KR20160094033A - Apparatus and method for performing hybrid automatic repeat request operation in wireless communication system supporting carrier aggregation - Google Patents

Abstract

The present invention relates to a device and a method for performing an HARQ operation in a wireless communications system supporting carrier aggregation. Disclosed is the method for performing the HARQ operation comprising: a step of receiving an upper layer signal, which instructs one or more cross carrier HARQ serving cells, from a base station; a step of receiving PDSCH from the base station on a sub serving cell of an unlicensed band; a step of transmitting HARQ NACK to the base station when the decoding of the PDSCH is failed; a step of receiving PDCCH including a flag, which instructs one of the cross carrier HARQ serving cells and the sub serving cell from the base station, from the base station; and a step of receiving retransmission PDSCH, which is instructed by the PDCCH, from the base station.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an apparatus and a method for performing an HARQ operation in a wireless communication system supporting carrier aggregation,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to wireless communication, and more particularly, to an apparatus and method for performing an HARQ operation in a wireless communication system supporting carrier wave aggregation.

Carrier aggregation (CA) supports multiple carriers and is sometimes referred to as spectrum aggregation or bandwidth aggregation. The individual unit carriers tied by the carrier aggregation are referred to as component carriers (CC). Each element carrier is defined as the bandwidth and center frequency. With CA, it is possible to achieve the same effect as using a logically large band band by bundling a plurality of physically continuous or non-continuous bands in the frequency domain.

However, as wireless communication traffic has surged recently, it is still urgent to secure more frequencies. Accordingly, a method of performing a CA using frequencies of an unlicensed band as well as a licensed band exclusively allocated to a mobile communication provider is being discussed. The LTE (Long Term Evolution) standard uses a system serving as a primary serving cell (PCell) on a licensed band while setting carrier waves on a license-exempt band as a secondary serving cell (SCell) using system information (SI) Or LAA (Licensed Assisted Access) for setting at least one or more auxiliary serving cells.

Meanwhile, a downlink HARQ (Hybrid Automatic Repeat reQuest) operation is performed in an asynchronous manner. For example, the asynchronous downlink HARQ operation only defines a timing relationship between a Physical Downlink Shared CHannel (PDSCH) and HARQ-ACK (ACKnowledgment) transmission, and a timing relationship between the PDSCH and HARQ-NACK Is not defined. That is, when the UE reports HARQ-NACK to the BS, the BS performs PDSCH retransmission only within a predetermined time according to the implementation of downlink scheduling. This also applies to the PDCCH (Physical Downlink Control CHannel) which instructs semi-persistent scheduling in the main serving cell.

Since the occupancy of the license-exempt band is not always guaranteed when the base station and the terminal communicate using the carriers of the license-exempt band based on the LAA, the HARQ retransmission in the license-exempt band is uncertain. As a result, a large delay is caused in the retransmission, which may lead to deterioration of efficiency and deterioration of performance of data transmission and reception. Accordingly, there is a need for a method that can effectively perform HARQ operation in a wireless communication system based on LAA.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus and method for performing HARQ operations in a wireless communication system supporting carrier wave aggregation.

According to an aspect of the present invention, there is provided a method for performing HARQ (Hybrid Automatic Repeat reQuest) operation in a wireless communication system supporting carrier aggregation. The method includes receiving an upper layer signal indicative of at least one cross-carrier HARQ serving cell from a base station, receiving a Physical Downlink Shared (PDSCH) from a base station on a secondary serving cell (SCell) A step of transmitting a HARQ NACK to the base station when decoding of the PDSCH fails, a step of receiving a flag indicating to which one of the at least one of the at least one of the at least one of the cross- Receiving a PDCCH (Physical Downlink Contrl CHannel) from the BS, the PDCCH including a PDCCH, and receiving a retransmission PDSCH indicated by the PDCCH from the BS.

The retransmission PDSCH may be received on a serving cell indicated by the flag, and the PDCCH may be received on a different serving cell than the retransmission PDSCH.

The at least one cross-carrier HARQ serving cell may be included in a license band and the at least one cross-carrier HARQ serving cell may be selected from among serving cells included in one serving cell group specific to the UE.

The method further includes transmitting an HARQ ACK to the base station when decoding of the PDSCH is successful, wherein the received flag for the HARQ ACK can be ignored.

In the LAA environment, the UE can recognize which PDSCH retransmission is performed on a serving cell through a flag, and improve the link performance by combining the data of the retransmitted PDSCH in the HARQ process of the corresponding serving cell stored in the UE memory .

Figure 1 shows examples of LAA deployment scenarios to which the present invention is applied.
2 is an explanatory view illustrating a concept of a cross-carrier HARQ operation in an LAA according to an embodiment.
3 is a flowchart illustrating a cross-carrier HARQ operation according to an exemplary embodiment of the present invention.
Fig. 4 is an embodiment embodying the description of the flowchart of Fig.
5 is a flowchart illustrating a cross-carrier HARQ operation according to another embodiment.
Fig. 6 is an embodiment embodying the description of the flowchart of Fig.
FIG. 7 illustrates a case where a plurality of CCs are used in the LAA according to an embodiment.
FIG. 8 is a flowchart illustrating a cross-carrier HARQ operation according to another embodiment.
Fig. 9 is an embodiment embodying the description of the flowchart of Fig.
FIG. 10 is a flowchart illustrating a method of selecting a retransmission serving cell based on priority in a base station according to an exemplary embodiment of the present invention.
11 is a block diagram illustrating a terminal and a base station according to an example of the present invention.

The present invention will be described with reference to a wireless communication network. A task performed in a wireless communication network may be performed in a process of controlling a network and transmitting data by a system (e.g., a base station) The operation can be performed in the terminal connected to the terminal.

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

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

Hereinafter, a downlink refers to a communication or communication path from a base station to a terminal, and an uplink refers to a communication or communication path from a terminal to a base station. In the downlink, the transmitter may be part of the base station, and the receiver may be part of the terminal. In the uplink, the transmitter may be part of the terminal, and the receiver may be part of the base station. The layers of the radio interface protocol between the terminal and the base station can be divided into a first layer L1, a second layer L2 and a third layer L3. Among them, the physical layer belonging to the first layer provides an information transfer service using a physical channel.

The physical layer is connected to a MAC layer (Media Access Control) layer through a transport channel. The data is transmitted between the MAC layer and the physical layer through a transmission channel. The transport channel is classified according to how the data is transmitted over the air interface. Further, data is transmitted through physical channels between different physical layers (i.e., between the physical layer of the terminal and the base station). The physical channel can be modulated by an Orthogonal Frequency Division Multiplexing (OFDM) scheme, and uses time, frequency, and space generated by a plurality of antennas as radio resources.

For example, a physical downlink control channel (PDCCH) of a physical channel notifies a UE of resource allocation of a paging CHannel (DLH), a downlink shared channel (DL-SCH), and Hybrid Automatic Repeat Request (HARQ) And an uplink scheduling grant informing the UE of the resource allocation of the uplink transmission. A Physical Uplink Shared Channel (PDSCH) carries a DL-SCH including downlink data. In addition, the Physical Uplink Control CHannel (PUCCH) carries uplink control information such as HARQ ACK / NACK for downlink transmission, a scheduling request, and a CQI. The Physical Uplink Shared CHannel (PUSCH) carries an uplink shared channel (UL-SCH) including uplink data. If necessary, the PUSCH may include CSI (Channel State Information) information such as HARQ ACK / NACK and CQI according to the setup and request of the base station.

Simple cell segmentation of macro and micro cells makes it difficult to meet the growing demand for data services. Accordingly, a method of performing wireless communication using frequencies of an unlicensed band (UB) such as a WiFi band as well as a licensed band (LB) is being discussed. Wireless communication in the license-exempt band may be provided with the support of the licensed band's communication techniques to facilitate the wireless communication in the license-exempt band. License assisted access (LAA) refers to the operation of CA operations on one or more secondary serving cells operating in the license-exempt band or license-exempt spectrum, based on the assistance of the primary serving cell operating in the licensed band or spectrum. And the like. In other words, the LAA is a technique of bundling the licensed band and the license-exempted band using a CA as an anchor for a licensed carrier (LC) of the LTE license band. In this case, one of the serving cells in the license band is used as the main serving cell, and the serving cells in the license-exempted band can always be configured as the serving cell. Also, the license-exempt band is activated only through the CA, and may not perform LTE communication by itself. The terminal may access the network by using the license band and use the service, and the base station may combine the licensed band and the license-exempted band with the CA to offload the traffic of the license band to the license-exempt band.

Figure 1 shows examples of LAA deployment scenarios to which the present invention is applied. In each scenario, the number of licensed carriers and unlicensed carriers may be one or more, respectively.

Referring to FIG. 1, a scenario 1 is a case where a macro cell using a license carrier F1 (frequency 1) and a small cell using a license-exempt carrier F3 are connected to each other through a carrier aggregation (CA). In this case, the macro cell and the small cell may be non-co-located and may be connected to each other with an ideal back hole. Scenario 2 is a case where small cell # 1 using F2, which is a license carrier, and small cell # 2 using F3, which is a license-exempt carrier, are connected to carrier aggregation in addition to macro cell coverage. Scenario 3 is a case where there is a macro cell and a small cell # 1 using a license carrier F1 and a small cell # 1 using the small cell # 1 and a small cell # 2 using a license-exempt carrier F3 are connected to a carrier aggregation. In the scenario 4, there are a macro cell using the license carrier F1, a small cell # 1 using the license carrier F2, and a small cell # 2 using the license-exempt carrier F3. The small cell # 1 and the small cell # It is the case that it is connected to the aggregation.

Since the LAA creates an opportunistic channel occupancy environment, the base station performs a procedure for securing an unlicensed carrier (UC), which includes dynamic carrier selection (DCS) and CCA (Clear Channel Assessment). The base station checks the occupancy status of the license-exempt frequency resource through the DCS and the CCA, and performs transmission and reception of wireless data by occupying the resource for a predetermined time if available. However, since the occupation of the license-exempted band is not always guaranteed, if the occupation in the license-exempt band is not secured at the time of HARQ retransmission, it is uncertain whether the HARQ retransmission is successful or not. As a result, a large delay is caused in the retransmission, which may lead to deterioration of efficiency and deterioration of performance of data transmission and reception. Accordingly, there is a need for a method that can effectively perform HARQ operation in a wireless communication system based on LAA.

2 is an explanatory view illustrating a concept of a cross-carrier HARQ operation in an LAA according to an embodiment.

Referring to FIG. 2, it is assumed that the base station and the terminal are configured on the LB and the UB based on the LAA. LB includes a main serving cell composed of a DL primary component carrier (PCC) and an uplink PCC (UL PCC), and UB includes a UC as a supplementary DL (SDL). "D" in each subframe means that downlink transmission occurs, and "U" means that uplink transmission occurs. Downlink transmission includes transmission of PDSCH carrying data, and uplink transmission includes transmission of PUCCH carrying HARQ ACK / NACK.

When the BS occupies the first six subframes of the UC and transmits the PDSCH1 to the UE on the first subframe of the UC, the UE attempts to decode the PDSCH1. If the UE fails to decode the PDSCH1, the UE transmits an HARQ NACK to the BS through the UL PCC. The base station receiving the HARQ NACK retransmits the data on the PDSCH1, but if the UC is no longer occupied, a separate resource is required for retransmission. The separate resource may be, for example, a DL PCC in the LB. In this case, the base station transmits the data to be retransmitted on the PDSCH2 to the UE through the DL PCC. In this manner, an operation in which retransmission of PDSCH (or data) by HARQ NACK occurs in a serving cell different from that of a previous serving cell is referred to as a cross-carrier HARQ operation. In other words, the operation in which the retransmission of PDSCH by HARQ NACK is performed by frequency hopping may be referred to as a cross-carrier HARQ operation. In this specification, a serving cell in which PDSCH retransmission is performed by frequency hopping is referred to as a cross carrier HARQ serving cell for the sake of convenience.

In the case where the BS fails to occupy the UC, the PDSCH retransmission is performed by the cross-carrier HARQ operation, but if occupation of the UC continues, the cross-carrier HARQ operation may be unnecessary. Therefore, the cross-carrier HARQ operation can be dynamically determined according to the occupation state of the UC by the base station. If the serving cell in which the PDSCH retransmission is performed according to the cross-carrier HARQ operation is changed, the UE must be aware of the situation to prepare for retransmission PDSCH reception. For this purpose, the BS can dynamically dictate to the UE which serving cell the retransmission of the PDSCH is performed. Referring to FIG. 2, a serving cell candidate in which retransmission of a PDSCH (i.e., transmission of PDSCH2) is performed may basically include both a serving cell of a UB (i.e., a UC that transmitted PDSCH1) and a serving cell of LB .

The present disclosure posts various embodiments relating to the parameters and detailed procedures necessary for the implementation of such a cross-carrier HARQ operation.

As a parameter required for implementing a cross-carrier HARQ operation, first, cross control information indicating a serving cell in which retransmission of a PDSCH is performed is required.

According to an embodiment of the present invention, since the crossover control information is a flag and the flag must quickly reflect a channel that changes momentarily, the (E) PDCCH including the downlink control information (DCI) Channel.

In one aspect, the flag may indicate one serving cell of UC and LB as one bit. Alternatively, the flag may indicate two UCs as one bit. That is, the flag indicates any one of the two serving cells. The index of the serving cell in the LB may be predetermined between the BS and the MS or may be previously informed to the MS by the BS as an upper layer signal. The corresponding relationship between the value indicated by the flag and the serving cell index can be defined by a table previously agreed between the UE and the BS. Herein, it is defined that the PDSCH retransmission is directed to the serving cell through the flag. However, in view of the operation, the flag may be dynamically informed to the UE whether to perform the cross-carrier HARQ operation. For example, if the flag is 1, it indicates that a cross-carrier HARQ operation is applied (i.e., PDSCH retransmission is performed in a serving cell of a predetermined LB), and if the flag is 0, a cross-carrier HARQ operation is not applied The retransmission of the PDSCH is performed).

In addition, if a serving cell that can be indicated by the flag referred to in the present invention is set for a cross-carrier HARQ operation by another UC by the RRC signal as well as the serving cell between the UC and LB, May be applied and operated between serving cells.

In another aspect, the flag may indicate up to three serving cells in the LB as well as the UC as two bits. That is, the flag indicates any one of the four serving cells. In this case, the index for each of the three serving cells may be a predetermined one between the BS and the MS, or the BS may inform the MS of the upper layer signal in advance. The corresponding relationship between the value indicated by the flag and the serving cell index can be defined by a table previously agreed between the UE and the BS.

In another aspect, the flag may indicate up to K serving cells, including UC and LB as N bits (N > 3). That is, the flag indicates any one of the K serving cells. For example, if K = 32, then N = 5. In this case, the index for each of the K serving cells may be an advance between the BS and the MS, or the BS may inform the MS of the upper layer signal in advance. The corresponding relationship between the value indicated by the flag and the serving cell index can be defined by a table previously agreed between the UE and the BS.

In yet another aspect, the flag may indicate L serving cells in a serving cell group as M bits. That is, the flag indicates any one of the L serving cells in a particular group.

According to another embodiment of the present invention, the crossover control information is a new data indicator (NDI), and the NDI is a control information for the PDSCH transmission, Signal (DCI (E) PDCCH). The NDI is indicated by being toggled to information for distinguishing whether the associated PDSCH is based on the HARQ retransmission or not, as one bit. When the NDI instructs HARQ retransmission, the PDSCH may be implicitly indicated to be transmitted through another serving cell other than the existing UC.

Next, based on the parameters, a specific procedure for the cross-carrier HARQ operation procedure is posted.

3 is a flowchart illustrating a cross-carrier HARQ operation according to an exemplary embodiment of the present invention. In describing the flowchart of Fig. 3, reference is made to Fig. 4 as a specific example.

3 and 4, the BS transmits an upper layer signal indicating a cross-carrier HARQ serving cell to the MS (S300). The upper layer signal indicates to which serving cell the retransmission of the PDSCH should be performed in order to support the cross-carrier HARQ operation for the terminal for which the LAA is established. This upper layer signal is used to preset the serving cell on which the PDSCH (retransmission) is to be performed for PDSCH scheduling on the UC. The upper layer signal may be RRC configuration information for a secondary serving cell set up on the UC. In this case, a service associated with a cross-carrier HARQ operation (i.e., retransmission PDSCH) in the configuration information for the secondary serving cell set on the UC The index of the cell is included.

For example, FIG. 4 shows a case where a main serving cell composed of DL PCC and UL PCC is used as a cross-carrier HARQ serving cell indicated by RRC signaling, and a base station transmits an upper layer signal (RRC message) indicating the main serving cell, To the terminal. The set up cross-carrier HARQ serving cell may be the same as or different from the cross-carrier scheduling serving cell for scheduling the PDSCH of the UC. In FIG. 4, the cross-carrier HARQ serving cell is a main serving cell and the cross-carrier scheduling serving cell is a different serving cell (DL SCC + UL SCC).

Referring back to FIG. 3, the base station transmits PDCCH1 through the DL SCC and transmits PDSCH1 indicated by the PDCCH1 to the terminal through the UC of the SDL (S305). The operation in which PDCCH and PDSCH are transmitted on different serving cells is referred to as cross-carrier scheduling. Here, it is assumed that the base station sees that it can occupy through CCA or DCS before using SDL, and occupies SDL UC.

The UE attempts to decode the PDSCH1 after receiving the PDSCH1, and transmits the HARQ NACK to the BS through the UL PCC when decoding fails (S310).

The base station should perform retransmission of data as it receives the HARQ NACK. In order to retransmit the data, the base station should check whether the UC of the SDL can be continuously used (i.e., occupied) (S315).

If it is determined that the occupation of the SDL UC is sustainable, the base station continues to use the UC of the SDL (i.e., its own serving cell where the current data transmission occurs) to perform retransmission of the PDSCH (i.e., transmission of PDSCH2) At the same time, the serving cell transmitting PDSCH2 transmits a PDCCH2 including a flag indicating that the serving cell is the UC of the SDL to the UE (S320). In this case, the UE recognizes that retransmission of the PDSCH by the HARQ NACK is performed in the UC of the SDL based on the flag, and receives the PDSCH2 from the UC of the SDL.

However, if it is determined that the occupation of SDL UC is impossible, the base station performs retransmission of the PDSCH (i.e., transmission of PDSCH2) through the main serving cell (DL PCC) set as the cross-carrier HARQ serving cell in step S300 (S325) (PDCCH2) indicating that the serving cell in which the PDSCH2 is transmitted is a serving cell set by the RRC (i.e., a cross-carrier HARQ serving cell, in FIGs. 3 and 4, indicates a DL PCC) to the UE in step S325. In this case, the UE recognizes that retransmission of the PDSCH by the HARQ NACK is performed in the DL PCC based on the flag, and receives the PDSCH2 in the DL PCC.

When a flag of 1 bit is used, an example of contents indicated by each flag value is shown in the following table.

FLAG bit (1 bit example) Serving cell indication for PDSCH retransmission 0 DL SCell (UC) One Cross Carrier HARQ Serving Cell # 0 (set by RRC)

Table 1 shows a UC or a cross-carrier HARQ serving cell # 0 with a flag of 1 bit.

On the other hand, according to the present embodiment, the number of bits of the flag can also be changed according to the number of serving cells indicated by the higher layer signal. For example, the base station may set a set of potential cross-carrier HARQ serving cells. If three downlink serving cells are set by an upper layer signal, a 2-bit flag can be indicated to the UE by the DCI.

When the 2-bit flag is used, an example of the content indicated by each flag value is shown in the following table.

FLAG bit (1 bit example) Serving Cell Instruction for SCH retransmission 00 DL SCell (UC) 01 The cross-carrier HARQ serving cell # 0 (RRC configured) 10 The cross-carrier HARQ serving cell # 1 (RRC configured) 11 The cross-carrier HARQ serving cell # 2 (RRC configured)

The cross-carrier HARQ serving cell indices # 0, # 1 and # 2 are previously set by the upper layer signal of step S300, and the flag values 01, 10 and 11 are respectively set to the cross- .

When the UE successfully decodes the data from the retransmitted PDSCH2, the UE performs combining with data according to the decoding result of the existing PDSCH1 (S330).

According to this embodiment, the base station can select the serving cell to which the PDSCH2 is to be transmitted (i.e., the PDSCH is to be retransmitted) based on the cross-carrier HARQ operation, which includes an upper layer signal for setting up a cross-carrier HARQ serving cell and a DCI Lt; / RTI > Also, although the PDCCH1 and the PDCCH2 are used in the present embodiment, it is needless to say that the E-PDCCH may be used.

On the other hand, if the UE transmits an HARQ-ACK in step S310 and the base station receives the HARQ-ACK, the flag can be set to 0 as a default. Alternatively, the MS may ignore the value of the flag received from the BS after transmitting the HARQ-ACK.

3 and 4 define the downlink HARQ operation, but these embodiments are equally applicable to the uplink HARQ operation. That is, if the uplink HARQ is assumed to be based on an asynchronous scheme, the same method can be applied. In the case of the uplink HARQ, a method for selecting and indicating a serving cell in which a PUSCH retransmission is performed is a method in which a PDSCH retransmission is performed This is the same as the method of performing. For example, in FIG. 3 and FIG. 4, the PDSCH will be replaced with a PUSCH, and the HARQ NACK will be changed from being transmitted from the base station to the terminal. And the upper layer signals and flags can be applied equally. However, when NACK is indicated through the PHICH, the PUSCH retransmission can be performed in the serving cell in which the corresponding PHICH is transmitted. In this case, the cross-carrier HARQ serving cell and the cross-carrier scheduling serving cell are equal. This is because the serving cell to which the PHICH is transmitted is the same as the serving cell to which the (E) PDCCH (UL grant) indicating the PUSCH transmission is transmitted.

5 is a flowchart illustrating a cross-carrier HARQ operation according to another embodiment. In describing the flowchart of Fig. 5, reference is made to Fig. 6 as a concrete example. 5 does not require an upper layer signal indicating (or setting) a cross-carrier HARQ serving cell, only a cross-carrier setting for activating a carrier indicator field need.

Referring to FIGs. 5 and 6, a base station transmits SDC UC to a mobile station, and transmits cross-carrier setting information indicating a serving cell (scheduling serving cell) to be used for scheduling SDL UC to a mobile station in operation S500. For example, FIG. 6 shows a case where DL SCC is set as a scheduling serving cell for SDL UC.

Referring again to FIG. 5, the base station transmits the PDCCH1 through the DL SCC and transmits the PDSCH1 indicated by the PDCCH1 to the terminal through the UC of the SDL (S505).

After receiving PDSCH1 and attempting to decode the PDSCH1, the UE transmits an HARQ NACK to the BS through UL PCC (S510).

The base station should perform retransmission of data as it receives the HARQ NACK. In order to retransmit the data, the base station should check whether the UC of the SDL can be continuously used (i.e., occupied) (S515).

If it is determined that the occupation of the SDL UC is sustainable, the base station continues to use the UC of the SDL (i.e., its own serving cell where the current data transmission occurs) to perform retransmission of the PDSCH (i.e., transmission of PDSCH2) At the same time, the PDCCH2 transmits a PDCCH2 including a flag indicating that the serving cell to which the PDSCH2 is transmitted is the UC of the SDL to the UE (S520). In this case, the UE recognizes that retransmission of the PDSCH by the HARQ NACK is performed in the UC of the SDL based on the flag, and receives the PDSCH2 from the UC of the SDL.

However, if it is determined that the occupation of the SDL UC is impossible, the base station performs retransmission of the PDSCH (i.e., transmission of the PDSCH2) through the secondary serving cell (DL SCC) set as the scheduling serving cell in step S500 (S525) The PDCCH2 including the flag indicating that the serving cell is the DL SCC is transmitted to the UE through the DL SCC (S525). In this case, the UE recognizes that retransmission of the PDSCH by HARQ NACK is performed in the DL SCC based on the flag, and receives the PDSCH2 in the DL SCC. According to this, even if the UE is configured with the cross-carrier scheduling, it can be regarded as operating as self-scheduling.

When one-bit flag is used in step S520 and step S525, the contents indicated by each flag value are as shown in the following table.

FLAG bit (1 bit example) Serving cell indication for PDSCH retransmission 0 DL SCell (UC) One Scheduling Serving Cell # 0 (Scheduling Serving Cell Set by RRC for Cross Carrier Scheduling)

The cross-carrier HARQ serving cell index # 0 is previously set by the cross-carrier setting information of step S500, and the flag value 1 corresponds to the cross-carrier HARQ serving cell index # 0.

FIG. 7 illustrates a case where a plurality of CCs are used in the LAA according to an embodiment.

Referring to FIG. 7, a total of sixteen CCs are shown, but this is only an example, and the number of CCs can be expanded to N. CC1 through CC6 are included in the license band, and CC7 through CC16 are included in the license-exempt zone. When the base station constructs a plurality of CCs (or serving cells) on the basis of the LAA, it can be configured as a group based. In the case of FIG. 7, 16 CCs are classified into four groups.

Considering the B5C configuration using 32 CCs, it is possible to set up to 4 serving cell groups (groups that can be composed of a maximum of 8 serving cells) (4 * 32 = 32 CCs) The embodiment of Fig. 5 can be applied.

For example, if a cross-carrier HARQ serving cell is selected to be selected only within a UE-specific group, a maximum 3-bit flag (number of serving cells in one group> 4) without an upper layer signal as in step S300, It can indicate the serving cell. Of course, the number of flag bits may also vary depending on the number of serving cells in the serving cell group. If a maximum of eight serving cells can be included in one serving cell group, a 3-bit flag can be used to indicate a cross-carrier HARQ serving cell in a UE-specific group.

On the other hand, if the concept of the serving cell group is not applied, the flag can indicate up to K serving cells, including UC and LB as N bits (N > 3). In the case of FIG. 7, since it is sixteen CCs, a flag of 4 bits is sufficient. However, if up to 32 CCs are supported, N = 5, that is, a 5-bit flag can be used.

FIG. 8 is a flowchart illustrating a cross-carrier HARQ operation according to another embodiment. In describing the flowchart of Fig. 8, reference is made to Fig. 9 as a concrete example. The embodiment of FIG. 8 does not require flags, unlike the embodiment of FIG. 3, and NDI is used to replace it. The 1-bit NDI field defined in the current DCI format is reused. When the NDI field indicates retransmission of the PDSCH, retransmission of the PDSCH to the cross-carrier HARQ serving cell is performed.

8 and 9, the BS transmits an upper layer signal indicating a cross-carrier HARQ serving cell to the MS (S800). The upper layer signal indicates to which serving cell the retransmission of the PDSCH should be performed in order to support the cross-carrier HARQ operation for the terminal for which the LAA is established. Or one predefined serving cell without the higher layer signaling may be a cross-carrier HARQ serving cell. For example, in this case, step S800 may be omitted.

The base station transmits the PDSCH1 to the mobile station through the UC of the SDL (S805).

The UE attempts to decode the PDSCH1 after receiving the PDSCH1, and transmits the HARQ NACK to the BS through the UL PCC when decoding fails (S810).

Regardless of the occupation of the SDL UC, the base station retransmits the PDSCH (that is, the PDSCH) through the main serving cell (DL PCC) set as the cross-carrier HARQ serving cell in step S800, PDCCH2) (S815), and transmits the PDCCH2 including the NDI indicating that the serving cell to which the PDSCH2 is transmitted is the DL PCC to the UE through the DL PCC (S815). After receiving the NDI, the UE can implicitly recognize that the retransmission of the PDSCH2 is performed by the cross-carrier HARQ serving cell when the NDI indicates retransmission.

The cross-carrier HARQ serving cell index # 0 is previously set by the upper layer signal of step S800, and the flag value 1 corresponds to the cross-carrier HARQ serving cell index # 0.

According to the present embodiment, "retransmission PDSCH is transmitted on the serving cell set to the upper layer signal (for example, RRC)" or "retransmission PDSCH is transmitted on the main serving cell" This provision is meaningful when NDI directs retransmission. In the case of retransmission of a PDSCH only in a specific serving cell predefined between a Node B and a UE, such as a cross-carrier HARQ operation based on NDI, the retransmission serving cell is not dynamically changed.

Accordingly, when the NDI instructs retransmission, the UE can recognize that retransmission of the PDSCH is performed through a specific serving cell that is implicitly predefined. That is, even if the additional flag bit is not introduced, the UE can receive the retransmitted PDSCH in the other serving cell through the NDI. This scheme may be effective in some regions or countries where the subframe (time) that can be occupied after one CCA run is shorter than the time required for retransmission. For example, in Japan, since the maximum time that can be occupied through one CCA is 4 ms, this time is shorter than the time to expect retransmission (e.g., HARQ retransmission timing ≥8 ms). In this case, since the retransmission occurs in the serving cell other than the UC to which the PDSCH is initially transmitted, it is unnecessary to dictate the serving cell for retransmission of the PDSCH.

On the other hand, in the cross-carrier HARQ operation based on the NDI, the BS and the UE can implicitly derive a specific serving cell defined in advance according to a certain rule.

In one aspect, retransmission for a PDSCH that is initially transmitted on the UC is performed on a scheduling serving cell (indicated by the cross-carrier setting information) or a cross-carrier HARQ serving cell (indicated by the upper layer signal) The UE and the BS can deduce the retransmission serving cell to be equal to each other according to this rule.

In another aspect, it is possible to rule that retransmissions for a PDSCH initially transmitted on UC1 are performed on UC2 other than UC1. At this time, another UC2 may be indicated by a higher layer signal as a cross-carrier HARQ serving cell.

In another aspect, retransmission for a PDSCH initially transmitted on UC1 is performed on i) a UC2 (indicated by a higher layer signal) that is not primarily UC1, but ii) if UC2 is also a resource available for retransmission (I.e., when UC2 is not occupied), it is possible to rule out retransmission of the PDSCH on an LC such as a secondary serving cell (a so-called fallback method). Therefore, the UE and the BS must confirm availability (or occupation state) of the serving cell UC1 and the cross-carrier HARQ serving cell UC2 in which the initial PDSCH is transmitted. If all resources are not acquired in UC1 and UC2, the PDSCH retransmission can be finally performed in the main serving cell. Here, it is assumed that the base station and the UE know whether the channels of UC1 and UC2 are occupied by the serving eNB. These rules are more generalized as shown in FIG.

FIG. 10 is a flowchart illustrating a method of selecting a retransmission serving cell based on priority in a base station according to an exemplary embodiment of the present invention. This embodiment is intended to allow retransmission of a PDSCH in serving cells set to UC as much as possible. Therefore, the present embodiment provides a method of selecting a retransmission serving cell based on a priority, on the assumption that it can succeed in occupying a plurality of UCs (SCell).

Referring to FIG. 10, the BS transmits an initial PDSCH on a secondary serving cell of the UC (S1000). The UE receives the initial PDSCH on the serving cell of the UC. If decoding of the initial PDSCH fails, the UE transmits an HARQ NACK to the BS.

The base station receives the HARQ NACK from the UE (S1005).

The base station confirms whether it has acquired resources for the retransmission PDSCH on the secondary serving cell of the UC (S1010).

If there is a resource for the retransmission PDSCH in the secondary serving cell of the UC (i.e., if the base station succeeds in occupying the UC), the base station retransmits the PDSCH in the corresponding UC (S1015).

On the other hand, if there is no resource for the retransmission PDSCH in the secondary serving cell of the UC (i.e., if the base station fails to occupy the UC), the base station confirms whether it has acquired resources for retransmission of the PDSCH on the secondary serving cell of another UC ).

If there is no resource for retransmission of the PDSCH on the serving cell of another UC (that is, the base station fails to occupy another UC), the base station may retransmit the PDSCH in the primary serving cell or a pre- (S1025).

If there is a resource for retransmission of the PDSCH on the secondary serving cell of another UC (i.e., if the base station succeeds in occupying another UC), the base station determines whether the number of UCs successful in resource acquisition is greater than one (S1030).

If the number of the serving cells of another UC that has acquired the resource is not greater than 1 (i.e., if the number is 1), the base station performs retransmission of the PDSCH on the serving cell of one other UC having the resource (S1035).

If the number of the serving cell of another UC that acquires the resource is greater than 1, the base station retransmits the PDSCH on the secondary serving cell of the selected UC based on the priority (S1040).

Specifically, among the secondary serving cells of a plurality of UCs, the priority of a secondary serving cell for performing PDSCH retransmission is, for example, as follows.

i) the serving cell of the UC having the smallest or largest value of the secondary serving cell index value, or

ii) the serving cell of the UC that obtained the most recent or oldest channel, or

iii) The serving cell of the UC, set to the highest priority, if the priority for the serving cell of the UC is set to RRC.

In step S1040, the BS performs retransmission of the PDSCH in the selected secondary serving cell based on the priority.

Steps S1010 to S1025 are performed by the UE in the same manner, so that the UE can find the retransmission serving cell.

According to the present embodiment, when the resource acquisition is not possible in the UC in which the initial PDSCH is transmitted, the BS and the UE can select and check the retransmission serving cell based on the flag without any upper layer signal and the predetermined priority. Meanwhile, in the present embodiment, the flag only informs the UE of information that the PDSCH will be retransmitted in another serving cell during HARQ retransmission. Specifically, what the serving cell is can be determined by the flowchart of FIG.

Although FIG. 10 illustrates the cross-carrier HARQ operation based on the flag or the NDI, the retransmission serving cell may be determined without control information such as a flag or an NDI. According to this embodiment, the base station obtains a resource (empty channel) through CCA and transmits a specific signal (preamble or PDCCH) to the UE before retransmission, thereby notifying the base station of the channel occupation state. If the base station has already acquired an idle channel at the timing of receiving the retransmission PDSCH, the terminal can also assume that it knows the fact (or information that the base station has acquired an idle channel) through the specific signal in advance. Accordingly, the UE can recognize the serving cell in which the retransmission PDSCH is transmitted according to whether the BS acquires the channel. Here, if the initial PDSCH fails to secure an idle channel for the UC to which the initial PDSCH is transmitted, the BS performs retransmission PDSCH with the serving cell indicated or designated by the RRC signal in advance. The UE can also know whether the retransmission PDSCH will be transmitted to which serving cell because the UE can know whether to acquire a channel on the corresponding UC of the BS through a specific signal transmitted from the BS in advance.

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

Referring to FIG. 11, a UE 1100 and a Node B 1150 perform a cross-carrier HARQ operation as disclosed herein.

The terminal 1100 includes a processor 1110, an RF unit 1120, and a memory 1125.

Processor 1110 implements the functions, processes, and / or methods suggested herein. Specifically, the processor 1110 implements all the operations of the UE described in the embodiments of FIGS. 3 to 10 and performs a cross-carrier HARQ operation. The memory 1125 is coupled to the processor 1110 and stores various information for driving the processor 1110. [ The RF unit 1120 is coupled to the processor 1110 to transmit and / or receive wireless signals. For example, the RF unit 1120 may transmit an HARQ ACK / NACK to the base station 1150 or receive a PDSCH, a PDCCH, a flag, an NDI, an upper layer signal, and the like from the base station 1150.

The processor 1100 decodes and analyzes the PDCCH, the PDSCH, the flag, the NDI, the upper layer signal, and the like received by the RF unit 1120, and performs a cross-carrier HARQ operation according to the decoding. RF section 1120 receives a higher layer signal indicating the at least one cross-carrier HARQ serving cell from the base station and receives the PDSCH from the base station on a secondary serving cell (SCell) on the license-exempt band.

When the PDCCH or PDSCH decoding fails, the processor 1100 generates an HARQ NACK and transmits the HARQ NACK to the base station 1150 through the RF unit 1120. [

In one embodiment, the RF unit 1120 receives from the base station 1150 a PDCCH that includes a flag indicating either the at least one cross-carrier HARQ serving cell and the secondary serving cell, And receives a retransmission PDSCH indicated by the PDCCH from the BS 1150. The contents indicated by the flags are as shown in Tables 1 to 3. Here, the RF unit 1120 may receive a retransmission PDSCH on a serving cell indicated by the flag, and may receive a PDCCH on a different serving cell than the retransmission PDSCH. The at least one cross-carrier HARQ serving cell may be included in the license band. The at least one cross-carrier HARQ serving cell may be selected from among serving cells included in one serving cell group specific to the UE.

The RF unit 1120 receives from the Node B 1150 a PDCCH including an NDI indicating that retransmission of a PDSCH is performed on a predefined serving cell between the UE 1100 and the Node B 1150, Together with the retransmission PDSCH indicated by the PDCCH, from the base station 1150. The contents indicated by NDI are shown in Table 4. Here, the RF unit 1120 may receive a retransmission PDSCH according to the NDI on a predetermined serving cell.

As another example, the processor 1100 may perform a cross-carrier HARQ scheme based on the priority according to FIG.

As another example, if processor 1100 successfully decodes the PDSCH, it may send an HARQ ACK to base station 1150, in which case processor 1100 may ignore the received flag for the HARQ ACK.

Base station 1150 includes memory 1155, processor 1160, and RF section 1165.

Processor 1160 implements the functions, processes, and / or methods suggested herein. Specifically, the processor 1160 implements all of the operations of the base station described in the embodiments of FIGS. 3 to 10, which are herein disclosed, and performs a cross-carrier HARQ operation. The memory 1155 is coupled to the processor 1160 to store various information for driving the processor 1160. The RF unit 1165 is coupled to the processor 1160 to transmit and / or receive wireless signals. For example, the RF unit 1165 may receive an HARQ ACK / NACK from the UE 1100 or may transmit a PDSCH, a PDCCH, a flag, an NDI, an upper layer signal, and the like to the UE 1100.

More specifically, the processor 1160 generates a PDCCH, a PDSCH, a flag, an NDI, an upper layer signal, and the like received by the RF unit 1165 and performs a cross-carrier HARQ operation according to the generated PDCCH. The RF unit 1165 transmits an upper layer signal indicating the at least one cross-carrier HARQ serving cell to the UE 1100 and transmits the PDSCH to the UE 1100 on the secondary serving cell SCell on the license-exempt band.

In one embodiment, the RF unit 1165 transmits a PDCCH including a flag indicating one of the at least one cross-carrier HARQ serving cell and the secondary serving cell to the UE 1100, And transmits the retransmission PDSCH indicated by the PDCCH to the UE 1100. The contents indicated by the flags are as shown in Tables 1 to 3. Here, the RF unit 1165 may transmit a retransmission PDSCH on a serving cell indicated by the flag, and may transmit a PDCCH on a different serving cell than the retransmission PDSCH. The at least one cross-carrier HARQ serving cell may be included in the license band. The at least one cross-carrier HARQ serving cell may be selected from among serving cells included in one serving cell group specific to the UE.

The RF unit 1165 transmits to the UE 1100 a PDCCH including an NDI indicating that retransmission of a PDSCH is performed on a predefined serving cell between the UE 1100 and the Node B 1150, And transmits the retransmission PDSCH indicated by the PDCCH to the UE 1100. The contents indicated by NDI are shown in Table 4. Here, the RF unit 1165 can transmit a retransmission PDSCH according to the NDI on a predetermined serving cell.

As another example, the processor 1160 may perform a cross-carrier HARQ scheme based on the priority according to FIG.

In the above-described exemplary system, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders . It will also be understood by those skilled in the art that the steps shown in the flowchart are not exclusive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the invention.

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

Claims (6)

A method for performing a Hybrid Automatic Repeat reQuest (HARQ) operation by a terminal in a wireless communication system supporting carrier aggregation,
Receiving an upper layer signal from the base station indicating at least one cross carrier HARQ serving cell;
Receiving a Physical Downlink Shared CHannel (PDSCH) from the base station on a secondary serving cell (SCell) on a license-exempted band;
Transmitting a HARQ NACK to the base station if decoding of the PDSCH fails;
Receiving a PDCCH (Physical Downlink Contrl CHannel) from the BS, the PDCCH including a flag for indicating at least one of the at least one of the at least one of the at least one of the at least one of the first and second serving cells; And
And receiving a retransmission PDSCH indicated by the PDCCH from the base station. The method according to claim 1,
Wherein the retransmission PDSCH is received on a serving cell indicated by the flag. The method according to claim 1,
Wherein the PDCCH is received on a different serving cell than the retransmission PDSCH. The method according to claim 1,
Wherein the at least one cross-carrier HARQ serving cell is included in a license band. The method according to claim 1,
Wherein the at least one cross-carrier HARQ serving cell is selected from among serving cells included in one serving cell group specific to the UE. The method according to claim 1,
And transmitting an HARQ ACK to the base station when decoding of the PDSCH is successful,
And the received flag for the HARQ ACK is ignored.

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