阅读说明：本技术 无线通信网络中用于处理条件切换(cho)的方法和装置 (Method and apparatus for handling Conditional Handover (CHO) in a wireless communication network ) 是由 F.A.拉瑟夫 M.A.因加尔 H.范德韦尔德 于 2020-08-11 设计创作，主要内容包括：本公开涉及通信方法和系统,用于将第五代(5G)通信系统与物联网(IoT)技术融合,以支持超越第四代(4G)系统的更高数据速率。本公开可应用于基于5G通信技术和IoT相关技术的智能服务,诸如智能家居、智能建筑、智能城市、智能汽车、联网汽车、医疗保健、数字教育、智能零售、安保和安全服务。本公开提供了用于在无线通信网络中处理条件切换(CHO)的装置和方法。(The present disclosure relates to communication methods and systems for fusing fifth generation (5G) communication systems with internet of things (IoT) technology to support higher data rates beyond fourth generation (4G) systems. The present disclosure is applicable to smart services based on 5G communication technologies and IoT related technologies, such as smart homes, smart buildings, smart cities, smart cars, networked cars, healthcare, digital education, smart retail, security, and security services. The present disclosure provides apparatus and methods for handling Conditional Handover (CHO) in a wireless communication network.)

1. A method performed by a source Base Station (BS) in a wireless communication system, the method comprising:

sending a switching request message for the terminal to the candidate target BS, wherein the switching request message comprises source cell configuration information;

receiving a handover request confirm message including first Conditional Handover (CHO) configuration information corresponding to the source cell configuration information from the candidate target BS;

transmitting a first Radio Resource Control (RRC) message including first CHO configuration information to the terminal based on the handover request confirm message; and

transmitting a second RRC message for configuring the updated source cell configuration information for the terminal to the terminal,

wherein the first CHO configuration information is released based on the second RRC message.

2. The method of claim 1, further comprising:

sending a handover request message including the updated source cell configuration information to the candidate target BS;

receiving a handover request confirm message including second CHO configuration information corresponding to the updated source cell configuration information from the candidate target BS; and

transmitting a third RRC message including the second CHO configuration information to the terminal,

wherein the terminal performs the CHO to the candidate target base station in case that a triggering condition of the CHO based on the second CHO configuration information is satisfied.

3. The method of claim 1, further comprising:

transmitting a fourth RRC message to the terminal instructing the terminal to enter an RRC inactive state,

wherein the stored CHO configuration information is released based on the fourth RRC message.

4. The method of claim 1, further comprising:

receiving a CHO cancel message from a candidate target BS; and

transmitting a fifth RRC message to the terminal for releasing the stored CHO configuration information based on the CHO cancel message,

wherein the stored CHO configuration information is released based on a fifth RRC message.

5. A method performed by a candidate target Base Station (BS) in a wireless communication system, the method comprising:

receiving a handover request message for a terminal from a source BS, the handover request message including source cell configuration information;

transmitting a handover request confirm message including first Conditional Handover (CHO) configuration information corresponding to the source cell configuration information to the source BS;

receiving a handover request message including updated source cell configuration information from a source BS;

transmitting a handover request confirm message including second CHO configuration information corresponding to the updated source cell configuration information to the source BS; and

a CHO cancel message is sent to the source BS,

wherein the stored CHO configuration information is released based on RRC messages from the source base station, an

Wherein, based on the CHO cancel message, an RRC message is sent to the terminal for releasing the stored CHO configuration information.

6. A method performed by a terminal in a wireless communication system, the method comprising:

receiving a first Radio Resource Control (RRC) message from a source Base Station (BS), the first RRC message including first Conditional Handover (CHO) configuration information for a terminal to a candidate target BS, the first CHO configuration information corresponding to source cell configuration information;

in case of receiving a second RRC message for configuring updated source cell configuration information for the terminal from the source BS, releasing the first CHO configuration information,

receiving a third RRC message including second CHO configuration information from the source BS;

determining whether a triggering condition of the CHO of the candidate target BS is satisfied based on the second CHO configuration information; and

in case the trigger condition is fulfilled, CHO to the candidate target BS is performed.

7. The method of claim 6, further comprising:

receiving a fourth RRC message instructing the terminal to enter an RRC inactive state from the source BS; and

based on the fourth RRC message, the stored CHO configuration information is released.

8. A source Base Station (BS) in a wireless communication system, the source BS comprising:

a transceiver configured to transmit and receive signals; and

a controller coupled with the transceiver and configured to:

transmitting a handover request message for the terminal to the candidate target BS, the handover request message including source cell configuration information,

receiving a handover request confirm message including first Conditional Handover (CHO) configuration information corresponding to the source cell configuration information from the candidate target BS,

transmitting a first Radio Resource Control (RRC) message including first CHO configuration information to the terminal based on the handover request confirm message, an

Transmitting a second RRC message for configuring the updated source cell configuration information for the terminal to the terminal,

wherein the first CHO configuration information is released based on the second RRC message.

9. The source BS of claim 8,

wherein the controller is further configured to:

sending a handover request message including the updated source cell configuration information to the candidate target BS;

receiving a handover request confirm message including second CHO configuration information corresponding to the updated source cell configuration information from the candidate target BS, and

transmitting a third RRC message including the second CHO configuration information to the terminal, an

Wherein the terminal performs the CHO to the candidate target base station in case that a triggering condition of the CHO based on the second CHO configuration information is satisfied.

10. The source BS of claim 8,

wherein the controller is further configured to send a fourth RRC message to the terminal indicating that the terminal enters an RRC inactive state, an

Wherein the stored CHO configuration information is released based on the fourth RRC message.

11. The source BS of claim 8,

wherein the controller is further configured to:

receiving a CHO cancel message from a candidate target BS, an

Transmitting a fifth RRC message to the terminal for releasing the stored CHO configuration information based on the CHO cancel message, an

Wherein the stored CHO configuration information is released based on a fifth RRC message.

12. A candidate target Base Station (BS) in a wireless communication system, the candidate target BS comprising:

a transceiver configured to transmit and receive signals; and

a controller coupled with the transceiver and configured to:

receiving a handover request message for the terminal from the source BS, the handover request message including source cell configuration information,

transmitting a handover request confirm message including first Conditional Handover (CHO) configuration information corresponding to the source cell configuration information to the source BS,

receiving a handover request message including updated source cell configuration information from the source BS,

transmitting a handover request confirm message including second CHO configuration information corresponding to the updated source cell configuration information to the source BS, an

Receiving a message for performing CHO to the candidate target base station from the terminal in case that a triggering condition of CHO based on the second CHO configuration information is satisfied,

wherein the first CHO configuration information is released based on the updated source cell configuration information.

13. The candidate target BS of claim 12,

wherein the controller is further configured to transmit a CHO cancel message to the source BS,

wherein the stored CHO configuration information is released based on RRC messages from the source base station, an

Wherein, based on the CHO cancel message, an RRC message is sent to the terminal for releasing the stored CHO configuration information.

14. A terminal in a wireless communication system, the terminal comprising:

a transceiver configured to transmit and receive signals; and

a controller coupled with the transceiver and configured to:

receiving a first Radio Resource Control (RRC) message from a source Base Station (BS), the first RRC message including first Conditional Handover (CHO) configuration information for a terminal to a candidate target BS, the first CHO configuration information corresponding to source cell configuration information,

in case of receiving a second RRC message for configuring updated source cell configuration information for the terminal from the source BS, releasing the first CHO configuration information,

receiving a third RRC message including second CHO configuration information from the source BS,

determining whether a triggering condition of the CHO of the candidate target BS is satisfied based on the second CHO configuration information; and

in case the trigger condition is fulfilled, CHO to the candidate target BS is performed.

15. The terminal of claim 14, wherein the controller is further configured to:

receiving a fourth RRC message from the source BS instructing the terminal to enter an RRC inactive state, an

Based on the fourth RRC message, the stored CHO configuration information is released.

Technical Field

The present disclosure relates to the field of wireless communication networks, and more particularly, to controlling enhanced mobility in a wireless communication network by configuring a Conditional Handover (CHO) to a User Equipment (UE) and optimizing performance of the CHO.

Background

In order to meet the increasing demand for wireless data services since the deployment of 4 th generation (4G) communication systems, efforts have been made to develop improved 5 th generation (5G) or pre-5G (pre-5G) communication systems. Accordingly, a 5G or pre-5G communication system is also referred to as an "beyond 4G network" or a "Long Term Evolution (LTE) system". The 5G communication system is considered to be implemented in a higher frequency (millimeter wave) band (e.g., 60GHz band), thereby achieving a higher data rate. In order to mitigate propagation loss of radio waves and increase transmission distance, beamforming, large-capacity multiple-input multiple-output (MIMO), full-dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and massive antenna techniques are discussed in a 5G wireless communication system. Further, in the 5G communication system, development of improvement of a system network based on advanced small cells, a cloud Radio Access Network (RAN), an ultra-dense network, device-to-device (D2D) communication, a wireless backhaul, a mobile network, cooperative communication, coordinated multi-point (CoMP), receiving end interference cancellation, and the like is in progress. In the 5G system, hybrid Frequency Shift Keying (FSK) and Quadrature Amplitude Modulation (QAM) modulation (FQAM) and Sliding Window Superposition Coding (SWSC) as Advanced Coding Modulation (ACM), and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and Sparse Code Multiple Access (SCMA) as advanced access technologies have been developed.

The Internet is a human-centric connected network in which humans generate and consume information, and is now evolving towards the Internet of Things (IoT), where distributed entities, such as Things, can exchange and process information without human intervention. Internet of everything (IoE) has emerged, which is a combination of IoT technology and big data processing technology through connection with a cloud server. As the IoT implements the demand for technical elements such as "sensing technology", "wired/wireless communication and network infrastructure", "service interface technology", and "security technology", sensor networks, machine-to-machine (M2M) communication, Machine Type Communication (MTC), and the like have recently been studied. Such an IoT environment can provide an intelligent internet technology service that creates new value for human life by collecting and analyzing data generated between connected things. In this case, IoT may be applied to various fields including smart homes, smart buildings, smart cities, smart cars or networked cars, smart grids, healthcare, smart homes, and advanced medical services through convergence and combination between existing Information Technology (IT) and various industrial applications.

In this regard, various attempts have been made to apply the 5G communication system to the IoT network. For example, technologies such as sensor networks, Machine Type Communication (MTC), and machine-to-machine (M2M) communication may be implemented through beamforming, MIMO, and array antennas. The application of cloud Radio Access Networks (RANs) as the big data processing technology described above can also be considered as an example of convergence between 5G technology and IoT technology.

Meanwhile, various researches on technologies such as conditional access (CHO) in a wireless communication system are underway to protect and enhance mobility in various communication environments.

Disclosure of Invention

Technical problem

A primary object of embodiments herein is to disclose methods and systems for controlling enhanced mobility in a wireless communication network by configuring at least one user equipment with a Conditional Handover (CHO) configuration of CHO candidate target Base Stations (BSs).

It is another object of embodiments herein to disclose the method and system for reconfiguring the at least one UE with an updated CHO configuration when at least one event occurs after configuring the at least one UE with the CHO configuration, wherein the at least one event comprises at least one of a change in source cell configuration and a change in target cell configuration.

It is another object of embodiments herein to disclose a method and system for reconfiguring at least one UE by performing one of a one-step reconfiguration method and a two-step reconfiguration method.

It is another object of embodiments herein to disclose methods and systems for enabling a CHO candidate target BS to release a CHO configuration previously configured on at least one UE when the CHO candidate target cell is not serving the at least one UE.

It is another object of embodiments herein to disclose methods and systems for enabling a CHO candidate target BS to serve at least one UE by retrieving a UE context and SeqUEnce Number (SN) status transmission from an old source cell when the at least one UE encounters at least one failure on the old source cell.

It is another object of embodiments herein to disclose methods and systems for enabling at least one UE to release the CHO configuration of a CHO candidate target cell upon transition from a Radio Resource Control (RRC) connected state to an RRC inactive state.

Technical scheme

Accordingly, embodiments herein provide methods and systems for handling Conditional Handover (CHO) in a wireless communication network. A method disclosed herein includes configuring, by a source Base Station (BS), a User Equipment (UE) with at least one CHO candidate target cell configuration and at least one CHO trigger condition of at least one CHO candidate target BS. The method further includes reconfiguring the UE with at least one updated CHO candidate target cell configuration of the at least one CHO candidate target BS upon detecting the occurrence of the at least one reconfiguration event. The method further comprises performing, by the UE, CHO on one of the CHO candidate target cells of the at least one CHO candidate target BS based on the updated CHO candidate target cell configuration of the at least one CHO candidate target BS and the at least one CHO trigger condition.

Accordingly, embodiments herein provide a wireless communication network that includes a plurality of User Equipments (UEs) and a plurality of Base Stations (BSs). A source BS of the plurality of BSs is configured to configure a UE of the plurality of UEs with at least one CHO candidate target cell configuration of at least one CHO candidate target BS of the plurality of BSs and at least one CHO trigger condition. The source BS is further configured to reconfigure the UE using at least one updated CHO candidate target cell configuration of the at least one CHO candidate target BS upon detecting the occurrence of the at least one reconfiguration event. The UE is configured to perform CHO on one of the CHO candidate target cells of the at least one CHO candidate target BS based on the updated CHO candidate target cell configuration of the at least one CHO candidate target BS and the at least one CHO trigger condition.

These and other aspects of the example embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating exemplary embodiments and numerous specific details thereof, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the example embodiments of the present disclosure without departing from the spirit thereof, and the example embodiments of the present disclosure include all such modifications.

Advantageous effects

According to the embodiments, an apparatus and method capable of effectively controlling enhanced mobility in a wireless communication system may be provided.

Drawings

Embodiments herein are illustrated in the accompanying drawings in which like reference numerals refer to corresponding parts throughout the various views. The embodiments herein will be better understood by the following description with reference to the accompanying drawings, in which:

fig. 1 depicts a wireless communication network in accordance with embodiments disclosed herein;

fig. 2 is a block diagram depicting hardware components of a Base Station (BS)/cell in accordance with embodiments disclosed herein;

FIG. 3 is a block diagram depicting hardware components of a User Equipment (UE) in accordance with embodiments disclosed herein;

fig. 4 is a sequence diagram depicting a one-step reconfiguration of a UE in accordance with embodiments disclosed herein;

fig. 5 is an example sequence diagram depicting a two-step reconfiguration of a UE according to embodiments disclosed herein;

6A, 6B, and 6C are example sequence diagrams depicting the initiation of release of a Conditional Handover (CHO) target cell configuration by a CHO candidate target cell when the target cell is no longer serving the UE, in accordance with embodiments disclosed herein;

fig. 7 is an example sequence diagram depicting a rejection of a handover cancel request of a CHO candidate target cell according to embodiments disclosed herein;

8A, 8B, and 8C are example sequence diagrams depicting example procedures in which a Radio Resource Control (RRC) reconfiguration message is sent to a UE to instruct the UE to remove a CHO candidate target cell, in accordance with embodiments disclosed herein;

fig. 9A and 9B are exemplary diagrams depicting a fall-back to connection establishment procedure after a UE encounters at least one failure on a source cell, in accordance with embodiments disclosed herein;

fig. 10A is an example sequence diagram depicting a fallback procedure to connection re-establishment after a UE encounters at least one failure on a source cell in accordance with embodiments disclosed herein;

fig. 10B depicts an example RRC reconfiguration complete message including information about an old source cell according to embodiments disclosed herein;

fig. 10C depicts example signaling provided to a UE for a procedure to implement fallback to RRC establishment in accordance with an embodiment disclosed herein;

fig. 11 is an example sequence diagram illustrating retrieval of Sequence Number (SN) status transmissions by a CHO candidate target cell to serve a UE after the UE encounters at least one failure on a source cell according to embodiments disclosed herein;

fig. 12A is an example sequence diagram illustrating the association of CHO trigger conditions with CHO target cell configurations of CHO candidate target cells according to embodiments disclosed herein; and

fig. 12B depicts a CHO configuration of CHO candidate target cells according to embodiments disclosed herein.

Detailed Description

The exemplary embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The description herein is intended merely to facilitate an understanding of ways in which the example embodiments herein may be practiced and to further enable those of skill in the art to practice the example embodiments herein. Accordingly, the disclosure should not be construed as limiting the scope of the example embodiments herein.

Generally, a wireless communication network monitors the behavior of a User Equipment (UE) and provides the UE with the necessary resources to perform one or more operations. Examples of wireless communication networks may be, but are not limited to, Long Term Evolution (LTE)/4G networks, New Radio (NR)/5G networks, and the like. Examples of one or more operations may be, but are not limited to, uplink data transmission, downlink data transmission, and the like. The signal strength and quality experienced by a UE in performing one or more operations may vary based on the proximity of the UE to (i.e., distance from) a base station/Radio Access Network (RAN) node (gbdeb)/enodeb (enb)) and the interference experienced by the UE from neighboring BSs. UEs close to the BS/cell may have better signal strength than UEs far away from the BS (i.e., cell edge case). Furthermore, when the serving BS/cell and the neighbor BSs/cells have low loads, the UE experiences less interference.

In a wireless communication network, a BS/RAN node may always maintain the context of a UE in an active Radio Resource Control (RRC) connected state. At any point in time, the serving BS/source cell may perform a handover of the UE from its control to another BS/cell (hereinafter referred to as a target BS/cell) for various reasons, such as, but not limited to, a weak signal condition, heavy loading on the serving BS, etc. Performing handover involves transmitting the entire context of the UE from the source cell to the target cell and changing the primary cell (PCell) of the UE. The serving cell performs handover of the UE to the target cell upon receiving the assistance information from the UE. The assistance information comprises measurement reports of neighbouring cells. The serving cell configures the UE to measure the signal strength of the serving cell and the neighboring cells on the same frequency or different frequencies that may belong to different BSs/cells. The serving cell further configures the UE with specific measurement and reporting criteria. When the configured measurement and reporting criteria are met, the UE sends assistance information to the serving cell for handover.

In a typical handover method, a serving cell triggers a Handover (HO) procedure by sending a HO request to a target cell. Upon receiving an Acknowledgement (ACK) from the target cell in response to the HO request, the serving cell initiates handover of the UE by sending an RRC reconfiguration to the UE. The RRC reconfiguration includes a HO command and configuration of the target cell. Upon receiving the RRC reconfiguration from the serving cell, the UE initiates a Random Access procedure for handover by sending a Physical Random Access Channel (PRACH) preamble to the target cell. However, when the UE moves or rotates when initiating a handover, the UE may experience a very fast degradation of signal strength because the UE is able to perform one or more operations at frequency range 2(FR2) or higher. At FR2 or higher frequency ranges, the change in signal strength and the degradation in signal strength may be more unfavorable than the change at frequency range 1(FR1) or lower. Such rapid degradation of signal strength may result in a higher probability of handover failure. In addition, the UE may not be able to receive the HO command from the serving cell due to the rapid degradation of signal strength. Resulting in handover failure.

In order to reduce handover failures due to rapid degradation of signal strength, 3GPP defines Conditional Handover (CHO).

In conventional CHO approaches, the serving cell, upon receiving measurements from one or more neighboring cells of the UE, initiates CHO preparation with the one or more neighboring cells of the UE. The serving cell receives acknowledgements from one or more neighboring cells that have successfully prepared (i.e., admission control was successful) the serving UE. The one or more neighboring cells that send the acknowledgement to the serving cell may be CHO candidate target cells/CHO candidate target cells. The acknowledgement received from the target/neighbor cell includes the configuration of the target cell/CHO configuration that the UE must apply when performing a CHO handover to the target cell. The serving cell sends an RRC reconfiguration message to the UE, which includes the CHO configurations of the one or more candidate target cells. The serving cell additionally provides the UE with one or more trigger conditions associated with the CHO configuration. The UE may use one or more trigger conditions to evaluate whether handover to any configured CHO candidate target cell may be triggered. Unlike typical handover methods, the UE does not initiate handover execution upon receiving an RRC reconfiguration message including a CHO configuration. The UE stores the received CHO configuration. Once the one or more trigger conditions associated with the CHO configuration have been met, the UE evaluates the one or more trigger conditions associated with the CHO configuration and automatically initiates handover execution. Thus, CHO ensures that RRC reconfiguration messages (including CHO configuration of CHO candidate target cells) are provided to the UE in advance to cope with poor radio signaling conditions. Providing the UE with an RRC reconfiguration message in advance reduces the probability of failure due to not receiving a HO command from the serving BS/cell, which further improves mobility robustness.

In the conventional CHO method, when a UE performs a transition from an RRC connected state to an RRC inactive state, the UE stores an Application Server (AS) context. The AS context includes RRC reconfiguration messages (including CHO configuration of CHO candidate target cells) and configuration of special cells (spcells). Once the UE recovers the RRC connected state from the RRC inactive state, the UE applies the CHO configuration to initiate HO execution with one of the CHO candidate target cells. However, the CHO configuration may be invalid when the UE resumes the RRC connected state. Thus, an increase in the amount of signaling results.

Further, the configuration of the serving cell may change when the UE recovers the RRC connected state from the RRC inactive state. The configuration change of the serving cell also affects the configuration of the CHO candidate target cell. Therefore, in such a case, the UE may have an invalid CHO configuration.

Furthermore, once the UE is configured with CHO, the loading conditions on the CHO candidate target cell may change and the CHO candidate target cell may no longer serve the UE. The conventional CHO approach does not involve any signaling that allows the CHO candidate target cell to modify or cancel the HO for the UE that has been confirmed and prepared.

Embodiments herein disclose methods and systems for controlling enhanced mobility in a wireless communication network by configuring a User Equipment (UE) with Conditional Handover (CHO) and optimizing performance of the CHO.

Referring now to the drawings, and more particularly to fig. 1 through 12B, wherein like reference numerals designate corresponding features consistently throughout the figures, there is shown an exemplary embodiment.

Fig. 1 depicts a wireless communication network 100 in accordance with embodiments disclosed herein. Examples of the wireless communication network 100 may be, but are not limited to, a Long Term Evolution (LTE)/4G network, an LTE-advanced network, a new radio-over-air (NR)/5G network, a Universal Mobile Telecommunications Service (UMTS), a Global System for Mobile Communications (GSM), and an enhanced data rates for GSM evolution (EDGE) radio access network (GERAN) System, or any other next generation network.

The wireless communication network 100 includes a plurality of User Equipments (UEs) 102, at least one Core Network (CN)104, and a plurality of base stations/Radio Access Network (RAN) nodes 106.

The UE(s) 102 referred to herein may be user equipment capable of supporting the wireless communication network 100. Examples of the UE102 may be, but are not limited to, a mobile phone, a smartphone, a tablet, a handheld phone, a Personal Digital Assistant (PDA), a laptop, a computer, a wearable computing device, a vehicle infotainment device, an internet of things (IoT) device, a Virtual Reality (VR) device, a wireless fidelity (Wi-Fi) router, an adapter (USB dongle), a robot, an automated guided vehicle, or any other device that supports the wireless communication network 100.

UE102 may connect with at least one BS 106 over an interface supported by wireless communication network 100 to perform one or more operations. Examples of interfaces may be, but are not limited to, a wired interface, a wireless interface (e.g., air interface, Nu interface, etc.), a wireless fronthaul interface, a wired or wireless backhaul interface, or any structure that supports communication over a wired or wireless connection. Examples of operations may be, but are not limited to, uplink data transmission, downlink data transmission, and the like. In examples herein, the data may be, but is not limited to, at least one of voice packets, video packets, data packets, and the like.

The UE102 may operate in various states such as, but not limited to, a Radio Resource Control (RRC) connected state, an RRC inactive/idle state, and so on. The RRC connected state may be a state in which the UE102 has established an RRC connection with at least one BS 106 to perform one or more operations. The RRC inactive state may be a state in which the UE102 has not established an RRC connection with any BS 106.

The CN 104 referred to herein may be one of an Evolved Packet Core (EPC), a 5G Core (5GC) network, and the like, but is not limited thereto. CN 104 may be connected to one or more BSs 106 and external data networks (not shown). Examples of external Data networks may be, but are not limited to, the internet, Packet Data Networks (PDNs), Internet Protocol (IP) multimedia core Network subsystems, and the like. CN 104 may be configured to connect at least one UE102 (connected with associated BS 106) to an external data network to perform one or more operations.

The BS/RAN node(s) 106 referred to herein may be nodes such as, but not limited to, evolved node (eNB), new air interface node (gNB), etc. BS(s) 106 may be associated with one or more cells. In an embodiment, the terms traversal document, such as BS 106 and cell 106, may be used interchangeably. The BS 106 may connect one or more UEs 106 with the CN 104. BS 106 may be configured to perform radio resource management functions such as, but not limited to, radio bearer control, radio admission control, connection mobility control, dynamic allocation of resources (scheduling) to UEs in the uplink/downlink, and the like.

The BS(s) 106 referred to herein may act as a serving BS/cell or a neighbor BS/cell for the UE 102. The BS 106 connected to the UE102 is referred to herein as a source BS/cell. Embodiments herein use terms such as, but not limited to, "serving BS/cell," source BS/cell, "" primary cell (PCell), "primary BS," and the like, which are used interchangeably for the BS/cell currently connected with the UE 102. BSs/cells 106 that may be present in the vicinity of the UE102 are referred to herein as neighbor BSs/cells (i.e., not connected to the UE).

The source BS/cell 106 may be configured to maintain a context of the UE102 (hereinafter referred to as UE context). The UE context may be necessary information needed to maintain and provide communication services (e.g., voice packets, video packets, data packets, etc.) to the UE 102. The UE context may include information such as, but not limited to, UE state information (e.g., RRC connected state, RRC inactive state, etc.), security information, UE capability information, an identification of the UE associated logical S1 connection, and the like.

The source BS/cell 106 may also be configured to monitor the behavior/mobility of the UE102 and perform handover of the UE102 to the target BS/cell 106. The target BS/cell 106 may be one of the neighboring BSs/cells of the UE 102. The handover of the UE102 involves transferring the UE context from the source BS/cell 106 to the target BS/cell 106.

In an embodiment, the source cell 106 may be configured to control enhanced mobility of the UE102 by configuring Conditional Handover (CHO) to the UE102 and optimizing performance of the CHO.

The source cell 106 initiates CHO candidate cell preparation upon receiving measurements of one or more neighboring cells from the UE 102. When the UE102 experiences degradation in signal strength associated with the source cell and degradation in the quality of the communication service being accessed by the UE102, the source cell 106 may receive measurements of one or more neighboring cells from the UE 102. During CHO candidate cell preparation, the source cell 106 sends its configuration, which is the current configuration available on the UE (hereinafter referred to as serving/source cell configuration), to one or more cells. In an embodiment, the one or more cells may be cells of the source BS 106 or the neighbor BSs 106. The source cell 106 may send the source cell configuration to one or more cells 106 in a handover request as handover preparation. Upon receiving the source cell configuration, one or more cells on the BS (having received the handover request) may perform admission control and reserve resources for the UE 102. One or more cells that traverse the document, perform admission control, and reserve resources for the UE102 for handover are referred to as CHO candidate target cells. With respect to reserving resources for the UE102, each CHO candidate target cell 106 prepares a target cell configuration (i.e., the UE102 may apply the configuration if the UE102 chooses to perform a CHO handover to the corresponding candidate target cell). In an embodiment, each CHO candidate target cell 106 may prepare the target cell configuration as an increment of the source cell configuration. The delta in which the target cell configuration is prepared as the source cell configuration means that the target cell configuration is ready without releasing the source cell configuration (i.e. the target cell configuration is ready with respect to the received source cell configuration or the target cell configuration has been updated on an existing source configuration).

The one or more CHO candidate target cells 106 may also include a target cell configuration prepared as an increment of the source cell configuration in a container (container). The container referred to herein may be an RRC message that enables the source cell 106 to skip the decoding process that must be performed on the container. Embodiments herein may use terms such as "container," "RRC reconfiguration message," and the like interchangeably to refer to an RRC message that may skip the decoding process. Thus, the target cell configuration of one or more CHO candidate target cells 106 may be expressed as:

target cell configuration source cell configuration + container (target cell configuration prepared as an increment of source cell configuration)

Embodiments herein may use terms such as "CHO target cell configuration", "CHO candidate target cell configuration", "target cell configuration", and the like interchangeably to refer to the configuration of the CHO candidate target cell 106.

In an embodiment, one or more CHO candidate target cells 106 may prepare a CHO target cell configuration based on the UE capability coordination and the source cell configuration. Thus, the source cell or target cell configuration may be reconfigured by ensuring that the reconfigured source cell or target cell configuration may be within the UE capability coordination sphere and may be complied with by the UE 102. The one or more CHO candidate target cells 106 include the CHO target cell configuration in the RRC reconfiguration message. The one or more CHO candidate target cells 106 send an RRC reconfiguration message to the source cell 106 in a handover request confirm message.

The source cell 106 encapsulates the containers received from the one or more CHO candidate target cells 106 into the RRC reconfiguration message and identifies the CHO target cell configuration included in the RRC reconfiguration message. The source cell 106 prepares a CHO configuration for one or more CHO candidate target cells by associating a trigger condition/CHO trigger condition with the CHO target cell configuration of each CHO candidate target cell. Thus, the CHO configuration includes a CHO target cell configuration for each CHO candidate target cell 106 and a CHO trigger condition associated with each CHO target cell configuration. The CHO trigger condition may be based on a measurement event such as, but not limited to, event A3, event a5, etc.

The CHO trigger conditions for each CHO candidate target cell 106 include measurement objects and reporting configurations. The measurement object may be, but is not limited to, Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), and the like. The measurement object may indicate the frequency at which the CHO candidate target cell 106 may operate. The reporting configuration may state that at least one condition of the associated CHO candidate target cells must be met so that the UE102 may initiate CHO execution for handover to one of the CHO candidate target cells 106. The source cell 106 designs a reporting configuration for CHO regardless of whether the handover is configured to the same frequency. The source cell 106 may use CHO in addition to normal handover. Normal handover may be used for improved network control and CHO may be used to improve the robustness of the handover. The source cell 106 may design a reporting configuration for CHO based on one or more options. Examples of these options may be, but are not limited to, using a separate reporting configuration for CHO (i.e., blind configuration), using a reporting configuration already used for normal handover for CHO, using a reporting configuration for CHO by adding a CHO offset in the reporting configuration used for normal handover, etc. Similarly, the source cell 106 may design the measurement object based on one or more options. Examples of options may be, but are not limited to, reusing measurement objects configured for other Radio Resource Management (RRM) purposes (the same parameter values may be used), configuring measurement objects separately for CHO (i.e., blind configuration), etc.

The source cell 106 links the measurement object and the reporting configuration using a measurement identifier (e.g., an ID or IE). The measurement identifier holds a unique integer value that cannot be applied to any other CHO candidate target cell 106. Thus, using the measurement identifier, the UE102 may uniquely identify the CHO candidate target cell associated with the CHO trigger condition. Alternatively, the source cell 106 may configure a new identifier or measurement identifier within the CHO configuration for linking measurement objects and reporting configurations. The new identifier may incur more overhead, but may be used if the same CHO trigger condition is applied to multiple candidates. Furthermore, the use of the new identifier automatically avoids RRM (i.e. does not trigger measurement reporting when CHO trigger conditions are met).

The source cell 106 may provide a measurement identifier associated with the CHO trigger condition to one or more target cells 106 along with the source cell configuration in the handover request. One or more CHO candidate target cells 106 may add a measurement identifier in a container carrying the CHO target cell configuration. Adding the measurement identifier in the container enables the UE102 to fully understand the association between the CHO trigger condition and the CHO target cell configuration. Thus, the CHO configuration may comprise a container with a CHO target cell configuration and a measurement identifier corresponding to the CHO trigger condition. Alternatively, the source cell 106 may include the reporting configuration and the measurement object (configured for CHO) within the existing measurement configuration rather than within the CHO target cell configuration (i.e., not within the RRC container). Alternatively, the source cell 106 may enable the target cell 106 to add the CHO trigger condition outside the RRC container. In such a scenario, if the UE102 performs an autonomous release of the CHO configuration, the UE102 has to remove the CHO trigger condition alone.

In an embodiment, the source cell 106 may associate the same CHO trigger condition with the CHO target cell configuration of one or more CHO candidate target cells. In such a case, the source cell 106 uses the new unique identifier to uniquely identify the CHO candidate cell associated with the CHO trigger condition. The source cell 106 signals the new unique identifier to one or more CHO candidate target cells 106. The one or more CHO candidate target cells 106 may add a value indicative of the new unique identifier in the CHO target cell configuration. The one or more CHO candidate target cells 106 may also add a value indicative of the new unique identifier as part of the in-container RRC reconfiguration message.

In an embodiment, the source cell 106 may associate a plurality of CHO trigger conditions with the CHO target cell configurations of one or more CHO candidate target cells. The source cell 106 may associate multiple CHO trigger conditions for each CHO candidate target cell 106 by combining two events, such as, but not limited to, event A3, event a5, etc. To avoid measurement burden on the UE102, the source cell 106 may use events over different triggering quantities. For example, event A3 may be an RSRP-based event, while event a5 may be an RSRQ-based event, or vice versa. The source cell 106 may combine these two events using a single logical "AND" operation. The support of two trigger conditions combined by a single logical "AND" operation can only be an enhancement to CHO operations. CHO trigger conditions (including a combination of two events) cannot be applied to measurement reporting. The measurement ID or new equivalent ID for the link and report configuration within the CHO configuration may have the option of linking two report configurations (including two events).

The source cell 106 sends CHO configurations for one or more CHO candidate target cells 106 to the UE102, where each CHO configuration corresponding to each CHO candidate target cell may include a CHO target cell configuration and associated CHO trigger conditions. Upon receiving the CHO configurations of the one or more CHO candidate target cells, the UE102 stores the CHO configurations in a CHO candidate target list. Since the received CHO target cell configuration includes a combination of the source cell configuration and the container with the target cell configuration prepared for the increment of the source cell configuration, the UE102 may apply the source cell configuration to continue in the source cell 106 before performing the CHO execution. The UE102 may perform CHO execution for handover when a CHO trigger condition associated with one of the CHO candidate target cells is met. CHO performs a target cell configuration involving applying an increment prepared for the source cell configuration to handover to one of the CHO candidate target cells satisfying the CHO trigger condition. Thus, handover failures may be reduced by providing a CHO configuration to the UE102 in advance in poor cell edge radio conditions.

In an embodiment, the UE102 may select one of the CHO candidate target cells for handover based on its implementation when the CHO trigger conditions associated with the two or more CHO candidate target cells have been met. In an embodiment, when the CHO trigger conditions associated with two or more CHO candidate cells have been met, the UE102 may select (from among the two or more CHO candidate target cells) a CHO candidate target cell for handover having the highest CHO trigger condition in terms of radio quality (i.e., reference signal received power). In an embodiment, the UE102 may select a CHO candidate target cell from the two or more CHO candidate target cells based on a random access, RA, resource configuration (e.g., if contention-free resources are configured, etc.) when a CHO trigger condition associated with the two or more CHO candidate target cells has been satisfied. In an embodiment, when the CHO trigger conditions associated with two or more CHO candidate target cells have been met, the UE102 may select a CHO candidate target cell from among the two or more CHO candidate target cells based on a combination of two events (combination events) associated with each CHO candidate target cell. In an example, the combined events may include RSRP-based event A3 and RSRP-based event a 4. In such a scenario, the UE102 may specify a combined event by applying a weighting factor w to event A3 and applying (1-w) to event a4, where the value of the weighting factor w is less than 1. In another example, the combined event may include RSRP-based event A3 and RSRQ-based event a4, or vice versa. In such a case, the UE102 may specify a combined event by applying a weighting factor w to event A3 and (1-w) to event a4, where the value of the weighting factor w is less than 1. Alternatively, the UE102 may apply equal weight to the two events. In selecting a CHO candidate cell 106 for handover, the UE102 applies the CHO target cell configuration of the selected CHO candidate target to handover to the selected CHO candidate cell 106.

Embodiments herein enable the UE102 to release the stored CHO configuration when performing a transition from the RRC connected state to the RRC inactive state. The UE102 may transition to the RRC inactive state when a CHO configuration of one or more candidate target cells 106 is received from the source cell 106. The UE102 may receive an RRC release message from the source cell 106 with the suspend configuration, which enables the UE102 to transition from an RRC connected state to an RRC inactive state. However, the suspend configuration does not explicitly instruct the UE102 to release the CHO configuration. In such a scenario, the UE102 releases the stored CHO configuration upon transitioning to the RRC inactive state. Therefore, handover failures may be reduced due to changes in the CHO configuration.

Embodiments herein enable the source cell 106 to reconfigure the UE102 with an updated CHO configuration upon detecting the occurrence of at least one event after providing the CHO configuration of one or more CHO candidate target cells 106 to the UE 102. Examples of the at least one event may be, but are not limited to, a change in a source cell configuration, a change in a target cell configuration, and the like.

In an embodiment, upon detecting the occurrence of at least one event after providing the CHO configuration of one or more CHO candidate target cells 106 to the UE102, the source cell 106 may reconfigure the UE102 independently with the updated source cell configuration and target cell configuration. Consider an example event in which, after providing the CHO configuration to the UE102, the source cell configuration has changed and the changed source cell configuration does not affect the target cell configuration. In such an event, the source cell 106 may provide only the changed/updated source cell configuration to the UE102 in an RRC reconfiguration message. The source cell configuration may be reconfigured as an increment of the existing source cell configuration. Throughout this document, the reconfigured/updated source cell configuration is referred to as an incremental source cell configuration. Thus, the UE102 may receive the updated source cell configuration without changing the already stored CHO target cell configuration. Consider another example event in which the CHO target cell configuration of the CHO candidate target cell 106 has been changed/reconfigured after the configuration of the CHO configuration is provided to the UE102, and the changed target cell configuration does not affect the source cell configuration. In such an event, the source cell 106 receives the reconfigured/updated target cell configuration from the CHO candidate target cell 106. The target cell configuration may be reconfigured to an increment of the source cell configuration available to the CHO candidate target cell 106. Throughout this document, the reconfigured/updated CHO target cell configuration is referred to hereinafter as the incremental CHO target cell configuration. The source cell 106 provides the UE102 with a delta CHO target cell configuration. The UE102 forms a CHO configuration of CHO candidate target cells for handover as a combination of the source cell configuration currently available at the UE102 and the received incremental CHO target cell configuration.

In an embodiment, the source cell 106 does not independently provide the UE102 with the updated source cell configuration and the updated CHO target cell configuration in one or more scenarios, wherein the source cell configuration affects the CHO target cell configuration and vice versa. Consider an example scenario in which, after the CHO configuration is provided to the UE102, the source cell configuration has changed, and the changed source cell configuration may affect the CHO target cell configuration. In such a scenario, if the source cell 106 sends an RRC reconfiguration message to the UE102 that only includes the source cell configuration, a potential CHO target cell configuration may result, which may be generated as a combination of the changed/updated source cell configuration and the CHO target cell configuration already available. Consider another example scenario in which the CHO target cell configuration of the CHO candidate target cell 106 changes after the CHO configuration is provided to the CHE configuration, and the target cell configuration may affect the source cell configuration. In such a scenario, updating the UE102 with the changed/updated CHO target cell configuration (prior to updating the source cell configuration) may result in an invalid CHO target cell configuration that has been generated as a combination of the source cell configuration available at the UE102 and the updated incremental target cell configuration (sent to the UE102 by the CHO candidate target cell). Thus, in the example scenario described above, the source cell 106 does not independently update the source cell configuration and the target cell configuration to the UE 102.

In an embodiment, upon detecting at least one event after providing the CHO configuration to the UE102, the source cell 106 may reconfigure the UE102 by performing a one-step reconfiguration. One-step reconfiguration of the UE102 includes sending both the updated/delta source and CHO target cell configurations to the UE102 at once in a single RRC reconfiguration message. When the source cell configuration has changed after providing the CHO configuration to the UE102, the source cell 106 sends an incremental source cell configuration (i.e., a change in the source cell configuration relative to the earlier/previous source cell configuration based on which each candidate target cell generated the CHO configuration) to the CHO candidate target cells in the handover request. When receiving the incremental source cell configuration, the CHO candidate target cell 106 prepares an updated/incremental CHO target cell configuration in a container. Preparing an updated CHO configuration involves updating the CHO target cell configuration to an increment of the incremental source cell configuration. Thus, the updated/incremental CHO target configuration includes an incremental source cell configuration and a container including an incremental target cell configuration prepared as an incremental source cell configuration. The CHO candidate target cell 106 sends the incremental CHO target cell configuration to the source cell 106 in a handover request acknowledge message. Upon receiving the handover request confirm message, the source cell 106 sends an RRC reconfiguration message to the UE 102. The RRC reconfiguration message includes the incremental CHO target cell configuration of the CHO candidate target cell 106. The incremental CHO target cell configuration of each CHO candidate target cell 106 includes an incremental source cell configuration and a container including a corresponding target cell configuration prepared as an increment of the incremental source cell configuration.

In an embodiment, if the source cell 106 initiates a configuration change that affects the target cell configuration, the source cell 106 sends a handover modification request to one or more CHO candidate target cells 106. The source cell 106 waits to receive acknowledgements and incremental CHO target cell configurations from one or more candidate target cells 106. The source cell 106 forms an RRC reconfiguration message that includes the incremental source cell configuration and the incremental CHO target cell configuration. The source cell 106 sends an RRC reconfiguration message to the UE 102.

Upon receiving the RRC reconfiguration message, the UE102 first updates the source cell configuration in the stored CHO configuration with the received incremental source cell configuration. The UE102 then updates the CHO target cell configuration in the stored CHO configurations with the received incremental CHO target cell configuration. Thus, the stored CHO configuration is updated.

One-step reconfiguration of the UE102 may be applicable to scenarios where the updated source or target cell configuration may be sent to the UE102 with a delay. For example, transmission of the updated/delta source cell configuration to the UE102 may be delayed until the source cell 106 receives the updated/delta CHO target cell configuration from the CHO candidate target cell 106. For example, transmission of the updated/incremental CHO target cell configuration to the UE102 may be delayed until the source cell 106 generates an updated/incremental source cell configuration. However, in scenarios where the transmission of the updated cell configuration to the UE102 cannot be delayed, the updated source cell configuration must be immediately sent to the UE102 to ensure good quality of service (QoS) and uninterrupted service (i.e., the change in source cell configuration must be immediately updated at the UE102 without waiting for an acknowledgement from the CHO candidate target cell 106). In such a scenario, the CHO target cell configuration may become invalid if only the updated source cell configuration is provided to the UE102, as the CHO target cell configuration stored at the UE102 may be a combination of the updated source cell configuration and the existing CHO target cell configuration. Thus, in such a scenario, embodiments herein enable the source cell 106 to reconfigure the UE102 by performing a two-step reconfiguration.

In the two-step reconfiguration of the UE102, when the source cell 106 reconfigures its configuration, the source cell 106 sends a first RRC reconfiguration message to the UE 102. The first RRC reconfiguration message includes the updated/incremental source cell configuration and the release of the CHO configuration corresponding to all CHO candidate target cells 106. Upon receiving the first RRC reconfiguration message from the source cell 106, the UE102 releases the stored CHO configuration and stores the updated/delta source cell configuration received from the source cell 106. Upon sending the first RRC message to the UE102, the source cell 106 sends a handover modification request to the CHO candidate target cell 106. In response to the handover modification request, the source cell 106 receives the updated/delta CHO target cell configuration from the CHO candidate target cell 106 in a handover request acknowledgement. Once the updated/delta CHO target cell configuration is received, the source cell 106 sends a second RRC reconfiguration message to the UE102, where the second RRC reconfiguration message includes a container with the delta target cell configuration. Further, the source cell 106 may include a source cell configuration that does not affect the CHO target cell configuration in the second RRC reconfiguration message. Upon receiving the second RRC reconfiguration message, the UE102 stores the CHO target cell configuration of the CHO candidate target cell 106 by including a delta CHO target cell configuration relative to the received delta source cell configuration in the first RRC reconfiguration message.

Embodiments herein enable the CHO candidate target cell 106 to send a handover cancel request to the source cell 106 if the CHO candidate target cell 106 can no longer serve a CHO-prepared UE 102. Based on the handover request received from the source cell 106, the CHO candidate target cell 106 performs admission control and reserves resources for the UE 102. In reserving resources for the UE102, the CHO candidate target cell 106 sends a handover request acknowledgement to the source cell 106 in response to the handover request. However, when sending a handover request acknowledgement to the source cell 106, the CHO candidate target cell 106 may reallocate resources to the UE102 in one or more scenarios. Examples of scenarios may be, but are not limited to, load changes of the CHO candidate target cell 106, reallocation of resources of the UE102 configured with CHO configurations of other UEs 102, etc. For example, the UE102 may perform CHO execution to handover to only one CHO candidate target cell 106 when an associated CHO trigger condition is met. Since there is uncertainty as to when the UE102 may initiate the actual CHO execution, the CHO candidate target cell 106 may reallocate the reserved resources of the UE102 configured with the CHO configuration to other UEs that are attempting to access the CHO candidate target cell. Thus, the CHO candidate target cell 106 does not want to serve the UE102 configured with its CHO configuration. For example, the load on the CHO candidate target cell 106 may increase when a handover request acknowledgement is sent to the source cell 106. In such a scenario, the CHO candidate target cell 106 does not want to serve the UE102 configured with its CHO configuration.

When a CHO candidate target cell 106 does not wish to serve a UE102 configured with its CHO configuration, the CHO candidate target cell 106 initiates a release of the CHO configuration provided for the UE 102. The CHO candidate target cell 106 initiates the release of the CHO configuration by sending a handover release/cancel request or a CHO configuration release request to the source cell 106. Upon receiving the handover cancel request, the source cell 106 accepts the handover cancel request and sends a handover cancel request acknowledgement to the CHO candidate target cell 106. Further, upon receiving the handover cancel request, the source cell 106 requests the UE102 to release the CHO configuration of the CHO candidate target cell 106.

In an embodiment, the source cell 106 may accept the handover cancel request and send a handover cancel request acknowledgement to the CHO candidate target cell 106 by ensuring that the UE102 has released the CHO configuration of the CHO candidate target cell 106. Upon receiving a handover cancel request or a CHO configuration release request from a CHO candidate target cell 106, the source cell 106 sends an RRC reconfiguration message to the UE102 to release the CHO configuration of the corresponding CHO candidate target cell 106. In an embodiment, upon receiving the RRC reconfiguration message to release the CHO configuration of the candidate target cell 106, the UE102 releases the CHO configuration of the candidate target cell 106 and sends an RRC reconfiguration complete message to the source cell 106. Releasing the CHO configuration on the UE102 involves removing the stored CHO target cell configuration and associated CHO trigger conditions of the CHO candidate target cell 106 from the CHO candidate target cell list. In an embodiment, upon receiving the RRC reconfiguration message to release the CHO configuration of the candidate target cell 106, the UE102 releases the CHO configuration of the candidate target cell 106 and sends a Radio Link Control (RLC) acknowledgement to the source cell 106 as an RRC reconfiguration complete message. Upon receiving the RRC reconfiguration complete message from the UE102, the source cell 106 accepts the handover cancellation of the CHO candidate target cell and sends a handover cancellation request acknowledgement to the CHO candidate target cell 106.

Embodiments herein enable the source cell 106 to reject handover cancellations received from the CHO candidate target cell 106 when the UE102 cannot receive an RRC reconfiguration message from the source cell 106 to release the CHO configuration of the CHO candidate target cell 106. The UE102 configured with the CHO configuration of the CHO candidate target cell 106 continuously evaluates the associated CHO trigger conditions to initiate CHO execution for handover. Once the CHO trigger condition associated with one of the CHO candidate target cells is satisfied, the UE102 initiates a CHO execution to handover to the corresponding CHO candidate target cell 106. During CHO execution, sometimes, due to its hardware capabilities, the UE102 may not be able to connect to the source cell 106 to receive any information from the source cell 106. In such a scenario, the UE102 instead tunes its Radio Frequency (RF) to the frequency of the CHO candidate target cell 106 for which the CHO trigger condition is fulfilled for cell synchronization and subsequent handover execution procedures, e.g. initiating random access on the CHO candidate target cell 106. However, when the CHO candidate target cell 106 does not wish to serve the UE102 configured with its CHO configuration, the CHO candidate target cell 106 may send a handover cancel request to the source cell 106. Thus, a scenario results in which: the UE102 attempts to initiate a CHO execution to handover to a CHO candidate cell that has sent a request to the source cell 106 to cancel/release the CHO configuration and thus the handover of the UE102 may fail.

In an embodiment, to avoid handover failure, when the UE102 fails to receive an RRC reconfiguration from the source cell 106 to release the CHO configuration of the CHO candidate target cell 106, the source cell 106 rejects the handover cancellation request received from the CHO candidate target cell 106. Upon receiving a handover cancel request or a CHO configuration release request from a CHO candidate target cell 106, the source cell 106 sends an RRC reconfiguration message to the UE102 to release the CHO configuration of the CHO candidate target cell 106. If the UE102 is unable to receive the RRC configuration message from the source cell 106, the source cell 106 rejects the handover cancel request received from the CHO candidate target cell 106 and sends a handover cancel reject message to the CHO candidate target cell 106. Upon receiving the handover cancel reject message from the source cell 106, the CHO candidate target cell 106 retains the CHO configuration provided to the UE 102. Thus, handover failures may be avoided.

Embodiments herein enable the source cell 106 to send an RRC reconfiguration message in various procedures/methods to instruct the UE102 to release the CHO configuration of the CHO candidate target cell.

In an example procedure, the source cell 102 sends an RRC reconfiguration message to the UE102 including a CHO release message to release the CHO configuration of the CHO candidate target cell 106. The CHO release message indicates the CHO configuration of the CHO candidate target cells that must be released. In such a scenario, upon releasing the CHO configuration of the indicated candidate target cell 106, the UE102 sends an RRC reconfiguration complete message to the source cell 106.

In another example procedure, the source cell 106 sends an RRC reconfiguration message to the UE102 including only the source cell configuration for releasing the CHO configuration of the CHO candidate target cell 106. In such a scenario, upon releasing the CHO configuration of the candidate target cell 106, the UE102 sends an RRC reconfiguration complete message to the source cell 106.

In another example procedure, the source cell 106 sends an RRC reconfiguration message to the UE102 including only the CHO target cell configuration for releasing the CHO configuration of the CHO candidate target cell 106. In such a scenario, the UE102 does not send an RRC reconfiguration complete message to the source cell 106. The UE102 may send an RRC reconfiguration complete message to the CHO candidate target cell 106 upon successful completion of the CHO execution.

In another example procedure, the source cell 106 sends an RRC reconfiguration message to the UE102 including the CHO candidate target cell 106 update/delta source cell configuration and the CHO target cell configuration to release the CHO configuration of the CHO candidate target cell 106. In such a scenario, the UE102 sends an RRC reconfiguration complete message to the source cell 106 indicating that the UE102 has complied with the received updated/delta source cell configuration. The UE102 does not send an RRC reconfiguration complete message to the source cell 106 to confirm the update of the CHO target cell configuration. However, when the CHO execution to the CHO candidate target cell 106 is successfully completed, the UE102 sends a reconfiguration complete message to the CHO candidate target cell 106.

In another example procedure, the source cell 106 sends an RRC reconfiguration message to the UE102 including the updated/delta CHO target cell configuration to release the CHO configuration. In such a scenario, the UE102 sends an RRC reconfiguration complete message to the source cell 106 indicating that the UE102 has released the CHO configuration of the indicated CHO candidate target cell.

In another example procedure, the source cell 106 sends an RRC reconfiguration message to the UE102 including an updated/incremental source cell configuration and a CHO release message to release the CHO configuration of the CHO candidate target cell 106. In such a scenario, the UE102 sends a joint/combined RRC reconfiguration complete message to the source cell 106. The joint RRC reconfiguration complete message includes a reconfiguration complete message for updated/incremental source cell configuration and an embedded reconfiguration complete message indicating release of the CHO configuration of the CHO candidate target cell 106. Alternatively, the RRC reconfiguration complete message comprises a reconfiguration complete message for an updated/incremental source cell configuration and a new Indicator (IE) indicating the release of the CHO configuration of the indicated CHO candidate target cell 106.

Embodiments herein enable the target cell 106 to send an RRC release message for RRC reestablishment when the UE102 encounters at least one failure on the source cell 106. When the UE102 configured with the CHO configuration of the CHO candidate target cell 106 encounters at least one failure, the UE102 initiates a recovery procedure by performing a cell selection procedure. Examples of failures may be, but are not limited to, Radio Link Failure (RLF), handover Failure when accessing a CHO candidate target cell, integrity verification Failure, reconfiguration Failure of RRC messages, and the like. The cell selection process involves selecting at least one BS/cell present in the vicinity of the UE102 to camp on. When selecting a cell by performing cell selection, the UE102 uses the CHO configuration stored in the CHO candidate target cell list to determine whether the selected cell is a CHO candidate target cell. If the selected cell is not a CHO candidate target cell, the UE initiates an RRC reestablishment procedure.

If the selected cell is a CHO candidate target cell configured to the UE102 before encountering at least one failure on the source cell 106, the UE102 performs a CHO execution and sends an RRC reconfiguration complete message to the selected cell/CHO candidate target cell 106. The RRC reconfiguration complete message sent to the selected cell/CHO candidate cell may be an unexpected message for the selected cell since the selected cell/CHO candidate target cell 106 has released the UE context and resources reserved for the UE 102. Upon receiving an indication from the source cell 106 after identifying at least one failure encountered by the UE102, the CHO candidate target cell 106 may release the UE context and resources reserved for the UE 102. Thus, the CHO candidate target cell 106 may only expect the RRC reestablishment request message from the UE102 when the UE102 encounters at least one failure. In such a scenario, the CHO candidate target cell 106 may send an RRC release message to the UE102 in response to an unexpected RRC reconfiguration message. Upon receiving the RRC release message, the UE102 may initiate an RRC connection establishment procedure.

Embodiments herein enable the target cell 106 to perform a fallback to connection establishment procedure when the UE102 configured with the CHO configuration encounters at least one failure on the source cell 102. The target cell 106 may be a cell selected by the UE102 upon encountering at least one failure, and the selected cell is a CHO candidate target cell. In the fallback to connection setup procedure, the CHO candidate target cell 106 may initiate a connection setup procedure with the UE102 upon receiving an unexpected RRC reconfiguration complete message. The connection establishment procedure involves sending an RRC setup message to the UE102 in response to the unexpected RRC reconfiguration complete message. The RRC setup message includes the configuration of the CHO candidate target cell 106. Initiating the connection establishment procedure by the CHO candidate target cell 106 reduces over-the-air Signaling and enables data bearers (Signaling Radio Bearer (SRB) and Dedicated Radio Bearer (DRB)) to resume the ongoing data transmission prior to the at least one failure encountered by the UE 102. Upon receiving the RRC setup message from the CHO candidate target cell 106, the UE102 releases all existing CHO configurations of the CHO candidate target cell and applies the configuration of the target cell 106 received in the RRC setup message for connecting with the CHO candidate target cell 106.

When a CHO-configured configuration UE102 encounters at least one failure on the source cell 106, embodiments herein enable the target cell 106 to serve the UE102 by retrieving the UE context from the source cell 106. The target cell 106 may be a cell selected by the UE102 upon encountering at least one failure, and the selected cell is a CHO candidate target cell.

Upon encountering at least one failure on the source cell, the UE102 includes information about the source cell 106 in an unexpected RRC reconfiguration complete message. The source cell 106 may be an old source cell that has served the UE102 before encountering at least one failure. The UE102 sends an unexpected RRC reconfiguration complete message with information of the old source cell 106 to the CHO candidate target cell 106. The information about the source cell 106 includes an indicator indicating the identity of the old source cell 106 and an authentication token for the old source cell 106 (which is required to verify the UE 102).

Upon receiving an unexpected RRC reconfiguration complete message from the UE102 with information of the old source cell 106, the CHO candidate target cell 106 may determine the old source cell 106 of the UE 102. The CHO candidate target cell 106 sends a retrieve UE CONTEXT message to the old source cell 106 and requests the UE CONTEXT from the old source cell 106. The UE context may provide information about the bearers that have been established at the UE102 before encountering the at least one failure so that the corresponding bearers can be re-established on the CHO candidate target cell 106. The old source cell 106 provides the UE context to the CHO candidate target cell 106.

Upon receiving the UE context from the old source cell 106, the CHO candidate target cell 106 sends an RRC reconfiguration message to the UE102 based on the received UE context. The RRC reconfiguration message may include a new configuration of the CHO candidate target cell 106. Upon receiving the RRC reconfiguration message from the CHO candidate target cell 106, the UE102 applies the new configuration and sends an RRC reconfiguration complete message to the CHO candidate target cell 106.

Embodiments herein enable the target cell 106 to serve the UE102 by retrieving UE context and Sequence Number (SN) status transmissions from the source cell 106 when the CHO-configured UE102 encounters at least one failure on the source cell 106. The target cell 106 may be a cell selected by the UE102 upon encountering at least one failure, and the selected cell is a CHO candidate target cell.

Upon receiving an unexpected RRC reconfiguration complete message from the UE102 including information about the old source cell 106, the CHO candidate target cell 106 requests the old source cell 106 and retrieves the UE context. Upon receiving the UE context from the old source cell 106, the CHO candidate target cell 106 sends an RRC reconfiguration message to the UE102 based on the received UE context. The RRC reconfiguration message may include the configuration of the CHO candidate target cell 106. Upon receiving the RRC reconfiguration message from the CHO candidate target cell 106, the UE102 applies the received configuration and sends an RRC reconfiguration complete message to the CHO candidate target cell 106.

Upon receiving the RRC reconfiguration complete message from the UE102, the CHO candidate target cell 106 requests the old source cell 106 for SN status transmission. The SN status transmission includes a Packet Data Convergence Protocol (PDCP) sequence number. The PDCP sequence number may be the first lost data unit if at least one failure is encountered on the UE102 during uplink data transmission. The PDCP sequence number may be the next sequence number that must be assigned to the UE102 if at least one failure is encountered on the UE102 during downlink data transmission. In an embodiment, the CHO candidate target cell 106 sends an XN-U address indication for the SN status transfer message. The XN-U address indication comprises the address of the CHO candidate target cell to which the forwarding address to the source cell 106 is to be informed, thereby informing the source cell 106, that status transmission and data forwarding have to be performed. The CHO candidate target cell 106 receives an SN status transmission from the source cell 106 in response to the transmitted XN-U address indication. The CHO candidate target cell 106 may use SN status transmission messages to ensure that less loss of failed recovery is incurred.

In an embodiment, the CHO candidate target cell 106 resumes data transmission to the UE102 if SN state transmissions are already available on the CHO candidate target cell 106 prior to receiving the RRC reconfiguration complete message from the UE 102. Data transmission may be resumed in an increasing order of SNs indicated in the SN status transmissions received from the old source cell 106 on which the UE 106 encountered at least one failure.

In an embodiment, if the cell selected by the UE102 by performing cell selection (after encountering at least one failure) is not a CHO candidate target cell, the UE102 sends a reestablishment request including information about the old source cell 106 to the selected cell/new target cell 106. In such a scenario, the new target cell 106 requests the old source cell and retrieves the UE context from the old source cell 106. Upon successful re-establishment of the connection between the UE102 and the new target cell 106, the new target cell 106 may further request the old source cell 106 for SN status transmission. Upon receiving the SN status transmission from the old source cell 106, the new target cell 106 reverts to data transmission to the UE102 in the ascending order of SN indicated in the received SN status transmission.

Fig. 1 shows exemplary elements of a wireless communication network 100, but it should be understood that other embodiments are not so limited. In other embodiments, the wireless communication network 100 may include a fewer or greater number of elements. Furthermore, the labels or names of the elements are for illustration purposes only and do not limit the scope of the embodiments herein. One or more elements may be combined together to perform the same or substantially similar functions in the wireless communication network 100.

Fig. 2 is a block diagram depicting hardware components of BS 106 in accordance with embodiments disclosed herein. BS 106 (source BS/cell and target BS/cell) includes memory 202, communication interface 204, and controller 206. BS 106 also includes at least one antenna, at least one RF transceiver, processing circuits, and the like (not shown).

Memory 202 can store at least one of a UE context, a source cell configuration, a CHO target cell configuration, an incremental source cell configuration, a CHO configuration configured with respect to UE102, SN status transmissions, and the like. Examples of memory 202 may be, but are not limited to, NAND, embedded Multimedia Card (eMMC), Secure Digital (SD) Card, Universal Serial Bus (USB), Serial Advanced Technology Attachment (SATA), solid-state drive (SSD), and the like. Memory 202 may also include one or more computer-readable storage media. The memory 202 may also include non-volatile storage elements. Examples of such non-volatile storage elements may include magnetic hard disks, optical disks, floppy disks, flash memory, or forms of electrically programmable memories (EPROMs) or electrically erasable and programmable memories (EEPROMs). Additionally, in some examples, memory 202 may be considered a non-transitory storage medium. The term "non-transitory" may indicate that the storage medium is not embodied in a carrier wave or propagated signal. However, the term "non-transitory" should not be construed to mean that the memory 202 is not removable. In some instances, a non-transitory storage medium may store data that may change over time (e.g., in Random Access Memory (RAM) or cache).

Communication interface 204 may be configured to enable BS 106 to communicate with at least one external entity (e.g., UE102, other BSs 106, CN 104, etc.), examples of which may be at least one of a wired or wireless fronthaul interface, a wired or wireless backhaul interface, or any structure supporting communication over wired or wireless connections.

The controller 206 may be at least one of a single processor, multiple processors, multiple homogeneous or heterogeneous cores, multiple heterogeneous Central Processing Units (CPUs), a microcontroller, special media, and other accelerators. The controller 206 may be a general purpose processor such as a Central Processing Unit (CPU), Application Processor (AP), Digital Signal Processor (DSP), or the like.

When BS 106 is a source cell 106, controller 206 is configured to prepare a source cell configuration or an updated/incremental source configuration. When BS 106 is a source cell 106, controller 206 is further configured to enable source cell 106 to:

sending a handover request to a CHO candidate target cell 106 for CHO target cell configuration, wherein the CHO candidate target cell 106 may be a cell of the source BS 106 or at least one neighboring BS 106;

associating a CHO trigger condition with the CHO target cell configuration of each CHO candidate target cell 106;

configuring the UE102 with a CHO configuration of CHO candidate target cells 106, wherein the CHO configuration of each CHO candidate cell includes a CHO target cell configuration and associated CHO trigger conditions;

independently reconfigure the UE102 with the updated source cell configuration and CHO target cell configuration;

performing a one-step reconfiguration of the UE 102;

performing a two-step reconfiguration of the UE 102; and

when the CHO candidate target cell can no longer serve UE102, requesting UE102 to release the CHO configuration of the CHO candidate target cell.

When BS 106 is the target cell 106, controller 206 is configured to prepare the target cell configuration as an incremental or updated/incremental target cell configuration of the source cell configuration. When BS 106 is a target cell 106, controller 206 is further configured to enable target cell 106 to:

sending the CHO target cell configuration to the source cell 106;

initiating release of the CHO configuration of the UE102 when the target cell 106 can no longer serve the UE 102;

performing a fallback connection procedure when an unexpected RRC reconfiguration message is received from the UE102 after encountering at least one failure on the source cell 106;

upon receiving an unexpected RRC reconfiguration message from the UE102 that includes information about the old source cell 106, retrieve a UE context from the old source cell 106 to serve the UE 102; and

upon receiving an unexpected RRC reconfiguration message from the UE102 that includes information about the old source cell 106, an XN-U address indication is sent to the old source cell 106 and an SN status transmission is retrieved from the old source cell 106 to serve the UE 102.

Fig. 2 shows exemplary elements of BS 106, but it should be understood that other embodiments are not limited thereto. In other embodiments, BS 106 may include a fewer or greater number of cells. Furthermore, the labels or names of the elements are for illustration purposes only and do not limit the scope of the embodiments herein. One or more elements may be combined together to perform the same or substantially similar functions in BS 106.

Fig. 3 is a block diagram depicting hardware components of UE102 in accordance with embodiments disclosed herein. UE102 includes memory 302, a communication interface 304, and a controller 306. UE102 also includes at least one antenna, at least one RF transceiver, processing circuitry, a display, input/output (I/O) ports, and the like (not shown).

The memory 302 may store, but is not limited to, at least one of a CHO candidate target cell list, a CHO configuration of the CHO candidate target cells 106, an updated source/CHO target cell configuration, information about the source cell 106, and the like. Examples of the memory 302 may be, but are not limited to, NAND, embedded multimedia card (eMMC), Secure Digital (SD) card, Universal Serial Bus (USB), Serial Advanced Technology Attachment (SATA), Solid State Drive (SSD), and the like. Memory 302 may also include one or more computer-readable storage media. The memory 302 may also include non-volatile storage elements. Examples of such non-volatile storage elements may include magnetic hard disks, optical disks, floppy disks, flash memory, or forms of electrically programmable memory (EPROM) or electrically erasable and programmable memory (EEPROM). Additionally, in some examples, memory 302 may be considered a non-transitory storage medium. The term "non-transitory" may indicate that the storage medium is not embodied in a carrier wave or propagated signal. However, the term "non-transitory" should not be construed to mean that the memory 302 is not removable. In certain examples, a non-transitory storage medium may store data that may change over time (e.g., in Random Access Memory (RAM) or cache).

Communication interface 304 may be configured to enable UE102 to communicate with at least one external entity (BS 106, other UEs 102, etc.) over an interface supported by wireless communication network 100, a wired or wireless backhaul interface, or any structure supporting communication over a wired or wireless connection.

The controller 306 may be at least one of a single processor, multiple processors, multiple homogeneous or heterogeneous cores, multiple heterogeneous Central Processing Units (CPUs), a microcontroller, special media, and other accelerators. The controller 306 may be a general purpose processor such as a Central Processing Unit (CPU), Application Processor (AP), Digital Signal Processor (DSP), or the like.

The controller 306 may be configured to enable the UE102 to:

storing the CHO configuration of the CHO candidate target cells in the CHO candidate target cell list of the memory 302;

enabling the CHO execution for handover when a CHO triggering condition associated with one of the CHO candidate target cells is satisfied;

selecting a CHO candidate target cell 106 for handover when CHO trigger conditions associated with two or more CHO candidate target cells are met;

updating the CHO configuration upon receiving updated source cell and CHO target cell configurations from the source cell 106;

releasing the stored CHO configuration of the CHO candidate target cell 106 upon receiving an RRC reconfiguration message from the source cell 106 to release the CHO configuration; and

the stored CHO configuration of the CHO candidate target cell 106 is released when a transition from the RRC connected state to the RRC inactive state is performed.

Fig. 3 shows exemplary elements of UE102, but it should be understood that other embodiments are not limited thereto. In other embodiments, the UE102 may include a fewer or greater number of cells. Furthermore, the labels or names of the elements are for illustration purposes only and do not limit the scope of the embodiments herein. One or more elements may be combined together to perform the same or substantially similar functions in the UE 102.

Fig. 4 is a sequence diagram depicting one-step reconfiguration of the UE102 according to embodiments disclosed herein. The embodiments herein further explain, for example, treating the source and target cells 106 as gnbs, but it will be apparent to those skilled in the art that the source and target cells 106 may be any other RAN nodes. The source cell 106 may be referred to hereinafter as SgNB 106, and the target cell 106 may be referred to hereinafter as TgNB 106.

In step 401, UE102 sends a measurement report to SgNB 106, where the measurement report includes measurements of TgNB 106. Upon receiving the measurement report from UE102, SgNB 106 sends a handover request (CHO) to TgNB 106 at step 402. The handover request includes a source cell configuration. Upon receiving the handover request from SgNB 106, TgNB 106 performs admission control and reserves resources for UE102, step 403. In reserving resources for the UE102, the TgNB 106 prepares a CHO target cell configuration. The CHO target cell configuration includes a source cell configuration and a container (including the incremental target cell configuration prepared for the received source cell configuration). In step 404, TgNB 106 sends a handover request acknowledgement to SgNB 106, which includes the CHO target cell configuration.

Upon receiving the CHO target cell configuration from the TgNB 106, the SgNB 106 associates the CHO trigger condition with the CHO target cell configuration and sends the CHO configuration of the TgNB 106 to the UE102 in an RRC reconfiguration message, step 405. The CHO configuration of TgNB 106 includes a CHO target cell configuration and CHO trigger conditions. In step 406, the UE102 applies the source cell configuration received in the CHO configuration to continue on the source cell. UE102 performs CHO execution if the CHO trigger condition of TgNB 106 has been met. CHO execution involves applying the CHO target cell configuration of the TgNB 106 for handover.

In step 407, SgNB 106 reconfigures the source cell configuration. SgNB 106 may reconfigure the source cell configuration to an increment over the existing source cell configuration (incremental source cell configuration). At step 408, SgNB 106 sends a handover modification request to TgNB 106, where the handover modification request includes the incremental source cell configuration. Upon receiving the incremental source cell configuration, the TgNB 106 updates the CHO target cell configuration (incremental CHO target cell configuration) by updating the CHO target cell configuration to an increment over the incremental source cell configuration at step 409. TgNB 106 sends the incremental CHO target cell configuration to SgNB 106 in a handover request acknowledgement.

Upon receiving the incremental CHO target cell configuration, SgNB 106 sends the incremental source cell configuration and the incremental CHO target cell configuration to UE102 in an RRC reconfiguration message, step 410. In step 411, the UE102 updates the CHO configuration of the TgNB 106. The UE102 first updates the source cell configuration in the (CHO-configured) stored CHO configuration with the incremental source configuration. Subsequently, the UE102 updates the CHO target configuration stored in the CHO configuration of the TgNB 106 with the incremental target cell configuration. In step 412, upon updating the CHO configuration of TgNB 106, UE102 sends an RRC reconfiguration complete message to SgNB 106 indicating a successful update of the CHO configuration of TgNB 106.

Fig. 5 is an example sequence diagram depicting a two-step reconfiguration of the UE102 according to embodiments disclosed herein.

In step 501, UE102 sends a measurement report to SgNB 106, where the measurement report includes measurements of TgNB 106. Upon receiving the measurement report from UE102, SgNB 106 sends a handover request (CHO) to TgNB 106 at step 502. The handover request includes a source cell configuration. Upon receiving the handover request from SgNB 106, TgNB 106 performs admission control and reserves resources for UE102, step 503. In reserving resources for the UE102, the TgNB 106 prepares a CHO target cell configuration. The CHO target cell configuration includes a source cell configuration and a container (including the incremental target cell configuration prepared for the received source cell configuration). In step 504, TgNB 106 sends a handover request acknowledgement to SgNB 106, which includes the CHO target cell configuration.

Upon receiving the CHO target cell configuration from the TgNB 106, the SgNB 106 associates the CHO trigger condition with the CHO target cell configuration and sends the CHO configuration of the TgNB 106 to the UE102 in an RRC reconfiguration message, step 505. The CHO configuration of TgNB 106 includes a CHO target cell configuration and CHO trigger conditions. In step 506, the UE102 applies the source cell configuration received in the CHO configuration to continue on the source cell. UE102 performs CHO execution if the CHO trigger condition of TgNB 106 has been met. CHO execution involves applying the CHO target cell configuration of the TgNB 106 for handover.

In step 507, SgNB 106 reconfigures the source cell configuration. SgNB 106 may reconfigure the source cell configuration to an increment of the existing source cell configuration (incremental source cell configuration). In step 508, upon reconfiguring the source cell configuration, SgNB 106 sends a first RRC reconfiguration message to UE 102. The first RRC reconfiguration message includes the incremental source cell configuration and a request to release the CHO target cell configuration for the TgNB 106 in the CHO configuration. Upon sending the first RRC reconfiguration message to UE102, SgNB 106 sends a handover modification request to TgNB 106 in step 509.

Upon receiving the first RRC reconfiguration message from SgNB 106, UE102 updates the source cell configuration in the CHO configuration with the incremental source cell configuration and releases the CHO target cell configuration of TgNB 106 at step 510. In step 511, upon releasing the CHO target cell configuration of the TgNB 106, the UE102 transmits an RRC reconfiguration complete message to the SgNB 106 in response to the first RRC reconfiguration message.

Upon receiving the handover modification request from SgNB, TgNB 106 updates the CHO target cell configuration and sends the updated/incremental CHO target cell configuration to SgNB 106 in a handover request acknowledgement, step 512. The incremental CHO target cell configuration may be prepared by updating the CHO target cell configuration to the increment of the received incremental source cell configuration.

Upon receiving the incremental CHO target cell configuration, SgNB 106 sends a second RRC reconfiguration message to UE102 at step 513. The second RRC reconfiguration message includes a delta CHO target cell configuration. At step 514, upon receiving the second RRC reconfiguration message, the UE102 updates the CHO target cell configuration in the CHO configuration of the TgNB 106 with the received incremental CHO target cell configuration.

Fig. 6A, 6B, and 6C are example sequence diagrams depicting initiation of release of a CHO target cell configuration by a CHO candidate target cell 106 when the target cell 106 is no longer serving the UE102, according to embodiments disclosed herein.

In an embodiment, as shown in fig. 6A, TgNB 106 initiates release of the CHO target cell configuration of UE102 by sending a handover cancel request to SgNB 106, and SgNB 106 immediately accepts the handover cancel request. When TgNB 106 is no longer serving UE102 due to allocation of resources reserved for UE102 to at least one of another UE102, an increase in load on TgNB, etc., TgNB 106 may initiate release of the CHO target cell configuration for UE 102. As shown in fig. 6A, in step 611, TgNB 106 sends a handover cancel request or a CHO configuration release request to SgNB 106 to allow the TgNB to release the CHO target cell configuration previously configured on UE 102. In step 612, SgNB 106 accepts the received handover cancel request and sends a handover cancel request acknowledgement to TgNB 106.

In an embodiment, as shown in fig. 6B, TgNB 106 initiates release of the CHO target cell configuration of UE102 by sending a handover cancel request to SgNB 106, and upon successful release of the CHO target cell configuration of TgNB 106 at UE102, SgNB 106 accepts the handover cancel request. As shown in fig. 6B, in step 621, TgNB 106 sends a handover cancel request to SgNB 106 to allow the TgNB to release the CHO target cell configuration previously configured on UE 102. In step 622, SgNB 106 sends an RRC reconfiguration message to UE102 to release the CHO target cell configuration of TgNB 106. In step 623, UE102 releases the CHO target cell configuration of TgNB 106 and sends an RRC reconfiguration complete message to SgNB 106 indicating the indicated release of the CHO target cell configuration of TgNB 106. Upon receiving the RRC reconfiguration complete message from UE102, SgNB 106 accepts the handover cancel request received from TgNB 106 and sends a handover cancel request acknowledgement to TgNB 106, step 624.

In an embodiment, as shown in fig. 6C, upon receiving an RLC acknowledgement from UE102, SgNB 106 allows TgNB 106 to release the CHO target cell configuration previously provided to UE 102. As shown in fig. 6C, in step 631, TgNB 106 sends a handover cancel request to SgNB 106 to allow the TgNB to release the CHO target cell configuration previously configured on UE 102. In step 632, SgNB 106 sends an RRC reconfiguration message to UE102 to release the CHO target cell configuration of TgNB 106. In step 633, the UE102 releases the CHO target cell configuration of the TgNB 106 and sends an RLC acknowledgement to the SgNB 106 indicating the indicated release of the CHO target cell configuration of the TgNB 106. Upon receiving the RRC reconfiguration complete message from UE102, SgNB 106 accepts the handover cancel request received from TgNB 106 and sends a handover cancel request acknowledgement to TgNB 106 in step 634.

Fig. 7 is an example sequence diagram depicting a rejection of a handover cancel request of a CHO candidate target cell 106 according to embodiments disclosed herein.

In step 701, TgNB 106 sends a handover cancel request to SgNB 106 to allow the TgNB to release the CHO target cell configuration previously configured on UE 102. In step 702, SgNB 106 sends an RRC reconfiguration message to UE102 to release the CHO target cell configuration of TgNB 106 and determines that UE102 cannot receive the RRC reconfiguration message. In step 703, upon determining that UE102 cannot receive the RRC reconfiguration message, SgNB 106 cancels the received handover cancel request of TgNB 106 and sends a handover cancel reject to TgNB 106.

Fig. 8A, 8B, and 8C are example sequence diagrams depicting example procedures in which a Radio Resource Control (RRC) reconfiguration message is sent to the UE102 to instruct the UE102 to remove the CHO candidate target cell 106, according to embodiments disclosed herein.

In the example procedure shown in fig. 8A, SgNB 106 sends an RRC reconfiguration message to UE102 to release the CHO target cell configuration of TgNB 106 in step 811, wherein the RRC reconfiguration message includes a CHO release message. The CHO release message indicates the CHO configuration/CHO target cell configuration of the TgNB that must be released. In step 812, the UE102 releases the CHO target cell configuration of the TgNB 106 and sends an RRC reconfiguration complete message to the SgNB 106.

In another example procedure, as shown in fig. 8B, SgNB 106 sends an RRC reconfiguration message to UE102 to release the CHO target cell configuration of TgNB 106 at step 821, where the RRC reconfiguration message includes a source cell configuration and a CHO release message. In step 822, UE102 releases the CHO target cell configuration of TgNB 106 and sends a combined RRC reconfiguration complete message to SgNB 106. The combined RRC reconfiguration complete message includes a reconfiguration complete message for an updated/delta source cell configuration and an embedded reconfiguration complete message for indicating release of the CHO target cell configuration of the TgNB 106.

In another example procedure, as shown in fig. 8C, SgNB 106 sends an RRC reconfiguration message to UE102 to release the CHO target cell configuration of TgNB 106 at step 831, wherein the RRC reconfiguration message includes a source cell configuration and a CHO release message. In step 832, UE102 releases the CHO target cell configuration of TgNB 106 and sends an RRC reconfiguration complete message to SgNB 106. The RRC reconfiguration complete message includes a CHO release Indicator (IE) indicating a successful release of the indicated CHO target cell configuration of the TgNB 106.

Fig. 9A and 9B are exemplary diagrams depicting a fallback to connection establishment procedure after the UE102 encounters at least one failure on the source cell 106, in accordance with embodiments disclosed herein.

As shown in fig. 9A and 9B, in step 901, UE102 sends a measurement report to SgNB 106, where the measurement report includes measurements of TgNB 106. Upon receiving the measurement report from UE102, SgNB 106 sends a handover request (CHO) to TgNB 106 at step 902. The handover request includes a source cell configuration. In step 903, upon receiving a handover request from SgNB 106, TgNB 106 performs admission control and reserves resources for UE 102. In reserving resources for the UE102, the TgNB 106 prepares a CHO target cell configuration. The CHO target cell configuration includes a source cell configuration and a container (including the incremental target cells prepared for the received source cell configuration). In step 904, TgNB 106 sends a handover request acknowledgement to SgNB 106, which includes the CHO target cell configuration.

Upon receiving the CHO target cell configuration from the TgNB 106, the SgNB 106 associates the CHO trigger condition with the CHO target cell configuration and sends the CHO configuration of the TgNB 106 to the UE102 in an RRC reconfiguration message, step 905. The CHO configuration of TgNB 106 includes a CHO target cell configuration and CHO trigger conditions. In step 906, the UE102 applies the source cell configuration received in the CHO configuration to continue on the source cell. UE102 performs CHO execution if the CHO trigger condition of TgNB 106 has been met. CHO execution involves applying the CHO target cell configuration of the TgNB 106 for handover.

In step 907, the UE102 encounters at least one failure (e.g., RLF) on the SgNB 106. At step 908, upon encountering at least one failure, the UE102 performs a cell selection procedure and selects a gNB that exists in the vicinity of the UE102, wherein the selected gNB may be a CHO candidate target cell/TgNB 106. In step 909, UE102 sends an RRC reconfiguration complete message to TgNB 106. In step 910, because TgNB 106 does not have UE context, TgNB 106 treats the received RRC reconfiguration complete message as an unexpected RRC reconfiguration complete message.

In the embodiment shown in fig. 9A, in step 911a, upon receiving an unexpected RRC reconfiguration message, TgNB 106 sends an RRC release message to UE 102. Upon receiving the RRC release message, the UE102 may initiate an RRC connection establishment procedure.

In the embodiment shown in fig. 9B, in step 911B, upon receiving the unexpected RRC reconfiguration message, TgNB 106 sends an RRC setup message to UE102, wherein the RRC setup message includes the configuration of TgNB 106. In step 911c, upon receiving the RRC setup message, the UE102 applies the configuration of the TgNB 106 in the received RRC setup message and transmits an RRC setup complete message to the TgNB 106.

Fig. 10A is an example sequence diagram depicting a fallback procedure to connection re-establishment after the UE102 encounters at least one failure on the source cell 106 according to embodiments disclosed herein.

In step 1001, the UE102 sends a measurement report to the SgNB 106, where the measurement report includes measurements of the TgNB 106. In step 1002, upon receiving a measurement report from UE102, SgNB 106 sends a handover request (CHO) to TgNB 106. The handover request includes a source cell configuration. Upon receiving the handover request from SgNB 106, TgNB 106 performs admission control and reserves resources for UE102 in step 1003. In reserving resources for the UE102, the TgNB 106 prepares a CHO target cell configuration. The CHO target cell configuration includes a source cell configuration and a container (including the incremental target cell configuration prepared for the received source cell configuration). In step 1004, TgNB 106 sends a handover request acknowledgement to SgNB 106, which includes the CHO target cell configuration.

Upon receiving the CHO target cell configuration from the TgNB 106, the SgNB 106 associates the CHO trigger condition with the CHO target cell configuration and sends the CHO configuration of the TgNB 106 to the UE102 in an RRC reconfiguration message, step 1005. The CHO configuration of TgNB 106 includes a CHO target cell configuration and CHO trigger conditions. In step 1006, the UE102 applies the source cell configuration received in the CHO configuration to continue on the source cell. UE102 performs CHO execution if the CHO trigger condition of TgNB 106 has been met. CHO execution involves applying the CHO target cell configuration of the TgNB 106 for handover.

In step 1007, UE102 encounters at least one failure (e.g., RLF) on SgNB 106. At step 1008, upon encountering the at least one failure, the UE102 performs a cell selection procedure and selects a gNB that exists in a vicinity of the UE102, wherein the selected gNB may be a CHO candidate target cell/TgNB 106. In step 1009, the UE102 sends an RRC reconfiguration complete message to the TgNB 106, wherein the RRC reconfiguration complete message includes information about the old SgNB 106 (the gbb used as the source cell 106 for the UE102 before encountering at least one failure). The information about the old SgNB 106 includes information about the identity of the old SgNB 106 and the authentication token of the old SgNB 106. An example RRC reconfiguration complete message including information about the old source cell is depicted in fig. 10B.

Upon receiving the RRC reconfiguration message including information about the old SgNB 106, the TgNB 106 requests the old SgNB 106 and retrieves the UE context, in step 1010. In step 1011, upon retrieving the UE context, TgNB 106 sends signaling to UE102 to perform RRC reestablishment. Example signaling instructing the UE102 to perform RRC reestablishment when at least one failure is encountered is depicted in fig. 10C. In step 1012, the UE102 performs RRC reestablishment and sends an RRC reestablishment complete to the TgNB 106.

Fig. 11 is an example sequence diagram illustrating retrieval of an SN status transmission by a CHO candidate target cell to serve the UE102 after the UE102 encounters at least one failure on the source cell 106 according to embodiments disclosed herein.

In step 1101, UE102 sends a measurement report to SgNB 106, wherein the measurement report includes measurements of TgNB 106. Upon receiving the measurement report from UE102, SgNB 106 sends a handover request (CHO) to TgNB 106 at step 1102. The handover request includes a source cell configuration. Upon receiving the handover request from SgNB 106, TgNB 106 performs admission control and reserves resources for UE102 in step 1103. In reserving resources for the UE102, the TgNB 106 prepares a CHO target cell configuration. The CHO target cell configuration includes a source cell configuration and a container (including the incremental target cell configuration prepared for the received source cell configuration). In step 1104, TgNB 106 sends a handover request acknowledgement to SgNB 106, which includes the CHO target cell configuration.

Upon receiving the CHO target cell configuration from the TgNB 106, the SgNB 106 associates the CHO trigger condition with the CHO target cell configuration and sends the CHO configuration of the TgNB 106 to the UE102 in an RRC reconfiguration message, step 1105. The CHO configuration of TgNB 106 includes a CHO target cell configuration and CHO trigger conditions. In step 1106, the UE102 applies the source cell configuration received in the CHO configuration to continue on the source cell. UE102 performs CHO execution if the CHO trigger condition of TgNB 106 has been met. CHO execution involves applying the CHO target cell configuration of the TgNB 106 for handover.

In step 1107, the UE102 encounters at least one failure (e.g., RLF) on the SgNB 106. Upon encountering at least one failure, the UE102 performs a cell selection procedure and selects a gNB present in the vicinity of the UE102, wherein the selected gNB may be a CHO candidate target cell/TgNB 106, step 1108. In step 1109, the UE102 sends an RRC reconfiguration complete message to the TgNB 106, wherein the RRC reconfiguration complete message includes information about the old SgNB 106 (the gbb used as the source cell 106 of the UE102 before encountering at least one failure). The information about the old SgNB 106 includes information about the identity of the old SgNB 106 and the authentication token of the old SgNB 106. In step 1110, upon receiving the RRC reconfiguration message including information about the old SgNB 106, the TgNB 106 determines that the TgNB 106 does not have the UE context. In step 1111, TgNB 106 identifies old SgNB 106 from the RRC reconfiguration message received by UE102 and sends the retrieved UE context to old SgNB 106 for the UE context. In step 1112, the old SgNB 106 sends a retrieve UE context response including the UE context to the TgNB 106.

In step 1113, upon receiving the UE context from old SgNB 106, TgNB 106 sends an RRC reestablishment message to UE 102. Upon receiving the RRC reestablishment message, UE102 sends an RRC reestablishment complete message to TgNB 106 in step 1114. In step 1115, TgNB 106 sends an Xn-U address indication to old SgNB 106 for SN status transmission. In step 1116, old SgNB 106 sends an SN status transmission to TgNB 106, enabling TgNB 106 to recover the ongoing data transmission to UE102 prior to the at least one failure encountered by UE 102.

Fig. 12A is an example sequence diagram depicting the association of CHO trigger conditions with the CHO target cell configuration of a CHO candidate target cell 106, according to embodiments disclosed herein.

Embodiments herein enable SgNB 106 to associate a CHO trigger condition with the CHO target cell configuration of TgNB 106 during CHO preparation by UE 102. The CHO trigger conditions may include measurement objects and reporting configurations. SgNB 106 uses the measurement identifier or any other unique ID to link the measurement object and the reporting configuration. SgNB 106 further enables TgNB 106 to include measurement identifiers in its container of CHO target cell configuration.

As shown in fig. 12A, SgNB 106 sends a handover request to TgNB 106, the handover request including the source cell configuration and the measurement identifier, in step 1201. Upon receiving the handover request, the TgNB 106 prepares a CHO target cell configuration and sends the CHO target cell configuration to the SgNB 106 in a handover request acknowledgement, step 1202. The CHO target cell configuration includes a source cell configuration and an RRC container including a target cell configuration prepared for the source cell configuration and an increment in a measurement identifier.

Upon receiving the CHO target cell configuration, SgNB 106 prepares the CHO configuration for TgNB 106 by associating a CHO trigger condition with the CHO target cell configuration and sends the CHO configuration for TgNB 106 to UE102 in an RRC reconfiguration message, step 1203. UE102 stores the CHO configuration of TgNB 106 in the CHO candidate target cell list (already stored in memory 202).

As shown in fig. 12B, the CHO configuration of the TgNB 106 in the RRC reconfiguration message includes a CHO target cell configuration, measurement objects, reporting configuration, identified measurements, and the like. The CHO target cell configuration includes a source cell configuration and a container, wherein the RRC container includes a target cell configuration prepared for the source cell configuration and an increment in the measurement identifier.

The embodiments disclosed herein may be implemented by at least one software program running on at least one hardware device and performing network management functions to control these elements. The elements shown in fig. 1-12A may be at least one of a hardware device or a combination of a hardware device and a software module.

Embodiments disclosed herein describe methods and systems for managing Conditional Handover (CHO) in a wireless communication network. It will thus be appreciated that the scope of protection extends to such programs and that such computer readable storage means contain, in addition to computer readable means having messages therein, program code means for implementing one or more steps of the method when the program is run on a server, a mobile device or any suitable programmable device. The method is implemented in a preferred embodiment by or together with a software program written in another programming language, for example very high speed integrated circuit hardware description language (VHDL), or by one or more VHDLs or software modules executed on at least one hardware device. The hardware device may be any programmable portable device. The apparatus may also comprise means which may be, for example, hardware means (e.g. an ASIC), or a combination of hardware and software means (e.g. an ASIC and an FPGA), or at least one microprocessor and at least one memory having software modules located therein. The method embodiments described herein may be implemented partly in hardware and partly in software. Alternatively, the present disclosure may be implemented on different hardware devices, e.g., using multiple CPUs.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Thus, while the embodiments herein have been described in terms of embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments described herein.