KR101833065B1 - Method and apparatus for transmitting reference signal in multi-node system - Google Patents

Abstract

There is provided a method of transmitting a reference signal in a multi-node system including a plurality of nodes and a base station controlling the plurality of nodes. The method includes transmitting node information to a terminal and transmitting a reference signal to at least one of the plurality of nodes based on the node information, wherein the node information includes a reference signal transmitted from the at least one node, And the plurality of nodes transmit different reference signals, respectively.

Description

TECHNICAL FIELD [0001] The present invention relates to a method and apparatus for transmitting a reference signal in a multi-

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

Recently, the data transmission amount of the wireless communication network is rapidly increasing. This is due to the advent and spread of various devices such as machine-to-machine (M2M) communications and smart phones and tablet PCs that require high data throughput. A carrier aggregation technique, a cognitive radio technique, and the like that efficiently use more frequency bands in order to satisfy a required high data transmission amount, and a multi-antenna technology and a multi-base-station cooperation Technology and the like have recently emerged.

In addition, the wireless communication network evolves toward a higher density of nodes that can access the user. Here, the node means an antenna or a group of antennas separated by a predetermined distance or more in a distributed antenna system (DAS), but is not limited to this meaning and can be used in a broader sense. That is, the node may be a pico-cell base station (PeNB), a home base station (HeNB), a remote radio head (RRH), a remote radio unit (RRU) Wireless communication systems with such high density nodes can exhibit higher system performance by cooperation between nodes. That is, when each node operates as an independent base station (BS, Advanced BS (ABS), Node-B (NB), eNode-B (eNB), Access Point (AP) If each node manages transmission and reception by one control station and operates as an antenna or antenna group for one cell, much better system performance can be obtained. Hereinafter, a wireless communication system including a plurality of nodes is referred to as a multi-node system.

In a multi-node system, a node transmitting a signal to the terminal may be different for each terminal, and a node receiving a signal from the terminal may also be different for each terminal. In consideration of the characteristics of the multi-node system, there is a need for a reference signal transmission method and apparatus capable of identifying each node in a multi-node system.

A method and an apparatus for transmitting a reference signal in a multi-node system.

According to an aspect of the present invention, there is provided a method of transmitting a reference signal in a multi-node system including a plurality of nodes and a base station controlling the plurality of nodes, the method comprising: transmitting node information to a terminal; Wherein the node information includes information capable of identifying a reference signal transmitted from the at least one node, wherein the plurality of nodes transmit different reference signals to the terminal, .

Each of the plurality of nodes may transmit a reference signal generated by using a different cell ID as a node ID.

Each of the plurality of nodes can transmit a reference signal generated using a node ID composed of a function of only a part of a cell ID used by the base station.

If the cell ID used by the base station is composed of a cell ID group and an ID in the cell ID group, the node ID of each of the plurality of nodes may include the same bit as the cell ID group.

When the cell ID used by the base station is composed of the cell ID group and the ID in the cell ID group, the node ID of each of the plurality of nodes may include the same bit as the ID in the cell ID group.

Each of the plurality of nodes may transmit a reference signal corresponding to a different antenna port.

Each of the plurality of nodes may transmit a reference signal corresponding to a different reference signal setting number.

Each of the plurality of nodes transmits a reference signal corresponding to the same cell ID, the same antenna port, and the same reference signal setting number, but can transmit a reference signal using different time, frequency, or code.

The node information may include at least one of a node ID, an antenna port information, and reference signal setting information used by each of the plurality of nodes.

Each of the plurality of nodes may be an antenna or an antenna group wired to the base station.

The base station further comprises receiving feedback information from the terminal through at least one of the plurality of nodes, wherein the feedback information includes at least one of a cell ID used when each of the plurality of nodes transmits the reference signal, an antenna port number, And a reference signal setting number.

According to another aspect of the present invention, there is provided a reference signal transmission apparatus including: an RF unit transmitting and receiving a radio signal; And a processor coupled to the RF unit, wherein the RF unit includes a plurality of nodes, the processor transmits node information to the terminal, and at least one of the plurality of nodes, based on the node information, The reference signal is transmitted to the terminal, and the node information includes information for identifying a node transmitting the reference signal, and the reference signal is transmitted through each of the plurality of nodes.

The reference signal may be transmitted through each of the plurality of nodes using one of the node ID, the antenna port information, and the reference signal setting information of each of the plurality of nodes.

A method and apparatus for transmitting a reference signal capable of identifying each node in a multi-node system are provided. According to the present invention, each node can identify each node using a cell ID, an antenna port number, a reference signal setting number, a reference signal division index, and the like. Therefore, in a multi-node system, a terminal can accurately report feedback information for each node, and system performance can be improved by using such feedback information.

1 shows an example of a multi-node system.
2 shows a distributed antenna system as an example of a multi-node system.
3 shows the structure of a Frequency Division Duplex (FDD) radio frame in 3GPP LTE.
4 shows a time division duplex (TDD) radio frame structure in 3GPP LTE.
5 is an exemplary diagram illustrating a resource grid for one downlink slot.
6 shows an example of a downlink subframe structure.
Figure 7 shows the mapping of the CRS in the normal CP. Figure 8 shows the mapping of the CRS in the extended CP.
Figure 8 shows the mapping of the CRS in the extended CP.
FIG. 9 shows a mapping of a CSI-RS to a CSI setting 0 in a normal CP, and FIG. 10 shows a mapping of a CSI-RS to a CSI setting 0 in an extended CP.
11 illustrates a reference signal transmission method of a multi-node system according to an embodiment of the present invention.
12 shows a method (method 1) of transmitting a reference signal corresponding to a different cell ID for each node.
13 shows a reference signal transmission method (method 2) using different antenna port numbers for each node.
14 shows a method (method 3) of transmitting a reference signal with different reference signal settings for each node.
15 shows a method (method 4) of alternately transmitting reference signals corresponding to the same cell ID, the same antenna port, and the same reference signal setting at each node in the multi-node system.
16 is a block diagram showing a base station and a terminal.

The following description is to be understood as illustrative and not restrictive, with reference to the accompanying drawings, in which: FIG. 1 is a block diagram of a mobile communication system according to an embodiment of the present invention; And may be used in a variety of multiple access schemes as well. CDMA may be implemented in radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. The TDMA may be implemented in a wireless technology such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in wireless technologies such as IEEE (Institute of Electrical and Electronics Engineers) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, and Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) is a part of E-UMTS (Evolved UMTS) using E-UTRA, adopting OFDMA in downlink and SC-FDMA in uplink. LTE-A (Advanced) is the evolution of LTE.

1 shows an example of a multi-node system.

Referring to FIG. 1, a multi-node system includes a base station and a plurality of nodes.

In FIG. 1, the node indicated by the antenna node may be a macro base station, a picosel base station (PeNB), a home base station (HeNB), a remote radio head (RRH), a repeater, or a distributed antenna. These nodes are also referred to as points.

In a multi-node system, if all the nodes manage transmission and reception by one base station controller and each node operates as a part of one cell, the system may be a distributed antenna system (DAS) system . In a distributed antenna system, individual nodes may be given separate node IDs or may operate as some antenna groups in a cell without a separate node ID. In other words, a distributed antenna system (DAS) refers to a system in which antennas (i.e., nodes) are distributed at various locations in a cell and the base stations manage such antennas. The distributed antenna system is different from the conventional CAS in that the antennas of the base station are concentrated at the cell center.

In a multi-node system, if individual nodes have individual cell IDs and perform scheduling and handover, this can be viewed as a multi-cell (e.g., macrocell / femtocell / picocell) system. If these multiple cells are configured to overlap according to their coverage, this is called a multi-tier network.

2 shows a distributed antenna system as an example of a multi-node system.

Referring to FIG. 2, a distributed antenna system (DAS) is composed of a base station (BS) and a plurality of base station antennas (e.g., ant 1 to ant 8, hereinafter abbreviated as antennas). The antennas ant 1 to ant 8 may be wired to the base station BS. Unlike a conventional centralized antenna system (CAS), a distributed antenna system is arranged such that the antennas are dispersed at various locations in a cell without being concentrated at a specific point of the cell 15a, for example, at the center of the cell. As shown in FIG. 2, the antenna may include one antenna (antenna 1 to antenna 4, antenna 6 to antenna 8) at each spaced apart place in the cell, and multiple antennas 111-1, 111-2, and 111-3 may be distributed in a concentrated form. The densely existing antennas can constitute one antenna node.

The antenna coverage of the antennas may overlap so that transmission of rank 2 or higher is possible. For example, the antenna coverage of each antenna may extend to an adjacent antenna. In this case, the strength of a signal received from a plurality of antennas may be variously changed according to a position in a cell, a channel state, and the like. Referring to the example of FIG. 2, the UE 1 can receive signals having high reception sensitivity from the antennas 1, 2, 5, and 6. On the other hand, the signals transmitted from the antennas 3, 4, 7, and 8 may have little effect on the terminal 1 due to the path loss.

The terminal 2 (UE2) can receive a signal having a good reception sensitivity from the antennas 6 and 7, and the signal transmitted from the remaining antennas may be insignificant. Similarly, in the case of the UE 3 (UE 3), it is possible to receive a signal of good reception sensitivity only from the antenna 3 and to have a weak enough strength to neglect the signals of the remaining antennas.

In a distributed antenna system, it may be easy to perform MIMO communication for terminals spaced apart from each other in a cell. In the above example, the terminal 1 is communicated via the antennas 1, 2, 5, and 6, and the terminal 2 can communicate with the antenna 7 and the terminal 3 with the antenna 3. The antennas 4 and 8 may transmit a signal for the terminal 2 or the terminal 3 and may not transmit any signal. That is, the antennas 4 and 8 may be operated in the off state as occasion demands.

As described above, when MIMO communication is performed in the distributed antenna system, there may be various layers per layer (i.e., number of transport streams). In addition, antennas (or antenna groups) allocated to each terminal may be different from each other. In other words, the distributed antenna system can support a specific antenna (or a specific antenna group) among all the antennas in the system for each terminal. The antennas supported by the terminal may be changed over time.

        3 shows the structure of a Frequency Division Duplex (FDD) radio frame in 3GPP LTE. This radio frame structure is referred to as a frame structure type 1.

Referring to FIG. 3, a radio frame is composed of 10 subframes, and one subframe is defined as two consecutive slots. The time taken for one subframe to be transmitted is called a transmission time interval (TTI). The time length of the radio frame, T _f = 307200 * T _s = 10 ms, is composed of 20 slots. The time length of the _slot is T _slot = 15360 * T _s = 0.5 ms and is numbered from 0 to 19. The downlink in which each node or the base station transmits a signal to the terminal and the uplink in which the terminal transmits signals to each node or the base station are classified in the frequency domain.

4 shows a time division duplex (TDD) radio frame structure in 3GPP LTE. This radio frame structure is referred to as a frame structure type 2.

Referring to FIG. 4, one radio frame is composed of two half-frames having a length of 10 ms and a length of 5 ms. One half frame is composed of five subframes having a length of 1 ms. One subframe is designated as one of a UL subframe, a DL subframe, and a special subframe. One radio frame includes at least one uplink subframe and at least one downlink subframe. One subframe is defined as two consecutive slots. For example, the length of one subframe may be 1 ms and the length of one slot may be 0.5 ms.

The special subframe is a specific period for separating the uplink and downlink between the uplink subframe and the downlink subframe. At least one special subframe exists in one radio frame, and the special subframe includes a downlink pilot time slot (DwPTS), a guard period, and an uplink pilot time slot (UpPTS). DwPTS is used for initial cell search, synchronization, or channel estimation. UpPTS is used to match the channel estimation at the base station and the uplink transmission synchronization of the terminal. The guard interval is a period for eliminating the interference occurring in the uplink due to the multipath delay of the downlink signal between the uplink and the downlink.

One slot in an FDD and a TDD radio frame includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in a time domain and a plurality of resource blocks (RBs) in a frequency domain. The OFDM symbol is used to represent one symbol period since 3GPP LTE uses OFDMA in the downlink and may be called another term such as an SC-FDMA symbol according to the multiple access scheme. A resource block includes a plurality of consecutive subcarriers in one slot in a resource allocation unit.

The structure of the radio frame described with reference to FIGS. 3 and 4 is described in 3GPP TS 36.211 V8.3.0 (2008-05) " Technical Specification Group Radio Access Network, Evolved Universal Terrestrial Radio Access (E-UTRA) 8) "in Section 4.1 and Section 4.2.

 The structure of the radio frame is merely an example, and the number of subframes included in a radio frame, the number of slots included in a subframe, and the number of OFDM symbols included in a slot can be variously changed.

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

Referring to FIG. 5, one downlink slot includes a plurality of OFDM symbols in a time domain. Herein, one downlink slot includes 7 OFDMA symbols and one resource block (RB) includes 12 subcarriers in the frequency domain, but the present invention is not limited thereto.

Each element on the resource grid is called a resource element, and one resource block (RB) includes 12 × 7 resource elements. The number N ^DL of resource blocks included in the downlink slot is dependent on the downlink transmission bandwidth set in the cell. The resource grid for the downlink slot described above can also be applied to the uplink slot.

6 shows an example of a downlink subframe structure.

Referring to FIG. 6, a subframe includes two consecutive slots. A maximum of 3 OFDM symbols preceding a first slot in a subframe may be a control region to which control channels are assigned and the remaining OFDM symbols may be a data region to which a physical downlink shared channel (PDSCH) is allocated.

The downlink control channel includes a Physical Control Format Indicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH), and a Physical Hybrid-ARQ Indicator Channel (PHICH). The PCFICH transmitted in the first OFDM symbol of the subframe carries information on the number of OFDM symbols (i.e., the size of the control region) used for transmission of the control channels in the subframe. The control information transmitted through the PDCCH is referred to as downlink control information (DCI). DCI indicates uplink resource allocation information, downlink resource allocation information, and uplink transmission power control commands for arbitrary UE groups. The PHICH carries an ACK (Acknowledgment) / NACK (Not-Acknowledgment) signal for HARQ (Hybrid Automatic Repeat Request) of the uplink data. That is, the ACK / NACK signal for the uplink data transmitted by the UE is transmitted on the PHICH.

The PDSCH is a channel through which control information and / or data is transmitted. The UE can decode the control information transmitted through the PDCCH and read the data transmitted through the PDSCH.

Hereinafter, a method of transmitting a reference signal in a multi-node system will be described.

LTE Rel-8 uses CRS (cell specific reference signal) for channel measurement and channel estimation for PDSCH.

Figure 7 shows the mapping of the CRS in the normal CP. Figure 8 shows the mapping of the CRS in the extended CP.

Referring to FIGS. 7 and 8, in the case of multiple antenna transmission using a plurality of antennas, a resource grid exists for each antenna, and at least one reference signal for each antenna may be mapped to each resource grid. The reference signal for each antenna consists of reference symbols. Rp represents the reference symbol of antenna port p (p ∈ {0, 1, 2, 3}). R0 to R3 are not mapped to overlapping resource elements.

In one OFDM symbol, each Rp may be located at six subcarrier spacing. The number of R0 and the number of R1 in the subframe are the same, and the number of R2 and the number of R3 are the same. The number of R2, R3 in the subframe is less than the number of R0, R1. Rp is not used for any transmission through other antennas except for antenna p.

In the LTE-A, a channel status information reference signal (CSI-RS) may be used separately from the CRS for channel measurement and channel estimation for the PDSCH. Hereinafter, the CSI-RS will be described.

Unlike CRS, CSI-RS has up to 32 different settings to reduce inter-cell interference (ICI) in multi-cell environments including heterogeneous network environments.

The setting for the CSI-RS differs depending on the number of antenna ports in the cell, and is given to be as different as possible among adjacent cells. The CSI-RS is classified according to the CP type. The CSI-RS is configured to apply both the frame structure type 1 and the frame structure type 2 according to the frame structure type (FDD for frame structure type 1 and TDD for frame structure type 2) 2 < / RTI >

Unlike CRS, CSI-RS supports up to 8 antenna ports, and antenna port p is supported by {15}, {15, 16}, {15,16,17,18}, {15, ..., 22} do. That is, it supports one, two, four, and eight antenna ports. The spacing? F between subcarriers is defined only for 15 kHz.

The sequence rl _{, ns} (m) for CSI-RS is generated as follows.

[Equation 1]

In Equation (1), n _s is a slot number in a radio frame, and l is an OFDM symbol number in a slot. c (i) is a pseudo-random sequence and starts in each OFDM symbol with c _init . N _ID ^cell denotes a physical layer cell ID.

In the subframes set to transmit CSI-RS, the reference signal sequence rl _{, ns} (m) is mapped to a complex-valued modulation symbol a _{k, l} ^(p) used as a reference symbol for antenna port p.

The relation between r _{l, n s} (m) and a _{k, l} ^(p) is as follows.

[Formula 2]

(K ', l') and n _s in the above Equation 2 are given in Tables 1 and 2 to be described later. CSI-RS can be transmitted in the downlink slots that meet the conditions shown in Table 1 and Table 2 to be described later is (n _s mod 2) (mod means a modular operation, that is, the remainder obtained by dividing the n _s 2 it means).

The following table shows the CSI-RS settings for the normal CP.

[Table 1]

The following table shows the CSI-RS settings for the extended CPs.

[Table 2]

In addition, the CSI-RS can be transmitted in a subframe satisfying the conditions of Table 3 below.

That is, the subframe including the CSI-RS must satisfy the following equation.

[Formula 3]

The following Table 3 shows the CSI-RS subframe settings associated with the duty cycle. n _f is the system frame number.

[Table 3]

In Table 3, 'CSI-RS-SubframeConfig', that is, I _CSI-RS indicates a CSI-RS subframe setting with a value given by an upper layer. T _CSI-RS represents the cell specific subframe setup period, and [Delta] _CSI-RS represents the cell specific subframe offset. The CSI-RS supports five duty cycles according to CQI / CSI feedback and can be transmitted with different subframe offset in each cell.

FIG. 9 shows a mapping of a CSI-RS to a CSI setting 0 in a normal CP, and FIG. 10 shows a mapping of a CSI-RS to a CSI setting 0 in an extended CP.

9 and 10, two consecutive identical resources for two antenna ports, for example p = {15,16}, {17,18}, {19,20}, {21,22} Element, and transmits the CSI-RS using the orthogonal cover code (OCC).

A plurality of CSI-RS settings can be used in a given cell. One CSI-RS configuration in which the UE assumes non-zero transmission power and one CSI-RS configuration in which the UE assumes zero transmission power can be set .

The CSI-RS is not transmitted in the following cases.

1. Special subframe of frame structure type 2

2. In case of conflict with synchronization signal, PBCH, SIB

3. The subframe where the paging message is sent

The resource element (k, l) used for transmission of the CSI-RS to an arbitrary antenna port of the set S is not used for transmission of the PDSCH for an arbitrary antenna port in the same slot. Also, the resource element (k, l) is not used for CSI-RS transmission to any other antenna port except S in the same slot. Here, the antenna ports included in the set S are {15, 16}, {17,18}, {19,20}, {21, 22}.

The parameters necessary for transmission of the CSI-RS are as follows: 1. CSI-RS port number, 2. CSI-RS setting information, 3. CSI-RS subframe setting (I _CSI-RS ) _CSI-RS ), 5. Sub-frame offset [Delta] _CSI-RS, etc. These parameters are cell specific and are given via higher layer signaling.

The base station can apply reference signals such as the CRS and the CSI-RS described above so that the terminal can identify each node in the multi-node system.

In a multi-node system, a node receiving a signal transmitted from the terminal to the base station may be some antenna or group of antennas in the multi-node system. Also, in a multi-node system, the UE can transmit only CSI (CQI, PMI, RI, etc.) feedback information corresponding to some nodes preferred to the BS. Therefore, the terminal needs to identify each node in the multi-node system. To this end, the base station can transmit UE-specific node information (node ID, number of nodes, number of antenna ports, etc., described below) to the UE. Using the node information, the terminal can distinguish reference signals transmitted by the respective nodes. Hereinafter, a case where CSI-RS is used as a reference signal transmitted by each node will be described as an example. However, the present invention is not limited to CSI-RS, and other reference signals such as a positioning RS (PRS), a CRS and the like may be used.

11 illustrates a reference signal transmission method of a multi-node system according to an embodiment of the present invention.

Referring to FIG. 11, the BS transmits node information to the MS (S11). Herein, the node information is information that allows the terminal to distinguish the reference signal transmitted from each node. The node information includes a node ID used in each node, antenna port information, reference signal setting information, a sharing indicator indicating whether a plurality of nodes share one reference signal pattern, and whether several nodes share the same reference signal pattern And a reference signal resource division index that indicates when a plurality of nodes share one reference signal resource.

For example, the base station transmits the reference signal 1 to the terminal through the node 1 (S12), and transmits the reference signal 2 to the terminal through the node 2 (S13). Here, the node 1 and the node 2 may be a node, for example, an antenna or an antenna group controlled and managed by the base station.

The mobile station identifies which node has transmitted the signal using the reference signal (S14), and generates a required operation, for example, feedback information and transmits it to the destination node, for example, node 2 (S15).

Hereinafter, a method for transmitting a reference signal in a plurality of nodes controlled and controlled by a base station of a multi-node system will be described in detail. In a multi-node system, it is possible to transmit different reference signals for each node in order for the terminal to distinguish the nodes. Such a reference signal can be reused according to the distance between nodes, transmission power, and the like. In a multi-node system, there are four methods for transmitting different reference signals at each node.

Method 1: A reference signal transmission method corresponding to a different cell ID for each node.

Method 2: Each node in a multi-node system transmits reference signals corresponding to different antenna ports. At this time, the cell IDs of the nodes are the same.

Method 3: Each node in a multi-node system transmits a reference signal according to different reference signal settings. At this time, reference signal setting includes subframe setting.

Method 4: In each node in the multi-node system, the same cell ID, the same antenna port, and the reference signal corresponding to the same reference signal setting are alternately transmitted.

Each of the above-mentioned four methods will be described in detail below.

12 shows a method (method 1) of transmitting a reference signal corresponding to a different cell ID for each node. In FIG. 12, the terminal may have received node information including a node ID for each node from the base station.

Referring to FIG. 12, node 1 transmits reference signal 1 using node ID 1 (S31), and node 2 transmits reference signal 2 using node ID 2 (S32).

As the node ID of each node, a certain cell ID can be directly used in the same format as the cell ID (physical layer cell ID), but it can be used in another format by modifying the cell ID. For example, the node ID can be configured as a function of the cell ID. In this case, in order to reduce the signaling overhead, the node ID included in the node information may be configured as a function of only a part of the constituent elements constituting the cell ID.

For example, in LTE, there are 504 physical layer cell IDs in total. The physical layer cell IDs are grouped into 168 unique physical layer cell ID groups, and each group contains three unique IDs. Each physical layer cell ID is included in a unique physical layer cell ID group.

That is, in LTE, the cell ID is configured as N _ID ^cell = 3 N _ID ⁽¹⁾ + N _ID ⁽²⁾ . Here, N _ID ⁽¹⁾ represents a cell ID group, and may be a value from 0 to 167. [ N _ID ⁽²⁾ represents a cell ID in the cell ID group and may be a value of any of 0 to 2. At this time, N _ID ⁽¹⁾ is represented by 8 bits, and N _ID ⁽²⁾ is represented by two bits. The node ID assigned to the nodes connected to the same base station can be defined such that some of the above-mentioned N _ID ⁽¹⁾ and / or N _ID ⁽²⁾ are the same. For example, all nodes connected to the same base stations may have the same N _ID ^(1). Then, each node is distinguished by N _ID ⁽²⁾ .

In the case where the node ID is formed by a function of only a part of the constituent elements constituting the cell ID, the base station does not need to signal the entire cell ID allocated to the node through the node information, but can only signal N _ID ⁽²⁾ have.

In addition, the terminal may not need to feed back the whole cell ID can only be sent N _ID ⁽²⁾ of the node in order to feed back the preferred node. Therefore, when the terminal desires to feed back the node to the base station, it can transmit only 2 bits of information instead of 10 bits of information in order to identify the node.

Or all of the nodes connected to the same base station have the same N _ID ^(2), can be defined as the upper four bits of the N _ID ⁽¹⁾ the same. In this case, each node can be distinguished only by the lower 4 bits of N _ID ⁽¹⁾ . Thus, the overhead in signaling related to the node is reduced.

The relationship between the node ID and the cell ID (i.e., the base station ID, which may be referred to as a BS ID in this sense) may be variously set. For example, when a node ID is composed of N bits, nodes having the same M bits (N> M) among them may be set as a node group, a node group ID may be assigned, and then a cell ID may be mapped to the node group ID . That is, a node group ID is generated for each cell and a cell ID is assigned. Then, the terminal can acquire the node ID and the group ID at the same time, and if the mapping relation between the group ID and the cell ID is known, the terminal can distinguish the cell ID.

Alternatively, the base station may have an independent cell ID (i.e., BS ID) and assign a node ID according to a specific rule to each node connected to the base station. For example, if the number of nodes connected to the base station is N, the base station can assign IDs from 0 to N-1 to N nodes. That is, the node ID (N _ID ^node ) can be expressed by N _ID ^node = f (N _ID ^cell , N _ID ⁽³⁾ ) or N _ID ^node = f (N _ID ⁽³⁾ ). Here, N _ID ⁽³⁾ may be a new seed number for generating the ID of each node. That is, the node ID may be generated as a function of the cell ID, or may be generated using a new seed number separately from the cell ID.

The node ID can be used for signaling information either explicitly or implicitly. As described above, if the node ID is a function of the cell ID, a node ID having a reduced amount of information in signaling can be used. If the relationship between the cell ID and the node ID is specified, the cell ID may be used as the node ID. At this time, it is also possible to limit the range of the cell ID usable as the node ID to a specific range. Alternatively, it is possible to set the range of the cell ID used as the node ID to a range out of the range of the existing cell ID (0 to 503 in LTE).

For example, when two nodes exist in a cell, two cell IDs having different values (e.g., cell ID 1, cell ID 1, cell ID 2, 2 to generate CSI-RSs, and then transmit the CSI-RSs generated by the cell IDs 1 and 2, respectively, as reference signals of the respective nodes. In this case, the cell ID 1 and the cell ID 2 serve as node IDs of the two nodes, respectively.

The terminal identifies each node by using a reference signal separated by each node ID (S33). As described in Equation 1, the sequence used for the reference signal is determined by the cell ID. Each node directly uses a different cell ID or applies a sequence generated using the modified cell ID to the reference signal. The terminal can know the node ID of each node (given the same format as the cell ID or given as a function of the cell ID) using the node information, and identify each node through the reference signal using the node ID. After measuring the reference signal, the UE can transmit feedback information to the Node B to the Node B.

13 shows a reference signal transmission method (method 2) using different antenna port numbers per node. In FIG. 13, the terminal may have received node information including antenna port information for each node from the base station.

Referring to FIG. 13, node 1 transmits reference signal 1 to antenna port N ₁ (S41), and node 2 transmits reference signal 2 to antenna port N ₂ (S42). The terminal receives the reference signal classified by the antenna port number and identifies each node (S43). That is, the antenna port number serves as an ID of each node. At this time, the node ID of each node may be the same as the cell ID of the base station.

Alternatively, the reference signal may be a CSI (for example, cell ID 1 or cell ID 2) having a different value for a cell ID (for example, cell ID 0 used in the base station) -RS and transmits a reference signal pattern according to the antenna port of the CSI-RS generated by the cell ID 1 or the cell ID 2 to the reference signal of each node. In this case, the cell ID 1, the cell ID 2, and the antenna port number serve as IDs of the respective nodes.

Each node may generate a CSI-RS using the same cell ID as the cell ID of the multi-node system, and then transmit a reference signal pattern for different antenna ports to identify each node. Alternatively, It is possible to identify each node by generating a CSI-RS using a cell ID different from the cell ID of the node system and transmitting a reference signal pattern for different antenna ports according to each node.

The antenna port number included in the node information may be directly used or may be used in a modified form. For example, the antenna port number in which the CSI-RS is used may be any one of {15, 16, ..., 22}. At this time, in order to signal the antenna port number itself, the number of necessary bits becomes 5 bits, which can be a waste. Signaling of the antenna port number (15) through the node information enables the antenna port number to be expressed by a number from 0 to 7, and the required number of bits is reduced to 3 bits.

In the case of using the above-described method 2, a feedback mode supporting feedback to the CSI for each transmit antenna port can be defined. This feedback mode may allow the UE to measure CSI values for each antenna port or set of antenna ports and then feed back all or some of the measured CSI values to the base station. The antenna port set may be configured according to a predetermined rule, or may be arbitrarily configured by the base station. For example, CSI-RS antenna port grouping information indicating which terminal should group the antenna port (hereinafter, referred to as CSI-RS antenna port) transmitting the CSI-RS and measure the CSI is added to the downlink control information . The feedback information may include a CQI for a CSI-RS antenna port and / or a CQI for a CSI-RS antenna port preferred by the UE and / or a PMI and / or a CQI for a specific antenna port group designated by the base station. The downlink control information may include physical layer control information (e.g., Downlink Control Information in LTE) and upper layer control information (e.g., Radio Resource Control Protocol in LTE).

14 shows a method (method 3) of transmitting a reference signal with different reference signal settings for each node. In FIG. 14, the terminal may have received node information including reference signal setting information for each node from the base station. Here, the reference signal setting information may include, for example, a CSI-RS setting number in Table 1 and Table 2 and a CSI-RS subframeConfig in Table 3 for each node.

Referring to FIG. 14, each node transmits a reference signal using different cell IDs and antenna port numbers but using different reference signal settings. That is, the node 1 transmits the reference signal 1 using the reference signal setting N ₁ (S51), and the node 2 transmits the reference signal 2 using the reference signal setting N ₂ (S52).

For example, when the reference signal used in each node is the above-described CSI-RS, each node refers to the CSI-RS setting described in Table 1 and Table 2 and the CSI-RS subframe setting in Table 3 differently Signal can be transmitted.

That is, in the method 3, the CSI-RS setting number (Table 1, Table 2) and the CSI-RS subframe setting number (Table 3) serve as the ID of each node. Therefore, when the UE feeds back the CSI for a plurality of nodes to the base station, the CSI-RS setting number and / or the CSI-RS subframe setting number may be used as the node ID capable of distinguishing each node. Alternatively, the node ID may be configured as a function of the CSI-RS setting number and / or the CSI-RS subframe setting number. For example, the terminal may feed back the CSI-RS setting number of the preferred node to the base station with the ID of the preferred node. For the implementation of method 3, a plurality of CSI-RS settings with non-zero transmit power can be specified.

A case where a reference signal different in CSI-RS subframe setting is transmitted from each node will be described. For example, if node 1 transmits CSI-RS with cell ID 0 and antenna port number 15 in subframe {0, 10, 20, 30, 25, 35, ....} to CSI-RS with cell ID 0 and antenna port number 15. In this case, node 1 and node 2 use different CSI-RS subframe set numbers (I _CSI-RS ). That is, referring to Table 3, the I _CSI-RS of the node 1 may be 5 and the I _CSI-RS of the node 2 may be 10. For an existing terminal, that is, a terminal operating according to standards up to LTE Rel-10, it is possible to define multiple subframe settings for CSI-RS with non-zero transmit power.

FIG. 15 shows a method (method 4) of transmitting reference signals corresponding to the same cell ID, the same antenna port, and the same reference signal setting in each node in the multi-node system. In FIG. 15, a terminal includes a sharing indicator (referred to as 'Flag_shared') indicating whether a plurality of nodes share one reference signal pattern, a shared node information indicating that several nodes share the same reference signal pattern, (Hereinafter, referred to as 'N_shared_nodes'), a state in which node information including a reference signal resource division index ('ID_shared_node') informing a corresponding node when a plurality of nodes share one reference signal resource have.

Referring to FIG. 15, each node transmits a reference signal in a method of dividing and using predetermined reference signal patterns, thereby identifying a node. That is, the node 1 transmits the reference signal by the reference signal pattern P (S61), and the node 2 also transmits the reference signal by the reference signal pattern P (S62). The reference signal pattern is a pattern defined according to the cell ID, antenna port, and reference signal setting. That is, the node 1 and the node 2 transmit the same reference signal pattern, but transmit them by dividing them into time, frequency, and code. In other words, the method of dividing the reference signal pattern includes a method (TDM) in which each node alternately uses in the time domain, a method of alternately transmitting in the frequency domain (FDM), a method of using the same reference signal pattern by applying different orthogonal codes (CDM). At this time, it is also possible to use TDM, FDM, and CDM in combination.

An example in which a reference signal is divided into TDM and transmitted at each node will be described.

For example, if node 1 is subframe {0, 10, 20, 30, ...} and node 2 is the same cell ID and antenna port in subframe {5, 15, 25, 35, RS, and the base station can set the CSI-RS subframe setting I _CSI-RS = 0 to have a period of 5 subframes. That is, the Node-1 and the Node-2 have the same CSI-RS setup number and CSI-RS subframe setup. The Node B notifies the UE of any number of nodes, that is, Node 1, and node 2 share the reference signal pattern. Also, information ('Flag_shared' = yes) indicating whether each node shares a reference signal and the number of corresponding nodes, that is, information indicating that two nodes share a reference signal pattern ('N_shared_nodes' = 2)

Through the node information, the terminal measures the CSI of the node 2 in the CSI of the node 1, the subframe {5, 15, 25, 35, ...} in the subframe {0, 10, 20, 30, Feedback can be made. When the UE feeds back the CSI, the reference signal resource division index ('ID_shared_node') can be added to the preferred node information.

That is, in method 4, the reference signal resource division index can serve as an ID of each node.

The four methods described above are not only used independently in a multi-node system. That is, some or all of the above-mentioned four methods can be used together. For example, some nodes among a plurality of nodes connected to one base station transmit reference signals corresponding to different cell IDs, and some nodes transmit reference signals corresponding to different antenna ports with the same cell ID .

In the above description, the CSI-RS is used as an example of the reference signal in the multi-node system. However, the CSI-RS is not limited to this and other reference signals (Positioning RS, CRS, etc.) can be used. It can also be used in other standards other than LTE (IEEE 802.16x). Further, the node in the present invention may be any antenna group. For example, a base station composed of a cross polarized antenna can be considered as a node composed of a vertical polarity antenna and a node composed of a horizontal polarity antenna.

16 is a block diagram showing a base station and a terminal.

The base station 100 includes a processor 110, a memory 120, and a radio frequency (RF) unit 130. The processor 110 implements the proposed functions, processes and / or methods. That is, the BS can broadcast the node information to the UE and perform scheduling based on the feedback information transmitted from the UE. The memory 120 is connected to the processor 110 and stores various information for driving the processor 110. [ The RF unit 130 is connected to the processor 110 to transmit and / or receive a radio signal. The RF unit 130 may be composed of a plurality of nodes connected to the base station 100 by wire.

The terminal 200 includes a processor 210, a memory 220, and an RF unit 230. The processor 210 receives node information from the base station and receives a reference signal from each node. The processor 210 may use the node information and the reference signal to identify which node transmitted the signal, and generate and transmit feedback information. The memory 220 is connected to the processor 210 and stores various information for driving the processor 210. The RF unit 230 is connected to the processor 210 to transmit and / or receive a radio signal.

The processors 110 and 210 may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, data processing devices, and / or converters for converting baseband signals and radio signals. The memory 120, 220 may comprise a read-only memory (ROM), a random access memory (RAM), a flash memory, a memory card, a storage medium, and / The RF units 130 and 230 may include one or more antennas for transmitting and / or receiving wireless signals. When the embodiment is implemented in software, the above-described techniques may be implemented with modules (processes, functions, and so on) that perform the functions described above. The modules may be stored in memory 120, 220 and executed by processors 110, 210. The memories 120 and 220 may be internal or external to the processors 110 and 210 and may be coupled to the processors 110 and 210 in a variety of well known ways.

The present invention may be implemented in hardware, software, or a combination thereof. (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- , Other electronic units, or a combination thereof. In software implementation, it may be implemented as a module that performs the above-described functions. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. It will be understood that various modifications and changes may be made without departing from the spirit and scope of the invention. Accordingly, modifications of the embodiments of the present invention will not depart from the scope of the present invention.

Claims (13)

A reference signal transmission method in a multi-node system including a plurality of nodes and a base station controlling the plurality of nodes,
Transmits the node information to the terminal,
At least one of the plurality of nodes transmits a reference signal to the terminal based on the node information,
Wherein the node information includes information capable of identifying the reference signal transmitted by the at least one node,
Wherein the information is one of antenna port information or reference signal setting information used by each of the plurality of nodes,
Wherein each of the plurality of nodes transmits the reference signal generated using a node ID composed of a function of only a part of a cell ID used by the base station to the terminal,
Receiving feedback information from the terminal through at least one of the plurality of nodes,
Wherein the feedback information includes one of the antenna port information or the reference signal setting information. delete delete 2. The method of claim 1, wherein, when the cell ID used by the base station is composed of a cell ID group and an ID in the cell ID group, the node ID of each of the plurality of nodes includes the same bit as the cell ID group Lt; / RTI > 2. The method of claim 1, wherein, when the cell ID used by the base station is composed of a cell ID group and an ID in the cell ID group, the node ID of each of the plurality of nodes is the same as the ID in the cell ID group ≪ / RTI > 2. The method of claim 1, wherein each of the plurality of nodes transmits a reference signal corresponding to a different antenna port. 2. The method of claim 1, wherein each of the plurality of nodes transmits a reference signal corresponding to a different reference signal setting number. 2. The method of claim 1, wherein each of the plurality of nodes transmits a reference signal corresponding to the same cell ID, the same antenna port, and the same reference signal setting number, but transmits a reference signal using a different time, frequency, or code Lt; / RTI > delete 2. The method of claim 1, wherein each of the plurality of nodes is an antenna or antenna group wired to the base station. delete An RF unit for transmitting and receiving a radio signal; And
And a processor coupled to the RF unit,
Wherein the RF unit includes a plurality of nodes,
Transmits the node information to the terminal,
At least one of the plurality of nodes transmits a reference signal to the terminal based on the node information,
Wherein the node information includes information capable of identifying a node transmitting the reference signal,
Wherein the information is one of antenna port information or reference signal setting information used by each of the plurality of nodes,
Each of the plurality of nodes transmits the reference signal generated using a node ID composed of a function of only a part of a cell ID (identification) used by the base station,
Receiving feedback information from the terminal through at least one of the plurality of nodes,
Wherein the feedback information includes one of the antenna port information and the reference signal setting information. delete

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