KR20220083611A - Method of managing delays for long distance communication, and apparatus for the same - Google Patents

Abstract

A delay time management method performed by a terminal in a non-terrestrial network includes: receiving, from a non-terrestrial node, information on a changed delay time or scheduling offset to be applied to uplink transmission; and performing the uplink transmission to the non-terrestrial node by applying the delay time or scheduling offset, wherein the information on the changed delay time or scheduling offset is a system information block (SIB) from the non-terrestrial node. is included and received, and whether the SIB includes information on the changed delay time or scheduling offset is indicated by a paging message received in the first change period of the SIB, and the changed delay time or scheduling The information on the offset may be received in a second change period after the first change period.

Description

Delay time management method for long-distance communication and apparatus therefor {Method of managing delays for long distance communication, and apparatus for the same}

The present invention relates to a non-terrestrial network (NTN), and more particularly, to prevent power consumption of a terminal in a non-terrestrial network based on a 5G NR (new radio) system and an efficient delay for reducing signaling overhead It relates to a time management method and an apparatus therefor.

It is necessary to develop mobile satellite communication technology in preparation for communication disruption that may occur in cellular shadow areas such as mountainous areas, desert areas, island areas, and the sea, and in areas where the terrestrial network collapses due to various disasters such as earthquakes, tsunamis, and war. Since the satellite communication network is maintained even when the terrestrial network is disrupted due to a disaster or disaster, the disaster or disaster area is connected without being disconnected from the outside, making it possible to maintain individual survival and safety.

In addition, the need for mobile satellite communication technology is increasing for the establishment of a hyper-connected society that provides mobile communication services even in areas where communication was not possible in the past, such as in mountains and remote areas where there is no communication infrastructure. In the 3rd generation partnership project (3GPP), based on 5G new radio (NR) technology, a non-terrestrial base station (eg, a base station using an airborne platform such as a satellite base station or an airship) Standardization of a non-terrestrial network (NTN) used is in progress On the other hand, in a non-terrestrial network, there is a problem in that a delay between a terminal and a base station increases as the size of a cell increases and a communication distance increases. Such a large delay is the size of a random access preamble, a timing advance value, and a random access response (RAR) in initial access performed by the terminal to the base station. ) affects the size of the window, which can also affect the performance of the entire system.

An object of the present invention for solving the above problems is to provide an efficient delay time management method for reducing power consumption of a terminal and signaling overhead between a terminal and a base station in a non-terrestrial network.

It is an object of the present invention to solve the above problems, to provide a configuration of a terminal and a base station that performs efficient delay time management to reduce power consumption of the terminal and signaling overhead between the terminal and the base station in a non-terrestrial network.

An embodiment of the present invention for achieving the above object is a delay time management method performed by a terminal in a non-terrestrial network, from a non-terrestrial node, information about a changed delay time or scheduling offset to be applied to uplink transmission receiving; and performing the uplink transmission to the non-terrestrial node by applying the delay time or scheduling offset, wherein the information on the changed delay time or scheduling offset is a system information block (SIB) from the non-terrestrial node. is included and received, and whether the SIB includes information on the changed delay time or scheduling offset is indicated by a paging message received in the first change period of the SIB, and the changed delay time or scheduling The information on the offset may be received in a second change period after the first change period.

According to embodiments of the present invention, in a non-terrestrial network, a large delay time between a base station and a terminal, which varies according to various non-terrestrial node types and mobility of a non-terrestrial node, is a terminal state (idle state) or connected state (connected state). state)) can be updated efficiently. Accordingly, the effect of reducing the signaling overhead between the terminal and the base station and the effect of reducing the power consumption of the terminal can be obtained.

1A and 1B are conceptual diagrams illustrating a communication environment to which embodiments of the present invention are applied.
2 is a conceptual diagram for explaining the concepts of a common delay time and a differential delay time according to a location of a terminal in long-distance communication.
3 is a conceptual diagram for explaining a concept in which a common delay time is defined for a specific beam.
4 is a conceptual diagram for explaining various common delays existing in a non-terrestrial network environment.
5 is a block diagram illustrating an embodiment of a communication node according to the present invention.

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing each figure, like reference numerals have been used for like elements.

Terms such as first, second, A, and B may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component. The term “and/or” includes a combination of a plurality of related listed items or any of a plurality of related listed items.

When an element is referred to as being “connected” or “connected” to another element, it is understood that it may be directly connected or connected to the other element, but other elements may exist in between. it should be On the other hand, when it is said that a certain element is "directly connected" or "directly connected" to another element, it should be understood that the other element does not exist in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

A wireless communication network to which embodiments according to the present invention are applied will be described. A wireless communication network to which embodiments according to the present invention are applied is not limited to the content described below, and embodiments according to the present invention may be applied to various wireless communication networks. Here, a wireless communication network may be used in the same meaning as a wireless communication system.

Hereinafter, for convenience of description, the term 'satellite base station' is used as a term representing a non-terrestrial base station or a mobile base station. However, the methods and apparatuses described below may be applied not only to a satellite base station but also to a base station using an airborne platform - such as an airship.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

1A and 1B are conceptual diagrams illustrating a communication environment to which embodiments of the present invention are applied.

Referring to FIG. 1A, in a non-terrestrial network environment in which standardization is in progress in 3GPP, the base stations gNB, 112, 113, and 123 are on the ground while the satellites 111, 121, and 122 perform the role of a relay. can That is, in this case, the satellite base station operates as a transparent node defined in 3GPP NTN.

Referring to FIG. 1B , central units (CUs) 133 and 142 of the base station may be located on the ground, and distributed units (DUs) of the base station may be located on satellites 131 , 132 and 141 . Alternatively, the base station (gNB) itself may be located in the satellite. That is, in this case, the satellite base station operates as a regenerative node defined in 3GPP NTN.

One or more NR Cells may be defined through one satellite. In addition, one gNB may provide services via more than one satellite. A satellite may be classified into a low earth orbit (LEO), a medium earth orbit (MEO), or a geostationary equatorial orbit (GEO).

In this case, as the cell radius and the height of the base station (eg, the satellite base station) increase, a large difference may occur in signal transmission times according to the locations of the terminals.

2 is a conceptual diagram for explaining the concept of a common delay time and a differential delay time according to a location of a terminal in long-distance communication.

Referring to FIG. 2 , a delay time (ie, common delay time) according to a distance 211 between the terminal 210 and the satellite base station 201 positioned below the vertical direction within the area of the satellite base station 201 . And, delay times (ie, common delay time+differential delay) according to the distance 221 between the terminal 220 and the satellite base station 201 located at various points are shown.

That is, the delay time of the terminal 210 and the delay time of the terminal 220 may have a difference by the differential delay time. In this case, the arrival time of the signal transmitted from the terminal 210 at the satellite base station 201 and the arrival time of the signal transmitted from the terminal 220 at the satellite base station 201 have a difference by the differential delay time. .

That is, the common delay time is the unidirectional delay time of the shortest distance, the average distance, or the longest distance at a specific point in time between the base station and the terminal within the corresponding area, or a specific value defined by the base station (or system) (eg, satellite height) can be

3 is a conceptual diagram for explaining a concept in which a common delay time is defined for a specific beam.

Referring to FIG. 3 , the common delay time is a delay time at the center of a beam of a base station (a point where the elevation angle of the beam is 0 degrees or a point where the gain of the beam is greatest) at a specific point in time in relation to the beam or the corresponding It may also be defined as a delay time for a point having the largest signal to noise ratio (SNR) in the region.

4 is a conceptual diagram for explaining various common delays existing in a non-terrestrial network environment.

Referring to FIG. 4 , at least three types of radio links may exist in a non-terrestrial network environment. At least three types of radio links are a service link 431 between the terminal 410 and the satellite base station 421 , an inter-satellite link (ISL) 441 , and a terrestrial connection to the data network 470 . It may include a feeder link (451, 452) between the gateway 460 and the satellite base stations (421, 422).

In this case, the common delay time ( _DS ) of the service link, the common delay time ( _DI ) of the inter-satellite link, and the common delay time ( _DF ) of the feeder link may exist, and the common delay described in FIGS. 2 and 3 . is mainly corresponding to the common delay ( _DS ) of the service link.

When the terminal knows the type of satellite (eg, LEO, MEO, or GEO) and the orbit of the satellite, it can infer an elevation angle with the satellite and the distance from the satellite. Since the type of satellite and the orbit of the satellite greatly affect the signal delay and signal strength between the terminal and the satellite base station, it is important for the terminal to know the type and orbit of the satellite for initial access, handover, paging ( It is helpful in various control procedures such as paging).

As described above, the types of satellites can be largely classified into geostationary orbiting satellites (GEO) and non-geostationary orbiting satellites (MEO/LEO). Compared to a geostationary orbit satellite whose service area does not change over time, a non-geostationary orbit satellite has a characteristic that the service area changes over time. The service area that is changed due to the mobility of the non-geostationary orbit satellite is divided into two types, an earth fixed beam and a moving beam. In the case of the terrestrial fixed beam, even if the satellite moves, the terrestrial cell is not changed, and in the mobile beam, the cell information is changed together with the moving satellite.

The satellite communication delay may vary depending on the position of the satellite, the position of the ground station, and the position of the terminal. First, delay variation may occur according to satellite mobility in a terminal in a fixed location. In the case of GEO, a maximum of 16 ms is expected, and in the case of LEO serving at 1200 km, a maximum of 6.44 ms is expected. A delay difference may occur depending on the location of the terminal in the beam serviced by the satellite at the same time. The value may have a large difference depending on the size of the beam. Finally, the distance between the satellite and the ground station may vary depending on the time of the ground station connected to the satellite, and if the LOS environment is not supported, the ground station may be connected to the ground station through connection with other satellites. These connections may change according to satellite deployment. In summary, in the case of the transparent mode, the satellite communication delay is defined as the delay considering the location between the terminal and the satellite, and in the case of the regenerative mode, it is defined as the delay considering the location between the satellite and the ground station as well as the delay considering the location between the terminal and the satellite. should be

In 5G satellite communication, both a type of terminal capable of knowing its own location information and a type of terminal that does not know its own location information should be supported. In this case, the location information of the terminal may be obtained through a GPS reception function or at least one of Assisted Global Navigation Satellite System (A-GNSS), Observed Time Differential Of Arrival (OTDOA), and Enhanced Cell ID (E-CID).

In a non-terrestrial network, due to a large cell size and a high altitude of a non-terrestrial node, a large delay may occur between the terminal and the base station. An increase in the delay time between the base station and the terminal may affect various parameters related to time applied in the existing communication, which may affect the performance of the entire system. In order to solve this problem, by introducing various offsets to the existing delay time related parameters, the influence on the existing parameters can be minimized.

For example, during initial access, timing is compensated so that the base station can receive preambles transmitted by all terminals in a cell at a similar time, or a scheduling offset between uplink resource allocation information and uplink transmission time is calculated between the base station and the terminal. It may be determined based on the delay time, or there may be an offset for various timers that need to consider RTT. These offsets should be determined based on the delay time between the base station and the terminal.

For example, timing advance (TA) may be configured as Common TA + UE specific TA. Common TA is determined by a delay time from a non-terrestrial node to a reference point in the cell. In this case, the Common TA may be configured with a service link delay and/or a feeder link delay. Upon initial access, the TA is set through a random access procedure, and a new adjustment value, TA, may be updated through a TA command in a periodic or event-driven manner. The TA command may be transmitted through the MAC CE or may be transmitted through a random access response (RAR). In particular, in the case of RAR, there is a problem in that the size of the RAR needs to be changed due to the large delay time of the non-terrestrial node. In addition, there is a problem in that a TA command must be frequently transmitted in order to reflect a large change in delay time in uplink reception. In the embodiments of the present invention, a method of updating the common TA in order to maintain the existing TA command and reflect the amount of delay time change due to the mobility of the non-terrestrial node is presented. Since the distance between the base station and the terminal varies with time according to the mobility of the non-terrestrial node, frequent updates are required. Also, the amount of delay time change can be defined as a negative number or a positive number. Hereinafter, an efficient delay time management (updating) method for preventing power consumption of the terminal and reducing signaling overhead between the terminal and the base station is proposed.

Hereinafter, a method of updating the delay time according to the connected state of the terminal (RRC idle state or RRC connected state) will be described first.

Terminal in RRC idle state

When performing the initial access, the terminal receives information on the common delay time (minimum delay time or maximum delay time) for each beam or cell from the base station, and the terminal receives information on its own location and the location information of non-terrestrial nodes based on the MSG1 may be transmitted by determining an offset for MSG1 transmission for random access and reflecting the determined offset in the transmission timing of MSG1. The base station may perform transmission of MSG2 and resource allocation for MSG3 based on uplink resource allocation for each beam or cell and a scheduling offset to be applied to resource timing. The UE may transmit MSG3 using the broadcast scheduling offset information. In this case, the terminal may report a value obtained by subtracting the common delay time from the offset determined by the terminal to the base station.

The UE in the RRC idle state may receive information on a common delay time or common scheduling/timing offset for each beam or cell through a system information block (SIB). When a delay time or a scheduling/timing offset is changed due to the mobility of a non-terrestrial node, an SIB update procedure is required.

Method 1-1) A method in which a delay time or a scheduling offset is changed for each modification period of the SIB

Due to the fast mobility of the non-terrestrial node, the distance between the terminal and the non-terrestrial node is continuously changed, but the SIB (SIB1 or SIB2) related to the transmission delay and the scheduling offset does not change in the corresponding transmission period, and according to the change period of the SIB A changed delay time or scheduling offset may be signaled. If the SIB change period has a large value, the difference between the actual delay time and the broadcast delay time becomes large, and thus the size of the preamble, the timing advance value, and the size of the RAR window are affected, which in turn affects the size of the entire system. will affect performance.

In order to prevent this problem, a new change period may be defined to enable setting of a period different (or shorter) from the existing SIB change period. When a new SIB change period for the non-terrestrial network is not defined, the UE may know that the non-terrestrial network-related system information is changed according to the existing modification period (modificationPeriodCoeff). The base station may notify the SIB change using a paging message during the change period, and transmit the changed SIB in the next change period. Since the UE must receive the SIB that is changed even in the RRC idle state at maximum every change period, power consumption of the UE may increase.

To improve this, even if the SIB is changed, it may be indicated that there is no change in the delay time or the scheduling offset using a change indication transmitted through a short message transmitted to the P-RNTI. Alternatively, by using a new bit (reserved bit(s)) not used in a short message, a non-terrestrial SIB-only change notification is defined, and only when the corresponding bit is set to 1, the non-terrestrial SIB is changed. It can be defined to notify. However, the notification may be applied only to the terminal in the RRC connected state. Even if the terminal in the idle state receives the corresponding message, the terminal does not immediately receive the changed SIB, but receives the non-terrestrial SIB at the time of performing the initial access, thereby obtaining information on the delay time and the scheduling offset.

On the other hand, considering a case in which a cell is changed, in the earth fixed scenario, when a satellite serving a corresponding cell is changed and serves with the same cell ID, a handover procedure is not driven and a beam change is performed. Since the service must be provided through the same cell, system information must be maintained even if the satellite is changed. However, since the position of the satellite is changed, all parameters related to the delay time between the terminal and the satellite need to be updated. That is, the previous satellite before the change informs the terminal that the satellite will be changed, and the terminal must be able to receive the changed SIB.

For example, the timing of changing the service area of a satellite may be preset through network management, a network, or an X2 message between base stations connected to two satellites. The distance between the satellite serving the current cell and the terminal may be different from the distance between the satellite to be served next and the terminal. Among the system information messages, if delay time, scheduling offset, timer offset, etc. affected by the distance between the base station and the terminal are provided in the SIB message, the corresponding information needs to be changed and the change must be notified to the terminal.

First, the currently serving base station may notify the terminal of the change of the non-terrestrial SIB by using the bit(s) of the paging message during the change period before the time when the satellite is changed. For example, when the corresponding bit is set to 1, it can be notified that the non-terrestrial SIB is changed in the next change period. The base station serving the new satellite may transmit the changed non-terrestrial SIB in a change period after the time point of the satellite change. The terminal may acquire the changed SIB information in the corresponding change period.

Alternatively, the currently serving base station may inform the terminal that the satellite is to be changed by using the bit(s) of the paging message during the change period before the time when the satellite is changed. For example, when the corresponding bit is set to 1, the terminal may acquire the changed SIB of the satellite in the next change period.

UE in RRC-connected state

A delay time, a scheduling offset, and/or a timer offset changed by the mobility of a non-terrestrial node with respect to the connected state terminal may be updated by the base station. Since the TA (Timing Advance) may change as the non-terrestrial node moves, when the existing TA update method is applied, a relatively large value must be updated and frequent update may be required. For example, whenever an uplink transmission from the terminal is received, a problem of having to transmit a TA command may occur. In addition, if uplink transmission does not occur for a certain period of time, due to a large difference between the configured TA value and the delay time between the actual base station and the terminal, a synchronization problem may occur, and the failure of synchronization may cause radio link failure (RLF). , which may cause a delay as the RRC re-establishment procedure is performed.

Method 2-1) How to broadcast latency update

This is a method of notifying the amount of delay time change due to the movement of the non-terrestrial node to the terminals belonging to the beam to which the terminal belongs or a set of adjacent beams. The base station may set up one beam or several beam groups including adjacent beams to update the common delay time, and may allocate a common TA group ID for distinguishing each group. In addition, the base station may determine a period (update period) to update the delay time variation. For example, an SI modification period may be used.

The base station may set a common TA group ID to which a beam providing a service to the terminal belongs during the access procedure of the terminal. After the update period, the base station may broadcast a common TA update command message to the terminals. The delay time for each Common TA group ID varies depending on the position of the beam. A list of Common TA group IDs may be defined in the Common TA update command message. When the delay time variation for each common TA group ID is transmitted to the UE, the UE may apply the delay time variation to the next uplink transmission in addition to the preset TA value. When the UE receives the Command TA update command message, the UE may set or reset TimeAlignmentTimer.

The above method can reduce signaling overhead by broadcasting a common TA to UEs, but has a disadvantage in that periodic updates must be performed according to an update period.

Method 2-2) How the UE requests TA update

The base station may set the uplink transmission timer, which is the maximum time until the common delay time update, based on the location information, elevation angle, or delay time update period of the terminal, to the terminal using an RRCReconfiguration message or MAC CE. Upon receiving the message, the terminal receives uplink data resource allocation and drives a corresponding timer when data is transmitted. When new uplink data allocation occurs, the UE may cancel the corresponding timer and restart the corresponding timer after transmission is complete.

When the uplink transmission timer expires, the terminal may transmit a Common TA Update request message to the base station. When a TA update is required, the base station transmits a TA command.

Offsets and scheduling offsets for starting various timers may be configured for each UE through RRC or MAC CE.

Hereinafter, a method for updating a delay time of a terminal having the capability to determine its own location information and a terminal not having the corresponding capability will be described.

A terminal that can know its location information

Hereinafter, an initial access method when the terminal can know its own location (eg, GNSS location) and the location of a satellite (eg, GNSS location) will be described. In addition, a TA update method of a terminal in an RRC connected state and a terminal in an RRC idle state or an RRC inactive state will be described.

(1) Example #1 of initial access method

i. The terminal may use its own location information and previously received satellite information (satellite ephemeris) to determine the location of a satellite connected to a base station that will provide its service (to which it intends to access). The terminal may calculate a delay between the terminal and the satellite by using the distance from the satellite connected to the base station to be accessed, and calculate a TA to be applied to transmission of a preamble for random access (RACH preamble) based on the calculated delay. The UE may select a RACH transmission opportunity (occasion) and apply the calculated TA to transmit the RACH preamble on the selected RACH occasion.

ii. The base station receiving the RACH preamble from the terminal transmits a TA adjustment value having a positive (+) or negative (-) value to the terminal through a random access response (RAR) for TA adjustment can

iii. Upon receiving the TA adjustment value from the base station through RAR, the terminal additionally reflects the TA adjustment value received from the base station to the TA calculated based on its own position and the position of the satellite, and then sends an uplink message (eg, a 4-step RA procedure). MSG3 for , or msg B) for 2-step RA procedure may be transmitted.

iv. Meanwhile, the base station may periodically or aperiodically update (positively or negatively) the TA adjustment value set by the base station using the TA command MAC CE. The UE may transmit an uplink message by periodically or aperiodically reflecting the TA calculated by the UE and the updated TA adjustment value.

v. If necessary, the terminal may report the TA value (at least one of TA calculated by the terminal, TA adjustment value, and TA used for transmission) applied to the uplink transmission to the base station through an RRC message or MAC CE to the base station.

(2) Embodiment #2 of initial access method

i. In step (iii) of the above-described embodiment #1, the terminal may include its location information in MSG3 (msg B in the case of a 2-step RA procedure) and transmit it to the base station. In this case, the base station may directly set the new TA value calculated by the base station based on the location information of the terminal to the terminal. The UE may transmit an uplink message based on the new TA.

The base station may update the TA adjustment value periodically or aperiodically (eg, when the TA for the terminal is changed by exceeding the TA difference threshold). The terminal may report the location of the terminal to the base station periodically or aperiodically (eg, when the location change of the terminal exceeds the location change threshold). In this case, the TA difference threshold and the location change threshold may be set to the terminal by using a broadcast/multicast or dedicated channel from the base station.

On the other hand, when the terminal reports its location information and movement speed information to the base station, the base station multicasts terminals having similar location and movement speed characteristics based on the location information and movement speed information collected from multiple terminals in one multicast. It can be set as a group. Since the moving speed of the terminal is relatively slow compared to the moving speed of the satellite, it is expected that there will be many TA changes mainly due to the mobility of the satellite. , and terminals belonging to the same TA multicast group may apply the same update value.

ii. If necessary, the terminal may report the TA value (at least one of TA calculated by the terminal, TA adjustment value, and TA used for transmission) applied to the uplink transmission to the base station through an RRC message or MAC CE to the base station.

(3) TA update method of UE in RRC connected (connected) state

i. When the TA value calculated by the terminal is not reported to the base station, the TA adjustment value may be periodically or aperiodically updated by the base station. For example, if the TA for the terminal is changed by exceeding the TA difference threshold (a value preset in the system) while the base station receives uplink data due to the movement of the mobile base station or the terminal, the base station adjusts the TA value can be set in the terminal using a broadcast/multicast or dedicated channel.

ii. When the TA value (at least one of the TA calculated by the terminal, the TA adjustment value, and the TA used for transmission) is reported to the base station, the base station periodically sends the TA adjustment value or the new TA value to the terminal through an RRC message or MAC CE Alternatively, it may be configured in the terminal using a broadcast/multicast or dedicated channel in an aperiodic (eg, event triggering method). For example, the base station may perform aperiodic configuration when the TA for the terminal is changed by exceeding a TA difference threshold (a value preset in the system) while performing uplink reception.

iii. Due to a characteristic of a large delay deviation in a satellite cell having a large cell size, when the TA adjustment value becomes too large, the TA command of the MAC CE should be defined to be large. As one method, there is a method of defining the number of bits of the TA command as large as possible to express a possible TA offset in one cell. Alternatively, when the maximum value of the TA command defined in NR is exceeded, the base station may set the maximum TA to the terminal using a dedicated channel and set an additional TA adjustment value using the TA command. That is, the base station uses a dedicated channel to indicate that a TA adjustment value exceeding the maximum value of the TA command is used, and sets the difference between the maximum value of the TA command and the TA adjustment value (an additional TA adjustment value) using the TA command. can Upon receiving this, the UE may perform uplink transmission by applying (TA calculated by itself + TA set by the base station). The base station receiving the uplink transmission from the terminal may periodically or aperiodically update the TA adjustment value. If the base station knows the TA value used by the terminal, the base station may newly set the TA value to the terminal using an RRC message or MAC CE. The terminal may perform uplink transmission by applying the newly set TA value, and the base station may periodically or aperiodically set the TA adjustment value.

iv. When the base station knows the location of the terminal, if it is determined that the TA for the terminal is changed by exceeding the threshold of the TA difference by using the location of the satellite and the location information of the terminal, the base station sends a new TA value to the RRC message or MAC CE Through the broadcast/multicast or dedicated channel, it can be set in the terminal. This method has an advantage that the base station can update the TA in anticipation of the TA change without an uplink message from the terminal.

v. On the other hand, since the location information of the terminal is sensitive information, it may be difficult for the terminal to share it with the base station. When the location information of the terminal is not provided to the base station, the base station determines the approximate value of the terminal based on the TA value (at least one of the TA calculated by the terminal, the TA adjustment value, and the TA used for transmission) or the change used in the terminal enemy location can be inferred. Additionally, by using information on neighboring cells reported through a measurement report of the UE, it is possible to know the approximate location of the UE in the cell.

vi. Since the terminal can calculate its own location information and location information according to the trajectory of the satellite, the terminal can transmit to the base station by applying the newly calculated TA value during uplink transmission. This method is more useful in consideration of a terminal having fast mobility as well as mobility of a satellite.

vi-1. The TA value used for transmission may be transmitted to the base station by the terminal using an RRC message or MAC CE. Alternatively, the UE may notify the base station that the new TA has been applied using L1 signaling, MAC CE, or RRC message. The base station receives the uplink data received from the terminal, and when the TA for the terminal is changed by exceeding the TA difference threshold (a value preset in the system), a new TA adjustment value is set to the terminal through an RRC message or MAC CE. can In the next uplink transmission, the UE may perform uplink transmission by reflecting the TA value and the TA adjustment value calculated by the UE.

vi-2. Alternatively, the UE may not notify the base station that the new TA has been applied. If the base station determines that TA adjustment is necessary when receiving uplink data, a positive or negative TA adjustment value for TA adjustment may be transmitted to the terminal using a broadcast/multicast or dedicated channel through an RRC message or MAC CE. . During the next uplink transmission, the UE may perform uplink transmission by reflecting the TA value and the TA adjustment value calculated by the UE.

vi-3. When the UE does not notify that the new TA has been applied, the new TA may be limitedly applied only to transmission of a scheduling request (SR) or an RA preamble (other than a previously promised message, L1 signaling, or MAC CE). If the base station anticipates that TA may be changed only for the uplink data promised in advance and determines that TA adjustment is necessary, a positive or negative TA adjustment value for TA adjustment of the received signal may be transmitted to the terminal. The base station may transmit the TA adjustment value to the terminal using broadcast/multicast or a dedicated channel through an RRC message or MAC CE. During the next uplink transmission, the UE may perform uplink transmission by reflecting the TA value and the TA adjustment value calculated by the UE.

(4) TA update method of UE in RRC idle state or RRC inactive state

When uplink data transmission is required, the terminal calculates a relative distance using its own location information at the time and location information of the base station (obtained by using satellite orbit information), and acquires a new TA value based on this. can The UE may transmit an uplink message (preamble, etc.) by applying a new TA value. The subsequent operation may be the same as in (1), (2), and (3) described above.

A terminal whose location information cannot be known

Hereinafter, an initial access method when the terminal cannot know its location information will be described. Also, a TA update method of a UE in an RRC connected state and a UE in an RRC idle state or RRC inactive state will be described.

(1) Initial connection method

i. The base station broadcasts a minimum delay value within a serving beam or cell. For example, the minimum delay value may be defined based on a 90 degree elevation angle. Alternatively, a delay value at a specific location in the cell closest to the satellite in the cell may be used as the minimum delay value. The terminal may infer a delay value according to the altitude of the satellite from the corresponding value.

ii. Since the delay difference according to the location of the UE in the satellite cell is large, there is a disadvantage in that the RACH capacity is reduced. Therefore, a method for inferring the location of the terminal is required. In addition to the delay described above, the base station may utilize signal strength (eg, RSRP, RSRQ) and neighboring cell information as a method for inferring the relative position within the cell of the terminal.

The base station may provide a delay offset according to an application criterion (eg, a threshold and a measurement time, etc.) for a differential delay to be additionally applied by the terminal. The UE may determine a delay offset to be applied to the UE based on the measurement result of the signal strength of the neighboring cell for a predetermined time. For example, the terminal may determine the delay offset in the following case.

A. When no surrounding cells are found

B. When a neighboring cell is found, but the signal strength of the neighboring cell is worse than threshold1

C. When the signal strength of the neighboring cell is better than threshold1, but the difference between the signal of the current serving cell and the neighboring cell is greater than threshold2 or the signal of the serving cell is greater than threshold3

D. When the signal strength of the neighboring cell is better than threshold1, and the signal difference between the current serving cell signal and the neighboring cell is less than threshold 2 or when the signal of the serving cell is less than threshold 3

iii. The UE may determine a delay offset that meets the condition based on the signal strength measured by the UE. The UE may determine the TA by applying (delay broadcasted by the base station + delay offset) and transmit the RACH preamble on the selected RACH occasion.

iv. The base station receiving the preamble transmitted from the terminal may transmit a positive or negative TA adjustment value for TA adjustment to the terminal through the RAR.

v. Upon receiving the TA adjustment value, the terminal may transmit an uplink message by additionally reflecting the TA adjustment value set by the base station to the TA calculated by the terminal.

vi. The base station may periodically or aperiodically update (positive or negative) the TA adjustment value set by the base station through the TA command MAC CE message. The UE may transmit an uplink message by reflecting the TA calculated by the UE and the updated TA adjustment value.

vii. The UE may report the TA value (including all or part of the TA calculated by the UE, TA adjustment value, TA used for transmission, etc.) to the base station during uplink transmission to the base station through an RRC message or MAC CE.

(2) TA update method of RRC connected (connected) state terminal

It can be performed in the same manner as '(3) TA update method of a terminal in an RRC connected state' for the 'terminal that can know its own location information' described above.

(3) TA update method of UE in RRC idle state or RRC inactive state

i. If the delay value broadcast by the base station is changed periodically or aperiodically, in order to prevent the terminal from performing an unnecessary system information update (SIB update) procedure, it is related to the update of the TA adjustment value before uplink data transmission occurs. action may not be performed.

ii. A terminal that wants to transition to an idle state or an in-active state uses the TA value (TA calculated by the terminal, TA adjustment value, and transmission) used in the message transmitted to the base station for state transition. Including all or only a part of the TA, etc.) may be transmitted to the base station in advance. When the base station transmits a paging message or a RAN paging message to the terminal, if the TA adjustment value caused by the mobility of the satellite exceeds the threshold compared to the previous TA adjustment value received from the terminal, the newly calculated TA adjustment value is combined with the paging message It can be transmitted to the terminal together. The UE may transmit the RA preamble by using the corresponding adjustment value.

iii. The terminal may attempt access using the above-described initial access method.

Even if the terminal can know the location information, when the calculated TA is not used, the terminal can perform the same operation as the terminal that does not know the location information.

Integrated operation plan

When a terminal capable of knowing its own location information and a terminal capable of knowing its own location information are mixed in one base station, an integrated operation method is required.

(1) Method to classify RACH Occasion

RACH occasions that can be used by a terminal that can know location information and a terminal that can't know location information can be distinguished. Since the uplink data received from the terminal that can know its location information has a small delay offset error, the delay offset error of the terminal that does not know its location information can be large, so the preamble in the base station Due to a reception error, it is necessary to define a large interval between RACH occasions, which may affect RACH capacity. Accordingly, a narrow RACH occasion may be defined for a UE that can know location information, and a wide RACH occasion interval may be defined for a UE that does not know location information.

The base station can broadcast configuration information on the RACH occasion by dividing the RACH occasion to be attempted by two types of terminals. The UE may transmit a RACH preamble by selecting a RACH occasion according to its type (a UE capable of knowing location information/a UE unable to know location information).

Alternatively, the base station may variously define intervals between RACH resources repeated for each RACH occasion (eg, Minimum delay*2 ~ Maximum delay*2) and broadcast. The UE may perform the selection of the RACH occasion. A terminal to perform the RACH procedure may be divided into a terminal to which TA information is configured (or a terminal capable of direct calculation) and a terminal to which TA information is not configured. In the case of a terminal for which TA information is set (that is, in the case of a terminal in which TA is established and TA is maintained through a random access procedure for previous initial access, or by using its own location and satellite location, it is possible to calculate its own TA value. In case of the terminal), the RACH resource interval is greater than or equal to its TA value *2 and may select the same RACH occasion. A UE for which TA information is not configured may transmit a RACH preamble by selecting a RACH occasion set at an interval equal to the Maximum delay *2 value provided by the base station or greater than the Maximum delay *2 value. The base station can accurately identify the RACH resource time (subframe) transmitted by the terminal when the preamble is received. Meanwhile, even if the terminal can calculate location information, if it does not use the TA calculated by itself, it may operate as a terminal for which TA is not configured.

(2) Method considering feeder link delay

Referring to FIG. 4 , two delays may be applied to the radio interface delay between the terminal and the base station: the delay between the terminal and the satellite and the delay between the satellite and the gateway on the ground. For example, when the base station is located on the ground, the terminal can calculate only the delay between the terminal and the satellite. Since the delay between the satellite and the terrestrial gateway may vary depending on network deployment or the mobility of the satellite, it is difficult for the terminal to obtain the corresponding information.

The first method is a method in which the base station broadcasts the feeder link delay. In the case of a base station in transparent mode or regenerative mode, the base station may broadcast the feeder link delay. In this case, a service link delay between the terminal and the satellite may also be additionally broadcast.

The second method is to leave the management of feeder link delay to a satellite or terrestrial gateway. That is, the base station in the transparent mode or the regenerative mode may consider only the service link delay excluding the feeder link delay. For example, in the transparent mode, the base station may broadcast only the service link delay. The feeder link delay may be commonly applied by terrestrial base stations.

The third method is to transmit a common delay including the feeder link delay. When the base station is on the ground, the base station can broadcast a delay including the service link delay and the feeder link delay. In the case of a regenerative mode base station, only the service link delay is broadcast. In the case of a terminal capable of knowing its own location information, a delay may be derived based on the calculation of the distance between the satellite and the terminal. In this case, when the delay value calculated by the terminal is greater than or smaller than the common delay value broadcast by the base station, the terminal may use the common delay instead of the delay value calculated by the terminal. In this case, it corresponds to the operation when the terminal cannot know its own location information.

When the terminal transmits the preamble in the above-described operations, the terminal may transmit the preamble by applying a delay value provided by the base station as an initial TA value.

(3) Message transmission/reception and scheduling offset

1) MSG3 Scheduling Offset

i. When the terminal determines the TA (terminal-specific propagation delay) (that is, when the terminal transmits the preamble by calculating the TA with the base station by using the location information of the terminal in the initial access step), the base station does not have information about the TA value used by the UE. Since the base station does not have information on the TA value used by the terminal, when the MSG3 resource is allocated, the time point at which the terminal transmits the MSG3 cannot be specified, so that the base station cannot know the subframe in which the MSG3 is received. Upon receiving MSG2, the UE may transmit MSG3 after (existing MSG2 reception processing + time required for MSG3 transmission preparation). However, in consideration of a long propagation delay (that is, in consideration of a TA value for MSG3 transmission in the terminal), the base station must perform scheduling. When transmitting MSG3, the UE transmits MSG3 in advance by applying <TA set by itself + TA adjustment value set by the base station> after the existing message preparation time. If the base station does not know the TA value set by the terminal in the MSG3 transmission step, the base station stops receiving the MSG3 message at the maximum delay time expected to receive the MSG3, that is, (maximum delay*2 + MSG2 reception processing + MSG3 transmission preparation time). can be expected When this time is referred to as n, the UE transmits MSG3 at time n-TA. Alternatively, if it is assumed that the time when the terminal receives the message from the base station is t, the terminal may transmit MSG3 at (t+MSG2 reception processing + MSG3 transmission preparation time + maximum delay - TA).

If the uplink scheduling time is set to (maximum delay *2), the initial access time is delayed, and if the initial access attempt fails, the delay time may be large enough to not be ignored. To solve this, there is a method of using the interval time of the RACH occasion selected by the UE instead of the maximum delay. When the UE selects the RACH occasion, since the RACH occasion larger than the TA (ie, the propagation delay calculated by the UE) is selected, the base station may assume that the maximum value of the delay between the UE and the base station is the interval between the RACH resources. If it is assumed that the base station expects to receive the uplink message (ie, (RO resource interval *2 + MSG2 reception processing + MSG3 transmission preparation time)) is n, the terminal may transmit MSG3 at n-TA time. Alternatively, if it is assumed that the time when the terminal receives the message from the base station is t, the terminal may transmit MSG3 at (t+ MSG2 reception processing + MSG3 transmission preparation time + RO resource interval - TA).

ii. The TA configured by the UE after the initial access procedure may be transmitted in MSG3 or MSG5 step. Alternatively, the terminal may transmit a TA update message to notify the base station of the TA value used by the terminal, and the base station may respond. The TA value set in this way may then be used as a scheduling offset. For example, TA may be applied at the start time of the RAR window operated by the UE for preamble transmission and RAR reception after preamble transmission in a random access procedure occurring after initial access. In addition, TA may be applied when MSG3 is transmitted after receiving MSG2, and the base station may operate to receive MSG3 after MSG2 transmission time (MSG processing time + TA*2). Alternatively, if it is assumed that the terminal receives the MSG2 message from the base station as t, MSG3 may be transmitted at <t+ MSG2 reception processing + MSG3 transmission preparation time>.

iii. When the base station determines TA (terminal specific propagation delay), the terminal without delay information between the terminal and the base station may apply the TA by using common delay information provided by the base station. The base station receiving the preamble may transmit a TA adjustment value through RAR. At this time, the base station knows the TA information of the terminal. The base station can expect to receive MSG3 after the MSG2 transmission time (MSG processing time + TA time*2). Alternatively, if it is assumed that the time when the terminal receives the message from the base station is t, the terminal may transmit MSG3 at (t+MSG2 reception processing + MSG3 transmission preparation time).

2) DATA Scheduling Offset

After the initial connection, when a TA is established, a new TA may be configured periodically or aperiodically (when the TA offset differs by more than a threshold). TA is a value reflecting long propagation delay in satellite communication. Since it may be changed according to the location of the terminal or the location of the satellite, the TA may be set for each terminal through terminal-specific signaling. When the base station sets TA to the terminal by using dedicated signaling, the scheduling time for uplink data reception may be determined as (downlink data reception processing time + TA time*2).

(4) Handover scheme

Since the location information of the terminal is sensitive information, it may be difficult to share it with the base station. When the location information of the terminal is not provided to the base station, the base station determines the approximate value of the terminal based on the TA value (at least one of the TA calculated by the terminal, the TA adjustment value, and the TA used for transmission) or the change used in the terminal. enemy location can be inferred. Additionally, by using information on neighboring cells reported through a measurement report from the UE, it is possible to know the approximate location of the UE in the cell.

The base station may have TA values at a plurality of predefined positions in the cell in advance. By additionally using the candidate cell list for handover reported by the terminal, the location is assumed to be the closest point to a predefined location, and TA with the target base station during handover is the distance from each satellite base station based on the location can be calculated and set in advance to the terminal.

Alternatively, the terminal may notify the target base station of information on whether it is a terminal capable of knowing location information or a terminal that cannot know location information. The target base station may omit providing the TA when the corresponding terminal is a terminal that can know location information. In the case of a terminal whose location information is unknown, uplink data transmission may be performed using the TA value received from the target base station.

5 is a block diagram illustrating an embodiment of a communication node according to the present invention.

The communication node illustrated in FIG. 5 may be a terminal or a satellite base station according to embodiments of the present invention. Referring to FIG. 5 , the communication node 500 may include at least one processor 510 , a memory 520 , and a transceiver 530 connected to a network to perform communication. In addition, the communication node 500 may further include an input interface device 540 , an output interface device 550 , a storage device 560 , and the like. Each of the components included in the communication node 500 may be connected by a bus 570 to communicate with each other.

The processor 510 may execute a program command stored in at least one of the memory 520 and the storage device 560 . The processor 510 may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present invention are performed. Each of the memory 520 and the storage device 560 may be configured as at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 520 may be configured as at least one of a read only memory (ROM) and a random access memory (RAM).

The methods according to the present invention may be implemented in the form of program instructions that can be executed by various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the computer-readable medium may be specially designed and configured for the present invention, or may be known and available to those skilled in the art of computer software.

Examples of computer-readable media may include hardware devices specially configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions may include not only machine language codes such as those generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as at least one software module to perform the operations of the present invention, and vice versa.

In addition, the above-described method or apparatus may be implemented by combining all or part of its configuration or function, or may be implemented separately.

Although the above has been described with reference to the preferred embodiment of the present invention, those skilled in the art can variously modify and change the present invention within the scope without departing from the spirit and scope of the present invention as described in the claims below. You will understand that it can be done.

Claims (1)

As a delay time management method performed by a terminal in a non-terrestrial network,
Receiving, from a non-terrestrial node, information on a changed delay time or a scheduling offset to be applied to uplink transmission; and
performing the uplink transmission to the non-terrestrial node by applying the delay time or the scheduling offset;
The information on the changed delay time or scheduling offset is received by being included in a system information block (SIB) from the non-terrestrial node, and whether the SIB includes information on the changed delay time or scheduling offset is determined by the SIB. Indicated by a paging message received in the first change period, and the information on the changed delay time or scheduling offset is received in a second change period after the first change period,
How to manage latency.

Images