KR101585698B1 - Method and apparatus of transmitting reference signal in multiple input multiple output communication system - Google Patents

Abstract

The present invention provides a method for transmitting a channel state information-reference signal (CSI-RS) for measuring a transmission channel in a wireless communication system. The method includes transmitting configuration information for setting a CSI-RS; And transmitting the CSI-RS according to the setting information. Here, the setting information may include subframe setting information indicating a subframe in which the CSI-RS is transmitted and wireless setting information indicating a CSI-RS allocation pattern. When the CSI-RS is transmitted by two or more antenna ports, the CSI-RS transmitted by the two or more antenna ports transmits at least two REs (Resource) in only one of the two slots of the subframe Element) so that the CSI-RS can be transmitted in two consecutive REs on the same subcarrier of only one of the two slots.

Description

TECHNICAL FIELD [0001] The present invention relates to a reference signal transmission method and apparatus for a multi-input / output (I / O) communication system,

The present invention relates to resource allocation in a communication system, and more particularly, to reference signal allocation and transmission for channel measurement in a multi-antenna communication system.

When data is transmitted in a wireless communication system, since data to be transmitted is transmitted through a wireless channel, signal distortion may occur during transmission. In order to properly decode the distorted signal on the receiving side, it is necessary to determine the information of the channel and to correct the distortion of the transmission signal by the channel information in the received signal. In order to find the information of the transmission channel, the receiving side transmits a signal known to both the transmitting side and the receiving side, and when the signal is received to the receiving side through the transmission channel, the information of the channel can be obtained referring to the degree of distortion of the transmission signal At this time, a transmission signal known to both the transmitting side and the receiving side is referred to as a pilot signal or a reference signal.

Recently, in most mobile communication systems, transmission / reception data efficiency is improved by employing a multiple input / multiple output (MIMO) scheme using multiple transmit antennas and multiple receive antennas when transmitting data. In the MIMO communication system as described above, an independent channel is formed for each transmission antenna, so that an independent reference signal is transmitted to each transmission antenna so that the channel status between each transmission antenna and the reception antenna can be grasped.

Generally, in a communication system, a reference signal RS can be classified into a reference signal for acquiring channel information and a reference signal used for data demodulation.

The reference signal for the purpose of channel information acquisition is for the terminal to acquire the downlink channel information. The reference signal must be transmitted in a wide band. A terminal that does not receive downlink data in a specific subframe also receives the reference signal, it must be able to measure. Also, the target reference signal for channel information acquisition is used for measurement such as handover.

A reference signal for data demodulation is a reference signal transmitted together with a corresponding resource when the base station transmits data in the downlink. The terminal receives the reference signal, performs channel estimation, and demodulates the received data . Therefore, the reference signal for data demodulation is transmitted in the area where the data is transmitted.

Meanwhile, LTE (Long Term Evolution) system and LTE-Advanced system, which are in the process of standardization, are required to support data transmission / reception through a plurality of transmission antennas in a downlink of a base station, but a base station supports up to 8 transmission antennas There is a problem that an efficient reference signal allocation and transmission method is not defined.

Meanwhile, in order to reduce inter-cell interference in a multi-cell environment and to improve communication performance of a terminal located at an edge of a cell, a coordinated multi-point transmission (hereinafter referred to as "CoMP" ) Technique has been proposed.

Using the CoMP technique, the UE can receive jointly data and control information from multiple cell base stations, thereby improving the communication performance of the UE located at the edge of the cell. In order to perform CoMP, The determination of the CoMP cluster (cluster), which is an aggregate of the base station (BS, eNB, cell, Access Point, etc.), should be given priority. The method of configuring the clusters can be divided into two methods according to the configuration subject, that is, a method in which a system or a separate base station controller configures and manages clusters, and a method in which each UE configures and manages its own cluster.

12 is a diagram schematically showing a method of configuring CoMP clusters.

FIG. 12A illustrates a method of configuring a cluster. First, each UE measures an amount of interference from a neighboring base station to a corresponding UE, and averages the interference for a predetermined period of time, and transmits the average to the system. The system uses the transmitted information to construct clusters by collecting eNBs which are expected to have the greatest performance improvement when CoMP is used because of the large amount of interferences. The number of base stations per cluster may vary depending on environments and may have different values for different clusters. However, for convenience of description, the number of base stations per cluster is limited to three in FIG. 12 (a).

FIG. 12 (b) illustrates a method of configuring a cluster, in which UE1 and UE2 each measure the amount of interference from a neighboring base station to a corresponding UE, average the same over a predetermined period of time, use the CoMP In this paper, we propose a new method to improve the performance of the proposed system. 12 (b), it is assumed that one cluster is composed of three base stations as in FIG. 12 (a). Actually, the number of base stations belonging to one cluster can be varied, and each cluster may have a different value have.

Even in the CoMP system, a reference signal must be allocated and transmitted for channel measurement and data demodulation. However, there is a problem that an efficient reference signal allocation and transmission method is not defined in the CoMP system.

The present invention provides a reference signal allocation method for channel measurement and a data transmission method therefor in a multi-antenna communication system.

Also, even when the base station supports four or more and up to eight transmit antennas as in the LTE-A system, the present invention provides an efficient reference signal allocation method and transmission method.

Also, an efficient reference signal allocation method and transmission method are provided in a system using a CoMP method.

According to an aspect of the present invention, there is provided a channel state information (CSI) signal for measuring a transmission channel for each antenna in a multiple input / multiple output (MIMO) A reference signal CSI-RS (CSI-RS) allocation method is a method for allocating two resource blocks in a subframe including a plurality of OFDM symbols in a time domain and a plurality of resource blocks in a frequency domain, ; Allocating the channel measurement reference signal at eight frequency resource element intervals to two resource blocks set as the basic allocation unit; Allocating a data signal to an extra frequency resource element of the two resource blocks; And transmitting a data packet to which the reference signal and the data signal are allocated, wherein the channel measurement reference signal for each antenna is allocated to different frequency resource elements, and the number of frequency resource elements to which the data signal is allocated Are allocated such that the two resource blocks are different from each other.

According to an aspect of the present invention, there is provided a channel state information (CSI) signal for measuring a transmission channel for each antenna in a multiple input / multiple output (MIMO) A method of transmitting a data signal with a reference signal CSI-RS includes the steps of: allocating the channel measurement reference signal at intervals of K frequency resource elements on a frequency, where K is an arbitrary integer greater than 6; And 12 is M, the M / 12 resource blocks are transmitted as one cycle, and the channel measurement reference signal is repeatedly transmitted in units of M / 12 resource blocks in the frequency domain. Here, one resource block includes 12 frequency resource elements in the frequency domain and is composed of a plurality of OFDM symbols in the time domain.

Preferably, in the above method, K is 8 and M is 24, and the channel measurement reference signal is repeatedly transmitted in units of two resource blocks in the frequency domain with two resource blocks as one cycle .

Preferably, the step of allocating the channel measurement reference signal further comprises allocating the data signal to an excess frequency resource element of the M / 12 resource blocks, The reference signal is allocated to different frequency resource elements, and the number of frequency resource elements to which the data signal is allocated is allocated such that the M / 12 resource blocks are different from each other.

According to an aspect of the present invention, there is provided a channel state information (CSI) signal for measuring a transmission channel for each antenna in a multiple input / multiple output (MIMO) Reference Signal (CSI-RS) and a device for transmitting a data signal include a plurality of transmission antennas; An RF transmitter for transmitting a data packet to which the reference signal and the data signal are mapped; And a controller for mapping a channel measurement reference signal for the plurality of transmit antennas and the data signal to resource elements of the subframe, wherein the controller includes a plurality of OFDM symbols in the time domain and a plurality of resource blocks in the frequency domain The two resource blocks are set as a basic allocation unit for allocating the channel measurement reference signal and the two resource blocks are mapped to eight frequency resource element intervals for two resource blocks set as the basic allocation unit, Wherein the channel measurement reference signal for the transmission and reception antennas is mapped to different frequency resource elements and the number of frequency resource elements to which the data signal is allocated is mapped such that the two resource blocks are different from each other.

According to the present invention, an efficient reference signal allocation method and a transmission method are provided even when the base station supports up to eight transmission antennas, such as the LTE-A system, and even if there are a plurality of transmission antennas of the base station, The transmission rate is not lowered.

1 is a diagram illustrating a structure of a downlink radio frame according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a resource grid for one downlink slot according to an embodiment of the present invention. Referring to FIG.
3 is a diagram illustrating a downlink subframe structure according to an embodiment of the present invention.
4 is a diagram illustrating an uplink subframe structure according to an embodiment of the present invention.
5 is a diagram illustrating a resource allocation pattern of a common reference signal according to an embodiment of the present invention.
FIG. 6 shows a pattern of the common reference signal R0 for antenna port 0.
7 is a diagram illustrating a CSI-RS pattern of 8 RE intervals according to an embodiment of the present invention.
FIG. 8 is a diagram illustrating a CSI-RS pattern when 24 resource elements according to an embodiment of the present invention are used for DM-RS transmission.
9 is a diagram illustrating a CSI-RS pattern when 12 resource elements according to an embodiment of the present invention are used for DM-RS transmission.
10 is a diagram illustrating a CSI-RS transmission pattern for eight antenna ports according to an embodiment of the present invention.
11 is a block diagram schematically showing a reference signal transmission apparatus according to an embodiment of the present invention.
12 is a diagram schematically showing a method of configuring CoMP clusters.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein like reference numerals refer to like or similar elements throughout the several views, and redundant description thereof will be omitted. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. It is to be noted that the accompanying drawings are only for the purpose of facilitating understanding of the present invention, and should not be construed as limiting the scope of the present invention with reference to the accompanying drawings.

The communication system of the present invention includes a base station and a terminal as a system for providing various communication services such as voice and packet data, and a LTE (Long Term Evolution) system or an LTE-Advanced system will be described as a representative example.

The terminal of the present invention may be called a subscriber station (SS), a user equipment (UE), a mobile equipment (ME), a mobile station Such as a portable device or a PC, or a vehicle-mounted device.

The base station of the present invention is a fixed point communicating with a terminal and can be used as an evolved NodeB (eNB), a base station (BS), a base transceiver system (BTS), and an access point. One or more cells may exist in one base station and an interface for transmitting user traffic or control traffic may be used between the base stations. Also, a downlink means a communication channel from a base station to a terminal, and an uplink means a communication channel from a terminal to a base station.

The multiple access scheme applied to the wireless communication system of the present invention can be applied to various wireless communication systems such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Single Carrier- Frequency Division Multiple Access) or other modulation techniques known in the art.

In addition, the multiple access scheme for downlink and uplink transmission may be different from each other. For example, an OFDMA scheme may be used for the downlink and an SC-FDMA scheme may be used for the uplink.

1 is a diagram illustrating a structure of a downlink radio frame according to an embodiment of the present invention.

A downlink radio frame according to an embodiment of the present invention is composed of 10 subframes, and one subframe is composed of two slots. The downlink radio frame may be configured by a Frequency Division Duplex (FDD) or a Time Division Duplex (TDD). The time at which one subframe is transmitted is called a transmission time interval (TTI). For example, one subframe length may be 1 ms and a slot length may be 0.5 ms. One slot includes a plurality of OFDM symbols in a time domain and a plurality of resource blocks in a frequency domain.

FIG. 2 is a diagram illustrating a resource grid for one downlink slot according to an embodiment of the present invention. Referring to FIG.

As shown in FIG. 2, a downlink slot includes a plurality of OFDM symbols in a time domain and a plurality of resource blocks (RBs) in a frequency domain. The number of OFDM symbols included in one slot may vary according to the configuration of a CP (Cyclic Prefix), and the illustrated example corresponds to a case where a CP is composed of a general CP. In this case, the number of OFDM symbols included in one slot is 7, and since the length of one OFDM symbol is increased when the CP is configured by an extended CP, the number of OFDM symbols included in one slot is smaller than that of a general CP And can be composed of six. When the extended CP is applied, it corresponds to a case where the channel state is unstable, for example, when the UE moves at a high speed, and an extended CP may be used to further reduce inter-symbol interference.

Referring to FIG. 2, one downlink slot includes 7 OFDM symbols, and one resource block (RB) includes 12 subcarriers. In addition, each element on the resource grid is called a resource element, and one resource block includes 84 resource elements (12 X 7 = 84). The interval of each subcarrier is 15 kHz, and one resource block includes about 180 kHz in the frequency domain. N ^DL is the number of resource blocks included in the downlink slot, and is dependent on the downlink transmission bandwidth (bandwidth) set by the scheduling of the base station.

2, one subframe is composed of 14 OFDM symbols, and the first two or three OFDM symbols of each subframe are allocated to PDCCH (Physical Downlink Control Channel), and the remaining The OFDM symbol may be allocated to a PDSCH (Physical Downlink Shared Channel).

3 is a diagram illustrating a downlink subframe structure according to an embodiment of the present invention.

As shown in FIG. 3, a maximum of three OFDM symbols located at the beginning of a first slot in one subframe are allocated as a channel as a control region. The remaining OFDM symbols are allocated to the PDSCH as a data area. The control channel may include a Physical Control Format Indicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH), a Physical Hybrid ARQ Indicator Channel (PHICH), and the like.

4 is a diagram illustrating an uplink subframe structure according to an embodiment of the present invention.

Referring to FIG. 4, the uplink subframe includes a control region and a data region in a frequency domain. A PUCCH (Physical Uplink Control Channel) for transmitting uplink control information is allocated to the control region. A PUSCH (Physical Uplink Shared Channel) for transmitting user data is allocated to the data area.

A PUCCH of one UE is allocated as a resource block pair in one subframe and resource blocks included in a resource block pair are located in different slots in two slots.

Hereinafter, the downlink reference signal will be described in detail.

The DL reference signal includes two reference signals, a common reference signal (CRS) shared by all terminals in a cell and a dedicated reference signal (DRS) dedicated to a specific terminal.

The common reference signal is used for information acquisition and handover measurement of the channel state, and the dedicated reference signal is used for data demodulation. The common reference signal is a cell-specific reference signal, and the dedicated reference signal is a UE-sepcific reference signal.

The UE measures the common reference signal and notifies the base station of feedback information such as CQI (Channel Quality Information), PMI (Pecoding Matrix Indicator) and RI (Rank Indicator), and the base station transmits the downlink frequency Area scheduling is performed.

The BS calculates the amount of radio resources to be allocated to the reference signal, the exclusive position of the common reference signal and the dedicated reference signal, the position of the synchronization channel (SCH) and the broadcast channel (BCH) And the like.

In this case, when a relatively large amount of resources are allocated to the reference signal, a high channel estimation performance can be obtained, but a data rate is relatively decreased. When a relatively small resource is allocated to a reference signal, a high data rate can be obtained. However, And deterioration of the channel estimation performance may occur. Therefore, efficient resource allocation of reference signal considering channel estimation and data transmission rate can be an important factor in system performance.

5 is a diagram illustrating a resource allocation pattern of a common reference signal according to an embodiment of the present invention.

The common reference signal is transmitted for each subframe for a wideband, and a reference signal is transmitted for each antenna port according to the number of antennas of the base station.

5 shows a case where the number of base station antennas is four, and common reference signals R0, R1, R2 and R3 for four antenna ports are transmitted in one resource block (RB), respectively. When a common reference signal is mapped to a resource in the time-frequency domain, the common reference signal for one antenna port in the frequency domain is mapped and transmitted at six resource element (RE) intervals. Therefore, since one resource block (RB) is composed of 12 resource elements (RE) in total in the frequency domain, a resource element (RE) for transmission of a reference signal for one antenna port is allocated to each resource block Two are used.

FIG. 6 shows a pattern of the common reference signal R0 for antenna port 0, where R0 is mapped to two resource elements at intervals of six resource elements in the frequency domain of one resource block.

However, if the number of downlink transmission antennas of a base station increases, and a maximum of eight transmission antennas are supported, a common reference signal for each of the eight antennas must be supported. For example, in the LTE-A system, the base station defines four or more transmit antennas to support up to eight transmit antennas, and the common reference signal must be further defined and designed. In addition, when supporting up to eight antennas, a dedicated reference signal for data demodulation as well as a common reference signal for channel measurement needs to be designed.

One of the important considerations in designing an LTE-A system is that the terminal and the system must support it so that the LTE system is backward compatible, that is, the LTE terminal works well in the LTE-A system.

When viewed from the viewpoint of transmission of the reference signal RS, the common reference signal designed as shown in Figs. 5 and 6 is transmitted to each of the sub- A signal can be added. However, in the LTE-A system, if the reference signal pattern for up to 8 transmit antennas is added to all bands in every subframe in the same manner as the common reference signal in the existing LTE system, the overhead of the reference signal becomes excessively large.

Accordingly, a reference signal is newly designed in a system supporting a plurality of transmission antennas, such as an LTE-A system. A newly designed reference signal is a channel measurement reference signal for channel measurement for selecting MCS, PMI, And a data demodulation-RS (DM-RS) for demodulating data transmitted through an Information-RS or Channel State Indication-RS and 8 transmission antennas. Unlike the above-described common reference signal (CRS) used for demodulating data simultaneously with the purpose of measurement such as channel measurement and handover, the CSI-RS for channel measurement purposes is designed for channel measurement-oriented purposes . Of course, CSI-RS can also be used for measurement purposes such as handover.

Since the CSI-RS is transmitted only for obtaining information on the channel state, unlike the CRS, the CSI-RS is not transmitted every subframe. Therefore, in order to reduce the overhead of the CSI-RS, the CSI-RS is transmitted intermittently on the time axis, and the dedicated DM-RS is transmitted to the UE scheduled in the corresponding time-frequency domain for data demodulation. That is, the DM-RS of a specific terminal can transmit only the time-frequency domain in which the corresponding terminal receives the scheduled domain, i.e., data.

If the base station supports CSI-RS for all the supported transmit antenna ports and supports up to 8 transmit antennas, transmitting the CSI-RS for each of the 8 antenna ports every subframe has a drawback that the overhead increases Therefore, the CSI-RS may be transmitted intermittently on the time axis without being transmitted every subframe, thereby reducing the overhead. That is, the CSI-RS may be periodically transmitted with a period of an integral multiple of one subframe or may be transmitted in a specific transmission pattern. At this time, the base station can configure the period or pattern in which the CSI-RS is transmitted.

In order to measure the CSI-RS, the UE must know the time-frequency location of the CSI-RS, the CSI-RS sequence, the CSI-RS frequency shift, and the like for each antenna port of the cell to which the UE belongs.

In the LTE system, the sequence of the common reference signal (CRS), the time-frequency position, and the frequency shift are tied by the Cell-ID, the subframe number, and the symbol number. However, in the LTE-A system, additional information such as a transmission period and a transmission offset is required for CSI-RS transmission, and such information can be transmitted from the system to the UE.

In the LTE-A system, the base station transmits CSI-RS for up to eight antenna ports, and the resources used for CSI-RS transmission of the different antenna ports must be orthogonal to each other. When one CSI-RS is transmitted to a different antenna port, one base station orthogonally configures these resources in an FDM scheme that maps CSI-RSs for the respective antenna ports to different frequencies, The CSI-RS may be transmitted in a CDM scheme for mapping the CSI-RS to a code having mutual orthogonality.

When a CSI-RS is transmitted from a base station, CSI-RSs for different antenna ports are mapped to different resource elements (REs) for each antenna port when the FDM scheme is applied. The CSI-RS for one antenna port preferably occupies one to two resource elements (RE) per resource block (RB).

Therefore, the base station needs to transmit CSI-RSs for a maximum of eight antenna ports, so that about 16 resource elements (REs) are required per CSI-RS transmission period in order to support eight transmission antennas. Even if CDM is used for antenna port classification, a similar number of resource elements (ie, 16 REs) as the FDM scheme is needed for CSI-RS mapping.

If the CSI-RS for one antenna port is mapped to have six resource element (RE) intervals as shown in FIGS. 5 and 6, since the frequency domain of one resource block (RB) is composed of 12 resource elements, The number of CSI-RS resources to support 8 transmit antennas is insufficient.

In the present invention, as one embodiment of the CSI-RS transmission, the resources of the CSI-RS for one antenna port have six resource elements (RE) intervals or more, preferably eight resource elements (RE) intervals on the frequency axis We propose a pattern.

Therefore, since resource mapping of the CSI-RS to one antenna port has an interval larger than 6RE on the frequency axis, the basic unit of CSI-RS allocation and transmission is a plurality of resource blocks (RBs) ) Unit.

For example, when a CSI-RS resource element for one antenna port is mapped at 8RE intervals, the basic unit of CSI-RS allocation and transmission is two resource blocks (RBs). In addition, the CSI-RS for one antenna port is mapped to three resource elements (RE) per two resource blocks (RB) and transmitted.

7 is a diagram illustrating a CSI-RS pattern of 8 RE intervals according to an embodiment of the present invention.

 For convenience of description, only the CSI-RS for one antenna port is shown in FIG. When the CSI-RS has a resource element (RE) interval of 6 RE or more, the number of resource elements (REs) used for CSI-RS transmission for each RB changes. Therefore, resource elements RE ).

If the CSI-RS for each antenna port is mapped to a resource element at intervals of 8REs, the number of resource elements used for CSI-RS transmission per RB depends on the number of resource blocks. That is, if the number of CSI-RS resource elements used for an even-numbered resource block is one for a specific antenna port, the number of resource elements of the CSI-RS used for an odd-numbered resource block is two.

Therefore, the number of resource elements that a channel estimator can use for channel estimation also depends on the resource block number.

The resource element to which data per resource block is allocated is allocated from the surplus resource element excluding the resource element used for control and CRS and CSI-RS in the entire resource element. Therefore, the resource element to which the data signal of the UE is mapped also varies in the number of resource elements used for data per resource block in consideration of the CSI-RS resource element mapping. That is, the number of resource elements allocated to data in an even-numbered resource block and the number of resource elements allocated to data in an odd-numbered resource block are different. Therefore, the number of resource elements RE used for control information transmission varies according to the resource block number (odd number or even number in this embodiment), and consequently resource block number (odd number or even number number in this embodiment) The number of resource elements (REs) used for data transmission varies.

According to another embodiment of the present invention, various CSI-RS intervals such as 7RE interval, 9RE interval, or 10RE interval may be used in addition to the CSI-RS transmission pattern of 8RE interval shown in FIG. That is, with respect to an arbitrary integer K, when the minimum common multiple of K and 12 (consisting of 1RB = 12RE) is M, the transmission pattern of CSI-RS is K RE, that is, M / 12 RB, .

At this time, if K is an integer larger than 6, the cycle of the CSI-RS transmission pattern becomes a plurality of RBs.

As shown in FIG. 7, when the transmission pattern K of the CSI-RS is 8 RE, the minimum common multiple M of 8 and 12 becomes 24, and the basic period of the RB that is the transmission pattern of CSI- RS is 2 RB RB).

As described above, if the CSI-RS pattern is repeated with a plurality of RB units as one period, the number of resource elements RE used for CSI-RS transmission may be different for each RB. Let N (= M / 12) be the number of a plurality of RBs forming one period of the CSI-RS pattern, and let N be a CSI-RS transmission period on the frequency axis. Then, the number and position of the resource elements RE used for the CSI-RS in each of the N RBs constituting one CSI-RS period are changed for each RB. Therefore, the number and location of resource elements RE allocated for transmission of data signals of the UE in each of the N RBs within the one period are different for each RB. At the same time, the number of resource elements (REs) allocated for transmission of a control signal of the UE in each of the N RBs within the one period is different for each RB.

Therefore, the channel estimator of the UE must estimate the channel using the number and pattern of different resource elements (REs) for each RB in each N RBs within one period.

Further, the CSI-RS has a pattern repeated over the entire frequency band on the frequency axis in the cycle of N RB.

FIG. 8 is a diagram illustrating a CSI-RS pattern when 24 resource elements according to an embodiment of the present invention are used for DM-RS transmission.

8 shows a CSI-RS pattern having a CSI-RS pattern period of a plurality of RB units as described above, in which 24 resource elements are used per resource block for DM-RS, The transmission pattern of the CSI-RS in the normal CP is shown in the case where the CRS is transmitted.

As shown, the CSI-RS pattern for one antenna port is transmitted at 8 RE intervals in one OFDM symbol, and the same CSI-RS pattern is repeated in units of 2 RBs on the frequency axis. The symbol index uses the same index as in FIG. 7, and the same number among the numbers listed in each resource element (RE) can be set as a CSI-RS for one antenna port. A maximum of 24 CSI -RS set can be derived. In this embodiment, it is assumed that the CSI-RS is transmitted in the remaining symbol periods except for the symbol interval in which the control information is transmitted, the symbol interval in which the CRS is transmitted, and the symbol interval in which the DM-RS is transmitted. For example, in FIG. 8, the CSI-RS can transmit symbol indexes in symbols 3, 9, and 10. This symbol index follows the symbol index used in FIG.

9 is a diagram illustrating a CSI-RS pattern when 12 resource elements according to another embodiment of the present invention are used for DM-RS transmission.

When 12 resource elements are used for DM-RS transmission, the set of REs to which the CSI-RS can be transmitted is 28 sets per 2RB.

However, the CSI-RS set numbers shown in FIGS. 8 and 9 are not absolute values but merely mean a set of resource elements RE to which the CSI-RS for one antenna port can be transmitted , The values of these numbers can be modified in various ways.

According to an embodiment of the present invention, the CSI-RS transmission pattern can be transmitted using different sets for each cell, and in some cases, CSI-RS transmission positions may be configured differently for each subframe.

Preferably, a reference position for CSI-RS transmission to the antenna port is defined for each cell, and a position of the CSI-RS is determined according to the number of resource elements used for DM-RS, It is possible to perform signaling from the base station to the mobile station with the CSI-RS set number of FIG.

The reference position of the CSI-RS with cell-specific characteristics unique to each cell is determined by reference position for a specific antenna port or antenna port group and time / frequency offset or CSI-RS time / frequency offset for the remaining antenna port or antenna port group The CSI-RS is signaled to the UE and the CSI-RS is transmitted to the corresponding position. In some cases, a CSI-RS set that does not overlap with the entire antenna port may be selected and signaled.

10 is a diagram illustrating a CSI-RS transmission pattern for eight antenna ports according to an embodiment of the present invention.

As shown in the figure, CSI-RS is used for eight antennas, RE 10 is set for antenna 0, RE 11 is set for antenna 1, RE 12 is set for antenna 2, RE 13 is set for antenna 3, Antenna # 5 RE # 19, antenna # 6 RE # 20 and antenna # 7 RE # 21. When the CSI-RS for each antenna is allocated and transmitted, when the CSI-RS transmission position is notified to the UE, for example, the reference position of the CSI-RS for the antenna port 0 is set to 10, The CSI-RS for the remaining antenna ports is transmitted at a position shifted by 1 to 3 from the CSI-RS set number for the antenna ports 1 to 3, And the antenna port is transmitted at a position shifted by 8 to 11 with CSI-RS set number, respectively.

The information indicating the CSI-RS transmission position for the antenna port is generalized as follows.

The position at which the CSI-RS is transmitted to each antenna port is defined as P _i (i = 0, 1, 2, ..., N-1: N is the number of CSI-RS antenna ports). Then, let's assume that the reference position at which the CSI-RS is transmitted to the antenna port # 0 is the CSI-RS position set # 10. In this case, a CSI-RS transmission position for another antenna port is determined in the same manner as in Equation (1).

&Quot; (1) "

P ₀ = 10

For (0 < _i ? 3) P _i = P _{i -1} + a _i ;

P ₄ = P ₀ +8

For (4? I <8) P _i = P _{i -1} + a _i

In Equation (1), a _i denotes an offset between P _i and P _{i -1} , and a _i Is set to &quot; 1 &quot;.

According to another embodiment of the present invention, a reference position of a CSI-RS to a reference antenna port is indicated, and a CSI-RS position of the remaining antenna port is cell-specific. , And may be randomly selected so as not to overlap with each other so as to be antenna specific.

In this case, the CSI-RS position for the remaining antenna port becomes dependent upon the reference position, and the reference position of the CSI-RS for the reference antenna port group is informed, The position for the antenna group can be randomly selected so as not to overlap with the position of the first antenna group and the position of the CSI-RS of other antenna ports in the group. In this case, the CSI-RS position for the remaining antenna ports is cell-specific, antenna specific, and dependent on the CSI-RS position of any one antenna port of the first antenna port group.

The base station signals the reference position of the CSI-RS with respect to the antenna port group to inform the terminal of the CSI-RS position of the antenna port, and determines the position of the CSI- Position, i.e. time / frequency shift or offset, to the terminal.

For example, when antenna ports 0 through 3 are grouped into one group for eight CSI-RS antenna ports, and antenna ports 4 through 7 are grouped into another group, antenna ports 0 through 3 And selects a CSI-RS set that does not overlap the reference positions of the CSI-RS with respect to the group. Referring to FIG. 10, the reference positions of the CSI-RSs for the antenna port groups 0 to 3 are indicated as CSI-RS sets 10 to 13, and for the CSI-RSs for the remaining antenna port groups 4 to 7, Lt; th &gt; antenna port group.

According to another embodiment of the present invention, as another method of notifying the CSI-RS transmission position to the UE, a base station selects a CSI-RS position set that does not overlap with all antenna ports to which the CSI-RS is to be transmitted It is also possible to signal all these positions.

In order to improve the channel estimation performance of the CSI-RS, the CSI-RSs between inter-cells must be designed so that they do not overlap at the same time / frequency positions.

According to an embodiment of the present invention, there is a method of multiplexing inter-cell CSI-RS in TDM of a subframe unit. At the same time, in order to perform orthogonal multiplexing between cells that transmit CSI-RS in the same subframe, different resource elements (RE) must be allocated for CSI-RS transmission. For this, reference positions of CSI-RS of different cells transmitted in the same subframe for each cell should be specified differently, and time / frequency shift and offset information should be specified so that CSI-RS transmission positions with neighboring cells do not overlap do.

However, considering a heterogeneous network environment in which not only a macro base station but also a relay, a femto base station (femto eNB), a Home eNB, and a pico eNB coexist, orthogonality of CSI- it is not always possible to guarantee orthogonality.

Particularly, in the CoMP system mentioned in the prior art, a CoMP cluster capable of performing a CoMP operation to perform CoMP will be defined first. CSI-RSs among cells in a CoMP cluster have orthogonal characteristics, The UE should be able to measure channel information of other cells. Therefore, in order to perform orthogonal multiplexing of CSI-RS between cells in the cluster, other cells in the cluster must leave the RE without transmitting other data but transmit the CSI-RS. That is, the corresponding RE is muting (nulling or puncturing).

That is, the UE must know the CSI-RS transmission pattern of the serving cell and know the location of the CSI-RS transmitted by other cells performing the CoMP. It should be noted that the UE performing CoMP should be aware of the CSI-RS location and pattern of other cells in the CoMP cluster, and that the CSI-RS of cells other than the serving cell is muting without data being transmitted. For this, information such as the CSI-RS pattern / location of the serving cell from the base station to the UE and the CSI-RS pattern / location of other cells in the CoMP cluster must be signaled. However, since the combination of cells performing CoMP in the CoMP cluster can be different for each UE according to the location and channel state of the UE, it is necessary for all UEs to know the exact location / pattern of the CSI-RS of the cells in the CoMP cluster It may be absent. Therefore, in order to reduce the burden of signaling, the CSI-RS transmission period and time offset of the CSI-RS of the cells in the CoMP cluster and the REs to which the CSI-RS is transmitted are informed and information such as the CSI- And the like. Then, the UE determines that the REs other than the location of the REs to which the CSI-RS of the serving cell is transmitted among the RE positions to which the CSI-RSs of all the cells in the CoMP cluster can be transmitted are not mutually transmitted You will know. In addition, when the UE actually performs CoMP with specific cells, the CSI-RS information of the corresponding cells must be received from the serving cell.

In addition, a scheme for multiplexing CSI-RS of cells which do not perform CoMP or belong to different CoMP Clusters should be provided. That is, it is desirable to design such that the CSI-RS between base stations that do not perform CoMP, or the CSI-RS between neighboring cells belonging to different CoMP Clusters do not continuously collide. If the location of the CSI-RS happens to be the same in all subframes and the CSI-RS transmission period is the same, then the CSI-RS of the two cells will always collide, resulting in performance degradation of channel estimation. In particular, if the transmission power of the CSI-RS is boosted and transmitted at higher power than the normal data, the performance degradation becomes larger. In addition, considering the small number of cells (Home eNB, Pico cell, Femto cell) that transmit downlink signals at low power in a heterogeneous network, if the CSI-RS continuously collides with the Macro eNB, .

Therefore, CSI-RS between cells belonging to different CoMP Cluster does not perform CSI-RS or CoMP, and randomizing the position of CSI-RS per cell and sub-frame so as not to overlap with the same cell continuously I suggest. In the present invention, a method of orthogonally multiplexing CSI-RS between cells belonging to the same CoMP cluster and randomly multiplexing CSI-RS between cells belonging to different CoMP clusters is proposed.

Therefore, according to an embodiment of the present invention, the CSI-RS between the inter-cells belonging to different CoMP clusters is randomly multiplexed, and the CSI-RS transmits the subframe time and the CSI- Therefore, it may be configured to hop at random. At this time, the hopping pattern of CSI-RS is configured to be cell-specific and antenna port-specific.

Therefore, when the base station informs the CSI-RS pattern to the UE, the subframe or CSI-RS transmission period, time offset, resource element (RE) through which the CSI-RS is transmitted, and / It tells the CSI-RS pattern of the cell.

(CSI-RS) pattern transmitted from the base station, etc., the UE transmits the remaining resources except for the location of the REs to which the CSI-RS of the serving cell is transmitted among the REs of the CSI- The elements RE can know that the base station does not transmit data and is muting.

According to another embodiment of the present invention, the BS transmits a location of a resource element (RE) to which a CSI-RS of a cell belonging to the same CoMP Cluster, that is, a subset of cells in a neighboring cell or network, And informs the CSI-RS pattern of the serving cell among them.

Similarly, the base station muts a resource element (RE) corresponding to a CSI-RS transmission position of another cell in the same CoMP Cluster.

However, if the cells in the CoMP cluster actually perform CoMP, the UE must separately inform the UE of the CSI-RS location / pattern and cell ID performing the CoMP.

In order for CSI-RS to perform random hopping and support orthogonal multiplexing, the subframe in which the CSI-RS is transmitted must be aligned between all cells or cells located in relatively close positions. That is, cells in the same cluster must transmit CSI-RS in the same subframe. RS is orthogonal multiplexing of CSI-RS between multiple cells by muting other resource elements (REs) in addition to resource elements (REs) in which a base station transmits CSI-RSs for all resource elements (REs) capable of CSI- .

Also, the CSI-RS may randomly hop for all resource elements (REs) capable of CSI-RS transmission on a subframe basis or a CSI-RS transmission period basis.

However, a resource element RE for allocating CSI-RS to all resource elements RE capable of CSI-RS transmission, for example, all CSI-RS sets 1 to 24 of FIG. 8, Muting all the remaining resource elements (REs) except for the CSI-RS has a problem that overhead of the CSI-RS is excessively generated.

Therefore, it is preferable that the CSI-RS transmission capable of CSI-RS transmission is performed between cells within a CoMP cooperative set, that is, a CoMP cooperative set, Specifies a set of RS resource elements (REs).

That is, in the case of FIG. 8, the CSI-RS sets 1 to 24 are transmitted only within the set 1 to 12 for a specific cell (eNB) group, and the CSI- RSs to transmit CSI-RSs within 24 sets of CSI-RSs. In other words, grouping CSI-RS sets to transmit CSI-RSs per CoMP cluster.

At this time, the cell group assigned the CSI-RS set 1 to 12 is muting the resource element (RE) in the CSI-RS set other than the CSI-RS set it transmits, but for the other sets 13 to 24 It is possible to transmit downlink data. Similarly, a cell group allocated with CSI-RS sets 13 to 24 transmits data for CSI-RSs 1 to 12, and resource elements for transmitting its own CSI-RSs in CSI-RS sets 13 to 24 (RE) other than the RE is muting without transmitting data. The CSI-RS hopping of the cells in the cell group may be performed in the allocated CSI-RS group. At this time, the CSI-RS allocation group (number set) may also be changed every subframe or CSI-RS transmission period. That is, a group of cells requiring CSI-RS coordination between cells for transmission of CSI-RS is grouped into one group, and a resource element (RE) capable of transmitting CSI-RS for CSI- ), And then allows the cells in the group to transmit the CSI-RS within the corresponding area. At the same time, the cell muts without transmitting data for the remaining resource elements (REs) in which the own CSI-RS is transmitted in the corresponding region. And the hopping of the CSI-RS transmission pattern of the cell is performed in the corresponding area. Of course, the area may also be configured to hop.

11 is a block diagram schematically showing a reference signal transmission apparatus according to an embodiment of the present invention.

The apparatus according to an embodiment of the present invention includes a channel state information-reference signal (CSI-RS) for measuring a transmission channel for each antenna in a MIMO wideband wireless communication system through a plurality of antennas, And a data signal.

The apparatus includes a plurality of transmit antennas 1101 and 1103, RF transmitters 1105 and 1107 for transmitting a sub-frame in which a reference signal and a data signal are mapped, a channel measurement criterion for a plurality of transmit antennas 1101 and 1103, And a control unit 1109 for mapping the signal and data signals to the resource elements of the subframe.

The plurality of transmission antennas 1101 and 1103 are constituted by four or more, preferably eight.

The controller 1109 preferably sets two resource blocks (RBs) as a basic allocation unit for channel measurement reference signal allocation in a subframe including a plurality of resource blocks.

A channel measurement reference signal for one antenna maps to eight frequency resource elements (RE) intervals for two resource blocks set as a basic allocation unit, and each channel measurement reference signal for the plurality of transmission antennas It is mapped to a resource element. Accordingly, the number of frequency resource elements to which the data signal is allocated is mapped so that the two resource blocks are different from each other.

Preferably, the channel measurement reference signal is transmitted periodically with a period of a specific integer multiple of one subframe in the time domain, and at least one of the resource element mapping position, transmission period, or transmission offset of the channel measurement reference signal The above information may be separately signaled and informed to the terminal.

The method according to the present invention described so far can be implemented in software, hardware, or a combination thereof. For example, the method according to the present invention may be stored in a storage medium (e.g., terminal internal memory, flash memory, hard disk, etc.) and executed by a processor Lt; RTI ID = 0.0 &gt; and / or &lt; / RTI &gt;

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, May be modified, modified, or improved.

Claims (13)

A method for transmitting a channel state information-reference signal (CSI-RS) for measuring a transmission channel in a wireless communication system,
Transmitting setting information for setting a CSI-RS; And
And transmitting the CSI-RS according to the setting information, wherein the setting information includes subframe setting information indicating a subframe in which the CSI-RS is transmitted and wireless setting information indicating a CSI-RS allocation pattern and;
When the CSI-RS is transmitted by two or more antenna ports, the CSI-RS transmitted by the two or more antenna ports transmits at least two REs (Resource) in only one of the two slots of the subframe Element of the CSI-RS, the CSI-RS is transmitted in two consecutive REs on the same subcarrier of only one of the two slots. The method of claim 1, wherein the subframe setting information indicates a period of a CSI-RS and a subframe offset of the CSI-RS. 2. The method of claim 1, wherein when the subframe includes a plurality of OFDM symbols in a time domain and a plurality of REs in a frequency domain,
Wherein the wireless configuration information represents OFDM symbols and REs. The method according to claim 1,
Wherein the setting information further indicates a muting RE to which a muted CSI-RS is transmitted. 2. The method according to claim 1,
Wherein the RRC message is transmitted through a radio resource control (RRC) message. A method for receiving a channel state information-reference signal (CSI-RS) for measuring a transmission channel in a wireless communication system,
Receiving setting information for setting a CSI-RS; And
Receiving the CSI-RS according to the setting information,
Here, the setting information includes subframe setting information indicating a subframe in which the CSI-RS is received and wireless setting information indicating a CSI-RS allocation pattern;
When the CSI-RS is received from two or more transmit antenna ports, the CSI-RS from each of the two or more transmit antenna ports is allocated to at least two REs (resources) in only one of the two slots of the subframe Element), whereby the CSI-RS is located in two consecutive REs on the same subcarrier of only one of the two slots. 7. The method of claim 6, wherein the subframe setup information indicates a period of a CSI-RS and a subframe offset of the CSI-RS. 7. The method of claim 6, wherein when the subframe includes a plurality of OFDM symbols in a time domain and a plurality of REs in a frequency domain,
Wherein the wireless configuration information represents OFDM symbols and REs. The method according to claim 6,
Wherein the setting information further indicates a muting RE in which a muted CSI-RS is received. 7. The method according to claim 6,
Wherein the RRC message is received through a radio resource control (RRC) message. An apparatus for transmitting a channel state information-reference signal (CSI-RS) for measuring a transmission channel in a wireless communication system,
Two or more transmit antenna ports;
A CSI-RS, and a controller for transmitting CSI-RS according to the setting information;
Here, the setting information includes subframe setting information indicating a subframe in which the CSI-RS is transmitted and wireless setting information indicating a CSI-RS allocation pattern;
When the CSI-RS is transmitted by two or more antenna ports, the CSI-RS transmitted by the two or more antenna ports transmits at least two REs (Resource) in only one of the two slots of the subframe Element), whereby the CSI-RS is transmitted in two consecutive REs on the same subcarrier of only one of the two slots. An apparatus for receiving a channel state information-reference signal (CSI-RS) for measuring a transmission channel in a wireless communication system,
At least one receiving antenna;
And a control unit for receiving the setting information for setting the CSI-RS and receiving the CSI-RS according to the setting information;
Here, the setting information includes subframe setting information indicating a subframe in which the CSI-RS is received and wireless setting information indicating a CSI-RS allocation pattern;
When the CSI-RS is received from two or more transmit antenna ports, the CSI-RS from each of the two or more transmit antenna ports is allocated to at least two REs (resources) in only one of the two slots of the subframe Element), whereby the CSI-RS is located in two consecutive REs on the same subcarrier of only one of the two slots. delete

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