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

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 and the allocated resources specified by the message 2 to transmit a message 3 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] [[ID=1**]]Conventional cellular communication standards stipulate a technique for extending coverage by repeatedly transmitting the same data in a plurality of consecutive time slots. 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, terminal devices existing in a wider area can connect to the base station device.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

[0005] The base station equipment instructs terminal equipment compliant with the Release 17 standard to repeatedly transmit message 3 in message 2. However, the base station equipment cannot recognize whether a terminal equipment complies with the Release 17 standard at the stage when it receives message 1 from that terminal equipment. Therefore, the base station equipment may instruct terminal equipment compliant with standards prior to Release 16 to repeatedly transmit. As a result, consecutive time slots are allocated to that terminal equipment for repeated transmission, but these time slots are not used, leading to a deterioration in frequency utilization efficiency. [Means for solving the problem]

[0006] This invention provides a technique that enables efficient repeated message transmission for coverage expansion in random access procedures.

[0007] A terminal device according to one aspect of the present invention includes: a first resource on which a device that cannot repeatedly transmit message 3 in a four-step random access procedure can transmit a random access preamble; and a second resource different from the first resource on which a device that can repeatedly transmit message 3 in a four-step random access procedure can transmit the random access preamble, the terminal device specifying which resource to use when transmitting the random access preamble; and a transmission means for transmitting the random access preamble to a base station device using the specified resource, wherein the specifying means, when the terminal device can perform the repeated transmission, Depending on the type of service to be provided Determine whether or not to use the repeated transmission, To perform communications for service types where the reliability of communication is paramount. If it is determined that the repeated transmission will be used, the second resource described above will be used. Other In this case, the first resource is identified as the resource to be used when transmitting the random access preamble. [Effects of the Invention]

[0008] According to the present invention, it is possible to efficiently perform repeated message transmission for coverage expansion in random access procedures. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram showing an example configuration of a wireless communication system. [Figure 2] This figure shows an example of the hardware configuration of base station equipment and terminal equipment. [Figure 3] This figure shows an example of the functional configuration of a terminal device. [Figure 4] This figure shows an example of the functional configuration of a base station device. [Figure 5] This diagram outlines the processing flow performed in a wireless communication system. [Modes for carrying out the invention]

[0010] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more features from the multiple features described in the embodiments may be combined arbitrarily. Furthermore, identical or similar configurations will be given the same reference numeral, and redundant descriptions will be omitted.

[0011] (System Configuration) Figure 1 shows an example configuration of a wireless communication system according to this embodiment. This wireless communication system may 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 one of the generations of 3GPP cellular wireless communication standards. For example, the base station device 101 broadcasts basic control information (e.g., SIB (System Information Block)), and the terminal device 102 acquires that control information. The terminal device 102 then establishes a connection with the base station device 101 by executing a random access procedure based on that control information.

[0012] Random access procedures can be either 4-step or 2-step.

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

[0014] When base station device 101 receives a random access preamble, it responds by sending a random access response (message 2) to terminal device 102. Message 2 contains information indicating the timing (timing advance) for when terminal device 102 should transmit a signal, as well as control information such as specifying the time and frequency resources for which message 3 should be sent. Terminal device 102 sends message 3 to base station device 101 requesting a connection at the RRC (Radio Resource Control) layer using the timing and resources specified by message 2. In response to message 3, base station device 101 sends message 4 to terminal device 102, which contains control information for RRC connection. Through this procedure, terminal device 102 can establish a connection with base station device 101. If base station device 101 fails to receive message 3, it can instruct terminal device 102 to resend message 3. If the base station device 101 fails to receive message 3 even after a predetermined number of retransmissions, it is determined that the terminal device 102 has failed to connect with the base station device 101.

[0015] In the two-step random access procedure, terminal device 102 transmits a first message corresponding to messages 1 and 3 described above, and base station device 101 responds by transmitting a second message corresponding to messages 2 and 4 described above. If base station device 101 detects the random access preamble portion of the first message but fails to decode message 3, it may proceed to the four-step random access procedure and have terminal device 102 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-side 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. In contrast, as described above, applying repeated transmission to message 3 of the random access procedure at the time of connection establishment has been studied. 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, and the frequency utilization efficiency will decrease.

[0018] Therefore, in this 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 first resource is provided that can transmit message 1 (random access preamble) to a terminal device that cannot repeatedly transmit message 3 in consecutive slots in a four-step random access procedure, and a second resource is provided that is different from the first resource and can transmit message 1 to a terminal device that can repeatedly transmit message 3 in consecutive slots. Here, the first resource and the second resource are set up as resources with different time and / or frequency, for example. For example, the first resource and the second resource may be different frequency resources in the same time slot, or different time slots in the same frequency, or resources that are different in both time slot and frequency. In addition to these, or instead, the first resource and the second resource may be set up so that they have different codes to be used for message 1. Furthermore, the sign may differ between the first and second resources by, for example, using different base sequences of the Zadoff-Chu series, or in addition to or instead of this, by using different Cyclic shift values. Other factors may also be used to differentiate between the first and second resources.

[0020] The terminal device 102 selects a resource to be used for transmitting Message 1 from among the first resource and the second resource based on the capability information (UE Capability) of its own device. 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 device that supports the retransmission of Message 3 transmits 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 device that supports 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 the synchronization signal or 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 even if the terminal device 102 determines that the retransmission of Message 3 is unnecessary due to other factors, it may also transmit Message 1 using the first resource. For example, the terminal device 102 may transmit Message 1 using the second resource when performing communication of a service type that values communication reliability according to the service type to be provided, and transmit Message 1 using the first resource in other cases.

[0022] The base station device 101 performs a message 1 detection process in the first resource and the second resource described above. Then, based on whether the resource that detected message 1 is the first resource or the second resource, the base station device 101 determines whether or not to instruct the terminal device 102 to repeatedly transmit message 3, and based on the result of that determination, it performs subsequent control for establishing the connection. If 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. In other words, it is assumed that a terminal device that transmits message 1 in the first resource does not support repeated transmission of message 3 or does not require repeated transmission of message 3, so repeated transmission is not instructed for such a terminal device.

[0023] On the other hand, if the base station device 101 detects message 1 from terminal device 102 using the second resource, it may further determine whether or not to instruct terminal device 102 to repeatedly transmit message 3. In other words, even if the base station device 101 detects message 1 from terminal device 102 using the second resource, it does not necessarily have to instruct terminal device 102 to repeatedly transmit message 3. For example, the base station device 101 may decide whether to have terminal device 102 repeatedly transmit message 3 based on radio quality such as the received signal strength of message 1. That is, if the radio quality such as the received signal strength of message 1 is sufficiently high, the base station device 101 may determine that the probability of successfully receiving message 3 is sufficiently high even without repeated transmission of message 3, and decide not to instruct terminal device 102 to repeatedly transmit message 3. On the other hand, if the radio quality such as the received signal strength of message 1 is below a certain level, the base station device 101 may instruct terminal device 102 to repeatedly transmit message 3. Furthermore, if the base station device 101 sends an instruction to the terminal device 102 to repeatedly transmit message 3, it will send that instruction in message 2.

[0024] The base station device 101 transmits information to the terminal device 102 that distinguishes between the first resource and the second resource. For example, the SIB may indicate information about the first resource in an information element that can be interpreted by terminal devices prior to release 16, and information about the second resource in an information element that can be interpreted by terminal devices from release 17 onwards. In this case, a terminal device from release 16 cannot interpret the information element that can be interpreted by terminal devices from release 17 onwards, and therefore can only obtain information about the first resource. On the other hand, a terminal device from release 17 can interpret both the information elements that can be interpreted by terminal devices prior to release 16 and the information elements that can be interpreted by terminal devices from release 17 onwards, and therefore can obtain information about both the first resource and the second resource. Note that this is just one example, and information about the second resource may be notified in an information element that is ignored by terminal devices that do not support repeated transmission of message 3. By obtaining such information, the terminal device 102 can distinguish and identify the first resource and the second resource.

[0025] Furthermore, when the terminal device 102 uses a two-step random access procedure, it may transmit the random access preamble portion of the first message to either the first resource or the second resource as described above. If the base station device 101 detects the random access preamble portion of the first message, successfully decodes the remaining portion, and establishes a connection, it will similarly transmit the second message to the terminal device 102, regardless of whether the resource to which the random access preamble portion was transmitted is the first resource or the second resource. On the other hand, if the base station device 101 detects the random access preamble portion of the first message but fails to decode the remaining portion, it will switch 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, but if, for example, the random access preamble portion was detected in the first resource, it will not instruct the terminal device 102 to repeatedly transmit message 3. On the other hand, if the base station device 101 detects, for example, the random access preamble portion in the second resource, it may instruct the terminal device 102 to repeatedly transmit message 3 as necessary. Whether or not repeated transmission of message 3 is necessary in this case can be determined based on the radio quality at the time of reception of the random access preamble portion, as described above. In other words, even if the random access preamble portion is detected in the second resource when transitioning from a two-step random access procedure to a four-step random access procedure, repeated transmission of message 3 is not necessarily instructed.

[0026] Furthermore, terminal device 102 may send message 1 of the random access procedure to establish synchronization on the uplink. In this case, since the process is completed up to message 2, terminal device 102 may randomly select either the first resource or the second resource and send message 1 on the selected resource. This is because, since message 3 is not sent, information indicating whether or not terminal device 102 supports repeated transmission of message 3 is meaningless.

[0027] (Device configuration) Next, an example of the hardware configuration of the base station device 101 and terminal device 102 that perform the above-described processing will be explained using Figure 2. In one example, the base station device 101 and terminal device 102 are configured to include a processor 201, ROM 202, RAM 203, storage device 204, and communication circuit 205. The processor 201 is a computer configured to include one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or ASIC (Application-Specific Integrated Circuit), and performs the overall processing of the base station device 101 and terminal device 102, as well as each of the above-described processing, by reading and executing programs stored in the ROM 202 and storage device 204. The ROM 202 is a read-only memory that stores information such as programs and various parameters related to the processing performed by the base station device 101 and terminal device 102. The RAM 203 functions as a workspace when the processor 201 executes programs and is a random-access memory that stores temporary information. The storage device 204 is configured, for example, by a removable external storage device. The communication circuit 205 is composed of, for example, a circuit for 5G wireless communication. Although Figure 2 shows one communication circuit 205, the base station device 101 and the terminal device 102 may have multiple communication circuits. For example, the base station device 101 and the terminal device 102 may have separate communication circuits 205 for each of the multiple usable frequency bands. Alternatively, the base station device 101 and the terminal device 102 may have a common communication circuit 205 for at least some of the multiple frequency bands. Furthermore, for example, the terminal device 102 may have not only a communication circuit 205 for cellular communication but also a communication circuit 205 that supports other wireless communication standards such as Wi-Fi.

[0028] Figure 3 shows an example of the functional configuration of the terminal device 102. The terminal device 102 has, for example, a resource information acquisition unit 301, a resource usage identification unit 302, and a random access processing unit 303. Note that Figure 3 shows only the functions particularly relevant to this embodiment, and various other functions that the terminal device 102 may have are omitted from the illustration. For example, the terminal device 102 naturally has other functions that terminal devices in cellular communication systems generally have. Also, the functional blocks in Figure 3 are shown schematically, and each functional block may be implemented as an integrated unit or further subdivided. Furthermore, each function in Figure 3 may be implemented, for example, by the processor 201 executing a program stored in the ROM 202 or storage device 204, or by a processor located inside the communication circuit 205 executing predetermined software. Note that the details of the processing performed by each functional unit will not be explained in detail here, and only the general functions will be outlined.

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

[0030] The resource usage identification unit 302 identifies the resource to transmit the random access preamble, based at least on the capability information of the terminal device 102. The resource usage identification unit 302 decides whether to use the first resource or the second resource identified by the resource information acquisition unit 301 to transmit the random access preamble. If the terminal device 102 does not support repeated transmission of message 3, the resource information acquisition unit 301 has not acquired information on the second resource, so the resource usage identification unit 302 identifies the first resource as the resource to be used. On the other hand, if the terminal device 102 supports repeated transmission of message 3, the resource usage identification unit 302 identifies either the first or second resource as the resource to be used, since both the first and second resources are available. In one example, the resource usage identification unit 302 determines that repeated transmission of message 3 may be necessary when the radio quality, such as the received strength of the synchronization signal or broadcast signal from the base station device 101, is below a predetermined value, and identifies the second resource as the resource to be used. On the other hand, if the resource usage identification unit 302 determines that the radio quality of the signal from the base station device 101 exceeds a predetermined quality and that repeated transmission of message 3 is not necessary, it may identify the first resource as the resource to be used. Furthermore, if the second resource is available (i.e., if repeated transmission of message 3 is supported), the resource usage identification unit 302 may identify 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 performs random access processing, which includes transmitting a random access preamble at the resource identified by the resource identification unit 302. For example, the random access processing unit 303 transmits a random access preamble at the identified resource and performs a four-step random access procedure. In this case, if the random access processing unit 303 is instructed to repeatedly transmit message 3 by message 2 (random access response) from the base station device 101, for example, it transmits the same message 3 repeatedly for the specified number of times at the time and frequency resource specified in message 2. Alternatively, the random access processing unit 303 may perform a two-step random access process, in which case it transmits a random access preamble at the identified resource and also transmits a first message containing information equivalent to message 3 to the base station device 101 at a separately specified resource. The random access processing unit 303 may receive a random access response from the base station device 101 instructing it to retransmit message 3 in response to this first message. In this case, the random access processing unit 303 can transition the processing to a four-step random access procedure and repeatedly send message 3 a specified number of times to the resource specified by the random access response.

[0032] Figure 4 shows an example of the functional configuration of the base station device 101. The base station device 101 has functions such as a resource information notification unit 401, a random access preamble detection unit 402, a repeatability determination unit 403, and a connection control unit 404. Note that Figure 4 shows only the functions particularly relevant to this embodiment, and various other functions that the base station device 101 may have are omitted from the illustration. For example, the base station device 101 naturally has other functions that a base station device in a cellular communication system generally has. Also, the functional blocks in Figure 4 are shown schematically, and each functional block may be implemented as an integrated unit or further subdivided. Furthermore, each function in Figure 4 may be implemented, for example, by the processor 201 executing a program stored in the ROM 202 or storage device 204, or by a processor located inside the communication circuit 205 executing predetermined software. Note that the details of the processing performed by each functional unit will not be explained in detail here, and only the general functions will be outlined.

[0033] The resource information notification unit 401 notifies terminal devices located in the area where the base station device 101 is deployed of the first resource and the second resource as described above. This notification is made using a broadcast signal such as SIB. The first resource and the second resource are notified in a distinguishable manner. In one example, only terminal devices compliant with the standard of Release 17 or later, or terminal devices that support repeated transmission of message 3, receive a broadcast signal in which the information elements are described in a format that allows the second resource to be identified. The random access preamble detection unit 402 performs random access preamble detection processing (e.g., correlation detection processing using known sequences) for the first resource and the second resource.

[0034] The repetition necessity determination unit 403 determines whether to instruct the repeated transmission of message 3, at least based on whether the resource from which the random access preamble was detected by the random access preamble detection unit 402 is a first resource or a second resource. If the random access preamble from terminal device 102 is detected as a first resource, the repetition necessity determination unit 403 does not instruct the terminal device 102 to repeatedly transmit message 3. On the other hand, if the random access preamble from terminal device 102 is detected as a second resource, the repetition necessity determination unit 403 determines whether to instruct the terminal device 102 to repeatedly transmit message 3, for example, based on the wireless quality such as the received strength of the random access preamble.

[0035] The connection control unit 404 performs control to establish a connection with the terminal device 102 by completing a 4-step or 2-step random access process. For example, in response to a random access preamble, the connection control unit 404 sends a random access response to the terminal device 102. If the 2-step random access procedure is used, and the connection control unit 404 detects the random access preamble contained in the first message and successfully decodes the remaining part, it sends a 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 contained in the first message but fails to decode the remaining part, it sends message 2 to the terminal device 102 instructing it to send message 3, thereby proceeding to the 4-step random access procedure. If the 4-step random access procedure is used, the connection control unit 404 sends a random access response upon detecting the random access preamble, causing the terminal device 102 to send message 3. When the connection control unit 404 controls the terminal device 102 to send message 3, for example, based on the determination of the repetition necessity determination unit 403, it sends a random access response to the terminal device 102 that includes information such as whether or not message 3 should be sent repeatedly, the number of repetitions, and the resources required for that transmission.

[0036] (Process flow) Next, an example of the processing flow executed by the base station device 101 and terminal device 102 according to this embodiment will be outlined with reference to Figure 5. Note that this is just one example, and the base station device 101 and terminal device 102 may perform various processes as illustrated above.

[0037] In this process, the base station device 101 notifies terminal devices within the area where the base station device 101 is deployed of information indicating resources available for transmitting a random access preamble, for example, by broadcast signal such as SIB (S501). This notification includes, for example, broadcast information containing the first resource and the second resource as described above. When terminal device 102 receives this resource information, it stores it as a resource to be used for transmitting a random access preamble when it needs to establish a connection with the base station device 101 (for example, when it receives a paging channel from the base station device 101 or when data to be transmitted is generated within terminal device 102). Terminal device 102 may operate based on its own capability information to store the first resource if it does not support repeated transmission of message 3 in a 4-step random access procedure, and store the second resource if it does support repeated transmission of message 3. Alternatively, terminal device 102 may store both the first and second resources if it supports repeated transmission of message 3.

[0038] Subsequently, the terminal device 102 identifies a resource for transmitting a random access preamble in response to the situation requiring the establishment of a connection with the base station device 101 (S502). The terminal device 102 decides whether to use the first resource or the second resource, for example, based on capability information such as whether or not its own device supports repeated transmission of message 3. Note that, for example, in S501, if only one of the first or second resources is stored, the terminal device 102 does not need to perform a selection process because it identifies the stored resource as the resource to be used. Subsequently, the terminal device 102 transmits a random access preamble using the resource identified in S502 (S503). Here, it is assumed that the terminal device 102 transmitted the random access preamble using the second resource, for example.

[0039] When the base station device 101 detects a random access preamble transmitted from the terminal device 102, it determines whether the terminal device 102 should repeatedly transmit message 3, at least based on whether the resource from which the random access preamble was detected is the first resource or the second resource (S504). For example, in S503, the base station device 101 determines whether the message 3 should be repeatedly transmitted 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 has determined that repeated transmission of message 3 is necessary. In this case, the base station device 101 transmits message 2 (random access response) to the terminal device 102, which contains information on the timing at which the terminal device 102 should transmit a signal and information specifying the time and frequency resources to which message 3 should be transmitted (S505). Here, when the base station device 101 instructs the terminal device 102 to repeatedly transmit message 3, it notifies the terminal device 102 of the number of repetitions in the repeated transmission and the amount of radio resources corresponding to that number. Furthermore, the base station device 101 may, for example, notify the terminal device 102 in advance (for example, at S501) of candidate numbers of repetitions for the repeated transmission of message 3, and at S505 notify the terminal device 102 which of the candidate numbers of repetitions should be used. This makes it possible to reduce the amount of information that needs to be individually notified to the terminal device 102.

[0040] Subsequently, the terminal device 102 repeatedly transmits message 3 to the specified resource for the number of repetitions specified in S505 (S506). The base station device 101 combines these multiple repeatedly transmitted messages 3 to obtain a single message 3. If the base station device 101 successfully receives this message 3, it sends message 4 to the terminal device 102 (S507) to establish a connection with the terminal device. If the base station device 101 fails to receive message 3, it may instruct the terminal device 102 to retransmit message 3. At this time, the base station device 101 may also perform processing such as increasing the number of repeated transmissions.

[0041] As described above, in this embodiment, the resource to which the random access preamble is sent can notify the base station device 101 whether or not the terminal device 102 supports repeated transmission of message 3. As a result, the base station device 101 can instruct terminal devices that support repeated transmission of message 3 to repeat the message 3 and reserve resources for such repeated transmission. This makes it possible to efficiently perform repeated transmission of messages for coverage expansion in the random access procedure.

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

Claims

1. A terminal device, Identification means for identifying either a first resource capable of transmitting a random access preamble to a device that cannot repeatedly transmit message 3 in consecutive slots in a four-step random access procedure, or a second resource different from the first resource, capable of transmitting the random access preamble to a device that can repeatedly transmit message 3 in consecutive slots, as the resource to be used by the terminal device when transmitting the random access preamble; In the identified resource, a transmission means for transmitting the random access preamble to the base station device, It has, The identifying means is characterized in that, when the terminal device is capable of performing the repeated transmission, it determines whether or not to use the repeated transmission depending on the type of service to be received, and if it determines that the repeated transmission should be used to perform communication for a service type in which the reliability of communication is important, it identifies the second resource as the resource to be used when transmitting the random access preamble, and otherwise identifies the first resource as the resource to be used.

2. The system further includes an acquisition means for acquiring information from the base station device that distinguishes between the first resource and the second resource. The terminal device according to feature 1.

3. When the transmission means uses a two-step random access procedure, it transmits the portion of the random access preamble of the message to be sent to the base station device in the random access procedure to the specified resource. The terminal device according to claim 1 or 2.

4. The first resource and the second resource are configured to differ in at least one of the following: frequency, time, and the code to be used in the random access preamble. The terminal device according to any one of claims 1 to 3.

5. A control method performed by a terminal device, The terminal device identifies either a first resource capable of transmitting a random access preamble to a device that cannot repeatedly transmit message 3 in consecutive slots in a four-step random access procedure, or a second resource different from the first resource, capable of transmitting the random access preamble to a device that can repeatedly transmit message 3 in consecutive slots, as the resource to be used when the terminal device transmits the random access preamble, wherein, when the terminal device is capable of repeated transmission, it determines whether to use repeated transmission depending on the type of service to be received, and if it determines to use repeated transmission for communication of a service type where the reliability of communication is important, it identifies the second resource as the resource to be used when transmitting the random access preamble, and otherwise identifies the first resource as the resource to be used. In the identified resource, the random access preamble is transmitted to the base station device, A control method characterized by including

6. A program for causing a computer installed in a terminal device to execute the control method described in claim 5.

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