KR20150018249A - Method and apparatus of pdcp reordering considering multi-flow in dual connectivity system - Google Patents

Abstract

The present invention relates to a method and an apparatus for reordering a packet data convergence protocol (PDCP) in a wireless communication system supporting dual connectivity. According to the present invention, provided is a method for reordering PDCP service data units (SDU) considering a multi-flow by a PDCP entity of user equipment (UE) that is configured for dual connectivity to a macro eNB and a small eNB. According to the present invention, when the dual connectivity of the user equipment to the macro eNB and the small eNB is configured and multi-flow downlink reception is performed, reordering of the PDCP SDUs is performed based on a wait timer that is driven when out-of-sequence PDCP packet data units (PDU) are received by the PDCP entity of the UE, the PDCP SDUs can be delivered to an upper layer in ascending order, and transmission efficiency can be improved.

Description

Technical Field [0001] The present invention relates to a PDCP reordering scheme, and more particularly, to a PDCP reordering scheme and a PDCP reordering scheme for a multi-

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication, and more particularly, to a PDCP reordering method and apparatus for multi-flow in a wireless communication system supporting dual connectivity.

In certain areas, such as a hotspot inside a cell, there is a particularly high demand for communication, and in certain areas, such as the cell edge or coverage hole, the reception sensitivity of the radio wave may be reduced. 2. Description of the Related Art As wireless communication technology has developed, small cells in a macro cell, for example, a pico cell, have been used for the purpose of enabling communication in an area such as a hot spot, a cell boundary, A pico cell, a femtocell, a micro cell, a remote radio head (RRH), a relay, and a repeater are installed together. Such a network is called a heterogeneous network (HetNet). In a heterogeneous network environment, a macro cell is a large cell with a large coverage and a small cell such as a femtocell and a picocell is a small cell. Small cells such as femtocell and picocell are called low power network (LPN) because they use low power compared to macro cell. In a heterogeneous network environment, coverage overlap occurs between a plurality of macro cells and small cells.

The UE can establish dual connectivity through two or more base stations of the at least one serving cell. A dual connection is an operation in which the UE consumes radio resources provided by at least two different network points (e.g., a macro base station and a small base station) in a RRC_CONNECTED mode. In this case, the at least two different network points may be connected to a non-ideal backhaul.

At this time, one of the at least two different network points may be referred to as a macro base station (or a master base station or an anchor base station), and the remainder may be referred to as a small base station (or a secondary base station or an assisting base station or a slave base station).

Generally, a wireless communication system is a single flow structure in which a service is provided to a terminal through one RB (radio bearer) for one EPS bearer service. However, in a wireless communication system supporting a dual connection, a single EPS bearer can be provided to a terminal through two RBs, which are respectively set in a macro cell and a small cell, instead of one RB. That is, the service can be provided to the terminal through multi-flow. In this case, one RB is provided only through a macro cell, and the other RB can be set via a macro cell and two base stations corresponding to a small cell. In other words, one RB can be set to a single base station, and the remaining one RB can be set to two base stations (Bearer split).

In the case of the RLC AM (acknowledged mode), the RLC entity of the UE on the downlink reorders the RLC PDU when the received RLC PDU (Packet Data Unit) is sequentially out of order. In the case of RLC AM, the receiving side may retransmit the missing RLC PDU from the transmitting side again. The RLC entity reassembles an RLC SDU (Service Date Unit) based on the rearranged RLC PDU and sequentially delivers the RLC SDU to an upper layer (i.e., a PDCP entity). In case of RLC AM, sequential transmission is possible through RLC PDU reordering and retransmission. In other words, the PDCP entity must receive the RLC SDUs sequentially, except for the re-establishment of the lower layer. However, in the case of a UE in which a multi-flow is configured, the RLC entity for the small base station and the RLC entity for the macro base station can be distinguished from each other to receive the respective RLC PDUs and deliver the RLC SDUs to the upper layer (i.e., the PDCP layer) The PDCP entity can not expect sequential reception of RLC SDUs. Therefore, in the case of a UE having a multi-flow structure, a PDCP rearrangement scheme for transferring ascending PDCP SDUs to an upper layer in a PDCP entity is required.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for rearranging a PDCP considering a multi-flow in a dual connection system.

Another aspect of the present invention is to provide a method and apparatus for transmitting a PDCP SDU to an upper layer in ascending order by a receiving end of a PDCP entity in a multi-flow structure.

Another aspect of the present invention is to perform PDCP reordering based on a timer in a multi-flow structure.

According to an aspect of the present invention, in a Packet Data Convergence Protocol (PDCP) entity of a UE configured with a macro base station (Macro eNB) and a small eNB and a dual connectivity, (PDU) SDU (Service Data Units) reordering considering multi-flow. The method of rearranging the PDCP SDUs comprises sequentially receiving a PDCP SN (sequence number) n PDCP PDUs (Packet Data Units) in sequence and a PDCP SN n (n) not a next expected PDCP SN n + 1 and driving a wait timer when a + k PDCP PDU is received.

According to another aspect of the present invention, there is provided a method of rearranging the PDCP SDU, the method comprising the steps of: starting from the PDCP SN n + 1 when the PDCP SN n + 1 PDCP PDU is received before the waiting timer expires; And delivering all stored PDCP SDUs with an associated PDCP SN value consecutively to an upper layer in ascending order.

According to another aspect of the present invention, there is provided a method of rearranging a PDCP SDU, the method comprising the steps of: when a PDCP SN n + 1 PDCP PDU is not received until the rearrangement timer expires, It may be determined that the PDCP SDUs not yet received associated with the SN value have been removed.

According to another aspect of the present invention, there is provided a method of rearranging the PDCP SDUs, wherein the PDCP SN n + 1 is removed when the PDCP SN n + 1 PDCP PDUs are not received until the rearrangement timer expires .

According to another aspect of the present invention, there is provided a method of rearranging the PDCP SDUs, the method comprising: if the PDCP SN n + 1 PDCP PDUs are not received until the rearrangement timer expires, starting from the PDCP SN n + k And delivering all stored PDCP SDUs of consecutively associated PDCP SN values to the upper layer in ascending order.

According to the present invention, when a UE is configured to have a dual connection with a macro base station and a small base station, when multi-flow downlink reception is performed, PDCP PDUs are transmitted to the PDCP entity of the UE in a non- It is possible to rearrange the PDCP SDUs based on the wait timer and perform the ascending sequence of the PDCP SDUs to the upper layer, thereby improving the transmission efficiency.

In addition, since the PDCP PDU is driven on the basis of the non-sequentially received PDCP PDU, the PDCP SDU can be rearranged smoothly even if time delay occurs during packet reception due to service disconnection.

1 shows 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 wireless protocol structure for a control plane.
4 is a diagram showing an outline of an example of an RLC sublayer model to which the present invention is applied.
5 is a diagram showing an outline of an example of a PDCP sublayer model to which the present invention is applied.
FIG. 6 shows an example of a dual connection situation of a terminal applied to the present invention.
FIG. 7 shows an example of an EPS bearer structure when a single flow is configured.
8 shows an example of a network structure of a macro base station and a small base station in a case of a single flow in a double connection situation.
9 shows an example of an EPS bearer structure in a case where a multi-flow is configured in a double connection situation.
10 shows an example of the network structure of the macro base station and the small base station when the multi-flow is performed.
11 shows a packet forwarding process in case of a single flow, considering a double connection.
12 shows a packet forwarding process in the case of a multi-flow when considering a double connection.
13 shows an example of the PDCP PDU reception timing in the PDCP entity of the UE.
14 is a diagram showing a case where a packet is intermittently received due to a service disconnection.
FIG. 15 shows a method of rearranging PDCP SDUs considering multi-flow according to an example of the present invention.
16 is a flowchart of a method of rearranging PDCP SDUs using a wait timer according to an embodiment of the present invention.
17 is a block diagram of a macro base station, a small base station, and a terminal according to the present invention.

Hereinafter, the contents related to the present invention will be described in detail with reference to exemplary drawings and embodiments, together with the contents of the present invention. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference symbols as possible even if they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear.

In addition, the present invention will be described with respect to a wireless communication network. The work performed in the wireless communication network may be performed in a process of controlling a network and transmitting data by a system (e.g., a base station) Work can be done at a terminal connected to the network.

1 shows a wireless communication system to which the present invention is applied. This may be a network structure of an E-UMTS system (Evolved-Universal Mobile Telecommunications System). The E-UMTS system may be an LTE (Long Term Evolution) or LTE-A (advanced) system. The wireless communication system can be classified into a Code Division Multiple Access (CDMA), a Time Division Multiple Access (TDMA), a Frequency Division Multiple Access (FDMA), an Orthogonal Frequency Division Multiple Access (OFDMA), a Single Carrier- , OFDM-TDMA, and OFDM-CDMA.

1, an E-UTRAN includes an evolved NodeB (eNB) 20 that provides a control plane (CP) and a user plane (UP) to a user equipment (UE) .

The terminal 10 may be fixed or mobile and may be referred to by other terms such as a mobile station (MS), an advanced MS (MS), a user terminal (UT), a subscriber station (SS) .

The base station 20 generally refers to a station that communicates with the terminal 10 and includes a base station (BS), a base transceiver system (BTS), an access point, a femto-eNB, , A pico-eNB, a home eNB, a relay, and the like. The base stations 20 may be interconnected via an X2 interface. The base station 20 is connected to an S-GW (Serving Gateway) through an MME (Mobility Management Entity) and an S1-U through an EPC (Evolved Packet Core) 30, more specifically, an S1-MME through an S1 interface. The S1 interface exchanges OAM (Operation and Management) information to support the movement of the terminal 10 by exchanging signals with the MME.

The EPC 30 includes an MME, an S-GW, and a packet data network-gateway (P-GW). The MME has information on the connection information of the terminal 10 and the capability of the terminal 10. This information is mainly used for managing the mobility of the terminal 10. [ The S-GW is a gateway having an E-UTRAN as an end point, and the P-GW is a gateway having a PDN (Packet Data Network) as an end point.

The E-UTRAN and the EPC 30 may be combined to form an EPS (Evolved Packet System), and the traffic flow from the wireless link connecting the terminal 10 to the base station 20 to the PDN connecting to the service entity can be referred to as IP (Internet Protocol).

The wireless interface between the terminal and the base station is called a Uu interface. The layers of the radio interface protocol between the terminal and the network are divided into a first layer (L1), a second layer (L1), and a second layer (L2) based on the lower three layers of an open system interconnection 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, and the RRC (Radio Resource Control) layer located at the third layer exchanges RRC messages, And the network.

FIG. 2 is a block diagram illustrating a radio protocol architecture for a user plane, and FIG. 3 is a block diagram illustrating a radio protocol structure for a control plane. The user plane is a protocol stack for transmitting user data, and the control plane is a protocol stack for transmitting control signals.

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

Also, data is transferred over the physical channel between different physical layers (i. E., Between the physical layer of the transmitter and the receiver). The physical channel can be modulated by an Orthogonal Frequency Division Multiplexing (OFDM) scheme, and uses time and frequency 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 (P-SCH), a downlink shared channel (DL-SCH), hybrid automatic repeat request (HARQ) The PDCCH may carry an uplink scheduling grant informing the UE of the resource allocation of the uplink transmission. Also, a physical control format indicator channel (PCFICH) informs the UE of the number of OFDM symbols used for PDCCHs and is transmitted every subframe. In addition, PHICH (Physical Hybrid ARQ Indicator Channel) carries HARQ ACK / NAK signal in response to uplink transmission. Also, a physical uplink control channel (PUCCH) carries uplink control information such as HARQ ACK / NAK, scheduling request and CQI for downlink transmission. Also, a physical uplink shared channel (PUSCH) carries an uplink shared channel (UL-SCH).

The MAC layer can perform multiplexing or demultiplexing into a transport block provided on a physical channel on a transport channel of a MAC SDU (service data unit) belonging to a logical channel and a mapping between a logical channel and a transport channel. The MAC layer provides service to the Radio Link Control (RLC) layer through a logical channel. The logical channel can be divided into a control channel for transferring control area information and a traffic channel for transferring user area information.

The function of the RLC layer includes concatenation, segmentation and reassembly of the RLC SDUs. In order to guarantee various QoS (Quality of Service) required by a radio bearer (RB), the RLC layer includes Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode , And AM).

RLC SDUs are supported in various sizes, and may be supported on a byte basis, for example. RLC protocol data units (RLC PDUs) are defined only when a transmission opportunity is notified from a lower layer (e.g., the MAC layer), and the RLC PDUs are delivered to the lower layer when the transmission opportunity is notified. The transmission opportunity may be notified with the size of the total RLC PDUs to be transmitted. The RLC layer will be described in detail with reference to FIG.

The functions of the Packet Data Convergence Protocol (PDCP) layer in the user plane include transmission of user data, header compression and ciphering. The function of the PDCP layer in the user plane includes transmission of control plane data and encryption / integrity protection.

The RRC layer is responsible for the control of logical channels, transport channels and physical channels in connection with the configuration, re-configuration and release of RBs. RB means a logical path provided by a first layer (PHY layer) and a second layer (MAC layer, RLC layer, PDCP layer) for data transmission between a UE and a 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 an operation method. The RB may be further classified into an SRB (Signaling RB) and a DRB (Data RB). The SRB is used as a path for transmitting the RRC message and the NAS (Non-Access Stratum) message in the control plane, and the DRB is used as a path for transmitting the user data in the user plane.

The NAS layer is located at the top of the RRC layer and 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 the RRC connected state, and if not, the UE is in the RRC idle state.

The downlink transmission channel for transmitting data from the network to the terminal includes a BCH (Broadcast Channel) for transmitting system information and a downlink SCH (Shared Channel) for transmitting user traffic or control messages. In case of a traffic or control message of a downlink multicast or broadcast service, it may be transmitted through a downlink SCH, or may be transmitted via a separate downlink MCH (Multicast Channel). Meanwhile, the uplink transmission channel for transmitting data from the UE to the network includes a random access channel (RACH) for transmitting an initial control message and an uplink SCH (Shared Channel) for transmitting user traffic or control messages.

A logical channel mapped to a transport channel is a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), a multicast traffic Channel).

A physical channel is composed of a plurality of subcarriers in a frequency domain and a plurality of symbols in a time domain. One sub-frame is composed of a plurality of OFDM symbols in the time domain. One subframe is composed of a plurality of resource blocks, and one resource block is composed of a plurality of symbols and a plurality of subcarriers. Also, each subframe may use specific subcarriers of the specific symbols (e.g., the first symbol) of the corresponding subframe for PDCCH (Physical Downlink Control Channel). The transmission time interval (TTI), which is the unit time at which data is transmitted, is 1 ms corresponding to one subframe.

4 is a diagram showing an outline of an example of an RLC sub-layer model to which an embodiment of the present invention is applied.

Referring to FIG. 4, an RLC entity is classified into different RLC entities according to a data transmission scheme. As an example, there are TM RLC entity 400, UM RLC entity 420, and AM RLC entity 440.

The UM RLC entity 400 may be configured to receive or transmit RLC PDUs over logical channels (e.g., DL / UL DTCH, MCCH, or MTCH). The UM RLC entity may also carry or receive a UMD PDU (Unacknowledged Mode Data PDU).

A UM RLC entity is composed of a transmitting UM RLC entity or a receiving UM RLC entity.

The transmitting UM RLC entity receives the RLC SDUs from the upper layer and transmits the RLC PDUs to the peer receiving UM RLC entity via the lower layer. When a transmitting UM RLC entity constructs UMD PDUs from RLC SDUs, if a specific transmission opportunity is notified by the lower layer, RLC SDUs are segmented or concatenated to determine the total size of RLC PDUs indicated by the lower layer UMD PDUs are configured to be within the UMD PDU, and the relevant RLC headers are included in the UMD PDU.

The receiving UM RLC entity delivers the RLC SDUs to the upper layer and receives the RLC PDUs from the peer receiving UM RLC entity through the lower layer. When the receiving UM RLC entity receives UMD PDUs, the receiving UM RLC entity detects whether UMD PDUs are received in duplicate and removes duplicate UMD PDUs, and if the UMD PDUs are out of sequence Reordering the order of the UMD PDUs, detecting the loss of UMD PDUs in the lower layer to avoid excessive rearrangement delays, reassembling the RLC SDUs from the rearranged UMD PDUs , Delivers the reassembled RLC SDUs to an upper layer in an ascending order of an RLC SN (sequence number), and transmits a UMD PDU that can not be reassembled into an RLC SDU due to a UMD PDU loss belonging to a specific RLC SDU in a lower layer Can be removed. Upon RLC re-establishment, the receiving UM RLC entity reassembles the RLC SDUs from the received UMD PDUs out of sequence, if possible, and passes them to the upper layer, leaving the remaining UMD PDUs that could not be reassembled with the RLC SDUs Remove all of them, initialize relevant state variables and stop related timers.

Meanwhile, the AM RLC entity 440 may be configured to receive or transmit RLC PDUs on a logical channel (e.g., DL / UL DCCH or DL / UL DTCH). The AM RLC entity transmits or receives an AMD PDU or an ADM PDU segment and forwards or receives an RLC control PDU (e.g., a STATUS PDU).

The AM RLC entity 440 forwards the STATUS PDUs to the peer AM RLC entity to provide positive and / or negative acknowledgment (ACK) information for the RLC PDUs (or portions thereof). This can be called STATUS reporting. A polling procedure from the peer AM RLC entity may be followed to trigger STATUS reporting. That is, the AM RLC entity may poll the peer AM RLC entity to trigger a STATUS report at its peer AM RLC entity.

If STATUS reporting is triggered and the blocking timer (t-StatusProhibit) is not running or has expired, the STATUS PDU is sent on the next transmission opportunity. Therefore, the UE estimates the size of the STATUS PDU and considers the STATUS PDU as data available for transmission in the RLC layer.

The AM RLC entity is composed of a transmitting side and a receiving side.

The transmitter of the AM RLC entity receives the RLC SDUs from the upper layer and transmits the RLC PDUs to the peer AM RLC entity through the lower layer. The AM RLC entity's transmitter may partition the RLC SDUs to fit within the total size of the RLC PDU (s) indicated by the lower layer when a particular transmission opportunity is noticed by the lower layer, when constructing AMD PDUs from the RLC SDUs segment or concatenate to form AMD PDUs. The transmitter of the AM RLC entity supports retransmission (ARQ) of RLC data PDUs. If the RLC data PDU to be retransmitted does not fit within the total size of the RLC PDU (s) indicated by the lower layer when a particular transmission opportunity is notified by the lower layer, the AM RLC entity re-segments the RLC data PDU into AMD PDU segments (re-segment).

At this time, the number of re-segmentation is not limited. When the transmitter of the AM RLC entity creates AMD PDUs from RLC SDUs received from the upper layer or creates AMD PDU segments from RLC data PDUs to be retransmitted, the relevant RLC headers are included in the RLC data PDU.

The receiver of the AM RLC entity delivers the RLC SDUs to the upper layer and receives the RLC PDUs from the peer AM RLC entity through the lower layer.

When receiving the RLC data PDUs, the receiver of the AM RLC entity detects whether the RLC data PDUs are received redundantly, removes the redundant RLC data PDUs, and receives the RLC data PDUs out of sequence Reorder the order of the RLC data PDUs, detect loss of RLC data PDUs occurring in the lower layer, request retransmission to the peer AM RLC entity, and reassemble the RLC SDUs from the rearranged RLC data PDUs reassembles the reassembled RLC SDUs and delivers the reassembled RLC SDUs to the upper layer in the reassembled sequence.

At the time of RLC resetting, the receiver of the AM RLC entity reassembles the RLC SDUs from the received RLC data PDUs out of the sequence if possible, transfers the RLC SDUs to the upper layer, and removes all remaining RLC data PDUs that can not be reassembled into RLC SDUs , Initialize relevant state variables, and stop associated timers.

5 is a diagram showing an outline of an example of a PDCP sublayer model to which the present invention is applied.

The PDCP sublayer includes at least one PDCP entity 500. Each RB (e.g., DRB and SRB, but not SRB0) is associated with one PDCP entity 500. Each PDCP entity may be associated with one or two RLC entity (s) according to the characteristics of the RB and the RLC mode.

The PDCP entity 500 receives user data from an upper layer (for example, an application layer) or transmits user data to an upper layer. Here, the user data is an IP packet. The user data may be delivered via PDCP-SAP (Service Access Point). The PDCP layer receives a PDCP configuration request (PDCP_CONFIG_REQ) message, which is signaling data, from the RRC layer. The PDCP configuration request message may be delivered via a C-SAP (Control-Service Access Point). The PDCP configuration request message is a message requesting to configure the PDCP according to the PDCP configuration parameters.

The trnasmitting side of the PDCP entity 500 starts a discard timer upon receipt of user data from an upper layer. The user data (i.e., the PDCP SDU) is subjected to header compression, integrity protection (in the control plane), encryption (cipering), and PDCP header is added to become a PDCP PDU (i.e., RLC SDU). The transmitting-end PDCP delivers the PDCP PDU to the lower layer (for example, the RLC layer). The PDCP PDU may include a PDCP Data PDU and a PDCP Control PDU. The PDCP Data PDU carries user plane data, control plane data, etc., and carries the PDCP SDU Sequence Number (SN). The PDCP SDU SN may be referred to as a PDCP SN. The PDCP Control PDU carries a PDCP status report and header compression control information.

The RLC SDU may be delivered to the RLC layer via the RLC-SAP. If the user data is not transmitted until the purging timer expires, the transmitting-end PDCP removes the user data (PDCP SDU including user data).

The receiving side of the PDCP entity 500 receives an RLC SDU (i.e., a PDCP PDU) from a lower layer. PDCP PDUs are PDCP SDUs through PDCP header decompression, deciphering, and integrity verification (in the control domain). The receiving end of the PDCP entity 500 delivers the PDCP SDU to an upper layer (for example, an application layer).

The receiving end of the PDCP entity 500 generally expects to receive RLC SDUs (i.e., PDCP PDUs) sequentially, except for the re-establishment of the lower layer. Therefore, the receiving end of the PDCP entity 500 can transfer the corresponding PDCP SDUs to the upper layer in ascending order, when receiving PDCP PDUs, except when RLC SDUs are received through re-establishment of lower layers. If there are stored PDCP SDUs, they are transferred to the upper layer in ascending order. For example, when the PDCP entity 500 receives a PDCP PDU for reasons other than a lower layer reset, the PDCP entity 500 transmits all stored PDCP SDUs (s) having count values lower than the count value of the received PDCP SDU to the upper layer in ascending order And delivers all stored PDCP SDUs (s) of the associated count value consecutively to the upper layer in ascending order starting from the count value of the received PDCP SDU.

FIG. 6 shows an example in which a terminal to which the embodiment of the present invention is applied has a dual connection.

6, a terminal 650 located in a service area of a macro cell in a macro base station (or a master base station or an anchor base station 600) is a small base station (or a secondary base station or an assisting base station or a slave base station, ) Into an over-laid area with the service area of my small cell.

In order to support the additional data service through the small cell in the small base station while maintaining the existing wireless connection and the data service connection through the macro cell in the macro base station, the network forms a dual connection to the terminal.

Accordingly, the user data arriving at the macro cell can be delivered to the terminal through the small cell in the small base station. Specifically, the F2 frequency band is allocated to the macro base station, and the F1 frequency band is allocated to the small base station. The UE can receive the service from the macro base station through the F2 frequency band and receive the service from the small base station through the F1 frequency band.

FIG. 7 shows an example of an EPS bearer structure when a single flow is configured.

Referring to FIG. 7, the RB is a bearer provided in the Uu interface to support the service of the user. In the wireless communication system, each bearer is defined for each interface to ensure independence between interfaces.

The bearer provided by the wireless communication system is collectively referred to as an evolved packet system (EPS) bearer. The EPS bearer is a transmission path generated between the terminal and the P-GW. The P-GW may receive an IP flow from the Internet or may transmit an IP flow over the Internet. The E-RAB can be divided into RB (Radio Bearer), S1 (Bearer), and E-RAB (Bearer). The EPS bearer can be divided into E-RAB (E-UTRAN Radio Access Bearer) It can be divided into bearers. That is, one EPS bearer corresponds to one RB, S1 bearer, and S5 / S8 bearer, respectively. Depending on which service (or application) is used, the IP flow may have different QoS (Quality of Service) characteristics, and IP flows having different QoS characteristics may be mapped and transmitted for each EPS bearer. EPS bearer can be distinguished based on EPS bearer identity. The EPS Bearer Identifier is allocated by the UE or the MME.

The P-GW (Packet Gateway) is a network node connecting between a wireless communication network (e.g., LTE network) and another network according to the present invention. The EPS bearer is defined between the terminal and the P-GW. The EPS bearer is further subdivided between nodes, and is defined as an RB between the UE and the base station, an S1 bearer between the base station and the S-GW, and an S5 / S8 bearer between the S-GW and the P- do. Each bearer is defined via QoS. QoS is defined through data rate, error rate, delay, and the like.

Therefore, once the QoS that the wireless communication system should provide as a whole is defined as the EPS bearer, QoS is determined for each interface. Each interface establishes a bearer according to the QoS it should provide. Since the bearer of each interface provides the QoS of the entire EPS bearer divided by interface, the EPS bearer, the RB, and the S1 bearer are basically in a one-to-one relationship.

That is, the LTE wireless communication system basically has a single flow structure, and one RB is configured for one EPS bearer. In other words, one EPS bearer is mapped to the S1 bearer through one RB. In the case of a single flow, one EPS bearer is serviced through one RB. In this case, one RB (for example, a PDCP entity, an RLC entity, a MAC entity, and a PHY layer) is set in the base station for the corresponding EPS bearer, and one RB is set in the terminal.

8 shows an example of a network structure of a macro base station and a small base station in a case of a single flow in a double connection situation. FIG. 8 shows a case where a service is provided to a terminal through two EPS bearers.

Referring to FIG. 8, the macro base station includes two PDCP entities, an RLC entity, a MAC entity, and a PHY layer, while a small base station includes an RLC entity, a MAC entity, and a PHY layer. The EPS bearer # 1 800 provides a service to the UE through an RB (PDCP / RLC / MAC / PHY) configured in the macro base station. On the other hand, the EPS bearer # 2 850 provides services to the UE through a PDCP entity configured in the macro base station and an RB (RLC / MAC / PHY) configured in the small base station. Therefore, the service is provided through one RB per single EPS bearer in a single flow.

9 shows an example of an EPS bearer structure in a case where a multi-flow is configured in a double connection situation.

Referring to FIG. 9, when a multi-flow is configured, a service is provided through two RBs configured for a macro base station and a small base station, respectively, rather than one RB for one EPS bearer. The UE can simultaneously receive services for one EPS bearer through the RB configured in the macro base station and the RB configured in the small base station. This is a form in which one EPS bearer provides service through two RBs. In the case where one EPS bearer provides service to the terminal through two or more RBs as described above, it can be considered that a multi-flow is configured in the terminal. Or a case in which a service is provided to a terminal through a macro base station and a small base station by dividing one RB, may be referred to as multi-flow. Or the RB that provides the service only through the macro base station and the macro base station and the other RB that provides one RB dividedly into the small base station are simultaneously provided to the terminal. A case where one RB is divided and a service is provided to a terminal through a macro base station and a small base station is referred to as a bearer split.

10 shows an example of the network structure of the macro base station and the small base station when the multi-flow is performed.

Referring to FIG. 10, the macro base station includes a PDCP entity, an RLC entity, a MAC entity, and a PHY layer, while a small base station includes an RLC entity, a MAC entity, and a PHY layer. In FIG. 10, unlike FIG. 8, RBs are provided to a macro base station and a small base station, respectively, for one EPS bearer 1000 to provide services to the terminal. That is, for a single EPS bearer, the macro base station and the small base station provide services to the terminal through the multi-flow.

In the case of a single flow and a multi-flow, the packet transmission process can be expressed as follows.

11 shows a packet forwarding process in case of a single flow, considering a double connection.

Referring to FIG. 11, the macro base station 1130 receives packets for each of the two EPS bearers through the P-GW and the S-GW. Where the flow through which packets are transmitted is mapped to each EPS bearer. It is assumed that packets transmitted through EPS bearer # 1 are packet 1 and packets transmitted through EPS bearer # 2 are packet 2.

PDCP 1135-1 of macro base station 1130 receives packet 1 from S-GW and PDCP 1135-2 receives packet 2 from S-GW. The PDCP 1135-1 generates a PDCP PDU1 based on the packet 1 and the PDCP PDU1 is transmitted to the RLC 1140 of the macro base station 1130 and is transmitted to the MAC entity 1145 and the PHY 1150 via the respective entities, And is transmitted to the terminal 1100. The terminal 1100 is connected to the Internet.

The PDCP 1135-2 of the macro base station 1130 generates a PDCP PDU2 based on the packet 2 and the PDCP PDU2 is transmitted to the RLC 1170 of the small base station 1160 and the MAC 1175, ), And is transmitted to the terminal 1100. The terminal 1100 is connected to the terminal 1100 via a network.

The terminal 1100 has a wireless protocol entity for each of the EPS bearer # 1 and the EPS bearer # 2. In other words, a PDCP / RLC / MAC / PHY entity (or a layer) exists for the EPS bearer # 1 and a PDCP / RLC / MAC / PHY entity (or layer) exists for the EPS bearer # 2 in the UE 1100 . Specifically, there are PHY 1105-1, MAC 1110-1, RLC 1115-1, and PDCP 1120-1 for EPS bearer # 1, and service data and packets for EPS bearer # 1 Lt; / RTI > There are PHY 1105-2, MAC 1110-2, RLC 1115-2 and PDCP 1120-2 for EPS bearer # 2 and service data and packets for EPS bearer # 2 .

Meanwhile, the macro base station 1130 and the small base station 1160 can be connected through the X2 interface. That is, the macro base station 1130 transmits the PDCP PDU 2 of the PDCP 1135-2 to the RLC 1140 of the small base station 1160 through the X2 interface. Where the X2 interface may be an X3 interface or other expression that refers to an interface between a macro base station and a small base station. In this case, if the X2 interface between the macro base station 1130 and the small base station 1160 is configured as a non-ideal backhaul, a transmission delay of about 20 to 60 ms may occur. The size of the transmission delay may be changed according to a transmission line, a system, or the like as an example.

In this case, however, the RLC 1115-1 and the PDCP 1120-1 for the EPS bearer # 1, the RLC 1115-2 and the PDCP 1120-2 for the EPS bearer # 2 are stored in the terminal 1100 Therefore, even when sequential delivery of the RLC SDU from the AM RLC entity to the PDCP entity is performed, no problem occurs. In other words, each PDCP entity corresponding to the PDCP 1120-1 and the PDCP 1120-2 is sequentially transmitted from each RLC entity corresponding to the RLC 1115-1 and the RLC 1115-2, There is no problem in that the change occurs.

12 shows a packet forwarding process in the case of a multi-flow when considering a double connection.

Referring to FIG. 12, the macro base station 1230 receives packets for one EPS bearer through the P-GW and the S-GW. For the one EPS bearer, the macro base station 1230 and the small base station 1260 constitute RBs, respectively. Specifically, the macro base station 1230 configures the PDCP 1235, the RLC 1240, the MAC 1245 and the PHY 1250, and the small base station 1240 configures the RLC 1270, the MAC 1275, the PHY 1280 ). The RBs configured by the small base station 1240 share the PDCP 1235 configured by the macro base station 1230. Therefore, one RB is divided into a macro base station 1230 and a small base station 1260.

The PDCP 1235 of the macro base station 1230 receives the packet from the S-GW. The PDCP 1235 generates PDCP PDUs based on the packets and transmits the PDCP PDUs to the RLC 1240 of the macro base station 1230 and the RLC 1270 of the small base station 1260 in accordance with a predefined rule or an arbitrary method. As appropriate. For example, a PDCP PDU having an odd SN among the PDCP PDUs is transmitted to the RLC 1240 of the macro BS 1230, and a PDCP PDU having an SN of an even number is transmitted to the RLC 1270 of the small base station 1260 .

The RLC PDU1 (s) is transformed into a format suitable for each entity and layer through the MAC 1245 and the PHY 1250 and is transmitted to the terminal 1200. The RLC PDU1 (s) The RLC PDU2 (s) is transformed into a format suitable for each entity and layer through the MAC 1275 and the PHY 1280 and transmitted to the terminal 1200 do.

The terminal 1200 has two wireless protocol entities for the EPS bearer. In other words, the terminal 1200 has a PDCP / RLC / MAC / PHY entity (or a layer) as an RB corresponding to the macro base station 1230 and an RLC / MAC / PHY entity (or layer) as an RB corresponding to the small base station 1260 Or layer). Specifically, the PHY 1205-1, the MAC 1210-1, the RLC 1215-1, and the PDCP 1220 corresponding to the macro base station 1230 exist for the EPS bearer, and the small base station 1260 There is a corresponding PHY 1205-2, MAC 1210-2, and RLC 1215-2. The PDCP 1220 is a PDCP entity corresponding to both the macro base station 1230 and the small base station 1260 at the same time. That is, in this case, two RLC entities 1215-1 and 1215-2 exist at the terminal 1200, but the two RLC entities 1215-1 and 1215-2 are one PDCP entity 1220, .

As described above, the macro base station 1230 and the small base station 1260 can be connected through the X2 (or Xn) interface. That is, the macro base station 1230 transmits a part of the PDCP PDUs of the PDCP 1235-2 to the RLC 1240 of the small framing station 1260 through the X2 interface. Where the X2 interface may be an Xn interface or other expression that refers to the interface between the macro base station and the small base station. In this case, when the X2 interface between the macro base station 1230 and the small base station 1260 is configured as a non-ideal backhaul, a transmission delay of about 20 to 60 ms may occur. The PDCP entity 1220 of the UE 1200 receives RLC SDUs (i.e., PDCP PDUs) from the two RLC entities 1215-1 and 1215-2, generates PDCP SDUs, and delivers the PDCP SDUs to the upper layer. The RLC SDUs (i.e., PDCP PDUs) received by the PDCP entity 1220 due to the transmission delay are received from the RLC entity 1215-1 and received from the RLC entity 1215-2, The PDCP entity 1220 may have a problem in performing the ascending transmission to the upper layer of the PDCP SDU.

12, one PDCP 1235 exists in the macro base station 1230 and one PDCP entity 1220 exists in the terminal 1200 for multi-flow in the double connection environment. There are RLC entities 1240 and 1270 in the macro base station 1230 and the small base station 1230 respectively and two RLC entities 1215-1 and 1215-2 corresponding to the RLC entities 1240 and 1270 in the terminal 1200 . That is, in-sequence delivery to the upper layer can be guaranteed at the RLC entities 1215-1 and 1215-2 of the UE 1210. However, in the PDCP entity 1220 of the UE 1210, the RLC SDUs (i.e., PDCP PDUs) are transmitted from the two RLC entities 1215-1 and 1215-2 instead of one RLC entity. Therefore, the sequential delivery at the RLC entities 1215-1 and 1215-2 does not guarantee sequential reception of PDCP PDUs at the PDCP entity end. The transmission of the PDCP PDU (s) from the PDCP entity 1235 of the macro base station 1230 to the RLC entity 1270 of the small base station 1260 may involve a transmission delay of 20 to 60 ms, A time delay may occur between the transmission of the PDCP PDU (s) to the RLC entity 1240 of the small base station 1230 and the transmission of the PDCP PDU (s) to the RLC entity 1270 of the small base station 1230. Even if the PDCP entity 1220 of the terminal 1200 receives the PDCP PDU (s) transmitted from the PDCP entity 1235 of the macro base station 1230 through the RLC sub-stage of the macro base station 1230, A difference occurs in the reception time in the transmission through the RLC sub-stage of the BS 1260 and it is difficult for the PDCP entity 1220 of the MS 1200 to expect sequential reception of the PDCP PDU (s).

13 shows an example of PDCP PDU reception timing in the PDCP entity of the UE. FIG. 13 exemplarily shows a time when a PDCP PDU transmitted through a macro base station and a PDCP PDU transmitted through a small base station arrive at a PDCP entity of the UE. The macro base station can determine the PDCP PDU to be transmitted through the macro base station and the PDCP PDU to be transmitted through the small base station with respect to the service for one EPS bearer. In FIG. 13, PDCP PDUs related to an odd number of PDCP SNs (Sequence Number) are transmitted to a UE through a macro base station, and PDCP PDUs associated with an even number are transmitted to a UE through a small base station.

Referring to FIG. 13, there is a time delay difference between a reception time of a PDCP PDU transmitted through a macro base station and a reception time of a PDCP PDU transmitted through a small base station. A transmission delay of about 20 to 60 ms may occur in a PDCP PDU transmitted through a small base station. This is mainly caused by the transmission delay occurring in the X2 (or Xn) interface when the PDCP PDU is transmitted from the macro base station to the small base station. In this case, the PDCP entity of the UE receives the PDCP PDU unsequentially due to the time difference of the RLC (SDU) SDUs received from the two RLC entities, and the PDCP entity processes the received PDCP PDU to the upper layer It is difficult to guarantee the ascending transmission of the PDCP SDUs. That is, in receiving the PDCP PDUs from the PDCP entity of the UE in the multi-flow structure, the PDCP PDUs transmitted from one PDCP entity of the macro base station are transmitted through the RLC entity of the macro base station and the RLC entity of the small base station, Therefore, there arises a problem in performing the ascending transmission of the PDCP SDU from the PDCP entity to the upper layer.

The PDCP entity of the UE deciphers the received PDCP PDU, performs header decompression, and transmits the PDCP SDU to the upper layer. At this time, if the PDCP SDUs having SNs smaller than the SN (sequence number) of the current PDCP SDU are stored, the PDCP SDUs are transmitted to the upper layer in the order of small SN to large SN.

Meanwhile, the transmission side of the PDCP entity may operate a discard timer. The duration of the purging timer may be configured from an upper layer, and a timer starts when a PDCP SDU is received from an upper layer. When the removal timer expires, the PDCP entity removes the corresponding PDCP SDU. Therefore, the PDCP SDU of a specific SN can be removed due to the expiration of the purging timer, and the receiving end of the PDCP entity can transmit all the PDCP SDUs in ascending order without having to sequentially transmit to the upper layer.

However, in the case of supporting the multi-flow in the above-described double connection situation, the PDCP entity can receive RLC SDUs (PDCP PDUs) from two RLC entities associated therewith. In this case, PDCP PDUs (in particular, RLC AMD SDUs) are not sequentially received in the PDCP entity, a PDCP PDU with a larger PDCP SN can be received first due to a problem of transmission path reception delay, PDCP SDUs may not be transmitted in ascending order.

Meanwhile, various communication services provided to the user may have a service gap due to various reasons. Service disconnection refers to a phenomenon such that the flow of a packet transmission between a user and a server does not continuously occur in providing an Internet service, and a packet transmission is interrupted or discontinuously transmitted for a specific time. The service provided on the Internet can be transmitted to the user from the application server through the Internet network. At this time, packets transmitted to the user may be discontinuously transmitted according to the load condition of the network and the like. Incoming packets may also be introduced discontinuously from the side of many nodes in the network. In addition, depending on the application, a packet may be generated discontinuously instead of continuously.

The packet for the service to the base station (for example, the macro base station) is not continuously received even in the network (for example, the LTE network) of the wireless communication system according to the present invention, .

14 is a diagram showing a case where a packet is intermittently received due to a service disconnection.

Referring to FIG. 14, a packet is transmitted from a GW (gateway) 1460 to a base station 1430 for a service provided to the AT 1400. The base station 1430 may be, for example, a macro base station. The application service may be provided through a server or the like, which is transmitted to the wireless network and transmitted to the base station 1430 through the GW 1460 in the form of a packet. At this time, packet traffic is generally continuously transmitted from the GW 1460 to the base station 1430. However, a service disconnection may occur in which a packet is not transmitted at a certain or arbitrary interval depending on a network situation or an application.

Although FIG. 14 shows that there is some interval from packet 1 to packet 4, this is for the purpose of explicitly illustrating the flow of the packet, and is practically transmitted with little or no time difference between packets. However, no packet is transmitted between packets 4 and 5 during a relatively long time interval corresponding to Gap 1. Also, no packet is transmitted during a relatively long time interval corresponding to Gap 2 between packet 8 and packet 9. Here, Gap1 and Gap2 can be treated as service disconnection. The base station 1430 receives the transmitted packets in order from the first packet. Packets received correspond to PDCP SDUs. That is, the received packet is stored in the PDCP buffer in the PDCP SDU format in the PDCP entity of the PDCP layer. At this time, the PDCP SDUs stored in the buffer are sequentially processed as PDCP PDUs and transferred to the lower layer. As described above, if there is a difference in the time interval during which the packets are received by the BS 1430 due to the service disconnection, a time interval may occur in the PDCP entity of the BS 1430 during the PDCP PDUs are transferred to the lower layer. That is, the PDCP PDUs processed with the PDCP SDUs corresponding to the packets 4, 5 and 8, 9 received by the base station 1430 at the time intervals of Gap1, Gap2 are also transmitted to the lower layer with a time difference .

In the case of a single flow situation, in general, when one terminal is configured for a dual connection, one PDCP entity is associated with one RLC entity. Therefore, even if a service disconnection occurs, there may be a time interval between PDCP PDUs received in the PDCP entity of the UE, but this situation does not cause a problem. PDCP PDUs generated in the PDCP entity are transmitted through the RLC entity of the lower layer, and in particular, the RLC AM supports sequential delivery. Therefore, the PDCP PDUs flowing in the time interval have to be processed after a predetermined time, and the service disconnection does not cause a particular problem in the system performance.

However, in the case of a multi-flow situation where a dual connection is configured in a terminal, the terminal can receive the packets through two different transmission paths. In other words, for one EPS bearer configured in the terminal and the network, the terminal receives the service through the macro base station and the small base station. For example, when there is one PDCP entity in the macro base station and one RLC entity exists in the macro base station and the small base station for one EPS bearer, the PDCP PDUs delivered from the PDCP entity of the macro base station are transmitted to the RLC Entity or the RLC entity of the small base station to the PDCP entity of the terminal. Accordingly, the PDCP entity of the UE receives PDCP PDUs that have undergone different path delays. In this case, a problem may occur such that a PDCP PDU having a larger PDCP SN arrives before a smaller PDCP PDU having a smaller PDCP SN, and therefore, a method of rearranging PDCP SDUs in the PDCP entity should be considered. A timer considering the path delay time can be used to rearrange the PDCP SDU in the PDCP entity. However, additional PDCP PDU transmission delay time due to service disconnection or the like must be considered together to rearrange PDCP SDUs.

If the time interval occurs due to the service disconnection, the service disconnection time may be much larger than the path delay time. Therefore, considering a path delay as well as a service disconnection, a PDCP SDU rearrangement method capable of transferring PDCP SDUs to an upper layer in an ascending order is required.

In the present invention, a wait timer driven when a PDCP entity receives a PDCP PDU out-of-sequence in consideration of a reception delay through a multipath and a service disconnection, , We propose a method to perform PDCP SDU rearrangement. Where the wait timer may be referred to as an out-of-sequence timer. The present invention can be applied to both the DL data transfer procedure and the UL data transfer procedure, and the downlink data transfer procedure will be mainly described hereinafter.

FIG. 15 shows a method of rearranging PDCP SDUs considering multi-flow according to an example of the present invention. 15, the PDCP PDUs of PDCP SNs 1 to 8 are transmitted through the RLC entity of the macro base station, and the PDCP PDUs of PDCP SNs 9, 10, 14, 15, 16, 23 and 24 are transmitted through the RLC entity of the small base station . In addition, FIG. 15 assumes that PDCP PDUs of a PDCP SN # 7 are delivered and that PDCP PDUs are not delivered for a certain time due to service disconnection.

15A shows a case where a PDCP SN 9 PDCP PDU is received without receiving a PDCP SN 8 PDCP PDU after receiving a PDCP SN 1, 2, 3, 4, 5, 6, 7 PDCP PDU in the PDCP entity of the UE.

Referring to FIG. 15A, a PDCP entity of a UE sequentially receives PDCP PDs 1 to 7 PDCP PDUs. The PDCP entity of the UE processes the received PDCP PDUs and forwards the corresponding PDCP SDUs to the upper layer. If PDCP PDUs are sequentially received, the PDCP entity of the UE does not start the wait timer. The PDCP entity of the UE can not receive other PDCP PDUs for a predetermined time, and receives the PDCP PDU No. 9 PDCP PDU. Since the PDCP entity of the UE has not yet received the PDCP PDU of PDCP SN 8, it is determined that the reception of the PDCP PDU of PDCP SN 9 is an unordered reception, and the standby timer is driven.

Here, the sequential reception may be determined according to the following criteria, for example. Next_PDCP_RX_SN is expressed by the following Equation 1 and Equation 2 if the PDCP SN of the last PDCP SDU transmitted to the upper layer is defined as Last_Submitted_PDCP_RX_SN and the PDCP SN of the PDCP SDU expected to be sequentially received next is defined as Next_PDCP_RX_SN You can follow one.

In Equation (2), Maximum_PDCP_SN indicates the maximum value of allowed PDCP SN. That is, Equation (2) indicates that the number starts from zero after the maximum value of the PDCP SN.

In addition, the wait timer may indicate a timer for a PDCP entity that has received an unordered PDCP PDU to wait for receipt of a sequential PDCP PDU. The wait timer may be set to a value of 20 to 60 ms, for example, in consideration of the path delay time of the X2 (or Xn) interface between the macro base station and the small base station.

When the waiting timer is driven on the basis of the non-sequential reception of the PDCP PDU as described above, it is possible to prevent the timer from expiring due to the time delay due to the service disconnection. For example, a timer for rearranging PDCP SDUs based on sequential reception of PDCP PDUs may be operated. However, in the case of the service disconnection described above, the timer may expire unexpectedly, PDCP PDUs can be mistakenly treated as removed. However, by operating the wait timer based on the non-sequential reception of the PDCP PDU as described above, it is possible to solve the problem caused by the time delay due to the service disconnection.

FIG. 15B assumes a case where the PDCP entity of the UE receives the PDCP SN # 8 PDCP PDU after receiving the PDCP SN 10, 14 PDCP PDUs and before the waiting timer expires.

Referring to FIG. 15B, the PDCP entity of the UE determines that the PDCP SNs of the PDCP SNs 10 and 14 are still unsynchronized. If a PDCP PDU of PDCP SN 8 is received afterwards, it is judged to be a sequential reception. When a PDCP PDU of PDCP SN # 8 is received, the PDCP entity of the UE stops the wait timer. Then, all the stored PDCP SDUs of consecutively associated PDCP SN values starting from PDCP SN 8 are transmitted to the upper layer in ascending order. For example, PDCP SN 8, 9, and 10 PDCP SDUs of the PDCP entity of the UE are delivered to the upper layer in ascending order.

 FIG. 15C assumes a case where the PDCP entity of the UE receives the PDCP PDU of PDCP SN # 15 after FIG. 15B.

Referring to FIG. 15C, when the PDCP entity of the UE receives the PDCP PDU of the PDCP SN # 15, it determines that the PDCP PDU is in the non-sequential reception mode, and drives the standby timer again. The PDCP entity of the UE waits until the PDCP SN # 11 PDCP PDU expected to be sequentially received is received until the wait timer expires.

If the PDCP SN 11 PDCP PDU is not received until the waiting timer expires, for example, the PDCP entity of the UE continuously stores all of the PDCP SN values continuously associated with the PDCP SN 11 when the waiting timer expires It is determined that the PDCP SDUs (e.g., PDCP SNs 11, 12, 13 PDCP SDUs) that have not yet been associated with the PDCP SNs are discarded and all PDCP PDUs PDCP SNs 14, 15 PDCP SDUs) to the upper layer.

As another example, the PDCP entity of the UE determines that all the unsaved PDCP SDUs continuously consecutively associated with the PDCP SN starting from the PDCP SN 11 are removed when the PDCP PDU is received for the first time after the expiration of the waiting timer, And transmits all stored PDCP PDUs of consecutively associated PDCP SN values to the upper layer.

According to the present invention as described above, when a terminal is configured to have a dual connection with a macro base station and a small base station, in performing multi-flow downlink reception, the PDCP entity of the UE may be non- Even if PDCP PDUs are received, the PDCP SDUs can be rearranged based on the wait timer, the PDCP SDUs can be transferred in ascending order to the upper layer, and the transmission efficiency can be improved.

In addition, since the PDCP PDU is driven on the basis of the non-sequentially received PDCP PDU, the PDCP SDU can be rearranged smoothly even if time delay occurs during packet reception due to service disconnection.

16 is a flowchart of a method of rearranging PDCP SDUs using a wait timer according to an exemplary embodiment of the present invention.

Referring to FIG. 16, when the PDCP entity of the UE sequentially receives PDCP SN n PDCP PDUs, the PDCP entity transmits the corresponding PDCP SDU to the upper layer (S1600). The PDCP entity of the UE can confirm whether the corresponding PDCP PDU is sequentially received based on the PDCP SN of the received PDCP PDU.

The PDCP entity of the UE drives a wait timer when a PDCP PDU of PDCP SN n + k (k is a natural number not 1) PDCP PDU is received that is not PDCP SN n + 1 in which sequential reception is expected (S1610) . The wait timer may refer to a timer that the PDCP entity that receives the non-sequential PDCP PDU waits to receive sequential PDCP PDUs.

For example, in FIG. 15A, after receiving a PDCP PDU corresponding to PDCP SN # 7, the UE may expect to receive PDCP PDU # 8 having PDCP SN 7 + 1. In this case, after a predetermined time elapses, the UE receives a PDCP PDU corresponding to SN 9, which is not PDCP SN 8, which is expected to be received. The UE drives a timer to wait for PDCP PDU # 8 reception after PDCP PDU # 9 has been received. At the time when the UE receives the PDCP PDU corresponding to the PDCP SN 9, the PDCP PDU corresponding to the PDCP SN 7 is transmitted to the upper layer and is not stored in the UE any more. However, the UE stores the SN of the PDCP PDU transmitted to the upper layer and knows the PDCP SN expected to be received next.

Referring to FIG. 15B, the UE transmits all PDCP PDUs corresponding to the PDCP SNs 8, 9, and 10 to the upper layer at the time of receiving the PDCP PDU 8. Accordingly, PDU to the upper layer. At this time, the UE grasps the PDCP SN that it expects to receive next time to be # 11. In FIG. 15C, when the UE receives the PDCP PDU corresponding to the PDCP SN # 15, it is different from the PDCP SN # 11 that is expected to be received next. Therefore, the UE drives the standby timer to wait for receiving the PDCP PDU corresponding to the PDCP SN # 11 . At this time, the UE stores PDCP PDUs 14 and 15. It is reasonable to judge that the PDCP PDU is transmitted through the macro or small base station before the PDCP PDUs 14 and 15 transmission even in the case of the PDCP PDUs 12 and 13 although the PDCP SN 11 is expected to be received and the standby timer is driven. Accordingly, when the UE receives the PDCP PDU 15, it is proper to receive the PDCP PDU 15 within the waiting timer operation period. If it is not received, it can be regarded as discarded. Accordingly, it can be determined that the PDCP PDUs that have not arrived at the expiration time of the wait timer driven by the terminal when receiving the PDCP PDU 15 are removed.

The PDCP entity of the UE confirms whether the PDCP PDU of PDCP SN n + 1 is received before the wait timer expires (S1620). The PDCP entity of the UE does not start / restart the wait timer even if the wait timer receives another non-sequential PDCP PDU in operation.

If the PDCP entity of the UE receives the PDCP SN n + 1 PDCP PDU before the wait timer expires in step S1620, the PDCP entity of the UE stops the wait timer and starts the PDCP SN n + 1 All stored PDCP SDUs of consecutively associated PDCP SN values are transferred to the upper layer in ascending order (S1630).

If the waiting timer expires in S1620, that is, if the PDCP entity of the UE does not receive the PDCP PDU of the PDCP SN n + 1 until the waiting timer expires, the PDCP entity of the UE is less than the PDCP SN n + k All PDCP SDUs associated with PDCP SN values that have not yet been received are considered to have been removed (S1640). That is, the PDCP entity of the UE removes the PDCP SDUs other than the currently stored PDCP SDUs among the associated PDCP SDUs starting from the PDCP SN value n + 1 expected to be sequentially received and smaller than the PDCP SN value n + k Can be considered. In this case, the PDCP entity of the UE transfers all the stored PDCP SDUs associated with the PDCP SN value smaller than the PDCP SN n + k to the upper layer (S1650). Then, all PDCP SNs having consecutively associated PDCP SN values starting from the PDCP SN n + And transfers the stored PDCP SDUs to an upper layer (S1660). For example, the PDCP entity of the UE transmits all stored PDCP SDUs associated with a PDCP SN value smaller than the PDCP SN n + k to the upper layer in ascending order at the expiration of the waiting timer, All stored PDCP SDUs with SN values can be transferred to the upper layer in ascending order. In another example, the PDCP entity of the UE transmits all stored PDCP SDUs associated with the PDCP SN value smaller than the PDCP SN n + k to the upper layer in ascending order at the reception of the first PDCP PDU for the first time after the reordering timer expires, all stored PDCP SDUs having consecutively associated PDCP SN values starting from n + k can be transmitted to the upper layer in ascending order.

Or all the unsaved PDCP SDUs starting from PDCP SN n + 1 to PDCP SN n + m that are consecutively associated PDCP SN values are considered to have been removed and the last (largest) PDCP SN value of the PDCP SDUs all stored PDCP SDUs of consecutively associated PDCP SN values starting from +1 of n + m may be transmitted to the upper layer in ascending order.

17 is a block diagram of a macro base station, a small base station, and a terminal according to the present invention.

Referring to FIG. 17, a terminal 1700 according to the present invention can configure daul connectivity with a macro base station 1730 and a small base station 1760. In addition, the terminal 1700, the macro base station 1730, and the small base station 1760 according to the present invention support the multi-flow described above.

The macro base station 1730 includes a macro transmission unit 1735, a macro reception unit 1740, and a macro processor 1750.

The macro receiving unit 1740 receives a packet for one EPS bearer from the S-GW. The macro processor 1750 controls the PDCP entity of the macro base station 1730 to process PDCP SDUs corresponding to the received packet and generate PDCP PDUs. The macro processor 1750 distributes the PDCP PDUs according to the reference and transfers (or transmits) the PDCP PDUs to the RLC entity of the macro BS 2140 and transmits the PDCP PDUs to the MS through the macro transmission unit 1735. The macro processor 1750 transmits (or delivers) the remaining part of the macrocell to the RLC entity of the small base station 1760 through the macro transmitting unit 1735. In this case, the PDCP SDUs corresponding to the PDCP PDUs can be identified and indicated as PDCP SNs.

In addition, the macro processor 1750 generates information on a wait timer for the PDCP SDU and transmits it to the terminal through the macro transmission unit 1735. The information on the wait timer may be signaled exclusively to the terminal 1700, or may be signaled in a broadcast manner. The macro transmitting unit 1735 may transmit the information on the waiting timer to the terminal 1700 through an RRC message (e.g., an RRC connection reconfiguration message).

The small base station 1760 includes a small transmission unit 1765, a small reception unit 1770, and a small processor 1780.

The small receiving unit 1770 receives the remaining PDCP PDUs from the macro base station 1730.

The small processor 1780 controls the RLC entity, the MAC entity, and the PHY layer of the small base station 2130 to process the PDCP PDU and transmits the PDCP PDU to the terminal through the small transmission unit 1565.

The terminal 1700 includes a terminal receiver 1705, a terminal transmitter 1710, and a terminal processor 1720. The terminal processor 1720 performs necessary functions and controls to implement the features of the present invention as described above.

The terminal receiving unit 1705 receives information on the waiting timer from the macro base station 1730. [ The information on the wait timer may be included in an RRC message (e.g., an RRC connection reconfiguration message) and may be received by the terminal receiver 1705. In this case, the terminal transmission unit 1710 may transmit an RRC connection reconfiguration completion message to the macro base station 1730.

In addition, the terminal reception unit 1705 receives data for PDCP PDUs from the macro base station 1730 and the small base station 1760, respectively.

The terminal processor 1720 analyzes the data and controls the PHY layer s, MAC entity s, RLC entity s and PDCP entity of the UE 1700 to obtain PDCP SDUs.

When the terminal processor 1720 sequentially receives the PDCP SN n PDCP PDUs in the PDCP entity, the terminal processor 1720 delivers the corresponding PDCP SDU to the upper layer. Here, the terminal processor 1720 can check whether the corresponding PDCP PDU is sequentially received in the PDCP entity based on the PDCP SN of the received PDCP PDU. For example, it is possible to determine the PDCP SN value of a PDCP SDU (or PDU) that is expected to be sequentially received based on Equation 1 or 2 described above.

The terminal processor 1720 drives a wait timer when a PDCP PDU of a PDCP SN n + k (k is a natural number not 1) received, which is not the PDCP SN n + 1 expected to be sequentially received by the PDCP entity.

If the PDCP SN n + 1 PDCP PDU is received in the PDCP entity before the wait timer expires, the terminal processor 1720 stops the wait timer. The terminal processor 1720 transmits all stored PDCP SDUs of consecutively associated PDCP SN values starting from the PDCP SN n + 1 to the upper layer of the PDCP entity in ascending order.

If the PDCP SN n + 1 PDCP PDU is not received until the waiting timer expires, that is, until the waiting timer expires in the PDCP entity, the terminal processor 1720 sets the PDCP SN value smaller than the PDCP SN n + k All associated unacknowledged PDCP SDUs can be viewed as removed.

In this case, the terminal processor 1720 delivers all stored PDCP SDUs related to the PDCP SN value smaller than the PDCP SN n + k to the upper layer in ascending order. In addition, the terminal processor 1720 transfers all stored PDCP SDUs of consecutively associated PDCP SN values from the PDCP SN n + k to the upper layer in ascending order.

For example, the terminal processor 1720 can forward all stored PDCP SDUs associated with PDCP SN values smaller than the PDCP SN n + k stored in the PDCP entity to the upper layer in ascending order at the expiration of the reordering timer, and the PDCP SN n + k All PDCP SDUs having consecutively associated PDCP SN values can be transmitted to the upper layer in ascending order. As another example, the terminal processor 1720 may allocate all the stored PDCP SDUs associated with the PDCP SN value smaller than the PDCP SN n + k stored in the PDCP entity at the time of the first arbitrary PDCP PDU after the reordering timer expires, Layer and can forward all PDCP SDUs of consecutively associated PDCP SN values from the PDCP SN n + k to the upper layer in ascending order.

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 falling within the scope of the same shall be construed as falling within the scope of the present invention.

Claims (11)

A PDCP (Packet Data Convergence Protocol) entity of a UE having a macro base station (Macro eNB) and a small eNB (Small eNB) and a dual connectivity is configured to use a multi- As a SDU (Service Data Unit) reordering method,
Sequentially receiving a PDCP SN (sequence number) n PDCP PDUs (Packet Data Units);
And if a PDCP PDU of a PDCP SN n + k other than the PDCP SN n + 1 whose next sequential reception is expected is received, a waiting timer is activated. How to rearrange. The method according to claim 1,
Wherein the value of the wait timer is set to an arbitrary value within 20 ms to 60 ms corresponding to an Xn interface path delay between the macro base station and the small base station. The method according to claim 1,
And when the PDCP PDU of the non-sequential recipient PDCP SN n + k is received, the waiting timer is driven only when the waiting timer is not in operation. The method according to claim 1,
And all PDCP SNs having a PDCP SN value consecutively associated starting from the PDCP SN n + 1 when the PDCP SN n + 1 PDCP PDUs are received before the waiting timer expires. And forwarding the PDCP SDUs to an upper layer in ascending order. 5. The method of claim 4,
If PDCP SN n + 1 PDCP PDUs are not received until the reordering timer expires, PDCP SDUs not yet received associated with a PDCP SN value less than the PDCP SN n + k are removed The method comprising the steps of: 6. The method of claim 5,
And forwarding all stored PDCP SDUs associated with PDCP SN values less than PDCP SN n + k to the upper layer in ascending order if the PDCP SN n + 1 PDCP PDUs are not received until the reordering timer expires And reordering the PDCP SDUs. The method according to claim 6,
And all stored PDCP SDUs having a PDCP SN value smaller than the PDCP SN n + k are delivered to the upper layer in ascending order at the time when the waiting timer expires. The method according to claim 6,
And all the stored PDCP SDUs having consecutively associated PDCP SN values starting from the PDCP SN n + k are delivered to the upper layer in ascending order at the time when an arbitrary PDCP PDU is received for the first time after the waiting timer expires. To the PDCP SDU array. The method according to claim 6,
If the PDCP SN n + 1 PDCP PDUs are not received until the reordering timer expires, all stored PDCP SDUs having consecutively associated PDCP SN values starting from PDCP SN n + k are transmitted to the upper layer in ascending order The method comprising the steps of: 10. The method of claim 9,
Wherein all the stored PDCP SDUs associated with a PDCP SN value smaller than the PDCP SN n + k are delivered to the upper layer in ascending order when the waiting timer expires. 10. The method of claim 9,
And all stored PDCP SDUs having consecutively associated PDCP SN values starting from the PDCP SN n + k are delivered to the upper layer in ascending order at the time when the first PDCP PDU is received after the waiting timer expires , PDCP SDU array method.

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