Device and method for performing group handover in wireless communication system

Abstract

An operation method of a base station in a wireless communication system is disclosed. The method comprises the steps of: receiving, from a plurality of terminals, a measurement report message including time information about a communication service; forming a handover group for the plurality of terminals on the basis of a processing time derived on the basis of the time information; transmitting a handover request to a target base station; receiving a handover request response from the target base station; and transmitting a handover command to the plurality of terminals.

Description

Device and method for performing group handover in a wireless communication system

[0001] The present disclosure relates to a wireless communication system, and more particularly, to a device and method for performing group handover in a wireless communication system.

[0002]

[0003] Mobile communication systems are evolving with each generation. Following the successful commercialization of the LTE (long term evolution) system, 5G (5 th The standardization and commercialization of 6G (6 generation) systems are in progress, and currently th There is also active discussion about the generation system.

[0004] Meanwhile, 3GPP (3 rd The Generation Partnership Project is working on standardization of non-terrestrial networks (NTNs) that are not spatially constrained to provide effective communication services.

[0005]

[0006] The present disclosure provides a device and method for efficiently performing handover in a wireless communication system.

[0007] The present disclosure provides a device and method for performing group handover in a wireless communication system.

[0008] The present disclosure provides a device and method for forming a handover group for a plurality of terminals in a wireless communication system.

[0009] The present disclosure provides an apparatus and method for performing a handover for a handover group in a wireless communication system.

[0010] The present disclosure provides a device and method for improving handover performance in a non-terrestrial network environment in a wireless communication system.

[0011] The present disclosure provides a device and method for forming a handover group through processing time based on time information.

[0012] The present disclosure provides a device and method for forming a handover group using time information regarding a service that guarantees an upper limit of delay time and a service that guarantees consistency of delay time.

[0013] The present disclosure provides a device and method for re-forming a handover group based on resources of a target base station in a wireless communication system.

[0014]

[0015] According to one aspect of the present disclosure, a method of operating a base station in a wireless communication system is disclosed. The method may include the steps of receiving a measurement report message including time information for a communication service from a plurality of terminals, forming a handover group for the plurality of terminals based on the processing time derived based on the time information, transmitting a handover request to a target base station, receiving a handover request response from the target base station, and transmitting a handover command to the plurality of terminals.

[0016]

[0017] According to another aspect of the present disclosure, a method for operating a terminal in a wireless communication system is disclosed. The method includes the steps of measuring signal strength, transmitting a measurement report message including time information for a communication service to a base station based on satisfaction of a handover condition, receiving a handover command from the base station, and performing a RACH (Random Access Channel) to a target base station, wherein the terminal is included in a handover group formed of a plurality of terminals based on a processing time, and the processing time can be calculated based on the time information.

[0018] According to another aspect of the present disclosure, a base station of a wireless communication system is disclosed. The base station includes a transceiver and a processor connected to the transceiver, wherein the processor controls to receive a measurement report message including time information for a communication service from a plurality of terminals, controls to form a handover group for the plurality of terminals based on the processing time derived based on the time information, controls to transmit a handover request to a target base station, controls to receive a handover request response from the target base station, and controls to transmit a handover command to the plurality of terminals.

[0019] According to another aspect of the present disclosure, a terminal of a wireless communication system is disclosed. The terminal includes a transceiver and a processor connected to the transceiver, wherein the processor comprises: a step of measuring signal strength; a step of controlling transmission of a measurement report message including time information for a communication service to a base station based on satisfaction of a handover condition; a step of controlling reception of a handover command from the base station; and a step of performing an RACH to a target base station, wherein the terminal is included in a handover group formed of a plurality of terminals based on a processing time, and the processing time can be calculated based on the time information.

[0020]

[0021] According to embodiments of the present disclosure, handover for terminals using a non-terrestrial network can be effectively performed.

[0022]

[0023] FIG. 1 illustrates an example of a satellite network according to one embodiment of the present disclosure.

[0024] Figure 2 illustrates an example of handover in a satellite network.

[0025] FIG. 3 illustrates another example of a satellite network according to one embodiment of the present disclosure.

[0026] FIG. 4 illustrates a configuration of a device in a wireless communication system according to one embodiment of the present disclosure.

[0027] Figure 5 illustrates elements of a measurement report in a wireless communication system.

[0028] Figure 6 illustrates an example of a measurement report in a wireless communication system.

[0029] FIG. 7 illustrates time-engineered service conditions in a wireless communication system according to one embodiment of the present disclosure.

[0030] FIG. 8 illustrates an NR subframe in a wireless communication system according to one embodiment of the present disclosure.

[0031] FIG. 9 illustrates an example of a group handover procedure in a wireless communication system according to one embodiment of the present disclosure.

[0032] FIG. 10 illustrates an example of an operation procedure of a terminal in a wireless communication system according to one embodiment of the present disclosure.

[0033] FIG. 11 illustrates an example of an operation procedure of a serving cell in a wireless communication system according to one embodiment of the present disclosure.

[0034] FIG. 12 illustrates an example of an operation procedure of a target cell in a wireless communication system according to one embodiment of the present disclosure.

[0035]

[0036] The terms used in these examples are selected from widely used, common terms, taking into account the functions they serve. However, these terms may vary depending on the intentions of engineers working in the field, precedents, the emergence of new technologies, etc. Furthermore, in certain cases, terms may be arbitrarily selected by the applicant, in which case their meanings will be described in detail in the relevant section. Therefore, the terms used in these examples should not be defined simply as names, but rather based on the meanings they embody and the overall content of these examples.

[0037] These embodiments may be modified in various ways and may take on various forms. Therefore, some embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit these embodiments to a specific disclosed form, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of these embodiments. The terminology used herein is solely for the purpose of describing the embodiments and is not intended to limit these embodiments.

[0038] Unless otherwise defined, the terms used in these examples have the same meaning as commonly understood by those of ordinary skill in the technical field to which these examples pertain. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an idealized or overly formal sense unless explicitly defined in these examples.

[0039] Meanwhile, unlike terrestrial network platforms, non-terrestrial network platforms move at very high speeds, requiring frequent handovers to support seamless communication services. Furthermore, non-terrestrial network platforms support relatively wide coverage, allowing multiple terminals to simultaneously perform handovers. Ultimately, the frequent handovers between multiple terminals in non-terrestrial network environments pose a significant disadvantage: signaling overhead is significantly higher than in terrestrial network environments.

[0040] Signaling overhead in communication networks can reduce communication system performance, resulting in delays, resource waste, and interference. Consequently, new procedures are needed to overcome the signaling overhead associated with frequent handovers in non-terrestrial network environments. Therefore, the present disclosure proposes a group handover technology for non-terrestrial network environments to address these issues.

[0041]

[0042] FIG. 1 illustrates an example of a satellite network according to one embodiment of the present disclosure.

[0043] Referring to FIG. 1, the satellite network includes a terminal (110), satellites (120-1, 120-2), and a gateway (130). The terminal (110) is a user device equipped with hardware and software that receives cellular data from the satellite (120-1), and may be a mobile or fixed device. For example, the terminal (110) may include a mobile phone, a smartphone, a wearable device, or a UE (User Equipment). In addition, the terminal (110) is not limited to the above-described examples, and any electronic device capable of cellular communication, such as a laptop or tablet PC, may be included. The terminal (110) is not limited to the above-described examples. Although the satellite network in FIG. 1 is illustrated as including only a single terminal (110), this is merely an exemplary embodiment, and the present invention is not limited thereto, and it is of course possible to include a plurality of terminals (110).

[0044] Specifically, the terminal (110) can support a communication protocol (e.g., LTE communication protocol, LTE-A communication protocol, NR communication protocol, etc.) specified in the 3GPP (3rd generation partnership project) standard. The plurality of communication nodes (110 to 130) can support CDMA (code division multiple access) technology, WCDMA (wideband CDMA) technology, TDMA (time division multiple access) technology, FDMA (frequency division multiple access) technology, OFDM (orthogonal frequency division multiplexing) technology, Filtered OFDM technology, CP (cyclic prefix)-OFDM technology, DFT-s-OFDM (discrete Fourier transform-spread-OFDM) technology, OFDMA (orthogonal frequency division multiple access) technology, SC (single carrier)-FDMA technology, NOMA (non-orthogonal multiple access) technology, GFDM (generalized frequency division multiplexing) technology, FBMC (filter bank multi-carrier) technology, UFMC (universal filtered multi-carrier) technology, SDMA (space division multiple access) technology, etc.

[0045] Satellites (120-1, 120-2) fly in fixed orbits and form beams toward the ground, thereby providing cells with a certain coverage area. In connection with the present disclosure, satellite (120-1) may be referred to as a serving satellite, and satellite (120-2) may be referred to as a target satellite, and these terms may be used interchangeably. Additionally, the serving satellite and target satellite may be referred to as a serving cell and a target cell, respectively, and these terms may be used interchangeably. The gateway (130) provides the satellites (120-1, 120-2) with links that enable them to access the network.

[0046] The link between the terminal (110) and the satellite (120-1) is called a service link and may be based on the NR standard defined by 3GPP. The link between the satellites (120-1, 120-2) and the gateway (130) is called a feeder link and may be based on a 3GPP or non-3GPP wireless interface. The inter-satellite link (ISL) may be primarily used for regenerative satellites.

[0047] For transparent satellites based on the NR-RAN architecture, the satellite radio interfaces for feeder and service links may be NR-Uu. For transparent satellites, the satellite performs radio frequency filtering, frequency conversion, and amplification. For regenerative satellites, onboard functions are built into the satellite, allowing the satellite to perform some or all base station functions, such as switching and routing, coding and modulation, and decoding and demodulation, in addition to radio frequency filtering, frequency conversion, and amplification.

[0048]

[0049] FIG. 2 illustrates an example of a handover in a satellite network. Referring to FIG. 2, each satellite according to the present disclosure (a serving satellite, a candidate satellite, and a target satellite in FIG. 2) can provide a cell with a certain size of coverage to a terminal. Additionally, each satellite can be connected to a gateway (130) via a feeder link. Here, the link may be a link based on the NR standard. Alternatively, a newly defined link in an evolved next-generation wireless communication system may be adaptively applied, or a link based on various interfaces of a communication system introduced due to industry needs other than the NR standard may be applied. Hereinafter, in relation to the present disclosure, a serving cell, a target cell, and a candidate cell may be mentioned, each corresponding to the serving satellite, the target satellite, and the candidate satellite, and may be used interchangeably.

[0050] A serving satellite may refer to a satellite currently connected to a terminal in a satellite network and providing communications. For example, a serving satellite may include, but is not limited to, geostationary satellites, low-Earth orbit satellites, medium-Earth orbit satellites, polar orbit satellites, elliptical orbit satellites, and the like. Furthermore, the satellites presented in this disclosure are not limited to a specific satellite configuration and may include any satellite or combination of satellites capable of providing functional connectivity between the gateway (130) and the terminal (110).

[0051] A target satellite may refer to a satellite that is replaced by a serving satellite when the strength of a signal received by the terminal (110) satisfies a handover condition as the terminal (110) moves out of the beam coverage of the serving satellite or is located near the boundary.

[0052] A candidate satellite can refer to a satellite that can be selected as a target satellite in a satellite network. That is, a candidate satellite can be determined based on at least the satellite's visibility, signal strength, connection stability, latency, and network load.

[0053] In connection with the present disclosure, the terminal (110) periodically measures the signal strength of the serving satellite and surrounding satellite base stations and reports the signal strength and the time corresponding to its communication service to the serving satellite. Subsequently, if the signal strength received from the serving satellite satisfies a predetermined handover condition, the terminal (110) attempts a handover to the target satellite. At this time, the serving satellite may wait for a waiting period before performing the handover to reduce signaling overhead resulting from frequent handovers.

[0054]

[0055] FIG. 3 illustrates another example of a satellite network according to one embodiment of the present disclosure. FIG. 3 illustrates an example of an NTN that provides non-terrestrial connectivity to a UE (210) using an NTN payload (220) and an NTN gateway (230). Here, the UE (210) may have substantially the same configuration as the terminal (110) described in FIG. 1. Referring to FIG. 2, the link between the NTN payload (220) and the UE (210) is a service link and may be based on a Uu interface. The link between the NTN payload (220) and the NTN gateway (230) is a feeder link. The link between the NTN gateway (230) and the AMF / UPF (240) may be based on an NG interface. The NTN payload (220) can transparently forward a wireless protocol received from the UE (210) via a service link to the NTN gateway (230). Similarly, the NTN payload (220) can transparently forward a wireless protocol received from the NTN gateway (230) via a feeder link to the UE (210).

[0056] To this end, the following connectivity may be supported by the NTN payload (220): A base station may service multiple NTN payloads; an NTN payload may be serviced by multiple base stations;

[0057] The NTN payload (220) can change the carrier frequency before retransmitting data on the service link. That is, the NTN payload (220) can use different carrier frequencies on the service link and the feed link. For the NTN, at least one of the AMF name, the NR cell global identifier (NCGI), the CgNB identifier (ID), the global gNB ID, the tracking area identity (TAI), the Single Network Slice Selection Assistance information (S-NSSAI), the Network Slice AS Group (NSAG), the Network Identifier (NID), the Closed Access Group (CAG) ID, and the local NG-RAN node ID (Identifier) ​​can be used as a network identifier, and additionally, a Mapped Cell ID can be further used. Here, the tracking area can correspond to a fixed geographical area.

[0058] Non-geosynchronous orbits (NGSOs) include low Earth orbits at altitudes of about 300 km to 1500 km and medium Earth orbits at altitudes of about 7000 km to 25000 km.

[0059] Service links can be categorized into three types: earth-fixed, quasi-earth-fixed, and earth-moving. The earth-fixed type provides beam(s) that continuously cover the same geographic area at all times. For example, a satellite in a geosynchronous orbit (GSO) can provide an earth-fixed service link. The quasi-earth-fixed type provides beam(s) that continuously cover the same geographic area for a limited period of time, and provides beams that cover different geographic areas for different periods of time. For example, a satellite in a non-earth-synchronous orbit can provide a quasi-earth-fixed service link using steerable beams. The earth-moving type provides beams whose coverage area slides over the surface of the Earth. For example, a satellite with a non-Earth-synchronous orbit could provide an Earth-mobile type service link using fixed or steerable beams.

[0060] Using a satellite in a non-Earth-synchronous orbit, the base station can provide quasi-Earth-fixed cell coverage or Earth-mobile cell coverage. Using a satellite in a geosynchronous orbit, the base station can provide Earth-fixed cell coverage. In the case of a non-Earth-synchronous orbit, a change in the service link may refer to a change in the serving satellite (120-1).

[0061]

[0062] FIG. 4 illustrates a configuration of a device in a wireless communication system according to one embodiment of the present disclosure. The device of FIG. 4 may be understood as a part of the structure of any one of the devices described with reference to FIG. 1, for example, a terminal (110), satellites (120-1, 120-2), and a gateway (130).

[0063] Referring to FIG. 4, the device may include a processor (210), a communication unit (220), and a memory (330).

[0064] The processor (310) can control the overall functions and operations of the device. The processor (310) can include an application-specific integrated circuit (ASIC), other chipsets, logic circuits, and / or data processing devices.

[0065] The communication unit (320) is connected to the processor (310) and transmits and receives wireless signals. The communication unit (320) may include a baseband circuit for processing wireless signals. For example, the communication unit (320) may include a short-range communication unit, a mobile communication unit, and a broadcast reception unit. In one embodiment, the communication unit (320) may transmit and receive data with other devices, such as base stations, satellites, etc.

[0066] The memory (330) is a hardware that stores various data processed by the processor (310). For example, the memory (330) may store an SIR value for a transmission target terminal of a transmitting terminal, information about a transmission target terminal group for each transmitting terminal, etc. In addition, the memory (330) may store applications, drivers, etc. to be driven by the processor (310). The memory (330) may include a random access memory (RAM) such as a dynamic random access memory (DRAM), a static random access memory (SRAM), a read-only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), a CD-ROM, a Blu-ray or other optical disk storage, a hard disk drive (HDD), a solid state drive (SSD), or a flash memory.

[0067] The structure of FIG. 4 can be understood as at least a portion of a terminal, a base station, a satellite, or a gateway. If the structure of FIG. 4 is part of a satellite, the satellite may further include other hardware devices necessary for orbital flight in addition to the components illustrated in FIG. 4. If the structure of FIG. 4 is part of a gateway or base station, the gateway or base station may further include components that support wired communications, etc.

[0068]

[0069] Figure 5 illustrates elements of a measurement report in a wireless communication system. The measurement report of Figure 5 corresponds to at least some of the elements of a measurement report defined in 3GPP.

[0070] Specifically, a measurement configuration may include a measurement object, a reporting configuration, measurement identities, a quantity configuration, and a measurement gap.

[0071] A measurement object may refer to a terminal that is the subject of measurement, and the object may vary depending on the measurement type, such as intra-frequency, inter-frequency, and inter-RAT (radio access technology). The object that is the subject of measurement may include network elements such as frequency, time, location, cell-specific offset, and a list of cells included in a blacklist / whitelist. The object ID may link the measurement object to each serving cell.

[0072] The reporting configuration defines how the terminal reports the measurement results, and may include, for example, triggering conditions, reporting volume, reporting criteria, and reporting quantity. For example, the triggering condition may include whether a measurement report is triggered when the terminal detects a specific event. For example, the triggering condition may be defined so that a report occurs when the signal strength falls below a certain level. For example, the reporting volume may include the measurement quantity and data type to be included in the measurement report. The measurement quantity may be related to the type of measurement signal, such as SS / PBCH (Synchronization Signal / Physical Broadcast Channel) or CSI-RS (Channel State Information-Reference Signal). The reporting criteria may include the criteria for performing the measurement report, and may include, for example, criteria for the reporting cycle and reporting event. The reporting quantity may include, for example, information on the quantity of data to be reported in the measurement report and the reporting interval.

[0073] A measurement ID may refer to a list of identifiers that link a measurement object to a reporting configuration. Specifically, a measurement ID may define a mapping relationship between a measurement object and a reporting configuration.

[0074] A quantity configuration may include filtering of measured data and configuration of quantities included in measurement reporting. For example, a quantity configuration may include filter coefficients applied to evaluate and report measured data.

[0075] The measurement interval may include the time interval during which the terminal performs measurements. During the measurement interval, the terminal may focus on measurements rather than communications.

[0076]

[0077] Figure 6 illustrates an example of a measurement report in a wireless communication system. Referring to Figure 6, the measurement report may include the signal strength of a serving cell and the signal strength of a neighboring cell. For example, the neighboring cell may include a target satellite and a candidate satellite. That is, the terminal transmits at least one of reference signal received power (RSRP), reference signal received quality (RSRQ), or signal to interference and noise ratio (SINR) through the measurement report.

[0078]

[0079] FIG. 7 illustrates time-engineered service conditions in a wireless communication system according to one embodiment of the present disclosure.

[0080] Referring to Figure 7, network services can be categorized into in-time communication services and on-time communication services. In-time services refer to services that guarantee an upper limit on delay time, while on-time services refer to services that guarantee delay consistency. Specifically, in-time services refer to communication services that require delay time to remain within a quantifiable limit, while on-time services may include communication services that require delay time to remain constant or to have as little variation as possible.

[0081]

[0082] FIG. 8 illustrates an NR subframe in a wireless communication system according to an embodiment of the present disclosure. Referring to FIG. 8, a frequency band can be separated into a time domain and a frequency domain, and the time domain and the frequency domain can be divided into minimum units. That is, the grid of FIG. 8 can be referred to as a resource grid (RG), and a resource consisting of one symbol (e.g., an OFDM symbol) in the time domain and one subcarrier in the frequency domain can be defined as a resource element (RE). Resources consisting of one OFDM symbol in the time domain and K subcarriers in the frequency domain can be defined as a resource element group (REG). That is, a REG can include K REs. A REG can be used as a basic unit for resource allocation in the frequency domain. OFDM symbols can be used as a basic unit for resource allocation in the time domain.

[0083] A resource block (RB) can refer to a unit of REs in the frequency domain. For example, in OFDM, if the subcarrier spacing (SCS) is 15 kHz, 12 REs can be grouped together to form a single resource block, occupying a frequency band of 180 kHz. A resource block is the minimum scheduling unit, and its number can vary depending on the bandwidth size.

[0084]

[0085] Figure 9 illustrates an example of a group handover procedure in a wireless communication system according to one embodiment of the present disclosure. Before explaining further, it should be noted that 3GPP is currently working on standardization related to handover in non-terrestrial networks. Unlike terrestrial networks, non-terrestrial networks move at very high speeds and support communications over relatively wide coverage, allowing multiple terminals to simultaneously perform handovers. When multiple terminals perform handovers simultaneously, there is a concern that signaling overhead due to measurement reports, handover command messages, random access (RA), and handover confirm messages may increase dramatically. Signaling overhead can cause a decrease in the performance of the communication system. To prevent the increase in signaling overhead in non-terrestrial networks, handovers without a random access procedure and group handovers may be considered, and when using group handovers, handover command messages can be significantly reduced.

[0086] Referring to FIG. 9, in step S901, each terminal (910-1, 910-2, 910-3, 910-4) measures the signal strength. Specifically, each terminal (910-1, 910-2, 910-3, 910-4) measures the signal strength of the serving cell and the signal strength of the adjacent cell. For example, each terminal (910-1, 910-2, 910-3, 910-4) can measure at least the SINR, RSRQ, and RSRP of the serving cell and the adjacent cell. For example, the terminals (910-1, 910-2, 910-3, 910-4) can measure the SINR, RSRQ, and RSRP of the serving satellite (920-1) and the candidate satellite (920-3). In addition, each terminal (910-1, 910-2, 910-3, 910-4) can measure, but is not limited to, the RSSI (Received Signal Strength Indicator), which is the power intensity of the received signal, and the SNR (Signal to Noise Ratio), which is the ratio between the signal and noise.

[0087] In step S903, each terminal (910-1, 910-2, 910-3, 910-4) transmits a measurement report. Specifically, each terminal (910-1, 910-2, 910-3, 910-4) transmits a measurement report message to the serving satellite (920-1) according to satisfaction of the handover condition. While the existing terminal transmits only the signal strength of the target satellite, the terminal (910-1, 910-2, 910-3, 910-4) according to the embodiment of the present disclosure transmits the time according to the communication service in the measurement report message. The time according to the communication service is t in_n or t on_n may include t in_n and t on_nEach may mean a quantified delay limit time by an in-time communication service and a quantified variation limit time by an on-time communication service. The serving satellite (920-1) receives a measurement report message and a time according to the communication service from each terminal (910-1, 910-2, 910-3, 910-4).

[0088] At step S905, the serving satellite (920-1) does not proceed with the handover immediately, but forms a waiting and handover group during the waiting time. The waiting time is t w may be referred to as and may be used interchangeably. Waiting time t w is the waiting time to form a group of each terminal (910-1, 910-2, 910-3, 910-4), and can correspond to the physical time for a packet to be transmitted from a transmitter to a receiver.

[0089] In step S907, the serving satellite (920-1) requests a handover to the target satellite (920-2). The serving satellite (920-1) transmits a handover request message to the target satellite (920-2), and the message may include information about all terminals (910-1, 910-2, 910-3, 910-4) formed as a group. In addition, the handover request message includes information equal to the number of terminals (910-1, 910-2, 910-3, 910-4). For example, information about the terminals may include UE Identity, source cell ID, target cell ID, terminal context, target satellite information, E-RAB (E-UTRAN Radio Access Bearer), etc. In connection with the present disclosure, the handover request message may include a time according to the communication service reported by the terminal (910-1, 910-2, 910-3, 910-4). For example, the handover request message may include a quantified delay limit time according to the in-time communication service and a quantified variable limit time according to the on-time communication service.

[0090] In step S909, the target satellite (920-2) calculates available resources. For example, the target satellite (920-2) may calculate available bandwidth, frequency resources, cell capacity, and Quality of Service requirements.

[0091] In step S911, the target satellite (920-2) responds to the handover request. Specifically, the target satellite (920-2) transmits a handover request response message to the serving satellite (920-1). The serving satellite (920-1), which receives the response to the handover request, can compare the available resources of the target satellite (920-2) with the resources required by the handover group to determine whether to perform a handover. For example, the serving satellite (920-1) can determine that a handover is possible if the available resources of the target satellite (920-2) are greater than the resources required by each terminal (910-1, 910-2, 910-3, 910-4) belonging to the handover group. On the other hand, the serving satellite (920-1) may determine that the handover is impossible if the available resources of the target satellite (920-2) are less than the resources required by each terminal (910-1, 910-2, 910-3, 910-4) belonging to the handover group. As another example, the serving satellite (920-1) may delay the handover, exclude some terminals, or reallocate the resources of the serving satellite (920-1) if the handover is impossible. The following description is made on the assumption that the terminals (910-1, 910-2, 910-3, 910-4) are included in a single handover group.

[0092] In step S913, the serving satellite (920-1) transmits a handover command to each terminal. To this end, the serving satellite (920-1) may assign an RNTI (e.g., G(group)-RNTI, C-RNTI) for broadcast or multicast to the terminals (910-1, 910-2, 910-3, 910-4). The RNTI may be provided in advance through system information or together with measurement settings.

[0093] In step S915, after receiving a handover command, each terminal (910-1, 910-2, 910-3, 910-4) performs a RACH (Random Access Channel) and handover to the target satellite (920-2). Specifically, each terminal (910-1, 910-2, 910-3, 910-4) performs random access to the target satellite (920-2). The terminals performing random access may be limited to terminals included in the handover group in which the handover is performed. The terminals (910-1, 910-2, 910-3, 910-4) transmit a preamble to the target satellite (920-2), and the target satellite (920-2) transmits a response to the random access to the terminal.

[0094]

[0095] FIG. 10 illustrates an example of an operation procedure of a terminal in a wireless communication system according to one embodiment of the present disclosure.

[0096] Referring to FIG. 10, in step S1001, a terminal measures the signal strength. Specifically, the terminal measures the signal strength of a serving cell and the signal strength or quality of a neighboring cell according to a predefined period. The terminal may be configured in multiple numbers. Specifically, each terminal measures the signal strength of the serving cell and the signal strength of the neighboring cell. For example, each terminal may measure at least SINR, RSRQ, and RSRP of the serving cell and the neighboring cell. In addition, each terminal may measure, but is not limited to, RSSI, which is the power intensity of a received signal, and SNR, which is the ratio between a signal and noise.

[0097] The terminal can measure the signal strength and quality at a predetermined interval. For example, the default value for the interval at which the terminal measures the signal strength and quality can be set to 200 ms. For example, each terminal can measure at least the SINR, RSRQ, and RSRP of the serving cell and neighboring cells at the predetermined interval. In addition, each terminal can measure, but is not limited to, the RSSI, which is the power intensity of the received signal, and the SNR, which is the signal-to-noise ratio.

[0098] In step S1003, the terminal determines whether the handover condition is satisfied based on the measured signal strength. If the handover condition is not satisfied, the terminal periodically or continuously re-measures the signal strength. For example, if the measured signal strength or quality falls below a predefined threshold or enters a predetermined range, the terminal may determine that the handover condition is satisfied. In addition, for example, if the signal strength or quality of a neighboring cell is higher than a specific threshold value of the signal strength or quality provided by the serving cell, the terminal may determine that the handover condition is satisfied.

[0099] In step S1005, the terminal transmits a measurement report including the communication service time. Specifically, the terminal transmits a measurement report message to the serving satellite according to the handover condition satisfaction. While the existing terminal transmits only the signal strength of the target satellite, the terminal (110) according to the embodiment of the present disclosure transmits the time (t) according to the communication service in the measurement report message. in_n or t on_n ) is transmitted. t in_n and t on_n may respectively mean a quantified delay limit time by an in-time communication service and a quantified variation limit time by an on-time communication service.

[0100] In step S1007, the terminal (110) performs RACH and handover according to the reception of a handover command. The terminal that received the handover command message from the serving cell may belong to a single handover group. Thereafter, the terminal performs RACH and handover to the target cell. When the handover is completed, the terminal may transmit a handover confirmation message to the target cell, and the target cell may transmit a handover completion message for each serving cell. When the handover is completed, the terminal releases the connection with the serving cell, and the serving cell releases the resources allocated to the terminal.

[0101]

[0102] FIG. 11 illustrates an example of an operation procedure of a serving cell in a wireless communication system according to one embodiment of the present disclosure.

[0103] Referring to Figure 11, in step S1101, the serving cell receives a measurement report from a terminal and waits for a waiting time. Specifically, the serving cell receives a measurement report message from each terminal and waits for a waiting time t w Wait for a while. Waiting time t w is the waiting time for forming a group of terminals, which can correspond to the physical time for transmitting a packet from a transmitter to a receiver. That is, the serving cell receives measurement report messages from terminals during the waiting time to form a group.

[0104] For example, the waiting time t w The value of t phydelay ~ t measure can be set to the value of t phydelay can be determined based on the propagation delay time and margin time caused by the physical distance from the transmitter to the receiver. For example, if the serving cell is a low-orbit satellite at an altitude of 300 km, t phydelay can be set to 11ms, reflecting the propagation delay time of 10ms and the margin time of 1ms. Similarly, if the serving cell is a satellite at an altitude of 1500km, tphydelay It can be set to 51ms by reflecting the margin time of 1ms in addition to the physically occurring propagation delay time of 50ms. The altitude of the low-orbit satellite is not limited to the above example and can be the same as defined in 3GPP. t measure may refer to the period during which the terminal periodically measures the strength of the signal. For example, t measure can be set to 200ms and may vary depending on user or system settings.

[0105] In step S1103, the serving cell calculates the processing time. Specifically, the serving cell calculates the processing time t for forming a handover group based on the received measurement report. p Calculate t p can be interpreted as a critical time for forming a handover group. For example, t p can be determined based on the time conditions of the time-engineered service conditions included in the measurement report. For example, t p can be based on the quantified variation limit time by the on-time communication service. Specifically, the serving cell is t from each terminal. on_n After receiving the value of t p can be calculated. t p can be calculated as shown in the following mathematical formula 1.

[0106]

[0107] That is, t p t received from each terminal (110) on_n can be determined as the lowest value among them. As another example, t p may be based on quantified variable limit time by in-time communication services.

[0108] In step S1105, the serving cell forms a handover group. For example, the serving cell may have a time condition of the time-engineered service condition included in the measurement report t pIn the relationship with, terminals included within a preset range can be formed into a handover group. For example, the serving cell can form a handover group based on the quantified delay limit time by the in-time communication service. Specifically, the serving cell can form a handover group based on the quantified delay limit time by the in-time communication service. in_n After receiving the value of , the processing time t p A handover group can be formed based on . The handover group can be formed according to mathematical formula 2.

[0109]

[0110] X represents a terminal included in the handover group, and the number of x can be configured as many as the remaining resources (R) of the target cell. The remaining resources R can mean the available resources of the target cell. The serving cell is t in_n The value of processing time t p A handover group can be formed by grouping terminals corresponding to the following.

[0111] In step S1107, the serving cell transmits a handover request and receives a handover request acknowledgment. Specifically, the serving cell processes the handover request for a processing time t p After waiting for a corresponding time, a handover request message is transmitted to the target cell, and a handover request response is received from the target cell. The handover request message may include information corresponding to a terminal included in the formed handover group. According to one embodiment, the handover request message may include UE Identity, source cell ID, target cell ID, terminal context, target satellite information, E-RAB, etc.

[0112] The handover request response may include available resources R of the target cell. For example, the resources R may include available bandwidth, frequency resources, cell capacity, and QoS requirements available to the target cell.

[0113] In step S1109, the serving cell compares available resources with the handover group. For example, if the available resources of the target cell are greater than or equal to the handover group, the serving cell transmits a handover command to the terminal. Specifically, the serving cell transmits a handover command message to each terminal included in the handover group. For this purpose, the serving cell may assign an RNTI (e.g., G(group)-RNTI, C-RNTI) for broadcast or multicast to each terminal. The RNTI may be provided in advance through system information or together with the measurement settings.

[0114] In step S1111, if the available resources of the target cell are less than the handover group, the serving cell re-forms the handover group as much as the available resources. Specifically, the serving cell, after processing time t p and t in_n The handover group can be re-formed based on the order of the value size of . For example, the serving cell may receive t in_n The value of processing time t p Assuming the following, t received from the terminal in_n After arranging the values ​​in order of size, t in_n In this small order, as many terminals as available resources can be configured into the re-formed handover group. In step S1113, the serving cell can transmit a handover command to the terminals included in the re-formed handover group.

[0115]

[0116] FIG. 12 illustrates an example of an operation procedure of a target cell in a wireless communication system according to one embodiment of the present disclosure.

[0117] Referring to FIG. 12, in step S1201, the target cell calculates available resources R upon receiving a handover request message from the serving cell. Specifically, the target cell can calculate available bandwidth, frequency resources, cell capacity, and QoS requirements.

[0118] In step S1203, the target cell transmits a handover request response. Specifically, the target cell transmits a handover request response including available resources R to the serving cell.

[0119] The handover request response may include available resources R of the target cell. For example, the resources R may include available bandwidth, frequency resources, cell capacity, and QoS requirements available to the target cell.

[0120] In step S1205, the target cell receives the RACH and completes the handover. After receiving the handover command, the target cell performs the RACH and handover with the terminal. Specifically, each terminal included in the handover group and the target cell perform random access. The terminal performing the random access may be limited to the terminal included in the handover group in which the handover is performed. The terminal transmits a preamble to the target cell, and the target cell transmits a response to the random access to the terminal.

[0121]

[0122] According to the various embodiments described above, a conditional handover can be performed without a RACH for the target cell. The RACH-less conditional handover according to the various embodiments can be performed in various scenarios. For example, if the target cell is a satellite base station, the RACH-less conditional handover described above can be performed. For example, if there are multiple target cells, including at least one satellite base station and at least one terrestrial base station, the RACH-less conditional handover can be applied only to the satellite base station, and the RACH-enabled conditional handover can be performed only to the terrestrial base station. In this case, the timing-related information and uplink grant information described above can be provided only to the target cell that is the satellite base station.

[0123] Meanwhile, those skilled in the art will appreciate that the present invention can be implemented in modified forms without departing from the essential characteristics of the above-described description. Therefore, the disclosed methods should be considered illustrative rather than restrictive. The scope of the present disclosure is set forth in the claims, not the foregoing description, and all differences within the scope equivalent thereto should be construed as being encompassed by the present disclosure.

[0124]

[0125] The present invention can be used in a device required to perform group handover in a wireless communication system.

Claims

1. In a method of operating a base station in a wireless communication system, A step of receiving a measurement report message including time information for a communication service from a plurality of terminals; A step of forming a handover group for the plurality of terminals based on the processing time derived based on the time information; A step of transmitting a handover request to a target base station; A step of receiving a handover request response from the target base station; and A method comprising the step of transmitting a handover command to the plurality of terminals.

2. In paragraph 1, The above communication service comprises a service that guarantees an upper limit of delay time and a service that guarantees consistency of delay time.

3. In paragraph 1, The above time information includes at least a delay limit time and a fluctuation limit time for the communication service, The above delay limit time includes a threshold time for a service that guarantees an upper limit of the delay time, The above variable limit time is a method including a threshold time for a service that ensures consistency of delay time.

4. In paragraph 1, The step of receiving the above measurement report message is: A method comprising the step of receiving the measurement report message during a waiting time based on a physical distance from the plurality of terminals to the base station.

5. In paragraph 4, The above waiting time is determined based on the propagation delay time caused by the physical distance and the period for measuring the strength of the signal.

6. In paragraph 1, A method in which the above processing time is determined as the lowest value among the fluctuation limit times for the communication services of the plurality of terminals.

7. In paragraph 1, A method in which the above handover group is formed by grouping terminals whose delay limit time for the communication service is less than the processing time.

8. In paragraph 1, The steps of forming the above handover group are: A step of comparing available resources of the target base station with resources required for the handover group; a step of transmitting the handover command to the plurality of terminals included in the handover group when the available resources are greater than the required resources; and A method comprising the step of re-forming the handover group so that the required resource is equivalent to the available resource, if the available resource is less than the required resource.

9. In paragraph 8, The steps for re-forming the above handover group are: A method comprising the step of grouping terminals based on the order of the magnitude of the delay limit time included in the above time information.

10. In a terminal operation method of a wireless communication system, A step of measuring the strength of a signal; A step of transmitting a measurement report message including time information for a communication service to a base station based on satisfaction of a handover condition; A step of receiving a handover command from a base station; Comprising a step of performing RACH (Random Access Channel) to a target base station, The above terminal is included in a handover group formed by multiple terminals based on processing time, The above processing time is calculated based on the above time information.

11. In paragraph 10, The above communication service comprises a service that guarantees an upper limit of delay time and a service that guarantees consistency of delay time.

12. In paragraph 10, The above time information includes at least a delay limit time and a fluctuation limit time for the communication service, The above delay limit time includes a threshold time for a service that guarantees an upper limit of the delay time, The above variable limit time is a method including a threshold time for a service that ensures consistency of delay time.

13. In paragraph 10, The step of sending the above measurement report message is: A method comprising the step of transmitting the measurement report message during a waiting time based on a physical distance to the base station.

14. In paragraph 13, The above waiting time is determined based on the propagation delay time caused by the physical distance and the period for measuring the strength of the signal.

15. In paragraph 10, A method in which the above processing time is determined as the lowest value among the fluctuation limit times for the communication services of the plurality of terminals.

16. In paragraph 10, A method wherein the above handover group is formed by grouping a plurality of terminals whose delay limit time for the communication service is less than the processing time.

17. In paragraph 10, The step of receiving the above handover command is: A method comprising the step of receiving the handover command when the available resources of the target base station are greater than the resources required for the handover group.

18. In paragraph 11, The step of receiving the above handover command is: A method comprising the step of receiving the handover command only when the terminal is included in the re-formed handover group based on the order of the delay limit time included in the time information, if the available resources are less than the required resources.

19. In a base station of a wireless communication system, Transmitter and receiver; and comprising a processor connected to the transceiver; The above processor, Control to receive a measurement report message including time information on a communication service from multiple terminals, Control to form a handover group for the plurality of terminals based on the processing time derived based on the above time information, Control to transmit a handover request to the target base station, Control to receive a handover request response from the target base station, A base station that controls transmission of a handover command to the above multiple terminals.

20. In a terminal of a wireless communication system, Transmitter and receiver; and comprising a processor connected to the transceiver; The above processor, A step of measuring the strength of a signal; Based on the satisfaction of the handover condition, control is provided to transmit a measurement report message including time information for the communication service to the base station, Control to receive a handover command from a base station, Comprising a step of performing RACH to a target base station, The above terminal is included in a handover group formed by multiple terminals based on processing time, The above processing time is calculated based on the above time information.

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