KR20100129237A - Method for efficient transmission of precoded referece signal in wireless communication system and apparatus thereof - Google Patents

Abstract

PURPOSE: A method and an apparatus for transmitting pre-coded reference signal in order to prevent load of a DCI format are provided to transmit the pre-coded reference signal without increasing CDM(Code Division Multiplexing) resource. CONSTITUTION: A pre-coding module(440) pre-codes a signal mapped to a layer according to a pre-coding vector. Resource element mapping modules multiplexes the pre-coded signal. The resource element mapping modules map the multiplexed signals to the resource elements. A transmission module transmits signals mapped to the resource elements through a multiple antenna. A processor is connected to a layer mapping module, the pre-coding module, the resource element mapping module and the transmission module.

Description

METHOD FOR EFFICIENT TRANSMISSION OF PRECODED REFERECE SIGNAL IN WIRELESS COMMUNICATION SYSTEM AND APPARATUS THEREOF}

The following description relates to a wireless communication system, and more particularly, to a method and apparatus for efficiently transmitting a precoded reference signal in a wireless communication system.

MIMO, which stands for Multiple-Input Multiple-Output, refers to a method that can improve transmit / receive data efficiency by adopting multiple transmit antennas and multiple receive antennas, away from the use of one transmit antenna and one receive antenna. . That is, a technique for increasing capacity or improving performance by using multiple antennas in a transmitter or receiver of 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.

)에 하기의 수학식 1의 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 a case where only a plurality of antennas are used 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 transmission rate and significantly improve frequency efficiency. The transmission rate according to the increase of channel transmission capacity is theoretically the maximum transmission rate when using one antenna

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 theoretical transmission rate of four times 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 WLAN. 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 describe the communication method in the multi-antenna system in a more specific manner, it can be represented as follows mathematically. As shown in FIG. 1, it is assumed that there are N _T transmit antennas and N _R receive antennas. First, referring to a transmission signal, when there are N _T transmit antennas, since 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 전송신호(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 전송안테나와

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 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 transmission 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, 전송안테나의 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,

It is noted that the order of the indexes 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 도착하는 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 expressed through the matrix representation as shown in Equation 7, Equation 8 below.

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.

의 행과 열의 수는 전송안테나와 수신 안테나의 개수에 의해 결정된다. 채널 행렬

에서 행의 수는 수신 안테나의 개수(N_R)과 동일하고, 열의 수는 전송 안테나의 개수(N_T)와 동일하다. 즉, 채널 행렬 H는 N_R ⅹ N_T 행렬로 표시될 수 있다. 일반적으로, 행렬의 랭크는 서로 독립적인 행의 수와 열의 수 중에서 더 작은 수에 의해 정의된다. 그러므로, 행렬의 랭크는 행렬의 행의 수나 열의 수보다 더 큰 값을 가질 수 없다. 채널 행렬

의 랭크는 다음의 수학식 11에 의해 표현될 수 있다. On the other hand, the channel matrix indicating the channel status

The number of rows and columns of is determined by the number of transmit antennas and receive antennas. Channel matrix

The number of rows is equal to the number of receive antennas N _R , and the number of columns is equal to the number of transmit antennas N _T. That is, the channel matrix H is N _R Ⅹ N _T It can be represented by a matrix. In general, the rank of a matrix is defined by the smaller of the number of rows and columns independent of each other. Therefore, the rank of the matrix cannot have a value larger than the number of rows or columns of the matrix. Channel matrix

The rank of may be expressed by the following equation (11).

In the MIMO system, precoding may provide beamforming gain and diversity gain to the transmitting / receiving side, thereby providing high system throughput. However, the precoding scheme should be appropriately designed in consideration of antenna setting, channel environment, and system structure.

In general, a MIMO system that performs precoding to minimize complexity and control signaling overhead uses a codebook based precoding technique. The codebook includes a predetermined number of precoding vectors / matrices predetermined between the transmitting and receiving end according to the transmission rank and the number of antennas. The transmitter selects a specific precoding vector / matrix in the codebook according to the channel state information received from the receiver to perform precoding on the transmission signal to transmit. In some cases, the transmitter may transmit a signal after performing precoding by selecting a precoding matrix according to a predetermined rule without receiving channel state information from the receiver.

A method of estimating a channel in a MIMO transmission system using precoded spatial multiplexing will be described. A reference signal (RS) is provided for channel estimation. When using a non-precoded reference signal, each channel from the transmit antenna ports is estimated from the reference signal, and an equivalent channel can be obtained by the combination of the estimated channel matrix and the precoding weight. Meanwhile, when using the precoded reference signal, since the precoded reference signal is precoded by the same precoding weight as that of data transmission, an equivalent channel can be directly obtained from the precoded reference signal. The equivalent channel matrix is composed of the channel vectors experienced by each layer, each channel vector being frequency division multiplexed (FDM), time division multiplexed (TDM) or code division multiplexed (Code Division). It can be estimated by the Multiplexing (CDM) method.

In the rank 2 or more MIMO transmission scheme, the precoded reference signals for two or more layers may be multiplexed using the CDM scheme and transmitted through one resource element (time and frequency resource). At this time, as many CDM resources as the number of transport ranks (or the number of transport layers) are required. That is, two CDM resources are needed for rank 2 transmission and three CDM resources are needed for rank 3 transmission.

As the rank increases, in case of using a lot of CDM resources, the overhead of transmitting control information for indicating this increases. For example, a demodulation reference signal (DMRS) for uplink transmission may be multiplexed using a cyclic shift (CS) as a CDM resource. The CS value for the DMRS may be downlink control information (DM). It is indicated to the UE through a Downlink Control Information (DCI) format. If the CS value to be indicated to the UE is different according to the rank, various DCI formats need to be defined accordingly, and the burden of the UE blind decoding the DCI format may be increased.

Even when the transmission rank is increased, a method of efficiently transmitting the CDM resource for transmitting the precoded RS is required.

In order to solve the above technical problem, a method of transmitting a reference signal in multi-antenna transmission according to an embodiment of the present invention includes the steps of determining a precoding vector for each of M (M≥3, M is a natural number) layers. Precoding reference signals for each of the M layers according to the precoding vector; precoding for N (N <M, N is a natural number) of precoded reference signals for each of the M layers The method may include multiplexing a coded reference signal using N codes, and transmitting the multiplexed precoded reference signal to a receiver.

The multiplexing may further include multiplexing a precoded reference signal for each of the M layers at least once.

The transmitting may include transmitting power of a precoded reference signal for a layer having a greater number of times than the precoded reference signal for the remaining layers, and transmitting the precoded reference signal for the remaining layers. The method may further include setting and transmitting lower than power.

The multiplexing may include precoding a reference signal for a layer having an element having a zero value in the precoding vector, and precoding a layer having no element having a zero value in the precoding vector. The method may further include multiplexing with the received reference signal.

In addition, M may be 3, and N may be 2.

In order to solve the above technical problem, an apparatus for transmitting a reference signal in multi-antenna transmission according to another embodiment of the present invention includes a layer mapping module for mapping a signal to be transmitted to a layer and a signal mapped to the layer to a precoding vector. A precoding module for precoding according to the present invention, a resource element mapping module for multiplexing the precoded signal and mapping it to a resource element, a transmission module for transmitting the signal mapped to the resource element through the multiple antennas, the layer mapping module, And a processor communicatively coupled to the precoding module, the resource element mapping module, and the transmission module, wherein the processor is configured to each of M (M ≧ 3, M is natural numbers) layers through the precoding module. Determine a precoding vector for each of the M layers according to the determined precoding vector. Control the signal to be precoded, and, through the resource element mapping module, precoded reference signals for N (N <M, N is a natural number) of precoded reference signals for each of the M layers Can be controlled to multiplex using two codes, and can be controlled to transmit the multiplexed precoded reference signal to a receiver through the transmission module.

In addition, the processor may control to multiplex the precoded reference signals for each of the M layers through the resource element mapping module.

Also, the processor may transmit, through the transmission module, the transmit power of the precoded reference signal for the layer having a greater number of times of transmission than the precoded reference signal for the remaining layer. It may be controlled to transmit by setting lower than the transmission power of the reference signal.

The processor may further include a precoded reference signal for a layer having an element having a zero value in the precoding vector and an element having a zero value in the precoding vector through the resource element mapping module. It can be controlled to multiplex with a precoded reference signal for a non-layer.

In addition, M may be 3, and N may be 2.

According to the present invention, even if the transmission rank is increased, it is possible to provide a method and apparatus for efficiently transmitting a precoded reference signal without increasing CDM resources for transmitting the precoded reference signal.

The effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned above may be clearly understood by those skilled in the art from the following description. will be.

1 is a configuration diagram of a multiple antenna (MIMO) communication system.
2 is a diagram illustrating a channel from a plurality of transmit antennas to a receive antenna.
3 is a diagram illustrating an example of a precoding matrix according to the present invention.
4 is a diagram illustrating a configuration of a transmission apparatus according to an embodiment of the present invention.

The following embodiments are a combination of elements and features of the present invention in a predetermined form. Each component or feature may be considered to be optional unless otherwise stated. Each component or feature may be implemented in a form that is not combined with other components or features. In addition, some of the elements and / or features may be combined to form an embodiment of the present 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.

In the present specification, embodiments of the present invention will be described based on a relationship between data transmission and reception between a base station and a terminal. Here, the base station has a meaning as a terminal node of the network that directly communicates with the terminal. The specific operation described as performed by the base station in this document may be performed by an upper node of the base station in some cases.

That is, it is obvious that various operations performed for communication with a terminal in a network composed of a plurality of network nodes including a base station may be performed by the base station or other network nodes other than the base station. A 'base station (BS)' may be replaced by terms such as a fixed station, a Node B, an eNode B (eNB), an access point (AP), and the like. The repeater may be replaced by terms such as relay node (RN) and relay station (RS). In addition, the term “terminal” may be replaced with terms such as a user equipment (UE), a mobile station (MS), a mobile subscriber station (MSS), a subscriber station (SS), and the like.

Specific terms used in the following description are provided to help the understanding of the present invention, and the use of such specific terms may be changed to other forms without departing from the technical spirit of the present invention.

In some instances, well-known structures and devices may be omitted or shown in block diagram form centering on the core functions of the structures and devices in order to avoid obscuring the concepts of the present invention. In addition, the same components will be described with the same reference numerals throughout the present specification.

Embodiments of the present invention may be supported by standard documents disclosed in at least one of the wireless access systems IEEE 802 system, 3GPP system, 3GPP LTE and LTE-Advanced (LTE-A) system and 3GPP2 system. That is, steps or parts which are not described to clearly reveal the technical spirit of the present invention among the embodiments of the present invention may be supported by the above documents. In addition, all terms disclosed in the present document can be described by the above standard document.

The following techniques include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and the like. It can be used in various radio access systems. CDMA may be implemented with a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented with wireless technologies such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in a wireless technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) long term evolution (LTE) is part of an Evolved UMTS (E-UMTS) using E-UTRA, and employs OFDMA in downlink and SC-FDMA in uplink. LTE-A (Advanced) is the evolution of 3GPP LTE. WiMAX can be described by the IEEE 802.16e standard (WirelessMAN-OFDMA Reference System) and the advanced IEEE 802.16m standard (WirelessMAN-OFDMA Advanced system). For clarity, the following description focuses on 3GPP LTE and LTE-A systems, but the technical spirit of the present invention is not limited thereto.

In the following description, 'rank' indicates the number of paths through which signals can be independently transmitted, and 'number of layers' indicates the number of signal streams transmitted through each path. In general, since the transmitting end transmits the number of layers corresponding to the number of ranks used for signal transmission, unless otherwise specified, the rank has the same meaning as the number of layers. In addition, in the precoding matrix, it is assumed that a row corresponds to each antenna and a column corresponds to a rank or each layer signal.

In the 3GPP LTE (3RD Generation Partnership Project Long Term Evolution) release 8 system, when the MIMO scheme is applied to uplink signal transmission from the terminal to the base station, problems such as PAPR (Peak-to-Average Ratio) / Cubic Metric (CM) characteristics deterioration Therefore, the MIMO transmission scheme is defined only for downlink signal transmission from the base station to the terminal. However, the uplink signal transmitted by the terminal to the base station is also discussed in the direction of applying the MIMO technique for increasing the transmission rate, obtaining the diversity gain, and the like (3GPP LTE-Advanced or 3GPP LTE-A). ), The specific method of applying MIMO technique to uplink signal transmission is discussed.

When transmitting the precoded reference signal in the uplink MIMO transmission scheme, it is necessary to consider the compatibility with the existing 3GPP LTE system. That is, in consideration of the DMRS used in the existing 3GPP LTE system, it is necessary to design a DMRS for uplink multi-antenna transmission of the 3GPP LTE-A system.

The DMRS defined in the existing 3GPP LTE standard (release 8 or 9) will be described.

DMRS is defined in a physical uplink shared channel (PDSCH) for uplink data transmission. For each terminal, DMRS is transmitted on the bandwidth over which the PUSCH of that terminal is scheduled. In the MIMO system, the DMRS for this PUSCH is multiplexed as follows. In the case of single-input multiple-output transmission, DMRSs of respective terminals may be multiplexed in an FDM scheme by using different frequency resources for each terminal. In the case of multi-user MIMO (MU-MIMO) transmission, DMRSs of each UE can be orthogonalized by allocating different cyclic shift (CS) values to each UE. Different cyclic shift values may be used in different slots of the subframe. In the case of a normal CP (Normal Cyclic Prefix), the DMRS for a PUSCH is located on a fourth OFDM symbol, and in case of an extended CP, it is located on a third OFDM symbol. The cyclic shift in the slot is given by (12).

의 값은 상위계층에 의해서 브로드캐스팅되는 값이고,

는 다중사용자 MIMO에 대한 상향링크 그랜트에 포함된다.

는 의사-랜덤(pseudo-random) 시퀀스인

에 의하여 주어지고,

는 셀-특정(cell-specific)으로 적용된다. 상향링크 그랜트의 순환시프트 필드와

값의 매핑관계는 표 1과 같다.In Equation 12,

Is the value broadcast by the higher layer,

Is included in the uplink grant for multi-user MIMO.

Is a pseudo-random sequence

Given by

Is applied cell-specific. The cyclic shift field of the uplink grant

The mapping relationship of values is shown in Table 1.

Uplink grant
Circular shift field

000 0 001 6 010 3 011 4 100 2 101 8 110 10 111 9

In designing the DMRS for uplink multi-antenna transmission in the 3GPP LTE-A system in consideration of the uplink DMRS used in the existing 3GPP LTE system described above, the existing 3GPP by multiplexing and transmitting the DMRS for the multi-antenna in the CDM scheme Maintain compatibility with LTE system. In order to transmit the reference signal precoded by the CDM scheme, CDM resources are required for the number of transmission ranks (or the number of transport layers). In the uplink of the existing 3GPP LTE system, the cyclic shift is used as a resource of the CDM. Cyclic shift resources should be allocated by the number of ranks.

The data allocation for uplink transmission and the cyclic shift value of DMRS are indicated to the UE through a DCI format including control information for uplink transmission. When the number of CS values to be indicated differs according to each rank, various DCIs The format needs to be defined. In this case, the number of blind decodings for acquiring uplink transmission control information increases. To remove this inefficiency, the DCI format for uplink transmission should consist of a fixed bit field regardless of the number of transmission ranks. Also, in order to satisfy this, the cyclic shift needs to be composed of fixed bits.

In an embodiment of the present invention, a method of transmitting a reference signal using CDM resources smaller than the number of ranks in the transmission of rank 3 or higher is proposed. For example, a method of transmitting a reference signal using N (N <M) CDM resources in rank M transmission will be described. The number N of CDM resources may have a fixed value even if the rank M increases.

Of the three layers constituting rank 3 transmission, the precoded reference signals for any two layers are multiplexed using two code resources and transmitted on one and the same resource element A (one resource element on the time axis Unit of one OFDM symbol and one subcarrier in the frequency axis). In addition, on a different resource element B (resource element B may have a different time and / or frequency position from resource element A), precoded reference signals for any two layers are multiplexed and transmitted using two code resources. do. That is, in rank M (M = 3) transmission, a precoded reference signal for M layers may be transmitted by multiplexing using N (N = 2 <M) CDM resources. Accordingly, it is possible to efficiently transmit a precoded reference signal for multiple layers by efficiently using CDM resources.

At this time, the code resource used for the CDM on the resource element A is the same as the code resource used for the CDM on the resource element B. In addition, the layer in which the reference signal precoded on the resource element A is multiplexed by the CDM scheme may be the same layer as the layer in which the reference signal precoded on the resource element B is multiplexed by the CDM scheme.

In a resource block and subframe allocated to RS transmission, precoded RSs for all three layers need to be transmitted at least once, and two or more time and / or frequency resources are used for this purpose. do.

According to the above-described scheme, the precoded reference signal for one of the three layers may be transmitted a relatively large number of times compared to the precoded reference signal for the other layers. In this case, the precoded reference signal for a layer that is transmitted relatively much may be transmitted at a relatively low power compared to the precoded reference signal for another layer when transmitted once.

For example, consider a 4x3 precoding matrix that represents the precoding weight for three layers (columns) at four antenna ports (rows). In the 4x3 precoding matrix W1 of FIG. 3, in the first transmission, CDM resources are precoded and transmitted with precoding vectors for the first and second layers, and in the second transmission, the preambles for the second and third layers are precoded. The CDM resource is precoded with coded vectors and transmitted. That is, in the first transmission, precoding reference signals for the first and second layers with precoding vectors for the first and second layers (columns), and multiplexing the precoded reference signals using CDM resources. Can be transmitted on the first resource element. In the second transmission, precoding reference signals for the second and third layers with precoding vectors for the second and third layers (columns), and multiplexing the precoded reference signals by using CDM resources. Can be transmitted on the resource element.

In this case, the transmission power may be adjusted, and the first and third precoded reference signals for the second layer transmitted in both transmissions are transmitted at a power of a and only once in each of the two transmissions. The precoded reference signals for the layers may be set to be transmitted at a power of 2a, respectively.

In the precoding matrix including a zero value element in a layer (column), such as the precoding matrix W2 of FIG. 3, the precoded reference signal for the first layer is transmitted in all four antenna ports, whereas Precoded reference signals for the second and third layers are transmitted only at two antenna ports (precoded reference signals for the second layer are transmitted only at the first and second antenna ports and precoded for the third layer Reference signal is transmitted only in the third and fourth antenna ports). In the case of using a precoding matrix including an element of zero value such as the precoding matrix W2, the precoded reference signals for the first and second layers are multiplexed and transmitted in the first transmission, and the second in the second transmission. And multiplexing and transmitting the precoded reference signal for the third layer, the antenna port (row corresponding to the element of 0 value in the precoding matrix) that is not transmitted for the second and third layers during signal transmission. There is a situation that the transmission power is lowered. In order to maintain the transmit power of the antenna port, the precoded reference signals for the first and second layers are multiplexed and transmitted in the first resource element, and the precoded for the first and third layers in the second resource element. The reference signal may be multiplexed and transmitted. By doing so, a precoded reference signal (a precoded reference signal for the first layer) is transmitted to both the first to fourth antenna ports in both the first transmission and the second transmission, thereby reducing the transmit power of the antenna port during signal transmission. You can avoid the situation of sudden lowering.

For example, the DMRS for the physical uplink shared channel is transmitted on two SC-FDMA symbols (hereinafter, referred to as first and second DMRS transmitted SC-FDMA symbols) in one subframe. According to an example, precoded DMRSs for the first and second layers are multiplexed and transmitted in the CDM scheme in the first DMRS transmitted SC-FDMA symbol, and in the first and third layers in the second DMRS transmitted SC-FDMA symbol. Precoded DMRS for the multiplexed in the CDM scheme can be configured to be transmitted. Accordingly, since the precoded DMRS for the first layer in both the first and second DMRS transmit SC-FDMA symbols is transmitted on all four transmit antenna ports, the first and second DMRS transmit SC-FDMA symbols are applied to the second and third layers including the element having a value of zero. According to the precoding vector, the situation of lowering the power of the transmitting antenna during signal transmission does not occur.

Although the above-described embodiment of the present invention has exemplarily described the case of rank 3 transmission, it may be applied to the case of rank 4 or more. That is, a reference signal for any two layers among the precoded reference signals for the four layers constituting the rank 4 transmission may be multiplexed and transmitted using two CDM resources, and the reference for any two different layers may be used. Signals can be transmitted by multiplexing using two CDM resources.

In addition, although the above-described embodiment of the present invention has described transmission of a precoded reference signal in uplink, an embodiment of the present invention is precoded for each layer in downlink transmission of rank 3 or higher. It will be apparent to those skilled in the art that the present invention can be applied even when transmitting a reference signal. In addition, in the transmission of rank 3 or more, an effect of the present invention that efficiently utilizes CDM resources by transmitting precoded reference signals using CDM resources less than the number of ranks is effective in transmitting uplink and downlink precoded reference signals. The same is achieved.

4 is a view for explaining the configuration of a transmission device having multiple antennas according to an embodiment of the present invention.

Referring to FIG. 4, the transmitting device includes an encoder (410-1, ..., 410-K), a modulation module (420-1, ..., 420-K), a layer mapping module (layer) mapping module 430, precoding module 440, resource element mapping module 450-1, ..., 450-K, transmission module 460-1, ..., 460-K) and Nt transmit antennas 470-1,..., 470-Nt.

The encoders 410-1,..., 410 -K encode the input data according to a predetermined coding scheme to form coded data. The modulation modules 420-1, ..., 420-K map the coded data to modulation symbols representing positions on the signal constellation. The modulation scheme is not limited and may be m-Phase Shift Keying (m-PSK) or m-Quadrature Amplitude Modulation (m-QAM). For example, m-PSK may be BPSK, QPSK or 8-PSK. m-QAM may be 16-QAM, 64-QAM or 256-QAM.

The layer mapping module 430 defines a layer of modulation symbols so that the precoding module 440 can distribute antenna-specific symbols to the path of each antenna. The layer is defined as an information path input to the precoding module 440. The information path before the precoding module 440 may be referred to as a virtual antenna or layer.

The precoding module 440 processes the modulation symbols by the MIMO scheme according to the multiple transmit antennas 470-1,..., 470 -Nt and outputs antenna specific symbols. The precoding module 440 distributes the antenna specific symbol to the resource element mapping module 450-1,..., 450-K of the path of the corresponding antenna. Each information path sent by the precoding module 440 to one antenna is called a stream. This may be referred to as a physical antenna.

The resource element mapping module 450-1,..., 450 -K assigns an antenna specific symbol to an appropriate resource element and multiplexes it according to a user. The transmission module 460-1, ..., 460-K modulates the antenna specific symbol according to a predetermined multiplexing technique. In the case of a transmission module of a base station transmitting a downlink signal, an OFDM symbol is output by modulating an antenna specific symbol by an OFDM scheme. In the case of a transmission module of a terminal for transmitting an uplink signal, the antenna-specific symbol is modulated by the SC-FDMA scheme to output an SC-FDMA symbol. In the case of downlink, the transmission modules 460-1,..., 460-K may perform inverse fast fourier transform (IFFT) on antenna-specific symbols, and CP (cyclic) in a time domain symbol on which IFFT is performed. prefix) may be inserted. The CP is a signal inserted in a guard interval to remove inter-symbol interference due to multiple paths in the OFDM transmission scheme. The OFDM symbol is transmitted through each transmit antenna 470-1,..., 470 -Nt.

In the apparatus for transmitting a reference signal in multi-antenna transmission according to an embodiment of the present invention, the precoding module 440 is each of the M (M ≥ 3, M is a natural number) received from the layer mapping module 430 A precoded reference signal is generated by precoding according to a precoding vector for.

The resource element mapping module 450 multiplexes the precoded reference signal by CDM and maps the resource element. More specifically, among the precoded reference signals for each of the M layers, the precoded reference signals for N (N <M, N is a natural number) layers are multiplexed using N codes. A plurality of multiplexing is performed such that all of the reference signals of the M layers are multiplexed at least once each. For example, when M is 3 and N is 2, three combinations of the first and second layers, the first and third layers, or the second and third layers are possible, at least of these three combinations. According to the combination of the two, the precoded reference signal for each layer may be multiplexed by the CDM scheme. In addition, in selecting such a combination, an element having a zero value exists in a precoding vector for a second layer and a third layer, and an element having a zero value does not exist in a precoding vector for a first layer. Can assume In this case, the reference signal of the layer corresponding to the precoding vector having no zero value may be multiplexed with the reference signal of another layer. That is, the precoded reference signals for the first and third layers may be multiplexed, and the precoded reference signals for the first and third layers may be multiplexed.

The transmission module 460 may map the multiplexed precoded reference signal to a resource element and transmit it to the receiver. In this case, when the number of times the precoded reference signal for one layer is transmitted is greater than that of the precoded reference signal for another layer, the transmit power of the precoded reference signal for the layer is increased. It may be set lower than the transmission power of the precoded reference signal. For example, it is assumed that when M is 3, precoded reference signals for the first and second layers are multiplexed, and precoded reference signals for the first and third layers are multiplexed and transmitted. . In this case, the precoded reference signal for the first layer is transmitted twice, whereas the precoded reference signal for the second and third layers is transmitted once, and thus the precoded reference signal for the first layer. The transmission power of may be a, and the transmission power of the precoded reference signals for the second and third layers may be 2a.

Meanwhile, the transmission device may further include a processor that controls the constituent modules of the transmission device and performs a function of calculating and processing information received from the transmission device, information to be transmitted to the outside, and the like. It may further include a memory that can be stored for a predetermined time.

Embodiments of the present invention described above 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 implementation in hardware, a method according to embodiments of the present invention may include one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), and Programmable Logic Devices (PLDs). It may be implemented by 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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing description of the preferred embodiments of the invention disclosed herein has been presented to enable any person skilled in the art to make and use the present invention. While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. For example, those skilled in the art can utilize each of the configurations described in the above-described embodiments in a manner of mutually combining them. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

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 interpreted 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. The present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. In addition, the claims may be combined to form an embodiment by combining claims that do not have an explicit citation relationship or may be incorporated as new claims by post-application correction.

410 Encoder 420 Modulation Module
430 Layer Mapping Module 440 Precoding Module
450 Resource Element Mapping Module 460 Transmission Module
470 transmit antennas

Claims (10)

A method of transmitting a reference signal in multi-antenna transmission,
Determining a precoding vector for each of the M (M ≧ 3, M is natural numbers) layers;
Precoding reference signals for each of the M layers according to the precoding vector;
Multiplexing the precoded reference signals for N (N <M, N is natural numbers) layers using N codes among the precoded reference signals for each of the M layers; And
And transmitting the multiplexed precoded reference signal to a receiver. The method of claim 1,
The multiplexing step,
And multiplexing a precoded reference signal for each of the M layers at least once. The method of claim 1,
The transmitting step,
Setting and transmitting a transmit power of a precoded reference signal for a layer having a greater number of times than a precoded reference signal for the remaining layers, than a transmit power of a precoded reference signal for the remaining layers. Further comprising a reference signal transmission method. The method of claim 1,
The multiplexing step,
Multiplexing a precoded reference signal for a layer having an element with a zero value in the precoding vector with a precoded reference signal for a layer for which no element with a zero value exists in the precoding vector. Further comprising, a reference signal transmission method. The method of claim 1,
M is 3, and N is 2, the reference signal transmission method. An apparatus for transmitting a reference signal in multi-antenna transmission,
A layer mapping module for mapping a signal to be transmitted to a layer;
A precoding module for precoding a signal mapped to a layer according to a precoding vector;
A resource element mapping module for multiplexing the precoded signal and mapping the resource element;
A transmission module for transmitting a signal mapped to the resource element through the multiple antennas; And
A processor communicatively coupled to the layer mapping module, the precoding module, the resource element mapping module, and the transmission module,
The processor comprising:
Through the precoding module, determine a precoding vector for each of M (M 3, M is a natural number) layers, and control to precode reference signals for each of the M layers according to the determined precoding vector. and,
Through the resource element mapping module, control to multiplex the precoded reference signals for N (N <M, N is a natural number) of the precoded reference signals for each of the M layers using N codes. and,
And transmits the multiplexed precoded reference signal to a receiving side through the transmitting module. The method of claim 5, wherein
The processor comprising:
And control the multiplexed precoded reference signals for each of the M layers at least once through the resource element mapping module. The method of claim 5, wherein
The processor comprising:
Through the transmission module, the transmit power of the precoded reference signal for the layer having a greater number of times than the precoded reference signal for the remaining layers is greater than the transmit power of the precoded reference signal for the remaining layers. A reference signal transmission device for controlling to transmit by setting low. The method of claim 5, wherein
The processor comprising:
Through the resource element mapping module, a precoded reference signal for a layer in which an element having a zero value exists in the precoding vector, and a precoding for a layer in which an element having a zero value does not exist in the precoding vector. And a reference signal transmission device for controlling to multiplex with the received reference signal. The method of claim 5, wherein
Wherein M is 3 and N is 2;

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