WO2010087646A2 - Method and apparatus for transmitting reference signal in wireless communication system - Google Patents

Abstract

A method and an apparatus for transmitting a reference signal in a wireless communication system are provided. The method comprises the steps of: allocating M reference signals for M antennas (wherein, M is a natural number) in an advanced subframe; and transmitting the M reference signals, wherein said M reference signals are allocated to a portion of resource elements which is located at the same position as that of the resource element in which N reference signals for N antennas (wherein, N is a natural number) are disposed in a legacy subframe, wherein M is larger than N. The present invention provides a method and apparatus for transmitting a reference signal for an advanced system which uses an increased number of antennas while maintaining a reference signal overhead of a legacy system.

Description

Method and apparatus for transmitting reference signal in wireless communication system

The present invention relates to wireless communication, and more particularly, to a method and apparatus for transmitting a reference signal in a wireless communication system.

The next generation multimedia wireless communication system, which is being actively researched recently, requires a system capable of processing and transmitting various information such as video, wireless data, etc., out of an initial voice-oriented service. The purpose of a wireless communication system is to enable a large number of users to communicate reliably regardless of location and mobility. However, a wireless channel is a Doppler due to path loss, noise, fading due to multipath, intersymbol interference (ISI), or mobility of UE. There are non-ideal characteristics such as the Doppler effect. Various techniques have been developed to overcome the non-ideal characteristics of the wireless channel and to improve the reliability of the wireless communication.

A technique for supporting reliable high speed data service is MIMO (multiple input multiple output). MIMO technology uses multiple transmit antennas and multiple receive antennas to improve data transmission and reception efficiency. MIMO techniques include spatial multiplexing, transmit diversity, beamforming, and the like. The MIMO channel matrix according to the number of receive antennas and the number of transmit antennas may be decomposed into a plurality of independent channels. Each independent channel is called a layer or stream. The number of layers is called rank.

In a wireless communication system, a signal known to both a transmitter and a receiver is required for channel state measurement and data demodulation. A signal known to both the transmitter and the receiver is called a reference signal (RS). The reference signal may also be called a pilot.

The receiver may measure a channel quality indicator (CQI) through a reference signal and feed back the CQI to the transmitter. In addition, the receiver may estimate a channel between the transmitter and the receiver through a reference signal and demodulate data using the estimated channel. Since the signal transmitted from the transmitter undergoes a corresponding channel for each transmission antenna or layer, the reference signal may be allocated for each transmission antenna or layer. Reference signals for each transmission antenna or layer may be distinguished by using resources such as time, frequency, and code. When there are a plurality of transmit antennas, the reference signal overhead can be greatly increased. The reference signal overhead may be defined as the ratio of resources used for transmitting the reference signal with respect to all resources. If the reference signal overhead is large, channel estimation performance can be improved and reliability of wireless communication can be improved. However, if the reference signal overhead is large, there is a problem of reducing the resources that can actually transmit data. This reduces data throughput and lowers spectral efficiency. This can degrade the performance of the entire system.

The number of transmit antennas used in the existing wireless communication system (hereinafter, legacy system) may be up to four. In case of designing a reference signal in a new wireless communication system (hereinafter, advanced system) that uses the number of transmit antennas to eight, for example, it is designed to support legacy user equipment operating in a legacy system. It is preferable. That is, it is desirable to support backward compatibility with legacy terminals. When a reference signal of an advanced system is located in a resource in which data is transmitted in a legacy system, the legacy terminal recognizes the reference signal as data. Accordingly, the legacy terminal attempts to demodulate data with respect to the reference signal, and as a result, may degrade the data demodulation performance of the legacy terminal.

There is a need for a method and apparatus for transmitting a reference signal for an extended antenna that maintains backward compatibility with a legacy terminal and does not increase the overhead of the reference signal.

An object of the present invention is to provide a method and apparatus for transmitting a reference signal in a wireless communication system.

A reference signal transmission method performed by a transmitter in a wireless communication system is provided. The method includes allocating M reference signals for M antennas (where M is a natural number) in an advanced subframe; And transmitting the M reference signals, wherein the M reference signals are partially located at the same position as the resource element in which N reference signals for N antennas (N is a natural number) are arranged in a legacy subframe. Assigned to a resource element, M is greater than N.

An apparatus for wireless communication includes a radio frequency (RF) unit for transmitting and / or receiving a radio signal; And a processor connected to the RF unit to allocate M reference signals for M antennas (M is a natural number) and transmit the M reference signals in an advanced subframe, wherein the M reference signals include: In the legacy subframe, N (N is a natural number) N reference signals for the antennas are allocated to some resource elements at the same position as the resource element where the arrangement is, and M is greater than N.

It is possible to provide a method and apparatus for transmitting a reference signal for an advanced system using an extended number of antennas while maintaining a reference signal overhead of a legacy system.

Since backward compatibility with legacy systems is provided, degradation of data demodulation performance of each terminal can be reduced even when legacy terminals operating in legacy systems and terminals operating in advanced systems are mixed.

1 is a block diagram illustrating a wireless communication system.

2 shows an example of a radio frame structure.

3 is an exemplary diagram illustrating a resource grid for one downlink slot.

4 shows an example of a structure of a radio frame and a downlink subframe.

5 shows an example of a structure of a downlink subframe.

6 is a block diagram illustrating an example of a transmitter structure.

7 illustrates an example of reference signal mapping for one antenna in the case of a normal CP.

8 illustrates an example of reference signal mapping for two antennas in the case of a normal CP.

9 illustrates an example of reference signal mapping for four antennas in the case of a normal CP.

10 illustrates an example of reference signal mapping for one antenna in case of an extended CP.

11 illustrates an example of reference signal mapping for two antennas in case of an extended CP.

12 shows an example of reference signal mapping for four antennas in the case of an extended CP.

13 shows an example of MBSFN reference signal mapping.

14 shows an example of reference signal mapping in a unicast subframe.

15 shows an example of reference signal mapping in an MBSFN subframe.

16 is a flowchart illustrating a reference signal transmission method performed by a transmitter according to an embodiment of the present invention.

17 shows examples of legacy subframes and advanced subframes.

18 shows an example of RS mapping in an advanced subframe.

19 shows another example of RS mapping in an advanced subframe.

20 illustrates an example of reference signal mapping in a legacy subframe in the case of a normal CP.

21 illustrates an example of reference signal mapping in a legacy subframe in case of an extended CP.

22 shows a first example of reference signal mapping in an advanced subframe in case of a normal CP.

FIG. 23 shows a second example of RS mapping in an advanced subframe in case of a normal CP.

24 illustrates a first example of RS mapping in an advanced subframe in case of an extended CP.

FIG. 25 illustrates a second example of RS mapping in an advanced subframe in case of an extended CP.

FIG. 26 shows a third example of RS mapping in an advanced subframe in case of a normal CP.

27 illustrates a fourth example of RS mapping in an advanced subframe in case of a normal CP.

FIG. 28 shows a third example of RS mapping in an advanced subframe in case of an extended CP.

29 shows a fourth example of RS mapping in an advanced subframe in case of an extended CP.

30 illustrates a fifth example of RS mapping in an advanced subframe in case of a normal CP.

Indicates.

31 illustrates a sixth example of RS mapping in an advanced subframe in case of a normal CP.

Indicates.

32 illustrates a fifth example of RS mapping in an advanced subframe in case of an extended CP.

Indicates.

33 is a sixth diagram of RS mapping in an advanced subframe in case of an extended CP.

For example.

34 shows an example of an advanced subframe structure in case of a normal CP.

35 shows another example of an advanced subframe structure in the case of a normal CP.

36 is a block diagram illustrating an apparatus for wireless communication, in which an embodiment of the present invention is implemented.

It is also.

The following technologies include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier-frequency division multiple access (SC-FDMA), and the like. The same can be used for various multiple access schemes. CDMA may be implemented with a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented with wireless technologies such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in a wireless technology such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) long term evolution (LTE) is part of an Evolved UMTS (E-UMTS) using E-UTRA, and employs OFDMA in downlink and SC-FDMA in uplink. LTE-A (Advanced) is the evolution of 3GPP LTE.

For clarity, the following description focuses on 3GPP LTE / LTE-A, but the technical spirit of the present invention is not limited thereto.

1 is a block diagram illustrating a wireless communication system.

Referring to FIG. 1, the wireless communication system 10 includes at least one base station 11 (BS). Each base station 11 provides a communication service for a particular geographic area (generally called a cell) 15a, 15b, 15c. The cell can in turn be divided into a number of regions (called sectors). A user equipment (UE) 12 may be fixed or mobile, and may include a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), It may be called other terms such as a wireless modem and a handheld device. The base station 11 generally refers to a fixed station communicating with the terminal 12, and may be called in other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, and the like. have.

Hereinafter, downlink (DL) means communication from the base station to the terminal, and uplink (UL) means communication from the terminal to the base station. In downlink, a transmitter may be part of a base station, and a receiver may be part of a terminal. In uplink, a transmitter may be part of a terminal, and a receiver may be part of a base station.

The wireless communication system can support multiple antennas. The transmitter may use a plurality of transmit antennas (Tx antennas), and the receiver may use a plurality of receive antennas (Rx antennas). A transmit antenna refers to a physical or logical antenna used to transmit one signal or stream, and a receive antenna refers to a physical or logical antenna used to receive one signal or stream. If the transmitter and receiver use multiple antennas, the wireless communication system may be called a multiple input multiple output (MIMO) system.

2 shows an example of a radio frame structure.

Referring to FIG. 2, a radio frame consists of 10 subframes, and one subframe consists of two slots. Slots in a radio frame are numbered with slots # 0 through # 19. The time taken for one subframe to be transmitted is called a transmission time interval (TTI). TTI may be referred to as a scheduling unit for data transmission. For example, one radio frame may have a length of 10 ms, one subframe may have a length of 1 ms, and one slot may have a length of 0.5 ms.

The structure of the radio frame is merely an example, and the number of subframes included in the radio frame or the number of slots included in the subframe may be variously changed.

3 is an exemplary diagram illustrating a resource grid for one downlink slot.

Referring to FIG. 3, a downlink slot includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in a time domain and an N (DL) resource block (RB) in a frequency domain. It includes. The OFDM symbol is used to represent one symbol period, and may be called another name such as an OFDMA symbol or an SC-FDMA symbol according to a multiple access scheme. The number N (DL) of resource blocks included in the downlink slot depends on the downlink transmission bandwidth set in the cell. In 3GPP LTE, N (DL) may be any one of 6 to 110. One resource block includes a plurality of subcarriers in the frequency domain.

Each element on the resource grid is called a resource element (RE). Resource elements on the resource grid may be identified by index pairs (k, l) in the slot. Where k (k = 0, ..., N (DL) × 12-1) is the subcarrier index in the frequency domain, and l (l = 0, ..., 6) is the OFDM symbol index in the time domain.

Here, an example of one resource block includes 7 × 12 resource elements including 7 OFDM symbols in the time domain and 12 subcarriers in the frequency domain, but the number of OFDM symbols and the number of subcarriers in the resource block is equal to this. It is not limited. The number of OFDM symbols may vary depending on the length of a cyclic prefix (CP) and subcarrier spacing. For example, the number of OFDM symbols is 7 for a normal CP and the number of OFDM symbols is 6 for an extended CP. The resource grid for the downlink slot illustrated in FIG. 3 may also be applied to the resource grid for the uplink slot.

4 shows an example of a structure of a radio frame and a downlink subframe.

Referring to FIG. 4, a radio frame includes 10 subframes, and the subframe includes two consecutive slots. Subframes within a radio frame are numbered from 0 to 9 subframes. In the case of a normal CP, a subframe includes 14 OFDM symbols. In the case of an extended CP, a subframe includes 12 OFDM symbols.

A synchronization channel (SCH) may be transmitted for every radio frame. The synchronization channel is a channel for cell search. The cell search is a process in which the UE acquires time synchronization and frequency synchronization with a cell and detects a cell ID of the cell. The synchronization channel includes a primary-SCH (P-SCH) and a secondary-SCH (S-SCH). A primary synchronization signal (PSS) is transmitted through the P-SCH, and a secondary synchronization signal (SSS) is transmitted through the S-SCH. The P-SCH may be transmitted through the last OFDM symbol of the first slot (slot numbers # 1, # 10) of subframes having subframe numbers 0 and 5 in the radio frame. In case of a normal CP, an OFDM symbol having an OFDM symbol index of 6 is an OFDM symbol, and in case of an extended CP, an OFDM symbol having an OFDM symbol index of 5 is an OFDM symbol. The S-SCH may be transmitted on an OFDM symbol immediately before the OFDM symbol on which the P-SCH is transmitted.

PBCH (physical broadcast channel) carries system information (SI). System information is essential information that the terminal needs to know in order to communicate with the base station. System information transmitted on the PBCH includes the most essential and most frequently transmitted parameters. The parameters are needed to obtain other information from the cell. Examples of the parameter may include a downlink transmission bandwidth, a system frame number (SFN), which is a radio frame number. In this case, the UE needs to receive system information on the PBCH in order to know the number N (DL) of resource blocks included in the downlink slot in the frequency domain. In 3GPP LTE, the base station may transmit system information on 6 resource blocks (6 RB) in the frequency domain.

System information is transmitted during four consecutive radio frames. The SFN of the radio frame where the system information transmission starts may satisfy SFN mod 4 = 0. The system information is an OFDM symbol having an OFDM symbol index l (L) of 0 to 3 in a second slot (slot number # 1) of a subframe having a subframe number of 0 in each radio frame. Can be sent through the network. However, this is merely an example and does not limit an area to which a PBCH is allocated in a radio frame.

5 shows an example of a structure of a downlink subframe.

Referring to FIG. 5, the downlink subframe includes two consecutive slots. The preceding three OFDM symbols of the first slot in the downlink subframe are the control region, and the remaining OFDM symbols are the data region. Here, it is merely an example that the control region includes 3 OFDM symbols.

In 3GPP LTE, a downlink subframe may be classified into a unicast subframe and a multimedia broadcast multicast service single frequency network (MBSFN) subframe. Unicast subframe is a subframe for supporting point-to-point communication. The MBSFN subframe is a subframe for supporting a multimedia broadcast and multicast service (MBMS). During the MBSFN subframe, a time-synchronized common waveform is transmitted from multiple cells. MBSFN transmission seems to be a transmission from a single large cell to the terminal. MBMS is a point-to-multipoint service where data is sent from one transmitter to multiple receivers. In the unicast subframe, the control region may consist of 4 OFDM symbols or less, and in the MBSFN subframe, the control region may consist of 2 OFDM symbols or less.

A physical downlink shared channel (PDSCH) may be allocated to the data region in the unicast subframe. Downlink data may be transmitted on the PDSCH. A physical multicast channel (PMCH) may be allocated to the data region in the MBSFN subframe. MBMS data may be transmitted on the PMCH. The MBSFN subframe may be transmitted on a carrier that supports both PMCH and PDSCH. Alternatively, the MBSFN subframe may be transmitted on a carrier that does not support PDSCH.

In the control region, control channels such as a physical control format indicator channel (PCFICH), a physical automatic repeat request (HICH) indicator channel (PHICH), and a physical downlink control channel (PDCCH) may be allocated.

The PHICH carries HARQ acknowledgment (NACK) / negative acknowledgment (NACK) for uplink data.

The PCFICH carries information on the number of OFDM symbols used for transmission of PDCCHs in a subframe to the UE. The number of OFDM symbols used for PDCCH transmission may be changed every subframe. The number of OFDM symbols used for PDCCH transmission in the unicast subframe may be one of 1, 2, and 3. If the downlink transmission bandwidth is smaller than a specific threshold, the number of OFDM symbols used for PDCCH transmission in a unicast subframe may be one of 2, 3, and 4. When the PMCH in the MBSFN subframe is transmitted on a carrier supporting both the PMCH and the PDSCH, up to two OFDM symbols of the first slot in the MBSFN subframe may be reserved for non-MBSFN transmission.

The PDCCH carries downlink control information. The downlink control information includes downlink scheduling information, uplink scheduling information, or an uplink power control command. The downlink scheduling information is also called a downlink grant, and the uplink scheduling information is also called an uplink grant.

6 is a block diagram illustrating an example of a transmitter structure. Here, the transmitter may be part of the terminal or the base station.

Referring to FIG. 6, the transmitter 100 includes a reference signal generator 110, a data processor 120, and Nt resource element mappers 130-1,..., 130. -Nt), Nt OFDM signal generators (140-1, ..., 140-Nt) and Nt antennas 190-1, ..., 190-Nt (Nt is a natural number). ).

Each of the Nt resource element mappers 130-1,..., 130 -Nt is connected to each of the Nt OFDM signal generators 140-1,..., 140 -Nt, and each of the Nt OFDM signal generators 140. Each of -1, ..., 140-Nt) is connected to each of the Nt antennas 190-1, ..., 190-Nt. That is, the n-th resource element mapper 130-n is connected to the n-th OFDM signal generator 140-n, and the n-th OFDM signal generator 140-n is connected to the n-th antenna 190-n ( n = 1, ..., Nt). In the case of multi-antenna transmission, there is one resource grid defined for each antenna.

The reference signal generator 110 is connected to Nt resource element mappers 130-1,..., 130 -Nt to generate a reference signal sequence corresponding to the reference signal. The reference signal sequence is composed of a plurality of reference symbols. As the reference signal sequence, any sequence may be used without particular limitation.

The data processor 120 is connected to the Nt resource element mappers 130-1,..., 130 -Nt, and is configured to process data to generate data symbols. The data processor 120 is configured to generate a bit stream corresponding to data, generate a codeword by performing channel coding on the bit stream, and modulate-mapped the codeword to generate data symbols. Can be. Codewords may be plural. The data processor 120 may be configured to further perform layer mapping, precoding, etc. according to a transmission scheme. For example, transmission schemes include single antenna schemes, transmit diversity schemes, large delay cyclic delay diversity schemes, and closed-loop spatial multiplexing. ) And multiple user-MIMO (MU-MIMO) techniques.

Each of the Nt resource element mappers 130-1,..., 130 -Nt is configured to map data symbols and reference symbols to resource elements that are time-frequency resources. One data symbol or one reference symbol may be mapped to one resource element. The resource element to which the reference symbol is mapped is called a reference resource element. Each of the Nt OFDM signal generators 140-1, ..., 140-Nt are configured to generate a time-continuous OFDM signal. Each of the Nt OFDM signal generators 140-1,..., 140 -Nt may generate an OFDM signal through inverse fast Fourier transform (IFFT), CP insertion, or the like. Each OFDM signal is transmitted through each of the Nt antennas 190-1, ..., 190-Nt.

Reference signals include cell-specific reference signals and MBSFN reference signals. The cell specific reference signal is a reference signal associated with non-MBSFN transmission, and the MBSFN reference signal is a reference signal associated with MBSFN transmission.

The cell specific reference signal may be transmitted through all downlink subframes in a cell supporting non-MBSFN transmission. Only the first 2 OFDM symbols in the MBSFN subframe may be used for cell specific reference signal transmission. The cell specific reference signal may be transmitted on one or several antennas. In 3GPP LTE, cell specific reference signals are defined only for subcarrier spacing 15 kHz (kilohertz).

Hereinafter, an example of a reference signal sequence of a cell specific reference signal generated by the reference signal generator 110 will be described.

Equation 1 below shows an example of a reference signal sequence r (m).

Equation 1

Where m is 0,1, ..., 2N (max, DL) -1. N (max, DL) is the number of resource blocks corresponding to the maximum bandwidth supported in the wireless communication system. For example, N (max, DL) is 110 in 3GPP LTE. When the subframe has a bandwidth smaller than N (max, DL), only a portion of the reference signal sequence generated at 2 × N (max, DL) length can be selected and used.

c (i) is a pseudo-random (PN) sequence. The PN sequence may be defined by a Gold sequence of length-31. Equation 2 below shows an example of a 2 × N (max, DL) length sequence c (i).

Equation 2

Where Nc = 1600, x (i) is the first m-sequence and y (i) is the second m-sequence. For example, the first m-sequence may be initialized with x (0) = 1 and x (i) = 0 (i = 1,2, ..., 30) for every OFDM symbol. The second m-sequence may be initialized for every OFDM symbol according to a cell ID, a slot number in a radio frame, an OFDM symbol index in a slot, a type of CP, and the like.

Equation 3 below is an example of initialization of the second m-sequence.

Equation 3

Where n (s) is a slot number in a radio frame, l is an OFDM symbol index in a slot, and N (cell_ID) is a cell ID. In case of normal CP, N (CP) is 1, and in case of extended CP, N (CP) is 0.

Hereinafter, an example of how each of the resource element mappers 130-1,..., 130 -Nt maps the reference signal sequence to the resource element will be described.

The reference signal sequence r (m) may be mapped to a complex value a (k, l, p) used as a reference symbol for an antenna p. Where k is a slot subcarrier index and l is a slot OFDM symbol index. a (k, l.p) corresponds to the resource element (k.l) on antenna p.

Equation 4 shows an example in which the reference signal sequence r (m) is mapped to a complex a (k, l, p).

Equation 4

Here, N (symb) is the number of OFDM symbols in the slot, N (DL) is the number of resource blocks in the slot.

Variables v and v (shift) define the position in the frequency domain for other reference signals. Equation 5 below shows examples of the variables v and v (shift).

Equation 5

The resource element (k, l) used for transmitting a reference signal through an antenna in a slot is not used for any transmission through another antenna in the same slot. If the resource element (k, l) on antenna p is not used for any transmission, the complex number a (k, l, p) corresponding to the resource element (k, l) on antenna p may be set to zero. .

Hereinafter, resource elements used for RS transmission according to the method described above in FIGS. 7 to 12 are shown.

7 illustrates an example of reference signal mapping for one antenna in the case of a normal CP. 8 illustrates an example of reference signal mapping for two antennas in the case of a normal CP. 9 illustrates an example of reference signal mapping for four antennas in the case of a normal CP. 10 illustrates an example of reference signal mapping for one antenna in case of an extended CP. 11 illustrates an example of reference signal mapping for two antennas in case of an extended CP. 12 shows an example of reference signal mapping for four antennas in the case of an extended CP.

7 to 12, there is one resource grid defined for each antenna. One reference signal is transmitted for each antenna. Rp represents a resource element used for transmission of a reference signal through antenna p (p = 0, 1, 2, 3). That is, Rp is a reference resource element for antenna p. R0 to R3 do not overlap with each other. Each Rp in one OFDM symbol is located at 6 subcarrier intervals. Rp is not used for any transmission through any antenna other than antenna p. This is to avoid interference between antennas.

The reference resource element is a resource element used for transmitting a reference signal. The reference signal corresponds to the set of reference resource elements. Resource elements other than the reference resource element may be used for data transmission. Resource elements used for data transmission are called data resource elements. Reference symbols constituting the reference signal are mapped to the reference resource element, and data symbols constituting the data are mapped to the data resource element.

Next, the MBSFN reference signal will be described.

The MBSFN reference signal is transmitted only within a subframe allocated for MBSFN transmission. That is, the MBSFN reference signal is transmitted only through the MBSFN subframe. The MBSFN reference signal is defined only for the extended CP.

13 shows an example of MBSFN reference signal mapping.

Referring to FIG. 13, Rm denotes a resource element used for MBSFN reference signal transmission through antenna m. It is assumed that the MBSFN reference signal is transmitted on antenna m. In one OFDM symbol, Rm is located at two subcarrier intervals.

The drawings to be described below show an example of reference signal mapping on one resource unit. One resource unit is defined as one subframe in the time domain and one resource block in the frequency domain. It is assumed that one resource block includes 12 subcarriers in the frequency domain. In the case of a normal CP, it is assumed that one subframe includes 14 OFDM symbols in the time domain, and in case of an extended CP, one subframe includes 12 OFDM symbols in the time domain. The resource element on the resource unit may be identified by the OFDM symbol number in the subframe and the subcarrier number (0, 1, ..., 11) in the resource block. In case of a normal CP, the OFDM symbol numbers are 0,1, ..., 13, and in case of an extended CP, the OFDM symbol numbers are 0,1, ..., 11.

14 shows an example of reference signal mapping in a unicast subframe.

Referring to FIG. 14, a unicast subframe may include a control region to which a PDCCH is allocated and a data region to which a PDSCH is allocated. Control information and cell specific reference signals may be transmitted in the control region within the unicast subframe. Unicast data and cell specific reference signals may be transmitted in the data region within the unicast subframe.

15 shows an example of reference signal mapping in an MBSFN subframe.

Referring to FIG. 15, an MBSFN subframe may include a control region to which a PDCCH is allocated and a data region to which a PMCH is allocated. Control information and cell specific reference signals may be transmitted in the control region within the MBSFN subframe. In the data area within the MBSFN subframe, the MBSFN data and the MBSFN reference signal may be transmitted.

For unicast communication, the UE periodically measures a channel quality indicator (CQI) through a cell specific reference signal. The UE measures the CQI using a channel estimated through a cell-specific reference signal transmitted over the entire unicast subframe including the control region and the data region. However, in the data area in which the MBSFN reference signal is transmitted in the MBSFN subframe, the UE should avoid a process of acquiring the CQI for unicast communication. The UE can acquire the CQI only through the cell specific reference signal transmitted through the control region of the MBSFN subframe.

In the case of multi-antenna transmission, although there is one resource unit defined for each antenna, FIGS. 14 and 15 show reference resource elements for all antennas on the same resource unit for convenience.

As described above, the legacy system may support up to 4 antennas for downlink transmission. On the other hand, in an advanced system, more than 5 antennas may be supported for downlink transmission. Accordingly, there is a need for a reference signal transmission method for an antenna that is more extended than a legacy system in an advanced system. However, even if advanced systems are introduced, it is desirable that the advanced systems maintain backward compatibility with legacy systems. The compatibility between advanced and legacy systems is convenient for the user, and the operator can also reuse existing equipment. For example, 3GPP LTE is a legacy system and LTE-A is an advanced system.

Hereinafter, a terminal of a legacy system is called a legacy UE, and a terminal of an advanced system is called UE-A (UE-advanced, UE-A). If referred to only as a terminal, it includes both the legacy terminal and the terminal-A.

When a newly designed reference signal for an extended antenna in an advanced system is transmitted through a resource element used for data transmission in a legacy system, the legacy terminal recognizes the reference signal of the extended antenna as data and attempts to demodulate the data. Can be. This may cause serious deterioration in data reception of the legacy terminal. Therefore, when designing a reference signal for an extended antenna in an advanced system, it should be designed in a direction that does not affect data reception of the legacy terminal.

When designing a new reference signal for an extended antenna in an advanced system, it is not desirable to increase the reference signal overhead. This is because the data transfer rate is lowered.

In addition, advanced systems may be designed to support legacy terminals. Legacy terminals do not have information about advanced systems. In advanced systems, it is desirable from the standpoint of legacy system support to keep the frame structure the same as the legacy system. In addition, the frame of the advanced system may be designed by inheriting the cell-specific reference signal of the legacy system, the MBSFN subframe, the control region to which the PDCCH is transmitted, the position of the PBCH and the position of the SCH. Hereinafter, a subframe of a legacy system is called a legacy subframe, and a subframe of an advanced system is called an advanced subframe.

16 is a flowchart illustrating a reference signal transmission method performed by a transmitter according to an embodiment of the present invention. The transmitter may be part of the base station.

Referring to FIG. 16, the transmitter transmits N first reference signals through N antennas (N is a natural number) in a legacy subframe (S110). The transmitter transmits M second reference signals through M antennas (where M is a natural number) in the advanced subframe (S120). At this time, M is larger than N.

The transmitter may transmit data to the legacy terminal in the legacy subframe. The transmitter does not transmit data to the legacy terminal in the advanced subframe.

At least one of the M second reference signals may be transmitted through the resource element at the same position on the basis of the N frames and the subframes.

17 shows examples of legacy subframes and advanced subframes.

Referring to FIG. 17, an advanced subframe may be continued to a legacy subframe. Advanced Subframe The previous subframe and the advanced subframe subsequent subframes may both be legacy subframes. Herein, a subframe having a subframe number of 6 in the radio frame is represented as an advanced subframe, but this is only an example. The number, location, etc. of advanced subframes within a radio frame may vary.

Hereinafter, the transmission time of the advanced subframe will be described in detail.

The transmission time of the advanced subframe may be variously set. However, it is desirable for the compatibility with legacy systems not to use a subframe in which PBCH and / or SCH is transmitted as an advanced subframe.

As an example, the advanced subframe transmission timing may be fixed. For example, a subframe whose subframe number is 6 in a radio frame may be an advanced subframe. In this case, the base station may only signal the legacy terminal once for the advanced subframe.

As another example, the advanced subframe may be transmitted periodically. In this case, the base station can inform the user equipment of the transmission period and offset of the advanced subframe. For example, an advanced subframe may be a subframe that satisfies (subframe number) mod (transmission period) = offset.

As another example, a transmission time of an advanced subframe may be set semi-statically. A transmission time of an advanced subframe may be set through higher layer signaling of a physical layer. For example, the upper layer may be RRC (radio resource control) for controlling radio resources between the terminal and the network. A bitmap scheme may be used for signaling indicating an advanced subframe. For example, when a subframe having a subframe number of 6 is set as an advanced subframe in a radio frame including 10 subframes, the bitmap may be expressed as '0000001000'.

As another example, the base station may configure the advanced subframe in a manner that does not schedule downlink transmission for the legacy terminal in the advanced subframe.

18 shows an example of RS mapping in an advanced subframe.

Referring to FIG. 18, an advanced subframe may be composed of a control region and an advanced data region. The advanced data area is the data area of the advanced subframe. In the control region, the same cell specific reference signal as that of the legacy system is transmitted. In the advanced data area, a reference signal for an extended antenna is transmitted. Re is a resource element used for transmitting a reference signal through an extended antenna.

Here, Re is disposed at the same position on the basis of the subframe and the reference resource element of the legacy subframe. However, this is only an example and does not limit the position in the subframe of the reference resource element for the extended antenna.

As such, the reference signal structure of the advanced subframe may be designed in consideration of the control region. In 3GPP LTE, a control channel may be allocated to the preceding maximum 3 OFDM symbols of the first slot in the downlink subframe. Depending on the situation, one, two, or three OFDM symbols in the downlink subframe become control regions. In order to maintain compatibility between the advanced system and the legacy system, the reference signal structure in the control region of the advanced subframe may be set to be the same as the legacy subframe. That is, in the control region of the advanced subframe, a reference signal for the same antenna as the legacy subframe may be transmitted through the reference resource element at the same position on the basis of the legacy subframe and the subframe.

Of course, advanced systems may not be compatible with legacy systems in control channel transmission. In this case, the reference signal structure in the control region of the advanced subframe may be set differently from the legacy subframe.

The reference signal structure of the advanced subframe may be designed in consideration of the accessibility of the legacy UE to the advanced subframe.

First, legacy terminals may not have access to advanced subframes. In this case, the reference signal structure of the advanced subframe has no effect on the legacy terminal. Thus, the reference signal structure of the advanced subframe can be freely designed.

Second, the legacy terminal may access the control region of the advanced subframe, but may not access the advanced data region. In this case, the reference signal structure of the control region of the advanced subframe is set to be the same as the control region of the legacy subframe, and the reference signal structure of the advanced data region can be freely designed. The legacy terminal can measure the CQI through the reference signal only in the control region of the advanced subframe. For example, it may be a reference signal structure of an advanced subframe as shown in FIG. 18.

In this case, the advanced subframe may reuse the MBSFN subframe. That is, the MBSFN subframe is reused in an advanced subframe for unicast transmission through an extended antenna. The MBSFN subframe may be configured by higher layer signaling such as RRC. Higher layer signaling for indicating an MBSFN subframe may be reused as signaling for indicating an advanced subframe. The legacy terminal can recognize the transmission time of the advanced subframe through the signaling.

Third, the legacy terminal may be accessible to both the control region and the advanced data region of the advanced subframe. The base station does not schedule downlink transmission for the legacy terminal in the advanced subframe. In this case, although the legacy terminal does not receive downlink data through the advanced data region, the legacy terminal may measure the CQI in the advanced subframe. To this end, the reference signal structure of the legacy subframe is maintained in the advanced subframe, and a reference resource element for an extended antenna in the advanced data region may be additionally arranged. Since the legacy terminal does not receive downlink data in the advanced subframe, the reference resource element for the extended antenna in the advanced data region has no effect on the legacy terminal.

19 shows another example of RS mapping in an advanced subframe.

Referring to FIG. 19, Re is a reference resource element for an extended antenna. UE-A may receive downlink data through an extended antenna in an advanced subframe. The legacy terminal does not receive downlink data in the advanced subframe, but estimates a channel for each of antennas 0 to 3 through reference signals transmitted through R0 to R3 in the advanced subframe, and CQI. Can be measured.

In this case, the base station may configure the advanced subframe in such a manner that the downlink transmission for the legacy terminal is not scheduled in the advanced subframe. The base station does not transmit the PDCCH for the legacy terminal in the control region of the advanced subframe. Since the legacy terminal does not detect the PDCCH, the legacy terminal does not receive downlink data in the advanced data area. In this case, the base station may not inform the legacy terminal of the advanced subframe transmission time.

Hereinafter, a case in which a legacy subframe transmits four first reference signals through four antennas and an advanced subframe transmits eight second reference signals through eight antennas will be described as an example. However, this is merely an example and does not limit the number of antennas in each of the legacy subframe and the advanced subframe.

In the drawings to be described below, Rp represents a reference resource element of antenna p (p = 0, 1, ..., 7). Rp is not used for any transmission through any antenna other than antenna p. P shown in the drawings is only an example, and p may be changed in the drawings. For example, R4 can be changed to R5 and R6 can be changed to R7. In addition, the reference resource element in the resource unit may transition to the frequency domain and / or the time domain. The reference resource element in the resource unit may be shifted by m-subcarriers (m is a natural number). The reference resource element in the resource unit may be shifted by n-OFDM symbols (n is a natural number).

20 illustrates an example of reference signal mapping in a legacy subframe in the case of a normal CP. 21 illustrates an example of reference signal mapping in a legacy subframe in case of an extended CP.

20 and 21, Rp represents a reference resource element of antenna p (p = 0, 1, 2, 3). Reference resource elements of the same antenna in one OFDM symbol are located at 6 subcarrier intervals. Reference resource elements of different antennas in one OFDM symbol are located at three subcarrier intervals. The reference resource element may be shifted to the frequency domain within the subcarrier spacing. In FIG. 20, the reference resource element is located in an OFDM symbol having symbol numbers 0, 1, 4, 7, 8, and 11. In FIG. 21, a reference resource element is located in an OFDM symbol having symbol numbers 0, 1, 3, 6, 7, and 9. R0 and R1 are eight in one resource unit, and R2 and R3 are four in each.

First, in the advanced data area, the resource element at the same position on the basis of the subframe and the reference resource element in the legacy subframe may be used as the reference resource element of the extended antenna. The extended antenna may be antennas 0 to 7. Hereinafter, it is assumed that OFDM symbols having a symbol number of 0 and 1 in the advanced subframe are control regions, and the remaining OFDM symbols are advanced data regions.

22 shows a first example of reference signal mapping in an advanced subframe in case of a normal CP.

Referring to FIG. 22, Rp represents a reference resource element of antenna p (p = 0, 1, ..., 7). OFDM symbols with symbol numbers 2 through 13 are advanced data regions. In the advanced data area, resource elements of the same position on the subframe basis with reference resource elements R0 to R3 in the data area of the legacy subframe are used for transmitting the reference signals for the antennas 4 to 7. That is, R0 to R3 in the data region of the legacy subframe are simply converted to R4 to R7 in the advanced subframe. For example, R0 of the legacy subframe is converted to R4 in the advanced data area. Similarly, R1 is converted to R5, R2 to R6, and R3 to R7. This one-to-one conversion can be various other examples.

When the transmitter transmits data using eight antennas, the receiver may demodulate the data by estimating a channel from reference signals for antennas 0-7. However, R0 to R3 in the advanced subframe are located only in the OFDM symbol whose symbol number is 0,1. In the case of a time flat channel, there is no problem. In the case of a time selective channel, channel estimation performance may be degraded. If the channel estimation performance is poor, the reliability of the wireless communication is lowered. In this case, the reference signal transmitted in the subframe subsequent to the advanced subframe may be used to overcome the time selective characteristic of the channel. Coherent time is inversely proportional to Doppler spread. The coherent time may be used to determine whether the channel is a time selective channel or a time flat channel.

FIG. 23 shows a second example of RS mapping in an advanced subframe in case of a normal CP.

Referring to FIG. 23, R0 of the legacy subframe is converted to R5 in the advanced data area. Similarly, R1 is converted to R4, R2 to R6, and R3 to R7. FIG. 23 shows that R4 and R5 of FIG. 22 are changed from each other.

22 and 23 are merely examples, and R0 to R3 in the data region of the legacy subframe may be variously converted to R4 to R7 in the advanced subframe.

24 illustrates a first example of RS mapping in an advanced subframe in case of an extended CP. FIG. 25 illustrates a second example of RS mapping in an advanced subframe in case of an extended CP. In this manner, the case of the normal CP may be equally applied to the extended CP.

22 to 25, the number of each of R0 to R3 in the advanced subframe is two, the number of each of R4 and R5 is six, and the number of each of R6 and R7 is two. That is, as shown in FIGS. 22 to 25, when simply converting R0 to R3 in the data region of the legacy subframe from R4 to R7 in the advanced subframe, the channel estimation performance for each antenna is not equal.

Channel estimation performance is related to the reference signal density. If an equal number of reference resource elements are arranged for each antenna in the subframe, channel estimation performance for each antenna may be equalized.

Hereinafter, a method of equalizing the reference signal densities for each of antennas 4 to 7 will be described.

For the same number of reference resource element arrangements per antenna, the number of OFDM symbols including reference resource elements for any two antennas in the advanced subframe and the number of OFDM symbols including reference resource elements for the remaining two antennas are the same. Can be arranged to

The case of four OFDM symbols including R4 to R7 will be described as an example. In each OFDM symbol including a reference resource element, reference resource elements for two antennas are arranged.

FIG. 26 shows a third example of RS mapping in an advanced subframe in case of a normal CP.

Referring to FIG. 26, R4 and R5 are located in OFDM symbols having symbol numbers 4 and 8, and R7 and R8 are located in OFDM symbols having symbol numbers 7, 11. The first OFDM symbol of the two OFDM symbols including R4 and R5 is always located before the first OFDM symbol of the two OFDM symbols including R6 and R7. The second OFDM symbol of the two OFDM symbols including R4 and R5 is also always located before the second OFDM symbol of the two OFDM symbols including R6 and R7.

Each Rp is located at 6 subcarrier intervals within one OFDM symbol. Reference resource elements of different antennas in one OFDM symbol are located at three subcarrier intervals. In one OFDM symbol, R4 and R5 maintain three subcarrier spacings, and R6 and R7 also maintain three subcarrier spacings.

Since the number of each of R4 to R7 in the advanced subframe is four, the reference signal density per antenna is the same. Therefore, channel estimation performance of each of antennas 4 to 7 may be equal.

27 illustrates a fourth example of RS mapping in an advanced subframe in case of a normal CP. FIG. 27 is a diagram in which R4 and R5 of FIG. 26 are changed from each other. 27 is only an example, and R6 and R7 of FIG. 26 may also be changed from each other.

FIG. 28 shows a third example of RS mapping in an advanced subframe in case of an extended CP. 29 shows a fourth example of RS mapping in an advanced subframe in case of an extended CP.

28 and 29, R4 and R5 are located in OFDM symbols having symbol numbers 3 and 7, and R6 and R7 are located in OFDM symbols having 6 and 9 symbol numbers. Except for this, the example of the normal CP of FIGS. 26 and 27 is applied as it is. In this manner, the case of the normal CP may be equally applied to the extended CP.

26 to 29 are exemplary only and do not limit the positions of R4 to R7 in advanced subframes. If the reference resource element for any two antennas of R4 to R7 is arranged in the OFDM symbol including the reference resource element, the reference resource element for the other two antennas is arranged in another OFDM symbol. When there are two OFDM symbols including reference resource elements for any two antennas, the positions of the frequency domains of the reference resource elements for each antenna in the first OFDM symbol and the second OFDM symbol may be exchanged with each other.

The following table shows symbol numbers of OFDM symbols including reference resource elements for the extended antenna in the advanced subframe. 4 OFDM symbols including reference resource elements for the extended antenna.

Table 1

Each of Rx, Ry, Rz and Rw in Table 1 may be optionally designated with one of R4 to R7. For example, Rx may be designated as R4, Ry as R5, Rz as R6, and Rw as R7. However, this is merely an example and not a limitation. A subframe including an OFDM symbol using a normal CP includes 14 OFDM symbols and may configure a data region with OFDM symbols having a symbol number of 3 to 13. A subframe including an OFDM symbol using an extended CP includes 12 OFDM symbols and may configure a data region with OFDM symbols having a symbol number of 2 to 11. The numbers shown in the table indicate the symbol numbers of the OFDM symbols in the subframe.

Hereinafter, a method of equalizing the reference signal densities for each of antennas 0 to 7 in the advanced data region of the advanced subframe will be described.

30 shows a fifth example of RS mapping in an advanced subframe in case of normal CP.

Referring to FIG. 30, for the advanced data area, R0 and R1 are located in an OFDM symbol with a symbol number of seven, R2 and R3 are located in an OFDM symbol with a symbol number of eight, and R4 and R5 are OFDM with a symbol number of four. Located in the symbol, R6 and R7 is located in the OFDM symbol with the symbol number 11. That is, the reference resource element for the antenna port pair consisting of antenna 0 and antenna 1 is placed in symbol number 7, and the reference resource element for the antenna port pair consisting of antenna 2 and antenna 3 is symbol number 8 Is placed on. The reference resource element for antenna port pair consisting of antenna 4 and antenna 5 is placed in symbol number 4. The reference resource element for antenna port pair consisting of antenna 6 and antenna 7 is placed in symbol number 11. do. In the advanced data area, each of R0 to R7 is disposed so that the reference signal density is equal.

31 illustrates a sixth example of RS mapping in an advanced subframe in case of normal CP.

Comparing FIG. 31 with FIG. 30, the symbol numbers where reference resource elements for each antenna port pair are arranged are the same, but the position of the frequency domain of the reference resource element for each antenna is changed. That is, in the case of R0 and R1, they are arranged interchangeably with the positions in FIG. Similarly, the positions of R2 and R3, R4 and R5, R6 and R7 are also exchanged with each other as compared with FIG.

Each antenna port pair described above with reference to FIGS. 30 and 31 (ie, antenna 0 and antenna 1, antenna 2 and antenna 3, antenna 4 and antenna 5, antenna 6 and antenna 7 ), The symbol number of the OFDM symbol in which the reference resource element is disposed may be represented as {7, 8, 4, 11} for convenience. The symbol number for each antenna port pair can be variously modified as shown in Table 2 below.

TABLE 2

	Symbol number to which the reference symbol is assigned for the antenna port pair
Example	0 and 1 antennas	Antennas		2 and 3	Antennas 4 and 5	Antennas 6 and 7
One	8	4	11	7
2	4	11	7	8
3	11	7	8	4
4	7	4	8	11
5	4	8	11	7
6	8	11	7	4
7	11	7	4	8
8	7	11	4	8
9	11	4	8	7
10	4	8	7	11
11	8	7	11	4
12	7	4	11	8
13	4	11	8	7
14	11	8	7	4
15	8	7	4	11

Examples of reference signal mapping for the normal CP described with reference to FIGS. 30 and 31 may also be applied to the extended CP.

32 shows a fifth example of RS mapping in an advanced subframe in case of an extended CP. 33 shows a sixth example of RS mapping in an advanced subframe in case of an extended CP.

32 and 33, in the advanced data area, R0 and R1 are located in OFDM symbol with symbol number 6, R2 and R3 are located in OFDM symbol with symbol number 7, and R4 and R5 are symbol number 3 In the OFDM symbol, and R6 and R7 are located in the OFDM symbol with the symbol number 9. In the frequency domain, the example of the normal CP of FIGS. 30 and 31 is applied as it is. In this manner, the extended CP may be applied in the same manner as in the case of the normal CP. Reference resource elements of different antennas in one OFDM symbol are located at three subcarrier intervals. FIG. 33 differs from FIG. 32 in that positions R0 and R1, R2 and R3, R4 and R5, and R6 and R7 are exchanged.

In the advanced subframe, since the number of each of R0 to R7 in the advanced data region is two, the reference signal density per antenna is the same. Therefore, the channel estimation performance of each of antennas 0 to 7 may be equal.

Although the antennas included in the antenna port pair have consecutive antenna numbers in the embodiments described with reference to FIGS. 30 to 33, this is not a limitation. That is, two antennas arbitrarily selected from antennas 0 to 7 may configure an antenna port pair. For example, antenna 0 and antenna 7 may constitute one antenna port pair, and antenna 1 and antenna 6 may constitute another antenna port pair.

The reference signal structure of the advanced system described so far may be arranged throughout the downlink transmission bandwidth. Or, the reference signal structure of the advanced system may be arranged limited to some frequency period of the downlink transmission bandwidth. For example, reference resource elements of each of antennas 0 to 3 are disposed throughout the downlink transmission bandwidth, and reference resource elements of each of antennas 4 to 7 are arranged only in some frequency intervals of the downlink transmission bandwidth. Can be.

34 shows an example of an advanced subframe structure in case of a normal CP.

Referring to FIG. 34, an advanced subframe is divided into a control region and an advanced data region in the time domain, and includes a special region for an extended antenna (hereinafter, referred to as a special region) in the advanced data region. Include. That is, the special region is in the form of time division multiplexing (TDM) with the control region in the time domain and the frequency division multiplexing (FDM) in the frequency domain within the advanced subframe.

The special region may include at least one or more subcarriers or at least one or more resource blocks in the frequency domain. The special region may include a frequency band divided by one carrier when viewed in the frequency domain, or may correspond to a component carrier of a multi-carrier system. The special area may be allocated for signal transmission for the terminal-A. In this case, the reference resource element of each of antennas 4 to 7 as described above may be disposed in the special region, or the reference resource elements of each of antennas 0 to 7 may be disposed. Existing reference signals can be transmitted in the radio resource region except the special region in the advanced data region.

35 shows another example of an advanced subframe structure in the case of a normal CP.

Referring to FIG. 35, unlike in FIG. 34, an advanced subframe has a difference in that a frequency band in which a special region is arranged in slot units is different. That is, special regions are arranged in different frequency bands based on slot boundaries in the first slot and the second slot.

In the advanced subframe described with reference to FIGS. 34 and 35, allocation information about a special region may be informed through an upper layer signal such as an RRC. Alternatively, it may be indicated by a physical layer signal transmitted through a radio resource to which a downlink grant is allocated. The allocation information for the special area may be configured in the form of a bitmap. For example, if each unit carrier includes a 1-bit information value indicating whether or not the OFDM symbol is a special area in units, a 14-bit bitmap (for a normal CP) is a special area. Can tell you whether or not.

Alternatively, if a radio resource region to which a special region can be allocated is defined in advance, it may be informed through information on an allocation pattern of the special region. For example, the information on the allocation pattern of the special region may be composed of an initial band value composed of one or more bands and an allocation pattern indicator.

In the above-described embodiments, only the reference signal for the legacy terminal is placed in the control region of the advanced subframe. However, this is not a limitation and a reference signal for UE-A may be arranged together with a reference signal for legacy UE in the control region of the advanced subframe. The reference signal for UE-A may be configured based on a control channel element (CCE), a resource element group (REG), and a resource element (RE). The CCE may correspond to 9 resource element groups. The resource element group may consist of four resource elements.

In the design of advanced systems, there are cases where the channel state of each frequency band is suddenly changed in time and does not change rapidly. When the channel state changes rapidly with time, the UE may allocate and operate a special area in subframe units. If the channel state does not change rapidly over time, a special area may be allocated and operated based on statistical measurements of the UE-As.

36 is a block diagram illustrating an apparatus for wireless communication in which an embodiment of the present invention is implemented. The base station 50 includes a processor 51, a memory 52, and an RF unit 53. The processor 51 implements the proposed functions, processes and / or methods. That is, a reference signal for an extended antenna is generated, placed in an advanced subframe, and transmitted to the terminal. Layers of the air interface protocol may be implemented by the processor 51. The memory 52 is connected to the processor 51 and stores various information for driving the processor 51. The RF unit 53 is connected to the processor 51 and transmits and / or receives a radio signal.

The terminal 60 includes a processor 61, a memory 62, and an RF unit 63. The processor 61 receives the reference signal for the extended antenna, measures the channel state, and transmits feedback information such as a CQI to the base station. Layers of the air interface protocol may be implemented by the processor 61. The memory 62 is connected to the processor 61 and stores various information for driving the processor 61. The RF unit 63 is connected to the processor 61 and transmits and / or receives a radio signal.

Processors 51 and 61 may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, data processing devices, and / or converters that interconvert baseband signals and wireless signals. The transmitter of FIG. 6 may be implemented within the processors 51 and 61. The memory 52, 62 may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage devices. The RF unit 53,63 includes one or more antennas for transmitting and / or receiving radio signals. When the embodiment is implemented in software, the above-described technique may be implemented as a module (process, function, etc.) for performing the above-described function. Modules are stored in memories 52 and 62 and can be executed by processors 51 and 61. The memories 52 and 62 may be inside or outside the processors 51 and 61, and may be connected to the processors 51 and 61 by various well-known means.

As such, an efficient reference signal transmission method and apparatus can be provided in a wireless communication system. While backward compatibility with legacy systems is maintained, it can support a larger number of transmit antennas than legacy systems. In other words, advanced systems may support legacy systems while using more extended transmit antennas than legacy systems. Support for a larger number of transmit antennas can increase the transmission rate or increase the reliability of wireless communications. Thus, overall system performance can be improved.

In the exemplary system described above, the methods are described based on a flowchart as a series of steps or blocks, but the invention is not limited to the order of steps, and certain steps may occur in a different order or concurrently with other steps than those described above. Can be. In addition, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the flowcharts may be deleted without affecting the scope of the present invention.

Claims (15)

1. A reference signal transmission method performed by a transmitter in a wireless communication system,

   Allocating M reference signals for M antennas (where M is a natural number) in an advanced subframe; And

   Transmitting the M reference signals,

   The M reference signals are allocated to some resource elements at the same position as the resource elements in which N reference signals for N antennas (N is a natural number) are arranged in a legacy subframe, and M is larger than N. How to.
2. The method of claim 1, wherein the advanced subframe includes a control region in which control information is transmitted in the time domain and an advanced data region in which data is transmitted.

   And the M reference signals are transmitted in the advanced data area.
3. 3. The method of claim 2, wherein the advanced data region includes at least one frequency band less than the frequency band to which the control region is assigned.
4. 4. The method according to claim 3, wherein the advanced data area consists of different frequency bands bordering slots of a subframe.
5. The method of claim 1,

   The advanced subframe is a multimedia broadcast multicast service single frequency network (MBSFN) subframe.
6. The method of claim 1, wherein each of the M reference signals in the advanced data area is allocated to an equal number of resource elements.
7. The method of claim 1,

   When the M antennas are sequentially represented by antennas 0, 1, ..., M-1, and the N antennas are sequentially represented by 0, 1, ..., N-1 antennas, the advanced And transmitting a reference signal for antennas N, N + 1, ..., M-1 of the M antennas in the data area.
8. 8. The method of claim 7, wherein reference signals for antennas N, N + 1, ..., M-1 are allocated to the same number of resource elements, respectively.
9. The method of claim 1, wherein at least one or more orthogonal frequency division multiplexing (OFDM) symbols in the advanced subframe are allocated resource elements for two reference signals of the M reference signals.
10. The method of claim 1,

    And wherein the advanced subframe is set via radio resource control (RRC) signaling.
11. A radio frequency (RF) unit for transmitting and / or receiving a radio signal; And

    Connected to the RF unit,

    A processor for allocating M reference signals for M antennas (where M is a natural number) and transmitting the M reference signals in an advanced subframe,

    The M reference signals are allocated to some resource elements at the same position as the resource elements in which N reference signals for N antennas (N is a natural number) are arranged in a legacy subframe, and M is greater than N. Device for wireless communication.
12. 12. The apparatus of claim 11, wherein each of the M reference signals in the advanced data area is allocated to an equal number of resource elements.
13. The method of claim 11,

    When the M antennas are sequentially represented by antennas 0, 1, ..., M-1, and the N antennas are sequentially represented by 0, 1, ..., N-1 antennas, the advanced And transmitting a reference signal for N, N + 1, ..., M-1 antennas among the M antennas in a data area.
14. The apparatus of claim 13, wherein reference signals for antennas N, N + 1, ..., M-1 are allocated to the same number of resource elements, respectively.
15. 12. The apparatus of claim 11, wherein at least one or more orthogonal frequency division multiplexing (OFDM) symbols in the advanced subframe are allocated resource elements for two reference signals of the M reference signals. .

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