KR20150052512A - Apparatus and method for reporting channel state information in wireless communication system supporting small cells - Google Patents

Abstract

Disclosed in the present invention are a method and an apparatus for reporting channel state information in a wireless communication system supporting small cells. The method of controlling operation state of small cells by cell operation control unit in a wireless communication system may comprise: a step of receiving, from the terminal, channel state information which the terminal decides based on the discovery signals transmitted from small cells; and a step of controlling the operation state of small cells based on the channel state information. Also, the channel state information can be a response signal for the non-periodic CSI (channel state information) feedback request signal received by the terminal.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method and apparatus for reporting channel state information in a wireless communication system supporting a small cell,

The present invention relates to wireless communication, and more particularly, to a method and apparatus for reporting channel state information in a wireless communication system supporting a small cell.

In a next generation communication system such as LTE-A (Advanced), a small cell based on a low-power node as well as a macro cell based on a high-power node (F2 Research is underway to provide wireless communication services indoors and outdoors through the Internet.

The small cell can be considered both in the frequency band that is the coverage of the macrocell and in the frequency band other than the coverage of the macrocell, and can be provided both in the indoor environment (in the cube) and in the outdoor environment (outside the cube). Also, an ideal or non-ideal backhaul network may be supported between macrocells and small cells, and / or between small cells. And the small cell can be provided both in a low density sparse deployment environment and / or a dense deployment environment.

A terminal can search among a plurality of small cells distributed in a macro cell whether there is a small cell capable of providing service to the terminal. Small cell discovery is also known as small cell discovery. For the small cell search, the small cell transmits a discovery signal to the terminal, and the terminal can search for the small cell using the search signal. However, when the duty cycle of the search signals transmitted by a plurality of small cells is short or the duration is long and the duty cycle is high, interference occurs between the search signals, It can be difficult. Furthermore, power can be wasted on small, sensitive cells.

SUMMARY OF THE INVENTION The present invention provides a channel state information reporting method in a wireless communication system supporting a small cell.

Another aspect of the present invention is to provide an apparatus for reporting channel state information in a wireless communication system supporting a small cell.

It is another object of the present invention to provide a method and apparatus for controlling the operating state of a small cell in a wireless communication system.

According to another aspect of the present invention, there is provided a method of controlling an operation state of a small cell by a cell operation control unit in a wireless communication system, the method comprising: The method comprising: receiving channel state information from the UE; and controlling an operation state of the small cell based on the channel state information. The channel state information includes at least one of an aperiodic CSI information feedback response signal of the terminal. Wherein the operation state of the small cell includes a first operation state in which the small cell transmits the search signal, traffic data, and control data to the terminal through the downlink channel, and a second operation state in which the small cell transmits only the search signal And a second operating state in which the transmission is performed. The UE can receive non-periodic CSI process configuration information from an upper layer, and the UE can only receive the small cell corresponding to the identifier information of the small cell included in the aperiodic CSI process configuration information, Information can be determined. The aperiodic CSI feedback request signal may be transmitted from the serving cell serving the terminal to the terminal, and the search signal may be at least one of a downlink channel and a downlink signal transmitted from the small cell. The channel state information based on the search signal includes CQI (channel quality indicator) information, reference signal received power (RSRP) information, and RSRQ (reference signal strength) information determined based on the identifier information of the small cell and the search signal transmitted by the small cell and received quality information. The terminal may determine whether to transmit the channel state information according to a signal strength of the search signal. The CQI information may be determined based on a difference between a first CQI value determined based on the search signal transmitted by the small cell and a second CQI value determined based on a downlink signal of a serving cell serving the mobile station have. The RSRP information may be determined based on a difference between a first RSRP value determined based on the search signal transmitted by the small cell and a second RSRP value determined based on a downlink signal of a serving cell serving the mobile station have.

According to another aspect of the present invention, there is provided a cell operation control apparatus for controlling an operation state of a small cell in a wireless communication system, the cell operation control apparatus comprising: A radio frequency (RF) unit implemented for the mobile terminal; And a processor selectively connected to the RF unit, wherein the processor receives channel state information determined by the terminal based on a search signal transmitted from the small cell, and based on the channel state information, The channel state information may be a response signal of the UE to an aperiodic CSI (channel state information) feedback request signal received by the UE. Wherein the operation state of the small cell includes a first operation state in which the small cell transmits the search signal, traffic data, and control data to the terminal through the downlink channel, and a second operation state in which the small cell transmits only the search signal And a second operating state in which the transmission is performed. The UE can receive non-periodic CSI process configuration information from an upper layer, and the UE can only receive the small cell corresponding to the identifier information of the small cell included in the aperiodic CSI process configuration information, Information can be determined. The aperiodic CSI feedback request signal may be transmitted from the serving cell serving the terminal to the terminal, and the search signal may be at least one of a downlink channel and a downlink signal transmitted from the small cell. The channel state information based on the search signal includes CQI (channel quality indicator) information, reference signal received power (RSRP) information, and RSRQ (reference signal strength) information determined based on the identifier information of the small cell and the search signal transmitted by the small cell and received quality information. The terminal may determine whether to transmit the channel state information according to a signal strength of the search signal. The CQI information may be determined based on a difference between a first CQI value determined based on the search signal transmitted by the small cell and a second CQI value determined based on a downlink signal of a serving cell serving the mobile station have. The RSRP information may be determined based on a difference between a first RSRP value determined based on the search signal transmitted by the small cell and a second RSRP value determined based on a downlink signal of a serving cell serving the mobile station have.

It is possible to reduce the small cell on / off switching time required to obtain the gain through the small cell on / off operation by quickly obtaining the channel state information. That is, the switching time for switching the small cell on / off can be reduced by greatly reducing the time delay of transmitting the reported channel state information based on the search signal transmitted by the small cell, thereby improving the performance of the small cell .

1 is a block diagram illustrating a wireless communication system to which the present invention is applied.
2 and 3 schematically show the structure of a radio frame to which the present invention is applied.
4 and 5 show 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 conceptual diagram showing a deployment scenario of a small cell and a macro cell.
8 is a conceptual diagram illustrating that channel state information is reported from a UE to a base station based on RRC.
9 is a conceptual diagram illustrating a method for transmitting channel state information based on a search signal based on aperiodic CSI feedback according to an embodiment of the present invention.
10 is a conceptual diagram illustrating a method for performing CQI reporting or RSRP / RSRQ reporting based on a search signal according to an embodiment of the present invention.
11 is a flowchart illustrating a method for a BS to request channel state information of a small cell to a UE according to an embodiment of the present invention.
12 is a flowchart illustrating a method for a BS to request channel state information of a small cell to a UE according to an embodiment of the present invention.
13 is a block diagram illustrating a wireless communication system according to an embodiment of the present invention.

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

The present invention will be described with reference to a communication network. The work performed in the communication network may be performed in a process of controlling the network and transmitting data by a system (e.g., a base station) that manages the communication network, The work can be done.

1 is a block diagram illustrating a wireless communication system to which the present invention is applied.

Referring to FIG. 1, a wireless communication system 10 is widely deployed to provide various communication services such as voice, packet data, and the like. The wireless communication system 10 includes at least one base station 11 (BS). Each base station 11 provides communication services for a particular geographical area or frequency domain and may be referred to as a site. A site may be divided into a plurality of areas 15a, 15b, and 15c, which may be referred to as sectors, and the sectors may have different cell IDs.

A user equipment (UE) 12 may be fixed or mobile and may be a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, (personal digital assistant), a wireless modem, a handheld device, and the like. The base station 11 generally refers to a station that communicates with the terminal 12 and includes an evolved-NodeB (eNodeB), a base transceiver system (BTS), an access point, a femto base station (Femto eNodeB) (ENodeB), a relay, a remote radio head (RRH), and the like. The cells 15a, 15b and 15c should be interpreted in a comprehensive sense to indicate a partial area covered by the base station 11 and include all coverage areas such as megacell, macrocell, microcell, picocell, femtocell to be.

Hereinafter, a downlink refers to a communication or communication path from the base station 11 to the terminal 12, and an uplink refers to a communication or communication path from the terminal 12 to the base station 11 . In the downlink, the transmitter may be part of the base station 11, and the receiver may be part of the terminal 12. In the uplink, the transmitter may be part of the terminal 12, and the receiver may be part of the base station 11. There is no limit to the multiple access scheme applied to the wireless communication system 10. [ (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-FDMA , OFDM-CDMA, and the like. These modulation techniques increase the capacity of the communication system by demodulating signals received from multiple users of the communication system. The uplink transmission and the downlink transmission may be performed using a time division duplex (TDD) scheme transmitted at different times or a frequency division duplex (FDD) scheme using different frequencies.

The layers of the radio interface protocol between the terminal and the base station are divided into a first layer (L1), a second layer (L1), and a second layer (L2) based on the lower three layers of an Open System Interconnection A second layer (L2), and a third layer (L3). Among them, the physical layer belonging to the first layer provides an information transfer service using a physical channel.

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

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

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

Referring to FIGS. 2 and 3, a radio frame includes 10 subframes. One subframe includes two slots. The time (length) for transmitting one subframe is called a transmission time interval (TTI). Referring to FIG. 2, for example, the length of one subframe (1 subframe) may be 1 ms and the length of one slot may be 0.5 ms.

A slot may contain a plurality of symbols in the time domain. For example, in the case of a radio system using OFDMA (Downlink Frequency Division Multiple Access) in a downlink (DL), the symbol may be an Orthogonal Frequency Division Multiplexing (OFDM) symbol. On the other hand, the representation of the symbol period of the time domain is not limited by the multiple access scheme or the name. For example, in a time domain, a plurality of symbols may be a single-carrier-frequency division multiple access (SC-FDMA) symbol, a symbol period, etc. in addition to an OFDM symbol.

The number of OFDM symbols included in one slot may vary according to the length of a CP (Cyclic Prefix). For example, one slot includes seven OFDM symbols in case of a normal CP, and one slot may include six OFDM symbols in case of an extended CP.

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

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

)를 추정할 수 있다.Since the UE knows the information of the reference signal, the UE estimates the channel based on the received reference signal, compensates the channel value, and can accurately obtain the data transmitted from the base station. If the reference signal sent from the base station is p, the channel information experienced by the reference signal during transmission is h, the thermal noise generated by the terminal is n, and the signal received by the terminal is y, y = h p + n . Since the reference signal p is already known by the UE, if the LS (Least Square) scheme is used, the channel information

) Can be estimated.

&Quot; (1) "

는

값에 의존하게 되므로, 정확한 h값의 추정을 위해서는

이 0에 수렴시킬 필요가 있다. Here, the channel estimation value estimated using the reference signal p

The

Value, so for accurate estimation of the h value

It is necessary to converge to zero.

The reference signal is typically generated by generating a signal from a sequence of reference signals. The reference signal sequence may be one or more of several sequences having superior correlation characteristics. For example, a Constant Amplitude Zero Auto-Correlation (CAZAC) sequence such as a Zadoff-Chu (ZC) sequence or a PN (pseudo-noise) sequence such as an m-sequence, a Gold sequence or a Kasami sequence May be used as a sequence of reference signals, and various other sequences having superior correlation characteristics may be used depending on system conditions. The reference signal sequence may be cyclic extension or truncation to adjust the length of the sequence or may be used in various forms such as binary phase shift keying (BPSK) or quadrature phase shift keying (QPSK) And may be mapped to RE (Resource element).

The downlink reference signal includes a cell-specific RS, a MBSFN reference signal, a UE-specific RS, a position reference signal PRS, RS and a channel state information (CSI) reference signal (CSI-RS).

The UE-specific reference signal is a reference signal received by a specific UE or a specific UE group in a cell and can be called a Demodulation RS (DM-RS) since it is mainly used for data demodulation of a specific UE or a specific UE group. have.

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

The CSI-RS can be transmitted over one, two, four or eight antenna ports. The antenna ports used may be p = 15, p = 15,16, p = 15, ..., 18 and p = 15, ..., The CSI-RS can be defined only when the frequency interval? F between subcarriers is 15 kHz. The CSI-RS sequence rl _{, ns} (m) can be defined as Equation (2).

&Quot; (2) "

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

&Quot; (3) "

로 표현될 수 있다. N = 1600 and _C in equation (3), a 1 m- sequence x ₁ (i) are _{x 1 (0) = 1,} x 1 (n) = 0, (n = 1,2, ..., 30) Lt; / RTI > 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,

. ≪ / RTI >

The pseudorandom sequence c (i) may be initialized by Equation (4) at the beginning of each OFDM symbol.

&Quot; (4) "

In Equation (3), N _CP has a value of 1 in the normal CP and 0 in the extended CP. N _ID ^CSI can have any one of integers from 0 to 503. N _ID ^CSI may be a virtual cell ID (VCID) for CSI-RS when signaled from an upper layer. The N _ID ^CSI may be equal to the physical cell ID (PCI) if there is no signaling from the upper layer.

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

&Quot; (5) "

Referring to Equation (5 ⁾ , a _{k, l} ^(p) is a complex modulation symbol mapped to the kth subcarrier and the lth OFDM symbol of the pth antenna port. a _{k, l} ^(p) are mapped by being multiplied by the CSI-RS sequence r _{l, ns} (m ') and the orthogonal sequence w _{l "} .

Each parameter in Equation (5) can be defined by Equation (6).

&Quot; (6) "

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

The CSI-RS configuration includes a non-zero transmission power CSI-RS configuration indicating a pattern in which a CSI-RS is transmitted to each cell (or a transmission point (TP) RS for muting the PDSCH region corresponding to the CSI-RS transmission of the uplink RS and the downlink RS. Zero or one CSI-RS configuration per CSI process, or zero or multiple CSI RS configurations for a terminal assuming zero power CSI-RS for a terminal assuming non-power CSI-RS.

Information on one or more non-optical power CSI-RS configurations (hereinafter referred to as CSI-RS configurations) may be transmitted to each terminal of the corresponding cell. The information on the CSI-RS configuration includes 2-bit information indicating the number of antenna ports (hereinafter referred to as CSI-RS antenna ports) for transmitting non-linear power CSI-RSs as 1, 2, 4, And 5-bit information indicating a configurable CSI-RS pattern for each number of CSI-RS antenna ports.

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

<Table 1>

<Table 2>

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

Referring to Table 1, a total of 32 CSI-RS configurations are provided when the number of antenna ports is one or two in the case of a general CP, a total of 16 CSI-RS configurations are provided when the number of antenna ports is four, There are 8 CSI-RS configurations in total. Referring to Table 2, when the number of antenna ports is one or two, a total of 28 types of CSI-RS configurations are used for the extended CP, 14 types of CSI-RS configurations are used when the number of antenna ports is four, There are a total of seven CSI-RS configurations for eight.

Referring to Table 1 and Table 2, the location of a specific resource element to which the CSI-RS is mapped can be indicated for each CSI-RS antenna port number with respect to the CSI-RS configuration. That is, the location of the remaining resource elements to which the CSI-RS is mapped can be determined based on the location of the specific one resource element, and thus the location of the remaining resource elements to which the CSI-RS is mapped can be determined. You can see the pattern.

For example, when the CP type = the general CP, the number of the CSI-RS antenna ports = 8, and the value of the CSI-RS configuration = 2 (= 00010) ) = (9,2) and n _s mod 2 = 1 are indicated. Therefore, it can be seen that within a subframe configured for CSI-RS transmission, the CSI-RS is mapped to a resource element with an OFDM symbol index of 2 and a subcarrier index of the second slot is 9. The resource element indicated by Table 1 may be one of the positions of the resource element to which the CSI-RS to be transmitted through the first CSI-RS antenna port is mapped. The location of the remaining resource elements to which the CSI-RS is transmitted through the first CSI-RS antenna port and the location of the resource element to which the CSI-RS transmitted through the remaining CSI-RS antenna port are mapped, Lt; RTI ID = 0.0 &gt; 1 &lt; / RTI &gt;

4 and 5 show 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.

FIG. 4 shows a case of FDD + TDD, and FIG. 5 shows a CSI-RS pattern in the case of TDD. In FIGS. 4 and 5, the numbers indicated in each resource element indicate a CSI-RS configuration number. RS is an antenna port of a CSI-RS antenna port 15, 16 is a CSI-RS antenna port 17, 18 is a CSI-RS antenna port 19, 20 is a CSI-RS antenna port 19, Gt; CSI-RS &lt; / RTI &gt; A denotes the DMRS antenna port {7, 8, 11, 13}, and B denotes the DMRS transmission on the DMRS antenna port {9, 10, 12, 14}. C represents a resource element to which CRS is mapped. It is also assumed in FIGS. 4 and 5 that the number of CRS antenna ports is two and the control area (shaded area) is allocated to the first three OFDM symbols of the subframe.

The CSI-RS pattern of FIGS. 4 and 5 can be applied to a case where the number of CRS antenna ports is one, four, or even when CRS is not transmitted. In addition, the CSI-RS patterns of FIGS. 4 and 5 can be applied to a case where a control region is allocated to an OFDM symbol in the first to fourth subframes, or a control region is not allocated. 4 and 5, the DMRS includes two code division multiplexing (CDM) groups (A: DMRS antenna ports {7, 8, 11, 13}, B: DMRS antenna ports {9, 10, 12, 14} , The CSI-RS pattern of FIG. 4 can be applied to the case of using one CDM group.

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.

4 and FIG. 5, the numbers indicated in each resource element in FIG. 6 indicate the CSI-RS configuration number. RS is an antenna port of a CSI-RS antenna port 15, 16 is a CSI-RS antenna port 17, 18 is a CSI-RS antenna port 19, 20 is a CSI-RS antenna port 19, Gt; CSI-RS &lt; / RTI &gt; E indicates that the DMRS is transmitted on the DMRS antenna port {7, 8}. C represents a resource element to which CRS is mapped. It is also assumed in FIG. 6 that the number of CRS antenna ports is two and the control area (shaded area) is allocated to the first three OFDM symbols of the subframe.

The CSI-RS pattern of FIG. 6 can be applied to a case where the number of CRS antenna ports is 1, 4, or CRS is not transmitted. In addition, the CSI-RS pattern of FIG. 6 can be applied to a case where the control area is allocated to the first to fourth OFDM symbols in the subframe, or the control area is not allocated.

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

<Table 3>

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

&Quot; (7) &quot;

The zero-power CSI-RS configuration may be configured with 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 constituted by an upper layer, a terminal allocates a resource element corresponding to four CSI-RS antenna ports in Tables 1 and 2 to zero power CSI- RS. More specifically, the most significant bit (MSB) of a 16-bit bitmap corresponds to the first CSI-RS configuration index in the case where the number of CSI-RS antenna ports is four in Table 1 and Table 2. [ The following bits of the 16-bit bitmap correspond to the direction in which the CSI-RS configuration index increases in the case where the number of CSI-RS antenna ports is four in Tables 1 and 2. In the resource element set as the zero power CSI-RS, the PDSCH corresponding to the CSI-RS transmission of the adjacent cell or the TP is muted and the PDSCH can be transmitted in the resource element not set as the zero power CSI-RS.

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

1) Zero power CSI-RS configuration list: When the number of CSI-RS antenna ports is four in Table 1 or Table 2, a 16-bit bit map composed of one CSI-

2) Zero Power CSI-RS Subframe Configuration (I _CSI-RS ): Indicates a subframe configuration for zero power CSI-RS, similar to the subframeConfig parameter transmitted for non-power CSI-RS described later. The zero power CSI-RS subframe structure has a length of 8 bits and is divided into a period (T _CSI-RS ) and an offset (T _CSI-RS ) of a subframe used for transmission according to a zero power CSI- ? _CSI-RS ) can be determined.

In advanced wireless communication systems, there is a need for techniques for small cell enhancement indoors and outdoors. The small cell enhancement provides various aspects to improve the performance of a small cell, such as how to avoid interference between small cells, how to adaptively place small cells in changing traffic, and how to accurately measure interference between small cells. .

Hereinafter, in an embodiment of the present invention, a terminal acquires information on a channel state based on a discovery signal transmitted by a small cell, and on / off of a small cell based on the acquired channel state information, lt; / RTI &gt; operation is controlled. The on / off operation of the small cell can be performed by a control device capable of controlling on / off of the small cell. A control device capable of controlling ON / OFF of the small cell is referred to as an ON / OFF control portion of the small cell.

7 is a conceptual diagram showing a deployment scenario of a small cell and a macro cell.

The macro cell 700 indicates a cell having a relatively larger coverage than the small cell 750 and the small cell 750 indicates a micro cell or a pico cell with a cell having a relatively smaller coverage than the macro cell 700. [ Cell, a femto cell, or the like.

Referring to FIG. 7, a terminal can search among a plurality of small cells 750 distributed in a macro cell 700 to see if there is a small cell 750 capable of providing services to the terminal. The operation of searching for the small cell 700 by the terminal can be expressed by the term small cell discovery. A terminal may use a discovery signal 710 transmitted by a small cell for a small cell search. The search signal 710 may include, for example, a CSI (channel state information) -RS (reference signal), a CRS (cell specific reference signal), a PSS / SSS, a modified CRS, A secondary synchronization signal (SSS), a CSI-RS or a positioning reference signal (PRS), or a newly defined signal for searching for a small cell.

According to the embodiment of the present invention, the terminal receives the search signal 710 from the small cells 703 and 706, and the on / off control unit of the small cell transmits the reporting result (for example, CQI, RSRP , RSRQ, etc.) of the small cells 703 and 706 on the basis of the on / off operation of the small cells 703 and 706. Accordingly, performance for serving a terminal based on a small cell can be improved.

The small cell on / off operation may be an operation of setting the small cell 750 to an ON state or an OFF state according to a specific condition. When the small cell 750 is on, the small cell 750 may operate as a legacy carrier and may transmit a downlink signal such as a reference signal and a channel. For example, when the small cell 750 is on, the small cell 750 may transmit a reference signal for channel reporting and demodulation of downlink data to the UE. The terminal can access the small cell 750 in the ON state and receive the downlink data from the small cell 750. Conversely, when the small cell 750 is in an off state, the small cell 750 may not be able to transmit channels and signals transmitted through the legacy carrier. The terminal can not access the small cell 750 in the off state and can not receive the downlink data from the small cell 750. [ However, the search signal 710 can be transmitted even when the small cell 750 is in the off state. That is, the OFF state of the small cell 750 may include a state in which the small cell 750 does not transmit any signal other than the search signal 710. [

If the small cell 750 is off, the interference signal transmitted from the corresponding cell to the UE may be reduced. In particular, when a certain small cell is in an off state, the interference caused to the terminal due to a signal transmitted from the same resource, such as a CRS transmitted by the small cell 750, may be reduced. If interference due to small cell 750 is reduced, network throughput performance can be improved. If the traffic load of the network increases, the network may switch the off-state small cell 750 back on to cover the increased traffic load. It is possible to save power consumed in the small cell 750 by switching the small cell on / off state.

The ON state of the small cell may be expressed differently in terms of the first operation state and the OFF state of the small cell may be expressed in terms of the second operation state. The first operating state is a state in which the small cell transmits a search signal, traffic data, and control data to a mobile station through a downlink channel. In a second operating state, a small cell transmits only a search signal through a downlink channel. have.

The gain obtained by turning on / off the small cell 750 may be dependent on the magnitude of the on / off switching time of the small cell 750. The ON / OFF switching time of the small cell 750 may be a time used when the small cell 750 is switched from the ON state to the OFF state or from the OFF state to the ON state. If the size of the switching time of the small cell 750 is long, a decrease in the performance improvement due to the small cell on / off may occur.

When on / off of the small cell 750 is performed in a semi-static manner, the ON / OFF switching time of the small cell 750 required may be 20 to 80 ms. At present, the mobile station receives a channel status report from a mobile station based on a radio resource control (RRC) and determines whether the small cell 750 is on or off based on the received channel status report. When the UE performs a channel state report on a RRC basis with a serving small cell or a serving macro cell serving as a serving cell (hereinafter, referred to as a serving cell), the minimum value of the period of channel state reporting is set to ON / OFF It can be 120ms, which is greater than the switching time. Therefore, when the channel state is reported based on the RRC and the ON / OFF of the small cell 750 is determined through the reported channel state information, I can not decide whether to turn off / on. Therefore, when the serving cell receives the channel state information from the UE based on the RRC, the requirement for the ON / OFF switching time of the small cell 750 required to obtain the gain can not be satisfied.

Referring to FIG. 7, in the embodiment of the present invention, channel state information (RSRP (reference signal received (RSRP)) 704, which is determined based on the search signal 710 received from the small cells 703 and 706, power, RSQ (reference signal received quality), CQI (channel quality indicator), etc.) to the serving cell. In the embodiment of the present invention, the serving cell can be used as a term indicating a cell (macro cell or small cell) to which the present terminal is connected. Hereinafter, the term channel state information used in the embodiment of the present invention includes a parameter including information on channel states such as RSRP, RSRQ, CQI, precoding matrix index (PMI), rank index Can be used as a meaning.

By using the channel state information reporting method based on the search signal according to the embodiment of the present invention, the time delay for reporting the channel state information to the serving cell can be greatly reduced, The performance of the small cell 750 can be improved. The method for improving the small cell performance according to the embodiment of the present invention is a method for improving the performance of the small cell by determining whether or not the small cell exists in the coverage of the macro cell, whether the small cell is located outdoors and indoors, whether the back hole is ideal, Whether they are distributed or not.

8 is a conceptual diagram illustrating that channel state information is reported from a UE to a base station based on RRC.

8, the terminal 800 may transmit the measured channel state information (e.g., an RSRP report) to the base station 850. [ In transmitting the periodic RSRP report to the base station 850, the period for transmitting the RSRP report can be set as shown in Table 4 below.

<Table 4>

Referring to Table 4, ReportInterval can indicate a period of time in which a periodic report is performed. ms 120 corresponds to 120 ms (millisecond), and ms 240 corresponds to 240 ms. Also, min 1 may correspond to one minute and min 6 may correspond to six minutes. That is, the RSRP report may be sent to the serving cell with a period that is too large to be used to determine the small cell on / off switching time.

8, the UE 800 may transmit not only periodic reporting but also channel state information measured by a channel state information reporting request of the BS 850 to the serving cell base station 850. [ That is, RSRP, which is channel state information, may be reported from the terminal to the base station at the request of the base station 800.

8, the current RSRP report does not satisfy the requirements of the small cell on / off switching time because it is performed based on an upper layer such as the RRC layer.

Therefore, in the embodiment of the present invention, even if the small cell is in the off state, the mobile station can report the channel state information to the base station through the feedback operation performed in the lower layer such as the physical layer based on the search signal transmitted. In the embodiment of the present invention, a method for satisfying the requirement of small cell on / off switching time is disclosed by transmitting measured channel state information to a base station based on a layer capable of reporting to the base station as fast as a physical layer. In order to switch the small cell in the off state to the on state or to switch the small cell in the on state to the off state, the terminal receives the search signal transmitted by the small cell and reports the channel state information quickly based on the received search signal need.

According to an embodiment of the present invention, the terminal may also set up a channel state report based on the search signal when setting aperiodic CSI feedback.

When setting aperiodic CSI feedback, the upper layer may set one or more CSI processes if the terminal supports transmission mode 10. Each CSI process may be associated with a CSI-RS resource and a CSI-IM (interference measurement) resource. The CSI reported by the terminal may be information corresponding to the CSI process set by the upper layer.

For example, when the UE decodes the uplink DCI format 4 or the random access response grant received through the subframe n and the CSI request field included in the information is set to trigger the CSI report Can be assumed. In this case, the UE can transmit aperiodic CSI reporting in the subframe n + k to the serving cell base station using a physical uplink shared channel (PUSCH).

If the size of the CSI request field is 2 bits and the UE is set to the transmission mode 10 for at least one serving cell, the CSI report can be set according to the value of Table 5 corresponding to the value of the CSI request field.

<Table 5>

In the embodiment of the present invention, the UE can use the CSI reporting method (for example, non-periodic CSI feedback) in reporting the channel status information measured based on the search signal transmitted by the small cell to the base station of the serving cell . The aperiodic CSI feedback is an operation performed in the physical layer. Therefore, the UE can report the channel state information measured on the basis of the non-periodic CSI feedback based on the search signal to the base station of the serving cell more quickly. Hereinafter, in an embodiment of the present invention, channel state information measured based on a search signal is expressed by the term channel state information based on a search signal. Since CSI feedback is feedback performed in the physical layer, it can be processed faster than the RRC report. By transmitting the channel state information based on the search signal to the feedback based on the physical layer, the channel for setting the small cell on / Status information can be obtained.

9 is a conceptual diagram illustrating a method for transmitting channel state information based on a search signal based on aperiodic CSI feedback according to an embodiment of the present invention.

9, when a base station performs downlink transmission using, for example, a transmission mode 10 (for example, a coordinated multiple point (CoMP)), a plurality of aperiodic CSI feedback processes may be established have. The UE can report the channel state information 960 based on the search signal to the base station of the serving cell 900 based on a plurality of aperiodic CSI feedback processes. For convenience of description, the channel status information based on the search signal may be reported to the base station of the macro cell although it is represented by a small cell.

Various settings can be performed to the terminal for reporting the CSI-based channel state information based on the search signal. The terminal may transmit the channel state information based on the search signal to the small cell or the macro cell. The macro cell or the core network can control the on / off operation of the small cell based on the channel state information based on the search signal.

For example, a separate CSI process for reporting channel state information based on a search signal may be established or an additional process may be set for an existing aperiodic CSI feedback process, To the base station of the serving cell. A CSI feedback process for reporting the channel state information 960 based on the search signal during the aperiodic CSI feedback process may be triggered and in this case the UE may generate channel state information for determining which small cell to turn on / (E.g., RSRP) with other aperiodic CSI feedback to the base station of the serving cell. In addition, the terminal may set to receive the search signal 950 from any small cell 910, 920 and report the channel state information based on the received search signal 950. That is, the small cells 910 and 920 for determining the channel state information 960 based on the search signal may be separately set in the upper layer.

Table 6 below shows a case where the terminal receives the search signal 950 from the small cells 910 and 920 and sets information on the small cell to which the channel state information 960 based on the search signal is to be reported, .

<Table 6>

Referring to Table 6, based on the CellDiscoveryMeasureList, a mobile station can set a physical cell identifier (PhyCellId) for reporting channel status information 960 based on a search signal. The CellDiscoveryMeasureList may be a list that receives the search signal 950 and sets a cell to which channel status information is to be reported. The UE may set the CellDiscoveryMeasureList and receive the search signal 950 to determine the target cell to which the channel status information 960 is to be reported. For example, if the CellDiscoveryMeasureList includes a first cell identifier and a second cell identifier, which are identifiers of the first small cell 910 and the second small cell 920, the UE transmits the first small cell 910 and the second small cell 920, The first small cell 910 and / or the second small cell 920, which have received the search signal 950 transmitted from the small cell 920 and calculated based on the received search signal, can do.

In another method according to an embodiment of the present invention, the setting for reporting the channel state information 960 based on the search signal may be added to the setting of the existing aperiodic CSI feedback process. In this case, the search condition based channel state information 960 may be set as an additional field of CSI feedback. When this aperiodic CSI feedback process is triggered, the terminal may feed back the channel state information 960 based on the search signal to the base station with CSI feedback. Table 7 below shows that the UE receives the search signal and sets information on the target cell that reports the channel status information 960 based on the search signal.

<Table 7>

Referring to Table 7, as in Table 6, a physical cell identifier (PhyCellId) can be set based on the CellDiscoveryMeasureList. The UE can receive the search signal 950 from the small cells 910 and 920 specified by the CellDiscoveryMeasureList by setting the CellDiscoveryMeasureList to acquire information on the target cell to which the channel status information 960 is to be reported. If the terminal is a terminal that does not support transmission mode 10 and in this case, the CSI process may not be able to be established.

When the macro cell is assumed as P (primary) -cell and the small cell as S (secondary) -cell, the small cell on / off switching operation may be performed in the S-cell. Therefore, in the embodiment of the present invention, CSI setting in case of carrier aggregation (CA) can be considered. Carrier aggregation indicates to perform downlink or uplink transmission using a plurality of CCs. When Carrier Aggregation is performed using the CC of the P-cell (CC of the primary cell, P-Cell) and the CC of the S-cell (the secondary cell of the S-cell) - The carrier corresponding to the CC of the cell is referred to as PCC (primary cell component carrier), and the carrier corresponding to the CC of S-cell is referred to as a second cell component carrier (SCC) Cell can perform an initial connection establishment process or a connection re-establishment process to the S-cell. The S-cell can be activated based on the P-cell.

When carrier aggregation is performed, the CSI reporting of the terminal to the P-cell and the S-cell can be set independently. Thus, when the small cell is an S-cell, reporting the channel state information based on the search signal transmitted by the small cell can be set with the aperiodic CSI feedback of the S-cell or with the aperiodic CSI feedback of the S- have

Table 8 below shows the setting of the aperiodic CSI feedback of the S-cell when the UE supports carrier aggregation.

<Table 8>

Referring to Table 8, a physical cell identifier (PhyCellId) can be set based on the CellDiscoveryMeasureList in the same manner as Table 6. That is, the UE receives the search signal by receiving the CellDiscoveryMeasureList, and obtains information on the target cell to which the channel status information is to be reported.

Also, if no carrier aggregation is set, the small cell may be a P-cell for the UE and may have a non-periodic CSI report setup for the P-cell. In this case, the channel state information reporting based on the search signal may be set up with the aperiodic CSI feedback of the P-cell. Table 9 below shows the setting of the aperiodic CSI feedback of the small cell when the UE does not support carrier aggregation.

<Table 9>

Referring to Table 9, a physical cell identifier (PhyCellId) can be set based on the CellDiscoveryMeasureList as in Table 6. [ That is, the UE receives the search signal by receiving the CellDiscoveryMeasureList, and obtains information on the target cell to which the channel status information is to be reported.

As described above, the channel state information reporting based on the search signal is set up and the UE can transmit the channel state information to the base station based on the channel state information based on the search signal.

Hereinafter, an embodiment of the present invention will be described in detail with reference to a method of reporting channel state information transmitted from a mobile station based on a search signal. Hereinafter, the channel state information reporting method disclosed in the embodiment of the present invention may be used as one example, and various other methods may be used to report channel state information.

In performing CSI feedback, RI, PMI, and CQI may be included in the feedback content. In reporting the channel state information based on the search signal, the channel state information based on the search signal may be a measurement report based on CQI or a measurement report based on RSRP / RSRQ. Hereinafter, in the embodiment of the present invention, CQI reporting based on search signals is firstly disclosed.

10 is a conceptual diagram illustrating a method for performing CQI reporting or RSRP / RSRQ reporting based on a search signal according to an embodiment of the present invention.

Referring to FIG. 10, a mobile station can be set up for channel state information reporting based on a search signal based on an upper layer, and a search signal 1050 to be reported based on a search signal 1050 received from the small cells 1010 and 1020, Based channel state information 1060 based on the channel state information. The UE may transmit the channel state information 1060 based on the search signal along with the CSI feedback when the base station of the serving cell requests the CSI feedback. The terminal may transmit the channel state information 1060 based on the search signal to the small cell or the macro cell. The macro cell or the core network can control the on / off operation of the small cell based on the channel state information based on the search signal.

The search condition based channel state information 1060 may have various information formats. Hereinafter, the exemplary embodiment of the present invention will be described in detail with reference to a case where channel state information 1060 based on a search signal is CQI reporting based on a search signal or RSRP / RSRQ reporting based on a search signal.

The ON / OFF switching time of the small cell can be reduced based on the CQI reporting based on the search signal transmitted by the mobile station. For example, based on CQI reporting, a UE can determine CQI information to be used when receiving downlink data from a small cell. Compared with existing aperiodic CSI feedback, CQI reporting based on search signals may not include RI or PMI information. The following method can be used to determine the CQI based on the search signal transmitted by the small cell in the terminal.

The UE can determine the CQI based on rank 1 transmission. Also, the UE can determine the CQI by assuming that the number of antenna ports for the search signal is one. If the number of antenna ports for the search signal is 2, the UE can determine the CQI by assuming transmission diversity based on space-frequency block codes (SFBC) in the transmission modes 1 to 6. In the transmission modes 7 to 10, the UE can determine the CQI based on the first PMI index or the CQI based on the average of the PMI index corresponding to rank 1 in the codebook.

Also, the terminal can determine the CQI for the bandwidth set by the setting of the upper layer. The original CQI report can be calculated for a wide band and a subband. In determining the CQI based on the search signal, the bandwidth for determining the CQI may be the band through which the search signal is transmitted. To improve fluidity, subband CQIs may be supported for CQI reporting based on search signals. The subband CQI may be a CQI determined in some bandwidth rather than the entire bandwidth over which the CQI is transmitted.

A minimum physical resource block (6PRB) may be required to ensure measurement accuracy for the subband CQI. The bandwidth for the UE to determine the CQI can be determined by an upper layer such as RRC. For example, when a terminal reports a CQI determined based on a wide band that is a whole bandwidth through which a search signal is transmitted, and the terminal reports a CQI determined based on a subband that is a part of a bandwidth through which a search signal is transmitted And a case in which the UE reports both the CQI determined based on the wide band that is the bandwidth through which the search signal is transmitted and the CQI determined based on the subband that is a part of the bandwidth in which the search signal is transmitted, .

In performing CQI reporting based on a search signal, cell identifier information may be considered. For example, the UE can transmit only CQI information determined only for a small number of small cells (for example, three cells) among the small cells transmitting the search signal. Table 10 below is an exemplary table showing the information included in the CQI report based on the search signal.

<Table 10>

Referring to Table 10, a CQI value determined based on a search signal for a small cell having the strongest search signal strength, a small cell having the strongest search signal strength for the second strongest, and a third smallest strongest search signal strength To the base station of the serving cell.

According to another embodiment of the present invention, in order to determine the small cell on / off, only the CQI value determined based on the small cell transmitting the search signal most severely may be transmitted. The identifier of the smallest cell having the strongest search signal and the CQI determined based on the search signal can be expressed as shown in Table 11 below.

<Table 11>

Referring to Table 11, the channel state information based on the search signal transmitted by the UE may include an identifier of the smallest cell having the strongest search signal and a CQI determined based on the search signal.

The 4-bit CQI value included in the CQI report transmitted by the UE can indicate the MCS level. Based on the link level simulation results, the CQI value may also reflect the SINR level. The modulation method, the coding rate, and the SINR according to the CQI index can be as shown in Table 12 below.

<Table 12>

In another embodiment of the present invention, the CQI information may be transmitted in a different manner in order to reduce the overhead of the UE performing the feedback. The UE can transmit the CQI based on the search signals of the upper 3 small cells having strong search signals and the difference value calculated based on the CQI of the serving cell.

<Table 13>

The CQI difference based on the search signal may be the CQI difference between the other codewords between transmissions of Rank 2 or higher rank. The formula for obtaining the CQI difference value between the small cell in which the UE receives the search signal from the small cell and the CQI calculated in the small cell and the current serving cell of the UE can be defined as Equation 8 below.

&Quot; (8) &quot;

The CQI difference value based on the search signal can be represented by 2 bits. The difference value index can be expressed as shown in Table 14 below.

<Table 14>

Hereinafter, a method for performing RSRP / RSRQ reporting based on a search signal, rather than CQI reporting based on a search signal, will be described in the embodiment of the present invention.

The RSRP / RSRQ reporting based on the search signal may not include RI information and PMI information. However, the cell identifier information may be additionally considered as in the case of the above-described CQI reporting. The UE needs to feed back the RSRP / RSRQ values of several (e.g., three) small cells to the base station in order of stronger search signals. Table 15 below shows the feedback of the RSRP / RSRQ values of the three cells having the strongest search signal strength to the base station.

<Table 15>

Referring to Table 15, the RSRP / RSRQ value determined based on the search signal for the smallest cell having the strongest search signal strength, the smallest cell having the strongest search signal strength for the second strongest, and the smallest cell having the strongest search signal strength for the third strongest To the base station.

Similarly to the CQI reporting based on the search signal, the difference value of the RSRP / RSRQ value may be calculated to reduce the feedback overhead of the additional terminal, and information on the difference value may be transmitted to the base station as feedback information. The UE can feed back the cell identifiers of the three strong small cells and the RSRP difference value as shown in Table 16 below.

The RSRP difference value between the serving small cell and the small cell may be indicated by 2 bits or 3 bits. The difference value index can be shown in Table 16 and Table 17.

<Table 16>

<Table 17>

The formula for calculating the difference value between the report cell and the serving cell may be expressed by Equation (9) below.

&Quot; (9) &quot;

According to another embodiment of the present invention, channel state information based on the search signal may be reported to the serving cell base station through cyclic CSI feedback as well as aperiodic CSI feedback.

Reporting a measurement report based on a search signal through a periodic CSI report can be performed by a plurality of periodic CSI processes. If a plurality of periodic CSI processes in transmission mode 10 are set by periodic CSI feedback, one special CSI process may be set up to periodically transmit a measurement report based on the search signal to the base station of the serving cell. If the periodic measurement report CSI process based on the search signal is set, the UE can transmit the channel state information based on the search signal to the base station based on the measurement in the specific subframe with the time interval.

In periodic CSI feedback, the maximum payload size may be limited to 11 bits. In this case, the information on the channel state based on the search signal can be reported including only the channel information for the small cell transmitting only the strongest search signal. Table 18 below is a table for reporting information on cell identifiers and RSRP differences for the cell with the strongest search signal.

<Table 18>

11 is a flowchart illustrating a method for a BS to request channel state information of a small cell to a UE according to an embodiment of the present invention.

Referring to FIG. 11, a base station of a serving cell can set up a channel state information report based on a search signal of a terminal (step S1100). Step S1100 may be performed by embodiments relating to the setting of the channel state information report disclosed in this specification.

For example, as described above, it is possible to transmit based on the identifier information for the small cell to transmit the channel status information based on the search signal from the upper layer to the terminal. In addition, the terminal may receive various settings for reporting channel state information based on the search signal. For example, the UE may be configured to transmit channel status information based on a search signal when transmitting an aperiodic CSI feedback signal. The terminal receives the search signal from the small cell, measures the channel state information of the small cell based on the search signal, and reports to the base station or the core network.

The base station of the serving cell requests aperiodic CSI feedback to the UE (step S1110).

The base station of the serving cell serving the UE may request aperiodic CSI feedback to the UE to know the channel status information of the small cell. When the base station of the serving cell requests aperiodic CSI feedback to the terminal, the terminal may transmit not only aperiodic CSI feedback but also channel state information based on the search signal to the base station.

And receives channel state information based on the search signal from the terminal (step S1120).

The BS may receive channel state information, such as CQI, RSRP, or RSRQ, which the UE determines based on the search signal. The serving cell receiving the channel status based on the search signal from the terminal may be a small cell or a macro cell serving the terminal. Step S1120 may be performed by embodiments relating to the channel status information reporting method disclosed in this specification.

On / off of the small cell is controlled based on the channel state information (step S1130).

The operation of controlling on / off of the small cell based on the channel state information may be performed by a cell operation control unit for controlling an operation for controlling on / off of cells other than the base station of the serving cell. The base station of the serving cell can measure the interference amount of the small cell and control the on / off operation of a specific small cell to set an optimum network environment. The ON state of the small cell may be expressed differently in terms of the first operation state and the OFF state of the small cell may be expressed in terms of the second operation state.

In FIG. 11, only the aperiodic CSI feedback signal is disclosed. However, according to the embodiment of the present invention, the terminal may transmit channel state information based on the search signal based on the periodic CSI feedback signal.

12 is a flowchart illustrating a method for a BS to request channel state information of a small cell to a UE according to an embodiment of the present invention.

FIG. 12 illustrates a method for a BS to request channel state information of a small cell to a UE when the UE performs random access or scheduling in response to an uplink data transmission request.

Referring to FIG. 12, a base station of a serving cell may receive a random access request or a scheduling request from a terminal (step S1200).

If the UE has uplink data to be transmitted to the Node B, the UE can receive a random access request or a scheduling request. The base station of the serving cell may allow random access of the UE or schedule resources for transmitting uplink data.

The base station of the serving cell can set a channel state information reporting method based on the search signal of the terminal (step S1210).

The subsequent procedure can be performed similarly to the above-described Fig. For example, as described above, it is possible to transmit based on the identifier information for the small cell to transmit the channel status information based on the search signal from the upper layer to the terminal.

The base station of the serving cell requests aperiodic CSI feedback to the UE (step S1220).

The base station of the serving cell serving the UE may request aperiodic CSI feedback to the UE to know the channel status information of the small cell. When the base station of the serving cell requests aperiodic CSI feedback to the terminal, the terminal may transmit not only aperiodic CSI feedback but also channel state information based on the search signal to the base station.

The base station of the serving cell receives channel state information based on the search signal from the terminal (step S1230).

The BS may receive channel state information, such as CQI, RSRP, or RSRQ, which the UE determines based on the search signal.

On / off of the small cell is controlled based on the channel state information (step S1140).

13 is a block diagram illustrating a wireless communication system according to an embodiment of the present invention.

13, a base station 1300 includes a processor 1310, a memory 1320, and a radio frequency unit (RF) unit 1330. The memory 1320 is coupled to the processor 1310 and stores various information for driving the processor 1310. [ RF section 1320 is coupled to processor 1310 for receiving a radio signal (e.g., a search signal as disclosed herein) and / or receiving a radio signal (e.g., channel state information as described herein) do. The processor 1310 implements a setting method for reporting the channel state information based on the search signal, and a method for reporting the channel state information disclosed in this specification. The operation of the base station of the serving cell in the above-described embodiment may be implemented by the processor 1310. [

The wireless device (or terminal) 1350 includes a processor 1360, a memory 1370, and an RF section 1380. The memory 1370 is coupled to the processor 1360 to store various information for driving the processor 1360. RF section 1380 is coupled to processor 1360 to receive a radio signal (e.g., a search signal as disclosed herein) or to transmit a radio signal (e.g., channel state information as described herein) . Processor 1360 implements the proposed functionality, process and / or method. The operation of the terminal in all of the embodiments disclosed herein may be implemented by processor 1360. [

In addition, a cell operation control device for controlling the operation state of the small cell as described in Figs. 1 to 12 may be implemented. The cell operation control device may be a base station of a macro cell to which the radio device 1350 is connected, a base station of a small cell, or a core network. The cell motion control device may be implemented variously. The cell operation control apparatus receives an RF signal for receiving a radio signal (for example, channel state information based on a search signal transmitted from a radio device) and transmitting a radio signal (a control signal for controlling the ON / OFF operation of the small cell) .

Further, the cell operation control device may include a processor. The processor may be configured to receive channel state information determined by the wireless device based on the search signal transmitted from the small cell, and to control the operation state of the small cell based on the channel state information. As described above, the channel state information may be a response signal of the wireless device 1350 to the aperiodic CSI feedback request signal (or periodic CSI feedback request signal) received by the wireless device. In addition to this, the processor of the cell operation control device can perform the small cell control operation described in Figs.

The processor may comprise an application-specific integrated circuit (ASIC), other chipset, logic circuitry and / or a data processing device. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage devices. The RF unit may include a baseband circuit for processing the radio signal. 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 module is stored in memory and can be executed by the processor. The memory may be internal or external to the processor and may be coupled to the processor by any of a variety of well known means.

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

Claims (16)

A method of controlling an operation state of a small cell by a cell operation control unit in a wireless communication system,
Receiving channel state information determined by the mobile station based on a search signal transmitted from the small cell; And
And controlling an operation state of the small cell based on the channel state information,
Wherein the channel state information is a response signal of the UE to an aperiodic CSI (channel state information) feedback request signal received by the UE. The method according to claim 1,
The operation state of the small cell may be,
A first operating state in which the small cell transmits the search signal, traffic data, and control data to the terminal through a downlink channel;
And a second operating state in which the small cell transmits only the search signal through the downlink channel. The method according to claim 1,
The UE receives non-periodic CSI process configuration information from an upper layer,
Wherein the UE determines the channel state information based on the search signal only for the small cell corresponding to the identifier information of the small cell included in the aperiodic CSI process setting information. The method according to claim 1,
The aperiodic CSI feedback request signal is transmitted from the serving cell serving the UE to the UE,
Wherein the search signal is at least one of a downlink channel and a downlink signal transmitted from the small cell. The method according to claim 1,
The channel state information based on the search signal includes CQI (channel quality indicator) information, reference signal received power (RSRP) information, and RSRQ (reference signal strength) information determined based on the identifier information of the small cell and the search signal transmitted by the small cell received quality information of the small cell. 6. The method of claim 5,
Wherein the terminal determines whether to transmit the channel state information according to a signal strength of the search signal. The method according to claim 6,
The CQI information is determined based on a difference between a first CQI value determined based on the search signal transmitted by the small cell and a second CQI value determined based on a downlink signal of a serving cell serving the mobile station A method for determining the operating state of a small cell. The method according to claim 6,
The RSRP information is determined based on a difference between a first RSRP value determined based on the search signal transmitted by the small cell and a second RSRP value determined based on a downlink signal of a serving cell serving the mobile station A method for determining the operating state of a small cell. A cell operation control apparatus for controlling an operation state of a small cell in a wireless communication system,
A radio frequency (RF) unit configured to transmit and receive a wireless signal; And
And a processor selectively coupled to the RF unit,
Receiving, from the terminal, channel state information determined by the terminal based on a search signal transmitted from the small cell,
Wherein the controller controls the operating state of the small cell based on the channel state information,
Wherein the channel state information is a response signal of the UE to an aperiodic CSI (channel state information) feedback request signal received by the UE. 10. The method of claim 9,
The operation state of the small cell may be,
A first operating state in which the small cell transmits the search signal, traffic data, and control data to the terminal through a downlink channel;
And a second operating state in which the small cell transmits only the search signal through the downlink channel. 10. The method of claim 9,
The UE receives non-periodic CSI process configuration information from an upper layer,
Wherein the UE determines the channel state information based on the search signal only for the small cell corresponding to the identifier information of the small cell included in the aperiodic CSI process setting information. 10. The method of claim 9,
The aperiodic CSI feedback request signal is transmitted from the serving cell serving the UE to the UE,
Wherein the search signal is at least one of a downlink channel and a downlink signal transmitted from the small cell. 10. The method of claim 9,
The channel state information based on the search signal includes CQI (channel quality indicator) information, reference signal received power (RSRP) information, and RSRQ (reference signal strength) information determined based on the identifier information of the small cell and the search signal transmitted by the small cell received quality information of the cell. 14. The method of claim 13,
Wherein the terminal determines whether to transmit the channel state information according to a signal strength of the search signal. 15. The method of claim 14,
The CQI information is determined based on a difference between a first CQI value determined based on the search signal transmitted by the small cell and a second CQI value determined based on a downlink signal of a serving cell serving the mobile station Cell operation control device. 15. The method of claim 14,
The RSRP information is determined based on a difference between a first RSRP value determined based on the search signal transmitted by the small cell and a second RSRP value determined based on a downlink signal of a serving cell serving the mobile station Cell operation control device.

Images