KR20150105057A - Mobile terminal and control method thereof - Google Patents

Abstract

The present invention relates to a device and a method for controlling a terminal in a wireless communication system. According to the present invention, the method includes the steps of: transmitting a control signal to connect to the base station of a serving cell; determining the signal quality of the serving cell when a response signal related to the transmitted control signal is not received; comparing the signal quality of the determined serving cell and a threshold value; determining a connection retry number regarding the serving cell according to a comparison result; and retrying to connect to the base station of the serving cell according to the determined retry number. The threshold value is a reference value for determining the status of signal quality of the serving cell. The signal quality of the serving cell is determined by at least one of a reference signal′s signal to noise ratio (RS SNR) or a channel quality indicator (CQI).

Description

[0001] MOBILE TERMINAL AND CONTROL METHOD THEREOF [0002]

The present invention relates to a mobile terminal and a control method thereof in a wireless communication system, and more particularly, to a method and an apparatus relating to an RRC connection in a wireless communication system.

The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), a next generation communication of UMTS (Universal Mobile Telecommunication System), is introduced as 3GPP release 8. LTE uses orthogonal frequency division multiple access (OFDMA) in the downlink and single carrier-frequency division multiple access (SC-FDMA) in the uplink.

In addition, MIMO (Multiple Input Multiple Output) having up to four antennas is employed. Recently, LTE-A (LTE-Advanced), an evolution of LTE, is under discussion.

In LTE / LTE-A, physical channels can be divided into PDSCH (Physical Downlink Shared Channel), PDCCH (Physical Downlink Control Channel), PUSCH (Physical Uplink Shared Channel) and PUCCH (Physical Uplink Control) have.

The LTE system includes a terminal, a base station, and an Access Gateway (AG) located at the end of the network and connected to an external network. The base station may simultaneously transmit multiple data streams for a broadcast service, a multicast service, and / or a unicast service.

One base station may have more than one cell. The cell is set to one of the bandwidths of 1.25, 2.5, 5, 10, 15, and 20 MHz, and provides downlink or uplink services to a plurality of terminals. Different cells may be set up to provide different bandwidths. The base station can control data transmission / reception for a plurality of terminals.

It is an object of the present invention to provide a method and apparatus for RRC connection when a terminal is in an RRC idle mode in a wireless communication system.

It is another object of the present invention to provide a method and apparatus for cell reselection when a terminal fails in an RRC connection in an RRC idle mode in a wireless communication system.

It is another object of the present invention to provide a method and apparatus for cell reselection considering the quality of a serving cell when a terminal fails in an RRC connection in an RRC idle mode in a wireless communication system.

 It is still another object of the present invention to provide a method and apparatus for retransmitting a connection to a serving cell in consideration of the quality of a serving cell when a terminal fails in an RRC connection from a RRC idle mode to a serving cell And to provide a method and apparatus for determining whether or not to determine whether or not to use the device.

According to another aspect of the present invention, there is provided a method for transmitting a control signal to a serving cell, the method comprising: transmitting a control signal for connection with a base station of a serving cell; Determining a signal quality of the serving cell if a response signal associated with the transmitted control signal is not received; Comparing the signal quality of the determined serving cell with a threshold value; Determining a number of connection retries with the serving cell according to the comparison result; And retrying the connection with the base station of the serving cell according to the determined number of retries, wherein the threshold is a reference value for determining a state of the signal quality of the serving cell, Is determined by at least one of a reference signal (RS), a signal-to-noise ratio (SNR), and a channel quality indicator (CQI).

In addition, in the present invention, the step of determining the number of connection retries may include determining the number of connection retries as a first retry number when the signal quality of the serving cell is greater than a threshold value as a result of the comparison, Wherein the number of connection retries is determined as a second number of retries when the signal quality of the serving cell is less than a threshold value and the first retry number is greater than the second retry number. .

Also, in the present invention, the step of retrying the connection may further include a step of attempting connection with a neighboring cell when the number of connection attempts with the base station of the serving cell is equal to or greater than the determined number of retries.

In the present invention, the control signal may be a random access request signal or a signal requesting an RRC connection.

Further, in the present invention, the response signal may be a random access response signal or an RRC connection setup signal.

According to another aspect of the present invention, there is provided a mobile communication system comprising: a transmitter for transmitting a control signal for connection with a base station of a serving cell; A receiving unit for receiving a response signal related to the control signal from the base station; And determining a number of connection retries with the serving cell according to a result of the comparison. The method of claim 1, further comprising: determining a quality of the serving cell if the response signal is not received; Wherein the threshold is a reference value for determining a state of the signal quality of the serving cell and the signal quality of the serving cell is determined based on the number of retries of the serving cell, Is determined by at least one of a reference signal (RS), a signal-to-noise ratio (SNR), and a channel quality indicator (CQI).

In the present invention, if the signal quality of the serving cell is greater than the threshold value, the controller determines the number of connection retries to be the first retry count, and if the signal quality of the serving cell is greater than the threshold, The connection retry count is determined as the second retry count, and the first retry count is greater than the second retry count.

Also, in the present invention, when the number of connection attempts with the base station of the serving cell is equal to or greater than the determined number of retries, the controller attempts to connect to the neighboring cell.

In the present invention, the control signal may be a signal for requesting a random access or a signal for requesting an RRC connection.

Further, in the present invention, the response signal may be a random access response signal or an RRC connection setup signal.

The method and apparatus for controlling a terminal according to the present invention have the following effects.

According to the present invention, an efficient RRC connection method of a terminal in a wireless communication system can be provided.

According to the present invention, an Efficient RRC connection method of a UE can be provided by determining a signal quality of a serving cell in a wireless communication system.

According to the present invention, an efficient RRC connection method of a UE can be provided by adjusting the number of times of reconnection according to signal quality of a serving cell in a wireless communication system.

According to the present invention, it is possible to provide an efficient RRC connection method of a UE by adjusting the number of reconnection times by comparing a signal quality of a serving cell with a threshold value in a wireless communication system.

FIG. 1 illustrates a cellular system in a wireless communication system to which the present invention is applied.
2 shows the internal structure of a terminal to which the present invention is applied as a whole.
FIG. 3 shows a structure of a radio access protocol in a communication system to which the present invention is applied.
Figure 4 shows the protocol stack of the control plane for the network to which the present invention is applied.
5 to 6 show a first embodiment to which the present invention is applied, FIG. 5 shows an RRC connection process, and FIG. 6 shows an example when a RRC connection fails.
7 to 12 show a second embodiment to which the present invention is applied. FIG. 7 schematically shows an attempt to connect to an adjacent cell when a RRC connection fails with a serving cell, and FIG. And if the RRC connection with the base station fails, a connection to an adjacent cell is attempted.
FIG. 9 shows a process of setting the number of connection attempts differently according to the quality of a serving cell.
FIG. 10 illustrates a procedure for attempting RRC connection with a base station of a serving cell according to a first retry count, and FIG. 11 illustrates a procedure for RRC connection attempt with a base station of a serving cell according to a second retry count.
FIG. 12 shows details of connection retry between a serving cell and a neighbor cell when a RRC connection fails with a base station of a serving cell.

The above objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. It is to be understood, however, that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and similarities. Like reference numerals designate like elements throughout the specification. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

Hereinafter, a method and an apparatus according to the present invention will be described in detail with reference to the drawings. The suffix "module" and "unit" for constituent elements used in the following description are given or mixed in consideration of ease of specification, and do not have their own meaning or role.

The terminal described in this specification may include a mobile phone, a smart phone, a laptop computer, a digital broadcasting terminal, a PDA (Personal Digital Assistants), a PMP (Portable Multimedia Player), and navigation. However, it will be understood by those skilled in the art that the configuration according to the embodiments described herein may be applied to a fixed terminal such as a digital TV, a desktop computer, and the like, unless the configuration is applicable only to a mobile terminal.

A wireless device may be fixed or mobile and may be referred to by other terms such as a User Equipment (UE), a mobile station (MS), a user terminal (UT), a subscriber station (SS), a mobile terminal (MT) A base station generally refers to a fixed station that communicates with a wireless device and may be referred to by other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, and the like.

FIG. 1 illustrates a cellular system in a wireless communication system to which the present invention is applied.

Referring to FIG. 1, one example of a layout structure of a macro cell and a pico cell in a cellular system can be examined (100).

The conventional network arrangement method has a typical homogeneous network type centered on a macro cell. However, the arrangement of homogeneous networks is too complex, iterative, and the incidence of shaded areas in urban areas increases. Therefore, a heterogeneous network (100) has been discussed as a method for solving such a problem.

Such a heterogeneous network can increase the traffic capacity and increase the data rate in a specific area by supplementing the macro cell with a low power picocell.

The heterogeneous network generally includes a macro cell 110, a picocell 120, a femtocell, and the like. In FIG. 1, a heterogeneous network including the macro cell 110 and the picocell 120 is illustrated. In this heterogeneous network, the base station of the macro cell 110 transmits a signal with a high transmit power of about 40 W at 5 W, and the picocell base station 120 transmits a signal at a transmit power of about 100 W to about 2 W.

The terminal may receive a service through connection with the macro cell 110 or the picocell 120. The terminal may be divided into an RRC Idle state and an RRC_Connected state according to an operation mode and a communication state. This distinction can be distinguished according to whether the terminal is in logical connection with the RRC of the base station.

Since the base station can grasp the presence of a terminal in the RRC connection state on a cell basis, the base station can effectively control the terminal. However, the BS can not recognize the RRC idle (RRC_Idle) terminal in the cell unit. That is, the terminal in the RRC idle state (RRC_Idle) must transit to the RRC_Connected state in order to receive services such as voice or data from the cell.

In the present invention, when the UE fails to transition from the RRC_Idle state to the RRC_Connected state, it attempts to connect to the neighbor cell by changing the number of connection retries according to the quality of the serving cell, And proposes a method by which the terminal can receive a stable and efficient service.

2 shows the internal structure of a terminal to which the present invention is applied as a whole

2, a terminal 200 receiving a service from a base station 210 includes a transmitting and receiving antenna 220, an RF module 230, a demodulator 240, a modulator 240, A controller 250, a controller 260, and a memory 270. The components shown in FIG. 2 are not essential, and may be implemented in a terminal 200 having more or fewer components.

In FIG. 2, the transmitting and receiving antenna 220 is shown as one in the terminal 200, but may also include a plurality of antennas. Therefore, the terminal 200 according to the present invention can support a multiple input multiple output (MIMO) system.

The transmission / reception antenna 220 receives a signal transmitted from the base station 210 or another terminal and provides the signal to the receiver 231. The transceiving antenna 220 can receive not only a signal of a Serving Cell currently being serviced but also a signal of another adjacent cell.

The RF module 230 may include a receiver 231 and a transmitter 232 for transmitting or receiving a radio signal from the base station 210 or another terminal.

The receiver 231 can receive a signal transmitted from the base station 210 or another terminal. Here, the receiver 231 may receive a signal through the transmission / reception antenna 220 and transmit the signal to the demodulator 240. The receiver 231 may receive an RRC message, which is a control signal, from the BS 210, and the RRC message may include various control information.

The transmitter 232 may transmit the modulated signal from the modulator 250 to the base station 210 or another terminal. Here, the transmitter 232 may transmit an RRC Request message for requesting RRC connection to the BS 210 through the Tx / Rx antenna 220.

The demodulator 240 demodulates the received signals and transmits the demodulated signals to the controller 260.

The controller 260 can direct and manage all operations of the terminal, and can operate in cooperation with the respective devices. For example, if the RRC connection with the serving cell fails, the controller 260 may determine the quality of the serving cell and change the number of retries for the RRC connection.

The controller 260 may be referred to as a controller, a microcontroller, a microprocessor, etc. The controller 260 may be hardware, firmware, software, As shown in FIG.

The modulator 250 operates in a manner contrary to the demodulator, that is, when receiving data to be transmitted from the controller, the modulator 250 modulates the data and transmits the modulated data to the transmitter. The modulator 250 converts a signal received from the controller 260 into a modulated signal suitable for transmission, and modulates the modulated signal by transmitting the modulated signal on a carrier wave.

The memory 270 is connected to the controller 260 and stores programs, applications, general files, and input / output data for the operation of the controller 260 as temporary Can be stored.

The memory 270 may be a flash memory type, a hard disk type, a multimedia card micro type, a card type memory (for example, SD or XD memory) At least one of a random access memory (RAM), a static random access memory (SRAM), a read only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), a programmable read- Lt; / RTI > type of storage medium. The terminal 200 may operate in association with a web storage that performs a storage function of the memory unit 270 on the Internet.

FIG. 3 shows a structure of a radio access protocol in a communication system to which the present invention is applied.

3, the radio access protocol can be divided into two areas, a user plane 381 and a control plane 380 according to the type of data to be transmitted. In addition, the layer structure may include a physical layer 310 corresponding to a first layer, a MAC layer 330 belonging to a second layer, an RCL layer 350, and an RRC layer 370 belonging to a third layer. Each layer may be connected to a radio bearer 360, a logical channel 340, a transport channel 320, and the like.

In detail, the physical layer 310 transmits and receives data through a wireless channel, a physical layer HARQ (Hybrid Automatic Repeat reQuest) processing, a modulation, a multi-antenna processing, Mapping to a frequency resource, mapping a transmission channel to a physical channel, and the like. The physical layer 310 may be connected to the upper layer MAC layer 330 through the transport channel 320.

The MAC layer 330 selects an appropriate transport channel for multiplexing the logical channel 340, data for mapping between a logical channel and a transport channel, and transmits a MAC SDU (Medium Access Control Service Data Unit) to construct a MAC PDU (Medium Access Control Packet Data Unit). Also, it is possible to perform data multiplexing among component carriers when HARQ retransmission and uplink, downlink scheduling, and carrier aggregation are used. The MAC layer may be coupled to the RCL layer 350 via the logical channel 340 and may be coupled to the physical layer 310 via the transport channel 320.

The RLC layer 350 is located in the upper layer of the MAC layer 330 to guarantee reliable transmission of data. The transmitting RLC layer can perform segmentation and concatenation of the RLC SDUs transmitted from the upper layer to construct data of an appropriate size for wireless transmission. The receiving RLC layer may support data reassembly to recover the original RLC SDUs from the received RLC PDUs. Each RLC entity included in the RLC layer can operate in three modes: Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM), depending on the processing and transmission method of the RLC SDU.

A wireless channel must be established for the terminal to exchange information with the base station. The RRC (Radio Resource Control) layer 370 supervises the layer. The RRC layer 370 may provide control functions related to setting, changing, and releasing radio resources. To this end, the RRC layer 370 provides a path for receiving direct control information with the lower layer, which is referred to as a C-SAP (Control SAP) 390.

RRC procedures for exchanging control information are defined between the RRC layer 370 of the terminal and the RRC layer 370 of the base station. Most of the RRC procedures can be used for controlling the functions of the terminal .

The RRC layer 370 of the UE may be in two states: an RRC connection (RRC_Connected) and an RRC idle (RRC_Idle). An RRC context may be formed in the RRC_Connected state. That is, parameters required for the terminal and the base station to communicate with each other are known in both the terminal and the base station. A cell to which the terminal belongs is known and a C-RNTI (Cell Radio Network Temporary Identifier) used for signaling between the terminal and the base station may be set in the identity of the terminal.

The RRC_Connected state is a state in which the MS and the BS transmit and receive data, but discontinuous reception (DRX) may be established to reduce power consumption of the MS. Since the RRC_context is already set in the base station even in the DRX state in the RRC_Connected state, signaling for connection establishment is not required. Therefore, it is relatively difficult to terminate DRX and start sending / receiving data fast.

The RRC context does not exist in the RRC idle state (RRC_Idle) state and the UE does not belong to a specific cell. In this state, the terminal may not transmit data for most of the time to reduce battery consumption. Uplink synchronization is not maintained, and thus only possible uplink transmission is a random access performed to move to the RRC_Connected state.

According to the present invention, when an RRC connection request (RRC connection request) for transiting to the RRC_Connected state fails while the terminal exists in the RRC_Idle state, the terminal transmits RRC You can control the number of connection retries. The terminal adjusts the number of RRC connection retries according to the signal quality of the cell and attempts to connect to another neighboring cell when the number of retries exceeds the number of retries, thereby providing an efficient service to the user.

A data transmission service may be provided between the terminal and the base station through a radio bearer (Radio Bearer) 360. The radio bearer 360 may be a data transmission service provided to the upper layer by the second layer. The characteristics of the radio bearer 360 may be determined by characteristics of the lower protocol layer, the transport channel 320, the physical channel 310, and the like.

The radio bearer 360 for transmission of the control plane 381 data may be referred to as a Signaling Radio Bearer (SRB) for distinguishing it from the radio bearer 360 of the user plane 380 transmitting user data. have.

The radio bearer 360 may provide bidirectional or unidirectional services to an upper layer. The directionality of the provided service may be determined by the RLC entity in use.

In the RRC_Idle state, when the MS succeeds in an RRC connection with the BS, the MS can receive a notification that a user plane RB is established from a lower layer of the NAS (Non-Access Stratum) layer.

The user plane 381 is an area in which traffic information of a caller such as a voice or an IP packet can be transmitted. The control plane 380 is used for maintaining and managing a network interface and call Indicates an area where control information can be transmitted.

In the present invention, the RRC layer 370 may transmit an RRC connection request message to the lower layer through the control plane 380. The RRC connection request message transmitted to the lower layer may be transmitted to the BS through the physical layer 310. However, when the RRC connection request message is not transmitted to the BS, the MS can not transition to the RRC_Connected state, and the MS can retransmit the RRC connection request message to the BS again.

In this case, the number of RRC connection request messages to be retransmitted may be adjusted according to the signal quality of the cell to attempt connection to the neighboring cell, thereby attempting to connect with the adjacent cell.

Figure 4 shows the protocol stack of the control plane for the network to which the present invention is applied.

Referring to FIG. 4, an LTE (Long Term Evolution) network, which is a fourth generation communication network, can be roughly divided into E-UTRAN and CN (Core Network). The E-UTRAN is composed of a terminal, a base station, and an access gateway (AG), which is a connection gateway connected to an external network. The AG may be divided into a portion for processing user traffic and a portion for processing control traffic. One base station may have more than one cell.

The layers of the radio interface protocol between the terminal and the base station can be classified into L1 (first layer), L2 (second layer) and L3 (third layer). Here, The physical layer (PHY) 460 provides an information transmission service using a physical channel. The physical layer (PHY) 460 includes an upper layer, a Medium Access Control (MAC) layer 450, Can be connected.

The Medium Access Control (MAC) layer 450, which is the second layer, provides a service to a radio link control (RLC) layer 440, which is an upper layer, through a logical channel .

A Radio Resource Control (RRC) layer 420 located in the third layer controls radio resources between the UE and the BS. It is defined only in the control plane and controls logical channels, transport channels and physical channels in connection with the setting, resetting and release of radio bearers (RBs). For this, the RRC layer 420 exchanges RRC messages between the UE and the BS.

The non-access stratum (NAS) layer 410 located in the upper part of the RRC layer 420 may perform functions such as session management and mobility management.

The NAS layer 410 may define two states of EMM-REGISTERED and EMM-UNREGISTERED for EMM management for the mobility management of the MS, And can be applied to terminals and MMEs. Initially, the terminal is in the EMM unregistered state. In order for the terminal to access the network, the terminal registers in the network through an initial attach procedure. If the contact procedure is successfully performed, the terminal and the MME can be in the EMM registration state.

In the present invention, when the NAS layer 410 transmits a service request message to a lower layer to transit from an RRC Idle state to an RRC_Connected state, The number of times of reconnection of the cell can be changed according to the signal quality of the cell.

FIG. 5 illustrates a RRC connection procedure of a terminal according to a first embodiment to which the present invention is applied.

5, the upper layer of the terminal 500 can transmit a service request message for RRC connection to a lower layer (S506), and the lower layer that has received the RRC connection request message transmits the service request message to the base station To perform the RRC connection (S510).

When the terminal 500 is in the RRC idle state (RRC_Idle), it can not transmit / receive data. Therefore, the MS must transition to the RRC connection state in order to transmit / receive data.

When the terminal 500 is in the RRC idle state (RRC_Idle) state, the NAS (Non Access Stratum) layer 501, which is an upper layer of the base station, transmits a service request message to the RRC_Connected state To the RRC layer 502 (S505).

If the service request message is received (S505), the RRC layer 502 may transmit an RRC connection request message for RRC connection to the lower layer 503 (S506). The RRC connection request message may be transmitted through a Signaling Radio Bearer.

If the terminal 500 is in the RRC_Idle state, it can not transmit on the uplink. Therefore, the terminal must attempt to make an RRC connection through the random access procedure S507.

The terminal 500 can request a random access channel to the serving base station 504 for a random access procedure S507 for uplink synchronization at step S508. The step S508 of requesting the random access channel is a step in which the terminal 500 transmits a preamble so that the base station 504 can estimate the transmission timing of the terminal 500. [

The base station 504 having received the preamble may perform a random access response (S509). This means that the base station transmits a timing advance command so that the terminal 500 can adjust the transmission timing based on the timing estimation in step S507.

If the uplink is established, the terminal 500 may transmit the RRC connection request message to the BS 504 (S510). If the RRC connection request message is received, the BS 504 may transmit an RRC connection setup message to the MS in step S511.

The lower layer 503 of the terminal 500 receiving the RRC connection setup message may transmit the RRC connection setup message to the upper layer RRC layer 502. If the RRC connection setup message is received, the RRC layer 502 may set up a Signaling Radio Bearer 1 (SRB1) for RRC connection (S513).

The RRC layer 502 that has set up the SRB 1 can notify the NAS layer 501 that the RRC connection has been successful (S 514) and can transmit a message to the lower layer 503 indicating that the RRC connection is completed (S515).

The lower layer 503 that has received the RRC connection complete message can transmit the RRC connection completion message to the base station 504 in step S516 and the terminal 500 becomes the RRC_Connected state, Data can be exchanged with the data processing unit 504.

FIG. 6 shows an example of a case where the RRC connection fails in the first embodiment to which the present invention is applied.

The description of the same steps as those in Fig. 5 will be omitted. Referring to FIG. 6, the terminal 600 may repeatedly send a message for RRC connection when the connection with the base station 604 for transition from the RRC idle mode to the RRC connected mode fails.

Specifically, the terminal 500 can request a random access channel as in FIG. 5 (S608). However, the terminal 500 may not receive a response to the random access from the BS 604 (S609). In step S610, the terminal 600, which has not received a response to the random access request, can request the random access channel to the base station 604 again.

If the random access procedure fails in response to the random access request in step S607, the lower layer 603 of the terminal 600 may inform the RRC layer 602 that the RRC connection request is rejected (step S611 ).

The RRC layer 602 having received the RRC connection request rejection from the lower layer 603 may notify the NAS layer 601 that the RRC connection has failed (S612).

The NAS layer 601 having received an RRC connection failure from the RRC layer 602 may transmit a service request message for RRC connection to the RRC layer 602 in operation S613. The RRC layer 602 may send an RRC connection request message to the lower layer 603 in step S614 and the lower layer 603 may repeatedly request the base station 604 for a random access channel S616).

However, when the procedure for the random access channel fails again (S615), repeatedly repeatedly requesting the RRC connection to the base station 604 causes the data service to the user despite the neighborable cells The quality of the service may be degraded.

Therefore, in order to solve such a problem, a connection retry count considering the signal quality of the base station is set, and a connection attempt with a neighbor cell is attempted when the retry count exceeds the set retry count.

FIG. 7 schematically shows a second embodiment in which the present invention is applied and attempts to connect to an adjacent cell when a RRC connection with a serving cell fails.

Referring to FIG. 7, if the RRC connection fails to the serving BS 712, the MS 711 may attempt to establish RRC connection with the neighbor BS 713.

Specifically, the MS 711 exists in the RRC idle state (RRC_Idle), and transmits a RRC_Connected state to the RRC_Connected state for data transmission / reception with the serving BS 712. [ The RRC connection request can be made to the RRC connection request 712.

However, if a RRC connection with the serving cell's base station 712 is not possible, for example, a response to a random access channel request for uplink synchronization can not be received, 712) can request repeated RRC connections (a).

In this case, if the RRC connection is continuously attempted to the BS 712, the MS 711 can not continuously receive the data service, which may degrade the service quality. Therefore, when the UE 711 retries the RRC connection to the BS 712 a predetermined number of times, it must abandon the RRC connection with the BS 712 and attempt to make an RRC connection to the BS 713 of the neighboring cell .

Therefore, when the RRC connection fails, the terminal 711 can attempt to establish an RRC connection with the base station of the neighboring cell even if the RRC connection reconnection is attempted more than a certain number of times to the serving base station 712 ).

FIG. 8 is a flowchart illustrating an overall process of attempting to connect to an adjacent cell when a RRC connection with a base station of a serving cell is failed, according to a second embodiment of the present invention.

Referring to FIG. 8, the MS may transmit an RRC connection request message to a serving BS in order to transition from an RRC idle state (RRC_Idle) to an RRC connected state (RRC_Connected). If the terminal fails to make an RRC connection with the serving cell's base station, the terminal may try to connect to the neighboring cell's base station considering the signal quality of the serving cell's base station.

Specifically, the UE may be in the RRC_Idle state in the serving cell region. Since the UE can not transmit / receive data to / from the serving cell base station in the RRC_Idle state, the UE transmits a control signal for RRC connection to the base station of the serving cell for data transmission / reception (S810).

Since the UE is not in uplink synchronization with the serving cell base station in the RRC_Idle state, the UE may perform random access for uplink synchronization before transmitting data or control information, Process can be performed.

In this case, the MS may transmit a signal for the random access to the BS of the serving cell before transmitting the RRC connection request message to the BS. Therefore, the control signal may be an RRC connection request signal for RRC connection or a signal for random access.

The MS can determine whether a response signal to the transmitted control signal is received from the BS (S820). The RRC connection setup signal may be a random access response signal when the control signal is the signal for the random access and the RRC connection setup signal if the control signal is the RRC connection request signal.

When receiving the response signal from the base station of the serving cell, the MS can perform RRC connection with the serving cell and transmit / receive data to / from the serving cell (S880).

However, if a response signal is not received from the BS, the MS may determine a signal quality of the serving cell by measuring a signal transmitted from the BS of the serving cell (S830). Hereinafter, the signal quality of the serving cell is referred to as Q _cell .

The Q _cell may be determined in consideration of various factors of the serving cell. For example, the Q _cell may be determined by at least one of a signal-to-noise ratio (RNG) and a channel quality indicator (CQI) of a reference signal (RS) Simulation) can be obtained statistically.

The signal-to-noise ratio (RS SNR) of the reference signal is a ratio between a level of a reference signal to be transmitted and a level of noise that interferes with the reference signal, and can be generally expressed in dB. Also, the channel quality indicator (CQI) is a method for increasing the transmission capacity in a mobile communication system. The CQI measures a radio channel quality at a location where the terminal is located and transmits the measured CQI to the base station. Information to be used as basic information of the scheduler for managing the modulation method, the number of codes, etc., that is, channel information.

If the Q _cell is determined, the terminal can compare the Q _cell with a threshold (S840). The threshold value as a value for determining a state of the Q _cell, if the Q _cell is greater than the threshold Q state of the _cell may be determined to be good. That is, it can be determined that the signal strength of the serving cell is high or interference of peripheral signals is small. However, if the Q _cell is smaller than the threshold, the state of the Q _cell may be determined to be bad. That is, it can be determined that the signal strength of the serving cell is low or the interference of neighboring signals is high.

The MS may determine the number of connection retries with the BS of the serving cell based on the result of the comparison (S850). Without passing through the step (S850) of determining the number of connected retry the serving cell according to the comparison result from the step (S830) of determining the quality of the serving cell, i.e. the number of times even in the terminal without regard to the Q _cell the retry A problem may occur in which the signal quality of the neighboring cell is not better than the signal quality of the serving cell but attempts to connect to an adjacent cell whose signal quality is poor after a number of retries may occur.

The MS may attempt to establish an RRC connection with the serving cell's base station by the number of retries (S860). And can transmit and receive data with the base station of the serving cell when the RRC connection with the base station of the serving cell is successful within the retry count. However, if the number of retries exceeds the number of retries, the MS may attempt to establish an RRC connection with a neighbor cell (S870).

FIG. 9 shows a process of setting the number of connection attempts differently according to the quality of a serving cell according to a second embodiment of the present invention.

9, the number of RRC connection retries with the base station of the serving cell can be determined by comparing the signal quality of the serving cell, that is, the Q _cell and the threshold value.

Specifically, the terminal can determine a Q _cell . 8, it can be determined by at least one of a reference signal to noise ratio (RS SNR) and a channel quality indicator (CQI) of the reference signal.

When the Q _cell is determined, the terminal can compare the Q _cell with a threshold (S930). Here, the threshold value is a value that can determine the Q _cell state, as shown in FIG.

If the Q _cell is greater than the threshold value, the MS determines that the serving cell has a good signal quality and sets the number of connection retries to the first retry count (S950). However, if the Q _cell is smaller than the threshold value, the MS determines that the signal quality of the serving cell is not good and sets the number of connection retries to the number of second retries (S940).

Wherein the first retry count may be greater than the second retry count. This is because it is determined that the signal quality of the serving cell is good, so that it is more efficient to connect with the base station of the serving cell than to connect with the base station of the neighboring cell.

However, when the Q _cell is smaller than the threshold value, it is determined that the signal quality of the serving cell is not good. Therefore, it is more desirable to attempt to establish a connection with the base station of the neighboring cell than to make a connection with the base station of the serving cell a number of times Since efficient service can be provided, the number of second retries can be set small.

FIG. 10 is a flowchart illustrating an RRC connection attempt procedure with a base station of a serving cell according to a first retry count, according to a second embodiment of the present invention. FIG. 11 is a second embodiment to which the present invention is applied. 2 RRC connection procedure with the base station of the serving cell according to the number of retries.

Referring to FIG. 10 and FIG. 11, when the MS determines the number of connection retries as the first retry count or the second retry count in FIG. 9, the MS determines whether the first retry count or the second retry count The RRC connection with the base station of the serving cell can be attempted.

Hereinafter, the case where the number of retries is set as the first retry count will be described in detail. If the number of retries is set to the second number of retries, the procedure is the same as the procedure of changing the first number of retries to the second number of retries in the procedure of FIG.

Looking at this in detail, the mobile signal quality of Q _cell with a threshold if the value compared to the Q _cell exceeds the threshold claim wherein the number of connected retry determines the signal quality of the serving cell is good first of retries of the serving cell (S1010). The UE having set the retry count may retry the RRC connection with the serving cell base station (S 1020)

As a result of the RRC connection retry with the serving cell BS, the MS can determine whether the RRC connection with the serving cell BS has been established (S 1030).

As a result of the retry, when the RRC connection with the base station of the serving cell is successful, the UE transitions from the RRC_Idle state to the RRC_Connected state and can transmit / receive data to / from the connected serving cell S1040).

However, if the RRC connection with the base station of the serving cell is failed again, the MS may compare the number of retries of the RRC connection with the BS of the serving cell and the first number of retries (S1050).

If the number of RRC connection attempts is equal to or greater than the first retry count, the MS may attempt to establish an RRC connection with the neighboring cell BS in step S1060. However, if the number of RRC connection attempts is less than the first retry count, the MS may retry RRC connection with the serving cell base station (S1020).

FIG. 12 shows details of connection retry with a serving cell and connection attempt with a neighboring cell when a connection with a serving cell fails.

Referring to FIG. 12, the UE may attempt to establish an RRC connection to transition to a RRC connection state with a base station of a serving cell. As a result, when the RRC connection fails, the signal quality of the serving cell is determined and the number of times of retry is determined by the number of retry attempts. If the number of attempts to connect to the serving cell's base station exceeds the retry count, can do.

Specifically, the MS can transmit a control signal for RRC connection with the serving cell BS to the BS of the serving cell (S1201).

The terminal may be in the RRC idle state (RRC_Idle) in the area of the serving cell. Since the UE can not transmit / receive data to / from the serving cell base station in the RRC_Idle state, the UE transmits a control signal for RRC connection to the base station of the serving cell for data transmission / reception (S1201).

Since the UE is not in uplink synchronization with the base station of the serving cell in the RRC idle mode, the UE performs a random access procedure for uplink synchronization before transmitting data or control information .

In this case, the MS may transmit the random access signal to the serving BS before transmitting the RRC connection request message to the BS. Therefore, the control signal may be an RRC connection request signal for RRC connection or a signal for random access.

The MS may determine whether a response signal to the transmitted control signal is received from the base station of the serving cell (S1202). As a result of the determination, when receiving the response signal from the base station of the serving cell, the terminal can perform RRC connection with the base station of the serving cell (S1205).

However, if the UE does not receive the response signal, the UE can determine whether the serving cell is a cell for which connection is prohibited (S1203). As a result of the determination, if the access is prohibited, the terminal can not access the serving cell and can attempt to make an RRC connection with the base station of the neighboring cell without transmitting a control signal for RRC connection to the base station of the serving cell S1204).

If the serving cell is not a cell for which connection is prohibited, the terminal can determine the signal quality of the serving cell, i.e., Q _cell (S1206). Here, the process of determining the Qcell may be determined by at least one of RS SNR and CQI as described below, and may be implemented by the following algorithm as an example.

If {RS SNR <-100 (dB), CQI <6}

Q _cell <Th _{cell _ Retry} N _retry ≥MAX_retry _good

Otherwise,

Q _cell > Th _{cell _ Retry} N _retry ≥MAX_retry _weak

The Th _{cell _ Retry} corresponds to the threshold for determining the state of the Q _cell, MAX_retry _good is that indicates the maximum access attempts when the value of the Q _cell the threshold value is greater than the value of Th _{cell _ Retry} Value. N _retry indicates the number of times that the UE attempts to access the serving cell and if the N _retry value is equal to or greater than MAX_retry _good , the UE terminates the connection to the serving cell and tries to make an RRC connection with the neighboring cell's base station .

MAX_retry _weak represents the maximum value when the value of the Q _cell is less than the threshold, the value of Th _{cell _ Retry} the terminal may attempt to access the base station of the serving cell. As described above, if the N _retry value is equal to or greater than the MAX_retry _weak value, the MS can _retry the connection to the serving cell and attempt an RRC connection with the BS of the neighboring cell.

The subsequent steps may be performed in the same manner as described with reference to FIGS.

As another embodiment of the present invention, the present invention can be applied to a case where a terminal changes from an EMM_Idle state to an EMM connected state, which is a step of connecting to a network. That is, the present invention can be applied to a case where a terminal is disconnected from an EMM-Deregistered state (ECM-Idle, RRC-Idle) and then connected again to the network.

In this case, the MS can access the MS through a service request message in a network using only a packet switching scheme, and the present invention can be applied when the MS can not access the MS through the service request message.

In addition, in the network using the circuit switching together with the packet switching method, it is possible to access the network through an extended service request message, and the extended service request message The present invention can be applied.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. The present invention is not limited to the drawings.

200: terminal 231: receiver
232: Transmitter 260: Controller
270: Memory

Claims (10)

A method of controlling a terminal in a wireless communication system,
Transmitting a control signal for connection with a base station of a serving cell;
Determining a signal quality of the serving cell if a response signal associated with the transmitted control signal is not received;
Comparing the signal quality of the determined serving cell with a threshold value;
Determining a number of connection retries with the serving cell according to the comparison result; And
Retrying the connection with the base station of the serving cell according to the determined number of retries,
The threshold value is a reference value for determining a state of the signal quality of the serving cell,
Wherein the signal quality of the serving cell is determined by at least one of a reference signal to noise ratio (SNR) of a reference signal or a channel quality indicator (CQI). Control method. 2. The method of claim 1, wherein determining the number of connection retries comprises:
If the signal quality of the serving cell is greater than the threshold value, the number of connection retries is determined as the first retry count,
If the signal quality of the serving cell is less than the threshold value, the number of connection retries is determined as the number of second retries,
Wherein the first retry count is greater than the second retry count. 2. The method of claim 1,
Further comprising the step of attempting connection with a neighboring cell when the number of retries exceeds the determined number of retries. 2. The method of claim 1,
A random access request signal, or a signal for requesting an RRC connection. 2. The apparatus of claim 1,
A random access response signal, or an RRC connection setup signal. A transmitter for transmitting a control signal for connection with a base station of a serving cell;
A receiving unit for receiving a response signal related to the control signal from the base station; And
Determines the signal quality of the serving cell if the response signal is not received, compares the determined signal quality of the serving cell with a threshold value, and determines the number of connection retries with the serving cell according to the comparison result And a controller for retrying connection with the base station of the serving cell according to the determined number of retries,
The threshold value is a reference value for determining a state of the signal quality of the serving cell,
Wherein the signal quality of the serving cell is determined by at least one of a reference signal to noise ratio (SNR) of a reference signal or a channel quality indicator (CQI). 7. The apparatus of claim 6,
If the signal quality of the serving cell is greater than the threshold value, the number of connection retries is determined as the first retry number,
If the signal quality of the serving cell is less than the threshold value, the number of connection retries is determined as the number of second retries,
Wherein the first retry count is greater than the second retry count. 7. The apparatus of claim 6,
And attempts to connect to the neighboring cell when the number of retries exceeds the determined number of retries. 7. The method of claim 6,
A random access request signal or an RRC connection request signal. 7. The method of claim 6,
A random access response signal or an RRC connection setup signal.

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