Radio communication device, radio communication system, and radio communication method

Abstract

To continuously perform data communication in a non-communication mode.SOLUTION: A radio communication device of a plurality of radio communication devices includes: a reception unit for receiving a message for establishing communication to be transmitted by another radio communication device to the radio communication device selected from the plurality of radio communication devices; and a controlling unit capable of performing control so that when transmitting, to the radio communication device, identification information allocated to the radio communication device by a first other radio communication device and establishing communication with the other radio communication device in a non-communication mode, data communication permitted even in the non-communication mode selected by the other radio communication device can be performed and a cell formed by the first other radio communication device can be selected, as a cell to be used for the data communication, from a plurality of cell groups formed by the plurality of radio communication devices.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a wireless communication device, a wireless communication system, and a wireless communication method. [Background technology]

[0002] Generally, in a wireless communication system, processing of the RRC (Radio Resource Control) layer is performed. In the RRC layer processing, for example, connection setup, modification, release, etc. are performed between a base station device and a terminal device. For example, in LTE (Long Term Evolution) or LTE-A (LTE-Advanced), which are standard technologies for 4G, RRC connected mode (RRC_CONNECTED) and RRC idle mode (RRC_IDLE) are defined as RRC layer states. The RRC connected mode is, for example, a mode in which data communication can be performed between a base station device and a terminal device. The RRC idle mode is, for example, a mode in which data communication is not performed between a base station device and a terminal device, and in which the terminal device is in a power saving state.

[0003] In fifth-generation mobile communications (5G or NR (New Radio)), in addition to RRC connected mode and RRC idle mode, an RRC inactive mode (RRC_INACTIVE) is specified. RRC inactive mode has the same low power consumption as RRC idle mode and is a mode that allows for quick transition to RRC connected mode when transmitting data. In RRC inactive mode, the context of the terminal device (hereinafter referred to as "UE context") is held in the base station device. The UE context is identification information that identifies information about the terminal device, such as the terminal device's location, communication capabilities, and various parameters. Because the UE context is held in the base station device in this way, the core network considers the terminal device to be connected to the base station device even in the RRC inactive mode. As a result, when the terminal device returns from RRC inactive mode to RRC connected mode, signal transmission and reception between the base station device and the core network is omitted, and quick transition to the RRC connected mode is achieved.

[0004] The RRC inactive mode is a mode in which no data communication is performed between a base station apparatus and a terminal apparatus, except for data communication essential for establishing or maintaining communication between the base station apparatus and the terminal apparatus. The RRC idle mode is a mode in which the terminal apparatus is in a power-saving state, and no data communication is performed between the base station apparatus and the terminal apparatus. Meanwhile, recently, it has been considered to realize transmission of predetermined data (e.g., small data) even in these non-communication modes. That is, it is considered that small data, such as terminal apparatus failure information or sensor measurement values, may be transmitted from the terminal apparatus to the base station apparatus during the RRC inactive mode. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-048100 [Patent Document 2] International Publication No. 2020 / 196780 [Patent Document 3] International Publication No. 2019 / 065814 [Non-patent literature]

[0006] [Non-Patent Document 1] 3GPP TS36.133 V17.1.0(2021-03) [Non-patent document 2] 3GPP TS36.211 V16.5.0(2021-03) [Non-patent document 3] 3GPP TS36.212 V16.5.0(2021-03) [Non-patent document 4] 3GPP TS36.213 V16.5.0(2021-03) [Non-Patent Document 5] 3GPP TS36.214 V16.2.0(2021-03) [Non-patent document 6] 3GPP TS36.300 V16.5.0(2021-03) [Non-Patent Document 7] 3GPP TS36.321 V16.4.0(2021-03) [Non-patent document 8] 3GPP TS36.322 V16.0.0(2020-07) [Non-Patent Document 9] 3GPP TS36.323 V16.3.0(2020-12) [Non-Patent Document 10] 3GPP TS36.331 V16.4.0(2021-03) [Non-Patent Document 11] 3GPP TS36.413 V16.5.0(2021-04) [Non-Patent Document 12] 3GPP TS36.423 V16.5.0(2021-04) [Non-Patent Document 13] 3GPP TS36.425 V16.0.0(2020-07) [Non-Patent Document 14] 3GPP TS37.324 V16.2.0(2020-09)

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[0007] However, if the wireless quality between the terminal device and the base station device deteriorates during the non-communication mode, a data communication failure occurs, making it difficult to continue the data communication. That is, if a data communication failure occurs during the RRC inactive mode, the terminal device starts a predetermined timer and transitions to the RRC idle mode when the timer expires. After transitioning to the RRC idle mode, the terminal device again selects a cell with good wireless quality.

[0008] In this way, if a data communication failure occurs during the RRC inactive mode, a transition to the RRC idle mode and cell reselection are performed, making it difficult to continuously transmit data such as small data.

[0009] The disclosed technology has been made in consideration of the above points, and aims to provide a wireless communication device, a wireless communication system, and a wireless communication method that are capable of performing data communication continuously even during a non-communication mode. [Means for solving the problem]

[0010] In one aspect, the wireless communication device disclosed in the present application is a wireless communication device among a plurality of wireless communication devices, and includes: a receiving unit that receives a message for establishing communication that is sent by another wireless communication device to a wireless communication device selected from the plurality of wireless communication devices; and a control unit that transmits identification information assigned to the wireless communication device by a first other wireless communication device to the wireless communication device, and is capable of controlling the wireless communication device to select a cell formed by the first other wireless communication device as a cell to be used for data communication from a group of multiple cells formed by the plurality of wireless communication devices, which is selected by the other wireless communication device when communication is established with the other wireless communication device in a non-communication mode and which can perform data communication that is allowed even in the non-communication mode. [Effects of the Invention]

[0011] According to one aspect of the wireless communication device, the wireless communication system, and the wireless communication method disclosed in the present application, it is possible to achieve an effect of enabling data communication to be performed continuously during a non-communication mode. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of a wireless communication system according to the first embodiment. [Figure 2] FIG. 2 is a block diagram showing the configuration of the base station device. [Figure 3] FIG. 3 is a block diagram showing the configuration of the terminal device. [Figure 4] FIG. 4 is a sequence diagram showing a cell selection method according to the second embodiment. [Figure 5] FIG. 5 is a sequence diagram showing a small data transmission method. [Figure 6] FIG. 6 is a sequence diagram showing another small data transmission method. [Figure 7] FIG. 7 is a sequence diagram showing a cell selection method according to the third embodiment. [Figure 8] FIG. 8 is a sequence diagram showing a cell selection method according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of a wireless communication device, a wireless communication system, and a wireless communication method disclosed in the present application will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to these embodiments.

[0014] (Embodiment 1) 1 is a diagram showing an example of the configuration of a wireless communication system according to embodiment 1. The wireless communication system shown in FIG. 1 includes a plurality of first wireless communication devices 100-1 to 100-3 and a second wireless communication device 200 connected to a core network 10.

[0015] First wireless communication devices 100-1 to 100-3 are wireless communication devices that are connected to core network 10 and are capable of wireless communication with second wireless communication device 200 located within a cell. In Fig. 1, the cells formed by first wireless communication devices 100-1 to 100-3 are indicated by dashed lines.

[0016] When communicating with second wireless communication device 200, first wireless communication devices 100-1 to 100-3 have a control unit that can control the implementation of data communication selectively using a group of multiple cells that are selected when communication with second wireless communication device 200 in non-communication mode and that are capable of implementing data communication that is permitted even in non-communication mode. That is, first wireless communication devices 100-1 to 100-3 are selected as wireless communication devices that form multiple cells used for data communication by second wireless communication device 200 in non-communication mode, depending on the wireless quality with second wireless communication device 200. That is, while second wireless communication device 200 is in non-communication mode, multiple communication partners of second wireless communication device 200 are selected from first wireless communication devices 100-1 to 100-3. Then, when second wireless communication device 200 is implementing data communication in non-communication mode, if data communication with one selected first wireless communication device fails, second wireless communication device 200 executes data communication with another selected first wireless communication device. Therefore, even if data communication with one of the first wireless communication devices fails during the non-communication mode, the second wireless communication device 200 can continue to perform data communication.

[0017] When second wireless communication device 200 is located within a cell, second wireless communication device 200 is capable of wireless communication with first wireless communication devices 100-1 to 100-3 that form the cell. Second wireless communication device 200 can operate by switching between a communication mode such as an RRC connected mode and a non-communication mode such as an RRC inactive mode.

[0018] When communicating with first wireless communication devices 100-1 to 100-3, second wireless communication device 200 has a control unit that, under control of first wireless communication devices 100-1 to 100-3 as communication partners, can control the implementation of data communication selectively using a plurality of cell groups that are capable of implementing data communication that is permissible even in the non-communication mode and that were selected when communication with first wireless communication devices 100-1 to 100-3 was established in the non-communication mode. That is, second wireless communication device 200 selectively implements data communication with a plurality of wireless communication devices selected from first wireless communication devices 100-1 to 100-3.

[0019] In the non-communication mode, second wireless communication device 200 is set to communicate with a plurality of wireless communication devices selected from first wireless communication devices 100-1 to 100-3. Therefore, if data communication with one selected first wireless communication device fails in the non-communication mode, second wireless communication device 200 can execute data communication with another selected first wireless communication device, and can continuously perform data communication.

[0020] As described above, according to the present embodiment, multiple first wireless communication devices are selected as communication partners of the second wireless communication device during the non-communication mode, and even if data communication with one of the first wireless communication devices fails, the second wireless communication device continues to perform data communication with the other first wireless communication devices, thereby enabling continuous data communication during the non-communication mode.

[0021] (Embodiment 2) In the second embodiment, a case where a terminal device sets up a call with a plurality of base station devices while in a non-communication mode will be described. The configuration of the wireless communication system according to the second embodiment is the same as that of the first embodiment (FIG. 1), and therefore the description thereof will be omitted. The second embodiment is an embodiment that embodies the first embodiment as appropriate, and can be implemented in combination with the first embodiment within a range that does not contradict.

[0022] 2 is a block diagram showing a configuration of base station device 100 according to embodiment 2. Base station device 100 has a configuration equivalent to that of base station devices 100-1 to 100-3. Base station device 100 shown in FIG. 2 includes network interface (hereinafter abbreviated as "network IF") 110, processor 120, memory 130, and radio communication unit 140.

[0023] The network IF 110 is wired connected to the core network 10, and transmits and receives signals to and from devices such as an AMF (Access and Mobility management Function) that configure the core network 10. The network IF 110 also includes an interface, such as an X2 interface, that connects to other base station devices, and transmits and receives signals to and from other base station devices.

[0024] The processor 120 is a control unit that includes, for example, a CPU (Central Processing Unit), an FPGA (Field Programmable Gate Array), or a DSP (Digital Signal Processor), and performs overall control of the base station device 100. When communicating with the terminal device 200, the processor 120 controls the execution of data communication selectively using a group of multiple cells that can perform data communication in the non-communication mode, which group was selected when communication was established with the terminal device 200 in a non-communication mode such as an RRC inactive mode. That is, when data communication with one selected base station fails, the processor 120 controls the terminal device 200 in the non-communication mode to perform data communication with another selected base station.

[0025] The memory 130 includes, for example, a random access memory (RAM) or a read only memory (ROM), and stores information used in processing by the processor 120.

[0026] The wireless communication unit 140 performs wireless communication with the opposing terminal device 200. The wireless communication unit 140 transmits, for example, identification information related to the UE context generated by the processor 120 to the terminal device 200. The wireless communication unit 140 also receives data transmitted from the terminal device 200. Note that the wireless communication unit 140 can perform predetermined communication with the terminal device 200 even when the opposing terminal device 200 is in a non-communication mode.

[0027] 3 is a block diagram showing a configuration of a terminal device 200 according to Embodiment 2. The terminal device 200 shown in FIG.

[0028] The wireless communication unit 210 performs wireless communication with the opposing base station device 100. The wireless communication unit 210 transmits and receives various signals to and from the base station device 100 for switching the communication mode and non-communication mode of the terminal device 200. For example, when the terminal device 200 establishes communication with the base station device 100, the wireless communication unit 210 receives identification information related to the UE context from the base station device 100. Note that the wireless communication unit 210 can perform predetermined communication permitted by the base station device 100 even when the terminal device 200 is in the non-communication mode.

[0029] The processor 220 is a control unit that includes, for example, a CPU, an FPGA, or a DSP, and that performs overall control of the terminal device 200. Furthermore, under control of the base station device 100, the communication partner, the processor 220 controls the execution of data communication selectively using a group of multiple cells that can perform data communication that is permitted even in the non-communication mode, and that was selected when communication with the base station device 100 was established in the non-communication mode. That is, under control of the base station device 100, when data communication with one selected base station fails in the non-communication mode, the processor 220 performs control to perform data communication with another selected base station.

[0030] The memory 230 includes, for example, a RAM or a ROM, and stores information used in processing by the processor 220.

[0031] Next, a cell selection method in the wireless communication system configured as above will be described with reference to Fig. 4. In the following description, it is assumed that the wireless communication system includes base station devices 100-1 and 100-2 having the same configuration as base station device 100.

[0032] During the non-communication mode, the terminal device 200 measures the signal strength from surrounding base station devices including the base station devices 100-1 and 100-2, and selects multiple base stations as potential communication partners. Here, it is assumed that the terminal device 200 selects, for example, the base station device 100-1 with the highest signal strength as the primary base station with which to communicate with the highest priority, and the base station device 100-2 with the second highest signal strength as the secondary base station with which to communicate with the second highest priority.

[0033] Then, in the non-communication mode, the terminal device 200 transmits an access stratum (AS) message (hereinafter referred to as "AS message") requesting a connection in order to establish communication with the base station device 100-1, which is the primary base station (step S101). Examples of this AS message include an RRC connection request and a connection resume request.

[0034] In response to this AS message, the base station device 100-1 transmits an AS message for predetermined settings to the terminal device 200 (step S102), and the terminal device 200 transmits an AS message notifying the base station device 100-1 of the completion of the connection (step S103). The AS message notifying the completion of the connection includes information indicating that the base station device 100-1 is the primary base station. That is, the terminal device 200 can notify the base station device 100-1 that it has selected the base station device 100-1 as the primary base station. Upon receiving this notification, the base station device 100-1 can recognize that it is the primary base station and that it is the base station that performs control to cause the terminal device 200 to perform data communication selectively using multiple cells. Note that the information indicating that the base station device 100-1 is the primary base station may be included in the AS message requesting the connection in step S101.

[0035] When a connection between the terminal device 200 and the base station device 100-1 is established, a Non-Access Stratum (NAS) message (hereinafter referred to as a "NAS message") for registration (e.g., location registration) is transmitted from the terminal device 200 to the core network 10 via the base station device 100-1 (step S104). When the terminal device 200 is registered in the core network 10, a NAS message indicating that the registration has been accepted is transmitted from the core network 10 to the terminal device 200 via the base station device 100-1 (step S105).

[0036] Furthermore, in the base station device 100-1, a UE context related to the terminal device 200 is generated. Then, temporary identification information including identification information of the terminal device 200 and identification information of the base station device 100-1 is generated as identification information related to the UE context. As this temporary identification information, for example, an I-RNTI (Inactive-Radio Network Temporary Identifier) ​​can be used. The I-RNTI is 40-bit identification information that can simultaneously identify a terminal device and a base station device. Because the I-RNTI is 40-bit identification information, if the number of bits allocated to the identification information of the base station device is increased, the number of identifiable base station devices increases, but the number of identifiable terminal devices decreases. Furthermore, if the number of bits allocated to the identification information of the base station device is reduced, the number of identifiable base station devices decreases, but the number of identifiable terminal devices increases. As identification information related to the UE context, any information other than the I-RNTI that can identify the UE context can be used.

[0037] The generated UE context is held by the base station device 100-1, and identification information related to the UE context is notified to the terminal device 200, for example, by an AS message for releasing the connection (step S106). Upon receiving this notification, the terminal device 200 holds the identification information related to the UE context and releases the connection with the base station device 100-1. As a result, the terminal device 200 transitions to a non-communication mode, for example, an RRC inactive mode.

[0038] Then, the terminal device 200 transmits an AS message requesting connection to establish communication with the base station device 100-2, which is the secondary base station (step S107). In response to this AS message, the base station device 100-2 transmits an AS message for predetermined settings to the terminal device 200 (step S108), and the terminal device 200 transmits an AS message notifying the base station device 100-2 of completion of connection (step S109). The AS message notifying the completion of connection includes information indicating that the base station device 100-2 is a secondary base station. In other words, the terminal device 200 can notify the base station device 100-2 that it has selected the base station device 100-2 as a secondary base station. Upon receiving this notification, the base station device 100-2 can recognize that it is a secondary base station. Note that the information indicating that the base station device 100-2 is a secondary base station may be included in the AS message requesting connection in step S107.

[0039] Here, the terminal device 200 has already completed registration with the core network 10 via the base station device 100-1, which is the primary base station. Therefore, when the terminal device 200 establishes a connection with the base station device 100-2, the terminal device 200 omits registration with the core network 10. Therefore, no NAS message is transmitted or received between the terminal device 200 and the core network 10, and a UE context related to the terminal device 200 is generated in the base station device 100-2. Then, temporary identification information including identification information of the terminal device 200 and identification information of the base station device 100-2 is generated as identification information related to the UE context. As with the identification information generated by the base station device 100-1, for example, the I-RNTI can be used as this temporary identification information.

[0040] The generated UE context is held by the base station device 100-2, and identification information related to the UE context is notified to the terminal device 200, for example, by an AS message for releasing the connection (step S110). Upon receiving this notification, the terminal device 200 holds the identification information related to the UE context and releases the connection with the base station device 100-2. At this time, the terminal device 200 transitions to a non-communication mode, for example, an RRC inactive mode.

[0041] In this way, during the non-communication mode, the terminal device 200 selects a primary base station and a secondary base station according to signal strength, requests connection to each of the primary base station and the secondary base station, and receives notification of identification information related to the UE context from each of the primary base station and the secondary base station. Therefore, even during the non-communication mode, the terminal device 200 can selectively perform data communication with multiple base stations, and can perform data communication with the secondary base station if, for example, data communication with the primary base station fails.

[0042] FIG. 5 is a sequence diagram showing a small data transmission method of the terminal device 200 in the non-communication mode.

[0043] When the terminal device 200 receives an AS message for releasing a connection from, for example, the base station device 100-1 with which it is communicating (step S201), the terminal device 200 releases the connection with the base station device 100-1 and transitions to the RRC inactive mode. An example of this AS message is an RRC connection release.

[0044] When small data occurs during the RRC inactive mode, the terminal device 200 transmits the small data by the random access method to the base station device 100-1, which is the already selected primary base station. Specifically, the terminal device 200 transmits a message 1 (Msg1) including a random access preamble to the base station device 100-1 (step S202), and receives a message 2 (Msg2) including a random access response from the base station device 100-1 (step S203). Then, the terminal device 200 transmits a message 3 (Msg3) including identification information related to the UE context notified by the base station device 100-1 to the base station device 100-1 (step S204), and receives a message 4 (Msg4) that is a response to message 3 from the base station device 100-1 (step S205).

[0045] Terminal device 200 can transmit small data to base station device 100-1 along with the above-mentioned message 1 or message 3. Here, if, for example, the wireless quality between terminal device 200 and base station device 100-1 deteriorates and transmission of the small data fails, the procedures of steps S202 to S205 above will not be completed normally. In other words, terminal device 200 may not receive message 4 in step S205, for example.

[0046] In such a case, the terminal device 200 starts a predetermined timer and waits for a response from the base station device 100-1 while the timer is running. When the timer expires, the terminal device 200 switches the communication partner to the base station device 100-2, which is the already selected secondary base station, and transmits small data using the random access scheme with the base station device 100-2. For example, the timer is T319. Specifically, the terminal device 200 transmits message 1 (Msg1) including a random access preamble to the base station device 100-2 (step S206), and receives message 2 (Msg2) including a random access response from the base station device 100-2 (step S207). Then, the terminal device 200 transmits a message 3 (Msg3) including identification information related to the UE context notified by the base station device 100-2 to the base station device 100-2 (step S208), and receives a message 4 (Msg4) that is a response to message 3 from the base station device 100-2 (step S209).

[0047] In this way, terminal device 200 selectively transmits small data to the primary base station and secondary base station selected during non-communication mode as communication partners, so even if small data transmission to the primary base station fails, small data transmission to the secondary base station can be executed. As a result, data communication can be continuously performed during non-communication mode.

[0048] 6 is a sequence diagram showing another small data transmission method of the terminal device 200 in the non-communication mode. In FIG. 6, the same parts as in FIG. 5 are denoted by the same reference numerals.

[0049] When the terminal device 200 receives an AS message for releasing a connection from, for example, the base station device 100-1 with which it is communicating (step S201), the terminal device 200 releases the connection with the base station device 100-1 and transitions to the RRC inactive mode. An example of this AS message is an RRC connection release.

[0050] When small data occurs during RRC inactive mode, the terminal device 200 transmits the small data to the base station device 100-1, the already selected primary base station, by the CG (Configured Grant) method using radio resources previously allocated to the terminal device 200. Specifically, when the timing arrives for the radio resources previously allocated to the terminal device 200 by the base station device 100-1, the terminal device 200 transmits the small data using these radio resources (step S211). If the small data has been successfully received by the base station device 100-1, a reception acknowledgment to that effect is transmitted from the base station device 100-1 to the terminal device 200 (step S212).

[0051] Here, for example, if the wireless quality between the terminal device 200 and the base station device 100-1 is degraded and the transmission of the small data fails, the procedures of steps S211 and S212 described above will not be completed normally. In other words, the terminal device 200 may not receive the reception confirmation response of step S212, for example.

[0052] In such a case, the terminal device 200 starts a predetermined timer and waits for a response from the base station device 100-1 while the timer is running. When the timer expires, the terminal device 200 switches its communication partner to the already selected secondary base station, base station device 100-2, and transmits small data using the CG method between the terminal device 200 and the base station device 100-2. Specifically, when the timing arrives for the radio resources that have been allocated to the terminal device 200 in advance by the base station device 100-2, the terminal device 200 transmits the small data using these radio resources (step S213). If the small data has been successfully received by the base station device 100-2, a reception acknowledgment to that effect is transmitted from the base station device 100-2 to the terminal device 200 (step S214).

[0053] When T319 is used as the timer, the time set in T319 may be set shorter than usual to prompt switching of the communication partner, or the communication partner may be switched without waiting for the expiration of T319. Also, the time until the terminal device 200 switches the communication partner may be set to the time obtained by dividing the set time in T319 by the number of selected base stations.

[0054] In this way, terminal device 200 selectively transmits small data to the primary base station and secondary base station selected during non-communication mode as communication partners, so even if small data transmission to the primary base station fails, small data transmission to the secondary base station can be executed. As a result, data communication can be continuously performed during non-communication mode.

[0055] As described above, according to the present embodiment, the terminal device selects a primary base station and a secondary base station as potential communication partners during non-communication mode, and receives notification of identification information related to the UE context from the primary base station and the secondary base station. Then, when the terminal device transmits data during non-communication mode, it selectively transmits the data to the primary base station and the secondary base station. Therefore, even if data transmission to the primary base station fails, data transmission to the secondary base station can be executed, and data communication can be continuously performed during non-communication mode.

[0056] (Embodiment 3) In the third embodiment, a case will be described in which a primary base station acquires a result of measuring signal strength in a terminal device in RRC idle mode (IDLE Mode Measurement) and selects a secondary base station. The configuration of a wireless communication system according to the third embodiment is the same as that of the first embodiment (FIG. 1), and therefore description thereof will be omitted. Furthermore, the configurations of a base station device 100 and a terminal device 200 according to the third embodiment are the same as those of the second embodiment (FIGS. 2 and 3), and therefore description thereof will be omitted. The third embodiment is an embodiment that appropriately embodies the first embodiment, and can be implemented in combination with the first and second embodiments as long as there is no contradiction. Note that the IDLE Mode Measurement is radio measurement controlled by the network even when the terminal device 200 is in RRC idle mode or RRC inactive mode, and is different from radio measurement that the terminal device 200 independently performs when in RRC idle mode or RRC inactive mode.

[0057] 7 is a sequence diagram showing a cell selection method in a wireless communication system according to embodiment 3. In Fig. 7, the same components as in Fig. 4 are assigned the same reference numerals. In the following description, it is assumed that the wireless communication system includes base station devices 100-1 and 100-2 having the same configuration as base station device 100.

[0058] During the non-communication mode, the terminal device 200 measures the signal strength from surrounding base station devices including the base station devices 100-1 and 100-2, and selects a base station that can be a communication partner. Here, it is assumed that the terminal device 200 selects, for example, the base station device 100-1 with the highest signal strength as the primary base station with which to communicate with the highest priority.

[0059] Then, in the non-communication mode, the terminal device 200 transmits an AS message requesting a connection to establish communication with the base station device 100-1, which is the primary base station (step S101). Examples of this AS message include an RRC connection request and a connection resume request.

[0060] In response to this AS message, the base station device 100-1 transmits an AS message for predetermined settings to the terminal device 200 (step S102), and the terminal device 200 transmits an AS message notifying the base station device 100-1 of the completion of connection (step S103). The AS message notifying the completion of connection can include information indicating that the base station device 100-1 is the primary base station, as well as flag information indicating that the terminal device 200 is measuring signal strength in RRC idle mode. That is, the terminal device 200 can notify the base station device 100-1 that it has selected the base station device 100-1 as the primary base station, and can also notify the base station device 100-1 that it is a terminal device that supports IDLE Mode Measurement. Receiving this notification, the base station device 100-1 can recognize that it is the primary base station and that it is a base station that controls the terminal device 200 to perform data communication selectively using multiple cells. Note that the information indicating that the base station device 100-1 is the primary base station and the flag information may be included in the AS message requesting the connection in step S101.

[0061] When a connection between the terminal device 200 and the base station device 100-1 is established, a NAS message for registration is transmitted from the terminal device 200 to the core network 10 via the base station device 100-1 (step S104). When the terminal device 200 is registered in the core network 10, a NAS message indicating that the registration has been accepted is transmitted from the core network 10 to the terminal device 200 via the base station device 100-1 (step S105).

[0062] Then, the base station device 100-1, which has determined that it is the primary base station, requests the terminal device 200 to report the signal strength measurement results obtained by IDLE Mode Measurement (step S301). In response to this request, the terminal device 200 reports the signal strength measurement results measured in RRC idle mode to the base station device 100-1 (step S302). The signal strength measurement results include the signal strength measurement results from base station devices surrounding the terminal device 200, including the base station device 100-2.

[0063] Based on the signal strength measurement results, the base station device 100-1 selects a secondary base station that can be a communication partner of the terminal device 200, with second highest priority after the base station device itself. Specifically, the base station device 100-1 selects a base station device whose signal strength at the terminal device 200 is equal to or greater than a predetermined threshold as a secondary base station. Here, it is assumed that the base station device 100-2 is selected as the secondary base station. After selecting the secondary base station, the base station device 100-1 requests the base station device 100-2, which is the secondary base station, to generate a UE context to be assigned to the terminal device 200 (step S303). In response to this request, the base station device 100-2 generates a UE context for the terminal device 200 and notifies the base station device 100-1 of identification information related to the generated UE context (step S304).

[0064] Meanwhile, a UE context related to the terminal device 200 is also generated in the base station device 100-1. Then, temporary identification information including identification information of the terminal device 200 and identification information of the base station device 100-1 is generated as identification information related to the UE context. As this temporary identification information, for example, the I-RNTI can be used. Since the I-RNTI is 40-bit identification information, if the number of bits allocated to the identification information of the base station device is increased, the number of identifiable base station devices increases, but the number of identifiable terminal devices decreases. Also, if the number of bits allocated to the identification information of the base station device is reduced, the number of identifiable base station devices decreases, but the number of identifiable terminal devices increases. As identification information related to the UE context, any information other than the I-RNTI that can identify the UE context can be used.

[0065] The generated UE context is held by the base station device 100-1, and identification information related to the UE context is notified to the terminal device 200, for example, by an AS message for releasing the connection (step S305). At this time, the identification information related to the UE context generated by the base station device 100-1 is notified to the terminal device 200 together with the identification information related to the UE context notified by the base station device 100-2. That is, the identification information related to the UE context generated for the terminal device 200 by each of the base station devices 100-1 and 100-2 is notified together to the terminal device 200. Upon receiving this notification, the terminal device 200 holds the identification information related to the UE context and releases the connection with the base station device 100-1. As a result, the terminal device 200 transitions to a non-communication mode, for example, an RRC inactive mode.

[0066] In this way, during non-communication mode, the terminal device 200 selects a primary base station according to signal strength and requests connection, and the primary base station acquires signal strength measurement results from the terminal device 200 and selects a secondary base station. The primary base station then acquires identification information related to the UE context from the secondary base station and notifies the terminal device 200 of the identification information related to the UE context generated by the primary base station and the secondary base station. Therefore, the terminal device 200 can selectively perform data communication with multiple base stations even during non-communication mode, and can perform data communication with the secondary base station if, for example, data communication with the primary base station fails. That is, as in embodiment 2 (FIGS. 5 and 6), when transmission of small data from the terminal device 200 to the base station device 100-1 fails, the terminal device 200 switches the communication partner to the base station device 100-2 after a predetermined timer expires and transmits the small data to the base station device 100-2. This allows the terminal device 200 to continuously perform data communication during non-communication mode.

[0067] As described above, according to the present embodiment, when a terminal device selects a primary base station during non-communication mode, the primary base station selects a secondary base station and notifies the terminal device of identification information related to UE contexts generated by the primary base station and the secondary base station. Then, when the terminal device transmits data during non-communication mode, the terminal device selectively transmits the data to the primary base station and the secondary base station. Therefore, even if data transmission to the primary base station fails, data transmission to the secondary base station can be performed, and data communication can be continuously performed during non-communication mode.

[0068] In the above embodiments, examples have been described in which a primary base station with the highest priority and a secondary base station with the second highest priority are selected, but base stations with a third or higher priority may also be selected. That is, for example, in embodiment 2, terminal device 200 may select three or more base station devices that can be communication partners, transmit AS messages requesting connection to each of the base station devices, and receive notification of identification information related to the UE context from each of the base station devices.

[0069] Also, for example, in the third embodiment, base station devices 100-1 to 100-3 may be selected as base station devices that can communicate with each other, as shown in Fig. 8. As shown in Fig. 8, base station device 100-1, which is the primary base station, selects base station devices 100-2 and 100-3 as the second and third most preferred base stations in accordance with the signal strength at terminal device 200, and then requests these base stations to generate UE contexts to be allocated to terminal device 200 (step S303). In response to this request, base station devices 100-2 and 100-3 each generate UE contexts and notify base station device 100-1 of identification information related to the generated UE contexts (step S304).

[0070] By selecting three or more base station devices as potential communication partners in this way, even if data communication with the first and second priority base station devices fails during the non-communication mode, the terminal device 200 can still perform data communication with the third or higher priority base station devices. As a result, data communication can be continuously performed during the non-communication mode.

[0071] In the above embodiments, if data communication fails while the terminal device 200 is in non-communication mode, the base station of the communication partner is switched after a predetermined timer expires. For example, the T319 timer can be used as this predetermined timer. Alternatively, a timer set to a time shorter than the T319 timer may be used as the predetermined timer so that the base station of the communication partner is switched quickly when data communication fails.

[0072] Furthermore, the terminal device 200 may switch the base station as a communication partner when the number of data communication failures reaches a predetermined number, instead of when a predetermined timer expires. That is, the terminal device 200 may switch the communication partner to a secondary base station and execute small data transmission, for example, when small data transmission to the primary base station fails a predetermined number of times. These conditions are set in the terminal device 200 under control of the primary base station.

[0073] Furthermore, in the above embodiments, a case has been described in which the communication partner of the terminal device 200 is switched when data communication fails, but the above embodiments can also be applied to a case in which the terminal device 200 moves between cells. That is, for example, when the terminal device 200 moves from the cell of the primary base station to the cell of the secondary base station in the non-communication mode, it is possible for the primary base station to be the communication partner while the terminal device 200 is in the range of the cell of the primary base station, and for the secondary base station to be the communication partner after the terminal device 200 moves to the cell of the secondary base station. [Explanation of symbols]

[0074] 110 Network Interface 120, 220 processors 130, 230 memory 140, 210 Radio Communication Department

Claims

1. A wireless communication device among the plurality of wireless communication devices, a receiving unit that receives a message for establishing communication, the message being transmitted from another wireless communication device to the wireless communication device selected from the plurality of wireless communication devices; a control unit that transmits to the wireless communication device identification information assigned to the wireless communication device by a first other wireless communication device, and that controls the wireless communication device to select a cell formed by the first other wireless communication device as a cell to be used for data communication from a group of multiple cells formed by the multiple wireless communication devices, which is selected by the other wireless communication device when communication with the other wireless communication device in a non-communication mode can be performed and which is allowed even in the non-communication mode; A wireless communication device comprising:

2. the identification information is identification information that can simultaneously identify the device itself and the other wireless communication device; 2. The wireless communication device according to claim 1.

3. the receiving unit receives, from the other wireless communication device, information indicating whether the other wireless communication device has selected the primary base station; When the information indicates that the other wireless communication device is the primary base station, the control unit controls to transmit a message for registering the other wireless communication device to the core network to the core network.

2. The wireless communication device according to claim 1.

4. A wireless communication device capable of communicating with a plurality of other wireless communication devices, a transmitter that transmits a first message for establishing communication to a first other wireless communication device selected from the plurality of other wireless communication devices; a control unit that receives, from the first other wireless communication device, first identification information assigned to the wireless communication device by the first other wireless communication device, and that is capable of controlling selection of a cell to be used for data communication from a group of multiple cells formed by the multiple other wireless communication devices, the cell being selected by the wireless communication device when communication with the first other wireless communication device is established during a non-communication mode, and which is capable of performing data communication that is allowed even during the non-communication mode; A wireless communication device comprising:

5. the first identification information is identification information capable of simultaneously identifying the own device and the first other wireless communication device; 5. The wireless communication device according to claim 4.

6. the transmission unit transmits, to the first other wireless communication device, information indicating that the wireless communication device is a selected primary base station, and transmits, via the first other wireless communication device, a message for registering to a core network.

5. The wireless communication device according to claim 4.

7. The control unit performs data communication using a second cell included in the plurality of cell groups when data communication using a first cell included in the plurality of cell groups fails during the non-communication mode.

5. The wireless communication device according to claim 4.

8. the transmitting unit transmits a second message for establishing communication to a second other wireless communication device selected from the plurality of other wireless communication devices; the control unit receives, from the second other wireless communication device, second identification information assigned to the wireless communication device by the second other wireless communication device; 5. The wireless communication device according to claim 4.

9. A wireless communication system including a plurality of wireless communication devices and another wireless communication device, a first wireless communication device among the plurality of wireless communication devices receives a message for establishing communication, which is transmitted from the other wireless communication device to the first wireless communication device selected from the plurality of wireless communication devices, and transmits, to the other wireless communication device, identification information assigned to the wireless communication device by the first other wireless communication device; The other wireless communication device receiving the identification information, and being able to control selection of a cell to be used for data communication from a group of multiple cells formed by the multiple wireless communication devices, which is selected by the wireless communication device when establishing communication with the first other wireless communication device during a non-communication mode and is capable of performing data communication that is allowed even during the non-communication mode; A wireless communication system comprising:

10. A wireless communication method for a wireless communication device capable of communicating with a plurality of other wireless communication devices, comprising: transmitting a first message for establishing communication to a first other wireless communication device selected from the plurality of other wireless communication devices; receiving, from the first other wireless communication device, first identification information assigned to the wireless communication device by the first other wireless communication device; Controlling selection of a cell to be used for data communication from a group of multiple cells formed by the multiple other wireless communication devices, which cell was selected by the wireless communication device when communication with the first other wireless communication device was established during the non-communication mode and which can perform data communication that is allowed even during the non-communication mode; 1. A wireless communication method comprising the steps of:

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