Base station equipment, terminal equipment, and communication method

Abstract

To provide a base station device, a terminal device, and a communication method that can efficiently switch a terminal device in broadcast mode in an idle state to a unicast mode.SOLUTION: A base station device capable of information communication via broadcast and unicast includes a transmitting and receiving unit that broadcasts a first signal to a terminal device in an idle state (RRC_IDLE) and receives a second signal including negative acknowledgment (NACK) information indicating deterioration of communication quality from the terminal device on the basis of the first signal, a determination unit that determines whether it is difficult to continue broadcast communication with the terminal device on the basis of negative response information included in the second signal, and a control unit that instructs the transmitting and receiving unit to transmit a third signal containing switching notification information to unicast to the terminal device when the determination unit determines that broadcast communication is difficult.SELECTED DRAWING: Figure 4A

Description

Technical Field

[0004] , ,

[0005] , ,

[0001] One aspect of the present invention relates to a base station device, a terminal device, and a communication method.

Background Art

[0002] In 3GPP (3rd Generation Partnership Project) Release 17, MBS (Multicast and Broadcast Service) is being studied towards standardization. In the multicast mode, communication in the communication connection state is required to support signaling and ACK / NACK feedback transmission. On the other hand, in the broadcast mode, communication is possible not only in the communication connection state but also in the idle state. Further, in Patent Document 1, it has been studied to transmit ACK / NACK feedback with a preamble signal in the LTE (Long Term Evolution)_Idle state.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when communication quality deteriorates in broadcast reception in the idle state, the improvement procedure is not clearly defined. Therefore, good communication may be difficult in the broadcast mode. There is no description in Patent Document 1 about countermeasures in such a case. <骑射

[0005] One embodiment of the present invention provides a base station device, a terminal device, and a communication method that can efficiently switch a terminal device that is in broadcast mode in an idle state to unicast mode. [Means for solving the problem]

[0006] A base station device according to one embodiment of the present invention is a base station device capable of information communication by broadcast and unicast, comprising: a transmitting / receiving unit that transmits a first signal by broadcast to a terminal device in an idle state (RRC_IDLE) and receives a second signal from the terminal device that includes negative response (NACK) information indicating deterioration of communication quality based on the first signal; a determination unit that determines whether it is difficult to continue communication with the terminal device by broadcast based on the negative response information included in the second signal; and a control unit that, when the determination unit determines that it is difficult to communicate by broadcast, commands the transmitting / receiving unit to transmit a third signal that includes notification information for switching to unicast to the terminal device.

[0007] A terminal device according to one embodiment of the present invention is a terminal device capable of communicating information by broadcast and unicast, comprising: a transmitting and receiving unit that, in an idle state (RRC_IDLE), transmits a second signal to the base station device containing negative acknowledgment (NACK) information for a first signal transmitted by broadcast from the base station device and receives a third signal containing notification information for switching from broadcast to unicast; and a control unit that, upon receiving the third signal, switches the communication method with the base station device from broadcast to unicast.

[0008] A communication method according to one embodiment of the present invention comprises: a base station device broadcasting a first signal to a terminal device in an idle state (RRC_IDLE); the terminal device transmitting a second signal to the base station device that includes negative acknowledgment (NACK) information indicating a deterioration in communication quality based on the first signal; the base station device determining, based on the negative acknowledgment information contained in the second signal, whether it is difficult to continue broadcast communication with the terminal device; when it is determined that broadcast communication is difficult, the base station device transmitting a third signal to the terminal device that includes notification information for switching to unicast; and when the terminal device receives the third signal, switching the communication method with the base station device from broadcast to unicast. [Brief explanation of the drawing]

[0009] [Figure 1] Conceptual diagram of the communication system according to the first embodiment. [Figure 2A] Block diagram of the base station device according to the first embodiment. [Figure 2B] Block diagram of the terminal device according to the first embodiment. [Figure 3A] Conceptual diagram of the communication method according to the first embodiment. [Figure 3B] A conceptual diagram showing the sequence in the communication method according to the first embodiment. [Figure 4A] Conceptual diagram of the communication method according to the first embodiment. [Figure 4B] A conceptual diagram showing the sequence in the communication method according to the first embodiment. [Figure 5] Conceptual diagram of the preamble signal according to the first embodiment. [Figure 6A] A flowchart illustrating the operation of the base station device according to the first embodiment. [Figure 6B] A flowchart illustrating the operation of the terminal device according to the first embodiment. [Figure 7A] A conceptual diagram showing the sequence in the communication method according to the second embodiment. [Figure 7B] A conceptual diagram showing the sequence in the communication method according to the second embodiment. [Figure 8] Conceptual diagram of an RRC connection request signal according to the second embodiment. [Figure 9A] Flowchart showing the operation of a base station device according to the second embodiment. [Figure 9B] Flowchart showing the operation of a terminal device according to the second embodiment. [Figure 10A] Flowchart showing the operation of a base station device according to the third embodiment. [Figure 10B] Flowchart showing the operation of a terminal device according to the third embodiment. [Figure 11] Flowchart showing the operation of a terminal device according to a modification of the third embodiment A

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Regarding the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0011] <First Embodiment> The base station device, terminal device, and communication method according to the first embodiment of this invention will be described. This embodiment relates to a base station device, a terminal device, and a communication method in a 5G network, and relates to a method for switching from a broadcast mode to a unicast mode when the communication situation deteriorates while a terminal device in an idle state is communicating in the broadcast mode.

[0012] FIG. 1 is a conceptual diagram of a communication system according to this embodiment. As shown in the figure, the communication system 100 includes a core network device 200, a base station device 300, and a terminal device 400.

[0013] The core network device 200 is a backbone network, for example, a network that controls a mobile network. The core network device 200 is connected to the base station device 300 and can communicate with each other. The core network device 200 according to this embodiment may be a SA (Stand Alone)-compliant 5GC (5th Generation Core network), or may be a NSA (Non Stand Alone)-compliant EPC (Evolved Packet Core).

[0014] The base station device 300 is compatible with NR (New Radio) and is also called a gNodeB. The base station device 300 forms a cell 500 and communicates with the terminal device 400 located within the cell 500.

[0015] The terminal device 400 is located within the cell 500, communicates with the base station device 300 via NR, and is also called a UE (User Equipment). The terminal device 400 may be a communication terminal such as a smartphone, a tablet-type or laptop-type PC, etc. The terminal device 400 may also be an application for eMBB (Enhanced Mobile Broadband), URLLC (Ultra-Reliable & Low Latency Communications), and mMTC (massive Machine Type Communication). eMBB, URLLC, and mMTC are usage scenarios for NR and 5GC defined, for example, in 3GPP Release 15, etc.

[0016] Next, the details of the base station device 300 will be described using FIGURE 2A. FIGURE 2A is a block diagram of the base station device 300. The base station device 300 can communicate information with the terminal device 400 through broadcast and unicast, and as shown in FIGURE 2A, it includes a transmission / reception unit 310, a determination unit 320, a control unit 330, and a storage unit 340.

[0017] The transmitting / receiving unit 310 transmits and receives signals with the terminal device 400. In this embodiment, the transmitting / receiving unit 310 broadcasts a first signal to the terminal device 400 in an idle state (RRC_IDLE) according to the command of the control unit 330, and receives a second signal from the terminal device 400 that includes negative acknowledgment (NACK) information indicating a deterioration in communication quality based on the first signal. Furthermore, the transmitting / receiving unit 310 transmits a third signal to the terminal device 400 that includes notification information for switching from broadcast to unicast, according to the command of the control unit 330. Also, when the transmitting / receiving unit 310 receives an RRC connection (Radio Resource Control Connection) request signal from the terminal device 400, it transmits an RRC connection setting signal to the terminal device 400 according to the command of the control unit 330.

[0018] The first signal described above is not limited to any signal transmitted by broadcast. In this embodiment, the second signal is a preamble signal transmitted by the terminal device 400 in response to the first signal transmitted from the base station device 300. The third signal is a response to the said preamble signal and is a preamble reception response signal transmitted by the base station device 300. The second signal, the third signal, the RRC connection request signal, and the RRC connection setting signal are signals transmitted and received in a random access procedure for establishing an RRC connection between the base station device 300 and the terminal device 400. Hereinafter, in this embodiment, the second signal may be referred to as the preamble signal and the third signal as the preamble reception response signal. The preamble signal is transmitted using the first message (Msg1, message 1) in the random access procedure, and the preamble reception response signal is transmitted using the second message (Msg2, message 2). Furthermore, the RRC connection request signal is transmitted using the third message (Msg3, message 3) in the random access procedure, and the RRC connection setup signal is transmitted using the fourth message (Msg4, message 4).

[0019] Furthermore, the idle state (RRC_IDLE) described above is a state in which an RRC connection has not been established between the base station device 300 and the terminal device 400. In contrast, the RRC connected state (RRC_CONNECTED), which will be described later, is a state in which radio resources have been allocated to the terminal device 400 and an RRC connection has been established between the terminal device 400 and the base station device 300.

[0020] Furthermore, the above-mentioned negative response (NACK) is information indicating that the terminal device 400 was unable to properly receive the signal from the base station device 300, and will be referred to simply as NACK below. The above-mentioned negative response information includes NACK if the terminal device 400 was unable to properly receive the signal, and does not include NACK if it was able to properly receive the signal. In the following explanation, the negative response information will be simply referred to as NACK information, and if the base station device 300 receives NACK information containing NACK, it will be simply described as having received NACK.

[0021] Next, the determination unit 320 will be described. Based on the negative response information contained in the second signal (preamble signal) received by the transmitting / receiving unit 310, the determination unit 320 determines whether it is possible or difficult to continue broadcast communication with the terminal device 400. For example, the determination unit 320 can determine whether it is possible to continue broadcast communication with the terminal device 400 based on the number of times the second signal has been received within a predetermined period.

[0022] The control unit 330 controls the operation of the entire base station device 300. Furthermore, when the determination unit 320 determines that broadcast communication is difficult, the control unit 330 instructs the transceiver unit 310 to transmit a third signal (preamble reception response signal) containing notification information for switching to unicast to the terminal device 400.

[0023] The storage unit 340 stores information received from the core network device 200 and the terminal device 400. For example, in this embodiment, it can store the number of times a second signal including NACK has been received from the terminal device 400 within a predetermined period. The storage unit 340 may be, for example, RAM, ROM, flash memory, etc.

[0024] Note that Figure 2A only illustrates the elements necessary to switch the terminal device 400 from broadcast mode to unicast mode when the communication conditions deteriorate, and may include other control blocks. Furthermore, the base station device 300 may be configured to communicate with the terminal device 400 not only via NR but also via LTE. In addition, the determination unit 320 and the control unit 330 may be processors such as CPUs, and the processor may function as the determination unit 320 and the control unit 330 by executing a program held in the storage unit 340.

[0025] Next, the details of the terminal device 400 will be explained using Figure 2B. Figure 2B is a block diagram of the terminal device 400. The terminal device 400 is capable of communicating information with the base station device 300 via broadcast and unicast, and as shown in Figure 2B, it comprises a transmitting / receiving unit 410, a control unit 420, and a storage unit 430.

[0026] The transmitting / receiving unit 410 transmits and receives signals with the base station device 300. More specifically, when the terminal device 400 is in an idle state (RRC_IDLE), the transmitting / receiving unit 410 transmits a second signal (preamble signal) containing negative acknowledgment (NACK) information for the first signal broadcast from the base station device 300 to the base station device 300, in accordance with the command of the control unit 420. Furthermore, the transmitting / receiving unit 410 receives a third signal (preamble reception response signal) from the base station device 300 containing notification information for switching from broadcast to unicast. For example, the transmitting / receiving unit 410 receives the third signal from the base station device 300 when it has transmitted the second signal a predetermined number of times within a predetermined period.

[0027] The control unit 420 controls the operation of the entire terminal device 400. Furthermore, when the transceiver unit 410 receives the third signal, the control unit 420 switches the communication method with the base station device 300 from broadcast to unicast.

[0028] The memory unit 430 stores information received from the base station device 300 and information specific to the terminal device 400. The memory unit 430 may be, for example, RAM, ROM, or flash memory.

[0029] Note that, similar to Figure 2A, Figure 2B only shows the elements necessary for the terminal device 400 to switch from broadcast mode to unicast mode when the communication conditions deteriorate, and may include other control blocks. Also, like the base station device 300, the terminal device 400 may be configured to communicate with the base station device 300 not only via NR but also via LTE. Furthermore, the control unit 420 may be a processor such as a CPU, and the processor may function as the control unit 420 by executing a program held in the memory unit 430.

[0030] Next, in the communication system 100 with the above configuration, when the terminal device 400 is communicating in broadcast mode while idle, a specific example will be given to explain how to maintain broadcast mode or switch to unicast mode depending on the communication status.

[0031] First, we will explain the case where the communication conditions are good using Figures 3A and 3B. Figures 3A and 3B show the random access procedure according to this embodiment. Figure 3A is a schematic diagram of the communication system 100, similar to Figure 1, and Figure 3B is a sequence diagram showing the communication exchange between the base station device 300 and the terminal device 400. The terminal device 400 is in an idle state (RRC_IDLE).

[0032] As shown in Figures 3A and 3B, the base station device 300 and the terminal device 400 communicate via broadcast. When the base station device 300 transmits a first signal via broadcast, the terminal device 400 transmits a preamble signal for the first signal to the base station device 300. In this embodiment, the terminal device 400 can include NACK information in the preamble signal indicating whether or not the first signal was received correctly. This point will be explained later in the section on when the communication status deteriorates. The determination unit 320 of the base station device 300 determines whether or not the communication status between the base station device 300 and the terminal device 400 is good based on the NACK information included in the preamble signal, and based on this, determines whether or not it is possible to continue broadcast communication with the terminal device 400. In this example, since the communication status is good, the determination unit 320 determines that it is possible to continue broadcast communication. Based on this result, the transmitting / receiving unit 310 transmits a normal preamble reception response signal to the terminal device 400, without any notification information about switching to unicast, in accordance with the command of the control unit 330 of the base station device 300. The control unit 420 of the terminal device 400 then continues broadcast communication, and thereafter continues broadcast communication with the base station device 300 in the same manner.

[0033] Next, we will explain the case where the communication status deteriorates while broadcast communication is being performed as shown in Figures 3A and 3B above. Figures 4A and 4B show the random access procedure according to this embodiment, similar to Figures 3A and 3B above. Figure 4A is a schematic diagram of the communication system 100, similar to Figure 1, and Figure 4B is a sequence diagram showing the communication exchange between the base station device 300 and the terminal device 400. The terminal device 400 is in an idle state (RRC_IDLE).

[0034] As shown in Figures 4A and 4B, the base station device 300 and the terminal device 400 communicate via broadcast. When the base station device 300 broadcasts a first signal, the terminal device 400 sends a preamble signal for the first signal to the base station device 300. At this time, suppose the communication conditions between the base station device 300 and the terminal device 400 have deteriorated, the communication quality of the first signal has deteriorated, and the terminal device 400 has not been able to receive the first signal correctly. Then the control unit 420 of the terminal device 400 instructs the transmitting / receiving unit 410 to generate a preamble signal including NACK and send it to the base station device 300. The determination unit 320 of the base station device 300 determines whether it is possible to continue broadcast communication with the terminal device 400 based on the NACK information contained in the preamble signal. In this example, the communication conditions have deteriorated and the received preamble signal contains NACK, so the determination unit 320 determines that it is difficult to continue broadcast communication. Based on the results, the control unit 330 of the base station device 300 generates a preamble reception response signal including a notification to switch to unicast and instructs the transceiver unit 310 to transmit it to the terminal device 400. Upon receiving the preamble reception response signal including the notification to switch to unicast, the terminal device 400 instructs the transceiver unit 410 to generate an RRC connection request signal (Radio Resource Control Setup Request) and transmit it to the base station device 300 in order for the control unit to switch from broadcast to unicast. In response to receiving the RRC connection request signal, the control unit 330 of the base station device 300 generates an RRC connection setup signal (RRC Setup) including information necessary for unicast communication and instructs the transceiver unit 310 to transmit it to the terminal device 400. As a result, the terminal device 400 changes from an idle state to an RRC connected state (RRC_CONNECTED) and thereafter begins unicast communication with the base station device 300.

[0035] Figure 5 is a schematic diagram showing the preamble signal in the time domain according to this embodiment. In a random access procedure, the terminal device 400 can transmit a preamble on a random access channel (RACH), and 13 types of preamble formats are available. In this embodiment, the terminal device can generate a preamble signal containing information about the communication status between the base station device 300 and the terminal device 400, such as NACK information in this example, using the new preamble format shown in Figure 5. The preamble signal is transmitted using the first message in the random access procedure, as described above.

[0036] As shown in Figure 5, the preamble signal in this example consists of a cyclic prefix (CP) followed by sequence data (SEQ), and finally a gap (GP). The gap indicates, for example, the boundary with the next signal. The sequence data, which includes, for example, five time domains following the cyclic prefix, contains substantial data, and the terminal device 400 can include in this sequence data information for synchronization between the base station device 300 and the terminal device 400, as well as NACK information. If the terminal device 400 is able to accurately receive the signal from the base station device 300, the terminal device does not include NACK in the preamble signal, and the preamble signal is a signal containing normal sequence data. On the other hand, if the terminal device 400 is unable to accurately receive the signal from the base station device 300, the terminal device 400 transmits the sequence data to the base station device 300 with NACK included. The control unit 330 of the base station device 300 performs calculations on the sequence data contained in the five time domains received in the preamble signal, and performs, for example, synchronization processing between the base station device 300 and the terminal device 400. Similarly, if a NACK is included, it can recognize that a NACK has been received through calculations. To give an example for simplicity, if a NACK is not included, the control unit 330 obtains a predetermined waveform, while if a NACK is included, it obtains a different waveform indicating that a NACK is included.

[0037] The operation of the base station device 300 and terminal device 400 to realize the above figures 3A, 3B, 4A, and 4B will be explained using Figures 6A and 6B. Figures 6A and 6B are flowcharts showing the operation of the base station device 300 and terminal device 400, respectively.

[0038] First, the operation of the base station device 300 will be explained using Figure 6A. As shown in the figure, the transmitting / receiving unit 310 of the base station device 300 transmits a first signal to the terminal device 400 by broadcast in step S10, in accordance with the command of the control unit 330. Then, in step S11, the transmitting / receiving unit 310 of the base station device 300 receives a preamble signal from the terminal device 400 that includes NACK information for the signal transmitted in step S10.

[0039] In step S12, the determination unit 320 of the base station device 300 determines whether it is difficult to continue broadcast communication based on the NACK information contained in the preamble signal received in step S11. If it determines that it is possible to continue, in step S13, the control unit 330 generates a normal preamble reception response signal that does not include unicast switching notification information, and the transmitting / receiving unit 310 transmits this to the terminal device 400 according to the command of the control unit 330.

[0040] On the other hand, if the base station device 300 determines in step S12 that it is difficult to continue broadcast communication, in step S14 the control unit 330 generates a preamble reception response signal including notification information for switching to unicast, and the transmitting / receiving unit 310 transmits this to the terminal device 400 in accordance with the command of the control unit 330. Subsequently, in step S15 the transmitting / receiving unit 310 of the base station device 300 receives an RRC connection request signal from the terminal device 400, and in step S16 the control unit 330 generates an RRC connection setting signal, which the transmitting / receiving unit 310 transmits to the terminal device 400 in accordance with the command of the control unit 330. After that, in step S17 the control unit 330 of the base station device 300 communicates with the terminal device 400 by unicast.

[0041] Next, the operation of the terminal device 400 will be explained using Figure 6B. As shown in the figure, the transmitting / receiving unit 410 of the terminal device 400 receives the first signal transmitted from the base station device 300 by broadcast in step S20. Then, in step S21, the control unit 420 of the terminal device 400 generates a preamble signal containing NACK information for the signal transmitted in step S20, and the transmitting / receiving unit 410 transmits this to the base station device 300 according to the command of the control unit 420. As mentioned above, if the first signal is received correctly, the control unit 420 of the terminal device 400 does not include NACK in the NACK information, and includes NACK if it is not received correctly. Furthermore, in step S22, the transmitting / receiving unit 410 of the terminal device 400 receives a preamble reception response signal from the base station device 300 for the preamble signal transmitted in step S21.

[0042] The control unit 420 of the terminal device 400 determines whether the preamble reception response signal received in step S22 contains information about switching to unicast. If the information about switching to unicast is not included, the control unit 420 of the terminal device 400 continues broadcast communication in step S24.

[0043] On the other hand, if the control unit 420 of the terminal device 400 determines in step S23 that the information includes a notification of switching to unicast, in step S25 the control unit 420 generates an RRC connection request signal, which the transceiver 410 transmits to the base station device 300 according to the command of the control unit 420. Then, in step S26 the transceiver 410 of the terminal device 400 receives an RRC connection setting signal from the base station device 300, the terminal device 400 enters an RRC connection state, and in step S27 it communicates with the base station device 300 by unicast.

[0044] With the above configuration, when broadcast communication is being performed with an idle terminal device 400, the communication quality can be determined by the NACK information included in the preamble signal. If the communication quality deteriorates, a notification to switch to unicast is included in the preamble reception response signal, making it possible to appropriately switch to unicast communication. As a result, stable communication is possible even when the communication conditions deteriorate.

[0045] Furthermore, by including NACK information in the preamble signal and a notification to switch to unicast in the preamble reception response signal, it is possible to switch from broadcast to unicast in fewer sequences compared to a typical random access flow.

[0046] The determination in step S12, as described in Figure 6A, can be performed using various methods. For example, the control unit 330 may set multiple thresholds for the number of NACK receptions and determine that broadcast communication is difficult if these thresholds are reached within a predetermined period. In this case, the threshold for the number of NACK receptions, the predetermined period, and the number of NACK receptions for each terminal device 400 located within the cell 500 are stored, for example, in the storage unit 340. Alternatively, the control unit 330 may determine that broadcast communication is difficult when it receives a NACK once. In this case, since it is not necessary to store the number of NACK receptions for each terminal device 400 in the storage unit 340, the load on the control unit 330 can be reduced.

[0047] <Second Embodiment> Next, a base station device, terminal device, and communication method according to a second embodiment of the present invention will be described. In the first embodiment described above, a case was described in which NACK information was included in the preamble signal and a notification of switching to unicast was included in the preamble reception response signal. In contrast, in this embodiment, NACK information is included in the RRC connection request signal and a notification of unicast or broadcast connection is included in the RRC connection setting signal. Below, only the differences from the first embodiment will be described.

[0048] The configuration of the base station device 300 and terminal device 400 according to this embodiment is the same as that described in Figures 2A and 2B of the first embodiment. However, in this embodiment, the terminal device 400 transmits an RRC connection request signal as a second signal, and the base station device 300 transmits an RRC connection setting signal, which is a response to the RRC connection request signal, as a third signal. In this embodiment as well, the second and third signals are signals transmitted and received in a random access procedure for establishing an RRC connection between the base station device 300 and the terminal device 400. In addition to the negative acknowledgment (NACK) information described in the first embodiment, the second signal according to this embodiment further includes information regarding the communication status between the base station device 300 and the terminal device 400. This information regarding the communication status includes acknowledgment (ACK), RSSI (Received Signal Strength Indicator), RSRP (Reference Signal Received Power), and CQI (Channel Quality Indicator). The determination unit 320 of the base station device 300 then determines whether broadcast communication can be continued with the terminal device 400 based on the negative response (NACK) information contained in the second signal and information regarding the communication status between the base station device 300 and the terminal device 400. Hereinafter, in this embodiment, the second signal will be referred to as the RRC connection request signal, and the third signal will be referred to as the RRC connection setting signal.

[0049] Next, in the communication system 100 according to this embodiment, when the terminal device 400 is communicating in broadcast mode while idle, a specific example will be given to explain how to maintain broadcast mode or switch to unicast mode depending on the communication status.

[0050] First, let's explain the case where the communication status is good using Figure 7A. Figure 7A corresponds to Figure 3B described in the first embodiment and is a sequence diagram of the random access procedure according to this embodiment. The terminal device 400 is in an idle state (RRC_IDLE).

[0051] As shown in Figure 7A, the base station device 300 and the terminal device 400 communicate via broadcast. When the base station device 300 transmits a first signal via broadcast, the terminal device 400 transmits a preamble signal for the first signal to the base station device 300. Unlike the first embodiment, the preamble signal in this embodiment does not include NACK information and is transmitted using one of the 13 conventional preamble formats described above. The base station device 300 transmits a preamble reception response signal to the terminal device 400 for the received preamble signal. This preamble reception response signal is a normal preamble reception response signal as described using Figure 3B in the first embodiment and does not include a notification of switching to unicast. Upon receiving the preamble reception response signal, the terminal device 400's control unit 420 generates an RRC connection request signal including feedback for the broadcast and has the transceiver unit 410 transmit it to the base station device 300. The feedback for the broadcast includes, in addition to the NACK information described above, information regarding the communication status such as RSSI, RSRP, and CQI. The base station device 300's determination unit 320 then determines, based on the feedback included in the RRC connection request signal, whether the communication status between the base station device 300 and the terminal device 400 is good, and based on this, determines whether it is possible to continue broadcast communication with the terminal device 400. In this example, since the communication status is good, the determination unit 320 determines that it is possible to continue broadcast communication. Based on this result, the control unit 330 of the base station device 300 generates an RRC connection setting signal that includes information indicating that broadcast communication will be continued (broadcast connection notification), and has the transceiver unit 310 transmit this to the terminal device 400. The control unit 420 of the terminal device 400 then continues broadcast communication, and thereafter continues broadcast communication with the base station device 300 in the same manner.

[0052] Next, we will explain the case where the communication status deteriorates while broadcast communication is being performed as shown in Figure 7A above. Figure 7B shows the random access procedure according to this embodiment, similar to Figure 7A above, and is a sequence diagram showing the communication exchange between the base station device 300 and the terminal device 400. The terminal device 400 is in an idle state (RRC_IDLE).

[0053] As shown in Figure 7B, the base station device 300 and the terminal device 400 communicate via broadcast. Similar to Figure 7A, when the base station device 300 broadcasts a first signal, the terminal device 400 sends a preamble signal for the first signal to the base station device 300, and the base station device 300 sends a preamble reception response signal to the terminal device 400. The control unit 420 of the terminal device 400 then generates an RRC connection request signal including the aforementioned feedback for the broadcast and instructs the transceiver unit 410 to send it to the base station device 300. The determination unit 320 of the base station device 300 determines, based on the feedback included in the RRC connection request signal, whether it is possible to continue broadcast communication with the terminal device 400. In this example, the determination unit 320 determines, based on the received feedback, that the communication situation has deteriorated and it is difficult to continue broadcast communication. Based on this result, the control unit 330 of the base station device 300 generates an RRC connection setting signal including a notification to switch to unicast and instructs the transceiver unit 310 to send it to the terminal device 400. Upon receiving an RRC connection setting signal that includes a notification of switching to unicast, the terminal device 400 changes from an idle state to an RRC connected state (RRC_CONNECTED) and thereafter begins unicast communication with the base station device 300.

[0054] Figure 8 is a conceptual diagram of the RRC connection request signal according to this embodiment. The RRC connection request signal is transmitted using the third message in the random access procedure, as described above. As shown in the figure, the third message according to this embodiment includes TMSI (Temporary Mobile Subscriber Identity), random value, Establishment cause, and spare, as well as a NACK index. This NACK index corresponds to the NACK information described above. Although not shown in Figure 8, the third message may also include information such as acknowledgment (ACK), RSSI, RSRP, and CQI. The RRC connection setup signal is transmitted using the fourth message in the random access procedure, as described above. And, similar to the RRC connection request signal shown in Figure 8, the fourth message further includes a notification of switching to unicast.

[0055] The operation of the base station device 300 and terminal device 400 to realize Figures 7A and 7B above will be explained using Figures 9A and 9B. Figures 9A and 9B are flowcharts showing the operation of the base station device 300 and terminal device 400, respectively, and correspond to Figures 6A and 6B described in the first embodiment.

[0056] First, the operation of the base station device 300 will be explained using Figure 9A. As shown in the figure, the transmitting / receiving unit 310 of the base station device 300 transmits the first signal to the terminal device 400 by broadcast in step S10, similar to the first embodiment. Then, in step S30, the transmitting / receiving unit 310 of the base station device 300 receives a preamble signal from the terminal device 400 for the signal transmitted in step S10. As mentioned above, this preamble signal does not contain NACK information.

[0057] In step S31, the control unit 330 of the base station device 300 generates a normal preamble reception response signal that does not include a notification of switching to unicast, and the transmitting / receiving unit 310 transmits this to the terminal device 400 according to the command of the control unit 330. Subsequently, in step S32, the transmitting / receiving unit 310 of the base station device 300 receives an RRC connection request signal that includes feedback for broadcasting. Then, in step S33, the determination unit 320 of the base station device 300 determines whether it is difficult to continue broadcast communication based on the feedback included in the RRC connection request signal received in step S32. If it determines that it is possible to continue, in step S34, the control unit 330 generates an RRC connection setting signal that includes a broadcast connection notification, and the transmitting / receiving unit 310 transmits this to the terminal device 400 according to the command of the control unit 330. As a result, the base station device 300 and the terminal device 400 continue broadcast communication.

[0058] On the other hand, if the base station device 300 determines in step S33 that it is difficult to continue broadcast communication, in step S35 the control unit 330 generates an RRC connection setting signal including notification information for switching to unicast, and the transceiver unit 310 transmits this to the terminal device 400 in accordance with the command of the control unit 330. Thereafter, in step S17, the base station device 300 communicates with the terminal device 400 by unicast.

[0059] Next, the operation of the terminal device 400 will be explained using Figure 9B. As shown in the figure, the transmitting / receiving unit 410 of the terminal device 400 receives the first signal transmitted from the base station device 300 by broadcast in step S20, similar to the first embodiment. Then, in step S40, the transmitting / receiving unit 410 of the terminal device 400 transmits a preamble signal for the signal transmitted in step S20 to the base station device 300. As mentioned above, this preamble signal does not contain NACK information. Furthermore, in step S41, the transmitting / receiving unit 410 of the terminal device 400 receives a preamble reception response signal for the preamble signal transmitted in step S40 from the base station device 300. This preamble reception response signal also does not contain unicast switching notification information.

[0060] Next, in step S42, the control unit 420 of the terminal device 400 generates an RRC connection request signal including feedback for the broadcast, which the transceiver unit 410 transmits to the base station device 300 according to the command of the control unit 420. Furthermore, in step S43, the transceiver unit 410 of the terminal device 400 receives an RRC connection setting signal from the base station device 300.

[0061] In step S44, the control unit 420 of the terminal device 400 determines whether the RRC connection setting signal received in step S43 contains information about switching to unicast. If the information about switching to unicast is not included, the control unit 420 of the terminal device 400 continues broadcast communication in step S24.

[0062] On the other hand, if the control unit 420 of the terminal device 400 determines in step S44 that the information includes a notification to switch to unicast, the terminal device 400 enters an RRC connection state and communicates with the base station device 300 via unicast in step S27.

[0063] With the above configuration, when broadcast communication is performed with an idle terminal device 400, the communication quality can be determined by the feedback included in the RRC connection request signal. In this case, compared to the first embodiment, information such as RSSI, RSRP, and CQI can be received in addition to NACK information, so the communication quality status can be grasped more accurately. Therefore, it becomes possible to switch to unicast communication more appropriately.

[0064] Furthermore, by including feedback in the RRC connection request and including a notification to switch to unicast in the RRC connection setting signal, it is possible to switch from broadcast to unicast in fewer sequences compared to a typical random access flow. In this embodiment, the case in which the base station device 300 determines that it is possible to continue communication by broadcast and includes a broadcast connection notification in the RRC connection setting signal was described as an example, but it is also possible not to include a broadcast connection notification. Even in this case, the terminal device 400 can recognize that communication will continue by broadcast based on the fact that the RRC connection setting signal does not include a notification to switch to unicast.

[0065] <Third Embodiment> Next, a base station device, terminal device, and communication method according to a third embodiment of the present invention will be described. This embodiment relates to a combination of the first and second embodiments described above, and applies the method described in the second embodiment when it is difficult to determine whether broadcast communication using NACK information as described in the first embodiment is difficult. Below, only the differences from the first and second embodiments will be described.

[0066] The configuration of the base station device 300 and terminal device 400 according to this embodiment is the same as that described in Figures 2A and 2B of the first embodiment. However, this embodiment differs from the first and second embodiments in the following respects.

[0067] First, the base station device 300 will be described. The transmitting / receiving unit 310 of the base station device 300 receives a preamble signal as a second signal, similar to the first embodiment. The transmitting / receiving unit 310 also transmits a preamble reception response signal or an RRC connection setting signal, including a notification of switching to unicast, as a third signal, in accordance with the command of the control unit 330, similar to the first embodiment. The transmitting / receiving unit 310 can also transmit a preamble reception response signal, including a request for information regarding the communication status between the base station device 300 and the terminal device 400, as a fourth signal, similar to the second embodiment. Furthermore, in response to the fourth signal, the transmitting / receiving unit 310 receives an RRC connection request signal from the terminal device 400 as a fifth signal, which further includes information regarding the communication status between the base station device 300 and the terminal device 400 (the feedback mentioned above).

[0068] The determination unit 320 determines whether broadcast communication with the terminal device 400 can be continued based on the negative response (NACK) information contained in the second signal (preamble signal) or the information regarding the communication status between the base station device 300 and the terminal device 400 contained in the fifth signal (RRC connection request signal).

[0069] If the determination unit 320 has difficulty determining whether broadcast communication can continue based on the negative response (NACK) information contained in the second signal (preamble signal), the control unit instructs the transceiver unit 310 to transmit a preamble reception response signal to the terminal device 400 as a fourth signal. This preamble response is a response to the preamble signal and includes a request for information regarding the communication status between the base station device 300 and the terminal device 400.

[0070] In other words, in this embodiment, the second signal is transmitted from the terminal device 400, as in the first embodiment, and is a preamble signal containing NACK information. The third signal is transmitted from the base station device 300, as in the first and second embodiments, and is a preamble reception response signal or RRC connection setting signal containing notification information for switching to unicast. Furthermore, the fourth signal is transmitted from the base station device 300, as in the second embodiment, and is a preamble reception response signal containing a feedback request regarding the communication status. And the fifth signal is transmitted from the terminal device 400, as in the second embodiment, and is an RRC connection request signal containing feedback regarding the communication status.

[0071] Next, the terminal device 400 will be described. The transmitting / receiving unit 410 of the terminal device 400 transmits a preamble signal as a second signal, similar to the first embodiment. After transmitting the second signal, if the transmitting / receiving unit 410 receives a fourth signal from the base station device 300, which is a preamble reception response signal that is a response to the preamble signal and includes a request for the communication status between the base station device 300 and the terminal device 400, it transmits an RRC connection request signal as a fifth signal to the base station device 300 in response to the fourth signal, further including feedback regarding the communication status between the base station device 300 and the terminal device 400. Then, after transmitting the fifth signal, the transmitting / receiving unit 310 receives a third signal (RRC connection setting signal).

[0072] Next, in the communication system 100 according to this embodiment, when the terminal device 400 is communicating in broadcast mode while idle, a method for maintaining broadcast mode or switching to unicast mode depending on the communication status will be explained using Figures 10A and 10B. Figures 10A and 10B are flowcharts showing the operation of the base station device 300 and the terminal device 400, respectively, and correspond to Figures 6A and 6B described in the first embodiment, and Figures 9A and 9B described in the second embodiment.

[0073] First, the operation of the base station device 300 will be explained using Figure 10A. As shown in the figure, the transmitting and receiving unit 310 of the base station device 300 transmits a first signal to the terminal device 400 by broadcast in step S10, similar to the first embodiment, and receives a preamble signal containing NACK information from the terminal device 400 in step S11.

[0074] In step S12, the determination unit 320 of the base station device 300 determines, based on the preamble signal received in step S11, whether it is difficult to continue broadcast communication. If the base station device 300 is able to make this determination in step S12, the same processing as in the first embodiment is performed. That is, if it is determined in step S12 that continuation is possible, in step S13, it sends a normal preamble reception response signal to the terminal device 400 that does not include notification information about switching to unicast. On the other hand, if the base station device 300 determines in step S12 that it is difficult to continue broadcast communication, it executes the processing of steps S14 to S17 described in Figure 6A of the first embodiment, and the base station device 300 communicates with the terminal device 400 by unicast.

[0075] On the other hand, in step S12, it may be difficult for the determination unit 320 of the base station device 300 to determine whether it is difficult to continue communication via broadcast. In this case, in step S50, the control unit 330 generates a preamble reception response signal that includes a notification requesting feedback for the broadcast, and instructs the transmitting / receiving unit 310 to transmit the signal to the terminal device 400.

[0076] The subsequent processing is the same as steps S32 onwards described in the second embodiment. That is, in step S32, the base station device 300 receives an RRC connection request signal including feedback for the broadcast. Then, in step S33, the base station device 300 determines again whether it is difficult to continue communication by broadcast. The determination in step S33 is made based on the feedback received in step S32, but the determination may also take into account the NACK information received in step S11. If it is determined that it is possible to continue, in step S34, it sends an RRC connection setting signal including a broadcast connection notification to the terminal device 400. On the other hand, if the base station device 300 determines in step S33 that it is difficult to continue communication by broadcast, the processing in steps S35 and S17 is performed, and the base station device 300 communicates with the terminal device 400 by unicast.

[0077] Next, the operation of the terminal device 400 will be explained using Figure 10B. As shown in the figure, the transmitting and receiving unit 310 of the terminal device 400, in the same manner as in the first embodiment, responds to the first signal received in step S20 by transmitting a preamble signal including NACK information to the base station device 300 in step S21, and further receives a preamble reception response signal from the base station device 300 in step S22.

[0078] In step S22, the control unit 420 of the terminal device 400 receives a preamble reception response signal. In step S60, it checks whether the preamble reception response signal includes a notification to switch to unicast or a notification requesting feedback for broadcast.

[0079] In step S60, if the preamble reception response signal does not include a feedback request notification, the same processing as in the first embodiment is performed. That is, if the preamble reception response signal does not include a unicast switching notification, broadcast communication continues in step S24. On the other hand, if a unicast switching notification is included, the processing in steps S25 to S27 described in Figure 6B of the first embodiment is performed, and the terminal device 400 communicates with the base station device 300 by unicast.

[0080] In step S60, if the preamble reception response signal includes a feedback request notification, the processes described in steps S42-S44, S24, and S27 in the second embodiment are performed. Specifically, in step S42, the terminal device 400 transmits an RRC connection request signal including feedback for the broadcast to the base station device 300, and in step S43, it receives an RRC connection setting signal from the base station device 300.

[0081] Then, in step S44, it is determined whether the RRC connection setting signal received in step S43 contains information about switching to unicast. If it does not contain information about switching to unicast, the terminal device 400 continues broadcast communication in step S24.

[0082] On the other hand, if the terminal device 400 determines in step S44 that the information includes a notification to switch to unicast, the terminal device 400 enters an RRC connection state and communicates with the base station device 300 via unicast in step S27.

[0083] According to the above configuration, if it is possible to determine whether or not communication can be continued by broadcast based on NACK information, the base station device 300 will decide whether to continue broadcast communication or switch to unicast based on the NACK information, as described in the first embodiment. However, there may be cases where it is difficult to make a decision based on NACK information alone. For example, if the base station device 300 receives five NACKs in a short period of time, it is preferable to determine that the communication situation has deteriorated and switch to unicast. However, if five NACKs are received over a long period of time, it may be difficult to clearly determine that the communication situation has deteriorated. In this regard, according to this embodiment, if it is difficult to make a decision based on NACK information alone, the base station device 300 requests feedback on the broadcast from the terminal device 400 using the preamble reception response signal, and determines the communication situation including this feedback to decide whether to continue broadcasting or switch to unicast. Therefore, the optimal decision method can be adopted depending on the situation, and the sequence can also be made simpler depending on the situation. As a result, more appropriate and faster decisions can be made.

[0084] In the first embodiment, it was noted that the determination of whether or not it is difficult to continue broadcast communication may be made based on the reception of a single NACK. Even in this case, as in this embodiment, when a NACK is received once, it may be determined whether to switch to unicast based on the feedback received from the terminal device 400. The operation of the base station device 300 in such a case will be explained with reference to Figure 11. Figure 11 is a flowchart showing the operation of the base station device 300 according to a modified example of the third embodiment.

[0085] In this example, as shown in Figure 10A described in the third embodiment, the control unit 330 of the base station device 300 causes the transceiver unit 310 to transmit the fourth signal once it receives the second signal. That is, as shown in Figure 11, when the base station device 300 receives the preamble signal in step S11, if it is determined in step S70 that the NACK information of the preamble signal contains a NACK, the operation from step S50 onwards described in Figure 10A is executed.

[0086] <Variations, etc.> The embodiments described above are merely examples, and various modifications are possible. For example, the configuration of the base station device 300 and terminal device 400 described in the above embodiments is merely an example and is not limited to the configuration described above. Furthermore, in the second and third embodiments, ACK, RSSI, RSRP, and CQI were described as examples of feedback to broadcasts, but the invention is not limited to these, and any information that is useful for determining the communication quality between the base station device 300 and the terminal device 400 is acceptable. Moreover, the criteria for determining whether or not broadcast communication can be continued can be appropriately selected depending on the application and surrounding environment.

[0087] Furthermore, in the above embodiment, the processing performed by the determination unit 320 and the control units 330 and 420 was described as an example in which the processor executes a program held in the storage units 340 and 430. However, this program only needs to be held in a storage device (recording medium) that can be read by a computer (i.e., a processor), and this recording medium can be a "non-temporary tangible medium," such as tape, disk, card, semiconductor memory, or programmable logic circuit. The program may also be supplied to the computer via any transmission medium that can transmit data. Of course, at least a part of the processing performed by the determination unit 320 and the control units 330 and 420 may be implemented by hardware, or by a combination of hardware and software. Moreover, the order of the flowchart processing described in the above embodiment can be changed as much as possible.

[0088] Although several embodiments of the present invention have been described above, the invention is not limited to the above-described forms and can be modified as appropriate. Furthermore, the above configurations can be replaced with substantially similar configurations, configurations that produce similar effects, or configurations that can achieve similar objectives. [Explanation of Symbols]

[0089] 100...Communication system, 200...Core network, 300...Base station equipment, 310, 410...Transmitting / receiving unit, 320...Determination unit, 330, 420...Control unit, 340, 430...Storage unit, 400...Terminal equipment, 500...Cell

Claims

1. A base station device capable of broadcast and unicast information communication, A transmitting and receiving unit that transmits a first signal via broadcast to a terminal device in an idle state (RRC_IDLE) and receives a second signal from the terminal device that includes negative response (NACK) information indicating a deterioration in communication quality based on the first signal, A determination unit that determines whether it is difficult to continue communication with the terminal device via broadcast based on the negative response information contained in the second signal, When the determination unit determines that communication by broadcast is difficult, the control unit commands the transceiver to transmit a third signal, which includes notification information for switching to unicast, to the terminal device. It is equipped with, The second signal is a preamble signal, The third signal is a preamble reception response signal, which is a response to the preamble signal, in the base station device.

2. The base station device according to claim 1, wherein the determination unit determines whether it is difficult to continue broadcast communication with the terminal device based on the number of times the second signal has been received within a predetermined period.

3. A base station device capable of broadcasting and unicasting information, A transmitting and receiving unit that transmits a first signal via broadcast to a terminal device in an idle state (RRC_IDLE) and receives a second signal from the terminal device that includes negative response (NACK) information indicating a deterioration in communication quality based on the first signal, A determination unit that determines whether it is difficult to continue communication with the terminal device via broadcast based on the negative response information contained in the second signal, When the determination unit determines that communication by broadcast is difficult, the control unit commands the transceiver to transmit a third signal, which includes notification information for switching to unicast, to the terminal device. It is equipped with, The base station device is such that the second and third signals are signals transmitted and received in a random access procedure.

4. A base station device capable of broadcasting and unicasting information, A transmitting and receiving unit that transmits a first signal via broadcast to a terminal device in an idle state (RRC_IDLE) and receives a second signal from the terminal device that includes negative response (NACK) information indicating a deterioration in communication quality based on the first signal, A determination unit that determines whether it is difficult to continue communication with the terminal device via broadcast based on the negative response information contained in the second signal, When the determination unit determines that communication by broadcast is difficult, the control unit commands the transceiver to transmit a third signal, which includes notification information for switching to unicast, to the terminal device. It is equipped with, The base station device is a Radio Resource Control (RRC) Setup Request signal, the second signal of which further includes information regarding the communication status between the base station device and the terminal device.

5. The base station apparatus according to claim 4, wherein the third signal is an RRC connection setup signal (RRC Setup).

6. The base station device according to claim 4, wherein the determination unit determines whether it is difficult to continue broadcast communication with the terminal device based on the negative response information included in the second signal and information regarding the communication status between the base station device and the terminal device.

7. A base station device capable of broadcasting and unicasting information, A transmitting and receiving unit that transmits a first signal via broadcast to a terminal device in an idle state (RRC_IDLE) and receives a second signal from the terminal device that includes negative response (NACK) information indicating a deterioration in communication quality based on the first signal, A determination unit that determines whether it is difficult to continue communication with the terminal device via broadcast based on the negative response information contained in the second signal, When the determination unit determines that communication by broadcast is difficult, the control unit commands the transceiver to transmit a third signal, which includes notification information for switching to unicast, to the terminal device. It is equipped with, The second signal is a preamble signal, Based on the negative response information included in the second signal, the control unit commands the transceiver to transmit a preamble reception response signal to the terminal device as a fourth signal, which is a response to the preamble signal and includes a request for information regarding the communication status between the base station device and the terminal device. In response to the fourth signal, the transmitting / receiving unit receives an RRC Setup Request signal from the terminal device as a fifth signal, which further includes information regarding the communication status between the base station device and the terminal device. The determination unit determines, based on information regarding the communication status between the base station device and the terminal device included in the fifth signal, whether it is difficult to continue broadcast communication with the terminal device.

8. The base station device according to claim 7, wherein the control unit, upon receiving the second signal once, causes the transmission / reception unit to transmit the fourth signal.

9. A terminal device capable of broadcast and unicast information communication, In an idle state (RRC_IDLE), a transceiver transmits a second signal to the base station device containing negative response (NACK) information for the first signal transmitted by broadcast from the base station device, and receives a third signal containing notification information for switching from broadcast to unicast. A control unit that, upon receiving the third signal, switches the communication method with the base station device from broadcast to unicast. It is equipped with, The second signal is a preamble signal. The terminal device wherein the third signal is a preamble reception response signal, which is a response to the preamble signal.

10. When the transmitting / receiving unit transmits the second signal a predetermined number of times within a predetermined period, the base station device The terminal device according to claim 9, which receives the third signal from the terminal device.

11. A terminal device capable of broadcasting and unicasting information, In an idle state (RRC_IDLE), a transceiver transmits a second signal to the base station device containing negative response (NACK) information for the first signal transmitted by broadcast from the base station device, and receives a third signal containing notification information for switching from broadcast to unicast. A control unit that, upon receiving the third signal, switches the communication method with the base station device from broadcast to unicast. It is equipped with, The terminal device is one in which the second signal and the third signal are signals transmitted and received in a random access procedure.

12. A terminal device capable of broadcasting and unicasting information, In an idle state (RRC_IDLE), a transceiver transmits a second signal to the base station device containing negative response (NACK) information for the first signal transmitted by broadcast from the base station device, and receives a third signal containing notification information for switching from broadcast to unicast. A control unit that, upon receiving the third signal, switches the communication method with the base station device from broadcast to unicast. It is equipped with, The terminal device is a Radio Resource Control (RRC) Setup Request signal, the second signal of which further includes information regarding the communication status between the base station device and the terminal device.

13. The terminal device according to claim 12, wherein the third signal is an RRC connection setup signal (RRC Setup).

14. A terminal device capable of broadcasting and unicasting information, In an idle state (RRC_IDLE), a transceiver transmits a second signal to the base station device containing negative response (NACK) information for the first signal transmitted by broadcast from the base station device, and receives a third signal containing notification information for switching from broadcast to unicast. A control unit that, upon receiving the third signal, switches the communication method with the base station device from broadcast to unicast. It is equipped with, The second signal is a preamble signal, After transmitting the second signal, the transmitting / receiving unit receives a fourth signal from the base station device, which is a preamble reception response signal that is a response to the preamble signal and includes a request for the communication status between the base station device and the terminal device. In response to the fourth signal, the transmitting / receiving unit transmits to the base station device a fifth signal, an RRC Setup Request signal, which further includes information regarding the communication status between the base station device and the terminal device. The transmitting and receiving unit is a terminal device that receives the third signal (RRC Setup) after transmitting the fifth signal.

15. The base station equipment broadcasts the first signal to terminal equipment in an idle state (RRC_IDLE), The terminal device transmits a second signal to the base station device that includes negative response (NACK) information indicating a deterioration in communication quality based on the first signal. The base station device determines, based on the negative response information included in the second signal, whether it is difficult to continue the broadcast communication with the terminal device. When it is determined that communication via broadcast is difficult, the base station device transmits a third signal containing information about switching to unicast to the terminal device. When the third signal is received, the terminal device switches the communication method with the base station device from broadcast to unicast. It is equipped with, A communication method wherein the second signal and the third signal are signals transmitted and received in a random access procedure.

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