Method for performing a handover between a first cell and a second cell, user equipment, and a non-transient computer-readable medium

Abstract

The present invention relates to a method implemented by user equipment for performing a handover between a first cell and a second cell in a network including a satellite communication network, wherein the first cell and the second cell are supported by one or more satellites of the satellite communication network, the first cell corresponds to a first base station, the second cell corresponds to a second base station, and at least the first cell is supported by a non-geostationary satellite of the satellite communication network, and the method comprises: Determining the value to be used as a timing advance in the second cell, the value to be used as a timing advance in the second cell is, - Data related to the timing advance of the user equipment in the second cell received from the first base station, or from the base station to which the user equipment was connected prior to connecting to the first base station, or, - If there is no data related to the timing advance of the user equipment in the second cell received from the first base station or from the base station to which the user equipment was connected prior to connecting to the first base station, it is determined based on the value used as the timing advance in the first cell, and The present invention relates to a method including performing uplink transmission with a second base station using a value to be used as a timing advance in a second cell.

Description

Technology Field

[0001] The present invention relates generally to the field of communication systems, and more specifically to satellite communication systems. Background Technology

[0002] In satellite communication networks involving non-geostationary satellites, the satellites are in constant motion. In such networks, User Equipment (UE) often performs handovers to maintain continuous access to the network via the next satellite beam covering a specific geographical area. These handovers require a vast amount of signaling, which entails the consumption of radio resources.

[0003] When satellite beams cover a wide geographical area and the relative ground velocities of these satellites are very high, the amount of signaling increases. In practice, under these circumstances, the number of UEs covered by a single beam can be very large, and since the time each UE is covered by the same satellite beam is very short, many UEs can perform handovers in a very short period of time.

[0004] In these satellite communication networks, there is also the problem of a long Round-Trip Time (RTT) between the UE and the base station. Therefore, since the target cell (target base station) pre-allocates radio resources to the UE so that the UE can access the target cell more quickly than during initial access during handover, such a long RTT requires the target cell to pre-allocate more radio resources for the handover (HO) to the UE to avoid interference. Furthermore, a long RTT increases the signaling required during handover.

[0005] The present invention aims to improve this situation.

[0006] To that end, the present invention provides a method performed by user equipment to perform a handover between a first cell and a second cell in a network including a satellite communication network, wherein the first cell and the second cell are supported by one or more satellites of the satellite communication network, the first cell corresponds to a first base station, the second cell corresponds to a second base station, and at least the first cell is supported by a non-geostationary satellite of the satellite communication network, and the method comprises

[0007] Determining the value to be used as a timing advance in the second cell, the value to be used as a timing advance in the second cell is,

[0008] - Data related to the timing advance of the user equipment in the second cell received from the first base station or from the base station to which the user equipment was connected prior to connecting to the first base station, or

[0009] - In the event that there is no data related to the timing advance of the user equipment in the second cell received from the first base station or from the base station to which the user equipment was connected prior to connecting to the first base station, and is determined based on the value used as the timing advance in the first cell, and

[0010] The present invention relates to a method including performing uplink transmission with a second base station using a value to be used as a timing advance in a second cell.

[0011] Therefore, to perform uplink communication between the user equipment and the second base station—that is, the base station to which the user equipment connects after the handover—the user equipment no longer needs to receive timing advances from the second base station (which typically estimates the timing advances and transmits them to the UE during the handover). Consequently, the amount of signaling and computation required during the handover is reduced. Furthermore, this procedure does not require user equipment capable of localizing itself (e.g., using a global navigation satellite system) or user equipment with high computational power.

[0012] User equipment can perform a handover that requires less computation and at least less signaling than a conventional handover procedure. In practice, during a conventional handover procedure, a second base station (second cell or target cell) estimates a value to be used as the timing advance (TA) of the user equipment within the second cell based on a signal transmitted to the second base station by the user equipment. For example, in radio communication standards such as LTE, Advanced LTE, or New Radio, the estimation of the TA is performed based on the first message of the RACH procedure (Msg1 of the RACH procedure) received by the base station from the user equipment. Then, in the same RACH procedure, the value of the TA estimated by the base station (Msg2 of the RACH procedure) is transmitted to the UE, and the UE uses this to introduce a time delay when emitting a signal through the second cell.

[0013] Accordingly, the present invention can remove one message (e.g., a RACH preamble or a second message (Msg2) transmitted by the second base station during the RACH procedure and / or, in some cases, skipping the RACH procedure entirely) during a handover procedure in situations of most radio standards (e.g., LTE, Advanced LTE, or New Radio) that can reduce the amount of computation and signaling during the handover. Deleting these messages enables a reduction in handover latency. Additionally, if the user equipment (ultimately the second base station) has not yet implemented a time offset based on a timing advance value (to compensate for the time required to propagate the signal), the exchange performed between the second base station and the user equipment during the handover procedure requires the second base station to secure much more radio resources than conventional exchanges; therefore, deleting these messages (or at least applying a timing advance offset during the transmission of these messages) enables the release of a significant amount of radio resources. In practice, the second base station cannot predict (or predicts insufficiently) the reception time of these exchanges, and therefore, in order to avoid interference with other transmissions (and to reduce the number of failures in access procedures), the second base station must secure a large amount of wireless resources to account for delays that may occur due to signal propagation. Therefore, determining by the user equipment the value to be used as a timing advance in the second cell before performing the handover procedure and while the user equipment is connecting to the base station (i.e., from the first base station or the base station to which the user equipment was connected before connecting to the first base station) reduces the consumption of wireless resources.

[0014] The uplink transmission performed by the second base station using a value to be used as a timing advance in the second cell may be any one of the uplink transmission during the handover procedure (e.g., Msg1 or Msg3 of the 4-step RACH procedure or an uplink message during the modified RACH procedure) or the uplink transmission performed after the handover procedure (e.g., a first uplink transmission performed after the handover), or, for example, a first uplink transmission performed between the second base station and the RACH procedure when the RACH procedure is not required during the handover.

[0015] Accordingly, the present method may further include performing a handover procedure. This handover may be performed without transmitting data related to a value to be used as a timing advance of the user equipment in the second cell through the second cell (target cell). The performed uplink transmission may be performed as part of the handover procedure. However, the performed uplink transmission may also be performed outside the frame of the handover procedure, for example, after or before the handover procedure.

[0016] That is, the user equipment can connect to the second cell without receiving data related to the value to be used as the timing advance of the user equipment in the second cell through the second cell.

[0017] The second base station no longer needs to measure the value used as a timing advance of the user equipment in the second cell during the user equipment access procedure to the second base station.

[0018] However, the user equipment can still receive data regarding the value to be used as the timing advance of the user equipment in the second cell while performing a handover using the value to be used as the timing advance in the second cell. For example, to fine-tune the timing advance value used when performing an uplink transmission, the second base station may transmit data related to the value to be used as the timing advance of the user equipment in the second cell. However, in this case, the present invention enables a reduction in the radio resources required during the handover procedure (as described above) because the offset between the ideal value to be used and the determined value to be used is small.

[0019] The timing advance value, or the value used or to be used as the timing advance, is understood to be a value corresponding to the time it takes for a signal to reach the base station from the user equipment.

[0020] It is understood that by determining the value, the user equipment determines a value that the user equipment can use to configure uplink communication with at least the second base station. Accordingly, the output of this determination is a value that should be used as a timing advance for the second cell.

[0021] This decision may be based on data related to the timing advance of the user equipment of the second cell received from the first base station or from the base station to which the user equipment was connected before being connected to the first base station.

[0022] This data is received from the connected base station before the user equipment connects to the second base station. Therefore, this data is received before any uplink communication is performed between the user equipment and the second base station.

[0023] Additionally, this decision may be based on the value used as the timing advance in the first cell when there is no data related to the timing advance of the user equipment in the second cell received from the first base station or from the base station to which the user equipment was connected prior to being connected to the first base station. Accordingly, when there is no data related to the timing advance of the user equipment in the second cell, the user equipment may use the value used as the timing advance in the first cell to determine that the value is to be used as the timing advance in the second cell. For example, the user equipment determines that the value to be used as the timing advance in the second cell is the same as the value to be used as the timing advance in the first cell.

[0024] Additionally, this decision may be based on a function of variation in the timing advance of the user equipment in the second cell. Accordingly, the user equipment receives data representing variation in the timing advance of the user equipment in the second cell as data related to the timing advance of the user equipment in the second cell, for example, an index among a set of indices representing various functions regarding variation in the timing advance of the user equipment in the second cell, or a value representing a parameter to be set in a general function of variation in the timing advance of the user equipment in the second cell. Based on this index or value, the user equipment obtains a function of variation in the timing advance of the user equipment in the second cell, and based on this function, the user equipment can determine a value to be used as the timing advance value of the user equipment in the second cell. For example, as described in the present disclosure, the output of the function at t=0 may be a value to be used as the timing advance of the user equipment in the second cell. The user equipment can determine the next value to be used by the user equipment in the second cell based on the output of the function at t > 0, where t represents the elapsed time since the user equipment connected to the second base station. Therefore, updating the timing advance value in the second cell requires no signaling or minimal signaling (although signaling may be required to correct the timing advance value, if the timing advance value is not constantly updated via feedback from the second base station through the function, since the offset between the update value determined by the function and the correction value is smaller than the offset between the timing advance value used by the user equipment and the update value signaled by the second base station, such correction may be performed less frequently and / or require less signaling).

[0025] Additionally, this determination may be based on a function of variation in the timing advance of the user equipment in the first cell and / or the second cell. Optionally, a supplementary time difference may also be used in this determination. For example, as described in this disclosure, if the user equipment uses a timing advance value based on a function of variation in the timing advance of the user equipment in the first cell at time t', the output of the function of variation in the timing advance of the user equipment in the first cell and / or the second cell at t = t'+Δt may be a value to be used as the timing advance of the user equipment in the second cell at time t'+Δt.

[0026] It is understood that the value used as the timing advance of the first cell is one of the values ​​used as the timing advance of the first cell by the user equipment. In practice, when connected to a base station, the timing advance of the user equipment is continuously updated, especially in the case of a non-geostationary orbit satellite moving relative to the surface. The value used as the timing advance of the first cell, which serves as the basis when the user equipment determines the value to be used as the timing advance of the second cell, may be, for example, the first or last value used as the timing advance of the first cell. In another example, the value used as the timing advance of the first cell, which serves as the basis when the user equipment determines the value to be used as the timing advance of the second cell, may be, for example, a value or index of a function of the variation of the timing advance in the first cell.

[0027] It is understood that, based on the value used (or to be used) as the timing advance for the user equipment of a specific cell, the user equipment applies a time offset based on this value to compensate for the time required for the signal to propagate, i.e., travel, from the user equipment to the base station. Additionally, the base station corresponding to this specific cell may use this value to determine resources scheduled for the user equipment. Therefore, the base station and the user equipment may use this value.

[0028] It is understood that, based on the data related to the timing advance, this data enables the user equipment to determine the timing advance value.

[0029] It is understood that by performing a handover between the first cell and the second cell, user equipment connected to the first base station connects to the second base station. The connection with the first base station may be disconnected. Accordingly, communication established with the user equipment in the first cell or transmission of data to the user equipment through the first cell continues through the second cell unless completed.

[0030] It is understood that a satellite communication network is a communication network that performs communication with user equipment of the communication network by using satellites to receive radio signals from user equipment and / or emit radio signals to user equipment. A satellite communication network may use only satellites to establish a physical link with user equipment of the communication network, or it may use non-satellite equipment, such as ground antennas or gateways. A satellite communication network may be integrated into a hybrid network, that is, a satellite-ground network.

[0031] It is understood that, by the cell corresponding to the base station, this cell is a cell that enables user equipment to transmit or receive wireless signals when connected to the base station.

[0032] It is understood that transmitting to user equipment or receiving at user equipment through a cell supported by a satellite involves transmitting radio signals between user equipment and the satellite. The cell may include one or more beams.

[0033] A non-geostationary satellite is a satellite that moves relative to the Earth.

[0034] A non-geostationary satellite may be a satellite having a fixed beam, for example, equipped with an unoperable antenna panel and pointing in a fixed direction relative to the satellite, and having a beam that places a footprint moving relative to the Earth surface on the Earth surface by the movement of the satellite relative to the Earth.

[0035] According to one aspect of the present invention, data related to the timing advance of user equipment in a second cell is,

[0036] - Data related to the value to be used as the timing advance of the user equipment in the second cell,

[0037] - Data that notifies the user equipment that the value to be used as the timing advance of the user equipment in the second cell is different from the value used as the timing advance of the user equipment in the first cell,

[0038] - Includes at least one of the data that notifies the user equipment that the value to be used as the timing advance of the user equipment in the second cell is the same as the value used as the timing advance of the user equipment in the first cell.

[0039] Transmitting data to the user equipment notifying that the value to be used as the timing advance in the second cell is different from the value used as the timing advance in the first cell allows the signaling required to notify the user equipment that there is no need to update the timing advance when connecting to the second base station to be easily removed (i.e., the signaling notifying the user equipment that the value to be used as the timing advance in the second cell is the same as the value used as the timing advance in the first cell can be removed). Based on this data, the user equipment determines whether the value to be used as the timing advance in the second cell is different from the value used as the timing advance of the user equipment in the first cell, or whether the value to be used as the timing advance in the first cell should be updated when performing a handover from the first cell to the second cell. Therefore, when connecting to the second base station after connecting to the first base station, the user equipment may transmit data only when it is necessary to update the value of the timing advance. Therefore, during a handover where an update of the timing advance is not required, there may be no signaling or at least less signaling. Accordingly, in this case, if the value to be used as the timing advance of the user equipment in the second cell is the same as the value used as the timing advance of the user equipment in the first cell, the data related to the timing advance cannot be transmitted. Consequently, if the data related to the timing advance of the user equipment in the second cell is not received by the user equipment, the user equipment can determine that the value to be used as the timing advance in the second cell is the value used in the first cell (e.g., the final timing advance value used in the first cell). If an update of the timing advance value is required, the update can be performed using a conventional procedure.For example, if the first cell and the second cell are not supported by the same satellite or the first base station and the second base station are not in the same location, it may be performed to transmit such data to the user equipment notifying the user equipment that the value to be used as the timing advance of the user equipment of the second cell is different from the value used as the timing advance of the user equipment of the first cell.

[0040] It is understood that by updating the timing advance value or the value to be used as the timing advance value, the timing advance value of the user equipment changes between the value previously used by the user equipment as the timing advance in the first cell (the value last used while connected to the first base station) and the new value to be used in the second cell.

[0041] Transmitting data to user equipment notifying that the value to be used as the timing advance in the second cell is the same as the value used as the timing advance in the first cell allows the second base station to avoid calculating the timing advance value and transmitting this value during the handover procedure. In this case, when performing a handover from the first cell to the second cell, the update of the timing advance value of the user equipment is not performed. For example, if the first cell and the second cell are supported by the same satellite and the first base station and the second base station are jointly deployed, the transmission of such data notifying user equipment may be performed.

[0042] Transmitting data to the user equipment regarding the value to be used as the timing advance of the user equipment in the second cell enables the user equipment to determine the timing advance value to be used in the second cell even if the value to be used as the timing advance in the second cell is different from the value used in the first cell. This information is useful when the value to be used as the timing advance in the second cell is different from the value used as the timing advance in the first cell, for example, when the first cell and the second cell are not supported by the same satellite or when the first base station and the second base station are not in the same location.

[0043] This data regarding the value to be used as a timing advance of the user equipment in the second cell may include at least one of the following.

[0044] - Data corresponding to the value, for example, data containing this value, or data encoding this value, or data representing an index and / or function that enables the calculation of the value. Thus, the user device can directly determine from the data the timing advance value to be used in the second cell.

[0045] - Data corresponding to an offset from the value used as the timing advance of the user equipment of the first cell. Therefore, the user equipment can determine the timing advance value to be used in the second cell with a simple operation.

[0046] - Data corresponding to an offset from a universal value. Thus, user equipment can determine the timing advance value to be used in the second cell with a simple operation. This universal value may be known by user equipment when performing the initial connection to the satellite network, and may be stored by user equipment, for example. The universal value may be, for example, a network universal value or a satellite universal value (assigned to each satellite) or a base station universal value (i.e., assigned to each base station), or may be a value common to, for example, a beam, a beam group, a base station group, or a user group. The universal value may be an index of a function or a variation function.

[0047] - Data related to the value of the reference signal received power RSRP. Accordingly, the user equipment can determine the timing advance value to be used in the second cell based on the signaled RSRP threshold (e.g., the RSRP threshold of a conditional handover procedure) and the match between this value and the timing advance value of the target cell.

[0048] According to one aspect of the present invention, an uplink transmission performed with a second base station is a first uplink transmission performed with the second base station.

[0049] Therefore, in the first uplink transmission performed between the user equipment and the second base station, a value determined by the user equipment is used. Accordingly, the radio resources secured by the second base station to receive the first uplink transmission can be reduced. In practice, if the first uplink transmission is performed without introducing an accurate timing advance value (or without any timing advance), the first uplink transmission is not aligned at the second base station. Consequently, the second base station will need to secure more radio resources so that the first uplink transmission (the first signal emitted from the user equipment for the second base station) does not interfere with other uplink radio signals from other user equipment. Furthermore, in satellite communication situations, the value used as a timing advance by the user equipment in the same cell can be very large compared to terrestrial communication and can differ significantly from that in terrestrial communication situations. Therefore, the amount of radio resources secured for the first uplink transmission may increase. In the context of NR, these secured wireless resources correspond to a preamble receiving window configured in the context of a four-step RACH procedure performed, for example, during a handover procedure.

[0050] A second aspect of the present invention is user equipment configured to perform a handover procedure between a first cell and a second cell in a network including a satellite communication network, wherein the first cell and the second cell are supported by one or more satellites of the satellite communication network, the first cell corresponds to a first base station, the second cell corresponds to a second base station, and at least the first cell is supported by a non-geostationary satellite of the satellite communication network, and the user equipment,

[0051] processor and,

[0052] As a non-transient computer-readable medium that stores instructions, when the instructions are executed by a processor, user equipment,

[0053] Determining the value to be used as a timing advance in the second cell, the value to be used as a timing advance in the second cell is,

[0054] - Data related to the timing advance of user equipment in the second cell, received from the first base station or from the base station to which the user equipment was connected prior to being connected to the first base station, or,

[0055] - If there is no data related to the timing advance of the user equipment in the second cell received from the first base station or from the base station to which the user equipment was connected prior to connecting to the first base station, determine based on the value used as the timing advance in the first cell, and

[0056] Configured to perform uplink transmission with the second base station using a value to be used as a timing advance in the second cell.

[0057] This relates to user equipment comprising a non-transient computer-readable medium.

[0058] A third aspect of the present invention is a method for managing a handover of user equipment between a first cell and a second cell in a network including a satellite communication network, wherein the first cell and the second cell are supported by one or more satellites of the satellite communication network, the first cell corresponds to a first base station, the second cell corresponds to a second base station, and at least the first cell is supported by a non-geostationary satellite of the satellite communication network, and the method comprises

[0059] Determining a value to be used as a timing advance of the user equipment in the second cell before the second base station receives a signal from the user equipment, and

[0060] The present invention relates to a method comprising performing uplink transmission between a second base station and a user equipment using a value to be used as a timing advance of the user equipment in the second cell.

[0061] Accordingly, in order to perform uplink communication between the user equipment and the second base station, i.e., the base station to which the user equipment connects, it is no longer necessary for the second base station to estimate a timing advance value that it needs to know based on the uplink signal received from the user equipment so that the target base station can schedule uplink resources for the user equipment. Therefore, scheduling should be used as the timing advance of the user equipment in the second cell and can be performed based on a predetermined value. Furthermore, if the user equipment can determine the timing advance value to be used before performing a handover according to the present invention as described above or by using location information (e.g., using GNSS), it is no longer necessary for the second base station to transmit timing advance data via signaling. Additionally, the user equipment does not need to transmit timing advance data to the second base station. Consequently, the signaling required to enable the user equipment to connect to the second base station is reduced (e.g., during a handover).

[0062] In addition, since the value to be used as the timing advance of the user equipment in the second cell is determined before the second base station receives any signal from the user equipment, the amount of computation required to estimate the timing advance of the user equipment during the connection between the user equipment and the second base station is less. Therefore, less computation is required during the handover procedure of handing over the user equipment from the first cell to the second cell. It is no longer necessary for the second base station to measure the value to be used as the timing advance of the user equipment in the second cell during the handover procedure.

[0063] Accordingly, as described above, the present invention enables the deletion of one message (e.g., a RACH preamble or a second message (Msg2) transmitted from the second base station during the RACH procedure and / or, in some cases, skipping the RACH procedure entirely) during a handover procedure, in situations of, for example, most radio standards (e.g., LTE, Advanced LTE, or New Radio), which can reduce computational load and signaling during the handover. Deleting such a message enables the reduction of handover latency. Furthermore, in cases where the user equipment (ultimately the second base station) has not yet implemented a time offset based on a timing advance value (to compensate for the time required for signal propagation), the exchange performed between the second base station and the user equipment during the handover procedure requires the second base station to secure much more radio resources than conventional exchanges; therefore, deleting such a message (or at least applying a timing advance offset during the transmission of these messages) enables the release of a significant amount of radio resources. In practice, because the second base station cannot predict (or predicts insufficiently) the reception time of these exchanges, and to avoid interference with other transmissions (and thus to reduce the number of failures in access procedures), the second base station must secure a large amount of wireless resources to account for delays that may occur due to signal propagation. Therefore, before performing the handover procedure, determining by the network the value to be used as a timing advance in the second cell while the user equipment is connecting to the base station (i.e., the first base station or the base station to which the user equipment was connected before connecting to the first base station) can reduce the consumption of wireless resources.

[0064] The uplink transmission performed by the second base station using a value to be used as a timing advance in the second cell may be an uplink transmission performed during a handover procedure (e.g., Msg1 or Msg3 of a 4-step RACH procedure or an uplink message during a modified RACH procedure) or after a handover procedure (e.g., a first uplink transmission performed after the handover), or a first uplink transmission performed between the second base station and (e.g., when a RACH procedure is not required).

[0065] The method may further include performing a handover procedure from a first base station to a second base station. This handover may be performed through a second cell (target cell) without transmitting data related to a value to be used as a timing advance for the user equipment in the second cell to the user equipment. The performed uplink transmission may be performed as part of the handover procedure. However, the performed uplink transmission may be performed outside the frame of the handover procedure, for example, after or before the handover procedure. This method may further include performing a handover procedure that reduces the available radio resources.

[0066] It is understood that by performing uplink transmission between the second base station and the user equipment using a timing advance value, the second base station configures the uplink transmission based on the determined timing advance value. For example, the second base station can schedule uplink resources allocated to the user equipment based on the determined timing advance value.

[0067] It is understood that by determining the value to be used as the timing advance of the user equipment in the second cell, any other network entity (or any combination of two or more of these network entities) excluding the first base station, the second base station, or the user equipment in this determination determines the timing advance value to be used in the second cell. This determination is made before the second base station receives a signal from the user equipment, that is, this determination is made without any direct data exchange between the user equipment and the second base station. Thus, this determination may be made prior to the handover procedure of the user equipment between the first base station and the second base station.

[0068] The determination of the timing advance value is based on the satellite network topology (beam and satellite topology) and / or whether the satellites of the network supporting each cell and / or the base stations corresponding to each cell are on the ground (also called satellites carrying a through payload) or wholly or partially on the satellites (also called satellites carrying a regenerative payload) and / or the relative physical positional relationship between the base stations (whether they are in the same location). These factors may be known by the network entity determining the timing advance value (the first base station or the second base station or other entities (excluding user equipment) or some of these entities). That is, determining whether the first cell and the second cell are supported by the same satellite and whether the first base station and the second base station are in the same location is particularly possible because the satellite takes a deterministic orbit when configuring or reconfiguring the network and / or base station, or it can be done in a more dynamic way based on information regarding the location of other satellites and / or beams and / or exchanges between base stations (e.g., configuration exchanges between base stations via Xn links) that can be obtained through the configuration (e.g., operation and maintenance configuration (O&M)).

[0069] To determine this value, a network entity (excluding user equipment) determines whether the timing advance value to be used by the user equipment in the second cell is the same as or different from the timing advance value used by the user equipment in the first cell. If the timing advance value to be used by the user equipment in the second cell is different from the timing advance value used by the user equipment in the first cell, determining that value may also involve calculating the timing advance value to be used by the user equipment in the second cell. Several calculation methods can be seen below.

[0070] A network entity refers to any one of the first base station, the second base station, another base station of the satellite network, or any other entity of the satellite network other than the user equipment. The network entity determines the value to be used by the user equipment at least in the second cell. Additionally, for convenience of explanation, the term network entity below refers to cases where the network entity includes multiple network entities other than the user equipment (e.g., the first base station and the second base station).

[0071] According to one aspect of the present invention, when the first cell and the second cell are supported by the same satellite and the first base station and the second base station are in the same location, the determined value is the same as the value used as the timing advance of the user equipment in the first cell. As a variation, the determined value and the value used as the timing advance of the user equipment in the first cell are values ​​of the same function of the variation of the timing advance with respect to time.

[0072] Accordingly, under these specific conditions regarding the beam topology and the position of the second base station relative to the first base station, the network entity determines whether the same timing advance value (and / or the same variation function) used in the first cell can be used in the second cell. In practice, if the base stations are mounted at the same location on the same satellite (and thus, the cells corresponding to these base stations are supported by the same satellite), or if they are at the same location on the ground and the cells corresponding to these base stations are supported by the same satellite, the time at which a signal emitted from the user equipment reaches the first base station is the same as that of the second base station, and thus the timing advance value used in the first cell can be used in the second cell. Furthermore, the function describing the variation of the user equipment's timing advance with respect to the time when the user equipment passes through the first and second cells does not depend on the handover time.

[0073] Based on the network topology, the value to be used as the timing advance of the user equipment in the second cell is determined without requiring any complex calculations. The network entity determining the timing advance value can use the timing advance value used in the first cell as the timing advance value of the second cell.

[0074] Base stations in the same location mean base stations located in the same physically geographical location, for example, on the same satellite or ground base stations at the same location / gateway. By definition, if the time required for a signal emitted from these base stations to reach the satellite supporting the cell corresponding to these two base stations is always the same, then the two base stations are in the same location.

[0075] According to one aspect of the present invention, when the first cell and the second cell are supported by different satellites, or when the first base station and the second base station are not in the same location, the value to be used as the timing advance of the user equipment in the second cell is different from the value used as the timing advance of the user equipment in the first cell.

[0076] According to one aspect of the present invention, the determination (e.g., calculation) of a value to be used as a timing advance of user equipment in a second cell is based on at least one value that is used or previously used as a timing advance of other user equipment in the second cell.

[0077] Since at least one value used or previously used as a timing advance has already been calculated according to the method of the present disclosure or measured according to any existing method, using it as a timing advance for user equipment in a second cell allows for the accurate determination of the value to be used as a timing advance for user equipment in the second cell without requiring complex calculations. For example, the value to be used as a timing advance for user equipment in the second cell is a value that has been used or previously used as a timing advance for other user equipment in the second cell.

[0078] The determination of at least one value used as a timing advance for other user equipment in the second cell or previously used can be performed by a network entity, for example, a second base station.

[0079] According to one aspect of the present invention, at least one value used or previously used as a timing advance of another user equipment in a second cell is,

[0080] - Uplink transmission between another user device and the second base station prior to connecting to the second cell (e.g., during a handover procedure), or,

[0081] - Transmit the first uplink of another user device after connecting to the second cell

[0082] It was used or previously used as a timing advance for other user equipment in the second cell.

[0083] Accordingly, at least one value used for uplink transmission in the second cell is used while another user device is in a similar situation to that user device, that is, while two user devices are around the second cell. Therefore, it is more accurate to determine the value to be used as the timing advance of the user device in the second cell based on this at least one value. For example, a network entity may determine that the timing advance value of the user device is the same as the at least one value.

[0084] In addition, since another user device can perform a handover from the first cell to the second cell, the situation of the user device and the other user device is more similar than the situation of the user device and the other user device that performed a handover from another cell to the second cell. In reality, the overlap between the first cell and the second cell may differ from the overlap between the second cell and another cell. If the overlap becomes larger, the user device can perform a handover closer to the center of the cell to be connected than when the overlap size is small. Therefore, depending on the overlap between the two cells, the timing advance value used when the user device performs a handover between these two cells may differ. Considering the first cell and the second cell including the adjacent first and second beams, it is understood that the first and second cells are deployed parallel to the LEO orbit and numbered in the opposite direction to the movement of the LEO satellite, and because the satellite mobility is much higher than the mobility of the user equipment, most of the user equipment in the first cell is directed toward the second cell (not toward the other third cell) to perform a handover.

[0085] According to one aspect of the present invention, at least one value is associated with a time stamp, said time stamp corresponds to the moment of determination of at least one value, and the duration between the moment of determination of at least one value and the determination of a value to be used as a timing advance of a user device in a second cell is less than a predetermined threshold.

[0086] Therefore, if it takes a very long time to determine at least one value before determining the value to be used as the timing advance for the user equipment in the second cell, the value to be used as the timing advance for the user equipment in the second cell cannot be determined based on at least one value. This ensures that the user equipment and other user equipment are located within a limited geographical area (e.g., within or near the overlapping area between the first and second cells) because the determination of at least one value was made shortly thereafter. Thus, other user equipment is in a similar situation to the user equipment; that is, the two user equipment are within a limited geographical area and may be at similar altitudes. Therefore, it is more accurate to determine the value to be used as the timing advance for the user equipment in the second cell based on this at least one value.

[0087] According to one aspect of the present invention, at least one value is associated with a geographical area, and at the moment of determining at least one value, the geographical area intersects with the geographical communication range of a second cell, and when performing uplink transmission between a second base station and a user device, the geographical area intersects with the geographical communication range of the second cell.

[0088] Therefore, if at least one value is determined by chance (when a timing advance value is determined) while the other user equipment is too far from the actual location of the user equipment, the value to be used as the timing advance for the user equipment in the second cell cannot be determined based on at least one value. This ensures that the location of the user equipment and the location of the other user equipment are close when performing uplink transmission and when at least one value is determined. Thus, the other user equipment is in a similar situation to the user equipment, that is, the two user equipment may be geographically close and at similar altitudes. Therefore, it is more accurate to determine the value to be used as the timing advance for the user equipment in the second cell based on this at least one value.

[0089] It is understood that at least one beam footprint of the beam used by the second base station for communication with user equipment intersects the geographical area that intersects with the geographical communication range of the second cell. Additionally, the beam used by the second base station to communicate with user equipment is,

[0090] - Uplink transmission between the second base station and user equipment is performed, and / or

[0091] - The second base station may communicate with other user equipment using at least one value, or it may be a beam implemented through which communication has already been completed.

[0092] A geographic area can be defined as a predetermined area on the surface of the Earth. A geographic area may be one of several geographic areas covering at least a portion of the Earth's surface. The size of the geographic area may vary. The network can infer whether user equipment is within the beam footprint from exchanges with user equipment, and thus infer proximity to some geographic areas. Additionally, the network may obtain location information of some users acquired, for example, by positioning technology.

[0093] According to one aspect of the present invention, the value to be used as a timing advance of user equipment in the second cell is determined by the second base station.

[0094] In this case, the method may further include transmitting data related to the timing advance of the user equipment in the second cell to the base station to which the user equipment is connected or to be connected, by the second base station, before connecting to the first base station or to the first base station, wherein said data related to the timing advance of the user equipment in the second cell corresponds to a value to be used as the timing advance of the user equipment in the second cell determined by the second base station. Based on the value for the timing advance of the user equipment in the second cell, the first base station (or the base station to which the user equipment is connected or to be connected before connecting to the first base station)

[0095] - Data related to the timing advance of the user equipment in the second cell (the said data enables the user equipment to determine the value to be used as the timing advance in the second cell), which is identical to the data transmitted by the second base station to the first base station or data adapted to the user equipment (for example, this data may correspond to an offset between the value to be used as the timing advance of the user equipment in the second cell and the value used as the timing advance of the user equipment in the first cell), or,

[0096] - Before the user equipment connects to the first base station, it may be decided to transmit (or enable transmission of) data related to the timing advance of the user equipment of the second cell to the base station to which the user equipment is connected (directly or through another base station).

[0097] Based on data related to the timing advance of the user equipment in the second cell, the base station to which the user equipment connects (which may be the first base station) may also decide not to transmit any data regarding the timing advance to the user equipment, in particular, if the value to be used as the timing advance of the user equipment in the second cell is the same as the value to be used or used as the timing advance of the user equipment in the first cell.

[0098] According to one aspect of the present invention, a value to be used as a timing advance of user equipment in a second cell is determined based on at least one value used as a timing advance of user equipment in a first cell.

[0099] That is, the network entity determines the value to be used as the timing advance for the user equipment in the second cell based on the value used as the timing advance for the user equipment in at least the first cell. Therefore, the determined value takes into account the situation of the user equipment more accurately, and accordingly, accurately determines the value to be used as the timing advance for the user equipment in the second cell.

[0100] For example, the value to be used as the timing advance of the user equipment in the second cell is at least,

[0101] - Minimum value used as a timing advance for the user equipment of the first cell and / or

[0102] - As the center position of the second beam footprint relative to the center position of the first beam footprint, the first beam is used by the first base station to communicate with user equipment, and the second beam is used by the second base station to perform uplink transmission between the second base station and user equipment, and / or,

[0103] - Location of the geographic communication range of the first cell, and / or,

[0104] - Location of the geographic communication range of the second cell, and / or,

[0105] - A change (i.e., variation) in the value used as a timing advance of the user equipment of the first cell, and / or,

[0106] - A value used as a timing advance of the user equipment in the first cell, determined at a predetermined time after the user equipment performs a handover to connect to the first base station or at a predetermined time before the user equipment performs a handover to connect to the second base station, and / or,

[0107] - Direction of satellite movement

[0108] It can be determined based on.

[0109] When a value is determined based on the position of the center of the second beam footprint relative to the position of the center of the first beam footprint, the user equipment communicates with the first base station through the first beam while connected to the first base station. This connection with the first base station is made prior to the connection with the second base station.

[0110] The combination of beam footprints of the beams supporting the cell is understood by the geographical communication range of the cell. A beam supporting the cell is any beam that can be used for user equipment to communicate (transmit or receive) through the cell, that is, to communicate through the base station corresponding to the cell.

[0111] It is understood that the direction of movement of the satellite is, for example, the direction of movement on the satellite's orbit, or the projection of this movement onto the surface of the earth, or any equivalent form representing the above direction.

[0112] The fundamental elements capable of determining the value to be used as the timing advance for the user equipment in the second cell are known because the network entity receives them from the base station and / or from the configuration of the satellite network (e.g., the direction of satellite movement) and / or calculations (e.g., the location of the cell's geographical range, the estimated location of the user equipment, or approximate estimates related to the location relative to a reference point within the system, etc.). For example, if the network entity determining the value to be used as the timing advance for the user equipment in the second cell is the first base station, the second base station,

[0113] - The location of the geographic communication range of the second cell, or,

[0114] - Center position of the second beam footprint (based on this position, the first base station can calculate the center position of the second beam footprint relative to the center position of the first beam footprint)

[0115] Information related to can be transmitted to the first base station.

[0116] Accordingly, according to one aspect of the present invention, a value to be used as a timing advance of user equipment in a second cell is determined by a first base station. In this case, the value may be determined based on information provided by the second base station.

[0117] According to one aspect of the present invention, the method further comprises transmitting data related to a timing advance of user equipment in a second cell corresponding to a determined value from a first base station or from a base station connected before user equipment is connected to the first base station. By this data, the user equipment can retrieve a value to be used as a timing advance of user equipment in the second cell.

[0118] According to one aspect of the present invention, the method further comprises setting a handover mode to active or non-active and transmitting a message to a user device instructing to perform a handover according to the set handover mode, wherein the active handover mode is a handover mode in which the handover is executed according to the present invention, and the non-active handover mode is a mode in which the handover is performed according to a different handover procedure (e.g., a standard handover procedure). The active handover mode is,

[0119] - If the value used as the timing advance in the second cell is different from the value used as the timing advance in the first cell, a different handover procedure is performed and used as the timing advance in the second cell. If the value is the same as the value used as the timing advance in the first cell, a first mode implementing a handover according to the present invention,

[0120] - A second mode implementing a handover according to the present invention

[0121] It is divided into two modes.

[0122] A fourth aspect of the present invention is a second base station configured to manage the handover of user equipment between a first cell and a second cell in a network including a satellite communication network, wherein the first cell and the second cell are supported by one or more satellites of the satellite communication network, the first cell corresponds to a first base station, the second cell corresponds to a second base station, at least the first cell is supported by a non-geostationary satellite of the satellite communication network, and the second base station is

[0123] processor and,

[0124] As a non-transient computer-readable medium in which instructions are stored, when the instructions are executed by a processor, a second base station,

[0125] - Determine the value to be used as the timing advance of the user equipment in the second cell, and

[0126] - To perform uplink transmission between the second base station and the user equipment using a value to be used as the timing advance of the user equipment in the second cell.

[0127] This relates to a second base station comprising a non-transient computer-readable medium.

[0128] In this case, the network entity is the second base station. Therefore, in addition to determining the value, the network entity performs uplink transmission by the user equipment (i.e., receives and processes the uplink signal transmitted by the user equipment).

[0129] A fifth aspect of the present invention is a method for managing a handover of user equipment between a first cell and a second cell in a network including a satellite communication network, wherein the first cell and the second cell are supported by one or more satellites of the satellite communication network, the first cell corresponds to a first base station, the second cell corresponds to a second base station, and at least the first cell is supported by a non-geostationary satellite of the satellite communication network, and the method is

[0130] Determining the value to be used as the timing advance of the user equipment in the second cell, and

[0131] The present invention relates to a method comprising transmitting to the second base station and / or user equipment a value to be used as a timing advance of the user equipment in the second cell before the second base station receives a signal from the user equipment.

[0132] If the network entity is not the second base station, that is, if the determination of the value is performed by an entity other than the second base station, this network entity, the determined value,

[0133] - In particular, if the user equipment cannot keep itself in the same position and, consequently, cannot calculate the value to be used as a timing advance in the second cell, it can transmit to the user equipment, and

[0134] - The second base station may transmit to the second base station to avoid estimating and transmitting the timing advance during handover.

[0135] In this case, the network entity may be any other network entity excluding the first base station or user equipment and the second base station.

[0136] A sixth aspect of the present invention is a first base station configured to manage the handover of user equipment between a first cell and a second cell in a network including a satellite communication network, wherein the first cell and the second cell are supported by one or more satellites of the satellite communication network, the first cell corresponds to a first base station, the second cell corresponds to a second base station, at least the first cell is supported by a non-geostationary satellite of the satellite communication network, and the first base station is

[0137] processor and,

[0138] As a non-transient computer-readable medium storing instructions, when the instructions are executed by a processor, the first base station,

[0139] - Determine the value to be used as the timing advance of the user equipment in the second cell, and

[0140] - The invention relates to a first base station comprising a non-transient computer-readable medium configured to transmit to the second base station and / or user equipment a value to be used as a timing advance of the user equipment in the second cell before the second base station receives a signal from the user equipment.

[0141] A seventh aspect of the present invention relates to a non-transient computer-readable medium that stores instructions and performs the method described above when the instructions are executed by a processor.

[0142] Computer-readable media include, but are not limited to, both computer memory media and communication media, comprising any medium that facilitates the transfer of computer programs from one place to another. As used herein, “computer memory media” may be any physical medium accessible by a computer. Examples of computer memory media include, but are not limited to, flash drives or other flash memory devices (e.g., memory keys, memory sticks, key drives), CD-ROMs or other optical storage, DVDs, magnetic disk storage or other storage devices, memory chips, RAM, ROM, EEPROM, smart cards, solid-state drive (SSD) devices or hard disk drive (HDD) devices, or any other suitable medium that can be used to carry or store program code in the form of instructions or data structures readable by a computer processor. Additionally, various forms of computer-readable media, including routers, gateways, servers or other transmitting devices, wired (coaxial cable, fiber, twisted pair, DSL cable) or wireless (infrared, wireless, cellular, microwave), may transmit or send instructions to a computer. The commands are not limited but may include code in any computer programming language, including assembly, C, C++, Visual Basic, HTML, PHP, Java, Javascript, Python, and bash scripts.

[0143] Unless specifically stated otherwise, any discussion using terms such as processing, computing, calculation, determination, etc. in the following description shall be understood to refer to the operation or process of a computer or computing system or a similar electronic computing device that manipulates data expressed in physical quantities, such as electronic quantities within the registers or memory of a computing system, or converts such data into other data similarly expressed in physical quantities within the memory, registers, or other information storage, transmission, or display devices of a computing system. Brief explanation of the drawing

[0144] The present invention is illustrated as an example, not limited to, the accompanying drawings, and similar reference numerals refer to similar elements. Figure 1 is a diagram showing some of the satellites of a satellite communication network. FIG. 2 is a diagram illustrating a method for determining a value to be used as a timing advance of user equipment in a second cell according to the present invention. FIG. 3 is a diagram illustrating a method for determining a value to be used as a timing advance of user equipment in a second cell according to the present invention. FIG. 4 is a diagram illustrating a method for determining a value to be used as a timing advance of user equipment in a second cell according to the present invention. FIG. 5 is a diagram illustrating a method for determining a value to be used as a timing advance of user equipment in a second cell according to the present invention. FIG. 6 is a flowchart illustrating the steps implemented for a user device according to the present invention to perform a handover. FIG. 7 is a flowchart illustrating the steps implemented to manage handover in a satellite network according to the present invention. Specific details for implementing the invention

[0145] Referring to FIG. 1, a portion of a satellite communication network is illustrated. Although the present invention is not limited to specific specifications, for ease of explanation, the present invention is described in the context of New Radio (NR) standards. While NR standards use the term "user equipment" to refer to devices used by end users for communication, the present specification also includes any other term used to refer to any wireless device used to communicate at least through a satellite network (e.g., mobile terminal, mobile station, personal handheld terminal, wireless modem, portable device, etc.) in the term "user equipment."

[0146] The present invention described below can be used in various types or architectures of satellite communication networks, for example, hybrid networks including satellite network components.

[0147] In FIG. 1, three satellites Sat1, Sat2, and Sat3 are illustrated. Each satellite is linked to one or more gateway nodes Gw1-Gw4. Two satellites may be linked to the same gateway node, but this is not illustrated herein. Accordingly, these gateway nodes Gw1 through Gw4 are configured to communicate with one or more satellite nodes Sat1, Sat2, and Sat3. Additionally, these gateway nodes Gw1 through Gw4 are configured to communicate with a core network not illustrated herein.

[0148] Each satellite Sat1, Sat2, and Sat3 is configured to generate one or more satellite beams, and three satellite beams for each satellite are illustrated in FIG. 1. The first satellite Sat1 generates satellite beams SB11.1, SB12.1, and SB13.2. The second satellite Sat2 generates satellite beams SB21.3, SB22.3, and SB23.4. The third satellite Sat3 generates satellite beams SB31.5, SB32.5, and SB33.5.

[0149] Each satellite beam SB11.1 through SB33.4 is configured with a specific frequency band. Through each satellite beam SB11.1 through SB33.4, the corresponding satellite (i.e., the satellite generating the beam) can transmit and receive data according to the radio resources allocated to the frequency band configured for the beam. These radio resources can be shared according to frequency division multiplexing (e.g., Frequency Division Multiplexing (FDM) or Orthogonal Frequency Division Multiplexing (OFDM)), by time division multiplexing (e.g., Time Division Multiplexing (TDM)) or code division multiplexing (Code Division Multiplexing (CDM)), by polarization, or by a combination thereof.

[0150] The allocation of radio resources for each beam is realized by base stations BS1 through BS5. Each base station manages the radio resources of one or more satellite beams. For example, as illustrated in FIG. 1,

[0151] - BS1 manages the radio resources of satellite beams SB11.1 and SB12.1.

[0152] - BS2 manages the radio resources of the satellite beam SB13.2.

[0153] - BS3 manages the radio resources of satellite beams SB21.3 and SB22.3.

[0154] - BS4 manages the radio resources of the satellite beam SB23.4.

[0155] - BS5 manages the radio resources of satellite beams SB31.5 and SB33.5.

[0156] Each base station defines a cell in which wireless resources are allocated to user equipment according to the beam managed by the base station. That is, wireless resources of a satellite beam can be allocated to user equipment by the base station managing the satellite beam (provided that the user equipment receives sufficient wireless power from this satellite beam). Therefore, the user equipment is considered to be within the communication range of the cell corresponding to the base station. Thus, according to FIG. 1, BS1 forms a first cell C1 while covering the user equipment to receive sufficient wireless power from satellite beams SB11.1 and SB12.1. BS2 forms a second cell C2 while covering the user equipment to receive sufficient wireless power from satellite beam SB13.2. BS3 forms a third cell C3 while covering the user equipment to receive sufficient wireless power from satellite beams SB21.3 and SB22.3. BS5 forms a fifth cell C5 while covering the user equipment to receive sufficient wireless power from satellite beams SB31.5 and SB33.5. Therefore, the cell can correspond to a beam (e.g., C2 and C4) or a set of beams (e.g., C1, C3 and C5).

[0157] Base stations can be mounted on a satellite (BS5) or deployed on the ground (BS1 to BS4). If two base stations are physically located in the same geographical location, they are in the same location, which is the case for BS1 and BS2, but different for, for example, BS2 and BS3 or BS3 and BS4.

[0158] In order for wireless resources to be allocated by a base station, user equipment must receive sufficient wireless power from at least one beam managed by the base station (i.e., the user equipment must be within the communication range of a cell formed by the base station) and be connected to that base station. The connection procedure may be performed upon initial access to the base station or when the user equipment is already connected to another base station and accesses the current base station via a handover procedure.

[0159] In FIG. 1, multiple user devices UE1 to UE5 are shown. UE1 is connected to BS1 of the first cell C1 and is allocated radio resources of satellite beam SB11.1 generated by satellite Sat1. UE2 is connected to BS2 of the second cell C2 and is allocated radio resources of satellite beam SB13.2 generated by satellite Sat1. UE3 is connected to BS3 of the third cell C3 and is allocated radio resources of satellite beam SB21.3 generated by satellite Sat2. UE4 is connected to BS4 of the fourth cell C4 and is allocated radio resources of satellite beam SB23.4 generated by satellite Sat2. UE5 is connected to BS5 of the fifth cell C5 and is allocated radio resources of satellite beam SB31.5 generated by satellite Sat3.

[0160] In the context of a satellite network using non-geostationary satellites and fixed-beam satellites, the footprints of the satellites and their beams move predictably relative to the Earth's surface (since the dynamics of the satellite constellations can be predicted). In Figure 1, the relative movement of the satellites with respect to the Earth's surface is indicated by the arrow Sat Mouv.

[0161] Based on this predictable dynamic of the satellite constellation, and considering that the mobility of the UE is negligible relative to the mobility of the satellite, it is possible to predict the base station that user equipment must connect to (e.g., by performing a handover) in order to continue communication through the satellite communication network. According to Figure 1, UE1 connects to BS1 and, in most cases, is likely to perform a handover from BS1 to BS2, then a handover from BS2 to BS3, then a handover from BS3 to BS5, and so on. UE2 connects to BS2 and, in most cases, is likely to perform a handover from BS2 to BS3 and a handover from BS3 to BS5, and so on. UE3 connects to BS3 and, in most cases, is likely to perform a handover from BS3 to BS4, a handover from BS4 to BS5, and so on. UE4 connects to BS4 and, in most cases, is likely to perform a handover from BS4 to BS5, etc.

[0162] However, in order for the user equipment and the base station to which the user equipment is to connect (target base station or second base station) to communicate accurately, the base station and the user equipment must acquire the value of the timing advance used by the base station (located within the cell managed by this base station). In the NR standard, acquiring the value involves the base station (to which the user equipment connects) performing a RACH procedure while measuring and transmitting the value of the timing advance.

[0163] However, if the cell currently serving the user equipment (1st cell) and the target cell (2nd cell) are supported by the same satellite, and the base station connected to the current user equipment (1st base station) and the target base station (2nd base station) are in the same location, the value to be used at the 2nd base station is the same as the value used at the 1st base station. Therefore, according to FIG. 1, since BS1 and BS2 are in the same location and both C1 and C2 are supported by Sat1, the value to be used as the timing advance of UE1 at C2 is the same as the value used as the timing advance of UE1 at C1 (e.g., the value last used at C1). With the same explanation, considering that the timing advance value of UE1 varies with time while UE1 passes through C1, C2, etc., if the cell currently serving the user equipment (1st cell) and the target cell (2nd cell) are supported by the same satellite, and if the base station connected to the user equipment (1st base station) and the target base station (2nd base station) are in the same location, when the user equipment passes through C1 and C2, the function of the variation of the user equipment's timing advance with respect to time is continuous; that is, this function does not depend on the moment of handover. That is, the value to be used as the timing advance of UE1 in C1 and the value used as the timing advance of UE1 in C2 are values ​​of the same function of the variation of the timing advance with respect to time. In other words, the function of the variation of the timing advance of UE1 with respect to time in C1 is the same as the function of the variation of the timing advance of UE1 with respect to time in C2.

[0164] Meanwhile, if the cell currently serving the user equipment (the first cell) and the target cell (the second cell) are supported by different satellites, or if the base station currently connected to the user equipment (the first base station) and the target base station (the second base station) are not in the same location, the value to be used at the second base station is different from the value used at the first base station. Therefore, according to FIG. 1, since BS2 and BS3 are not in the same location or C2 and C3 are not supported by the same satellites Sat1 and Sat2, the value to be used as the timing advance of UE2 at C3 is different from the value used as the timing advance of UE2 at C2. Since BS3 and BS4 are not in the same location, the value to be used as the timing advance of UE3 at C4 is different from the value used as the timing advance of UE3 at C3. Because BS4 and BS5 are not in the same location or C4 and C5 are not supported by the same satellites Sat2 and Sat3, the value to be used as the timing advance for UE4 in C5 is different from the value used as the timing advance for UE4 in C4. In this case, it is necessary to estimate the value to be used as the timing advance in the second cell (C3, C4, and C5, respectively). By the same logic, considering that the timing advance value of UE1 varies with time while UE1 passes through C2, C3, etc., if the cell currently serving the user equipment (first cell) and the target cell (second cell) are not supported by the same satellite and / or if the base station connected to the current user equipment (first base station) and the target base station (second base station) are not in the same location, when the user equipment passes through C2 and C3, the function of the variation in the user equipment's timing advance with respect to time is discontinuous; that is, this function depends on the moment of handover.In other words, the value to be used as the timing advance of UE1 in C2 and the value used as the timing advance of UE1 in C3 are different, because this can be interpreted as different function values ​​of the variation of the timing advance with respect to time. That is, the function of the variation of UE1's timing advance with respect to time in C1 is identical to the function of the variation of UE1's timing advance with respect to time in C2.

[0165] Several methods for estimating (i.e., determining) the value of a timing advance according to the present invention are described below.

[0166] Each base station BS1 through BS5 includes a processing module PROC-BS and a memory unit MEM-BS. The memory unit MEM-BS includes a non-volatile unit that retrieves computer programs, and a volatile unit that retrieves values ​​used as timing advances in the second cell of other user equipment, timestamps associated with these values, information regarding geographic areas, functions of changes in the timing advance values ​​of user equipment in the first cell, the location of user equipment, the minimum timing advance value of user equipment in the first cell, the timing advance value received in the first cell at a given moment, the ephemeris of satellite constellations, information regarding the beam footprint of the satellite network, etc. The processing module PROC-BS is configured to calculate the location of user equipment, determine the value to be used as a timing advance for user equipment in the second cell, transmit data related to the timing advance of user equipment in the second cell, perform a handover, perform uplink transmission, and perform resource scheduling.

[0167] Each user device includes one communication module (COM_UE) 1.4, one processing module PROC-UE, and one memory unit MEM-UE. The memory unit MEM-UE includes a non-volatile unit that searches for a computer program and a volatile unit that searches for a value to be used as a timing advance in the second cell, a value used as a timing advance in the first cell, a universal value, a handover mode, a satellite universal value, a network universal value, a base station universal value, an offset from the value used as a timing advance in the first cell, and an offset from the universal value. The processing module PROC-UE is configured to receive and decode data related to the timing advance of the user device in the second cell, determine the value to be used as a timing advance in the second cell, and perform uplink transmission with the second base station using the value to be used as a timing advance in the second cell.

[0168] The user equipment can be mobile user equipment or fixed user equipment.

[0169] FIG. 2 illustrates a satellite communication network identical to the satellite communication network illustrated in FIG. 1. User equipment UE6 (also referred to as other user equipment in this application) is added. UE6 is connected to BS3, for example, after performing a handover from BS2 to BS3 (i.e., a handover from C2 to C3). As described above, since UE6 is connected to BS3, BS3 determines the value of the timing advance of UE6 at C3, and the intermediate value and / or variation thereof starting from the moment UE6 accesses BS3. The value of the timing advance of UE6 at C3 can be determined by any method (a conventional method or a method according to the present invention).

[0170] UE2 needs to connect to BS2 and perform a handover from BS2 (the first base station) to BS3 (the second base station). BS3 can determine a value to be used as the timing advance for the user equipment at C3 based on one or some of the values ​​used for UE6 at C3.

[0171] For example, BS3 can determine that the value to be used as the timing advance of the user equipment in C3 is the same as the value used in UE6 of C3 (for example, the value used in UE6 from C3 during the handover from C2 to C3 of UE6).

[0172] In addition, BS3 can determine the value to be used as the timing advance of the user equipment (UE2) in C3 based on the value used for the various user equipment connected to BS3.

[0173] For example, BS3 may determine that the value to be used as the timing advance of user equipment (UE2) in C3 is equal to the average of the values ​​of multiple user equipment used in C3 (e.g., the value used in multiple user equipment in C3 during the handover from C2 to C3). For example, BS3 may determine that the value to be used as the timing advance of user equipment (UE2) in C3 is the value of a function of the variation of the timing advance of other user equipment (e.g., UE6) in C3, or the average of the values ​​of a function of multiple user equipment.

[0174] Additionally, the value of UE2 over a specific time period can be determined using a value that serves as the basis for determining the value to be used as the timing advance of the user equipment (UE2) in C3. To this end, a timestamp is associated with each value, and this timestamp corresponds to the moment when each of these values ​​was determined. Values ​​for which the timestamp indicates that the moment of determination is older than the time threshold cannot be used to determine the value to be used as the timing advance of the user equipment (UE2) in C3. In other words, only sufficiently new values ​​can be used for estimation.

[0175] FIG. 3 illustrates a satellite communication network identical to the satellite communication network illustrated in FIG. 1. User equipment UE6 (also referred to as other user equipment in this application) is added. UE6 connected to BS3, for example, after performing a handover from BS2 to BS3, while Sat1 and Sat2 had previously passed through (for example, when the satellite follows a fixed orbit). Since UE6 is connected to BS3, BS3 determines the value of the timing advance of UE6 that was in use when UE6 connected to BS3. The value of the timing advance of UE6 used when UE6 connected to BS3 can be determined by BS3 by any method (a conventional method or a method according to the present invention). When UE6 connected to BS3, the geographic communication range of C3 intersected with the geographic area GeoA. The value of the timing advance of UE6 (e.g., the value used from C3 to UE6 during the handover of UE6 from C2 to C3) is associated with the geographic area GeoA. UE2 needs to connect to BS2 and perform a handover from BS2 (the first base station) to BS3 (the second base station). When UE2 performs a handover from BS2 to BS3, BS3 can determine the value to be used as the timing advance of the user equipment at C3 based on the value used for UE6 at C3 if the geographic communication range of C3 intersects with GeoA around the geographic area. Additionally, this embodiment can be implemented in combination with a time stamp.

[0176] These embodiments (shown in FIG. 2 and FIG. 3) include a second base station (BS3) capable of determining a value to be used as a timing advance in a second cell for UE2. However, in these embodiments, BS2 may also determine a value to be used as a timing advance in a second cell for UE2. In this case, BS3 transmits necessary information, for example, a value used as a timing advance in C3 by user equipment connected to BS3, to BS2, and enables BS2 to calculate, for example, the average of the values ​​used as a timing advance in C3, and this average may be considered as a value to be used as a timing advance in C2 for UE2.

[0177] Figure 4 illustrates the same satellite communication network as the satellite communication network shown in Figure 1.

[0178] UE2 connects to BS2. During the connection with BS2, BS2 tracks the timing advance of UE2 and continuously updates the value to be used as the timing advance for UE2 at C2. In FIG. 4, TA1 to TA9 represent the timing advance values ​​measured by BS2 for UE2. In FIG. 4, these values ​​are represented as satellite frames. These values ​​of UE2's timing advance (TA1 to TA9) (i.e., a function of the change in the timing advance value in the first cell), measured at the respective C2 at the moment of measurement, enable BS2 (or, if this information is transmitted to BS3, BS3) to obtain some information regarding the position of UE2 and / or predict the change in UE2's timing advance value at a future moment.

[0179] This position can be calculated using an equivalent technique. For example, the average timing advance value received from C2 allows determining an axis parallel to the direction of movement of Sat1. Intersecting the axis where UE2 exists with two circles described by two different timing advance values ​​for UE2 measured at BS1 allows obtaining the position of UE2.

[0180] As another example, it is possible to more accurately estimate the position of UE2 based on the timing advance value received from C2 (TA-C2) at a given moment, for example, at t1 millisecond after the handover. Variations in the timing advance value received from C2 are combined with other measurements depending on the case, thereby obtaining information related to the position of UE2 and / or making it possible to predict changes in the timing advance value of UE2 at future moments in the same cell or the next cell.

[0181] For example, in the specific case where the center of the beam footprint used for communication with UE2 corresponds to the nadir of Sat1 (i.e., the center corresponds to a point on the ground directly below the satellite), the minimum value of abs(timing advance, TA_ref) indicates that UE2 has reached the point closest to the center of the beam (SB13.2) in orbit, where abs(.) represents the absolute value and TA_ref is the reference timing advance value, which may be beam-specific (commonly known to all users within the beam) and corresponds to the timing advance of the user at the center of the beam. In this case, there are two possible positions for UE2 (as shown in Fig. 5, reaching the same minimum value at both points H' and being symmetric with respect to the Sat1 Mouv axis). In this case, additional information may be needed to distinguish which of these two locations UE2 actually is, for example, by using the reference signal received power (RSRP) of UE2 measured by another satellite in the constellation, or by using historical statistical information regarding the orbit of UE2 received from another base station.

[0182] In some embodiments, TA_ref may be transmitted to all users within the beam, for example (e.g., via a SIB or via an RRC parameter having a value common to all users within the beam). In this case, while communicating with a base station through a given beam, only the difference value of the UE's unique timing advance is transmitted to each UE, and the UE can calculate the timing advance value by combining the reference beam's unique value TA_ref and the UE's unique value individually transmitted by the service base station.

[0183] To complete the determination of the value to be used as the timing advance for UE2 in C3, additional information related to the topology of the satellite constellation may be required. This information is, for example, the position of the Sat2 nadir relative to the Sat1 nadir and the elevations of Sat1 and Sat2. This additional information may be obtained by the ephemeris of the satellite constellation (or at least the ephemeris of Sat1 and Sat2) or a map of the beam footprint of the satellite network or any other traditional method used to determine the value to be used in the second cell if the location of the user equipment is known (e.g., using the same method used to determine the timing advance value if the user equipment determines its location via the Global Navigation Satellite System).

[0184] Additionally, this additional information may include information regarding the physical location of the base station (BS2 and / or BS3) and / or, if the base station is not mounted on this satellite, the offset of the timing advance caused by transmission between the base station (BS2 and / or BS3) and the satellite (Sat1 and / or Sat2). Thus, finally, the first base station (BS2) can adjust the determination of the value to be used as the timing advance at C3.

[0185] If transmitting information regarding this position to BS3 is necessary to enable BS3 to determine the value to be used as a timing advance in UE2's C3, or to enable BS2 to complete the determination of the timing advance value, BS3 may transmit additional information to BS2. The types and formats of transmittable information are indicated below.

[0186] Referring to FIG. 5, the determination of the value to be used as the timing advance of the user equipment in the second cell is illustrated in detail according to the method described in FIG. 4. FIG. 5 is a top view of the same satellite communication network as the satellite communication network illustrated in FIG. 4. For simplicity of explanation, in the example of FIG. 5, the centers of the beam (C-SB13.2 and C-SB22.3) coincide with the nadir points of Sat1 and Sat2, respectively.

[0187] vector The position of C-SB22.3 relative to C-SB13.2, denoted by , and angle φ, can be determined from the constellation topology.

[0188] BS2 measures the timing advance of UE2 used in C2. UE2 is centered at the beam center (C-SB13.2) and has a radius It can be placed at any point on the circle (corresponding to the TA-C2 value of UE2). When connecting to BS3 at point H, UE2 is You must use the TA-C3 value corresponding to it.

[0189] To calculate, you must know the angle θ. The satellite's direction When moving to , SB2 estimates the TA-C2 value. The minimum absolute value of TA-C2 is observed when UE2 is closest to C-SB13.2, i.e., when UE2 is at position H', and the TA-C2 value corresponds to d. d and Based on this, θ can be calculated as shown in the following equation.

[0190]

[0191] thus, It can be calculated as follows.

[0192]

[0193] A UE that obtains its position via a global navigation satellite system may be unable to calculate its own timing advance due to limitations in computational power or a lack of knowledge regarding the network topology; therefore, it still requires auxiliary information from the network to accurately determine the timing advance value of the target cell. In this case, the method obtained by the present invention is still applied with a supplementary step in which the UE reports its position information to the network (e.g., to the source base station before and / or during handover, and to the target base station during and / or after handover). In this case, the network receives the position information from the UE and compares it with the timing advance value without needing to perform all the calculations described above. Thus, the determination of the timing advance by the network entity is simplified.

[0194] Referring to FIG. 6, a flowchart illustrating the steps implemented for a user device according to the present invention to perform a handover is shown.

[0195] In step S11, user equipment (e.g., UE2) is configured.

[0196] Although the steps of the method implemented by the user equipment are described in a general context and exemplified in the context of UE2, those skilled in the art will have no trouble modifying specific examples in the context of the other user equipment (UE1 to UE5) described above based on the description above.

[0197] Configuration of user equipment UE2 can be performed when connecting to a base station of a satellite network (when the user equipment first connects to the base station of the network, or whenever the user equipment performs an initial connection to the network, or during the user equipment's connection to the network), or while connected to the base station (e.g., via configuration and / or reconfiguration messages), or can be performed by factory default settings.

[0198] The configuration of UE2 may include setting a handover mode to be implemented while UE2 is connected to a satellite network or until the current configuration is changed by the network. For example, the mode may be Standard Mode (StaM) and performs a handover as described in the NR standard. The mode may be Simple Mode (SimM) and performs a handover as described in the NR standard only when the value to be used as the timing advance in the second cell is different from the value used as the timing advance in the first cell. The mode may be Full Mode (FulM) and performs only the handover according to the present invention.

[0199] Additionally, the configuration can set some parameters necessary for user equipment UE2 to acquire values ​​to be used as a timing advance in the second cell C3. For example, as follows.

[0200] - The network universal value, that is, the network timing advance, is expressed as the sum of the network universal value and the offset value.

[0201] - The satellite universal value, that is, the timing advance associated with the base station supported by the satellite, is expressed as the sum of the satellite's unique satellite universal value and the offset value.

[0202] - The base station universal value, that is, the timing advance associated with the base station, is expressed as the sum of the base station universal value unique to that base station and the offset value.

[0203] - The beam universal value, that is, the timing advance associated with the base station transmitting through the beam, is expressed as the sum of the beam's inherent beam universal value and the offset value.

[0204] In step S12, user equipment UE2 receives data related to the timing advance of the user equipment in the second cell. This data may be transmitted to UE2 by the first base station BS2 or by the base station to which the user equipment was connected before connecting to BS2, e.g., BS1. To receive this data, the handover mode is set to either SimM mode or FulM mode.

[0205] In SimM mode, the data related to the timing advance of the user equipment of the second cell is one of the following.

[0206] - Data notifying the user equipment that the value to be used as the timing advance for UE2 in C3 (referred to as TA-C3 to be used) is different from TA-C2 (e.g., setting the binary value to 1), or,

[0207] - Data notifying the user equipment that the TA-C3 to be used is identical to TA-C2 (e.g., setting the binary value to 0).

[0208] By configuring UE2 and the network, the transmission of any of these data to UE2 can be avoided. For example, the network and UE2 are configured as follows.

[0209] Data notifying user equipment UE2 that TA-C3 to be used is different from TA-C2 is still transmitted to UE2, and the next handover is performed based on this information.

[0210] - When performing a handover from C2 to C3, data notifying the user equipment that the TA-C3 to be used is the same as TA-C2 is not transmitted to UE2, and UE2 (set to SimM mode) assumes that the TA-C3 to be used is the same as TA-C2, and therefore performs the handover as if receiving this information.

[0211] The opposite is also possible, that is, data notifying the user device that the TA-C3 to be used is different from TA-C2 is not transmitted to UE2, and data notifying the user device that the TA-C3 to be used is the same as TA-C2 is transmitted to UE2.

[0212] Depending on the ratio of cells supported per satellite, one option or the other may be more advantageous regarding signaling.

[0213] In Full mode, the data related to the timing advance of the user equipment in the second cell is one of the following.

[0214] - Data notifying the user equipment that the TA-C3 to be used is identical to TA-C2,

[0215] - Data regarding TA-C3 to be used.

[0216] As in SimM mode, when UE2 and the network are configured in this way, data notifying the user equipment that the TA-C3 to be used is the same as TA-C2 cannot be transmitted to UE2. In this case, when performing the next handover, if the data related to the TA-C3 to be used is not received by UE2, UE2 (set to FullM mode) considers the TA-C3 to be the same as TA-C2 and performs the handover as if it had received this information.

[0217] Data regarding TA-C3 to be used may include the following.

[0218] - Data corresponding to the TA-C3 to be used, for example, UE2 may receive TA-C3 or any encoded version representing TA-C3,

[0219] - Data corresponding to the offset from TA-C2,

[0220] - Data corresponding to the offset from the general-purpose value (network general-purpose value, satellite general-purpose value, base station general-purpose value, beam general-purpose value).

[0221] In step S13, user equipment UE2 determines the TA-C3 to be used.

[0222] When UE2 receives data related to TA-C3, UE2 determines TA-C3 based on this data and the data stored during configuration or TA-C2. For example, UE2 obtains TA-C3 by summing the offset with a universal value. For example, UE2 decodes the data corresponding to TA-C3.

[0223] When UE2 receives data notifying that TA-C3 to be used is identical to TA-C2, UE2 can set TA-C3 to be identical to TA-C2. For example, the last TA-C2 is used by the UE2 of C2. If TA-C2 and / or TA-C3 consist of user-specific values ​​and universal values, the distribution between user-specific values ​​and universal values ​​may change during handover even if TA-C3 is identical to TA-C2.

[0224] When UE2 receives data notifying that TA-C3 to be used is different from TA-C2, UE2 can prepare to perform a standard handover without setting the value of TA-C3.

[0225] As described above, if UE2 does not receive any data related to TA-C3, it can set TA-C3 to be the same as TA-C2, and if the network and UE2 are configured such that data related to TA-C3 is not transmitted to UE2, UE2 assumes that the TA-C3 to be used is the same as TA-C2.

[0226] In step S14, UE2 performs a handover from C2 to C3.

[0227] If TA-C3 is not determined in step S13, UE2 performs a standard handover.

[0228] If UE2 determines TA-C3 in step S13, UE2 can perform uplink transmission with BS3 using TA-C3. That is, UE2 applies a time offset based on TA-C3 to compensate for the time required to propagate the signal.

[0229] This uplink transmission may be an uplink transmission as part of the RACH procedure.

[0230] For example, this uplink transmission may be a first uplink transmission performed by BS3 during a random access (RACH) procedure. For example, the first message of the RACH procedure is transmitted by UE2 to connect to BS3 using the TA-C3 offset.

[0231] For example, this uplink transmission may be a second uplink transmission performed by BS3 during RACH. For example, in an NR situation, the third message of the RACH procedure is transmitted by UE2 to connect to BS3 using the TA-C3 offset. Thus, the first message of the RACH procedure is transmitted according to the standard procedure, and BS3 can estimate TA-C3 without receiving the corresponding signaling data.

[0232] Since this uplink transmission may be an uplink transmission after a RACH-less handover procedure, it may represent a first standard uplink transmission, a second standard uplink transmission, or a future standard uplink transmission to BS3 prior to BS3 updating the value of the timing advance (e.g., through timing advance adjustment in connection mode so that BS3 transmits a MAC CE timing advance command to UE3 in the current NR procedure).

[0233] In this case, UE2 will not receive any TA-C3 from BS3 until a connection is established. Once a connection to BS3 is established, BS3 can continuously update TA-C3 until UE2 leaves C3.

[0234] Referring to FIG. 7, a flowchart illustrating the steps of a satellite network according to the present invention for managing handover is shown.

[0235] In step S21, a satellite network is configured.

[0236] The configuration of a satellite communication network includes setting a handover mode that the network can implement and configuring a method for determining a value to be used as a timing advance for user equipment in a second cell. Based on this method, the data required to determine this value is stored in various network entities.

[0237] Therefore, at least some of the following information is stored in each base station of a satellite communication network (more generally, any other network entity excluding user equipment).

[0238] - Ecliptic of satellite constellations, and / or,

[0239] - Beam topology, i.e., the distribution of the beam's footprint on the surface, and / or,

[0240] - Mapping between base stations and the satellites on which they are mounted, and / or

[0241] - Mapping between ground base stations and the gateways they link to the satellite, and / or

[0242] - The physical location of the gateway to which the base station links to the satellite, and / or

[0243] - The physical location of base stations relative to each other (whether they are in the same location).

[0244] According to the method configured to determine the value to be used as the timing advance of the user equipment in the second cell, the related network entity stores the following related data to determine this value.

[0245] - Value used as a timing advance in the second cell of another user's equipment,

[0246] - Timestamp associated with this value,

[0247] - Information regarding geographical areas,

[0248] - A function of the change in the timing advance value of the user equipment in the cell,

[0249] - Mapping between the function of the change in the timing advance value of the user equipment in the first cell and the position of the user equipment,

[0250] - Mapping between the minimum timing advance value of the user equipment in the first cell and / or the second cell and the position and / or RSRP and / or Doppler measurements of the user equipment,

[0251] - Mapping between the timing advance value received from the first cell at a given moment and the user equipment position and / or RSRP and / or Doppler measurements,

[0252] - Mapping between a function of the change in the timing advance value of the user equipment in the first cell and a function of the change in the timing advance value of the user equipment in the second cell,

[0253] - Ecological edicts of satellite constellations,

[0254] - Information regarding the beam footprint of a satellite network (e.g., a map of the satellite network's beam footprint), etc.

[0255] In step S22, the network entity determines whether the value to be used as the timing advance of the user equipment in the second cell (i.e., TA-C3 to be used for UE2 in the context of UE2) is the same as the value used as the timing of the user equipment in the first cell (i.e., TA-C2).

[0256] Although the steps of the method performed on the network side (all network entities excluding user equipment) are described in a general context and exemplified in the context of UE2, those skilled in the art will have no trouble adapting this example to the context of the other user equipment (UE1 to UE5) described above based on the above description.

[0257] The network entity determines whether the first cell and the second cell are supported by the same satellite and whether the first base station and the second base station are in the same location. The network entity determines this based on the configuration and information stored in step S21. This information may not be directly accessible to the network entity, and it may be necessary to receive part of the information from another network entity, for example, through an operation and maintenance configuration (O&M) and / or through an exchange between base stations (Xn links).

[0258] In the case of UE2, UE2 will need to connect to BS2 and perform a handover from BS2 to BS3. The network entity determines that BS3 and BS2 are not located in the same location and that C3 and C2 are supported by different satellites (Sat2 and Sat1, respectively), and therefore, TA-C3, which is to be used as already described in FIG. 1, is different from TA-C2.

[0259] The network entity can be BS2 or BS3.

[0260] Another case is explained in Fig. 1.

[0261] In step S22, if the network entity determines that the value to be used as the timing advance for user equipment UE2 in the second cell C3 (i.e., TA-C3 to be used for UE2) is different from the value used as the timing advance for user equipment UE2 in the first cell C2 (i.e., TA-C2), then in step S23, the network entity determines the value to be used as the timing advance for user equipment UE2 in the second cell C3.

[0262] To determine the value to be used as the timing advance for user equipment UE2 in the second cell C3, the network entity may implement one or more of the methods described in FIGS. 2, 3, and 4. These methods can be combined to more accurately determine the value to be used as the timing advance for user equipment UE2 in the second cell C3 (TA-C3 to be used).

[0263] The method described in FIGS. 2 and 3 explains determining a value from learning by a second base station (BS3 in the context of UE2) of the timing advance value of another user device. The network entity implementing the determination of the TA-C3 to be used may be BS2 or BS3 (or any network entity excluding the user device). However, if BS2 is the network entity determining the TA-C3 to be used for UE2, BS3 may transmit a learned value (or any corresponding information) to BS2 based on its ability to determine the TA-C3. This transmission may be performed via an exchange between base stations (Xn link).

[0264] The method described in FIG. 4 describes determining a value from a calculation based on user equipment-specific parameters related to the location of the user equipment acquired by the first base station (BS2 in the context of UE2). The network entity implementing the determination of the TA-C3 to be used may be BS2 or BS3 (any network entity excluding the user equipment). However, if BS3 is the network entity determining the TA-C3 to be used for UE2, BS2 may transmit the location of the user equipment UE2 (or any corresponding information) based on the ability of BS3 to determine the TA-C3. Meanwhile, if BS2 is the network entity determining the TA-C3 to be used for UE2, BS3 may transmit additional information of the user equipment UE2 (or any corresponding information) based on the ability of BS2 to determine the TA-C3 (as described above). In both cases, these transmissions may be performed through exchanges between these base stations (Xn links).

[0265] In step S24, the network entity that has determined the value to be used in the second cell for the user equipment transmits, if necessary, data related to the timing advance of the user equipment in the second cell to the second base station connected to the user equipment, and finally to the user equipment (particularly, if the user equipment cannot independently determine the value to be used in the second cell).

[0266] Accordingly, when the network entity that determined the value is the second base station (BS3 in the case of UE2), when the TA-C3 to be used is different from TA-C2, and when the handover mode is FulM, the second base station (BS3) transmits data related to the timing advance of the user equipment in the second cell to the first base station (BS2), thereby enabling the first base station to transmit data related to the timing advance of the user equipment in the second cell to the user equipment (UE2).

[0267] Data related to the timing advance of user equipment in the second cell transmitted by the first base station may include the following.

[0268] - Data corresponding to the TA-C3 to be used, for example, BS2 may transmit TA-C3 or any encoded version representing TA-C3,

[0269] - Data corresponding to the offset from TA-C2,

[0270] - Data corresponding to the offset from the general value.

[0271] The user equipment determines the timing advance value (TA-C3) to be used in the second cell based on data regarding the timing advance received from the first base station.

[0272] When the TA-C3 to be used is different from TA-C2 and the handover mode is SimM, the second base station (BS3) transmits data related to the timing advance of the user equipment in the second cell to the first base station (BS2), so that the first base station can transmit data related to the timing advance of the user equipment in the second cell to the user equipment (UE2). In this case, the data related to the timing advance of the user equipment may be data notifying the user equipment that an update of the timing advance value is required. Since the handover mode is SimM, the user equipment UE2 performs a standard handover between BS2 and BS3, and during this time, UE2 acquires the TA-C3 to be used.

[0273] When the value to be used as the timing advance of the user equipment in the second cell is the same as the value used as the timing advance of the user equipment in the first cell (in the case of UE1), and when the handover mode is FulM or SimM, the second base station (BS2 in the case of UE1) can transmit data related to the timing advance of the user equipment in the second cell to the first base station (BS1 in the case of UE1).

[0274] Depending on the configuration, the first base station may or may not transmit data related to the timing advance of the user equipment in the second cell to the user equipment. However, in either case, the user equipment sets a timing advance value to be used in the second cell C2 as, for example, the final timing advance value used in the first cell C1, based on the data related to the timing advance in the second cell received from the first base station or based on the fact that the user equipment does not receive any data related to the timing advance in the second cell.

[0275] As described above, data related to the timing advance of the user equipment in the second cell transmitted from the first base station to the user equipment (whereby the user equipment can determine the value to be used in the second cell based on this data) may be different from or may not be different from data related to the timing advance of the user equipment in the second cell transmitted from the second base station to the first base station (whereby the first base station can generate data related to the timing advance of the user equipment in the second cell transmitted to the user equipment based on this data).

[0276] If the network entity that determined the value is the first base station (BS2 in the case of UE2), if the TA-C3 to be used is different from TA-C2, and if the handover mode is FulM, the first base station (BS2) can directly transmit data related to the timing advance of the user equipment in the second cell to the user equipment (UE2). Additionally, the first base station (BS2) can directly transmit data related to the timing advance of the user equipment in the second cell to the user equipment (UE2).

[0277] Data related to the timing advance of user equipment in the second cell transmitted by the first base station may include the following.

[0278] - Data corresponding to the TA-C3 to be used, for example, BS2 may transmit TA-C3 or any encoded version representing TA-C3,

[0279] - Data corresponding to the offset from TA-C2,

[0280] - Data corresponding to the offset from the general value.

[0281] The user equipment determines the timing advance value (TA-C3) to be used in the second cell based on data regarding the timing advance received from the first base station.

[0282] The second base station determines the timing advance value (TA-C3) to be used in the second cell based on data regarding the timing advance received from the first base station.

[0283] If the TA-C3 to be used is different from TA-C2 and the handover mode is SimM, the first base station (BS2) may directly transmit data related to the timing advance of the user equipment in the second cell to the user equipment (UE2). In this case, the data related to the timing advance of the user equipment may be data notifying the user equipment that an update to the timing advance value is required. Since the handover mode is SimM, the user equipment UE2 performs a standard handover between BS2 and BS3, and during this time, UE2 acquires the TA-C3 to be used.

[0284] Additionally, the first base station (BS2) may transmit data related to the timing advance of user equipment in the second cell to the second base station (BS3). Based on the data regarding the timing advance received from the first base station, the second base station determines that the timing advance value will be updated by performing a standard handover to acquire the TA-C3 to be used by UE2.

[0285] If the value to be used as the timing advance of the user equipment in the second cell is the same as the value used as the timing advance of the user equipment in the first cell (in the case of UE1), and if the handover mode is FulM or SimM, the first base station (BS1 in the case of UE1) may or may not transmit data related to the timing advance of the user equipment in the second cell to the user equipment depending on the configuration. However, in both cases, the user equipment sets the timing advance value to be used in the second cell C2 as, for example, the final timing advance value used in the first cell C1, based on the data related to the timing advance in the second cell received from the first base station BS1 or based on the fact that user equipment UE1 has not received any data related to the timing advance in the second cell.

[0286] In addition, the first base station BS1 can transmit data related to the timing advance of user equipment in the second cell to the second base station (BS2 in the case of UE1).

[0287] The second base station determines a value to be used as the timing advance of the user equipment in the second cell based on data regarding the timing advance received from the first base station.

[0288] As described above, data related to the timing advance of the user equipment in the second cell transmitted from the first base station to the user equipment (whereby the user equipment can determine the value to be used in the second cell based on this data) may be different from or may not be different from the data related to the timing advance of the user equipment in the second cell transmitted from the first base station to the second base station (whereby the second base station can determine the value to be used in the second cell based on this data).

[0289] In step S25, the first base station and the second base station perform a handover of user equipment from the first base station to the second base station.

[0290] When the mode is SimM, if the value TA-C3, which is to be used for the timing advance of the user equipment UE2 in the second cell, cannot be determined, the handover performed from the first base station to the second base station is a standard handover.

[0291] The mode,

[0292] - FulM, or,

[0293] - In the case of SimM and when data related to the timing advance of the user equipment in the second cell is not transmitted to UE1, or when the transmitted data related to the timing advance is data notifying the user equipment that the value to be used as the timing advance of the user equipment in the second cell is the same as the value used as the timing advance of the user equipment in the first cell, a handover from the first base station to the second base station according to the present invention is performed, that is, a handover in which the second base station does not transmit to the user equipment the value to be used as the timing advance value of the user equipment in the second cell. For example, in the case of NR, the second message of the RACH procedure transmitted by this base station to connect to the second base station does not include the timing advance value. Once a connection to the second base station is established, the second base station can continuously update the timing advance value until the user equipment leaves the second cell.

[0294] Additionally, the second base station can schedule uplink resources for user equipment using the determined timing advance value. For example, in an NR situation, the second message of the RACH procedure transmitted by the second base station schedules uplink resources for user equipment so that the user equipment can transmit the third message of the RACH procedure. This is possible even if the second base station receives the first message of the RACH procedure from user equipment that may have already been corrected based on the timing advance value (since the second base station knows the timing advance value to be used), and therefore, timing advance estimation is not performed based on this first message of the RACH procedure.

Claims

Claim 1 A method implemented by user equipment to perform a handover between a first cell and a second cell within a network including a satellite communication network, wherein the first cell and the second cell are supported by one or more non-geostationary satellites of the satellite communication network, the first cell corresponds to a first base station and the second cell corresponds to a second base station, and the first base station or the second base station performs transmission and reception with the user equipment through the first cell or the second cell, but performs transmission and reception using a radio signal via the one or more non-geostationary satellites, and the method comprises determining a value to be used as a timing advance in the second cell before the user equipment transmits a first signal corresponding to an uplink transmission after a RACH-less handover procedure to the second base station, wherein the value to be used as a timing advance in the second cell is - received from the first base station or from the base station to which the user equipment is connected before being connected to the first base station, A method comprising—where data related to the timing advance of the user equipment in the second cell, or—data related to the timing advance of the user equipment in the second cell is not received from the first base station or from the base station to which the user equipment is connected before being connected to the first base station, determining based on the value used as the timing advance in the first cell, and performing an uplink transmission with the second base station using the value to be used as the timing advance in the second cell, which is determined by the user equipment before the user equipment transmits the first signal to the second base station. Claim 2 A method according to claim 1, wherein the data related to the timing advance of the user equipment in the second cell comprises: - data related to a value to be used as the timing advance of the user equipment in the second cell; - data notifying the user equipment that the value to be used as the timing advance of the user equipment in the second cell is different from the value used as the timing advance of the user equipment in the first cell; and - data notifying the user equipment that the value to be used as the timing advance of the user equipment in the second cell is the same as the value used as the timing advance of the user equipment in the first cell. Claim 3 In claim 2, the data related to the value to be used as a timing advance of the user equipment in the second cell comprises: - data corresponding to the value; - data corresponding to an offset from the value used as a timing advance of the user equipment in the first cell; and - at least one of the data corresponding to an offset from a universal value. Claim 4 A method according to any one of claims 1 to 3, wherein the uplink transmission performed with the second base station is a first uplink transmission performed with the second base station. Claim 5 User equipment configured to perform a handover procedure between a first cell and a second cell within a network including a satellite communication network, wherein the first cell and the second cell are supported by one or more non-geostationary satellites of the satellite communication network, the first cell corresponds to a first base station, and the second cell corresponds to a second base station, and the first base station or the second base station performs transmission and reception with the user equipment through the first cell or the second cell, but performs transmission and reception using radio signals via the one or more non-geostationary satellites, and the user equipment includes a processor and a non-transient computer-readable medium storing instructions, wherein when the instructions are executed by the processor, the user equipment determines a value to be used as a timing advance in the second cell before the user equipment transmits a first signal corresponding to an uplink transmission after a RACH-less handover procedure to the second base station, and the value to be used as a timing advance in the second cell A user device configured to determine a value based on a value used as a timing advance in the first cell, wherein the value is determined by the user device before transmitting the first signal to the second base station, using the value to be used as a timing advance in the second cell, which is determined by the user device before the user device transmits the first signal to the second base station. Claim 6 A method performed by a second base station to manage a handover of user equipment between a first cell and a second cell within a network including a satellite communication network, wherein the first cell and the second cell are supported by one or more non-geostationary satellites of the satellite communication network, the first cell corresponds to a first base station and the second cell corresponds to a second base station, and the first base station or the second base station performs transmission and reception with the user equipment through the first cell or the second cell, but performs said transmission and reception using wireless communication via the one or more non-geostationary satellites, and the method comprises determining a value to be used as a timing advance of the user equipment in the second cell before the second base station receives any signal corresponding to an uplink transmission after a RACH-less handover procedure from the user equipment, and transmitting data regarding said determined value to the user equipment through another base station, and before the second base station receives any signal from the user equipment, the A method comprising transmitting data to the user equipment, thereby enabling the user equipment to perform uplink transmission between the user equipment and the second base station using the value to be used as a timing advance of the user equipment in the second cell, wherein, if the first cell and the second cell are supported by the same satellite and the first base station and the second base station are co-localized, the determined value is the same as the value used as a timing advance of the user equipment in the first cell. Claim 7 delete Claim 8 In claim 6, the value to be used as a timing advance of the user equipment in the second cell is determined based on at least one value that is used as a timing advance of another user equipment in the second cell or was previously used. Claim 9 In claim 8, the at least one value used or previously used as a timing advance of the other user equipment in the second cell is a method used or previously used as a timing advance of the other user equipment in the second cell for - a first uplink transmission of the other user equipment after being connected to the second cell, or - an uplink transmission between the other user equipment and the second base station before being connected to the second cell. Claim 10 A method according to claim 8, wherein the at least one value is associated with a time stamp, the time stamp corresponds to the moment of determination of the at least one value, and the duration between the moment of determination of the at least one value and the determination of the value to be used as a timing advance of the user equipment in the second cell is less than a predetermined threshold. Claim 11 In claim 8, the method wherein at least one value is associated with a geographical area, and at the moment of determination of the at least one value, the geographical area intersects with the geographical communication range of the second cell, and when performing uplink transmission between the second base station and the user equipment, the geographical area intersects with the geographical communication range of the second cell. Claim 12 In claim 6, the value to be used as a timing advance of the user equipment in the second cell is determined by the second base station. Claim 13 In claim 12, the method further comprises transmitting data related to the timing advance of the user equipment in the second cell to the first base station or to the base station to which the user equipment is connected or will be connected in the future prior to being connected to the first base station, wherein the data related to the timing advance of the user equipment in the second cell corresponds to the value to be used as the timing advance of the user equipment in the second cell determined by the second base station. Claim 14 In claim 6, the value to be used as the timing advance of the user equipment in the second cell is determined based on at least one value to be used as the timing advance of the user equipment in the first cell. Claim 15 In claim 14, the method wherein the value to be used as a timing advance of the user equipment in the second cell is determined based on at least one of the following: - a minimum value used as a timing advance of the user equipment in the first cell; - a center position of the second beam footprint relative to the center position of the first beam footprint, wherein the first beam is used by the first base station to communicate with the user equipment, and the second beam is used by the second base station to perform the uplink transmission between the second base station and the user equipment; - a location of the geographic communication range of the first cell; - a location of the geographic communication range of the second cell; - a change in the value used as a timing advance of the user equipment in the first cell; - A value used as a timing advance of the user equipment in the first cell, determined at a given time after the user equipment performs a handover to connect to the first base station or at a given time before the user equipment performs a handover to connect to the second base station; and - the direction of movement of the satellite. Claim 16 In claim 14, the value to be used as a timing advance of the user equipment in the second cell is determined by the first base station based on information provided by the second base station. Claim 17 A method according to claim 6 further comprising transmitting to the user equipment data related to the timing advance of the user equipment in the second cell, corresponding to the determined value, from the first base station or from a base station connected before the user equipment is connected to the first base station. Claim 18 A second base station configured to manage the handover of user equipment between a first cell and a second cell in a network including a satellite communication network, wherein the first cell and the second cell are supported by one or more non-geostationary satellites of the satellite communication network, wherein the first cell corresponds to a first base station and the second cell corresponds to the second base station, and wherein the first base station or the second base station performs transmission and reception with the user equipment through the first cell or the second cell, and performs transmission and reception using radio signals via the one or more non-geostationary satellites, and wherein the second base station comprises a processor and a non-transient computer-readable medium storing instructions, and wherein, when the instructions are executed by the processor, the second base station determines a value to be used as a timing advance of the user equipment in the second cell before the second base station receives a signal corresponding to an uplink transmission after a RACH-less handover procedure from the user equipment, and the determined Data regarding a value is transmitted to the user equipment through another base station, and the user equipment is configured to perform uplink transmission between the user equipment and the second base station by transmitting the data to the user equipment before the second base station receives any signal from the user equipment, using the value to be used as a timing advance of the user equipment in the second cell, and the second base station, wherein, when the first cell and the second cell are supported by the same satellite and the first base station and the second base station are co-localized, the determined value is the same as the value used as a timing advance of the user equipment in the first cell. Claim 19 A method performed by a first base station to manage a handover of user equipment between a first cell and a second cell in a network including a satellite communication network, wherein the first cell and the second cell are supported by one or more non-geostationary satellites of the satellite communication network, wherein the first cell corresponds to a first base station and the second cell corresponds to a second base station, and the first base station or the second base station performs transmission and reception with the user equipment through the first cell or the second cell, wherein the transmission and reception are performed using radio signals via the one or more non-geostationary satellites, and the method comprises determining a value to be used as a timing advance of the user equipment in the second cell; transmitting said value to be used as a timing advance of the user equipment in the second cell to the user equipment before the second base station receives any signal corresponding to an uplink transmission after a RACH-less handover procedure from the user equipment; and the second base station receiving any A method comprising transmitting to the second base station, by the first base station, the value to be used as a timing advance of the user equipment in the second cell, before receiving a signal. Claim 20 A first base station configured to manage the handover of user equipment between a first cell and a second cell within a network including a satellite communication network, wherein the first cell and the second cell are supported by one or more non-geostationary satellites of the satellite communication network, wherein the first cell corresponds to the first base station and the second cell corresponds to the second base station, wherein the first base station or the second base station performs transmission and reception with the user equipment through the first cell or the second cell, but performs said transmission and reception using radio signals via the one or more non-geostationary satellites, wherein the first base station comprises a processor and a non-transient computer-readable medium storing instructions, wherein when the instructions are executed by the processor, the first base station determines a value to be used as a timing advance of the user equipment in the second cell, and before the second base station receives any signal corresponding to an uplink transmission after a RACH-less handover procedure from the user equipment, the A first base station that transmits the value to be used as a timing advance of the user equipment in the second cell to the user equipment, and, before the second base station receives any signal from the user equipment, transmits the value to be used as a timing advance of the user equipment in the second cell to the second base station by the first base station. Claim 21 A non-transient computer-readable medium storing instructions, wherein the instructions, when executed by a processor, perform the method described in any one of claims 1 to 3, claim 6 and claim 19.

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