Terminal device for coverage extension in random access procedure, control method, and program

Abstract

To provide a terminal device for efficiently executing repetitive transmission of a message for coverage extension in a random access procedure, and a control method and program therefor.SOLUTION: A radio communications system includes a terminal device for: identifying, as a resource for transmitting a random access preamble, any of a first resource in which a device incapable of repetitively transmitting a message 3 in a random access procedure of four steps using sequential slots is capable of transmitting the preamble, and a second resource differing from the first resource, in which a device capable of repetitively transmitting the message 3 using sequential slots is capable of transmitting the preamble; transmitting the preamble; when the repetitive transmission can be performed, determining whether or not to use the repetitive transmission; and identifying, as a preamble transmission resource, the second resource when it is determined to use the repetitive transmission and the first resource when it is determined not to use the repetitive transmission.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a coverage extension technique in a random access procedure.

Background Art

[0002] In the cellular communication standard of the 3rd Generation Partnership Project (3GPP), when a terminal device connects to a base station device, it is stipulated to execute a random access procedure. In the random access procedure, first, the terminal device transmits a Message 1 (random access preamble) to the base station device at a predetermined frequency and time resource for the random access procedure. In response to detecting the Message 1, the base station device transmits a Message 2 (random access response) including transmission timing and resource allocation information in the uplink (the link in the direction from the terminal device to the base station device). Then, the terminal device uses the timing specified by the Message 2 and the allocated resources to transmit a Message 3 for requesting a connection in the RRC (Radio Resource Control) layer to the base station device. The base station device transmits a Message 4 including control information for the RRC connection and the like to the terminal device in response to the Message 3. By this procedure, the terminal device can establish a connection with the base station device.

[0003] In the conventional cellular communication standard, a technique for extending coverage by repeatedly transmitting the same data in a plurality of consecutive time slots is stipulated. And in the standardization work of the 3GPP Release 17 standard, it has been studied to apply this coverage extension technique to the above-mentioned Message 3 of the random access procedure (Non-Patent Document 1). By repeatedly transmitting the Message 3, it becomes possible for terminal devices existing in a wider area to connect to the base station device.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

SUMMARY OF THE INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

[0005] In message 2, the base station device will instruct the terminal device compliant with the Release 17 standard to repeatedly transmit message 3. However, the base station device cannot recognize whether the terminal device complies with the Release 17 standard at the stage of receiving message 1 from the terminal device. For this reason, the base station device may also instruct the terminal device compliant with the standard prior to Release 16 to perform repeated transmission. As a result, consecutive time slots for repeated transmission are allocated to the terminal device, but the frequency utilization efficiency deteriorates because the time slots are not used.

MEANS FOR SOLVING THE PROBLEM

[0006] The present invention provides a technology capable of efficiently executing repeated transmission of a message for coverage expansion in a random access procedure.

[0007] A terminal device according to an aspect of the present invention includes: a first resource where a device that cannot repeatedly transmit Message 3 in a 4-step random access procedure can transmit a random access preamble; and a second resource different from the first resource, where a device that can repeatedly transmit the Message 3 in consecutive slots can transmit the random access preamble. Specific means for specifying either the first resource or the second resource as a resource to be used by the terminal device when transmitting the random access preamble; and transmission means for transmitting the random access preamble to a base station device in the specified resource. The specific means determines whether to use the repeated transmission when the terminal device can perform the repeated transmission. When it is determined to use the repeated transmission, the second resource is specified as the resource to be used when transmitting the random access preamble. When it is determined not to use the repeated transmission, the first resource is specified as the resource to be used when transmitting the random access preamble.

Effect of the Invention

[0008] According to the present invention, it is possible to efficiently execute repeated transmission of a message for coverage extension in a random access procedure.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiment for Carrying Out the Invention

[0010] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of the features described in the embodiments are essential to the invention. Two or more of the features described in the embodiments may be arbitrarily combined. Also, the same or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0011] (System Configuration) FIG. 1 shows a configuration example of a wireless communication system according to this embodiment. This wireless communication system can be a cellular communication system including a base station device 101 and a terminal device 102. The base station device 101 and the terminal device 102 perform wireless communication according to any generation of cellular wireless communication standards of 3GPP. For example, the base station device 101 broadcasts and transmits basic control information (such as SIB (System Information Block)), and the terminal device 102 acquires the control information. Then, the terminal device 102 executes a random access procedure based on the control information to establish a connection with the base station device 101.

[0012] There are a 4-step procedure and a 2-step procedure for the random access procedure.

[0013] In the 4-step random access procedure, first, the terminal device 102 transmits a random access preamble (message 1) in the time-frequency resources for transmitting the random access preamble specified by the control information broadcast from the base station device 101. As the random access preamble, a sequence known to both the base station device 101 and the terminal device 102 is transmitted. The base station device 101 can detect the reception of the random access preamble by performing correlation detection on the signal received in the resources for the random access procedure using the known sequence. The sequence transmitted as the random access preamble is generated by applying a Cyclic Shift selected by the terminal device 102 from those notified by the base station device 101 to the Zadoff-Chu sequence. By using such a sequence, even if a plurality of terminal devices transmit random access preambles in parallel, as long as different Cyclic Shifts are used, the base station device 101 can detect these random access preambles separately.

[0014] When the base station device 101 receives a random access preamble, in response, it transmits a random access response (message 2) to the terminal device 102. In message 2, control information such as information indicating the timing (timing advance) when the terminal device 102 transmits a signal and the designation of the time and frequency resources for transmitting the subsequent message 3 is transmitted to the terminal device 102. The terminal device 102 uses the timing specified by message 2 and the allocated resources to transmit message 3, which requests a connection in the RRC (Radio Resource Control) layer, to the base station device 101. The base station device 101 transmits message 4, which includes control information for the RRC connection, etc., to the terminal device 102 in response to message 3. Through this procedure, the terminal device 102 can establish a connection with the base station device 101. Note that when the base station device 101 fails to receive message 3, it can cause the terminal device 102 to retransmit message 3. Note that if the base station device 101 still fails to receive message 3 even after retransmission is performed a predetermined number of times, it is determined that the terminal device 102 has failed to connect to the base station device 101.

[0015] Note that in the two-step random access procedure, the terminal device 102 transmits a first message corresponding to the above-mentioned message 1 and message 3, and the base station device 101 transmits a second message corresponding to the above-mentioned message 2 and message 4 in response. Note that even if the base station device 101 detects, for example, the random access preamble part of the first message but fails to decode the message 3 part, it may shift to the four-step random access procedure and cause the terminal device 102 to retransmit message 3.

[0016] In a cellular communication system, a coverage extension technique by a method of repeatedly transmitting the same data in consecutive time slots is defined. This method is not a retransmission when the reception of data fails on the receiving side, but the same data is repeatedly transmitted from the initial transmission. In the receiving device, the radio quality can be improved by the gain obtained by repeatedly receiving the same data, and communication can be performed between the terminal device 102 and the base station device 101 that are located at positions where communication cannot be performed by a single transmission.

[0017] Conventional repeated transmission is performed after the connection is established. On the other hand, as described above, it has been considered to apply repeated transmission to message 3 of the random access procedure at the time of connection establishment. However, the base station device 101 cannot recognize whether the terminal device 102 supports the repeated transmission of message 3 at the stage of transmitting message 2. The base station device 101 can instruct the repeated transmission of message 3 even when the terminal device 102 does not support the repeated transmission of message 3 and can secure resources for the repeated transmission. However, when the terminal device 102 does not support the repeated transmission of message 3, it cannot recognize the instruction for the repeated transmission and will transmit message 3 only once. As a result, the radio resources secured by the base station device 101 for the repeated transmission of message 3 will not be used, resulting in a decrease in frequency utilization efficiency.

[0018] Therefore, in the present embodiment, the base station device 101 can determine whether the terminal device 102 supports the repeated transmission of message 3 at the stage of message 1.

[0019] In this embodiment, a terminal device that cannot repeatedly transmit Message 3 in consecutive slots in a 4-step random access procedure is provided with a first resource capable of transmitting Message 1 (random access preamble), and a second resource different from the first resource, where a terminal device capable of repeatedly transmitting Message 3 in consecutive slots is provided with a second resource capable of transmitting Message 1. Here, the first resource and the second resource are set as resources that are different in time and / or frequency from each other, for example. For example, the first resource and the second resource may be different frequency resources in the same time slot, different time slots at the same frequency, or resources that are different in both time slot and frequency resource. In addition to or instead of these, the first resource and the second resource may be set such that the codes to be used for Message 1 are different. Note that the codes may be made different between the first resource and the second resource, for example, by using different base sequences of the Zadoff-Chu sequence, and in addition to or instead of this, the value of the cyclic shift may be made different between the first resource and the second resource. Note that the first resource and the second resource may be set to be different by elements other than these.

[0020] The terminal device 102 selects a resource to be used for transmitting Message 1 from among a first resource and a second resource based on the device's own capability information (UE Capability). Then, the terminal device 102 transmits Message 1 on the selected resource. If the terminal device 102 does not support the retransmission of Message 3, it does not use the second resource. That is, only the terminal devices that support the retransmission of Message 3 are allowed to transmit using the second resource. Also, even if the terminal device 102 supports the retransmission of Message 3, if it does not indicate to the base station device 101 that it supports the retransmission of Message 3, it transmits Message 1 using the first resource. On the other hand, when the terminal device 102 supports the retransmission of Message 3 and indicates to the base station device 101 that it supports the retransmission of Message 3, it transmits Message 1 using the second resource. That is, the first resource can be used by all terminal devices regardless of whether they support the retransmission of Message 3, and the second resource can only be used when the terminal devices that support the retransmission of Message 3 should notify the base station device 101 of such support for the retransmission.

[0021] As an example, when the terminal device 102 that supports the retransmission of Message 3 determines that the radio quality when receiving a synchronization signal or a notification signal sent from the base station device 101 is sufficiently high and there is no need to retransmit Message 3, it can transmit Message 1 using the first resource. Note that this is just an example, and the terminal device 102 may also transmit Message 1 using the first resource when it determines that the retransmission of Message 3 is unnecessary due to other factors. For example, depending on the type of service to be provided, when performing communication of a service type that emphasizes communication reliability, the terminal device 102 may transmit Message 1 using the second resource, and in other cases, it may transmit Message 1 using the first resource.

[0022] The base station device 101 executes the detection process of Message 1 in the above-described first resource and second resource. Then, based on whether the resource in which Message 1 is detected is the first resource or the second resource, the base station device 101 determines whether to instruct the terminal device 102 to repeatedly transmit Message 3, and based on the result of the determination, executes control for subsequent connection establishment. When the base station device 101 detects Message 1 from the terminal device 102 in the first resource, it does not instruct the terminal device 102 to repeatedly transmit Message 3. That is, since it is considered that the terminal device that transmits Message 1 in the first resource does not support the repeated transmission of Message 3 or does not require the repeated transmission of Message 3, the repeated transmission is not instructed to such a terminal device.

[0023] On the other hand, when the base station device 101 detects Message 1 from the terminal device 102 in the second resource, it can further determine whether to instruct the terminal device 102 to repeatedly transmit Message 3. That is, even if the base station device 101 detects Message 1 from the terminal device 102 in the second resource, it does not necessarily have to instruct the terminal device 102 to repeatedly transmit Message 3. In one example, the base station device 101 can determine whether to cause the terminal device 102 to repeatedly transmit Message 3 based on radio quality such as the reception intensity of Message 1. That is, when the radio quality such as the reception intensity of Message 1 is sufficiently high, the base station device 101 can determine that the probability of successfully receiving Message 3 is sufficiently high even without repeatedly transmitting Message 3, and decide not to instruct the terminal device 102 to repeatedly transmit Message 3. On the other hand, when the radio quality such as the reception intensity of Message 1 is below a certain level, the base station device 101 can instruct the terminal device 102 to repeatedly transmit Message 3. When the base station device 101 transmits an instruction to repeatedly transmit Message 3 to the terminal device 102, it transmits the instruction in Message 2.

[0024] The base station device 101 transmits information that can distinguish between the first resource and the second resource to the terminal device 102. For example, in the information element interpretable by the terminal device before Release 16 of the SIB, the information of the first resource can be indicated, and in the information element interpretable by the terminal device after Release 17, the information of the second resource can be indicated. According to this, since the terminal device of Release 16 cannot interpret the information element interpretable by the terminal device after Release 17, it can only acquire the information of the first resource. On the other hand, since the terminal device of Release 17 can interpret both the information element interpretable by the terminal device before Release 16 and the information element interpretable by the terminal device after Release 17, it can acquire both the information of the first resource and the information of the second resource. Note that this is an example, and the information of the second resource can be notified in the information element ignored by the terminal device that does not support the repeated transmission of Message 3. By acquiring such information, the terminal device 102 can distinguish and specify the first resource and the second resource.

[0025] Note that when the terminal device 102 uses the two-step random access procedure, the random access preamble part of the first message can be transmitted in either the first resource or the second resource as described above. When the base station device 101 detects the random access preamble part of the first message, successfully decodes the remaining part, and establishes a connection, regardless of whether the resource where the random access preamble part is transmitted is the first resource or the second resource, the base station device 101 transmits the second message to the terminal device 102 in the same manner. On the other hand, when the base station device 101 detects the random access preamble part of the first message but fails to decode the remaining part, the base station device 101 shifts the random access procedure to a four-step random access procedure. In this case, the base station device 101 instructs the terminal device 102 to transmit Message 3. At this time, for example, when the random access preamble part is detected in the first resource, the base station device 101 does not instruct the terminal device 102 to repeatedly transmit Message 3. On the other hand, when the random access preamble part is detected in the second resource, for example, the base station device 101 may instruct the terminal device 102 to repeatedly transmit Message 3 as necessary. Whether or not to repeatedly transmit Message 3 at this time can be determined based on the radio quality at the time of receiving the random access preamble part, etc., as described above. That is, even when shifting from the two-step random access procedure to the four-step random access procedure and the random access preamble part is detected in the second resource, it is not always necessary to instruct the repeated transmission of Message 3.

[0026] Note that the terminal device 102 may transmit Message 1 of the random access procedure for establishing uplink synchronization. In this case, since the process is completed up to Message 2, the terminal device 102 may randomly select either the first resource or the second resource and transmit Message 1 on the selected resource. This is because, as long as Message 3 is not transmitted, the information indicating whether the terminal device 102 supports the retransmission of Message 3 has no meaning.

[0027] (Configuration of the device) Next, a hardware configuration example of the base station device 101 and the terminal device 102 that execute the above-described processing will be described with reference to FIG. 2. In one example, the base station device 101 and the terminal device 102 include a processor 201, a ROM 202, a RAM 203, a storage device 204, and a communication circuit 205. The processor 201 is a computer including one or more processing circuits such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and reads and executes programs stored in the ROM 202 and the storage device 204, thereby executing the overall processing of the base station device 101 and the terminal device 102 and each of the above-described processes. The ROM 202 is a read-only memory that stores information such as programs and various parameters related to the processing executed by the base station device 101 and the terminal device 102. The RAM 203 functions as a work space when the processor 201 executes a program, and is a random access memory that stores temporary information. The storage device 204 is configured by, for example, a removable external storage device or the like. The communication circuit 205 is configured by, for example, a circuit for 5G wireless communication. In FIG. 2, one communication circuit 205 is illustrated, but the base station device 101 and the terminal device 102 may have a plurality of communication circuits. For example, the base station device 101 and the terminal device 102 may each have a separate communication circuit 205 for each of the plurality of available frequency bands. Further, the base station device 101 and the terminal device 102 may have a common communication circuit 205 for at least a part of the plurality of frequency bands. Further, for example, the terminal device 102 may have not only a communication circuit 205 for cellular communication but also a communication circuit 205 corresponding to other wireless communication standards such as wireless LAN.

[0028] FIG. 3 is a diagram showing a functional configuration example of the terminal device 102. As its functions, the terminal device 102 has, for example, a resource information acquisition unit 301, a used resource specifying unit 302, and a random access processing unit 303. Note that FIG. 3 shows only the functions particularly related to the present embodiment, and illustration of other various functions that the terminal device 102 may have is omitted. For example, the terminal device 102 naturally has other functions that a terminal device in a cellular communication system generally has. Also, the functional blocks in FIG. 3 are schematically shown, and each functional block may be integrated and realized, or may be further subdivided. Further, each function in FIG. 3 may be realized, for example, by the processor 201 executing a program stored in the ROM 202 or the storage device 204, or may be realized, for example, by a processor existing inside the communication circuit 205 executing predetermined software. Note that details of the processing executed by each functional unit are not described here, and only the general functions are outlined.

[0029] The resource information acquisition unit 301 identifies resources that can be used for transmitting a random access preamble (message 1 in the 4-step random access procedure). Here, as resources that can be used for transmitting the random access preamble, a first resource and a second resource different from the first resource are identified. The first resource is a resource where a terminal device that cannot repeatedly transmit message 3 in consecutive slots in the 4-step random access procedure can transmit the random access preamble. On the other hand, the second resource is a resource where a terminal device that can repeatedly transmit message 3 in consecutive slots can transmit the random access preamble. As described above, the first resource and the second resource are set as resources that differ in at least one of time, frequency, and code (sequence). The resource information acquisition unit 301 acquires this setting information by receiving an SIB (System Information Block) or the like transmitted from the base station device 101. For example, a terminal device 102 compliant with Release 16 may be notified of the setting information in a format where it can acquire the information of the first resource but cannot acquire the information of the second resource. Also, even for a terminal device 102 compliant with Release 17, a terminal device 102 that does not support the repeated transmission of message 3 may be notified of the setting information in a format where it can acquire the information of the first resource but cannot acquire the information of the second resource. Note that not being able to acquire the information here includes receiving the information itself but ignoring its content or being unable to interpret it.

[0030] The used resource specifying unit 302 specifies a resource for transmitting a random access preamble based at least on the capability information of the terminal device 102. The used resource specifying unit 302 determines which of the first resource and the second resource specified by the resource information acquisition unit 301 is to be used for transmitting the random access preamble. When the terminal device 102 does not support the retransmission of Message 3, since the resource information acquisition unit 301 does not acquire the information of the second resource, the used resource specifying unit 302 specifies the first resource as the resource to be used. On the other hand, when the terminal device 102 supports the retransmission of Message 3, since both the first resource and the second resource can be used by the used resource specifying unit 302, it specifies either of them as the resource to be used. In one example, when the radio quality such as the reception intensity of the synchronization signal or the notification signal from the base station device 101 is equal to or lower than a predetermined value, the used resource specifying unit 302 determines that the retransmission of Message 3 may be necessary, and specifies the second resource as the resource to be used. On the other hand, when the radio quality of the signal from the base station device 101 exceeds the predetermined quality and the used resource specifying unit 302 determines that the retransmission of Message 3 is not necessary, the used resource specifying unit 302 may specify the first resource as the resource to be used. Note that when the second resource can be used (that is, when the retransmission of Message 3 is supported), the used resource specifying unit 302 may specify the second resource as the resource to be used regardless of the radio quality of the signal received from the base station device 101.

[0031] The random access processing unit 303 executes random access processing including transmitting a random access preamble in the resource specified by the used resource specifying unit 302. For example, the random access processing unit 303 transmits a random access preamble in the specified resource and executes a 4-step random access procedure. At this time, when the random access processing unit 303 is instructed to repeatedly transmit message 3 by, for example, message 2 (random access response) from the base station apparatus 101, it repeatedly transmits the same message 3 a specified number of times in the time-frequency resource specified by the message 2. Further, the random access processing unit 303 may execute 2-step random access processing. In this case, it transmits a random access preamble in the specified resource and transmits a first message including information corresponding to message 3 to the base station apparatus 101 in a separately specified resource. The random access processing unit 303 may receive a random access response instructing retransmission of message 3 from the base station apparatus 101 for this first message. In this case, the random access processing unit 303 may shift the processing to a 4-step random access procedure and repeatedly transmit message 3 a specified number of times in the resource specified by the random access response.

[0032] FIG. 4 is a diagram showing a functional configuration example of the base station apparatus 101. The base station apparatus 101 has, as its functions, for example, a resource information notification unit 401, a random access preamble detection unit 402, a repetition necessity determination unit 403, and a connection control unit 404. In FIG. 4, only the functions particularly related to the present embodiment are shown, and illustration of other various functions that the base station apparatus 101 may have is omitted. For example, the base station apparatus 101 naturally has other functions that are generally possessed by base station apparatuses in a cellular communication system. Further, the functional blocks in FIG. 4 are schematically shown, and each functional block may be integrated and realized, or may be further subdivided. Also, each function in FIG. 4 may be realized, for example, by a processor 201 executing a program stored in a ROM 202 or a storage device 204, or may be realized, for example, by a processor existing inside a communication circuit 205 executing predetermined software. Note that details of the processing executed by each functional unit are not described here, and only the general functions are outlined.

[0033] The resource information notification unit 401 notifies the first resource and the second resource as described above to terminal devices existing in the area where the base station apparatus 101 is deployed. This notification is performed using a notification signal such as an SIB. Note that the first resource and the second resource are notified in a distinguishable manner. In one example, only terminal devices compliant with the specifications after Release 17 or only terminal devices supporting the retransmission of Message 3 are transmitted a notification signal in which information elements are described in a form that can identify the second resource. The random access preamble detection unit 402 executes a random access preamble detection process (for example, a correlation detection process using a known sequence) in the first resource and the second resource.

[0034] The repetition necessity determination unit 403 determines whether to instruct the retransmission of Message 3 based at least on whether the resource in which the random access preamble is detected by the random access preamble detection unit 402 is the first resource or the second resource. When the random access preamble from the terminal device 102 is detected in the first resource, the repetition necessity determination unit 403 does not instruct the retransmission of Message 3 to that terminal device 102. On the other hand, when the random access preamble from the terminal device 102 is detected in the second resource, the repetition necessity determination unit 403 determines whether to instruct the retransmission of Message 3 to that terminal device 102 based on the radio quality such as the reception intensity of the random access preamble, for example.

[0035] The connection control unit 404 executes control to complete the 4-step or 2-step random access process and establish a connection with the terminal device 102. For example, the connection control unit 404 transmits a random access response to the terminal device 102 in response to the random access preamble. Note that when the 2-step random access procedure is used, if the connection control unit 404 detects the random access preamble included in the first message and succeeds in decoding the remaining part, it transmits the second message to the terminal device 102 to complete the establishment of the connection. On the other hand, if the connection control unit 404 detects the random access preamble included in the first message but fails to decode the remaining part, it transmits a message 2 instructing that message 3 should be transmitted to the terminal device 102 to shift to the 4-step random access procedure. Note that when the 4-step random access procedure is used, the connection control unit 404 transmits a random access response in response to detecting the random access preamble, so that the terminal device 102 transmits message 3. When the connection control unit 404 controls the terminal device 102 to transmit message 3, for example, based on the determination of the repetition necessity determination unit 403, it transmits a random access response including information such as the necessity and number of repetitions of the repeated transmission of message 3 and the resources for the transmission to the terminal device 102.

[0036] (Flow of processing) Subsequently, an example of the flow of processing executed by the base station device 101 and the terminal device 102 according to the present embodiment will be outlined with reference to FIG. 5. Note that this is an example, and the base station device 101 and the terminal device 102 may execute various processes as exemplified above.

[0037] In this process, the base station apparatus 101 notifies, by means of a notification signal such as an SIB, information indicating resources available for transmitting a random access preamble to the terminal apparatuses within the area where the base station apparatus 101 is deployed (S501). In this notification, for example, notification information including the first resource and the second resource as described above is transmitted. When the terminal apparatus 102 receives this resource information, if it is necessary to establish a connection with the base station apparatus 101 (for example, when receiving a paging channel from the base station apparatus 101 or when data to be transmitted is generated inside the terminal apparatus 102), it stores the resource to be used for transmitting the random access preamble. Note that the terminal apparatus 102 may operate to store the first resource if it does not support retransmission of message 3 in, for example, a 4-step random access procedure based on its own device capability information, and store the second resource if it supports retransmission of message 3. Also, when the terminal apparatus 102 supports retransmission of message 3, it may store both the first resource and the second resource.

[0038] After that, when the situation where the terminal apparatus 102 should establish a connection with the base station apparatus 101 occurs, the terminal apparatus 102 specifies a resource for transmitting a random access preamble (S502). The terminal apparatus 102 determines which of the first resource and the second resource to use based on, for example, its own device capability information indicating whether it supports retransmission of message 3. Note that, for example, in S501, if only one of the first resource and the second resource is stored, the terminal apparatus 102 does not need to execute a selection process to specify the stored resource as the resource to be used. After that, the terminal apparatus 102 transmits a random access preamble using the resource specified in S502 (S503). Here, it is assumed that the terminal apparatus 102 transmits a random access preamble using, for example, the second resource.

[0039] When the base station device 101 detects the random access preamble transmitted from the terminal device 102, it determines whether the terminal device 102 needs to retransmit message 3 based at least on whether the resource where the random access preamble is detected is the first resource or the second resource (S504). For example, in S503, the base station device 101 determines whether to retransmit message 3 based on the radio quality of the random access preamble detected in the second resource. Here, it is assumed that the base station device 101 determines that retransmission of message 3 is necessary. In this case, the base station device 101 transmits a message 2 (random access response) including information on the timing at which the terminal device 102 should transmit a signal and information specifying the time - frequency resource for transmitting message 3 to the terminal device 102 (S505). Here, when the base station device 101 instructs the terminal device 102 to retransmit message 3, it notifies information specifying the number of retransmissions in the retransmission and the corresponding amount of radio resources. Note that the base station device 101 may, for example, notify the terminal device 102 in advance (e.g., at the time of S501) of candidates for the number of retransmissions in the retransmission of message 3, and at the time of S505, notify the terminal device 102 which of the candidate numbers of retransmissions should be used. According to this, it is possible to suppress the amount of information to be individually notified to the terminal device 102.

[0040] Thereafter, the terminal device 102 repeats the transmission of message 3 a specified number of times in the specified resource (S506). The base station device 101 combines the multiple re - transmitted messages 3 to obtain one message 3. Then, when the base station device 101 successfully receives this message 3, it transmits message 4 to the terminal device 102 (S507) to establish a connection with the terminal device. Note that when the base station device 101 fails to receive message 3, it may instruct the terminal device 102 to re - transmit message 3. At this time, the base station device 101 may perform processing such as increasing the number of re - transmission times.

[0041] As described above, in this embodiment, the resource for transmitting the random access preamble can be used to notify the base station apparatus 101 whether or not the terminal apparatus 102 supports the retransmission of message 3. As a result, the base station apparatus 101 can instruct only the terminal apparatuses that support the retransmission of message 3 to retransmit message 3 and can secure resources for the retransmission. Thereby, it is possible to efficiently execute the retransmission of a message for coverage extension in the random access procedure.

[0042] The invention is not limited to the above-described embodiments, and various modifications and changes are possible within the scope of the gist of the invention.

Claims

1. A terminal device, a determination means for determining, as a resource to be used by the terminal device when transmitting the random access preamble, either a first resource by which a device that cannot repeatedly transmit a message 3 in consecutive slots in a four-step random access procedure can transmit a random access preamble, or a second resource different from the first resource by which a device that can repeatedly transmit the message 3 in consecutive slots can transmit the random access preamble; A transmitting means for transmitting the random access preamble to a base station device in the specified resource; having The terminal device is characterized in that the determination means, when the terminal device is capable of performing the repetitive transmission, determines whether or not to use the repetitive transmission, and when it is determined that the repetitive transmission is to be used, determines the second resource as the resource to be used when transmitting the random access preamble, and when it is determined that the repetitive transmission is not to be used, determines the first resource as the resource to be used when transmitting the random access preamble.

2. the identifying means identifies the second resource when the base station device indicates that the repeated transmission can be performed and that the message 3 can be repeatedly transmitted in consecutive slots; 2. The terminal device according to claim 1 .

3. the identifying means identifies the first resource when the repeated transmission cannot be performed or when the base station device is not informed that the message 3 can be repeatedly transmitted in consecutive slots; 3. The terminal device according to claim 1 or 2.

4. The method further includes acquiring information indicating the first resource and the second resource from the base station device in a distinguishable manner.

4. The terminal device according to claim 1, wherein the first and second terminals are connected to each other.

5. When a two-step random access procedure is used, the transmitting means transmits a part of a random access preamble of a message to be transmitted to the base station device in the random access procedure in the specified resource.

5. The terminal device according to claim 1, wherein the first and second terminals are connected to each other.

6. The first resource and the second resource are set to be different in at least one of a frequency, a time, and a code to be used for the random access preamble.

6. The terminal device according to claim 1, wherein the first and second terminals are connected to each other.

7. A control method executed by a terminal device, comprising: Identifying, as a resource to be used when the terminal device transmits the random access preamble, either a first resource from which a device that cannot repeatedly transmit a message 3 in consecutive slots in a four-step random access procedure can transmit a random access preamble, or a second resource different from the first resource from which a device that can repeatedly transmit the message 3 in consecutive slots can transmit the random access preamble, and when the terminal device is capable of performing the repetitive transmission, determining whether or not to use the repetitive transmission, and when it is determined that the repetitive transmission is to be used, identifying the second resource as the resource to be used when transmitting the random access preamble, and when it is determined that the repetitive transmission is not to be used, identifying the first resource as the resource to be used when transmitting the random access preamble; transmitting the random access preamble to a base station device in the specified resource; A control method comprising:

8. A program for causing a computer installed in a terminal device to execute the control method according to claim 7.

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