KR102225990B1 - METHOD AND APPARATUS TO TRANSMIT/RECEIVE DISCOVERY SIGNAL IN Wireless COMMUNICATION SYSTEMS - Google Patents

Abstract

The present invention relates to a cellular wireless communication system, and in particular, in order to operate a predetermined base station in a plurality of states such as an active state and a dormant state, a discovery signal is defined. Accordingly, the present invention relates to a method for a terminal to search for the base station (cell search), to recognize a state of the base station, to obtain time/frequency synchronization of the base station, and to measure the strength of a signal from the base station.

Description

Method and apparatus for transmitting/receiving discovery signals in wireless communication systems {METHOD AND APPARATUS TO TRANSMIT/RECEIVE DISCOVERY SIGNAL IN Wireless COMMUNICATION SYSTEMS}

The present invention relates to a cellular wireless communication system, and in particular, in order to operate a predetermined base station in a plurality of states such as an active state and a dormant state, a discovery signal is defined. Accordingly, the present invention relates to a method for a terminal to search for the base station (cell search), to recognize a state of the base station, to obtain time/frequency synchronization of the base station, and to measure the strength of a signal from the base station.

Mobile communication systems are evolving into high-speed, high-quality wireless packet data communication systems to provide data services and multimedia services, rather than initially providing voice-oriented services. Recently, 3GPP's High Speed Downlink Packet Access (HSDPA), HSUPA (High Speed Uplink Packet Access), LTE (Long Term Evolution), LTE-A (Long Term Evolution Advanced), 3GPP2's HRPD (High Rate Packet Data), and IEEE Various mobile communication standards such as 802.16 have been developed to support high-speed, high-quality wireless packet data transmission services. In particular, the LTE system is a system developed to efficiently support high-speed wireless packet data transmission, and maximizes the capacity of the wireless system by utilizing various wireless access technologies. The LTE-A system is an advanced wireless system of the LTE system and has improved data transmission capability compared to LTE.

In the LTE system, which is a representative example of a broadband wireless communication system, the downlink uses an OFDM (Orthogonal Frequency Division Multiplexing) method, and the uplink uses the SC-FDMA (Single Carrier Frequency Division Multiple Access) method. have. In the multiple access method as described above, data or control information for each user is allocated and operated so that the time-frequency resources for carrying data or control information for each user do not overlap with each other, that is, orthogonality is established. To distinguish.

1 is a diagram showing the basic structure of a time-frequency domain, which is a radio resource domain in which data or a control channel is transmitted in downlink of LTE and LTE-A systems. 1 shows a mapping relationship between a downlink physical channel and a signal in a basic structure of a radio resource region.

In FIG. 1, the horizontal axis represents the time domain and the vertical axis represents the frequency domain. The minimum transmission unit in the time domain is the OFDMA symbol 104, and N _symb ^DL (normally N _symb ^DL = 7) OFDM symbols are collected to form one slot 101. And two slots 101 are gathered to form one subframe 102 with a length of 1 ms, and 20 slots 101, that is, ten subframes 102 are gathered to form a radio frame 103 with a length of 10 ms. do. The minimum transmission unit in the frequency domain is the subcarrier 105, and the entire system transmission band 109 _{is composed of a total of N BW} subcarriers 105. N _BW has a value proportional to the system transmission bandwidth.

The basic unit of a resource in the time-frequency domain is a resource element (RE) 106 and may be defined as an OFDM symbol index and a subcarrier index. Resource Block (RB) (or Physical Resource Block; PRB) 107, 108 is N _symb ^DL consecutive OFDM symbols 104 _{in the time domain and N sc} ^RB in the frequency domain (normally N _sc ^RB = 12 ) Number of consecutive subcarriers 105. Thus, one RB (107, 108) is composed of N _symb ^DL x N _sc ^RB number of REs (106). In general, the minimum transmission unit of data or control information is an RB unit.

The downlink control channel 110 is transmitted within the first number of N OFDM symbols in the subframe 102. In general, N = {1, 2, 3}. Accordingly, the value of N varies for each subframe 102 according to the amount of control information to be transmitted to the current subframe 102. The control channel 110 includes a physical control format indicator channel (PCFICH) including an indicator indicating the N value, a physical downlink control channel (PDCCH) including uplink or downlink scheduling information, and a HARQ ACK/NACK signal. PHICH (Physical HARQ Indicator Channel) is transmitted. In addition, the downlink physical data channel PDSCH (Physical Downlink Shared Channel) 111 is transmitted during the remaining subframe period in which the downlink control channel 110 is not transmitted.

The base station transmits a reference signal (RS) for allowing the terminal to refer to measuring the downlink channel state or to refer to demodulating the PDSCH. The reference signal is also called a pilot signal. RS is a CRS (Cell-specific Reference Signal, 112) that UEs in the base station can jointly receive, and CSI-RS (Channel Status Information Reference Signal, 114) that uses relatively few resources per antenna port compared to CRS. ), a PDSCH scheduled for a predetermined terminal is divided into a DM-RS (Demodulation Reference Signal, 113) that the terminal refers to to demodulate. If the CSI-RS 114 and the DM-RS 113 are not transmitted in some or all of the resource regions to which the CSI-RS 114 and the DM-RS 113 can be mapped, they will be used for PDSCH transmission. I can.

The antenna port is a logical concept, and the CSI-RS 114 is defined for each antenna port and operated to measure a channel state for each antenna port. If the same CSI-RS 114 is transmitted from several physical antennas, the UE cannot distinguish each of the physical antennas and recognizes them as one antenna port.

The CSI-RS 114 may transmit by allocating a separate location for each base station. As described above, the allocation of time and frequency resources for CSI-RS transmission at different locations for each base station is to prevent CSI-RSs of different base stations from causing mutual interference with each other.

In the LTE and LTE-A systems, in order for the terminal to acquire the base station ID and to acquire the subframe 102 and the radio frame 103 synchronization and frequency synchronization, the base station is a PSS (Primary Synchronization Signal) and SSS (Secondary Synchronization Signal). ). The base station maps the PSS and SSS to a predetermined position in the radio frame 103 using a sequence determined respectively as the PSS and SSS, and transmits it repeatedly in units of radio frames.

2 is a diagram showing a time-frequency domain mapping structure of PSS and SSS of LTE and LTE-A systems. In FIG. 2, when the LTE and LTE-A systems use a frequency division duplex (FDD) scheme, specific mapping positions of PSS and SSS are shown.

In the time domain, the PSS is transmitted in OFDM symbols #6 (201, 203) of subframe #0 and subframe #5, respectively. In addition, the SSS is transmitted in OFDM symbols #5 (202, 204) of subframe #0 and subframe #5, respectively. In the frequency domain, PSS and SSS are mapped to 6 RBs 205 in the center of the system transmission band.

PSS and SSS are used by the terminal to continuously track the time and frequency of the cell, and in preparation for the terminal to handover to the neighboring base station, the neighboring base station is detected and measured from the PSS and SSS of the neighboring base station. It is also used for the purpose of performing.

A method of reducing the overhead of the LTE and LTE-A systems operating as described above and interference between adjacent base stations and increasing system energy efficiency at the same time has been discussed. For example, when a terminal requiring data communication does not exist within a predetermined base station radius, the corresponding base station can be operated in a dormant state. If the base station is in an idle state, some or all of the data channel, the control channel, and the RS are stopped, thereby reducing interference to an adjacent base station and reducing energy consumption of the base station. At this time, when a terminal requiring data communication occurs in the base station, the base station switches back to an active state to perform transmission and reception operations such as a general data channel, a control channel, and an RS.

In the above-described operation, there is a need for a method of efficiently notifying neighboring terminals whether a base station is in an active state or an idle state.

The present invention provides a method and apparatus for operating a base station in a plurality of states such as an active state and a dormant state.

In the present invention, by defining a discovery signal, the terminal searches for a base station (cell search), recognizes the state of the base station, acquires time/frequency synchronization of the base station, and the strength of the signal from the base station It provides a method and apparatus for measuring.

In a wireless communication system according to the present invention, a method for receiving a search signal of a terminal includes: receiving search signal setting information of a neighboring base station from a base station, detecting a search signal of the neighboring base station based on the setting information, and the detection And reporting a measurement result of the search signal to the base station.

In addition, the method for transmitting a discovery signal by a base station in a wireless communication system according to the present invention includes transmitting discovery signal setting information when entering an idle state, and transmitting the discovery signal according to the setting information, The discovery signal is characterized in that it is transmitted at intervals of m subframes within a transmission period in a period of n radio frames.

In addition, the terminal receiving the discovery signal in the wireless communication system receives the discovery signal setting information of the adjacent base station from the base station through the communication unit and the communication unit for performing data communication, and based on the setting information, the search of the adjacent base station And a control unit for controlling the communication unit to detect a signal and report a measurement result of the detected discovery signal to the base station.

In addition, the base station transmitting the discovery signal in the wireless communication system according to the present invention, when entering the communication unit performing data communication and the idle state, transmits discovery signal setting information, and transmits the discovery signal according to the setting information. And a control unit for controlling the communication unit so that the discovery signal is transmitted at intervals of m subframes within a transmission period in a period of n radio frames.

The present invention defines a discovery signal and operates a base station in a plurality of states such as an active state and a dormant state, thereby mitigating interference between base stations and increasing energy efficiency of the base station. Let it have an effect.

1 is a diagram showing a basic structure of a time-frequency domain in which data or control channels are transmitted in downlink of LTE and LTE-A systems.
2 is a diagram showing a time-frequency domain mapping structure of PSS and SSS of LTE and LTE-A systems.
3 is a diagram showing the concept of a system operation according to the present invention.
4 is a diagram showing the interaction between a terminal and a base station according to the present invention.
5 is a diagram showing a base station procedure according to the present invention.
6 is a diagram showing a terminal procedure according to the present invention.
7 is a diagram showing a discovery signal transmission time.
8 is a diagram showing a discovery signal multiplexed on a time axis.
9 is a diagram showing a CSI-RS signal configuration.
10 is a diagram showing a configuration of a multiplexed CSI-RS signal.
11 is a diagram showing a discovery signal multiplexed on a frequency axis.
12 is a diagram showing power control for a discovery signal.
13 is a diagram showing reception power of a terminal for a multiplexed discovery signal.
14 is a diagram showing power setting by discovery signal configuration.
15 is a diagram illustrating a method of classifying base station state information according to a discovery signal configuration.
16 is a diagram showing a configuration for discriminating between a PSS/SSS signal and a discovery signal.
17 is a diagram illustrating a base station apparatus according to an embodiment of the present invention.
18 is a diagram illustrating a terminal device according to an embodiment of the present invention.

Hereinafter, various embodiments of the present invention will be described in detail together with the accompanying drawings. In addition, when it is determined that detailed descriptions of known functions or configurations related to the present invention may unnecessarily obscure the subject matter of the present invention, detailed descriptions thereof will be omitted. In addition, terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of users or operators. Therefore, the definition should be made based on the contents throughout the present specification.

Hereinafter, the base station is a subject that performs resource allocation of the terminal, and may be at least one of an eNode B, an eNB, a Node B, a base station (BS), a radio access unit, a base station controller, or a node on a network. The terminal may include a user equipment (UE), a mobile station (MS), a cellular phone, a smart phone, a computer, or a multimedia system capable of performing a communication function.

And uplink (UL) refers to a radio link through which the UE transmits data or control signals to the base station, and downlink (DL) refers to a radio link through which the base station transmits data or control signals to the UE. .

Embodiments of the present invention may be applied to other communication systems having a similar technical background and/or channel type to the present invention. In addition, the embodiments of the present invention may be applied to other communication systems through some modifications without significantly departing from the scope of the present invention, as determined by a person having skilled technical knowledge. For example, in the HSPA system, the transmission/reception method according to an aspect of the embodiment of the present invention may be applied.

3 is a diagram showing the concept of a system operation according to the present invention. FIG. 3 shows an example in which pico base stations 303, 305, and 307 with relatively small coverages 304, 306, and 308 are disposed within the coverage 302 of the macro base station 301. Referring to FIG. The macro base station can transmit signals with relatively higher transmission power than the pico base station, and thus the coverage of the macro base station is relatively larger than that of the pico base station.

Since a signal to be transmitted by a terminal or a base station is less attenuated as a transmission path is shorter, a high-speed data service is possible with a relatively small transmission power, and there is a characteristic that there is less interference. Therefore, when there are multiple terminals within the coverage of a macro base station and you want to distribute data traffic to each pico base station (Case A), the throughput of the entire system is improved by operating each terminal to communicate with a nearby pico base station or macro base station. I can make it. That is, in the embodiment of FIG. 3, the terminal 312 communicates with the macro base station 301, the terminal 309 communicates with the pico base station 307, and the terminal 310 communicates with the pico base station 305, , The terminal 311 communicates with the pico base station 303.

If there are not many terminals requiring data communication within the coverage of the macro base station, and thus it is not necessary to distribute data traffic (Case B), the network according to the present invention operates the pico base stations 303, 305, 307 in an idle state. In addition, by operating the macro base station in an active state, interference between adjacent base stations can be mitigated and system energy efficiency can be increased.

In the embodiment of FIG. 3, since the macro base station has a relatively wide coverage, the macro base station maintains an active state as much as possible to support mobility of the terminal. That is, the terminal 309 communicates with the macro base station 301. In this case, the frequencies used by the macro base station and the pico base station may be the same frequency or different frequencies.

At this time, if multiple terminals within the coverage of the macro or pico base station require data communication again, it is necessary to switch to the active state for the idle base stations. That is, it is necessary to switch from Case B to Case A in FIG. 3. To this end, the terminal may search for the idle pico base stations 303, 305, and 307 and inform the macro base station to switch the base station to the active state.

In the present invention, in order for the UE to search for the idle base station and switch to the active state as described above, the idle base station may transmit a discovery signal every specific period.

4 is a diagram showing the interaction between a terminal and a base station according to the present invention. Specifically, FIG. 4 shows a series of processes in which a UE detects a discovery signal from an idle base station and handover to a corresponding base station. Currently, the terminal 401 accesses the base station 1 402 to perform communication, and the base station 2 403 is a neighboring base station of the base station 1 402 and transmits a discovery signal to support the base station discovery of the terminal 401. Assuming that.

First, in step 404, base station 2 403 notifies base station 1 402 of its own discovery signal configuration information. Discovery signal configuration information may include a transmission period of a discovery signal, a transmission time point, a bandwidth, resource mapping information, sequence information, and the like.

Base station 1 (402) notifies the discovery signal configuration information to (401) in step 405. At this time, discovery signal configuration information of other base stations other than base station 2 403 may also be reported.

Base station 2 403 transmits a discovery signal based on discovery signal configuration information (406). The terminal 401 refers to the acquired discovery signal configuration information, and detects the discovery signal transmitted by the base station 2 403 (407).

The terminal 401 acquires subframe/radio frame synchronization of the base station (or cell) from the detected discovery signal, and acquires a cell ID indicating the discovery signal transmitted from which base station (or cell) the discovery signal is.

The terminal 401 measures the reception strength of the detected discovery signal (407). In addition, the terminal 401 informs the base station 1 402 of the detection and measurement result of discovery signaling as a measurement report (408). The measurement report includes information such as cell ID and received signal strength of one or more detected discovery signals. In order to reduce unnecessary overhead of the terminal 401, the terminal may inform the base station by including information on the discovery signal in the measurement report only when the received signal strength of the discovery signal is greater than a predetermined threshold. The threshold value may be included in the discovery signal configuration information and may be notified by the base station to the terminal 401 or may be a preset fixed value.

Base station 1 (402) determines whether to handover the corresponding terminal (401) based on the measurement report of the terminal (401) (409). If the cell ID of the adjacent base station 2 403 is included in the measurement report of the terminal 401 and the received signal strength is sufficiently large, the base station 1 402 sends the terminal 401 to the base station 2 403. 2 (403) transmits a'handover preparation request' message requesting a handover (410). When base station 1 402 obtains a'handover preparation complete' message from base station 2 403 (411), base station 1 402 instructs terminal 401 to handover to base station 2 403 ( 412). The terminal 401 performs a handover to the base station 2 403 according to the handover command of the base station 1 402 (413).

5 is a diagram showing a base station procedure according to the present invention. Specifically, FIG. 5 shows a procedure of the base station in the process of FIG. 4.

In step 501, the base station acquires the discovery signal configuration information of the neighboring cell from the neighboring cell, and in step 502 notifies the UE of the discovery signal configuration information of the neighboring cell. In step 503, the base station obtains a measurement report for the discovery signal from the terminal, and determines whether to handover the terminal in step 504. If it is determined not to handover the terminal, the base station proceeds to step 503 to obtain the next measurement report of the terminal. If the base station determines to handover the UE in step 504, the base station transmits a'handover preparation request' message to a target cell to handover the UE in step 505. And, when the base station obtains a'handover preparation complete' message of the corresponding terminal from the destination cell in step 506, the base station instructs the terminal to handover to the destination cell in step 507. If the base station does not obtain the'handover preparation complete' message in step 506, it moves to step 505 and repeats the above-described handover preparation operation.

6 is a diagram showing a terminal procedure according to the present invention. Specifically, FIG. 6 shows a procedure of a terminal in the process of FIG. 4.

In step 601, the terminal acquires discovery signal configuration information of a neighboring cell from the base station. In step 602, the UE detects and measures a discover signal by referring to the acquired discovery signal configuration information of an adjacent cell. In step 603, the UE informs the base station of a measurement report for the measured discovery signal. Thereafter, in step 604, the UE determines whether a handover command has been received from the base station, and if the handover command is not received, the UE moves to step 602 and repeats the discovery detection/measurement and reporting procedure. If the UE receives the handover command in step 604, the UE performs handover to the destination cell indicated by the handover command in step 605.

In order to more efficiently perform the system operation as described above, various types of discovery signals are currently being discussed.

As an example, a PSS/SSS signal used for base station discovery and synchronization acquisition purposes in an existing LTE/LTE-A system as shown in FIG. 2 may be used as a discovery signal. That is, the idle base station may transmit the discovery signal in the same or relatively long period as the PSS/SSS transmission period by using the PSS/SSS signal in use as the discovery signal. In this case, the terminal may also receive a discovery signal based on an operation previously used to receive the PSS/SSS signal, and obtain information on idle base stations such as a corresponding base station ID and synchronization. At this time, different sequences may be used for the discovery signal of the idle base station and the PSS/SSS of the active base station to distinguish between the PSS/SSS-based discovery signal transmitted by the idle base station and the PSS/SSS transmitted by the active base station. have.

Currently, the PSS/SSS signals defined in LTE/LTE-A are transmitted using the same frequency resource region at the same location regardless of the base station. Therefore, if one or more idle base stations around the terminal transmit at the same discovery signal transmission period, or when there is more than one active base station around the terminal and a PSS/SSS signal is already being used, interference between PSS/SSS Therefore, there occurs a case in which the UE cannot properly receive the discovery signal. In particular, when a plurality of small base stations are distributed as shown in FIG. 3, a problem of interference of discovery signals of adjacent base stations may occur more frequently.

In order to solve the above problem, a method of transmitting a PSS/SSS signal-based discovery signal in different time domains may be considered. However, in this case, the UE must repeatedly perform a downlink signal reception operation in order to receive a discovery signal. In addition, when the PSS/SSS signal defined as 6RB is used as a discovery signal, the discovery signal reception performance of the UE may deteriorate. In order to improve the discovery signal reception performance of the UE, at least one PSS/SSS signal may be repeatedly received, but an additional time delay may occur when the UE detects an idle base station. The delay in the base station discovery time of the terminal increases the time it takes for the idle base station to switch to the active state, and thus the terminal and system efficiency may be degraded. Therefore, it is necessary to define a discovery signal that is more efficient than a discovery signal based on a PSS/SSS signal.

In the present invention, a discovery signal is defined for a terminal to more efficiently detect an idle base station.

7 is a diagram showing a discovery signal transmission time.

The discovery signal transmitted by the idle base station is set to be transmitted in a period 701 that is equal to or relatively long as the PSS/SSS transmission period transmitted in units of a conventional radio frame as shown in FIG. 7. As a result, the network can avoid the problem of increasing interference between adjacent cells and deteriorating energy efficiency due to unnecessary transmission of a discovery signal by an idle base station. In addition, the base station may transmit one or more discovery signals according to the period 703 in the discovery signal transmission period 702 in order to improve the discovery signal reception performance of the terminal. In this case, the UE may perform a cell search and synchronization acquisition operation by performing a discovery signal reception operation in the discovery signal transmission period 701 and the transmission period 702 of the base station.

According to the above-described embodiment of the present invention, system performance may be changed according to a discovery signal transmission period and a transmission period setting of the base station. For example, when the discovery signal transmission period of the base station is increased, the energy efficiency of the base station increases and the effect of reducing interference due to the discovery signal increases, but the time required for the mobile station to search for a cell in an idle state increases. . Conversely, when the discovery signal transmission period is reduced, energy efficiency decreases due to frequent discovery signal transmission by the base station and interference between adjacent cells increases, but the time required for cell discovery by the terminal decreases. In addition, when the discovery signal transmission period is increased, the discovery signal reception performance of the terminal is improved, but the energy efficiency of the base station is decreased and the interference of adjacent cells due to the discovery signal is increased. Conversely, when the discovery signal transmission period is reduced, the discovery signal reception performance of the terminal is degraded, but the energy efficiency of the base station is reduced and the interference problem due to the discovery signal is reduced. Accordingly, a discovery signal should be defined so as to reduce unnecessary transmission of the discovery signal by the base station, improve the discovery signal reception performance of the terminal, and minimize the time required for cell discovery and time/frequency synchronization of the terminal.

In addition, the UE should be able to perform discovery for as many cells as possible through the discovery signal. Currently, the number of small base stations existing in the macro base station area is gradually increasing. Therefore, as the number of small base stations increases, the number of idle base stations is also expected to increase. Therefore, the UE should maximize system performance by searching for as many cells as possible during the period in which the discovery signal is received.

To this end, the present invention defines several types of discovery signals. Hereinafter, the discovery signal according to the present invention will be described in more detail.

8 is a diagram showing a discovery signal multiplexed on a time axis.

As described above, in the present invention, a plurality of base stations may transmit a discovery signal using different times within the same discovery signal transmission period 802 as shown in FIG. 8. Specifically, referring to FIG. 8, in one discovery transmission period 802, the discovery signal transmission times of base stations A, base stations B, and C are divided into time axes by a constant offset 804, and base stations A, base stations B, and C May transmit a discovery signal without mutual interference.

In various embodiments, the plurality of base stations may transmit the discovery signal without mutual interference using each offset 803 within the same discovery signal transmission period 802 as the base stations B and C (807, 808). In addition, in various embodiments, the base station may transmit different discovery signals 805 and 806 in the same discovery signal transmission period in order to improve the discovery signal reception performance of the terminal, like base station A.

<First Example>

The first embodiment is a method for defining and using a CSI-RS signal used by a UE to measure channel quality from a base station as a discovery signal in an existing LTE/LTE-A system. In the following embodiment, the CSI-RS-based discovery signal is expressed as D-CSI-RS in order to distinguish the CSI-RS signal and the CSI-RS signal-based discovery signal used as described above. In addition, in the following embodiments, the discovery signal means a CSI-RS-based discovery signal (D-CSI-RS).

The CSI-RS is transmitted through at least one of the predefined CSI-RS resource regions 908 as shown in FIG. 9, and different periods and resources may be configured for each base station. 9 shows CSI-RS resource mapping corresponding to CSI-RS configuration 0 (909) when a given base station uses four CSI-RSs in a 1RB pair.

If the base stations use a CSI-RS signal multiplexed on a time axis as shown in FIG. 10, that is, when using different CSI-RS resources, interference between CSI-RS does not occur. 10 illustrates a case where two base stations use different CSI-RS configurations (1009, 1010).

9 and 10 illustrate an example in which four CSI-RS signals are used, but a different number of CSI-RS signals including 1, 2, or 8 in addition to the 4 CSI-RSs may be used. .

When a CSI-RS signal is used as a discovery signal (D-CSI-RS), an effect of interference between base stations due to a discovery signal between base stations can be minimized. In addition, it is possible to avoid interference received by a terminal in an active base station from a discovery signal by using a zero power CSI-RS (ZP-CSI-RS).

In addition, since the CSI-RS can be transmitted in the entire frequency band unlike the PSS/SSS signal, it is possible to obtain a base station discovery performance higher than the discovery signal reception performance based on the PSS/SSS signal based on the same time. Therefore, when the base station transmits the D-CSI-RS signal, the terminal can search more accurately than when the discovery signal based on the PSS/SSS signal is used during the same discovery time, so that the base station in a relatively idle state is detected more quickly. can do. In other words, when the D-CSI-RS signal is defined as described above, the idle base station can be switched to the active state faster than the PSS/SSS-based discovery signal.

Since the CSI-RS signal is different from the CSI-RS configuration used for each base station, the UE must receive information related to the CSI-RS of the corresponding base station from the base station. The base station is a CSI-RS-related information, CSI-RS resource configuration identity, number of CSI-RS ports, CSI-RS configuration, CSI-RS subframe configuration, transmission power relationship between PDSCH and CSI-RS, variables for random signal generation , quasi-co-location-related variables may be transmitted to the terminal including at least one or more.

In the case of the D-CSI-RS signal, similarly to the information related to the CSI-RS signal, it is necessary to receive some or all of the information related to the D-CSI-RS. In this case, the D-CSI-RS signal-related information may be set by reusing the same value as the CSI-RS-related information without defining an additional information variable according to the characteristics of the information, or by defining an additional variable.

For example, in the case of the transmission period of the D-CSI-RS signal, it can be set to be generally longer than the conventional CSI-RS transmission period. Accordingly, a variable such as a D-CSI-RS subframe configuration may be additionally defined for transmission of separate D-CSI-RS signal transmission period information. Alternatively, the transmission period of the D-CSI-RS signal is a value defined as a positive integer multiple (i=1, 2,...) of _{the CSI-RS periodicity (T CSI - RS) corresponding to the CSI-RS subframe configuration in use.} Can be used. That is, the D-CSI-RS periodicity may be expressed as a value such as _{T D - CSI - RS} = ixT _{CSI - SR.} In this case, the integer multiple (i) as described above may be defined in advance or may be included in D-CSI-RS-related information and transmitted to the terminal.

The D-CSI-RS signal transmission resource region can be used in the same manner as the CSI-RS signal transmission resource region. Therefore, the base station can additionally define the D-CSI-RS configuration variable and set it to the same or separate value as the CSI-RS configuration in use, or to reuse the existing CSI-RS configuration without additional variable definition. .

In addition, the information related to the D-CSI-RS may additionally include information on a frequency band (RB index) in which the D-CSI-RS discovery signal is transmitted.

If a new type of CSI-RS configuration is used for D-CSI-RS, information related to D-CSI-RS may include newly defined D-CSI-RS configuration information.

The discovery signal related information may be transmitted to the terminal through higher-layer signaling such as RRC signaling or L1 signaling, or may be transmitted to the terminal through SIB. In addition, the discovery signal related information may be defined in advance using at least one of information such as a base station identifier (cell ID), SFN, base station state, and usable frequency resource area (number of RBs) between the terminal and the base station. I can.

<Second Example>

In general, CSI-RS signals are transmitted in all frequency bands. Accordingly, the D-CSI-RS discovery signal can also be transmitted in all frequency bands. However, since the Rel-8 and Rel-9 terminals cannot know information on the periodically transmitted D-CSI-RS discovery signal, interference from the discovery signal cannot be avoided by using ZP-CSI-RS or the like. . Therefore, if the discovery signal is periodically transmitted through all frequency bands, Rel-8 and Rel-9 terminals receive interference by the discovery signal in all frequency bands. If the base station serving the Rel-8 and Rel-9 terminals knows the discovery signal related information for neighboring base stations, interference can be avoided by not scheduling the terminal as described above in the region where the discovery signal is transmitted. However, restrictions on base station operation and resource utilization are inevitable. Therefore, it is desirable to minimize the influence on existing terminals by transmitting the discovery signal in the minimum time/frequency resource domain.

In order to solve the above problem, in the second embodiment of the present invention, a D-CSI-RS discovery signal is defined to be transmitted only in a partial frequency domain.

In addition to the D-CSI-RS-related information mentioned in the first embodiment, the base station may add and transmit information on a discovery signal allocation resource region (eg, one or more RB indexes) to the terminal. Alternatively, the base station may set the discovery signal to be transmitted only in some predefined frequency domains without transmitting additional information.

When additional information on the discovery signal allocation resource region is transmitted to the UE to the base station, additional signaling overhead for transmission of the frequency domain related information is increased, and the UE is used for various frequency bands to receive one discovery signal. Since the reception operation must be performed, the complexity of the terminal may increase. Therefore, it may be efficient to transmit the discovery signal using a pre-defined band.

Referring to what is currently defined in the LTE/LTE-A standard, the LTE/LTE-A system can support a frequency band of various sizes from 1.4MHz to 20MHz. In this case, in the case of the 1.4 MHz frequency band using the smallest frequency band, the base station may use a maximum of 6 RBs. Since the discovery signal defined as described above should be usable in a system frequency band of various sizes, it is preferable that the discovery signal is set in units of at least 6 RBs to support a variable frequency band.

11 is a frame structure when a discovery signal is defined in units of C RB. At this time, C may be set to a positive integer multiple of 6RB (C=ix6, i=1, 2,...). When the discovery signal transmission in a fixed unit is defined as described above, since the terminal can perform a reception operation in units of the defined discovery signal area, the complexity of the terminal can be reduced. In addition, when a discovery signal transmission in a fixed unit is defined, the discovery signal defined as described above may be supported in all LTE/LTE-A system bands of various sizes. In addition, since the base station only needs to inform the terminal of a single frequency domain (RB index start point or end point) rather than a plurality of frequency domains, signaling overhead can be reduced.

The frequency resource related information (eg, RB index) used by the discovery signal may be delivered to the terminal through higher-layer signaling such as RRC signaling or L1 signaling, or may be delivered to the terminal through SIB. In addition, the information may be predefined between the terminal and the base station using at least one of information such as a base station identifier (cell ID), SFN, slot, base station state, and usable frequency resource area (number of RBs). .

When the discovery signal is defined in units of 6RB as described above, a plurality of base stations may transmit the discovery signal without interference by multiplexing radio resources on the frequency axis. For example, when base stations using 50RB transmit the discovery signal in units of 6RB, up to 8 base stations may transmit the discovery signal without mutual interference in different resource regions.

If a plurality of base stations use different CSI-RS configurations within one 6RB, a greater number of base stations may simultaneously transmit a discovery signal without mutual interference according to the CSI-RS configuration. In addition, as mentioned above, when different base stations transmit a discovery signal using a subframe offset in a discovery signal transmission period, more base stations can be multiplexed.

<Third Example>

The third embodiment is a power control method for improving the discovery signal reception performance of a terminal when using a frequency-multiplexed D-CSI-RS discovery signal as in the first and second embodiments.

As described above, when there are multiple idle base stations around the terminal, the terminal searches for a base station that can provide the best service to itself, and if the base station is idle, the base station quickly switches to the active state. Performance can be improved by receiving a service. Therefore, a discovery signal that enables the UE to quickly discover the base stations should be defined. That is, the discovery signal should be defined so that the UE can search for as many base stations as possible for a short time. To this end, the discovery signal may be allocated to use more resources in the time axis and the frequency axis. However, as mentioned above, in order to mitigate interference between an active base station and a terminal due to a discovery signal frequently transmitted by idle base stations and to use time/frequency resources efficiently, it is desirable to use a minimum time and frequency resource for the discovery signal. Do.

A third embodiment provides a power control method of a discovery signal for improving a discovery signal reception performance of a terminal. When a base station in an idle state transmits a discovery signal, the base station is free to use radio resources such as time, frequency, and power because there is no terminal to provide a data service. In addition, as in the second embodiment, when a discovery signal is transmitted in units of 6RB, signal transmission is not required outside the corresponding discovery signal transmission frequency domain. Accordingly, the base station can allocate higher transmission power to the frequency resource allocated for transmission of the discovery signal.

The operation related to transmission power control of the discovery signal as described above will be described with reference to FIG. 12 as follows.

12 is a diagram showing power control for a discovery signal. In FIG. 12, it is assumed that a predetermined base station operates as an idle base station without a terminal transmitting and receiving data services.

The idle base station may not transmit a data channel, a control channel, and an RS signal other than the discovery signal. Accordingly, the idle base station may allocate additional power to the discovery signal 1201.

In FIG. 12, the x-axis represents a frequency resource (RB index, 1203), and the y-axis represents the amount of transmission power 1202 for each frequency resource. When the base station transmits the discovery signal in the frequency domain 1201, the base station may transmit a power 1204 higher than the transmission power 1205 used for data channel transmission or CSI-RS transmission to the discovery signal. When the power control as described above is used, since the amount of power received by the UE to receive the discovery signal increases, the probability that the UE can correctly search for the base station through reception of the discovery signal increases. As a result, the terminal can reduce the base station discovery time than when the base station does not perform power control.

13 is a diagram showing reception power of a terminal for a multiplexed discovery signal. Specifically, FIG. 13 is a reception power of a terminal for discovery signals of idle base stations multiplexed on a frequency as in the second embodiment.

If two base stations (Cell A and Cell B) performing the idle operation transmit discovery signals (1301, 1302) using their own discovery signal transmission resource region according to the above-mentioned rule, the UE Discovery signals in A and Cell B can be received without interference. In addition, when different powers are allocated to the discovery signal for each base station, the terminal may receive the discovery signal with different received powers, such as 1305 and 1306. In FIG. 13, it is assumed that the size of the channel between the terminal and the base station A and the base station B is all 1.

The discovery signal transmission power (P _d ) used for each base station may be set to the same value as the ratio of PDSCH EPRE to CSI-RS EPRE ( _{P c)} used to inform the CSI-RS transmission power. In addition, the discovery signal transmission power used for each base station may be defined and used as a new D-CSI-RS transmission power value, such as a ratio of PDSCH EPRE to D-CSI-RS EPRE ( _{P d).} In addition, the discovery signal transmission power used for each base station is P _d (ratio of CSI-RS EPRE to D-CSI-RS EPRE), P _d (ratio of D-CSI-RS EPRE to CSI-RS EPRE), etc. It may be defined as an additional offset value for a predefined P _c.

Power-related information (eg, P _d ) used by the discovery signal may be delivered to the terminal through higher-layer signaling such as RRC signaling or L1 signaling, or may be delivered to the terminal through SIB. In addition, the information may be predefined between the terminal and the base station using at least one of information such as a base station identifier (cell ID), SFN, slot, base station state, and usable frequency resource area (number of RBs). .

The transmission power setting as described above may be applied differently according to the discovery signal configuration. For example, when a given base station transmits D-CSI-RS discovery signal type 1 (1409) as shown in FIG. 14, since only two REs are used in one OFDM symbol (1401), the average power per RE is compared. Up to about 6 times the power can be allocated to the D-CSI-RS signal. If, as in the case of D-CSI-RS discovery signal type 2 (1410), a discovery signal is transmitted, since only one RE is used in one OFDM symbol 1401, the maximum power of about 10 times the average power per RE is D- Can be allocated to the CSI-RS signal. When compared with the D-CSI-RS discovery signal type 1 (1409), energy of up to 4 times the average power per RE can be used for transmission of the discovery signal. The above method enables discovery signal transmission resource mapping and power allocation operations in various configurations including discovery signal type 3 (1411) and type 4 (1412).

<Fourth embodiment>

In the fourth embodiment, when a base station uses a D-CSI-RS discovery signal, an operation in which the terminal recognizes a state transition of the base station is related. Upon receiving the discovery signal of the idle base station, the terminal acquires synchronization using the received discovery signal, measures the channel quality of the corresponding base station, etc., and reports the measurement information to the base station connected to the terminal. At this time, the base station receiving the measurement information may switch the corresponding idle base station to the active state by using the reported information. The base station switched to the active state may stop transmission of a discovery signal or may maintain transmission of a discovery signal. The discovery signal transmitted by the active base station as described above may be a predefined PSS/SSS signal or a D-CSI-RS discovery signal defined in the present invention.

If the base station transferred to the active state stops transmitting the discovery signal, the terminal cannot recognize whether the base station has switched to the state. When the base station is switched to the active state, since the base station no longer transmits the discovery signal, the terminal cannot receive the discovery signal. In this case, the terminal cannot know whether the base station has been switched to an active state and has not received the discovery signal, or whether the base station has transmitted the discovery signal but the terminal itself has not correctly received it. Therefore, there is a need for a method of allowing the terminal to recognize the state transition of the base station as described above.

In the fourth embodiment, a description will be given of a method in which a terminal that has received a discovery signal from a base station as described above determines whether or not the base station changes state.

Method 1:

The terminal may determine whether the idle base station is in a state change by using the PSS/SSS signal transmitted by the active base station. When the base station transmitting the D-CSI-RS discovery signal in the idle state is switched to the active state, the base station may stop transmitting the D-CSI-RS discovery signal, but the PSS/SSS transmission operation must be performed. Accordingly, the terminal receiving the D-CSI-RS discovery signal can determine that the corresponding base station is active if it receives the PSS/SSS signal of the base station. If the active base station can transmit the D-CSI-RS discovery signal, the terminal simultaneously receives the D-CSI-RS and the PSS/SSS signal, or when only the PSS/SSS signal is received, the corresponding base station is activated. I can judge.

Method 2:

In order for the UE to determine whether the base station has switched state, a CSI-RS or D-CSI-RS configuration classified according to the base station state may be defined. For example, as shown in FIG. 15, when a discovery signal is transmitted according to a specific D-CSI-RS configuration 1509 or in a specific time/frequency domain 1510 or 1511, the terminal By using a combination, the state of the corresponding base station can be determined as an active state. For example, when a discovery signal is transmitted in a specific time/frequency domain 1512 in FIG. 15, the terminal may determine the state of the corresponding base station as an idle state. The D-CSI-RS configuration and time/frequency domain division as shown in FIG. 15 are only examples and may be configured in various combinations. For example, when a discovery signal is transmitted in area 1512, the terminal may be configured to determine the state of the corresponding base station as an active state.

Method 3:

The base station connecting to the terminal may directly inform the terminal whether the state of the idle base station is switched. For example, as in step 504 of FIG. 5, the terminal receiving the handover command from the base station may recognize that the base station has been switched to the active state. Alternatively, the base station notifies the time point at which the target base station (idle state base station) is switched to the active state in the handover command so that the terminal can know the time point for switching the active phase of the corresponding base station. Alternatively, the base station may inform the UE of the state information of the idle base station through higher-layer signaling such as RRC signaling or L1 signaling, or may inform the base station state information to the UE through SIB.

<Fifth Example>

As described in the second embodiment, when the discovery signal is defined in a predetermined frequency domain unit, for example, an integer multiple of 6RB or 6RB, a plurality of base stations may transmit the discovery signal without interference. For example, when base stations using 50RB transmit the discovery signal in units of 6RB, up to 8 base stations may transmit the discovery signal without mutual interference by using different resource regions. In addition, when different base stations use different CSI-RS configurations within the same 6RB, a greater number of base stations may simultaneously transmit the discovery signal according to the CSI-RS configuration. In addition, as mentioned in the above embodiment, when different base stations transmit a discovery signal using a subframe offset within a discovery signal transmission period, more base stations may be multiplexed.

If a plurality of base stations are multiplexed as described above to transmit a D-CSI-RS discovery signal, for example, when 8 base stations transmit discovery signals without interference in different frequency domains, PSS transmitted by an active base station The discovery signal may be transmitted at the same location as the /SSS signal. When the time when the active base station transmits the PSS/SSS and the time when the discovery signal transmitted by the base stations coincide, the PSS/SSS of the active base station may be affected by interference from the discovery signal. In particular, when higher power control is allocated to the discovery signal as in the above-described embodiment, the influence of interference on the PSS/SSS signal may increase.

Therefore, when transmitting a discovery signal according to a certain frequency region as described above, the base station is set not to transmit the discovery signal in the frequency region in which the PSS/SSS signal is transmitted, that is, the region corresponding to 6RB of the center band of the used frequency band. Can be. That is, the time/frequency band in which the discovery signal can be transmitted may be set to be different from the time/frequency band in which the PSS/SSS signal is transmitted. Accordingly, when the PSS/SSS signal is transmitted, transmission of the discovery signal may be restricted, or the discovery signal may be transmitted only in a region other than the frequency region in which the PSS/SSS signal is transmitted. In addition, as shown in FIG. 16, the discovery signal may be set to be transmitted only in the area 1610 except for the area 1611 in which PSS/SSS can be transmitted.

In the above case, since the PSS/SSS signal transmission region and the discovery signal transmission region are separated, the UE separately performs a reception operation for the PSS/SSS signal region and a reception operation for the discovery signal region, and thus the fourth embodiment. As described above, it is possible to recognize whether the state of a specific base station has changed. For example, a terminal receiving a PSS/SSS signal in area 1611 may recognize that the corresponding base station is active. In addition, for example, a terminal receiving a PSS/SSS signal in area 1611 and simultaneously receiving a discovery signal in area 1610 may recognize that the corresponding base station is active. In addition, for example, when a terminal that has not received a PSS/SSS signal in region 1611 receives a discovery signal in region 1610, the terminal may recognize that the corresponding base station is in an idle state.

17 is a diagram illustrating a base station apparatus according to an embodiment of the present invention. Devices not directly related to the present invention are omitted for convenience of description.

Referring to FIG. 17, the base station apparatus 1700 includes a transmission unit 1701 composed of a discovery signal block, a PSS/SSS block, a PDCCH block, a PDSCH block, a multiplexer, and a transmission RF block, and a PUCCH block, a PUSCH block, and a demultiplexer. , And a receiving unit 1703 and a control unit 1705 composed of a receiving RF block. The transmission unit 1701 and the reception unit 1703 may be collectively referred to as a communication unit, a transmission/reception unit, and an RF unit. The control unit 1705 controls the respective constituent blocks of the transmitting unit 1701 and the receiving unit 1703 to generate and obtain a promised signal, and determines whether to operate the base station 1700 in an idle state or an active state. Plays a role. If the base station 1700 is operated in an idle state, the control unit 1705 operates by minimizing signal transmission/reception operations other than the discovery signal. The discovery signal block generates a discovery signal so that it can be mapped to a predetermined time-frequency domain under the control of the controller 1705. The PSS/SSS block generates PSS/SSS under the control of the controller 1705. The PDCCH block generates a PDCCH (Physical Downlink Control Channel) by performing a process such as channel coding and modulation on downlink control information including scheduling information and the like under the control of the controller 1705. The PDSCH block generates a physical downlink shared channel (PDSCH) by performing a process such as channel coding and modulation on downlink data under the control of the controller 1705. Each Discovery signal block, PSS/SSS block, PDCCH block, Discover signal generated from PDSCH block, PSS/SSS, PDCCH, and PDSCH are multiplexed by a multiplexer and mapped to the time-frequency domain, and then signal processed in the transmitted RF block. After that, it is transmitted to the terminal. The receiving unit 1703 of the base station 1700 demultiplexes the signal received from the terminal and distributes it to a PUCCH block and a PUSCH block, respectively. The PUCCH block acquires information such as HARQ-ACK/NACK and CSI by performing a process such as demodulation and channel decoding on a PUCCH (Physical Uplink Control Channel) including UCI. The PUSCH block obtains uplink data transmitted by the terminal by performing a process such as demodulation and channel decoding on a physical uplink shared channel (PUSCH) including uplink data of the terminal. The receiving unit 1703 of the base station 1700 applies the output results of the PUCCH block and the PUSCH block to the control unit 1705 and uses them in the data transmission process.

18 shows a terminal device according to an embodiment of the present invention. Devices not directly related to the present invention are omitted for convenience of description.

Referring to FIG. 18, the UE 1800 includes a transmitter 1801 consisting of a PUCCH block, a PUSCH block, a multiplexer, and a transmission RF block, a discovery signal block, a PSS/SSS block, a PDCCH block, a PDSCH block, a demultiplexer, It is composed of a receiving unit 1803 and a control unit 1805 composed of a receiving RF block. The transmission unit 1801 and the reception unit 1803 may be collectively referred to as a communication unit, a transmission/reception unit, and an RF unit. The control unit 1805 controls a discovery signal reception operation of the terminal 1800 from the control information received from the base station, and controls each of the constituent blocks of the receiving unit 1803 and the transmitting unit 1801.

The discovery signal block in the receiving unit 1803 performs a process of acquiring a discovery signal in a time-frequency domain in which the terminal 1800 is previously promised. The PSS/SSS block performs a process in which the terminal 1800 acquires PSS/SSS in a predetermined time-frequency domain. The PDCCH block acquires downlink control information by performing a process such as demodulation and channel decoding on the PDCCH received by the terminal 1800. The PDSCH block acquires downlink data by performing a process such as demodulation and channel decoding on the PDSCH received by the terminal 1800.

The PUCCH block in the transmitter 1801 generates a PUCCH by performing a process such as channel coding and modulation for UCI including HARQ-ACK/NACK, CSI, and the like. The PUSCH block generates a PUSCH by performing a process such as channel coding and modulation on uplink data.

Each PUCCH block, PUCCH and PUSCH generated from the PUSCH block are multiplexed by the multiplexer, signal processed in the transmission RF block, and then transmitted to the base station.

On the other hand, the embodiments of the present invention disclosed in the present specification and drawings are merely provided with specific examples to easily explain the technical content of the present invention and to aid understanding of the present invention, and are not intended to limit the scope of the present invention. That is, it is apparent to those of ordinary skill in the art that other modifications based on the technical idea of the present invention can be implemented.

1700: base station 1701: transmitter
1703: receiving unit 1705: control unit
1800: terminal 1801: transmitter
1803: receiving unit 1805: control unit

Claims (20)

A method for receiving a search signal by a terminal in a wireless communication system,
Receiving search signal setting information of a second base station from a first base station;
Detecting a second discovery signal transmitted from the second base station based on the setting information;
Reporting a measurement result of the detected second discovery signal to the first base station; And
Determining whether the second base station is in an active state or an idle state based on the second discovery signal,
The second discovery signal is spaced apart from a third discovery signal transmitted from a third base station by a second offset in a second transmission period spaced apart from a first transmission period in which the first discovery signal of the first base station is transmitted and a first offset And transmitted,
The second discovery signal is transmitted in a second time-frequency domain excluding a first time-frequency domain for transmitting a Primary Synchronization Signal (PSS)/Secondary Synchronization Signal (SSS) in a time-frequency domain of the second transmission period. Become,
When the PSS/SSS of the second base station is detected in the first time-frequency domain and the second discovery signal is not detected in the second time-frequency domain, the second base station is determined to be active,
When the PSS/SSS of the second base station is not detected in the first time-frequency domain and the second discovery signal is detected in the second time-frequency domain, the second base station is determined to be in an idle state. How to receive. The method of claim 1, wherein the second search signal,
A receiving method, characterized in that the reception method is received within the second transmission period at n radio frame periods and at m subframe intervals within the second transmission period. The method of claim 1, wherein the second search signal,
A receiving method, characterized in that it is received through a resource element allocated for a channel status information reference signal (CSI-RS). The method of claim 1, wherein the second search signal,
Receiving method, characterized in that received through a predetermined frequency band of the entire transmission band. The method of claim 1, wherein the second search signal,
A receiving method, characterized in that it is received according to a preset transmission power. delete A method for transmitting a discovery signal of a second base station in a wireless communication system,
When the second base station enters the idle state, transmitting discovery signal setting information to the first base station; And
In accordance with the search signal setting information, including the step of transmitting a second search signal,
The second discovery signal is transmitted in a first transmission period in which the first discovery signal of the first base station is transmitted and a second transmission period spaced apart by a first offset,
The second search signal is transmitted by being spaced apart by a second offset from a third search signal transmitted from a third base station in the second transmission section,
The second search signal,
It is transmitted at m subframe intervals within the second transmission period in n radio frame periods,
The second discovery signal is transmitted in a second time-frequency domain excluding a first time-frequency domain for transmitting a Primary Synchronization Signal (PSS)/Secondary Synchronization Signal (SSS) in a time-frequency domain of the second transmission period. Become,
In the idle state, the second discovery signal is transmitted in the second time-frequency domain, the PSS/SSS of the second base station is not transmitted in the first time-frequency domain, and the second base station enters an active state. Then, the second search signal is not transmitted in the second time-frequency domain, and the PSS/SSS of the second base station is transmitted in the first time-frequency domain. The method of claim 7, wherein the second search signal,
A transmission method, characterized in that transmission through a resource element allocated for a channel status information reference signal (CSI-RS). The method of claim 7, wherein the second search signal,
Transmission method, characterized in that the transmission through a predetermined frequency band of the entire transmission band. The method of claim 7, wherein the second search signal,
Transmission method, characterized in that the transmission according to a preset transmission power. A terminal that receives a search signal in a wireless communication system,
A communication unit for performing data communication; And
Receives search signal setting information of a second base station from a first base station through the communication unit, detects a second search signal transmitted from the second base station based on the search signal setting information, and detects the detected second search signal And a control unit controlling the communication unit to report a measurement result of a signal to the first base station, and determining whether the second base station is in an active state or an idle state based on the second discovery signal,
The second discovery signal is spaced apart from a third discovery signal transmitted from a third base station by a second offset in a second transmission period spaced apart from a first transmission period in which the first discovery signal of the first base station is transmitted and a first offset And transmitted,
The second discovery signal is transmitted in a second time-frequency domain excluding a first time-frequency domain for transmitting a Primary Synchronization Signal (PSS)/Secondary Synchronization Signal (SSS) in a time-frequency domain of the second transmission period. Become,
When the PSS/SSS of the second base station is detected in the first time-frequency domain and the second discovery signal is not detected in the second time-frequency domain, the control unit determines the second base station as an active state. And, when the PSS/SSS of the second base station is not detected in the first time-frequency domain and the second discovery signal is detected in the second time-frequency domain, determining that the second base station is in an idle state. Terminal characterized by. The method of claim 11, wherein the second search signal,
A terminal, characterized in that the terminal is received within the second transmission period at n radio frame periods and at m subframe intervals within the second transmission period. The method of claim 11, wherein the second search signal,
A terminal, characterized in that it is received through a resource element allocated for a channel status information reference signal (CSI-RS). The method of claim 11, wherein the second search signal,
Terminal, characterized in that the reception through a predetermined frequency band of the entire transmission band. The method of claim 11, wherein the second search signal,
Terminal, characterized in that received according to a preset transmission power. delete A second base station that transmits a discovery signal in a wireless communication system,
A communication unit for performing data communication; And
When the second base station enters the idle state, and transmits discovery signal setting information to the first base station, and comprises a control unit for controlling the communication unit to transmit a second discovery signal to the terminal according to the discovery signal setting information,
The second discovery signal is transmitted in a first transmission period in which the first discovery signal of the first base station is transmitted and a second transmission period spaced apart by a first offset,
The second search signal is transmitted by being spaced apart by a second offset from a third search signal transmitted from a third base station in the second transmission section,
The second search signal,
It is transmitted at m subframe intervals within the second transmission period in n radio frame periods,
The second discovery signal is transmitted in a second time-frequency domain excluding a first time-frequency domain for transmitting a Primary Synchronization Signal (PSS)/Secondary Synchronization Signal (SSS) in a time-frequency domain of the second transmission period. Become,
The control unit transmits the second search signal in the second time-frequency domain in the idle state and does not transmit the PSS/SSS of the second base station in the first time-frequency domain, and the second base station When entering an active state, the second base station transmits the PSS/SSS of the second base station in the first time-frequency domain without transmitting the second discovery signal in the second time-frequency domain. The method of claim 17, wherein the second search signal,
A second base station, characterized in that it is transmitted through a resource element allocated for a channel status information reference signal (CSI-RS). The method of claim 17, wherein the second search signal,
The second base station, characterized in that the transmission through a predetermined frequency band of the entire transmission band. The method of claim 17, wherein the second search signal,
The second base station, characterized in that the transmission according to a preset transmission power.

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