Conditional Handover in Non-Terrestrial Wireless Networks (NTN)

Abstract

A mechanism is provided for a user equipment (UE) to perform a handover operation from a first base station in a serving cell to a second base station in a target cell under a condition. The UE can receive a conditional handover command including a channel quality condition for the handover operation and an additional condition for the handover operation. The UE can determine an operation order between testing the channel quality condition and testing the additional condition, and further determine whether the channel quality condition or the additional condition is satisfied. In response to determining that the channel quality condition is satisfied and determining that the additional condition is satisfied, the UE can perform the handover operation to handover the UE from the first base station to the second base station.

Description

[Technical field]

[0001] The described aspects generally relate to non-terrestrial wireless networks (NTNs), including conditional handover for user equipment (UE) in NTNs. [Background technology]

[0002] The wireless communication system may include a fifth generation (5G) system, a new wireless (NR) system, a long-term evolution (LTE) system, a combination thereof, or some other wireless system. In addition, the wireless communication system may support a wide range of use cases, such as enhanced mobile broadband (eMBB), massive machine type communications (mMTC), ultra-reliable and low-latency communications (URLLC), enhanced vehicle to anything communications (eV2X), among others. Enabling support for non-terrestrial networks (NTN) has been one direction of exploration in the 3rd Generation Partnership Project (3GPP). Summary of the Invention

[0003] Some aspects of the present disclosure relate to an apparatus and method for implementing a conditional handover technique for a user equipment (UE) to perform a handover operation from a first base station in a serving cell to a second base station in a target cell. The conditional handover may be indicated by a conditional handover command including a channel quality condition for the handover operation and an additional condition for the handover operation. The UE may determine an operation order between testing the channel quality condition and testing the additional condition, and further determine whether the channel quality condition or the additional condition is satisfied. In response to determining that the channel quality condition is satisfied and determining that the additional condition is satisfied, the UE may perform a handover operation to handover the UE from the first base station to the second base station. The implemented technique may be applicable to many wireless systems, for example, wireless communication systems based on Non-Terrestrial Wireless Networks (NTN), 3rd Generation Partnership Project (3GPP) Release 15 (Rel-15), Release 16 (Rel-16), Release 17 (Rel-17), or others.

[0004] Some aspects of the disclosure relate to a UE and a method performed by the UE. The UE may perform a method for conditional handover in a wireless communication network, such as an NTN. The method may include receiving a message including a conditional handover command to perform a handover operation from a first base station in a serving cell in the NTN to a second base station in a target cell in the NTN. The conditional handover command may include a channel quality condition for the handover operation and an additional condition for the handover operation. The method further includes determining an operation order between testing the channel quality condition and testing the additional condition. Thus, the method may include performing a measurement operation to measure a quality of a channel between the UE and the second base station in the target cell to test the channel quality condition, and determining whether the channel quality condition is met based on the measurement operation. In addition, the method may include determining whether the additional condition is met. In response to determining that the channel quality condition is met and determining that the additional condition is met, the method further includes performing a handover operation to handover the UE from the first base station to the second base station.

[0005] According to some aspects, the handover operation may include various operations such as initiating a handover procedure for the UE, performing target cell tracking, and transmitting a message from the UE to a second base station in the target cell in a random access channel.

[0006] According to some aspects, in response to determining that the additional condition is not satisfied, the UE can maintain a connection on a channel between the UE and a first base station in the serving cell. In some embodiments, the UE can receive a configuration from the first base station, the configuration indicating an order of operations between testing the channel quality condition and testing the additional condition. According to some aspects, the order of operations can indicate that testing the channel quality condition is performed before testing the additional condition.

[0007] According to some aspects, the additional condition may be a time condition indicating a start time T1 and an end time T2 for performing the handover operation during a time range from T1 to T2. Thus, determining whether the additional condition is satisfied includes testing that the start time T1 is satisfied and testing that the end time T2 is not exceeded. According to some aspects, the operation order may indicate that testing the additional condition is performed before testing the channel quality condition, and performing the measurement operation includes performing the measurement operation based on the start time T1 being satisfied. In response to determining that the end time T2 has been exceeded when performing the handover operation, maintain a connection on the channel between the UE and the first base station in the serving cell or terminate the handover operation and perform a radio resource control (RRC) re-establishment.

[0008] According to some aspects, the order of operations may indicate that testing the additional condition is performed after testing the channel quality condition. Thus, the method further includes performing a handover operation to handover the UE from the first base station to the second base station based on the start time T1 being satisfied in response to determining that the channel quality condition is satisfied.

[0009] According to some aspects, the additional condition may be a distance condition indicating at least a starting distance for performing a handover operation. Furthermore, the operation order may indicate that a test of the distance condition is performed before a test of the channel quality condition. Thus, determining whether the additional condition is satisfied includes performing a distance measurement to test whether the distance condition is satisfied. In some embodiments, performing the distance measurement includes performing a distance measurement based on Global Navigation Satellite System (GNSS) information obtained in the NTN. Furthermore, performing the measurement operation includes performing the measurement operation after performing the distance measurement.

[0010] According to some aspects, the additional condition may be a distance condition indicating at least a starting distance for performing a handover operation, and the operation order may indicate that testing the additional condition is performed after testing the channel quality condition. Further, determining whether the additional condition is satisfied includes performing a distance measurement to test whether the distance condition is satisfied after performing the measurement operation.

[0011] This summary of the invention is provided merely for the purpose of illustrating some aspects to provide an understanding of the subject matter described herein. Thus, the above features are merely examples and should not be construed as narrowing the scope or spirit of the subject matter in the present disclosure. Other features, aspects, and advantages of the present disclosure will become apparent from the following detailed description, figures, and claims.

[0012] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable one skilled in the art to make and use the present disclosure. [Brief description of the drawings]

[0013] [Figure 1] 1 illustrates a non-terrestrial wireless network (NTN) including a user equipment (UE) for performing a conditional handover in accordance with certain aspects of the present disclosure.

[0014] [Diagram 2] 1 illustrates a block diagram of a UE implementing conditional handover in an NTN in accordance with certain aspects of the present disclosure.

[0015] [Diagram 3] 1 illustrates an example process performed by a UE to perform a conditional handover in an NTN, according to certain aspects of the present disclosure.

[0016] [Figure 4A]1 illustrates an example process performed by a UE to perform a conditional handover in an NTN, according to certain aspects of the present disclosure. [Figure 4B] 1 illustrates an example process performed by a UE to perform a conditional handover in an NTN, according to certain aspects of the present disclosure. [Figure 4C] 1 illustrates an example process performed by a UE to perform a conditional handover in an NTN, according to certain aspects of the present disclosure. [Figure 4D] 1 illustrates an example process performed by a UE to perform a conditional handover in an NTN, according to certain aspects of the present disclosure. [Figure 4E] 1 illustrates an example process performed by a UE to perform a conditional handover in an NTN, according to certain aspects of the present disclosure. [Figure 4F] 1 illustrates an example process performed by a UE to perform a conditional handover in an NTN, according to certain aspects of the present disclosure. [Figure 4G] 1 illustrates an example process performed by a UE to perform a conditional handover in an NTN, according to certain aspects of the present disclosure. [Figure 4H] 1 illustrates an example process performed by a UE to perform a conditional handover in an NTN, according to certain aspects of the present disclosure.

[0017] [Diagram 5] 1 is an exemplary computer system for implementing some aspects or portion(s) of the present disclosure provided herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present disclosure is described with reference to the accompanying drawings, in which like reference numbers generally indicate identical or functionally similar elements, and in which the left-most digit(s) of a reference number generally identifies the drawing in which the reference number first appears.

[0019] There are various wireless communication systems or networks. For example, a non-terrestrial wireless network (NTN) is a wireless communication system. An NTN can refer to any network that includes non-terrestrial flying objects. An NTN can include a satellite communication network, a high altitude platform system (HAPS), an air-to-ground network, a low altitude unmanned aerial vehicle (UAV, also known as a drone), or any other NTN network. Due to the relative movement of a user equipment (UE) or a satellite in an NTN, the UE may experience a Doppler frequency shift and lose synchronization with a base station. Traditionally, for wireless communication in an NTN, actions may be taken by the UE to overcome the Doppler frequency shift based on the UE's Global Navigation Satellite System (GNSS) location.

[0020] When a UE of a wireless communication system moves from one location to another, the UE may be served by different base stations, for example, a first base station, a second base station, a primary base station, a secondary base station, or a combination thereof. A procedure when the UE leaves a serving cell managed by a first base station and enters a target cell managed by a second base station may be referred to as a handover procedure or operation for handing over the UE from the first base station to the second base station. The UE may perform a measurement operation to measure a quality of a channel between the UE and the second base station in the target cell to test whether a channel quality condition for handover is met. In a normal handover operation, when the UE determines that the channel quality condition is met based on the measurement operation, the handover operation may be performed. The handover operation may include various steps or operations, such as initiating a handover procedure for the UE, performing target cell tracking, and sending a message from the UE to the second base station in the target cell in a random access channel (RACH).

[0021] In the case of a conditional handover for a UE, the UE may receive a conditional handover (CHO) command or instruction to perform a handover operation from a first base station in a serving cell to a second base station in a target cell. The command or instruction is used interchangeably in the present description. The conditional handover command may include a channel quality condition for the handover operation, similar to a normal handover command. In addition, additional conditions for the handover operation may also be included in the conditional handover command. The embodiments herein present various implementation forms of the conditional handover command.

[0022] In some embodiments, the UE may receive a message including a conditional handover command to perform a handover operation from a first base station in a serving cell to a second base station in a target cell. The conditional handover command may include a channel quality condition and an additional condition for the handover operation. The UE may determine an operation order between testing the channel quality condition and testing the additional condition. The UE may then perform a measurement operation to measure a quality of a channel between the UE and the second base station in the target cell to test the channel quality condition, and determine whether the channel quality condition is met based on the measurement operation. Furthermore, the UE may determine whether the additional condition is met. When both the channel quality condition and the additional condition are met, the UE may perform a handover operation to handover the UE from the first base station to the second base station.

[0023] 1 illustrates an NTN 100 including a UE 101 for performing a conditional handover in accordance with some aspects of the present disclosure. The NTN 100 is provided for illustrative purposes only and is not intended to limit aspects of the disclosure.

[0024] NTN 100 may include, but is not limited to, UE 101, base station 107 in serving cell 111, and base station 109 in target cell 113. One or more satellites, for example, satellite 102 and satellite 106, may communicate with base station 107 and base station 109, and may communicate with UE 101 via base station 107 or base station 109. Satellite 102 and satellite 106 may communicate with gateway 104, base station 103, and core network 105. Satellite 102 and satellite 106 may include network nodes or transceivers for wireless communication.

[0025] There may be various implementations of the NTN 100. For example, the base stations 103 and the gateway 104 may be integrated into one unit instead of being separate components. The base stations 103 and the core network 105 may implement the functions as a normal terrestrial wireless network without satellites, and the gateway 104 may implement the functions between the terrestrial wireless network and the satellite 102 or the satellite 106.

[0026] In some embodiments, the NTN 100 may have a transmission payload and the base station 103 is located on the ground. In some embodiments, the NTN 100 may have a regeneration payload when the base station 103 may be located on the satellite 102 or the satellite 106. There may be multiple satellites with on-board base stations communicating with each other, such as communication between satellite 102 and satellite 106. There may be other network entities, such as a network controller, relay stations (not shown). The NTN may be referred to as a wireless network, a wireless communication system, or some other name known to those skilled in the art. The techniques disclosed for the embodiments herein may be applicable to many other wireless communication systems or networks.

[0027] In some embodiments, the NTN 100 may be an NTN having a non-terrestrial flying object, for example, satellite 102 or satellite 106. In some embodiments, the NTN 100 may include a satellite communication network including one satellite, for example, satellite 102, a HAPS, or an air-to-ground network, or a UAV. The satellite 102 or satellite 106 may be a low earth orbit (LEO) satellite, a medium earth orbit (MEO) satellite, or a geostationary earth orbit (GEO) satellite. The NTN 100 may be a HAPS, which may be an aerial platform including aircraft, balloons, and airships. For example, the NTN 100 may include an international mobile communications base station known as a HIBS. The HIBS system may provide mobile services on the same transmission frequencies used by terrestrial mobile networks. The NTN 100 may be an air-to-ground network to provide in-flight connectivity to aircraft by utilizing ground stations that act similarly to base stations in terrestrial mobile networks. The NTN 100 may be a mobile-enabled low altitude UAV.

[0028] In some examples, the NTN 100 may be a radio system including different radio technologies, e.g., NR, LTE, 5G, any other radio technology, or a combination thereof. The NTN 100 may support a wide range of use cases, such as enhanced mobile broadband (eMBB), massive machine type communications (mMTC), ultra-reliable and low-latency communications (URLLC), and enhanced vehicle to anything communications (eV2X).

[0029] In some embodiments, satellite 102 or satellite 106 may be a GEO satellite deployed at an altitude of 35786 Km and characterized by slow movement around its orbital position relative to a point on the Earth. Compared to terrestrial cellular systems, communication networks based on GEO satellites have large propagation delays and high propagation losses that must be considered in the overall design of the satellite network. Additionally and alternatively, satellite 102 or satellite 106 may be a LEO satellite at an altitude of 300-3000 km. As a result, satellite 102 or satellite 106 may have lower propagation delays, lower propagation losses, and higher Doppler frequency shifts than GEO satellites.

[0030] According to some aspects, base station 103, base station 107, or base station 109 may be a fixed station or a mobile station. In some embodiments, base station 103 may be mounted on satellite 102 or satellite 106. Base station 103, base station 107, or base station 109 may also be referred to by other names such as a base transceiver system (BTS), an access point (AP), a transmit / receive point (TRP), an evolved Node B (eNB), a next generation Node B (gNB), a 5G Node B (NB), or other equivalent terminology.

[0031] According to some aspects, the UE 101 may be stationary or mobile. The UE 101 may be a handheld terminal or a very small satellite earth station (VSAT) equipped with a parabolic antenna and typically mounted on a building or a vehicle. The UE 101 may be a cellular phone (e.g., a smartphone), a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop, a desktop, a cordless phone, a wireless local loop station, a tablet, a camera, a gaming device, a netbook, an ultrabook, a medical device or equipment, a biosensor or device, a wearable device (smart watch, smart clothing, smart glasses, smart jewelry such as a smart wristband, a smart ring, or a smart bracelet), an entertainment device (e.g., a music or video device, or a satellite radio), a vehicle component, a smart meter, an industrial manufacturing equipment, a global positioning system device, an Internet of Things (IoT) device, a machine type communication (MTC) device, an evolved or enhanced machine type communication (eMTC) device, or any other suitable device configured to communicate over a wireless medium. For example, MTC and eMTC devices may include robots, drones, location tags, etc.

[0032] According to some aspects, due to relative movement between the UE 101 and the satellite 102 or 106, the UE 101 may experience a Doppler frequency shift. In satellite communications, the Doppler frequency shift needs to be compensated for. Dynamic Doppler compensation is used in which the frequency of the signal is gradually changed during transmission so that the satellite receives a constant frequency signal. The dynamic Doppler compensation for the dynamic Doppler frequency shift may be calculated based on the location of the UE 101, e.g., the GNSS location.

[0033] According to some aspects, the base station 107 manages the serving cell 111 and the base station 109 manages the target cell 113. In some examples, the base station 107 may be a first primary base station, the serving cell 111 may be a first primary cell (PCell), the base station 109 may be a second primary base station, and the target cell 113 may be a second PCell. In some other examples, the primary base station may be called by other names known to those skilled in the art. Initially, the UE 101 may communicate with the base station 107. When the UE 101 moves toward the target cell 113, the UE 101 may perform a handover procedure to communicate with the base station 107 to replace the base station 109. During the handover operation, the UE 101 may establish dual connectivity in the serving cell 111 to communicate with the base station 107 and in the target cell 113 to communicate with the base station 109.

[0034] According to some aspects, the UE 101 may receive a message 121 from the base station 107. The message 121 may include a conditional handover command 123 to perform a handover operation from the base station 107 in the serving cell 111 to the base station 109 in the target cell 113. The conditional handover command 123 may include a channel quality condition 125 for the handover operation and an additional condition 127 for the handover operation. Based on the conditional handover command 123, the UE 101 may determine an operation order between testing the channel quality condition 125 and testing the additional condition 127. In some embodiments, the operation order between testing the channel quality condition 125 and testing the additional condition 127 may be a sequential order in which testing the channel quality condition 125 is performed before testing the additional condition 127. In some other embodiments, testing the channel quality condition 125 may be performed in parallel with testing the additional condition 127. Thus, the operations for testing the channel quality condition 125 and the operations for testing the additional condition 127 may be performed in parallel or in a pipelined manner, as shown in Figure 4G. In some embodiments, the UE 101 may receive a configuration 129 from the base station 107, which may indicate an order of operations between testing the channel quality condition 125 and testing the additional condition 127.

[0035] According to some aspects, the UE 101 may perform a measurement operation to measure a quality of a channel between the UE 101 and the base station 109 in the target cell 113 to test the channel quality condition 125. The UE 101 may further determine whether the channel quality condition 125 is met based on the measurement operation. The UE 101 may further determine whether an additional condition 127 is met. In response to determining that the channel quality condition 125 is met and determining that the additional condition 127 is met, the UE 101 may perform a handover operation to handover the UE 101 from the base station 107 to the base station 109. According to some aspects, the handover operation may include various operations such as initiating a handover procedure for the UE 101, performing tracking of the target cell 113, and transmitting a message from the UE 101 to the base station 109 in the target cell 113 in a random access channel (RACH).

[0036] According to some aspects, in response to determining that the additional condition 127 is not satisfied, the UE 101 can maintain a connection on a channel between the UE 101 and the base station 107 in the serving cell 111. According to some aspects, the order of operations can indicate that testing the channel quality condition 125 is performed before testing the additional condition 127.

[0037] According to some aspects, the additional condition 127 may be a time condition indicating a start time T1 and an end time T2 for performing a handover operation during a time range from T1 to T2. Thus, the conditional handover may not be performed before T1, which represents the earliest time point at which the UE 101 can perform a CHO to the target cell. Similarly, the conditional handover may not be performed after T2, which represents the end of the time window. Thus, the UE 101 may determine that the additional condition 127 is satisfied when the start time T1 is satisfied. When the operation order indicates that testing the additional condition 127 is performed before testing the channel quality condition 125, the UE 101 may perform a measurement operation of a channel between the UE 101 and the base station 109 in the target cell 113 based on the start time T1 being satisfied.

[0038] According to some aspects, when the operation order indicates that testing additional condition 127 is performed after testing channel quality condition 125, in response to determining that channel quality condition 125 is satisfied, UE 101 may perform a handover operation to handover UE 101 from base station 107 to base station 109 based on start time T1 being satisfied.

[0039] According to some aspects, the additional condition 127 may be a distance condition indicating at least a starting distance for performing a handover operation. In addition, the operation order may indicate that a test of the distance condition is performed before a test of the channel quality condition 125. Thus, the UE 101 may perform a distance measurement to test whether the distance condition is met. In some embodiments, the UE 101 may perform the distance measurement based on the GNSS information. Furthermore, the UE 101 may perform a measurement operation on a channel between the UE 101 and the base station 109 after performing the distance measurement.

[0040] According to some aspects, the additional condition 127 may be a distance condition indicating at least a starting distance for performing a handover operation, and the operation order may indicate that testing the additional condition 127 is performed after testing the channel quality condition 125. Furthermore, the UE 101 may perform a distance measurement to test that the distance condition is satisfied after performing the measurement operation.

[0041] According to some aspects, the UE 101 may be implemented according to a block diagram as shown in FIG. 2. Referring to FIG. 2, the UE 101 may have an antenna panel 217 coupled to the transceiver 203 and including one or more antenna elements for forming various transmit beams, e.g., transmit beam 213, controlled by the processor 209. The transceiver 203 and the antenna panel 217 (using the transmit beam 213) may be configured to enable wireless communication in a wireless network. In particular, the transceiver 203 may include a radio frequency (RF) circuit 216, a transmit circuit 212, and a receive circuit 214. The RF circuit 216 may include multiple parallel RF chains for one or more of the transmit or receive functions, each of which is connected to one or more antenna elements of the antenna panel. In addition, the processor 209 may be communicatively coupled to the memory 201, which is further coupled to the transceiver 203. Various data may be stored in the memory 201. In some examples, the memory 201 may store the message 121, the handover command 123, the channel quality condition 125, the additional condition 127, and a configuration 129 indicating an order of operations between testing the channel quality condition 125 and testing the additional condition 127.

[0042] In some embodiments, the memory 201 may include instructions that, when executed by the processor 209, perform operations described herein, such as operations to perform a conditional handover for the UE 101. Alternatively, the processor 209 may be "hard-coded" to perform the operations described herein.

[0043] In some embodiments, the processor 209 may be configured to receive the message 121 including the conditional handover command 123 for performing a handover operation from the base station 107 in the serving cell 111 to the base station 109 in the target cell 113. The processor 209 may be further configured to determine an operation order between testing the channel quality condition 125 and testing the additional condition 127. The processor 209 may be further configured to perform a measurement operation for measuring a quality of a channel between the UE 101 and the base station 109 in the target cell 113 to test the channel quality condition 125, and determine whether the channel quality condition 125 is met based on the measurement operation. In addition, the processor 209 may be configured to determine whether the additional condition 127 is met. In response to the determination that the channel quality condition 125 is met and the determination that the additional condition 127 is met, the processor 209 may be configured to perform a handover operation for handing over the UE 101 from the base station 107 to the base station 109.

[0044] 3 illustrates an example process 300 for a UE to perform a conditional handover in an NTN in accordance with certain aspects of the present disclosure. According to certain aspects, the process 300 may be performed by a UE 101.

[0045] In 301, the UE 101 may receive a message including a conditional handover command for performing a handover operation from a first base station in a serving cell to a second base station in a target cell, where the conditional handover command includes a channel quality condition for the handover operation and an additional condition for the handover operation. For example, as shown in FIG. 1, the UE 101 may receive a message 121 including a conditional handover command 123 for performing a handover operation from a base station 107 in a serving cell 111 to a base station 109 in a target cell 113, where the conditional handover command 123 includes a channel quality condition 125 and an additional condition 127 for the handover operation.

[0046] At 303, the UE 101 may determine an operation order between testing the channel quality condition and testing the additional condition. For example, as shown in FIG. 1, the UE 101 may determine an operation order between testing the channel quality condition 125 and testing the additional condition 127.

[0047] At 305, the UE 101 may perform a measurement operation to measure a quality of a channel between the UE 101 and a second base station in the target cell to test a channel quality condition. For example, as shown in FIG. 1, the UE 101 may perform a measurement operation to measure a quality of a channel between the UE 101 and a base station 109 in the target cell 113 to test a channel quality condition 125.

[0048] At 307, the UE 101 may determine whether a channel quality condition is met based on the measurement operation. For example, as shown in FIG. 1, the UE 101 may determine whether a channel quality condition 125 is met based on the measurement operation.

[0049] At 308, the UE 101 may determine whether an additional condition is met. For example, as shown in Figure 1, the UE 101 may determine whether an additional condition 127 is met. As will be described with reference to Figures 4B-4H, in some embodiments, step 308 may be performed before step 307 such that the additional condition is determined to be met before the channel condition is determined to be met.

[0050] At 309, in response to determining that the channel quality condition is met and determining that the additional condition is met, the UE 101 may perform a handover operation to handover the UE from the first base station to the second base station. For example, as shown in FIG. 1, in response to determining that the channel quality condition 125 is met and determining that the additional condition 127 is met, the UE 101 may perform a handover operation to handover the UE 101 from base station 107 to base station 109.

[0051] 4A-4H illustrate example processes 400, 410, 420, 430, 440, 450, 460, and 470 for a conditional handover process in a wireless network or NTN in accordance with certain aspects of the disclosure. Process 400 is a partial process to illustrate operations shared among processes 410, 420, 430, 440, 450, 460, and 470. Processes 410, 420, 430, 440, 450, 460, and 470 may be examples of process 300 shown with more, less, or different details that may be performed by UE 101.

[0052] As shown in Figure 4A, process 400 includes operations shared among processes 410, 420, 430, 440, 450, 460, and 470. More specifically, only the channel quality conditions for handover operation are described in Figure 4A. Implementations of additional conditions for handover operation are not described in Figure 4A, but are described in Figures 4B-4H.

[0053] In step 1, in 401, the UE 101 receives a CHO command or a conditional handover command in a radio resource control (RRC) message; step 2: the UE decodes the CHO command included in the RRC message and starts monitoring a channel between the UE 101 and the base station 109 in the target cell 113. In step 3, the channel conditions for the channel between the UE 101 and the base station 109 in the target cell 113 may be changed, for example, the channel quality in the channel is improved. The UE 101 may not perform any operation in step 3. Instead, the UE 101 may just wait for a change in the radio channel conditions. The operations performed in 401 may be examples of the operations performed in 301.

[0054] At 405, in step 4, the UE 101 may perform cell search and measurement on the target cell 113. Various detailed steps may be performed at 405. For example, the UE 101 may perform a measurement operation to measure the quality of a channel between the UE 101 and the base station 109 in the target cell 113 to test the channel quality condition. The operation performed at 405 may be an example of the operation performed at 305.

[0055] At 407, in step 5, based on the cell measurement results, the UE 101 may determine that the quality of the channel between the UE 101 and the base station 109 is above a threshold for CHO, where the threshold may be an example of a channel quality condition 125. The operations performed at 407 may be examples of the operations performed at 307.

[0056] In 409, the UE 101 may trigger a handover operation. In particular, in step 6, the UE 101 may initiate a CHO procedure and prepare hardware and / or software for CHO. In step 7, after preparation, the UE 101 may perform physical layer time / frequency tracking and RACH preparation for the target cell 113. Then, in step 8, the UE 101 may successfully transmit a RACH to the base station 109 in the target cell 113, and the CHO is completed in the UE 101. In some embodiments, some additional steps for the UE 101 and the network should be completed for the RACH, which will not be described in detail herein. The operations performed in 409 may be examples of the operations performed in 309.

[0057] FIG. 4A also shows a timeline of conditional handover operations. CHO The timeline can be defined as the time between the end of the last Transmission Time Interval (TTI) containing an RRC message with a conditional handover command and the start of the transmission of a new uplink PRACH, which can be expressed as: D CHO =T RRC +T イベント実行 +[T 測定 ]+T CHO_実行 +T 中断 Here, T RRC is the RRC procedure delay in step 2. T イベント実行 is the delay uncertainty in step 3, T 測定 is the measured time delay in step 4 of 405. T CHO_実行 T is the time in step 6 of the UE preparation time for conditional handover. 中断 is the delay in step 7, which is the time between when the UE 101 starts to perform the conditional handover to the target cell 113 and when the UE 101 starts to transmit the new PRACH.

[0058] Process 400 implements only the channel quality condition for the conditional handover operation. The implementation of additional conditions for the handover operation is described in Figures 4B-4H by processes 410, 420, 430, 440, 450, 460, and 470. Processes 410, 420, 430, 440, 450, 460, and 470 include operations 401, 405, 407, and 409 shown in Figure 4A, but will not be repeated in the following description for brevity. The additional operations shown in Figures 4B-4H will be further described.

[0059] 4B, the process 410 may be an example of the process 300 for performing a conditional handover based on a conditional handover command including a channel quality condition and an additional condition. The additional condition of the process 410 is a time condition indicating a start time T1 and an end time T2 for performing a handover operation during a time range T1 to T2. Determining whether the additional condition is satisfied includes testing whether the start time T1 is satisfied and testing whether the end time T2 is not exceeded.

[0060] Although not shown, based on the operation in 303, the UE 101 may determine an operation order for testing the channel quality condition after testing the time condition. In operation 418, the UE 101 may determine that the start time T1 of the time condition is met and is earlier than the radio condition change at the end of step 3. Operation 418 may be an example of an operation performed in 308. Thus, the operation performed in 405, e.g., the measurement operation, may be performed based on the start time T1 being met in operation 418. The operation in 405 is performed after the start time T1 is met in operation 418. In response to determining that the end time T2 has been exceeded when performing the handover operation, maintain the connection on the channel between the UE and the first base station in the serving cell, or terminate the handover operation and perform RRC re-establishment.

[0061] 4C, the process 420 may be an example of the process 300 for performing a conditional handover based on a conditional handover command including a channel quality condition and an additional condition. The additional condition of the process 420 is a time condition indicating a start time T1 and an end time T2 for performing a handover operation during a time range T1 to T2. Determining whether the additional condition is satisfied includes testing whether the start time T1 is satisfied and testing whether the end time T2 is not exceeded.

[0062] Although not shown, based on the operation in 303, the UE 101 can determine an operation order for testing the channel quality condition after testing the time condition. In operation 428, the UE 101 can determine that the start time T1 of the time condition is met. In this case, the start time T1 is met after the time interval 421 following the end of step 3. Thus, if the channel quality is improved at the end of step 3 but the start time T1 is not yet met, the UE 101 can wait in operation 428 until the start time T1 is met after the time interval 421. The operation 428 can be an example of an operation performed in 308. The UE 101 can determine whether the start time T1 is met by a timer. Furthermore, the operation performed in 405, e.g., a measurement operation, can be performed based on the start time T1 met in operation 428. In response to the determination that the end time T2 is exceeded when performing the handover operation, the UE 101 maintains the connection on the channel between the UE and the first base station in the serving cell, or terminates the handover operation and performs RRC re-establishment.

[0063] 4D, the process 430 may be an example of the process 300 for performing a conditional handover based on a conditional handover command including a channel quality condition and an additional condition. The additional condition of the process 430 is a time condition indicating a start time T1 and an end time T2 for performing a handover operation during a time range T1 to T2. Determining whether the additional condition is satisfied includes testing whether the start time T1 is satisfied and testing whether the end time T2 is not exceeded.

[0064] Although not shown, based on the operation at 303, the UE 101 may determine an operation order for testing the channel quality condition before testing the time condition. At 436, after the RRC message is decoded at step 2, the UE 101 may start searching and measuring the channel quality for the channel between the UE 101 and the base station 109. Operation 436 may be optional. Additionally and alternatively, the UE 101 may start searching and measuring the channel quality for the channel at step 4 for the operation at 405. At 438, the UE 101 may determine that a start time T1 of the time condition is met and is earlier than the end of the operation for step 4 at 405. Operation 438 may be an example of an operation performed at 308. Thus, the operation at 405 is performed before the start time T1 is met at operation 438. In response to determining that the end time T2 has been exceeded when performing the handover operation, maintain the connection on the channel between the UE and the first base station in the serving cell or end the handover operation and perform RRC re-establishment.

[0065] 4E, the process 440 may be an example of the process 300 for performing a conditional handover based on a conditional handover command including a channel quality condition and an additional condition. The additional condition of the process 440 is a time condition indicating a start time T1 and an end time T2 for performing a handover operation during a time range T1 to T2. Determining whether the additional condition is satisfied includes testing whether the start time T1 is satisfied and testing whether the end time T2 is not exceeded.

[0066] Although not shown, based on the operations at 303, the UE 101 may determine an order of operations for testing the channel quality condition before testing the time condition. At 446, after the RRC message is decoded at step 2, the UE 101 may start searching and measuring the channel quality for the channel between the UE 101 and the base station 109. Operation 446 may be optional. Additionally and alternatively, the UE 101 may start searching and measuring the channel quality for the channel at step 4 for the operation at 405. At 448, the UE 101 may determine that a start time T1 of the time condition is met and is after the end of the operation for step 4 at 405. There is a time interval 441 between the end of the operation for step 4 at 405 and the operation at 448. Operation 448 may be an example of an operation performed at 308. Thus, the operation at 405 is performed before the start time T1 is met at operation 448. In response to determining that the end time T2 has been exceeded when performing the handover operation, either maintain the connection on the channel between the UE and the first base station in the serving cell, or terminate the handover operation and perform RRC re-establishment.

[0067] In some embodiments, the UE 101 may determine an operation order between testing the channel quality condition and testing the time condition based on a network configuration or instruction. The base station 107 may configure the operation order between testing the channel quality condition and testing the time condition. The network indication may be satellite specific. For example, when the base stations 107 and 109 are communicating with the satellite 102, a first configuration for the operation order may be used, and when the base stations 107 and 109 are communicating with the satellite 106, a second configuration for the operation order different from the first configuration may be used. In some embodiments, the configuration for the operation order may depend on whether the satellite 102 is a LEO or GEO satellite. The configuration for the operation order from the network may be conveyed in a conditional handover instruction or command, or other dedicated RRC signaling or system information (SI).

[0068] In some embodiments, if the conditional handover command includes an additional condition as a time condition indicating a start time T1 and an end time T2 for performing a handover operation during a time range T1 to T2, there may be various restrictions on the end time T2. In some embodiments, T2 may be designed to be no earlier than the timing point at which the UE 101 identifies that the target cell quality is changed at the end of step 3, or no earlier than the start of the CHO execution / preparation in step 6. If T2 does not satisfy the condition, the UE 101 may drop the conditional handover command and initiate RRC re-establishment with the base station 107. In some embodiments, the UE 101 may fall back to the channel between the UE 101 and the base station 107 in the original serving cell 111 and resume the CHO procedure.

[0069] 4F, the process 450 may be an example of the process 300 for performing a conditional handover based on a conditional handover command including a channel quality condition and an additional condition. The additional condition of the process 450 is a distance condition indicating at least a starting distance for performing a handover operation. Determining whether the additional condition is satisfied includes performing a distance measurement to test whether the distance condition is satisfied, for example, performing a distance measurement based on GNSS information obtained at the NTN.

[0070] Although not shown, based on the operation in 303, UE 101 can determine an operation order for testing the distance condition before testing the channel quality condition. In 456, after the RRC message is decoded in step 2, UE 101 can start performing distance measurement based on the GNSS information. In 458, UE 101 can determine that the distance condition is met. UE 101 determines that the distance condition is met before the operation for step 4 in 405 is terminated. Thus, UE 101 can terminate the operation for step 4 in 405 to perform a measurement operation to test whether the channel quality condition is met. UE 101 can perform the measurement operation after determining that the distance condition is met.

[0071] 4G, the process 460 may be an example of the process 300 for performing a conditional handover based on a conditional handover command including a channel quality condition and an additional condition. The additional condition of the process 460 is a distance condition indicating at least a starting distance for performing a handover operation. Determining whether the additional condition is satisfied includes performing a distance measurement to test whether the distance condition is satisfied, for example, performing a distance measurement based on GNSS information obtained at the NTN.

[0072] Although not shown, based on the operation at 303, the UE 101 may determine an operation order for testing the distance condition before testing the channel quality condition. At 466, after the RRC message is decoded in step 2, the UE 101 may start performing distance measurements based on the GNSS information. At 468, the UE 101 may determine that the distance condition is met. The UE 101 may perform a measurement operation to measure the quality of the channel between the UE in the target cell and the second base station to test the channel quality condition after the operation at 468. Additionally and alternatively, as shown in FIG. 4G, the UE 101 may perform a measurement operation to measure the quality of the channel to test the channel quality condition in parallel with performing distance measurements based on the GNSS information. In some embodiments, the UE 101 may determine that the distance condition is met at 468 after the operation for step 4 at 405 is completed. After completing operations for step 4 at 405 to determine that the channel quality condition is met, the UE 101 may wait for a time interval 461 to determine that the distance condition is met at 468.

[0073] As shown in FIG. 4H, the process 470 may be an example of the process 300 for performing a conditional handover based on a conditional handover command including a channel quality condition and an additional condition. The additional condition of the process 470 is a distance condition indicating at least a starting distance for performing a handover operation. Determining whether the additional condition is satisfied includes performing a distance measurement to test whether the distance condition is satisfied, for example, performing a distance measurement based on GNSS information obtained at the NTN.

[0074] Although not shown, based on the operations at 303, the UE 101 may determine an order of operations for testing the distance condition after testing the channel quality condition. At 476, shown as the same time instance as the operations at 407, the UE 101 may begin performing distance measurements based on the GNSS information. At 478, the UE 101 may determine that the distance condition is met. The UE 101 determines that the distance condition is met after the operations for step 4 at 405 are completed. A time interval 471 may separate the end of the operations at 407 and the operations at 478. Thus, the UE 101 may complete the operations for testing the distance condition at 478 after the time interval 471 following the operations at 407 of determining that the channel quality condition is met based on the measurement operations. After the UE 101 determines that the channel quality condition is met, it may perform distance measurements to test that the distance condition is met.

[0075] In some embodiments, the UE 101 may determine an operation order between testing the channel quality condition and testing the distance condition based on a network configuration or instruction. The base station 107 may configure the operation order between testing the channel quality condition and testing the distance condition. The network indication may be satellite specific. For example, when the base stations 107 and 109 are communicating with the satellite 102, a first configuration for the operation order may be used, and when the base stations 107 and 109 are communicating with the satellite 106, a second configuration for the operation order that is different from the first configuration may be used. In some embodiments, the configuration for the operation order may depend on whether the satellite 102 is a LEO or GEO satellite. The configuration for the operation order from the network may be conveyed in a conditional handover instruction or command, or other dedicated RRC signaling or SI.

[0076] Various aspects may be implemented using one or more computer systems, such as computer system 500 shown in FIG. 5. Computer system 500 may be any computer capable of performing the functions described herein, such as UE 101, base station 103, base station 107, or base station 109 shown in FIG. 1 and FIG. 2 for the operations described for processor 209 or process 300, process 400, process 410, or process 470 shown in FIG. 3, FIG. 4A-4H. Computer system 500 includes one or more processors (also referred to as central processing units or CPUs), such as processor 504. Processor 504 is connected (e.g., by a bus) to a communication infrastructure 506. Computer system 500 also includes user input / output device(s) 503, such as a monitor, keyboard, pointing device, etc., that communicate with communication infrastructure 506 via user input / output interface(s) 502. Computer system 500 also includes a main or primary memory 508, such as a random access memory (RAM). The main memory 508 may include one or more levels of cache. The main memory 508 stores control logic (e.g., computer software) and / or data.

[0077] Computer system 500 may also include one or more secondary storage devices or memories 510. Secondary memory 510 may include, for example, a hard disk drive 512 and / or a removable storage device or drive 514. Removable storage drive 514 may be a floppy disk drive, a magnetic tape drive, a compact disk drive, an optical storage device, a tape backup device, and / or any other storage device / drive.

[0078] The removable storage drive 514 can interact with a removable storage unit 518. The removable storage unit 518 includes a computer usable or computer readable storage device having computer software (control logic) and / or data stored thereon. The removable storage unit 518 may be a floppy disk, magnetic tape, compact disk, DVD, optical storage disk, and / or any other computer data storage device. The removable storage drive 514 reads from and / or writes to the removable storage unit 518 in a well-known manner.

[0079] According to some aspects, secondary memory 510 may include other means, instrumentalities, or other techniques for making computer programs and / or other instructions and / or data accessible by computer system 500. Such means, media, or other techniques may include, for example, removable storage unit 522 and interface 520. Examples of removable storage unit 522 and interface 520 may include program cartridges and cartridge interfaces (such as those found in video game devices), removable memory chips (such as EPROMs or PROMs) and associated sockets, memory sticks and USB ports, memory cards and associated memory card slots, and / or any other removable storage unit and associated interface.

[0080] In some examples, main memory 508, removable storage unit 518, removable storage unit 522 may store instructions that, when executed by processor 504, cause processor 504 to perform operations for a UE or a base station, such as UE 101, or base station 103, base station 107, or base station 109 shown in Figures 1 and 2. In some examples, the operations include those shown and described with respect to process 300, process 400, processes 410-470 as shown in Figures 3, 4A-4H.

[0081] The computer system 500 may further comprise a communication or network interface 524. The communication interface 524 enables the computer system 500 to communicate and interact with any combination of remote devices, remote networks, remote entities, etc. (individually and collectively referred to by reference numeral 528). For example, the communication interface 524 may enable the computer system 500 to communicate with the remote devices 528 over a communication path 526, which may be wired and / or wireless and may include any combination of a LAN, a WAN, the Internet, etc. Control logic and / or data may be transmitted to and from the computer system 500 via the communication path 526. The operations of the communication interface 524 may be performed by a wireless controller and / or a cellular controller. The cellular controller may be a separate controller for managing communications according to different wireless communication technologies. The operations in the aforementioned aspects may be implemented in a wide variety of configurations and architectures. Thus, some or all of the operations in the aforementioned aspects may be performed in hardware, software, or both. In some aspects, a tangible non-transitory apparatus or article of manufacture is also referred to herein as a computer program product or program storage device that includes a tangible non-transitory computer usable or readable medium having control logic (software) stored thereon. This includes, but is not limited to, computer system 500, main memory 508, secondary memory 510, removable storage units 518 and 522, and tangible articles of manufacture embodying any combination of the foregoing. Such control logic, when executed by one or more data processing devices (such as computer system 500), causes such data processing devices to operate as described herein.

[0082] Based on the teachings contained herein, it will be apparent to one skilled in the relevant art(s) how to make and use aspects of the present disclosure using data processing devices, computer systems and / or computer architectures other than those shown in Figure 5. In particular, aspects may operate with software, hardware, and / or operating system implementations other than those described herein.

[0083] It is understood that it is the "Description of Embodiments" section, and not the "Summary" and "Abstract" sections, that are intended to be used to interpret the claims. The Summary and Abstract sections may describe one or more exemplary aspects of the disclosure, but not all of the exemplary aspects of the disclosure, as contemplated by the inventor(s), and thus are not intended to limit the scope of the disclosure or the appended claims in any way.

[0084] Although the present disclosure is described herein with reference to exemplary embodiments for exemplary fields and applications, it should be understood that the present disclosure is not limited to the exemplary embodiments. Other embodiments and variations of the embodiments are possible and are within the scope and spirit of the present disclosure. By way of example and without limiting the generality of this paragraph, the embodiments are not limited to the software, hardware, firmware, and / or entities shown in the figures and / or described herein. Moreover, the embodiments (whether or not explicitly described herein) have significant utility for fields and applications beyond the examples described herein.

[0085] Aspects have been described herein with the help of functional building blocks illustrating implementations of certain functions and relationships thereof. Boundaries of these functional building blocks have been arbitrarily defined herein for convenience of description. Alternative boundaries may be defined so long as the specified functions and relationships (or their equivalents) are appropriately performed. In addition, alternative aspects may perform functional blocks, steps, operations, methods, etc. using orders different from those described herein.

[0086] References herein to "one embodiment," "one embodiment," "exemplary embodiment," or similar phrases indicate that the described embodiment may include a particular feature, structure, or characteristic, but not all embodiments may necessarily include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with one embodiment, it is within the knowledge of one of ordinary skill in the relevant art(s) to incorporate such particular feature, structure, or characteristic in other aspects, whether or not expressly mentioned or described herein.

[0087] The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary aspects, but should be defined only in accordance with the following claims and their equivalents.

[0088] In one or more embodiments, for example, at least one of the components depicted in one or more of the preceding figures may be configured to perform one or more of the operations, techniques, processes, and / or methods as described in the Examples section below. For example, circuitry associated with a sled device, router, network element, etc. described above in connection with one or more of the preceding figures may be configured to operate according to one or more of the examples described in the Examples section below.

[0089] This disclosure contemplates that entities involved in the collection, analysis, disclosure, transmission, storage, or other use of such personal information data will adhere to robust privacy policies and / or privacy practices. Specifically, such entities should implement and consistently use privacy policies and practices that are generally recognized as meeting or exceeding industry or government requirements for keeping personal information data confidential and secure. Such policies should be easily accessible by users and should be updated as data collection and / or use changes. Personal information from users should be collected for the entity's lawful and legitimate use and should not be shared or sold except for those lawful uses. Furthermore, such collection / sharing should only be carried out after the user is informed and consented to. Moreover, such entities should consider taking all necessary measures to protect and secure access to such personal information data and ensure that others who have access to the personal information data adhere to their privacy policies and procedures. Furthermore, such entities may subject themselves to third-party assessments to attest to their adherence to widely accepted privacy policies and practices. Moreover, policies and practices should be adapted to the specific types of personal data collected and / or accessed, and should conform to applicable laws and standards, including jurisdiction-specific considerations. For example, in the United States, collection or access of certain health data may be governed by federal and / or state laws, such as the Health Insurance Portability and Accountability Act (HIPAA), while health data in other countries may be subject to other regulations and policies and should be addressed accordingly. Therefore, different privacy practices should be maintained with respect to different types of personal data in each country.

Claims

1. 1. A method for performing wireless communication with a user equipment (UE), comprising: receiving a message including a conditional handover command for performing a handover operation from a first base station in a serving cell to a second base station in a target cell, the conditional handover command including a channel quality condition for the handover operation and an additional condition for the handover operation, the first base station and the second base station being in a non-terrestrial wireless network (NTN); determining an order of operations between testing the channel quality condition and testing the additional condition; performing a measurement operation to measure a quality of a channel between the UE and the second base station in the target cell to test the channel quality condition; determining whether the channel quality condition is met based on the measurement operation; and determining whether said additional condition is satisfied; and and performing the handover operation to handover the UE from the first base station to the second base station in response to determining that the channel quality condition is met and determining that the additional condition is met.

2. The method of claim 1 , wherein the order of operations indicates that testing the channel quality condition is performed before testing the additional condition.

3. the additional condition is a time condition indicating a start time T1 and an end time T2 for performing a handover operation within a time range T1 to T2; 2. The method of claim 1, wherein determining whether the additional condition is satisfied comprises testing that the start time T1 is satisfied and testing that the end time T2 is not exceeded.

4. 4. The method of claim 3, further comprising, in response to determining that the end time T2 is exceeded when performing the handover operation, maintaining a connection on a channel between the UE and the first base station in the serving cell or aborting the handover operation to perform Radio Resource Control (RRC) re-establishment.

5. the order of operations indicates that testing the additional condition occurs before testing the channel quality condition; The method of claim 3 , wherein performing the measurement operation comprises performing the measurement operation based on the start time T1 being met.

6. The order of operations indicates that testing the additional condition is performed after testing the channel quality condition, and the method further comprises:

4. The method of claim 3, further comprising: in response to determining that the channel quality condition is met, performing the handover operation to handover the UE from the first base station to the second base station based on the start time T1 being met.

7. maintaining a connection on a channel between the UE and the first base station in the serving cell in response to determining that the additional condition is not satisfied; The method of claim 1 further comprising:

8. receiving a configuration from the first base station, the configuration indicating an order of operations between testing the channel quality condition and testing the additional condition; The method of claim 1 further comprising:

9. the additional condition is a distance condition indicating at least a starting distance for performing the handover operation; the order of operations indicates that the checking of the distance condition is performed before the checking of the channel quality condition; determining whether the additional condition is satisfied includes performing a distance measurement to test whether the distance condition is satisfied; The method of claim 1 , wherein performing the measurement operation comprises performing the measurement operation after determining that the distance condition is met.

10. the additional condition is a distance condition indicating at least a starting distance for performing the handover operation; the order of operations indicates testing the distance condition after testing the channel quality condition; 2. The method of claim 1, wherein the determining whether the additional condition is met comprises performing a distance measurement to test whether the distance condition is met after determining that the channel quality condition is met.

11. A user equipment (UE), a transceiver configured to enable wireless communication in a non-terrestrial wireless network (NTN); a processor communicatively coupled to the transceiver, the processor comprising: receiving a message including a conditional handover command for performing a handover operation from a first base station in a serving cell to a second base station in a target cell, the conditional handover command including a channel quality condition for the handover operation and an additional condition for the handover operation, the first base station and the second base station being within the NTN; determining an order of operations between testing the channel quality condition and testing the additional condition; performing a measurement operation to measure a quality of a channel between the UE and the second base station in the target cell to test the channel quality condition; determining whether the channel quality condition is met based on the measurement operation; determining whether said additional conditions are met; and configured to perform the handover operation to handover the UE from the first base station to the second base station in response to determining that the channel quality condition is met and determining that the additional condition is met.

12. 12. The UE of claim 11, wherein the additional condition is a time condition indicating a start time T1 and an end time T2 for performing the handover operation during a time range T1-T2, and the processor is further configured to determine whether the additional condition is met by testing that the start time T1 is met and the end time T2 is not exceeded.

13. 13. The UE of claim 12, in response to determining that the end time T2 is exceeded when performing the handover operation, the UE maintains a connection on a channel between the UE and the first base station in the serving cell or aborts the handover operation to perform radio resource control (RRC) re-establishment.

14. The processor, 12. The UE of claim 11, further configured to, in response to determining that the additional condition is not satisfied, maintain a connection on a channel between the UE and the first base station in the serving cell.

15. The processor, 12. The UE of claim 11, further configured to receive a configuration from the first base station, the configuration indicating an order of operations between testing the channel quality condition and testing the additional condition.

16. A non-transitory computer-readable medium storing instructions that, when executed by a processor of a user equipment (UE), cause the UE to perform operations, the operations including: receiving a message including a conditional handover command for performing a handover operation from a first base station in a serving cell to a second base station in a target cell, the conditional handover command including a channel quality condition for the handover operation and an additional condition for the handover operation, the first base station and the second base station being in a non-terrestrial wireless network (NTN); determining an order of operations between testing the channel quality condition and testing the additional condition; performing a measurement operation to measure a quality of a channel between the UE and the second base station in the target cell to test the channel quality condition; determining whether the channel quality condition is met based on the measurement operation; and determining whether said additional condition is satisfied; and and performing the handover operation to handover the UE from the first base station to the second base station in response to determining that the channel quality condition is met and determining that the additional condition is met.

17. 20. The non-transitory computer-readable medium of claim 16, wherein the order of operations indicates testing the channel quality condition is performed before testing the additional condition.

18. the additional condition is a time condition indicating a start time T1 and an end time T2 for performing the handover operation within a time range T1 to T2; 17. The non-transitory computer-readable medium of claim 16, wherein determining whether the additional condition is satisfied comprises testing that the start time T1 is satisfied and testing that the end time T2 is not exceeded.

19. 20. The method of claim 18, responsive to determining that the end time T2 is exceeded when performing the handover operation, maintaining a connection on a channel between the UE and the first base station in the serving cell or aborting the handover operation to perform radio resource control (RRC) re-establishment.

20. The operation, 17. The non-transitory computer-readable medium of claim 16, further comprising, in response to determining that the additional condition is not met, maintaining a connection on a channel between the UE and the first base station in the serving cell.

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