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

Abstract

The present invention relates to a method implemented by a user equipment for performing a handover between a first cell and a second cell in a network comprising a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to a first base station and the second cell corresponding to a second base station, at least the first cell being supported by a non-geostationary satellite of the satellite communication network, the method comprising the following steps: determining a value to be used as a timing advance in the second cell, the value to be used as the timing advance in the second cell being determined based on: - data related to the timing advance of the user equipment in the second cell received from the first base station or from a base station to which the user equipment was connected before being connected to the first base station, or - when no data related to the timing advance of the user equipment in the second cell is received from the first base station or from a base station to which the user equipment was connected before being connected to the first base station, the value to be used as the timing advance in the first cell; performing an uplink transmission with the second base station using the value to be used as the timing advance in the second cell.

Description

Technical Field

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

[0002] In satellite communication networks with non-geostationary satellites, the satellites are constantly moving. User equipment (UE) in such communication networks often performs handovers to stay connected to the network via the next satellite beam covering its geographical area. These handovers require a lot of signaling that consumes radio resources.

[0003] Since satellite beams often cover large geographical areas and the relative ground speed of these satellites is very important, the amount of signaling increases. In fact, in this case, the number of UEs covered by one beam can be very important, and the time each of these UEs is under the coverage of the same satellite beam is very short, so a large number of UEs may perform handovers in a very short time.

[0004] Another problem is related to the fact that in these satellite communication networks, there is a long round trip time (RTT) between the UE and the base station. Therefore, since during handover, the target cell (target base station) pre-allocates radio resources to the UE so that the UE can access the target cell faster than the initial access, this long RTT requires the target cell to pre-allocate more radio resources to the UE for handover (HO) to avoid interference. In addition, the long round trip time (RTT) also increases the signaling required during handover. Summary of the invention

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

[0006] To this end, the present invention relates to a method implemented by a user equipment for performing a handover between a first cell and a second cell in a network comprising a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to a first base station and the second cell corresponding to a second base station, at least the first cell being supported by a non-geostationary satellite of the satellite communication network, the method comprising the following steps:

[0007] determining a 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 being determined based on:

[0008] - data relating to the timing advance of the user equipment in the second cell received from the first base station or from a base station to which the user equipment was connected before connecting to the first base station, or

[0009] - when no data related to the timing advance of the user equipment in the second cell is received from the first base station or from the base station to which the user equipment was connected before connecting to the first base station, use as the value of the timing advance in the first cell; use the value to be used as the timing advance in the second cell to perform uplink transmission with the second base station.

[0010] Thus, 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 is connected after the handover), it is no longer necessary for the user equipment to receive the timing advance from the second base station (which typically estimates the timing advance and sends it to the UE during the handover). Thus, less signaling and less calculations are required during the handover. In addition, such a procedure does not require the user equipment to be able to locate itself (e.g., using a global navigation satellite system) or to have significant computing power.

[0011] The user equipment can perform a handover that requires less calculations and at least less signaling than a classic handover procedure. In practice, during a classic handover procedure, the second base station (second cell or target cell) estimates a value to be used as a timing advance (TA) for the user equipment in the second cell based on a signal sent by the user equipment to the second base station. For example, in wireless communication standards such as LTE, Advanced LTE or New Radio, the estimation of TA is performed based on the first message of a RACH procedure (Msg1 of the RACH procedure) received by the base station from the user equipment. Later in the same RACH procedure, the value of TA estimated by the base station is sent (Msg2 of the RACH procedure) to the UE, which the UE uses to introduce a delay when transmitting a signal through the second cell.

[0012] Thus, the present invention allows to reduce calculations and signaling during handover, for example in the context of most wireless standards (e.g. LTE, LTE-Advanced or New Radio) may allow to remove one message during the handover process (e.g. RACH preamble or second message (Msg2) sent by the second base station during the RACH process, and / or in some cases skip the RACH process altogether). Removing these messages allows to reduce handover delays. In addition, removing these messages (or at least applying a timing advance offset while sending these messages) also allows to release a large amount of radio resources, because during the handover process when the user equipment (and eventually the second base station) has not yet implemented a time offset based on the timing advance value (to compensate for the time required for signal propagation) the exchange performed between the second base station and the user equipment requires the second base station to reserve many more radio resources than the classic exchange. In fact, the second base station cannot (or only poorly) predict the reception time of these exchanges, so in order to avoid interference with other transmissions (and therefore reduce the number of unsuccessful access processes), the second base station must reserve important radio resources to take into account the possible delays caused by signal propagation. Therefore, the user equipment determines the value to be used as the timing advance in the second cell before performing the handover procedure and while the user equipment is connected to a base station (i.e., the first base station or a base station to which the user equipment was connected before connecting to the first base station) consumes less radio resources.

[0013] The uplink transmission performed with the second base station using the value to be used as the 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 the handover procedure (e.g., the first uplink transmission performed after the handover) or even the first uplink transmission performed with the second base station when, for example, a RACH procedure is not required during handover.

[0014] The method may therefore further comprise performing a handover procedure. Such a handover may be performed without sending data related to a value to be used as a timing advance of the user equipment in the second cell by the second cell (the 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 framework of the handover procedure, for example after or before the handover procedure.

[0015] That is, the user equipment can connect to the second cell without receiving data related to a value to be used as the timing advance of the user equipment in the second cell through the second cell.

[0016] During the access procedure of the user equipment to the second base station, the second base station no longer needs to measure a value to be used as the timing advance of the user equipment in the second cell.

[0017] However, the user equipment may still receive data related to the value to be used as the timing advance for the user equipment in the second cell while performing the handover using the value to be used as the timing advance in the second cell. For example, the second base station may send data related to the value to be used as the timing advance for the user equipment in the second cell to make a small correction to the timing advance value used to perform uplink transmissions. However, in this case, the present invention allows a reduction in the radio resources required during the handover process (as described above) because the offset between the ideal value to be used and the determined value to be used is smaller.

[0018] A timing advance value or a value to be used or used as timing advance is understood to be a value corresponding to the amount of time it takes for a signal to reach a base station from a user equipment.

[0019] Determining a value is understood as a value that the user equipment determines the user equipment will be able to use to at least configure uplink communications with the second base station.The output of this determination is thus a value to be used as the timing advance in the second cell.

[0020] The determination may be based on data relating to the timing advance of the user equipment in the second cell received from the first base station or from a base station to which the user equipment was connected prior to connecting to the first base station.

[0021] The data is received from a base station to which the user equipment was connected before connecting to the second base station. Thus, the data is received before any uplink communication is performed between the user equipment and the second base station.

[0022] The determination may also be based on the value used as the timing advance in the first cell when no data related to the timing advance of the user equipment in the second cell is received from the first base station or from a base station to which the user equipment was connected before connecting to the first base station. Thus, 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 the value 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 used as the timing advance in the first cell.

[0023] The determination may also be based on a function of a change in the timing advance of the user equipment in the second cell. Thus, the user equipment receives data representing a change 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, such as an index in a set of indices representing different functions of a change in the timing advance of the user equipment in the second cell, or a value of a parameter to be set in a general function representing a change in the timing advance of the user equipment in the second cell. Based on the index or value, the user equipment may retrieve a function of a change in the timing advance of the user equipment in the second cell, and based on the function, the user equipment may determine a value to be used as a timing advance value of the user equipment in the second cell. For example, 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, as described in the present disclosure. The user equipment may determine a subsequent value to be used for the user equipment in the second cell based on the output of the function at t>0, where t represents the time elapsed since the user equipment was connected to the second base station. Therefore, the update of the timing advance value in the second cell does not require signaling or at least less signaling (signaling may be required to correct the timing advance value, but such correction may be performed less frequently and / or may require less signaling because the offset between the updated value determined via the function and the corrected value is smaller than the offset between the timing advance value used by the user equipment and the updated value signaled by the second base station when the timing advance value is not continuously updated via the function but via feedback from the second base station).

[0024] The determination may also be based on a function of a change in the timing advance of the user equipment in the first and / or second cell. Optionally, a supplementary time difference may also be used in the determination. For example, if the user equipment uses a timing advance value at time t' based on a function of a change in the timing advance of the user equipment in the first cell, then at t=t'+Δt the output of the function of the change in the timing advance of the user equipment in the first and / or second cell may be the value to be used as the timing advance of the user equipment in the second cell at time t'+Δt, as described in the present disclosure.

[0025] The value used as the timing advance in the first cell is understood to be any value used as the timing advance in the first cell by the user equipment. In practice, once connected to the base station, the timing advance of the user equipment is continuously updated, in particular in the context of non-geostationary satellites moving relative to the surface of the earth. For example, the value used as the timing advance in the first cell based on which the user equipment determines the value to be used as the timing advance in the second cell may be the first value or the last value of the timing advance used in the first cell. In another example, for example, the value used as the timing advance in the first cell based on which the user equipment determines the value to be used as the timing advance in the second cell may be a value or index of a function of the change of the timing advance in the first cell.

[0026] The value used (or to be used) as the timing advance of the user equipment in a particular cell is understood as the time offset applied by the user equipment based on the value to compensate for the time required for the signal to propagate (i.e., travel) from the user equipment to the base station. The base station corresponding to the particular cell may also use the value to determine the resources scheduled to the user equipment. Therefore, the base station and the user equipment may use the value.

[0027] Data related to timing advance are understood to be data enabling the user equipment to determine the timing advance value.

[0028] Performing a handover between the first cell and the second cell is understood as the user equipment connected to the first base station being connected to the second base station. The connection with the first base station may be released. Thus, the communication established with the user equipment in the first cell or the data transmission to the user equipment via the first cell (if not completed) will continue via the second cell.

[0029] A satellite communication network is understood to be a communication network that uses satellites to receive radio signals from user equipment and / or transmit radio signals to user equipment to perform communications with user equipment of the communication network. A satellite communication network may use satellites exclusively to establish a physical link with user equipment of the communication network or may also use non-satellite equipment (e.g., ground antennas or gateways). A satellite communication network may be incorporated into a hybrid network (i.e., a satellite-terrestrial network).

[0030] A cell corresponding to a base station is understood to be a cell through which a user equipment can transmit or receive radio signals when connected to the base station.

[0031] A cell supported by a satellite is understood to mean that transmission to or reception from a user equipment through the cell involves sending radio signals between the user equipment and the satellite. A cell may comprise one or more beams.

[0032] Non-geostationary satellites are satellites that move relative to the Earth.

[0033] A non-geostationary orbit satellite may be a satellite with a fixed beam, such as a non-geostationary satellite equipped with a non-steerable antenna panel having a beam pointed in a fixed direction relative to the satellite, thereby deploying a coverage area on the surface of the Earth that moves relative to the surface of the Earth due to the movement of the satellite relative to the Earth.

[0034] According to an aspect of the present invention, the data related to the timing advance of the user equipment in the second cell includes at least one of the following:

[0035] - data relating to a value to be used as a timing advance of the user equipment in the second cell;

[0036] - data informing the user equipment of a value to be used as the timing advance of the user equipment in the second cell which is different from the value used as the timing advance of the user equipment in the first cell; and

[0037] - Informing the user equipment of data 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.

[0038] Transmitting data to the user equipment informing that the value to be used as the timing advance in the second cell is different from the value to be used as the timing advance in the first cell allows to easily remove the signaling required to inform the user equipment that the timing advance does not need to be updated when connected to the second base station (i.e., the signaling informing the user equipment 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 can be removed). Based on the data, the user equipment determines that the value to be used as the timing advance in the second cell is different from the value to be used as the timing advance of the user equipment in the first cell or, synonymously, that the value to be used as the timing advance should be updated when performing a handover from the first cell to the second cell. Therefore, data can be sent only when the user equipment needs to update the value of the timing advance when connecting to the second base station after connecting to the first base station. Therefore, no signaling or at least less signaling is required during the handover when the time advance does not need to be updated. Therefore, in this case, when 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 as the timing advance of the user equipment in the first cell, data related to the timing advance may not be sent. Thus, when the user equipment does not receive data related to the timing advance of the user equipment in the second cell, the user equipment may 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 last timing advance value used in the first cell). When the timing advance value needs to be updated, the update may be performed using a classical procedure. For example, transmitting to the user equipment such data that informs 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 may be performed when 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 co-located.

[0039] Updating the timing advance value or the value to be used as timing advance is understood as changing the timing advance value of the user equipment between the value previously used as timing advance by the user equipment in the first cell (the last value used while connected to the first base station) and a new value to be used in the second cell.

[0040] Transmitting data to the user equipment informing 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 avoiding the second base station from calculating the value of the timing advance and sending this during the handover procedure. In this case, when a handover is performed from the first cell to the second cell, an update of the timing advance value of the user equipment is not performed. For example, the transmission of such data informing the user equipment may be performed 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-located.

[0041] Transmitting data to the user equipment regarding the value to be used as the timing advance for 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 advantageous 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 the first base station and the second base station are not co-located.

[0042] Such data relating to a value to be used as the timing advance of the user equipment in the second cell may comprise at least one of the following:

[0043] - Data corresponding to the value, e.g. data comprising the value or data encoding the value or data representing an index and / or a function allowing calculation of the value. Thus, the user equipment may determine the timing advance value to be used in the second cell directly from the data.

[0044] - Data corresponding to an offset relative to the value used as the timing advance by the user equipment in the first cell. Thus, the user equipment can determine the timing advance value to be used in the second cell by a simple calculation.

[0045] - data corresponding to an offset relative to a common value. Thus, the user equipment can determine the timing advance value to be used in the second cell by a simple calculation. Such a common value may be known to the user equipment, for example stored by the user equipment when performing a first connection to the satellite network. The common value may be, for example, a network common value or a satellite common value (specified for each satellite) or a base station common value (i.e. specified for each base station), or may be, for example, a value common to a beam, a group of beams or a group of base stations or a group of users. The common value may also be an index to a function or a varying function.

[0046] - Data related to the value of reference signal received power RSRP. Therefore, the user equipment can determine the timing advance value to be used in the second cell based on the RSRP threshold signaled (e.g., the RSRP threshold in the conditional handover process) and the correspondence between this value and the timing advance value in the target cell.

[0047] According to an aspect of the present invention, the uplink transmission performed with the second base station is a first uplink transmission performed with the second base station.

[0048] Therefore, the value determined by the user equipment is used for the first uplink transmission performed between the user equipment and the second base station. This allows the second base station to reduce the radio resources reserved for the reception of the first uplink transmission. In fact, if the first uplink transmission is performed without achieving the correct timing advance value (or without any timing advance), the first uplink transmission will be misaligned on the second base station side. Therefore, the second base station will have to reserve more radio resources to ensure that the first uplink transmission (the first signal transmitted by the user equipment for the second base station) does not interfere with other uplink radio signals from other user equipment. In addition, in the context of satellite communications, the value used as timing advance by the user equipment in the same cell may be very important compared to terrestrial communications, and in addition, they may also be very different from each other compared to the terrestrial communication background. Therefore, the amount of reserved radio resources required for the first uplink transmission may be important. In the context of NR, these reserved radio resources correspond, for example, to the preamble reception window configured in the context of the 4-step RACH process performed during the switching process.

[0049] A second aspect of the present invention relates to a user equipment configured to perform a handover procedure between a first cell and a second cell in a network comprising a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to a first base station and the second cell corresponding to a second base station, at least the first cell being supported by a non-geostationary orbit satellite of the satellite communication network, the user equipment comprising:

[0050] Processor; and

[0051] A non-transitory computer-readable medium comprising instructions stored thereon that, when executed by a processor, configure a user device to:

[0052] determining a value to be used as a timing advance in the second cell, the value to be used as the timing advance in the second cell being determined based on:

[0053] - data relating to the timing advance of the user equipment in the second cell received from the first base station or from a base station to which the user equipment was connected before connecting to the first base station, or

[0054] - when no data related to the timing advance of the user equipment in the second cell is received from the first base station or from the base station to which the user equipment was connected before connecting to the first base station, use as the value of the timing advance in the first cell; perform uplink transmission with the second base station using the value to be used as the timing advance in the second cell.

[0055] A third aspect of the present invention relates to a method for managing handover of a user equipment between a first cell and a second cell in a network comprising a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to a first base station and the second cell corresponding to a second base station, at least the first cell being supported by a non-geostationary satellite of the satellite communication network, the method comprising the following steps:

[0056] determining, before the second base station receives any signal from the user equipment, a value to be used as a timing advance of the user equipment in the second cell;

[0057] Uplink transmission is performed between the second base station and the user equipment using a value to be used as a timing advance of the user equipment in the second cell.

[0058] Therefore, in order to perform uplink communication between a user equipment and a second base station (i.e., a base station to which the user equipment is connected), it is no longer necessary for the second base station to estimate the timing advance value that the target base station needs to know in order to be able to schedule uplink resources to the user equipment based on the uplink signal received from the user equipment. Therefore, scheduling can be performed based on a value to be used as a timing advance for the user equipment in the second cell and predetermined. In addition, if the user equipment can determine the timing advance value to be used before performing a handover according to the present invention or using location information (e.g., using GNSS) as described above, it is no longer necessary for the second base station to send timing advance data via signaling. It is also not necessary for the user equipment to send timing advance data to the second base station. Therefore, less signaling is required to enable the user equipment to be connected to the second base station (e.g., while performing a handover).

[0059] In addition, since the determination of the value to be used as the timing advance of the user equipment in the second cell is performed before the second base station receives any signal from the user equipment, fewer calculations are required to estimate the timing advance of the user equipment during the connection of the user equipment to the second base station. Therefore, fewer calculations are required to perform the handover of the user equipment from the first cell to the second cell during the handover process. The second base station no longer needs to measure the value to be used as the timing advance of the user equipment in the second cell during the handover process.

[0060] Thus, as previously mentioned, the present invention allows to reduce calculations and signaling during handover, for example in the context of most wireless standards (e.g. LTE, LTE-Advanced or New Radio) may allow to remove one message during the handover process (e.g. the RACH preamble or the second message (Msg2) sent by the second base station during the RACH process, and / or in some cases skip the RACH process altogether). Removing these messages allows to reduce handover delays. In addition, removing these messages (or at least applying the timing advance offset while sending these messages) also allows to release a large amount of radio resources, because the exchanges performed between the second base station and the user equipment during the handover process when the user equipment (and eventually the second base station) has not yet implemented a time offset based on the timing advance value (to compensate for the time required for signal propagation) require the second base station to reserve many more radio resources than the classic exchanges. In fact, the second base station cannot (or only poorly) predict the reception time of these exchanges, so in order to avoid interference with other transmissions (thus reducing the number of unsuccessful access processes), the second base station must reserve important radio resources to take into account the possible delays caused by signal propagation. Therefore, the network determines the value to be used as the timing advance in the second cell before performing the handover procedure and while the user equipment is connected to a base station (i.e. the first base station or a base station to which the user equipment was connected before connecting to the first base station) consumes less radio resources.

[0061] The uplink transmission performed with the second base station using the value to be used as the timing advance in the second cell may be an uplink transmission performed during the handover procedure (e.g., Msg1 or Msg3 of a 4-step RACH procedure or an uplink message during a modified RACH procedure) or after the handover procedure (e.g., the first uplink transmission performed after the handover) or even the first uplink transmission performed with the second base station (e.g., if the RACH procedure is not required).

[0062] The method may further include performing a handover procedure from the first base station to the second base station. Such a handover may be performed without sending data related to a value to be used as a timing advance of the user equipment in the second cell to the user equipment via 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 framework of the handover procedure, for example after or before the handover procedure. The method may further include performing the handover procedure with reduced reserved radio resources.

[0063] Performing uplink transmission between the second base station and the user equipment using the timing advance value is understood as the second base station configuring the uplink transmission based on the determined timing advance value. For example, the second base station may schedule uplink resources allocated to the user equipment based on the determined timing advance value.

[0064] Determining the value to be used as the timing advance of the user equipment in the second cell is understood as the first base station, the second base station or any other network entity other than the user equipment (or any combination of two or more of these network entities) determining the timing advance value to be used in the second cell. The determination is made before the second base station receives any signal from the user equipment, that is, the determination is made without any direct data exchange between the user equipment and the second base station. The determination can therefore be made between the first base station and the second base station before any handover process of the user equipment.

[0065] The determination of the timing advance value is based on the satellite network topology (beam and satellite topology) and / or which satellite of the network supports each cell and / or whether the base station corresponding to each cell is on the earth (also referred to as a satellite with a transparent payload) or on a satellite (completely or partially) (also referred to as a satellite with a regenerative payload) and / or the physical location of the base stations relative to each other (whether they are co-located). These elements may be known to the network entity (the first base station or the second base station or another entity (other than the user equipment) or multiple of these entities) that determines the timing advance value. That is, the determination of 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 co-located may be performed when configuring or reconfiguring the network and / or the base station (in particular, since the satellites follow deterministic orbits), or may be performed in a more dynamic manner based on position information of other satellites and / or beams that may be obtained through configuration (e.g., operation and maintenance configuration (O&M)) and / or exchange between base stations (e.g., configuration exchange between base stations via Xn links).

[0066] To determine the value, a network entity (other than the user equipment) determines whether a timing advance value to be used by the user equipment in the second cell is the same as or different from a timing advance value used by the user equipment in the first cell. When 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 the value may further include calculating the timing advance value to be used by the user equipment in the second cell. A number of calculation methods will be seen below.

[0067] The network entity refers to one of the first base station, the second base station, another base station of the satellite network, or any other entity other than the user equipment of the satellite network. The network entity at least determines the value to be used by the user equipment in the second cell. In addition, for simplicity, hereinafter, the term network entity also refers to the case where the network entity includes multiple network entities other than the user equipment (e.g., the first base station and the second base station).

[0068] According to an aspect of the 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 co-located, the determined value is the same as the value used as the timing advance of the user equipment in the first cell. In a variant, 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 timing advance variation over time.

[0069] Therefore, 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 that the same timing advance value (and / or the same variation function) as the one used in the first cell can be used in the second cell. In fact, when the base stations are co-located on the same satellite (so the cells corresponding to these base stations are supported by the same satellite) or co-located on the earth and the cells corresponding to these base stations are supported by the same satellite, then the signal transmitted by the user equipment takes the same time to reach the first base station as the second base station, so the timing advance value used in the first cell can be used in the second cell. In addition, the function describing the variation of the timing advance of the user equipment over time when the user equipment propagates through the first cell and the second cell does not depend on the switching time.

[0070] Based on the network topology, a value to be used as the timing advance of the user equipment in the second cell is determined without any complex calculations.The network entity determining the timing advance value may use the timing advance value used in the first cell as the timing advance value in the second cell.

[0071] Base station co-location means that the base stations are physically located in the same geographical location, such as on the same satellite or in the same location / gateway on Earth. Synonymously, two base stations are co-located if the signals transmitted by them always take the same time to reach the satellite supporting the cells corresponding to the two base stations.

[0072] According to an aspect of the present invention, when the first cell and the second cell are supported by different satellites or the first base station and the second base station are not co-located, 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.

[0073] According to an aspect of the invention, determining (eg calculating) a value to be used as a timing advance for the user equipment in the second cell is based on at least one value used or previously used as a timing advance for another user equipment in the second cell.

[0074] At least one value used or previously used as the timing advance has been calculated according to the method of the present disclosure or measured according to any existing method, and therefore, using it as the timing advance of the user equipment in the second cell allows the value to be used as the timing advance of the user equipment in the second cell to be accurately determined without any complex calculation. For example, the value to be used as the timing advance of the user equipment in the second cell is a value used or previously used as the timing advance of another user equipment in the second cell.

[0075] The determination of the at least one value used or previously used as the timing advance of another user equipment in the second cell may be performed by a network entity, eg by the second base station.

[0076] According to an aspect of the present invention, at least one value used or previously used as a timing advance for another user equipment in a second cell is used or previously used as a timing advance for another user equipment in the second cell for:

[0077] - uplink transmission between another user equipment and the second base station before connecting to the second cell (e.g. during a handover procedure), or

[0078] - A first uplink transmission by another user equipment once connected to the second cell.

[0079] Thus, while another user equipment is in a similar situation as the user equipment (i.e., both user equipments are around the second cell), at least one value for uplink transmission in the second cell is used. Thus, determining a value to be used as the timing advance of the user equipment in the second cell based on the at least one value is more accurate. For example, the network entity may determine the timing advance value of the user equipment to be the same as the at least one value.

[0080] In addition, another user equipment may also have performed a handover from the first cell to the second cell, and therefore, the similarity between the user equipment and the situation of the other user equipment that has performed a handover from the other cell to the second cell is greater than that of the user equipment and the other user equipment that has performed a handover from the other cell to the second cell. In fact, the overlap between the first cell and the second cell may be different from the overlap between the second cell and the other cell. When the overlap is more important, the user equipment may perform a handover while being closer to the center of the cell to which it is connected than when the overlap is less important. Therefore, according to the overlap between the two cells, the timing advance value used once the user equipment performs a handover between the two cells may be different. When processing the first cell and the second cell containing the adjacent first beam and the second beam, the first and the second are understood to be deployed in parallel to the LEO orbit and numbered in the opposite direction of the movement of the LEO satellite, then because the satellite mobility is much higher than the user equipment mobility, the vast majority of the user equipment of the first cell performs a handover toward the second cell (rather than to a different third cell).

[0081] According to an aspect of the present invention, the at least one value is associated with a timestamp corresponding to a moment in time when the at least one value is determined, and wherein a duration between the moment in time when the at least one value is determined and a value to be used as a timing advance of the user equipment in the second cell is determined is lower than a predetermined threshold.

[0082] Therefore, if the determination of at least one value occurs too long before the determination of the value to be used as the timing advance of the user equipment in the second cell, the value to be used as the timing advance of the user equipment in the second cell cannot be determined based on the at least one value. This allows ensuring that the user equipment and the other user equipment are in a limited geographical area (e.g., in or near the overlapping area between the first cell and the second cell) because the determination of the at least one value occurred not long ago. Therefore, the other user equipment is in a similar situation to the user equipment, that is, the two user equipments are in a limited geographical area and they may be at a similar altitude. Therefore, it is more accurate to determine the value to be used as the timing advance of the user equipment in the second cell based on the at least one value.

[0083] According to an aspect of the present invention, the at least one value is associated with a geographical area, so that at the moment of determining the at least one value, the geographical area intersects with the geographical coverage of the second cell, and when uplink transmission between the second base station and the user equipment is performed, the geographical area intersects with the geographical coverage of the second cell.

[0084] Therefore, if the determination of at least one value occurs when the other user equipment is in a position that is too far from the actual position of the user equipment (when determining its timing advance value), the value to be used as the timing advance of the user equipment in the second cell cannot be determined based on the at least one value. This allows ensuring that the position of the user equipment when performing uplink transmission is close to the position of the other user equipment when determining its at least one value. Therefore, the other user equipment is in a similar situation to the user equipment, that is, the two user equipments are geographically close and they may be at a similar altitude. Therefore, it is more accurate to determine the value to be used as the timing advance of the user equipment in the second cell based on the at least one value.

[0085] The intersection of the geographical area and the geographical coverage of the second cell is understood to mean that at least the beam coverage area of ​​the beam used by the second base station for communicating with the user equipment intersects with the geographical area. In addition, the beam used by the second base station for communicating with the user equipment may also be a beam used for:

[0086] - performing uplink transmission between the second base station and the user equipment, and / or

[0087] - The second base station communicates or has communicated with another user equipment using the at least one value.

[0088] A geographic area may be defined as a predetermined area on the surface of the earth. A geographic area may be one of other geographic areas that create coverage of at least a portion of the earth's surface. Geographic areas may be of different sizes. The network may infer from exchanges with the user equipment whether the user equipment is in a beam coverage area and therefore its proximity to a geographic area. The network may also have some location information of the user, such as obtained by positioning techniques.

[0089] According to an aspect of the invention, a value to be used as the timing advance of the user equipment in the second cell is determined by the second base station.

[0090] In this case, the method may further include: sending, by the second base station, 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 to be connected before connecting to the first base station, the data related to the timing advance of the user equipment in the second cell corresponding to a value determined by the second base station to be used as the timing advance of the user equipment in the second cell. Based on the data related to 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) may decide (and is able to):

[0091] - sending data relating to the timing advance of the user equipment in the second cell (the data enabling the user equipment to determine a value to be used as the timing advance in the second cell); the data may be the same as the data sent by the second base station to the first base station or may be adapted to the user equipment (for example, the data may correspond to an offset between a value to be used as the timing advance of the user equipment in the second cell and a value to be used as the timing advance of the user equipment in the first cell), or

[0092] - Sending data relating to the timing advance of the user equipment in the second cell to the base station to which the user equipment was connected (directly or via other base stations) before the user equipment became connected to the first base station.

[0093] Based on the data related to the timing advance of the user equipment in the second cell, the base station to which the user equipment is connected (which may be the first base station) may also decide not to send any data related to the timing advance to the user equipment, in particular when 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.

[0094] According to an aspect of the invention, a value to be used as the timing advance of the user equipment in the second cell is determined based at least on a value used as the timing advance of the user equipment in the first cell.

[0095] That is, the network entity determines the value to be used as the timing advance of the user equipment in the second cell based at least on the value used as the timing advance of the user equipment in the first cell. Therefore, the determined value more accurately takes into account the situation of the user equipment, thus resulting in an accurate determination of the value to be used as the timing advance of the user equipment in the second cell.

[0096] For example, the value to be used as the timing advance of the user equipment in the second cell may be determined based at least on:

[0097] - used as a minimum value for the timing advance of the user equipment in the first cell, and / or

[0098] - a center position of a second beam coverage area relative to a center position of a first beam coverage area, the first beam being used by the first base station for communicating with the user equipment and the second beam being used by the second base station for performing uplink transmissions between the second base station and the user equipment; and / or

[0099] - the geographical coverage location of the first cell, and / or

[0100] - the geographical coverage location of the second cell, and / or

[0101] - an evolution (ie a change) of a value used as a timing advance for the user equipment in the first cell; and / or

[0102] - 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 / or

[0103] - Satellite movement direction.

[0104] The user equipment communicates with the first base station through the first beam while connected to the first base station, with the value determined based on the center position of the second beam coverage area relative to the center position of the first beam coverage area. This connection to the first base station precedes the connection to the second base station.

[0105] The geographical coverage of a cell is understood as the union of the beam coverage areas of the beams supporting the cell.The beams supporting a cell are all beams that a user equipment can use to communicate (transmit or receive) through the cell, ie via the base station corresponding to the cell.

[0106] The direction of satellite movement is understood to be, for example, the direction in which the satellite moves in its orbit, or the projection of this movement on the Earth, or any equivalent representation of the above directions.

[0107] These elements based on which the value to be used as the timing advance of the user equipment in the second cell may be determined are known by the network entity by receiving them from the base station and / or the configuration of the satellite network (e.g., satellite movement direction) and / or calculation (e.g., the location of the geographical coverage of the cell, the estimated location of the user equipment or a rough estimate related to its location relative to a reference point in the system, etc.). For example, when the network entity determining the value to be used as the timing advance of the user equipment in the second cell is the first base station, the second base station may send information related to the following to the first base station:

[0108] - the location of the geographical coverage of the second cell, or

[0109] - a center position of the second beam coverage area, based on which the first base station can calculate the center position of the second beam coverage area relative to the center position of the first beam coverage area.

[0110] Therefore, according to an aspect of the present invention, the value to be used as the timing advance of the user equipment in the second cell is determined by the first base station. In this case, the value may be determined based on information provided by the second base station.

[0111] According to an aspect of the present invention, the method further comprises: sending 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 to which the user equipment was connected before connecting to the first base station. The data enables the user equipment to retrieve a value to be used as the timing advance of the user equipment in the second cell.

[0112] According to one aspect of the present invention, the method further includes: setting the switching mode to active or inactive and sending a message to the user equipment indicating that the switching is performed according to the set switching mode, the active switching mode is a switching mode in which the switching is performed according to the present invention, and the inactive switching mode is a mode in which the switching is performed according to another switching process (e.g., a standard switching process). The active switching mode can be divided into two modes:

[0113] - a first mode, wherein a further handover procedure is implemented 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, and wherein the handover is performed according to the invention when 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;

[0114] - A second mode, in which the handover is performed according to the invention.

[0115] A fourth aspect of the present invention relates to a second base station configured to manage handover of a user equipment between a first cell and a second cell in a network comprising a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to the first base station and the second cell corresponding to the second base station, at least the first cell being supported by a non-geostationary orbit satellite of the satellite communication network, the second base station comprising: a processor;

[0116] A non-transitory computer readable medium comprising instructions stored thereon that, when executed by a processor, configure a second base station:

[0117] - determining a value to be used as timing advance of the user equipment in the second cell;

[0118] - performing uplink transmission between the second base station and the user equipment using the value to be used as the timing advance of the user equipment in the second cell.

[0119] In this case, the network entity is the second base station. Hence, in addition to determining the value, the network entity performs uplink transmission with the user equipment (ie receives and processes uplink signals sent by the user equipment).

[0120] A fifth aspect of the present invention relates to a method for managing handover of a user equipment between a first cell and a second cell in a network comprising a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to a first base station and the second cell corresponding to a second base station, at least the first cell being supported by a non-geostationary satellite of the satellite communication network, the method comprising the following steps:

[0121] determining a value to be used as a timing advance of the user equipment in the second cell;

[0122] Before the second base station receives any signal from the user equipment, a value to be used as the timing advance of the user equipment in the second cell is sent to the second base station and / or the user equipment.

[0123] When the network entity is not the second base station, that is, when the determination of the value is performed by another entity other than the second base station, the network entity may send the determined value to:

[0124] - User equipment, in particular when the user equipment is unable to locate itself and eventually calculate the value to be used as timing advance in the second cell;

[0125] - The second base station, to avoid any estimation and transmission of the timing advance of the second base station during the handover.

[0126] In this case, the network entity may be the first base station or any other network entity except the user equipment and the second base station.

[0127] A sixth aspect of the present invention relates to a first base station configured to manage handover of a user equipment between a first cell and a second cell in a network including a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to the first base station and the second cell corresponding to the second base station, at least the first cell being supported by a non-geostationary orbit satellite of the satellite communication network, the first base station comprising: a processor;

[0128] A non-transitory computer readable medium comprising instructions stored thereon that, when executed by a processor, configure a second base station:

[0129] - determining a value to be used as timing advance of the user equipment in the second cell;

[0130] - before the second base station receives any signal from the user equipment, sending to the second base station and / or the user equipment a value to be used as the timing advance of the user equipment in the second cell.

[0131] A seventh aspect of the present invention relates to a non-transitory computer-readable medium comprising instructions stored thereon, wherein the instructions are executed by a processor for executing the aforementioned method.

[0132] Computer-readable media include, but are not limited to, both computer storage media and communication media, including any medium that facilitates the transmission of computer programs from one place to another. As used herein, "computer storage media" can be any physical medium accessible to a computer. Examples of computer storage 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, disk storage or other magnetic storage devices, memory chips, RAMs, ROMs, EEPROMs, smart cards, solid-state drives (SSD) devices or hard disk drives (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 that can be read by a computer processor. In addition, various forms of computer-readable media can send or carry instructions to a computer, including routers, gateways, servers or other transmission devices, wired (coaxial cables, optical fibers, twisted pairs, DSL cables) or wireless (infrared, radio, cellular, microwaves). Instructions may include the code of any computer programming language, including, but not limited to, assembly, C, C++, Visual Basic, HTML, PHP, Java, Javascript, Python, and bash scripts.

[0133] Unless otherwise specifically stated, it will be understood that throughout the following description, discussions utilizing terms such as processing, computing, determining, etc. refer to the actions or processes of a computer or computing system or similar electronic computing device that manipulates or transforms data represented as physical (e.g., electronic) quantities within the computing system's registers or memories into other data similarly represented as physical quantities within the computing system's memories, registers, or other such information storage, transmission, or display devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0134] The present invention is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references refer to similar elements.

[0135] [ Figure 1 ] Figure 1 Shown are a number of satellites in a satellite communications network.

[0136] [ Figure 2 ] Figure 2 A method of determining a value to be used as a timing advance for a user equipment in a second cell according to the present invention is shown.

[0137] [ Figure 3 ] Figure 3 A method of determining a value to be used as a timing advance for a user equipment in a second cell according to the present invention is shown.

[0138] [ Figure 4 ] Figure 4 A method of determining a value to be used as a timing advance for a user equipment in a second cell according to the present invention is shown.

[0139] [ Figure 5 ] Figure 5 A method of determining a value to be used as a timing advance for a user equipment in a second cell according to the present invention is shown.

[0140] [ Figure 6 ] Figure 6 A flow chart representing the steps implemented by a user equipment to perform a handover according to the present invention is shown.

[0141] [ Figure 7 ] Figure 7 A flow chart representing the steps implemented by a satellite network to manage handovers in accordance with the present invention is shown. DETAILED DESCRIPTION

[0142] Reference Figure 1, showing a portion of a satellite communication network. The present invention is not limited to a particular standard, however for simplicity the present invention will be described in the context of the New Radio (NR) standard. The NR standard uses the term user equipment to refer to a device used by an end user to communicate, however any other term used to refer to any wireless device used to communicate at least via a satellite network (e.g., mobile terminal, mobile station, personal digital assistant, wireless modem, handheld device, etc.) is encompassed herein within the term user equipment.

[0143] The invention described below may be used in satellite communication networks of various types or architectures, such as hybrid networks including satellite network components.

[0144] exist Figure 1 In the figure, three satellites are represented as Sat1, Sat2, Sat3. Each satellite is linked to one or more gateway nodes Gw1 to Gw4. Two satellites can be linked to the same gateway node (not shown here). These gateway nodes Gw1 to Gw4 are therefore configured to communicate with one or more satellite nodes Sat1, Sat2, Sat3. In addition, these gateway nodes Gw1 to Gw4 are configured to communicate with a core network (not shown here).

[0145] Each satellite Sat1, Sat2 or Sat3 is configured to generate one or more satellite beams. For each satellite, Figure 1 3 satellite beams are shown 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.

[0146] Each satellite beam SB11.1 to SB33.4 is configured in a specific frequency band. Through each satellite beam SB11.1 to SB33.4, the corresponding satellite (i.e., the satellite generating the beam) can send and receive data according to the radio resources allocated in the frequency band configured for the beam. These radio resources can be shared according to a frequency division scheme (e.g., frequency division multiplexing (FDM) or orthogonal frequency division multiplexing (OFDM)) or by a time division scheme (e.g., time division multiplexing (TDM)) or a code division scheme (code division multiplexing (CDM)) or according to polarity or a combination thereof.

[0147] The allocation of radio resources for each beam is implemented by base stations BS1 to BS5. Each base station manages the radio resources of one or more satellite beams. Figure 1 The above indicates:

[0148] -BS1 manages the radio resources of satellite beams SB11.1 and SB12.1,

[0149] -BS2 manages the radio resources of satellite beam SB13.2,

[0150] -BS3 manages the radio resources of satellite beams SB21.3 and SB22.3,

[0151] -BS4 manages the radio resources of satellite beam SB23.4,

[0152] -BS5 manages the radio resources of satellite beams SB31.5 and SB33.5.

[0153] Each base station defines a cell to which radio resources are allocated to a user equipment according to the beam managed by the base station. That is, a base station managing a satellite beam may allocate radio resources of the satellite beam to a user equipment (if the user equipment receives sufficient radio power from the satellite beam). The user equipment is therefore considered to be under the coverage of the cell corresponding to the base station. Figure 1 , BS1 forms a first cell C1, which covers user equipment that receives sufficient radio power from satellite beams SB11.1 and SB12.1. BS2 forms a second cell C2, which covers user equipment that receives sufficient radio power from satellite beam SB13.2. BS3 forms a third cell C3, which covers user equipment that receives sufficient radio power from satellite beams SB21.3 and SB22.3. BS5 forms a fifth cell C5, which covers user equipment that receives sufficient radio power from satellite beams SB31.5 and SB33.5. Thus, a cell may correspond to a beam (e.g., C2 and C4) or a set of beams (e.g., C1, C3, and C5).

[0154] Base stations may be located on a satellite (BS5) or on the earth (BS1 to BS4). Two base stations are co-located if they are physically located at the same geographical location, which is the case for BS1 and BS2, but not for example BS2 and BS3 or BS3 and BS4.

[0155] In order to allocate radio resources by the base station, the user equipment must receive sufficient radio power from at least one beam managed by the base station (i.e., the user equipment must be within the coverage of the cell formed by the base station) and connect to the base station. The connection process can be performed as an initial access to a base station or when the user equipment is already connected to another base station and accesses the current base station through a handover process.

[0156] exist Figure 1A plurality of user equipments UE1 to UE5 are shown above. UE1 is connected to BS1 in a first cell C1 and is allocated radio resources of a satellite beam SB11.1 generated by a satellite Sat1. UE2 is connected to BS2 in a second cell C2 and is allocated radio resources of a satellite beam SB13.2 generated by a satellite Sat1. UE3 is connected to BS3 in a third cell C3 and is allocated radio resources of a satellite beam SB21.3 generated by a satellite Sat2. UE4 is connected to BS4 in a fourth cell C4 and is allocated radio resources of a satellite beam SB23.4 generated by a satellite Sat2. UE5 is connected to BS5 in a fifth cell C5 and is allocated radio resources of a satellite beam SB31.5 generated by a satellite Sat3.

[0157] In the context of satellite networks using non-geostationary satellites and satellites with fixed beams, the satellites, and therefore the coverage areas of their beams, move relative to the Earth's surface in a predictable manner (because the satellite constellation dynamics are predictable). Figure 1 The top is indicated by the arrow Sat Mouv.

[0158] Based on the predictable satellite constellation dynamics, and because the UE's mobility is negligible relative to satellite mobility, it is possible to predict which base stations the user equipment will have to connect to (e.g., by performing a handover) in order to continue communicating over the satellite communications network. Figure 1 , UE1 is connected to BS1 and will most likely perform a handover from BS1 to BS2, then from BS2 to BS3, then from BS3 to BS5, etc. UE2 is connected to BS2 and will most likely perform a handover from BS2 to BS3, then from BS3 to BS5, etc. UE3 is connected to BS3 and will most likely perform a handover from BS3 to BS4, then from BS4 to BS5, etc. UE4 is connected to BS4 and will most likely perform a handover from BS4 to BS5, etc.

[0159] However, in order to be able to perform correct communication between the user equipment and the base station to which the user equipment is to be connected (the target base station or the second base station), the base station and the user equipment must obtain the value of the timing advance used with the base station (i.e., in the cell managed by the base station). In the NR standard, obtaining the value involves performing a RACH procedure during which the base station (to which the user equipment is connected) measures and sends the value of the timing advance for use.

[0160] However, when the cell currently serving the user equipment (the first cell) and the target cell (the second cell) are supported by the same satellite and when the base station to which the user equipment (the first base station) is currently connected and the target base station (the second base station) are co-located, the value to be used with the second base station is the same as the value to be used with the first base station. Figure 1 , since BS1 and BS2 are co-located and both C1 and C2 are supported by Sat1, the value to be used as the timing advance of UE1 in C2 is the same as the value used as the timing advance of UE1 in C1 (e.g., the last value used in C1). In an equivalent description, considering that the timing advance value of UE1 changes over time while UE1 crosses C1, C2, etc., when the cell currently serving the user equipment (the first cell) and the target cell (the second cell) are supported by the same satellite and when the base station to which the user equipment (the first base station) is currently connected and the target base station (the second base station) are co-located, the function of the change in the timing advance of the user equipment over time when the user equipment crosses C1 and C2 is continuous, that is, the function does not depend on the switching moment. In other words, 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 change in the timing advance over time. In other words, the function of the change in the timing advance of UE1 in C1 over time is the same as the function of the change in the timing advance of UE1 in C2 over time.

[0161] In contrast, when the cell currently serving the user equipment (first cell) and the target cell (second cell) are supported by different satellites or when the base station to which the user equipment (first base station) is currently connected and the target base station (second base station) are not co-located, the value used with the second base station is different from the value used with the first base station. Figure 1, the value to be used as the timing advance for UE2 in C3 is different from the value to be used as the timing advance for UE2 in C2, since BS2 and BS3 are not co-located or C2 and C3 are not supported by the same satellites Sat1 and Sat2. The value to be used as the timing advance for UE3 in C4 is different from the value to be used as the timing advance for UE3 in C3, since BS3 and BS4 are not co-located. The value to be used as the timing advance for UE4 in C5 is different from the value to be used as the timing advance for UE4 in C4, since BS4 and BS5 are not co-located or C4 and C5 are not supported by the same satellites Sat2 and Sat3. In these cases, the values ​​to be used as the timing advance in the second cell (C3, C4 and C5, respectively) must be estimated. In an equivalent description, taking into account that the timing advance value of UE1 varies over time while UE1 crosses C2, C3, etc., when the cell currently serving the user equipment (first cell) and the target cell (second cell) are not supported by the same satellite and / or when the base station to which the user equipment (first base station) is currently connected and the target base station (second base station) are not co-located, the function of the variation of the timing advance of the user equipment over time when the user equipment crosses C2 and C3 is discontinuous, that is, the function depends on the switching moment. In other words, the value to be used as the timing advance of UE1 in C2 is different from the value to be used as the timing advance of UE1 in C3 because they can be interpreted as values ​​of different functions of the variation of the timing advance over time. In other words, the function of the variation of the timing advance of UE1 in C1 over time is the same as the function of the variation of the timing advance of UE1 in C2 over time.

[0162] A number of methods of estimating (ie, determining) the value of the timing advance according to the present invention will be described below.

[0163] Each base station BS1 to BS5 comprises a processing module PROC-BS and a memory unit MEM-BS. The memory unit MEM-BS comprises a non-volatile unit for retrieving a computer program and a volatile unit for retrieving a value used as a timing advance for another user equipment in a second cell, a timestamp associated with the value, information relative to a geographical area, a function of the evolution of the timing advance value of the user equipment in the first cell, the location of the user equipment, the minimum timing advance value of the user equipment in the first cell, the experience of the timing advance value in the first cell at a given moment, the ephemeris of the satellite constellation, information about the beam coverage area of ​​the satellite network, etc. The processing module PROC-BS is configured to calculate the location of the user equipment, determine the value to be used as the timing advance of the user equipment in the second cell, send data related to the timing advance of the user equipment in the second cell, perform handover, perform uplink transmission, and perform resource scheduling.

[0164] Each user equipment comprises a communication module (COM_UE) 1.4, a processing module PROC-UE and a memory unit MEM-UE. The memory unit MEM-UE comprises a non-volatile unit for retrieving a computer program and a volatile unit for retrieving a value to be used as a timing advance in the second cell, a value to be used as a timing advance in the first cell, a common value, a switching mode, a satellite common value, a network common value, a base station common value, an offset relative to the value to be used as a timing advance in the first cell, an offset relative to the common value. The processing module PROC-UE is configured to receive and decode data related to the timing advance of the user equipment in the second cell, determine the value to be used as the timing advance in the second cell, and perform an uplink transmission with the second base station using the value to be used as the timing advance in the second cell.

[0165] The user equipment may also be a mobile user equipment or a fixed user equipment.

[0166] Figure 2 Representation and Figure 1 A satellite communication network is the same as the network represented in FIG. A user equipment UE6 (also referred to as another user equipment in the present application) is added. For example, after performing a handover from BS2 to BS3 (in other words, a handover from C2 to C3), UE6 is connected to BS3. As mentioned previously, since UE6 is connected to BS3, BS3 knows the value of the timing advance of UE6 in C3 and its intermediate value and / or the change starting from the moment UE6 accesses BS3. The value of the timing advance of UE6 in C3 can be determined by any method (existing method or method according to the present invention).

[0167] UE2 is connected to BS2 and will have to perform a handover from BS2 (first base station) to BS3 (second base station).BS3 may determine the value to be used as the timing advance for the user equipment in C3 based on one or some values ​​used for UE6 in C3.

[0168] For example, BS3 may determine that the value to be used as the timing advance for the user equipment in C3 is equal to the value used for UE6 in C3 (eg, the value used for UE6 in C3 during handover of UE6 from C2 to C3).

[0169] BS3 may also determine a value to be used as the timing advance of the user equipment (UE2) in C3 based on values ​​for a plurality of user equipments connected to BS3.

[0170] For example, BS3 may determine that the value to be used as the timing advance of the user equipment (UE2) in C3 is equal to the average of the values ​​used by multiple user equipments in C3 (e.g., the values ​​used by multiple user equipments in C3 during their switching from C2 to C3). For example, BS3 may determine that the value to be used as the timing advance of the user equipment (UE2) in C3 is a value that is a function of the change in the timing advance of another user equipment (e.g., UE6) in C3 or an average of the values ​​of the function of multiple user equipments.

[0171] In addition, the values ​​on which the determination of the value to be used as the timing advance of the user equipment (UE2) in C3 is based can be used to determine the value of UE2 within a certain amount of time. To this end, a timestamp is associated to each value, which timestamp corresponds to the moment when each of these values ​​is determined. Values ​​whose timestamp indicates the moment when the value is determined earlier 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. That is, only sufficiently recent values ​​are used for the estimation.

[0172] Figure 3 Representation and Figure 1 A satellite communication network is the same as the network represented in . A user equipment UE6 (also referred to as another user equipment in this application) is added. UE6 is connected to BS3 during previous passages of Sat1 and Sat2 (e.g., when the satellite follows a fixed orbit), for example, after a handover from BS2 to BS3 has been performed. Since UE6 is connected to BS3, BS3 knows the value of the timing advance of UE6 used when UE6 is connected to BS3. The value of the timing advance of UE6 used when UE6 is connected to BS3 can be determined by BS3 by any method (existing method or method according to the present invention). When UE6 is connected to BS3, the geographical coverage of C3 intersects with the geographical area GeoA. The value of the timing advance of UE6 (e.g., the value used for UE6 in C3 during the handover of UE6 from C2 to C3) is associated with the geographical area GeoA. UE2 is connected to BS2 and will have to perform a handover from BS2 (first base station) to BS3 (second base station). When UE2 performs a handover from BS2 to BS3, if the geographic coverage of C3 intersects with the geographic area GeoA, BS3 may determine the value to be used as the timing advance of the user equipment in C3 based on the value used for UE6 in C3. This implementation may also be implemented in combination with timestamps.

[0173] These implementations (expressed in Figure 2 and Figure 3) involves a second base station (BS3) which may determine a value to be used as a timing advance for UE2 in the second cell. However, in these implementations, BS2 may also determine a value to be used as a timing advance for UE2 in the second cell. In this case, BS3 sends the required information to BS2, e.g. the value used as timing advance in C3 by user equipment connected to BS3, so that, for example, BS2 can calculate an average of the values ​​used as timing advance in C3, which may be considered as the value to be used as timing advance for UE2 in C2.

[0174] Figure 4 Representation and Figure 1 The network represented in is the same satellite communication network.

[0175] UE2 is connected to BS2. During its connection to BS2, BS2 tracks the timing advance of UE2 to continuously update the value to be used as the timing advance of UE2 in C2. Figure 4 In , TA1 to TA9 represent the timing advance values ​​measured by BS2 for UE2. Figure 4 These values ​​(TA1 to TA9) of the timing advance of UE2 measured in C2, respectively associated with their measurement moments (i.e. a function of the evolution of the timing advance value in the first cell) may enable BS2 (or BS3 if this information is sent to BS3) to have some information about the location of UE2 and / or to predict the evolution of the timing advance value of UE2 at later moments.

[0176] This position can be calculated with equivalent techniques. For example, the experience of the average timing advance value in C2 allows to determine an axis parallel to the direction of movement of Sat1. Intersecting the two circles drawn by two different timing advance values ​​of UE2 measured by BS1 with the axis where UE2 lies allows to obtain the position of UE2.

[0177] In another example, the location of UE2 may be more accurately inferred based on the timing advance value experience (TA-C2) in C2 at a given time (e.g., t1 milliseconds after switching). The change in the timing advance value experience in C2 (possibly combined with other measurements) gives information about the location of UE2 and / or allows prediction of the evolution of the timing advance value of UE2 at a later time in the same cell or in a subsequent cell.

[0178] For example, in the specific case where the center of the beam coverage area used for communication with UE2 corresponds to the nadir point of Sat1 (i.e., the center corresponds to the point on the Earth's surface directly below the satellite), the minimum value of abs(timing advance - TA_ref) indicates that UE2 has reached the point on its trajectory that is closest to the center of the beam (SB13.2), where abs(.) represents an absolute value and TA_ref is a reference timing advance value, which may be beam-specific (known to all users in the beam), corresponding to the timing advance of the user at the center of the beam. In this case, two positions of UE2 are possible (reaching the same minimum at two points H', such as Figure 5 and which is symmetrical with respect to the axis Sat1 Mouv). In this case, further information may be needed to distinguish in which of the two positions UE2 is actually located, for example using the reference signal received power (RSRP) of UE2 measured by another satellite of the constellation or using previous statistics of the trajectory of UE2 received from other base stations.

[0179] In some implementations, TA_ref may be broadcasted to all users in a beam (e.g., via a SIB or via an RRC parameter with a common value for all users in a beam). In this case, only the UE-specific differential value of the timing advance is transmitted to each UE during its communication with the base station via a given beam, and the UE may calculate the timing advance value by combining the reference beam-specific value TA_ref and the UE-specific value separately transmitted by the serving base station.

[0180] In order to complete the determination of the value to be used as the timing advance for UE2 in C3, additional information relative to the topology of the satellite constellation may be needed. For example, the position of the nadir point of Sat2 relative to the nadir point of Sat1 and the altitudes of Sat1 and Sat2. This additional information may be given by the ephemeris of the satellite constellation (or at least the ephemeris of Sat1 and Sat2) or by the beam coverage map of the satellite network or any other classical method for determining the value to be used in the second cell when the position of the user equipment is known (for example, using the same method used to determine the timing advance value when the user equipment gets its position through a global navigation satellite system).

[0181] In addition, when the base station is not located on the satellite, the additional information may include information relative to the physical location of the base station (BS2 and / or BS3) and / or the timing advance offset caused by the transmission between the base station (BS2 and / or BS3) and the satellite (Sat1 and / or Sat2). Therefore, the first base station (BS2) can therefore adjust the determination of the value to be used as the timing advance in C3.

[0182] Information relative to this position may be sent to BS3 to enable BS3 to determine the value to be used as timing advance for UE2 in C3, or if necessary, BS3 may send additional information to BS2 to enable BS2 to complete the determination of the timing advance value. In the following we will see which type and form of information may be sent.

[0183] Reference Figure 5 , showing in more detail that according to Figure 4 The method described in determines a value to be used as a timing advance of a user equipment in a second cell. Figure 5 Representation and Figure 4 An overhead view of the same satellite communications network as shown in Figure 1. Figure 5 In the example shown in Figure 2, the centers of the beams (C-SB13.2 and C-SB22.3) coincide with the nadir points of Sat1 and Sat2, respectively.

[0184] By vector The position of C-SB22.3 relative to C-SB13.2, represented by the angle φ, is known from the constellation topology.

[0185] BS2 measures the timing advance of UE2 used in C2. UE2 may be located at the center of the beam (C-SB13.2) and the radius is When connected to BS3 at point H, UE2 should use the same Corresponding TA-C3 value.

[0186] To calculate The angle θ should be known. As the satellite moves in the direction When UE2 is closest to C-SB13.2, that is, when UE2 is at position H', the minimum absolute value of TA-C2 is observed, and the TA-C2 value corresponds to d. Based on d and θ can be calculated as

[0187]

[0188] therefore, can be calculated as:

[0189]

[0190] Due to limitations of its computing power or due to lack of knowledge of the network topology, a UE that obtains its position via a global navigation satellite system may not be able to calculate its own timing advance by itself and still requires auxiliary information from the network in order to correctly know the timing advance value in the target cell. In this case, the method given by the present invention is still applicable, with the supplementary step that the UE reports its location information to the network (e.g., to the source base station before and / or during the handover, to the target base station during and / or after the handover). In this case, the network receives the location information from the UE and matches it with the timing advance value without having to perform all the above calculations. Therefore, the determination of the timing advance by the network entity is simplified.

[0191] Reference Figure 6 , shows a flow chart representing steps implemented by a user equipment to perform a handover according to the present invention.

[0192] In step S11 , a user equipment (eg, UE2) is configured.

[0193] The method steps implemented by the user equipment will be described in a general context and illustrated in the context of UE2, however, based on the above description, those skilled in the art will find it easy to transfer the specific examples to the cases of the other user equipments (UE1 to UE5) mentioned above.

[0194] Configuration of the user equipment UE2 may be performed when connected to a base station of the satellite network (when the user equipment is connected to a base station of the network for the first time or each time the user equipment performs an initial connection to the network or during connection of the user equipment to the network) or while connected to the base station (e.g., via configuration and / or reconfiguration messages), or may be performed as a factory setting.

[0195] The configuration of UE2 may include setting a switching mode, which will be implemented during the connection of UE2 to the satellite network or until the network changes the current configuration. For example, the mode may be a standard mode (StaM), implementing switching as described in the NR standard. The mode may be a simple mode (SimM), implementing switching 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 a full mode (FulM), implementing only switching according to the present invention.

[0196] The configuration may also set some parameters required for the user equipment UE2 to retrieve the value to be used as the timing advance in the second cell C3. For example:

[0197] - a network common value, i.e. the timing advance in the network is represented as the sum of the network common value and the offset value;

[0198] - a satellite-generic value, i.e. the timing advance associated with a base station supported by a satellite is expressed as the sum of the satellite-generic value and an offset value specific to that satellite;

[0199] - a base station common value, i.e., the timing advance associated with a base station is expressed as the sum of the base station common value and the offset value specific to the base station;

[0200] - A beam-generic value, i.e. the timing advance associated with a base station transmitting via a beam is expressed as the sum of a beam-generic value specific to that beam and an offset value.

[0201] In step S12, the user equipment UE2 receives data related to the timing advance of the user equipment in the second cell. The data may be sent to UE2 by the first base station BS2 or by the base station (e.g., BS1) to which the user equipment is connected before connecting to BS2. In order to receive such data, the switching mode is set to SimM mode or FulM mode.

[0202] In SimM mode, the data related to the timing advance of the user equipment in the second cell is:

[0203] - data informing 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 a binary value to 1); or

[0204] - Inform the user equipment that TA-C3 to be used is the same data as TA-C2 (for example, set the binary value to 0). The UE2 and the network may be configured to avoid transmitting one of these data to the UE2. For example, the network and the UE2 are configured as follows:

[0205] - inform the user equipment UE2 to use TA-C3 different from TA-C2. Data is still sent to UE2, and the next handover is performed based on this information;

[0206] -When performing a handover from C2 to C3, data informing the user equipment that the TA-C3 to be used is the same as TA-C2 is not sent to UE2, UE2 (set in SimM mode) will assume that the TA-C3 to be used is the same as TA-C2, and will therefore perform the handover as if this information had been received.

[0207] Vice versa, that is, data informing the user equipment that TA-C3 to be used is different from TA-C2 is not sent to UE2 and data informing the user equipment that TA-C3 to be used is the same as TA-C2 is sent to UE2.

[0208] Depending on the ratio of supported cells per satellite, one or the other option is more advantageous in terms of signaling.

[0209] In the FulM mode, the data related to the timing advance of the user equipment in the second cell may be:

[0210] - inform the user equipment to use the same data as TA-C2 in TA-C3;

[0211] - Data related to the TA-C3 to be used.

[0212] As in SimM mode, if UE2 and the network are so configured, data notifying the user equipment that the TA-C3 to be used is the same as TA-C2 may not be sent to UE2. In this case, when performing the next handover, if UE2 does not receive data regarding the TA-C3 to be used, UE2 (set in FulM mode) will assume that the TA-C3 to be used is the same as TA-C2 and perform the handover as if this information was received.

[0213] Data related to the TA-C3 to be used may include:

[0214] - data corresponding to TA-C3 to be used, e.g. UE2 may receive TA-C3 or any coded version representing TA-C3;

[0215] - data corresponding to the offset relative to TA-C2;

[0216] -Data corresponding to the offset relative to a common value (network common value, satellite common value, base station common value, beam common value).

[0217] In step S13, the user equipment UE2 determines TA-C3 to be used.

[0218] If UE2 receives data related to TA-C3, based on the data and the data or TA-C2 stored during configuration, UE2 determines TA-C3. For example, UE2 sums the offset with the common value to retrieve TA-C3. For example, UE2 decodes the data corresponding to TA-C3.

[0219] If UE2 receives data informing that the TA-C3 to be used is the same as TA-C2, UE2 may set TA-C3 equal to TA-C2. For example, the last TA-C2 used by UE2 in C2. When TA-C2 and / or TA-C3 consist of user-specific and universal values, the redivision between the user-specific and universal values ​​may change during handover even if TA-C3 is the same as TA-C2.

[0220] If UE2 receives data notifying that TA-C3 to be used is different from TA-C2, UE2 may not set the value of TA-C3 and prepare to perform standard handover.

[0221] As previously mentioned, if the network and UE2 are configured such that when no data related to TA-C3 is sent to UE2, UE2 assumes that TA-C3 to be used is the same as TA-C2, then UE2 may also set TA-C3 to be equal to TA-C2 when no data related to TA-C3 is received.

[0222] In step S14, UE2 performs handover from C2 to C3.

[0223] If TA-C3 is not determined in step S13, UE2 performs a standard handover.

[0224] If UE2 determines TA-C3 in step S13, UE2 may 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 for signal propagation.

[0225] The uplink transmission may be an uplink transmission as part of a RACH procedure.

[0226] For example, the uplink transmission may be the first uplink transmission performed with BS3 during a random access (RACH) procedure. For example, UE2 sends a first message of the RACH procedure to connect to BS3 using a TA-C3 offset.

[0227] For example, the uplink transmission may be a second uplink transmission performed with BS3 during RACH. For example, in the context of NR, UE2 sends a third message of the RACH procedure to connect to BS3 using a TA-C3 offset. Thus, the first message of the RACH procedure is sent according to the standard procedure, so that BS3 can estimate TA-C3 without receiving signaling data corresponding thereto.

[0228] The uplink transmission may be an uplink transmission after a RACH-free handover procedure, thus representing a first / second / subsequent regular uplink transmission to BS3 before BS3 updates the value of the timing advance (e.g., by timing advance adjustment in connected mode, e.g., BS3 sends a MAC CE timing advance command to UE3 in the current NR procedure)

[0229] In these cases, UE2 will not receive any TA-C3 from BS3 until a connection is performed. Once a connection with BS3 is established, BS3 may continuously update TA-C3 until UE2 leaves C3.

[0230] Reference Figure 7 , showing a flow chart representing the steps implemented by a satellite network to manage handover according to the present invention.

[0231] In step S21, the satellite communication network is configured.

[0232] The configuration of the satellite communication network includes setting the switching patterns achievable by the network and configuring a method for determining the values ​​to be used as timing advance for the user equipment in the second cell. Based on the method, the data required to determine these values ​​are stored on different network entities.

[0233] Therefore, at least part of the information is stored at each base station of the satellite communication network (or more generally, any other network entity other than the user equipment), which is:

[0234] - Ephemeris of the satellite constellation; and / or

[0235] - beam topology, i.e. the distribution of beam footprints over the Earth's surface; and / or

[0236] - A mapping between base stations and the satellites on which they are located; and / or

[0237] - A mapping between base stations on Earth and the gateways through which they are linked to the satellites; and / or

[0238] - the physical location of the gateway through which the base station is linked to the satellite; and / or

[0239] - The physical location of the base stations relative to each other (co-located or not).

[0240] According to a method configured for determining a value to be used as a timing advance for a user equipment in a second cell, the network entities involved store data related to determining such a value.

[0241] - a value used as a timing advance for another user equipment in the second cell;

[0242] - a timestamp associated with the value;

[0243] - information relative to geographical areas;

[0244] - a function of the evolution of the timing advance value of the user equipment in the cell;

[0245] - a mapping between a function of the evolution of the timing advance value of the user equipment in the first cell and the location of the user equipment;

[0246] - a mapping between a minimum timing advance value of the user equipment in the first cell and / or the second cell and a location of the user equipment and / or RSRP and / or Doppler measurement;

[0247] - a mapping between the timing advance value experience in the first cell at a given moment and the location of the user equipment and / or RSRP and / or Doppler measurements;

[0248] - a mapping between a function of the evolution of the timing advance value of the user equipment in the first cell and a function of the evolution of the timing advance value of the user equipment in the second cell;

[0249] -Ephemeris of satellite constellation;

[0250] - information about the beam coverage of the satellite network (e.g. a beam coverage map of the satellite network);

[0251] -etc.

[0252] 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 advance of the user equipment in the first cell (i.e., TA-C2).

[0253] The method steps implemented on the network side (any network entity other than the user equipment) will be described in a general context and illustrated in the context of UE2, however, based on the above description, those skilled in the art will find it easy to transfer the illustration to the cases of the other user equipments (UE1 to UE5) mentioned above.

[0254] 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 co-located. 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 some information may need to be received from other network entities, for example, through operation and maintenance configuration (O&M) and / or through inter-base station exchange (Xn link).

[0255] In the case of UE2, UE2 is connected to BS2 and will have to perform a handover from BS2 to BS3. The network entity determines that BS3 and BS2 are not co-located and C3 and C2 are supported by different satellites (Sat2 and Sat1, respectively), so as before Figure 1 As mentioned in, the TA-C3 to be used is different from TA-C2.

[0256] The network entity may be BS2 or BS3.

[0257] Other situations Figure 1 Described in.

[0258] If, in step S22, the network entity determines that the value to be used as the timing advance of the user equipment UE2 in the second cell C3 (i.e., TA-C3 to be used for UE2) is different from the value to be used as the timing advance of the 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 of the user equipment UE2 in the second cell C3.

[0259] In order to determine a value to be used as the timing advance of the user equipment UE2 in the second cell C3, the network entity may implement Figure 2 , Figure 3 and Figure 4 These methods may be combined together to obtain higher accuracy in determining the value to be used as the timing advance (TA-C3 to be used) for the user equipment UE2 in the second cell C3.

[0260] Figure 2 and Figure 3 The method described in describes the value of determining the timing advance value of other user equipment from learning by a second base station (BS3 in the context of UE2). The network entity that implements the determination of the TA-C3 to be used may be BS2 or BS3 (or any network entity other than the user equipment). However, if BS2 is the network entity that determines the TA-C3 to be used for UE2, BS3 may send the learned value (or any corresponding information) that may determine TA-C3 to BS2. This transmission may be performed by an inter-base station exchange (Xn link).

[0261] Figure 4 The method described in describes determining a value from a calculation based on a user equipment specific parameter related to the location of the user equipment obtained by a first base station (BS2 in the context of UE2). The network entity that implements the determination of the TA-C3 to be used may be BS2 or BS3 (any network entity other than the user equipment). However, if BS3 is the network entity that determines the TA-C3 to be used for UE2, BS2 may send the location of the user equipment UE2 (or any corresponding information), based on which BS3 may determine the TA-C3. Conversely, if BS2 is the network entity that determines the TA-C3 to be used for UE2, BS3 may send additional information (as described above) of the user equipment UE2 (or any corresponding information), based on which BS2 may determine the TA-C3. In both cases, these transmissions may be performed via inter-base station exchanges (Xn links).

[0262] In step S24, if necessary, the network entity that determines the value to be used by the user equipment in the second cell ultimately sends data related to the timing advance of the user equipment in the second cell to the second base station to which the user equipment will be connected and to the user equipment (in particular if the user equipment cannot determine the value to be used in the second cell by itself) via other base stations.

[0263] Therefore, if the network entity that determines the value is the second base station (BS3 in the context of UE2) and if the TA-C3 to be used is different from TA-C2 and if the switching mode is FulM, the second base station (BS3) may send 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 send data related to the timing advance of the user equipment in the second cell to the user equipment (UE2).

[0264] The data related to the timing advance of the user equipment in the second cell sent by the first base station may include:

[0265] - data corresponding to the TA-C3 to be used, e.g. BS2 may send TA-C3 or any coded version representing TA-C3;

[0266] - data corresponding to the offset relative to TA-C2;

[0267] - Data corresponding to the offset relative to the common value.

[0268] Based on the data related to the timing advance received from the first base station, the user equipment determines a timing advance value to be used in the second cell (TA-C3).

[0269] If the TA-C3 to be used is different from TA-C2 and if the switching mode is SimM, the second base station (BS3) may send 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 send the 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 informing the user equipment that the timing advance value will have to be updated. Since the switching mode is SimM, the user equipment UE2 will perform a standard handover between BS2 and BS3, during which UE2 will acquire the TA-C3 to be used.

[0270] 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 (which is the case with UE1) and if the switching mode is FulM or SimM, the second base station (BS2 in the context of UE1) may send data related to the timing advance of the user equipment in the second cell to the first base station (BS1 in the context of UE1).

[0271] Depending on the configuration, the first base station sends or does not send data related to the timing advance of the user equipment in the second cell to the user equipment. However, in both cases, based on the data related to the timing advance in the second cell received from the first base station or based on the user equipment not receiving any data related to the timing advance in the second cell, the user equipment sets the timing advance value to be used in the second cell C2 to, for example, the last timing advance value used in the first cell C1.

[0272] As previously mentioned, the data related to the timing advance of the user equipment in the second cell sent to the user equipment by the first base station (enabling the user equipment to determine the value to be used in the second cell) may be different from or the same as the data related to the timing advance of the user equipment in the second cell sent to the first base station by the second base station (enabling the first base station to generate data related to the timing advance of the user equipment in the second cell that is sent to the user equipment).

[0273] If the network entity that determines the value is the first base station (BS2 in the context of UE2) and if the TA-C3 to be used is different from TA-C2 and if the switching mode is FulM, the first base station (BS2) may directly send data related to the timing advance of the user equipment in the second cell to the user equipment (UE2). In addition, the first base station (BS2) may directly send data related to the timing advance of the user equipment in the second cell to the user equipment (UE2).

[0274] The data related to the timing advance of the user equipment in the second cell sent by the first base station may include:

[0275] - data corresponding to the TA-C3 to be used, e.g. BS2 may send TA-C3 or any coded version representing TA-C3;

[0276] - data corresponding to the offset relative to TA-C2;

[0277] - Data corresponding to the offset relative to the common value.

[0278] Based on the data related to the timing advance received from the first base station, the user equipment determines a timing advance value to be used in the second cell (TA-C3).

[0279] Based on the data related to the timing advance received from the first base station, the second base station determines a timing advance value to be used in the second cell (TA-C3).

[0280] If the TA-C3 to be used is different from TA-C2 and if the switching mode is SimM, the first base station (BS2) may directly send 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 informing the user equipment that the timing advance value will have to be updated. Since the switching mode is SimM, the user equipment UE2 will perform a standard handover between BS2 and BS3, during which UE2 will acquire the TA-C3 to be used.

[0281] In addition, the first base station (BS2) may send data related to the timing advance of the user equipment in the second cell to the second base station (BS3). Based on the data related to 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, during which UE2 will acquire TA-C3 to be used.

[0282] 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 (which is the case for UE1) and if the switching mode is FulM or SimM, the first base station (BS1 in the context of UE1) may or may not send data related to the timing advance of the user equipment in the second cell to the user equipment according to the configuration. However, in both cases, the user equipment sets the timing advance value to be used in the second cell C2 to, for example, the last 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 the user equipment UE1 has not received any data related to the timing advance in the second cell.

[0283] In addition, the first base station BS1 may send data related to the timing advance of the user equipment in the second cell to the second base station (BS2 in the context of UE1).

[0284] Based on the data related to the timing advance received from the first base station, the second base station determines a value to be used as the timing advance for the user equipment in the second cell.

[0285] As previously mentioned, the data related to the timing advance of the user equipment in the second cell sent by the first base station to the user equipment (enabling the user equipment to determine the value to be used in the second cell) may be different from or the same as the data related to the timing advance of the user equipment in the second cell sent by the first base station to the second base station (enabling the second base station to determine the value to be used in the second cell).

[0286] In step S25, the first base station and the second base station perform handover of the user equipment from the first base station to the second base station.

[0287] If the mode is SimM and if the data related to the timing advance of the user equipment UE2 in the second cell cannot determine the value of TA-C3 to be used, the handover performed from the first base station to the second base station is a standard handover.

[0288] If the mode is:

[0289] -FulM, or

[0290] -SimM and no data related to the timing advance of the user equipment in the second cell is sent to UE1 or the data related to the timing advance sent is data informing 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, then the handover according to the present invention is performed from the first base station to the second base station, that is, the second base station does not send the user equipment a handover of the value to be used as the timing advance value of the user equipment in the second cell. For example, in the context of NR, the second message of the RACH procedure sent by the second base station to connect to it will not include the timing advance value. Once the connection with the second base station is established, the second base station may continuously update the timing advance value until the user equipment leaves the second cell.

[0291] In addition, the second base station may schedule uplink resources to the user equipment using the determined timing advance value. For example, in the context of NR, the second message of the RACH procedure sent by the second base station will schedule uplink resources to the user equipment to enable the user equipment to send 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 the user equipment (which may have been compensated based on the timing advance value) (because the second base station knows the timing advance value to be used), and therefore does not perform an estimation of the timing advance based on the first message of the RACH procedure.

Claims

1. A method implemented by a user equipment for performing a handover between a first cell and a second cell in a network comprising a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to a first base station and the second cell corresponding to a second base station, at least the first cell being supported by a non-geostationary satellite of the satellite communication network, the method comprising the following steps: Before the user equipment sends a first signal to the second base station, a value to be used as a timing advance in the second cell is determined, where the value to be used as the timing advance in the second cell is determined based on: - data relating to the timing advance of the user equipment in the second cell received from a base station to which the user equipment was connected before connecting to the first base station, or - determining a value used as the timing advance in the second cell based on a value used as the timing advance in the first cell for the user equipment when no data related to the timing advance of the user equipment in the second cell is received from the first base station or from a base station to which the user equipment was connected before connecting to the first base station; Uplink transmission is performed with the second base station using a value to be used as a timing advance in the second cell.

2. The method according to claim 1, wherein: The data related to the timing advance of the user equipment in the second cell includes at least one of the following: - data relating to a value to be used as a timing advance for said user equipment in said second cell; - informing the user equipment of data that a value to be used as the timing advance of the user equipment in the second cell is different from a value to be used as the timing advance of the user equipment in the first cell; as well as - informing the user equipment of data that is the same as the value used as the timing advance of the user equipment in the first cell, to be used as the timing advance of the user equipment in the second cell.

3. The method according to claim 2, wherein: The data related to the value to be used as the timing advance of the user equipment in the second cell comprises at least one of the following: - data corresponding to the value, - data corresponding to an offset relative to a value used as a timing advance of said user equipment in said first cell; - Data corresponding to the offset relative to the common value.

4. A method according to any one of the preceding claims, wherein: The uplink transmission performed with the second base station is a first uplink transmission performed with the second base station.

5. A user equipment configured to perform a handover procedure between a first cell and a second cell in a network comprising a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to a first base station and the second cell corresponding to a second base station, at least the first cell being supported by a non-geostationary satellite of the satellite communication network, the user equipment comprising: processor; as well as A non-transitory computer-readable medium comprising instructions stored thereon that, when executed by the processor, configure the user device to: Before the user equipment sends a first signal to the second base station, a value to be used as a timing advance in the second cell is determined, where the value to be used as the timing advance in the second cell is determined based on: - data relating to the timing advance of the user equipment in the second cell received from a base station to which the user equipment was connected before connecting to the first base station, or - determining a value used as the timing advance in the second cell based on a value used as the timing advance in the first cell for the user equipment when no data related to the timing advance of the user equipment in the second cell is received from the first base station or from a base station to which the user equipment was connected before connecting to the first base station; Uplink transmission is performed with the second base station using a value to be used as a timing advance in the second cell.

6. A method for managing handover of a user equipment between a first cell and a second cell in a network comprising a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to a first base station and the second cell corresponding to a second base station, at least the first cell being supported by a non-geostationary satellite of the satellite communication network, the method comprising the following steps: determining, before the second base station receives any signal from the user equipment, a value to be used as a timing advance of the user equipment in the second cell, data related to the value of the timing advance being sent to the user equipment via a base station to which the user equipment was connected before connecting to the first base station; Uplink transmission is performed between the second base station and the user equipment using a value to be used as a timing advance of the user equipment in the second cell.

7. The method according to claim 6, 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-located, the determined value is the same as the value used as the timing advance of the user equipment in the first cell.

8. The method according to claim 6, wherein: 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 used or previously used as the timing advance of another user equipment in the second cell.

9. The method according to claim 7, wherein: 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 used or previously used as the timing advance of another user equipment in the second cell.

10. The method according to claim 8, wherein: The at least one value used or previously used as a timing advance of the other user equipment in the second cell is 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 once connected to the second cell, or - Uplink transmission between the other user equipment and the second base station before connecting to the second cell.

11. The method according to claim 9, wherein: The at least one value used or previously used as a timing advance of the other user equipment in the second cell is 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 once connected to the second cell, or - Uplink transmission between the other user equipment and the second base station before connecting to the second cell.

12. The method according to claim 8, wherein: The at least one value is associated with a timestamp corresponding to a moment in time when the at least one value is determined, and wherein a duration between the moment in time when the at least one value is determined and a value to be used as a timing advance for the user equipment in the second cell is below a predetermined threshold.

13. The method according to claim 9, wherein: The at least one value is associated with a timestamp corresponding to a moment in time when the at least one value is determined, and wherein a duration between the moment in time when the at least one value is determined and a value to be used as a timing advance for the user equipment in the second cell is below a predetermined threshold.

14. The method according to claim 10, wherein: The at least one value is associated with a timestamp corresponding to a moment in time when the at least one value is determined, and wherein a duration between the moment in time when the at least one value is determined and a value to be used as a timing advance for the user equipment in the second cell is below a predetermined threshold.

15. The method according to claim 11, wherein: The at least one value is associated with a timestamp corresponding to a moment in time when the at least one value is determined, and wherein a duration between the moment in time when the at least one value is determined and a value to be used as a timing advance for the user equipment in the second cell is below a predetermined threshold.

16. The method according to claim 8, wherein: The at least one value is associated with a geographic area, so that at the moment of determining the at least one value, the geographic area intersects with the geographic coverage of the second cell, and when uplink transmission between the second base station and the user equipment is performed, the geographic area intersects with the geographic coverage of the second cell.

17. The method according to claim 9, wherein: The at least one value is associated with a geographic area, so that at the moment of determining the at least one value, the geographic area intersects with the geographic coverage of the second cell, and when uplink transmission between the second base station and the user equipment is performed, the geographic area intersects with the geographic coverage of the second cell.

18. The method according to claim 10, wherein: The at least one value is associated with a geographic area, so that at the moment of determining the at least one value, the geographic area intersects with the geographic coverage of the second cell, and when uplink transmission between the second base station and the user equipment is performed, the geographic area intersects with the geographic coverage of the second cell.

19. The method according to claim 11, wherein: The at least one value is associated with a geographic area, so that at the moment of determining the at least one value, the geographic area intersects with the geographic coverage of the second cell, and when uplink transmission between the second base station and the user equipment is performed, the geographic area intersects with the geographic coverage of the second cell.

20. The method according to any one of claims 6 to 19, wherein: A value to be used as the timing advance of the user equipment in the second cell is determined by the second base station.

21. The method according to claim 20, further comprising the steps of: Data related to the timing advance of the user equipment in the second cell are sent by the second base station to the first base station or to a base station to which the user equipment is connected or to be connected before connecting to the first base station, and the data related to the timing advance of the user equipment in the second cell corresponds to a value determined by the second base station to be used as the timing advance of the user equipment in the second cell.

22. The method according to any one of claims 6 to 19, wherein: The value to be used as the timing advance of the user equipment in the second cell is determined based at least on the value used as the timing advance of the user equipment in the first cell.

23. The method according to claim 22, wherein: A value to be used as the timing advance of the user equipment in the second cell is determined based on at least: - used as a minimum value of the timing advance of the user equipment in the first cell, and / or - a center position of a second beam coverage area relative to a center position of a first beam coverage area, the first beam being used by the first base station for communicating with the user equipment and the second beam being used by the second base station for performing uplink transmissions between the second base station and the user equipment; and / or - the location of the geographical coverage of said first cell, and / or - the location of the geographical coverage of the second cell, and / or - evolution of a value used as timing advance of said user equipment in said first cell; and / or - 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 handover to connect to the first base station or at a given time before the user equipment performs handover to connect to the second base station; and / or - Satellite movement direction.

24. The method according to claim 22, wherein: A value to be used as the 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.

25. The method according to claim 23, wherein: A value to be used as the 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.

26. The method according to any one of claims 6 to 19, further comprising the steps of: Data related to the timing advance of the user equipment in the second cell corresponding to the determined value is transmitted to the user equipment from the first base station or from a base station to which the user equipment was connected before being connected to the first base station.

27. The method according to claim 20, further comprising the steps of: Data related to the timing advance of the user equipment in the second cell corresponding to the determined value is transmitted to the user equipment from the first base station or from a base station to which the user equipment was connected before being connected to the first base station.

28. The method according to claim 21, further comprising the steps of: Data related to the timing advance of the user equipment in the second cell corresponding to the determined value is transmitted to the user equipment from the first base station or from a base station to which the user equipment was connected before being connected to the first base station.

29. The method according to claim 22, further comprising the steps of: Data related to the timing advance of the user equipment in the second cell corresponding to the determined value is transmitted to the user equipment from the first base station or from a base station to which the user equipment was connected before being connected to the first base station.

30. The method according to claim 23, further comprising the steps of: Data related to the timing advance of the user equipment in the second cell corresponding to the determined value is transmitted to the user equipment from the first base station or from a base station to which the user equipment was connected before being connected to the first base station.

31. The method according to claim 24, further comprising the steps of: Data related to the timing advance of the user equipment in the second cell corresponding to the determined value is transmitted to the user equipment from the first base station or from a base station to which the user equipment was connected before being connected to the first base station.

32. The method according to claim 25, further comprising the steps of: Data related to the timing advance of the user equipment in the second cell corresponding to the determined value is transmitted to the user equipment from the first base station or from a base station to which the user equipment was connected before being connected to the first base station.

33. A second base station configured to manage handover of a user equipment between a first cell and a second cell in a network comprising a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to a first base station and the second cell corresponding to the second base station, at least the first cell being supported by a non-geostationary satellite of the satellite communication network, the second base station comprising: processor; as well as a non-transitory computer-readable medium comprising instructions stored thereon that, when executed by the processor, configure the second base station to: - 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 from the user equipment; - performing uplink transmission between the second base station and the user equipment using a value to be used as a timing advance of the user equipment in the second cell, 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-located, the determined value is the same as the value used as the timing advance of the user equipment in the first cell.

34. A second base station configured to manage handover of a user equipment between a first cell and a second cell in a network comprising a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to a first base station and the second cell corresponding to the second base station, at least the first cell being supported by a non-geostationary satellite of the satellite communication network, the second base station comprising: processor; as well as a non-transitory computer-readable medium comprising instructions stored thereon that, when executed by the processor, configure the second base station to: - 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 from the user equipment; - performing uplink transmission between the second base station and the user equipment using a value to be used as a timing advance of the user equipment in the second cell, The value to be used as the timing advance of the user equipment in the second cell is determined based at least on the value used as the timing advance of the user equipment in the first cell.

35. A method for managing handover of a user equipment between a first cell and a second cell in a network comprising a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to a first base station and the second cell corresponding to a second base station, at least the first cell being supported by a non-geostationary satellite of the satellite communication network, the method comprising the following steps: determining, by the first base station, 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 from the user equipment, the first base station sends to the second base station and the user equipment a value to be used as a timing advance of the user equipment in the second cell.

36. A first base station configured to manage handover of a user equipment between a first cell and a second cell in a network comprising a satellite communication network, the first cell and the second cell being supported by one or more satellites of the satellite communication network, the first cell corresponding to the first base station and the second cell corresponding to a second base station, at least the first cell being supported by a non-geostationary satellite of the satellite communication network, the first base station comprising: processor; as well as a non-transitory computer-readable medium comprising instructions stored thereon that, when executed by the processor, configure the first base station to: - 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 from the user equipment, sending to the second base station and the user equipment a value to be used as the timing advance of the user equipment in the second cell.

37. A non-transitory computer readable medium comprising instructions stored thereon, which when executed by a processor perform the method of any one of claims 1 to 4, 6 to 32 and 35.

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