KR20100052288A - Method and apparatus for cell reselection of user equipment - Google Patents

Abstract

PURPOSE: A method and a device for cell reselection of mobile terminal are provided to reflect a priority setting of proceeded signal strength after scaling signal strength of femto cell to perform cell reselection of the femto cell. CONSTITUTION: If a signal strength of reference macro cell BS(Base Station) is bigger than a signal strength of femto cell BS, a terminal performs scaling signal strength of the femto cell BS(S355). The terminal determines a priority about cell selection according to a signal strength processed by the femto cell station and a signal strength of the standard macro cell base station(S325). The terminal selects a BS which is highest priority as a cell reselection target(S340).

Description

Method and apparatus for cell reselection of a mobile terminal {METHOD AND APPARATUS FOR CELL RESELECTION OF USER EQUIPMENT}

The present invention relates to a cell reselection method of a mobile terminal and an apparatus thereof. More specifically, the present invention relates to a method and apparatus for setting a cell reselection parameter for a terminal to perform cell reselection to a femtocell in a mobile communication system in which a macro cell and a femtocell coexist.

Femto Cell (Femto Cell) is a compact mobile communication base station connected to a mobile communication core network through a broadband network installed indoors, such as home or office. The name of a femto cell (or indoor micro base station) is a compound word of 'femto' which means 10 minus 15 wins (one hundredth of a trillion) and 'cell' which means the communication range of a mobile phone. Means a base station that can provide coverage of. Femtocells have various advantages to expand indoor coverage, improve call quality, and efficiently provide a variety of wired and wireless convergence services. Since femtocells aim to provide a higher level of data services to more users, they are attracting attention not only in existing 3rd generation mobile communication systems but also in next generation mobile communication systems such as 3GPP LTE (The 3rd Generation Partnership Project Long Term Evolution). Is getting. Such a femto cell has a very small cell coverage compared to a macro cell and assumes that the user installs it directly where desired.

On the other hand, cell reselection means a process in which an idle mode terminal selects a base station to maintain a camping state. To this end, the terminal sets a priority for the neighbor base station according to a predetermined condition, and then selects the neighbor base station having the highest priority as the cell reselection base station.

However, since the cell reselection process is set based on the macro cell environment, there is a concern that the cell reselection process desired by the user may not be performed according to the location of the femto cell in an environment where a plurality of femto cells are installed inside the macro cell. have. For example, when the femto cell is set at a location close to the macro cell base station, the strength of the signal transmitted from the macro cell base station is stronger than that of the signal transmitted by the femto cell. Therefore, in this case, since the priority of the macro cell base station is always higher than the priority of the femto cell base station, there is a problem that a user cannot perform a cell reselection process with the femto cell.

The present invention has been made to solve the above problems, and an object of the present invention is to perform a cell reselection process to a femto cell even when a plurality of femto cells are installed in a macro cell.

In addition, the terminal of the present invention is to scale the signal strength of the femto cell base station measured by itself, and reflects the signal strength of the scaled femto cell base station when setting the neighboring base station priority.

In the cell reselection method of the present invention for solving the above problems, a measurement step of measuring the signal strength of the base station to be a cell reselection, when the cell reselection, the measurement result, the signal strength of the reference macro cell base station is femto When the signal strength of the cell base station is greater than that, the scaling step of scaling the signal strength of the femto cell base station and the priority for cell reselection according to the signal strength of the scaled femto cell base station and the signal strength of the reference macro cell base station are determined. And selecting a base station having the highest priority as the base station of the cell reselection target. In this case, the scaling factor for scaling is calculated by dividing the signal strength of the cell base station by the reference mark measured by the mobile terminal by the limit value of the signal strength that can be provided with the femtocell service, or by the reference mark measured by the femtocell base station. The signal strength of the cell base station is calculated by dividing the signal strength limit value that can be provided with the femtocell service.

In addition, the cell reselection apparatus of the present invention for solving the above problems is a received signal strength measuring unit for measuring the signal strength of the base station to be the cell reselection, when the cell reselection, the measurement result, the reference macro cell base station If the signal strength is greater than the signal strength of the femto cell base station, the scaling unit for scaling the signal strength of the femto cell base station and the cell reselection according to the signal strength of the scaled femto cell base station and the signal strength of the reference macro cell base station And a cell reselection unit for determining the priority for the cell and selecting the base station having the highest priority as the base station of the cell reselection target. Similarly, the scaling factor for scaling is calculated by dividing the signal strength of the cell base station by the reference terminal measured by the mobile terminal by the limit value of the signal strength that can be provided with the femto cell service, or by the reference macro cell base station measured by the femto cell base station. It is characterized by calculating the signal strength of the divided by the limit value of the signal strength that can be provided femtocell service.

According to the cell reselection method of the present invention, even if the signal strength of the macro cell base station is strong, the terminal may perform a cell reselection process to a femto cell in an area where femto cell service is available. Since the conventional cell reselection process only considers the macro cell environment, there is a concern that the cell reselection to the femto cell may fail if the femto cell is still applied. However, in the present invention, since the signal strength of the femtocell measured by the terminal is scaled and reflected in the base station priority setting, the cell reselection to the femtocell may be performed.

The femtocell of the present invention may be used in a closed access mode serving only a user registered to the user (Closed Subscriber Grooup, hereinafter referred to as a 'CSG'), or in an open access femtocell providing a service to a user not registered to the user. It can work.

In addition, the signal strength of the present invention means the measurement strength of the signal received from the base stations to be the cell reselection. In addition, the received signal strength of the present invention means that the hysteresis value or offset value for preventing repetitive cell reselection is performed on the measured signal strength. In an embodiment of the present invention, the priority of base stations targeted for cell reselection may be determined based on the signal strength or the received signal strength. However, in the following detailed description, an embodiment in which priorities of base stations are determined based on received signal strength will be described. Referring to this, it will be apparent to those skilled in the art that priority of base stations is determined based on signal strength.

And the base station or cell of the present invention may be used in the same sense.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that, in the drawings, the same components are denoted by the same reference symbols as possible. Further, the detailed description of well-known functions and constructions that may obscure the gist of the present invention will be omitted.

1 is a conceptual diagram illustrating a cell reselection system for scaling a signal strength of a femtocell base station measured by a terminal and reflecting the signal strength of the scaled femtocell base station when setting a neighboring base station priority according to an embodiment of the present invention. . The cell reselection system of the present invention includes a macro cell 110, a first femto cell 120, a first femto cell base station 130, a second femto cell 140, a second femto cell base station 150, and a macro cell. The base station 160 and the terminal 170 are included.

The macro cell 110 includes a plurality of femto cells 120, 140, and the like. Here, the femto cell 120, 140 refers to a very small indoor base station used indoors, such as home or office. And it is assumed that the femto cell (120, 140, etc.) is installed directly where the users want.

The first femto cell base station 130 and the second femto cell base station 150 are base stations for the first femto cell 120 and the second femto cell 140, respectively. Here, the first and second femto cell base stations 130 and 150 provide the service not only to the femto cell dedicated subscribers subscribed to the first and second femto cell 120 and 140 services but also to general subscribers not subscribed to the femto cell service. Is a home base station. The first femto cell base station 130 and the second femto cell base station 150 are connected to a wireless network controller (not shown) and connected to a core network (not shown) to provide a mobile communication service to the terminal 170. In the present invention, a femto cell or a femto cell base station may be used in the same sense.

The macro cell base station 160 controls the macro cell 110 to provide a mobile communication service to terminals existing within a communication radius. In the present invention, the macro cell base station 160 or the macro cell may be used in the same sense.

The terminal 170 establishes a communication link with the macro cell base station 160 or the femto cell base stations 130 and 150 to receive a normal mobile communication service. The femto cell is assumed to be installed directly where users want it. Accordingly, the terminal 170 has a list of neighbor macro cells of the femto cell to which it can connect, which is called a fingerprint.

The terminal 170 according to an embodiment of the present invention may perform a cell reselection process for selecting a base station to maintain a camping state in an idle mode. In this case, the terminal 170 searches for neighboring base stations, sets the priority by measuring signal strength for each of the discovered base stations. Here, the adjacent base station includes a femto cell base station that controls a femto cell such as the first femto cell base station 130 and the second femto cell base station 150 as well as the macro cell base station 160. The terminal 170 selects the neighboring base station having the highest priority as the cell reselection base station.

When the cell reselection process is performed, the terminal 170 receives a signal strength for setting priorities of neighbor BSs as shown in Equation 1 below.

[Equation 1]

Rs = Q (means, s) + Q (hyst, s)

Equation 1 is a received signal strength measured from a serving base station that currently provides a service to the terminal 170. Q (means, s) is a value measured by the terminal 170, the signal strength transmitted from the serving base station, Q (hyst, s) is a hysteresis (Hysteresis) value for preventing repeated cell reselection. The terminal 170 receives the hysteresis value from the macro cell base station 160 together with the system information.

[Equation 2]

Rn = Q (means, n)-Q (offset, s, n)

Equation 2 is a received signal strength measured from an adjacent base station adjacent to the terminal 170. Q (means, n) is a value obtained by measuring the signal strength transmitted from a neighboring base station by the terminal 170, and Q (offset, s, n) is an offset value for preventing repeated cell reselection. Similarly, the terminal 170 receives the offset value along with the system information from the macro cell base station 160.

The terminal 170 sets the priority of each base station for cell reselection according to the received signal strengths of the serving base station and the neighboring base station according to Equations 1 and 2 above. According to another embodiment of the present invention, it is also possible to set the priority of each base station according to the signal strength, not the received signal strength. However, hereinafter, a method of setting the priority of the base station based on the received signal will be described. The terminal 170 selects the base station having the highest priority as the cell reselection target base station.

On the other hand, when the user enters the communication radius of the femto cell from the communication radius of the macro cell 110, there is a case that wants to camp to the femto cell due to the communication cost. The second femto cell 140 is located in the outer region of the macro cell 110. Therefore, when the terminal 170 compares the received signal strength Rs and Rn in the second femto cell 140, the received signal strength of the second femto cell 140 is measured higher than the received signal strength of the macro cell 110. . Accordingly, since the priority of the second femto cell 140 is set higher than that of the macro cell 110, the terminal 170 may camp to the second femto cell.

On the other hand, the first femto cell 120 is in a location adjacent to the macro cell base station 160. Therefore, when the terminal 170 compares Rs and Rn, which are received signal strengths measured by the first femto cell 120, the received signal strength of the macro cell 110 is greater than the received signal strength of the first femto cell 120. It is measured higher. In this case, the priority of the first femto cell 120 is measured lower than that of the macro cell base station 160. Accordingly, a problem occurs that the terminal 170 cannot reselect the first femto cell 120.

According to an embodiment of the present invention, if the femto cell cannot be reselected because the priority of the femto cell is low, the terminal 170 scales the signal strength of the femto cell, and the signal strength of the scaled femto cell base station is adjacent to the base station. It is characterized by reflecting when setting the priority of.

2 is a block diagram showing the internal structure of a terminal 170 according to an embodiment of the present invention. The terminal 170 of the present invention includes a wireless communication unit 210, a display unit 220, an input unit 230, a storage unit 240, and a control unit 250. The controller 250 includes a received signal strength measurer 250A, a scaling factor calculator 250B, a scaling performer 250C, and a cell reselector 250D.

The wireless communication unit 210 may include an RF transmitter for upconverting and amplifying a frequency of a transmitted signal, and an RF receiver for low noise amplifying and downconverting a received signal. The wireless communication unit 210 according to the embodiment of the present invention transmits a signal received from the serving base station and the adjacent base station to the received signal strength measuring unit 250A. In addition, the wireless communication unit 210 receives the signal strength of the macro cell base station 160 measured by the femto cell base station and transmits it to the scaling factor calculator 250C. The received signal strength value is used when calculating the scaling factor.

The display unit 220 may be formed of an LCD or the like, and displays various display data and operation states generated in the terminal on the screen. In addition, when the display unit 220 is implemented as a touch screen, the display unit 220 may also operate as an input unit.

The input unit 230 is a device that receives information related to user setting and control, and outputs a key input signal. In this case, the input unit 230 may include a plurality of numbers, letters, and / or function keys for inputting numbers and text information and setting various functions.

The storage unit 240 stores programs and data necessary for the overall operation of the terminal 170 according to an embodiment of the present invention. In particular, the storage unit 240 according to the embodiment of the present invention calculates a scaling factor for scaling the received signal strength of the femtocell, and the process of reflecting the signal strength of the scaled femtocell when setting the neighboring base station priority is programmed Saved programs can be saved.

The controller 250 controls the overall operation of the terminal 170. In particular, the controller 250 may include a received signal strength measurer 250A, a scaling factor calculator 250B, a scaling performer 250C, and a cell reselector 250D.

The received signal strength measuring unit 250A receives signals of the serving base station and neighboring base stations through the wireless communication unit 210. The received signal strength measuring unit 250A calculates Rs and Rn values described in Equations 1 and 2 above. In this case, the reception signal strength measuring unit 250A determines whether the femtocell has the highest priority when the signal strength of the femtocell is greater than or equal to a threshold value (hereinafter, referred to as 'rx (levlevinin)') that can receive femtocell service. To judge. In this case, when the priority of the femto cell is lower than the priority of the macro cell, the scaling factor calculator 250B instructs the calculation of the scaling factor.

When the scaling factor calculator 250B receives the scaling factor calculation instruction, the scaling factor calculator 250B calculates a scaling factor for scaling the signal strength of the femtocell base station measured by the terminal 170. In this case, the scaling factor calculator 250B may calculate the scaling factor by two methods. The first method is to calculate the scaling factor using the signal strength of the macro cell base station 160 measured by the terminal 170. The second method is to calculate the scaling factor using the signal strength of the macro cell base station 160 measured by the femto cell. The scaling factor calculation method will be described later.

In both the first method and the second method, the terminal 170 or the femto cell must measure the signal strength of the macro cell base station 160 in order to calculate the scaling factor. In the present invention, the macro cell base station at which the terminal 170 or the femto cell measures signal strength is referred to as a reference macro base station. In this case, the reference macro cell base station is basically set as a macro cell base station including a femto cell which is a cell reselection target. However, when signals of a plurality of macro cell base stations are received in the femto cell, such as a handover area, the macro cell base station having the highest priority may be set as the reference macro cell base station.

The method of the terminal 170 or the femto cell base station determines the information on the reference macro cell base station is as follows.

First, a femto cell base station may periodically set a priority setting procedure for an adjacent base station to set a macro cell base station having the highest priority as a reference macro cell base station.

If the reference macro cell base station is changed, the femto cell base station should inform the terminal 170. In this case, if the terminal 170 is present in the femto cell, the femto cell base station may transmit the changed reference mark cell base station information to the terminal 170 to inform the base station of the change. On the other hand, if the terminal 170 is not present in the femto cell, the femto cell base station may transmit the cell base station information to the higher network element with the changed reference mark, and the higher network element may transmit the terminal 170 to the terminal 170 again.

In the above, the femto cell base station has described a method of obtaining information about the cell base station with a reference mark and transmitting it to the terminal 170. However, according to another exemplary embodiment of the present invention, a method in which the terminal 170 acquires information on the base station as a reference mark and informs the femto cell base station of the reference mark is also possible. In this case, the terminal 170 identifies the cell base station by the reference mark by performing a priority setting process for the neighbor base station when the femto cell is manually selected. When the terminal 170 transmits the base station cell information to the femto cell base station with reference marks, the femto cell base station may also obtain information about the base station cell.

The scaling performer 250C scales the signal strength of the femtocell base station measured by the terminal 170 using the scaling factor calculated by the scaling factor calculator 250B. In addition, the scaling performer 250C reflects the signal strength of the scaled femto cell base station to the neighbor base station priority setting when the cell is reselected. In this case, the equation for the received signal strength used to set the priority of the base stations using the scaling result is shown in Equation 3 below.

&Quot; (3) "

R (macro) = Q (means, macro) + Q (hyst, macro)

R (scale, femto) = Q (scale, means, femto)-Q (offset, macro, femto)

Here, the signal strength of the macro cell base station 160 measured by the terminal 170 is Q (means, macro), and the result of scaling the signal strength of the femto cell base station measured by the terminal 170 is Q (scale, means, femto). In other words, the scaling result for Q (means, femto) becomes Q (scale, means, femto). In this case, the method of determining the scaling factor is as follows.

The cell reselection unit 250D determines the priority for cell reselection according to the signal strength of the scaled femto cell base station and the signal strength of the macro cell base station. According to an embodiment of the present invention, the priority may be determined according to the signal strength or the received signal strength of the base stations to be reselected. The cell reselection unit 250D selects a base station having the highest priority as the base station of the cell reselection target and performs a cell reselection procedure.

Hereinafter, the scaling factor calculator 250B calculates the scaling factor, and the scaling performer 250C performs scaling using the calculated scaling factor. In this case, two methods for calculating the scaling factor will be described separately.

<Method of using signal strength of macro cell base station measured by terminal>

The terminal 170 may calculate a scaling factor using the signal strength of the macro cell base station 160 measured by the terminal 170. In this case, the calculated scaling factor is a value described in Equation 4 below.

[Equation 4]

α (means, femto) = Q (means, macro) / Q (rxlevmin)

That is, the calculated scaling factor α (means, femto) is a value obtained by dividing the signal strength of the macro cell base station 160 measured by the terminal 170 by Q (rxlevmin), which is a limit value for camping in the femto cell.

The result of scaling the signal strength of the femto cell base station using the calculated scaling factor is expressed by Equation 5 below.

[Equation 5]

Q (scale means, femto) α (means, femto) = Q (means, femto) + Q (means, macro)-Q (rxlevmin)

Here, 'Q (scale means, femto) α (means, femto)' means a value in which the signal strength of the femtocell base station measured by the terminal 170 is scaled by the scaling factor 'α (means, femto)'. . As can be seen from Equation 5, the result of the scaling is the signal strength ('Q) measured from the macro cell base station to the signal strength (' Q (means, femto) 'portion) of the femto cell base station measured by the terminal 170. (means, macro) 'part).

When priority is set for neighbor base stations using the scaling result, a condition for cell reselection to a femto cell is expressed by Equation 6 below. Equation 6 is the same as the result of substituting Equation 4 and Equation 5 into Equation 3.

&Quot; (6) &quot;

R (scale, femto)> R (macro)

Q (mean, femto) + Q (means, macro)-Q (rxlevmin)-Q (offset, macro, femto)> Q (means, macro) + Q (hhyst, macro)

Q (means, femto)> Q (rxlevmin) + Q (hhyst, macro) + Q (offset, macro, femto)

As can be seen in Equation 6, it can be seen that the cell reselection to the femto cell after scaling is determined by the signal strength, the threshold value, the hysteresis, and the offset value of the femto cell. In addition, since the influence of the signal strength of the macro cell base station 160 is removed through scaling, it can be seen that cell reselection is possible even when the signal strength of the macro cell base station 160 is strong in the femto cell.

<Method of using signal strength of macro cell base station measured by femto cell>

According to another embodiment of the present invention, the terminal 170 may calculate a scaling factor using the signal strength of the macro cell base station 160 measured by the femto cell. In this case, the terminal 170 receives the signal strength of the macro cell base station 160 measured by the femto cell from the femto cell base station. In this case, the calculated scaling factor is a value described in Equation 7 below.

[Equation 7]

α (ref, femto) = Q (ref, macro) / Q (rxlevmin)

That is, the calculated scaling factor α (ref, femto) is a value obtained by dividing the signal strength of the macro cell base station 160 measured by the femto cell base station by Q (rxlevmin), which is a limit value for camping in the femto cell.

The result of scaling the received signal strength of the femto cell base station using the calculated scaling factor is expressed by Equation 8 below.

[Equation 8]

Q (scale means, femto) α (ref, femto) = Q (means, femto) + Q (ref, macro)-Q (rxlevmin)

Here, 'Q (scale means, femto) α (ref, femto)' means the value of the signal strength of the femto cell base station measured by the terminal 170 is scaled by the scaling factor 'α (ref, femto)'. As can be seen in Equation 8, the result of the scaling is the macro cell base station 160 measured by the femto cell base station to the signal strength ('Q (means, femto)' portion) of the femto cell base station measured by the terminal 170. This results in the signal strength ('Q (ref, macro)' part) being added.

In the case of setting priorities for neighboring base stations using the scaling result, a condition for cell reselection to a femto cell is expressed by Equation 9 below. Equation 9 is the same as the result of substituting Equation 7 and Equation 8 into Equation 3.

[Equation 9]

R (scale, femto)> R (macro)

Q (mean, femto) + Q (ref, macro)-Q (rxlevmin)-Q (offset, macro, femto)> Q (means, macro) + Q (hhyst, macro)

Q (means, femto)> {Q (means, macro)-Q (ref, macro)} + Q (rxlevmin) + Q (hhyst, macro) + Q (offset, macro, femto)

As can be seen in Equation 9, whether to perform cell reselection to the femto cell after scaling is determined by the signal strength, the threshold value, the hysteresis, the offset value, and the macro cell base station 160 measured by the terminal 170. It can be seen that the signal strength of is determined by the signal strength values of the macro cell base station 160 measured by the femto cell.

Accordingly, cell reselection to femtocells is possible depending on how much the signal strength of the macro cell base station 160 measured by the femto cell base station differs from the signal strength of the macro cell base station 160 measured by the terminal 170. It can be seen.

3 is a flowchart illustrating a process of performing cell reselection by the terminal 170 according to an embodiment of the present invention.

First, the terminal 170 determines whether to reselect a cell in step S305. If the terminal 170 determines the cell reselection, in step S310 receives a signal from the macro cell base station 160 and the femto cell base station to measure the signal strength. In operation S315, the terminal 170 determines whether the signal strength of the femtocell base station has a value greater than a limit value Q (rxlevmin) for receiving femtocell service. If the signal strength of the femto cell base station is smaller than the threshold value, the femto cell service cannot be provided, and thus the process returns to step S310.

However, when the signal strength of the femto cell base station is larger than the threshold, femto cell service can be provided. In this case, the terminal 170 determines the Rs value and the Rn value in order to give priority to the received signal strength of the base stations in step S320. The terminal 170 determines the priority of the base stations according to the determined Rs value and Rn value in step S325.

The terminal 170 checks whether the femtocell base station has the highest priority in step S330. When the femto cell base station has the highest priority, the terminal 170 determines whether the cell reselection condition is satisfied in step S335 and performs a cell reselection process in step S340.

On the other hand, the priority of the femto cell base station may not be the highest in step S330. In this case, although the terminal 170 may be provided with the femto cell service, the signal strength of the macro cell base station 160 is stronger than the signal strength of the femto cell base station, so that the terminal 170 may reselect the femto cell. May be absent. In this case, the terminal 170 needs to scale the signal strength of the femto cell base station measured by the terminal 170.

Accordingly, the terminal 170 determines whether scaling has been previously performed in step S345. In case of initial scaling, the terminal 170 calculates a scaling factor required to scale the signal strength of the femto cell base station in step S350. There are two methods for determining the scaling factor as described above. This will be described in detail with reference to FIG. 4.

After calculating the scaling factor, the terminal 170 scales the signal strength of the femtocell base station according to the calculated scaling factor in step S355. The terminal 170 returns to step S320 to calculate Rs and Rn values, which are received signal strengths. In operation S325, the terminal 170 re-determines priorities of the base stations using the calculated received signal strength.

If the priority of the femtocell base station among the re-determined base stations is the highest, the terminal 170 performs a reselection process to the femtocell. However, even though the priority of the base stations is re-determined, if the femto cell base station does not have the highest priority, the terminal 170 maintains camping at the currently accessed macro cell base station through steps S345 and S360.

4 is a flowchart illustrating a process of determining a scaling factor by a terminal 170 according to an embodiment of the present invention. The terminal 170 may determine the scaling factor using the signal strength of the macro cell base station 160 measured by the terminal 170, or may determine the scaling factor using the signal strength of the macro cell base station measured by the femtocell base station.

First, the terminal 170 determines whether to determine a scaling factor using the signal strength of the macro cell base station 160 measured by the terminal 170 in step S410. If the signal strength of the macro cell base station 160 measured by the terminal 170 is used, the scaling factor α (means, femto) is calculated using the equation described in Equation 4 in step S420. In this case, the scaling factor α (means, femto) is a value obtained by dividing the signal strength of the macro cell base station 160 measured by the terminal 170 by Q (rxlevmin), which is a limit value for camping in the femto cell.

Meanwhile, if the signal strength of the macro cell base station 160 measured by the terminal 170 is not used, the terminal 170 uses the signal strength of the macro cell base station 160 measured by the femto cell base station in step S430. Determine. If the signal strength of the macro cell base station 160 measured by the femto cell base station is used, the terminal 170 receives the signal strength value of the macro cell base station 160 measured by the femto cell base station in step S440. In operation S450, the terminal 170 calculates a scaling factor α (ref, femto) using the equation described in Equation 7. In this case, the scaling factor α (ref, femto) is a value obtained by dividing the signal strength of the macro cell base station 160 measured by the femto cell base station by Q (rxlevmin), which is a limit value for camping in the femto cell.

After performing the above process, the terminal 170 returns to step S350 of FIG. 3 to perform scaling.

FIG. 5 is a flowchart illustrating a process of performing scaling by a terminal 170 grasping a scaling factor when performing a cell reselection process according to an exemplary embodiment of the present invention.

First, the terminal 170 receives a cell reselection parameter from the macro cell base station 160 in step S505. Then, the terminal 170 measures the signal strength of the macro cell base station 160 and the signal strength of the femto cell base station in steps S510 and S515. In operation S520, the terminal 170 determines whether to perform a cell reselection process.

After determining that the cell reselection process is performed, the terminal 170 determines whether scaling of the received signal of the femtocell base station measured by the terminal is necessary in operation S525. As described in FIG. 3, although the signal strength of the femto cell base station is greater than a limit value (Q (rxlevmin)) at which the femto cell service can be provided, the priority of the femto cell base station is that of the macro cell base station. This may be the case below the priority.

If scaling is not necessary, the terminal 170 performs the cell reselection process in step S535 or less without performing the scaling process. This will be described later.

On the other hand, if scaling is required, the terminal 170 scales the received signal of the femto cell base station by using the scaling factor already known in step S530. The terminal 170 recalculates the priority of the base stations by calculating the received signal strength of the scaled femto cell base station.

When the cell to be reselected (the femto cell in this embodiment) is determined, the terminal 170 requests the cell reselection to the macro cell base station 160 in step S535. The macro cell base station 160 receiving the request transmits a cell reselection request to the femto cell base station in step S540.

Then, the femto cell base station transmits a cell reselection response to the macro cell base station 160 in response to the request in step S545. Then, the macro cell base station 160 instructs the terminal 170 to reselect the cell in step S550. Upon receiving the command, the terminal 170 performs a cell reselection process in step S555.

6 is a flowchart illustrating a process of performing scaling by a macro cell base station 160 that is aware of a scaling factor according to another embodiment of the present invention.

First, the terminal 170 receives a cell reselection parameter from the macro cell base station 160 in step S605. Then, the terminal 170 measures the signal strength of the macro cell base station 160 and the signal strength of the femto cell base station in steps S610 and S615. In operation S620, the terminal 170 reports the measurement result to the macro cell base station 160. The macro cell base station 160 receiving the measurement report determines whether the terminal 170 performs a cell reselection process in step S625.

When determining to perform cell reselection, the macro cell base station 160 determines whether scaling of the femtocell reception signal measured by the terminal 170 is necessary in operation S630. As described in FIG. 3, although the signal strength of the femto cell base station is greater than a limit value (Q (rxlevmin)) at which the femto cell service can be provided, the priority of the femto cell base station is that of the macro cell base station. This may be the case below the priority.

If scaling is not necessary, the macro cell base station 160 does not perform a scaling process and performs a cell reselection process in step S640 or below. This will be described later.

On the other hand, if scaling is necessary, the macro cell base station 160 scales the received signal of the femto cell base station using the scaling factor already known in step S635. The macro cell base station 160 calculates the received signal strength of the scaled femto cell base station and re-determines the priority of the base stations.

When the cell to be reselected (the femto cell in this embodiment) is determined, the macro cell base station 160 requests the cell reselection to the femto cell base station in step S640. Upon receiving the request, the femto cell base station transmits a cell reselection response to the macro cell base station 160 in step S645.

Then, the macro cell base station 160 instructs the end terminal 170 to reselect the cell in step S650. The terminal 170 receiving the command performs a cell reselection process in step S655.

The embodiments of the present invention disclosed in the present specification and drawings are merely illustrative of specific embodiments of the present invention and are not intended to limit the scope of the present invention in order to facilitate understanding of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention can be carried out in addition to the embodiments disclosed herein.

1 is a conceptual diagram illustrating a cell reselection system for scaling a signal strength of a femtocell base station measured by a terminal according to an embodiment of the present invention, and reflecting the signal strength of the scaled femtocell base station when setting a neighboring base station priority;

2 is a block diagram showing the internal structure of a terminal 170 according to an embodiment of the present invention.

3 is a flowchart illustrating a process in which a terminal 170 performs cell reselection according to an embodiment of the present invention.

4 is a flowchart illustrating a process of determining a scaling factor by a terminal 170 according to an embodiment of the present invention.

5 is a flowchart illustrating a process of performing scaling by a terminal 170 having grasped a scaling factor when performing a cell reselection process according to an embodiment of the present invention.

6 is a flowchart illustrating a process of performing scaling by a macro cell base station 160 that is aware of a scaling factor according to another embodiment of the present invention.

Claims (14)

In the cell reselection method of a mobile terminal, A measurement step of measuring signal strength of base stations targeted for cell reselection when the cell is reselected; A scaling step of scaling the signal strength of the femto cell base station when the signal strength of the reference macro cell base station is greater than that of the femto cell base station as a result of the measurement; And Reselection of cell reselection is determined according to the signal strength of the scaled femto cell base station and the signal strength of the reference macro cell base station, and reselection of selecting a base station having the highest priority as the base station of the cell reselection target. And a cell reselection method of a mobile terminal. The method of claim 1, The scaling step includes a scaling factor calculation step of calculating a scaling factor for the signal strength of the femto cell base station. The method of claim 2, wherein the scaling factor is And calculating the signal strength of the cell base station by the reference mark measured by the portable terminal by dividing the signal strength by a limit value of the signal strength capable of receiving femtocell service. The method of claim 2, wherein the scaling factor is The cell reselection method of a mobile terminal, characterized in that the reference strength measured by the femto cell base station is calculated by dividing the signal strength of the cell base station by a limit value of the signal strength capable of receiving femto cell service. The method of claim 4, wherein before the scaling factor calculation step, And receiving the signal strength of the cell base station by the reference mark measured by the femto cell base station from the femto cell base station. The method of claim 1, And the reference macro cell base station is a macro cell base station including the femto cell base station. The method of claim 6, And when the reference macro cell base station is changed, the femto cell base station transmitting information on the changed reference macro cell base station to the mobile terminal. The method of claim 6, And when the reference macro cell base station is changed, the portable terminal transmits information on the changed reference macro cell base station to the femto cell base station. The method of claim 1, And the scaling step is performed by the mobile terminal or the reference macro cell base station. The method of claim 1, And the scaling is performed when the signal strength of the femto cell base station is greater than or equal to a threshold value of the signal strength capable of receiving femto cell service. A reception signal strength measurement unit for measuring signal strength of base stations which are cell reselection targets when reselecting a cell; A scaling performer configured to scale the signal strength of the femto cell base station when the signal strength of the reference macro cell base station is greater than that of the femto cell base station as a result of the measurement; And Determine priority for cell reselection according to the signal strength of the scaled femto cell base station and the signal strength of the reference macro cell base station, and cell reselection for selecting a base station having the highest priority as a base station of a cell reselection target. And a cell reselection apparatus for a mobile terminal. The method of claim 11, And a scaling factor calculator for calculating a scaling factor for the signal strength of the femto cell base station. The method of claim 12, The scaling factor calculator calculates the scaling factor by dividing a signal strength of a cell base station by a reference mark measured by the portable terminal by a limit value of a signal strength capable of receiving femtocell service. Device. The method of claim 12, The scaling factor calculator calculates the scaling factor by dividing the signal strength of the cell base station by a reference mark measured by the femto cell base station by a limit value of a signal strength capable of receiving femtocell service. Optional device.

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