KR20150055383A - Apparatus and method of small cell discovery - Google Patents

Abstract

The present invention relates to a cell discovery operation method used in a terminal and a device thereof. The method is used to conduct a cell discovery operation when a small cell discovery signal which is distinct from a conventional primary synchronization signal or secondary synchronization signal (PSS/SSS) and cell specific reference signal (CRS) used for the cell discovery of a conventional system. According to the present invention, the device includes a control unit, a transmission unit, and a reception unit.

Description

[0001] Apparatus and method for small cell discovery [

The present invention proposes an efficient operation scheme for an arbitrary cell formed by an arbitrary base station / eNB / RRH / RU in a 3GPP LTE / LTE-A wireless mobile communication system. ENB / RRH / RU, which is a method of network adaptation to reduce power consumption of a base station / eNB / RRH / RU according to the number of terminals belonging to the cell or the amount of data traffic, The present invention provides a method for blocking all downlink radio signal transmission in a DTX mode and applying a dynamic cell on / off operation in a DTX mode.

In this regard, the present invention focuses on on / off of various types of small cell base stations / eNBs / RRHs / RUs formed by overlapping macro cells, but it is not necessarily limited to small cells, It is obvious that the same concept can be applied to the cell.

 The present invention relates to a method and apparatus for cell discovery of a terminal when a conventional PSS / SSS and a CRS used for cell discovery in an existing system and a small cell discovery signal are defined.

Figure 1 (A) shows the Deployment scenario of small cell.
Figure 2 (Figure B-1) shows the small cell deployment scenario.
Figure 3 (Figure B-2) shows the small cell deployment scenario # 1.
Figure 4 (Figure B-3) shows the small cell deployment scenario # 2a.
Figure 5 (Figure B-4) shows the small cell deployment scenario # 2b.
Figure 6 (Figure B-5) shows the small cell deployment scenario # 3.
7 is a mapping of downlink reference signals (normal cyclic prefix).
8 is a diagram illustrating a configuration of a base station according to another embodiment of the present invention.
9 is a diagram illustrating a configuration of a user terminal according to another embodiment of the present invention.

Hereinafter, some embodiments of the present invention 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 numerals even though they are shown in different drawings. In the following description 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 invention rather unclear.

The wireless communication system in the present invention is widely deployed to provide various communication services such as voice, packet data and the like. A wireless communication system includes a user equipment (UE) and a base station (BS, or eNB). The user terminal in this specification is a comprehensive concept of a terminal in wireless communication. It is a comprehensive concept which means a mobile station (MS), a user terminal (UT), an SS (User Equipment) (Subscriber Station), a wireless device, and the like.

A base station or a cell generally refers to a station that communicates with a user terminal and includes a Node-B, an evolved Node-B (eNB), a sector, a Site, a BTS A base transceiver system, an access point, a relay node, a remote radio head (RRH), a radio unit (RU), and a small cell.

That is, the base station or the cell in this specification is interpreted as a comprehensive meaning indicating a partial region or function covered by BSC (Base Station Controller) in CDMA, NodeB in WCDMA, eNB in LTE or sector (site) And covers various coverage areas such as megacell, macrocell, microcell, picocell, femtocell and relay node, RRH, RU, and small cell communication range.

Since the various cells listed above exist in the base station controlling each cell, the base station can be interpreted into two meanings. i) a device itself providing a megacell, a macrocell, a microcell, a picocell, a femtocell, or a small cell in relation to a wireless region, or ii) the wireless region itself. i indicate to the base station all devices that are controlled by the same entity or that interact to configure the wireless region as a collaboration. An eNB, an RRH, an antenna, an RU, an LPN, a point, a transmission / reception point, a transmission point, a reception point, and the like are exemplary embodiments of a base station according to a configuration method of a radio area. ii) may indicate to the base station the wireless region itself that is to receive or transmit signals from the perspective of the user terminal or from a neighboring base station.

Therefore, a base station is collectively referred to as a megacell, a macrocell, a microcell, a picocell, a femtocell, a small cell, an RRH, an antenna, an RU, a low power node (LPN), a point, an eNB, Quot;

Herein, the user terminal and the base station are used in a broad sense as the two transmitting and receiving subjects used to implement the technical or technical idea described in this specification, and are not limited by a specific term or word. The user terminal and the base station are used in a broad sense as two (uplink or downlink) transmitting and receiving subjects used to implement the technology or technical idea described in the present invention, and are not limited by a specific term or word. Here, an uplink (UL, or uplink) means a method of transmitting / receiving data to / from a base station by a user terminal, and a downlink (DL or downlink) .

There are no restrictions on multiple access schemes applied to wireless communication systems. Various multiple access schemes such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), OFDM-FDMA, OFDM- Can be used. An embodiment of the present invention can be applied to asynchronous wireless communication that evolves into LTE and LTE-Advanced via GSM, WCDMA, and HSPA, and synchronous wireless communication that evolves into CDMA, CDMA-2000, and UMB. The present invention should not be construed as limited to or limited to a specific wireless communication field and should be construed as including all technical fields to which the idea of the present invention can be applied.

A TDD (Time Division Duplex) scheme in which uplink and downlink transmissions are transmitted using different time periods, or an FDD (Frequency Division Duplex) scheme in which they are transmitted using different frequencies can be used.

In systems such as LTE and LTE-Advanced, the uplink and downlink are configured on the basis of one carrier or carrier pair to form a standard. The uplink and the downlink are divided into a Physical Downlink Control Channel (PDCCH), a Physical Control Format Indicator CHannel (PCFICH), a Physical Hybrid ARQ Indicator CHannel, a Physical Uplink Control CHannel (PUCCH), an Enhanced Physical Downlink Control Channel (EPDCCH) Transmits control information through the same control channel, and is configured with data channels such as PDSCH (Physical Downlink Shared CHannel) and PUSCH (Physical Uplink Shared CHannel), and transmits data.

On the other hand, control information can also be transmitted using EPDCCH (enhanced PDCCH or extended PDCCH).

In this specification, a cell refers to a component carrier having a coverage of a signal transmitted from a transmission point or a transmission point or transmission / reception point of a signal transmitted from a transmission / reception point, and a transmission / reception point itself .

The wireless communication system to which the embodiments are applied may be a coordinated multi-point transmission / reception system (CoMP system) or a coordinated multi-point transmission / reception system in which two or more transmission / reception points cooperatively transmit signals. antenna transmission system, or a cooperative multi-cell communication system. A CoMP system may include at least two multipoint transmission / reception points and terminals.

The multi-point transmission / reception point includes a base station or a macro cell (hereinafter referred to as 'eNB'), and at least one mobile station having a high transmission power or a low transmission power in a macro cell area, Lt; / RTI >

Hereinafter, a downlink refers to a communication or communication path from a multiplex transmission / reception point to a terminal, and an uplink refers to a communication or communication path from a terminal to a multiplex transmission / reception point. In the downlink, a transmitter may be a part of a multipoint transmission / reception point, and a receiver may be a part of a terminal. In the uplink, the transmitter may be a part of the terminal, and the receiver may be a part of multiple transmission / reception points.

Hereinafter, a situation in which a signal is transmitted / received through a channel such as PUCCH, PUSCH, PDCCH, EPDCCH, and PDSCH is expressed as 'PUCCH, PUSCH, PDCCH, EPDCCH and PDSCH are transmitted and received'.

In the following description, an indication that a PDCCH is transmitted or received or a signal is transmitted or received via a PDCCH may be used to mean transmitting or receiving an EPDCCH or transmitting or receiving a signal through an EPDCCH.

That is, the physical downlink control channel described below may mean a PDCCH, an EPDCCH, or a PDCCH and an EPDCCH.

Also, for convenience of description, EPDCCH, which is an embodiment of the present invention, may be applied to the portion described with PDCCH, and EPDCCH may be applied to the portion described with EPDCCH according to an embodiment of the present invention.

Meanwhile, the High Layer Signaling described below includes RRC signaling for transmitting RRC information including RRC parameters.

The eNB performs downlink transmission to the UEs. The eNB includes a physical downlink shared channel (PDSCH) as a main physical channel for unicast transmission, downlink control information such as scheduling required for reception of a PDSCH, A physical downlink control channel (PDCCH) for transmitting scheduling grant information for transmission in a Physical Uplink Shared Channel (PUSCH). Hereinafter, the transmission / reception of a signal through each channel will be described in a form in which the corresponding channel is transmitted / received.

Various techniques for applying various CoMP technologies with macro cells formed by high power eNB in 3GPP LTE / LTE-A rel-11 system and small cells formed by low power RRH connected with corresponding high power eNBs Various interference control techniques have been proposed in heterogeneous network scenarios where pico cells or micro cells overlap with macro cells to support hot spots or coverage holes. In 3GPP LTE / LTE-A rel-12, various small cell enhancement techniques are being researched.

The following describes a small cell deployment scenario to which the proposals described in the present invention can be applied.

Figure 1 (Figure A) shows the deployment scenario of small cells.

Figure A shows a general picture in the case of small cell and macro cell coexistence. In figure B below, whether there is macro coverage, whether the corresponding small cell is for outdoor or indoor, dense, whether it is the same frequency spectrum as the macro in terms of spectrum or not.

First, Figure B-1 below shows a typical representative picture for the scenario of Figure B-2 ~ 5. Explanations of each scenario are given in the preceding figure of each scenario.

Figure 2 (Figure B-1) is a small cell deployment scenario.

Scenario 1 is a co-channel deployment scenario for small cells and macro in the presence of an overlaid macro and is an outdoor small cell scenario.

Figure 3 (Figure B-2) shows Small cell deployment scenario # 1.

Scenario 2a is a deployment scenario in which small cells and macros use different frequency spectrum in the presence of an overlaid macro and is an outdoor small cell scenario.

Figure 4 (Figure B-3) shows the Small cell deployment scenario # 2a.

Scenario 2b is a deployment scenario in which small cells and macros use different frequency spectrum in the presence of overlaid macros and is an indoor small cell scenario.

Figure 5 (Figure B-4) shows the Small cell deployment scenario # 2b.

Scenario 3 is an indoor small cell scenario with no macro coverage.

Figure 6 (Figure B-5) shows the Small cell deployment scenario # 3.

In this way, when a plurality of small cells are overlapped with an arbitrary macro cell coverage, the overall system throughput is increased through the cell splitting gain. However, the interference problem between the small cell and the macro cell, which reduces the effect of the corresponding cell splitting gain, There is a disadvantage in that the system power consumption is increased through the introduction of the base station and the maintenance cost is increased. In particular, even when there is no UE connected in the corresponding small cell coverage, the small cell base station / eNB / RU / RRH continuously transmits the downlink signal including the PSS / SSS and the PBCH or CRS, / eNB / RU / RRH, as well as unnecessary interference to data transmission / reception in the adjacent cell.

In order to solve this problem, it is determined whether or not downlink signals including PSS / SSS, PBCH and CRS are transmitted in the corresponding small cell base station / eNB / RU / RRH according to the number of terminals connected to the small cell or the presence or absence of terminals Discussions are underway to support small cell on / off operations. However, the support of small cell on / off can be influenced by cell measurement procedure based on PSS / SSS and CRS.

In the heterogeneous network environment in which the macro cell and the plurality of small cells are overlapped, the number of the UEs connected to the Node B / eNB / RRH / RU, the number of the UEs connected to the UE, We propose a small cell discovery method to support / off operation.

In the existing 3GPP LTE / LTE-A rel-11 and below systems, the base station / eNB / RU / RRH that form an arbitrary cell can perform downlink channel measurement for mobility management such as handover and cell selection / reselection specific reference signal (CRS) in all downlink subframes except the MBSFN subframe according to the number of antenna ports installed in the base station as shown in Fig. However, in the downlink subframe set with the MBSFN subframe, the corresponding CRS is transmitted only through the first OFDM symbol of the first slot or the second OFDM symbol.

Figure 7 (Figure 1) is a mapping of downlink reference signals (normal cyclic prefix).

Accordingly, the UE connected to the corresponding base station receives the CRS transmitted through the corresponding downlink subframe for a predetermined time, measures the RSRP / RSRQ and reports the measured RSRP / RSRQ to the base station, and the base station, on the basis of which the downlink It is decided whether to perform the mobility management procedure of the terminal such as handover as well as scheduling. Also, since the CRS transmitted by the corresponding base station is also used for channel measurement for determination of a handover target base station according to movement of a terminal connected to a neighbor base station and channel measurement for cell selection / reselection of idle terminals, The corresponding base station has to always transmit the CRS through all the downlink subframes even if there is no terminal connected thereto.

However, as described above, when a plurality of small cells are overlapped with a macro cell, it is often the case that no terminal is connected to a corresponding small cell. In this case, Downlink signals such as PSS / SSS or PBCH may unnecessarily interfere with macro cells or adjacent small cells. In addition, unnecessary power consumption always occurs in the corresponding small cell base station / eNB / RU / RRH in order to transmit CRS through each downlink subframe.

As a method to solve this problem, a dynamic small cell on / off method of turning off a corresponding small cell when there is no terminal connected to any small cell or when there is no data traffic is discussed. In other words, off duration which does not perform the existing downlink PSS / SSS, CRS or other downlink signal and channel transmission at 1ms subframe level or 10ms radio frame level for any cell and down duration PSS / SS, CRS, etc., or when an arbitrary terminal enters the corresponding small cell coverage after repeating an arbitrary small cell according to the presence or absence of the access terminal and the data traffic, a small cell an on / off operation has been proposed. In this case, when a corresponding small cell cell is applied with a corresponding dynamic small cell on / off operation, the corresponding small cell does not transmit a CRS for downlink channel measurement in all downlink subframes, A new small cell discovery signal can be defined.

The present invention proposes a method of cell discovery of a UE when a conventional PSS / SSS and a CRS used for cell discovery in the existing system and a small cell discovery signal are defined. In particular, when a new discovery signal is defined for the corresponding small cell discovery, a small cell discovery procedure based on the new discovery signal is defined.

However, the present invention proposes a small cell discovery procedure based on the assumption of a new small cell discovery signal, which can be applied regardless of a specific discovery signal structure and design.

Point 1. UE-specific discovery signal configuration

It is possible to define discovery signal setting information for a small cell in which a cell or a base station should perform measurement for each UE in a UE-specific or cell-specific manner. That is, an arbitrary cell or a base station can set small cell measurement configuration information through UE-specific RRC signaling or cell-specific RRC signaling to UEs in the corresponding cell. The measurement configuration information includes information related to the small cell ID to be performed by the UE and discovery signal setting information transmitted by the corresponding small cell. The discovery signal setting information includes time / frequency resource allocation information for transmitting the discovery signal, subframe configuration information such as periodicity and subframe offset to which the discovery signal is transmitted, and RE (RE) s) allocation information. In addition, it includes information related to the operation mode (dynamic small cell on / off operation mode vs. normal mode) of the small cell transmitting the discovery signal or information on the current corresponding small cell state (off state vs. on state) can do.

In addition, a zero power discovery signal configuration for any terminal can be defined. Specific or cell-specific RRC signaling is used to reduce the interference of neighbor cells in time / frequency resources used for discovery signal transmission of small cell base stations supporting any small cell on / off operation. And perform a zero-power discovery signal configuration for any of the terminals.

Point 2. Cell selection / reselection procedure for new UEs

RRM / RLM measurement for cell selection / reselection based on discovery signal can be defined for rel-12 or subsequent UEs in any idle state. In this case, a cell selection / reselection procedure for establishing an RRC connection or receiving paging based on the discovery signal measurement and the existing PSS / SSS and CRS based measurement results can be newly defined. As an example of this, an arbitrary UE performs a newly defined discovery signal based measurement together with existing PSS / SSS and CRS based measurement, and performs a measurement based on a discovery signal based on a new discovery signal, The cell access or reselection is performed based on the CRS-based measurement result, and the initial access procedure for switching from the idle state to the active state (RRC connected state) is performed with the best cell according to the cell selection or the cell reselection result . However, the discovery signal-based measurement results of PSS / SSS and any small cell that does not transmit CRS in the best cell and RRC connection terminal are compared with the best cell selected based on current PSS / SSS and CRS measurement. In the latter case, the UE may report the measurement results to the corresponding cell or base station via a UE-specific RRC signaling after the initial access procedure message (eg, via msg 3 on the random access procedure) or after the connection. Or the discovery channel based measurement performed by the terminal.

8 is a diagram illustrating a configuration of a base station according to another embodiment of the present invention.

8, a base station 1000 according to another embodiment includes a controller 1010, a transmitter 1020, and a receiver 1030.

The control unit 1010 performs a cell discovery operation of the UE when the existing PSS / SSS and the CRS used for cell discovery in the existing system and the small cell discovery signal are defined. Thereby controlling the overall operation of the base station.

The transmitting unit 1020 and the receiving unit 1030 are used to transmit and receive signals, messages, and data necessary for carrying out the present invention to and from the terminal.

9 is a diagram illustrating a configuration of a user terminal according to another embodiment of the present invention.

9, a user terminal 1100 according to another embodiment of the present invention includes a receiving unit 1110, a control unit 1120, and a transmitting unit 1130.

The receiving unit 1110 receives downlink control information, data, and messages from the base station through the corresponding channel.

In addition, the controller 1120 may perform a cell discovery operation of the UE when the existing PSS / SSS and the CRS used for cell discovery in the existing system, and a small cell discovery signal, And controls the overall operation of the terminal according to the performance.

The transmitter 1130 transmits uplink control information, data, and a message to the base station through the corresponding channel.

The standard content or standard documents referred to in the above-mentioned embodiments constitute a part of this specification, for the sake of simplicity of description of the specification. Therefore, it is to be understood that the content of the above standard content and portions of the standard documents are added to or contained in the scope of the present invention.

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 (1)

A cell discovery method of a terminal when existing PSS / SSS and CRS used for cell discovery in the existing system and a small cell discovery signal are defined.

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