Base station, wireless terminal, communication method, and program for performing efficient cell search

Abstract

To allow a terminal to efficiently perform a cell search in a mobile communication system.SOLUTION: A base station communicates with a wireless terminal based on the cellular communication standard of the Third Generation Partnership Project (3GPP). The base station sets one or more measurement gaps (MGs) for measuring signals of other base stations in one or more second frequency bands different from a first frequency band used for the communication, and transmits a measurement instruction including designation information designating whether measurement should be performed and, if measurement should be performed, which of the second frequency bands to measure to the wireless terminal in each MG.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a technique for performing cell search in a mobile communication system.

Background Art

[0002] In a mobile communication system compliant with the cellular communication standard of the 3rd Generation Partnership Project (3GPP (registered trademark)), in order for a terminal (also called User Equipment, UE) to identify a cell to which it can connect, search and measurement (cell search) of neighboring cells are performed. A terminal connected to a base station such as a gNB (next Generation Node B) or an eNB (evolved Node B) performs cell search during a set Measurement Gap (MG) period and reports the measurement results to the base station. Non-Patent Documents 1 and 2 define the definition of MG set for a terminal.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The base stations defined in Non-Patent Documents 1 and 2 set a period (MG) for a terminal to measure using MGL (MG Length) and MGRP (MG Repetition Periodicity). However, it is not clear how the terminal uses the MG for measurement. Therefore, depending on the measurement method executed by the terminal, the time until cell search is completed may vary significantly, and as a result, problems such as throughput degradation and inability to perform handover within a predetermined period may occur. The present invention provides a technique for efficiently performing cell search in a mobile communication system.

Means for Solving the Problems

[0005] A base station according to an aspect of the present invention is a base station that communicates with a wireless terminal based on the cellular communication standard of the 3rd Generation Partnership Project (3GPP), and in one or more second frequency bands different from the first frequency band used for the communication, setting means for setting one or more Measurement GAPs (MGs) for measuring signals of other base stations, and in each of the MGs, a measurement instruction including designation information for designating whether to perform the measurement and, if the measurement is to be performed, which of the second frequency bands to measure, and transmitting means for transmitting the measurement instruction to the wireless terminal.

[0006] A wireless terminal according to an aspect of the present invention is a wireless terminal that communicates with a base station based on the cellular communication standard of the 3rd Generation Partnership Project (3GPP), and in one or more second frequency bands different from the first frequency band used for the communication, receiving means for receiving a setting of one or more Measurement GAPs (MGs) for measuring signals of other base stations and a measurement instruction including designation information for designating whether to perform the measurement and, if the measurement is to be performed, which of the second frequency bands to measure from the base station, and in each of the MGs, measurement means for executing the measurement of the second frequency band designated by the designation information.

Advantages of the Invention

[0007] According to the present invention, in a mobile communication system, a terminal can efficiently perform cell search.

Brief Description of the Drawings

[0008]

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Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of the features described in the embodiments are essential to the invention. Two or more of the features described in the embodiments may be arbitrarily combined. Also, the same or similar configurations are denoted by the same reference numerals, and redundant descriptions are omitted.

[0010] (System Configuration) FIG. 1 shows a configuration example of a mobile communication system according to the present embodiment. The mobile communication system of the present embodiment is, for example, a cellular communication system compliant with the cellular communication standard of the 3rd Generation Partnership Project (3GPP (registered trademark)). However, it is not limited thereto, and the following discussion can be applied to a mobile communication system compliant with any wireless communication standard. This mobile communication system includes, for example, a terminal 101, a first base station 111, a second base station 112, and a third base station 113. The first base station 111, the second base station 112, and the third base station 113 may be collectively referred to as the base station 110. The base station 110 exchanges wireless signals with the terminal 101 via a wireless medium. The base station 110 includes, for example, a gNB (next Generation Node B), an eNB (evolved Node B), etc. Each of the base stations 110 is connected to a core network (not shown). The core network may be, for example, an Evolved Packet System (EPS) or a 5G Core Network (5GC). The terminal 101 is a terminal used by a user and exchanges wireless signals with the base station 110 via a wireless medium. The terminal 101 may be called a User Equipment (UE). The terminal 101 includes, for example, a smartphone, a mobile phone, a personal computer, a tablet terminal, a wearable terminal, an IoT (Internet of Things) terminal, etc. The terminal 101 may be called a wireless terminal. The base station 110 and the terminal 101 can communicate using wireless signals in frequency bands such as the 3.7 GHz band, 4.5 GHz band, 28 GHz band, etc. Also, the base station 110 and the terminal 101 can communicate using wireless signals in frequency bands such as the 700 MHz band, 800 MHz band, 900 MHz band, 1.5 GHz band, 1.7 GHz band, 2 GHz band, 2.5 GHz band, 3.4 GHz band, 3.5 GHz band, etc. Further, the base station 110 and the terminal 101 can communicate using wireless signals such as the 2.6 GHz band, 4.9 GHz band, 26 GHz band, 40 GHz band, etc. For example, in FIG. 1, it is assumed that the first base station 111 and the terminal 101 are communicating using a wireless signal in the 2.6 GHz band.Also, it is assumed that the second base station 112 and the third base station 113 can communicate with the terminal 101 using radio signals in the 800 MHz band and the 2 GHz band, respectively. That is, it is assumed that the first base station 111 and the terminal 101 are in a connected state, or an RRC (Radio Resource Control)_Connected state, and that the second base station 112 and the third base station 113 and the terminal 101 are not in a connected state, or are in an RRC_Idle state (or an RRC_Inactive state).

[0011] While the terminal 101 is communicating with the first base station 111, it can perform cell search based on the notification from the first base station 111. Cell search means that the terminal 101 searches for a cell to which it can connect. A cell is, for example, a range within which communication is possible with the base station 110 that provides this cell. As an example, when the terminal 101 and the first base station 111 are in the RRC_Connected state, cell search can be performed as follows. First, the first base station 111 notifies the terminal 101 to perform measurements of received signals from each base station 110 including its own device. For example, the first base station 111 can use an RRC Connection Reconfiguration message to notify the terminal 101 of measurement settings for performing measurements. The measurement configuration can include a measurement object and a report configuration. Also, measurement identities can be set for combinations of the measurement object and the report configuration. Further, the measurement configuration may include an MG (Measurement Gap) etc. indicating a period during which data transmission and reception are not performed for measurement. The measurement object includes the carrier frequency that the terminal 101 should measure and the bandwidth to be measured. Also, the report configuration can be used to notify the terminal 101 of the type of trigger for a measurement report, the parameters used for the trigger, the reporting period, the number of reports, etc. For example, when a trigger for a measurement report occurs (for example, the conditions for reporting are satisfied) in the terminal 101, the first base station 111 can receive a measurement report from the terminal 101. The triggers for a measurement report can include periodic triggers and event triggers.

[0012] When the terminal 101 receives a measurement setting from the base station 110, it executes cell search according to the measurement setting. For example, the terminal 101 identifies the carrier frequency and bandwidth to be measured from the measurement targets included in the acquired measurement setting (i.e., identifies the frequency band), and attempts to detect signals in that frequency band. For example, the terminal 101 detects the synchronization signal included in the radio frame transmitted by the base station 110 in the frequency band of the measurement target. The synchronization signal (which may also be called Synchronization Signal, SS) may be composed of a Primary SS (PSS) and a Secondary SS (SSS). The terminal 101 can perform symbol timing synchronization and Local ID detection using the PSS, and perform radio frame synchronization and cell group ID detection using the SSS. The terminal 101 can obtain the physical ID (PCI) of the cell by combining these pieces of information. Also, the terminal 101 can measure the received power of the cell (which may also be called Reference Signal Receive Power, RSRP), the received quality (which may also be called Reference Signal Receive Quality, RSRQ), etc. based on the received SSS. The terminal 101 can transmit a measurement report including PCI, RSRP, RSRQ, etc. to the first base station 111. Note that the terminal 101 can perform a measurement report to the first base station 111 when the trigger indicated in the acquired report setting occurs. For example, the event type trigger indicated by the report setting may include that the RSRP of an adjacent cell is greater than the value obtained by adding a predetermined value to the RSRP of the serving cell (also called event A3), or that the RSRP of the serving cell is lower than a predetermined threshold and the RSRP of an adjacent cell is higher than the threshold (also called event A5), etc.

[0013] Synchronization signals can be transmitted at different periods in each cell. For example, the base station 110 corresponding to Long Term Evolution (LTE) can transmit synchronization signals at a period of 5 ms (milliseconds). Also, the base station 110 corresponding to 5G New Radio (NR) can transmit synchronization signals at any one of the periods of 5 ms, 10 ms, 20 ms, 40 ms, 80 ms, or 160 ms. On the other hand, the terminal 101 performs measurements during the period of the MG included in the measurement settings notified by the first base station 111 and attempts to detect synchronization signals transmitted from other base stations 110. The MG is a parameter composed of an MG Length (MGL) and an MG Repetition Periodicity (MGRP). For example, the MGL notified by the base station 110 corresponding to LTE can be selected from among 3 ms, 4 ms, and 6 ms. Also, the MGL notified by the base station 110 corresponding to NR can be selected from among 1.5 ms, 3 ms, 3.5 ms, 4 ms, 5.5 ms, and 6 ms. On the other hand, the MGRP notified by the base station 110 corresponding to LTE or the base station 110 corresponding to NR can be selected from among 20 ms, 40 ms, 80 ms, or 160 ms.

[0014] As described above, the first base station 111 can execute cell search in order to connect the terminal 101 communicating with the own device to a more suitable cell. For example, the first base station 111 can recognize, by receiving a measurement report from the terminal 101, that there is a cell more suitable for the terminal 101 than the one provided by the own device. Therefore, when the first base station 111 finds that the trigger notified to the terminal 101 in the reporting setting has occurred, the first base station 111 can cause the terminal 101 to perform a handover to the base station that caused the trigger (for example, the second base station 112 or the third base station 113). Also, when there are certain usage restrictions on the frequency band used for communication with the terminal 101, the first base station 111 can cause the terminal 101 to perform a handover to another base station based on the restrictions. For example, in FIG. 1, the 2.6 GHz band used by the first base station 111 for communication with the terminal 101 is available for a system that performs data transmission in Japan. That is, there is a usage restriction that voice traffic cannot be communicated using this 2.6 GHz band. For this reason, when the first base station 111 detects that voice traffic has occurred in communication with the terminal 101, the first base station 111 can cause the terminal 101 to perform a handover to a cell using another frequency band (for example, the second base station 112 or the third base station 113) so that voice traffic is not communicated in the 2.6 GHz band. Note that the reasons for the first base station 111 to cause the terminal 101 to perform a handover to another base station are not limited to these. For example, when the first base station 111 finds that it cannot meet the quality requirements for traffic with certain quality requirements, the first base station 111 may cause the terminal 101 to perform a handover to another base station. Here, in the current cellular communication standard of 3GPP, the first base station 111 can set the MG for the terminal 101 to perform measurements and set the conditions to be satisfied for reporting the measurement results, but cannot instruct how the terminal 101 performs measurements for each frequency band. Therefore, depending on the cell search method for each terminal 101, the time required until the completion of the cell search may vary greatly.As a result, if the terminal 101 uses a large number of MGs before completing cell search, the throughput of the terminal 101 may decrease. This is because the terminal 101 cannot communicate data during the MG period. Also, when communicating using the 2.6 GHz band, if a handover cannot be executed until voice traffic exchange starts, voice traffic may be communicated in the 2.6 GHz band, and thus it may not be possible to comply with the usage restrictions of this frequency band.

[0015] In view of such circumstances, the first base station 111 in the present embodiment sets an MG for the terminal 101 to perform measurements, and in each of the set MGs, issues an instruction (measurement instruction) including information (designation information) specifying whether to perform measurements and which frequency band to measure when performing measurements, to the terminal 101. Then, when the terminal 101 receives the measurement instruction from the first base station 111, it performs measurements on each frequency band based on the measurement instruction. Thereby, the terminal 101 can efficiently execute cell search. For example, the first base station 111 may be able to utilize information on measurement reports of past cell searches by other terminals connected to its own device, and cell arrangement information of base stations possessed by a base station management system (not shown). In this case, the first base station 111 can perform measurement settings so as to preferentially perform cell search on frequency bands where cells are likely to be detected based on such information, and notify the terminal 101 as a measurement instruction. As an example, the first base station 111 can determine the frequency band to be preferentially measured based on information on neighboring cells (such as the frequency used, RSRP, RSRQ, etc.) that have been detected and reported by other terminals connected to its own device in the past, and generate measurement settings. Also, the first base station 111 can generate measurement settings so as to preferentially measure the frequency band used by a base station located geographically close to its own device based on the cell arrangement information managed in a base station management system such as an Element Management System (EMS). Thus, by the first base station 111 issuing a measurement instruction to the terminal 101, an efficient cell search independent of the unique implementation of the terminal 101 becomes possible.

[0016] Also, the first base station 111 can cause the terminal 101 to continuously execute multiple measurements for one frequency band. For example, if the distance between the base station 110 to be measured and the terminal 101 is large, the possibility that the terminal 101 fails to detect the synchronization signal in cell search increases. In this case, by increasing the number of measurement times, the possibility of detecting the signal can be increased. Therefore, the first base station 111 can perform measurement settings such that the higher the priority frequency band, the larger the number of consecutive measurements. Also, by continuously measuring the frequencies with high priority, if a cell is detected promptly, cell search can be completed in a short period. Furthermore, the first base station 111 can set a shorter measurement period for the higher priority frequency bands. By setting a shorter measurement period, a cell can be detected promptly. The frequency band to be measured, the priority level (the order in which it should be preferentially measured) set for each frequency band, the number of consecutive measurements for each frequency band, the measurement period (measurement interval) of each frequency band, etc. can be included in the measurement instruction as specified information. Note that the specified information may include information other than these.

[0017] Further, the first base station 111 can determine whether to issue a measurement instruction according to the type of traffic communicated with the terminal 101. For example, assume that the first base station 111 detects that voice traffic occurs in the communication with the terminal 101. As an example, when the terminal 101 establishes a session for voice communication, a SIP (Session Initiation Protocol) Invite signal is transmitted to the network via the first base station 111. In response, a request for creating a bearer for transmitting the voice traffic or a request for establishing a QoS flow for setting the bearer is notified from the network side to the first base station 111. The first base station 111 can detect that voice traffic occurs in the communication with the terminal 101 by detecting these requests from the network side. At this time, when the frequency band used in the communication between the first base station 111 and the terminal 101 is a frequency band in which voice traffic cannot be communicated, in order to cause the terminal 101 to perform a handover to a cell using another frequency band, it is necessary to quickly identify the next base station 110 to be the connection destination. In this case, for example, the first base station 111 can determine to select the frequency band in which the terminal 101 should perform cell search and issue an instruction for setting a priority for each frequency band. As an example, as the frequency bands in which the terminal 101 should perform cell search, there are two bands of 800 MHz and 2 GHz, and if the 800 MHz band is more suitable for transmitting voice traffic because it has advantages such as a wider coverage than the 2 GHz band, a high priority can be set for the 800 MHz band. In this way, by the first base station 111 issuing a measurement instruction only when it is necessary to quickly complete cell search according to the type of traffic, the processing load for the first base station 111 to generate a measurement instruction every time cell search is performed and the communication traffic generated therefor can be reduced.

[0018] An example of an operation for controlling cell search of a terminal will be described in which the first base station 111 notifies the terminal 101 of a measurement instruction including specified information. For example, the first base station 111 can notify the terminal 101 of the specified information using a predetermined IE (e.g., a measurement configuration (measConfig) IE). Note that IE is an abbreviation for Information Element. FIG. 2 shows an example of a sequence when the first base station 111 gives a measurement instruction to the terminal 101. For example, the first base station 111 transmits a measurement instruction including a measurement configuration IE to the terminal 101 using an RRC Connection Reconfiguration message (S201). The measurement configuration IE can include the above-described specified information. For example, the measurement configuration IE includes one or more measurement objects (measObject), and each measurement object can include a frequency band (carrierFreq), a priority, a measurement period or measurement interval (periodicity), a measurement count (contdMeas), and the like. Also, a measurement object identifier (measObjectId) can be set for each measurement object. The frequency band indicates the frequency band to be measured. The information indicating the frequency band can be, for example, an earfcnDl. EarfcnDl is an abbreviation for E-UTRAN absolute radio-frequency channel number. E-UTRAN is an abbreviation for Evolved Universal Terrestrial Radio Access Network. The information indicating the frequency band can be other information, for example, a combination of the center frequency and the bandwidth of the frequency band. The priority indicates the degree to which this measurement object should be preferentially measured. In FIG. 2, priorities can be assigned to each measurement object such that the higher the value of the priority, the higher the priority order to be measured. Note that priorities can be assigned to each measurement object such that the lower the value of the priority, the higher the priority order to be measured. The measurement period (or measurement interval) indicates the temporal interval at which the measurement is performed. For example, the unit of the measurement period (or measurement interval) can be ms (milliseconds). Note that the unit of the measurement period (or measurement interval) can be a radio frame (e.g., 10 ms) or the like, as long as it is information that can specify the timing at which the terminal 101 should perform the measurement.The number of measurements indicates the number of times the measurement target should be continuously measured. In Figure 2, for measurement target 1 with measurement target identifier 1 (measObjectId 1) set, the frequency band is the 2 GHz band (earfcnDl is 100), the priority is 1 (low priority), the measurement interval is 40 ms, and the number of measurements is set to 2 times. Also, for measurement target 2 with measurement target identifier 2 (measObjectId 2) set, the frequency band is the 800 MHz band (earfcnDl is 5900), the priority is 2 (high priority), the measurement interval is 40 ms, and the number of measurements is set to 3 times. Note that the measurement interval can be set based on the MG defined in the 3GPP cellular communication standard. For example, as the measurement interval, values such as 20 ms, 40 ms, 80 ms, 160 ms, etc., which are defined as possible values of MGRP, can be specified. Note that the specified information may include the measurement period of each measurement. As the measurement period, values such as 1.5 ms, 3 ms, 3.5 ms, 4 ms, 5.5 ms, 6 ms, etc., which are defined as possible values of MGL in the 3GPP cellular communication standard, can be specified. Note that values other than these parameters can be specified as the measurement interval or measurement period. Also, the expression methods of these parameters are not limited to the above, and any method that can specify the priority, measurement period or interval, number of measurements, etc. of each measurement target is acceptable. Also, the information included in the measurement target may be a part of these, or other information may be included.

[0019] When the terminal 101 receives a measurement instruction including specified information from the first base station 111, it determines whether to accept the measurement instruction, and if it accepts, it transmits a response (S202). The response can be, for example, an RRC Connection Reconfiguration Complete message. When accepting the measurement instruction, the terminal 101 executes measurements according to the received specified information. FIG. 3 shows an example of the flow of measurements executed by the terminal 101. When the terminal 101 acquires the specified information (S301), it selects the measurement target with the highest priority among the measurement targets included in the specified information (S302). For example, the terminal 101 selects measurement target 2 with a priority set to 2. As a result, 800 MHz is selected as the frequency band to be measured first. Then, the terminal 101 determines whether to execute measurements for each MG (S303). For example, when the terminal 101 executes the first measurement in the most recent MG, it determines whether to execute the second measurement in the next MG based on whether this MG matches the measurement timing based on the measurement interval of measurement target 2. For example, when the measurement period is set to 40 ms, if the next MG after the MG used for the first measurement is set 40 ms after the MG used for the first measurement, the terminal 101 determines to execute the measurement (YES in S304). On the other hand, for example, when the next MG after the MG used for the first measurement is set 20 ms after the MG used for the first measurement, the terminal 101 determines not to execute the measurement (NO in S304). When the terminal 101 performs a measurement, it can acquire the cell identifier (Physical Cell Identifier, PCI) and RSRP and RSRQ based on the signal detected during the measurement. Also, when a measurement report trigger occurs due to the measurement, the terminal 101 can execute a measurement report to the first base station 111. The terminal 101 may complete the measurement assuming that the measurement instruction has been completed by performing the measurement report. Each time the terminal 101 executes a measurement, it determines whether it has executed the set number of measurements for the measurement target (S305).For example, when the number of measurements is set to three, if the terminal 101 performs three consecutive measurements in the 800 MHz frequency band (YES in S305), it determines whether there is another frequency band to be measured (S306). On the other hand, if the number of consecutive measurements in the 800 MHz frequency band is less than three (NO in S305), it returns to S303 to continue the measurement. When a series of measurements for measurement target 2 is completed, the terminal 101 then selects the measurement target 1 with a higher priority (i.e., the 2 GHz band) (S307) and performs the measurement (YES in S306). Then, when the measurement of measurement target 1 is completed, since the series of measurements shown in the measurement settings is completed (NO in S306), the terminal 101 returns to S302 to continue the measurement.

[0020] Figure 4 is an example of a time chart when the terminal 101 executes measurement. Figure 4 shows an example of the case where the terminal 101 performs measurement based on the measurement instruction included in the RRC connection Reconfiguration shown in Figure 2. The vertical axis of Figure 4 indicates the passage of time in units of radio frames (10 ms). Note that SFN is an abbreviation of System Frame Number. That is, the numbers 0 to 20 on the vertical axis indicate the serial numbers assigned to each radio frame. The horizontal axis of Figure 4 indicates the passage of time within one radio frame. One radio frame is composed of 10 subframes each with a length of 1 ms, and one subframe is composed of 2 slots each with a length of 0.5 ms. In Figure 4, the synchronization signal (PS) is transmitted in the 0th slot and the 10th slot of each radio frame. That is, the synchronization signal is periodically transmitted every 5 ms. Here, assume that as the MG setting in the measurement setting, MGRP = 40 ms and MGL = 6 ms are set. The terminal 101 starts the first measurement using the 6-ms-long MG set from the 2nd slot to the 7th slot of the 0th radio frame. Here, the terminal 101 executes measurement in the 800 MHz band, which is the frequency band specified by the relatively high-priority measurement target 2. The terminal 101 can detect the synchronization signal transmitted in the 10th slot during the first measurement. Then, according to the measurement interval (40 ms) and the number of measurements (3 times) specified by the measurement target 2, the terminal 101 uses the two MGs set 40 ms after (radio frame with SFN = 4) and 80 ms after (radio frame with SFN = 8) the first measurement to execute the second and third measurements. When the measurement for the measurement target 2 is completed by these three measurements, the terminal 101 executes the measurement for the measurement target 1. That is, the terminal 101 executes measurement in the 2 GHz band using the MGs set 40 ms after the third measurement and 40 ms after that (radio frames with SFN = 12 and 16). When the measurement for the measurement target 1 is completed by these two measurements, the series of measurements indicated by the measurement instruction is completed. The terminal 101 returns to the measurement of the measurement target 2 and continues the measurement.

[0021] FIG. 5 shows an example of a time chart when the measurement interval specified for measurement target 1 in the measurement instruction included in the RRC connection Reconfiguration shown in FIG. 2 is 80 ms. The difference from FIG. 4 is that measurement is not performed in the MG set in the radio frame with SFN = 16. First, the terminal 101 executes the measurement of the 800 MHz band indicated by measurement target 2 three times at a measurement interval of 40 ms. Then, the terminal 101 executes the measurement of the 2 GHz band indicated by measurement target 1 two times at a measurement interval of 80 ms. That is, the terminal 101 executes the measurement in the MG in the radio frame with SFN = 20 set 80 ms after the fourth measurement as the next measurement after the fourth measurement. As a result, the measurement in the MG in the radio frame with SFN = 16 arranged 40 ms after the fourth measurement is not executed. In this way, the terminal 101 can determine whether to execute the measurement in each MG based on the measurement period indicated in the measurement setting and the period in which the MG is arranged.

[0022] In addition, the first base station 111 can perform resource allocation for transmitting and receiving data and the like to the terminal 101 during the MG period in which it is known in advance that the terminal 101 does not perform measurements. That is, the first base station 111 can release the setting of the period for the MG in which measurements are not performed. In order for the first base station 111 to recognize the MG in which measurements by the terminal 101 are not performed, the MG in which the terminal 101 starts measurements may be shared between the first base station 111 and the terminal 101. For example, in addition to the above-described specified information, the first base station 111 notifies the terminal 101 of measurement settings including the SFN of the radio frame in which the MG for starting measurements is set. For example, in the time chart of FIG. 5, the radio frame in which the MG for starting measurements is set is the 0th radio frame. By notifying the radio frame for starting measurements using the designation of this SFN, the first base station 111 can recognize whether the terminal 101 is performing measurements in each MG and which frequency band is being measured. Also, for example, the terminal 101 can recognize that data and the like can be transmitted and received during the period when measurements are not performed by the inclusion of the notification of the SFN of the radio frame in which the MG for starting measurements is set in the specified information. By releasing the setting of the MG in which measurements by the terminal 101 are not performed, the throughput of the terminal 101 can be improved.

[0023] The method by which the first base station 111 specifies whether or not to execute measurements in each MG for the terminal 101 and which frequency band to measure when executing measurements is not limited to the above. For example, a bitmap specifying the frequency band to be measured for each MG may be used. As an example, the first base station 111 assigns an identifier to each of the frequency bands to be measured. For example, the first base station 111 assigns identifiers 1, 2, and 3 to the 800 MHz band, 2 GHz band, and 2.6 GHz band, respectively. Then, the first base station 111 associates each MG with the frequency band to be measured. For example, taking FIG. 4 as an example, assuming the MGs are in order of earlier time (MG1, MG2, ···, MG5, MG6), the frequency bands to be measured in each MG are expressed as (1, 1, 1, 2, 2). Here, since a series of measurements are completed by 5 MGs, the number of elements constituting the bitmap is 5. Also, taking FIG. 5 as an example, the frequency bands to be measured in each MG are expressed as (1, 1, 1, 2, 0, 2). Here, since a series of measurements are completed by 6 MGs including an MG that does not perform measurement (expressed as 0), the number of elements constituting the bitmap is 6. For example, the first base station 111 may transmit this bitmap to the terminal 101 instead of the specified information in measConfig in FIG. 2. The terminal 101 may execute cell search while changing the frequency band to be measured according to this bitmap.

[0024] In addition, the first base station 111 can update the measurement settings for the terminal 101 based on the measurement results received from the terminal 101. For example, the first base station 111 transmits a measurement instruction including a reporting setting including a periodic trigger to the terminal 101, and the terminal 101 can periodically transmit a measurement report to the first base station 111 based on the reporting period included in the reporting setting. When there is a measurement target for which a cell is not detected in the measurement report, the first base station 111 can change the designation information of the measurement target. For example, the first base station 111 can update the designation information of the measurement target by any one or a combination of the following: setting the priority of the measurement target to be low, setting the measurement period or measurement interval to be long, or setting the number of measurements to be small. Note that the first base station 111 may change the settings of other measurement targets in order to achieve the same effect. That is, the designation information of the measurement target can be updated by any one or a combination of the following: setting the priority of other measurement targets to be high, setting the measurement period or measurement interval to be short, or setting the number of measurements to be large. The first base station 111 can notify the terminal 101 of the updated designation information. For example, the first base station 111 can notify the terminal 101 of the updated designation information using the measurement setting IE included in the RRC connection Reconfiguration. When the terminal 101 receives the RRC connection Reconfiguration including the measurement setting IE, the terminal 101 can perform measurements using the received measurement setting IE. By the first base station 111 updating the measurement settings based on the measurement report received from the terminal 101, it is possible to reduce the time required for measurements in a frequency band where there is no cell or the cell cannot be detected. As a result, it becomes possible to complete cell search earlier.

[0025] The method by which the first base station 111 updates the measurement settings is not limited to the above. For example, the base station 111 may update the measurement settings based on a measurement setting change request received from the terminal 101. For example, the terminal 101 may transmit a measurement setting change request using a UE Assistance Information message. As an example, the base station 111 may receive from the terminal 101 a request (measurement setting release request) indicating that measurements for one or more of a plurality of measurement targets should be released or terminated. Also, as an example, the base station 111 may receive from the terminal 101 a request (for example, a request indicating that the number of times should be reduced (number reduction request) or a request indicating that the measurement period should be extended (period extension request), etc.) indicating that the measurement frequency for one or more of a plurality of measurement targets should be reduced.

[0026] FIG. 6 shows an example of a sequence for causing the first base station 111 to cause the terminal 101 to perform a measurement release request (or a request for reducing the number of times, extending the period, etc., which may be collectively referred to as a request hereinafter). For example, the first base station 111 transmits a measurement instruction including a measurement setting IE to the terminal 101 using an RRC Connection Reconfiguration message (S601). The measurement setting IE may include conditions for transmitting a request in addition to the specified information shown in FIG. 2, for example. For example, the condition for transmitting a request is the number of consecutive measurement failures (outOfCovNum). In the present embodiment, the number of consecutive measurement failures (measurement failure count) is used as an example of the condition for transmitting a request, but the condition for transmitting a request may be other conditions, and may be a condition that can determine that a cell cannot be detected in the frequency band of the measurement target. In the example of FIG. 6, when the terminal 101 fails to detect a cell continuously five times in the measurement of measurement target 1, the terminal 101 transmits a request to the first base station 111. On the other hand, for measurement target 2, since infinity is set as the threshold value of the measurement failure count, the terminal 101 does not transmit a request regardless of the measurement failure count. Note that 0 or the maximum value that can be set using this IE may be set as another threshold value of the measurement failure count when it is not desired to cause the terminal 101 to transmit a request. When the terminal 101 receives a measurement instruction including specified information from the first base station 111, the terminal 101 determines whether to accept the measurement instruction, and if it accepts, transmits a response (S602).

[0027] FIG. 7 shows an example of a sequence when the terminal 101 transmits a measurement release request. For example, when the terminal 101 satisfies a condition (e.g., the number of measurement failures reaches a threshold, etc.) to be notified, which is included in the measurement instruction received from the first base station 111 (S701), the terminal 101 notifies the first base station 111 of a measurement release request (S702). As an example, the terminal 101 may notify the first base station 111 of a measurement release request by transmitting a UE Assistance Information message including a measurement release request (MeasConfigRel) IE. The measurement release request may include a measurement object identifier of the measurement object for which the measurement should be terminated (measurement object 1 in FIG. 7). When receiving the measurement release request, the first base station 111 updates the measurement setting (S703). For example, the first base station 111 determines that the measurement of measurement object 1 (i.e., the frequency band of 2 GHz) should be terminated, and deletes measurement object 1 from the measurement setting. The first base station 111 notifies the terminal 101 of the updated measurement setting (S704). In FIG. 7, the measurement setting notified by the first base station 111 in S704 includes only one measurement object, and the value of the measurement object identifier set for this measurement object has been incremented to 1. The terminal 101 performs measurements based on this measurement setting. Note that the first base station 111 may further update the measurement setting to add a measurement of the 2 GHz band as a measurement object after a certain time has elapsed since the transmission of the updated measurement setting, and notify this measurement setting to the terminal 101. For example, when the positional relationship between the terminal 101 and the third base station 113 that communicates using a signal in the 2 GHz band changes due to the movement of the terminal 101, the terminal 101 may be able to receive a signal in the 2 GHz band. Therefore, the first base station 111 may add a measurement object that has been deleted once to the measurement setting according to the passage of time.

[0028] FIG. 8 shows an example of a sequence when the terminal 101 transmits a reduction request. For example, when the terminal 101 satisfies the condition to be notified of the request included in the measurement instruction received from the first base station 111 (S801), the terminal 101 notifies the first base station 111 of the reduction request (S802). As an example, the terminal 101 may notify the first base station 111 of the reduction request by transmitting a UE Assistance Information message including a ReduceContdMeas IE. The reduction request may include a measurement object identifier of the measurement object for which the number of measurements should be reduced (measurement object 1 in FIG. 8). When the first base station 111 receives the reduction request, it updates the measurement setting (S803). For example, the first base station 111 changes the number of measurements of measurement object 1 from 3 to 2. Note that the number by which the number of measurements is reduced may be determined by the first base station 111 or requested by the terminal 101. When the first base station 111 determines, the first base station 111 may reduce the number one by one. Also, when requested by the terminal 101, the terminal 101 may notify the number of measurements to be requested and the number to be reduced using the UE Assistance Information message. Then, the first base station 111 notifies the terminal 101 of the updated measurement setting (S804). In FIG. 8, in the measurement setting notified by the first base station 111, the value of contdMeas of measurement object 1 is changed to 2. The terminal 101 performs measurements based on this measurement setting.

[0029] Figure 9 shows an example of a sequence when the terminal 101 transmits a periodic extension request. For example, when the terminal 101 satisfies the condition to be notified of the request included in the measurement instruction received from the first base station 111 (S901), it notifies the first base station 111 of the periodic extension request (S902). As an example, the terminal 101 may notify the first base station 111 of the periodic extension request by transmitting a UE Assistance Information message including an IncreasePeriodicityMeas IE. The IncreasePeriodicityMeas IE may have other names. For example, it may be a ReduceFrequency IE. The periodic extension request may include a measurement object identifier of the measurement object for which the measurement period (or measurement interval) should be extended (measurement object 1 in Figure 9). When the first base station 111 receives the periodic extension request, it updates the measurement setting (S903). For example, the first base station 111 changes the measurement period of measurement object 1 from 40 to 80. The first base station 111 notifies the terminal 101 of the updated measurement setting (S904). In Figure 9, in the measurement setting notified by the first base station 111, the value of periodicity of measurement object 1 is changed to 80. The terminal 101 performs measurements based on this measurement setting. Note that the terminal 101 may notify the first base station 111 of both the count reduction request and the periodic extension request at once. In this case, the first base station 111 may update both periodicity and contdMeas simultaneously. Also, in the above, as an example of the condition for transmitting a request, a threshold value of the number of measurement failures is commonly used for each request. However, the condition for transmitting each request may be set individually for each of the measurement release request, the count reduction request, and the periodic extension request. Thereby, it becomes possible for the first base station 111 to pre-associate the condition for transmitting a request with the parameter of the measurement setting to be changed, and to finely control the measurement setting according to this association. Also, the terminal 101 may simply notify a request for changing the measurement setting without distinguishing between the measurement release request, the count reduction request, and the periodic extension request, and the first base station 111 may determine whether to end the measurement of the requested measurement object, reduce the number of measurements, or extend the measurement period, and notify the terminal 101.In this case, the terminal 101 can notify the first base station 111 of a request to change the measurement settings and the measurement target identifier to be targeted. The first base station 111 can determine which parameters to change according to the remaining time that can be spent on cell search.

[0030] As described above, the first base station 111 notifies the terminal 101 of the designation information (or measurement settings) that specifies whether to execute the measurement and the frequency band to be measured in each of the MGs for cell search measurement, and the terminal 101 executes the measurement based on this designation information. As a result, since the measurement executed by the terminal 101 can be controlled by a device on the network side (including the base station), the cell search can be completed promptly, and the terminal 101 can be made to perform a handover in a short period. Further, the first base station 111 updates the measurement settings based on the measurement report received from the terminal 101 and the requests (measurement setting release request, number reduction request, period extension request, etc.), and notifies the terminal 101. By preventing the terminal 101 from performing measurements in a frequency band where measurement failure is highly likely, the terminal 101 can effectively use the MG and promptly complete the cell search. (Modification example) In the above description, an example was described in which the first base station 111 issues an instruction (measurement instruction) including information (designation information) for designating whether to execute measurement in each of the MGs set for the terminal 101 to perform measurement, and which frequency band to measure when executing measurement, and the terminal 101 performs measurement of each frequency band based on the instruction. In this modified example, the first base station 111 issues a measurement instruction including a condition for the terminal 101 to end measurement, and the terminal 101 ends measurement when the condition is satisfied. Further, the base station 111 controls such that when the condition is satisfied for the terminal 101, the terminal 101 ends measurement and requests to disconnect the connection state with the first base station 111. For example, the first base station 111 notifies the terminal 101 of setting information for requesting disconnection of the connection state based on the occurrence of a specific type of communication different from the use of the first frequency used for communication with the terminal 101 and associated with the terminal 101. Then, when a specific type of communication associated with the terminal 101 occurs, the terminal 101 issues a connection disconnection request when a predetermined condition based on this setting information is satisfied. For example, the specific type of communication may be voice communication. In this case, the first base station 111 may notify the terminal 101 of a measurement instruction including a deadline for the terminal 101 to end measurement due to the occurrence of voice communication traffic associated with the terminal 101. Thereby, even when another base station to be handed over is not found in cell search, it becomes possible to execute appropriate communication in accordance with the frequency band use restriction. For example, it becomes possible to disconnect the connection before voice traffic is communicated in a frequency band where voice traffic cannot be transmitted. Note that the operation to be taken by the terminal 101 when a predetermined condition is satisfied is not limited to the request for disconnection of the connection, and may be any operation that does not cause a type of communication that is not allowed to be used.

[0031] FIG. 10 shows an example of a sequence between the first base station 111 and the terminal 101 when the first base station 111 notifies the terminal 101 of a measurement instruction including the time at which the measurement should end. The first base station 111 transmits a measurement instruction to the terminal 101 using an RRC Connection Reconfiguration message including a measurement configuration IE (S1001). For example, the first base station 111 may transmit a measurement instruction to the terminal 101 when it detects that voice traffic will occur because a request to create a bearer for transmitting voice traffic from the network side or a request to establish a QoS flow for setting a bearer has been notified. The measurement configuration (measConfig) IE may include one measurement object (measObject) including, for example, a frequency band (carrierFreq), a measurement period (tIFsearch), and an operation to be taken when the measurement period has been reached. For example, the operation to be executed when the measurement period has been reached may be a transition of the RRC state (requestedRRC-State). In the example of FIG. 10, in the measurement configuration, as the frequency band to be measured, the 2.6 GHz band (earfcnDl is 41040), the measurement period is 1000 ms, and as the operation to be taken when the measurement period has been reached, a request to transition the RRC state to RRC_Idle is set to be transmitted. When the frequency band of the cell provided by the own device (the first base station 111) is specified as the frequency band to be measured, the terminal 101 may perform measurements on measurement objects other than this measurement object. That is, this measurement object may be used to set the measurement period. On the other hand, when no measurement object other than this measurement object is notified, the terminal 101 may perform measurements in each MG without receiving a special designation. When the terminal 101 receives a measurement instruction including designation information from the first base station 111, it determines whether to accept the measurement instruction, and if it accepts, it transmits a response (S1002). Then, the terminal 101 performs the measurement (S1003). When the measurement period (1000 ms from the start of the measurement) has been reached without the occurrence of the measurement report trigger notified from the first base station 111, the terminal 101 notifies the first base station 111 that it will perform the operation to be executed shown in the measurement configuration (S1004). In the case of FIG. 10, the terminal 101 notifies that it will transition to the RRC_Idle state.This notification may be performed using the UE Assistance Information message, and the UE Assistance Information may include the preferredRRC_State-r16 idle IE. When the first base station 111 receives this notification from the terminal 101, it transmits an RRC Connection Release message to transition the terminal 101 to the RRC_Idle state (S1005). Note that the terminal 101 can perform a cell search to detect a new connection destination even when not connected to the first base station 111. If a connectable base station 110 is detected by the cell search, the terminal 101 attempts to connect using the random access procedure. Note that the first base station may notify the terminal 101 of the recommended frequency band using the redirectedCarrierInfo IE in the RRC Connection Release message. Thus, when it is detected that a predetermined type of traffic occurs, the first base station 111 notifies the terminal 101 of a measurement instruction including a certain measurement period and the operation to be performed when the measurement period is reached. The terminal 101 performs measurements according to the measurement instruction and, when the measurement period is reached, performs the operation to be performed (for example, a request to disconnect the connection with the first base station 111). For example, the measurement period can be set based on the time when it is predicted that voice traffic communication will start. Thereby, it can be avoided that a type of traffic that cannot be used in the frequency band used for communication between the first base station 111 and the terminal 101 occurs due to the measurement taking a long time. Also, it is possible to avoid a decrease in the throughput of the terminal 101 by continuing to set the MG without completing the cell search.

[0032] The method by which the first base station 111 detects a predetermined type of traffic is not limited to the above. For example, the terminal 101 may detect that a predetermined type of traffic has occurred or has occurred, and notify the first base station 111 of this. In the terminal 101, when a predetermined type of traffic is detected, the first base station 111 can recognize the occurrence of traffic earlier than when receiving a request from the network side. FIG. 11 shows an example of a sequence when the terminal 101 is made to detect the occurrence of a predetermined type of traffic. First, the first base station 111 transmits a measurement instruction including the type of traffic (ulGenProtocol) to be detected and the operation to be executed when detected (S1101). In FIG. 11, RTP (Real-time Transport Protocol) is notified as the type of traffic to be detected, and transitioning to the RRC_Idle state is notified as the operation to be executed. RTP is a protocol used in voice services such as VoLTE (Voice over LTE). Note that the terminal 101 can detect a predetermined type of traffic by a method other than RTP detection. When the terminal 101 receives a measurement instruction including specified information from the first base station 111, it determines whether to accept the measurement instruction, and if it accepts, it transmits a response (S1102). Then, in S1103, when the terminal 101 detects the occurrence of an RTP packet, the terminal 101 notifies the first base station 111 that it will perform the operation to be executed when detected (in FIG. 11, the request to transition to the RRC_Idle state) (S1104). This notification can be made, for example, by a UE Assistance Information message including a preferredRRC-State-r16 idle IE. By this notification, the first base station 111 can infer that an RTP packet has occurred in the terminal 101. That is, the first base station 111 infers that an RTP packet has occurred because the operation notified by itself has been executed by the terminal 101. In this case, the first base station 111 can cause the terminal 101 to execute a cell search with a measurement period set without transmitting an RRC Connection Release message in response to the notification from the terminal 101 (S1105 to S1110).That is, the first base station 111 does not immediately disconnect the connection with the terminal 101 in response to the notification from the terminal 101, but can confirm whether the terminal 101 can perform handover within the deadline. Since the sequences of S1105 to S1110 are the same as those of S1001 to S1005 in FIG. 10, the description thereof is omitted. In this case, the first base station 111 can issue an instruction (measurement instruction) including information (designation information) specifying whether to perform measurement and, if measurement is to be performed, which frequency band to measure for each of the MGs, in addition to the measurement deadline, regarding the measurement performed by the terminal 101. For example, the first base station 111 may include a measurement setting including a plurality of measurement targets in the measurement instruction notified in S1001 of FIG. 10 or S1105 of FIG. 11. By the first base station 111 notifying the designation information for measurement together with the measurement deadline, the possibility that the terminal 101 can complete cell search within the measurement deadline can be increased. In this way, when the terminal 101 detects a predetermined type of traffic and notifies the first base station 111, and the first base station 111 causes the terminal 101 to perform cell search based on this notification, the cell search can be started at an earlier timing.

[0033] Also, in the above example, the first base station 111 can autonomously disconnect the connection with the terminal 101 based on the measurement deadline notified to the terminal 101 (for example, can cause the terminal 101 to transition to the RRC_Idle state). For example, the first base station 111 notifies the measurement deadline to the terminal 101 and also starts a timer in its own device. When the timer reaches the deadline without receiving a measurement report from the terminal 101, the first base station 111 can notify the terminal 101 of an RRC Connection Release message regardless of whether a UE Assistance Information message has been received from the terminal 101. Thereby, since the first base station 111 can quickly disconnect the connection without performing sequence exchange with the terminal 101, it becomes possible to reduce the resources required for the sequence between the first base station 111 and the terminal 101 and avoid communication of unusable types of traffic.

[0034] On the one hand, when a predetermined type of traffic is detected at the terminal 101 or when the first base station 111 receives a notification from the terminal 101 that it has transitioned to the RRC_Idle state due to the detection, the first base station 111 may cause the terminal 101 to transition to the RRC_Idle state without performing a cell search. By quickly disconnecting the connection, it becomes possible to more reliably avoid communication of traffic of a type that cannot be used in the frequency band used for communication between the first base station 111 and the terminal 101. FIG. 12 shows an example of a sequence when the connection is disconnected without causing the terminal 101 to perform a cell search after detecting the occurrence of a predetermined type of traffic at the terminal 101. For the same sequence as in FIG. 11, the same reference numbers are assigned and the description is omitted. That is, in FIG. 12, the terminal 101 detects the generation of RTP packets in S1103 and notifies the first base station 111 of the transition to the RRC_Idle state (S1104). In response to the notification from the terminal 101, the first base station 111 transmits an RRC Connection Release message to cause the terminal 101 to transition to the RRC_Idle state (S1201). Then, the terminal 101 can continue to perform a cell search in a state where there is no connection with the first base station 111. When a connectable base station 110 is detected by the cell search, the terminal 101 attempts to connect using a random access procedure. Note that the first base station 111 may notify the terminal 101 of the recommended frequency band in the RRC Connection Release message using the redirectedCarrierInfo IE.

[0035] As described above, in this modified example, the first base station 111 gives an instruction including the conditions for the terminal 101 to end the measurement. When the conditions are satisfied, the terminal 101 ends the measurement and executes a predetermined operation. Thereby, even when no other base station to be handed over is found in cell search, it is possible to execute appropriate communication in accordance with the usage restrictions of the frequency band. Further, when the first base station 111 detects that a predetermined type of traffic has occurred in the terminal 101, the first base station 111 notifies the terminal 101 to execute a predetermined operation, and based on the fact that the terminal 101 has executed the predetermined operation, the communication of the terminal 101 is disconnected. Thereby, it is made more certain that traffic with usage restrictions is not communicated, and the terminal 101 can execute cell search for handover. Note that the parameters used in the description of this embodiment may have other names. (Circuit Configuration) A configuration example of the base station 110 and the terminal 101 as described above will be described. FIG. 13 is a diagram showing the hardware configurations of the base station 110 and the terminal 101. In one example, the base station 110 and the terminal 101 include a processor 1301, a ROM 1302, a RAM 1303, a storage device 1304, and a communication circuit 1305. The processor 1301 is a computer including one or more processing circuits such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit). The processor 1301 reads and executes programs stored in the ROM 1302 and the storage device 1304 to execute the overall processing of the device and each of the above-described processes. The ROM 1302 is a read-only memory in which information such as programs and various parameters related to the processes executed by the base station 110 and the terminal 101 is recorded. The RAM 1303 functions as a work space when the processor 1301 executes a program and is a random access memory in which temporary information is recorded. The storage device 1304 is constituted by, for example, a removable external storage device or the like. The communication circuit 1305 includes, for example, circuits for wired communication or wireless communication of the base station 110 and the terminal 101. For example, the base station 110 and the terminal 101 can communicate with each other using the communication circuit 1305 for LTE or 5G. (Functional Configuration) FIG. 14 is a diagram showing a functional configuration example of the base station 110 (for example, the first base station 111). The base station 110 includes, as its functions, for example, an MG setting unit 1401, a measurement instruction transmission unit 1402, and a report reception unit 1403. FIG. 14 shows the functional configuration of the base station 110 according to the present embodiment, and for example, the general configuration of the base station 110 is omitted. Note that these functional units can be realized, for example, when the processor 1301 executes programs stored in the ROM 1302 and the storage device 1304 and controls the communication circuit 1305 as necessary. However, the present invention is not limited to this, and for example, dedicated hardware for realizing each function may be prepared.

[0036] The MG setting unit 1401 sets an MG for the terminal 101 to perform measurements. The MG may be arranged periodically or aperiodically according to the need for measurement. The MG setting unit 1401 can set the arrangement of the MG according to the measurement target. Also, the MG setting unit 1401 may set the arrangement of the MG based on a predetermined period. The measurement instruction transmission unit 1402 transmits, for each of the MGs, a measurement instruction including designation information specifying whether the terminal 101 should perform a measurement and, if a measurement is to be performed, which frequency should be measured, to the terminal 101. The measurement instruction may include a plurality of measurement targets. The designation information may include a frequency band to be measured, a priority level set for each frequency band, the number of times to continuously measure each frequency band, the measurement period (or measurement interval) of each frequency band. Also, the designation information may include a condition under which the terminal 101 should send a request (e.g., the number of consecutive measurement failures). Further, the designation information may include a measurement deadline, information specifying the type of traffic to be detected, and an operation to be performed when the measurement deadline is reached or when a predetermined type of traffic is detected. The measurement instruction transmission unit 1402 can transmit the designation information when the frequency band used by the base station 110 in communication with the terminal 101 is a frequency that cannot be used for a predetermined type of communication. Note that the designation information may be transmitted in a message different from the measurement instruction. Also, the measurement instruction transmission unit 1402 can transmit a measurement instruction including the designated information when it detects the occurrence of a predetermined type of traffic. The measurement instruction transmission unit can update the measurement instruction when it receives a measurement report or request from the terminal 101 and transmit the updated measurement instruction to the terminal 101. The report receiving unit 1403 receives a measurement report and a request from the terminal 101. The report receiving unit 1403 notifies the received measurement report and request to the measurement instruction transmission unit 1402.

[0037] FIG. 15 is a diagram showing a functional configuration example of the terminal 101. The terminal 101 includes, as its functions, for example, a measurement instruction receiving unit 1501, a measurement unit 1502, and a report transmission unit 1503. FIG. 15 shows the functional configuration of the terminal 101 of the present embodiment, and for example, the general configuration of the terminal 101 is omitted. Note that these functional units can be realized, for example, when the processor 1301 executes programs stored in the ROM 1302 and the storage device 1304 and controls the communication circuit 1305 as necessary. However, the present invention is not limited to this, and for example, dedicated hardware for realizing each function may be prepared.

[0038] The measurement instruction receiving unit 1501 receives a measurement instruction from the base station 110. The measurement unit 1502 performs measurements according to the measurement instruction. For example, based on the measurement instruction, the measurement unit 1502 determines whether to perform measurements in each of the set MGs and which frequency band to measure when performing measurements, and then performs the measurements. The report transmission unit 1503 transmits reports and requests of measurement results to the base station 110. For example, when the trigger for the measurement report included in the measurement instruction occurs, the report transmission unit 1503 transmits a measurement report to the base station 110. The measurement report from the terminal 101 may include the physical ID (PCI) of the detected cell, the received signal strength (RSRP), and the received signal quality (RSRQ). In addition, when the conditions for transmitting a request included in the measurement instruction are met, the report transmission unit 1503 can transmit a measurement setting release request, a count reduction request, a period extension request, etc. to the base station 110. Furthermore, when the measurement deadline included in the measurement instruction is reached or when it is detected that a predetermined type of traffic has occurred, the report transmission unit 1503 can notify the base station 110.

[0039] As described above, according to the present embodiment, the first base station 111 notifies, in each of the MG for cell search measurement, designation information (or measurement setting) that specifies whether to execute the measurement and the frequency band to be measured, and the terminal 101 executes the measurement based on this designation information. As a result, since it becomes possible to control the measurement executed by the terminal 101 from a device on the network side (including the base station), the cell search can be completed promptly, and it becomes possible to cause the terminal 101 to perform handover in a short period. Further, the first base station 111 updates the measurement setting based on the measurement report received from the terminal 101 and requests (such as a measurement setting release request, a count reduction request, a period extension request, etc.), and notifies the terminal 101. As a result, by preventing the terminal 101 from performing measurement in a frequency band where measurement is likely to fail, the terminal 101 can effectively use the MG and promptly complete the cell search. Furthermore, the first base station 111 gives a measurement instruction including the time when the terminal 101 should end the measurement, and when the terminal 101 reaches that time, the terminal 101 ends the measurement and executes a predetermined operation. As a result, even when no other base station to be handed over is found in the cell search, it becomes possible to execute appropriate communication in accordance with the usage restriction of the frequency band. In addition, when the first base station 111 detects that a predetermined type of traffic has occurred in the terminal 101, the first base station 111 notifies the terminal 101 to execute a predetermined operation, and based on the fact that the terminal 101 has executed the predetermined operation, the communication of the terminal 101 is disconnected. As a result, it is possible to more surely prevent traffic with usage restrictions from being communicated, and it becomes possible for the terminal 101 to execute cell search for handover. Therefore, it becomes possible to contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0040] The invention is not limited to the above-described embodiment, and various modifications and changes are possible within the scope of the gist of the invention.

Explanation of Reference Numerals

[0041] 101: Terminal, 111: First base station, 112: Second base station, 113: Third base station, 1401: MG setting unit, 1402: Measurement instruction transmission unit, 1501: Measurement instruction reception unit, 1502: Measurement unit, 1503: Report transmission unit

Claims

1. A base station that communicates with a wireless terminal based on the cellular communication standard of the Third Generation Partnership Project (3GPP), comprising: setting means for setting one or more Measurement Gaps (MGs) for measuring signals of other base stations in one or more second frequency bands different from a first frequency band used for the communication; transmission means for transmitting, to the wireless terminal, a measurement instruction including designation information indicating whether to perform the measurement in each of the MGs and, if the measurement is to be performed, which of the second frequency bands to measure; A base station characterized by the above.

2. The transmission means transmits the designation information to the wireless terminal when the first frequency band is a frequency band that cannot be used for a predetermined type of communication. The base station according to claim 1, characterized by the above.

3. The transmission means transmits the designation information to the wireless terminal when it detects that traffic of the predetermined type of communication occurs. The base station according to claim 2, characterized by the above.

4. The transmission means updates the designation information using a measurement report or request received from the wireless terminal. The base station according to claim 1, characterized by the above.

5. The transmission means updates the designation information based on receiving, from the wireless terminal, information indicating that measurement of at least any one of the one or more second frequency bands should be terminated. The base station according to claim 4, characterized by the above.

6. The transmission means updates the designation information based on receiving, from the wireless terminal, information indicating that the frequency of measuring at least any one of the one or more second frequency bands should be reduced. The base station according to claim 4, characterized by the above.

7. A wireless terminal that communicates with a base station based on the cellular communication standard of the Third Generation Partnership Project (3GPP), comprising: receiving means for receiving, from the base station, setting of one or more Measurement Gaps (MGs) for measuring signals of other base stations in one or more second frequency bands different from a first frequency band used for the communication, and a measurement instruction including designation information indicating whether to perform the measurement in each of the MGs and, if the measurement is to be performed, which of the second frequency bands to measure; In each of the MGs, measurement means for performing measurement of the second frequency band designated by the designation information; A wireless terminal characterized by the above. **Claim 8** The receiving means receives the designation information when the first frequency band is a frequency band that cannot be used for a predetermined type of communication. The wireless terminal according to claim 7, characterized in that. **Claim 9** The receiving means acquires the designation information when it detects that traffic of the predetermined type of communication has occurred. The wireless terminal according to claim 8, characterized in that. **Claim 10** The wireless terminal according to claim 7 further includes transmission means for performing a measurement report or request to the base station. The wireless terminal according to claim 7, characterized in that. **Claim 11** The transmission means reports information indicating that at least one of the one or more second frequency bands should be measured. The wireless terminal according to claim 10, characterized in that. **Claim 12** The transmission means reports information indicating that the frequency of measuring at least one of the one or more second frequency bands should be reduced. The wireless terminal according to claim 10, characterized in that. **Claim 13** A communication method executed by a base station that communicates with a wireless terminal based on the cellular communication standard of the Third Generation Partnership Project (3GPP), a setting step of setting one or more Measurement Gaps (MGs) for measuring signals of other base stations in one or more second frequency bands different from the first frequency band used for the communication; a transmission step of transmitting, to the wireless terminal, a measurement instruction including designation information for designating whether to perform the measurement and, if the measurement is to be performed, which of the second frequency bands to measure, in each of the MGs; A communication method characterized by the above. **Claim 14** A communication method executed by a wireless terminal that communicates with a base station based on the cellular communication standard of the Third Generation Partnership Project (3GPP), a receiving step of receiving, from the base station, a setting of one or more Measurement Gaps (MGs) for measuring signals of other base stations in one or more second frequency bands different from the first frequency band used for the communication, and a measurement instruction including designation information for designating whether to perform the measurement and, if the measurement is to be performed, which of the second frequency bands to measure, in each of the MGs; In each of the MG, a measurement step of performing measurement of the second frequency band specified by the specified information A communication method characterized by the above.

15. In a computer included in a base station that communicates with a wireless terminal based on the cellular communication standard of the Third Generation Partnership Project (3GPP), One or more Measurement GAPs (MG) for measuring signals of other base stations are set in one or more second frequency bands different from the first frequency band used for the communication, In each of the MG, a measurement instruction including specified information for specifying whether to perform the measurement and, if the measurement is to be performed, which of the second frequency bands to measure is transmitted to the wireless terminal For the program.

16. In a computer included in a wireless terminal that communicates with a base station based on the cellular communication standard of the Third Generation Partnership Project (3GPP), Setting one or more Measurement GAPs (MG) for measuring signals of other base stations in one or more second frequency bands different from the first frequency band used for the communication, and in each of the MG, receiving from the base station a measurement instruction including specified information for specifying whether to perform the measurement and, if the measurement is to be performed, which of the second frequency bands to measure In each of the MG, causing measurement to be performed on the second frequency band specified by the specified information For the program.

Images