizing precoder <MAT> are connected in series, <MAT>.

Accordingly, the kth user's digital beamforming information may be obtained based on information about the kth user's null precoder <MAT> and information about the kth user's transmit layer parallelizing precoder <MAT>.

According to various embodiments, the base station may obtain information about the null precoder <MAT> and, based on the obtained information about the null precoder <MAT>, then obtain information about the stream parallelizing precoder Vpk, thereby obtaining information about the kth user's digital precoder VBB,k.

For example, according to various embodiments, the base station may obtain information about the null precoder based on the analog beamforming information and channel information as shown, in operation <NUM> and obtain information about the transmit layer parallelizing precoder based on the information about the null precoder obtained in operation <NUM> and the channel information and analog beamforming information, as shown, in operation <NUM>, thereby obtaining digital beamforming information.

In operation <NUM>, the base station may obtain the information about the null precoder based on the analog beamforming information and channel information.

The base station may obtain the information about the null precoder based on the channel information matrix obtained based on the channel information and analog beamforming information.

According to various embodiments, the null precoder information may be information regarding the kth user's null precoder <MAT>, and the kth user's null precoder <MAT>. may be obtained based on the channel information matrix H̃ considering the influence from the analog precoder VRF.

For example, the kth user's channel information matrix <MAT> considering influence from VRF may be obtained based on information regarding the channel information matrix Hk for the kth user and the information regarding the analog precoder VRF for all the users/subcarriers and be represented as <MAT>.

For example, Hk means the channel information matrix in subcarrier index k or the kth terminal having a size of Nr × Nt, and VRF means the precoding matrix (weight matrix) for analog beamforming in all the users/subcarriers having a size of <MAT>.

According to various embodiments, the kth user's null precoder <MAT> may use the null space or orthogonality to minimize interference from the multiple users.

For example, the kth user's null precoder <MAT> may be obtained based on the channel information matrix H̃ considering the analog precoder VRF.

For example, the kth user's null precoder <MAT> may be obtained according to the criterion as shown in Equation <NUM> using nullspace(. ) after excluding the kth user's <MAT> considering the analog precoder VRF of the channel information matrix H̃ considering influence from VRF.

To that end, ΣK-<NUM>Nr,k×NRF matrix H̃T,k in the form as shown in Equation <NUM> may be considered, and the matrix H̃T,k is a set of the other channels except for the kth user's channel information matrix <MAT> considering VRF from the channel information matrix H̃ considering influence from VRF.

According to various embodiments, information about the kth user's null precoder <MAT> may be obtained using a scheme via singular value interpretation.

For example, since the total number of the streams of all the users, transmittable simultaneously, may not exceed the number of RF chains, the condition Nt»NRF≥ ΣKNs,k needs to be met.

Thus, since ĤT,k may be decomposed as shown in Equation <NUM> by singular value interpretation, the null precoder <MAT>, according to various embodiments, may be obtained as a matrix having a size of NRF × Ns,k corresponding to singular value <NUM> among the right singular matrixes.

According to various embodiments, information about the kth user's null precoder <MAT> may be obtained using a scheme using a codebook.

For example, when the codebook set is defined as a NRF×L matrix C ≐ {c<NUM> ··· cL}, the columns c<NUM> of matrix C may be assumed to be orthogonal to one another. That is, cl⊥cm, l≠m.

According to various embodiments, codebook C may be generated in various methods to implement a constant phase over a unit circle.

For example, codebook C may be generated in such a manner that a codebook is generated with a Zadoff-Chu sequence and orthogonality is given using the cyclic shift.

For example, codebook C may be configured as a Fourier matrix having orthogonality using the discrete Fourier transform (DFT) matrix.

For example, codebook C may be configured as a steering vector set having the Vandermonde matrix, such as a steering matrix of array.

For example, codebook C may be implemented in the form of a phase shift matrix constituting the analog precoder VRF.

According to various embodiments, <MAT>. may be implemented as a criterion as shown in Equation <NUM> based on the codebook C generated according to various embodiments.

For example, the null precoder <MAT> may be obtained as <MAT> having the smallest value of ∥(H̃T,k)Hcl∥F.

According to various embodiments, different analog beamforming information may be configured per user or per stream.

For example, when the analog precoder VRF may be selected per user upon implementing the null precoder, VRF in Equation <NUM> described above may be changed to a peruser analog precoder, such as VRF,k, and VRF,k may be obtained according to the baseband algorithm of obtaining a scheduler or digital beamforming information.

For example, when VRF,k is implemented to be used instead of the null precoder <MAT>, , Equation <NUM> may be modified as shown in Equation <NUM>.

For example, the kth user's analog precoder VRF,k may be implemented via the null space as shown in Equation <NUM> or may be obtained by a method, such as Equation <NUM>, in the codebook set predefined.

According to various embodiments, the hybrid beamforming structure includes the digital precoder (baseband precoder) VBB,k configured as a cascade structure of the null precoder <MAT> and the transmit layer parallelizing precoder <MAT>, thereby minimizing multi-user interference and maximizing the transmission rate for each user. Thus, the total data transmission rate may be maximized.

In operation <NUM>, the base station may obtain information about the transmit layer parallelizing precoder based on the channel information, the analog beamforming information, and the obtained null precoder information.

According to various embodiments, the base station may obtain the information about the transmit layer parallelizing precoder based on the effective channel information obtained based on the information about the null precoder obtained in operation <NUM> and channel information and the analog beamforming information.

For example, the information about the transmit layer parallelizing precoder is information regarding the kth user's transmit layer parallelizing precoder <MAT>.

For example, the effective channel information matrix Heff,k may be obtained based on the information regarding the channel matrix Hk for the kth user, information regarding the analog precoder VRF for all the users, and the information regarding the kth user's null precoder <MAT> obtained in operation <NUM> and may be represented as <MAT>.

According to various embodiments, the transmit layer parallelizing precoder <MAT> is a precoder necessary to easily implement the transmit power allocation of the transmit stream to meet the criterion to transmit transmit power, which is one major criterion of the precoder, with it adjusted to specific power. That is, it is a pre-processing precoder to distribute the transmit stream power into <MAT> and to secure the maximum transmission rate.

For example, according to various embodiments, the information about the transmit layer parallelizing precoder <MAT> may be obtained based on the effective channel information matrix Heff,k, using at least one or more of zero forcing (ZF), minimum mean squared error (MMSE), and right singular precoding (RSP).

The above-described type of precoder is as shown in Table <NUM> below. In this case, Kn,k is the noise covariance matrix defined in Equation <NUM>.

Although not shown in the drawings, the base station may allocate transmit power to the data stream of each user based on the transmit layer parallelizing precoder <MAT> obtained in operation <NUM>.

According to various embodiments, the kth user's digital precoder <MAT> may be configured to allocate power per stream while meeting the power constraints by parallelizing the effective channel information matrix Heff,k.

<FIG> is a flowchart illustrating an example of performing decoding based on a minimum scheduling unit applied to a base station, by a terminal, according to various embodiments.

According to various embodiments, the minimum scheduling unit is the unit in which beamforming is applied in the base station and the unit in which channel estimation and data decoding are applied in the terminal.

For example, the subcarrier group, as the minimum scheduling unit, may be configured in the base station, on a per-channel estimation basis and on a per-beamforming basis, and may be configured in the terminal on a per-channel state information feedback unit, on a per-channel estimation basis, or on a per-data decoding basis.

In operation <NUM>, the terminal may identify the subcarrier group information.

According to various embodiments, the terminal may receive and identify the subcarrier group information from the base station.

For example, the subcarrier group information may be transmitted from the base station to the terminal via downlink control information.

For example, the subcarrier group information may include information regarding the subcarrier group which is the minimum scheduling unit to which beamforming has been applied in the base station.

For example, the subcarrier group information may include indication information indicating the type of the subcarrier group, and the indication information may be configured as a bit stream.

For example, the first subcarrier group (SCG type <NUM>) including <NUM> subcarriers may be indicated with a bit stream of <NUM>, the second subcarrier group (SCG type <NUM>) including six subcarriers may be indicated with a bit stream of <NUM>, the third subcarrier group (SCG type <NUM>) including four subcarriers may be indicated with a bit stream of <NUM>, and the fourth subcarrier group (SCG type <NUM>) including three subcarriers may be indicated with a bit stream of <NUM>.

According to various embodiments, the terminal may identify the subcarrier group based on the indication information included in the subcarrier group information received from the base station and identify the identified subcarrier group as the minimum scheduling unit to which beamforming has been applied in the base station. This is described below in further detail with reference to <FIG>.

In operation <NUM>, the terminal may perform channel estimation and data decoding using the identified subcarrier group information.

According to various embodiments, the terminal may estimate the channel in the minimum scheduling unit identified based on the subcarrier group information received from the base station and perform data decoding.

For example, the minimum scheduling unit may be the subcarrier group to which beamforming has been applied in the base station and in which the terminal may estimate the channel on a per-subcarrier group basis and perform decoding on the data received from the base station, on a per-subcarrier group basis.

<FIG> is a view illustrating the operation of identifying, by a terminal, a minimum scheduling unit applied in a base station and configuring the identified minimum scheduling unit in the terminal, according to various embodiments.

In operation <NUM>, the terminal may receive the subcarrier group information and the downlink data to which hybrid beamforming has been applied on a per-subcarrier group basis.

For example, the subcarrier group information may be transmitted from the base station to the terminal via downlink control information (DCI format).

For example, the downlink data to which hybrid beamforming has been applied on a per-subcarrier group basis may be transmitted from the base station to the terminal via a downlink message.

In operation <NUM>, the terminal may identify the subcarrier group information corresponding to the subcarrier group.

For example, as shown in <FIG>, the first subcarrier group (SCG type <NUM>) including <NUM> subcarriers may be indicated with a bit stream of <NUM>, the second subcarrier group (SCG type <NUM>) including six subcarriers may be indicated with a bit stream of <NUM>, the third subcarrier group (SCG type <NUM>) including four subcarriers may be indicated with a bit stream of <NUM>, and the fourth subcarrier group (SCG type <NUM>) including three subcarriers may be indicated with a bit stream of <NUM>.

In operation <NUM>, the terminal may identify whether the indication information included in the subcarrier group information is <NUM>.

According to various embodiments, the terminal may identify the minimum scheduling unit applied to beamforming in the base station, based on the indication information included in the subcarrier group information.

For example, since the value of the indication information may be determined based on the bit stream of the indication information, and the bit stream of the indication information corresponds to each subcarrier group, the subcarrier group of the minimum scheduling unit applied to beamforming may be identified in the base station based on the value of the indication information.

For example, as shown in <FIG>, the value of the indication information of the first subcarrier group (SCG type <NUM>) for which the bit stream of the indication information is <NUM> may be <NUM>, the value of the indication information of the second subcarrier group (SCG type <NUM>) for which the bit stream of the indication information is <NUM> may be <NUM>, the value of the indication information of the third subcarrier group (SCG type <NUM>) for which the bit stream of the indication information is <NUM> may be <NUM>, and the value of the indication information of the fourth subcarrier group (SCG type <NUM>) for which the bit stream of the indication information is <NUM> may be <NUM>.

In operation <NUM>, when the value of the indication information included in the subcarrier group information identified by the terminal is <NUM>, this means that the minimum scheduling unit to which beamforming has been applied in the base station is the first subcarrier group including <NUM> subcarriers. In operation <NUM>, the terminal may set one resource block unit including <NUM> subcarriers as the minimum scheduling unit in the terminal.

In operation <NUM>, unless the value of the indication information included in the subcarrier group information identified by the terminal is <NUM>, this means that the minimum scheduling unit to which beamforming has been applied in the base station is a subcarrier group including a smaller number of subcarriers than <NUM>. In operation <NUM>, the terminal may set the subcarrier group unit as the minimum scheduling unit in the terminal.

Although not shown in the drawings, the terminal may perform channel estimation and decoding in the minimum scheduling unit set in operation <NUM> or <NUM>.

<FIG> is a block diagram illustrating components of a base station <NUM> according to various embodiments.

A wireless communication system includes a base station <NUM> and a plurality of terminals <NUM> positioned in the coverage of the base station.

Referring to <FIG>, the base station <NUM> may include a transceiver <NUM> and a processor <NUM>.

Although not shown in the drawings, the base station <NUM> may further include a memory (not shown).

For example, the base station <NUM> may further include a memory storing a basic program for operating the base station <NUM>, application programs, control information or other data.

The memory is connected with the processor <NUM> to store various pieces of information for driving the processor <NUM>. The memory may be positioned inside or outside the processor <NUM> and be connected with the processor <NUM> via various known means.

For example, the memory may include at least one type of storage medium of flash memory types, hard disk types, multimedia card micro types, card types of memories (e.g., SD or XD memory cards), magnetic memories, magnetic disks, or optical discs, random access memories (RAMs), static random access memories (SRAMs), read-only memories (ROMs), programmable read-only memories (PROMs), or electrically erasable programmable read-only memories (EEPROMs). The processor <NUM> may perform various operations using various programs, contents, or data stored in the memory.

The processor <NUM> implements the functions, processes, and/or methods proposed above. Wireless interface protocol layers may be implemented by the processor <NUM>.

The base station <NUM> shown in <FIG> and/or the terminal <NUM> shown in <FIG> may have multiple antennas. In particular, according to the present invention, the base station <NUM> and the terminal <NUM> may be implemented to support the above-described massive MIMO system.

According to various embodiments, the transceiver <NUM> is connected with the processor <NUM> to transmit and/or receive wireless signals. For example, according to various embodiments of the present invention, the transceiver <NUM> may transmit and receive signals, information, or data.

According to various embodiments, the transceiver <NUM> may receive channel state-related information from the terminal <NUM>.

According to various embodiments, the channel state-related information may include a reference signal transmitted from the terminal <NUM> via uplink.

For example, the reference signal transmitted from the terminal <NUM> via uplink may include a sounding reference signal (SRS).

According to various embodiments, the channel state-related information may include feedback information transmitted to the terminal <NUM> via uplink, in response to the reference signal transmitted via downlink.

For example, the feedback information transmitted from the terminal <NUM> via uplink may include channel state information about the downlink estimated on a per-subcarrier group basis.

For example, the feedback information may be fed back from the terminal <NUM> on a per-subcarrier group basis.

For example, the feedback information may include channel state information (CSI) estimated on a per-subcarrier group basis, based on the channel state information reference signal (CSI-RS) received by the terminal <NUM> from the base station <NUM> via downlink and be fed back from the terminal <NUM> to the base station <NUM> on a per-subcarrier group basis.

According to various embodiments, the transceiver <NUM> may transmit the subcarrier group information corresponding to the subcarrier group which is the minimum scheduling unit to which beamforming has been applied in the base station <NUM>.

For example, the subcarrier group may include the same or smaller number of subcarriers as/than a plurality of subcarriers included in one resource block.

For example, the subcarrier group information includes indication information indicating the type of the subcarrier group. The indication information included in the subcarrier group information may be constituted of a bit stream corresponding to the subcarrier group.

For example, the subcarrier spacing of the subcarriers included in the subcarrier group may include at least one of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

According to an embodiment, the processor <NUM> may control the overall operation of the base station <NUM>. The processor <NUM> may control the overall operation of the base station <NUM> according to various embodiments as described above.

According to various embodiments, the processor <NUM> may identify the channel state information estimated on a per-subcarrier group basis based on the channel state-related information transmitted from the terminal <NUM>.

For example, the channel state information estimated on a per-subcarrier group basis may be channel state information about downlink and may include at least one or more of the precoding matrix index (PMI), rank indicator (RI), and channel quality indicator (CQI).

For example, the base station <NUM> may perform channel estimation on a per-subcarrier group basis, based on the sounding reference signal (SRS) transmitted from the terminal <NUM> via uplink and may obtain and identify the channel state information about the downlink estimated on a per-subcarrier group basis.

For example, the base station <NUM> may identify the channel state information about the downlink estimated on a per-subcarrier group basis based on the feedback information fed back from the terminal <NUM>.

According to various embodiments, the processor <NUM> may obtain analog beamforming information and digital beamforming information based on the channel state information estimated on a per-subcarrier group basis.

For example, the precoding matrix (weight matrix) for digital beamforming in subcarrier index k or the kth terminal <NUM> may be the kth user's digital precoder VBB,k having a size of <MAT>, and the digital precoder may differ per user or per stream.

According to various embodiments, the base station <NUM> may obtain the information about the null precoder <MAT> based on the analog beamforming information and the channel information and, based on the obtained information about the null precoder Vnullk, then obtain the information about the transmit layer parallelizing precoder <MAT>, thereby obtaining the information about the digital precoder VBB,K.

For example, the kth user's null precoder <MAT> may be obtained using the nullspace(. ) after excluding the kth user's <MAT> considering the analog precoder VRF of the channel information matrix H̃ considering the influence from VRF to minimize multi-user interference.

According to various embodiments, the information about the null precoder may be obtained based on the codebook.

According to various embodiments, the information about the transmit layer parallelizing precoder may be obtained based on the obtained null precoder information, the analog beamforming information and the channel information.

For example, the effective channel information matrix Heff,k may be obtained based on the information regarding the channel matrix Hk for the kth user, the information regarding the analog precoder VRF for all the users, and the information regarding the kth user's null precoder <MAT>, and may be represented as <MAT>.

For example, according to various embodiments, the information about the transmit layer parallelizing precoder Vpk may be obtained based on the effective channel information matrix Heff,k, using at least one or more of zero forcing (ZF), minimum mean squared error (MMSE), and right singular precoding (RSP).

<FIG> is a block diagram illustrating components of a terminal <NUM> according to various embodiments.

Referring to <FIG>, the terminal <NUM> may include a transceiver <NUM> and a processor <NUM>.

For example, the terminal <NUM> may further include a memory storing a basic program for operating the terminal <NUM>, application programs, control information or other data.

According to various embodiments, the transceiver <NUM> may transmit channel state-related information to the base station <NUM>.

For example, the channel state-related information may include a reference signal transmitted on an uplink or feedback information transmitted on the uplink, in response to a reference signal may receive ed on a downlink.

For example, the feedback information may include channel state information (CSI) estimated on a per-subcarrier group basis, based on the channel state information reference signal (CSI-RS) received by the terminal <NUM> from the base station <NUM> and be fed back from the terminal <NUM> to the base station <NUM> on a per-subcarrier group basis.

According to various embodiments, the transceiver <NUM> may receive the subcarrier group information corresponding to the subcarrier group unit which is the minimum scheduling unit to which beamforming has been applied in the base station <NUM>, from the base station <NUM>.

According to various embodiments, the transceiver <NUM> may receive, from the base station <NUM>, the downlink data to which hybrid beamforming has been applied on a per-subcarrier group basis.

According to an embodiment, the processor <NUM> may control the overall operation of the terminal <NUM>. The processor <NUM> may control the overall operation of the terminal <NUM> according to various embodiments as described above.

According to various embodiments, the processor <NUM> may perform channel estimation and decoding based on the subcarrier information received from the base station <NUM>.

For example, the subcarrier group information may include information regarding the subcarrier group which is the minimum scheduling unit to which beamforming has been applied in the base station <NUM>.

For example, the subcarrier group information may include indication information indicating the type of the subcarrier group, and the indication information may be configured as a bit stream corresponding to the subcarrier group.

According to various embodiments, the processor <NUM> may identify the minimum scheduling unit applied to beamforming in the base station <NUM>, based on the indication information included in the identified subcarrier group information.

For example, since the value of the indication information may be determined based on the bit stream of the indication information, and the bit stream of the indication information corresponds to each subcarrier group, the subcarrier group of the minimum scheduling unit applied to beamforming may be identified in the base station <NUM> based on the value of the indication information.

According to various embodiments, the processor <NUM> may perform channel estimation and decoding based on the identified minimum scheduling unit.

For example, the processor <NUM> may set the identified minimum scheduling unit, to which beamforming has been applied in the base station <NUM>, as the minimum scheduling unit in the terminal <NUM>.

For example, the subcarrier group, as the minimum scheduling unit, may be configured in the base station <NUM>, on a per-channel estimation basis and on a per-beamforming basis, and may be configured in the terminal <NUM> on a per-channel state information feedback unit, on a per-channel estimation basis, or on a per-data decoding basis.

For example, the processor <NUM> may estimate channel and perform data decoding in the units of the subcarrier group to which beamforming has been applied in the base station <NUM>.

The above-described embodiments regard predetermined combinations of the components and features of the disclosure. Each component or feature should be considered as optional unless explicitly mentioned otherwise. Each component or feature may be practiced in such a manner as not to be combined with other components or features.

Further, some components and/or features may be combined together to configure an embodiment of the disclosure. The order of the operations described in connection with the embodiments of the disclosure may be varied. Some components or features in an embodiment may be included in another embodiment or may be replaced with corresponding components or features of the other embodiment. It is obvious that the claims may be combined to constitute an embodiment unless explicitly stated otherwise or such combinations may be added in new claims by an amendment after filing.

The embodiments of the disclosure may be implemented by various means, e.g., hardware, firmware, software, or a combination thereof.

When implemented in hardware, an embodiment of the disclosure may be implemented with, e.g., one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs).

Processors, controllers, micro-controllers, or micro-processors. When implemented in firmware or hardware, an embodiment of the disclosure may be implemented as a module, procedure, or function performing the above-described functions or operations. The software code may be stored in a memory and driven by a processor. The memory may be positioned inside or outside the processor to exchange data with the processor by various known means.

Claim 1:
A method for performing downlink beamforming by a base station (<NUM>, <NUM>) in a wireless access system, the method comprising:
receiving (<NUM>) channel state-related information from a terminal (<NUM>, <NUM>), wherein the channel state-related information includes feedback information transmitted on an uplink from the terminal, in response to a reference signal, such as a channel state information reference signal, CSI-RS, transmitted by the base station on a downlink;
identifying (<NUM>) channel state information estimated on a per-subcarrier group basis, based on the channel state-related information;
obtaining (<NUM>) analog beamforming information and digital beamforming information based on the channel state information;
performing (<NUM>), based on the analog beamforming information and the digital beamforming information, hybrid beamforming, which is a combination of analog beamforming and digital beamforming, on a per-subcarrier group basis as a minimum scheduling unit;
transmitting (<NUM>) downlink control information including scheduling information for scheduling physical resources in uplink or downlink and subcarrier group information , wherein the subcarrier group information includes indication information regarding a subcarrier group which is the minimum scheduling unit to which beamforming is applied in the base station, and wherein the subcarrier group includes a number of subcarriers less than a number of a plurality of subcarriers included in one resource block; and
transmitting downlink data to which beamforming is applied on a per-subcarrier group basis depending on the subcarrier group information,
wherein the indication information indicates one of a plurality of subcarrier group, SCG, types as a value of a bit stream, the plurality of SCG types respectively indicate a plurality of subcarrier groups including different numbers of subcarriers.