Terminal, method, base station and communication system

Abstract

A terminal according to one aspect of the present disclosure comprising: a receiver configured to receive an indication of a switching time from a first mode to a second mode and a length of a transmission window that starts at the switching time; a processor configured to determine a transmission time within the transmission window; and a transmitter configured to initiate a transmission at the determined transmission time. According to one aspect of the present disclosure, preventing traffic surges, reduced signaling overhead, and / or improving overall system efficiency / throughput can be achieved appropriately.

Description

TERMINAL, METHOD, BASE STATION AND COMMUNICATION SYSTEMCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on and claims priority to U.S. Provisional Application No. 63 / 716,842, filed on November 6, 2024, the contents of which are incorporated herein by reference in their entirety.

[0002] Apparatuses and methods consistent with the present disclosure relate generally to communications, more specifically, methods, systems, and devices for distributed access control, for example, when satellite cell operation switches from store-and-forward mode to real-time mode.

[0003] Modern mobile communication services utilize both terrestrial and non-terrestrial networks (NTN). Third Generation Partnership Project (3GPP) radio interfaces incorporate NTN features (Non Patent Literature 1).

[0004] For NTNs, the 3GPP starts considering a Store & Forward (S&F) mode, allowing satellites to collect data from users when feeder links are unavailable and sending it to ground stations once feeder link connections are restored.

[0005] A significant traffic surge can occur when a satellite switches from a delay-tolerant S&F mode back to a real-time operational mode. To manage such surges, conventional methods like access class barring or probabilistic access class barring could be applied. These methods control network access by either progressively allowing different user classes to connect or by having users defer their access attempts based on a broadcasted randomization parameter.

[0006] 3GPP TS 38.300 V18.3.0, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; NR and NG-RAN Overall Description; Stage 2 (Release 18)”

[0007] However, applying these conventional techniques to the NTN S&F scenario has several drawbacks. They are often slow, depend on complex centralized algorithms executed by the network, and create considerable signaling overhead because system information needs to be repeatedly updated and re-acquired by user equipment. This is particularly inefficient in a satellite environment where resources are constrained.

[0008] Therefore, one object of the present disclosure is to provide a terminal, a method, a base station and a communication system that can efficiently prevent traffic surges when a satellite system switches from a store-and-forward mode to a real-time mode. Another object is to achieve this with reduced signaling overhead and / or without the need for complex centralized control algorithms, thereby improving overall system efficiency or throughput.

[0009] A terminal according to one aspect of the present disclosure comprising: a receiver configured to receive an indication of a switching time from a first mode to a second mode and a length of a transmission window that starts at the switching time; a processor configured to determine a transmission time within the transmission window; and a transmitter configured to initiate a transmission at the determined transmission time.

[0010] According to one aspect of the present disclosure, preventing traffic surges, reduced signaling overhead, and / or improving overall system efficiency / throughput can be achieved appropriately.

[0011] FIG. 1 is a schematic diagram illustrating a system for some embodiments of the present disclosure.

[0012] FIG. 2 is a schematic diagram illustrating an exemplary functional configuration of each device for some embodiments of the present disclosure.

[0013] FIG. 3 is a schematic diagram illustrating an exemplary hardware configuration of each device for some embodiments of the present disclosure.

[0014] FIG. 4 is a schematic diagram illustrating an exemplary flow chart of a procedure for probabilistic access class barring.

[0015] FIG. 5 is a schematic diagram illustrating an exemplary flow chart of a procedure for distributed radio frame counting based access control.

[0016] The present disclosure may introduce a method and apparatus for distributed access control when satellite cell operation switches from store-and-forward mode to real-time mode.

[0017] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the present disclosure. Instead, they are merely examples of systems, apparatuses, and methods consistent with aspects related to the present disclosure as recited in the appended claims.

[0018] In the present disclosure, "A / B," “A and / or B” and "at least one of A and B" may be used interchangeably. In the present disclosure, "A / B / C," “A and / or B and / or C” and "at least one of A, B and C" may be used interchangeably.

[0019] <System> FIG. 1 is a schematic diagram illustrating a system for some embodiments of the present disclosure. The system 1 may be a system implementing a communication using Long Term Evolution (LTE), 5th generation mobile communication system New Radio (5G NR) and so on the specifications of which have been drafted by Third Generation Partnership Project (3GPP). The system 1 may include at least one of Evolved Packet System (EPS), 5G system (5GS), and so on. The system 1 may include one or more user equipment (UE) 10, one or more base stations (BS) 20, one or more core networks (CN) 30.

[0020] In the present disclosure, terms “system,” “radio system,” “radio communication system,” “radio interface,” and “network (NW)” are used as general terms which include one or both of terrestrial network systems and non-terrestrial network (NTN) systems such as satellite systems. In the present disclosure, these terms may be used interchangeably.

[0021] The UE 10 may be a terminal supporting at least one of communication schemes such as LTE, 5G NR, and so on. The UE 10 may be connected to at least one of plurality of BS 20. The UE 10 may take any form, including but not limited to, a vehicle, a component mounted in a vehicle, a road-side unit, a laptop computer, a wireless terminal including a mobile phone, a wireless handheld device, or wireless personal device.

[0022] In the present disclosure, a UE, a mobile station, a mobile node and a terminal may be used interchangeably.

[0023] The plurality of base stations 10 may be connected each other by a wired connection (for example, optical fiber) or a wireless connection (for example, an NR communication). The base station 10 may be connected to a core network 30 through another base station 10 or directly.

[0024] In the present disclosure, a BS may be referred to as the terms such as a NodeB, an eNodeB (eNB), a gNodeB (gNB), a radio access network (RAN), a carrier, a component carrier, a sector, a cell, a cell group, a super cell, a macro cell, a small cell, a femto cell, a pico cell, and so on. In the present disclosure, a network may mean an apparatus (for example, a BS) included in the network.

[0025] In the present disclosure, a term “node” is used as a general term which includes user equipment (UE), a relay node, a vehicle mounted module, a station, a network infrastructure node such as a base station (BS), a roadside unit, a repeater, a transponder, a wireless router, a controller, an access point, a transmission point (TP), a reception point (RP), a transmission / reception point (TRP), a panel, and sub-systems thereof. In the present disclosure, these entities (apparatuses, devices) may be used interchangeably.

[0026] The communication between UE 10 and BS 20 may be transferred via one or more apparatuses for NTN, e.g., a Geostationary Earth Orbit (GEO) satellite, a Medium-Earth Orbit (MEO), a Low Earth Orbit (LEO) satellite, a High Altitude Platform Station (HAPS), an NTN payload and an NTN gateway. In the present disclosure, the BS 20 may include a BS in a terrestrial network and / or a BS in NTN (or the BS on / within the above one or more apparatuses for NTN). In the present disclosure, the BS and the above one or more apparatuses for NTN may be used interchangeably.

[0027] The NTN (or the system 1) may provide a non-terrestrial NR access to the UE 10 by means of the NTN payload and the NTN Gateway. A wireless link between the NTN payload and the UE 10 may be called as a service link, and a wireless link between the NTN Gateway and the NTN payload may be called as a feeder link.

[0028] A satellite, such as GEO, MEO, LEO and HAPS, may be a space-borne vehicle orbiting the Earth embarking the NTN payload. The NTN payload may be a network node, embarked on board the satellite, providing connectivity functions, between the service link and the feeder link. The NTN Gateway may be an earth station (also referred to as a ground station) located at the surface of the earth, providing connectivity to the NTN payload using the feeder link.

[0029] The NTN payload may transparently forward the radio protocol received from the UE 10 (via the service link) to the NTN Gateway (via the feeder link) and vice-versa.

[0030] A satellite may directly communicate with another satellite via inter-satellite link (ISL). The ISL may work as a satellite backhaul.

[0031] The core network 30 may include at least one of Evolved Packet Core (EPC), 5G Core Network (5GCN), and so on.

[0032] In the system 1, an orthogonal frequency division multiplexing (OFDM)-based wireless access scheme may be used. For example, in at least one of the downlink (DL) communication and the uplink (UL) communication, Cyclic Prefix OFDM (CP-OFDM), Discrete Fourier Transform Spread OFDM (DFT-s-OFDM), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA), and the like may be used.

[0033] <Functional / Hardware Configuration of Device> FIG. 2 is a schematic diagram illustrating an exemplary functional configuration of each device for some embodiments of the present disclosure. For example, the UE 10 may have a control unit 110, a communication unit 120, an input / output unit 130, and a storage unit 140.

[0034] The BS 20 may have similar functional configurations. For this reason, in this exemplary functional configuration, the sign of the functional block corresponding to each device is also shown with the largest digit of the sign indicating each device (e.g., the largest digit "2" of "20" for BS 20) replaced with "1". In the following, the functional blocks relating to the UE 10 will be explained, but it is understood that the same explanation applies to other devices as well.

[0035] In this example, the functional blocks of the characteristic parts of the system are mainly shown, and each device may also have other functional blocks necessary for other processes. The configuration may also not include some of the functional blocks.

[0036] Note that in the present disclosure, the words such as an apparatus, a circuit, a device, a section, a unit, and so on may be interchangeably interpreted.

[0037] The control unit 110 implements control of the UE 10 and provides various functions. For example, the control unit 110 may control communication with other devices via the communication unit 120. The control unit 110 may also obtain information necessary for processing based on information received via the communication unit 120. The control unit 110 may be referred to as a processing unit.

[0038] The communication unit 120 communicates (transmits / receives) with other devices via wired / wireless communication. The communication unit 120 may obtain information from the received signal and output it to the control unit 110, or it may convert information input from the control unit 110 into a signal and transmit it. The communication unit 120 may perform measurement on the received signal and output the measurement result to the control unit 110. The communication unit 120 may be referred to as a transmitter, receiver, or transmitter / receiver. The communication unit 120 may be referred to as a measurement unit.

[0039] The input / output unit 130 may include an input unit that accepts input from a person. The input unit may be connected to a predetermined device, storage medium, etc., and may accept data input. The input unit may output input results to, for example, the control unit 110.

[0040] The input / output unit 130 may also include an output unit that outputs data, content, etc. in a format that can be perceived by humans. The output unit may comprise a display unit that displays images, an audio output unit that outputs sound, and the like.

[0041] The storage unit 140 stores (holds) various information used by the management unit 10 for processing. The control unit 110 may instruct the storage unit 140 to read and write data.

[0042] The functional blocks (components) in FIG. 2 may be implemented in arbitrary combinations of at least one of hardware and software. Each functional block may be realized by one apparatus that is physically or logically coupled, or may be realized by directly or indirectly connecting two or more physically or logically separate apparatuses (for example, via wire, wireless, or the like) and using these apparatuses. The functional blocks may be implemented by combining softwares into the apparatus described above or the plurality of apparatuses described above.

[0043] FIG. 3 is a schematic diagram illustrating an exemplary hardware configuration of each device for some embodiments of the present disclosure. For example, the UE 10, the BS 20, and the other devices in the present disclosure may function as a computer that executes the processes of the radio communication method(s) in the present disclosure. Each device may have an antenna 910, a Radio Frequency (RF) circuit 920, a processor 930, a network interface 940, an input device / output device 950, a memory 960, and a storage 970.

[0044] For example, the above control unit X10 (e.g., X = 1, 2; same below) described above may be implemented by the processor 930. The communication unit X20 may be implemented by the antenna 910 / RF circuit 920 / network interface 940. The input / output unit X30 may be implemented by the input device / output device 950. The storage unit X40 may be implemented by the memory 960 / storage 970.

[0045] The hardware configuration of each device may be configured to include one or more of the elements shown in this exemplary hardware configuration, or may be configured without some of the elements. For example, the UE 10 may not have a network interface 940.

[0046] The antenna 910 converts signals into radio waves and radiates said radio waves into space. The antenna 910 also receives radio waves in space and converts said radio waves into signals. The antenna 910 may be mounted in plurality, may include a transmitting antenna and a receiving antenna, or may include a single antenna for transmitting and receiving. The antenna 910 may include a directional antenna or may include multiple antenna elements. The antenna 910 may include one or more antenna elements and may enable different input-output antenna configurations.

[0047] The RF circuit 920 performs analog processing of signals transmitted and received via antenna 910. The RF circuit 920 may include filters (e.g., high frequency filters, low pass filters), amplifiers, modulators, frequency synthesizers, analog-to-digital conversion circuit, digital-analog conversion circuit, Fast Fourier Transform (FFT) / Inverse Fast Fourier Transform (IFFT) processing circuit, etc.

[0048] The RF circuit 920 may perform amplification, filter processing, demodulation to a baseband signal, etc. on the received radio frequency band signal and output to processor 930 RF circuit 920 may perform modulation to a radio frequency band, filter processing, amplification and transmit the radio frequency band signals via the transmitter / receiver antenna 910. The RF circuit 920 may perform physical layer processing (e.g., processing of lower functions of the physical layer), and may perform beamforming processing such as analog beamforming and digital beamforming processing.

[0049] The processor 930 may control the entire device. The processor 930 may read programs (program code), software (software modules), data, and the like from the storage 970 to the memory 960 and perform various processes according to these. For example, the processor 930 may execute and control an operating system (OS) program that is loaded into the memory 960. The programs are used to allow computers to execute at least part of methods (operations) shown in embodiments of the present disclosure. For example, the control unit 110 (210) may be implemented by control programs that are stored in the memory 960 and that operate on the processor 930, and other functional blocks may be implemented likewise.

[0050] The processor 930 may be configured by a central processing unit (CPU), which may include interfaces to peripheral devices, control units, arithmetic units, registers, and the like. The processor 930 may also be a microprocessor, Digital Signal Processor (DSP), Application Specific Integrated Circuit (ASIC), Programmable Logic Device (PLD), Field Programmable Gate Array (FPGA), Graphics Processing Unit (GPU), Neural Processing Unit (NPU), etc.

[0051] The processor 930 may perform digital processing of signals transmitted and received via the antenna 910 and the RF circuit 920. Said digital processing may include physical layer processing (e.g., processing of higher functions of the physical layer), processing of layers above the Medium Access Control (MAC) layer, modulation, demodulation, coding, decoding, scrambling, etc. The processor 930 also processes signals sent and received via network interface 940.

[0052] The processor 930 may include a plurality of processors or may be a single processor. The multiple processors may include a baseband processor that performs the digital processing described above and one or more processors that perform other processing (e.g., overall control).

[0053] The network interface 940 may be, for example, a network adapter, which may be wired to an external network to send and receive signals.

[0054] The RF circuit 920 / baseband processor / network interface 940 may be an integral part of the RF circuit 920 / baseband processor / network interface 940. The network interface 940 may be referred to as a network controller, network card, communication module, etc.

[0055] The input device / output device 950 may comprise an input device that accepts external input (e.g., keyboard, mouse, microphone, switches, buttons, sensors, etc.), an output device that performs external output (e.g., display, speaker, Light Emitting Diode (LED) lamp etc.), and a device (e.g., a touch panel) that integrates these devices. The sensors may include a locator (e.g., a receiver corresponding to Global Navigation Satellite System (GNSS)) to obtain position information.

[0056] The memory 960 is a computer-readable, non-transitory storage medium that stores a program to be executed by the processor 930, parameters related to said program, and various other information. The memory 960 is at least one of Read Only Memory (ROM), Erasable Programmable ROM (EPROM), Electrically EPROM (EEPROM), Random Access Memory (RAM), and flash memory. All or part of the memory 960 may be contained within processor 930. Memory 960 may be referred to as a register, cache, main memory (main storage), etc.

[0057] The storage 970 is a computer-readable, non-transitory storage medium that stores a variety of information. The storage 970 may include, for example, flexible disks, floppy (registered trademark) disks, magneto-optical disks (e.g., compact disc (Compact Disc ROM (CD-ROM), digital versatile disk, Blu-ray (registered trademark) disk), a removable disk, a hard disk drive (Hard Disc Drive (HDD)), a smart card, a flash memory device (e.g., Solid State Drive (SSD)), or at least one other. The storage 970 may be referred to as an auxiliary storage device.

[0058] The processor 930, memory 960, and other devices may be connected by a bus for communicating information. A single bus may be used within a device, or different buses may be used between devices.

[0059] The BS 20 may be separated into three elements: the Radio Unit (RU), the Distributed Unit (DU), and the Central Unit (CU). The RU implements RF processing and lower functions of the physical layer. The DU implements the upper functions of the physical layer, the functions of the MAC layer, and the functions of the Radio Link Control (RLC) layer. The CU realizes the functions of the Packet Data Convergence Protocol (PDCP) layer, the Service Data Adaptation Protocol (SDAP), and the Radio Resource Control (RRC) layer.

[0060] In this disclosure, BS 20 may include one device that realizes all the functions of RU, DU and CU, or may include multiple devices that each realize some of the functions of RU, DU and CU.

[0061] Other devices in the present disclosure may also be implemented by multiple devices that are physically located apart from each other. Conversely, a plurality of different devices in this disclosure may be implemented as a single device.

[0062] Some or all of the devices in this disclosure may also mean logical devices realized by virtual machines, containers, Docker, etc., or physical devices that operate such logical devices.

[0063] <Store & Forward (S&F) mode for Non-Terrestrial Network (NTN)> Modern mobile communication services may utilize both terrestrial and non-terrestrial networks (NTN). For instance, 3GPP radio interfaces incorporate NTN features for 4G and 5G.

[0064] The key difference is that terrestrial networks have fixed-location nodes, while NTNs rely on satellite-based nodes. While radio protocols are similar, deployment of data transport methods varies; terrestrial networks use fiber optics or point-to-point microwave links, whereas satellites rely on radio feeder links with ground stations. A geostationary satellite's feeder link functions like a terrestrial network, where a feeder link acts like a cable or point-to-point microwave link. In contrast, low orbit moving satellites need to switch between various ground stations. Maintaining continuous connections through feeder links requires a dense and costly ground station deployment for moving satellites, which is not always practical.

[0065] To resolve this, 3GPP is standardizing a Store & Forward (S&F) mode (see RP-240776; “Revised WID on Non-Terrestrial Networks (NTN) for Internet of Things (IoT) Phase 3”), allowing satellites to collect data from users when feeder links are unavailable and sending it to ground stations once feeder link connections are restored.

[0066] The S&F mode is suitable exclusively for mobile-originated data that can tolerate delays. The satellite informs the user segment of its operational mode, whether it is in S&F or real-time mode. In S&F mode, users engaged in real-time traffic are either released from the system or placed on hold until the feeder link is restored. When real-time mode is activated, the backlogged real-time users may quickly access the system. Without proper traffic control, their access requests may lead to numerous collisions. Users who successfully connect immediately after the switch (i.e., switch from the S&F mode to the real-time mode) may also cause a surge in paging requests. As a result, transitioning back to real-time mode can cause a sudden increase in traffic, leading to congestion and rendering the system nearly inoperable until the issue is resolved.

[0067] Note that, in the present disclosure, “user segment” may be interchangeably read as the as “user,” “UE,” and the like. In the present disclosure, “S&F mode” may be interchangeably read as “non-real-time mode,” “delay-tolerant mode,” “regenerative mode,” “barred mode,” “first mode,” and the like. In the present disclosure, “real-time mode” may be interchangeably read as “non-S&F mode,” “transparent mode,” “non-barred mode,” “second mode,” and the like.

[0068] One existing method is access class barring, which categorizes users into different classes. Initially, it prevents the users from accessing the system, and then progressively allows each class access through signaling via system information broadcasts (MIB / SIB). This commonly employed method in terrestrial networks mitigates traffic surges and prevents congestion, particularly following a node restart, which is comparable to a mode change. Another existing method involves randomization, where the network sends a parameter in broadcast system information. The user generates a random number and sees the cell as barred if it doesn't meet the parameter's criterion. This approach allows for a gradual traffic increase by adjusting the randomization parameter.

[0069] Although both techniques could be used for NTN after S&F mode switching, they are slow, dependent on complex centralized algorithms, and create considerable signaling overhead since system information needs to be updated and re-acquired at each step.

[0070] In S&F capable satellites, the switching times from S&F mode back to real-time mode may be known in advance and advertised to the user segment. This may facilitate local management of traffic surges during mode switching without necessitating frequent system information updates or centralized algorithms. One of key ideas of some embodiments in the present disclosure is that the user segment receives the switching time information and independently randomizes their individual access times within a parameterized transmission window after the switching instant, thereby enabling a distributed approach for traffic congestion avoidance.

[0071] One of the closest prior arts is probabilistic access class barring, which involves network signaling of a randomization parameter. Figure 4 exemplifies a procedure of probabilistic access class barring, where p is the randomization parameter (barring parameter), and r is a user's random number.

[0072] In step S101, the user receives the barring parameter p. In step S102, the user draws the random number r which is greater than zero but less than or equal to one. In step S103, the user checks whether the random number r is equal to or exceeds the parameter p.

[0073] When r is equal to or exceeds p, the user considers the cell barred and computes a barring timer value, and starts the timer in step S104. When r is not equal to or do not exceed p, the user considers the cell is not barred in step S106 and stops the procedure.

[0074] The user retries after the timer expires (step S105), repeating until access is granted. The network iteratively adjusts randomization parameters to manage traffic load, ensuring users are not indefinitely barred.

[0075] In contrast, some embodiments in the present disclosure may use a finite transmission window that begins at the mode switching instant. Users may choose their access attempt time within this window by utilizing, e.g., a random and uniform selection method. The process may permit an access attempt per user within the transmission window, with random transmission delays but without barring any users. These individual delays may help manage traffic surges from returning and arriving real-time users by distributing access attempts evenly over a period.

[0076] One of benefits of some embodiments in the present disclosure is its distributed nature, which may simplify operations by eliminating the need for centralized algorithms. Furthermore, it may avoid the necessity for system information updates, thereby reducing signaling load and minimizing the frequency with which users must re-acquire system information.

[0077] <Method> The methods (wireless (or radio) communication methods, control methods) described below may be applied in the system 1 described above. A transmitter (or receiver) in the methods may be the UE 10 and may be considered as a UE. A receiver (or transmitter) in the methods may be the BS 20 and may be considered as a BS.

[0078] The present disclosure may disclose a method and apparatus for distributed access control preventing traffic surges during S&F mode switching.

[0079] The method can be applied to any wireless communication system but, in the rest of the disclosure, the method is exemplified with, but not limited to, non-terrestrial mobile radio communication systems, such as 3GPP LTE and / or NR radio access technology.

[0080] The method may make use of radio parameters that may be provided to a user through dedicated signaling, broadcast system information blocks (SIBs), system information blocks via dedicated signaling upon request, master information blocks (MIBs), or pre-configurations. For example, a parameter may be sent in a connection release message when the user is released from the system. Pre-configuration may involve smart card settings, network signaling, or fixed specification values. Examples of such parameters are instant of time and window sizes as exemplified below.

[0081] In one embodiment, a S&F capable network node may signal (indicate, announce, communicate) a point of time for switching from S&F mode to real-time mode. The switching point of time may be provided to a user, for example, through broadcast system information (MIB, SIB, etc.). In the present disclosure, the switching point of time may be referred to as the mode switching time, the switching time, and the like. The mode switching time may be expressed, for example, in terms of system frame number, slot number, absolute time, relative time to another event such as switching to S&F mode whereof it may be inferred implicitly from a duration of S&F operating mode.

[0082] The mode switching time may also be communicated in advance through a pre-arranged schedule, such as a list or another type of signaled or indicated data structure. In the present disclosure, the data structure may be any data structure such as a vector, array, list, table, and the like.

[0083] The announced switching time may be accompanied by the length of a transmission window. The window length may be conveyed through separate system information broadcasts (MIB / SIB) or dedicated signaling. The window length may be expressed, for example, in terms of system frame numbers, radio frames, sub-frames, slots, symbols, hyper-frames, absolute time, or relative time compared to the switching instant.

[0084] Upon or after reception of the switching point, the user may select one or more transmission time(s) within the window.

[0085] In another embodiment, the transmission time selection may be based on random and / or uniform methods. For example, if the window length is expressed in terms of absolute or relative time, the user may draw a random number from the switching point of time (or zero or one) to the end of the window (or window length), start a timer that is set to the randomized time. The transmission time within the window may be the time of the timer expiry.

[0086] In another example, the selection may be based on radio frame counting and the window length may be set in radio frames. The user may pick a random integer between one and the window length, and may count radio frames post S&F mode switching. Transmission may occur when this count matches the random integer. Figure 5 shows this method with a window of N frames (hereinafter N means transmission window length) and a random frame number (i.e., transmission time) n.

[0087] In step S201, the user receives indication of switching from the S&F mode to the real-time mode and the transmission window length N.

[0088] In step S202, the user randomizes the transmission time n, where n is greater than 0 and less than or equal to N.

[0089] In step S203, the user checks whether the current radio frame is the nth radio frame (or, the nth radio frame post S&F mode switching).

[0090] When the current radio frame is the nth radio frame, the user also checks whether data is in transmitter buffer in step S204. When the data is in the transmitter buffer, the user initiates transmission in the nth radio frame in step S205. When the data is not in the transmitter buffer, the user stops the procedure.

[0091] In another embodiment, the transmission time selection may be derived from the user’s access class. For example, the access class number or access class identity may be used as the radio frame number for the transmission attempt (i.e., transmission time). The access class number or access class identity may be sent to the user.

[0092] In another embodiment, the transmission time selection may be derived from the user’s identity. For example, the first or last digit(s) of the user identity may be used as the radio frame number for the transmission attempt. The user’s identity may be International Mobile Subscriber Identity (IMSI), Temporary Mobile Subscriber Identity (TMSI), Serving Temporary Mobile Subscriber Identity (S-TMSI), Radio Network Temporary Identity (RNTI), UE Contention Resolution Identity, and the like.

[0093] In the present disclosure, “S-TMSI” may mean “System Architecture Evolution(SAE)-Temporary Mobile Subscriber Identity,” “5G-Short(S)-Temporary Mobile Subscriber Identity,” and the like. In the present disclosure, “RNTI” may be Cell-RNTI (C-RNTI), Temporary Cell RNTI (TC-RNTI), Random Access RNTI (RA-RNTI), RNTI for Diversity Slotted ALOHA (DSA), RNTI for Contention Resolution DSA (CRDSA), and the like.

[0094] In another embodiment, the transmission time selection may be derived from an earlier event. For example, it may be derived from the time when the UE switched last from Radio Resource Control (RRC) Connected mode to RRC Idle mode, or vice-versa. In other examples, it may be derived from the time when the UE last acquired a specific system information broadcast message (e.g., MIB, SIB1, SIBX (X is an integer)), when the UE last performed cell selection or cell re-selection or received a specific message such as RRC reconfiguration message. In another example, it may be derived from the time when the UE initiated a transmission as from any embodiment in the present disclosure.

[0095] In another embodiment, the User Equipment (UE) may store the window length value in its memory. In case the signalling of window length value fails, or the value is absent, the stored value may be used.

[0096] In another embodiment, the window length may have a default value. In case the signalling of window length value fails, or the value is absent, the default value may be used.

[0097] In another embodiment, one or more of the transmission selection parameters may be associated with the user’s access class.

[0098] While the example embodiments in the present disclosure relate to the user segment or UE, embodiments in the present disclosure may be implemented by any node.

[0099] While the example embodiments in the present disclosure relate to real-time traffic users, embodiments in the present disclosure may be implemented to any other type of traffic that may be barred in S&F mode.

[0100] While the example embodiments in the present disclosure relate to the example S&F mode, embodiments in the present disclosure are not limited to the S&F mode and may be implemented for example for any scenario where there may be a switching from barred mode to non-barred mode, or from non real-time mode to real time mode.

[0101] The present disclosure may describe a method for distributed access control to prevent traffic congestion in non-terrestrial networks when switching from store-and-forward to real-time mode. It may reduce algorithm complexity and signalling overhead compared to prior art centralized solutions, making it suitable for satellite-based NTN deployments. The key feature may be using local decisions in the user segment with random and / or uniform methods within a configured transmission window after the store-and-forward mode switch.

[0102] <Supplementary Notes> Regarding embodiments of the present disclosure, the following supplementary notes are given. <Supplementary Note 1> A terminal comprising: a receiver configured to receive an indication of a switching time from a first mode to a second mode and a length of a transmission window that starts at the switching time; a processor configured to determine a transmission time within the transmission window; and a transmitter configured to initiate a transmission at the determined transmission time. <Supplementary Note 2> The terminal according to supplementary note 1, wherein the processor is configured to determine one or more transmission times within the transmission window. <Supplementary Note 3> The terminal according to any one of supplementary notes 1 to 2, wherein the processor is configured to determine the transmission time based on an access class of the terminal. <Supplementary Note 4> The terminal according to any one of supplementary notes 1 to 3, wherein the processor is configured to determine the transmission time based on an identity of the terminal. <Supplementary Note 5> The terminal according to any one of supplementary notes 1 to 4, wherein the identity of the terminal is one of an International Mobile Subscriber Identity (IMSI), a Temporary Mobile Subscriber Identity (TMSI), or a Radio Network Temporary Identity (RNTI). <Supplementary Note 6> The terminal according to any one of supplementary notes 1 to 5, wherein the processor is configured to determine the transmission time based on a time of a previously occurred event. <Supplementary Note 7> The terminal according to any one of supplementary notes 1 to 6, wherein the length of the transmission window is expressed in a number of radio frames, and the processor determines a radio frame number within said number of radio frames as the transmission time. <Supplementary Note 8> The terminal according to any one of supplementary notes 1 to 7, further comprising a memory configured to store a pre-configured value for the length of the transmission window, wherein the processor is configured to use the stored value when the length of the transmission window is not received. <Supplementary Note 9> The terminal according to any one of supplementary notes 1 to 8, wherein the processor is configured to use a default value for the length of the transmission window when the length of the transmission window is not received. <Supplementary Note 10> The terminal according to any one of supplementary notes 1 to 9, wherein the first mode is a store-and-forward mode and the second mode is a real-time mode for a non-terrestrial network. <Supplementary Note 11> A method performed by a terminal, the method comprising: receiving an indication of a switching time from a first mode to a second mode and a length of a transmission window that starts at the switching time; determining a transmission time within the transmission window; and initiating a transmission at the determined transmission time. <Supplementary Note 12> A base station comprising: a processor configured to determine a switching time for a terminal to switch from a first mode to a second mode and a length of a transmission window that starts at the switching time; and a transmitter configured to transmit, to the terminal, an indication of the switching time and the length of the transmission window. <Supplementary Note 13> A communication system comprising a terminal according to any one of supplementary notes 1 to 10 and a base station according to supplementary note 12.

[0103] <Variations> Embodiments in the present disclosure may be used for any 3GPP radio access technologies, for example, 3GPP 4G technology referred to as Long Term Evolution (LTE), 3GPP 5G technology referred to as New Radio (NR) or future 3GPP radio technology generations such as 6G or 7G. While the examples in the present disclosure relate to 3GPP technologies, embodiments in the present disclosure could be used for non-3GPP technologies, for example, Bluetooth, Institute of Electrical and Electronics Engineers (IEEE) and its 802.11 variants, Wi-Fi, Worldwide Interoperability for Microwave Access (WiMAX), etc.

[0104] In the present disclosure, any signals (e.g., for indication, configuration and notification of some information) from a node to another node may be transmitted using any one or combinations of Radio Resource Control (RRC) layer signaling, Medium Access Control (MAC) layer signaling, and physical (PHY) layer signaling, even if not explicitly stated.

[0105] The RRC layer signaling may be an RRC message or an RRC information element. The MAC layer signaling may be a MAC control element (MAC CE) or a MAC Protocol Data Unit (PDU). The PHY layer signaling may be downlink control information (DCI), uplink control information (UCI), or sidelink control information (SCI).

[0106] Furthermore, a BS in the present disclosure may be interpreted as a UE. For example, each embodiment of the present disclosure may be applied to the case where a communication between a BS and a UE is replaced with a communication between a plurality of UEs. In the case, the UE may have the functions of the BS described above. In the case, "uplink" and "downlink" may be interpreted as a UE-to-UE link (for example, "sidelink"). For example, an uplink channel, a downlink channel and so on may be interpreted as a sidelink channel.

[0107] Any parameters, values and information in the present disclosure may be indicated from a node to another node, even if not explicitly stated. In the present disclosure, “X” and “information on X” may be used interchangeably.

[0108] In the present disclosure, a time unit for radio communication may be replaced with (or interchangeably used as) another time unit for radio communication. For example, a radio frame (frame), a hyper frame, a subframe, a slot, a sub-slot, and a symbol all express time units for radio communication.

[0109] In the present disclosure, the terms “notify,” “report,” “indicate,” “designate,” “activate,” “deactivate,” “select,” “configure,” “pre-configure,” “update,” “determine,” and any variation of the terms may be read interchangeably.

[0110] In the present disclosure, "equal to or smaller than," "smaller than," "equal to or larger than," "larger than," "equal to," and the like may be interchangeably used. In the present disclosure, words such as "good," "bad," "much," "little," "large," "small," "high," "low," "early," "late," "wide," "narrow," and the like may be interchangeably used irrespective of positive degree, comparative degree, and superlative degree. In the present disclosure, the words (such as "good," "bad," ...) and expressions obtained by adding "i-th" (i is any integer) to the words may be interchangeably used irrespective of positive degree, comparative degree, and superlative degree (for example, "best" may be interpreted as "i-th best," and vice versa).

[0111] In the present disclosure, "of," "for," "regarding," "related to," "associated with," and the like may be used interchangeably.

[0112] As used in the present disclosure, use of the term “or” in a list of items indicates an inclusive list. The list of items may be prefaced by a phrase such as “at least one of” or “one or more of.” For example, a list of at least one of A, B, or C includes A or B or C or AB (i.e., A and B) or AC or BC or ABC (i.e., A and B and C). Also, as used in the present disclosure, prefacing a list of conditions with the phrase “based on” shall not be construed as “based only on” the set of conditions and rather shall be construed as “based at least in part on” the set of conditions. For example, an outcome described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure.

[0113] In the present disclosure, the terms “comprise,” “include,” or “contain” may be used interchangeably and have the same meaning and are to be construed as inclusive and open-ended. The terms “comprise,” “include,” or “contain” may be used before a list of elements and indicate that at least all of the listed elements within the list exist but other elements that are not in the list may also be present. For example, if A comprises B and C, both {B, C} and {B, C, D} are within the scope of A.

[0114] The present disclosure, in connection with the accompanied drawings, describes example configurations that are not representative of all the examples that may be implemented or all configurations that are within the scope of the present disclosure. The term “exemplary” should not be construed as “preferred” or “advantageous compared to other examples” but rather “an illustration, an instance or an example.” By reading the present disclosure, including the description of the embodiments and the drawings, it will be appreciated by a person of ordinary skills in the art that the technology disclosed herein may be implemented using alternative embodiments. The person of ordinary skill in the art would appreciate that the embodiments, or certain features of the embodiments described herein, may be combined to arrive at yet other embodiments for practicing the technology described in the present disclosure. Thus, the disclosure is not limited to the examples and designs described herein but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.

[0115] The flowcharts and block diagrams in the figures illustrate examples of the architecture, functionality, and operation of possible implementations of systems, methods, and devices according to various embodiments. It should be noted that, in some alternative implementations, the functions noted in blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments.

[0116] It is understood that the described embodiments are not mutually exclusive, and elements, components, materials, or steps described in connection with one example embodiment may be combined with, or eliminated from, other embodiments in suitable ways to accomplish desired design objectives. Any embodiment (two or more) used in the present disclosure may be used in combination.

[0117] Reference herein to “some embodiments” or “some exemplary embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment. The appearance of the phrases “one embodiment,” “some embodiments” or “another embodiment” in various places in the present disclosure do not all necessarily refer to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. In the present disclosure, “an / one embodiment,” “(some) embodiments” and “another embodiment” may be used interchangeably.

[0118] The articles “a” and “an” as used in the present disclosure and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form.

[0119] Unless explicitly stated otherwise, each numerical value and range in the present disclosure may be interpreted as being approximate as if the word “about” or “approximately” preceded the value of the value or range.

[0120] The term "connected" or any variation of the term as used in the present disclosure mean all direct or indirect connections between two or more elements, and may include the presence of one or more intermediate elements between two elements that are "connected" to each other. The connection between the elements may be physical, logical, or a combination thereof. For example, "connection" may be interpreted as "access."

[0121] Although the elements in the following method claims, if any, are recited in a particular sequence, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

[0122] It is appreciated that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the present disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the present disclosure. Certain features described in the context of various embodiments are not essential features of those embodiments, unless noted as such.

[0123] It will be further understood that various modifications, alternatives, and variations in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of described embodiments may be made by those skilled in the art without departing from the scope. Accordingly, the following claims embrace all such alternatives, modifications, and variations that fall within the terms of the claims.

Claims

1. A terminal comprising: a receiver configured to receive an indication of a switching time from a first mode to a second mode and a length of a transmission window that starts at the switching time; a processor configured to determine a transmission time within the transmission window; and a transmitter configured to initiate a transmission at the determined transmission time.

2. The terminal according to claim 1, wherein the processor is configured to determine one or more transmission times within the transmission window.

3. The terminal according to claim 1, wherein the processor is configured to determine the transmission time based on an access class of the terminal.

4. The terminal according to claim 1, wherein the processor is configured to determine the transmission time based on an identity of the terminal.

5. The terminal according to claim 4, wherein the identity of the terminal is one of an International Mobile Subscriber Identity (IMSI), a Temporary Mobile Subscriber Identity (TMSI), or a Radio Network Temporary Identity (RNTI).

6. The terminal according to claim 1, wherein the processor is configured to determine the transmission time based on a time of a previously occurred event.

7. The terminal according to claim 1, wherein the length of the transmission window is expressed in a number of radio frames, and the processor determines a radio frame number within said number of radio frames as the transmission time.

8. The terminal according to claim 1, further comprising a memory configured to store a pre-configured value for the length of the transmission window, wherein the processor is configured to use the stored value when the length of the transmission window is not received.

9. The terminal according to claim 1, wherein the processor is configured to use a default value for the length of the transmission window when the length of the transmission window is not received.

10. The terminal according to claim 1, wherein the first mode is a store-and-forward mode and the second mode is a real-time mode for a non-terrestrial network.

11. A method performed by a terminal, the method comprising: receiving an indication of a switching time from a first mode to a second mode and a length of a transmission window that starts at the switching time; determining a transmission time within the transmission window; and initiating a transmission at the determined transmission time.

12. A base station comprising: a processor configured to determine a switching time for a terminal to switch from a first mode to a second mode and a length of a transmission window that starts at the switching time; and a transmitter configured to transmit, to the terminal, an indication of the switching time and the length of the transmission window.

13. A communication system comprising a terminal according to any one of claims 1 to 10 and a base station according to claim 12.

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