KR20160075570A - Cell selection method and measurement method for cell reselection - Google Patents

Abstract

According to an embodiment of the present invention, a cell reselection method of a terminal is presented. The cell reselection method includes receiving a common parameter and a category-specific parameter to be used for a cell selection procedure from a serving cell; Performing measurements on one or more of the serving cell and neighboring cells; And determining whether the measurement result value meets a cell selection criterion. Here, when the UE is set to use the category-specific parameter, the cell reselection can be evaluated by reflecting the category-specific parameter to the measurement result value.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a cell selection method and a cell selection method,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication, and more particularly, to a cell selection method and a measurement method for cell reselection.

The 3rd Generation Partnership Project (3GPP) long term evolution (LTE), an enhancement of Universal Mobile Telecommunications System (UMTS), is introduced as 3GPP release 8. 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in the downlink and single carrier-frequency division multiple access (SC-FDMA) in the uplink. MIMO (multiple input multiple output) with up to four antennas is adopted. Recently, 3GPP LTE-A (LTE-Advanced), an evolution of 3GPP LTE, is under discussion.

On the other hand, handover is referred to as movement of a mobile terminal in a 3GPP system to another cell, and movement of a mobile station in an idle state to another cell is referred to as cell reselection.

On the other hand, in recent years, there has been a lot of research on MTC (Machine Type Communication) communication without human interaction, that is, communication between devices or between devices and servers without human intervention. As such, MTC is expected to use less traffic than human to human communications.

Therefore, even though the quality of the cell is low, the MTC-based device can receive service from the cell unlike a general communication device. Nevertheless, applying the existing cell selection and cell reselection schemes to the MTC device may be inefficient.

The disclosure herein is directed to improving the cell selection procedure and the cell reselection procedure.

According to an embodiment of the present invention, a cell reselection method of a UE is disclosed. The cell reselection method includes receiving a common parameter and a category-specific parameter to be used for a cell selection procedure from a serving cell; Performing measurements on one or more of the serving cell and the i.us cell; And determining whether the measurement result value meets a cell selection criterion. Here, when the UE is set to use the category-specific parameter, the cell reselection can be evaluated by reflecting the category-specific parameter to the measurement result value of the UE.

According to an embodiment of the present invention, a measurement method for cell reselection of a terminal is provided. The method includes receiving a common parameter and a category-specific parameter to be used for a cell reselection procedure from a serving cell; Performing measurements on the serving cell; And determining whether the measurement condition for the neighboring cell is satisfied according to the measurement result of the serving cell. When the UE is set to use the category-specific parameter, a value corresponding to the category-specific parameter is added to a measurement result value for the serving cell, .

According to one disclosure of the present disclosure, as the number of cell selection and reselection is reduced compared to the prior art, it is possible to stay in a cell that is already camped on for a longer time. In addition, according to one disclosure of the present specification, the number of times of measurement for cell selection and reselection is reduced, thereby preventing battery consumption. Also, according to one disclosure of the present specification, the performance of circuit switching fallback (CSFB) is improved and the call success rate is further increased. In addition, the call connection speed is increased.

1 shows a wireless communication system to which the present invention is applied.
2 is a block diagram illustrating a radio protocol architecture for a user plane.
3 is a block diagram illustrating a wireless protocol structure for a control plane.
4 shows a state transition process in the RRC idle state.
5 is a flowchart illustrating a process in which a UE in an idle state performs cell selection.
FIG. 6 is a flowchart illustrating the cell reselection process shown in FIG. 5 in detail.
7 is a flowchart illustrating an exemplary process of performing Inter-RAT cell reselection and inter-frequency cell reselection.
8 shows an example of MTC (Machine Type communication) communication.
Figures 9A-9C are exemplary diagrams illustrating a scheme according to one disclosure of the present disclosure.
Fig. 10A shows an operation according to the prior art, and Fig. 10B shows an application example of one embodiment.
Fig. 11A shows another operation according to the prior art, and Fig. 11B shows an application example of one embodiment.
12 is a block diagram illustrating a wireless communication system in which an embodiment of the present invention is implemented.

It is noted that the technical terms used herein are used only to describe specific embodiments and are not intended to limit the invention. It is also to be understood that the technical terms used herein are to be interpreted in a sense generally understood by a person skilled in the art to which the present invention belongs, Should not be construed to mean, or be interpreted in an excessively reduced sense. Further, when a technical term used herein is an erroneous technical term that does not accurately express the spirit of the present invention, it should be understood that technical terms that can be understood by a person skilled in the art are replaced. In addition, the general terms used in the present invention should be interpreted according to a predefined or prior context, and should not be construed as being excessively reduced.

Also, the singular forms "as used herein include plural referents unless the context clearly dictates otherwise. In the present application, the term "comprising" or "comprising" or the like should not be construed as necessarily including the various elements or steps described in the specification, Or may be further comprised of additional components or steps.

Furthermore, terms including ordinals such as first, second, etc. used in this specification can be used to describe various elements, but the elements should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

When an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but other elements may be present in between. On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein like reference numerals refer to like or similar elements throughout the several views, and redundant description thereof will be omitted. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. It is to be noted that the accompanying drawings are only for the understanding of the present invention and should not be construed as limiting the scope of the present invention. The spirit of the present invention should be construed as extending to all modifications, equivalents, and alternatives in addition to the appended drawings.

Hereinafter, although a terminal is shown in the drawing, the terminal may be a user equipment (UE), a mobile equipment (ME), a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, A handheld device, and an AT (access terminal). The terminal may be a portable device having a communication function such as a mobile phone, a PDA, a smart phone, a wireless modem, and a notebook, or may be a portable device such as a PC or a vehicle-mounted device .

1 shows a wireless communication system to which the present invention is applied.

This may be referred to as Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN) or Long Term Evolution (LTE) / LTE-A system.

The E-UTRAN includes a base station (BS) 20 that provides a control plane and a user plane to a user equipment (UE) 10. The UE 10 may be fixed or mobile and may also be referred to as another term such as a Terminal, a UT (User Terminal), a Mobile Station (SS), a Subscriber Station (SS), a Mobile Terminal (MT) Lt; / RTI > The base station 20 is a fixed station that communicates with the UE 10 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.

The base stations 20 may be interconnected via an X2 interface. The base station 20 is connected to an S-GW (Serving Gateway) through an MME (Mobility Management Entity) and an S1-U through an EPC (Evolved Packet Core) 30, more specifically, an S1-MME through an S1 interface.

The EPC 30 is composed of an MME, an S-GW, and a P-GW (Packet Data Network-Gateway). The MME has information about the UE's access information and the capability of the UE, and this information is mainly used for managing the mobility of the UE. The S-GW is a gateway having an E-UTRAN as an end point, and the P-GW is a gateway having a PDN as an end point.

The layers of the radio interface protocol between the UE and the network are classified into L1 (first layer), L1 (second layer) based on the lower three layers of the Open System Interconnection (OSI) A physical layer belonging to a first layer provides an information transfer service using a physical channel, and a physical layer (physical layer) An RRC (Radio Resource Control) layer located at Layer 3 controls radio resources between the UE and the network. To this end, the RRC layer exchanges RRC messages between the UE and the base station.

2 is a block diagram illustrating a radio protocol architecture for a user plane. 3 is a block diagram illustrating a wireless protocol structure for a control plane.

The data plane is a protocol stack for transmitting user data, and the control plane is a protocol stack for transmitting control signals.

Referring to FIGS. 2 and 3, a physical layer (PHY) provides an information transfer service to an upper layer using a physical channel. The physical layer is connected to a MAC (Medium Access Control) layer, which is an upper layer, through a transport channel. Data is transferred between the MAC layer and the physical layer through the transport channel. The transport channel is classified according to how the data is transmitted through the air interface.

Data moves between different physical layers, i. E., Between the transmitter and the physical layer of the receiver, over the physical channel. The physical channel can be modulated by an Orthogonal Frequency Division Multiplexing (OFDM) scheme, and uses time and frequency as radio resources.

The function of the MAC layer includes a mapping between a logical channel and a transport channel and a multiplexing / demultiplexing into a transport block provided as a physical channel on a transport channel of a MAC SDU (service data unit) belonging to a logical channel. The MAC layer provides a service to a Radio Link Control (RLC) layer through a logical channel.

The function of the RLC layer includes concatenation, segmentation and reassembly of the RLC SDUs. The RLC layer includes a Transparent Mode (TM), an Unacknowledged Mode (UM), and an Acknowledged Mode (RB) in order to guarantee various QoSs required by a radio bearer (RB) , And AM). AM RLC provides error correction via automatic repeat request (ARQ).

The functions of the Packet Data Convergence Protocol (PDCP) layer in the user plane include transmission of user data, header compression and ciphering. The function of the Packet Data Convergence Protocol (PDCP) layer in the user plane includes transmission of control plane data and encryption / integrity protection.

 The Radio Resource Control (RRC) layer is defined only in the control plane. The RRC layer is responsible for the control of logical channels, transport channels and physical channels in connection with the configuration, re-configuration and release of radio bearers. The RB means a logical path provided by the first layer (PHY layer) and the second layer (MAC layer, RLC layer, PDCP layer) for data transmission between the UE and the network.

The setting of the RB means a process of defining characteristics of a radio protocol layer and a channel to provide a specific service, and setting each specific parameter and an operation method. RB can be divided into SRB (Signaling RB) and DRB (Data RB). The SRB is used as a path for transmitting the RRC message in the control plane, and the DRB is used as a path for transmitting the user data in the user plane.

When an RRC connection is established between the RRC layer of the UE and the RRC layer of the E-UTRAN, the UE is in an RRC connected state (or an RRC connected mode), and if not, the RRC idle state RRC idle) state (or RRC idle mode).

The downlink transmission channel for transmitting data from the network to the UE includes a BCH (Broadcast Channel) for transmitting system information and a downlink SCH (Shared Channel) for transmitting user traffic or control messages. In case of a traffic or control message of a downlink multicast or broadcast service, it may be transmitted through a downlink SCH, or may be transmitted via a separate downlink MCH (Multicast Channel). Meanwhile, as an uplink transport channel for transmitting data from the UE to the network, there are RACH (Random Access Channel) for transmitting an initial control message and an uplink SCH (Shared Channel) for transmitting user traffic or control messages.

A logical channel mapped to a transport channel is a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), a multicast traffic Channel).

A physical channel is composed of several OFDM symbols in the time domain and a plurality of sub-carriers in the frequency domain. One sub-frame is composed of a plurality of OFDM symbols in the time domain. A resource block is a resource allocation unit, and is composed of a plurality of OFDM symbols and a plurality of sub-carriers. In addition, each subframe can use specific subcarriers of specific OFDM symbols (e.g., first OFDM symbol) of a corresponding subframe for a physical downlink control channel (PDCCH), i.e., an L1 / L2 control channel. The TTI (Transmission Time Interval) is the unit time of the subframe transmission.

Hereinafter, the RRC state (RRC state) and the RRC connection method of the UE will be described in detail.

The RRC state refers to whether or not the RRC layer of the UE is a logical connection with the RRC layer of the E-UTRAN. If the RRC layer is connected, the RRC connected state is established. If the RRC layer is not connected, State (RRC idle state). Since the RRC-connected terminal has an RRC connection, the E-UTRAN can grasp the existence of the corresponding terminal on a cell-by-cell basis, thereby effectively controlling the terminal. On the other hand, the terminal in the RRC idle state can not be grasped by the E-UTRAN and is managed by the CN (core network) in units of a tracking area (Tracking Area) larger than the cell. That is, the UEs in the RRC idle state are only detected on the basis of a large area, and in order to receive ordinary mobile communication services such as voice and data, they must move to the RRC connection state.

When the user first turns on the power of the terminal, the terminal first searches for the appropriate cell and then stays in the RRC idle state in the cell. When the RRC idle terminal needs to establish an RRC connection, it establishes an RRC connection with the E-UTRAN through an RRC connection procedure and transitions to the RRC connection state. There are many cases where the UE in the RRC idle state needs to make an RRC connection. For example, if uplink data transmission is required due to a user's call attempt or the like, or a paging message is received from the E-UTRAN And transmission of a response message to the received message.

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

In order to manage the mobility of the terminal in the NAS layer, two states of EMM-REGISTERED (EPS Mobility Management-REGISTERED) and EMM-DEREGISTERED are defined, and these two states are applied to the terminal and the MME. The initial terminal is in the EMM-DEREGISTERED state, and the terminal performs a process of registering with the network through an initial attach procedure to access the network. When the Attach procedure is successfully performed, the UE and the MME enter the EMM-REGISTERED state.

In order to manage the signaling connection between the terminal and the EPC, two states of ECM (EPS Connection Management) -IDLE state and ECM-CONNECTED state are defined, and these states are applied to the terminal and the MME. When the UE in the ECM-IDLE state establishes the RRC connection with the E-UTRAN, the UE enters the ECM-CONNECTED state. The MME in the ECM-IDLE state enters the ECM-CONNECTED state when it makes an S1 connection with the E-UTRAN. When the UE is in the ECM-IDLE state, the E-UTRAN does not have context information of the UE. Accordingly, the UE in the ECM-IDLE state performs the UE-based mobility-related procedure such as the cell selection procedure or the cell reselection procedure without receiving the command of the network. Here, the cell selection procedure means that the terminal selects a cell to access the network service. And the cell reselection procedure means to find the best cell that can be set as a serving cell.

On the other hand, when the terminal is in the ECM-CONNECTED state, the mobility of the terminal is managed by the command of the network. If the location of the terminal differs from the location known by the network in the ECM-IDLE state, the terminal notifies the network of the location of the terminal through a Tracking Area Update procedure.

The following describes the system information.

The system information includes essential information that the terminal needs to know in order to access the base station. Therefore, the terminal must receive all the system information before connecting to the base station, and always have the latest system information. Since the system information is information that must be known by all terminals in a cell, the base station periodically transmits the system information.

According to Section 5.2.2 of 3GPP TS 36.331 V8.7.0 (2009-09) "Radio Resource Control (RRC), Protocol specification (Release 8)", the system information includes MIB (Master Information Block), SB (Scheduling Block) , And SIB (System Information Block). The MIB allows the UE to know the physical configuration of the cell, for example, the bandwidth. The SB informs the transmission information of the SIBs, for example, the transmission period. An SIB is a collection of related system information. For example, some SIBs only contain information of neighboring cells, and some SIBs only contain information of uplink radio channels used by the UE.

Generally, the service provided by the network to the terminal can be classified into the following three types. Also, the terminal recognizes the type of the cell differently depending on what service can be provided. In the following, the service type is first described, and the type of the following cell is described.

1) Limited service: This service provides an emergency call and an earthquake and tsunami warning system (ETWS) and can be provided in an acceptable cell.

2) Normal service: This service is a general purpose general service, and can be provided in a regular cell.

3) Operator service: This service refers to a service for a network operator. This cell can only be used by a network operator and can not be used by a general user.

With respect to the service type provided by the cell, the type of the cell can be divided as follows.

1) Acceptable cell: A cell in which a terminal can receive a limited service. This cell is not barred for the terminal, but is a cell that satisfies the cell selection criterion of the terminal.

2) Suitable cell: A cell where the terminal can receive regular service. This cell satisfies the conditions of the acceptable cell and satisfies the additional conditions at the same time. As an additional condition, this cell must belong to a PLMN (Public Land Mobile Network) that the terminal can access, and the cell should not be prohibited from performing the tracking area update procedure of the terminal. If the corresponding cell is a CSG cell, the terminal must be a cell capable of connecting to this cell as a CSG member.

3) Barred cell: It is a cell that broadcasts information that a cell is prohibited through system information.

4) Reserved cell: It is a cell that broadcasts information that a cell is a reserved cell through system information.

Now, we describe the measurement and the measurement report.

It is essential to support the mobility of the terminal in the mobile communication system. Accordingly, the UE continuously measures the quality of the serving cell and the quality of the neighboring cell that provide the current service. The terminal reports the measurement result to the network at an appropriate time, and the network provides optimal mobility to the terminal through handover or the like.

In addition to the purpose of mobility support, the terminal can perform a specific purpose measurement set by the network and report the measurement result to the network in order to provide information that can help the operator to operate the network. For example, the terminal receives broadcast information of a specific cell set by the network. The terminal may store a cell identifier of the particular cell (also referred to as a global cell identifier), location identification information (e.g., Tracking Area Code) to which the particular cell belongs and / For example, whether it is a member of a closed subscriber group (CSG) cell).

If the mobile terminal confirms that the quality of a specific area is very bad, it can report the location information and measurement results of bad quality cells to the network. The network can optimize the network based on the report of the measurement results of the terminals supporting the operation of the network.

In a mobile communication system with a frequency reuse factor of 1, mobility is mostly made between different cells in the same frequency band. Therefore, in order to ensure mobility of the UE, the UE must be able to measure the quality and cell information of neighbor cells having the same center frequency as the center frequency of the serving cell. The measurement for a cell having the same center frequency as the center frequency of the serving cell is called an intra-frequency measurement. The terminal performs in-cell measurements and reports the measurement results to the network at an appropriate time so that the purpose of the corresponding measurement results is achieved.

The mobile communication service provider may operate the network using a plurality of frequency bands. In a case where a service of a communication system is provided through a plurality of frequency bands, in order to guarantee optimal mobility to the UE, the UE can measure the quality and cell information of neighboring cells having center frequencies different from the center frequency of the serving cell . Thus, a measurement on a cell having a center frequency different from the center frequency of the serving cell is called inter-frequency measurement. The terminal shall be able to perform inter-cell measurements and report the measurement results to the network at the appropriate time.

If the UE supports measurements on a heterogeneous network, measurements may be made on the cells of the heterogeneous network by setting the BS. Such measurements on heterogeneous networks are referred to as inter-RAT (Radio Access Technology) measurements. For example, the RAT may include UTRAN (UMTS Terrestrial Radio Access Network) and GERAN (GSM EDGE Radio Access Network) conforming to the 3GPP standard, and may also include a CDMA 2000 system conforming to the 3GPP2 standard.

Hereinafter, a procedure for selecting a cell by the UE will be described in detail with reference to 3GPP TS 36.304 V8.8.0 (2009-12) "User Equipment (UE) procedures in idle mode (Release 8)".

4 shows a state transition process in the RRC idle state.

As shown, whenever a PLMN is selected, it starts at the location indicated by number 1, and a cell selection procedure is performed. Here, the UE may perform the measurement procedure for cell selection (or cell reselection).

The UE can select the appropriate cell based on the measurement in the idle mode and the cell selection criterion. To quickly perform the cell selection procedure, stored cell information for multiple RATs may be used.

If the UE is camp-on normally in the appropriate cell, the UE may periodically search for a better cell according to the cell reselection criterion. If a better cell is found, the UE may reselect the cell and camp on.

On the other hand, after camping on the corresponding cell, the UE enters the RRC connection mode, acquires system information or the like from the cell, and transits to the RRC idle state. If the UE transitions from the RRC connection mode state to the RRC idle state, the UE performs the cell selection procedure again.

Hereinafter, the cell selection procedure will be described in detail.

5 is a flowchart illustrating a process in which a UE in an idle state performs cell selection.

FIG. 5 shows a procedure in which a terminal whose power is turned on is registered in the network via a cell selection process, and then, when necessary, performs cell reselection.

Referring to FIG. 5, the MS selects a radio access technology (RAT) for communicating with a public land mobile network (PLMN), which is a network to which the MS desires to receive services (S410). Information on the PLMN and the RAT may be selected by a user of the UE or may be stored in a universal subscriber identity module (USIM).

In step S420, the UE selects a cell having the largest signal strength among the cells of which the measured signal strength or quality is greater than a predetermined value. This may be referred to as an initial cell selection in which a terminal that is powered on performs cell selection. The cell selection procedure will be described later in detail. After the cell selection, the terminal receives the system information periodically transmitted by the base station.

The parameters of the cell selection criterion used by the UE in the cell selection process are expressed by Equation (1).

Where Srxlev and Squal are defined as follows:

The Srxlev value is calculated based on a reference signal received power (hereinafter referred to as RSRP) in the LTE system and is calculated by a received signal code power (hereinafter referred to as RSCP) in UMTS . The squal value is calculated based on a reference signal reception quality (hereinafter referred to as RSRQ) in the LTE system and is calculated as Ec / No in UMTS. This value is calculated per chip of a pilot channel Is a value obtained by dividing the received power Ec by the total noise power density N0.

Specifically, in LTE, Srxlev is the cell selection reception (RX) level value (dB), _Qrxlevmeas is the reception level of the measured cell (RSRP), _Qrxlevmin is the minimum required reception level (dBm) in the cell, _{Qrxlevminoffset} is offset (offset), Pcompensation = max for _{Q rxlevmeas (P EMAX - P UMAX} , 0) (dB), P EMAX is good up to a transmit power (dBm) even if the terminal is transmitted in the cell, P _UMAX is the performance of the terminal Is the maximum transmission power (dBm) of the terminal radio transmission unit (RF) according to the following equation. In addition, the above described Squal is the cell selection quality value (dB) in the LTE, Q _qualmeas means RSRQ, and Q _qualmin refers to the minimum quality level (dB) is required in the cell, and Q _{qualminoffset} is offset to the Q _qualmin Value.

In Equations (1) and (2), it can be seen that the UE selects a cell whose strength and quality are greater than a specific value determined by a cell providing the service. The parameters used in Equations 1 and 2 are broadcast through the system information, and the terminal receives the parameter values and uses the parameters for the cell selection criterion.

If the terminal needs to register the network (S430), the terminal performs the network registration procedure (S440). The terminal registers its information (eg, IMSI) to receive services (eg, paging) from the network. The UE does not register with the network to which it is connected every time the cell is selected. When the information of the network received from the system information (for example, Tracking Area Identity (TAI) do.

The UE performs cell re-selection based on the service environment provided in the cell or the environment of the UE (S450).

For example, if the measured strength or quality of a signal for a currently connected cell is lower than a value measured from a neighboring cell's base station, the terminal may select one of the other cells providing better signal characteristics than the cell connected to the terminal Reselect. This process is called cell re-selection by distinguishing it from the initial cell selection. Also, once the UE has selected a cell through the cell selection process, the strength or quality of the signal between the UE and the BS may be changed due to mobility of the UE or change of the radio environment. Thus, if the quality of the selected cell degrades, the terminal may reselect other cells providing better quality. When the cell is reselected in this way, the cell reselecting normally provides a better signal quality than the currently selected cell. At this time, a time constraint is set in order to prevent the cell from being reselected frequently according to the change of the signal characteristics. The cell reselection procedure will be described later in detail.

In order to select a cell for reselection in the cell reselection, there is a method of selecting or reselecting a cell according to the signal characteristics of the wireless environment, There may be a choice.

- Inter-RAT cell reselection: The terminal reselects a cell using a RAT different from the RAT being camped on

- Intra-frequency cell reselection: reselects cells with the same center-frequency as the RAT such as the cell in which the terminal is camping (camping)

- Inter-frequency cell reselection: reselects cells with the same center frequency as the RAT of the cell the terminal is camping on

First, the Inter-RAT cell reselection and the Intra-frequency cell reselection are based on priority. The network may provide priority to inter-RAT (RAT) and frequency priorities that are commonly applied by terminals in the cell through broadcast signaling, or may be provided with different priority .

According to this priority, if the RAT having a higher priority than the serving cell and the neighboring cell using a frequency having a higher priority than the serving cell satisfy Equation (1), the UE reselects the neighboring cell.

However, if the priorities of the serving cell and the neighboring cell are the same, then ranking is based. Intra-frequency cell reselection is also based on ranking. Ranking is the task of defining the index values for the cell reselection evaluation and ordering the cells by the index value size using the index values. Cells with the best indicator are often called best ranked cells. The cell index value is a value obtained by applying a frequency offset or a cell offset as necessary based on a value measured by the terminal for the corresponding cell.

The ranking will be described as follows. A ranking criterion is defined as Equation (3).

Qmeas, s is the quality value measured by the UE with respect to the serving cell, Qmeas, n is the quality value measured by the UE with respect to neighboring cells, Q _hyst is the ranking index of the serving cell, Rn is the rank index of the neighboring cell, Is the hysteresis value for ranking, and Q _offset is the offset between two cells.

Q _offset = Q _{offsets, n,} and Qoffset = 0 if the UE does not receive Q _{offsets, n} when the UE receives offset (Q _{offsets, n} ) between the serving cell and the neighboring cell.

If the ranking indicator Rs of the serving cell and the ranking indicator Rn of the neighboring cell fluctuate in a state similar to each other, the ranking of the fluctuation result ranking is reversed, and the terminal can reselect the cells while alternating between the two cells. Qhyst is a parameter to give hysteresis in cell reselection and to prevent the terminal from alternating between two cells.

The UE measures the Rs of the serving cell and the Rn of the neighboring cell according to the above equation and regards the cell having the highest ranking index value as the best ranked cell and reselects this cell.

FIG. 6 is a flowchart illustrating the cell reselection process shown in FIG. 5 in detail.

The UE 100 receives the cell reselection information from the base station (S451). The cell reselection information may include two thresholds, S _intrasearch and S _{non-intrasearch} . The S _intrasearch is the S _intrasearchP S _intrasearchQ . S _intrasearchP is expressed as a threshold of Srxlev for intra-frequency measurement in dB. S _intrasearchQ is the squared threshold for intra-frequency measurements in dB. In addition, S _{non-intrasearch} can be divided into S _{non-intraseachP} and S _{non-intraseachQ} . S _{non-intraserachP} is expressed as a threshold of _Srxlev for inter-frequency and inter-RAT measurements in dB. Also, S _{non-intraserachQ} is expressed in dB as a threshold of _squal for inter-frequency and inter-RAT measurements.

The UE measures the serving cell (S452). The measurement result of the serving cell is expressed as Srxlev Or Squal is used.

The UE performs a comparison as shown in Equation (4) below as a reference for measuring neighboring cells existing on the same frequency as the serving cell (S453).

If Srxlev > S _IntraSearchP or Squal > S _IntraSearchQ is satisfied, the UE performs measurements on neighboring cells on the same frequency as the serving cell (S453-1). However, if Srxlev > S _IntraSearchP or Squal > S _IntraSearchQ are not met, the UE may omit measurements on neighboring cells that are on the same frequency as the serving cell.

If the cell reselection information does not include S _intrasearch , then the UE can not omit measurements on neighboring cells of the same frequency as the serving cell.

Meanwhile, the UE performs a comparison as a reference for measuring neighboring cells existing on different frequencies from the serving cell as shown in Equation (5) below (S454).

If Srxlev> S _{non-intraserachP} or Squal> S _{non-intraserachQ} is not satisfied, the UE performs an inter-frequency measurement, that is, a measurement on a cell existing on a different frequency from the serving cell (S454-1). However, if the quality of the serving cell is better and the Srxlev > S _{non-intraserachP} or Squal > S _{non-intraserachQ} is met, then the UE may omit measurements on neighboring cells that are on a different frequency than the serving cell.

If the cell reselection information does not include S _{non-intrasearch} , then the UE can not omit measurements on neighboring cells that are on a different frequency than the serving cell.

The UE 100 calculates the measurement result S _{nonServingCell, x} for the neighbor cell x (S455).

Then, the UE 100 _{reselects the} corresponding cell when S _{nonServingCell} of the cell x at the frequency to be measured is greater than the Thresh _{x, high} value (S456) during a time period called T _{reselectionRAT} (S457 ). The S _{nonServingCell} , x may be the Srxlev value or the Squal value of the cell x at the frequency to be measured.

7 is an exemplary flowchart illustrating a process of performing Inter-RAT cell reselection and inter-frequency cell reselection.

Referring to FIG. 7, it is shown that the LTE-based eNodeB 200-1 uses the frequency F1 and the UMTS-based NodeB 200-2 uses the frequency F2.

The UE 100 performs an initial cell selection process. First, the UE 100 receives a synchronization signal, that is, a PSS (Primary Synch Signal), an SSS (Secondary Synch Signal), and acquires the cell ID through the synchronization signal, thereby identifying the cell.

Then, the UE 100 performs cell measurement based on a reference signal, for example, a cell-specific reference signal (CRS). A brief description of what CRS is to understand is as follows. CRS is a reference signal shared by all UEs in a cell, and is used for information acquisition and handover measurement of a channel state. The UE measures the CRS and measures RSRP (reference signal received power) and RSRQ (reference signal received quality). Also, the UE can calculate feedback information such as CQI (channel quality information), PMI (pecoding matrix indicator), and RI (rank indicator) through the CRS.

Then, the UE 100 performs initial cell selection according to the above-described contents (S420).

If the UE 100 selects the LTE-based eNodeB 200-1, the UE 100 camps on the cell of the eNodeB 200-1.

Accordingly, in FIG. 7, the eNodeB 200-1 is represented as a serving cell. Then, the UE 100 establishes an RRC connection and receives system information such as MIB (Master Information Block) and SIB (system information block) from the serving cell eNodeB 200-1. The MIB may be received via a physical broadcast channel (PBCH), and the SIB may be received via a PDSCH (Physical Downlink Shared Channel). The system information, e.g., SIB, may include an inter-RAT (RAT) priority and a frequency priority.

The UE 100 reselects the cell of the Node B 200-2 according to the inter-RAT priority and the frequency priority (S450).

Then, the UE 100 camps on a cell of the NodeB 200-2 and makes an RRC connection.

Hereinafter, the MTC will be described.

8 shows an example of MTC (Machine Type communication) communication.

Machine Type Communication (MTC) is a method for exchanging information between MTC devices 100 without human interaction through the base station 200 or exchanging information between the MTC device 100 and the MTC server 700 Exchange.

The MTC server 700 is an entity that communicates with the MTC device 100. The MTC server 700 executes the MTC application and provides the MTC specific service to the MTC device.

The MTC device 100 is a wireless device that provides MTC communication, and may be fixed or mobile.

The service provided through MTC is different from the service in existing human intervention, and various kinds of services such as tracking, metering, payment, medical service, exist. More specifically, services provided through the MTC may include meter reading, water level measurement, utilization of surveillance cameras, inventory reporting of vending machines, and the like.

Since the specificity of the MTC device is small and the transmission / reception of the up / down data occurs occasionally, it is effective to lower the cost of the MTC device and reduce the battery consumption in accordance with the low data rate.

The following table summarizes the characteristics according to the types of MTC devices.

Types of MTC devices Data processing request speed Error rate requirements Delay sensitivity Smart meter lowness lowness lowness Fleet management lowness lowness Heavy price Point of sale terminal (POS) lowness middle height Live video lowness lowness lowness

As described above, the MTC device does not require a wide range of services, unlike a general UE, but requires only a very small number of special services. Therefore, it is sufficient that the MTC apparatus is camped on only a cell that can provide a low-quality service, so that it is not necessary to perform the cell reselection procedure a large number of times.

≪ Method according to one embodiment of the present specification >

One disclosure set forth herein provides a method for streamlining the number of times that a device requiring only a predetermined service, for example, an MTC device, performs a cell selection procedure and a reselection procedure. At this time, the cell selection procedure and the cell reselection procedure are performed on the basis of comparing parameters such as a predetermined threshold and a power intensity of a signal received from the cell. Thus, one embodiment of the present disclosure provides different category-specific parameters used for evaluation for cell selection and cell reselection.

Here, the category is a system classified according to delay tolerance, i.e., how sensitive to delay.

For example, categories can be divided as follows.

Various criteria can be used to identify categories.

a) It is possible to classify the category according to the delay sensitivity of the service to be started by the terminal. For example, different service delay sensitivities can be categorized into different categories even if they require sensitivity.

b) The terminal can identify the category according to the error rate requirement of the service to be started. For example, if different error rates are required, they can be classified into different categories.

c) The terminal can distinguish categories according to the data rate requirements of the service to be started. For example, different minimum data rates can be categorized into different categories if required.

d) Categories may be classified according to the operational power efficiency requirements required by the terminal. For example, when operating in the power saving mode, and when not operating, different categories can be distinguished.

Hereinafter, more detailed description will be made with reference to the drawings.

Figures 9A-9C are exemplary diagrams illustrating a scheme according to one disclosure of the present disclosure.

9A, the base station 200 may provide other parameters to the UE 10 and the MTC 100 in general. For example, the base station 200 may provide the UE 10 with the cell-common parameters to be used in the cell selection and cell reselection procedures, while providing the MTC device 100 with the cell- Can provide category specific parameters. Details of these category specific parameters will be described later.

As can be seen with reference to FIG. 9B, when the cell selection procedure is triggered, the MTC device 100 acquires broadcast information from the cell after detecting the cell. The broadcast information may include cell-common parameters to be used in the cell selection and cell reselection procedures, as described above. In addition, the category specific parameter may be included in the broadcast information. At this time, the category specific parameter may include only an offset value for the cell common parameter. Alternatively, the category specific parameter may not be received included in the broadcast information, but may be preset to the MTC device or received via another network signal.

Subsequently, it is determined whether the MTC device 100 is set to use a specific category, and furthermore, it is set to apply a parameter for the specific category. To this end, the network may deliver a signal indicating that the MTC device 100 should apply the category specific parameters. In this case, when the MTC device 100 does not receive the signal, the MTC device 100 may determine that the category specific parameter is not applied. Conversely, the network may deliver a signal indicating that the MTC device 100 should not apply the category specific parameters. In this case, when the MTC device 100 does not receive the signal, the MTC device 100 may determine that the category specific parameter should be applied.

If the MTC device 100 is set to use a specific category and furthermore, the MTC device 100 is set to apply the parameters for the specific category, the MTC device 100 applies the parameters for the specific category, Evaluate selection criteria.

On the other hand, when the MTC device 100 is not set to use a specific category or is not set to apply the parameter for the specific category, the MTC device 100 applies the cell common parameter Evaluate cell selection criteria.

Referring to FIG. 9C, when the MTC device 100 starts the cell reselection procedure in the idle state, it determines whether a parameter for a specific category should be applied. To this end, the network may deliver a signal indicating that the MTC device 100 should apply the category specific parameters. In this case, when the MTC device 100 does not receive the signal, the MTC device 100 may determine that the category specific parameter is not applied. Conversely, the network may deliver a signal indicating that the MTC device 100 should not apply the category specific parameters. In this case, when the MTC device 100 does not receive the signal, the MTC device 100 may determine that the category specific parameter should be applied.

If the MTC device 100 is set to use a specific category and furthermore, the MTC device 100 is set to apply the parameters for the specific category, the MTC device 100 applies the parameters for the specific category, Evaluate the reselection criterion.

On the other hand, when the MTC device 100 is not set to use a specific category or is not set to apply the parameter for the specific category, the MTC device 100 applies the cell common parameter Evaluate cell reselection criteria.

Hereinafter, parameters for a specific category used in cell selection will be described.

First, according to one embodiment, the parameters Srxlev and Squal, which are used as cell selection criteria, can be improved for a particular category as the following equation.

Comparing Equation (6) and Equation (2) above, Q _rxlevmin Changes to _{rxlevmin_category} Q, Q is _rxlevmin it can be seen that changes in Q _{rxlevmin_category.} As described above with reference to Equation (2), Q _rxlevmin and Q _rxlevmin are broadcast through system information as a cell common parameter. However, Q _{rxlevmin_category} and Q _{rxlevmin_category} are category specific parameters provided according to one disclosure of the present disclosure. Here, the value of Q is smaller than the value of Q _{rxlevmin_category rxlevmin} to reduce the number of times of cell selection, and the value of Q _{rxlevmin_category} may be smaller than the value of Q _rxlevmin to reduce the number of times of cell selection. The values of Q _{rxlevmin_category} and Q _{rxlevmin_category} may be different for each category. At this time, the cell can _provide the value of Q _{rxlevmin_category} differently for each category. Similarly, a cell can provide values of Q _{rxlevmin_category} differently for each category. Alternatively, the cell may provide values of Q _{rxlevmin_category} and Q _{rxlevmin_category} for a particular category. At this time, the values of Q _{rxlevmin_category} and Q _{rxlevmin_category} for other categories can be defined as offset values. The offset value may be a value that the MTC device has in advance for each category or may be acquired by the MTC device through a separate signal.

Next, according to another embodiment, the parameters Srxlev and Squal, which are used as the cell selection criterion, may be improved as follows for a particular category.

Comparing Equation (7) and Equation (2) above, it can be seen that Qrxthres_category and Qqualthres_category are additionally added. The Qrxthres_category is a threshold value of a reception level for each category as a category specific parameter provided according to another embodiment of the present invention. The reason why the Qrxthres_category is added in addition to the above equation (2) is that the cell selection criterion Srxlev > 0 shown in Equation (1) is satisfied. Likewise, the reason why the Qrxthres_category is added in addition to the above Equation (2) is that the cell selection criterion Squal> 0 shown in Equation (1) is satisfied. On the other hand, the Qrxthres_category and Qqualthres_category may have different values for each category. At this time, the cell can provide the values of Qrxthres_category and Qqualthres_category by different categories. Alternatively, the cell may provide values of Qrxthres_category and Qqualthres_category for a particular category. At this time, the values of Qrxthres_category and Qqualthres_category for other categories can be defined as offset values. The offset value may be a value that the MTC device has in advance for each category or may be acquired by the MTC device through a separate signal.

In the following, parameters for a specific category used in cell reselection will be described.

First, according to one embodiment, the parameters Srxlev and Squal, which are used as criteria of measurement for cell reselection, may be improved according to one embodiment as follows for a particular category.

Comparing Equation (8) and Equation (4) above, it can be seen that Q _{rxlevmeasoffset_category} and Q _{qualmeasoffest_category} are added according to the embodiment of the present invention. The Q _{rxlevmeasoffset_category} is a category specific parameter provided according to an embodiment of the present invention, and may be an offset value for a reception level for each category, and the value may be different for each category. The Q _{qualmeasoffest_category} may be a category specific parameter provided according to an embodiment of the present invention, and may be an offset value for each category quality value, and the value may be different for each category. On the other hand, the cell can provide different values of Q _{rxlevmeasoffset_category} and Q _{qualmeasoffest_category} for each category. Alternatively, the cell may provide values of Q _{rxlevmeasoffset_category} and Q _{qualmeasoffest_categor} for a particular category. At this time, the values of Q _{rxlevmeasoffset_category} and Q _{qualmeasoffest_category} for other categories can be defined as delta values. The delta value may be a value that the MTC device has in advance for each category or may be acquired by the MTC device through a separate signal. The MTC unit Srxlev + Q _{rxlevmeasoffset_category>} S if they meet the _IntraSearchP or Squal + Q _{qualmeasoffest_category>} satisfy the S _{IntraSearchQ,} the serving cell can be determined better than the neighboring cell, if not a measurement for the inter-frequency cell reselection And may not perform measurements for inter-RAT frequency cell reselection with lower or equal priority.

Next, a ranking criterion used as a criterion for cell reselection when the priority between the serving cell and the neighboring cell is the same can be improved according to the following equation according to an embodiment.

Comparing Equation (9) and Equation (3), it can be seen that Q _category is additionally added to Rs, which is a rank indicator of the serving cell, according to an embodiment of the present invention. The Q _category may be different for each _category . Here, the cell can provide the value of Q _category differently for each _category . According to Equation (9), since the ranking indicator of the serving cell, i.e., Rs, becomes higher than the ranking indicator of the neighboring cell, i.e., Rn, the MTC device can stay in the serving cell for as long as possible.

The above equation (9) can be modified as shown in the following equation.

Comparing Equation (10) with Equation (10) above, Q _{category, n} is added to the ranking index for neighboring cells, that is, Rn.

On the other hand, an evaluation for reselecting a lower priority cell than a serving cell can be improved as follows.

If, Thresh _X _Q (for example, for the serving cell Thresh _{Serving, LowQ)} when received, with respect to the serving cell Squal + Q _{qaualoffset_category} <Thresh _{Serving, LowQ} are met, priority is Squal for low neighboring cell> Thresh _{X, LowQ} are satisfied during the time period _Treselection , the MTC device can reselect the low priority neighbor cell. The Q q _{airoffset_category} is an offset value for the received level added in accordance with an embodiment of the present disclosure. Alternatively, when Srxlev + _{Qrxlevoffset_category} <Thresh _{Serving, LowP} is satisfied for the serving cell and Srxlev> Thresh _{X, LowP} time period _Treselection for the low priority neighbor cell is satisfied, the MTC device has the lower priority The neighboring cell can be reselected. The Q _{rxlevoffset_category} is a quality offset value added in accordance with an embodiment of the present disclosure.

Hereinafter, modifications of the above-mentioned scheme will be described.

In performing an evaluation for cell reselection for a serving cell and a neighbor cell having a different priority, the network may transmit priorities to the MTC device in addition to the absolute priority. If the category priority is received, the MTC device may use the category priority for cell evaluation and measurement. Thereby, the MTC device may re-prioritize cell reselection for some frequencies for a particular category. On the other hand, the MTC device may or may not use the priority according to the category according to a specific situation. For example, if the MTC device has limited transmission and reception of general data, it may be better for the MTC device to move a cell-based cell than a LTE-based cell. In this situation, the priorities of the CS-based cells can be made higher through the priorities of the categories, so that the MTC device can reselect the CS-based cells. As another way for MTC devices to use category-specific priorities according to a particular situation, it may be considered that the category-specific cell reselection priority set is associated with the region. In this method, priority information for each category applied in a specific area is stored in advance in the terminal or separately signaled. The UE selectively applies the cell reselection priority according to the current location and the service category. For example, let the cell reselection priority set of category a applicable in region A be P_Aa and the cell reselection priority set of category b applicable in the same region be P_Ab. In addition, let P_Ba be the cell reselection priority set of category a applicable in region B, and P_Bb be the cell reselection priority set of category b applicable in the same region. Based on this setting, the UE performs cell reselection using P_Aa when it wants to start a service belonging to category a in region A, and when it wants to start a service belonging to category b in region B, Perform the selection.

Fig. 10A shows an operation according to the prior art, and Fig. 10B shows an application example of one embodiment.

It is assumed that the MTC device 100 shown in FIG. 10A is installed as a smart meter in a place where the signal intensity from the cell 200 of the base station is weak, for example, under the building. At this time, it is assumed that there is only one cell in which the MTC device 100 can camp on. At this time, the signal intensity of the cell measured by the MTC device 100 is -110 dBm. Therefore, in this situation, the service provided from the cell is very poor (for example, high delay and high error rate), and it can be determined that the service is impossible if the UE is a general UE. However, if the MTC apparatus 100 does not require a high data transmission rate when the MTC apparatus 100 applies the category-specific parameter Qrxlevmin_category according to an embodiment of the present invention, It can be determined that the service can be provided from the cell even if the delay is somewhat high.

Fig. 11A shows another operation according to the prior art, and Fig. 11B shows an application example of one embodiment.

A general LTE based UE performs neighbor cell measurements when the received signal strength (or quality) of the serving cell drops below a certain threshold. Referring to FIG. 11A, when the received signal strength (or quality) of the cell 1 corresponding to the serving cell falls below a certain threshold value, the MTC device 100 measures cell 2 and reselects cell 2 accordingly . However, referring to FIG. 11B, when applying a category-specific offset in accordance with an embodiment of the present disclosure, it is not possible to perform a measurement on a neighboring cell, cell 2, and thereby not to reselect cell 2. FIG. Thus, according to one embodiment of the present disclosure, the MTC device can stay in the serving cell for as long as possible by reducing the number of measurements to maximize the battery saving effect while reducing the number of cell reselections.

The embodiments described so far can be implemented by various means. For example, embodiments of the present invention may be implemented by hardware, firmware, software, or a combination thereof. This will be described in detail with reference to FIG.

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

The base station 200 includes a processor 201, a memory 202 and an RF unit (radio frequency unit) 203. The memory 202 is connected to the processor 201 and stores various information for driving the processor 201. [ The RF unit 203 is connected to the processor 201 to transmit and / or receive a radio signal. The processor 201 implements the proposed functions, procedures and / or methods. In the above-described embodiment, the operation of the base station can be implemented by the processor 201. [

The MTC apparatus 100 includes a processor 101, a memory 102, and an RF unit 103. The memory 102 is connected to the processor 101 and stores various information for driving the processor 101. [ The RF unit 103 is connected to the processor 101 to transmit and / or receive a radio signal. The processor 101 implements the proposed functions, procedures and / or methods. In the above-described embodiment, the operation of the MTC apparatus can be implemented by the processor 101. [

The processor may comprise an application-specific integrated circuit (ASIC), other chipset, logic circuitry and / or a data processing device. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage devices. The RF unit may include a baseband circuit for processing the radio signal. When the embodiment is implemented in software, the above-described techniques may be implemented with modules (processes, functions, and so on) that perform the functions described above. The module is stored in memory and can be executed by the processor. The memory may be internal or external to the processor and may be coupled to the processor by any of a variety of well known means.

In the above-described exemplary system, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders . It will also be understood by those skilled in the art that the steps shown in the flowchart are not exclusive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the invention.

Claims (10)

A cell reselection method of a terminal,
Receiving a common parameter and a category-specific parameter to be used for a cell selection procedure from a serving cell;
Performing measurements on one or more of the serving cell and neighboring cells;
Determining whether the measurement result value meets a cell selection criterion,
Wherein, when the UE is configured to use the category-specific parameter, the cell selection is evaluated by reflecting the category-specific parameter to the measurement result value. 2. The method according to claim 1, wherein in the receiving step
And a parameter is received for each category. 3. The method of claim 2,
Wherein the categories are classified according to delay tolerance. The method according to claim 1,
Wherein the measurement result value for the serving cell is represented by Srxlev or Squal, and when the cell selection criterion is Srxlev> 0 or Squal> 0, the category-specific parameter increases the value of Srxlev or the value of Squal Cell selection method. 1. A measurement method for cell reselection of a terminal,
Receiving a common parameter and a category-specific parameter to be used for a cell reselection procedure from a serving cell;
Performing measurements on the serving cell;
Determining whether a measurement execution condition for a neighboring cell is satisfied according to a measurement result value for the serving cell,
When the UE is set to use the category-specific parameter, a value corresponding to the category-specific parameter is added to a measurement result value for the serving cell, Wherein the cell reselection comprises: 7. The method of claim 6, wherein in the receiving step
And a parameter is received for each category. The method according to claim 6,
Wherein the categories are classified according to delay tolerance. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; 6. The method of claim 5, wherein the category-
A first parameter to be used in a case where a first measurement performance condition for a neighboring cell on a frequency different from the serving cell is satisfied and a second parameter to be used in meeting a second measurement performance condition for a neighbor cell on the same frequency as the serving cell, And the parameters are classified into parameters. A terminal for performing cell reselection,
A transceiver for receiving a common parameter and a category-specific parameter to be used for a cell selection procedure from a serving cell;
And a processor for controlling the transceiver to perform measurements on the serving cell and determining whether a measurement result for the serving cell satisfies a cell selection criterion,
Wherein if the UE is configured to use the category-specific parameter, the processor increases the frequency at which the cell selection criterion is met by increasing the measurement result for the serving cell by the value of the category-specific parameter Terminal. A terminal that performs measurements for cell reselection,
A transceiver for receiving a common parameter and a category-specific parameter to be used for a cell reselection procedure from a serving cell; And
The mobile station performs the measurement on the serving cell by controlling the transceiving unit and determines whether the measurement performing condition for the neighboring cell is satisfied according to the measurement result value of the serving cell
Wherein if the UE is configured to use the category-specific parameter, the processor adds a value according to the category-specific parameter to a measurement result value for the serving cell to determine if the measurement performing condition for the neighboring cell is satisfied So that the frequency is reduced.

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