JP2012249132A - Radio communication system, base station, handover optimization method and handover method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio communication system having handover suppression means with a particular neighboring cell, capable of improving a handover success rate in the overall cell, without increasing abnormal communication disconnection when a handover failure rate with the particular neighboring cell is high.SOLUTION: The radio communication system comprises a base station for managing a first cell to which a mobile terminal is connected. The mobile terminal can be handed over from the first cell to a second cell. Based on measurement information of radio quality for each cell, reported from the mobile terminal, the radio communication system includes an alternate cell detection unit for detecting a third cell, having the radio quality of a predetermined value or higher, from cells excluding the second cell; and based on the detection result of the third cell by the alternate cell detection unit, a handover suppression unit for suppressing handover to the second cell.

Description

  The present invention relates to a wireless communication system having a handover suppressing function, a base station, a handover optimization method, and a handover method.

  In a wireless communication system, when a mobile terminal moves from a connection-destination radio cell (source cell) to another radio cell, the mobile terminal performs a connection-destination radio cell switching process called handover, and continues communication. In order to implement handover of the mobile terminal, the base station managing the source cell instructs the mobile terminal to transmit a measurement report when a predetermined event occurs. The predetermined event is, for example, deterioration of the radio quality of the source cell. The measurement report generated by the mobile terminal includes the measurement results of the radio quality of the source cell and its neighboring cells. When the base station receives the measurement report from the mobile terminal, the base station determines a switching destination radio cell (target cell) based on the measurement report, and starts a handover procedure including signaling between the mobile terminal and the target cell.

Here, one of the measurement report transmission events defined in 3GPP technical specifications (3GPP TS 36.331 V8.11.0) related to LTE (Long Term Evolution) / E-UTRAN (Evolved UTRAN) will be introduced. The essential part of the reporting event defined as Event A3 (Neighbor becomes offset better than serving) in the technical specification is expressed by the following equation (1).
P _S + O _S <P _T + O _T (1)

P _S in the formula (1) is a wireless quality measurement result of the source cell, P _T is the measurement result of the radio quality of the neighboring cell. If LTE, employed is _{P S} and _{P T,} the received power of the downlink reference signal (RSRP: Reference Signal Received Power) or reference signal received quality: a (RSRQ Reference Signal Received Quality). RSRQ is the ratio of RSRP to the total received power (RSSI: Received Signal Strength Indicator). Also, O _S in formula (1) is an offset value for the radio quality of the source cell, it acts on the radio quality of the downlink reference signal source cell. On the other hand, O _T is the offset value for the radio quality of the neighboring cells, acting on the radio quality of the downlink reference signals of neighboring cells.

O _T is generally in the cell individual offset: a handover parameter called (CIO Cell Individual Offset), for each neighboring cell registered in the neighbor list, it is possible to set different offset values. The CIO is included in the neighbor list notified from the base station to the mobile terminal connected to the radio cell managed by the base station.

  When the operating condition of Expression (1) is set in the base station, the operating condition of Expression (1) is notified to the mobile terminal connected to the radio cell managed by the base station. The mobile terminal transmits a measurement report to the base station that manages the source cell, triggered by the measurement results of the radio quality of the source cell and the radio quality of the neighboring cell satisfying the condition of Equation (1).

Conventionally, techniques for dynamically adjusting handover parameters such as the offset value O _t (CIO) and Time to Trigger (TTT) described above are known. Note that TTT is a protection time from when the measurement report transmission condition such as the above-described equation (1) is satisfied until the measurement report is transmitted. For example, the mobile terminal transmits a measurement report when the period that satisfies the condition of Expression (1) continues beyond the period defined as TTT. In other words, the longer the TTT, the later the start timing of the handover and the more difficult the handover occurs.

  Patent Document 1 discloses a method for reducing handover failures (Too Late Handover, Too Early Handover) by dynamically adjusting handover parameters (TTT, CIO, etc.) based on a measurement report of a mobile terminal. Yes. For example, when the timing of handover with the target cell is too early and fails (Too Early Handover), the success rate of handover is improved by delaying the timing of handover by reducing the CIO.

However, the radio cells that can notify the mobile terminal of the offset value O _t are limited to the neighbor cells registered in the neighbor list. In general, there is an upper limit on the number of radio cells that can be registered in the neighbor list. Therefore, the offset value O _t cannot be notified to the mobile terminal for radio cells that cannot be registered in the neighbor list. In this case, because it can not timing adjustment regulation by the mobile terminal a handover offset value O _t, for example, as in Patent Document 1, it becomes difficult to realize the improvement of the handover success rates based on the adjustment of the offset value O _t .

  The 3GPP technical specification (3GPP TS 36.300 V8.12.0) for LTE / E-UTRAN specifies an interface that can set a handover prohibition flag for each neighboring cell even for neighboring cells that are not registered in the neighboring list. Yes. FIG. 18 is a diagram illustrating the contents of a Neighbor Relation Table (NRT) that manages flag settings for each adjacent cell. In some cases, the handover success rate can be improved by suppressing the handover to the neighboring cell in which the NoHO flag is set in the NRT.

  FIG. 19 is a diagram illustrating a case where the success rate of handover is improved by suppressing handover to a specific neighboring cell. In FIG. 19, the handover to the adjacent cell A (second cell) is performed due to the deterioration of the radio quality (RSRQ) of the source cell (first cell), but the RSRQ of the adjacent cell A suddenly increases. This shows a situation in which an abnormal disconnection of communication occurs when the handover to another neighboring cell is not in time and the RSRQ of the neighboring cell A falls below the required quality. After abnormal disconnection, the mobile terminal reconnects to the adjacent cell B (third cell) that exceeds the required quality.

  In such a case, the handover success rate can be improved by suppressing the handover to the adjacent cell A that causes abnormal disconnection of communication. That is, handover from the source cell to the adjacent cell B is performed, and abnormal disconnection of communication in the adjacent cell A is avoided. Hereinafter, an alternative adjacent cell that can avoid abnormal disconnection in the target cell, such as the adjacent cell B, will be referred to as an alternative cell.

International Publication No. 2010/002926

3GPP TS36.331 v.8.11.0, "Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification", 2010. 3GPP TS 36.300 v8.12.0: "Radio Access (E-UTRA) and Radio Access Network (E-UTRAN); Overall description; Stage 2", 2010. 3GPP TS 36.423 v9.5.0: "Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 application protocol (X2AP)", 2010.

  Even if handover to an adjacent cell that causes abnormal disconnection of communication is suppressed, abnormal disconnection of communication may not be avoided. FIG. 20 is a diagram for explaining a case where the handover success rate cannot be improved even if the handover to a specific neighboring cell is suppressed.

In FIG. 20, as in FIG. 19, after a handover to adjacent cell A is performed, abnormal communication disconnection occurs in adjacent cell A, and the mobile terminal reconnects to adjacent cell B after the abnormal disconnection. Is shown. In this case, since there is a time point (T _Fail ) in which both the RSRQ of the source cell and the neighboring cell B are lower than the required quality between the handover request and the reconnection, even if the handover to the neighboring cell A is suppressed, Before the RSRQ of the cell falls below the required quality, it is not possible to perform handover to another neighboring cell that exceeds the required quality, and an abnormal disconnection of communication occurs at the time (T _Fail ).

As described above, when there is no other neighboring cell serving as a substitute cell for the neighboring cell A, if the handover to the neighboring cell A is suppressed, abnormal disconnection of communication may increase. For example, when the moving speed of the terminal is low, the RSRQ of the adjacent cell A decreases relatively gradually, so that handover to another adjacent cell may be in time, but abnormal disconnection at the time (T _Fail ) Since there is no neighboring cell whose RSRQ exceeds the required quality other than the neighboring cell A that suppresses the handover, abnormal disconnection of communication occurs in all the mobile terminals. Therefore, if the handover to the adjacent cell A is suppressed, there is a possibility that the total number of abnormal disconnections increases by the amount of abnormal disconnection of the low-speed mobile terminal at the time point (T _Fail ).

  In an actual source cell, a place where there is a substitute cell as shown in FIG. 19 and a place where there is no substitute cell as shown in FIG. 20 are mixed. Therefore, when the number of times that the mobile terminal passes through a place where there is no alternative cell of the target cell is larger than the number of handover failures from the source cell to the target cell, If handover to adjacent cells that cause abnormal disconnection of communication is uniformly suppressed by setting the prohibition flag, there is a problem that abnormal disconnection of communication may be increased.

  Therefore, in view of the above problems, the present invention provides a wireless communication system, a base station, and handover optimization that can improve the success rate of handover of the entire cell without increasing abnormal communication disconnection when there is no alternative neighboring cell that can be handed over It is an object to provide a method and a handover method.

  A radio communication system according to the present invention is a radio communication system including a base station that manages a first cell to which a mobile terminal is connected, wherein the mobile terminal can be handed over from the first cell to a second cell. Alternative cell detection means for detecting a third cell having a radio quality equal to or higher than a required value from cells other than the second cell based on measurement information of radio quality for each cell reported from the mobile terminal And a handover suppression unit that suppresses a handover to the second cell based on a detection result of the third cell by the alternative cell detection unit.

  The base station of the present invention is a base station that manages a first cell to which a mobile terminal is connected and processes a handover of the mobile terminal from the first cell to a second cell. Based on measurement information of radio quality for each cell reported from the terminal, an alternative cell detection means for detecting a third cell having a radio quality equal to or higher than a required value from cells other than the second cell; Handover suppression means for suppressing handover to the second cell based on the detection result of the third cell by the alternative cell detection means.

  The handover optimization method of the present invention is a handover optimization method for setting a handover parameter for suppressing handover of the mobile terminal from the first cell to which the mobile terminal is connected to the second cell, Based on the measurement information of radio quality for each cell measured by the mobile terminal, a third cell having a radio quality equal to or higher than a required value is detected from the cells other than the second cell, and the third cell Based on the detection result, a handover parameter for suppressing handover to the second cell is set.

Further, in the handover method of the present invention, in the handover process in which the mobile terminal switches the connection destination cell, the mobile terminal reports radio quality measurement information for each cell to the base station at the time of the handover request, and the base station Handover characteristics between the first cell to which the mobile terminal is connected and the second cell notified as the handover destination are inferior to a predetermined standard, and the first cell and the second In the measurement information of the cells other than the second cell, when there is a third cell whose radio quality is equal to or higher than a required value, the handover is performed to the third cell.

  Advantageous Effects of Invention According to the present invention, a radio communication system, a base station, a handover optimization method, and a handover that can improve the success rate of handover of the entire cell without increasing abnormal communication disconnection when there is no alternative neighboring cell that can be handed over A method can be provided.

It is a figure which shows the outline | summary of this invention. It is a block diagram which shows the structure of the radio | wireless communications system of the 1st Embodiment of this invention. It is a figure which shows an example of the management table of the handover statistical information which the quality statistics storage part shown in FIG. 2 manages. 3 is a flowchart for explaining the operation of the base station shown in FIG. It is a flowchart explaining the operation | movement of the alternative cell detection part shown in FIG. It is a flowchart explaining operation | movement of the HO suppression part shown in FIG. 3 is a flowchart illustrating an operation using CIO in the parameter setting unit shown in FIG. 2. 3 is a flowchart illustrating an operation that does not use CIO in the parameter setting unit illustrated in FIG. 2. 6 is a flowchart for explaining the operation of an alternative cell detection unit using radio quality when handover fails in the radio communication system according to the second embodiment of the present invention. It is a flowchart explaining the operation | movement of the alternative cell detection part which used the time series for radio | wireless quality in the radio | wireless communications system of the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the radio | wireless communications system of the 3rd Embodiment of this invention. It is a flowchart explaining the operation | movement of the HO suppression part shown in FIG. It is a block diagram which shows the structure of the radio | wireless communications system of the 4th Embodiment of this invention. It is a flowchart explaining operation | movement of the base station shown in FIG. It is a flowchart explaining operation | movement of the moving speed discrimination | determination part shown in FIG. It is a block diagram which shows the structure of the base station of the 5th Embodiment of this invention. 17 is a flowchart for explaining the operation of the base station shown in FIG. 16. It is a figure which shows an example of the management table of the flag setting for every adjacent cell. It is a figure explaining the case where a handover success rate is improved by the handover suppression to a specific adjacent cell. It is a figure explaining the case where a handover success rate cannot be improved even if it suppresses the handover to a specific neighboring cell.

  In describing each embodiment of the present invention, an outline of the present invention will be described first.

  As shown in FIG. 1, the present invention is characterized in that, in a radio communication system in which a mobile terminal performs handover from a currently connected serving cell (first cell) to another cell, the mobile terminal includes an alternative cell detection unit and a handover suppression unit. .

  In the radio system of the present invention, a cell (second cell) that can be handed over is determined based on measurement information of radio quality reported from a mobile terminal. Here, the alternative cell detection means newly provided in the wireless communication system detects the alternative cell (third cell) based on the radio quality measurement information reported from the mobile terminal. At this time, the alternative cell detection means detects an alternative cell from the cells excluding the cells that have a radio quality equal to or higher than a required value and that can be handed over, based on the measurement information.

  The handover suppressing means is a means for suppressing handover performed in the wireless communication system. Specifically, when handover characteristics to the second cell are inferior, the handover to the second cell is suppressed. . Here, the handover suppression unit performs the suppression based on the detection result of the third cell in the alternative cell detection unit.

  As described above, the radio communication system of the present invention does not uniformly suppress handover for cells having poor handover characteristics, but detection obtained by the detection means for detecting an alternative cell that satisfies a predetermined condition. Based on the result, it is determined whether or not to suppress handover.

  With such a configuration, handover suppression suitable for each situation can be performed, so that the success rate of handover of the entire cell can be improved. Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are denoted by the same reference numerals, and redundant description is omitted as necessary for the sake of clarity.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a diagram illustrating a configuration example of a wireless communication system having a handover suppressing function according to the present embodiment.

  The base station 30A manages the handover optimization target cell 35A and performs the handover process of the mobile terminal 10 under its control. Here, the optimization target cell is a cell to be optimized for handover, and is a cell (source cell) to which the mobile terminal 10 is connected before the handover. Since the optimization target cell is a cell that provides a service to the mobile terminal 10 before the handover, the optimization target cell may be hereinafter referred to as a serving cell.

  The base station 30A includes a handover control unit (hereinafter referred to as HO control unit) 101, a handover characteristic management unit (hereinafter referred to as HO characteristic management unit) 102, and an alternative cell detection unit 103, and is connected to the network management system 90. .

  The network management system 90 includes a handover suppression unit 96 (hereinafter referred to as an HO suppression unit) and a quality statistics storage unit 104. The HO suppression unit 96 includes a parameter setting unit 105.

  The base station 30B manages the neighboring cell 35B of the optimization target cell 35A. When receiving a handover request for the mobile terminal 10 from the base station 30A, the base station 30B performs an acceptance process for the mobile terminal 10. The base station 30B includes a failure information notification unit 106, and when the handover of the mobile terminal 10 fails, the failure information notification unit 106 notifies the base station 30A of handover failure information.

  When receiving a handover request from the mobile terminal 10, the HO control unit 101 acquires measurement information regarding the radio quality of neighboring cells from the mobile terminal 10. The HO control unit 101 determines a target cell based on the acquired measurement information and executes a handover to the target cell.

The alternative cell detection unit 103 acquires measurement information at the time of a handover request of the mobile terminal 10 from the HO control unit 101, and detects an alternative cell from neighboring cells included in the measurement information. However, the neighbor cell (suppression target cell) that has already been set with the NoHO flag and is the target of suppression of handover from the optimization target cell 35A, and the neighbor cell selected as the target cell at the time of detection are excluded. Here, the NoHO flag is a flag indicating that it is an adjacent cell that is a target for suppressing handover, and specifically, is a prohibition flag indicating that handover to the adjacent cell is prohibited.

  The HO characteristic management unit 102 acquires information regarding success or failure of the handover from the failure information notification unit 106 and further acquires a detection result of the alternative cell from the alternative cell detection unit 103. Here, the information regarding success or failure of the handover is specifically failure information indicating that the handover has failed. The HO characteristic management unit 102 counts the number of handover attempts for each adjacent cell and counts the number of handover failures for each adjacent cell for each presence / absence of an alternative cell based on the acquired information. The HO characteristic management unit 102 periodically transmits the hand-over statistical information collected in this way to the network management system 90.

  When the handover of the mobile terminal 10 fails, the failure information notification unit 106 notifies the failure information of the handover to the base station 30A. The handover failure information includes the identification information of the source cell and the target cell in the handover source radio cell, and the identification information of the radio cell to which the mobile terminal 10 has reconnected after the handover failure. As such handover failure information, for example, HANDOVER REPORT defined in 3GPP technical specifications (3GPP TS 36.423 V9.5.0) regarding LTE / E-UTRAN can be used.

The quality statistics storage unit 104 is an area for storing handover statistical information (hereinafter referred to as HO statistical information) received from the HO characteristic management unit 102 in the network management system 90. FIG. 3 is a diagram illustrating an example of a management table of HO statistical information stored in the quality statistical storage unit 104. As shown in FIG. 3, in the management table, the number of handover attempts (A _i ) and the number of handover failures when there is an alternative cell (F _i ) regarding the handover performed from the optimization target cell 35A to the neighboring cell i. ), The number of handover failures (F ^′ _i ) when there is no alternative cell is recorded.

  The HO suppression unit 96 determines a suppression target cell based on the HO statistical information recorded in the quality statistics storage unit 104, and sets a handover parameter for suppressing handover for the suppression target cell. This setting is performed by the parameter setting unit 105.

  The parameter setting unit 105 uses, for example, the aforementioned NRT NoHO flag or CIO as a handover parameter for suppressing handover. Specifically, the handover to the suppression target cell is suppressed by enabling the NoHO flag of the suppression target cell. Alternatively, when the suppression target cell is registered in the neighbor list, a significantly large negative CIO is set for the suppression target cell such that the suppression target cell is not included in the measurement information of the mobile terminal 10. The handover parameter set by the parameter setting unit 105 is notified from the HO suppression unit 96 to the base station 30.

  The HO control unit 101 performs the target cell determination process described above in accordance with the handover parameter notified from the HO suppression unit 96. That is, when the NoHO flag is used as a handover suppression unit, the HO control unit 101 determines a target cell from neighboring cells in which the NoHO flag is invalid among neighboring cells included in the measurement information of the mobile terminal 10. On the other hand, when the CIO is used as a handover suppression unit, the HO control unit 101 has a significantly large negative CIO set in the suppression target cell so that the measurement target cell does not include the suppression target cell. Is notified to the mobile terminal 10.

  Next, the operation of the wireless communication system having the handover suppressing function according to this embodiment will be described. FIG. 4 is a flowchart for explaining the operation of the base station 30A.

  The HO control unit 101 acquires, from the mobile terminal 10 connected to the base station 30A, the measurement information of the radio quality of the neighboring cell reported by the mobile terminal at the time of the handover request (Step S101).

  Next, the HO control unit 101 determines a target cell from neighboring cells in which the NoHO flag is invalid based on the acquired measurement information (step S102). Next, the HO control unit 101 performs handover for the target cell determined in step S102 (step S103).

When the HO control unit 101 executes a handover, the HO characteristic management unit 102 counts the number of handover attempts (A _i ) of the target cell among the number of handover attempts (A) for each adjacent cell managed by the base station 30A. Is increased by one (step S104).

  The HO control unit 101 acquires the failure information of the handover performed in step S103 from the failure information notification unit 106 of the base station 30B (step S105). That is, when the handover of the mobile terminal 10 performed in step S103 fails, the failure information notification unit 106 notifies the base station 30A of handover failure information.

  The HO control unit 101 determines the success or failure of the handover according to the presence / absence of failure information (step S106). That is, the HO control unit 101 determines that the handover has succeeded when failure information is not notified from the failure information notification unit 106, and determines that the handover has failed when failure information is notified. If it is determined in step S106 that the handover has succeeded, the HO control unit 101 ends the entire process.

  On the other hand, if it is determined in step S106 that the handover has failed, the alternative cell detection unit 103 acquires measurement information at the time of the handover request of the mobile terminal 10 from the HO control unit 101 and detects an alternative cell (step S106). S107).

  The HO characteristic management unit 102 totals the number of handover failures according to the presence / absence of an alternative cell based on the detection result of the alternative cell detection unit 103 according to the processing flow of steps S108 to S110 below.

  That is, the HO characteristic management unit 102 inputs the result of the detection process performed by the alternative cell detection unit 103 in step S107, and determines whether there is an alternative cell (step S108).

If the HO characteristic management unit 102 determines in step S108 that there is no replacement cell, the handover failure number (F ^′) when there is no replacement cell among the number of handover failures for each adjacent cell managed by the base station 30A. _i ) is incremented by one to update the handover statistical information (step S109), and the whole process is terminated.

On the other hand, if the HO characteristic management unit 102 determines in step S103 that there is an alternative cell, the number of handover failures when there is an alternative cell among the number of handover failures for each adjacent cell managed by the base station 30A ( F _i ) is incremented by 1 to update the handover statistical information (step S110), and the whole process is terminated.

  Next, an alternative cell detection method will be described. FIG. 5 is a flowchart for explaining the operation of the alternative cell detection unit 103.

  As shown in FIG. 5, the alternative cell detection unit 103 initializes the set S to an empty set (step S301). Next, the alternative cell detection unit 103 acquires, from the control unit 101, measurement information of the radio quality of the neighboring cell reported by the mobile terminal 10 at the time of the handover request (Step S302).

  Next, the alternative cell detection unit 103 stores, in the set S, neighboring cells that can be handed over other than the suppression target cell and the target cell among the neighboring cells included in the measurement information (step S303). At this time, the alternative cell detection unit 103 selects a radio cell whose radio quality such as reception power (RSRP in LTE) or signal-to-interference wave ratio (RSRQ in LTE) included in the measurement information is equal to or higher than a threshold value, Extracted as a neighbor cell that can be handed over.

  Next, the alternative cell detection unit 103 determines whether or not the set S is an empty set (step S304). If the result of determination in step S304 is that the set S is an empty set, the alternative cell detection unit 103 determines that no alternative cell has been detected (step S305), and ends the entire process. On the other hand, if the adjacent cell is included in the set S, the alternative cell detection unit 103 determines that an alternative cell has been detected (step S306), and ends the entire process.

  Next, a method for suppressing handover will be described. FIG. 6 is a flowchart for explaining the operation of the HO suppressing unit 96.

  As illustrated in FIG. 6, the HO suppressing unit 96 selects an optimization target cell (step S201). When the optimization target cell is selected in step S201, the HO suppression unit 96 sequentially selects all the wireless cells 35 under the network management system 90, for example. Alternatively, the HO suppression unit 96 may select a radio cell 35 whose handover failure rate of the entire cell is equal to or greater than a threshold as an optimization target cell.

  Next, the HO suppression unit 96 accesses the quality statistics storage unit 104 and refers to the HO statistical information of the optimization target cell selected in step S201 (step S202).

Next, the HO suppression unit 96 extracts neighboring cells whose radio quality at the time of HO request is equal to or higher than a threshold based on the HO statistical information referred to in step S202 (step S203). Specifically, for each neighboring cell (j), the HO suppression unit 96 determines the number of handover attempts (A _j ) for the neighboring cell (j), the number of handover failures (F _j ) when there is an alternative cell, and the alternative cell. The handover failure rate (R _{HoFail, j} ) of the neighboring cell ( _j ) is calculated with reference to the number of handover failures (F ^′ _j ) in the case of none, and the failure rate (R _{HoFail, j is} determined as a cell with inferior handover characteristics. ) Is extracted adjacent cells (adjacent cell k) having a threshold value or more.

The handover failure rate (R _{HoFail, j} ) can be calculated using Equation (1), for example.
(Expression 1) R _{HoFail, j} = (F _j + F ^' _j ) / A _j

  In addition, when extracting the adjacent cell (adjacent cell k) in step S203, the HO suppressing unit 96 uses other handover characteristics such as the number of handover failures and the average stay time after handover to the adjacent cell, in addition to the handover failure rate. It doesn't matter. That is, the HO suppression unit 96 may extract neighboring cells having the number of failed handovers equal to or greater than a threshold and neighboring cells having an average stay time after handover equal to or less than the threshold as cells having handover characteristics inferior to a predetermined criterion. Further, the HO suppressing unit 96 may extract a neighboring cell (neighboring cell k) by combining a plurality of handover characteristics.

HO suppression unit 96, to the adjacent cell k extracted in step S203, to calculate the occupation ratio of the alternate cells have a handover failure number _{(F k) (R Share,} k), occupancy (R _{Share, k)} Is greater than or equal to a threshold (Th _Share ) (step S204). As a result of the determination, if the occupation ratio (R _{Share, k} ) is less than the threshold value (Th _Share ), the HO suppression unit 96 ends the entire process. On the other hand, when the occupation ratio (R _{Share, k} ) is equal to or greater than the threshold (Th _Share ), the HO suppression unit 96 regards the adjacent cell k as the suppression target cell. Note that the HO suppressing unit 96 can calculate the occupation ratio (R _{Share, k} ) using, for example, the following formula (2).
(Equation _{2) R Share, k = F} k / (F k + F 'k)

If it is determined in step S204 that the occupation ratio (R _{Share, k} ) is equal to or greater than the threshold value (Th _Share ), the HO suppression unit 96 causes the parameter setting unit 105 to perform handover parameters for suppressing handover to the adjacent cell k. Is set for the optimization target cell (step S205).

  The HO suppression unit 96 notifies the handover parameter set by the parameter setting unit 105 to the base station that manages the optimization target cell (step S206), and ends the entire process.

  As described above, the HO suppressing unit 96 determines whether or not to suppress the handover after taking into consideration the detection result of the alternative cell for the cell whose handover characteristic is inferior to the predetermined reference.

  Next, a method for setting handover parameters will be described. FIG. 7 is a flowchart for explaining the operation of the parameter setting unit 105.

  As illustrated in FIG. 7, the parameter setting unit 105 determines whether or not the suppression target cell is registered in the neighbor list (step S501). As a result of the determination, if the suppression target cell is not registered in the neighbor list, the parameter setting unit 105 sets a NoHO flag for the suppression target cell (step S504) and ends the entire process. On the other hand, when the suppression target cell is registered in the neighbor list, the parameter setting unit 105 determines whether or not the CIO of the suppression target cell has reached the lower limit (step S502). If the CIO has reached the lower limit value, the parameter setting unit 105 sets a NoHO flag for the suppression target cell (step S504), and ends the entire process. On the other hand, when the CIO of the suppression target cell has not reached the lower limit value, the parameter setting unit 105 sets the lower limit value for the CIO of the suppression target cell (step S503) and ends the entire process.

  Note that the handover parameter setting method performed by the parameter setting unit 105 is not limited to the above setting method. For example, the configuration may be set according to a flowchart for explaining the operation of the parameter setting unit 105 shown in FIG.

  In FIG. 8, the parameter setting unit 105 determines whether or not the suppression target cell is registered in the neighbor list (step S501). If it is determined that the suppression target cell is not registered in the neighbor list, the parameter setting unit 105 sets a NoHO flag for the suppression target cell (step S504) and ends the entire process. On the other hand, if it is determined that the suppression target cell is registered in the neighbor list, the suppression target cell is deleted from the neighbor list (step S505), and then the NoHO flag is set for the suppression target cell (step S504). ), The entire process is terminated. The handover parameter setting method may be configured by such processing.

  As described above, the radio communication system according to the present embodiment has a radio quality of the cell excluding the target cell (second cell) based on the radio quality measurement information for each cell reported from the mobile terminal. An alternative cell detection means for detecting an alternative cell (third cell) that is equal to or greater than a required value is provided. And the handover suppression means which suppresses the hand-over to a 2nd cell based on the detection result of the 3rd cell by an alternative cell detection means is further provided. By adopting such a configuration, since handover of the target cell is suppressed in consideration of the existence of an alternative cell, the success rate of handover of the entire cell can be improved.

  More specifically, according to the present embodiment, when the handover characteristic is inferior to a predetermined criterion such as a high handover failure rate from the optimization target cell to a specific neighboring cell, there is an alternative neighboring cell that can be handed over Only suppress handover to neighboring cells with a high failure rate. That is, according to the present embodiment, the handover failure rate is determined not by uniformly suppressing handovers to neighboring cells having a high handover failure rate as in the prior art, but by considering the existence of alternative cells that can be handed over. Suppresses handover to a neighboring cell having a high value. As a result, the success rate of handover of the entire cell can be improved without increasing abnormal communication disconnection when there is no alternative neighboring cell that can be handed over.

(Second Embodiment)
The wireless communication system according to the present embodiment is characterized in that a substitute cell is detected based on measurement information of wireless quality at a plurality of points in time, as compared with the first embodiment. Hereinafter, it explains in detail using a drawing. The block configuration of the wireless communication system is the same as that of the first embodiment, and will be described with reference to FIG.

  FIG. 9 is a flowchart for explaining the operation of the alternative cell detection unit 103 in the wireless communication system of this embodiment. In FIG. 9, the same processes as those in FIG.

  The failure information notification unit 106 according to the present embodiment newly adds the measurement information of the radio quality of the neighboring cell measured by the mobile terminal 10 at the time of handover failure to the failure information and notifies the base station 30A. The time of handover failure means, for example, a point in time when an abnormal disconnection of the radio line occurs during the handover from the source cell to the target cell. Alternatively, it means a point in time when an abnormal disconnection of the radio line occurs within a certain period immediately after the handover from the source cell to the target cell is completed.

  When the neighboring cell is included in the set S in step S304, that is, when the substitute cell is detected, the alternative cell detecting unit 103 fails the measurement information of the radio quality of the adjacent cell when the handover of the mobile terminal 10 fails. Obtained from the information (step S401).

  The alternative cell detection unit 103 determines whether there is an adjacent cell whose wireless quality at the time of handover failure is equal to or higher than a threshold among the adjacent cells included in the set S (step S402). If the result of determination in step S402 is that there is no adjacent cell that satisfies the condition, it is determined that no alternative cell has been detected (step S305), and the entire process ends. On the other hand, if such an adjacent cell exists, it is determined that an alternative cell has been detected (step S306), and the entire process ends.

  If the failure information notification unit 106 can notify the base station 30A of the time information of the radio quality measurement information of the neighboring cell between the time when the mobile terminal 10 requests handover and the time of failure, the failure information notification unit 106 can notify the base station 30A. The operation shown in FIG. 10 can be performed as the operation of the alternative cell detection unit 103 in the embodiment.

  In the operation illustrated in FIG. 10, when the neighboring cell is included in the set S in step S <b> 304, i.e., when an alternative cell is detected, the alternative cell detection unit 103 performs the process from the time when the mobile terminal 10 requests handover until the time when the mobile terminal 10 fails. A time series of measurement information of radio quality of neighboring cells is acquired from the failure information (step S410).

  The alternative cell detection unit 103 determines whether or not a neighboring cell whose radio quality is always equal to or higher than the threshold value is included in the set S from the time of the handover request to the time of the handover failure (step S411). If the result of determination in step S411 is that there is no neighboring cell that satisfies the condition, it is determined that no alternative cell has been detected (step S305), and the entire process is terminated. On the other hand, if such an adjacent cell exists, it is determined that an alternative cell has been detected (step S306), and the entire process ends.

  As described above, according to the present embodiment, an alternative cell is detected based on measurement information of radio quality at a plurality of points in time, and a handover to a specific neighboring cell having a high handover failure rate is suppressed according to the detection result of the alternative cell. To do.

  In the first embodiment, there are cases where a neighboring cell whose radio quality is lower than the required quality after the handover request is erroneously detected as an alternative cell. On the other hand, according to the present embodiment, such a false detection can be reduced because the alternative cell is detected based on the radio quality at a plurality of points in time after the handover request.

(Third embodiment)
Compared with the first and second embodiments, the wireless communication system according to the present embodiment is newly provided with a mechanism for monitoring a change in handover characteristics after suppressing a handover to a specific neighboring cell. It is characterized in that it is configured to be able to release the immediately preceding suppression when the characteristics deteriorate. Hereinafter, the wireless communication system according to the present embodiment will be described in detail with reference to the drawings.

  FIG. 11 is a diagram illustrating a configuration of the wireless communication system according to the present embodiment. In FIG. 11, the same components as those in FIG.

  As shown in FIG. 11, the present embodiment is different from the first and second embodiments in that the HO suppression unit 96 further includes a quality monitoring unit 201. The quality monitoring unit 201 refers to the HO statistical information stored in the quality statistical storage unit 104, and when the handover characteristic is deteriorated due to the suppression performed by the HO suppression unit 96, the quality monitoring unit 201 determines the parameter immediately before the parameter setting unit 105. Request release of changes.

  Next, the operation of the wireless communication system of this embodiment will be described. FIG. 12 is a flowchart for explaining the operation of the HO suppression unit 96 in the wireless communication system of the present embodiment. In FIG. 12, the same processes as those in FIG.

  The quality monitoring unit 201 waits until a predetermined period (T) elapses after the HO suppressing unit 96 notifies the handover parameter to the base station that manages the optimization target cell (step S501). The quality monitoring unit 201 accesses the quality statistics storage unit 104 when a certain period (T) has elapsed, and performs HO statistical information on the optimization target cell when the certain period (T) has elapsed since the handover parameter was changed. Is referred to (step S502).

  The quality monitoring unit 201 determines whether or not the handover characteristics of the optimization target cell have deteriorated based on the acquired statistical information (step S503). As a result of the determination, if the handover characteristics are not degraded, the handover suppressing unit 96 ends the entire process. On the other hand, when the handover characteristic is deteriorated, the quality monitoring unit 201 requests the parameter setting unit 105 to cancel the handover suppression (step S504).

  Note that the quality monitoring unit 201 determines that the handover characteristics have deteriorated when, for example, the abnormal disconnection rate of communication of the entire source cell or the handover failure rate to the alternative cell increases by a certain value or more compared to before the handover suppression. To do. At this time, the quality monitoring unit 201 can calculate the handover failure rate using, for example, Equation (1).

  The parameter setting unit 105 receives a request for canceling suppression from the quality monitoring unit 201 and sets a handover parameter for canceling handover suppression to the suppression target cell. That is, settings such as returning the CIO to the value before the change or invalidating the NoHO flag are performed. The HO suppression unit 96 notifies the handover parameter set by the parameter setting unit 105 for canceling the suppression to the base station 30A that manages the optimization target cell (step S505), and ends the entire process.

  As described above, the wireless communication system according to the present embodiment monitors a change in handover characteristics after suppressing a handover to a specific neighboring cell, and releases the immediately preceding suppression when the handover characteristics deteriorate due to the suppression. .

  In the first and second embodiments, when communication quality of an optimization target cell deteriorates due to suppression of handover to a specific neighboring cell, the deterioration cannot be alleviated. On the other hand, according to the present embodiment, when the handover characteristic deteriorates due to the suppression, the immediately preceding suppression is released, and thus such deterioration can be mitigated.

(Fourth embodiment)
Compared with the first to third embodiments, the wireless communication system according to the present embodiment is newly provided with a mechanism for determining the moving speed of the mobile terminal 10 and suppresses handover to a specific neighboring cell. The difference is that it can be applied only to.

  FIG. 13 is a diagram illustrating a configuration of the wireless communication system according to the present embodiment. In FIG. 13, the same components as those in FIG.

  As illustrated in FIG. 13, the present embodiment is different from the first to third embodiments in that the HO control unit 101 includes a moving speed determination unit 301. The moving speed discriminating unit 301 obtains history information of wireless cells connected in the past from the mobile terminal 10 and discriminates whether the terminal is a high speed mobile terminal or a low speed mobile terminal based on the obtained information. The moving speed determination unit 301 notifies the HO control unit 101 of the determination result.

  Next, the operation of the wireless communication system of this embodiment will be described. FIG. 14 is a flowchart for explaining the operation of the base station 30A in the wireless communication system of this embodiment. In FIG. 14, the same processes as those in FIG.

  The moving speed determination unit 301 determines whether the mobile terminal 10 is a high-speed mobile terminal or a low-speed mobile terminal, and notifies the determination result to the HO control unit 101 (step S601).

  The HO control unit 101 determines a target cell according to the determination result of the moving speed in the moving speed determining unit 301. That is, when the HO control unit 101 determines that the mobile terminal 10 is a high-speed mobile terminal based on the determination result notified from the moving speed determination unit 301 (step S602), among the adjacent cells included in the measurement information Then, a target cell is determined from neighboring cells in which the NoHO flag is invalid (step S102). On the other hand, when it is determined that the mobile terminal 10 is a low-speed mobile terminal (step S602), a target cell is determined from all neighboring cells included in the measurement information (step S603).

  Next, a method for determining the moving speed of the terminal will be described. FIG. 15 is a flowchart for explaining the operation of the moving speed determination unit 301.

  As illustrated in FIG. 15, the moving speed determination unit 301 acquires history information of wireless cells to which the mobile terminal 10 has connected in the past from the mobile terminal 10 (step S701). Next, the moving speed determination unit 301 acquires the stay time of the cell connected immediately before from the history information (step S702).

  Next, the moving speed determination unit 301 determines the moving speed of the mobile terminal according to the stay time. Specifically, based on the history information acquired in step S702, the moving speed determination unit 301 compares the stay time of the cell to which the mobile terminal 10 has just connected with the reference period (P) (step S703). ).

  As a result of the comparison in step S703, when the stay time is shorter than the period (P), the moving speed determination unit 301 determines the mobile terminal 10 as a high-speed mobile terminal (step S704). On the other hand, when the stay time is longer than the period (P), the mobile terminal 10 is determined as a low-speed mobile terminal (step S705).

  In the present embodiment, as an example, the history information of the wireless cell connected in the past is acquired from the mobile terminal 10, but the history information is acquired from the base station to which the mobile terminal 10 was connected immediately before. It does not matter in the form.

  Thus, according to this embodiment, the moving speed of the terminal is determined, and handover to a specific neighboring cell is suppressed only for the high-speed mobile terminal.

  In the first to third embodiments, the suppression of handover to a specific neighboring cell is uniformly applied to all moving speeds connected to the source cell. Therefore, in an environment where terminals with various mobile speeds coexist, it is necessary to apply handover suppression unnecessarily to low-speed mobile terminals to promote handovers to neighboring cells with lower radio quality, resulting in lower throughput, etc. There was a possibility of causing deterioration of communication quality. On the other hand, according to the present embodiment, since handover suppression is applied only to high-speed mobile terminals, such deterioration of communication quality can be prevented.

(Fifth embodiment)
Compared with the first to fourth embodiments, the radio communication system according to the present embodiment includes a mechanism for determining whether handover suppression to a specific neighboring cell is appropriate in the base station, and each handover request of a mobile terminal. The difference is that the base station can determine and apply handover suppression each time.

  FIG. 16 is a diagram illustrating the configuration of the base station according to the present embodiment. In FIG. 16, the same components as those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIG. 16, the present embodiment is different from the first to fourth embodiments in that the base station 30A includes a quality statistics storage unit 401 and the HO control unit 101 includes a HO suppression unit 402. .

The quality statistics storage unit 401 is an area for storing handover statistical information such as the number of handover attempts (a _i ) and the number of handover failures (f _i ) regarding the handover performed from the optimization target cell 35 to the adjacent cell i. is there.

  The HO suppression unit 402 acquires the HO statistical information regarding the target cell determined by the HO control unit 101 based on the measurement report of the mobile terminal from the quality statistical storage unit 401, and acquires the detection result of the alternative cell from the alternative cell detection unit 103. Based on the acquired information, it is determined whether or not the handover to the alternative cell is necessary. The HO suppression unit 402 notifies the HO control unit 101 of the determination result.

  Next, the operation of the base station of this embodiment will be described. FIG. 17 is a flowchart for explaining the operation of the base station 30A of the present embodiment. In FIG. 17, the same processes as those in FIG. 4 are denoted by the same reference numerals, and the description thereof is omitted.

  The HO control unit 101 determines a target cell (neighboring cell (i)) based on the measurement report of the mobile terminal (step S801).

The HO suppression unit 402 acquires HO statistical information related to the target cell from the quality statistical storage unit 401 (step S802). Next, the HO suppressing unit 402 calculates the handover failure rate (R ^′ _{HoFail, i} ) of the neighboring cell (i) and determines whether the failure rate (R ^′ _{HoFail, i} ) exceeds the threshold (Th _HoFail ). Determination is made (step S803).

The handover failure rate (R ^′ _{HoFail, i} ) is calculated using Equation (3) based on the number of handover attempts (a _i ) and the number of handover failures (f _i ) for the neighboring cell (i), for example. Can do.
(Equation 3) R ^′ _{HoFail, i} = f _i / a _i

If it is determined in step S803 that the handover failure rate (R ^′ _{HoFail, i} ) is equal to or less than the threshold (Th _HoFail ), the HO control unit 101 performs handover for the target cell determined in step S801. (Step S103). On the other hand, if it is determined in step S803 that the handover failure rate (R ^′ _{HoFail, i} ) exceeds the threshold (Th _HoFail ), the alternative cell detection unit 103 uses the measurement information at the time of the handover request of the mobile terminal 10 as HO. Obtained from the control unit 101, and detects an alternative cell (step S107).

  As in the first embodiment, as the quality index in step S803, the number of handover failures and the average stay time after handover to the target cell may be used in addition to the handover failure rate.

  Alternatively, in step S803, instead of evaluating the handover failure rate, the presence / absence of NoHO setting for the neighboring cell (i) is checked. If NoHO is not set, the process proceeds to step S103, where NoHO is set. Alternatively, the process may move to step S107.

  In step S108, the HO suppressing unit 402 branches the process depending on the presence / absence of an alternative cell based on the detection result of the alternative cell detection unit 103. That is, when it is determined that there is no alternative cell, a handover is executed for the target cell determined in step S801 (step S103). On the other hand, if it is determined that there is an alternative cell, in step S804, a target cell is determined from the alternative cells detected by the alternative cell detection unit 103, and a handover to the determined target cell is executed (step S103).

  Even if it is determined in step S108 that there is an alternative cell, the handover to the alternative cell is executed in step S103 only when the handover characteristics of the alternative cell are not inferior. In other cases, step S801 is performed. Handover may be executed for the target cell determined in step (1).

  Thus, according to this embodiment, when the handover failure rate of the target cell determined based on the measurement report of the mobile terminal is high, the base station determines the presence / absence of an alternative cell based on the measurement report of the mobile terminal. If there is an alternative cell, the target cell is reselected from the alternative cells and the handover is executed.

  In the first to fourth embodiments, the suppression target cell is determined based on the result of counting the detection results of the alternative cells in units of adjacent cells. Therefore, in an environment where there are places where there are no alternative cells and where there are no alternative cells in the source cell, handover suppression is applied when there is no alternative cell, or abnormal communication disconnection without applying handover suppression even if there is an alternative cell. There was a possibility that handover mismatch would occur. On the other hand, according to the present embodiment, whether or not handover suppression is appropriate is determined for each handover request of a mobile terminal, and thus such mismatch of handover suppression can be prevented.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. For example, the present invention can take the following forms.

(1) A wireless communication system including a base station that manages a first cell to which a mobile terminal is connected, wherein the mobile terminal can be handed over from the first cell to a second cell, from the mobile terminal Based on the reported radio quality measurement information for each cell, an alternative cell detection means for detecting a third cell having a radio quality equal to or higher than a required value from cells other than the second cell, and the alternative cell A wireless communication system comprising: a handover suppressing unit that suppresses a handover to the second cell based on a detection result of the third cell by the detecting unit.
(2) When the handover characteristic to the second cell is inferior to a predetermined standard, the handover suppressing unit is configured to transfer the second cell to the second cell based on the detection result of the third cell by the alternative cell detecting unit. The wireless communication system according to (1), wherein handover is suppressed.
(3) The handover characteristic includes at least one of a handover failure rate to the second cell, a number of handover failures, and an average stay time after handover to the second cell. Wireless communication system.
(4) The radio communication system according to (1), wherein the radio quality includes at least one of reception power of a reference signal or a signal-to-interference wave and a noise power ratio transmitted from a base station that manages the cell.
(5) The handover suppression means includes statistics of the number of handover failures to the second cell when the third cell exists, and the second cell when the third cell does not exist The wireless communication system according to any one of (1) to (4), wherein it is determined to suppress handover to the second cell based on statistics of the number of handover failures.
(6) The alternative cell detecting means detects the third cell for each handover request from the mobile terminal, and the handover suppressing means is provided on the condition that the third cell is detected. The wireless communication system according to any one of (1) to (4), wherein handover to the second cell is suppressed.
(7) The handover suppressing unit suppresses handover to the second cell by notifying the mobile terminal of an offset value to be added to the radio quality measurement result of the second cell. ) Wireless communication system.
(8) The wireless communication system according to (5), wherein the handover suppressing unit suppresses a handover to the second cell by setting a handover prohibition flag for the second cell.
(9) The radio communication system according to (5), wherein the handover suppressing unit suppresses handover to the second cell only for a mobile terminal that moves at a high speed among the mobile terminals.
(10) The radio communication system according to (9), wherein the mobile terminal that moves at high speed is a mobile terminal in which a stay time of a cell connected immediately before the connected cell is equal to or less than a threshold value.
(11) The handover suppressing means includes quality monitoring means for monitoring the communication quality of the first cell after suppressing the handover to the second cell, and the communication quality of the first cell The wireless communication system according to (5) or (6), wherein the suppression of the handover to the second cell is released when the deterioration occurs before the suppression.
(12) The quality monitoring means includes an abnormal disconnection rate of communication of the entire first cell, a handover failure rate to the third cell, the number of handover failures, and an average stay time after handover to the third cell The wireless communication system according to (11), wherein deterioration of communication quality of the first cell is evaluated using at least one of the following.
(13) Any one of (1) to (4), wherein the alternative cell detection means detects, as the third cell, a cell whose radio quality at the time of a handover request reported from the mobile terminal is a required value or more. The wireless communication system according to item 1.
(14) The alternative cell detection unit detects, as the third cell, a cell in which radio quality at a plurality of time points reported from the mobile terminal is equal to or higher than a required value, (1) to (4) The wireless communication system according to any one of the above.
(15) The alternative cell detection means detects, as the third cell, a cell in which the radio quality at the time of the handover request reported from the mobile terminal and the radio quality at the time of the handover failure are both higher than a required value. The wireless communication system according to (13).
(16) The alternative cell detection means detects, as the third cell, a cell whose radio quality time series between the handover request time and the handover failure time reported from the mobile terminal is always a required value or more. (14) The wireless communication system according to (14).
(17) A base station that manages a first cell to which the mobile terminal is connected and processes a handover of the mobile terminal from the first cell to the second cell, the cell reported from the mobile terminal Based on measurement information of radio quality for each cell, a substitute cell detection means for detecting a third cell having a radio quality equal to or higher than a required value from cells excluding the second cell; A handover suppressing unit that suppresses handover to the second cell based on a detection result of the third cell.
(18) The handover suppressing unit may be configured to switch to the second cell based on a detection result of the third cell by the alternative cell detecting unit when a handover characteristic to the second cell is inferior to a predetermined standard. The base station according to (17), which suppresses a handover.
(19) A handover optimization method for setting a handover parameter for suppressing handover of the mobile terminal from a first cell to a second cell to which the mobile terminal is connected, for each cell measured by the mobile terminal Based on the measurement information of the radio quality, a third cell having a radio quality equal to or higher than a required value is detected from the cells other than the second cell, and the second cell is detected based on the detection result of the third cell. A handover optimization method for setting a handover parameter for suppressing handover to a cell.
(20) The handover according to (19), wherein the setting of the handover parameter is performed based on a detection result of the third cell when a handover characteristic to the second cell is inferior to a predetermined criterion. Optimization method.
(21) The handover optimization method according to (20), wherein the handover parameter includes at least one of a handover prohibition flag and an offset value added to a radio quality measurement result by the mobile terminal.
(22) In a handover process in which a mobile terminal switches a connection destination cell, the mobile terminal reports radio quality measurement information for each cell to a base station at the time of a handover request, and the base station is connected to the mobile terminal Cell having a handover characteristic between the first cell of the first cell and the second cell notified as the handover destination is inferior to a predetermined standard, and of the measurement information, the cell excluding the first cell and the second cell A handover method for performing handover to the third cell when there is a third cell having a radio quality equal to or higher than a required value in the measurement information.

DESCRIPTION OF SYMBOLS 10 Mobile terminal 30 Base station 30A Base station 30B Base station 35 Radio cell 35A Optimization object cell 35B Adjacent cell 90 Network management system 96 Handover suppression part 101 Handover control part 102 Handover characteristic management part 103 Alternative cell detection part 104 Quality statistics storage part 105 Parameter setting unit 106 Failure information notification unit 201 Quality monitoring unit 301 Movement speed determination unit 401 Quality statistics storage unit 402 Handover suppression unit

Claims (20)

A wireless communication system comprising a base station that manages a first cell to which a mobile terminal is connected, wherein the mobile terminal can be handed over from the first cell to a second cell;
An alternative cell detection means for detecting a third cell having a radio quality equal to or higher than a required value from cells excluding the second cell based on measurement information of radio quality for each cell reported from the mobile terminal; ,
A handover suppressing unit for suppressing a handover to the second cell based on a detection result of the third cell by the alternative cell detecting unit;
A wireless communication system. The handover suppressing unit suppresses handover to the second cell based on a detection result of the third cell by the alternative cell detecting unit when a handover characteristic to the second cell is inferior to a predetermined standard. To
The wireless communication system according to claim 1. The handover characteristics include at least one of a handover failure rate to the second cell, a number of handover failures, and an average stay time after handover to the second cell.
The wireless communication system according to claim 2. The radio quality includes at least one of a received power of a reference signal or a signal-to-interference wave and a noise power ratio transmitted from a base station that manages the cell.
The wireless communication system according to claim 1. The handover suppression means includes statistics of the number of handover failures to the second cell when the third cell exists, and the number of handover failures to the second cell when the third cell does not exist. Determining to suppress handover to the second cell based on the statistics of
The radio | wireless communications system of any one of Claims 1 thru | or 4. The alternative cell detection means detects the third cell for each handover request from the mobile terminal,
The handover suppressing means suppresses handover to the second cell on condition that the third cell is detected;
The radio | wireless communications system of any one of Claims 1 thru | or 4. The handover suppressing means suppresses a handover to the second cell by notifying the mobile terminal of an offset value to be added to a measurement result of radio quality of the second cell;
The wireless communication system according to claim 5. The handover suppressing means suppresses handover to the second cell by setting a handover prohibition flag for the second cell;
The wireless communication system according to claim 5. The handover suppressing means suppresses handover to the second cell only for mobile terminals that move at high speed among the mobile terminals.
The wireless communication system according to claim 5. The mobile terminal moving at high speed is a mobile terminal whose stay time of a cell connected immediately before the connected cell is equal to or less than a threshold value.
The wireless communication system according to claim 9. The handover suppressing unit includes a quality monitoring unit that monitors communication quality of the first cell after suppressing a handover to the second cell,
When the communication quality of the first cell is deteriorated before the suppression of the handover, the suppression of the handover to the second cell is canceled.
The radio | wireless communications system of Claim 5 or Claim 6. The quality monitoring means includes at least one of an abnormal disconnection rate of communication of the entire first cell, a handover failure rate to the third cell, a number of handover failures, and an average stay time after handover to the third cell. The degradation of the communication quality of the first cell using
The wireless communication system according to claim 11. The alternative cell detection means detects, as the third cell, a cell whose radio quality at the time of a handover request reported from the mobile terminal is a required value or more,
The radio | wireless communications system of any one of Claims 1 thru | or 4. The alternative cell detection means detects, as the third cell, a cell whose radio quality at a plurality of time points reported from the mobile terminal is higher than a required value.
The radio | wireless communications system of any one of Claims 1 thru | or 4. The alternative cell detection means detects, as the third cell, a cell in which both the radio quality at the time of the handover request reported from the mobile terminal and the radio quality at the time of the handover failure are equal to or higher than a required value,
The wireless communication system according to claim 13. The alternative cell detection means detects, as the third cell, a cell whose radio quality time series between the handover request time and the handover failure time reported from the mobile terminal is always a required value or more.
The wireless communication system according to claim 14. A base station that manages a first cell to which a mobile terminal is connected and processes a handover of the mobile terminal from the first cell to a second cell,
An alternative cell detection means for detecting a third cell having a radio quality equal to or higher than a required value from cells excluding the second cell based on measurement information of radio quality for each cell reported from the mobile terminal; ,
A handover suppressing unit for suppressing a handover to the second cell based on a detection result of the third cell by the alternative cell detecting unit;
Base station with A handover optimization method for setting a handover parameter for suppressing handover of the mobile terminal from a first cell to a second cell to which the mobile terminal is connected, comprising:
Based on the measurement information of radio quality for each cell measured by the mobile terminal, a third cell having a radio quality equal to or higher than a required value is detected from among cells excluding the second cell;
Based on the detection result of the third cell, setting a handover parameter that suppresses handover to the second cell;
Handover optimization method. The handover parameter includes at least one of a handover prohibition flag and an offset value added to a measurement result of radio quality by the mobile terminal.
The handover optimization method according to claim 18. In the handover process in which the mobile terminal switches the connection destination cell,
The mobile terminal reports measurement information of radio quality for each cell to the base station at the time of a handover request,
The base station has a handover characteristic inferior to a predetermined standard between a first cell to which the mobile terminal is connected and a second cell notified as a handover destination, and the first measurement information includes the first cell In the measurement information of the cells excluding the second cell and the second cell, if there is a third cell whose radio quality is equal to or higher than a required value, a handover is made to the third cell.
Handover method.

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