Patent Description:
The present disclosure generally relates to mobile communication field, and more particularly, to a conditional handover method and apparatus.

In a mobile communication system, if a terminal has any one of an integrity check failure, a Radio Resource Control (RRC) connection reconfiguration failure, a primary cell group synchronization failure, a handover failure and a radio link failure, an RRC re-establishment procedure is triggered for the terminal. During the RRC re-establishment procedure, it may fail as a target base station does not have context information of the terminal. In addition, the base station also performs access control on the terminal performing the RRC re-establishment procedure, and may refuse an access of the terminal, which further increases possibility of an RRC re-establishment failure.

The document "<NPL>) discloses conditional handover. NR should offer the possibility to associate the HO command (RRCConnectionReconfiguration with mobilityControllnfo) with a condition. As soon as the UE determines the condition to be fulfilled, it executes the handover in accordance with the handover command. Such a condition could, e.g., be that the UE detects out-of-synch for a configurable amount of time after sending the measurement report (same principle as T312 timer in LTE). Another example could be that the quality of the mobility RS (MRS) of the target cell or beam becomes X dB stronger than the mobility RS (MRS) of the serving cell.

The document "<NPL>) discloses conditional handover in NR. The source gNB may be unaware of the conditional handover execution, which could result in radio resource waste and larger interruption time. Proposal <NUM>: A timer associated with the conditional handover command can be configured to the UE. Proposal <NUM>: Explicit signalling from the UE can be used to indicate the execution or expiration of the conditional handover command.

Therefore, a mechanism is needed to enable the terminal to quickly recovery a connection after the above connection failure occurs.

The invention is set out in the appended set of independent claims.

In an embodiment of the present disclosure, a conditional handover method is provided, including: receiving a measurement report and transmitting a handover preparation instruction to a neighboring base station; and transmitting a conditional handover command to a terminal, wherein the conditional handover command is configured to enable the terminal to perform a handover procedure in a target cell or an RRC re-establishment procedure in a case of a connection failure, wherein the conditional handover command includes a first signal condition, and the first signal condition includes signal quality of a neighboring cell or a signal quality difference between the neighboring cell and a source cell.

Optionally, the conditional handover command further includes a resource reservation condition, and the resource reservation condition includes at least one of a first timer and a second timer, wherein if the resource reservation condition includes the first timer, the resource reservation condition is that the first timer does not exceed a first preset time threshold; if the resource reservation condition only includes the second timer, the resource reservation condition is that the second timer does not exceed a second preset time threshold; or if the resource reservation condition includes the first timer and the second timer, the terminal uses one of the first and second timers, wherein the first timer includes a valid period for allowing the terminal to perform a conditional handover, and the second timer includes a valid period for a dedicated random access resource for the conditional handover.

Optionally, the first signal condition includes that the signal quality of the neighboring cell exceeds a first threshold, or the signal quality difference between the neighboring cell and the source cell is greater than a second threshold.

Optionally, the conditional handover command further includes a second signal condition, and the second signal condition includes that the signal quality of the neighboring cell exceeds a third threshold, or the signal quality difference between the neighboring cell and the source cell is greater than a fourth threshold, wherein the third threshold is less than the first threshold, and the fourth threshold is less than the second threshold.

In all embodiments of the present invention, the conditional handover command further includes indication information for indicating whether the handover procedure can be initiated when the connection failure occurs, wherein if the indication information indicates that the handover procedure can be initiated, the handover procedure is performed, or if the indication information indicates that the handover procedure cannot be initiated, the RRC re-establishment procedure is performed.

Optionally, the target cell is a cell with the highest priority among a plurality of neighboring cells.

Optionally, for each of the plurality of neighboring cells, a priority of the cell is indicated by the conditional handover command, or determined based on a measurement result of the terminal on the cell.

In an embodiment of the present disclosure, a conditional handover method is provided, including: receiving a handover preparation instruction; performing handover preparation based on the handover preparation instruction; and receiving a handover request from a terminal, or performing an RRC re-establishment procedure for the terminal.

In an embodiment of the present disclosure, a conditional handover method is provided, including: transmitting a measurement report to a source base station; receiving a conditional handover command from the source base station; and when a connection failure occurs, performing a handover procedure in a target cell or an RRC re-establishment procedure, wherein the conditional handover command includes a first signal condition, and the first signal condition includes signal quality of a neighboring cell or a signal quality difference between the neighboring cell and a source cell.

Optionally, when the connection failure occurs, if the first signal condition is met, the handover procedure is performed in the target cell; or if the first signal condition is not met, the RRC re-establishment procedure is performed.

Optionally, the conditional handover command further includes a second signal condition, the second signal condition includes signal quality of the target cell or a signal quality difference between the source cell and the target cell, and a satisfaction standard of the second signal condition is lower than a satisfaction standard of the first signal condition, wherein when the connection failure occurs, if the second signal condition is met, the handover procedure is performed in the target cell; or if the second signal condition is not met, the RRC re-establishment procedure is performed.

Optionally, the conditional handover command further includes a resource reservation condition, and the resource reservation condition includes at least one of a first timer and a second timer, wherein if the resource reservation condition includes the first timer, the resource reservation condition is that the first timer does not exceed a first preset time threshold; if the resource reservation condition only includes the second timer, the resource reservation condition is that the second timer does not exceed a second preset time threshold; or if the resource reservation condition includes the first timer and the second timer, one of the first and second timers is used, wherein the first timer includes a valid period for allowing performing a conditional handover, and the second timer includes a valid period for a dedicated random access resource for the conditional handover.

Optionally, when the connection failure occurs, if the resource reservation condition is met, the handover procedure is performed in the target cell; if the resource reservation condition is not met, the RRC re-establishment procedure is performed.

Optionally, when the connection failure occurs, if the first signal condition and the resource reservation condition are met, the handover procedure is performed in the target cell; or if the first signal condition or the resource reservation condition is not met, the RRC re-establishment procedure is performed.

Optionally, the conditional handover command further includes a second signal condition, the second signal condition includes signal quality of the target cell or a signal quality difference between the source cell and the target cell, and a satisfaction standard of the second signal condition is lower than a satisfaction standard of the first signal condition, wherein when the connection failure occurs, if the second signal condition and the resource reservation condition are met, the handover procedure is performed in the target cell; or if the second signal condition or the resource reservation condition is not met, the RRC re-establishment procedure is performed.

Optionally, the connection failure includes a radio link failure.

Optionally, the target cell is a cell with the highest priority among a plurality of neighboring cells, and for each of the plurality of neighboring cells, a priority of the cell is indicated by the conditional handover command, or determined based on a measurement result on the cell.

Optionally, performing the handover procedure in the target cell includes: selecting the one with the highest priority from the plurality of neighboring cells as the target cell to perform the handover procedure.

Optionally, performing the RRC re-establishment procedure includes: selecting the one with the highest priority from the plurality of neighboring cells as the target cell to perform the RRC re-establishment procedure.

In an embodiment of the present disclosure, a conditional handover apparatus on a source base station side including a memory and a processor, wherein the memory has computer instructions stored therein, and when the processor executes the computer instructions, the above conditional handover method on the source base station side is performed.

In an embodiment of the present disclosure, a conditional handover apparatus on a target base station side including a memory and a processor, wherein the memory has computer instructions stored therein, and when the processor executes the computer instructions, the above conditional handover method on the target base station side is performed.

In an embodiment of the present disclosure, a conditional handover apparatus on a terminal side including a memory and a processor, wherein the memory has computer instructions stored therein, and when the processor executes the computer instructions, the above conditional handover method on the terminal side is performed.

In the embodiments of the present disclosure, a terminal may initiate a handover procedure in a case of a connection failure, thereby increasing a speed of connection recovery after the connection failure, increasing a success rate of connection establishment, reducing interruption of data transmission, and improving user experience.

Further, the terminal performs an RRC re-establishment procedure when the handover procedure cannot be triggered or fails, thereby avoiding a connection failure, improving robustness of a connection between the terminal and a base station, guaranteeing transmission of user data, and improving user experience.

The present disclosure may be applied to <NUM> (Fifth Generation) communication systems, <NUM> or <NUM> communication systems, or various subsequently evolutionary communication systems, such as <NUM> or <NUM>.

Referring to <FIG> is a flow chart of a conditional handover method on a source base station side according to an embodiment.

In S11, a measurement report is received, and a handover preparation instruction is transmitted to a target base station.

In some embodiments, the source base station receives the measurement report from a terminal, and transmits a handover preparation instruction to a base station of each neighboring cell. The measurement report may include signal strength of each neighboring cell detected by the terminal, where the target cell is one neighboring cell. The measurement report may further include signal strength of a serving cell. The signal strength may be in the form of Reference Signal Receiving Power (RSRP), Reference Signal Receiving Quality (RSRQ), or Signal to Interference plus Noise Ratio (SINR).

In S12, a conditional handover command is transmitted to a terminal, where the conditional handover command is configured to enable the terminal to perform a handover procedure in a target cell or an RRC re-establishment procedure in a case of a connection failure.

In some embodiments, the conditional handover command may be carried in an RRC message, including but not limited to an RRC reconfiguration message.

In some embodiments, in the case of the connection failure, the terminal selects the target cell from a plurality of neighboring cells to perform the handover procedure or the RRC re-establishment procedure.

In some embodiments, the conditional handover command includes a first signal condition, where the first signal condition includes signal quality of a neighboring cell or a signal quality difference between the neighboring cell and a source cell.

In some embodiments, the conditional handover command further includes a resource reservation condition, and the resource reservation condition includes at least one of a first timer and a second timer.

In some embodiments, if the resource reservation condition includes the first timer, that is, the resource reservation condition only includes the first timer, or the resource reservation condition includes the first timer and the second timer, the resource reservation condition is that the first timer does not exceed a first preset time threshold, where the first preset time threshold is a valid period for allowing the terminal to perform a conditional handover.

If the resource reservation condition only includes the second timer, the resource reservation condition is that the second timer does not exceed a second preset time threshold, where the second preset time threshold is a valid period for a dedicated random access resource for the conditional handover. The first preset time threshold and the second preset time threshold may be configured by the base station.

If the resource reservation condition includes the first timer and the second timer, the terminal uses one of the first and second timers. One possible rule is that the base station instructs the terminal to use one of the first timer and the second timer through signaling, and another possible rule is that the terminal uses one of the first timer and the second timer which has a longer duration. In some embodiments, when the terminal receives the conditional handover command, the first timer and the second timer start timing.

With the above configuration, it is ensured that when the terminal performs a random access procedure (i.e., the handover procedure) to the target cell, there are random access resources in the target cell for the terminal to use, thereby improving a success rate of random access.

In some embodiments, the first signal condition includes that the signal quality of the neighboring cell exceeds a first threshold or the signal quality difference between the neighboring cell and the source cell is greater than a second threshold. The first threshold and the second threshold are set by the source base station. In some embodiments, if RSRP is adopted, a range of the first threshold may be -144dBm to -44dBm. In some embodiments, the range of the first threshold may be -144dBm to 44dBm. A range of the second threshold may be 0dB to 100dB.

In some embodiments, the conditional handover command further includes a second signal condition, and the second signal condition includes the signal quality of the neighboring cell exceeds a third threshold or the signal quality difference between the neighboring cell and the source cell is greater than a fourth threshold. The third threshold is less than the first threshold, and the fourth threshold is less than the second threshold. The third threshold and the fourth threshold may be set in absolute values respectively, or may be set in a form of offsets of the first threshold and the second threshold respectively.

By setting the second signal condition with lower requirements, it is possible to increase possibility of handover to the target cell when the terminal fails to connect to the source cell, thereby increasing a speed of connection recovery and a success rate of connection establishment, reducing interruption of data transmission, and improving user experience.

In all embodiments of the present invention, the conditional handover command further includes indication information for indicating whether the terminal can initiate the handover procedure when the connection failure occurs. If the indication information indicates that the terminal can initiate the handover procedure, the handover procedure is performed, or if the indication information indicates that the terminal cannot initiate the handover procedure, the RRC re-establishment procedure is performed.

By setting the indication information in the conditional handover command, it is possible to decide whether to use the conditional handover method provided by the embodiments of the present disclosure according to different scenarios, so as to improve flexibility of systems.

The handover procedure means that the terminal uses a random access resource in the handover command to initiate random access in the target cell, so as to realize a handover from the source cell to the target cell.

In some embodiments, the target cell is a cell with the highest priority among a plurality of neighboring cells.

In some embodiments, for each of the plurality of neighboring cells, a priority of the cell may be indicated by the conditional handover command, or determined based on a measurement result of the terminal on the cell. The terminal may select one of the plurality of neighboring cells as the target cell for handover based on the priority of each cell, thereby improving handover performance.

In some embodiments, the priority may be indicated by the source base station through the conditional handover command. The priority may include the priority of the target cell and the priority of a frequency where the target cell is located. The priority of the target cell may be expressed by a numerical value, for example, <NUM>, <NUM>, <NUM>,. , <NUM>, where <NUM> represents the highest priority, and <NUM> represents the lowest priority. The priority of the frequency of the cell may also be represented by a numerical value, for example, <NUM>, <NUM>, <NUM>,. , <NUM>, where <NUM> represents the highest priority, and <NUM> represents the lowest priority.

In some embodiments, the priority of the cell may be determined based on the measurement result on the cell by the terminal. That is, the source base station does not need to indicate the priority of each neighboring cell through the conditional handover command, but determines the priority of each neighboring cell in a predetermined manner.

In some embodiments, the priority of each neighboring cell may be determined based on signal quality of the neighboring cell. For example, a neighboring cell with higher absolute signal quality has a higher priority, and a neighboring cell with lower absolute signal quality has a lower priority.

In some embodiments, the priority of each neighboring cell may be determined based on a difference between the signal quality of the neighboring cell and the first threshold. For example, the neighboring cell with the smallest difference between the signal quality and the first threshold has the highest priority, and the neighboring cell with the largest difference between the signal quality and the first threshold has the lowest priority.

In some embodiments, the priority of each neighboring cell may be determined based on the number of beams exceeding a certain signal quality threshold. For example, the neighboring cell with the largest number of beams exceeding the certain signal quality threshold has the highest priority, and the adjacent cell with the smallest number of beams exceeding the certain signal quality threshold has the lowest priority. The signal quality threshold may be a signal quality threshold corresponding to a handover trigger condition, or may be another signal quality threshold configured by the network, for example, a signal quality threshold defined by a certain measurement event. In some embodiments, if the number of beams exceeding the signal quality threshold in cell A is <NUM>, and the number of beams exceeding the signal quality threshold in cell B is <NUM>, the priority of cell B is higher than that of cell B.

In some embodiments, the priority of each neighboring cell may be determined based on a remaining duration of a timer corresponding to the neighboring cell, and the timer may be the first timer or the second timer. For example, among the neighboring cells, the neighboring cell with the longest remaining time of the corresponding timer has the highest priority, and the neighboring cell with the shortest remaining time of the corresponding timer has the lowest priority. Information about the first timer and the second timer has been described above, and is not repeated here.

<FIG> is a flow chart of a conditional handover method on a target base station side according to an embodiment. The conditional handover method on the target base station side includes S21, S22 and S23.

In S21, a handover preparation instruction is received.

In some embodiments, each neighboring base station receives a handover preparation instruction from a source base station.

In S22, handover preparation is performed based on the handover preparation instruction.

It should be noted that the handover preparation of each neighboring base station includes preparation for resources required by the terminal for handover in the target base station, which may specifically include random access resources required by the terminal for a handover procedure in the target cell. After the handover preparation is completed, handover preparation acknowledgement information is transmitted to the source base station.

In S23, a handover request is received from a terminal, or an RRC re-establishment procedure is performed for the terminal.

In some embodiments, when a connection between the terminal and the source base station fails, a cell with the highest priority among neighboring cells (i. e;, the target cell) receives the handover request from the terminal, or performs the RRC re-establishment procedure with the terminal.

<FIG> is a flow chart of a conditional handover method on a terminal side according to an embodiment.

In S31, a measurement report is transmitted to a source base station.

Specifically, the measurement report may include signal strength of each neighboring cell detected by the terminal.

In S32, a conditional handover command is received from the source base station.

In some embodiments, the conditional handover command includes a first signal condition, and the first signal condition includes signal quality of a neighboring cell or a signal quality difference between the neighboring cell and a source cell. Before a connection failure, if the terminal meets the first signal condition, the terminal performs a handover procedure.

In S33, when a connection failure occurs, a handover procedure in the target cell or an RRC re-establishment procedure is performed.

In some embodiments, the conditional handover command includes the first signal condition, and when the connection failure occurs, the terminal performs the handover procedure in the target cell.

In some embodiments, the conditional handover command includes the first signal condition. When the connection failure occurs, if the first signal condition is met, the terminal performs the handover procedure in the target cell; if the first signal condition is not met, the terminal performs the RRC re-establishment procedure. The RRC re-establishment procedure includes that the terminal transmits an RRC Connection Reestablishment Request message to the base station, and the base station determines whether to reestablish an RRC connection with the terminal upon reception of the RRC Connection Reestablishment Request message.

In some embodiments, the conditional handover command further includes a second signal condition, the second signal condition includes signal quality of the target cell or a signal quality difference between the source cell and the target cell, and a satisfaction standard of the second signal condition is lower than a satisfaction standard of the first signal condition,.

In some embodiments, the conditional handover command includes the first signal condition and the second signal condition. When the connection failure between the terminal and the source base station occurs, if the second signal condition is met, the terminal performs the handover procedure in the target cell; or if the second signal condition is not met, the RRC re-establishment procedure is performed.

In some embodiments, the conditional handover command further includes a resource reservation condition, and the resource reservation condition includes at least one of a first timer and a second timer. If the resource reservation condition includes the first timer, the resource reservation condition is that the first timer does not exceed a first preset time threshold; if the resource reservation condition only includes the second timer, the resource reservation condition is that the second timer does not exceed a second preset time threshold; or if the resource reservation condition comprises the first timer and the second timer, one of the first and second timers is used by the terminal. The first timer includes a valid period for allowing performing a conditional handover, and the second timer includes a valid period for a dedicated random access resource for the conditional handover.

In some embodiments, if the resource reservation condition includes the first timer and the second timer, the base station may instruct the terminal to use one of the first timer and the second timer through signaling. Alternatively, one of the first timer and the second timer which has a longer duration may be used.

In some embodiments, the conditional handover command includes the first signal condition and the resource reservation condition. When the connection failure occurs, if the resource reservation condition is met, the terminal performs the handover procedure in the target cell; or if the resource reservation condition is not met, the RRC re-establishment procedure is performed.

In some embodiments, the conditional handover command includes the first signal condition and the resource reservation condition. When the connection failure occurs, if the first signal condition and the resource reservation condition are met, the terminal performs the handover procedure in the target cell; or if the first signal condition or the resource reservation condition is not met, the RRC re-establishment procedure is performed.

In some embodiments, the conditional handover command includes the first signal condition, the second signal condition and the resource reservation condition. When the connection failure occurs, if the second signal condition and the resource reservation condition are met, the terminal performs the handover procedure in the target cell; or if the second signal condition or the resource reservation condition is not met, the RRC re-establishment procedure is performed.

In the above six cases, if the terminal fails in the handover procedure in the target cell, the RRC re-establishment procedure is performed.

In some embodiments, the first signal condition includes that the signal quality of the neighboring cell exceeds a first threshold or the signal quality difference between the neighboring cell and the source cell is greater than a second threshold. The first threshold and the second threshold are set by the base station. In some embodiments, if RSRP is adopted, a range of the first threshold may be -144dBm to -44dBm. In some embodiments, the range of the first threshold may be -144dBm to 44dBm. A range of the second threshold may be 0dB to 100dB.

In some embodiments, the second signal condition includes the signal quality of the neighboring cell exceeds a third threshold or the signal quality difference between the neighboring cell and the source cell is greater than a fourth threshold. The third threshold is less than the first threshold, and the fourth threshold is less than the second threshold. The third threshold and the fourth threshold may be set in absolute values respectively, or may be set in a form of offsets of the first threshold and the second threshold respectively.

In some embodiments, the connection failure merely includes a radio link failure. In some embodiments, the connection failure may be any connection failure, including but not limited to an integrity check failure, an RRC connection reconfiguration failure, a primary cell group synchronization reconfiguration failure and a radio link failure.

The conditional handover command further includes indication information for indicating whether the terminal can initiate the handover procedure when the connection failure occurs. If the indication information indicates that the terminal can initiate the handover procedure, the handover procedure is performed, or if the indication information indicates that the terminal cannot initiate the handover procedure, the RRC re-establishment procedure is performed.

Therefore, if the indication information indicates that the terminal can initiate the handover procedure, when the terminal fails to connect with the source cell, the solution proposed in the embodiment of the present disclosure is adopted to decide whether to perform the handover procedure. If the indication information indicates that the terminal cannot initiate the handover procedure, when the connection between the terminal and the source cell fails, the terminal directly performs the RRC re-establishment procedure.

In some embodiments, the target cell is a cell with the highest priority among a plurality of neighboring cells, and the priority is indicated by the conditional handover command, or determined based on a measurement result on the cell.

In some embodiments, performing the handover procedure in the target cell includes: selecting the one with the highest priority from the plurality of neighboring cells as the target cell to perform the handover procedure.

In some embodiments, performing the RRC re-establishment procedure includes: selecting the one with the highest priority from the plurality of neighboring cells as the target cell to perform the RRC re-establishment procedure. That is, , the priority of each neighboring cell is also considered in the RRC re-establishment procedure.

In some embodiments, for each of the plurality of neighboring cells, the priority of the cell is indicated by the conditional handover command, or determined based on a measurement result of the terminal on the cell.

In some embodiments, the priority may be indicated by the source base station through the conditional handover command, including a priority of the target cell and a priority of a frequency where the target cell is located. Therefore, the terminal may select the neighbor cell with the highest priority as the target cell for the handover procedure based on the priority of the target cell and the priority of the frequency where the target cell is located.

In some embodiments, the priority may be determined based on the measurement result of the terminal on the cell. That is to say, the source base station does not need to indicate the priority of each neighboring cell through the conditional handover command, but determines the priority of each neighboring cell through a predetermined manner. Specifically, the terminal may determine the priority of each neighboring cell based on the signal quality of the neighboring cell, the difference between the signal quality of the neighboring cell and the first threshold, the number of beams exceeding the certain signal quality threshold, or a remaining time of the timer corresponding to the neighboring cell.

Referring to <FIG> is a signaling interaction diagram of a conditional handover method according to an embodiment.

In the embodiment as shown in <FIG>, base station <NUM> is a source base station, and base station <NUM> and base station <NUM> are neighboring base stations. The terminal transmits a measurement report to base station <NUM>, and base station <NUM> transmits a handover preparation instruction to base station <NUM> and base station <NUM>, and receives handover preparation acknowledgement information from base station <NUM> and base station <NUM>. After completing the handover preparation, base station <NUM> transmits a conditional handover instruction to the terminal. The handover preparation instruction includes a first signal condition, a resource reservation condition and a second signal condition. After the terminal fails in connection, if both the base station <NUM> and the base station <NUM> meet the resource reservation condition and the second signal condition, the terminal may select the base station <NUM> with higher priority for handover based on priority information.

Referring to <FIG> is a structural diagram of a conditional handover apparatus on a source base station side according to an embodiment. The apparatus includes a memory <NUM> and a processor <NUM>. The memory <NUM> stores computer instructions that can run on the processor <NUM>. The computer instructions stored on the memory <NUM> are instructions that implement steps of the above conditional handover apparatus on the source base station side. The processor <NUM> implements the steps when executing the computer instructions. The memory <NUM> may include a Read Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk. The steps can be referred to the above descriptions, and are not described in detail here.

<FIG> is a structural diagram of a conditional handover apparatus on a target base station side according to an embodiment. The apparatus includes a memory <NUM> and a processor <NUM>. The memory <NUM> stores computer instructions that can run on the processor <NUM>. The computer instructions stored on the memory <NUM> are instructions that implement steps of the above conditional handover apparatus on the target base station side. The processor <NUM> implements the steps when executing the computer instructions. The memory <NUM> may include a ROM, a RAM, a magnetic disk or an optical disk. The steps can be referred to the above descriptions, and are not described in detail here.

<FIG> is a structural diagram of a conditional handover apparatus on a terminal side according to an embodiment. The apparatus includes a memory <NUM> and a processor <NUM>. The memory <NUM> stores computer instructions that can run on the processor <NUM>. The computer instructions stored on the memory <NUM> are instructions that implement steps of the above conditional handover apparatus on the terminal side. The processor <NUM> implements the steps when executing the computer instructions. The memory <NUM> may include a ROM, a RAM, a magnetic disk or an optical disk. The steps can be referred to the above descriptions, and are not described in detail here.

Claim 1:
A conditional handover method performed in a source base station, comprising the steps of:
receiving a measurement report from a terminal and transmitting a handover preparation instruction to a neighboring base station; and
transmitting a conditional handover command to the terminal, wherein the conditional handover command is configured to enable the terminal to perform a handover procedure in a target cell or a Radio Resource Control, RRC, re-establishment procedure in a case of a connection failure,
wherein the conditional handover command comprises a first signal condition, and the first signal condition comprises signal quality of a neighboring cell or a signal quality difference between the neighboring cell and a source cell,
characterized in that the conditional handover command further comprises indication information for indicating whether the handover procedure can be initiated when the connection failure occurs, wherein if the indication information indicates that the handover procedure can be initiated, the handover procedure is performed, wherein if the indication information indicates that the handover procedure cannot be initiated, the RRC re-establishment procedure is performed.