WO2015020508A1

WO2015020508A1 - Method and apparatus for reordering pdcp while considering multi-flow in dual connectivity system

Info

Publication number: WO2015020508A1
Application number: PCT/KR2014/007457
Authority: WO
Inventors: 정명철; 허강석; 권기범; 안재현
Original assignee: 주식회사 팬택
Priority date: 2013-08-09
Filing date: 2014-08-11
Publication date: 2015-02-12

Abstract

The present invention relates to a method and an apparatus for reordering a PDCP while considering a multi-flow in a wireless communication system supporting dual connectivity. According to the present invention, PDCP SN values of PDCP PDUs, which are transmitted through a macro eNB and a small eNB, can be compared, the PDCP SDUs removed based on a timer can be identified, and the PDCP SDUs can be reordered. According to the present invention, when receiving a multi-flow downlink when dual connectivity is configured between a terminal and the macro eNB and the small eNB, the PDCP SDUs can be delivered to an upper layer, in ascending order, and transmission efficiency can be improved, even if the PDCP PDUs are received non-sequentially by a PDCP entity of the user equipment due to a delay of a transmission path.

Description

Method and apparatus for rearranging PDC in consideration of multi-flow in dual connectivity system

The present invention relates to wireless communication, and more particularly, to a PDCP reordering method and apparatus therefor in consideration of multi-flow in a wireless communication system supporting dual connectivity.

In particular areas, such as hot spots inside the cell, there is a great demand for communication, and in certain areas such as cell edges or coverage holes, the reception sensitivity of radio waves may be reduced. With the development of wireless communication technology, small cells, such as pico cells, within a macro cell for the purpose of enabling communication in areas such as hot spots, cell boundaries, and coverage holes. (Pico Cell), femto cell (Femto Cell), micro cell (Micro Cell), remote radio head (RRH), relay (relay), repeater (repeater) is installed together. Such a network is called a heterogeneous network (HetNet). In a heterogeneous network environment, a macro cell is a large coverage cell, and a small cell such as a femto cell and a pico cell is a small coverage cell. Compared to macro cells, small cells such as femto cells and pico cells use low power and are also referred to as low power networks (LPNs). Coverage overlap occurs between multiple macro cells and small cells in a heterogeneous network environment.

The terminal may configure dual connectivity through two or more base stations among the base stations configuring at least one serving cell. Dual connectivity is an operation in which the terminal consumes radio resources provided by at least two different network points (eg, macro base station and small base station) in a radio resource control connection (RRC_CONNECTED) mode. In this case, the at least two different network points may be connected by non-ideal backhaul.

In this case, one of the at least two different network points may be called a macro base station (or a master base station or an anchor base station), and the rest may be called small base stations (or secondary base stations or assisting base stations or slave base stations).

In general, a wireless communication system has a single flow structure in which a service is provided to a terminal through one radio bearer (RB) for one EPS bearer service. However, in a wireless communication system supporting dual connectivity, one EPS bearer may provide a service to a terminal through two RBs configured in a macro cell and a small cell instead of one RB. That is, the service may be provided to the terminal through multi-flow. In the above, one RB may be provided through only the macro cell, and the other RB may be configured through two base stations corresponding to the macro cell and the small cell. In other words, one RB may be configured in a single base station and the other RB may be configured in a bearer split into two base stations.

In the case of an RLC acknowlegdged mode (AMC), when a received RLC packet data unit (RDU PDU) is received out of order in downlink, the RLC entity reorders the RLC PDUs. In the case of RLC AM, the missing RLC PDU may be retransmitted at the receiver. The RLC entity reassembles an RLC Service Date Unit (SDU) based on the rearranged RLC PDUs and sequentially delivers them to a higher layer (ie, PDCP entity). In the case of RLC AM, sequential delivery is possible through reordering and retransmission of the RLC PDU. In other words, the PDCP entity should receive the RLC SDUs sequentially, except for re-establishment of the lower layer. However, in case of a UE configured with multi-flow, an RLC entity for a small base station and an RLC entity for a macro base station may be divided to receive each RLC PDU, and the RLC SDU may be delivered to a higher layer (ie, a PDCP layer). If the PDCP entity does not expect the sequential reception of the RLC SDU. Therefore, in case of a UE configured with multi-flow, a PDCP rearrangement method for ascending delivery of PDCP SDUs to a higher layer in a PDCP entity is required.

An object of the present invention is to provide a method and apparatus for rearranging PDCP in consideration of multi-flow in a dual connectivity system.

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

Another technical problem of the present invention is to perform PDCP SDU rearrangement based on PDCP SN comparison in a multiflow structure.

Another technical problem of the present invention is to perform PDCP rearrangement based on a timer.

According to an aspect of the present invention, in a Packet Data Convergence Protocol (PDCP) entity of a UE configured for dual connectivity with a macro base station (Macro eNB) and a small eNB (small eNB), multi-flow A method of reordering PDCP Service Data Units (SDUs) considering multi-flow is provided. The PDCP SDU rearrangement method may include receiving PDCP PDUs through the macro base station and the small base station, and if PDCP SN n PDCP PDUs are received through any one of the macro base station and the small base station, Driving an array timer.

According to another aspect of the present invention, a PDCP entity of a terminal configured with dual connectivity with a macro base station and a small base station provides a method for rearranging PDCP SDUs in consideration of multiflow. The PDCP SDU rearrangement method may further include receiving PDCP PDUs through the macro base station and the small base station, and when PDCP SN n PDCP PDUs are received through any one of the macro base station and the small base station, And checking whether a maximum PDCP SN value k of at least one PDCP PDU received through another base station is greater than n.

According to another aspect of the present invention, there is provided a method for rearranging PDCP SDUs in consideration of multiflow in a PDCP entity of a terminal having dual connectivity with a macro base station and a small base station. The PDCP SDU rearrangement method includes receiving PDCP PDUs through the macro base station and the small base station, and if the rearrangement timer is not running, driving a rearrangement timer when any PDCP PDU is received. It is characterized by.

According to the present invention, when the terminal is dual-linked with the macro base station and the small base station, in performing multi-flow downlink reception, due to a transmission path delay, PDCP PDUs are sequentially arranged in the PDCP entity of the terminal. Even if received, the PDCP SDUs may be rearranged, the ascending order of PDCP SDUs may be performed to an upper layer, and transmission efficiency may be improved.

1 shows a wireless communication system to which the present invention is applied.

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

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

4 is a diagram illustrating an outline of an example of an RLC sublayer model to which the present invention is applied.

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

6 shows an example of a dual connection situation of a terminal applied to the present invention.

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 single flow in a dual connectivity situation.

9 shows an example of an EPS bearer structure when a multi flow is configured in a dual connection situation.

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

11 illustrates a packet forwarding process in the case of a single flow when considering dual connectivity.

12 illustrates a packet forwarding process in the case of multi-flow when considering dual connectivity.

13 shows an example of a PDCP PDU reception timing in a PDCP entity of a terminal.

14A to 14B illustrate examples of performing a PDCP SDU rearrangement based on a PDCP SN comparison according to an embodiment of the present invention.

15A to 15B illustrate an example of performing PDCP SDU removal determination based on a PDCP SN comparison according to an embodiment of the present invention.

16A to 16B illustrate a case where a problem occurs in PDCP PDU transmission through a small base station in a situation in which a multi-flow is configured with a macro base station and a small base station in the terminal.

17A to 17B illustrate examples of a PDCP SDU rearrangement scheme using a rearrangement timer when PDCP PDUs are not suddenly received through a small base station according to another embodiment of the present invention.

18 is a flowchart of a PDCP SDU rearrangement method based on PDCP SN comparison according to an embodiment of the present invention.

19 is a flowchart illustrating a rearrangement timer based PDCP SDU rearrangement method according to another embodiment of the present invention.

20A to 20B illustrate a PDCP removal confirmation method according to another example of the present invention.

21 illustrates an example of performing PDCP removal determination based on a PDCP SN comparison and rearrangement timer for each base station according to another embodiment of the present invention.

22 is a flowchart of a PDCP SDU rearrangement method based on a PDCP SN comparison and rearrangement timer for each base station according to another embodiment of the present invention.

23A to 23E illustrate examples of a PDCP SDU rearrangement method based on a rearrangement timer according to another example of the present invention.

24A to 24D illustrate another example of a PDCP SDU rearrangement method based on a rearrangement timer according to another embodiment of the present invention.

25 is a flowchart of a rearrangement timer based PDCP SDU rearrangement method according to another embodiment of the present invention.

26 is a block diagram of a macro base station, a small base station and a terminal 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 done at the terminal coupled to the network.

1 shows a wireless communication system to which the present invention is applied. This may be a network structure of an Evolved-Universal Mobile Telecommunications System. The E-UMTS system may be a 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, the E-UTRAN provides a base station 20 (evolved NodeB: eNB) which provides a control plane (CP) and a user plane (UP) to a user equipment (UE). Include.

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). .

The base station 20 generally refers to a station communicating with the terminal 10, and includes a base station (BS), a base transceiver system (BTS), an access point, and a femto-eNB. It may be called other terms such as a pico base station (pico-eNB), a home base station (Home eNB), a relay (relay). The base stations 20 may be connected to each other through an X2 interface. The base station 20 is connected to a Serving Gateway (S-GW) through an MME (Mobility Management Entity) and an S1-U through an Evolved Packet Core (EPC) 30, more specifically, an S1-MME through an S1 interface. The S1 interface exchanges OAM (Operation and Management) information for supporting 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 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.

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

The radio 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 based on the lower three layers of the Open System Interconnection (OSI) reference model, which are well known in a communication system. 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 network and network.

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 a medium access control (MAC) layer, which is an upper 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 through 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 time and frequency as radio resources.

For example, the physical downlink control channel (PDCCH) of the physical channel informs the UE of resource allocation of a paging channel (PCH) and downlink shared channel (DL-SCH) and hybrid automatic repeat request (HARQ) information related to the DL-SCH. The PDCCH may carry an uplink scheduling grant informing the UE of resource allocation of uplink transmission. In addition, 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, the PHICH (physical hybrid ARQ Indicator Channel) carries a HARQ ACK / NAK signal in response to 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, a physical uplink shared channel (PUSCH) carries an uplink shared channel (UL-SCH).

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.

Functions of the RLC layer include concatenation, segmentation, and reassembly of RLC SDUs. In order to guarantee the various quality of service (QoS) required by the radio bearer (RB), the RLC layer has a transparent mode (TM), an unacknowledged mode (UM), and an acknowledged mode (Acknowledged Mode). Three modes of operation (AM).

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 when the transmission opportunity is notified, the RLC PDUs are delivered to the lower layer. The transmission opportunity may be informed with the size of the total RLC PDUs to be transmitted. Hereinafter, the RLC layer will be described in detail with reference to FIG. 4.

Functions of the Packet Data Convergence Protocol (PDCP) layer in the user plane include delivery of user data, header compression, and ciphering. Functions of the PDCP layer in the user plane include the transfer 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 configuration, re-configuration, and release of RBs. RB means a logical path provided by the first layer (PHY layer) and the 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 further 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 NAS layer is located above 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 an RRC connected state, otherwise it is in an RRC idle state.

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

It is located above the transport channel, and the logical channel mapped to the transport channel is a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), and a multicast traffic (MTCH). Channel).

The physical channel is composed of several symbols in the time domain and several sub-carriers in the frequency domain. One sub-frame consists of a plurality of OFDM symbols in the time domain. One subframe consists of a plurality of resource blocks, and one resource block consists of a plurality of symbols and a plurality of subcarriers. In addition, each subframe may use specific subcarriers of specific symbols (eg, the first symbol) of the corresponding subframe for the physical downlink control channel (PDCCH). The transmission time interval (TTI), which is a unit time for transmitting data, is 1 ms corresponding to one subframe.

4 is a diagram illustrating an example of an example of an RLC sublayer model to which an embodiment of the present invention is applied.

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

The UM RLC entity 400 may be configured to receive or forward RLC PDUs over logical channels (eg, DL / UL DTCH, MCCH or MTCH). In addition, the UM RLC entity may deliver or receive a UMD PDU (Unacknowledged Mode Data PDU).

The UM RLC entity consists of a sending UM RLC entity or a receiving UM RLC entity.

The transmitting UM RLC entity receives the RLC SDUs from the upper layer and sends the RLC PDUs to the peer receiving UM RLC entity via the lower layer. When the sending UM RLC entity constructs UMD PDUs from the RLC SDUs, the total size of the RLC PDUs indicated by the lower layer by segmenting or concatenating the RLC SDUs when a specific transmission opportunity is notified by the lower layer. The UMD PDUs are configured to be within and the related 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 the UMD PDUs have been received in duplicate, removes the duplicate UMD PDUs, and when the UMD PDUs are received out of sequence. Reorder the UMD PDUs, detect loss of UMD PDUs in the lower layer to avoid excessive reordering delays, reassemble RLC SDUs from the rearranged UMD PDUs, and In addition, the reassembled RLC SDUs are delivered to an upper layer in an ascending order of an RLC sequence number, and UMD PDUs cannot be reassembled into an RLC SDU due to a loss of UMD PDUs belonging to a specific RLC SDU in a lower layer. Can be removed. Upon RLC re-establishment, the receiving UM RLC entity, if possible, reassembles the RLC SDUs from the received UMD PDUs out of sequence and forwards them to the higher layer, and the remaining UMD PDUs that could not be reassembled into RLC SDUs. Remove all, initialize the relevant state variables and stop the associated timers.

Meanwhile, the AM RLC entity 440 may be configured to receive or deliver RLC PDUs through logical channels (eg, DL / UL DCCH or DL / UL DTCH). The AM RLC entity delivers or receives an AMD PDU or ADM PDU segment, and delivers or receives an RLC control PDU (eg, a STATUS PDU).

AM RLC entity 440 delivers STATUS PDUs to peer AM RLC entities to provide positive and / or negative acknowledgment of RLC PDUs (or portions thereof). This may be called STATUS reporting. A polling procedure may be involved from the peer AM RLC entity to trigger STATUS reporting. That is, an AM RLC entity may poll the peer AM RLC entity to trigger STATUS reporting at its peer AM RLC entity.

If a STATUS report is triggered and the t-StatusProhibit is not running or has expired, the STATUS PDU is sent at the next transmission opportunity. Accordingly, 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 sends the RLC PDUs to the peer AM RLC entity via the lower layer. When the transmitter of the AM RLC entity configures AMD PDUs from RLC SDUs, it splits 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 notified by the lower layer. Segment or concatenate to configure AMD PDUs. The transmitter of the AM RLC entity supports retransmission of RLC data PDUs (ARQ). 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 informed by the lower layer, then the AM RLC entity repartitions 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 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 via the lower layer.

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

When resetting the RLC, the receiver of the AM RLC entity, possibly out of sequence, reassembles the RLC SDUs from the received RLC data PDUs and delivers them to the higher layer, all remaining RLC data PDUs that cannot be reassembled into RLC SDUs. Remove it, initialize the relevant state variables and stop the associated timers.

The PDCP sublayer includes at least one PDCP entity 500. Each RB (eg, DRB and SRB, except SRB0) is associated with one PDCP entity 500. Each PDCP entity may be associated with one or two RLC entity (s) depending on the characteristics of the RB and the RLC mode.

The PDCP entity 500 receives user data from a higher layer (eg an application layer) or passes user data to a higher layer. The user data here is an IP packet. User data may be delivered via a Service Access Point (PDCP-SAP). 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 through a control-service access point (C-SAP). The PDCP configuration request message is a message requesting to configure PDCP according to the PDCP configuration parameters.

The transmitting side of the PDCP entity 500 starts a discard timer upon receipt of user data from a higher layer. User data (i.e. PDCP SDU) is subject to PDCP headers (i.e., RLC SDUs) through header compression, flawless protection (in the control plane), and encryption. The transmitter PDCP delivers the PDCP PDU to the lower layer (eg, 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, and the like, and carries a PDCP SDU Sequence Number (SN). PDCP SDU SN may be called 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 through the RLC-SAP. If the user data is not transmitted until the removal timer expires, the transmitting PDCP removes the user data (PDCP SDU including the user data).

The receiving side of the PDCP entity 500 receives an RLC SDU (ie PDCP PDU) from a lower layer. PDCP PDUs become 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 SDUs to higher layers (eg, application layers).

The receiving end of the PDCP entity 500 generally expects to receive sequentially RLC SDUs (ie, PDCP PDUs), except for re-establishment of lower layers. Accordingly, except when the receiving end of the PDCP entity 500 receives the RLC SDU through the resetting of the lower layer, when the PDCP PDU is received, the receiving end of the PDCP entity 500 may transmit the corresponding PDCP SDU to the upper layer in ascending order. If there are stored PDCP SDUs, they are delivered to the upper layer in ascending order. For example, if the PDCP entity 500 receives a PDCP PDU for a reason other than a reset of a lower layer, the PDCP entity 500 will check all associated stored PDCP SDU (s) with a count value less than the associated count value of the received PDCP SDU. It delivers to the upper layer in ascending order and delivers all stored PDCP SDU (s) of consecutively associated count values starting from the count value of the received PDCP SDU to the upper layer in ascending order.

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

Referring to FIG. 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) may be a small base station (or a secondary base station or an assisting base station or a slave base station, 610). In this case, the mobile station enters an area overlaid with the service area of the small cell.

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

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

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

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

Bearers provided by the wireless communication system are collectively referred to as EPS (Evolved Packet System) bearers. The EPS bearer is a transmission path generated between the UE and the P-GW. The P-GW may receive IP flows from the Internet or send IP flows to the Internet. One or more EPS bearers may be configured per terminal, each EPS bearer may be divided into an E-UTRAN Radio Access Bearer (E-RAB) and an S5 / S8 bearer, and the E-RAB may be a Radio Bearer (RB) or an S1. 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 Quality of Service (QoS) characteristics, and IP flows having different QoS characteristics may be mapped and transmitted for each EPS bearer. The EPS bearer may be classified based on an EPS bearer identity. The EPS bearer identifier is allocated by the UE or MME.

P-GW (Packet Gateway) is a network node connecting between a wireless communication network (for example, LTE network) and another network according to the present invention. EPS bearer is defined between the terminal and the P-GW. EPS bearer is further subdivided between nodes, defined as RB between UE and BS, S1 bearer between BS and S-GW, and S5 / S8 bearer between S-GW and P-GW in EPC. do. Each bearer is defined through 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 an EPS bearer, each QoS is determined for each interface. Each interface establishes a bearer according to the QoS that it must provide. Since bearers of each interface provide QoS of all EPS bearers by interface, EPS bearers, RBs, and S1 bearers are basically in a one-to-one relationship.

That is, the LTE wireless communication system is basically a single flow structure, one RB is configured for one EPS bearer. In other words, one EPS bearer is mapped with 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 (eg, PDCP entity, RLC entity, MAC entity, PHY layer) is configured for the corresponding EPS bearer, and one RB is configured in the terminal.

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

Referring to FIG. 8, a 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 terminal through the RB (PDCP / RLC / MAC / PHY) configured in the macro base station. On the other hand, the EPS bearer # 2 850 provides a service to the terminal through the PDCP entity configured in the macro base station and the RB (RLC / MAC / PHY) configured in the small base station. Therefore, a service is provided through one RB per EPS bearer in a single flow.

Referring to FIG. 9, when multi-flow is configured, a service is provided through two RBs configured for the macro base station and the small base station instead of one RB for one EPS bearer. The terminal may simultaneously receive a service through one RB configured in the macro base station and one RB configured in the small base station for one EPS bearer. This is a form in which one EPS bearer provides a service through two RBs. As described above, when one EPS bearer provides a service to a terminal through two or more RBs, it may be regarded that multi-flow is configured in the terminal. Alternatively, multi-flow may be configured in the terminal when a service is provided to the terminal through the macro base station and the small base station by dividing one RB. Alternatively, the multi-flow may be configured when the RB providing the service only through the macro base station and another RB providing the RB divided into the macro base station and the small base station are simultaneously provided to the terminal. The case of providing a service to a terminal through a macro base station and a small base station by dividing one RB may be referred to as bearer split.

Referring to FIG. 10, a 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, an RB is configured at a macro base station and a small base station for one EPS bearer 1000 to provide a service to a terminal. That is, a macro base station and a small base station provide a service to a terminal through multiflow for one EPS bearer.

On the other hand, in consideration of dual connectivity, in the case of single flow and multi-flow, the packet forwarding process may be represented as follows.

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

The PDCP 1135-1 of the macro base station 1130 receives Packet 1 from the S-GW, and the PDCP 1135-2 receives Packet 2 from the S-GW. The PDCP 1135-1 generates PDCP PDU1 based on Packet 1, and the PDCP PDU1 is delivered to the RLC 1140 of the macro base station 1130, and each entity and the MAC 1145 through the PHY 1150. It is transformed into a form suitable for a layer and transmitted to the terminal 1100.

The PDCP 1135-2 of the macro base station 1130 generates a PDCP PDU2 based on Packet 2, and delivers the PDCP PDU2 to the RLC 1170 of the small base station 1160, and sends the MAC 1175 and the PHY 1180. ) Is transformed into a format suitable for each entity and layer and transmitted to the terminal 1100.

In the terminal 1100, a radio protocol entity exists for each of the EPS bearer # 1 and the EPS bearer # 2. In other words, the PDCP / RLC / MAC / PHY entity (or layer) exists in the EPS bearer # 1 and the PDCP / RLC / MAC / PHY entity (or layer) exists in the EPS bearer # 2. . In more detail, PHY 1105-1, MAC 1110-1, RLC 1115-1, and PDCP 1120-1 exist with respect to EPS bearer # 1. To deal with. The PHY 1105-2, the MAC 1110-2, the RLC 1115-2, and the PDCP 1120-2 exist for the EPS bearer # 2, and service data and packets for the EPS bearer # 2 are present. Process.

Meanwhile, the macro base station 1130 and the small base station 1160 may be connected through an X2 interface. That is, the macro base station 1130 transmits the PDCP PDU2 of the PDCP 1135-2 to the RLC 1140 of the small base station 1160 through the X2 interface. Herein, the X2 interface may use other expressions indicating an X3 interface or an interface between other macro base stations and small base stations. In this case, when the X2 interface between the macro base station 1130 and the small base station 1160 is configured with 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 or a method as an example.

However, even in this case, the terminal 1100 includes the RLC 1115-1 for the EPS bearer # 1, the PDCP 1120-1 for the EPS bearer # 2, and the RLC 1115-2 for the EPS bearer # 2 and the PDCP 1120-2. Since it is configured separately, no problem occurs even when sequential delivery of RLC SDUs is performed from the RLC entity of the AM to the PDCP entity. In other words, each PDCP entity corresponding to PDCP 1120-1 and PDCP 1120-2 is sequentially processed if it is processed in the order transmitted from each RLC entity corresponding to RLC 1115-1 and RLC 1115-2. Problem does not occur.

Referring to FIG. 12, the macro base station 1230 receives packets for one EPS bearer through the P-GW and the S-GW. The macro base station 1230 and the small base station 1260 each constitute an RB for the one EPS bearer. Specifically, the macro base station 1230 constitutes a PDCP 1235, an RLC 1240, a MAC 1245, and a PHY 1250, and the small base station 1240 is an RLC 1270, a MAC 1275, and a PHY 1280. ). The RB configured by the small base station 1240 shares 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 packets, and generates the PDCP PDUs according to a predefined rule or any method according to the RLC 1240 of the macro base station 1230 and the RLC 1270 of the small base station 1260. Properly distribute to For example, PDCP PDUs having odd SNs among PDCP PDUs are transmitted to the RLC 1240 of the macro base station 1230, and PDCP PDUs having even SNs are transmitted to the RLC 1270 of the small base station 1260. Can be.

The RLC 1240 generates an RLC PDU1 (s), and the RLC PDU1 (s) is transformed into a format suitable for each entity and layer through the MAC 1245 and the PHY 1250 and transmitted to the terminal 1200. In addition, the RLC 1270 generates an RLC PDU2 (s), and 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 radio protocol entities for the EPS bearer. In other words, the terminal 1200 includes a PDCP / RLC / MAC / PHY entity (or layer) as an RB corresponding to the macro base station 1230, and an RLC / MAC / PHY entity (as an RB corresponding to the small base station 1260). Or hierarchy). In detail, 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 is present. There is a corresponding PHY 1205-2, MAC 1210-2, and RLC 1215-2. The PDCP 1220 is a PDCP entity corresponding to the macro base station 1230 and the small base station 1260 simultaneously. 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. Corresponds to.

As described above, the macro base station 1230 and the small base station 1260 may be connected through an X2 (or Xn) interface. That is, the macro base station 1230 transfers some of the PDCP PDUs of the PDCP 1235-2 to the RLC 1240 of the small base station 1260 through the X2 interface. Herein, the X2 interface may use other expressions indicating an Xn interface or an interface between other macro base stations and small base stations. In this case, when the X2 interface between the macro base station 1230 and the small base station 1260 is configured with a non-ideal backhaul, a transmission delay of about 20 to 60 ms may occur. The PDCP entity 1220 of the UE 1200 should receive RLC SDUs (ie, PDCP PDUs) from two RLC entities 1215-1 and 1215-2, respectively, generate PDCP SDUs, and deliver them to a higher layer. Due to the transmission delay, a time difference occurs between the RLC SDUs (ie, PDCP PDUs) received by the PDCP entity 1220 from those received from the RLC entity 1215-1, and from the RLC entity 1215-2. The PDCP entity 1220 may have problems in performing ascending transmission to the upper layer of the PDCP SDU.

As shown in FIG. 12, one PDCP 1235 exists in the macro base station 1230 and one PDCP entity 1220 exists in the UE 1200 for multi-flow in a dual connectivity environment. In addition, the

RLC entities

1240 and 1270 are present in the macro base station 1230 and the small base station 1230, respectively, and two RLC entities 1215-1 and 1215-2 are also present in the terminal 1200. . That is, in the RLC entities 1215-1 and 1215-2 of the terminal 1210, in-sequence delivery to the upper layer may be guaranteed. However, at the PDCP entity 1220 end of the terminal 1210, RLC SDUs (ie PDCP PDUs) are transmitted from two RLC entities 1215-1 and 1215-2 instead of one RLC entity. Thus, sequential delivery at the RLC entity 1215-1, 1215-2 end does not guarantee sequential reception of PDCP PDUs at the PDCP entity end. In addition, 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, and the macro base station 1230 There may be a time delay between transmission of PDCP PDU (s) towards RLC entity 1240 and transmission of PDCP PDU (s) to RLC entity 1270 of small base station 1230. As a result, even when the PDCP PDU (s) transmitted from the PDCP entity 1235 of the macro base station 1230 is received by the PDCP entity 1220 of the terminal 1200, transmission and small through the RLC sub-terminal of the macro base station 1230 are performed. In the transmission through the RLC stage of the base station 1260, a difference occurs in the reception time, and the PDCP entity 1220 of the terminal 1200 is difficult to expect the sequential reception of the PDCP PDU (s).

13 illustrates an example of timing of reception of PDCP PDUs in a PDCP entity of a UE. 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 a terminal. The macro base station may determine a PDCP PDU to be transmitted through the macro base station and a PDCP PDU to be transmitted through the small base station for the service for one EPS bearer. In FIG. 13, PDCP PDUs associated with an odd number of PDCP sequence numbers (SN) 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 at a terminal of a PDCP PDU transmitted through a macro base station and a reception time at a terminal of a PDCP PDU transmitted through a small base station. A transmission delay of about 20 to 60 ms may occur in the PDCP PDU transmitted through the small base station. This is mainly caused by 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, due to the time difference between the RLC (AMD) SDUs received from the two RLC entities, the PDCP entity of the terminal receives the PDCP PDUs out of order, and the PDCP entity processes them to a higher layer (for example, an application layer). In case of transmission, it is difficult to guarantee the ascending transmission of PDCP SDUs. That is, since the PDCP PDUs transmitted from one PDCP entity of the macro base station in the multi-flow structure are transmitted through the RLC entity of the macro base station and the RLC entity of the small base station, the PDCP PDU of the UE receives a time delay. Therefore, a problem arises in performing ascending transmission of the PDCP SDU from the PDCP entity to the higher layer.

The PDCP entity of the UE reads the received PDCP PDU and performs header decompression, and transmits the PDCP SDU to the upper layer. At this time, if the PDCP SDU of the SN smaller than the SN (sequence number) of the current PDCP SDU is stored, the PDCP SDU is transmitted to the upper layer in order from the smallest SN to the largest SN.

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

However, when supporting the multi-flow in the aforementioned dual connectivity situation, the PDCP entity may receive RLC SDUs (PDCP PDUs) from the two RLC entities with which it is associated. In this case, PDCP PDUs (particularly, RLC AMD SDUs) are not sequentially received at the PDCP entity, and PDCP PDUs with a larger PDCP SN may be received first due to transmission path reception delay, and the PDCP entity is moved to a higher layer. There may be cases where PDCP SDU ascending transmission is not guaranteed. In consideration of the path delay caused by the multi-flow, a PDCP SDU rearrangement method is required, which enables the PDCP entity to deliver the PDCP SDUs to the upper layer in ascending order.

The PDCP SDU rearrangement method based on the PDCP SN comparison proposed in the example of the present invention is as follows. The present invention can be applied to both a downlink data transfer procedure and an uplink data transfer procedure, and the following description will focus on the downlink data transfer procedure.

14 shows an example of performing a PDCP SDU rearrangement based on a PDCP SN comparison according to an embodiment of the present invention.

Referring to FIG. 14, PDCP PDUs of

PDCP SNs

1, 2, 3, 4, 5, 11, 12, 13, 17, 18, 19, 20, 21, 22, and 26 are transmitted through an RLC entity of a macro base station. It is assumed that PDCP PDUs of

PDCP SNs

6, 7, 8, 9, 10, 14, 15, 16, and 23 are transmitted through an RLC entity of a small base station. Hereinafter, it is assumed that a PDCP entity of a terminal can distinguish whether received PDCP PDUs are transmitted through an RLC entity of a macro base station or through an RLC entity of a small base station.

FIG. 14A illustrates a PDCP PDU of PDCP SN 19 after receiving PDCP PDUs of

PDCP SN

1, 2, 3, 4, 5, 11, 12, 6, 13, 7, 17, 8, 18, and 9 from a PDCP entity of a UE. Is received.

The PDCP entity of the terminal sequentially receives PDCP PDUs of

PDCP SNs

1, 2, 3, 4, and 5 through the macro base station (the RLC entity), and then receives the PDCP PDUs of PDCP SN 11. In this case, since the PDCP entity of the terminal has received PDCP PDUs of PDCP SN 11 through the macro base station, it can be seen that there is no possibility of receiving PDCP SN 6 to 10 PDCP PDUs through the macro base station even after a longer time. However, there is a possibility of receiving PDCP PDUs 6 to 10 PDCP PDUs through a small base station (of RLC entity). Therefore, the PDCP entity of the terminal does not immediately transmit the corresponding PDCP SDU when receiving PDCP PDUs of PDCP SN 11 and stores them in a buffer, and then checks whether PDCP SN 6 to 10 PDCP PDUs are received through the small base station.

When the PDCP entity of the terminal receives the PDCP PDU of PDCP SN No. 12 through the macro base station, the PDCP entity stores the corresponding PDCP SDU in the buffer. After receiving the PDCP PDU of PDCP SN No. 6 through the small base station, the PDCP entity of the terminal transmits the corresponding PDCP SDU to the higher layer. After receiving the PDCP PDU of PDCP SN No. 13 through the macro base station, the PDCP entity of the terminal stores the corresponding PDCP SDU in the buffer. After receiving the PDCP PDU of PDCP SN No. 7 through the small base station, the PDCP entity of the terminal transfers the corresponding PDCP SDU to the higher layer. After receiving the PDCP PDU of PDCP SN 17 through the macro base station, the PDCP entity of the terminal stores the corresponding PDCP SDU in the buffer. After receiving the PDCP PDU of PDCP SN No. 8 through the small base station, the PDCP entity of the terminal transmits the corresponding PDCP SDU to the higher layer. After receiving the PDCP PDU of PDCP SN No. 18 through the macro base station, the PDCP entity of the terminal stores the corresponding PDCP SDU in the buffer. After receiving the PDCP PDU of PDCP SN No. 9 through the small base station, the PDCP entity of the terminal transmits the corresponding PDCP SDU to the upper layer. After receiving the PDCP PDU of PDCP SN 19 through the macro base station, the PDCP entity of the terminal stores the corresponding PDCP SDU in the buffer.

Meanwhile, if PDCP PDUs of PDCP SN greater than PDCP SN 11 are received as the PDCP entity of the terminal through the small base station in a situation where PDCP SNs 6 to 10 PDCP PDUs are not received, the PDCP entity of the terminal is the PDCP SN. 6 to 10 PDCP PDUs may no longer be transmitted through the small base station. In this case, the PDCP entity of the terminal may deliver the PDCP SDU of PDCP SN 11 to a higher layer.

FIG. 14B assumes a case where the PDCP entity of the UE receives the PDCP PDU of PDCP SN 10 after FIG. 14A.

Referring to FIG. 14B, when a PDCP entity of a terminal receives a PDCP PDU of PDCP SN 10,

PDCP SN

10, 11, 12, and 13 PDCPs, which are all stored PDCP SDUs of PDCP SN values consecutively associated with the PDCP 10 starting from PDCP 10, are received. Deliver SDUs to higher layers.

15 illustrates an example of performing PDCP SDU removal determination based on a PDCP SN comparison according to an embodiment of the present invention.

Referring to FIG. 15, PDCP PDUs of

PDCP SNs

FIG. 15a illustrates that a PDCP entity of a UE receives PDCP SN 13 and PDCP PDUs without receiving PDCP PDUs of PDCP SN 6 after

PDCP SN

1, 2, 3, 4, 5, 11, and 12 PDCP PDUs are received. If it is.

Referring to FIG. 15A, after a PDCP entity of PDCP SN 5 receives PDCP PDUs of PDCP SN 5, PDCP SN 13 of PDCP SN 13 through a macro base station without receiving PDCP PDUs of PDCP SN 6, and PDCP PDUs of PDCP SN 7 through a small base station Received. In this case, since the PDCP entity of the terminal receives the PDCP PDUs of PDCP SN No. 7 through the small base station, it can be seen that the PDCP PDUs of PDCP SN No. 6 which are smaller PDCP SNs will not be transmitted through the small base station. In this case, the PDCP entity of the terminal checks the reception status of PDCP PDUs through the macro base station. If a PDCP PDU having a PDCP SN value greater than PDCP SN 6 is received to the PDCP entity of the terminal through the macro base station, the PDCP entity of the terminal will no longer transmit the PDCP PDUs of PDCP SN 6 to the macro base station. Able to know. In FIG. 15A, since PDCP PDUs of

PDCP SNs

11, 12, and 13 greater than PDCP SN 6 are received through the macro base station, it can be seen that PDCP PDUs of PDCP SN 6 are not transmitted through the macro base station. Therefore, in this case, the PDCP PDUs of PDCP SN 6 are no longer viewed as removed, and the PDCP PDUs of PDCP SN 7 already received are transferred to higher layers. As such, when PDCP SDU rearrangement is performed based on a comparison of PDCP SNs without a separate timer for PDCP SDU rearrangement, PDCP PDU removal can be grasped even before the timer expires, and the upper layer of the remaining PDCP SDUs can be identified. Ascending can be performed with

FIG. 15B illustrates a case where a plurality of PDCP PDUs are removed. After 15 (a), the PDCP entity of the UE receives PDCP SN 17 and PDCP PDUs of 18 times, and then

PDCP SN

19 and 9 without receiving PDCP PDUs of PDCP SN 8. It is the case that one PDCP PDU is received.

Referring to FIG. 15B, the PDCP entity of the terminal receives the PDCP PDU of the PDCP SN 9 through the small base station without receiving the PDCP PDU of the PDCP SN 8. Accordingly, PDCP PDUs of PDCP SN 8, which are smaller than PDCP SN 9, are no longer received via the small base station. Therefore, in this case, the PDCP PDU of PDCP SN No. 8 should be examined for the possibility of being received through the macro base station. In this case, since the PDCP entity of the current terminal has received PDCP PDUs of PDCP SN 19 through the macro base station, PDCP PDUs of PDCP SN 8 smaller than PDCP SN 19 may no longer be received through the macro base station. Therefore, in this case, the PDCP entity of the terminal determines that the PDCP PDUs of PDCP SN 8 are removed, and delivers the PDCP SDUs associated with PDCP SN 9 to a higher layer.

When the rearrangement is performed using only the PDCP SN as described above, the PDCP entity of the terminal is a peer configured in the terminal corresponding to the RLC entity of the macro base station through the macro base station (RLC entity of) or the small base station (RLC entity). (peer) distinguishes PDCP PDUs received through a RLC entity or a peer RLC entity configured in a terminal corresponding to an RLC entity of a small base station, and PDCP SNs of PDCP PDUs received through one base station and the other base station Compares PDCP SNs of PDCP PDUs received through the PDCP PDUs and reports the PDCP PDUs of the missing PDCP SNs as removed and forwards the stored PDCP SDUs to a higher layer according to certain rules, or PDCPs of the missing PDCP SNs. It may be decided whether to wait for more PDUs. In other words, not waiting for the PDCP PDU of the missing PDCP SN may mean that the PDCP PDU (or PDCP SDU) of the PDCP SN is removed. Here, the removal of a PDCP PDU (or PDCP SDU) of a specific SN may be referred to as PDCP removal of a specific SN. Also, hereinafter, simply PDCP removal may mean PDCP removal of a specific SN.

Meanwhile, in a dual connectivity situation, the small base station may be considered as a resource additionally used by the terminal to the macro base station. The radius of the cell of the small base station is also smaller than the radius of the cell of the macro base station. Therefore, from the terminal side, a small base station may be added or removed. In addition, it may be difficult to perform transmission through the small base station according to a wireless situation. In other words, a problem may occur in transmission through the small base station in a multi-flow situation.

FIG. 16 illustrates a case where a problem occurs in PDCP PDU transmission through a small base station in a situation in which a multi-flow is configured with a macro base station and a small base station in the terminal. 16 shows PDCP PDUs of

PDCP SN

1, 2, 3, 4, 5, 11, 12, 13, 17, 18, 19, 20, 21, 22, 26, 27, 33, 34, and 35. PDCP PDUs of

PDCP SN

6, 7, 8, 9, 10, 14, 15, 16, 23, 24, 25, 28, and 29 are transmitted through the small base station (the RLC entity). In this case, there is a problem in PDCP PDU transmission of

PDCP SN

15, 16, 23, 24, 25, 28, 29 through a small base station. This may be a situation in which transmission failures in which PDCP PDUs are not transmitted from the UE through the small base station due to the movement of the UE or the bad situation of the radio section are continued.

FIG. 16a illustrates a PDCP entity of a terminal receives

PDCP PDUs

13 and 7 without receiving PDCP PDUs of PDCP SN 6 after

PDCP SN

1, 2, 3, 4, 5, 11 and 12 PDCP PDUs are received. In this case,

PDCP SN

18 and 8 PDCP PDUs are received without receiving PDCP PDUs of PDCP SN 17.

Referring to FIG. 16A, the PDCP entity of the terminal receives PDCP PDUs of PDCP SN 18 without receiving PDCP PDUs of PDCP SN 17, but when the reception status is confirmed in the small base station, PDCP SN 7 is received.

PDCP SN

14, 15, 16, 17 PDCP PDUs are determined to be received through the small base station, the PDCP SDU associated with PDCP SN 18 is stored in a buffer, PDCP PDUs of

PDCP SN

14, 15, 16, 17 Wait until the PDCP DPU of the PDCP SN, which is received through the small base station or larger, is received through the small base station to confirm the removal.

FIG. 16B illustrates a case in which a PDCP entity of the UE receives

PDCP SN

8, 19, 9, 20, 10, 21, and 14 PDCP PDUs after 16 (a).

Referring to FIG. 16B, the PDCP entity of the terminal does not transfer PDCP SDUs corresponding to PDCP PDUs of

PDCP SN

19, 20, and 21 received after receiving PDCP PDUs of PDCP SN 18 to a higher layer and stores them in a buffer. . At this time, PDCP PDUs from PDCP SN 15 are not transmitted due to a problem in transmission through the small base station. In this case, even if the PDCP entity of the UE no longer waits, the PDCP entity cannot determine whether it can deliver the PDCP PDU of PDCP SN 18 to a higher layer. In a situation where a PDCP PDU to be compared is not received through a small base station (or a macro base station), such as when a small base station or the like causes a problem and no more PDCP PDUs are transmitted, it is determined whether to treat a PDCP PDU as removed. Problems that can't be judged and still pending can occur.

17 illustrates an example of a PDCP SDU rearrangement scheme using a waiting timer when PDCP PDUs are not suddenly received through a small base station according to another embodiment of the present invention. In the present invention, the wait timer may be referred to as a rearrangement timer or a PDCP rearrangement timer. FIG. 17 shows PDCP PDUs of

PDCP SN

1, 2, 3, 4, 5, 11, 12, 13, 17, 18, 19, 20, 21, 22, 26, 27, 33, 34, 35. PDCP PDUs of

PDCP SN

15, 16, 23, 24, 25, 28, 29 through a small base station.

FIG. 17a illustrates a PDCP entity of a terminal receives

PDCP SNs

13 and 7 without receiving PDCP PDUs of PDCP SN 6 after

PDCP SN

1, 2, 3, 4, 5, 11 and 12 PDCP PDUs are received. Receives PDCP PDUs of

PDCP SN

18, 8, 19, 9, 20, 10, 21, and 14 without receiving PDCP PDUs of PDCP SN 17, and transmits the PDCP SN 22 through the macro base station due to a transmission problem through the small base station. This is the case where only PDCP PDUs of Nos., 26, 27, 33, 34, and 35 are received.

Referring to FIG. 17A, when the PDCP PDUs of PDCP SN 18 are received by the PDCP entity of the UE through the macro base station, PDCP PDUs of

PDCP SNs

14, 15, 16, and 17 may be received through the small base station. At this time, the PDCP entity of the terminal drives the rearrangement timer for the PDCP PDU of PDCP SN 18, and stores the PDCP SDU associated with PDCP SN 18 in the buffer. At this time, while the rearrangement timer is running, the terminal checks the PDCP PDU received through the small base station.

If the PDCP entity of the terminal receives a PDCP PDU of the PDCP SN greater than PDCP SN # 18 through the small base station during the rearrangement timer driving period, the PDCP entity of the terminal stops the rearrangement timer. In this case, the PDCP entity of the terminal may determine that the PDCP PDUs of PDCP SN 14 to 17 have been removed and may deliver the PDCP SDU associated with PDCP SN 18 to a higher layer.

If the PDCP entity of the terminal receives PDCP PDUs through the small base station during the rearrangement timer driving period, PDCP PDUs are not received through the small base station of PDCP SN greater than PDCP SN 18 until the rearrangement timer expires. If not, the PDCP entity of the terminal drives the rearrangement timer again after the rearrangement timer expires. In this case, PDCP SDUs received through the macro base station associated with PDCP SN greater than PDCP SN 18 are stored in a buffer. Accordingly, when the PDCP entity of the terminal receives the PDCP PDUs of PDCP SN 35, the PDCP entities store PDCP SDUs associated with

PDCP SNs

18, 19, 20, 21, 22, 26, 27, 33, 34, and 35 in a buffer.

If the PDCP entity of the terminal does not receive PDCP PDUs at all through the small base station during the rearrangement timer driving period, the PDCP entity of the terminal delivers the stored PDCP SDUs to a higher layer after the rearrangement timer expires.

FIG. 17B illustrates a case in which the rearrangement timer expires without receiving a PDCP PDU through the small base station after FIG. 17A.

Referring to FIG. 17B, the PDCP entity of the terminal has no second PDCP PDU received through the small base station during the second rearrangement timer driving period, and thus no more PDCP PDUs are transmitted through the small base station. It may be determined that it will not be, and the stored PDCP SDUs may be delivered to a higher layer.

By setting the rearrangement timer as described above, it is possible to determine the reception status of PDCP PDUs transmitted through the small base station, and the PDCP PDUs transmitted through the small base station are not received by the PDCP entity of the terminal due to a problem such as the small base station. If not, the PDCP SDUs corresponding to the PDCP PDUs previously received in the PDCP entity of the UE may be delivered to the upper layer.

In addition, the PDCP entity of the UE during the rearrangement timer driving period is an example of delivering the stored PDCP SDUs to the upper layer after the rearrangement timer expires, only when the PDCP entity has not received any PDCP PDUs through the small base station. Therefore, in addition, if the number of repetitions of the large timer is set to, for example, three times, and the timer operates in three repetitions, and at this time, the PDCP PDU of the PDCP SN, which is expected to receive sequentially, is not received, the PDCP of the UE The entity may deliver the stored PDCP SDUs to higher layers. Alternatively, by setting the length of the rearrangement timer to an appropriate value, after the rearrangement timer expires, the PDCP entity of the terminal may unconditionally deliver the stored PDCP SDUs to a higher layer.

Referring to FIG. 18, a PDCP entity of a terminal receives PDCP PDUs through a macro base station and a small base station configured with multi-flow with the terminal (S1800).

When the PDCP entity of the UE receives PDCP SN n PDCP PDUs through one of the macro base station and the small base station, the PDCP entity checks whether the maximum PDCP SN values k of PDCP PDUs received through the other base station are greater than n. (S1810).

If k> n in S1810, the PDCP entity of the terminal determines that the PDCP SDUs not yet received associated with a PDCP SN value smaller than PDCP SN n are removed (S1820). The PDCP entity of the UE delivers all stored PDCP SDUs associated with a PDCP SN value smaller than PDCP SN n to a higher layer (S1830), starting from PDCP SN n (starting from), and all stored PDCPs of consecutively related PDCP SN values. The SDUs are delivered to the upper layer in ascending order (S1840).

If k <n in S1810, the PDCP entity of the terminal waits to receive a PDCP PDU of the PDCP SN value greater than PDCP SN n times through the other base station, and repeats the operation of S1800 or less.

Meanwhile, in preparation for a situation in which PDCP PDUs are not transmitted due to a problem in transmitting PDCP PDUs through another base station, the PDCP entity of the UE may operate a rearrangement timer.

Referring to FIG. 19, a PDCP entity of a terminal receives PDCP PDUs through a macro base station and a small base station configured with multi-flow with the terminal (S1900).

When the PDCP entity of the terminal receives a PDCP PDU of PDCP SN n through any one of the macro base station and the small base station, the PDCP entity drives the rearrangement timer (S1910).

The PDCP entity of the terminal checks whether at least one PDCP PDU is received through the other base station during the rearrangement timer driving period (S1920).

If, at S1920, at least one PDCP PDU is received through the other base station during the rearrangement timer driving period, the PDCP entity of the terminal is at least one received through the other base station during the rearrangement timer driving period. It is checked whether the maximum PDCP SN value k in the PDCP PDU is greater than n (S1930).

If the maximum PDCP SN value k of at least one PDCP PDU received through the other base station in S1930 is greater than the n, that is, if a PDCP PDU of PDCP SN k greater than the PDCP SN n times is received, The rearrangement timer is stopped (S1940). The PDCP entity of the terminal determines that PDCP SDUs not yet received associated with a PDCP SN value smaller than PDCP SN n are removed (S1950). The PDCP entity of the UE transmits all stored PDCP SDUs associated with a PDCP SN value smaller than PDCP SN n to a higher layer (S1960), starting with PDCP SN n and sequentially storing all stored PDCP SDUs of associated PDCP SN values in ascending order. Transfer to the upper layer (S1970).

If the maximum PDCP SN value k of at least one PDCP PDU received through the other base station is not greater than n in S1930, the PDCP entity of the terminal drives the rearrangement timer again after the rearrangement timer expires ( S1980). The PDCP entity of the terminal receives PDCP PDUs through the other base station during the rearrangement timer driving period, but the PDCP PDU having a PDCP SN value of PDCP SN greater than PDCP SN n times through the other base station until the rearrangement timer expires. If not received.

If the PDCP entity of the terminal does not receive PDCP PDUs at all through the other base station during the rearrangement timer driving period in S1920, the PDCP entity of the terminal after the reordering timer expires, all stored PDCP SDUs in ascending order. Transfer to the upper layer (S1990).

As described above, the PDCP entity of the UE may perform PDCP SDU rearrangement by comparing PDCP SNs of PDCP PDUs transmitted from the macro base station and the small base station, each of which has dual connectivity with the terminal, and at least one of the macro base station and the small base station. When PDCP PDUs are not continuously received through one base station, the PDCP PDUs received through the other base station may be processed based on the rearrangement timer.

In the above, an example of determining (or determining) PDCP removal using only SN and determining PDCP removal based on the rearrangement timer has been described. When the PDCP removal is determined by the SN alone, the PDCP removal may be determined more quickly than when the PDCP removal is determined by using a timer, and the remaining PDCP SDUs may be transmitted to a higher layer. That is, in this case, there is an advantage in that a gain can be obtained in terms of transmission efficiency. In addition, if the PDCP removal is determined based on the rearrangement timer, there is an advantage of securing stability than when determining the PDCP removal only with SN.

The method of determining the PDCP removal and performing the PDCP rearrangement described above may be used to solve a problem in which sequential delivery in the PDCP layer is not guaranteed in a situation in which dual connectivity is configured in the terminal. In the above-described example, when the in-sequence PDCP PDU is not received at the PDCP layer, the rearrangement timer may be started when the out-of-sequence PDCP PDU is received. The rearrangement timer is set in consideration of the transmission delay time of the X2 interface between the macro base station and the small base station in which the dual connection is configured in the terminal (about 20 to 60 ms, but this may vary depending on the network layout and the backhaul network environment, for example). Can be.

In summary, when dual connectivity is configured in the terminal, packets transmitted from the upper layer of the macro base station to the PDCP layer (through the macro cell) are processed through header compression and ciphering. The PDCP PDUs are processed in a layer, and the PDCP PDUs are classified according to a predetermined criterion, and partly transmitted to the terminal through the macro cell of the macro base station, and the other part is transmitted to the terminal through the small cell of the small base station. Each of the PDCP PDUs is indicated by an SN, and even when an out-of-sequence reception occurs in which the PDCP PDUs are not received in the SN order at the terminal, the terminal once receives the PDCP PDU (ie, the missing SN). Instead of determining that the PDCP PDU corresponding to the sequential reception has been removed (PDCP removal), the rearrangement timer set in consideration of the above-described transmission delay is driven. If the PDCP PDU of the SN is not received until the rearrangement timer expires, then the PDCP PDU of the SN is determined (or determined) to be removed. After the PDCP PDU (PDCP PDU corresponding to sequential reception) of the missing SN is determined to be removed, the PDCP PDUs of the SN larger than the missing SN are transferred (sequentially) to higher layers.

In FIG. 20A, the UE expects to receive a PDCP PDU of SN6 after receiving a PDCP PDU of SN5. The PDCP PDU of the SN6, which the UE expects to receive, may be regarded as a PDCP PDU of an in-sequence SN. However, the terminal configured with dual connectivity may receive the PDCP PDU of the SN11 in some cases. According to the present invention, upon receiving the PDCP PDU of the SN11, the UE determines that the PDCP PDU of the non-sequential SN is received and drives a rearrangement timer (PDCP rearrangement timer).

Thereafter, the terminal may receive PDCP PDUs of

SN

12, 13, 7, 8, and 9. However, in this case, since the rearrangement timer is running and the PDCP PDU of the SN6 has not been received yet, PDCP SDUs associated with the received PDCP PDU are stored in a buffer and are not delivered to the upper layer. For example, the upper layer may correspond to a transmission protocol such as TCP (Transmission Control Protocol), through which an actual service may be performed at an application stage. Therefore, if the PDCP SDUs that cannot be delivered to the upper layer for a certain time or the PDCP SDUs rapidly reach the upper layer, this may lead to a lowering of the transmission rate and may cause a deterioration of quality of service. Therefore, it is desirable that PDCP SDUs be delivered to the upper layer as soon as possible.

20B illustrates an operation in the PDCP layer of the terminal when the rearrangement timer expires. The terminal determines (or determines) that the PDCP PDU of the SN6 has been removed at the time when the rearrangement timer expires. Therefore, PDCP SDUs stored in the buffer and associated with PDCP PDUs of SN larger than SN6 may be delivered (in ascending order) to a higher layer. Here, PDCP SDUs associated with PDCP PDUs of PDCP SN 7 to 13 may be delivered to a higher layer.

Meanwhile, according to another example of the present invention, PDCP removal and sequential delivery of PDCP SDUs can be supported based on both a rearrangement timer-based scheme and a base station-based PDCP PDU SN comparison scheme.

Referring to FIG. 21, PDCP PDUs of

PDCP SNs

6, 7, 8, 9, 10, 14, 15, 16, and 23 are transmitted through an RLC entity of a small base station.

21 is a PDCP entity of the terminal after receiving PDCP PDUs of

PDCP SN

1, 2, 3, 4, 5, 11, 12, without receiving PDCP PDUs of PDCP SN 6, PDCP SN 13, PDCP PDUs 7 received If it is.

Referring to FIG. 21, after a PDCP entity of PDCP SN 5 receives a PDCP PDU of PDCP SN 5, a PDCP entity of the terminal drives a rearrangement timer when the PDCP PDU of PDCP SN 11 is received through a macro base station without receiving PDCP PDU of PDCP SN 6. Thereafter, the PDCP entity of the terminal receives the PDCP PDU of PDCP SN 7 through the small base station. In this case, the UE may know that the received PDCP PDU of PDCP SN 7 is transmitted from the RLC entity corresponding to the small cell of the small base station. The individual RLC entity delivers the PDCP PDUs to the PDCP entity in ascending order in RLC AM mode. If the rearrangement timer is driven by out-of-sequence PDCP PDU reception from the macro base station (macro cell), it is possible to receive sequential PDCP PDUs from the small base station (small cell), in which case the PDCP stored even before the rearrangement timer expires. SDUs can be delivered to higher layers.

Using both the PDCP rearrangement timer and the base station SN comparison method can quickly determine PDCP removal and solve the stability (or reliability) problem of using only the base station SN comparison method without a timer. have.

In more detail, a method of performing PDCP removal determination based on PDCP SN comparison and rearrangement timer for each base station according to another embodiment of the present invention will be described.

Referring to FIG. 22, a PDCP entity of a terminal receives PDCP PDUs through a macro base station and a small base station configured with multi-flow with the terminal (S2200). For example, the PDCP entity of the terminal may sequentially receive PDCP PDUs up to PDCP SN a.

The PDCP entity of the terminal may store PDCP SDUs associated with the received PDCP PDUs in a buffer.

When the PDCP entity of the terminal receives the PDCP PDUs of PDCP SN n times through any one of the macro base station and the small base station, the PDCP entity checks whether the PDCP PDU reception of the PDCP SN n times is a PDCP PDU reception of a non-sequential SN (S2210). ). For example, the terminal may check whether the reception is non-sequential based on whether a + 1 = n.

When the PDCP PDU of the non-sequential SN is received in S2210, the PDCP entity of the terminal drives the rearrangement timer (S2220). In other words, in the present embodiment, when the PDCP PDU of the non-sequential SN is received, the rearrangement timer is driven.

The PDCP entity of the terminal determines whether n is greater than the PDCP SN value k of the PDCP PDU received through another base station (S2230).

If n> k in S2230, the PDCP entity of the terminal determines that PDCP PDUs of PDCP SN (a + 1) to (k-1) are PDCP removed (S2240). When the PDCP entity of the terminal excludes the SN determined to remove the PDCP, the PDCP entity, which is determined to be sequential, transfers the PDCP SDUs related to the received PDCP PDUs to an upper layer in ascending order (S2250).

For example, when the PDCP entity is a = 5, n = 11, and k = 7, since n> k (11> 7), the PDCP PDU of the SN corresponding to a + 1 = 6 is determined to be removed. The PDCP rearrangement timer was driven by receiving a PDCP PDU with SN n = 11 through a macro cell in a state of sequentially receiving PDCP PDUs up to SN a = 5, and then SN k through a small cell rather than a macro cell. It may be the case that a PDCP PDU corresponding to = 7 is received. Therefore, the PDCP PDU corresponding to SN 6 can no longer be received through the small cell, and since the PDCP PDU with SN n = 11 is received in the macro cell, it is determined that the PDCP PDU corresponding to SN6 can no longer be received. Can be.

Accordingly, when the PDCP entity of the UE receives a PDCP PDU corresponding to SN7 (k = 7), the PDCP PDU of SN6 determines that PDCP is removed, and the corresponding PDCP PDU is removed because the PDCP PDU of SN6 is removed. Except for the PDCP PDUs of the SN determined to be determined, the PDCP SDUs associated with the received PDCP PDUs determined to be sequential (eg, SN7) may be delivered to the upper layer in ascending order.

If n <k in S2240, the PDCP entity of the terminal determines that PDCP PDUs of PDCP SN (a + 1) to (n-1) are PDCP removed (S2260). When the PDCP entity of the terminal excludes the SN determined to remove the PDCP, the PDCP entity, which is determined to be sequential, transfers the PDCP SDUs associated with the received PDCP PDUs to an upper layer in ascending order (S2270).

For example, if the PDCP entity is a = 5, n = 11, and k = 15, n <k (11> 15), so PDCP of SN corresponding to 6 (a + 1) to 10 (n-1) PDUs are determined to be removed. The PDCP rearrangement timer was driven by receiving a PDCP PDU with SN n = 11 through a macro cell in a state of sequentially receiving PDCP PDUs up to SN a = 5, and then SN k through a small cell rather than a macro cell. This may be the case when a PDCP PDU corresponding to = 15 is received. Therefore, the PDCP PDUs of SNs ranging from 6 (a + 1) to 10 (n-1) can no longer be received through the small cell, and since the PDCP PDUs of SN n = 11 are also received from the macro cell, It may be determined that PDCP PDUs corresponding to SN6 through SN10 cannot be received.

Therefore, when the PDCP entity of the UE receives a PDCP PDU corresponding to SN15 (k = 15), the PDCP PDUs of SN6 to 10 are determined to be PDCP removed, except for PDCP PDUs of the SN determined to be removed. PDCP SDUs associated with the received PDCP PDUs determined to be may be delivered to the upper layer in ascending order.

When the PDCP entity received during the PDCP rearrangement timer operation does not satisfy S2230, the PDCP entity of the UE may store the PDCP SDU associated with the PDCP PDU of the received SN k in a buffer.

When the rearrangement timer expires, the PDCP SDUs stored in the buffer are transferred to the upper layer in ascending order (S2280).

As described above, the PDCP SNs of the PDCP PDUs transmitted from the macro base station and the small base station configured with the dual connectivity with the terminal may be compared, and the PDCP removal determination and the PDCP SDU rearrangement may be performed more efficiently based on the rearrangement timer. have.

Meanwhile, in the present invention, PDCP SDU rearrangement may be performed based on a fixed timer as well as the above-described method, and the ascending order of PDCP SDUs may be guaranteed. In order to proceed with the PDCP SDU rearrangement in the PDCP layer of the UE, a process when a PDCP PDU is received that does not correspond to a PDCP SN that the PDCP entity of the UE expects to receive sequentially is problematic. The PDCP entity of the UE may deliver the rearranged PDCP SDUs to the upper layer in ascending order after PDCP SDU rearrangement according to the PDCP SN value of the PDCP PDU received after waiting a certain time, or correspond to the PDCP SN expected to be sequentially received. The PDCP PDU (or SDU) may be considered to have already been removed, and the remaining PDCP SDUs may be delivered to the upper layer in ascending order. For this purpose, a method of driving a timer in a specific situation may be used, but in this case, the operation of the existing PDCP layer must be accompanied by a condition for driving a specific timer, a stopping condition, or a timer value. The problem arises that the complexity of. Therefore, another example of the present invention proposes a PDCP SDU rearrangement method based on a fixed timer to solve the above problem.

The PDCP SDU rearrangement method based on the fixed rearrangement timer proposed in another example of the present invention is as follows. The present invention can be applied to both the downlink data transfer procedure and the uplink data transfer procedure, and will be described below with reference to the downlink data transfer procedure.

23 illustrates a PDCP SDU rearrangement method based on a rearrangement timer according to another embodiment of the present invention. 20 shows that PDCP PDUs of

PDCP SNs

1, 2, 3, 4, 5, 11, 12, 13, 17, 18, 19, 20, 21, 22, 26, 27, 33 represent a macro base station (the RLC entity of). PDCP PDUs of

PDCP SN

6, 7, 8, 9, 10, 14, 15, 16, 23, 24, 25 are transmitted through a small base station (the RLC entity).

FIG. 23A assumes a case where a PDCP entity of a terminal receives PDCP PDUs of

PDCP SNs

1, 2, 3, 4, 5, 11, 12, 6, 13, 7, and 17. FIG.

Referring to FIG. 23A, when the PDCP entity of the terminal receives the PDCP PDU of PDCP SN 1, the rearrangement timer does not operate previously, and thus, the rearrangement timer is driven. At this time, the value of the rearrangement timer may be a predetermined value. The value of the rearrangement timer may be transmitted from the macro base station to the terminal. The macro base station may transmit the rearrangement timer value to the terminal through dedicated signaling or broadcasting. When the rearrangement timer is running, the PDCP entity of the terminal does not stop according to a specific situation. That is, once the rearrangement timer is driven, it is maintained for a set time.

While the rearrangement timer is running (or maintained), PDCP SDUs corresponding to PDCP PDUs of the PDCP SN received out of order are stored in a buffer. While the rearrangement timer is running, PDCP SDUs corresponding to PDCP PDUs of the PDCP SN corresponding to sequential reception are delivered to a higher layer.

The non-sequential reception may mean a case where a PDCP PDU of another PDCP SN is received without receiving a PDCP PDU of a PDCP SN that is expected to be sequentially received. In this case, the sequential reception may be determined based on, for example, the following criteria. If the PDCP SN of the last PDCP SDU delivered 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, Next_PDCP_RX_SN is represented by Equation 1 and Equation 2 below. You can follow one.

Equation 1

Equation 2

In Equation 2, Maximum_PDCP_SN represents the maximum value of the allowed PDCP SN. That is, Equation 2 indicates that the number starts again from 0 after the maximum value of the PDCP SN.

Referring again to FIG. 23A, the rearrangement timer expires after receiving PDCP PDUs of PDCP SN # 5 from the PDCP entity of the UE, and when the PDCP entity of the UE receives PDCP PDUs of PDCP SN # 11 which is the next PDCP PDU The timer is running.

FIG. 23B assumes a case where the PDCP entity of the UE receives

PDCP SN

8, 18, 9, 19, and 10 PDCP PDUs after FIG. 23A.

Referring to FIG. 23B, when the PDCP entity of the terminal receives the PDCP PDU of PDCP SN 11, the rearrangement timer is started. Then, PDCP PDUs of

PDCP SN

12, 13, 17, and 18 that are sequentially received by the PDCP entity of the terminal are operated. PDCP SDUs corresponding to the PDCP SDUs are stored in a buffer, and PDCP SDUs corresponding to the PDCP PDUs of

PDCP SN

6, 7, 8, which are sequentially received are transferred to a higher layer. The rearrangement timer expires after receiving PDCP PDUs of PDCP SN 18, and PDCP SDUs corresponding to PDCP PDUs of

PDCP SNs

11, 12, 13, 17, and 18 are delivered to a higher layer even if the rearrangement timer expires. It is stored in a buffer. After the rearrangement timer expires, if a PDCP PDU of PDCP SN 9 is received, the rearrangement timer is newly started.

Thereafter, when the PDCP entity of the PDCP SN 19 PDCP PDUs are received out of order, the PDCP entity stores the corresponding PDCP SDU in the buffer. When the PDCP entity of the terminal receives PDCP PDUs of PDCP SN 10, this is regarded as sequential reception, starting with the PDCP SN values of the sequentially received PDCP PDUs, and all stored PDCP SDUs of consecutively related PDCP SN values are transferred to a higher layer. To pass. That is, the PDCP entity of the terminal delivers PDCP SDUs of

PDCP SN

10, 11, 12, and 13 to a higher layer.

FIG. 23C illustrates a case where PDCP SDUs associated with

PDCP SN

7, 10 to be transmitted through the small base station are removed. FIG. 23C illustrates that a PDCP entity of a terminal receives PDCP PDUs of

PDCP SNs

1, 2, 3, 4, 5, 11, 12, 6, and 13, and does not receive PDCP PDUs of PDCP SN 7 and does not receive

PDCP SNs

17, 8, and 18. It is assumed that PDCP PDUs of Nos. 9 and 19 are received, and PDCP PDUs of

PDCP

20 and 14 are received without receiving PDCP PDUs of

PDCP SN

10 and 19. In addition, it is assumed that when the PDCP entity of the terminal receives PDCP PDUs of

PDCP SNs

1, 11, and 9, the rearrangement timer is driven.

Referring to FIG. 23C, even if the PDCP entity of the UE receives the PDCP PDUs of PDCP SN 8, the PDCP PDUs of PDCP SN 7 that are expected to be sequentially received have not yet been received. Can't deliver. In the situation where the rearrangement timer is running, it is not yet possible to determine whether the PDCP PDU of PDCP SN 7 can be received. When the rearrangement timer expires, the PDCP entity of the terminal determines that the PDCP PDU 7 has been removed. Thereafter, when the terminal receives the PDCP PDU of PDCP SN 9, the terminal drives the rearrangement timer again. Subsequently, even if the PDCP entity of the terminal receives PDCP PDUs of

PDCP SNs

19, 20, and 14, PDCP PDUs of PDCP SN 10, which are expected to be sequentially received, have not yet been received, so that

PDCP SNs

11, 12, 13, 14, 17, Store the PDCP SDUs associated with 18, 19 and 20 in the buffer.

FIG. 23D illustrates a case in which a PDCP entity of the UE receives PDCP PDUs of

PDCP SNs

14, 21, and 15 after FIG. 23C.

Referring to FIG. 23D, the PDCP entity of the terminal receives PDCP PDUs of

PDCP SN

14, 21, and 15 while the rearrangement timer is driven. Since the rearrangement timer has not expired and PDCP PDUs of PDCP SN # 10 that are expected to be sequentially received have not yet been received, the PDCP entity of the UE additionally stores PDCP SDUs associated with

PDCP SNs

21 and 15 in a buffer.

FIG. 23E assumes that the PDCP entity of the terminal receives PDCP PDUs of

PDCP SN

22 and 16 after FIG. 23D and then the rearrangement timer expires.

Referring to FIG. 23E, after the PDCP PDU of PDCP SN # 16 receives the PDCP PDU, the PDCP entity determines that the PDCP PDUs (and SDUs) of PDCP SN # 10 have been removed. At this time, except for the PDCP SDU associated with the removed PDCP SN 10, the portion of the stored PDCP SDUs, which can be viewed as sequential reception, is transferred to the upper layer in ascending order. That is, PDCP SDUs associated with PDCP SNs 11 to 22 are delivered to the upper layer in ascending order.

By using the rearrangement timer described above, it may be determined whether the PDCP PDU not received is removed. However, in the case of the rearrangement timer, the timer is driven when a certain PDCP PDU is received when the timer is not being driven, instead of driving the timer in a specific situation such as sequential reception or non-sequential reception of the PDCP PDU. Therefore, when the rearrangement timer is used, rearrangement between PDCP PDUs received by the UE may be performed during a predetermined time interval, but it may not be determined whether the PDCP PDUs not received are removed even after the timer expires.

24 shows another example of a PDCP SDU rearrangement method based on a rearrangement timer according to another embodiment of the present invention. 24 shows that PDCP PDUs of

PDCP SNs

PDCP SN

6, 8, 9, 14, 15, 16, 23, 24, and 25 are transmitted through a small base station (an RLC entity). In FIG. 21, PDCP PDUs (or SDUs) of

PDCP SN

7, 10 to be transmitted through the small base station are removed.

FIG. 24a illustrates a PDCP entity of a terminal receiving PDCP PDUs of

PDCP SNs

1, 2, 3, 4, 5, 11, 12, 6, and 13, and without receiving PDCP PDUs of PDCP SN 7,

PDCP SNs

17, 8, and 18; After receiving PDCP PDUs, it is assumed that the rearrangement timer driven upon reception of PDCP PDUs of PDCP SN 11 expires.

Referring to FIG. 24A, the PDCP entity of the terminal may not determine that the PDCP PDU of PDCP SN 7 is removed even when the PDCP PDU of PDCP SN 8 is received and the rearrangement timer expires thereafter. When the rearrangement timer is driven, the timer is started for a predetermined time from the reception of any PDCP PDU when the rearrangement timer is not running, not considering the reception status of a specific PDCP PDU, and after the timer expires. This is because the timer is driven again when an arbitrary PDCP PDU is received.

For example, when the PDCP SNs are listed in the order of receiving PDCP PDUs from the PDCP entity of the UE, 1, 2, 3, 4, 5, 11, 12, 6, 13, 17, 8, and 18 are the same. Here, when the rearrangement timer expires, all

PDCP SN

7, 9, 10, 14, 15, and 16 PDCP PDUs that have not been received cannot be determined to be removed. Accordingly, the following operation may be further performed to determine whether to remove PDCP PDUs (or SDUs) based on the proposed rearrangement timer.

Hereinafter, the section in which each rearrangement timer is driven is divided into section A / section B / section C / section D. In FIG. 24A, PDCP PDUs received by the PDCP entity of the UE in interval B are PDCP PDUs of

PDCP SN

12, 6, 13, 17, 8, and 18. At this time, PDCP PDUs of

PDCP SN

7, 9, 10, 14, 15 and 16 have not been received in interval B yet. These unreceived PDCP PDUs may then be received in interval C. However, the PDCP PDU expected to be received after the reception of the last received PDCP PDU in the interval B should be received within a time duration of at least one rearrangement timer. That is, if PDCP PDUs not received in interval B are not received in interval C, the corresponding PDCP PDUs may be determined to be removed. That is, the next rearrangement timer expires among PDCP SDUs not yet received that are associated with a PDCP SN value that is smaller than the largest PDCP SN value among PDCP PDUs of PDCP PDUs received until the reordering timer of interval B expires. PDCP SDUs not received by the time point are determined to have been removed.

24B is a rearrangement timer is driven when the PDCP entity of the terminal receives the PDCP PDU of PDCP SN 9 (ie, start of section C) after FIG. 24A, and then

PDCP SN

19, 20, 14, 21, 15, 22, and 16 When one PDCP PDU has been received and the rearrangement timer has expired.

Referring to FIG. 24B, the PDCP SDU associated with PDCP SN 7 may not be determined to be removed even if the interval B for receiving the PDCP PDU of PDCP SN 8, etc., expires. However, if the PDCP PDUs of PDCP SN 7 are not received until the interval C expires, the PDCP SDUs associated with PDCP SN 7 are determined to be removed. And, the PDCP entity of the terminal delivers the PDCP SDUs associated with

PDCP SN

8, 9 to the upper layer in ascending order.

FIG. 24C illustrates a rearrangement timer when the PDCP entity of the UE receives PDCP PDUs of PDCP SN 26 (that is, start of segment D) after FIG. 24B, and then receives PDCP PDUs of

PDCP SNs

23, 27, 24, and 33. Assume the case.

Referring to FIG. 24C, when the rearrangement timer is running, the PDCP entity of the terminal may not determine whether the PDCP SDU associated with PDCP SN 10 that is not received in the interval C is removed. Therefore, even if PDCP PDUs after PDCP SN 10 are received, the PDCP entity of the UE does not deliver the corresponding PDCP SDUs to the upper layer in ascending order and stores them in the buffer.

24D, it is assumed that after FIG. 24C, the PCDP entity of the terminal receives the PDCP PDU of PDCP SN 25 and the rearrangement timer expires.

Referring to FIG. 24D, when the rearrangement timer expires (that is, when the interval D expires), the PDCP entity of the terminal determines that the PDCP SDU associated with PDCP SN 10 that has not yet been received is removed. Therefore, except for PDCP SN 10, successively stored PDCP SDUs are delivered to the upper layer in ascending order.

Referring to FIG. 25, a PDCP entity of a terminal receives PDCP PDUs through a macro base station and a small base station configured with multi-flow with the terminal (S2500).

When the rearrangement timer is not running, the PDCP entity of the terminal drives the l (L) order rearrangement timer when an arbitrary PDCP PDU is received (S2510).

The PDCP entity of the terminal checks the maximum PDCP SN value k of the received PDCP PDUs until the first order rearrangement timer expires (S2520).

When the PDCP entity of the terminal receives the PDCP PDU for the first time after the first rearrangement timer expires, the PDCP entity drives the l + 1st rearrangement timer (S2530).

The PDCP entity of the terminal determines that the PDCP SDUs that are not yet received associated with the PDCP SN value less than the PDCP SN k have been removed until the l + 1st rearrangement timer expires (S2540), and PDCP Starting from SN k, all stored PDCP SDUs of PDCP SN values consecutively associated are transferred to the upper layer in ascending order (S2550).

Referring to FIG. 26, the terminal 2600 according to the present invention may configure a dual connectivity with the macro base station 2630 and the small base station 2660. In addition, the terminal 2600, the macro base station 2630, and the small base station 2660 according to the present invention support the above-described multiflow.

The macro base station 2630 includes a macro transmitter 2635, a macro receiver 2640, and a macro processor 2650.

The macro receiver 2640 receives a packet for one EPS bearer from the S-GW. The macro processor 2650 controls the PDCP entity of the macro base station 2630 to process PDCP SDUs corresponding to the received packet and generate PDCP PDUs. The macro processor 2650 distributes the PDCP PDUs according to a reference, transfers (or transmits) a part of the PDCP PDUs to the RLC entity of the macro base station 2640, and transmits the PDCP PDUs to the terminal through the macro transmitter 2635. The macro processor 2650 transmits (or delivers) the remaining part to the RLC entity of the small base station 2660 through the macro transmitter 2635. In this case, PDCP SDUs corresponding to PDCP PDUs may be identified and indicated as PDCP SN.

In addition, the macro processor 2650 generates information on the PDCP layer timer and transmits the information to the terminal through the macro transmitter 2635. The information about the timer may be signaled exclusively to the terminal 2600 or may be signaled in a broadcast manner. The macro transmitter 2635 may transmit the information about the timer to the terminal 2600 through an RRC message (eg, an RRC connection reconfiguration message).

The small base station 2660 includes a small transmitter 2665, a small receiver 2670, and a small processor 2680.

The small receiver 2670 receives the remaining PDCP PDUs from the macro base station 2630.

The small processor 2680 processes the PDCP PDU by controlling the RLC entity, MAC entity, and PHY layer of the small base station 2660 and transmits the PDCP PDU to the terminal through the small transmitter 2665.

The terminal 2600 includes a terminal receiver 2605, a terminal transmitter 2610, and a terminal processor 2620. The terminal processor 2620 performs functions and controls necessary for implementing the above-described features of the present invention.

The terminal receiver 2605 receives information on a PDCP layer timer from the macro base station 2630. The rearrangement timer information may be included in an RRC message (eg, an RRC connection reconfiguration message) and received by the terminal receiver 2605. In this case, the terminal transmitter 2610 may transmit an RRC connection reconfiguration complete message to the macro base station 2630.

In addition, the terminal receiving unit 2605 receives data for PDCP PDUs from the macro base station 2630 and the small base station 2660, respectively.

The terminal processor 2620 interprets the data and controls the PHY layer (s), the MAC entity (s), the RLC entity (s), and the PDCP entity of the terminal 2600 to obtain PDCP SDUs.

The terminal processor 2620 controls the PDCP entity, performs rearrangement of PDCP SDUs, and transfers the rearranged PDCP SDUs to an upper layer of the PDCP layer in ascending order. Here, the terminal processor 2620 may check whether the corresponding PDCP PDU is sequentially received by the PDCP entity based on the PDCP SN of the received PDCP PDU. For example, the PDCP SN value of the PDCP SDU (or PDU) which is expected to be sequentially received based on

Equation

1 or 2 may be determined.

For example, when the PDCP PDU of PDCP SN n is received through one of the macro base station 2630 and the small base station 2660, the terminal processor 2620 may receive the maximum number of PDCP PDUs received through the other base station. Check if PDCP SN value k is greater than n. If k> n, the terminal processor 2620 determines that not yet received PDCP SDUs associated with a PDCP SN value smaller than PDCP SN n are removed. The terminal processor 2620 transfers all stored PDCP SDUs associated with a PDCP SN value smaller than PDCP SN n to a higher layer of the PDCP layer, and sequentially stores all stored PDCP SDUs of the associated PDCP SN values starting from PDCP SN n. Transfer to the upper layer.

As another example, the terminal processor 2620 drives the rearrangement timer when a PDCP PDU of PDCP SN n is received through one of the macro base station 2630 and the small base station 2660. The terminal processor 2620 confirms whether at least one PDCP PDU is received through the other base station during the rearrangement timer driving period. If at least one PDCP PDU is received through the other base station during the rearrangement timer driving period, the terminal processor 2620 receives at least one received through the other base station during the rearrangement timer driving period. It is checked whether the maximum PDCP SN value k in the PDCP PDU is greater than n. If k is greater than n, then the rearrangement timer is stopped and the PDCP SDUs not yet received associated with a PDCP SN value less than PDCP SN n are determined to have been removed. The terminal processor 2620 transfers all stored PDCP SDUs associated with a PDCP SN value smaller than PDCP SN n to a higher layer of the PDCP layer, and sequentially stores all stored PDCP SDUs of the associated PDCP SN values starting from PDCP SN n. Transfer to the upper layer. If k is not greater than n, the terminal processor 2620 drives the rearrangement timer again after the rearrangement timer expires. And, if the PDCP entity configured in the terminal 2600 is not receiving PDCP PDUs at all through the other base station during the rearrangement timer driving period, the terminal processor 2620 after all the PDCP stored after the rearrangement timer expires. Deliver SDUs to the upper layer.

As another example, the terminal processor 2620 may perform PDCP removal determination based on both a PDCP SN comparison and a rearrangement timer based method for each base station. In detail, the terminal processor 2620 sequentially receives PDCP PDUs up to SN a through the macro base station and the small base station, and when PDCP PDUs of PDCP SN n are received through any one of the macro base station and the small base station, If the PDCP PDU reception of the PDCP SN n times the PDCP PDU reception of the non-sequential SN, and if the PDCP PDU of the non-sequential SN is received, the PDCP entity of the terminal drives the rearrangement timer. The terminal processor 2620 receives PDCP PDUs through another base station, checks whether n is greater than the PDCP SN value k of the PDCP PDU received through the other base station, and when n> k, the terminal processor 2620 PDCP PDUs of PDCP SN (a + 1) to (k-1) are determined to be PDCP removed, and if n <k, the terminal processor 2620 determines that PDCP SNs (a + 1) to (n-1) PDCP PDUs are determined to be PDCP removed. Subsequently, when the UE processor 2620 excludes the SN determined to remove the PDCP, the terminal processor 2620 transfers the PDCP SDUs associated with the received PDCP PDUs to the upper layer in ascending order. Meanwhile, when the rearrangement timer expires, the terminal processor 2620 transfers PDCP SDUs stored in a buffer to an upper layer in ascending order.

As another example, the terminal processor 2620 operates a fixed rearrangement timer. When the rearrangement timer is not running, the terminal processor 2620 drives the rearrangement timer l (L) when an arbitrary PDCP PDU is received. Check the maximum PDCP SN value k of PDCP PDUs received until the reordering timer expires. The terminal processor 2620 drives the first order rearrangement timer when the PDCP PDU is received for the first time after the first order rearrangement timer expires, and is greater than the PDCP SN k until the time of the l + 1st rearrangement timer expires. The PDCP SDUs that are not yet received associated with the low PDCP SN value are determined to have been removed. In addition, the terminal processor 2620 transfers all stored PDCP SDUs of PDCP SN values continuously associated with the PDCP SN k to the upper layer of the PDCP layer in ascending order.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Claims

PDCP considering multi-flow in the Packet Data Convergence Protocol (PDCP) entity of a UE configured for dual connectivity with a macro eNB and a small eNB By reordering service data units (SDUs),

Receiving PDCP PDUs through the macro base station and the small base station; And

And if a PDCP PDU of PDCP SN n has been received through any one of the macro base station and the small base station, driving a rearrangement timer.
The method of claim 1,

During the rearrangement timer driving period, confirming whether at least one PDCP PDU is received through the other base station.
The method of claim 2,

During the rearrangement timer driving period, if at least one PDCP PDU is received through another base station, checking whether a maximum PDCP SN value k of at least one PDCP PDU received through the other base station is greater than n; PDCP SDU rearrangement method, characterized in that.
The method of claim 3, wherein

And if k is greater than n, determining that not yet received PDCP PDUs associated with a PDCP SN value less than PDCP SN n are removed.
The method of claim 4, wherein

If k is greater than n, transferring all stored PDCP SDUs associated with a PDCP SN value less than PDCP SN n to an upper layer in ascending order.
The method of claim 3, wherein

And if k is not greater than n, driving the rearrangement timer again after expiration of the rearrangement timer.
The method of claim 2,

During the rearrangement timer driving period, when at least one PDCP PDU is received through another base station, after the rearrangement timer expires, transferring all stored PDCP SDUs to an upper layer in ascending order. How to rearrange PDCP SDUs.
In a wireless communication system supporting dual connectivity with a macro eNB and a small eNB, reordering PDCP Service Data Units (SDUs) in consideration of multi-flow UE to perform,

A receiver configured to receive PDCP PDUs through the macro base station and the small base station; And

And a processor for driving a rearrangement timer when a PDCP PDU of PDCP SN n is received through any one of the macro base station and the small base station.
The method of claim 8,

The processor, during the rearrangement timer driving period, characterized in that the receiver receives at least one PDCP PDU via the other base station, the terminal.
The method of claim 9,

When the receiver receives at least one PDCP PDU through another base station during the rearrangement timer driving period, the processor has a maximum PDCP SN value k of at least one PDCP PDU received through the other base station than n. The terminal, characterized in that a large check.
The method of claim 10,

And wherein if k is greater than n, the processor determines that not yet received PDCP PDUs associated with PDCP SN value less than PDCP SN n are removed.
The method of claim 11,

And the processor transfers all stored PDCP SDUs associated with a PDCP SN value less than the PDCP SN n to an upper layer when k is greater than n, in ascending order.
The method of claim 10,

The processor, if the k is not greater than the n, characterized in that for driving the rearrangement timer again after the rearrangement timer expires.
The method of claim 9,

During the rearrangement timer driving period, when the receiver receives at least one PDCP PDU through another base station, after the rearrangement timer expires, the processor transfers all stored PDCP SDUs to an upper layer in ascending order. Terminal.