WO2015020461A1

WO2015020461A1 - Method and apparatus for transmitting buffer state report in wireless communication system

Info

Publication number: WO2015020461A1
Application number: PCT/KR2014/007337
Authority: WO
Inventors: 권기범
Original assignee: 주식회사 팬택
Priority date: 2013-08-07
Filing date: 2014-08-07
Publication date: 2015-02-12
Also published as: KR102082000B1; KR20150017592A

Abstract

Disclosed are a method and an apparatus for transmitting a buffer state report in a wireless communication system. A method for transmitting a buffer state report of a terminal in a wireless communication system comprises the steps of: configuring a single radio bearer between base stations and the terminal on the basis of a dual connectivity; generating buffer size information which identifies the amount of uplink data available on a logical channel group corresponding to the single radio bearer and defined for each of the base stations; generating a buffer state report which includes an ID identifying the logical channel group and the buffer size information; and transmitting the buffer state report.

Description

Buffer status report transmission method and device in wireless communication system

The present invention relates to a wireless communication, and more particularly, when a terminal is dually connected to two or more different base stations and a single bearer is configured or formed between the two or more different base stations and the terminal. A method and apparatus for operating a state report (buffer state report).

In a wireless communication system, a terminal may perform wireless communication through two or more base stations of at least one base station constituting at least one serving cell. This is called dual connectivity. In other words, dual connectivity may be referred to as an operation in which a terminal consumes radio resources provided by at least two other network points. Here, the at least two other network points may be a plurality of base stations physically or logically separated. One of the plurality of base stations may be a macro base station, and the other base stations may be small base stations.

In dual connectivity, each base station transmits downlink data and receives uplink data through an evolved packet system bearer or a radio bearer (RB) configured for one terminal. . In this case, one RB may be configured in one base station or may be configured through two or more different base stations.

In this case, basically, uplink data generated in each RB in the terminal should be delivered to the base station in which the RB corresponding to the corresponding RB is configured. However, since only the form of transmitting the buffer state information defined in the logical channel group (LCG) unit in the terminal is supported, the BSR is transmitted in the LC unit mapped to the RB allocated to the specific base station. Could not. Although, even though the buffer status information may be transmitted in units of LCs mapped to each RB allocated to a specific base station, when a single RB is configured by a plurality of base stations, the terminal should select a target base station to which the buffer status information is transmitted. There was no.

An object of the present invention is to provide a buffer status report transmission method and apparatus in a wireless communication system.

Another technical problem of the present invention is to provide a signaling request and a buffer state for a logical channel mapped to a single radio bearer configured by a terminal through a plurality of base stations in a wireless communication system. It provides a method for transmitting a report).

Another technical problem of the present invention is that if a terminal is dually connected to two or more different base stations and a single radio bearer is configured in the terminal through the two or more different base stations, the logical channel mapped to the single radio bearer The present invention provides a reference for a base station to transmit a scheduling request and a buffer status report.

According to an aspect of the present invention, a method for transmitting a buffer status report of a terminal in a wireless communication system includes configuring a single radio bearer between base stations and the terminal based on dual connectivity, wherein the single radio Generating buffer size information that identifies the amount of available uplink data with respect to a logical channel group corresponding to a bearer and defined for each of the base stations And generating a buffer state report including an ID for identifying the logical channel group and the buffer size information, and transmitting the buffer state report.

According to another aspect of the present invention, a method for transmitting a buffer status report of a terminal in a wireless communication system includes a single radio bearer configured in at least two or more base stations having dual connectivity with the terminal and an RLC of the base stations. (Radio Link Control) When the layers are connected to each other, the base station for transmitting the buffer status report according to the priority of the data arrived in the buffer based on the uplink resource situation, uplink reliability and uplink transmission rate of each base station. And transmitting a buffer status report to the selected base station.

According to another aspect of the present invention, a terminal transmitting a buffer status report in a wireless communication system corresponds to a single radio bearer configured between base stations and the terminal based on dual connectivity and the base stations Regarding the logical channel group defined for each, generating buffer size information that identifies the amount of available uplink data and identifying the logical channel group It may include a generation unit for generating a buffer state report including an ID and the buffer size information, and a transmission unit for transmitting the buffer state report.

According to another aspect of the present invention, a terminal for transmitting a buffer status report in a wireless communication system is configured in at least two or more base stations having a single radio bearer (dual connectivity) with the terminal and the When the radio link control (RLC) layers are connected to each other, the base station to transmit the buffer status report is selected according to the priority of the data arriving in the buffer based on the uplink resource status of each base station, the reliability of the uplink, and the uplink transmission rate. And a transmitter for transmitting a buffer status report to the selected base station.

In a wireless communication system, a terminal may transmit a buffer state report in logical channel units mapped to a radio bearer allocated to a specific base station.

Scheduling request for a logical channel mapped to the single radio bearer when the terminal is dually connected to two or more different base stations and a single radio bearer is configured in the terminal through the two or more different base stations. Request and the base station to send the buffer status report can be determined.

1 is a diagram illustrating a network structure of a wireless communication system to which the present invention is applied.

2 is a block diagram illustrating a radio protocol architecture for a user plane.

3 is a block diagram illustrating a radio protocol architecture for a control plane.

4 is a diagram illustrating a structure of a bearer service in a wireless communication system to which the present invention is applied.

5 is a diagram illustrating a dual connection situation of a terminal applied to the present invention.

6 is a diagram illustrating a process of transmitting data to a base station by a terminal applied to the present invention.

7 is a diagram illustrating a case in which a terminal applied to the present invention fails to transmit data.

8 illustrates a MAC control element of a buffer status report to which the present invention is applied.

9 is a diagram illustrating logical channel configuration information to which the present invention is applied.

10 is a diagram illustrating buffer status report related parameters.

FIG. 11 is a diagram illustrating an Infinite Source Delay System. FIG.

FIG. 12 is a diagram illustrating a Tandem Queuing System. FIG.

13 to 15 are exemplary diagrams illustrating a case in which a terminal is dually connected to a small base station and a macro base station.

16 is a flowchart illustrating an example of a method of transmitting a buffer status report according to the present invention.

17 illustrates a format of a buffer status report according to the present invention.

18 is a diagram illustrating a case where a base station for transmitting a buffer status report is determined by a network.

19 is a diagram illustrating a case where a base station for transmitting a buffer status report is determined by a determination of a terminal.

20 is a block diagram illustrating an example of an apparatus for transmitting a buffer status report according to the present invention.

Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings and examples, together with the contents of the present disclosure. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are used as much as possible even though they are shown in different drawings. In addition, in describing the embodiments of the present specification, when it is determined that a detailed description of a related well-known configuration or function may obscure the gist of the present specification, the detailed description thereof will be omitted.

In addition, the present specification describes a wireless communication network, the operation performed in the wireless communication network is performed in the process of controlling the network and transmitting data in the system (for example, the base station) that is in charge of the wireless communication network, or the corresponding wireless Work may be performed in a terminal included in the network.

1 illustrates a network structure of an Evolved-Universal Mobile Telecommunications System (E-UMTS system) as an example of a wireless communication system. The E-UMTS system may be an Evolved-UMTS Terrestrial Radio Access (E-UTRA) or Long Term Evolution (LTE) or LTE-A (Advanced) system. Wireless communication systems include 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), and OFDM-FDMA Various multiple access schemes such as OFDM, TDMA, and OFDM-CDMA may be used.

Referring to FIG. 1, an Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN) is a base station providing a control plane (CP) and a user plane (UP) to a user equipment (UE) 10. (eNB: evolved NodeB, 20).

The terminal 10 may be fixed or mobile, and may be called by other terms such as mobile station (MS), advanced MS (AMS), user terminal (UT), subscriber station (SS), and wireless device (Wireless Device). have.

The base station 20 generally refers to a station for communicating with the terminal 10, and includes a base station (BS), a base transceiver system (BTS), an access point, an femto base station, and a pico-eNB. It may be called other terms such as a base station (pico-eNB), a home base station (Home eNB), a relay, and the like. The base stations 20 are physically connected through an optical cable or a digital subscriber line (DSL), and may exchange signals or messages with each other through an X2 interface. Hereinafter, the description of the physical connection will be omitted and the logical connection will be described. As shown in FIG. 1, the base station 20 is connected to an Evolved Packet Core (EPC) 30 through an S1 interface. More specifically, the base station 20 is connected to the Mobility Management Entity (MME) through the S1-MME interface, and is connected to the Serving Gateway (S-GW) through the S1-U interface. The base station 20 exchanges contents information of the MME and context information of the terminal 10 and information for supporting mobility of the terminal 10 through the S1-MME interface. In addition, the S-GW and the data to be serviced to each terminal 10 through the S1-U interface.

Although not shown in FIG. 1, the EPC 30 includes MME, S-GW, and Packet Data Network Gateway (P-GW). The MME has access information of the terminal 10 or information on the capability of the terminal 10, and this information is mainly used for mobility management of the terminal 10. The S-GW is a gateway having an E-UTRAN as an endpoint, and the P-GW is a gateway having a PDN (Packet Data Network) as an endpoint.

The E-UTRAN and the EPC 30 may be integrated to be referred to as EPS (Evolved Packet System), and the traffic flows from the radio link to which the terminal 10 connects to the base station 20 to the PDN connected to the service entity are all IP. It works based on (Internet Protocol).

The air interface between the terminal 10 and the base station 20 is called a "Uu interface". Layers of the radio interface protocol between the terminal 10 and the network may include a first layer L1 defined in a 3GPP (3rd Generation Partnership Project) -based wireless communication system (UMTS, LTE, LTE-Advanced, etc.), It may be divided into a second layer L2 and a third layer L3. Among these, the physical layer belonging to the first layer provides an information transfer service using a physical channel, and the RRC (Radio Resource Control) layer located in the third layer exchanges an RRC message for the UE. Control radio resources between the network and the 10.

FIG. 2 is a block diagram showing a radio protocol architecture for a user plane, and FIG. 3 is a block diagram showing a radio protocol architecture for a control plane. The user plane is a protocol stack for user data transmission, and the control plane is a protocol stack for control signal transmission.

2 and 3, a physical layer (PHY) layer provides an information transfer service to a higher layer using a physical channel. The physical layer is connected to the upper layer by a medium access control (MAC) layer through a transport channel. Data is transmitted through a transport channel between the MAC layer and the physical layer. Transport channels are classified according to how data is transmitted over the air interface.

In addition, data is transmitted over a physical channel between different physical layers (ie, between physical layers of a transmitter and a receiver). The physical channel may be modulated by an orthogonal frequency division multiplexing (OFDM) scheme and utilizes space generated by time, frequency, and a plurality of antennas as radio resources.

For example, a physical downlink control channel (PDCCH) of a physical channel informs a terminal of resource allocation of a PCH (Paging CHannel) and DL-SCH (DownLink Shared CHannel) and HARQ (Hybrid Automatic Repeat Request) information related to the DL-SCH, The terminal may carry an uplink scheduling grant informing of resource allocation of uplink transmission. In addition, the Physical Control Format Indicator CHannel (PCFICH) informs the UE of the number of OFDM symbols used for the PDCCHs and is transmitted every subframe. In addition, the PHICH (Physical Hybrid ARQ Indicator CHannel) carries a HARQ ACK / NAK signal in response to the uplink transmission. In addition, the physical uplink control channel (PUCCH) carries uplink control information such as HARQ ACK / NAK, scheduling request, and CQI for downlink transmission. In addition, the PUSCH (Physical Uplink Shared CHannel) carries an UL-SCH (UpLink Shared CHannel). If necessary according to the configuration and request of the base station, the PUSCH may include channel state information (CSI) information such as HARQ ACK / NACK and CQI.

The MAC layer may perform multiplexing or demultiplexing into a transport block provided as a physical channel on a transport channel of a MAC service data unit (SDU) belonging to the logical channel and mapping between the logical channel and the transport channel. The MAC layer provides a service to a Radio Link Control (RLC) layer through a logical channel. The logical channel may be divided into a control channel for transmitting control region information and a traffic channel for delivering user region information. As an example, services provided from the MAC layer to a higher layer include data transfer or radio resource allocation.

Functions of the RLC layer include concatenation, segmentation, and reassembly of RLC SDUs. The RLC layer uses a transparent mode (TM), an unacknowledged mode (UM), and an acknowledgment mode (AM) in order to guarantee various quality of services (QoS) required by a radio bearer (RB). Three modes of operation are provided: Acknowledgment Mode.

In general, transparent mode is used to set up an initial connection.

Unacknowledged mode is for real-time data transmission, such as data streaming or Voice over Internet Protocol (VoIP), which focuses on speed rather than reliability of data. The acknowledgment mode, on the other hand, focuses on the reliability of the data and is suitable for large data transmissions or data transmissions that are less sensitive to transmission delays. The base station determines the mode of the RLC in the RB corresponding to each EPS bearer based on the Quality of Service (QoS) information of each EPS bearer configured to be connected to the terminal, and configures the parameters in the RLC to satisfy the QoS.

The RLC SDUs are supported in various sizes, and for example, may be supported in units of bytes. RLC Protocol Data Units (PDUs) are defined only when a transmission opportunity is notified from a lower layer (eg, MAC layer) and delivered to the lower layer. The transmission opportunity may be informed with the size of the total RLC PDUs to be transmitted. In addition, the transmission opportunity and the size of the total RLC PDUs to be transmitted may be separately informed.

Functions of the Packet Data Convergence Protocol (PDCP) layer in the user plane include the transfer of user data, header compression and ciphering, and the transfer and control of encryption / integrity protection of control plane data.

The RRC layer is responsible for the control of logical channels, transport channels, and physical channels in connection with configuration, re-configuration, and release of RBs. A radio bearer (RB) refers to a logical path provided by a first layer (PHY layer) and a second layer (MAC layer, RLC layer, PDCP layer) for data transmission between the terminal and the network. The configuration of the RB means a process of defining characteristics of a radio protocol layer and a channel to provide a specific service, and setting each specific parameter and operation method. The RB may be classified into a signaling RB (SRB) and a data RB (DRB). The SRB is used as a path for transmitting RRC messages and non-access stratum (NAS) messages in the control plane, and the DRB is used as a path for transmitting user data in the user plane.

The non-access stratum (NAS) layer located above the RRC layer performs functions such as session management and mobility management. If there is an RRC connection between the RRC layer of the UE and the RRC layer of the E-UTRAN, the UE is in an RRC connected state, otherwise it is in an RRC idle state. do.

In order for a terminal to transmit user data (eg, an IP packet) to an external internet network or to receive user data from an external internet network, the terminal exists between mobile communication network entities existing between the terminal and the external internet network. Resources must be allocated to different paths. Thus, a path in which resources are allocated between mobile communication network entities and data transmission and reception is possible is called a bearer.

4 shows a path in which end-to-end service is provided between a terminal and an internet network. Here, the end-to-end service refers to a service that requires a path between the terminal and the P-GW (EPS Bearer) and a P-GW and an external bearer for the Internet network and data service. Here, the external path is a bearer between the P-GW and the Internet network.

When the terminal transmits data to the external internet network, the terminal first transmits the data to the base station eNB through the RB. Then, the base station transmits the data received from the terminal to the S-GW through the S1 bearer. The S-GW delivers the data received from the base station to the P-GW via the S5 / S8 bearer, and finally the data is delivered through the external bearer to a destination existing in the P-GW and the external Internet network.

Similarly, in order to transmit data from the external Internet network to the terminal, the data can be delivered to the terminal through each bearer in the reverse direction as described above.

As described above, in the wireless communication system, each bearer is defined for each interface to ensure independence between the interfaces. The bearer at each interface will be described in more detail as follows.

The bearers provided by the wireless communication system are collectively called an Evolved Packet System (EPS) bearer. An EPS bearer is a delivery path established between a UE and a P-GW for transmitting IP traffic with a specific QoS. The P-GW may receive IP flows from the Internet or send IP flows to the Internet. Each EPS bearer is set with QoS decision parameters that indicate the nature of the delivery path. One or more EPS bearers may be configured per UE, and one EPS bearer uniquely represents a concatenation of one E-UTRAN Radio Access Bearer (E-RAB) and one S5 / S8 bearer.

The S5 / S8 bearer is a bearer of the S5 / S8 interface. Both S5 and S8 are bearers present at the interface between the S-GW and the P-GW. The S5 interface exists when the S-GW and the P-GW belong to the same operator, and the S8 interface belongs to the provider (Visited PLMN) roamed by the S-GW, and the P-GW has subscribed to the original service (Home). PLMN).

The E-RAB uniquely represents the concatenation of the S1 bearer and the corresponding RB. When there is one E-RAB, one-to-one mapping is established between the E-RAB and one EPS bearer. That is, one EPS bearer corresponds to one RB, S1 bearer, and S5 / S8 bearer, respectively. The S1 bearer is a bearer at the interface between the base station and the S-GW.

RB means two types of data radio bearer (DRB) and signaling radio bearer (SRB). However, in the present invention, RB is a DRB provided in the Uu interface to support a service of a user. . Therefore, the RB expressed without distinction is distinguished from the SRB. The RB is a path through which data of the user plane is transmitted, and the SRB is a path through which data of the control plane, such as the RRC layer and NAS control messages, are delivered. One-to-one mapping is established between RB, E-RAB and EPS bearer.

EPS bearer types include a default bearer and a dedicated bearer. When the terminal accesses the wireless communication network, an IP address is assigned, a PDN connection is created, and a default EPS bearer is created at the same time. That is, a default bearer is first created when a new PDN connection is created. When a user uses a service (for example, the Internet, etc.) through a default bearer, and uses a service (for example, VoD, etc.) that the default bearer cannot provide QoS properly, the user may be on-demand. A dedicated bearer is created. In this case, the dedicated bearer may be set to a different QoS from the bearer that is already set. QoS decision parameters applied to the dedicated bearer are provided by a Policy and Charging Rule Function (PCRF). Upon creation of a dedicated bearer, the PCRF may receive subscription information of a user from a Subscriber Profile Repository (SPR) to determine QoS determination parameters. Up to 15 dedicated bearers may be created, for example. However, four of the above 15 are not used in the LTE system. Therefore, up to 11 dedicated bearers may be generated in an LTE system.

The EPS bearer includes a QoS Class Identifier (QCI) and Allocation and Retention Priority (ARP) as basic QoS decision parameters. EPS bearers are classified into GBR (Guaranteed Bit Rate) bearers and non-GBR bearers according to QCI resource types. The default bearer is always set to a non-GBR type bearer, and the dedicated bearer may be set to a GBR type or non-GBR type bearer. The GBR bearer has GBR and MBR (Maximum Bit Rate) as QoS decision parameters in addition to QCI and ARP. After the QoS that the wireless communication system must provide as a whole is defined as an EPS bearer, each QoS is determined for each interface. Each interface sets up a bearer according to the QoS it needs to provide.

5 is a diagram illustrating an example of a dual connectivity situation of a terminal applied to an embodiment of the present invention.

In FIG. 5, for example, the terminal 550 enters an area in which the service area of the macro cell F2 in the macro base station 500 and the service area of the small cell F1 in the small base station 510 overlap. The case is shown.

In this case, in order to support an additional data service through the small cell F1 in the small base station 510 while maintaining the existing wireless connection and data service connection through the macro cell F2 in the macro base station 500, Configure a dual connection for the terminal 550. Accordingly, user data arriving at the macro base station 500 may be transmitted to the terminal through the small base station 510. Specifically, the F2 frequency band is allocated to the macro base station 500, and the F1 frequency band is allocated to the small base station 510. The terminal 550 may receive the service through the F2 frequency band from the macro base station 500 and may receive the service through the F1 frequency band from the small base station 510. In the above example, the macro base station 500 uses F2 and the small base station 510 is described as using the F1 frequency band. However, the present invention is not limited thereto, and both the macro base station 500 and the small base station 510 have the same F1 or F2 frequency. Bands can also be used.

6 is a diagram illustrating a process in which a terminal to which an embodiment of the present invention is applied transmits data to a base station, and FIG. 7 is a diagram illustrating a case in which a terminal to which the embodiment of the present invention is applied fails to transmit data.

As shown in FIG. 6, when the UE has data to be transmitted through uplink and a buffer state report (BSR) is triggered (S610), the UE induces the base station to allocate uplink resources. A scheduling request (SR) is transmitted (S620). The SR is transmitted through the PUCCH, and the base station allocates resources for transmitting the SR to each terminal.

When the terminal receives an uplink grant (UL grant) for the SR from the base station (S630), and transmits the BSR (S640). The BSR is for informing the base station that there is data to be transmitted by the terminal through the uplink, and to provide QoS aware packet scheduling support for the uplink. In other words, the BSR procedure is performed after the SR transmission and is used to provide the serving base station with information about the amount of available data in the uplink buffer of the terminal.

The terminal configures a BSR based on data buffered in each logical channel group (LCG) in the terminal. Up to four LCGs may be configured in the terminal. The BSR has a short format for reporting the buffer status of one LCG and a long format for reporting the buffer status of four LCGs. The format of the BSR may refer to FIG. 8 to be described later.

The base station may configure a periodic BSR timer (periodicBSR-Timer) and a retransmission BSR timer (retxBSR-Timer) through signaling defined in the RRC layer, and control a BSR procedure for a logical channel in each terminal. That is, since the BSR is performed for the LCG, the base station may transmit logical channel configuration information including the syntaxes of FIGS. 9 and 10 to the terminal.

In the BSR procedure, the UE should consider a suspended radio bearer (RB) and all unreserved RBs.

On the other hand, BSRs include a regular BSR, a padding BSR, and a periodic BSR. The general BSR is triggered when the uplink data that can be transmitted to a logical channel having a higher priority than other logical channels that already have transmittable data is present in the RLC entity or PDCP entity for the logical channel included in the LCG. . In addition, the general BSR is triggered even when the retxBSR-Timer expires and the UE has data that can be transmitted on a logical channel in the LCG. The padding BSR is triggered when uplink resources are allocated and the number of padding bits is equal to or greater than the size for BSR transmission. Periodic BSR is triggered when the periodicBSR-Timer expires.

The UE performs a BSR procedure when at least one of the BSRs is triggered and is not canceled. If an uplink resource for a new transmission is allocated to this transmission time interval (TTI), the UE instructs a multiplexing and assembly procedure for generating a BSR MAC control element, starts or restarts a periodicBSR-Timer. Start or restart the retxBSR-Timer. Here, the procedure of starting or restarting the periodicBSR-Timer is excluded when a shortened BSR (Truncated BSR) is generated. When a normal BSR is triggered, if the uplink grant is not configured or if the normal BSR is not triggered due to the presence of uplink data that can be transmitted on a specific logical channel for which SR masking is set up by a higher layer, then the SR is It must be triggered. That is, the SR is triggered when a general BSR is triggered by a specific logical channel for which SR masking is not set up.

At this time, one MAC PDU should include only one MAC control element even if multiple BSRs are triggered. And, if a general BSR and a periodic BSR can be transmitted, this always takes precedence over the padding BSR. In addition, upon confirming receipt of an indicator indicating transmission of new data for all UL-SCHs, the terminal should restart the retxBSR-Timer. All triggered BSRs should be canceled when they receive an UL grant that can send all pending data but cannot send additional BSR MAC control elements. In addition, all triggered BSRs must be canceled when the BSR is included in the MAC PDU. The terminal should transmit one general / periodic BSR in one TTI. If the UE is required to transmit a plurality of MAC PDUs in one TTI, one padding BSR may be included in any MAC PDUs that do not include a general / periodic BSR. All BSRs always reflect the buffer status after all MAC PDUs are configured in the TTI over which the BSR is sent. Each LCG must report one buffer status value per TTI, and the buffer status values must be reported through the BSR for the LCG within every BSR. That is, one BSR value should be transmitted for each LCG in the same TTI, and the buffer status value for the LCG should be the same value for all BSRs transmitted in the same TTI. On the other hand, the padding BSR is not allowed to cancel the general / periodic BSR. The padding BSR is triggered for a specific MAC PDU, and the trigger of the padding BSR is canceled when a specific MAC PDU is generated.

6 again, when the terminal receives an uplink grant for the buffer status report from the base station (S650), since resources for the transmission of the uplink data are allocated, substantial data transmission is then performed (S660).

Next, referring to FIG. 7, if the number of terminals currently connected to the base station is greater than the amount of resources to transmit the SR to the base station, the terminal may not be allocated an SR resource. Alternatively, even though the SR is transmitted, uplink resource allocation from the base station may be performed after a specific period, or data transmission may not be performed even if the number of SR transmissions exceeds a specific number. In this case, the UE starts a contention-based random access (RA) procedure through the primary serving cell or the serving cell transmitting the corresponding SR as an alternative corresponding to the purpose of the SR.

In detail, when the SR is triggered and there is no SR currently pending, the terminal sets the SR count (SR_COUNTER) to zero. However, the SR is pending and there is a valid PUCCH resource to send the SR in this Transmission Time Interval (TTI), this TTI is not part of the measurement gap and a timer (sr) to prohibit SR transmission. If ProhibitTimer is not in progress, if the SR_COUNTER value is less than the maximum number of transmissions of the SR, the SR count value is increased by 1 and the physical layer is instructed to transmit the SR signal through the PUCCH, and then sr-ProhibitTimer is started. However, if the SR_COUNTER value is greater than or equal to the maximum number of transmissions, RRC is notified of the release of PUCCH and SRS (Sounding Reference Signal), and all configured downlink allocations and uplink grants are cleared. It then initializes the random access procedure and cancels all pending SRs.

Meanwhile, if the SR is pending but there is no UL-SCH resource available for transmission in any TTI, the UE initializes the random access procedure and cancels all the pending SRs.

Therefore, when the wrong power is set from the base station as shown in FIG. 7 (S710), the UE transmits the SR until the SR_COUNTER value is equal to the maximum number of transmissions of the SR (S720 and S730). If the SR_COUNTER value is equal to the maximum number of transmissions of the SR, the terminal releases uplink resources and initializes a random access procedure (S740), and then transmits a random access preamble (S750).

8 illustrates a MAC control element of a buffer status report to which an embodiment of the present invention is applied.

Referring to FIG. 8, the MAC control element (a) of the short BSR and the divided BSR includes an LCG ID field and a buffer size (BS) field. In addition, the MAC control element (b) of the long BSR is composed of four buffer size fields corresponding to four LCG IDs (LCG ID # 0 to LCD ID # 3). The BSR format is identified by a value of a logical channel identifier (LCID) included in a sub header of a MAC PDU as shown in Table 1 below.

Table 1

index	LCID value
00000	CCCH
00001-01010	Logical Channel Identification
01011-11000	Spare
11001	Extended Power Remaining Report
11010	Power Remaining Report
11011	C-RNTI
11100	Partitioned BSR
11101	Short BSR
11110	Long BSR
11111	padding

The LCG ID field is for identifying a group of logical channels whose buffer status is reported to the base station. The LCD ID field is 2 bits long. The buffer size field is used to identify the total amount of data available on all logical channels in the LCG after all MAC PDUs for the TTI have been established, and contains information about all data that can be transmitted in the RLC layer and the PDCP layer. do. Here, the RLC header and PDCP header are not taken into account in the buffer size calculation. The length of the buffer size field is 6 bits. In the case of not the extended BSR size (extendedBSR-size), the value of the buffer size field is shown in Table 2, and in the case of the extended BSR size, the value of the buffer size field is shown in Table 3.

TABLE 2

index	Buffer size value (bytes)	index	Buffer size value (bytes)
0	BS = 0	32	1132 <BS <= 1326
One	0 <BS <= 10	33	1326 <BS <= 1552
2	10 <BS <= 12	34	1552 <BS <= 1817
3	12 <BS <= 14	35	1817 <BS <= 2127
4	14 <BS <= 17	36	2127 <BS <= 2490
5	17 <BS <= 19	37	2490 <BS <= 2915
6	19 <BS <= 22	38	2915 <BS <= 3413
7	22 <BS <= 26	39	3413 <BS <= 3995
8	26 <BS <= 31	40	3995 <BS <= 4677
9	31 <BS <= 36	41	4677 <BS <= 5476
10	36 <BS <= 42	42	5476 <BS <= 6411
11	42 <BS <= 49	43	6411 <BS <= 7505
12	49 <BS <= 57	44	7505 <BS <= 8787
13	57 <BS <= 67	45	8787 <BS <= 10287
14	67 <BS <= 78	46	10287 <BS <= 12043
15	78 <BS <= 91	47	12043 <BS <= 14099
16	91 <BS <= 107	48	14099 <BS <= 16507
17	107 <BS <= 125	49	16507 <BS <= 19325
18	125 <BS <= 146	50	19325 <BS <= 22624
19	146 <BS <= 171	51	22624 <BS <= 26487
20	171 <BS <= 200	52	26487 <BS <= 31009
21	200 <BS <= 234	53	31009 <BS <= 36304
22	234 <BS <= 274	54	36304 <BS <= 42502
23	274 <BS <= 321	55	42502 <BS <= 49759
24	321 <BS <= 376	56	49759 <BS <= 58255
25	376 <BS <= 440	57	58255 <BS <= 68201
26	440 <BS <= 515	58	68201 <BS <= 79846
27	515 <BS <= 603	59	79846 <BS <= 93479
28	603 <BS <= 706	60	93479 <BS <= 109439
29	706 <BS <= 826	61	109439 <BS <= 128 125
30	826 <BS <= 967	62	128 125 <BS <= 150000
31	967 <BS <= 1132	63	BS> 150000

TABLE 3

index	Buffer size value (bytes)	index	Buffer size value (bytes)
0	BS = 0	32	4940 <BS <= 6074
One	0 <BS <= 10	33	6074 <BS <= 7469
2	10 <BS <= 13	34	7469 <BS <= 9185
3	13 <BS <= 16	35	9185 <BS <= 11294
4	16 <BS <= 19	36	11294 <BS <= 13888
5	19 <BS <= 23	37	13888 <BS <= 17077
6	23 <BS <= 29	38	17077 <BS <= 20999
7	29 <BS <= 35	39	20999 <BS <= 25822
8	35 <BS <= 43	40	25822 <BS <= 31752
9	43 <BS <= 53	41	31752 <BS <= 39045
10	53 <BS <= 65	42	39045 <BS <= 48012
11	65 <BS <= 80	43	48012 <BS <= 59039
12	80 <BS <= 98	44	59039 <BS <= 72598
13	98 <BS <= 120	45	72598 <BS <= 89272
14	120 <BS <= 147	46	89272 <BS <= 109774
15	147 <BS <= 181	47	109774 <BS <= 134986
16	181 <BS <= 223	48	134986 <BS <= 165989
17	223 <BS <= 274	49	165989 <BS <= 204111
18	274 <BS <= 337	50	204111 <BS <= 250990
19	337 <BS <= 414	51	250990 <BS <= 308634
20	414 <BS <= 509	52	308634 <BS <= 379519
21	509 <BS <= 625	53	379519 <BS <= 466683
22	625 <BS <= 769	54	466683 <BS <= 573866
23	769 <BS <= 945	55	573866 <BS <= 705666
24	945 <BS <= 1162	56	705666 <BS <= 867737
25	1162 <BS <= 1429	57	867737 <BS <= 1067031
26	1429 <BS <= 1757	58	1067031 <BS <= 1312097
27	1757 <BS <= 2161	59	1312097 <BS <= 1613447
28	2161 <BS <= 2657	60	1613447 <BS <= 1984009
29	2657 <BS <= 3267	61	1984009 <BS <= 2439678
30	3267 <BS <= 4017	62	2439678 <BS <= 3000000
31	4017 <BS <= 4940	63	BS> 3000000

9 is a diagram illustrating logical channel configuration information to which an embodiment of the present invention is applied, and FIG. 10 is a diagram illustrating parameters related to buffer status reporting.

Referring to FIG. 9, logical channel configuration information includes information elements included in logical channel configuration. "priority" indicates a logical channel priority. The terminal is a MAC control element for data from UL-CCCH (Uplink-Common Control Channel) or Cell-Radio Network Temporary Identifier (C-RNTI), MAC control element for BSR except for BSR with padding, extended PHR or The MAC control element for the PHR takes precedence over the data in all logical channels for transmitting user data separately from the priority of the logical channel. In the case of the MAC control element for the BSR with padding, it has a lower priority than the data in all the logical channels. "prioritisedBitRate" represents the priority bit rate for the priority of the logical channel. The value of "prioritisedBitRate" is in kilobytes / second, kBps8 corresponds to 8 kB / second, and kBps16 corresponds to 16 kB / second. The value of "prioritisedBitRate" applies infinity for SRB1 and SRB2. "BucketSizeDuration" represents bucket size time for logical channel priority. The value of "BucketSizeDuration" is in milliseconds, ms50 corresponds to 50ms, ms100 corresponds to 100ms. "logicalChannelGroup" represents a logical channel mapped to LCG for BSR reporting. "logicalChannelSR-Mask" controls SR triggering based on a logical channel when an uplink grant is configured. Meanwhile, "SRmask" and "UL" fields may exist conditionally in the logical channel configuration. The "SRmask" field is optionally present depending on the existence of an uplink specific parameter (ul-SepcificParameter). The "UL" field is mandatory when an uplink logical channel exists and does not exist when an uplink logical channel does not exist.

Next, referring to FIG. 10, the MAC main setting (MAC-MainConfig) includes information about an extended BSR size (extendedBSR-Sizes-r10). The default MAC main configuration parameters are "maxHARQ-tx", "periodicBSR-Timer", "retxBSR-Timer", "ttiBunding", "drx-Config", "phr-Config" and "sr-ProhibitTimer". have.

For the purpose of MAC buffer status reporting, the UE may perform retransmission in RLC AM mode among RLC SDUs or segments of the RLC SDUs and RLC data PDUs or portions of RLC data PDUs. The reserved data should be considered as data that can be transmitted in the RLC layer. If the STATUS PDU is triggered and the t-StatusProhibit timer is not in progress or has expired, the UE must estimate the size of the STATUS PDU to be transmitted at the next transmission opportunity, and this can also be transmitted in the RLC layer included in the MAC buffer status report. Consider data.

In addition, the UE is not yet processed by PDCP for the SDUs for the PDUs that are not delivered to the lower layer, or PDCP control PDUs as well as the PDU in which the SDU is processed by the PDCP layer Consider data that can be transferred from

In addition, if the PDCP entity previously performed a re-establishment procedure for radio bearers mapped to the confirmation mode among the RLC's operating modes, the UE has not yet been processed by the PDCP in the SDU, The PDUs processed once by the PDU should be considered as data transmittable at the PDCP layer. In this case, if the PDCP status report is received from the SDUs starting from the first SDU whose delivery of the PDUs is not confirmed from the lower layer among the SDUs corresponding to the PDUs delivered only to the lower layer prior to the PDCP re-establishment. SDUs that have been successfully delivered through PDCP status reporting are excluded.

FIG. 11 is a diagram illustrating an Infinite Source Delay System, and FIG. 12 is a diagram illustrating a Tandem Queuing System.

In order to calculate the total buffer state for the BSR, the traffic arriving at the buffer first may be formulated as in Equation 1 below.

Equation 1

Where T _A is the random inter-arrival time, A (t) is the cumulative distribution function (CDF) for the arrival time interval, and A '(t) is the probability for the arrival time interval. Probability Density Function (PDF) E [TA] is the average arrival time interval and λ is the arrival rate.

In addition, the serviced traffic may be formulated as in Equation 2 below.

Equation 2

Where T _H is the Random Service (holding time), H (t) is the cumulative distribution function for the arrival time interval, H '(t) is the probability density function for the arrival time interval, and E [T _H ] Represents the expected average time between arrivals, and ε represents the termination rate.

Therefore, in the case of the Infinite source delay system having a single buffer as shown in FIG. 11, the arrival process (Arrival Process (M)) and the service process (Service Process (M)) are shown in Equations 3 and 4, respectively. Can be expressed as:

Equation 3

Equation 4

Based on this, the tamdom queuing system having a PDCP buffer and an RLC buffer may be expressed as shown in FIG. 12. Therefore, state equations for equilibrium state for stationary probabilities of state

Based on the number of average data in Station i is shown in Equation 5 below.

Equation 5

Therefore, the total buffer state for BSR transmission may be calculated using Equation 5.

First, referring to FIG. 13, both the macro base station and the small base station include a PDCP, RLC, MAC, and PHY layers. The first RB (# 1 RB) is configured through the PDCP layer and RLC layer of the terminal and the PDCP layer and RLC layer of the macro base station, and the second RB (# 2 RB) is the PDCP layer, RLC layer and small base station of the terminal It is composed of PDCP layer and RLC layer. The RBs may be configured to include a part of MAC layer related to logical channel configuration. The terminal is connected to the P-GW through a first EPS bearer (# 1 EPS bearer) and is connected to the P-GW through a second EPS bearer (# 2 EPS bearer). As such, each base station receives CN data through an EPS bearer (# 1 EPS bearer and # 2 EPS bearer) or RB (# 1 RB and # 2 RB) configured for one UE. Also called).

Next, a bearer split case is shown in FIGS. 14 and 15. The bearer split refers to a structure in which one RB is configured through a plurality of base stations to divide and transmit data into two flows (or more flows). Alternatively, when a single radio bearer is configured between the base stations and the terminal based on dual connectivity, a logical channel group defined for each of the base stations corresponding to the single radio bearer may be defined as a bearer split. The bearer split may be called multi flow, multiple node (eNB) transmission, inter-eNB carrier aggregation, etc. in that information is transmitted through a plurality of flows. Can be.

In the case of a bearer split, each base station may include a PDCP layer, a MAC layer and an RLC layer, but the layer responsible for flow control is included in only one base station (ie, macro base station). If the layer in charge of the flow control is a PDCP layer, the PDCP layer is included only in the macro base station.

The MAC layer of the base station in the existing LTE system delivers information on the amount of data, transmission opportunities, etc. to the RLC layer. The RLC layer configures an RLC PDU by splitting or combining the RLC SDU data received from the PDCP layer located in the same base station based on the information received from the MAC layer. Thereafter, the MAC layer receives the RLC PDU configured in the RLC from the RLC layer in the form of a MAC SDU. However, in the case of a bearer split, even if the RLC layer in the small base station processes the data according to the data amount and the transmission opportunity required by the MAC layer in the small base station, information on the processed data amount and the transmission opportunity exists in the upper RLC layer. Inform macro flow control layer in the macro base station.

To this end, the PDCP layer of the macro base station may be connected to the RLC layer of the small base station using the Xn interface protocol, as shown in FIG. 14. In this case, the Xn interface protocol is defined as an interface between the MeNB and the SeNB. The Xn interface protocol may be an X2 interface protocol defined between base stations in the LTE system. In this case, the PDCP layer of one macro base station is connected to both the RLC layer of the macro base station and the RLC layer of the small base station. Here, the RLC layer of the macro base station is referred to as # 1 sub-entity, and the RLC layer of the small base station is referred to as # 2 sub-entity. Sub-entities are divided into one-to-one matching between transmission and reception. The sub-entity may be called an entity.

In the case of FIG. 14, the RLC layer exists in a duplicated form. Each sub entity is independent but there are two sub entities (# 1 sub entity and # 2 sub entity) within one RB (ie, # 1 RB). In this case, RLC parameters should be configured separately for the RLC-AM # 1 sub-entity and the RLC-AM # 2 sub-entity, respectively. Because delay time that occurs when data serviced through each RLC-AM sub-entity is delivered to the UE may be different, timer values to be set in consideration of the delay time are different from each other. Because you can. If the delay times of the data transmitted through each sub-entity are the same, values of timers to be set for each sub-entity may be the same. This may be determined at the macro base station or at the small base station, or may be determined at a network including the macro base station and the small base station. Accordingly, data to be delivered via PDCP in the same RB may be transmitted through one of the RLC-AM # 1 sub-entities or the RLC-AM # 2 sub-entity. Here, an identifier may be further transmitted by the terminal that receives the data to identify which sub-entity the data is transmitted through.

The example of FIG. 14 is also called a sub-entity RLC type, a separated RLC type, or an independent RLC type among bearer split cases. However, the example of FIG. 14 is not necessarily applied only to the bearer split.

Meanwhile, referring to FIG. 15, the macro base station includes the PDCP, RLC, MAC, and PHY layers, but the small base station includes the RLC, MAC, and PHY layers. The RLC layer of the macro base station is connected to the RLC layer of the small base station using the Xn interface protocol. In this case, the RLC layer of the macro base station is called a master RLC layer, and the RLC layer of the small base station is called a slave RLC layer.

In the case of downlink, additional division is possible for the AMD / UM PDU of the slave RLC layer of the UE. The splitting operation of the slave RLC includes a grouping of a plurality of RLC PDUs or a grouping of AMD PDU segments divided in a macro RLC. In addition, concatenation is possible for the AMD / UM PDU of the slave RLC layer of the base station.

In the case of uplink, when the base station receives data through the slave RLC layer, the small base station forwards it to the macro RLC layer. Therefore, the same data may be received through the slave RLC layer or the MAC of the macro base station to the master RLC layer. Therefore, uplink transmission between the terminal and the base station may be a single transmission instead of TDM transmission.

On the other hand, the dynamic scheduling of radio resources is mainly responsible for the MAC scheduler in each base station. Since the situation of the MAC layer of the macro base station and the situation of the MAC layer of the small base station are different, the master RLC layer allocates (or splits, concatenates, or recombines) PDUs based on information provided by the MAC layer of the macro base station, and the slave RLC layer. Splits or connects based on information provided by the MAC layer of the small base station.

In the uplink, only one RLC layer exists from the terminal's point of view. In downlink, since the MAC layer is divided into two or more different base stations, and there is a difference in downlink radio conditions for each base station, the downlink data is divided or recombined in different ways in the RLC layer, whereas in uplink Since the slave RLC layer in the small base station simply forwards the received data to the macro RLC layer, only the RLC layer processing uplink data is the master RLC layer. Therefore, the dually connected UE includes only one PDCP layer and RLC layer in a single RB for data to be transmitted to two or more different base stations during uplink transmission. In addition, only one MAC layer may control uplink transmission according to uplink resource allocation information received from two or more different base stations for uplink transmission. Therefore, it is also possible to perform uplink transmission only to the macro base station in terms of uplink data transmission (for example, PUSCH) (also referred to as "single uplink").

The example of FIG. 15 is also called a master-slave RLC type among bearer split cases. However, the example of FIG. 15 is not necessarily applied only to the bearer split.

As described above with reference to FIGS. 13 to 15, in case of dual connectivity, each base station transmits downlink data through each component of an RB configured in each base station or a single RB configured redundantly in each base station for one UE and Process reception of uplink data. Therefore, data generated in each RB in the terminal should be delivered to the base station in which the RB corresponding to the corresponding RB is configured. Therefore, the terminal should generate a BSR based on the data present in the PDCP / RLC constituting each RB in the terminal and deliver it to each base station.

However, in the past, since only BSR defined in the UE-specific LCG unit was transmitted in the UE unit, the BSR could not be transmitted in the LC unit mapped to the RB allocated to the specific BS. Although the BSR may be transmitted in the LC unit mapped to each RB allocated to a specific base station, in the case of a bearer split, since the same RB and LC may be configured in a plurality of base stations, the base station to which the SR and the BSR should be transmitted should be selected. There was no standard for that.

Accordingly, the present invention provides a method for transmitting a scheduling request and a buffer status report for an LC mapped to a single RB when a single RB is configured through a plurality of base stations, that is, a bearer split.

When the scheduler of each base station can independently schedule uplink with respect to the terminal, that is, when a dynamic resource allocation (DRA) packet scheduling function exists independently for each base station among RRM functions, one of the following embodiments BSR can be sent.

In the following embodiment, it is assumed that the PDCP layer or the master RLC layer performs the flow control function of the flow control layer. However, it is not excluded that the flow control layer may be configured in the macro base station separately from the PDCP layer or the master RLC layer. In addition, it is assumed that a terminal configures dual connectivity with a macro cell in a macro base station and a small cell in a small base station and configures RRC (Radio Resource Control) for supporting the dual connection. In particular, although a configuration of a bearer split limited to a single RB is described as an example, the scope of the present invention is not limited thereto, and the present invention may be applied to a bearer split for a plurality of RBs.

In this case, in the case of a control plane (CP) (eg, generation and transmission of RRC signaling), a bearer split for a signaling radio bearer may be configured, and in this case, a user plane (UP) The defined bearer split scheme can be equally applied to SRBs defined in the control plane. That is, the configuration may be the same.

In addition, the terminal applied to the present invention may provide information distinguished for each RB (that is, information on whether or not a bearer split is applied in each RB) or a plurality of RBs (eg, logical channel groups). (logical channel group) may be used to provide common information. At this time, the configuration information for each RB is independent of each other. For example, when the first RB includes information for configuring a bearer split (eg, "MF on"), the information on the second RB transmitted simultaneously with the information on the first RB may be RB flow reconfiguration ( RB flow reconfiguration) information (eg, "MF off") may be included.

First embodiment: when the bearer is not split

For example, in the case of a CN split as shown in FIG. 13, each base station needs to know which uplink data is to be preferentially processed according to a priority value set for each logical channel in each LCG. Therefore, BSRs for all RBs (# 1 RB and # 2 RB) configured in all base stations (macro base station and small base station) included in the dual connection may be shared among all the base stations. Furthermore, when the terminal can simultaneously transmit uplink to each base station, when the base station allocates uplink resources to the corresponding terminal, transmission power for allocating the uplink resources is allocated, so that other base stations allocate uplink resources to the corresponding terminal. This should be considered. Accordingly, the schedulers in each base station may share the BSR received from the terminal with each other to determine the amount of uplink resources to be set in the base station using the priority value and the BSR value of the logical channel for the counterpart base station.

However, if the terminal operates in TDM during uplink transmission, the terminal cannot transmit uplink data to two or more base stations at the same time. That is, time slots (subframes or radio frame units) allocated to each base station are distinguished from each other. Therefore, in this case, it may not be a problem even if the BSR for the logical channel allocated to the counterpart base station is not shared.

Second Embodiment: When a Bearer is Split and Separated PDCP or Separate RLC Type

16 is a flowchart illustrating an example of a method of transmitting a buffer status report according to the present invention, and FIG. 17 is a diagram illustrating a format of a buffer status report according to the present invention. Hereinafter, referring to FIGS. 14, 16, and 17, a single RB is configured in at least two or more base stations dually connected with the terminal, and a single RB in the terminal is split into a plurality of separate PDCP entities or separate RLC entities. When configured, a method of generating and transmitting a BSR is described.

Referring to FIG. 16, a terminal configures a single radio bearer between a macro base station / small base station and the terminal based on dual connectivity (S1610).

The terminal calculates a buffer size that identifies the amount of available uplink data with respect to a logical channel group defined for each of the macro base station and the small base station by the bearer split, and indicates the buffer size. Buffer size information is generated (S1620).

In the case of the separated RLC or the separated PDCP, there are a plurality of LCGs separated from each other for logical channels configured as bearer splits. Here, the LCGs may be defined for different base stations. For example, if a logical channel consisting of a bearer split is # 4 LC, # 5 LC, # 7 LC, the LCG including the LCs may be divided into LCG 2 to be transmitted to the macro base station and LCG 3 to be transmitted to the small base station. . At this time, the terminal generates first buffer size information on LCG 2 and generates second buffer size information on LCG 3.

As shown in FIG. 14, when a single radio bearer is configured as a single PDCP layer corresponding to all of the base stations and a plurality of RLC entities respectively corresponding to each of the base stations, a method of generating buffer size information may be various. There can be.

For example, the UE may generate buffer size information based on the sum of the buffer size of a single PDCP layer and the buffer size of one RLC entity among a plurality of RLC entities, as shown in FIG. 17 (a).

As another example, as shown in FIG. 17B, the UE has a value different from a 'a' corresponding to the ratio of the buffer size of one RLC entity among the buffer sizes of the plurality of RLC entities in the buffer size of the single PDCP layer. The buffer size of the single PDCP layer is separated by a value '(1-a)' corresponding to the ratio of the buffer size of the RLC entity of the unit, and the ratio of the buffer size of the one RLC entity to the buffer size corresponding to the RLC entity Buffer size information for each LCG may be generated based on the sum of the buffer sizes of the single PDCP layer separated by a value corresponding to.

As another example, as shown in FIG. 17C, the UE may generate the buffer size information using only buffer size information for each RLC entity.

In the above embodiments, when the UE calculates the buffer size, the method described with reference to FIGS. 11 and 12 and Equations 1 to 5 may be used.

Referring back to FIG. 16, the terminal generates an ID (eg, LCG 2 and LCG 3) identifying each logical channel group and a buffer status report including the buffer size information, respectively (S1630). For example, in the above example, the terminal may generate a first buffer status report including LCG2 and first buffer size information and a second buffer status report including LCG3 and second buffer size information.

The terminal may transmit the buffer status report generated for each base station to the corresponding base station, respectively (S1640 and S1650).

That is, as shown in FIG. 14, in the case of the separated RLC among the bearer split cases, the terminal may generate and generate buffer size information to be reported to each base station.

Third Embodiment: Bearer Split and Master-Slave RLC Type

In the master-slave RLC scheme as shown in FIG. 15, the BSR for a single RB configured in all base stations included in the dual connection may be transmitted only to one of the base stations. The subject that determines which base station the BSR is transmitted to may be a terminal or a base station.

FIG. 18 is a diagram illustrating a case where a base station to which a terminal transmits a buffer status report is determined by a network, and FIG. 19 is a diagram illustrating a case where a base station to transmit a buffer status report is determined by a terminal.

18 illustrates an example in which a terminal transmits a buffer status report to a small base station by the macro base station. In this case, when the macro base station receives a measurement report from the terminal (S1810), after determining the dual connectivity configuration, and determines the uplink transmission through the small base station for the RB consisting of the bearer split (S1820). In operation S1830, information for requesting allocation of an SR resource for a corresponding UE from among PUCCH resources in a specific serving cell in the small base station is transmitted through the dual connection establishment request. Thereafter, upon receiving a response to the dual connectivity establishment request from the small base station (S1840), the macro base station delivers the SR resource configuration information to the terminal through an RRC reconfiguration procedure (S1850). The terminal may confirm that the base station to which the BSR is to be transmitted is the small base station based on the SR resource configuration information. In this case, when the RRC layer exists in the small base station according to the dual connectivity configuration, the RRC reconfiguration procedure may be performed by the small base station. Thereafter, if the traffic arriving at the RLC / PDCP buffer is identified (S1860), the terminal transmits an SR to the small base station (S1870). When an uplink grant is received from the small base station (S1880), the BSR is transmitted (S1890). Meanwhile, FIG. 19 illustrates a case in which the terminal transmits a buffer status report to the small base station by the determination of the terminal.

In this case, when the macro base station receives a measurement report from the terminal (S1910), it transmits a dual connection establishment request to the small base station (S1920). When receiving the acceptance of the dual connectivity configuration from the small base station (S1930), the SR resource configuration information is transmitted to the terminal through the RRC reconfiguration procedure (S1940). In this case, when the RRC layer exists in the small base station according to the dual connectivity configuration, the RRC reconfiguration procedure may be performed by the small base station.

Thereafter, the terminal identifies traffic arriving at the RLC / PDCP buffer (S1950), and determines an uplink path for user data to a base station that is advantageous for uplink transmission according to the priority of the traffic (S1960). At this time, if the determined path is a path through the small base station, the terminal transmits the SR to the small base station (S1970), and when receiving the uplink grant (S1980), and transmits the BSR to the small base station (S1990).

As described above, in the master-slave RLC scheme, since the RLC entity of the macro base station and the RLC entity of the small base station are connected, it does not matter to which base station, all PDCP control PDUs and RLC control PDUs including the RLC status report are transmitted. Accordingly, the terminal may transmit a BSR to a base station that can easily receive uplink resource allocation. That is, the terminal may transmit the BSR to the base station determined by the network as shown in FIG. 18 or transmit the BSR to the base station determined to be advantageous in uplink transmission as determined by the terminal as shown in FIG. 19. For example, the UE includes a serving cell configured with a PUCCH (for example, a primary cell or a special cell) or a serving cell configured with a PUCCH configured to transmit a PRACH to replace a serving cell or a scheduling request allocated with SR resources. The BSR can be transmitted to the established base station.

The UE is (1) which base station is most likely to be allocated an uplink resource (2) which base station uplink transmission is efficient (throughput) (3) which base station uplink transmission can be performed quickly (delay ) May determine a base station advantageous for uplink transmission and transmit the BSR to the determined base station.

The uplink situation may be affected by feedback information for downlink transmission. Accordingly, a low loading factor having a good uplink resource situation is a base station having a small number of RRC connected users. Therefore, the terminal has a high probability of being allocated uplink resources from a small base station having a small number of terminals. However, in the case of TDM, the base station that can be allocated more time slots may vary according to the actual time slot allocation configuration.

Meanwhile, uplink transmission is efficient for a high SINR of uplink reliability. In the case of a base station relatively close to the terminal, it is highly likely to maintain a high reliability due to low PL. Therefore, a small base station having a probability small service radius has high reliability of uplink. However, in the case of TDM, the base station that can be allocated more time slots has a higher uplink reliability. Therefore, this case may be determined differently according to the actual time slot allocation configuration.

In addition, when the BSR is directly transmitted to the macro base station, since the delay time between the non-ideal backhaul existing between the macro base station and the small base station does not have to be considered, it can be quickly delivered.

In consideration of such matters, the terminal may transmit a BSR to a small base station or a base station with many uplink time slot assignments when the first data that arrives in the buffer corresponds to a low priority logical channel. However, when data having a higher priority than data currently stored in the buffer is received and the BSR is triggered, the triggered BSR is transmitted to the macro base station because the high priority data must be delivered quickly.

On the other hand, the BSR for the SRB may be transmitted limited to the base station capable of RRC transmission. If the base station capable of RRC transmission is a plurality of base stations, the BSR for the SRB may be determined based on the same criteria as the BSR for the DRB, and specific for each logical channel for each SRB based on the RRC message previously received from the base station. It may be limited to the base station and transmitted. For example, the BSR for the LCG including LC0, LC1, and LC2 corresponding to SRB0,1,2 may be transmitted to the macro base station, and the BSR for the LCG included in LC3 corresponding to SRB3 may be transmitted to the small base station. It can be transmitted in a limited manner.

Fourth Embodiment: Bearer Split

When the terminal is dually connected to two or more different base stations and a single RB is configured in the terminal through the two or more different base stations, the buffer size information may be shared among all base stations included in the dual connection.

For example, a plurality of logical channels included in a single LCG may be configured with a bearer split. In this case, BSR _{total, which} is a BSR for the single LCG, may be BSR _MeNB + BSR _SeNB . In this case, because the buffer size information of the BSR _total is shared to each base station, the uplink resource allocation scheduled by all base stations included in the dual connection may be 2BSR _total , which may cause inefficiency of uplink resources. have. However, when an uplink grant is received even when there is no data to be transmitted, the base station can further inform the base station that the current buffer size value is 0 by transmitting a padding BSR for the uplink grant, so that the base station no longer transmits to the corresponding user equipment. Do not proceed with link resource allocation. Therefore, inefficiency of uplink resources is not a big problem.

However, in case of the separated PDCP / separated RLC scheme, if BSR _total (50) = BSR _MeNB (0) + BSR _SeNB (50), the buffer size information reported to the base stations is only BSR _total . Due to the sharing of the buffer size information between the total uplink resources allocated by the macro base station and the small base station may be allocated twice, that is, 100 times the actual reported buffer size. In this case, 50 resources are used for uplink data transmission by the small base station, but since the uplink data to be transmitted to the macro base station is 0, the remaining 50 resources are not used. Accordingly, when the terminal receives an uplink grant from the macro base station, the terminal transmits a padding BSR and reports 50 as the padding BSR value. At this time, when the scheduler of each base station receives the padding BSR by checking the received uplink data, the scheduler of the base station ignores the value of the data in the padding BSR and determines that the buffer size information of the base station is 0.

20 is a block diagram illustrating an example of an apparatus for transmitting a buffer status report according to the present invention. Referring to FIG. 20, the terminal 2000 may include a generator 2010 and a transmitter 2020.

The generation unit 2010 generates a buffer state report (BSR) to provide the serving base station with information about the amount of data that can be transmitted to the uplink buffer of the terminal 2000. As an example, in the case of the separated RLC or the separated PDCP, the generation unit 2010 corresponds to a single RB configured between the base stations and the terminal 2000 based on dual connectivity and is defined for each of the base stations. A buffer size identifying the amount of available uplink data is calculated and information indicating the buffer size is generated. A BSR including an ID for identifying each LCG and the buffer size information is generated, respectively. In this case, the transmitter 2020 may transmit the BSR configured for each base station to the corresponding base station. Here, as illustrated in FIG. 14, when a single RB is configured as a single PDCP layer corresponding to all of the base stations and a plurality of RLC entities corresponding to each of the base stations, as illustrated in FIG. 14, the generation unit 2010. As shown in FIG. 17 (a), buffer size information is generated based on the sum of the buffer size of a single PDCP layer and the buffer size of one RLC entity among the plurality of RLC entities, or shown in FIG. 17 (b). As shown, the buffer size is based on the sum of the buffer sizes of one RLC entity and the buffer size of one of the plurality of RLC entities in the buffer size of a single PDCP layer. Information can be generated. In addition, as shown in FIG. 17C, the buffer size information may be generated as the buffer size information for the RLC entity.

In this case, each base station may share the BSR received from the terminal 2000 with each other. In this case, if the BSR is a padding buffer status report (padding BSR), the base station may ignore the data value in the padding BSR and determine that the buffer size information for the base station is zero.

Meanwhile, when a single RB is configured in at least two or more base stations dually connected to the terminal 2000 and the RLC layers of the base stations are connected to each other, the uplink resource situation of each base station, the reliability of the uplink, and the uplink It may include a selection unit (not shown) for selecting a base station to transmit the buffer status report according to the priority of the data arriving in the buffer based on the link transmission speed. In this case, the transmitter 2020 may transmit a buffer status report to the base station selected by the selector.

In the exemplary system described above, the methods are described based on a flowchart as a series of steps or blocks, but the invention is not limited to the order of steps, and certain steps may occur in a different order or concurrently with other steps than those described above. Can be. In addition, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the flowcharts may be deleted without affecting the scope of the present invention.

The above-described embodiments include examples of various aspects. Although not all possible combinations may be described to represent the various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, the invention is intended to embrace all other replacements, modifications and variations that fall within the scope of the following claims.

Claims

A method for transmitting a buffer status report by a terminal having dual connectivity with two or more base stations in a wireless communication system,

Generate a first buffer state report including buffer size information for a first logical channel group (LCG) and an identifier (ID) of the first LCG, and generate a second buffer state report Generating a second buffer status report comprising buffer size information for an LCG and an ID of the second LCG; And

Transmitting the first buffer status report to the first base station based on the first LCG ID, and transmitting the second buffer status report to the second base station based on the second LCG ID. Report transmission method.
The method of claim 1,

Configuring a single radio bearer corresponding to both the first base station and the second base station based on the logical channel configuration information received from the first base station,

And the first LCG and the second LCG are mapped to the single radio bearer.
The method of claim 2,

The logical channel configuration information,

And the first LCG and the second LCG indicate corresponding base stations.
The method of claim 2,

The first buffer size information and the second buffer size information,

When the single radio bearer is composed of a single Packet Data Convergence Protocol (PDCP) layer corresponding to all of the base stations and a plurality of Radio Link Control (RLC) entities corresponding to each of the base stations,

And a buffer size of the single PDCP layer and a buffer size of one RLC entity among the plurality of RLC entities.
The method of claim 2,

The first buffer size information and the second buffer size information,

If the single radio bearer is composed of a single PDCP layer corresponding to all of the base stations and a plurality of RLC entities respectively corresponding to each of the base stations,

And a value corresponding to a ratio of the buffer size of one RLC entity among the buffer sizes of the plurality of RLC entities to the buffer size of the single PDCP layer, and the sum of the buffer sizes of the one RLC entity. Buffer status report transmission method.
The method of claim 2,

The first buffer size information and the second buffer status report,

If the single radio bearer is composed of a single PDCP layer corresponding to all of the base stations and a plurality of RLC entities respectively corresponding to each of the base stations,

And generating a buffer status report based on a buffer size of one of the plurality of RLC entities.
The method of claim 1,

The first buffer status report and the second buffer status report,

The buffer status report transmission method, characterized in that shared between the base stations.
The method of claim 1,

The first buffer status report and the second buffer status report,

And a padding buffer status report, wherein the data value in the padding buffer status report is ignored.
A method for transmitting a buffer status report by a terminal having dual connectivity with two or more base stations in a wireless communication system,

When the terminal is configured with a single radio bearer (radio bearer) corresponding to all of the base stations and the Radio Link Control (RLC) layers of the base stations are connected to each other, the uplink resource situation of each base station, uplink reliability and uplink Selecting a base station to transmit a buffer status report according to the priority of data arriving at the buffer based on at least one of the link transmission rates; And

And transmitting a buffer status report to the selected base station.
The method of claim 9,

The buffer status report,

The buffer status report transmission method, characterized in that shared between the base stations.
The method of claim 9,

The buffer status report,

And a padding buffer status report, wherein the data value in the padding buffer status report is ignored.
A terminal configured with dual connectivity with two or more base stations in a wireless communication system,

Generate a first buffer state report including buffer size information for a first logical channel group (LCG) and an ID of the first LCG, and generate a first buffer state report for the second LCG A generation unit for generating a second buffer status report including buffer size information and an ID of the second LCG; And

And a transmitter configured to transmit the first buffer status report to the first base station based on the first LCG ID and to transmit the second buffer status report to the second base station based on the second LCG ID.
The method of claim 12,

And a single radio bearer is configured between the base stations and the terminal, and the first LCG and the second LCG are mapped to the single radio bearer.
The method of claim 13,

The single radio bearer is,

And a terminal configured based on logical channel configuration information received from the first base station.
The method of claim 14,

The logical channel configuration information,

And the first LCG and the second LCG each indicate a corresponding base station.
The method of claim 13,

The generation unit,

When the single radio bearer is composed of a single Packet Data Convergence Protocol (PDCP) layer corresponding to all of the base stations and a plurality of Radio Link Control (RLC) entities corresponding to each of the base stations,

And generating the buffer size information based on a sum of the buffer size of the single PDCP layer and the buffer size of one RLC entity among the plurality of RLC entities.
The method of claim 13,

The generation unit,

If the single radio bearer is composed of a single PDCP layer corresponding to all of the base stations and a plurality of RLC entities respectively corresponding to each of the base stations,

The buffer size information based on a sum of a buffer size of one RLC entity among the buffer sizes of the plurality of RLC entities and a buffer size of the one RLC entity in the buffer size of the single PDCP layer; Terminal, characterized in that for generating.
The method of claim 12,

The generation unit,

If the single radio bearer is composed of a single PDCP layer corresponding to all of the base stations and a plurality of RLC entities respectively corresponding to each of the base stations,

And generating the buffer size information based on a buffer size of one RLC entity among the plurality of RLC entities.
The method of claim 12,

The first buffer status report and the second buffer status report,

The terminal characterized in that shared between the base stations.
The method of claim 12,

The first buffer status report and the second buffer status report,

In case of padding buffer status report (padding BSR), characterized in that the data value in the padding buffer status report is ignored.