PATENT DOCUMENT

Publication Number: US-11864257-B2
Application Number: US-202117448788-A
Country: US
Kind Code: B2

Title: Cell selection optimization during RRC reestablishment

Abstract:
A user equipment (UE) is configured to receive a mobility configuration from a source cell of a network, wherein the mobility configuration includes at least one mobility measurement object, determine 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 and reestablish the RRC connection with the PCell.

Claims:
The invention claimed is: 
     
       1. A processor of a user equipment (UE) configured to perform operations comprising:
 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) only on frequencies associated with the at least one mobility measurement object to reestablish a radio resource control (RRC) connection; 
 determining, when a conditional handover (CHO) PCell is found during the searching, whether the CHO PCell satisfies an A5 event power threshold, wherein the UE continues the searching for the PCell when the CHO PCell does not satisfy the A5 event power threshold; and 
 reestablishing the RRC connection with the CHO PCell when the CHO PCell satisfies the A5 event power threshold. 
 
     
     
       2. The processor of  claim 1 , wherein the mobility configuration is a conditional handover (CHO) configuration, wherein the at least one mobility measurement object is a CHO measurement object corresponding to at least one target cell. 
     
     
       3. The processor of  claim 2 , wherein the operations further comprise:
 searching for the PCell on other frequencies not associated with CHO measurement object when the CHO PCell is not found. 
 
     
     
       4. The processor of  claim 2 , wherein the operations further comprise:
 omitting acquisition of a system information block 1 (SIB1) of the CHO PCell when the CHO PCell satisfies preconfigured conditions for a CHO execution. 
 
     
     
       5. The processor of  claim 2 , wherein the operations further comprise:
 omitting acquisition of a system information block 1 (SIB1) of the CHO PCell when the SIB1 has already been received in an RRC Reconfiguration air-message included in the CHO configuration. 
 
     
     
       6. The processor of  claim 1 , wherein, when the CHO PCell satisfies the A5 event power threshold, a cell suitability check is not performed. 
     
     
       7. 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. 
 
     
     
       8. 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 report configuration (ReportConfig) configured to use a T312 timer. 
     
     
       9. The processor of  claim 8 , 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 frequencies associated with the T312 measurement object. 
 
     
     
       10. 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 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) only on frequencies associated with the at least one mobility measurement object to reestablish a radio resource control (RRC) connection; 
 determining, when a conditional handover (CHO) PCell is found during the searching, whether the CHO PCell satisfies an A5 event power threshold, wherein the UE continues the searching for the PCell when the CHO PCell does not satisfy the A5 event power threshold; and 
 reestablishing the RRC connection with the CHO PCell when the CHO PCell satisfies the A5 event power threshold. 
 
 
     
     
       11. The UE of  claim 10 , wherein the mobility configuration is a conditional handover (CHO) configuration, wherein the at least one mobility measurement object is a CHO measurement object corresponding to at least one target cell. 
     
     
       12. The UE of  claim 11 , wherein the operations further comprise:
 searching for the PCell on other frequencies not associated with CHO measurement object when the CHO PCell is not found. 
 
     
     
       13. The UE of  claim 11 , wherein the operations further comprise:
 omitting acquisition of a system information block 1 (SIB1) of the CHO PCell when the CHO PCell satisfies preconfigured conditions for a CHO execution. 
 
     
     
       14. The UE of  claim 11 , wherein the operations further comprise:
 omitting acquisition of a system information block 1 (SIB1) of the CHO PCell when the SIB1 has already been received in an RRC Reconfiguration air-message included in the CHO configuration. 
 
     
     
       15. The UE of  claim 10 , wherein, when the CHO PCell satisfies the A5 event power threshold, a cell suitability check is not performed. 
     
     
       16. The UE of  claim 10 , wherein the operations further comprise:
 transmitting an RRC reconfiguration complete message to the CHO PCell to facilitate reestablishment of the RRC connection. 
 
     
     
       17. The UE of  claim 10 , 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 report configuration (ReportConfig) configured to use a T312 timer. 
     
     
       18. The UE of  claim 17 , 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 frequencies associated with the T312 measurement object.

Description:
BACKGROUND INFORMATION 
     While a user equipment (UE) is in a radio resource control (RRC) connected mode, the UE may need to reestablish the connection with the wireless network based on different triggers such as, for example, a radio link failure (RLF), a handover (HO) failure, etc. To reestablish the connection, the UE initiates an RRC connection reestablishment procedure that is defined by the 3GPP standards. From the time the RRC connection reestablishment procedure is initiated until it is successfully completed, user-plane data transfer is suspended. 
     SUMMARY 
     Some exemplary embodiments are related 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) only on 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. 
     Other exemplary embodiments are related 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 the 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) only on 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 THE DRAWINGS 
         FIG.  1    shows an exemplary network arrangement according to various exemplary embodiments. 
         FIG.  2    shows an exemplary user equipment (UE) according to various exemplary embodiments. 
         FIG.  3    shows an exemplary base station according to various exemplary embodiments. 
         FIG.  4 A  shows a method of searching for a suitable primary cell (PCell) during a radio resource control (RRC) connection reestablishment procedure according to various exemplary embodiments. 
         FIG.  4 B  shows an exemplary conditional handover (CHO) configuration according to various exemplary embodiments. 
         FIG.  5    shows a method of searching for a suitable PCell during an RRC connection reestablishment procedure according to various exemplary embodiments. 
         FIGS.  6 A and  6 B  show a method of performing an RRC connection reestablishment procedure according to various exemplary embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The exemplary embodiments may be further understood with reference to the following description and the related appended drawings, wherein like elements are provided with the same reference numerals. The exemplary embodiments relate to operations by a user equipment (UE) for improving a radio resource configuration (RRC) connection reestablishment procedure. 
     In the following description, reference to a “suitable” primary cell (PCell) is used. The meaning of the term “suitable” or “suitable cell” should be understood to be the same as that term is defined in the 3GPP standards, including TS 36.304 and TS 38.304, and any standards referenced by these standards. 
     A UE may be configured with a mobility configuration. The mobility configuration may include a conditional handover (CHO) configuration that indicates a target cell ID for each of the target cells for handover in a source configuration received from a source cell. The UE is not required to parse radio resource control (RRC) configuration data for the target cell(s), thus reducing a UE processing burden. In some exemplary embodiments, a downlink (DL) frequency is also provided to the UE for each measurement object corresponding to the target cells. 
     The mobility configuration may alternatively or additionally be a T312 Fast Failure Recovery configuration that includes measurement IDs corresponding to measurement objects on which the UE may perform measurements when a time to trigger (TTT) timer has expired. The UE then transmits measurement report(s) based on these measurements to the network. Successful reception of the measurement report(s) by the network may 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 expiration of the T312 timer, the UE may initiate an RRC connection reestablishment procedure instead of waiting for expiration of a T310 timer. 
     In some cases, although the UE may be configured with a CHO, the UE may still attempt to perform an RRC connection reestablishment with a neighboring cell that is not a CHO configured cell but is found to be suitable based on its power. In such a scenario, the time that the user-plane data transfer is suspended is prolonged compared with a CHO RRC reestablishment because the UE must conduct the entire RRC connection reestablishment procedure. 
     In some exemplary embodiments, a UE that has been configured with a CHO may be configured to prioritize frequencies associated with the CHO measurement objects when searching for a suitable primary cell (PCell) with which to perform an RRC connection reestablishment. As a result, the probability that a CHO PCell is selected is increased, thus also increasing the likelihood of decreasing the user plane data transfer suspension time. 
     Another issue that arises is that a PCell with which the UE performs an RRC connection reestablishment may not be able to retrieve the UE context data from the last serving cell. In such a scenario, the UE would need to perform the entire RRC connection procedure with the new PCell (e.g., including access stratum (AS) security context), which requires an even longer period of time than an RRC connection reestablishment procedure in which the UE context information is retrievable from the last serving cell. 
     In some exemplary embodiments, a UE that has been configured with CHO measurement objects or T312 measurement objects may prioritize the frequencies associated with those measurement objects during its search for a suitable PCell with which to perform an RRC connection reestablishment. Because either of the CHO measurement objects or the T312 measurement objects lead to 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 independently found by the UE after RLF detection). 
       FIG.  1    shows an exemplary network arrangement  100  according to various exemplary embodiments. The exemplary network arrangement  100  includes a UE  110 . It should be noted that any number of UE may be used in the network arrangement  100 . Those skilled in the art will understand that the UE  110  may be any type of electronic component that is configured to communicate via a network, e.g., mobile phones, tablet computers, desktop computers, smartphones, phablets, embedded devices, wearables, Internet of Things (IoT) devices, etc. It should also be understood that an actual network arrangement may include any number of UEs being used by any number of users. Thus, the example of a single UE  110  is merely provided for illustrative purposes. 
     The UE  110  may be configured to communicate with one or more networks. In the example of the network configuration  100 , the networks with which the UE  110  may wirelessly communicate are a 5G New Radio (NR) radio access network (5G NR-RAN)  120 , an LTE radio access network (LTE-RAN)  122  and a wireless local access network (WLAN)  124 . However, it should be understood that the UE  110  may also communicate with other types of networks and the UE  110  may also communicate with networks over a wired connection. Therefore, the UE  110  may 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 . 
     The 5G NR-RAN  120  and the LTE-RAN  122  may be portions of cellular networks that may be deployed by cellular providers (e.g., Verizon, AT&amp;T, T-Mobile, etc.). These networks  120 ,  122  may include, for example, cells or base stations (Node Bs, eNodeBs, HeNBs, eNBS, gNBs, gNodeBs, macrocells, microcells, small cells, femtocells, etc.) that are configured to send and receive traffic from UE that are equipped with the appropriate cellular chip set. The WLAN  124  may include any type of wireless local area network (WiFi, Hot Spot, IEEE 802.11x networks, etc.). 
     The UE  110  may connect to the 5G NR-RAN  120  via the gNB  120 A and/or the gNB  120 B. The gNBs  120 A and  120 B may be configured with the necessary hardware (e.g., antenna array), software and/or firmware to perform massive multiple in multiple out (MIMO) functionality. Massive MIMO may refer to a base station that is configured to generate a plurality of beams for a plurality of UE. During operation, the UE  110  may be within range of a plurality of gNBs. Reference to two gNBs  120 A,  120 B is merely for illustrative purposes. The exemplary embodiments may apply to any appropriate number of gNBs. Further, the UE  110  may communicate with the eNB  122 A of the LTE-RAN  122  to transmit and receive control information used for downlink and/or uplink synchronization with respect to the 5G NR-RAN  120  connection. 
     Those skilled in the art will understand that any association procedure may be performed for the UE  110  to connect to the 5G NR-RAN  120 . For example, as discussed above, the 5G NR-RAN  120  may be associated with a particular cellular provider where the UE  110  and/or the user thereof has a contract and credential information (e.g., stored on a SIM card). Upon detecting the presence of the 5G NR-RAN  120 , the UE  110  may transmit the corresponding credential information to associate with the 5G NR-RAN  120 . More specifically, the UE  110  may associate with a specific base station (e.g., the gNB  120 A of the 5G NR-RAN  120 ). 
     In addition to the networks  120 ,  122  and  124  the network arrangement  100  also includes a cellular core network  130 , the Internet  140 , an IP Multimedia Subsystem (IMS)  150 , and a network services backbone  160 . The cellular core network  130  may be considered to be the interconnected set of components that manages the operation and traffic of the cellular network. The cellular core network  130  also manages the traffic that flows between the cellular network and the Internet  140 . The IMS  150  may be generally described as an architecture for delivering multimedia services to the UE  110  using the IP protocol. The IMS  150  may communicate with the cellular core network  130  and the Internet  140  to provide the multimedia services to the UE  110 . The network services backbone  160  is in communication either directly or indirectly with the Internet  140  and the cellular core network  130 . The network services backbone  160  may be generally described as a set of components (e.g., servers, network storage arrangements, etc.) that implement a suite of services that may be used to extend the functionalities of the UE  110  in communication with the various networks. 
       FIG.  2    shows an exemplary UE  110  according to various exemplary embodiments. The UE  110  will be described with regard to the network arrangement  100  of  FIG.  1   . The UE  110  may represent any electronic device and may include a processor  205 , a memory arrangement  210 , a display device  215 , an input/output (I/O) device  220 , a transceiver  225  and other components  230 . The other components  230  may include, for example, an audio input device, an audio output device, a battery that provides a limited power supply, a data acquisition device, ports to electrically connect the UE  110  to other electronic devices, one or more antenna panels, etc. For example, the UE  110  may be coupled to an industrial device via one or more ports. 
     The processor  205  may be configured to execute a plurality of engines of the UE  110 . For example, the engines may include an RRC management engine  235 . The RRC management engine  235  may perform various operations related to performing an RRC connection reestablishment on a primary cell (PCell) as configured by the network  100 . Exemplary operations will be described in greater detail below. 
     The above referenced engine being an application (e.g., a program) executed by the processor  205  is only exemplary. The functionality associated with the engine may also be represented as a separate incorporated component of the UE  110  or may be a modular component coupled to the UE  110 , e.g., an integrated circuit with or without firmware. For example, the integrated circuit may include input circuitry to receive signals and processing circuitry to process the signals and other information. The engines may also be embodied as one application or separate applications. In addition, in some UE, the functionality described for the processor  205  is split among two or more processors such as a baseband processor and an applications processor. The exemplary embodiments may be implemented in any of these or other configurations of a UE. 
     The memory arrangement  210  may be a hardware component configured to store data related to operations performed by the UE  110 . The display device  215  may be a hardware component configured to show data to a user while the I/O device  220  may be a hardware component that enables the user to enter inputs. The display device  215  and the I/O device  220  may be separate components or integrated together such as a touchscreen. The transceiver  225  may be a hardware component configured to establish a connection with the 5G NR-RAN  120 , the LTE-RAN  122 , the WLAN  124 , etc. Accordingly, the transceiver  225  may operate on a variety of different frequencies or channels (e.g., set of consecutive frequencies). 
       FIG.  3    shows an exemplary network base station, in this case gNB  120 A, according to various exemplary embodiments. The gNB  120 A may represent any access node of the 5G NR network through which the UEs  110  may establish a connection. The gNB  120 A illustrated in  FIG.  3    may also represent the gNB  120 B. 
     The gNB  120 A may include a processor  305 , a memory arrangement  310 , an input/output (I/O) device  320 , a transceiver  325 , and other components  330 . The other components  330  may include, for example, a power supply, a data acquisition device, ports to electrically connect the gNB  120 A to other electronic devices, etc. 
     The processor  305  may be configured to execute a plurality of engines of the gNB  120 A. For example, the engines may include an RRC management engine  335  for performing operations including configuring the UE  110  with measurement objects corresponding to target cells in a conditional handover (CHO) or T312 Fast Failure Recovery configuration. Examples of the operations will be described in greater detail below. 
     The above noted engine being an application (e.g., a program) executed by the processor  305  is only exemplary. The functionality associated with the engines may also be represented as a separate incorporated component of the gNB  120 A or may be a modular component coupled to the gNB  120 A, e.g., an integrated circuit with or without firmware. For example, the integrated circuit may include input circuitry to receive signals and processing circuitry to process the signals and other information. In addition, in some gNBs, the functionality described for the processor  305  is split among a plurality of processors (e.g., a baseband processor, an applications processor, etc.). The exemplary aspects may be implemented in any of these or other configurations of a gNB. 
     The memory  310  may be a hardware component configured to store data related to operations performed by the UEs  110 ,  112 . The I/O device  320  may be a hardware component or ports that enable a user to interact with the gNB  120 A. The transceiver  325  may be a hardware component configured to exchange data with the UE  110  and any other UE in the system  100 . The transceiver  325  may operate on a variety of different frequencies or channels (e.g., set of consecutive frequencies). Therefore, the transceiver  325  may include one or more components (e.g., radios) to enable the data exchange with the various networks and UEs. 
       FIG.  4 A  shows a method  400  of searching for a suitable primary cell (PCell) during a radio resource control (RRC) connection reestablishment procedure according to various exemplary embodiments.  FIG.  4 B  shows an exemplary conditional handover (CHO) configuration according to various exemplary embodiments. The method  400  will be described with reference to the exemplary conditional handover (CHO) configuration of  FIG.  4 B . 
     At  405 , the UE  110  receives a CHO configuration (Conditional Reconfiguration IE  452 ) from a base station (e.g., gNB  120 A). As shown in  FIG.  4 B , the CHO configuration includes a conditional reconfiguration add/mod list  454  that includes a plurality of conditional reconfiguration entries ( 8  shown in the example of  FIG.  4 B ). Each conditional reconfiguration entry  456  includes a conditional reconfiguration ID  458 , conditional execution/trigger conditions  460  that must be met for the CHO to be triggered, and a conditional RRC reconfiguration air-message  462  corresponding to the cell associated with the conditional reconfiguration entry  456 . Once the conditions are met, the UE  110  may transmit a RRC configuration complete message to the corresponding cell to complete the RRC connection reestablishment instead of performing the typical RRC connection reestablishment procedure. 
     As illustrated in  FIG.  4 B , each condition of the conditional execution/trigger conditions  460  may include a measurement ID  464  that includes (i) a report configuration  466  in which the reportType information element (IE) is set to cond. Trigger Config and (ii) a measurement object  468  having a frequency corresponding to the candidate cell. 
     Returning to  FIG.  4 A , 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  may be configured with multiple measurement objects in addition to CHO measurement objects. By prioritizing the CHO frequencies, the probability that the UE  110  finds a CHO PCell is increased because the UE  110  will connect with the CHO PCell even if it finds another (non-CHO) PCell with better power than the CHO PCell. As a result, the probability of shortening the duration during which user plane data transfer is suspended is improved. 
     At  420 , the UE  110  determines if a CHO PCell has been found. If a CHO PCell has been found, in some exemplary embodiments, the UE  110  may determine, at  425 , whether that CHO PCell meets an A5 event power threshold (Mn+Ofn+Ocn−Hys&gt;Thresh2) as defined in TS 38.331 of 3GPP standards. If the CHO PCell does not meet the A5 event power threshold, then 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 met for a cell to be considered suitable for connection reestablishment. If the CHO PCell passes the cell suitability check, then the UE  110  selects the CHO PCell at  430 . If, however, the CHO PCell does not pass the cell suitability check, then, at  440 , the UE  110  continues searching for other PCells on CHO frequencies as well as other frequencies (e.g., on frequencies of other measurement objects other than the CHO frequencies). At  445 , the UE performs the RRC connection reestablishment procedure with the PCell found at  440 . 
     If, however, the CHO PCell does meet the A5 event power threshold at  425 , then the UE  110  selects the CHO PCell at  430 . At  435 , the UE  110  transmits the RRC reconfiguration complete message to the CHO PCell to establish the RRC connection with the CHO PCell. In some embodiments, because the CHO PCell meets the A5 event power threshold, the UE  110  may skip the cell power suitability check defined in section 5.2.3.2 of 3GPP TS 36.304 or TS 38.304. 
     If the UE  110  does not find a CHO PCell at  420 , then the method proceeds to  440 , where the UE  110  continues searching for other PCells on CHO frequencies as well as other frequencies (e.g., on frequencies of other measurement objects other than the CHO frequencies). At  445 , the UE performs the RRC connection reestablishment procedure with the PCell found at  440 . 
       FIG.  5    shows a method  500  of searching for a suitable PCell during an RRC connection reestablishment procedure according to various exemplary embodiments. At  505 , the UE  110  receives a CHO or T312 configuration. The CHO configuration has been discussed above. A T312 configuration may 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 (ReportConfigs) that are configured to use the T312 timer. In some embodiments, the frequencies associated with these measurements IDs trigger the network (e.g., gNB  120 A) to send a HO commend to the UE  110 . 
     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 CHO/T312 configurations. The UE  110  may be configured with multiple measurement objects in addition to CHO/T312 measurement objects. At  520 , the UE  110  determines if a PCell has been found on a frequency corresponding to a CHO/T312 measurement object. If a PCell on a CHO/T312 frequency has been found, then the UE  110  selects that PCell at  525  and performs an RRC connection reestablishment with that PCell at  530 . If, however, no suitable PCell is found at  520 , then the UE  110  searches for PCells on other frequencies corresponding to other measurement objects at  535 . At  540 , the UE  110  performs the normal RRC connection reestablishment procedure with such a PCell (non-CHO/T312). 
     Because any PCell on a CHO frequency is a preconfigured CHO PCell, the CHO PCell will be able to retrieve the UE context information from the original serving cell. Similarly, because any PCell on a T312 frequency is a PCell to which the network would trigger the HO command, that PCell will be able to retrieve the UE context information from the original serving cell. As such, by prioritizing the search for a PCell on frequencies corresponding to a CHO or T312 configuration, the probability that the PCell is able to retrieve the UE context information from the original serving cell is increased. 
     In addition to increasing the probability of finding a CHO PCell and/or of finding a suitable PCell that will be able to successfully retrieve the UE context data from the original serving cell, the methods  500  and  600  may also reduce the time required to find a suitable PCell. For example, in some exemplary embodiments, during a search for a suitable CHO PCell, the UE  110  may skip acquiring the system information block 1 (SIB1), which is typically used for the TS 36.304/38.304 cell suitability check, if one or more predetermined conditions are met. In some exemplary embodiments, the predetermined conditions may include the CHO PCell satisfies the conditional execution/trigger conditions  458 , but the CHO execution is not triggered because a TTT timer has not expired. In some exemplary embodiments, the predetermined conditions may include that the SIB1 is already provided in the Conditional RRC Reconfiguration air-message associated with the CHO PCell. Because the UE  110  can avoid acquiring the SIB1 in any of these scenarios, the time spent acquiring the SIB1 for a TS 36.304/38.304 suitability check is avoided, thus reducing the time required to find a suitable PCell. 
       FIGS.  6 A and  6 B  show a method  600  of performing an RRC connection reestablishment according to various exemplary embodiments. The method  600  begins with the 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  120 A). If the UE  110  has received a CHO configuration, then, at  615 , the UE  110  searches for a CHO PCell on frequencies associated with measurement objects identified in the CHO configuration. If more than one candidate frequency is available, then the UE  110  begins with frequencies having the highest power based on CHO PCells that have already been found. If, however, the UE  110  has not received a CHO configuration at  615 , then the method  600  proceeds to  625 , which is discussed below. 
     At  620 , the UE  110  determines if a CHO PCell has been found. If a CHO PCell has been found, then the UE  110  transmits the RRC reconfiguration complete message to the CHO PCell at  695 . If, however, a CHO PCell has not been found, then, at  625 , the UE  110  searches for any PCell on (i) the frequency of the original serving cell if the cause for the connection reestablishment is not RLF, and (ii) the frequencies of the measurement objects associated with CHO or T312 configurations having cells that were previously detected by the UE  110  (e.g., during connected mode measurements or previous scan iterations). At  630 , the UE  110  determines if a suitable PCell has been found as a result of the search at  625 . If a suitable PCell has been found, then the method  600  proceeds to  690 , where the UE  110  initiates the RRC connection reestablishment procedure on the that PCell. 
     If, however, a suitable PCell has not been found, then, at  635 , the UE  110  searches for any PCell on frequencies of measurement objects associated with CHO or T312 configurations having cells that were not previously detected by the UE  110 . At  640 , the UE  110  determines if a suitable PCell has been found as a result of the search at  635 . If a suitable PCell has been found, then the method  600  proceeds to  690 , where the UE  110  initiates the RRC connection reestablishment procedure on the that PCell. 
     If, however, a suitable PCell has not been found, then, at  645 , the UE  110  searches for any PCell on frequencies of any remaining measurement objects with which the UE  110  is configured and having cells that were previously detected by the UE  110 . At  650 , the UE  110  determines if a suitable PCell has been found as a result of the search at  645 . If a suitable PCell has been found, then the method  600  proceeds to  690 , where the UE  110  initiates the RRC connection reestablishment procedure on the that PCell. 
     If, however, a suitable PCell has not been found, then, at  655 , the UE  110  searches for any PCell on frequencies of any remaining measurement objects with which the UE  110  is configured and having cells that were not previously detected by the UE  110 . At  660 , the UE  110  determines if a suitable PCell has been found as a result of the search at  655 . If a suitable PCell has been found, then the method  600  proceeds to  690 , where the UE  110  initiates the RRC connection reestablishment procedure on the that PCell. 
     If, however, a suitable PCell has not been found, then, at  665 , the UE  110  searches for any PCell on the frequency of the original serving cell if the cause for the connection reestablishment is RLF. At  670 , the UE  110  determines if a suitable PCell has been found as a result of the search at  665 . If a suitable PCell has been found, then the method  600  proceeds to  690 , where the UE  110  initiates the RRC connection reestablishment procedure on the that PCell. 
     If, however, a suitable PCell has not been found, then, at  675 , the UE  110  searches for any PCell on frequencies of any remaining measurement objects with which the UE  110  is configured and other frequency bands based on information stored on the UE  110 . At  680 , the UE  110  determines if a suitable PCell has been found as a result of the search at  675 . If a suitable PCell has been found, then the method  600  proceeds to  690 , where the UE  110  initiates the RRC connection reestablishment procedure on the that PCell. 
     If, however, a suitable PCell has not been found, then, at  683 , the UE  110  determines if a T311 timer that defines the time allowed for a connection reestablishment cell selection has expired. If the T311 timer has expired, then, at  685 , the UE  110  performs an RRC connection reestablishment failure procedure. If, however, the T311 timer has not expired, then the method  600  returns to  610 , where the UE  110  determines if a CHO configuration has been received. 
     Those skilled in the art will understand that the above-described exemplary embodiments may be implemented in any suitable software or hardware configuration or combination thereof. An exemplary hardware platform for implementing the exemplary embodiments may include, for example, an Intel x86 based platform with compatible operating system, a Windows OS, a Mac platform and MAC OS, a mobile device having an operating system such as iOS, Android, etc. In a further example, the exemplary embodiments of the above-described method may be embodied as a program containing lines of code stored on a non-transitory computer readable storage medium that, when compiled, may be executed on a processor or microprocessor. 
     Although this application described various embodiments each having different features in various combinations, those skilled in the art will understand that any of the features of one embodiment may be combined with the features of the other embodiments in any manner not specifically disclaimed or which is not functionally or logically inconsistent with the operation of the device or the stated functions of the disclosed embodiments. 
     It is well understood that the use of personally identifiable information should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users. 
     It will be apparent to those skilled in the art that various modifications may be made in the present disclosure, without departing from the spirit or the scope of the disclosure. Thus, it is intended that the present disclosure cover modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.

Metadata:
Filing Date: 20210924
Publication Date: 20240102
Grant Date: 20240102
Priority Date: 20210924
Inventors: MOSTAFA, Amr
TAHIR, Ammar
KEMMER, BERND H.
ELBEHAIDY, Karim
ASHTEKAR, PRASAD P.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W36/362", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W76/19", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W36/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/0058", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W76/19", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W36/0061", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/305", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/362", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/08", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 83362549