WO2019148677A1

WO2019148677A1 - Communication handover method and apparatus

Info

Publication number: WO2019148677A1
Application number: PCT/CN2018/084646
Authority: WO
Inventors: Ting Zhou; Yuling OUYANG; Zhenhong Li; Xin XIA
Original assignee: JRD Communication Shenzhen Ltd
Current assignee: JRD Communication Shenzhen Ltd
Priority date: 2018-01-31
Filing date: 2018-04-26
Publication date: 2019-08-08
Anticipated expiration: 2020-07-31
Also published as: CN110099419A; CN110099419B

Abstract

The present disclosure provide a communication handover method comprising: determining at least two candidate base stations for a user equipment by a source base station, and the candidate base stations comprising at least one primary candidate base station; sending a pre-handover instruction to the user equipment by the source base station, and the pre-handover instruction being configured to instruct the user equipment to enter a dual connectivity state; the user equipment in the dual connectivity state connecting to the source base station and the candidate base station simultaneously, and receiving user plane data from the primary candidate base station by the user equipment, wherein the source base station serves as a primary base station, and the candidate base station serves as a secondary base station; determining a target base station for the user equipment by the source base station, and the target base station belonging to the candidate base station; assisting the user equipment to apply the handover to the target base station by the source base station. The present further provide a communication handover apparatus. By the above-mentioned implementation, a possibility of the mobility interruptions may be reduced.

Description

COMMUNICATION HANDOVER METHOD AND APPARATUS

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201810098953.4, field on January 31, 2018 in the China Intellectual Property Office, the contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The described embodiments relate to a communication technology, and more particularly, to a communication handover method and an apparatus.

BACKGROUND

A handover is one of the most basic and important procedures in a mobility management. In the related art, the mobility management of a radio resource control (RRC) state is controlled by a network, that is, the network determines a connection relationship between a user equipment and a cell.

Generally, in a network controlling handover procedure, the user equipment disconnects a source base station first, and then connects to a target base station. However, after the user equipment disconnected the source base station, and before the user equipment establishes a connection with the target base station, there is no connection between the user equipment and the source base station, and no connection between the user equipment and target base station. In this case, user plane data of the user equipment cannot be transmitted (including sending download user plane data to the user equipment and/or receiving upload user plane data from the user equipment) , resulting in a mobility interruption that user plane data transmits for a long time in the handover procedure.

SUMMARY

The purpose of the present disclosure is to provide a communication handover method and an apparatus, which may solve the problem of the mobility interruption in the handover procedure for a long time in the related art.

The technical solution adopted by the present disclosure for solving the above-mentioned technical problem is to provide a communication handover method comprising: determining at least two candidate base stations for a user equipment by a source base station, and the candidate base stations comprising at least one primary candidate base station; sending a pre-handover instruction to the user equipment by the source base station, and the pre-handover instruction being configured to instruct the user equipment to enter a dual connectivity state; the user equipment in the dual connectivity state connecting to the source base station and the candidate base station simultaneously, and receiving user plane data from the primary candidate base station by the user equipment, wherein the source base station serves as a primary base station, and the candidate base station serves as a secondary base station; determining a target base station for the user equipment by the source base station, and the target base station belonging to the candidate base station; assisting the user equipment to apply the handover to the target base station by the source base station.

The technical solution adopted by the present disclosure for solving the above-mentioned technical problem is to provide a communication handover method comprising: reporting a first measurement report to a source base station by a user equipment; receiving a pre-handover instruction from the source base station by the user equipment, and the pre-handover instruction being configured to instruct the user equipment to enter a dual connectivity state; the user equipment in the dual connectivity state connecting to the source base station and at least two candidate base stations simultaneously, and receiving user plane data from at least one primary candidate base station, wherein the source base station serves as a primary base station, and the candidate base station serves as a secondary base station, the candidate base station is determined by the source base station for the user equipment, and the primary candidate base station belongs to the candidate base station; entering the dual connectivity state in response to the pre-handover instruction by the user equipment; reporting a second measurement report to the source base station in the dual connectivity state by the user equipment; assisting the user equipment to apply the handover to a target base station by the source base station, and the target base station belonging to the candidate base station.

The technical solution adopted by the present disclosure for solving the above-mentioned technical problem is to provide a communication handover method comprising: receiving a secondary base station addition request by a candidate base station from a source base station; the secondary base station addition request including user equipment information; and the candidate base station being determined by the source base station for the user equipment; sending a confirmation message of the secondary base station addition request by the candidate base station to the source base station; establishing a connection with the user equipment by the candidate base station; receiving a role switch request from the source base station by the candidate base station, and the role switch request being a first role switch request or a second role switch request; the candidate base station being applied the handover to a new primary base station in response to the first role switch request, or the candidate base station releasing resources of the user equipment in response to the second role switch request.

The technical solution adopted by the present disclosure for solving the above-mentioned technical problem is to provide a communication handover apparatus comprising a processor and a communication circuit, the processor connecting to the communication circuit; wherein the processor is configured to execute instructions to implement any one of the above-mentioned methods.

The technical solution adopted by the present disclosure for solving the above-mentioned technical problem is to a communication handover apparatus storing instructions, wherein the instructions are configured to execute instructions to implement any one of the above-mentioned methods.

The present disclosure has following beneficial effects: determining at least two candidate base stations for a user equipment by a source base station, and the candidate base stations comprising at least one primary candidate base station; sending a pre-handover instruction to the user equipment by the source base station, and the pre-handover instruction being configured to instruct the user equipment to enter a dual connectivity state; the user equipment in the dual connectivity state connecting to the source base station and the candidate base station simultaneously, and receiving user plane data from the primary candidate base station by the user equipment, wherein the source base station serves as a primary base station, and the candidate base station serves as a secondary base station; determining a target base station for the user equipment by the source base station, and the target base station belonging to the candidate base station; assisting the user equipment to apply the handover to the target base station by the source base station. In the handover procedure, the user equipment is in the dual connectivity state, not only as a source base station of a primary base station but also to connect to at least two candidate base stations. User plane data may be received from the primary candidate base station, and the possibility of the mobility interruption may be reduced. A determination of the candidate base station is before the user equipment actually applies the handover to the target base station, which means that the radio environment where the user equipment is located during the actual handover, may be different from when determining the candidate base station, and in particular in the case of using a high working frequency band or a ultra-density small cell deployment scenario. Because the number of the candidate base stations is higher than one, even though any changes in the radio environment may make certain candidate base stations no longer to be suitable as a target for the handover. There may still be some base stations that are suitable as targets for the handover, so that comparing with a case of only one candidate base station, a possibility of a handover failure may be reduced. The handover failure may result in a failure of the source base station activating a traditional handover, or even result in a failure of the user equipment entering a radio data link, and both may result in the mobility interruptions. The number of candidate base stations may be higher than one, so that a possibility of the mobility interruptions may be further reduced.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a flow chart of a communication handover method in accordance with a first embodiment of the present disclosure;

Fig. 2 is a flow chart of a communication handover method in accordance with a second embodiment of the present disclosure;

Fig. 3 is a flow chart of a block S141 in Fig. 2;

Fig. 4 is a flow chart of a communication handover method in accordance with a third embodiment of the present disclosure;

Fig. 5 is a flow chart of a communication handover method in accordance with a fourth embodiment of the present disclosure;

Fig. 6 is a flow chart of a communication handover method in accordance with a fifth embodiment of the present disclosure;

Fig. 7 is a flow chart of a communication handover method in accordance with a sixth embodiment of the present disclosure;

Fig. 8 is a flow chart of a communication handover method in accordance with a seventh embodiment of the present disclosure;

Fig. 9 is a flow chart of a communication handover method in accordance with an eighth embodiment of the present disclosure;

Fig. 10 is a flow chart of a communication handover method in accordance with a ninth embodiment of the present disclosure;

Fig. 11 is a flow chart of a communication handover method in accordance with a tenth embodiment of the present disclosure;

Fig. 12 is a flow chart of a communication handover method in accordance with an eleventh embodiment of the present disclosure;

Fig. 13 is a schematic diagram of an application scenario in accordance with an embodiment of the present disclosure;

Fig. 14 is a schematic diagram of a handover procedure in a case where a moving path of a user equipment is AB, in a communication handover method in accordance with an embodiment of the present disclosure;

Fig. 15 is a schematic diagram of a handover procedure in a case where a moving path of the user equipment is AB’, in a communication handover method in accordance with an embodiment of the present disclosure;

Fig. 16 is a structural illustration of a communication handover apparatus in accordance with a first embodiment of the present disclosure;

Fig. 17 is a structural illustration of a communication handover apparatus in accordance with a second embodiment of the present disclosure;

Fig. 18 is a structural illustration of a communication handover apparatus in accordance with a third embodiment of the present disclosure;

Fig. 19 is a structural illustration of a communication handover apparatus in accordance with a fourth embodiment of the present disclosure.

DETAILED DESCRIPTION

In order to give a better and thorough understanding to the whole and other intended purposes, features and advantages of the technical solution of the present disclosure, detailed description will be given with respect to preferred embodiments provided and illustrated here below in accompanied drawings. The non-conflicting embodiments in the following may be combined with each other.

An execution body of a communication handover method in accordance with a first embodiment of the present disclosure may be a base station, and the base station may serve as a source base station in a handover procedure, i.e., the base station which a user equipment currently connects to. The base station may connect to a core network and perform a radio communication with the user equipment, to provide a communication coverage for a corresponding geographical area. The base station may be a macro base station, a micro base station, a pico base station or a femtocell. In some embodiments, the base station may also be referred to as a radio base station, an access point, a node B, an evolved node B (eNodeB, or eNB) , a gNB, or other suitable terminology. As shown in Fig. 1, the embodiment may comprise:

S11: a source base station determines at least two candidate base stations for a user equipment.

The source base station may determine at least two candidate base stations according to a first measurement report, and the first measurement report may be reported by the user equipment. For a specific procedure, reference may be made to descriptions of subsequent embodiments.

After the source base station completed the determination of the candidate base stations, a secondary base station addition procedure may be performed to assist the user equipment to add the candidate base station as a secondary base station. After the secondary base station addition procedure was completed, the user equipment may change from connecting to only the source base station to a dual connectivity.

The user equipment needs to establish a connection with the candidate base station to enter the dual connectivity state in maintaining the connection with the source base station. This procedure may make a certain delay, especially when the user equipment needs to perform a random access to synchronize to the candidate base station, and the delay cannot be ignored. Before the delay expires, i.e., the user equipment has not established the connection with the candidate base station, if a radio link between the source base station and the user equipment is deteriorated to be unable to continue serving the user equipment, the user equipment may not be able to enter the dual connectivity state, and may even enter a radio link failure (RLF) and perform a RRC connection re-establishment, finally resulting in a mobility interruption. In order to reduce an occurrence of the above-mentioned situation, when the source base station determines the candidate base stations, a channel condition of the source base station on the user equipment side may be better than a handover procedure in the related art.

Although the user equipment entering the dual connectivity state connects the source base station and all the candidate base stations simultaneously, because there may be a capability limitation of the user equipment, e.g., a number of antennas, a limitation of a power consumption, etc., the user equipment in the dual connectivity state may not perform user plane data transmission with all the candidate base stations. The candidate base station that performs the user plane data transmission with the user equipment in the dual connectivity state may be referred to a primary candidate base station, and the candidate base station that does not perform the user plane data transmission with the user equipment in the dual connectivity state may be referred to a backup candidate base station. The candidate base station may include at least one the primary candidate base station. A number of the candidate base stations may be zero, i.e., all the candidate base stations may be the primary candidate base stations; or a number of the backup candidate base stations may be higher than zero.

S12: the source base station sends a pre-handover instruction to the user equipment.

The pre-handover instruction may include candidate base station information. If the candidate base stations include the primary candidate base stations and the backup candidate base stations, the information of each candidate base station may include a type tag, which may be configured to indicate whether the candidate base station is a primary candidate base station or a backup candidate base station. If all the candidate base stations are primary candidate base stations, the information of each candidate base station may still include a type tag, or may not.

The pre-handover instruction may be configured to instruct the user equipment to enter the dual connectivity state. The user equipment in the dual connectivity state may connect to the source base station and the candidate base station simultaneously, and user plane data may be received from the primary candidate base station. The source base station may serve as a primary base station, and the candidate base station may serve as a secondary base station. The pre-handover instruction may be a RRC signaling, such as a RRC_Connection_Reconfiguration signaling.

All RRC signaling messages and functions required for the user equipment in the dual connectivity state may be managed by the primary base station, such as a public radio resource configuration, a dedicated radio resource configuration, a measurement, a mobility management, and so on.

The source base station as the primary base station may not perform the user plane data transmission with the user equipment in the dual connectivity state. In this case, only a main candidate base station and the user equipment transmit the user plane data, and a bearer mode of the user plane data may be a secondary cell group (SCG, i.e., a serving cell group controlled by the secondary base station) . The source base station may still perform the user plane data transmission with the user equipment in the dual connectivity state to further reduce the possibility of mobility interruption. In this case, both the source base station and the primary candidate base station transmit the user plane data with the user equipment, and the bearer mode of the user plane data may be split. For example, a main cell group (MCG, i.e., a serving cell group controlled by the primary base station) is split or a secondary cell group is split. No matter in which case, the backup candidate base station may give up a radio bearer.

S13: the source base station determines a target base station for the user equipment.

The source base station may determine the target base station according to a second measurement report, and the second measurement report may be reported by the user equipment. For a specific procedure, reference may be made to descriptions of subsequent embodiments. The target base station may belong to the candidate base station and may be the primary candidate base station or the backup candidate base station.

Compared with when determining the candidate base station, when the source base station determines the target base station, the channel condition of the source base station on the user equipment side is worse, and/or the channel condition of the candidate base station is better.

S14: the source base station assists the user equipment to apply the handover to the target base station.

The source base station may perform a role switch procedure to assist the user equipment to apply the handover to the target base station, so as to complete an actual handover. In the role switch procedure, the RRC signaling messages and the functions of the user equipment may be migrated from the source base station to the target base station, so that the target base station may be converted from the secondary base station to a new primary base station, and the source base station may be converted from the primary base station to a new secondary base station. After the role switch procedure was completed, the user equipment may disconnect all the secondary base stations (including the source base station) , and change from the dual connection to only connect to the target base station.

By the above-mentioned embodiment, the source base station determines at least two the candidate base stations for the user equipment, and the candidate base stations comprises at least one the primary candidate base station; the source base station sends the pre-handover instruction to the user equipment, the pre-handover instruction is configured to instruct the user equipment to enter the dual connectivity state; the user equipment in the dual connectivity state connects to the source base station and the candidate base station simultaneously, and receiving user plane data from the primary candidate base station by the user equipment, wherein the source base station serves as the primary base station, and the candidate base station serves as the secondary base station; the source base station determines the target base station for the user equipment, and the target base station belonging to the candidate base station; the source base station assist the user equipment to apply the handover to the target base station. In the handover procedure, the user equipment is in the dual connectivity state, not only as the source base station of the primary base station but also to connect to at least two the candidate base stations. The user plane data may be received from the primary candidate base station, and the possibility of the mobility interruption may be reduced.

In addition, a determination of the candidate base station is before the user equipment actually applies the handover to the target base station, which means that the radio environment where the user equipment is located during the actual handover, may be different from when determining the candidate base station, and in particular in the case of using a high working frequency band or a ultra-density small cell deployment scenario. Because the number of the candidate base stations is higher than one, even though any changes in the radio environment may make certain candidate base stations no longer to be suitable as a target for handover, there may still be some base stations that are suitable as targets for the handover, so that comparing with the case of only one candidate base station, a possibility of a handover failure may be reduced. The handover failure may result in a failure of the source base station activating a traditional handover, or even result in a failure of the user equipment entering a radio data link, and both may result in the mobility interruptions. The number of candidate base stations may be higher than one, so that a possibility of the mobility interruptions may be further reduced.

As shown in Fig. 2, Fig. 2 is a flow chart of a communication handover method in accordance with a second embodiment of the present disclosure, which is based on the first embodiment, and S14 may comprise:

S141: a role switch is performed between the source base station and the target base station.

In a role switch procedure, the target base station may be converted from a secondary base station to a new primary base station, and other secondary base stations except the target base station may be converted to a release state.

As shown in Fig. 3, in an embodiment of the present disclosure, S141 may specifically comprise:

S1411: the source base station sends a role switch request to each of the candidate base station.

The source base station may send a role switch request to each of the candidate base station. The role switch request may include a first role switch request and a second role switch request. The first role switch request may be sent to the target base station and may be configured to instruct the target base station to be converted to a new primary base station, and the second role switch request may be sent to other candidate base stations except the target base station and may be configured to instruct other the candidate base stations except the target base station to be converted to a release state, i.e., resources of the user equipment may be released. For example, in the case that the target base station is a backup candidate base station or another primary candidate base station, the second role switch request may be further configured to instruct the primary candidate base station to transmit the user plane data that was unsuccessfully sent, to the target base station.

The role switch request may comprise an updating role identifier, and the updating role identifier may be configured to indicate that the role switch request is the first role switch request or the second role switch request. For example, the update role identifier may be an one bit binary number. When the binary number is 0, it may be indicated that the role switch request is the first role switch request, and the candidate base station receiving the first role switch request needs to perform the role switch. When the binary number is 1, it may be indicated that the role switch request is the second role switch request, and the candidate base station receiving the second role switch request does not need to perform the role switch. The updating role identifier may also be reversed, i.e., when the binary number is 0, it may be indicated that the role switch request is the second role switch request, and when the binary number is 1, it may be indicated that the role switch request is the first role switch request.

S1412: the source base station receives a role switch confirmation message from the candidate base station.

S142: the source base station sends an actual handover instruction to the user equipment.

The actual handover instruction may be configured to instruct the user equipment to modify the target base station as a new primary base station and modify the source base station as a new secondary base station, and all the secondary base stations including the source base station are disconnected. The actual handover instruction may be the RRC signaling, such as the RRC_Connection_Reconfiguration signaling.

Sequences of execution between the present block and S141 are merely a signaling, and the actual sequence may be exchanged or performed simultaneously.

S143: the source base station releases resources of the user equipment.

The resources of the user equipment may refer to the resources allocated by the base station for the user equipment, such as contexts of the user equipment.

As shown in Fig. 4, Fig. 4 is a flow chart of a communication handover method in accordance with a third embodiment of the present disclosure which is based on the first embodiment, and S11 may comprise:

S111: the source base station receives the first measurement report reported by the user equipment.

A reporting of the first measurement report may be periodic or aperiodic, such as an event-triggered report. Before the first measurement report is received, the source base station may send a measurement configuration message to the user equipment to be indicated when to start to measure and report the first measurement report.

S112: the source base station determines whether the first measurement report satisfies a pre-handover threshold.

The first measurement report may include a channel condition between the source base station on the user equipment side and a measurement object. The pre-handover threshold may include that a channel condition of the source base station is lower than a first threshold. In addition, the pre-handover threshold may further include that a channel condition of a specified number of measurement objects is higher than a second threshold, or a channel condition of a difference between a specified number of measurement objects and the source base station is higher than a third threshold.

If the first measurement report satisfies the pre-handover threshold, skip to S113; otherwise, the source base station may continue to wait for the user equipment to report the first measurement report.

S113: the source base station determines at least two the candidate base stations according to the first measurement report.

The source base station may select at least two base stations as candidate base stations from the measurement objects according to a channel condition of the measurement object in the first measurement report. In a procedure of selecting the candidate base station, in addition to the measurement report, the source base station may also refer to a current position of the user equipment, a motion direction of the user equipment, and a load of the candidate base station.

The source base station may select the N measurement objects that channel conditions are higher than a specified threshold as the candidate base stations according to the first measurement report. The source base station may also arrange the measurement objects in a descending order of channel conditions, and take the front of N measurement objects as candidate base stations. N may be a specified number of candidate base stations and may be an integer higher than 1. The measurement object may be a base station that is geographically close to the source base station, or may be a base station that the source base station can directly obtain information through an inter-base station interface.

S114: the source base station sends a secondary base station addition request to the candidate base station.

The secondary base station addition request may include user equipment information, which is configured to perform a handover preparation by the candidate base station. The candidate base station may perform an admission control before the handover preparation, to determine whether there are enough resources to receive the user equipment. If there are enough resources, a confirmation message of the secondary base station addition request may be sent to the source base station. If there are not enough resources, a denied message of the secondary base station addition request may be sent to the source base station.

If the source base station receives the denied message of the secondary base station addition request, the candidate base station may be removed. If the number of candidate base stations does not meet the requirement after removing the candidate base station, (e.g., 1) , the source base station may perform the present block after supplementing several candidate base stations from rest measurement objects. The user equipment may also be notified to re-select the candidate base station after updating the first measurement report.

S115: the source base station receives a confirmation message of the secondary base station addition request from the candidate base station.

The confirmation message of the secondary base station addition request may be indicated that the admission control of the candidate base station has been successful.

As shown in Fig. 5, Fig. 5 is a flow chart of a communication handover method in accordance with a fourth embodiment of the present disclosure which is based on the first embodiment, and S11 may further comprise:

S15: the source base station sends a secondary base station reconfiguration complete message to the candidate base station.

The secondary base station reconfiguration complete message may be configured to indicate that the user equipment has completed the RRC_Connection_Reconfiguration signaling, and the candidate base station is added as a secondary base station. The secondary base station reconfiguration complete message may comprise a priority identifier, and the priority identifier may be configured to indicate whether the candidate base station that receives the secondary base station reconfiguration complete message is the primary candidate base station.

Similarly, the priority identifier may be an one bit binary number. When the binary number is 0, it may be indicated that the candidate base station is the primary candidate base station. When the binary number is 1, it may be indicated that the candidate base station is the backup candidate base station. The priority identifier may also be reversed, i.e., when the binary number is 0, it may be indicated that the candidate base station is the backup candidate base station, and when the binary number is 1, it may be indicated the candidate base station is the primary candidate base station.

As shown in Fig. 6, Fig. 6 is a flow chart of a communication handover method in accordance with a fifth embodiment of the present disclosure which is based on the first embodiment, and S13 may further comprise:

S131: the source base station receives a second measurement report reported by the user equipment.

Similarly, a reporting of the first measurement report may be periodic or aperiodic, such as an event-triggered report. Before the first measurement report is received, the source base station may send a measurement configuration message to the user equipment to be indicated when to start to measure and report the first measurement report. A measurement configuration message for indicating when to report the first measurement report and the second measurement report may be the same or different.

S132: the source base station determines whether the first measurement report satisfies an actual handover threshold.

The second measurement report may include a channel condition between the source base station on the user equipment side and a measurement object. The actual handover threshold may include that a channel condition of the source base station is lower than a fourth threshold. In addition, the actual handover threshold may further include that a channel condition of the candidate base station is higher than a fifth threshold, or a channel condition of a difference between the candidate base station and the source base station is higher than a sixth threshold. In general, the first threshold may be higher than the fourth threshold, the second threshold may be less than the fifth threshold, and the third threshold may be less than the sixth threshold.

If the second measurement report satisfies the actual handover threshold, skip to S133; otherwise, the source base station may continue to wait for the user equipment to report the second measurement report.

S133: the source base station selects the target base station from the candidate base stations according to the second measurement report.

The source base station may select one of the candidate base stations as the target base station according to the channel condition of the candidate base station in the second measurement report. For example, the source base station may directly select the candidate base station with a best channel condition as the target base station.

In addition to the channel condition, the source base station may select the target base station in combination with the priority of the candidate base station. For example, the candidate base station may comprise the primary candidate base station and backup candidate base stations, and the primary candidate base station may have a higher priority than the backup candidate base stations have. The source base station may screen the channel condition which is higher than a default threshold according to the second measurement report, i.e., the source base station may screen the candidate base station which is suitable to a handover target. If a screening result includes the primary candidate base station, the primary candidate base station with the best channel condition may be selected as the target base station. If the screening result includes only the backup candidate base stations, the backup candidate base station with the best channel condition may be selected as the target base station.

As shown in Fig. 7, an execution body a communication handover method in accordance with a sixth embodiment of the present disclosure may be the base station, and the base station serves as the candidate base station during the handover procedure. The present embodiment may comprise:

S21: the candidate base station receives the secondary base station addition request from a source base station.

The secondary base station addition request may include user equipment information, which is configured to perform a handover preparation by the candidate base station. The candidate base station may be a primary candidate base station or a backup candidate base station. The candidate base station may be determined by the source base station for the user equipment. For a specific determination procedure, reference may be made to descriptions of a communication handover method in accordance with the first and third embodiments of the present disclosure

S22: the candidate base station sends the confirmation message of the secondary base station addition request to the source base station.

Before performing the present block, the candidate base station may perform the admission control to determine whether there is enough resources to receive the user equipment. If there are enough resources, the present block may be performed. If there are not enough resources, a denied message of the secondary base station addition request may be sent to the source base station.

S23: the candidate base station establishes a connection with the user equipment.

For a specific procedure, reference may be made to descriptions of subsequent embodiments. After the connection was established, if the candidate base station is a primary candidate base station, the user plane data may be transmitted with the user equipment. If the candidate base station is a backup candidate base station, the user plane data may be not transmitted with the user equipment.

S24: the candidate base station receives the role switch request from the source base station.

If the candidate base station is selected as a target base station, the role switch request may be the first role switch request for instructing the candidate base station to be converted to a new primary base station. If the candidate base station is not selected as the target base station, the role switch request may be the second role switch request for instructing the candidate base station to be converted to a release state, i.e., resources of the user equipment may be released. There is not a necessary association relationship between whether the candidate base station is the primary candidate base station and whether the backup candidate base station is selected as the target base station.

S25: the candidate base station is applied the handover to a new primary base station in response to the first role switch request, or the candidate base station releases resources of the user equipment in response to the second role switch request.

If the candidate base station is the primary candidate base station, when the candidate base station receives the second role switch request, the primary candidate base station may transmit the user plane data that was unsuccessfully sent, to the target base station

By the above-mentioned embodiment, in the handover procedure, the user equipment is in the dual connectivity state, not only as the source base station of the primary base station but also to connect to at least two the candidate base stations. The user plane data may be received from the primary candidate base station, and the possibility of the mobility interruption may be reduced.

In addition, a determination of the candidate base station is before the user equipment actually applies the handover to the target base station, which means that the radio environment where the user equipment is located during the actual handover, may be different from when determining the candidate base station, in particular in the case of using a high working frequency band or a ultra-density small cell deployment scenario. Because the number of the candidate base stations is higher than one, even though any changes in the radio environment may make certain candidate base stations no longer to be suitable as a target for handover, there may still be some base stations that are suitable as targets for the handover, so that comparing with the case of only one candidate base station, a possibility of a handover failure may be reduced. The handover failure may result in a failure of the source base station activating a traditional handover, or even result in a failure of the user equipment entering a radio data link, and both may result in the mobility interruptions. The number of candidate base stations may be higher than one, so that a possibility of the mobility interruptions may be further reduced.

As shown in Fig. 8, Fig. 8 is a flow chart of a communication handover method in accordance with a seventh embodiment of the present disclosure, which is based on the sixth embodiment, and after S22 may further comprise:

S26: the candidate base station receives a secondary base station reconfiguration complete message from the source base station.

The secondary base station reconfiguration complete message may be configured to indicate that the user equipment has completed the RRC_Connection_Reconfiguration signaling, and the candidate base station is added as a secondary base station. The secondary base station reconfiguration complete message may comprise a priority identifier, and the priority identifier may be configured to indicate whether the candidate base station is the primary candidate base station.

As shown in Fig. 9, Fig. 9 is a flow chart of a communication handover method in accordance with a eighth embodiment of the present disclosure, which is based on the sixth embodiment, and after S24 may further comprise:

S27: sending a role switch request confirmation message to the source base station by the candidate base station.

An execution body of a ninth embodiment in accordance with a first embodiment of the present disclosure may be an user equipment. The user equipment may be fixed or mobile, and may be a cellular phone, a personal digital assistant (PDA) , a wireless modem, a tablet computer, a laptop, a cordless phone, and so on. As shown in Fig. 10, the present embodiment may comprise:

S31: the user equipment reports the first measurement report to a source base station.

The source base station may determine at least two candidate base stations for the user equipment according to the first measurement report, when the first measurement report satisfies a pre-handover threshold, and the candidate base station may include at least one primary candidate base station. For a specific determination procedure, reference may be made to descriptions of a communication handover method in accordance with the first and third embodiments of the present disclosure.

S32: the user equipment receives the pre-handover instruction from the source base station.

The pre-handover instruction may be configured to instruct the user equipment to enter the dual connectivity state. The user equipment in the dual connectivity state may connect to the source base station and at least two the candidate base station simultaneously, and user plane data may be received from at least one the primary candidate base station. The source base station may serve as a primary base station, and the candidate base station may serve as a secondary base station. The pre-handover instruction may be a RRC signaling, such as a RRC_Connection_Reconfiguration signaling.

S33: the user equipment enters the dual connectivity state in response to the pre-handover instruction.

The user equipment may establish a connection with the candidate base station to enter the dual connectivity state described above.

S34: the user equipment reports the second measurement report to the source base station in the dual connectivity state.

The source base station may determine the target base station for the user equipment according to the first measurement report, when the second measurement report satisfies the actual handover threshold. The target base station may belong to the candidate base station and may be the primary candidate base station or the backup candidate base station. For a specific determination procedure, reference may be made to descriptions of a communication handover method in accordance with the first and fifth embodiments of the present disclosure.

S35: the source base station assists the user equipment to apply the handover to the target base station.

The source base station may perform the role switch procedure to assist the user equipment to apply the handover to the target base station, so as to complete an actual handover. In the role switch procedure, the RRC signaling messages and the functions of the user equipment may be migrated from the source base station to the target base station, so that the target base station may be converted from the secondary base station to a new primary base station, and the source base station may be converted from the primary base station to a new secondary base station. After the role switch procedure was completed, the user equipment may disconnect all the secondary base stations (including the source base station) , and change from the dual connection to only connect to the target base station.

As shown in Fig. 11, Fig. 11 is a flow chart of a communication handover method in accordance with a tenth embodiment of the present disclosure, which is based on the ninth embodiment, and S33 may comprise:

S331: the user equipment establishes a connection with the candidate base station in maintaining a connection with the source base station.

Specifically, after receiving the pre-handover instruction, the user equipment may modify its RRC connection to add all candidate base stations as secondary base stations, and may send a RRC_Connection_Reconfiguration signaling complete message to the source base station after modifying. The source base station may send a confirmation message of the secondary base station addition request to each candidate base station in response to the RRC_Connection_Reconfiguration signaling complete message, and may establish a connection between the user equipment and the candidate base station at L3 (e.g., a RRC layer) . The user equipment may complete a synchronization with each the candidate base station, so as to complete to establish the connection with the candidate base station. The user equipment may also complete the synchronization with each the candidate base station first, after receiving the pre-handover instruction, and then may directly send the RRC_Connection_Reconfiguration signaling complete message to each the candidate base station, or may transmit it by the source base station, so as to complete the connection with the candidate base station.

In the above-mentioned procedure of establishing the connection, the user equipment may perform the synchronization by performing a random access to the candidate base station. If a timing advance (TA) of the candidate base station is the same as the source base station, or the TA of the candidate base station is 0 (e.g., the candidate base station is a base station of a small cell) , the user equipment may have completed the synchronization with the candidate base station, the random access to the candidate base station may be omitted.

After the user equipment established the connection with the candidate base station, data may be transmitted between the user equipment and the candidate base station. In the procedure of establishing the connection between the user equipment and the candidate base station, the user equipment may maintain a connection with the source base station.

S332: the user equipment receives the user plane data from the primary candidate base station.

As shown in Fig. 12, Fig. 12 is a flow chart of a communication handover method in accordance with a eleventh embodiment of the present disclosure, which is based on the tenth embodiment, and S35 may comprise:

S351: the user equipment receives the actual handover instruction from the source base station.

S352: the user equipment modifies the target base station as a new primary base station in response to the actual handover instruction, and modifies the source base station as a new secondary base station.

S353: the user equipment disconnects all the secondary base stations including the source base station.

The detailed description set forth below is intended as a description of the specific handover procedure with reference to the appended figures and embodiments.

As shown in Fig. 13, a gNB1 and a gNB2 and gNB3 may be adjacent. The user equipment may start at point O and may be served by the gNB1, i.e., the gNB1 is a source base station. When the user equipment moves to a point A, the source base station may decide to perform a secondary base station addition procedure, and may select the gNB2 and the gNB3 as candidate base stations, wherein the gNB2 is the candidate base station and the gNB3 is a backup candidate base station. A moving path of the user equipment may be divided into two cases. In one case, the user equipment may move from the point A to a point B in a range of the gNB3. The moving path may be represented by a solid line. The user equipment may perform the actual handover at the point B, and a target base station may be the gNB3. In another case, the user equipment may move from the point A to a point B'in a range of the gNB2. The moving path may be represented by a dashed line, the user equipment may perform the actual handover at the point B', and the target base station may be the gNB2. In the following, the two cases will be specifically described by ways of example respectively, and same parts as those of the above-mentioned embodiment will not be repeated. In Fig. 14, dashed lines may represent the transmission of user plane data, and solid lines may represent the transmission of control data.

As shown in fig. 14, in the case of the moving path of the user equipment is AB, the handover procedure may specifically comprise:

S101: the gNB1 sends a measurement configuration message to the user equipment.

S102: the user equipment transmits the user plane data with the gNB1.

The user plane data may come from a MCG bearer and may be ciphered with a key of the gNB1.

An order of execution between the present block and S101, S103-S107 is not limited.

S103: the user equipment sends the first measurement report to the gNB1.

S104: the gNB1 selects the gNB2 and the gNB3 as the candidate base stations for the user equipment according to the first measurement report.

S105: the gNB1 sends the secondary base station addition request to the gNB2 and the gNB3 respectively.

S106: the gNB2 and the gNB3 send the confirmation message of the secondary base station addition request to the gNB1.

S107: the gNB1 sends the RRC_Connection_Reconfiguration signaling to the user equipment.

The RRC_Connection_Reconfiguration signaling may serve as the pre-handover instruction and may include information of the gNB2 and the gNB3.

S108: the user equipment sends the RRC_Connection_Reconfiguration signaling complete message to the gNB1.

S109: the gNB1 sends the secondary base station reconfiguration complete message to the gNB2 and the gNB3 respectively.

The secondary base station reconfiguration complete message may comprise a priority identifier. The priority identifier of the secondary base station reconfiguration complete message sent to the gNB2 may be indicated a primary candidate base station, and the priority identifier of the secondary base station reconfiguration complete message sent to the gNB3 may be indicated a backup candidate base station.

S110: the user equipment completes a random access to the gNB2 and the gNB3 respectively.

S111: the user equipment and the gNB1 transmit the user plane data.

The user plane data may come from the split bearer and may be ciphered with a key of the gNB1.

The order of execution between the present block and S101, S103-S107 is not limited.

S112: the user equipment transmits the user plane data with the gNB2.

The user plane data may come from the split bearer and may be ciphered with a key of the gNB2.

The order of execution between the present block, S103-S107, and S111 is not limited.

S113: the user equipment sends a second measurement report to the gNB1.

S114: the gNB1 selects the gNB3 as a target base station for the user equipment according to the second measurement report.

S115: the gNB1 sends the second role switch request to the gNB2.

S116: The gNB2 transmits the user plane data that was unsuccessfully sent, to the gNB3.

If gNB2 does not have sent the user plane data successfully, the present block may be omitted.

S117: the gNB1 sends the first role switch request to the gNB3.

The order of execution between the present block, and S115-S116 is not limited.

S118: The gNB2 and the gNB3 send the role switch confirmation message to the gNB1.

S119: the gNB1 sends the RRC_Connection_Reconfiguration signaling to the user equipment.

The RRC_Connection_Reconfiguration signaling may serve as an actual handover instruction.

S120: the user equipment sends the RRC_Connection_Reconfiguration signaling complete message to the gNB1.

S121: the user equipment transmits the user plane data with the gNB3.

The user plane data may come from the split bearer and may be ciphered with a key of the gNB3.

Download user plane data sent from the gNB3 to the user equipment may be from a core network, the gNB1, or the gNB2 (transmitted in S116) .

The user equipment may continue to transmit the user plane data with the gNB1.

S122: the gNB2 releases resources of the user equipment.

The present block may only need to be executed after S115, and the order of execution between other blocks after S115 is not limited.

S123: the user equipment distinguishes the user plane data from the gNB1 and the gNB3.

S124: the user equipment disconnects a connection of the gNB1 and a connection of the gNB2.

S125: the gNB1 sends a sequence number status transfer message to the gNB3.

The sequence number status transition message may be configured to transmit a packet data convergence protocol (PDCP) sequence number to notify the gNB3 a the data transmission state of the gNB1.

S126: the gNB3 notifies the gNB1 to release a context of the user equipment.

S127: the gNB1 releases the resources of the user equipment.

As shown in Fig. 15, in the case of the moving path of the user equipment is AB’, the handover procedure may specifically comprise:

S201: the gNB1 sends a measurement configuration message to the user equipment.

S202: the user equipment transmits the user plane data with the gNB1.

The user plane data may come from the MCG bearer and may be ciphered with the key of the gNB1.

An order of execution between the present block and S201, S203-S207 is not limited.

S203: the user equipment sends the first measurement report to the gNB1.

S204: the gNB1 selects the gNB2 and the gNB3 as the candidate base stations for the user equipment according to the first measurement report.

S205: the gNB1 sends the secondary base station addition request to the gNB2 and the gNB3 respectively.

S206: the gNB2 and the gNB3 send the confirmation message of the secondary base station addition request to the gNB1.

S207: the gNB1 sends the RRC_Connection_Reconfiguration signaling to the user equipment.

S208: the user equipment sends the RRC_Connection_Reconfiguration signaling complete message to the gNB1.

S209: the gNB1 sends the secondary base station reconfiguration complete message to the gNB2 and the gNB3 respectively.

The secondary base station reconfiguration complete message may comprise a priority identifier. The priority identifier of the secondary base station reconfiguration complete message sent to the gNB2, may be indicated a primary candidate base station; and the priority identifier of the secondary base station reconfiguration complete message sent to the gNB3, may be indicated a backup candidate base station.

S210: the user equipment completes a random access to the gNB2 and the gNB3 respectively.

S211: the user equipment transmits the user plane data with the gNB1.

The user plane data may come from the split bearer and may be ciphered with the key of the gNB1.

The order of execution between the present block and S201, S203-S207 is not limited.

S212: the user equipment and the gNB2 transmit the user plane data.

The order of execution between the present block, S203-S207, and S211 is not limited.

S213: the user equipment sends the second measurement report to the gNB1.

S214: the gNB1 selects the gNB2 as a target base station for the user equipment according to the second measurement report.

S215: the gNB1 sends the first role switch request to the gNB2.

S216: the gNB1 sends the second role switch request to the gNB3.

The order of execution between the present block and S215 is not limited.

S217: The gNB2 and the gNB3 send the role switch confirmation message to the gNB1.

S218: the gNB1 sends the RRC_Connection_Reconfiguration signaling to the user equipment.

The RRC_Connection_Reconfiguration signaling may serve as the actual handover instruction.

S219: the user equipment sends the RRC_Connection_Reconfiguration signaling complete message to the gNB1.

S220: the gNB3 releases resources of the user equipment.

The present block may only need to be executed after S215, and the order of execution between other blocks after S215 is not limited.

S221: the user equipment distinguishes the user plane data from the gNB1 and the gNB2.

Before the present block, the user equipment may still receive the user plane data from the gNB1 and the gNB2.

S222: the user equipment disconnects a connection of the gNB1 and a connection of the gNB3.

S223: the gNB1 sends a sequence number status transfer message to the gNB2.

The sequence number status transition message may be configured to transmit a PDCP sequence number to notify the gNB3 a the data transmission state of the gNB1.

S224: the gNB2 notifies the gNB1 to release a context of the user equipment.

S225: the gNB1 releases the resources of the user equipment.

As shown in Fig. 16, Fig. 16 is a structural illustration of a communication handover apparatus in accordance with a first embodiment of the present disclosure, which may comprise a processor 110 and a communication circuit 120, and the processor 110 may be connected to the communication circuit 120.

The communication circuit 120 may be configured to send and receiving user data, and may be an interface which the communication handover apparatus communicates with other communication apparatuses.

The processor 110 may control operations of the communication handover apparatus, and the processor 110 may also be referred to as a central processing unit (CPU) . The processor 110 may be an integrated circuit chip with signal processing capabilities. The processor 110 may also be a general purpose processor, a digital signal processor (DSP) , an application specific integrated circuit (ASIC) , a field programmable gate array (FPGA) , or other programmable logic devices, a discrete gate, or a transistor logic device, a discrete hardware component. The general purpose processor may be a microprocessor, or the processor may be any conventional processor or the like.

The processor 110 may be configured to execute instructions to implement the communication handover method in accordance with one of the first to the eighth embodiments of the present disclosure and any non-conflicting combination.

The communication handover apparatus in the present embodiment may be a base station, or may be an independent component that may be integrated in the base station, such as a baseband board.

As shown in Fig. 17, Fig. 17 is a structural illustration of a communication handover apparatus in accordance with a second embodiment of the present disclosure, which may comprise a processor 210 and a communication circuit 220, and the processor 210 may be connected to the communication circuit 220.

The communication circuit 220 may be configured to send and receiving user data, and may be an interface which the communication handover apparatus communicates with other communication apparatuses.

The processor 210 may control operations of the communication handover apparatus, and the processor 110 may also be referred to as a CPU. The processor 210 may be an integrated circuit chip with signal processing capabilities. The processor 210 may also be a general purpose processor, a DSP, an ASIC, a FPGA, or other programmable logic devices, a discrete gate, or a transistor logic device, a discrete hardware component. The general purpose processor may be a microprocessor, or the processor may be any conventional processor or the like.

The processor 210 may be configured to execute instructions to implement the communication handover method in accordance with one of the ninth to the eleventh embodiments of the present disclosure and any non-conflicting combination.

The communication handover apparatus in the present embodiment may be a user equipment, or may be an independent component that may be integrated in the user equipment, such as a baseband chip.

As shown in Fig. 18, Fig. 18 is a structural illustration of a communication handover apparatus in accordance with a second embodiment of the present disclosure, which may comprise a memory 310. The memory 310 may store instructions, and the instructions may be configured to be executed instructions to implement the communication handover method in accordance with one of the first to the eighth embodiments of the present disclosure and any non-conflicting combination.

The memory 310 may include a read-only memory (ROM) , a random access memory (RAM) , a flash memory, a hard disk, an optical disk, and the like.

As shown in Fig. 19, Fig. 19 is a structural illustration of a communication handover apparatus in accordance with a second embodiment of the present disclosure, which may comprise a memory 410. The memory 410 may store instructions, and the instructions may be configured to be executed instructions to implement the communication handover method in accordance with one of the ninth to the eleventh embodiments of the present disclosure and any non-conflicting combination.

The memory 410 may include a ROM, a RAM, a flash memory, a hard disk, an optical disk, and the like.

In several embodiments provided by the present disclosure, it should be understood that the disclosed methods and apparatus may be implemented in other ways. For example, the apparatus described above are merely schematic. For example, the division of the modules or units is only a logical function division, and an actual implementation may have another division manner, e.g., multiple units or components may be combined or may be integrated into another system, or some features can be ignored or not be performed. In addition, the illustrated or discussed mutual coupling or the direct coupling or the communication connection may be indirect coupling or may be a communication connection via some interfaces, devices or units, and may be electrical, mechanical or other forms.

The units described as separate parts may or may not be physically separated, and the parts displayed as units may or may not be physical units, i.e., which may be located in one place, or may be distributed on multiple network units. Some or all of the units may be selected to achieve the purpose of the solution of the present embodiment according to actual needs.

In addition, each functional unit in each embodiment of the present disclosure may be integrated in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit. The above-mentioned integrated unit can be implemented either in hardware or in software.

If the integrated unit is implemented in the form of a software functional unit and sold or used as a stand-alone product, it may be stored in a computer-readable storage medium. Based on such understanding, a part of the technical solution of the present disclosure that contributes to the related art or all the part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and may include instructions for enabling a computer device (which may be a personal computer, a server, or a network device, etc. ) or a processor to perform all or part of blocks of the method according to various embodiments of the present disclosure. The above-mentioned storage medium may include various media that can store program codes, such as a flash disk, a removable hard disk, a read-only memory (ROM) , a random access memory (RAM) , a magnetic disk, or a CD.

It is understood that the descriptions above are only embodiments of the present disclosure. It is not intended to limit the scope of the present disclosure. Any equivalent transformation in structure and/or in scheme referring to the instruction and the accompanying drawings of the present disclosure, and direct or indirect application in other related technical field, are included within the scope of the present disclosure.

Claims

A communication handover method comprising:

determining at least two candidate base stations for a user equipment by a source base station, and the candidate base stations comprising at least one primary candidate base station;

sending a pre-handover instruction to the user equipment by the source base station, and the pre-handover instruction being configured to instruct the user equipment to enter a dual connectivity state; the user equipment in the dual connectivity state connecting to the source base station and the candidate base station simultaneously, and receiving user plane data from the primary candidate base station by the user equipment, wherein the source base station serves as a primary base station, and the candidate base station serves as a secondary base station;

determining a target base station for the user equipment by the source base station, and the target base station belonging to the candidate base station;

assisting the user equipment to apply the handover to the target base station by the source base station.
The method according to claim 1, wherein the assisting the user equipment to apply the handover to the target base station by the source base station comprises:

performing a role switch between the source base station and the target base station;

sending an actual handover instruction to the user equipment by the source base station, the actual handover instruction being configured to instruct the user equipment to modify the target base station as a new primary base station and modify the source base station as a new secondary base station, and disconnecting all the secondary base stations including the source base station;

releasing resources of the user equipment by the source base station.
The method according to claim 2, wherein the performing the role switch between the source base station and the target base station comprises:

sending a role switch request to each of the candidate base station by the source base station, and the role switch request including a first role switch request and a second role switch request; the first role switch request being sent to the target base station and configured to instruct the target base station to be converted to a new primary base station; the second role switch request being sent to other candidate base stations except the target base station, and being configured to instruct other the candidate base stations except the target base station to release resources of the user equipment;

receiving a role switch confirmation message from the candidate base station by the source base station.
The method according to claim 3, wherein the second role switch request sent to the primary candidate base station is further configured to instruct the primary candidate base station to transmit the user plane data that was unsuccessfully sent, to the target base station.
The method according to claim 3, wherein the role switch request comprises an updating role identifier, and the updating role identifier is configured to indicate that the role switch request is the first role switch request or the second role switch request.
The method according to any one of claims 1-5, wherein the determining at least two candidate base stations for the user equipment by the source base station comprises:

receiving a first measurement report by the source base station, and the first measurement report being reported by the user equipment;

determining whether the first measurement report satisfies a pre-handover threshold, by the source base station;

when the pre-handover threshold is satisfied, determining at least two the candidate base stations according to the first measurement report by the source base station.
The method according to claim 6, wherein the determining at least two the candidate base stations according to the first measurement report by the source base station further comprises:

sending a secondary base station addition request by the source base station to the candidate base station;

receiving a confirmation message of the secondary base station addition request from the candidate base station by the source base station.
The method according to any one of claims 1-5, wherein the determining at least two candidate base stations for the user equipment by the source base station further comprises:

sending a secondary base station reconfiguration complete message to the candidate base station by the source base station.
The method according to claim 8, wherein the secondary base station reconfiguration complete message comprises a priority identifier, and the priority identifier is configured to indicate whether the candidate base station that receives the secondary base station reconfiguration complete message is the primary candidate base station.
The method according to any one of claims 1-5, wherein the determining the target base station for the user equipment by the source base station comprises:

receiving a second measurement report by the source base station, and the second measurement report being reported by the user equipment;

determining whether the first measurement report satisfies an actual handover threshold, by the source base station;

when the actual handover threshold is satisfied, selecting the target base station from the candidate base stations according to the second measurement report by the source base station.
The method according to claim 10, wherein the candidate base station further comprises a backup candidate base station, the backup candidate base station is different from the primary candidate base station, and the target base station belongs to the backup candidate base station.
The method according to any one of claims 1-5, wherein the pre-handover instruction comprises information of the candidate base station.
The method according to claim 12, wherein the candidate base station further comprises a backup candidate base station, and the backup candidate base station is different from the primary candidate base station; information of each of the candidate base station comprises a type tag of the candidate base station, and the type tag is configured to indicate that the candidate base station is the primary candidate base station or the backup candidate base station.
A communication handover method comprising:

reporting a first measurement report to a source base station by a user equipment;

receiving a pre-handover instruction from the source base station by the user equipment, and the pre-handover instruction being configured to instruct the user equipment to enter a dual connectivity state; the user equipment in the dual connectivity state connecting to the source base station and at least two candidate base stations simultaneously, and receiving user plane data from at least one primary candidate base station, wherein the source base station serves as a primary base station, and the candidate base station serves as a secondary base station; the candidate base station is determined by the source base station for the user equipment, and the primary candidate base station belongs to the candidate base station;

entering the dual connectivity state in response to the pre-handover instruction by the user equipment;

reporting a second measurement report to the source base station in the dual connectivity state by the user equipment;

assisting the user equipment to apply the handover to a target base station by the source base station, and the target base station belonging to the candidate base station.
The method according to claim 14, wherein the entering the dual connectivity state in response to the pre-handover instruction by the user equipment comprises:

establishing a connection with the candidate base station in maintaining a connection with the source base station by the user equipment;

receiving user plane data from the primary candidate base station by the user equipment.
The method according to claim 15, wherein the establishing the connection with the candidate base station by the user equipment comprises:

random accessing to the candidate base station by the user equipment.
The method according to claim 14, wherein the assisting the user equipment to apply the handover to the target base station by the source base station comprises:

receiving an actual handover instruction from the source base station by the user equipment;

modifying the target base station as a new primary base station in response to the actual handover instruction by the user equipment, and modifying the source base station as a new secondary base station;

disconnecting all the secondary base stations including the source base station by the user equipment.
The method according to any one of claims 14-17, wherein the pre-handover instruction comprises information of the candidate base station.
The method according to claim 18, wherein the candidate base station further comprises a backup candidate base station, and the backup candidate base station is different from the primary candidate base station; information of each of the candidate base station comprises a type tag of the candidate base station, and the type tag is configured to indicate that the candidate base station is the primary candidate base station or the backup candidate base station.
A communication handover method comprising:

receiving a secondary base station addition request by a candidate base station from a source base station; the secondary base station addition request including user equipment information; and the candidate base station being determined by the source base station for the user equipment;

sending a confirmation message of the secondary base station addition request by the candidate base station to the source base station;

establishing a connection with the user equipment by the candidate base station;

receiving a role switch request from the source base station by the candidate base station, and the role switch request being a first role switch request or a second role switch request;

the candidate base station being applied the handover to a new primary base station in response to the first role switch request, or the candidate base station releasing resources of the user equipment in response to the second role switch request.
The method according to claim 20, wherein after the establishing the connection with the user equipment by the candidate base station further comprises:

sending user plane data to the user equipment by the candidate base station.
The method according to claim 21, wherein before the candidate base station releasing resources of the user equipment in response to the second role switch request further comprises:

transmitting the user plane data that was unsuccessfully sent, to the target base station by the candidate base station.
The method according to any one of claims 20-22, after the sending the confirmation message of the secondary base station addition request by the candidate base station to the source base station, further comprising:

receiving a secondary base station reconfiguration complete message from the source base station by the candidate base station; the secondary base station reconfiguration complete message comprising a priority identifier, and the priority identifier being configured to indicate whether the candidate base station is the primary candidate base station.
The method according to any one of claims 20-22, wherein the role switch request comprises an updating role identifier, and the updating role identifier is configured to indicate that the role switch request is the first role switch request or the second role switch request.
The method according to any one of claims 20-22, wherein after the receiving the role switch request from the source base station by the candidate base station further comprises:

sending a role switch request confirmation message to the source base station by the candidate base station.
A communication handover apparatus comprising a processor and a communication circuit, the processor connecting to the communication circuit;

wherein the processor is configured to execute instructions to implement methods of any one of claims 1-25.
A communication handover apparatus storing instructions, wherein the instructions are configured to be executed to implement methods of any one of claims 1-25.