KR20090076769A - Method of reselecting a cell based on priorities - Google Patents

Abstract

A reselecting method based on priority is provided to guarantee QoS(Quality of Service) to a terminal in a wireless communication system and reduce power consumption for moving the terminal. A signal of a candidate cell is measured(S1010). When signal property of the candidate cell satisfies a predetermined condition for a predetermined time, the candidate cell is selected(S1030). The predetermined time is changed according to priority of the candidate cell. The priority is the priority for a frequency, an RAT(Radio Access Technology), or combination of the frequency and the RAT.

Description

Cell reselection based on priority {METHOD OF RESELECTING A CELL BASED ON PRIORITIES}

The present invention relates to a wireless communication system, and more particularly, to a method for reselecting a cell in a wireless communication system.

The basic purpose of selecting a cell is to register with a network and receive a service from a base station. If the strength or quality of the signal between the terminal and the base station is degraded due to the mobility of the terminal, the terminal reselects another cell to maintain the transmission quality of the data. In this specification, the characteristics of a physical signal related to the strength of the signal or the ratio of the signal and noise / interference are simply referred to as signal characteristics.

The cell reselection method may be classified according to Radio Access Technology (RAT) and frequency characteristics of a cell participating in cell reselection as follows.

Intra-frequency cell reselection: UE reselects a cell having the same center-frequency as the RAT as the serving cell

Inter-frequency cell reselection: UE reselects a cell having a center frequency different from the same RAT as the serving cell

Inter-RAT cell reselection: UE reselects a cell using a RAT different from the RAT being used in the serving cell

FIG. 1 illustrates an operation of a terminal in an idle mode when the terminal is powered on. Referring to FIG. 1, when the power is turned on, the terminal selects a RAT for communicating with a PLMN (Public Land Mobile Network), which is a network to be serviced automatically or manually (S110). The PLMN and RAT information may be selected by a user of the terminal or may be stored in a Universal Subscriber Identity Module (USIM).

Thereafter, the terminal performs an initial cell selection process for selecting a cell having the largest value among the measured base station and a cell whose signal strength or quality is greater than a reference value (S120). The reference value refers to a value defined in the system to ensure the quality of the physical signal in data transmission and reception. Therefore, the value may vary depending on the RAT applied. Thereafter, the terminal receives system information (SI) periodically transmitted by the base station. System information includes basic and essential information for the terminal to access the network. In addition, the system information may include information (Neighbor Cell List; NCL) related to the cells adjacent to the serving cell. Therefore, the terminal should receive all the system information before accessing the base station and should always have the latest system information. The terminal selects a cell to receive the system information in the idle mode when the power is initially turned on.

The terminal registers its information (eg IMSI) in the network in order to receive a service (eg paging) from the network (S150). When the UE selects a cell, the UE does not register with the network, but registers with the network when the network information received from the SI (eg, Tracking Area Identity; TAI) is different from the network information known to the user (S140 and S170).

If the strength or quality of the signal measured from the base station of the serving cell is lower than the value measured from the base station of the neighboring cell, the terminal selects one of the other cells that provides better signal characteristics than the cell of the base station to which the terminal is connected. In addition, when priority (priority) is defined between the frequency or RAT, the cell may be selected in consideration of the priority (S160). This process is referred to as cell reselection, distinguished from initial cell selection in step S120. In the LTE system, Reference Symbol Received Power (RSRP), Reference Symbol Received Quality (RSRQ), and Received Signal Strength Indicator (RSSI) are discussed as signal measurement values.

In FIG. 1, the basic operation of reselecting a cell according to signal characteristics has been described. In LTE, cell selection is required and the following matters are also considered.

UE capability

-Subscriber Information

Camp load balancing

Traffic load balancing

UE capability refers to selecting a cell according to a frequency band selectable by the terminal because the frequency band available for the terminal itself may be limited. The terminal may be configured to select or not select a specific cell according to user subscription information or operator policy. Subscriber information corresponds to this. Camp Load Balancing refers to selecting a cell that is being used by a small number of terminals in order to reduce the data load generated when idle terminals are activated in one cell. Similarly, in terms of reducing data load generated in activated terminals, traffic load balancing is a standard for changing a cell.

In particular, the LTE system is likely to expand the frequency band based on the existing UTRAN for the purpose of installation / maintenance / maintenance. In order to efficiently use radio resources, terminals of the same cell need to balance loads among cells in order to efficiently use radio resources. Therefore, Camp / Traffic Load Balancing is defined as an essential requirement in LTE system.

In the LTE system, in order to efficiently implement the above-described cell selection process, priority is defined for each selectable frequency or RAT so that the UE may preferentially select a specific frequency or RAT during cell selection or cell reselection. can do. In addition, the priority may have different priorities when there are a plurality of frequencies / RATs, or some may have the same priority or may all have the same priority. The LTE system is defined to be a cell reselection target only for a frequency or RAT having priority.

First, a brief description will be given of an operation of performing cell reselection according to a priority of a frequency or a RAT. When the signal characteristic value of the serving cell does not satisfy the threshold (eg, Snonintrasearch), the terminal measures a signal for a cell having a frequency / RAT other than the frequency / RAT of the serving cell. At this time, when reselecting a cell using a frequency having a different priority or the same RAT as the serving cell, the UE is a condition for cell reselection as one condition regardless of the priority of the candidate cell (eg, Treselection). _EUTRAN ) only. That is, the constraint time for reselecting a cell having a higher priority than the serving cell is the same as the constraint time for reselecting a cell having a lower priority than the serving cell. Therefore, in the case of evaluating whether a period in which a signal characteristic value of a candidate cell is greater than or equal to a threshold satisfies a constraint time, the possibility that the evaluation fails due to radio variability is the same in all candidate cells regardless of priority. do.

2 illustrates a process in which the UE reselects cells having different priorities. Referring to FIG. 2, since the signal characteristic value of the serving cell is equal to or less than a specific threshold (eg, Thresh_serving), the UE starts searching and measuring for reselecting another cell. At this time, the cell of frequency 1 has a lower priority than the serving cell and the signal characteristic value is above a certain threshold Threshold_L. In addition, the cell of frequency 2 has a higher priority than the serving cell and the signal characteristic value is above a certain threshold Thresh_H. The UE checks whether the cells satisfy conditions for cell reselection during the Treselection _EUTRAN . In FIG. 2, it is assumed that the Treselection _EUTRAN value is 10 seconds. Therefore, in order for the UE to select a cell of a higher frequency than the serving cell, the cell of frequency 2 has a signal characteristic value greater than or equal to a threshold (eg, Thresh_H) for 10 seconds. However, the frequency 2 cell has no signal characteristic value above the threshold for 10 seconds due to radio fluctuation. Thus, the timer evaluating the signal characteristic value for the cell at frequency 2 is stopped. On the other hand, since the cell of frequency 1 lower than the priority of the serving cell satisfies the signal characteristic value for 10 seconds, the terminal reselects the cell of frequency 1 having a lower priority.

When the UE receives a service at a low priority frequency or RAT, the UE performs measurement periodically or continuously to go to a high priority frequency or RAT. For example, the base station may assign the highest priority to a specific frequency (eg, frequency 2) for the purpose of load balancing and assign a low priority to another specific frequency (eg, frequency 1). In this case, the terminal receives the service at the highest priority frequency (eg, frequency 2). However, when the signal characteristic value of the frequency having the highest priority is lowered due to the mobility of the terminal, the terminal may reselect a cell of another frequency (eg, frequency 1) having a lower priority. A UE receiving a service in a low priority cell continuously measures to select a cell of a high priority frequency (eg, frequency 2). In other words, even if the signal characteristic value of the cell receiving the service is higher than a specific signal characteristic value, the terminal should make a measurement to periodically select a cell having a high priority. Therefore, a terminal that selects a low priority cell may seriously waste power in order to reselect a high priority cell.

In addition, when priority is used for load balancing purposes, the higher the priority of frequency / RAT, the lower the load. Therefore, when the terminal selects a cell of a low frequency / RAT, the amount of bandwidth provided from the cell is reduced. That is, if a cell of a low priority frequency is selected, the load may be relatively high, and thus, the terminal may not be sufficiently allocated radio resources as desired. Therefore, it is difficult to guarantee sufficient quality-of-service (QoS) to be provided to the terminal. In addition, the bandwidth allocated to the cell may not be used efficiently.

As described above, when the terminal is serviced in a cell of low priority frequency or RAT, power consumption may occur by periodically measuring a high priority cell that is difficult to provide sufficient QoS or bandwidth to the user.

The present invention has been made to solve the problems of the prior art as described above, an object of the present invention is to ensure the quality of service (QoS) to the terminal in a wireless communication system, power consumption for the movement of the terminal To provide a way to reduce this.

Another object of the present invention is to provide a method in which reselection eases according to priorities when the UE reselects a cell.

Still another object of the present invention is to provide a method in which reselection eases depending on a relative priority with a serving cell when the terminal reselects a cell having a different priority from the serving cell.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

In one aspect of the present invention, a method for performing cell reselection based on priority in a wireless communication system, the method comprising: measuring a signal of a candidate cell, and a signal characteristic of the candidate cell satisfies a predetermined condition for a specific time; And selecting the candidate cell, wherein the specific time is dependent on the priority of the candidate cell.

In another aspect of the present invention, a method for transmitting control information regarding cell reselection in a wireless communication system, the method comprising: transmitting information about cell priority to a terminal and a signal characteristic of a candidate cell satisfying a predetermined condition; And transmitting information about a specific time to be maintained while the specific time depends on the priority of the candidate cell.

According to embodiments of the present invention has the following effects.

First, it is possible to guarantee a quality of service (QoS) to the terminal and to reduce power consumption for the movement of the terminal.

Second, the terminal may reselect a cell having a higher priority more easily than a cell having a low priority.

Third, when the UE reselects a cell having a priority different from that of the serving cell, the ease of reselection may be restricted according to a relative priority.

Effects obtained in the present invention are not limited to the above-mentioned effects, and other effects not mentioned above may be clearly understood by those skilled in the art from the following description. will be.

The construction, operation, and other features of the present invention will be readily understood by the embodiments of the present invention described with reference to the accompanying drawings. The embodiments described below are examples in which technical features of the present invention are applied to an Evolved Universal Mobile Telecommunications System (E-UMTS).

3 shows a network structure of an E-UMTS. The E-UMTS system is an evolution 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 a Long Term Evolution (LTE) system. For details of technical specifications of UMTS and E-UMTS, refer to Release 7 and Release 8 of the "3rd Generation Partnership Project; Technical Specification Group Radio Access Network", respectively.

Referring to FIG. 3, an E-UMTS is mainly composed of an access gateway (AG) located at an end of a user equipment (UE), a base station, and an network (E-UTRAN) and connected to an external network. Typically, a base station can transmit multiple data streams simultaneously for broadcast service, multicast service and / or unicast service. The AG may be divided into a part that handles user traffic and a part that handles control traffic. In this case, a new interface may be used to communicate with each other between the AG for processing new user traffic and the AG for controlling traffic. One or more cells exist in one eNB. An interface for transmitting user traffic or control traffic may be used between eNBs. CN (Core Network) may be configured with a network node for the user registration of the AG and the UE. An interface for distinguishing between E-UTRAN and CN may be used. AG manages the mobility of the terminal in units of a tracking area (TA). The TA is composed of a plurality of cells, and when the UE moves from one TA to another, the AG notifies the AG of the change of the TA.

4 shows a network structure of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The E-UTRAN system is an evolution from the existing UTRAN system. The E-UTRAN consists of base stations, and eNBs are connected via an X2 interface. The eNB is connected to the terminal through a wireless interface, and is connected to the Evolved Packet Core (EPC) through the S1 interface.

5A and 5B illustrate a control plane and a user plane (U-Plane, User-Plane) structure of a radio interface protocol between a terminal and an E-UTRAN based on 3GPP radio access network standards, respectively. Indicates. The air interface protocol consists of a physical layer, a data link layer, and a network layer horizontally, and vertically a user plane and control signal for data information transmission. (Signaling) It is divided into control plane for transmission. The protocol layers of FIGS. 5A and 5B are based on the lower three layers of the Open System Interconnection (OSI) reference model, which are well known in communication systems, based on L1 (first layer), L2 (second layer), and L3. (The third layer).

The control plane refers to a path through which control messages used by the terminal and the network to manage a call are transmitted. The user plane refers to a path through which data generated at an application layer, for example, voice data or Internet packet data, is transmitted. Hereinafter, each layer of the control plane and the user plane of the radio protocol will be described.

The physical layer, which is the first layer, provides an information transfer service to an upper layer by using a physical channel. The physical layer is connected to the upper layer of the medium access control layer through a transport channel. Data moves between the medium access control layer and the physical layer through the transport channel. Data moves between the physical layer between the transmitting side and the receiving side through the physical channel. The physical channel is modulated by an orthogonal frequency division multiplexing (OFDM) scheme and utilizes time and frequency as radio resources.

The medium access control (MAC) layer of the second layer provides a service to a radio link control (RLC) layer, which is a higher layer, through a logical channel. The RLC layer of the second layer supports reliable data transmission. The functionality of the RLC layer may be implemented as a functional block inside the MAC. In this case, the RLC layer may not exist. The PDCP (Packet Data Convergence Protocol) layer of the second layer performs a header compression function to reduce unnecessary control information in order to efficiently transmit an IP packet such as IPv4 or IPv6 over a narrow bandwidth interface. .

The radio resource control (RRC) layer located at the bottom of the third layer is defined only in the control plane, and the configuration, re-configuration, and release of radio bearers (RBs) are performed. It is in charge of controlling logical channels, transport channels and physical channels. RB 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 terminal and the network. If there is an RRC connected (RRC Connected) between the RRC layer of the terminal and the RRC layer of the wireless network, the terminal is in the RRC connected mode (Connected Mode), otherwise it is in the RRC idle mode (Idle Mode).

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

One cell constituting the eNB is set to one of the bandwidth, such as 1.25, 2.5, 5, 10, 20Mhz to provide a downlink or uplink transmission service to multiple terminals. Different cells may be configured to provide different bandwidths.

The downlink transmission channel for transmitting data from the network to the UE includes a broadcast channel (BCH) for transmitting system information, a paging channel (PCH) for transmitting a paging message, and a downlink shared channel (SCH) for transmitting user traffic or control messages. have. Traffic or control messages of a downlink multicast or broadcast service may be transmitted through a downlink SCH or may be transmitted through a separate downlink multicast channel (MCH). Meanwhile, the uplink transmission channel for transmitting data from the terminal to the network includes a random access channel (RACH) for transmitting an initial control message and an uplink shared channel (SCH) for transmitting user traffic or a control message.

It is located above the transport channel, and the logical channel mapped to the transport channel is a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), and an MTCH (multicast). Traffic Channel).

6 shows 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 consists of a plurality of symbols on the time axis. One subframe consists of a plurality of resource blocks, and one resource block consists of a plurality of symbols and a plurality of subcarriers. In addition, each subframe may use specific subcarriers of specific symbols (eg, the first symbol) of the corresponding subframe for the physical downlink control channel (PDCCH), that is, the L1 / L2 control channel. 5 shows an L1 / L2 control information transmission region (PDCCH) and a data transmission region (PDSCH). In an E-UMTS (Evolved Universal Mobile Telecommunications System) system currently under discussion, a radio frame of 10 ms is used, and one radio frame includes 10 subframes. In addition, one subframe consists of two consecutive slots. One slot is 0.5ms long. In addition, one subframe includes a plurality of OFDM symbols, and some symbols (eg, first symbols) of the plurality of OFDM symbols may be used to transmit L1 / L2 control information. The transmission time interval (TTI), which is a unit time for transmitting data, is 1 ms.

In general, except for a specific control signal or specific service data, a base station and a terminal transmit and receive data through a PDSCH, which is a physical channel, mostly using a DL-SCH, which is a transport channel. Data of the PDSCH is transmitted to which UE (one or a plurality of UEs), and information on how the UEs should receive and decode the PDSCH data is included in the PDCCH and transmitted.

For example, a specific PDCCH is CRC masked with a Radio Network Temporary Identity (RNTI) of A, a radio resource (for example, frequency location) of B, and transmission type information of C (for example, a transport block). It is assumed that information about data transmitted using size, modulation, coding information, etc.) is transmitted through a specific subframe. In this case, one or more terminals in the corresponding cell monitor the PDCCH using the RNTI information that they have, and if there is one or more terminals having A RNTI, the terminals receive the PDCCH and information on the received PDCCH. Receives the PDSCH indicated by B and C through.

7 shows an example of a transmission and reception method using a call message. A method of transmitting and receiving a call message will be described with reference to FIG. 7. The paging message includes a paging record composed of a paging cause and a UE identifier. When receiving the call message, the terminal may perform a discontinuous reception cycle (DRX) for the purpose of reducing power consumption. Specifically, the network configures a plurality of paging occasions (Paging Occasion) for each time period called a paging DRX Cycle, and a specific terminal can receive only a specific paging opportunity time to obtain a paging message. The terminal does not receive a call channel at a time other than the specific call opportunity time and may be in a sleep state to reduce power consumption. One call opportunity time corresponds to one TTI. The base station and the terminal use a paging indicator (PI) as a specific value indicating the transmission of the call message. The base station may define a specific identifier (for example, Paging-Radio Network Temporary Identity (P-RNTI)) for the purpose of the PI to inform the terminal of the call information transmission. For example, the UE wakes up every DRX cycle and receives one subframe to know whether a call message is present. If the P-RNTI is present in the L1 / L2 control channel (PDCCH) of the received subframe, the UE may know that there is a call message in the PDSCH of the corresponding subframe. In addition, if the terminal message has its own terminal identifier (eg, IMSI), the terminal receives the service by responding to the base station (eg, RRC connection).

8 illustrates an example of a method of reselecting a cell according to priority when priority is defined for each frequency or RAT. If priorities are defined between different frequencies or different RATs, the UE is a high priority frequency or RAT within a range that satisfies a minimum signal characteristic or a specific signal characteristic defined by the system. Select the cell corresponding to Exceptionally, the terminal may select the cell having the highest signal characteristic value without considering the priority when selecting the initial cell.

Referring to FIG. 8, when the UE selects a cell having the highest priority and receives a service (S820), a signal characteristic value of a cell (serving cell) receiving a service is equal to or greater than a specific value (eg, S _{nonintrasearch} ). In this case, since the measurement for the low priority cell may not be performed, power consumption may be effectively reduced (S840 and S842). On the other hand, even if the serving cell has the highest priority, if the signal characteristic value of the serving cell falls below a specific value, the UE may select another cell having a lower priority satisfying the specific signal characteristic value through a measurement process ( S844, S846). If there are several cells satisfying a specific value, a cell satisfying a specific condition (eg, a cell having the highest priority, a cell having the highest signal characteristic value, etc.) may be selected from the cells (S846). .

On the other hand, if the UE does not receive the service by selecting the cell using the highest priority frequency and / or RAT (that is, when selecting a cell of low priority) (S820), the signal characteristic value of the serving cell is specific Even if the value is greater than a value (eg, S _{nonintrasearch} ), cells that use frequency and / or RAT of high priority are found periodically (S830 and S832). The period for searching for another cell may be an implicitly determined value between the base station and the terminal, and may be determined by either the base station or the terminal and informed to the other side.

Hereinafter, the cell reselection process according to the priority will be described in more detail.

First, when the UE reselects another cell having the same priority as the serving cell, the UE reselects the cell having the largest signal characteristic value through a ranking process for comparing signal strength and quality. Choose. The equation used for the ranking procedure between cells having the same priority is as follows.

R _s = Q _{meas, s} + Qhyst _s

R _n = Q _{meas, n} -Qoffset

Here, Q _{meas, s} is an RSRP value measured by the UE for the serving cell, and Q _{meas, n} is an RSRP value measured by the UE for neighboring cells. Qhyst _s is a hysteresis value for weighting a serving cell, and Qoffset represents at least one of a deviation value between cells and a deviation value between different frequencies.

In the ranking procedure, the terminal selects a cell corresponding to Rn if the cell having the largest signal characteristic value satisfies the condition that Rn> Rs for a specific time (Treselection _EUTRAN ). That is, the cell having the best signal characteristic is reselected among the cells having the better signal characteristic than the serving cell. In the conventional WCDMA, a cell having the highest signal characteristic value is reselected through the above-described ranking procedure without using priority information regarding frequency or RAT.

The Treselection value is used to restrict the cell reselection condition for a predetermined time or more in order to prevent the UE from repeatedly selecting a specific cell. The base station transmits the information to the UE through the system information (SI). Intra _- frequency cell reselection and inter-frequency cell reselection use the value of Treselection _EUTRAN . For inter-RAT cell reselection, the Treselection _UTRAN value is used for cell reselection to WCDMA cells and for cell reselection to GSM cells. Each of the Treselection _GERAN values is used. That is, the cell reselection time limit is defined for each RAT so that the cell reselection time can be differentially applied to different RATs. Hereinafter, TreselectionRAT is used to indicate the cell reselection constraint time from the serving cell to the cell to be subjected to cell reselection without RAT classification.

In addition, when the terminal speed is fast, in order to speed up cell reselection, TreselectionRAT ^* (= TreselectionRAT × Scaling) is applied by applying the TreselectionRAT value transmitted by the base station through SI and the scaling factor_S (SF_S) applied by the terminal. After factor_S), it may be applied as a constraint time of cell re-selection. '*' Is used to indicate that the time limit is finally applied at the time of cell reselection.

9 is a flowchart illustrating a method of reselecting a cell of higher priority than a serving cell. Referring to FIG. 9, a reselection to a cell corresponding to a frequency or RAT having a higher priority than a frequency or RAT of the serving cell in the process of FIG. 8 will be described in detail. Referring to FIG. 9, the UE has a condition in which a signal characteristic value (eg, Snonserving_H) of cells corresponding to a frequency or RAT of higher priority than a serving cell has a specific threshold value (eg, Thresh_H) higher than a serving cell. To select a cell that satisfies for a specific time (TreselectionRAT) (S910, S920). At this time, a cell having a frequency or a RAT belonging to the highest priority among the corresponding cells is selected, and when there are several cells having the same priority, the cell having the highest signal characteristic value is selected according to the ranking procedure. (S930).

10 is a flowchart illustrating a method of reselecting a cell of lower priority than a serving cell. Referring to FIG. 10, a reselection to a cell corresponding to a frequency or RAT having a lower priority than a frequency or RAT of the serving cell in the process of FIG. 8 will be described in detail. If the UE does not find a cell having a priority higher than that of the serving cell, if a signal characteristic value of the serving cell is lower than a specific threshold (eg, Sserving <Threshold), the UE has a lower priority than the serving cell's frequency or RAT. The cell of frequency or RAT is reselected. In this case, a cell whose signal characteristic value (eg, Snonserving_H) of a cell having a lower priority frequency or RAT than the serving cell (eg, Snonserving_H) satisfies a condition equal to or greater than a certain threshold (eg, Thresh_L) for a specific time (TreselectionRAT) is selected. (S1010-S1030).

The criteria for the network to prioritize according to the frequency or radio access technology may be to meet various purposes as follows. In addition, the following purposes can be seen as a case where a cell selection process of the terminal is required.

Qos (quality of service) for providing to the terminal: refers to setting the priority according to the quality of service or type of service to be provided to the terminal. For example, a terminal using only VoIP may set a high priority on a frequency or RAT related to VoIP. As another example, a RAT (eg, E-UTRAN) providing a high data rate may be set to a high priority for a UE using a service requiring a high data rate. In addition, the UE using the MBMS service can set a high priority to the frequency or RAT providing the MBMS.

-Network sharing: network sharing (network sharing): different PLMNs are shared to provide a service to the terminal, the terminal may determine the priority for the frequency or RAT to select a cell provided by the available PLMN.

Subscriber type: This means setting priorities according to subscriber information. For example, a user who subscribes to a service requiring only low speed voice communication may set a high priority for a low speed RAT (eg UTRAN) and a low priority for a high speed RAT (eg E-UTRAN). You can set the rank. As another example, users who subscribe to multimedia services that require high data rates may set high priority for high speed RATs (e.g., E-UTRAN) and low priority for relatively low speed RATs (e.g., UTRAN). Can be set.

Closed Subscriber Group (CSG) or Home NodeB: A CSG cell refers to a cell that can be used only by one or more specific users or terminals. A specific terminal accessible to a CSG cell may set a high priority for a frequency or RAT associated with the CSG. An example of a CSG is a Home Node installed and used by a user in the same place as a home.

Load balancing: The above mentioned camp / traffic load balancing is included here. For example, an example is to load balance between cells by setting a low frequency or RAT with a high priority so that the UE preferentially selects a cell having a low load and receives service. In addition, load balancing of a cell, a tracking area, a registration area consisting of a plurality of tracking areas, and a PLMN unit may be performed according to a range of an area to which frequency or RAT priority is applied.

Operator Policy: In addition to the above-mentioned criteria, a specific frequency or RAT may be given a high priority according to the policy of the network operator.

The validity of the frequency or RAT priority information allocated to the UE and the range / scope applied thereto may be as follows.

Priority is determined in units of a tracking area (TA), and prior to the tracking area update (TAU-process in which the terminal registers identification information such as its IMSI in the network), the priority is prioritized. Does not change For example, the priority assigned in the previous TAU process in the TAU process may be invalidated. If the priority information is received from the network after the TAU process or the TAU, the priority becomes valid until the next TAU.

Priority is determined on a cell-by-cell basis, and priority is not changed before reselecting another cell. For example, when a cell serviced by a UE changes, priorities previously assigned may be invalidated. If the priority is received from the network through the system information after the cell reselection process or the cell reselection, the priority becomes effective until the next cell reselection or until the system information is received after the next cell reselection.

It may have a validity or coverage of a PLMN unit.

The terminal may have a validity or an application range of a PLMN registered, that is, a registered PLMN (RPLMN) unit.

In addition, priority information may be invalidated as the terminal state transitions from an idle mode to a connected mode. That is, the priority may be invalidated by a specific RRC signal for the UE to go from the idle mode to the connected mode. For example, the priority is invalidated when the terminal sends an RRC connection request, when the RRC connection setup is received from the base station, or when the RRC connection complete is sent to the base station. Can be. On the contrary, priority information may be invalidated as the terminal state transitions from the connected mode to the idle mode. That is, the priority may be invalidated by a specific RRC signal for the UE to go from the connected mode to the idle mode. For example, priority may be invalidated by an RRC connection release.

The terminal may receive priority from the base station in the following manner.

Receive selectable frequency / RAT information and priority information from the base station at the time of TAU.

Receive selectable frequency / RAT information from the base station at the time of TAU. Thereafter, priority information for a specific frequency / RAT is received through SI (system information).

-Receive selectable frequency / RAT information and priority information through SI. In addition, the SI may receive priority information of the neighbor cell together with the neighbor cell list (NCL).

Frequency / RAT information and priority information thereof can be received through the RRC signal. The RRC signal may be, for example, an RRC connection release, an RRC connection request, an RRC connection setup, a radio bearer setup, or a radio bearer reconfiguration. The signal may be related to an RRC connection reconfiguration and an RRC connection reestablishment.

Frequency or RAT information and priority information thereof may be received through L1 / L2 control signaling and PDCP / RLC / MAC PDU.

The terminal may receive the priority from the network in one or more ways described above. Priority information for frequencies or RATs received in different ways may be the same or different. When the terminal receives the duplicated priorities in different ways, the terminal may apply priority to the priorities received in a specific method having a different priority. For example, after receiving the priority through the system information, the terminal may receive the priority once more through the RRC connection release. In this case, the terminal may ignore the priority received from the system information and perform measurement and cell reselection according to the priority received through the RRC connection release. Subsequently, the terminal in the idle mode may establish an RRC connection with the base station to receive a service from the base station, and may invalidate a priority previously received by the RRC disconnection in this process. In addition, if the terminal has not received the priority from the network when the RRC disconnection after receiving the service from the base station, the terminal returned to idle mode performs the cell reselection using the priority before the RRC connection, or from the system information Cell reselection may be performed using the newly received priority.

In the state where the UE knows the priority for each frequency / RAT, the UE may know the existence of each frequency or RAT from the neighbor cell list NCL received through the system information SI. The terminal determines the priority of each cell using the priority of each frequency / RAT and the neighbor cell list or receives the priority of each cell from the base station, and then reselects the cell using the priority of each cell. Can be performed. In addition, even if the terminal does not have an NCL, the terminal may detect the presence of another frequency or RAT by performing a scanning process by itself.

Example Differentiation of Ease of Cell Reselection According to Priority

Performing cell reselection according to frequency or RAT priority has the following advantages. First, in accordance with absolute priority, the signal measurement / cell reselection rule can be simplified. Second, when the UE selects a cell of the highest priority frequency or RAT that satisfies a predetermined condition (eg, S_intra_frequency), power consumption is reduced because no other frequency or RAT is measured.

However, when the UE does not select a cell of a high priority frequency or RAT, the UE must continuously measure a cell of high priority and QoS is not guaranteed. Therefore, in order to enjoy the advantages of cell reselection according to priority, it is necessary to ensure that the UE easily selects a cell of high priority.

To this end, the present invention proposes that the ease of cell reselection is different according to the priority. Specifically, the present invention provides a method for performing cell reselection based on priority, the method comprising: measuring a signal of a candidate cell, and when a signal characteristic of the candidate cell satisfies a predetermined condition for a specific time, selecting the candidate cell; And selecting, but applying the specific time differently according to the priority of the candidate cell.

The priority indicates priority for frequency, RAT, or a combination thereof. The criteria for determining the priority of the network, the validity and range / area applied to the priority information assigned to the terminal, and the method of receiving the priority information from the network have been described in detail above. Preferably, whether the predetermined condition is satisfied is determined by whether a signal characteristic value of the candidate cell is equal to or greater than a specific threshold value. Preferably, the specific time is a cell reselection timeout (Treselection).

Differentiation of cell reselection timeout according to priority

11 is a conceptual diagram illustrating cell reselection according to an embodiment of the present invention. Referring to FIG. 11, a terminal is provided with a service in a serving cell of frequency 3. Due to the mobility of the terminal, the signal characteristic value of the serving cell falls below Thresh _serving , and the terminal performs cell searching for cell reselection. Currently, a cell of frequency 1 and a cell of frequency 2 exist at the boundary of the serving cell, and the terminal starts signal measurement for the two cells. That is, the two cells become candidate cells for cell reselection. It is assumed that the priority of frequency 1 is lower than that of frequency 2. The frequency priority of the serving cell may be the same as any one of the frequency 1 or the frequency 2, or may be in the middle of the frequency 1 and the frequency 2.

At the time when the UE starts measuring signals with respect to the candidate cell, both the cell of frequency 1 and the cell of frequency 2 have a signal characteristic value equal to or greater than (or greater than) a specific threshold Threshold_H / L. Accordingly, the terminal operates the first timer for the cell of frequency 1 and monitors the time when the signal characteristic value satisfies Thresh_L. In addition, the terminal operates a second timer for the cell of frequency 2 and monitors the time when the signal characteristic value satisfies Thresh_H.

Since the frequency 1 has a lower priority than the frequency 2, the terminal sets the expiration time of the first timer and the second timer differently (first timer: TreselectionRAT_low, second timer: TreselectionRAT_high). Specifically, the terminal sets the expiration time of the first timer for the cell having a lower priority than the expiration time of the second timer. If there are more candidate cells that the terminal can select, the terminal may set a timer individually or for each group in consideration of the priority of each candidate cell. In case of setting timers individually, the UE sets a timer expiration time as the priority of each candidate cell is lower. When setting the timer for each group, the terminal classifies the candidate cells based on the relative priority of the candidate cells determined based on the priority of the serving cell. That is, the candidate cell may be classified into a cell having a higher priority than the serving cell, a cell having the same priority as the serving cell, or a cell having a lower priority than the serving cell. Based on the classification, the timer expiration time may be set identically to candidate cells having the same relative priority. This will be described in detail with reference to FIG. 12.

Although the first timer and the second timer are started at the same time, the second timer is terminated first because the expiration time of the second timer is shorter than the expiration time of the first timer. Since the signal characteristic value of the cell of frequency 2 satisfies Thresh_H until the second timer expires, the terminal stops the first timer and reselects the cell of frequency 2. Referring to FIG. 2, it can be seen that, under the same condition, a cell of frequency 2 having a high priority is not selected due to radio variability. On the other hand, in the embodiment of the present invention, by varying the length of the constraint time applied to the high priority cells, it is ensured that the high priority cells are easily reselected. That is, it is sufficient if the constraint time of the high priority cell is relatively short compared to the constraint time of the low priority cell. The absolute length of each constraint time may be determined in consideration of the wireless environment, the mobility of the terminal, and the like. In addition, for the sake of compatibility with the related art, only a constraint time applied to a cell having a high priority may be set to be shorter than a conventional constraint time. In addition, only a constraint time applied to a cell having a low priority may be set longer than a conventional constraint time.

Cell reselection timeout differentiation based on relative priority

12 is a timing diagram at cell reselection according to an embodiment of the present invention.

Referring to FIG. 12, when the cell reselection process is started, the UE starts measuring signals with respect to the candidate cell (S1210). Four candidate cells are shown in FIG. 12. Each candidate cell was marked RAT_1, RAT_2 and RAT_3 based on RAT. The RAT may be selected from EUTRAN, UTRAN, GSM / EDGE Radio Access Network (GERAN), CDMA_HRPD and CDMA_1xRTT, respectively. The priority of each candidate cell is indicated as P_L or P_H, respectively. P_L means low priority, and P_H means high priority. That is, the priority shown in FIG. 12 is the relative priority of the candidate cell determined based on the priority of the serving cell. As a previous step for determining the relative priority, the absolute priority of each cell is determined according to frequency, RAT or a combination thereof.

 In FIG. 12, there are four candidate cells represented by RAT_1 (P_H), RAT_1 (P_L), RAT_2 (P_H), and RAT_3 (P_L). The priority shown in FIG. 12 is a relative priority, and the priority of the serving cell is not separately illustrated. When using relative priority, the cell reselection constraint time is divided into a first specific time and a second specific time, and the length of each specific time may be a first specific time <second specific time:

First specific time: the priority of the candidate cell is higher than that of the serving cell; And

Second specific time: The priority of the candidate cell is lower than the priority of the serving cell.

Further, the cell reselection constraint time is divided into the following first to third specific times, and the length of each specific time is equal to the first specific time <second specific time ≤ third specific time or first specific time ≤ second specific time. Time <may be a third specific time:

First specific time: the priority of the candidate cell is higher than that of the serving cell;

Second specific time: the priority of the candidate cell is equal to the priority of the serving cell; And

Third specific time: the priority of the candidate cell is lower than that of the serving cell.

In FIG. 12, RAT_1 (P_H) and RAT_1 (P_L) using the same RAT will be described. Since the two cells use the same RAT, the priority between them will be determined by the frequency priority. Since the priority of the cell of RAT_1 (P_H) is higher than that of the cell of RAT_1 (P_L), the constraint time 1220 of the cell of RAT_1 (P_H) is shorter than the constraint time 1222 of the cell of RAT_1 (P_L). Is set. For example, if RAT_1 is EUTRAN, the constraint time may be represented as Treselection _EUTRAN _high (1220; eg, 10 seconds) <Treselection _EUTRAN _low (1222; eg, 14 seconds).

Next, a cell of RAT_2 (P_H) and a cell of RAT_3 (P_L) will be described together. The cells illustrated in FIG. 12 have different RATs. One of RAT_1, RAT_2 or RAT_3 may be the same as the RAT of the serving cell. When the RATs used between the cells are different as described above, the priority of the cells may be determined only by the RATs or in combination with the frequency priorities. For example, the serving cell is {EUTRAN, frequency_1, priority: 2}, and the candidate cell is {UTRAN, frequency_2, priority: 1}, {UTRAN, frequency_3, priority: 3}. Can be. Since the cells of RAT_1 (P_H), the cells of RAT_2 (P_H), and the cells of RAT_3 (P_L) all have high priority, the cell reselection timeout will be shorter than that of the corresponding low priority cells. However, since the cells use different RATs, cell reselection timeouts applied to the cells may be basically different. For example, assuming that RAT_1 is EUTRAN, RAT_2 is UTRAN, and RAT_3 is GERAN, the cell reselection timeout applied to each cell may be as follows.

-If you use different RATs:

Treselection _EUTRAN _high (1220) <Treselection _GERAN _high (1240)

<Treselection _UTRAN _high (1230)

-If you use the same RAT:

Treselection _EUTRAN _high (1220) <Treselection _EUTRAN _low (1222)

Treselection _UTRAN _high (1230) <Treselection _UTRAN _low (not shown)

Treselection _GERAN _high (1240) <Treselection _GERAN _low (not shown)

Cell reselection process of UE according to differentiated constraint time

To differentiate timeouts by priority, you can consider:

-Use a plurality of constraint time set differently according to the priority

Setting one base time constraint and one or more scaling factors (SF) multiplied by the base time constraint.

The plurality of constraint time or basic constraint time may be set differently for each RAT. In addition, in order to distinguish the SF applied according to the priority from other types of SF (eg, SF_S in consideration of mobility), it is indicated as SF_P. The SF_P may be set differently for each frequency or for each RAT.

Hereinafter, an example of a method of performing cell reselection using differentiated constraint times according to priorities will be described with reference to FIGS. 13 to 15.

Case 1: Use multiple time constraints set according to priority

13 illustrates a case where cell reselection constraint time is individually set according to priority. In FIG. 13, the UE sets TreselectionRAT_high and TreselectionRAT_low as differentiated constraint times according to priorities (S1310). The constraint time may be further modified in consideration of the mobility of the terminal. For example, the constraint time actually applied to the cell reselection may be modified as follows in consideration of the mobility of the terminal.

Treselection _EUTRAN _high ^* = Treselection _EUTRAN _high × SF_S

^{_{Treselection EUTRAN _low * = Treselection EUTRAN _low}} × SF_S

Here, '*' indicates that the constraint time is finally applied when the cell is reselected, and SF_S is a scaling factor in consideration of mobility of the terminal. If an additional element such as SF_S is not considered, Treselection _EUTRAN _high ^* = Treselection _EUTRAN _high and Treselection _EUTRAN _low ^* = Treselection _EUTRAN _low.

When cell reselection is initiated, the UE starts to measure the signal of the candidate cell (S1320). The signal measurement process is continued until the cell reselection process is completed. In the actual cell reselection process, the signal characteristic value obtained from the measured signal is used. Examples of signal characteristic values include Reference Symbol Received Power (RSRP), Reference Symbol Received Quality (RSRQ), and Received Signal Strength Indicator (RSSI). While measuring the signal for the candidate cell, the terminal determines whether the priority of the candidate cell is higher than the priority of the serving cell (S1330). Thereafter, the terminal determines whether the candidate cell satisfies a condition for cell reselection in consideration of the relative priority of the candidate cell (S1332 and S1334). Thereafter, the terminal selects a candidate cell that satisfies the condition (S1340). The condition for cell reselection may be as follows according to the relative priority of the candidate cell.

Candidate cells with higher priority than the serving cell:

(Snonserving_H> Thresh_H) _{Satisfaction time}

> TreselectionRAT_high ^* = TreselectionRAT_high

Candidate cells with the same or lower priority as the serving cell:

(Snonserving_L> Thresh_L) _{Satisfaction time}

> TreselectionRAT_low ^* = TreselectionRAT_low

Here, Snonserving_H / L represents a signal characteristic value of the candidate cell, and Thresh_H / L represents a threshold value that the signal characteristic value of the candidate cell should satisfy.

For example, when the RAT of the candidate cell is EUTRAN, the timeout may be set to Treselection _EUTRAN _high = 10 seconds and Treselection _EUTRAN _low = 14 seconds.

In FIG. 13, candidate cells having the same or lower priority as the serving cell are treated identically. However, an additional constraint time may be defined for candidate cells having the same priority as the serving cell. For example, the following condition may be added to FIG. 13. In this case, the flowchart can be modified accordingly.

Candidate cells with the same priority as the serving cell:

(Snonserving_E> Thresh_E) _{Satisfaction time} > TreselectionRAT_equal

Case 2: Use default timeouts and multiple SF_Ps

14 illustrates a case in which a plurality of scaling factors _P (SF_Ps) to be applied are set according to a cell reselection constraint time and priority set for each RAT. In order to simplify system operation, the UE may use only two types of SP_Ps for the high priority frequency and the low priority frequency. In addition, the UE may use only two types of SP_Ps for the high priority RAT and the low priority RAT.

The UE sets TreselectionRAT, SF_P_high and SF_P_low to differentiate the time constraints according to the priority (S1410). When cell reselection is initiated, the UE starts to measure the signal of the candidate cell (S1420). The signal measurement process is continued until the cell reselection process is completed. In the actual cell reselection process, the signal characteristic value obtained from the measured signal is used. Examples of signal characteristic values include Reference Symbol Received Power (RSRP), Reference Symbol Received Quality (RSRQ), and Received Signal Strength Indicator (RSSI). While measuring the signal for the candidate cell, the terminal determines whether the priority of the candidate cell is higher than the priority of the serving cell (S1430). Thereafter, the terminal determines whether the candidate cell satisfies a condition for cell reselection in consideration of the relative priority of the candidate cell (S1432 and S1434). Thereafter, the terminal selects a candidate cell that satisfies the condition (S1440). The condition for cell reselection may be as follows according to the relative priority of the candidate cell.

Candidate cells with higher priority than the serving cell:

(Snonserving_H> Thresh_H) _{Satisfaction time}

> TreselectionRAT_high ^* = TreselectionRAT × SF_P_high

Candidate cells with the same or lower priority as the serving cell:

(Snonserving_L> Thresh_L) _{Satisfaction time}

> TreselectionRAT_low ^* = TreselectionRAT × SF_P_low

Here, Snonserving_H / L represents a signal characteristic value of the candidate cell, and Thresh_H / L represents a threshold value that the signal characteristic value of the candidate cell should satisfy.

For example, when the RAT of the candidate cell is EUTRAN, Treselection _EUTRAN = 10 seconds, SF_P_high = 1 and SF_P_low = 1.4. In this case, two kinds of time constraints are used for cell reselection, depending on the priority of the candidate cell. That is, Treselection _EUTRAN _ high ^* = 10 seconds and Treselection _EUTRAN _ low ^* = 14 seconds.

In FIG. 14, it is exemplified to treat candidate cells having the same or lower priority as the serving cell. However, an additional constraint time may be defined for candidate cells having the same priority as the serving cell. In this case, the following conditions are added to FIG. 14, and the flowchart may be modified accordingly.

Candidate cells with the same priority as the serving cell:

(Snonserving_E> Thresh_E) _{Satisfaction time} > TreselectionRAT × SF_P_equal

Case 3: Use default timeout and one SF_P

FIG. 15 illustrates a case in which one scaling factor_P (SF_P) to be applied is set according to a cell reselection constraint time and priority set for each RAT.

The UE sets TreselectionRAT and SF_P in order to differentiate the time limit according to the priority (S1510). When cell reselection is initiated, the UE starts to measure the signal of the candidate cell (S1520). The signal measurement process is continued until the cell reselection process is completed. In the actual cell reselection process, the signal characteristic value obtained from the measured signal is used. Examples of signal characteristic values include Reference Symbol Received Power (RSRP), Reference Symbol Received Quality (RSRQ), and Received Signal Strength Indicator (RSSI). While measuring the signal for the candidate cell, the terminal determines whether the priority of the candidate cell is higher than the priority of the serving cell (S1530). Thereafter, the terminal determines whether the candidate cell satisfies a condition for cell reselection in consideration of the relative priority of the candidate cell (S1532 and S1534). Thereafter, the terminal selects a candidate cell that satisfies the condition (S1540). The condition for cell reselection may be as follows according to the relative priority of the candidate cell.

Candidate cells with higher priority than serving cells:

(Snonserving_H> Thresh_H) _{Satisfaction time}

> TreselectionRAT_high ^* = TreselectionRAT

Candidate cells with the same or lower priority as the serving cell:

(Snonserving_L> Thresh_L) _{Satisfaction time}

> TreselectionRAT_low ^* = TreselectionRAT × SF_P

Here, Snonserving_H / L represents a signal characteristic value of the candidate cell, and Thresh_H / L represents a threshold value that the signal characteristic value of the candidate cell should satisfy.

For example, when the RAT of the candidate cell is EUTRAN, Treselection _EUTRAN = 10 seconds and SF_P = 1.4. In this case, two kinds of time constraints are used for cell reselection, depending on the priority of the candidate cell. That is, Treselection _EUTRAN _ high ^* = 10 seconds and Treselection _EUTRAN _ low ^* = 14 seconds.

Receive / Set Cell Reselection Timeout

Information for differentiating the constraint time according to the priority may be predefined between the terminal and the base station or may be received from the base station. The information about the constraint time may indicate a plurality of constraint time set differently according to priority, and indicate the basic constraint time and one or more SF_P. The plurality of constraint time and the basic constraint time may be set differently for each RAT. In addition, the SF_P may be set differently for each frequency or for each RAT.

16A illustrates an example of receiving information about the time limit from a base station according to an embodiment of the present invention. The information about the time limit may be transmitted to the UE through system information (SI), an RRC message, an L1 / L2 control signaling (eg, PDCCH) or a MAC / RLC / PDCP PDU. The RRC signal may be a signal associated with an RRC connection release, an RRC connection request, an RRC connection establishment, a radio bearer establishment, a radio bearer reset, an RRC connection reset, or an RRC connection reestablishment.

Referring to FIG. 16A, the terminal receives information regarding the time limit from the network (S1610). The information on the constraint time may be (TreselectionRAT, SF_P), (TreselectionRAT, SF_P_1, SF_P_2), (TreselectionRAT, SF_P_1, ..., SF_P_n) or (TreselectionRAT_high, TreselectionRAT_low). Thereafter, the UE performs cell reselection by changing TreselectionRAT ^* according to the priority of the cell (S1630).

The information about the time limit may be UE-common or UE-specific. When the information about the time limit is terminal-common, the information about the time limit may include a PLMN unit, a registered area unit, a tracking area (TA) unit, a cell unit, a group unit, or a RAT. Can be common in units. For example, the information about the time limit may be delivered to all terminals in the cell through system information. In addition, when the information about the time limit is terminal-specific, the information about the time limit is transmitted through the RRC disconnection so that only a specific terminal can perform the operation according to the embodiment of the present invention. That is, depending on whether the information about the time limit is terminal-common or terminal-specific, the method of transmitting the information about the time limit to the terminal and the range of the terminal to be applied may vary.

The information about the time constraint may be indicated by the base station periodically / aperiodically. Also, the information about the constraint time may be invalidated in some cases. For example, when the information about the time limit is terminal-common, if the PLMN, registration area, tracking area, cell, group, or RAT is changed, the information about the time limit may be invalidated. As another example, when the information about the time limit is terminal-specific, the information about the time limit may be invalidated while the terminal state transitions from the idle mode to the connected mode. That is, the information about the time limit may be invalidated by a specific RRC signal for the UE to go from the idle mode to the connected mode. For example, when the UE sends an RRC connection request, when the UE receives an RRC connection setup or when the UE sends an RRC connection complete to the base station, Information may be invalidated. Conversely, as the terminal state transitions from the connected mode to the idle mode, the information about the time limit may be invalidated. That is, the information about the time limit may be invalidated by a specific RRC signal for the UE to go from the connected mode to the idle mode. For example, the information about the time limit may be invalidated by RRC connection release.

In addition, the terminal may invalidate the information about the time limit when a predetermined time elapses after receiving the information about the time limit.

FIG. 16B illustrates an example of cell reselection when the information regarding the time limit is repeatedly received according to an embodiment of the present invention.

The terminal may receive information on the time limit overlapping from the network. In this case, the timeouts indicated by the network may be the same or may be different. When the terminal receives duplicate information about the time limit, the terminal may apply the terminal-specific information in preference to the terminal-common information. In addition, the terminal may preferentially apply the information on the constraint time received in a specific method to the information on the constraint time received in another method. Referring to FIG. 16B, the terminal may receive SF_P_1 through system information (S1610), and may receive SF_P_2 through RRC connection release (S1612). In this case, the UE may ignore the SF_P_1 received from the system information and perform cell reselection using the TreselectionRAT set for each SF_P_2 and RAT received through RRC disconnection (S1620, S1622, and S1630). Thereafter, the terminal in the idle mode may establish an RRC connection with the base station to receive a service from the base station, and in this process may invalidate the SF_P_2 previously received by the RRC disconnection. In addition, if the terminal receives the service from the base station, and does not receive the information on the timeout when the RRC disconnection from the base station, the mobile station returns to the idle mode using the information on the timeout before the RRC connection to reselect the cell Alternatively, the cell reselection may be performed using information on the new constraint time received from the system information.

In one embodiment of the present invention, the terminal may apply a constraint time for cell reselection in consideration of priority according to frequency, RAT, or a combination thereof. Therefore, the constraint time for reselecting the cells of high priority can be set to be shorter than the constraint time for reselecting the cells of low priority. Accordingly, the terminal can increase the chance of receiving a service in a high priority cell compared to a low priority cell. In addition, it is possible to effectively reduce the power consumption due to the movement of the terminal by reducing the process of measuring a high priority cell. In addition, it is possible to ensure the quality of service for the terminal by first selecting a cell of a high priority.

The embodiments described above are the components and features of the present invention are combined in a predetermined form. Each component or feature is to be considered optional unless stated otherwise. Each component or feature may be embodied in a form that is not combined with other components or features. It is also possible to combine some of the components and / or features to form an embodiment of the invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment. It is obvious that the claims may be combined to form an embodiment by combining claims that do not have an explicit citation relationship in the claims or as new claims by post-application correction.

In this document, embodiments of the present invention have been mainly described based on data transmission / reception relations between a terminal and a base station. Certain operations described in this document as being performed by a base station may in some cases be performed by an upper node thereof. That is, it is obvious that various operations performed for communication with the terminal in a network including a plurality of network nodes including a base station may be performed by the base station or other network nodes other than 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. In addition, the term "terminal" may be replaced with terms such as a user equipment (UE), a mobile station (MS), a mobile subscriber station (MSS), and the like.

Embodiments according to the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of a 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), FPGAs ( field programmable gate arrays), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, procedure, function, etc. that performs the functions or operations described above. The software code may be stored in a memory unit and driven by a processor. The memory unit may be located inside or outside the processor, and may exchange data with the processor by various 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 detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included as part of the detailed description in order to provide a thorough understanding of the present invention, provide an embodiment of the present invention and together with the description, illustrate the technical idea of the present invention.

1 illustrates a procedure in which a terminal selects a cell in an idle mode.

2 shows an example of a timing diagram applied when cell reselection is performed.

Figure 3 shows the network structure of the E-UMTS.

4 is a schematic diagram of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN).

5A and 5B illustrate a control plane and a user plane structure of a radio interface protocol between a UE and an E-UTRAN, respectively.

6 shows an example of a physical channel structure used in an E-UMTS system.

7 shows an example of a transmission and reception method using a call message.

8 illustrates a method in which an idle terminal reselects a cell according to priority.

9 illustrates a method of reselecting a cell having a higher priority than a serving cell.

10 illustrates a method of reselecting a cell having a lower priority than a serving cell.

11 is a conceptual diagram of cell reselection according to an embodiment of the present invention.

12 is a timing diagram at cell reselection according to an embodiment of the present invention.

13 is a flowchart for performing cell reselection according to an embodiment of the present invention.

14 is a flowchart of cell reselection according to another embodiment of the present invention.

15 is a flowchart for performing cell reselection according to another embodiment of the present invention.

16A illustrates an example of receiving information regarding a cell reselection constraint time according to an embodiment of the present invention.

16B illustrates an example of performing cell reselection when a scaling factor regarding a cell reselection constraint time is repeatedly received according to an embodiment of the present invention.

Claims (25)

A method for performing cell reselection based on priority in a wireless communication system, Measuring a signal of a candidate cell; And If the signal characteristic of the candidate cell satisfies a predetermined condition for a specific time, selecting the candidate cell; Wherein the specific time depends on the priority of the candidate cell. The method of claim 1, Wherein the priority is a priority for frequency, RAT, or a combination thereof. The method of claim 1, And determining whether or not the predetermined condition is satisfied based on whether a signal characteristic value of the candidate cell is equal to or greater than a specific threshold value. The method of claim 1, And wherein the specific time is UE-common or UE-specific. The method of claim 1, And wherein the specific time is longer as the priority of the candidate cell is lower. The method of claim 1, And wherein the specific time depends on the relative priority of the candidate cell determined based on a serving cell. The method of claim 6, The specific time may be divided into a first specific time and a second specific time, and the length of each specific time may be a first specific time <second specific time. First specific time: the priority of the candidate cell is higher than that of the serving cell; And Second specific time: The priority of the candidate cell is lower than the priority of the serving cell. The method of claim 6, The specific time is divided into the following first to third specific times, and the length of each specific time is equal to the first specific time <second specific time ≤ third specific time or first specific time ≤ second specific time <third specific time. Method for performing cell reselection, characterized in that time: First specific time: the priority of the candidate cell is higher than that of the serving cell; Second specific time: the priority of the candidate cell is equal to the priority of the serving cell; And Third specific time: the priority of the candidate cell is lower than that of the serving cell. The method of claim 1, And receiving information from the network regarding the specific time. The method of claim 9, And wherein the information includes a plurality of specific times applied according to the priority of the candidate cell. The method of claim 9, And the information includes one or more scaling factors multiplied by the specific time according to a specific time defined for each RAT and the priority of the candidate cell. The method of claim 1, The information includes at least one of system information, a radio resource control message (RRC) message, L1 / L2 control signaling, medium access control (MAC), radio link control (RLC), and packet data convergence protocol (PDCP) protocol data unit (PDU). Method for performing cell reselection, characterized in that received using one. The method of claim 1, And wherein said cell reselection is inter-frequency cell reselection or inter-RAT cell reselection. A method of transmitting control information regarding cell reselection in a wireless communication system, Transmitting information regarding a priority of a cell to a terminal; And Transmitting information about a specific time that a signal characteristic of a candidate cell must be maintained while satisfying a predetermined condition, to the terminal, And the specific time depends on the priority of the candidate cell. The method of claim 14, The priority is characterized in that the priority for the frequency, RAT or a combination thereof. The method of claim 14, It is determined whether or not the predetermined condition is satisfied based on whether a signal characteristic value of the candidate cell is equal to or greater than a specific threshold value. The method of claim 14, The specific time is characterized in that the UE-common (UE-common) or UE-specific (UE-specific), the transmission method of the control information. The method of claim 14, The specific time is characterized in that the lower the priority of the candidate cell, the longer, transmission method of the control information. The method of claim 14, The specific time is characterized in that it depends on the relative priority of the candidate cell determined based on the serving cell, the control information transmission method. The method of claim 19, The specific time may be divided into a first specific time and a second specific time, and the length of each specific time may be a first specific time <second specific time. First specific time: the priority of the candidate cell is higher than that of the serving cell; And Second specific time: The priority of the candidate cell is lower than the priority of the serving cell. The method of claim 19, The specific time is divided into the following first to third specific times, and the length of each specific time is equal to the first specific time <second specific time ≤ third specific time or first specific time ≤ second specific time <third specific time. Method of transmitting the control information, characterized in that the time: First specific time: the priority of the candidate cell is higher than that of the serving cell; Second specific time: the priority of the candidate cell is equal to the priority of the serving cell; And Third specific time: the priority of the candidate cell is lower than that of the serving cell. The method of claim 14, The information about the specific time comprises a plurality of specific times applied according to the priority of the candidate cell, transmission method of the control information. The method of claim 14, The information about the specific time includes a specific time defined for each RAT and one or more scaling factors multiplied by the specific time according to the priority of the candidate cell. The method of claim 14, The specific time information may include system information, RRC message (radio resource control message), L1 / L2 control signaling, medium access control (MAC) / radio link control (RLC) / packet data convergence protocol (PDCP) protocol data and transmitting at least one of the unit). The method of claim 14, Wherein the cell reselection is inter-frequency cell reselection or inter-RAT cell reselection.

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