KR20100048871A - Method of dl transmitting reference signal in a wireless communication having multiple antennas - Google Patents

Abstract

PURPOSE: A method for transmitting downlink reference signals in a multi-antenna wireless communication system is provided to efficiently transmit downlink reference signals when the number of antennas increase in a multi-antenna wireless communication system. CONSTITUTION: UE(User Equipment) generally includes a control system(402), a baseband processor(404), transmit circuitry(406), receive circuitry(408), multiple antennas(410), and a user interface(412). The receive circuitry receives a radio signal carrying information from one or more base stations through multiple antennas. Preferably, a low noise amplifier and a filter amplify the received signal and cancel broadband interference from the amplified signal. A down-conversion and analog-to-digital conversion circuitry down-converts the filtered signal to an IF or baseband signal and digitizes the IF or baseband signal to one or more digital streams. The baseband processor processes the digital signal and extracts information or data bits from the processed signal. The processing includes demodulation, decoding, error correction, etc. The baseband processor is configured usually with one or more DSPs(Digital Signal Processors) and ASICs(Application Specific Integrated Circuits). For transmission, the baseband processor receives digital data carrying voice, data, or control information from the user interface under the control of the control system and encodes the digital data. The transmit circuitry modulates the encoded data to a carrier having a desired transmission frequency or frequencies. A power amplifier amplifies the modulated carrier signal to a power level appropriate for transmission. The amplified signal is transmitted through the multiple antennas.

Description

METHOOD OF DL TRANSMITTING REFERENCE SIGNAL IN A WIRELESS COMMUNICATION HAVING MULTIPLE ANTENNAS}

The present invention relates to a method of performing communication in a wireless communication system. More specifically, the present invention relates to a method for downlink transmission of a reference signal in a wireless communication system having multiple antennas.

3rd Generation Partnership Project (3GPP) wireless communication systems based on Wideband Code Division Multiple Access (WCDMA) radio access technology are widely deployed around the world. High Speed Downlink Packet Access (HSDPA), which can be defined as the first evolution of WCDMA, provides 3GPP with a highly competitive wireless access technology in the mid-term future.

E-UMTS is to provide high competitiveness in the long term future. E-UMTS is an evolution from the existing WCDMA UMTS and is being standardized in 3GPP. E-UMTS is also called a Long Term Evolution (LTE) system. For details of technical specifications of UMTS and E-UMTS, refer to Release 7 and Release 8 of the "3rd Generation Partnership Project; Technical Specification Group Radio Access Network", respectively.

The E-UMTS is largely composed of an access gateway (AG) located at an end of a user equipment (UE), a base station, and an network (E-UTRAN) and connected to an external network. Typically, a base station can transmit multiple data streams simultaneously for broadcast service, multicast service and / or unicast service. In the LTE system, orthogonal frequency divisional multiplexing (OFDM) and multi-input multi-out (MIMO) are used for downlink transmission of various services.

OFDM represents a high speed data downlink access system. The advantage of OFDM is the high spectral efficiency that the entire spectrum allocated can be used by all base stations. In OFDM modulation, the transmission band is divided into a plurality of orthogonal subcarriers in the frequency domain and divided into a plurality of symbols in the time domain. Since OFDM divides a transmission band into a plurality of subcarriers, bandwidth per subcarrier is reduced and modulation time per carrier is increased. Since the plurality of subcarriers are transmitted in parallel, the digital data or symbol rate of a particular subcarrier is lower than that of a single carrier.

A multiple input mulple output (MIMO) system is a communication system using a plurality of transmit and receive antennas. The MIMO system can linearly increase the channel capacity without increasing the additional frequency bandwidth as the number of transmit / receive antennas increases. MIMO technology uses a spatial diversity scheme that can improve transmission reliability by using symbols that pass through various channel paths, and each antenna simultaneously transmits separate data streams using a plurality of transmit antennas, thereby providing a transmission rate. There is a method of spatial multiplexing that increases.

The MIMO technology can be broadly classified into an open-loop MIMO technology and a closed-loop MIMO technology according to whether the transmitter knows channel information. In the open-loop MIMO technique, the transmitting end does not know channel information. Examples of the open-loop MIMO technique include per antenna rate control (PARC), per common basis rate control (PCBRC), BLAST, STTC, random beamforming, and the like. On the other hand, in the closed-loop MIMO technology, the transmitting end knows channel information. The performance of a closed loop MIMO system depends on how accurately the channel information is known. Examples of the closed-loop MIMO technology include per stream rate control (PSRC), TxAA, and the like.

Channel information refers to radio channel information (eg, attenuation, phase shift, or time delay) between a plurality of transmit antennas and a plurality of receive antennas. In a MIMO system, various stream paths exist by a combination of a plurality of transmit / receive antennas, and have a fading characteristic in which a channel state changes irregularly in a time / frequency domain due to a multipath time delay. Therefore, the transmitter calculates channel information through channel estimation. Channel estimation estimates channel information necessary to recover a distorted transmission signal. For example, channel estimation refers to estimating the magnitude and reference phase of a carrier. That is, channel estimation estimates a frequency response of a radio section or a radio channel.

As a channel estimating method, there is a method of estimating a reference value based on reference signals (RS) of several base stations using a two-dimensional channel estimator. In this case, RS refers to a symbol having a high output although not actually having data in order to help carrier phase synchronization and base station information acquisition. The transmitting side and the receiving side may perform channel estimation using such RS. The channel estimation by RS estimates a channel through a symbol commonly known by the transmitting and receiving side, and restores data using the estimated value. RS is also referred to as pilot.

MIMO systems support time division duplex (TDD) systems and frequency division duplex (FDD) systems. In a time division duplex (TDD) system, since the forward link transmission and the reverse link transmission are on the same frequency domain, it is possible to estimate the forward link channel from the reverse link channel by the reciprocity principle.

Wireless communication technology has been developed to LTE based on WCDMA, but the demands and expectations of users and operators are continuously increasing. In addition, as other radio access technologies continue to be developed, new technological evolution is required to be competitive in the future. Reduced cost per bit, increased service availability, flexible use of frequency bands, simple structure and open interface, and adequate power consumption of the terminal are required.

In this regard, 3GPP is preparing work to standardize subsequent technologies for LTE. In the present specification, the above technique is referred to as "LTE-Advanced" or "LTE-A". One of the major differences between LTE and LTE-A systems is the number of multiple antennas supported. Currently, LTE systems are designed to support up to four multiple antennas. LTE-A systems, on the other hand, aim to support up to eight multiple antennas. Therefore, the LTE-A system should be able to support the downlink transmission of the reference signal for up to eight antennas. In particular, in the LTE-A system, LTE terminals capable of recognizing up to four antennas and LTE-A terminals capable of recognizing up to eight antennas will coexist.

The present invention has been made to solve the problems of the prior art as described above, an object of the present invention is to provide a method for efficiently transmitting a downlink reference signal in a wireless communication system having multiple antennas.

Another object of the present invention is to provide a method for efficiently transmitting a downlink reference signal when the number of multiple antennas is expanded.

It is still another object of the present invention to provide a method of downlink transmission of a reference signal with backward compatibility when extending the number of multiple antennas.

Another object of the present invention is to provide a method for efficiently transmitting a reference signal in an environment in which terminals having different capabilities coexist.

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

In one aspect of the present invention, in a method of downlink transmission of a reference signal in a wireless communication system having multiple antennas, a reference signal for a first antenna group is allocated to a subframe including a specific region having different accessibility according to a terminal capability. And pairing a reference signal for a second antenna group with the first antenna group in the specific region and assigning the same by a code division multiplexing scheme, and transmitting the subframe in a downlink region. A method of downlink transmission of a signal is provided.

According to another aspect of the present invention, in a method of downlink transmission of a reference signal in a wireless communication system having multiple antennas, the reference signal for the first antenna group is provided in a subframe including a specific area having different accessibility according to the terminal capability. Allocating a reference signal for a second antenna group in the specific region with the first antenna group in a code division multiplexing scheme if the rank is greater than or equal to a predetermined value; A downlink transmission method of a reference signal including downlink transmission is provided.

In still another aspect of the present invention, there is provided a method for estimating a channel in a wireless communication system having multiple antennas, the method comprising: receiving subframes to which reference signals for first and second antenna groups are allocated; Extracting a reference signal for a second antenna group, and performing channel estimation with the extracted reference signal, wherein the subframe includes a specific region defined to prevent access of a terminal having a predetermined capability; There is provided a channel estimation method in which a reference signal for the second antenna group is paired with the first antenna group in the specific region and allocated in a code division multiplexing scheme.

In still another aspect of the present invention, there is provided a method for estimating a channel in a wireless communication system having multiple antennas, the method comprising: receiving subframes to which reference signals for first and second antenna groups are allocated; Extracting a reference signal for a second antenna group, and performing channel estimation with the extracted reference signal, wherein the subframe includes a specific region having different accessibility according to a terminal capability; When a reference signal for an antenna group has a rank equal to or greater than a predetermined value, a channel estimation method is provided for pairing with the first antenna group in the specific region and assigning the coded multiplexing scheme.

In another aspect of the present invention, a method for downlink transmission of a reference signal in a wireless communication system having multiple antennas, the method comprising: assigning a reference signal for a first antenna group to a subframe, and a dedicated reference signal in the subframe Allocating a reference signal for a second antenna group in a code division multiplexing scheme to a specific position where a dedicated reference signal (DRS) is assigned, wherein the specific position is a frequency within the subframe such that a frequency interval is constant. And a downlink transmission method of a reference signal distributed in a time domain.

In still another aspect of the present invention, there is provided a method for estimating a channel in a wireless communication system having multiple antennas, the method comprising: receiving subframes to which reference signals for first and second antenna groups are allocated; And extracting a reference signal for a second antenna group, and performing channel estimation with the extracted reference signal, wherein the reference signal for the second antenna group is a dedicated reference signal (DRS). Is assigned in a code division multiplexing scheme to a specific position defined to be assigned, and the specific position is distributed in the frequency and time domain within the subframe such that the frequency interval is constant.

According to the embodiments of the present invention, the following effects are obtained.

First, in a wireless communication system having multiple antennas, the reference signal can be efficiently transmitted downward.

Second, in case of extending the number of multiple antennas, the reference signal can be efficiently transmitted downward.

Third, when extending the number of multiple antennas, the reference signal may be transmitted downward while having backward support.

Fourth, it is possible to efficiently transmit a reference signal in an environment in which terminals having different capabilities coexist.

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.

The construction, operation, and other features of the present invention will be readily understood by the preferred embodiments of the present invention described with reference to the accompanying drawings. The embodiments described below are examples in which the technical features of the present invention are applied to an OFDM system having multiple antennas.

Modeling of Multiple Antenna (MIMO) Systems

1 is a block diagram of a wireless communication system having a general multiple antenna. 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 , the theoretical channel transmission capacity is proportional to the number of antennas, unlike when the transmitter or the receiver uses multiple antennas. This increases. Therefore, the transmission rate can be improved and the frequency efficiency can be significantly improved. As the channel transmission capacity is increased, the transmission rate can theoretically increase as the rate of increase rate R _i multiplied by the maximum transmission rate R _o when using a single antenna.

For example, in a MIMO communication system using four transmit antennas and four receive antennas, a transmission rate four times higher than a single antenna system may be theoretically obtained. Since the theoretical capacity increase of multi-antenna systems was proved in the mid 90's, various techniques to actively lead to the actual data rate improvement have been actively studied. In addition, some technologies are already being reflected in various wireless communication standards such as 3G mobile communication and next generation WLAN.

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

The communication method in a multi-antenna system will be described in more detail using mathematical modeling. It is assumed that there are N _T transmit antennas and N _R receive antennas in the system.

Looking at the transmission signal, when there are N _T transmit antennas, the maximum information that can be transmitted is N _T. The transmission information may be expressed as follows.

는 전송 전력이 다를 수 있다. 각각의 전송 전력을

라고 하면, 전송 전력이 조정된 전송 정보는 다음과 같이 표현될 수 있다.Each transmission information

The transmit power may be different. Each transmit power

In this case, the transmission information whose transmission power is adjusted may be expressed as follows.

는 전송 전력의 대각행렬

를 이용해 다음과 같이 표현될 수 있다.Also,

Is the diagonal of the transmit power

Can be expressed as

에 가중치 행렬

가 적용되어 실제 전송되는 N _T 개의 송신신호

가 구성되는 경우를 고려해 보자. 가중치 행렬

는 전송 정보를 전송 채널 상황 등에 따라 각 안테나에 적절히 분배해 주는 역할을 한 다.

는 벡터

를 이용하여 다음과 같이 표현될 수 있다.Information vector with adjusted transmission power

Weighting matrix

N _T transmitted signals actually applied by applying

Consider the case where is configured. Weighting matrix

Plays a role in properly distributing transmission information to each antenna according to transmission channel conditions.

Vector

It can be expressed as follows.

는 i번째 송신 안테나와 j번째 정보간의 가중치를 의미한다.

는 프리코딩 행렬이라고도 불린다.From here,

Denotes a weight between the i th transmit antenna and the j th information.

Is also called a precoding matrix.

은 벡터로 다음과 같이 표현될 수 있다.Received signal is received signal of each antenna when there are N _R receiving antennas

Can be expressed as a vector as

로 표시하기로 한다.

에서, 인덱스의 순서가 수신 안테나 인덱스가 먼저, 송신 안테나의 인덱스가 나중임에 유의한다. In the case of modeling a channel in a multi-antenna wireless communication system, channels may be divided according to transmit / receive antenna indexes. From the transmit antenna j to the channel through the receive antenna i

It is indicated by.

Note that in the order of the index, the receiving antenna index is first, and the index of the transmitting antenna is later.

2 shows a channel from N _T transmit antennas to receive antenna i . The channels may be bundled and displayed in vector and matrix form. In FIG. 2, a channel arriving from a total of N _T transmit antennas to a receive antenna i may be represented as follows.

Accordingly, all channels arriving from the N _T transmit antennas to the N _R receive antennas may be expressed as follows.

에서 행의 수는 수신 안테나의 수 N _R 과 같고, 열의 수는 송신 안테나의 수 N _T 와 같다. 즉, 채널 행렬

는 행렬이 N _R ㅧN _T 된다.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

The matrix is N _R ㅧ N _T.

를 거친 후에 백색잡음(AWGN; Additive White Gaussian Noise)이 더해진다. N _R 개의 수신 안테나 각각에 더해지는 백색잡음

은 다음과 같이 표현될 수 있다.Channel matrix on the actual channels

After passing through, Additive White Gaussian Noise (AWGN) is added. White noise added to each of N _R receive antennas

Can be expressed as

The received signal may be expressed as follows through the above-described mathematical modeling.

의 랭크(

)는 다음과 같이 제한된다.Meanwhile, the rank of the matrix is defined as the minimum number of rows or columns that are independent of each other. Thus, the rank of the matrix cannot be greater than the number of rows or columns. Channel matrix

Rank of (

) Is limited to

Another definition of rank may be defined as the number of nonzero eigenvalues when the matrix is eigenvalue decomposition. Similarly, another definition of rank may be defined as the number of nonzero singular values when singular value decomposition is performed. Therefore, the physical meaning of rank in the channel matrix is the maximum number that can send different information in a given channel.

Transmitter and Receiver of Multiple Antenna (MIMO) System

3 is a block diagram of a base station that can be applied to an embodiment of the present invention.

Referring to FIG. 3, a base station generally includes a control system 302, a baseband processor 304, a transmit circuit 306, a receive circuit 308, a multiple antenna 310, and a network interface 312. . The receiving circuit 308 receives the radio signal transmitted from the terminal through the multi-antenna 310. Preferably, low noise amplifiers and filters (not shown) amplify the signal and eliminate broadband interference. Downconversioin and digitization circuits (not shown) downconvert the filtered received signal into an intermediate or baseband frequency signal and digitize it into one or more digital streams.

The baseband processor 304 processes the digitized received signal to extract information or data bits from the received signal. The processing includes demodulation, decoding, error correction and the like. Baseband processor 304 is typically implemented with one or more digital signal processors (DSPs). Thereafter, the received information is transmitted through the wireless network via the network interface or to another terminal served by the base station. The network interface 312 interacts with a circuit switched network that forms part of a wireless network that may be connected to a central network controller and a public switched telephone network (PSTN).

On the transmitting side, the baseband processor 304 receives digitized data from the network interface 312 under control of the control system 302 and encodes the data for transmission, which may represent voice, data or control information. The encoded data is input to the transmitting circuit 306. In the transmission circuit 306, the encoded data is modulated by a carrier having a desired transmission frequency or frequencies. A power amplifier (not shown) amplifies the modulated carrier signal to a level suitable for transmission. The amplified signal is delivered to the multiple antenna 310.

4 is a block diagram of a terminal that can be applied to an embodiment of the present invention.

Referring to FIG. 4, the terminal may include a control system 402, a baseband processor 404, a transmission circuit 406, a reception circuit 408, a multiple antenna 410, and a user interface circuit 412. . Receiving circuit 408 receives a wireless signal containing information from multiple antennas 410 from one or more base stations. Preferably, a low noise amplifier and filter (not shown) amplify the signal and eliminate broadband interference. The downconversion and digitization circuit (not shown) then downconverts the received signal filtered into an intermediate or baseband frequency signal. The signal is then digitized into one or more digital streams. Baseband processor 404 processes the digitized received signal to extract information or data bits from the received signal. The process includes demodulation, decoding, and error correction operations. Baseband processor 404 is typically implemented with one or more digital signal processors (DSPs) and application specific integrated circuits (ASICs).

At the transmitting side, the baseband processor 404 receives digitized data from the user interface 312 under control of the control system 402 and encodes the data for transmission, which may represent voice, data or control information. The encoded data is input to the transmitting circuit 406. In the transmission circuit 406, the encoded data is modulated by a carrier having a desired transmission frequency or frequencies. A power amplifier (not shown) amplifies the modulated carrier signal to a level suitable for transmission. The amplified signal is delivered to the multiple antenna 410.

5 shows a block diagram of a transmitter that can be applied to an embodiment of the present invention.

Referring to FIG. 5, although the transmitter structure has been described with reference to a base station, those skilled in the art will appreciate that the structure shown may be used for uplink and downlink transmission. In addition, the transmission structure represents various multiple access structures including, but not limited to, code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), and orthogonal frequency division multiplexing (OFDM). It was intended to be.

Initially, the network transmits data to the base station to transmit to the terminal. The scheduled data, which is a bit stream, is scrambled in a manner that reduces the peak to average power ratio associated with the data using the data scramble module 504. A cyclic redundancy check (CRC) for the scrambled data is determined by the CRC addition module 506 and appended to the scrambled data. In order to facilitate data recovery and error correction at the terminal, channel coding is performed using the channel encoder module 508. Channel coding can effectively add redundancy to the data. The channel encoder module 508 may use turbo encoding technology.

The processed data bits are systematically mapped to corresponding symbols by the mapping module 514 depending on the selected baseband modulation. Quadrature amplitude modulation (QAM) or quadrature phase shift key (QPSK) modulation forms may be used. The group of bits is mapped to symbols representing positions in amplitude and phase constellations. The symbol block is then processed by the space time code (STC) encoder module 518. The STC encoder module 518 will process the symbols according to the selected STC encoding mode and provide N outputs corresponding to the number of multiple transmit antennas 310 of the base station. The symbol stream output from the STC encoder module 518 is inverse Fourier transformed by the IFFT processing module 520. The prefix and RS addition module 522 then adds a cyclic prefix (CP) and RS to the inverse Fourier transformed signal. Thereafter, the digital upconversion (DUC) module and the digital-to-analog (D / A) conversion module 524 upconvert the previously processed signal in the digital domain to an intermediate frequency and convert it into an analog signal. The analog signal is then modulated, amplified and transmitted simultaneously at the desired RF frequency via the RF module 526 and multiple antenna 310.

6 shows a block diagram of a receiver that can be applied to an embodiment of the present invention.

Referring to FIG. 6, the receiver structure has been described with reference to a terminal, but those skilled in the art will appreciate that the structure shown for uplink and downlink transmission may be used. When the transmitted signal arrives at the multiple transmit antenna 410, each signal is demodulated and amplified by the corresponding RF module 602. For convenience, only one of the multiple receive paths in the receiver is shown. Analog-to-digital (A / D) conversion and downconversion module (DCC) 604 digitizes and downconverts the analog signal for digital processing. The digitized signal may be used in an automatic gain control module (AGC) 606 to control the amplifier gain in the RF module 602 based on the received signal level.

Thereafter, the CRC checked data is recovered by the descrambling module 646 to the original data 648.

Reference Signal (RS)

When transmitting a packet in a wireless communication system, since the transmitted packet is transmitted through a wireless channel, signal distortion may occur during the transmission process. In order to correctly receive the distorted signal at the receiving end, the distortion must be corrected in the received signal using the channel information. In order to find out the channel information, a method of transmitting the signal known to both the transmitting side and the receiving side and finding the channel information with the distortion degree when the signal is received through the channel is mainly used. The signal is called a pilot signal or a reference signal. When transmitting and receiving data using multiple antennas, it is necessary to know the channel condition between each transmitting antenna and the receiving antenna to receive the correct signal. Therefore, a separate reference signal must exist for each transmit antenna.

7 illustrates the structure of 3GPP LTE downlink RS. 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. In case of normal CP, each slot is composed of 7 symbols [7 (a)]. In the case of an extended CP, each slot consists of six symbols [7 (b)]. Extended CPs are commonly used in environments with long delays. The number of supported base station transmit antennas is four, and resources used when transmitting RS signals for each antenna port 0-3 are shown as '0', '1', '2' and '3'. RS of antenna ports 0-3 is a common RS (CRS). 1 denotes an OFDM symbol index and sc denotes a subcarrier index.

RS time / frequency spacing

Considering a 20 MHz system in 3GPP LTE, one symbol consists of 2048 samples. At this time, the symbol duration (duration) is 66.67us (1us = 10- ⁶ second). In the case of a normal CP, the first symbol among the seven symbols uses 160 samples as CPs, and the remaining six symbols use 144 samples as CPs. Accordingly, the first symbol and the remaining symbols using the normal CP may cover channel delay spreads of 5.2us and 4.69us, respectively. In the case of an extended CP, the CP consists of 6 symbols of 512 samples. Thus, a symbol using an extended CP can cover as many as 16.67us of channel delay spread. Referring to FIG. 7 (a) (b), the RS for a specific antenna has a frequency spacing of 6 in one symbol. However, since the staggering of the RS for a specific antenna in a slot or in a subframe, the frequency interval between RSs becomes 3 as a result. Here, the frequency interval means subcarrier spacing between adjacent RSs on the frequency axis. In this case, adjacent RSs need not be in the same OFDM symbol, and may be distributed to several OFDM symbols, slots, and subframes on a time axis. The frequency interval may vary depending on the profile of the OFDM system. As an example, the frequency interval may be 15 kHz.

The relationship between the frequency spacing of the RS and the channel estimation capability will be described in more detail using a formula.

에 IDFT (Inverse Discrete Fourier Transform)를 취하면 다음과 같이 표현될 수 있다.For example, a sequence

If the IDFT (Inverse Discrete Fourier Transform) is taken, it can be expressed as follows.

가 된다.

에 IDFT를 취하면 다음과 같이 표현될 수 있다.Assuming that the frequency interval of RS is 'Z + 1', there are Z data signals between each RS. Suppose that only RS is transmitted to observe the effect of RS's frequency spacing on channel estimation. In this case, Z zeros are filled as data signals between each RS, and the transmission sequence is

Becomes

Taking an IDFT in, can be expressed as

과

는

이다.From here,

and

Is

to be.

와

의 관계를 살펴보면, 다음과 같이

신호가 0의 개수만큼 반복적으로 나타남을 알 수 있다.Using Equations 11 and 12

Wow

Looking at the relationship of,

It can be seen that the signal appears repeatedly as many as zero.

8 and 9 show the RS observed in the time domain when the frequency interval of the RS is 6. FIG. Referring to the figure, it can be seen that, according to Equation 13, RS appears in six repeated forms within one OFDM symbol duration. Assuming that the OFDM symbol duration is 66.66us, the RS appears repeatedly in a period of 11.11us in the time domain. Thus, if the channel delay spread does not exceed 11.11us, the original recovery of the RS signal is theoretically possible. When a normal CP is applied (CP length: 5.2us or 4.69us), it is assumed that a wireless environment in which channel delay of up to 5.2us or 4.69us occurs. Therefore, in an environment to which a general CP is applied, even if the frequency interval of the RS is 6, since there is no interference between each RS, the original restoration of the RS is possible (FIG. 8). On the other hand, when an extended CP is applied (CP length: 16.67us), it is assumed that a wireless environment in which a channel delay of up to 16.67us occurs. Therefore, in an environment to which an extended CP is applied, interference may exist between RSs when the frequency interval of the RS is 6 (FIG. 9).

In order to compensate for this problem, LTE has staggered the RS of each antenna so that the RS frequency interval is set to three. FIG. 10 shows the RS observed in the time domain when the frequency interval of the RS is 3. FIG. Referring to FIG. 10, since the frequency interval of the RS is 3, it can be seen that the RS appears in three repeated forms within one OFDM symbol duration. Assuming the OFDM symbol duration is 66.66us, the RS appears repeatedly in a period of 22.22us in the time domain. That is, since the covertable channel delay spread is 22.22us, the original restoration of the RS is possible regardless of the CP length.

Code division multiplexing (cdm)-cyclic delay in time domain

와 같은 형태일 수 있다. 주파수 도메인에서 직교 코드를 곱함으로써, RS는 시간 도메인에서 순환 지연(Cyclic dealy)될 수 있다. 시퀀스

에 직교 코드를 곱한 경우에, 시간 도메인에서 순환 지연되는 것을 수학식 15에 나타내었다.Assigning RSs for different antennas to the same resource region is called multiplexing. Multiplexing methods include time division multiplexing, frequency division multiplexing, or code division multiplexing. Among them, code division multiplexing means that an orthogonal code (sequence) set differently for each antenna is multiplied by RS in the frequency domain and allocated to the same radio resource (frequency / time). The orthogonal code is

It may be in the form of. By multiplying orthogonal codes in the frequency domain, the RS may be cyclically delayed in the time domain. sequence

In the case of multiplying the orthogonal codes, the cyclic delay in the time domain is shown in equation (15).

를 곱하면 시간축 상에서 순환 지연된다.Thus, in the frequency domain

Multiplying results in a circular delay on the time base.

Evolution from LTE to LTE-A: Expansion of Multiple Antenna Systems

One embodiment of the present invention relates to a method of transmitting downlink RSs when the number of transmitting antennas is extended to M (> N) in a conventional N-number system. In LTE, the number of downlink antennas is assumed to be 4 (= N). Therefore, the LTE terminal can also recognize up to four antennas. On the other hand, LTE-A considers that the number of antennas used for downlink transmission will be extended to 8 (= M). Although an embodiment of the present invention described below is illustrated using LTE-A, it should be noted that the same principle may be applied to any MIMO system that satisfies the condition of M> N.

In the above environment, within the cell of the base station supporting LTE-A, up to 8 (= M) antennas and user equipment (UE) and 8 (= M) antennas that can recognize only 4 (= N) existing transmit antennas can be recognized. LTE-A terminal coexist. In this case, in addition to the reference signal for supporting the existing N antennas, a reference signal for supporting 4 (= M-N) antennas should be additionally transmitted. In this case, it is necessary to efficiently transmit data and reference signals to an LTE UE that recognizes only four antennas in an environment in which an LTE-A UE that recognizes eight antennas is added without additional signaling. LTE defines antenna port 5 when in closed loop rank 1 transmission mode, but for the sake of convenience, antenna ports for LTE-A systems that extend to eight antennas will be 0-7. To be defined.

On the other hand, as shown in Figure 7 (a), the overhead of RS is 14.3% based on the normal CP. Therefore, one embodiment of the present invention will propose an RS transmission technique using CDM so that the overhead does not exceed 15% even if the number of antennas is increased. Until now, the term “normal CP” or “extended CP” has been used based on the LTE system. However, one embodiment of the present invention described below can also be used in a system that covers multiple channel delays. Therefore, the following description will be made of the case where the channel delay is small and the channel delay is large.

First Embodiment: Subframe Terminal accessibility to  8Tx Antenna Design

As described above, in the LTE-A system, the LTE UE and the LTE-A UE will coexist. In this case, in order to maintain backward compatibility for the LTE UE, the LTE-A system may operate a plurality of subframes having different accessibility according to the terminal capability. For convenience, subframes to be used in the LTE-A system are classified into two subframes according to UE accessibility (first subframe and second subframe).

In the present specification, the first subframe means a subframe that all terminals can freely access regardless of their capabilities. On the other hand, the second subframe refers to a subframe including a specific region having different accessibility according to the terminal capability. In an extreme example, the entire area of the second subframe may be configured only with a specific area having different accessibility according to the terminal capability. The difference in accessibility according to the terminal capability means that a terminal having a predetermined capability is restricted from access, or that only a terminal having a specific capability can access. For example, the first subframe can be read by both the LTE UE and the LTE-A UE. In contrast, the second subframe includes (i) an area that both the LTE UE and the LTE-A UE can access and an area that only the LTE-A UE can access, or (ii) only the LTE-A UE can access. It can consist of an area. Therefore, in case of (i), the LTE system may use only a part of the second subframe. In the case of (ii), the LTE system cannot use the entire area of the second subframe (eg, slot 1: l = 0 to slot 2: l = 5 (6)). The second subframe may include a multimedia broadcast / multicast single frequency network (MBSFN) subframe defined in an LTE system.

Accordingly, one embodiment of the present invention proposes to transmit downlink RS for an antenna added to an LTE system using a second subframe. Hereinafter, an embodiment of the present invention will be described in detail by taking MBSFN subframes as an example. In the present invention, examples of LTE, LTE-A, LTE UE, LTE-A UE, MBSFN subframes are intended to help the understanding of the present invention, and are not intended to limit the scope of the present invention to these.

11 shows the structure of the MBSFN subframe. MBSFN includes "Multi-Media Broadcast over a Single Frequency Network", "Multimedia Broadcast / multicast (MBMS) over a Single Frequency Network", "MBMS Single Frequency Network", "Multicast / Broadcast over a Single Frequency Network", "Multicast Broadcast" Single frequency network "," Multicast broadcast single frequency network "and the like can be used in various ways. Referring to FIG. 11, the MBSFN consists of two slots. One slot consists of seven OFDM symbols in the case of a normal CP and six OFDM symbols in the case of an extended CP. Resource block (RB) included in MBSFN consists of 12 subcarriers in the frequency domain.

Meanwhile, when the LTE system signals the LTE UE to the MBSFN subframe, the LTE UE does not read the data portion of the MBSFN subframe and does not use channel information. That is, when the LTE UE is signaled that the received subframe is an MBSFN subframe, it uses only information of l = 0 and l = 1 of slot 1 (denoted as 'LTE UE'). Accordingly, the remaining symbols except for the two OFDM symbols are resources that the LTE-A UE can freely use regardless of the operation of the LTE UE (shaded portion, denoted as 'LTE-A'). That is, the LTE UE is restricted from accessing and reading information about slot 1: l = 2-5 (6) and slot 2: l = 0-5 (6) of the MBSFN subframe. On the other hand, the LTE-A UE can freely access and read information about slot 1: l = 2-5 (6) and slot 2: l = 0-5 (6). Thus, it is possible to transmit the RS for the LTE-A UE in slot 1: l = 2-5 (6) and slot 2: l = 0-5 (6).

12 is a flowchart illustrating an example of downlink transmission of RSs of antenna ports 0-7 using a second subframe according to an embodiment of the present invention.

Referring to FIG. 12, the base station allocates an RS for the first antenna group to a subframe including a specific region having different accessibility according to the terminal capability (S1210). The specific area may be an area defined such that a terminal supporting only antenna ports 0-3 cannot be read. The terminal includes an LTE UE. The subframe may be an MBSFN subframe. The specific area may be slot 1: l = 0 to slot 2: l = 5 (6). When the subframe is an MBSFN subframe, the specific region may be slot 1: l = 2 to slot 2: l = 5 (6). The first antenna group is composed of an antenna used in a conventional multi-antenna system. The existing multi-antenna system may be a system supporting 1-4 multi-antennas. Preferably, the existing multi-antenna system may be an LTE system. For example, the first antenna group consists of antenna ports 0-3. The RS may be a common RS (CRS) or a dedicated RS (DRS).

Thereafter, the base station pairs the reference signal for the second antenna group with the first antenna group in the specific region and allocates the reference signal by the code division multiplexing method (S1220, FIG. 12 (a)). As another example, the base station pairs the reference signal for the second antenna group with the first antenna group in the specific region only when the rank is greater than or equal to a predetermined value and allocates the coded multiplexing scheme in operation S1220 and FIG. b)). The predetermined value may vary depending on the system. For example, if the system supports eight multiple antennas, the predetermined value may be five. If the code division multiplexing scheme is applied when the rank is smaller than the predetermined value, the RS transmission power is reduced. Therefore, when the rank size is smaller than a predetermined value, it may be more efficient to operate like the LTE system than to reduce the transmit power of the antenna in half. The second antenna group includes an antenna newly added to an existing multi-antenna system. The second antenna group may include 1-4 antennas. The system to which the second antenna group is applied is a system supporting multiple antennas of antenna ports 4-7. The system to which the second antenna group is applied may be an LTE-A system. For example, the second antenna group consists of antenna ports 4-7.

Thereafter, the base station transmits the subframe downward (S1230).

FIG. 13 illustrates a flowchart of estimating a channel in a terminal when RSs of antenna ports 0-7 are transmitted using a second subframe according to another embodiment of the present invention.

Referring to FIG. 13, the terminal receives subframes to which reference signals for the first and second antenna groups are allocated (S1310). The subframe includes a specific region having different accessibility according to the terminal capability, and the reference signal for the second antenna group is assigned to the specific region by code division multiplexing by pairing with the first antenna group ( Figure 13 (a)). As another example, the reference signal for the second antenna group is allocated in a code division multiplexing scheme by pairing with the first antenna group in the specific region only when the rank is greater than or equal to a predetermined value (FIG. 13 (b)). ). The predetermined value may vary depending on the system. For example, if the system supports eight multiple antennas, the predetermined value may be five. The RS may be a common RS (CRS) or a dedicated RS (DRS). Thereafter, the terminal extracts reference signals for the first and second antenna groups (S1320). The terminal performs channel estimation with the extracted reference signal (S1330). The terminal is a terminal capable of supporting antenna ports 4-7. The terminal includes an LTE-A UE. The first antenna group, the second antenna group, the terminal capability, and the specific area are the same as those described with reference to FIG. 12.

 Hereinafter, a method of allocating RS for the LTE-A UE in the MBSFN subframe will be described with a specific example.

In the LTE system, the number of RSs is defined as shown in Table 1 to maintain the maximum overhead of less than 15% when transmitting RS. The LTE system supports antenna ports 0-3 and the number of RSs is designed to be 8, 8, 4, and 4 per subframe. Since the number of RSs for the antenna ports 2 and 3 is 4, respectively, when the LTE-A system supports the antenna ports 0-7, the number of RSs for the additional antenna ports 4-7 can be limited to 4 each. Suggest that. The larger the number of RSs, the more accurate channel estimation is possible. However, in the LTE environment in which four antennas are supported, the RS of antenna ports 2-3 is limited to four RSs. The limit on the number of RSs for the added antenna port is shown in the dark portion of Table 1 below.

As can be seen from Table 1, 16 RSs are additionally required for antenna ports 4-7 of the LTE-A UE. In this regard, referring to the MBSFN subframe of FIG. 7, in LTE, the number of RSs transmitted through the remaining symbols except for the previous two symbols is 16. Therefore, one embodiment of the present invention proposes to use the same position as that of the LTE UE even for the RS for the antenna added in the LTE-A UE. When the RS position used by the LTE UE is used as it is, the LTE-A UE has an advantage of using the hardware used in the LTE UE as it is.

Antenna pairing is performed to apply CDM to RS transmitted to antenna ports 0-3 and RS transmitted to antenna ports 4-7. Antenna ports 0-3 used in the LTE system and antenna ports 4-7 added in the LTE-A system may be paired in any combination. As an example, the RS for the antenna ports 0-3 may be allocated as a pattern 1-1 or 1-2 to a specific area set so that the LTE UE cannot read the MBSFN subframe. The specific area is l = 2-5 (6) in slot 1 and l = 0-5 (6) in slot 2.

[Pattern 1-1]

[Pattern 1-2]

Here, l represents an OFDM symbol index, the number in the table represents a subcarrier index in the resource block, '-' indicates that no reference signal is assigned,

Here, antenna ports 0-3 can be permuted and the reference signal can be shifted along the frequency axis or time axis. The transition may be determined using a cell identifier (ID) or the like.

A) When the channel delay is small

In order to cover a small channel delay such as 5-6us, the frequency interval of the RS may have 3 or 6. RS patterns for pairing antenna ports 0-3 and antenna ports 4-7 are illustrated in FIGS. 14A and 14B. In the figure, only the specific region (ie, the region defined not to be read by the LTE terminal) to which the CDM is applied is shown. In the figure, reference signals for antenna ports 0-7 are shown as 0-7, respectively.

The reference signal patterns in FIGS. 14A and 14B are summarized as follows.

[Pattern 1-3]

[Pattern 1-4]

Here, l represents the OFDM symbol index, the number in the table represents the subcarrier index in the resource block, '-' indicates that no reference signal is assigned, the number in parentheses indicates the paired antenna,

Here, antenna ports 0-3 and antenna ports 4-7 may each be permuted independently, and the reference signal may be shifted along the frequency axis or time axis. The transition may be determined using a cell identifier (ID) or the like.

Referring to patterns 1-3 shown in FIG. 14A, antenna pairing is performed in slot 2 with (0, 4), (1, 5), (2, 6), and (3, 7). However, since the number of RSs of antenna ports 0 and 1 is larger than the number of RSs of antenna ports 2 and 3, the pairing is different from slots (0,7) and (1,6).

Referring to patterns 1-4 shown in FIG. 14B, antenna pairing is performed in slot 2 with (0,6), (1,7), (2,4), and (3,5). However, since the number of RSs in antenna ports 0 and 1 is greater than the number of RSs in antenna ports 2 and 3, slots (0, 5) and (1, 4) make pairing different.

On the other hand, orthogonality must be maintained between RSs using a code / sequence so as not to cause interference between RSs of paired antennas. As an example of CDM, it is proposed to give an appropriate cyclic delay value on the time axis as shown in Equation (14).

FIG. 15 shows an example in which CDM is applied to a part of the antenna pair illustrated in FIG. 14 (a).

와 안테나 포트 2

은 안테나 포트 6의 RS에 각각 CDM으로 페어링된다[슬롯 1:(1,6), 슬롯 2:(2,6)]. 즉, 안테나 포트 6은 슬롯 1과 슬롯 2에서 페어링되는 안테나가 달라진다. 따라서, 도 15에서 안테나 포트 6에 대한 RS는 주파수 간격이 3으로 보이지만, 실제 주파수 간격은 6이 된다. 안테나 포트 6에 대한 RS의 주파수 간격이 6이므로, 페어링되는 모든 안테나의 RS 시퀀스에

을 곱해준다. 이와 같이, 모든 안테나 페어에

을 곱함으로써 CDM 방법으로 기존의 안테나와 추가된 안테나를 구분할 수 있다.Referring to Figure 15 (a), antenna port 1

With antenna port 2

Are paired by CDM to RS of antenna port 6 (slot 1: (1, 6), slot 2: (2, 6)). That is, antenna port 6 is different from the antenna paired in slot 1 and slot 2. Thus, the RS for antenna port 6 in FIG. 15 appears to have a frequency spacing of 3, but the actual frequency spacing is six. Since the frequency spacing of RSs for antenna port 6 is 6, the RS sequence of all paired antennas

Multiply by. As such, on all antenna pairs

By multiplying by CDM method, the existing antennas and added antennas can be distinguished.

Referring to FIG. 15B, the RS of the antenna port 6 in the time domain is expressed in a cyclic delay with respect to the RS of the paired antenna port 1 or 2. In FIG. 15 (a), the CDM code multiplied by the paired RS causes a phase difference of π in the frequency domain, so that the RS of antenna port 6 in the time domain is 1/2 cycle for the RS of antenna port 1 or 2 in the time domain. Cyclic delay. Therefore, the RS of the added antenna port 6 can be distinguished from the RS of the existing antenna port 1 or 2. The RS at antenna port 6 is 11.11 / 2us apart on the time axis from the RS at antenna port 1 or 2, so it can cover a small channel delay such as 5-6us.

As described above, although the same CDM cyclic delay may be applied to all antenna pairs, different cyclic delays may be applied to each antenna pair. FIG. 16 shows an example in which CDM is applied in a manner different from that of FIG. 15.

을 곱해준다. 여기에서, θ는 시간 도메인에서 CDM 코드가 곱해진 RS의 순환 지연 값을 결정한다. 시간 도메인에서의 순환 지연 값은 Pㅧ(θㆇ2π)로 결정된다. P는 CDM 코드가 곱해지는 RS의 주기를 나타낸다. 따라서, 상기 θ는 RS의 순환 지연을 무선 환경에 따라 허용된 채널 딜레이 보다 크거나 같게 하는 값 가운데서 독립적으로 선택될 수 있다. 예를 들어, 상기 θ는 순환 지연 값을 5-6us 보다 크게 하는 임의의 값일 수 있다. 예를 들어, θ는 π/2≤θ≤3π/2 일 수 있다. 이 경우, RS는 시간 도메인에서 페어링된 RS의 1/4 내지 3/4 주기 순환 지연된다. 도 16(b)에 θ의 변화에 따라 안테나 포트 4의 RS가 소정 범위 내에서 순환 지연되는 것을 나타냈다. 이와 같이, 주파수 간격이 3인 안테나 페어에

을 곱함으로써 CDM 방법으로 기존의 안테나와 추가된 안테나를 구분할 수 있다. 그러나, 간단한 필터 디자인을 위해, 페어링되는 안테나의 RS 시퀀스에

을 곱해줄 수 있다. 상기 경우를 도 16(c)에 도시하였다. θ가 π이므로 추가된 안테나의 RS는 1/2 주기 순환 지연된다(11.11us).Referring to slot 2 of FIG. 14A, antenna port 4 is paired with antenna port 0 (0, 4). Within slot 2, antenna port 0 has a frequency spacing of 3 by staggering. Therefore, the RS of antenna port 4 paired with antenna port 0 also has a frequency interval of 3. Since the frequency interval of RS is 3, the RS sequence of the antenna to be paired

Multiply by. Here, θ determines the cyclic delay value of RS multiplied by the CDM code in the time domain. The cyclic delay value in the time domain is determined by P ㅧ ( θ 2π). P represents the period of RS by which the CDM code is multiplied. Thus, [ theta] can be independently selected from among values that make the cyclic delay of RS greater than or equal to the allowed channel delay according to the wireless environment. For example, θ may be any value that makes the cyclic delay value greater than 5-6us. For example, θ may be π / 2≤ θ ≤ 3π / 2. In this case, the RS is cyclically delayed 1/4 to 3/4 of the paired RS in the time domain. 16 (b) shows that the RS of the antenna port 4 is cyclically delayed within a predetermined range according to the change of θ . Thus, to an antenna pair with a frequency interval of 3

By multiplying by CDM method, the existing antennas and added antennas can be distinguished. However, for simple filter design, the RS sequence of the antenna being paired

Can be multiplied by This case is shown in Fig. 16 (c). Since θ is π, the RS of the added antenna is cyclically delayed 1/2 cycle (11.11us).

을 곱해 CDM 방법으로 안테나를 구분하는 예를 나타낸다.17 shows an RS sequence of an antenna to be paired when the frequency interval of RS is 3;

Multiply by to show an example of distinguishing antennas by the CDM method.

Referring to slot 2 of FIG. 14A, antenna port 4 is paired with antenna port 0 (0, 4). In this case, the receiver may think that the frequency interval of RS is 6 based on one OFDM symbol. In addition, it can be considered that the frequency interval of the RS is 3 based on one slot.

와

로 구분되고, 각각

및

이 곱해진 형태가 된다. 이 경우,

와

로부터 형성된 RS는 시간 도메인에서 1/2 주기만큼 순환 천이된다. 한 슬롯을 기준으로 RS 처리가 이뤄지면,

에

이 곱해진 형태가 된다.

로부터 형성된 RS는 시간 도메인에서 1/4 주기 순환 천이된다.When RS processing is performed based on one OFDM symbol, the RS of the paired antenna port 0 is

Wow

Separated by

And

Is multiplied. in this case,

Wow

The RS formed from is cyclically shifted by one-half period in the time domain. If RS processing is performed based on one slot,

on

Is multiplied.

The RS formed from the cyclic shift in quarter cycle in the time domain.

B) If the channel delay is large

It is proposed to apply the proposed RS transmission scheme when the channel delay is small when the channel delay is large. As described above, the frequency interval of the RS should be 3 to cover the case where the channel delay is as large as 16.67us. However, the proposed method in the case of "A) channel delay is small may have a frequency interval of 6 RS.

In this regard, referring back to FIG. 14 (a) (b), antenna pairing did not match correctly in slot 1 and slot 2. Therefore, some antennas have a frequency interval of 6 and apply CDM. Therefore, in consideration of the environment having a long channel delay spread, it is proposed to change the RS position of the antenna ports 0-3 so that the frequency interval is three.

18A and 18B show an example in which the position of the antenna is changed so that the frequency interval of RS becomes three. In the figure, only the specific region (ie, the region defined not to be read by the LTE terminal) to which the CDM is applied is shown. In the figure, reference signals for antenna ports 0-7 are shown as 0-7, respectively.

The reference signal patterns in FIGS. 18A and 18B are summarized as follows.

[Pattern 1-5]

[Pattern 1-6]

Here, l represents the OFDM symbol index, the number in the table represents the subcarrier index in the resource block, '-' indicates that no reference signal is assigned, the number in parentheses indicates the paired antenna,

Here, antenna ports 0-3 and antenna ports 4-7 may each be permuted independently, and the reference signal may be shifted along the frequency axis or time axis. The transition may be determined using a cell identifier (ID) or the like.

By changing the RS positions of antenna ports 0-3, as in patterns 1-5 and 1-6, antenna ports 0-3 and additional antenna ports 4-7 can be paired correctly to apply CDM to staggering. . In patterns 1-5, all antennas of the MBSFN subframe are paired with (0, 4), (1, 5), (2, 6), and (3, 7), and then the CDM scheme is applied to each antenna. Similarly, CDM can be considered in the same manner in patterns 1-6. As described above, by changing the RS position of the antenna ports 0-3, the frequency interval of the added antenna ports 4-7 can be reduced to three.

19 and 20 illustrate RSs observed in the time domain when RSs are assigned to patterns 1-5 or the like. Referring to FIG. 19, it can be seen that the RS of antenna port 6 is 11.11us cyclically delayed compared to the RS of paired antenna port 0. Therefore, if the channel delay spread exceeds 11.11us, interference may occur between the RSs of the antennas. However, since the signal strength of the RS signal decreases exponentially along the time axis, the interference is not expected to be large. On the other hand, if the channel delay is large, it is required to cover the channel delay spread up to 16.67us, but in the environment where antenna ports 0-7 are used, the channel delay spread rarely reaches 16.67us. However, if the channel delay is large, it is suggested to apply the above method in an environment in which a 11.11us channel delay spread can be covered (FIG. 20).

Currently, LTE-A discusses RS for channel measurement and RS for data demodulation. The present invention can transmit the newly increased RS of the antenna using the CDM to support LTE-A in the MBSFM subframe. The present invention has the advantage that it can be used for both RS for channel measurement and RS for data demodulation.

Example 2: Dedicated RS Design for 8Tx Antennas

The method of transmitting the downlink RS using the MBSFN subframe has a problem that the UE can be informed only when the MBSFN subframe is transmitted. Accordingly, there is a need for a method capable of transmitting downlink RSs for up to eight multi-antennas even when transmitting a general subframe. In the LTE-A UE, it may be possible to use the DRS location defined in LTE as the RS for the antenna ports 4-7. Accordingly, another embodiment of the present invention proposes to use a dedicated RS (DRS) transmitted in all subframes for 5-8 antennas for a supporting terminal.

21 is a flowchart illustrating a CDM scheme of assigning RSs of antenna ports 4-7 to DRS positions according to an embodiment of the present invention.

Referring to FIG. 21, the base station allocates an RS for the first antenna group to a subframe (S2110). The first antenna group is composed of an antenna used in a conventional multi-antenna system. The existing multiple antenna system may be a system supporting multiple antennas of antenna ports 0-3. The existing multi-antenna system may be an LTE system. For example, the first antenna group consists of antenna ports 0-3. The RS for the first antenna group may be a common RS (CRS).

Thereafter, the base station allocates the RS for the second antenna group in a code division multiplexing scheme to a specific position where the DRS is allocated in the subframe (S2120).

In this case, the base station may allocate the RS for the first antenna group and the RS for the second antenna group in a code division multiplexing scheme to a specific position where the DRS is allocated in the subframe.

The specific position may be distributed in the frequency and time domain in the subframe such that the frequency interval is constant. The frequency interval may be 3 or less in case of using a normal CP and 1 in case of using an extended CP. In addition, the specific position may be staggered between OFDM symbols. In addition, the specific position may be 2 or 3 frequency interval in the same OFDM symbol. The second antenna group includes an antenna newly added to an existing multi-antenna system. The second antenna group may include one to four antennas. The system to which the second antenna group is applied is a system supporting 5-8 multiple antennas. The system to which the second antenna group is applied may be an LTE-A system. For example, the second antenna group consists of antenna ports 4-7.

Thereafter, the base station transmits the subframe allocated with the RS to the terminal (S2130).

The base station may transmit the subframe identification information to the terminal indicating that the subframe is for a specific terminal supporting 5-8 multiple antennas. The subframe identification information may be transmitted to the UE through system information (SI), an RRC message, an L1 / L2 control signaling (eg, PDCCH), or a MAC / RLC / PDCP PDU. The RRC signal may be a signal associated with an RRC connection release, an RRC connection request, an RRC connection establishment, a radio bearer establishment, a radio bearer reset, an RRC connection reset, or an RRC connection reestablishment.

FIG. 22 is a flowchart of estimating a channel in a terminal when an RS of antenna ports 4-7 is transmitted using a DRS position according to another embodiment of the present invention.

Referring to FIG. 22, the terminal receives subframes to which reference signals for the first and second antenna groups are allocated (S2210). The reference signal for the second antenna group is allocated in a code division multiplexing scheme to a specific position where a dedicated reference signal (DRS) is assigned, and the specific position is a frequency within the subframe such that a frequency interval is constant. And in the time domain. Alternatively, the specific location may be coded multiplexed and allocated to the dedicated reference signal for the first antenna group and the dedicated reference signal for the second antenna group.

Thereafter, the terminal extracts reference signals for the first and second antenna groups (S2220). The terminal performs channel estimation with the extracted reference signal (S2230). The first antenna group and the second antenna group are the same as those described with reference to FIG. 21. In addition, the terminal may receive subframe identification information indicating that the subframe is for a specific terminal supporting 5-8 multi-antennas from the base station.

FIG. 23 (a) shows a subframe using a generic CP used for downlink transmission in an LTE system. In the figure, RSs for antenna ports 0-3 are shown as 0-4, respectively. RS of antenna ports 0-3 is a common RS (CRS). The DRS location is marked with a D on the resource element. 1 denotes an OFDM symbol index and sc denotes a subcarrier index.

Referring to FIG. 23A, a frequency interval between DRSs is two. Thus, the RS assigned to the DRS location appears twice in one symbol in the time domain. If the duration of the symbol is 66.67us, the decodeable time resolution of the RS assigned to the DRS position is 33.33us. Therefore, when the RS for four antennas added in the LTE-A system is allocated to the DRS position by the CDM method, each RS occupies 33.33 / 4 = 8.33us. Since the channel delay expected in the normal CP is 5-6us, it is possible to transmit the RS for antennas 4-7 at the DRS position without interference. In addition, in the case of a subframe using the normal CP, it may be possible to arrange the DRS such that the frequency interval between the DRS is 1 or 2.

FIG. 23 (b) shows a subframe using an extended CP used for downlink transmission in the LTE system. In the figure, RSs for antenna ports 0-3 are shown as 0-3, respectively. Antenna ports 0-3 RS are Common RS (CRS). The DRS location is marked with a D on the resource element. 1 denotes an OFDM symbol index and sc denotes a subcarrier index.

Referring to FIG. 23B, the extended CP has a frequency interval of 3 between DRSs. Thus, the RS assigned to a location in the DRS appears three times in one symbol in the time domain. If the duration of the symbol is 66.67us, the decodeable time resolution of the RS assigned to the DRS position is 22.22us. Therefore, when RSs for four antennas added in the LTE-A system are allocated to the DRS position by the CDM method, each RS occupies 22.22 / 4 = 5.55us. The expected channel delay in the extended CP is about 15us. Therefore, when the RS of the antenna ports 4-7 at the DRS position is transmitted by the CDM method, interference may occur between the RSs of the antenna. That is, performance transmission may occur when RSs of antenna ports 4-7 are transmitted using the DRS positions of subframes using the extended CP of the LTE system.

Accordingly, an embodiment of the present invention proposes 10 DRS patterns capable of transmitting RSs of antenna ports 4-7 without degradation in performance in a long channel delay environment.

24 shows an example of allocating a DRS position to a subframe using an extended CP according to an embodiment of the present invention. The allocation pattern is summarized as follows.

[Pattern 2-1]

Where l represents the OFDM symbol index, the number in the table represents the subcarrier index in the resource block, '-' indicates that no reference signal is assigned, and the reference signal shifts along the frequency axis or time axis. Can be.

Referring to RS pattern 2-1, the frequency interval between DRSs is maintained at 3 in one OFDM symbol. However, within one subframe, three OFDM symbols are staggered such that the frequency interval between DRSs is one. That is, the DRSs allocated to OFDM symbols l = 4 of the first slot and the DRSs allocated to OFDM symbols l = 1 and l = 4 of the second slot do not overlap each other in the frequency domain. In this case, the frequency interval between the DRS may finally be 1. If the RS for the antenna ports 4-7 is allocated to the DRS position by the CDM scheme, the resolution of the RS of each antenna can estimate the channel is 66.66us / 4 = 16.67us. The maximum channel delay spread expected in wireless environments with long channel delays is 15us. For each antenna, a longer time resolution than the maximum channel delay spread is ensured, thereby enabling channel estimation without deterioration of performance.

25 shows an example of allocating a DRS position to a subframe using an extended CP according to another embodiment of the present invention. The allocation pattern is summarized as follows.

[Pattern 2-2]

Where l represents the OFDM symbol index, the number in the table represents the subcarrier index in the resource block, '-' indicates that no reference signal is assigned, and the reference signal shifts along the frequency axis or time axis. Can be.

The method of arranging DRS in RS pattern 2-2 is basically the same as that described in RS pattern 2-1. However, in RS pattern 2-2, the DRS is not located in the OFDM symbol to which the CRS of antenna ports 0-3 is transmitted. In general, in order to improve the performance of the RS, it is possible to boost the power used for the RS higher than the power used for other resource elements. If boosting the power of all RSs in the resource block, the power range that the power amplifier must support depends on the number of RSs allocated in the same OFDM symbol. For example, referring to pattern 2-1, four RSs are generally allocated to one OFDM symbol, while eight RSs are allocated to l = 1 OFDM symbol in slot 2. Therefore, the power range that the power amplifier must support to boost eight RSs should be designed high. In addition, if the power is boosted for only four RSs like other OFDM symbols to uniformly adjust the total transmit power, the remaining four RSs may have relatively low power, which may degrade RS performance. In the RS pattern 2-2, the number of RSs included in the OFDM symbol is uniform, which does not cause the above power problem.

FIG. 26 shows an example of allocating a DRS position to a subframe using an extended CP according to another embodiment of the present invention. FIG. The allocation pattern is summarized as follows.

[Pattern 2-3]

Where l represents the OFDM symbol index, the number in the table represents the subcarrier index in the resource block, '-' indicates that no reference signal is assigned, and the reference signal shifts along the frequency axis or time axis. Can be.

The method of arranging DRS in RS pattern 2-3 is basically the same as that described in RS pattern 2-1. However, in the RS pattern 2-3, the DRS is arranged as far as possible in the time domain to maximize the time interpolation effect during channel estimation. RS pattern 2-3 characteristically does not place DRS in the last OFDM symbol (l = 5 in slot 2). This is because an RS for channel measurement may be transmitted in the last OFDM symbol.

27 illustrates an example of allocating a DRS position to a subframe using an extended CP according to another embodiment of the present invention. The allocation pattern is summarized as follows.

[Pattern 2-4]

Where l represents the OFDM symbol index, the number in the table represents the subcarrier index in the resource block, '-' indicates that no reference signal is assigned, and the reference signal shifts along the frequency axis or time axis. Can be.

If the number of DRSs included in each slot is different, there may be a power problem described in RS pattern 2-2 in boosting the RS at the base station. Accordingly, in pattern 2-4, one OFDM symbol is arranged in each slot. However, by changing the total number of OFDM symbols arranged in the DRS to 2, the frequency interval between the DRS in one OFDM symbol is changed from 3 to 2. In this case, the frequency interval between the DRS is finally one. Therefore, even in extended CP, channel estimation can be performed without deterioration of performance. The characteristic of RS patterns 2-4 is that channel estimation can be performed using two OFDM symbols located relatively close in time. Since it is not necessary to perform channel estimation by pulling all RSs spread over three OFDM symbols spread in the time domain, it is possible to improve performance when channel values change over time in a high speed environment.

28 shows an example of allocating a DRS position to a subframe using an extended CP according to an embodiment of the present invention. The allocation pattern is summarized as follows.

[Pattern 2-5]

Where l represents the OFDM symbol index, the number in the table represents the subcarrier index in the resource block, '-' indicates that no reference signal is assigned, and the reference signal shifts along the frequency axis or time axis. Can be.

The method of arranging DRS in RS pattern 2-5 is basically the same as that described in RS pattern 2-1. However, the pattern for staggering OFDM symbols is different. That is, in RS pattern 2-1, DRSs allocated to OFDM symbols l = 4 of the first slot are allocated to subcarriers 1, 4, 7, and 10, and DRSs allocated to OFDM symbols l = 4 of the second slot are assigned to subcarrier 0. , 3, 6, and 9. In RS pattern 2-5, DRSs allocated to OFDM symbols l = 4 of the first slot are allocated to subcarriers 0, 3, 6, and 9, and OFDM symbols l = of the second slot. DRSs assigned to 4 are allocated to subcarriers 1, 4, 7, and 10.

29 shows an example of allocating a DRS position to a subframe using an extended CP according to an embodiment of the present invention. The allocation pattern is summarized as follows.

[Pattern 2-6]

Here, l represents the OFDM symbol index, the number in the table represents the subcarrier index in the resource block, '-' indicates that no reference signal is assigned, the reference signal is shifted along the frequency axis or time axis Can be.

The method of arranging DRS in RS pattern 2-6 is basically the same as that described in RS pattern 2-5. However, in RS pattern 2-6, the DRS is not located in the OFDM symbol to which the CRS of antenna ports 0-3 are transmitted. This is to solve the power boosting problem as described in RS pattern 2-2.

30 shows an example of allocating an RS position to a subframe using an extended CP according to an embodiment of the present invention. The allocation pattern is summarized as follows.

[Pattern 2-7]

Where l represents the OFDM symbol index, the number in the table represents the subcarrier index in the resource block, '-' indicates that no reference signal is assigned, and the reference signal shifts along the frequency axis or time axis. Can be.

RS pattern 2-7 is a modification of the OFDM symbol to which the DRS is allocated in RS pattern 2-6.

31 shows an example of allocating an RS position to a subframe using an extended CP according to an embodiment of the present invention. The allocation pattern is summarized as follows.

[Pattern 2-8]

Where l represents the OFDM symbol index, the number in the table represents the subcarrier index in the resource block, '-' indicates that no reference signal is assigned, and the reference signal shifts along the frequency axis or time axis. Can be.

The method of arranging DRS in RS pattern 2-8 is basically the same as that described in RS pattern 2-1. However, the pattern for staggering OFDM symbols is different. That is, in RS pattern 2-1, DRSs allocated to OFDM symbols l = 4 of the first slot are allocated to subcarriers 1, 4, 7, and 10, and DRSs allocated to OFDM symbols l = 1 of the second slot are assigned to subcarrier 2. DRSs assigned to OFDM symbols l = 4 of the second slot are allocated to subcarriers 0, 3, 6, and 9, and in the RS pattern 2-8, OFDM symbols l = of the first slot. DRSs assigned to 4 are allocated to subcarriers 0, 3, 6, and 9, DRSs assigned to OFDM symbol l = 1 of the second slot are allocated to subcarriers 1, 4, 7, and 10, and OFDM symbols of the second slot. DRSs assigned to l = 4 are allocated to subcarriers 2, 5, 8, and 11.

32 shows an example of allocating a DRS position to a subframe using an extended CP according to an embodiment of the present invention. The allocation pattern is summarized as follows.

[Pattern 2-9]

Where l represents the OFDM symbol index, the number in the table represents the subcarrier index in the resource block, '-' indicates that no reference signal is assigned, and the reference signal shifts along the frequency axis or time axis. Can be.

The method of arranging DRS in RS pattern 2-9 is basically the same as that described in RS pattern 2-8. However, in RS pattern 2-9, the DRS is not located in the OFDM symbol to which the CRS of antenna ports 0-3 are transmitted. This is to solve the power boosting problem as described in RS pattern 2-2.

33 shows an example of allocating a DRS position to a subframe using an extended CP according to an embodiment of the present invention. The allocation pattern is summarized as follows.

[Pattern 2-10]

Where l represents the OFDM symbol index, the number in the table represents the subcarrier index in the resource block, '-' indicates that no reference signal is assigned, and the reference signal shifts along the frequency axis or time axis. Can be.

RS pattern 2-10 is a modification of the OFDM symbol to which the DRS is allocated in RS pattern 2-9.

The patterns 2-1 to 2-10 illustrate a case in which the RSs of the antennas 4-7 are allocated to the resource elements denoted by D in FIGS. 24 to 33 in a code division multiplexing scheme. From RS 33 to RS, antennas 0-7 may be allocated to the resource element denoted by D in a code division multiplexing scheme.

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.

Embodiments according to the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of a hardware implementation, an embodiment of the present invention may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), FPGAs ( field programmable gate arrays), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, procedure, function, etc. 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.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit 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.

The present invention can be applied to a method of performing communication in a wireless communication system. More specifically, the present invention can be applied to a method of downlink transmission of a reference signal in a wireless communication system having multiple antennas.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included as part of the detailed description in order to provide a thorough understanding of the present invention, provide an embodiment of the present invention and together with the description, illustrate the technical idea of the present invention.

1 shows an antenna configuration of a multi-antenna system.

2 shows a channel from an N _T transmit antenna to a receive antenna i.

3 is a block diagram of a base station that can be applied to an embodiment of the present invention.

4 is a block diagram of a terminal that can be applied to an embodiment of the present invention.

5 shows a block diagram of a transmitter that can be applied to an embodiment of the present invention.

6 shows a block diagram of a receiver that can be applied to an embodiment of the present invention.

FIG. 7 illustrates a structure in which a reference signal (RS) is allocated to a subframe using a normal CP and an extended CP in 3GPP LTE.

FIG. 8 illustrates channel delay spreading of an RS observed in the time domain when the frequency interval of the RS is 6 in an environment where a general CP is applied.

9 illustrates channel delay spreading of the RS observed in the time domain when the frequency interval of the RS is 6 in an environment in which an extended CP is applied.

FIG. 10 illustrates channel delay spreading of the RS observed in the time domain when the frequency interval of the RS is 3 in the environment where the normal CP and the extended CP are applied.

11 shows an example of allocating RS to an MBSFN subframe in an environment having a small channel delay.

12 is a flowchart illustrating an example of transmitting an RS of a 5-8 Tx antenna using an MBSFN subframe according to an embodiment of the present invention.

FIG. 13 shows a flowchart of estimating a channel in a terminal when an RS of a 5-8 Tx antenna is transmitted using an MBSFN subframe according to another embodiment of the present invention.

14 (a) and (b) show the RS pattern when the channel delay is small as the CDM scheme is applied to antenna pairing according to an embodiment of the present invention.

15 (a) shows an example of applying the CDM scheme to antenna pairing when the frequency interval of RS is 6 according to another embodiment of the present invention. FIG. 15B is a representation of FIG. 15A in the time domain.

FIG. 16 (a) shows an example of applying the CDM scheme to antenna pairing when the frequency interval of RS is 3 and 6 according to another embodiment of the present invention. 16 (b) and (c) represent FIG. 16 (a) in the time domain.

17 shows an example of applying the CDM scheme to antenna pairing when the frequency interval of RS is 3 according to another embodiment of the present invention.

18 (a) and (b) show an RS pattern to which the CDM scheme is applied when the position of RS for antennas 0 to 3 is changed according to another embodiment of the present invention.

FIG. 19 illustrates channel delay spreading of the RS observed in the time domain when the RS pattern of FIG. 18 is applied in an environment having a large channel delay.

FIG. 20 illustrates channel delay spreading of the RS observed in the time domain when the RS pattern of FIG. 18 is applied in a small channel delay environment.

21 is a flowchart for allocating RSs of antennas 4-7 to the DRS position by the CDM scheme according to an embodiment of the present invention.

22 illustrates a flowchart of estimating a channel in a terminal when an RS of a 5-8 Tx antenna is transmitted using a DRS position according to another embodiment of the present invention.

23 (a) and (b) show a structure in which a demodulation reference signal (RS) is allocated to a subframe using a normal CP and an extended CP in 3GPP LTE, respectively.

24 shows an example of allocating a DRS position to a subframe using an extended CP according to an embodiment of the present invention.

25 shows another example of allocating a DRS position to a subframe using an extended CP according to another embodiment of the present invention.

26 shows another example of allocating a DRS position to a subframe using an extended CP according to another embodiment of the present invention.

27 shows another example of allocating a DRS position to a subframe using an extended CP according to another embodiment of the present invention.

28 shows another example of allocating DRS positions to subframes using an extended CP according to another embodiment of the present invention.

29 shows another example of allocating a DRS position to a subframe using an extended CP according to another embodiment of the present invention.

30 shows another example of allocating a DRS position to a subframe using an extended CP according to another embodiment of the present invention.

31 shows another example of allocating a DRS position to a subframe using an extended CP according to another embodiment of the present invention.

32 shows another example of allocating a DRS position to a subframe using an extended CP according to another embodiment of the present invention.

33 shows another example of allocating a DRS position to a subframe using an extended CP according to another embodiment of the present invention.

Claims (40)

In the method for downlink transmission of a reference signal in a wireless communication system having multiple antennas, Allocating a reference signal for the first antenna group to a subframe including a specific region having different accessibility according to the terminal capability; Pairing a reference signal for a second antenna group with the first antenna group in the specific region and allocating the reference signal in a code division multiplexing scheme; And Downlink transmission of the reference frame; In the method for downlink transmission of a reference signal in a wireless communication system having multiple antennas, Allocating a reference signal for the first antenna group to a subframe including a specific region having different accessibility according to the terminal capability; Pairing a reference signal for a second antenna group with the first antenna group in the specific region by a code division multiplexing method when the rank is greater than or equal to a predetermined value; And Downlink transmission of the reference frame; The method according to claim 1 or 2, The specific region is a downlink transmission method of a reference signal, characterized in that the terminal supporting only four or less multi-antenna is defined not to be read. The method according to claim 1 or 2, The subframe includes a multimedia broadcast / multicast single frequency network (MBSFN) subframe. The method according to claim 1 or 2, The reference signal is a downlink transmission method of a reference signal, characterized in that the common reference signal (CRS) or dedicated reference signal (DRS). The method according to claim 1 or 2, The reference signal for the first antenna group is a downlink transmission method of the reference signal, characterized in that allocated to the specific region using a pattern 1-1 or 1-2: [Pattern 1-1]

[Pattern 1-2]

Here, l represents an OFDM symbol index, the number in the table represents a subcarrier index in the resource block, '-' indicates that no reference signal is assigned, Here, antenna ports 0-3 can be permuted and the reference signal can be shifted along the frequency axis or time axis. The method according to claim 1 or 2, And the second antenna group includes one to four antennas. The method according to claim 1 or 2, And the number of reference signals for each antenna belonging to the second antenna group is independently four or less. The method according to claim 1 or 2, And a reference signal for each antenna belonging to the second antenna group has a frequency interval of 3 or 6 independently. The method according to claim 1 or 2, A reference signal for each antenna belonging to the second antenna group is cyclic delay in the time domain, and the cyclic delay value is independently selected from a value greater than or equal to the allowed channel delay. Downlink transmission method. The method of claim 10, The cyclically delayed value is a downlink transmission method of a reference signal, characterized in that 1/4 to 3/4 period of the paired reference signal. The method of claim 11, The cyclically delayed value is 1/4, 1/2 or 3/4 when the frequency interval of the reference signal is 3, and 1/2 when the frequency interval of the reference signal is 6, the downlink transmission method of the reference signal . The method according to claim 1 or 2, The reference group for the first and the second antenna group is a downlink transmission method of the reference signal, characterized in that allocated using any one of the patterns selected from the following patterns 1-3 to 1-6: [Pattern 1-3]

[Pattern 1-4]

[Pattern 1-5]

[Pattern 1-6]

Here, l represents the OFDM symbol index, the number in the table represents the subcarrier index in the resource block, '-' indicates that no reference signal is assigned, the number in parentheses indicates the paired antenna, Here, antenna ports 0-3 and antenna ports 4-7 may each be permuted independently, and the reference signal may be shifted along the frequency axis or time axis. A method for estimating a channel in a wireless communication system having multiple antennas, Receiving a subframe to which reference signals for the first and second antenna groups are allocated; Extracting reference signals for the first and second antenna groups; And Performing channel estimation with the extracted reference signal, The subframe includes a specific region having different accessibility according to terminal capability, and a reference signal for the second antenna group is allocated to the specific region by code division multiplexing by pairing with the first antenna group. Estimation method. A method for estimating a channel in a wireless communication system having multiple antennas, Receiving a subframe to which reference signals for the first and second antenna groups are allocated; Extracting reference signals for the first and second antenna groups; And Performing channel estimation with the extracted reference signal, The subframe includes a specific region having different accessibility according to terminal capability, and the reference signal for the second antenna group is coded by pairing with the first antenna group in the specific region when the rank is equal to or greater than a predetermined value. Channel estimation method assigned by division multiplexing. The channel estimation method of claim 14 or 15, wherein the specific region is defined such that a terminal supporting only four or less multi-antennas cannot be read. The method according to claim 14 or 15, Wherein the subframe comprises a multimedia broadcast / multicast single frequency network (MBSFN) subframe. The method according to claim 14 or 15, And the reference signal is a common reference signal (CRS) or a dedicated reference signal (DRS). The method of claim 14 or 15, wherein the reference signal for the first antenna group is allocated using the pattern 1-1 or 2-1 in the specific region. [Pattern 1-1]

[Pattern 1-2]

Here, l represents an OFDM symbol index, the number in the table represents a subcarrier index in the resource block, '-' indicates that no reference signal is assigned, Here, antenna ports 0-3 can be permuted and the reference signal can be shifted along the frequency axis or time axis. 16. The method of claim 14 or 15, wherein the second antenna group comprises one to four antennas. 16. The method of claim 14 or 15, wherein the number of reference signals for each antenna belonging to the second antenna group is independently four or less. The method of claim 14 or 15, wherein the reference signal for each antenna belonging to the second antenna group has a frequency interval of 3 or 6 independently. The method according to claim 14 or 15, wherein a reference signal for each antenna belonging to the second antenna group is cyclic delayed in the time domain, and the cyclic delay value is greater than or equal to the allowed channel delay. Channel estimation method, characterized in that independently selected. 24. The method of claim 23, The cyclically delayed value is a channel estimation method, characterized in that 1/4 to 3/4 periods of the paired reference signal. The method of claim 24, The cyclically delayed value is 1/4, 1/2 or 3/4 when the frequency interval of the reference signal is 3, and 1/2 when the frequency interval of the reference signal is 6. The method of claim 14 or 15, wherein the reference groups for the first and second antenna groups are allocated using any one pattern selected from the following patterns 1-3 to 1-6. : [Pattern 1-3]

[Pattern 1-4]

[Pattern 1-5]

[Pattern 1-6]

Where l denotes an OFDM symbol index, a number in the table indicates a subcarrier index in a resource block, '-' indicates that a reference signal is not assigned, a number in parentheses indicates a paired antenna, Here, antenna ports 0-3 and antenna ports 4-7 may each be permuted independently, and the reference signal may be shifted along the frequency axis or time axis. In the method for downlink transmission of a reference signal in a wireless communication system having multiple antennas, Assigning a reference signal for the first antenna group to the subframe; Allocating a reference signal for a second antenna group in a code division multiplexing scheme to a specific position where a dedicated reference signal (DRS) is allocated in the subframe; And Downlinking the subframe; And the specific position is distributed in a frequency and time domain within the subframe such that a frequency interval is constant. The method of claim 27, The frequency interval is a downlink transmission method of a reference signal, characterized in that 3 or less when using a normal cyclic prefix (CP), 1 when using an extended cyclic prefix (CP). The method of claim 27, And the specific position is staggered between OFDM symbols. The method of claim 27, The reference signal for the first antenna group and the reference signal for the antenna group for the second group is not allocated in the same OFDM symbol, characterized in that the downlink transmission method. The method of claim 27, And transmitting to the terminal subframe identification information indicating that the subframe is for a terminal supporting five or more multi-antennas. The method of claim 27, And a reference signal for the first antenna group and a reference signal for the second antenna group are allocated to the specific position in a code division multiplexing scheme. The method of claim 27, The reference group for the first and the second antenna group is allocated by using any one of the patterns selected from the patterns 2-1 to 2-10 below. [Pattern 2-1]

[Pattern 2-2]

[Pattern 2-3]

[Pattern 2-4]

[Pattern 2-5]

[Pattern 2-6]

[Pattern 2-7]

 [Pattern 2-8]

 [Pattern 2-9]

[Pattern 2-10]

Here, l represents an OFDM symbol index, the number in the table represents a subcarrier index in the resource block, '-' indicates that no reference signal is assigned, Here, the reference signal may be shifted along the frequency axis or the time axis. A method for estimating a channel in a wireless communication system having multiple antennas, Receiving a subframe to which reference signals for the first and second antenna groups are allocated; Extracting reference signals for the first and second antenna groups; And Performing channel estimation with the extracted reference signal, The reference signal for the second antenna group is allocated in a code division multiplexing scheme to a specific position where a dedicated reference signal (DRS) is assigned, and the specific position is a frequency within the subframe such that a frequency interval is constant. And a channel estimation method distributed in the time domain. The method of claim 34, wherein The frequency interval is a channel estimation method, characterized in that 3 or less when using a normal cyclic prefix (CP), and 1 when using an extended cyclic prefix (CP). The method of claim 34, wherein And the specific position is staggered between OFDM symbols. The method of claim 34, wherein And the reference signal for the first antenna group and the reference signal for the antenna group for the second group are not allocated in the same OFDM symbol. The method of claim 34, wherein And receiving subframe identification information indicating that the subframe is for a terminal supporting five or more multi-antennas. The method of claim 34, wherein And a reference signal for the first antenna group and a reference signal for the second antenna group are allocated to the specific position in a code division multiplexing scheme. The method of claim 34, wherein The reference group for the first and second antenna group is allocated using any one of the patterns selected from the patterns 2-1 to 2-10 below: [Pattern 2-1]

[Pattern 2-2]

[Pattern 2-3]

[Pattern 2-4]

[Pattern 2-5]

[Pattern 2-6]

[Pattern 2-7]

[Pattern 2-8]

 [Pattern 2-9]

[Pattern 2-10]

Here, l represents an OFDM symbol index, the number in the table represents a subcarrier index in the resource block, '-' indicates that no reference signal is assigned, Here, the reference signal may be shifted along the frequency axis or the time axis.

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