KR20120082315A

KR20120082315A - Methods for transmitting and receiving channel state information and apparatus for performing the same

Info

Publication number: KR20120082315A
Application number: KR1020110031366A
Authority: KR
Inventors: 좌혜경
Original assignee: 한국전자통신연구원
Priority date: 2011-01-13
Filing date: 2011-04-05
Publication date: 2012-07-23

Abstract

PURPOSE: A method for transmitting and receiving channel state information and an apparatus for performing the same are provided to efficiently performing a channel adaptive transmission considering an actual beam forming gain and an interference removing gain. CONSTITUTION: A resource demapping unit(330) extracts one of data, a terminal specific reference signal, or a cell specific reference signal from an OFDM(Orthogonal Frequency Division Multiplexing) demodulated signal. A channel estimation unit(340) estimates downlink channel based on one of the terminal specific reference signal or the cell specific reference signal. A CSI(Channel State Information) producer(370) calculates a cell specific CQI(Channel Quality Indicator), a terminal specific CQI, or a switched beam selection information.

Description

METHODS FOR TRANSMITTING AND RECEIVING CHANNEL STATE INFORMATION AND APPARATUS FOR PERFORMING THE SAME}

The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for transmitting and receiving channel state information of a wireless communication system.

Multiple input multiple output (MIMO) technology for increasing the capacity of a system in a wireless communication system has been developed in various forms by incorporating a communication system using Orthogonal Frequency Division Multiple Access (OFDMA) technology.

MIMO is a technology for transmitting signals using a plurality of transmit and / or receive antennas. MIMO can be broadly classified into transmit diversity, spatial multiplexing, and beamforming. These are all reflected in the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE). In addition, a closed loop MIMO technique using channel state information has been applied to further improve the capacity of a wireless communication system.

When the wireless communication system operates in the beamforming mode, the base station is usually equipped with an array antenna having a distance of 0.5λ (where λ means wavelength) between antennas, and a beamforming weight vector is added to the data and reference signals. Apply and transmit to the terminal. In the beamforming mode, beamforming gain can be basically obtained, and in the dual layer beamforming mode reflected in LTE Release-9, interference by signals of other terminals allocated to the same frequency and time resources can be reduced.

The beamforming weight vector may be calculated by using eigen decomposion of a channel covariance matrix and using an array response vector, and the above methods may be performed when the base channel state information is known to the base station. Only the beamforming weight vector can be calculated.

In general, in a wireless communication system using a frequency division duplex (FDD) scheme, since the frequency bands of the uplink and the downlink are different, the base station can receive the downlink channel state information from the user equipment. Meanwhile, in a wireless communication system using a time division duplex (TDD) scheme, since uplink and downlink frequency bands are the same, the uplink and downlink channel conditions are assumed to be the same, and the uplink measurement reference signal (Sounding Reference) After predicting the channel state of the downlink through a signal, etc., the beamforming weight vector is calculated using the predicted channel state information, but there is a problem that the channel state may be different depending on whether the antenna is calibrated.

Channel state information in downlink transmission mode 7, which is a beamforming mode of the current LTE Release-8, exists only as a channel quality indicator (CQI), and does not include information for obtaining a beamforming weight vector. In this case, since the CQI is calculated using a cell-specific reference signal on the assumption that the transmission mode is the transmission diversity mode, the base station should perform channel adaptive transmission by estimating the beamforming gain.

In addition, in downlink transmission mode 8, which is a dual layer beamforming mode reflected in LTE Release-9, only a CQI may be transmitted according to a setting of a higher layer, and a CQI and a precoding matrix index (PMI) are transmitted. Are separated. In the mode of transmitting only CQI, the CQI is fed back in the same manner as the downlink transmission mode 7 of Release-8, and includes the above disadvantage. On the other hand, in the mode of transmitting CQI and PMI, the PMI having the best signal-to-noise ratio (SNR) among the precoding matrices defined in 3GPP TS 36.211 is selected, and the CQI when the selected PMI is applied is selected. Because the feedback is calculated and the actual beamforming gain is not reflected.

SUMMARY OF THE INVENTION An object of the present invention for overcoming the above disadvantages is to provide a channel state information transmitting / receiving apparatus capable of obtaining information necessary for transmitting data in a beamforming mode and efficiently performing channel adaptive transmission. will be.

Another object of the present invention is to provide a method for transmitting and receiving channel state information of the apparatus for transmitting and receiving channel state information.

Technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

In accordance with an aspect of the present invention, an apparatus for transmitting channel state information includes an OFDM demodulator for performing OFDM demodulation on a received signal, data from an OFDM demodulated signal, a terminal specific reference signal, and the like. A resource demapping unit for extracting at least one of a cell specific reference signal, a channel estimator for estimating a downlink channel based on at least one of the terminal specific reference signal and a cell specific reference signal, and estimated channel information of the estimated downlink And a channel state information calculator configured to calculate at least one of a cell-specific channel quality indicator (CQI), a terminal-specific CQI, and switched beam selection information.

Here, the channel estimator provides a terminal specific channel estimation result of estimating a downlink channel based on the terminal specific reference signal to the channel estimator and a downlink based on the cell specific reference signal. And a cell specific channel estimator for providing a cell specific channel estimation result of estimating a channel of the channel estimator.

In this case, when the CQI calculation point is reached, the channel state information calculator calculates the signal-to-noise ratio of the received signal using the cell-specific channel estimation result, and converts the calculated signal-to-noise ratio into CQI bits having a predetermined number of bits. The CQI can be calculated.

When the CQI calculation point is reached, the channel state information calculator calculates a signal-to-noise ratio of a received signal using the terminal-specific channel estimation result, and converts the calculated signal-to-noise ratio into CQI bits having a predetermined number of bits to identify the terminal. The CQI can be calculated.

The channel state information calculator may select one switched beam from among a plurality of predetermined switched beams and generate selected switched beam index information (SBI) when it is time to calculate a precoding matrix index (PMI). Can be.

Here, the channel state information calculation unit configures a covariance matrix using the cell-specific channel estimation result, and then eigen resolves to select an eigenvector having the largest eigenvalue, and then correlates most with the selected eigenvector among a plurality of switched beams. It is possible to choose a switched beam with a high degree of intensity.

Here, the channel state information calculator calculates a signal-to-noise ratio of the received signal by multiplying the cell-specific channel estimation result by a vector of each of the plurality of switched beams, and then selects the switched beam having the largest signal-to-noise ratio.

In addition, the apparatus for receiving channel state information according to an aspect of the present invention for achieving the object of the present invention is based on each terminal based on at least one of cell-specific CQI, terminal-specific CQI and switched beam selection information transmitted from a plurality of terminals, respectively. A scheduler for determining a code rate and a modulation scheme, a location of a subcarrier to insert a terminal specific reference signal, a beamforming weight vector of each terminal, and a channel for channel encoding the bit stream according to the determined code rate A coding unit, a modulation unit for modulating channel-coded data according to the determined modulation scheme, a resource mapping unit and a resource mapping unit for inserting a terminal specific reference signal of each of at least one terminal according to the position of the determined subcarrier The signal is divided into signals for each antenna by applying the beamforming weight vector of each terminal to the signal. And it includes a beam formation of assigning a specific signal based on the signal separated by each cell antenna.

Here, when only the cell specific CQI and the switched beam selection information are transmitted from a specific terminal, the scheduler may determine a modulation scheme and a code rate in consideration of the beamforming gain through the beamforming weight vector and the cell specific CQI.

Here, when the cell-specific CQI, the UE-specific CQI, and the switched beam selection information are transmitted from a specific UE, the scheduler may determine a modulation scheme and a code rate in consideration of beamforming gain and interference cancellation gain.

Here, the scheduler considers the switched beam selection information transmitted from a plurality of terminals when the apparatus for receiving the channel state information operates in the dual layer beamforming mode in the downlink transmission mode and in the multi-user MIMO (MU-MIMO). To select a transmission target terminal.

Here, the scheduler is a beamforming weight vector of a vector represented by a switched beam index (SBI), which is the switched beam selection information transmitted from each of the plurality of terminals, or a precoding vector having the highest correlation with a vector represented by the switched beam index. Can be determined.

In addition, the channel state information transmission and reception method according to an aspect of the present invention for achieving another object of the present invention, the channel state information transmission apparatus of the cell-specific reference signal and the terminal-specific reference signal extracted from the received signal when the CQI calculation point Estimating a downlink channel by extracting at least one; calculating, by the apparatus for transmitting channel state information, at least one of a cell specific CQI and a terminal specific CQI based on a channel estimation result; Selects a predetermined switched beam from among a plurality of predetermined switched beams and the channel state information transmitting apparatus receives at least one of the cell specific CQI, the terminal specific CQI, and the switched beam selection information when the PMI is calculated. Transmitting to the device.

In the estimating of the downlink channel, when the downlink transmission mode is the beamforming mode, the UE-specific reference signal is transmitted in a frequency axis direction of a resource block (RB) region in which PDSCH resources of a downlink subframe are allocated. Extracting every four subcarriers, and when the downlink transmission mode is a dual-layer beamforming mode, the UE-specific reference signal is divided into five subcarriers in the frequency axis direction of a resource block (RB) region in which PDSCH resources of a downlink subframe are allocated. And extracting a downlink channel based on the extracted UE specific reference signal.

The calculating of at least one of the cell-specific CQI and the UE-specific CQI may include: calculating a signal-to-noise ratio of a received signal by using a channel estimation result estimated using the cell-specific reference signal when the CQI calculation time is reached; And calculating the cell-specific CQI by converting the calculated signal-to-noise ratio into CQI bits having a predetermined number of bits.

The calculating of at least one of the cell-specific CQI and the UE-specific CQI may include calculating a signal-to-noise ratio of a received signal using a channel estimation result estimated using the terminal-specific reference signal when the CQI calculation time is reached; And calculating the terminal specific CQI by converting the calculated signal to noise ratio into CQI bits having a predetermined number of bits.

In the selecting of the switched beams among the plurality of switched beams, a covariance matrix is formed by using a cell-specific channel estimation result estimated by using the cell-specific reference signal, and then eigen-decomposed to obtain the eigenvalue. After selecting a large eigenvector, a switched beam having the highest correlation with the selected eigenvector among a plurality of switched beams may be selected.

In the selecting of the switched beams among the plurality of switched beams, a signal-to-noise ratio of the received signal is calculated by multiplying a cell-specific channel estimation result estimated using the cell-specific reference signal and a vector of each of the plurality of switched beams. Then, the switched beam with the largest signal-to-noise ratio can be selected.

The channel state information transmitting / receiving method may include a code rate, a modulation scheme, and a terminal, based on at least one of the cell-specific CQI, the terminal-specific CQI, and the switched beam selection information transmitted from the channel state information transmitting apparatus. The method may further include a scheduling step of determining at least one of a position of a subcarrier and a beamforming weight vector to insert a specific reference signal.

Here, the scheduling may include a vector represented by a switched beam index (SBI), which is the switched beam selection information transmitted from each of the plurality of channel state information transmitting apparatuses, or a precoding vector having the highest correlation with a vector represented by the switched beam index. It may be determined by the beamforming weight vector.

According to the method and apparatus for transmitting and receiving channel state information as described above, the terminal operating in the beamforming mode has the best signal-to-noise ratio among the predetermined number of switched beams using a cell-specific reference signal, or inherent decomposition of the channel covariance matrix. After selecting the switched beam having the most correlation with the information of the selected switched beam is transmitted to the base station. In addition, the UE transmits the UE-specific CQI calculated based on the assumption that the downlink transmission mode is the diversity transmission mode and the cell-specific CQI calculated using the cell-specific reference signal and / or the beamforming transmission mode to the base station.

The base station determines the beamforming weight vector based on the switched beam selection information transmitted from the terminal, the cell specific CQI, and the terminal specific CQI information, and determines a code rate and a modulation method.

Accordingly, channel adaptive transmission can be efficiently performed in consideration of the actually reflected beamforming gain and interference cancellation gain, and beamforming mode transmission can be efficiently performed. In addition, the switched beam selection information transmitted from the terminal has an advantage that can be utilized as the location information of the terminal.

1 and 2 illustrate a downlink subframe structure applied to a method for transmitting and receiving channel state information according to an embodiment of the present invention.
3 is a block diagram illustrating a configuration of an apparatus for transmitting channel state information according to an embodiment of the present invention.
4 is a flowchart illustrating a method of calculating channel state information according to an embodiment of the present invention.
FIG. 5 is a conceptual diagram illustrating a process of selecting a switched beam in the process of calculating channel state information shown in FIG. 4.
6 is a block diagram illustrating a configuration of an apparatus for receiving channel state information according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be interpreted in an ideal or overly formal sense unless explicitly defined in the present application Do not.

The term "terminal" used in the present application is a mobile station (MS), a mobile terminal (MT), a user terminal, a user equipment (UE), a user terminal (UT: User Terminal), a wireless terminal, Access Terminal (AT), Subscriber Unit, Subscriber Station (SS), Wireless Device, Wireless Communication Device, Wireless Transmit / Receive Unit (WTRU), Mobile Node, Mobile Or other terms.

In addition, the 'base station' used in the present application generally refers to a fixed point for communicating with a terminal, and includes a base station, a Node-B, an eNode-B, and a BTS. It may be called other terms such as (Base Transceiver System), Access Point.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, the same reference numerals are used for the same components in the drawings, and duplicate descriptions of the same components are omitted.

1 and 2 illustrate a downlink subframe structure applied to a method for transmitting and receiving channel state information according to an embodiment of the present invention, and FIG. 1 is applied to downlink transmission mode 7 (beamforming mode) of a 3GPP LTE system. 2 shows a subframe structure applied to downlink transmission mode 8 (dual layer beamforming mode) of the 3GPP LTE system.

First, referring to FIG. 1, a system bandwidth of a downlink subframe includes 6 resource blocks (RBs), and one resource block includes 12 subcarriers. Here, one resource block may have a bandwidth of 180 kHZ in the LTE system. The system bandwidth may consist of up to 110 resource blocks, in which case the bandwidth is 20 MHz. In addition, when a normal CP (normal cyclic prefix) is applied, one subframe includes 14 OFDM symbols in the time axis direction.

When a maximum number of transmitting antennas is considered as four, a cell specific reference signal is allocated for every six subcarriers in the frequency axis direction of the downlink subframe.

The UE specific reference signal is allocated only to a resource block region to which a Physical Downlink Shared Channel (PDSCH) resource is allocated, and one UE is allocated to every four subcarriers in the frequency axis direction as shown in FIG. 1.

Referring to FIG. 2, in the dual layer beamforming mode of downlink transmission mode 8, the cell-specific reference signal is allocated as shown in FIG. 1.

One UE-specific reference signal is allocated for every five subcarriers in the frequency axis direction, and two UE-specific reference signals are allocated adjacent to each other in the time axis direction in an orthogonal code division scheme, thereby allowing data to be transmitted to two terminals using the same frequency and time resources. A multi-user MIMO scheme may be used for transmission, or a single user MIMO scheme may be used for transmitting two data streams to one UE.

3 is a block diagram illustrating a configuration of an apparatus for transmitting channel state information according to an embodiment of the present invention, wherein the apparatus for transmitting channel state information may be a terminal having a plurality of antennas.

Referring to FIG. 3, an apparatus for transmitting channel state information (hereinafter, referred to as a terminal) includes an RF receiver 310, an OFDM demodulator 320, a resource demapping unit 330, a channel estimator 340, and a decoding. A grandfather 350, a decoder 360 and a channel state information calculator 370 may be included.

The RF receiver 310 samples the signals received through the plurality of antennas and converts the received signals into basebands. For this purpose, the RF receiver 310 may include the same number of RF receivers as the number of antennas P, and each RF receiver converts an RF signal received through a corresponding antenna connected to the baseband signal into a baseband signal. Provided to the OFDM demodulator.

The OFDM demodulator 320 may include the same number of OFDM demodulators as the number of antennas and the number of RF receivers 310, and each OFDM demodulator performs OFDM demodulation on a baseband signal provided from the corresponding RF receiver 310. Perform

The resource demapping unit 330 receives the OFDM demodulated signal from the OFDM demodulation unit 320 and extracts data, the UE specific reference signal, and the cell specific reference signal from the corresponding subcarrier positions of the OFDM demodulated signal. Here, when the downlink transmission mode is the beamforming mode, the resource demapping unit 330 may extract the UE-specific reference signal allocated for every four subcarriers in the frequency axis direction of the downlink subframe as shown in FIG. 1. If the downlink transmission mode is the dual layer beamforming mode, as shown in FIG. 2, the corresponding UE is identified from among UE-specific signals allocated adjacent to each other in the time axis direction for every five subcarriers in the frequency axis direction of the downlink subframe. The reference signal can be extracted.

The channel estimator 340 is configured to estimate a channel between the base station and the terminal based on the terminal specific reference signal provided from the resource demapping unit 330, and the cell provided from the resource demapping unit 330. And a cell specific channel estimator 343 for estimating a channel between the base station and the terminal based on the specific reference signal.

The demodulator 350 demodulates the data provided from the resource demapping unit 330 using the channel estimation information estimated by the terminal specific channel estimator 341.

The decoder 360 decodes the demodulated data provided from the demodulator 350 to restore the data.

The channel state information calculator 370 calculates channel state information based on the terminal specific channel estimation information and the cell specific channel estimation information provided from the terminal specific channel estimating unit 341. The calculated channel state information is fed back to the base station. The channel state information may include a cell specific CQI calculated based on cell specific channel estimation information, a terminal specific CQI calculated based on terminal specific channel estimation information, and switched beam information selected from a plurality of switched beams. have.

In detail, the channel state information calculator 370 calculates a signal-to-noise ratio (SNR) of the received signal using the channel estimation result provided from the cell-specific channel estimator 343, and then calculates the calculated signal-to-noise ratio. Convert to CQI (cell specific CQI) having a predetermined number of bits.

In addition, the channel state information calculator 370 calculates the signal-to-noise ratio of the received signal using the channel estimation result provided from the terminal-specific channel estimator 333 and converts the calculated signal-to-noise ratio into a CQI (terminal specific CQI). .

In addition, the channel state information calculator 370 selects any one of a predetermined number of switched beams and generates the selected switched beam index (SBI). Here, the switched beam information is fed back to the base station.

4 is a flowchart illustrating a method of calculating channel state information according to an embodiment of the present invention, and the channel state information performed by the channel state information calculator 370 of the apparatus (or terminal) of the channel state information transmitter shown in FIG. 3. The calculation process is shown in detail. 5 is a conceptual diagram illustrating a process of selecting a switched beam in the process of calculating channel state information shown in FIG. 4.

4 and 5, the terminal first determines whether it is time to calculate the CQI (step 410). Here, the CQI calculation time point may be determined corresponding to the CQI reporting method, and the CQI reporting method may be performed periodically or aperiodically according to the decision of the base station. For example, when CQI reporting is performed periodically and the FDD scheme is used, the CQI reporting period may be any one of 2, 5, 10, 20, 32, 40, 64, 80, 128, and 160 ms.

If it is determined in step 410 that it is time to calculate the CQI, the UE calculates the signal-to-noise ratio (SNR) of the received signal using the channel estimation result estimated based on the cell-specific reference signal (step 421), and the calculated signal-to-noise ratio Is converted into a CQI having a predetermined number of bits (step 423). Here, the UE may assume the downlink transmission mode as the transmit diversity mode and calculate a signal-to-noise ratio of the received signal, and the number of CQI bits may be configured as 4 bits, for example. Hereinafter, a CQI obtained based on a cell specific reference signal is referred to as a cell specific CQI.

In addition, the terminal calculates the signal-to-noise ratio of the received signal using the channel estimation result including the beamforming weight vector estimated based on the terminal-specific reference signal (step 431), and converts the calculated signal-to-noise ratio to the CQI ( Step 433). Here, the terminal may calculate the signal-to-noise ratio of the received signal assuming the downlink transmission mode as the beamforming transmission mode. Hereinafter, as described above, the CQI obtained based on the UE-specific reference signal is called a UE-specific CQI.

Thereafter, the terminal transmits the cell-specific CQI and / or the terminal-specific CQI obtained through steps 423 and 433 to the base station (step 440).

In FIG. 4, for example, steps 421 and 423, and steps 431 and 433 are performed at the same time, but steps 421 and 423 may be performed before steps 431 and 433, and steps 431 and 433 may be performed. It may be performed before step 421 and step 423.

The difference between the cell specific CQI and the terminal specific CQI becomes a beamforming gain.

In addition, the terminal determines whether it is time to calculate the PMI (step 450). Here, the PMI calculation time point may be determined corresponding to the PMI reporting method, and the PMI reporting method may be performed periodically or aperiodically according to the determination of the base station.

According to an embodiment of the present invention, when the terminal operates in downlink transmission mode 7 or 8, when it is time to calculate the PMI, one of a predetermined number of switched beams is selected without calculating the PMI. (Step 460), the selected Switched Beam Index (SBI) information is transmitted to the base station (step 470).

For example, when there are eight array antennas of a base station, as shown in FIG. 5, the spaced at -60 to 60 degrees may be divided into 12 spaces and configured as a switched beam. Here, the number of switched beams may be configured according to the number of PMI bits. For example, when the PMI is configured with 4 bits, the switched beams may be configured with 16 bits. At this time, the vector representing the switched beam becomes an array response vector in each direction.

If the number of array antennas of the base station is P, the spacing between the antennas is d λ, and the B switched beams are configured between −60 and 60 degrees, a vector representing each switched beam is expressed by Equation 1 below. Can be represented.

In Equation 1, i denotes an index of the switched beam, and θ _i denotes a phase of the i-th switched beam.

The following two methods can be used to select a switched beam that can best represent spatial information of the UE among the B switched beams.

That is, the covariance matrix of the channel is configured through the cell-specific channel estimation result (step 461), and then eigen decomposition to select the eigenvector having the largest eigenvalue (step 462). Then, the correlation between the selected eigenvectors and each of the B switched beams is calculated to select the switched beam having the highest correlation (step 463).

Alternatively, the signal-to-noise ratio of the received signal is calculated by multiplying the cell-specific channel estimation result by the vector of each switched beam (step 466), and then the switched beam having the largest signal-to-noise ratio of the received signal is selected (step 467). Hereinafter, the index of the switched beam selected through one of the two methods described above is referred to as a switched beam index (SBI).

The terminal feeds back at least one of the cell specific CQI, the terminal specific CQI, and the SBI calculated as described above to the base station, and the scheduler of the base station uses the information fed back according to the downlink transmission mode.

In FIG. 4, for example, steps 410 to 440, which are processes for acquiring a cell specific CQI and a terminal specific CQI, are performed first, and then steps 450 to 470, which are processes for obtaining switched beam index information, are illustrated. According to another embodiment of the present invention, steps 450 to 470 which are the processes of obtaining the switched beam index information may be performed first, and then steps 410 to 440 which are the processes of obtaining the cell specific CQI and the UE specific CQI may be performed.

6 is a block diagram illustrating a configuration of a channel state information receiving apparatus according to an embodiment of the present invention, wherein the channel state information receiving apparatus performs beamforming and channel adaptive transmission based on channel state information fed back from a plurality of terminals. It may be a base station to perform.

In addition, the apparatus for receiving channel state information shown in FIG. 6 includes a plurality of antennas, and operates in a dual layer beamforming mode of downlink transmission mode 8 of the LTE system, thereby providing two different terminals (that is, a first terminal and a first terminal). For example, a case in which different data streams are transmitted to two terminals) is illustrated.

Referring to FIG. 6, the apparatus for receiving channel state information (hereinafter, referred to as a “base station”) includes a scheduler 610, an encoder 620, a modulator 630, a resource mapper 640, and a beamformer 650. ), An OFDM modulator 660, and an RF transmitter 670.

The scheduler 610 transmits data to each terminal 300a or 300b based on at least one of cell-specific CQI, terminal-specific CQI, and SBI, which are information fed back from the first terminal 300a and the second terminal 300b. A channel code rate and modulation scheme for channel adaptive transmission of a stream are determined. Here, when only the cell-specific CQI and the SBI are transmitted from the specific UE and the UE-specific CQI is not transmitted, the scheduler 610 determines the modulation scheme and the code rate by considering only the beamforming gain through the beamforming weight vector and the cell-specific CQI. When all cell-specific CQIs, SBIs, and UE-specific CQIs are transmitted from the UE, the modulation scheme and the code rate may be determined in consideration of the interference cancellation gain obtained in addition to the beamforming gain.

In addition, the scheduler 610 determines a position of a subcarrier to map a modulated signal and a subcarrier position to insert a terminal specific reference signal, and is based on information fed back from the first terminal 300a and the second terminal 300b, respectively. The beamforming weight vector of each terminal 300a or 300b is determined. Here, the scheduler 610 may determine a vector representing the switched beam as a beamforming weight vector using the SBI transmitted from each terminal, and beam the precoding vector having the most correlation with the vector representing the switched beam. It may be determined by the formation weight vector.

In addition, when the downlink transmission mode operates in the dual layer beamforming mode and uses the multi-user MIMO (MU-MIMO) mode, the scheduler 110 allocates a plurality of terminals for transmitting signals at the same subcarrier and time. Considering the SBI transmitted from the terminal of the two terminals with the largest difference of the SBI can be allocated to the signal transmission target.

The encoder 620 may include a first channel encoder 621 for encoding a data stream to be transmitted to the first terminal 300a and a second channel encoder 623 for encoding a data stream to be transmitted to the second terminal 300b. The first channel encoder 621 and the second channel encoder 623 may perform channel encoding according to a code rate determined by the scheduler 610.

The modulator 630 may include a first modulator 631 and a second modulator 633. The first modulator 631 and the second modulator 633 modulate the encoded data provided from the first channel encoder 621 and the second channel encoder 623 according to the modulation scheme determined by the scheduler 610. Here, the first modulator 631 and the second modulator 633 may perform quadratura amplitude modulation (QAM) modulation.

The resource mapping unit 640 may include a first resource mapper 641 and a second resource mapper 643. The first resource mapper 641 maps the modulated signal provided from the first modulator 631 according to the subcarrier position determined by the scheduler 610 and inserts the UE-specific reference signal 1 (UE-RS1). The second resource mapper 643 also maps the modulated signal provided from the second modulator 633 according to the subcarrier position determined by the scheduler 610 and inserts the UE-specific reference signal 2 (UE-RS2).

Here, the UE-specific reference signal 1 (UE-RS1) and the UE-specific reference signal 2 (UE-RS2) may be allocated to one of every five subcarriers in the frequency axis direction of the downlink subframe, as shown in FIG. In the orthogonal code division scheme, the two terminal specific reference signals may be allocated adjacent to each other in the time axis direction.

The beamformer 650 may include a first beamformer 651 and a second beamformer 653. The first beamformer 651 multiplies a signal mapped through the first resource mapper 641 by a beamforming weight vector of the first terminal 300a determined by the scheduler 610 and separates the signal into antenna signals. In addition, the second beamformer 653 separates the signal mapped through the second resource mapper 643 into a signal for each antenna by multiplying the beamforming weight vector of the second terminal 300b determined by the scheduler 610.

In addition, the beamformer 650 inserts the cell-specific reference signals P ₁ , P ₂ ,..., P _TX into the signals separated for each antenna as described above. 1 and 2, the cell specific reference signal may be allocated to each of six subcarriers in the frequency axis direction of the downlink subframe and may be allocated to each antenna.

The OFDM modulator 660 may include the same number of OFDM modulators as the number of antennas, and each OFDM modulator performs OFDM modulation on a signal provided from a corresponding beamformer.

The RF transmitter 670 may be configured with the same number of RF transmitters as the number of antennas. Each RF transmitter converts a signal provided from a corresponding OFDM modulator into an analog signal, and then amplifies and converts the signal into an RF band signal. Transmit through the antenna.

Although described with reference to the embodiments above, those skilled in the art will understand that the present invention can be variously modified and changed without departing from the spirit and scope of the invention as set forth in the claims below. Could be.

310: RF receiver 320: OFDM demodulator
330 resource demapping unit 340 channel estimation unit
350: demodulator 360: decoder
370: channel state information calculator 610: scheduler
620: encoder 630: modulator
640: resource mapping unit 650: beam forming unit
660: OFDM modulator 670: RF transmitter

Claims

An OFDM demodulator for performing OFDM demodulation on the received signal;
A resource demapping unit configured to extract at least one of data, a terminal specific reference signal, and a cell specific reference signal from the OFDM demodulated signal;
A channel estimator estimating a downlink channel based on at least one of the terminal specific reference signal and a cell specific reference signal; And
And a channel state information calculation unit for calculating at least one of a cell specific channel quality indicator (CQI), a terminal specific CQI, and switched beam selection information based on the estimated downlink channel information.

The method of claim 1, wherein the channel estimator
A terminal specific channel estimator configured to provide a terminal specific channel estimation result of estimating a downlink channel based on the terminal specific reference signal to the channel estimator; And
And a cell specific channel estimator for providing a cell specific channel estimation result of estimating a downlink channel based on the cell specific reference signal to the channel estimator.

3. The apparatus of claim 2, wherein the channel state information calculator
When the CQI is calculated, the signal-to-noise ratio of the received signal is calculated using the cell-specific channel estimation result, and the cell-specific CQI is calculated by converting the calculated signal-to-noise ratio into CQI bits having a predetermined number of bits. Channel status information transmission device.

3. The apparatus of claim 2, wherein the channel state information calculator
When the CQI is calculated, the signal-to-noise ratio of the received signal is calculated using the UE-specific channel estimation result, and the UE-specific CQI is calculated by converting the calculated signal-to-noise ratio into CQI bits having a predetermined number of bits. Channel status information transmission device.

3. The apparatus of claim 2, wherein the channel state information calculator
When the PMI (Precoding Matrix Index) calculation point is reached, the channel state information transmission comprises selecting any one of a plurality of predetermined switched beams and generating selected switched beam index information (SBI). Device.

The method of claim 5, wherein the channel state information calculation unit
After constructing the covariance matrix using the cell-specific channel estimation result, eigen decomposition is used to select the eigenvector having the largest eigenvalue, and then select the switched beam having the highest correlation with the selected eigenvector among a plurality of switched beams. Channel state information transmission apparatus, characterized in that.

The method of claim 5, wherein the channel state information calculation unit
And multiplying the cell-specific channel estimation result by a vector of each of the plurality of switched beams to calculate a signal-to-noise ratio of the received signal, and then selecting the switched beam having the largest signal-to-noise ratio.

Determine a code rate and a modulation scheme of each terminal based on at least one of cell specific CQI, terminal specific CQI, and switched beam selection information transmitted from a plurality of terminals, and determine a location of a subcarrier to insert the terminal specific reference signal. A scheduler for determining a beamforming weight vector of each terminal;
A channel encoder for channel encoding the bit stream according to the determined code rate;
A modulator for modulating channel-coded data according to the determined modulation scheme;
A resource mapping unit for inserting a terminal specific reference signal of each of at least one terminal according to the determined position of the subcarrier; And
Apparatus for receiving channel state information including a beamforming unit for applying a beamforming weight vector of each terminal to the signal provided from the resource mapping unit, separating the signal into antenna signals, and then assigning a cell-specific reference signal to the signal separated for each antenna. .

The method of claim 8, wherein the scheduler is
When only the cell specific CQI and the switched beam selection information are transmitted from a specific terminal, a modulation scheme and a code rate are determined in consideration of a beamforming gain through a beamforming weight vector and a cell specific CQI, and the cell specific from the specific terminal. And transmitting the CQI, the UE-specific CQI, and the switched beam selection information to determine a modulation scheme and a code rate in consideration of the beamforming gain and the interference cancellation gain.

The method of claim 8, wherein the scheduler is
When the apparatus for receiving channel state information operates in a downlink transmission mode in a dual layer beamforming mode and in a multi-user MIMO (MU-MIMO), the apparatus for receiving a channel state information may be selected in consideration of switched beam selection information transmitted from a plurality of terminals. Channel state information receiving apparatus, characterized in that for selecting.

The method of claim 8, wherein the scheduler is
Determining a beamforming weight vector as a vector represented by a switched beam index (SBI), which is the switched beam selection information transmitted from each of the plurality of terminals, or a precoding vector having a highest correlation with a vector represented by the switched beam index. A channel state information receiving apparatus.

The method of claim 8, wherein the resource mapping unit
When the downlink transmission mode is the beamforming mode, the UE-specific reference signal is inserted every four subcarriers in the frequency axis direction of the resource block (RB) region in which the PDSCH resource of the downlink subframe is allocated. In the dual layer beamforming mode, the UE-specific reference signal of each UE is inserted every five subcarriers in a frequency axis direction of a resource block (RB) region in which PDSCH resources of a downlink subframe are allocated, and the time axis of the downlink subframe Channel state information receiving apparatus, characterized in that inserted in a position adjacent to the direction.

Estimating a downlink channel by extracting at least one of a cell-specific reference signal and a terminal-specific reference signal extracted from the received signal when the apparatus for transmitting channel state information arrives at the CQI calculation time point;
Calculating, by the apparatus for transmitting channel state information, at least one of a cell specific CQI and a terminal specific CQI based on a channel estimation result;
Selecting, by the apparatus for transmitting channel state information, a predetermined switched beam from among a plurality of predetermined switched beams when the PMI calculation point is reached; And
And transmitting, by the apparatus for transmitting channel state information, at least one of the cell specific CQI, the terminal specific CQI, and the switched beam selection information to a channel state information receiving device.

The method of claim 13, wherein estimating the channel of the downlink
When the downlink transmission mode is the beamforming mode, the UE-specific reference signal is extracted every four subcarriers in the frequency axis direction of the RB region to which the PDSCH resource of the downlink subframe is allocated. In the dual layer beamforming mode, extracting the UE-specific reference signal for every five subcarriers in a frequency axis direction of a resource block (RB) region to which PDSCH resources of a downlink subframe are allocated; And
And estimating a downlink channel based on the extracted terminal specific reference signal.

The method of claim 13, wherein the calculating of at least one of the cell specific CQI and the terminal specific CQI comprises:
Calculating a signal-to-noise ratio of the received signal using the channel estimation result estimated using the cell specific reference signal when the CQI calculation time point is reached; And
And converting the calculated signal-to-noise ratio into CQI bits having a predetermined number of bits to calculate the cell specific CQI.

The method of claim 13, wherein the calculating of at least one of the cell specific CQI and the terminal specific CQI comprises:
Calculating a signal-to-noise ratio of the received signal using the channel estimation result estimated using the terminal specific reference signal when the CQI calculation time point arrives; And
And converting the calculated signal-to-noise ratio into CQI bits having a predetermined number of bits to calculate the terminal specific CQI.

The method of claim 13, wherein the step of selecting a predetermined switched beam of the plurality of switched beams,
After constructing a covariance matrix using the cell-specific channel estimation result estimated using the cell-specific reference signal, eigen decomposition is performed to select the eigenvector having the largest eigenvalue, and then selects the eigenvector and the selected one among the plurality of switched beams. A method for transmitting and receiving channel state information comprising selecting a switched beam having high correlation.

The method of claim 13, wherein the step of selecting a predetermined switched beam of the plurality of switched beams,
A channel-specific channel estimation result estimated using the cell-specific reference signal is multiplied by a vector of each of the plurality of switched beams to calculate a signal-to-noise ratio of a received signal, and then the switched channel having the largest signal-to-noise ratio is selected. How to send and receive status information.

The method of claim 13, wherein the channel state information transmission / reception method is as follows.
The position of the subcarrier to insert a code rate, a modulation scheme, and a terminal specific reference signal based on at least one of the cell specific CQI, the terminal specific CQI, and the switched beam selection information transmitted from the channel state information transmitting apparatus. And a scheduling step of determining at least one of the beamforming weight vectors.

20. The method of claim 19, wherein said scheduling step
The beamforming weight vector determines a vector represented by a switched beam index (SBI), which is the switched beam selection information transmitted from each of the plurality of channel state information transmitting apparatuses, or a precoding vector having the highest correlation with a vector represented by the switched beam index. Channel state information transmitting and receiving device, characterized in that.