WO2012093888A2 - Device and method for selecting cell in wireless communication system - Google Patents

Abstract

The present invention relates to a device and a method for selecting a cell in a wireless communication system. The invention enables a terminal to receive a first cell range expansion (CRE) bias through a first message and to receive a second CRE bias, in which the first CRE bias is modified, through a second message such that a cell is selected on the basis of said second CRE bias. In this case, said first and second CRE biases are offsets which are added to the signal strength of a micro cell, and thus, said terminal selects the micro cell if a sum of the second CRE bias and the signal strength of the micro cell is larger than the signal strength of a macro cell. Since the present invention provides different CRE bias values to an unallowed user for a CSG cell and an allowed user therefor, the unallowed user for the CSG cell can confirm the CSG cell in advance, thereby preventing a radio link failure (RLF).

Description

Apparatus and method for cell selection in a wireless communication system

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

Wireless communication systems are widely deployed to provide various kinds of communication services such as voice and data. A wireless communication system is a multiple access system that can support communication with multiple users by sharing available system resources (bandwidth, transmission power, etc.). Examples of multiple access systems include code division multiple access (CDMA) systems, frequency division multiple access (FDMA) systems, time division multiple access (TDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and single carrier frequency (SC-FDMA). division multiple access) system.

As various communication systems emerge, a heterogeneous network environment in which various cells coexist in a short distance is being considered. For example, there is a micro cell having relatively low power transmission power, such as a pico cell and a femto cell, in the coverage of one macro cell. In addition, the cell can be classified into an open access (OA) cell that can be serviced at any time if necessary without a separate access restriction, and a closed subscriber group (CSG) cell that allows access only to specific users. Can be.

On the other hand, cell selection is a technique for the UE to select a specific cell to receive the service. The cell selection may include initial cell selection for selecting a cell to be initially connected after the terminal is powered on, and cell reselection for selecting a cell again while the terminal stays in the cell. Hereinafter, unless otherwise specified, cell selection includes initial cell selection and cell reselection. The terminal searches for a radio channel for cell selection. When the UE finds a suitable cell that satisfies the cell selection criteria, the UE selects the corresponding cell.

Meanwhile, as cells having various coverages appear in heterogeneous networks, it is required to perform cell selection and handover more efficiently.

For example, when the signal strengths of the macro base station and the pico base station are similar, since the pico cell provides a higher data rate than the macro cell, the terminal having a high data traffic may select the pico cell. On the other hand, if too many terminals are concentrated in the pico cell, the quality of service may be deteriorated. Therefore, a load balancing technique for properly distributing terminals between the pico cell and the macro cell is needed.

In consideration of such a network environment, in a next-generation wireless communication system, a cell selection method considering heterogeneous networks requires a method for satisfying load balancing without changing actual transmission power. In addition, when offset values are used without actually controlling the transmission power to balance the load, a method of compensating for performance degradation caused by intercell interference power in an extended cell region is urgently needed.

The present invention provides an apparatus and method for performing cell selection between a macro cell and a micro cell in a wireless communication system.

The present invention provides an apparatus and method for performing handover between a macro cell and a micro cell in a wireless communication system.

The present invention provides an apparatus and method for pre-detecting a closed user group (CSG) cell between a macro cell and a micro cell in a wireless communication system.

The present invention provides an apparatus and method for adjusting cell coverage in a wireless communication system.

The present invention provides an apparatus and method capable of effectively adjusting the load between cells in a wireless communication system.

The present invention provides an apparatus and method for preventing a terminal from detecting a CSG cell in advance and falling into a radio link failure state in a wireless communication system.

According to an aspect of the present invention, in a wireless communication system, a method in which a terminal performs detection / cell selection / handover of a CSG cell in advance may include receiving a first cell range expansion (CRE) bias through a first message; Receiving a second CRE bias with a modified 1 CRE bias via a second message and performing cell selection / handover based on the second CRE bias, wherein the first and second CRE bias are micro ( Macro) is an offset added to the signal strength of the cell, and the sum of the signal strength of the second CRE bias and the micro (macro) cell is greater than the signal strength of the macro (micro) cell and is allowed to the micro (macro) cell (allowed-UE ), The micro (macro) cell is selected / handed over.

In this case, when the sum of the CRE bias of the second micro cell and the signal strength of the micro cell is greater than the signal strength of the macro cell for a predetermined time, the micro cell may be selected by the terminal.

Here, the first and second messages may be cell specific messages of the serving / neighbor cell, or may be terminal specific messages of the serving cell, and the first message is a cell specific message of the serving / neighbor cell and the second message. May be a terminal specific message of the serving cell.

According to another aspect of the present invention, a method for adjusting cell coverage by a base station in a wireless communication system includes receiving a measurement result or terminal capability from at least one terminal or network in a cell, based on the measurement result Determining whether to adjust the coverage; correcting the CRE bias when the coverage of the cell is determined; and transmitting the modified CRE bias to the at least one terminal.

According to another aspect of the present invention, a cell selection and handover method of a terminal in a wireless communication system includes the steps of: determining, by the terminal, whether the cell is a CSG cell to which the terminal cannot access; transmitting a CRE bias to the terminal; Receiving a measurement result reflecting the CRE bias from the terminal; And if it is determined that the measurement restriction is necessary based on the measurement result, transmitting a measurement limit setting command to the terminal.

In this case, the at least one terminal performs cell selection / handover based on the modified CRE bias, wherein the modified CRE bias is an offset added to the signal strength of the micro cell, and the modified CRE bias and the signal strength of the micro cell are adjusted. If the sum is greater than the signal strength of the macro cell, the micro cell may be selected / handed over.

The modified CRE bias may be transmitted through a cell specific message or may be transmitted through a terminal specific message.

If the neighboring micro cell is a CSG, the CSG bias value of the CSG cell is given to an unauthorized terminal, thereby preventing the UE from entering the CSG cell and detecting the CSG cell in advance before falling into the RLF due to severe interference from the CSG base station. It may be.

According to the present invention, load balancing between cells in a wireless communication system can be made more efficient, and cell coverage can be effectively adjusted.

In addition, the terminal can guarantee a higher quality of service (QoS), and in particular, the terminal that is not allowed to the closed subscriber group (CSG) cell detects the CSG cell in advance and falls into a radio link failure (RLF). It has the advantage of being preventable.

1 is a diagram schematically illustrating the concept of a network consisting of a macro cell, a femto cell and a pico cell.

2 illustrates cell selection or handover according to an embodiment of the present invention.

3 illustrates cell selection or handover according to an embodiment of the present invention.

4 illustrates cell selection or handover according to an embodiment of the present invention.

5 illustrates cell selection or handover according to an embodiment of the present invention.

6 illustrates cell selection or handover according to an embodiment of the present invention.

7 is a flowchart illustrating a general handover process.

8 is a flowchart illustrating a handover process according to an embodiment of the present invention.

9 illustrates an example in which a CRE bias is not applied based on a terminal category according to an embodiment of the present invention.

10 illustrates an example of applying a CRE bias based on a terminal category according to an embodiment of the present invention.

11 is a flowchart illustrating an operation of a terminal in an RRC connected state for performing handover according to the present invention.

12 is a flowchart illustrating a process of reselecting a cell using a cell selection offset according to the present invention.

13 illustrates another example of a cell reselection process using a cell selection offset according to the present invention.

14 is a flowchart illustrating the operation of a base station according to an embodiment of the present invention.

15 is a flowchart schematically illustrating an embodiment in which a CSG cell is present in a system to which the present invention is applied.

FIG. 16 is a diagram schematically illustrating an embodiment in which a CSG cell is present in a system to which the present invention is applied.

17 is a block diagram of a transmission and reception apparatus according to an embodiment of the present invention.

Hereinafter, some embodiments will be described in detail with reference to the accompanying drawings. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are assigned to the same components as much as possible even though they are shown in different drawings. In addition, in describing the embodiments of the present specification, when it is determined that a detailed description of a related well-known configuration or function may obscure the gist of the present specification, the detailed description thereof will be omitted.

Herein, the wireless communication system will be described as an example, and in particular, a next generation wireless communication system supporting a plurality of CCs will be described as an example. However, one embodiment of the present specification provides asynchronous wireless communication that evolves to Long Term Evolution (LTE) and LTE-advanced (LTE-A) through GSM, WCDMA, and HSPA, and synchronous evolution to CDMA, CDMA-2000, and UMB. It can be applied to a wireless communication system.

In the present specification, a wireless communication system includes a user equipment (UE) and a base station (evolved Node-B, eNB), and the terminal may be fixed or mobile, and may have a mobile station (MS) and a mobile terminal (MT). It may be called other terms such as a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant, a wireless modem, a handheld device, and the like. It may also be called a terminal, a user and a user device.

A base station (eNB) generally refers to a fixed station for communicating with a terminal, and may be referred to by other terms such as a base transceiver system (BTS) and an access point. The eNB may provide services for one or more cells. Meanwhile, a cell may be classified into a macro cell or a micro cell based on coverage (or maximum transmission power). Macro cells have wider coverage or greater transmit power than micro cells. The micro cell may be referred to in other terms, such as a pico cell, a femto cell.

A heterogeneous network may be configured as a network in which a micro cell exists within the coverage of a macro cell. In the present specification, the use of micro cells such as pico cells and femto cells is not particularly limited, but in general, pico cells are communication shadow areas that are not covered by macro cells alone, or areas where data service demands are high, so-called hot zones. It can be used to. For example, femto cells may be generally used in indoor offices or homes.

1 is a diagram schematically illustrating a concept of a heterogeneous network including a macro cell, a femto cell, and a pico cell. Although FIG. 1 illustrates a heterogeneous network composed of a macro cell, a femto cell, and a pico cell for convenience of description, the heterogeneous network may include a relay or another type of cell.

Referring to FIG. 1, a macro cell 10, a femto cell 20, and a pico cell 30 are operated together in a heterogeneous network. The macro cell 10, femto cell 20, and pico cell 30 each have their own cell coverages 10, 20, 30. A femto cell is a low power wireless access point, which is a small base station for mobile communication used indoors such as a home or an office. A femto cell can access a mobile communication core network using DSL or cable broadband in a home or office.

Cells may be classified into open access (OA) cells and closed subscriber group (CSG) cells according to user accessibility. The CSG cell basically aims to provide specialized services only to members belonging to the CSG. The micro cell may be an OA cell or a CSG cell.

The terminal may be defined and used as a pico-cell user equipment (PUE) and a macro-cell user equipment (MUE). PUE is a terminal that uses a micro cell such as a pico cell as a serving cell. In the present invention, not only the pico cell but also the femto cell, the terminal including the micro cell as the serving cell is referred to as PUE. The MUE is a terminal having a macro cell as a serving cell.

The state of the UE is divided into an RRC connected state and an RRC idle state according to whether the RRC is connected to the radio resource control (RRC).

First, in the RRC idle state, the UE operates as follows. At this time, one or several of the following operations may be performed simultaneously or sequentially. In each state, you can do the following, but that doesn't mean that they happen sequentially:

The terminal is configured with UE-specific Discontinuous Reception (DRX) by non-access stratum (NAS). Here, DRX is a function of controlling the terminal to stop the reception operation and sleep (sleep) in order to reduce the power consumption of the terminal. In addition, a cell selection and cell reselection process may be performed to find a suitable cell as a serving cell to a corresponding UE among neighbor cells. Here, the cell reselection process refers to a process for moving to the best cell in the state of cell selection.

The terminal monitors system information (SI) transmitted from a serving cell. The serving cell refers to a cell that has completed camp-on. Here, the camp-on refers to a state in which the terminal completes a cell selection or reselection process and monitors system information and paging information.

The terminal monitors a paging channel.

Second, in the RRC connected state, the terminal operates as follows. At this time, one or several of the following operations may be performed simultaneously or sequentially. In each state, you can do the following, but that doesn't mean that they happen sequentially:

The terminal may transmit / receive unicast data. The terminal may configure and operate a terminal specific DRX defined by a media access control (MAC) layer of the base station. In addition, the terminal monitors the paging channel, SIB1 (System Information Block Type 1), system information, control channel, and the like. At this time, the monitor is progressed at a different period from the RRC idle state (generally shorter than the cycle of the RRC idle state).

The base station may transmit information constituting the operation of the terminal so that the terminal can obtain the channel information, the terminal transmits the channel quality information (CQI), measurement information and the like to the base station according to the configured information You can report.

When the base station determines that the signal strength of the neighbor cell is more suitable for the terminal based on a rule determined based on the information reported by the terminal, the base station may handover the terminal to the neighbor cell. Herein, the cell to be handed over may be another base station of the same frequency band (hereinafter, an intra-frequency base station), the same base station of another frequency band or another base station (hereinafter, an inter-frequency base station). Or an inter-RAT (inter-RAT (Radio Access Technologies)) base station using another radio transmission scheme.

Cell range expansion (CRE) refers to increasing the coverage of a micro cell in order to benefit from network load balancing. As the coverage of the microcells increases, the number of acceptable terminals also increases. Here, load balancing may be performed when traffic loads of several cells are unevenly distributed. For example, when over-traffic occurs in a cell, a user may be sent from the cell where the over-traffic occurs to another cell through a handover or a cell reselection method.

According to the present specification, CRE bias refers to an offset added to the signal strength of a cell to apply CRE. Hereinafter, the signal strength of the micro cell is denoted by Smc, the signal strength of the macro cell is denoted by Smm, and the CRE bias is denoted by Sb. Sb1 refers to the first CRE bias, Sb2 refers to the second CRE bias, and Sb3 refers to the third CRE bias.

For example, if Smc + Sb> Smm is maintained for a predetermined time, the MUE may perform handover to the micro cell. The larger Sb is, the higher the probability that the MUE is handed over to the micro cell, and serves to increase the coverage of the micro cell.

As an example of the CRE bias, a variable used in the handover process may be used. Variables used in the handover process include Ocn and Ocs. Here, Ocn is a cell specific offset value added to the measured value of the adjacent cell, and Ocs is a cell specific offset value added to the measured value of the serving cell. Default values of the Ocn and the Ocs may be set to 0, and the Ocn and the Ocs are transmitted through an RRC message. In this case, when the value of the Ocn and Ocs has the same value for a plurality of terminals, it may be transmitted through a cell specific message, when the different Ocn and Ocs is set for each terminal, the value of the Ocn and Ocs May be transmitted through a terminal specific message.

Hereinafter, the UE specific message is a message transmitted to a specific UE in a cell, and includes an RRC message and a MAC message, and the messages are transmitted through a physical downlink shared channel (PDSCH) or a physical downlink control channel (PDCCH). Can be sent through.

In addition, the cell specific message may include an RRC message including system information transmitted to all UEs in the cell, and the RRC message may be transmitted through a PDSCH or through a broadcasting channel (PBCH).

Meanwhile, the signal strength is an index indicating power / quality of a corresponding cell, and parameters such as CQI (Channel Quality Indicator), RSRP (Reference Signal Received Power) and / or RSRQ (Reference Signal Received Quality) may be used. Here, the RSRP refers to a linear average of power of resource elements (REs) carrying a cell-specific reference signal (CRS) in a measurement frequency band. RSRQ may be expressed as N * RSRP / (E-UTRA carrier RSSI), where N denotes the number of RBs in the Evolved Universal Terrestrial Radio Access (E-UTRA) carrier RSSI measurement band, and the E-UTRA carrier RSSI (Received) Signal Strength Indicator) refers to a linear average value of a signal received in an entire OFDM symbol including RS of antenna port 0 at a measurement frequency. The RSSI is a value that includes both interference and thermal noise of adjacent channels.

2 illustrates cell selection or handover according to an embodiment of the present invention.

Referring to FIG. 2, the PUE 300 is in the first coverage 210 of the micro cell 200 and uses the micro cell 200 as a serving cell. Assume that the CRE bias at this time is Sb1. That is, the first coverage 210 of the micro cell 200 is set to Sb1.

The micro cell 200 adjusts the CRE bias Sb1 to inform the PUE 300 of the CRE bias Sb2 having a smaller value than before. The adjusted CRE bias Sb2 may inform the PUE 300 by the micro cell 200 through a terminal specific message.

Since Sb2 has a smaller value than Sb1, the second coverage 220 of the adjusted micro cell 200 is smaller than the first coverage 210 in the determination for cell selection or handover.

Therefore, when Smc + Sb2 <Smm, the PUE 300 may select the macro cell 100 or perform a handover to the macro cell 100.

3 illustrates cell selection or handover according to an embodiment of the present invention.

Referring to FIG. 3, the adjusted CRE bias Sb2 informs the PUE 300 through the cell specific message by the micro cell 200. All terminals in the micro cell 200 may receive the adjusted CRE bias Sb2.

Since Sb2 220 has a smaller value than Sb1 210, the second coverage 220 of the adjusted micro cell 200 becomes smaller than the first coverage 210 in the determination for cell selection or handover. .

Therefore, when Smc + Sb2 <Smm, the PUE 300 may select the macro cell 100 or perform a handover to the macro cell 100.

4 illustrates cell selection or handover according to an embodiment of the present invention.

Referring to FIG. 4, the MUE 300 is within the coverage of the macro cell 100 and uses the macro cell 100 as a serving cell. Let CRE bias be Sb1.

The macro cell 100 adjusts the CRE bias Sb1 to inform the MUE 300 of the CRE bias Sb3 having a larger value than before. The adjusted CRE bias Sb3 may inform the MUE 300 through the UE-specific message by the macro cell 100.

Since Sb3 has a larger value than Sb1, the second coverage 260 of the adjusted micro cell 200 is larger than the first coverage 250 in the determination for cell selection or handover.

Accordingly, the MUE 300 may perform handover or cell selection to the micro cell 200.

5 illustrates cell selection or handover according to an embodiment of the present invention.

Referring to FIG. 5, the adjusted CRE bias Sb3 (CRE bias with a larger value than before) is transmitted through a cell specific message of the micro cell 200, and the MUE 300 listens to the adjusted CRE bias Sb3 ( listen).

Since Sb3 has a larger value than Sb1, the second coverage 260 of the adjusted micro cell 200 becomes larger than the first coverage 250 in the determination for cell selection or handover.

Accordingly, the MUE 300 may perform cell selection or handover to the micro cell 200.

6 illustrates cell selection or handover according to an embodiment of the present invention. The coverage boundary of the cell may be in various forms such as an actual circle or an ellipse.

Referring to FIG. 6, in cell reselection determination, cell coverage may be applied in various forms. For example, although the MUE 310 belongs to the coverage of the macro cell in the determination of cell reselection even if it is separated by the same distance from the base station of the micro cell, the MUE 300 may belong to the coverage of the micro cell. That is, it is conceivable to induce cell reselection or handover by adjusting the CRE bias only for the MUE 300.

The adjusted CRE bias Sb3, that is, the CRE bias Sb3 having a larger value than before, is transmitted to the MUE 300 through a terminal specific message of the macro cell 100.

Since Sb3 has a larger value than Sb1, in the determination for cell selection or handover, the adjusted second coverage 260 of the micro cell 200 becomes larger than the first coverage 250.

Accordingly, the MUE 300 may perform cell selection or handover to the micro cell 200.

The micro cell (pico cell) becomes a hot spot zone. Here, the hot spot area refers to a cell with a relatively high load. If the value of the CRE bias is fixed, a situation in which the micro cell cannot cover all the terminals may occur when the load of the micro cell is increased. On the contrary, consider the case where the number of terminals in the micro cell is small and the number of terminals in the macro cell is relatively large. If the bias value is fixed, it is difficult to balance the load because it is difficult to handover the terminal to the micro cell.

When the CRE bias is sent through the UE-specific message, a unique CRE bias can be designated for each UE. Even in a terminal located at the same location, link reliability (e.g., an error rate) varies depending on the capability of the terminal, so that a CRE bias can be specified for each terminal to provide an appropriate service to each terminal. have. The coverage of the micro cell may vary for each terminal.

7 is a flowchart illustrating a general handover process.

Referring to FIG. 7, when the terminal reports the measurement result to the source base station (S710), the source base station prepares for handover with the target base station (S720). When the source base station notifies the terminal of the RRC connection reconfiguration (S730), it performs a random access procedure (S740). The UE informs the target base station of the RRC connection reconfiguration complete (S750).

Hereinafter, a cell selection or handover method for balancing a load using a CRE bias will be described by dividing a case where the UE is in an RRC connected state and a case where the UE is in an RRC idle state.

1. When the terminal is in the RRC connection state

8 is a flowchart illustrating the handover of a UE in an RRC connected state according to the present invention. Hereinafter, in the description of FIG. 8, the UE may be a MUE or a PUE. When the terminal is MUE, the base station means a macro base station, and when the terminal is a PUE, the base station means a pico base station (or femto base station).

Referring to FIG. 8, first, a UE in an RRC connection state reports a measurement result to a base station (S810). The measurement result may be a measurement result of reporting a measurement result measured periodically, or may be an event-triggering measurement result measured when an event occurs.

The following Table 1 shows an example of an event that the terminal reports to the base station.

Table 1

event	Report purpose
A1	The signal strength of the serving cell is greater than the threshold
A2	The signal strength of the serving cell is less than the threshold
A3	The signal strength of the neighboring cell is offset by more than the serving cell plus the additional margin
A4	NAVER cell has signal strength above threshold
A5	The signal strength of the serving cell is less than the first threshold and the signal strength of the neighbor cell is greater than the second threshold.
B1	Signal strength of inter RAT neighbor cell is higher than threshold
B2	The signal strength of the serving cell is less than the first threshold, and the signal strength of the inter RAT navigator cell is greater than the second threshold.

The terminal reports the events of A1 to B2 to the base station according to each purpose. The occurrence report of the event and the measurement result measured at this time may be the selection criteria of the handover.

Subsequently, the base station requests a change of the CRE bias from the mobility management entity (MME) based on the measurement result or the performance of the terminal (S820). The base station may change the CRE bias value based on the measurement result.

The MME informs the base station of the changed CRE bias in response to the request (S830). If the MME can command the change of the CRE bias value without the request of the base station, the base station may change the CRE bias value based on the CRE bias transmitted by the MME. In this case, step S810 or S820 may be omitted.

Alternatively, when MMEs managing cells affected by the changed CRE bias are different, information exchange between MMEs (loading of cells managed by MMEs, base station configuration information (paging configuration), and the number of antennas of a base station) , Frequency band to be used) and the like can be used to change the CRE bias value. For example, in a situation where a change in the CRE bias of the pico cell is required, and the macro cell is affected by such a change in the CRE bias, the MME managing the macro base station is referred to as MME1, and the MME managing the pico base station is called. Let's call it MME2. If the pico base station requests the MME2 to change the CRE bias, the MME2 may exchange this information with the MME1 and then inform each base station of the changed CRE bias.

The information transmitted to the base station by the MME may be an RFSP index (RAT / Frequency Selection Priority Index) determined by the MME based on an operator's policy and context information of the terminal. The RFSP index is terminal specific and is a value received by the MME from a home subscriber server (HSS). The base station receiving this information can change the CRE bias value based on this information.

On the other hand, the base station can change the CRE bias without the response of the MME based on the measurement result or the performance of the terminal measured in step S810. In this case, steps S820 and S830 may be omitted.

Alternatively, the base station itself may determine the load balance to change the CRE bias value. In this case, steps S810, S820, and S830 may be omitted.

In this way, the base station determines whether it is necessary to balance the load based on information (eg, over-traffic or the like) for the neighbor cell, and changes the CRE bias value (S840). Step S840 does not change the CRE bias value when it is desired to change the CRE bias value for reasons other than load balancing or when it is not necessary to balance the load. That is, step S840 is optionally performed.

The base station transmits a CRE bias to the terminal (S850). The modified CRE bias is transmitted through steps S810 to S840. If the CRE bias is not changed as all or part of steps S810 to S840 are omitted, the CRE bias is transmitted without changing the CRE bias. The CRE bias may be transmitted through a cell specific message or a terminal specific message. The CRE bias may be transmitted through a broadcast channel or a common channel, or may be transmitted through a dedicated channel.

The terminal performs a handover process based on the received CRE bias (S860). The handover process is performed by applying the received CRE bias to the measurement result. The handover process may proceed simultaneously with the UE receiving the CRE bias from the base station in step S850.

As another embodiment of the present invention, steps S810 to S860 described in FIG. 8 may also be applied to an example in which the UE hands over from a serving cell to a target cell.

First, the terminal reports the measurement result to the serving cell. The measurement result may be a measurement result measured periodically or an event-triggered measurement result measured when an event occurs.

Subsequently, the serving cell requests the target cell to change the CRE bias based on the measurement result or the performance of the UE. The serving cell may change the CRE bias value based on the measurement result.

The target cell informs the serving cell of the changed CRE bias in response to the request. If the target cell can instruct the change of the CRE bias value without the request of the serving cell, the serving cell can change the CRE bias value based on the CRE bias transmitted to the target cell. On the other hand, the serving cell can change the CRE bias based on the measurement result or the performance of the UE measured without the response of the target cell. Alternatively, the serving cell may determine the load balance by itself and change the CRE bias value.

As described above, the serving cell determines whether the load needs to be balanced based on information on the neighbor cell (for example, whether over traffic or the like), and changes the CRE bias value. If you want to change the CRE bias value for reasons other than load balancing, or if you do not need to balance the load, do not change the CRE bias value.

The serving cell transmits a CRE bias to the terminal. If the CRE bias is changed in the previous procedure, the changed CRE bias is transmitted. If the CRE bias is not changed, the CRE bias is transmitted without changing the CRE bias. The CRE bias may be transmitted through a cell specific message or a terminal specific message. The CRE bias may be transmitted over a broadcast channel or a shared channel, or may be transmitted over a dedicated channel.

The terminal performs handover based on the received CRE bias. Handover is performed by applying the received CRE bias to the measurement result. Handover may proceed simultaneously with the UE receiving the CRE bias from the serving cell.

The CRE bias may be transmitted through a cell specific message or may be transmitted through a terminal specific message. That is, CRE bias can be applied cell-specifically, but UE-specific can also be applied. For example, cell selection or handover may be performed by applying a CRE bias based on a terminal category. Here, the category of the terminal may be a category for distinguishing whether the terminal is a high-end terminal or a low-end terminal, and other types of categories may be possible.

9 and 10 will be described below, which is more effective when the CRE bias is applied to the UE specificly than when the CRE bias is applied to the cell. Hereinafter, the description of the pico cell may be applied to the femto cell.

9 illustrates an example in which a CRE bias is not applied based on a terminal category.

Referring to FIG. 9, in the case of the region 920 of the pico cell adjusted to load balance by applying a cell-specific CRE bias to an area 910 of the first pico cell, too many terminals are pico cells. There is room for over-traffic in the pico cell.

In this case, rather than applying the cell-specific CRE bias to reduce the pico cell area again to balance the load, the CRE bias based on the category of the UE in order to balance the load effectively while maintaining the system throughput through the CRE bias. You can apply the value.

10 illustrates an example in which a CRE bias is applied based on a terminal category according to the present invention.

Referring to FIG. 10, a terminal-specific CRE bias value is applied. The CRE bias is applied to include the high-end terminal and not the low-end terminal based on the category of the terminal. At this time, the area of the pico cell is extended to the range including the high-end terminal. However, the low-end terminal is not included. Therefore, the number of UEs included in the region 930 of the extended pico cell is smaller than when the cell-specific CRE bias value is applied. Thus, it is more selective and effective to load balance while maintaining the gain (eg system gain) that can be gained by using CRE.

11 is a flowchart illustrating an operation of a terminal in an RRC connected state in performing a handover according to the present invention.

Referring to FIG. 11, the terminal receives a CRE bias (S1110). The measurement result is reported to the base station based on the received CRE bias value (S1120). Here, the measurement result may include at least one of RSRP, RSRQ, CQI, and an event. Refer to Table 1 above regarding events. For example, when it is measured that the signal strength of the neighbor cell is stronger than the serving cell, the terminal reports the event A3 to the base station.

Based on the measurement result received by the base station from the terminal, the base station proceeds to handover according to the present invention from the serving cell to the neighbor cell (S1130). For example, the handover described with reference to FIGS. 8 to 10 may be performed.

2. When the terminal is in the RRC idle state.

Hereinafter, a method of performing cell selection by applying a CRE bias to a UE in an RRC idle state will be described.

First, the cell selection criteria are as follows.

Equation 1

Here, S _rxlev is a cell selection reception (RX) level value and a unit is decibel (dB). S _qual is a cell selection quality value and the unit is decibels. Q _rxlevmeas is the measured cell RX level value and Q _qualmeas is the measured cell quality value. Q _rxlevmin is the minimum value of the required RX level in the cell, and the unit is dBm. dBm is the actual power (milliwatt) converted to dB (decibels). Q _qualmin is the minimum of the required quality level in the cell and is in dB. Q _{rxlevminoffset} is an offset value used to determine the S _rxlev value, and periodically searches for the original land network (PLNM) when camping on another site (VLMN). By performing a search, the offset value is given to the user's network so that the user's network can be accessed. Q _{qualminoffset is} also an offset value used to determine S _{qual for} the same purpose. P _compensation is the larger value of PEMAX-P _powerClass and 0, PEMAX is the maximum value of the uplink Transmission (TX) power level used by the terminal allowed by the upper layer, P _PowerClass is the terminal The maximum value of the RF (Radio Frequency) output power of a terminal according to a power class.

The cell reselection criteria are as follows.

Equation 2

Here, Q _meas is the RSRP measurement value (quantity) to be used in the cell reselection, Qoffset is intra- If a case that the frequency cell reselection, Qoffset _{s, n} is present, and Qoffset _{s, n} value, and if not 0 to be. Also, Qoffset inter-frequency cell when the Qoffset _s with respect to the case of _{reselection, n} present the sum of the Qoffset _{s, n} and Q _{offsetfrequency} value, otherwise has a Q value _{offsetfrequency.} Here, the Qoffset value refers to an offset value additionally applied to the RSRP measurement value of the neighbor cell in the cell reselection process. Qoffset _{s, n} is an offset between the serving cell and the neighbor cell. The Qoffset _{s, n} value may have a value of −24 dB to 24 dB and may be set in units of 2 dB. Q _{offsetfrequency} can be used when inter-frequency cell reselection (because one base station operates differently for each frequency, there is a concept of handover and reselection). ) Offset, which is a variable used to give priority to each frequency in the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) of LTE. For example, this offset can be used to balance the load to prevent the user from being concentrated in the preferred frequency band. Therefore, the higher the R value including both the R value, that is, R _s and R _n values, the terminal preferentially selects the corresponding cell when the cell is reselected.

Meanwhile, the definition of RSRQ considered in the present invention is as follows.

In the LTE system to which the present invention is applied, the RSRQ may be expressed as N * RSRP / (E-UTRA carrier RSSI), where N is an Evolved Universal Terrestrial Radio Access (E-UTRA) carrier RSSI measurement block in all RBs in a frequency band ) Means the number. In general, it may be the downlink frequency bandwidth of one cell.

In addition, the E-UTRA carrier RSSI (Received Signal Strength Indicator) is a linear average of signals received on all OFDM symbols with respect to OFDM symbols including RS among the signals transmitted through antenna port 0 at the RSSI measurement frequency. It means the value. The RSSI is a value that includes both interference and thermal noise of adjacent channels. If the UE receives an indication of the subframe for the RSRQ measurement from a higher layer (for example, when the UE receives information for distinguishing between the RSRQ measurable subframe and the RSRQ non-measurable subframe), the UE at the RSSI measurement All OFDM symbols of the indicated subframe are measured, not just the OFDM symbols including the RS. The measured RSRQ value may be applied to the RRC idle mode and the RRC connected mode, and may also be applied to the same frequency band and different frequency band as the current serving cell for each mode. The RSRQ value is measured at an antenna connector of the UE.

In the present invention, when it is confirmed that the absolute value of the offset (Qoffset _{s, n} ) value has a predetermined value or a value exceeding a threshold transmitted through a broadcasting channel, the terminal in the macro cell or pico cell is determined from an upper layer. It is assumed that the subframe for the RSRQ measurement is received, and the idle mode UE starts measuring the RSSI in all OFDM symbols of the subframe in which the RSRQ measurement is indicated during the RSRQ measurement. If the UE does not have information for distinguishing between the RSRQ measurable subframe and the RSRQ non-measurable subframe from the eNB, the UE determines that RSRQ measurement has been indicated for all subframes. In addition, the terminal may activate a Time Divisino Multiplexing (TDM) enhanced Inter Cell Interference Coordination (eICIC) mode. In addition, in order to measure RSRP and / or RSRQ in Layer 1 (physical layer), an RRM measurement cycle that can be configured in the terminal may be changed. The measurement period is set in subframe units. When the RRM measurement cycle is changed, the FDD is changed to a cycle other than a multiple of 40 ms, and the TDD is changed to a cycle that is not a multiple of 20 ms and 70 ms and 50 ms.

The predetermined specific value may be set to a fixed value, and may be set to one of 5 dB or 10 dB or 15 dB or 20 dB. In addition, the threshold transmitted through the broadcasting channel may be transmitted through SIB4 and may be configured as shown in Table 2 below.

TABLE 2

SystemInformationBlockType4 :: = SEQUENCE {

...,

threshTDMeICIC ReselectionThreshold, OPTIONAL,-Need ON

...,

}

Here, the ReselectionThreshold value may be expressed as an integer having a value of 0 to 31, and the actual application value may be applied as it is or set to N times. For example, if the ReselectionThreshold value is 5 and N is 2, the actual value applied is 5 * 2 = 10dB. If the value is not set, one of 5 dB or 10 dB or 15 dB or 20 dB may be set as an initial value.

For example, a terminal configured to set a macro cell or a pico cell as a serving cell may operate as follows. First, the terminal checks the information of the broadcasting channel received from the serving cell. It is checked whether there is a Qoffset _{s, n} value for a neighbor cell among the information transmitted through the broadcasting channel. If the value does not exist, the value of Qoffset _{s, n} neighbor cells is set to zero. If at least one piece of information on a neighbor cell whose absolute value of Qoffset _{s, n} for a particular neighbor cell is greater than or equal to a threshold value is identified, the UE regards the subframe for measuring the RSRQ from an upper layer and receives the RSRQ in the idle mode. In the measurement, an operation of measuring RSSI in all OFDM symbols of a subframe indicated by RSRQ measurement is started.

In addition, in the present invention, when the UE which sets the macro cell or the pico cell or the cell corresponding thereto as the serving cell confirms that the CSG cell such as the femto cell exists in the neighbor cell, the UE performs subframes for the RSRQ measurement from an upper layer. It is assumed that the indication is received, and when the RSRQ measurement is performed in the idle mode, the operation of measuring the RSSI in all OFDM symbols of the indicated subframe RSRQ measurement is started. If the UE does not have information for distinguishing between the RSRQ measurable subframe and the RSRQ non-measurable subframe from the eNB, the UE determines that RSRQ measurement has been indicated for all subframes. In addition, the terminal may activate the TDM eICIC mode for the idle mode. In addition, in order to measure RSRP and / or RSRQ in Layer 1 (physical layer), an RRM measurement cycle that can be configured in the terminal may be changed. The measurement period is set in subframe units. When the RRM measurement cycle is changed, the FDD is changed to a cycle other than a multiple of 40 ms, and the TDD is changed to a cycle that is not a multiple of 20 ms and 70 ms and 50 ms.

The idle mode terminal may check a range of physical cell ID (PCI) values of CSG cells among information currently provided through a broadcasting channel in a camp-on cell, that is, a serving cell.

TABLE 3

SystemInformationBlockType4 :: = SEQUENCE {

...,

csg-PhysCellIdRange PhysCellIdRange

...,

}

The csg-PhysCellIdRange field may not always be present when the cell transmitting the broadcasting channel is not a CSG cell. For example, if a CSG cell does not exist in a corresponding range within the cell and around the cell, the field may not exist. However, in the case of CSG, the csg-PhysCellIdRange field should always be included in the broadcasting channel.

The PhysCellIdRange field defining the range value of PCI may be defined as follows.

Table 4

PhysCellIdRange :: = SEQUENCE {

start PhysCellId,

range ENUMERATED {

n4, n8, n12, n16, n24, n32, n48, n64, n84,

n96, n128, n168, n252, n504, spare2,

spare1} OPTIONAL-Need OP

}

Here, the meaning of a field value such as n4 indicates the number of consecutive PCI range values from the start value. For example, if the starting PCI value is 52 and the range value is n8, the PCI values that CSG cells may have are 52, 53,... , 59.

The idle mode terminal measures RSRP of neighbor cells. At this time, in order to distinguish each adjacent cell, PCI information included in a synchronization channel is checked and RSRP is measured using the checked PCI information. At this time, it is checked whether the checked PCI information exists within a range of PCI values of CSG cells through the broadcasted information. If the PCI value is determined to be a PCI value that is determined to be a CSG cell, the idle mode UE considers that the subframe for the RSRQ measurement is received from a higher layer, and the RSRQ measurement is indicated when the RSRQ measurement is instructed in the idle mode. The operation of measuring RSSI in all OFDM symbols starts.

In addition, the present invention intends to use the offset (Qoffsets, n) value as a CRE bias value.

Hereinafter, a method of selecting a cell by applying the CRE bias according to the present invention will be described.

When the RRC idle state UE wants to select a cell, the CRE bias may be transmitted through system information. A variable for giving the CRE bias value to the UE for cell selection may additionally be included in the cell selection criteria. This variable may be transmitted through system information (for example, System Information Block 4 (SIB4)). Herein, a variable added to give a CRE bias value may be referred to as a cell selection offset (Offset_Cell_selection). That is, the variable called cell selection offset is an offset value used for the UE in the RRC idle state to apply the CRE bias.

For example, the cell selection offset may be defined as an offset value added to the Q _rxlevmeas or Q _qualmeas value described in Equation 1 above. In addition, the cell selection offset may have two values. For example, the CRE bias value for the low-end terminal and the CRE bias value for the high-end terminal may be included and transmitted based on the category of the terminal. In this case, the terminal receiving the cell selection offset may select an offset value corresponding to its category and apply the CRE bias value to select the cell.

Alternatively, the base station may change the CRE bias value of the terminal based on the RFSP index received from the MME. The RFSP index is UE-specific and is a value received by the MME from the HSS. Upon receiving the changed CRE bias value, the UE may perform cell reselection based on this value.

12 is a flowchart illustrating a process of reselecting a cell using a cell selection offset according to the present invention. The UE may be a MUE or a PUE. FIG. 12 is an embodiment when the UE is a MUE. The UE may perform cell reselection from a macro base station to a pico base station.

SIB4 and SIB5 (System Information Block 5) of the system information can be received while the terminal is camped on, and includes information on neighbor cells. SIB4 includes information of an intra-frequency neighbor cell, and SIB5 includes information of an inter-frequency neighbor cell.

The cell selection offset may be transmitted through system information such as SIB4 or SIB5. For example, the Qoffset value described in Equation 2 may be used as a cell selection offset for applying a CRE bias value. Qoffest refers to an offset value additionally applied to RSRP measurement values of neighbor cells in a cell reselection process.

Referring to FIG. 12, the terminal UE camps on the macro base station (S1210). The camp-on terminal receives system information from the camp-on one serving cell (here, the macro cell) (S1220). The camp-on state is a cell selection state, and the selected cell becomes a serving cell. The terminal receives system information such as SIB4 or SIB5 from the serving cell.

The base station (here, the macro base station) of the serving cell transmits a cell selection offset value through system information. The UE measures and compares the signal strengths of the serving cell and the neighbor cell by applying the cell selection offset value received through the system information (S1230).

The cell is reselected based on the measurement result (S1240). For example, when the signal strength of a micro cell such as a pico cell is expressed as Smc, the signal intensity of a macro cell as Smm, and the cell selection offset is Qoffset, when "Smc + Qoffset> Smm" is maintained for a predetermined time, the macro cell The MUE that has been camped on may perform cell reselection with a micro cell such as a pico cell. As a result of comparing the measured values of the neighbor cell and the serving cell is different due to the received cell selection offset value, the cell reselection process may be performed when the most suitable cell becomes the neighbor cell.

13 illustrates another example of a cell reselection process using a cell selection offset according to the present invention. When the terminal is a PUE, the PUE is an embodiment for cell reselection from the macro base station to the pico base station.

Referring to FIG. 13, the terminal PUE camps on a pico cell (S1310). The camp-on terminal receives system information from the camp-on one serving cell (here, the pico cell) (S1320). The base station of the serving cell transmits a cell selection offset value through system information. The terminal measures and compares the signal strengths of the serving cell and the neighbor cell by applying the cell selection offset value received through the system information (S1330). The cell reselection process is performed based on the measurement result.

For example, when the signal strength of a micro cell, such as a pico cell, is represented by Smc, the macro cell signal strength is Smm, and the cell selection offset value is Qoffset, when "Smc + Qoffset <Smm" is maintained for a predetermined time, The PUE camping on the same micro cell as the cell may perform cell reselection to the macro cell. As a result of comparing the measured values of the neighbor cell and the serving cell is different due to the received cell selection offset value, the cell reselection process may be performed when the most suitable cell becomes the neighbor cell.

14 is a flowchart illustrating the operation of a base station according to an embodiment of the present invention.

The base station receives information of the terminal and the network, such as measurement results and terminal performance from the terminal and the network (S1410). In consideration of the load balance and / or the measurement result and / or the terminal performance of the terminal, the base station determines whether to modify the CRE bias value of the terminal (S1420). The CRE bias value is set to cell-specific or zero by default.

For example, the base station may determine to modify the CRE bias value when the number of terminals in the cell increases. Or, if the channel state of the terminal worsens, the base station may determine to modify the CRE bias value. Alternatively, the correction of the CRE bias value may be determined according to the terminal performance.

The terminal performance may be, for example, a terminal category configured based on a transmit / receive capacity for the uplink / downlink of the terminal (for example, a memory size in the terminal), or a frequency supported by the corresponding terminal. It can be a band. In this case, the supportable frequency band may be set based on the sizes of uplink and downlink frequency bands within a single serving cell, or when a plurality of serving cells are configured, based on the number and combination of serving cells configurable by the corresponding UE. Can be set. The serving cell combination includes configurability for continuous serving cells and continuity for discontinuous serving cells. In this case, the serving cell may consist of only a downlink component carrier or may include both a downlink component carrier and an uplink component carrier.

In addition, the terminal performance may be the maximum number of antenna ports that the terminal can support. In this case, the number of antenna ports is defined by dividing downlink and uplink and may be configured independently.

In addition, the terminal performance may be defined as a combination of a frequency band that the terminal can support and the maximum number of antenna ports that can be supported. For example, the frequency band that the terminal can support is 20 MHz per serving cell, the maximum number of serving cells that can be supported is three, and the maximum number of antenna ports is eight for downlink and four for uplink. The combination of the possible frequency band and the maximum number of antenna ports that can be supported can be shown in Table 5.

Table 5

CA and MIMO capability index	Maximum Supported Serving Cell Combinations	Maximum Supported Antenna Ports
One	1 serving cell (1.4 to 20 MHz)	8
2	2 continuous serving cells	Four
3	2 non-continuous serving cells	2
4	3 continuous serving cells	Four

If there is no need to modify the CRE bias value in step S1420, the next step does not occur. If it is determined to correct the CRE bias value, the base station corrects the CRE bias (S1430). For example, if the CRE bias value is set differently based on the terminal category, the terminal whose terminal category is higher than or equal to a certain level (high-end, 'high-end') and lower (low-end, 'low-end') Other CRE bias values can be set for the UE. For example, if the terminal category is composed of eight as shown in Table 6, when the terminal is defined as the performance between the terminal category step 4 to step 8, it is divided into high-end base station to the terminal for the high-end If the CRE bias value is set, and the UE is less than the UE category 4 step, it is divided into low-ends and the base station sets a CRE bias value for the low-end to the UE.

Table 6

UE Category	Max. Data rate (DL / UL) (Mbps)	DL				UL
		Max. num. of DL-SCH TB bits per TTI	Max. num. of DL-SCH per TB per TTI	Total num. of soft channel bits	Max. num. of spatial layers	Max. num of UL-SCH TB bits per TTI	Max. num of UL-SCH per TB per TTI	Support for 64QAM
Category
1	10 Mbps / 5 Mbps	10296	10296	250368	One	5160	5160	No
Category 2	50 Mbps / 25 Mbps	51024	51024	1237248	2	25456	25456	No
Category 3	100 Mbps / 50 Mbps	102048	75376	1237248	2	51024	51024	No
Category 4	150 Mbps / 50 Mbps	150752	75376	1827072	2	51024	51024	No
Category 5	300 Mbps / 75 Mbps	299552	149776	3667200	4	75376	75376	Yes
Category 6	300 Mbps / 50 Mbps	301504	149776 (4layers) 75376 (2layers)	3667200	2 or 4	51024	51024	No
Category 7	300 Mbps / 150 or 100 Mbps	301504	149776 (4layers) 75376 (2layers)	3667200	2 or 4	102048	51024	No
Category 8	1200 Mbps / 600 Mbps	2998560	299856	35982720	8	1497760	149776	Yes

The base station transmits the modified CRE bias to the terminal (S1440). The modified CRE bias may be transmitted through a cell specific message or a terminal specific message.

15 is a flowchart schematically illustrating an embodiment in which a CSG cell is present in a system to which the present invention is applied. If the UE of the user adjacent to the CSG cell is a UE that is not allowed to access the CSG cell, the base station may adjust the CRE bias for the UE of the user so that the UE may respond to interference from the CSG cell in advance. .

Referring to FIG. 15, the serving cell checks whether the serving cell is a CSG cell which is a neighbor cell of the (not allowed) (S1510). The UE checks the PCI of the CSG cell and checks the CSG ID on its white list to inform the serving cell of whether the UE is allowed in the CSG cell or not. Here, the white list is a set of cells that the terminal can enter, which is received from a higher layer.

If it is confirmed that the neighbor cell of the terminal is a CSG cell that is not allowed to access the terminal, the serving cell transmits the CRE bias considering the CSG cell to the terminal (S1520). The serving cell transmits a CRE bias only to a terminal that is not allowed to access the CSG cell, thereby preventing the terminal receiving the CRE bias from receiving more interference from the CSG cell. The prevention is the introduction of eICIC technology, which deliberately feels that an unauthorized user is subjected to interference from the CSG cell before being severely interrupted by the CSG cell, thereby allowing the serving cell to measure eICIC technology early. For example, the measurement of the serving cell may be applied only to the ABS (Almost Blank Subframe) of the CSG cell. In this case, ABS is used to protect a resource that is interfered with by an aggressive cell. The ABS reduces or does not transmit power such as control information, data information, and signaling (signals transmitted for channel measurement and synchronization) transmitted through the subframe. Of course, it is necessary to transmit control information, data information, signaling, and system information necessary for the terminal for backwards compatibility. In addition, an ABS may use a multimedia broadcast single frequency network (MBSFN) subframe.

For example, the serving cell may transmit a CRE bias only to a terminal that is not allowed to access the CSG cell. The CRE bias is a value greater than zero.

In addition, the serving cell may transmit different CRE biases to the UE that is allowed to access the CSG cell and the UE that is not allowed to access the CSG cell.

By transmitting the CRE bias to the terminal, the base station can apply the measurement limitation to the terminal early, thereby preventing unnecessary handover requests, RLF generation, and the like.

The serving cell may determine whether the corresponding terminal is a terminal that can access the CSG cell in various ways.

The CRE bias may be transmitted through a terminal specific message. The CRE bias can be transmitted through a broadcast channel or a common channel. The CRE bias may be sent over a dedicated channel. The CRE bias may be a variable used in the existing measurement process. This variable may be a cell specific message or a terminal specific message.

The UE may perform measurement (hereinafter, referred to as 'measurement') related to channel state or communication quality and report this to the serving cell (S1530). At this time, the terminal reports the measured value reflecting the CRE bias to the serving cell.

The serving cell receiving the measured value reflecting the CRE bias may transmit a command for setting a limit to the measurement performed by the UE in advance before the UE is greatly influenced by the interference from the CSG cell (S1540).

If the measurement value without the CRE bias is not yet significantly affected by the interference from the CSG cell, the serving cell determines that the measurement value needs to be limited by determining the measurement value with the CRE bias reflected. Restrictions necessary for the measurement of the terminal can be added. For example, the serving cell may limit the measurement to the UE to perform measurement on a subframe in which interference is low among the downlink subframe patterns used by the CSG cell.

If the measurement of the UE is performed on a subframe in which interference is strongly occurring, the reliability of the measurement is deteriorated, and the serving cell receiving the measurement report may misrecognize a channel state or a communication state. Therefore, when the UE enters the CSG cell and already receives a large amount of interference from the CSG cell, in case of limiting the measurement or taking necessary measures, the UE may be in a RLF (Radio Link Failure) state due to interference from the CSG cell. have. Therefore, the serving cell may allow the UE to set measurement limits in consideration of interference from neighboring CSG cells before the UE is affected by the interference.

Upon receiving the command for setting a limit on the measurement, the UE may perform the measurement based on the restricted content and report it to the serving cell (S1550).

In this case, the limitation of the measurement is that the measurement is performed on a subframe that can receive less interference from the CSG cell as described above, and thus, the measurement results on the subframe that is severely interfered with the CSG cell, thereby falling into an unnecessary RLF state. The phenomenon can be prevented. Therefore, the serving cell may perform appropriate inter-cell interference coordination so that the UE can avoid the interference of the CSG cell.

In this case, the CRE bias is transmitted to the terminal and the measurement result reflecting the measurement result is confirmed, and then the measurement limit setting command is transmitted to the terminal. However, based on the previously received measurement result, the CRE bias and the measurement limit setting command are transmitted together to the terminal. Can be. For example, if an Ocn variable value for an unacceptable cell is received above 0, the terminal may start measurement restriction. When the UE receives the CRE bias and the measurement limit setting command together, the UE may perform the measurement in which the measurement limit is reflected without performing an unnecessary operation (no longer) such as requesting a handover to the corresponding CSG cell.

FIG. 16 is a diagram schematically illustrating an embodiment in which a CSG cell is present in a system to which the present invention is applied. 16, the embodiment described with reference to FIG. 15 may be specifically confirmed.

In FIG. 16, UE 1 (UE 1; 1640) and UE 2 (UE 2; 1650) are terminals having a macro cell 1610 as a serving cell. For the CSG cell 1630 existing in the cell area of the macro cell 1610, the terminal 1 1640 is a terminal that is not allowed to access, and the terminal 2 1650 is a terminal that is allowed to access. Accordingly, in case of entering the CSG cell, UE 2 1650 does not need to take additional action by handing over to the CSG cell, but UE 1 1640 cannot handover to the CSG cell and is affected by interference by the CSG cell.

At this time, the macro cell base station 1610 confirms that the terminal 1 1640 is adjacent to the CSG cell, and transmits a CRE bias to the terminal 1 1640, before the terminal 1 1640 enters the CSG cell and the RLF is removed For example, the necessary measures can be performed in advance.

Referring to FIG. 16, when applying the present invention, with respect to the terminal 1 1640 which receives the CRE bias and performs the measurement by reflecting the CRE bias, the area of the CSG cell is the terminal 2 1650 that does not receive the CRE bias. It can be seen that can be determined differently. Accordingly, the UE 1640 may perform necessary measures such as setting a measurement limit in advance before entering the original CSG cell area.

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

The base station 50 includes a processor 51, a memory 52, and an RF unit 53. The RF unit 53 is connected to the processor 51 and transmits and / or receives a radio signal. The RF unit 53 may receive a measurement result report from the terminal, receive information related to an adjacent cell, for example, whether or not it can access a CSG cell, and transmit a CRE bias and a measurement limit command to the terminal. have. In addition, the RF unit 53 may transmit and receive necessary information between other cells. For example, the base station may transmit and receive a CRE bias change request and a CRE bias change response between adjacent cells through the RF unit 53.

The memory 52 is connected to the processor 51 and stores various information for driving the processor 51. The memory 52 may include information about a measurement report transmitted by a terminal, information about a CRE bias transmitted to a terminal, information about a CSE bias transmitted and received between neighboring cells, and / or a relationship between a terminal and a neighboring cell, such as The terminal may store information on whether the terminal is a member of a specific CSG cell.

The processor 51 may be connected to the memory 52 and the RF unit 53 to control them. The processor 51 may determine the CRE bias based on the measurement report received from the terminal, and may perform a procedure regarding a CRE change among other cells in this regard. Meanwhile, the processor 51 may determine whether the cell adjacent to the terminal is a CSG cell, the terminal is a member of the corresponding CSG cell, and determine a CRE bias to be transmitted to the terminal. It may be determined whether to make a setting and delivered to the terminal.

The terminal 60 includes a processor 61, a memory 62, and an RF unit 63.

The RF unit 63 is connected to the processor 61 and transmits and / or receives a radio signal. The RF unit 63 may transmit a measurement result or information about a neighboring cell, such as whether the neighboring cell is a CSG cell or can be connected to the corresponding CSG cell, to the base station, and information on the CRE bias and / or measurement limitation from the base station. A setup command can be received.

The memory 62 is connected to the processor 61 and stores various information for driving the processor 61. For example, the memory 62 may store information on the CRE bias received from the base station, and may store the information about the CRE bias when the base station transmits a measurement limit setting command.

The processor 61 is connected to the RF unit 63 and the memory 62 to control them. Processor 61 performs the measurements to report to the base station. In this case, the processor 61 may perform the measurement by reflecting the CRE bias received from the base station, and may perform the measurement by reflecting the measurement limit received from the base station. In addition, the processor 61 may transmit information about an adjacent cell to the base station through the RF unit 63. For example, if it is confirmed that the neighboring cell is a CSG cell to which it cannot connect, the processor 61 may transmit information related thereto to the base station.

The processor may include application-specific integrated circuits (ASICs), other chipsets, logic circuits, and / or data processing devices. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and / or other storage device. The RF unit may include a baseband circuit for processing a radio signal. When the embodiment is implemented in software, the above-described technique may be implemented as a module (process, function, etc.) for performing the above-described function. The module may be stored in memory and executed by a processor. The memory may be internal or external to the processor and may be coupled to the processor by various well known means.

In the exemplary system described above, the methods are described based on a flowchart as a series of steps or blocks, but the invention is not limited to the order of steps, and certain steps may occur in a different order or concurrently with other steps than those described above. Can be. In addition, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the flowcharts may be deleted without affecting the scope of the present invention.

Claims (18)

1. A method of operating a terminal in a handover process of a wireless communication system,

   Receiving a first cell range expansion (CRE) bias via a first message;

   Receiving a second CRE bias in which the first CRE bias is modified through a second message; And

   Proceeding to the handover procedure based on the second CRE bias,

   The first and second CRE bias is an offset added to the signal strength of the micro cell,

   If the sum of the second CRE bias and the signal strength of the micro cell is greater than the signal strength of the macro cell, the handover procedure is a handover process to the micro cell.
2. The method of claim 1,

   And if the sum of the second CRE bias and the signal strength of the micro cell is greater than the signal strength of the macro cell for a predetermined time, handover to the micro cell.
3. The method of claim 1,

   And the first message and the second message are cell specific messages of a serving cell or cell specific messages of a neighbor cell, respectively.
4. The method of claim 1,

   Wherein the first message and the second message are terminal specific messages of a serving cell, respectively.
5. The method of claim 1,

   The first message is a cell specific message of a serving cell or a cell specific message of a neighbor cell,

   The second message is a terminal specific message of the serving cell.
6. A method for adjusting cell coverage by a base station in a wireless communication system,

   Receiving a measurement result from at least one terminal in a cell;

   Determining whether to adjust the coverage of the cell based on the measurement result;

   If the adjustment of the coverage of the cell is determined, correcting a CRE bias; And

   Transmitting the modified CRE bias to the at least one terminal.
7. The method of claim 6,

   The at least one terminal further comprises the step of performing cell selection or handover based on the modified CRE bias,

   The modified CRE bias is an offset added to the signal strength of the micro cell, and if the sum of the modified CRE bias and the signal strength of the micro cell is greater than the signal strength of the macro cell, the micro cell is selected or handed over. How to.
8. The method of claim 6,

   The at least one terminal performs cell selection or handover based on the modified CRE bias,

   The modified CRE bias is an offset added to the signal strength of the macro cell, and if the sum of the modified CRE bias and the signal strength of the macro cell is greater than the signal strength of the micro cell, the macro cell is selected or handed over. How to.
9. The method of claim 6,

   Wherein the modified CRE bias is transmitted via a cell specific message.
10. The method of claim 6,

    The modified CRE bias is transmitted via a terminal specific message.
11. A method of operating a terminal in a handover process of a wireless communication system,

    Receiving a first cell range expansion (CRE) bias via a first message;

    Receiving a second CRE bias in which the first CRE bias is modified through a second message; And

    Proceeding to the handover procedure based on the second CRE bias,

    The first and second CRE bias are offsets added to the signal strength of the macro cell, and if the sum of the second CRE bias and the signal strength of the macro cell is greater than the signal strength of the micro cell, the handover process to the macro cell proceeds. Characterized in that the method.
12. A method in which a terminal performs cell selection or reselection in a wireless communication system,

    Receiving a first cell range expansion (CRE) bias via a first message;

    Receiving a second CRE bias in which the first CRE bias is modified through a second message; And

    Performing cell selection or reselection based on the second CRE bias;

    The first and second CRE bias are offsets added to the signal strength of the micro cell, and if the sum of the second CRE bias and the signal strength of the micro cell is greater than the signal strength of the macro cell, the micro cell is selected or reselected. Characterized in that the method.
13. A method in which a terminal performs cell selection or reselection in a wireless communication system,

    Receiving a first cell range expansion (CRE) bias via a first message;

    Receiving a second CRE bias in which the first CRE bias is modified through a second message; And

    Performing cell selection / reselection based on the second CRE bias;

    The first and second CRE bias are offsets added to the signal strength of the macro cell, and if the sum of the second CRE bias and the signal strength of the macro cell is greater than the signal strength of the micro cell, the macro cell is selected or reselected. Characterized in that the method.
14. As an operation method of a terminal in a wireless communication system,

    Transmitting information about an adjacent cell to a base station;

    Receiving a CRE bias from a base station;

    Performing measurement by reflecting the received CRE bias;

    Receiving a measurement limit setting command considering the influence of an adjacent CSG cell from a serving cell; And

    And performing a measurement reflecting the measurement limit setting command.
15. 15. The method of claim 14, wherein the information about the neighbor cell comprises information about a physical cell ID (PCI) of the neighbor cell, characteristics of the neighbor cell, or whether the neighbor cell can be connected to the neighbor cell.
16. As an operation method of a terminal in a wireless communication system,

    Determining whether a cell adjacent to the terminal is a CSG cell to which the terminal cannot access based on the information received from the terminal;

    If it is determined that the cell adjacent to the terminal is a CSG cell to which the terminal cannot access, transmitting a CRE bias to the terminal;

    Receiving a measurement result reflecting the CRE bias from the terminal; And

    And if it is determined that measurement limitation is necessary based on the measurement result, transmitting a measurement limit setting command to the terminal.
17. 17. The method of claim 16, wherein the CRE bias is transmitted only to terminals that cannot access the CSG cell.
18. 17. The method of claim 16, wherein the CRE bias has a different value from the CRE bias transmitted to a terminal that can access the CSG cell.

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