Communication device, and method employing communication device

Abstract

A terminal device 10 includes a control unit 110 and a communication unit 120. The control unit 110 and the communication unit 120 receive an RRC message, and if, on the basis of information included in the RRC message indicating a remaining time threshold for RLC retransmission, in a packet data convergence protocol PDCP layer, the remaining time until a discard timer for a PDCP SDU expires is less than the remaining time threshold, the control unit 110 and the communication unit 120 provide, to an RLC layer, a first indication to the PDCP PDU, receive a second indication for an RLC SDU from the PDCP layer in the RLC layer, and consider the RLC SDU to be a target for retransmission on the basis that no ACK is indicated in the RLC SDU.

Description

Communication device and method using the communication device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority based on Japanese Patent Application No. 2024-130990, filed on August 7, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a communication device and a method therefor.

[0003] In recent years, technological development related to extended reality (XR) has progressed. XR is a concept that includes multimedia integration technologies such as virtual reality (VR), augmented reality (AR), mixed reality (MR), and substitutional reality (SR). In XR, three-dimensional time-series image data in real space and / or virtual space, audio data of multiple channels (stereo, 5.1ch, etc.), other data presented to the user, control data, etc. are transmitted and received in parallel. XR requires low latency and high reliability to maintain and improve the quality of the user's experience.

[0004] Non-Patent Document 1 describes technical specifications defined by the Third Generation Partnership Project (3GPP (registered trademark)). Specifically, Non-Patent Document 1 describes technical specifications for a Radio Link Control (RLC) layer.

[0005] 3GPP TS 38.322 V18.1.0 (2024-06)

[0006] According to the description in Non-Patent Document 1, in the RLC layer, a transmitting side transmits a protocol data unit (PDU) to a receiving side in acknowledged mode (AM). If the receiving side fails to receive the PDU correctly, the transmitting side retransmits the PDU to the receiving side. Data transmission in AM is suitable for data communications that do not require real-time performance but require reliability.

[0007] XR is operated under various requirements, including a requirement for low latency. In consideration of this, a low latency requirement is imposed on data transmission in AM, and an enhancement thereof has been proposed. However, Non-Patent Document 1 does not disclose a specific means for achieving low latency for data transmission in AM.

[0008] In view of the above circumstances, the present disclosure provides a technique for achieving low latency in AM data transmission.

[0009] In order to achieve the above object, a terminal device in the present disclosure includes a control unit and a communication unit, wherein the control unit and the communication unit receive a Radio Resource Control (RRC) message, and, in a Packet Data Convergence Protocol (PDCP) layer, based on information indicating a remaining time threshold for retransmission of a Radio Link Control (RLC) included in the RRC message, provide a first indication for the PDCP Service Data Unit (SDU) to an RLC layer if a remaining time until a discard timer for the PDCP Service Data Unit (SDU) expires is less than the remaining time threshold, and receive a second indication for the RLC SDU from the PDCP layer in the RLC layer, and consider the RLC SDU to be a target for retransmission based on the fact that a positive acknowledge (ACK) is not indicated for the RLC SDU.

[0010] Furthermore, a method executed by a terminal device in the present disclosure includes receiving a Radio Resource Control (RRC) message; and, in a Packet Data Convergence Protocol (PDCP) layer, providing a first indication for a PDCP Service Data Unit (SDU) to an RLC layer based on information indicating a remaining time threshold for retransmission of a Radio Link Control (RLC) included in the RRC message, when a remaining time until a discard timer for the PDCP Service Data Unit (SDU) expires is less than the remaining time threshold; and receiving, in the RLC layer, a second indication for the RLC SDU from the PDCP layer and determining the RLC SDU as a target for retransmission based on the fact that a positive acknowledgement is not indicated for the RLC SDU.

[0011] According to the above configuration, a PDU is retransmitted when the remaining time until the PDU is received by the receiving side is short, and as a result, the PDU can be retransmitted without receiving the reception result of the PDU. Note that the above configuration may achieve other effects instead of or in addition to the above effect.

[0012] 1 is a diagram illustrating a communication system S. 1 is a diagram illustrating a protocol stack of the U-plane. 2 is a diagram illustrating a protocol stack of the C-plane. 3 is a block diagram illustrating a schematic hardware configuration of a terminal device 10. 4 is a block diagram illustrating a schematic functional configuration of the terminal device 10. 5 is a block diagram illustrating a schematic hardware configuration of a base station device 20. 6 is a block diagram illustrating a schematic functional configuration of a base station device 20. 7 is a diagram illustrating a radio frame configuration. 8 is a diagram illustrating a format of an AMD PDU. 9 is a diagram illustrating a format of a STATUS PDU. 10 is a flowchart illustrating a procedure for transmitting a STATUS PDU and retransmitting an RLC SDU according to the prior art. 11 is a flowchart illustrating a procedure for retransmitting an RLC SDU according to the first embodiment. 12 is a flowchart illustrating a procedure for retransmitting an RLC SDU according to another example of the first embodiment. 13 is a flowchart illustrating a procedure for retransmitting an RLC SDU according to yet another example of the first embodiment. 14 is a flowchart illustrating a procedure for retransmitting an RLC SDU according to a second embodiment. 15 is a diagram illustrating new transmission or retransmission of HARQ according to the value of NDI. 16 is a flowchart illustrating a procedure for retransmitting an RLC SDU according to another example of the second embodiment. 17 is a flowchart illustrating a procedure for retransmitting an RLC SDU according to a third embodiment. Fig. 10 is a flowchart showing a procedure for retransmitting an RLC SDU according to another example of the third embodiment Fig. 11 is a flowchart showing a procedure for transmitting a STATUS PDU and retransmitting an RLC SDU according to a fourth embodiment.

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and drawings, elements that can be similarly described will be designated by the same reference numerals, and redundant description may be omitted.

[0014] Each embodiment described below is merely an example of a configuration that can realize this embodiment. Each embodiment described below can be modified or changed as appropriate depending on the configuration of the device to which this embodiment is applied and various conditions. Not all combinations of elements included in each embodiment described below are necessarily essential to realize this embodiment, and some elements can be omitted as appropriate. Therefore, the scope of this embodiment is not limited to the configurations described in each embodiment described below. As long as there are no mutual contradictions, a configuration that combines multiple configurations described in the embodiments described below can also be adopted.

[0015] 1. First Embodiment 1.1. Communication System As shown in FIG. 1, a communication system S includes one or more terminal apparatuses (Terminal Apparatus) 10, one or more base station apparatuses (Base Station Apparatus) 20, and a core network 30. The communication system S is configured in accordance with predetermined technical specifications. For example, the communication system S may comply with technical specifications (e.g., 5G, 5G Advanced, 6G, etc.) defined by 3GPP.

[0016] In the communication system S, a user plane where user data is transmitted and received and a control plane where control data is transmitted and received are configured separately. That is, the communication system S supports C / U separation. The user plane is abbreviated as U-plane, and the control plane is abbreviated as C-plane.

[0017] The terminal device 10 is a device that wirelessly communicates with the base station device 20 and may be, for example, user equipment (UE) that operates in accordance with the 3GPP 5G NR technical specifications. The terminal device 10 may also be a device that complies with other older or newer 3GPP technical specifications.

[0018] The terminal device 10 may be, for example, a mobile phone terminal such as a smartphone, a tablet terminal, a laptop PC, a communication module, a communication card, or an IoT device such as a surveillance camera or a robot. The terminal device 10 may be a vehicle (e.g., a car, a train, etc.) or a device provided therein. The terminal device 10 may be a transport vehicle other than a vehicle (e.g., a ship, an airplane, etc.) or a device provided therein. The terminal device 10 may be a sensor or a device provided therein. Note that the terminal device 10 may be called by other names such as a terminal, a mobile station, a mobile terminal, a mobile device, a mobile unit, a subscriber station, a subscriber terminal, a subscriber device, a subscriber unit, a wireless station, a wireless terminal, a wireless device, a wireless unit, a remote station, a remote terminal, a remote device, or a remote unit. The terminal device 10 may be a device adapted to one or more of enhanced Mobile Broadband (eMBB), Ultra-Reliable and Low Latency Communications (URLLC), and massive Machine Type Communications (mMTC).

[0019] The terminal devices 10 are connected to each other via a predetermined interface (e.g., a PC5 interface). This type of communication is called sidelink communication. Note that the terminal devices 10 may be connected to each other via other interfaces with different functions or names.

[0020] The base station device 20 manages at least one cell. A cell constitutes the smallest unit of a communication area. For example, one cell belongs to one frequency (e.g., carrier frequency) and is composed of one component carrier. The term "cell" can refer to wireless communication resources and can also refer to a communication target of the terminal device 10. The base station device 20 wirelessly communicates with the terminal device 10 located in its own cell in the U-plane and C-plane. In other words, the base station device 20 terminates the U-plane protocol and C-plane protocol for the terminal device 10.

[0021] The base station device 20 communicates with the core network 30 in the U-plane and the C-plane. More specifically, the core network 30 includes multiple logical nodes including an Access and Mobility Management Function (AMF) and a User Plane Function (UPF). The base station device 20 connects to the AMF in the C-plane and connects to the UPF in the U-plane.

[0022] The base station device 20 may be, for example, a gNB that provides the terminal device 10 with a U-plane and a C-plane conforming to the 3GPP 5G NR technical specifications and connects to the 3GPP 5GC (5G Core Network). The base station device 20 may also be a device conforming to other older or newer 3GPP technical specifications.

[0023] The base station device 20 may be configured by a plurality of unit devices. For example, the base station device 20 may be configured by a central unit (CU), a distributed unit (DU), and a radio unit (RU).

[0024] A radio access network (RAN) is formed by interconnecting multiple base station devices 20. The radio access network formed by the base station devices 20 that are gNBs may be referred to as an NG-RAN. The base station devices 20 that are gNBs may be referred to as NG-RAN nodes.

[0025] The plurality of base station devices 20 are connected to each other via a predetermined interface (for example, an Xn interface). More specifically, for example, the plurality of base station devices 20 are connected to each other via an Xn-U interface in the U-plane and via an Xn-C interface in the C-plane. Note that the plurality of base station devices 20 may also be connected to each other via other interfaces with different functions or names.

[0026] Each base station device 20 is connected to the core network 30 via a predetermined interface (for example, an NG interface). More specifically, for example, each base station device 20 is connected to the UPF of the core network 30 via an NG-U interface in the U-plane, and is connected to the AMF of the core network 30 via an NG-C interface in the C-plane. Note that each base station device 20 may be connected to the core network 30 via another interface with a different function or name.

[0027] The radio protocol architecture between the terminal device 10 and the base station device 20 will be described with reference to Fig. 2. The radio protocol architecture between the terminal device 10 and the base station device 20 and between the terminal device 10 and the core network 30 will be described with reference to Fig. 3.

[0028] 2, the U-plane protocol stack includes, from the bottom up, a physical (PHY) layer, a media access control (MAC) layer, an RLC layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer. Each of the above layers is terminated at the base station device 20 on the network side.

[0029] Although not shown, the U-plane protocol stack shown in Fig. 2 is also applied to sidelink communication. That is, a PHY layer, a MAC layer, an RLC layer, a PDCP layer, and an SDAP layer are provided between two terminal devices 10.

[0030] As shown in Fig. 3 , the C-plane protocol stack includes, from the bottom up, a physical (PHY) layer, a media access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, a radio resource control (RRC) layer, and a non-access stratum (NAS). The above-mentioned layers other than the non-access stratum are terminated at the base station device 20 on the network side. The non-access stratum is terminated at the AMF of the core network 30 on the network side.

[0031] Although not shown, the C-plane protocol stack shown in Fig. 3 is also applied to sidelink communication. That is, a PHY layer, a MAC layer, an RLC layer, a PDCP layer, and an RRC layer are provided between two terminal devices 10.

[0032] 4, the terminal device 10 has, as hardware elements, a processor 101, a memory 102, an input / output interface 103, a transceiver 104, and an antenna 105. The above elements provided in the terminal device 10 are connected to each other by an internal bus. Note that the terminal device 10 may have hardware elements other than the elements shown in FIG. 4.

[0033] The processor 101 is a computing element that realizes various functions of the terminal device 10. The processor 101 may be a system-on-a-chip (SoC) that includes elements such as a central processing unit (CPU), a graphics processing unit (GPU), and a memory controller.

[0034] The memory 102 is composed of at least one storage medium such as a RAM (Random Access Memory) or an eMMC (embedded Multi Media Card). The memory 102 is an element that temporarily or permanently stores programs and data used to execute various processes in the terminal device 10. The programs include one or more instructions for operating the terminal device 10. The processor 101 implements the functions of the terminal device 10 by expanding and executing the programs stored in the memory 102 in the memory 102 and / or a system memory (not shown).

[0035] The input / output interface 103 is an interface that receives operations on the terminal device 10 and supplies the operations to the processor 101, and presents various information to the user. The input / output interface 103 is, for example, a touch panel.

[0036] The transceiver 104 is a circuit that performs various signal processing to realize wireless communication, and includes a baseband processor and an RF circuit. The transceiver 104 transmits and receives wireless signals to and from the base station device 20 via the antenna 105.

[0037] 5, the terminal device 10 has, as functional blocks, a control unit 110 and a communication unit 120. The communication unit 120 has at least one transmission unit 121 and at least one reception unit 122.

[0038] The control unit 110 may include at least one processor 101 and at least one memory 102. In other words, the control unit 110 may be realized by the processor 101 and the memory 102. The control unit 110 executes various control processes in the terminal device 10. For example, the control unit 110 controls wireless communication with the base station device 20 via the communication unit 120. That is, the control unit 110 transmits and receives data / information / messages via the communication unit 120.

[0039] The communication unit 120 includes the transceiver 104 and the antenna 105. In other words, the communication unit 120 is realized by the transceiver 104 and the antenna 105. The communication unit 120 wirelessly communicates with the base station device 20 by transmitting and receiving radio signals to and from the base station device 20. Two or more transceivers 104 and two or more antennas 105 may be included in the communication unit 120.

[0040] The control unit 110 operates to execute various processes of the terminal device 10 .

[0041] 6, the base station device 20 has, as hardware elements, a processor 201, a memory 202, a network interface 203, a transceiver 204, and an antenna 205. The above elements provided in the base station device 20 are connected to each other by an internal bus. Note that the base station device 20 may have hardware elements other than the elements shown in FIG.

[0042] The processor 201 is a computing element that realizes various functions of the base station device 20. The processor 201 may be a CPU, and may further include other processors such as a GPU.

[0043] The memory 202 is configured by at least one storage medium such as a read-only memory (ROM), a RAM, a hard disk drive (HDD), or a solid state drive (SSD). The memory 202 is an element that temporarily or permanently stores programs and data used to execute various processes in the base station device 20. The programs include one or more instructions for operating the base station device 20. The processor 201 implements the functions of the base station device 20 by expanding and executing the programs stored in the memory 202 in the memory 202 and / or a system memory (not shown).

[0044] The network interface 203 is an interface used to transmit and receive signals to and from other base station devices 20 and the core network 30 .

[0045] The transceiver 204 is a circuit that performs various signal processing to realize wireless communication, and includes a baseband processor and an RF circuit. The transceiver 204 transmits and receives wireless signals to and from the terminal device 10 via the antenna 205.

[0046] 7, the base station device 20 has, as functional blocks, a control unit 210, a communication unit 220, and a network communication unit 230. The communication unit 220 has at least one transmission unit 221 and at least one reception unit 222.

[0047] The control unit 210 may include at least one processor 201 and at least one memory 202. In other words, the control unit 210 may be realized by the processor 201 and the memory 202. The control unit 210 executes various control processes in the base station device 20. For example, the control unit 210 controls wireless communication with the terminal device 10 via the communication unit 220. That is, the control unit 210 transmits and receives data / information / messages via the communication unit 220. Furthermore, for example, the control unit 210 controls communication with other nodes (e.g., other base station devices 20, nodes of the core network 30) via the network communication unit 230.

[0048] The communication unit 220 includes a transceiver 204 and an antenna 205. In other words, the communication unit 220 is realized by the transceiver 204 and the antenna 205. The communication unit 220 wirelessly communicates with the terminal device 10 by transmitting and receiving radio signals to and from the terminal device 10. Two or more transceivers 204 and two or more antennas 205 may be included in the communication unit 220.

[0049] The network communication unit 230 includes the network interface 203. In other words, the network communication unit 230 is realized by the network interface 203. The network interface 203 transmits and receives signals to and from the network (and thus to the other nodes described above).

[0050] The control unit 210 operates to execute various processes in the base station device 20 .

[0051] 1.2 Radio Resources The terminal device 10 and the base station device 20 communicate with each other wirelessly using radio resources in the frequency domain and the time domain. Radio resources will be explained below.

[0052] The transmission method for downlink communication from the base station device 20 to the terminal device 10 is, for example, Orthogonal Frequency Division Multiplexing (OFDM) using a cyclic prefix (CP), i.e., CP-OFDM. The transmission method for uplink communication from the terminal device 10 to the base station device 20 is, for example, the above-mentioned CP-OFDM or DFTS-OFDM in which CP-OFDM is applied after transform precoding that performs discrete Fourier transform (DFT) spreading.

[0053] A cyclic prefix is ​​a redundant signal that functions as a guard period (GP) to prevent inter-symbol interference and inter-carrier interference, and is inserted at the beginning of an OFDM symbol. There are two types of cyclic prefixes: a normal cyclic prefix and an extended cyclic prefix.

[0054] As radio resources in the frequency domain of OFDM, multiple subcarriers that are orthogonal to each other are used. The multiple subcarriers are arranged in the frequency domain at a predetermined subcarrier spacing (sub-carrier spacing, SCS) Δf. Multiple subcarrier spacings Δf can be applied in a communication system S. The subcarrier spacing Δf can be expressed, for example, by the following equation: Δf=2 μ ・15 [kHz]

[0055] Here, μ is an integer equal to or greater than 0 and can take on at least one of the values ​​0, 1, 2, 3, 4, 5, and 6. Therefore, the subcarrier spacing Δf [kHz] can take on at least one of the values ​​15, 30, 60, 120, 240, 480, and 960. Note that μ may also take on a value of 7 or greater.

[0056] In the time domain of OFDM, a layered radio frame structure is used as shown in Figure 8. One radio frame includes 10 subframes. Subframes are assigned subframe numbers that count up by one from 0 to 9. One radio frame is divided into two half frames. The time length of a radio frame is 10 ms, the time length of a half frame is 5 ms, and the time length of a subframe is 1 ms. These time lengths do not depend on the subcarrier spacing Δf.

[0057] One subframe includes one or more slots (slot(s)). The number Ns of slots included in one subframe depends on the value of μ described above, and further depends on the subcarrier spacing Δf. The number Ns of slots is expressed by the following formula, for example: Ns=2 μ

[0058] One slot contains multiple symbols. The number of symbols in one slot depends on the type of cyclic prefix. For example, if a normal cyclic prefix is ​​used, one slot contains 14 symbols. For example, if an extended cyclic prefix is ​​used, one slot contains 12 symbols.

[0059] As described above, the number of slots and the number of symbols included in each of a radio frame, half frame, and subframe, each of which has a fixed time length, are variable. Therefore, the time length of a slot and the time length of a symbol are also variable.

[0060] A resource element (RE) is a radio resource unit in the time-frequency domain consisting of one subcarrier and one symbol, and a resource block (RB) is a radio resource unit in the time-frequency domain consisting of 12 subcarriers and multiple symbols.

[0061] Each radio frame is assigned a system frame number (SFN), which counts up by one from 0 to 1023. SFN "0" corresponds to the initial value of the SFN, and SFN "1023" corresponds to the maximum value of the SFN. Therefore, the radio frame following a radio frame assigned SFN 1023 is assigned SFN 0. Since the time length of a radio frame is 10 ms, the time length of one cycle of the system frame number is 10,240 ms (= 10.24 seconds).

[0062] Here, the base station device 20 may configure one or more serving cells for the terminal device 10. The serving cell may correspond to a component carrier in the downlink and / or a component carrier in the uplink. The technology in which one or more serving cells are configured and the base station device 20 and the terminal device 10 perform wireless communication may also be referred to as carrier aggregation.

[0063] Furthermore, the base station device 20 may configure one or more bandwidth parts (Bandwidth Parts, BWPs) for the terminal device 10 with respect to each of one or more serving cells. For example, a Downlink Bandwidth Part (DL-BWP) may be configured in the downlink of one serving cell. Furthermore, an Uplink Bandwidth Part (UL-BWP) may be configured in the uplink of one serving cell. Herein, the DL-BWP may include an initial DL-BWP and / or a dedicated DL-BWP. Furthermore, the UL-BWP may include an initial UL-BWP and / or a dedicated UL-BWP. Hereinafter, the BWP may include a DL-BWP and / or a UL-BWP.

[0064] 1.3 Channels and Control Information The terminal device 10 and the base station device 20 transmit and receive user data and control information to and from each other. The transmission and reception of control information in the downlink and uplink will be exemplified below.

[0065] The terminal device 10 and the base station device 20 transmit and receive user data and control information using a plurality of hierarchical channels. The physical channel is a channel used for physical communication between the terminal device 10 and the base station device 20. Examples of the physical channel include a physical downlink control channel (PDCCH), a physical broadcast channel (PBCH), and a physical uplink control channel (PUCCH).

[0066] A transport channel is a channel located above a physical channel and is mapped to a physical channel in the PHY layer. Multiple transport channels may be mapped to one physical channel. Examples of transport channels include a Downlink Shared Channel (DL-SCH) and an Uplink Shared Channel (UL-SCH). For example, data in the downlink may also be referred to as DL-SCH data. Furthermore, for example, data in the uplink may also be referred to as UL-SCH data. Here, DL-SCH data includes user data in the downlink. Furthermore, UL-SCH data includes user data in the uplink.

[0067] A logical channel is a channel located above a transport channel and is mapped to the transport channel in the MAC layer. Multiple logical channels may be mapped to one transport channel, and one logical channel may be mapped to multiple transport channels. Logical channels are classified according to the characteristics of the information they transmit. Examples of logical channels include a Broadcast Control Channel (BCCH), a Common Control Channel (CCCH), and a Dedicated Control Channel (DCCH).

[0068] The base station device 20 transmits downlink control information (DCI) to the terminal device 10 using the PDCCH, which is a physical channel. The DCI includes information on downlink and uplink resource allocation for the terminal device 10, and control information for the terminal device 10. The DCI is mapped to the PDCCH and corresponds to Layer 1 signaling.

[0069] Here, one or more formats may be defined for transmission of DCI in the PDCCH. The formats defined for transmission of DCI in the PDCCH may be referred to as DCI formats. For example, the DCI formats may include DCI formats used for scheduling a Physical Downlink Shared Channel (PDSCH) (e.g., formats referred to as DCI format 1_0, DCI format 1_1, and / or DCI format 1_2). Furthermore, for example, the DCI formats may include DCI formats used for scheduling a Physical Uplink Shared Channel (PUSCH) (e.g., formats referred to as DCI format 0_0, DCI format 0_1, and / or DCI format 0_2). Furthermore, the DCI formats may include DCI formats not used for scheduling the PDSCH and / or the PUSCH. The DCI formats used for scheduling the PDSCH and / or the PUSCH may be referred to as scheduling DCI formats. A DCI format that is not used for scheduling the PDSCH and / or PUSCH may be referred to as a non-scheduling DCI format. Hereinafter, for ease of explanation, a "DCI format" may be simply referred to as a "PDCCH." Furthermore, a "DCI generated according to a DCI format" may be simply referred to as a "DCI format."

[0070] For example, the base station device 20 may configure frequency domain resources and / or time domain resources that the terminal device 10 monitors (i.e., monitors) a PDCCH candidate set. For example, the frequency domain resources that the terminal device 10 monitors the PDCCH candidate set may be referred to as a control resource set (CORESET). Furthermore, the time domain resources that the terminal device 10 monitors the PDCCH candidate set may be referred to as a search space set (SSS). The terminal device 10 may monitor the PDCCH candidate set in one or more CORESETs in the DL-BWP of a serving cell for which PDCCH monitoring is configured, according to the corresponding search space set. Here, monitoring may imply attempting to decode each PDCCH candidate according to the monitored DCI format. The above configuration may be referred to as blind decoding.

[0071] Here, a Cyclic Redundancy Check (CRC) scrambled with a Radio Network Temporary Identifier (RNTI) may be added to the DCI (or DCI format) transmitted on the PDCCH. The CRC may also be referred to as a CRC parity bit. Multiple types of RNTI are defined. For example, the base station device 20 may set each RNTI by transmitting an RRC message including at least one of information indicating a C-RNTI (Cell-RNTI), information indicating a Modulation and Coding Scheme Cell-RNTI (MCS-C-RNTI), and information indicating a Configured Scheduling-RNTI (CS-RNTI). That is, a CRC scrambled with at least one of the C-RNTI, MCS-C-RNTI, and CS-RNTI may be added to the DCI (or DCI format) transmitted on the PDCCH.

[0072] The terminal device 10 may monitor (and / or receive) the PDCCH and detect (and / or receive) the DCI format.

[0073] The terminal device 10 transmits uplink control information (UCI) to the base station device 20 using the PUCCH, which is a physical channel. The UCI includes control information such as a scheduling request (SR), a hybrid automatic repeat reQuest (HARQ) ACK / NACK, and channel state information (CSI). The UCI is mapped to the PUCCH or PUSCH and corresponds to layer 1 signaling.

[0074] The base station device 20 uses the DL-SCH, which is a transport channel, to transmit a control element (CE) of the MAC layer to the terminal device 10. The downlink MAC CE is mapped to the PDSCH via the DL-SCH and corresponds to Layer 2 signaling.

[0075] The terminal device 10 transmits a control element (CE) of the MAC layer to the base station device 20 using the UL-SCH, which is a transport channel. The uplink MAC CE includes control information such as a buffer status report (BSR). The uplink MAC CE is mapped to a PUSCH via the UL-SCH and corresponds to Layer 2 signaling.

[0076] The base station device 20 transmits (or broadcasts) system information (SI) to the terminal device 10 using the BCCH, which is a logical channel. The SI includes minimum system information (MSI) and other system information (OSI). The MSI includes a master information block (MIB) and system information block 1 (SIB1). SIB1 may be referred to as remaining minimum system information (RMSI). The OSI includes system information blocks (SIB2 onward) other than SIB1. Of the BCCH, the MIB is mapped to the PBCH via the BCH (Broadcast CHannel), and the SIB is mapped to the PDSCH via the DL-SCH.

[0077] The base station device 20 transmits control information in the RRC layer to the terminal device 10 using a signaling radio bearer (SRB) established between the terminal device 10 and the base station device 20 in the RRC layer. Hereinafter, messages exchanged between the base station device 20 and the terminal device 10 in the RRC layer may be referred to as RRC messages. There are multiple types of SRBs (e.g., SRB0, SRB1, SRB2, SRB3, SRB4). The SRBs are used to transmit and receive RRC messages as well as NAS messages containing control information in the NAS layer. The CCCH or DCCH is used to transmit RRC messages from the base station device 20 to the terminal device 10. The CCCH and DCCH are each mapped to the PDSCH via the DL-SCH. The RRC message corresponds to Layer 3 signaling.

[0078] As an example of a downlink RRC message, an RRC reconfiguration message will be described. The RRC reconfiguration message is an RRC message transmitted from the base station device 20 to the terminal device 10 using SRB1 or SRB3. The DCCH is used to transmit the RRC reconfiguration message. The RRC reconfiguration message is used to reconfigure or modify the connection between the base station device 20 and the terminal device 10.

[0079] The terminal device 10 transmits an RRC message to the base station device 20 using the above-mentioned SRB. The CCCH or DCCH is used to transmit the RRC message from the terminal device 10 to the base station device 20. The CCCH and DCCH are each mapped to the PUSCH via the UL-SCH. The RRC message corresponds to Layer 3 signaling.

[0080] As an example of an uplink RRC message, a user equipment capability information (UECapabilityInformation) message will be described. The user equipment capability information message is an RRC message transmitted from the terminal device 10 to the base station device 20 using SRB1. The DCCH is used to transmit the user equipment capability information message. The user equipment capability information message is used to notify the base station device 20 of information related to the radio access capability of the terminal device 10.

[0081] As an example of an uplink RRC message, a user equipment assistance information (UE Assistance Information, UAI) message will be described. The UAI message is an RRC message transmitted from the terminal device 10 to the base station device 20 using SRB1 or SRB3. The DCCH is used to transmit the UAI message. The UAI message is used to notify the base station device 20 of various information related to the terminal device 10 (e.g., UE assistance information).

[0082] 1.4. Processing in the RLC Layer 1.4.1. RLC PDU

[0083] When transmitting and receiving data between a terminal device 10 and a base station device 20, an RLC entity in the RLC layer on the transmitting side transmits an RLC PDU to an RLC entity on the receiving side via a lower layer. In uplink communication, the terminal device 10 is the transmitting side, and the base station device 20 is the receiving side. In downlink communication, the terminal device 10 is the receiving side, and the base station device 20 is the transmitting side. In sidelink communication, one of the two terminal devices 10 is the transmitting side, and the other is the receiving side.

[0084] An RLC PDU is data in which an RLC header is added to a data packet called a Service Data Unit (SDU). A PDCP entity in the PDCP layer generates a PDCP PDU by adding a PDCP header to data (SDU) received from an upper layer and submits it to the RLC layer. The RLC entity generates an RLC PDU by adding an RLC header to the PDCP PDU and submits it to a lower layer. In the RLC layer, the PDCP PDU is called an RLC SDU.

[0085] AM supports RLC data PDUs transmitted and received in the U-plane and RLC control PDUs transmitted and received in the C-plane. RLC data PDUs transmitted in AM are called AMD PDUs. AMD PDUs are data sent by a transmitting AM RLC entity to a receiving AM RLC entity. RLC control PDUs include a STATUS PDU. The STATUS PDU is sent to a transmitting AM RLC entity to indicate whether the receiving AM RLC entity has successfully or unsuccessfully received the RLC SDU contained in the AMD PDU.

[0086] An AM RLC entity can segment an RLC SDU into multiple RLC SDUs in response to a notification from a lower layer, for example, a notification of a transmission opportunity. For example, if an RLC SDU is segmented into three RLC SDUs, an RLC header is added to each of the three RLC SDUs, generating three RLC PDUs (AMD PDUs). Segmenting an RLC SDU is called segmentation, and the segmented RLC SDUs are called RLC SDU segments. Alternatively, an AM RLC entity may not segment an RLC SDU into multiple RLC SDU segments. In this case, an RLC header is added to a single complete, unsegmented RLC SDU, generating one RLC PDU (AMD PDU). That is, an AMD PDU contains either one complete RLC SDU or one RLC SDU segment. Hereinafter, when referring to an RLC SDU, the RLC SDU also includes an RLC SDU segment.

[0087] The AMD PDU has a predetermined format. As shown in Fig. 9, the AMD PDU is composed of a header field and a data field. The header field may include a D / C (Data / Control) field, a P (Polling Bit) field, an SI (Segmentation Info) field, an SN (Sequence Number) field, and an SO (Segment Offset) field. In addition to the format shown in Fig. 9, other formats of the AMD PDU are also defined, such as a format that does not include an SO field.

[0088] The D / C field indicates whether the PDU is a control PDU or a data PDU. The P field indicates whether the receiving AM RLC entity is requested to transmit a STATUS PDU as a status report (to be described later). If the P field is set to "1: Status report is requested", the receiving AM RLC entity may transmit a STATUS PDU indicating whether the RLC SDU has been successfully received to the transmitting AM RLC entity. That is, the receiving AM RLC entity may transmit a STATUS PDU indicating a positive acknowledge (ACK) or negative acknowledge (NACK) for the RLC SDU to the transmitting AM RLC entity.

[0089] The SN field is a sequence number assigned to each RLC SDU corresponding to an AMD PDU, and identifies the RLC SDU corresponding to the transmitted AMD PDU. The receiving AM RLC entity reassembles the RLC SDU based on the value set in the SN field.

[0090] The SI field indicates whether the RLC SDU is segmented, and if so, whether it is the first RLC SDU segment, the last RLC SDU segment, or an RLC SDU segment that is neither the first nor the last. The SO field indicates the position of the RLC SDU segment in the RLC SDU.

[0091] The STATUS PDU also has a predetermined format. As shown in Fig. 10, the STATUS PDU includes a D / C field, an ACK_SN field, a NACK_AN field, etc. Note that Fig. 10 shows only a part of the format of the STATUS PDU.

[0092] The ACK_SN field indicates the sequence number (SN) of the next missed RLC SDU that is not reported missing in a STATUS PDU. When a transmitting AM RLC entity receives a STATUS PDU, it considers that all RLC SDUs up to the RLC SDU with the SN indicated in the ACK_SN field have been received by the receiving AM RLC entity, except for the RLC SDU with the SN indicated in the ACK_SN field and the RLC SDUs indicated by NACK_SN, as described below.

[0093] The NACK_SN field may indicate a sequence number set in an RLC SDU when the receiving AM RLC entity fails to receive the RLC SDU successfully. The NACK_SN field may be set to a value set in the SN field of the RLC SDU that the receiving AM RLC entity fails to receive successfully. That is, the NACK_SN field indicates the SN of the RLC SDU (or RLC SDU segment) that is detected as lost by the receiving AM RLC entity.

[0094] 1.4.2 AM RLC Entity If a receiving AM RLC entity fails to receive an RLC SDU successfully, the transmitting AM RLC entity can retransmit the RLC SDU (or the AMD PDU corresponding to the RLC SDU) to the receiving AM RLC entity. The RLC SDU may be retransmitted if the STATUS PDU transmitted by the receiving AM RLC entity indicates NACK. That is, the condition for retransmission of the RLC SDU may be that the STATUS PDU indicates NACK. The STATUS PDU indicates NACK, meaning that the NACK_SN field shown in FIG. 10 is set to a predetermined value. That is, if the NACK_SN field included in the STATUS PDU indicates a NACK for a certain RLC SDU, the RLC SDU (or the AM RLC PDU corresponding to the RLC SDU) may be considered for retransmission, i.e., the transmitting AM RLC entity may retransmit the RLC SDU.

[0095] For a receiving AM RLC entity to transmit a STATUS PDU every time it receives an AMD PDU would result in signaling overhead. To avoid this, 3GPP TS 23.2100-10.2504 discloses that transmission of STATUS PDUs is restricted under certain conditions.

[0096] The P field of an AMD PDU transmitted by a transmitting AM RLC entity may be set to '1' based on the conditions described below. Otherwise, it may be set to '0: Status report not requested'. Hereinafter, setting the P field to '1' and including a poll in an AMD PDU are considered to have the same meaning. Based on receiving an AMD PDU with the P field set to '1' from a lower layer, the receiving AM RLC entity may trigger (or transmit) a status report (i.e., transmission of a STATUS PDU).

[0097] The transmitting AM RLC entity may include a poll in the AMD PDU in response to transmitting a predetermined number of AMD PDUs or a predetermined number of bytes of AMD PDUs, i.e., in response to transmitting a predetermined number of AMD PDUs, the transmitting AM RLC entity requests the receiving AM RLC entity to report whether the AMD PDUs to be transmitted have been successfully received.

[0098] For example, assume that a transmitting AM RLC entity transmits 10 AMD PDUs consecutively, corresponding to 10 RLC SDU segments. In this case, the transmitting AM RLC entity increments PDU_WITHOUT_POLL by one each time it transmits an AMD PDU. PDU_WITHOUT_POLL is a counter that counts the number of AMD PDUs to be transmitted. Note that PDU_WITHOUT_POLL may also be incremented when transmitting an AMD PDU that includes a previously untransmitted RLC SDU or RLC SDU segment. Furthermore, each time it transmits an AMD PDU, the transmitting AM RLC entity increments BYTE_WITHOUT_POLL by the number of bytes in the data field of the AMD PDU. BYTE_WITHOUT_POLL is a counter that counts the number of bytes in the data field of the AMD PDU to be transmitted. Note that BYTE_WITHOUT_POLL may be incremented when transmitting an AMD PDU that includes a previously untransmitted RLC SDU or an RLC SDU segment.

[0099] The transmitting AM RLC entity then checks whether the condition PDU_WITHOUT_POLL >= PollPDU or BYTE_WITHOUT_POLL >= PollByte is met. If the above condition is met, the transmitting AM RLC entity transmits an AMD PDU including a poll. After transmitting the AMD PDU, the transmitting AM RLC entity polls to receive a STATUS PDU from the receiving AM RLC entity.

[0100] The Poll PDU is set to a threshold value for the number of AMD PDUs transmitted by the transmitting AM RLC entity. When the number of AMD PDUs to be transmitted (PDU_WITHOUT_POLL) exceeds the threshold value (Poll PDU), the transmitting AM RLC entity includes a poll in the AMD PDU. The Poll Byte is set to a threshold value for the number of bytes in the data field of the AMD PDU transmitted by the transmitting AM RLC entity. When the number of bytes in the AMD PDU to be transmitted (PDU_WITHOUT_BYTE) exceeds the threshold value (Poll Byte), the transmitting AM RLC entity includes a poll in the AMD PDU. The Poll PDU and Poll Byte are IEs included in the RLC-Config IE. The RLC-Config IE is transmitted from the base station device 20 to the terminal device 10 via an RRC message.

[0101] For example, if the Poll PDU is set to "4," the above condition is met when transmitting the fourth AMD PDU out of ten AMD PDUs. In this case, the transmitting AM RLC entity includes a Poll in the AMD PDU when transmitting the fourth AMD PDU. That is, the transmitting AM RLC entity sets "1" based on the P field of the AMD PDU. Furthermore, when including a Poll in the AMD PDU, the transmitting AM RLC entity sets PDU_WITHOUT_POLL and BYTE_WITHOUT_POLL to "0." That is, when transmitting the eighth AMD PDU, the above condition is met again, and the transmitting AM RLC entity may include a Poll in the eighth AMD PDU.

[0102] The transmitting AM RLC entity may also include a poll in an AMD PDU if both its transmission buffer and retransmission buffer are empty after the transmission of the AMD PDU (except for transmitted RLC SDUs or RLC SDU segments that are awaiting ACK), or if it is unable to transmit a new RLC SDU after the transmission of the AMD PDU (e.g., due to window stalling).

[0103] Furthermore, when t-Reassembly expires, the receiving AM RLC entity may trigger a status report (i.e., transmission of a STATUS PDU). That is, the receiving AM RLC entity may transmit a STATUS PDU based on the expiration of t-Reassembly. t-Reassembly is a timer used by the receiving AM RLC entity to detect the loss of an AMD PDU. t-Reassembly is an IE included in the RLC-Config IE.

[0104] The transmitting AM RLC entity may (re)initiate t-PollRetransmit based on the inclusion of a poll in an AMD PDU and sending it to the lower layer. t-PollRetransmit is the timer used by the transmitting AM RLC entity to retransmit a poll. t-PollRetransmit is an IE included in the RLC-Config IE.

[0105] Based on the expiration of t-PollRetransmit, the transmitting AM RLC entity may include a poll in the AM PDU and may consider unacknowledged RLC SDUs for retransmission if both the transmission and retransmission buffers are empty when t-PollRetransmit expires, or if no new RLC SDUs can be transmitted.

[0106] The receiving AM RLC entity transmits a STATUS PDU under the above conditions. However, to avoid continuous STATUS PDU transmission, the receiving AM RLC entity may not transmit a STATUS PDU while t-StatusProhibit is running. t-StatusProhibit is a timer used by the receiving AM RLC entity to prohibit STATUS PDU transmission. t-StatusProhibit is an IE included in the RLC-Config IE. The receiving AM RLC entity may start t-StatusProhibit when it transmits a STATUS PDU to lower layers.

[0107] Non-Patent Document 1 describes the procedure for transmitting a STATUS PDU and retransmitting an AMD PDU. This procedure will be explained with reference to FIG.

[0108] 11, the transmitting AM RLC entity transmits 10 AMD PDUs consecutively corresponding to 10 RLC SDU segments. First, the transmitting AM RLC entity increments PDU_WITHOUT_POLL and BYTE_WITHOUT_POLL based on the RLC SDUs transmitted from the PDCP layer (step S1101).

[0109] The transmitting AM RLC entity increments PDU_WITHOUT_POLL for the AMD PDU to be transmitted as follows: PDU_WITHOUT_POLL = PDU_WITHOUT_POLL + 1. The transmitting AM RLC entity also increments BYTE_WITHOUT_POLL for the AMD PDU to be transmitted as follows: BYTE_WITHOUT_POLL = BYTE_WITHOUT_POLL + Byte of AMD PDU, where Byte of AMD PDU is the number of bytes in the data field of the AMD PDU.

[0110] Next, the transmitting AM RLC entity checks whether the condition PDU_WITHOUT_POLL >= PollPDU or BYTE_WITHOUT_POLL >= PollByte is met. If the condition is met (Yes in step S1102), the transmitting AM RLC entity sets "1" in the P field in the header added to the RLC SDU (step S1103). If the condition is not met (No in step S1102), the transmitting AM RLC entity sets "0" in the P field (step S1104).

[0111] In addition to the condition in step S1102, the transmitting AM RLC entity may set the P field to “1” if both the transmission buffer and the retransmission buffer are empty after transmitting the AMD PDU (except for transmitted RLC SDUs or RLC SDU segments that are waiting for ACK), or if no new RLC SDUs can be transmitted after transmitting the AMD PDU (e.g., due to window stalling).

[0112] Next, the transmitting AM RLC entity sets values ​​corresponding to each of the 10 RLC SDUs (or RLC SDU segments) in the SN field in the RLC header (step S1105). For example, for the fourth AMD PDU, the SN field is set to "4." After setting predetermined values ​​in the other fields in the RLC header, the transmitting AM RLC entity adds a header to the RLC SDU to generate an AMD PDU, and transmits the AMD PDU to the receiving AM RLC entity via lower layers (step S1106).

[0113] Upon receiving the AMD PDU, the receiving AM RLC entity determines whether to trigger a status report (i.e., transmission of a STATUS PDU) based on the value of the P field in the header (step S1107). As a result, if the P field is set to "1" (Yes in step S1107), the receiving AM RLC entity may transmit a STATUS PDU with an ACK or NACK set, indicating whether the RLC SDU was received successfully (step S1108). If the P field is set to "0" (No in step S1107), the receiving AM RLC entity may not transmit a STATUS PDU.

[0114] As mentioned above, if t-StatusProhibit is active when a status report is triggered, the STATUS PDU does not need to be transmitted. For example, the STATUS PDU may be transmitted at the first transmission opportunity after t-StatusProhibit expires. Also, if t-Reassembly expires, the receiving AM RLC entity may trigger a status report.

[0115] Upon receiving the STATUS PDU, the transmitting AM RLC entity checks whether the STATUS PDU indicates an ACK or NACK (step S1109). If the STATUS PDU indicates an ACK for a certain RLC SDU (Yes in step S1109), the transmitting AM RLC entity may notify the upper layer that the RLC SDU has been successfully received and update TX_NEXT_ACK (step S1110). TX_NEXT_ACK holds the SN value of the next RLC SDU for which an ACK is consecutively received, and serves as the lower limit of the transmission window. It is initially set to '0' and is updated each time the transmitting AM RLC entity receives an ACK for an RLC SDU with SN = TX_Next_Ack.

[0116] If the STATUS PDU indicates a NACK for a certain RLC SDU (No in step S1109), the transmitting AM RLC entity may consider the RLC SDU to be a target for retransmission and perform retransmission of the RLC SDU (step S1111). The transmitting AM RLC entity may determine that a NACK for the RLC SDU is indicated based on the value of the NACK_SN field included in the STATUS PDU. The NACK_SN field may be set to the sequence number set in the RLC SDU of the AMD PDU that the receiving AM RLC entity was unable to receive successfully. Thus, the transmitting AM RLC entity can identify one or more RLC SDUs to retransmit based on the value of the NACK_SN field of the PDU.

[0117] In the procedure shown in Figure 11, the receiving AM RLC entity may not transmit a STATUS PDU until it receives an AMD PDU containing a poll or until t-Reassembly expires. This means that the transmitting AM RLC entity may need a certain amount of time to receive the STATUS PDU, and if the receiving AM RLC entity cannot receive an RLC SDU successfully, retransmission of the RLC SDU may be delayed.

[0118] Although it is preferable for the receiving AM RLC entity to be restricted from transmitting STATUS PDUs under the above-mentioned conditions in order to avoid signaling overhead, it may not be preferable in situations where low latency is required. In this embodiment, the time required for retransmission of RLC SDUs that have low latency requirements is reduced.

[0119] 1.5 Low-Delay Requirement Data In this embodiment, the transmitting AM RLC entity reduces the time required for retransmission of data that has a low-delay requirement. Hereinafter, data that has a low-delay requirement may be referred to as low-delay requirement data.

[0120] The low-delay requirement data may be delay-critical data as described in Non-Patent Document 1. The delay-critical data may include delay-critical RLC SDUs and / or delay-critical PDCP SDUs. The delay-critical RLC SDUs correspond to PDCP PDUs marked as "delay-critical" in the PDCP layer. The PDCP PDUs correspond to delay-critical PDCP SDUs.

[0121] A delay-critical PDCP SDU refers to a PDCP SDU for which the remaining time until the PDCP discard timer expires is below a remaining time threshold. In response to receiving a PDCP SDU from a higher layer, the PDCP entity may start the PDCP discard timer. When the PDCP discard timer expires, the PDCP entity may discard the PDCP SDU and its corresponding PDCP PDU. If the corresponding PDCP PDU has already been submitted to a lower layer, the PDCP entity may notify a lower layer (e.g., the RLC layer) of the discard. The PDCP discard timer may be configured for a Data Radio Bearer (DRB). The PDCP discard timer may be either discardTimer or discardTimerForLowImportance. The discardTimerForLowImportance may be used for data with relatively low importance (i.e., data with a relatively high PDU Set Importance (PSI) value). For the remaining time threshold, remainingTimeThreshold is used.

[0122] The 3GPP 5G NR technical specifications prescribe that a PDCP entity transmits a Delay Status Report (DSR) to report a delay situation to a base station device 20 when the remaining time until the PDCP discard timer expires falls below a remaining time threshold. discardTimer and discardTimerForLowImportance are IEs included in a PDCP-Config IE. Furthermore, remainingTimeThreshold is an IE included in a MAC-CellGroupConfig IE, and may be set for a logical channel group (LCG). The MAC-CellGroupConfig IE and the PDCP-Config IE are transmitted from the base station device 20 to the terminal device 10 via an RRC message.

[0123] As described above, a delay-critical PDCP SDU refers to a PDCP SDU for which the time remaining until the PDCP discard timer expires is below a remaining time threshold.

[0124] In this embodiment, the transmitting AM RLC entity retransmits the RLC SDU even if it has not received a STATUS PDU. The RLC SDU may be, for example, data to which a low delay requirement is imposed. Note that the low delay requirement data in this embodiment includes the delay critical data defined in the 3GPP 5G NR technical specifications, but this is merely an example, and the low delay requirement data may be defined separately from the delay critical data.

[0125] 1.6. Determination of Low Delay Requirement Data and Retransmission Procedure 1.6.1. Determination of Low Delay Requirement Data in the PDCP Layer A procedure for retransmitting an RLC SDU according to this embodiment will be described with reference to FIG. 12. In this embodiment, an example will be described in which a terminal device 10 retransmits an RLC SDU to a base station device 20 in uplink communication. However, this embodiment may also be applied to downlink communication, i.e., a case in which a base station device 20 retransmits an RLC SDU to a terminal device 10, and to sidelink communication, i.e., a case in which one of two terminal devices 10 retransmits an AMD PDU to the other.

[0126] 12 , the terminal device 10 performs processing in the PDCP layer and the RLC layer. These processings are performed by the control unit 110 and the communication unit 120, but in the PDCP layer, the processing is performed by a PDCP entity implemented by the control unit 110. In addition, in the RLC layer, the processing is performed by an AM RLC entity implemented by the control unit 110.

[0127] In step S1201, the control unit 110 starts a PDCP discard timer in the PDCP layer upon receiving a PDCP SDU from an upper layer. The PDCP discard timer may be, but is not limited to, discardTimer or discardTimerForLowImportance. Alternatively, a timer for determining whether a delay has occurred may be used. Furthermore, upon receiving a PDCP SDU from an upper layer in the PDCP layer, the control unit 110 may start a timer for controlling RLC retransmission, separate from the PDCP discard timer. The timer for controlling RLC retransmission may be a timer for controlling retransmission in the RLC layer based on the remaining time. The base station device 20 may transmit to the terminal device 10 an RRC message including a parameter indicating the timer for determining whether a delay has occurred and / or the timer for controlling RLC retransmission. For example, the parameter may be included in the PDCP-Config IE.

[0128] Next, the control unit 110 adds a PDCP header to the PDCP SDU in the PDCP layer to generate a PDCP PDU, and passes the PDCP PDU to the RLC layer (step S1202).

[0129] Next, the control unit 110 adds an RLC header to the PDCP PDU (RLC SDU) passed from the PDCP layer in step S1202 in the RLC layer to generate an RLC PDU (AMD PDU), and passes the RLC PDU to the lower layer (step S1203). Through this process, the communication unit 120 transmits the AMD PDU to the RLC entity of the base station device 20 via the lower layer.

[0130] In step S1203, processing such as incrementing PDU_WITHOUT_POLL and setting values ​​in the P field and SN field of the RLC header may also be performed. These processing are performed according to the conventional technology described with reference to Fig. 11, and therefore detailed description thereof will be omitted.

[0131] Next, the control unit 110 checks whether the remaining time until the PDCP discard timer expires in the PDCP layer is below a remaining time threshold (step S1204). The remaining time threshold may be the remaining time threshold remainingTimeThreshold. Alternatively, without being limited thereto, a remaining time threshold for controlling RLC retransmission may be used as the remaining time threshold. The base station device 20 may transmit to the terminal device 10 an RRC message including a parameter indicating the remaining time threshold for controlling RLC retransmission. For example, the parameter may be included in any of the PDCP-Config IE, the RLC-Config, or the MAC-CellGroupConfig IE. Furthermore, the control unit 110 may check whether the timer for controlling RLC retransmission in the PDCP layer has expired.

[0132] If the processing of step S1204 indicates that the remaining time until the PDCP discard timer for a certain PDCP SDU expires is below the remaining time threshold, the control unit 110 may provide an indication to the RLC layer indicating that the remaining time until the PDCP discard timer associated with the PDCP PDU corresponding to the PDCP SDU expires is below the remaining time threshold. For example, if the processing of step S1204 indicates that the remaining time until the PDCP discard timer for a certain PDCP SDU expires is below the remaining time threshold, the control unit 110 may consider the PDCP SDU to be low-delay requirement data. The low-delay requirement data may be a delay-critical PDCP SDU. If the control unit 110 has already passed a PDCP PDU corresponding to the delay-critical PDCP SDU to the RLC layer in step S1202, the control unit 110 may provide an indication (delay-critical indication) indicating that the PDCP PDU is delay-critical to the RLC layer (step S1205). Furthermore, the control unit 110 may provide an indication to the RLC layer in the PDCP layer that a timer for controlling RLC retransmission has expired.

[0133] Next, the control unit 110 identifies, in the RLC layer, an RLC SDU to be retransmitted from among the RLC SDUs corresponding to the AMD PDU transmitted in step S1203 (step S1206). The control unit 110 may determine, as a retransmission target, an RLC SDU corresponding to a PDCP PDU for which the PDCP layer indicates that the remaining time until the PDCP discard timer expires has fallen below a remaining time threshold. For example, the control unit 110 may determine, as a retransmission target, an RLC SDU corresponding to a PDCP PDU for which the PDCP layer indicates that the timer for controlling RLC retransmission has expired (i.e., a delay-critical RLC SDU). Alternatively, the control unit 110 may determine, as a retransmission target, an RLC SDU corresponding to a PDCP PDU for which the PDCP layer indicates that the timer for controlling RLC retransmission has expired. That is, the control unit 110 may determine, based on an instruction from the PDCP layer, an RLC SDU to be retransmitted. The RLC SDU to be retransmitted may be an RLC SDU for which normal reception by the base station device 20 has not been confirmed (i.e., an RLC SDU for which no ACK has been indicated). That is, when an indication (e.g., an indication indicating that the RLC SDU is delay-critical) is indicated from the PDCP layer for an RLC SDU for which no ACK has been indicated, the control unit 110 may consider the RLC SDU to be a target for retransmission.

[0134] As described above, the procedure according to the conventional technique described with reference to Fig. 11 is also executed in addition to the process according to this embodiment. Therefore, at the time of the process of step S1206, a STATUS PDU indicating an ACK may already be received from the base station device 20.

[0135] Next, the control unit 110 sets "1" in the P field of the RLC header for the AMD PDU corresponding to the RLC SDU identified as the retransmission target in step S1206 in the RLC layer (step S1207). That is, when an RLC SDU is identified as the retransmission target based on an instruction from the PDCP layer, a poll may be included in the AMD PDU corresponding to the RLC SDU.

[0136] Next, the control unit 110 adds an RLC header to the RLC SDU identified as the retransmission target in the RLC layer to form a new AMD PDU, and passes the new AMD PDU to the lower layer (step S1208). As described above in step S1207, the P field of the RLC header may be set to "1." This process allows the communication unit 120 to retransmit the AMD PDU to the RLC entity of the base station device 20 via the lower layer.

[0137] Note that the control unit 110 may (re)segment the RLC SDU as necessary when retransmitting the RLC SDU. In this case, a new AMD PDU may be formed from the (re)segmented RLC SDU.

[0138] 12 may be executed only when the terminal device 10 is designated in advance to execute the process. For example, when setting information for RLC retransmission is set, the terminal device 10 may execute the process. For example, when setting information for RLC retransmission is set, the terminal device 10 may execute a process to identify data to be retransmitted (e.g., an RLC SDU) based on an instruction from the PDCP layer, and may include a poll in an AMD PDU corresponding to the identified RLC SDU.

[0139] The base station device 20 may transmit an RRC message including configuration information for RLC retransmission to the terminal device 10. That is, the terminal device 10 may receive an RRC message including configuration information for RLC retransmission from the base station device 20. For example, the configuration information for RLC retransmission may be included in any one of a PDCP-Config IE, an RLC-Config, or a MAC-CellGroupConfig IE. Note that the base station device 20 may transmit the configuration information for RLC retransmission to the terminal device 10 using at least one of an RRC message, a MAC CE, and a DCI.

[0140] The setting information for RLC retransmission may be information that explicitly indicates that the terminal device 10 is allowed to retransmit data (e.g., an RLC SDU) based on an instruction from the PDCP layer. The setting information for RLC retransmission may be information that explicitly indicates that the terminal device 10 is allowed to retransmit data based on the remaining time of a timer (e.g., a PDCP discard timer and / or a timer for controlling RLC retransmission). For example, the setting information for RLC retransmission may be information that indicates whether the terminal device 10 is allowed to retransmit data (e.g., an RLC SDU) based on an instruction from the PDCP layer. The "information indicating whether the terminal device 10 is allowed to retransmit data based on an instruction from the PDCP layer" may be a flag that indicates "the terminal device 10 is allowed to retransmit data based on an instruction from the PDCP layer" or "the terminal device 10 is not allowed to retransmit data based on an instruction from the PDCP layer." For example, the configuration information for RLC retransmission may be a flag indicating to the RLC entity in which the configuration information is set, or to an RLC entity associated with the PDCP entity in which the configuration information is set, that "the terminal device 10 is permitted to retransmit data based on instructions from the PDCP layer" or "the terminal device 10 is not permitted to retransmit data based on instructions from the PDCP layer."

[0141] 12 may be executed only when a parameter used for determining whether to perform retransmission in the process of Fig. 12 is notified, such as remainingTimeThreshold, a parameter indicating a remaining time threshold for controlling RLC retransmission, discardTimer, discardTimerForLowImportance, and / or a parameter indicating a timer for controlling RLC retransmission. That is, the configuration information for RLC retransmission may be remainingTimeThreshold, a parameter indicating a remaining time threshold for controlling RLC retransmission, discardTimer, discardTimerForLowImportance, and / or a parameter indicating a timer for controlling RLC retransmission.

[0142] 1.6.2 Determination of Low Delay Requirement Data in the RLC Layer In the process shown in Fig. 12, the PDCP entity determines the low delay requirement data and instructs the lower layer, so that the RLC entity determines the data (e.g., RLC SDUs) to be retransmitted. As another example of the process shown in Fig. 12, a case where the low delay requirement data is determined by the AM RLC entity will be described.

[0143] In this example, a parameter indicating a PDU retransmission timer (e.g., t-PDURetransmit) and / or a parameter indicating a remaining time threshold for the PDU retransmission timer (e.g., remainingTimeThreshold-R19) may be notified to the terminal device 10 via an RRC message. For example, the parameters may be included in the RLC-Config IE.

[0144] A procedure for retransmitting an RLC SDU according to another example of this embodiment will be described with reference to Fig. 13. The matters mentioned for the process shown in Fig. 12 also apply to the process shown in Fig. 13.

[0145] In step S1301, the control unit 110 may start a PDU retransmission timer in the RLC layer when receiving a PDCP PDU (RLC SDU) from the PDCP layer. That is, the control unit 110 may start a PDU retransmission timer for the RLC SDU based on reception of the RLC SDU from the upper layer. Although t-PDURetransmit is used as the PDU retransmission timer, t-PDURetransmit is merely an example.

[0146] Next, the control unit 110 adds an RLC header to the RLC SDU in the RLC layer to generate an RLC PDU (AMD PDU) and passes it to the lower layer (step S1302). Through this process, the communication unit 120 transmits the AMD PDU to the RLC entity of the base station device 20 via the lower layer. The PDU retransmission timer may be started in step S1302. In this case, the PDU retransmission timer does not need to be started in step S1301. For example, the control unit 110 may start the PDU retransmission timer for a certain RLC SDU based on submitting an AMD PDU including that RLC SDU to the lower layer. The RLC SDU may be an RLC SDU that has not been previously transmitted. In other words, the control unit 110 may start the PDU retransmission timer for the RLC SDU based on submitting an AMD PDU including that RLC SDU to the lower layer. In step S1302, the process shown in FIG. 11 may be executed simultaneously.

[0147] Next, the control unit 110 may check whether the remaining time until the PDU retransmission timer expires in the RLC layer is below a remaining time threshold (step S1303). Although remainingTimeThreshold-R19 is used as the remaining time threshold, remainingTimeThreshold-R19 is merely an example. Alternatively, in step S1303, the control unit 110 may check whether the PDU retransmission timer expires.

[0148] If the processing of step S1303 indicates that the time remaining until the PDU retransmission timer expires is below the remaining time threshold, the control unit 110 identifies an RLC SDU to be retransmitted from among the RLC SDUs corresponding to the AMD PDU transmitted in step S1302 (step S1304). The control unit 110 may determine an RLC SDU as a retransmission target if the time remaining until the PDU retransmission timer for that RLC SDU expires is below the remaining time threshold. Alternatively, the control unit 110 may determine an RLC SDU as a retransmission target if the PDU retransmission timer for that RLC SDU expires. That is, the control unit 110 may identify an RLC SDU to be retransmitted based on the PDU retransmission timer and / or the remaining time threshold for the PDU retransmission timer. The RLC SDU to be retransmitted may be an RLC SDU for which the base station apparatus 20 has not confirmed that it has received it normally (i.e., an RLC SDU for which no ACK has been indicated). That is, the control unit 110 may consider an RLC SDU for which no ACK has been indicated as a target for retransmission when the remaining time until the PDU retransmission timer for the RLC SDU for which no ACK has been indicated expires is below a remaining time threshold. The control unit 110 may also consider an RLC SDU for which no ACK has been indicated as a target for retransmission when the PDU retransmission timer for the RLC SDU for which no ACK has been indicated expires.

[0149] Next, the control unit 110 sets "1" to the P field of the RLC header for the RLC SDU identified as a retransmission target in step S1305 in the RLC layer (step S1305). That is, when an RLC SDU is identified as a retransmission target based on the PDU retransmission timer and / or the remaining time threshold for the PDU retransmission timer, a poll may be included in the AMD PDU corresponding to the RLC SDU.

[0150] Next, the control unit 110 adds an RLC header to the RLC SDU identified as the retransmission target in the RLC layer to form a new AMD PDU, and passes the new AMD PDU to the lower layer (step S1306). As described above in step S1305, the P field of the RLC header may be set to "1." This process allows the communication unit 120 to retransmit the AMD PDU to the RLC entity of the base station device 20 via the lower layer.

[0151] 13 may be executed when the terminal device 10 is designated in advance to execute the process. For example, when configuration information for RLC retransmission is set, the terminal device 10 may execute the process. For example, when configuration information for RLC retransmission is set, the terminal device 10 may execute a process to identify data (e.g., an RLC SDU) to be retransmitted based on a PDU retransmission timer and / or a remaining time threshold for the PDU retransmission timer, and may include a poll in an AMD PDU corresponding to the identified RLC SDU.

[0152] The configuration information for RLC retransmission may be information that explicitly indicates that the terminal device 10 is allowed to retransmit data (e.g., an RLC SDU) based on a PDU retransmission timer and / or a remaining time threshold for the PDU retransmission timer. For example, the configuration information for RLC retransmission may be information that indicates whether the terminal device 10 is allowed to retransmit data (e.g., an RLC SDU) based on a PDU retransmission timer and / or a remaining time threshold for the PDU retransmission timer. Furthermore, the processing shown in FIG. 13 may be executed only when a parameter used to determine whether to perform retransmission in the processing of FIG. 13 , such as t-PDURetransmit and / or remainingTimeThreshold-R19, is notified. That is, the configuration information for RLC retransmission may be t-PDURetransmit and / or remainingTimeThreshold-R19.

[0153] 1.6.3 Determining Retransmission Based on PSI In the processes shown in Figures 12 and 13, an RLC SDU is retransmitted by determining whether the remaining time on a timer associated with the RLC SDU is running low. As yet another example of the processes shown in Figures 12 and 13, an example will be described in which an RLC SDU is retransmitted by determining whether the remaining time on a timer associated with the RLC SDU is running low depending on the type of data. The type of data may be determined (identified) based on the value of the PSI associated with the data.

[0154] In communications that require real-time performance, such as XR, the Real-time Transport Protocol (RTP) is assumed to be used. An RTP packet includes an RTP payload, an RTP header, and the like.

[0155] The 3GPP 5G NR technical specifications define fields included in the RTP header extension. The PDU set importance (i.e., PSI) is included in the RTP header extension. The PSI is associated with a PDU set and indicates its importance compared to other PDU sets within the same QoS flow.

[0156] The PSI is represented by, for example, 4 bits. The PSI may have a value between 0 and 15. The lower the PSI value, the higher the importance of the PDU set associated with that PSI. For example, a PDU set associated with a PSI of "0" has the highest importance. A PDU set associated with a PSI of "15" has the lowest importance. Therefore, in the following description, the expression "a relatively small PSI value" may be rephrased as "the importance of the corresponding data (i.e., PDU set) is relatively high." The expression "a relatively large PSI value" may be rephrased as "the importance of the corresponding data (i.e., PDU set) is relatively low."

[0157] A procedure for retransmitting an RLC SDU according to another example of this embodiment will be described with reference to Figure 14. The matters mentioned for the processes shown in Figures 12 and 13 also apply to the process shown in Figure 14.

[0158] In step S1401, the control unit 110 identifies a PDCP SDU having a specific importance level by referring to a PSI value associated with a PDU set to which the PDCP SDU belongs. The PSI value may be notified from a higher layer. Whether a PDCP SDU has a specific importance level may be determined by comparing the PSI value associated with the PDU set to which the PDCP SDU belongs with an importance threshold or an importance rank. For example, the PDCP-Config IE may include such an importance threshold or importance rank, such as an IE such as ImportanceThreshold, and such an IE may be notified to the terminal device 10 via an RRC message. Furthermore, whether a PDCP SDU has a specific importance level may be determined (identified) based on the implementation of the terminal device 10. Whether a PDCP SDU has a specific importance level may be rephrased as whether the PDCP SDU has high importance level, low importance level, or a specific type.

[0159] Instead of the PSI, other information indicating a priority or importance set for data may be used. Subsequent processing may be performed only on PDCP SDUs determined to have a specific importance based on the value of the PSI or other information. For example, subsequent processing may be performed only on PDCP SDUs belonging to a PDU set with a high importance.

[0160] Next, the control unit 110 starts a PDCP discard timer for the PDCP SDU in the PDCP layer (step S1402). The PDCP SDU may be a PDCP SDU with a specific importance. The PDCP discard timer is as described above.

[0161] Next, the control unit 110 adds a PDCP header to the PDCP SDU in the PDCP layer to generate a PDCP PDU, and passes the PDCP PDU to the RLC layer (step S1403).

[0162] Next, in the RLC layer, the control unit 110 adds an RLC header to the PDCP PDU (RLC SDU) passed from the PDCP layer in step S1403 to generate an RLC PDU (AMD PDU), and passes the RLC PDU to the lower layer (step S1404). Through this process, the communication unit 120 transmits the AMD PDU to the RLC entity of the base station apparatus 20 via the lower layer. Note that the process shown in FIG. 11 may be executed simultaneously in step S1404.

[0163] Next, the control unit 110 checks whether the remaining time until the PDCP discard timer expires is below the remaining time threshold in the PDCP layer (step S1405). The remaining time threshold is as described above.

[0164] If the processing of step S1405 indicates that the remaining time until the PDCP discard timer for a certain PDCP SDU expires is below the remaining time threshold, the control unit 110 may provide an indication to the RLC layer indicating that the remaining time until the PDCP discard timer associated with the PDCP PDU corresponding to the PDCP SDU expires is below the remaining time threshold. For example, if the processing of step S1405 indicates that the remaining time until the PDCP discard timer for a certain PDCP SDU expires is below the remaining time threshold, the control unit 110 may consider the PDCP SDU to be a delay-critical PDCP SDU. If a PDCP PDU corresponding to the delay-critical PDCP SDU has already been passed to the RLC layer in step S1403, the control unit 110 may provide an indication to the RLC layer indicating that the PDCP PDU is delay-critical (step S1406).

[0165] Next, the control unit 110 identifies, in the RLC layer, an RLC SDU to be retransmitted from among the RLC SDUs corresponding to the AMD PDU transmitted in step S1404 (step S1407). The control unit 110 may determine, as a retransmission target, an RLC SDU corresponding to a PDCP PDU for which the PDCP layer indicates that the remaining time until the PDCP discard timer expires has fallen below a remaining time threshold. For example, the control unit 110 may determine, as a retransmission target, an RLC SDU corresponding to a PDCP PDU for which the PDCP layer indicates that the timer for controlling RLC retransmission has expired (i.e., a delay-critical RLC SDU). Alternatively, the control unit 110 may determine, as a retransmission target, an RLC SDU corresponding to a PDCP PDU for which the PDCP layer indicates that the timer for controlling RLC retransmission has expired. That is, the control unit 110 may determine, based on an instruction from the PDCP layer, an RLC SDU to be retransmitted. The RLC SDU to be retransmitted may be an RLC SDU for which the base station device 20 has not confirmed that it has received it normally (i.e., an RLC SDU for which no ACK is indicated). The RLC SDU to be retransmitted may be a PDCP SDU for which the corresponding PDCP SDU has a specific importance. That is, when the PDCP SDU corresponding to the RLC SDU for which no ACK is indicated is a PDCP SDU with a specific importance and an indication (e.g., an indication indicating that the RLC SDU is delay-critical) is indicated for the RLC SDU from the PDCP layer, the control unit 110 may consider the RLC SDU to be a target for retransmission.

[0166] Next, in the RLC layer, the control unit 110 sets "1" in the P field of the RLC header for the AMD PDU corresponding to the RLC SDU identified as the retransmission target in step S1407 (step S1408).

[0167] Next, the control unit 110 adds an RLC header to the RLC SDU identified as the retransmission target in the RLC layer to form a new AMD PDU, and passes the AMD PDU to the lower layer (step S1409). Through this process, the communication unit 120 may retransmit the AMD PDU to the RLC entity of the base station apparatus 20 via the lower layer.

[0168] The processing shown in FIG. 14 may also be executed only when the terminal device 10 is specified in advance to execute the processing. For example, when configuration information for RLC retransmission is configured, the terminal device 10 may execute the processing. Furthermore, the base station device 20 may transmit to the terminal device 10 an RRC message including information indicating that data to be retransmitted may be determined according to the data type. When configuration information for RLC retransmission and / or information indicating that data to be retransmitted may be determined according to the data type is configured, the terminal device 10 may execute the processing shown in FIG. 14. This information may be included in the configuration information for RLC retransmission. Furthermore, the processing shown in FIG. 14 may be executed only when parameters used to determine whether to perform retransmission in the processing of FIG. 14, such as remainingTimeThreshold, discardTimer, and / or discardTimerForLowImportance, are notified. That is, the configuration information for RLC retransmission may be remainingTimeThreshold, discardTimer, and / or discardTimerForLowImportance, etc.

[0169] In the process shown in Fig. 14, whether the remaining time is running low is determined in the PDCP layer, but whether the remaining time is running low may be determined in the RLC layer according to the process shown in Fig. 13. In this case, the determination of the data type based on the value of the PSI or other data may be performed in the PDCP layer or in the RLC layer.

[0170] As described above, the first embodiment has been described. In the first embodiment, regardless of whether a STATUS PDU is received or not, the transmitting AM RLC entity considers an RLC SDU to be a target for retransmission when the remaining time on the timer associated with the RLC SDU is low. This reduces the time required for retransmission of RLC SDUs with low latency requirements, especially for data of high importance.

[0171] Furthermore, the conditions for the receiving AM RLC entity to transmit a STATUS PDU are in accordance with the prior art, so that the number of STATUS PDU transmissions is not increased due to retransmission of at least the first RLC SDU, and as a result, signaling overhead is also avoided.

[0172] Furthermore, when an RLC SDU is retransmitted, a poll is included in the AM RLC PDU, allowing the transmitting AM RLC entity to request an early report indicating whether the retransmitted RLC SDU was successfully received by the receiving AM RLC entity.

[0173] The low-delay requirement data described in the first embodiment is merely an example. The low-delay requirement data may be determined by a method other than the method described in the first embodiment.

[0174] 2. Second Embodiment 2.1 Retransmission Based on the Number of HARQ Retransmissions Next, a second embodiment will be described. In the second embodiment, an example will be described in which an RLC SDU is retransmitted when the number of HARQ retransmissions reaches a predetermined threshold.

[0175] As described above, the terminal device 10 transmits the UL-SCH to the base station device 20. HARQ retransmission control is applied to the UL-SCH. HARQ is a technology that improves communication quality of a transmission path by combining Automatic Repeat reQues (ARQ) and Forward Error Correction (FEC).

[0176] In HARQ retransmission control for UL-SCH, the terminal device 10 transmits data to the base station device 20 using the UL-SCH, and if the base station device 20 is unable to successfully decode the data, it transmits a NACK to the terminal device 10. In response to receiving the NACK, the terminal device 10 retransmits the data. On the other hand, if the base station device 20 is able to successfully decode the data, it transmits an ACK to the terminal device 10. In response to receiving the ACK, the terminal device 10 transmits the next data.

[0177] In this embodiment, when the number of HARQ retransmissions reaches a predetermined threshold, the RLC SDU is retransmitted. The predetermined threshold is a threshold that defines an upper limit of the number of HARQ retransmissions. Such a threshold may be transmitted from the base station device 20 to the terminal device 10 via an RRC message.

[0178] The procedure for retransmitting an RLC SDU according to this embodiment will be described with reference to Fig. 15. In this embodiment, an example will also be described in which the terminal device 10 retransmits an RLC SDU to the base station device 20 in uplink communication.

[0179] 15 , the terminal device 10 performs processing in the RLC layer and the MAC layer. These processings are performed by the control unit 110 and the communication unit 120, but in the RLC layer, the processing is performed by an AM RLC entity implemented by the control unit 110. In addition, in the MAC layer, the processing is performed by a MAC entity implemented by the control unit 110.

[0180] In step S1501, when the control unit 110 receives a PDCP PDU (RLC SDU) from the PDCP layer in the RLC layer, it adds an RLC header to the RLC SDU to generate an RLC PDU (AMD PDU) and passes it to a lower layer. Through this process, the communication unit 120 transmits the AMD PDU to the RLC entity of the base station device 20 via the lower layer. Note that the process shown in FIG. 11 may be executed simultaneously in step S1501.

[0181] Next, the control unit 110 counts the number of HARQ retransmissions in the MAC layer (step S1502). As described above, for scheduling the PUSCH to which the UL-SCH is mapped, the base station apparatus 20 transmits DCI to the terminal apparatus 10 using the PDCCH. For scheduling the UL-SCH, DCI format 0_0, DCI format 0_1, DCI format 0_2, or DCI format 0_3 is used.

[0182] DCI format 0_0, DCI format 0_1, DCI format 0_2, or DCI format 0_3 all include data fields called HARQ process number, new data indicator (NDI), and redundancy version (RV).

[0183] The HARQ process number identifies the process that performs the HARQ retransmission. The NDI indicates whether the transmission is a transmission of new data or a retransmission of already transmitted data. The RV indicates which bits are selected for transmission; a different RV from the RV in the previous transmission indicates that a different set of bits is transmitted.

[0184] When transmitting data via HARQ, the control unit 110 can calculate the number of HARQ retransmissions based on at least one of the HARQ process number, NDI, and RV indicated by the DCI. HARQ retransmissions are performed in parallel by multiple HARQ processes. The number of HARQ retransmissions may be counted for each HARQ process. For example, when it is determined that a HARQ retransmission is to be performed based on at least one of the HARQ process number, NDI, and RV indicated by the DCI, a counter that counts the number of retransmissions may be incremented (e.g., by one). At this time, the counter corresponding to the HARQ process number indicated by the DCI may be incremented. Furthermore, for example, when it is determined that a new transmission is to be performed based on at least one of the HARQ process number, NDI, and RV indicated by the DCI, the counter may be initialized or set to "0." At this time, the counter corresponding to the HARQ process number indicated by the DCI may be initialized or set to "0."

[0185] The NDI indicates whether the data to be transmitted is a "new transmission" or a "retransmission." Whether the data to be transmitted is a "new transmission" or a "retransmission" may be determined based on whether the NDI field is toggled, or may be determined based on whether the value set in the NDI field indicates "0" or "1." The example shown in FIG. 16 indicates a state in which three HARQ processes having HARQ process numbers "#1," "#2," and "#3" have performed new transmissions or retransmissions, respectively.

[0186] 16, row No. 1 indicates the first transmission by the HARQ process having HARQ process number "#1", and the NDI indicates that the transmission is a new transmission. Rows No. 2 and 3 indicate the second and third transmissions by the HARQ process having HARQ process number "#1", respectively, and the NDI indicates that the transmission is a retransmission.

[0187] 16 shows that the HARQ process having the HARQ process number "#1" performs two HARQ retransmissions, and the HARQ process having the HARQ process number "#3" performs one HARQ retransmission. When the DCI indicates the above-described data, the control unit 110 increments the counter for the number of HARQ retransmissions. In this way, HARQ retransmissions may be counted for each HARQ process.

[0188] The number of HARQ retransmissions may be counted across HARQ process numbers. In this case, in the example shown in Fig. 16, two retransmissions by the HARQ process having the HARQ process number "#1" and one retransmission by the HARQ process having the HARQ process number "#3" are summed up, and the total number of HARQ retransmissions is counted as three.

[0189] Next, the control unit 110 determines whether the number of HARQ retransmissions counted in step S1502 has reached a threshold in the MAC layer (step S1503). If the number of HARQ retransmissions is counted for each HARQ process number, the number of HARQ retransmissions may be compared with the threshold for each HARQ process number. Alternatively, the maximum value among the counted number of retransmissions may be compared with the threshold. In other words, the number of retransmissions when the process that performed the most HARQ retransmissions among multiple HARQ processes performed retransmissions is compared. Alternatively, if the number of HARQ retransmissions is counted for each HARQ process number, the average value of the counted number of retransmissions may be compared with the threshold.

[0190] Furthermore, if the number of HARQ retransmissions is counted across HARQ process numbers, the total number of retransmissions may be compared with a threshold value. The total number of HARQ retransmissions performed by each of the multiple HARQ processes is compared.

[0191] As a result of the process at step S1503, if the number of HARQ retransmissions reaches the threshold (Yes at step S1503), the control unit 110 provides an indication to the RLC layer requesting retransmission of the RLC SDU (step S1504).

[0192] Next, the control unit 110 identifies an RLC SDU to be retransmitted from among the RLC SDUs corresponding to the AMD PDU transmitted in step S1501 in the RLC layer (step S1505). The control unit 110 may identify the RLC SDU to be retransmitted based on an indication from the MAC layer. The RLC SDU to be retransmitted may be an RLC SDU that the base station apparatus 20 has not confirmed to have been received successfully. In other words, when an indication is received from the MAC layer for an RLC SDU for which no ACK is indicated, the control unit 110 may consider the RLC SDU to be retransmitted.

[0193] Next, the control unit 110 sets "1" in the P field of the RLC header of the AMD PDU corresponding to the RLC SDU identified as the retransmission target in step S1505 in the RLC layer (step S1506). That is, when an RLC SDU is identified as the retransmission target based on an instruction from the MAC layer, a poll may be included in the AMD PDU corresponding to the RLC SDU.

[0194] Next, the control unit 110 adds an RLC header to the RLC SDU identified as the retransmission target in the RLC layer to form a new AMD PDU, and passes the AMD PDU to the lower layer (step S1507). Through this process, the communication unit 120 may retransmit the AMD PDU to the RLC entity of the base station apparatus 20 via the lower layer.

[0195] The process shown in Fig. 15 may be executed only when the terminal device 10 is designated in advance to execute the process. For example, when configuration information for RLC retransmission is set, the terminal device 10 may execute the process. Furthermore, the process shown in Fig. 15 may be executed only when a parameter used to determine whether to perform retransmission in the process of Fig. 15, such as a predetermined threshold value for the number of retransmissions of HQRQ, is notified. That is, the configuration information for RLC retransmission may be a predetermined threshold value for the number of retransmissions of HQRQ, etc.

[0196] 2.2. Data Type Determination In the process shown in Figure 15, an RLC SDU is retransmitted based on the number of HARQ retransmissions reaching a threshold. As another example of the process shown in Figure 15, an RLC SDU may be retransmitted based on the number of HARQ retransmissions reaching a threshold for data having a specific type.

[0197] The data having a specific type may be low-delay requirement data. For example, the data having a specific type may be delay-critical data. That is, the data may be an SDU determined to be "delay-critical" in the PDCP layer. In this case, a timer such as a PDCP discard timer is compared with a remaining time threshold in the PDCP layer. The data having a specific type may also be an SDU determined to be "delay-critical" in the RLC layer. For example, the data having a specific type may be data (e.g., an RLC SDU) for which the remaining time until the PDU retransmission timer expires in the RLC layer is below the remaining time threshold.

[0198] Furthermore, data having a specific type may be determined based on a value indicating the importance or priority of the data, such as a PSI. The importance or priority of the data may be determined in the PDCP layer or the RLC layer. Hereinafter, in this embodiment, data determined to be delay-critical or to have a specific importance / priority is data having a first type and is referred to as "specific data." On the other hand, data determined to be not delay-critical and / or not to have a specific importance / priority is data having a second type and is referred to as "normal data."

[0199] A procedure for retransmitting an RLC SDU according to another example of this embodiment will be described with reference to Fig. 17. The matters mentioned for the process shown in Fig. 15 also apply to the process shown in Fig. 17.

[0200] 17 , the terminal device 10 performs processing in the PDCP layer and the RLC layer. These processings are performed by the control unit 110 and the communication unit 120, but in the PDCP layer, the processing is performed by a PDCP entity implemented by the control unit 110. In addition, in the RLC layer, the processing is performed by an AM RLC entity implemented by the control unit 110.

[0201] First, when the control unit 110 receives a PDCP SDU from an upper layer in the PDCP layer, the control unit 110 determines the type of data, i.e., whether it is specific data or normal data (step S1701). As described above, the type of data may be determined based on whether the PDCP SDU is "low delay requirement data" or the value of the PSI. Alternatively, the process of step S1701 may be performed in the RLC layer. In this case, the type of data may be determined based on whether the RLC SDU is "low delay requirement data" or the like, as described above.

[0202] Next, the control unit 110 adds a PDCP header to the PDCP SDU in the PDCP layer to generate a PDCP PDU, and passes the PDCP PDU to the RLC layer (step S1702).

[0203] Next, when the RLC layer receives a PDCP PDU (RLC SDU) from the PDCP layer, it adds an RLC header to the RLC SDU to generate an RLC PDU (AMD PDU) and passes it to the lower layer (step S1703). Through this process, the communication unit 120 transmits the AMD PDU to the RLC entity of the base station device 20 via the lower layer. Note that the process shown in FIG. 11 may be executed simultaneously in step S1703.

[0204] Next, the control unit 110 counts the number of HARQ retransmissions for data having a specific type in the MAC layer as a result of the process of step S1701 (step S1704). The details of counting the number of HARQ retransmissions are the same as the process of step S1502 in Fig. 15, and therefore a detailed description thereof will be omitted.

[0205] Next, the control unit 110 determines whether the number of HARQ retransmissions counted in step S1704 has reached a threshold in the MAC layer (step S1705). If the number of HARQ retransmissions has reached the threshold (Yes in step S1705), the control unit 110 provides an indication to the RLC layer requesting retransmission of the RLC SDU (step S1706).

[0206] Next, the control unit 110 identifies an RLC SDU to be retransmitted from among the RLC SDUs corresponding to the AMD PDU transmitted in step S1703 in the RLC layer (step S1707). The control unit 110 may identify the RLC SDU to be retransmitted based on an indication from the MAC layer. The RLC SDU to be retransmitted may be an RLC SDU that the base station apparatus 20 has not confirmed to have been received successfully. That is, when an indication is received from the MAC layer for an RLC SDU for which no ACK is indicated, the control unit 110 may consider the RLC SDU to be retransmitted.

[0207] Next, in the RLC layer, the control unit 110 sets "1" in the P field of the RLC header for the AMD PDU corresponding to the RLC SDU identified as the retransmission target in step S1707 (step S1708).

[0208] Next, the control unit 110 adds an RLC header to the RLC SDU identified as the retransmission target in the RLC layer to form a new AMD PDU, and passes the AMD PDU to the lower layer (step S1709). Through this process, the communication unit 120 may retransmit the AMD PDU to the RLC entity of the base station apparatus 20 via the lower layer.

[0209] As described above, the second embodiment has been described. In the second embodiment, the transmitting AM RLC entity considers an RLC SDU to be retransmitted based on the number of HARQ retransmissions reaching a threshold, regardless of whether a STATUS PDU is received. Therefore, the second embodiment can also reduce the time required for retransmission of an RLC SDU.

[0210] In the sidelink communication, sidelink control information (SCI) is transmitted from the base station device 20 to the terminal device 10 to schedule a physical sidelink shared channel (PSSCH). The HARQ process number, NDI, and RV are also included in SCI format 1-A, etc. Therefore, when the second embodiment is applied to the sidelink communication, the number of HARQ retransmissions may be determined based on the value of the NDI, etc. indicated by the SCI.

[0211] 3. Third Embodiment 3.1 Retransmission Based on Available Resource Capacity Next, a third embodiment will be described. In the third embodiment, an example will be described in which an RLC SDU is retransmitted when the available resource capacity on the transmitting side is equal to or greater than a predetermined amount.

[0212] The terminal device 10 generates a Medium Access Control Protocol Data Unit (MAC PDU) for uplink transmission in accordance with an uplink grant from the base station device 20. When a new transmission is to be performed, the terminal device 10 multiplexes data from different logical channels (Logical CHannel, LCH) to generate a MAC PDU. At this time, the terminal device 10 generates the MAC PDU in accordance with Logical Channel Prioritization (LCP). LCP is a priority process for multiplexing data from different LCHs.

[0213] The 3GPP 5G NR technical specifications stipulate that the MAC entity reports to the base station how much data is in the buffer. This report is called a buffer status report (BSR). In the BSR, LCHs are assigned to logical channel groups (LCGs). Each LCG includes one or more LCHs. The terminal device 10 calculates the buffer size of uplink data for each LCG. The terminal device 10 transmits the buffer size corresponding to each LCG as a BSR to the base station device 20.

[0214] In this embodiment, if there is no data available in the buffer for transmission and there are remaining resources, the RLC SDU is retransmitted.

[0215] The procedure for retransmitting an RLC SDU according to this embodiment will be described with reference to Fig. 18. In this embodiment, an example will also be described in which the terminal device 10 retransmits an RLC SDU to the base station device 20 in uplink communication.

[0216] 18 , the terminal device 10 performs processing in the RLC layer and the MAC layer. These processings are performed by the control unit 110 and the communication unit 120, but in the RLC layer, the processing is performed by an AM RLC entity implemented by the control unit 110. In addition, in the MAC layer, the processing is performed by a MAC entity implemented by the control unit 110.

[0217] In step S1801, when the control unit 110 receives a PDCP PDU (RLC SDU) from the PDCP layer in the RLC layer, it adds an RLC header to the RLC SDU to generate an RLC PDU (AMD PDU) and passes it to a lower layer. Through this process, the communication unit 120 transmits the RLC SDU to the RLC entity of the base station device 20 via the lower layer. Note that the process shown in FIG. 11 may be executed simultaneously in step S1801.

[0218] Next, the control unit 110 determines whether there is data available for transmission in the buffer at the MAC layer and / or the RLC layer and whether there are remaining resources (step S1802). The determination of whether there is available data at step S1802 may be based on whether the transmission buffer and / or the retransmission buffer (e.g., at the RLC layer) is empty. That is, if the transmission buffer and / or the retransmission buffer is empty, it may be determined that there is no available data. The determination of whether there is available data at step S1802 may also be based on whether data from all LCHs selected in the resource allocation (e.g., at the MAC layer) has been used up. That is, if data from all LCHs selected in the resource allocation has been used up, it may be determined that there is no available data. The determination of whether there are remaining resources at step S1802 may be performed after determining that there is no available data. The determination of whether there are remaining resources at step S1802 may also be based on whether the remaining resources are equal to or greater than a predetermined amount. That is, after determining that no data is available, if the remaining resources are equal to or greater than a predetermined amount, it may be determined that there are remaining resources. The predetermined amount may be zero, or may be the sum of the size of the data to be retransmitted in the process described below and its subheader.

[0219] As a result of the processing in step S1802, if there is no data available for transmission in the buffer and resources remain (Yes in step S1802), the control unit 110 may provide an indication to the RLC layer to retransmit the RLC SDU (step S1803).

[0220] Next, when an indication is provided in the RLC layer in step S1804, the control unit 110 identifies an RLC SDU to be retransmitted from among the RLC SDUs transmitted in step S1801 (step S1804). The RLC SDU to be retransmitted may be an RLC SDU for which the base station apparatus 20 has not confirmed that it has received it correctly. That is, when an indication is provided from the MAC layer for an RLC SDU for which no ACK is provided, the control unit 110 may consider the RLC SDU to be retransmitted. The details of identifying the RLC SDU to be retransmitted are the same as those of step S1206 in FIG. 12, and therefore a detailed description thereof will be omitted.

[0221] Next, in the RLC layer, the control unit 110 sets "1" in the P field of the RLC header for the AMD PDU corresponding to the RLC SDU identified as the retransmission target in step S1804 (step S1805).

[0222] Next, the control unit 110 adds an RLC header to the RLC SDU identified as the retransmission target in the RLC layer to form a new AMD PDU, and passes the AMD PDU to the lower layer (step S1806). Through this process, the communication unit 120 may retransmit the AMD PDU to the RLC entity of the base station apparatus 20 via the lower layer.

[0223] As described above, in the process shown in Fig. 18, the execution of LCP determines whether there is data available for transmission, but the execution of LCP is not necessarily required. In this case, the control unit 110 determines whether there is data available in the buffer, regardless of the LCH / LCG.

[0224] The processing shown in Fig. 18 may be executed only when it is specified in advance that the terminal device 10 executes the processing. For example, when setting information for RLC retransmission is set, the terminal device 10 may execute the processing. Furthermore, the processing shown in Fig. 18 may be executed only when a parameter used to determine whether to perform retransmission in the processing of Fig. 18 is notified.

[0225] 3.2. Data Type Determination In the process shown in Figure 18, an RLC SDU is retransmitted when the available resource capacity is equal to or greater than a predetermined amount. As another example of the process shown in Figure 18, for data having a specific type, an RLC SDU may be retransmitted when the available resource capacity is equal to or greater than a predetermined amount.

[0226] A procedure for retransmitting an RLC SDU according to another example of this embodiment will be described with reference to Fig. 19. The matters mentioned for the process shown in Fig. 18 also apply to the process shown in Fig. 19.

[0227] 19 , the terminal device 10 performs processing in the PDCP layer and the RLC layer. These processings are performed by the control unit 110 and the communication unit 120, but in the PDCP layer, the processing is performed by a PDCP entity implemented by the control unit 110. In addition, in the RLC layer, the processing is performed by an AM RLC entity implemented by the control unit 110.

[0228] First, when the control unit 110 receives a PDCP SDU from an upper layer in the PDCP layer, the control unit 110 determines the type of data, i.e., whether the data is specific data or normal data (step S1901). The details of determining the type of data are the same as the process in step S1701 in Fig. 17, and therefore detailed description thereof will be omitted.

[0229] Next, the control unit 110 adds a PDCP header to the PDCP SDU in the PDCP layer to generate a PDCP PDU, and passes the PDCP PDU to the RLC layer (step S1902).

[0230] Next, when the RLC layer receives a PDCP PDU (RLC SDU) from the PDCP layer, it adds an RLC header to the RLC SDU to generate an RLC PDU (AMD PDU) and passes it to the lower layer (step S1903). Through this process, the communication unit 120 transmits the AMD PDU to the RLC entity of the base station device 20 via the lower layer. Note that the process shown in FIG. 11 may be executed simultaneously in step S1903.

[0231] Next, the control unit 110 determines in the MAC layer, as a result of the process of step S1901, whether data available for transmission for the specific type of data exists in the buffer and whether resources remain (step S1904). The details of this determination are the same as the process of step S1802 in Fig. 18, and therefore a detailed description thereof will be omitted.

[0232] If the result of the process in step S1904 shows that there is no data available for transmission in the buffer and resources remain (Yes in step S1904), the control unit 110 provides an indication to the RLC layer to retransmit the RLC SDU (step S1905).

[0233] Next, the control unit 110 identifies an RLC SDU to be retransmitted from among the RLC SDUs corresponding to the AMD PDU transmitted in step S1903 in the RLC layer (step S1906). The RLC SDU to be retransmitted may be an RLC SDU that the base station apparatus 20 has not confirmed as having received successfully. That is, when an indication is received from the MAC layer for an RLC SDU for which no ACK is indicated, the control unit 110 may consider the RLC SDU to be retransmitted. The details of identifying the RLC SDU to be retransmitted are the same as those of step S1206 in FIG. 12, and therefore will not be described in detail here.

[0234] Next, the control unit 110 sets "1" in the P field of the RLC header for the RLC layer corresponding to the RLC SDU identified as the retransmission target in step S1906 (step S1907).

[0235] Next, the control unit 110 adds an RLC header to the RLC SDU identified as the retransmission target in the RLC layer to form a new AMD PDU, and passes the AMD PDU to the lower layer (step S1908). Through this process, the communication unit 120 may retransmit the AMD PDU to the RLC entity of the base station apparatus 20 via the lower layer.

[0236] As described above, the third embodiment has been described. In the third embodiment, regardless of whether a STATUS PDU is received or not, the transmitting AM RLC entity retransmits the RLC SDU when there is no data available for transmission in the buffer and resources remain. Therefore, the third embodiment also reduces the time required for retransmission of the RLC SDU.

[0237] 4. Fourth Embodiment Next, a fourth embodiment will be described. In the fourth embodiment, the receiving AM RLC entity notifies the transmitting AM RLC entity of the reception result of the RLC SDU for data having a specific type within a shorter time.

[0238] As mentioned above, to determine whether to include a poll in an AMD PDU, the transmitting AM RLC entity compares a counter that counts the number of AMD PDUs / bytes transmitted by the transmitting AM RLC entity with a threshold. The counter uses PDU_WITHOUT_POLL and BYTE_WITHOUT_POLL, as described in Non-Patent Document 1. The threshold uses PollPDU and PollByte, as described in Non-Patent Document 1.

[0239] In this embodiment, counters different from PDU_WITHOUT_POLL and BYTE_WITHOUT_POLL (e.g., DELAY_PDU_WITHOUT_POLL and DELAY_BYTE_WITHOUT_POLL) may be used for data of a specific type (e.g., delay-critical data, specific data). That is, the counter to be used may be determined based on whether the data has a specific type. The transmitting AM RLC entity may increment DELAY_PDU_WITHOUT_POLL by one instead of PDU_WITHOUT_POLL every time it transmits an AMD PDU corresponding to data of a specific type. In this case, PDU_WITHOUT_POLL and DELAY_PDU_WITHOUT_POLL may also be incremented by one. Note that the AMD PDU may be an RLC SDU that has not been transmitted before, or an AMD PDU that includes an RLC SDU segment.

[0240] Alternatively, the transmitting AM RLC entity may increment DELAY_PDU_WITHOUT_POLL instead of PDU_WITHOUT_POLL by the number of bytes in the data field of the AMD PDU each time it transmits an AMD PDU corresponding to data of a specific type. In this case, PDU_WITHOUT_POLL and DELAY_PDU_WITHOUT_POLL may be incremented by the number of bytes in the data field of the AMD PDU. Note that the AMD PDU may be an AMD PDU containing a previously untransmitted RLC SDU or an RLC SDU segment. If a poll is included in an AMD PDU corresponding to data of a specific type, the transmitting AM RLC entity may set DELAY_PDU_WITHOUT_POLL and DELAY_BYTE_WITHOUT_POLL to '0'. If a poll is included in an AM RLC PDU corresponding to data that does not have a specific type (e.g., non-delay critical data, normal data), the transmitting AM RLC entity may not set DELAY_PDU_WITHOUT_POLL and DELAY_BYTE_WITHOUT_POLL to "0".

[0241] In addition, in this embodiment, for data having a specific type, for example, PollPDU-R19 and PollByte-R19 may be used instead of PollPDU and PollByte. A value smaller than PollPDU may be set for PollPDU-R19. Similarly, a value smaller than PollByte may be set for PollByte-R19.

[0242] As described above, the transmitting AM RLC entity includes a poll in an AMD PDU when the counter that counts the number of AMD PDUs / bytes transmitted by the transmitting AM RLC entity reaches a threshold. Therefore, by using PollPDU-R19 and PollByte-R19, which are set to values ​​smaller than PollPDU and PollByte, a poll can be included in an AMD PDU within a shorter time for data of a specific type. Furthermore, by using a counter for data of a specific type, a poll can be included in an AMD PDU at an appropriate timing.

[0243] As mentioned above, when the timer used by the receiving AM RLC entity to detect the loss of an AMD PDU expires, the receiving AM RLC entity is triggered to transmit a STATUS PDU. For this timer, the t-Reassembly described in Non-Patent Document 1 is used.

[0244] In this embodiment, for example, t-Reassembly-R19 is used instead of t-Reassembly for data having a specific type. t-Reassembly-R19 is set to a value smaller than t-Reassembly.

[0245] As described above, the receiving AM RLC entity may be triggered to transmit a STATUS PDU when t-Reassembly expires. Therefore, by using t-Reassembly-R19, which is set to a value smaller than t-Reassembly, it is possible to transmit a STATUS PDU within a shorter time for data of a specific type.

[0246] Furthermore, it has been mentioned above that when the timer used by the transmitting AM RLC entity to retransmit a poll expires, the transmitting AM RLC entity transmits an AMD PDU containing a poll, and for this timer, the t-PollRetransmit timer described in Non-Patent Document 1 is used.

[0247] In this embodiment, for example, t-PollRetransmit-R19 may be used instead of t-PollRetransmit for data having a specific type. t-PollRetransmit-R19 may be set to a value smaller than t-PollRetransmit. The transmitting AM RLC entity may (re)initiate t-PollRetransmit-R19 instead of t-PollRetransmit based on transmitting an AMD PDU corresponding to data having a specific type and including a poll to a lower layer. The transmitting AM RLC entity may also (re)initiate t-PollRetransmit based on transmitting an AMD PDU corresponding to data not having a specific type and including a poll to a lower layer. That is, when the transmitting AM RLC entity transmits an AMD PDU including a poll to a lower layer, it may select a timer to start based on whether the AMD PDU contains data of a specific type. t-PollRetransmit-R19 may be stopped (or reset) based on receiving a STATUS PDU indicating an ACK or NACK for the corresponding RLC SDU. If t-PollRetransmit-R19 expires, RLC SDUs corresponding to data of a particular type that have not yet received an ACK may be considered for retransmission.

[0248] As described above, the transmitting AM RLC entity transmits an AMD PDU including a poll in response to the expiration of t-PollRetransmit. Therefore, by using t-PollRetransmit-R19, which is set to a value smaller than t-PollRetransmit, it is possible to include a poll in an AMD PDU within a shorter time for data of a specific type.

[0249] Furthermore, as mentioned above, the receiving AM RLC entity does not transmit a STATUS PDU while the timer used to prohibit the receiving AM RLC entity from transmitting a STATUS PDU is running. For this timer, the t-StatusProhibit timer described in Non-Patent Document 1 is used.

[0250] In this embodiment, for data having a specific type, for example, t-StatusProhibit-R19 is used instead of t-StatusProhibit, and a value smaller than t-StatusProhibit is set for t-StatusProhibit-R19.

[0251] As described above, when t-StatusProhibit is active, the receiving AM RLC entity does not transmit a STATUS PDU. Therefore, by using t-StatusProhibit-R19, which is set to a value smaller than t-StatusProhibit, the time during which STATUS PDU transmission is restricted for data of a specific type is shortened, and as a result, STATUS PDUs can be transmitted within a shorter time.

[0252] For data having a specific type, it is not necessary to use all of the above-described PollPDU-R19, PollByte-R19, t-Reassembly-R19, t-PollRetransmit-R19, and t-StatusProhibit-R19, and some of them may be used. For example, for data having a specific type, PollPDU-R19 and PollByte-R19 with smaller values ​​set may be used, and t-Reassembly, t-PollRetransmit, and t-StatusProhibit described in Non-Patent Document 1 may be used. PollPDU-R19, PollByte-R19, t-Reassembly-R19, t-PollRetransmit-R19, and t-StatusProhibit-R19 may be transmitted from the base station device 20 to the terminal device 10 via an RRC message. For example, they may be included in an RLC-Config IE. When PollPDU-R19, PollByte-R19, t-Reassembly-R19, t-PollRetransmit-R19, and t-StatusProhibit-R19 are configured via an RRC message, the configured parameters may be used for data having a specific type.

[0253] Alternatively, for data of a particular type, the counter that counts the number of AMD PDUs / bytes transmitted by the transmitting AM RLC entity may be incremented by a larger number. For example, each time an AMD PDU is transmitted, PDU_WITHOUT_POL is incremented as follows: PDU_WITHOUT_POLL = PDU_WITHOUT_POLL + N, where N is a number equal to or greater than 2. Each time an AMD PDU is transmitted, the transmitting AM RLC entity increments BYTE_WITHOUT_POLL as follows: BYTE_WITHOUT_POLL = BYTE_WITHOUT_POLL + (Byte of AMD PDU * N) or BYTE_WITHOUT_POLL = BYTE_WITHOUT_POLL + (Byte of AMD PDU + M). Byte of RLC SDU is the number of bytes in the data field of the AMD PDU, N is a number equal to or greater than 2, and M is a number equal to or greater than 1.

[0254] As described in the second embodiment, data having a specific type is data that is determined to be delay-critical or to have a specific level of importance / priority, that is, data having a first type, and is referred to as “specific data.” In contrast to the specific data, data that is determined to not be delay-critical and / or not to have a specific level of importance / priority is data having a second type, and is referred to as “normal data.”

[0255] The procedure for transmitting a STATUS PDU and retransmitting an RLC SDU according to this embodiment will be described with reference to Fig. 20. In this embodiment, an example will also be described in which a terminal device 10 retransmits an RLC SDU to a base station device 20 in uplink communication.

[0256] 20 , the terminal device 10 performs processing in the PDCP layer and the RLC layer. These processings are performed by the control unit 110 and the communication unit 120, but in the PDCP layer, the processing is performed by a PDCP entity implemented by the control unit 110. In addition, in the RLC layer, the processing is performed by an AM RLC entity implemented by the control unit 110.

[0257] 20, the terminal device 10 transmits 10 AMD PDUs consecutively corresponding to 10 RLC SDUs (or RLC SDU segments). At least one of PollPDU-R19, PollByte-R19, and t-PollRetransmit-R19 may be used to determine whether or not to include a poll in the AMD PDU.

[0258] First, when the control unit 110 receives a PDCP SDU from an upper layer in the PDCP layer, the control unit 110 determines the type of data, i.e., whether the data is specific data or normal data (step S2001). The details of determining the type of data are the same as the process in step S1701 in Fig. 17, and therefore detailed description thereof will be omitted.

[0259] As a result of the process of step S2001, the terminal device 10 increments a counter that counts the number of AMD PDUs / bytes in the RLC layer based on the AMD PDUs to be transmitted (step S2002). The increment of the counter that counts the number of AMD PDUs / bytes is the same as the process described with reference to Fig. 11. The number of AMD PDUs / bytes to be transmitted by the transmitting AM RLC entity may be incremented by a larger number.

[0260] Next, the control unit 110 checks whether the result of the process in step S2001 in the RLC layer satisfies the condition PDU_WITHOUT_POLL >= PollPDU-R19 or BYTE_WITHOUT_POLL >= PollByte-R19 for the specific data (step S2003). Note that as a result of the process in step S2001, PollPDU and PollByte may be used for normal data instead of PollPDU-R19 and PollByte-R19.

[0261] If the above condition is met as a result of the processing in step S2003 (Yes in step S2003), the control unit 110 sets "1" in the P field in the header added to the RLC SDU in the RLC layer (step S2004). If the above condition is not met (No in step S2003), the control unit 110 sets "0" in the P field in the RLC layer (step S2005).

[0262] Next, the control unit 110 sets values ​​corresponding to each of the 10 RLC SDUs (or RLC SDU segments) in the SN field in the RLC header in the RLC layer (step S2006). After setting predetermined values ​​in the other fields in the RLC header in the RLC layer, the control unit 110 adds a header to the RLC SDU to generate an AMD PDU and passes it to lower layers (step S2007). Through this process, the communication unit 120 transmits the AMD PDU to the RLC entity of the base station device 20 via the lower layers.

[0263] When the control unit 210 of the base station device 20 receives the AMD PDU in the RLC layer, it determines whether to trigger transmission of a STATUS PDU based on the value of the P field in the header (step S2008). As a result, if "1" is set in the P field (Yes in step S2008), the control unit 210 generates a STATUS PDU with an ACK or NACK set, indicating whether the RLC SDU was received normally, and passes the STATUS PDU to the lower layer (step S2009). Through this process, the communication unit 220 transmits the STATUS PDU to the RLC entity of the terminal device 10 via the lower layer.

[0264] If "0" is set in the P field (No in step S2008), the control unit 210 does not need to transmit a STATUS PDU in the RLC layer.

[0265] Furthermore, the control unit 210 of the base station device 20 may start t-Reassembly-R19 in the RLC layer upon receiving an AMD PDU (step S2010). Note that t-Reassembly may be used for normal data instead of t-Reassembly-R19. In order for the base station device 20 to determine whether to use t-Reassembly or t-Reassembly-R19, the terminal device 10 may notify the base station device 20 of the type of data by, for example, setting a value indicating the type of data in the RLC header.

[0266] Even if the P field is set to "1", a STATUS PDU is not transmitted if t-StatusProhibit-R19 is active. t-StatusProhibit-R19 is also initiated by the control unit 210 for specific data. A STATUS PDU may also be transmitted if t-Reassembly-R19 expires.

[0267] The control unit 110 of the terminal device 10 may initiate t-PollRetransmit-R19 after passing an AMD PDU corresponding to data having a specific type to a lower layer in the RLC layer. If PollRetransmit-R19 expires before the terminal device 10 receives a STATUS PDU indicating an ACK or NACK for the corresponding RLC SDU, the control unit 110 transmits an AMD PDU including a poll in the RLC layer. t-PollRetransmit-R19 may be stopped or reset in response to receiving a STATUS PDU indicating an ACK or NACK for the corresponding RLC SDU.

[0268] When the control unit 110 receives a STATUS PDU in the RLC layer, the control unit 110 checks whether the STATUS PDU indicates ACK or NACK (step S2011). If the STATUS PDU indicates ACK (Yes in step S2011), the control unit 110 may notify the upper layer that the RLC SDU was successfully received and update TX_NEXT_ACK (step S2012).

[0269] If the STATUS PDU indicates a NACK (No in step S2011), the control unit 110 determines an AMD PDU to be retransmitted in the RLC layer based on the value of the NACK_SN field of the STATUS PDU and passes the AMD PDU to a lower layer (step S2013). Through this process, the communication unit 120 retransmits the STATUS PDU to the RLC entity of the base station device 20 via the lower layer. The NACK_SN field may be set to the sequence number set in the RLC SDU of the AMD PDU that the base station device 20 was unable to receive successfully. Thus, the terminal device 10 can identify one or more RLC SDUs to be retransmitted based on the value of the NACK_SN field of the PDU.

[0270] 20 may be executed when the terminal device 10 is designated in advance to execute the process. For example, when setting information related to a poll is set, the terminal device 10 may execute the process. For example, when setting information related to a poll is set, the terminal device 10 may execute the above-described process for data having a specific type.

[0271] 20 may be executed only when a parameter used to determine whether to perform transmission including a poll in the processing of Fig. 20, such as PollPDU-R19, PollByte-R19, t-Reassembly-R19, t-PollRetransmit-R19, and / or t-StatusProhibit-R19, is notified. That is, the setting information related to a poll may be PollPDU-R19, PollByte-R19, t-Reassembly-R19, t-PollRetransmit-R19, and / or t-StatusProhibit-R19.

[0272] As described above, the fourth embodiment has been described. In the fourth embodiment, the transmitting AM RLC entity is notified of the reception result of the RLC SDU for specific data within a shorter period of time. Therefore, the fourth embodiment also reduces the time required for retransmission of the RLC SDU.

[0273] 5. Modifications Although the embodiments for carrying out the present invention have been described above, the present invention is not limited to the above-described embodiments. It is to be understood that the above-described embodiments are merely examples and that various modifications are possible. Furthermore, the order of steps in the methods according to the embodiments does not necessarily have to be performed in the order shown, and the steps may be performed in a different order, some steps may be omitted, or other steps not shown may be added.

[0274] All embodiments of the present disclosure are applicable to uplink communication, downlink communication, and sidelink communication. Therefore, the entities that execute the processes in the embodiments are a transmitting device and a receiving device, both of which are referred to as communication devices. The transmitting communication device is referred to as a "first communication device," and the receiving communication device is referred to as a "second communication device."

[0275] The words, phrases, and other expressions used in the above embodiments are merely examples and may be replaced with substantially identical or similar expressions. In particular, since the technology according to the above embodiments relates to technical specifications, the expressions in the above embodiments may be replaced with substantially identical or similar expressions in technical specifications (e.g., technical specifications cited in this specification).

[0276] The information transmitted and received in the above embodiment may be contained in the same or a different message or element already described in the technical specifications, or may be contained in a newly defined message or element. The information transmitted and received in the above embodiment may be transmitted and received using a different layer and / or a different channel than those in the above embodiment.

[0277] The means and / or functions provided by the devices described in the above embodiments can be provided by software recorded in a tangible memory device and a computer that executes the software, software alone, hardware alone, or a combination thereof. For example, if any of the above devices is provided by an electronic circuit that is hardware, it can be provided by a digital circuit including a large number of logic circuits, or an analog circuit.

[0278] The device described in the above embodiment executes a program stored in a non-transitory tangible storage medium, and the execution of the program executes a method corresponding to the program.

[0279] 6. Supplementary Note: Some or all of the above-described embodiments and modified examples may also be described as in the following supplementary notes, but are not limited to the contents of the supplementary notes. Hereinafter, a relationship is expressed in which a supplementary note that is dependent on multiple supplementary notes is dependent on another supplementary note that is dependent on multiple supplementary notes. All of the dependency relationships of the supplementary notes expressed below are included in the above-described embodiments.

[0280] (Supplementary Note 1) A first communication device (10) comprising a control unit (110) and a communication unit (120), wherein the control unit and the communication unit: start a timer; transmit a protocol data unit (PDU) to a second communication device (20); determine whether the remaining time of the timer is below a threshold value of the remaining time until the PDU is received by the second communication device; and retransmit the PDU to the second communication device in response to determining that the remaining time is below the threshold value.

[0281] (Supplementary Note 2) The first communication device according to Supplementary Note 1, wherein when the control unit and the communication unit retransmit the PDU, the control unit and the communication unit include a poll in the PDU to be retransmitted.

[0282] (Supplementary Note 3) The first communication device according to Supplementary Note 1 or 2, wherein the control unit and the communication unit, in a Packet Data Convergence Protocol (PDCP) layer, start the timer; determine whether the remaining time is below the remaining time threshold; provide an indication to a Radio Link Control (RLC) layer in response to determining that the remaining time is below the remaining time threshold; and retransmit the PDU to the second communication device in the RLC layer in response to the indication.

[0283] (Supplementary Note 4) The first communication device described in Supplementary Note 1 or 2, wherein the control unit and the communication unit, in the RLC layer, start the timer, determine whether the remaining time is below the remaining time threshold, and retransmit the PDU to the second communication device in response to determining that the remaining time is below the remaining time threshold.

[0284] (Supplementary Note 5) The first communication device described in any one of Supplementary Notes 1 to 4, wherein the control unit and the communication unit: determine whether the PDU has a specific type; if it is determined that the PDU has the specific type, start the timer; determine whether the remaining time is below the remaining time threshold; and in response to determining that the remaining time is below the remaining time threshold, retransmit the PDU to the second communication device.

[0285] (Supplementary Note 6) The first communication device according to Supplementary Note 5, wherein determining whether the PDU has a specific type is based on an importance level set for the data.

[0286] (Supplementary Note 7) The first communication device according to Supplementary Note 5, wherein determining whether the PDU has a particular type is based on a priority set for the data.

[0287] (Supplementary Note 8) The first communication device described in any one of Supplementary Notes 1 to 7, wherein the control unit and the communication unit receive a parameter, start the timer according to the value of the parameter, determine whether the remaining time is below the remaining time threshold, and retransmit the PDU to the second communication device in response to determining that the remaining time is below the remaining time threshold.

[0288] (Supplementary Note 9) The first communication device according to Supplementary Note 8, wherein the parameter indicates whether or not the first communication device performs the determining and the retransmitting.

[0289] (Supplementary Note 10) The first communication device according to Supplementary Note 8, wherein the parameters include the timer.

[0290] (Supplementary Note 11) The first communication device according to Supplementary Note 8 or 10, wherein the parameters include the remaining time threshold.

[0291] (Supplementary Note 12) The first communication device according to any one of Supplementary Notes 1 to 11, wherein the control unit and the communication unit: include a poll in the PDU to be transmitted when transmitting the PDU; receive a report from the second communication device indicating a reception result of the PDU; retain a sequence number set in the PDU that was successfully received by the second communication device based on the report; and identify the PDU to be retransmitted based on the sequence number.

[0292] (Supplementary Note 13) A method performed by a first communication device (10), comprising: starting a timer; transmitting a Protocol Data Unit (PDU) to a second communication device (20); determining whether the remaining time of the timer is below a threshold time remaining until the PDU is received by the second communication device; and retransmitting the PDU to the second communication device in response to determining that the remaining time is below the threshold time remaining.

[0293] (Supplementary Note 14) A program that, when executed, causes a processor (101) in a first communication device (10) to: start a timer; transmit a protocol data unit (PDU) to a second communication device (20); determine whether the remaining time of the timer is below a threshold value for the remaining time until the PDU is received by the second communication device; and retransmit the PDU to the second communication device in response to determining that the remaining time is below the threshold value.

[0294] (Supplementary Note 15) A computer-readable non-transitory tangible recording medium having stored thereon a program that, when executed, causes a processor (101) in a first communication device (10) to perform the following: start a timer; transmit a Protocol Data Unit (PDU) to a second communication device (20); determine whether the remaining time of the timer is below a threshold value for the remaining time until the PDU is received by the second communication device; and retransmit the PDU to the second communication device in response to determining that the remaining time is below the threshold value.

[0295] (Supplementary Note 16) A first communication device (10) comprising a control unit (110) and a communication unit (120), wherein the control unit and the communication unit: transmit a Protocol Data Unit (PDU) to a second communication device (20); count a number of Hybrid Automatic Repeat reQuest (HARQ) retransmissions; determine whether the number of HARQ retransmissions reaches a threshold; and retransmit the PDU to the second communication device in response to determining that the number of HARQ retransmissions reaches the threshold.

[0296] (Supplementary Note 17) The first communication device according to Supplementary Note 1, wherein when the control unit and the communication unit retransmit the PDU, the control unit and the communication unit include a poll in the PDU to be retransmitted.

[0297] (Supplementary Note 18) The first communication device according to Supplementary Note 16 or 17, wherein the control unit and the communication unit count the number of HARQ retransmissions based on a value of a New Data indicator (NDI) notified by scheduling information.

[0298] (Supplementary Note 19) The first communication device according to Supplementary note 18, wherein the control unit and the communication unit count the number of HARQ retransmissions further based on a HARQ process number notified by scheduling information.

[0299] (Supplementary Note 20) The first communication device according to Supplementary Note 16 or 17, wherein the control unit and the communication unit count the number of HARQ retransmissions based on a value of a redundancy version (RV) notified by scheduling information.

[0300] (Supplementary Note 21) The first communication device according to Supplementary note 20, wherein the control unit and the communication unit count the number of HARQ retransmissions further based on a HARQ process number notified by scheduling information.

[0301] (Supplementary Note 22) The first communication device according to Supplementary Note 16 or 17, wherein the control unit and the communication unit count the number of HARQ retransmissions based on a value of CBG transmission information (CBGTI) notified by scheduling information.

[0302] (Supplementary Note 23) The first communication device according to Supplementary note 22, wherein the control unit and the communication unit count the number of HARQ retransmissions further based on a HARQ process number notified by scheduling information.

[0303] (Supplementary Note 24) The first communication device described in any one of Supplementary Notes 16 to 23, wherein the control unit and the communication unit: determine whether the PDU has a specific type; if it is determined that the PDU has the specific type, count the number of HARQ retransmissions; determine whether the number of HARQ retransmissions reaches a threshold; and retransmit the PDU to the second communication device in response to determining that the number of HARQ retransmissions has reached the threshold.

[0304] (Supplementary Note 25) The first communication device according to Supplementary Note 24, wherein determining whether the PDU has a particular type is based on an importance level set for the data.

[0305] (Supplementary Note 26) The first communication device according to Supplementary Note 24, wherein determining whether the PDU has a particular type is based on a priority set for the data.

[0306] (Supplementary Note 27) The first communication device described in any one of Supplementary Notes 16 to 26, wherein the control unit and the communication unit receive a parameter, count the number of HARQ retransmissions according to the value of the parameter, determine whether the number of HARQ retransmissions reaches a threshold, and retransmit the PDU to the second communication device in response to determining that the number of HARQ retransmissions reaches the threshold.

[0307] (Supplementary Note 28) The first communication device according to Supplementary Note 27, wherein the parameters include the threshold value.

[0308] (Supplementary Note 29) The first communication device described in any one of Supplementary Notes 16 to 28, wherein the control unit and the communication unit: include a poll in the PDU to be transmitted when transmitting the PDU; receive a report from the second communication device indicating a reception result of the PDU; retain a sequence number set in the PDU that was successfully received by the second communication device based on the report; and identify the PDU to be retransmitted based on the sequence number.

[0309] (Supplementary Note 30) A method performed by a first communication device (10), comprising: transmitting a Protocol Data Unit (PDU) to a second communication device (20); counting a number of Hybrid Automatic Repeat reQuest (HARQ) retransmissions; determining whether the number of HARQ retransmissions reaches a threshold; and retransmitting the PDU to the second communication device in response to determining that the number of HARQ retransmissions reaches the threshold.

[0310] (Supplementary Note 31) A program that, when executed, causes a processor (101) in a first communication device (10) to execute the following: transmit a Protocol Data Unit (PDU) to a second communication device (20); count a number of Hybrid Automatic Repeat reQuest (HARQ) retransmissions; determine whether the number of HARQ retransmissions reaches a threshold; and retransmit the PDU to the second communication device in response to determining that the number of HARQ retransmissions reaches the threshold.

[0311] (Supplementary Note 32) A computer-readable non-transitory tangible recording medium storing a program that, when executed, causes a processor (101) in a first communication device (10) to perform the following: transmit a Protocol Data Unit (PDU) to a second communication device (20); count a number of Hybrid Automatic Repeat reQuest (HARQ) retransmissions; determine whether the number of HARQ retransmissions reaches a threshold; and retransmit the PDU to the second communication device in response to determining that the number of HARQ retransmissions reaches the threshold.

[0312] (Supplementary Note 33) A first communication device (10) comprising a control unit (110) and a communication unit (120), wherein the control unit and the communication unit: transmit a protocol data unit (PDU) to a second communication device (20); determine whether available data exists in a buffer and whether resources remain; and retransmit the PDU to the second communication device in response to determining that the available data does not exist in the buffer and that the resources remain.

[0313] (Supplementary Note 34) The first communication device according to Supplementary Note 33, wherein when the control unit and the communication unit retransmit the PDU, the control unit and the communication unit include a poll in the PDU to be retransmitted.

[0314] (Supplementary Note 35) The first communication device according to Supplementary Note 33 or 34, wherein the control unit and the communication unit determine, in a Media Access Control (MAC) layer, whether the available data exists in a buffer and whether the resources remain, provide an indication to a Radio Link Control (RLC) layer in response to determining that the available data does not exist in the buffer and that the resources remain, and retransmit the PDU to the second communication device in the RLC in response to the indication.

[0315] (Supplementary Note 36) The first communications device according to any one of Supplementary Notes 33 to 35, wherein determining whether there is available data in a buffer comprises determining whether resources are allocated for transmission, and determining whether there are remaining resources comprises determining whether a number of padding bits is greater than or equal to a size of a Buffer Status Reporting (BSR) MAC CE plus a subheader.

[0316] (Supplementary Note 37) The first communication device described in any one of Supplementary Notes 33 to 36, wherein the control unit and the communication unit: determine whether the PDU has a specific type; if it is determined that the PDU has the specific type, determine whether the available data exists in the buffer and whether the resources remain; and in response to determining that the available data does not exist in the buffer and that the resources remain, retransmit the PDU to the second communication device.

[0317] (Supplementary Note 38) The first communication device according to Supplementary Note 37, wherein determining whether the PDU has a particular type is based on an importance level set for the data.

[0318] (Supplementary Note 39) The first communication device according to Supplementary Note 37, wherein determining whether the PDU has a particular type is based on a priority set for the data.

[0319] (Supplementary Note 40) The first communication device described in any one of Supplementary Notes 33 to 39, wherein the control unit and the communication unit receive a parameter, determine whether the available data exists in the buffer and whether the resources remain according to the value of the parameter, and retransmit the PDU to the second communication device in response to determining that the available data does not exist in the buffer and that the resources remain.

[0320] (Supplementary Note 41) The first communication device according to Supplementary Note 40, wherein the parameter indicates whether the first communication device performs the determining and the retransmitting.

[0321] (Supplementary Note 42) The first communication device described in any one of Supplementary Notes 33 to 41, wherein the control unit and the communication unit: include a poll in the PDU to be transmitted when transmitting the PDU; receive a report from the second communication device indicating a reception result of the PDU; retain a sequence number set in the PDU that was successfully received by the second communication device based on the report; and identify the PDU to be retransmitted based on the sequence number.

[0322] (Supplementary Note 43) A method performed by a first communication device (10), comprising: transmitting a Protocol Data Unit (PDU) to a second communication device (20); determining whether there is available data in a buffer and whether there are remaining resources; and in response to determining that there is no available data in the buffer and that there are remaining resources, retransmitting the PDU to the second communication device.

[0323] (Supplementary Note 44) A program that, when executed, causes a processor (101) in a first communication device (10) to: transmit a protocol data unit (PDU) to a second communication device (20); determine whether available data exists in a buffer and whether resources remain; and, in response to determining that the available data does not exist in the buffer and that the resources remain, retransmit the PDU to the second communication device.

[0324] (Supplementary Note 45) A computer-readable non-transitory tangible recording medium having stored thereon a program that, when executed, causes a processor (101) in a first communication device (10) to perform the following: transmit a protocol data unit (PDU) to a second communication device (20); determine whether available data exists in a buffer and whether resources remain; and retransmit the PDU to the second communication device in response to determining that the available data does not exist in the buffer and that the resources remain.

[0325] (Supplementary Note 46) A first communication device (10) comprising a control unit (110) and a communication unit (120), wherein the control unit and the communication unit: determine whether a Protocol Data Unit (PDU) to be transmitted has a first type or a second type; if it is determined that the PDU has the first type, determine whether a poll is included in the PDU to be transmitted using a first parameter; if it is determined that the PDU has the second type, determine whether a poll is included in the PDU to be transmitted using a second parameter, wherein the first parameter is set to a value smaller than the second parameter; and transmit the PDU including the poll to a second communication device.

[0326] (Supplementary Note 47) The first communication device according to Supplementary Note 46, wherein the control unit and the communication unit count the number of PDUs to be transmitted and determine whether to include a poll in the PDU to be transmitted by comparing the counted number of PDUs with the first parameter.

[0327] (Supplementary Note 48) The first communication device according to Supplementary Note 46 or 47, wherein the control unit and the communication unit count the number of bytes of the PDU to be transmitted and compare the counted number of bytes with the first parameter to determine whether to include a poll in the PDU to be transmitted.

[0328] (Supplementary Note 49) A first communication device (10) comprising a control unit (110) and a communication unit (120), wherein the control unit and the communication unit: determine whether a Protocol Data Unit (PDU) to be transmitted has a first type or a second type; include a poll in the PDU to be transmitted; transmit the PDU including the poll to a second communication device; if it is determined that the PDU has the first type, use a first parameter to retransmit the PDU including the poll to the second communication device when a report indicating a reception result of the PDU is not received from the second communication device; if it is determined that the PDU has the second type, use a second parameter to retransmit the PDU including the poll to the second communication device when a report indicating a reception result of the PDU is not received from the second communication device, wherein the first parameter is set to a value smaller than the second parameter.

[0329] (Supplementary Note 50) A first communication device (10) comprising a control unit (110) and a communication unit (120), wherein the control unit and the communication unit: determine whether a Protocol Data Unit (PDU) to be transmitted has a first type or a second type; determine whether to include a poll in the PDU to be transmitted by comparing a counter with a threshold; if it is determined that the PDU has the first type, increment the counter by a larger value compared to when it is determined that the PDU has the second type; and transmit the PDU including the poll to a second communication device. The first communication device according to any one of Supplementary Notes 46 to 49.

[0330] (Supplementary Note 51) The first communications device described in any one of Supplementary Notes 46 to 50, wherein the control unit and the communications unit determine whether the PDU has the first type or the second type by: starting a timer; determining whether the remaining time of the timer is below a threshold value for the remaining time until the PDU is received by the second communications device; and retransmitting the PDU to the second communications device in response to determining that the remaining time is below the threshold value.

[0331] (Supplementary Note 52) The first communication device according to any one of Supplementary Notes 46 to 51, wherein the control unit and the communication unit determine whether the PDU has the first type or the second type based on an importance set to data.

[0332] (Supplementary Note 53) The first communication device according to any one of Supplementary Notes 46 to 51, wherein the control unit and the communication unit determine whether the PDU has the first type or the second type based on a priority set for data.

[0333] (Supplementary Note 54) A method executed by a first communication device (10), comprising: determining whether a Protocol Data Unit (PDU) to be transmitted has a first type or a second type; if it is determined that the PDU has the first type, determining whether to include a poll in the PDU to be transmitted using a first parameter; if it is determined that the PDU has the second type, determining whether to include a poll in the PDU to be transmitted using a second parameter, wherein the first parameter is set to a value smaller than the second parameter; and transmitting the PDU including the poll to a second communication device.

[0334] (Supplementary Note 55) A program that, when executed, causes a processor (101) in a first communication device (10) to execute the following: determine whether a Protocol Data Unit (PDU) to be transmitted has a first type or a second type; if it is determined that the PDU has the first type, determine whether a poll is included in the PDU to be transmitted using a first parameter; if it is determined that the PDU has the second type, determine whether a poll is included in the PDU to be transmitted using a second parameter, wherein the first parameter is set to a value smaller than the second parameter; and transmit the PDU including the poll to a second communication device.

[0335] (Supplementary Note 56) A computer-readable non-transient tangible recording medium having stored thereon a program which, when executed, causes a processor (101) in a first communication device (10) to execute the following: determine whether a Protocol Data Unit (PDU) to be transmitted has a first type or a second type; if it is determined that the PDU has the first type, determine whether to include a poll in the PDU to be transmitted using a first parameter; if it is determined that the PDU has the second type, determine whether to include a poll in the PDU to be transmitted using a second parameter, wherein the first parameter is set to a value smaller than the second parameter; and transmit the PDU including the poll to a second communication device.

[0336] The disclosures of the above prior art documents and references are incorporated herein by reference.

Claims

1. A terminal device (10) comprising: a communication unit that receives a Radio Resource Control (RRC) message; and a control unit including a Packet Data Convergence Protocol (PDCP) layer and a Radio Link Control (RLC) layer, wherein the PDCP layer provides an indication to the RLC layer when the remaining time until a discard timer for a PDCP service data unit (SDU) expires falls below the remaining time threshold, based on information indicating a remaining time threshold for retransmission in the RLC layer, which information is included in the RRC message; and the RLC layer receives the indication for an RLC SDU from the PDCP layer and, based on the absence of a positive acknowledgement (ACK) for the RLC SDU, considers the RLC SDU to be a target for retransmission.

2. The terminal device according to claim 1, wherein in the PDCP layer, the indication is an indication for a PDCP packet data unit (PDU) corresponding to the PDCP SDU, and the PDCP layer provides the indication to the RLC layer if the PDCP layer has already submitted the PDCP PDU to the RLC layer.

3. The terminal device according to claim 1, wherein the PDCP layer provides the indication to the RLC layer when the RRC message includes information indicating a remaining time threshold for retransmission in the RLC layer.

4. The terminal device according to claim 1, wherein the RRC message includes information indicating a discard timer, and the PDCP layer starts the discard timer for the PDCP SDU based on receiving the PDCP SDU.

5. A method executed by a terminal device (10), comprising: receiving a Radio Resource Control (RRC) message; and, in a Packet Data Convergence Protocol (PDCP) layer, providing an indication to a Radio Link Control (RLC) layer if the remaining time until a discard timer for a PDCP Service Data Unit (SDU) expires is less than the remaining time threshold, based on information indicating a remaining time threshold for retransmission in the RLC layer, included in the RRC message; and, in the RLC layer, receiving the indication for an RLC SDU from the PDCP layer and determining that the RLC SDU is to be retransmitted based on the absence of a positive acknowledgement (ACK) for the RLC SDU.

6. The method of claim 5, wherein, at the PDCP layer, the indication is an indication for a PDCP packet data unit (PDU) corresponding to the PDCP SDU, and the method further comprises, when the PDCP layer has already submitted the PDCP PDU to the RLC layer, providing the indication to the RLC layer.

7. The method of claim 5, further comprising: in the PDCP layer, if the RRC message includes information indicating a remaining time threshold for retransmission in the RLC layer, providing the indication to the RLC layer.

8. The method of claim 5, wherein the RRC message includes information indicating a discard timer, and the method further includes, in the PDCP layer, starting the discard timer for the PDCP SDU based on receiving the PDCP SDU.

9. A program that, when executed, causes a processor (101) in a terminal device (10) to perform the following: receive a Radio Resource Control (RRC) message; in a Packet Data Convergence Protocol (PDCP) layer, based on information indicating a remaining time threshold for retransmission in a Radio Link Control (RLC) layer included in the RRC message, provide an indication to an RLC layer if the remaining time until a discard timer for a PDCP Service Data Unit (SDU) expires is less than the remaining time threshold; and in the RLC layer, receive the indication for an RLC SDU and consider the RLC SDU to be a target for retransmission based on the fact that a positive acknowledgment (ACK) is not indicated for the RLC SDU.

10. The program according to claim 9, wherein, in the PDCP layer, the indication is an indication for a PDCP packet data unit (PDU) corresponding to the PDCP SDU, and the program further causes the processor to provide the indication to the RLC layer if the PDCP layer has already submitted the PDCP PDU to the RLC layer.

11. The program of claim 9, further causing the processor to provide the indication to the RLC layer when the RRC message includes, at the PDCP layer, information indicating a remaining time threshold for retransmission at the RLC layer.

12. The program according to claim 9, wherein the RRC message includes information indicating a discard timer, and the program further causes the processor to start the discard timer for the PDCP SDU based on reception of the PDCP SDU in the PDCP layer.

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