KR101563008B1 - Method of releasing radio bearer in wireless communication system and receiver - Google Patents

Abstract

A method and apparatus for releasing a radio bearer are provided. Release of an RLC (Radio Link Control) entity and a PDCP (Packet Data Convergence Protocol) entity is determined. The RLC entity is released after transferring an RLC SDU (service data unit) extracted in response to a release request of the RNC entity to the PDCP entity. The PDCP entity stores the first PDCP SDU obtained by processing the RLC SDU in the reception buffer. The PDCP entity is released after transferring the first PDCP SDU in the reception buffer to an upper layer.

Description

TECHNICAL FIELD [0001] The present invention relates to a method and a device for releasing a radio bearer in a wireless communication system,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication, and more particularly, to a method and apparatus for releasing a radio bearer in a wireless communication system.

BACKGROUND OF THE INVENTION Wireless communication systems are becoming widespread to provide voice or packet services. Multiple access systems support communication to multiple users by sharing available system resources. Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, and an orthogonal frequency division multiple access (OFDMA) system.

The 3rd Generation Partnership Project (3GPP) long term evolution (LTE), an enhancement of Universal Mobile Telecommunications System (UMTS), is introduced as 3GPP release 8. 3GPP LTE uses OFDMA in the downlink and SC-FDMA (Single Carrier-FDMA) in the uplink. MIMO (multiple input multiple output) with up to four antennas is adopted. Recently, 3GPP LTE-A (LTE-Advanced), an evolution of 3GPP LTE, is under discussion.

A radio bearer is a logical path for data transmission between a user and a network and can be created, re-established and released at any time by a user or network request. In general, when the radio bearer is released, all data stored in the buffers of each layer is discarded without any processing.

However, when the radio bearer is released, discarding all data immediately may lead to inefficient use of resources. This is because the data successfully transmitted by releasing the radio bearer may be discarded and the data may be transmitted again and again.

SUMMARY OF THE INVENTION The present invention is directed to a radio bearer release method and a receiver for preventing loss of data stored in a buffer.

In an aspect, a method of releasing a radio bearer in a wireless communication system is provided. The method includes determining a release of a Radio Link Control (RLC) entity and a Packet Data Convergence Protocol (PDCP) entity, delivering an RLC SDU (service data unit) extracted according to a release request of the RLC entity to the PDCP entity, Releases the RLC entity, stores the first PDCP SDU obtained by processing the RLC SDU in the PDCP entity in the reception buffer, and transfers the first PDCP SDU in the reception buffer to the upper layer and releases the PDCP entity .

And forward the second PDCP SDU previously stored in the reception buffer to the upper layer. A plurality of PDCP SDUs in the reception buffer may be transmitted to the upper layer in ascending order of SN (sequence number) of each PDCP SDU. The plurality of PDCP SDUs in the receive buffer may be all PDCP SDUs in the receive buffer.

The PDCP entity may perform decoding and header recovery on the RLC SDU to obtain the first PDCP SDU. The RLC SDU may be obtained by recombining at least one RLC PDU (protocol data unit) received from a transmitter.

The number of RLC SDUs transmitted to the PDCP entity is a plurality, and the plurality of RLC SDUs can be transmitted to the PDCP entity in ascending order of the SN of each RLC SDU.

In another aspect, the receiver includes a radio frequency (RF) unit and a processor coupled to the RF unit to release the radio bearer. Wherein the processor determines release of an RLC entity and a Packet Data Convergence Protocol entity and delivers an RLC SDU (service data unit) extracted in response to the release request of the RLC entity to the PDCP entity, Releases the RLC entity, stores the first PDCP SDU obtained by processing the RLC SDU in the PDCP entity in the reception buffer, and transfers the first PDCP SDU in the reception buffer to the upper layer and releases the PDCP entity .

It is possible to prevent redundant data transmission and efficiently use radio resources. It is possible to prevent loss of discontinuous received data blocks.

1 is a block diagram illustrating a wireless communication system. This may be a network structure of 3rd Generation Partnership Project (3GPP) long term evolution (LTE) / LTE-A (Advanced). The Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN) includes a base station (BS) 20 that provides a control plane and a user plane to a user equipment (UE) do. The terminal 10 may be fixed or mobile and may be referred to by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a mobile terminal (MT) . The base station 20 is a fixed station that communicates with the terminal 10 and may be referred to as another term such as an evolved NodeB (eNB), a base transceiver system (BTS), an access point, or the like. One base station 20 may have more than one cell. An interface for transmitting user traffic or control traffic may be used between the base stations 20. The base stations 20 may be interconnected via an X2 interface. The base station 20 is connected to an S-GW (Serving Gateway) 30 through an EPC (Evolved Packet Core), more specifically, a S1-MME through an S1 interface and an MME (Mobility Management Entity) The S1 interface supports many-to-many-relations between the base station 20 and the MME / SAE gateway 30.

Hereinafter, downlink refers to communication from the base station 20 to the terminal 10, and uplink refers to communication from the terminal 10 to the base station 20. In the downlink, the transmitter may be part of the base station 20 and the receiver may be part of the terminal 10. In the uplink, the transmitter may be part of the terminal 10 and the receiver may be part of the base station 20.

2 is a block diagram illustrating a functional split between the E-UTRAN and the EPC. The hatched box represents the radio protocol layer and the white box represents the functional entity of the control plane. The base station performs the following functions. (1) Radio Resource Control such as Radio Bearer Control, Radio Admission Control, Connection Mobility Control, and Dynamic Resource Allocation to the UE (RRM) function, (2) Internet Protocol (IP) header compression and encryption of user data streams, (3) routing of user plane data to the S-GW, (4) Scheduling and transmission of broadcast information, (6) measurement and measurement reporting setup for mobility and scheduling. The MME performs the following functions. (1) NAS (Non-Access Stratum) signaling, (2) NAS signaling security, (3) Idle mode UE reachability, (4) Tracking Area list management, , (5) Roaming, and (6) Authentication. The S-GW performs the following functions. (1) mobility anchoring, (2) lawful interception. The P-GW (PDN-Gateway) performs the following functions. (1) terminal IP (internet protocol) allocation, and (2) packet filtering.

3 is a block diagram illustrating a radio protocol architecture for a user plane. 4 is a block diagram illustrating a wireless protocol structure for a control plane. The data plane is a protocol stack for transmitting user data, and the control plane is a protocol stack for transmitting control signals.

Referring to FIGS. 3 and 4, a physical layer (PHY) provides an information transfer service to an upper layer using a physical channel. The physical layer is connected to a MAC (Medium Access Control) layer, which is an upper layer, through a transport channel. Data is transferred between the MAC layer and the physical layer through the transport channel. The transport channel is classified according to how the data is transmitted through the air interface. Data is transferred between the different physical layers, that is, between the transmitter and the physical layer of the receiver through a physical channel.

There are several physical control channels used in the physical layer. The physical downlink control channel (PDCCH) informs the UE of resource allocation of a paging channel (PCH), a 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 the resource allocation of the uplink transmission. A physical control format indicator channel (PCFICH) informs the UE of the number of OFDM symbols used for PDCCHs and is transmitted every subframe. PHICH (Physical Hybrid ARQ Indicator Channel) carries HARQ ACK / NAK signal in response to uplink transmission. A physical uplink control channel (PUCCH) carries uplink control information such as HARQ ACK / NAK, scheduling request and CQI for downlink transmission. A physical uplink shared channel (PUSCH) carries an uplink shared channel (UL-SCH).

The function of the MAC layer includes a mapping between a logical channel and a transport channel and a multiplexing / demultiplexing into a transport block provided as a physical channel on a transport channel of a MAC SDU (service data unit) belonging to a logical 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 transferring control area information and a traffic channel for transferring user area information.

The function of the RLC layer includes concatenation, segmentation and reassembly of the RLC SDUs. The RLC layer includes a Transparent Mode (TM), an Unacknowledged Mode (UM), and an Acknowledged Mode (RB) in order to guarantee various QoSs required by a radio bearer (RB) , And AM). AM RLC provides error correction via automatic repeat request (ARQ).

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

The Radio Resource Control (RRC) layer is defined only in the control plane. The RRC layer is responsible for the control of logical channels, transport channels and physical channels in connection with the configuration, re-configuration and release of radio bearers. RB means a logical path provided by a first layer (PHY layer) and a second layer (MAC layer, RLC layer, PDCP layer) for data transmission between a UE and a network. The setting of the RB means a process of defining characteristics of a radio protocol layer and a channel to provide a specific service, and setting each specific parameter and an operation method. RB can be divided into SRB (Signaling RB) and DRB (Data RB). The SRB is used as a path for transmitting the RRC message in the control plane, and the DRB is used as a path for transmitting the user data in the user plane.

The non-access stratum (NAS) layer located at the top of the RRC layer performs functions such as session management and mobility management.

5 is a flowchart showing HARQ and ARQ. The RLC entity 110 of the transmitter 100 transmits an RLC PDU (Protocol Data Unit) having a sequence number (SN) 0 to the MAC entity 120 (S110). The MAC entity 120 of the transmitter 100 sends the MAC PDU1 (s) corresponding to the RLC PDUs with SN = 0 to the MAC entity 220 of the receiver 200 (S112). The MAC entity 220 that successfully received the MAC PDU is sent to the RLC entity 210 (S114).

The RLC entity 120 of the transmitter 100 sends an RLC PDU with SN = 1 to the MAC entity 120 (S120). The MAC entity 120 of the transmitter 100 sends the MAC PDU2 (s) corresponding to the RLC PDU with SN = 1 to the MAC entity 220 of the receiver 200 (S122). It is said that the HARQ is in progress for the MAC PDU2 due to deterioration of the radio channel.

The RLC entity 110 of the transmitter 100 sends the RLC PDU with SN = 2 to the MAC entity 120 (S130). The MAC entity 120 of the transmitter 100 sends the MAC PDU 3 (s) corresponding to the RLC PDU with SN = 2 to the MAC entity 220 of the receiver 200 (S132). The MAC entity 220 that successfully received the MAC PDU 3 is sent to the RLC entity 210 (S134).

Then, the HARQ of the MAC PDU2 (s) corresponding to the RLC PDU with SN = 1 is completed (S135), and the RLC entity 210 obtains the RLC PDU with SN = 1 (S136). RLC PDUs having non-continuous SNs may be received by the RLC entity 210 according to the HARQ process. This is called HARQ reordering.

The RLC entity 110 of the transmitter 100 sends an RLC PDU with SN = 3 to the MAC entity 120 (S140). At this time, a polling bit is set in the header of the RLC PDU, and a status report is requested. The MAC entity 120 of the transmitter 100 sends the MAC PDU 4 (s) corresponding to the RLC PDUs with SN = 3 to the MAC entity 220 of the receiver 200 (S142). The MAC entity 220 that successfully received the MAC PDU 4 is sent to the RLC entity 210 (S 144). The RLC entity 210 requesting the status report constructs a status PDU and sends the status PDU to the RLC entity 110 of the transmitter 100 (S150).

A PDU is a data block that a layer sends to a lower layer, and an SDU is a block of data that a layer receives from an upper layer. For example, the RLC PDU is a data block sent by the RLC to the MAC, and the RLC SDU is a data block received by the RLC from the PDCP. Conversion from PDU to SDU or from SDU to PDU may differ depending on the function of the layer.

An RLC entity supporting ARQ is referred to as an Acknowledged Mode (AM) RLC entity, and an RLC entity not supporting ARQ is referred to as an unacknowledged mode (UM) RLC entity.

The UM RLC entity of the transmitter includes a SN (Sequence Number) in the header of each PDU so that the UM RLC entity of the receiver can know which PDU is lost during transmission. The UM RLC is responsible for the transmission of broadcast / multicast data in the user plane and the transmission of real-time packet data such as voice in the packet service domain (eg Voice over Internet Protocol (VoIP) or streaming) In the control plane, a RRC message to be transmitted to a specific terminal or a specific terminal group in the cell is responsible for transmission of an RRC message which does not require acknowledgment.

The UM RLC entity of the receiver checks the SN of the PDU first after receiving the PDU. If the received PDU is an in-sequence PDU for a previously received PDU, the SDU obtained by processing the PDU is transferred to an upper layer (e.g., PDCP). However, if the received PDU is not a sequential PDU, the PDU is stored in the buffer and waits until a sequential PDU is received.

There are two main reasons why an RLC entity receives PDUs in an unordered manner. One is that PDUs are lost during transmission, and the other is due to HARQ rearrangement in the lower layer. If the first reason, non-sequential reception due to PDU loss occurs, it is recommended that the UM RLC entity of the receiver transmit the PDUs received to the higher layer as soon as possible. The second reason is that if non-sequential reception due to HARQ rearrangement occurs, sequential PDUs will be received after a certain period of time, so it is preferable that the UM RLC entity of the receiver waits for a certain period of time to sequentially receive and process the PDUs.

In order to solve the problem of non-sequential reception of the opposite PDU, the UM RLC entity of the receiver defines a timer. If a PDU is out of sequence, it stores the PDU in the buffer and starts the timer at the same time. If a sequential PDU is not received until the timer expires, it is determined that it is a non-sequential reception due to PDU loss. If a PDU is received in an unordered manner, the PDU will wait in the buffer until the timer expires or a previous sequential PDU is received.

Like the UM RLC entity, the AM RLC entity includes an SN in the PDU header. However, unlike the UM RLC entity, the AM RLC entity sends an acknowledgment to the transmitter in response to the received PDU. The response is used to request retransmission to the transmitter for PDUs that the receiver did not receive. AM RLC is intended to guarantee error-free data transmission through retransmission. AM RLC is mainly responsible for the transmission of non real-time packet data such as TCP / IP (Transmission Control Protocol / Internet Protocol) of the packet service area in the user plane. In the control plane, the RRC message And is responsible for the transmission of the required RRC message.

As with the UM RLC entity, the AM RLC entity first checks the SN of the PDU when it receives the PDU. If the received PDU is an in-sequence PDU for a previously received PDU, the SDU obtained by processing the PDU is transferred to an upper layer. However, if the received PDU is not a sequential PDU, the PDU is stored in the buffer and waits until a sequential PDU is received.

The reason why AM RLC receives PDUs out of order is the same as UM RLC. However, since the AM RLC supports retransmission, when the timer expires, the PDUs that are not sequentially received are not forwarded to the upper layer, but the status report is sent to the AM RLC of the transmitter to request the retransmission of the PDU that has not been received. Thus, the AM RLC entity of the receiver will continue to buffer until a previous PDU is received, if any PDUs are received on a non-contiguous basis.

The PDCP layer receives the PDCP PDU from the lower RLC layer, deciphers it, decompresses the header, and delivers the restored PDCP SDU to the upper layer. In general, the PDCP SDU does not wait in the buffer of the PDCP layer. This is because the lower layer, the UM RLC or the AM RLC, always delivers PDCP PDUs in ascending order of the SN, so the PDCP processes the received PDCP PDUs in order and delivers them to the upper layer.

A radio bearer (RB) is a path through which data is transmitted, and can be generated and released at any time by a request of a terminal or a network. However, as described above, the RLC buffer and / or the PDCP buffer may store PDUs or SDUs due to non-sequential reception such as HARQ rearrangement. When the radio bearer is released, data stored in the RLC buffer and / If you dispose of them immediately, resource utilization can be inefficient.

Therefore, in the following, a technique for minimizing the loss of data even when the radio bearer is released by allowing the data stored in the buffer to be processed when the radio bearer is released is proposed.

6 is a flowchart showing an example of radio bearer release. This method can be performed by the processor of the receiver.

In step S610, the receiver determines release of the radio bearer. The RRC sends the release of the radio bearer to the RLC and PDCP and requests release of the RLC and PDCP. The RLC may be UM RLC or AM RLC.

In step S620, the RLC of the receiver reassembles the RLC PDU stored in the RLC reception buffer to obtain the RLC SDU, and delivers the reassembled RLC SDU to the PDCP. The RLC of the receiver removes the header for RLC PDUs successfully received and stored in the RLC receive buffer (UMD PDU, AMD PDU, and / or AMD PDU segment), and recombines to obtain a complete RLC SDU. If an incomplete RLC SDU is obtained due to a missing PDU, discard the incomplete RLC SDU. The reassembled RLC SDU is delivered to the PDCP, and the RLC SDU to be delivered corresponds to the PDCP PDU. The reassembled RLC SDUs can be delivered to the PDCP in ascending order of the SN.

In step S630, after the RLC SDU is transmitted to the PDCP, the RLC is released.

In step S640, the PDCP of the receiver processes the PDCP PDU stored in the PDCP receiving buffer and / or the PDCP PDU delivered from the RLC to acquire the PDCP SDU, and delivers the PDCP SDU to the upper layer. The PDCP deciphers and header decompresses the PDCP PDUs stored in the PDCP reception buffer and the PDCP PDUs received from the RLCs to obtain the complete PDCP SDUs and stores them in the PDCP reception buffer. All complete PDCP SDUs in the PDCP receive buffer are forwarded to the upper layer of the PDCP. An upper layer of the PDCP refers to a layer that can receive and process a PDCP SDU such as an application layer. PDCP SDUs can be delivered to higher layers in ascending order of SN.

In step S650, the PDCP is released after transferring the PDCP SDU to the upper layer.

Release of the radio bearer may occur in an abnormal situation. For example, the channel condition between the UE and the network temporarily deteriorates, or the radio resources temporarily become insufficient. When the radio bearer is released, the previously received data is transferred to the upper layer, so that the existing data can be maintained and data loss can be prevented when the radio bearer is reset.

Although the RLC and PDCP release are described here, the technical idea of the present invention can be applied to release between at least two layers. For example, when the first layer is the RLC layer and the second layer is the PDCP layer, the data blocks are transferred according to the release of the two layers. The technical idea of the present invention can be applied as it is for releasing between layers constituting other radio interface protocols.

7 is a conceptual diagram showing release of a radio bearer. The RRC requests release to the RLC and PDCP for release of the radio bearer. The RLC stores an RLC PDU 702 with SN = 6, an RLC PDU 703 with SN = 7, and an RLC PDU 705 with SN = 9 in an RLC reception buffer. The RLC PDU 704 with SN = 8 is awaiting reception. In response to the RLC release request, the RLC extracts the first RLC SDU 711 from the RLC PDU 702 with SN = 6 and the RLC PDU 703 with SN = 7, and extracts the first RLC SDU 711 from the RLC PDU 705 with SN = And extracts the second RLC SDU 712. After transmitting the extracted first RLC SDU 711 and the second RLC SDU 712 to the PDCP, the RLC is released.

The first RLC SDU 711 and the second RLC SDU 712 delivered to the PDCP are the first PDCP PDU and the second PDCP PDU, respectively. The PDCP decrypts and decompresses the first PDCP PDU 711 and the second PDCP PDU 712 received from the RLC to obtain the first PDCP SDU 721 and the third PDCP SDU 723, And stores it in the receive buffer. In addition, the PDCP obtains the second PDCP SDU 722 from the PDCP PDU previously stored in the PDCP receiving buffer and stores it in the PDCP receiving buffer. After the first PDCP SDU 721, the second PDCP SU 722 and the third PDCP SDU 723 in the reception buffer are transferred to the upper layer of the PDCP, the PDCP is released.

8 is a block diagram illustrating a wireless communication system in which an embodiment of the present invention is implemented. Transmitter 50 and receiver 60 may be part of a terminal, base station or repeater. The transmitter 50 includes a processor 51, a memory 52 and an RF unit (radio frequency) unit 53. [ The processor 51 implements the proposed functions, procedures and / or methods. The layers of the air interface protocol may be implemented by the processor 51. The memory 52 is connected to the processor 51 and stores various information for driving the processor 51. [ The RF unit 53 is connected to the processor 51 to transmit and / or receive a radio signal. The receiver 60 includes a processor 61, a memory 62 and an RF unit 63. [ The processor 61 implements the proposed functions, procedures and / or methods. The layers of the air interface protocol may be implemented by the processor 61. The memory 62 is connected to the processor 61 and stores various information for driving the processor 61. [ The RF unit 63 is connected to the processor 61 to transmit and / or receive a radio signal.

Processors 51 and 61 may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, and / or data processing devices. The memory 52, 62 may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium, and / The RF units 53 and 63 may include a baseband circuit for processing a radio signal. When the embodiment is implemented in software, the above-described techniques may be implemented with modules (processes, functions, and so on) that perform the functions described above. The module is stored in the memory 52, 62 and can be executed by the processor 51, 61. The memories 52, 62 may be internal or external to the processors 51, 61 and may be connected to the processors 51, 61 by various well known means.

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

The above-described embodiments include examples of various aspects. While it is not possible to describe every possible combination for expressing various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the invention include all alternatives, modifications and variations that fall within the scope of the following claims.

1 is a block diagram illustrating a wireless communication system.

2 is a block diagram showing functional division between E-UTRAN and EPC.

3 is a block diagram illustrating a wireless protocol structure for a user plane.

4 is a block diagram illustrating a wireless protocol structure for a control plane.

5 is a flowchart showing HARQ and ARQ.

6 is a flowchart showing an example of radio bearer release.

7 is a conceptual diagram showing release of a radio bearer.

8 is a block diagram illustrating a wireless communication system in which an embodiment of the present invention is implemented.

Claims (10)

A method for releasing a radio bearer in a wireless communication system, Transmitting a radio bearer request for requesting release of an RLC (Radio Link Control) entity and a PDCP (Packet Data Convergence Protocol) entity from an RRC (Radio Resource Control) terminal to a RLC terminal and a PDCP terminal of the receiver; The step of transmitting the RLC SDU from the RLC end of the receiving end to the PDCP end of the receiving end in ascending order of a sequence number (SN) of each RLC SDU (Service Data Unit) Is obtained by reassembling RLC packet data units (PDUs) successfully received and stored in the RLC receive buffer before a radio bearer request is transmitted; Releasing the RLC entity after the RLC SDU is transmitted to the PDCP end of the receiver;  Transferring PDCP SDUs from the PDCP end of the receiving end to the upper end in ascending order of the SNs of the respective PDCP SDUs after the RLC entity is released; And releasing the PDCP entity after the PDCP SDU is delivered to the upper layer. The method of claim 1, further comprising storing the PDCP PDU in a PDCP receive buffer. The method of claim 1, further comprising receiving the PDCP PDU from the RLC entity. The radio bearer releasing method according to claim 1, further comprising a step of decrypting and performing header decompression on the PDCP PDU stored in the PDCP reception buffer and received from the RLC entity to obtain the PDCP SDU . The method as claimed in claim 1, wherein the RLC SDU is obtained by removing a header of the RLC PDU stored in the RLC reception buffer. An RF (Radio Frequency) unit; And And a processor coupled to the RF unit to release the radio bearer, Transmitting a radio bearer request for requesting release of an RLC (Radio Link Control) entity and a PDCP (Packet Data Convergence Protocol) entity from an RRC (Radio Resource Control) end of a receiver to an RLC and a PDCP end of a receiver; The step of transmitting the RLC SDU from the RLC end of the receiving end to the PDCP end of the receiving end in ascending order of a sequence number (SN) of each RLC SDU (Service Data Unit) Is obtained by reassembling RLC packet data units (PDUs) successfully received and stored in the RLC receive buffer before a radio bearer request is transmitted; Release the RLC entity after the RLC SDU is transmitted to the PDCP end of the receiver; Transferring PDCP SDUs from the PDCP end of the receiving end to the upper end in ascending order of the SNs of the respective PDCP SDUs after the RLC entity is released; And configured to facilitate to release the PDCP entity after the PDCP SDU is delivered to the upper layer. 7. The receiver of claim 6, wherein the processor is configured to store the PDCP PDU in a PDCP receive buffer. 7. The receiver of claim 6, wherein the processor is configured to receive the PDCP PDU from the RLC entity. 7. The receiver of claim 6, wherein the processor is configured to store the PDCP receive buffer and perform a decode and header decompression on the PDCP PDU received from the RLC entity to obtain the PDCP SDU. 7. The receiver of claim 6, wherein the processor is configured to obtain the RLC SDU by removing a header of the RLC PDU stored in the RLC receive buffer.

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