KR20210038361A - Initial access method for long distance communication, and apparatus for the same - Google Patents

Abstract

An initial access method to a base station performed by a terminal in a non-terrestrial network may comprise: a step of receiving configuration information on random access channel (RACH) transmission occasions from the base station; a step of selecting a RACH occasion with reference to the configuration information for the RACH occasion according to whether or not the terminal is a terminal that can know the location information or a terminal that does not know the location information; and a step of transmitting a RACH preamble to the base station on the selected RACH occasion. Therefore, the present invention is capable of improving the RACH performance of the system.

Description

Initial access method for long distance communication, and apparatus for the same TECHNICAL FIELD

The present invention relates to a non-terrestrial network, and more particularly, to a method for performing an initial connection in a non-terrestrial network and an apparatus therefor.

It is necessary to develop a mobile satellite communication technology in preparation for communication disruption that may occur in areas of cellular shading such as mountain areas, desert areas, island areas and oceans, and terrestrial network collapse areas caused by various disasters such as earthquakes, tsunamis, and wars. Since the satellite communication network is maintained even when the terrestrial network collapses due to a disaster or disaster, the area where the disaster or disaster occurs is connected without being disconnected from the outside, enabling individual survival and maintenance of safety.

In addition, the necessity of mobile satellite communication technology is increasing in order to establish a hyperconnected society, which provides mobile communication services even in areas where communication was not possible in the past, such as mountains and remote areas without communication infrastructure. In 3GPP (3rd generation partnership project), based on 5G NR (new radio) technology, non-terrestrial base stations (e.g., base stations using an airborne platform such as a satellite base station or an airship) are used. Standardization of a non-terrestrial network (NTN) to be 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 cell size is large and the 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 the initial access performed by the UE to the base station. ) It affects the size of the window, which can affect the performance of the entire system.

An object of the present invention for solving the above problems is to provide an initial access method and apparatus performed by a terminal and a base station in a non-terrestrial network.

An embodiment of the present invention for achieving the above object is an initial access method for a base station performed by a terminal in a non-terrestrial network, and configuration information for random access channel (RACH) transmission opportunities from the base station is provided. Receiving; Selecting a RACH occasion with reference to the setting information for the RACH occasion according to whether the terminal is a terminal that can know location information or a terminal whose location information is unknown; And transmitting a RACH preamble to the base station at the selected RACH occasion, wherein the RACH occasions are set at narrow intervals for terminals that can know location information, and for terminals whose location information is unknown. Can be set at wide intervals.

Since the timing advance value may vary according to various satellite types and mobility in a non-terrestrial network having a long round trip delay time characteristic, according to embodiments of the present invention, timing advance by calculating or inferring the distance to the satellite according to the capability of the terminal. By adjusting the value, the RACH performance of the system can be improved.

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

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to a specific embodiment, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention. In describing each drawing, similar reference numerals have been used for similar 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 component. For example, without departing from the scope of the present invention, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. The term “and/or” includes a combination of a plurality of related described items or any of a plurality of related described items.

When a component is referred to as being "connected" or "connected" to another component, it is understood that it may be directly connected or connected to the other component, but other components may exist in the middle. It should be. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that there is no other component 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. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof does not preclude in advance.

Unless otherwise defined, all terms used herein including technical or scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms as defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as 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. The wireless communication network to which the embodiments according to the present invention are applied is not limited to the contents described below, and the embodiments according to the present invention can be applied to various wireless communication networks. Here, the wireless communication network may be used with the same meaning as a wireless communication system.

Hereinafter, for convenience of description,'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, 123) are on the ground and the satellites (111, 121, 122) perform the role of relays. I can. That is, in this case, the satellite base station operates as a transparent node defined in 3GPP NTN.

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

One or more NR cells may be defined through one satellite. In addition, one gNB may provide a service through one or more satellites. Satellites can 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 altitude of the base station (eg, 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 illustrating 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 (that is, a common delay) according to a distance 211 between a terminal 210 and a satellite base station 201 located vertically below the area of the satellite base station 201 And, the delay time according to the distance 221 between the terminal 220 and the satellite base station 201 located at various points (ie, a common delay time + a differential delay time) is shown.

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

That is, the common delay time is the shortest distance, average distance, or unidirectional delay time of the longest distance at a specific time point between the base station and the terminal within the corresponding area, or a specific value defined by the base station (or system) (e.g., satellite Altitude).

3 is a conceptual diagram illustrating 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 or a corresponding 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 the point where the gain of the beam is greatest) at a specific point in time in relation to the beam. It may be defined as a delay time for a point in which the signal to noise ratio (SNR) is the largest in the region.

4 is a conceptual diagram illustrating 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 include a service link 431 between the terminal 410 and the satellite base station 421, an inter-satellite link (ISL) 441, and a terrestrial link connected to the data network 470. It may include feeder links 451 and 452 between the gateway 460 and the satellite base stations 421 and 422.

At this time, there may be a common delay time (D _S ) of a service link, a common delay time of an inter-satellite link (D _I ), and a common delay time (D _F ) of a feeder link, and the common delay described in FIGS. 2 and 3 Mainly corresponds to the common delay (D _S ) 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 the elevation angle with the satellite and the distance with 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, and paging. It is useful for various control procedures such as paging).

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

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

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

Due to the characteristics of satellite communication with a large cell size, a large delay may occur between the terminal and the base station. In order for the base station to receive uplink data transmitted by all terminals in the cell at a similar time during initial access, the base station sends a timing advance (TA) to each terminal by a random access response (RAR). It is set through, and thereafter, the base station may periodically or aperiodically adjust the TA value set in the terminal. The large delay affects the size (length) of the random access preamble (RACH preamble), the TA value, and the size of the RAR reception window during initial access, which may affect the performance of the entire system. For example, when the TA value is large, the interval between RACH transmission opportunities must be increased, and the window size in the receiving unit for preamble and RAR reception must be increased. This may reduce the capacity of the random access channel (RACH), which may deteriorate overall system performance. TA can be adjusted with a MAC control element (CE) message. For a large TA due to a large delay, it is necessary to define a large MAC message. In the following, a method of managing a large TA for efficient system operation is proposed.

Terminal that can know its own location information

Hereinafter, an initial access method when the terminal can know its own location (eg, GNSS location) and satellite location (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 is described.

(1) Example #1 of the initial connection method

i. The terminal can determine the location of a satellite connected to a base station that will provide a service to it (they are trying to access) by using its location information and previously received satellite information (satellite ephemeris). 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 an RACH transmission opportunity 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 for TA adjustment to the terminal through a random access response (RAR). I can.

iii. The terminal receiving the TA adjustment value from the base station through the RAR additionally reflects the TA adjustment value received from the base station to the TA calculated based on its position and the position of the satellite earlier, and an uplink message (e.g., 4-step RA procedure). For MSG3 or for 2-step RA procedure, MSG B) may be transmitted.

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

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

(2) Example #2 of the initial connection 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 a new TA value calculated by the base station to the terminal based on the location information of 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 from the base station to the terminal using broadcast/multicast or a dedicated channel.

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 position and movement speed characteristics based on the location information and movement speed information collected from multiple terminals. Can be set in groups. 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 changes in the TA due to the mobility of the satellite, so the update value for the TA adjustment value due to the movement of the satellite is set as multicasting. And, UEs belonging to the same TA multicast group may apply the same update value.

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

(3) TA update method of the terminal in the 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, due to the movement of the mobile base station or the terminal, if the TA for the terminal is changed by exceeding the threshold of the TA difference (a value preset in the system) while the base station receives uplink data, the base station adjusts the TA value. Can be set in the terminal using broadcast/multicast or a dedicated channel.

ii. When the TA value (at least one of the TA calculated by the terminal, the TA adjustment value, and the TAs 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, broadcast/multicast or a dedicated channel may be used for aperiodic (for example, event triggering) configuration in the terminal. For example, while performing uplink reception, the base station may perform aperiodic configuration when the TA for the terminal is changed by exceeding the threshold of the TA difference (a value preset in the system).

iii. In a satellite cell having a large cell size, when the TA adjustment value is too large due to the large deviation of the delay, the TA command of the MAC CE must be largely defined. As one method, there is a method of defining the number of bits of the TA command as large as possible to represent the possible TA offset in one cell. Alternatively, when the maximum value of the TA command defined in the 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 indicates using a dedicated channel that the TA adjustment value exceeding the maximum value of the TA command is used, and the difference between the maximum value of the TA command and the TA adjustment value (additional TA adjustment value) is set using the TA command. I can. Upon receiving this, the UE may perform uplink transmission by applying (the TA calculated by itself + the 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 UE performs uplink transmission by applying a 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, when it is determined that the TA for the terminal has been 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 an RRC message or MAC CE. Through broadcast/multicast or a dedicated channel, the terminal can be set. This method has the advantage that the base station can anticipate and update the TA change without the uplink message of the terminal.

v. Meanwhile, since the location information of the terminal is sensitive information, it may be difficult for the terminal to share it with the base station. If the location information of the terminal is not provided to the base station, the base station approximates the TA value used by the terminal (at least one of the TA calculated by the terminal, the TA adjustment value, and the TAs used for transmission) or a change thereof. You can infer the typical location. In addition, if information on neighboring cells reported through a measurement report of the terminal is used, the approximate location of the terminal in the cell can be known.

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 a newly calculated TA value during uplink transmission. This method is more useful when considering a terminal having fast mobility as well as satellite mobility.

vi-1. The TA value used for transmission can be transmitted from the UE to the base station 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. When the base station receives the uplink data received from the terminal and the TA for the terminal is changed by exceeding the threshold of the TA difference (a value preset in the system), the base station sets a new TA adjustment value to the terminal through an RRC message or MAC CE. I 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 terminal may not inform the base station that the new TA has been applied. When the base station determines that TA adjustment is necessary when receiving uplink data, the base station may transmit a positive or negative TA adjustment value for TA adjustment 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 pre-promised messages or L1 signaling, MAC CE). The base station can transmit a positive or negative TA adjustment value for TA adjustment of the received signal to the terminal when it anticipates that the TA may be changed and TA adjustment is necessary for only the uplink data promised in advance. The base station may transmit the TA adjustment value to the terminal through 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.

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

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

Terminals whose location information is unknown

Hereinafter, an initial access method when the terminal cannot know its own location information 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 is 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 an elevation angle of 90 degrees. Alternatively, a delay value at a specific position in the cell closest to the satellite within the cell may be used as the minimum delay value. The terminal can infer a delay value according to the altitude of the satellite with the corresponding value.

ii. Since the difference in delay according to the location of the terminal in the satellite cell is large, there is a disadvantage in that the RACH capacity is reduced. Therefore, there is a need for a method to infer the location of the terminal. In addition to the above-described delay, the base station may utilize signal strength (eg, RSRP, RSRQ) and neighboring cell information as a method for inferring the relative position in 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) for a differential delay to be additionally applied by the terminal. The UE may determine a delay offset to be applied by the UE based on the measurement result of the signal strength of the neighboring cells for a predetermined period of time. For example, the terminal may determine the delay offset in the following cases.

A. If no surrounding cells are found

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

C. The signal strength of the neighboring cell is better than the 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 threshold 3

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

iii. The terminal may determine a delay offset suitable for the condition based on the signal strength measured by the terminal. The UE may determine a TA by applying (a delay broadcast by the base station + a delay offset) and transmit a RACH preamble on a 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. The terminal receiving the TA adjustment value 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 itself through a TA command MAC CE message. The UE may transmit an uplink message by reflecting the TA calculated by itself and the updated TA adjustment value.

vii. The UE may report a TA value (including all or only part of the TA calculated by the UE, a TA adjustment value, and a TA used for transmission) applied 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 state terminal

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

(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 periodically or aperiodically changed, 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 the uplink data transmission occurs. The operation may not be performed.

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

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

Even if the terminal can know location information, if the calculated TA is not used, it can perform an operation like a terminal whose location information is unknown.

Integrated operation plan

In a case where a terminal that can know its location information and a terminal that cannot know its location information are mixed in one base station, an integrated operation method is required.

(1) How to classify RACH Occasion

RACH occasions that can be used by a terminal whose location information is known and a terminal whose location information is not known can be distinguished. The uplink data received from a terminal whose location information is known has a small delay offset error, whereas a delay offset error of a terminal whose location information is unknown can be large, so the preamble at 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 whose location information is known, and a wide RACH occasion may be defined for a UE whose location information is unknown.

The base station may broadcast configuration information for the RACH occasion by distinguishing the RACH occasions to be attempted by the two types of terminals. The UE may select a RACH occasion according to its type (a UE with known location information/a UE with unknown location information) and transmit a RACH preamble.

Alternatively, the base station may variously define intervals between RACH resources repeated for each RACH occasion (eg, Minimum delay*2 to Maximum delay*2) and broadcast. The UE can perform the selection of the RACH occasion. A terminal that intends to perform the RACH procedure may be divided into a terminal for which TA information is set (or a terminal that can be directly calculated) and a terminal for which TA information is not set. A terminal for which TA information is set (i.e., through a random access procedure for previous initial access, in the case of a terminal in which a TA is established and maintains a TA, or can calculate its own TA value by itself using its own location and satellite location) In the case of the UE) can select a RACH occasion with a RACH resource interval greater than or equal to its TA value *2. A UE in which TA information is not configured may transmit a RACH preamble by selecting a RACH occasion set at an interval equal to or greater than the maximum delay *2 value provided by the base station. When receiving the preamble, the base station can accurately identify the RACH resource time (subframe) transmitted by the terminal. Meanwhile, even if a terminal capable of calculating location information does not use a TA calculated by itself, it may operate like a terminal in which no TA is set.

(2) Consideration of feeder link delay

Referring to FIG. 4, two delays may be applied to a radio interface delay between a terminal and a base station: a delay between a terminal and a satellite and a delay between a satellite and a gateway on the ground. For example, when the base station is located on the ground, the terminal can only calculate 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 to obtain the corresponding information from the terminal.

The first method is a method in which the base station broadcasts the feeder link delay. In the case of a transparent mode or regenerative mode base station, the base station may broadcast a 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 the 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 case of a transparent mode, the base station can broadcast only the service link delay. The feeder link delay can 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 may broadcast a delay including a service link delay and a 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 that can know its own location information, the delay can be derived based on the calculation of the distance between the satellite and the terminal. In this case, if the delay value calculated by the base station is larger 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, the operation corresponds to the case in which 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 and reception and scheduling offset

1) MSG3 scheduling offset

I. When the terminal determines the TA (terminal-specific propagation delay) (that is, when the terminal calculates a TA with the base station using the location information of the terminal in the initial access stage and transmits the preamble), the base station There is no information on 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 is allocated resources, the time point at which the terminal transmits the MSG3 cannot be specified, and the base station cannot know the subframe in which the MSG3 is received. The terminal receiving MSG2 may transmit MSG3 after (existing MSG2 reception processing + time used for preparation for MSG3 transmission). 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 applies <the TA set by itself + the TA adjustment value set by the base station> after the existing message preparation time, and transmits the MSG3 in advance. If the base station does not know the TA value set by the terminal in the MSG3 transmission step, the base station receives the MSG3 message at the maximum delay time expected to receive 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 terminal transmits MSG3 at n-TA time. Alternatively, assuming that the time point at which the terminal receives the message from the base station is t, the terminal can 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 not to 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 it selects a RACH occasion larger than the TA (ie, the propagation delay calculated by the UE), the BS may assume that the maximum value of the delay between the UE and the BS is an interval between RACH resources. Assuming that the base station expects to receive an uplink message (that is, (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 point at which 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. After the initial access procedure, the TA set by the terminal may be transmitted in the MSG3 or MSG5 step. Alternatively, the terminal transmits a TA update message to inform 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 be used as a scheduling offset later. For example, in a random access procedure that occurs after initial access, TA may be applied at the start point of the RAR window operated by the terminal for preamble transmission and RAR reception after preamble transmission. In addition, TA is applied when MSG3 is transmitted after MSG2 is received, and the base station can operate to receive MSG3 after MSG2 transmission time (MSG processing time + TA*2). Alternatively, if the terminal assumes that the time point at which the MSG2 message is received from the base station is t, MSG3 may be transmitted at <t+MSG2 reception processing + MSG3 transmission preparation time>.

Iii. When the base station determines the TA (terminal specific propagation delay), the terminal without delay information between the terminal and the base station can apply the TA by using common delay information provided by the base station. The base station receiving the preamble may transmit the TA adjustment value through the 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, assuming that the time point at which the terminal receives the message from the base station is t, the terminal can transmit MSG3 at (t+MSG2 reception processing + MSG3 transmission preparation time).

2) DATA scheduling offset

After the initial access, if a TA is set, a new TA may be set periodically or aperiodically (when the TA offset differs by more than a threshold). TA is a value that reflects a long propagation delay in satellite communication. Since it can be changed according to the location of the terminal or the location of the satellite, the TA can be set for each terminal through terminal-specific signaling. When the base station configures the TA by using dedicated signaling to the terminal, 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. If the location information of the terminal is not provided to the base station, the base station approximates the TA value used by the terminal (at least one of the TA calculated by the terminal, the TA adjustment value, and the TAs used for transmission) or a change thereof. You can infer the typical location. Additionally, by using information on neighboring cells reported through a measurement report from the terminal, it is possible to know the approximate location of the terminal in the cell.

The base station may have TA values in a number of predefined locations in the cell in advance. By additionally using the candidate cell list for handover reported by the terminal, the position is assumed as the point closest to the predefined position, and the TA with the target base station during handover is the distance to each satellite base station based on the corresponding position. Can be calculated and set in advance to the terminal.

Alternatively, the terminal may inform the target base station of information on whether it is a terminal that can know location information or a terminal that cannot know location information. If the target base station is a terminal capable of knowing location information, the target base station may omit provision of the TA. 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 showing 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 transmission/reception device 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, and a storage device 560. 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 in which methods according to embodiments of the present invention are performed. Each of the memory 520 and the storage device 560 may be configured with at least one of a volatile storage medium and a nonvolatile storage medium. For example, the memory 520 may be composed of at least one of read only memory (ROM) and random access memory (RAM).

The methods according to the present invention may be implemented in the form of program instructions that can be executed through 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 usable to those skilled in 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 high-level language codes that can be executed by a computer using an interpreter or the like as well as machine language codes such as those produced by a compiler. The above-described hardware device may be configured to operate as at least one software module to perform the operation 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 preferred embodiments of the present invention, those skilled in the art will variously modify and change the present invention within the scope not departing from the spirit and scope of the present invention described in the following claims. You will understand that you can do it.

Claims (1)

As an initial access method for a base station performed by a terminal in a non-ground network,
Receiving configuration information on random access channel (RACH) transmission opportunities from the base station;
Selecting a RACH occasion with reference to the setting information for the RACH occasion according to whether the terminal is a terminal that can know location information or a terminal whose location information is unknown; And
Including the step of transmitting a RACH preamble (preamble) to the base station on the selected RACH occasion,
The RACH occasions are set at narrow intervals for terminals that can know location information, and set at wide intervals for terminals whose location information is unknown,
Initial connection method.

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