Communication control method

Abstract

One aspect relates to a communication control method in a mobile communication system. The communication control method comprises a step for transmitting, to a user device, a skip notification indicating skipping of transmission of a transmission packet if a base station does not retransmit the transmission packet, and setting a timer value of a high-speed retransmission timer shorter than a timer value of a reference timer in the user device if retransmission of the transmission packet is performed.

Description

Communication Control Method

[0001] The present disclosure relates to a communication control method in a mobile communication system.

[0002] The Third Generation Partnership Project (3GPP) (registered trademark; the same applies hereinafter), a standardization project for mobile communication systems, has approved XR (eXtended Reality) for Release 18 of its specifications. XR is a broad term that includes virtual reality (VR), augmented reality (AR), and mixed reality (MR), and describes an environment that blends the real world with a virtual space. XR describes a blended environment of real space and virtual space generated by computer technology and wearable devices, and represents the interaction between humans and machines.

[0003] RP-213587, 3GPP TSG RAN Meeting #94e, “Study on XR Enhancements for NR”, Nokia, Dec. 6-17,20213GPP TR 38.838 V17.0.0 (2021-12)

[0004] According to one aspect, a communication control method for a mobile communication system includes a step of: a base station transmitting, to a user equipment device, a skip notification indicating that transmission of the transmission packet will be skipped if the base station does not retransmit the transmission packet; and, if the base station retransmits the transmission packet, setting, to the user equipment device, a timer value of a fast retransmission timer having a timer value shorter than a reference timer.

[0005] According to one aspect, there is provided a communication control method in a mobile communication system, the communication control method including a step of, when a user device does not retransmit a transmission packet, transmitting a skip notification to a base station indicating that transmission of the transmission packet will be skipped.

[0006] FIG. 1 is a diagram illustrating an example of the configuration of a mobile communication system according to the first embodiment. FIG. 2 is a diagram illustrating an example of the configuration of a UE (user equipment) according to the first embodiment. FIG. 3 is a diagram illustrating an example of the configuration of a gNB (base station) according to the first embodiment. FIG. 4 is a diagram illustrating an example of the configuration of a protocol stack related to a user plane according to the first embodiment. FIG. 5 is a diagram illustrating an example of the configuration of a protocol stack related to a control plane according to the first embodiment. FIGS. 6(A) and 6(B) are diagrams illustrating an example of operation according to the first embodiment. FIG. 7 is a diagram illustrating an example of operation according to the second embodiment.

[0007] An object of one aspect of the present disclosure is to provide a communication control method that enables appropriate communication using XR.

[0008] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0009] [First embodiment] (Configuration of mobile communication system) Fig. 1 is a diagram showing the configuration of a mobile communication system according to the first embodiment. The mobile communication system 1 conforms to the 5th Generation System (5GS) of the 3GPP standard. Although the following description will be given using 5GS as an example, the mobile communication system may also be at least partially based on an LTE (Long Term Evolution) system. Alternatively, the mobile communication system may also be at least partially based on a 6th Generation (6G) system.

[0010] The mobile communication system 1 includes a user equipment (UE) 100, a 5G radio access network (NG-RAN: Next Generation Radio Access Network) 10, and a 5G core network (5GC: 5G Core Network) 20. Hereinafter, the NG-RAN 10 may be simply referred to as the RAN 10. Furthermore, the 5GC 20 may be simply referred to as the core network (CN) 20.

[0011] The UE 100 is a mobile wireless communication device. The UE 100 may be any device that is used by a user. For example, the UE 100 may be a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC, a communication module (including a communication card or a chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0012] The UE 100 includes an XR device. The XR device is, for example, a device capable of XR processing. Specific examples of XR devices include a head-mounted display (HMD) that can be worn on a human head, eyeglass-type AR glasses (or smart glasses), a handheld mobile handset, a wristwatch-type device (smart watch), and a smartphone. These XR devices may also be referred to as wearable devices. The HMD includes a display, lenses, a tracking sensor, a camera, a control unit (e.g., a central processing unit (CPU) or a graphics processing unit (GPU)) that performs XR-related processing, and a communication function. The AR glasses have a function for transmitting images. The mobile handset may include various sensors such as a tracking sensor. The HMD, AR glasses, wristwatch-type device, and mobile handset have a communication function that supports a 5G system, etc. In the following, the UE 100 will be described as including such an XR device.

[0013] The NG-RAN 10 includes a base station (called a "gNB" in a 5G system) 200. The gNBs 200 are connected to each other via an Xn interface, which is an interface between base stations. The gNB 200 manages one or more cells. The gNB 200 performs wireless communication with a UE 100 that has established a connection with its own cell. The gNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, and the like. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate a function or resource for wireless communication with the UE 100. One cell belongs to one carrier frequency (hereinafter simply referred to as "frequency").

[0014] In addition, gNBs can also be connected to the Evolved Packet Core (EPC), which is the core network of LTE. LTE base stations can also be connected to 5GC. LTE base stations and gNBs can also be connected via an inter-base station interface.

[0015] The 5GC20 includes an Access and Mobility Management Function (AMF) and a User Plane Function (UPF) 300. The AMF performs various mobility controls for the UE 100. The AMF manages the mobility of the UE 100 by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. The UPF controls data forwarding. The AMF and the UPF are connected to the gNB 200 via an NG interface, which is an interface between a base station and a core network.

[0016] 2 is a diagram showing the configuration of the UE 100 (user equipment) according to the first embodiment. The UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 constitute a wireless communication unit that performs wireless communication with the gNB 200.

[0017] The receiving unit 110 performs various types of reception under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130.

[0018] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0019] The control unit 130 performs various controls and processes in the UE 100. Such processes include processes of each layer described below. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processes by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation, encoding / decoding, etc. of baseband signals. The CPU executes programs stored in the memory to perform various processes. Note that the control unit 130 may perform each process or operation in the UE 100 in each of the embodiments described below.

[0020] 3 is a diagram showing the configuration of a gNB 200 (base station) according to the first embodiment. The gNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240. The transmitter 210 and the receiver 220 constitute a wireless communication unit that performs wireless communication with the UE 100. The backhaul communication unit 240 constitutes a network communication unit that communicates with the CN 20.

[0021] The transmitting unit 210 performs various transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0022] The receiving unit 220 performs various types of reception under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 230.

[0023] The control unit 230 performs various controls and processes in the gNB 200. Such processes include processes for each layer described below. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processes by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation, encoding / decoding, etc. of baseband signals. The CPU executes programs stored in the memory to perform various processes. Note that the control unit 230 may perform each process or operation in the gNB 200 in each of the embodiments described below.

[0024] The backhaul communication unit 240 is connected to adjacent base stations via an Xn interface, which is an interface between base stations. The backhaul communication unit 240 is connected to the AMF / UPF 300 via an NG interface, which is an interface between a base station and a core network. Note that the gNB 200 is composed of a CU (Central Unit) and a DU (Distributed Unit) (i.e., functionally divided), and the two units may be connected by an F1 interface, which is a fronthaul interface.

[0025] FIG. 4 is a diagram showing the configuration of a protocol stack of a radio interface of a user plane that handles data.

[0026] The user plane radio interface protocol includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer.

[0027] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of gNB200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from gNB200 on a physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires the successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from gNB200 has a CRC parity bit scrambled by the RNTI added.

[0028] The MAC layer performs data priority control, retransmission processing using hybrid ARQ (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of UE100 and the MAC layer of gNB200 via a transport channel. The MAC layer of gNB200 includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to UE100.

[0029] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the gNB 200 via a logical channel.

[0030] The PDCP layer performs header compression / decompression, encryption / decryption, and the like.

[0031] The SDAP layer maps IP flows, which are units for Quality of Service (QoS) control by the core network, to radio bearers, which are units for QoS control by the Access Stratum (AS). Note that if the RAN is connected to the EPC, SDAP may not be required.

[0032] FIG. 5 is a diagram showing the configuration of a protocol stack of a radio interface of a control plane that handles signaling (control signals).

[0033] The protocol stack of the radio interface of the control plane has a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) instead of the SDAP layer shown in FIG.

[0034] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of gNB200. The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of gNB200, UE100 is in an RRC idle state. When the connection between the RRC of UE100 and the RRC of gNB200 is suspended, UE100 is in an RRC inactive state.

[0035] The NAS, which is located above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS of the UE 100 and the NAS of the AMF 300. Note that the UE 100 has an application layer and the like in addition to the radio interface protocol. Also, the layer below the NAS is called an Access Stratum (AS).

[0036] (About XR) As described above, XR is a broad term that includes, for example, virtual reality (VR), augmented reality (AR), and mixed reality (MR), and describes an environment that combines the real world and a virtual space. XR is also, for example, a general term for such various types of realities. XR is also, for example, a general term for technology that combines the real world and a virtual space to enable perception of things that do not exist in reality.

[0037] In XR, human-to-machine and human-to-human communication is performed with the aid of a portable or wearable end-user device, the UE 100. Such communication enables XR to be applied in various application areas such as entertainment, healthcare, or education.

[0038] Along with XR, cloud gaming (CG) is one of the use cases in future mobile systems. Cloud gaming is a general term for use cases in which, for example, most of the calculations related to a game are offloaded to an edge server or a remote server. In cloud gaming, the UE 100 transmits information related to pose and / or control. The cloud performs calculations related to video data and the like based on this information and provides the UE 100 with video and other game-related data.

[0039] Virtual reality (VR) refers to the creation of an environment that is not the original (or real world) but is essentially functionally the same as the original by stimulating the user's senses. In virtual reality (VR), the user typically wears an HMD, the user's field of vision is replaced with simulated visual elements, and accompanying audio is provided to the user through headphones. Virtual spaces are designed to mimic sensory stimuli such as sight and hearing in the real world as naturally as possible. Virtual reality (VR) can also include the metaverse, a virtual space (or service) built on a computer or computer network that is different from the real world.

[0040] Augmented reality (AR) is a technology that displays a virtual space overlaid on the real world. Augmented reality (AR) also provides additional information (artificially generated items or content) overlaid on the user's real environment. The additional information can be perceived directly without sensors or indirectly via sensors.

[0041] Furthermore, mixed reality (MR) is a technology that combines and / or blends the real world and a virtual space to create a space in which they interact with each other in real time. Mixed reality (MR) is an advanced form of augmented reality (AR) and is constructed with the intention of inserting virtual elements into a physical scene to give the illusion that they are part of the actual scene.

[0042] Typical forms of XR include virtual reality (VR), augmented reality (AR), and mixed reality (MR), but areas that interpolate between these may also be included in XR.

[0043] Many XR and cloud gaming (CG) use cases are characterized by video stream traffic in the DL direction and a combination of pose and / or control traffic and video stream traffic in the UL direction. The video stream has a higher data rate than other use cases, and data related to pose and / or control is updated frequently. Furthermore, XR and cloud gaming (CG) are characterized by the fact that DL traffic and UL traffic are more sensitive to delays than other use cases.

[0044] (XR Traffic Model) The following describes the XR traffic model. XR traffic models include (1) a general traffic model and (2) a specific traffic model. First, (1) the general traffic model will be described. The (1) general traffic model includes (1.1) a traffic model in the DL direction and (1.2) a traffic model in the UL direction.

[0045] (1) General traffic model

[0046] (1.1) Traffic Model in DL Direction There are two types of traffic models in the DL direction: a single-stream DL traffic model and a multi-stream DL traffic model. The two traffic models can be summarized as follows:

[0047] (1.1.1) Single-Stream DL Traffic Model: A Sequence of Video Frames

[0048] (1.1.2) Multi-Stream DL Traffic Model:

[0049] (1.1.2.1) Option #1: Two streams, the first stream being an I (Intra-coded) stream and the second stream being a P (Predicted) stream. Option #1 includes a slice-based traffic model (Option #1A) and a GOP (Group-Of-Picture)-based traffic model (Option #1B).

[0050] (1.1.2.1A) Option #1A (Slice-based): The first stream is an I slice (I stream), and the second stream is a P slice (P stream). Here, an I slice is, for example, a slice in which all macroblocks included in the I slice are coded by intra-frame prediction. A P slice is, for example, a slice in which all macroblocks included in the P slice are coded by intra-frame prediction or inter-frame prediction. When a video frame is sliced ​​into N slices, one slice can be an I slice, and the remaining (N-1) slices can be P slices.

[0051] (1.1.2.1B) Option #1B (GOP-based): The first stream is an I-frame (I-stream), and the second stream is a P-slice (P-stream). Here, an I-frame is a frame encoded using a video frame without using other video frames. A P-frame is a frame encoded using a video frame preceding it in time. If the GOP size is K frames, an I-frame is transmitted every K frames. A GOP includes one I-frame and (K-1) P-frames.

[0052] (1.1.2.2) Option #2: A traffic model with two streams, where the first stream is video and the second stream is audio and / or data.

[0053] (1.1.2.3) Option #3: A traffic model in which the first stream is a field of view (FOV) and the second stream is an omnidirectional view. For example, the FOV is video data from the user's line of sight, and the omnidirectional view is omnidirectional video data centered on the user, including video data from the user's line of sight.

[0054] (1.2) Traffic Model in UL Direction The traffic model in the UL direction includes an attitude and / or control stream traffic model, in which the UE 100 transmits data related to attitude and / or control.

[0055] (2) Specific Traffic Models Specific traffic models include (2.1) virtual reality (VR), (2.2) augmented reality (AR), and (2.3) cloud gaming (CG) traffic models.

[0056] (2.1) Traffic Model of Virtual Reality (VR) The traffic model of virtual reality (VR) can be summarized as follows:

[0057] (2.1.1) DL Stream: Single-stream model: Same as above (1.1.1) "Single-stream DL traffic model" (series of video frames) Multi-stream model: Same as above (1.1.2.2) "Option #2" (first stream is video, second stream is audio and / or data)

[0058] (2.1.2) UL stream: Same as (1.2) "Traffic model in UL direction" above

[0059] (2.2) Traffic Model of Augmented Reality (AR) The traffic model of augmented reality (AR) can be summarized as follows.

[0060] (2.2.1) DL stream: same as (2.1.1) above

[0061] (2.2.2) UL Stream: Model #1: 1-stream model Model #2: 2-stream model: the first stream is attitude and / or control, the second stream is a combination of scene (e.g. continuous video), video, data, and audio Model #3A: 3-stream Model A: the first stream is attitude and / or control, the second stream is a combination of scene stream and video stream, the third stream is a combination of audio and data Model #3B: 3-stream Model B: the first stream is attitude and / or control, the second stream is video I stream, the third stream is video P stream

[0062] (2.3) Cloud Gaming (CG) Traffic Model The traffic model for cloud gaming (CG) can be summarized as follows:

[0063] (2.3.1) DL Stream Single-stream model: Same as above (1.1.1) "Single-stream DL traffic model" (series of video frames) Multi-stream model: Same as above (1.1.2) "Multi-stream DL traffic model"

[0064] (2.3.2) UL stream: Same as (1.2) "Traffic model in UL direction" above

[0065] (Communication control method according to the first embodiment) As described above, XR traffic may use a video stream, and may transmit a large amount of data compared to other traffic. Furthermore, XR traffic may require real-time performance, such as cloud gaming (CG), and may require low latency compared to other traffic.

[0066] In addition, since XR traffic is likely to generate traffic periodically, such as video streams, it is expected that a scheduling method called SPS (Semi-Persistent Scheduling) or CG (Configured Grant), which enables periodic transmission or reception, will be used. SPS and CG are scheduling methods that initially allocate radio resources using DCI (Downlink Control Information), and thereafter, can use the radio resources periodically without using DCI. In 5G systems, SPS is a scheduling method for the DL direction, and CG is a scheduling method for the UL direction.

[0067] Here, assume a case where, in XR traffic, if transmission or reception of a packet fails, the packet is retransmitted. 3GPP supports Hybrid Automatic Repeat Request (HARQ) in the MAC layer. HARQ is a retransmission control method that combines Automatic Repeat Request (ARQ) and Forward Error Correction (FEC). In HARQ, for example, the transmitting side retransmits data in units of code blocks constituting a transport block (TB) (MAC PDU), and the receiving side combines (soft combines) already received data stored in a buffer with the retransmitted data to obtain a transmission packet. ARQ is also supported in the RLC layer. In ARQ in the RLC layer, when the receiving side detects a loss of an RLC SDU or an RLC SDU segment, the receiving side transmits an RLC status report to the transmitting side, and the transmitting side retransmits the RLC SDU or the RLC SDU segment based on the RLC status report. The ARQ in the RLC layer serves to compensate for residual errors in the HARQ in the MAC layer, for example.

[0068] Although the mobile communication system 1 also supports such a retransmission control method, there are cases where retransmission packets are unnecessary for XR traffic. For example, if the next video stream has already been transmitted, the delayed packet becomes unnecessary on the receiving side. Furthermore, for example, if the orientation of the HMD has changed, the delayed packet becomes unnecessary on the receiving side. In such cases, even if retransmission such as HARQ is performed, the retransmission packet may become unnecessary on the receiving side. In this case, if the transmitting side unilaterally stops transmitting the retransmission packet, the receiving side will wait for the retransmission packet while storing the already received packet in a buffer, which may result in normal reception or delay in delivery of the packet to the upper layer.

[0069] Therefore, in XR traffic, performing retransmission control such as HARQ may not necessarily result in efficient communication.

[0070] On the other hand, in XR traffic, when a retransmission occurs due to an important scene, it may be better to perform the retransmission. In this case, it is preferable to perform the retransmission earlier than normal retransmission.

[0071] Therefore, in one embodiment, when the transmission packet is not retransmitted, the transmitting device transmits a skip notification to the receiving device indicating that the transmission of the transmission packet is skipped. On the other hand, when the transmission packet is retransmitted, the gNB 200 sets a fast retransmission timer for the UE 100 having a timer value shorter than the reference timer.

[0072] Specifically, if a base station (e.g., gNB200) does not retransmit a transmission packet, it transmits a skip notification to a user device (e.g., UE100) indicating that transmission of the transmission packet will be skipped, and if the base station retransmits the transmission packet, it sets the timer value of a fast retransmission timer with a timer value shorter than the reference timer to the user device.

[0073] In this way, when retransmission is not performed, a skip notification is transmitted, and the receiving side can perform appropriate processing, such as outputting the received packet awaiting retransmission to an upper layer. On the other hand, when retransmission is performed, the UE 100 can start a fast retransmission timer with a timer value that is shorter than the expiration time of the reference timer. Therefore, the UE 100 can receive the retransmission packet after the timer expires, and can receive the retransmission packet earlier than when the reference timer is used. Therefore, in the mobile communication system 1, communication using XR can be performed appropriately.

[0074] In the first embodiment, a case where retransmission is not performed will be described. That is, an example of a skip notification will be described in the first embodiment. In the second embodiment, a case where retransmission is performed, that is, an example of a fast retransmission timer will be described.

[0075] (Operation Example of First Embodiment) FIGS. 6A and 6B are diagrams showing an operation example according to the first embodiment.

[0076] Regarding retransmission, it may be performed by gNB200 in the DL direction or by UE100 in the UL direction. In other words, regarding retransmission, there are cases where the transmitting side is gNB200 and the receiving side is UE100 (i.e., DL direction), and cases where the transmitting side is UE100 and the receiving side is gNB200 (i.e., UL direction). Therefore, in the operation example according to the first embodiment, it will be described as the transmitting side and the receiving side. In this case, when the transmitting side (or transmitting device) is gNB200, the receiving side (or receiving device) is UE100, and when the transmitting side is UE100, the receiving side is gNB200.

[0077] 6(A) and 6(B) are consecutive in time, but it is assumed that, for example, before the operation of Fig. 6(B) is started, the state is as follows: That is, it is assumed that the transmitting side has transmitted a transmission packet to the receiving side, but the receiving side has not been able to receive the transmission packet and has transmitted a retransmission request (for example, a NACK of HARQ-feedback) to the transmitting side.

[0078] As shown in Figure 6 (A), in step S10, gNB200 may transmit a skip condition to UE100. In this case, with respect to retransmission, UE100 is the transmitter of the transmission packet, and gNB200 is the receiver of the transmission packet. The skip condition is applied to the retransmission of the transmission packet from UE100.

[0079] The skip conditions are, for example, as follows:

[0080] First, the skip condition may be a residence time of a transmission packet. The residence time of a transmission packet may represent an upper limit of the time from when the transmitting AS receives the transmission packet from the application layer until the transmission of the transmission packet to the receiving side is completed (or the reception of an ACK is completed). The residence time of a transmission packet may be a timer value of a timer that counts the residence time.

[0081] Second, the skip condition may be the number of retransmissions. The number of retransmissions may be the upper limit number of retransmissions by HARQ. Alternatively, the number of retransmissions may be the upper limit number of retransmissions by ARQ in the RLC layer. The two upper limits may be set to different upper limits or the same upper limit number. The number of retransmissions may be the upper limit number of times a NACK is received from the receiving side.

[0082] The skip condition may be transmitted before the retransmission. Alternatively, the skip condition may be transmitted during the retransmission. The gNB 200 may transmit the skip information including in a DCI, a MAC PDU, an RRC message, or the like.

[0083] As shown in FIG. 6(B), in step S11, the transmitting side retransmits the transmission packet and recognizes that the expiration date of the transmission packet has expired. The transmitting side may recognize that the transmission of the transmission packet is no longer necessary. The transmitting side may recognize that the expiration date of the transmission packet has expired when the transmission packet satisfies a condition related to the expiration date of the transmission packet. The condition related to the expiration date may be a skip condition (step S10). For example, the UE 100 (transmitting side) recognizes that the expiration date of the transmission packet has expired when the transmission packet satisfies the skip condition (step S10). The condition related to the expiration date may also be a QoS condition indicated in the QoS setting. For example, if the transmission packet does not satisfy the QoS condition indicated in the QoS setting, the gNB 200 (transmitting side) recognizes that the expiration date of the transmission packet has expired (or that the transmission of the packet is no longer necessary). The QoS condition may be expressed as 5QI.

[0084] In step S12, the transmitting side transmits a skip notification to the receiving side indicating that transmission of the transmission packet will be skipped. For example, the transmitting side transmits the skip notification to the receiving side when the transmission packet satisfies the condition regarding the expiration date of the transmission packet (step S11). Alternatively, for example, the UE 100 transmits the skip notification to the gNB 200 when the transmission packet satisfies the skip condition (step S10).

[0085] First, the skip notification may be transmitted using, for example, the following message: That is, the transmitting side may transmit an SDAP Control PDU including the skip notification to the receiving side. Since the SDAP layer performs mapping between QoS flows and radio bearers (DRBs), the transmitting side can transmit the skip notification for each QoS flow by using the SDAP Control PDU. Alternatively, the transmitting side may transmit a PDCP Control PDU including the skip notification to the receiving side. In this case, for example, the transmitting side can transmit the skip notification for each PDCP PDU. Furthermore, the transmitting side may transmit an RLC Control PDU including the skip notification to the receiving side. In this case, for example, the transmitting side can transmit the skip notification for each RLC SDU segment (or each RLC SDU). Furthermore, the transmitting side may transmit an RRC message including the skip notification.

[0086] Second, the skip notification may include, for example, the following content: That is, the skip notification includes the SN (Sequence Number) of the transmission packet to be skipped. When multiple transmission packets are to be skipped, the skip notification may include a range of SNs of the transmission packets to be skipped. The SNs to be skipped may be represented by PDCP SNs. Alternatively, the SNs to be skipped may be represented by a COUNT value that is a combination of a Hyper Frame Number (HFN) and a PDCP SN. Furthermore, the SNs to be skipped may be represented by RLC SNs. Furthermore, the skip notification may include information indicating that the next packet will not be transmitted, rather than the SNs of the transmission packets to be skipped. When the transmission of multiple packets is to be skipped, the skip notification may include information indicating that the next N packets (e.g., the number of SNs to be skipped or the number of packets to be skipped) will be skipped. The skip notification may include information specifying a state variable of the receiving window on the receiving side. The receiving window may be a PDCP receiving window (reordering window), and the state variable may be RX_NEXT indicating the COUNT value of the next PDCP SDU expected to be received.

[0087] The transmitting side may discard the transmission packet that is the target of the skip notification.

[0088] In step S13, in response to receiving the skip notification, the receiving side performs processing as if it had received a transmission packet.

[0089] First, the PDCP layer performs, for example, the following process. That is, the PDCP layer on the receiving side may output a received transmission packet that is awaiting retransmission to a layer above the PDCP layer. This, for example, eliminates a state in which a received packet remains stuck in a buffer or the like, thereby suppressing a delay in delivering the received packet to a layer above the PDCP layer. Furthermore, the PDCP layer on the receiving side may set the lower limit of the reception window to the next PDCP SN (or COUNT value) of the transmission packet. Since the PDCP SN is included in the skip notification, the PDCP layer may use this. Furthermore, the PDCP layer on the receiving side may notify a lower layer (such as the RLC layer) that packet reception will be skipped.

[0090] Second, the RLC layer may perform the following process: the receiving RLC layer may discard the received RLC SDU or RLC SDU segment, set the lower limit of the reception window to the next SN of the transmission packet, and notify an upper layer (such as the PDCP layer) that packet reception will be skipped.

[0091] Thus, in the first embodiment, when the gNB 200 (transmitting device) does not retransmit the transmission packet, it transmits a skip notification indicating that the transmission of the transmission packet will be skipped to the UE 100 (receiving device). Also, in the first embodiment, when the UE 100 (transmitting device) does not retransmit the transmission packet, it transmits a skip notification indicating that the transmission of the transmission packet will be skipped to the base station (receiving device).

[0092] Second Embodiment In a second embodiment, an example in which a transmission packet is retransmitted will be described.

[0093] In XR traffic, real-time performance may be required in use cases such as augmented reality (AR) or cloud gaming (CG). Therefore, XR traffic requires low latency compared to other traffic. In such a situation, if retransmission of XR traffic occurs, one solution is for the transmitting side to send a skip notification to the receiving side under certain conditions, as in the first embodiment, so that the transmitting side does not retransmit. On the other hand, as described above, retransmission may occur for video scenes that are more important than others. In such cases, retransmission is preferable, and further, due to the low latency requirement of XR traffic, retransmission is preferably performed earlier than normal retransmission.

[0094] Therefore, in the second embodiment, an example will be described in which a fast retransmission timer having a timer value shorter than that of the reference timer is used.

[0095] Specifically, a base station (e.g., gNB200) sets a timer value of a fast retransmission timer that is shorter than the reference timer to a user equipment (e.g., UE100). Furthermore, first, the base station transmits the timer value of the fast retransmission timer to the user equipment. Second, when the user equipment fails to receive a transmission packet, the fast retransmission timer is started. Third, when the timer value of the fast retransmission timer expires, the user equipment attempts to receive the transmission packet.

[0096] As a result, for example, even if the UE 100 fails to receive a transmission packet transmitted from the gNB 200, the UE 100 can attempt to receive the transmission packet with an expiration time shorter than that of the reference timer, so that the retransmission packet can be received faster than when the reference timer is used. Therefore, in the mobile communication system 1, it is possible to appropriately perform communication using XR.

[0097] (Example of Operation According to Second Embodiment) FIG. 7 is a diagram showing an example of operation according to the second embodiment.

[0098] As shown in Figure 7, in step S20, the gNB200 sets the timer value of a reference RTT (Round Trip Timer) timer and the timer value of a fast retransmission RTT timer having a timer value shorter than the reference RTT timer. For example, the reference timer is a reference RTT timer, and the fast retransmission timer is a fast retransmission RTT timer. The reference RTT timer is, for example, a HARQ RTT timer used in retransmission control (HARQ) for DRX (Discontinuous Reception).

[0099] In DRX, by discontinuously monitoring the PDCCH of the target UE 100, it is possible to reduce the power consumption of the UE 100 compared to when continuously monitoring the PDCCH. When the UE 100 enters the DRX cycle, it starts an on-duration timer (OnDurationTimer) and monitors the PDCCH for the period until the timer expires (on-duration). In the UE 100, if reception of a transmission packet is instructed using the PDCCH in the on-duration but the transmission packet cannot be received, the MAC layer of the UE 100 performs retransmission control using HARQ and requests the gNB 200 to retransmit the transmission packet. In the MAC layer, the HARQ RTT timer is started when the transmission packet cannot be received (or when a retransmission request is made). Since it takes a certain time from a retransmission request of a transmission packet to reception of the transmission packet, the HARQ RTT timer can be started to put UE 100 into sleep mode for a certain time (the timer value of the HARQ RTT timer). Then, in the MAC layer, when the HARQ RTT timer expires, a DRX retransmission timer (drx-RetransmissionTimer) is started, and reception of the transmission packet (i.e., the retransmission packet) is attempted while the DRX retransmission timer is running. When the MAC layer receives a transmission packet, the DRX retransmission timer is stopped, and if the transmission packet cannot be received, reception of the transmission packet is attempted until the DRX retransmission timer expires. In the second embodiment, fast retransmission is realized by using a fast retransmission RTT timer having a timer value shorter than the timer value of the HARQ RTT timer and activating the DRX retransmission timer at a time earlier than the HARQ RTT timer. Therefore, the gNB 200 sets two timer values, a timer value X of the HARQ RTT timer and a timer value Y of the fast retransmission RTT timer, so that X > Y. The gNB 200 transmits the two timer values ​​that have been set to the UE 100. The gNB 200 may transmit the two timer values ​​that have been set by including them in an RRC message, a MAC PDU, or a DCI, etc.

[0100] It is assumed that gNB200 has performed DRX configuration for UE100 prior to step S20.

[0101] In step S21, gNB200 transmits data to UE100.

[0102] In step S22, UE100 receives a PDCCH during a DRX active period (DRX active time). The DRX active period is, for example, a period during which an on-duration timer (OnDurationTimer) is operating. The gNB200 may use the PDCCH to instruct the application of the fast retransmission RTT timer. For example, the gNB200 may use the PDCCH to transmit to the UE100 a new DCI format that indicates the application of the fast retransmission RTT timer. Also, for example, the gNB200 may use DCI information (bits) to instruct the application of the fast retransmission RTT timer.

[0103] In step S23, the UE 100 attempts to receive the PDSCH by using the DCI received by using the PDCCH. Here, it is assumed that the UE 100 has failed to decode the PDSCH.

[0104] In step S24, the UE 100 transmits a NACK as HARQ-feedback, and in step S25, the UE 100 starts the fast retransmission RTT timer. Steps S24 and S25 may be performed simultaneously. In step S24, the UE 100 may notify the gNB 200 that the fast retransmission RTT timer is applied (started). This notification may be performed on a PUCCH (Physical Up-link Control Channel) or may be indicated by a special NACK signal.

[0105] In step S26, when the fast retransmission RTT timer expires, the UE 100 starts a DRX retransmission timer (drx-RetransmissionTimer). That is, when the fast retransmission RTT timer expires, the UE 100 attempts to receive a transmission packet (retransmission packet) transmitted using the PDSCH. The UE 100 attempts to receive the transmission packet while the DRX retransmission timer is operating.

[0106] [Other embodiments] A program may be provided that causes a computer to execute each process performed by the UE 100 or the gNB 200. The program may be recorded on a computer-readable medium. Using a computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM and / or a DVD-ROM.

[0107] In addition, circuits that perform each process performed by UE100 or gNB200 may be integrated, and at least a portion of UE100 or gNB200 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

[0108] Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to the above, and various design changes can be made within the scope of the gist. Furthermore, it is also possible to combine all or part of each embodiment, each operation, each process, and each step within the scope of consistent combinations.

[0109] As used in this disclosure, the terms "based on" and "depending on" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "based only on" and "at least in part on." Furthermore, "obtain" may mean obtaining information from stored information, obtaining information from information received from another node, or obtaining information by generating the information. The terms "include," "comprise," and variations thereof do not mean including only the listed items, but may also mean including only the listed items or including additional items in addition to the listed items. Furthermore, as used in this disclosure, the term "or" is not intended to mean an exclusive or. Furthermore, any reference to an element using a designation such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient method of distinguishing between two or more elements. Thus, reference to a first and a second element does not imply that only two elements may be employed therein, or that the first element must precede the second element in some way. In this disclosure, when articles are added by translation, such as a, an, and the in English, these articles are intended to include the plural unless the context clearly dictates otherwise.

[0110] This application claims priority from Japanese Patent Application No. 2022-073808 (filed April 27, 2022), the entire contents of which are incorporated herein by reference.

[0111] (Additional Note) In one embodiment, (Additional Note 1) a communication control method in a mobile communication system, the communication control method in the mobile communication system may include a step in which, when a base station does not retransmit a transmission packet, it transmits a skip notification to a user device indicating that transmission of the transmission packet will be skipped, and, when the base station retransmits the transmission packet, it sets, to the user device, a timer value of a fast retransmission timer having a timer value shorter than a reference timer.

[0112] (Supplementary Note 2) The communication control method of (Supplementary Note 1) above may further include a step in which the user device, upon receiving the skip notification, performs processing as if it had received the transmission packet.

[0113] (Supplementary Note 3) In the communication control method of (Supplementary Note 1) or (Supplementary Note 2) above, the setting step may include a step in which the base station transmits the skip notification to the user equipment when the transmission packet satisfies a condition regarding the expiration date of the transmission packet.

[0114] (Supplementary Note 4) In any of the communication control methods described above in (Supplementary Note 1) to (Supplementary Note 3), the method may further include the steps of: the base station transmitting the timer value of the fast retransmission timer to the user equipment; the user equipment starting the fast retransmission timer when it fails to receive the transmission packet; and the user equipment attempting to receive the transmission packet when the timer value of the fast retransmission timer expires.

[0115] In addition, in one embodiment, (Supplementary Note 5) a communication control method in a mobile communication system may include a step in which, when a user device does not retransmit a transmission packet, the user device transmits a skip notification to a base station indicating that transmission of the transmission packet will be skipped.

[0116] (Supplementary Note 6) The communication control method of (Supplementary Note 5) above may further include a step in which the base station processes the transmission packet as if it had been received in response to receiving the skip notification.

[0117] (Supplementary Note 7) In the communication control method of (Supplementary Note 5) or (Supplementary Note 6) above, the base station may further include a step of transmitting a skip condition to the user device, and the step of transmitting the skip notification may include a step of the user device transmitting the skip notification to the base station when the transmission packet satisfies the skip condition.

[0118] (Supplementary Note 8) In the communication control methods of (Supplementary Note 1) to (Supplementary Note 7) above, the transmission packets may be transmission packets for XR traffic.

[0119] 1: Mobile communication system 20: CN 100: UE 110: Receiving unit 120: Transmitting unit 130: Control unit 200: gNB 210: Transmitting unit 220: Receiving unit 230: Control unit 300: AMF

Claims

1. A communication control method in a mobile communication system, comprising: When the network node does not retransmit a transmission packet, the network node transmits a skip notification to the user device indicating that transmission of the transmission packet is to be skipped, and when the network node retransmits the transmission packet, the network node sets a timer value of a fast retransmission timer, the timer value of which is shorter than a reference timer, to the user device. Communications control method.

2. The method further includes: the user device, in response to receiving the skip notification, performing processing as if the transmission packet had been received. The communication control method according to claim 1.

3. The setting includes the network node transmitting the skip notification to the user equipment when the transmission packet satisfies a condition regarding an expiration date of the transmission packet. The communication control method according to claim 1.

4. said network node transmitting said timer value of said fast retransmission timer to said user equipment; starting the fast retransmission timer when the user equipment fails to receive the transmission packet; and wherein the user equipment attempts to receive the transmitted packet when the timer value of the fast retransmit timer expires. The communication control method according to claim 1.

5. A communication control method in a mobile communication system, comprising: If the user equipment does not retransmit the transmission packet, the user equipment transmits a skip notification to the network node indicating that the transmission of the transmission packet is to be skipped. Communications control method.

6. The network node, in response to receiving the skip notification, processes the transmission packet as having been received. The communication control method according to claim 5.

7. The network node further comprises transmitting a skip condition to the user equipment; The sending of the skip notification includes the user equipment sending the skip notification to the network node when the transmission packet satisfies the skip condition. The communication control method according to claim 5.

8. the transmission packet is a transmission packet for XR traffic; The communication control method according to claim 1 or 5.

9. A user device, A receiving unit that receives, when the network node does not retransmit the transmission packet, a skip notification indicating that transmission of the transmission packet is to be skipped from the network node; The receiving unit receives, from the network node, setting information for setting a timer value of a fast retransmission timer having a timer value shorter than a reference timer when retransmitting the transmission packet. User equipment.

10. A user device, comprising: A transmission unit that transmits a skip notification to a network node when the transmission packet is not to be retransmitted, the skip notification indicating that the transmission of the transmission packet is to be skipped. User equipment.