KR20140121244A - Method and apparatus of transmitting reference signal in small cell environment - Google Patents

Abstract

A method and apparatus for transmitting a reference signal in a small cell environment are provided. The method includes generating a reference signal sequence to perform a resource element (RE) mapping, generating an orthogonal frequency division multiplexing (OFDM) signal including a reference signal based on the RE mapping, Wherein the RE mapping pattern of the reference signal is defined by two PRBs in frequency and one subframe in time, and two PRBs on the frequency and one subframe on time And is a pattern mapped to a total of 12 REs per CDM (Code Division Multiplexing) group.

Description

TECHNICAL FIELD [0001] The present invention relates to a reference signal transmission method and apparatus,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to wireless communication, and more particularly, to an apparatus and method for efficiently transmitting a reference signal in a small cell environment.

In certain areas, such as a hotspot inside a cell, there is a particularly high demand for communication, and in certain areas, such as the cell edge or coverage hole, the reception sensitivity of the radio wave may be reduced. As the wireless communication technology develops, a pico cell, a femtocell, a femtocell, etc. are provided in a macro cell for the purpose of enabling communication in an area such as a hot spot, a cell boundary, And a small cell such as a remote radio head (RRH) may be installed together. At this time, the macro cell may be a large cell with a large coverage and the small cell may be a cell with a small coverage.

The UE can perform communication with any cell and perform cell change according to the channel environment or the movement state. For example, a terminal may disconnect from a macro cell due to deterioration of a channel state while connected to a macro cell, and may connect to another macro cell or a small cell. Or, as the terminal moves while connected to the macro cell, it can disconnect from the macro cell and connect to another macro cell or a small cell.

Since the small cell has a narrow coverage, the supporting terminal receiving the service from the small cell usually has little or no movement. Accordingly, a method in which the base station transmits the reference signal more effectively to the terminal is considered.

SUMMARY OF THE INVENTION It is an object of the present invention to determine a pattern of a reduced reference signal to be transmitted from a base station to a mobile station in a small cell.

Another object of the present invention is to transmit a reference signal having a reduced pattern to a mobile station in a small cell.

Another aspect of the present invention is to maintain a channel characteristic while transmitting a reference signal having a reduced pattern.

According to an aspect of the present invention, a method for transmitting a reference signal by a base station in a small cell environment includes: generating a reference signal sequence to perform resource element (RE) mapping; Generating an orthogonal frequency division multiplexing (OFDM) signal including a reference signal based on the RE mapping, and transmitting the OFDM signal to a terminal, wherein the RE mapping pattern of the reference signal includes two PRB and a subframe in time, and is a pattern mapped to a total of 12 PRs per CDM (Code Division Multiplexing) group in two PRBs on the frequency and one subframe in time .

According to another aspect of the present invention, a base station for transmitting a reference signal in a small cell environment includes: an RE mapping unit for generating a reference signal sequence and performing a resource element (RE) mapping; An OFDM signal generator for generating an Orthogonal Frequency Division Multiplexing (OFDM) signal, and a transmitter for transmitting the OFDM signal to a terminal, wherein the RE mapping pattern of the reference signal includes two PRBs in frequency and one And is a pattern that is mapped to a total of twelve REs per CDM (Code Division Multiplexing) group in two PRBs on the frequency and one subframe in time on the time axis.

According to the present invention, the risk of the channel environment can be dispersed while the overhead due to the transmission of the reference signal is reduced.

According to the present invention, power balancing is possible on a symbol basis.

1 shows a wireless communication system to which the present invention is applied.
2 is a flowchart illustrating an example of a method of transmitting a DMRS to which the present invention is applied.
Fig. 3 is a view for schematically explaining the concept of a small cell environment.
FIG. 4 shows an example of a resource element mapping pattern of a downlink DMRS when a normal cyclic prefix is used.
5 is a diagram illustrating an example of a plurality of subframe scheduling to which the present invention is applied.
6 is a flowchart illustrating an example of a method and apparatus for transmitting a reference signal using a DMRS pattern according to the present invention.
Figures 7 and 8 show an example of a reduced DMRS pattern in accordance with the present invention.
Figures 9 and 10 show another example of a reduced DMRS pattern in accordance with the present invention.
11 and 12 show another example of a reduced DMRS pattern according to the present invention.
13 is a flowchart showing an example of the operation of the terminal according to the present invention.
14 is a block diagram showing an example of an apparatus for transmitting and receiving a reference signal according to the present invention.

Hereinafter, some embodiments will be described in detail with reference to exemplary drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference symbols as possible even if they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear.

Hereinafter, the term 'transmitting a channel' can be interpreted as meaning that information is transmitted through a specific channel. Here, the channel includes both a control channel and a data channel, and the control channel may be a physical downlink control channel (PDCCH) or a physical uplink control channel (PUCCH), for example. And the data channel may be a Physical Downlink Shared CHannel (PDSCH) or a Physical Uplink Shared CHannel (PUSCH), for example.

1 shows a wireless communication system to which the present invention is applied.

Referring to FIG. 1, a wireless communication system 10 is widely deployed to provide various communication services such as voice, packet data, and the like. The wireless communication system 10 includes at least one base station 11 (evolved-NodeB, eNodeeB). Each base station 11 provides communication services to specific cells (15a, 15b, 15c). One base station may be responsible for a plurality of cells. In the present invention, the base station 11 refers to a transmitting / receiving end for performing information sharing and control information sharing with a terminal for cellular communication and includes a base station (BS), a base transceiver system (BTS), an access point A femto base station, a home node B, a relay, and the like. Cells are meant to cover various coverage areas such as megacell, macrocell, microcell, picocell, and femtocell.

A user equipment (UE) 12 may be fixed or mobile and may be a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, (personal digital assistant), a wireless modem, a handheld device, or other term, such as a terminal device or a wireless device.

Hereinafter, the downlink refers to a transmission link from the base station 11 to the terminal 12, and the uplink refers to a transmission link from the terminal 12 to the base station 11 it means. In the downlink, the transmitter may be part of the base station 11, and the receiver may be part of the terminal 12. In the uplink, the transmitter may be part of the terminal 12, and the receiver may be part of the base station 11. There are no restrictions on multiple access schemes applied to wireless communication systems. (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiplexing Access (OFDMA), Single Carrier-FDMA , OFDM-CDMA, and the like. A TDD (Time Division Duplex) scheme in which uplink and downlink transmissions are transmitted using different time periods, or an FDD (Frequency Division Duplex) scheme in which they are transmitted using different frequencies can be used.

The layers of the radio interface protocol between the terminal 12 and the base station 11 are based on the lower three layers of the Open System Interconnection (OSI) model well known in the communication system, Layer L1, a second layer L2, and a third layer L3. Among them, the physical layer belonging to the first layer provides an information transfer service using a physical channel.

There are several physical channels used in the physical layer. The physical downlink control channel (PDCCH) includes a resource allocation and transmission format of a downlink shared channel (DL-SCH), a resource of an uplink shared channel (UL-SCH) Resource allocation of an upper layer control message such as allocation information, a random access response transmitted on a physical downlink shared channel (PDSCH), transmission power control for individual terminals in an arbitrary terminal group : TPC) commands, and so on. A plurality of PDCCHs can be transmitted in the control domain, and the UE can monitor a plurality of PDCCHs.

The control information of the physical layer mapped to the PDCCH is referred to as downlink control information (DCI). That is, the DCI is transmitted on the PDCCH. The DCI may include an uplink or downlink resource allocation field, an uplink transmission power control command field, a control field for paging, a control field for indicating a random access response (RA response), and the like.

The wireless communication system 10 may be a multiple antenna system. A multi-antenna system may be referred to as a multiple-input multiple-output (MIMO) system. Or a multiple antenna system may be a multiple input single output (MISO) system or a single input multiple output (SIMO) system. A MIMO system uses multiple transmit antennas and multiple receive antennas. The MISO system uses multiple transmit antennas and one receive antenna. The SIMO system uses one transmit antenna and multiple receive antennas. In contrast, a single input single output (SISO) system uses one transmit antenna and one receive antenna

A multi-antenna transmission / reception scheme used for operation of a multi-antenna system includes a frequency switched transmit diversity (FSTD), a space frequency block code (SFBC), a space time block code (STBC), a cyclic delay diversity (CDD) , Time-switched transmit diversity (TSTD), or the like may be used.

In the wireless communication system 10, it is necessary to estimate an uplink channel or a downlink channel for data transmission / reception, system synchronization acquisition, channel information feedback, and the like. A process of compensating for a distortion of a signal caused by a sudden change in channel environment and restoring a transmission signal is called channel estimation. It is also necessary to measure the channel state of the cell to which the terminal 12 belongs or the other cell. In general, a reference signal (RS) known to each other by the terminal 12 and the base station 11 can be used for channel estimation or channel state measurement.

The terminal 12 that knows the information of the reference signal can accurately obtain the data sent from the base station 11 by estimating the channel based on the received reference signal and compensating the channel value.

The reference signal may be allocated to all subcarriers or between data subcarriers transmitting data. In a scheme in which a reference signal is allocated to all subcarriers, a signal of a specific transmission timing is made only of a reference signal in order to obtain a gain of channel estimation performance. According to a method in which a reference signal is allocated between data subcarriers, the amount of data to be transmitted can be increased. In a multi-antenna system, reference signals of each antenna need to be transmitted separately from reference signals of other antennas in consideration of interference.

The downlink reference signal includes a CSI (Channel State Information) reference signal (CSI-RS) and a DMRS (DeModulation RS). The transmission pattern and configuration information are different for each reference signal.

<1. CSI-RS>

The CSI-RS may be used for estimation of channel state information (CSI). The CSI-RS is arranged in the frequency domain or the time domain. A channel quality indicator (CQI), a precoding matrix indicator (PMI), a rank indicator (RI), and the like are used to estimate channel state information using CSI- As shown in FIG.

The wireless communication system 10 may operate in accordance with various transmission modes. For example, transmission mode 0 may be a mode supporting only a single antenna port, and transmission mode 9 may be a mode capable of supporting up to 8 antenna ports.

In a multi-antenna system, the same or different antenna ports may be mapped to each physical antenna. For example, antenna port 0 to antenna port 3 may be sequentially mapped to each of the four physical antennas.

The number of antenna ports and the resource grid unique to each antenna port are determined depending on the reference signal configuration in the cell. For example, if there are a total of eight physical antennas, the number of antenna ports supporting CSI-RS depends on the configuration of the CSI-RS and the arrangement of the CSI-RS ports on the physical antennas: {1, 2, 4, 8 }, And may have a unique pattern carrying CSI-RS for each antenna port. Hereinafter, a pattern in which an antenna port carries a CSI-RS or a pattern in which a CSI-RS is mapped to a resource element is referred to as a 'CSI-RS pattern'.

<2. DMRS>

A network system can design a DMRS that supports multiple layers. Up to 8 layers can be supported for a single user MIMO of a terminal for transmission of DMRS. For multi-user MIMO, up to 4 layers Could be supported.

The reference signal is generally transmitted in a sequence. The reference signal sequence may be a sequence having an excellent correlation property. As an example, the reference signal sequence may use a Constant Amplitude Zero Auto-Correlation (CAZAC) sequence. The CAZAC sequence includes a Zadoff-Chu based sequence, and the ZC-based sequence may be cyclic extended or truncated depending on the usage. As another example, the reference signal sequence may use a PN (pseudo-random) sequence. PN sequences include m-sequences, computer-generated PN sequences, Gold sequences, and Kasami sequences.

Among the parameters used for generating the DMRS sequence, the antenna port number, the scrambling identity n _SCID, and the number of layers may be included in the DCI and transmitted.

2 is a flowchart illustrating an example of a method of transmitting a DMRS to which the present invention is applied.

Referring to FIG. 2, the base station determines a sequence generation value (S200).

The base station generates a DCI including the determined sequence generation value (S205). The sequence generation value indicates an antenna port number, a scrambling identifier, and the number of layers, and may be 3-bit information, for example.

The base station maps the DCI including the determined sequence generation value to the PDCCH and transmits it to the UE (S210). The terminal monitors the PDCCH to which the DCI is mapped to receive the DCI from the base station. If the UE successfully decodes the PDCCH, it obtains the DCI. The information field in the DCI is analyzed to check the antenna port number, the scrambling identifier, and the number of layers indicated by the sequence generation value.

The base station transmits the DMRS to the terminal using the determined DMRS sequence based on the sequence generation value (S215). The UE performs channel estimation by comparing a DMRS sequence derived using an antenna port number, a scrambling identifier, and the number of layers indicated by a sequence generation value with a DMRS sequence obtained from a DMRS transmitted from the base station and received by the UE.

Fig. 3 is a view for schematically explaining the concept of a small cell environment. For example, a small cell may be a femtocell and a picocell. A femtocell is a low power wireless access point, for example, a base station for ultra small mobile communication used in a room such as a home or office. The femtocell can be connected to the mobile communication core network using a home or office DSL or cable broadband. Alternatively, the small cell may be configured to include other types of cells than the femtocell and the picocell, such as a remote wireless head (RRH).

Referring to FIG. 3, the macro cell 310 and the small cell 320 can be operated together. The macro cell 310 and the small cell 320 each have a unique cell coverage.

The small cell 320 may be used as a low power wireless access point, for example, indoors, such as a home or office. The small cell 320 can be connected to the mobile communication core network using a home or office DSL or cable broadband.

Also, the small cell 320 may be connected to a mobile communication network through a wired network such as the Internet network. A terminal in a small cell can access a mobile communication network or an internet network.

The small cell 320 may cover the coverage of the macrocell 310 and may cover an area other than the coverage of the macrocell 310. [

Or the small cell 320 may be located in the room 330 or outdoors.

Or, it may be connected between the macro cell 310 and the small cell 320 or the small cell 320 by using an ideal backhaul and a non-ideal backhaul.

Alternatively, the small cells 320 may be dense deployed, and may be sparse rather than compact.

A method and apparatus for transmitting a reference signal in a small cell environment according to the present invention will now be described.

Since a mobile terminal in a small cell environment is expected to have a small mobility, there is a characteristic that the change is not large in existing channels and signals. Accordingly, it is possible to improve the performance of the UE in a small cell environment by reducing the overhead of the UE-specific reference signal (e.g., DMRS).

As an example, a DMRS pattern with PRB or sub-frame bundling is proposed. The DMRS pattern with reduced overhead for RE mapped to a subset of the DMRS pattern of FIG. 4, which is a conventional DMRS pattern, can be used.

Hereinafter, a PRB refers to a physical resource block, and a resource block (RB) refers to a resource area corresponding to 0.5 ms on a time axis and 180 KHz on a frequency axis. In this case, 0.5 ms corresponds to one slot, and if a normal cyclic prefix (CP) is used, 7 OFDM symbols in the downlink may correspond to the slot. Also, 180Khz may correspond to a total of 12 subcarriers when the subcarrier interval is 15Khz. A PRB pair may mean an RB pair over two slots, and the N PRBs may correspond to N RBs in frequency.

FIG. 4 shows an example of a resource element (RE) mapping pattern of a downlink DMRS when a normal cyclic prefix is used. The RE mapping pattern of the DMRS may be abbreviated as DMRS pattern.

The downlink DMRS can be transmitted using up to eight antenna ports (antenna ports # 7, # 8, # 9, # 10, # 11, # 12, # 13, # 14). When one layer is used for transmission of PDSCH, the base station uses DMRS corresponding to antenna port # 7 or # 8. Alternatively, when 'v' layers are used for transmission of the PDSCH, the base station transmits the antenna ports # 7, # 8, ... , and # v + 6 are used.

In addition, antenna ports # 7, # 8, # 11 and # 13 may be referred to as CDM (Code Division Multiplexing) group 1, and antenna ports # 9, # 10, # 12 and # 14 may be referred to as CDM group 2. In this case, different CDM groups are classified into a frequency division multiplexing (FDM) scheme and a time division multiplexing (TDM) scheme using different resource elements (RE), that is, different DMRS patterns. Antenna ports are classified by the CDM method through an orthogonal sequence such as OCC (Orthogonal Cover Code).

Referring to FIG. 4, antenna ports # 7, # 8, # 9, and # 10 are used.

(Resource element corresponding to CDM group 1) for antenna ports # 7 and # 8 and resource element (corresponding to CDM group 2) for antenna ports # 9 and # 10 , The resource element for CDM group 2 in general is a resource element corresponding to the subcarrier immediately below the frequency axis on the same time axis in comparison with the resource element for CDM group 1.

The DMRS exists when the PDSCH is associated with the corresponding antenna port, and the DMRS is a valid reference for PDSCH demodulation. Also, the DMRS is transmitted only through the RB to which the corresponding PDSCH is mapped.

This DMRS has an overhead for the resource element RE used according to the rank.

As an example, in the rank # 1 and rank # 2 PDSCH transmissions of a normal downlink subframe with a common CP, there are 12 DMRS REs per RPB pair. An overhead of approximately 7% occurs.

As another example, in a PDSCH transmission of rank # 3 or higher of a normal downlink subframe with a normal CP, there are 12 x 2 = 24 DMRS REs per PRB pair. An overhead of approximately 14% occurs.

On the other hand, by reducing the overhead of the control channel, the performance of a UE in a small cell environment can be improved.

For example, the PDCCH overhead can be reduced through a plurality of sub-frame scheduling or cross sub-frame scheduling.

The scheduling parameters (e.g., MCS or resource allocation) in a small cell may not be changed every subframe because the channel characteristics do not change well due to the characteristics of the small cell. In particular, the probability of successive scheduling for a secondary serving cell is higher.

5 is a diagram illustrating an example of a plurality of subframe scheduling to which the present invention is applied.

Referring to FIG. 5, the RE 510 stored for not transmitting the PDCCH 500 in the next subframes may be used for transmission of user data.

6 is a flowchart illustrating an example of a reference signal transmission method and apparatus using a DMRS pattern according to the present invention.

Referring to FIG. 6, the base station generates a reference signal sequence, multiplies the OCC by RE, and performs RE mapping (S600). After the RE mapping, an OFDM signal is generated (S605). The OFDM signal including the reference signal is transmitted to the terminal (S610).

In step S600, the RE mapping is performed based on the DMRS pattern according to the present invention.

In one embodiment, it may be a reduced DMRS pattern in the frequency domain. Some of the DMRSs are removed.

In another embodiment, it may be a reduced DMRS pattern in the frequency domain and the time domain.

Since the reduced DMRS pattern in the frequency or time domain can be different according to the DMRS transmission rank, it is possible to use the case where the rank is 1 or 2 (i.e., antenna port # 7 and / or # 8 is used) (That is, antenna ports # 7 to # 11, # 7 to # 12, # 7, and # 7) To # 13 or # 7 to # 14). Here, the rank refers to the number of independent layers.

<When there are one or two ranks>

The reduced DMRS pattern according to the present invention may be limited in the subframe dimension, limited in the slot dimension, or limited in the slot and subframe dimension.

Figures 7 and 8 show an example of a reduced DMRS pattern in accordance with the present invention. Slot and subframe based reduced DMRS pattern. FIG. 7 shows an example of a normal subframe, and FIG. 8 shows an example of a special subframe.

Referring to FIG. 7, in a PRB, three DMRS mapping RE pairs (two, seventh, and tenth subcarriers in one PRB (subcarrier indices within one PRB are respectively # (The subcarrier index in one PRB is # 6 in one PRB) in the even-numbered slots of the even-numbered PRBs in the even-numbered PRBs (# 1, # 6, # 11) ) Is removed, and the second DMRS mapping RE pair is removed in the odd-numbered slot of the even-numbered PRB. On the other hand, in the odd-numbered PRB, the second DMRS mapping RE pair is removed, and in the odd-numbered slot of the odd-numbered PRB, the remaining DMRS mapping RE pair excluding the second DMRS mapping RE pair is removed.

7, but the DMRS mapping RE pair removed in the even PRB and the odd PRB may be applied in reverse. That is, three DMRS mapping RE pairs (two, seventh, and tenth subcarriers in one PRB (the subcarrier indexes in one PRB are # 1 and # 6 , # 11), the second DMRS mapping RE pair in the even-numbered slot of the even-numbered PRB (the seventh sub-carrier in each PRB (the sub-carrier index # 6 in one PRB) And the remaining DMRS mapping RE pair excluding the second DMRS mapping RE pair may be removed in the odd-numbered slot of the even-numbered PRB. Also, in the even-numbered slots of the odd-numbered PRB, the remaining DMRS mapping RE pair excluding the second DMRS mapping RE pair is removed, and the second DMRS mapping RE pair in the odd-numbered slot of the odd-numbered PRB may be removed.

That is, the reduced DMRS pattern is a diamond structure, and the DMRS REs are uniformly distributed in all subframes and PRBs. In particular, the pattern of the odd-numbered slot of the even-numbered PRB is the same as the pattern of the even-numbered slot of the odd-numbered PRB, and the pattern of the even-numbered slot of the even-

Referring to FIG. 8, a structure similar to that of FIG. 7 and taking into consideration the characteristics of a special subframe will be described. In FIG. 7, in the even-numbered slot, DMRS RE is mapped in the OFDM symbol # 5 and # 6, and in the odd-numbered slot, the DMRS is mapped in the OFDM symbol # 5 and # 6 . That is, the first and second OFDM symbols to which the DMRS is mapped in one subframe are the symbols corresponding to the OFDM symbol indexes # 5 and # 6 in the even-numbered slots, respectively, and the third and fourth OFDM symbols to which the DMRS is mapped in one subframe Symbols are symbols corresponding to the OFDM symbol indexes # 5 and # 6 in the odd-numbered slots, respectively.

However, in the case of the special subframe, the position of the OFDM symbol to which the DMRS is mapped can be changed. In the case of the special subframe configuration # 1, # 2, # 6 or # 7, the DMRS is not mapped in the odd-numbered slot and the OFDM symbol indexes # 2 and # 3, and # 5 and # 6. That is, the first, second, third, and fourth OFDM symbols to which the DMRS is mapped in one subframe are mapped to OFDM symbols in the even- Symbols # 2, # 3, # 4, and # 5. (b) is a special subframe setting # 3, # 4, # 8, or # 9, the OFDM symbol indexes # 2 and # 3 in the even slot and the OFDM symbol index # DMRS can be mapped to an OFDM symbol corresponding to # 2, # 3. That is, the first and second OFDM symbols to which the DMRS is mapped in one subframe are symbols corresponding to the OFDM symbol indexes # 2 and # 3 in the even-numbered slots, respectively, and the third and fourth OFDM symbols to which the DMRS is mapped in one subframe Symbols are symbols corresponding to the OFDM symbol indexes # 2 and # 3 in the odd-numbered slots, respectively.

8, in the same manner as in FIG. 7, in a PRB, three DMRS mapping RE pairs (two, seventh, and tenth subcarriers in one PRB (subcarrier indices in one PRB In the first and second OFDM symbols to which the DMRS is mapped in one subframe of the even-numbered PRBs among the second DMRS mapping RE pairs (the seventh sub- (The subcarrier index # 6 in one PRB) is removed, and in the third and fourth OFDM symbols in which the DMRS is mapped in one subframe of the even PRB, the second DMRS mapping RE pair is removed. On the other hand, in the first and second OFDM symbols to which the DMRS is mapped in one subframe of the odd-numbered PRB, the second DMRS mapping RE pair is removed, and the third and fourth OFDM symbols The remaining DMRS mapping RE pair excluding the second DMRS mapping RE pair is removed.

Or the DMRS mapping RE pair removed in the even PRB and the odd PRB may be applied in reverse. That is, three DMRS mapping RE pairs (two, seventh, and tenth subcarriers in one PRB (the subcarrier indexes in one PRB are # 1 and # 6 , # 11), in the first and second OFDM symbols to which the DMRS is mapped in one subframe of the even-numbered PRB, the second DMRS mapping RE pair (the seventh subcarrier in one PRB The subcarrier index # 6) in the even-numbered PRB is removed, and in the third and fourth OFDM symbols to which the DMRS is mapped in one subframe of the even-numbered PRB, the remaining DMRS mapping RE pair excluding the second DMRS mapping RE pair is removed It is possible. Also, in the first and second OFDM symbols to which the DMRS is mapped in one subframe of the odd-numbered PRB, the remaining DMRS mapping RE pair except for the second DMRS mapping RE pair is removed, and in the one subframe of the odd- The second DMRS mapping RE pair may be removed in the third and fourth OFDM symbols mapped.

Figures 9 and 10 show another example of a reduced DMRS pattern in accordance with the present invention. Slot-based reduced DMRS pattern, FIG. 9 is an example of a normal sub-frame, and FIG. 10 is an example of a special sub-frame.

Referring to FIGS. 9 and 10, DMRS mapping is performed on four existing OFDM symbols in one subframe. In the first and second OFDM symbols, the DMRS mapping RE pair is removed without mapping DMRS, and only the third and fourth OFDM symbols Map the DMRS. In the odd-numbered PRB, the DMRS mapping pair RE is removed without mapping the DMRS in the third and fourth OFDM symbols, and the DMRS is mapped only in the first and second OFDM symbols.

9 and 10, but the DMRS mapping RE pair removed in the even PRB and the odd PRB may be applied in reverse. That is, in the even-numbered PRB, the DMRS mapping pair RE is removed without mapping the DMRS in the third and fourth OFDM symbols, and the DMRS is mapped only in the first and second OFDM symbols. In the odd PRB, the first and second OFDM symbols do not map the DMRS, but the DMRS mapping RE pair is removed and the third and fourth OFDM symbols only map the DMRS.

9, the first and second OFDM symbols may be symbols corresponding to OFDM symbol indexes # 5 and # 6 in an even-numbered slot, respectively, and the third and fourth OFDM symbols may be odd-numbered Th slot may be a symbol corresponding to OFDM symbol indexes # 5 and # 6.

In the special subframe configuration # 1, # 2, # 6, or # 7 in the case of using the special subframe as shown in FIG. 10, the first, second, third and fourth OFDM symbols are transmitted in the even- OFDM symbol indexes # 2, # 3, # 5, and # 6. In the special subframe setting # 3, # 4, # 8 or # 9, the first and second OFDM symbols may be symbols corresponding to the OFDM symbol indexes # 2 and # 3 in the even-numbered slots, respectively. The fourth OFDM symbol may be a symbol corresponding to the OFDM symbol indexes # 2 and # 3 in the odd-numbered slot, respectively.

11 and 12 show another example of a reduced DMRS pattern according to the present invention. FIG. 11 is an example of two PRB bundling, and FIG. 12 is an example of three PRB bundling.

Referring to FIG. 11, even-numbered PRBs are removed and odd-numbered PRBs are maintained in the first sub-frame. On the other hand, even-numbered PRBs are held and odd-numbered PRBs are removed in the second sub-frame. In the third subframe, even-numbered PRBs are removed and odd-numbered PRBs are maintained.

In this case also, the sub-frame and PRB are combined and the remaining DMRS REs are diamond-structured.

The reduced DMRS pattern based on the subframe bundling is the same DMRS pattern as the normal subframe in the special subframe.

Referring to FIG. 12, the first PRB is maintained and the second PRB and the third PRB are removed in the first subframe. In the second subframe, the second PRB is maintained and the first PRB is removed. In the third subframe, the third PRB is retained and the first PRB and the second PRB are removed.

&Lt; Case where there are 3 to 8 ranks >

If the rank is greater than 2 (e.g., 3 to 8), there are 24 REs in one subframe. 24 REs belong to two CDM groups. It is possible to remove the DMRS for the first CDM group and maintain the DMRS for the second CDM group in one subframe (for example, the odd subframe). It is also possible to maintain the DMRS for the first CDM group and remove the DMRS for the second CDM group in another subframe (e.g., even-numbered subframe).

If subframe bundling is not applied, the existing DMRS pattern is used as it is.

If PRB bundling is applied, 1) use the existing DMRS pattern in the first subframe, and use the reduced DMRS pattern from the second subframe. 12 REs per subframe are maintained. 2) The DMRS for CDM group 2 (antenna ports # 9, # 10, # 12 and / or # 14) is removed in the second subframe. Therefore, only the DMRS for CDM group 1 (antenna ports # 7, # 8, # 11 and / or # 13) exists in the second subframe and CDM group 2 (antenna ports # 9, # 10, 12 and / or &lt; RTI ID = 0.0 &gt;# 14). &Lt; / RTI &gt;

On the other hand, the reduced DMRS pattern based on the CDM group for the plurality of PRBs is 1) in the even PRB, the DMRS for the CDM group 1 of the even subframe is maintained and the DRMS for the CDM group 2 is removed, while the CDM group 1 is removed and the DMRS for CDM Group 2 is maintained. 2) In the odd PRB, the DMRS for CDM group 1 in the even subframe is removed and the DRMS for CDM group 2 is maintained, while the DMRS for CDM group 1 in the odd subframe is maintained and the DMRS for CDM group 2 is maintained Removed.

13 is a flowchart showing an example of the operation of the terminal according to the present invention.

The terminal receives the OFDM signal including the reference signal from the base station (S1300). The pattern of the reference signal may correspond to one of Figs. 7 to 12.

The UE derives a reference signal sequence by RE demapping the OFDM signal (S 1305).

A sequence generated based on information related to the DMRS received by the base station from a sequence extracted by the terminal (e.g., sequence generated and transmitted from the base station and received and extracted by the terminal through the channel) The sequence can be generated based on information related to the DMRS transmitted to the base station) (S1310).

14 is a block diagram showing an example of an apparatus for transmitting and receiving a reference signal according to the present invention.

Referring to FIG. 14, a base station 1400 for transmitting a reference signal in a small cell environment includes an RE mapping unit 1405 for performing resource element mapping to a reference signal sequence, an OFDM signal An OFDM signal generator 1410 for generating an OFDM signal and a transmitter 1415 for transmitting the OFDM signal to a terminal.

The RE mapping unit maps two PRB pairs into a unit pattern, and maps the PRB pairs to be distributed regularly in the sub-frame bundling or PRB.

For example, the RE mapping unit may map the patterns of FIGS. 7 to 12.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (10)

A method for transmitting a reference signal in a small cell environment,
Generating a reference signal sequence to perform resource element (RE) mapping;
Generating an OFDM (Orthogonal Frequency Division Multiplexing) signal including a reference signal based on the RE mapping; And
And transmitting the OFDM signal to a terminal,
The RE mapping pattern of the reference signal is defined by two PRBs in frequency and one subframe in time, two PRBs on the frequency, and a Code Division Multiplexing (CDM) in one subframe in time. ) &Lt; / RTI &gt; is a pattern mapped to a total of 12 REs per group. The method according to claim 1,
The reference signal sequence is mapped using a total of four OFDM symbols for one subframe in time,
In one subframe, the RE mapping pattern of the reference signal mapped in the first and second OFDM symbols of the even PRB and the RE mapping pattern of the reference signal mapped in the third and fourth OFDM symbols of the odd PRB are the same, The RE mapping pattern of the reference signal mapped in the third and fourth OFDM symbols of the PRB and the RE mapping pattern of the reference signal mapped in the first and second OFDM symbols of the odd PRB are the same. 3. The method of claim 2,
In the first and second OFDM symbols of even-numbered PRBs and the third and fourth OFDM symbols of odd-numbered PRBs, the reference signal sequence is mapped to two subcarriers per CDM group among 12 subcarriers in one PRB,
The reference signal sequence is mapped to one subcarrier per CDM group among 12 subcarriers in one PRB in the third and fourth OFDM symbols of the even PRB and the first and second OFDM symbols of the odd PRB. . 3. The method of claim 2,
The reference signal sequence is mapped to one subcarrier per CDM group among 12 subcarriers in one PRB in the first and second OFDM symbols of the even PRB and the third and fourth OFDM symbols of the odd PRB,
The reference signal sequence is mapped to two subcarriers per CDM group among 12 subcarriers in one PRB in the third and fourth OFDM symbols of the even PRB and the first and second OFDM symbols of the odd PRB. . 3. The method of claim 2,
The reference signal sequence is mapped to three subcarriers per CDM group among 12 subcarriers in one PRB in the first and second OFDM symbols of the even PRB and the third and fourth OFDM symbols of the odd PRB,
The reference signal sequence is not mapped to 12 subcarriers in one PRB in the third and fourth OFDM symbols of even-numbered PRBs and first and second OFDM symbols of odd-numbered PRBs. 3. The method of claim 2,
The reference signal sequence is not mapped to 12 subcarriers in one PRB in the first and second OFDM symbols of the even PRB and the third and fourth OFDM symbols of the odd PRB,
The reference signal sequence is mapped to three subcarriers per CDM group among 12 subcarriers in one PRB in the third and fourth OFDM symbols of the even PRB and the first and second OFDM symbols of the odd PRB. . A base station for transmitting a reference signal in a small cell environment,
A RE mapping unit for generating a reference signal sequence to perform resource element (RE) mapping;
An OFDM signal generator for generating an orthogonal frequency division multiplexing (OFDM) signal including a reference signal based on the RE mapping; And
And a transmitter for transmitting the OFDM signal to a mobile station,
The RE mapping pattern of the reference signal is defined by two PRBs in frequency and one subframe in time, two PRBs on the frequency, and a Code Division Multiplexing (CDM) in one subframe in time. ) &Lt; / RTI &gt; is a pattern mapped to a total of 12 REs per group. 8. The method of claim 7,
The reference signal sequence is mapped using a total of four OFDM symbols for one subframe in time,
In one subframe, the RE mapping pattern of the reference signal mapped in the first and second OFDM symbols of the even PRB and the RE mapping pattern of the reference signal mapped in the third and fourth OFDM symbols of the odd PRB are the same, The RE mapping pattern of the reference signal mapped in the third and fourth OFDM symbols of the PRB and the RE mapping pattern of the reference signal mapped in the first and second OFDM symbols of the odd PRB are the same. 9. The method of claim 8,
In the first and second OFDM symbols of even-numbered PRBs and the third and fourth OFDM symbols of odd-numbered PRBs, the reference signal sequence is mapped to two subcarriers per CDM group among 12 subcarriers in one PRB,
The reference signal sequence is mapped to one subcarrier per CDM group among 12 subcarriers in one PRB in the third and fourth OFDM symbols of the even PRB and the first and second OFDM symbols of the odd PRB. . 9. The method of claim 8,
The reference signal sequence is mapped to three subcarriers per CDM group among 12 subcarriers in one PRB in the first and second OFDM symbols of the even PRB and the third and fourth OFDM symbols of the odd PRB,
The reference signal sequence is not mapped to 12 subcarriers in one PRB in the third and fourth OFDM symbols of even-numbered PRBs and first and second OFDM symbols of odd-numbered PRBs.

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