Controller, control method, and program for controlling target reception power

Abstract

To provide a mobile communication system that improves throughput of a cell of a control object while suppressing occurrence of quality degradation in a periphery cell.SOLUTION: A controller in a radio communication network including a plurality of base station devices identifies a first base station device, which is included in the plurality of base station devices and is connected to one or more terminal devices whose transmission power should be increased; notifies the first base station device of a target value of reception power in the first base station device receiving signals transmitted by the terminal devices, the terminal devices being to be notified of the target value by the first base station device; determines whether or not predetermined quality degradation on communication quality has occurred in a cell configured by a second base station device differing from the first base station device of the plurality of base station devices; and performs control so as to increase the target value until occurrence of the predetermined quality degradation.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a technique for controlling transmission power in the uplink direction in a mobile communication system. [Background technology]

[0002] The cellular communication standards for Long Term Evolution (LTE) and fifth-generation mobile communication systems (5G), established by the Third Generation Partnership Project (3GPP), stipulate the transmission power control that a terminal (user equipment) should use when transmitting data in the uplink. For example, open-loop power control, which is one type of terminal transmission power control, stipulates that transmission power control be performed using a target received power, which is a target value for the received power when a radio signal transmitted by the terminal is received by a base station. Furthermore, Patent Document 1 describes a method of uplink transmission power control that combines open-loop power control and closed-loop power control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-086431 Summary of the Invention [Problem to be solved by the invention]

[0004] In open-loop power control, setting a high target received power enables the use of a transmission method with a higher transmission rate, thereby increasing the throughput in a cell. However, setting a high target received power may increase interference with neighboring cells with at least a partial overlap in frequency bands, potentially reducing the throughput in those neighboring cells. In response to this, for example, by determining the target received power based on the distance between a terminal transmitting a wireless signal and each base station constituting each cell, the transmit power of each terminal can be controlled to optimize the throughput in each cell. However, performing such control requires keeping track of the locations of all terminals connected to each cell, and requires sequentially calculating the target received power as each terminal moves, which can complicate the control. The present invention provides an uplink transmit power control technique for a mobile communication system that improves the throughput of a cell being controlled while suppressing quality degradation in neighboring cells, without requiring such complex calculations. [Means for solving the problem]

[0005] A control device according to one embodiment of the present invention is a control device in a wireless communication network including a plurality of base station devices, and includes: an identification means for identifying a first base station device included in the plurality of base station devices, the first base station device for which the transmission power of one or more terminal devices connected to the first base station device should be increased; a notification means for notifying the first base station device of a target value of received power when a signal transmitted by the terminal device is received at the first base station device, the target value being notified to the terminal device from the first base station device; a determination means for determining whether a predetermined quality deterioration related to communication quality has occurred in a cell constituted by a second base station device different from the first base station device included in the plurality of base station devices; and a control means for controlling to increase the target value until the predetermined quality deterioration occurs. [Effects of the Invention]

[0006] According to the present invention, in a mobile communication system, it is possible to improve the throughput of a cell to be controlled while suppressing the occurrence of quality degradation in surrounding cells. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a mobile communication system. [Figure 2] FIG. 2 is a diagram illustrating an example of a hardware configuration of a control device. [Figure 3] FIG. 2 is a diagram illustrating an example of a functional configuration of a control device. [Figure 4] 10 is an example of a flowchart when the control device executes control of the target received power. [Figure 5] 10 is a sequence example when the control device controls the target received power. [Figure 6] FIG. 1 is a diagram illustrating an example of the configuration of a mobile communication system. [Figure 7] 10A and 10B are diagrams illustrating an example of an operation when the control device controls the target received power. [Figure 8] 10A and 10B are diagrams illustrating an example of an operation when the control device controls the target received power. [Figure 9] 10 is an example of a flowchart when the control device executes control of the target received power. [Figure 10] 10A and 10B are diagrams illustrating an example of an operation when the control device controls the target received power. [Figure 11] 10A and 10B are diagrams illustrating an example of an operation when the control device controls the target received power. [Figure 12] FIG. 10 is a diagram illustrating an example of the distribution of terminal devices when there are multiple cells. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be arbitrarily combined. Furthermore, the same reference numerals are used for the same or similar components, and redundant explanations will be omitted.

[0009] (System Configuration) FIG. 1 shows an example of the configuration of a mobile communication system according to this embodiment. The mobile communication system is, for example, a cellular communication system conforming to the cellular communication standard of the Third Generation Partnership Project (3GPP (registered trademark)). However, the present invention is not limited to this, and the following discussion can be applied to a mobile communication system conforming to any wireless communication standard. The mobile communication system is configured to include, for example, a control device 101, a base station 111, a base station 112, a terminal 121, and a terminal 122. The control device 101 is a network device for configuring and controlling the base station 111 and the base station 112. For example, the control device 101 can be a RAN Intelligent Controller (RIC) in an Open-Radio Access Network (O-RAN). The O-RAN is a radio access network based on standards for making the radio access network (RAN) open and intelligent. The RIC is a control device in the O-RAN that designs and configures RAN parameters, automates and optimizes RAN operations, and so on. The control device 101 may be configured to include a Non-RealTime RIC and a Near-RealTime RIC as defined in the O-RAN standard. The Non-RealTime RIC may determine policies for controlling the long-term behavior of the entire system. The Near-RealTime RIC may control the RAN in accordance with policies generated by the Non-RealTime RIC. The control device 101 may be configured to include either a Non-RealTime RIC or a Near-RealTime RIC.

[0010] The base station 111 exchanges radio signals with the terminal 121 via a wireless medium. The base station 111 is a so-called base station, and includes, for example, a gNB (next generation Node B) and an eNB (evolved Node B). On the other hand, the base station 112, like the base station 111, also exchanges radio signals with the terminal 122 via a wireless medium. The base station 112 also includes, for example, a gNB (next generation Node B) and an eNB (evolved Node B). Note that the base station 111 and the base station 112 may be referred to as the base station 110 without distinction. An area configured by the base station 111 and the base station 112 and capable of communicating with the base station 111 and the base station 112 is called a cell. For example, in FIG. 1, the base station 111 and the base station 112 configure a cell 131 and a cell 132, respectively.

[0011] The terminal 121 and the terminal 122 are terminals used by users, and exchange wireless signals with the base station 111 and the base station 112, respectively, via a wireless medium. The terminal 121 and the terminal 122 may be referred to as the terminal 120 without distinction. The terminal 120 may be referred to as User Equipment (UE). The terminal 120 includes, for example, a smartphone, a mobile phone, a personal computer, a tablet terminal, a wearable terminal, an IoT (Internet of Things) terminal, and the like.

[0012] Each of the base stations 111 and 112 is connected to the control device 101 via a network. The network may be a wired network or a wireless network. Furthermore, the base station 110 and the terminal 120 are connected to each other via a wireless medium. FIG. 1 illustrates an example in which the base station 111 and the terminal 121, and the base station 112 and the terminal 122 communicate with each other via a wireless medium, but two or more terminals 120 may be connected to one base station 110. Furthermore, one terminal 120 may be connected to two or more base stations 110. Each of the base stations 111 and 112 is connected to a core network (not shown). The core network may be a fifth-generation core network (5GC), an evolved packet core network (EPC), or the like. The base station 110 transfers information such as data between the core network and the terminal 120, allowing the terminal 120 to receive various information services from the network.

[0013] An overview of the procedure from when the terminal 120 accesses the mobile communication system to when it establishes a connection with the base station 110 will be described. When the terminal 120 is powered on, it performs a cell search to search for a cell to which it can connect. For example, the terminal 120 can detect a cell to which it can connect by receiving a synchronization signal transmitted by the base station 110. When the terminal 120 detects a cell, it acquires system information related to the cell. For example, the terminal 120 acquires the allocation of a random access channel (PRACH) in a radio frame, which should transmit a preamble for accessing the base station 110, by receiving a master information block (MIB) included in a downlink physical broadcast channel (PBCH) transmitted by the base station 110. The terminal 120 exchanges messages with the base station 110 using a random access procedure to establish a radio resource control (RRC) connection. By establishing the RRC connection with the base station 110, the terminal 120 can perform radio communication based on control information transmitted from the base station 110. For example, the terminal 120 requests the base station 110 to allocate radio resources necessary for transmitting data, etc., and transmits the data, etc., using the radio resources allocated by the base station. The radio resources may be called resource blocks. The control information notified by the base station 110 may include information for specifying the transmission power, MCS (Modulation and Coding Scheme), etc., to be used when the terminal 120 performs transmission.

[0014] The transmission power to be used when the terminal 120 transmits a wireless signal may be determined based on the received power to be received at the base station 110. For example, the base station 110 may notify, as one piece of system information, a target value of the received power at the terminal 120 when receiving a wireless signal transmitted by the terminal 120 connected to the terminal 120. This target value may be referred to as the target received power. The base station 110 may also transmit a reference signal that enables the terminal 120 to determine the loss (path loss) of the wireless signal on the propagation path between the terminal 120 and the base station 110. The terminal 120 may calculate the path loss between the terminal 120 and the base station 110 based on the received power of the reference signal. The terminal 120 may then determine the transmission power to be used based on, for example, the equation: Transmission Power = P0 + α × PL. Here, P0 is the target received power notified by the base station 110, and PL is the path loss. α is a predetermined coefficient, and may be, for example, a value equal to or less than 1. In this way, a transmission power control method that controls the transmission power to be used when the terminal 120 transmits based on the target reception power notified by the base station 110 can be called open-loop transmission power control (open-loop power control). Note that the target reception power may be determined by the base station 110, or may be determined by the control device 101 and notified to the base station.

[0015] A radio signal transmitted from terminal 120 to base station 110 may become an interference signal to other base stations or terminals. For example, in FIG. 1 , terminal 121 is located at the boundary between cells where cell 131 and cell 132 overlap. Therefore, the radio signal transmitted from terminal 121 may not only be received by base station 111 but also reach base station 112. In this case, if at least a portion of the frequency bands used in cells 131 and 132 overlap, the radio signal transmitted by terminal 122 may not be properly received by base station 112. That is, a radio signal transmitted from terminal 121 using the same frequency band at the same timing as a radio signal transmitted from terminal 122 to base station 112 using the overlapping frequency band may become an interference signal. In open-loop power control, in order to mitigate interference to other cells from terminals located at such cell boundaries, for example, a target received power may be set low. However, when the target received power is set low, the received power at the base station 110 is lower than when the target received power is set high, making the received signal more susceptible to noise and interference signals. In this case, a highly reliable MCS may be selected for transmission from the terminal 120. A highly reliable MCS is a combination of a modulation scheme with a low modulation level and a coding method with a low coding rate, and using these makes the signal less susceptible to noise and interference signals. However, using a highly reliable MCS may reduce intra-cell throughput. On the other hand, setting the target received power high with an emphasis on intra-cell throughput may increase interference with other cells, degrading the communication quality in those cells. As such, because there is a trade-off between cells in controlling the target received power, controlling the target received power in each cell may become complicated.

[0016] In consideration of these circumstances, in the mobile communication system of this embodiment, the control device 101 controls the target received power in stages for a base station 110 that needs to increase its cell throughput while determining whether degradation in communication quality is occurring in other cells included in the mobile communication system. For example, the control device 101 identifies a first base station, which is one of the base stations 110 included in the mobile communication system, and which should increase the transmission power of one or more terminals 120 connected to that base station. The control device 101 also notifies the first base station of the target received power (a target value of the received power when a signal transmitted by the terminal device 120 is received at the first base station). For example, the control device 101 may notify the first base station of the target received power of the first base station at the time the first base station was identified, plus a predetermined increase. The target received power notified to the first base station is then notified to the terminal 120 by the first base station. Meanwhile, after notifying the first base station of the target received power, the control device 101 determines whether a predetermined quality degradation in communication quality has occurred in a cell configured by a base station 110 (second base station) different from the first base station. The control device 101 then gradually controls the target received power of the first base station to further increase it until communication quality degradation occurs in other cells. Furthermore, if quality degradation occurs in other cells as a result of the control, the control device 101 lowers the target received power until the quality degradation is resolved and then stops the control. For example, the control device 101 uses a predetermined increase amount when increasing the target received power and a predetermined decrease amount when decreasing the target received power. Each time the target received power is changed, the control device 101 checks whether quality degradation has occurred in the second cell and determines whether further control is performed based on the check result. In this way, the control device 101 controls the first base station to increase its target received power while determining whether communication quality degradation has occurred in the cell provided by the second base station. This makes it possible to maximize the target received power of the first base station within a range that does not affect the cell of the second base station.

[0017] Furthermore, the control device 101 can perform control such that when increasing the target received power, it increases it stepwise using a predetermined increment, and when decreasing the target received power, it decreases it stepwise using a predetermined decrement, and when quality degradation occurs in a cell configured by the second base station, it decreases it by the predetermined decrement until the quality degradation is resolved. At this time, the control device 101 determines the predetermined decrement so that the predetermined decrement does not fall below the predetermined increment. As a result, if quality degradation occurs in another cell as a result of the control, it becomes possible to control so that the quality degradation is quickly resolved.

[0018] Furthermore, the control device 101 collects first information indicating the communication quality between the second base station and one or more terminals connected to the second base station, and each time the target received power is increased by one step, determines the timing for determining whether quality degradation has occurred in the cell configured by the second base station based on the characteristics of a set including at least a portion of the first information as an element.The control device 101 then determines whether quality degradation has occurred at the determined timing, and controls the target received power to be increased in steps until it is determined that quality degradation has occurred.This makes it possible to evaluate the impact on the second cell of increasing the target received power by one step at an appropriate time, and then determine whether to further control the target received power.The following describes the configuration and processing flow for implementing such a control device 101.

[0019] (Device configuration) FIG. 2 is a diagram illustrating an example of the hardware configuration of the control device 101. In one example, the control device 101 includes a processor 201, a ROM 202, a RAM 203, a storage device 204, and a communication circuit 205. The processor 201 is a computer including one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit). The processor 201 reads and executes programs stored in the ROM 202 or the storage device 204, thereby executing the overall processing of the device and each of the above-mentioned processes. The ROM 202 is a read-only memory that stores programs related to the processing executed by the control device 101, various parameters, and other information. The RAM 203 functions as a workspace when the processor 201 executes a program, and is a random access memory that stores temporary information. The storage device 204 is, for example, a removable external storage device. The communication circuit 205 is, for example, configured to include a circuit for communicating with other devices. Although one communication circuit 205 is shown in FIG. 2, each device may have multiple communication circuits.

[0020] FIG. 3 is a diagram illustrating an example of the functional configuration of the control device 101. The control device 101 includes, as its functions, a base station identification unit 301, a target value notification unit 302, a quality degradation determination unit 303, a target value control unit 304, a base station selection unit 305, a control amount determination unit 306, an information collection unit 307, and a timing determination unit 308, for example. FIG. 3 illustrates the functional configuration of the control device 101 of this embodiment, and omits, for example, the general configuration of the control device 101. These functional units may be realized, for example, by the processor 201 executing a program stored in the ROM 202 or the storage device 204 and controlling the communication circuit 205 as necessary. However, this is not limiting, and for example, dedicated hardware may be provided to realize each function. In the following description, the base station 110 whose target received power is to be controlled is referred to as the first base station, and the base station 110 whose target received power is to be controlled and whose determination of whether quality degradation has occurred due to control of the target received power of the first base station is referred to as the second base station.

[0021] The base station identifying unit 301 identifies a first base station whose target received power should be controlled. For example, the base station identifying unit 301 may acquire information indicating the congestion status of communication traffic in the cell constituted by each base station 110 included in the mobile communication system from each base station 110, identify a cell in which congestion is occurring or is likely to occur as a cell in which throughput needs to be increased, and identify the base station 110 constituting that cell as the first base station. Information indicating the congestion status of communication traffic in a cell may be, for example, the amount of resource blocks used, the resource block usage rate, or the delay time until data transmission is completed. Furthermore, if quality degradation is occurring in a specific cell, the base station identifying unit 301 may identify a base station constituting a cell adjacent to that specific cell as the first base station. The target value notifying unit 302 notifies the first base station of the target received power. For example, the target value notifying unit 302 may notify the first base station of the target received power determined under the control of the target value control unit 304.

[0022] The quality degradation determination unit 303 determines whether quality degradation is occurring in a cell constituted by the second base station. For example, the quality degradation determination unit 303 may make the determination using information (first information) associated with quality degradation of communication at the second base station collected by the information collection unit 307. For example, the quality degradation determination unit 303 may determine that quality degradation has occurred when the interference power (interfered power) measured at the second base station exceeds a predetermined threshold. The quality degradation determination unit 303 may also determine that predetermined quality degradation has occurred when the delay time from when data is generated at the terminal 120 connected to the second base station until the data transmission is completed exceeds a predetermined threshold. Here, the predetermined threshold may be a fixed value set in advance by an operator or may be a value determined based on a difference from a statistical amount, etc. The quality degradation determination unit 303 may make the determination at a timing determined by the timing determination unit 308.

[0023] The target value control unit 304 controls the target received power. For example, the target value control unit 304 may control the target received power of the first base station to increase or decrease in stages using the predetermined increase and decrease amounts determined by the control amount determination unit 306. Furthermore, the target value control unit 304 may control the target received power of the first base station to increase in stages until the quality degradation determination unit 303 determines that quality degradation has occurred in the cell configured by the second base station. On the other hand, if the target value control unit 304 determines that quality degradation has occurred in the cell configured by the second base station, the target value control unit 304 may control the target received power of the first base station to decrease in stages until the quality degradation is resolved. Each time the target received power is changed, the target value control unit 304 may check whether quality degradation has occurred and, depending on the check result, determine whether to perform further control. Furthermore, when gradually decreasing the target received power, the target value control unit 304 may control the target received power so that it does not fall below a value set as the initial value of the target received power.

[0024] The base station selection unit 305 selects the second base station. For example, the base station selection unit 305 can select the second base station from among base stations that provide cells adjacent to the cell configured by the first base station.

[0025] The control amount determination unit 306 determines a control amount used to control the target received power. For example, the control amount determination unit 306 determines a predetermined increase amount when gradually increasing the target received power or a predetermined decrease amount when gradually decreasing the target received power as the control amount used to control the target received power. Note that the control amount determination unit 306 can determine the predetermined decrease amount so that it does not fall below the predetermined increase amount.

[0026] The information collecting unit 307 collects, from the first base station and the second base station, information related to communications in the cells formed by the respective base stations. For example, the information collecting unit 307 collects, from the second base station, first information indicating the communication quality between the second base station and the terminal 120 and information capable of identifying the time period in which the information was generated. The information collecting unit 307 also collects second information capable of identifying the amount of communication in the cell formed by the first base station and information capable of identifying the time period in which the information was generated. Furthermore, the information collecting unit 307 collects third information capable of identifying the amount of communication in the cell formed by the second base station and information capable of identifying the time period in which the information was generated.

[0027] The timing determination unit 308 determines the timing for determining whether quality degradation is occurring in the second base station. For example, the timing determination unit 308 may determine the timing based on information collected by the information collection unit 307. As an example, the timing determination unit 308 may determine the timing at which the characteristics of a set including at least a part of the first information collected by the information collection unit 307 as an element satisfy a predetermined condition as the timing for making the determination.

[0028] (Processing flow) (Processing example 1) FIG. 4 shows an example of the flow of processing executed by the control device 101 in this embodiment. In this example, the control device 101 identifies one of the base stations 110 to be controlled and controls the target received power of that base station 110. First, the control device 101 identifies a first base station to be controlled for target received power (target value) (S401). For example, the control device 101 may identify a base station 110 constituting a cell in which congestion is occurring or is likely to occur as a control target. For example, if the control device 101 is a RIC and communication is established with the base station 110 using the E2 interface or the O1 interface, the control device 101 may acquire information such as the resource block usage rate, resource block usage amount, and delay time until data transmission is completed for each base station 110. Based on the acquired information, the control device 101 may identify, for example, a base station 110 whose resource block usage rate exceeds a predetermined threshold as a first base station to be controlled for target received power. In this example, it is assumed that a large number of terminals 121 are connected to and communicating with the base station 111 in Fig. 1, causing the resource block usage rate to exceed a predetermined threshold, and therefore the base station 111 is identified as the first base station. Note that the method by which the control device 101 identifies the first base station is not limited to the above, and any method that can determine that target received power control should be performed may be used.

[0029] The control device 101 notifies the identified first base station of the target received power (S402). For example, the control device 101 may notify the first base station of the target received power obtained by adding a predetermined increase to the current target received power of the identified first base station as the new target received power. That is, if the target received power used by the base station 111 at time t is P0(t), P0(t)+ΔP0 may be notified to the base station 111 as the new target received power. Here, ΔP0 is the predetermined increase. Note that, when the control device 101 is a RIC, the control device 101 may notify the base station 110 of various control information including the setting of the target received power using the E2 interface.

[0030] Then, the control device 101 acquires information (quality information) associated with quality degradation in cells constituted by base stations 110 other than the first base station (S403). For example, if the control device 101 is a RIC, the control device 101 may acquire, as information associated with quality degradation, information such as the amount of interference power, a packet error rate, a packet loss rate, and a delay time until data transmission is completed, using the E2 interface or the O1 interface. The control device 101 may acquire each measurement value measured by the base station 110, or may acquire statistical information obtained by performing statistical processing or the like by the base station 110. The control device 101 may periodically acquire quality information from each base station 110, or may request the other base stations 110 to provide quality information after notifying the first base station 110 of the target received power. The control device 101 uses the acquired quality information to determine whether quality degradation has occurred (S404). For example, the control device 101 may determine that quality degradation has not occurred as long as a value indicating quality degradation identified based on the quality information (such as interference power, packet error rate, packet loss rate, or delay time from data generation to data transmission completion) does not exceed a predetermined threshold value, since the value is within an acceptable range. On the other hand, the control device 101 may determine that quality degradation has occurred when a value indicating quality degradation identified based on the quality information exceeds a predetermined threshold value. Thus, in this embodiment, even if quality degradation occurs in a cell configured by a second base station in response to control of the target received power of the first base station, quality degradation is determined not to have occurred as long as the value is within an acceptable predetermined range, and quality degradation is determined to have occurred when the value exceeds the acceptable predetermined range.

[0031] When the control device 101 determines that no quality degradation has occurred (NO in S404), it executes the first control and returns to S402 to execute the process. For example, the control device 101 may execute control to further increase the target received power as the first control. Even after increasing the target received power of the base station 111, if the quality degradation at the base station 112 is within an acceptable range (for example, the interference power does not exceed a predetermined threshold), there is a possibility that the quality degradation at the base station 112 will remain within an acceptable range (the interference power will not reach the predetermined threshold) even if the target received power of the base station 111 is further increased. In such a case, by gradually increasing the target received power, it is possible to further increase the throughput in the cell 131 formed by the base station 111. The control device 101 may execute control to add a predetermined increment ΔP0 to the target received power until it is determined that quality degradation has occurred at another base station 110. That is, when the control device 101 determines that no quality degradation will occur, it notifies the first base station of the target received power that has been further increased by a predetermined increment (S402), and can further determine whether quality degradation will occur in other base stations (S403, S404). Note that, when an upper limit value of the allowable target received power is predetermined in the mobile communication system, the control device 101 can control the target received power to be increased within a range that does not exceed the upper limit value (S407).

[0032] On the other hand, when the control device 101 determines that quality degradation has occurred (YES in S404), it executes the second control and ends the processing. For example, as the second control, the control device 101 may lower the target received power by ΔP0′. If quality degradation occurs in another cell, it may have an impact such as a decrease in throughput in that cell. Therefore, the control device 101 may perform control to lower the target received power of the first base station, assuming that the target received power has been excessively increased. Note that the increase amount ΔP0 when increasing the target received power and the decrease amount ΔP0′ when decreasing the target received power may be the same value. By returning the target received power to the value determined to be free of quality degradation, it is possible to maximize the target received power while reliably avoiding quality degradation in other cells. Furthermore, the decrease amount ΔP0′ may be smaller than the increase amount ΔP0. In other words, by using a target received power higher than the target received power confirmed not to cause quality degradation, it is possible to increase the throughput in the first base station while mitigating quality degradation in other cells. In this case, the control device 101 may gradually reduce the target received power multiple times until the occurrence of quality degradation is resolved. By setting ΔP0′ to a small value and gradually reducing the target received power, it becomes easier to identify the maximum target received power in the cell to be controlled within a range in which quality degradation does not occur in other cells. Furthermore, the control device 101 may set ΔP0′ to a value greater than ΔP0. By using a target received power lower than the target received power at which it has been confirmed that quality degradation does not occur, it becomes possible to prevent quality degradation in other cells from occurring even if interference increases due to a subsequent change in communication conditions in the cell configured by the first base station. After executing the second control, the control device 101 may determine whether the quality degradation in the cell configured by the second base station has been resolved, and terminate the processing if the quality degradation has been resolved. In this case, the control device 101 may further execute the second control if the quality degradation in the cell configured by the second base station has not been resolved.Furthermore, when quality degradation is resolved by performing the second control by making ΔP0' larger than ΔP0, the control device 101 may perform control to increase the target received power again using a value smaller than ΔP0. In this case, when quality degradation occurs again in the cell configured by the second base station, the control device 101 may perform control to return the target received power to the level immediately before the quality degradation occurred, and terminate the process.

[0033] FIG. 5 shows an example of a sequence of messages exchanged between the control device 101 and the first base station and the second base station. In this example, it is assumed that the control device 101 identifies the base station 111 as a target (first base station) for which target received power should be controlled. The control device 101 notifies the base station 111 of the target received power (target value). Upon receiving the notification of the target received power, the base station 111 notifies the terminal 120 connected to the base station of the notified target received power for the cell that the base station 111 configures (S502). The notification of the target received power for the cell may be notified as system information or individual control information. Then, the control device 101 requests the base station 112 to provide quality information (S503). The base station 112 provides the quality information to the control device 101 (S504). If the control device 101 regularly receives quality information from the base station 112, S503 may not be executed. The control device 101 uses the quality information acquired from the base station 112 to determine whether or not degradation in communication quality is occurring in the cell formed by the base station 112 (S505). Then, based on the determination result, if the control device determines that no quality degradation is occurring, the control device controls the base station 111 to further increase the target received power, and if the control device determines that quality degradation is occurring, the control device controls the base station 111 to decrease the target received power (S506).

[0034] As described above, in this processing flow, the control device 101 identifies a base station 110 for which the transmission power of the terminal 120 connected to the base station should be increased, and while determining whether quality degradation is occurring in cells constituted by other base stations, increases the target received power of the identified base station 110 until quality degradation occurs. If the control device 101 determines that quality degradation is occurring in a cell constituted by another base station, it decreases the target received power until the quality degradation is resolved. This makes it possible to increase the throughput of a cell in which congestion, a shortage of resource blocks, or the like is occurring or is likely to occur, while keeping the effects of interference occurring in other cells within an acceptable range.

[0035] (Quality information used to determine quality deterioration) Here, the quality information used by the control device 101 to determine whether quality degradation is occurring in the cell constituted by the second base station when controlling the target received power of the first base station will be described. For example, in S404 of FIG. 4, the control device 101 determines whether quality degradation is occurring in the cell constituted by the second base station. At this time, examples of quality information that the control device 101 can use to determine whether quality degradation is occurring include the amount of interference power, the packet error rate, and the packet loss rate. However, even if interference from other cells occurs within a cell, quality degradation may not be apparent at the service level. For example, by selecting a highly reliable MCS as described above, communication is possible even in an environment where interference is occurring. It is also possible to adjust the scheduling of resource blocks used in communication so as to be less susceptible to the effects of interference. In this way, it is possible to prevent quality degradation at the service level from becoming apparent even when interference occurs. However, using a highly reliable MCS requires more resource blocks to communicate the same amount of data. Furthermore, if the resource block usage rate within a cell becomes high and avoidance by resource block scheduling becomes impossible, there will be a shortage of resource blocks that can be allocated to terminal requests. In such a case, if interference power or the like is used to determine the occurrence of quality degradation, it becomes easier to determine that quality degradation has occurred even if the interference is at a level that is tolerable at the service level.

[0036] Therefore, the control device 101 may use the delay time from when data is generated until the data transmission is completed as quality information. If the delay time until the data transmission is completed becomes large, quality degradation at the service level may become apparent depending on the delay time. For example, if there are quality requirements such as an allowable delay time for the data to be communicated, exceeding this limit may be recognized as quality degradation by the user. In this way, by using the delay time until the data transmission is completed to determine whether quality degradation has occurred, it becomes possible to determine whether interference caused by controlling the target received power is tolerable at the service level.

[0037] The delay time until data transmission is completed may be referred to as a transmission delay time. For example, the transmission delay time may be the time required from the time when the terminal 120 notifies the base station 110 that a packet has been generated in order to transmit uplink data to the time when the uplink data is transmitted from the terminal 120 and successfully received by the base station 110. For example, the terminal 120 may notify the base station 110 of the generation of a packet using a scheduling request. Furthermore, the time when the uplink data from the terminal 120 is successfully received by the base station 110 may be the time when the base station 110 successfully completes packet processing, or may be the time when the terminal 120 receives an acknowledgment from the base station 110. The control device 101 may acquire from the base station 110 the transmission delay time in the cell and its statistics (average, maximum, etc.) and compare them with a predetermined threshold to determine whether quality degradation is occurring in the cell of the base station 110. The predetermined threshold may be a preset allowable delay time. The predetermined threshold may be a value determined based on the allowable delay time. For example, a value obtained by subtracting a predetermined fixed value from the allowable delay time may be used. By using a value obtained by subtracting a predetermined fixed value from the allowable delay time, the control device 101 can detect and prevent possible quality degradation before the allowable delay time is reached.

[0038] The control device 101 may determine quality degradation using the transmission delay times of all terminals 120 connected to the base station 110, or may determine quality degradation using the transmission delay times of some of the terminals 120. For example, when communication of a specific terminal 120 is associated with a specific network slice (hereinafter, sometimes simply referred to as a slice), specific quality requirements (such as an allowable delay time and a packet loss rate) for that communication may be defined. Furthermore, the quality requirements for communication may differ for each slice. Therefore, the control device 101 may determine quality degradation based on the transmission delay time for each slice with different quality requirements. For example, the control device 101 may determine quality degradation using an allowable delay time corresponding to each slice and the transmission delay time of data of the terminal 120 associated with that slice. For example, the control device 101 may determine that quality degradation has occurred if the average or maximum transmission delay time of communication associated with any slice exceeds the allowable delay time corresponding to that slice. Furthermore, the control device 101 may determine that quality degradation has occurred if the average transmission delay time or the maximum transmission delay time of communication of a specific slice in a specific cell exceeds the allowable delay time corresponding to that slice. In this case, even if the transmission delay time of communication of other slices in that specific cell exceeds the allowable delay time, the control device 101 may determine that quality degradation has not occurred if the transmission delay time of communication of the specific slice is below the allowable delay time. In this way, by using the transmission delay time to determine quality degradation, it is possible to determine, at a service level that a user can perceive, whether interference caused by increasing the target received power is tolerable.

[0039] (Timing for determining quality deterioration) The timing at which the control device 101 determines whether quality degradation is occurring in the cell formed by the second base station when controlling the target received power of the first base station will be described. For example, in S404 of FIG. 4, the control device 101 determines whether quality degradation is occurring in the cell formed by the second base station. At this time, the control device 101 can control the timing of this determination depending on the situation. Generally, in a mobile communication system, the communication environment in a cell can change over time due to changes in the movement of each terminal 120, the type of communication, the amount of communication, etc. Therefore, even if quality degradation occurs in the cell formed by the second base station after increasing the target received power of the first base station, depending on the communication environment, it may not be due to the increase in the target received power of the first base station. For example, if a large number of terminals 120 are connected to the cell formed by the first base station and their movement speeds are high, the change in interference to the second base station will be significant. When the communication environment changes significantly, the variance of the quality information measured in the cell of the second base station increases. Therefore, if a determination is made using the average value of the quality information, for example, a small number of quality information items used for the determination may make it difficult to accurately determine whether quality degradation has occurred. In other words, to determine the impact of controlling the target received power when the variance of the quality information is large, it may be necessary to collect a certain number of quality information items until the variance converges. On the other hand, for example, if the terminal 120 in the cell of the first base station hardly moves, the change in interference to the second base station may be relatively small. In such a communication environment, the variance is small and the fluctuation converges quickly, so the impact of controlling the target received power may be appropriately determined even with a small number of quality information items. Here, even in a communication environment where the variance of the collected quality information may be large, it may be possible to reduce the impact of the variance of the collected quality information and quickly determine whether quality degradation has occurred by using, for example, a portion of the quality information collected from the second base station that was generated when the characteristics of the communication environment met certain conditions.

[0040] Therefore, the control device 101 in this embodiment determines whether quality degradation has occurred in the cell of the second base station at a timing when a predetermined condition is satisfied after performing control to increase the target received power of the first base station. For example, the control device 101 determines the timing to determine whether quality degradation has occurred based on the characteristics of a set including at least a portion of the quality information collected from the second base station as elements. For example, the elements included in the set are information that satisfies a predetermined condition among the quality information collected from the second base station, and the characteristic of the set is the number of elements. The control device 101 may perform the determination at a timing when the number of elements exceeds a predetermined threshold. The quality information may include the amount of interference power, packet error rate, packet loss rate, resource utilization rate, transmission delay time, number of handover attempts, etc.

[0041] The quality information satisfying the predetermined conditions constituting the elements of the set may be information generated during a predetermined time period. For example, the communication environment in a cell may vary depending on the time of day. For example, the communication volume in a cell of a base station installed in an office district or the like is high during the daytime and low at night. On the other hand, the communication volume in a cell of a base station installed in a busy shopping district or the like is low during the daytime and high at night. Therefore, the control device 101 identifies, from the quality information collected from the second base station, those belonging to the same time period as elements of the set. Then, when the number of elements of the set exceeds a predetermined threshold, the control device 101 may use the elements of the set to determine whether quality degradation exists. By using quality information generated during the same time period, the variance of the elements included in the set is reduced, allowing for appropriate determination even if the number of elements is relatively small. Note that the same time period may include the same time period on multiple days. In this case, the control device 101 may collect, from the second base station, a combination of the date and time or time period at which the quality information was generated and the quality information.

[0042] The control device 101 may also identify quality information generated in a cell configured by a second base station as an element of a set during a time period in which the communication volume in the cell configured by the first base station falls within a predetermined range. The variance of the quality information in the cell configured by the second base station may depend on changes in the communication environment in the interfering cell. For example, the control device 101 collects information associated with the communication environment in the cell configured by the first base station from the first base station and identifies a time period in which the information satisfies a predetermined condition. The control device 101 generates a set using the quality information generated in the cell configured by the second base station during that time period as an element. Then, when the number of elements exceeds a predetermined number, the control device 101 determines whether quality degradation has occurred using the elements of the set. This may reduce the variance of the elements included in the set, enabling appropriate determination even if the number is relatively small. In this case, the control device 101 may acquire information from the first base station that can identify the communication volume in the cell configured by the first base station and the time period in which the communication volume falls within a predetermined range. Furthermore, the control device 101 can acquire quality information in the cell of the second base station and the time period in which the information was generated.

[0043] The information associated with the communication environment in the cell configured by the first base station and the predetermined condition that the information must satisfy may be that the communication volume and the change in the communication volume in the cell configured by the first base station fall within a predetermined range. For example, the control device 101 may collect information (communication volume) that can identify the number of terminals currently communicating in the cell of the first base station, the resource block usage rate, the electric field distribution of the terminals 120 currently communicating, etc. from the first base station, and identify a time period in which the values ​​fall within a predetermined range. The predetermined range may be, for example, an average resource block usage rate of 40 to 60% with a standard deviation of 10%. Alternatively, the predetermined range may be, for example, an average number of terminals currently communicating of 10 to 20 with a standard deviation of 5. The predetermined range is not limited to these, and the information collected from the first base station may be a combination of these values.

[0044] Furthermore, the control device 101 may identify quality information generated in the cell of the second base station during a time period in which the communication volume in the cell of the second base station falls within a predetermined range as an element of the set. The variance of the quality information in the cell of the second base station may also depend on changes in the communication environment in the cell of the second base station that is subject to interference. For example, the control device 101 collects information associated with the communication environment in the cell of the second base station from the second base station and identifies a time period in which the information satisfies a predetermined condition. The control device 101 generates a set using the quality information generated in the cell of the second base station during that time period as an element. Then, when the number of elements exceeds a predetermined number, the control device 101 determines whether quality degradation has occurred using the elements of the set. This may reduce the variance of the elements included in the set, making it possible to make an appropriate determination even if the number of elements is relatively small. In this case, the control device 101 can obtain from the second base station the communication volume in the cell constituted by the second base station, information that can identify the time period in which that communication volume falls within a specified range, and quality information in the cell of the second base station and the time period in which that information was generated.

[0045] The information associated with the communication environment in the cell configured by the second base station and the predetermined condition that the information must satisfy may be that the communication volume or the change in the communication volume in the cell configured by the second base station falls within a predetermined range. For example, the control device 101 may collect information (communication volume) that can identify the number of terminals currently communicating in the cell of the second base station, the resource block usage rate, the electric field distribution of the terminals 120 currently communicating, etc. from the second base station, and identify a time period in which the value falls within a predetermined range. Note that the control device 101 may use a combination of the time period in which the communication volume in the cell configured by the first base station falls within a predetermined range and the time period in which the communication volume in the cell configured by the second base station falls within a predetermined range. Using quality information for a time period in which the characteristics of the communication environments in both the interfering cell and the interfered cell fall within a predetermined range may reduce the variance of the elements included in the set.

[0046] The control device 101 may also identify, from the quality information collected from the second base station, data related to a specific network slice as an element of the set. For example, when a slice is associated with a specific service or communication or a specific terminal 120, the control device 101 may determine whether quality degradation has occurred using quality information about the data associated with each slice. For example, the control device 101 may collect, from the second base station, transmission delay times measured for data of a specific slice and their average values, and when the number of such times exceeds a predetermined number, determine whether quality degradation has occurred using the elements of the set. Since data assigned to a slice may be associated with predetermined quality requirements (such as an allowable delay time or a packet loss rate), using quality information about communications that are significantly affected by quality degradation to determine quality degradation enables more direct determination. In this case, the control device 101 may acquire, from the second base station, information in which a measured value of the transmission delay time and an identifier of the slice of the data to be measured are paired.

[0047] The above describes a method in which the control device 101 reduces the variance by using quality information collected from the second base station that satisfies a predetermined condition to make a determination. However, the method by which the control device 101 determines the timing for determining quality degradation is not limited to this. For example, the control device 101 may treat all quality information collected from the second base station as elements of a set, calculate the variance thereof, and determine quality degradation at the timing when the calculated variance satisfies a predetermined condition. As an example, when the control device 101 controls the target received power at the first base station, it collects quality information from the second base station and calculates the variance of the collected quality information at a predetermined period. Then, when the variation in the variance falls below a predetermined threshold, the control device 101 may determine whether quality degradation has occurred using the quality information collected up to that point. This makes it possible to determine the impact of controlling the target received power based on the quality information after the variation in the variance has stabilized.

[0048] The control device 101 may determine whether the fluctuation in the variance of the quality information collected after controlling the target received power has stabilized by comparing it with the variance of quality information collected in the past. For example, the control device 101 periodically collects quality information from the second base station and calculates and stores the variance of the quality information. Then, when the control device 101 acquires quality information from the second base station after increasing the target received power of the first base station, the control device 101 calculates the variance of the acquired quality information, compares the calculated variance with the stored variance, and determines whether quality degradation has occurred if the difference between the calculated variance and the stored variance satisfies a predetermined threshold. In this way, determining whether quality degradation has occurred when the fluctuation in the variance of the quality information has stabilized enables appropriate determination of the impact of the target received power. The control device 101 may calculate the variance by excluding elements corresponding to quality information outside a predetermined range from a set whose elements are the quality information collected from the second base station. If the quality information includes outliers, excluding these outliers enables appropriate detection of the convergence of the variance fluctuation. For example, the elements exceeding a predetermined range may be the minimum and maximum values ​​included in the set, or a predetermined number of elements from each of the minimum and maximum values.

[0049] The control device 101 may periodically collect information necessary for determining the timing of determining quality degradation, such as quality information, communication volume, and information that can identify the time period in which the information was generated, from the first base station and the second base station, or information for determining quality degradation. Alternatively, the control device 101 may notify the first base station and the second base station of predetermined conditions, and each base station 110 may provide information to the control device 101 when the predetermined conditions are satisfied. Alternatively, the control device 101 may collect information from the first base station and the second base station when the predetermined conditions are satisfied. By collecting information when the predetermined conditions are satisfied, it is possible to reduce the load on the control device 101 and the network. Meanwhile, by periodically notifying the information, the control device 101 can timely and flexibly determine quality degradation. Alternatively, the control device 101 may acquire the information itself, such as the quality information and communication volume, generated by the first base station and the second base station, or may acquire statistical values ​​of the information calculated by the first base station or the second base station.

[0050] (Processing example 2) In the processing example 1, an example in which the control device 101 identifies one first base station has been described. In this processing example, an example in which the control device 101 identifies two or more first base stations will be described. FIG. 6 illustrates a configuration in which the mobile communication system illustrated in FIG. 1 further includes a base station 113 and a terminal 123. The base station 113 has the same configuration as the base station 111 and the base station 112, and is connected to the control device 101 via a network. The base station 113 is also connected to the terminal 123 via a wireless medium. The base stations 111 to 113 may be referred to as base station 110 without distinction. The terminal 123 has the same configuration as the terminal 121 and the terminal 122, and is connected to the base station 113 via a wireless medium. The terminals 121 to 123 may be referred to as terminal 120 without distinction. The terminal 123 is located at the boundary between the overlapping cells of the cell 133 formed by the base station 113 and the cell 132 formed by the base station 112. Therefore, signals transmitted from each of terminal 121, terminal 122, and terminal 123 arrive at base station 112. For this reason, for example, if control device 101 controls both base station 111 and base station 113 to increase the target received power, cell 132 will simultaneously receive increased interference from both cell 131 and cell 133, making quality degradation more likely to occur. On the other hand, it may be difficult for base station 112 to determine whether the increased interference in cell 132 is due to an increase in the target received power of base station 111 or base station 113.

[0051] In this processing example, the control device 101 identifies two or more base stations 110 (e.g., a first base station and a third base station) as base stations 110 to be controlled for target reception power. For example, the first base station and the third base station may be base station 111 and base station 113, respectively. The control device 101 notifies each of the identified base stations 110 of the target reception power. For example, the control device 101 may notify the first base station of the first target reception power (target value) and the second base station of the second target reception power (target value). Each target reception power may be obtained by adding a predetermined increase to the target reception power of each base station 110 at the time the control device 101 identified the first base station and the third base station. After notifying each base station 110 of the target reception power, the control device 101 determines whether quality degradation is occurring in the cell constituted by the second base station, and controls the first target reception power and the second target reception power based on the determination result. While Fig. 6 shows a state in which the mobile communication system includes three base stations, it may include four or more base stations. Also, Fig. 6 shows a state in which the base station 112 receives interference signals from two adjacent cells, but it may also receive interference signals from three or more cells. Also, in this example, an example will be described in which the control device 101 controls the target received power of two base stations (base station 111 and base station 113), but this example can also be applied to a case in which the control device 101 controls the target received power of three or more base stations.

[0052] The configuration of the control device 101 in this example is the same as in processing example 1, so a description thereof will be omitted. The processing flow will be described using FIG. 4, as in processing example 1. Note that a description of operations that are the same as in processing example 1 will be omitted. First, the control device 101 identifies a base station 110 for which the target received power (target value) should be controlled (S401). In this example, it is assumed that a large number of terminals 121 and a large number of terminals 123 are connected to and communicating with each of the base stations 111 (first base station) and 113 (third base station) in FIG. 6, and therefore the usage rates of resource blocks at each of the base stations exceed a predetermined threshold, and therefore the base stations 111 and 113 are identified as the first base station and the third base station, respectively.

[0053] The control device 101 notifies each of the first base station and the third base station of the target received power (S402). For example, if the target received powers used by the base station 111 and the base station 113 at time t when the control device 101 identifies the base station 111 and the base station 113 are P01(t) and P02(t), respectively, the control device 101 may notify the base station 111 and the base station 113 of the first target received power = P01(t) + ΔP0 and the second target received power = P02(t) + ΔP0, respectively. Here, ΔP0 is a predetermined increase. Note that ΔP0 may be different for each base station 110 that is notified, or may be the same for each base station 110. For example, the control device 101 may change ΔP0 depending on the type of data being communicated by each base station 110. In this case, a larger value of ΔP0 may be used for the target received power of a base station 110 that is communicating a type of data that requires higher throughput or low delay. In this example, a description will be given assuming that each target received power is controlled using a common ΔP0.

[0054] Then, the control device 101 acquires quality information in a cell formed by base stations 110 other than the first base station and the third base station (S403). For example, the control device 101 may acquire quality information from the base station 112 (second base station). The control device 101 uses the acquired quality information to determine whether quality degradation has occurred (S404). If the control device 101 determines that quality degradation has not occurred (NO in S404), it executes first control and returns to S402 to execute the process. For example, as the first control, the control device 101 may execute control to further increase each target received power. The control device 101 may execute control to add a predetermined increase amount ΔP0 to each target received power until it is determined that quality degradation has occurred in the second base station. That is, when the control device 101 determines that no quality degradation will occur, it notifies the first base station and the third base station of a target received power that has been further increased by a predetermined amount (S402), and can further determine whether quality degradation has occurred in the second base station (S403, S404).

[0055] On the other hand, when it is determined that quality degradation has occurred (YES in S404), the control device 101 executes the second control and ends the processing. For example, as the second control, the control device 101 may lower each target received power by ΔP0′. The increase amount ΔP0 when increasing the target received power and the decrease amount ΔP0′ when decreasing the target received power may be the same or different. Furthermore, the ΔP0′ used in the control of the first target received power and the control of the second target received power may be the same or different. Then, if quality degradation is resolved after lowering each target received power, the control device 101 may maximize the throughput of each cell by increasing each target received power within a range where quality degradation does not occur. Such control operation of each target received power by the control device 101 will be described with reference to FIG. 7.

[0056] FIG. 7 shows an overview of the operation when the control device 101 controls the reception power of each target. In FIG. 7, the horizontal axis represents the passage of time, and the vertical axis represents the set values ​​of the first target reception power and the second target reception power. The first target reception power is represented by the height of the unshaded bar, and the second target reception power is represented by the height of the shaded bar. For example, the time when the control device 101 identifies the first base station and the third base station is assumed to be t0 (not shown). The target reception powers at this time are assumed to be first target reception power = P01(t0) and second target reception power = P02(t0), respectively. The control device 101 adds ΔP0 to each target reception power and notifies it at time t1. That is, the first target reception power P01(t1) = P01(t0) + ΔP0 and the second target reception power P02(t1) = P02(t0) + ΔP0 are notified to the first base station and the third base station, respectively. When each target received power is notified from each base station in each cell, the transmission power of the terminal 120 in each cell increases. If the control device 101 determines that no quality degradation has occurred in a second base station (e.g., base station 112) as a result of controlling the target received power at time t1, it notifies each base station of the target received power plus ΔP0 at time t2. Note that the value of the target received power increased by the control device 101 at time t2 may be the same as ΔP0 or may be a value different from ΔP0. For example, when the control device 101 controls the target received power using ΔP0 at time t2, the first target received power P01(t2) = P01(t0) + 2 × ΔP0, and the second target received power P02(t2) = P02(t0) + 2 × ΔP0. If the control device 101 determines that no quality degradation has occurred in the second base station as a result of controlling the target reception power at time t2, it further increases each target reception power by ΔP0 and issues a notification (time=t3). Then, at time t3, it is assumed that the control device 101 determines that quality degradation has occurred in the second base station. In this case, the control device 101 controls each target reception power to be lowered. For example, the control device 101 lowers each target reception power by ΔP0' and issues a notification.That is, the first target received power P01(t4)=P01(t0)+3×ΔP0-ΔP0', and the second target received power P02(t4)=P02(t0)+3×ΔP0-ΔP0'. In this case, if ΔP0'=P0, each target received power will have the same value as at time t2.

[0057] If the control device 101 determines that no quality degradation has occurred in the other base stations as a result of controlling the target reception power at time t4, it can individually control the target reception power of each base station. For example, at time t5, the control device 101 increases the value of the first target reception power by ΔP0 while maintaining the second target reception power, and notifies the first base station of the increase. That is, the first target reception power P01(t5) = P01(t0) + 4 × ΔP0 - ΔP0'. At this time, the control device 101 may or may not notify the third base station. If notification is performed, the same value as the target reception power at time t4 may be notified. The same applies when any of the target reception powers is maintained in the following steps; the maintained target reception power may or may not be notified. If the control device 101 determines that quality degradation has occurred in the second base station as a result of controlling the target reception power at time t5, the control device 101 controls to lower the first target reception power and increase the second target reception power. That is, the first target received power P01(t6) = P01(t0) + 4 × ΔP0 - 2 × ΔP0', and the second target received power P02(t6) = P02(t0) + 4 × ΔP0 - ΔP0'. If the control of the target received power at time t6 determines that no quality degradation has occurred in the second base station, the control device 101 controls to further increase the second target received power while maintaining the first target received power. That is, the second target received power P02(t7) = P02(t0) + 5 × ΔP0 - ΔP0'. If the control of the target received power at time t7 determines that quality degradation has occurred in another base station, the control device 101 controls to decrease the second target received power while maintaining the first target received power. That is, the second target received power P02(t8) = P02(t0) + 5 × ΔP0 - 2 × ΔP0'. If it is determined that no quality degradation has occurred in the second base station as a result of the control of the target received power at time t8, the control device 101 ends the second control.

[0058] As described above, the control device 101 in this example performs the second control to lower the first target received power and the second target received power when quality degradation occurs, and then adjusts each target received power individually when the quality degradation is resolved after lowering the first target received power and the second target received power. That is, the control device 101 controls to increase the first target received power while maintaining the second target received power until quality degradation occurs. If quality degradation occurs thereafter, the control device 101 controls to decrease the first target received power until the quality degradation is resolved, and after the quality degradation is resolved, the control device 101 controls to increase the second target received power while maintaining the first target received power until quality degradation occurs. Then, if quality degradation occurs after increasing the second target received power while maintaining the first target received power, the control device 101 controls to decrease the second target received power until the quality degradation is resolved, and stops the control after the quality degradation is resolved. This makes it possible to increase the throughput of multiple specific cells while keeping quality degradation due to interference from other cells within an acceptable range.

[0059] Note that the control device 101 may use a method other than the above for the second control. For example, when quality degradation occurs, the control device 101 may perform control to lower the first target received power to a first provisional value while maintaining the second target received power at a first time point when the quality degradation occurred, and if the quality degradation is subsequently resolved, set the first provisional value as the first target received power, and if the quality degradation is not resolved, perform control to return the first target received power to the first target received power at the first time point and lower the second target received power to a second provisional value, and if the quality degradation is subsequently resolved, set the second provisional value as the second target received power, and if the quality degradation is not resolved, perform control to set the first provisional value as the first target received power and the second provisional value as the second target received power. At this time, if quality degradation is resolved after lowering the first target received power to the first provisional value, the control device 101 may increase the second target received power until quality degradation occurs, and in response to the occurrence of quality degradation, lower the second target received power until the quality degradation is resolved, and then stop control.Also, if quality degradation is resolved after lowering the second target received power to the second provisional value, the control device 101 may increase the first target received power until quality degradation occurs, and in response to the occurrence of quality degradation, lower the first target received power until the quality degradation is resolved, and then stop control.

[0060] FIG. 8 shows an overview of the operation when the control device 101 operates as described above to perform the second control. The operation from time t1 to t3 is the same as that shown in FIG. 7, and therefore a description thereof will be omitted. If the control device 101 determines that quality degradation has occurred in the other base stations as a result of the control of the target reception power at time t3, it individually controls the target reception power of each base station. For example, at time t4, the control device 101 maintains the second target reception power while lowering the value of the first target reception power by ΔP0′ and notifies the first base station. That is, the first target reception power P01(t4)=P01(t0)+3×ΔP0-ΔP0′. Here, the value of the first target reception power obtained by lowering ΔP0′ is set as the first provisional value. If the control of the target reception power at time t4 determines that quality degradation has occurred in the second base station, the control device 101 returns the first target reception power to the first target reception power at time t3 and performs control to lower the second target reception power. That is, the first target received power P01(t5) = P01(t0) + 3 × ΔP0, and the second target received power P02(t5) = P02(t0) + 3 × ΔP0 - ΔP0'. Here, the value of the second target received power obtained by lowering ΔP0' is set to the second provisional value. If, as a result of controlling the target received power at time t5, it is determined that quality degradation is occurring in the second base station, the control device 101 sets the first provisional value as the first target received power, performs control to set the second provisional value as the second target received power, and then stops the control.

[0061] If the control device 101 determines at time t4 that no quality degradation has occurred in the second base station, it may maintain the second target received power at time t4 as the second target received power, set a first provisional value as the first target received power, and stop control. At this time, the control device 101 may set the first target received power to the first provisional value, and then control the second target received power to increase. In this case, the control device 101 may increase the second target received power until quality degradation occurs, and then, in response to the occurrence of quality degradation, decrease the second target received power until the quality degradation is resolved, and stop control.

[0062] Furthermore, if the control device 101 determines at time t5 that no quality degradation has occurred in the second base station, it may maintain the first target received power at time t5 as the first target received power, set a second provisional value as the second target received power, and stop control. At this time, the control device 101 may set the second target received power to the second provisional value, and then control the first target received power to increase. In this case, the control device 101 may increase the first target received power until quality degradation occurs, and then, upon occurrence of quality degradation, decrease the first target received power until the quality degradation is resolved, and then stop control. In this way, after quality degradation has occurred, the control device 101 checks whether the quality degradation has been resolved when each target received power is decreased using a predetermined provisional value, and ends control using a provisional value that resolves the quality degradation, thereby enabling the quality degradation to be resolved early.

[0063] (Processing example 3) In the processing example 1, when the control device 101 identifies a base station 110 for which the target received power should be controlled, the control device 101 identifies a base station whose cell throughput needs to be increased due to communication traffic congestion or the like. As described above, as the terminal 120 moves within a cell or between cells, the terminals and the number of terminals connected to each base station 110, or the types of communication and services, may change. Therefore, even if the target received power of each base station 110 in the mobile communication system is set so as not to cause quality degradation in other cells, quality degradation may occur in one of the cells due to a subsequent change in the communication environment. In this example, an example of the operation of the control device 101 when quality degradation occurs in one of the cells and the control device 101 controls the target received power of a specific base station 110 will be described.

[0064] The control device 101 in this example first determines whether quality degradation is occurring in each cell in the mobile communication system. For example, if the control device 101 is a RIC and communication is established with the base station 110 using the E2 interface or the O1 interface, the control device 101 may acquire information associated with quality degradation from the base station 110, such as the amount of interference power, the packet error rate, the packet loss rate, and the transmission delay time. When the control device 101 determines that quality degradation is occurring in a specific cell, the control device 101 identifies a base station (first base station) to which a terminal whose transmission power should be reduced is connected. For example, if the control device 101 has a database storing information on the geographical locations of the base stations 110, the control device 101 may identify each of the base stations 110 constituting a cell adjacent to the cell in which quality degradation is occurring as the first base station. The method by which the control device 101 identifies the first base station is not limited to this. For example, the control device 101 may identify the first base station from among the base stations 110 located within a predetermined geographical distance from the cell in which quality degradation is occurring, based on the target received power set for each base station 110. For example, the control device 101 may identify a base station 110 whose target received power exceeds a predetermined threshold as the first base station. Also, the control device 101 may identify a predetermined number of base stations 110 ranked from the top of the base stations 110 whose target received power is high as the first base station.

[0065] The control device 101 then controls the target received power of the identified first base station to be reduced until the quality degradation is resolved. At this time, the control device 101 controls the target received power of the first base station so that it does not fall below the initial value of the target received power. This can prevent excessive throughput degradation in the cell of the first base station from occurring by lowering the target power of the cell of the first base station to resolve the quality degradation that has occurred in the specific cell. The control device 101 also determines the predetermined reduction amount used when gradually reducing the target received power so that the reduction amount is greater than the predetermined increase amount used when gradually increasing the target received power. If the quality degradation that has occurred in the specific cell is not resolved quickly, communication congestion, connection failures, and the like may spread, potentially resulting in a continued degradation of the communication experience. Therefore, the control device 101 can determine the predetermined reduction amount used when gradually reducing the target received power of the first base station based on the occurrence of quality degradation in the specific cell so that the predetermined reduction amount is greater than the predetermined increase amount used when gradually increasing the target received power to increase the throughput in the specific cell.

[0066] The operation of the control device 101 will be described using the example flowchart of FIG. 9. In this example, it is assumed that quality degradation has occurred in the cell 132 in FIG. 1, and that the control device 101 controls the target received power of the base station 111. That is, the base station 111 and the base station 112 correspond to the first base station and the second base station, respectively. First, the control device 101 determines whether or not there is a cell in which quality degradation has occurred (S901). For example, the control device 101 may periodically acquire quality information from each base station 110, and determine whether or not quality degradation has occurred based on whether or not the acquired quality information exceeds a predetermined threshold. If there is a cell in which quality degradation has occurred (YES in S901), the control device 101 performs the process of S902, and if there is no cell in which quality degradation has occurred, the control device 101 periodically executes the determination of S901. In this example, it is assumed that the cell 132 constituted by the base station 112 has been identified.

[0067] Then, the control device 101 identifies a base station whose target received power should be controlled (S902). For example, the control device 101 identifies the base station 111 that configures the cell 131 adjacent to the cell 132 configured by the base station 112 as the first base station whose target received power should be controlled. The control device 101 notifies the identified base station of the target received power (S903). For example, if the target received power used by the base station is P0(t), the control device 101 notifies the base station 111 of P0(t)-ΔP0' as a new target received power. Here, ΔP0' is a predetermined amount of decrease, and its determination method will be described later. The target received power notified to the base station 111 is notified from the base station 111 to the terminal 121. By using the new target received power in the transmission power control in the terminal 121, interference in the cell 132 is mitigated, and quality degradation can be resolved. After notifying the target received power, the control device 101 acquires quality information from the base station constituting the cell in which quality degradation is occurring (S904). The quality information may be the same type of information as the information acquired in S901. The control device 101 determines whether the quality degradation has been resolved based on the acquired quality information (S905). For example, the control device 101 determines whether the quality degradation in the cell 132 has been resolved based on the quality information acquired from the base station 112. If the quality degradation has not been resolved (NO in S905), the control device 101 executes a first control (S906), and if the quality degradation has been resolved (YES in S905), the control device 101 executes a second control (S907). In the first control, the control device 101 performs control to further reduce the target received power by a predetermined reduction amount. That is, if the control device 101 determines that the quality degradation has not been resolved, it notifies the second base station of a target received power that has been further reduced by a predetermined amount (S903), and can further determine whether the quality degradation at the first base station has been resolved (S904 and S905).

[0068] On the other hand, if the quality degradation is resolved (YES in S905), the control device 101 may increase the target reception power by ΔP0 in the second control. Lowering the target reception power of the first base station to resolve the quality degradation in other cells may have an effect such as a decrease in throughput in the cell configured by the first base station. Therefore, the control device 101 may perform control to increase the target reception power of the first base station so that it does not decrease excessively. After increasing the target reception power by ΔP0 and notifying the first base station, the control device 101 determines whether quality degradation has occurred in the second base station. If quality degradation has occurred, the control device 101 returns the target reception power to the level before the second control and terminates the processing. Furthermore, if quality degradation does not occur, the control device 101 may perform control to further increase the target reception power by ΔP0. The control device 101 gradually increases the target reception power until quality degradation occurs. If quality degradation occurs, the control device 101 returns the target reception power to the value of the previous level and terminates the processing. In this way, when quality degradation occurs in a specific cell, the control device 101 identifies the base station 110 that caused the quality degradation and controls the base station 110 to lower the target received power until the quality degradation is resolved, thereby enabling the quality degradation to be resolved early. Furthermore, after the quality degradation is resolved, the control device 101 controls the first base station to raise the target power within a range where no quality degradation occurs, thereby preventing an excessive decrease in throughput in the cell constituted by the first base station.

[0069] (Method for determining the control amount of target received power) A method for specifying a predetermined control amount (increase or decrease) when the control device 101 controls to reduce the target received power of the first base station will be described. When quality degradation occurs in a specific cell, the higher the target received power set in the surrounding cells, the more likely it is that the cells are generating stronger interference. In a cell configured by a base station 110 with high target received power, the higher the transmission power used by the terminal 120, making it more likely to cause interference to other cells. By quickly reducing the transmission power of the terminal in such a cell, the quality degradation is more likely to be resolved quickly. Therefore, the control device 101 can determine the predetermined decrease amount based on the target received power set in each first base station when it is determined that quality degradation is occurring. For example, the control device 101 can determine the product of the target received power set in the first base station and a predetermined coefficient as the predetermined decrease amount. In other words, the control device 101 can determine a predetermined ratio of the target received power of the first base station as the predetermined decrease amount. As a result, the higher the target received power, the shorter the period in which the target received power can be reduced.

[0070] The control device 101 may also determine the predetermined decrease amount based on the difference between the target received power of the first base station when it is determined that quality degradation is occurring and an initial value. Here, the initial value is a reference value when controlling the target received power of the first base station, and may be, for example, a predetermined fixed value set in the first base station. As an example, the initial value may be the target received power initially set when the base station 110 is started up. When lowering the target received power of the first base station to resolve quality degradation in the second base station, if the target received power falls below the initial value of the first base station, the possibility of quality degradation occurring in the cell of the first base station increases. Therefore, the control device 101 may determine the predetermined decrease amount as the product of the difference between the target received power of the first base station when it is determined that quality degradation is occurring and the initial value and a predetermined coefficient. In other words, the control device 101 may determine the predetermined decrease amount as a predetermined percentage of the difference between the target received power of the first base station and the initial value. By determining the predetermined decrease amount in this manner, it is possible to prevent the target received power after control to lower the target received power of the first base station from falling below the initial value. This makes it possible to eliminate quality degradation in the second base station while suppressing the possibility of quality degradation occurring in the cell of the first base station. Note that the control device 101 can set any value between 0 and 1 as the predetermined coefficient (i.e., predetermined ratio). For example, when determining the predetermined decrease amount as the product of the difference between the target received power of the first base station when it is determined that quality degradation is occurring and the initial value and the predetermined coefficient, the control device 101 can set 0.5 as the predetermined coefficient. In this case, the target received power can be reduced to half the cumulative value of the increase in the target received power due to control up to that point.

[0071] On the other hand, the control device 101 may find that the predetermined decrease calculated as described above is smaller than the predetermined increase when controlling to increase the target received power. In this case, the control device 101 may determine the predetermined decrease as the same as the predetermined increase. This allows control to be performed to decrease the target received quality at least as quickly as when controlling to increase the target received power. Furthermore, when controlling the target received power of the first base station using the determined predetermined decrease, the control device 101 may compare the target received power after control with an initial value, and if the initial value is higher, notify the first base station of the initial value as the target received power. This may prevent the first base station from setting an excessively low target received power. In this case, the control device 101 may use a fixed value other than the initial value. For example, the control device 101 may compare the target received power after control with a predetermined fixed value, and if the predetermined fixed value is higher, notify the first base station of the predetermined fixed value as the target received power. This allows the target received power to be controlled flexibly using a value other than the initial value.

[0072] The method by which the control device 101 determines the predetermined decrease amount is not limited to the above. For example, the control device 101 may determine the predetermined decrease amount using a predetermined statistical value associated with communication in a cell configured by the first base station. As an example, the control device 101 may determine the predetermined decrease amount using the number of handover attempts in the cell of the first base station. When the terminal 120 detects a base station 110 that can provide a better connection than the base station 110 to which the terminal 120 is connected, the terminal 120 reports this to the base station 110 to which the terminal 120 is connected. The base station 110 that receives the report notifies the terminal 120 of a handover instruction. The terminal 120 that receives the instruction attempts a handover to another base station 110. Based on this procedure, the terminal 120 located on the boundary where multiple cells geographically overlap is likely to attempt a handover, and signals transmitted by this terminal 120 are likely to reach multiple cells and therefore cause interference to other cells.

[0073] Therefore, the control device 101 may determine the predetermined decrease amount using the number of handover attempts notified by the first base station such that the greater the number of handover attempts, the greater the predetermined decrease amount. The number of handover attempts may be, for example, the number of handover attempts that occurred at the first base station. The number of handover attempts may be notified to the control device 101 from the first base station, for example, using the E2 interface or the O1 interface. As an example, the control device 101 may set two values ​​as the predetermined decrease amount, and use the first decrease amount when the number of handover attempts exceeds a predetermined threshold, and use the second decrease amount when the number of handover attempts falls below the predetermined threshold. Here, the first decrease amount is assumed to be greater than the second decrease amount. As a result, the target received power can be reduced more quickly for a cell with a larger number of handover attempts, thereby enabling quality degradation to be resolved more quickly. Note that the control device 101 may set three or more values ​​as the predetermined decrease amount. In this case, the control device 101 may set multiple thresholds, and may use a first decrease amount when the number of handover attempts exceeds a first threshold, a second decrease amount when the number is equal to or less than the first threshold but exceeds a second threshold, and so on. If the number is equal to or less than an (N-1)th threshold but exceeds an Nth threshold, the Nth decrease amount may be used. Here, the first decrease amount > the second decrease amount > > the Nth decrease amount. Furthermore, the statistical value of the cell of the first base station that can be used by the control device 101 is not limited to the number of handover attempts. For example, the control device 101 may determine the predetermined decrease amount using the resource block usage rate in the cell of the second base station. If the resource block usage rate is high, the chances of interfering with other cells may increase. Therefore, the control device 101 may determine the predetermined decrease amount so that the higher the resource block usage rate in the cell of the second base station, the larger the predetermined decrease amount.

[0074] The control device 101 may also determine the predetermined decrease amount based on the geographical location of the second base station that constitutes the cell in which quality degradation is occurring. Generally, the higher the station density (the number of base stations deployed per unit area), the easier it is for signals to reach each other between cells, resulting in greater mutual interference. Therefore, if quality degradation occurs in one or more cells of multiple base stations 110 deployed in a location with high station density, the likelihood of quality degradation also occurring in other nearby cells increases. Therefore, the control device 101 may determine the predetermined decrease amount so that the greater the station density in the geographical location where the second base station is deployed, the greater the predetermined decrease amount in controlling the target received power of the first base station. For example, the control device 101 may determine the predetermined decrease amount based on the distance between the first base station and the second base station (referred to as inter-site distance, ISD) so that the smaller the ISD, the greater the predetermined decrease amount. For example, the control device 101 may set two values ​​as the predetermined decrease amount, and use the first decrease amount when the ISD exceeds a predetermined threshold, and use the second decrease amount when the ISD falls below the predetermined threshold. Here, the first decrease amount is smaller than the second decrease amount. The control device 101 may set three or more values ​​as the predetermined decrease amount. In this case, the control device 101 may set multiple thresholds, and use the first decrease amount when the ISD exceeds the first threshold, the second decrease amount when the ISD is equal to or less than the first threshold but exceeds the second threshold, and so on. If the ISD is equal to or less than the (N-1)th threshold but exceeds the Nth threshold, the Nth decrease amount may be used. Here, the first decrease amount < the second decrease amount < < the Nth decrease amount. This allows the target received power to be reduced more quickly as the ISD decreases, thereby quickly eliminating quality degradation. For example, if the control device 101 has information indicating the geographical location of each base station 110 included in the mobile communication system or is able to obtain such information, the control device 101 may determine the predetermined decrease amount using the station density in a predetermined area including the second base station or the distance between the first base station and the second base station.

[0075] The control device 101 may also determine the predetermined decrease amount using past trends in the target received power at the first base station. For example, the control device 101 may determine the predetermined decrease amount based on the average value of the target received power set at the first base station over a predetermined period in the past or the lowest target received power value. As an example, the control device 101 may store the target received power notified to the first base station and the time period in which the target received power was notified, and determine the predetermined decrease amount using the target received power used in the past during the time period in which the target received power of the first base station is to be controlled. Using a target received power that has been used in the past makes it possible to quickly resolve quality degradation occurring in the cell of the first base station. The control device 101 may also use a target received power that is lower by a predetermined fixed value than the target received power determined using the past target received power. Using a target received power that is lower than the target received power that has been used in the past makes it possible to reliably resolve quality degradation.

[0076] (Processing example 4) In the processing example 3, the case where the control device 101 identifies one base station 110 has been described. In this processing example, the case where the control device 101 identifies two or more base stations 110 will be described. In this example, the control device 101 first determines whether quality degradation is occurring in each cell in the mobile communication system. If the control device 101 determines that quality degradation is occurring in a specific cell, it identifies a base station (first base station) to which a terminal whose transmission power should be reduced is connected. In this example, two or more base stations 110 (for example, a first base station and a third base station) are identified. The control device 101 controls each of the target received powers of the two or more identified base stations 110 to reduce the target received power until the quality degradation is resolved. Then, when the control device 101 confirms that the quality degradation has been resolved, it controls the target received powers of the first base station and the third base station to be maximized within a range where quality degradation does not occur.

[0077] The configuration of the control device 101 in this example is the same as in Processing Example 1, so its description will be omitted. The processing flow will be described using FIG. 9, as in Processing Example 3. Note that descriptions of operations that are the same as in Processing Example 3 will be omitted. In addition, this example will be described using the network configuration of FIG. 6. That is, the control device 101 detects that quality degradation is occurring in the cell 132 configured by the base station 112 (second base station), and controls the target received power of the base station 111 and the base station 113 (first base station and third base station). FIG. 6 shows a state in which the base station 112 receives interference signals from two adjacent cells, but there is also a case in which the base station 112 receives interference signals from three or more cells. In this example, an example in which the control device 101 controls the target received power of two base stations (base station 111 and base station 113) will be described, but this example can also be applied to a case in which the control device 101 controls the target received power of three or more base stations.

[0078] First, the control device 101 determines whether or not there is a cell in which quality degradation has occurred (S901). If there is a cell in which quality degradation has occurred (YES in S901), the control device 101 performs the process of S902, and if there is no cell in which quality degradation has occurred, the control device 101 periodically performs the determination of S901. In this example, the cell 132 configured by the base station 112 is identified. Then, the control device 101 identifies the base station whose target received power should be controlled (S902). For example, the control device 101 identifies the base station 111 and the base station 113 that respectively configure the cell 131 and the cell 133 adjacent to the cell 132 configured by the base station 112 as the first base station and the third base station whose target received power should be controlled. The control device 101 notifies the first base station and the third base station of the target received power (S903). For example, if the target received powers used by the base stations 111 and 113 at time t when the control device 101 identifies the base stations 111 and 113 are P01(t) and P02(t), respectively, the control device 101 may notify the base stations 111 and 113 of a first target received power = P01(t) - ΔP0' and a second target received power = P02(t) - ΔP0' as new target received powers, respectively. Here, ΔP0' is a predetermined decrease amount. Note that ΔP0' may be different for each notifying base station 110, or may be the same for each notifying base station 110. In this example, it is assumed that each target received power is controlled using a common ΔP0'. After notifying the target received power, the control device 101 acquires quality information from the second base station constituting the cell in which quality degradation is occurring (S904). Based on the acquired quality information, the control device 101 determines whether the quality degradation has been resolved (S905). For example, the control device 101 determines whether or not quality degradation in the cell 132 has been resolved based on quality information acquired from the base station 112. If the quality degradation has not been resolved (NO in S905), the control device 101 executes a first control (S906), and if the quality degradation has been resolved (YES in S905), the control device 101 executes a second control (S907).

[0079] In the first control, the control device 101 performs control to further reduce each of the target reception powers by a predetermined amount. That is, if the control device 101 determines that the quality degradation has not been resolved, it notifies the first base station and the third base station of the target reception power further reduced by the predetermined amount (S903), and may further determine whether the quality degradation in the second base station has been resolved (S904 and S905). On the other hand, if the control device 101 determines that the quality degradation has been resolved (YES in S905), it performs the second control and ends the processing. For example, as the second control, the control device 101 may increase any of the target reception powers by ΔP0. The increase amount ΔP0 when increasing the target reception power and the decrease amount ΔP0' when decreasing the target reception power may be the same or different. Furthermore, the ΔP0 used in the first target reception power control and the second target reception power control may be the same or different. The control device 101 then increases one target received power so as not to cause quality degradation, and then increases the other target received power so as not to cause quality degradation. By controlling the target received powers of the first base station and the third base station in this manner, it is possible to maximize the throughput of each cell while eliminating quality degradation. Such control operation of each target received power by the control device 101 will be described using FIG. 10.

[0080] FIG. 10 shows an outline of the operation when the control device 101 controls the reception power of each target. In FIG. 10, the horizontal axis indicates the passage of time, and the vertical axis indicates the set values ​​of the first target reception power and the second target reception power. The first target reception power is indicated by the height of the unshaded bar, and the second target reception power is indicated by the height of the shaded bar. For example, let t0 be the time when the control device 101 identifies the second base station (base station 112), the first base station, and the third base station (base station 111 and base station 113). At this time, let us assume that the target reception powers of the base station 111 and the base station 113 are first target reception power = P01(t0) and second target reception power = P02(t0), respectively. The control device 101 notifies the respective target reception powers reduced by ΔP0′ at time t1. That is, the first target received power P01(t1) = P01(t0) - ΔP0' and the second target received power P02(t1) = P02(t0) - ΔP0' are notified to the first base station and the third base station, respectively. If the control device 101 determines that the quality degradation in the cell of the base station 112 has not been resolved as a result of controlling the target received power at time t1, it further reduces the target received power by ΔP0' at time t2 and notifies the first base station and the third base station of the respective target received powers. That is, the first target received power P01(t2) = P01(t0) - 2 × ΔP0' and the second target received power P02(t2) = P02(t0) - 2 × ΔP0'. If the control device 101 determines that the quality degradation in the cell of the base station 112 has been resolved as a result of controlling the target received power at time t2, it increases one of the target received powers by ΔP0 and notifies the result. In this example, a notification to increase the first target received power is sent (time t3). That is, the first target received power P01(t3)=P01(t0)-2×ΔP0'+ΔP0, and the second target received power P02(t3)=P02(t0)-2×ΔP0'. Then, it is assumed that the control device 101 determines that quality degradation has occurred in the cell of the base station 112. In this case, the control device 101 controls to decrease the first target received power. For example, the control device 101 decreases the first target received power by ΔP0 and sends a notification (time t4).That is, the first target received power P01(t4) = P01(t0) - 2 × ΔP0'. Then, the control device 101 issues a notification to increase the second target received power (time t4). That is, the second target received power P02(t4) = P02(t0) - 2 × ΔP0' + ΔP0. If the control device 101 determines that no quality degradation has occurred in the cell of the base station 112 as a result of controlling the target received power at time t4, it issues a notification to further increase the received power of the second target (time t5). That is, the second target received power P02(t5) = P02(t0) - 2 × ΔP0' + 2 × ΔP0. At this time, the control device 101 may or may not issue a notification to the base station 111. If a notification is issued, the same value as the target received power at time t4 may be notified. If it is determined that quality degradation has occurred in the cell of the base station 112 as a result of controlling the target received power at time t5, the control device 101 performs control to lower the second target received power and ends the process. That is, the second target received power P02(t6)=P02(t0)-2×ΔP0'+ΔP0. Because the second target received power notified at time t6 is the same as the second target received power at time t4, it has been confirmed that quality degradation will not occur in the cell of the base station 112.

[0081] As described above, the control device 101 in this example performs the second control by individually adjusting the first target received power and the second target received power when quality degradation is resolved. That is, the control device 101 controls the first target received power to be increased while maintaining the second target received power until quality degradation occurs, and when quality degradation occurs, controls the first target received power to be decreased. Then, the control device 101 controls the second target received power to be increased while maintaining the first target received power until quality degradation occurs, and when quality degradation occurs, controls the first target received power to be decreased until quality degradation is resolved, and then stops the control. This makes it possible to increase the throughput of multiple specific cells while keeping quality degradation due to interference from other cells within an acceptable range.

[0082] The control device 101 may use a method other than the above for the second control. For example, when quality degradation is resolved, the control means 101 increases the first target received power and the second target received power until quality degradation occurs in the cell of the base station 112. Then, the control device 101 controls the first target received power to be lowered to a first provisional value while maintaining the second target received power at the first time point when the quality degradation occurred. After lowering the first target received power to the first provisional value, if the quality degradation is resolved, the control device 101 sets the first provisional value as the first target received power and stops the control. On the other hand, when the quality degradation is not resolved, the control device 101 controls the first target received power to be returned to the first target received power at the first time point and lowers the second target received power to the second provisional value. Then, after lowering the second target value to the second provisional value, if the quality degradation is resolved, the control device 101 stops control with the second provisional value as the second target received power, and if the quality degradation is not resolved, the control device 101 sets the first provisional value as the first target received power and stops control with the second provisional value as the second target received power.

[0083] FIG. 11 shows an overview of the operation when the control device 101 operates as described above to execute the second control. The operation from time t0 to t2 is the same as that shown in FIG. 10, and therefore a description thereof will be omitted. If the control device 101 determines that quality degradation has been resolved in the cell of the base station 112 as a result of controlling the target received power at time t2, the control device 101 controls each target received power to increase it (time t3). The increase amount ΔP0 of the target received power at this time may be smaller than the decrease amount ΔP0' when the target received power was reduced from time t0 to t2. By making ΔP0 smaller than ΔP0', it is possible to quickly resolve quality degradation, suppress the influence of subsequent quality degradation, and maximize throughput in the cell of the second base station. If the control device 101 determines that quality degradation has not occurred in the cell of the base station 112 as a result of controlling the target received power at time t2, the control device 101 controls each target received power to further increase it (time t4). Then, when the control device 101 determines that quality degradation has occurred in the cell of the base station 112 as a result of controlling the target received power at time t4, it controls each target received power individually. For example, at time t5, the control device 101 maintains the second target received power while lowering the value of the first target received power by ΔP0″ and notifies the base station 111. That is, the first target received power P01(t5)=P01(t0)-2×ΔP0′+2×ΔP0-ΔP0″. Here, the value of the first target received power obtained by lowering ΔP0″ is set to the first provisional value. Note that if ΔP0″=P0, the first target received power at time t5 will be the same as the first target received power at time t3. If it is determined that quality degradation is occurring in the cell of the base station 112 as a result of controlling the target received power at time t5, the control device 101 returns the first target received power to the first target received power at time t4 and performs control to lower the second target received power. That is, the first target received power P01(t6) = P01(t0) - 2 × ΔP0' + 2 × ΔP0, and the second target received power P02(t6) = P02(t0) - 2 × ΔP0' + 2 × ΔP0 - ΔP0" Here, the value of the second target received power obtained by lowering ΔP0" is set to the second provisional value.If, as a result of controlling the target received power at time t6, it is determined that quality degradation is occurring in the cell of base station 112, control device 101 performs control to set a first provisional value as the first target received power and a second provisional value as the second target received power, and then stops the control.

[0084] If the control device 101 determines at time t5 that no quality degradation has occurred in the cell of the base station 112, it may maintain the second target received power at time t5 as the second target received power, set a first provisional value as the first target received power, and stop control. At this time, the control device 101 may set the first target received power to the first provisional value, and then control to increase the second target received power. In this case, the control device 101 may increase the second target received power until quality degradation occurs, and then, in response to the occurrence of quality degradation, decrease the second target received power until the quality degradation is resolved, and stop control.

[0085] Furthermore, if the control device 101 determines at time t6 that no quality degradation has occurred in the cell of the base station 112, it may maintain the first target received power at time t6 as the first target received power, set a second provisional value as the second target received power, and stop control. At this time, the control device 101 may set the second target received power to the second provisional value, and then control to increase the first target received power. In this case, the control device 101 may increase the first target received power until quality degradation occurs, and then, upon occurrence of quality degradation, lower the first target received power until the quality degradation is resolved, and then stop control. In this way, after quality degradation has occurred, the control device 101 checks whether the quality degradation has been resolved when each target received power is lowered using a predetermined provisional value, and ends control using a provisional value that resolves the quality degradation, thereby enabling the quality degradation to be resolved early.

[0086] (First base station identification method) An example of a method for identifying a first base station whose target received power should be controlled in the control device 101 operating as described above will be described. Generally, when quality degradation occurs in a specific cell and multiple cells exist in the vicinity of that cell, it can be difficult to identify which cell is causing interference that is causing the quality degradation. In this case, for example, if control is performed to lower the target received power for all base stations 110 constituting multiple cells adjacent to the cell where quality degradation is occurring, throughput will also decrease in cells that did not originally need to lower their target received power, potentially causing quality degradation in those cells. For example, FIG. 12 shows an example of a mobile communication system consisting of multiple cells. Assume that the mobile communication system includes multiple cells, each represented by a pentagon, including cells 1201 to 1203. Cells 1201 and 1203 may correspond to cells 131 and 133 in FIG. 6, respectively. Shaded areas 1211 and 1212 indicate areas where a large number of terminals 120 are present. Assume that quality degradation is occurring in cell 1202 in FIG. 12. Cell 1202 may correspond to cell 132 in FIG. 6. In this case, since many terminals 120 are located in area 1211 on the boundary between cells 1201 and 1202, it is highly likely that quality degradation in cell 1202 will be resolved by lowering the target received power of cell 1201. Terminals 120 located in such an area where multiple cells geographically overlap may be referred to as interfering terminals. On the other hand, since many terminals 120 in cell 1203 are located in area 1212, which is far from cell 1202, it is unlikely that quality degradation in cell 1202 will be resolved even if the target received power of cell 1203 is lowered. Therefore, the control device 101 identifies the base station 110 whose target received power should be controlled based on the geographical distribution of terminals 120, thereby efficiently controlling the target received power.

[0087] For example, the control device 101 controls the target received power for a base station 110 that satisfies a predetermined condition. For example, the predetermined condition may be that multiple terminals 120 are located in an area that geographically overlaps with a cell where quality degradation is occurring. As an example, the base station 110 acquires location information of the terminals 120 connected to the base station 110 using a specific method and notifies the control device 101. For example, if the base station 110 has a function for estimating the location of the terminal 120 using a global positioning system (GPS) or an observed time difference of arrival (OTDOA), the location information of the terminal 120 may be acquired based on communication with the terminal 120. Then, the control device 101 may identify a first base station for which the target received power should be controlled based on the acquired location information of each terminal 120. For example, if the control device 101 has access to information indicating the geographical location of the base station 110, the base station 110 that configures a cell adjacent to a cell configured by a second base station may be identified as a candidate for the first base station. The control device 101 then determines the number of terminals 120 located in a predetermined geographical area between the second base station and the first base station candidate and connected to the first base station. For example, the predetermined geographical area may be a circle whose diameter is a line segment starting from the geographical location of the first base station candidate and ending at the geographical location of the second base station. Alternatively, the predetermined geographical area may be a circle whose center is a predetermined point between the geographical locations of the first base station candidate and the second base station. The predetermined geographical area may be set by other methods. If the number of terminals 120 located in the predetermined geographical area exceeds a predetermined threshold, the control device 101 determines the first base station candidate as the first base station. The method by which the control device 101 determines the second base station may be another method, as long as it can determine the first base station from among the first base station candidate candidates for which target reception power control is to be performed, based on the geographical distribution of terminals 120.

[0088] The method by which the control device 101 identifies the first base station that controls the target received power is not limited to the above. For example, the control device 101 may use setting information of each base station 110 (such as the setting of the target received power) or statistics associated with communications in the cell configured by the base station 110 (such as the resource block usage rate or the number of handover attempts). As an example, the control device 101 may identify, as the first base station candidate, cells adjacent to the cell where quality degradation has occurred or surrounding cells that satisfy predetermined geographical conditions, and identify, from among them, the base station 110 with high target received power. In this case, the control device 101 may identify, as the first base station, the base station 110 whose target received power exceeds a predetermined threshold or the base station 110 whose cumulative increase from the initial value of the target received power exceeds a predetermined threshold. Furthermore, from among the candidate first base stations, the control device 101 may identify, as the first base station, the base station 110 that increased the target received power during a predetermined period of time from the time when quality degradation occurred. Furthermore, the control device 101 may identify, from among the candidates for the first base station, a base station 110 that constitutes a cell in which the resource block usage rate is higher than a predetermined threshold or the number of handover attempts is higher than a predetermined threshold as the first base station.

[0089] When the control device 101 identifies the first base station using the configuration information of the base station 110 or statistics related to communications in the cell, the control device 101 may determine the predetermined control amount (decrease amount) when controlling the target received power based on the information used for the identification. For example, when the control device 101 identifies the first base station based on the number of interfering terminals, the control device 101 may set the predetermined decrease amount to a larger value as the number of interfering terminals increases. When the control device 101 identifies the first base station based on the amount of frequency resources used by the interfering terminals or the frequency resource utilization rate, the control device 101 may set the predetermined decrease amount to a larger value as the amount of frequency resources used by the interfering terminals or the frequency resource utilization rate increases. When the control device 101 identifies the first base station based on the target received power of the base station 110, the control device 101 may set the predetermined decrease amount to a larger value as the target received power increases. When the control device 101 identifies the first base station based on the number of handover attempts in the cell of the base station 110, the control device 101 may set the predetermined decrease amount to a larger value as the number of handover attempts increases. The control device 101 may determine the predetermined decrease amount using information different from the information used to identify the first base station. For example, when the control device 101 identifies the base station 110 that configures a cell with a high resource block utilization rate as the first base station, the control device 101 may increase the predetermined decrease amount as the target received power of the first base station increases.

[0090] As described above, according to this embodiment, when it becomes necessary to increase the throughput of a specific cell included in the mobile communication system, the control device 101 controls the target received power to be increased in stages using a predetermined increment, and with each increase, determines whether degradation of communication quality is occurring in other cells. The control device 101 then controls the target received power to be increased until it is determined that quality degradation has occurred in other cells, and if quality degradation occurs, controls the target received power to be decreased in stages until the quality degradation is resolved. This configuration makes it possible to increase the throughput of the necessary cells while suppressing the occurrence of quality degradation in the mobile communication system.

[0091] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the invention. [Explanation of symbols]

[0092] 101: control device, 111: base station, 112: base station, 121: terminal, 122: terminal

Claims

1. A control device in a wireless communication network including a plurality of base station devices, a first base station device included in the plurality of base station devices, and a specifying means for specifying the first base station device for which transmission power of one or more terminal devices connected to the first base station device should be increased; a notification means for notifying the first base station device of a target value of received power when a signal transmitted by the terminal device is received at the first base station device, the target value being notified to the terminal device from the first base station device; a determination means for determining whether a predetermined quality deterioration related to communication quality has occurred in a cell configured by a second base station device different from the first base station device included in the plurality of base station devices; a control means for controlling the target value to be increased until the predetermined quality deterioration occurs; A control device characterized by:

2. When the predetermined quality deterioration occurs as a result of the control, the control means lowers the target value until the predetermined quality deterioration is eliminated, and then stops the control.

2. The control device according to claim 1.

3. The control means uses a predetermined increase amount when increasing the target value and a predetermined decrease amount when decreasing the target value, and checks whether the predetermined quality deterioration has occurred each time the target value is changed, and determines whether further control should be performed depending on the check result.

3. The control device according to claim 1 or 2.

4. the identifying means further identifies a third base station device included in the plurality of base station devices, the third base station device being different from the first base station device and the second base station device; the notification means notifies the first base station device of a first target value that is the target value for the first base station device, and notifies the third base station device of a second target value that is the target value for the third base station device; The control means controls the first target value and the second target value to increase until the predetermined quality deterioration occurs.

2. The control device according to claim 1.

5. the control means controls the first target value and the second target value to be lowered when the predetermined quality deterioration occurs, When the predetermined quality deterioration is eliminated after the first target value and the second target value are reduced, control is performed so as to increase the first target value while maintaining the second target value until the predetermined quality deterioration occurs; if the predetermined quality deterioration occurs after the first target value is increased while maintaining the second target value, control is performed to decrease the first target value until the predetermined quality deterioration is eliminated, and after the predetermined quality deterioration is eliminated, control is performed to increase the second target value while maintaining the first target value until the predetermined quality deterioration occurs; If the predetermined quality deterioration occurs after the second target value is increased while the first target value is maintained, the second target value is controlled to be decreased until the predetermined quality deterioration is eliminated, and the control is stopped after the predetermined quality deterioration is eliminated.

5. The control device according to claim 4.

6. the control means performs control when the predetermined quality deterioration occurs so as to lower the first target value to a first provisional value while maintaining the second target value at a first time point when the predetermined quality deterioration occurs; After lowering the first target value to the first provisional value, When the predetermined quality deterioration is eliminated, the first provisional value is set as the first target value; If the predetermined quality deterioration is not resolved, control is performed so that the first target value is returned to the first target value at the first time point and the second target value is reduced to a second provisional value; After lowering the second target value to the second provisional value, When the predetermined quality deterioration is eliminated, the second provisional value is set as the second target value; If the predetermined quality deterioration is not resolved, the first provisional value is set as the first target value, and the second provisional value is set as the second target value.

5. The control device according to claim 4.

7. The control means If the predetermined quality deterioration is eliminated after the first target value is reduced to the first provisional value, the second target value is increased until the predetermined quality deterioration occurs, and in response to the occurrence of the predetermined quality deterioration, the second target value is reduced until the predetermined quality deterioration is eliminated, and control is stopped.

7. The control device according to claim 6.

8. The control means If the predetermined quality deterioration is eliminated after the second target value is reduced to the second provisional value, the first target value is increased until the predetermined quality deterioration occurs, and in response to the occurrence of the predetermined quality deterioration, the first target value is reduced until the predetermined quality deterioration is eliminated, and control is stopped.

7. The control device according to claim 6.

9. The determining means determines that the predetermined quality degradation has occurred when the interference power measured by the second base station device exceeds a predetermined threshold.

2. The control device according to claim 1.

10. The determining means determines that a predetermined quality degradation has occurred when a delay time until data transmission by a terminal device connected to the second base station device is completed exceeds a predetermined threshold.

2. The control device according to claim 1.

11. and a selection unit for selecting the second base station device from among base station devices that provide cells adjacent to a cell configured by the first base station device.

2. The control device according to claim 1.

12. The control device functions as a Radio Intelligent Controller (RIC) in an Open-Radio Access Network (O-RAN).

2. The control device according to claim 1.

13. A control method executed by a control device in a wireless communication network including a plurality of base station devices, a step of identifying a first base station device included in the plurality of base station devices, the first base station device being one that should increase transmission power of one or more terminal devices connected to the first base station device; a notification step of notifying the first base station device of a target value of received power when a signal transmitted by the terminal device is received at the first base station device, the target value being notified from the first base station device to the terminal device; a determination step of determining whether a predetermined quality deterioration regarding communication quality has occurred in a cell configured by a second base station device different from the first base station device included in the plurality of base station devices; a control step of controlling the target value to be increased until the predetermined quality deterioration occurs. A control method comprising:

14. A computer included in a control device in a wireless communication network including a plurality of base station devices, identifying a first base station device included in the plurality of base station devices, the first base station device being one that should increase transmission power of one or more terminal devices connected to the first base station device; notifying the first base station device of a target value of received power when a signal transmitted by the terminal device is received at the first base station device, the target value being notified to the terminal device from the first base station device; determining whether a predetermined quality degradation related to communication quality has occurred in a cell configured by a second base station device different from the first base station device included in the plurality of base station devices; Control is performed so as to increase the target value until the predetermined quality deterioration occurs. Program for.

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