KR20100092656A - System and method for controlling hand-over target cell by compensating the error of traffic load - Google Patents

Abstract

PURPOSE: A handover method following error correction of a traffic load amount and a system for executing the same are provided to correct deviation of a traffic load amount, thereby accurately determining a target base station for handover of a mobile communication terminal. CONSTITUTION: A serving BS(Base Station)(100) receives at least one RSSI(Received Signal Strength Indication) per candidate BS from a mobile communication terminal(200). The serving BS checks a traffic load amount per candidate BS corresponding to the received RSSI. The serving BS calculates an expense function by the RSSI per candidate BS and the traffic load amount. The serving BS determines one target base station among the candidate base stations(300) according to the calculated expense function.

Description

Handover method and system performing the same according to error correction of traffic load {SYSTEM AND METHOD FOR CONTROLLING HAND-OVER TARGET CELL BY COMPENSATING THE ERROR OF TRAFFIC LOAD}

The present invention relates to a handover method and a system for performing the same, and more particularly, to determine a target base station using traffic loads exchanged between base stations in a system supporting multi-service, and to perform a handover to the determined target base station and performing the same. It is about the system.

Handover means that when a mobile communication terminal moves between sectors in a cell or moves from one cell to another cell, the current communication channel is automatically switched to a base station managing a cell where the mobile communication terminal is located. In general, a method for performing handover between base stations may be as follows. A method of performing handover between base stations will be described with reference to FIG. 1. 1 is a diagram illustrating a configuration of a system in which a handover according to the prior art is performed.

Referring to FIG. 1, it is assumed that a mobile communication terminal 200 is connected to a serving base station 100 that manages one cell among at least two adjacent cells.

The mobile communication terminal 200 connected to the serving base station 100 is moved to a cell managed by the candidate base station 300. As the position of the mobile communication terminal 200 moves closer to the cell managed by the candidate base station 300, the strength of the signal transmitted / received between the serving base station 100 and the mobile communication terminal 200 becomes weaker than the set signal strength. When the strength of a signal transmitted and received between the mobile communication terminal 200 and the candidate base station 300 becomes stronger than the set signal strength, handover between the serving base station 100 and the candidate base station 300 is performed. In more detail, it may be as follows.

The serving base station 100 and the mobile communication terminal 200 periodically measure parameter values necessary for handover determination. In this case, the parameter values include the strength of the transmission signal between the neighboring base stations 100 and 300 and the mobile communication terminal 200, the traffic load on the neighboring base stations 100 and 300, and the communication formed between the serving base station 100 and the mobile communication terminal 200. Information on the quality of the channel.

If the measured parameter values meet various handover conditions determined by the network manager, the serving base station 100 determines the base station to which the mobile communication terminal 200 is to be handed over. Referring to FIG. 1, the mobile communication terminal 200 moves to a cell managed by the candidate base station 300. Accordingly, the base station to which the mobile communication terminal 200 is to be handed over becomes the candidate base station 300. The conditions set by the network manager may include electric field strength of the received signal between the mobile communication terminal and the base stations, bit error rate, distance between the mobile communication terminal and the base station, service radius of the base station, and traffic load control on the network.

When the handover is determined, the previously established communication link between the serving base stations 100 is released, and then a new communication link to the target base station 300 is attempted.

The method of selecting a base station to be handed over according to the double traffic load can easily determine the base station to be handed over when a certain cell has a heavy traffic load. However, in this case, a problem arises in that a lot of handovers may occur according to a change in traffic load.

In addition, in order to select the base station to be handed over, the reliability of the information about the traffic load must be high. However, if the time taken to determine the handover is delayed, there is a problem that the reliability of the information about the traffic load is lowered.

In order to solve the above problems, the present invention provides a method for performing a handover by correcting an error of a traffic load and a system for performing the same.

In order to achieve the above object, a handover method according to an embodiment of the present invention includes the steps of: a serving base station receiving received signal strengths of at least one candidate base station from a mobile communication terminal; Checking, by the serving base station, the traffic load for each candidate base station corresponding to the received received signal strength; Calculating, by the serving base station, a cost function that is a traffic load when handover is performed by using the received signal strength and the traffic load for each candidate base station; Determining, by the serving base station, one of the candidate base stations as the target base station according to the calculated cost function; And the terminal handing over to the target base station according to the determination of the serving base station.

In addition, to achieve the above object, a handover system according to an embodiment of the present invention includes at least one candidate base station is determined as the target base station to be handed over; The mobile communication terminal transmitting a received signal strength received from the at least one candidate base station to a serving base station providing a service when performing a handover; And when the received signal strength is received, determine a traffic load for each candidate base station, calculate a cost function using the received signal strength and the traffic load amount, and convert the candidate base station into the target base station according to the calculated cost function. The serving base station is determined to be.

According to the present invention, as the error of the traffic load is corrected, the target base station to which the mobile communication terminal is to be handed over can be accurately determined. In addition, the cost function value has the advantage that the target base station to be handed over can be determined by predicting the traffic load of the target base station at the time when the handover is performed. And, as the target base station to be handed over is accurately determined, the success rate of handover is increased.

'Serving base station' refers to a base station capable of performing a service with a mobile communication terminal.

The candidate base station refers to a base station adjacent to the serving base station and selected as a target base station to be handed over according to the strength of a signal transmitted and received with the mobile communication terminal.

The 'target base station' refers to a base station to which a mobile communication terminal is newly connected when handover is performed.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. At this time, it should be noted that the same components in the accompanying drawings are represented by the same reference numerals as possible. Further, the detailed description of well-known functions and constructions that may obscure the gist of the present invention will be omitted.

2 is a diagram schematically illustrating a configuration of a base station according to an embodiment of the present invention.

Referring to FIG. 2, the base station includes a base station communication unit 110, a base station storage unit 120, and a base station control unit 130. Here, the base station is divided into the serving base station 100 and the candidate base station 300 according to the mobile communication terminal 200 and whether the service is performed.

The base station communication unit 110 may transmit a measurement control including a system information block (SIB) under the control of the base station control unit 130. The SIB includes information on signal strength between the mobile communication terminal 200 and the base station, communication channel quality between the mobile communication terminal 200 and the base station, neighbor cell list (NCL), hysteresis value, and length of time to trigger. Contains information related to the same handover. Here, hysteresis means electric field sensitivity for determining handover.

The base station communication unit 110 transmits the measurement report transmitted from the mobile communication terminal 200 to the base station control unit 130. The measurement report includes received signal strength measured for each candidate base station and cell ID which is identification information for each candidate base station.

The base station communication unit 110 may transmit and receive base station information including information related to the traffic load of neighboring base stations under the control of the base station control unit 130. In this case, the base station information includes the number of subchannels requested by the mobile communication terminal 200 to the candidate base station 300, the number of subchannels currently allocated and used by the candidate base station 300, and the total number of subchannels of the candidate base station 300. Information about may be included. Through this information, the traffic load can be confirmed.

The base station storage unit 120 may store an algorithm for selecting a target base station to be handed over. The algorithm refers to a mathematical formula for confirming a traffic load, a waveform distribution function for calculating a traffic load correction value, and a mathematical formula for calculating a cost function. The base station storage unit 120 may store a cost function threshold 125 for selecting a target base station to be handed over according to traffic load.

The base station controller 130 controls the states and operations of the components constituting the base station 100 or 300. Here, the base station controller 130 will be described based on the serving base station 100. When the measurement report including the received signal strength of each candidate base station is received from the mobile communication terminal 200, the base station controller 130 determines the traffic load for each candidate base station 300. The base station controller 130 calculates a cost function using the traffic load of the candidate base station 300. The base station controller 130 determines a target base station to which the mobile communication terminal 200 will hand over the candidate base station whose calculated cost function is equal to or greater than the set cost function threshold.

In other words, the base station controller 130 checks the received signal strength of each candidate base station included in the measurement report received from the mobile communication terminal 200. Next, the base station controller 130 transmits and receives base station information with the candidate base station 300 corresponding to the received signal strength received from the mobile communication terminal 200. The base station information includes information about the total number of subchannels of the candidate base station and the number of subchannels currently used by the candidate base station.

The base station controller 130 checks the traffic load for each candidate base station by using the information included in the base station information. In this case, the traffic load may be expressed by Equation 1.

Where R _{k, j} is the traffic load. r _{k, j} is the number of subchannels requested by the mobile communication terminal 200 to the candidate base station 300, and A _j is the number of subchannels currently allocated to other mobile communication terminals in the candidate base station 300. . N _j is the total number of subchannels of the candidate base station 300.

Next, the base station controller 130 calculates a traffic load correction value for correcting an error caused by a change in traffic load that may occur between the time point at which the target base station is determined and the time point when the handover is performed. The base station controller 130 calculates a cost function for each candidate base station 300 by using the received signal strength, the confirmed traffic load, and the traffic load correction value. Here, the traffic load amount used for the cost function and the correction value of the traffic load amount may be traffic loads of the candidate base station predicted based on the time point at which the handover is performed.

The base station controller 130 determines the candidate base station having the largest calculated cost function as the target base station. At this time, the base station controller 130 compares the calculated cost function with the cost function threshold 125 stored in the storage. If the calculated cost function is greater than or equal to the cost function threshold, the base station controller 130 determines the candidate base station 300 corresponding to the calculated cost function as the target base station. To do this, the base station controller 130 includes a target base station selector 140.

The target base station selection unit 140 includes a traffic load correction value calculator 145 and a cost function calculator 147 for determining a target base station to be handed over.

The traffic load correction value calculator 145 calculates the traffic load correction value. In more detail, the traffic load of the target base station identified before the handover may be changed when the handover is performed. Therefore, when the traffic load of the target base station increases at the time when the handover is performed, the handover of the mobile communication terminal 200 may not be performed. Accordingly, the traffic load correction value calculating unit 145 estimates a change in traffic load in advance and calculates a correction value for correcting the traffic load change amount of the target base station that may be generated when performing the handover.

The traffic load correction value may be calculated using a wavelet distribution function generated in accordance with the exchange of the communication system. The wavelet distribution function for calculating the traffic load correction value may be calculated through data previously measured in an experiment in the environment of various communication systems. In other words, the wavelet distribution function may be calculated using parameters calculated through experiments. The wavelet distribution function is defined as in Equation 2.

Here, k1 and k2 are parameters for adjusting the influence range of the probability distribution according to the environment of the communication system. If the time for updating base station information between base stations becomes long, or if the time required for performing handover becomes long, the ranges of k1 and k2 become small. On the contrary, if the time for updating base station information between base stations or the time required for performing handover is short, the ranges of k1 and k2 become long. a and b are parameters adjusted so that the wavelet distribution function has an equal probability. Where k1, k2, a, b can be determined as follows.

For example, it is assumed that a user can use up to four services simultaneously in a cellular mobile communication environment having a Haxagon shape and 19 base stations. In addition, it is assumed that the moving speed of the mobile communication terminal 200 has an arbitrary value with an equal probability in the range of 3 km / h to 120 km / h. Under these experimental conditions, the parameter a of the wavelet distribution function may be determined as 0.4, b as 0.3, k1 as 0.35, and k2 as 0.56. Then, the traffic load correction value calculating unit 145 calculates the wave distribution function by substituting the parameters determined in Equation (2). Next, the traffic load correction value calculator 145 checks a random variable according to the determined wavelet distribution function. In this case, the identified random variable may be a traffic load correction value.

Next, the cost function calculator 147 may calculate the cost function using the received signal strength, the traffic load amount, and the traffic load correction value. Here, the cost function means the traffic load of the target base station to which the mobile communication terminal 200 to be handed over, which is predicted based on the time point at which the handover is performed. The cost function can be calculated through Equation 3.

Where f _{k, j} is a cost function and P _i is the received signal strength. R _{k, j} denotes a traffic load, and E _{k, j} denotes a traffic load correction value that is a random variable according to the distribution of Equation 2.

The base station controller 130 determines a candidate base station corresponding to the largest cost function among the cost functions calculated by the cost function calculator 147 as the target base station. In this case, the base station controller 130 compares the calculated cost function with the cost function threshold 125 stored in the base station storage 120. If the calculated cost function is greater than or equal to the cost function threshold, the base station controller 130 may determine the candidate base station 300 as the target base station. For example, even if the cost function corresponding to the candidate base station A is higher than the other candidate base stations, if the cost function is not greater than or equal to the cost function threshold 125 stored in the base station storage unit 120, the base station control unit 130 selects the candidate base station A as the target base station. Do not decide.

In the above, the structure which comprises the base station for determining a target base station was demonstrated. Next, a configuration of the mobile communication terminal 200 for determining the target base station will be described in detail with reference to FIG. 3.

3 is a diagram illustrating a configuration of a mobile communication terminal according to an embodiment of the present invention.

Referring to FIG. 3, the mobile communication terminal 200 includes a mobile terminal communication unit 210, a mobile terminal control unit 220, and a mobile terminal storage unit 230.

The mobile terminal communication unit 210 performs a service with the serving base station 100. In addition, the mobile terminal communication unit 210 transmits the measurement control received from the serving base station 100 to the mobile terminal control unit 220. Here, the measurement control includes a system information block (SIB). SIB signal strength between the mobile communication terminal 200 and the base station, communication channel quality between the mobile communication terminal 200 and the base station, neighbor cell list (NCL; Neighbor Cell List), the conditions for handover Hysteresis, Time to trigger, etc. Include information about The mobile terminal communication unit 210 transmits a measurement report to the serving base station 100 under the control of the mobile terminal control unit 220. The measurement report includes information on received signal strength measured for each candidate base station.

The mobile terminal controller 220 controls the states and operations of the components constituting the mobile communication terminal 200. The mobile terminal controller 220 includes a received signal strength measuring unit 225 for checking the strength of a received signal received from a neighboring base station. Herein, the mobile terminal controller 220 can periodically measure the received signal strength of the neighboring base stations. Alternatively, if the received signal strength of the serving base station 100 is weaker than the signal strength threshold 235 stored in the mobile terminal storage unit 230, the mobile terminal controller 220 may measure the received signal strength of the neighboring base stations.

The mobile terminal controller 220 determines whether the received signal strength of at least one neighboring base station measured by the received signal strength measuring unit 225 is greater than or equal to the signal strength threshold 235 stored in the mobile terminal storage 230. The mobile terminal controller 220 transmits the received signal strength measured to the stored base station 100 through the mobile terminal communication unit 210 to the serving base station 100.

The mobile terminal storage unit 230 may store various data generated when an application program and a function related to a function that may be performed in the mobile communication terminal 200 are executed. The mobile terminal storage 230 stores the signal strength threshold 235. Here, the signal strength threshold 235 is a preset value for determining the handover. The signal strength threshold 235 means hysteresis included in the SIB received from the serving base station 100 when the mobile communication terminal 200 is camped or connected to a cell managed by the serving base station 100.

4 is a flowchart illustrating a method of determining a target base station in a system consisting of a mobile communication terminal and a plurality of base stations according to an embodiment of the present invention.

Referring to FIG. 4, when the handover between the serving base station 100 and the mobile communication terminal 200 starts, the serving base station 100 transmits measurement control for handover to the mobile communication terminal 200 in step 410. . In this case, the measurement control includes a candidate base station list (NCL) corresponding to call ID which is identification information of candidate base stations adjacent to the serving base station 100. In step 420, the mobile communication terminal 200 measures the received signal strength of the candidate base stations 300 corresponding to the NCL included in the measurement control. Herein, the mobile terminal 200 may determine whether the received signal strength received from the candidate base station 300 is measured to be greater than or equal to the signal strength threshold 235.

In operation 425, the mobile communication terminal 200 transmits a measurement report including the received signal strength measured for each candidate base station and the call ID of the candidate base station to the serving base station 100. Herein, the mobile communication terminal 200 transmits a received signal strength measured above the signal strength threshold 235 and call IDs of candidate base stations corresponding thereto. Then, the serving base station 100 checks the call ID included in the measurement report, and checks the traffic load of the candidate base station 300 by exchanging base station information with each candidate base station 300 in step 430. For example, as shown in FIG. 4, if there are three candidate base stations 300, the serving base station 100 checks the traffic load of each candidate base station 300a. The base station information exchanged between the serving base station 100 and the candidate base station 300 includes the number of subchannels required for each base station, the number of subchannels currently allocated and used for each base station, the total number of subchannels in each base station, and the like. Can be.

 Next, the serving base station 100 calculates a traffic load correction value in step 435. In this case, the traffic load correction value is a random variable according to the wavelet distribution function, and is calculated to reduce an error that may occur according to the traffic load that may change when the handover is performed.

The serving base station 100 calculates the cost function f _{k, i} using the received signal strength, traffic load, and traffic load correction value in step 440. In this case, the serving base station 100 may calculate a cost function f _{k, i} for each candidate base station 300 corresponding to the call ID received from the mobile communication terminal 200. Here, the cost function f _{k, i} represents a candidate base station traffic load at the time when handover is performed.

The serving base station 100 selects the target base station according to the cost function f _{k, i} calculated in step 445. In more detail, the serving BS 100 may determine the candidate access point having a cost function computed for each candidate access point f _k, the largest cost function in f _{i k, i} to the target base station. At this time, the serving base station 100 must determine whether the largest cost function f _{k, i} is greater than or equal to the predetermined cost function threshold 125. Accordingly _, even if the cost function f _{k, i, which} is the largest among the cost functions f _{k, i} calculated for each candidate base station, is not equal to or more than the preset cost function threshold 125, the serving base station 100 calculates the calculated cost function f _{k, i. The} candidate base station corresponding to _i is not determined as the target base station. The serving base station 100 receives the measurement report from the mobile communication terminal 200 again, and calculates a cost function for determining the target base station. It is assumed here that the target base station is determined as the candidate base station 300a. When the target base station is determined in this way, the mobile communication terminal 200 may be handed over to the target base station according to the determination of the serving base station.

To this end, the serving base station 100 transmits a handover request signal to the target base station 300a determined in step 450. The handover request signal includes a service performed between the serving base station 100 and the mobile communication terminal 200 and identification information of the mobile communication terminal 200. Upon receiving the handover request signal, the target base station 300a transmits a handover request ACK, which is a response signal to the handover request, to the serving base station 100 in step 455.

In step 460, the serving base station 100 receives the handover commend to the mobile communication terminal 200. The serving base station 100 recovers the radio resources allocated to the mobile communication terminal 200. The mobile communication terminal 200 receiving the handover commend transmits a handover confirm to the target base station 300a in step 470.

Next, a method of selecting a target base station for performing a handover in the mobile communication terminal 200 which constitutes a communication system will be described with reference to FIG. 5. 5 is a flowchart illustrating a method of determining a target base station of a mobile communication terminal according to an embodiment of the present invention.

Referring to FIG. 5, the mobile communication terminal 200 performs a service with the serving base station 100 in step 510. The service may include a service capable of transmitting and receiving various data such as voice data and image data, a call waiting service, and the like.

The mobile communication terminal 200 determines whether a measurement control for controlling handover is received from the serving base station 100 in step 520. The measurement control includes candidate base station list (NCL) corresponding to identification information about candidate base stations adjacent to the serving base station 100 and information on the length of Hysteresis and Time to trigger which are conditions for performing handover.

When the measurement control is received, the mobile communication terminal 200 checks candidate base station identification information included in the measurement control in step 530. In addition, the mobile communication terminal 200 measures the received signal strength of the candidate base stations 300 corresponding to the identification information identified in step 540. At this time, the mobile communication terminal 200 determines whether the measured received signal strength of each candidate base station 300 is greater than or equal to the stored received signal threshold.

Next, the mobile communication terminal 200 serves a measurement base station including a measurement report including received signal strength of the candidate base station 300 measured in step 550 and Call ID, which is identification information of the candidate base station 300 in which each received signal strength is measured. Send to 100.

Although not shown in the figure, the mobile communication terminal 200 may be handed over to the target base station selected by the serving base station 100. If the handover is made, the mobile communication terminal 200 releases the communication channel established with the serving base station 100 that is currently providing the service. Next, the mobile communication terminal 200 may newly establish a communication channel with the handed over target base station to perform a service. Alternatively, the mobile communication terminal 200 may newly establish a communication channel with the handed-over target base station and then release the communication channel established with the serving base station 100 providing the service.

Up to now, the process of transmitting the received signal strength of the candidate base stations 300 to the serving base station 100 in order to determine the target base station for handover in the mobile communication terminal 200 has been described. Next, a method of determining the target base station in the serving base station 100 will be described with reference to FIG. 6. 6 is a flowchart illustrating a method of determining a target base station of a serving base station according to an embodiment of the present invention.

Referring to FIG. 6, the serving base station 100 provides a service to the mobile communication terminal 200 in step 610. In operation 615, the serving base station 100 determines whether a measurement report including the received signal strength measured for each candidate base station 300 is received from the mobile communication terminal 200.

If the measurement report is received from the mobile communication terminal 200, the serving base station 100 checks the received signal strength of each candidate base station 300 included in the measurement report in step 620. The serving base station 100 determines the traffic load for each candidate base station in step 625. Here, the serving base station 100 may check the traffic load through the base station information transmitted and received with the candidate base station 300.

The serving base station 100 calculates a traffic load correction value using a wavelet distribution function in step 630. The trickle load correction value is a value calculated to correct a traffic load that may change when a handover is performed. The serving base station 100 calculates the cost function f _{k, i} using the received signal strength, traffic load, and traffic load correction in step 635. The cost function is a value that predicts the traffic load of the base station to be handed over when the handover is performed. Since the cost function f _{k, i} is calculated in FIG. 2, the detailed description thereof is omitted.

The serving base station 100 determines the candidate base station 300 selected as the target base station according to the cost function f _{k, i} calculated in step 640. For example _{, the} candidate base station 300 having the smallest cost function f _{k, i} may be the target base station. If the calculated cost function f _{k, i} is not less than the previously stored cost function threshold 125, the serving base station 100 does not determine the candidate base station 300 as the target base station. Although not shown in the figure, if the target base station is not determined, the serving base station 100 again determines whether the received signal strength is received from the mobile communication terminal 200. When the received signal strength is received, the serving base station 100 may again calculate a cost function to determine the target base station.

If the target base station is determined, the serving base station 100 determines in step 645 whether it is time to perform a handover. If the handover is not performed, the serving base station 100 continues the service that was originally performed with the mobile communication terminal 200 in step 650.

On the other hand, when the handover is performed, the serving base station 100 recovers the radio resources allocated to the mobile communication terminal 200 in step 660. The serving base station 100 performs a handover in step 670. In more detail, when the handover is performed, the serving base station 100 transmits a handover request signal to the target base station. At this time, the serving base station 100 includes the identification information of the mobile communication terminal 200 and the information on the service being performed in the handover request signal and transmits them together to the target base station. When the handover response signal is received from the target base station, the serving base station 100 transmits a handover commend to the mobile communication terminal 200. Next, the serving base station 100 recovers the radio resources allocated to the mobile communication terminal 200 and completes the handover.

Next, a result when handover is performed according to each condition and a result when handover is performed according to the present invention will be described with reference to FIG. 7. When the target base station is determined according to the received signal strength, when the target base station is determined according to the received signal strength and traffic load, and the target base station is determined according to the cost function, the probability of handover is described with reference to FIG. 7. FIG. . 7 is a graph illustrating a drop rate of handover according to the present invention.

Referring to FIG. 7, the horizontal axis represents a new call service try, and the vertical axis represents a handover drop rate. The method for determining the target base station for handover includes determining a target base station using only received signal strength, determining a target base station according to received signal strength and traffic load, and receiving signal strength, traffic load, and traffic load correction values. A method of determining the target base station according to the cost function calculated using the above was used.

The parameter values for the wave probability distribution are determined as shown in Table 1.

parameter a b k1 k2 value 0.4 0.3 0.35 0.56

In addition, the size of the signal strength threshold for performing the handover is set to 3.5dB, the length of the Time To Trigger is 300ms, and the base station information exchanged between the base stations is updated every 100ms. The result of the handover using the conditions set as described above is shown in a graph shown in FIG. 7.

Looking at the graph, it can be seen that the handover drop rate is the highest when the target base station is determined based on the received signal strength. And it can be seen that the handover drop rate is the lowest when the target base station is determined by calculating the cost function. Accordingly, it can be seen that the performance is good when the target base station is determined through the cost function.

In the above description, embodiments of the present invention disclosed in the specification and drawings are merely illustrative of the technical contents of the present invention, and specific examples are provided for the understanding of the present invention, and are not intended to limit the scope 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 diagram illustrating a configuration of a system in which a handover according to the prior art is performed.

2 is a diagram schematically illustrating a configuration of a base station according to an embodiment of the present invention.

3 is a diagram illustrating a configuration of a mobile communication terminal according to an embodiment of the present invention.

4 is a flowchart illustrating a method of determining a target base station in a system consisting of a mobile communication terminal and a plurality of base stations according to an embodiment of the present invention.

5 is a flowchart illustrating a method of determining a target base station of a mobile communication terminal according to an embodiment of the present invention.

6 is a flowchart illustrating a method of determining a target base station of a serving base station according to an embodiment of the present invention.

7 is a graph of the performance probability of handover according to the present invention.

Claims (12)

In the handover method of the communication system, Receiving, by a serving base station, received signal strengths of at least one candidate base station from a mobile communication terminal; Checking, by the serving base station, the traffic load for each candidate base station corresponding to the received received signal strength; Calculating, by the serving base station, a cost function that is a traffic load when handover is performed by using the received signal strength and the traffic load for each candidate base station; Determining, by the serving base station, one of the candidate base stations as a target base station according to the calculated cost function; And And handing over the terminal to the target base station according to the determination of the serving base station. The method of claim 1, wherein the calculating of the cost function Calculating a traffic load correction value for each candidate base station to correct the traffic load that may change when the handover is performed; And And calculating a cost function for each candidate base station by using the received signal strength, the traffic load amount, and the traffic load correction value. The method of claim 1, wherein the determining of the target base station is performed. And determining a candidate base station corresponding to the largest cost function among the calculated cost function for each candidate base station as the target base station. The method of claim 1, wherein the determining of the target base station is performed. Determining whether the calculated cost function for each candidate base station is greater than or equal to a set cost function threshold; And If the calculated cost function is greater than or equal to the cost function threshold, the candidate base station corresponding to the calculated cost function is determined as the target base station, and if it is less than the cost function threshold, the candidate base station is not determined as the target base station. Handover method characterized in that it further comprises a process. The method of claim 1, And transmitting the received signal strength to the serving base station when the received signal strength is equal to or greater than a set signal strength threshold. In a communication system in which handover is performed, At least one candidate base station determined as a target base station to be handed over; The mobile communication terminal transmitting a received signal strength received from the at least one candidate base station to a serving base station providing a service when performing a handover; And When the received signal strength is received, determine a traffic load for each candidate base station, calculate a cost function using the received signal strength and the traffic load, and transfer the candidate base station to the target base station according to the calculated cost function. Handover system consisting of the serving base station to determine. The method of claim 6, wherein the serving base station A traffic load correction value for correcting the traffic load that can be changed during handover is calculated, and a cost function is calculated using the received signal strength, the traffic load, and the traffic load correction value. Handover system. The method of claim 7, wherein the serving base station And a candidate base station corresponding to the largest cost function among the calculated cost function for each candidate base station is determined as the target base station. The method of claim 7, wherein the serving base station It is determined whether the calculated cost function is greater than or equal to a set cost function threshold. If the cost function is greater than or equal to the cost function threshold, the candidate base station is determined as the target base station. If the cost function is less than the cost function threshold, the candidate base station is less. Handover system, characterized in that not to determine the target base station The method of claim 7, wherein the mobile communication terminal It is determined whether the received signal strength received from the candidate base station is greater than or equal to a set signal strength threshold value, and if the received signal strength is greater than or equal to the signal strength threshold value, the received signal strength is transmitted to the serving base station. system. The method of claim 7, wherein the traffic load correction value is Handover system characterized in that the random variable generated by using a wavelet distribution function obtained from previously measured data. The method of claim 11, wherein the wavelet distribution function And a parameter for calculating an updated wavelet distribution function according to the environment of the communication system, and calculating the parameter using the determined parameter.

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