Communication device, control method, and program for preventing unnecessary transmission in RLC-am

Abstract

This communication device generates an RLC PDU including at least one PDCP PDU and transmits the RLC PDU to a counterpart device of communication by RLC-AM. The communication device manages an allowable delay time that is an allowable value of a delay until the transmitted PDCP PDU is successfully received by the counterpart device in the PDCP layer, discards the PDCP PDU of which the allowable delay time is expired, acquires information identifying the discarded PDCP PDU in the RLC layer, identifies a sequence number of the RLC PDU including the discarded PDCP PDU, discards the RLC PDU including the discarded PDCP PDU, and notifies the counterpart device of the sequence number of the discarded RLC PDU.

Description

Communication device, control method, and program for preventing unnecessary transmission in RLC-AM

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

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

[0003] There is user data for which a delay tolerance (tolerable delay time, packet delay budget) is set until the data reaches the other device. For example, user data that requires real-time performance is naturally assumed to have a short tolerable delay time. Here, when transmitting user data with such a short tolerable delay time in RLC-AM, it is assumed that the tolerable delay time will be exceeded when transmitting or retransmitting the user data. User data that exceeds the tolerable delay time becomes data that no longer needs 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.

[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 generation of Packet Data Convergence Protocol (PDCP) Protocol Data Units (PDDUs) 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 the delay until the transmitted PDCP PDU is successfully received by the communication partner device, and when a PDCP PDU that exceeds the allowable delay time is received, the PDCP processing means manages an allowable delay time, which is an allowable value for the delay until the transmitted PDCP PDU is successfully received by the communication partner device, and when a PDCP PDU that exceeds the allowable delay time is received, the PDCP processing means manages an allowable delay time. The RLC processing means acquires information for identifying the discarded PDCP PDU from the PDCP processing means, identifies the sequence number of the RLC PDU including the discarded PDCP PDU, discards the RLC PDU including the discarded PDCP PDU, and notifies the other device of the sequence number of the RLC PDU to be discarded.

[0006] A communication device according to another aspect of the present invention is a communication device conforming to the cellular communication standard of the Third Generation Partnership Project (3GPP), and includes: RLC processing means for receiving an RLC Protocol Data Unit (PDU) from a communication partner device in Radio Link Control (RLC)-Acknowledge Mode (AM) and outputting one or more RLC Service Data Units (SDUs) included in the RLC PDU; and PDCP processing means for acquiring the RLC SDU as a Packet Data Convergence Protocol (PDCP) PDU and performing 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 outputs the RLC SDU of the notified sequence number. If a PDU is not received, it does not request a retransmission of that RLC PDU.

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

[0008] Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which the same or similar elements are designated by the same reference numerals.

[0009] The accompanying drawings are incorporated in and constitute a part of the specification, illustrate embodiments of the present invention, and together with the description are used to explain the principles of the present invention. A diagram showing an example of the configuration of a wireless communication system. A diagram showing an example of the hardware configuration of a base station device and a terminal device. A diagram showing an example of the functional configuration of a base station device and a terminal device. A diagram explaining processing performed in a wireless communication system.

[0010] 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.

[0011] (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) or 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.

[0012] (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 the 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 the 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 also 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. While 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 also 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 a 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 the multiple available frequency bands, or may have a common communication circuit 205 for at least some of the frequency bands.

[0013] 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. Furthermore, the functional blocks in FIG. 3 are shown schematically, and the respective functional blocks may be realized as an integrated unit or may be 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 by a processor present within the communication circuit 205 executing predetermined software. Since the details of the processes executed by each functional unit have been described above, only the general functions of the base station device 101 and the terminal device 111 will be outlined here.

[0014] 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.

[0015] 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. In this case, one RLC SDU may be segmented and included in multiple RLC PDUs.

[0016] The MAC processing unit 303 performs processing of the Medium Access Control (MAC) layer. The MAC processing unit 303 treats 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 as a radio signal to the other device.

[0017] 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. Furthermore, one RLC SDU may be segmented and included in multiple RLC PDUs. Therefore, the RLC processing unit 302 segments or concatenates portions of the payload included in the RLC PDU to reconstruct each RLC SDU. Then, the RLC processing unit 302 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 packets) of the transmitting communication device (the terminal device 111 in the case of the uplink, or the base station device 101 in the case of the downlink) reaches the receiving communication device (the base station device 101 in the case of the uplink, or the terminal device 111 in the case of the downlink).

[0018] 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. The PDCP processing unit 301 discards the PDCP PDU if the elapsed time from the generation of the user data (input to the PDCP processing unit 301) exceeds the allowable delay time. The allowable delay time in this case 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 the wireless line, such as 5QI (5G QoS Identifier), received from the core network device, and notify the terminal device of the determined allowable delay time as a discardTimer, which is part of the PDCP parameters.

[0019] 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 it. Then, the RLC processing unit 302 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 the 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."

[0020] When communication control is performed using RLC-AM, if a receiving communication device fails to successfully 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 layer may no longer need to retransmit the RLC PDU containing the PDCP PDU, 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 will 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 will perform unnecessary transmission. Furthermore, the RLC processing unit 302 in the receiving communication device is unable to recognize that the RLC PDU no longer needs to be transmitted because the permissible delay time for the user data has elapsed, and so continues to transmit the retransmission request.

[0021] In view of the above circumstances, this embodiment provides a technique for suppressing unnecessary transmission of RLC PDUs.

[0022] 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 a PDCP SDU including the user data), the PDCP processing unit 301 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 the 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 of the transmitting device discards the RLC PDU with that sequence number and further notifies the RLC processing unit 302 of 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. Furthermore, by receiving information on the sequence number of the discarded RLC PDU, the receiving device can avoid sending a retransmission request for that RLC PDU to the transmitting device even if the RLC PDU with that sequence number is not received.

[0023] The transmitting apparatus may notify the receiving apparatus of the sequence number of the discarded RLC PDU each time an RLC PDU is discarded, or may periodically notify the receiving apparatus of (a list of) the sequence numbers of the discarded RLC PDUs at a predetermined interval. In this case, information that can identify the predetermined interval may be notified from the base station apparatus 101 when the transmitting apparatus is the terminal apparatus 111. Even when the transmitting apparatus is the base station apparatus 101, information that can identify the predetermined interval may be notified from the terminal apparatus 111 to the base station apparatus 101. When the transmitting apparatus notifies the receiving apparatus of the sequence number of the discarded RLC PDU, the transmitting apparatus may activate a prohibit timer to prevent further notification of the sequence number of the discarded RLC PDU for a predetermined period. That is, the transmitting apparatus may prevent the sequence number of the discarded RLC PDU from being notified frequently, and after a sequence number has been notified once, prevent similar notification for a certain period. The transmitting apparatus may transmit only information regarding the sequence numbers of the discarded RLC PDUs to the receiving apparatus, or may include information regarding the sequence numbers of the discarded RLC PDUs in an RLC PDU (Acknowledge Mode Data (AMD) PDU) containing user data to be transmitted to the receiving apparatus and transmit the resulting RLC PDU to the receiving apparatus. Alternatively, the transmitting apparatus may generate a STATUS PDU including information regarding the sequence numbers of the discarded RLC PDUs and transmit the STATUS PDU to the receiving apparatus. This STATUS PDU may be newly defined to notify the discarded RLC PDUs. 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 smallest sequence number of the discarded RLC PDUs and the number of discarded RLC PDUs. Furthermore, if an RLC PDU is discarded before it is transmitted for the first time, the transmitting device may advance the sequence numbers of other RLC PDUs to be transmitted after that RLC PDU, and may not notify the user of the sequence numbers of the discarded RLC PDUs.For example, if a first RLC PDU with a sequence number "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.

[0024] 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 the 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. Therefore, when the transmitting device receives a retransmission request for 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 for which a retransmission request is requested. 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.

[0025] Furthermore, when an 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.

[0026] 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 discard has not been received (as if it had been received). Note that reception management may also be performed in the receiving device using a sequence number window or the like. In this case, when receiving notification of the sequence number of the discarded RLC PDU, if the sequence number corresponds to the minimum value of the window, the receiving device may shift the range of the window so that it does not include the sequence number.

[0027] The terminal device 111 may notify the base station device 101 of capability information indicating whether 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 it has 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 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 a discarded RLC PDU, 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 not including the discarded RLC PDU as the target of NACK in the above-mentioned STATUS PDU, the base station apparatus 101 can prevent the terminal apparatus 111 from retransmitting the RLC PDU. Furthermore, in this case, if the base station apparatus 101 requests retransmission of the discarded RLC PDU, the terminal apparatus 111 can retransmit the RLC PDU. That is, the terminal apparatus 111 may only notify the sequence number and not perform other processing. That is, provided that the base station apparatus 101 is capable of performing functions including control of internal variables, the terminal apparatus 111 may not be capable of performing all of the above-mentioned processing. Note that if the terminal apparatus 111 is only capable of performing the function of notifying the sequence number of the discarded RLC PDU, but the base station apparatus 101 is not capable of performing the above-mentioned processing, the notification is simply ignored, and conventional operation can be performed. That is, the terminal device 111 notifies 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 apparatus 101 is unable to interpret the above-mentioned notification, the RLC PDU corresponding to the discarded user data is 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.

[0028] 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 may instruct the terminal device 111 to execute all of the processing corresponding to the capabilities of the terminal device 111, or may 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, for example, by an RRC Reconfiguration message.

[0029] (Processing Flow) Next, an example of the processing flow 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 are possible. Note that it is assumed that notification of the capability information of the terminal device 111 has already been performed, and notification of the sequence number and change of the internal variable are performed.

[0030] Assume that the transmitting device transmits RLC PDUs with sequence numbers 1 to 9, for example. While FIG. 4 shows an example in which RLC PDUs with sequence numbers 1 to 9 are initially generated, 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 the 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 number 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 (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."

[0031] In addition, a receiving device manages a reception window, and the lower limit of the sequence number defined by the window is managed by the variable RX_Next. Furthermore, in the receiving device, the last sequence number successfully received is managed by the variable RX_Next_Highest. In the example of FIG. 4, the receiving device initially holds RX_Next = 1. 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 sequence number that has been successfully received is 2, and sets RX_Next to "3" because the sequence number of the next RLC PDU to be received is 3.

[0032] Upon receiving the ACK of 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." This shifts the window to the range of 3 to 5, and the transmitting device transmits the RLC PDUs with sequence numbers 4 and 5, which have not yet been initially transmitted, to the receiving device (S403). At this point, the sequence number of the RLC PDU to be transmitted next, which has not yet been initially transmitted, becomes "6," so the variable TX_Next is changed to "6." Furthermore, the receiving device transmits 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 acknowledgment (ACK) in this case may be a STATUS PDU including NACK_SN=3 and ACK_SN=5. At timing 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 successfully received sequence number is 4, so the value of RX_Next_Highest is changed to "4" while the value of RX_Next remains "3." 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.

[0033] It is assumed that the transmitting device then determines 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). 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." The transmitting device then shifts the window so that the sequence number starts from 5, and transmits the RLC PDUs with sequence numbers 6 and 7, whose initial transmissions have not yet been completed within that window, to the receiving device (S406). Furthermore, with this transmission, the transmitting device changes the value of TX_Next to "8".

[0034] 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, since the receiving device successfully receives the RLC PDU with sequence number 4, it changes the value of RX_Next to "5." Thereafter, 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, since the receiving device has not successfully received the RLC PDU with sequence number 5, it keeps the value of RX_Next at "5" and changes the value of RX_Next_Highest to "7".

[0035] 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. For example, if such a STATUS PDU is transmitted earlier than S405, NACK_SN = 3 and ACK_SN = 5 are set. In contrast, the STATUS PDU reported between S405 and S406 includes only ACK_SN = 5, and does not include a NACK_SN. In S406, upon receiving 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, at a timing after S406, a STATUS PDU with NACK_SN=5 and ACK_SN=8 specified may be transmitted.

[0036] In this way, it is possible to prevent unnecessary transmission of RLC PDUs due to discarding of user data in the PDCP layer, thereby contributing to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0037] 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.

[0038] This application claims priority based on Japanese Patent Application No. 2024-056620, filed March 29, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A communication device conforming to the cellular communication standard of the Third Generation Partnership Project (3GPP), comprising: PDCP processing means for performing PDCP layer processing including generation of 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 the 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: a communication device that acquires information identifying a discarded PDCP PDU from the PDCP processing means; identifies a sequence number of an RLC PDU including the discarded PDCP PDU; discards the RLC PDU including the discarded PDCP PDU; and notifies the counterpart device of the sequence number of the RLC PDU to be discarded.

2. The communication device according to claim 1, wherein the RLC processing means notifies the counterpart device of the sequence number of the RLC PDU to be discarded every time the RLC processing means discards an RLC PDU including the discarded PDCP PDU.

3. The communication device according to claim 1, wherein, when the RLC processing means notifies the other device of the sequence number of the RLC PDU to be discarded, the RLC processing means starts a timer that prevents further notifications from being made for a predetermined period of time after the notification.

4. The communication device according to claim 1, wherein said RLC processing means periodically notifies said counterpart device of the sequence number of the discarded RLC PDU at a predetermined interval.

5. The communication device according to claim 4, wherein the predetermined period is notified by the other device.

6. The communication device according to claim 1, wherein said RLC processing means includes information about the sequence number of the first RLC PDU to be discarded in an Acknowledge Mode Data (AMD) PDU, which is a second RLC PDU that is not discarded, and transmits the AMD PDU to said counterpart device.

7. The communication device according to claim 1, wherein said RLC processing means includes information on the sequence number of the RLC PDU to be discarded in a STATUS PDU and transmits the STATUS PDU to said counterpart device.

8. The communication device according to claim 1, wherein said RLC processing means transmits a list of sequence numbers of RLC PDUs to be discarded to said counterpart device.

9. The communication device according to claim 1, wherein said RLC processing means transmits to said counterpart device, as information on one or more RLC PDUs to be discarded, information indicating the smallest value of the sequence numbers of said one or more RLC PDUs and the number of RLC PDUs to be discarded.

10. The communication device according to claim 1, wherein, when the RLC processing means discards a first RLC PDU that has not been transmitted to the other device, the RLC processing means advances the sequence number of a second RLC PDU that is transmitted after the first RLC PDU, and does not notify the other device of the sequence number that was assigned to the first RLC PDU.

11. The communication device according to claim 1, wherein said RLC processing means, when receiving from said other device a signal requesting retransmission of an RLC PDU having said sequence number notified to said other device, retransmits said sequence number of the discarded RLC PDU to said other device.

12. The communication device according to claim 1, wherein the RLC processing means discards the RLC PDUs including the discarded PDCP PDUs and the PDCP PDUs that are not discarded, generates an RLC PDU including the PDCP PDUs that are not discarded, and transmits the RLC PDU to the counterpart device.

13. The communication device according to claim 1, wherein, when the smallest sequence number in a window for specifying a range of sequence numbers for identifying an RLC PDU to be transmitted corresponds to the sequence number corresponding to a discarded RLC PDU, the RLC processing means shifts the window to a range that does not include the sequence number corresponding to the discarded RLC PDU.

14. A communication device conforming to the cellular communication standard of the Third Generation Partnership Project (3GPP), comprising: RLC processing means for receiving an RLC Protocol Data Unit (PDU) from a communication partner device in Radio Link Control (RLC)-Acknowledge Mode (AM) and outputting one or more RLC Service Data Units (SDUs) included in the RLC PDU; and PDCP processing means for acquiring the RLC SDU as a Packet Data Convergence Protocol (PDCP) PDU and performing reception processing for 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 outputs the RLC SDU of the notified sequence number. The communication device does not request retransmission of an RLC PDU even if the PDU is not received.

15. The communications device according to claim 14, wherein said RLC processing means is configured to transmit information indicating the reception status of an RLC PDU to said counterpart device, and generates said reception status so as not to indicate that an RLC PDU of said notified sequence number has not been received.

16. A communication device according to any one of claims 1 to 15, wherein the communication device is a terminal device and the counterpart device is a base station device.

17. The communication device according to claim 16, further comprising a transmitting means for transmitting capability information indicating whether or not the communication device has capability related to notification of the sequence number of an RLC PDU to be discarded to the other device.

18. The communication device according to claim 17, wherein said capability information further includes information indicating whether or not said device has a function for controlling an internal variable associated with said notification.

19. A communication device according to any one of claims 1 to 15, wherein the communication device is a base station device and the counterpart device is a terminal device.

20. The communication device according to claim 19, further comprising receiving means for receiving, from the counterpart device, capability information indicating whether or not the counterpart device has capability for notifying the sequence number of an RLC PDU to be discarded.

21. The communication device according to claim 20, wherein the capability information further includes information indicating whether or not the device has a function for controlling an internal variable associated with the notification.

22. A control method executed by a communication device that conforms to the cellular communication standard of the Third Generation Partnership Project (3GPP), and includes: a PDCP function that performs PDCP layer processing, including generating Packet Data Convergence Protocol (PDCP) Protocol Data Units (PDUs) including user data; and a Radio Link Control (RLC) function that acquires PDCP PDUs from the PDCP function, generates Radio Link Control (RLC) PDUs including one or more PDCP PDUs, and transmits the RLC PDUs 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 for the delay until the transmitted PDCP PDU is successfully received by the communication partner device; and discarding PDCP PDUs that exceed the allowable delay time; and in the RLC function, acquiring information identifying a discarded PDCP PDU from the PDCP function; identifying a sequence number of an RLC PDU including the discarded PDCP PDU; discarding the RLC PDU including the discarded PDCP PDU; and notifying the other device of the sequence number of the RLC PDU to be discarded.

23. A control method executed by a communication device that conforms to the cellular communication standard of the Third Generation Partnership Project (3GPP), includes: an RLC function that receives an RLC Protocol Data Unit (PDU) from a communication partner device in Radio Link Control (RLC)-Acknowledge Mode (AM) and outputs one or more RLC Service Data Units (SDUs) included in the RLC PDU; and a PDCP function that acquires the RLC SDU as a Packet Data Convergence Protocol (PDCP) PDU and performs reception processing for the PDCP PDU, the method comprising: receiving, from the communication partner device, a notification of a sequence number of an RLC PDU to be discarded; and not requesting retransmission of the RLC PDU even if the PDU is not received.

24. A program for causing a computer installed in a communication device to execute the control method according to claim 22.

25. A program for causing a computer installed in a communication device to execute the control method according to claim 23.

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