WO2018037512A1 - Control device, terminal device, and control method - Google Patents

Abstract

This control device controls a plurality of transmission points, and is provided with a notification unit, reception unit, interference control unit, and transmission unit. The notification unit notifies a terminal, which is connected to at least one transmission point among a plurality of transmission points, of the number of the transmission points to be used for terminal communication. The reception unit receives, via at least one transmission point among the transmission points, information indicating that reception power at the terminal has exceeded a threshold value. When the interference control unit receives the information, the interference control unit selects a transmission point to be subjected to interference control, and performs the interference control with respect to the transmission point thus selected. The transmission unit transmits control information relating to the interference control to the transmission point, to which the control information is to be transmitted.

Description

Control device, terminal device, and control method

The present invention relates to a control device, a terminal device, and a control method.

As a successor system of LTE-A (Long Term Evolution-Advanced), a system called fifth generation mobile communication (5G, the 5th generation Generation mobile communication) is being studied. The specifications of 5th generation mobile communication are being studied by 3GPP standardization organizations (3rd Generation Generation Partnership Project, 3GPP) and the like. In the 5G wireless system, it is expected that the number of communication increases because communication between things without human intervention is performed by IoT (Internet of Things). Furthermore, it is predicted that the amount of information transferred will also increase. As described above, it is difficult to realize a system in which both the number of communication and the throughput required for communication are rapidly increased only by a macro base station having a wide area range. Therefore, a system using both a macro base station and a small base station has been proposed.

FIG. 1 is a diagram illustrating an example of a communication system. In the communication system shown in FIG. 1, a plurality of base stations 5 (5a to 5k) are installed at a high density in a macro cell 8 formed by radio waves from the macro base station radio section 15. Each base station 5 forms a small cell 7 (7a to 7k). Here, the small cell 7 is a cell in which the cell radius and the number of simultaneously accessible users are smaller than those of the macro cell 8. Each of the base stations 5 is connected to a BBU (BaseＢBand） Unit) 10 of the macro base station. When the terminal 2 is located in the small cell 7, the terminal 2 can communicate via the base station 5 that forms the small cell 7. In the example of FIG. 1, the terminal 2 is located in the small cell 7e and performs communication via the base station 5e.

Thus, by arranging a plurality of small cells 7 in the macro cell 8, it is possible to improve the number of simultaneously accessible users and the communication throughput of each user, but depending on the arrangement and setting of the base station 5 Interference may occur. Accordingly, interference mitigation techniques have been proposed.

FIG. 2 is a diagram illustrating an example of an interference mitigation technique called CoMP (Coordinated Multi Point Operation). CoMP is standardized as an interference mitigation technique in LTE-A. CoMP is used when one terminal 2 receives radio waves from a plurality of base stations 5, such as when the terminal 2 exists at a position where the small cells 7 formed by each of the plurality of base stations 5 overlap. In CoMP, the signal is adjusted between the base stations 5 so that the plurality of base stations 5 strengthens the signal strength at the position of the terminal 2 with respect to the terminals 2 receiving signals from the plurality of base stations 5. For example, in the example of FIG. 2, the terminal 2 is located at the boundary between the small cell 7a and the small cell 7b. The small cell 7a is formed by the base station 5a, and the small cell 7b is formed by the base station 5b. Further, the terminal 2 can receive signals from both the base station 5a and the base station 5b. In this state, the base station 5a and the base station 5b communicate with each other through the optical fiber 4 to transmit signals in a coordinated manner so that the signal strength at the terminal 2 increases.

As a related technique, a communication system has been proposed in which base station devices measure the amount of interference, exchange results obtained between base stations, and determine an interference arbitration method from the exchanged information (for example, Patent Documents). 1). When the maximum value of received signal power received from multiple base stations is greater than or equal to a predetermined threshold, communication is performed with the base station that has obtained the maximum received power, and the maximum value of received signal power is smaller than the predetermined threshold In this case, a terminal that performs communication with a plurality of base stations has also been proposed (for example, Patent Document 2). Furthermore, a method in which access points coordinate transmission power has also been proposed (for example, Patent Document 3).

JP 2010-178237 A JP 2011-23852 A JP-T-2015-534418

In CoMP described in the background art, when a certain terminal is connected to a plurality of base stations, the plurality of base stations coordinate transmission signals using feedback from the terminals. However, since the transmission conditions at the base station are not changed depending on the communication status of the terminals that are not connected, a transmission signal from the base station to which another terminal is connected may become an interference source. In particular, when a plurality of terminals connected to different base stations are close to each other, interference is likely to occur and communication quality is likely to deteriorate. Similar problems may occur even when the method for transmission power coordination described as the related technique is used. Furthermore, even if the number of connections is adjusted on the terminal side, interference from a base station that is not transmitting a signal addressed to the terminal is not reduced. The connection destination of the terminal may be a transmission point other than the base station. Such a problem can also occur when the terminal is connected to a plurality of transmission points.

An object of the present invention is, as one aspect, to reduce interference caused by transmission signals from a plurality of transmission points.

A control device according to a certain aspect controls a plurality of transmission points, and includes a notification unit, a reception unit, an interference control unit, and a transmission unit. The notification unit notifies a terminal connected to at least one transmission point of the plurality of transmission points of the number of transmission points used for communication of the terminal. The receiving unit receives information indicating that the reception power at the terminal has exceeded a threshold value via at least one transmission point of the plurality of transmission points. When receiving the information, the interference control unit selects a target transmission point to be subjected to interference control, and performs interference control for the selected target transmission point. The transmission unit transmits control information related to the interference control to the target transmission point.

∙ Interference due to transmission signals from multiple transmission points can be reduced.

It is a figure explaining the example of a communication system. It is a figure explaining the example of an interference reduction technique. It is a figure explaining the example of the control method concerning an embodiment. It is a figure explaining the example of a structure of a control apparatus. It is a figure explaining the example of the hardware constitutions of a control apparatus. It is a figure explaining the example of a structure of a terminal. It is a figure explaining the example of the hardware constitutions of a terminal. It is a figure explaining the example of the control method for reducing interference. It is a figure explaining an example in case interference does not occur. It is a flowchart explaining the example of the process which a terminal performs. It is a figure explaining the example of the control method for reducing interference. It is a figure explaining the example of a detection of an interference wave. It is a figure explaining the example of base station information. It is a figure explaining the example of control processing. It is a flowchart explaining the example of the process which a control apparatus performs. It is a figure explaining the modification of control processing. It is a figure explaining the modification of control processing. It is a figure explaining the modification of control processing. It is a figure explaining the example of the change process of the number of base stations used for communication. It is a flowchart explaining the example of the process which a control apparatus performs.

FIG. 3 is a diagram illustrating an example of a control method according to the embodiment. Case C1 in FIG. 3 is an example of a range in which a downlink signal (downlink signal, DL signal) transmitted from the base station 5 reaches when the base stations 5 (5a to 5e) are arranged with high density. It is shown. In case C1, a part of the DL signal transmitted from each base station 5 is illustrated. In the following description, the transmission source of the DL signal is described as the base station 5, but the transmission source of the DL signal is not limited to the base station, and may be a small base station radio unit or the like. The transmission source of the DL signal may be described as a transmission point (TP, transmission point). Note that the transmission point is a transmission source of an arbitrary DL signal, and may be, for example, the base station 5.

In case C1, a signal indicated by DL1 is transmitted from the base station 5a, and a signal indicated by DL2 is transmitted from the base station 5b. Furthermore, DL3a and DL3b signals are transmitted from the base station 5c. In addition, a DL4 signal is transmitted from the base station 5d, and a DL5 signal is transmitted from the base station 5e. Here, the base stations 5a to 5e are connected to the control device 20 via a control line. In this state, the terminal 50a is present at a position where it can receive the signal DL1 transmitted from the base station 5a, the signal DL2 transmitted from the base station 5b, and the signal DL3a transmitted from the base station 5c. Further, the terminal 50b is present at a position where it can receive the signal DL3b transmitted from the base station 5c, the signal DL4 transmitted from the base station 5d, and the signal DL5 transmitted from the base station 5e. For this reason, when transmission data to each terminal 50 is transmitted using two downlink signals, in case C1, a signal that is not used for data transmission becomes an interference source.

Sequence SE1 shows an example of a control method according to the embodiment. In the sequence SE1, in order to make the drawing easier to see, processing in a part of the base station 5 illustrated as the case C1 and the terminal 50a is shown. First, the control device 20 determines the number of base stations 5 used for communication of each terminal 50 located in the macro cell 8. The control device 20 notifies the determined number of base stations to each terminal 50 in the macro cell 8 cells. The notification of the number of base stations may be performed via the base station 5 or may be performed via a connection with the macro base station radio unit 15 connected to the control device 20. Here, it is assumed that the terminal 50a acquires the notification from the control device 20 using the connection with the macro base station radio unit 15 (step S1). In FIG. 3, it is assumed that the number of base stations (n) is determined to be 2. The terminal 50a stores the notified number of base stations.

It is assumed that the terminal 50a receives a downlink signal from each of the base station 5a and the base station 5b (step S2). The terminal 50a compares the threshold value stored in advance with the strength of the received signal. The threshold value is a value that can be used to determine whether to select a connection destination, and it is assumed that the terminal 50a can establish a connection with a transmission source of a downlink signal that is equal to or greater than the threshold value. The terminal 50a establishes a connection with the same number of base stations 5 notified from the control device 20 among the base stations 5 in which the received power intensity of the downlink signal is equal to or greater than the threshold. Here, it is notified that the signal from both the base station 5a and the base station 5b has an intensity exceeding the threshold and the number of base stations n is 2. Therefore, the terminal 50a establishes a connection between both the base station 5a and the base station 5b. Therefore, at this time, the terminal 50a is communicating with the same number of base stations 5 as the notified number of base stations n (step S3).

Suppose that the terminal 50a also receives the signal DL3a from the base station 5c during communication with the same number of base stations 5 as the notified number of base stations n (step S4). Hereinafter, the base station 5 detected during communication with the same number of notified base stations n may be referred to as the (n + 1) th base station. The terminal 50a compares the received power from the (n + 1) th base station (base station 5c) with a threshold value and notifies the control device 20 of the comparison result (steps S5 and S6). The notification of the comparison result at the terminal 50a may be performed via either the base station 5a or the base station 5b.

The control device 20 determines whether the downlink signal transmitted from the base station 5c is an interference source of communication of the terminal 50a using the comparison result notified from the terminal 50a, and uses the comparison result in the terminal 50a. The corresponding control is performed (step S7). For example, when the received power intensity from the base station 5c in the terminal 50a is equal to or greater than the threshold, the control device 20 determines that interference has occurred because the influence of the downlink signal from the base station 5c is large. Therefore, the control device 20 determines to reduce the transmission power at the base station 5c in order to reduce interference at the terminal 50a. The control device 20 transmits a control signal for reducing transmission power to the base station 5c. When receiving the control signal from the control device 20, the base station 5c reduces the transmission power according to the control signal. For this reason, both beam ranges of the downlink signals DL3a and DL3b transmitted from the base station 5c are narrowed. As a result, the strength of the signal DL3a reaching the terminal 50a is reduced, and interference at the terminal 50a due to the signal DL3a is reduced. On the other hand, when the received power intensity from the base station 5c in the terminal 50a is less than the threshold value, the control device 20 is not greatly affected by the downlink signal from the base station 5c, so that interference does not occur or can be ignored. Judge that there is. Then, the control apparatus 20 determines not to change the setting for the base station 5c.

In the sequence SE1, the example of the control based on the comparison result in the terminal 50a has been described, but the same control is performed based on the comparison result notified from the other terminal 50 such as the terminal 50b. By performing the processing described with reference to FIG. 3, even when the base stations 5 are in a dense state, interference due to transmission signals from a plurality of base stations is reduced.

<Device configuration>
FIG. 4 is a diagram illustrating an example of the configuration of the control device 20. The control device 20 includes a CPRI (Common Public Radio Interface) -IF unit 21, an I / Q signal processing unit 25, a baseband processing unit 26, a control unit 30, and a storage unit 40. The CPRI-IF unit 21 includes a transmission unit 22 and a reception unit 23. The control unit 30 includes a notification unit 31, a determination unit 32, a relay processing unit 33, and a selection unit 34, and an adjustment unit 35 as an option. The storage unit 40 stores base station information 41. The control device 20 can be realized as, for example, a BBU.

The transmission unit 22 transmits data to the base station 5. Further, the transmission unit 22 may transmit data to the terminal 50 in the macro cell 8 via the macro base station radio unit 15. In this case, the data transmitted from the transmission unit 22 is converted into a radio signal by the macro base station radio unit 15. The receiving unit 23 receives data from the base station 5. The receiving unit 23 may process a signal received via the macro base station radio unit 15. The I / Q signal processing unit 25 processes an I / Q signal to be transmitted / received. The baseband processing unit 26 processes a baseband signal.

The notification unit 31 performs processing for notifying the terminal 50 of the number of base stations 5 (number of base stations n) used for communication with the terminal 50 located in the macro cell 8. Here, the number of base stations may be a value stored in the notification unit 31 as a predetermined value, or may be a value obtained by adjustment in the adjustment unit 35. The determining unit 32 determines the control content when the terminal 50 is notified of information on the base station 5 that is an interference source in the communication of the terminal 50. For example, the determination unit 32 can determine a decrease in transmission power of the base station 5 serving as an interference source, a change in beam direction, a change in beam shape, and the like. The determination unit 32 generates control information for notifying the determined base station 5 of the determined setting.

The relay processing unit 33 performs processing for relaying transmission data addressed to the connection destination terminal 50 to the base station 5 that has established a connection with the terminal 50. For example, the relay processing unit 33 performs processing such as selection of the relay destination base station 5 according to the transmission data. When the base station 5 serving as an interference source notified from a certain terminal 50 is used for communication in another terminal 50, the selection unit 34 selects which terminal 50 communication is given priority. . The adjustment unit 35 determines the number of base stations 5 (number of base stations n) used for communication with the terminal 50 located in the macro cell 8. The determination of the number of base stations in the adjustment unit 35 will be described later.

The base station information 41 is associated with identification information for each of the base stations 5 installed in the macro cell 8, information on the terminal 50 notified by using the base station 5, and setting of the base station 5 Information is recorded. The base station information 41 can be used for processing in the selection unit 34, for example.

FIG. 5 is a diagram illustrating an example of a hardware configuration of the control device 20. The control device 20 includes an FPGA (field-programmable gate array) 101, a processor 105, and a memory 106. The FPGA 101 operates as the CPRI-IF unit 21. The processor 105 is an arbitrary processing circuit. For example, a central processing unit (CPU), a digital signal processor (DSP), a network processor (NMP), and a microprocessor (MPU) can be used as the processor 105. The processor 105 operates as an I / Q signal processing unit 25, a baseband processing unit 26, and a control unit 30 by executing a program. The memory 106 operates as the storage unit 40. The memory 106 includes a RAM (Random Access Memory) and a ROM (Read Only Memory).

FIG. 5 is an example of the hardware configuration of the control device 20. For example, the type and number of processors 105 held by the control device 20 can be changed according to the implementation. The number of memories 106 can also be changed according to the implementation. When there are a plurality of processors 105, the wireless signal processing unit 25, the baseband processing unit 26, and the control unit 30 may be realized by different processors 105, or may be realized by the same processor 105. .

FIG. 6 is a diagram for explaining an example of the configuration of the terminal 50. The terminal 50 includes an antenna 51, a reception unit 55, a control unit 60, and a transmission unit 80. The receiving unit 55 includes a radio unit 56, an orthogonal multiple access processing unit 57, and a demodulation / decoding unit 58. The control unit 60 includes a detection unit 70, a data processing unit 61, a system information extraction unit 62, a control signal extraction unit 63, a pilot extraction unit 64, a synchronization unit 65, a line control unit 66, a radio control unit 67, and a system information storage unit 68. Have The transmission unit 80 includes an encoding modulation unit 81, an orthogonal multiple access processing unit 82, and a radio unit 83.

The radio unit 56 receives a radio signal via the antenna 51 and outputs the received signal to the orthogonal multiple access processing unit 57. The orthogonal multiple access processing unit 57 performs IQ separation on the input signal, thereby removing the carrier wave and generating a baseband signal. The demodulation / decoding unit 58 performs demodulation processing and decoding processing on the baseband signal.

The detecting unit 70 measures the received power intensity and associates the obtained received power intensity with the identification information of the base station 5 that is the transmission source of the downlink signal. The identification information of the base station 5 is arbitrary information that can identify each base station 5. As identification information of the base station 5, for example, an ID (pilot ID) of a pilot signal can be used. The detection unit 70 holds the number of base stations notified from the control device 20 as a detection number threshold 71. The detection unit 70 compares the number of base stations that are the transmission source of the downlink signal received by the terminal 50 with the detection number threshold 71. When the downlink signal is received after receiving the downlink signals from the same number of base stations 5 as the detection number threshold 71, the detection unit 70 compares the received power intensity of the downlink signal with the threshold Th. The detection unit 70 outputs a comparison result between the received power intensity of the downlink signal and the threshold Th to the line control unit 66. Further, the detection unit 70 outputs the data input from the demodulation / decoding unit 58 to the system information extraction unit 62, the control signal extraction unit 63, the pilot extraction unit 64, and the data processing unit 61. The data processing unit 61 processes received data and appropriately generates transmission data.

The system information extraction unit 62 extracts information such as SIB (System Information Block) from the input information. The system information extraction unit 62 outputs the extracted system information to the line control unit 66. The control signal extraction unit 63 extracts a control signal transmitted from the control device 20 or the base station 5 from the input information. For example, the control signal extraction unit 63 extracts the number of base stations in the control information transmitted from the control device 20 and notifies the line control unit 66 of it. The pilot extraction unit 64 extracts a pilot signal from the input information and outputs the pilot signal to the synchronization unit 65. The synchronization unit 65 performs synchronization processing using the pilot signal. The line control unit 66 performs control for notification processing using the information extracted by the system information extraction unit 62 and the control signal extraction unit 63. Further, the line control unit 66 stores the system information acquired from the system information extraction unit 62 in the system information storage unit 68, and uses the number of base stations extracted by the control signal extraction unit 63 as the detection number threshold 71. Notify The radio control unit 67 controls operations of the antenna 51, the radio unit 56, and the radio unit 83.

The encoding / modulation unit 81 encodes and modulates data input from the line control unit 66 and the data processing unit 61. The encoding modulation unit 81 outputs the processed data to the orthogonal multiple access processing unit 82. The orthogonal multiple access processing unit 82 generates a transmission signal using the input baseband signal, and transmits the transmission signal via the radio unit 83 and the antenna 51.

FIG. 7 is a diagram for explaining an example of the hardware configuration of the terminal 50. The terminal 50 includes an antenna 51, an RF (Radio Frequency) circuit 111, a BB (baseband) processing circuit 112, a processor 113, and a memory 114. The RF circuit 111 implements a wireless unit 56 and a wireless unit 83. The BB processing circuit 112 operates as an orthogonal multiple access processing unit 57, a demodulation decoding unit 58, an encoding modulation unit 81, and an orthogonal multiple access processing unit 82. The processor 113 operates as a data processing unit 61, a system information extraction unit 62, a control signal extraction unit 63, a pilot extraction unit 64, a synchronization unit 65, a line control unit 66, a radio control unit 67, and a detection unit 70. The memory 114 stores the detection number threshold 71 and the like, and operates as the system information storage unit 68.

<First Embodiment>
In the first embodiment, in order to make it easy to understand, a case where one terminal 50 is located in the vicinity of a plurality of base stations 5 is taken as an example, and control performed to reduce interference detection and interference An example of processing will be described. Furthermore, in 1st Embodiment, the notification part 31 in the control apparatus 20 shall hold | maintain the value determined beforehand about the number n of base stations which the terminal 50 uses for communication.

FIG. 8 is a diagram for explaining an example of a control method for reducing interference. In case C11, the terminal 50 is located near the base stations 5a to 5c. Each of the base stations 5a to 5c is connected to the control device 20. In the following description, it is assumed that the pilot ID used by the base station 5a is PIDa. Further, it is assumed that the pilot ID used by the base station 5b is PIDb and the pilot ID used by the base station 5c is PIDc.

In case C11, it is assumed that the terminal 50 first receives the signal DL1 from the base station 5a when moving to the vicinity of the base stations 5a to 5c. When measuring the strength of the signal DL1 received from the base station 5a, the detecting unit 70 stores the obtained received power strength in association with the pilot ID used by the base station 5a. For example, assuming that the received power intensity of the signal DL1 is R1, the data processing unit 61 stores pilot ID = PIDa and received power intensity = R1 in association with each other. It is assumed that the line control unit 66 determines to connect to the base station 5a because the received power strength R1 exceeds the signal strength usable for communication. Then, the terminal 50 establishes a connection with the base station 5a by processing of the line control unit 66 and the radio control unit 67.

Meanwhile, the notification unit 31 in the control device 20 generates a control signal including the number of base stations n. The transmission unit 22 transmits the control signal generated by the notification unit 31 via the base stations 5a to 5c. The terminal 50 receives a control signal via the base station 5a. The control signal is processed by the reception unit 55 and output to the detection unit 70. The detection unit 70 determines from the pilot ID in the downlink signal used for transmission of the control signal that the information is received via the connected base station 5a. Further, the control signal extraction unit 63 extracts the number of base stations n from the control signal. The base station number n is stored as the detection number threshold 71. In the description of FIG. 8, it is assumed that the number of base stations n is two.

Thereafter, it is assumed that the terminal 50 receives the signal DL2 from the base station 5b and further receives the signal DL3 from the base station 5c. Through the processing in the control unit 60 and the detection unit 70, the strength of the received signal from each base station 5 is obtained. The detection unit 70 associates the obtained received power intensity with the pilot ID of the signal transmission source. For example, assume that the following information is obtained.
First received signal: pilot ID = PIDa, strength R1
Second received signal: pilot ID = PIDb, strength R2
Third received signal: pilot ID = PIDc, strength R3

Here, since the detection number threshold 71 is 2, the first received signal is the (n−1) th received signal. The second received signal is the nth received signal, and the third received signal is the (n−1) th received signal.

Case C12 shows the downlink signals received by the terminal 50 in the order in which the terminal 50 starts receiving. That is, in the terminal 50, the signal DL1 (pilot ID = PIDa) from the base station 5a corresponds to the downlink signal received by the terminal 50 at the (n-1) th. Further, since the signal DL2 (pilot ID = PIDb) from the base station 5b is a downlink signal received by the terminal 50 n-th, the terminal 50 also starts communication via the base station 5b. In the control device 20, when the relay processing unit 33 specifies that the terminal 50 is connected to the base station 5a and the base station 5b, the data addressed to the terminal 50 is transmitted via the base station 5a and the base station 5b. Processing for relaying to the terminal 50 is performed.

On the other hand, the signal DL3 (pilot ID = PIDc) from the base station 5c is a downlink signal received by the terminal 50 n + 1th. The detector 70 compares the received power intensity of the signal DL3 received n + 1th with the threshold Th. When the strength of the (n + 1) th received downlink signal exceeds the threshold Th, the detecting unit 70 determines that the n + 1th received downlink signal is an interference wave.

Case C13 illustrates the determination result of the detection unit 70. Here, since the terminal 50 is connected to both the base station 5a and the base station 5b, for the terminal 50, the signal DL1 and the signal DL2 are both signals (effective waves) used for communication. The detection unit 70 determines that the strength of the (n + 1) th downlink signal exceeds the threshold Th and that the pilot ID used in the base station 5 that is the transmission source of the (n + 1) th downlink signal is PIDc. The control unit 66 is notified. The line control unit 66 uses the notified information to generate control information for notifying the control device 20 of the comparison result between the strength of the (n + 1) th downlink signal and the threshold Th. The line control unit 66 transmits the generated control information to the control device 20 via the transmission unit 80.

In case C14, the control device 20 receives control information from the terminal 50. The determination unit 32 determines using the control information that the transmission signal from the base station 5 using the pilot signal of pilot ID = PIDc is interfering with the communication of the terminal 50. The determining unit 32 uses the base station information 41 to specify that the base station 5c is using a pilot signal with pilot ID = PIDc. Therefore, the determination unit 32 determines the setting of the base station 5c in order to reduce interference at the terminal 50. In the example of FIG. 8, it is assumed that the determination unit 32 determines to decrease the transmission power of the base station 5c. The determination unit 32 transmits a control signal for applying the determined setting to the base station 5c. When receiving the control signal from the control device 20, the base station 5 c reduces the transmission power in response to a request from the control device 20. For this reason, as shown in case C14, the reach range of the signal DL3 transmitted from the base station 5c is narrowed, and the received power intensity of the signal DL3 at the terminal 50 is reduced. For this reason, the interference with respect to communication in the terminal 50 is reduced.

FIG. 9 is a diagram for explaining an example when no interference occurs. Even if the terminal 50 can receive signals from the base station 5 whose number is equal to or greater than the detection number threshold 71, interference does not occur when the strength of the n + 1-th received signal is low. Case C21 in FIG. 9 is an example of a positional relationship when the terminal 50 is located in the vicinity of the base stations 5a to 5c, as in the situation described with reference to the case C11 in FIG.

Case C22 shows an example in which the terminal 50 starts receiving downlink signals from the base station 5a, base station 5b, and base station 5c in this order, and is notified of the number of base stations n = 2. In case C22, it is assumed that the following information is obtained in the terminal 50.
First received signal: pilot ID = PIDa, strength R1
Second received signal: pilot ID = PIDb, strength R2
Third received signal: pilot ID = PIDc, strength R4

The detection unit 70 compares the received power intensity of the (n + 1) th received signal DL4 with the threshold Th. In the example of FIG. 9, it is assumed that the received power intensity R4 of the signal DL4 is less than the threshold Th. In this case, the detection unit 70 determines that interference due to the (n + 1) th received downlink signal has not occurred.

Case C23 illustrates the determination result of the detection unit 70. As in the case C13 of FIG. 8, since the terminal 50 is connected to both the base station 5a and the base station 5b, the terminal 50 receives the signal DL1 received from the base station 5a and the base station 5b. Each of the signals DL2 is an effective wave. The signal DL3 is neither an effective wave nor an interference wave for the terminal 50. The detecting unit 70 indicates that the strength of the (n + 1) th downlink signal does not exceed the threshold Th and that the pilot ID used in the base station 5 (base station 5c) that is the transmission source of the (n + 1) th downlink signal is PIDc. The line control unit 66 is notified of this. The line control unit 66 generates control information for notifying the control device 20 of the notified information, and transmits the generated control information to the control device 20.

In case C24, the control device 20 receives control information from the terminal 50. Using the control information, the determination unit 32 determines that the transmission signal from the base station 5 (base station 5c) using the pilot signal of pilot ID = PIDc does not interfere with the communication of the terminal 50. Since no interference has occurred, the determination unit 32 ends the process without determining the changed setting. For this reason, the reach of the signal DL3 transmitted from the base station 5c is not changed, but there is no problem because the terminal 50 does not cause interference due to the signal DL3.

FIG. 10 is a flowchart for explaining an example of processing performed by the terminal 50. In FIG. 10, the constant n is the value of the detection number threshold 71. The radio unit 56 receives the signal transmitted from the base station 5 and demodulates the received signal in the demodulation / decoding unit 58 (steps S11 and S12). The detector 70 determines whether a signal has been received from the n + 1th detected base station 5 (step S13). When the signal is not received from the (n + 1) th detected base station 5, the detection unit 70 ends the process (No in step S13).

When a signal is received from the n + 1th detected base station 5, the detection unit 70 determines whether the intensity of the signal from the n + 1th detected base station 5 exceeds the threshold Th (Yes in step S13, step S13). S14). When the intensity of the signal from the base station 5 detected n + 1 exceeds the threshold Th, the detection unit 70 determines that the signal from the base station 5 detected n + 1 is an interference wave (Yes in step S14). Step S15). On the other hand, when the intensity of the signal from the n + 1-th detected base station 5 does not exceed the threshold Th, the detector 70 determines that the signal from the n + 1-th detected base station 5 is an effective wave (in step S14). No, step S16). When the process of step S15 or step S16 is completed, the line control unit 66 notifies the determination result to the control device 20 using an uplink (uplink, UL) signal (step S17).

In the first embodiment, the control device 20 can recognize which base station 5 is an interference source in each terminal 50. Furthermore, the control device 20 controls the setting of the base station 5 that is an interference source, using information obtained from the terminal 50. For this reason, even if the base stations 5 are in a dense state, interference due to transmission signals from a plurality of base stations is reduced.

<Second Embodiment>
In the second embodiment, an example of control processing performed to detect interference waves and reduce interference will be described, taking as an example the case where the terminals 50a and 50b are located in the vicinity of a plurality of base stations 5. . Hereinafter, a case where a signal not used for communication of any terminal 50 is an interference wave and a case where a signal used for communication by one terminal is an interference wave of the other terminal 50 will be described separately.

Also in the second embodiment, it is assumed that the notification unit 31 in the control device 20 holds a predetermined value for the number n of base stations used by the terminal 50 for communication. In the following description, in order to make it easy to understand which terminal 50 is the process, the same alphabet as the end of the code of the terminal 50 that executes the process may be added to the end of the code. For example, the detection unit 70a is the detection unit 70 in the terminal 50a, and the detection unit 70b is the detection unit 70 in the terminal 50b.

(1) When a signal that is not used for communication of any terminal 50 is an interference wave FIG. 11 is a diagram illustrating an example of a control method for reducing interference. In case C31, the terminal 50a is located near the base stations 5a to 5c, and the terminal 50b is located near the base stations 5c to 5e. Each of the base stations 5a to 5e is connected to the control device 20. In the following description, it is assumed that the pilot ID used by each base station 5 is PIDa in the base station 5a, PIDb in the base station 5b, PIDc in the base station 5c, PIDd in the base station 5d, and PIDe in the base station 5e.

In case C31, it is assumed that the terminal 50a first establishes a connection with the base station 5a by receiving the signal DL1 from the base station 5a among the base stations 5a to 5c. On the other hand, it is assumed that the terminal 50b establishes a connection with the base station 5e by first receiving the signal DL5 from the base station 5e among the base stations 5c to 5e.

The notification unit 31 in the control device 20 transmits a control signal including the number of base stations n used by the terminal 50 for communication via the base stations 5a to 5e. The terminal 50a receives a control signal via the base station 5a, and the terminal 50b receives a control signal via the base station 5e. Also in the description of FIG. 11, it is assumed that the number of base stations n is two. The base station number n is held as the detection number threshold 71 in each terminal 50. Thereafter, when receiving a downlink signal transmitted from other than the communicating base station 5, each terminal 50 performs the same processing as described with reference to cases C11 and C12 in FIG. And the pilot ID are stored in association with each other. Furthermore, each terminal 50 also stores the order in which signal reception is started.

Case C32 shows the downlink signals received by the terminals 50 in the order in which the terminals 50 started receiving. For example, assume that the terminal 50a stores the following information.
First received signal: pilot ID = PIDa, strength R1
Second received signal: pilot ID = PIDb, strength R2
Third received signal: pilot ID = PIDc, strength R3
That is, in the example of FIG. 11, the terminal 50a starts receiving the downlink signal in the order of the signal DL1 from the base station 5a, the signal DL2 from the base station 5b, and the signal DL3a from the base station 5c. Therefore, for the terminal 50a, the signal DL1 is the n−1th received signal, the signal DL2 is the nth received signal, and the signal DL3a is the n + 1th received downlink signal. For this reason, the terminal 50a starts communication via the base station 5b in addition to communication with the base station 5a.

On the other hand, it is assumed that the terminal 50b stores the following information.
First received signal: pilot ID = PIDe, strength R11
Second received signal: pilot ID = PIDd, strength R12
Third received signal: pilot ID = PIDc, strength R13
The terminal 50b starts receiving downlink signals in the order of the signal DL5 from the base station 5e, the signal DL4 from the base station 5d, and the signal DL3b from the base station 5c. Therefore, for the terminal 50b, the signal DL5 is the n−1th received signal, the signal DL4 is the nth received signal, and the signal DL3b is the n + 1th received downlink signal. For this reason, the terminal 50b starts communication via the base station 5d in addition to communication with the base station 5e.

The control device 20 also recognizes that each terminal 50 has started communication with the same number of base stations 5 as the number of base stations n. For this reason, in the base station information 41, the information of the terminal in communication with each base station 5 is updated. Hereinafter, it is assumed that the base station information 41 includes the following information.
PIDa (base station 5a): data transmission to terminal 50a PIDb (base station 5b): data transmission to terminal 50a PIDc (base station 5c): no connection PIDd (base station 5d): data transmission to terminal 50b PIDe (base station 5e) ): Data transmission to terminal 50b Note that the relay processing unit 33 can appropriately determine the transfer destination of transmission data using the base station information 41.

Case C33 is an example of a determination result of whether the received signal at each terminal 50 is an interference wave. Here, since the terminal 50a is connected to both the base station 5a and the base station 5b, the signal DL1 and the signal DL2 are both effective waves for the terminal 50a. The detection unit 70a determines whether the signal DL3a is an interference wave by using a result obtained by comparing the received power intensity of the signal DL3a with the threshold Th because the signal DL3a is the n + 1th signal started to be received in the terminal 50a. To do. Since the intensity of the signal DL3a exceeds the threshold Th, the detection unit 70a determines that the signal is an interference wave. Accordingly, the relationship between the downlink signal transmitted from each of the base stations 5a to 5c and the communication status at the terminal 50a is as shown in case C33. Therefore, the detection unit 70a notifies the line control unit 66a that the strength of the signal DL3a exceeds the threshold Th and that the pilot ID used in the base station 5 that is the transmission source of the signal DL3a is PIDc. To do. Using the notified information, the line control unit 66a generates control information including the information that the signal DL3a exceeds the threshold Th and pilot ID = PIDc. The transmission unit 80a transmits control information to the control device 20.

On the other hand, since the terminal 50b is connected to both the base station 5e and the base station 5d, the signal DL5 and the signal DL4 received from the base station 5e are both effective waves for the terminal 50b. The detection unit 70b determines whether the signal DL3b is an interference wave using the result obtained by comparing the received power intensity of the signal DL3b with the threshold Th because the signal DL3b is the n + 1th signal started to be received in the terminal 50b. To do. The detector 70b determines that the signal DL3b is not an interference wave because the intensity of the signal DL3b is less than the threshold Th. Therefore, the relationship between the downlink signal transmitted from each of the base stations 5c to 5e and the communication status at the terminal 50b is as shown in case C33. Therefore, the detection unit 70b notifies the line control unit 66b that the strength of the signal DL3b is less than the threshold Th and that the pilot ID used in the base station 5c that is the transmission source of the signal DL3b is PIDc. Using the notified information, the line control unit 66b generates control information including information that the signal DL3b is less than the threshold Th and pilot ID = PIDc, and transmits the control information to the control device 20.

In Case C34, the control device 20 receives control information from each of the terminal 50a and the terminal 50b. Using the control information, the determination unit 32 determines that the transmission signal from the base station 5 using the pilot signal with pilot ID = PIDc is interfering with the communication of the terminal 50a. The determination unit 32 further recognizes that the transmission signal from the base station 5 using the pilot signal of pilot ID = PIDc does not interfere with the communication of the terminal 50b. The determining unit 32 uses the base station information 41 to specify that the base station 5c is using a pilot signal with pilot ID = PIDc. Furthermore, the determination unit 32 acquires from the base station information 41 that the downlink signal from the base station 5c is not used in any communication between the terminal 50a and the terminal 50b.

Therefore, it is assumed that the determination unit 32 determines to reduce the transmission power of the base station 5c in order to reduce interference at the terminal 50a. The determination unit 32 transmits a control signal for applying the determined setting to the base station 5c. When receiving the control signal from the control device 20, the base station 5 c reduces the transmission power in response to a request from the control device 20. For this reason, as shown in case C34, the reach ranges of the signal DL3a and the signal DL3b transmitted from the base station 5c are narrowed. Therefore, the received power intensity of the signal DL3a at the terminal 50a is reduced, and interference with communication at the terminal 50a is reduced. On the other hand, since the signal DL3b is not used for communication in any of the terminals 50, there is no problem in communication with the terminal 50b.

As described above, when the interference is caused by the downlink signal that is not used for communication of any terminal 50, the control device 20 sets the base station 5 that is transmitting the signal that is the interference source. By changing, interference can be reduced.

(2) When a signal used by one terminal for communication is an interference wave of the other terminal FIG. 12 is a diagram illustrating an example of detecting an interference wave. Case C41 shows an example of the reach of the terminal 50a, the terminal 50b, the base stations 5a to 5e, and the downlink signal transmitted from each base station 5. The relationship among the reach of signals from the terminal 50a, the terminal 50b, the base stations 5a to 5e, and the base station 5 in the case C41 is the same as that in the case C31 described with reference to FIG. Also in the case C41, it is assumed that the terminal 50a is connected to the base station 5a, and the terminal 50b is connected to the base station 5e. The terminal 50 a and the terminal 50 b obtain the number of base stations n from the control device 20.

Case C42 shows the downlink signal received by each terminal 50 together with the order in which the terminal 50 started reception. For example, assume that the terminal 50a receives the following signals in the following order.
First received signal: pilot ID = PIDa, strength R1
Second received signal: pilot ID = PIDb, strength R2
Third received signal: pilot ID = PIDc, strength R3
In this case, as in the example of FIG. 11, the terminal 50a starts receiving downlink signals in the order of the signal DL1 from the base station 5a, the signal DL2 from the base station 5b, and the signal DL3a from the base station 5c. . For this reason, the terminal 50a communicates with the base station 5a via the base station 5b. For terminal 50a, signal DL1 is the n−1th received signal, signal DL2 is the nth received signal, and signal DL3a is the n + 1th received downlink signal.

In the case C42, it is assumed that the terminal 50b starts receiving downlink signals in the order of the signal DL5 from the base station 5e, the signal DL3b from the base station 5c, and the signal DL4 from the base station 5d. In this case, for the terminal 50b, the signal DL5 is the n−1th received signal, the signal DL3b is the nth received signal, and the signal DL4 is the n + 1th received downlink signal. Here, it is assumed that the terminal 50b stores the following information.
First received signal: pilot ID = PIDe, strength R21
Second received signal: pilot ID = PIDc, strength R22
Third received signal: pilot ID = PIDd, strength R23
In this case, the terminal 50b communicates through both the base station 5e and the base station 5c.

FIG. 13 is a diagram for explaining an example of the base station information 41. In the example of FIG. 13, the base station information 41 includes a pilot ID, transmission data destination, transmission power, and beam tilt angle. FIG. 13 reflects the information notified from each of the terminal 50a and the terminal 50b in case C42 of FIG. For this reason, the base station information 41 records that the terminal 50a is connected to the base station 5a and the base station 5b, and that the terminal 50b is connected to the base station 5c and the base station 5e.

Transmission power is power used for transmission processing from each base station 5. In the example of FIG. 13, transmission processing is performed at 20 dB at the base station 5a, 25 dB at the base station 5b, 30 dB at the base station 5c, 27 dB at the base station 5d, and 23 dB at the base station 5e. The tilt angle is the tilt angle of the beam formed at each base station 5. In the example of FIG. 13, the base station 5a uses ta, the base station 5b uses tb, the base station 5c uses tc, the base station 5d uses td, and the base station 5e uses te. The determination unit 32 can appropriately use the base station information 41 when determining whether to change the setting of the base station 5 that is an interference source or when determining the change contents of the setting.

FIG. 14 is a diagram for explaining an example of the control process. FIG. 14 illustrates an example of processing performed after the state of case C42 in FIG. It is assumed that the base station information 41 is as shown in FIG.

Case C43 is an example of a determination result of whether the received signal at each terminal 50 is an interference wave. Since the terminal 50a is connected to both the base station 5a and the base station 5b, the signal DL1 and the signal DL2 are both effective waves for the terminal 50a. The detection unit 70a compares the received power intensity of the signal DL3a received by the terminal 50a with the (n + 1) th time with the threshold Th. Assume that the detection unit 70a determines that the signal DL3a is an interference wave because the intensity of the signal DL3a exceeds the threshold Th. Therefore, the relationship between the downlink signal transmitted from each of the base stations 5a to 5c and the communication status at the terminal 50a is as shown in case C43. For this reason, the control information including the information that the signal DL3a exceeds the threshold Th and the pilot ID = PIDc is transmitted to the control device 20 by the same processing as described with reference to FIG. The

On the other hand, since the terminal 50b is connected to both the base station 5c and the base station 5e, the signal DL3b and the signal DL5 are both effective waves for the terminal 50a. The detection unit 70b compares the received power intensity (R23) of the signal DL4 received by the terminal 50b with the (n + 1) th time with the threshold Th. Assume that the detection unit 70b determines that the signal DL4 is an interference wave because the intensity of the signal DL4 exceeds the threshold Th. Accordingly, the relationship between the downlink signal transmitted from each of the base stations 5c to 5e and the communication status at the terminal 50b is as shown in case C43. The terminal 50b performs the same processing as that of the terminal 50a, so that the control information including the information that the signal DL4 exceeds the threshold Th and pilot ID = PIDd is transmitted to the control device 20.

In Case C44, the control device 20 receives control information from each of the terminal 50a and the terminal 50b. The determining unit 32 uses the control information and the base station information 41 (FIG. 13), and the transmission signal from the base station 5c using the pilot signal with the pilot ID = PIDc interferes with the communication of the terminal 50a. judge. The determination unit 32 also recognizes that the transmission signal from the base station 5c is used for communication of the terminal 50b by referring to the base station information 41. In this case, if the interference at the terminal 50a is reduced by the control of the base station 5c, the communication quality at the terminal 50b may be deteriorated.

As described above, when a signal used by one terminal 50 for communication is an interference wave of another terminal 50, the selection unit 34 selects a preferred terminal 50 in accordance with a previously stored scheduling policy.

For example, as a scheduling policy, it may be set to determine a preferred terminal 50 using QoS (Quality Service) associated with data. In this case, the selection unit 34 gives priority to the communication quality at the terminal 50 that transmits and receives data with high QoS. For example, it is assumed that high QoS is applied to data used for remote surgery using a network. In this case, the selection unit 34 sets the terminal 50 that is transmitting and receiving data used for remote surgery as a priority terminal. Further, fairness among terminals 50 may be used as a scheduling policy. In this case, the selection unit 34 selects the priority terminal 50 so that the throughput amount is fair among the terminals 50.

The selection unit 34 notifies the determination unit 32 of the selected terminal 50. The determination unit 32 determines whether to change the setting according to the terminal 50 that has been notified of priority. When the terminal 50a is prioritized, it is determined to reduce the interference of the terminal 50a even if the communication quality at the terminal 50b is reduced. For this reason, as described with reference to case C34 of FIG. 11, the interference of the terminal 50a is reduced by changing the setting of the base station 5c.

Case C44 in FIG. 14 shows an example when it is determined that the terminal 50b is given priority. In this case, even if the interference of the terminal 50a occurs, the setting that reduces the communication quality at the terminal 50b is not changed. For example, if a decrease in transmission power at the base station 5c is set, the range in which the signal DL3b reaches may be narrowed, and the communication quality at the terminal 50b may deteriorate. Therefore, as illustrated in case C44, the determination unit 32 does not decrease the transmission power of the base station 5c. The signal DL4 is notified that it is an interference source for the terminal 50b, but is not used for communication with other terminals 50 (FIG. 13). For this reason, the determination part 32 reduces the transmission power of the base station 5d. For this reason, the arrival status of the signal after control is as shown in case C44.

If the interference of the terminal 50a can be reduced without degrading the communication quality of the terminal 50b by changing the beam shape or the like, the determining unit 32 may determine to change the beam shape or the like. In this case, the determination unit 32 notifies the base station 5c of the determined setting change, and the base station 5c performs control according to the notification from the control device 20.

FIG. 15 is a flowchart for explaining an example of processing performed by the control device 20. The process shown in the flowchart of FIG. 15 is performed for each notified interference wave. The determination unit 32 determines whether there is an interference wave notification from the terminal 50 (step S21). Here, it is assumed that a notification including that the received power intensity of the (n + 1) th signal exceeds the threshold value Th is handled as an interference wave notification. When the notification of the interference wave is not received, the determination unit 32 ends the process.

When the notification of the interference wave is received, the determination unit 32 determines whether the interference source base station 5 is used for communication with any one of the terminals 50 (Yes in Step S21, Step S22). Here, the base station 5 of the interference source is a base station 5 that transmits an interference wave. When the base station 5 of the interference source is used for communication with any one of the terminals 50, the selection unit 34 selects the terminal 50 having priority according to the scheduling policy (Yes in Step S22, Step S23). The determination unit 32 determines whether interference has occurred in the priority terminal 50 (step S24). When interference does not occur in the priority terminal 50, the determination unit 32 ends the process (No in step S24).

On the other hand, when the interference is occurring in the priority terminal 50, the determination unit 32 determines the setting for reducing the interference that the interference source base station 5 gives to the terminal 50 (Yes in Step S24, Step S25). The determination unit 32 transmits the determined setting to the interference source base station 5 via the transmission unit 22 (step S26).

In step S22, when it is determined that the interference source base station 5 is not used for communication in any of the terminals 50, the processing after step S25 is performed (No in step S22). As an example of the case where it is determined No in step S22, the case described with reference to FIG. 11 and the case described as the first embodiment can be given. Further, when it is determined in step S21 that no interference wave has been notified, the determination unit 32 ends the process (No in step S21).

FIGS. 16A to 16C are diagrams for explaining a modification of the control process determined by the determination unit 32. FIG. In the above description, the case where the setting content is mainly a decrease in the transmission power from the interference source base station 5 has been described as an example. However, the processing performed on the interference source base station 5 is a decrease in the transmission power. Other than that.

16C, it is assumed that the signal DL3 transmitted from the base station 5c is notified to the control device 20 as an interference source of the terminal 50a. Furthermore, it is assumed that the signal DL3 transmitted from the base station 5c is not used for any terminal 50 communication. Then, the determination unit 32 may determine to stop transmission of signals from the base station 5c. When the determination unit 32 notifies the base station 5c that the signal transmission is stopped, the base station 5c stops the signal transmission, as shown in case C52. For this reason, in the example of FIG. 16A, interference of the base station 5c with respect to communication of the terminal 50a is eliminated.

Also in case C53 in FIG. 16B, it is assumed that the signal DL3 transmitted from the base station 5c is notified to the control device 20 as an interference source of the terminal 50a. Further, it is assumed that the signal DL3 transmitted from the base station 5c is not used for any terminal 50 communication. Then, the determination part 32 may determine the change of the beam direction of the signal from the base station 5c. When the determination unit 32 notifies the base station 5c of the change in the beam direction of the signal, the base station 5c changes the beam direction as shown in case C54. For this reason, interference of the base station 5c with respect to communication with the terminal 50a is reduced. In addition, when changing the direction of a beam, the determination part 32 may notify the beam information used when forming the beam after a change in the base station 5c. Here, the beam information is a matrix index or a matrix value of a matrix to be multiplied with the transmission signal in order to form a beam in the base station 5c. In the system in which the control device 20 generates a transmission signal transmitted from each base station 5 and outputs the I / Q signal to each base station 5, the determination unit 32 sends the beam-related information to the base station 5. You do not have to send it.

Furthermore, in order to determine how to change the beam direction, the determination unit 32 causes the terminal 50 to calculate both the value of the beam matrix as the change candidate and the value of the beam matrix that causes interference. May be performed. The determination unit 32 uses the calculation result obtained from the terminal 50 to determine the beam state after the change.

In case C55 in FIG. 16C, the signal DL3 transmitted from the base station 5c is notified to the control device 20 as an interference source of the terminal 50a, and the signal DL3 transmitted from the base station 5c Also not used for communication at 50. In this case, the determination unit 32 may determine a change in the beam shape of the signal from the base station 5c. The processing performed when the determination unit 32 determines the change of the beam shape of the signal is the same as the case where the change of the beam direction of the signal is determined. When the beam shape is changed as shown in case C56, the interference of the base station 5c with respect to the communication at the terminal 50a is reduced.

As described above, in the second embodiment, even if an interference wave for a part of the plurality of terminals 50 is not an interference wave for the other terminals 50, it is used for communication of the other terminals 50. If not, processing for reducing interference is performed. On the other hand, when interference waves for some of the terminals 50 are used for communication of other terminals 50, the terminal 50 that prioritizes communication quality is selected, and interference occurs in the priority terminal 50 The process for reducing the interference is performed. For this reason, even if both the base station 5 and the terminal 50 are in a dense state, it is easy to reduce interference due to transmission signals from a plurality of base stations.

<Third Embodiment>
In the third embodiment, an example will be described in which the value of the number of base stations n is changed according to the distribution of terminals 50 and the like. Note that the controller 20 used in the third embodiment includes an adjustment unit 35.

FIG. 17 is a diagram for explaining an example of processing for changing the number of base stations used for communication. In case C61, the base stations 5a to 5e are connected to the control device 20, the terminal 50a is located near the base stations 5a to 5c, and the terminal 50b is located near the base stations 5c to 5e. At this time, the adjustment unit 35 is set to the number of base stations n = 2. For this reason, both the terminal 50a and the terminal 50b are connected to the two base stations 5, and interference by the third received signal is caused by the comparison result between the received power of the third received signal and the threshold Th. Determine if it has occurred. In the case C61, as in the example described with reference to FIG. 11, the terminal 50a transmits the signal DL1 transmitted from the base station 5a, the signal DL2 transmitted from the base station 5b, and the base station 5c. Assume that signals are received in the order of the signal DL3. Therefore, the terminal 50a communicates with the base station 5a and the base station 5b. On the other hand, it is assumed that the terminal 50b receives the signal DL5 transmitted from the base station 5e, the signal DL4 transmitted from the base station 5d, and the signal DL3 transmitted from the base station 5c in this order. Accordingly, the terminal 50b communicates with the base station 5e and the base station 5d. That is, in the case C61, the following information is recorded as the base station information 41.
PIDa (base station 5a): data transmission to terminal 50a PIDb (base station 5b): data transmission to terminal 50a PIDc (base station 5c): no connection PIDd (base station 5d): data transmission to terminal 50b PIDe (base station 5e) ): Data transmission to terminal 50b

Case C62 shows an example in which only the terminal 50a is present at a position relatively close to the base stations 5a to 5e because the terminal 50b has moved from the state of the case C61. In this case, the base station information 41 is changed as follows.
PIDa (base station 5a): data transmission to terminal 50a PIDb (base station 5b): data transmission to terminal 50a PIDc (base station 5c): no connection PIDd (base station 5d): no connection PIDe (base station 5e): connection None

The adjustment unit 35 refers to the base station information 41 and determines that the density of the terminals 50 in the macro cell 8 is lower than in the case C61. Therefore, it is determined whether the number of base stations 5 used for communication by the terminal 50 in the macro cell 8 can be made larger than in the case C61. In the example of FIG. 17, it is assumed that the adjustment unit 35 has decided to increase the number of base stations 5 used by the terminal 50 for communication. For example, it is assumed that the adjustment unit 35 changes the number of base stations 5 (number of base stations n) used by the terminal 50 for communication from 2 to 3. Then, the notification unit 31 notifies the terminal 50a of the number of base stations n changed by the adjustment unit 35.

The detection unit 70a in the terminal 50a updates the detection number threshold 71 by processing control information notifying that the number of base stations n has been changed from 2 to 3. The details of the update processing of the detection number threshold 71 are the same as the processing described in the first embodiment. The line control unit 66 determines to increase the number of base stations 5 used for communication to three because the detection number threshold 71a has been changed from 2 to 3. The line control unit 66a determines to connect to the base station 5c that is the transmission source of the third received signal. It is assumed that the terminal 50a establishes a connection with the base station 5c by the connection process in the radio control unit 67a. Then, as shown in case C62, the downlink signal transmitted from each of the base stations 5a to 5c becomes an effective wave for the terminal 50a.

Thereafter, it is assumed that the terminal 50c has moved to the vicinity of the base stations 5c to 5e. Then, since the number of base stations n = 3, the terminal 50c establishes connections with the base stations 5c to 5e. For this reason, the information in the base station information 41 is changed as follows.
PIDa (base station 5a): data transmission to terminal 50a PIDb (base station 5b): data transmission to terminal 50a PIDc (base station 5c): data transmission to terminals 50a and 50c PIDd (base station 5d): data to terminal 50c Transmission PIDe (base station 5e): Data transmission to terminal 50c

The adjustment unit 35 refers to the base station information 41 and determines that the density of the terminals 50 in the macro cell 8 is higher than that in the case C62 due to the movement of the terminals 50c. Therefore, it is determined whether the number of base stations 5 used for communication by the terminal 50 in the macro cell 8 is smaller than in the case C62. In the example of FIG. 17, the adjustment unit 35 changes the number of base stations 5 (number of base stations n) used by the terminal 50 for communication from 3 to 2. Then, the notification unit 31 notifies the terminal 50a and the terminal 50c of the number of base stations n changed by the adjustment unit 35.

The detection unit 70a in the terminal 50a updates the detection number threshold 71 by processing control information notifying that the number of base stations n has been changed from 3 to 2. The line control unit 66 decides to reduce the number of base stations 5 used for communication to two because the detection number threshold 71 has been changed from 3 to 2. The line control unit 66a determines to disconnect the connection with the base station 5c that is the transmission source of the third received signal. It is assumed that the terminal 50a ends the connection with the base station 5c by the processing in the radio control unit 67a. Then, as shown in case C63, the downlink signal transmitted from the base station 5a and the base station 5b becomes an effective wave for the terminal 50a. In the example of case C63, since the received power intensity of the signal DL3 from the base station 5c at the terminal 50a is less than the threshold Th, the signal DL3 is not an interference source for communication at the terminal 50a.

Also in the terminal 50c, when control information notifying that the number of base stations n has been changed from 3 to 2 is notified from the control device 20, the same processing as the terminal 50a is performed. For this reason, the base station 5 to which the terminal 50c is connected is changed from three to two. In case C63, it is assumed that the terminal 50c disconnects the connection with the base station 5d. Then, the downlink signal transmitted from the base station 5c and the base station 5e becomes an effective wave for the terminal 50c. In the example of case C63, since the received power intensity of the signal DL4 from the base station 5d at the terminal 50c exceeds the threshold Th, the signal DL4 is an interference source for communication at the terminal 50c. For this reason, in the case C63, as described with reference to FIGS. 12 to 15, processing for reducing interference is performed.

In FIG. 17, in order to make the drawing easier to see, the number of base stations 5 is set to be small and the number of terminals 50 in the macro cell 8 is also reduced. However, in the implementation, the base station 5 in one macro cell 8 is implemented. The number of terminals 50 is arbitrary. Further, the number of base stations n may be adjusted according to the distribution status of the terminals 50 and the small cells 7 without being limited to the density of the terminals 50.

For example, it is assumed that there are 40 base stations 5 under the control device 20 and 40 small cells 7 are generated. Furthermore, although there are not a large number of terminals 50 in total, it is assumed that a large number of terminals 50 are concentrated in the adjacent five small cells 7 in the 40 small cells 7. In such a case, there is a possibility that the communication status may deteriorate in an area where the terminals 50 are crowded. Therefore, the adjustment unit 35 performs communication according to the situation of the area where the terminals 50 are crowded. The number n of base stations to be used for the above is determined. For example, if the number of base stations n is set to 3 before the terminals 50 are crowded, the adjustment unit 35 detects that the terminals 50 are concentrated on the five small cells 7, and then adjusts the number of base stations n. Is set to 2. The changed number of base stations n = 2 is applied to all terminals 50 in the macro cell 8.

FIG. 18 is a flowchart illustrating an example of processing performed by the control device 20. In the example of FIG. 18, it is assumed that the adjustment unit 35 stores a default value of the number of base stations n used by the terminal 50 for communication. Note that changes such as changes in the order of steps S41 and S42 can be added to the process shown in FIG. 18 according to the implementation.

The adjustment unit 35 substitutes the default value of the base station 5 used by the terminal 50 for communication into the variable n (step S41). The adjustment unit 35 refers to the base station information 41, and acquires the number (X) of small cells 7 whose number of terminals exceeds the threshold Tha (step S42). The adjustment unit 35 determines whether the number (X) of small cells 7 whose number of terminals exceeds the threshold value Tha is equal to or greater than the threshold value Thb (step S43). When X is equal to or greater than the threshold Thb, the adjustment unit 35 determines whether the small cells 7 whose number of terminals exceeds the threshold Tha are adjacent to each other (Yes in Step S43, Step S44). When the small cells 7 whose number of terminals exceeds the threshold Tha are adjacent to each other, the adjustment unit 35 changes the number of base stations used by the terminal 50 to n−1 (Yes in step S44, step S45). That is, in step S45, the number of base stations used by the terminal 50 is one smaller than the default value. The notification unit 31 notifies each terminal 50 in the macro cell 8 of the changed number of base stations (step S48).

On the other hand, when the small cells 7 whose number of terminals exceeds the threshold value Tha are not adjacent to each other, the adjustment unit 35 does not change the number of base stations n (No in step S44).

When it is determined in step S43 that the number (X) of small cells 7 whose number of terminals exceeds the threshold Tha is not equal to or greater than the threshold Thb, the adjustment unit 35 determines whether X is equal to or less than the threshold Thc (step S43). No, step S46). That is, in step S46, the adjustment unit 35 determines whether or not the crowded small cells 7 are equal to or less than the threshold value Thc. The threshold value Thc is a value smaller than the threshold value Thb. When the number of small cells 7 in which the number of terminals exceeds the threshold Tha exceeds the threshold Thc, the adjustment unit 35 does not change the number n of base stations (No in Step S46). On the other hand, when the number (X) of small cells 7 in which the number of terminals exceeds the threshold Tha is equal to or less than the threshold Thc, the adjustment unit 35 changes the number of base stations used by the terminal 50 to n + 1 (Yes in step S46). Step S47). That is, in step S47, the number of base stations used by the terminal 50 is one larger than the default value. The notification unit 31 notifies each terminal 50 in the macro cell 8 of the changed number of base stations (step S48).

In the system using the third embodiment, the base station 5 can be effectively used by changing the number of base stations n according to the communication environment such as the distribution status of the terminals 50. Furthermore, also in the third embodiment, since the control according to the first and second embodiments is performed, interference is reduced.

<Others>
The embodiment is not limited to the above, and can be variously modified. Some examples are described below.

In the above description, the case where the number of base stations n used by the terminal 50 for communication has been described as being many, but this is merely an example. The number n of base stations used for communication by the terminal 50 can be set to an arbitrary value of 1 or more depending on the implementation.

The information element in the base station information 41 illustrated in the above description is an example. That is, the elements in the base station information 41 can be changed according to the implementation. Further, information such as a scheduling policy may be held in the control unit 30 or may be stored in the storage unit 40.

2, 50 terminal 4 optical fiber 5 base station 7 small cell 8 macro cell 10 BBU
DESCRIPTION OF SYMBOLS 15 Macro base station radio | wireless part 20 Control apparatus 21 CPRI- IF part 22, 80 Transmission part 23, 55 Reception part 25 I / Q signal processing part 26 Baseband processing part 30, 60 Control part 31 Notification part 32 Determination part 33 Relay process Unit 34 selection unit 35 adjustment unit 40 storage unit 41 base station information 51 antenna 56, 83 radio unit 57, 82 orthogonal multiple access processing unit 58 demodulation decoding unit 61 data processing unit 62 system information extraction unit 63 control signal extraction unit 64 pilot extraction Unit 65 synchronization unit 67 wireless control unit 68 system information storage unit 70 detection unit 71 detection number threshold 81 encoding modulation unit 101 FPGA
104 SW
105, 113 Processor 106, 114 Memory 111 RF circuit 112 BB processing circuit

Claims (10)

1. A control device for controlling a plurality of transmission points,
   A notification unit for notifying a terminal connected to at least one transmission point of the plurality of transmission points of the number of transmission points used for communication of the terminal;
   A receiving unit that receives information indicating that the received power at the terminal has exceeded a threshold via at least one of the plurality of transmission points;
   Upon receiving the information, an interference control unit that selects a target transmission point to be subjected to interference control, and performs interference control for the selected target transmission point;
   A control apparatus comprising: a transmission unit configured to transmit control information related to the interference control to the target transmission point.
2. A relay processing unit that relays transmission data to the terminal to each of the first terminal and the second terminal via the same number of transmission points as the number of transmission points used for the communication;
   When the transmission point set by the relay processing unit as a relay destination of transmission data to the second terminal is notified from the first terminal as the target transmission point, the first terminal and the second terminal A selection unit for selecting a terminal to be preferentially communicated among
   When the first terminal is selected as a priority terminal, the interference control unit reduces the interference given to the first terminal by the transmission point notified from the first terminal as the target transmission point. Determine the settings,
   The control device according to claim 1, wherein the transmission unit transmits a setting request for requesting application of the determined setting to a transmission point notified as the target transmission point from the first terminal. .
3. When transmission points whose number of connected terminals exceeds the first threshold are distributed at a predetermined density or more, the number of transmission points used for the communication is reduced, and the number of connected terminals is the first threshold. An adjustment unit that increases the number of transmission points used for the communication when the number of transmission points exceeding the second threshold value is less than or equal to the second threshold;
   When the number of transmission points used for the communication is changed by the adjustment unit, the notification unit connects the number of transmission points used for communication after the change to any of the plurality of transmission points. The control device according to claim 1, wherein the control device is notified to an existing terminal.
4. The information determined as a setting for reducing interference by the interference control unit is information on one or more of transmission power, beam shape, and beam direction of a transmission point notified as the target transmission point. 4. The control device according to any one of 1 to 3.
5. A terminal device connectable to a plurality of transmission points controlled by a control device,
   A receiving unit that receives notification information for notifying the number of transmission points used for communication by the terminal device from the control device;
   A control unit that generates control information including identification information of the target transmission point when a target transmission point whose received power intensity newly exceeds a threshold value during communication with the same number of transmission points as the number of transmission points;
   A terminal device comprising: a transmission unit that transmits the control information to the control device.
6. The controller is
   When the first value is notified as the number of transmission points, communication is established with the same number of transmission points as the first value,
   When a second value is notified as the number of transmission points during communication with the same number of transmission points as the first value, the number of transmission points used for communication by the terminal device is changed to the same number as the second value. And
   The terminal device according to claim 5, wherein when the target transmission point is detected during communication with the same number of transmission points as the second value, control information including identification information of the target transmission point is generated. .
7. When the control unit newly detects a transmission point whose received power intensity is less than a threshold during communication with the same number of transmission points as the number of transmission points, the control unit receives the identification information of the detected transmission point and the reception from the detected transmission point. Generate other control information notifying that the power intensity is less than the threshold,
   The terminal device according to claim 5, wherein the transmission unit transmits the other control information to the control device.
8. A control device that controls a plurality of transmission points,
   Notifying a terminal connected to at least one transmission point of the plurality of transmission points of the number of transmission points used for communication of the terminal,
   Via at least one transmission point of the plurality of transmission points, receiving information indicating that the received power at the terminal exceeds a threshold;
   When receiving the information, select a target transmission point to be subject to interference control,
   The control method characterized by performing the process which transmits the control information regarding the interference control about the said target transmission point to the selected said target transmission point.
9. Relaying transmission data to each of the first terminal and the second terminal via the same number of transmission points as the number of transmission points used for the communication,
   When a transmission point set as a relay destination of transmission data to the second terminal is notified as the target transmission point from the first terminal, among the first terminal and the second terminal, Select a device to communicate with priority,
   When the first terminal is selected as a priority terminal, a setting for reducing interference that the transmission point notified from the first terminal as the target transmission point gives to the first terminal is determined,
   9. The control according to claim 8, wherein the control device performs a process of transmitting a setting request for requesting application of the determined setting to a transmission point notified from the first terminal as the target transmission point. Method.
10. When transmission points where the number of connected terminals exceeds the first threshold are distributed at a predetermined density or more, the number of transmission points used for the communication is reduced,
    If the number of transmission points where the number of connected terminals exceeds the first threshold is less than or equal to the second threshold, increase the number of transmission points used for the communication,
    When the number of transmission points used for the communication is changed, the control device notifies the terminal connected to one of the plurality of transmission points of the number of transmission points used for the communication after the change. The control method according to claim 8, wherein the control method is performed.

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