WO2015065077A1

WO2015065077A1 - Apparatus and method for configuring reference signal in wireless communication system to support small cells

Info

Publication number: WO2015065077A1
Application number: PCT/KR2014/010330
Authority: WO
Inventors: 윤성준
Original assignee: 주식회사 아이티엘
Priority date: 2013-11-01
Filing date: 2014-10-31
Publication date: 2015-05-07
Also published as: KR102180254B1; KR20150050999A

Abstract

The present invention relates to an apparatus and a method for configuring a reference signal in a wireless communication system to support small cells. Disclosed in the present specification is a method for transmitting a reference signal (RS) by using a base station (BS) in a wireless communication system, comprising the steps of: generating channel state information-RS_discovery signal (CSI-RS_DS) configuration information for indicating patterns of CSI-RS configured for k number of small cells; and transmitting the CSI-RS_DS configuration information to user equipment (UE).

Description

Apparatus and Method for Constructing Reference Signal in Wireless Communication System Supporting Small Cell

The present invention relates to wireless communication, and more particularly, to an apparatus and method for configuring a reference signal in a wireless communication system supporting a small cell.

In next-generation communication systems such as LTE-A (Advanced), not only a macro cell (F1) based on a high-power node, but also a small cell (F2) based on a low-power node In order to provide a wireless communication service to the indoor (indoor) and outdoor (outdoor) through the ().

The small cell may be considered both in the frequency band which is the coverage of the macro cell and in the frequency band other than the coverage of the macro cell, and may be provided in both an indoor environment (in a cube) and an outdoor environment (out of a cube). In addition, an ideal or non-ideal backhaul network may be supported between the macro cell and the small cell and / or between the small cells. In addition, the small cell may be provided in both a low density deployment environment and / or a high density deployment environment.

The terminal may discover a small cell capable of providing a service to itself among a plurality of small cells distributed in the macro cell. This operation is called small cell discovery. The small cell transmits a discovery signal to the terminal so that the small cell can be found by the terminal, and the terminal can discover the small cell using the discovery signal. If a large amount of resources are allocated to transmit a discovery signal, the detection accuracy of the discovery signal may be increased, but there is a concern that the overhead is increased and power is wasted in a power-sensitive small cell. On the contrary, if a small resource is allocated to transmit a discovery signal, the overhead is reduced, while the detection accuracy of the discovery signal may be lowered.

In consideration of this aspect, there is a need for allocating an appropriate level of resources for discovery signals, and specifically, a definition of how much resources are allocated and how to allocate them is required.

An object of the present invention is to provide an apparatus and method for configuring a reference signal in a wireless communication system supporting a small cell.

Another object of the present invention is to provide an apparatus and method for configuring a CSI-RS as a discovery signal.

Another technical problem of the present invention is to provide an apparatus and method for transmitting a CSI-RS using four resource elements in a time-frequency resource region corresponding to one subframe and one RB on a time axis. have.

According to an aspect of the present invention, a method for transmitting a reference signal (RS) by a base station (BS) in a wireless communication system is provided. The method includes generating CSI-RS_DS (discovery signal) configuration information indicating patterns of channel state information (CSI) -RS configured for k small cells, and the CSI- And transmitting the RS_DS configuration information to a user equipment (UE).

According to another aspect of the present invention, there is provided a base station (BS) for transmitting a reference signal (RS) in a wireless communication system. The base station generates a radio resource control (RRC) for generating CSI-RS_DS (discovery signal) configuration information indicating patterns of channel state information (CSI) -RS configured for k small cells. A control unit and a transmission unit for transmitting the CSI-RS_DS configuration information to a user equipment (UE).

According to another aspect of the present invention, there is provided a method for receiving a reference signal (RS) by a user equipment (UE) in a wireless communication system. The method includes CSI-RS_DS (discovery signal) configuration information indicating patterns of channel state information (CSI) -RS configured for k small cells from a serving base station. And receiving the CSI-RS from at least one small cell based on the CSI-RS_DS configuration information.

According to another aspect of the present invention, a user equipment (UE) for receiving a reference signal (RS) in a wireless communication system is provided. The terminal receives CSI-RS_DS (discovery signal) configuration information indicating patterns of channel state information (CSI) -RS configured in k small cells from a serving base station. And a receiver configured to receive the CSI-RS from at least one small cell based on the CSI-RS_DS configuration information.

Here, the sequence used to generate the CSI-RS is one orthogonal frequency division in a time-frequency resource region corresponding to one subframe on a time axis and one resource block on a frequency axis. On a multiplexing symbol, one sequence value according to one sequence index may be repeatedly mapped to two resource elements.

Alternatively, a sequence used to generate the CSI-RS is one orthogonal frequency division in a time-frequency resource region corresponding to one resource frame on one subframe and one frequency block on a time axis. On a multiplexing symbol, two sequence values according to two consecutive sequence indices may be mapped to two resource elements, respectively.

When the CSI-RS patterns are used for transmission of a discovery signal of a small cell, discovery signals having orthogonality to each other for a plurality of small cells may be transmitted. In addition, since these discovery signals are orthogonal to each other, interference can be minimized.

1 is a diagram illustrating a communication system in which a high power node and a low power node are disposed.

2 is a block diagram showing a wireless communication system to which the present invention is applied.

3 and 4 schematically show the structure of a radio frame to which the present invention is applied.

5A and 5B illustrate an example of a CSI-RS configuration and a CSI-RS pattern according to the number of CSI-RS antenna ports in a general CP.

6 shows an example of a CSI-RS configuration and a CSI-RS pattern according to the number of CSI-RS antenna ports in an extended CP.

7 is a flowchart illustrating a configuration and transmission method of a CSI-RS according to an example of the present invention.

8 illustrates a CSI-RS pattern according to an example of the present invention. This is according to the CSI-RS configuration according to Table 1 or Table 2.

9 illustrates a CSI-RS pattern according to another example of the present invention. This is according to the CSI-RS configuration according to Table 11 or Table 12.

10 is a block diagram illustrating a terminal and a base station according to an example of the present invention.

Hereinafter, some embodiments will be described in detail with reference to the accompanying drawings. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are used as much as possible even though they are shown in different drawings. In addition, in describing the embodiments of the present specification, when it is determined that a detailed description of a related well-known configuration or function may obscure the gist of the present specification, the detailed description thereof will be omitted.

The present specification describes a communication network, and the work performed in the communication network is performed in the process of controlling the network and transmitting data in a system (for example, a base station) that manages the communication network, or a terminal linked to the network. Work can be done in

Referring to FIG. 2, the wireless communication system 10 is widely deployed to provide various communication services such as voice and packet data. The wireless communication system 10 includes at least one base station (BS) 11. Each base station 11 provides a communication service for a specific geographic area or frequency area and may be called a site. The site may be divided into a plurality of

regions

15a, 15b, and 15c, which may be called sectors, and the sectors may have different cell IDs.

The UE 12 may be fixed or mobile and may have a mobile station (MS), a mobile terminal (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, or a PDA. (personal digital assistant), wireless modem (wireless modem), a handheld device (handheld device) may be called other terms. The base station 11 generally refers to a station communicating with the terminal 12, and includes an evolved-nodeb (eNodeB), a base transceiver system (BTS), an access point, an femto base station, a femto eNodeB, and a household It may be called other terms such as a base station (Home eNodeB: HeNodeB), a relay, a remote radio head (RRH), and the like.

Cells

15a, 15b, and 15c should be interpreted in a comprehensive sense indicating some areas covered by the base station 11, and encompass all of the various coverage areas such as megacells, macrocells, microcells, picocells, and femtocells. to be.

Hereinafter, downlink refers to a communication or communication path from the base station 11 to the terminal 12, and uplink refers to a communication or communication path from the terminal 12 to the base station 11. . In downlink, the transmitter may be part of the base station 11 and the receiver may be part of the terminal 12. In uplink, the transmitter may be part of the terminal 12 and the receiver may be part of the base station 11. There is no limitation on the multiple access scheme applied to the wireless communication system 10. Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-FDMA (SC-FDMA), OFDM-FDMA, OFDM-TDMA For example, various multiple access schemes such as OFDM-CDMA may be used. These modulation techniques demodulate signals received from multiple users of a communication system to increase the capacity of the communication system. The uplink transmission and the downlink transmission may use a time division duplex (TDD) scheme transmitted using different times or a frequency division duplex (FDD) scheme transmitted using different frequencies.

The layers of the radio interface protocol between the terminal and the base station are based on the lower three layers of the Open System Interconnection (OSI) model, which is well known in the communication system. It may be divided into 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) is 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 upper layer control messages, such as allocation information, random access response transmitted on a physical downlink shared channel (PDSCH), and transmission power control for individual terminals in any terminal group : TPC) can carry a set of commands. A plurality of PDCCHs may be transmitted in the control region, and the terminal may monitor the plurality of PDCCHs.

Control information of the physical layer mapped to the PDCCH is referred to as downlink control information (DCI). That is, DCI is transmitted through 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.

3 and 4, a radio frame includes 10 subframes. One subframe includes two slots. The time (length) of transmitting one subframe is called a transmission time interval (TTI). For example, one subframe may have a length of 1 ms, and one slot may have a length of 0.5 ms.

One slot may include a plurality of symbols in the time domain. For example, in a wireless system using orthogonal frequency division multiple access (OFDMA) in downlink (DL), the symbol may be an orthogonal frequency division multiplexing (OFDM) symbol. Meanwhile, the representation of the symbol period in the time domain is not limited by the multiple access scheme or the name. For example, the plurality of symbols in the time domain may be a Single Carrier-Frequency Division Multiple Access (SC-FDMA) symbol, a symbol interval, or the like in addition to the OFDM symbol.

The number of OFDM symbols included in one slot may vary depending on the length of a cyclic prefix (CP). For example, one slot may include seven OFDM symbols in the case of a normal CP, and one slot may include six OFDM symbols in the case of an extended CP.

A resource element (RE) represents the smallest time-frequency unit to which a modulation symbol of a data channel or a modulation symbol of a control channel is mapped. A resource block (RB) is a resource allocation unit and includes time-frequency resources corresponding to 180 kHz on the frequency axis and 1 slot on the time axis. Meanwhile, a resource block pair (PBR) refers to a resource unit including two consecutive slots on the time axis.

In a wireless communication system, 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. The process of restoring a transmission signal by compensating for distortion of a signal caused by a sudden change in channel environment is called channel estimation. In addition, it is also necessary to measure the channel state (channel state) for the cell to which the terminal belongs or other cells. In general, a reference signal (RS) that is known between a terminal and a transmission / reception point is used for channel estimation or channel state measurement.

Since the terminal knows the information of the reference signal, the terminal can accurately obtain data received on the corresponding channel by estimating the channel based on the received reference signal and compensating for the channel value. If p is the reference signal transmitted by the base station, h is channel information experienced by the reference signal during transmission, n is thermal noise generated at the terminal, and y is the signal received at the terminal, it can be expressed as y = h · p + n. . In this case, since the reference signal p is already known by the terminal, when the LS (Least Square) method is used, channel information (

) Can be estimated.

Equation 1

Here, the channel estimate estimated using the reference signal p

Is

Depends on the value, so to get an accurate estimate of

Needs to converge to zero.

The reference signal is generally transmitted by generating a signal from a sequence of reference signals. In the reference signal sequence, one or more of various sequences having excellent correlation characteristics may be used. For example, pseudo-noise (PN) such as Constant Amplitude Zero Auto-Correlation (CAZAC) sequences such as Zadoff-Chu (ZC) sequences, m-sequences, Gold sequences, and Kasami sequences. ) May be used as the sequence of the reference signal, and various other sequences having excellent correlation characteristics may be used depending on the system situation. In addition, the reference signal sequence may be used by cyclic extension or truncation to adjust the length of the sequence, and may be various forms such as binary phase shift keying (BPSK) or quadrature phase shift keying (QPSK). May be modulated and mapped to a resource element.

The downlink reference signal includes a cell-specific RS (CRS), a multimedia broadcast and multicast single frequency network (MBSFN) reference signal, a UE-specific RS (RS), and a position reference signal (PRS). RS and channel state information (CSI) reference signals (CSI-RS).

The UE-specific reference signal is a reference signal received by a specific terminal or a specific terminal group in a cell, and is mainly used for data demodulation of a specific terminal or a specific terminal group and may be called a demodulation reference signal (DMRS).

The CSI-RS is used for channel estimation for the physical downlink shared channel (PDSCH) of the LTE-A terminal. The CSI-RSs are arranged relatively sparse in the frequency domain or the time domain. Channel quality indicator (CQI), precoding matrix indicator (PMI), rank indicator (RI), etc. may be reported from the UE when necessary through estimation of CSI.

The CSI-RS may be transmitted through one, two, four or eight antenna ports. In this case, the antenna ports used may be p = 15, p = 15,16, p = 15, ..., 18 and p = 15, ..., 22, respectively. CSI-RS is defined for the case where the frequency spacing Δf between subcarriers is 15 kHz. The CSI-RS sequence r _{l, ns} (m) may be defined as in Equation 2.

Equation 2

In Equation 2, n _s is a slot number in a radio frame and l is an OFDM symbol number in a slot. Referring to Equation 2, the m-th CSI-RS sequence is generated by normalizing the real part and the imaginary part through a pseudo-random sequence c (i), respectively. c (i) may be defined by a Gold sequence of length-31. c (i) may have a value of 0 or 1 as a binary pseudo-random sequence. Therefore, as shown in Equation 2, 1-2 · c (i) may represent a value of 1 or -1, and the 2m-th sequence corresponding to an even number in the real part and the odd number in the imaginary part (2m Use the +1) th sequence. The output sequence c (n) of length M _PN (n = 0,1, ..., M _PN-1 ) may be defined as in Equation 3.

Equation 3

In Equation 3, N _C = 1600, and the first m-sequence x ₁ (i) is x ₁ (0) = 1, x ₁ (n) = 0, (n = 1,2, ..., 30) Can be initialized to The initialization of the second m-sequence x ₂ (i) may be initialized to different values depending on the system parameter values used in the channel or signal to which the sequence is applied.

It can be expressed as.

The pseudo random sequence c (i) may be initialized by Equation 4 at the start of each OFDM symbol.

Equation 4

In Equation 4, N _CP has a value of 1 in a general CP and 0 in an extended CP. The N _ID ^CSI may have any one of integers from 0 to 503. The N _ID ^CSI may be a virtual cell ID (VCID) for CSI-RS when signaled from a higher layer. The N _ID ^CSI may be equal to a physical cell ID (PCID) if there is no signaling from a higher layer.

In the subframe configured for transmission of the CSI-RS, the CSI-RS sequence r _{l, ns} (m) is a complex-valued modulation symbol a _k used as a reference symbol on the antenna port p according to Equation 5 _{, l} ^(p) can be mapped.

Equation 5

Referring to Equation 5, a _{k, l} ^(p) is a complex modulation symbol mapped to the k th subcarrier and the l th OFDM symbol of the p th antenna port. a _{k, l} ^(p) is mapped by multiplying the CSI-RS sequence r _{l, ns} (m ') and the orthogonal sequence w _l'' .

Each parameter of Equation 5 may be defined by Equation 6.

Equation 6

Referring to Equation 6, the requirements for (k ', l') and n _s can be given by Tables 1 and 2 described below.

The CSI-RS configuration includes a non-zero transmission power CSI-RS configuration indicating a pattern in which a CSI-RS is transmitted to a terminal of each cell (or transmission point (TP)), and a neighboring cell (or It may be classified into a zero transmission power CSI-RS configuration for muting a PDSCH region corresponding to CSI-RS transmission of TP). Zero or one CSI-RS configuration per CSI process may be used for a terminal assuming non-zero power CSI-RS, and zero or several CSI RS configurations may be used for a terminal assuming zero power CSI-RS.

Information about one or more non-zero power CSI-RS configuration (hereinafter, referred to as CSI-RS configuration) may be transmitted to each terminal of the corresponding cell. The information on the CSI-RS configuration includes 2-bit information indicating whether the number of antenna ports (hereinafter, CSI-RS antenna ports) for transmitting non-zero power CSI-RS is any one of 1, 2, 4, and 8; 5 bit information indicating a CSI-RS pattern configurable for each number of CSI-RS antenna ports may be included.

Table 1 shows the mapping of the CSI-RS configuration and (k ', l'), that is, the CSI-RS pattern in Equation 6, in the general CP, and Table 2 shows the CSI-RS configuration and (k) in Equation 6 in the extended CP. ', l'), that is, mapping of the CSI-RS pattern.

Table 1

	CSI-RS configuration	Number of CSI-RSs
		1 or 2		4		8
		(k ', l')	n _s mod 2	(k ', l')	n _s mod 2	(k ', l')	n _s mod 2
Frame structure type 1 and 2	0	(9,5)	0	(9,5)	0	(9,5)	0
	One	(11,2)	One	(11,2)	One	(11,2)	One
	2	(9,2)	One	(9,2)	One	(9,2)	One
	3	(7,2)	One	(7,2)	One	(7,2)	One
	4	(9,5)	One	(9,5)	One	(9,5)	One
	5	(8,5)	0	(8,5)	0
	6	(10,2)	One	(10,2)	One
	7	(8,2)	One	(8,2)	One
	8	(6,2)	One	(6,2)	One
	9	(8,5)	One	(8,5)	One
	10	(3,5)	0
	11	(2,5)	0
	12	(5,2)	One
	13	(4,2)	One
	14	(3,2)	One
	15	(2,2)	One
	16	(1,2)	One
	17	(0,2)	One
	18	(3,5)	One
	19	(2,5)	One
Frame structure type 2 only	20	(11,1)	One	(11,1)	One	(11,1)	One
	21	(9,1)	One	(9,1)	One	(9,1)	One
	22	(7,1)	One	(7,1)	One	(7,1)	One
	23	(10,1)	One	(10,1)	One
	24	(8,1)	One	(8,1)	One
	25	(6,1)	One	(6,1)	One
	26	(5,1)	One
	27	(4,1)	One
	28	(3,1)	One
	29	(2,1)	One
	30	(1,1)	One
	31	(0,1)	One

TABLE 2

	CSI-RS configuration	Number of CSI-RSs
	CSI-RS configuration	1 or 2		4		8
		(k ', l')	n _s mod 2	(k ', l')	n _s mod 2	(k ', l')	n _s mod 2
Frame structure type 1 and 2	0	(11,4)	0	(11,4)	0	(11,4)	0
	One	(9,4)	0	(9,4)	0	(9,4)	0
	2	(10,4)	One	(10,4)	One	(10,4)	One
	3	(9,4)	One	(9,4)	One	(9,4)	One
	4	(5,4)	0	(5,4)	0
	5	(3,4)	0	(3,4)	0
	6	(4,4)	One	(4,4)	One
	7	(3,4)	One	(3,4)	One
	8	(8,4)	0
	9	(6,4)	0
	10	(2,4)	0
	11	(0,4)	0
	12	(7,4)	One
	13	(6,4)	One
	14	(1,4)	One
	15	(0,4)	One
Frame structure type 2 only	16	(11,1)	One	(11,1)	One	(11,1)	One
	17	(10,1)	One	(10,1)	One	(10,1)	One
	18	(9,1)	One	(9,1)	One	(9,1)	One
	19	(5,1)	One	(5,1)	One
	20	(4,1)	One	(4,1)	One
	21	(3,1)	One	(3,1)	One
	22	(8,1)	One
	23	(7,1)	One
	24	(6,1)	One
	25	(2,1)	One
	26	(1,1)	One
	27	(0,1)	One

In Table 1 and Table 2, frame structure type 1 means FDD and frame structure type 2 means TDD.

Referring to Table 1, in case of a general CP, 32 CSI-RS configurations are used when the number of antenna ports is 1 or 2, 16 CSI-RS configurations are used when the number of antenna ports is 4, and the number of antenna ports is There are eight CSI-RS configurations when there are eight. Referring to Table 2, in case of the extended CP, 28 CSI-RS configurations in total with one or two antenna ports, 14 CSI-RS configurations in total with four antenna ports, and the number of antenna ports In eight, there are a total of seven CSI-RS configurations.

Referring to Tables 1 and 2, the location of one specific resource element to which the CSI-RS is mapped may be indicated for each CSI-RS antenna port with respect to the CSI-RS configuration. That is, the location of the remaining resource elements to which the CSI-RS is mapped may be determined by Equation 6 based on the location of the one specific resource element, and thus the total CSI-RS configurable for each number of CSI-RS antenna ports. The pattern can be seen.

For example, if the number of CSI-RS antenna ports is 8 and the value of the CSI-RS configuration is 2 (= 00010), corresponding to (k ', l') = (9,2) according to Table 1 And n _s mod 2 = 1. Accordingly, it can be seen that within the subframe configured for CSI-RS transmission, the CSI-RS is mapped to a resource element having a subcarrier index of 9 and an OFDM symbol index of 2 in the second slot. The resource element indicated by Table 1 may be one of locations of resource elements to which CSI-RSs transmitted through the first CSI-RS antenna port are mapped. The positions of the remaining resource elements to which the CSI-RSs transmitted through the first CSI-RS antenna port are mapped and the positions of the resource elements to which the CSI-RSs are transmitted through the remaining CSI-RS antenna port are mapped according to Equation (6). It may be located at a predetermined distance from the resource element indicated by 1.

FIG. 5A is a case where it can be applied in frame structure type 1 (FDD) and frame structure type 2 (TDD), and FIG. 5B shows a CSI-RS pattern when it is applicable only in frame structure type 2 (TDD). In FIG. 5A and FIG. 5B, numerals denoted for each resource element indicate a CSI-RS configuration number.

a is CSI-RS antenna port {15, 16}, b is CSI-RS antenna port {17, 18}, c is CSI-RS antenna port {19, 20}, d is CSI-RS antenna port {19, 20 } This shows transmitting the CSI-RS. A denotes DMRS antenna ports {7, 8, 11, 13}, and B denotes transmission of DMRS on DMRS antenna ports {9, 10, 12, 14}. C represents a resource element to which the CRS is mapped. In addition, in FIG. 5, it is assumed that the number of CRS antenna ports is two, and the control region (shading part) is allocated to the first three OFDM symbols of the subframe.

The CSI-RS pattern of FIGS. 5A and 5B may be applied even when the number of CRS antenna ports is one or four or when no CRS is transmitted. In addition, the CSI-RS pattern of FIGS. 5A and 5B may be applied even when a control region is allocated to an OFDM symbol in the first 1 to 4 subframes, or when the control region is not allocated. 5A and 5B, DMRS is divided into two code division multiplexing (CDM) groups (A: DMRS antenna ports {7, 8, 11, 13}, and B: DMRS antenna ports {9, 10, 12, 14}). Although assumed to use, the CSI-RS pattern of Figures 5a and 5b can be applied to the case of using one CDM group.

Like FIG. 5A and FIG. 5B, the numerals indicated in each resource element in FIG. 6 indicate CSI-RS configuration numbers. a is CSI-RS antenna port {15, 16}, b is CSI-RS antenna port {17, 18}, c is CSI-RS antenna port {19, 20}, d is CSI-RS antenna port {19, 20 } This shows transmitting the CSI-RS. E indicates transmitting DMRS on DMRS antenna port {7, 8}. C represents a resource element to which the CRS is mapped. In addition, in FIG. 6, it is assumed that the number of CRS antenna ports is two, and the control region (shading part) is allocated to the first three OFDM symbols of the subframe.

The CSI-RS pattern of FIG. 6 may be applied even when the number of CRS antenna ports is one or four or when no CRS is transmitted. In addition, the CSI-RS pattern of FIG. 6 may be applied even when a control region is allocated to an OFDM symbol in the first 1 to 4 of the subframe, or when the control region is not allocated.

Table 3 shows an example of a subframe configuration in which the CSI-RS is transmitted.

TABLE 3

CSI-RS-Subframe Configuration I _CSI-RS	CSI-RS CycleT _CSI-RS (subframe)	CSI-RS subframe offset Δ _CSI-RS (subframes)
0-4	5	I _CSI-RS
5-14	10	I _CSI-RS -1
15-34	20	I _CSI-RS -15
35-74	40	I _CSI-RS -35
75-154	80	I _CSI-RS -75

Referring to Table 3, the period (CSI-RS period, T _CSI-RS ) and offset (Δ _CSI-RS ) of the subframe in which the CSI-RS is transmitted according to the CSI-RS subframe configuration (I _CSI-RS ) Can be determined. The CSI-RS subframe configuration may be configured separately for the non-zero power CSI-RS and zero-power CSI-RS. On the other hand, the subframe for transmitting the CSI-RS needs to satisfy the equation (7).

Equation 7

The zero power CSI-RS configuration may include a 16-bit bitmap corresponding to the CSI-RS pattern when each bit has four CSI-RS antenna ports. That is, for a bit set to 1 in a 16-bit bitmap configured by a higher layer, the UE selects a resource element corresponding to the case where the number of CSI-RS antenna ports is 4 in Tables 1 and 2, and zero-power CSI-. Can be set to RS. More specifically, the most significant bit (MSB) of the 16-bit bitmap corresponds to the first CSI-RS configuration index when the number of CSI-RS antenna ports is 4 in Tables 1 and 2. Subsequent bits of the 16-bit bitmap correspond to the direction in which the CSI-RS configuration index increases when the number of CSI-RS antenna ports is 4 in Tables 1 and 2. The resource element set to the zero power CSI-RS may mute the PDSCH corresponding to the CSI-RS transmission of the neighbor cell or the TP, and transmit the PDSCH to the resource element not set to the zero power CSI-RS.

The parameters transmitted in the RRC layer for zero power CSI-RS are as follows.

1) Zero power CSI-RS configuration list: 16-bit bitmap composed of one CSI-RS configuration as one bit when the number of CSI-RS antenna ports is 4 in Table 1 or Table 2.

2) Zero Power CSI-RS Subframe Configuration (I _CSI-RS ): Like the subframeConfig parameter transmitted for the non-zero power CSI-RS described below, it indicates a subframe configuration for the zero power CSI-RS. The zero-power CSI-RS subframe configuration has a length of 8 bits, and the period (T _CSI-RS ) and offset (T _CSI-RS ) of the subframe in which the zero-power CSI-RS is used for transmission according to the zero-power CSI-RS subframe configuration Δ _CSI-RS ) can be determined.

The terminal may discover a small cell capable of providing a service to itself among a plurality of small cells distributed in the macro cell. This operation is called small cell discovery. The small cell transmits a discovery signal to the terminal so that the small cell can be found by the terminal, and the terminal can discover the small cell using the discovery signal. If a large amount of resources are allocated to transmit a discovery signal, the detection accuracy of the discovery signal may be increased, but there is a concern that the overhead is increased and power is wasted in a power-sensitive small cell. On the contrary, if a small resource is allocated to transmit a discovery signal, the overhead is reduced, while the detection accuracy of the discovery signal may be lowered. In consideration of this aspect, it is necessary to allocate an appropriate level of resources for the discovery signal, and in particular, a definition of how much resources are allocated is required, and information on this may be transmitted from the base station to the terminal.

In this embodiment, the discovery signal may include a CSI-RS. Of course, as the discovery signal, one or more of physical signals such as CRS, PSS / SSS, modified CRS, modified PSS / SSS, CSI-RS, or PRS may be included, but in the present embodiment, CSI-RS is included. Explain in the case of. In addition, the following describes the technical features of the present invention as a discovery signal using the CSI-RS, but the technical features based on the CSI-RS may be equally applicable to the case where all other physical signals are used as the discovery signal.

According to Table 1 and Table 2, when configuring the CSI-RS through one or two antenna ports, a total of two resource elements in a time-frequency resource region consisting of one subframe on the time axis and one RB on the frequency axis Is used for transmission of the CSI-RS. Up to 20 CSI-RS patterns with orthogonality on a time-frequency resource consisting of one subframe on the time axis with normal CP and one RB on the frequency axis (but maximum when extended CP is used) 16 (when FDD) or 28 (when TDD) CSI-RS patterns) may be defined. When the CSI-RS patterns are used for transmission of a discovery signal of a small cell, discovery signals having orthogonality to each other may be transmitted in up to 20 small cells. Since these discovery signals are orthogonal to each other, interference can be minimized.

Meanwhile, in the present embodiment, in configuring the CSI-RS through one or two antenna ports as a discovery signal, a total of four within a time-frequency resource region including one subframe on the time axis and one RB on the frequency axis Resource elements (not two) are used to transmit CSI-RS. According to this, on time-frequency resources in one subframe in which normal CPs are used, up to 10 CSI-RS patterns having orthogonality (except in case of extended CPs, up to 8 (in case of FDD) or 14) CSI-RS pattern) in the case of TDD) may be defined. When these CSI-RS patterns are used for transmission of a discovery signal of a small cell, discovery signals having orthogonality to each other may be transmitted in up to 10 small cells.

According to the dense small cell scenario currently considered, one small cell cluster may be composed of up to 10 small cells. When a maximum of 10 CSI-RS patterns using 4 resource elements are applied to a dense small cell scenario, the orthogonality is minimized and interference is minimized for all 10 small cells included in one small cell cluster. Discovery signals may be sent. As such, when the CSI-RS is mapped and transmitted to an appropriate number of resource elements, and the CSI-RS is used as the discovery signal, the overhead burden may be reduced and the detection accuracy of the discovery signal may be improved.

Hereinafter, a method of configuring a CSI-RS for signaling four resource elements, that is, a CSI-RS, and a method of signaling the same will be described.

Referring to FIG. 7, the base station generates CSI-RS_DS configuration information (S700). The base station provides a serving cell to the terminal. The CSI-RS_DS configuration information includes a configuration related to transmission of a discovery signal (DS). The CSI-RS_DS configuration information may be referred to simply as CSI-RS configuration information. The CSI-RS_DS configuration information may be selectively generated and transmitted by the base station. As an example, when CSI-RS_DS configuration information is not generated and transmitted, only CRS may be used as a discovery signal. As another example, when CSI-RS_DS configuration information is generated and transmitted, both CRS and CSI-RS_DS may be used as a discovery signal. The CSI-RS_DS configuration information may have various embodiments.

As a first embodiment, the CSI-RS_DS configuration information may include at least one of a resource configuration list field and a subframe configuration field. In some cases, the CSI-RS_DS configuration information may further include a CSI-RS_DS configuration ID field. Table 4 below is an example in which the CSI-RS_DS configuration information includes all of a CSI-RS_DS configuration ID field, a resource configuration list field, and a subframe configuration field.

Table 4

-ASN1START

...

CSI-RS_DS-config CSI-RS_DS-Config ----- {Optional}

...

CSI-RS_DS-Config :: = SEQUENCE {

csi-RS_DS-ConfigId CSI-RS_DS-ConfigId,

resourceConfigList BIT STRING (SIZE (Z)),

subframeConfig INTEGER (0..154),

...

}

-ASN1STOP

Referring to Table 4, the CSI-RS_DS configuration ID field is used to identify a resource configuration for transmitting the CSI-RS when CoMP (Coordinated Multiple Point) is supported. The first embodiment may include an embodiment in which the CSI-RS_DS configuration ID field is excluded from Table 4 above.

The resource configuration list field is a bitmap of length Z and provides information on CSI-RS patterns configured in k small cells. A specific CSI-RS pattern may be mapped to each of the Z bits of the resource configuration list field. Here, the specific CSI-RS pattern may be a CSI-RS pattern when four antenna ports are used. For example, in Table 1, four antenna port-based CSI-RS patterns may be 16 kinds, such as CSI-RS patterns 0 to 9 and 20 to 25, based on subframes of a normal CP. In this case, when the length Z = 16 of the resource configuration list field (that is, the resource configuration list field is 16 bits), the 16 CSI-RS patterns may be mapped 1: 1 to the 16 bits.

The information provided by the resource configuration list field is as follows. If any bit in the resource configuration list field is 0, it is indicated that the CSI-RS pattern corresponding to the arbitrary bit is not configured in any small cell. On the contrary, if an arbitrary bit in the resource configuration list field is 1, it is indicated that a CSI-RS pattern corresponding to the arbitrary bit is configured in at least one small cell.

According to the first embodiment, the CSI-RS_DS configuration information may further include at least one of an ID list field of small cells transmitting the CSI-RS and a number field of antenna ports. Table 5 shows CSI-RS_DS configuration information further including a small cell ID list field.

Table 5

-ASN1START

CSI-RS_DS-Config :: = SEQUENCE {

csi-RS_DS-ConfigId CSI-RS_DS-ConfigId,

resourceConfigList BIT STRING (SIZE (Z)),

subframeConfig INTEGER (0..154),

smallcellIDlist Small_CELL_ID_list,

...

}

Small_CELL_ID_list :: = SEQUENCE (SIZE (1 ... maxSmallCell)) {

smallcellID PhysCellId

}

-ASN1STOP

Referring to Table 5, the small cell ID list field may include up to maxSmallCell as small cell IDs. Here, maxSmallCell may be 10. The small cell ID included in the small cell ID list field may be a physical cell ID (PhysCellID) identifying a physical ID of each small cell. Here, the small cell ID may be 9 bits.

In Table 5, the small cell ID list field includes only the IDs of the small cells, but as shown in Table 6, the small cell ID list field may further include the antenna port number and / or the Pc field in addition to the small cell ID. have.

Table 6

-ASN1START

CSI-RS_DS-Config :: = SEQUENCE {

csi-RS_DS-ConfigId CSI-RS_DS-ConfigId,

resourceConfigList BIT STRING (SIZE (Z)),

subframeConfig INTEGER (0..154),

smallcellIDlist Small_CELL_ID_list,

...

}

Small_CELL_ID_list :: = SEQUENCE (SIZE (1 ... maxSmallCell)) {

smallcellID PhysCellId,

antennaPortsCount ENUMERATED {an1, an2},

Pc INTEGER (-8..15)

}

-ASN1STOP

Referring to Table 6, the small cell ID list field may include an antenna port count field and a P-c field of antenna ports having an1 or an2. Here, an1 represents the number of antenna ports = 1, and an2 represents the number of antenna ports = 2 (1 bit is used). Of course, when the number of antenna ports for transmitting the CSI-RS as the discovery signal is fixed to one, the number field of the antenna ports may be omitted in Table 6. For example, the P-c field may indicate the strength of the CSI-RS transmission power in a range of -8 to 15 dB. If all the small cells transmit the CSI-RS with the same power strength, the P-c field may be omitted in Table 6.

Meanwhile, as another example, the small cell ID list field may include only the ID of the small cell configured with the CSI-RS pattern corresponding to the bit indicated by 1 in the resource configuration list field. According to this, the small cell ID list field does not include the small cell IDs of maxSmallCell as shown in Table 5 or Table 6, but the small cell ID list field is composed of the CSI-RS pattern corresponding to the bit indicated by 1 in the resource configuration list field. It includes as many small cell IDs. In this case, the small cell IDs may be listed in order according to the bit indicated by 1 in the resource configuration list field.

As a second embodiment, the CSI-RS_DS configuration information may include at least one of k small cell resource configuration list (resourceConfigList_small) fields and a subframe configuration field. In some cases, the CSI-RS_DS configuration information may further include a CSI-RS_DS configuration ID field. Table 7 below is an example in which the CSI-RS_DS configuration information includes all of the CSI-RS_DS configuration ID field, k small cell resource configuration list fields, and a subframe configuration field.

TABLE 7

-ASN1START

CSI-RS_DS-Config :: = SEQUENCE {

csi-RS_DS-ConfigId CSI-RS_DS-ConfigId,

resourceConfigList_small ResourceConfigList_Small

subframeConfig INTEGER (0..154),

...

}

ResourceConfigList_Small :: = SEQUENCE (SIZE (1 ... k)) {

smallcellID PhysCellId,

resourceConfigList BIT STRING (SIZE (Z)),

}

-ASN1STOP

Referring to Table 7, the second embodiment may include an embodiment in which the CSI-RS_DS configuration ID field is excluded from Table 7. The small cell resource configuration list field includes an ID field of the small cell and a resource configuration list field indicating a CSI-RS pattern configured in the small cell. The resource configuration list field is a length Z bitmap. The combination of the ID field / resource list field of the small cell may be defined individually for a total of k small cells.

The second embodiment may further include that the number of antenna ports field and / or the P-c field are included in the small cell resource configuration list field. In this case, the small cell resource configuration list field may be expressed as shown in the following table.

Table 8

-ASN1START

CSI-RS_DS-Config :: = SEQUENCE {

csi-RS_DS-ConfigId CSI-RS_DS-ConfigId,

resourceConfigList_small ResourceConfigList_Small

subframeConfig INTEGER (0..154),

...

}

ResourceConfigList_Small :: = SEQUENCE (SIZE (1 ... k)) {

smallcellID PhysCellId,

resourceConfigList BIT STRING (SIZE (Z)),

antennaPortsCount ENUMERATED {an1, an2},

Pc INTEGER (-8..15)

}

-ASN1STOP

As a third embodiment, the CSI-RS_DS configuration information may include at least one of a resourceConfig field and a subframeConfig field. In some cases, the CSI-RS_DS configuration information may further include a CSI-RS_DS configuration ID field. Table 9 below is an example in which the CSI-RS_DS configuration information includes all of the CSI-RS_DS configuration ID field, resource configuration field, and subframe configuration field.

Table 9

-ASN1START

CSI-RS_DS-Config :: = SEQUENCE {

csi-RS_DS-ConfigId CSI-RS_DS-ConfigId,

resourceConfig INTEGER (0 ... 31),

subframeConfig INTEGER (0..154),

...

}

-ASN1STOP

Referring to Table 9, the CSI-RS_DS Configuration ID field is used to identify a resource configuration for transmitting the CSI-RS as a discovery signal. The third embodiment may further include an embodiment in which the CSI-RS_DS configuration ID field is excluded from Table 9 above.

The resource configuration field indicates 32 CSI-RS patterns provided in Table 1 or Table 2 as indices 0 to 31. Here, the CSI-RS pattern indicated by the resource configuration field means a CSI-RS pattern configured in the small cell transmitting the discovery signal. For example, 4 or 5 bits may be allocated to the resource configuration field. Meanwhile, the CSI-RS_DS configuration information may further include a P-c indicating the power of the CSI-RS transmitted in the CSI-RS pattern indicated by the resource configuration field.

As a fourth embodiment, CSI-RS_DS configuration information may be included in non-zero power CSI-RS configuration information. The non-zero power CSI-RS configuration information includes an antenna port count (antennaPortsCount) and a resource configuration (resourceConfig) field. In addition, for example, the non-zero power CSI-RS configuration information may be defined as shown in Table 10 below.

Table 10

-ASN1START

CSI-RS-ConfigNZP :: = SEQUENCE {

csi-RS-ConfigNZPId CSI-RS-ConfigNZPId,

antennaPortsCount ENUMERATED {an1, an2, an4, an8},

resourceConfig INTEGER (0..31),

subframeConfig INTEGER (0..154),

scramblingIdentity INTEGER (0..503),

qcl-CRS-Info SEQUENCE {

qcl-ScramblingIdentity INTEGER (0..503),

crs-PortsCount ENUMERATED {n1, n2, n4, spare1},

mbsfn-SubframeConfigList CHOICE {

release NULL,

setup SEQUENCE {

subframeConfigList MBSFN-SubframeConfigList

}

} OPTIONAL-Need ON

} OPTIONAL,-Need OR

...

}

-ASN1STOP

Referring to Table 10, the resource configuration field indicates indexes 0 to 31, and each index corresponds to the CSI-RS pattern of Table 1. In this case, when the number of antenna ports indicates an4 (that is, four), indexes 10 to 19 and 26 to 31 according to Table 1 are code points that remain unused. The present embodiment includes using the remaining code points to indicate the CSI-RS pattern configured in the small cell. Here, one antenna port may be used for the CSI-RS transmitted in the small cell, and two antenna ports may be used. The number of antenna ports for the CSI-RS of the small cell may be previously regulated between the terminal and the base station.

Each parameter name described in Examples 1 to 4 and Tables 5 to 9 is a parameter name arbitrarily described for convenience of description in the present invention, and the parameter name does not change the meaning or indication of each parameter. Each parameter name may be described otherwise.

7 again, the base station transmits CSI-RS_DS configuration information to the terminal (S705). The CSI-RS_DS configuration information may be transmitted to the terminal in the form of an RRC message. In particular, the CSI-RS_DS configuration information may be selectively included in an RRC connection reconfiguration message. The UE may receive the CSI-RS_DS configuration information and perform reconfiguration of the RRC connection as indicated by the CSI-RS_DS configuration information. And, based on the CSI-RS_DS configuration information, the UE can know the CSI-RS pattern configured in the small cell.

The small cell generates a discovery signal, that is, a CSI-RS (S710). In detail, the method for generating the CSI-RS by the small cell may include the following examples.

(1) An example of a method of generating a CSI-RS includes: i) generating a sequence for the CSI-RS according to Equations 2 to 4, ii) from the CSI-RS sequence according to Equation 5 Obtaining a complex modulation symbol a _{k, l} ^(p) , and iii) mapping the complex modulation symbol to a resource element designated according to Equation 8 below. In step i), the same sequence generated in Equations 2 to 4 is mapped twice to two resource elements in one physical RB on one OFDM symbol. That is, one sequence value according to one sequence index (corresponding to m in Equation 2) is repeatedly mapped twice. In step iii), Equation 8 for obtaining the resource element to which the CSI-RS is mapped is as follows.

Equation 8

Referring to Equation 8, an antenna port p = {115, 116} for CSI-RS is defined. That is, up to two antenna ports for the CSI-RS of the small cell may be supported. The subcarrier k to which the CSI-RS is mapped is k '+ 12m + {-0 or -6} in the case of a general CP, and two subcarriers k exist in one PRB. This means that there are two resource elements to which CSI-RSs are mapped on one OFDM symbol in a time-frequency resource region corresponding to one subframe on the time axis and one RB on the frequency axis. In addition, since the value of "l" is 2, the CSI-RS is transmitted on two OFDM symbols. That is, the CSI-RS may be transmitted using a total of four resource elements (2 OFDM symbols * 2 subcarriers).

In this example, the CSI-RS_DS configuration information according to the above-described four embodiments may be applied as the CSI-RS_DS configuration information. Meanwhile, in this example, the antenna port number of the CSI-RS for discovery signal is distinguished from the antenna port for the existing CSI-RS, and for convenience, the antenna port number of the first antenna is 115 and the antenna port number of the second antenna is 116. However, it is not limited thereto. In addition, although Equation 8 has been described as using one or two antenna ports in the CSI-RS for discovery signals, technical details related to the second antenna port (p = 116) in Equation 9 when only one antenna port is used. May be omitted.

(2) Another example of the method of generating the CSI-RS includes: i) generating a sequence for the CSI-RS according to Equation 9, Equation 3, and Equation 4 below, ii) Equation 5 Obtaining a complex modulation symbol a _{k, l} ^(p) from the CSI-RS sequence, and iii) mapping the complex modulation symbol to a resource element designated according to Equation 10 below. In step i), sequences generated in

Equations

9, 3 and 4 are mapped to two resource elements in one physical RB on one OFDM symbol. In this case, two sequence values according to two consecutive sequence indices (for example, m = a and m = a + 1 in Equation 2) are mapped to the two resource elements.

Equation 9

Referring to Equation 9, unlike Equation 2, the maximum value of m is 2N _RB ^maxDL-1 . Accordingly, sequences having a length doubled as compared with Equation 2 may be generated. In this case, one sequence represented by Equation 9 is mapped to each of two resource elements in one PRB on one OFDM symbol. Originally, a sequence for the CSI-RS is generated according to Equations 2 to 4, but a sequence for the CSI-RS to be used for the discovery signal is generated according to

Equations

9, 3, and 4.

Meanwhile, in step iii), Equation 10 for obtaining the resource element to which the CSI-RS is mapped is as follows.

Equation 10

Referring to Equation 10, an antenna port p = {115, 116} for CSI-RS is defined. That is, up to two antenna ports for the CSI-RS of the small cell may be supported. In the case of a general CP, two subcarriers to be mapped to the CSI-RS exist in one PRB as k = k '+ 6m + {-6} (because of the variable' 6m ', two subcarriers may be allocated in one PRB. Can be). This means that there are two resource elements to which CSI-RSs are mapped on one OFDM symbol in a time-frequency resource region corresponding to one subframe on the time axis and one RB on the frequency axis. In addition, since the value of "l" is 2, the CSI-RS is transmitted on two OFDM symbols. That is, the CSI-RS may be transmitted using a total of four resource elements (2 OFDM symbols * 2 subcarriers).

In this example, the antenna port number of the CSI-RS for the discovery signal is distinguished from the antenna port for the existing CSI-RS for convenience, and the antenna port number of the first antenna is 115 and the antenna port number of the second antenna is 116. It is not limited. In addition, although Equation 8 has been described as using one or two antenna ports (that is, two or less) in the CSI-RS for discovery signals, the second antenna port (p) in Equation 9 is used when only one antenna port is used. 116) may be omitted.

7 again, the small cell transmits the CSI-RS to the terminal using four resource elements according to the CSI-RS pattern (S715). The small cell uses one or two (ie two or less) antenna ports for CSI-RS transmission, and within a time-frequency resource region consisting of one subframe on the time axis and one RB on the frequency axis. Four resource elements are used. 8 or 9 illustrates a tendency of mapping CSI-RS to four resource elements (ie, CSI-RS pattern).

Referring to FIG. 8, when FIG. 8- (a) is applied to frame structure type 1 (FDD) and frame structure type 2 (TDD) in a general CP, FIG. 8- (b) shows only a frame structure type in a general CP. CSI-RS pattern when applied to 2 (TDD). 8- (c) shows a CSI-RS pattern in case of an extended CP. In FIG. 8, numbers indicated on each resource element indicate a CSI-RS configuration number. a indicates transmitting the CSI-RS on the CSI-RS antenna ports {115, 116}. A is the DMRS antenna port {7, 8, 11, 13} in the generic CP, B is the DMRS antenna port {9, 10, 12, 14} in the generic CP, E is the DMRS antenna port {7, 8} in the extended CP DMRS is transmitted. C represents a resource element to which the CRS is mapped. In addition, in FIG. 8, it is assumed that a control region (shaded portion) is allocated to the first three OFDM symbols of a subframe.

The CSI-RS pattern of FIG. 8 may be applied even when the number of CRS antenna ports is one or two, or when the CRS is not transmitted. In addition, the CSI-RS pattern of FIG. 8 may be applied even when a control region is allocated to an OFDM symbol in the first 1 to 4 of the subframe, or when the control region is not allocated. In addition, in FIG. 8, DMRS uses two code division multiplexing (CDM) groups (A: DMRS antenna ports {7, 8, 11, 13}, and B: DMRS antenna ports {9, 10, 12, 14}). It is assumed, but the CSI-RS pattern of FIG. 8 may be applied even when using one CDM group.

For example, if CP type = general CP, the number of CSI-RS antenna ports = 1 (that is, p = 115), and the CSI-RS configuration = 2 (= 00010), corresponding to Table 1 ( k ', l') = (9,2) and n _s mod 2 = 1. Substituting this in Equation 8, within the subframe configured for CSI-RS transmission, the CSI-RS is a resource element {k, l} = {{9,2}, {9,3}, {3,2} , {3,3}}.

Referring to FIG. 9, when FIG. 9- (a) is applied to frame structure type 1 (FDD) and frame structure type 2 (TDD) in a general CP, FIG. 9- (b) shows only a frame structure type in a general CP. The CSI-RS pattern in the case of 2 (TDD) is shown. 9- (c) shows a CSI-RS pattern in case of an extended CP. In FIG. 9, numbers indicated on each resource element indicate a CSI-RS configuration number. a indicates transmitting the CSI-RS on the CSI-RS antenna ports {115, 116}. A is the DMRS antenna port {7, 8, 11, 13} in the generic CP, B is the DMRS antenna port {9, 10, 12, 14} in the generic CP, E is the DMRS antenna port {7, 8} in the extended CP DMRS is transmitted. C represents a resource element to which the CRS is mapped. In addition, in FIG. 9, it is assumed that a control region (shading part) is allocated to the first three OFDM symbols of a subframe.

Looking at the CSI-RS configuration index, unlike in Figure 8, in the case of the general CP CSI-RS configuration index 0/1/2/3/4/5/6/7/8/9/20/21/22/23/24 / 25 is converted to 10/11/12/13/14/15/16/17 / 18/19/26/27/28/29/30/31 respectively. In other words, CSI-RS configuration indices 0-9 and 20-25 represent existing CSI-RS patterns on four antenna ports, while CSI-RS configuration indices 10-19 and 26-31 are not used on existing four antenna ports. The unused CSI-RS pattern is used as the CSI-RS pattern for the discovery signal. This allows you to take advantage of unused code points on four antenna ports.

When considering the CSI-RS pattern configured in the small cell using the normal CP, Table 1 may be modified as shown in Table 11 below.

Table 11

	CSI-RS configuration	Number of CSI-RSs
		1 or 2		4		8
		(k ', l')	n _s mod 2	(k ', l')	n _s mod 2	(k ', l')	n _s mod 2
Frame structure type 1 and 2	0	(9,5)	0	(9,5)	0	(9,5)	0
	One	(11,2)	One	(11,2)	One	(11,2)	One
	2	(9,2)	One	(9,2)	One	(9,2)	One
	3	(7,2)	One	(7,2)	One	(7,2)	One
	4	(9,5)	One	(9,5)	One	(9,5)	One
	5	(8,5)	0	(8,5)	0
	6	(10,2)	One	(10,2)	One
	7	(8,2)	One	(8,2)	One
	8	(6,2)	One	(6,2)	One
	9	(8,5)	One	(8,5)	One
	10	(3,5)	0	(9,5)	0
	11	(2,5)	0	(11,2)	One
	12	(5,2)	One	(9,2)	One
	13	(4,2)	One	(7,2)	One
	14	(3,2)	One	(9,5)	One
	15	(2,2)	One	(8,5)	0
	16	(1,2)	One	(10,2)	One
	17	(0,2)	One	(8,2)	One
	18	(3,5)	One	(6,2)	One
	19	(2,5)	One	(8,5)	One
Frame structure type 2 only	20	(11,1)	One	(11,1)	One	(11,1)	One
	21	(9,1)	One	(9,1)	One	(9,1)	One
	22	(7,1)	One	(7,1)	One	(7,1)	One
	23	(10,1)	One	(10,1)	One
	24	(8,1)	One	(8,1)	One
	25	(6,1)	One	(6,1)	One
	26	(5,1)	One	(11,1)	One
	27	(4,1)	One	(9,1)	One
	28	(3,1)	One	(10,1)	One
	29	(2,1)	One	(8,1)	One
	30	(1,1)	One	(6,1)	One
	31	(0,1)	One	(11,1)	One

Meanwhile, for the extended CP, CSI-RS configuration indexes 0/1/2/3/4/5/6/7/16/17/18/19/20/21 are 8/9/10/11/12 / 13/14/15/22/23/24/25 / 26/27 When considering the CSI-RS pattern configured in the small cell using the extended CP, Table 2 may be modified as shown in Table 12 below.

Table 12

	CSI-RS configuration	Number of CSI-RSs
	CSI-RS configuration	1 or 2		4		8
		(k ', l')	n _s mod 2	(k ', l')	n _s mod 2	(k ', l')	n _s mod 2
Frame structure type 1 and 2	0	(11,4)	0	(11,4)	0	(11,4)	0
	One	(9,4)	0	(9,4)	0	(9,4)	0
	2	(10,4)	One	(10,4)	One	(10,4)	One
	3	(9,4)	One	(9,4)	One	(9,4)	One
	4	(5,4)	0	(5,4)	0
	5	(3,4)	0	(3,4)	0
	6	(4,4)	One	(4,4)	One
	7	(3,4)	One	(3,4)	One
	8	(8,4)	0	(11,4)	0
	9	(6,4)	0	(9,4)	0
	10	(2,4)	0	(10,4)	One
	11	(0,4)	0	(9,4)	One
	12	(7,4)	One	(5,4)	0
	13	(6,4)	One	(3,4)	0
	14	(1,4)	One	(4,4)	One
	15	(0,4)	One	(3,4)	One
Frame structure type 2 only	16	(11,1)	One	(11,1)	One	(11,1)	One
	17	(10,1)	One	(10,1)	One	(10,1)	One
	18	(9,1)	One	(9,1)	One	(9,1)	One
	19	(5,1)	One	(5,1)	One
	20	(4,1)	One	(4,1)	One
	21	(3,1)	One	(3,1)	One
	22	(8,1)	One	(11,1)	One
	23	(7,1)	One	(10,1)	One
	24	(6,1)	One	(9,1)	One
	25	(2,1)	One	(5,1)	One
	26	(1,1)	One	(4,1)	One
	27	(0,1)	One	(3,1)	One

Referring back to FIG. 7, the terminal may receive the CSI-RS transmitted from the small cell based on the CSI-RS pattern configured in the small cell. Meanwhile, the terminal may discover the small cell using the CSI-RS of the small cell (S715).

The present invention relates to any one of the CSI-RS_DS configuration information of the first embodiment described in step S700 to the CSI-RS_DS configuration information of the fourth embodiment, any one of the CSI-RS generation methods described in step S710, and Includes all embodiments derived from any combination of the CSI-RS patterns described in S715.

Referring to FIG. 10, the serving base station 1050 includes a transmitter 1055, a receiver 1060, and a base station processor 1070. The base station processor 1070 includes a reference signal generator 1071 and an RRC controller 1072.

The RRC control unit 1072 generates CSI-RS_DS configuration information about the small cell as described in step S700. The CSI-RS_DS configuration information indicates patterns of channel state information (CSI) -RS configured for k small cells. In addition, the RRC control unit 1072 may selectively generate the CSI-RS configuration information for the serving base station 1050. The generated CSI-RS_DS configuration information may include all the embodiments described throughout this specification. For example, the CSI-RS_DS configuration information includes a resource configuration list field, the resource configuration list field is a 16-bit bitmap, and the bitmap includes the CSI-RS patterns in at least one of the k small cells. It can indicate whether or not. Meanwhile, the resource configuration list field may further include physical cell IDs of the k small cells.

The reference signal generator 1071 generates a CSI-RS and sends it to the transmitter 1055.

The transmitter 1055 transmits the CSI-RS configuration information and / or the CSI-RS_DS configuration information received from the RRC control unit 1072 to the terminal 1000. In addition, the transmitter 1055 transmits the CSI-RS received from the reference signal generator 1071 to the terminal 1000. In particular, the transmitter 1055 transmits the CSI-RS to the terminal 1000 as a CSI-RS pattern determined based on the CSI-RS configuration information about the serving base station 1050.

As an example, the transmitter 1055 transmits CSI-RS_DS mapped to two or less antenna ports and four resource elements to the terminal 1000 based on the CSI-RS_DS configuration information.

As another example, the transmitter 1055 transmits the CSI-RS using a sequence, but includes a time-frequency resource region corresponding to one subframe on a time axis and one resource block on a frequency axis. On one orthogonal frequency division multiplexing (OFDM) symbol, one sequence value according to one sequence index may be repeated twice on two resource elements and mapped to the CSI-RS.

As another example, the transmitter 1055 may include one orthogonal frequency division multiplexing (OFDM) symbol in a time-frequency resource region corresponding to one subframe on a time axis and one resource block on a frequency axis. ), Two sequence values according to two consecutive sequence indexes to two resource elements may be mapped to the CSI-RS, respectively.

The receiving unit 1060 receives the CSI-RS configuration information, the CSI-RS of the small base station 1090 or the CSI-RS of the serving base station 1050, the corresponding response message (for example, CSI report ( report), etc.) or an uplink signal.

The terminal 1000 performing wireless communication with the base station 1050 includes a receiver 1050, an RRC controller 1010, and a transmitter 1015.

The receiver 1050 receives the CSI-RS configuration information, the CSI-RS_DS configuration information, and the CSI-RS from the serving base station 1050. In addition, the receiver 1050 receives the CSI-RS for the discovery signal from the small base station 1090 that provides the small cell. Here, the CSI-RS for the discovery signal is generated according to any one of the CSI-RS generation methods (1) and (2) described herein as described above, and the receiver 1050 generates the CSI-RS generation method (1). , CSI-RS is received by a method corresponding to any one of (2). For example, the receiver 1050 is mapped to four resource elements and two or less antenna ports in a time-frequency resource region corresponding to one subframe on a time axis and one resource block on a frequency axis. The CSI-RS may be received.

The RRC control unit 1010 interprets the CSI-RS configuration information and the CSI-RS_DS configuration information. The RRC control unit 1010 performs a configuration for receiving the CSI-RS from the serving base station 1050 as indicated by the CSI-RS configuration information. The RRC control unit 1010 performs a configuration for receiving the CSI-RS from the small base station 1090 as indicated by the CSI-RS_DS configuration information.

Thereafter, the RRC controller 1010 performs small cell discovery according to the CSI-RS_DS configuration information. For small cell discovery, the RRC controller 1010 may control the receiver 1005 to receive the CSI-RS from the small base station 1090 according to a specific CSI-RS pattern. Or, if the CSI-RS_DS configuration information is not included in the RRC message, the RRC control unit 1010 recognizes that only the CRS is used as a discovery signal.

The transmitter 1015 transmits CSI-RS configuration information, CSI-RS_DS configuration information, and a message or uplink signal corresponding to receiving the CSI-RS to the base station 1050.

The small base station 1090 includes a reference signal generator 1093 and a transmitter 1096.

The reference signal generator 1093 generates the CSI-RS according to any one of the CSI-RS generation methods (1) and (2) and sends the CSI-RS to the transmitter 1096. The transmitter 1096 transmits the CSI-RS received from the reference signal generator 1093 to the terminal 1000. In this case, the transmitter 1096 transmits the CSI-RS to the terminal 1000 using the CSI-RS pattern shown in FIG. 8 or 9 and the antenna ports 115 and / or 116.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Claims

A method of transmitting a reference signal (RS) by a base station (BS) in a wireless communication system,

generating CSI-RS_DS (discovery signal) configuration information indicating patterns of channel state information (CSI) -RS configured for k small cells;

Transmitting the CSI-RS_DS configuration information to a user equipment (UE); And

Transmitting CSI-RS_DS mapped to two or less antenna ports and four resource elements to the terminal based on the CSI-RS_DS configuration information.
The method of claim 1,

The CSI-RS_DS configuration information includes a resource configuration list field,

The resource configuration list field is a 16-bit bitmap,

And wherein the bitmap indicates whether the CSI-RS patterns are configured in at least one of the k small cells.
The method of claim 1,

The resource configuration list field further includes a physical cell ID of the k small cells.
A base station (BS) for transmitting a reference signal (RS) in a wireless communication system,

a radio resource control (RRC) control unit for generating CSI-RS_DS (discovery signal) configuration information indicating patterns of channel state information (CSI) -RS configured for k small cells; And

Transmitting the CSI-RS_DS configuration information to a user equipment (UE), and transmitting the CSI-RS_DS mapped to two or less antenna ports and four resource elements to the terminal based on the CSI-RS_DS configuration information. A base station comprising a transmission unit.
The method of claim 4, wherein

The CSI-RS_DS configuration information includes the resource configuration list field,

The resource configuration list field is a 16-bit bitmap,

And wherein the bitmap indicates whether the CSI-RS patterns are configured in at least one of the k small cells.
The method of claim 4, wherein

The resource configuration list field, characterized in that further comprises a physical cell ID of the k small cells, the base station.
A method of receiving a reference signal (RS) by a user equipment (UE) in a wireless communication system,

Receiving CSI-RS_DS (discovery signal) configuration information indicating patterns of channel state information (CSI) -RS configured for k small cells from a serving base station ; And

Receiving the CSI-RS from at least one small cell based on the CSI-RS_DS configuration information.
The method of claim 8,

The CSI-RS is mapped to four resource elements and two or less antenna ports in a time-frequency resource region corresponding to one subframe on a time axis and one resource block on a frequency axis. A method of receiving a reference signal, characterized in that.
The method of claim 8,

The sequence used to generate the CSI-RS is one orthogonal frequency division multiplexing (OFDM) in a time-frequency resource region corresponding to one subframe on a time axis and one resource block on a frequency axis. The method for receiving a reference signal, characterized in that one sequence value according to one sequence index is repeatedly mapped to two resource elements on a symbol.
The method of claim 8,

The sequence used to generate the CSI-RS is one orthogonal frequency division multiplexing (OFDM) in a time-frequency resource region corresponding to one subframe on a time axis and one resource block on a frequency axis. 2. A method of receiving a reference signal, characterized in that on a symbol, two sequence values according to two consecutive sequence indices are mapped to two resource elements, respectively.
A user equipment (UE) for receiving a reference signal (RS) in a wireless communication system,

receiving CSI-RS_DS (discovery signal) configuration information indicating patterns of channel state information (CSI) -RS configured for k small cells from a serving base station, And a receiver configured to receive the CSI-RS from at least one small cell based on the CSI-RS_DS configuration information.
The method of claim 11,

The CSI-RS is mapped to four resource elements and two or less antenna ports in a time-frequency resource region corresponding to one subframe on a time axis and one resource block on a frequency axis, and the receiving unit is mapped to the receiver. Characterized in that received by the terminal.
The method of claim 11,

The sequence used to generate the CSI-RS is one orthogonal frequency division multiplexing (OFDM) in a time-frequency resource region corresponding to one subframe on a time axis and one resource block on a frequency axis. The terminal, characterized in that one sequence value according to one sequence index is repeatedly mapped to two resource elements.
The method of claim 11,

A sequence used for generating the CSI-RS is one orthogonal frequency division multiplexing (OFDM) in a time-frequency resource region corresponding to one subframe on a time axis and one resource block on a frequency axis. On the symbol, characterized in that two sequence values according to two consecutive sequence indexes are mapped to two resource elements, respectively.