Terminal device, base station device, and control method for preventing unnecessary transmission in RLC-am

Abstract

To prevent transmission of data that exceeds an allowable delay time in RLC-AM.SOLUTION: A communications device that generates an RLC PDU containing one or more PDCP PDUs and transmits the RLC PDU to a communications partner device using RLC-AM manages, in the PDCP layer, an allowable delay time, which is an allowable value for the delay until the transmitted PDCP PDU is successfully received by the communications partner device, discards PDCP PDUs that exceed the allowable delay time, and, in the RLC layer, acquires information for identifying the discarded PDCP PDU, identifies the sequence number of the RLC PDU containing the discarded PDCP PDU, discards the RLC PDU containing the discarded PDCP PDU, and notifies the communications partner device of the sequence number of the RLC PDU to be discarded.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a data transmission technique using RLC-AM in a cellular communication system. [Background technology]

[0002] The cellular communication standard of the Third Generation Partnership Project (3GPP (registered trademark)) has introduced a mechanism called Radio Link Control (RLC)-Acknowledge Mode (AM) to improve the reliability of user data communication. This mode is a mode in which user data is retransmitted when an acknowledgement (ACK) indicating that the user data to be transmitted has been received by the other device is not received. Summary of the Invention [Problem to be solved by the invention]

[0003] There is user data for which a delay tolerance (tolerable delay time, packet delay badge) is set until the data reaches the remote device. For example, user data that requires real-time performance is naturally expected to have a short tolerable delay time. Here, when transmitting user data with such a short tolerable delay time in RLC-AM, it is expected that the tolerable delay time will be exceeded when transmitting or retransmitting the user data. User data that exceeds the tolerable delay time is no longer required to be transmitted. However, the RLC-AM entity cannot stop processing such as retransmission, which can result in waste, such as the transmission of unnecessary data. [Means for solving the problem]

[0004] The present invention provides a technique for preventing data transmission that exceeds the allowable delay time in RLC-AM.

[0005] A communication device according to one aspect of the present invention is a communication device that complies with the cellular communication standard of the Third Generation Partnership Project (3GPP), and includes: PDCP processing means for performing PDCP layer processing, including generating Packet Data Convergence Protocol (PDCP) Protocol Data Units (PDUs) including user data; and Radio Link Control (RLC) processing means for acquiring PDCP PDUs from the PDCP processing means, generating Radio Link Control (RLC) PDUs including one or more PDCP PDUs, and transmitting the RLC PDUs to a communication partner device in RLC-Acknowledge Mode (RLC-AM), wherein the PDCP processing means manages an allowable delay time, which is an allowable value for delay until the transmitted PDCP PDU is successfully received by the communication partner device, and discards PDCP PDUs that exceed the allowable delay time, and the RLC processing means acquires information for identifying the discarded PDCP PDU from the PDCP processing means, identifies a sequence number of the RLC PDU including the discarded PDCP PDU, discards the RLC PDU including the discarded PDCP PDU, and discards the discarded RLC PDU. The PDU sequence number is notified to the other device.

[0006] A communication device according to another aspect of the present invention is a communication device that complies with the cellular communication standard of the Third Generation Partnership Project (3GPP), and includes: Radio Link Control (RLC) processing means that receives an RLC Protocol Data Unit (PDU) from a communication partner device in RLC-Acknowledge Mode (AM) and outputs one or more RLC Service Data Units (SDUs) included in the RLC PDU; and Packet Data Convergence Protocol (PDCP) processing means that acquires the RLC SDU as a PDCP PDU and performs reception processing of the PDCP PDU, wherein the RLC processing means receives a notification of a sequence number of an RLC PDU to be discarded from the communication partner device, and does not request retransmission of the RLC PDU even if the RLC PDU with the notified sequence number is not received. [Effects of the Invention]

[0007] According to the present invention, it is possible to prevent transmission of data that exceeds the allowable delay time in RLC-AM. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. [Figure 2] FIG. 2 is a diagram illustrating an example of the hardware configuration of a base station device and a terminal device. [Figure 3] FIG. 2 is a diagram illustrating an example of the functional configuration of a base station device and a terminal device. [Figure 4] FIG. 1 is a diagram illustrating a process executed in a wireless communication system. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any desired manner. Furthermore, the same reference numerals are used to designate identical or similar components, and redundant descriptions will be omitted.

[0010] (System Configuration) FIG. 1 shows an example of the configuration of a wireless communication system according to this embodiment. This wireless communication system is a wireless communication system that complies with cellular communication standards such as Long Term Evolution (LTE) and fifth generation (5G) of the Third Generation Partnership Project (3GPP (registered trademark)), or successor standards. This wireless communication system includes a base station device 101 and a terminal device 111. The terminal device 111 is a communication device that establishes a connection with the base station device 101, transmits user data on an uplink (a link in the direction from the terminal device 111 to the base station device 101), and receives user data on a downlink (a link in the direction from the base station device 101 to the terminal device 111). Similarly, the base station device 101 is a communication device that transmits downlink user data to the connected terminal device 111, and receives uplink user data.

[0011] (Device configuration) FIG. 2 shows an example of the hardware configuration of the base station device 101 and the terminal device 111 according to this embodiment. In one example, the base station device 101 and the terminal device 111 are configured to 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 configured to include one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and executes overall control processing of the device and each of the above-mentioned processes by reading and executing programs stored in the ROM 202 or the storage device 204. The ROM 202 is a read-only memory that stores information such as programs and various parameters related to processes executed by the base station device 101 and the terminal device 111. The RAM 203 functions as a workspace when the processor 201 executes a program 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 configured, for example, by a circuit for wireless communication of LTE, 5G, or a successor standard. Although FIG. 2 illustrates one communication circuit 205, the base station device 101 and the terminal device 111 may have multiple communication circuits. For example, the base station device 101 and the terminal device 111 may have wireless communication circuits for LTE, 5G, and a successor standard, respectively, and a common antenna for these circuits. The base station device 101 and the terminal device 111 may have separate antennas suitable for each standard. The base station device 101 may also have a wired communication circuit used when communicating with other base station devices or nodes in the core network. The terminal device 111 may also have a communication circuit compliant with a wireless communication standard other than the cellular communication standard, such as a wireless local area network (LAN) or Bluetooth (registered trademark). The base station device 101 and the terminal device 111 may have separate communication circuits 205 for each of multiple available frequency bands, or may have a common communication circuit 205 for at least some of these frequency bands.

[0012] FIG. 3 shows an example of the functional configuration of the base station device 101 and the terminal device 111 according to this embodiment. Both the base station device 101 and the terminal device 111 include a PDCP processing unit 301, an RLC processing unit 302, a MAC processing unit 303, and a PHY processing unit 304. Note that FIG. 3 only shows functions particularly related to this embodiment, and does not illustrate various other functions that the base station device and the terminal device may have. For example, the terminal device naturally has other functions that terminal devices compliant with 5G and subsequent standards generally have. The functional blocks in FIG. 3 are shown schematically, and the respective functional blocks may be integrated or further subdivided. Furthermore, 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 within the communication circuit 205 executing predetermined software. Since the details of the processing performed by each functional unit are as described above, only the general functions of the base station device 101 and the terminal device 111 will be outlined here.

[0013] The PDCP processing unit 301 executes processing of the Packet Data Convergence Protocol (PDCP) layer. When the PDCP processing unit 301 acquires an Internet Protocol (IP) packet containing user data, it handles the packet as a PDCP Service Data Unit (SDU) to be transmitted. The PDCP processing unit 301 then adds a PDCP layer header (PDCP header) to the PDCP SDU to generate a PDCP Protocol Data Unit (PDU). The PDCP processing unit 301 outputs the PDCP PDU to the RLC processing unit 302.

[0014] The RLC processing unit 302 performs processing of the Radio Link Control (RLC) layer. The RLC processing unit 302 converts the PDCP PDU input from the PDCP processing unit 301 into an RLC SDU, adds an RLC layer header (RLC header) to the RLC SDU to generate an RLC PDU, and outputs the RLC PDU to the MAC processing unit 303. Note that the RLC processing unit 302 can concatenate multiple RLC SDUs to generate one RLC PDU. At this time, one RLC SDU may be divided and included in multiple RLC PDUs.

[0015] The MAC processing unit 303 executes processing of the Medium Access Control (MAC) layer. The MAC processing unit 303 takes the RLC PDU generated by the RLC processing unit 302 as a MAC SDU, adds a MAC layer header (MAC header) and padding to the MAC SDU to generate a MAC PDU, and outputs the MAC PDU to the PHY processing unit 304. The PHY processing unit 304 uses the MAC PDU as a transport block to generate a subframe to be transmitted, and transmits the subframe to the other device as a radio signal.

[0016] Up to this point, the processing units of the transmitting communication device have been described. The receiving communication device performs the reverse procedure. That is, the PHY processing unit 304 receives a radio signal (subframe) including a transport block from the remote device and outputs the transport block to the MAC processing unit 303. The MAC processing unit 303 converts the transport block into a MAC PDU, removes the MAC header and padding from it, extracts a MAC SDU, and outputs the MAC SDU to the RLC processing unit 302. The RLC processing unit 302 converts the MAC SDU into an RLC PDU, removes the RLC header, and extracts the RLC SDU. Note that an RLC PDU may contain multiple RLC SDUs. Also, one RLC SDU may be divided into multiple RLC PDUs. Therefore, the RLC processing unit 302 segments or concatenates the payload portion included in the RLC PDU to reconstruct each RLC SDU. The RLC processing unit 302 then outputs the reconstructed RLC SDU to the PDCP processing unit 301. The PDCP processing unit 301 removes the PDCP header from the RLC SDU and extracts the IP packet. In this way, the user data (IP packet) from the transmitting communication device (terminal device 111 for uplink, base station device 101 for downlink) reaches the receiving communication device (base station device 101 for uplink, terminal device 111 for downlink).

[0017] The PDCP processing unit 301 in the transmitting communication device manages an allowable delay time, which is the allowable delay value until user data (IP packets) are successfully received by the other communication device. If the time elapsed since the generation of user data (input to the PDCP processing unit 301) exceeds the allowable delay time, the PDCP processing unit 301 discards the PDCP PDU. In this case, the allowable delay time can be notified from the base station device, which is the receiving communication device, to the terminal device, which is the transmitting communication device. The base station device can determine the allowable delay time based on information indicating the quality required for a wireless line, such as 5QI (5G QoS Identifier), received from the core network device, and notify the terminal device of the allowable delay time as a discardTimer, which is part of the PDCP parameters.

[0018] Furthermore, the RLC processing unit 302 can use an acknowledgement and retransmission mechanism called RLC-Acknowledge Mode (AM). In RLC-AM, the RLC processing unit 302 assigns a sequence number to an RLC PDU to be transmitted and transmits the PDU. The RLC processing unit 302 then receives an acknowledgement (status information) indicating the sequence number of an RLC PDU that was not successfully received by the RLC processing unit 302 of the other communication device, and retransmits the RLC PDU that was not successfully received. For example, a STATUS PDU indicating the reception status of the RLC PDU is received from the other communication device. The STATUS PDU includes, for example, information indicating the sequence number of an RLC PDU that was not successfully received and the sequence number next to the sequence number of an RLC PDU that was successfully received (i.e., the sequence number of an RLC PDU that should be newly received next). For example, if RLC PDUs with sequence numbers 1 to 3 have been transmitted, and the RLC PDU with sequence number 2 has not been successfully received, but the RLC PDUs with sequence numbers 1 and 3 have been successfully received, the STATUS PDU may contain the sequence number "2" of the RLC PDU that was not successfully received and the sequence number "4" of the RLC PDU that is to be received next. In response to receiving the STATUS PDU, the RLC processing unit 302 may retransmit the RLC PDU with sequence number "2" and transmit the RLC PDU with sequence number "4."

[0019] When communication control is performed using RLC-AM, if a receiving communication device fails to receive an RLC PDU, the transmitting communication device repeatedly transmits the RLC PDU. At this time, for example, if the PDCP processing unit 301 determines that the time since the generation of the user data to be transmitted using the RLC PDU has exceeded the allowable delay time, the PDCP processing unit 301 discards the PDCP PDU related to the user data. At this point, the RLC PDU containing the PDCP PDU may no longer need to be retransmitted in the RLC layer, but the RLC processing unit 302 cannot recognize that retransmission is no longer necessary. Furthermore, for user data with a short allowable delay time, it is conceivable that the time since the generation of the user data may exceed the allowable delay time while the RLC processing unit 302 is preparing to transmit the RLC PDU containing the user data. In such a case, the RLC processing unit 302 performs unnecessary transmission. Furthermore, the RLC processing unit 302 in the receiving communication device cannot recognize that the RLC PDU no longer needs to be transmitted because the allowable delay time for the user data has elapsed, and continues to transmit a retransmission request.

[0020] In view of the above circumstances, this embodiment provides a technique for suppressing unnecessary transmission of RLC PDUs.

[0021] In this embodiment, in a communication device on the transmitting side (hereinafter referred to as the "transmitting device"), when the PDCP processing unit 301 discards user data (a PDCP PDU or PDCP SDU including the user data), it notifies the RLC processing unit 302 of information identifying the discarded user data. The PDCP processing unit 301 can, for example, notify the RLC processing unit 302 of information identifying the PDCP PDU or PDCP SDU. The RLC processing unit 302 identifies the sequence number of the RLC PDU including the discarded user data based on the notified information. Then, the RLC processing unit 302 in the transmitting device discards the RLC PDU with that sequence number, and further notifies the RLC processing unit 302 in the communication device on the receiving side (hereinafter referred to as the "receiving device") of the sequence number of the discarded RLC PDU. This makes it possible to prevent the transmitting device from transmitting unnecessary RLC PDUs. In addition, by receiving information about the sequence number of the discarded RLC PDU, the receiving device can avoid sending a retransmission request for the RLC PDU to the transmitting device even if the RLC PDU with that sequence number is not received.

[0022] The transmitting device may notify the receiving device of the sequence number of the discarded RLC PDU every time an RLC PDU is discarded, or may notify the receiving device of (a list of) the sequence numbers of the discarded RLC PDUs periodically at a predetermined period. In this case, information that can identify the predetermined period may be notified from the base station device 101 when the transmitting device is the terminal device 111. Even when the transmitting device is the base station device 101, information that can identify the predetermined period may be notified from the terminal device 111 to the base station device 101. When the transmitting device notifies the receiving device of the sequence number of the discarded RLC PDU, the transmitting device may start a prohibit timer to prevent further notification of the sequence number of the discarded RLC PDU for a predetermined period. In other words, the transmitting device may prevent the sequence number of the discarded RLC PDU from being notified frequently, and after the sequence number has been notified once, prevent similar notification for a certain period. The transmitting apparatus may transmit only information regarding the sequence number of the discarded RLC PDU to the receiving apparatus, or may include information regarding the sequence number of the discarded RLC PDU in an RLC PDU (Acknowledge Mode Data (AMD) PDU) containing user data to be transmitted to the receiving apparatus and transmit the resulting PDU to the receiving apparatus. The transmitting apparatus may also generate a STATUS PDU including information regarding the sequence number of the discarded RLC PDU and transmit the STATUS PDU to the receiving apparatus. This STATUS PDU may be newly defined to notify the discarded RLC PDU. The information notified by the transmitting apparatus is not limited to (a list of) the sequence numbers of the discarded RLC PDUs, but may also be information consisting of the minimum sequence number of the discarded RLC PDUs and the number of discarded RLC PDUs. Furthermore, if an RLC PDU is discarded before its first transmission, the transmitting apparatus may advance the sequence numbers of other RLC PDUs to be transmitted after the discarded RLC PDU and not notify the sequence number of the discarded RLC PDU.For example, if a first RLC PDU with a sequence number of "n" is discarded without being transmitted to the receiving device, the sequence number of the second RLC PDU that was scheduled to be transmitted with a sequence number set to "n+1" may be reassigned to "n" so that notification of the sequence number of the first RLC PDU is not made. Because the first RLC PDU has never been transmitted, the receiving device is not aware of the existence of the first RLC PDU and will not request retransmission of the first RLC PDU.

[0023] Note that, after notifying a receiving device of the sequence number of a discarded RLC PDU, if the transmitting device receives a retransmission request from the receiving device for an RLC PDU with that sequence number, the transmitting device may retransmit the notification of the sequence number of the discarded RLC PDU to the receiving device without transmitting the RLC PDU. This is because it is assumed that the notification of the sequence number of the discarded RLC PDU has not arrived at the receiving device due to the receipt of the retransmission request. Note that, to perform this process, the transmitting device may manage transmitted RLC PDUs and discarded RLC PDUs separately. That is, the transmitting device manages transmission using a window of a predetermined size to identify RLC PDUs having sequence numbers within a predetermined range as those to be transmitted. However, this management alone cannot distinguish between discarded RLC PDUs and RLC PDUs that may be retransmitted. For this reason, when the transmitting device receives a request to retransmit a discarded RLC PDU, the transmitting device may manage information that enables it to identify that the RLC PDU is not to be retransmitted. The transmitting device may determine, for example, based on this information, whether to retransmit the RLC PDU that is the target of the retransmission request. That is, the transmitting device may determine not to retransmit the discarded RLC PDU even if a retransmission request is received, and may determine to retransmit the RLC PDU if a retransmission request is received for the non-discarded RLC PDU. Furthermore, for example, if an RLC PDU with the smallest sequence number within the range of sequence numbers specified by the above-mentioned window is discarded, the transmitting device may shift the window to a range that does not include the discarded sequence number, thereby changing the range of transmission targets.

[0024] Furthermore, when a single RLC PDU includes a discarded first PDCP PDU and an undeleted second PDCP PDU, the transmitting device may discard the RLC PDU including the first PDCP PDU and generate an RLC PDU including only the second PDCP PDU. The transmitting device may then transmit the RLC PDU to the receiving device. Note that the sequence number of the discarded RLC PDU may be reused, or a different sequence number may be assigned to the RLC PDU. In this case, the RLC PDU including the discarded first PDCP PDU and the undeleted second PDCP PDU may not be discarded, and conventional processing, including retransmission of the RLC PDU, may be continued.

[0025] As described above, the receiving device does not send a retransmission request for a discarded RLC PDU even if it is not received. The RLC processing unit 302 of the receiving device handles the discarded RLC PDU in the same way as if it had been successfully received. In one example, the receiving device may generate the above-mentioned STATUS PDU and transmit it to the transmitting device so as not to indicate that the RLC PDU with the sequence number notified of the discarding has not been received (as if it had been received). Note that the receiving device may also manage reception using a sequence number window or the like. In this case, when receiving notification of the sequence number of the discarded RLC PDU, if that sequence number corresponds to the minimum value of the window, the receiving device may shift the range of the window so that it no longer includes that sequence number.

[0026] The terminal device 111 may notify the base station device 101 of capability information indicating whether or not it has the capability to perform the above-described processing. That is, the terminal device 111 may notify the base station device 101 of whether or not it has the capability to notify the sequence number of a discarded RLC PDU, or whether or not it has the capability to notify the base station device 101 of the capability to notify the sequence number of a discarded RLC PDU, or the capability to not request retransmission of the discarded RLC PDU upon receiving such notification. The capability information may also include information indicating whether or not it is possible to control internal variables for the above-described window control, etc. Note that the control of internal variables does not need to be notified. That is, the terminal device 111 may notify the base station device 101 of information indicating that it supports only some, but not all, of the processing described in this embodiment. For example, if the terminal device 111 supports only the processing related to the notification of the sequence number of an RLC PDU to be discarded, the base station device 101 can prevent the terminal device 111 from transmitting unnecessary RLC PDUs without processing internal variables by performing the same processing as when the RLC PDU is successfully received. That is, by the base station apparatus 101 not marking the discarded RLC PDU as a target for NACK in the above-mentioned STATUS PDU, it is possible to prevent the terminal apparatus 111 from retransmitting that RLC PDU. Also, in this case, when the terminal apparatus 111 is requested by the base station apparatus 101 to retransmit the discarded RLC PDU, it can retransmit that RLC PDU. That is, the terminal apparatus 111 may only notify the sequence number and not perform other processes. That is, provided that the base station apparatus 101 is capable of performing processes including control of internal variables, the terminal apparatus 111 may not be capable of performing all of the above-mentioned processes. Note that, when the terminal apparatus 111 is only capable of performing the function of notifying the sequence number of the RLC PDU to be discarded, if the base station apparatus 101 is not capable of performing the above-mentioned processes, it simply ignores the notification and can operate as usual. That is, the terminal device 111 notifies the base station device 101 of the sequence number of the RLC PDU to be deleted, but does not discard the RLC PDU until it is notified that the RLC PDU has been received normally by the base station device 101.Therefore, if the base station device 101 cannot interpret the above-mentioned notification, an RLC PDU corresponding to the discarded user data will be transmitted. However, it is possible to prevent an operation in which the discarded RLC PDU does not exist and the notification is not interpreted even if it is retransmitted.

[0027] In addition, the base station device 101 can determine the processing to be executed by the terminal device 111 in response to receiving the capability information. That is, the base station device 101 can instruct the terminal device 111 to execute all of the processing corresponding to the capabilities of the terminal device 111, or can instruct the terminal device 111 to execute only some of the functions, such as only the above-mentioned sequence number notification processing. This instruction can be notified to the terminal device 111 by, for example, an RRC Reconfiguration message.

[0028] (Processing flow) Next, an example of the flow of processing executed in the wireless communication system of this embodiment will be described with reference to Fig. 4. Note that the processing shown here is an example, and various modifications such as those described above can be made. Note that it is assumed that notification of capability information of the terminal device 111 has already been made, and notification of a sequence number and change of an internal variable are to be made.

[0029] Assume that the transmitting device transmits RLC PDUs with sequence numbers 1 to 9, for example. Note that FIG. 4 shows an example in which RLC PDUs with sequence numbers 1 to 9 are initially generated, but these RLC PDUs may be generated sequentially, and at least some data may not be generated initially. The transmitting device uses a window to identify RLC PDUs to be transmitted. In the example of FIG. 4, the window size is 3, and initially, a range of sequence numbers 1 to 3 may be identified as the transmission targets. The transmitting device transmits RLC PDUs with sequence numbers 1 to 3 specified by the window to the receiving device (S401). At this time, the transmitting device manages the oldest sequence number among those for which no ACK has been received from the receiving device, using a variable TX_Next_Ack. At the time of S401, RLC PDUs with sequence numbers 1 to 3 have been transmitted, and no ACK has been received for any of them, so TX_Next_Ack is set to "1." This TX_Next_Ack corresponds to the lower limit of the sequence numbers specified in the window. That is, the window is set so that RLC PDUs with sequence numbers from TX_Next_Ack to TX_Next_Ack+Window Size-1 are to be transmitted. The transmitting device also manages the sequence number of the RLC PDU to be transmitted next (that is, not yet transmitted) using the variable TX_Next. In this case, since RLC PDUs with sequence numbers 1 to 3 have been transmitted, TX_Next is set to "4."

[0030] In addition, a receiving device manages a receiving window, and the lowest value of the sequence number defined by the window is managed by a variable RX_Next. In addition, in the receiving device, the last sequence number that was successfully received is managed by a variable RX_Next_Highest. In the example of FIG. 4, RX_Next=1 is initially stored in the receiving device. Here, it is assumed that the receiving device has successfully received only the RLC PDUs with sequence numbers 1 to 2 out of the RLC PDUs with sequence numbers 1 to 3 transmitted in S401. In this case, the receiving device transmits, for example, an acknowledgement (ACK) indicating successful reception of the RLC PDUs with sequence numbers 1 to 2 to the transmitting device (S402). In this case, the acknowledgement (ACK) may be a STATUS PDU including ACK_SN=3. At this point, the transmitting device sets RX_Next_Highest to "2" because the highest successfully received sequence number is 2, and sets RX_Next to "3" because the sequence number of the next RLC PDU to be received is 3.

[0031] Upon receiving the ACK in S402, the transmitting device recognizes that the RLC PDUs with sequence numbers 1 and 2 have been successfully transmitted, and changes TX_Next_Ack to "3." As a result, the window shifts to the range of 3 to 5, and the transmitting device transmits the RLC PDUs with sequence numbers 4 and 5, of the RLC PDUs with sequence numbers 3 to 5, whose initial transmission has not been completed, to the receiving device (S403). At this point, the sequence number of the RLC PDU to be transmitted next, whose initial transmission has not been completed, becomes "6," so the variable TX_Next is changed to "6." Furthermore, it is assumed that the receiving device has transmitted an ACK indicating that only the RLC PDU with sequence number 4 has been successfully received among the RLC PDUs with sequence numbers 4 and 5 (S404). The acknowledgement (ACK) in this case may be a STATUS PDU including NACK_SN=3 and ACK_SN=5. At the timing of S404, the receiving device can determine that the RLC PDU with sequence number 3 has not been successfully received, and can transmit a STATUS PDU including NACK_SN=3. In this case, the RLC PDU with sequence number 3 has not been received, and the highest value of the successfully received sequence number is 4, so the value of RX_Next remains "3" while RX_Next_Highest is changed to "4." On the other hand, even when the transmitting device receives this ACK, it does not change the value of TX_Next_Ack or TX_Next.

[0032] After that, it is assumed that the transmitting device decides to discard the transmitted RLC PDU with sequence number 3 in response to the discarding of user data in the PDCP layer. In response to this decision, the transmitting device notifies the receiving device of the sequence number "3" of the RLC PDU to be discarded (S405). At this time, after discarding the RLC PDU with sequence number 3, the transmitting device changes the internal variable for that RLC PDU in the same way as when transmission is successful. That is, the transmitting device changes TX_Next_Ack in the same way as when an ACK is received for the RLC PDU with sequence number 3. In this case, since the transmitting device has received a notification of successful reception for the RLC PDU with sequence number 4, it changes the value of TX_Next_Ack to "5." Then, the transmitting device shifts the window so that the sequence number starts from 5, and transmits the RLC PDUs with sequence numbers 6 and 7, whose initial transmission has not been completed within that window, to the receiving device (S406). Furthermore, the transmitting device changes the value of TX_Next to "8" after this transmission.

[0033] On the other hand, when the receiving device receives notification of the sequence number of the RLC PDU to be discarded in S405, it changes its internal variables in the same way as when it successfully receives the RLC PDU with the notified sequence number 3. That is, because the receiving device successfully receives the RLC PDU with sequence number 4, it changes the value of RX_Next to "5." After that, for example, if the receiving device successfully receives the RLC PDUs with sequence numbers 6 and 7 transmitted from the transmitting device in S406, it returns an ACK in response (S407). The acknowledgment (ACK) in this case may be a STATUS PDU including NACK_SN=5 and ACK_SN=8. At the timing of S407, the receiving device can determine that it did not successfully receive the RLC PDU with sequence number 5, and can transmit a STATUS PDU including NACK_SN=5. In this case, because the receiving device did not successfully receive the RLC PDU with sequence number 5, it maintains the value of RX_Next as "5" and changes the value of RX_Next_Highest to "7."

[0034] The receiving device transmits a STATUS PDU indicating the reception status of the RLC PDU to the transmitting device, including a NACK_SN indicating the sequence number of the RLC PDU that was not successfully received and an ACK_SN indicating the sequence number next to the sequence number of the most recently successfully received RLC PDU. If such a STATUS PDU is transmitted, for example, earlier than S405, the settings are NACK_SN=3 and ACK_SN=5. In contrast, a STATUS PDU reported between S405 and S406 includes only ACK_SN=5 and does not include a NACK_SN. In S406, in response to the reception of the RLC PDU with sequence number 6, the receiving device can determine that the RLC PDU with sequence number 5 was not successfully received. Therefore, a STATUS PDU with NACK_SN=5 and ACK_SN=8 may be transmitted later than S406.

[0035] This prevents unnecessary RLC PDU transmission due to discarded user data at the PDCP layer, contributing to Goal 9 of the United Nations Sustainable Development Goals (SDGs), which is to "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0036] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention.

Claims

1. A communication device conforming to a cellular communication standard of the Third Generation Partnership Project (3GPP), comprising: a PDCP processing means for performing PDCP layer processing including generation of a Packet Data Convergence Protocol (PDCP) Protocol Data Unit (PDU) containing user data; a Radio Link Control (RLC) processing means for acquiring the PDCP PDU from the PDCP processing means, generating an RLC PDU including one or more PDCP PDUs, and transmitting the RLC PDU to a communication partner device in an RLC-Acknowledge Mode (RLC-AM); and the PDCP processing means manages an allowable delay time, which is an allowable value of delay until a transmitted PDCP PDU is successfully received by the other device, and identifies a PDCP PDU that exceeds the allowable delay time; The RLC processing means acquiring, from the PDCP processing means, information identifying the PDCP PDU identified as having exceeded the allowable delay time; Identifying a sequence number of an RLC PDU including a PDCP PDU identified as exceeding the tolerable delay time; performing RLC retransmission control to exclude the RLC PDU having the specified sequence number from targets for RLC retransmission; A communication device comprising:

2. 2. The communication device according to claim 1, wherein the communication device is a terminal device, and the counterpart device is a base station device.

3. 3. The communication device according to claim 2, further comprising a transmitting unit configured to transmit capability information indicating whether or not the communication device has capability related to the RLC retransmission control to the other device.

4. 2. The communication device according to claim 1, wherein the communication device is a base station device, and the counterpart device is a terminal device.

5. 5. The communication device according to claim 4, further comprising a receiving unit configured to receive capability information indicating whether or not the communication device has capability related to the RLC retransmission control from the counterpart device.

6. A communication device as described in Claim 3, characterized in that it further has a receiving means for receiving an instruction to execute processing corresponding to the capability information from the base station device.

7. A control method executed by a communication device that conforms to a cellular communication standard of the Third Generation Partnership Project (3GPP), includes: a Packet Data Convergence Protocol (PDCP) function that performs PDCP layer processing, including generating a Packet Data Convergence Protocol (PDCP) Protocol Data Unit (PDU) including user data; and a Radio Link Control (RLC) function that acquires a PDCP PDU from the PDCP function, generates a Radio Link Control (RLC) PDU including one or more PDCP PDUs, and transmits the RLC PDU to a communication partner device in RLC-Acknowledge Mode (RLC-AM), the method comprising: In the PDCP function, Managing an allowable delay time, which is an allowable value of delay until the transmitted PDCP PDU is successfully received by the other device; Identifying a PDCP PDU that exceeds the allowable delay time; In the RLC function, obtaining, from the PDCP function, information identifying a PDCP PDU identified as exceeding the tolerable delay time; Identifying a sequence number of an RLC PDU including a PDCP PDU identified as exceeding the tolerable delay time; performing RLC retransmission control to exclude the RLC PDU having the specified sequence number from targets for RLC retransmission; A control method comprising:

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

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