Cell selection optimization during rrc reestablishment

Abstract

The present disclosure relates to cell selection optimization during RRC reestablishment. A user equipment (UE) configured to receive a mobility configuration from a source cell of a network, wherein the mobility configuration comprises at least one mobility measurement object; determine that a radio link failure (RLF) event has occurred on the source cell; search for a primary cell (PCell) on only frequencies associated with the at least one mobility measurement object to reestablish a radio resource control (RRC) connection; and reestablish the RRC connection with the PCell.

Description

BACKGROUND

[0001] When a user equipment (UE) is in a radio resource control (RRC) connected mode, the UE can need to reestablish a connection with a wireless network based on different triggers, such as, for example, a radio link failure (RLF), a handover (HO) failure, and the like. To reestablish the connection, the UE initiates an RRC connection reestablishment procedure defined by 3GPP standards. From the initiation of the RRC connection reestablishment procedure until its successful completion, user plane data transmission is suspended. SUMMARY

[0002] Some example embodiments relate to a processor of a user equipment (UE) configured to perform operations. The operations include receiving a mobility configuration from a source cell of a network, wherein the mobility configuration includes at least one mobility measurement object; determining that a radio link failure (RLF) event has occurred on the source cell; searching for a primary cell (PCell) on only frequencies associated with the at least one mobility measurement object to reestablish a radio resource control (RRC) connection; and reestablishing the RRC connection with the PCell.

[0003] Other example embodiments relate to a user equipment (UE) having a transceiver configured to communicate with a network and a processor communicatively coupled to the transceiver and configured to perform operations. The operations include receiving a mobility configuration from a source cell of a network, wherein the mobility configuration includes at least one mobility measurement object; determining that a radio link failure (RLF) event has occurred on the source cell; searching for a primary cell (PCell) on only frequencies associated with the at least one mobility measurement object to reestablish a radio resource control (RRC) connection; and reestablishing the RRC connection with the PCell. BRIEF DESCRIPTION OF DRAWINGS

[0004] Figure 1 An example network arrangement is shown in accordance with various example embodiments.

[0005] Figure 2 An example user equipment (UE) is shown in accordance with various example embodiments.

[0006] Figure 3 An example base station is shown in accordance with various example embodiments.

[0007] Figure 4A A method of searching for a suitable primary cell (PCell) during a radio resource control (RRC) connection reestablishment procedure is shown in accordance with various example embodiments.

[0008] Figure 4BExemplary conditional handover (CHO) configurations are shown in accordance with various example embodiments.

[0009] Figure 5 Methods of searching for a suitable PCell during an RRC connection reestablishment procedure are shown in accordance with various example embodiments.

[0010] Figure 6A and Figure 6B Methods of performing an RRC connection reestablishment procedure are shown in accordance with various example embodiments. DETAILED DESCRIPTION

[0011] The example embodiments can be further understood with reference to the following description and related drawings, wherein like elements are referred to with like reference numerals. The example embodiments relate to operations of a user equipment (UE) for improving a radio resource configuration (RRC) connection reestablishment procedure.

[0012] In the following description, reference is made to a “suitable” primary cell (PCell). The meaning of the term “suitable” or “suitable cell” should be understood to be the same as the term defined in 3GPP standards, including TS 36.304 and TS 38.304, and any standards cited by these standards.

[0013] A UE can be configured with a mobility configuration. The mobility configuration can include a conditional handover (CHO) configuration that indicates a target cell ID for each of the target cells in a target cell for handover from a source configuration received from a source cell. The UE does not need to parse radio resource control (RRC) configuration data of the target cell, thereby reducing the UE processing burden. In some example embodiments, a downlink (DL) frequency is also provided to the UE for each measurement object corresponding to a target cell.

[0014] Alternatively or in addition, the mobility configuration can be a T312 fast failure recovery configuration that includes a measurement ID corresponding to a measurement object on which the UE can perform measurements when a time-to-trigger (TTT) timer has expired. The UE would then transmit a measurement report based on these measurements to the network. Successful reception of the measurement report by the network can trigger the network to transmit a handover (HO) command to the UE. However, if the UE does not receive the HO command from the network before the T312 timer expires, the UE can initiate an RRC connection reestablishment procedure instead of waiting for the T310 timer to expire.

[0015] In some cases, although a UE can be configured with CHO, the UE can still attempt to perform RRC connection reestablishment with a cell that is not a CHO configuration but is found to be a suitable neighbor cell based on its power. In this case, since the UE has to perform the entire RRC connection reestablishment procedure, the time that the user plane data transmission is suspended is extended compared to CHO RRC reestablishment.

[0016] In some example embodiments, a UE that has been configured with CHO can be configured to prioritize frequencies associated with CHO measurement objects when searching for a suitable primary cell (PCell) for performing RRC connection reestablishment. As a result, the probability of a CHO PCell being selected is increased, thereby also increasing the likelihood of reducing the user plane data transmission suspension time.

[0017] Another problem that arises is that the PCell that the UE uses to perform RRC connection reestablishment can not be able to retrieve the UE context data from the last serving cell. In this scenario, the UE will need to perform the entire RRC connection procedure (e.g., including access stratum (AS) security context) with the new PCell, which takes an even longer period of time than the RRC connection reestablishment procedure in which the UE context information is able to be retrieved from the last serving cell.

[0018] In some example embodiments, a UE that has been configured with CHO measurement objects or T312 measurement objects can prioritize frequencies associated with those measurement objects during its search for a suitable PCell for performing RRC connection reestablishment. Since either of the CHO measurement objects or T312 measurement objects results in a HO to a PCell configured by the network, there is a high likelihood that the PCell will be able to obtain the UE context data from the last serving cell (compared to a cell that is found independently by the UE after RLF detection).

[0019] Figure 1 An example network arrangement 100 according to various example embodiments is shown. The example network arrangement 100 includes a UE 110. It should be noted that any number of UEs can be used in the network arrangement 100. Those skilled in the art will understand that the UE 110 can be any type of electronic component configured to communicate via a network, such as a mobile phone, tablet, desktop computer, smart phone, phablet, embedded device, wearable device, Internet of Things (IoT) device, etc. It should also be understood that an actual network arrangement can include any number of UEs used by any number of users. Thus, only an example with a single UE 110 is provided for illustrative purposes.

[0020] The UE 110 can be configured to communicate with one or more networks. In the example of network configuration 100, the networks with which the UE 110 can wirelessly communicate are a 5G New Radio (NR) Radio Access Network (5G NR-RAN) 120, a LTE Radio Access Network (LTE-RAN) 122, and a Wireless Local Area Network (WLAN) 124. However, it should be understood that the UE 110 can also communicate with other types of networks, and that the UE 110 can also communicate with networks through wired connections. Thus, the UE 110 can include a 5G NR chipset to communicate with the 5G NR-RAN 120, an LTE chipset to communicate with the LTE-RAN 122, and an ISM chipset to communicate with the WLAN 124.

[0021] The 5G NR-RAN 120 and the LTE-RAN 122 can be part of a cellular network that can be deployed by a cellular provider (e.g., Verizon, AT&T, T-Mobile, etc.). These networks 120, 122 can include, for example, cells or base stations (NodeBs, eNodeBs, HeNBs, eNBS, gNBs, gNodeBs, macrocell base stations, microcell base stations, small cell base stations, femtocell base stations, etc.) configured to send and receive traffic from UEs equipped with the appropriate cellular chipset. The WLAN 124 can include any type of wireless local area network (WiFi, hotspots, IEEE 802.1 lx networks, etc.).

[0022] The UE 110 can connect to the 5G NR-RAN 120 via gNB 120A and / or gNB 120B. The gNBs 120A and 120B can be configured with the necessary hardware (e.g., antenna arrays), software, and / or firmware to perform massive Multiple-Input Multiple-Output (MIMO) functionality. Massive MIMO can refer to a base station configured to generate multiple beams for multiple UEs. During operation, the UE 110 can be within range of multiple gNBs. The reference to two gNBs 120A, 120B is for illustrative purposes only. The example embodiments can apply to any appropriate number of gNBs. Additionally, the UE 110 can communicate with eNB 122A of the LTE-RAN 122 to transmit and receive control information for downlink and / or uplink synchronization relative to the 5G NR-RAN 120 connection.

[0023] Those skilled in the art will appreciate that any relevant procedures can be performed for UE 110 to connect to 5G NR-RAN 120. For example, as described above, 5G NR-RAN 120 can be associated with a particular cellular provider at which UE 110 and / or its user has agreement and credential information (e.g., stored on a SIM card). Upon detecting the presence of 5G NR-RAN 120, UE 110 can transmit corresponding credential information in order to associate with 5G NR-RAN 120. More specifically, UE 110 can associate with a particular base station (e.g., gNB 120A of 5G NR-RAN 120).

[0024] In addition to networks 120, 122, and 124, network arrangement 100 includes cellular core network 130, Internet 140, IP Multimedia Subsystem (IMS) 150, and network services backbone 160. Cellular core network 130 can be viewed as an interconnected set of components that manage the operation and traffic of a cellular network. Cellular core network 130 also manages traffic that flows between the cellular network and Internet 140. IMS 150 can generally be described as an architecture for delivering multimedia services to UE 110 using IP protocols. IMS 150 can communicate with cellular core network 130 and Internet 140 to provide multimedia services to UE 110. Network services backbone 160 communicates with Internet 140 and cellular core network 130, either directly or indirectly. Network services backbone 160 can generally be described as a set of components (e.g., servers, network storage arrangements, etc.) that implement a suite of services that can be used to extend the functionality of UE 110 in communicating with various networks.

[0025] Figure 2 An exemplary UE 110 is shown in accordance with various example embodiments. UE 110 will be described with reference to network arrangement 100 of Figure 1 UE 110 can represent any electronic device and can include processor 205, memory arrangement 210, display device 215, input / output (I / O) device 220, transceiver 225, and other components 230. Other components 230 can include, for example, an audio input device, an audio output device, a battery providing a limited power source, a data acquisition device, a port for electrically connecting UE 110 to other electronic devices, one or more antenna panels, etc. For example, UE 110 can be coupled to an industrial device via one or more ports.

[0026] Processor 205 can be configured to execute a number of engines of UE 110. For example, the engines can include RRC management engine 235. RRC management engine 235 can perform various operations related to performing an RRC connection reestablishment on a primary cell (PCell) as configured by network 100. Exemplary operations will be described in greater detail below.

[0027] The above engines are exemplary only as applications (e.g., programs) executed by the processor 205. The functionality associated with the engines can also be represented as standalone components of the UE 110, or can be modular components coupled to the UE 110, e.g., integrated circuits with or without firmware. For example, the integrated circuits can include input circuitry for receiving signals and processing circuitry for processing signals and other information. The engines can also be embodied as one application or as multiple applications separate from one another. Moreover, in some UEs, the functionality described with respect to the processor 205 is split between two or more processors, such as a baseband processor and an application processor. The exemplary embodiments can be implemented in any of these or other configurations of the UE.

[0028] The memory arrangement 210 can be a hardware component configured to store data related to operations performed by the UE 110. The display device 215 can be a hardware component configured to display data to a user, while the I / O device 220 can be a hardware component that enables a user to make inputs. The display device 215 and the I / O device 220 can be separate components or can be integrated together, such as a touchscreen. The transceiver 225 can be a hardware component configured to establish a connection with the 5G NR-RAN 120, the LTE-RAN 122, the WLAN 124, etc. Thus, the transceiver 225 can operate on multiple different frequencies or channels (e.g., contiguous sets of frequencies).

[0029] Figure 3 An exemplary network base station, in this case a gNB 120A, is shown in accordance with various exemplary embodiments. The gNB 120A can represent any access node of a 5G NR network with which the UE 110 can establish a connection. Figure 3 The gNB 120A shown can also represent the gNB 120B.

[0030] The gNB 120A can include a processor 305, a memory arrangement 310, input / output (I / O) devices 320, a transceiver 325, and other components 330. The other components 330 can include, for example, a power source, a data acquisition device, ports that electrically connect the gNB 120A to other electronic devices, etc.

[0031] The processor 305 can be configured to execute a number of engines of the gNB 120A. For example, the engines can include an RRC management engine 335 for performing operations including configuring the UE 110 with measurement objects corresponding to target cells in conditional handover (CHO) or T312 fast failure recovery configurations. Examples of these operations are described in greater detail below.

[0032] The above engines are exemplary only as applications (e.g., programs) executed by the processor 305. The functionality associated with the engines can also be represented as stand-alone integrated components of the gNB 120A or can be modular components coupled to the gNB 120A, e.g., integrated circuits with or without firmware. For example, the integrated circuits can include input circuitry to receive signals and processing circuitry to process the signals and other information. Further, in some gNBs, the functionality described with respect to the processor 305 is split among multiple processors (e.g., a baseband processor, an application processor, etc.). The exemplary aspects can be implemented in any of these or other configurations of the gNB.

[0033] The memory 310 can be a hardware component that is configured to store data related to operations performed by the UE 110, 112. The I / O device 320 can be a hardware component or port that enables a user to interact with the gNB 120A. The transceiver 325 can be a hardware component that is configured to exchange data with the UE 110 and any other UE in the system 100. The transceiver 325 can operate on various different frequencies or channels (e.g., a set of contiguous frequencies). Thus, the transceiver 325 can include one or more components (e.g., radio components) to enable data exchange with various networks and UEs.

[0034] Figure 4A A method 400 of searching for a suitable primary cell (PCell) during a radio resource control (RRC) connection re-establishment procedure is shown in accordance with various exemplary embodiments. Figure 4B An exemplary conditional handover (CHO) configuration is shown in accordance with various exemplary embodiments. The method 400 will be described with reference to the exemplary conditional handover (CHO) configuration of Figure 4B .

[0035] At 405, the UE 110 receives a CHO configuration (conditional reconfiguration IE 452) from a base station (e.g., gNB 120A). As shown in Figure 4B , the CHO configuration includes a conditional reconfiguration addition / modification list 454 that includes a plurality of conditional reconfiguration entries (456). Each conditional reconfiguration entry 456 includes a conditional reconfiguration ID 458, a condition execution / trigger condition 460 that must be satisfied for the CHO to be triggered, and a conditional RRC reconfiguration over-the-air message 462 corresponding to a cell associated with the conditional reconfiguration entry 456. Once these conditions are satisfied, the UE 110 can transmit an RRC configuration complete message to the corresponding cell to complete the RRC connection re-establishment instead of performing a typical RRC connection re-establishment procedure. Figure 4B

[0036] Figure 4B ​​As shown, each condition in the conditional execution / triggering conditions 460 can include a measurement ID 464 that includes (i) a report configuration 466 in which a reportType information element (IE) is set to cond. TriggerConfig and (ii) a measurement object 468 having a frequency corresponding to a candidate cell.

[0037] Returning to Figure 4A At 410, the UE 110 detects a radio link failure (RLF) on the serving PCell. At 415, the UE 110 searches for a suitable PCell, but prioritizes frequencies associated with measurement objects (measurement objects 468) corresponding to CHO configurations. The UE 110 can be configured with multiple measurement objects in addition to the CHO measurement objects. By prioritizing the CHO frequencies, the UE 110 has an increased probability of finding a CHO PCell, as even if the UE 110 finds another (non-CHO) PCell with better power than the CHO PCell, it will connect with the CHO PCell. Thus, the probability of shortening the duration of suspending user plane data transmission is improved.

[0038] At 420, the UE 110 determines whether a CHO PCell has been found. In some example embodiments, if a CHO PCell has been found, the UE 110 can determine at 425 whether the CHO PCell satisfies an A5 event power threshold (Mn+Ofn+Ocn–Hys>Thresh2) as defined in 3GPP standard TS 38.331. If the CHO PCell does not satisfy the A5 event power threshold, the UE 110 performs a cell power suitability check at 455, which is defined in Section 5.2.3.2 of 3GPP TS 36.304 or TS 38.304, both of which define conditions that should be satisfied for a cell to be considered suitable for connection reestablishment. If the CHO PCell passes the cell suitability check, the UE 110 selects the CHO PCell at 430. However, if the CHO PCell does not pass the cell suitability check, at 440, the UE 110 continues to search for other PCells on the CHO frequencies as well as other frequencies (e.g., on frequencies of other measurement objects in addition to the CHO frequencies). At 445, the UE performs an RRC connection reestablishment procedure with the PCell found at 440.

[0039] However, if the CHO PCell does satisfy the A5 event power threshold at 425, the UE 110 selects the CHO PCell at 430. At 435, the UE 110 transmits an RRC reconfiguration complete message to the CHO PCell to establish an RRC connection with the CHO PCell. In some embodiments, because the CHO PCell satisfies the A5 event power threshold, the UE 110 can skip the cell power suitability check defined in Section 5.2.3.2 of 3GPP TS 36.304 or TS 38.304.

[0040] If the UE 110 does not find a CHO PCell at 420, the method proceeds to 440, where the UE 110 continues to search for other PCells on the CHO frequency as well as other frequencies (e.g., on frequencies that are other measurement object frequencies in addition to the CHO frequency). At 445, the UE performs an RRC connection reestablishment procedure with a PCell found at 440.

[0041] Figure 5 A method 500 of searching for a suitable PCell during an RRC connection reestablishment procedure is shown, in accordance with various example embodiments. At 505, the UE 110 receives a CHO or T312 configuration. The CHO configuration has been discussed above. The T312 configuration can be associated with one or more measurement objects associated with one or more measurement IDs. These measurement IDs are also associated with one or more measurement report configurations (ReportConfig) configured to use a T312 timer. In some embodiments, a frequency triggered network (e.g., gNB 120A) sends a HO command to the UE 110 associated with these measurement IDs.

[0042] At 510, the UE 110 detects a radio link failure (RLF) on the serving PCell. At 515, the UE 110 searches for a suitable PCell, but prioritizes frequencies associated with measurement objects corresponding to the CHO / T312 configuration. The UE 110 can be configured with multiple measurement objects in addition to the CHO / T312 measurement objects. At 520, the UE 110 determines whether a PCell has been found on a frequency corresponding to the CHO / T312 measurement objects. If a PCell has been found on the CHO / T312 frequency, the UE 110 selects that PCell at 525 and performs an RRC connection reestablishment with that PCell at 530. However, if a suitable PCell is not found at 520, the UE 110 searches for a PCell on other frequencies corresponding to other measurement objects at 535. At 540, the UE 110 performs a normal RRC connection reestablishment procedure with such a PCell (non-CHO / T312).

[0043] Because any PCell on a CHO frequency is a preconfigured CHO PCell, the CHO PCell will be able to retrieve UE context information from the original serving cell. Similarly, because any PCell on a T312 frequency is a PCell for which the network will trigger a HO command, that PCell will be able to retrieve UE context information from the original serving cell. In this way, by prioritizing searching for a PCell on a frequency corresponding to a CHO or T312 configuration, the probability that a PCell is able to retrieve UE context information from the original serving cell is increased.

[0044] In addition to increasing the probability of finding a CHO PCell and / or increasing the probability of finding a suitable PCell that will be able to successfully retrieve UE context data from the original serving cell, the methods 500 and 600 can also reduce the time required to find a suitable PCell. For example, in some example embodiments, during the search for a suitable CHO PCell, the UE 110 can skip acquiring a system information block 1 (SIB1), which is typically used for TS 36.304 / 38.304 cell suitability checks, if one or more predetermined conditions are met. In some example embodiments, the predetermined conditions can include that, although a CHO execution / trigger condition 458 is met, the CHO execution is not triggered because the TTT timer has not expired. In some example embodiments, the predetermined conditions can include that the SIB1 has been provided in a conditional RRC reconfiguration over-the-air message associated with the CHO PCell. Because the UE 110 can avoid acquiring the SIB1 in any of these scenarios, the time taken to acquire the SIB1 for TS 36.304 / 38.304 suitability checks is avoided, reducing the time required to find a suitable PCell.

[0045] Figure 6A and Figure 6B A method 600 of performing RRC connection reestablishment is shown, in accordance with various example embodiments. The method 600 begins with an RRC connection reestablishment cell search at 605. At 610, the UE 110 determines whether a CHO configuration has been received from the network (e.g., gNB 120A). If the UE 110 has received a CHO configuration, at 615, the UE 110 searches for a CHO PCell on a frequency associated with a measurement object identified in the CHO configuration. If more than one candidate frequency is available, the UE 110 starts with the frequency having the highest power based on the CHO PCell that has been found. However, if the UE 110 has not received a CHO configuration at 615, the method 600 proceeds to 625, which is discussed below.

[0046] At 620, the UE 110 determines whether a CHO PCell has been discovered. If a CHO PCell has been discovered, the UE 110 transmits an RRC reconfiguration complete message to the CHO PCell at 695. However, if a CHO PCell has not been discovered, at 625, the UE 110 searches for any PCell on (i) the frequency of the original serving cell (if the cause of the connection reestablishment is not RLF) and (ii) the frequencies of the measurement objects associated with CHO or T312 configurations of cells previously detected by the UE 110 (e.g., during connection mode measurements or a previous scan iteration). At 630, the UE 110 determines whether a suitable PCell has been discovered as a result of the search at 625. If a suitable PCell has been discovered, the method 600 proceeds to 690, where the UE 110 initiates an RRC connection reestablishment procedure on the PCell.

[0047] However, if a suitable PCell has not been discovered, at 635, the UE 110 searches for any PCell on the frequencies of the measurement objects associated with CHO or T312 configurations of cells that the UE 110 has not previously detected. At 640, the UE 110 determines whether a suitable PCell has been discovered as a result of the search at 635. If a suitable PCell has been discovered, the method 600 proceeds to 690, where the UE 110 initiates an RRC connection reestablishment procedure on the PCell.

[0048] However, if a suitable PCell has not been discovered, at 645, the UE 110 searches for any PCell on the frequencies of any remaining measurement objects that the UE 110 is configured for and cells that the UE 110 has previously detected. At 650, the UE 110 determines whether a suitable PCell has been discovered as a result of the search at 645. If a suitable PCell has been discovered, the method 600 proceeds to 690, where the UE 110 initiates an RRC connection reestablishment procedure on the PCell.

[0049] However, if a suitable PCell has not been discovered, at 655, the UE 110 searches for any PCell on the frequencies of any remaining measurement objects that the UE 110 is configured for and cells that the UE 110 has not previously detected. At 660, the UE 110 determines whether a suitable PCell has been discovered as a result of the search at 655. If a suitable PCell has been discovered, the method 600 proceeds to 690, where the UE 110 initiates an RRC connection reestablishment procedure on the PCell.

[0050] However, if a suitable PCell has not been found, at 665, if the cause of the connection reestablishment is RLF, the UE 110 searches for any PCell on the frequency of the original serving cell. At 670, the UE 110 determines whether a suitable PCell has been found as a result of the search at 665. If a suitable PCell has been found, the method 600 proceeds to 690, where the UE 110 initiates an RRC connection reestablishment procedure on the PCell.

[0051] However, if a suitable PCell has not been found, at 675, the UE 110 searches for any PCell on the frequencies and other bands of any remaining measurement objects configured on the UE 110 based on information stored on the UE 110. At 680, the UE 110 determines whether a suitable PCell has been found as a result of the search at 675. If a suitable PCell has been found, the method 600 proceeds to 690, where the UE 110 initiates an RRC connection reestablishment procedure on the PCell.

[0052] However, if a suitable PCell has not been found, at 683, the UE 110 determines whether the T311 timer, which defines the time allowed for connection reestablishment cell selection, has expired. If the T311 timer has expired, at 685, the UE 110 performs an RRC connection reestablishment failure procedure. However, if the T311 timer has not expired, the method 600 returns to 610, where the UE 110 determines whether a CHO configuration has been received.

[0053] Those skilled in the art will appreciate that the exemplary embodiments described above can be implemented in any suitable software configuration or hardware configuration, or a combination thereof. Exemplary hardware platforms for implementing the exemplary embodiments can include, for example, Intel x86-based platforms with compatible operating systems, Windows OS, Mac platforms and MAC OS, mobile devices with operating systems such as iOS, Android, and the like. In other examples, the exemplary embodiments of the above-described methods can be embodied as a program including lines of code stored on a non-transitory computer readable storage medium, which when compiled can be executed on a processor or microprocessor.

[0054] While this patent application describes various combinations of various embodiments each having different features, those skilled in the art will appreciate that any feature of one embodiment can be combined with features of another embodiment or features that are not inconsistent with the operation or functioning of the devices of the embodiments disclosed or the functions described in any manner not expressly disclosed.

[0055] It is well understood that, when using personal identifiable information, privacy policies and practices shall be followed that are generally recognized as satisfying or exceeding industry or governmental requirements for maintaining privacy. Specifically, personal identifiable information data shall be managed and handled in a manner that minimizes the risk of unintentional or unauthorized access or use, and the nature of authorized use shall be clearly indicated to users.

[0056] It will be apparent to those skilled in the art that various modifications can be made to the disclosed implementations without departing from the spirit or scope of the disclosure. Thus, it is intended that the disclosure cover modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.

Claims

1. A processor of a user equipment (UE), the processor configured to perform operations comprising: receiving a mobility configuration from a source cell of a network, wherein the mobility configuration comprises at least one mobility measurement object; determining that a radio link failure (RLF) event has occurred on the source cell; searching for a primary cell (PCell) on a frequency associated with the at least one mobility measurement object to reestablish a radio resource control (RRC) connection; when a conditional handover (CHO) PCell is found during the searching, determining whether the CHO PCell satisfies an A5 event power threshold, wherein when the CHO PCell does not satisfy the A5 event power threshold, the UE performs a suitability check to determine whether the CHO PCell passes the suitability check, and wherein when the CHO PCell does not pass the suitability check, the UE continues to search for other PCells on a CHO frequency and other frequencies; when the CHO Pcell satisfies the A5 event power threshold, reestablishing the RRC connection with the CHO PCell; and when the CHO Pcell does not satisfy the A5 event power threshold, receiving a CHO configuration comprising one or more trigger conditions that trigger when the CHO is to be satisfied, wherein when the one or more trigger conditions comprise a measurement ID, the measurement ID comprises (i) a reporting configuration in which a reportType information element (IE) is set to cond. TriggerConfig and (ii) a measurement object with a frequency corresponding to the PCell, wherein when the trigger conditions are satisfied, transmitting an RRC configuration complete message to the CHO PCell to complete the RRC connection reestablishment.

2. The processor of claim 1, wherein the mobility configuration is a CHO configuration, wherein the at least one mobility measurement object is a CHO measurement object corresponding to at least one target cell. when the CHO PCell satisfies the A5 event power threshold, no cell suitability check is performed.

3. The processor of claim 1, wherein, 4. The processor of claim 1, wherein the operations further comprise: transmitting an RRC reconfiguration complete message to the CHO PCell to facilitate reestablishment of the RRC connection.

5. The processor of claim 2, wherein the operations further comprise: when the CHO PCell satisfies a preconfigured condition for CHO execution, omitting acquisition of a system information block 1 (SIB1) of the CHO PCell.

6. The processor of claim 2, wherein the operations further comprise: when a system information block 1 (SIB1) has been received in an RRC reconfiguration over the air message included in the CHO configuration, omitting acquisition of the SIB1 of the CHO PCell. ​ 7. The processor of claim 1, wherein the mobility configuration is a T312 configuration, wherein the at least one measurement object is a T312 measurement object corresponding to a measurement ID, and wherein the measurement ID is associated with a measurement reporting configuration, ReportConfig, configured to use a T312 timer.

8. The processor of claim 7, wherein the operations further comprise: searching for the PCell on other frequencies not associated with the T312 measurement object when the PCell is not found on a frequency associated with the T312 measurement object.

9. A user equipment (UE), comprising: a transceiver configured to communicate with a network; and a processor communicatively coupled to the transceiver and configured to perform operations comprising: receiving a mobility configuration from a source cell of the network, wherein the mobility configuration comprises at least one mobility measurement object; determining that a radio link failure (RLF) event has occurred on the source cell; searching for a primary cell (PCell) only on frequencies associated with the at least one mobility measurement object to reestablish a radio resource control (RRC) connection; when a conditional handover (CHO) PCell is found during the searching, determining whether the CHO PCell satisfies an A5 event power threshold, wherein when the CHO PCell does not satisfy the A5 event power threshold, the UE performs a suitability check to determine whether the CHO PCell passes the suitability check, and wherein when the CHO PCell does not pass the suitability check, the UE continues to search for other PCells on CHO frequencies and other frequencies; when the CHO PCell satisfies the A5 event power threshold, reestablishing the RRC connection with the CHO PCell; and when the CHO PCell does not satisfy the A5 event power threshold, receiving a CHO configuration comprising one or more triggering conditions that trigger when the CHO is to be satisfied, wherein when the one or more triggering conditions comprise a measurement ID, the measurement ID comprises (i) a reporting configuration in which a reportType information element (IE) is set to cond. TriggerConfig and (ii) a measurement object having a frequency corresponding to the PCell, wherein when the triggering conditions are satisfied, transmitting an RRC configuration complete message to the CHO PCell to complete the RRC connection reestablishment.

10. The UE of claim 9, wherein the mobility configuration is a CHO configuration, wherein the at least one mobility measurement object is a CHO measurement object corresponding to at least one target cell. when the CHO PCell satisfies the A5 event power threshold, no cell suitability check is performed.

11. The UE of claim 9, wherein, 12. The UE of claim 9, wherein the operations further comprise: searching for the PCell on other frequencies not associated with the T312 measurement object when the PCell is not found on a frequency associated with the T312 measurement object. transmitting an RRC reconfiguration complete message to the CHO PCell to facilitate reestablishment of the RRC connection.

13. The UE of claim 10, wherein the operations further comprise: omitting acquisition of system information block 1 (SIB1) for the CHO PCell when the CHO PCell satisfies a preconfigured condition for CHO execution.

14. The UE of claim 10, wherein the operations further comprise: omitting acquisition of system information block 1 (SIB1) for the CHO PCell when the SIB1 has been received in an RRC reconfiguration over the air message included in the CHO configuration.

15. The UE of claim 9, wherein the mobility configuration is a T312 configuration, wherein the at least one measurement object is a T312 measurement object corresponding to a measurement ID, and wherein the measurement ID is associated with a measurement reporting configuration (ReportConfig) configured to use a T312 timer.

16. The UE of claim 15, wherein the operations further comprise: searching for the PCell on other frequencies not associated with the T312 measurement object when the PCell is not found on a frequency associated with the T312 measurement object.

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