KR20100066298A - Reference signal transmission method for downlink multiple input multiple output system - Google Patents

Abstract

PURPOSE: A reference signal transmission method for downlink multiple input multiple output system is provided to effectively transmit a reference signal in environment which LTE UE(User Equipment) and LTE-A(LTE-Advanced) UE coexists. CONSTITUTION: A first UE recognizes four transmission antennas among eight transmission antennas. A second UE recognizes the eight transmission antenna. In the base station, one reference signal transmission mode is selected between a plurality of reference signal transmission modes according to rank(S601). In the base station, the reference signal is transmitted according to the selected reference signal transmission mode(S602). The second reference signal transmission mode uses a pre-coded demodulation-common reference signal as the reference signal toward the transmission eight antennas.

Description

RS transmission method in downlink MIO system {REFERENCE SIGNAL TRANSMISSION METHOD FOR DOWNLINK MULTIPLE INPUT MULTIPLE OUTPUT SYSTEM}

The present invention relates to a method for efficiently providing data and a reference signal in an environment where an antenna is added to an existing system in a multiple antenna (MIMO) communication system.

Multiple antennas ( MIMO Definition of technology

MIMO is an abbreviation of Multiple-Input Multiple-Output, and it is a method that can improve the transmit / receive data efficiency by adopting multiple transmit antennas and multiple receive antennas. . That is, a technique of increasing capacity or improving performance by using multiple antennas in a transmitter or receiver in a wireless communication system. MIMO will be referred to herein as multiple antennas.

Multi-antenna technology is an application of a technique of gathering and completing fragmented pieces of data received from multiple antennas without relying on a single antenna path to receive a message. The multi-antenna technology is a next generation mobile communication technology that can be widely used in a mobile communication terminal and a repeater because it can improve the data transmission speed in a specific range or increase the system range for a specific data transmission speed. The technology is attracting attention as a next generation technology capable of overcoming the transmission limitation of mobile communication, which has reached a limit situation due to the expansion of data communication.

MIMO System in modelling

)에 하기의 수학식 1의 레이트 증가율(

)이 곱해진 만큼 증가할 수 있다.1 is a configuration diagram of a general multiple antenna (MIMO) communication system. As shown in FIG. 1, when the number of transmitting antennas is increased to N _{T and the} number of receiving antennas is increased to N _R at the same time, unlike the case where a plurality of antennas are used only in a transmitter or a receiver, the number of antennas is theoretically proportional to the number of antennas. The transmission capacity is increased. Therefore, it is possible to improve the transmission rate and to significantly improve the frequency efficiency. The transmission rate according to the increase in the channel transmission capacity is theoretically the maximum transmission rate when using one antenna (

) Rate increase rate of the following equation (1)

Can be multiplied by

For example, in a MIMO communication system using four transmit antennas and four receive antennas, a transmission rate of four times theoretically can be obtained for a single antenna system. Since the theoretical capacity increase of the multi-antenna system was proved in the mid-90s, various technologies have been actively studied to lead to substantial data rate improvement. Some of these technologies have already been developed for 3G mobile communication and next-generation wireless LAN. Is reflected in the various standards of wireless communication.

The research trends related to multi-antennas to date include information theory aspects related to calculation of multi-antenna communication capacity in various channel environments and multi-access environments, research on wireless channel measurement and model derivation of multi-antenna systems, and improvement of transmission reliability and transmission rate. Active research is being conducted from various viewpoints, such as the study of space-time signal processing technology.

In order to mathematically model the communication method in the antenna system in a more specific manner, it may be represented as follows. As shown in FIG. 1, it is assumed that there are N _T transmit antennas and N _R receive antennas. First, referring to the transmission signal, when there are N _T transmit antennas, since the maximum transmittable information is N _T , the transmission information may be represented by a vector shown in Equation 2 below.

에 있어 전송 전력을 다르게 할 수 있으며, 이때 각각의 전송 전력을

라 하면, 전송 전력이 조정된 전송 정보를 벡터로 나타내면 하기의 수학식 3과 같다.Meanwhile, each transmission information

Can have different transmit powers.

In this case, the transmission information of which transmission power is adjusted is represented by a vector as shown in Equation 3 below.

를 전송 전력의 대각행렬

를 이용하여 나타내면 하기의 수학식 4와 같다.Also,

Diagonal of transmit power

When expressed using the equation (4) below.

에 가중치 행렬

가 적용되어 실제 전송되는 N_T 개의 송신신호(transmitted signal)

가 구성되는 경우를 고려해 보자. 여기서, 가중치 행렬은 전송 정보를 전송 채널 상황 등에 따라 각 안테나에 적절히 분배해 주는 역할을 수행한다. 이와 같은 전송신호

는 벡터

를 이용하여 하기의 수학식 5와 같이 나타낼 수 있다. 여기서

는

번째 송신안테나와

번째 정보 간의 가중치를 의미한다.

는 가중치 행렬(Weight Matrix) 또는 프리코딩 행렬(Precoding Matrix)이라고 불린다.On the other hand, information vector with adjusted transmission power

Weighting matrix

N _T transmitted signals that are actually transmitted by applying

Consider the case where is configured. Here, the weight matrix plays a role of properly distributing transmission information to each antenna according to a transmission channel situation. Such a transmission signal

Vector

It can be expressed as shown in Equation 5 below. here

Is

With the first transmit antenna

It means the weight between the first information.

Is called a weight matrix or a precoding matrix.

을 벡터로 나타내면 하기의 수학식 6과 같다.Receive signal of each antenna when there are N _R receiving antennas

When expressed as a vector is as shown in Equation 6 below.

로부터 수신 안테나

를 거치는 채널을

로 표시하기로 한다. 여기서,

의 인덱스의 순서는 수신 안테나 인덱스가 먼저, 송신안테나의 인덱스가 나중임에 유의한다.Meanwhile, when modeling a channel in a multi-antenna communication system, channels may be classified according to transmit / receive antenna indexes and transmit antennas.

Receiving antenna from

Channel through

It is indicated by. here,

Note that the order of the indices is that the reception antenna index is first, and the transmission antenna index is later.

로의 채널을 도시한 도면이다.These channels can be grouped together and displayed in vector and matrix form. An example of the vector display is described as follows. 2 is a reception antenna in N _T transmit antennas

It is a figure which shows the channel of a furnace.

로 도착 하는 채널은 다음과 같이 표현 가능하다.Receive antennas from a total of N _T transmit antennas as shown in FIG.

A channel arriving at can be expressed as follows.

In addition, when all the channels passing from the N _T transmit antennas to the N _R receive antennas are represented as shown in Equation 7, Equation 8 may be represented.

를 거친 후에 백색잡음(AWGN; Additive White Gaussian Noise)이 더해지게 되므로, N_R개의 수신안테나 각각에 더해지는 백색잡음

을 벡터로 표현하면 하기의 수학식 9와 같다.The actual channel is the same channel matrix as above

After passing through, white noise (AWGN) is added, and thus white noise is added to each of the _R reception antennas.

When expressed as a vector is expressed by the following equation (9).

The received signal obtained using the above equations is shown in Equation 10 below.

reference  signal( Reference Signal ; RS )

When transmitting a packet in a mobile communication system, since the transmitted packet is transmitted through a wireless channel, signal distortion may occur during the transmission process. In order to receive such a distorted signal correctly, the receiver must find out the channel information and correct the distortion of the transmission signal by the channel information in the received signal. In order to find out the information of the channel, it is mainly used to find out the information of the channel with the degree of distortion of the signal when the signal is transmitted from both the transmitting side and the receiving side. A signal known to both the transmitting side and the receiving side is referred to as a pilot signal or a reference signal (hereinafter referred to as RS). RS is classified into four types according to the purpose as shown in Table 1 below.

characteristic CQI-CRS It refers to common RS for channel measurement, and the user equipment (UE) determines channel quality indicator (CQI), precoding matrix index (PMI), and rank indicator (RI) based on this information. Therefore, it is good to distribute evenly over the whole band. DM-CRS It means a common RS for demodulation, but can be used for channel measurement. Since several UEs use the DM-CRS for channel measurement, the precoding scheme of a specific UE cannot be applied to the DM-CRS. Therefore, when a physical downlink shared channel (PDSCH) is precoded, signaling through a physical downlink control channel (PDCCH) is required. NDM-DRS Dedicated RS for demodulation not precoded. PDM-DRS It means a dedicated RS for precoded demodulation, and since the same precoding is applied to the PDM-DRS and PDSCH, signaling is not required for the PDCCH.

In most mobile communication systems, when transmitting and receiving data using multiple antennas, a separate reference signal exists for each transmitting antenna, and a channel signal between each transmitting antenna and the receiving antenna needs to be known for correct signal transmission. Can be received.

On the other hand, Figure 3 is a 3GPP LTE (3 ^rd Generation Project Partnership Long Term Evolution) standard cyclic prefix in; will showing an RS structure (normal Cyclic Prefix normal CP) and 4 extended cyclic prefix in the 3GPP LTE (extended Cyclic Prefix ; shows an RS structure of extended CP). Currently, the 3GPP LTE downlink RS structure is the same as in FIGS. 3 and 4. For one resource block, the horizontal axis represents the time axis and the vertical axis represents the frequency axis. One subframe consists of two slots. 3 corresponds to a case of a standard CP, and each slot includes seven symbols. 4 corresponds to a case of an extended CP, and each slot includes six symbols. The extended CP is generally used in a long delay environment. The number of supported base station transmit antenna ports is 4, and resources used when transmitting RS signals for each antenna port 0-3 are represented by 0, 1, 2, and 3.

Meanwhile, when an LTE UE capable of recognizing only four transmit antennas and an LTE-Advanced (LTE-A) UE capable of recognizing up to eight antennas coexist, an additional four signals in addition to a reference signal for supporting the existing four antennas are present. Transmission of a reference signal to support the antenna is required.

Therefore, when the LTE-A UE that recognizes 8 antennas is added while minimizing the impact on the performance of the existing LTE UE that recognizes only 4 antennas, efficient reference signal transmission and a new codebook precoding matrix are required.

In case of coexistence of LTE UE capable of recognizing existing four transmit antennas and LTE-A UE capable of recognizing up to eight antennas, reference signals for supporting additional four antennas in addition to reference signals for supporting existing four antennas We need a transmission and a precoding matrix of. That is, when an LTE-A UE that recognizes 8 antennas is added while minimizing the impact on the performance of the existing LTE UE that recognizes only 4 antennas, an efficient method of transmitting a reference signal and a new codebook for precoding are required.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and in the downlink MIMO system, a new codebook for an efficient method of transmitting a reference signal and precoding when an LTE UE and an LTE-A UE coexist. To provide.

In order to solve the above problems, a first UE (User Equipment) for recognizing four transmit antennas of the eight transmit antennas provided in the base station according to an aspect of the present invention and a second UE for recognizing the eight transmit antennas In a downlink Multi Input Multi Output (MIMO) system supporting a method, a method of transmitting a reference signal may include selecting, at the base station, one reference signal transmission mode among a plurality of reference signal transmission modes; And transmitting, at the base station, a reference signal according to the selected reference signal transmission mode.

Preferably, the plurality of reference signal transmission modes use a demodulation-common reference signal (DM-CRS) as a reference signal for the four transmission antennas, and reference signals for the remaining four transmission antennas. A first reference signal transmission mode using a non-precoded demodulation-common reference signal (NDM-DRS) as a reference signal, and a dedicated reference signal precoded as a reference signal for the eight transmit antennas. It includes a second reference signal transmission mode using a (Precoded Demodulation-Common Reference Signal; PDM-DRS).

At this time, preferably, in the selecting step, the first reference signal transmission mode is selected when the rank is 5 or more, and the second reference signal transmission mode is selected when the rank is less than 5.

,

,

,

의 값은 각각, 랭크 4의 프리코딩 행렬 인덱스 i의 프리코딩 행렬 W_{4 ,i}의According to another aspect of the present invention, a downlink MIMO supporting a first user equipment (UE) that recognizes four transmit antennas among eight transmit antennas and a second UE that recognizes the eight transmit antennas are provided. In an input multi output) system, a method of precoding a codeword includes modulating the codeword at the base station; And at the base station, precoding the modulated codeword using a codebook, wherein the elements of the precoding matrix W _{N , i} of the precoding matrix index i of rank N of rank N of five or more of the precoding matrices of the codebook. medium

,

,

,

Are the values of the precoding matrix W _{4 , i} of the rank 4 precoding matrix index i, respectively.

,

,

,

과 동일하고

,

,

,

Same as

 X1, X2, X3, and X4 may have any one of 1 to 8 as different values.

W _{N , i} and the W _{4 , i} are each

to be.

Preferably, X1, X2, X3 and X4 are 1, 2, 3 and 4, respectively,

W _{4 , i} is

to be.

In this case, preferably, W _{N , i} is

to be.

을 만족하는 W_n 의 요소로부터 선택되고 상기 I는 4 x 4 단위 행렬이고, 상기 U_n 은

,

,

,

,

,

,

,

,

,

,

,

,

,

,

및

중 어느 하나이다.In this case, preferably, each element from the first row to the fourth row of W _{4 , i} is

Is selected from the elements of W _n satisfying i and the I is a 4 x 4 unit matrix and the U _n silver

,

,

,

,

,

,

,

,

,

,

,

,

,

,

And

Which is either.

The present invention provides an efficient method of transmitting a reference signal and a codebook in an environment in which an LTE user equipment and an LTE-Advanced (LTE-A) UE coexist in a downlink MIMO system.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description set forth below in conjunction with the appended drawings is intended to explain exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. The following detailed description includes specific details to assist in a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details. For example, the following description will focus on certain terms, but need not be limited to these terms and may refer to the same meaning even when referred to as any term. In addition, the same or similar components throughout the present specification will be described using the same reference numerals.

Hereinafter, a method of transmitting a reference signal (hereinafter referred to as RS) in an environment in which an LTE user equipment (LTE UE) and an LTE-A UE coexist according to the first aspect of the present invention will be described.

FIG. 3 shows a subframe for transmitting an RS in case of normal Cyclic Prefix (normal CP) in 3GPP LTE, and FIG. 4 shows an extended cyclic prefix (extended CP) in 3GPP LTE. A subframe for transmitting RS is shown. In the 3GPP LTE downlink, four antennas are used, and reference signals (hereinafter, referred to as RSs) for the four antennas are as shown in FIGS. 3 and 4.

However, since LTE-A (LTE-Advanced) supports MIMO in which the number of transmit antenna ports for downlink is increased, the number of RSs must be increased accordingly. In defining the RS pattern of each antenna port, there are various methods, such as a code division multiplexing (CDM) method, a frequency division multiplexing (FDM), or a time division multiplexing (TDM).

Table 2 shows the type of the method for transmitting the RS for the antenna ports 4 to 7 to be added. Antenna ports 0 to 3 are antenna ports supported together by LTE and LTE-A.

A technique considered as a method of transmitting an additional RS for an LTE-A UE with minimal impact on performance of an existing LTE user equipment (hereinafter, referred to as UE). There is method 4.

How to transmit the RS of the added antenna port Method 1 DM-CRS (antenna port 0 to 3) + DM-CRS (antenna port 4 to 7) Method 2 DM-CRS (antenna port 0 to 3) + NDM-DRS (antenna port 4 to 7) Method 3 PDM-DRS (antenna port 0 to 7) Method 4 DM-CRS (antenna port 0 to 3) + PDM-DRS (antenna port 4 to 7)

DM-CRS, NDM-DRS, and PDM-DRS described in Table 2 have the following characteristics.

DM-CRS (DeModulation Common RS) means a common RS for demodulation (demodulation). However, DM-CRS can also be used for channel measurement. Since several UEs use the DM-CRS for channel measurement, the precoding scheme of a specific UE cannot be applied to the DM-CRS. Therefore, when a physical downlink shared channel (PDSCH) is precoded, signaling for precoding is required through a physical downlink control channel (PDCCH).

Non-precoded DeMdulation Dedicated RS (NDM-DRS) means dedicated RS for demodulation that is not precoded.

PDM-DRS (Precoded DeModulation Dedicated RS) means a dedicated RS for precoded demodulation, and since the same precoding is applied to PDM-DRS and PDSCH, no separate signaling through PDCCH is required.

Hereinafter, a method of transmitting RS of the added antenna port of Table 2 will be described in detail.

Method 1 sends DM-CRS to RS for added antenna ports 4 to 7 of the LTE-A system for demodulation. The method of transmitting the DM-CRS to the RS for the antenna ports 4-7 is the same as the method of transmitting the RS for the antenna ports 0-3 in the LTE system. In this case, even though the LTE UE does not know the location of the DM-CRS of the antenna ports 4 to 7, the LTE UE should be minimally influenced therefrom, and thus uses resources of a physical downlink control channel (PDCCH) or a virtual multiple input multiple. Output; virtual MIMO) can be used. Since DM-CRS is a CRS, it can be used simultaneously for channel measurement and demodulation.

However, DM-CRS has a disadvantage that it should always be transmitted regardless of whether there is data to be transmitted. In addition, even though the number of antennas is 8, there is a case in which a low rank such as 1 or 2 needs to be used, and thus there is a disadvantage in that resources may be wasted for the LTE-A UE. .

Method 2 transmits RS defined in the existing LTE system to RS for antenna ports 0 to 3 for demodulation in LTE-A system and transmits NDM-DRS to RS for added antenna ports 4 to 7 to be. Since NDM-DRS is transmitted only when data is transmitted, it saves resources compared to transmitting DM-CRS. However, because DRS cannot perform channel measurement, CQI-CRS is not available through other subframes. Should be sent.

However, in the same manner as in Method 1, although the number of antennas is 8, Rank 1

Alternatively, since there is a case where a low rank such as rank 2 is required, resources may be wasted on the LTE-A UE's side.

Method 3 is a method of transmitting a PDM-DRS to an RS for antenna ports 0 to 7 according to a rank regardless of the CRSs for the existing antenna ports 0 to 3 for demodulation in the LTE-A system. Although it does not use the CRS of the existing LTE system, the LTE-A UE that uses a lower rank, such as rank 1 or rank 2 has the advantage of reducing the waste of resources.

Method 4 uses the DM-CRS defined in the existing LTE system as the RS for the antenna ports 0 to 3 for demodulation in the LTE-A system, and uses the PDM-DRS as the RS for the added antenna ports 4 to 7. How to use. Since PDM-DRS is transmitted only when data is transmitted, it saves resources compared to DM-CRS. Since the data and RS are multiplied by a precoding matrix, the number of transmissions of DRS is determined according to the rank. This allows for more efficient use of resources.

내지

은 각 안테나 포트 0 내지 7로 전송되는 RS를 의미하며

내지

은 항상 전송이 되며

내지

은 랭크에 따라 전송 유무가 결정이 된다.FIG. 5 is a schematic diagram illustrating a structure in which an antenna port and a reference signal are mapped according to Method 4. FIG. As shown in FIG. 5, the RSs for antenna ports 0 to 3 are CRSs, so the RSs are not multiplied by the precoding matrix, but the RSs for antenna ports 4 to 7 are PDM-DRSs. Are multiplied and sent.

To

Means RS transmitted to each antenna port 0 to 7

To

Is always sent

To

The presence or absence of transmission depends on the rank.

Example

As described above, since each of the methods 1 to 4 has advantages and disadvantages, it is preferable to switch the methods 1 to 4 according to a system or an operating environment.

6 shows a flowchart of a method of transmitting a reference signal of an embodiment according to the first aspect of the present invention.

As shown in FIG. 6, one method is selected from among a plurality of methods (corresponding to any one of the methods 1 to 4) for transmitting an RS according to a predetermined condition (step 601).

Preferably, the plurality of transmission methods may be the method 2 and the method 3, and one of the method 2 and the method 3 is selected and used according to a predetermined condition.

Using method 3 when the system is low rank has the advantage of making efficient use of resources. However, when the PDM-DRS is transmitted for all ranks, as the rank increases, the overhead of the RS becomes very high, and resources for data transmission are relatively insufficient. This is because the CRS for the LTE UE should be considered.

As a solution to this problem, if the rank is increased, the method 2 may be selected to use DM-CRS as an RS for antenna ports 0 to 3 and use the DM-CRS as a DRS like NDM-DRS. For example, if the rank is 5 or more, method 2 may be selected to demodulate using DM-CRS for antenna ports 0 to 3 and NDM-DRS as RS for antenna ports 4 to 7. Therefore, the predetermined condition in step 601 may be the size of the rank.

Then, the RS signal is transmitted to the UE according to the switched method (step 602).

Meanwhile, the existing LTE system supports up to four antennas, but the LTE-A system needs to support up to eight antennas. Therefore, a new codebook considering an 8ⅹ8 precoding matrix is needed.

Therefore, the present invention proposes to define a codebook for the LTE-A system by using a precoding matrix defined in the codebook used in the existing LTE system.

Hereinafter according to the second aspect of the present invention A method of defining a codebook for an LTE-A system will be described.

Example  One

7 is a configuration diagram of a precoding matrix constituting a codebook for the LTE-A system of the first embodiment according to the second aspect of the present invention.

As shown on the right side of FIG. 7, the precoding matrix defined in the codebook for the LTE-A system uses the components of the precoding matrix of the codebook of the existing LTE system, and newly added antenna ports 4 to 7 It is constructed by adding column components. That is, the portion indicated by the 4x4 LTE codebook in FIG. 7 shows the precoding matrix of the codebook used in the LTE system, and the portion indicated by the 8x4 LTE-A codebook indicates the newly added antenna ports 4 to 7 in the precoding matrix. Heat component. However, if the rank is 4 or less, the existing part uses the codebook used in the LTE system as it is.

Hereinafter, a method of defining a codebook for an LTE-A system will be described using a determinant.

,

,

,

의 값은 각각, 랭크 4의 프리코딩 행렬 인덱스 i의 프리코딩 행렬 W_{4 ,i}의

,

,

,

과 동일하고Among the elements of the precoding matrix W _{N , i} of the precoding matrix index i of rank N of 5 or more among the precoding matrices of the LTE-A codebook according to the present invention.

,

,

,

Are the values of the precoding matrix W _{4 , i} of the rank 4 precoding matrix index i, respectively.

,

,

,

Same as

X1, X2, X3, and X4 have different values and have any one of 1 to 8.

W _{N , i} and the W _{4 , i} are each

It is expressed as

,

,

,

의 각 요소는

을 만족하는 W_n의 요소로부터 선택되고 상기 I는 4 x 4 단위 행렬이고, 상기 U_n 은

,

,

,

,

,

,

,

,

,

,

,

,

,

,

및

중 어느 하나이다.Further, the above W _{4 , i}

,

,

,

Each element of

Is selected from the elements of W _n satisfying i and the I is a 4 x 4 unit matrix and the U _n silver

,

,

,

,

,

,

,

,

,

,

,

,

,

,

And

Which is either.

,

,

,

의 각 요소는 상기 W_n 의 요소로부터 선택된다. Precoding matrix of a codebook for the LTE-A system in accordance with the present invention because it uses a precoding matrix of a codebook used in the LTE system, the W _{4, i}

,

,

,

Each element of W _n is Is selected from the elements.

를 만족하는 경우를 나타낸다.In the case of FIG. 8, X1, X2, X3 and X4 are 1, 2, 3 and 4, respectively, and W _{4, i} is

Indicates a case where

On the other hand, it is preferable to add an orthogonal characteristic to the column components constituting the precoding matrix of FIG.

8 is a configuration diagram of a precoding matrix constituting a codebook for an LTE-A system according to a second embodiment of the present invention.

As shown in FIG. 8, a fifth matrix of rows 5 through 8 of columns 1 through 4 of the precoding matrix of the codebook for the LTE-A system is set as the fifth column. The rows except for the first to fourth rows from to eighth column are regarded as zero matrix. By constructing as described above, it is possible to give the orthogonal characteristics to the column components of the precoding matrix.

When the precoding matrix of the codebook for the LTE-A system given the orthogonal characteristics is expressed in a determinant, W _{N , i} is

를 만족하게 된다.

Will be satisfied.

In the MIMO system, since the total power is the same regardless of the number of antennas used, the larger the number of antennas, the smaller the power that can be allocated to one antenna. If the RS is transmitted in the above manner, when the rank is less than 4, only 4Tx antennas are used, so twice the power is allocated to one antenna compared to the environment supporting the rank 5 or more.

The embodiments described above are the components and features of the present invention are combined in a predetermined form. Each component or feature is to be considered optional unless stated otherwise. Each component or feature may be implemented in a form that is not combined with other components or features. It is also possible to combine some of the components and / or features to form an embodiment of the invention. The order of the operations described in the embodiments of the present invention may be changed. Some configurations or features of certain embodiments may be included in other embodiments, or may be replaced with corresponding configurations or features of other embodiments. It is obvious that the claims may be combined to form an embodiment by combining claims that do not have an explicit citation relationship in the claims or as new claims by post-application correction.

In the present invention, a user equipment (UE) may be replaced with terms such as a mobile station (MS), a subscriber station (SS), a mobile subscriber station (MSS), or a mobile terminal.

Meanwhile, the UE of the present invention includes a PDA (Personal Digital Assistant), a cellular phone, a Personal Communication Service (PCS) phone, a Global System for Mobile (GSM) phone, a Wideband CDMA (WCDMA) phone, a Mobile Broadband System (MBS) phone, and the like. Can be used.

Embodiments of the invention may be implemented through various means. For example, embodiments of the present invention may be implemented by hardware, firmware, software, or a combination thereof.

For a hardware implementation, the method according to embodiments of the present invention may be implemented in one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs) , Field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of an implementation by firmware or software, the method according to the embodiments of the present invention may be implemented in the form of a module, a procedure, or a function that performs the functions or operations described above. The software code may be stored in a memory unit and driven by a processor. The memory unit may be located inside or outside the processor, and may exchange data with the processor by various known means.

The invention can be embodied in other specific forms without departing from the spirit and essential features of the invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention. In addition, claims that do not have an explicit citation in the claims may be combined to form an embodiment or included in a new claim by amendment after the application.

The present invention can be used in a terminal, base station, or other equipment of a wireless mobile communication system.

1 is a block diagram of a general multi-antenna communication system.

개의 송신 안테나에서 수신 안테나

로의 채널을 도시한 것이다.2 is

Antennas from two transmit antennas

Shows a channel to.

3 illustrates a subframe for transmitting an RS in case of a standard cyclic prefix (CP) in 3GPP LTE.

4 illustrates a subframe for transmitting an RS in case of an extended CP in 3GPP LTE.

4 shows the output of symbols over time when the transmission interval of RS is 6;

5 is a schematic diagram illustrating a structure in which an antenna port and a reference signal are mapped according to the present invention.

6 shows a flowchart of a method of transmitting a reference signal according to the first aspect of the present invention.

7 is a configuration diagram of a precoding matrix constituting a codebook for the LTE-A system of the first embodiment according to the second aspect of the present invention.

8 is a configuration diagram of a precoding matrix constituting a codebook for an LTE-A system according to a second aspect of the present invention.

Claims (7)

In a downlink Multi Input Multi Output (MIMO) system supporting a first UE (User Equipment) for recognizing four transmit antennas among eight transmit antennas provided in a base station and a second UE for recognizing the eight transmit antennas, As a method of transmitting a reference signal, Selecting, at the base station, one reference signal transmission mode among a plurality of reference signal transmission modes according to the rank; And At the base station, transmitting a reference signal in accordance with the selected reference signal transmission mode; Reference signal transmission method. The method of claim 1, The plurality of reference signal transmission modes A dedicated reference for demodulation that is not precoded as a reference signal for the four other transmit antennas using a demodulation-common reference signal (DM-CRS) as a reference signal for the four transmit antennas. A first reference signal transmission mode using a non-coded Demodulation-Common Reference Signal (NDM-DRS), and And a second reference signal transmission mode using a precoded dedicated reference signal (PDM-DRS) as reference signals for the eight transmit antennas. Reference signal transmission method. The method of claim 2, In the step of selecting, If the rank is 5 or more, the first reference signal transmission mode is selected. If the rank is less than 5, the second reference signal transmission mode is selected. Reference signal transmission method. In a downlink Multi Input Multi Output (MIMO) system supporting a first UE (User Equipment) for recognizing four transmit antennas among eight transmit antennas provided in a base station and a second UE for recognizing the eight transmit antennas, As a method of precoding a codeword, Modulating the codeword at the base station; And At the base station, precoding the modulated codeword using a codebook, Among the elements of the precoding matrix W _{N , i} of the precoding matrix index i of rank N of 5 or more among the precoding matrices of the codebook.

,

,

,

The value of each of the rank 4 precoding matrix index i for the precoding matrix W _4, the precoding matrix of the precoding matrix index i, _i of rank 4 W _{4, i}

,

,

,

Same as, X1, X2, X3, and X4 have different values and have any one of 1 to 8, W _{N , i} and the W _{4 , i} are each

sign Precoding method. The method of claim 4, wherein X1, X2, X3 and X4 are 1, 2, 3 and 4, respectively W _{4 , i} is

sign, Precoding method. The method of claim 5, W _{N , i} is

sign, Precoding method. The method of claim 5, Wherein W _4, each element of each element to the fourth row from the first row of the _{4 W, i} from the first row to the fourth row of the _i

Is selected from the elements of W _n satisfying i, and I is a 4 x 4 unit matrix, U _n silver

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,

,

,

,

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And

Any one of Precoding method.

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