WO2018062786A1

WO2018062786A1 - Method and apparatus for controlling srb

Info

Publication number: WO2018062786A1
Application number: PCT/KR2017/010535
Authority: WO
Inventors: 이영대; 김상원; 이재욱
Original assignee: 엘지전자 주식회사
Priority date: 2016-09-28
Filing date: 2017-09-25
Publication date: 2018-04-05

Abstract

Provided are a method for a terminal controlling a signaling radio bearer (SRB) in a wireless communication system and an apparatus supporting same. The method comprises the steps of: establishing a radio resource control (RRC) connection with a first base station and setting a first SRB; setting a second base station and a second SRB, wherein the second SRB is temporarily suspended; and resuming the temporarily suspended second SRB when the quality of a cell in the first base station is worse than a first critical value.

Description

Methods and Devices for Controlling SRBs

The present invention relates to a wireless communication system, and more particularly, to a method for a terminal to control a signaling radio bearer (SRB) and an apparatus supporting the same.

Efforts have been made to develop an improved 5th-generation (5G) communication system or a pre-5G communication system to meet the increasing demand for wireless data traffic since the commercialization of a 4th-generation (4G) communication system. For this reason, a 5G communication system or a pre-5G communication system is called a system after a 4G network (beyond 4G network) or after a long term evolution (LTE) system (post LTE).

The terminal continuously measures to maintain the quality of the radio link with the serving cell receiving the service. The terminal determines whether communication is impossible in the current situation due to deterioration of the quality of the radio link with the serving cell. If the quality of the serving cell is so low that communication is almost impossible, the terminal determines the current situation as a Radio Link Failure (RLF). If the radio link failure is determined, the UE abandons communication maintenance with the current serving cell, selects a new cell through a cell selection (or cell reselection) procedure, and attempts to reestablish RRC connection to the new cell.

On the other hand, in general, the reliability of the RRC connection is important. If a connection failure occurs, not only the terminal but also the base station cannot use a data radio bearer (DRB), and thus data transmission is impossible. For example, while the RRC connection reestablishment procedure is in progress, the UE cannot perform data transmission / reception. Therefore, in order to secure the reliability of the RRC connection, a method for controlling a signaling radio bearer (SRB) by the terminal and an apparatus supporting the same need to be proposed.

In one embodiment, a method for controlling a signaling radio bearer (SRB) by a terminal in a wireless communication system is provided. The method includes: establishing a radio resource control (RRC) connection with a first base station and establishing a first SRB; Establishing a second SRB with a second base station, wherein the second SRB is in a suspended state; And if the quality of the cell at the first base station is worse than a first threshold, resuming the suspended second SRB.

The method may further include suspending the first SRB.

The method may further include resuming the suspended second SRB if the quality of the cell at the second base station is better than a second threshold.

The method may further include resuming the suspended second SRB when a radio link failure related timer or a handover failure related timer is started.

The method may further include resuming the suspended second SRB when a re-establishment procedure for the RRC connection is initiated.

The method may further include resuming the suspended second SRB when the terminal determines to suspend the first SRB.

The second SRB may be a temporary SRB.

The first base station may be a base station in which an RRC entity for the terminal is located, and the second base station may be a base station in which an RRC entity for the terminal is not located.

In another embodiment, a method for controlling a signaling radio bearer (SRB) by a terminal in a wireless communication system is provided. The method comprises: establishing a radio resource control (RRC) connection and a first SRB with a first base station, wherein the first SRB is in a suspended state; Establishing a second base station and a second SRB; And if the quality of the cell at the first base station is better than a first threshold, resuming the suspended first SRB.

The method may further include suspending the second SRB.

The method may further include resuming the suspended first SRB if the quality of the cell at the second base station is worse than a second threshold.

The method may further include resuming the suspended first SRB when the radio link failure related timer or the handover failure related timer is stopped.

The method may further include resuming the suspended first SRB when the terminal determines to suspend the second SRB.

In another embodiment, a terminal for controlling a signaling radio bearer (SRB) in a wireless communication system is provided. The terminal includes a memory; Transceiver; And a processor connecting the memory and the transceiver, wherein the processor establishes a radio resource control (RRC) connection and a first SRB and a second base station and a second SRB. The SRB is in a suspended state, and may be configured to resume the suspended second SRB if the quality of the cell at the first base station is worse than a first threshold.

The reliability of the RRC connection can be improved.

1 shows a structure of an LTE system.

2 shows an air interface protocol of an LTE system for a control plane.

3 shows an air interface protocol of an LTE system for a user plane.

4 shows an RRC connection establishment procedure.

5 shows an RRC connection reconfiguration procedure.

6 shows an RRC connection reestablishment procedure.

7 illustrates a procedure of controlling an SRB by a terminal according to an embodiment of the present invention.

8 illustrates a procedure of controlling an SRB by a terminal according to an embodiment of the present invention.

9 illustrates an example in which a temporary SRB is set according to an embodiment of the present invention.

FIG. 10 illustrates a method for maintaining an RRC connection through a temporary SRB and a procedure for a UE to reestablish an RRC connection when a connection fails according to an embodiment of the present invention.

11 is a block diagram illustrating a method of controlling an SRB by a terminal according to an embodiment of the present invention.

12 is a block diagram illustrating a method of controlling an SRB by a terminal according to an embodiment of the present invention.

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

The following techniques include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and the like. It can be used in various wireless communication systems. CDMA may be implemented with a radio technology such as universal terrestrial radio access (UTRA) or CDMA2000. TDMA may be implemented with wireless technologies such as global system for mobile communications (GSM) / general packet radio service (GPRS) / enhanced data rates for GSM evolution (EDGE). OFDMA may be implemented by wireless technologies such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), and the like. IEEE 802.16m is an evolution of IEEE 802.16e and provides backward compatibility with systems based on IEEE 802.16e. UTRA is part of a universal mobile telecommunications system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is part of evolved UMTS (E-UMTS) using evolved-UMTS terrestrial radio access (E-UTRA), which employs OFDMA in downlink and SC in uplink -FDMA is adopted. LTE-A (advanced) is the evolution of 3GPP LTE. 5G communication system is the evolution of LTE-A.

For clarity, the following description focuses on LTE-A / 5G, but the technical spirit of the present invention is not limited thereto.

1 shows a structure of an LTE system. Communication networks are widely deployed to provide various communication services such as IMS and Voice over internet protocol (VoIP) over packet data.

Referring to FIG. 1, an LTE system structure includes one or more UEs 10, an evolved-UMTS terrestrial radio access network (E-UTRAN), and an evolved packet core (EPC). The terminal 10 is a communication device moved by a user. The terminal 10 may be fixed or mobile and may be called by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), and a wireless device.

The E-UTRAN may include one or more evolved node-eB (eNB) 20, and a plurality of terminals may exist in one cell. The eNB 20 provides an end point of a control plane and a user plane to the terminal. The eNB 20 generally refers to a fixed station communicating with the terminal 10, and may be referred to in other terms such as a base station (BS), a base transceiver system (BTS), an access point, and the like. . One eNB 20 may be arranged per cell. There may be one or more cells within the coverage of the eNB 20. One cell may be configured to have one of bandwidths such as 1.25, 2.5, 5, 10, and 20 MHz to provide downlink (DL) or uplink (UL) transmission service to various terminals. In this case, different cells may be configured to provide different bandwidths.

Hereinafter, DL means communication from the eNB 20 to the terminal 10, and UL means communication from the terminal 10 to the eNB 20. In the DL, the transmitter may be part of the eNB 20 and the receiver may be part of the terminal 10. In the UL, the transmitter may be part of the terminal 10 and the receiver may be part of the eNB 20.

The EPC may include a mobility management entity (MME) that serves as a control plane, and a system architecture evolution (SAE) gateway (S-GW) that serves as a user plane. The MME / S-GW 30 may be located at the end of the network and is connected to an external network. The MME has information about the access information of the terminal or the capability of the terminal, and this information may be mainly used for mobility management of the terminal. S-GW is a gateway having an E-UTRAN as an endpoint. The MME / S-GW 30 provides the terminal 10 with the endpoint of the session and the mobility management function. The EPC may further include a packet data network (PDN) -gateway (GW). PDN-GW is a gateway with PDN as an endpoint.

The MME includes non-access stratum (NAS) signaling to the eNB 20, NAS signaling security, access stratum (AS) security control, inter CN (node network) signaling for mobility between 3GPP access networks, idle mode terminal reachability ( Control and execution of paging retransmission), tracking area list management (for terminals in idle mode and active mode), P-GW and S-GW selection, MME selection for handover with MME change, 2G or 3G 3GPP access Bearer management, including roaming, authentication, and dedicated bearer settings, SGSN (serving GPRS support node) for handover to the network, public warning system (ETWS) and commercial mobile alarm system (PWS) It provides various functions such as CMAS) and message transmission support. S-GW hosts can be based on per-user packet filtering (eg, through deep packet inspection), legal blocking, terminal IP (Internet protocol) address assignment, transport level packing marking in DL, UL / DL service level charging, gating and It provides various functions of class enforcement, DL class enforcement based on APN-AMBR. For clarity, the MME / S-GW 30 is simply represented as a "gateway", which may include both MME and S-GW.

An interface for user traffic transmission or control traffic transmission may be used. The terminal 10 and the eNB 20 may be connected by the Uu interface. The eNBs 20 may be interconnected by an X2 interface. Neighboring eNBs 20 may have a mesh network structure by the X2 interface. The eNBs 20 may be connected with the EPC by the S1 interface. The eNBs 20 may be connected to the EPC by the S1-MME interface and may be connected to the S-GW by the S1-U interface. The S1 interface supports a many-to-many-relation between eNB 20 and MME / S-GW 30.

The eNB 20 may select for the gateway 30, routing to the gateway 30 during radio resource control (RRC) activation, scheduling and transmission of paging messages, scheduling channel information (BCH), and the like. Perform connection mobility control in transmission, dynamic allocation of resources from the UL and DL to the terminals 10, configuration and provisioning of eNB measurements, radio bearer control, radio admission control (RAC) and LTE activation can do. As mentioned above, the gateway 30 may perform paging initiation, LTE idle state management, user plane encryption, SAE bearer control, and encryption and integrity protection functions of NAS signaling in the EPC.

2 shows an air interface protocol of an LTE system for a control plane. 3 shows an air interface protocol of an LTE system for a user plane.

The layer of the air interface protocol between the UE and the E-UTRAN is based on the lower three layers of the open system interconnection (OSI) model, which is well known in communication systems, and includes L1 (first layer), L2 (second layer), and L3 (third layer). Hierarchical). The air interface protocol between the UE and the E-UTRAN may be horizontally divided into a physical layer, a data link layer, and a network layer, and vertically a protocol stack for transmitting control signals. ) Can be divided into a control plane and a user plane which is a protocol stack for transmitting data information. Layers of the radio interface protocol may exist in pairs in the UE and the E-UTRAN, which may be responsible for data transmission of the Uu interface.

The physical layer (PHY) belongs to L1. The physical layer provides an information transmission service to a higher layer through a physical channel. The physical layer is connected to a higher layer of a media access control (MAC) layer through a transport channel. Physical channels are mapped to transport channels. Data may be transmitted between the MAC layer and the physical layer through a transport channel. Data between different physical layers, that is, between the physical layer of the transmitter and the physical layer of the receiver may be transmitted using radio resources through a physical channel. The physical layer may be modulated using an orthogonal frequency division multiplexing (OFDM) scheme, and utilizes time and frequency as radio resources.

The physical layer uses several physical control channels. A physical downlink control channel (PDCCH) reports resource allocation of a paging channel (PCH) and a downlink shared channel (DL-SCH), and hybrid automatic repeat request (HARQ) information related to the DL-SCH to the UE. The PDCCH may carry an uplink grant to report to the UE regarding resource allocation of uplink transmission. The physical control format indicator channel (PCFICH) informs the UE of the number of OFDM symbols used for the PDCCH and is transmitted every subframe. A physical hybrid ARQ indicator channel (PHICH) carries a HARQ ACK (non-acknowledgement) / NACK (non-acknowledgement) signal for UL-SCH transmission. A physical uplink control channel (PUCCH) carries UL control information such as HARQ ACK / NACK, a scheduling request, and a CQI for downlink transmission. The physical uplink shared channel (PUSCH) carries an uplink shared channel (UL-SCH).

The physical channel includes a plurality of subframes in the time domain and a plurality of subcarriers in the frequency domain. One subframe consists of a plurality of symbols in the time domain. One subframe consists of a plurality of resource blocks (RBs). One resource block is composed of a plurality of symbols and a plurality of subcarriers. In addition, each subframe may use specific subcarriers of specific symbols of the corresponding subframe for the PDCCH. For example, the first symbol of the subframe may be used for the PDCCH. The PDCCH may carry dynamically allocated resources, such as a physical resource block (PRB) and modulation and coding schemes (MCS). A transmission time interval (TTI), which is a unit time at which data is transmitted, may be equal to the length of one subframe. One subframe may have a length of 1 ms.

The transport channel is classified into a common transport channel and a dedicated transport channel depending on whether the channel is shared or not. A DL transport channel for transmitting data from a network to a UE includes a broadcast channel (BCH) for transmitting system information, a paging channel (PCH) for transmitting a paging message, and a DL-SCH for transmitting user traffic or control signals. And the like. The DL-SCH supports dynamic link adaptation and dynamic / semi-static resource allocation by varying HARQ, modulation, coding and transmit power. In addition, the DL-SCH may enable the use of broadcast and beamforming throughout the cell. System information carries one or more system information blocks. All system information blocks can be transmitted in the same period. Traffic or control signals of a multimedia broadcast / multicast service (MBMS) are transmitted through a multicast channel (MCH).

The UL transport channel for transmitting data from the terminal to the network includes a random access channel (RAC) for transmitting an initial control message, a UL-SCH for transmitting user traffic or a control signal, and the like. The UL-SCH can support dynamic link adaptation due to HARQ and transmit power and potential changes in modulation and coding. In addition, the UL-SCH may enable the use of beamforming. RACH is generally used for initial connection to a cell.

The MAC layer belonging to L2 provides a service to a radio link control (RLC) layer, which is a higher layer, through a logical channel. The MAC layer provides a mapping function from a plurality of logical channels to a plurality of transport channels. The MAC layer also provides a logical channel multiplexing function by mapping from multiple logical channels to a single transport channel. The MAC sublayer provides data transfer services on logical channels.

The logical channel may be divided into a control channel for information transmission in the control plane and a traffic channel for information transmission in the user plane according to the type of information to be transmitted. That is, a set of logical channel types is defined for other data transfer services provided by the MAC layer. The logical channel is located above the transport channel and mapped to the transport channel.

The control channel is used only for conveying information in the control plane. The control channel provided by the MAC layer includes a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), and a dedicated control channel (DCCH). BCCH is a downlink channel for broadcasting system control information. PCCH is a downlink channel used for transmitting paging information and paging a terminal whose cell-level location is not known to the network. CCCH is used by the terminal when there is no RRC connection with the network. MCCH is a one-to-many downlink channel used to transmit MBMS control information from the network to the terminal. DCCH is a one-to-one bidirectional channel used by the terminal for transmitting dedicated control information between the terminal and the network in an RRC connection state.

The traffic channel is used only for conveying information in the user plane. The traffic channel provided by the MAC layer includes a dedicated traffic channel (DTCH) and a multicast traffic channel (MTCH). DTCH is used for transmission of user information of one UE in a one-to-one channel and may exist in both uplink and downlink. MTCH is a one-to-many downlink channel for transmitting traffic data from the network to the terminal.

The uplink connection between the logical channel and the transport channel includes a DCCH that can be mapped to the UL-SCH, a DTCH that can be mapped to the UL-SCH, and a CCCH that can be mapped to the UL-SCH. The downlink connection between the logical channel and the transport channel is a BCCH that can be mapped to a BCH or DL-SCH, a PCCH that can be mapped to a PCH, a DCCH that can be mapped to a DL-SCH, a DTCH that can be mapped to a DL-SCH, MCCH that can be mapped to MCH and MTCH that can be mapped to MCH.

The RLC layer belongs to L2. The function of the RLC layer includes adjusting the size of the data by segmentation / concatenation of the data received from the upper layer in the radio section such that the lower layer is suitable for transmitting data. In order to guarantee the various QoS required by the radio bearer (RB), the RLC layer is divided into three modes: transparent mode (TM), unacknowledged mode (UM) and acknowledged mode (AM). Provides three modes of operation. AM RLC provides retransmission through automatic repeat request (ARQ) for reliable data transmission. Meanwhile, the function of the RLC layer may be implemented as a functional block inside the MAC layer, in which case the RLC layer may not exist.

The packet data convergence protocol (PDCP) layer belongs to L2. The PDCP layer introduces an IP packet, such as IPv4 or IPv6, over a relatively low bandwidth air interface to provide header compression that reduces unnecessary control information so that the transmitted data is transmitted efficiently. Header compression improves transmission efficiency in the wireless section by transmitting only the information necessary for the header of the data. In addition, the PDCP layer provides security. Security functions include encryption to prevent third party inspection and integrity protection to prevent third party data manipulation.

The radio resource control (RRC) layer belongs to L3. The RRC layer at the bottom of L3 is defined only in the control plane. The RRC layer serves to control radio resources between the terminal and the network. To this end, the UE and the network exchange RRC messages through the RRC layer. The RRC layer is responsible for the control of logical channels, transport channels and physical channels in connection with the configuration, re-configuration and release of RBs. RB is a logical path provided by L1 and L2 for data transmission between the terminal and the network. That is, RB means a service provided by L2 for data transmission between the UE and the E-UTRAN. Setting up an RB means defining the characteristics of the radio protocol layer and channel to provide a particular service, and determining each specific parameter and method of operation. RBs may be classified into two types: signaling RBs (SRBs) and data RBs (DRBs). The SRB is used as a path for transmitting RRC messages in the control plane, and the DRB is used as a path for transmitting user data in the user plane.

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

Referring to FIG. 2, the RLC and MAC layers (end at the eNB at the network side) may perform functions such as scheduling, ARQ and HARQ. The RRC layer (ended at the eNB at the network side) may perform functions such as broadcast, paging, RRC connection management, RB control, mobility function, and UE measurement report / control. The NAS control protocol (terminated at the gateway's MME at the network side) may perform functions such as SAE bearer management, authentication, LTE_IDLE mobility handling, paging initiation at LTE_IDLE, and security control for signaling between the terminal and the gateway.

Referring to FIG. 3, the RLC and MAC layer (end at the eNB at the network side) may perform the same function as the function in the control plane. The PDCP layer (terminating at the eNB at the network side) may perform user plane functions such as header compression, integrity protection and encryption.

4 shows an RRC connection establishment procedure.

The terminal sends an RRC connection request message to the network requesting an RRC connection (S410). The network sends an RRC connection setup message in response to the RRC connection request (S420). After receiving the RRC connection setup message, the terminal enters the RRC connection mode.

The UE sends an RRC Connection Setup Complete message to the network, which is used to confirm successful completion of RRC connection establishment (S430).

5 shows an RRC connection reconfiguration procedure.

RRC connection reset is used to modify an RRC connection. It is used to set / modify / release RBs, perform handovers, and set up / modify / release measurements.

The network sends an RRC connection reconfiguration message for modifying the RRC connection to the terminal (S510). In response to the RRC connection reconfiguration, the UE sends an RRC connection reconfiguration complete message used to confirm successful completion of the RRC connection reconfiguration to the network (S520).

6 shows an RRC connection reestablishment procedure.

Referring to FIG. 6, the UE stops using all radio bearers which are set except for Signaling Radio Bearer # 0 (SRB 0) and initializes various sublayers of an access stratum (AS) (S610). In addition, each sublayer and physical layer are set to a default configuration. During this process, the UE maintains an RRC connection state.

The UE performs a cell selection procedure for performing an RRC connection reestablishment procedure (S620). The cell selection procedure of the RRC connection reestablishment procedure may be performed in the same manner as the cell selection procedure performed by the UE in the RRC idle state, although the UE maintains the RRC connection state.

After performing the cell selection procedure, the terminal checks system information of the corresponding cell to determine whether the corresponding cell is a suitable cell (S630). If it is determined that the selected cell is an appropriate E-UTRAN cell, the UE transmits an RRC connection reestablishment request message to the cell (S640).

On the other hand, if it is determined through the cell selection procedure for performing the RRC connection reestablishment procedure that the selected cell is a cell using a different RAT other than E-UTRAN, the RRC connection reestablishment procedure is stopped, the terminal is in the RRC idle state Enter (S650).

The terminal may be implemented to complete the confirmation of the appropriateness of the cell within a limited time through the cell selection procedure and receiving system information of the selected cell. To this end, the UE may drive a timer as the RRC connection reestablishment procedure is initiated. The timer may be stopped when it is determined that the terminal has selected a suitable cell. If the timer expires, the UE may consider that the RRC connection reestablishment procedure has failed and may enter the RRC idle state. This timer is referred to hereinafter as a radio link failure timer. In LTE specification TS 36.331, a timer named T311 may be used as a radio link failure timer. The terminal may obtain the setting value of this timer from the system information of the serving cell.

When the RRC connection reestablishment request message is received from the terminal and the request is accepted, the cell transmits an RRC connection reestablishment message to the terminal.

Upon receiving the RRC connection reestablishment message from the cell, the UE reconfigures the PDCP sublayer and the RLC sublayer for SRB1. In addition, it recalculates various key values related to security setting and reconfigures the PDCP sublayer responsible for security with newly calculated security key values. Through this, SRB 1 between the UE and the cell is opened and an RRC control message can be exchanged. The UE completes the resumption of SRB1 and transmits an RRC connection reestablishment complete message indicating that the RRC connection reestablishment procedure is completed to the cell (S660).

On the contrary, if the RRC connection reestablishment request message is received from the terminal and the request is not accepted, the cell transmits an RRC connection reestablishment reject message to the terminal.

If the RRC connection reestablishment procedure is successfully performed, the cell and the terminal perform the RRC connection reestablishment procedure. Through this, the UE recovers the state before performing the RRC connection reestablishment procedure and guarantees the continuity of the service to the maximum.

On the other hand, in general, the reliability of the RRC connection is important. If a connection failure occurs, not only the terminal but also the base station cannot use a data radio bearer (DRB), and thus data transmission is impossible.

In LTE, the RRC function supports recovery of an RRC connection by using an RRC connection reestablishment procedure. When the RRC connection reestablishment procedure is triggered, the UE may perform cell selection and access to the selected cell. After the RRC connection reconfiguration, the terminal may resume data transmission. However, it may take time until the RRC connection reestablishment procedure is completed, and data transmission may be impossible during the corresponding time. Due to the interruption time as described above, user plane latency may be surpassed and packet delay may be increased. Therefore, reliable RRC connections are very important to minimize interruption time in connection failure cases.

In small cell enhancement of LTE, RRC diversity has been regarded as a potential solution for improving mobility robustness. Due to RRC diversity, RLF can be prevented as long as the terminal can maintain a connection with at least one cell. This may prevent the RRC reestablishment procedure from being performed.

In the end, however, RRC diversity was not reflected in the LTE standard. In fact, it is also not clear to support RRC diversity when the RRC connection is in good condition. Moreover, various means exist to improve the reliability of RRC message delivery. In LTE, all RRC messages are carried over the MCG. For example, all RRC messages are carried over the MCG regardless of the SRB used in both downlink and uplink. This is also acceptable for LTE / NR interworking and standalone NR as long as the RRC connection is not jeopardized (eg, connection failure case). Thus, a mechanism to improve the reliability of the RRC connection may be needed only in connection failure cases. Hereinafter, a method for controlling a signaling radio bearer (SRB) by a terminal and an apparatus supporting the same according to an embodiment of the present invention will be described.

Referring to FIG. 7, in step S710, the UE may make an RRC connection with the first base station and set up the first base station and the first SRB. The first base station may be a master eNB or a gNB. The first base station may be a base station where an RRC entity for the terminal is located. The first SRB may provide exchange of RRC messages between the RRC entity of the first base station and the RRC entity of the terminal. The first SRB may be one or more.

In step S720, the terminal may set up a radio resource (and radio bearer) with the second base station, and set up the second base station and the second SRB. The second base station may be a secondary eNB or a gNB. The second base station may be a base station where an RRC entity for the terminal is not located. The second base station may be connected to the first base station. The second SRB may provide exchange of RRC messages between the RRC entity of the first base station and the RRC entity of the terminal. The second SRB may be one or more. The second SRB may be a temporary SRB.

In operation S730, the second SRB may be suspended. Preferably, the first SRB may be in a non-suspended state, while the second SRB may be in a suspended state.

In step S740, the terminal may detect a condition for resuming the suspended second SRB. Alternatively, the terminal may detect a condition of suspending the first SRB. The conditions for resuming the suspended second SRB or the conditions for suspending the first SRB are as follows.

1-1 condition: The cell quality of the cell at the second base station is better than the threshold value.

Condition 1-2: Cell quality of the cell at the first base station is worse than the threshold.

Condition 1-3: The timer associated with the radio link failure is started.

Condition 1-4: The timer associated with the handover failure is started.

Condition 1-5: An RRC connection reestablishment procedure for the terminal is initiated.

Condition 1-6: The UE decides to suspend the first SRB. For example, if data cannot be transmitted over the first SRB through the first base station, the terminal may decide to suspend the first SRB.

In operation S750, when at least one of the conditions 1-1 to 1-6 is detected, the terminal may resume the suspended second SRB. Furthermore, the terminal may suspend the first SRB.

Referring to FIG. 8, in step S810, the UE may establish an RRC connection with the first base station and set up the first base station and the first SRB. The first base station may be a master eNB or a gNB. The first base station may be a base station where an RRC entity for the terminal is located. The first SRB may provide exchange of RRC messages between the RRC entity of the first base station and the RRC entity of the terminal. The first SRB may be one or more.

In step S820, the terminal may set up a radio resource (and radio bearer) with the second base station, and set up the second base station and the second SRB. The second base station may be a secondary eNB or a gNB. The second base station may be a base station where an RRC entity for the terminal is not located. The second base station may be connected to the first base station. The second SRB may provide exchange of RRC messages between the RRC entity of the first base station and the RRC entity of the terminal. The second SRB may be one or more. The second SRB may be a temporary SRB.

In operation S830, the first SRB may be suspended. Preferably, the second SRB may be in a non-suspended state, while the first SRB may be in a suspended state.

In step S840, the terminal may detect a condition for resuming the suspended first SRB. Alternatively, the terminal may detect a condition of suspending the second SRB. The conditions for resuming the suspended first SRB or the conditions for suspending the second SRB are as follows.

2-1 condition: The cell quality of the cell at the first base station is better than the threshold value.

2-2 Condition: The cell quality of the cell at the second base station is worse than the threshold value.

Condition 2-3: The timer associated with the radio link failure is stopped.

Condition 2-4: The timer associated with the handover failure is stopped.

Condition 2-5: The RRC connection reestablishment procedure for the terminal is successfully completed.

2-6 condition: The terminal decides to suspend the second SRB. For example, if data cannot be transmitted over the second SRB through the second base station, the terminal may decide to suspend the second SRB.

In operation S850, when at least one of the 2-1 to 2-6 conditions is detected, the terminal may resume the suspended first SRB. Furthermore, the terminal may suspend the second SRB.

Referring to FIG. 9, the temporary SRB may be a signaling radio bearer (SRB) set over an MCG and one or more SCGs. The RRC message generated by the RRC in the MCG may be temporarily transmitted through the SCG resource when the connection fails. For example, even when the SRB is in an unavailable state, the terminal may receive an RRC message from the RRC entity of the MCG using the temporary SRB.

Referring to FIG. 10, in step S1010, the UE may establish an RRC connection with an old master cell group cell. And, the UE can set up the old MCG cell and SRB1. The SRB1 may be a normal SRB.

In step S1020, the UE having set up the old MCG cell and SRB1 in the RRC connection establishment procedure may perform SCG establishment (establishment). During SCG establishment, the UE may set up a temporary SRB with a secondary cell group cell (SCG cell). The temporary SRB may be called t-SRB. The temporary SRB may be in a suspended state until a connection failure occurs. When the RRC connection between the UE and the old MCG cell is in a good state, the UE may not use the temporary SRB.

In step S1030, when the RRC connection between the UE and the old MCG cell is in a bad state, the UE may start using the temporary SRB instead of SRB1. In this case, SRB1 may be suspended, and RRC connection may be maintained through the temporary SRB. For example, if RRC signaling through SRB1 is disabled due to RLF, the UE may begin using a temporary SRB instead of SRB1. For example, if the quality of the old MCG cell is lower than the threshold, the terminal may start using the temporary SRB instead of SRB1. For example, if the quality of the SCG cell is better than the threshold, the terminal may start using the temporary SRB instead of SRB1. For example, if the quality of the old MCG cell is worse than the threshold value, the quality of the SCG cell is better than the threshold value, the terminal may start using the temporary SRB instead of SRB1. For example, if the handover fails, the terminal can start using the temporary SRB instead of SRB1. For example, when an RLF or HOF related timer (eg, T310 or T311) starts, the terminal may start using a temporary SRB instead of SRB1. Although SRB1 is suspended in the RRC connection reestablishment procedure, the temporary SRB can be used to maintain the RRC connection. Data transmission via the DRB may still proceed on the SCG of the SCG bearer or split bearer.

In parallel with maintaining the RRC connection of the MCG on the temporary SRB through the SCG resources, the UE may still perform the RRC connection reestablishment procedure. For example, the RRC connection reestablishment procedure may follow a legacy LTE procedure when the MCG is in the E-UTRAN. Hereinafter, steps S1040a to S1040c may be selectively performed.

(1) When the UE performs cell reestablishment with the old MCG cell

In step S1040a, if the RRC connection between the UE and the old MCG cell is in a good state, the UE may suspend the temporary SRB and resume SRB1. For example, if the RRC connection reestablishment procedure for the old MCG cell is successfully completed, the UE may suspend the temporary SRB and resume SRB1. For example, if the quality of the old MCG cell is better than the threshold, the terminal may suspend the temporary SRB and resume SRB1. For example, if the quality of the SCG cell is worse than the threshold, the terminal may suspend the temporary SRB and resume SRB1. For example, if the quality of the old MCG cell is better than the threshold, and the quality of the SCG cell is worse than the threshold, the terminal may suspend the temporary SRB and resume SRB1. Therefore, after reestablishing the RRC connection in the old MCG cell, the UE may switch from the temporary SRB to SRB1 to maintain the RRC connection.

(2) UE performs cell reestablishment with new MCG cell

Alternatively, in step S1040b, the terminal may establish an RRC connection with a new master cell group cell (MCG cell). The UE may set up a new MCG cell and SRB2. The SRB2 may be a normal SRB. For example, if the RRC connection reestablishment procedure for the new MCG cell is successfully completed, the terminal may suspend the temporary SRB and set up SRB2. For example, if the quality of the new MCG cell is better than the threshold, the terminal may suspend the temporary SRB and set up SRB2. For example, if the quality of the SCG cell is worse than the threshold, the terminal may suspend the temporary SRB and set up SRB2. For example, if the quality of the new MCG cell is better than the threshold and the quality of the SCG cell is worse than the threshold, the terminal may suspend the temporary SRB and set up SRB2. Therefore, after reestablishing the RRC connection in the new MCG cell, the UE may switch from the temporary SRB to SRB2 to maintain the RRC connection.

(3) When the UE performs cell reestablishment with the existing SCG cell

Alternatively, in step S1040c, the terminal may establish an RRC connection with the SCG cell. The UE may set up the SCG cell and the SRB3. The SRB3 may be a normal SRB. That is, the terminal may re-establish the RRC connection with the SCG cell. In this case, if the RRC connection reestablishment procedure for the SCG cell is successfully completed, the SCG cell may be changed to the MCG cell. For example, if the RRC connection reestablishment procedure for the SCG cell is successfully completed, the terminal may suspend the temporary SRB and set up SRB3. In this case, the UE that has set up the SCG cell and the SRB3 in the RRC connection establishment procedure may perform SCG establishment with another SCG cell and may set up the temporary SCB with another SCG cell during the SCG establishment.

(4) When the UE fails to reestablish the cell

On the other hand, in step S1040d, the RRC connection reestablishment procedure may not be completed successfully. If the RRC connection reestablishment procedure is not completed successfully, the terminal may perform at least one of the following options.

First option: The terminal enters the RRC_IDLE state. In this case, all radio bearers including the temporary SRB can be released.

Second option: The terminal enters a new RRC state. The new RRC state may be a new RRC state that is neither an RRC_IDLE state nor an RRC_CONNECTED state. After the UE enters a new RRC state, the UE may select a cell in the new RRC state. For example, the new RRC state may be a state in which the UE may perform a cell reselection procedure and maintain the ECM_CONNECTED state. For example, the new RRC state may be an RRC_INACTIVE state.

Third option: The terminal may perform handover to the cell according to the following steps. In the first step, the UE may optionally transmit an RRC message requesting handover to the RRC entity of the MCG through the temporary SRB. In the second step, the RRC entity of the MCG may transmit a handover command message for the target cell to the terminal through the temporary SRB. In a third step, the terminal may move to the target cell, and transmit a handover complete message to the cell. The cell may be configured as a PCell in MCG.

According to an embodiment of the present disclosure, when the first SRB is unavailable, the terminal may still receive the RRC message using the second SRB, thereby improving reliability of RRC message delivery.

Referring to FIG. 11, in step S1110, the UE may establish a radio resource control (RRC) connection and a first SRB with a first base station. The first base station may be a base station where an RRC entity for the terminal is located.

In step S1120, the terminal may configure the second base station and the second SRB. The second SRB may be in a suspended state. The second SRB may be a temporary SRB. The second base station may be a base station in which an RRC entity for the terminal is not located.

In step S1130, if the quality of the cell at the first base station is lower than the first threshold value, the terminal may resume the suspended second SRB.

Additionally, the terminal may suspend the first SRB.

Additionally, if the quality of the cell at the second base station is better than the second threshold value, the terminal may resume the suspended second SRB.

Additionally, when the radio link failure related timer or the handover failure related timer is started, the terminal may resume the suspended second SRB.

In addition, when the re-establishment procedure for the RRC connection is initiated, the terminal may resume the suspended second SRB.

Additionally, if the terminal determines to suspend the first SRB, the terminal may resume the suspended second SRB.

Referring to FIG. 12, in step S1210, the UE may establish a radio resource control (RRC) connection and a first SRB with a first base station. The first SRB may be in a suspended state. The first base station may be a base station where an RRC entity for the terminal is located.

In step S1220, the terminal may configure the second base station and the second SRB. The second SRB may be a temporary SRB. The second base station may be a base station in which an RRC entity for the terminal is not located.

In step S1230, if the quality of the cell in the first base station is better than the first threshold value, the terminal may resume the suspended first SRB.

Additionally, the terminal may suspend the second SRB.

Additionally, if the quality of the cell at the second base station is worse than the second threshold value, the terminal may resume the suspended first SRB.

Additionally, when the radio link failure related timer or the handover failure related timer is stopped, the terminal may resume the suspended first SRB.

Additionally, if the terminal determines to suspend the second SRB, the terminal may resume the suspended first SRB.

In addition, when the reestablishment procedure for the RRC connection is completed, the terminal may resume the suspended first SRB.

The base station 1300 includes a processor 1301, a memory 1302, and a transceiver 1303. The memory 1302 is connected to the processor 1301 and stores various information for driving the processor 1301. The transceiver 1303 is connected to the processor 1301 to transmit and / or receive a radio signal. The processor 1301 implements the proposed functions, processes, and / or methods. In the above-described embodiment, the operation of the base station may be implemented by the processor 1301.

The terminal 1310 includes a processor 1311, a memory 1312, and a transceiver 1313. The memory 1312 is connected to the processor 1311 and stores various information for driving the processor 1311. The transceiver 1313 is connected to the processor 1311 to transmit and / or receive a radio signal. The processor 1311 implements the proposed functions, processes and / or methods. In the above-described embodiment, the operation of the terminal may be implemented by the processor 1311.

The processor may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, and / or data processing devices. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and / or other storage device. The transceiver may include baseband circuitry for processing wireless signals. When the embodiment is implemented in software, the above technique may be implemented as a module (process, function, etc.) for performing the above-described function. The module may be stored in memory and executed by a processor. The memory may be internal or external to the processor and may be coupled to the processor by various well known means.

Based on the examples described above, various techniques in accordance with the present disclosure have been described with reference to the drawings and reference numerals. For convenience of description, each technique described a number of steps or blocks in a specific order, but the specific order of these steps or blocks does not limit the invention described in the claims, and each step or block may be implemented in a different order, or In other words, it is possible to be performed simultaneously with other steps or blocks. In addition, it will be apparent to those skilled in the art that the steps or blocks have not been described in detail, and that at least one other step may be added or deleted without departing from the scope of the invention.

The above-described embodiments include various examples. Those skilled in the art will appreciate that not all possible combinations of examples of the inventions can be described, and that various combinations can be derived from the description herein. Therefore, the protection scope of the invention should be judged by combining various examples described in the detailed description within the scope of the claims described below.

Claims

In the method for controlling the signaling radio bearer (SRB) in the wireless communication system,

Establishing a radio resource control (RRC) connection and a first SRB with a first base station;

Establishing a second SRB with a second base station, wherein the second SRB is in a suspended state; And

And if the quality of the cell at the first base station is worse than a first threshold, resuming the suspended second SRB.
The method of claim 1,

Suspending the first SRB.
The method of claim 2,

If the quality of the cell at the second base station is better than a second threshold, resuming the suspended second SRB.
The method of claim 2,

Resuming the suspended second SRB when a radio link failure related timer or a handover failure related timer is initiated.
The method of claim 2,

When the re-establishment procedure for the RRC connection is initiated, resuming the suspended second SRB.
The method of claim 2,

If the terminal decides to suspend the first SRB, resuming the suspended second SRB.
The method of claim 1,

And the second SRB is a temporary SRB.
The method of claim 1,

Wherein the first base station is a base station in which an RRC entity for the terminal is located, and the second base station is a base station in which an RRC entity for the terminal is not located.
In the method for controlling the signaling radio bearer (SRB) in the wireless communication system,

Establishing a radio resource control (RRC) connection and a first SRB with a first base station, wherein the first SRB is in a suspended state;

Establishing a second base station and a second SRB; And

And if the quality of the cell at the first base station is better than a first threshold, resuming the suspended first SRB.
The method of claim 9,

Suspending the second SRB.
The method of claim 10,

If the quality of the cell at the second base station is worse than a second threshold value, resuming the suspended first SRB.
The method of claim 10,

When the radio link failure related timer or the handover failure related timer is stopped, resuming the suspended first SRB.
The method of claim 10,

If the terminal determines to suspend the second SRB, resuming the suspended first SRB.
The method of claim 9,

Wherein the first base station is a base station in which an RRC entity for the terminal is located, and the second base station is a base station in which an RRC entity for the terminal is not located.
In a terminal for controlling a signaling radio bearer (SRB) in a wireless communication system,

Memory; Transceiver; And a processor connecting the memory and the transceiver, wherein the processor

Establish a radio resource control (RRC) connection and a first SRB with a first base station,

Establish a second SRB with a second base station, wherein the second SRB is in a suspended state; and

And if the quality of the cell at the first base station is worse than a first threshold, resume the suspended second SRB.