Communication device, control method, and program for enhancing retransmission control in RLC layer of cellular communication system

Abstract

This communication device of a cellular communication system transmits, to another communication device, a Radio Link Control (RLC) Protocol Data Unit (PDU) which includes a Packet Data Convergence Protocol (PDCP) Service Data Unit (SDU). After the RLC PDU is transmitted, the communication device performs control so as to use a first setting value for increasing the transmission frequency of a STATUS PDU on the basis of the fact that the remaining time of a PDCP discard Timer activated for the PDCP SDU included in the RLC PDU falls below a prescribed threshold, and so as to use a second setting value at which the transmission frequency of the STATUS PDU becomes lower than the first setting value on the basis of the fact that the remaining time exceeds the prescribed threshold.

Description

Communication device, control method, and program for enhancing retransmission control in the RLC layer of a cellular communication system

[0001] The present invention relates to a retransmission control technique in an RLC layer in a cellular communication system.

[0002] Wireless communication systems conforming to cellular communication standards such as the Long Term Evolution (LTE) and fifth generation (5G) standards of the Third Generation Partnership Project (3GPP (registered trademark)) have been widely deployed. In cellular communication systems, in order to ensure that data is reliably delivered from a transmitting communication device to a receiving communication device, there is a mode called RLC-AM in which the receiving communication device transmits an acknowledgement response to allow the transmitting communication device to confirm whether or not the data has been successfully received. Note that RLC stands for Radio Link Control, and AM stands for Acknowledgement Mode.

[0003] In a cellular communication system, various types of user data are transmitted and received. Among the transmitted and received user data, there is data for which an allowable delay time is set between when the data is generated in a transmitting communication device and when it reaches a receiving communication device. When data with a short allowable delay time (e.g., requiring real-time performance) is transmitted using RLC-AM, if the allowable delay time is exceeded during transmission or retransmission of the data, the data is discarded. If such data discarding occurs frequently, the communication efficiency of the entire system may decrease.

[0004] The present invention provides a technique that enables efficient execution of RLC-AM data transmission.

[0005] A communication device according to one aspect of the present invention is a communication device in a cellular communication system, comprising: communication means for at least transmitting Radio Link Control (RLC) Protocol Data Units (PDUs) including Packet Data Convergence Protocol (PDCP) Service Data Units (SDUs) to another communication device; and control means for controlling the communication means to use a first setting value for increasing the transmission frequency of STATUS PDUs based on a remaining time of a PDCP discard timer activated for the PDCP SDU included in the RLC PDU after the RLC PDU has been transmitted, and to use a second setting value for decreasing the transmission frequency of the STATUS PDUs from the first setting value based on the remaining time exceeding the predetermined threshold.

[0006] A communication device according to another aspect of the present invention is a communication device for a cellular communication system, comprising: communication means for receiving a Radio Link Control (RLC) Protocol Data Unit (PDU) including a Packet Data Convergence Protocol (PDCP) Service Data Unit (SDU) from another communication device and transmitting a STATUS PDU; and a PDCP discard timer for increasing the frequency of transmission of the STATUS PDU when a remaining time of a PDCP discard timer activated for the PDCP SDU included in the RLC PDU after the RLC PDU is transmitted from the other communication device falls below a predetermined threshold, and a PDCP discard timer for increasing the frequency of transmission of the STATUS PDU from the first setting value when the remaining time exceeds the predetermined threshold. and control means for controlling the communication means to use a second setting value that reduces the frequency of PDU transmission.

[0007] According to the present invention, it is possible to efficiently perform RLC-AM data transmission.

[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. Figure 1 is a diagram showing an example of the configuration of a wireless communication system. Figure 2 is a diagram showing an example of the hardware configuration of a communication device. Figure 3 is a diagram showing a first example of the functional configuration of a communication device on the data transmitting side. Figure 4 is a diagram showing a first example of processing executed by the communication device on the data transmitting side. Figure 5 is a diagram showing a second example of the functional configuration of a communication device on the data transmitting side. Figure 6 is a diagram showing a second example of the functional configuration of a communication device on the data receiving side. Figure 7 is a diagram showing a first example of processing executed by the communication device on the data transmitting side. Figure 8 is a diagram showing a first example of processing executed by the communication device on the data receiving side.

[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 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 5th 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 102. The terminal device 102 is a communication device that establishes a connection with the base station device 101 and communicates with the base station device 101. The terminal device 102 transmits user data on an uplink (a link from the terminal device 102 to the base station device 101) to the base station device 101 and receives user data on a downlink (a link from the base station device 101 to the terminal device 102) from the base station device 101. Similarly, the base station device 101 is a communication device that transmits downlink user data to the connected terminal device 102 and receives uplink user data from the terminal device 102.

[0012] In this embodiment, it is assumed that retransmission control of user data is used in the Radio Link Control (RLC) layer. A communication device (e.g., terminal device 102) on the transmitting side of user data uses RLC-Acknowledge Mode (RLC-AM) to confirm whether data of the RLC layer has been successfully received in a communication device (e.g., base station device 101) on the receiving side, and if there is data that has not been successfully received, retransmits that data. The communication device on the transmitting side aggregates or segments data of the Packet Data Convergence Protocol (PDCP) layer (PDCP Protocol Data Unit (PDU)) to generate an RLC PDU. The communication device then aggregates one or more RLC PDUs or segments one RLC PDU to generate a Medium Access Control (MAC) PDU. The communication device then transmits a physical layer radio signal using the MAC PDU as a transport block. The receiving communication device then extracts the MAC PDU from the received physical layer radio signal and extracts the RLC PDU from the MAC PDU. The receiving communication device then determines whether each RLC PDU was successfully received and, based on the result of the determination, transmits a retransmission request to the transmitting communication device for the RLC PDUs that were not successfully received. Upon receiving the retransmission request, the transmitting communication device retransmits the RLC PDUs specified in the retransmission request. In one example, this retransmission request is information that can identify whether each RLC PDU was successfully received and is transmitted to the transmitting communication device as information called a STATUS PDU. The transmitting communication device identifies the RLC PDUs that were not successfully received based on the STATUS PDU and retransmits the RLC PDUs to the receiving communication device. In this way, the reliability of communication can be improved by repeatedly transmitting the RLC PDUs that the receiving communication device failed to receive.

[0013] On the other hand, a permissible delay time (Packet Delay Budget) is sometimes set for user data, which is the time from when the user data is generated at a transmitting communication device until the user data reaches a receiving communication device. In such a case, if the permissible delay time elapses while the transmitting communication device is waiting for a STATUS PDU or while the transmitting communication device is preparing to transmit an RLC PDU containing the user data, the RLC PDU will be discarded. If such discarding of user data (RLC PDUs) occurs frequently, the communication efficiency of the entire wireless communication system may decrease.

[0014] In view of the above circumstances, this embodiment provides a technique for reducing the probability of user data being discarded and suppressing a decrease in communication efficiency. Note that, in the following, an example will be described in which the transmitting communication device is the terminal device 102 and the receiving communication device is the base station device 101, but similar processing can also be performed in the case in which the base station device 101 is the transmitting communication device and the terminal device 102 is the receiving communication device.

[0015] (Device Configuration) FIG. 2 shows an example of the hardware configuration of the base station device 101 and the terminal device 102 according to this embodiment. In one example, the base station device 101 and the terminal device 102 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 102. 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 102 may have multiple communication circuits. For example, the base station device 101 and the terminal device 102 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 102 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 102 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 102 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.

[0016] (Processing Example) Next, an example of processing executed in the wireless communication system will be described.

[0017] <Processing Example 1> In this processing example, after a terminal device 102 operating in RLC-AM transmits data that may exceed the allowable delay time, the terminal device 102 retransmits the data without waiting for a retransmission request (or STATUS PDU) from the base station device 101 based on the satisfaction of a predetermined condition. That is, a transmitting communication device operating in RLC-AM typically receives a retransmission request or STATUS PDU from a receiving communication device and performs processing to retransmit RLC PDUs that were transmitted from the transmitting communication device but not received by the receiving communication device. Note that the retransmission processing in the case of autonomous retransmission is performed in the same manner as retransmission when a retransmission request or the like is received. That is, when it is determined that autonomous retransmission is to be performed, the terminal device 102 stores the data to be autonomously retransmitted in a transmission buffer and transmits a radio signal including the data using radio resources (frequency and time resources) allocated by the base station device 101. In response to this, the transmitting communication device (terminal device 102) according to this processing example executes retransmission of the RLC PDU without receiving a retransmission request or a STATUS PDU. Such retransmission performed without receiving a retransmission request or a STATUS PDU may be referred to hereinafter as a spontaneous retransmission. The predetermined condition may be, for example, that the remaining time of a timer that counts down the timing to discard an RLC PDU containing data with a predetermined delay requirement falls below a predetermined value. The data with a predetermined delay requirement may be data in a layer higher than the RLC layer, such as the RLC layer or PDCP layer, whose discard timing is measured by a timer. In the following description, this data is assumed to be data classified as a delay-critical PDCP SDU in the 3GPP (registered trademark) standard. SDU stands for Service Data Unit. In the following description, it is assumed that the timer is a PDCP discard timer that is activated in the PDCP layer.

[0018] When the remaining time of a PDCP discard timer activated for a delay-critical PDCP SDU falls below a predetermined threshold, the terminal device 102 targets an RLC PDU containing the delay-critical PDCP SDU for autonomous retransmission. Here, the predetermined threshold may be specified by a parameter called remainingTimeThreshold, for example. Note that this is just one example, and the predetermined threshold may be specified by a parameter with a different name. The terminal device 102 does not target the RLC PDU for autonomous retransmission while the remaining time of the PDCP discard timer exceeds a threshold remainingTimeThreshold. Note that this threshold remainingTimeThreshold may be notified to the terminal device 102 in advance from the base station device 101.

[0019] The above-mentioned comparison of the remaining time of the PDCP discard timer with the threshold and determination can be performed by the PDCP processing function of the terminal device 102 for each PDCP SDU. Then, for example, when a PDCP SDU whose remaining time is below the threshold exists, information for identifying the PDCP SDU is notified from the PDCP processing function of the terminal device 102 to the RLC processing function. Based on the information notified from the PDCP processing function, the RLC processing function identifies an RLC PDU (i.e., corresponding to the PDCP SDU) including an RLC SDU associated with the PDCP SDU, and determines that the RLC PDU is to be subject to autonomous retransmission. In this case, an RLC PDU that has already been determined to be retransmitted and is waiting for retransmission in the RLC processing function (waiting for allocation of radio resources necessary for retransmission) can be excluded from the subjects of autonomous retransmission. Furthermore, an RLC PDU for which retransmission has already been determined in the RLC processing function and for which the lower layer (MAC) has been notified of the RLC PDU to be retransmitted may be determined to be a target for autonomous retransmission even if the RLC PDU has not actually been transmitted to the base station apparatus 101. In other words, even for an RLC PDU that has never been transmitted to the base station apparatus 101, processing for autonomous retransmission may be initiated for the RLC PDU that has been processed in the RLC layer and transferred to the lower layer. Furthermore, when the PDCP processing function determines that there is a PDCP SDU whose remaining time exceeds a threshold, the PDCP processing function notifies the RLC processing function of information for identifying the PDCP SDU. The RLC processing function may then identify the RLC PDU corresponding to the PDCP SDU as an RLC PDU that is not a target for autonomous retransmission.

[0020] Furthermore, the comparison and determination of the remaining time of the PDCP discard timer with a threshold value may be performed in the RLC processing function, rather than in the PDCP processing function. For example, when the RLC processing function receives a PDCP SDU (RLC SDU) from the PDCP processing function, it starts a timer for determining whether to perform autonomous retransmission. Then, the RLC processing function determines the remaining time of the timer and the threshold value, and identifies RLC PDUs that should be subject to autonomous retransmission and RLC PDUs that should not be subject to autonomous retransmission. In this case, the timer value of the timer started in the RLC processing function for determining whether to perform autonomous retransmission can be determined based on the PDCP discard timer. The PDCP discard timer may be used as the timer value as is, or a timer value obtained by subtracting the time required for PDCP processing from the PDCP discard timer may be used. Furthermore, in the RLC processing function, information for calculating the timer to be started from the PDCP discard timer may be notified in advance from the base station apparatus 101 to the terminal apparatus 102. As described above, when the RLC processing function compares the remaining time with a threshold and makes a determination, it is not necessary to notify information for identifying PDCP SDUs that are below (or above) the threshold, which makes it easier to implement the function according to this embodiment in the terminal apparatus 102. Note that, when the RLC processing function is notified by the PDCP processing function before retransmission of an RLC PDU that is determined to be subject to autonomous retransmission, that PDCP SDU should be discarded, the RLC processing function can discard the RLC PDU without autonomous retransmission.

[0021] Here, for data to be subject to autonomous retransmission, such as a delay-critical PDCP SDU, when the user data to be transmitted is notified from the PDCP layer processing function unit to the RLC layer processing function unit in the terminal device 102, information indicating that the allowable delay time is short and that different processing from that for a normal PDCP SDU may be performed may be added in addition to the user data. Furthermore, the determination of whether an RLC PDU is subject to autonomous retransmission may be performed for each RLC PDU or for each logical channel. When determining whether an RLC PDU is subject to autonomous retransmission for each logical channel, the remaining time of the PDCP discard timer is specified for SDUs (PDCP SDUs / RLC SDUs) that have not yet been transmitted by a MAC PDU among all SDUs buffered in each LCG (Logical Channel Group). Then, based on the remaining time for each LCG, the terminal device 102 determines whether to subject SDUs belonging to that LCG to autonomous retransmission. For example, it identifies values ​​indicating characteristics of the remaining time for SDUs belonging to that LCG whose reception has not been confirmed, such as the minimum, maximum, average, or median remaining time, and determines whether the SDU whose reception has not been confirmed is subject to autonomous retransmission based on whether any (or all) of these values ​​are below (or above) a threshold. The terminal device 102 generates and retransmits (transmits) a MAC PDU including SDUs belonging to the LCG whose reception has not been confirmed. In this way, data of a specific logical channel with roughly the same delay requirement is subject to autonomous retransmission collectively when the remaining time falls below a predetermined threshold. Therefore, for example, when autonomous retransmission of data with strict delay requirements is performed, data with a relatively long remaining time is also retransmitted, thereby improving the probability that the delay requirement for that data can be met. In addition, data of a common logical channel is spontaneously retransmitted in bulk, and the base station device 101 receives the data of that logical channel normally, which reduces the amount of data whose remaining time falls below the threshold in a short period of time, thereby preventing frequent spontaneous retransmissions.

[0022] Furthermore, during communication of transmission data with a short allowable delay time, the terminal device 102 (its RLC-AM entity) may perform the above-mentioned autonomous retransmission uniformly for all data, rather than processing for each RLC PDU or each logical channel. Note that an RLC PDU corresponding to data that has already been discarded in the PDCP layer may be excluded from the autonomous retransmission because there is no point in performing autonomous retransmission.

[0023] After determining whether an RLC PDU is a target for autonomous retransmission, the terminal device 102 may start the retransmission process when a trigger (event) for starting autonomous retransmission occurs. The terminal device 102 may start the autonomous retransmission process of the RLC PDU that is a target for autonomous retransmission, for example, when HARQ transmission of the RLC PDU fails a specified number of times (for example, specified by the parameter REPETITION_NUMBER). Furthermore, the terminal device 102 may start the autonomous retransmission process of the RLC PDU that is a target for autonomous retransmission, for example, when HARQ transmission fails a second specified number of times different from REPETITION_NUMBER before the number of HARQ transmission failures reaches the above-mentioned specified number. Furthermore, the terminal device 102 may initiate autonomous retransmission of an RLC PDU when it does not receive a STATUS PDU related to the RLC PDU within a predetermined time period after the transmission of the RLC PDU. Alternatively, the terminal device 102 may perform autonomous retransmission only when multiple of the above-mentioned triggers occur. For example, the terminal device 102 may perform autonomous retransmission of an RLC PDU only when two conditions are met: it does not receive a STATUS PDU related to the RLC PDU within a predetermined time period after the transmission of the RLC PDU, and HARQ transmission has failed a predetermined number of times. Furthermore, performing autonomous retransmission consumes more radio resources. For this reason, additional conditions may be set so that autonomous retransmission is performed only under certain conditions. For example, the base station device 101 may monitor the usage status of radio resources and transmit a predetermined instruction to the terminal device 102 permitting autonomous retransmission only when the usage amount of radio resources is equal to or less than a certain value. In this case, the terminal device 102 can perform autonomous retransmission of the data to be autonomously retransmitted only when it receives the predetermined instruction from the base station device 101 (and when the above-mentioned conditions are satisfied). This makes it possible to prevent a decrease in the efficiency and quality of communication of other terminal devices due to the autonomous retransmission of a specific terminal device in an environment where excessive consumption of radio resources due to autonomous retransmission should be prevented, such as when a large number of terminal devices are connected to a base station device.

[0024] The terminal device 102 counts the number of retransmissions of an RLC PDU, and if the number of retransmissions exceeds the maximum number of retransmissions maxRetxThreshold specified by the base station device 101, determines that a radio link failure (RLF) has occurred and starts reconnection processing. Here, the terminal device 102 may include spontaneous retransmissions in the count of retransmissions used to determine RLF. When spontaneous retransmissions are performed, many retransmissions may be performed in a short period of time. For this reason, if spontaneous retransmissions are counted as retransmissions when determining whether the number of retransmissions has reached the maximum number of retransmissions, RLF may be more likely to be detected in situations where wireless quality is insufficient. For this reason, when spontaneous retransmissions are counted as retransmissions in the terminal device 102, the above-mentioned maximum number of retransmissions maxRetxThreshold may be changed to another value (larger than when spontaneous retransmissions are not counted as retransmissions). The base station device 101 may notify the terminal device 102 in advance of two types of maxRetxThreshold. That is, in addition to the conventional first maxRetxThreshold, a second maxRetxThreshold for counting spontaneous retransmissions as the number of retransmissions may be notified from the base station device 101 to the terminal device 102 and set in the terminal device 102. Furthermore, the terminal device 102 may not count spontaneous retransmissions as the number of retransmissions when determining whether the number of retransmissions has reached the maximum number of retransmissions. Furthermore, whether or not to count spontaneous retransmissions as the number of retransmissions when determining whether the number of retransmissions has reached the maximum number of retransmissions may be dynamically switched based on the radio quality of the received signal at the terminal device 102. For example, the terminal device 102 may determine not to count spontaneous retransmissions as the number of retransmissions when the fluctuations in the wireless quality are large enough to exceed a predetermined value, and to count spontaneous retransmissions as the number of retransmissions when the fluctuations in the wireless quality are small enough to be below the predetermined value. This determination may also be made in the base station device 101. For example, the base station device 101 may make this determination based on the wireless quality of a signal arriving from the terminal device 102. In this case, the base station device 101 may notify the terminal device 102 of the determination result (whether to count spontaneous retransmissions as the number of retransmissions). Note that the base station device 101 may also notify the terminal device 102 of a value indicating the magnitude of fluctuations in the wireless quality.In addition, the base station device 101 may notify the terminal device 102 of the above-mentioned predetermined value so that the terminal device 102 can determine whether or not to count spontaneous retransmission as a retransmission count.

[0025] Furthermore, for an RLC PDU that may exceed the allowable delay time, the number of HARQ retransmissions REPETITION_NUMER may be changed to a value larger than the previous value, thereby allowing more HARQ retransmissions to be performed. In this case, the base station apparatus 101 may notify the terminal apparatus 102 in advance of two different setting values ​​for the number of HARQ retransmissions REPETITION_NUMER, and the terminal apparatus 102 may determine which setting value to apply depending on the situation and conditions (or, in some cases, based on instructions from the base station apparatus 101). Note that the terminal apparatus 102 may use multiple setting values ​​for the count of the number of retransmissions and the number of HARQ retransmissions depending on the situation and conditions, as described above, or may uniformly apply the value instructed by the base station apparatus 101 in an RLC-AM entity that handles transmission data with a short allowable delay time.

[0026] FIG. 3 shows an example of the functional configuration of the terminal device 102 that executes this processing example. The terminal device 102 includes, for example, a setting receiving unit 301 and a retransmission control unit 302. Note that FIG. 3 only schematically illustrates functions related to this processing example, and omits other functions. For example, the terminal device 102 naturally has functions that a terminal device (User Equipment, UE) in a cellular communication system generally has. Furthermore, the functions shown in FIG. 3 may be implemented, for example, in a form in which a processor included in the communication circuit 205 executes instructions stored in memory, or in a form in which the processor 201 executes instructions stored in the ROM 202, the storage device 204, or the like to control the communication circuit 205.

[0027] The setting receiver 301 receives setting information from the base station device 101, such as information about spontaneous retransmission (e.g., information indicating conditions for executing spontaneous retransmission, various settings for counting spontaneous retransmissions as the number of retransmissions for determining RLF, etc.) and information about the number of HARQ retransmissions. Details of the setting information have been described above, and therefore will not be repeated here. For example, the setting receiver 301 notifies the base station device 101 of capability information indicating that the terminal device 102 has the capability to execute spontaneous retransmission, and the base station device 101 can transmit the above-described setting information, etc. to the terminal device 102 based on the capability information. The retransmission controller 302 performs various controls related to retransmission. For example, the setting receiver 301 determines whether to perform the above-described spontaneous retransmission, and if spontaneous retransmission is to be performed, performs control to store the data (RLC PDU) to be spontaneous retransmitted in a transmission buffer and perform transmission processing when a retransmission request, etc. has not been received from the base station device 101.

[0028] In addition, the base station device 101 has functions that are generally possessed by base station devices in a cellular communication system, and can be configured to notify the terminal device 102 of the above-mentioned capability information, for example, when it receives information indicating whether the terminal device 102 has the capability of spontaneous retransmission.

[0029] An example of the flow of processing executed by the terminal device 102 in this processing example will be outlined using FIG. 4 . Note that this processing shows processing when the terminal device 102 performs spontaneous retransmission. Various modifications of the processing are possible, as described in this embodiment. First, the terminal device 102 notifies the base station device 101 of capability information (S401) and receives configuration information (S402). The configuration information may include, for example, information on a remaining time threshold value, remainingTimeThreshold. Note that if no special configuration information for spontaneous retransmission exists (for example, because it is pre-installed in the terminal device 102), the processing of S401 and S402 may be omitted in the processing related to spontaneous retransmission. Thereafter, the terminal device 102 starts communication with the base station device 101 (S403).

[0030] Thereafter, when the terminal device 102 detects data to be retransmitted autonomously, for example, when the remaining time of the PDCP discard timer for the transmitted data falls below a predetermined value (YES in S404), the terminal device 102 determines, for example, whether autonomous retransmission is possible (S405). For example, the terminal device 102 determines that autonomous retransmission is possible when it receives a predetermined instruction from the base station device 101 indicating that autonomous retransmission is permitted. When it determines that autonomous retransmission is possible (YES in S405), the terminal device 102 determines whether an event to start the autonomous retransmission process has occurred (S406). The autonomous retransmission process is started when an event such as the above-mentioned event occurs, such as when a STATUS PDU related to an RLC PDU is not received within a predetermined time period after transmission of the RLC PDU. If an event for starting the autonomous retransmission process has occurred (YES in S406), the terminal device 102 determines whether the PDCP layer data (PDCP SDU) included in the RLC PDU to be autonomously retransmitted has already been discarded (S407). If the data to be retransmitted has not been discarded (NO in S407), the terminal device 102 performs autonomous retransmission of the RLC PDU including that data (S408). Note that if there is no data to be autonomously retransmitted, the terminal device 102 does not perform the autonomous retransmission process (NO in S404) and waits for the occurrence of data to be autonomously retransmitted. If the terminal device 102 is in a state where autonomous retransmission is not possible (NO in S405) or if there is no event for starting the autonomous retransmission process (NO in S406), the terminal device 102 does not perform the autonomous retransmission process and returns the process to S404. Furthermore, the terminal device 102 returns the process to S404 without retransmitting data that has already been discarded (YES in S407).

[0031] In this way, by enabling the terminal device 102 to autonomously retransmit the RLC PDU, data for which a required delay is set can be retransmitted quickly, reducing the probability of data being discarded and improving communication efficiency.

[0032] <Processing Example 2> When the terminal device 102 can receive STATUS PDUs from the base station device 101 with high frequency, it can quickly retransmit RLC PDUs that were not successfully received at the base station device 101. When the RLC-AM entity of the terminal device 102 (the transmitting communication device) desires to receive a status report such as a STATUS PDU from the base station device 101 (the receiving communication device), it can set a poll bit in the RLC PDU and transmit it. Upon receiving the poll bit, the RLC-AM entity of the base station device 101 transmits a STATUS PDU related to that RLC PDU to the terminal device. Therefore, in this processing example, the setting value related to the poll bit of the RLC-AM entity (which can also be referred to as the setting value related to the STATUS PDU report) is changed when there is a possibility that data to be transmitted exists that cannot satisfy the allowable delay time, so that STATUS PDUs are transmitted with high frequency.

[0033] As an example, when there is a possibility that data to be transmitted exists that cannot satisfy the allowable delay time, the t-PollRetransmit used in the RLC-AM entity of the terminal device 102 is changed to a smaller value. That is, the set value of t-PollRetransmit is changed so that the second value of t-PollRetransmit, which is used when there is a possibility that data to be transmitted exists that cannot satisfy the allowable delay time, is smaller than the first value of t-PollRetransmit, which is used when there is no possibility that data to be transmitted exists that cannot satisfy the allowable delay time. For example, when the first value is 1000 ms, the set value of t-PollRetransmit is changed so that the second value becomes 100 ms. This allows the terminal device 102 to set poll bits at 100 ms intervals when transmitting an RLC PDU, thereby enabling it to frequently receive STATUS PDUs from the base station device 101 and quickly retransmit RLC PDUs. Whether or not there is a possibility that data to be transmitted that cannot satisfy the allowable delay time exists can be determined by whether or not the remaining time of the PDCP discard timer is below a predetermined threshold, as in Processing Example 1. Furthermore, the value PollPDU, which specifies the number of RLC PDUs for which a poll bit can be set, or the value PollByte, which specifies the number of bytes for which a poll bit can be set, may be changed instead of t-PollRetransmit. For example, the value of PollPDU may be changed from a first value that allows a poll bit to be set every n RLC PDUs to a second value that allows a poll bit to be set every n / 10 RLC PDUs. Similarly, the value of PollByte may be changed from a first value that allows a poll bit to be set (every n bytes) if n bytes of data have been transmitted since the last poll bit was transmitted, to a second value that allows a poll bit to be set every n / 10 bytes.

[0034] The base station device 101 also maintains a timer called t-Reassembly (and t-ReassemblyExt), and when this timer expires, it transmits a STATUS PDU to the terminal device 102 to request retransmission of unreceived RLC PDUs. Therefore, the RLC-AM entity of the base station device 101 can also increase the frequency of STATUS PDU transmission by changing the value of t-Reassembly (or t-ReassemblyExt) used to a smaller value. Furthermore, when the timer t-StatusProhibibit for suppressing STATUS PDU transmission is active, the base station device 101 suppresses STATUS PDU transmission and determines that a STATUS PDU can be transmitted only after t-StatusProhibibit expires. Therefore, in order to transmit STATUS PDUs more frequently, t-StatusProhibit may be changed to a smaller value, or t-StatusProhibit may be disabled, thereby disabling the function of suppressing STATUS PDU transmission by the timer.

[0035] As the setting values ​​related to the transmission of the above-mentioned STATUS PDU (e.g., t-PollRetransmit, PollPDU, PollByte, t-Reassembly, t-ReassemblyExt, t-StatusProhibibit), a plurality of setting values ​​may be prepared, including a setting value used in normal times and a setting value used only when a specific condition is met. These multiple setting values ​​may then be notified in advance from the base station device 101 to the terminal device 102. Furthermore, the specific condition may be, for example, as in the above-mentioned processing example 1, for each logical channel or RLC-AM entity, when the remaining time until the tolerable delay time (e.g., shorttest remaining-time) falls below a threshold, starting to use a setting value different from the normal setting value; and when the remaining time subsequently exceeds the threshold due to completion of data retransmission, ending to use of the setting value and starting to use the normal setting value. In this case, the terminal device 102 determines the start and end of the use of different setting values ​​based on the remaining time until the allowable delay time (shortest remaining-time), and switches the setting value to be used between a first setting value for normal use notified in advance by the base station device 101 and a second setting value different from normal use. Furthermore, when the terminal device 102 should use a setting value different from normal use, it transmits a predetermined notification to the base station device 101, and when the base station device 101 receives the predetermined notification, it changes the setting values ​​of t-Reassembly, t-ReassemblyExt, and t-StatusProhibibit to be used from the first value for normal use to a second value different from normal use. When the terminal device 102 notifies the base station device 101 of the shorttest remaining-time, the base station device 101 may determine whether or not to change the setting values. That is, the base station device 101 can compare the shortest remaining-time with a threshold value and determine whether or not to change the setting value. Note that the value of shorttest remaining-time can be notified to the base station device 101 from the terminal device 102.

[0036] Furthermore, changing the setting value related to the STATUS PDU may result in more radio resources being consumed. For this reason, the base station device 101 may monitor the usage status of radio resources and permit the use of the setting value for transmitting STATUS PDUs at a high frequency only when the amount of radio resources used is equal to or less than a certain value. In this case, the base station device 101 may uniformly apply the setting value before the change when the amount of radio resources used exceeds the certain value, or may determine to apply the changed setting value on the condition that, in addition to the amount of radio resources used falling below the certain value, the value of the MAC delay status reporting (shortest remaining-time) notified from the terminal device 102 is equal to or less than a certain value. The base station device 101 then notifies the terminal device 102 that the setting value change is permitted, and if the value of the MAC delay status reporting (shortest remaining-time) exceeds a certain value, the base station device 101 can notify the terminal device 102 that the setting value change is not permitted.

[0037] Furthermore, when there is a possibility that data to be transmitted exists that cannot satisfy the allowable delay time, the terminal device 102 may transmit an RLC PDU with a poll bit set only once when transmitting an RLC PDU. In this case, the terminal device 102 may leave the timer and control related to the poll bit unchanged as usual, and, for example, when the shorttest remaining-time is equal to or less than a threshold, may assign a poll bit to an RLC PDU to be transmitted that would not normally have a poll bit assigned, and transmit the RLC PDU to the base station device 101.

[0038] In this case, too, the base station device 101 can notify the terminal device 102 whether or not to transmit an RLC PDU with the poll bit set, on the condition that the value of the MAC delay status reporting (shortest remaining-time) notified from the terminal device 102 is equal to or less than a certain value. Furthermore, the terminal device 102 can notify the base station device 101 that the poll bit to be transmitted in this case is a bit different from the poll bit used in normal cases. Normally, upon receiving a poll bit, the base station device 101 determines whether t-Status Prohibit is active. If t-Status Prohibit is active, the base station device 101 transmits a STATUS PDU after the t-Status Prohibit expires, thereby reducing the frequency of STATUS PDU transmissions. For this reason, even if the terminal device 102 transmits an RLC PDU with the poll bit set, there may be cases where it is unable to transmit a STATUS PDU to the base station device 101. In response to this, as described above, the terminal device 102 can notify the base station device 101 that the bit is different from the normal poll bit (i.e., that it is a poll bit for a STATUS PDU that is not subject to the transmission suppression function by t-StatusProhibibit), thereby enabling the STATUS PDU to be transmitted from the base station device 101 at an earlier stage.

[0039] Furthermore, if an RLC PDU with the poll bit set is transmitted only once each time the remaining time of the PDCP discard timer falls below a predetermined threshold, the event of the remaining time falling below the predetermined threshold may occur repeatedly, resulting in high-frequency transmission of RLC PDUs with the poll bit set. In this case, the terminal device 102 may activate the ProhibitTimer at the time of transmission of an RLC PDU with the poll bit set, and suppress transmission of RLC PDUs with the poll bit set while the ProhibitTimer is activated. This makes it possible to prevent high-frequency transmission of RLC PDUs with the poll bit set. The terminal device 102 may also transmit an RLC PDU with the poll bit set only once when a specified number of events occur in which the remaining time of the PDCP discard timer falls below the predetermined threshold. This also makes it possible to prevent high-frequency transmission of RLC PDUs with the poll bit set. The ProhibitTimer and the specified number of times used to suppress transmission of the RLC PDU in which the poll bit is set can be notified in advance from the base station apparatus 101 to the terminal apparatus 102 .

[0040] Alternatively, instead of preventing the terminal device 102 from frequently transmitting RLC PDUs with a poll bit set, the base station device 101 may use t-StatusProhibit to prevent STATUS PDUs from being transmitted frequently. In this case, a value different from that used in normal operation may be used as t-StatusProhibit. Furthermore, the t-StatusProhibit applied to a STATUS PDU transmitted in response to a normal poll bit and the t-StatusProhibit applied to a STATUS PDU transmitted in response to a poll bit set when the remaining time falls below a predetermined threshold may be treated as separate timers. Note that the base station device 101 may change the t-StatusProhibit from the setting value used in normal operation to a specific value related to this process upon receiving a poll bit set when the remaining time until the allowable delay time of an RLC PDU (PDCP SDU) falls below a predetermined threshold. Furthermore, the poll bit transmitted when the above-described specific condition is satisfied can be processed separately from the poll bit transmitted in response to a normal t-PollRetransmit or PollByte. That is, the satisfaction of the above-described specific condition (which results in the transmission of an RLC PDU with the poll bit set according to this processing example) can be prevented from affecting the t-PollRetransmit timer control or the PollByte counter control. Conversely, when the above-described specific condition is satisfied, the terminal device 102 may transmit an RLC PDU with the poll bit set, and may also control the restart of the t-PollRetransmit timer and the initialization of the PollByte counter.

[0041] FIG. 5 shows an example of the functional configuration of the base station device 101 that executes this processing example. The base station device 101 includes, for example, a setting change permission unit 501 and a setting change unit 502. Note that FIG. 5 only schematically illustrates functions related to this processing example, and omits other functions. For example, the base station device 101 naturally has functions that a base station device (such as a gNodeB) in a cellular communication system generally has. Furthermore, the functions shown in FIG. 5 may be implemented, for example, in a form in which a processor included in the communication circuit 205 executes instructions stored in memory, or in a form in which the processor 201 executes instructions stored in the ROM 202, the storage device 204, or the like to control the communication circuit 205.

[0042] The setting change permission unit 501 determines whether to permit or deny a change to setting information related to a change in the transmission frequency of STATUS PDUs. If a change to the setting information is permitted, the setting change unit 502 transmits a predetermined instruction to the terminal device 102 or changes the setting within its own device, taking into consideration, for example, other conditions.

[0043] For example, setting change permission unit 501 permits or denies control to increase the transmission frequency of STATUS PDUs depending on the amount of radio resources used, etc. When control to increase the transmission frequency of STATUS PDUs is permitted, setting change unit 502 further determines whether or not to actually perform that control.

[0044] For example, the setting change unit 502 may determine to perform control to increase the transmission frequency of STATUS PDUs when it receives a MAC delay status reporting (shortest remaining-time) from the terminal device 102 and finds that an RLC PDU whose remaining time is below a predetermined threshold exists in the terminal device 102. For example, when increasing the transmission frequency of STATUS PDUs, the setting change unit 502 uses first setting values ​​such as setting t-Reassembly and t-ReassemblyExt in its own device to relatively small values, setting t-StatusProhibit to a relatively small value, or disabling the function of suppressing transmission of STATUS PDUs by t-StatusProhibibit. Furthermore, the setting change unit 502 may determine not to perform control to increase the transmission frequency of STATUS PDUs when control to increase the transmission frequency of STATUS PDUs is prohibited or when there are no RLC PDUs in the terminal device 102 for which the remaining time until the expiration of the allowable delay time is below a predetermined threshold. In this case, the setting change unit 502 uses a second setting value, such as relatively increasing the values ​​of t-Reassembly and t-ReassemblyExt in the own device (at least more than the first setting value), relatively increasing the value of t-StatusProhibit (at least more than the first setting value), or resuming the function of suppressing transmission of STATUS PDUs using t-StatusProhibit. Note that the first setting value and the second setting value may be prepared in advance. Note that the second setting value may be a conventional setting value.

[0045] Furthermore, the setting change unit 502 notifies the terminal device 102 of a first setting value when the STATUS PDU transmission frequency is to be increased and a second setting value when the STATUS PDU transmission frequency is not to be increased. Here, the first setting value and the second setting value may be, for example, the setting values ​​of t-PollRetransmit, PollPDU, and PollByte. For example, the first setting values ​​of t-PollRetransmit, PollPDU, and PollByte may be smaller than the second setting values ​​of t-PollRetransmit, PollPDU, and PollByte, respectively. Note that the setting change unit 502 may notify the terminal device 102 of the first setting value when the STATUS PDU transmission frequency should be increased, and may not notify the terminal device 102 of the first setting value when the STATUS PDU transmission frequency should not be increased. Furthermore, the setting change unit 502 may notify the terminal device 102 of the first setting value (in addition to the second setting value) regardless of whether or not the transmission frequency of STATUS PDUs should be increased. Note that the second setting value may be a conventional setting value. Note that when both the first setting value and the second setting value are notified to the terminal device 102, the terminal device 102 may independently (without an instruction from the base station device 101) determine which setting value to use.

[0046] FIG. 6 shows an example of the functional configuration of the terminal device 102 that executes this processing example. The terminal device 102 includes, for example, a setting receiving unit 601 and a setting change processing unit 602. Note that FIG. 6 only schematically illustrates functions related to this processing example, and omits other functions. For example, the terminal device 102 naturally has functions that a terminal device (User Equipment, UE) in a cellular communication system generally has. The terminal device 102 may also have functions such as those shown in FIG. 3. The functions shown in FIG. 6 may be implemented, for example, by a processor included in the communication circuit 205 executing instructions stored in memory, or by the processor 201 executing instructions stored in the ROM 202, the storage device 204, or the like to control the communication circuit 205.

[0047] The setting receiver 601 receives from the base station device 101 a predetermined instruction indicating whether or not control for increasing the STATUS PDU transmission frequency is permitted. The setting receiver 601 also receives a first setting value to be used when control for increasing the STATUS PDU transmission frequency is to be performed, and a second setting value to be used when such control is not to be performed. As described above, the first setting value and the second setting value are the setting values ​​for t-PollRetransmit, PollPDU, and PollByte. The setting change processor 602 executes control for increasing the STATUS PDU transmission frequency when such control is permitted. For example, when control for increasing the STATUS PDU transmission frequency is permitted, the setting change processor 602 determines whether or not to execute such control, and operates to use the first setting value when it is determined that control is to be executed. Furthermore, the setting change processing unit 602 operates to use the second setting value when control to increase the transmission frequency of STATUS PDUs is not permitted, or when such control is permitted but, for example, there is no RLC PDU whose remaining time until the expiration of the allowable delay time is below a predetermined threshold, etc. Furthermore, the setting change processing unit 602 can transmit a MAC delay status reporting (shortest remaining-time) to the base station device 101, for example, to cause a setting change in the base station device 101.

[0048] An example of processing executed by the base station device 101 will be described using FIG. 7 . Note that the base station device 101 can be modified in various ways as described in this embodiment, and the processing shown in FIG. 7 is merely one example of processing. First, the base station device 101 receives capability information from the terminal device 102 (S701) and starts communication with the terminal device 102 (S702). Based on the capability information, the base station device 101 can determine whether the terminal device 102 is capable of executing control processing to increase the transmission frequency of STATUS PDUs (e.g., whether t-PollRetransmit, PollPDU, PollByte, etc. for increasing the transmission frequency of STATUS PDUs are capable of being set). Then, if the base station device 101 determines that the terminal device 102 is capable of executing such control processing, it can execute the following processing. At this stage (e.g., during connection processing), the base station device 101 may notify the terminal device 102 of the first set values ​​(set values ​​when increasing the transmission frequency of STATUS PDUs) and second set values ​​(set values ​​under normal conditions) of t-PollRetransmit, PollPDU, and PollByte, as described above.

[0049] The base station device 101 then determines whether to permit the execution of a control process to increase the transmission frequency of STATUS PDUs. For example, the base station device 101 determines whether the usage of radio resources (frequency and time resources) is below a predetermined value (S703). If the usage of resources is below the predetermined value (YES in S703), the base station device 101 permits the execution of the control process. Note that if the terminal device 102 can configure settings such as t-PollRetransmit, PollPDU, and PollByte to increase the transmission frequency of STATUS PDUs, the base station device 101 transmits a predetermined notification to the terminal device 102 permitting the change of settings (S704). Along with this predetermined notification, the base station device 101 may also notify the terminal device 102 of the first and second setting values ​​of the t-PollRetransmit, PollPDU, and PollByte that the terminal device 102 should use. On the other hand, if the resource usage exceeds a predetermined value (NO in S703), the base station device 101 may decide not to permit the execution of the control process. In this case, if the terminal device 102 can make the above-mentioned settings for increasing the transmission frequency of STATUS PDUs, the base station device 101 may transmit a predetermined notification to the terminal device 102 indicating that the setting change is not permitted (S705).

[0050] Furthermore, the base station device 101 can determine, for example, whether the terminal device 102 holds an RLC PDU whose remaining time until the tolerable delay time is below a predetermined threshold (S706). Note that the base station device 101 can make this determination, for example, by receiving a MAC delay status reporting (shortest remaining-time) from the terminal device 102. If the value indicated by the MAC delay status reporting (shortest remaining-time) is below the predetermined threshold, the base station device 101 can determine that the terminal device 102 holds an RLC PDU whose remaining time until the tolerable delay time is below the predetermined threshold. Then, when the base station device 101 determines that the terminal device 102 holds an RLC PDU whose remaining time until the tolerable delay time is below a predetermined threshold (YES in S706), it executes processing to use a first setting value for increasing the transmission frequency of the STATUS PDU (S707). For example, if the base station device 101 can itself execute settings for increasing the transmission frequency of the STATUS PDU, it transitions to a state in which the first setting value is used, such as by reducing the values ​​of the above-mentioned t-Reassembly, t-ReassemblyExt, and t-StatusProhibibit. Furthermore, for example, if the terminal device 102 can increase the transmission frequency of the STATUS PDU by setting the above-mentioned t-PollRetransmit, PollPDU, and PollByte, the base station device 101 may notify the terminal device 102 of the first setting values ​​of these parameters at this time. Furthermore, the base station device 101 may instruct the terminal device 102 to use the first setting value notified in advance.

[0051] On the other hand, if the base station device 101 determines not to permit the execution of the control process, or if it determines that the terminal device 102 does not hold an RLC PDU whose remaining time until the allowable delay time is below a predetermined threshold (NO in S706), it executes a process to use second setting values ​​so as to perform normal state processing without increasing the transmission frequency of STATUS PDUs (S708). For example, the base station device 101 transitions to a state in which second setting values ​​are used, such as by increasing the values ​​of t-Reassembly, t-ReassemblyExt, and t-StatusProhibit above the first setting values. Furthermore, the base station device 101 may instruct the terminal device 102 to use the second setting values ​​of t-PollRetransmit, PollPDU, and PollByte, which it notified in advance.

[0052] Note that at least one of the setting in the base station device 101 and the setting in the terminal device 102 may be executed. That is, the setting in S707 or S708 may be executed only in the base station device 101, only in the terminal device 102, or in both the base station device 101 and the terminal device 102.

[0053] An example of processing executed by the terminal device 102 will be described using Figure 8. Note that the terminal device 102 can be modified in various ways as described in this embodiment, and the processing shown in Figure 8 is merely one example of processing. First, the terminal device 102 transmits capability information to the base station device 101 (S801) and starts communication with the base station device 101 (S802). The terminal device 102 can notify the base station device 101 as capability information whether it is capable of executing control processing to increase the transmission frequency of STATUS PDUs (for example, whether it is possible to set t-PollRetransmit, PollPDU, PollByte, etc. to increase the transmission frequency of STATUS PDUs). Note that it is assumed here that the terminal device 102 is capable of executing control processing to increase the transmission frequency of STATUS PDUs. At this point, the terminal device 102 can also acquire from the base station device 101 first setting values ​​(setting values ​​when increasing the transmission frequency of STATUS PDUs) and second setting values ​​(setting values ​​under normal conditions) of t-PollRetransmit, PollPDU, and PollByte.

[0054] The terminal device 102 determines whether it has received a predetermined notification from the base station device 101 indicating permission for the configuration change (S803). If the configuration change is permitted, the terminal device 102 determines whether it holds an RLC PDU whose remaining time until the allowable delay time is below a predetermined threshold (S804). If the terminal device 102 holds an RLC PDU whose remaining time is below the predetermined threshold (YES in S804), it enters a state in which it uses a first configuration value for increasing the transmission frequency of STATUS PDUs (S805). On the other hand, if the configuration change is not permitted (NO in S803) or if the terminal device 102 does not hold an RLC PDU whose remaining time until the allowable delay time is below the predetermined threshold (NO in S804), it enters a state in which it uses a second configuration value that should be used normally (S806). That is, in S805, the configuration is changed so that the values ​​of t-PollRetransmit, PollPDU, PollByte, etc. are smaller than those in S806. Furthermore, for example, when the terminal device 102 is using the first setting value and reaches a state where it does not hold any RLC PDUs whose remaining time until the allowable delay time is below a predetermined threshold, it changes the values ​​of t-PollRetransmit, PollPDU, PollByte, etc. to second setting values ​​that are larger than the first setting value.

[0055] The above-described control process by at least one of the base station device 101 and the terminal device 102 makes it possible to control the frequency of STATUS PDU transmission in the base station device 101. As a result, for example, when there is an RLC PDU with a short remaining time until the allowable delay time, it is possible to transmit STATUS PDUs at a high frequency, thereby enabling data retransmissions to be performed at a high frequency.

[0056] In the above-described processing example 1 and processing example 2, the configuration information (such as a threshold for determining whether to perform autonomous retransmission of an RLC PDU, the maximum number of retransmissions, and the setting values ​​of various timers) can be notified from the base station device 101 to the terminal device 102 by a downlink control message such as a Radio Resource Control (RRC) Reconfiguration message, a Medium Access Control-Control Element (MAC CE), or Downlink Control Information (DCI). Furthermore, the determination result in the terminal device 102 can be notified from the terminal device 102 to the base station device 101 by an uplink control message such as a UE Assistance Information message, a MAC CE, or Uplink Control Information (UCI). Furthermore, in the process of autonomous retransmission of an RLC PDU, for example, a threshold value for determining whether or not an RLC PDU is to be subject to autonomous retransmission (a threshold value used to determine the remaining time of a PDCP discard timer) may be included in an RRC Reconfiguration message instructing the start of communication, and an instruction to permit or disallow autonomous retransmission may be included in a subsequent STATUS PDU, MAC CE, or DCI and notified to the terminal device 102.

[0057] As described above, the terminal device 102 may transmit capability information (UE Capabilities) indicating whether the terminal device 102 has the autonomous retransmission function of Processing Example 1 or the function of changing the setting value related to the STATUS PDU of Processing Example 2 to the base station device 101. The base station device 101 may issue an instruction to enable the autonomous retransmission function at the start of communication of the terminal device 102 only if the terminal device 102 has capability information indicating that the terminal device 102 has the autonomous retransmission function of Processing Example 1. Furthermore, if the base station device 101 determines that there are insufficient radio resources for autonomous retransmission, the base station device 101 may issue an instruction to the terminal device 102 at the start of communication not to enable the autonomous retransmission function. The base station device 101 may detect a change in the situation and, when it becomes possible to secure radio resources to be used for autonomous retransmission, issue an instruction to the terminal device 102 currently communicating to newly enable the autonomous retransmission function. This instruction to enable / disable (permit / disable) spontaneous retransmission can be transmitted from the base station device 101 to the terminal device 102 by, for example, an RRC Reconfiguration message, a STATUS PDU, a MAC CE, or a DCI. Furthermore, the base station device 101 may use an RRC Reconfiguration message to instruct the terminal device 102 to enable / disable (permit / disable) spontaneous retransmission at the start of communication, and then, when changing the enable / disable (permit / disable) during communication, may use a MAC CE or a DCI to transmit an instruction to change the setting to the terminal device 102. Note that the default setting value may indicate permission for spontaneous retransmission or may indicate disallowance of spontaneous retransmission.

[0058] Furthermore, multiple RLC-AM entities can be used simultaneously. For example, when the terminal device 102 is the transmitting communication device and the base station device 101 is the receiving communication device, communication is performed using two logical channels: a first RLC-AM entity with logical channel number 1 and a second RLC-AM entity with logical channel number 2. User data for which an allowable delay time is set is mapped to the first RLC-AM entity. In this case, if a determination of spontaneous retransmission is made for each RLC PDU, the terminal device 102 makes that determination for each RLC PDU transmitted by the first RLC-AM entity, determines spontaneous retransmission based on the determination result, and does not make that determination for RLC PDUs transmitted by the second RLC-AM entity. Furthermore, with regard to changing the timer value of the poll bit, the terminal device 102 compares the threshold value for each RLC PDU transmitted by the first RLC-AM entity to determine the start and end of use of a setting value different from that used in normal situations, but does not perform this determination for RLC PDUs transmitted by the second RLC-AM entity. Furthermore, in PDCP duplication control for Ultra-Reliable and Low Latency Communication (URLLC), for user data for which an allowable delay time is set, data transmitted by the first RLC-AM entity may be duplicated and transmitted by the second RLC-AM entity. In this case, the above-described determination is performed for each RLC PDU transmitted by the first RLC-AM entity and the RLC PDU transmitted by the second RLC-AM entity, and control related to spontaneous retransmission and poll bits may be performed depending on the determination results.

[0059] In the above-described embodiment, an example was shown in which the terminal device 102 is a transmitting communication device and the base station device 101 is a receiving communication device, but the base station device 101 may be a transmitting communication device and the terminal device 102 may be a receiving communication device. In this case, in processing example 1, the base station device 101 may retransmit a downlink RLC PDU without waiting for a STATUS PDU from the terminal device 102. Also, in processing example 2, the base station device 101 may change transmitting-side setting values ​​such as t-PollRetransmit, and the terminal device 102 may change receiving-side setting values ​​such as t-StatusProhibibit, so that STATUS PDUs are transmitted more frequently.

[0060] Furthermore, UL-AM-RLC, in which the terminal device 102 is the transmitting communication device and the base station device 101 is the receiving communication device, and DL-AM-RLC, in which the base station device 101 is the transmitting communication device and the terminal device 102 is the receiving communication device, may be used simultaneously. In this case, the base station device 101 and the terminal device 102 can each make decisions and perform control regarding spontaneous retransmissions and poll bits.

[0061] As described above, this embodiment provides an advanced retransmission technique in the RLC layer based on the remaining time until the tolerable delay time of user data, which can contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0062] 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.

[0063] This application claims priority to U.S. Provisional Patent Application No. 63 / 644,602, filed May 9, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A communication device for a cellular communication system, comprising: communication means for at least transmitting a Radio Link Control (RLC) Protocol Data Unit (PDU) including a Packet Data Convergence Protocol (PDCP) Service Data Unit (SDU) to another communication device; and control means for controlling the communication means to use a first setting value for increasing the frequency of STATUS PDU transmission when the remaining time of a PDCP discard timer activated for the PDCP SDU included in the RLC PDU falls below a predetermined threshold after the RLC PDU is transmitted, and to use a second setting value for decreasing the frequency of STATUS PDU transmission from the first setting value when the remaining time exceeds the predetermined threshold.

2. The communication device according to claim 1, wherein the first set value and the second set value are set values ​​of t-PollRetransmit, PollPDU, or PollByte, and the first set value has a value smaller than the second set value.

3. The communication device according to claim 1 or 2, wherein the communication device is a terminal device and the other communication device is a base station device, and the communication means receives the first setting value and the second setting value from the base station device.

4. The communication device according to claim 3, wherein the communication means receives a notification from the base station device indicating whether or not use of the first setting value is permitted, and the control means controls the communication means to use the first setting value based on the notification that use of the first setting value is permitted being received and the remaining time falling below the predetermined threshold.

5. The communication device according to any one of claims 1 to 4, wherein said control means determines for each RLC PDU whether the remaining time is below said predetermined threshold value.

6. The communications device according to any one of claims 1 to 4, wherein the control means identifies the remaining time for PDCP SDUs belonging to a common logical channel, and determines, for each logical channel, whether to use the first setting value or the second setting value based on the remaining time for the PDCP SDUs belonging to the common logical channel.

7. The communication device according to claim 6, wherein the control means determines whether the minimum, maximum, or average value of the remaining time for the PDCP SDUs belonging to the common logical channel is below the predetermined threshold.

8. A communication device for a cellular communication system, comprising: communication means for receiving a Radio Link Control (RLC) Protocol Data Unit (PDU) including a Packet Data Convergence Protocol (PDCP) Service Data Unit (SDU) from another communication device and transmitting a STATUS PDU; and control means for controlling the communication means to use a first setting value for increasing the transmission frequency of the STATUS PDU when the remaining time of a PDCP discard timer activated for the PDCP SDU included in the RLC PDU after the RLC PDU is transmitted from the other communication device falls below a predetermined threshold, and to use a second setting value for decreasing the transmission frequency of the STATUS PDU from the first setting value when the remaining time exceeds the predetermined threshold. A communication device having:

9. A communication device according to claim 8, wherein the first set value and the second set value are at least one of t-Reassembly and t-ReassemblyExt, and the first set value has a value smaller than the second set value.

10. The communications device according to claim 8 or 9, wherein the first set value and the second set value are set values ​​of t-StatusProhibit for suppressing transmission of the STATUS PDU, and the first set value is either smaller than the second set value or is a set value that stops suppression of transmission of the STATUS PDU by the t-StatusProhibibit.

11. The communication device according to any one of claims 8 to 10, wherein the control means receives information about the remaining time from the communication device.

12. A control method executed by a communication device in a cellular communication system, comprising: transmitting a Radio Link Control (RLC) Protocol Data Unit (PDU) including a Packet Data Convergence Protocol (PDCP) Service Data Unit (SDU) to another communication device; and, after the RLC PDU is transmitted, controlling the communication device to use a first setting value for increasing the transmission frequency of a STATUS PDU based on the remaining time of a PDCP discard timer activated for the PDCP SDU included in the RLC PDU falling below a predetermined threshold, and to use a second setting value for decreasing the transmission frequency of the STATUS PDU compared to the first setting value based on the remaining time exceeding the predetermined threshold.

13. A control method executed by a communication device in a cellular communication system, comprising: receiving a Radio Link Control (RLC) Protocol Data Unit (PDU) including a Packet Data Convergence Protocol (PDCP) Service Data Unit (SDU) from another communication device; transmitting a STATUS PDU; and, after the RLC PDU is transmitted from the other communication device, controlling the use of a first setting value for increasing the transmission frequency of the STATUS PDU based on the remaining time of a PDCP discard timer activated for the PDCP SDU included in the RLC PDU falling below a predetermined threshold, and controlling the use of a second setting value for decreasing the transmission frequency of the STATUS PDU compared to the first setting value based on the remaining time exceeding the predetermined threshold. A control method comprising:

14. A program for causing a computer provided in a terminal device of a cellular communication system to execute the control method according to claim 12.

15. A program for causing a computer provided in a terminal device of a cellular communication system to execute the control method according to claim 13.

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