CN113767671A

CN113767671A - Method and apparatus for handover without interruption of data transmission and reception in next generation mobile communication system

Info

Publication number: CN113767671A
Application number: CN202080032217.4A
Authority: CN
Inventors: 金东建; 金成勳
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2019-03-28
Filing date: 2020-03-30
Publication date: 2021-12-07
Also published as: KR20200114994A

Abstract

The present disclosure relates to a communication method and system for converging fifth generation (5G) communication systems that support higher data rates than fourth generation (4G) systems and internet of things (IoT) technologies. The present disclosure may be applied to smart services based on 5G communication technologies and IoT related technologies, such as smart homes, smart buildings, smart cities, smart cars, networked cars, healthcare, digital education, smart retail, security, and security services. The method of the terminal in the wireless communication system according to the present disclosure includes: receiving a message from a first base station through Radio Resource Control (RRC) signaling, the message including a handover command from the first base station to a second base station; identifying that the message includes information indicating a dual protocol stack switch; and receiving data from the first base station until a cell of the first base station is released, in case the message comprises information indicating a dual protocol stack handover.

Description

Method and apparatus for handover without interruption of data transmission and reception in next generation mobile communication system

Technical Field

The present disclosure relates to a method and apparatus for efficient handover without interruption of data transmission or reception during handover in a next generation mobile communication system.

Background

In order to meet the increasing demand for wireless data services since the deployment of 4G communication systems, efforts have been made to develop an improved 5G or quasi-5G communication system. Accordingly, the 5G or quasi-5G communication system is also referred to as a "super 4G network" or a "post-LTE system". 5G communication systems are considered to be implemented at higher frequency (mmWave) bands (e.g., 60GHz band) in order to achieve higher data rates. In order to reduce propagation loss of radio waves and increase transmission distance, beamforming, massive Multiple Input Multiple Output (MIMO), full-dimensional MIMO (FD-MIMO), array antenna, analog beamforming, massive antenna techniques are discussed in the 5G communication system. In addition, in the 5G communication system, development of system network improvement based on advanced small cells, a cloud Radio Access Network (RAN), an ultra-dense network, device-to-device (D2D) communication, a wireless backhaul, a mobile network, cooperative communication, coordinated multipoint (CoMP), reception-side interference cancellation, and the like is ongoing. In 5G systems, hybrid FSK and QAM modulation (FQAM) and Sliding Window Superposition Coding (SWSC) have been developed as Advanced Coding Modulation (ACM), and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA), and Sparse Code Multiple Access (SCMA) as advanced access techniques.

The internet, which is a human-centric connectivity network in which humans generate and consume information, is now evolving into the internet of things (IoT), where distributed entities, such as objects, exchange and process information without human intervention. Internet of everything (IoE), which is a combination of IoT technology and big data processing technology through connection with a cloud server, has emerged. Since IoT implementations require technical elements such as "sensing technology", "wired/wireless communication and network infrastructure", "service interface technology", and "security technology", sensor networks, machine-to-machine (M2M) communication, Machine Type Communication (MTC), etc. have recently been studied. Such IoT environments can provide intelligent internet technology services that create new value for human life by collecting and analyzing data generated between connected objects. IoT can be applied in a variety of fields including smart homes, smart buildings, smart cities, smart cars or networked cars, smart grids, healthcare, smart home appliances, and advanced medical services through fusion and combination between existing Information Technology (IT) and various industrial applications.

Accordingly, various attempts have been made to apply the 5G communication system to the IoT network. For example, techniques such as sensor networks, Machine Type Communication (MTC), and machine-to-machine (M2M) communication may be implemented through beamforming, MIMO, and array antennas. The application of cloud Radio Access Network (RAN) as the big data processing technology described above may also be considered as an example of the convergence of 5G technology with IoT technology.

The above information is merely background information to aid in understanding the present disclosure. No determination has been made, nor has an assertion been made, as to whether any of the above can be applied as prior art to the present disclosure.

Disclosure of Invention

[ problem ] to provide a method for producing a semiconductor device

In the next generation mobile communication system, a method for efficient handover is required to support a seamless data service with low transmission delay.

[ problem solution ] to provide a solution

In order to solve the above problem, the present disclosure provides a method of a terminal in a wireless communication system, which may include: receiving a message from a first base station through Radio Resource Control (RRC) signaling, the message including a handover command from the first base station to a second base station; identifying whether the message includes information indicating a dual protocol stack switch; and receiving data from the first base station until the cell of the first base station is released, in case the message comprises information indicating a dual protocol stack handover.

In addition, to solve the above problem, the present disclosure provides a method of a first base station in a wireless communication system, which may include: transmitting a message to the terminal through Radio Resource Control (RRC) signaling, the message including a handover command to the second base station; and in case the message includes information indicating a dual protocol stack handover, transmitting data to the terminal until the cell of the first base station is released.

In addition, to solve the above problem, the present disclosure provides a terminal in a wireless communication system, the terminal may include: a transceiver; and a controller configured to receive a message from the first base station through Radio Resource Control (RRC) signaling via the transceiver, the message including a handover command from the first base station to the second base station; identifying whether the message includes information indicating a dual protocol stack switch; and receiving data from the first base station via the transceiver until the cell of the first base station is released, in case the message comprises information indicating a dual protocol stack handover.

Further, to solve the above problem, the present disclosure provides a first base station in a wireless communication system, the first base station may include: a transceiver; and a controller configured to transmit a message to the terminal through Radio Resource Control (RRC) signaling via the transceiver, the message including a handover command to the second base station; and in case the message comprises information indicating a dual protocol stack handover, transmitting data to the terminal via the transceiver until the cell of the first base station is released.

[ advantageous effects of the invention ]

The present disclosure proposes various methods for efficient handover to prevent occurrence of data interruption time due to handover when handover is performed in a next generation mobile communication system, thereby supporting seamless data service.

Before proceeding with the following detailed description, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms "include" and "comprise," as well as derivatives thereof, mean inclusion without limitation; the term "or" is inclusive, meaning and/or; the phrases "associated with," and "associated with," as well as derivatives thereof, may mean including, included within, interconnected with, contained within, connected to, or connected to, coupled to, or coupled with, communicable with, cooperative with, interleaved, juxtaposed, proximate to, bound to, or bound with,. having,. properties, and so forth; and the term "controller" means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely.

Further, the various functions described below may be implemented or supported by one or more computer programs, each computer program formed from computer readable program code and embodied in a computer readable medium. The terms "application" and "program" refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in suitable computer readable program code. The phrase "computer readable program code" includes any type of computer code, including source code, object code, and executable code. The phrase "computer readable medium" includes any type of medium capable of being accessed by a computer, such as Read Only Memory (ROM), Random Access Memory (RAM), a hard disk drive, a Compact Disc (CD), a Digital Video Disc (DVD), or any other type of memory. A "non-transitory" computer-readable medium excludes wired, wireless, optical, or other communication links that convey transitory electrical or other signals. Non-transitory computer-readable media include media in which data can be stored permanently and media in which data can be stored and later rewritten, such as rewritable optical disks or erasable memory devices.

Definitions for certain words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.

Drawings

For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like reference numbers represent like parts:

fig. 1 is a diagram showing a structure of an LTE system to which the present disclosure can be applied;

fig. 2 is a diagram showing a radio protocol structure of an LTE system to which the present disclosure can be applied;

fig. 3 is a diagram showing the structure of a next generation mobile communication system to which the present disclosure can be applied;

fig. 4 is a diagram showing a radio protocol structure of a next generation mobile communication system to which the present disclosure can be applied;

fig. 5 is a diagram illustrating a procedure in which a terminal switches from an RRC idle mode to an RRC connected mode and establishes a connection with a network in the present disclosure;

fig. 6 is a diagram illustrating a signaling procedure for performing handover in a next generation mobile communication system;

FIG. 7 is a diagram illustrating a first embodiment of an efficient handoff method for minimizing data disruption time due to handoff in the present disclosure;

Fig. 8 is a diagram illustrating second and third embodiments of an efficient handover method for minimizing data interruption time due to handover in the present disclosure;

FIG. 9 is a diagram illustrating a fourth embodiment of an efficient handoff method for minimizing data disruption time due to handoff in the present disclosure;

fig. 10 is a diagram illustrating a fifth embodiment of an efficient handover method for minimizing data interruption time due to handover in the present disclosure;

fig. 11 is a diagram illustrating a structure of a high efficiency PDCP entity that can be applied to the embodiment;

fig. 12 is a diagram illustrating an operation of a terminal to which the embodiments presented in the present disclosure can be applied;

fig. 13 shows a structure of a terminal to which the embodiment can be applied; and is

Fig. 14 shows a block diagram of a TRP in a wireless communication system to which the embodiments may be applied.

Detailed Description

Figures 1 through 14, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device.

Hereinafter, the operational principle of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description of the present disclosure, a detailed description of known functions or configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear. The terms to be described below are terms defined in consideration of functions in the present disclosure, and may be different according to a user, a user's intention, or a habit. Therefore, the definition of the terms should be determined based on the contents throughout the entire specification.

In the following description of the present disclosure, a detailed description of known functions or configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear. Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

In the following description, terms for identifying an access node, terms for referring to network entities, terms for referring to messages, terms for referring to interfaces between network entities, terms for referring to various identification information, and the like are illustratively used for convenience. Accordingly, the present disclosure is not limited to the terms used below, and other terms regarding the subject matter having an equivalent technical meaning may be used.

In the following description, for ease of description, the present disclosure uses terms and names defined in the third generation partnership project long term evolution (3GPP LTE) standard. However, the present disclosure is not limited to these terms and names, and may be applied in the same manner to systems conforming to other standards. In this disclosure, for ease of description, the term "eNB" may be used interchangeably with the term "gNB". That is, a base station described as "enB" may refer to "gbb".

The present disclosure proposes a seamless handover method capable of minimizing a data interruption time due to handover, or reducing the data interruption time to 0ms in a next generation mobile communication system.

In particular, the efficient handover methods presented in the present disclosure may have one or more of the following features.

If a terminal that transmits and receives data (uplink transmission or downlink data reception) to and from a source base station through respective protocol entities (PHY entity, MAC entity, RLC entity, or PDCP entity) of a plurality of first bearers receives a handover command message (or RRC reconfiguration message) from the source base station, the terminal may configure a new protocol entity of a plurality of second bearers corresponding to the protocol entities of the plurality of first bearers (e.g., having the same bearer identifier), and may maintain data transmission and reception (uplink transmission or downlink data reception) with the source base station through the plurality of first bearers (without stopping the data transmission and reception), thereby performing data transmission and reception (uplink transmission or downlink data reception).

-protocol entities (PHY entity, MAC entity, RLC entity or PDCP entity) of the plurality of second bearers reconfigured after receiving the handover command message as described above, may be configured to transmit and receive data to and from the target base station based on bearer configuration information or protocol entity information included in the handover command message.

The terminal may perform a procedure of randomly accessing the target base station through the protocol entities (e.g., MAC entities) of the plurality of second bearers while transmitting and receiving data to and from the source base station through the protocol entities of the plurality of first bearers (uplink transmission or downlink data reception). In this case, the random access procedure may include transmitting a preamble, receiving a random access response, or transmitting a message 3.

The terminal may complete a procedure of randomly accessing the target base station through the protocol entities (e.g., MAC entities) of the plurality of second bearers while transmitting and receiving data to and from the source base station through the protocol entities of the plurality of first bearers (uplink transmission and downlink data reception), and may transmit a handover complete message to the target base station through the protocol entities of the plurality of second bearers.

The terminal may complete a process of randomly accessing the target base station through the protocol entities (e.g., MAC entities) of the plurality of second bearers while transmitting and receiving data to and from the source base station through the protocol entities of the plurality of first bearers (uplink transmission and downlink data reception), may transmit a handover complete message to the target base station through the protocol entities of the plurality of second bearers, and may perform (uplink or downlink) data transmission and reception.

When the procedure of random access to the target base station is completed { e.g., when a random access response is received, when a handover complete message (e.g., a "rrcrconfiguration" message) is transmitted to the target base station, or when data is initially transmitted to the target base station using PUCCH or PUSCH uplink transmission resources }, the terminal may stop transmitting and receiving data to and from the source base station through the protocol entities of the plurality of first bearers.

-upon receiving the handover command message, the terminal may continue to transmit and receive data (uplink transmission or downlink data reception) to and from the source base station through the protocol entities of the plurality of first bearers, and may perform a procedure of randomly accessing the target base station through the protocol entities of the plurality of second bearers, and upon receiving a random access response, upon transmitting a handover complete message to the target base station, or upon initially transmitting data using PUCCH or PUSCH uplink transmission resources, the terminal may stop transmitting uplink data to the source base station through the protocol entities of the plurality of first bearers, and may transmit uplink data to the target base station only through the protocol entities of the plurality of second bearers, and the terminal may continue to receive downlink data from the source base station through the protocol entities of the plurality of first bearers, and may continue to receive downlink data from the target base station over the protocol entities of the plurality of second bearers.

In the following, the present disclosure proposes an efficient handover procedure without data interruption time based on the above features.

Fig. 1 is a diagram showing the structure of an LTE system to which the present disclosure can be applied.

Referring to fig. 1, a radio access network of an LTE system may include evolved node bs (hereinafter referred to as "ENB", "node B", or "base station") 105, 110, 115, and 120; a Mobility Management Entity (MME)125 and a serving gateway (S-GW)130, as shown in fig. 1. The user equipment (hereinafter referred to as "UE" or "terminal") 135 accesses an external network through the ENBs 105 to 120 and the S-GW 130.

In fig. 1, the ENBs 105 to 120 may correspond to existing node bs of a UMTS system. The ENB may be connected to the UE 135 via a radio channel and may play a more complex role than an existing node B. In the LTE system, all user traffic including real-time services provides services through a shared channel, such as voice over IP (VoIP) over internet protocol. Therefore, an apparatus for collecting status information (such as buffer status, available transmission power status, and channel status) of the UE and performing scheduling is used. The ENBs 105 to 120 serve as such devices. One ENB generally controls a plurality of cells. For example, to achieve a data rate of 100Mbps, the LTE system uses orthogonal frequency division multiplexing (hereinafter, referred to as "OFDM") in, for example, a 20MHz bandwidth as a radio access technology. In addition, an adaptive modulation and coding (hereinafter, referred to as "AMC") scheme is applied to determine a modulation scheme and a channel coding rate according to a channel state of a terminal. S-GW130 is a device for providing a data bearer, and generates or removes a data bearer under the control of MME 125. The MME is a device that performs various control functions as well as a mobility management function of the terminal, and may be connected to a plurality of base stations.

Fig. 2 is a diagram showing a radio protocol structure of an LTE system to which the present disclosure can be applied.

Referring to fig. 2, the radio protocols of the LTE system include a Packet Data Convergence Protocol (PDCP)205 or 240, a Radio Link Control (RLC)210 or 235, and a Medium Access Control (MAC)215 or 230 in the terminal and the ENB, respectively. The Packet Data Convergence Protocol (PDCP)205 or 240 performs operations such as IP header compression/decompression and the like. The main functions of PDCP are summarized as follows.

Header compression and decompression (ROHC only)

-transfer of user data

-in-order delivery of upper layer PDUs in PDCP re-establishment procedure for RLC AM

Sequence reordering { for a separate bearer in DC (RLC AM only supported): PDCP PDU routing for transmission and PDCP PDU reordering for reception }

-repeatedly detecting lower layer SDUs during PDCP re-establishment procedure for RLC AM

-resending PDCP SDUs at handover for RLC AM and PDCP PDUs during PDCP data recovery for split bearers in DC

-encryption and decryption

Timer based SDU discard in uplink.

The Radio Link Control (RLC)210 or 235 reconfigures PDCP PDUs (packet data units) to an appropriate size and performs an ARQ operation, etc. The main functions of the RLC are summarized as follows.

Data transfer function (transfer of upper layer PDU)

ARQ function { error correction by ARQ (for AM data transfer only) }

Concatenation, segmentation and reassembly of RLC SDUs (for UM and AM data transfer only)

Re-segmentation of RLC data PDUs (for AM data transfer only)

Reordering of RLC data PDUs (for UM and AM data transfer only)

Duplicate detection (for UM and AM data transfer only)

Protocol error detection (for AM data transfer only)

RLC SDU discard (for UM and AM data transfer only)

RLC re-establishment

The

MAC

215 or 230 is connected to a plurality of RLC entities configured in the terminal, multiplexes RLC PDUs into MAC PDUs, and demultiplexes RLC PDUs from the MAC PDUs. The main functions of the MAC are summarized below.

Mapping between logical channels and transport channels

-multiplexing/demultiplexing MAC SDUs belonging to one or different logical channels into/from Transport Blocks (TBs) delivered on a transport channel from the physical layer

-scheduling information reporting

HARQ function (error correction by HARQ)

Priority handling between logical channels of one UE

-priority handling between UEs by means of dynamic scheduling

-MBMS service identification

-transport format selection

-filling

The

physical layers

220 and 225 channel-encode and modulate upper layer data and convert the upper layer data into OFDM symbols and then transmit the OFDM symbols through a radio channel, or demodulate and channel-decode OFDM symbols received through a radio channel and then transmit the OFDM symbols to an upper layer.

Fig. 3 is a diagram showing the structure of a next generation mobile communication system to which the present disclosure can be applied.

Referring to fig. 3, a radio access network of a next generation mobile communication system (hereinafter referred to as "NR" or "5G") may include a new radio node B (hereinafter referred to as "NR gbb" or "NR base station") 310 and a new radio core network (hereinafter referred to as "NR CN") 305. A new radio user equipment (hereinafter referred to as "NR UE" or "terminal") 315 accesses an external network through NR gNB 310 and NR CN 305.

In fig. 3, NR gNB 310 corresponds to an evolved node b (enb) in an existing LTE system. The NR gNB 310 is connected to the NR UE 315 through a radio channel 320 and can provide better service than the existing node B. In the next generation mobile communication system, all user services are served through a shared channel. Therefore, an apparatus for collecting status information (such as buffer status, available transmission power status, and channel status) of the UE and performing scheduling is used. The NR NB 310 serves as such a device.

One NR gbb may control a plurality of cells. In order to achieve an ultra-high data rate with respect to the existing LTE system, the next-generation mobile communication system may have a bandwidth equal to or greater than the maximum bandwidth of the existing system. In addition, the next generation mobile communication system may use Orthogonal Frequency Division Multiplexing (OFDM) as a radio access technology, and may employ a beamforming technology in addition thereto. In addition, an adaptive modulation and coding (hereinafter, referred to as "AMC") scheme may be applied to determine a modulation scheme and a channel coding rate according to a channel state of a terminal.

The NR CN 305 performs functions such as mobility support, bearer configuration, and QoS configuration. The NR CN is a device that performs various control functions as well as a mobility management function of the terminal, and may be connected to a plurality of base stations. In addition, the next generation mobile communication system may interwork with the existing LTE system, and the NR CN may be connected to the MME 325 through a network interface. The MME may be connected to the eNB 330 as an existing base station.

Fig. 4 is a diagram showing a radio protocol structure of a next generation mobile communication system to which the present disclosure can be applied.

Referring to fig. 4, the radio protocol of the next generation mobile communication system includes

NR SDAP

401 or 445,

NR PDCP

405 or 440,

NR RLC

410 or 435, and

NR MAC

415 or 430 in the terminal and NR base station, respectively.

The primary functions of

NR SDAP

401 or 445 may include some of the following functions.

-transfer of user plane data

Mapping between QoS flows and DRBs for both downlink and uplink

Marking QoS flow IDs in both downlink and uplink packets

Mapping of reactive QoS flows to DRBs for UL SDAP PDUs

For the SDAP entity, the terminal may receive a configuration indicating whether to use a header of the SDAP entity or whether to use a function of the SDAP entity for each PDCP entity, for each bearer or for each logical channel through an RRC message. In the case of configuring the SDAP header, the 1-bit NAS reflective QoS configuration indicator and the 1-bit AS reflective QoS configuration indicator of the SDAP header may instruct the terminal to update or reconfigure mapping information between QoS flows and data bearers in uplink and downlink. The SDAP header may include QoS flow ID information indicating QoS. The QoS information may be used as data processing priority information, scheduling information, etc. for supporting a valid service.

The main functions of the

NR PDCP

405 or 440 may include some of the following functions.

Header compression and decompression (ROHC only)

-transfer of user data

In-order delivery of upper layer PDUs

Out-of-order delivery of upper layer PDUs

Sequence reordering (PDCP PDU reordering for reception)

Duplicate detection of lower layer SDU

-retransmission of PDCP SDU

-encryption and decryption

Timer-based SDU discard in uplink

The above-described re-ordering function of the NR PDCP entity means a function of re-ordering PDCP PDUs received from a lower layer based on PDCP Sequence Numbers (SNs), may include a function of transmitting data to an upper layer in a re-ordered order, may include a function of directly transmitting data to the upper layer regardless of order, may include a function of re-ordering a sequence and recording lost PDCP PDUs, may include a function of transmitting a status report of the lost PDCP PDUs to a transmitting end, and may include a function of requesting re-transmission of the lost PDCP PDUs.

The main functions of

NR RLC

410 or 435 may include some of the following functions.

Data transfer function (transfer of upper layer PDU)

In-order delivery of upper layer PDUs

Out-of-order delivery of upper layer PDUs

ARQ capabilities (error correction by ARQ)

Concatenation, segmentation and reassembly of RLC SDUs

-re-segmentation of RLC data PDUs

Reordering of RLC data PDUs

-duplicate detection

-protocol error detection

RLC SDU discard

RLC re-establishment

The above-described sequential delivery function of the NR RLC entity denotes a function of sequentially delivering RLC SDUs received from a lower layer to an upper layer, may include a function of reassembling and transmitting one original RLC SDU, in a case where the RLC SDU is divided into a plurality of RLC SDUs and received, may include a function of reordering received RLC PDUs based on an RLC Sequence Number (SN) or a PDCP Sequence Number (SN), may include a function of reordering a sequence and recording missing RLC PDUs, may include a function of transmitting a status report of missing RLC PDUs to a transmitting end, may include a function of requesting retransmission of missing RLC PDUs, may include a function of sequentially transmitting RLC SDUs preceding only the missing RLC SDU to the upper layer in a case where there is a missing RLC SDU, may include a function of, even if there is a missing RLC SDU, if a predetermined timer expires, the function of sequentially transmitting all RLC SDUs received before the timer is started to the upper layer, or may include a function of sequentially transmitting all RLC SDUs received so far to the upper layer if a predetermined timer expires even if there is a missing RLC SDU. In addition, the RLC PDUs may be processed in the order received (in the order of arrival, regardless of their sequence numbers or sequence numbers) and may be sent to the PDCP entity in an out-of-order delivery manner. In the case of fragments, the fragments stored in a buffer or to be received later may be received and reconfigured into one complete RLC PDU, and the RLC PDU may be processed and transmitted to the PDCP entity. The NR RLC layer may not include a concatenation function, which may be performed in the NR MAC layer or may be replaced with a multiplexing function of the NR MAC layer.

The out-of-order delivery of the NR RLC entity means a function of directly delivering RLC SDUs received from a lower layer to an upper layer regardless of order, may include a function of reassembling and delivering the RLC SDUs in a case where one original RLC SDU is divided into a plurality of RLC SDUs and received, and may include a function of storing and ordering RLC SNs or PDCP SNs of the received RLC PDUs, thereby recording missing RLC PDUs.

The

NR MAC

415 or 430 may be connected to a plurality of NR RLC entities configured in a single terminal, and the main functions of the NR MAC may include some of the following functions.

Mapping between logical channels and transport channels

-multiplexing/demultiplexing of MAC SDUs

-scheduling information reporting

HARQ function (error correction by HARQ)

Priority handling between logical channels of one UE

-priority handling between UEs by means of dynamic scheduling

-MBMS service identification

-transport format selection

-filling

The NR PHY layers 420 and 425 may perform an operation of channel-coding and modulating upper layer data into OFDM symbols and transmitting the OFDM symbols through a radio channel, or an operation of demodulating and channel-decoding OFDM symbols received through a radio channel and transmitting them to an upper layer.

Fig. 5 is a diagram illustrating a procedure in which a terminal switches from an RRC idle mode to an RRC connected mode and establishes a connection with a network in the present disclosure.

In fig. 5, if a terminal transmitting and receiving data in an RRC connected mode does not transmit and receive data for a predetermined reason or within an executed period, a base station may transmit an "RRCConnectionRelease" message to the terminal, so that the terminal switches to an RRC idle mode (501).

Thereafter, if a currently unconnected terminal (hereinafter, referred to as "idle mode UE") has data to transmit, the terminal performs an RRC connection setup procedure with the base station. The terminal may establish reverse transmission synchronization with the base station through a random access procedure and may transmit an "RRCConnectionRequest" message to the base station (505). The message may contain an identifier of the terminal, a reason for establishing a connection (estabilishmentiuse), and the like. The base station may send an "RRCConnectionSetup" message to cause the terminal to establish an RRC connection (510).

The message includes configuration information per service/bearer/RLC device, per logical channel or per bearer, information on whether each bearer/logical channel is to use ROHC, ROHC configuration information (e.g., information on ROHC version, initial information, etc.), "status report required" information (information by which the base station indicates the terminal to report PDCP status), "drb-conteinurohc" information { this is configuration information indicating that the ROHC configuration information is maintained and used as it is, and may be included in PDCP entity configuration information (PDCP-config) to then be transmitted }. In addition, the message may include RRC connection configuration information, and the like. The RRC-connected bearer is also referred to as a "Signaling Radio Bearer (SRB)" and may be used to transmit and receive an RRC message, which is a control message between the terminal and the base station.

The terminal having established the RRC connection transmits an "rrcconnectionsetupcomplete" message to the base station (515). The message may include a control message, referred to as a "service request," by which the terminal requests the MME to configure a bearer for the predetermined service. The base station transmits a message "service request" included in the "rrcconnectitupcompute" message to the MME or the AMF (520), and the MME or the AMF determines whether to provide the service requested by the terminal.

As a result of the determination, if the terminal determines to provide the requested service, the MME or the AMF may transmit an "initial context setup request" message to the base station (525). The message may include information such as quality of service (QoS) information to be applied when configuring a Data Radio Bearer (DRB) and security-related information (e.g., which may include at least one of a security key, a security algorithm, etc.) to be applied to the DRB.

In addition, if the base station fails to receive the capability information of the terminal from the MME or the AMF, the base station may transmit a UE capability information request message to the terminal to identify the capability information of the terminal (526). Upon receiving the UE capability information request message, the terminal may configure and generate and transmit a UE capability information message to the base station (527).

The UE capability information message may include types of handover methods supported by the terminal. An indicator for each handover method may be defined, and the base station may recognize the UE capability information and may transmit an indicator indicating a handover type to the terminal using a handover command message when indicating handover.

The base station may exchange a "SecurityModeCommand" message (530) and a "SecurityModeComplete" message (535) with the terminal to establish security. When security is established, the base station transmits an "RRCConnectionReconfiguration" message to the terminal (540).

The message includes configuration information per service/bearer/RLC device, per logical channel or per bearer, information on whether each bearer/logical channel is to use ROHC, ROHC configuration information (e.g., information on ROHC version, initial information, etc.), "status report required" information (information by which the base station indicates the terminal to report PDCP status), "drb-conteinurohc" information { this is configuration information indicating that the ROHC configuration information is maintained and used as it is, and may be included in PDCP entity configuration information (PDCP-config) to then be transmitted }. In addition, the message contains RRC connection configuration information and the like. The RRC-connected bearer is also referred to as a "Signaling Radio Bearer (SRB)" and is used to transmit and receive an RRC message, which is a control message between the terminal and the base station.

In addition, the message includes configuration information on the DRB in which the user data is processed, and the terminal configures the DRB by applying the above information and transmits an "rrcconnectionreconfiguration complete" message to the base station (545). After completing the DRB configuration with respect to the terminal, the base station transmits an "initial context setup complete" message to the MME or the AMF (550). Upon receiving the messages, the MME or the AMF exchanges an "S1 bearer setup" message and an "S1 bearer setup response" message with the S-GW to configure an S1 bearer (555 and 560). The S1 bearer is a connection for transmitting data, which is established between the S-GW and the base station, and corresponds to the DRB in a one-to-one correspondence. When all the above processes are completed, the terminal transmits and receives data to and from the base station through the S-GW (565 and 570). The general data transmission process described above basically comprises three steps: RRC connection establishment, security configuration, and DRB configuration. In addition, the base station may send an "rrcconnectionreconfiguration" message to the terminal to indicate a new configuration to the terminal, to add another configuration, or to modify a configuration for some reason (575).

In the present disclosure, the bearers may include SRBs and DRBs, the SRBs may represent "signaling radio bearers", and the DRBs may represent "data radio bearers". The SRB is mainly used to transmit and receive RRC messages of the RRC entity, and the DRB is mainly used to transmit and receive user layer data. In addition, UM DRB refers to DRB using an RLC entity operating in Unacknowledged Mode (UM), and AM DRB refers to DRB using an RLC entity operating in Acknowledged Mode (AM).

Fig. 6 is a diagram illustrating a signaling procedure for performing handover in a next generation mobile communication system.

The terminal 601 in the RRC connected mode may periodically or when a certain event is satisfied transmit a cell measurement report to the current source base station (source eNB)602 (605).

The source base station may determine whether the terminal is to perform handover to a neighboring cell based on the measurement report. "handover" is a technique of handing over a source base station, which provides a service to a terminal in a connected mode, to another base station (or another cell of the same base station). If the source base station determines handover, the source base station may request handover by transmitting a Handover (HO) request message to a new base station, i.e., "target base station (target eNB)" 603(610) that will serve the terminal. If the target base station accepts the handover request, the target base station may send a "HO request confirm" message to the source base station (615).

Upon receiving the message, the source base station may transmit a Handover (HO) command message to the terminal (620). The source base station may transmit a handover command message to the terminal using the RRC connection reconfiguration message.

Upon receiving the message, the terminal may stop transmitting and receiving data to and from the source base station, and may start a timer T304 (625). If the terminal fails to perform handover to the target base station within a predetermined period of time, the timer T304 causes the terminal to return to its original configuration and switch to the RRC idle state. The source base station may transmit a Sequence Number (SN) status of uplink/downlink data to the target base station and, if there is downlink data, downlink data to the target base station (630 and 635).

The terminal may attempt random access to the target cell indicated by the source base station (640). Random access is intended to inform the target cell that the terminal is moving for handover and to match uplink synchronization. For random access, the terminal transmits a preamble corresponding to a preamble ID provided from the source base station or a randomly selected preamble ID to the target cell.

After transmitting the preamble, the terminal may monitor whether a Random Access Response (RAR) message is received from the target cell when a certain number of subframes pass. The monitored time period is referred to as a "random access response window (RAR window)".

If a Random Access Response (RAR) is received during a specific time period (645), the terminal may transmit a Handover (HO) complete message to the target base station using an RRC reconfiguration complete message (655). That is, the terminal may include information indicating handover completion in the RRC reconfiguration complete message and may transmit the message to the target base station.

Upon successful receipt of the random access response from the target base station as described above, the terminal may terminate the timer T304 (650). The target base station may request path modification to the MME/S-GW/AMF 604 to modify the path of the bearer configured for the source base station (660 and 665), and may send a request to delete the UE context of the terminal to the source base station (670). Accordingly, the terminal attempts to receive data from the target base station from the start time of the RAR window (675), and transmits an RRC reconfiguration complete message after receiving the RAR, thereby starting transmission and reception of data to and from the target base station.

The present disclosure proposes a seamless handover method capable of minimizing a data interruption time due to handover or reducing the data interruption time to 0ms in a next generation mobile communication system.

The terminal can configure a plurality of first bearers with respect to the source base station, perform transmission and reception (uplink transmission or downlink data reception) of data through respective protocol entities (PHY entity, MAC entity, RLC entity, or PDCP entity) of the bearers, and hereinafter, for convenience of description, an example of the terminal having one bearer will be shown and described in the drawings and the description.

Fig. 7 is a diagram illustrating a first embodiment of an efficient handover method for minimizing data interruption time due to handover in the present disclosure. Although described herein as various embodiments, such as the first embodiment or the second embodiment, this description should not be construed in a limiting sense. The various embodiments may be combined or separated into separate embodiments without departing from the scope of the disclosure.

Referring to fig. 7, in step 701, even if the terminal 720 receives a handover command from the source base station 705 while transmitting and receiving data to and from the source base station, the terminal may continue to transmit and receive data to and from the source base station to minimize a data interruption time occurring during handover.

Accordingly, in step 702, when the terminal 720 performs a random access procedure, transmits a preamble, or transmits initial data to the target base station 710 indicated by the handover command message through an uplink transmission resource (e.g., PUCCH or PUSCH transmission resource), the terminal 720 may stop transmitting and receiving data to and from the source base station (uplink data transmission and downlink data reception).

In addition, in step 703, the terminal 720 may complete a process of randomly accessing the target base station, may transmit a handover complete message, and may start transmitting and receiving data to and from the target base station (uplink data transmission and downlink data reception)

Fig. 8 is a diagram illustrating second and third embodiments of an efficient handover method for minimizing a data interruption time due to handover in the present disclosure.

Referring to fig. 8, in a second embodiment of the efficient handover method, even if the terminal 820 receives a handover command from the source base station 805 while transmitting and receiving data to and from the source base station, the terminal may continue to transmit and receive data to and from the source base station through the protocol entity 822 of the first bearer in step 801 to minimize a data interruption time occurring during handover.

In addition, a protocol entity (PHY entity, MAC entity, RLC entity, or PDCP entity) 821 for the second bearer of the target base station may be pre-configured or established according to the configuration included in the received handover command message. The second bearer may be configured and established to have the same bearer identifier as the first bearer to prevent data outage times per bearer. In addition, even if the terminal receives the handover command message from the source base station, the terminal may continue to transmit and receive data due to HARQ retransmission to prevent data loss, and thus may not initialize the MAC entity of the first bearer.

In step 802, even when the terminal 820 performs a random access procedure on the target base station 810 indicated by the handover command message through the protocol entity of the second bearer (e.g., before receiving a random access response after transmitting the preamble), the terminal may continue to transmit and receive data to and from the source base station through the protocol entity of the first bearer (uplink data transmission and downlink data reception).

In addition, in step 803, the terminal 820 may complete a process of randomly accessing the target base station 810 through a protocol entity of the second bearer, and may transmit and receive data (downlink data reception and uplink data transmission).

In addition, if the first condition is satisfied, the terminal may stop transmitting and receiving data to and from the source base station 805 through the protocol entity 822 of the first bearer. In addition, the PDCP entity 821 of the second bearer can continue to perform seamless data transmission and reception to and from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, etc., stored in the PDCP entity 822 of the first bearer. The first condition may include at least one of the following conditions.

When the terminal performs a random access procedure to the target base station through the entity 821 of the second bearer and receives a random access response

-when the terminal performs a procedure of randomly accessing the target base station through the entity of the second bearer, receives a random access response, and configures and transmits a handover complete message to the target base station

-when the terminal completes the process of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources

-when the base station configures a separate timer for the terminal by RRC message and the timer expires

The timer may be started when: when the terminal receives a handover command message from the source base station; when the terminal starts random access to the target base station (when the preamble is transmitted); when the terminal receives a random access response from the target base station; when the terminal sends a switching completion message to the target base station; or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.

-when the terminal performs a process of randomly accessing the target base station through the entity of the second bearer, receives a random access response, and configures and sends a handover complete message to the target base station and when a successful sending of the handover complete message is recognized by the MAC entity (HARQ ACK) or the RLC entity (RLC ACK)

-when the terminal performs a procedure of random access to the target base station through an entity of the second bearer, receives a random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources

The source base station may determine a time to stop transmitting downlink data to the terminal or a time to release a connection with the terminal based on a predetermined method when performing the efficient handover proposed in the present disclosure. For example, the predetermined method may include at least one of: when a predetermined timer expires (the timer may be started after the handover indication) or when an indication is received from the target base station indicating that the terminal has successfully performed a handover to the target base station.

In addition, if downlink data is not received from the source base station within a predetermined period of time, the terminal may determine that the connection with the source base station is released and may release the connection.

-when the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resource allocated by the target base station or receives the indication of the first uplink transmission resource

E.g., more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) }is allocated

When the terminal transmits a predetermined preamble to the cell of the target base station and receives a Random Access Response (RAR) message, the terminal may determine that the random access procedure is successfully completed. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the first condition is satisfied.

Alternatively, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is contention-based random access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated))

When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included, or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that a process of randomly accessing the target base station is successfully completed. Thus, when the terminal monitors the PDCCH and initially receives the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal or initially receives an indication of the uplink transmission resource, the terminal may then determine that the first condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the first condition is satisfied.

In case the handover command message received by the terminal indicates a handover method that does not require a random access procedure (handover without RACH)

If the handover command message includes uplink transmission resources to the target base station

When the terminal transmits a message 3 (e.g., a handover complete message or a "rrcreeconfigurationcomplete" message) using uplink transmission resources of the target base station and receives a UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.

In case the handover command message does not include uplink transmission resources for the target base station

When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "rrcreeconfiguration complete" message) using the uplink transmission resource and receives a UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.

Meanwhile, referring to fig. 8, in the third embodiment of the efficient handover method, even if the terminal 820 receives a handover command from the source base station 805 while transmitting and receiving data to and from the source base station, the terminal may continue to transmit and receive data to and from the source base station through the protocol entity 822 of the first bearer in order to minimize a data interruption time occurring during handover in step 801.

In addition, a protocol entity (PHY entity, MAC entity, RLC entity, or PDCP entity) 821 for the second bearer of the target base station may be pre-configured or established according to the configuration contained in the received handover command message. The second bearer may be configured and established to have the same bearer identifier as the first bearer to prevent data outage times per bearer.

In addition, the handover command message may include uplink transmission resources of the target base station and may then be transmitted to the terminal to omit a random access procedure of the terminal to the target base station through a protocol entity of the second bearer.

As another method, in case the handover command message indicates handover without a random access procedure, the terminal may synchronize with the target base station without a random access procedure and may receive uplink transmission resources from the target base station by monitoring the PDCCH. As described above, the data interruption time can be minimized by omitting the random access procedure.

In addition, even if the terminal receives the handover command message from the source base station, the terminal may continue to transmit and receive data due to HARQ retransmission to prevent data loss, and thus may not initialize the MAC entity of the first bearer. In addition, in case of RLC in AM, RLC retransmission may be continuously performed.

In the third embodiment, in step 802, the operation of the terminal 820 performing the random access procedure on the target base station 810 indicated by the handover command message through the protocol entity of the second bearer may be omitted. The terminal may configure the handover complete message and may send the handover complete message to the target base station through the protocol entity of the second bearer using the transmission resource of the target base station indicated by the handover command message.

As another method, in case that the handover command message indicates handover without a random access procedure but does not include uplink transmission resources to the target base station, the terminal may synchronize with the target base station without a random access procedure and may receive uplink transmission resources from the target base station by monitoring the PDCCH, thereby transmitting a handover complete message to the target base station. The terminal may continue to transmit and receive data to and from the source base station (uplink data transmission and downlink data reception) through the protocol entity of the first bearer.

In the third embodiment, in step 803, the terminal 820 may transmit and receive data (downlink data reception and uplink data transmission) using the protocol entities of the second bearer.

The source base station may determine a time to stop transmitting downlink data to the terminal or a time to release a connection with the terminal based on a predetermined method when performing the efficient handover proposed in the present disclosure. For example, the predetermined method may include at least one of: when a predetermined timer expires (the timer may be started after the handover indication); or when an indication is received from the target indicating that the terminal has successfully performed a handover to the target base station.

When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included, or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that a process of randomly accessing the target base station is successfully completed. Accordingly, the terminal may determine that the first condition is satisfied when the terminal thereafter monitors the PDCCH and initially receives the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal or initially receives an indication of the uplink transmission resource. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the first condition is satisfied.

Fig. 9 is a diagram illustrating a fourth embodiment of an efficient handover method for minimizing a data interruption time due to handover in the present disclosure.

Referring to fig. 9, in step 901, even if the terminal 920 receives a handover command from the source base station 905 while transmitting and receiving data to and from the source base station, the terminal may continue to transmit and receive data to and from the source base station through the protocol entity 922 of the first bearer to minimize a data interruption time occurring during handover.

In addition, the protocol entity (PHY entity, MAC entity, RLC entity, or PDCP entity) 921 for the second bearer of the target base station may be pre-configured or established according to the configuration included in the received handover command message. The second bearer may be configured and established to have the same bearer identifier as the first bearer to prevent data outage times per bearer.

In addition, in the fourth embodiment, the PDCP entity of the first bearer and the PDCP entity of the second bearer may logically operate as a single PDCP entity, and a more detailed operation method thereof will be described with reference to fig. 11.

In addition, in the case where the terminal is allowed to transmit uplink data to both the source base station and the target base station, there may be a problem of a decrease in coverage due to insufficient transmission power of the terminal, or a problem of determining a base station to which transmission resources are to be requested and uplink data is transmitted when transmitting uplink data (link selection problem). Therefore, in order to avoid the above-described problem, in the fourth embodiment, the terminal may transmit uplink data to the source base station and the target base station at different times through a Time Domain Multiplexing (TDM) scheme when transmitting the uplink data to the source base station or the target base station.

As another method, the base station may configure a threshold value through an RRC message, and the terminal may transmit uplink data to the source base station (or the target base station) in a case where the size of the uplink data of the terminal is less than the threshold value, and may transmit uplink data to both the source base station and the target base station in a case where the size of the uplink data of the terminal is greater than the threshold value. The transmission of uplink data may be accompanied by a Buffer Status Report (BSR) procedure or a scheduling request procedure for reporting the size of data to be transmitted.

In addition, even if the terminal receives the handover command message from the source base station, the terminal may continue to transmit and receive data due to HARQ retransmission to prevent data loss, and thus may not initialize the MAC entity of the first bearer. In addition, in case of the RLC entity in the AM, RLC retransmission may be continuously performed.

In step 902, the terminal 920 may continue to transmit and receive data (uplink data transmission and downlink data transmission) to and from the source base station through the protocol entity of the first bearer of the terminal even when the random access procedure is performed on the target base station 910 indicated by the handover command message through the protocol entity of the second bearer.

In step 903, the terminal 920 may complete a process of randomly accessing the target base station 910 through the protocol entity of the second bearer, may transmit and receive data (uplink data transmission and downlink data transmission), and may continue to transmit and receive data to and from the source base station through the protocol entity of the first bearer (uplink data transmission and downlink data transmission).

In step 904, the terminal 920 may stop transmitting data to and receiving data from the source base station 805 through the protocol entity 922 of the first bearer if the first condition is met. In addition, the PDCP entity 921 of the second bearer may continue to perform seamless data transmission and reception to and from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, etc., stored in the PDCP entity 922 of the first bearer. The first condition may include at least one of the following conditions.

When the terminal performs a random access procedure to the target base station through the entity 921 of the second bearer and receives a random access response

When the terminal receives an indication { e.g., an RRC message (e.g., "RRCREConfiguration" message), a MAC CE, an RLC control PDU, or a PDCP control PDU } from the target base station to release the connection with the source base station

When the terminal receives an indication { e.g., an RRC message (e.g., "RRCREConfiguration" message), a MAC CE, an RLC control PDU, or a PDCP control PDU } from the source base station to release the connection with the source base station

If the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is contention-based random access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated))

When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included, or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that a process of randomly accessing the target base station is successfully completed. Thus, thereafter, when the terminal monitors the PDCCH and initially receives the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal or initially receives an indication of the uplink transmission resource, the terminal may determine that the first condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the first condition is satisfied.

Fig. 10 is a diagram illustrating a fifth embodiment of an efficient handover method for minimizing a data interruption time due to handover in the present disclosure.

Referring to fig. 10, in the fifth embodiment, in step 1001, even if the terminal 1020 receives a handover command from the source base station 1005 while transmitting and receiving data to and from the source base station, the terminal may continue to transmit and receive data to and from the source base station through the protocol entity 1022 of the first bearer to minimize a data interruption time occurring during handover.

In addition, a protocol entity (PHY entity, MAC entity, RLC entity, or PDCP entity) 1021 for the second bearer of the target base station may be pre-configured or established according to the configuration included in the received handover command message. The second bearer may be configured and established to have the same bearer identifier as the first bearer to prevent data outage times per bearer.

In addition, in the fifth embodiment, the PDCP entity of the first bearer and the PDCP entity of the second bearer may logically operate as a single PDCP entity, and a more detailed operation method thereof will be described with reference to fig. 11.

In addition, in the fifth embodiment, in the case where the terminal is allowed to transmit uplink data to both the source base station and the target base station, there may be a problem of a decrease in coverage due to insufficient transmission power of the terminal, or a problem of determining a base station to which transmission resources are to be requested and uplink data is transmitted when transmitting uplink data (a link selection problem). Therefore, in order to avoid the above-described problem, in the fifth embodiment, the terminal may transmit uplink data to only one of the source base station or the target base station.

Accordingly, the terminal may request scheduling to only one of the source and target base stations, may report only a size { e.g., a Buffer Status Report (BSR) } of data to be transmitted in the PDCP entity to one of the source and target base stations, may receive uplink transmission resources, and may then transmit uplink data to only one base station. In addition, even if the terminal receives the handover command message from the source base station, the terminal may continue to transmit and receive data due to HARQ retransmission to prevent data loss, and thus may not initialize the MAC entity of the first bearer. In addition, in case of the RLC entity in the AM, RLC retransmission may be continuously performed.

In the fifth embodiment, in step 1002, even when the random access procedure is performed on the target base station 1010 indicated by the handover command message through the protocol entity of the second bearer, the terminal 1020 may continue to transmit and receive data (uplink data transmission and downlink data transmission) to and from the source base station through the protocol entity of the first bearer.

In the fifth embodiment, in step 1003, the terminal 1020 may stop transmitting and receiving data to and from the source base station through the protocol entity 1022 of the first bearer, may transmit uplink data to the target base station through the protocol entity 1021 of the second bearer, and may continue receiving downlink data from the source base station and the target base station through the protocol entities of the first bearer and the second bearer, if the second condition is satisfied. In addition, the PDCP entity 1021 of the second bearer can continue to perform seamless data transmission and reception to and from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, etc., stored in the PDCP entity 1022 of the first bearer.

The second condition may include at least one of the following conditions.

When the terminal performs a random access procedure to the target base station through the entity 1021 of the second bearer and receives a random access response

When the terminal receives an indication { e.g., an RRC message (e.g., "RRCREConfiguration" message), a MAC CE, an RLC control PDU, or a PDCP control PDU } from the target base station to release the connection with the source base station and handover the uplink to the target base station

When the terminal receives an indication { e.g., an RRC message (e.g., "RRCREConfiguration" message), a MAC CE, an RLC control PDU, or a PDCP control PDU } from the source base station to release the connection with the source base station and handover the uplink to the target base station

When the terminal transmits a predetermined preamble to the cell of the target base station and receives a Random Access Response (RAR) message, the terminal may determine that the random access procedure is successfully completed. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the second condition is satisfied.

When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included, or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that a process of randomly accessing the target base station is successfully completed. Thus, thereafter, when the terminal monitors the PDCCH and initially receives the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal or initially receives an indication of the uplink transmission resource, the terminal may determine that the second condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the second condition is satisfied.

When the terminal transmits a message 3 (e.g., a handover complete message or a "rrcreeconfigurationcomplete" message) using uplink transmission resources of the target base station and receives a UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the second condition is satisfied. As another method, the terminal may determine that the second condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.

When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "rrcreeconfiguration complete" message) using the uplink transmission resource and receives a UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the second condition is satisfied. As another method, the terminal may determine that the second condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.

In order to facilitate reception of downlink data from the source base station (or target base station) or to facilitate transmission of downlink data by the source base station (or target base station) in the case where the terminal can continue to receive downlink data from the source base station and the target base station through the protocol entities of the first bearer and the second bearer, for an AM bearer, RLC status reports other than data are allowed to be continuously transmitted to the source base station (or target base station) through the protocol entities of the first bearer (or the second bearer) in an uplink. This is due to the fact that: after the AM bearer transmits data to the transmitting terminal, if there is no RLC status report indicating successful delivery (that is, if no RLC status report is received), the AM bearer cannot continue to transmit data thereafter.

In addition, in the fifth embodiment, in step 1003, even if the terminal 1020 stops transmitting uplink data to the source base station through the protocol entity 1022 of the first bearer because the second condition is satisfied and switches to start transmitting uplink data to the target base station through the protocol entity 1021 of the second bearer, in order to facilitate receiving downlink data from the source base station (or the target base station) or to facilitate transmitting downlink data to the source base station (or the target base station), the terminal may allow HARQ ACK or HARQ NACK information or PDCP control data (e.g., PDCP status report or ROHC feedback information) to be continuously transmitted through the protocol entity of the first bearer (or the second bearer).

In addition, in the fifth embodiment, in step 1003, even if the terminal 1020 stops transmitting uplink data to the source base station through the protocol entity 1022 of the first bearer because the second condition is satisfied and switches to start transmitting uplink data to the target base station through the protocol entity 1021 of the second bearer, the terminal may continue transmitting data due to HARQ retransmission of the MAC entity or continue transmitting data due to retransmission of the RLC entity in the AM to prevent data loss to the source base station.

In addition, in the fifth embodiment, in step 1003, if the terminal 1020 stops transmitting uplink data to the source base station through the protocol entity 1022 of the first bearer because the second condition is satisfied, and switches to start transmitting uplink data to the target base station through the protocol entity 1021 of the second bearer, the source base station or the target base station may allocate transmission resources to the terminal by dividing time so that the uplink transmission resources to the target base station and the uplink transmission resources to the source base station do not collide (or overlap) with each other. If the uplink transmission resource to the target base station overlaps with the uplink transmission resource to the source base station, the terminal may prioritize the uplink transmission resource of the source base station to maintain transmission of downlink data from the source base station, thereby performing data transmission to the source base station.

Alternatively, if the uplink transmission resource to the target base station overlaps with the uplink transmission resource to the source base station, the terminal may prioritize the uplink transmission resource of the target base station to maintain the transmission of the downlink data from the target base station, thereby performing the data transmission to the target base station.

Specifically, in the case of being instructed to handover corresponding to the fifth embodiment of the present disclosure upon receiving the handover command message, the terminal may perform a scheduling request through the first protocol entity until the second condition is satisfied, may transmit a buffer status report to the source base station, may receive uplink transmission resources, may transmit uplink data, and may receive downlink data from the source base station.

However, if the second condition is satisfied, the terminal may no longer transmit data to the source base station, may switch the uplink to perform a scheduling request by the second protocol entity, may transmit a buffer status report to the target base station, may receive uplink transmission resources, and may transmit uplink data to the target base station.

However, the terminal may continue to receive downlink data from the source base station, and may continue to transmit HARQ ACK, HARQ NACK, RLC status report, or PDCP control data (e.g., PDCP status report or ROHC feedback information) corresponding to the downlink data. The terminal may also receive downlink data from the target base station if the second condition is satisfied.

In the fifth embodiment, in step 1004, the terminal 1020 may stop receiving downlink data from the source base station 1005 via the protocol entity 1022 of the first bearer if the first condition is satisfied. In addition, the PDCP entity 1021 of the second bearer can continue to perform seamless data transmission and reception to and from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, etc., stored in the PDCP entity 1022 of the first bearer. The first condition may include at least one of the following conditions.

-when the terminal fails to receive downlink data from the source base station within a predetermined time period

Fig. 10 may illustrate steps in embodiment 5-2 of an efficient handoff method for minimizing data disruption time due to handoff in the present disclosure.

Referring to fig. 10, in the 5-2 embodiment, in step 1001, even if the terminal 1020 receives a handover command from the source base station 1005 while transmitting and receiving data to and from the source base station, the terminal may continue to transmit and receive data to and from the source base station through the protocol entity 1022 of the first bearer to minimize a data interruption time occurring during handover.

In addition, in the 5 th-2 nd embodiment, the PDCP entity of the first bearer and the PDCP entity of the second bearer may logically operate as a single PDCP entity, and a more detailed operation method thereof will be described with reference to fig. 11.

In addition, in the 5-2 embodiment, in addition, in the case where the terminal is allowed to transmit uplink data to both the source base station and the target base station, there may be a problem of a decrease in coverage due to an insufficient transmission power of the terminal, or a problem of determining a base station to which transmission resources are to be requested and uplink data is transmitted when transmitting uplink data (a link selection problem). Therefore, in order to avoid the above problem, in the 5 th-2 nd embodiment, the terminal may transmit uplink data to only one of the source base station and the target base station.

Accordingly, the terminal may request scheduling to only one of the source and target base stations, may report only a size { e.g., a Buffer Status Report (BSR) } of data to be transmitted in the PDCP entity to one of the source and target base stations, may receive uplink transmission resources, and may then transmit uplink data to only one base station. In addition, even if the terminal receives the handover command message from the source base station, the terminal may continue to transmit and receive data due to HARQ retransmission to prevent data loss, and thus may not initialize the MAC entity of the first bearer.

In the 5-2 embodiment, in step 1002, even when the random access procedure is performed on the target base station 1010 indicated by the handover command message through the protocol entity of the second bearer, the terminal 1020 may continue to transmit and receive data (uplink data transmission and downlink data transmission) to and from the source base station through the protocol entity of the first bearer.

In the 5-2 embodiment, in step 1003, the terminal 1020 may stop transmitting uplink data to the source base station through the protocol entity 1022 of the first bearer, may transmit uplink data to the target base station through the protocol entity 1021 of the second bearer, and may continue receiving downlink data from the source base station and the target base station through the protocol entities of the first bearer and the second bearer, if the second condition is satisfied. In this case, when stopping transmission of uplink data to the source base station through the protocol entity 1022 of the first bearer, the terminal may perform an RLC re-establishment procedure for a transmission RLC entity among the protocol entities. In addition, the PDCP entity 1021 of the second bearer can continue to perform seamless data transmission and reception to and from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, etc., stored in the PDCP entity 1022 of the first bearer. The second condition may include one of the following conditions.

In addition, in order to facilitate reception of downlink data from the source base station (or the target base station) or transmission of downlink data by the source base station (or the target base station), HARQ ACK or HARQ NACK information or PDCP control data (e.g., PDCP status report or ROHC feedback information) may be allowed to be continuously transmitted through a protocol entity of the first bearer (or the second bearer).

Specifically, in the case of being instructed to handover corresponding to the 5 th-2 nd embodiment of the present disclosure upon receiving the handover command message, the terminal may perform a scheduling request through the first protocol entity until the second condition is satisfied, may transmit a buffer status report to the source base station, may receive uplink transmission resources, may transmit uplink data, and may receive downlink data from the source base station.

However, the terminal may continue to receive downlink data from the source base station, and may continue to transmit HARQ ACK, HARQ NACK, RLC status report, or PDCP control data (e.g., PDCP status report or ROHC feedback information) corresponding to the downlink data. The terminal may also receive downlink data from the target base station when the second condition is satisfied.

In the 5-2 embodiment, in step 1004, the terminal 1020 may stop receiving downlink data from the source base station 1005 via the protocol entity 1022 of the first bearer if the first condition is satisfied. In addition, the PDCP entity 1021 of the second bearer can continue to perform seamless data transmission and reception to and from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, etc., stored in the PDCP entity 1022 of the first bearer. The first condition may include one of the following conditions.

Meanwhile, indicators of the proposed embodiments of the present disclosure may be defined. Therefore, when transmitting the handover command message to the terminal (620) in fig. 6, the base station may indicate to the terminal a handover procedure corresponding to a specific embodiment to be triggered through the handover command message (e.g., rrcreeconfiguration message), as described above. In addition, the terminal may perform a handover procedure according to a handover method indicated by the handover command message, thereby performing handover to the target base station while minimizing a data interruption time.

As another method, indicators for the embodiments proposed by the present disclosure may be defined for respective bearers. Thus, the base station may use the handover command message to more specifically indicate the embodiment and bearer to which the handover applies. For example, the embodiments may be applied only to an AM bearer that drives an RLC entity under AM, or may be extended to an UM bearer that drives an RLC entity under UM.

In addition, it is assumed that the embodiments presented in the present disclosure are applied to DRBs. However, if necessary (e.g., when the terminal maintains the SRB of the source base station and cannot perform handover to the target base station, thereby reporting a handover failure message or recovering through the SRB of the source base station), the embodiments proposed in the present disclosure may be extended to be applied to the SRB.

In an embodiment, when the terminal transmits and receives data to and from the source base station through the protocol entity of the first bearer and when the terminal transmits and receives data to and from the target base station through the protocol entity of the second bearer, the MAC entity of the first bearer and the MAC entity of the second bearer may use separate Discontinuous Reception (DRX) periods to reduce battery consumption of the terminal. That is, the terminal may continue to apply the DRX period of the MAC entity, which has been applied when transmitting and receiving data through the protocol entity of the first bearer, even after receiving the handover command message, and may stop the DRX according to the first condition or the second condition in the present disclosure. In addition, the terminal may apply the DRX period to the MAC entity of the second bearer separately according to the indication of the target base station.

In addition, in the present disclosure, the operation in which the terminal stops uplink transmission to the source base station through the protocol entity of the first bearer and stops downlink transmission from the source base station refers to an operation in which the terminal reestablishes, initializes or releases the protocol entity (PHY entity, MAC entity, RLC entity or PDCP entity) of the first bearer.

For convenience of description, the case where the terminal has the first bearer for the source base station or the second bearer for the target base station has been described in the above embodiments, and the embodiments can be easily extended and applied to the case where the terminal has a plurality of first bearers for the source base station or a plurality of second bearers for the target base station in the same manner.

In addition, embodiments of the present disclosure can be easily extended and applied to the case where multiple bearers are configured for multiple target base stations in the same manner. For example, the terminal may configure the second bearer while performing a handover procedure to the first target base station, and if the handover is unsuccessful, the terminal may configure the second bearer while performing a handover procedure to the second target base station. As described above, the terminal may search for and determine a cell satisfying a predetermined condition (e.g., having a predetermined signal strength or stronger than the predetermined signal strength) among a plurality of target base stations, thereby performing a handover procedure.

Fig. 11 is a diagram illustrating a structure of a high efficiency PDCP entity that can be applied to the embodiment.

The present disclosure proposes a structure of an efficient PDCP entity as shown in fig. 11. The structure of the PDCP entity shown in fig. 11 may be applied to the second, third, fourth, or fifth embodiment of the efficient handover method for minimizing the data interruption time proposed in the present disclosure.

In fig. 11, a terminal 1120 may transmit and receive data to and from a source base station 1105 through a protocol entity of a first bearer, and may simultaneously transmit and receive data to and from a target base station 1110 through a protocol entity of a second bearer.

Although the PDCP entity of the first bearer and the PDCP entity of the second bearer are configured in the terminal, respectively, the PDCP entity of the first bearer and the PDCP entity of the second bearer may logically operate as a single PDCP entity, as shown in fig. 11. Specifically, a single PDCP entity can be implemented to have one upper layer PDCP entity 1123 and two lower

layer PDCP entities

1121 and 1122 for the source and target base stations, respectively, according to the functions of the PDCP entities.

The upper layer transmitting PDCP entity 1123 may be configured to assign a PDCP sequence number to data received from the upper layer entity. In addition, the upper layer transmitting PDCP entity 1123 may perform header compression. In addition, the lower layer

transmission PDCP entities

1121 and 1122 for the source and target base stations may apply an integrity protection procedure to a PDCP header and data (PDCP SDU) in the case where integrity protection is configured using security keys set for the source and target base stations, respectively, the lower layer

transmission PDCP entities

1121 and 1122 for the source and target base stations may apply a ciphering procedure to the PDCP header and data, and may transmit the PDCP header and data to the transmission RLC entity of the first bearer or the transmission RLC entity of the second bearer.

In order to increase the data processing speed, the lower layer transmitting

PDCP entities

1121 and 1122 can perform parallel processing in which header compression, integrity protection, and/or ciphering processes are performed in parallel, and can perform the integrity protection or ciphering processes using different security keys. In addition, in one transmitting PDCP entity logically, integrity protection or ciphering procedures can be performed on different data using different security keys or security algorithms.

The upper layer receiving PDCP entity 1123 may perform a duplicate detection function on data received from the lower layer entity based on the PDCP sequence number. In addition, the upper layer receiving PDCP entity 1123 may sort the received data in an ascending order of PDCP sequence numbers and may sequentially transmit the data to the upper layer. In addition, the upper layer receiving PDCP entity 1123 may perform header decompression.

Further, in case that integrity protection is configured using separate security keys set for the source and target base stations, the lower layer

reception PDCP entities

1121 and 1122 for respective one of the source and target base stations may apply an integrity verification process to the PDCP header and data (PDCP SDU), the lower layer

reception PDCP entities

1121 and 1122 for respective one of the source and target base stations may apply a decryption process to the PDCP header and data, and may transmit the PDCP header and data to the upper layer reception PDCP entity, thereby processing the data.

To reduce unnecessary integrity verification or deciphering processes, the lower receiving PDCP entity may perform a process of discarding data outside the window and discarding duplicate data based on the PDCP sequence number, and may perform an integrity verification or deciphering process only on valid data within the window.

In order to increase data processing speed, the lower layer transmitting PDCP entity may perform parallel processing of performing header compression, integrity protection, and ciphering processes in parallel based on the PDCP sequence number, and may perform an integrity protection verification or deciphering process using different security keys. In addition, in one transmitting PDCP entity logically, integrity protection or ciphering procedures can be performed on different data using different security keys or security algorithms. In addition, the lower layer receiving PDCP entity can perform an out-of-order deciphering or integrity verification process on each piece of received data regardless of the order of the PDCP sequence numbers.

An entity of a first bearer (or a first RLC entity) and an entity of a second bearer (or a second RLC entity) of a single PDCP entity are distinguished as follows: by considering that they are connected to different MAC entities, by allowing them to have different logical channel identifiers, by considering that they are different RLC entities connected to different MAC entities, or using different encryption keys based on them, and uplink data and downlink data can be encrypted or decrypted using different security keys, and uplink data and downlink data can be compressed or decompressed using different compression protocol contexts.

When the fourth or fifth embodiment proposed in the present disclosure can be indicated to the terminal through the handover command message. At this time, if each bearer satisfies the following fourth condition, the terminal may convert, change or reset the PDCP entity for each bearer to the efficient PDCP entity set forth in fig. 11 before receiving the handover command message, and may apply the efficient PDCP entity. The fourth condition may be one or more of the following conditions.

-in case the terminal receives a handover command message from the source base station indicating a method of performing handover using the fourth or fifth embodiment proposed in the present disclosure or indicating application of the efficient PDCP entity structure proposed in fig. 11

When the terminal transmits a predetermined preamble to the cell of the target base station and receives a Random Access Response (RAR) message, the terminal may determine that the random access procedure is successfully completed. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the fourth condition is satisfied.

When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included, or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that a process of randomly accessing the target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal or initially receives an indication of the uplink transmission resource, the terminal may determine that the fourth condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the fourth condition is satisfied.

When the terminal transmits a message 3 (e.g., a handover complete message or a "rrcreeconfigurationcomplete" message) using uplink transmission resources of the target base station and receives a UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the fourth condition is satisfied. As another method, the terminal may determine that the fourth condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.

When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "rrcreeconfiguration complete" message) using the uplink transmission resource and receives a UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the fourth condition is satisfied. As another method, the terminal may determine that the fourth condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.

In addition, when the fourth or fifth embodiment proposed in the present disclosure is indicated to the terminal through the handover command message, if each bearer satisfies the fourth condition, the terminal may convert, change or reset the PDCP entity for each bearer before receiving the handover command message to the efficient PDCP entity proposed in fig. 11, and may apply the efficient PDCP entity.

Further, if the fifth condition is satisfied, the terminal may stop receiving downlink data from the source base station, and may re-convert, change or reset the structure of the PDCP entity that has been converted, changed or reset to the efficient PDCP entity set forth in fig. 11 to the PDCP entity for each bearer before receiving the handover command message. The fifth condition may be one or more of the following conditions.

When the terminal transmits a predetermined preamble to the cell of the target base station and receives a Random Access Response (RAR) message, the terminal may determine that the random access procedure is successfully completed. Accordingly, when the terminal receives the first uplink transmission resource allocated, included, or indicated in the random access response message, the terminal may determine that the fifth condition is satisfied.

When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included, or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that a process of randomly accessing the target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal or initially receives an indication of the uplink transmission resource, the terminal may determine that the fifth condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the fifth condition is satisfied.

When the terminal transmits a message 3 (e.g., a handover complete message or a "rrcreeconfigurationcomplete" message) using uplink transmission resources of the target base station and receives a UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the fifth condition is satisfied. As another method, the terminal may determine that the fifth condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.

When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "rrcreeconfiguration complete" message) using the uplink transmission resource and receives a UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the fifth condition is satisfied. As another method, the terminal may determine that the fifth condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.

As another method, if the fifth condition is satisfied, the terminal may stop receiving downlink data from the source base station, may release the RLC entity or the MAC entity, which is the first protocol entity, for each bearer, and may apply the structure of the efficient PDCP entity, which is proposed in fig. 11, to the respective bearers, thereby using the structure of the efficient PDCP entity.

Fig. 12 is a display diagram illustrating an operation of a terminal that can be applied to the embodiments presented in the present disclosure.

Referring to fig. 12, a terminal may receive a handover command message (1205). The terminal may establish a protocol entity for a second bearer for the target base station indicated by the message (1210).

Then, the terminal may perform a process of randomly accessing the target base station through the established protocol entity (1215). The terminal may continue to transmit and receive data (uplink and downlink data transmissions) to and from the source base station through the protocol entity of the first bearer while performing the random access procedure (1220).

The terminal may identify whether a second condition is satisfied (1225), and if the second condition is satisfied, the terminal may stop transmitting uplink data to the source base station through the protocol entity of the first bearer and may transmit uplink data to the target base station through the protocol entity of the second bearer while continuing to receive downlink data from the source base station and the target base station through the protocol entities of the first bearer and the second bearer (1230). In addition, the PDCP entity of the second bearer can continue seamless data transmission to and reception from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, etc., stored in the PDCP entity of the first bearer. The second condition may be one of the following conditions.

-when the terminal performs a procedure of random access to the target base station through the entity of the second bearer and receives a random access response

If the second condition is not satisfied in the above-described steps, the terminal may repeatedly check the second condition while continuing the existing procedure, that is, the procedure of transmitting and receiving data to and from the source base station and connecting to the target base station (1235).

Meanwhile, if the first condition is satisfied (1240), the terminal may stop receiving downlink data from the source base station through the protocol entity of the first bearer (1245). In addition, the PDCP entity of the second bearer can continue seamless data transmission to and reception from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, etc., stored in the PDCP entity of the first bearer. The first condition may be one of the following conditions.

The source base station may determine a time to stop transmitting downlink data to the terminal or a time to release a connection with the terminal based on a predetermined method when performing the efficient handover proposed in the present disclosure. For example, the predetermined method may include at least one of: when a predetermined timer expires (the timer may be started after the handover indication); or when an indication is received from the target indicating that the terminal has successfully performed a handover to the target base station. In addition, if downlink data is not received from the source base station within a predetermined period of time, the terminal may determine that the connection with the source base station is released and may release the connection.

If the first condition is not satisfied in the above step, the terminal may repeatedly check the first condition while continuing the existing procedure (1250).

In the present disclosure, the operation of the PDCP entity is to prevent the occurrence of data interruption time and data loss while performing the embodiment (the first, second, third, fourth, fifth, or 5-2 embodiment) of the handover procedure proposed in the present disclosure for minimizing the data interruption time. Therefore, hereinafter, an embodiment of a PDCP entity procedure supporting the handover procedure proposed by the present disclosure to minimize a data interruption time is proposed.

Indicators may be defined for various embodiments of the handover procedure set forth in this disclosure for minimizing data interruption time. Accordingly, when the base station transmits a handover command message to the terminal (620) in fig. 6, an embodiment of a PDCP entity procedure supporting a handover procedure for minimizing a data interruption time according to the present disclosure may indicate a handover procedure corresponding to a specific embodiment to be triggered to the terminal using the handover command message (e.g., rrcreeconfiguration message). Accordingly, the terminal can perform a handover procedure according to the handover method indicated by the handover command message, thereby performing handover to the target base station while minimizing the data interruption time.

In addition, an indicator of an embodiment of a PDCP entity procedure in a handover procedure proposed in the present disclosure for minimizing a data interruption time may be defined for each bearer or each PDCP entity. Accordingly, the base station may indicate a PDCP entity procedure corresponding to a specific embodiment to be triggered to the terminal using a handover command message (e.g., rrcreeconfiguration message), so that the terminal may perform the indicated PDCP entity procedure.

Hereinafter, the present disclosure proposes a first embodiment of a PDCP entity procedure supporting the handover procedure for minimizing a data interruption time proposed in the present disclosure.

In a first embodiment of the PDCP entity procedure proposed in the present disclosure, specific operations of the transmitting PDCP entity and the receiving PDCP entity are as follows. The first embodiment may be referred to as "PDCP re-establishment".

If an upper layer entity (e.g., an RRC entity) requests a first embodiment of a PDCP entity procedure for a certain bearer, or if an indicator indicates the first embodiment of the PDCP entity procedure when a handover command message or a "rrcreeconfiguration" message is received by a terminal, a transmitting PDCP entity may perform at least one of the following procedures.

1. If there is no indicator that UM DRB and AM DRB continue to use the header compression protocol, the transmitting PDCP entity may initialize the header compression protocol and start the header compression protocol in a unidirectional (U) mode of Initialization and Refresh (IR) state.

2. The transmitting PDCP entity sets a window state variable (e.g., TX _ NEXT) of the UM DRB and the SRB to an initial value.

3. As for the SRB, the transmitting PDCP entity discards all stored data (e.g., PDCP SDUs or PDCP PDUs) (since data is an RRC message generated for transmission to the source base station, it discards them to avoid transmitting them to the target base station).

4. The transmitting PDCP entity applies the new security key and the new ciphering algorithm received from the upper layer entity (e.g., the RRC entity).

5. The transmitting PDCP entity applies the new security key and the new integrity protection algorithm received from the upper layer entity (e.g., RRC entity).

6. As for the UM DRB, the transmitting PDCP entity regards data (e.g., PDCP SDUs), which has been allocated a PDCP sequence number but has not been transmitted to a lower entity (after discarding all existing stored PDCP PDUs), as data received from an upper layer (e.g., an SDAP entity or a TCP/IP entity), and transmits the data in an ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment. In addition, the transmitting PDCP entity does not restart the data discard timer. Specifically, the transmitting PDCP entity performs a new header compression procedure on data (PDCP SDU), performs an integrity procedure or a ciphering procedure again, configures a PDCP header, and transmits it to a lower entity.

7. As for the AM DRB, the transmitting PDCP entity may perform a new header compression process on data (after discarding all existing stored PDCP PDUs) in ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment, starting from the first data (e.g., PDCP SDU) that the lower layer entity (e.g., RLC entity) has not yet confirmed its successful delivery, may perform an integrity process or ciphering process again, configure a PDCP header, and may transmit it to the lower layer entity, thereby performing retransmission or transmission. In other words, the transmitting PDCP entity performs retransmission by accumulating data starting from the first data for which successful delivery has not been acknowledged.

If an upper layer entity (e.g., an RRC entity) requests a first embodiment of a PDCP entity procedure for a certain bearer or if the first embodiment of the PDCP entity procedure is indicated when a terminal receives a handover command message or an RRC reconfiguration message, the receiving PDCP entity may perform the following procedure.

1. The receiving PDCP entity processes data (e.g., PDCP PDUs) received from a lower layer entity due to re-establishment of the lower layer entity (e.g., RLC entity).

2. As for the SRB, the receiving PDCP entity discards all stored data (e.g., PDCP SDUs or PDCP PDUs) (the receiving PDCP entity discards the date since the data is an RRC message received from the source base station).

3. The receiving PDCP entity may stop and reset the timer if a reordering timer is running for the SRB and UM DRB. In addition, the receiving PDCP entity may perform a header decompression procedure on all data (e.g., PDCP SDUs) stored for the UM DRB and transmit it to an upper entity.

4. If there is no indicator to continue using the header decompression protocol for the AM DRB, the receiving PDCP entity performs a header decompression procedure on the stored data (e.g., PDCP SDUs).

5. If there is no indicator to continue using the header decompression protocol for the UM DRB and the AM DRB, the receiving PDCP entity initializes the downlink header decompression protocol and starts the downlink header decompression protocol in a unidirectional (U) mode without a context (NC) state.

6. The receiving PDCP entity sets window variables (e.g., RX _ NEXT and RX _ DELIV) of UM DRB and SRB to an initial value.

7. The receiving PDCP entity applies the new security key and the new ciphering/deciphering algorithm received from the upper entity (e.g., the RRC entity).

8. The receiving PDCP entity applies the new security key and the new integrity protection/verification algorithm received from the upper entity (e.g., RRC entity).

Hereinafter, the present disclosure proposes a second embodiment of a PDCP entity procedure supporting the handover procedure for minimizing the data interruption time proposed in the present disclosure.

In a second embodiment of the PDCP entity procedure proposed in the present disclosure, the specific operations of the transmitting PDCP entity and the receiving PDCP entity are as follows. The second embodiment may be referred to as "PDCP data recovery".

If an upper layer entity (e.g., RRC entity) requests the second embodiment of the PDCP entity procedure for a certain bearer, or if the indicator indicates the second embodiment of the PDCP entity procedure when the terminal receives a handover command message or a "rrcreeconfiguration" message, the transmitting PDCP entity may perform at least one of the following procedures.

1. If an upper layer entity (e.g., an RRC entity) requests a PDCP data recovery procedure for the AM DRB, the transmitting PDCP entity may perform the following procedure.

A. The transmitting PDCP entity may perform selective retransmission only on all data, of which the lower layer entity (e.g., RLC entity) has not yet confirmed its successful transmission (RLC ACK), among data (e.g., PDCP PDUs) previously transmitted to the re-established AM RLC entity or the disconnected AM RLC entity in ascending order of the count value (or PDCP sequence number). The transmission and retransmission may be performed on data previously stored in the buffer, or in the case where data has not been generated, the data may be generated first and then the transmission and retransmission may be performed on the generated data.

Hereinafter, the present disclosure proposes a third embodiment of a PDCP entity procedure supporting the handover procedure for minimizing the data interruption time proposed in the present disclosure.

In a third embodiment of the PDCP entity procedure proposed in the present disclosure, the specific operations of the transmitting PDCP entity and the receiving PDCP entity are as follows. The third embodiment may be referred to as "PDCP extension" or another name. In addition, the third embodiment may be configured as the 3 rd to 1 st embodiment and the 3 rd to 2 nd embodiment.

If an upper layer entity (e.g., an RRC entity) requests a 3 rd-1 embodiment of a PDCP entity procedure for a certain bearer or if an indicator indicates the 3 rd-1 embodiment of the PDCP entity procedure when a handover command message or a "rrcreeconfiguration" message is received by a terminal, a transmitting PDCP entity may perform one or more of the following procedures.

As another method, if the handover command message includes an indicator indicating the fourth or fifth embodiment proposed for handover in the present disclosure, the transmitting PDCP entity may perform one or more of a plurality of procedures in the following 3-1 embodiment.

1. If there is no indicator to continue using the header compression protocol for UM DRBs and AM DRBs, the sending PDCP entity initializes the header compression protocol and starts the header compression protocol in a one-way (U) mode of Initialization and Refresh (IR) state.

2. Since data transmission to the source and target base stations is continued to minimize the data interruption time, the transmitting PDCP entity does not initialize a window variable (e.g., TX _ NEXT) for the UM DRB.

3. If the handover command message is received from the source base station, the terminal may set a window state variable (e.g., TX _ NEXT) of the SRB to an initial value since the terminal no longer transmits and receives RRC messages to and from the source base station. Alternatively, the terminal may release the SRB of the source base station. In addition, the terminal may also set a window state variable (e.g., TX _ NEXT) to an initial value for the SRB of the second bearer for the target base station.

As another method, if the terminal cannot perform handover to the target base station, the terminal may transmit a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration request message through the SRB of the source base station while maintaining the SRB connection with the source base station, thereby reducing transmission delay due to the handover failure. As another method, the terminal may discard data (PDCP SDU or PDCP PDU) stored in the SRB while maintaining the SRB connection with the above source base station, and may set its window state variable (e.g., TX _ NEXT) to an initial value, thereby preventing a gap of PDCP sequence numbers from occurring later when a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration message is transmitted through the SRB of the source base station.

4. If a handover command message is received from the source base station, the terminal may discard all data (e.g., PDCP SDUs or PDCP PDUs) stored for the SRBs, since it is no longer necessary to send and receive RRC messages to and from the source base station (since data is a resulting RRC message intended for the source base station, the terminal discards the data to avoid sending it to the target base station).

5. The transmitting PDCP entity may store and prepare the new security key and the new ciphering algorithm received from an upper entity (e.g., RRC entity), and may apply them to the PDCP entity for the second bearer of the target base station and to data. In addition, the transmitting PDCP entity may continue to apply the old security key and ciphering algorithm used before receiving the new security key and ciphering algorithm from the upper entity to the PDCP entity for the first bearer of the source base station and to the data.

6. The transmitting PDCP entity may store and prepare the new security key and the new integrity protection algorithm received from an upper entity (e.g., RRC entity), and may apply them to the PDCP entity for the second bearer of the target base station and to data. In addition, the transmitting PDCP entity may continue to apply the security key and the integrity protection algorithm used before receiving the new security key and integrity protection algorithm from the upper entity to the PDCP entity for the first bearer of the source base station and to the data.

7. The transmitting PDCP entity may transmit a PDCP status report to the source base station when necessary, configured, or indicated, or at any time, thereby reporting the current transmission/reception status of data (e.g., successful or unsuccessful data reception).

8. If a user data compression process (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize buffers for the user data compression process for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using the dictionary information. As another method, the terminal may initialize the buffer if there is no indicator of the buffer contents for continuing to use the user data compression process. As another method, if dictionary information is predefined, the buffer may be initialized using the dictionary information. In addition, the terminal may apply user data compression configuration to the target base station and may initialize the buffer.

If an upper layer entity (e.g., an RRC entity) requests a 3 rd-1 embodiment of a PDCP entity procedure for a certain bearer or if an indicator indicates the 3 rd-1 embodiment of the PDCP entity procedure when a handover command message or an RRC reconfiguration message is received by a terminal, the receiving PDCP entity may perform one or more of the following procedures.

As another method, if the handover command message includes an indicator indicating the fourth or fifth embodiment proposed in the present disclosure for handover, the receiving PDCP entity may perform one or more of a plurality of procedures in the following 3-1 embodiment.

1. If a handover command message is received from the source base station, the terminal may discard all data (e.g., PDCP SDUs or PDCP PDUs) stored for the SRBs (data is discarded because it is an RRC message received from the source base station) since the terminal no longer transmits and receives RRC messages to and from the source base station.

In addition, the terminal may stop the reordering timer if the reordering timer is running. Alternatively, the terminal may release the SRB for the source base station. In addition, the terminal may set window variables (e.g., RX _ NEXT and RX _ DELIV) to initial values for the SRB of the second bearer for the target base station, and may stop the reordering timer if the reordering timer is running.

As another method, if the terminal cannot perform handover to the target base station, the terminal may transmit a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration request message through the SRB of the source base station while maintaining the SRB connection with the source base station, thereby reducing transmission delay due to the handover failure. As another method, the terminal may discard data (PDCP SDU or PDCP PDU) stored in the SRB while maintaining the SRB connection with the above source base station, and may set a window state variable (e.g., RX _ NEXT) to an initial value, thereby preventing a gap of PDCP sequence numbers from occurring later when a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration message is transmitted to the SRB of the source base station.

2. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of data, there is no need to separately process stored data for the UM DRB.

3. If the reordering timer is running for the SRB and the UM DRB, the receiving PDCP entity stops and resets the timer, performs a header decompression procedure on all data (e.g., PDCP SDUs) stored for the UM DRB, and transmits it to an upper layer entity.

6. Since data continues to be received from the source or target base station without interrupting the transmission and reception of data, the receiving PDCP entity does not set window state variables (e.g., RX _ NEXT and RX _ DELIV) to initial values for the UM DRB.

7. The receiving PDCP entity may store and prepare the new security key and the new ciphering algorithm received from the upper entity (e.g., RRC entity), and may apply them to the PDCP entity for the second bearer of the target base station and to data. In addition, the receiving PDCP entity may continue to apply the security key and the ciphering algorithm used before receiving the new security key and the ciphering algorithm from the upper entity to the PDCP entity for the first bearer of the source base station and to the data.

8. The receiving PDCP entity may store and prepare the new security key and the new integrity protection algorithm received from an upper entity (e.g., RRC entity), and may apply them to the PDCP entity for the second bearer of the target base station and to data. In addition, the receiving DCP entity may continue to apply the security key and integrity protection algorithm used before receiving the new security key and integrity protection algorithm from the upper entity to the PDCP entity for the first bearer of the source base station and to the data.

9. Upon receiving the PDCP status report, the receiving PDCP entity may read the current status of transmitted data to and received data from the source or target base station (e.g., successful or unsuccessful data reception), and may reflect it on the transmission or retransmission of the data. For example, the receiving PDCP entity may not perform transmission or retransmission of data for which successful delivery has been acknowledged.

10. If a user data compression process (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize buffers for the user data compression process for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using the dictionary information. As another method, the terminal may initialize the buffer if there is no indicator of the buffer contents for continuing to use the user data compression process. As another method, if dictionary information is predefined, the buffer may be initialized using the dictionary information. In addition, the terminal may apply user data compression configuration to the target base station and may initialize the buffer.

If an upper layer entity (e.g., an RRC entity) requests a 3 rd-2 embodiment of a PDCP entity procedure for a certain bearer, or if a third condition is satisfied, a transmitting PDCP entity of the terminal may perform the 3 rd-2 embodiment, and specifically, perform one or more of the following procedures.

1. The transmitting PDCP entity may apply the new security key and the new ciphering algorithm, which are received and stored from an upper entity (e.g., an RRC entity), to the PDCP entity for the second bearer of the target base station and to data. In addition, the transmitting PDCP entity may release or discard the security key and the ciphering algorithm applied to the PDCP entity of the first bearer of the source base station before receiving the new security key and the ciphering algorithm from the upper entity.

As another method, the transmitting PDCP entity may release a security key and a ciphering algorithm applied to the PDCP entity of the first bearer of the source base station in an uplink, and may maintain the security key and the ciphering algorithm and apply them to data received in a downlink. As another method, the transmitting PDCP entity may discard or release the security key and ciphering algorithm applied to the PDCP entity of the first bearer of the source base station when the connection (e.g., downlink data reception) with the source base station is completely released, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.

2. The transmitting PDCP entity may apply the new security key and the integrity verification algorithm, which are received and stored from an upper layer entity (e.g., RRC entity), to the PDCP entity for the second bearer of the target base station and to data. In addition, the transmitting PDCP entity may release or discard the security key and integrity verification algorithm applied to the PDCP entity of the first bearer of the source base station before receiving the new security key and ciphering algorithm from the upper entity.

3. The transmitting PDCP entity may transmit a PDCP status report to the source or target base station when necessary, configured, or indicated, or at any time, thereby reporting the current transmission/reception status of data (e.g., successful or unsuccessful data reception).

4. As for the UM DRB, the transmitting PDCP entity regards data (e.g., PDCP SDUs), which has been allocated a PDCP sequence number but has not been transmitted to a lower entity (after discarding all existing stored PDCP PDUs), as data received from an upper layer (e.g., an SDAP entity or a TCP/IP entity), and transmits the data in an ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment. In addition, the terminal does not restart the data discard timer. Specifically, the transmitting PDCP entity performs a new header compression procedure on data (PDCP SDU), performs an integrity procedure or a ciphering procedure again, configures a PDCP header, and transmits it to a lower entity.

5. As for AM DRB, the transmitting PDCP entity may perform a new header compression procedure on data (after discarding all existing stored PDCP PDUs) in ascending order of count values (or PDCP sequence numbers) assigned before PDCP re-establishment (or before satisfying a third condition or before receiving an RRC message) starting from the first data (e.g., PDCP SDU) for which the lower layer entity (e.g., RLC entity) has not yet acknowledged its successful delivery. In addition, the transmitting PDCP entity may perform the integrity procedure or the ciphering procedure again, configure a PDCP header, and may transmit it to a lower layer entity, thereby performing retransmission or transmission. That is, the transmitting PDCP entity performs retransmission by accumulating data starting from the first data whose successful delivery has not been confirmed.

As another approach, when performing retransmission, the transmitting PDCP entity may perform retransmission only for data whose successful delivery has not been acknowledged by the lower layer entity (e.g., RLC entity). More specifically, as for the AM DRB, the transmitting PDCP entity (after discarding all stored PDCP PDUs to be transmitted to the source base station through the first protocol entity previously connected to the PDCP entity) may release a lower layer entity (e.g., an RLC entity or a MAC entity) that is the first protocol entity for transmitting data to the source base station. In addition, the transmitting PDCP entity may start from first data (e.g., PDCP SDU) whose successful transmission has not been confirmed by a lower layer entity (e.g., RLC entity) as a first protocol entity for transmitting data to the source base station, perform a new header or data compression procedure by applying a security key or a header compression (or data compression) protocol context corresponding to the target base station in an ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment (or before a third condition is satisfied or before an RRC message is received), may perform an integrity or ciphering procedure again, may configure a PDCP header, and may transmit it to a lower layer entity as a second protocol entity for transmitting data to the target base station, thereby performing retransmission or transmission. That is, the transmitting PDCP entity can perform retransmission by accumulating data from the first data whose successful delivery has not been confirmed.

As another method, when performing retransmission, the transmitting PDCP entity transmits only data, whose successful delivery has not been confirmed by a lower layer entity (e.g., RLC entity) that is a first protocol entity for transmitting data to the source base station, to a lower layer entity that is a second protocol entity for transmitting data to the target base station, thereby performing selective retransmission. As another method, a transmission or retransmission operation may be performed after releasing a lower layer entity (e.g., an RLC entity or a MAC entity) that is a first protocol entity for transmitting data to the source base station.

6. If a user data compression process (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize buffers for the user data compression process for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using the dictionary information. In addition, the terminal may release the user compression configuration for the source base station and may release the buffer.

If an upper layer entity (e.g., an RRC entity) requests a 3 rd-2 embodiment of a PDCP entity procedure for a certain bearer, or if a third condition is satisfied, a receiving PDCP entity of the terminal may perform the 3 rd-2 embodiment, and specifically, perform one or more of the following multiple procedures.

1. If data (e.g., PDCP PDUs) are received from a lower layer entity due to re-establishment of the lower layer entity (e.g., RLC entity), the receiving PDCP entity processes the data.

3. Since data continues to be received from the source or target base station without interrupting the transmission and reception of data, the receiving PDCP entity does not set window state variables (e.g., RX _ NEXT and RX _ DELIV) to initial values for AM DRBs or UM DRBs.

4. The receiving PDCP entity may apply the new security key and the new ciphering algorithm, which are received and stored from an upper entity (e.g., an RRC entity), to the PDCP entity for the second bearer of the target base station and to data. In addition, if downlink data is no longer received from the source base station, the receiving PDCP entity may release or discard the security key and ciphering algorithm applied to the PDCP entity of the first bearer of the source base station before receiving a new security key and ciphering algorithm from the upper layer entity.

As another method, the receiving PDCP entity may release a security key and a ciphering algorithm applied to the PDCP entity of the first bearer of the source base station in an uplink, and may maintain the security key and the ciphering algorithm and apply them to data received in a downlink. As another method, the receiving PDCP entity may discard or release the security key and ciphering algorithm applied to the PDCP entity of the first bearer of the source base station when the connection (e.g., downlink data reception) with the source base station is completely released, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.

5. The receiving PDCP entity may apply the new security key and the new integrity verification algorithm, which are received and stored from an upper entity (e.g., an RRC entity), to the PDCP entity for the second bearer of the target base station and to data. In addition, if downlink data is no longer received from the source base station, the receiving PDCP entity may release or discard the security key and ciphering algorithm applied to the PDCP entity of the first bearer of the source base station before receiving the new security key and integrity verification algorithm from the upper layer entity.

6. Upon receiving the PDCP status report, the receiving PDCP entity may read the current status of transmitted data to and received data from the source or target base station (e.g., successful or unsuccessful data reception), and may reflect it on the transmission or retransmission of the data. For example, the receiving PDCP entity may not perform transmission or retransmission of data for which successful delivery has been acknowledged.

7. If a user data compression process (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize buffers for the user data compression process for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using the dictionary information. In addition, the terminal may release the user compression configuration for the source base station and may release the buffer.

The third condition may be one of the following conditions.

When the terminal receives an indication { e.g., an RRC message (e.g., "RRCREConfiguration" message), a MAC CE, an RLC control PDU, or a PDCP control PDU } from the target base station to handover the uplink to the target base station

When the terminal receives an indication { e.g., an RRC message (e.g., "RRCREConfiguration" message), a MAC CE, an RLC control PDU, or a PDCP control PDU } from the source base station to handover the uplink to the target base station

-when the terminal releases the connection with the source base station and releases the first protocol entity

When the terminal transmits a predetermined preamble to the cell of the target base station and receives a Random Access Response (RAR) message, the terminal may determine that the random access procedure is successfully completed. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the third condition is satisfied.

When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included, or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that a process of randomly accessing the target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal or initially receives an indication of the uplink transmission resource, the terminal may determine that the third condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the third condition is satisfied.

When the terminal transmits a message 3 (e.g., a handover complete message or a "rrcreeconfigurationcomplete" message) using uplink transmission resources of the target base station and receives a UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the third condition is satisfied. As another method, the terminal may determine that the third condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.

When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "rrcreeconfiguration complete" message) using the uplink transmission resource and receives a UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the third condition is satisfied. As another method, the terminal may determine that the third condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.

If the third condition is not satisfied in the above-described steps, the terminal may repeatedly check the third condition while continuing the existing procedure.

Hereinafter, the present disclosure proposes a fourth embodiment of a PDCP entity procedure supporting the handover procedure for minimizing the data interruption time proposed in the present disclosure.

In a fourth embodiment of the PDCP entity procedure proposed in the present disclosure, the specific operations of the transmitting PDCP entity and the receiving PDCP entity are as follows. The fourth embodiment may be referred to as "PDCP extension" or another name. In addition, the fourth embodiment may be configured as the 4 th-1 st embodiment and the 4 th-2 nd embodiment. In the fourth embodiment, since data continues to be transmitted and received, a process for initializing or handling a header compression protocol is not required.

If an upper layer entity (e.g., an RRC entity) requests a 4 th-1 th embodiment of a PDCP entity procedure for a certain bearer or if an indicator indicates the 4 th-1 th embodiment of the PDCP entity procedure when a handover command message or a "rrcreeconfiguration" message is received by a terminal, a transmitting PDCP entity may perform one or more of the following procedures.

As another method, if the handover command message contains an indicator applying the fourth embodiment or the fifth embodiment proposed in the present disclosure to the handover, the transmitting PDCP entity may perform one or more of the following processes in the 4 th-1 th embodiment.

1. Since data transmission to the source and target base stations is continued to minimize the data interruption time, the transmitting PDCP entity does not initialize a window variable (e.g., TX _ NEXT) for the UM DRB.

2. If a handover command message is received from the source base station, the terminal may set a window state variable (e.g., TX _ NEXT) to an initial value for the SRB or may release the SRB for the source base station since the terminal is no longer transmitting and receiving RRC messages to and from the source base station. In addition, the terminal may set a window state variable (e.g., TX _ NEXT) to an initial value for the SRB of the second bearer for the target base station.

3. If a handover command message is received from the source base station, the terminal may discard all data (e.g., PDCP SDUs or PDCP PDUs) stored for the SRBs, since it is no longer necessary to send and receive RRC messages to and from the source base station (since data is a resulting RRC message intended for the source base station, the terminal discards the data to avoid sending it to the target base station).

As another method, if the terminal cannot perform handover to the target base station, the transmitting PDCP entity may transmit a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration request message through the SRB of the source base station while maintaining the SRB connection with the source base station, thereby reducing transmission delay due to the handover failure. As another method, the terminal may discard data (PDCP SDU or PDCP PDU) stored in the SRB while maintaining the SRB connection with the above source base station, and may set a window state variable (e.g., TX _ NEXT) to an initial value, thereby preventing a gap of PDCP sequence numbers from occurring later when a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration message is transmitted to the SRB of the source base station.

4. The transmitting PDCP entity may store and prepare the new security key and the new ciphering algorithm received from an upper entity (e.g., RRC entity), and may apply them to the PDCP entity for the second bearer of the target base station and to data. In addition, the transmitting PDCP entity may continue to apply the security key and the ciphering algorithm used before receiving the new security key and ciphering algorithm from the upper entity to the PDCP entity for the first bearer of the source base station and to the data.

5. The transmitting PDCP entity may store and prepare the new security key and the new integrity protection algorithm received from an upper entity (e.g., RRC entity), and may apply them to the PDCP entity for the second bearer of the target base station and to data. In addition, the transmitting PDCP entity may continue to apply the security key and the integrity protection algorithm used before receiving the new security key and integrity protection algorithm from the upper entity to the PDCP entity for the first bearer of the source base station and to the data.

6. The transmitting PDCP entity may transmit a PDCP status report to the source base station when necessary, configured, or indicated, or at any time, thereby reporting the current transmission/reception status of data (e.g., successful or unsuccessful data reception).

7. If a user data compression process (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize buffers for the user data compression process for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using the dictionary information. As another method, the terminal may initialize the buffer if there is no indicator of the buffer contents for continuing to use the user data compression process. As another method, if dictionary information is predefined, the buffer may be initialized using the dictionary information. In addition, the terminal may apply user data compression configuration to the target base station and may initialize the buffer.

If an upper layer entity (e.g., an RRC entity) requests a 4 th-1 th embodiment of a PDCP entity procedure for a certain bearer or if an indicator indicates the 4 th-1 th embodiment of the PDCP entity procedure when a handover command message or an RRC reconfiguration message is received by a terminal, the receiving PDCP entity may perform one or more of the following procedures.

As another method, if the handover command message includes an indicator indicating the fourth or fifth embodiment proposed for handover in the present disclosure, the accepting PDCP entity may perform one or more of a plurality of procedures in the following 4-1 embodiment.

As another method, if the terminal cannot perform handover to the target base station, the terminal may transmit a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration request message to the SRB of the source base station while maintaining the SRB connection with the source base station, thereby reducing transmission delay due to the handover failure. As another method, while maintaining the SRB connection with the above source base station, the receiving PDCP entity may discard data (PDCP SDUs or PDCP PDUs) stored in the SRB, and may set a window state variable (e.g., RX _ NEXT) to an initial value, thereby preventing a gap of PDCP sequence numbers from occurring later when a handover failure message, an RRC connection reestablishment message, or an RRC connection resumption message is transmitted to the SRB of the source base station.

3. Since data continues to be received from the source or target base station without interrupting the transmission and reception of data, the receiving PDCP entity does not set window state variables (e.g., RX _ NEXT and RX _ DELIV) to initial values for the UM DRB.

4. The receiving PDCP entity may store and prepare the new security key and the new ciphering algorithm received from the upper entity (e.g., RRC entity), and may apply them to the PDCP entity for the second bearer of the target base station and to data. In addition, the receiving PDCP entity may continue to apply the security key and the ciphering algorithm used before receiving the new security key and the ciphering algorithm from the upper entity to the PDCP entity for the first bearer of the source base station and to the data.

5. The receiving PDCP entity may store and prepare the new security key and the new integrity protection algorithm received from an upper entity (e.g., RRC entity), and may apply them to the PDCP entity for the second bearer of the target base station and to data. In addition, the receiving DCP entity may continue to apply the security key and integrity protection algorithm used before receiving the new security key and integrity protection algorithm from the upper entity to the PDCP entity for the first bearer of the source base station and to the data.

If an upper layer entity (e.g., an RRC entity) requests a 4 th-2 embodiment of a PDCP entity procedure for a certain bearer, or if a third condition is satisfied, a transmitting PDCP entity of the terminal may perform the 4 th-2 embodiment, and specifically, perform one or more of the following procedures.

2. The transmitting PDCP entity may apply the new security key and the new integrity verification algorithm, which are received and stored from an upper layer entity (e.g., an RRC entity), to the PDCP entity for the second bearer of the target base station and to data. In addition, the transmitting PDCP entity may release or discard the security key and integrity verification algorithm applied to the PDCP entity of the first bearer of the source base station before receiving the new security key and ciphering algorithm from the upper entity.

4. As for the UM DRB, the transmitting PDCP entity regards data (e.g., PDCP SDUs), which has been allocated a PDCP sequence number but has not been transmitted to a lower entity (after discarding all existing stored PDCP PDUs), as data received from an upper layer (e.g., an SDAP entity or a TCP/IP entity), and transmits the data in an ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment. In addition, the transmitting PDCP entity does not restart the data discard timer. Specifically, the transmitting PDCP entity performs a new header compression procedure on data (PDCP SDU), performs an integrity procedure or a ciphering procedure again, configures a PDCP header, and transmits it to a lower entity.

5. As for AM DRB, the transmitting PDCP entity may perform a new header compression procedure on data (after discarding all existing stored PDCP PDUs) in ascending order of count values (or PDCP sequence numbers) assigned before PDCP re-establishment (or before satisfying a third condition or before receiving an RRC message) starting from the first data (e.g., PDCP SDU) for which the lower layer entity (e.g., RLC entity) has not yet acknowledged its successful delivery. In addition, the transmitting PDCP entity may perform the integrity procedure or the ciphering procedure again, configure a PDCP header, and may transmit it to a lower layer entity, thereby performing retransmission or transmission. That is, the transmitting PDCP entity can perform retransmission by accumulating data from the first data whose successful delivery has not been confirmed.

As another approach, when performing retransmission, the transmitting PDCP entity may perform retransmission only for data whose successful delivery has not been acknowledged by the lower layer entity (e.g., RLC entity). More specifically, as for the AM DRB, the transmitting PDCP entity (after discarding all stored PDCP PDUs to be transmitted to the source base station through the first protocol entity previously connected to the PDCP entity) may release a lower layer entity (e.g., an RLC entity or a MAC entity) that is the first protocol entity for transmitting data to the source base station. The transmitting PDCP entity may start from first data (e.g., PDCP SDU) whose successful transmission has not been confirmed by a lower layer entity (e.g., RLC entity) as a first protocol entity for transmitting data to the source base station, perform a new header or data compression procedure by applying a security key or a header compression (or data compression) protocol context corresponding to the target base station in an ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment (or before a third condition is satisfied or before an RRC message is received), may perform an integrity or ciphering procedure again, may configure a PDCP header, and may transmit it to the lower layer entity as a second protocol entity for transmitting data to the target base station, thereby performing retransmission or transmission. That is, the transmitting PDCP entity can perform retransmission by accumulating data from the first data whose successful delivery has not been confirmed.

As another method, when performing retransmission, the transmitting PDCP entity transmits only data, whose successful delivery has not been confirmed by a lower layer entity (e.g., RLC entity) that is a first protocol entity for transmitting data to the source base station, to a lower layer entity that is a second protocol entity for transmitting data to the target base station, thereby performing selective retransmission. As another method, a transmission or retransmission operation may be performed after releasing a lower layer entity (e.g., RLC entity) that is a first protocol entity for transmitting data to the source base station.

If an upper layer entity (e.g., RRC entity) requests the 4 th-2 embodiment of the PDCP entity procedure for a certain bearer, or if a third condition is satisfied, a receiving PDCP entity of the terminal may perform the 4 th-2 embodiment, and specifically, perform one or more of the following procedures.

4. The receiving PDCP entity may apply the new security key and the new ciphering algorithm, which are received and stored from an upper entity (e.g., an RRC entity), to the PDCP entity for the second bearer of the target base station and to data. In addition, if downlink data is no longer received from the source base station, the receiving PDCP entity may release or discard the security key and ciphering algorithm applied to the PDCP entity of the first bearer of the source base station before receiving a new security key and ciphering algorithm from the upper layer entity. As another method, the receiving PDCP entity may release a security key and a ciphering algorithm applied to the PDCP entity of the first bearer of the source base station in an uplink, and may maintain the security key and the ciphering algorithm and apply them to data received in a downlink.

As another method, the receiving PDCP entity may discard or release the security key and ciphering algorithm applied to the PDCP entity of the first bearer of the source base station when the connection (e.g., downlink data reception) with the source base station is completely released, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.

6. Upon receiving the PDCP status report, the receiving PDCP entity may read the current status of the transmission data of the source or target base station and the reception data from the source or target base station (e.g., successful or unsuccessful data reception) and may reflect it on the transmission or retransmission of the data. For example, the receiving PDCP entity may not perform transmission or retransmission of data for which successful delivery has been acknowledged.

The third condition may be one of the following conditions.

Hereinafter, the present disclosure proposes a fifth embodiment of a PDCP entity procedure supporting the handover procedure for minimizing the data interruption time proposed in the present disclosure.

In a fifth embodiment of the PDCP entity procedure proposed in the present disclosure, the specific operations of the transmitting PDCP entity and the receiving PDCP entity are as follows. The fifth embodiment may be referred to as "PDCP extension" or another name. In addition, the fifth embodiment may be configured as the 5 th-1 st embodiment and the 5 th-2 nd embodiment.

In a fifth embodiment of the PDCP entity procedure of the present disclosure, in the PDCP entity structure shown in fig. 11, the respective lower

layer PDCP entities

1121 and 1122 can perform a header compression procedure on data to be transmitted based on different header compression protocol contexts (e.g., ROHC contexts), and can cipher the procedure using different security keys.

Specifically, the first lower layer PDCP entity 1121 may apply a header compression procedure to data (e.g., PDCP SDUs) received from an upper layer based on a first header compression protocol context (e.g., ROHC context), and may cipher the data using a first security key (a security key configured from a source base station or a target base station). In addition, the second lower layer PDCP entity 1122 can apply a header compression procedure to data (e.g., PDCP SDU) received from the upper layer based on a second header compression protocol context (e.g., ROHC context), and can cipher the data using a second security key (configured from the source base station or the target base station). The two lower layer PDCP entities can perform a header compression process and a ciphering process in parallel, thereby reducing a data processing time and a data interruption time that may occur during handover.

In a fifth embodiment of the PDCP entity procedure of the present disclosure, referring to the PDCP entity structure shown in fig. 11, the lower

layer PDCP entities

1121 and 1122 can perform a deciphering procedure on data to be received using different security keys, and can perform a header decompression procedure using different header compression protocol contexts (e.g., ROHC contexts).

In particular, the first lower layer PDCP entity 1121 may apply a header decompression process to data (e.g., PDCP SDUs) received from a lower layer entity based on a first header compression protocol context (e.g., ROHC context), and may decrypt the data using a first security key (a security key configured from a source base station or a target base station). In addition, the second lower layer PDCP entity 1122 can apply a header decompression process to data (e.g., PDCP SDUs) received from the lower layer entity based on a second header compression protocol context (e.g., ROHC context), and can decrypt the data using a second security key (configured from the source base station or the target base station). The two lower layer PDCP entities can perform a header decompression process and a deciphering process in parallel, thereby reducing data processing time and data interruption time that may occur during handover.

In the above PDCP entity structure, if an upper layer entity (e.g., RRC entity) requests the 5 th-1 st embodiment of the PDCP entity procedure for a certain bearer, or if the indicator indicates the 5 th-1 st embodiment of the PDCP entity procedure when the terminal receives a handover command message or a "rrcreeconfiguration" message, the transmitting PDCP entity may perform one or more of the following procedures.

2. If a handover command message is received from the source base station, the terminal may set a window state variable (e.g., TX _ NEXT) to an initial value for the SRB or may release the SRB for the source base station since the terminal is no longer transmitting and receiving RRC messages to and from the source base station. In addition, the terminal may also set a window state variable (e.g., TX _ NEXT) to an initial value for the SRB of the second bearer for the target base station.

As another method, if the terminal cannot perform handover to the target base station, the terminal may transmit a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration request message to the SRB of the source base station while maintaining the SRB connection with the source base station, thereby reducing transmission delay due to the handover failure. As another method, the terminal may discard data (PDCP SDU or PDCP PDU) stored in the SRB while maintaining the SRB connection with the above source base station, and may set a window state variable (e.g., TX _ NEXT) to an initial value, thereby preventing a gap of PDCP sequence numbers from occurring later when a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration message is transmitted to the SRB of the source base station.

4. The transmitting PDCP entity may store and prepare the new security key and the new ciphering algorithm received from the upper layer entity (e.g., RRC entity), and may apply them to a PDCP entity (e.g., a second lower layer PDCP entity) for the second bearer of the target base station and then to data. In addition, the transmitting PDCP entity may continue to apply the security key and the ciphering algorithm used before receiving the new security key and ciphering algorithm from the upper entity to the PDCP entity (e.g., the first lower layer ODCO entity) for the first bearer of the source base station and then to the data.

5. The transmitting PDCP entity may store and prepare the new security key and the new integrity protection algorithm received from the upper layer entity (e.g., RRC entity), and may apply them to a PDCP entity (e.g., a second lower layer PDCP entity) for the second bearer of the target base station and then to data. In addition, the transmitting PDCP entity may continue to apply the security key and integrity protection algorithm used before receiving the new security key and integrity protection algorithm from the upper layer entity to a PDCP entity (e.g., a first lower layer PDCP entity) for the first bearer of the source base station and to data.

7. If a user data compression process (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize buffers for the user data compression process for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using the dictionary information. As another method, the terminal may initialize the buffer if there is no indicator for continuing to use the buffer contents for the user data compression process. As another method, if dictionary information is predefined, the buffer may be initialized using the dictionary information. In addition, the terminal may apply user data compression configuration to the target base station and may initialize the buffer.

If an upper layer entity (e.g., an RRC entity) requests a 5 th-1 th embodiment of a PDCP entity procedure for a certain bearer or if an indicator indicates the 5 th-1 th embodiment of the PDCP entity procedure when a handover command message or a "rrcreeconfiguration" message is received by a terminal, the receiving PDCP entity may perform one or more of the following procedures.

1. If the handover command message does not have an indicator to continue using the header compression protocol for each bearer of the UM DRB and the AM DRB, the terminal may initialize the header compression protocol in a PDCP entity of the second bearer (e.g., a second lower layer PDCP entity) and may start the header compression protocol in a unidirectional (U) mode of Initializing and Refreshing (IR) status.

If the handover command message has an indicator to continue using the header compression protocol, the terminal may continue using the header compression protocol of the PDCP entity (e.g., the first lower layer PDCP entity) for the first bearer of the source base station, or may perform a header decompression procedure. In addition, the terminal can continue to use the header compression protocol context without initializing the header compression protocol in a PDCP entity (e.g., a first lower layer PDCP entity) for the first bearer of the source base station.

2. If the handover command message is received from the source base station, the receiving PDCP entity discards all data (e.g., PDCP SDUs or PDCP PDUs) stored for the SRBs (data is discarded because it is an RRC message received from the source base station) since the terminal no longer transmits and receives RRC messages to and from the source base station. In addition, the terminal may stop the timer if the reordering timer is running. Alternatively, the terminal may release the SRB for the source base station. In addition, the terminal may set window variables (e.g., RX _ NEXT and RX _ DELIV) to initial values for the SRB of the second bearer for the target base station, and may stop the reordering timer if the reordering timer is running.

3. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of data, there is no need to separately process stored data for the UM DRB.

4. The terminal may stop and reset the timer if a reordering timer is running for the SRB. As for the AM DRB, if there is no indicator to continue using the header decompression protocol for the PDCP entity corresponding to the second (or first) bearer of the target (or source) base station { e.g., the second (or first) lower layer PDCP entity }, the receiving PDCP entity may perform a header decompression procedure on the stored data (e.g., PDCP SDU) using the existing header compression protocol context. Thereafter, the receiving PDCP entity may initialize a header compression protocol context.

5. If there is no indicator to continue using the header decompression protocol for the UM DRB and AM DRB, the receiving PDCP entity initializes a downlink header decompression protocol for a PDCP entity corresponding to the second (or first) bearer of the target (or source) base station { e.g., a second (or first) lower layer PDCP entity }, and starts in a unidirectional (U) mode without a context (NC) state.

7. The receiving PDCP entity may store and prepare the new security key and the new ciphering algorithm received from the upper entity (e.g., RRC entity), and may apply them to the PDCP entity for the second bearer of the target base station and to data, or may perform deciphering. In addition, the receiving PDCP entity may continue to apply the security key and the ciphering algorithm used before receiving the new security key and the ciphering algorithm from the upper entity to the PDCP entity for the first bearer of the source base station and to the data, or may perform deciphering.

8. The receiving PDCP entity may store and prepare the new security key and the new integrity protection algorithm received from an upper entity (e.g., RRC entity), and may apply them to the PDCP entity for the second bearer of the target base station and to data, or may perform integrity protection. In addition, the receiving DCP entity may continue to apply the security key and integrity protection algorithm used before receiving the new security key and integrity protection algorithm from the upper entity to the PDCP entity for the first bearer of the source base station and to the data, or may perform integrity protection.

9. Upon receiving the PDCP status report, the receiving PDCP entity may read the current status of transmitted data to and received data from the source or target base station (e.g., successful or unsuccessful data reception) and may reflect it on the data transmission or retransmission of the transmitting PDCP entity for the source or target base station. For example, the receiving PDCP entity may not perform transmission or retransmission of data for which successful delivery has been acknowledged.

10. If a user data compression process (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize buffers for the user data compression process for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using the dictionary information. As another method, the terminal may initialize the buffer if there is no indicator for continuing to use the buffer contents for the user data compression process. As another method, if dictionary information is predefined, the buffer may be initialized using the dictionary information. In addition, the terminal may apply user data compression configuration to the target base station and may initialize the buffer.

If an upper layer entity (e.g., an RRC entity) requests a 5 th-2 embodiment of a PDCP entity procedure for a certain bearer, or if a third condition is satisfied, a transmitting PDCP entity of a terminal may perform the 5 th-2 embodiment, and specifically, perform one or more of the following procedures.

1. If the handover command message does not have an indicator to continue using the header compression protocol for each bearer of the UM DRB and the AM DRB, the terminal may initialize the header compression protocol in a PDCP entity (e.g., a second lower layer PDCP entity) for the second bearer of the target base station and may start in a unidirectional (U) mode of Initializing and Refreshing (IR) status.

If the handover command message has an indicator to continue using the header compression protocol, the terminal may continue using the header compression protocol in the PDCP entity (e.g., the first lower layer PDCP entity) for the first bearer of the source base station, or may perform a header decompression procedure.

2. The transmitting PDCP entity may apply the new security key and the new ciphering algorithm, which are received and stored from an upper entity (e.g., an RRC entity), to the PDCP entity for the second bearer of the target base station and to data. In addition, the transmitting PDCP entity may release or discard the security key and the ciphering algorithm applied to the PDCP entity of the first bearer of the source base station before receiving the new security key and the ciphering algorithm from the upper entity.

3. The transmitting PDCP entity may apply the new security key and the new integrity verification algorithm, which are received and stored from an upper layer entity (e.g., an RRC entity), to the PDCP entity for the second bearer of the target base station and to data. In addition, the transmitting PDCP entity may release or discard the security key and integrity verification algorithm applied to the PDCP entity of the first bearer of the source base station before receiving the new security key and ciphering algorithm from the upper entity.

4. The transmitting PDCP entity may transmit a PDCP status report to the source or target base station when necessary, configured, or indicated, or at any time, thereby reporting the current transmission/reception status of data (e.g., successful or unsuccessful data reception).

5. As for the UM DRB, the transmitting PDCP entity regards data (e.g., PDCP SDUs), which has been allocated a PDCP sequence number but has not been transmitted to a lower entity (after discarding all existing stored PDCP PDUs), as data received from an upper layer (e.g., an SDAP entity or a TCP/IP entity), and transmits the data in an ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment. In addition, the terminal does not restart the data discard timer. Specifically, the transmitting PDCP entity performs a new header compression procedure on data (PDCP SDU), performs an integrity procedure or a ciphering procedure again, configures a PDCP header, and transmits it to a lower entity.

6. As for AM DRB, the transmitting PDCP entity may perform a new header compression procedure on data (after discarding all existing stored PDCP PDUs) in ascending order of count values (or PDCP sequence numbers) assigned before PDCP re-establishment (or before satisfying a third condition or before receiving an RRC message) starting from the first data (e.g., PDCP SDU) for which the lower layer entity (e.g., RLC entity) has not yet acknowledged its successful delivery. In addition, the transmitting PDCP entity may perform the integrity procedure or the ciphering procedure again, configure a PDCP header, and may transmit it to a lower layer entity, thereby performing retransmission or transmission. That is, the transmitting PDCP entity can perform retransmission by accumulating data from the first data whose successful delivery has not been confirmed.

As another approach, when performing retransmission, the transmitting PDCP entity may perform retransmission only for data whose successful delivery has not been acknowledged by the lower layer entity (e.g., RLC entity). Alternatively, the transmitting PDCP entity may perform selective retransmission based on the PDCP status report. More specifically, as for the AM DRB, the transmitting PDCP entity (after discarding all stored PDCP PDUs to be transmitted to the source base station through the first protocol entity previously connected to the PDCP entity) may release a lower layer entity (e.g., an RLC entity or a MAC entity) that is the first protocol entity for transmitting data to the source base station. The transmitting PDCP entity may start from first data (e.g., PDCP SDU) whose successful transmission has not been confirmed by a lower layer entity (e.g., RLC entity) as a first protocol entity, perform a new header or data compression procedure by applying a security key or a header compression (or data compression) protocol context corresponding to the target base station in ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment (or before a third condition is satisfied or before an RRC message is received), may perform an integrity or ciphering procedure again, may configure a PDCP header, and may transmit it to the lower layer entity as a second protocol entity for transmitting data to the target base station, thereby performing retransmission or transmission. That is, the transmitting PDCP entity can perform retransmission by accumulating data from the first data whose successful delivery has not been confirmed.

If an upper layer entity (e.g., RRC entity) requests the 5 th-2 embodiment of the PDCP entity procedure for a certain bearer, or if a third condition is satisfied, a receiving PDCP entity of the terminal may perform the 5 th-2 embodiment, and specifically, perform one or more of the following procedures.

The third condition may be one of the following conditions.

The embodiments of PDCP entity procedure proposed in this disclosure can be extended and applied to such a structure: wherein the upper layer PDCP entity performs a header compression process on data transmitted in the PDCP entity structure shown in fig. 11 using a common header compression protocol context (e.g., ROHC context), and wherein the respective lower

layer PDCP entities

1121 and 1122 perform a ciphering process on the data using different security keys.

In addition, the embodiments of the PDCP entity procedure proposed in this disclosure can be extended and applied to such a structure: wherein the respective lower

layer PDCP entities

1121 and 1122 perform a deciphering process on data received in the PDCP entity structure shown in fig. 11 using different security keys, and wherein the upper layer PDCP entity performs a header decompression process on the data using a common header compression protocol context (e.g., ROHC context).

According to a specific embodiment of the PDCP entity proposed in the present disclosure, different procedures may be performed as follows depending on a handover type indicated by a handover command message received by a terminal.

-if the handover type indicated in the handover command message received by the terminal from the source base station is a first handover (e.g. normal handover procedure)

The terminal may perform a first embodiment of the PDCP entity proposed in this disclosure (e.g., PDCP re-establishment).

If the handover type indicated in the handover command message received by the terminal from the source base station is the second handover (e.g. the handover method of the fourth or fifth embodiment proposed in this disclosure)

The terminal may perform the third, fourth, or fifth embodiments of the PDCP entity proposed in this disclosure (e.g., PDCP entity continuation).

In addition, in a case where the source base station in the present disclosure instructs the terminal to perform handover applying the embodiments proposed in the present disclosure, the source base station may start forwarding data to the target base station when the following fifth condition is satisfied. The fifth condition may mean that one or more of the following conditions are satisfied.

When the terminal receives an indication from the target base station indicating that the handover has been successfully completed

-when a handover command message is sent to the terminal

-when a handover command message is sent to the terminal and successful delivery of the handover command message (HARQ ACK, NACK, RLC ACK or NACK) is acknowledged

-when the source base station receives an indication { e.g. RRC message (e.g. "rrcreeconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the terminal to release the connection with the source base station

-when a predetermined timer is driven after sending a handover command message to the terminal and then the timer expires

-when an acknowledgement of successful transmission of downlink data (HARQ ACK, NACK, RLC ACK or NACK) is not received from the terminal within a predetermined time

Fig. 13 shows a structure of a terminal to which the embodiment can be applied.

Referring to fig. 13, the terminal includes a Radio Frequency (RF) processor 1310, a baseband processor 1320, a memory unit 1330, and a controller 1340.

The RF processor 1310 performs functions of transmitting and receiving signals through a wireless channel, such as band conversion and amplification of the signals. That is, the RF processor 1310 up-converts a baseband signal provided from the baseband processor 1320 into an RF band signal, thereby transmitting the RF band signal through an antenna, and down-converts an RF band signal received through the antenna into a baseband signal. For example, the RF processor 1310 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), and the like. Although only one antenna is shown in fig. 13, the terminal may have a plurality of antennas. In addition, the RF processor 1310 may include a plurality of RF chains. In addition, the RF processor 1310 may perform beamforming. To perform beamforming, the RF processor 1310 may adjust the phase and amplitude of signals transmitted and received through multiple antennas or antenna elements. In addition, the RF processor may perform MIMO and may receive a plurality of layers when performing MIMO operation. The RF processor 1310 may perform receive beam scanning by appropriately setting a plurality of antennas or antenna elements under the control of the controller, or may adjust the direction and beam width of a receive beam so that the receive beam is coordinated with a transmit beam.

The baseband processor 1320 performs a function of converting between a baseband signal and a bit string according to the physical layer specification of the system. For example, in case of data transmission, the baseband processor 1320 encodes and modulates a transmission bit string, thereby generating complex symbols. In addition, upon receiving data, the baseband processor 1320 demodulates and decodes a baseband signal provided from the RF processor 1310, thereby restoring a reception bit string. For example, in case of applying an Orthogonal Frequency Division Multiplexing (OFDM) scheme, when transmitting data, the baseband processor 1320 generates complex symbols by encoding and modulating a transmission bit string, maps the complex symbols to subcarriers, and then configures the OFDM symbols by an Inverse Fast Fourier Transform (IFFT) operation and Cyclic Prefix (CP) insertion. In addition, when receiving data, the baseband processor 1320 divides a baseband signal provided from the RF processor 1310 into OFDM symbol units, restores a signal mapped to a subcarrier through a Fast Fourier Transform (FFT) operation, and then restores a received bit string through demodulation and decoding.

The baseband processor 1320 and the RF processor 1310 transmit and receive signals as described above. Accordingly, the baseband processor 1320 and the RF processor 1310 may be referred to as a "transmitter", "receiver", "transceiver", or "communication unit". Further, at least one of the baseband processor 1320 and the RF processor 1310 may include a plurality of communication modules to support a plurality of different radio access technologies. In addition, at least one of the baseband processor 1320 and the RF processor 1310 may include different communication modules to process signals of different frequency bands. For example, the different radio access technologies may include LTE networks, NR networks, and the like. In addition, the different frequency bands may include an ultra high frequency (SHF) (e.g., 2.5Ghz or 5Ghz) band and a millimeter wave (e.g., 60Ghz) band.

The storage unit 1330 stores data such as basic programs for the operation of the terminal, application programs, and configuration information. The storage unit 1330 provides the stored data in response to a request from the controller 1340.

The controller 1340 controls the overall operation of the terminal. For example, the controller 1340 transmits and receives signals through the baseband processor 1320 and the RF processor 1310. In addition, the controller 1340 records and reads data in and from the storage unit 1330. To this end, the controller 1340 may include at least one processor. For example, the controller 1340 may include a Communication Processor (CP) for controlling communication and an Application Processor (AP) for controlling an upper layer such as an application program. In some embodiments, controller 1340 includes a multi-connection processor 1342.

As shown in fig. 14, the base station includes an RF processor 1410, a baseband processor 1420, a backhaul transceiver 1430, a storage unit (or memory) 1440, and a controller 1450.

The RF processor 1410 performs functions of transmitting and receiving signals, such as band conversion and amplification of the signals, through a radio channel. That is, the RF processor 1410 up-converts a baseband signal provided from the baseband processor 1420 into an RF band signal, thereby transmitting the RF band signal through an antenna, and down-converts an RF band signal received through the antenna into a baseband signal. For example, the RF processor 1410 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, and the like. Although only one antenna is shown in the drawing, the first access node may have a plurality of antennas. In addition, the RF processor 1410 may include a plurality of RF chains. Further, the RF processor 1410 may perform beamforming. To perform beamforming, the RF processor 1410 may adjust phases and amplitudes of signals transmitted and received through a plurality of antennas or antenna elements. The RF processor may perform downlink MIMO operations by transmitting one or more layers.

The baseband processor 1420 performs a function of converting between a baseband signal and a bit string according to a physical layer specification of the first radio access technology. For example, in case of data transmission, the baseband processor 1420 encodes and modulates a transmission bit string, thereby generating complex symbols. In addition, upon receiving data, the baseband processor 1420 demodulates and decodes a baseband signal provided from the RF processor 1410, thereby restoring a reception bit string. For example, in case of applying the OFDM scheme, when transmitting data, the baseband processor 1420 generates complex symbols by encoding and modulating a transmission bit string, maps the complex symbols to subcarriers, and then configures the OFDM symbols through an IFFT operation and CP insertion. In addition, when receiving data, the baseband processor 1420 divides a baseband signal provided from the RF processor 1410 into OFDM symbol units, restores a signal mapped to subcarriers through an FFT operation, and then restores a received bit string through demodulation and decoding. The baseband processor 1420 and the RF processor 1410 transmit and receive signals as described above. Accordingly, the baseband processor 1420 and the RF processor 1410 may be referred to as a "transmitter", "receiver", "transceiver", "communication unit" or "wireless communication unit".

The transceiver 1430 provides an interface for performing communication with other nodes in the network.

The storage unit 1440 stores data such as a basic program for the operation of the main base station, an application program, and configuration information. Specifically, the storage unit 1440 may store information on bearers allocated to the connected terminals, measurement results reported from the connected terminals, and the like. In addition, the storage unit 1440 may store information as a criterion for determining whether multi-connection is provided to the terminal or released. In addition, the storage unit 1440 provides stored data in response to a request from the controller 1450.

The controller 1450 controls the overall operation of the main base station. For example, controller 1450 transmits and receives signals through baseband processor 1420 and RF processor 1410 or backhaul transceiver 1430. In addition, the controller 1450 records data in and reads data from the storage unit 1440. To this end, the controller 1450 may include at least one processor. In some embodiments, controller 1450 includes a multi-connection processor 1452.

Meanwhile, the order in which the methods of the present disclosure are explained with reference to the drawings does not necessarily correspond to the order in which the methods are performed, and the order thereof may be changed or performed in parallel.

Alternatively, only some elements may be included and some elements omitted from the drawings describing the methods of the present disclosure without departing from the scope of the present disclosure.

Additionally, the methods of the present disclosure may be performed in conjunction with some or all of the content included in the various embodiments without departing from the scope of the present disclosure.

Further, information contained in a message of the present disclosure is intended to explain examples of the present disclosure, and some information may be omitted therefrom or additional information may be included therein.

While the present disclosure has been described with various embodiments, various changes and modifications may be suggested to one skilled in the art. The present disclosure is intended to embrace such alterations and modifications as fall within the scope of the appended claims.

Claims

1. A method of a terminal in a wireless communication system, the method comprising:

receiving a message from a first base station through radio resource control, RRC, signaling, the message including a handover command from the first base station to a second base station;

identifying that the message includes information indicating a dual protocol stack switch; and

receiving data from the first base station until a cell of the first base station is released, in case the message comprises information indicating a dual protocol stack handover.

2. The method of claim 1, further comprising:

transmitting uplink data to the first base station until a random access procedure to the second base station is successfully completed; and

and transmitting uplink data to the second base station when the random access process is successfully completed.

3. The method of claim 1, wherein receiving the message comprising the handover command comprises:

establishing a medium access control, MAC, entity and a radio link control, RLC, entity for a second bearer corresponding to the second base station on receipt of the message, an

Reconfiguring a packet data convergence protocol, PDCP, entity for the second bearer.

4. The method according to claim 3, wherein header compression and decompression ROHC functions and security are performed on data for the first base station and the second base station in a packet data convergence protocol, PDCP, entity for the first base station and the second base station.

5. The method of claim 1, wherein a state variable of a packet data convergence protocol PDCP entity is not initialized.

6. A method of a first base station in a wireless communication system, the method comprising:

Transmitting a message to the terminal through radio resource control, RRC, signaling, the message including a handover command to the second base station; and

transmitting data to the terminal until the cell of the first base station is released, in case the message includes information indicating a dual protocol stack handover.

7. The method of claim 6, further comprising receiving uplink data from the terminal until a random access procedure for the second base station is successfully completed,

wherein reception of the uplink data is stopped in response to successful completion of the random access procedure.

8. The method as claimed in claim 6, wherein header compression and decompression ROHC functions and security are performed on data in a packet data convergence protocol PDCP entity.

9. A terminal in a wireless communication system, the terminal comprising:

a transceiver; and

a controller configured to:

control the transceiver to receive a message from a first base station via the transceiver by radio resource control, RRC, signaling, the message comprising a handover command from the first base station to a second base station;

Control the transceiver to receive data from the first base station until a cell of the first base station is released, in case the message comprises information indicating a dual protocol stack handover.

10. The terminal of claim 9, wherein the controller is configured to:

controlling the transceiver to transmit uplink data to the first base station until a random access procedure to the second base station is successfully completed; and

control the transceiver to transmit uplink data to the second base station on a successful completion of the random access procedure.

11. The terminal of claim 9, wherein the controller is configured to:

12. The terminal of claim 11, wherein header compression and decompression ROHC functions and security are performed on data for the first base station and the second base station in a packet data convergence protocol PDCP entity for the first base station and the second base station.

13. The terminal as claimed in claim 9, wherein a state variable of the packet data convergence protocol PDCP entity is not initialized.

14. A first base station in a wireless communication system, the first base station comprising:

a transceiver; and

a controller configured to:

controlling the transceiver to send a message to the terminal by radio resource control, RRC, signaling, the message comprising a handover command to the second base station, an

In case the message comprises information indicating a dual protocol stack handover, controlling the transceiver to transmit data to the terminal until the cell of the first base station is released.

15. The first base station of claim 14, wherein the controller is configured to:

control the transceiver to receive uplink data from the terminal until a random access procedure to the second base station is successfully completed,

wherein reception of the uplink data is stopped in case the random access procedure is successfully completed, an

Wherein header compression and decompression ROHC functions and security are performed on data in a packet data convergence protocol PDCP entity.