JP2011166435A - Base station device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform control to suppress interference which corresponds to the temporal change of radio resource allocation in another base station device. <P>SOLUTION: A base station device includes: control units 23, 24 for performing control to suppress interference with respect to another base station device and/or a terminal device which communicates with another base station device; and a determination unit 27 for determining the temporal change of radio resource allocation to the terminal device by another base station device. The control units 23, 24 perform control to adjust how to suppress the interference, on the basis of the determination result of the determination unit 27. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a base station apparatus that performs wireless communication with a terminal apparatus.

In a wireless communication system including a plurality of base station apparatuses, when communication areas (cells) set by the plurality of base station apparatuses overlap, a signal transmitted from a base station apparatus It may reach the terminal device in the cell of the base station device and become an interference signal for the terminal device.
It is well known that such interference can be suppressed by beam forming. That is, while directing a beam to a terminal device in its own cell (hereinafter also referred to as its own terminal device), to a terminal device (hereinafter also referred to as another terminal device) in a cell of another base station device. By performing the beam forming so that the null beam is directed, the signal (interference signal) from the own base station apparatus becomes difficult to reach other terminal apparatuses, and the interference is suppressed. 1).

Nobuyoshi Kikuma, "Adaptive signal processing by array antenna", Science and Technology Publishing, November 25, 1998

By the way, in the said radio | wireless communications system, as a base station apparatus, the macro base station apparatus which forms the cell (macro cell) of the magnitude | size of several kilometers, for example, and the comparatively small cell (about several dozen meters installed in the said macro cell ( There is one provided with a femto base station apparatus that forms a femto cell) in the macro cell.
In the wireless communication system, a femto cell formed by a femto base station apparatus may be formed in a macro cell, and almost the entire area thereof may overlap with the macro cell. Further, since the femto base station apparatus may be installed at any place in the macro cell by the user, the downlink signal of the femto base station apparatus may interfere with the terminal apparatus connected to the macro base station apparatus or the femto base station apparatus. In addition to the case where the uplink signal transmitted by the terminal device connected to the base station device gives interference to the macro base station device, a plurality of femto base station devices that form femto cells adjacent to each other and the terminal devices connected thereto In some cases, mutual interference may occur, and there may be various cases in which interference occurs.
For this reason, even if the base station apparatus uses the beam forming, there are cases where it is difficult to suitably suppress interference in the various situations described above.

In order to suppress such interference, a base station device that may cause interference, such as a femto base station device, grasps the radio resource allocation status performed by other base station devices (particularly macro base station devices). It is possible to keep it.
That is, if a radio resource used in uplink or downlink of another base station apparatus is grasped, use of the radio resource can be avoided. The interference can also be suppressed by reducing the transmission power.

  Here, it is not always easy to grasp radio resource assignments in other base station apparatuses in complete real time. For example, if the time change of radio resource allocation is large, grasping the status of radio resource allocation in other base station apparatuses and attempting to suppress interference accordingly, another resource allocation occurs at that time. There is a risk.

  On the other hand, when the radio resource allocation in the other base station apparatus is a fixed allocation that continuously allocates the same radio resource (frequency) to the same user in time, the radio resource in the other base station apparatus Once the allocation is grasped, the allocation state continues for a while, so that it is possible to efficiently perform interference suppression control according to radio resource allocation in other base station apparatuses.

  In view of the circumstances as described above, it is an object of the present invention to enable appropriate control of interference suppression depending on the situation.

(1) The inventors of the present invention should change the way of interference suppression control between when the time variation of the radio resource allocation status to the terminal device by other base station devices is large and when it is small. I got the idea. For example, when there is little time variation of radio resources by other base station devices, it is easy to grasp unused radio resources that are not used by other base station devices for transmission and reception. If used, there is little risk of interference with other cells even if the transmission power is increased somewhat. On the other hand, when the time variation of radio resources by other base station apparatuses is small, it is difficult to grasp unused radio resources that are not used by other base station apparatuses for transmission and reception, and the allocation to other cells is difficult. In order to suppress the interference, it is preferable to control the transmission power to be low.

  The present invention is based on the above idea. That is, the present invention includes a control unit that performs control for suppressing interference with a terminal device that communicates with the other base station device and / or the other base station device, and wireless communication to the terminal device by the other base station device. A determination unit configured to determine temporal variation of resource allocation status, wherein the control unit performs control to adjust a method of suppressing the interference based on a determination result by the determination unit. Base station apparatus.

  According to the present invention, the determination unit can determine the time variation of the radio resource allocation status to the terminal device by another base station device, and suppress the interference according to the time variation. The way can be adjusted appropriately.

(2) The control unit performs control to suppress the interference by adjusting the magnitude of the transmission power of the own base station apparatus and / or the magnitude of the transmission power of the terminal apparatus communicating with the own base station apparatus. It is preferred to do so. In this case, appropriate interference control can be performed by adjusting the magnitude of the transmission power.

(3) The determination unit may determine whether the radio resource allocation to the terminal apparatus by the other base station apparatus is a fixed allocation with a relatively small temporal variation or a variable allocation with a relatively large temporal variation. It is preferable to determine whether or not. In this case, the method of interference suppression control can be adjusted according to whether the allocation is fixed or variable.

(4) When it is determined that the radio resource allocation to the terminal device by the other base station device is the fixed allocation, the control unit is configured to transmit the radio resource allocated to the terminal device by the other base station device. It is preferable to perform control to suppress the interference by performing control so that radio resources other than resources are allocated to terminal devices that communicate with the own base station device. In this case, since radio resources that are not used in other base station apparatuses are used, interference can be suppressed.

(5) The control unit allocates radio resources other than radio resources allocated to the terminal device by the other base station device to a terminal device communicating with the own base station device, and then It is preferable to perform control to reduce the magnitude of the transmission power and / or the magnitude of the transmission power of the terminal apparatus communicating with the own base station apparatus over time. In this case, even if the appropriateness of resource allocation decreases with the lapse of time after resource allocation, the transmission power is reduced, so that the possibility of occurrence of interference can be reduced.

(6) When it is determined that the radio resource allocation to the terminal device by the other base station device is the variable allocation, the control unit determines the magnitude of the transmission power of the own base station device and / or the own base station device. It is preferable to perform control to suppress the interference by adjusting the magnitude of the transmission power of the terminal device communicating with the base station device. In this case, by suppressing the magnitude of the transmission power, it is possible to suppress the interference regardless of radio resource allocation in other base station apparatuses.

(7) The control unit adjusts the magnitude of the transmission power of the own base station apparatus and / or the magnitude of the transmission power of the terminal apparatus communicating with the own base station apparatus by determining that it is the variable allocation. After that, it is possible to perform control for decreasing the magnitude of the transmission power of the own base station apparatus and / or the magnitude of the transmission power of the terminal apparatus communicating with the own base station apparatus as time elapses. In this case, even when the appropriateness of the adjusted transmission power decreases with the passage of time after adjusting the transmission power, the transmission power becomes low, so that interference can be suppressed.

(8) The control unit performs control to adjust the method of suppressing the interference based on the determination result of the fixed allocation or the variable allocation, and It is configured to perform power reduction control for reducing the magnitude of transmission power and / or the magnitude of transmission power of a terminal device communicating with its own base station apparatus over time, and the control unit further includes the variable It is preferable that the power reduction amount in the power reduction control when it is determined to be an allocation is larger than the power reduction amount in the power reduction control when it is determined to be a fixed allocation. The decrease over time in the appropriateness of adjustment of how to suppress interference is larger in the case of variable allocation than in the case of fixed allocation, so the power when it is determined that the allocation is variable By increasing the amount of power reduction in the reduction control, it is possible to suppress interference.

(9) Information that can be used to determine the temporal variation from information included in a radio frame transmitted from the other base station device to a terminal device that communicates with the other base station device It is preferable that the determination part performs the determination of the temporal variation based on the information acquired by the acquisition part. In this case, the determination can be made based on information included in a radio frame in another cell.

(10) The determination unit includes an acquisition unit that acquires information that can be used to determine the temporal variation via a backbone network in which the other base station device and the own base station device are connected. Preferably, the temporal variation is determined based on the information acquired by the acquisition unit. In this case, the determination can be made based on information obtained via the backbone network.

(11) The information acquired by the acquisition unit as information that can be used for determining the temporal variation is information indicating whether a radio resource allocation method is a localized FDMA or a distributed FDMA. Is preferred.

(12) The information acquired by the acquisition unit as information that can be used for determining the temporal variation is preferably information indicating a type of a scheduling algorithm for radio resource allocation.

(13) The information acquired by the acquisition unit as information usable for determining the temporal variation is information indicating an application type of data transmitted or received by the other base station device. Is preferred.

(14) A measurement unit that periodically measures a communication signal of communication performed between the other base station device and a terminal device, and the determination unit is configured to periodically measure the communication signal measured by the measurement unit. It is preferable to determine the temporal variation based on the above. In this case, the determination can be made based on the measurement results of the signals of other cells.

(15) The determination unit calculates a temporal variation in the received power of the communication signal periodically measured by the measurement unit, so that the time base of radio resource allocation to the terminal device by another base station device is calculated. It is preferable to determine the variation. In this case, the determination can be made based on temporal fluctuations in received power of other cells.

(16) It is preferable that the measurement unit adjusts a cycle of measuring the communication signal according to a determination result by the determination unit. In this case, the measurement cycle can be adjusted according to the time variation of radio resource allocation.

  According to the base station apparatus of the present invention, it is possible to appropriately control interference suppression according to the radio resource allocation status to the terminal apparatus by other base station apparatuses.

It is the schematic which shows the structure of the radio | wireless communications system provided with the base station apparatus which concerns on 1st embodiment of this invention. It is a figure which shows the structure of each uplink and downlink radio frame in LTE. It is a figure which shows the detailed structure of DL frame. It is a figure which shows the detailed structure of a UL frame. In FIG. 1, it is a block diagram which shows the structure of femto BS. It is a figure which shows the allocation condition by SPS. It is a flowchart which shows the process of Localized / Distributed determination (1st example). It is a figure which shows the example which changes the upper limit of transmission power with progress of time. It is a flowchart which shows the process of scheduling algorithm determination (2nd example). It is a flowchart which shows the process of application determination (3rd example). It is a figure which shows the example of fixed allocation and variable allocation. It is a flowchart which shows the process of the determination (4th example) based on the electric power fluctuation amount measurement by measurement.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[First embodiment]
[1. Configuration of communication system]
FIG. 1 is a schematic diagram illustrating a configuration of a wireless communication system including a base station apparatus according to the first embodiment of the present invention.
The wireless communication system includes a plurality of base station devices 1 and a plurality of terminal devices 2 (mobile terminals) that can perform wireless communication with the base station device 1.
The plurality of base station apparatuses 1 are compared with a plurality of macro base station apparatuses (Macro Base Stations) 1a forming a communication area (macrocell) MC having a size of several kilometers, for example, and are installed in the macrocell MC. A plurality of femto base station apparatuses (Femto Base Stations) 1b forming a small femtocell FC.

A macro base station apparatus (hereinafter also referred to as “macro BS”) 1a can perform wireless communication with a terminal apparatus 2 in its own macro cell MC.
Further, the femto base station apparatus (hereinafter also referred to as “femto BS”) 1b is disposed, for example, in a place where it is difficult to receive the radio wave of the macro BS 1a, for example, indoors, and forms the femto cell FC. The femto BS 1b can wirelessly communicate with a terminal device (hereinafter also referred to as “MS”) 2 in the femto cell FC formed by the femto BS 1b. In this system, the radio wave of the macro BS 1a is difficult to receive. Even at a location, by installing a femto BS 1b that forms a relatively small femto cell FC at the location, it is possible to provide services to the MS 2 with sufficient throughput.
In the following description, the MS 2 connected to the femto BS 1b is also referred to as a femto MS 2b, and the MS 2 connected to the macro BS 1a is also referred to as a macro MS 2a.

  The radio communication system according to the present embodiment is a system for mobile phones to which, for example, LTE (Long Term Evolution) is applied, and communication based on LTE is performed between each base station device and a terminal device. . In LTE, a frequency division duplex (FDD) scheme can be adopted. In the present embodiment, the communication system will be described as adopting an FDD scheme. Note that the communication system is not limited to the LTE and is not limited to the FDD system, and may be a TDD (Time Division Duplex) system, for example.

[2. LTE frame structure]
In the FDD scheme that can be adopted in LTE that the communication system according to the present embodiment complies with, an uplink signal (a transmission signal from the terminal device to the base station device) and a downlink signal (a transmission signal from the base station device to the terminal device) By assigning different use frequencies to each other, uplink communication and downlink communication are simultaneously performed.
Further, in the present embodiment, OFDM (Orthogonal Frequency Division Multiplexing) is adopted for downlink radio communication, and SC-FDMA (Single Carrier-Frequency Division Multiple Access) is adopted for uplink radio communication.

FIG. 2 is a diagram illustrating the structure of uplink and downlink radio frames in LTE. The radio frame (DL frame) and the uplink radio frame (UL frame), which are downlink basic frames in LTE, each have a time length of 10 milliseconds, from # 0 to # 9. It is composed of 10 subframes. These DL frames and UL frames are arranged in the time axis direction with their timings aligned.
Note that the timings of the DL frame and the UL frame are aligned between the base station apparatuses, and communication in each cell is performed in a state in which so-called inter-base station synchronization is established.

FIG. 3 is a diagram illustrating a detailed structure of a DL frame. In the figure, the vertical axis direction represents frequency, and the horizontal axis direction represents time.
Each subframe constituting the DL frame is composed of two slots (for example, slots # 0 and # 1). One slot is composed of seven (# 0 to # 6) OFDM symbols (in the case of Normal Cyclic Prefix).
In the figure, a resource block (RB: Resource Block), which is a basic unit region (minimum unit for user allocation) in data transmission, is 12 subcarriers in the frequency axis direction and 7 OFDM symbols (1 slot in the time axis direction). ). Therefore, for example, when the frequency bandwidth of the DL frame is set to 5 MHz, 300 subcarriers are arranged, so that 25 resource blocks are arranged in the frequency axis direction.

  As shown in FIG. 3, a transmission area for the base station apparatus to allocate a control channel necessary for downlink communication to the terminal apparatus is secured at the head of each subframe. This transmission area is allocated with symbols # 0 to # 2 (three symbols at the maximum) of the slot located at the head side in each subframe, and PDSCH (PDSCH: Physical Downlink Shared Channel, where user data is stored) Control channel configuration indication channel for notifying downlink control channel (PDCCH: Physical Downlink Control Channel) including allocation information and the like of PUSCH (explained) and PUSCH (PDSCH: Physical Uplink Shared Channel, explained later) and information on PDCCH (PCFICH: Physical Control Format Indicator Channel), hive for PUSCH Hybrid ARQ indication channel (PhysicalHydrogenARB) for transmitting a reception success notification (ACK: Acknowledgement) and a reception failure notification (NACK: Negative Acknowledgment) of a hybrid automatic repeat request (HARQ: Hybrid Automatic Repeat Request) Assigned.

  In addition to the allocation information, the PDCCH includes information related to uplink transmission power control information, which will be described later, and a report instruction for downlink CQI (Channel Quality Indicator).

Also, in the DL frame, a broadcast channel (PBCH: Physical Broadcast Channel) for notifying the terminal device of the system bandwidth and the like by broadcast transmission is assigned to the first subframe # 0. PBCH is arranged with four symbol widths at the positions of symbols # 0 to # 3 in the slot on the rear side in first subframe # 0 in the time axis direction, and in the frequency axis direction, the center of the bandwidth of the DL frame Are allocated for 6 resource block widths (72 subcarriers). This PBCH is configured to be updated every 40 milliseconds by transmitting the same information over four frames.
PBCH stores main system information such as a communication bandwidth, the number of transmission antennas, and a structure of control information.
Also, in the PBCH, information on an allocation position of a system information block (SIB) 1 stored in the PDSCH and transmitted to the MS connected thereto, and a radio frame number necessary for demodulation of the corresponding PDSCH A master information block (MIB: Master Information Block) including the.

  Of the 10 subframes constituting the DL frame, each of the first (# 0) and sixth (# 5) subframes is a signal for identifying a base station apparatus or a cell. One synchronization signal and second synchronization signal (P-SCH: Primary Synchronization Channel, S-SCH: Secondary Synchronization Channel) are assigned.

P-SCH is arranged with a single symbol width at the position of symbol # 6 which is the last OFDM symbol of the leading slot in each of subframe # 0 and subframe # 5 in the time axis direction, and in the frequency axis direction. , 6 resource block widths (72 subcarriers) are arranged at the center of the DL frame bandwidth. The P-SCH is information for the terminal device to identify each of a plurality (three) sectors obtained by dividing the cell of the base station device, and three patterns are defined.
S-SCH is arranged with a single symbol width at the position of symbol # 5, which is the second OFDM symbol from the end of the first slot in each of subframe # 0 and subframe # 5, in the time axis direction. In the axial direction, 6 resource block widths (72 subcarriers) are arranged at the center of the DL frame bandwidth. This S-SCH is information for the terminal device to identify each of communication areas (cells) of a plurality of base station devices, and 168 patterns are defined.

P-SCH and S-SCH define 504 types (168 × 3) of patterns by combining with each other. The terminal apparatus can recognize in which sector of which base station apparatus the terminal is present by acquiring the P-SCH and S-SCH transmitted from the base station apparatus.
A plurality of patterns that can be taken by P-SCH and S-SCH are predetermined in the communication standard and are known in each base station apparatus and each terminal apparatus. That is, P-SCH and S-SCH are known signals that can take a plurality of patterns, respectively.

Resource blocks in other areas to which the above-described channels are not allocated are used as the above-described downlink shared channel (PDSCH) for storing user data and the like. The PDSCH is an area shared and used by a plurality of terminal devices, and stores user data, control information for each terminal device, and the like.
As the control information to be stored, the above-described SIB1 can be cited. SIB1 includes, for example, information related to information allocation positions such as SIB2 that is a flag indicating whether the currently connected BS1 is a macro or a femto, and SIB9 that indicates downlink transmission power of the BS1. Yes.
The allocation of user data stored in the PDSCH is notified to the terminal device by downlink allocation information regarding downlink radio resource allocation stored in the PDCCH allocated at the head of each subframe. This downlink allocation information is information indicating radio resource allocation for each PDSCH, and the terminal apparatus can determine whether or not data for itself is stored in the subframe based on this downlink allocation information.

FIG. 4 is a diagram illustrating a detailed structure of the UL frame. In the figure, the vertical axis direction represents frequency, and the horizontal axis direction represents time.
The structure of the UL frame is basically the same as that of the DL frame, and each subframe is composed of two slots (for example, slots # 0 and # 1), and one slot has seven (# 0 to # 6) OFDM symbols.
The same applies to a resource block (RB) as a basic unit area in data transmission, and is defined by 12 subcarriers in the frequency axis direction and 7 OFDM symbols (1 slot) in the time axis direction.

  A physical random access channel (PRACH) used for communication for the first access before the terminal apparatus connects to the base station apparatus is assigned to the UL frame. The PRACH has a frequency bandwidth of 6 resource blocks (72 subcarriers), and the allocation is notified to the terminal device by the PBCH (broadcast channel) of the DL frame.

An uplink control channel (PUCCH: Physical Uplink Control Channel) is allocated to both ends of each subframe in the frequency axis direction. The PUCCH is used for transmission of information on HARQ ACK and NACK for PDSCH, information on downlink CQI, and the like. The allocation of the PUCCH is notified to the terminal device by the PBCH of the DL frame.
Also, a sounding reference signal (SRS) used for measuring the CQI of the uplink signal of the terminal apparatus is assigned to the last symbol of each subframe.

Resource blocks in other areas to which the above-described channels are not allocated are used as the above-described uplink shared channel (PUSCH) for storing user data and the like. The PUSCH is an area shared and used by a plurality of terminal apparatuses, and stores control information and the like in addition to user data.
The user data allocation for the PUSCH is notified to the terminal apparatus by uplink allocation information related to uplink radio resource allocation stored in the PDCCH of the DL frame. The uplink allocation information is information indicating radio resource allocation of each PUSCH, and the terminal apparatus can recognize the PUSCH used for its own transmission by this uplink allocation information.

[3. Configuration of base station apparatus]
FIG. 5 is a block diagram showing the configuration of the femto BS 1b in FIG. Here, the configuration of the femto BS 1b will be described, but the configuration of the macro BS 1a is also substantially the same as that of the femto BS 1b.
The femto BS 1b is configured to perform signal processing of transmission / reception signals exchanged between the antenna 3, the transmission / reception unit (RF unit) 4 to which the antenna 3 is connected, and the RF unit 4, and other cells (bases of other cells). And a signal processing unit 5 that performs processing for suppressing interference given to a station device or a terminal device.

[3.1 RF section]
The RF unit 4 includes an upstream signal reception unit 11, a downstream signal reception unit 12, and a transmission unit 13. The uplink signal receiving unit 11 is for receiving an uplink signal from the MS 2, and the downlink signal receiving unit 12 is for receiving a downlink signal from another macro BS 1a or another femto BS 1b. The transmission unit 13 is for transmitting a downlink signal to the MS 2.

In addition, the RF unit 4 includes a circulator 14. The circulator 14 is for giving a reception signal from the antenna 3 to the upstream signal reception unit 11 and the downstream signal reception unit 12 side, and giving a transmission signal output from the transmission unit 13 to the antenna 3 side. The filters included in the circulator 14 and the transmission unit 13 prevent the reception signal from the antenna 3 from being transmitted to the transmission unit 13 side.
Further, the filter included in the circulator 14 and the upstream signal receiving unit 11 prevents the transmission signal output from the transmitting unit 13 from being transmitted to the upstream receiving unit 11 side. Further, the filters included in the circulator 14 and the upstream signal receiving unit 12 prevent the transmission signal output from the transmitting unit 13 from being transmitted to the upstream signal receiving unit 12 side.

  The upstream signal receiving unit 11 includes a filter that allows only the upstream signal frequency band to pass, an amplifier, an A / D converter, and the like, acquires an upstream signal from the MS 2 from the reception signal received by the antenna 3, Is converted into a digital signal and output to the signal processing unit 5. As described above, the uplink signal receiving unit 11 is a receiving unit configured in conformity with reception of the uplink signal from the MS 2, and is a receiving unit that is essentially necessary as a base station apparatus.

  The transmission unit 13 includes a D / A converter, a filter, an amplifier, and the like. The transmission unit 13 receives a transmission signal output as a digital signal from the signal processing unit 5, converts it into an analog signal, amplifies it, and amplifies it from the antenna 3. It has a function of transmitting as a downlink signal.

The femto BS 1b of this embodiment further includes a downlink signal receiving unit 12. This downlink signal receiving unit 12 is for receiving (measuring) a downlink signal transmitted by another BS1 (other base station apparatus) other than itself.
In this embodiment, the downlink signal of another BS1 received by the downlink signal receiving unit 12 is used for acquisition of resource allocation status by the other BS1.

The downlink signal receiving unit 12 includes a filter, an amplifier, an A / D conversion unit, and the like that pass only the frequency band of the downlink signal from the other BS1, and from other BS1 than the received signal received by the antenna 3. Are received, amplified, converted into a digital signal, and output.
The downlink reception signal output from the downlink signal receiving unit 12 is given to the signal processing unit 5 and processed by the modem unit 21 and the measurement unit 22.

[3.2 Signal Processing Unit]
The signal processing unit 5 includes a modulation / demodulation unit 21 for performing signal processing of a transmission / reception signal transmitted / received between an upper layer of the signal processing unit 5 and the RF unit 4. The modem unit 21 has a function of demodulating the uplink signal given from the uplink signal receiving unit 11 as uplink received data and outputting the demodulated signal to the upper layer and modulating various transmission data given from the upper layer. The modulation unit 21 can also demodulate the downlink signal of another cell received by the downlink signal reception unit 12 or demodulate the uplink signal of another cell received by the uplink signal reception unit 12. .
The modem unit 21 modulates the transmission data given from the higher layer by a predetermined method for each predetermined data unit based on the instruction of the scheduling unit 21, and performs DL data for each resource block unit on the modulated data. It has a function of assigning to frames and generating its own downlink transmission signal.

  In this signal processing unit 5, when generating its own downlink transmission signal, the power control unit 23 generates uplink transmission power control information for allowing the terminal device connected to itself to adjust the transmission power of the uplink transmission signal. It has a function of adjusting the transmission power of the terminal device by storing it in the PDCCH of the downstream transmission signal and transmitting it to the terminal device.

  Further, the signal processing unit 5 has a function of setting the transmission power of its own downlink transmission signal and the transmission power of the uplink transmission signal of the terminal device connected to itself for each resource block. Based on the output downlink transmission power control information, the transmission power of its own downlink transmission signal is adjusted for each resource block. Similarly, the transmission power of the uplink transmission signal of the terminal apparatus is adjusted for each resource block by the terminal apparatus according to the uplink transmission power control information transmitted to the terminal apparatus.

The power control unit 23 adjusts the transmission power of itself (own base station apparatus) and / or the transmission power of the terminal apparatus communicating with the own base station apparatus, thereby giving power to the base station apparatus or terminal apparatus of another cell. It functions as a control unit that performs control to suppress interference.
That is, when there is a possibility of causing interference to another cell, the power control unit 23 performs control so as to suppress the transmission power (upper limit value) of the terminal device in itself or in its own cell, A signal transmitted from a terminal device in the own cell is prevented from becoming an interference signal in another cell.

  The signal processing unit 5 also includes a scheduling control unit 24 as a control unit that performs control for suppressing interference. The scheduling control unit 24 controls the scheduling unit 26 that assigns radio resources (resource blocks). The scheduling unit 26 can execute a plurality of types of scheduling algorithms, and the scheduling control unit 24 selects which scheduling algorithm to execute and makes other settings related to scheduling, and performs scheduling according to the set contents. 26 can be executed.

Examples of scheduling algorithms that can be executed by the scheduling unit 26 include a Round Robin (RR) method, a Proportional Fairness (PF) method, and a Maximum CIR method.
The RR method is a method of sequentially allocating resources to each user without considering the condition of the transmission path and the like, and is a method in which the time variation of resource allocation tends to increase.
The PF method is a method of performing scheduling so that the communication speeds of the respective users are uniform, and the temporal variation of resource allocation is smaller than that of the PR method.
The Maximum CIR method is a method in which CIR (Carrier to Interference Ratio) is preferentially allocated to the best user, and has less temporal variation in resource allocation than the PR method and the PF method, and is close to fixed allocation. Become.

The scheduling unit 26 can also perform Semi-Persistent Scheduling (SPS) based on the LTE standard.
As shown in FIG. 6, SPS is a method of fixing an allocation position (allocation resource block) across a plurality of subframes for a specific user terminal device (in FIG. 6, “user 1”). This method is suitable for application data that requires fixed allocation, such as the above data.

The transmission power adjustment by the power control unit 23 and the scheduling control by the scheduling control unit 24 are performed according to the determination result in the determination unit 27.
The determination unit 27 determines temporal variations in radio resource allocation to terminal devices by other base station devices (particularly, the macro BS 1a). The temporal variation of radio resource allocation refers to a change in the way of resource allocation between subframes that are different in terms of time, and if the method of resource allocation between subframes that are different in terms of time is exactly the same, It can be said that the temporal variability is zero. Also, the resource allocation method between subframes that are different in terms of time is partly the same, but if they are partly different, the degree of temporal variability increases slightly, and resource allocation between subframes that are different in terms of time If the way is completely different, the time variation is the maximum.

  When the time variation of resource allocation is small, even if the resource allocation status of another base station apparatus grasped at a certain time point is used for prediction of resource allocation in the subsequent subframe, the validity of the prediction becomes high. On the other hand, when the time variation of resource allocation is large, the validity of the prediction is low when the resource allocation status of another base station apparatus grasped at a certain time point is used for prediction of resource allocation in the subsequent subframe. Therefore, when the time variation of resource allocation is small, interference suppression is performed by avoiding the use of resources used by the other base station apparatus according to the resource allocation status of the other base station apparatus. It becomes easy.

As described above, when the time variation of the resource allocation is large, the resource allocation becomes highly uncertain. The magnitude of this temporal change in resource allocation indicates the predictability of future resource allocation.
The determination unit 27 determines the temporal variation of resource allocation for the interference suppression control by the power control unit 23 and the scheduling control unit 24 using the above points. Details of the determination of temporal variation will be described later.

  The determination unit 27 uses other base station devices, terminal devices communicating with other base station devices, devices for controlling other base station devices, etc. To make a decision.

  Information that can be used to determine temporal changes in resource allocation in other base station apparatuses includes localized / distributed information, scheduling algorithm type information, data application type information, and power fluctuation information obtained by measurement. . The determination unit 21 performs determination based on these pieces of information.

The Localized / Distributed information is information indicating whether the radio resource allocation method is Localized FDMA that is fixed allocation or Distributed FDMA that is variable allocation.
Scheduling algorithm type information is information indicating the type of scheduling algorithm executed in another base station apparatus, and as described above, the algorithm type is an index indicating the degree of temporal variation in resource allocation.

  The application type information is information indicating the application type (VoIP, streaming, WEB) of data. Since VoIP and streaming data are required to be provided continuously so that the data is not interrupted, they are fixedly allocated. On the other hand, since WEB data is allowed even if there is a slight data delay, it is often assigned discretely (in a burst manner), resulting in a large temporal variation.

  The power fluctuation information is obtained by measuring the power of each subframe in the uplink and / or downlink in another cell, and if it is a fixed assignment, the power fluctuation between subframes different in time is The smaller and more variable, the greater the power fluctuation.

  The determination unit 27 can acquire the above information from the modem unit 21, the measurement unit 22, and the information acquisition unit 28. When obtaining the above information from the modem unit 21 as an acquisition unit, it is only necessary to sniff communication between the base station apparatus and the terminal apparatus in another cell and extract each of the above information from the message included in the radio frame.

  According to the LTE standard, the Localized / Distributed information for the downlink is stored as a PDCCH Format 1A and Format 1B message, and the Localized / Distributed information for the uplink is stored as a PDCCH Format 0 message. Therefore, Localized / Distributed information can be obtained by intercepting other cell communications and reading the message.

Further, if the scheduling type information and the application type information are also included in the (downstream) frame of another cell, such information can be obtained by intercepting the other cell communication.
Furthermore, information such as Localized / Distributed information, scheduling type information, application type information, and power fluctuation information in other cells is acquired in the terminal device connected to the own base station device, and the information acquired by the terminal device is used as an uplink. The information may be received from the terminal device by transmitting to the base station device.

In addition, each piece of information may be acquired from another base station apparatus or an apparatus (server) that controls another base station apparatus via a backbone network (wired network) that connects the base stations. The signal processing unit 5 includes a network interface 29 for a backbone network, and the information acquisition unit 28 uses the interface 29 to locate localized / distributed information, scheduling type information, application, and the like via the backbone network. Information such as type information can be acquired.
Note that the application type information is also acquired from the host device via the backbone network because the host device (server) that controls other base station devices is also known.

The power fluctuation information can be obtained by measuring a signal (signal strength; power amount) of other cell communication by the measurement unit 22. The measurement unit 22 can measure the power of uplink and / or downlink signals of other cells for each resource block, and obtain the amount of power for each resource block. Based on the amount of power, the determination unit 27 generates and acquires power fluctuation information by itself and uses it for determination.
The method of determining temporal variations in resource allocation of other cells based on the power measured by the measurement unit 22 is advantageous when the localized / distributed information, scheduling type information, and application type information cannot be obtained.
The measurement by the measurement unit 22 can be performed by periodically suspending communication in the own cell and acquiring signals of other cells during the suspension.

[How to adjust interference suppression control (first example)]
FIG. 7 shows an adjustment method of interference suppression control based on determination of temporal variation of resource allocation in another cell and the determination result using Localized / Distributed information.
First, the localized / distributed information of uplink and / or downlink of another cell (macro BS) is acquired (step S1). As described above, this information can be acquired by reading a message in a frame of another cell, acquiring via a backbone network, or the like.

  Subsequently, based on the Localized / Distributed information, it is determined whether the allocation method in the other cell (macro BS) is a fixed Localized FDMA or a variable Distributed FDMA (Step S12). If it is determined in step S12 that it is a distributed FDMA, it is difficult to control interference suppression in units of resource blocks according to the resource allocation of other cells because the resource allocation varies greatly. Therefore, the power control unit 23 suppresses interference with other cells by limiting the upper limit value of transmission power over the entire used communication band (step S13).

  That is, in step S13, the power control unit 23 determines that the maximum value of the transmission power transmitted by the own base station device and the maximum value of the transmission power of the terminal device communicating with the own base station device are in a normal state (suppressing interference suppression). The upper limit value is set so as to be smaller than the state not considered). In addition, when the first upper limit value is set as the upper limit value of the transmission power in the normal state, the power control unit 23 sets the second upper limit value lower than the first upper limit value as the transmission power upper limit value in Step 13. Set to change to.

  By setting an upper limit value of transmission power over the entire used communication band in step S13, a signal transmitted from the own base station device or a terminal device communicating with the own base station device reaches another cell. This makes it difficult to suppress interference with other cells. In addition, since transmission power is suppressed over the entire used communication band, even if the time variation of resource allocation is large and it is difficult to grasp used resource blocks in other cells, interference suppression can be realized.

  On the other hand, if it is determined in step S12 that the resource allocation method of the other base station apparatus (macro BS) is Localized FDMA, an unused resource block that is not used in the cell of the base station apparatus is detected. (Step S14). This detection can be performed by reading the resource allocation information in another base station apparatus from the downlink frame of the other base station apparatus. Further, the power of the downlink signal of the other base station apparatus is measured in resource block units by the measurement unit 22, and a resource block whose power is smaller than a threshold is detected as an unused resource block or a resource block that hardly causes interference. May be.

Subsequently, the scheduling control unit 24 controls the scheduling unit 26 so that the resource allocation in the own cell is also performed by the localized FDMA (step S15). In this case, an unused resource block in another cell or a resource block that hardly causes interference is used fixedly in the own cell. Corresponding to the fixed resource allocation in other cells, the own cell also uses another resource block in a fixed manner, so that interference can be efficiently avoided.
That is, even if an unused resource block in another cell is used for communication in the own cell, it does not interfere with another cell. Therefore, the power control unit 23 can perform communication efficiently by increasing the transmission power in the own cell communication for the unused resource block in the other cell to increase the communication speed.

  Moreover, even if it is a resource block used in another cell, when the base station apparatus and terminal device of another cell are located far away, the detected electric power becomes small. Such a resource block is considered to be a resource block that does not easily cause interference, and even if communication is performed with a slightly large transmission power, it may be attenuated before reaching another cell to reduce the degree of interference. it can. Also in this case, it is possible to increase the transmission power in the own cell communication, increase the communication speed, and perform communication efficiently.

  Note that resource blocks that are used by other cells and that may cause interference may not be used in the own cell, or transmission power may be sufficiently suppressed to suppress interference.

  The resource allocation and transmission power settings performed in step 15 are continuously used until the resource allocation status of other cells is reacquired (step S11). That is, even if the status of resource allocation in other cells is fixed, it may be changed after the processes of steps S12 and S14 are performed. Therefore, the set value in step S15 is less reliable over time and may not correspond to the resource allocation status of other cells in real time.

Therefore, the power control unit 23 performs control (power reduction control) for reducing the upper limit value of the transmission power once set in step S15 as time elapses. That is, as illustrated in FIG. 8A, at the time of step S15, the power control unit 23 sets the upper limit value of the transmission power to a relatively high first for a frequency region (resource block) where other cells are not used. Set the upper limit value to increase communication efficiency, and set the upper limit value of transmission power to a relatively low second upper limit value for the frequency region (resource block) used by other cells to suppress interference Shall be.
Then, the set value of FIG. 8A is not used invariably until the re-acquisition of the resource allocation status of other cells is performed, but when the time elapses as shown in FIG. The control unit 23 reduces the upper limit value of transmission power. In particular, for a range set to the first upper limit value that may cause interference when other cells use resources, at least the second upper limit that does not cause interference even when other cells use resources. It is preferable to lower the value.

  In this way, when time elapses after acquiring the resource allocation status of other cells, the possibility that the status is maintained decreases, and the appropriateness of the interference suppression control for each resource block in the own cell decreases. To do. In such a situation, it is appropriate to reduce the transmission power in the entire communication frequency band used as the interference suppression control.

  The power reduction control may be performed not only after step S15 but also after step S13. That is, it is determined that it is distributed (variable allocation), and once the upper limit value of the transmission power is set, the magnitude of the transmission power of the own base station apparatus and / or the transmission of the terminal apparatus communicating with the own base station apparatus It is possible to perform power reduction control that reduces the magnitude of power over time. This power reduction control is performed in the entire used communication frequency band.

  The power reduction amount in the power reduction control when it is determined that the allocation is variable (Distributed) is made larger than the power reduction amount in the power reduction control when it is determined that the allocation is fixed (Localized). The decrease over time in the appropriateness of adjustment of how to suppress interference is larger in the case of variable allocation than in the case of fixed allocation, so the power when it is determined that the allocation is variable By increasing the amount of power reduction in the reduction control, it is possible to suppress interference.

[How to adjust interference suppression control (second example)]
FIG. 9 shows a second example of a determination method of interference suppression control based on the determination of temporal variation of resource allocation in another cell and the determination result using scheduling algorithm type information.
First, scheduling algorithm type information in another base station apparatus (macro BS) is acquired (step S21). This information acquisition is easy to acquire from another base station apparatus via the backbone network, but when the information is included in a frame of another cell, it is based on reading a message in the frame. You may get it.

  Subsequently, the type of the scheduling algorithm in the other base station apparatus is determined based on the scheduling algorithm type information in order to determine the temporal variation of the resource allocation in the other cell (step S22). Then, as in the RR method, when it is determined that the resource allocation predictability is very low and the allocation is variable, control for suppressing the transmission power of the entire used communication frequency band is performed as in step S13 of FIG. This is performed (step S23).

  On the other hand, in the case of the PF method, the PF method, the Maximum CIR method, and the SPS in which the aspect of fixed allocation is recognized to some extent, the resource block used by another base station apparatus is detected (step S24). The scheduling control unit 24 of the base station apparatus 1 performs scheduling in the own base station apparatus using an algorithm corresponding to the algorithm of the other base station apparatus (step S25).

  Here, the temporal variability of resource allocation decreases in the order of the RR method, the PF method, the Maximum CIR method, and the SPS. Therefore, in step S25, for example, when the algorithm of another base station apparatus is SPS, the resource block used in another cell is fixed in a predetermined period. Resource blocks are fixedly assigned by SPS.

Also, when the other cell is the PF method or Maximum CIR method, unlike the RR method, a specific resource block is fixedly used for a specific user for reasons such as the communication environment at that time. It becomes easy to be done.
Therefore, if the own base station apparatus preferentially uses resource blocks other than the resource blocks used in the other cells and performs scheduling by the PF method or the Maximum CIR method, the base station device can perform the same for other cells as compared to the RR method. The probability of giving interference can be kept low. However, in this case, even if resource blocks other than the resource blocks used in other cells are used, the probability of causing interference to other cells is higher than that of SPS. Control.

  Further, when the PF method and the Maximum CIR method are compared, the Maximum CIR method has less time variation in resource allocation. Therefore, in the base station apparatus, when scheduling is performed by the Maximum CIR method using resource blocks other than the resource blocks used in other cells, the probability of causing interference to other cells is smaller than that in the PF method. When the interference probability is small, even if the transmission power in the own cell is increased, interference can be prevented from actually occurring, so that the transmission power in the own cell can be increased.

  In this way, the scheduling algorithm of other base station devices affects the degree of temporal fluctuation. Therefore, if the type of the algorithm can be grasped, the transmission power (upper limit value) for each resource block and resource block to be used is determined. By appropriately adjusting, interference with other cells can be suppressed.

  9, similarly to steps S13 and S15 in FIG. 7, when the time has elapsed since the scheduling algorithm type of another base station apparatus was acquired, power reduction control for reducing transmission power is performed. be able to.

[How to adjust interference suppression control (third example)]
FIG. 10 shows a third example of the determination method of the time variation of the resource allocation in the other cell and the adjustment method of the interference suppression control based on the determination result using the application type information of the communication data in the other cell.
First, the application type information of the data transmitted / received in another base station apparatus (macro BS) is acquired (step S31). This information acquisition is easy to acquire from another base station device or a host device of another base station device via the backbone network, but when the information is included in the frame of another cell It may be obtained by reading a message in the frame.

  Subsequently, in order to determine temporal variations in resource allocation in other cells, the application type of data that is a target of communication (particularly downlink) in the other cell is determined based on the application type information (step S32). ). Then, when it is determined that the application type is an application type with variable allocation, such as when the application type is WEB, control is performed to suppress the transmission power of the entire used communication frequency band as in step S13 of FIG. Is performed (step S33).

  On the other hand, when the application type is VoIP or streaming, since the allocation is fixed, a resource block that is not used by another base station apparatus (macro BS) is detected (step S34), and then the own base station The scheduling control unit 24 of the device 1 performs scheduling using resource blocks that are not used by other base station devices (step S35). In steps S33 and S35, as in steps S13 and S15 of FIG. 7, the upper limit value of the transmission power is adjusted, or the power reduction control is performed to lower the upper limit value of the transmission power as time elapses. May be.

[How to adjust interference suppression control (fourth example)]
11 and 12, the measurement unit 22 performs power measurement of communication signals in other cells, determines temporal variation of resource allocation in other cells, and adjusts interference suppression control based on the determination result. The 4th example of the method of doing is shown.

In the case of fixed allocation as shown in FIG. 11A, there is no temporal variation in the frequency domain (resource block) allocated to user A and the frequency domain (resource block) allocated to user B. On the other hand, in the case of variable allocation as shown in FIG. 11 (b), since resource allocation varies with time, temporal variation is recognized.
Therefore, by measuring the signal power (reception power) of another cell for each frequency (resource block) by the measurement unit 22, it can be determined whether or not the resource allocation of the other cell is fixed. For example, “measurement timing 1” in FIG. 11: power P _RX (t, f) of each frequency (resource block) f is measured at t, and “measurement timing 2” which is the next measurement timing after T _{M has} elapsed. ": t + T _M at each frequency (resource block) f of the power P _RX (t, f) when measuring, if fixed, measurement results at both time points whereas almost coincide, it is fluctuating For example, the difference between the measurement results at both time points becomes large.

Therefore, as shown in FIG. 12, in the determination unit 27, first, the fluctuation amount (power fluctuation information) A of the average received power for each frequency (resource block) at the measurement interval T _M is calculated based on the equation in the figure. (Step S41). If the fluctuation amount A is large, the temporal variation degree of resource allocation in other cells is large, and if the fluctuation amount A is small, the temporal fluctuation is small.

Then, the determination unit 27, the variation is compared with a predetermined threshold value B (step S42), when the change amount A is larger than the predetermined value B, and measurement interval T _M, narrowing as delta _T. When the resource allocation of other cells is variable, the measurement interval T _M is shortened, so that subsequent measurements are frequently performed, and the power level of other cells and the resource allocation status of other cells are more frequently determined. Can grasp.

On the other hand, when the fluctuation amount A is smaller than the predetermined value B (when the measurement interval T _M is short, it is returned), the transmission power P _TX in the own cell is based on the fluctuation amount A. Is obtained (step S44). Specifically, first, the reception power (gain) C from another base station apparatus (macro BS) is obtained from the measurement result based on the formula shown in the figure. Here, D in the figure is the default transmission power (the upper limit value of the transmission power in the normal state).

When the received power C from the other base station apparatus is large, the signal attenuation (path loss) from the other base station apparatus is small, so when the own base station apparatus (femto BS) performs transmission, There is also a high possibility of causing interference to the base station apparatus. Therefore, when the reception power C is large, the transmission power _PTX of the own cell should be set small to suppress interference.

Further, if the fluctuation amount A is large, even if the reception power C is small, the probability that it greatly changes is high. That is, if the fluctuation amount A is large, even if the received power C is small and the other base station apparatus is considered not to use much resources, the other base station apparatus suddenly has many resources. It can be said that there is a high possibility of changing to use. When other base station apparatuses use many resources, the probability that the own base station apparatus uses the same resources increases, and as a result, the probability of causing interference to other cells increases. Therefore, when the probability is high, the transmission power _PTX in the own cell should be reduced to reduce the probability of occurrence of interference.

Therefore, in the present embodiment, even when the fluctuation amount A is large and the probability of causing interference to other cells increases, the transmission power _PTX in the own cell is reduced to suppress the interference (step S44). That is, the power control unit 23 determines the transmission power P _TX = DAC in its own cell.
The above transmission power control may be performed for each frequency (resource block).

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Base station apparatus 1a Macro base station apparatus 1b Femto base station apparatus 21 Modulation / demodulation part (acquisition part)
22 Measurement unit 23 Power control unit (control unit)
24 Scheduling control unit (control unit)
26 Scheduling unit 27 Judgment unit 28 Information acquisition unit MC Macrocell FC Femtocell

Claims (16)

A control unit that performs control for suppressing interference with another base station device and / or a terminal device communicating with the other base station device;
A determination unit configured to determine temporal variation of radio resource allocation to terminal devices by other base station devices;
With
The base station apparatus, wherein the control unit performs control to adjust a method of suppressing the interference based on a determination result by the determination unit. The control unit performs control to suppress the interference by adjusting a magnitude of transmission power of the own base station apparatus and / or a magnitude of transmission power of a terminal apparatus communicating with the own base station apparatus. The base station apparatus according to 1. The determination unit determines whether the radio resource allocation to the terminal device by the other base station apparatus is a fixed allocation with a relatively small temporal variation or a variable allocation with a relatively large temporal variation. The base station apparatus according to claim 1 or 2, wherein the determination is performed. When it is determined that the radio resource allocation to the terminal device by the other base station device is the fixed allocation, the control unit is configured to transmit a radio resource other than the radio resource allocated to the terminal device by the other base station device. The base station apparatus according to claim 3, wherein control is performed to suppress the interference by performing control so that radio resources are allocated to a terminal apparatus that communicates with the base station apparatus. The control unit allocates radio resources other than radio resources allocated to the terminal device by the other base station device to a terminal device communicating with the base station device, and then transmits transmission power of the base station device. The base station apparatus according to claim 4, wherein control is performed to reduce the magnitude and / or the magnitude of transmission power of a terminal apparatus communicating with the own base station apparatus over time. When it is determined that the radio resource allocation to the terminal device by the other base station device is the variable allocation, the control unit determines the magnitude of the transmission power of the own base station device and / or the own base station device. The base station apparatus of any one of Claims 3-5 which performs control which suppresses the said interference by adjusting the magnitude | size of the transmission power of the terminal device which communicates with. The control unit adjusts the magnitude of the transmission power of the own base station apparatus and / or the magnitude of the transmission power of the terminal apparatus communicating with the own base station apparatus by determining that it is the variable allocation, The base station apparatus according to claim 6, wherein control is performed to reduce the magnitude of transmission power of the own base station apparatus and / or the magnitude of transmission power of a terminal apparatus communicating with the own base station apparatus as time elapses. The control unit performs control for adjusting a method of suppressing the interference based on a determination result of the fixed allocation or the variable allocation, and then transmits the transmission power of the base station apparatus. It is configured to perform power reduction control for reducing the magnitude and / or the magnitude of the transmission power of the terminal device communicating with the own base station device over time,
Further, the control unit has a power reduction amount in the power reduction control when determined to be the variable allocation larger than a power reduction amount in the power reduction control when determined to be the fixed allocation. The base station apparatus according to any one of claims 3 to 7. Acquire information usable for determining the temporal variation from information included in a radio frame transmitted from the other base station device to a terminal device communicating with the other base station device. With an acquisition unit,
The base station apparatus according to claim 1, wherein the determination unit determines the temporal variation based on the information acquired by the acquisition unit. Via an backbone network to which the other base station device and the own base station device are connected, an acquisition unit that acquires information that can be used to determine the temporal variation,
The base station apparatus according to any one of claims 1 to 9, wherein the determination unit determines the temporal variation based on the information acquired by the acquisition unit. 10. The information acquired by the acquisition unit as information that can be used for determining the temporal variation is information indicating whether a radio resource allocation method is a localized FDMA or a distributed FDMA. Or the base station apparatus of 10. The information acquired by the acquisition unit as information that can be used to determine the temporal variation is information indicating a type of a scheduling algorithm for radio resource allocation. The base station apparatus according to the item. The information acquired by the acquisition unit as information that can be used to determine the temporal variation is information indicating an application type of data transmitted or received by the other base station device. The base station apparatus according to any one of 12. A measurement unit that periodically measures a communication signal of communication performed between the other base station device and the terminal device;
The base station apparatus according to claim 1, wherein the determination unit determines the temporal variation based on the communication signal periodically measured by the measurement unit. The determination unit determines a temporal variation in radio resource allocation to the terminal device by another base station device by calculating a temporal variation in received power of the communication signal periodically measured by the measurement unit. The base station apparatus according to claim 14. The base station apparatus of Claim 14. The said measurement part adjusts the period which measures the said communication signal according to the determination result by the said determination part.

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