KR101622219B1 - Method and apparatus for RRC connection reestablishment in wireless communication system - Google Patents

Abstract

Hereinafter, a method for reestablishing an RRC (Radio Resource Control) connection in a wireless communication system is disclosed. The UE selects the target cell based on the cell quality information corresponding to each of the one or more cells and judges the type of the selected target cell so that only the first type cell providing both the emergency service and the general service can transmit the RRC And transmits a connection reset request message. Also, if the selected target cell is the second type cell providing only the emergency service, the terminal selects the target cell again.

Cell selection, RRC connection reset, Suitable cell

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method and apparatus for re-establishing an RRC connection in a wireless communication system,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication system, and more particularly, to a method of selecting a cell in an RRC connection reset process in a wireless communication system.

The terminal performs a cell selection procedure and registers itself in the network in order to receive a service from the cell. Also, if the strength or quality of the signal between the UE and the cell deteriorates due to the mobility of the UE, the UE performs a cell reselection procedure to maintain the data transmission quality.

The 3GPP standard document TS 36.304 distinguishes the cell selection procedure as follows.

The first is an initial cell selection process, which is performed when the UE does not have advance information on a wireless channel. In this case, the terminal searches all the radio channels to find an appropriate cell, and selects a cell corresponding to the radio channel having the strongest signal quality among the searched radio channels.

Secondly, a stored information cell selection process using stored information is performed when the UE has already stored information on the wireless channel. In this case, since the terminal already has information on the radio channel, the cell can be selected quickly in comparison with the above-described initial cell selection process.

Equation 1 below represents a cell selection criterion in an LTE (Long Term Evolution) system disclosed in 3GPP standard document TS 36.304.

Srxlev = Q _rxlevmeas - (Q _rxlevmin + Q _{rxlevminoffset} ) - Pcompensation> 0

The parameters used in Equation 1 are shown in Table 1 below.

Qrxlevmeas The received level of the measured cell (RSRP). Q _rxlevmin Minimum required receive level (dBm) in the cell Q _{rxlevminoffset} Q offset for _rxlevmin Pcompensation max (P _EMAX - P _UMAX , 0) (dB) P _EMAX The maximum transmission power (in dBm) P _UMAX The maximum transmission power (dBm) of the terminal radio transmission unit (RF)

The terminal receives the parameters of Table 2 through the system information (SI), and proceeds with the cell selection procedure using the cell selection criterion of Equation (1).

Meanwhile, the above-described system information includes essential information that the terminal needs to know in order to access the cell. Therefore, the terminal must have the latest system information before connecting to the cell. Since the system information is information that must be known by all terminals in a cell, the cell periodically transmits the system information.

Such system information is classified into MIB (Master Information Block), SB (Scheduling Block), SIB (System Information Block), and the like. The MIB allows the terminal to know information such as the physical configuration of the cell, for example, bandwidth. An SIB is a collection of related system information. For example, some SIBs only contain information of surrounding cells, and some SIBs only contain information of uplink radio channels used by the UE. The SB informs the transmission information of the SIBs, for example, the transmission period.

Meanwhile, after the UE has selected a cell through the cell selection procedure, the strength or quality of the signal between the UE and the cell may be changed due to mobility of the UE or change of the radio environment. If the quality of the selected cell degrades, the terminal may select another cell that provides better quality. When the cell is reselected in this way, a cell is selected that generally provides better signal quality than the currently selected cell. This is called a cell reselection procedure.

The cell reselection procedure has a basic purpose in terms of the quality of the radio signal, in general, to select a cell that provides the best quality to the terminal. In addition to the quality of the radio signal, the network can determine the priority for each frequency and notify the terminal. The UE receiving this priority takes priority over the radio signal quality criterion in the cell reselection procedure. Such a cell reselection procedure can be classified as shown in Table 2 according to the radio access technology (RAT) and frequency characteristics of the cell.

Intra-frequency cell reselection A cell with a center-frequency such as RAT like a serving cell is reselected Inter-frequency cell reselection Cells with a different center frequency than the RAT like the serving cell are reselected Inter-RAT cell reselection Reselect a cell using a different RAT from the RAT being used in the serving cell

1 is a flowchart illustrating an operation of a terminal when a terminal is powered on in an LTE (Long Term Evolution) system.

Referring to FIG. 1, in step 110, when the terminal is powered on, the terminal automatically or manually selects a public land mobile network (PLMN) and a radio access technology (RAT) for communication. The PLMN and RAT information may be selected by a user of the terminal or may use information stored in a Universal Subscriber Identity Module (USIM). In this case, the UE measures a signal transmitted from the cell periodically or non-periodically, that is, a reference signal or a pilot signal, as shown in step 130, so that the signal strength and noise / interference ratio The cell quality information is calculated using the characteristics of the physical signal.

Thereafter, in step 120, the UE performs a cell selection process for selecting a cell having the largest value among the cells whose measured cell quality information is larger than the reference value. The reference value refers to a value defined in the system in order to guarantee the quality of a physical signal in data transmission / reception. Therefore, the value may be different according to the applied RAT, and in the LTE system, Equation 1 can be used.

Then, the UE receives the system information transmitted periodically by the cell, and uses its own information (e.g., International Mobile Subscriber Identity, IMSI) to receive service from the network in step 150, . If the information of the network (e.g., Tracking Area Identity, TAI) received from the SI and the information of the network known by the terminal are different from each other, as in steps 140 and 170, .

If the strength or quality of the signal measured from the cell of the serving cell is lower than the value measured from the cell of the neighboring cell in step 160, . This process is referred to as cell reselection in a manner different from the cell selection in step 120. At this time, a time constraint (for example, a cell selection timer) may be set to prevent the cell from being frequently re-selected according to the change of the signal characteristics.

Meanwhile, when the conventional cell selection procedure is directly applied to the RRC connection re-establishment process, the UE transmits an RRC connection reestablishment request message to the selected cell regardless of the selected cell type. That is, even if the selected cell is a cell that can not provide a normal service, the RRC connection re-establishment request message is transmitted, and the cell transmits an RRC connection re-establishment rejection message to the UE. In this case, there is a problem in that the mobile station must reconnect the RRC connection in order to continue to provide the service, and perform all the steps for receiving the service normally.

In addition, the object of the conventional cell selection procedure considers cells using all radio access technologies (RAT) supported by the UE. Therefore, in the cell selection procedure during the RRC connection re-establishment process, the UE can select a cell using RAT other than Evolved Universal Terrestrial Radio Access (E-UTRA). However, since a cell using a RAT other than the E-UTRA does not have the configuration and configuration context of the corresponding UE, the UE does not have a time to search for a cell using E-UTRA, There is a problem that the connection reset process is considered to have failed and transition to the RRC hibernation state.

If the conventional cell selection procedure is directly applied to the RRC connection re-establishment process, the continuity of the RRC connection of the UE can not be ensured.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cell selection method and an RRC connection resetting method capable of increasing the probability of success of RRC connection re-establishment.

Another object of the present invention is to propose a cell selection method and an RRC connection resetting method that can reduce a service interruption time of a terminal caused by an RRC connection resetting process.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, unless further departing from the spirit and scope of the invention as defined by the appended claims. It will be possible.

In order to accomplish the above object, a method for performing RRC connection re-establishment between a cell using a specific RAT (Radio Access Technology) in a wireless communication system and a multiple RAT supporting terminal in a RRC (Radio Resource Control) connected state is disclosed . Wherein the RRC connection re-establishment method comprises: constructing a set of candidate cells by excluding one or more cells using RAT other than the specific RAT in one or more cells; Selecting a target cell based on the information, and transmitting an RRC connection re-establishment request message to the selected target cell. And configuring the candidate cell set is a step of stopping a receiver of the RAT other than the specific RAT.

More preferably, the method further comprises starting a cell selection timer before execution of the step of configuring the candidate cell set, and entering the RRC idle state if the target cell is not selected until the cell selection timer expires do. The method may further include receiving an RRC connection reset acceptance message from the selected target cell after transmitting the RRC connection re-establishment request message, and transmitting an RRC connection re-establishment acknowledgment message to the selected target cell.

According to another aspect of the present invention, there is provided a method for performing RRC connection re-establishment between a cell using a specific RAT (Radio Access Technology) in a wireless communication system and a multiple RAT supporting terminal in a RRC (Radio Resource Control) Measuring cell quality information corresponding to each of the one or more cells using the received signal from the cell, excluding cell quality information of cells using RAT other than the specific RAT in the cell quality information, Generating quality information, selecting a target cell based on the candidate cell quality information, and transmitting an RRC connection re-establishment request message to the target cell.

More preferably, the method further comprises starting a cell selection timer before execution of the step of configuring the candidate cell set, and entering the RRC idle state if the target cell is not selected until the cell selection timer expires do. The method may further include receiving an RRC connection reset acceptance message from the selected target cell after transmitting the RRC connection re-establishment request message, and transmitting an RRC connection re-establishment acknowledgment message to the selected target cell.

According to another aspect of the present invention, there is provided a method for reconfiguring an RRC connection of a terminal in a radio resource control (RRC) connected state in a wireless communication system, comprising: selecting a target cell based on cell quality information corresponding to each cell; Determining a type of the selected target cell and transmitting the RRC connection re-establishment request message to the selected target cell when the selected target cell is a first type cell providing both the emergency service and the general service.

And if the selected target cell is not the first type cell, repeating the step of selecting the target cell if the selected target cell is a second type cell providing only emergency services, And releasing the connection state.

Preferably, only when the selected target cell is a first type cell providing both an emergency service and a general service and is a cell using Evolved Universal Terrestrial Radio Access (E-UTRA), an RRC connection re- To the base station.

More preferably, the method further comprises starting a cell selection timer before execution of the step of configuring the candidate cell set, and entering the RRC idle state if the target cell is not selected until the cell selection timer expires do. The method may further include receiving an RRC connection reset acceptance message from the selected target cell after transmitting the RRC connection re-establishment request message, and transmitting an RRC connection re-establishment acknowledgment message to the selected target cell.

According to another aspect of the present invention, there is provided a mobile communication system including a plurality of RAT supporting terminals in a RRC (Radio Resource Control) connection state with a cell using a specific RAT (Radio Access Technology) in a wireless communication system, A radio signal measurement module for measuring cell quality information using the received signal, and a target cell selection unit for selecting a target cell based on the measured cell quality information A processor including a cell selection module, and a transmission module for transmitting an RRC connection re-establishment request message to the selected target cell.

According to another aspect of the present invention, there is provided a method for measuring a cell quality of a cell in a wireless communication system, the method comprising: The cell quality information corresponding to each of the at least one cell is measured using the received signal, and a cell quality of the cells using RAT other than the specific RAT is measured in the cell quality information, And a cell selection module for selecting a target cell based on the candidate cell quality information, and a processor for transmitting an RRC connection re-establishment request message to the selected target cell And a transmission module.

According to another aspect of the present invention, there is provided a terminal device including a receiving module for receiving a signal for measuring cell quality information from one or more cells, a cell quality information measuring module for measuring cell quality information corresponding to each cell using the received signal, A processor including a radio signal measurement module and a cell selection module for selecting a target cell based on the cell quality information and a transmission module for transmitting a Radio Resource Control (RRC) connection re-establishment request message to the selected target cell, The processor controls the transmitting module to transmit the RRC connection re-setting request message to the selected target cell only when the selected target cell is a first type cell providing both the emergency service and the general service. Preferably, the processor reselects the target cell if the selected target cell is a second type cell providing only emergency services.

When the RRC connection resetting process is performed by the method and apparatus for resetting the RRC connection in the wireless communication system according to the present invention, not only the probability of success of RRC connection re-establishment is increased but also the service interruption time of the UE decreases, Continuity is guaranteed.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. The detailed description set forth below in conjunction with the appended drawings is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. The following detailed description includes specific details for a better understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details. For example, in the following description, certain terms are mainly described, but they need not be limited to these terms, and they may have the same meaning when they are referred to as arbitrary terms. Further, the same or similar elements throughout the present specification will be described using the same reference numerals.

Also, the terms and words used in the present specification and claims should not be construed to be limited to ordinary or dictionary meanings, and the inventor is not limited to the concept of terms in order to describe his invention in the best way. It should be construed in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be properly defined.

Prior to describing the present invention, the Evolved Universal Mobile Telecommunications System (E-UMTS), which is a technical field to which the present invention is applied, and related technical features will be described below.

2 is a diagram conceptually showing a network structure of an E-UMTS. In particular, the E-UMTS system has evolved from the existing WCDMA UMTS system, and is currently undergoing basic standardization work in the 3rd Generation Partnership Project (3GPP). E-UMTS is also called Long Term Evolution (LTE) system. For details of the technical specifications of UMTS and E-UMTS, refer to Release 7 and Release 8 of "3rd Generation Partnership Project (Technical Specification Group Radio Access Network)" respectively.

Referring to FIG. 2, an E-UMTS is an Access Gateway (hereinafter referred to as AG) located at the end of a UE, a cell (eNB), and a network (E-UTRAN) . Typically, an eNB may simultaneously transmit multiple data streams for broadcast services, multicast services, and / or unicast services. An interface for transmitting user traffic or control traffic may be used between eNBs.

The AG may be divided into a part for handling user traffic and a part for processing control traffic. At this time, a new interface between the AG for processing new user traffic and the AG for processing control traffic can be communicated with each other. Also, the AG manages the mobility of the UE in a TA (Tracking Area) unit, and the TA is composed of a plurality of cells. If the terminal moves from one TA to another TA, it informs AG that the TA where it is located has changed.

The CN (Core Network) can be configured as a network node for user registration of AG and UE. An interface for distinguishing E-UTRAN and CN may be used.

3 is a conceptual diagram illustrating a network structure of an evolved universal terrestrial radio access network (E-UTRAN). Especially, the E-UTRAN system is an evolved system in the existing UTRAN system. The E-UTRAN is composed of cells (eNBs), and the cells are connected via the X2 interface. The cell is connected to the terminal through the air interface, and is connected to the EPC (Evolved Packet Core) through the S1 interface.

EPC is composed of MME (Mobility Management Entity), S-GW (Serving-Gateway) and PDN-GW (Packet Data Network-Gateway). The MME has information on the access information of the terminal or the capability of the terminal, and this information is mainly used for managing the mobility of the terminal. The S-GW is a gateway having an E-UTRAN as an end point, and the PDN-GW is a gateway having a PDN (Packet Data Network) as an end point.

Meanwhile, the 3GPP standard document TS 36.304 classifies the services provided by the E-UTRAN to the terminal into the following three types as shown in Table 3 below.

Limited service Emergency call and ETWS (Earthquake and Tsunami Warning System) are provided. Normal service Provide general purpose public use services. Operator service Provide services for network operators

Also, in 3GPP standard document TS 36.304, cell types are classified as shown in Table 4 with respect to a service type in which cells are provided to UEs.

Acceptable cell Cells where the terminal can receive limited service Suitable cell Cells where the terminal can receive normal service Barred cell Cells designated as Barred cells in System Information Reserved cell Cells designated as reserved cells in system information

Here, the acceptable cell is a cell which is not barred for the UE and satisfies the cell selection criterion of the UE, and is a cell that can receive only limited services such as emergency call and ETWS.

Also, a suitable cell satisfies the condition of the acceptable cell and satisfies the additional conditions at the same time. As an additional condition, this cell should belong to a PLMN that the corresponding terminal can access, and should not be inhibited from performing the TA update procedure of the terminal. If the corresponding cell is a closed subscriber group (CSG) cell, the terminal must be a cell capable of being connected as a CSG member.

For reference, the 3GPP standard document TS 25.304 defines a service and a cell type provided by a Universal Terrestrial Radio Access Network (UTRAN) to a terminal, and a Global System for Mobile communication (GSM) is provided to a terminal in the 3GPP standard document TS 43.022 Service and cell types are defined. In particular, the limited services provided by UTRAN and GSM support only emergency calls except ETWS.

4A and 4B illustrate a control plane and a U-plane (User-Plane) structure of a radio interface protocol between a UE and an E-UTRAN based on the 3GPP radio access network standard Fig. In particular, the wireless interface protocol consists of a physical layer, a data link layer, and a network layer vertically, and horizontally includes a user plane for data information transmission and a control plane And a control plane for signal transmission.

The protocol layers of FIGS. 4A and 4B are based on an Open System Interconnection (OSI) reference model widely known in communication systems. The lower three layers are referred to as L1 (first layer), L2 (second layer) , And L3 (third layer).

The control plane is a path through which control messages used by the UE and the network to manage calls are transmitted. The user plane means a path through which data generated in the application layer, for example, voice data or Internet packet data, is transmitted. Hereinafter, the layers of the control plane and the user plane of the wireless protocol will be described.

The physical layer as the first layer provides an information transfer service to an upper layer using a physical channel. The physical layer is connected to the upper layer of Medium Access Control (MAC) layer through a transport channel. Data is transferred between the MAC layer and the physical layer through the transport channel. Data is transferred between the transmitting side and the receiving side physical layer through the physical channel. The physical channel is modulated by an Orthogonal Frequency Division Multiplexing (OFDM) scheme, and uses time and frequency as radio resources.

The MAC layer of the second layer provides a service to a radio link control (RLC) layer, which is an upper layer, through a logical channel. The RLC layer of the second layer supports reliable data transmission. The function of the RLC layer may be implemented as a function block inside the MAC. In this case, the RLC layer may not exist. The Packet Data Convergence Protocol (PDCP) layer of the second layer performs a header compression function to reduce unnecessary control information for efficient transmission in an air interface having a narrow bandwidth when transmitting IP packets such as IPv4 or IPv6 .

A Radio Resource Control (RRC) layer located at the bottom of the third layer is defined only on the control plane and includes a configuration, reconfiguration, and release of radio bearers (RBs) And controls the logical channels, the transport channels, and the physical channels. The radio bearer means a service provided by the second layer for data transmission between the UE and the E-UTRAN. To this end, the RRC layer exchanges RRC messages between the UE and the network.

Hereinafter, the RRC state of the UE and the RRC connection method will be described. The RRC state refers to whether or not the RRC of the UE is a logical connection with the RRC of the E-UTRAN. If the RRC is connected, the RRC connection state (RRC_CONNECTED) is established. If not, the RRC idle state (RRC_IDLE) .

Since the E-UTRAN can grasp the presence of the UE in the RRC-connected state on a cell-by-cell basis, the E-UTRAN can effectively control the UE. On the other hand, the E-UTRAN can not grasp the RRC idle terminal in the cell unit, and the CN manages the TA unit, which is a larger area unit than the cell. That is, in order for the UE in the RRC idle state to receive services such as voice or data from the cell, the UE must transition to the RRC connected state.

In particular, when the user first turns on the power of the UE, the UE first searches for an appropriate cell and stays in the RRC idle state in the cell. The UE which has stayed in the RRC idle state performs the RRC connection establishment process with the RRC of the E-UTRAN only when it is necessary to establish the RRC connection, and transits to the RRC connection state. Here, the case where the RRC connection needs to be established means that uplink data transmission is required due to a user's call attempt or the like, or when a paging message is received from the E-UTRAN, a response message should be transmitted.

As described above, since the cell selection procedure is performed in a state in which the UE does not currently determine the cell in which the RRC is in the idle state, it is most important to select the cell as quickly as possible. Therefore, even if the cell is not a cell providing the best radio signal quality to the UE, that is, it is an acceptable cell but not a suitable cell, it can be selected in the cell selection procedure of the UE have.

On the other hand, if the UE can not perform normal communication due to deteriorated quality of the radio channel or mismatch between the UE and the network, the UE determines that the current communication link is faulty and starts the RRC connection reestablishment procedure .

In the 3GPP standard document TS 36.331, if the UE determines that there is a serious problem with the downlink communication link quality based on the result of radio quality measurement of the physical layer of the UE as an example in which the normal communication can not be performed, Random Access procedure is continuously failed or the uplink data transmission in the RLC sublayer continues to fail and it is determined that there is a serious problem in the uplink transmission, the handover has failed or the message received by the terminal is subjected to an integrity check integrity check, and so on.

In FIG. 4A, the Non-Access Stratum (NAS) layer at the top of the RRC layer performs functions such as session management and mobility management. In the NAS layer, two states of EMM (EPS Mobility Management) registration state (EMM-REGISTERED) and EMM unregistered state (EMM-UNREGISTERED state) are defined for terminal mobility management, and these states are applied to the terminal and the MME. The initial terminal is an EMM unregistered state, and the terminal performs a process of registering with the network through an initial attach procedure to access the network. When the contact procedure is successfully performed, the terminal and the MME are in the EMM registration state.

In the NAS layer, two types of ECM (EPS Connection Management) idle state (ECM_IDLE) and ECM connection state (ECM_CONNECTED) are defined to manage a signaling connection between a terminal and an EPC. . When the UE in the ECM idle state establishes the RRC connection with the E-UTRAN, the UE enters the ECM connected state. ECM The MME in the idle state is connected to the ECM when it makes an S1 connection with the E-UTRAN.

When the UE is in the ECM idle state, the E-UTRAN does not have a context of the UE. Therefore, the terminal in the ECM idle state performs terminal-based mobility-related procedures such as cell selection or cell re-selection procedure without receiving commands from the network. On the other hand, when the terminal is in the ECM connection state, the mobility of the terminal is managed by a command of the network. If the position of the terminal differs from the position known to the network in the ECM idle state, the terminal informs the network of the corresponding position of the terminal through a TA update (Tracking Area Update) procedure.

5 is a diagram illustrating an example of a physical channel structure used in an E-UMTS system. The physical channel is composed of several subframes on the time axis and several subcarriers on the frequency axis. Here, one sub-frame is composed of a plurality of symbols on the time axis. One subframe is composed of a plurality of resource blocks, and one resource block is composed of a plurality of symbols and a plurality of subcarriers. In the E-UMTS system currently under discussion, a radio frame of 10 ms is used and one radio frame is composed of 10 subframes. Also, one subframe consists of two consecutive slots. The length of one slot is 0.5 ms, and the TTI (Transmission Time Interval), which is a unit time in which data is transmitted, is 1 ms.

Referring to FIG. 5, each subframe may use specific subcarriers of specific OFDM symbols (e.g., first symbol) of a corresponding subframe for a physical downlink control channel (PDCCH), i.e., an L1 / have. FIG. 5 shows an L1 / L2 control information transmission region (PDCCH) 501 and a data transmission region (PDSCH) 502.

The BS and the UE generally transmit and receive data through the PDSCH 502, which is a physical channel, using a DL-SCH, which is mostly a transport channel, except for a specific control signal or specific service data. Data of the PDSCH 502 is transmitted to a terminal (one or a plurality of terminals), and information on how the terminals receive and decode the PDSCH data is included in the PDCCH 501 and transmitted.

For example, when a specific PDCCH 501 is CRC masked with an RNTI (Radio Network Temporary Identity) A, and a radio resource (for example, a frequency location) B and transmission format information C , Transport block size, modulation, coding information, and the like) is transmitted through a specific subframe. In this case, one or more UEs in the corresponding cell monitor the PDCCH 501 using RNTI information it has, and if there is more than one UE having an A RNTI, the UEs receive the PDCCH 501, And receives the PDSCH 502 indicated by B and C through the information of one PDCCH 501. [

6 is a diagram for explaining a general transmission / reception method using a paging message.

Referring to FIG. 6, the paging message includes a paging record composed of a paging cause and a UE identity. Upon receiving the paging message, the UE may perform Discontinuous Reception (DRX) for the purpose of reducing power consumption.

Specifically, the network configures a plurality of paging occasions for each time period called a paging DRX cycle, and a specific terminal receives only a specific call opportunity time to acquire a paging message. The terminal does not receive the paging channel at times other than the specific paging opportunity time and may be in a sleep state to reduce power consumption. One call opportunity time corresponds to one TTI.

The BS and the UE use a paging indicator (PI) as a specific value for informing the transmission of the paging message. The base station can define a specific identifier (e.g., Paging-Radio Network Temporary Identity) for the purpose of the PI and notify the UE of the paging information transmission. For example, the UE wakes up every DRX cycle and receives one subframe to know whether a paging message is present or not. If the UE has a P-RNTI in the L1 / L2 control channel (PDCCH) of the received subframe, it can know that there is a paging message on the PDSCH of the corresponding subframe. Also, if there is an own terminal identifier (e.g., IMSI) in the paging message, the terminal receives a service by responding to the base station (for example, RRC connection).

Hereinafter, the RRC connection resetting process will be described in more detail. 7 is a flowchart illustrating a general RRC connection re-establishment procedure of the UE.

Referring to FIG. 7, in step 701, the UE stops using all radio bearers except for Signaling Radio Bearer # 0 (SRB 0), initializes various sub layers of an AS (Access Stratum) And the physical layer to the default configuration. The important point here is that the terminal maintains the RRC connection state.

In step 702, the UE performs a cell selection procedure to perform the RRC connection re-establishment process. In the conventional RRC connection reset procedure, the cell selection procedure is the same as the cell selection procedure performed by the UE in the RRC idle state even though the UE remains connected.

If it is determined in step 702 that the selected cell is a cell using E-UTRA (step 703), the UE transmits an RRC connection reset request message to the corresponding cell in step 704.

On the other hand, if it is determined in step 702 that the selected cell is a cell using another RAT other than the E-UTRAN (step 703), the RRC connection reset process is stopped, At 707, the RRC enters the idle state. Also, even if the UE fails to select a cell within a limited time, the UE enters the RRC Idle state as in step 707, assuming that the RRC connection reset process has failed.

Subsequently, when the cell accepts the RRC connection reset request message of the UE, the cell transmits an RRC connection reset acceptance message to the UE. In step 705, if the UE receives the RRC connection reconfiguration acknowledgment message, the UE reconfigures the PDCP sublayer and the RLC sublayer for SRB 1. Also, various key values related to the security setting are recalculated, and the PDCP sublayer responsible for security is reconfigured with newly calculated security key values. Thus, the terminal and the inter-cell SRB 1 are opened and the RRC control message can be exchanged. The MS completes the resumption of the SRB 1 and transmits a confirm message to the cell that the RRC connection reset process is completed in step 706. 8 is a flowchart showing steps 704, 705, and 706, that is, when the RRC connection re-establishment process is successful.

Therefore, if the RRC connection re-establishment process is successful, the cell performs an RRC connection reconfiguration procedure with the UE, restores the state before the UE performs the RRC connection re-establishment process, and ensures the continuity of the service to the maximum.

Meanwhile, when the cell rejects the RRC connection re-establishment request message of the UE, the cell transmits an RRC connection re-establishment reject message to the UE. When the UE receives the RRC Connection Rejection Reject message, the UE releases the RRC connection state and switches to the RRC Idle state. 9 is a flowchart showing a case where the RRC connection resetting process fails.

After the UE enters the RRC idle state, the RRC of the UE releases all the radio resources in use, i.e., the RLC entity, the MAC configuration, and the PDCP entity for all the configured RBs, disconnects the RRC from the NAS of the UE You will be notified. Thereafter, the AS of the UE performs an initial cell selection procedure for selecting a cell for waiting for the UE in the RRC idle state.

Hereinafter, problems of the conventional RRC connection resetting process will be described with reference to FIG. 10, which illustrates a part of the RRC connection resetting process.

When the RRC connection resetting process is started, the operation of the cell selection timer is started in step 1001. In this case, the terminal still maintains the RRC connection state. In step 1002, the UE measures a radio signal from the candidate cells for the cell selection procedure, and the UE selects a target cell for RRC connection re-establishment among the candidate cells in step 1003. In this case, the cell to be selected includes all RAT cells supported by the UE, including the E-UTRAN.

Also, the cell selection procedure of steps 1002 and 1003 may limit the maximum allowable time for selecting a cell during the RRC connection re-establishment process by the cell selection timer. That is, if no cell is selected until the cell selection timer is terminated as in step 1004, the UE releases the RRC connection state and switches to the RRC idle state in step 1007.

If the UE selects a cell using E-UTRA as a result of step 1003, it transmits an RRC connection re-establishment request message to the corresponding cell in step 1006. If the UE selects a cell using RAT other than E-UTRA as a result of step 1003, the UE considers that the RRC connection reset has failed and releases the RRC connection state and switches to the RRC idle state in step 1007.

As described above, in step 1003, the UE can select a cell using a RAT other than E-UTRA. This is called inter-RAT (Inter-RAT) cell selection. In order for the RRC connection re-establishment procedure to succeed, the selected cell must have a context for the UE. However, since a cell using a RAT other than E-UTRA does not have such information, it can not support the RRC connection re-establishment process of the UE. Therefore, a UE selecting a cell using a RAT other than E- 1005, the RRC connection state is released and the RRC idle state can not be avoided. The terminal switched to the RRC idle state must perform all the steps to continue to provide the service. That is, although the UE has a chance to find a cell using E-UTRA because the timer for cell selection has not expired yet, the UE immediately releases the RRC connection state, switches to the RRC idle state, Is inefficient in terms of service interruption time of the terminal.

Therefore, in the cell selection procedure for the RRC connection re-establishment process of the present invention, unlike the prior art in which all the cells using the E-UTRAN and the other RATs are considered as the cell selection targets, UTRA that can be excluded from the cell selection object is selected.

In order to implement this, the UE must first determine whether the current cell selection is a cell selection procedure for the RRC connection re-establishment process, based on whether or not the cell selection timer operates. When the UE performs a cell selection procedure for the RRC connection re-establishment process in order to exclude a cell using a RAT other than the E-UTRA from the cell selection target, . In addition, a method of preventing a cell using another RAT from satisfying a cell selection criterion by ignoring a measurement value for a cell using a RAT other than E-UTRA in the cell selection criterion or forcibly assuming a very low value It is possible.

Meanwhile, even if the UE selects a cell using E-UTRA in the cell selection procedure, the success or failure of the RRC connection re-establishment process may depend on the type of cell selected. That is, a cell using E-UTRA may be a suitable cell for providing a general service defined in 3GPP standard document TS 36.304 to a terminal or an acceptable cell which does not satisfy all conditions of a suitable cell. The UE always transmits an RRC connection reset request message to the selected E-UTRAN cell irrespective of whether the selected cell is a suitable cell or an acceptable cell through the cell selection procedure of the RRC connection re-establishment process.

However, the Acceptable cell can not support the RRC connection reconfiguration process because it does not have the configuration and configuration context of the UE performing the RRC connection reconfiguration process. Therefore, the Acceptable cell does not accept the RRC connection reset request and sends a reject message. As described above, the RRC connection re-establishment process can not be successful in an acceptable cell. In this case, if the UE selects an Acceptable cell that is not suitable for the RRC connection resetting process, the timer for cell selection has not yet expired and the UE still has a chance to find a suitable cell.

Therefore, transmitting the RRC connection re-establishment request message directly to the acceptable cell as in the prior art only results in the failure of the RRC connection re-establishment process. When the RRC connection state is released and the RRC is put into the idle state, Again, it is inefficient in terms of service interruption time of the terminal.

Therefore, in the present invention, the UE selects a cell using E-UTRA in the cell selection procedure of the RRC connection re-establishment process, and transmits an RRC connection re-establishment request message only when the selected cell is a suitable cell. If the UE confirms that the selected E-UTRAN cell is an acceptable cell which is not suitable, the UE performs the cell selection procedure again without transmitting the RRC connection re-establishment request message.

Hereinafter, in order to solve the problem caused by cell selection between inter-RAT, a method of excluding a cell using RAT other than E-UTRAN from a cell selection target and a method of transmitting an RRC connection reset request message only when a selected cell is a suitable cell And then, an improved RRC connection resetting method in which both methods are applied will be described.

<Method of excluding cells of RATs other than E-UTRAN from cell selection targets>

11 is a diagram illustrating a cell selection procedure during the RRC connection re-establishment process according to an embodiment of the present invention. In particular, the embodiment disclosed in FIG. 11 is a case in which a radio receiver of a RAT other than the E-UTRAN is turned off when the UE performs a cell selection procedure for the RRC connection re-establishment process, and uses a RAT other than E-UTRAN Cell is excluded.

Referring to FIG. 11, when the RRC connection resetting process is started, the operation of the cell selection timer is started in step 1101.

When performing the cell selection procedure, the UE determines whether it is a cell selection procedure for the RRC connection re-establishment process. That is, in step 1102, the UE checks whether the cell selection timer is in progress and confirms whether the cell selection process is a cell selection process for the RRC connection re-establishment process.

If the corresponding cell selection procedure is not a cell selection procedure for the RRC connection re-establishment process, that is, if it is confirmed in step 1102 that the cell selection timer does not proceed, the UE proceeds to step 1104 to determine a cell using all RATs supported by the UE Cell selection target.

On the other hand, if the corresponding cell selection procedure is a cell selection procedure for the RRC connection re-establishment process, that is, if it is confirmed in step 1102 that the cell selection timer is in progress, the UE uses another RAT in addition to E-UTRAN in the cell of cell selection The candidate cell set is configured. That is, the UE stops the operation of the RAT receiver other than the E-UTRAN and adds a constraint condition that the cell selection object does not consider a cell using a RAT other than E-UTRAN.

Subsequently, in step 1104, a radio signal transmitted from one or more cells is measured for a cell selection procedure, and based on this, a cell is selected in step 1105. If it is determined that the corresponding cell selection procedure is a cell selection procedure for the RRC connection re-establishment process, the target cell is selected based on the constraint condition added in step 1103, i.e., the candidate cell set, It is a cell using UTRA. On the other hand, if it is determined that the corresponding cell selection procedure is not a cell selection procedure for the RRC connection re-establishment process, the cell selected in step 1105 may be a cell using E-UTRA or a cell using another RAT.

If the cell selection timer is terminated before the cell is selected through the cell selection procedure as shown in step 1106, the UE releases the RRC connection state and switches to the RRC idle state in step 1108. On the other hand, if it is determined in step 1105 that a cell using E-UTRA is selected in the corresponding cell selection procedure, the UE transmits an RRC connection re-establishment request message to the selected cell in step 1107. Thereby, the UE continues the RRC connection reset process.

12 is a diagram illustrating a cell selection procedure during the RRC connection re-establishment process according to another embodiment of the present invention. In particular, the cell selection procedure during the RRC connection re-establishment procedure of FIG. 12 ignores the measurement values for cells using RATs other than E-UTRAN in the cell selection criterion, or forcibly assumes a very low value, .

Referring to FIG. 12, when the RRC connection resetting process is started, the operation of the cell selection timer starts in step 1201. In this case, the terminal still maintains the RRC connection state. In step 1202, the terminal also measures radio signals from candidate cells for cell selection.

Subsequently, the UE checks whether it is a cell selection procedure for the RRC connection reset process. That is, in step 1203, the UE checks whether the cell selection timer is in progress and confirms whether the cell selection procedure is a cell selection process for the RRC connection re-establishment process.

If the corresponding cell selection procedure is not the cell selection procedure for the RRC connection re-establishment process, that is, if it is confirmed in step 1203 that the cell selection timer does not proceed, the UE proceeds to step 1205 and uses the cell quality information measured in step 1202 as it is And proceeds to the cell selection procedure.

If the corresponding cell selection procedure is the cell selection procedure for the RRC connection re-establishment process, that is, if it is confirmed in step 1203 that the cell selection timer is in progress, the UE determines in step 1204 that the cell quality information measured in step 1202 The value of the cell quality information for the cell using the RAT is adjusted to generate the candidate cell quality information. That is, in the cell selection criterion, a measurement value for a cell using a RAT other than E-UTRAN is ignored or forced to be a very low value so that the cell selection criterion can not be satisfied.

Subsequently, in step 1205, the UE selects the target cell of the RRC connection re-establishment using the cell quality information measured in step 1202 or the value of the candidate cell quality information generated in step 1204. If it is determined that the corresponding cell selection procedure is a cell selection procedure for the RRC connection re-establishment process, the cell selection is performed based on the candidate cell quality information, and the selected cell is a cell using E-UTRA. Meanwhile, if it is determined that the cell selection procedure is not a cell selection procedure for the RRC connection re-establishment process, the cell selected in step 1205 may be a cell using E-UTRA or a cell using another RAT.

If the cell selection timer is terminated before the target cell is selected through the cell selection procedure as shown in step 1206, the UE releases the RRC connection state in step 1208 and switches to the RRC idle state. On the other hand, if it is determined in step 1205 that a cell using E-UTRA is selected in the corresponding cell selection procedure, the UE transmits an RRC connection re-establishment request message to the selected cell in step 1207. Thereby, the UE continues the RRC connection reset process.

<How to send RRC connection reset request message only when it is a suitable cell>

13 is a diagram showing a part of the RRC connection resetting process according to the embodiment of the present invention. In particular, FIG. 13 illustrates a method of transmitting an RRC connection re-establishment request message only when a selected cell is a suitable cell, and a method of excluding a cell using a RAT other than the E-UTRAN described above from a cell selection target is not applied .

Referring to FIG. 13, when the RRC connection resetting process is started, the operation of the cell selection timer is started in step 1301, the radio signal is measured for cell selection in step 1302, and the cell is selected in step 1303 based on the measurement . The selected cell may be a cell using E-UTRA or a cell using another RAT.

On the other hand, if the cell selection timer is terminated before the cell is selected through the cell selection procedure as shown in step 1304, the UE releases the RRC connection state and switches to the RRC idle state in step 1308. If the cell selected in step 1303 is a cell using another RAT other than E-UTRA, the UE stops the RRC connection reset process and releases the RRC connection state and the RRC idle state in step 1308.

If the cell selected in step 1303 is a cell using E-UTRA, the UE proceeds to step 1306 to check the type of the cell before transmitting the RRC connection re-establishment request message. The terminal can read the system information of the cell selected for the cell type check or utilize the information stored in the terminal. If it is determined that the selected cell is a suitable cell, the UE transmits an RRC connection reset request message to the corresponding cell in step 1307.

On the other hand, if the selected cell is an acceptable cell, the UE does not send an RRC connection reset request message to the corresponding cell, and proceeds to step 1302 and subsequent steps to search for a suitable cell unless the cell selection timer expires.

&Lt; Improved RRC connection reset method >

14 is a diagram illustrating an improved RRC connection resetting process according to an embodiment of the present invention. In particular, although the embodiment shown in FIG. 14 exemplifies the case where the UE turns off the radio receiver of the RAT other than the E-UTRAN when performing the cell selection procedure for the RRC connection re-establishment procedure, It should be apparent to those skilled in the art that the present invention can also be applied to the case of excluding measurement values for cells using RAT.

In addition, since the processes of steps 1401 to 1406 are the same as those of steps 1101 to 1106 of FIG. 11, a detailed description will be omitted.

Referring to FIG. 14, when it is confirmed in step 1402 that the cell selection timer is in progress, in step 1403, the UE excludes cells using RATs other than E-UTRAN in the cell selection object, that is, the candidate cell

Subsequently, in step 1404, a radio signal is measured from the candidate cells for the cell selection procedure, and based on this, a cell is selected in step 1405, and the selected cell is necessarily a cell using E-UTRA. Also, the UE proceeds to step 1407 for type checking of the cell before transmitting the RRC connection re-establishment message to the selected cell using E-UTRA. If it is determined that the selected cell is a suitable cell, the UE transmits an RRC connection reset request message to the corresponding cell in step 1408.

If the selected cell is an Acceptable cell, the UE does not send an RRC connection reset request message to the corresponding cell. If the selected cell does not expire, the UE proceeds to step 1404 and repeats the following steps to search for a suitable cell among the cells using E-UTRA do.

15 is a block diagram of a terminal device according to an embodiment of the present invention.

15, the terminal device of the present invention includes a receiving module 1510, a processor 1520 and a transmitting module 1530. Particularly, the processor 1520 includes a radio signal measuring module 1540, Module 1550. &lt; RTI ID = 0.0 &gt;

Receiving module 1510 may receive information necessary for cell selection and cell reselection procedures from cells other than general data transmitted from cells. In particular, the receiving module 1510 may receive an RRC Connection Reset Accept message and an RRC Connection Reset Reject message from the cell. The receiving module 1510 may receive a reference signal or a pilot signal for measuring the cell quality information required for the cell selection and the cell reselection procedure.

The processor 1520 controls the overall operation of the terminal, and generates control signals, for example, an RRC connection reset request message and an RRC connection reset complete message, for transmission to the cell in the cell selection procedure and the cell reselection procedure.

A radio signal measurement module 1540 included in the processor 1520 also measures signal characteristics for a cell selection or cell reselection procedure. Here, the signal characteristic refers to a characteristic of a physical signal such as a strength of a reference signal or a pilot signal received by the receiving module 1510, a ratio of noise / interference, and the like.

In addition, the cell selection module 1550 included in the processor 1520 searches for cells to be subjected to cell selection or cell reselection based on the signal characteristics measured by the radio signal measurement module 1540. In particular, the cell selection module 1550 determines whether the corresponding cell selection procedure is a cell selection procedure for the RRC connection reset procedure. In this case, it is preferable that the cell selection timer is checked to see if the corresponding cell selection procedure is a cell selection procedure for the RRC connection re-establishment process.

Also, the cell selection module 1550 preferably excludes cells using RAT other than E-UTRA from the cell selection object if the corresponding cell selection procedure is a cell selection procedure for the RRC connection re-establishment procedure.

As a first method, the cell selection module 1550 constructs a candidate cell set by excluding one or more cells using RAT other than the specific RAT in the cell, and selects a target cell in the candidate cell set. This can be implemented by turning off the radio receiver of the RAT other than the E-UTRAN if the cell selection procedure is a cell selection procedure for the RRC connection re-establishment procedure.

As a second method, the radio signal measurement module 1540 measures cell quality information corresponding to each of the one or more cells using a signal received from one or more cells, and measures RAT It is possible to ignore the cell quality information of the cells using the cell quality information or force the cell quality information to be a very low value to generate the candidate cell quality information. In this case, the cell selection module 1550 can select the target cell based on the candidate cell quality information.

Also, in the cell selection procedure for the RRC connection re-establishment process, the processor 1520 determines a suitable cell as a target cell in the RRC connection re-establishment process among the cells using the selected E-UTRA. That is, in the case of an Acceptable cell other than a suitable cell, the processor 1520 does not send an RRC connection reset request message to the cell, and controls the cell selection module 1550 to search for a suitable cell again unless the cell selection timer expires .

The transmitting module 1530 may transmit uplink data or control information to the cell and may transmit an RRC connection reset request message and an RRC connection reset complete message during the RRC connection reset process. In particular, the transmission module 1530 can transmit an RRC connection re-establishment request message to the cell only when the cell selection module 1550 selects a suitable cell among the cells using E-UTRA in the RRC connection re-establishment process.

The embodiments described above are those in which the elements and features of the present invention are combined in a predetermined form. Each component or feature shall be considered optional unless otherwise expressly stated. Each component or feature may be implemented in a form that is not combined with other components or features. It is also possible to construct embodiments of the present invention by combining some of the elements and / or features. The order of the operations described in the embodiments of the present invention may be changed. Some configurations or features of certain embodiments may be included in other embodiments, or may be replaced with corresponding configurations or features of other embodiments. It is clear that the claims that are not expressly cited in the claims may be combined to form an embodiment or be included in a new claim by an amendment after the application.

In this document, the embodiments of the present invention have been mainly described with reference to the data transmission / reception relationship between the terminal and the base station. The specific operation described herein as being performed by the base station may be performed by its upper node, in some cases. That is, it is apparent that various operations performed for communication with a terminal in a network including a plurality of network nodes including a base station can be performed by a network node other than the base station or the base station. A 'base station' may be replaced by terms such as a fixed station, a Node B, an eNode B (eNB), an access point, and the like. The term 'terminal' may be replaced with terms such as User Equipment (UE), Mobile Station (MS), and Mobile Subscriber Station (MSS).

Embodiments in accordance with the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of hardware implementation, an embodiment of the present invention may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs) field programmable gate arrays, processors, controllers, microcontrollers, microprocessors, and the like.

In the case of an implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, a procedure, a function, or the like which performs the functions or operations described above. The software code can be stored in a memory unit and driven by the processor. The memory unit may be located inside or outside the processor, and may exchange data with the processor by various well-known means.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit of the invention. Accordingly, the above description should not be construed in a limiting sense in all respects and should be considered illustrative. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the scope of equivalents of the present invention are included in the scope of the present invention.

Although the cell reselection method and apparatus for cell reselection in the wireless communication system as described above have been described with reference to an example applied to the 3GPP LTE system, other types of cell reselection schemes other than the 3GPP LTE system, It is possible to apply it to a communication system.

1 is a flowchart illustrating an operation of a terminal when the terminal is turned on in the LTE system,

2 is a diagram conceptually showing a network structure of an E-UMTS,

3 is a diagram conceptually showing a network structure of an E-UTRAN,

4A and 4B are diagrams showing a wireless interface protocol structure between a terminal and an E-UTRAN based on a 3GPP radio access network standard;

5 is a diagram showing an example of a physical channel structure used in an E-UMTS system,

6 is a diagram for explaining a general transmission / reception method using a paging message,

FIG. 7 is a flowchart showing a general RRC connection resetting procedure of a terminal,

8 is a flowchart showing a case where the RRC connection re-establishment process is successful;

FIG. 9 is a flowchart showing a case where the RRC connection resetting process fails;

10 is a diagram showing a part of a general RRC connection resetting process,

11 is a diagram illustrating a cell selection procedure in an RRC connection re-establishment process according to an embodiment of the present invention;

12 is a diagram illustrating a cell selection procedure during an RRC connection reset process according to another embodiment of the present invention;

13 is a diagram showing a part of an RRC connection resetting process according to an embodiment of the present invention;

FIG. 14 is a diagram illustrating an improved RRC connection resetting process according to an embodiment of the present invention,

15 is a block diagram of a terminal device according to an embodiment of the present invention.

Claims (17)

A method for performing RRC connection re-establishment between a cell using a specific RAT (Radio Access Technology) in a wireless communication system and a multiple RAT supporting terminal in a RRC (Radio Resource Control) connection state, Determining whether a cell selection procedure is a communication RRC reconnection state through a cell selection timer verification process; Generating cell quality information by forcibly applying a measured value of at least one cell using another RAT except the specific RAT to a low value; Configuring a candidate cell set by excluding the one or more cells from one or more cells if the current cell selection procedure is in the RRC reconnect state; Selecting a target cell based on cell quality information corresponding to each of one or more cells included in the candidate cell set; And And transmitting an RRC connection re-establishment request message to the selected target cell, Wherein the target cell has configuration information and context of the terminal and is configured to allow a tracking update (TA) How to reset the RRC connection. The method according to claim 1, Wherein configuring the candidate cell set comprises: Stopping a receiver of the RAT other than the specific RAT, How to reset the RRC connection. The method according to claim 1, Starting a cell selection timer before execution of the step of constructing the candidate cell set; And And entering the RRC idle state if the target cell is not selected until the cell selection timer expires. How to reset the RRC connection. The method according to claim 1, Receiving an RRC connection reestablishment acceptance message from the selected target cell after executing the step of transmitting the RRC connection reestablishment request message; And Further comprising transmitting an RRC connection re-establishment acknowledgment message to the selected target cell. How to reset the RRC connection. delete delete delete delete delete delete delete delete delete delete A multi-RAT supporting terminal apparatus in a radio communication system in a RRC (Radio Resource Control) connection state with a cell using a specific RAT (Radio Access Technology) A receiving module for receiving a signal for cell quality information measurement from one or more cells; The UE determines whether the cell selection procedure is in a communication RRC reconnection state through a cell selection timer check process and forcibly applies a measurement value of one or more cells using RATs other than the specific RAT to a low value, Generates candidate cell quality information by excluding the cell quality information of the one or more cells from the cell quality information when the current cell selection procedure is in the RRC reconnection state and generates candidate cell quality information based on the candidate cell quality information, A processor to select; And And a transmission module for transmitting an RRC connection re-establishment request message to the selected target cell, Wherein the target cell has configuration information and context of the terminal and is configured to allow a tracking update (TA) Multiple RAT capable terminals. delete delete

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