Patent Description:
To meet the demand for wireless data traffic having increased since deployment of <NUM> communication systems, efforts have been made to develop an improved <NUM> or pre-<NUM> communication system, also referred to as a 'beyond <NUM> network' or a 'post LTE system'. The <NUM> communication system is considered to be implemented in higher frequency (mmWave) bands, such as <NUM> bands, so as to accomplish higher data rates.

In addition, in <NUM> communication systems, development for system network improvement is being made based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like. In the <NUM> system, hybrid frequency shift keying (FSK) and frequency quadrature amplitude modulation (QAM) (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.

The Internet is now evolving to the Internet of things (IoT) where distributed entities, such as things, exchange and process information without human intervention. As technology elements, such as "sensing technology", "wired/wireless communication and network infrastructure", "service interface technology", and "security technology" have been required for IoT implementation, a sensor network, a machine-to-machine (M2M) communication, machine type communication (MTC), and so forth have been
recently researched.

Accordingly, research has been conducted to apply <NUM> communication systems to IoT networks. Application of a cloud radio access network (RAN) as the above-described big data processing technology may also be considered to be as an example of convergence between the <NUM> and IoT technologies.

A network supporting a next-generation mobile communication system can also support an LTE system and can provide services for UEs via a next-generation mobile communication base station and an LTE base station which are installed. In the network, a UE may receive services by accessing the next-generation mobile communication base station or the LTE base station. However, when the UE simultaneously accesses the next-generation mobile communication base station and the LTE base station, the network requires a procedure for changing an LTE PDCP-layer device, which processes data served through the LTE base station, to a new radio (NR) PDCP-layer device of the next-generation mobile communication system in order to enable the next-generation mobile communication base station, which is capable of operating a larger number of transmission resources and has improved performance, to manage all traffic for the UE. However, data loss occurs when an LTE PDCP-layer device of the UE is changed to an NR PDCP-layer device due to a change between the PDCP-layer devices of the two different systems or when the LTE PDCP-layer device is changed to the NR PDCP-layer device.

As such, it is necessary to prevent such data loss when a change occurs between the PDCP-layer devices of the two different systems.

In a discussion paper to <NPL>, RLC and MAC handling for EN-DC operation was discussed and principles on the L2 handling for EN-DC operation were proposed.

<CIT> relates to a pre-<NUM>th-Generation (<NUM>) or <NUM> communication system to be provided for supporting higher data rates Beyond <NUM>th-Generation (<NUM>) communication system such as Long Term Evolution (LTE). This document describes a UE for managing a user plane operation in a wireless communication system. The UE includes a user plane management unit coupled to a memory and a processor. The user plane management unit is configured to receive a signaling message from a gNodeB. Further, the user plane management unit is configured to determine whether the signaling message includes control information comprising one of a PDCP re-establish indication and a security key change indication. Further, the user plane management unit is configured to perform the at least one operation for at least one data radio bearer based on the determination.

<CIT> relates to a communication technique for converging a <NUM> communication system, which is provided to support a higher data transmission rate beyond a <NUM> system with an IoT technology, and a system therefor. This technique may be applied to intelligent services (e.g., smart home, or the like) based on the <NUM> communication technology and the IoT related technology. This document discloses a method and an apparatus for supporting a multiple access in next generation mobile communication systems.

In a discussion paper to <NPL>, different views concerning bearer type change were discussed in general.

The same topic was also subject matter of a further discussion paper to <NPL>, and in <NPL>.

A network supporting a next-generation mobile communication system can also support an LTE system and can provide services for UEs via a next-generation mobile communication base station and an LTE base station which are installed. In the network, a UE may receive services by accessing the next-generation mobile communication base station or the LTE base station. However, when the UE simultaneously
accesses the next-generation mobile communication base station and the LTE base station, the network requires a procedure for changing an LTE PDCP-layer device, which processes data served through the LTE base station, to an NR PDCP-layer device of the next-generation mobile communication system in order to enable the next-generation mobile communication base station, which is capable of operating a larger number of transmission resources and has improved performance, to manage all traffic for the UE. Further, when an LTE PDCP-layer device of the UE is changed to an NR PDCP-layer device due to a change between the PDCP-layer devices of the two different systems or when the LTE PDCP-layer device is changed to the NR PDCP-layer device, it is necessary to prevent data loss.

In accordance with an embodiment of the disclosure, a method by a terminal is provided as defined in the appended claims.

In accordance with another embodiment of the disclosure, a terminal in a communication system is provided as defined in the appended claims.

Accordingly, an aspect of the disclosure is to provide a method and an apparatus for changing a long term evolution (LTE) PDCP-layer device to an NR PDCP-layer device.

Another aspect of the disclosure is to provide a method and an apparatus for changing an NR PDCP-layer device to an LTE PDCP-layer device.

Another aspect of the disclosure is to provide a network which, when a UE simultaneously accesses a next-generation mobile communication base station and an LTE base station, performs a procedure for changing an LTE PDCP-layer device, which processes data served through the LTE base station, to an NR PDCP-layer device of the next-generation mobile communication system in order to enable the next-generation mobile communication base station, which is capable of operating a larger number of transmission resources and has improved performance, to manage all traffic for the UE.

Another aspect of the disclosure is to provide a method and an apparatus for preventing data loss in a process of changing the version of a PDCP-layer device of the UE (when an LTE PDCP-layer device of the UE is changed to an NR PDCP-layer device or when the LTE PDCP-layer device of the UE is changed to the NR PDCP-layer device) in the procedure, to prevent unnecessary retransmission by an upper-layer device, thus preventing a transmission delay and the waste of transmission resources.

Hereinafter, embodiments of the disclosure will be described with reference to accompanying drawings, in which a size of each component may be exaggerated for convenience. Detailed descriptions of known functions and configurations incorporated herein will be omitted for the sake of clarity and conciseness.

The terms which will be described below are defined in consideration of the functions in the disclosure, and may be different according to users, intentions of the users, or customs. Therefore, the definitions of the terms, such as for identifying an access node, referring to network entities, referring to messages, referring to an interface between network objects, and referring to various identification information, should be made based on the contents throughout the specification. The disclosure is not limited by the following terms, and other terms referring to objects having equivalent technical meanings may be used.

For convenience of explanation, embodiments herein use terms and words defined in the third generation partnership project long term evolution (3GPP LTE) standard. However, the disclosure is not limited by these terms and words and may be equally applied to systems in accordance with other standards. In embodiments, the term evolved Node B (eNB) may be used interchangeably with gNB (<NUM> base station or next generation node B) for convenience of explanation. That is, an eNB illustrated as a base station may refer to a gNB. The term "terminal" or "UE" may refer to a mobile phone, narrow band-Internet of things (NB-IoT) devices, sensors, and other wireless communication devices.

A PDCP, RLC, medium access control (MAC), and physical (PHY) may be used interchangeably with a PDCP layer, an RLC layer, a MAC layer, and a PHY layer, respectively, or with a PDCP-layer device, an RLC-layer device, a MAC-layer device, and a PHY-layer device, respectively. An existing version of a PDCP-layer device may be defined as a first PDCP-layer device, and a new version of the PDCP-layer device may be defined as a second PDCP-layer device.

A network supporting a next-generation mobile communication system can also support an LTE system and can provide services for UEs via a next-generation mobile communication base station (NR base station) and an LTE base station which are installed. In the network, a UE may receive services by accessing the next-generation mobile communication base station or the LTE base station. However, when the UE simultaneously accesses the next-generation mobile communication base station and the LTE base station, the network requires a procedure for changing an LTE PDCP-layer device, which processes data served through the LTE base station, to an NR PDCP-layer device of the next-generation mobile communication system in order to enable the next-generation mobile communication base station (NR base station), which is capable of operating a larger number of transmission resources and has improved performance, to manage all traffic for the UE.

Data loss may occur when an LTE PDCP-layer device of the UE is changed to an NR PDCP-layer device due to a change between the PDCP-layer devices of the two different systems or when the LTE PDCP-layer device of the UE is changed to the NR PDCP-layer device. Also, when the UE (non-standalone: NSA) simultaneously connected to the NR base station and the LTE base station is disconnected from the NR base station and is thus served only by the LTE base station, data loss may occur during a procedure for changing the changed NR PDCP-layer device back to the LTE PDCP-layer device is required.

Therefore, disclosed herein is a procedure for changing a PDCP-layer device without data loss when a UE receives an RRC message from an LTE base station or an NR base station and a change from an LTE PDCP-layer device to an NR PDCP-layer device or a change from the NR PDCP-layer device to the LTE PDCP-layer device is indicated for a bearer having the same bearer identifier. Specifically, before the version of a PDCP-layer device is changed, the UE transmits pieces of data stored in the LTE PDCP-layer device before the change to a newly changed (NR) PDCP-layer device or newly stores the data in the newly changed PDCP-layer device so that the newly changed NR PDCP-layer device considers the data as being newly received and processes the data.

The UE may determine data to transmit to or store in the newly changed PDCP-layer device among the pieces of data stored in the LTE PDCP-layer device before the change according to one of the following methods.

In another method, the successful delivery of data of a PDCP-layer device may be identified using not only an RLC status report (RLC status PDU) of an RLC-layer device but also a PDCP status report of the PDCP-layer device.

<FIG> illustrates the structure of an LTE system according to an embodiment.

Referring to <FIG>, a radio access network of the LTE system includes an evolved node B (hereinafter, referred to as an eNB, a Node B or a base station) <NUM>, <NUM>, <NUM> or <NUM>, a mobility management entity (MME) <NUM>, and a serving gateway (S-GW) <NUM>. A user equipment (UE or terminal) <NUM> accesses an external network through the eNBs <NUM>, <NUM>, <NUM>, and <NUM> and the S-GW <NUM>.

In <FIG>, the eNBs <NUM>, <NUM>, <NUM>, and <NUM> correspond to existing node B's of a universal mobile telecommunication system (UMTS), are connected to the UE <NUM> over a wireless channel, and perform a more complex role than that of the existing Nodes B. In the LTE system, since all user traffic including a real-time service, such as a voice over Internet protocol (VoIP) service, is provided through a shared channel, a device that collects state information, such as UEs' buffer status, available transmission power state, and channel state, and performs scheduling is required. The eNBs <NUM>, <NUM>, <NUM>, and <NUM> are responsible for these functions. One eNB generally controls a plurality of cells.

For example, in order to realize a transmission speed of <NUM> Mbps, the LTE system uses orthogonal frequency division multiplexing (FDM) as a radio access technology, such as at a bandwidth of <NUM>. In addition, the LTE system applies adaptive modulation & coding (AMC), which determines a modulation scheme and a channel coding rate according to the channel state of a UE. The S-GW <NUM> provides a data bearer and generates or removes a data bearer under the control of the MME <NUM>. The MME <NUM> performs not only a mobility management function for the UE <NUM> but also various control functions and is connected to a plurality of base stations <NUM>, <NUM>, <NUM>, and <NUM>.

<FIG> illustrates the wireless protocol structure of an LTE system according to an embodiment.

Referring to <FIG>, a wireless protocol of the LTE system includes packet data convergence protocols (PDCPs) <NUM> and <NUM>, radio link controls (RLCs) <NUM> and <NUM>, and medium access controls (MACs) <NUM> and <NUM> respectively at a UE and an eNB. The PDCPs <NUM> and <NUM> are responsible for IP header compression/decompression or the like.

Main functions of the PDCPs are summarized as follows.

The RLCs <NUM> and <NUM> reconstruct a PDCP PDU into a proper size and perform an automatic repeat request (ARQ) operation. Main functions of the RLCs are summarized as follows.

The MACs <NUM> and <NUM> are connected to a plurality of RLC-layer devices configured in one device, multiplex RLC PDUs into a MAC PDU, and demultiplex a MAC PDU into RLC PDUs. Main functions of the MACs are summarized as follows.

Physical (PHY) layers <NUM> and <NUM> perform channel coding and modulation of upper-layer data and convert the data into OFDM symbols to transmit the OFDM symbols via a wireless channel, or demodulate OFDM symbols received via a wireless channel and perform channel decoding of the OFDM symbols to deliver the OFDM symbols to an upper layer.

<FIG> illustrates the structure of a next-generation mobile communication system according to an embodiment.

Referring to <FIG>, a radio access network of the next-generation mobile communication system (NR or <NUM>) includes a new radio node B (NR gNB or NR base station) <NUM> and a new radio core network (NR CN) <NUM>. A new radio user equipment (NR UE or terminal) <NUM> accesses an external network through the NR gNB <NUM> and the NR CN <NUM>.

In <FIG>, the NR gNB <NUM> corresponds to an eNB of an existing LTE system, and is connected to the NR UE <NUM> over a wireless channel to provide a more advanced service than that of the existing eNB. In the next-generation mobile communication system, since all user traffic is served through a shared channel, a device that collects state information, such as UEs' buffer status, available transmission power state, and channel state, and performs scheduling is required, and is the responsibility of the NR gNB <NUM>.

One NR gNB generally controls a plurality of cells. In order to realize ultrahigh-speed data transmission compared to current LTE, the NR may have a bandwidth greater than the existing maximum bandwidth and may employ a beamforming technique in addition to OFDM as a radio access technology. The NR applies AMC, which determines a modulation scheme and a channel coding rate according to the channel state of a UE. The NR CN <NUM> performs functions of mobility support, bearer setup, and quality of service (QoS) setup. The NR CN <NUM> performs not only a mobility management function for a UE but also various control functions and is connected to a plurality of base stations. The next-generation mobile communication system may also interwork with the existing LTE system, in which case the NR CN <NUM> is connected to an MME <NUM> through a network interface. The MME <NUM> is connected to the eNB <NUM>, which is an existing base station.

<FIG> illustrates the wireless protocol structure of a next-generation mobile communication system according to an embodiment.

Referring to <FIG>, a wireless protocol of the next-generation mobile communication system includes NR service data adaptation protocols (SDAPs) <NUM> and <NUM>, NR PDCPs <NUM> and <NUM>, NR RLCs <NUM> and <NUM>, and NR MACs <NUM> and <NUM> respectively at a UE and an NR base station (NR gNB).

Main functions of the NR SDAPs <NUM> and <NUM> may include some of the following functions.

Regarding the SDAP-layer devices, the UE may receive a configuration about whether to use a header of the SDAP-layer devices or whether to use the SDAP-layer devices for each PDCP-layer device, each bearer, or each logical channel via an RRC message. When an SDAP header is configured, a one-bit non-access stratum (NAS) QoS reflective indicator (NAS reflective QoS) and a one-bit AS QoS reflective indicator (AS reflective QoS) of the SDAP header may be used for indication to enable the UE to update or reconfigure uplink and downlink QoS flows and mapping information for a data bearer. The SDAP header may include QoS flow ID information indicating QoS. The QoS information may be used as a data processing priority or scheduling information in order to support a desired service.

Main functions of the NR PDCPs <NUM> and <NUM> may include some of the following functions.

Among the above functions, the reordering function of the NR PDCP devices refers to rearranging PDCP PDUs received in a lower layer in order based on the PDCP sequence number (SN) and may include transmitting the data to an upper layer in the order of rearrangement or immediately transmitting the data regardless of order. In addition, the reordering function may include recording lost PDCP PDUs via reordering, may include reporting the state of lost PDCP PDUs to a transmitter, and may include requesting retransmission of lost PDCP PDUs.

Main functions of the NR RLCs <NUM> and <NUM> may include the following.

Among the above functions, the in-sequence delivery function of the NR RLC devices refers to delivering RLC SDUs received from a lower layer to an upper layer in order, and may include reassembling and delivering a plurality of RLC SDUs when one original RLC SDU is divided into the plurality of RLC SDUs to be received, rearranging received RLC PDUs based on the RLC SN or the PDCP SN, and recording lost RLC PDUs via reordering.

In addition, the in-sequence delivery function may include reporting the state of lost RLC PDUs to a transmitter, requesting retransmission of lost RLC PDUs, and, if there is a lost RLC SDU, may include delivering only RLC SDUs before the lost RLC SDU to an upper layer in order. The in-sequence delivery function may include delivering all RLC SDUs, received before a timer starts, to an upper layer in order when the timer has expired despite the presence of a lost RLC SDU, or delivering all RLC SDUs received so far to an upper layer in order when the timer expires despite the presence of a lost RLC SDU.

The NR RLC devices may process RLC PDUs in order of reception (the order of arrival regardless of the order of SNs) and may deliver the RLC PDUs to the PDCP devices in an out-of-sequence manner. For a segment, the NR RLC devices may receive segments that are stored in a buffer or are to be received later, may reconstruct the segment into one whole RLC PDU, may process the RLC PDU, and may deliver the RLC PDU to the PDCP devices. The NR RLC layers may not include a concatenation function, and the concatenation function may be performed in the NR MAC layers or may be replaced with a multiplexing function of the NR MAC layers.

The out-of-sequence delivery function of the NR RLC devices refers to delivering RLC SDUs received from a lower layer directly to an upper layer regardless of order, and may include reassembling and delivering a plurality of RLC SDUs when one original RLC SDU is divided into the plurality of RLC SDUs to be received, and recording lost RLC PDUs by storing and reordering the RLC SNs or PDCP SNs of received RLC PDUs.

The NR MACs <NUM> and <NUM> may be connected to a plurality of NR RLC-layer devices configured in one device, and main functions of the NR MACs may include some of the following.

NR PHY layers <NUM> and <NUM> may perform channel coding and modulation of upper-layer data and convert the data into OFDM symbols to transmit the OFDM symbols via a wireless channel, or demodulate OFDM symbols received via a wireless channel and perform channel decoding of the OFDM symbols to deliver the OFDM symbols to an upper layer.

<FIG> illustrates a procedure in which a UE establishes an RRC connection with a base station when establishing a connection with a network in a next-generation mobile communication system according to an embodiment.

Referring to <FIG>, when the UE transmitting or receiving data in an RRC-connected mode neither transmits nor receives data for a reason or for a certain time, the base station (gNB) may transmit an RRCConnectionRelease message to the UE in step <NUM>, so that the UE switches to an RRC-idle mode. When there is data to transmit, the UE currently not connected (hereinafter, idle-mode UE) may perform an RRC connection establishment process with the base station in step <NUM>.

The UE establishes reverse transmission synchronization with the base station through a random access procedure and transmits an RRCConnectionRequest message to the base station in step <NUM>. The RRCConnectionRequest message may include an identifier of the UE and a reason for establishing a connection (establishmentCause).

The base station transmits an RRCConnectionSetup message so that the UE establishes an RRC connection in step <NUM>. The RRCConnectionSetup message may include at least one of configuration information of each logical channel, configuration information of each bearer, configuration information of a PDCP-layer device, configuration information of an RLC-layer device, and configuration information of a MAC-layer device.

The RRCConnectionSetup message may indicate configurations of the PDCP-layer device, the RLC-layer device, the MAC-layer device, and a PHY-layer device for a bearer corresponding to a signaling radio bearer (SRB) identifier or a data radio bearer (DRB) identifier, and may indicate, for a bearer corresponding to a bearer identifier, whether to configure or release an LTE PDCP-layer device and whether to configure or release an NR PDCP-layer device. The RRCConnectionSetup message may indicate, for a bearer corresponding to a bearer identifier, whether to release the LTE PDCP-layer device to change to the NR PDCP-layer device and to connect the NR PDCP-layer device to an LTE RLC-layer device, and whether to release the NR PDCP-layer device to change to the LTE PDCP-layer device and to reconnect the LTE PDCP-layer device to the LTE RLC-layer device.

When the RRCConnectionSetup message includes a configuration for releasing the LTE PDCP-layer device corresponding to a first bearer identifier, the RRC message (RRCConnectionSetup message) does not include NR PDCP configuration information corresponding to the first bearer identifier, and the NR PDCP-layer device for the first bearer identifier is already configured, the NR PDCP-layer device may establish a connection with the LTE RCP-layer device, which has been connected with the released LTE PDCP-layer device (version change procedure of the PDCP-layer device, which is a change from the LTE PDCP to the NR PDCP). This procedure may be defined as a first condition.

When the RRCConnectionSetup message includes a configuration for releasing the NR PDCP-layer device for the first bearer identifier, which is configured by the connection of the NR PDCP-layer device and the LTE RLC-layer device, and includes LTE PDCP configuration information corresponding to the first bearer identifier, the LTE PDCP-layer device may establish a connection with the LTE RLC-layer device, which has been connected with the released NR PDCP-layer device (version change procedure of the PDCP-layer device, which is a change from the NR PDCP to the LTE PDCP). This procedure may be defined as a second condition.

Upon establishing the RRC connection, the UE transmits an RRCConnetionSetupComplete message to the base station in step <NUM>. The RRCConnetionSetupComplete message may include a control message, such as a SERVICE REQUEST for the UE to request an access management function (AMF) or an MME to configure a bearer for a service. The base station transmits a SERVICE REQUEST message included in the RRCConnetionSetupComplete message to the AMF or the MME in step <NUM>. The AMF or MME may determine whether to provide the service requested by the UE.

When it is determined to provide the service requested by the UE, the AMF or the MME transmits an INITIAL CONTEXT SETUP REQUEST message to the base station in step <NUM>. The INITIAL CONTEXT SETUP REQUEST message may include QoS information to be applied when a DRB is configured and security-related information, such as a security key or a security algorithm, to be applied to the DRB.

The base station transmits a SecurityModeCommand message to the base station in order to enable security with the UE in step <NUM> and receives a SecurityModeComplete message from the UE in step <NUM>. When security is completely enabled, the base station transmits an RRCConnectionReconfiguration message to the UE in step <NUM>.

The RRCConnectionReconfiguration message may indicate configurations of the PDCP-layer device, the RLC-layer device, the MAC-layer device, and a PHY-layer device for a bearer corresponding to a bearer identifier (for example, an SRB identifier or a DRB identifier). The RRCConnectionReconfiguration message may indicate, for a bearer corresponding to a bearer identifier, whether to configure or release the LTE PDCP-layer device and to configure or release the NR PDCP-layer device, whether to release the LTE PDCP-layer device to change to the NR PDCP-layer device and to connect the NR PDCP-layer device to the LTE RLC-layer device, or whether to release the NR PDCP-layer device to change to the LTE PDCP-layer device and to reconnect the LTE PDCP-layer device to the LTE RLC-layer device.

When the RRCConnectionReconfiguration message includes a configuration for releasing the LTE PDCP-layer device corresponding to the first bearer identifier, the RRCConnectionReconfiguration message does not include NR PDCP configuration information corresponding to the first bearer identifier, and the NR PDCP-layer device for the first bearer identifier is already configured, the NR PDCP-layer device may establish a connection with the LTE RCP-layer device, which has been connected with the released LTE PDCP-layer device (version change procedure of the PDCP-layer device, which is a change from the LTE PDCP to the NR PDCP). This procedure may be defined as the first condition.

When the RRCConnectionReconfiguration message includes a configuration for releasing the NR PDCP-layer device for the first bearer identifier, which is configured by the connection of the NR PDCP-layer device and the LTE RLC-layer device, and includes LTE PDCP configuration information corresponding to the first bearer identifier, the LTE PDCP-layer device may establish a connection with the LTE RLC-layer device, which has been connected with the released NR PDCP-layer device (version change procedure of the PDCP-layer device, which is a change from the NR PDCP to the LTE PDCP). This procedure may be defined as the second condition.

The RRCConnectionReconfiguration message may include configuration information about a DRB for processing user data, and the UE configures a DRB by applying this information and transmits an RRCConnectionReconfigurationComplete message to the base station in step <NUM>. After completely configuring the DRB with the UE, the base station may transmit an INITIAL CONTEXT SETUP COMPLETE message to the AMF or MME, thereby completing the connection in step <NUM>.

When the above process is completed, the UE transmits and receives data to and from the base station through the AMF and a core network, in step <NUM>. The data transmission process is largely divided into RRC connection setup, security setup, and DRB setup. In addition, the base station may transmit an RRCConnectionReconfiguration message to the UE in order to renew, add, or change a configuration for a reason, in step <NUM>.

The RRCConnectionReconfiguration message may indicate configurations of the PDCP-layer device, the RLC-layer device, the MAC-layer device, and a PHY-layer device for a bearer corresponding to a bearer identifier (for example, an SRB identifier or a DRB identifier), and may indicate, for a bearer corresponding to a bearer identifier, whether to configure or release the LTE PDCP-layer device or the NR PDCP-layer device, whether to release the LTE PDCP-layer device to change to the NR PDCP-layer device, and to connect the NR PDCP-layer device to the LTE RLC-layer device, and whether to release the NR PDCP-layer device to change to the LTE PDCP-layer device and to reconnect the LTE PDCP-layer device to the LTE RLC-layer device.

When the RRCConnectionReconfiguration message includes a configuration for releasing the LTE PDCP-layer device corresponding to the first bearer identifier, the RRC message does not include NR PDCP configuration information corresponding to the first bearer identifier, and the NR PDCP-layer device for the first bearer identifier is already configured, the NR PDCP-layer device may establish a connection with the LTE RCP-layer device, which has been connected with the released LTE PDCP-layer device (version change procedure of the PDCP-layer device, which is a change from the LTE PDCP to the NR PDCP).

When the RRCConnectionReconfiguration message includes a configuration for releasing the NR PDCP-layer device for the first bearer identifier, which is established by the connection of the NR PDCP-layer device and the LTE RLC-layer device, and includes LTE PDCP configuration information corresponding to the first bearer identifier, the LTE PDCP-layer device may establish a connection with the LTE RLC-layer device, which has been connected with the released NR PDCP-layer device (version change procedure of the PDCP-layer device, which is a change from the NR PDCP to the LTE PDCP).

The procedure for establishing the connection between the UE and the base station may be applied to both the establishment of a connection between the UE and an LTE base station and the establishment of a connection between the UE and the NR base station.

A UM DRB denotes a DRB using an RLC-layer device operating in an unacknowledged mode (UM), and an AM DRB denotes a DRB using an RLC-layer device operating in an acknowledged mode (AM). A procedure for changing the version of a PDCP-layer device disclosed herein may be applied to both a change from an NR PDCP to an LTE PDCP and a change from an LTE PDCP to an NR PDCP and may be applied to both a DRB and an SRB. That is, this procedure may be applied to a PDCP version change procedure for a DRB and, if necessary, may also be applied to a PDCP version change procedure for an SRB in an extended manner. The UE may receive an RRC message indicating the procedure for changing the version of the PDCP-layer device from an LTE base station or an NR base station.

<FIG> illustrates a protocol structure in which a UE establishes a connection with an LTE base station and transmits and receives data according to an embodiment.

Referring to <FIG>, when a UE <NUM> is in LTE cell coverage <NUM> supported by an LTE base station <NUM>, the UE <NUM> may establish an RRC connection with the LTE base station <NUM>, as described in <FIG>, and may transmit and receive data for a first bearer <NUM>. Downlink data for the first bearer <NUM> is processed via an LTE PDCP-layer device, an LTE RLC-layer device, an LTE MAC-layer device, and an LTE PHY-layer device of the LTE base station <NUM>, is transmitted via a radio link, and is received and processed via an LTE PHY-layer device, an LTE MAC-layer device, an LTE RLC-layer device, and an LTE PDCP-layer device of the UE <NUM>. Uplink data for the first bearer <NUM> is processed via the LTE PDCP-layer device, the LTE RLC-layer device, the LTE MAC-layer device, and the LTE PHY-layer device of the UE <NUM>, is transmitted via the radio link, and is received and processed via the LTE PHY-layer device, the LTE MAC-layer device, the LTE RLC-layer device, and the LTE PDCP-layer device of the LTE base station <NUM>.

<FIG> illustrates a protocol structure in which a UE establishes a connection with an LTE base station, establishes a connection with an NR base station, and transmits and receives data according to an embodiment.

An NR base station may have a central unit (CU)-distributed unit (DU)-split structure. That is, a CU <NUM> may operate an SDAP-layer device or a PDCP-layer device, and a DU <NUM> connected with the CU <NUM> in a wired manner may operate an RLC-layer device, a MAC-layer device, and a PHY-layer device. gNB DU coverge <NUM> is managed by the gNB DU1 <NUM> and gNB DU coverage <NUM> is managed by the gNB DU2.

Referring to <FIG>, when a UE <NUM> is in LTE cell coverage <NUM> supported by an LTE base station (eNB) <NUM>, the UE <NUM> may establish an RRC connection with the LTE base station <NUM>, as described in <FIG>, and may transmit and receive data for a first bearer <NUM>. When the UE <NUM> is in NR cell coverage <NUM> supported by an NR base station having gNB CU <NUM> and gNB DU1 <NUM>, the UE <NUM> may establish an RRC connection with the NR base station, as described in <FIG>, and may transmit and receive data for a second bearer <NUM>.

Downlink data for the second bearer <NUM> is processed via an NR PDCP-layer device, an NR RLC-layer device, an NR MAC-layer device, and an NR PHY-layer device of the gNB CU <NUM> and gNB DU1 <NUM>, is transmitted via a radio link, and is received and processed via an NR PHY-layer device, an NR MAC-layer device, an NR RLC-layer device, and an NR PDCP-layer device of the UE <NUM>. Uplink data for the second bearer <NUM> is processed via the NR PDCP-layer device, the NR RLC-layer device, the NR MAC-layer device, and the NR PHY-layer device of the UE <NUM>, is transmitted via the radio link, and is received and processed via the NR PHY-layer device, the NR MAC-layer device, the NR RLC-layer device, and the NR PDCP-layer device of the gNB CU <NUM> and gNB DU1 <NUM>.

However, as illustrated in <FIG>, when the UE <NUM> establishes the RRC connections to the LTE base station <NUM> and the gNB CU <NUM> and gNB DU1 704at the same time and transmits and receives data, if the first bearer <NUM> is managed by the LTE base station <NUM>, and the second bearer <NUM> is managed by the gNB CU <NUM> and gNB DU1 <NUM>, the management of a network may be complicated. In order to manage data traffic for one UE <NUM> by two different base stations (the LTE base station <NUM> and the gNB CU <NUM> and gNB DU1 <NUM>) together, it is necessary to exchange control signals between the base stations, thus causing a transmission delay and difficulty in the management.

Accordingly, disclosed herein is a method and a device in which a network enables an NR base station, which is capable of operating a larger number of transmission resources and has improved performance, to manage all traffic for a UE when the UE simultaneously accesses the next-generation mobile communication base station (NR base station) and an LTE base station. To this end, a method and a device are provided that enable the NR base station to manage all the traffic of the UE by changing an LTE PDCP-layer device, which processes data served through the LTE base station, to an NR PDCP-layer device of the next-generation mobile communication system.

<FIG> illustrates a protocol structure in which a UE changes the version of a PDCP-layer device and transmits and receives data when establishing a connection with an LTE base station and establishing a connection with an NR base station according to an embodiment. gNB DU coverge <NUM> is managed by the gNB DU1 <NUM> and gNB DU coverage <NUM> is managed by the gNB DU2.

Referring to <FIG>, when a UE <NUM> is in LTE cell coverage <NUM> supported by an LTE base station <NUM>, the UE <NUM> may establish an RRC connection with the LTE base station <NUM> and may transmit and receive data for a first bearer <NUM> as described in <FIG>. When the UE <NUM> is in NR cell coverage <NUM> supported by an NR base station having gNB CU <NUM> and gNB DU1 <NUM>, the UE <NUM> may establish an RRC connection with the NR base station, as described in <FIG>. When establishing the RRC connection, the UE <NUM> may establish a connection between an NR PDCP-layer device and an LTE RLC-layer device for the first bearer by releasing an LTE PDCP-layer device for the first bearer and by newly configuring the NR PDCP-layer device, and may transmit and receive data. The UE <NUM> may configure a second bearer <NUM> and may transmit and receive data.

Downlink data for the first bearer <NUM> is processed via an NR PDCP-layer device of the gNB CU <NUM> and gNB DU1 <NUM>, an interface between the base stations, such as a gNB DU1 coverage or X2 interface <NUM>, an LTE RLC-layer device, an LTE MAC-layer device, and an LTE PHY-layer device of the LTE base station <NUM>, is transmitted via a radio link, and is received and processed via an LTE PHY-layer device, an LTE MAC-layer device, an LTE RLC-layer device, and an NR PDCP-layer device of the UE <NUM>. Uplink data for the first bearer <NUM> is processed via the NR PDCP-layer device, the LTE RLC-layer device, the LTE MAC-layer device, and the LTE PHY-layer device of the UE <NUM>, is transmitted via the radio link, and is received and processed via the LTE PHY-layer device, the LTE MAC-layer device, the LTE RLC-layer device of the LTE base station <NUM>, the interface between the base stations, such as the gNB DU1 coverage or X2 interface <NUM>, and the NR PDCP-layer device of the NR base station <NUM> and <NUM>.

Downlink data for the second bearer <NUM> is processed via the NR PDCP-layer device, an NR RLC-layer device, an NR MAC-layer device, and an NR PHY-layer device of the gNB CU <NUM> and gNB DU1 <NUM>, is transmitted via a radio link, and is received and processed via an NR PHY-layer device, an NR MAC-layer device, an NR RLC-layer device, and the NR PDCP-layer device of the UE <NUM>. Uplink data for the second bearer <NUM> is processed via the NR PDCP-layer device, the NR RLC-layer device, the NR MAC-layer device, and the NR PHY-layer device of the UE <NUM>, is transmitted via the radio link, and is received and processed via the NR PHY-layer device, the NR MAC-layer device, the NR RLC-layer device, and the NR PDCP-layer device of the gNB CU <NUM> and gNB DU1 <NUM>.

As described above, the NR base station <NUM> and <NUM> can manage any bearer or any data traffic for the UE <NUM> as indicated by reference numerals <NUM> and <NUM>, thus preventing unnecessary signaling between the LTE base station <NUM> and the NR base station <NUM> and <NUM>, and enabling one of the gNB CU <NUM> or gNB DU1 <NUM> to effectively manage the traffic of the UE <NUM>.

<FIG> illustrates a procedure in which a UE changes the version of a PDCP-layer device when establishing a connection with an LTE base station and establishing a connection with an NR base station according to an embodiment.

Referring to <FIG>, when a UE <NUM> is in LTE cell coverage supported by an LTE base station <NUM>, the UE <NUM> may establish an RRC connection with the LTE base station <NUM> and may transmit and receive data for a first bearer <NUM> as described in <FIG>. When the UE <NUM> is in NR cell coverage supported by an NR base station having gNB CU <NUM> and gNB DU1 <NUM>, the UE <NUM> may establish an RRC connection with the gNB CU <NUM> and gNB DU1 <NUM>, as described in <FIG>. When establishing the RRC connection or receiving an RRC message from the LTE base station, the UE <NUM> may establish a connection between an NR PDCP-layer device <NUM> and an LTE RLC-layer device <NUM> for the first bearer <NUM> by releasing an LTE PDCP-layer device <NUM> for the first bearer <NUM> and by newly configuring the NR PDCP-layer device <NUM>, thereby changing a PDCP-layer device version <NUM>, and may transmit and receive data through the changed NR PDCP-layer device <NUM>.

Accordingly, the NR base station <NUM> and <NUM> can manage the first bearer <NUM>, which has been managed by the LTE base station <NUM>, as a first bearer <NUM> in the gNB CU <NUM> and gNB DU1 <NUM>, along with a second bearer <NUM>. The gNB CU <NUM> and gNB DU <NUM><NUM> may transmit and receive data for the first bearer <NUM> through an interface <NUM> between the base stations.

When the UE having accessed the LTE base station and the NR base station is disconnected from the NR base station due to departure from the NR cell coverage or an indication from a network, the NR PDCP-layer device, which has established the connection with the LTE RLC-layer device due to the PDCP version change, may be changed back to the LTE PDCP-layer device. That is, the PDCP version change <NUM> may be performed in reverse according to an indication of an RRC message.

<FIG> illustrates a procedure of processing data in a PDCP-layer device and an RLC-layer device of a UE according to an embodiment.

Referring to <FIG>, when receiving data, such as an IP packet or a PDCP SDU <NUM>, from an upper-layer device, a PDCP-layer device <NUM> of a UE may apply an integrity protection procedure to the PDCP SDU and a PDCP header <NUM> using a security key configured by a base station. The PDCP-layer device <NUM> may configure a PDCP PDU <NUM> by applying a ciphering procedure only to PDCP SDU using the security key and may transmit the PDCP PDU <NUM> to a lower-layer device <NUM>.

Upon receiving an RLC SDU (or PDCP PDU) <NUM> from an upper-layer device <NUM>, the RLC-layer device <NUM> of the UE may generate an RLC header corresponding to the RLC SDU, may configure an RLD PDU <NUM>, and may transmit the RLD PDU <NUM> to a lower-layer device, such as a MAC-layer device.

<FIG> illustrates a method of changing the version of a PDCP-layer device according to an embodiment, which may be applied to a change from an LTE PDCP-layer device to an NR PDCP-layer device or from an NR PDCP-layer device to an LTE PDCP-layer device.

Referring to <FIG>, a UE may receive an RRC message from an LTE base station or an NR base station. When the RRC message indicates a change of the version of a PDCP-layer device for a certain bearer, such as when the RRC message includes a configuration for releasing an LTE PDCP-layer device corresponding to a first bearer identifier (DRB ID1)<NUM>, the RRC message includes does not include NR PDCP configuration information corresponding to the first bearer identifier <NUM>, and an NR PDCP-layer device for the first bearer identifier <NUM> is already configured (when an LTE PDCP-layer device for a bearer is changed to an NR PDCP-layer device) or when the RRC message includes a configuration for releasing the NR PDCP-layer device for the first bearer identifier <NUM>, which is established for the NR PDCP-layer device and the LTE RLC-layer device, and includes LTE PDCP configuration information corresponding to the first bearer identifier <NUM> (when an NR PDCP-layer device for a bearer is changed to an LTE PDCP-layer device), the following procedure may be performed. DRB ID <NUM><NUM> corresponds to an NR RLC layer associated with an NR PDCP layer.

A network supporting a next-generation mobile communication system can also support an LTE system and can provide services for UEs via an NR base station and an LTE base station which are installed. In the network, a UE may receive services by accessing the next-generation mobile communication base station or the LTE base station. However, when the UE simultaneously accesses the next-generation mobile communication base station and the LTE base station, the network requires a procedure for changing an LTE PDCP-layer device, which processes data served through the LTE base station, to an NR PDCP-layer device of the next-generation mobile communication system in order to enable the NR base station, which is capable of operating a larger number of transmission resources and has improved performance, to manage all traffic for the UE. When an LTE PDCP-layer device of the UE is changed to an NR PDCP-layer device due to a change between the PDCP-layer devices of the two different systems or when the LTE PDCP-layer device is changed to the NR PDCP-layer device, data loss may occur.

In contrast, when the UE (non-standalone (NSA)) simultaneously connected to the NR base station and the LTE base station is disconnected from the NR base station and is thus served only by the LTE base station, a procedure for changing the changed NR PDCP-layer device back to the LTE PDCP-layer device is required, in which case data loss may also occur. That is, as shown in <FIG>, in step <NUM> of changing the PDCP-layer device, all stored data is discarded and the new PDCP-layer device is configured while releasing the currently configured PDCP-layer device, and thus data loss may occur with respect to the first bearer <NUM>.

Therefore, the following discloses a procedure for changing a PDCP-layer device without data loss when a UE receives an RRC message from an LTE base station or an NR base station and a change from an LTE PDCP-layer device to an NR PDCP-layer device or a change from the NR PDCP-layer device to the LTE PDCP-layer device is indicated for a bearer having the same bearer identifier. Specifically, before the version of a PDCP-layer device is changed, the UE transmits pieces of data (for example, PDCP SDUs) stored in the PDCP-layer device (for example, the LTE PDCP layer device) before the change to a newly changed PDCP-layer device (for example, the NR PDCP layer device) or newly stores the data in the newly changed PDCP-layer device so that the newly changed PDCP-layer device (for example, the NR PDCP layer device) considers the data as being newly received and processes the data.

The UE may determine data to transmit to or store in the newly changed PDCP-layer device among the pieces of data (for example, PDCP SDUs) stored in the PDCP-layer device before the PDCP version change according to one of the following methods.

In another method, the successful delivery of data of a PDCP-layer device may be identified using not only an RLC status report of an RLC-layer device but also a PDCP status report of the PDCP-layer device.

<FIG> illustrates a method of changing the version of a PDCP-layer device without loss according to an embodiment, which may be applied to a change from an LTE PDCP-layer device to an NR PDCP-layer device or a change from an NR PDCP-layer device to an LTE PDCP-layer device.

In <FIG>, a UE may receive an RRC message from an LTE base station or an NR base station. When the RRC message indicates a change of the version of a PDCP-layer device for a certain bearer, for example, when the RRC message includes a configuration for releasing an LTE PDCP-layer device corresponding to a first bearer identifier <NUM>, the RRC message includes does not include NR PDCP configuration information corresponding to the first bearer identifier <NUM>, and an NR PDCP-layer device for the first bearer identifier <NUM> is already configured (when an LTE PDCP-layer device for a bearer is changed to an NR PDCP-layer device) or when the RRC message includes a configuration for releasing the NR PDCP-layer device for the first bearer identifier <NUM>, which is established for the NR PDCP-layer device and the LTE RLC-layer device, and includes LTE PDCP configuration information corresponding to the first bearer identifier <NUM> (when an NR PDCP-layer device for a bearer is changed to an LTE PDCP-layer device), the following procedure may be performed. DRB ID <NUM><NUM> corresponds to an NR RLC layer associated with an NR PDCP layer.

When the UE receives RRC messages from the LTE base station or the NR base station and receives an indication to change the version of a PDCP-layer device for a certain bearer, the UE performs a second embodiment as follows.

As described above, when the UE receives RRC messages from the LTE base station or the NR base station and receives an indication to change the version of a PDCP-layer device for a certain bearer, the UE performs a third embodiment according to the disclosure.

As described above, when a UE receives an RRC message and receives an indication to change the version of a PDCP-layer device, in order to prevent the loss of uplink data of a first bearer, the UE releases an existing version of a PDCP-layer device corresponding to the first bearer and delivers pieces of data (for example, PDCP SDUs) stored in the existing version of the PDCP-layer device to a newly configured version of a PDCP-layer device before discarding the data so that the new version of the PDCP-layer device processes the data again, such as by configuring a PDCP PDU by newly configuring a PDCP header for the delivered PDCP SDUs according to the configuration of the new PDCP-layer device and by performing integrity protection or encryption with a new security key, regarding the data as being received from an upper-layer device, and transmits the data.

The same method of changing the version of the PDCP-layer device without loss disclosed herein may also be applied to base stations for downlink data in an extended manner. For example, when a base station transmits an indication to change the version of a PDCP-layer device to a UE via an RRC message, in order to prevent the loss of downlink data of a first bearer, the base station having an existing version of a PDCP-layer device corresponding to the first bearer may release the PDCP-layer device and may deliver pieces of data (for example, PDCP SDUs) stored in the existing version of the PDCP-layer device to a base station having a newly configured version of a PDCP-layer device before discarding the data so that the new version of the PDCP-layer device may process the data again, such as by configuring a PDCP PDU by newly configuring a PDCP header for the delivered PDCP SDUs according to the configuration of the new PDCP-layer device and by performing integrity protection or encryption with a new security key, regarding the data as being received from an upper-layer device, and may transmit the data. The first embodiment, the second embodiment, or the third embodiment of the method of changing the version of the PDCP-layer device without loss disclosed herein may also be applied to an LTE base station and an NR base station which transmit downlink data in an extended manner.

<FIG> illustrates a UE operation in a procedure for changing the version of a PDCP-layer device without loss according to an embodiment.

In <FIG>, a UE receives an RRC message in step <NUM>. The RRC message may be either an RRC connection setup message (RRCConnectionSetup message) or an RRC connection reconfiguration message (RRCConnectionReconfiguration message), without being limited thereto.

The UE identifies whether an indication to change the version of a PDCP-layer device is received based on the RRC message in step <NUM>. When the indication to change the version of the PDCP-layer device is received, in order to prevent the loss of uplink data of a first bearer, the UE releases an existing version of a PDCP-layer device corresponding to the first bearer and delivers pieces of data (for example, PDCP SDUs) stored in the existing version of the PDCP-layer device to a newly configured version of a PDCP-layer device before discarding the data in step <NUM>. The new version of the PDCP-layer device regards the data delivered from the existing PDCP-layer device as being data received from an upper-layer device and processes the data again, such as by configuring a PDCP PDU by newly configuring a PDCP header for the delivered PDCP SDUs according to the configuration of the new PDCP-layer device and by performing integrity protection or encryption with a new security key, and transmits the data in step <NUM>.

In the UE operation, pieces of data to transmit to a PDCP-layer device after a version change among pieces of data (for example, PDCP SDUs) stored in a PDCP-layer device before the version change may be determined according to the first embodiment, the second embodiment, or the third embodiment provided in the disclosure.

Although <FIG> illustrates uplink transmission of a UE as an example, the foregoing operation may be equally applied to the downlink operation of a base station. The UE or the base station may be defined as a transmission device. When the transmission device identifies a PDCP-layer device version change through an RRC message or the like, the transmission device may change a PDCP-layer device and prevent data loss according to the methods herein, thus transmitting data via a new version of a PDCP-layer device.

<FIG> illustrates a detailed UE operation in a procedure for changing the version of a PDCP-layer device without loss according to an embodiment.

The UE identifies whether a first condition is satisfied in step <NUM>.

When the first condition is satisfied, such as when the RRC message including a configuration for releasing an LTE PDCP device corresponding to a first bearer identifier does not include NR PDCP configuration information corresponding to the first bearer identifier and an NR PDCP for the first bearer identifier is already configured, i.e., when it is indicated to change the LTE PDCP-layer device to the NR PDCP-layer device, the UE performs step <NUM> as follows.

When a second condition is satisfied rather than the first condition in step <NUM>, i.e., when the RRC message including a configuration for releasing the NR PDCP device for the first bearer identifier, for which the NR PDCP device and the LTE RLC device are configured, includes configuration information about the LTE PDCP-layer device corresponding to the first bearer identifier, the UE performs step <NUM> as follows.

When neither the first condition nor the second condition is satisfied and it is indicated to release the LTE PDCP-layer device or the NR PDCP-layer device in step <NUM>, the UE performs step <NUM> in which the UE discards PDCP SDUs and PDCP PDUs and releases the LTE PDCP-layer device or the NR PDCP-layer device.

Although <FIG> illustrates uplink transmission of a UE as an example, the foregoing operation may be equally applied to the downlink operation of a base station.

In the following embodiments, data loss that may occur due to the configuration of a PDCP reordering timer in a reception PDCP-layer device is illustrated, and a solution thereto is disclosed.

A PDCP-layer device may operate a PDCP reordering timer, and the PDCP reordering timer operates or starts when a PDCP sequence number gap occurs relative to a PDCP sequence number in the reception PDCP-layer device. When data corresponding to the PDCP sequence number gap is not received until the PDCP reordering timer expires, pieces of data are transmitted to an upper-layer device in ascending order of PDCP sequence numbers or COUNT values and a reception window is moved after the transmitted PDCP sequence number. Therefore, when the data corresponding to the PDCP sequence number gap is received after the expiration of the PDCP reordering timer, since the data is not data within the reception window, the reception PDCP-layer device discards the data, resulting in data loss.

Therefore, in order to prevent data loss, when an AM DRB is configured for a UE via an RRC message, a PDCP-layer device of the AM DRB of the UE does not use a PDCP reordering timer. Alternatively, when the AM DRB is configured, the PDCP-layer device of the AM DRB of the UE sets a PDCP reordering timer to an infinite value. Alternatively, when a base station configures an AM DRB for the UE, the base station does not configure a PDCP reordering timer of a PDCP-layer device corresponding to the AM DRB or set a PDCP reordering timer to an infinite value.

<FIG> illustrates the configuration of a UE according to an embodiment.

Referring to <FIG>, the UE includes a radio frequency (RF) processor <NUM>, a baseband processor <NUM>, a storage unit <NUM>, and a controller <NUM>. The controller <NUM> may include a multi-connection processor <NUM>.

The RF processor <NUM> transmits or receives a signal through a wireless channel, such as band conversion and amplification of a signal. That is, the RF processor <NUM> upconverts a baseband signal, provided from the baseband processor <NUM>, into an RF band signal to transmit the RF band signal through an antenna and downconverts an RF band signal, received through the antenna, into a baseband signal. The RF processor <NUM> may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), and an analog-to-digital converter (ADC). Although <FIG> shows only one antenna, the UE may include a plurality of antennas. In addition, the RF processor <NUM> may include a plurality of RF chains.

The RF processor <NUM> may perform beamforming by adjusting the phase and strength of each of signals transmitted and received through a plurality of antennas or antenna elements. The RF processor may perform MIMO and may receive a plurality of layers when performing MIMO, may perform reception beam sweeping by appropriately setting the plurality of antennas or antenna elements under the control of the controller <NUM>, or may adjust the orientation and width of a reception beam such that the reception beam is coordinated with a transmission beam.

The baseband processor <NUM> converts a baseband signal and a bit stream according to the physical-layer specification of a system. For example, in data transmission, the baseband processor <NUM> encodes and modulates a transmission bit stream, thereby generating complex symbols. In data reception, the baseband processor <NUM> demodulates and decodes a baseband signal, provided from the RF processor <NUM>, thereby reconstructing a reception bit stream. For example, according to OFDM, in data transmission, the baseband processor <NUM> generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and constructs OFDM symbols through inverse fast Fourier transform (IFFT) and cyclic prefix (CP) insertion. In data reception, the baseband processor <NUM> divides a baseband signal, provided from the RF processor <NUM>, into OFDM symbols, reconstructs signals mapped to subcarriers through fast Fourier transform (FFT), and reconstructs a reception bit stream through demodulation and decoding.

As described above, the baseband processor <NUM> and the RF processor <NUM> transmit and receive signals, and thus, may be referred to as a transmitter, a receiver, a transceiver, or a communication unit. At least one of the baseband processor <NUM> and the RF processor <NUM> may include a plurality of communication modules to support a plurality of different radio access technologies such as LTE and NR networks, and may include different communication modules for processing signals in different frequency bands. The different frequency bands may include a super high frequency (SHF) band (for example, <NUM> and <NUM>) and a millimeter wave band (for example, <NUM>).

The storage unit <NUM> stores data, such as a default program, an application, and configuration information for operating the UE, and provides stored data upon request from the controller <NUM>.

The controller <NUM> controls overall operations of the UE. For example, the controller <NUM> transmits and receives signals through the baseband processor <NUM> and the RF processor <NUM>, and records and reads data in the storage unit <NUM>. To this end, the controller <NUM> may include at least one processor, such as a communication processor to perform control for communication and an application processor (AP) to control an upper layer, such as an application.

<FIG> illustrates the configuration of a base station according to an embodiment.

Referring to <FIG>, the base station includes an RF processor <NUM>, a baseband processor <NUM>, a communication unit <NUM>, a storage unit <NUM>, and a controller <NUM>. The controller <NUM> may include a multi-connection processor <NUM>.

The RF processor <NUM> transmits or receives a signal through a wireless channel, such as band conversion and amplification of a signal. That is, the RF processor <NUM> upconverts a baseband signal, provided from the baseband processor <NUM>, into an RF band signal to transmit the RF band signal through an antenna and downconverts an RF band signal, received through the antenna, into a baseband signal. The RF processor <NUM> may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, and an ADC. Although <FIG> shows only one antenna, the base station may include a plurality of antennas. In addition, the RF processor <NUM> may include a plurality of RF chains, and may perform beamforming by adjusting the phase and strength of each of signals transmitted and received through a plurality of antennas or antenna elements. The RF processor may transmit one or more layers, thereby performing downlink MIMO.

The baseband processor <NUM> converts a baseband signal and a bit stream according to the physical-layer specification of a first radio access technology. For example, in data transmission, the baseband processor <NUM> encodes and modulates a transmission bit stream, thereby generating complex symbols. In data reception, the baseband processor <NUM> demodulates and decodes a baseband signal, provided from the RF processor <NUM>, thereby reconstructing a reception bit stream. For example, according to OFDM, in data transmission, the baseband processor <NUM> generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and constructs OFDM symbols through IFFT and CP insertion. In data reception, the baseband processor <NUM> divides a baseband signal, provided from the RF processor <NUM>, into OFDM symbols, reconstructs signals mapped to subcarriers through FFT, and reconstructs a reception bit stream through demodulation and decoding. The baseband processor <NUM> and the RF processor <NUM> transmit and receive signals, and thus, may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

The communication unit <NUM> provides an interface for performing communication with other nodes in a network.

The storage unit <NUM> stores data, such as a default program, an application, and configuration information for operating the base station. In particular, the storage unit <NUM> may store information on a bearer allocated to a connected UE, a measurement result reported from a connected UE, and the like. In addition, the storage unit <NUM> may store information as a criterion for determining whether to provide or stop a multi-connection to a UE. The storage unit <NUM> provides stored data upon request from the controller <NUM>.

Claim 1:
A method performed by a terminal in a wireless communication system, the method comprising:
receiving (<NUM>; <NUM>), from a base station, a radio resource control, RRC, message including information instructing a change from a first packet data convergence protocol, PDCP, entity for a bearer to a second PDCP entity for the bearer, the first PDCP entity and the second PDCP entity being in the terminal, the method being characterized by:
identifying whether the first PDCP entity for the bearer is changed to the second PDCP entity for the bearer based on the information indicating the change;
transferring (<NUM>) first data from the first PDCP entity to the second PDCP entity, in case that the first PDCP entity for the bearer is changed to the second PDCP entity for the bearer;
releasing the first PDCP entity;
configuring a new PDCP header associated with the first data; and
encrypting the first data with a new security key,
wherein the first data is associated with a first PDCP sequence number which is greater than or equal to a second PDCP sequence number for which successful transmission is not acknowledged, from a radio link control, RLC, entity.