WO2012108643A2

WO2012108643A2 - Apparatus and method for transmitting uplink signal in multiple component carrier system

Info

Publication number: WO2012108643A2
Application number: PCT/KR2012/000826
Authority: WO
Inventors: Ki Bum Kwon; Jong Nam Kim; Jae Hyun Ahn
Original assignee: Pantech Co., Ltd.
Priority date: 2011-02-09
Filing date: 2012-02-03
Publication date: 2012-08-16
Also published as: WO2012108643A3

Abstract

The present invention relates to an apparatus and method for transmitting an uplink signal in a multiple component carrier system. The present invention discloses a user equipment (UE) for transmitting a sounding reference signal (SRS) used to estimate an uplink channel, comprising a reception unit configured to receive serving cell configuration information about a serving cell to be configured in the UE and configured to receive an activation indicator to instruct activation or deactivation of the serving cell, an SRS transmission processing unit configured to trigger the transmission of the SRS in the serving cell when the activation indicator is received in an nth subframe, and a transmission unit configured to aperiodically transmit the SRS in a predefined (n+m)th subframe based on a specific criterion. According to the present invention, uplink scheduling can be precisely performed because a delay in the transmission of the ASRS is reduced.

Description

APPARATUS AND METHOD FOR TRANSMITTING UPLINK SIGNAL IN MULTIPLE COMPONENT CARRIER SYSTEM

The present invention relates to wireless communication and, more particularly, to a method and apparatus for transmitting an uplink signal in a multiple component carrier system.

In general, a wireless communication system uses one bandwidth for data transmission. For example, the 2nd generation wireless communication system uses a bandwidth of 200 KHz to 1.25 MHz, and the 3rd generation wireless communication system uses a bandwidth of 5 MHz to 10 MHz. In order to support an increasing transmission capacity, the bandwidth of the recent 3GPP LTE or 802.16m has extended to 20 MHz or higher. In order to increase the bandwidth may be considered to be indispensable so as to increase the transmission capacity, but to support a high bandwidth even when the quality of service required is low may generate great power consumption.

In order to solve the problem, there has emerged a multiple component carrier system in which a component carrier having one bandwidth and the center frequency is defined and data is transmitted or received through a plurality of component carriers using a wide band. That is, a narrow band and a wide band are supported at the same time by using one or more component carriers. For example, if one component carrier corresponds to a bandwidth of 5 MHz, a maximum 20 MHz bandwidth can be supported by using four component carriers.

The network of a wireless communication system uses several control signals in order to obtain information about an uplink or downlink channel environment. For example, a reference signal may be used. For example, In a Long Term Evolution (LTE) system, a mobile station transmits a Sounding Reference Signal (SRS) to a base station as a channel estimation reference signal to indicate an uplink channel state. The reference signal for this channel estimation, etc. may be transmitted periodically or aperiodically. If the SRS is not properly transmitted either periodically or aperiodically, a base station is unable to properly perform uplink scheduling. In a multiple component carrier system, there is a need for a method of efficiently transmitting an uplink signal.

An object of the present invention is to provide a method and apparatus for transmitting an uplink signal in a multiple component carrier system.

Another object of the present invention is to provide an apparatus and method for implicitly triggering the transmission of an aperiodic sounding reference signal by using the activation indicator of a serving cell.

Yet another object of the present invention is to provide an apparatus and method for transmitting an aperiodic sounding reference signal when there is implicit triggering.

Further yet another object of the present invention is to provide an apparatus and method for transmitting an aperiodic sounding reference signal in a predefined subframe when there is implicit triggering.

Still yet another object of the present invention is to provide an apparatus and method for transmitting a specific one of a plurality of sounding reference signals when there is implicit triggering.

In an aspect, a user equipment (UE) for transmitting a sounding reference signal (SRS) used to estimate an uplink channel is provided. The UE includes: a reception unit configured to receive serving cell configuration information about a serving cell to be configured in the UE and configured to receive an activation indicator instructing activation or deactivation of the serving cell, an SRS transmission processing unit configured to trigger the transmission of the SRS in the serving cell when the activation indicator is received in an nth subframe, and a transmission unit configured to aperiodically transmit the SRS in a predefined (n+m)th subframe based on a specific criterion.

In another aspect, a method of transmitting a sounding reference signal (SRS) used to estimate an uplink channel performed by a user equipment (UE), is provided. The method includes: receiving serving cell configuration information about a serving cell to be configured in the UE, receiving an activation indicator to instruct activation or deactivation of the serving cell, triggering transmission of the SRS in the serving cell when the activation indicator is received in an nth subframe, and aperiodically transmitting the SRS in a predefined (n+m)th subframe based on a specific criterion.

In yet another aspect, a base station (BS) for receiving a sounding reference signal (SRS) used to estimate an uplink channel is provided. The BS includes: an information generation unit configured to generate serving cell configuration information about a serving cell to be configured in a user equipment (UE) and an activation indicator to instruct activation or deactivation of the serving cell, a transmission unit configured to transmit at least one of the serving cell configuration information and the activation indicator to the UE in an nth subframe, a reception unit configured to receive the SRS from the UE in a predefined (n+m)th subframe in response to the activation indicator, and a scheduling unit configured to perform uplink scheduling for the UE by using the SRS.

In still yet another aspect, a method of receiving a sounding reference signal (SRS) used to estimate an uplink channel performed by a base station (BS) is provided. The method includes: transmitting an activation indicator, instructing a serving cell configured in a user equipment (UE) to be activated or deactivated, to the UE in an nth subframe, receiving the SRS from the UE in a predefined (n+m)th subframe in response to the activation indicator, and performing uplink scheduling for the UE in response to the SRS.

According to the present invention, additional signaling overhead necessary to trigger the transmission of an ASRS can be reduced because a subframe in which the ASRS is transmitted is previously agreed between a UE and a BS by using implicit triggering. Furthermore, uplink scheduling can be precisely performed because a delay in the transmission of the ASRS is reduced.

The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:

FIG. 1 is shows a wireless communication system;

FIG. 2 is an explanatory diagram illustrating an intra-band contiguous carrier aggregation;

FIG. 3 is an explanatory diagram illustrating an intra-band non-contiguous carrier aggregation;

FIG. 4 is an explanatory diagram illustrating an inter-band carrier aggregation;

FIG. 5 shows a linkage between a downlink component carrier and an uplink component carrier in a multiple carrier system;

FIG. 6 is an explanatory diagram illustrating the concept of a serving cell and neighbor cells;

FIG. 7 is an explanatory diagram illustrating the concept of a primary serving cell and a secondary serving cell;

FIG. 8 shows an example in which the transmission of a Periodic Sounding Reference Signal (PSRS) is triggered according to the present invention;

FIG. 9a shows an example in which the transmission of an Aperiodic Sounding Reference Signal (ASRS) is triggered according to the present invention;

FIG. 9b shows another example in which the transmission of an ASRS is triggered according to the present invention;

FIG. 10 is a flowchart illustrating a method of transmitting an SRS according to an embodiment of the present invention;

FIG. 11 is a flowchart illustrating a method of a mobile station transmitting an SRS according to an embodiment of the present invention;

FIG. 12 is a flowchart illustrating a method of a base station receiving an SRS according to an embodiment of the present invention;

FIG. 13 is a block diagram showing a mobile station and a base station according to an embodiment of the present invention; and

FIG. 14 shows multiple Timing Alignment Groups (TAGs) configured for a mobile station according to an embodiment of the present invention.

Some embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is to be noted that in assigning reference numerals to respective elements in the drawings, the same reference numerals designate the same elements although they are shown in different drawings. Furthermore, in describing the embodiments of the present invention, a detailed description of known constructions or functions will be omitted if it is deemed to make the gist of the present invention unnecessarily vague.

Furthermore, in this specification, a communication network is chiefly described. However, tasks performed in the communication network may be performed in a process in which a system (e.g., a base station) managing the communication network controls the communication network and sends data or may be performed in a mobile station connected to the communication network.

FIG. 1 shows a wireless communication system. The wireless communication systems are widely deployed in order to provide a variety of communication services, such as voice and packet data. Meanwhile, multiple access schemes applied to the wireless communication systems are not limited. A variety of 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), Single Carrier- FDMA (SC-FDMA), OFDM-FDMA, OFDM-TDMA, and OFDM-CDMA, may be used.

Referring to FIG. 1, the wireless communication systems 10 are widely deployed in order to provide a variety of communication services, such as voice and packet data. The wireless communication system 10 includes one or more Base Stations (BS) 11. The BS 11 commonly refers to a station communicating with user equipments (UEs) 12, and it may also be called another terminology, such as an evolved NodeB (eNB), a BTS (Base Transceiver System), or an access point. The BSs 11 provide communication services through respective areas (commonly called cells) 15a, 15b, and 15c. The cell should be interpreted as a comprehensive meaning indicating some areas covered by the BS 11. The cell has a meaning to cover all various coverage areas, such as a mega cell, a macro cell, a micro cell, a pico cell, and a femto cell. The cell may be divided into a plurality of areas (called sectors).

The UE 12 may be fixed or mobile and may also be called another terminology, such as mobile station (MS), an mobile terminal (MT), a user terminal (UT), an subscriber station (SS), a wireless device, a personal digital assistant (PDA), a wireless modem, or a handheld device.

Hereinafter, downlink (DL) refers to communication from the BS 11 to the UE 12, and uplink (UL) refers to communication from the UE 12 to the BS 11. In downlink, a transmitter may be part of the BS 11, and a receiver may be part of the UE 12. In uplink, a transmitter may be part of the UE 12, and a receiver may be part of the BS 11. In uplink transmission and downlink transmission, a Time Division Duplex (TDD) scheme in which transmission and reception are performed at different points of time may be used or a Frequency Division Duplex (FDD) scheme in which transmission and reception are performed using different frequencies may be used.

The layers of a radio interface protocol between a mobile station and a network may be classified into a first layer L1, a second layer L2, and a third layer L3 on the basis of three lower layers of an Open System Interconnection (OSI) which has been widely known in the communication systems.

A physical layer (i.e., the first layer) is connected to a higher Medium Access Control (MAC) layer through a transport channel. Data between the MAC layer and the physical layer is moved through the transport channel. Furthermore, data between different physical layer (i.e., the physical layers on the transmission side and on the reception side) is moved through a physical channel. There are some control channels used in the physical layer.

A Physical Downlink Control Channel (PDCCH) through which physical control information is transmitted informs a mobile station of the resource allocation of a paging channel (PCH) and a downlink shared channel (DL-SCH) and of Hybrid Automatic Repeat Request (HARQ) information related to the DL-SCH. The PDCCH may carry an uplink grant, informing a mobile station of the resource allocation of uplink transmission. A Physical Control Format Indicator Channel (PCFICH) is used to inform a mobile station of the number of OFDM symbols used in the PDCCHs and is transmitted for every frame. A Physical Hybrid ARQ Indicator Channel (PHICH) carries HARQ ACK/NAK signals in response to uplink transmission. A Physical Uplink Control Channel (PUCCH) carries the HARQ ACK/NAK signals for downlink transmission, a scheduling request, and uplink control information, such as Channel Quality Information (CQI). A Physical Uplink Shared Channel (PUSCH) carries an uplink shared channel (UL-SCH).

A radio data link layer (i.e., the second layer) includes an MAC layer, an RLC layer, and a Packet Data Convergence Protocol (PDCP) layer. The MAC layer is a layer responsible for mapping between a logical channel and a transport channel. The MAC layer selects a proper transport channel suitable for sending data received from the RLC layer and adds necessary control information to the header of an MAC Protocol Data Unit (PDU).

A Radio Resource Control (RRC) layer (i.e., the third layer) controls a lower layer and also exchanges pieces of radio resource control information between a mobile station and a network. A variety of RRC states, such as an idle mode and an RRC connected mode, are defined according to the communication state of a mobile station. A mobile station may transfer between the RRC states, if necessary. Various procedures related to the management of radio resources, such as system information broadcasting, an RRC access management procedure, a multiple component carrier configuration procedure, a configuration procedure related to the transmission of a Sounding Reference Signal (SRS), a radio bearer control procedure, a security procedure, a measurement procedure, and a mobility management procedure (handover), are defined in the RRC layer.

A Carrier Aggregation (CA) supports a plurality of carriers. The CA is also called a spectrum aggregation or a bandwidth aggregation. An individual unit carrier aggregated by the carrier aggregation is called a Component Carrier (CC). Each CC is defined by the bandwidth and the center frequency. The CA is introduced to support an increased throughput, prevent an increase of the costs due to the introduction of wideband RF (radio frequency) devices, and guarantee compatibility with the existing system. For example, if five CCs are allocated as the granularity of a carrier unit having a 5 MHz bandwidth, a maximum bandwidth of 20 MHz can be supported.

The carrier aggregation may be classified into an intra-band contiguous carrier aggregation, such as that shown in FIG. 2, an intra-band non-contiguous carrier aggregation, such as that shown in FIG. 3, and an inter-band carrier aggregation, such as that shown in FIG. 4.

First, referring to FIG. 2, the intra-band contiguous carrier aggregation is formed between continuous CCs in the same band. For example, aggregated CCs, that is, a CC#1, a CC#2, a CC#3 to a CC #N are contiguous to each other.

Referring to FIG. 3, the intra-band non-contiguous carrier aggregation is formed between discontinuous CCs. For example, aggregated CCs, that is, a CC#1 and a CC#2 are spaced apart from each other by a specific frequency.

Referring to FIG. 4, the inter-band carrier aggregation is of a type in which, if a plurality of CCs exists, one or more of the CCs are aggregated on different frequency bands. For example, an aggregated CC, that is, a CC #1 exists in a band #1, and an aggregated CC, that is, a CC #2 exists in a band #2.

The number of carriers aggregated in downlink and the number of carriers aggregated in uplink may be differently set. A case where the number of DL CCs is identical with the number of UL CCs is called a symmetric aggregation, and a case where the number of DL CCs is different from the number of UL CCs is called an asymmetric aggregation.

Furthermore, CCs may have different sizes (i.e., bandwidths). For example, assuming that 5 CCs are used to configure a 70 MHz band, the configuration of the 70 MHz band may be a 5 MHz CC (carrier #0) + a 20 MHz CC (carrier #1) + a 20 MHz CC (carrier #2) + a 20 MHz CC (carrier #3) + a 5 MHz CC (carrier #4).

A multiple carrier system hereinafter refers to a system supporting the carrier aggregation. In the multiple carrier system, the contiguous carrier aggregation or the non-contiguous carrier aggregation or both may be used. Furthermore, either the symmetric aggregation or the asymmetric aggregation may be used.

FIG. 5 shows a linkage between a DownLink Component Carrier (DL CC) and an UpLink Component Carrier (UL CC) in a multiple carrier system.

Referring to FIG. 5, in downlink, Downlink Component Carriers (hereinafter referred to as ‘DL CC’) D1, D2, and D3 are aggregated. In uplink, Uplink Component Carriers (hereinafter referred to as ‘UL CC’) U1, U2, and U3 are aggregated. Here, Di is the index of a DL CC, and Ui is the index of a UL CC (where i=1, 2, 3).

In an FDD system, a DL CC and a UL CC are linked to each other in a one-to-one manner. Each of pairs of D1 and U1, D2 and U2, and D3 and U3 is linked to each other in a one-to-one manner. A mobile station sets up pieces of linkage between the DL CCs and the UL CCs on the basis of system information transmitted on a logical channel BCCH or a UE-dedicated RRC message transmitted on a DCCH. Each of the pieces of linkage may be set up in a cell-specific way or a UE-specific way.

Examples of an UL CC linked to a DL CC are as follows.

1) A UL CC through which a UE will transmit ACK/NACK information with respect to data transmitted by a BS through a DL CC.

2) A DL CC through which a BS will transmit ACK/NACK information with respect to data transmitted by a UE through an UL CC.

3) A DL CC through which a BS will transmit a response to a Random Access Preamble (RAP), transmitted through an UL CC by a UE which starts a random access procedure, when the BS receives the RAP.

4) A UL CC to which uplink control information is applied when a BS transmits the uplink control information through a DL CC.

FIG. 5 illustrates only the 1:1 linkage between the DL CC and the UL CC, but pieces of linkage, such as 1:n or n:1, may be set up. Furthermore, the index of a CC does not coincide with the order of the CC or the position of the frequency band of the CC.

FIG. 6 is an explanatory diagram illustrating the concept of a serving cell and neighbor cells.

Referring to FIG. 6, a system frequency band is classified into a plurality of carrier frequencies. Here, the carrier frequency means the center frequency of a cell. The cell may mean downlink frequency resources and uplink frequency resources. In some embodiments, the cell may mean a combination of downlink frequency resources and optional uplink frequency resources. Furthermore, when a carrier aggregation is not taken into consideration, one cell always consists of a pair of uplink and downlink frequency resources.

A serving cell 605 refers to a cell in which service is being provided to a UE. A neighbor cell refers to a cell adjacent to the serving cell 605 geographically or one the frequency band. Neighbor cells using the same carrier frequency on the basis of the serving cell 605 are called

intra-frequency neighbor cells

600 and 610. Furthermore, neighbor cells using different carrier frequencies on the basis of the serving cell 605 are called

inter-frequency neighbor cells

615, 620, and 625. That is, both a serving cell and neighbor cells (i.e., not only cells using the same frequency as the serving cell, but also cells using a different frequency from the serving cell) may be called neighbor cells.

What a UE performs handover from the serving cell 605 to the

intra-frequency neighbor cell

600 or 610 is called intra-frequency handover. Meanwhile, what a UE performs handover from the serving cell 605 to the

inter-frequency neighbor cell

615, 620, or 625 is called inter-frequency handover.

In order for packet data to be transmitted and received through a specific cell, a UE first has to configure a specific cell or CC. The term ‘configuration’ means a state in which the reception of system information necessary for data transmission and reception for a relevant cell or CC has been completed.

For example, the configuration may include the entire process of receiving common physical layer parameters necessary for data transmission and reception, MAC layer parameters, or parameters necessary for a specific operation in the RRC layer. A configured cell or CC is in a state in which packets can be instantly transmitted and received when only signaling information, indicating that packet data can be transmitted, is received.

Meanwhile, a configured cell may exist in an activation state or a deactivation state. The reason why the state of the configured cell is divided into the activation state and the deactivation states is to allow a UE to monitor or receive a control channel (PDCCH) and a data channel (PDSCH) only in the activation state and to allow a channel quality information measurement operation in downlink in order to minimize the battery consumption of the UE.

The activation state means that a cell is transmitting or receiving traffic data and is in a ready state. In order to check resources (e.g., frequency and time) allocated thereto, the UE can monitor or receive the control channel (PDCCH) and the data channel (PDSCH) of an activated cell. Furthermore, a channel quality information measurement operation in downlink may be performed.

The deactivation state means that a cell cannot transmit or receive traffic data, but can perform measurement or transmit and receive minimal information. A UE can receive system information (SI) necessary to receive packets from a deactivated cell. However, a UE does not monitor or receive the control channel (PDCCH) and the data channel (PDSCH) of a deactivated cell in order to check resources (e.g., frequency and time) allocated thereto.

FIG. 7 is an explanatory diagram illustrating the concept of a primary serving cell and a secondary serving cell.

Referring to FIG. 7, a primary serving cell PCell 705 refers to one serving cell which provides security input and NAS mobility information in an RRC establishment or re-establishment state. At least one cell, together with the primary serving cell 705, may be configured to form a set of serving cells according to the capabilities of a UE. Here, the at least one cell is called a secondary serving cell 720.

Accordingly, a set of serving cells configured for one UE may consist of only the one primary serving cell 705 or may consist of the one primary serving cell 705 and the at least one secondary serving cell 720.

The

intra-frequency neighbor cells

700 and 710 of the primary serving cell 705 belong to the same carrier frequency, and the

intra-frequency neighbor cells

715 and 725 of the secondary serving cell 720 belong to the same carrier frequency. Furthermore, the

inter-frequency neighbor cells

730, 735, and 740 of the primary serving cell 705 and the secondary serving cell 720 belong to a different carrier frequency from the primary serving cell 705 and the secondary serving cell 720.

A DL CC corresponding to the primary serving cell 705 is called a DownLink Primary Component Carrier (DL PCC), and an UL CC corresponding to the primary serving cell 705 is called an UpLink Primary Component Carrier (UL PCC). Furthermore, in downlink, a CC corresponding to the secondary serving cell 720 is called a DownLink Secondary Component Carrier (DL SCC). In uplink, a CC corresponding to the secondary serving cell 720 is called an UpLink Secondary Component Carrier (UL SCC).

The PCC is a CC to which a UE is connected or RRC connected at the early stage, from among several CCs. The PCC is a special CC which is responsible for connection or RRC connection for signaling regarding a number of CCs and for the management of UE context information (i.e., connection information related to the UE). Furthermore, the PCC is always in the activation state, when it is connected to a UE and in an RRC connected mode.

The SCC is a CC allocated to a UE in addition to the PCC. The SCC is a carrier extended for the additional allocation of resources to a UE in addition to the PCC. The state of the SCC may be divided into the activation state and the deactivation state. The primary serving cell 705 and the secondary serving cell 720 have the following characteristics.

First, the primary serving cell 705 is used to transmit a PUCCH.

Second, the primary serving cell 705 is always activated, whereas the secondary serving cell 720 is activated or deactivated depending on specific conditions.

Third, when the primary serving cell 705 experiences a Radio Link Failure (RLF), RRC re-establishment is triggered. When the secondary serving cell 720 experiences an RLF, however, RRC re-establishment is not triggered.

Fourth, the primary serving cell 705 may be changed by a change of a security key or a handover procedure accompanied by a Random Access Channel (RACH) procedure. In case of UEG4 (contention resolution), however, only a PDCCH to indicate UEG4 must be transmitted through the primary serving cell 705, and UEG4 information may be transmitted through the primary serving cell 705 or the secondary serving cell 720.

Fifth, Non-Access Stratum (NAS) information is received through the primary serving cell 705.

Sixth, in the primary serving cell 705, a DL PCC and an UL PCC are always configured in pairs.

Seventh, a different CC may be configured for the primary serving cell 705 for every UE.

Eighth, procedures, such as the reconfiguration, adding, and removal of the secondary serving cell 720, may be performed by the RRC layer. In adding the new secondary serving cell 720, RRC signaling may be used to transmit system information about a dedicated secondary serving cell.

In a multiple carrier system, one UE performs communication with a BS through a plurality of CCs or a plurality of serving cells. A plurality of serving cells configured to a UE may have different propagation delays. In this case, the UE has to apply different uplink transmission timing T to each of the serving cells. This is called Multiple Timing Alignment (MTA). If each MTA value always has a value greater than 0 (in other words, an uplink synchronization time point is earlier than a current downlink subframe synchronization position and uplink synchronization time points are different for a plurality of serving cells), the MTA value may be defined as a multiple timing advanced value. If a UE performs a random access procedure for each serving cell in order to obtain MTA values, overhead may occur in limited uplink resources, and the complexity of random access may be increased.

Accordingly, a BS or a UE reduces the system complexity by using a timing alignment group (TAG) with the same timing alignment (TA) value, wherein the TAG includes at least one serving cell using the same timing reference. For example, if a first serving cell and a second serving cell belong to the same TAG (TAG1), the same TA value is applied to the first serving cell and the second serving cell. A UE may obtain a TA value for the two serving cells in a single random access procedure. A TAG including a primary serving cell is called a primary TAG (pTAG). In some embodiments, the TAG may do not include a primary serving cell, but may include at least one secondary serving cell. In this case, the TAG is called a secondary TAG (sTAG). The initial group configuration and group reorganization of the TAG are determined by a BS, and the TAG is transmitted to a UE through RRC signaling.

A primary serving cell does not change a TAG. Furthermore, if MTA values are required, a UE must be able to support at least two TAGs. For example, a UE must be able to support a TAG divided into a pTAG including a primary serving cell and an sTAG not including a primary serving cell. Here, only one pTAG exists, and one or more sTAGs may exist if MTA values are required.

A serving BS and a UE may perform the following operation in order to obtain and maintain a TA value for each TAG.

1. The TA value of a pTAG is always obtained and maintained through a primary serving cell. Furthermore, a timing reference that is a reference for the downlink synchronization for calculating the TA value of a pTAG always becomes a DL CC within a primary serving cell.

2. In order to obtain an initial uplink TA value for a sTAG, a random access procedure reset by a BS must be used.

3. A timing reference for a sTAG is the UL CC and System Information Block 2 (SIB2)-linked DL CC of a secondary serving cell that has transmitted an RAP in the most recent random access procedure. Here, the SIB2 is one of system information blocks transmitted through a broadcasting channel. The SIB2 information is transmitted through an RRC reconfiguration procedure from a BS to a UE when a relevant secondary serving cell is configured. Uplink center frequency information is included in the SIB2, and downlink center frequency information is included in SIB1. Accordingly, an SIB2 linkage means a linkage between a DL CC and a UL CC which are configured based on the information within the SIB2 of a corresponding secondary serving cell

4. Each TAG has one timing reference and one Timing Alignment Timer (TAT). Each TAT may be configured according to a different timer expiration value. The TAT is started and restarted right after a TA value is obtained from a serving BS in order to determine the validity of the TA value obtained and applied by each TAG.

5. If the TAT of a pTAG expires, the TAT of all TAGs including the pTAG expires. Furthermore, a UE flushes the HARQ buffers of all the serving cells. Furthermore, the UE clears all the resource allocation configurations for downlink and uplink. For example, if periodic resource allocation is configured without control information which is transmitted for downlink/uplink resource allocation, such as a PDCCH, as in a Semi-Persistent Scheduling (SPS) method, the SPS configuration is flushed. Furthermore, the configuration of PUCCHs and type 0 (periodic) SRS of all the serving cells is released.

6. If only the TAT of an sTAG expires, the following procedure is performed.

A. SRS transmission through the UL CC of secondary serving cells within an sTAG is stopped.

B. A type 0 (periodic) SRS configuration is released. A type 1 (aperiodic) SRS configuration remains intact.

C. Configuration information about a CSI report remains intact.

D. HARQ buffers for the uplink of the secondary serving cells within the sTAG are flushed.

7. Although all the secondary serving cells within the sTAG have been deactivated, a UE does not stop the TAT of the relevant sTAG.

8. If the last secondary serving cell within the sTAG has been removed, that is, if any secondary serving cell within the sTAG has not been configured, the TAT within the relevant sTAG is stopped.

9. A random access procedure for the secondary serving cell may be performed when a BS transmits the indication of a PDCCH to an activated secondary serving cell. The random access procedure may be performed in a non-contention-based random access procedure or contention-based random access procedure way.

10. A PDCCH for RAR transmission may be transmitted through another serving cell other than a secondary serving cell through which the RAP has been transmitted.

11. A path attenuation reference of a pTAG may become a primary serving cell or a secondary serving cell within the pTAG. A BS may differently set up the path attenuation reference through RRC signaling every serving cell within the pTAG.

The path attenuation reference of UL CCs of each serving cell within the sTAG is each SIB2-linked DL CC.

In case of the No. 7 operation, although all the secondary serving cells within the sTAG have been deactivated, a UE does not stop the TAT of the relevant sTAG. This means that the validity of a TA value of the relevant sTAG is guaranteed through the TAT in the state in which the UE does not transmit an SRS for a specific time because of the deactivation of all the secondary serving cells within the sTAG.

The technical spirit of the present invention regarding the characteristics of the primary serving cell 705 and the secondary serving cell 720 are not necessarily limited to the above description, but may include more examples.

A DL CC may configure one serving cell. Or a DL CC and a UL CC are linked to configure one serving cell. However, the serving cell is not configured by only one UL CC.

The activation of/deactivation of a CC is equal to the concept of the activation of/deactivation of a serving cell. For example, assuming that a serving cell1 is configured by a DL CC1, the activation of the serving cell1 means the activation of the DL CC1. Assuming that a serving cell2 includes a DL CC2 and a UL CC2 that are linked, the activation of the serving cell2 means the activation of the DL CC2 and the UL CC2. Furthermore, a primary serving cell corresponds to a PCC, and the secondary serving cell corresponds to an SCC.

A UE may perform the following operations, such as those listed in Table 1 below, depending on which a serving cell is in the activation or deactivation state.

Table 1

State of Serving Cell	Deactivation	Activation
Operation of UE	If a periodic SRS is configured, the UE stops the transmission of an SRS. The UE disregards all uplink grants for an UL CC.	If a periodic SRS is configured, the UE restarts the transmission of an SRS. The UE receives an uplink grant for an UL CC.
Operation of UE	The UE does not consider UE-specific search space for an UL CC into consideration.	The UE receives a PDCCH in UE-specific search space for an UL CC.

In particular, the operations of a UE regarding the activation and deactivation of a secondary serving cell may be performed as follows.

First, if the secondary serving cell is changed from the activation state to the deactivation state, the UE may be operated as follows. First, the UE stops a deactivation timer operation for the secondary serving cell. Second, with respect to a DL CC for configuring the secondary serving cell, the UE stops the monitoring of a PDCCH for the control information transmission region of the secondary serving cell. Furthermore, the UE stops the monitoring of a control information transmission region configured to schedule a secondary serving cell deactivated in a control information transmission region within a secondary serving cell configured based on cross carrier scheduling. Third, the UE does not receive information about downlink and uplink resource allocation for the secondary serving cell. Fourth, the UE does not respond to downlink and uplink resource allocation for the secondary serving cell. Here, the term ‘respond’ may mean ACK/NACK transmission for resource allocation. Fifth, the UE does not perform downlink and uplink resource allocation for the secondary serving cell. Here, the ‘perform’ may include both a reception operation and a reaction operation. Sixth, with respect to an UL CC for configuring the secondary serving cell, the UE stops the transmission of a type 0 SRS and a type 1 SRS, the report of channel quality information, or the transmission/retransmission of a Physical Uplink Shared Channel (PUSCH). Here, the type 0 SRS is a periodic SRS, and the type 1 SRS is aperiodic SRS.

Next, if the secondary serving cell is changed from the deactivation state to the activation state, the UE starts all operations stopped in the deactivation state. Furthermore, the UE starts a deactivation timer.

A message indicating activation or deactivation about the secondary serving cell is transmitted in a MAC Control Element (CE) format. The MAC CE includes a Logical Channel ID (LCID) indicating whether a corresponding MAC CE is about the activation or deactivation of the secondary serving cell and an activation indicator. Table 2 is an example of the LCID.

Table 2

Index	LCID value
00000	CCCH
00001-01010	Identity of logical channel
01011-11000	Reserved
11001	SCell activation/deactivation
11010	Power Headroom Report
11011	C-RNTI
11100	Truncated BSR
11101	Short BSR
11110	Long BSR
11111	Padding

Referring to Table 2, if the LCID value is 11001, it means that a corresponding MAC CE is about the activation or deactivation of the secondary serving cell. The activation indicator has a bitmap form, and each bit of the activation indicator may correspond to the index of each serving cell. For example, the least significant bit may correspond to a serving cell index 0, and the most significant bit may correspond to a serving cell index 7. The least significant bit may correspond to the cell index of a primary serving cell. In this case, the least significant bit does not have the meaning of the activation indicator. If the bit of the activation indicator is 1, it means that the serving cell of a relevant index is activated. If the bit of the activation indicator is 0, it means that the serving cell of a relevant index is deactivated.

It is preferred that a primary serving cell be always activated from a viewpoint of compatibility with the existing system (e.g., LTE) and the transmission of system information. However, a secondary serving cell needs not to be always activated and may be adaptively activated deactivated depending on efficient spectrum distribution and a scheduling condition. In an LTE communication system that is one of the recent wireless communication schemes, a Demodulation Reference Signal (DMRS) and a Sounding Reference Signal (SRS) are defined in uplink. In order to perform frequency selective uplink scheduling, a BS must obtain information about an uplink frequency channel. To this end, a UE transmits a reference signal for uplink channel estimation that is a kind of a reference signal to a single BS. The channel estimation reference signal may include, for example, an SRS. The SRS has the same function as a pilot channel for an uplink channel.

Hereinafter, a method of aperiodically transmitting an uplink signal is described. A reference signal for uplink channel estimation and an SRS that is an embodiment thereof are chiefly described as embodiments of the uplink signal, but the present invention is not limited to the SRS. It is to be noted that the present invention should be interpreted as a concept including all kinds of control signals used in uplink.

The SRS must be able to transmit uplink channel information about all bands, including not only a band to be used by each UE, but a band that may be used by each UE, to a BS. That is, the SRS must be transmitted over the entire subcarrier band.

The sequence of the SRSs is generated according to Math Figure 1 below, and the generated sequence is transmitted after being subject to resource mapping.

MathFigure 1

Here, M^RS _SC=mN^RB _SC is the length of an SRS sequence, 1≤m≤N^max,UL _RB, u is a PUCCH sequence group number, v is a base sequence number, and a Cyclic Shift (CS) α=2πn^sc _SRS/8. n^sc _SRS is an integer value of one of 0 to 7 and set by a higher layer for every UE.

There are two types of methods of transmitting the SRS. The type 0 SRS is Periodic SRS (PSRS) periodically transmitted by a UE, and the type 1 SRS is Aperiodic SRS (ASRS) aperiodically transmitted by a UE. In the type 0, both the transmission of resource information for the SRS and the triggering of SRS transmission are performed through higher layer signaling, such as RRC signaling. In type 1, the transmission of resource information for the SRS is performed through higher layer signaling, such as RRC signaling, and the triggering of SRS transmission is performed through Downlink Control Information (DCI). For example, the transmission of the type 1 SRS is triggered by a DCI format for uplink, such as a format 0 or a format 4.

Parameters related to the type 1 SRS is based on an ‘SRS common configuration parameter’ which is also applied to the type 0 SRS. Here, the SRS common configuration parameter is a parameter applied to all the users within a cell in common. In other words, parameters set for only the type 0 SRS or the type 1 SRS exist independently, but parameters for the type 0 SRS and the type 1 SRS share the category of parameters defined in the SRS common configuration parameter in common.

In order to transmit an SRS, a UE must receive parameters, such as resources necessary to transmit the SRS, a point of time at which the resources are transmitted, and the duration of the transmission, from a BS and set the parameters. Information, including the parameters necessary to transmit the SRS, is called SRS configuration information. Table 3 is an example of the SRS configuration information. The SRS configuration information may be an information element generated in the RRC layer.

Table 3

Referring to Table 3, the SRS configuration information includes an SRS common configuration parameter SoundingRS-UL-ConfigCommon, a PSRS configuration parameter SoundingRS-UL-ConfigDedicated, SoundingRS-UL-ConfigDedicated-v10x0, and an ASRS configuration parameter SoundingRS-UL-ConfigDedicatedAperiodic.

The SRS common configuration parameter includes an SRS bandwidth configuration parameter srs-BandwidthConfig, an SRS subframe configuration parameter srs-SubframeConfig, an Ack/Nack-SRS simultaneous transmission parameter ackNackSRS-SimultaneousTransmission, and an SRS UpPt parameter srsMaxUpPt. The SRS bandwidth configuration parameter may set an SRS bandwidth, for example, as in Table 4.

Table 4

SRS bandwidth configuration C_SRS	SRS-bandwidthB_SRS=0		SRS-bandwidthB_SRS=1		SRS-bandwidthB_SRS=2		SRS-bandwidthB_SRS=3
	m_SRS,0	N₀	m_SRS,1	N₁	m_SRS,2	N₂	m_SRS,3	N₃
0	36	1	12	3	4	3	4	1
1	32	1	16	2	8	2	4	2
2	24	1	4	6	4	1	4	1
3	20	1	4	5	4	1	4	1
4	16	1	4	4	4	1	4	1
5	12	1	4	3	4	1	4	1
6	8	1	4	2	4	1	4	1
7	4	1	4	1	4	1	4	1

Referring to Table 4, actual bandwidth configuration parameters bw0, bw1, …, bw7 based on an uplink bandwidth refer to respective

configuration index values

0, 1, …, 7. When the configuration index is determined, m_srs,b and N_b are determined based on the determined configuration index. m_srs,b is a parameter to determine the sequence length of an SRS, and N_b is a parameter to determine a frequency position index when frequency hopping of an SRS is possible.

The SRS subframe configuration parameter is information to designate a subframe on which the SRS is transmitted. Table 5 is an example of the SRS subframe configuration parameter.

Table 5

SRS Subframe Configuration Parameter	Binary Number	Configuration PeriodT_SFC (subframes)	Transmission Offset Δ_SFC (subframes)
0	0000	1	{0}
1	0001	2	{0}
2	0010	2	{1}
3	0011	5	{0}
4	0100	5	{1}
5	0101	5	{2}
6	0110	5	{3}
7	0111	5	{0,1}
8	1000	5	{2,3}
9	1001	10	{0}
10	1010	10	{1}
11	1011	10	{2}
12	1100	10	{3}
13	1101	10	{0,1,2,3,4,6,8}
14	1110	10	{0,1,2,3,4,5,6,8}
15	1111	Reserved	Reserved

Table 5 is the subframe configuration table of an SRS in an FDD system. In Table 5, each configuration srsSubframeConfiguration is defined by 4 bits, and it defines a transmission period and an offset of an actually transmitted subframe. For example, if the srsSubframeConfiguration value is 8 (1000 in a binary number), a UE transmits an SRS in second and third subframes for every 5 subframe periods.

The Ack/Nack-SRS simultaneous transmission parameter controls an ACK/NACK signal and an SRS so that they are transmitted in the same subframe. For example, if an SRS and an ACK/NACK signal or a PUCCH on which a positive Scheduling Request (SR) is transmitted in the same subframe are configured, a UE may determine an operation based on an Ack/Nack-SRS simultaneous transmission parameter value. For example, if the Ack/Nack-SRS simultaneous transmission parameter is configured as 'FALSE', the UE does not transmit the SRS and the PUCCH at the same time. For another example, if the Ack/Nack-SRS simultaneous transmission parameter is configured as 'TRUE', the UE transmits the SRS and the PUCCH at the same time. Since the Ack/Nack-SRS simultaneous transmission parameter is not applied to a secondary serving cell, the UE may regard the Ack/Nack-SRS simultaneous transmission parameter value when the secondary serving cell transmits the SRS.

The SRS UpPt parameter is a parameter that configures whether a value for UpPTS will be reconfigured in a TDD system.

Next, the ASRS configuration parameter includes an SRS bandwidth parameter srs-BandwidthAp, a frequency domain position parameter freqDomainPositionAp, an SRS hopping bandwidth parameter srs-HoppingBandwidthAp, duration, a SRS configuration index srs-ConfigIndex, transmisionComb, and a cyclic shift cyclicShift.

The SRS bandwidth parameter indicates B_SRS in Table 4. The frequency position parameter is a parameter used to obtain the index value n_b of the frequency domain which is defined when SRS frequency hopping is possible. The transmisionComb is a parameter to define an UpPTS section that belongs to a special subframe in a TDD system. The SRS configuration index is a parameter to determine the position and offset of a subframe in which an SRS is transmitted. The cyclic shift is a parameter to generate a sequence for the transmission of an ASRS.

A difference between triggering the PSRS (type 0) transmission and triggering the ASRS (type 1) transmission is described below. The PSRS is transmitted based on a predefined subframe period and offset. If a plurality of serving cells are configured in a UE, the PSRS or the ASRS may be transmitted for every serving cell. Here, parameters may be differently configured and may be identically configured for every serving cell, which is an issue of implementation. If an SRS is sought to be transmitted in a serving cell, the serving cell must be activated.

FIG. 8 shows an example in which the transmission of a PSRS is triggered according to the present invention.

Referring to FIG. 8, after there is an activation indication of a serving cell in a 3rd subframe, a serving cell is activated in a 7th subframe after k subframes (e.g., 4 subframes). Next, after there is a deactivation indication of the serving cell in a 10th subframe, the serving cell is deactivated in a 14th subframe . Meanwhile, it is assumed that a PSRS is configured to be transmitted in the fifth and the sixth subframes of each radio frame. Accordingly, the PSRS is scheduled to be transmitted in the 15th and 16th subframes which are the 5th and the 6th subframes of a second radio frame. However, a UE cannot transmit the PSRS in a serving cell because the serving cell has already been deactivated in a 14th subframe. In this case, the transmission of the SRS cannot be triggered.

FIG. 9a shows an example in which the transmission of an ASRS is triggered according to the present invention.

Referring to FIG. 9a, a UE receives an activation indicator for a serving cell in a 3rd subframe from a BS. The UE considers the reception of the activation indicator as implicit triggering for ASRS transmission. Alternatively, the UE considers activation for the serving cell as implicit triggering for ASRS transmission. Accordingly, the UE can activate the serving cell and also trigger the ASRS transmission in response to the activation indicator. Here, timing when the serving cell is activated and timing when the ASRS is transmitted may be previously defined between the UE and the BS. The UE may activate the serving cell in a predefined subframe or predefined timing and transmit the ASRS. The predefined subframe may be spaced apart from a subframe in which the activation indicator is received at a specific interval. Various embodiments may exist regarding the predefined subframe or timing.

For example, the predefined subframe for the activation of the serving cell and the predefined subframe for the transmission of the ASRS may be different. For example, the UE may activate the serving cell in a (3+k)th subframe after a lapse of k subframes from a 3rd subframe and transmit the ASRS in a (3+m)th subframe after a lapse of m subframes from the 3rd subframe (k≠m). In case of k=4 and m=8, the UE activates the serving cell in a 7th subframe and transmits the ASRS in the serving cell in an 11th subframe.

For another example, the predefined subframe for the activation of the serving cell and the predefined subframe for the transmission of the ASRS may be the same. For example, the UE may activate the serving cell and transmit the ASRS, in the (3+k)th subframe after a lapse of k subframes from the 3rd subframe. Here, k=m.

For yet another example, the UE may determine the foremost subframe in which the ASRS can be foremost transmitted as the predefined subframe and transmit the ASRS in the foremost subframe. Here, the UE checks a frequency band and sequence in which the ASRS can be transmitted. In this case, a minimum value of m may be 0, and a maximum value of m may be 10.

A BS may inform a UE of information about the predefined subframe in which the ASRS is transmitted based on implicit triggering, and the information about the predefined subframe may be previously known to both the UE and the BS. In some embodiments, the predefined subframe may be variously determined by a specific pattern, and the UE and the BS may know the specific pattern.

If the predefined subframe in which the ASRS is transmitted is previously defined between the UE and the BS based on implicit triggering, additional signaling overhead necessary to trigger to the ASRS can be reduced. Furthermore, a delay in the transmission of the ASRS can also be reduced because the ASRS can be immediately transmitted.

In FIG. 9a, it has been described that the timing (or subframe) when the ASRS is transmitted is determined based on the timing when the activation indicator is received, but this is only illustrative. For example, the timing (or subframe) when the ASRS is transmitted may be determined based on timing when the serving cell is activated. In this case, a subframe in which the ASRS is transmitted is 3+k+m, and m=4.

FIG. 9b shows another example in which the transmission of an ASRS is triggered according to the present invention. FIG. 9b shows a method in which a UE determines a predefined subframe based on position information about the subframe in which the ASRS can be transmitted.

Referring to FIG. 9b, a primary serving cell (PCell) and a secondary serving cell (SCell) are configured in a UE. The UE receives an activation indicator, indicating the activation of the secondary serving cell, through the MAC CE of the primary serving cell in an nth subframe. Thus, the transmission of an ASRS is implicitly triggered. Meanwhile, in relation to position information of a subframe regarding the secondary serving cell, a subframe in which a UE may transmit the ASRS in the secondary serving cell is defined as an (n+10)th subframe, an (n+15)th subframe, …. That is, the predefined subframe depends on position information (e.g., an SRS configuration index) of a subframe in which the ASRS may be transmitted, from among pieces of ASRS-related configuration information. The position information of the subframe regarding the secondary serving cell may be configured in a cell-specific way or in a UE-specific way.

Assuming that the time that the secondary serving cell is substantially activated from the reception of the activation indicator is eight subframes, the secondary serving cell continues in the deactivation state from an nth subframe to an (n+7)th subframe. Here, the type 0 SRS (i.e., the PSRS) cannot be transmitted. Meanwhile, the secondary serving cell is activated in an (n+8)th subframe. However, a UE can transmit the type 1 SRS (i.e., the ASRS) in an (n+10)th subframe which is the fastest timing when the UE can transmit the ASRS after the secondary serving cell is activated. This is because the UE can transmit the ASRS in the (n+10)th subframe, the (n+15)th subframe, …

Meanwhile, since the secondary serving cell has been activated, the UE can transmit the PSRS separately from the ASRS. The PSRS can be transmitted in a subframe (e.g., an (n+320)th subframe) that is determined based on SRS configuration information. As described above, the foremost subframe in which a UE can transmit an ASRS is determined based on timing when an activation indicator for a secondary serving cell is received and position information about a subframe regarding the secondary serving cell.

FIG. 10 is a flowchart illustrating a method of transmitting an SRS according to an embodiment of the present invention.

Referring to FIG. 10, a BS transmits a first message, including configuration information about a serving cell (or serving cell configuration information), to a UE at step S1000. The serving cell may be a secondary serving cell or a primary serving cell. Meanwhile, the first message may be an RRC message. In this case, the first message may be any one of an RRC connection establishment-related message for inducing initial RRC connection establishment, an RRC connection re-establishment-related message for inducting the reconfiguration of RRC establishment in a situation, such as a Radio Link Failure, and an RRC connection reconfiguration-related message for inducing the reconfiguration of RRC establishment. In some embodiments, the first message may be either a Medium Access Control (MAC) message or the message of the physical layer. From a viewpoint of a serving cell configured as a CC, configuration information about the serving cell may also be called CC configuration information. The CC configuration information is information indicating that a DL CC or an UL CC or both should be configured in a UE.

The UE completes the configuration of the serving cell based on the configuration information about the serving cell and transmits a second message, indicating that the configuration of the serving cell has been completed, to the BS at step S1005. For example, if the first message is the RRC connection reconfiguration message, the second message may be an RRC connection reconfiguration completion message. For another example, if the first message is the RRC connection re-establishment message, the second message may be an RRC connection re-establishment completion message. For yet another example, if the first message is the RRC connection establishment message, the second message may be an RRC connection establishment completion message.

The BS transmits an activation indicator, indicating the activation or deactivation of the configured serving cell, to the UE at step S1010. The activation indicator may be a control message generated in the physical layer, the MAC layer, or the RRC layer.

The UE triggers ASRS transmission in the configured serving cell at step S1015. The reception of the activation indicator corresponds to implicit triggering for the ASRS transmission. Meanwhile, if the configured serving cell needs to be changed into an activation state before the ASRS transmission is triggered, the UE may activate the configured serving cell in response to the activation indicator.

The UE checks SRS configuration information about the configured serving cell at step S1020. For example, the SRS configuration information may have a format, such as that shown in Table 4. The SRS configuration information includes configuration information which is related to the transmission of the ASRS. The SRS configuration information may be included in the first message and transmitted.

The UE transmits the ASRS in a predefined subframe of the configured serving cell at step S1025. The predefined subframe may be identical with or different from a subframe in which the configured serving cell is activated. In some embodiments, the predefined subframe may be a subframe in which the ASRS can be foremost transmitted. For example, the predefined subframe may be determined as described above with reference to FIGS. 9a and 9b.

FIG. 11 is a flowchart illustrating a method of a UE transmitting an SRS according to an embodiment of the present invention.

Referring to FIG. 11, the UE receives a first message, including configuration information about a serving cell, from a BS at step S1100. The first message may be an RRC message. In this case, the first message may be any one of an RRC connection establishment-related message for inducing initial RRC connection establishment, an RRC connection re-establishment-related message for inducting the reconfiguration of RRC establishment in a situation, such as a Radio Link Failure, and an RRC connection reconfiguration-related message for inducing the reconfiguration of RRC establishment. In some embodiments, the first message may be either a Medium Access Control (MAC) message or the message of the physical layer. From a viewpoint of a serving cell configured as a CC, configuration information about the serving cell may also be called CC configuration information. Assuming that a primary serving cell has almost been configured and activated, the configuration information about the serving cell is chiefly for configuring a secondary serving cell.

The UE completes the configuration of the serving cell based on the configuration information about the serving cell and transmits a second message, indicating that the configuration of the serving cell has been completed, to the BS at step S1105. Here, the UE may set the initial state of the serving cell whose configured has been completed as a deactivation state. The initial state of the serving cell means a state first set by the configured serving cell, from among the activation and deactivation states. The initial state may be set simultaneously when the serving cell is configured or may be set after the serving cell is configured. The initial state may also be called a default state. An expression that the initial state of the configured serving cell is set may be replaced with an expression that the configured serving cell is initialized. The initial state of the configured serving cell is any one of the activation and deactivation states. If the initial state of the configured serving cell is basically the deactivation state, a BS must transmit additional signaling related to activation to a UE in order to activate the configured serving cell.

The UE receives an activation indicator, indicating the activation or deactivation of the configured serving cell, from the BS in an nth subframe at step S1110. The activation indicator may be a control message generated in the physical layer, the MAC layer, or the RRC layer. The UE may perform the following operations depending on which the initial state of the configured serving cell is the activation state or the deactivation state. i) If the initial state is the deactivation state and the activation indicator indicates the activation of the configured serving cell, the UE starts an operation related to the activation of the configured serving cell in an (n+k)th subframe. For example, k=8. ii) If the initial state is the deactivation state and the activation indicator indicates the activation of the configured serving cell, the UE restarts the deactivation timer of the configured serving cell. iii) If the initial state is the activation state and the activation indicator indicates the deactivation of the configured serving cell, the UE stops an operation related to the activation of the configured serving cell. iv) If the initial state is the deactivation state and the activation indicator indicates the deactivation of the configured serving cell, the UE does not perform a special operation.

The UE triggers ASRS transmission in the configured serving cell at step S1115. The reception of the activation indicator corresponds to implicit triggering for ASRS transmission.

The UE checks ASRS configuration information about the configured serving cell at step S1120). For example, the UE may check an SRS bandwidth parameter, a frequency domain position parameter, an SRS hopping bandwidth parameter, duration, an SRS configuration index, transmisionComb, and a cyclic shift. The ASRS configuration information may be included in SRS configuration information, such as that shown in Table 3. The ASRS configuration information may be included in the first message and transmitted.

The UE transmits the ASRS in a predefined subframe at step S1125. The predefined subframe is determined based on position information (e.g. an SRS configuration index) about a subframe in which the ASRS can be transmitted, from among pieces of ASRS-related configuration information. After the activation indicator is received, the UE transmits the ASRS based on information about a subframe configured for the UE.

For example, it is assumed that one radio frame includes 0th to 9th subframes and subframes in which an SRS can be transmitted according to the SRS common configuration parameter are first, third, fifth, and ninth subframes.

For example, if subframes in which an ASRS allocated to a first UE can be transmitted are the first, the fifth, and the ninth subframes and a subframe (n) in which an activation indicator is received is the second subframe, the first UE can transmit the ASRS in a (2+8(the time that a serving cell is actually taken to be activated after the activation indicator is received) mod 10 (i.e., the first subframe switched to an activation state).

For another example, if subframes in which an ASRS allocated to a first UE can be transmitted are the first, the fifth, and the ninth subframes and a subframe (n) in which an activation indicator is received is the third subframe, the first UE cannot transmit the ASRS in a (3+8) mod 10 (i.e., the second subframe switched to an activation state)). Accordingly, the UE can transmit the ASRS in the fifth subframe which is the foremost, from among the subframes in which the ASRS can be transmitted.

Here, the ASRS is transmitted based on the checked SRS configuration information. The predefined subframe may be identical with or different from a subframe in which the configured serving cell is activated. In some embodiments, the predefined subframe may be a subframe in which the ASRS can be foremost transmitted after an (n+k)th subframe. For example, the predefined subframe may be an (n+k+m)th subframe. Here, a range of an m value may be 0≤m≤10.

The UE must take some cases into consideration when transmitting the ASRS in the predefined subframe. First, there is a case where the ASRS and a PSRS contend with each other. That is, there is a case in which the ASRS and the PSRS have been scheduled so that they are transmitted in the same subframe. For example, timing when the type 0 SRS (i.e., the PSRS) will be transmitted and timing when the ASRS will be transmitted may be identically set as an (n+k+m)th subframe). Here, the UE transmits the ASRS or the PSRS according to priorities. If the ASRS is precedent to the PRSR, the UE transmits only the ASRS in the (n+k+m)th subframe. If the PSRS is precedent to the ASRS, however, the UE transmits only the PSRS in the (n+k+m)th subframe. From a standpoint of a BS, there is no practical use according to the priorities because an SRS has only to be received although the SRS is the ASRS or the PSRS.

Second, there is a case in which a plurality of SRSs are transmitted on a plurality of serving cells. The plurality of SRSs may include only the ASRS, only the PSRS, or both the ASRS and the PSRS. For example, it is assumed that the transmission of a first ASRS is triggered in a first serving cell, the transmission of a second ASRS is triggered in a second serving cell, and the first ASRS and the second ASRS are scheduled to be transmitted in an (n+k+m)th subframe. In this case, a UE may simultaneously transmit the first ASRS and the second ASRS through the respective serving cells or may transmit only one ASRS selected according to a criterion for selection. For example, the criterion for selection may be great or small in the SRS transmission power. For example, the transmission of an SRS requiring greater transmission power may be selected. If power for the transmission of the first ASRS is greater than power for the transmission of the second ASRS, the UE may transmit only the first ASRS through the first serving cell, but may not transmit the second ASRS.

For another example, the criterion for selection may be a type of a serving cell. For example, the transmission of an ASRS through a primary serving cell may be selected. Accordingly, the UE may transmit only the ASRS for the primary serving cell, but may not transmit the ASRS for all the secondary serving cells.

For yet another example, the criterion for selection may be a serving cell whose state has changed from a deactivation state to an activation state. If the number of serving cells whose states have been changed is 2 or more, a primary serving cell may always have the top priority, and the remaining secondary serving cells may sequentially transmit ASRSs in order of a cell index (or a serving cell index or a secondary serving cell index).

For another example, it is assumed that the transmission of an ASRS is triggered in a first serving cell, the transmission of a PSRS is configured in a second serving cell, and the ASRS and the ASRS are scheduled to be transmitted in an (n+k+m)th subframe. In this case, a UE may simultaneously transmit the ASRS and the PSRS through respective serving cells or may give priority to the ASRS or the PSRS and transmit only one SRS selected according to the priorities. In some embodiment, the criterion for selection may be a type of a serving cell. For example, the transmission of an SRS (an ASRS or a PSRS) through a primary serving cell may be selected. Accordingly, a UE may transmit only the SRS (the ASRS or the PSRS) of the primary serving cell, but may not transmit the SRS (the ASRS or the PSRS) for all the secondary serving cells.

FIG. 12 is a flowchart illustrating a method of a BS receiving an SRS according to an embodiment of the present invention.

Referring to FIG. 12, the BS transmits a first message, including configuration information about a serving cell, to a UE at step S1200. The serving cell may be a secondary serving cell or a primary serving cell. The first message may be an RRC message. In this case, the first message may be any one of an RRC connection establishment-related message for inducing initial RRC connection establishment, an RRC connection re-establishment-related message for inducting the reconfiguration of RRC establishment in a situation, such as a Radio Link Failure, and an RRC connection reconfiguration-related message for inducing the reconfiguration of RRC establishment. In some embodiments, the first message may be either a MAC message or the message of the physical layer. From a viewpoint of a serving cell configured as a CC, configuration information about the serving cell may also be called CC configuration information. The configuration information about the serving cell is chiefly for configuring the secondary serving cell. This is because only the primary serving cell is configured when a BS first sets up Radio Resources Connection (RRC) with a UE. Accordingly, the BS transmits an RRC reconfiguration message, including configuration information about a secondary serving cell, to the UE in order to configure a plurality of serving cells in the UE. Here, the configuration information about the secondary serving cell may include a DL CC configuration information and UL CC configuration information that is optional.

The BS receives a second message from the UE at step S1205. For example, if the first message is an RRC connection reconfiguration message, the second message may be an RRC connection reconfiguration completion message. For another example, if the first message is an RRC connection re-establishment message, the second message may be an RRC connection re-establishment completion message. For yet another example, if the first message is an RRC connection establishment message, the second message may be an RRC connection establishment completion message.

The BS transmits an activation indicator, indicating the activation or deactivation of the configured serving cell, to the UE at step S1210. The activation indicator may be a control message generated in the physical layer, the MAC layer, or the RRC layer.

The BS receives an ASRS from the UE in a predefined subframe of the configured serving cell at step S1215. The predefined subframe may be identical with or different from a subframe in which the configured serving cell is activated. In some embodiments, the predefined subframe may be a subframe in which the ASRS can be foremost transmitted.

FIG. 13 is a block diagram showing a UE and a BS according to an embodiment of the present invention.

Referring to FIG. 13, the UE 1300 includes a reception unit 1305, a serving cell configuration unit 1310, an SRS transmission processing unit 1315, and a transmission unit 1320.

The reception unit 1305 receives information about a frequency band in which a first message, an activation indicator, or a repeater is installed from the BS 1350. The first message may include configuration information about a serving cell (or serving cell configuration information) and ASRS configuration information. The ASRS configuration information may be configured as in Table 3. The first message the first message may be an RRC message. In this case, the first message may be any one of an RRC connection establishment-related message for inducing initial RRC connection establishment, an RRC connection re-establishment-related message for inducting the reconfiguration of RRC establishment in a situation, such as a Radio Link Failure, and an RRC connection reconfiguration-related message for inducing the reconfiguration of RRC establishment. In some embodiments, the first message may be either a MAC message or the message of the physical layer.

Because a serving cell is configured by a CC, configuration information about the serving cell may also be called CC configuration information. The CC configuration information is chief for configuring a secondary serving cell. This is because only a primary serving cell is configured when a BS first sets up RRC with a UE. Accordingly, the BS transmits an RRC reconfiguration message, including configuration information about the secondary serving cell, to the UE in order to configure a plurality of serving cells in the UE. Here, the configuration information about the secondary serving cell may include DL CC configuration information and optional UL CC configuration information.

The activation indicator is information to indicate the activation or deactivation of a configured serving cell and may be a control message generated in the physical layer, the MAC layer, or the RRC layer.

The serving cell configuration unit 1310 configures a primary serving cell or a secondary serving cell for the UE 1300 based on the serving cell configuration information. Furthermore, when an activation indicator for a specific serving cell is received, the serving cell configuration unit 1310 activates or deactivates the specific serving cell according to the activation indicator.

When an activation indicator for a specific serving cell is received, the SRS transmission processing unit 1315 triggers ASRS transmission in the specific serving cell. When the transmission of the ASRS is triggered, the SRS transmission processing unit 1315 checks ASRS configuration information and generates an ASRS based on a frequency band and sequence in which the ASRS can be transmitted, etc. The SRS transmission processing unit 1315 controls the transmission unit 1320 so that the generated ASRS can be transmitted in a predefined subframe. To this end, the SRS transmission processing unit 1315 may store information about the predefined subframe. Various embodiments for the predefined subframe or timing may exist.

For example, for the activation of a serving cell and the transmission of an ASRS, the predefined subframe may differ. For example, the serving cell configuration unit 1310 may activate the serving cell in an (n+k)th subframe after a lapse of k subframes from an nth subframe. The SRS transmission processing unit 1315 may perform control so that the ASRS is transmitted in an (n+m)th subframe after a lapse of m subframes from the nth subframe (k≠m).

For another example, for the activation of a serving cell and the transmission of an ASRS, the predefined subframe may be the same. For example, the serving cell configuration unit 1310 may activate the serving cell in an (n+k)th subframe after a lapse of k subframes from an nth subframe. The SRS transmission processing unit 1315 may transmit the ASRS in the (n+k)th subframe (k=m).

For yet another example, the SRS transmission processing unit 1315 may determine the foremost subframe in which an ASRS can be foremost transmitted as the predefined subframe and perform control so that the ASRS is transmitted in the foremost subframe. Here, the SRS transmission processing unit 1315 checks a frequency band and sequence in which the ASRS can be transmitted. A minimum value of m may be 0, and a maximum value of m may be 10.

The BS 1350 may inform the UE 1300 of information about the predefined subframe in which the ASRS is transmitted by implicit triggering, and the information about the predefined subframe may be previously known to the UE 1300 and the BS 1350. In some embodiments, the predefined subframe may be variably determined by a specific pattern, and the UE 1300 and the BS 1350 may recognize the specific pattern.

The SRS transmission processing unit 1315 may control the transmission of an ASRS in the following cases. First, there is a case in which an ASRS and a PSRS contend with each other. For example, timing when a type 0 SRS (i.e., the PSRS) will be transmitted and timing when the ASRS will be transmitted may be identically set as an (n+k+m)th subframe. In this case, the SRS transmission processing unit 1315 selects ASRS transmission or PSRS transmission according to priorities. If the ASRS is prior to the PSRS, the SRS transmission processing unit 1315 performs control so that only the ASRS is transmitted in the (n+k+m)th subframe. If the PSRS is precedent to the ASRS, the SRS transmission processing unit 1315 performs control so that only the PSRS is transmitted in the (n+k+m)th subframe.

Second, there is a case in which a plurality of SRSs is transmitted on a plurality of serving cells. The plurality of SRSs may include only an ASRS, only a PSRS, or both the ASRS and the PSRS. For example, it is assumed that the transmission of a first ASRS is triggered in a first serving cell, the transmission of a second ASRS is triggered in a second serving cell, and the first ASRS and the second ASRS are scheduled to be transmitted in an (n+k+m)th subframe. In this case, the SRS transmission processing unit 1315 may simultaneously transmit the first ASRS and the second ASRS through the respective serving cells or may transmit only one ASRS selected according to a criterion for selection. For example, the criterion for selection may be great or small in the SRS transmission power. For example, the transmission of an SRS requiring greater transmission power may be selected. If power for the transmission of the first ASRS is greater than power for the transmission of the second ASRS, a UE may transmit only the first ASRS through the first serving cell, but may not transmit the second ASRS.

For another example, the criterion for selection may be a type of a serving cell. For example, the transmission of an ASRS through a primary serving cell may be selected. Accordingly, the SRS transmission processing unit 1315 may perform control so that only the ASRS for the primary serving cell is transmitted, but the ASRS for all the secondary serving cells is not transmitted.

For another example, it is assumed that the transmission of an ASRS is triggered in a first serving cell, the transmission of a PSRS is configured in a second serving cell, and the ASRS and the ASRS are scheduled to be transmitted in an (n+k+m)th subframe. In this case, the SRS transmission processing unit 1315 may perform control so that the ASRS and the PSRS are simultaneously transmitted through respective serving cells or priority is given to the ASRS or the PSRS and only one SRS selected according to the priorities is transmitted. In some embodiment, the criterion for selection may be a type of a serving cell. For example, the transmission of an SRS (an ASRS or a PSRS) through a primary serving cell may be selected. Accordingly, the SRS transmission processing unit 1315 may perform control so that only the SRS (the ASRS or the PSRS) of the primary serving cell is transmitted, but the SRS (the ASRS or the PSRS) for all the secondary serving cells is not transmitted.

Meanwhile, the SRS transmission processing unit 1315 may divide the state of the UE 1300 when the activation indicator is received into the following cases i), ii), and iii) and determine a condition for implicit triggering. i) If the Timing Alignment Timer (TAT) of an a Secondary Timing Alignment Group (sTAG) has expired and all the secondary serving cells within the sTAG are in the deactivation state, the SRS transmission processing unit 1315 determines that a random access procedure has been initialized for a secondary serving cell within the sTAG that has been instructed to be activated. That is, implicit triggering is not taken into consideration. ii) If the TAT of an sTAG has not expired and all the secondary serving cells within the sTAG are in the deactivation state, the SRS transmission processing unit 1315 determines that implicit triggering is instructed for the transmission of an ASRS for a secondary serving cell within the sTAG that has been instructed to be activated. iii) If the TAT of an sTAG has not expired and at least one secondary serving cell within the sTAG is in the activation state, the SRS transmission processing unit 1315 activates a specific secondary serving cell, but does not perform other operations according to the original meaning of an activation indicator. That is, implicit triggering is not taken into consideration.

Meanwhile, the reception unit 1305 receives an activation indicator for secondary serving cells placed in a frequency band on the basis of information about the frequency band in which a repeater is installed. Here, the SRS transmission processing unit 1315 considers the activation indicator as implicit triggering for the transmission of an ASRS. That is, the SRS transmission processing unit 1315 determines whether a secondary serving cell is placed or configured in a specific frequency band in which the repeater is operated and selectively instructs the transmission of the ASRS to be triggered only when the secondary serving cell is configured in the specific frequency band. Information about the frequency band in which the repeater is installed and operated is shown in Table 6 below.

The BS 1350 includes an information generation unit 1355, a transmission unit 1360, a reception unit 1365, and a scheduling unit 1370.

The information generation unit 1355 generates a first message or an activation indicator. Alternatively, the information generation unit 1355 generates information about a frequency band in which a repeater is installed.

The transmission unit 1360 transmits the first message, the activation indicator, or information about the frequency band in which the repeater is installed to the UE 1300. The reception unit 1365 receives an ASRS from the UE 1300. The scheduling unit 1370 estimates an uplink channel by using the received ASRS and performs uplink scheduling for the UE 1300.

FIG. 14 shows multiple Timing Alignment Groups (TAGs) configured for a UE according to an embodiment of the present invention.

FIG. 14 shows an example in which a pTAG and an sTAG are configured in the UE, the pTAG includes only a primary serving cell, and the sTAG includes only one secondary serving cell.

Referring to FIG. 14, the primary serving cell 1410 and the secondary serving cell 1420 configured in the UE 1400 have different TA values TA3 and TA1. Accordingly, a BS may group the primary serving cell 1410 into the pTAG and group the secondary serving cell 1420 into the sTAG.

At the time when the UE 1400 moves from a position ⓐ to a position ⓑ, the secondary serving cell 1420 configured in the UE 1400 is deactivated. In this state, the UE 1400 continues to move to a position ⓒ that is a cell provided by a repeater 1430. Furthermore, at the position ⓒ, the UE 1400 receives an activation indicator for the secondary serving cell 1420. If the TAT of the sTAG has not expired at the position ⓒ, however, the UE 1400 may determine that the previous TA value TA1 is valid and start uplink transmission, such as SRS transmission.

However, the TA value TA1 is not valid because a TA value for the cell provided by the repeater 1430 is TA2 at the position ⓒ. If the UE 1400 transmits an uplink signal according to uplink synchronization on the basis of the previous TA value TA1, other UEs transmitting signals through a frequency band 2 F2 experience interference because it is not synchronized. In particular, in a wireless communication system according to an OFDM transmission scheme, uplink transmission generates interference for the entire system band because time is not synchronized.

Accordingly, the BS must detect an environment in which the TA value of the sTAG has changed from TA1 to TA2 as soon as possible and update the TA value of the sTAG. The prior art does not disclose a method capable of preventing uplink interference generated owing to a difference between TA values if the TAT of an sTAG expires or before an environment in which the TA has changed from TA1 to TA2 is detected, after the secondary serving cell 1420 within the sTAG of the UE 1400 starts the transmission of an uplink signal. Accordingly, a BS must first check whether the TA value of the secondary serving cell 1420 has to be changed right after the secondary serving cell 1420 of the UE 1400 is activated or deactivate, and a method of supporting the check is as follows.

1. Indicate random access start

A method of a BS tracking a change of the uplink TA value of a UE is to use a random access procedure. For example, when the BS instructs the UE on the random access start and the UE transmits a random access preamble to the BS, the BS checks timing when the random access preamble is received and checks whether uplink synchronization has changed. However, the method using the random access procedure is not a method of the BS checking that there is a problem in what UE and then instructing a random access start for a specific secondary serving cell. That is, the BS cannot determine whether a TA value for all the secondary serving cells just activated needs to be updated. Accordingly, there is a possibility that the BS may start a random access procedure for a secondary serving cell whose TA value needs not to be updated. This may unnecessarily consume the time and frequency resources of the BS and the UE and unnecessarily consume UE battery.

2. Receive periodic (type 0) SRS (PSRS)

As another method, an uplink signal known to a UE and a BS may be used. For example, the UE and the BS may know that a PSRS is transmitted using what time/frequency resources and what sequence signal. Accordingly, the BS may check a change of uplink synchronization in response to the PSRS. This method is useful because additional signaling for SRS transmission is not required between the BS and the UE. The transmission period of the PSRS signal may be set to a maximum of 320 ms. Accordingly, it is difficult for the UE to check a change of uplink synchronization before the PSRS signal is transmitted after a secondary serving cell was activated. It is also difficult for the BS to schedule uplink transmission in the state in which whether a TA value has changed has not been checked.

3. Triggering of aperiodic (type 1) SRS (ASRS) transmission

As yet another method, a BS transmits ASRS configuration information to a UE and transmits a triggering indicator, triggering the transmission of an ASRS, to the UE if necessary. When the triggering indicator is received, the UE may transmit the ASRS to the BS based on the ASRS configuration information, and the BS may check a change of uplink synchronization regarding a secondary serving cell by using the ASRS.

This method is useful because SRS transmission can be induced on desired timing through minimum signaling between the BS and the UE. However, the triggering indicator is transmitted only through DCI having a specific format. For example, the DCI of the specific format may include a

DCI format

0 or 4 for transmitting information related to uplink resource allocation and a DCI format 1A or 2B or 2C (TDD) for transmitting information related to downlink resource allocation.

That is, the triggering indicator is transmitted along with the information related to uplink or downlink resource allocation. In this case, the BS transmits a PDCCH, instructing uplink data to be transmitted in a secondary serving cell just activated, to the UE and checks an SRS signal received from the UE. According to this method, if a network knows information about the operating frequency band of a repeater, the BS may selectively trigger the transmission of an ASRS only in the secondary serving cell of the operating frequency band. In this method, however, a PDCCH for triggering the transmission of the ASRS needs to be transmitted, and downlink radio resources may be unnecessarily consumed.

4. Implicit triggering 1 according to an activation indicator

As further yet another method, when a BS transmits an activation indicator indicative of implicit triggering to a UE, the UE transmits an ASRS to the BS through a secondary serving cell, just activated, on the basis of ASRS configuration information. Accordingly, the BS can check a change of uplink synchronization.

This method is useful because SRS transmission can be induced on timing when an SRS can be foremost transmitted even without signaling between the BS and the UE. In this method, however, all the secondary serving cells right after they are activated are instructed to transmit ASRS signals. Accordingly, the BS must calculate timing when an activation indicator is transmitted to a specific secondary serving cell by taking a situation in which the ASRS resources of the secondary serving cells are allocated to each UE into consideration in order to prevent a plurality of UEs from being instructed to transmit the ASRS signals for the same SRS resources at the same time. For this reason, the scheduling complexity of the BS may be increased, and activation indication for downlink transmission may be delayed.

5. Implicit triggering 2 according to an activation indicator

As still yet another method, uplink interference due to a secondary serving cell right after activation can be quickly checked while obviating the scheduling complexity of the BS and a restriction on the basis of the No. 4 method. In this method, if a UE receives an activation indicator for at least one secondary serving cell is received, the state of the UE when the activation indicator was received may be classified into 1), 2), and 3) below, and the implicit triggering operation of the UE may be differently defined.

1) The TAT of an sTAG = expired, all the secondary serving cells within the sTAG = deactivated:

The UE determines that a random access procedure has been indicated for the secondary serving cells within the sTAG that have been indicated to be activated.

2) The TAT of an sTAG ≠ expired, all the secondary serving cells within the sTAG = deactivated:

The UE determines that type 1 SRS triggering has been indicated for the secondary serving cells within the sTAG that have been indicated to be activated.

3) The TAT of an sTAG ≠ expired, at least one secondary serving cell within the sTAG = activated:

The UE activates a specific secondary serving cell, but does not perform other operations according to the original meaning of an activation indicator.

6. Implicit triggering 3 according to an activation indicator

A BS transmits information about a frequency band in which a repeater is installed to a UE. The UE receives an activation indicator for secondary serving cells configured in the frequency band on the basis of the information about the frequency band. Here, the UE determines that the activation indicator implicitly triggers the transmission of a type 1 SRS. In this method, if a UE has information about a specific frequency band in which a repeater is installed and operated, aperiodic SRS transmission triggering for a secondary serving cell configured in the relevant frequency band may be selectively indicated. However, there is a need for additional signaling for transmitting the information about the frequency band in which the repeater is installed and operated.

In this method, the information about the frequency band in which the repeater is installed and operated is transmitted to the UE through the following signaling.

Table 6

As in Table 6, a configuration (nonUL-Configuration) field for the DL CC of a secondary serving cell includes a downlink repeater field FS-Repeater-DL. The downlink repeater field has a Boolean value. The downlink repeater field is set to ‘1’ or ‘true’ when a repeater is operated in a frequency band in which the relevant secondary serving cell is configured. If the repeater is not operated in the frequency band in which the relevant secondary serving cell is configured, however, the downlink repeater field is set to ‘0’ or ‘false’. An uplink repeater field UL-Configuration is also set like the downlink repeater field.

All the functions described above may be executed by a microprocessor, a controller, a microcontroller, or a processor such as an ASIC (Application Specific Integrated Circuit) according to software or program codes coded to execute the functions. The design, development and/ implementation of the codes may be said to be evident to those skilled in the art based on the description of the present invention.

Although the some embodiments of the present invention have been described above, a person having ordinary skill in the art will appreciate that the present invention may be modified and changed in various ways without departing from the technical spirit and scope of the present invention. Accordingly, the present invention is not limited to the embodiments and the present invention may be said to include all embodiments within the scope of the claims below.

Claims

A user equipment (UE) for transmitting a sounding reference signal (SRS) used to estimate an uplink channel, the UE comprising:

a reception unit configured to receive serving cell configuration information about a serving cell to be configured in the UE and configured to receive an activation indicator instructing activation or deactivation of the serving cell;

an SRS transmission processing unit configured to trigger the transmission of the SRS in the serving cell when the activation indicator is received in an nth subframe; and

a transmission unit configured to aperiodically transmit the SRS in a predefined (n+m)th subframe based on a specific criterion.
The UE as claimed in claim 1, further comprising:

a serving cell configuration unit configured to configure the serving cell in the UE and configured to activate or deactivate the serving cell based on instruction of the activation indicator.
The UE as claimed in claim 1, wherein:

the SRS transmission processing unit generates a sequence used to transmit the SRS, and

the transmission unit transmits the SRS by using the sequence.
The UE as claimed in claim 1, wherein the specific criterion is defined as in which subframe the SRS is foremost transmitted after the serving cell is activated.
The UE as claimed in claim 1, wherein:

the serving cell belongs to a timing alignment group (TAG) which is a set of serving cells to which a timing alignment (TA) value for adjusting uplink synchronization is identically applied, and

the SRS transmission processing unit operates a timing alignment timer (TAT) applied to the TAG.
The UE as claimed in claim 5, wherein the SRS transmission processing unit triggers the transmission of the SRS in the serving cell, if the TAT does not expire in the nth subframe and all serving cells within the TAG are in a deactivation state.
The UE as claimed in claim 1, wherein:

the reception unit receives information about a frequency band in which a repeater is installed, and

the SRS transmission processing unit examines whether the serving cell is placed in the frequency band and triggers the transmission of the SRS in the serving cell based on the examination.
A method of transmitting a sounding reference signal (SRS) used to estimate an uplink channel performed by a user equipment (UE), the method comprising:

receiving serving cell configuration information about a serving cell to be configured in the UE;

receiving an activation indicator to instruct activation or deactivation of the serving cell;

triggering transmission of the SRS in the serving cell when the activation indicator is received in an nth subframe; and

aperiodically transmitting the SRS in a predefined (n+m)th subframe based on a specific criterion.
The method as claimed in claim 8, further comprising:

configuring the serving cell in the UE; and

activating or deactivating the serving cell based on the instruction of the activation indicator.
The method as claimed in claim 8, further comprising:

generating a sequence used to transmit the SRS, and

transmitting the SRS by using the sequence.
The method as claimed in claim 8, wherein the specific criterion is defined as in which subframe the SRS is foremost transmitted after the serving cell is activated.
The method as claimed in claim 8, wherein:

the serving cell belongs to a timing alignment group (TAG) which is a set of serving cells to which a timing alignment (TA) value for adjusting uplink synchronization is identically applied, and

a timing alignment timer (TAT) is applied to the TAG.
The method as claimed in claim 12, wherein the transmission of the SRS in the serving cell is triggered, if the TAT does not expire in the nth subframe and all serving cells within the TAG are in a deactivation state.
The method as claimed in claim 8, further comprising:

receiving information about a frequency band in which a repeater is installed, and

determining whether the secondary serving cell is placed in the frequency band,

wherein the transmission of the SRS in the serving cell is triggered based on the determination.
A base station (BS) for receiving a sounding reference signal (SRS) used to estimate an uplink channel, the BS comprising:

an information generation unit configured to generate serving cell configuration information about a serving cell to be configured in a user equipment (UE) and an activation indicator to instruct activation or deactivation of the serving cell;

a transmission unit configured to transmit at least one of the serving cell configuration information and the activation indicator to the UE in an nth subframe;

a reception unit configured to receive the SRS from the UE in a predefined (n+m)th subframe in response to the activation indicator; and

a scheduling unit configured to perform uplink scheduling for the UE by using the SRS.
The BS as claimed in claim 15, wherein the information generation unit generates the activation indicator by using a Medium Access Control (MAC) layer.
The BS as claimed in claim 15, wherein:

the information generation unit generates information about a frequency band in which a repeater is installed, and

the transmission unit transmits the information about the frequency band.
A method of receiving a sounding reference signal (SRS) used to estimate an uplink channel performed by a base station (BS), the method comprising:

transmitting an activation indicator, instructing a serving cell configured in a user equipment (UE) to be activated or deactivated, to the UE in an nth subframe;

receiving the SRS from the UE in a predefined (n+m)th subframe in response to the activation indicator; and

performing uplink scheduling for the UE in response to the SRS.
The method as claimed in claim 18, further comprising:

generating information about a frequency band in which a repeater is installed; and

transmitting the information about the frequency band.