Method and system for single carrier wideband hybrid beamforming based on limited feedback

A communication system and an operating method thereof are for single carrier wideband hybrid beamforming based on limited feedback. A transmitter having a plurality of Tx antennas may be configured to receive limited channel information from at least one receiver each having at least one Rx antenna, schedule a RF beam for at least one stream in the receiver using the limited channel information, and perform baseband beamforming based on the RF beam.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and claims priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2019-0128488, filed on Oct. 16, 2019, in the Korean Intellectual Property Office, the disclosures of which is herein incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Technical Field

Various embodiments relate to a method and system for single carrier wideband hybrid beamforming based on limited feedback.

2. Description of the Related Art

A beamforming technology is a technology for focusing a transmission signal on a specific direction using multiple antennas. In particular, in a high frequency channel, such as mmWave communication considered in a 5G mobile communication system, high path attenuation can be overcome through beamforming and space resources can be efficiently used by forming a narrow beam width using multiple antennas. In order to apply the existing digital MIMO technology using multiple antennas, RF chains corresponding to the number of antennas are necessary. However, if multiple antennas are used, a system implementation is made impossible because hardware complexity and power consumption are significantly increased.

A transmitter needs to have channel state information (CSI) feedback from a receiver in order to design beamforming. However, in a large-scale antenna system using tens or hundreds of antennas, high feedback overhead is unrealistically necessary due to a too large channel size.

A mmWave beamforming system, that is, a core technology of a 5G mobile communication system, uses a wide range of frequency resources, and thus a radio channel has a wideband or frequency selective characteristic. In the existing mobile communication system, an orthogonal frequency division multiplexing (OFDM) technology is a lot used to overcome the wideband characteristic of a channel. Accordingly, a given ratio of overhead is necessary because a cyclic prefix is used to remove inter-symbol interference.

SUMMARY OF THE INVENTION

Various embodiments provide a communication system capable of reducing feedback overhead from a receiver to a transmitter and an operating method thereof.

Various embodiments provide a communication system capable of reducing hardware complexity and power consumption while using multiple antennas and an operating method thereof.

Various embodiments provide a communication system capable of controlling inter-symbol interference and an operating method thereof.

A communication system and an operating method thereof according to various embodiments provide a method and system for single carrier wideband hybrid beamforming based on limited feedback.

A communication system according to various embodiments may include at least one receiver including at least one receive (Rx) antenna and configured to feedback limited channel information and a transmitter including a plurality of transmit (Tx) antennas and configured to receive the limited channel information, schedule a radio frequency (RF) beam for at least one stream in the receiver using the limited channel information, and perform baseband beamforming based on the RF beam.

An operating method of a communication system according to various embodiments may include receiving, by a transmitter including a plurality of transmit (Tx) antennas, limited channel information from at least one receiver each including at least one receive (Rx) antenna, scheduling, by the transmitter, a RF beam for at least one stream in the receiver using the limited channel information, and performing, by the transmitter, baseband beamforming based on the RF beam.

DETAILED DESCRIPTION

Hereinafter, various embodiments of this document are described with reference to the accompanying drawings.

FIG. 1is a diagram illustrating a communication system100according to various embodiments.

Referring toFIG. 1, the communication system100according to various embodiments may be implemented as a wideband mmWave beamforming system of a 5G mobile communication system, and may include a transmitter110and at least one, for example, U receivers120. In this case, the transmitter110and the receiver120may transmit and receive signals through a plurality of wideband mmWave channels130.

The transmitter110may include a plurality of transmit (Tx) antennas, for example, NtTx antennas111. For example, the transmitter110may include a base station (BS). The transmitter110may perform beamforming for at least one of the receivers120using limited channel information feedback from each of the receivers120, and may transmit a signal to the receiver120.

The transmitter110may further include a transmission processor113and a scheduler115. The transmission processor113may include transmission processors, such as a plurality of RF antennas, for example, NRFtRF chains. In this case, the number of transmission processors, for example, NRFtmay be equal to the number of Tx antennas111, for example, Nt, or may be smaller than the number of Tx antennas111, for example, Nt. The scheduler115may select at least any one, for example, K receivers120among all, that is, the U receivers120. The scheduler115may not allocate or allocate at least one, for example, Lu(0≤Lu≤NRFf) stream to the selected receiver120. In this case, the number of streams for the selected receiver120may be represented as a spatial multiplexing number. Furthermore, the number of stream allocated in the transmitter110may be represented as a total number of stream for the selected receiver120

According to various embodiments, the transmitter110may transmit a signal using baseband beamforming and RF beamforming. The transmitter110may perform baseband beamforming based on a baseband beamforming matrix (FBB=[F1BB, . . . , FUBB]∈□NRFt×L) in accordance with the number of transmission processors, for example, NRFt, and may perform RF beamforming based on an RF beamforming matrix (FRF∈□Nt×NRFt) in accordance with the number of Tx antennas111, for example, Nt.

The receiver120may include at least one receive (Rx) antenna, for example, NrRx antennas121. For example, the receiver120is a user equipment, and may include at least one of a portable communication device, a computer device, a portable multimedia device, a portable medical device, a camera, a wearable device, or home appliances. The receiver120may feedback limited channel information to the transmitter110. Furthermore, the receiver120may perform beamforming, and thus may receive a signal from the transmitter110.

The receiver120may further include a reception processor123. The reception processor123may include reception processors, such as a plurality of RF chains, for example, NRFrRF chains. In this case, the number of reception processors, for example, NRFrmay be equal to the number of Rx antennas121, for example, Nror may be smaller than the number of Rx antennas121, for example, Nr.

According to one embodiment, the receiver120may receive a signal using RF beamforming. The receiver120may perform RF beamforming based on an RF beamforming matrix (WuRF∈□Nr×NRFr) in accordance with the number of Rx antennas121, for example, Nr. According to another embodiment, the receiver120may receive a signal using RF beamforming and baseband beamforming. The receiver120may perform RF beamforming based on the RF beamforming matrix (WuRF∈□Nr×NRFr) in accordance with the number of Rx antennas121, for example, Nr, and may additionally perform baseband beamforming based on a baseband beamforming matrix (WuBB∈□NRFr×Lu) in accordance with the number of reception processors, for example, NRFr. Furthermore, the reception processor123may receive at least one stream, for example, Lustreams allocated to the receiver120, and may compensate for a delay of a channel path for the stream, that is, a delay value. InFIG. 1, “delay d*u,n,” may mean that a delay of a channel path value d*u,nfor the n-th stream of a u-th receiver120is compensated for.

According to various embodiments, a delay-d multiple input multiple output (MIMO) channel matrix (Hu,d∈□Nr×Nt, d=0, . . . , D−1) may be given between the transmitter110and any one of the receivers120, that is, the u-th receiver120like Equation 1.

In Equation 1, {tilde over (H)}uindicates a large-scale channel gain. Nclindicates the number of clusters of scatters present in a channel. Nrayindicates the number of multiple path components present within a single cluster. αu,i,lindicates a path gain. prc(τ) indicates a raised-cosine pulse-shaping function at τ seconds for a Tsinterval signal. θu,i,lt/ϕu,i,ltindicates an elevation/azimuth angle of each path component that goes out to the Tx antennas. θu,i,lr/ϕu,i,lr, indicates an elevation/azimuth angle of each path component that enters the Rx antenna. at(⋅)/ar(⋅) indicates the normalized array response vector of a Tx/Rx antenna. at(⋅)/ar(⋅) may be determined depending on the type of array antenna.

According to various embodiments, a received signal of the u-th receiver120in a time index k may be represented like Equation 2. In this case, if the receiver120uses RF beamforming and baseband beamforming, the received signal of the receiver120may be represented like Equation 3. In this case, assuming that a delay for an n-th received stream of a u-th user is d*u,n, the received signal may be represented like Equation 4 by compensating for the delay.

In Equation 2, P (P=diag( . . . , pu,n, . . . )) may indicates a diagonal matrix indicative of Tx power allocation by the transmitter110, and may satisfy Tr(P)≤Pt. P may indicate maximum Tx power of a base station (BS). x may indicate the transmission signal vector of a signal transmitted by the transmitter110. nu[k] may indicate the noise vector of the u-th receiver120in a k-th time index.

In Equation 4,yu,n[k] may be represented like Equation 5.

In this case, Pnmay indicate noise power.

According to various embodiments, the communication system100may be based on a hybrid beamforming technology for maximizing a weighted sum rate like Equation 6 so that importance for each user, that is, for each receiver120, can be incorporated.

In Equation 6, quis the weight of a u-th user, that is, the receiver120. The SINR may be calculated like Equation 7.

In Equation 7, Plmay be calculated like Equation 8.

FIG. 2is a diagram illustrating an operating method of the communication system100according to various embodiments.

Referring toFIG. 2, at operation210, each of all receivers, that is, each of the U receivers120, may feedback limited channel information to the transmitter110. Each of the receivers120may detect a channel matrix with the transmitter110. The channel matrix may be configured with a plurality of delay components. Each of the receivers120may extract beam space channel coefficients for each delay component of the channel matrix. Each of the receivers120may extract a predetermined number of elements from the beam space channel coefficients. Each of the receivers120may configure limited channel information using extracted elements with respect to all the delay components of the channel matrix. Each of the receivers120may transmit the limited channel information to the transmitter110. Accordingly, the transmitter110may receive the limited channel information from all receivers, that is, the U receivers120.

At operation220, the transmitter110may schedule a RF beam for at least one stream in the receiver120using the limited channel information. In this case, the transmitter110may schedule the transmitter110and a RF beam therefor in a beam domain so that inter-symbol interference and inter-stream interference are mitigated. Furthermore, the transmitter110may configure the RF beamforming matrix (FRF) of the transmitter110and the RF beamforming matrix (WuRF) of the receiver120.

At operation230, the transmitter110may perform baseband beamforming based on the RF beam. In this case, the transmitter110may design the baseband beamforming matrix (FBB) of the transmitter110. Specifically, the transmitter110may design the baseband beamforming matrix (FBB) of the transmitter110using the RF beamforming matrix (FRF) of the transmitter110and the RF beamforming matrix (WuRF) of the receiver120. Furthermore, the transmitter110may allocate power to the RF beamforming matrix (FRF) and baseband beamforming matrix (FBB) of the transmitter110.

At operation240, the transmitter110and the receiver120may communicate with each other. In this case, the transmitter110may transmit a signal by performing baseband beamforming based on the baseband beamforming matrix (FBB) and performing RF beamforming based on the RF beamforming matrix (FRF). According to one embodiment, the receiver120may receive a signal using RF beamforming. The receiver120may perform RF beamforming based on an RF beamforming matrix (WuRF∈□Nr×NRFr) in accordance with the number of Rx antennas121, for example, Nr. According to another embodiment, the receiver120may receive a signal using RF beamforming and baseband beamforming. The receiver120may perform RF beamforming based on the RF beamforming matrix (WuRF∈□Nr×NRFr) in accordance with the number of Rx antennas121, for example, Nr, and may additionally perform baseband beamforming based on a baseband beamforming matrix (WuBB∈□NRFr×Lu) in accordance with the number of reception processors, for example, NRFr.

FIG. 3is a diagram illustrating an operating method of the receiver120according to various embodiments.

Referring toFIG. 3, at operation310, the receiver120may feedback limited channel information to the transmitter110. The receiver120may include at least one Rx antenna, for example, NrRx antennas121. For example, the receiver120is a user equipment, and may include at least one of a portable communication device, a computer device, a portable a multimedia device, a portable medical device, a camera, a wearable device, or home appliances.

FIG. 4is a diagram illustrating a limited channel information feedback operation ofFIG. 3.

Referring toFIG. 4, at operation410, the receiver120may detect a channel matrix. The channel matrix may be configured with a plurality of delay components, for example, D delay components. At operation420, the receiver120may extract beam space channel coefficients for each of the delay components of the channel matrix. The receiver120may convert each of the delay components into a beam domain representation. In this case, the receiver120may detect a d-th delay component like Equation 9 by decomposing the channel matrix using orthogonal bases. Furthermore, the receiver120may extract a beam space channel coefficient (su,d∈□NtNr×1,∀d) like Equation 10 based on Equation 9.

In Equation 9, (ūnr,vnr), (ūmt,vmt) may indicate uniformly sampled virtual angles in a directional cosine domain in order to form orthogonal basis matrices H(i). su,d,imay indicate a beam space channel coefficient and may be represented as a vector like Equation 10.
Su,d□vec(Hu,dt)=[Su,d,1, . . . ,Su,d,NtNr]T[Equation 10]

At operation430, the receiver120may extract a predetermined number of elements, for example, Nfelements from the beam space channel coefficients. At operation440, the receiver120may configure limited channel information using the extracted elements with respect to all the delay components of the channel matrix. In this case, the receiver120may configure the limited channel information using NfD elements, for example. At operation450, the receiver120may transmit the limited channel information to the transmitter110. Thereafter, the receiver120may return to the process ofFIG. 3.

Referring back toFIG. 3, at operation320, the receiver120may receive a signal from the transmitter110. According to one embodiment, the receiver120may receive a signal using RF beamforming. The receiver120may perform RF beamforming based on an RF beamforming matrix (WuRF∈□Nr×NRFr) in accordance with the number of Rx antennas121, for example, Nr. According to another embodiment, the receiver120may receive a signal using RF beamforming and baseband beamforming. The receiver120may perform RF beamforming based on the RF beamforming matrix (WuRF∈□Nr×NRFr) in accordance with the number of Rx antennas121, for example, Nr, and may additionally baseband beamforming based on a baseband beamforming matrix (WuBB∈□NRFr×Lu) in accordance with the number of reception processors, for example, NRFr. Furthermore, the reception processor123may receive at least one stream allocated to the receiver120, for example, Lustreams, and may compensate for a delay for the stream.

FIG. 5is a diagram illustrating an operating method of the transmitter110according to various embodiments.

Referring toFIG. 5, at operation510, the transmitter110may receive limited channel information from all receives, that is, U receivers120. At operation520, the transmitter110may select at least any one of the receivers120using the limited channel information, and may schedule a RF beam for at least one stream in the selected receiver120. In this case, the transmitter110may schedule the transmitter110and a RF beam therefor in a beam domain so that inter-symbol interference and inter-stream interference are mitigated. Furthermore, the transmitter110may configure the RF beamforming matrix (FRF) of the transmitter110and the RF beamforming matrix (WuRF) of the receiver120. In this case, column vectors that configure the RF beamforming matrix (FRF) of the transmitter110and the RF beamforming matrix (WuRF) of the receiver120may be selected within a given beam codebook. The receivers120, that is, Lu>0, may correspond to the selected receivers120. A different number of streams may be allocated to each receiver120based on a channel state.

FIG. 6is a diagram illustrating a user and beam scheduling operation ofFIG. 5.FIG. 7is a diagram for describing the user and beam scheduling operation ofFIG. 5.

Referring toFIG. 6, at operation610, the transmitter110may estimate a beam space channel coefficient (ŝu,d) for each of the receivers120based on the limited channel information. The transmitter110may estimate beam space channel coefficients (ŝu,d) configured with a predetermined number of elements, for example, Nfelements and (NtNr−Nf) 0s based on the limited channel information. At operation620, the transmitter110may restore a channel matrix (Ĥu,d) based on all the beam space channel coefficients (ŝu,d) in accordance with each of the receivers120. The transmitter110may restore the channel matrix (Ĥu,d) based on the beam space channel coefficients (ŝu,d) like Equation 12.

In Equation 12, ŝu,d,inmay indicate an element having an n-th size among ŝu,delements.

At operation630, the transmitter110may form a channel coefficient matrix (Gd) using the beam space channel coefficients (ŝu,d) of all receivers, that is, the U receivers120. The transmitter110may form the channel coefficient matrix (Gd) like Equation 13.
Gd=[G1,dT, . . . ,GU,dT],d=0, . . . ,D−1  [Equation 13]

In Equation 13,Gu,dmay be defined using the elements of the beam space channel coefficient (ŝu,d) like Equation 14. WhenGu,dis configured, a value of each element smaller than a threshold (γu) may be processed as 0.

At operation640, the transmitter110may schedule a RF beam (n*) in each of the selected receivers120based on the channel coefficient matrix (Gd). In this case, the transmitter110may select the delay component (d*), row (m*) and column (l*) of an element having the largest magnitude in the channel coefficient matrix (Gd) like Equation 15. Thereafter, the transmitter110may select the receiver (u*)120based on the selected column (l*) and the number of Rx antennas121(Nr) like Equation 16. Furthermore, the transmitter110may determine a RF beam (n*) for the selected receiver (u*)120based on the selected column (l*), the number of Rx antennas121(Nr), and the selected receiver (u*)120like Equation 17. Accordingly, the transmitter110may configure a combination of the selected receiver (u*)120, the selected delay component (d*), the determined RF beam index at the selected receiver (n*), and the selected RF beam index at the transmitter (m*) as a combination (Ωsel=Ωsel∪{(u*,d*,n*,m*)}) of the RF beam (n*).

According to one embodiment, the transmitter110may convert columns having a value not 0, in the selected row (m*) of a channel coefficient matrix

(∑d=0D-1⁢G__d),
into 0, and may convert rows having a value not 0, in the selected column (l*) of the channel coefficient matrix

(∑d=0D-1⁢G__d),
into 0. Accordingly, the column and row having 0 in the channel coefficient matrix

(∑d=0D-1⁢G__d)
are excluded from scheduling, and thus inter-symbol interference and inter-stream interference can be controlled. In order to consider the number of reception processors such as the RF chains of all receivers, that is, K selected receivers120, for example, all the columns of a channel coefficient matrix (Gd,∀d) corresponding to receivers120from which NRFrbeams have been selected may be converted into 0. This may be repeated until the number of RF beams to be transmitted with respect to the remaining values of the channel coefficient matrix (Gd,∀d) becomes NRFtor all the columns of the channel coefficient matrix (Gd,∀d) not 0 disappear, for example.

For example, the transmitter110may obtain scheduling results, such as those illustrated inFIG. 7. Assuming that the number of Tx antennas111(Nt), the number of Rx antennas121(Nr) and the number of delay components (D) are 8, 4 and 2, respectively, the elements of channel coefficient matrices (G0,G1) may be obtained as illustrated inFIG. 7. In this case, the number of streams allocated to the receivers120, that is, users, may be represented as {Lu}u=1U={1,1,1,1,0,2}, and a set of receivers120selected from the receivers may be represented as U={1,2,3,4,6}.

At operation650, the transmitter110may configure the RF beamforming matrix (FRF) of the transmitter110and the RF beamforming matrix (WuRF) of the receiver120using a combination of (Ωsel=Ωsel∪{(u*,d*,n*,m*)}) of the scheduled RF beam (n*). In this case, a delay component (d*) may be compensated in the receiver120. Thereafter, the transmitter110may return toFIG. 5.

According to one embodiment, the transmitter110may select at least any one of the receivers120using the limited channel information based on an algorithm represented like Table 1, and may schedule a RF beam for at least one stream in the selected receiver120.

In this case, the set Ωsel(a)may indicate a set of only a-th elements in each tuple belonging to the set Ωsel. The set Ωsel(a,b)may indicate a set of index pairs of only an a-th element and a b-th element in each tuple belonging to the set Ωsel.

Referring back toFIG. 5, at operation530, the transmitter110may perform baseband beamforming based on the RF beam. In this case, the transmitter110may design the baseband beamforming matrix (FBB) of the transmitter110. Specifically, the transmitter110may design the baseband beamforming matrix (FBB) of the transmitter110using the RF beamforming matrix (FRF) of the transmitter110and the RF beamforming matrix (WuRF) of the receiver120. Furthermore, the transmitter110may allocate power to the RF beamforming matrix (FRF) and baseband beamforming matrix (FBB) of the transmitter110.

FIG. 8is a diagram illustrating a baseband beamforming and power allocation operation ofFIG. 5.

Referring toFIG. 8, at operation810, the transmitter110may design the baseband beamforming matrix (FBB) of the transmitter110using the RF beamforming matrix (FRF) of the transmitter110and the RF beamforming matrix (WuRF) of the receiver120. According to one embodiment, assuming that the receiver120uses only RF beamforming (WuBB=ILu), the transmitter110may design the baseband beamforming matrix (FBB) of the transmitter110like Equation 18 so that a signal to leakage plus noise ratio (SLNR) is maximized.
FBB=[F1BB| . . . |FUBB]  [Equation 18]

In Equation 18, FuBB=[fu,1BB| . . . |fu,LuBB] is a baseband beamforming matrix for a u-th receiver120. Each vector component may be designed like Equation 19.
fu,nBB=cu,n((FRF)HAu,nFRF)−1(FRF)HHu,d*u,nHwu,nRF,u,n[Equation 19]

In Equation 19, wu,nRFis the n-th column vector of WuRF, and the matrix Au,nmay be defined like Equation 20.

In this case, cu,nmay indicate a constant for satisfying ∥FRFfu,nBB∥=1.

At operation820, the transmitter110may allocate power to the RF beamforming matrix (FRF) and baseband beamforming matrix (FBB) of the transmitter110. In this case, the transmitter110may allocate power to the RF beamforming matrix (FRF) and baseband beamforming matrix (FBB) of the transmitter110based on a power allocation algorithm for maximizing a weighted sum rate under the Tx power limit condition of the transmitter110. To this end, for example, Equation 21 may be defined. An algorithm using an iterative water-filling method, such as Equation 22, may be proposed based on Equation 21. Thereafter, the transmitter110may return toFIG. 5.

In Equation 22, λ is a parameter indicative of a water level, and may satisfy a maximum Tx power condition.

According to one embodiment, the transmitter110may perform baseband beamforming and power allocation based on an algorithm represented like Table 2. In this case, the transmitter110may perform baseband beamforming and power allocation using Equation 19 and Equation 22.

Referring back toFIG. 5, at operation540, the transmitter110may transmit a signal to the selected receiver120. The transmitter110may transmit the signal by performing baseband beamforming based on the baseband beamforming matrix (FBB) and performing RF beamforming based on the RF beamforming matrix (FRF).

According to one embodiment, if the receiver120receives a signal using RF beamforming, the transmitter110may provide the receiver120with a codebook index for a RF beam. Furthermore, the transmitter110may transmit a signal to the receiver120using baseband beamforming and RF beamforming. Accordingly, the receiver120may receive the signal using RF beamforming based on the codebook index. According to another embodiment, if the receiver120receives a signal using RF beamforming and baseband beamforming, the transmitter110may provide the receiver120with information on a codebook index for a RF beam and the baseband beamforming matrix of the receiver120. Furthermore, the transmitter110may transmit a signal to the receiver120using baseband beamforming and RF beamforming. Accordingly, the receiver120may receive the signal using RF beamforming based on the codebook index and using baseband beamforming based on the provided information.

According to various embodiments, feedback overhead from the receiver120to the transmitter110in the communication system100can be reduced in such a manner that the receiver120feedbacks limited channel information to the transmitter110. In this case, the limited channel information may be extracted using the spatial characteristic of a channel and may be represented as a virtual beam domain.

According to various embodiments, multiple antennas can be used in the communication system100and hardware complexity and power consumption can be reduced because the transmitter110performs hybrid beamforming using baseband beamforming and RF beamforming together. In this case, spectral efficiency of the communication system100can be improved because each of the transmitter110and the receiver120uses multiple RF chains. According to one embodiment, the receiver120in addition to the transmitter110may use hybrid beamforming. Furthermore, the transmitter110may transmit multiple streams to the receiver120. Furthermore, if the transmitter110performs beamforming to maximize a weighted sum rate, the priority of the receiver120or fairness between the receivers120can be incorporated.

According to various embodiments, by implementing the communication system100into a wideband mmWave beamforming system of a 5G mobile communication system, inter-symbol interference can be controlled even without using a cyclic prefix. Furthermore, a different number of streams can be allocated to each of the plurality of receivers120and a weight for each of the receivers120can be considered because the communication system100uses a wideband mmWave channel.

Accordingly, the communication system100and the operating method thereof according to various embodiments can be implemented based on a hybrid beamforming technology capable of controlling inter-symbol interference of a wideband channel using limited feedback information in the single carrier system100.

The communication system100according to various embodiments may include at least one receiver120including at least one Rx antenna and configured to feedback limited channel information, and a transmitter110including a plurality of Tx antennas and configured to receive the limited channel information, schedule a RF beam for at least one stream in the receiver120using the limited channel information, and perform baseband beamforming based on the RF beam.

According to various embodiments, the receiver120may be configured to extract a beam space channel coefficient for each of delay components of a channel matrix, extract a predetermined number of elements from the beam space channel coefficient, configure the limited channel information using the extracted elements with respect to all the delay components of the channel matrix, and transmit the limited channel information to the transmitter110.

According to various embodiments, the transmitter110may be configured to configure an RF beamforming matrix of the transmitter110and an RF beamforming matrix of the receiver120.

According to various embodiments, the transmitter110may be configured to estimate a beam space channel coefficient for each of the receivers120based on the limited channel information, restore a channel matrix based on the beam space channel coefficient, form a channel coefficient matrix using the beam space channel coefficients of all the receivers120, schedule the RF beam in each of the receivers120based on the channel coefficient matrix, and configure the RF beamforming matrix of the transmitter110and the RF beamforming matrix of the receiver120using a combination of the scheduled RF beams.

According to various embodiments, the transmitter110may be configured to select a delay component, row and column of an element having the largest magnitude in the channel coefficient matrix, select the receiver120based on the selected column and the number of Rx antennas, determine a RF beam for the selected receiver120based on the selected column, the number of Rx antennas and the selected receiver120, and configure a combination of the selected receiver120, the selected delay component, the determined RF beam and the selected row as a combination of the scheduled RF beams.

According to various embodiments, the transmitter110may be configured to convert columns having a value not 0 in the selected row of the channel coefficient matrix into 0 and to convert rows having a value not 0 in the selected column of the channel coefficient matrix into 0.

According to various embodiments, the transmitter110may be configured to design a baseband beamforming matrix of the transmitter110using the RF beamforming matrix of the transmitter110and the RF beamforming matrix of the receiver120and to perform the baseband beamforming based on the baseband beamforming matrix.

According to various embodiments, the transmitter110may be configured to allocate power to the RF beamforming matrix and baseband beamforming matrix of the transmitter110.

According to one embodiment, the transmitter110may be configured to provide a codebook index for the RF beam to the receiver120and to transmit a signal to the receiver120using the baseband beamforming and RF beamforming.

According to one embodiment, the receiver120may be configured to receive the signal using RF beamforming based on the codebook index.

According to another embodiment, the transmitter110may be configured to provide the receiver120with information on a codebook index for the RF beam and a baseband beamforming matrix of the receiver120and to transmit a signal to the receiver120using the baseband beamforming and RF beamforming.

According to another embodiment, the receiver120may be configured to receive the signal using RF beamforming based on the codebook index and using baseband beamforming based on the provided information.

An operating method of the communication system100according to various embodiments may include receiving, by the transmitter110having a plurality of transmit (Tx) antennas, limited channel information from at least one receiver120each having at least one Rx antenna, scheduling, by the transmitter110, a RF beam for at least one stream in the receiver120using the limited channel information, and performing, by the transmitter110, baseband beamforming based on the RF beam.

According to various embodiments, the operating method may further include extracting, by the receiver120, beam space channel coefficients with respect to each of delay components of a channel matrix, extracting, by the receiver120, a predetermined number of elements from the beam space channel coefficients, configuring, by the receiver120, the limited channel information using the extracted elements with respect to all the delay components of the channel matrix, and transmitting, by the receiver120, the limited channel information to the transmitter110.

According to various embodiments, in the scheduling of the RF beam, may configure a radio frequency (RF) beamforming matrix of the transmitter110and an RF beamforming matrix of the receiver120by the transmitter110.

According to various embodiments, the scheduling of the RF beam may include estimating, by the transmitter110, beam space channel coefficients for each of the receivers120based on the limited channel information, restoring, by the transmitter110, a channel matrix based on the beam space channel coefficients, forming, by the transmitter110, a channel coefficient matrix using the beam space channel coefficients of all the receivers120, scheduling, by the transmitter110, the RF beam in each of the receivers120based on the channel coefficient matrix, and configuring, by the transmitter110, the RF beamforming matrix of the transmitter110and the RF beamforming matrix of the receiver120using a combination of the scheduled RF beams.

According to various embodiments, the scheduling of the RF beam may include selecting, by the transmitter110, a delay component, row and column of an element having the largest magnitude in the channel coefficient matrix, selecting, by the transmitter110, the receiver120based on the selected column and the number of Rx antennas, determining, by the transmitter110, a RF beam for the selected receiver120based on the selected column, the number of Rx antennas and the selected receiver120, and configuring, by the transmitter110, a combination of the selected receiver120, the selected delay component, the determined RF beam and the selected row as a combination of the scheduled RF beams.

According to various embodiments, the scheduling of the RF beam may further include converting, by the transmitter110, columns having a value not 0 in the selected row of the channel coefficient matrix into 0, and converting, by the transmitter110, rows having a value not 0 in the selected column of the channel coefficient matrix into 0.

According to various embodiments, the performing of the baseband beamforming may include designing, by the transmitter110, a baseband beamforming matrix of the transmitter110using the RF beamforming matrix of the transmitter110and the RF beamforming matrix of the receiver120and performing, by the transmitter110, the baseband beamforming based on the baseband beamforming matrix.

According to various embodiments, the performing of the baseband beamforming may further include allocating, by the transmitter110, power to the RF beamforming matrix and baseband beamforming matrix of the transmitter110.

According to various embodiments, the operating method may further include providing, by the transmitter110, a codebook index for the RF beam to the receiver120, transmitting, by the transmitter110, a signal to the receiver120using the baseband beamforming and RF beamforming, and receiving, by the receiver120, the signal using RF beamforming based on the codebook index.

According to various embodiments, the operating method may further include providing, by the transmitter110, the receiver120with information on a codebook index for the RF beam and a baseband beamforming matrix of the receiver120, transmitting, by the transmitter110, a signal to the receiver120using the baseband beamforming and RF beamforming, and receiving, by the receiver120, the signal using RF beamforming based on the codebook index and using baseband beamforming based on the provided information.

The embodiments of this document and the terms used in the embodiments are not intended to limit the technology described in this document to a specific embodiment, but should be construed as including various changes, equivalents and/or alternatives of a corresponding embodiment. Regarding the description of the drawings, similar reference numerals may be used in similar elements. An expression of the singular number may include an expression of the plural number unless clearly defined otherwise in the context. In this document, an expression, such as “A or B”, “at least one of A or/and B”, “A, B or C” or “at least one of A, B and/or C”, may include all of possible combinations of listed items together. Expressions, such as “a first,” “a second,” “the first” and “the second”, may modify corresponding elements regardless of the sequence and/or importance, and are used to only distinguish one element from the other element and do not limit corresponding elements. When it is described that one (e.g., first) element is “(operatively or communicatively) connected to” or “coupled with” the other (e.g., second) element, one element may be directly connected to the other element or may be connected to the other element through another element (e.g., third element).

The “module” used in this document includes a unit configured with hardware, software or firmware, and may be interchangeably used with a term, such as logic, a logical block, a part or a circuit. The module may be an integrated part, a minimum unit to perform one or more functions, or a part thereof. For example, the module may be configured with an application-specific integrated circuit (ASIC).

Various embodiments of this document may be implemented in the form of software including one or more instructions stored in a storage medium readable by a machine (e.g., the transmitter110, the receiver120). For example, the processor of the machine may fetch at least one of one or more stored instructions from a storage medium, and may execute the one or more instructions. This enables the machine to perform at least one function based on the fetched at least one instruction. The one or more instructions may include code generated by a complier or code executable by an interpreter. The storage medium readable by the machine may be provided in the form of a non-transitory storage medium. In this case, ‘non-transitory’ means that a storage medium is a tangible device and does not include a signal (e.g., electromagnetic waves). The term is not used regardless of whether data is semi-persistently stored in a storage medium and whether data is temporally stored in a storage medium.

According to various embodiments, each (e.g., module or program) of the described elements may include a single entity or a plurality of entities. According to various embodiments, one or more of the aforementioned elements or operations may be omitted or one or more other elements or operations may be added. Alternatively or additionally, a plurality of elements (e.g., modules or programs) may be integrated into one element. In such a case, the integrated elements may perform one or more functions of each of a plurality of elements identically with or similar to that performed by a corresponding one of the plurality of elements before the elements are integrated. According to various embodiments, module, operations performed by a program or other elements may be executed sequentially, in parallel, repeatedly, or heuristically, or one or more of the operations may be executed in different order or may be omitted, or one or more other operations may be added.

According to various embodiments, feedback overhead from a receiver to a transmitter in a communication system can be reduced because the receiver feedbacks limited channel information to the transmitter.

According to various embodiments, multiple antennas can be used in a communication system and hardware complexity and power consumption can be reduced because a transmitter performs hybrid beamforming using baseband beamforming and RF beamforming together.

According to various embodiments, inter-symbol interference can be controlled even without a cyclic prefix because a communication system is implemented as a wideband mmWave beamforming system of a 5G mobile communication system.

Accordingly, the communication system and operating method thereof according to various embodiments can be implemented based on a hybrid beamforming technology capable of controlling inter-symbol interference of a wideband channel using limited feedback information in a single carrier system.