JP5696775B2 - COMMUNICATION CONTROL DEVICE, TERMINAL DEVICE, AND COMMUNICATION CONTROL METHOD - Google Patents

Description

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

  In LTE-A (Long Term Evolution-Advanced), which is a next generation cellular communication standard discussed in 3GPP (Third Generation Partnership Project), introduction of a technology called Carrier Aggregation (CA) has been studied. Yes. Carrier aggregation is the integration of a plurality of frequency bands supported in LTE, for example, communication channels between a terminal device (UE: User Equipment) and a base station (BS: Base Station or eNB: evolved Node B). This is a technique for improving communication throughput. Each frequency band included in one communication channel formed by carrier aggregation is referred to as a component carrier (CC). The bandwidth of the frequency band that can be used in LTE is 1.4 MHz, 3.0 MHz, 5.0 MHz, 10 MHz, 15 MHz, or 20 MHz. Therefore, for example, if five 20 MHz frequency bands are aggregated as component carriers, a communication channel of 100 MHz in total can be formed.

  In carrier aggregation, component carriers included in one communication channel do not necessarily have to be adjacent to each other in the frequency direction. A mode in which component carriers are arranged adjacent to each other in the frequency direction is referred to as a contiguous mode. A mode in which component carriers are arranged without being adjacent to each other is referred to as a non-contiguous mode.

  Further, in carrier aggregation, the number of component carriers in the uplink and the number of component carriers in the downlink are not necessarily equal. A mode in which the number of component carriers in the uplink and the number of component carriers in the downlink are equal is referred to as a symmetric mode. A mode in which the number of component carriers in the uplink and the number of component carriers in the downlink are not equal is referred to as an asymmetric mode. For example, when two component carriers are used in the uplink and three component carriers are used in the downlink, it can be said that the carrier aggregation is asymmetric.

  Further, in LTE, either FDD (Frequency Division Duplex) or TDD (Time Division Duplex) can be used as a duplex method. Among these, in the case of FDD, since the link direction (uplink or downlink) of each component carrier does not change with time, FDD is more suitable for carrier aggregation than TDD.

  On the other hand, handover, which is a basic technique for realizing mobility of a terminal device in the cellular communication standard, is also one of important themes in LTE-A. In LTE, a terminal device measures a communication quality with a serving base station (a connected base station) and a communication quality with a neighboring base station, and a measurement report including the measurement results (measurements). (Measurement report) is transmitted to the serving base station. Next, the serving base station that has received the measurement report determines whether to perform handover based on the measurement result included in the report. When it is determined that the handover should be performed, the source base station (serving base station before the handover), the terminal device, and the target base station (serving base station after the handover) are followed according to a predetermined procedure. Handover is performed (see, for example, Patent Document 1 below).

JP 2009-232293 A

  However, there has not yet been reported a case in which a specific study has been made on how to proceed with a handover procedure in wireless communication involving carrier aggregation.

  For example, in general, in order to measure the communication quality with a base station, the terminal device is required to synchronize with the downlink channel from the base station. At this time, the frequency band to be synchronized is not necessarily the same as the frequency band currently used for communication. Therefore, in the terminal device, it may be necessary to change the operating frequency band of the wireless communication unit in the physical layer. In order to change the operating frequency band, the base station allocates a period called a measurement gap to the terminal device. And since a base station does not transmit data to the said terminal device in the period of a measurement gap, it can measure by changing an operating frequency band, without losing data in a terminal device. However, when carrier aggregation is involved, the number of component carriers constituting one communication channel is plural. In this case, if a measurement gap is allocated to each component carrier as in the conventional case, an increase in the measurement gap increases the possibility of causing a decrease in throughput and a delay in handover.

  Further, such a problem related to allocation of measurement gaps may occur not only in handover but also in changing or adding a component carrier in a cell of one base station in radio communication involving carrier aggregation. For example, it is assumed that there is a request to further improve the throughput in a state where wireless communication with carrier aggregation is performed between the terminal device and the base station. At that time, after measuring (that is, measuring) the communication quality of the frequency band that is not used at that time, the operating frequency band of the component carrier in use is changed to a frequency band where good quality can be obtained, or By newly adding a component carrier whose frequency band where quality can be obtained is an operation frequency band, throughput is improved. In this case as well, there is a need to allocate a measurement gap to the component carrier in use, but the allocation of the measurement gap may cause a temporary decrease in throughput or a delay in processing.

  Therefore, the present invention provides a new and improved communication control device, terminal device, and communication control method capable of suppressing a decrease in throughput due to an increase in a measurement gap or a delay in processing such as a handover due to an increase in a measurement gap in radio communication involving carrier aggregation. Is to provide.

  According to an embodiment of the present invention, a wireless communication unit that performs wireless communication with a terminal device on a communication channel formed by integrating a plurality of component carriers, and a measurement gap for the terminal device And a control unit that controls allocation for each component carrier, wherein the control unit allocates measurement gaps to more component carriers as the channel quality of the communication channel is lower.

  According to another embodiment of the present invention, a wireless communication unit that performs wireless communication with a base station on a communication channel formed by integrating a plurality of component carriers, and channel quality of the communication channel And a measurement unit that performs measurement for handover using a measurement gap assigned to each component carrier according to the number of component carriers. An assigned terminal device is provided.

  According to another embodiment of the present invention, there is provided a communication control method for controlling wireless communication between a terminal device and a base station on a communication channel formed by integrating a plurality of component carriers. Assigning a measurement gap for each component carrier for the terminal device in the base station, wherein the measurement gap is assigned to more component carriers as the channel quality of the communication channel is lower. A control method is provided.

  According to another embodiment of the present invention, a wireless communication unit that performs wireless communication with a terminal device on a communication channel formed by integrating a plurality of component carriers, and used by the terminal device And a control unit that causes the terminal device to use more component carriers for measurement when the channel quality of the communication channel is lower when adding or changing a component carrier is provided. .

  According to another embodiment of the present invention, a wireless communication unit that performs wireless communication with a base station on a communication channel formed by integrating a plurality of component carriers, and used by the wireless communication unit There is provided a terminal device including a control unit that performs measurement using more component carriers as the channel quality of the communication channel is lower when adding or changing a component carrier to be performed.

  According to another embodiment of the present invention, there is provided a communication control method for controlling wireless communication between a terminal device and a base station on a communication channel formed by integrating a plurality of component carriers. In the base station, when adding or changing a component carrier used by the terminal device, the lower the channel quality of the communication channel, the more component carriers are used for the terminal device for measurement. A communication control method is provided.

  As described above, according to the communication control device, the terminal device, and the communication control method according to the present invention, it is possible to suppress a decrease in throughput due to an increase in a measurement gap or a delay in processing such as a handover due to an increase in a measurement gap in carrier communication. Can do.

It is a sequence diagram for demonstrating the flow of a general handover procedure. It is explanatory drawing for demonstrating an example of a structure of a communication resource. It is explanatory drawing for demonstrating a measurement gap. It is a schematic diagram which shows the outline | summary of the radio | wireless communications system which concerns on one Embodiment. It is explanatory drawing for demonstrating the subject regarding the measurement gap at the time of a carrier aggregation. It is a block diagram which shows an example of a structure of the terminal device which concerns on one Embodiment. It is a block diagram which shows an example of a detailed structure of the radio | wireless communication part which concerns on one Embodiment. It is a block diagram which shows an example of a structure of the base station which concerns on one Embodiment. It is a block diagram which shows an example of a detailed structure of the determination part which concerns on one Embodiment. It is a flowchart which shows an example of the flow of the emergency determination process which concerns on one Embodiment. It is a flowchart which shows an example of the detailed flow of the measurement gap allocation process which concerns on one Embodiment. It is explanatory drawing for demonstrating the 1st example of allocation of a measurement gap. It is explanatory drawing for demonstrating the 2nd example of allocation of a measurement gap. It is explanatory drawing for demonstrating the 3rd example of allocation of a measurement gap. It is a flowchart which shows an example of the detailed flow of the measurement gap allocation process which concerns on one modification. It is explanatory drawing for demonstrating the change and addition of a component carrier.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

Further, the “DETAILED DESCRIPTION OF THE INVENTION” will be described in the following order.
1. 1. Description of Related Technology 1-1. Handover procedure 1-2. Measurement gap 2. Overview of wireless communication system 2-1. Overall view of system 2-2. 2. Issues related to career aggregation 3. Configuration example of apparatus according to one embodiment 3-1. Configuration example of terminal device 3-2. 3. Configuration example of base station Example of processing according to one embodiment 4-1. Flow of processing 4-2. Example of measurement gap allocation 4-3. Modified example 4. 4. Example of processing according to one embodiment 5. Example of application to change or addition of component carrier Summary

<1. Explanation of related technology>
[1-1. Handover procedure]
First, a technique related to the present invention will be described with reference to FIGS. 1, 2A, and 2B. FIG. 1 shows a flow of a handover procedure based on LTE in wireless communication without carrier aggregation as an example of a general handover procedure. Here, a terminal apparatus (UE), a source base station (Source eNB), a target base station (Target eNB), and an MME (Mobility Management Entity (mobility management entity)) are involved in the handover procedure.

  As a pre-handover stage, first, the terminal device reports the channel quality of the communication channel between the terminal device and the source base station to the source base station (step S2). The channel quality report may be periodically performed, or may be performed when the channel quality falls below a predetermined reference value. The terminal device can measure the channel quality of the communication channel with the source base station by receiving the reference signal included in the downlink channel from the source base station.

  Next, the source base station determines whether or not measurement is necessary based on the quality report received from the terminal device, and allocates a measurement gap to the terminal device when measurement is necessary (step S4). The measurement gap will be described in more detail later.

  Next, the terminal device searches for a downlink channel from a neighboring base station (that is, performs a cell search) during the allocated measurement gap period (step S12). The terminal device can know the surrounding base stations to be searched according to a list provided in advance from the source base station.

  Next, when the terminal apparatus acquires synchronization with the downlink channel, the terminal apparatus performs measurement using the reference signal included in the downlink channel (step S14). During this time, the source base station restricts allocation of data communication related to the terminal device so that data transmission by the terminal device does not occur.

  The terminal device that has finished the measurement transmits a measurement report including the measurement result to the source base station (step S22). The result of the measurement included in the measurement report may be an average value or a representative value of the measurement values over a plurality of measurements. Further, the measurement result may include data for a plurality of frequency bands.

  The source base station that has received the measurement report determines whether or not to execute handover based on the content of the measurement report. For example, when the channel quality of other base stations in the vicinity is better than a predetermined threshold value than the channel quality of the source base station, it can be determined that a handover is necessary. In that case, the source base station determines to proceed with the handover procedure with the other base station as the target base station, and transmits a handover request message (Handover Request) to the target base station (step S24).

  The target base station that has received the handover request message determines whether or not the terminal device can be accepted according to the availability of a communication service provided by itself. If the terminal device can be accepted, the target base station transmits a handover approval message (Handover Request Confirm) to the source base station (step S26).

  The source base station that has received the handover approval message transmits a handover command (Handover Command) to the terminal device (step S28). Then, the terminal device acquires synchronization with the downlink channel of the target base station (step S32). Next, the terminal apparatus performs random access to the target base station using a random access channel provided in a predetermined time slot (step S34). During this time, the source base station transfers data that is addressed to the terminal device to the target base station (step S36). When the random access is successful, the terminal device transmits a handover complete message (Handover Complete) to the target base station (step S42).

  The target base station that has received the handover complete message requests the MME to update the route for the terminal device (step S44). When the MME updates the route of user data, the terminal device can communicate with another device via a new base station (that is, a target base station). Then, the target base station transmits an acknowledgment (Acknowledgement) to the terminal device (step S46). Thereby, a series of handover procedures is completed.

[1-2. Measurement gap]
FIG. 2A shows a configuration of communication resources in LTE as an example of a configuration of communication resources to which the present invention can be applied. Referring to FIG. 2A, communication resources in LTE are divided into individual radio frames having a length of 10 msec in the time direction. Further, one radio frame includes 10 subframes, and one subframe is composed of two 0.5 ms slots. In LTE, in the time direction, this subframe is one unit of communication resource allocation to each terminal device. Such a unit is referred to as a resource block. One resource block includes 12 subcarriers in the frequency direction. That is, one resource block has a size of 1 msec × 12 subcarriers in the time-frequency domain. As more resource blocks are allocated for data communication within the same bandwidth and the same time length, the throughput of data communication increases.

  FIG. 2B is an explanatory diagram for explaining a general measurement gap. Referring to FIG. 2B, a measurement gap MG1 is allocated at a position corresponding to the second radio frame from the left in the time direction. Further, a measurement gap MG2 is assigned to a position corresponding to the fourth radio frame from the left. Each measurement gap typically has a length of 6 msec. Among them, the terminal device can use the central 5.166 msec for measurement (see MG1a in the figure). The first half of the remaining part of the measurement gap is used for the terminal device to tune the operating frequency band to the frequency band targeted for measurement (see MG1b in the figure). The latter half of the remaining part of the measurement gap is used by the terminal device to retune the operating frequency band from the frequency band targeted for measurement to the original frequency band (see MG1c in the figure). The period of the measurement gap is usually set to be an integral multiple of the radio frame length. When the frequency band targeted for measurement is the same as the original operating frequency band, the measurement gap need not be assigned. In this case, the terminal device can perform measurement without changing its own operating frequency band in the physical layer. Such a measurement gap is assigned to the terminal apparatus in the previous stage of the handover procedure as shown in FIG. 1, and can also be assigned to the terminal apparatus when a component carrier is changed or added.

<2. Overview of Wireless Communication System>
[2-1. Overall view of the system]
Next, an outline of a wireless communication system to which the present invention can be applied will be described using FIG. 3 and FIG.

  FIG. 3 is a schematic diagram showing an outline of the wireless communication system 1 according to an embodiment of the present invention. Referring to FIG. 3, the radio communication system 1 includes a terminal device 100, a base station 200a, and a base station 200b. Among these, the base station 200 a is assumed to be a serving base station for the terminal device 100.

  The terminal device 100 is located inside a cell 202a where a wireless communication service is provided by the base station 200a. The terminal device 100 performs data communication with another terminal device (not shown) via the base station 200a on a communication channel formed by integrating a plurality of component carriers (that is, by carrier aggregation). It can be performed. However, since the distance between the terminal apparatus 100 and the base station 200a is not short, the terminal apparatus 100 may need to be handed over. Furthermore, the terminal device 100 is located inside a cell 202b in which a radio communication service is provided by the base station 200b. Accordingly, the base station 200b can be a target base station candidate for the handover of the terminal device 100.

  The base station 200a can communicate with the base station 200b via a backhaul link (for example, X2 interface). Between the base station 200a and the base station 200b, for example, various messages in the handover procedure as described with reference to FIG. 1 or scheduling information about terminal devices belonging to each cell can be transmitted and received. Furthermore, the base station 200a and the base station 200b can communicate with the MME, which is an upper node, for example via the S1 interface.

  In the following description of the present specification, when it is not necessary to distinguish the base stations 200a and 200b from each other, the alphabet at the end of the code is omitted and these are collectively referred to as the base station 200. The same applies to other components.

[2-2. Issues related to career aggregation]
In the situation where there is a possibility of handover as shown in FIG. 3, when the terminal apparatus 100 performs carrier aggregation, there is a problem as to how measurement gaps should be assigned to a plurality of component carriers constituting a communication channel. It becomes. FIG. 4 is an explanatory diagram for explaining a problem related to the measurement gap at the time of such carrier aggregation.

  In general, even when carrier aggregation is not performed, there are a plurality of frequency band candidates after handover to be measured. When carrier aggregation is involved, the required number of measurements increases according to the number of component carriers. In the example of FIG. 4, three component carriers CC1 to CC3 that are partially discontinuously arranged in the frequency direction constitute a communication channel between the terminal device and the serving base station. In addition, there are three candidate component carriers for each component carrier that are to be subjected to measurement accompanied by a change in the operating frequency band. In the example of FIG. 4, even if measurement is performed only once for overlapping candidates, measurement for seven component carriers in the target base station is required for the entire communication channel. If the number of component carriers in use is three and the number of candidate component carriers after handover for each component carrier is three, the maximum number of measurements is 3 × 3 = 9. Cost.

  Increasing the required number of measurements means that more measurement gaps must be allocated for changing the operating frequency band during measurement (ie, including tuning and retuning). This leads to a decrease in throughput and a delay in handover due to the suspension of data communication during the measurement gap. Therefore, in the wireless communication system 1 in which carrier aggregation is performed, it is beneficial to efficiently allocate measurement gaps by the method according to an embodiment described in the next section.

<3. Configuration Example of Device According to One Embodiment>
Hereinafter, an example of the configuration of the terminal device 100 and the base station 200 included in the wireless communication system 1 according to an embodiment of the present invention will be described with reference to FIGS.

[3-1. Example of terminal device configuration]
FIG. 5 is a block diagram illustrating an example of the configuration of the terminal device 100 according to the present embodiment. Referring to FIG. 5, the terminal device 100 includes a wireless communication unit 110, a signal processing unit 150, a control unit 160, and a measurement unit 170.

(Wireless communication part)
The wireless communication unit 110 performs wireless communication with the base station 200 on a communication channel formed by integrating a plurality of component carriers using a carrier aggregation technique.

  FIG. 6 is a block diagram illustrating an example of a more detailed configuration of the wireless communication unit 110. Referring to FIG. 6, the wireless communication unit 110 includes an antenna 112, a switch 114, an LNA (Low Noise Amplifier) 120, a plurality of down converters 122a to 122c, a plurality of filters 124a to 124c, and a plurality of ADCs (Analogue to Digital Converter). 126a to 126c, demodulator 128, modulator 130, a plurality of digital to analog converters (DACs) 132a to 132c, a plurality of filters 134a to 134c, a plurality of upconverters 136a to 136c, a combiner 138, and a PA (Power Amplifier) 140).

  When the antenna 112 receives a radio signal transmitted from the base station 200, the antenna 112 outputs the received signal to the LNA 120 via the switch 114. The LNA 120 amplifies the received signal. The down converter 122a and the filter 124a separate the baseband signal of the first component carrier (CC1) from the reception signal amplified by the LNA 120. The separated baseband signal is converted into a digital signal by ADC 126 a and output to demodulation section 128. Similarly, the down converter 122b and the filter 124b separate the baseband signal of the second component carrier (CC2) from the reception signal amplified by the LNA 120. The separated baseband signal is converted into a digital signal by ADC 126 b and output to demodulation section 128. The down converter 122c and the filter 124c separate the baseband signal of the third component carrier (CC3) from the reception signal amplified by the LNA 120. The separated baseband signal is converted into a digital signal by ADC 126 c and output to demodulation section 128. Thereafter, the demodulation unit 128 generates a data signal by demodulating the baseband signal of each component carrier, and outputs the data signal to the signal processing unit 150.

  When a data signal is input from the signal processing unit 150, the modulation unit 130 modulates the data signal and generates a baseband signal for each component carrier. Among these baseband signals, the baseband signal of the first component carrier (CC1) is converted into an analog signal by the DAC 132a. Then, the filter 134a and the up-converter 136a generate a frequency component corresponding to the first component carrier in the transmission signal from the analog signal. Similarly, the baseband signal of the second component carrier (CC2) is converted into an analog signal by the DAC 132b. Then, a frequency component corresponding to the second component carrier in the transmission signal is generated from the analog signal by the filter 134b and the up-converter 136b. The baseband signal of the third component carrier (CC3) is converted into an analog signal by the DAC 132c. Then, the frequency component corresponding to the third component carrier in the transmission signal is generated from the analog signal by the filter 134c and the up-converter 136c. Thereafter, the frequency components corresponding to the three generated component carriers are combined by the combiner 138 to form a transmission signal. The PA 140 amplifies the transmission signal and outputs it to the antenna 112 via the switch 114. Then, the antenna 112 transmits the transmission signal to the base station 200 as a radio signal.

  In addition, although the example which the radio | wireless communication part 110 handles three component carriers was demonstrated in FIG. 6, the number of the component carriers which the radio | wireless communication part 110 handles may be two, or four or more, Also good.

  Further, the radio communication unit 110 may process the signal of each component carrier in the digital domain instead of processing the signal of each component carrier in the analog domain as in the example of FIG. In the latter case, at the time of reception, the digital signal converted by one ADC is separated into the signal of each component carrier by the digital filter. At the time of transmission, the digital signal of each component carrier is frequency-converted and synthesized, and then converted into an analog signal by one DAC. In general, when the signal of each component carrier is processed in the analog domain, the load on the ADC and the DAC is smaller. On the other hand, when processing the signal of each component carrier in the digital domain, the sampling frequency for AD / DA conversion becomes high, so that the load on the ADC and DAC can increase.

(Signal processing part)
Returning to FIG. 5, the description of an example of the configuration of the terminal device 100 is continued.

  The signal processing unit 150 performs signal processing such as deinterleaving, decoding, and error correction on the demodulated data signal input from the wireless communication unit 110. Then, the signal processing unit 150 outputs the processed data signal to the upper layer. The signal processing unit 150 performs signal processing such as encoding and interleaving on the data signal input from the upper layer. Then, the signal processing unit 150 outputs the processed data signal to the wireless communication unit 110.

(Control part)
The control unit 160 controls the overall functions of the terminal device 100 using a processing device such as a CPU (Central Processing Unit) or a DSP (Digital Signal Processor). For example, the control unit 160 controls the timing of data communication by the wireless communication unit 110 according to the scheduling information that the wireless communication unit 110 receives from the base station 200. Further, the control unit 160 causes the measurement unit 170 to measure the channel quality using the reference signal from the base station 200 serving as a serving base station, and transmits the channel quality report to the base station 200 via the wireless communication unit 110. Further, in the present embodiment, when a measurement gap is allocated to the terminal device 100 by the base station 200, the control unit 160 causes the measurement unit 170 to execute the measurement during the allocated measurement gap.

(Measurement part)
For example, the measurement unit 170 measures the channel quality for each component carrier using the reference signal from the base station 200 according to the control from the control unit 160. In addition, when a measurement gap is allocated to the terminal device 100 by the base station 200, the measurement unit 170 performs a measurement for handover using the allocated measurement gap.

  In the present embodiment, the measurement gap is allocated for each component carrier by the base station 200, as will be described later. Therefore, the control unit 160, for example, in the measurement gap period assigned to the first component carrier, the operating frequency band for the first component carrier of the wireless communication unit 110 (for example, the down converter shown in FIG. 6). 122a, the filter 124a, and the operating frequency band of the ADC 126a) are tuned to a predetermined frequency band to be measured. Next, the measurement unit 170 performs measurement for the frequency band. Then, the control unit 160 retunes the operation frequency band for the first component carrier of the wireless communication unit 110 to the original frequency band before the measurement gap period ends. Such a measurement is similarly performed for the second and third component carriers.

  The result of the measurement for each component carrier executed by the measurement unit 170 in this way is shaped into a predetermined format for the measurement report by the control unit 160 and transmitted to the base station 200 via the wireless communication unit 110. Thereafter, the base station 200 determines whether or not to perform handover for the terminal device 100 based on the measurement report.

[3-2. Example of base station configuration]
FIG. 7 is a block diagram showing an example of the configuration of the base station 200 according to this embodiment. Referring to FIG. 7, the base station 200 includes a radio communication unit 210, an interface unit 250, a component carrier (CC) management unit 260, a determination unit 270, and a control unit 280.

(Wireless communication part)
The specific configuration of the wireless communication unit 210 may be similar to the configuration of the wireless communication unit 110 of the terminal device 100 described with reference to FIG. 6, although the number of component carriers to be supported and processing performance requirements are different. The wireless communication unit 210 performs wireless communication with a terminal device on a communication channel formed by integrating a plurality of component carriers using a carrier aggregation technique.

(Interface part)
The interface unit 250 mediates communication between the wireless communication unit 210 and the control unit 280 and the upper node via, for example, the S1 interface illustrated in FIG. Further, the interface unit 250 mediates communication between the wireless communication unit 210 and the control unit 280 and other base stations via, for example, the X2 interface illustrated in FIG.

(CC Management Department)
The CC management unit 260 holds data representing which component carrier each terminal device uses for each terminal device belonging to the cell of the base station 200. Such data can be updated by the control unit 280 when a new terminal device joins the cell of the base station 200 or when an existing terminal device changes a component carrier. Therefore, for example, the determination unit 270 and the control unit 280 can know which component carrier the terminal apparatus 100 is using by referring to the data held by the CC management unit 260.

(Judgment part)
Based on the received signal received from the terminal device by the wireless communication unit 210, the determination unit 270 determines the urgency level of the handover of the terminal device. More specifically, the determination unit 270 may determine that the urgent degree of handover of the terminal device is higher as the moving speed of the terminal device detected based on the received signal received from the terminal device is higher. . Further, the determination unit 270 may determine that the urgency level of handover of the terminal device is higher as the channel quality included in the received signal received from the terminal device is lower.

  FIG. 8 is a block diagram illustrating an example of a more detailed configuration of the determination unit 270. Referring to FIG. 8, the determination unit 270 includes a quality acquisition unit 272, a speed detection unit 274, and an urgency level determination unit 276.

  The quality acquisition unit 272 acquires the quality level of the communication channel between the terminal device and the base station 200 for each component carrier based on the received signal from the terminal device. For example, the quality acquisition unit 272 may acquire a quality level for each component carrier by receiving a channel quality report transmitted from the terminal device. Moreover, the quality acquisition part 272 may acquire the quality level for every component carrier by measuring parameters, such as the received signal strength of a received signal from a terminal device, or an error rate itself. The quality acquisition unit 272 outputs the quality level for each component carrier acquired in this way to the urgency level determination unit 276.

  The speed detection unit 274 detects the moving speed of the terminal device based on the received signal received from the terminal device. For example, when the terminal device has a GPS (Global Positioning System) function, position data representing the position of the terminal device measured by the GPS function is included in the received signal. In that case, after acquiring the position data from the received signal, the speed detection unit 274 detects the moving speed of the terminal device by calculating the change over time of the position of the terminal device using the acquired position data. be able to. Further, the moving speed may be calculated in the terminal device from the position measured by the GPS function. In that case, the speed detection unit 274 can be notified of the moving speed from the terminal device. Further, the speed detection unit 274 may detect the moving speed of the terminal device from the measurement result of the received signal from the terminal device, for example, the change in the signal delay amount of the received signal. Furthermore, the speed detection unit 274 may calculate the moving speed of the terminal device by measuring the position of the terminal device using a known positioning technique based on a radio signal. The speed detection unit 274 outputs the movement speed of the terminal device thus detected to the urgency level determination unit 276.

  The urgency level determination unit 276 determines the urgency level of the handover of the terminal device according to the channel quality level input from the quality acquisition unit 272 and the moving speed of the terminal device input from the speed detection unit 274. FIG. 9 is a flowchart illustrating an example of the flow of urgency determination processing by the determination unit 270 according to the present embodiment.

  Referring to FIG. 9, first, the quality acquisition unit 272 acquires the quality level for each component carrier (step S102). Next, the moving speed of the terminal device is detected by the speed detector 274 (step S104).

  Next, the urgency determination unit 276 determines whether or not the channel quality is lower than a predetermined reference using the quality level for each component carrier (step S106). More specifically, for example, the urgency determining unit 276 compares a parameter such as an average value or a minimum value of quality levels for each component carrier with a predetermined reference value that is determined in advance. If it is determined that the channel quality is lower than the predetermined reference, the process proceeds to step S112. On the other hand, if it is determined that the channel quality is not lower than the predetermined reference, the process proceeds to step S108.

  In step S108, the urgency determining unit 276 determines whether or not the moving speed of the terminal device is faster than a predetermined reference value determined in advance (step S108). Here, when it is determined that the moving speed of the terminal device is faster than the predetermined reference, the process proceeds to step S112. On the other hand, if it is determined that the moving speed of the terminal device is not faster than the predetermined reference, the process proceeds to step S110.

  In step S110, since the channel quality is not lower than the predetermined reference and the moving speed of the terminal device is not higher than the predetermined reference, the urgency determination unit 276 determines that the urgency of the handover of the terminal device is low ( Step S110). On the other hand, in step S112, since the channel quality is higher than the predetermined reference or the moving speed of the terminal device is higher than the predetermined reference, the urgency determination unit 276 determines that the urgency of the handover of the terminal device is high ( Step S112).

  The urgency level determination unit 276 outputs the urgency level determined in this way to the control unit 280. Further, the quality acquisition unit 272 outputs the quality level for each component carrier to the control unit 280. Note that FIG. 9 illustrates an example in which it is determined that the urgency level of the handover of the terminal apparatus is “high” or “low”. However, the present invention is not limited to this example, and the urgency level of handover may be classified into more levels. Further, for example, in step S106 of FIG. 9, the reference value to be compared with a parameter such as an average value or a minimum value of the quality level for each component carrier may change dynamically. For example, the reference value can be dynamically changed based on the number of terminal devices connected to the base station or the surrounding electric field condition. Thereby, a flexible system operation becomes possible. Similarly, the reference value to be compared with the moving speed of the terminal device in step 108 may also change dynamically.

(Control part)
The control unit 280 controls the overall functions of the base station 200 using a processing device such as a CPU or a DSP. Moreover, in this embodiment, the control part 280 controls allocation of the measurement gap for a terminal device for every component carrier according to the emergency degree determined as a result of the emergency degree determination process by the determination part 270 mentioned above. .

  More specifically, the control unit 280 can assign measurement gaps to more component carriers as the urgency level of handover is higher. For example, as described with reference to FIG. 9, a case is assumed where the urgency level of handover is classified as either “high” or “low”. In this case, when it is determined that the urgency level of the handover is high, the control unit 280 allocates a measurement gap to all the component carriers used by the terminal device. Further, when it is determined that the urgency level of the handover is low, the control unit 280 allocates a measurement gap to a part (for example, any one) of component carriers used by the terminal device. As a result, when handover urgency is low, a relatively long time is taken to avoid a decrease in throughput, and when handover urgency is high, measurement is performed in a short time. Thus, a delay in handover can be prevented.

  Further, the control unit 280 may change the measurement gap allocation pattern according to the channel quality quality level for each component carrier acquired by the quality acquisition unit 272.

  More specifically, for example, when assigning measurement gaps to some component carriers, the control unit 280 may preferentially assign measurement gaps to component carriers with low quality levels. In addition, when assigning measurement gaps to two or more component carriers, the control unit 280 assigns the measurement gap period assigned to the first component carrier to the second component carrier having a lower quality level. May be longer. As a result, the ratio of measurement gaps to communication resources for component carriers with a high quality level is reduced, so that a reduction in throughput is suppressed compared to the case where measurement gaps are uniformly allocated to all component carriers regardless of the quality level. can do.

  Further, for example, when assigning measurement gaps to two or more component carriers, the control unit 280 determines the assignment of measurement gaps so that the timing of one measurement gap does not coincide with the timing of other measurement gaps. Also good. As a result, it is possible to avoid a data transmission delay caused by a time during which no data transmission can be performed.

  In addition, for example, when two or more component carriers are adjacent in the frequency direction, or when the distance in the frequency direction of two or more component carriers is closer than a predetermined threshold, the control unit 280 The measurement gap may be allocated only for any one of the two or more component carriers. In such a case, for example, the result of the measurement for one component carrier is substituted for another component carrier that is adjacent or close in the frequency direction, thereby reducing the time required for the measurement and avoiding a handover delay. In addition, a decrease in throughput can be suppressed.

  In addition, for example, when the number of component carriers that can be used for measurement is notified from the terminal device, the control unit 280 prevents the number of component carriers to which the measurement gap is allocated from exceeding the notified number. The allocation of measurement gaps may be controlled. Thereby, it is possible to avoid useless allocation of measurement gaps and suppress a decrease in throughput.

<4. Example of Processing According to One Embodiment>
[4-1. Process flow]
FIG. 10 is a flowchart showing an example of a detailed flow of measurement gap allocation processing by the base station 200 according to the present embodiment.

  Referring to FIG. 10, first, the wireless communication unit 210 receives a channel quality report from the terminal device (step S202). Radio communication section 210 then outputs the received channel quality report to control section 280.

  Next, the control unit 280 determines whether or not measurement for handover is necessary based on the channel quality report (step S204). Here, for example, when it is determined that the measurement for handover is unnecessary because the channel quality is good, the measurement gap is not allocated (step S206), and the measurement gap allocation process is completed. To do. On the other hand, if it is determined that measurement for handover is necessary, the process proceeds to step S208.

  In step S208, the determination unit 270 performs the urgency determination process described with reference to FIG. 9 (step S208). Then, the determination unit 270 outputs the determined urgency level of the handover to the control unit 280.

  Next, the control unit 280 determines whether or not the handover urgency level determined by the determination unit 270 is high (step S210). If the urgency level of the handover is high, the process proceeds to step S212. On the other hand, if the urgency level of the handover is not high, the process proceeds to step S214.

  In step S212, the control unit 280 allocates a measurement gap to all component carriers used by the terminal device (step S212). On the other hand, in step S214, the control unit 280 assigns a measurement gap to some component carriers used by the terminal device (step S214). Then, the measurement gap allocation process ends.

[4-2. Example of measurement gap allocation]
FIG. 11A to FIG. 11C each show an example of a measurement gap pattern assigned as a result of the measurement gap assignment processing by the control unit 280.

(Pattern A)
Referring to FIG. 11A, three component carriers CC1 to CC3 constitute one communication channel. The component carriers CC1 to CC3 are not located near each other in the frequency direction. Further, it is assumed that the determination unit 270 determines that the urgency level of the handover is high.

  In this case, the control unit 280 assigns a measurement gap to all the component carriers CC1 to CC3. In the example of FIG. 11A, measurement gaps MG11, MG12,... Are assigned to the component carrier CC1. Further, measurement gaps MG13, MG14,... Are allocated to the component carrier CC2. Further, measurement gaps MG15... Are assigned to the component carrier CC3. Therefore, the terminal device can perform the handover early by performing the measurement in a short time.

(Pattern B)
Referring to FIG. 11B, as in FIG. 11A, three communication carriers CC1 to CC3 constitute one communication channel. Among these, the component carriers CC1 and CC2 are located near each other in the frequency direction. Further, it is assumed that the determination unit 270 determines that the urgency level of the handover is high. Furthermore, the quality level of the component carrier CC1 is higher than the quality level of the component carrier CC2.

  In this case, the control unit 280 allocates a measurement gap to, for example, the component carrier CC2 having a lower quality level among the component carriers CC1 and CC2 that are located near each other in the frequency direction. Further, the control unit 280 assigns a measurement gap to the component carrier CC3. In the example of FIG. 11B, measurement gaps MG21, MG22,... Are assigned to the component carrier CC2. Further, measurement gaps MG23, MG24,... Are assigned to the component carrier CC3. On the other hand, a measurement gap is not allocated to a component carrier CC1 having a large contribution to throughput (ie, a high quality level). Therefore, in pattern B, a decrease in throughput due to the allocation of measurement gaps is effectively suppressed.

(Pattern C)
Referring to FIG. 11C, as in FIGS. 11A and 11B, three component carriers CC1 to CC3 constitute one communication channel. Further, it is assumed that the determination unit 270 determines that the urgency level of the handover is low. Furthermore, the quality level for each component carrier is assumed to be lower in the order of component carriers CC1, CC2, and CC3.

  In this case, the control unit 280 allocates more communication resources for the measurement gap as the quality level for each component carrier is lower. In the example of FIG. 11C, the measurement gap is not allocated to the component carrier CC3 having the highest quality level. On the other hand, measurement gaps MG31, MG32, MG33,... Are allocated to the component carrier CC1. Further, measurement gaps MG34, MG35,... Are allocated to the component carrier CC2. However, the measurement gap cycle T1 in the component carrier CC1 is 2 radio frames, and the measurement gap cycle T2 in the component carrier CC2 is 4 radio frames. That is, by reducing the period of the measurement gap of the component carrier CC2 having a higher quality level, it is possible to effectively suppress a decrease in throughput of the entire communication channel.

  Further, through the example of FIGS. 11A to 11C, the timing of one measurement gap is determined not to be the same as the timing of another measurement gap. As a result, there is no time during which data transmission cannot be performed at all, so that a delay in data transmission is avoided.

[4-3. Modified example]
In the embodiment described above, an example has been described in which the base station determines the urgency level of the handover of the terminal device and then controls the allocation of the measurement gap according to the urgency level and the quality level for each component carrier. However, it is also possible for the base station to control the allocation of measurement gaps according to the quality level for each component carrier without determining the urgency of the handover of the terminal device. FIG. 12 shows an example of the flow of measurement gap allocation processing according to such a modification of the present embodiment.

  Referring to FIG. 12, first, the wireless communication unit 210 receives a channel quality report from the terminal device (step S302). Radio communication section 210 then outputs the received channel quality report to control section 280.

  Next, the control unit 280 determines whether or not measurement for handover is necessary based on the channel quality report (step S304). Here, for example, when it is determined that the measurement for the handover is unnecessary because the channel quality is good, the measurement gap is not allocated (step S306), and the measurement gap allocation process is completed. To do. On the other hand, if it is determined that measurement for handover is necessary, the process proceeds to step S308.

  In step S308, the control unit 280 allocates a measurement gap for each component carrier according to the quality level for each component carrier acquired by the quality acquisition unit 272 (step S308). At this time, for example, as described with reference to FIGS. 11B and 11C, the measurement gap can be preferentially assigned to the component carrier having a low quality level. In addition, a measurement gap with a shorter period can be assigned to a component carrier with a low quality level. Then, the measurement gap allocation process ends.

  In such a measurement gap allocation process or the measurement gap allocation process described with reference to FIG. 10, for example, a constraint condition regarding the number of component carriers to which a measurement gap can be allocated may be determined in advance. For example, the number of component carriers to which the measurement gap can be assigned is always one, and the measurement gap may be assigned to the component carrier having the lowest quality level. Further, when one or a plurality of component carriers (or RF circuits) capable of performing the measurement are defined in advance, a measurement gap may be assigned to the one or a plurality of component carriers (or RF circuits). Good.

<5. Example of application to change or addition of component carrier>
The above-described method related to measurement gap allocation control can be applied to the change of the component carrier (change of the operating frequency band of the component carrier) of the terminal device 100 or the addition of the component carrier in the cell of one base station 200. It is.

  FIG. 13 is an explanatory diagram for describing an example in which the above-described embodiment is applied to change or addition of a component carrier. In the scenario of FIG. 13, it is assumed that the terminal device 100 performs wireless communication with carrier aggregation with the base station 200 which is a serving base station. On the right side of FIG. 13, a sequence diagram regarding a procedure for changing a component carrier between the terminal device 100 and the base station 200 is shown. The left side of FIG. 13 shows the status of the operating frequency band at each stage of the sequence.

  Referring to FIG. 13, first, the terminal device 100 performs wireless communication with the base station 200 using three component carriers CC1 to CC3. The operating frequency bands of the component carriers CC1, CC2, and CC3 are the first frequency band (# 1), the second frequency band (# 2), and the third frequency band (# 3), respectively.

  First, the terminal device 100 reports the channel quality for each component carrier to the base station 200 (step S402). The channel quality report may be performed periodically, or may be performed when the channel quality falls below a predetermined reference value. Further, the terminal apparatus 100 may transmit a component carrier change (or addition) request for improving the throughput to the base station 200 instead of the channel quality report.

  Next, the base station 200 allocates a measurement gap to the terminal device 100 by, for example, the measurement gap allocation process described with reference to FIG. 10 or FIG. 12 (Step S404). That is, for example, a measurement gap can be preferentially assigned to a component carrier having a low quality level among the component carriers CC1, CC2, and CC3. In addition, a measurement gap with a shorter period can be assigned to a component carrier with a low quality level.

  Next, the terminal apparatus 100 acquires synchronization with the downlink channel from the base station 200 for the frequency band not in use during the allocated measurement gap, and uses the reference signal included in the downlink channel. Measurement is then performed (step S412). In the example of FIG. 13, the measurement for the fourth frequency band (# 4) is performed during the measurement gap assigned to the component carrier CC2. Further, the measurement for the fifth frequency band (# 5) is performed during the measurement gap assigned to the component carrier CC3.

  Next, the terminal device 100 that has finished the measurement transmits a measurement report including the measurement result to the base station 200 (step S414). The result of the measurement included in the measurement report may be an average value or a representative value of the measurement values over a plurality of measurements.

  The base station 200 that has received the measurement report determines whether or not the component carrier of the terminal device 100 needs to be changed or added based on the content of the measurement report. For example, when there is a frequency band having better quality than any of the channel quality of the component carriers CC1 to CC3, the operating frequency band of the component carrier should be changed to the frequency band having the good quality. It can be determined that there is. Further, when the number of component carriers currently used in the terminal device 100 is smaller than the number of usable component carriers, and there is another frequency band having good quality, the good quality is reduced. It may be determined that a component carrier whose operating frequency band is the existing frequency band should be added. In the example of FIG. 13, the base station 200 changes the operating frequency band of the component carrier CC3 from the third frequency band (# 3) to the fourth frequency band (# 4) based on the content of the measurement report. It is decided that it should be.

  Accordingly, the base station 200 next transmits a component carrier deletion command specifying the component carrier CC3 to the terminal device 100 (step S422). In response, in the terminal device 100, the component carrier CC3 is deleted from the component carrier in use (step S424). Next, base station 200 designates the fourth frequency band (# 4) and transmits a component carrier addition command to terminal apparatus 100 (step S426). Accordingly, in order to add a component carrier CC3 having the fourth frequency band (# 4) as an operating frequency band in the terminal device 100, the terminal device 100 is connected to the downlink channel of the fourth frequency band (# 4). Synchronization is acquired (step S428). Unlike the case of handover, when changing or adding a component carrier within the cell of the same base station 100, no new timing adjustment is required, and therefore random access may not be performed.

  Through such a procedure, the terminal device 100 uses the component carriers CC1 to CC3 that newly set the first, second, and fourth frequency bands to the base station 200 as wireless communication. Communication is continued (step S430).

  Note that when it is determined to add a component carrier instead of changing the component carrier, for example, steps S422 and S424 illustrated in FIG. 13 may be omitted. Then, for example, in step S426, a component carrier addition command that uses the fourth or fifth frequency band as the operating frequency band is transmitted from the base station 200 to the terminal device 100.

  Moreover, the case where a component carrier is added is a case where the unused component carrier (or unused RF circuit etc.) remains in the terminal device 100. FIG. In such a case, the terminal device 100 may perform the measurement using an unused component carrier without receiving the allocation of the measurement gap. However, when a component carrier should be added urgently, measurement can be performed at higher speed by using a component carrier in use and an unused component carrier in parallel. Further, even when it is not desired to activate the sleeping RF circuit for the purpose of power saving or the like, the measurement can be performed using the component carrier in use.

<6. Summary>
So far, the terminal device 100 and the base station 200 included in the wireless communication system 1 according to an embodiment of the present invention have been described with reference to FIGS. According to the present embodiment, in the base station 200, the allocation of measurement gaps is controlled for each component carrier by the control unit 280 in accordance with the urgency level of handover determined by the determination unit 270. Also, the measurement gap allocation pattern is controlled according to the quality level of each component carrier. Then, in the terminal device 100, the measurement for handover is performed using the measurement gap allocated by the base station 200. Accordingly, it is possible to suppress a decrease in throughput or a delay in handover processing due to an increase in a measurement gap in wireless communication involving carrier aggregation.

  Further, according to the present embodiment, not only for handover but also when changing or adding a component carrier, the measurement gap allocation pattern can be controlled for each component carrier according to the quality level of each component carrier. Thereby, it is possible to suppress a decrease in throughput and a processing delay due to the change or addition of the component carrier.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Wireless communication system 100 Terminal device 110 Wireless communication part 160 Control part 170 Measurement part 200 Base station 210 Wireless communication part 270 Determination part 280 Control part

Claims (24)

A wireless communication unit that performs wireless communication with a terminal device on a communication channel formed by integrating a plurality of component carriers;
A control unit for controlling allocation of measurement gaps for the terminal device for each component carrier;
With
The controller assigns a measurement gap to more component carriers as the channel quality of the communication channel is lower.
Communication control device.   The communication control according to claim 1, further comprising: a quality acquisition unit that acquires the channel quality of the communication channel based on a reception signal received from the terminal device by the wireless communication unit. apparatus. The communication control device further includes a quality acquisition unit that acquires the channel quality for each component carrier based on a reception signal received from the terminal device by the wireless communication unit,
The control unit preferentially allocates a measurement gap to a component carrier having a low channel quality;
The communication control apparatus according to claim 1 or 2. The communication control device further includes a quality acquisition unit that acquires the channel quality for each component carrier based on a reception signal received from the terminal device by the wireless communication unit,
When assigning a measurement gap to two or more component carriers, the control unit sets a period of the measurement gap to be assigned to the first component carrier to a second component carrier having a channel quality lower than that of the first component carrier. Longer than the measurement gap period assigned to
The communication control apparatus according to claim 1.   When assigning measurement gaps to two or more component carriers, the control unit sets the measurement gaps to the two or more component carriers so that the timing of one measurement gap does not coincide with the timing of other measurement gaps. The communication control device according to claim 1, wherein assignment is determined.   The control unit allocates a measurement gap so that the number of component carriers to which a measurement gap is allocated does not exceed the number of component carriers that can be used for measurement notified from the terminal device via the wireless communication unit. The communication control device according to claim 1, which controls the communication control device. A wireless communication unit that performs wireless communication with a base station on a communication channel formed by integrating a plurality of component carriers;
A measurement unit that performs a measurement for handover using a measurement gap assigned to each component carrier according to the channel quality of the communication channel;
With
The measurement gap is allocated to more component carriers as the channel quality of the communication channel is lower.
Terminal device.   The terminal device according to claim 7, wherein the channel quality of the communication channel is determined based on a transmission signal transmitted to the base station by the wireless communication unit. The channel quality is determined for each component carrier,
The measurement gap is preferentially assigned to the component carrier with low channel quality.
The terminal device according to claim 7 or 8. The channel quality is determined for each component carrier,
When the measurement gap is allocated to two or more component carriers, the period of the measurement gap allocated to the first component carrier is allocated to the second component carrier having a channel quality lower than that of the first component carrier. Longer than the measurement gap period,
The terminal device according to claim 7.   When the measurement gap is allocated to two or more component carriers, the allocation of the measurement gap to the two or more component carriers is such that the timing of one measurement gap does not coincide with the timing of another measurement gap. The terminal device according to claim 7, wherein   The number of component carriers to which the measurement gap is allocated is controlled so as not to exceed the number of component carriers that can be used for measurement notified to the base station via the wireless communication unit. The terminal device described. A communication control method for controlling wireless communication between a terminal device and a base station on a communication channel formed by integrating a plurality of component carriers,
Allocating a measurement gap for each component carrier for the terminal device in the base station;
Including
The measurement gap is allocated to more component carriers as the channel quality of the communication channel is lower.
Communication control method.   The communication control method according to claim 13, wherein the base station determines the channel quality of the communication channel based on a reception signal received from the terminal device.   The base station acquires the channel quality for each component carrier based on a received signal received from the terminal device, and preferentially allocates a measurement gap to the component carrier having the low channel quality. Item 15. The communication control method according to Item 14.   The base station acquires the channel quality for each component carrier based on a received signal received from the terminal device, and assigns a measurement gap to two or more component carriers and assigns it to a first component carrier The communication control method according to claim 13, wherein a measurement gap period is set longer than a measurement gap period allocated to a second component carrier having a channel quality lower than that of the first component carrier.   When the base station allocates measurement gaps to two or more component carriers, the base station sets the measurement gaps to the two or more component carriers so that the timing of one measurement gap does not coincide with the timing of other measurement gaps. The communication control method according to claim 13, wherein allocation is determined.   The base station controls allocation of measurement gaps such that the number of component carriers to which a measurement gap is allocated does not exceed the number of component carriers that can be used for measurement notified from the terminal device. The communication control method described. A wireless communication unit that performs wireless communication with a terminal device on a communication channel formed by integrating a plurality of component carriers;
When adding or changing a component carrier used by the terminal device, a control unit that causes the terminal device to use more component carriers for measurement as the channel quality of the communication channel is lower;
A communication control device comprising:   The communication control device according to claim 19, wherein the control unit preferentially allocates a measurement gap to the component carrier having a low channel quality. A wireless communication unit that performs wireless communication with a base station on a communication channel formed by integrating a plurality of component carriers;
When adding or changing a component carrier used by the wireless communication unit, a control unit that performs measurement using more component carriers as the channel quality of the communication channel is lower,
A terminal device comprising:   The terminal device according to claim 21, wherein a measurement gap is preferentially assigned to the component carrier having a low channel quality. A communication control method for controlling wireless communication between a terminal device and a base station on a communication channel formed by integrating a plurality of component carriers,
In the base station, when adding or changing a component carrier used by the terminal device, the lower the channel quality of the communication channel, the more the component carrier is used by the terminal device for measurement,
Including a communication control method. The communication control method according to claim 23, wherein the base station preferentially allocates a measurement gap to the component carrier having a low channel quality.

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