KR20170074570A - Method and apparatus for performing a soft handover - Google Patents

Abstract

A method for selecting a reference serving cell during handover and a terminal apparatus therefor are disclosed. A method for a soft handover of a terminal in a wireless communication system includes receiving an active set update message instructing to update an active set comprising at least one serving cell set in the terminal, Adding or removing at least one serving cell to the set and selecting a new reference serving cell from the updated active set if the preset reference serving cell is removed from the terminal by the active set update message, The selection of the reference serving cell is performed based on a priority for providing a reference of uplink synchronization to the terminal in the uplink transmission of the terminal for the other serving cells in the active set, Each serving cell supports May be determined based on the transport channel.

Description

[0001] METHOD AND APPARATUS FOR PERFORMING A SOFT HANDOVER [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to wireless communication, and more particularly, to a method of selecting a reference serving cell and a terminal apparatus therefor.

Handover refers to a function in which a mobile station automatically tunes to a new communication channel of a neighboring base station and continuously maintains a communication state when a mobile station moves from a cell boundary to a neighboring base station service area. The call disconnection time during the automatic change of the call channel is about 15 ms or less. In such a short period of time, it is difficult for the subscriber in the call to perform the message communication between the base station and the terminal to hardly detect the momentary call disconnection state. Due to the development of wireless communication technology, the number of terminals is rapidly increasing and heterogeneous networks using different wireless communication methods are expanding. Heterogeneous network or media handover techniques have also been developed.

The handover method includes hard handover (HHO) and soft handover. Soft handover techniques include macro diversity handover (MDHO) and fast base station switching Switching, FBSS).

In a WCDMA (Wideband Code Division Multiple Access) system, when a UE establishes an RRC connection, it selects a serving cell designated by the network as a reference serving cell and maintains a radio link. However, when the reference serving cell is removed, there is no clear criterion as to which cell to add as the reference serving cell among the added serving cells.

It is an object of the present invention to provide a method and apparatus for selecting a reference serving cell.

According to one aspect, a method for a terminal to perform soft handover in a wireless communication system includes receiving an active set update message instructing to update an active set comprising at least one serving cell set in the terminal, Adding or removing at least one serving cell to the active set based on the message and selecting a new reference serving cell from the updated active set if the preset reference serving cell is removed from the terminal by the active set update message Wherein the selection of a reference serving cell is performed based on a priority for providing a reference of uplink synchronization to the terminal in an uplink transmission of the terminal for other serving cells in the active set, Each of the It may be determined based on the transmission channel to the ice-cell support.

The priority determines the serving cell that supports at least one of the HS-DSCH transmission channel and the E-DCH transmission channel among the serving cells included in the updated active set as a first rank, and determines the other serving cells as second rank .

When there are a plurality of serving cells having the same priority, the serving cell having the highest received signal level among the serving cells determined with the same priority can be selected as the reference serving cell.

The received signal level may be the Receiving Signal Code Power (RSCP).

If the received signal level value of the predetermined reference serving cell is less than or equal to the threshold value, the UE can transmit a measurement report for the predetermined reference serving cell.

The transport channel information may be included in the active set update message.

The transport channel information may be provided through upper layer signaling.

According to another aspect, a terminal performing soft handover in a wireless communication system includes a communication module and a processor for receiving an active set update message instructing to update an active set including at least one serving cell set in the terminal , The processor adds or removes at least one serving cell to the active set based on the received active set update message and if the active set update message has removed the preset reference serving cell from the terminal, Selecting a new reference serving cell, wherein selection of a reference serving cell is performed based on a priority for providing uplink synchronization criteria to the terminal in uplink transmission of the terminal for other serving cells in the active set, The ranking is based on the updated active tax And it may be determined based on each transmission channel for the serving cell is included in the support.

The priority determines the serving cell that supports at least one of the HS-DSCH transmission channel and the E-DCH transmission channel among the serving cells included in the updated active set as a first rank, and determines the other serving cells as second rank .

When there are a plurality of serving cells having the same priority, the serving cell having the highest received signal level among the serving cells determined with the same priority can be selected as the reference serving cell.

The received signal level may be the Receiving Signal Code Power (RSCP).

The processor may transmit a measurement report for a predetermined reference serving cell if the received signal level value of the predetermined reference serving cell is less than or equal to a threshold value.

The transport channel information may be included in the active set update message.

The transport channel information may be provided through upper layer signaling.

According to an embodiment of the present invention, when a UE performs soft handover, when a reference serving cell designated by the network is removed, a method of selecting a reference serving cell is provided to efficiently maintain a wireless link, An effect of preventing link failure can be obtained.

1 is a diagram conceptually showing a network structure of an E-UMTS.
2 is a conceptual diagram illustrating a network structure of an evolved universal terrestrial radio access network (E-UTRAN).
3 and 4 illustrate a control plane and a U-Plane (User-Plane) structure of a radio interface protocol between a UE and an E-UTRAN based on the 3GPP radio access network standard Fig.
5 is a flowchart illustrating a method for updating an active set by a terminal according to an embodiment.
6 and 7 are flow charts for selecting a reference serving cell according to an embodiment.
8 is a block diagram of a terminal according to an embodiment.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, those skilled in the art will recognize that the present invention may be practiced without these specific details. For example, the following detailed description assumes that the mobile communication system is an Institute of Electrical and Electronics Engineers (IEEE) 802.16 system or a 3GPP (3rd Generation Partnership Project). However, the IEEE 802.16 system, The present invention is applicable to any other mobile communication system.

In some instances, well-known structures and devices may be omitted or may be shown in block diagram form, centering on the core functionality of each structure and device, to avoid obscuring the concepts of the present invention. In the following description, the same components are denoted by the same reference numerals throughout the specification.

In the following description, it is assumed that the UE collectively refers to a mobile stationary or stationary user equipment such as a UE (User Equipment), an MS (Mobile Station), and an AMS (Advanced Mobile Station). It is also assumed that the base station collectively refers to any node at a network end that communicates with a terminal such as a Node B, an eNode B, a BS (Base Station), and an AP (Access Point).

In a mobile communication system, a mobile station can receive information from a base station through a downlink, and the mobile station can also transmit information through an uplink. The information transmitted or received by the terminal includes data and various control information, and various physical channels exist depending on the type of information transmitted or received by the terminal.

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

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

Referring to FIG. 1, an E-UMTS is an Access Gateway (hereinafter referred to as AG) located at the end of a UE, a cell (eNB), and a network (E-UTRAN) . Typically, an eNB may simultaneously transmit multiple data streams for broadcast services, multicast services, and / or unicast services. An interface for transmitting user traffic or control traffic may be used between eNBs.

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

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

2 is a conceptual diagram illustrating a network structure of an evolved universal terrestrial radio access network (E-UTRAN).

Referring to FIG. 2, the E-UTRAN system is an evolved system in an existing UTRAN system. The E-UTRAN is composed of cells (eNBs), and the cells are connected via the X2 interface. The cell is connected to the terminal through the air interface, and is connected to the EPC (Evolved Packet Core) through the S1 interface.

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

3 and 4 illustrate a control plane and a U-Plane (User-Plane) structure of a radio interface protocol between a UE and an E-UTRAN based on the 3GPP radio access network standard Fig.

In particular, the wireless interface protocol consists of a physical layer, a data link layer, and a network layer vertically, and horizontally includes a user plane for data information transmission and a control plane And a control plane for signal transmission.

The protocol layers of FIGS. 3 and 4 are based on an Open System Interconnection (OSI) reference model widely known in communication systems. The lower three layers are referred to as L1 (first layer), L2 (second layer) , And L3 (third layer).

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

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

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

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

In FIG. 3, the Non-Access Stratum (NAS) layer at the top of the RRC layer performs functions such as session management and mobility management. The NAS layer exists in the Mobility Management Entity (MME) of the UE and the network.

The MME is a key control-node in an LTE access network. The MME is responsible for the tracking and paging procedures for the idle terminal. In addition, the MME participates in the radio bearer activation / deactivation process and is responsible for selecting a Serving Gateway (SGW) at the time of 'Initial Attach' or during an intra-LTE handover including a core network relocation. do. The MME takes charge of terminal authentication through interaction with a Home Subscriber Server (HSS). The NAS signaling is terminated at the MME, and the MME is responsible for creating and assigning a temporary identifier to the terminal. The MME verifies that the terminal has the authority to camp-on the service provider's PLMN (Public Land Mobile Network). MME is the endpoint for encryption / integrity protection for NAS signaling in the network and is responsible for security key management. The MME provides a control plane function for mobility between LTE and 2G / 3G access networks.

In the NAS layer, two states of EMM (EPS Mobility Management) registration state (EMM-REGISTERED) and EMM unregistered state (EMM-UNREGISTERED state) are defined for terminal mobility management, and these states are applied to the terminal and the MME. The initial terminal is an EMM unregistered state, and the terminal performs a process of registering with the network through an initial attach procedure to access the network. When the contact procedure is successfully performed, the terminal and the MME are in the EMM registration state.

In the NAS layer, two types of ECM (EPS Connection Management) idle state (ECM_IDLE) and ECM connection state (ECM_CONNECTED) are defined in order to manage signaling connection between the terminal and the EPC, . When an ECM idle terminal establishes an RRC connection with an E-UTRAN, the UE becomes an ECM connected state. ECM An idle MME becomes an ECM connection when it makes an S1 connection with an E-UTRAN. When the UE is in the ECM idle state, the E-UTRAN has no context of the UE. Therefore, the UE in the idle state of the ECM performs a mobility-related procedure based on a terminal such as a cell selection or a cell reselection procedure without receiving a command of the network. On the other hand, when the terminal is in the ECM connection state, the mobility of the terminal is managed by a command of the network. If the location of the terminal is different from the location known by the network in the ECM idle state, the terminal notifies the network of the corresponding location of the terminal through a TA (Tracking Area Update) procedure.

Traditionally, the handover service is intended to prevent data disconnection while setting the terminal 100 to communicate with the target base station in the event that the signal strength from the serving base station becomes gradually smaller. That is, when the terminal 100 is expected to be out of coverage of the serving base station, the terminal 100 changes the communication target to the target base station adjacent to the terminal 100, So as to be continuously provided.

5 is a flowchart illustrating a method for updating an active set by a terminal according to an embodiment.

For example, the UE may be a UE supporting at least one of CDMA 1x, CDMA 1x EVDO, WCDMA, evolved High Rate Packet Data (eHRPD), and LTE communication. Also, the wireless access network may be any one of a UTRAN (Universal Terrestrial Radio Access Network) and an E-ETRAN (Evolved-UTRAN). UTRAN is a UMTS radio access network supporting W-CDMA radio access technology, which means a network structure located between a terminal and a core network. UTRAN has been introduced for improved wireless access technology and network management over the existing GSM radio access network. The UTRAN can support radio access and mobility of UEs (Mobile Terminals, User Equipment) and can provide various functions for efficient management of radio resources. The UTRAN is composed of a plurality of RNSs (Radio Network Subsystems), and each RNS may be composed of one RNC (Radio Network Controller) and several Node Bs. The Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) is an evolved and extended wireless access network for use in LTE in the existing UTRAN. It is composed of a plurality of eNodeBs, interconnected by eNodeBs through an X2 interface, Core) to the S1 interface.

It can be assumed that the wireless access network of the present embodiment is composed of three serving cells (for example, psc 100, psc 200, and psc 300) having different primary scrambling codes (psc). Here, the number of serving cells is only an example, and the number of serving cells is not limited thereto. In addition, using primary scrambling code as a criterion for distinguishing a serving cell is merely an example, and different types of serving cells can be distinguished from each other.

Referring to FIG. 5, if the UE performs initialization, it may send a request for an RRC connection to a wireless access network (510) and receive an RRC connection setup from a wireless access network (520). At this time, the radio access network can transmit information on the serving cell (psc 100) to the UE, and the UE can select the serving cell set by the radio access network as the reference serving cell while setting the RRC connection (530) .

Thereafter, the level and the channel state of the signal received from each cell may change according to the movement of the terminal. For example, a terminal located near the serving cell psc 100 can move near the serving cell psc 200 and the serving cell psc 300. In this case, the serving cell psc The receiving signal level from the serving cell psc 200 and the receiving signal level from the serving cell psc 300 can be increased.

If the received signal level or the channel status changes due to the movement of the terminal, the terminal may transmit a measurement report including information on the current received signal level or the like to the wireless access network.

The measurement report according to one example may be one of Event 1A, Event 1B, and Event 1C. Event 1A is for adding a new cell to the active set at the time of soft handover and is a measurement report performed when the received signal level of the adjacent base station is higher than a certain reference level. Event 1B is for removing cells included in the active set during soft handover, and is a measurement report performed when the received signal level of an adjacent base station becomes lower than a predetermined standard. When the reception level of the adjacent base station is better than the reception level of the cell included in the active set in a state where the cell is included in the maximum number of cells that can be included in the active set, This is a measurement report that is performed to remove the worst cell of the signal quality and replace it with a new cell.

For example, if the received signal level of the new serving cell psc (200), psc (300) is measured to be higher than a certain reference level according to the movement of the UE, the UE transmits a new serving cell psc ), psc (300)) (540). On the other hand, when the signal level of the serving cell psc (100) included in the active set has been measured to be less than a predetermined reference level according to the movement of the UE, the UE calculates an Event 1B measurement A report may be sent 550. In this case, the wireless access network adds an active set to the serving cell psc (200), psc (300) to update the active set of the current terminal, and sets an active set An update message may be transmitted (560). Then, the terminal receives the active set update message and updates the active set of the terminal.

In this case, for example, when the preset reference serving cell is maintained in the updated active set (i.e., the reference serving cell is not removed), the UE operates based on the preset reference serving cell, Only the update to the serving cell can be performed. However, as another example, if the reference serving cell previously set by the active set update is removed, the UE needs to select a new reference serving cell.

For example, if the preset reference serving cell is the serving cell psc 100, if the serving cell psc 100 is removed by the above described active set update 560, (570).

Work In the embodiment  Criteria according to serving  How to choose

6 and 7 are flow charts for selecting a reference serving cell according to an embodiment.

Referring to FIG. 6, when the level of the received signal from the serving cell changes due to the movement of the UE, the UE can transmit the measurement report to the radio access network, receive the active update message from the radio access network, (610). At this time, the UE can determine whether a preset reference serving cell has been removed in the updated active set (620). If the preset reference serving cell is removed, the UE can select a new reference serving cell for acquiring timing synchronization (630).

Referring to FIG. 7, the UE may determine the priority of serving cells included in the active set to select a reference serving cell (631). In one example, the priority may be determined based on the transport channel supported by each serving cell included in the updated active set. At this time, the transport channel information may be provided in the active set update message or may be provided through upper layer signaling.

For example, the serving cell that supports at least one of the HS-DSCH transmission channel and the E-DCH transmission channel among the serving cells included in the updated active set is determined as a first rank, . For example, if the serving cell psc (200), psc (300) is added to the active set and the reference serving cell psc (100) 300) can be selected as the serving cell, and when the serving cell psc 200 supports the HS-DSCH / E-DCH transport channel, the serving cell psc 300 may be determined to be in a second order if the HS-DSCH / E-DCH transmission channel is not supported by the HS-DSCH / E-DCH. In this case, the UE can select the serving cell psc (200) in the first rank as the reference serving cell.

After that, the UE can determine whether there is a serving cell determined as a first rank (633), and if there is a serving cell determined as a first rank, the UE can determine the number of first serving cells (635). In this case, for example, when there is one serving cell as the first serving cell, the UE can select the serving cell as a reference serving cell.

However, as another example, when there are two or more determined serving cells, the serving cell determined as the first order may be sorted to the received signal level (637), and the serving cell having the highest received signal level may be sorted into the reference serving cell (639). For example, when both the serving cells psc (200) and psc (300) support the HS-DSCH / E-DCH transport channel, both cells are determined to be in a first rank, . In this case, the UE may need different decision criteria and can use the received signal level of each serving cell for this purpose. At this time, the received signal level may be the receiving signal code power (RSCP). For example, if the RSCP of the serving cell psc 200 is -60dB and the RSCP of the serving cell psc 300 is -55dB, the serving cell psc 300 can be selected as the reference serving cell .

As another example, if there is no serving cell determined as a first rank, the second determined serving cell may be sorted to a received signal level (634), and a serving cell having the highest received signal level may be selected as a reference serving cell (639). For example, if all the serving cells psc (200) and psc (300) do not support the HS-DSCH / E-DCH transport channel, the serving cells psc (200) and psc (300) The UE can use the received signal level of each serving cell to determine a reference serving cell, and the RSCP of the serving cell psc 200 is -60 dB, When the RSCP of the cell (psc 300) is -55 dB, the serving cell psc (300) can be selected as the reference serving cell.

As described above, when selecting a reference serving cell based on a transmission channel supported by a serving cell, the UE can select a serving cell having a timing signal robust against noise and interference as a reference serving cell, thereby obtaining more accurate timing synchronization . In addition, even when the reference serving cell is selected based on the received signal level, it is possible to receive a signal of a better quality, thereby accurately acquiring the timing synchronization.

A reference serving selection method according to a further embodiment

According to another embodiment, a UE determines a priority based on a transmission channel supported by a serving cell, and selects a serving cell having a higher priority as a reference serving cell. When there are a plurality of serving cells having the same priority, The reference serving cell can be selected based on the increase amount of the received signal level of each serving cell.

For example, when both the serving cells psc (200) and psc (300) support the HS-DSCH / E-DCH transport channel, both cells are determined to be in a first rank, . In this case, the UE can select the reference serving cell based on the increase amount of the received signal level of each serving cell. For example, if the RSCP increase of the serving cell psc 200 is 5dB and the RSCP increase of the serving cell psc 300 is 10dB, then the serving cell psc 300 may be selected as the reference serving cell .

According to another embodiment, the UE can determine a priority by assigning a predetermined weight to a transmission channel supported by a serving cell and a received signal level of each serving cell, and can select a reference serving cell based on the priority. For example, the weights of the transmission channel supported by the serving cell and the reception signal level may be set to 0.5: 0.5. At this time, a point of the serving cell supporting the HS-DSCH / E-DCH transmission channel is set to '1', and if it is not supported, the point can be set to '0'. In addition, the point for the received signal level can be calculated as the reciprocal of the received signal power. For example, when the received signal level is -10 dB, it can be calculated as 1/10 = 0.1 point.

In this case, for example, if the serving cell psc 200 supports the HS-DSCH / E-DCH transport channel and the received signal level is -60 dB, the point of the serving cell psc 200 is 1 * 0.5) + (1/60 * 0.5) = 0.5083. On the other hand, when the serving cell psc 300 does not support the HS-DSCH / E-DCH transmission channel and the received signal level is -55 dB, the point of the cell psc 300 is (0 * (1/55 * 0.5) = 0.0091. Therefore, in such a case, the UE can select the serving cell psc (200) as the reference serving cell.

According to another embodiment of the present invention, a UE selects a reference serving cell by setting a transmission channel supported by a serving cell as a first rank, and when the received signal level of the serving cell is less than a predetermined reference level, Another serving cell of the serving cell can be selected as the reference serving cell.

For example, it is possible to set not to select a serving cell having a received signal level of -55 dB or less. At this time, if the serving cell psc 200 supports the HS-DSCH / E-DCH transmission channel, the reception signal level is -60 dB, and the serving cell psc 300 is the HS- And the received signal level is -50 dB, the UE can prioritize the serving cell psc (200) in order of priority. However, the terminal may not select the serving cell psc (200) as the reference serving cell because the received signal level of the serving cell (psc 200) is -55 dB or less. On the other hand, the serving cell (psc 300) may be selected as a second serving cell or a bar serving as a reference serving cell with a signal level of -50 dB. At this time, if a plurality of serving cells satisfying the same criterion are collided, the terminal can select the reference serving cell based on the received signal level.

According to another embodiment, a UE selects a reference serving cell by setting a transmission channel supported by a serving cell as a first priority, and when the UE has a decreasing trend in a received signal level of the serving cell, Another serving cell of the rank can be selected as the reference serving cell.

For example, if the serving cell psc 200 supports the HS-DSCH / E-DCH transport channel, the received signal level is decreasing, and the serving cell psc 300 is the HS- When the reception signal level is increased without supporting the transmission channel, the UE can prioritize the serving cell psc (200) in order of priority. However, if the received signal level of the serving cell psc 200 is in a decreasing trend, the UE can determine that the UE is moving away from the serving cell psc 200 and minimize the change of the additional reference serving cell The serving cell psc 200 may not be selected as the reference serving cell.

On the other hand, if the serving cell psc 300 does not support the HS-DSCH / E-DCH transport channel and the received signal level increases, the UE determines that it is approaching the serving cell psc 300 It is determined that the possibility of the change of the reference serving cell is low, and the serving cell psc (300) can be selected as the reference serving cell.

When a plurality of serving cells having the same priority are in contention, the UE selects a serving cell having the best received signal level as a reference serving cell, or selects a serving cell having a higher received signal level as a reference serving cell .

8 is a block diagram of a terminal 800 according to an embodiment.

8, a terminal 800 for performing the above-described methods according to the present invention includes a processor 830 and a communication module 810 that can access and execute software codes stored in the memory 850 .

According to one example, the communication module 810 may receive an active set update message that instructs the terminal 800 to update the active set that includes at least one or more serving cells. The communication module 810 may transmit a measurement report of a predetermined reference serving cell generated by the processor to the radio access network when the value of the received signal level of the preset reference serving cell is less than or equal to a threshold value.

According to one example, the processor 830 may add or remove at least one serving cell to the active set based on the received active set update message, and the active set update message may remove , A new reference serving cell may be selected from the updated active set. At this time, the method of selecting the reference serving cell may be performed based on a priority for providing a reference of uplink synchronization required for uplink transmission of the UE to other serving cells in the active set, Can be determined based on the transport channels supported by each serving cell included in the active set.

The various embodiments and features described herein may be implemented in software, hardware, or a combination thereof. For example, a computer program executing a method and apparatus for performing embodiments of the present invention (executed by a processor, controller, CPU, etc., mobile terminal and / or network device of a computer) And may include at least one program code section or module. Likewise, a software tool that performs methods and apparatus for performing embodiments of the present disclosure (executed by a processor, controller, CPU, etc., mobile terminal and / or network device of a computer) And may include at least one program code section or module for performing the functions described herein.

Methods and apparatus for performing the embodiments of the present disclosure are compatible with various types of techniques and standards. The embodiments described herein relate to standards such as 3GPP (Global System for Mobile Communications (GSM), Wideband Code Division Multiple Access (WCDMA), UMTS, LTE, LTE-Advanced, etc.), IEEE 802, However, the above exemplary standards do not limit other related standards and techniques applicable to the various embodiments and features described herein.

The embodiments and features described herein may be implemented in various types of user devices (e.g., mobile terminals, handsets, wireless communication devices, etc.) and / or network devices, entities, components that support MTC and / .

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The detailed description above should not be construed as limiting unless expressly specified otherwise, and should be interpreted broadly within the scope of the claims. Accordingly, it is intended that all changes and modifications within the equivalent scope of the invention be included within the scope of the present invention and interpreted within the scope of the claims.

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

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 or essential characteristics thereof. Accordingly, the above description should not be construed in a limiting sense in all respects and should be considered illustrative. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the scope of equivalents of the present invention are included in the scope of the present invention.

800: terminal 810: communication module
830: Processor 850: Memory

Claims (14)

A method for performing a soft handover in a wireless communication system,
Receiving an active set update message instructing to update an active set including at least one serving cell set in the terminal;
Adding or removing at least one serving cell to the active set based on the active set update message; And
Selecting a new reference serving cell from the updated active set if a predetermined reference serving cell is removed from the terminal by the active set update message; , ≪ / RTI &
Wherein the selection of the reference serving cell is performed based on a priority for providing a reference of uplink synchronization to the terminal in uplink transmission of the terminal to other serving cells in the active set,
Wherein the priority is determined based on a transport channel supported by each serving cell included in the updated active set. The method according to claim 1,
The priority order is determined such that the serving cell supporting at least one of the HS-DSCH transmission channel and the E-DCH transmission channel among the serving cells included in the updated active set is determined as a first rank, Determining a ranking. The method according to claim 1,
When a plurality of serving cells having the same priority are present, selecting a serving cell having a highest received signal level among serving cells determined to have the same priority as a reference serving cell. The method of claim 3,
Wherein the received signal level is a Receiving Signal Code Power (RSCP). The method according to claim 1,
Transmitting a measurement report for the predetermined reference serving cell if the received signal level value of the preset reference serving cell is less than or equal to a threshold value; ≪ / RTI > The method according to claim 1,
Wherein the transport channel information is included in the active set update message. The method according to claim 1,
Wherein the transport channel information is provided via upper layer signaling. 1. A terminal performing soft handover in a wireless communication system,
A communication module for receiving an active set update message instructing to update an active set including at least one serving cell set in the terminal; And
A processor; / RTI >
The processor
Adding or removing at least one serving cell to the active set based on the received active set update message,
Selecting a new reference serving cell from the updated active set if the preset serving cell is removed from the active set by the active set update message,
Wherein the selection of the reference serving cell is performed based on a priority for providing a reference of uplink synchronization to the terminal in uplink transmission of the terminal to other serving cells in the active set,
Wherein the priority is determined based on a transport channel supported by each serving cell included in the updated active set. 9. The method of claim 8,
The priority order is determined such that the serving cell supporting at least one of the HS-DSCH transmission channel and the E-DCH transmission channel among the serving cells included in the updated active set is determined as a first rank, Determining a ranking of the terminal. 9. The method of claim 8,
And selects, as a reference serving cell, a serving cell having a highest received signal level among the serving cells determined to have the same priority, when a plurality of serving cells having the same priority exist. 11. The method of claim 10,
Wherein the received signal level is a Receiving Signal Code Power (RSCP). 9. The method of claim 8,
Wherein the processor transmits a measurement report for the predetermined reference serving cell if the received signal level value of the predetermined reference serving cell is less than or equal to a threshold value. 9. The method of claim 8,
Wherein the transport channel information is included in the active set update message. 9. The method of claim 8,
Wherein the transport channel information is provided through upper layer signaling.

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