Patent Description:
The background description provided in this disclosure is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

In a wireless communication system, a base station that supports a certain Radio Access Technology (RAT) communicates with a user equipment (UE) using, among other protocols, a protocol for controlling radio resources corresponding to the RAT. The protocol for controlling radio resources may be, for example, a Radio Resource Control (RRC) protocol utilized by <NUM>, <NUM>, <NUM>, or later-generation wireless communication systems. Upon establishing a radio connection via the base station, the UE operates in a connected state of the protocol for controlling radio resources, which may be RAT-specific (e.g., EUTRA-RRC CONNECTED, NR-RRC CONNECTED).

The UE and the base station can use signaling radio bearers (SRBs) to exchange RRC messages as well as non-access stratum (NAS) messages. There are several types of SRBs: SRB1 resources carry RRC messages and in some cases NAS messages over a dedicated control channel (DCCH); SRB2 resources support RRC messages that include logged measurement information or NAS messages, also over the DCCH but with lower priority than SRB1 resources; SRB3 resources support RRC messages related to measurement configuration and reporting, for example, of a secondary cell group (SCG) when the UE operates in dual connectivity (DC); and SRB4 resources support RRC messages that include application-layer measurement reporting information, also over the DCCH.

Further, the UE and the base station use data radio bearers (DRBs) to transport data on a user plane.

There are several scenarios in which the (first) base station and/or the UE determines that the UE should establish a radio connection with another (second) base station. For example, the first base station can determine to hand the UE over to the second base station, and initiate a handover procedure. In another scenario, the UE can detect radio link failure (RLF) on the radio connection with the first base station and subsequently select the second base station for re-establishing the radio connection. In yet another scenario, the first base station can detect a below-threshold activity for the UE over some period of time over the established connection and instruct the UE to transition to an inactive state of the RAT protocol (e.g., EUTRA-RRC INACTIVE, NR-RRC INACTIVE). At a later time, such as when the UE has moved into a different coverage area and has payload data to transmit to the wireless communication system, the UE operating in the inactive state selects or reselects the second base station and subsequently transitions back to the connected state.

In some of these scenarios, the UE and the first base station use an SRB4, which the second base station may not support. The second base station is generally unaware of an unsupported configuration of an SRB and, as a result, the second base station may provide a configuration to the UE that conflicts with the SRB4 configuration, or the UE can continue using the SRB4 to transmit information which the second base station does not process.

As a more particular example, an SRB or a DRB has a distinct logical channel identity. For example, an SRB4 can have a logical channel identity value of "<NUM>. " When the second base station supports SRB4s, the second base station is aware of the logical channel identity value which the first base station assigned to the SRB4 of the UE. Accordingly, when the second base station configures a new radio bearer for the UE, the second base station does not use the logical channel identity value already assigned to the SRB4. However, when the second base station does not support the SRB4 configuration, the second base station is unaware of the existence of the SRB4 configuration and its logical channel identity value. As a result, the second base station can associate a DRB with the same logical channel identity value the first base station assigned to the SRB4. This conflict in logical channel identity assignment can result in communication failure between the UE and the second base station.

Further, when the second base station supports SRB4s, the second base station in some cases can apply full configuration to the radio connection between the UE and the second base station. For example, the second base station can provide the full configuration when the second base station does not recognize at least one configuration of the connection, or when the second base station attempts to conserve processing resources by not filtering through the configuration(s) associated with the connection between the UE and the first base station. As another example, the second base station can be manufactured or operated by a different entity than the first base station. The 3rd Generation Partnership Project (3GPP) specification, and specifically 3GPP TS <NUM> v15. <NUM>, does not address the scenario in which the second base station provides a UE with a full configuration that involves an SRB4. Different UEs thus can handle the full configuration differently, and the second base station and the UE as a result can fail to communicate properly. <CIT> describes a method of handling radio resource reconfiguration for a mobile device in a wireless communication system. The method includes establishing at lease one data radio bearer (DRB) and an Evolved Packet System (EPS)-bearer identity of the least one DRB, wherein the least one DRB is associated with a first radio resource configuration; indicating that establishment of the at least one DRB and the EPS-bearer identity of the at least one DRB is illegal when the mobile device reverts back to a second radio resource configuration from the first radio resource configuration. <CIT> describes a bearer management apparatus and method, and a communication system. The method comprises: a user equipment (UE) receives an indication message, sent by a base station, for changing a bearer type of a bearer or releasing the bearer under dual connectivity; and changes the bearer type of the bearer or releases the bearer according to the indication message. <CIT> describes a method for handling a user plane by a UE configured for dual connectivity operation. The method includes receiving a RRC reconfiguration message including one or more Layer <NUM> indications and a Layer <NUM> configuration corresponding to one or more radio bearers from one of a MN and a SN involved in a dual connectivity operation of the UE. Further, the method includes performing, by the UE, one of: reestablishing of a RLC entity and a data recovery procedure for a PDCP entity corresponding to the radio bearer based on the one or more Layer <NUM> indications and the Layer <NUM> configuration received in the RRC reconfiguration message, and reestablishing of a RLC entity and reestablishing of a PDCP entity corresponding to the radio bearer based on the one or more Layer <NUM> indications and the Layer <NUM> configuration received in the RRC reconfiguration message. <CIT> describes a method and system for performing a bearer type change of a plurality of radio bearers configured for a User Equipment (UE). The proposed method includes changing the bearer type of specific bearer by the network. Further, the proposed method includes checking any changes in keys or PDCP termination point or PDCP version change. Furthermore, the proposed method includes notifying the UE to change the bearer type either through reconfiguration procedure without handover or SN change procedure or reconfiguration procedure with handover or SN change procedure. The network indicates one or more operations to the UE for performing the bearer type change.

In a radio access network (RAN) of this disclosure, a first base station (e.g., an evolved NodeB (eNB)) configures a UE with an SRB4, and the UE subsequently establishes or re-establishes a radio connection with a second base station (e.g., another eNB), as a part of a handover procedure, a connection re-establishment procedure, a connection resume procedure, etc. The second base station in some of the implementations causes the UE to release the SRB4 and establish a radio bearer of another type to communicate with the second base station. In other implementations, the second base station causes the UE to reconfigure the SRB4 for communicating with the second base station.

In various implementations, the second base station causes the UE to release the SRB4 by including a configuration for a DRB, omitting a configuration for the SRB4, including an explicit indicator instructing the UE to release the SRB4, omitting an explicit indicator instructing the UE to keep the SRB4, providing a full configuration that omits the SRB4 configuration, etc. The second base station can use one of these techniques when formatting a handover command, an RRC reconfiguration command, an RRC resume command, etc. Because the second base station in at least some of these scenarios communicates with the UE via the first base station, the first base station in some implementations modifies the message the second base station addresses to the UE. By causing the UE to release the SRB4 before applying the DRB configuration, the second base station prevents the UE from using the same logical channel identity with two different radio bearers.

In another implementation, the UE reconfigures the SRB4 in accordance with a message from the second base station. The term "reconfigure" as used herein can refer to the UE (i) reconfiguring an existing SRB4 to generate a new SRB4 configuration for use with the second base station or (ii) releasing the existing SRB4 and generating a new SRB4 according to a new configuration provided by the second base station. That is, if the second base station supports SRB4, the second base station can transmit the message that includes the new SRB4 configuration to cause the UE to replace the SRB4 configuration previously provided by the first base station with the new SRB4 configuration. If the second base station does not support SRB4, the second base station can transmit the message that includes the configuration for a DRB to the UE, causing the UE to release the SRB4 before applying the DRB configuration.

Generally, the techniques disclosed in this disclosure apply to wireless communication systems having one or more Radio Access Networks that support the same or different types of Radio Access Technologies (RATs), e.g., via unlicensed portions of the radio spectrum, such as the fourth generation of mobile or cellular data technology ("<NUM>"), <NUM> in accordance with the Long-Term Evolution standard ("<NUM>-LTE"), the fifth generation of mobile or cellular data technologies (referred to as "<NUM>"), <NUM> New Radio ("NR" or "NR-U"), <NUM> Evolved Universal Terrestrial Radio Access ("EUTRA" or "E-UTRA"), the sixth generation of mobile or cellular data technologies ("<NUM>"), etc. The various different types of radio access technologies may be connected to any suitable type of Core Network ("CN"), such as an Evolved Packet Core Network ("EPC"), a generation of Core Network subsequent to EPC (such as 5GC), a generation of Core Network later than 5GC, etc..

The techniques described in this disclosure apply to a certain type of a radio bearer, an SRB4, when the UE establishes or re-establishes a radio connection with a base station. However, these techniques also can apply to other radio bearers which some but not all of the base stations operating in a RAN support.

As illustrated in <FIG>, the system <NUM> includes a first base station <NUM> and a second base station <NUM> of a RAN <NUM> that each supports a same or different RAT. For example, base station <NUM> may support NR, and base station <NUM> may support EUTRA, or vice versa. Generally speaking, a base station that supports an NR RAT operates as a gNodeB (gNB), and a base station that supports an E-UTRA RAT and connects to a 5GC Core Network (E-UTRA/5GC) operates as a next generation evolved Node B (ng-eNB). A base station that supports an E-UTRA RAT and connects to an EPC Core Network (E-UTRA/EPC) operates as an evolved NodeB (eNB), and a base station that supports both E-UTRA/EPC and E-UTRA/5GC operates as both an ng-eNB and an eNB. Each base station <NUM>, <NUM> may communicatively connect to the same CN (e.g., EPC or 5GC) or different core networks (EPC and 5GC). Base station <NUM> supports a cell <NUM>, and base station <NUM> supports a cell <NUM>. The cells <NUM> and <NUM> may partially overlap, as illustrated in <FIG>.

Each base station <NUM>, <NUM> may support other types of Radio Access Technologies instead of or in addition to NR and/or EUTRA. Although <FIG> illustrates two base stations <NUM>, <NUM> that are connected to a single CN <NUM>, the system <NUM> may be configured with any number of base stations supporting any number of RANs, each of which is respectively connected to any number of CNs.

Base station <NUM> and UE <NUM> establish a connection via which data payload is transmitted between UE <NUM> and base station <NUM>, e.g., wirelessly. Upon establishing the connection via base station <NUM>, UE <NUM> is in a connected state of the RAT protocol for controlling radio resources (e.g., EUTRA-RRC_CONNECTED, NR-RRC CONNECTED). Base station <NUM> maintains a context of UE <NUM>, where the context of the UE <NUM> includes configuration and other information associated with the connection of UE <NUM> with base station <NUM>. The context of UE <NUM> may be included in or implemented as an AS, for example. The context of UE <NUM> may include configurations of an SRB1, an SRB2, an SRB4, a DRB, and/or other configurations (e.g., security configuration) associated with the connection between UE <NUM> and base station <NUM>.

At some point in time, UE <NUM> establishes, resumes or re-establishes a radio connection with base station <NUM> for servicing. This may occur in various scenarios. In one scenario ("the handover scenario"), base station <NUM> may determine that UE <NUM> is to handover to base station <NUM>. In another scenario ("the re-establishment scenario"), UE <NUM> may detect radio link failure (RLF) over the established connection with base station <NUM> or detect integrity check failure on the SRB1, SRB2 or SRB4, and subsequently select base station <NUM> for servicing. In yet another scenario ("the re-selection scenario"), base station <NUM> may detect that below-threshold or no-data activity for UE <NUM> has occurred over some interval of time over the established connection. Upon this detection, base station <NUM> instructs UE <NUM> to enter into an inactive state of the RAT protocol (e.g., EUTRA-RRC INACTIVE, NR-RRC INACTIVE). At some point in time thereafter, such as when UE <NUM> has moved into a different coverage area and has payload data to transmit to the system, UE <NUM> (which is in the inactive state) selects or reselects base station <NUM> for servicing.

In each of the scenarios described above, a new connection is established between UE <NUM> and base station <NUM>, which causes base station <NUM> to create a second instance of the context or AS of UE <NUM>, and populate the second instance of the context/AS with configuration information associated with the connection between UE <NUM> and base station <NUM>. In some cases, base station <NUM> may not support or recognize at least one configuration (e.g., an SRB4 configuration) associated with the connection between UE <NUM> and base station <NUM>, and therefore, base station <NUM> is generally unaware of such unsupported or unrecognizable configurations. In some cases, base station <NUM> may support or recognize the configurations associated with the connection between UE <NUM> and base station <NUM>, yet provide its own configurations (e.g., full configuration, delta configuration) to UE <NUM>, and base station <NUM> stores information gathered during these procedures and the locally-accessible second instance of the context/AS.

In each of the scenarios described above, base station <NUM> is configured to include or omit an indication in the message for releasing or reconfiguring the SRB4 configuration from the context of UE <NUM> maintained by base station <NUM>. For example, in the handover scenario, the re-establishment scenario, or the re-selection scenario, base station <NUM> is configured to include or omit an indication in a Handover Command message, an RRC Reconfiguration message, or a RRC Resume message, respectively, for releasing or reconfiguring the SRB4 configuration.

UE <NUM> is equipped with processing hardware <NUM> that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and/or special-purpose processing units. The processing hardware <NUM> in an example implementation includes an RRC controller <NUM> configured to receive messages from the base stations <NUM>, <NUM> during the handover scenario, the re-establishment scenario, or the re-selection scenario and release or reconfigure an existing SRB4 <NUM> (i.e., maintained by base station <NUM>) stored in non-transitory computer-readable memory in response to the messages in accordance with one or more of the methods, principles, and techniques disclosed in this disclosure.

Base station <NUM> is equipped with processing hardware <NUM> that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and/or special-purpose processing units. The processing hardware <NUM> in an example implementation includes an RRC controller <NUM> configured to initiate the handover scenario or the re-selection scenario in accordance with one or more of the methods, principles, and techniques disclosed in this disclosure.

Base station <NUM> is equipped with processing hardware <NUM> that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and/or special-purpose processing units. The processing hardware <NUM> in an example implementation includes an RRC controller <NUM> configured to complete the handover scenario, the re-establishment scenario, or the re-selection scenario in accordance with one or more of the methods, principles, and techniques disclosed in this disclosure.

Although not shown, processing hardware <NUM>, <NUM>, <NUM> may include UE and base station interfaces via which the processing hardware <NUM>, <NUM>, <NUM> may communicate with each other.

<FIG> and <FIG> generally illustrate example message flow diagrams of the handover scenario between UE <NUM> and base stations <NUM>, <NUM> of wireless communication system <NUM>.

Turning now to <FIG>, at the beginning of a scenario <NUM>, RRC controller <NUM> of UE <NUM> and RRC controller <NUM> of base station <NUM> perform <NUM> a measurement procedure to establish a manner in which UE <NUM> performs measurements and provides results of the measurements in a report to base station <NUM>. To begin performing <NUM> the measurement procedure, UE <NUM> operates <NUM> in a connected state (e.g., EUTRA-RRC_CONNECTED, NR-RRC CONNECTED) with base station <NUM>. When base station <NUM> determines <NUM> to request UE <NUM> to perform a measurement (e.g., an application layer measurement report (e.g., a qoe-MeasReport), MDT measurement report, SON measurement report, RLF measurement report, RACH measurement report, connection establishment failure report and/or mobility history report) and provide a corresponding report to base station <NUM> via a particular SRB4, base station <NUM> transmits <NUM> an RRC Reconfiguration message to UE <NUM>. In some embodiments, the RRC Reconfiguration message includes an SRB4 configuration that is associated with a particular logical channel identity value (e.g., "<NUM>"), and a measurement configuration (e.g., an application layer measurement configuration, MDT measurement configuration or/and a SON measurement configuration). In other embodiments, base station <NUM> can include and transmit <NUM> the measurement configuration in a second RRC Reconfiguration message.

In response, UE <NUM> applies <NUM> the SRB4 configuration and measurement configuration, and proceeds to perform measurements and generate a report. To transmit the requested report, UE <NUM> includes the report in an RRC message (e.g., a MeasReportAppLayer message, UEInformationResponse message, a UEAssistanceInformation message, or newly defined RRC message) and transmits <NUM> the RRC message to base station <NUM> via the configured SRB4 (associated with logical channel identity value <NUM>), thereby completing <NUM> the measurement procedure. In one embodiment, the newly defined RRC message may contain a segment of an RRC message.

After a period of time, base station <NUM> determines <NUM> to handover UE <NUM> to base station <NUM>. Accordingly, base station <NUM> transmits <NUM> a Handover Request message to base station <NUM>. In response, base station <NUM> determines <NUM> to configure UE <NUM> with a DRB configuration associated with the same logical channel identity value as the configured SRB4, either because base station <NUM> does not support or is otherwise unaware of the configured SRB, or because base station <NUM> supports the configured SRB4 yet intends to release the configured SRB4 (i.e., hence the logical channel identity value that was assigned to the configured SRB4 is available for assignment by base station <NUM>). Base station <NUM> includes a configuration for a DRB in a Handover Command message, and subsequently transmits <NUM> a Handover Request Acknowledge message including the Handover Command message (e.g., an RRCConnectionReconfiguration message, an RRCReconfiguration message) to base station <NUM>. In turn, base station <NUM> transmits <NUM> the Handover Command message to UE <NUM>.

The Handover Command message causes UE <NUM> to release <NUM> the SRB4 and apply <NUM> the DRB configuration indicated in the Handover Command message. Accordingly, and advantageously, UE <NUM> validates the Handover Command message because the logical channel identity value associated with the DRB configuration is only associated with the DRB configuration and not the SRB4 configuration. In some embodiments, UE <NUM> can also release the measurement configuration provided by base station <NUM> at events <NUM> or <NUM>.

In turn, UE <NUM> transmits <NUM> a Handover Complete message (e.g., an RRCConnectionReconfigurationComplete message, an RRCReconfigurationComplete message) to base station <NUM>, thereby successfully completing the handover scenario. Accordingly, UE <NUM> operates <NUM> in a connected state with base station <NUM>, and therefore UE <NUM> and base station <NUM> can exchange <NUM> data via the logical channel identity mapped to the DRB. For example, UE <NUM> can transmit a packet (e.g., an internet protocol (IP) packet) via the DRB. The UE <NUM> can transmit a measurement report or other suitable report in a Packet Data Convergence Protocol (PDCP) Protocol Data Unit (PDU) to base station <NUM> via the DRB (i.e., instead of the previously configured SRB4 due to releasing the SRB4 configuration). Particularly, UE <NUM> can generate a PDCP SDU including the report, encrypt the PDCP SDU, and construct a PDCP PDU including the encrypted PDCP SDU according to the DRB configuration. UE <NUM> transmits the PDCP PDU associated to the DRB to base station <NUM>. In response, base station <NUM> successfully processes the PDCP PDU according to the DRB configuration. Similarly, UE <NUM> can receive a PDCP PDU associated to the DRB from base station <NUM> and successfully process the PDCP PDU according to the DRB configuration (i.e., instead of the SRB4 configuration due to releasing the SRB4 configuration).

Turning now to <FIG>, at the beginning of a scenario <NUM>, UE <NUM> and base station <NUM> perform <NUM> the measurement procedure. After a period of time, base station <NUM> determines <NUM> to handover UE <NUM> to base station <NUM>. Accordingly, base station <NUM> transmits <NUM> a Handover Request message to base station <NUM>. In response, base station <NUM> determines to configure UE <NUM> with a configuration (e.g., a security configuration in contrast to a DRB configuration illustrated in <FIG>), includes the configuration in a Handover Command message (e.g., an RRCConnectionReconfiguration message, an RRCReconfiguration message), and subsequently transmits <NUM> a Handover Request Acknowledge message including the Handover Command message to base station <NUM>. In turn, base station <NUM> transmits <NUM> the Handover Command message to UE <NUM>.

The Handover Command message causes UE <NUM> to apply <NUM> the configuration included in the Handover Command message.

In turn, UE <NUM> transmits <NUM> a Handover Complete message (e.g., an RRCConnectionReconfigurationComplete message, an RRCReconfigurationComplete message) to base station <NUM>, thereby successfully completing the handover scenario. Accordingly, UE <NUM> operates <NUM> in a connected state with base station <NUM>.

In contrast to base station <NUM> illustrated in <FIG>, base station <NUM> illustrated in <FIG> initiates <NUM> a reconfiguration procedure, by determining <NUM> to configure UE <NUM> with a DRB configuration associated with the same logical channel identity value as the configured SRB4 after successful completion of the handover scenario, either because base station <NUM> does not support or is otherwise unaware of the configured SRB, or because base station <NUM> supports the configured SRB4 yet intends to release the configured SRB4 (i.e., hence the logical channel identity value that was assigned to the configured SRB4 is available for assignment by base station <NUM>). Base station <NUM> includes the DRB configuration in a RRC Reconfiguration message, and subsequently transmits <NUM> the RRC Reconfiguration message to UE <NUM>.

The RRC Reconfiguration message causes UE <NUM> to release <NUM> the SRB4 and apply <NUM> the DRB configuration included in the RRC Reconfiguration message. Accordingly, and advantageously, UE <NUM> validates the RRC Reconfiguration message because the logical channel identity value associated with the DRB configuration is only associated with the DRB configuration and not the SRB4 configuration. In some embodiments, UE <NUM> can also release the measurement configuration provided by base station <NUM> at event <NUM>.

In turn, UE <NUM> transmits <NUM> an RRC Connection Reconfiguration Complete message (e.g., an RRCConnectionReconfiguration message or an RRCReconfiguration message) to base station <NUM>. Accordingly, and as described above in <FIG>, UE <NUM> operates <NUM> in a connected state with base station <NUM>, and therefore UE <NUM> and base station <NUM> can exchange <NUM> data via the logical channel identity mapped to the DRB, thereby completing <NUM> the reconfiguration procedure.

Turning now to <FIG>, at the beginning of a scenario <NUM>, UE <NUM> and base station <NUM> perform <NUM> a measurement procedure, similar to event <NUM> discussed above. Also similar to events <NUM>, <NUM> discussed above, base station <NUM> determines <NUM> to handover UE <NUM> to base station <NUM> and subsequently transmits <NUM> a Handover Request message to base station <NUM>.

In some embodiments, in response to the Handover Request message, base station <NUM> determines <NUM> to configure UE <NUM> with a full configuration or delta configuration, which may include a DRB configuration (similar to event <NUM>) and omit an SRB4 configuration. For example, base station <NUM> may determine to provide a full configuration or delta configuration when base station <NUM> does not recognize at least one configuration (e.g., an SRB4 configuration) associated with the connection between UE <NUM> and base station <NUM>, or when base station <NUM> determines to conserve processing resources by not filtering through the configuration(s) associated with the connection between UE <NUM> and base station <NUM>. As another example, base station <NUM> may simply be operated by a different vendor than that of base station <NUM>.

The base station <NUM> includes a full configuration or delta configuration and omits an SRB4 configuration in a Handover Command message, and subsequently transmits <NUM> a Handover Request Acknowledge message including the Handover Command message to base station <NUM>, which in turn transmits <NUM> the Handover Command message to UE <NUM>, similar to events <NUM> and <NUM>.

Similar to events <NUM> and <NUM>, the Handover Command message causes UE <NUM> to release <NUM> the SRB4 and apply <NUM> the DRB configuration indicated in the Handover Command message. Accordingly, and advantageously, UE <NUM> validates the Handover Command message because the logical channel identity value associated with the DRB configuration is only associated with the DRB configuration and not the SRB4 configuration. In some embodiments, UE <NUM> can also release the measurement configuration provided by base station <NUM> at event <NUM>.

In other embodiments, in response to the Handover Request message, base station <NUM> determines <NUM> to include the full configuration or delta configuration and include the SRB4 configuration in a Handover Command message, and subsequently transmits <NUM> a Handover Request Acknowledge message including the Handover Command message to base station <NUM>, which in turn transmits <NUM> the Handover Command message to UE <NUM>, similar to events <NUM> and <NUM>. However, in contrast to events <NUM> and <NUM>, the Handover Command message causes UE <NUM> to reconfigure <NUM> the SRB4 in view of the SRB4 configuration indicated in the Handover Command message. It should be noted that UE <NUM> may reconfigure the existing SRB4 maintained by base station <NUM> into the new SRB4 configuration provided by base station <NUM>, or release the existing SRB4 and apply the new SRB4 configuration provided by the base station <NUM>, and optionally keep the previous SRB4 configuration as-is, in addition to the new SRB4 configuration. Accordingly, and advantageously, because both UE <NUM> and base station <NUM> are configured to communicate via the new SRB4, UE <NUM> is able to communicate with base station <NUM> via the new SRB.

In response to either applying <NUM> the DRB configuration or reconfiguring <NUM> the SRB, UE <NUM> transmits <NUM> a Handover Complete message to base station <NUM>, similar to event <NUM>. Accordingly, UE <NUM> operates <NUM> in a connected state with base station <NUM> via the DRB or the new SRB, and therefore UE <NUM> and base station <NUM> can communicate via the DRB or the new SRB.

Turning now to <FIG>, at the beginning of a scenario <NUM>, UE <NUM> and base station <NUM> perform <NUM> a measurement procedure, similar to event <NUM> discussed above. Similar to event <NUM> discussed above, base station <NUM> determines <NUM> to handover UE <NUM> to base station <NUM>. Base station <NUM> includes the SRB4 configuration in a Handover Request message, and subsequently transmits <NUM> the Handover Request message to base station <NUM>, similar to event <NUM>.

In response to the Handover Request message, base station <NUM>, which does not support SRB4 in scenario <NUM>, determines <NUM> to omit the SRB4 configuration and include a DRB configuration for UE <NUM>. Base station <NUM> omits an SRB4 configuration and includes a configuration for a DRB in a Handover Command message, and subsequently transmits <NUM> a Handover Request Acknowledge message including the Handover Command message to base station <NUM>, similar to event <NUM>. In turn, base station <NUM> transmits <NUM> the Handover Command message to UE <NUM>, similar to event <NUM>.

In response, UE <NUM> and base station <NUM> proceed to events <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

In some embodiments, in response to the Handover Request message, base station <NUM> determines <NUM> to provide an SRB4 release indication or omit an SRB4 kept indication for UE <NUM>. Base station <NUM> includes an SRB4 release indication and omits an SRB4 kept indication in a dedicated field of a Handover Command message, and subsequently transmits <NUM> a Handover Request Acknowledge message including the Handover Command message to base station <NUM>, which in turn transmits <NUM> the Handover Command message to UE <NUM>, similar to events <NUM> and <NUM>. In response, UE <NUM> and base station <NUM> proceed to events <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

Although not illustrated, base station <NUM> instead of base station <NUM> may determine to provide the SRB4 release indication or omit the SRB4 kept indication for UE <NUM>. As such, base station <NUM> includes an SRB4 release indication and omits an SRB4 kept indication in the Handover Command message, and subsequently transmits the Handover Command message to UE <NUM>. Accordingly, because base station <NUM> communicates with UE <NUM> via base station <NUM>, base station <NUM> modifies the Handover Command message the base station <NUM> transmits to UE <NUM>.

In other embodiments, in response to the Handover Request message, base station <NUM> determines <NUM> to omit the SRB4 release indication and include the SRB4 kept indication in a Handover Command message, and subsequently transmits <NUM> a Handover Request Acknowledge message including the Handover Command message to base station <NUM>, which in turn transmits <NUM> the Handover Command message to UE <NUM>, similar to events <NUM> and <NUM>. In response, UE <NUM> and base station <NUM> proceed to events <NUM>, <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, <NUM>, and <NUM>.

Turning now to <FIG>, at the beginning of a scenario <NUM>, UE <NUM> and base stations <NUM>, <NUM> proceed to events <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In response to receiving <NUM> the Handover Command message, UE <NUM> proceeds to events <NUM>, <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, <NUM>, and <NUM>. As such, UE <NUM> releases SRB4 automatically in response to the Handover Command message or after the handover scenario is complete. For example, in embodiments in which the RATs of base station <NUM> and base station <NUM> are different, UE <NUM> releases SRB4 automatically due to inter-RAT handover from base station <NUM> to base station <NUM>.

Turning now to <FIG>, at the beginning of a scenario <NUM>, UE <NUM> and base station <NUM> perform <NUM> the measurement procedure, similar to event <NUM>. After a period of time, base station <NUM> may determine <NUM> to not only handover UE <NUM> to base station <NUM>, but also release SRB4. In other words, base station <NUM> may determine to handover UE <NUM> to base station <NUM> and release SRB4 if an SRB4 release condition is the same as a handover condition. For example, when base station <NUM> receives an indication that a measurement result for cell <NUM> or <NUM> at the UE <NUM> satisfies a certain threshold (e.g., a fixed threshold, an offset value), base station <NUM> determines that the measurement result satisfies the handover condition as well as the SRB4 release condition, and subsequently sends <NUM> the RRC reconfiguration message (e.g., an RRCConnectionReconfiguration message or an RRCReconfiguration message) to UE <NUM>, to cause UE <NUM> to release <NUM> the SRB4. Base station <NUM> may include a dedicated field (e.g., a SRB4 release indicator, a srb-ToReleaseListExt-r15 or a SRB4 configuration) in the RRC Reconfiguration message to cause UE <NUM> to release SRB4. Subsequently, base station <NUM> sends <NUM> the Handover Request message to base station <NUM>.

In one implementation, the measurement result indicates signal strength or quality for cell <NUM> satisfies a threshold. For example, the measurement result may include an event identity indicating an event. The event can be Event A3 (indicating a neighbor cell becomes better than a serving cell (e.g., primary cell (PCell), primary SCell (PSCell)) by an offset), Event A4 (indicating a neighbor cell becomes better than a threshold), or Event A5 (a serving cell becomes worse than a first threshold and a neighbor cell becomes better than a second threshold). In another example, the measurement result may include a value of the signal strength or quality for cell <NUM> (e.g., reference signal received power (RSRP), reference signal received quality (RSRQ) or signal to noise and interference ratio (SINR)). In response to determining that the measurement result indicating cell <NUM> signal strength or quality satisfies a threshold, the base station <NUM> decides to hand over UE <NUM> to base station <NUM>. In response to the handover decision, the base station <NUM> decides to release the SRB4 configuration before handing over UE <NUM> to base station <NUM>. In some implementations, the offset and/or threshold may be predetermined by base station <NUM>. In some implementations, base station <NUM> may transmit the offset and/or threshold to UE <NUM>.

In another implementation, the measurement result indicates signal strength or quality for cell <NUM> does not satisfy a threshold. For example, the measurement result may include an event identity indicating an event. The event can be Event A2 (indicating a serving cell becomes worse than a threshold). In another example, the measurement result may include a value of the signal strength or quality for cell <NUM> (e.g., RSRP, RSRQ or SINR). In response to determining that the measurement result indicating signal strength or quality for cell <NUM> does not satisfy the threshold, base station <NUM> decides to release the SRB4 and hand over UE <NUM> to base station <NUM> (i.e., always release SRB4 upon handover). In some implementations, the threshold may be predetermined by base station <NUM>. In some implementations, base station <NUM> may transmit the threshold to UE <NUM>.

In other implementations, base station <NUM> can determine that it should release the SRB4 if the SRB4 release condition is similar but not identical to the handover condition. For example, with reference to <FIG>, when base station <NUM> receives an indication that a measurement result for cell <NUM> at the UE <NUM> satisfies a first predetermined threshold but does not satisfy a second predetermined threshold, the base station <NUM> determines <NUM> that the measurement result satisfies the SRB4 release condition but does not satisfy the handover condition. Base station <NUM> in this scenario sends <NUM> the RRC reconfiguration message to UE <NUM>. If the base station <NUM> subsequently determines <NUM> that the measurement result satisfies the second predetermined threshold, the base station <NUM> determines that the measurement result now satisfies the handover condition, and subsequently sends <NUM> the Handover Request message to base station <NUM>.

In one implementation, base station <NUM> receives a first measurement result indicating that signal strength or quality for cell <NUM> is below the first predetermined threshold and not yet below the second predetermined threshold. Based on the first measurement result, base station <NUM> determines that UE <NUM> may be leaving coverage of base station <NUM>. In response to the determination, base station <NUM> decides to release the SRB4 configuration. Subsequently, base station <NUM> receives a second measurement result indicating that signal strength or quality for cell <NUM> is below the second predetermined threshold. Based on the second measurement result, base station <NUM> decides to hand over UE <NUM> to base station <NUM>. For example, the first measurement result may include a first event identity indicating a first event. The first event can be Event A2 (indicating a serving cell becomes worse than the first predetermined threshold). The second measurement result may include a second event identity indicating a second event. The second event can be Event A2 (indicating a serving cell becomes worse than the second predetermined threshold). In some implementations, base station <NUM> may transmit the first predetermined threshold and/or the second predetermined threshold to UE <NUM>.

In another implementation, base station <NUM> receives a first measurement result indicating that signal strength or quality for cell <NUM> does not satisfy the first predetermined threshold. Based on the first measurement result, base station <NUM> determines that UE <NUM> may be leaving coverage of base station <NUM>. In response to the determination, base station <NUM> decides to release the SRB4 configuration. Subsequently, base station <NUM> receives a second measurement result indicating that signal strength or quality for cell <NUM> is above the second predetermined threshold. Based on the second measurement result, base station <NUM> decides to hand over UE <NUM> to base station <NUM>. For example, the first measurement result may include a first event identity indicating a first event. The first event can be Event A2 (indicating a serving cell becomes worse than the first predetermined threshold). The second measurement result may include a second event identity indicating a second event. The second event can be Event A2 (indicating a serving cell becomes worse than the second predetermined threshold). In some implementations, base station <NUM> may transmit the first predetermined threshold and/or the second predetermined threshold to UE <NUM>.

As such, base station <NUM> in scenarios illustrated in <FIG> and <FIG> may determine to release the SRB4 based on measurement results indicating signal strength or quality for cell <NUM> or cell <NUM>. In releasing the SRB4, base station <NUM> prevents radio bearer non-capability issues that may result when base station <NUM> does not recognize at least one configuration (e.g., an SRB4 configuration) associated with the connection between UE <NUM> and base station <NUM>. As another example, base station <NUM> may release SRB4 because base station <NUM> is operated by a different vendor than that of base station <NUM>.

In some implementations, base station <NUM> transmits <NUM> a Handover Request message to base station <NUM> after transmitting <NUM> the RRC Reconfiguration message to UE <NUM>. In other implementations, base station <NUM> transmits <NUM> the Handover Request message to base station <NUM> before transmitting <NUM> the RRC Reconfiguration message to UE <NUM>. In yet other implementations, base station <NUM> transmits the Handover Request message to base station <NUM> and the RRC Reconfiguration message to UE <NUM> at the same time.

In response to the Handover Request message, base station <NUM> may transmit <NUM> a Handover Request Acknowledge message to base station <NUM>.

In response to receiving <NUM> the RRC Reconfiguration message, UE <NUM> transmits <NUM> an RRC Reconfiguration Complete message (e.g., an RRCConnectionReconfigurationComplete message, an RRCReconfigurationComplete message) to base station <NUM>, thereby completing the SRB4 release. Base station <NUM> may receive the RRC Reconfiguration Complete message from UE <NUM> before receiving the Handover Request Acknowledge message (which includes a Handover Command message) from base station <NUM> (i.e., as illustrated in the scenario of <FIG>), after receiving the Handover Request Acknowledge message from base station <NUM> (not illustrated in <FIG>), depending on the relative completion timing at UE <NUM> and base station <NUM>, or after receiving the Handover Request Acknowledge message from base station <NUM> (i.e., as illustrated in the scenario of <FIG>).

Base station <NUM> transmits <NUM> the Handover Command message to UE <NUM> in response to receiving the RRC Reconfiguration Complete message (i.e., as illustrated in the scenario of <FIG>), before receiving the RRC Reconfiguration Complete message (not illustrated in <FIG>), or after receiving the RRC Reconfiguration Complete message (i.e., as illustrated in the scenario of <FIG>).

In response to receiving <NUM> the Handover Command message, UE <NUM> transmits <NUM> a Handover Complete message (e.g., an RRCConnectionReconfigurationComplete message, an RRCReconfigurationComplete message) to base station <NUM>, thereby completing the handover scenario. Accordingly, UE <NUM> operates <NUM> in a connected state with base station <NUM>.

Because base station <NUM> causes UE <NUM> to release SRB4, which base station <NUM> may not support, base station <NUM> avoids providing a configuration to UE <NUM> that could have conflicted with the released SRB4. That is, if base station <NUM> determines to configure UE <NUM> with a DRB configuration or a new SRB4 configuration (included in the Handover Command message, or separately in an RRC Reconfiguration message, similar to event <NUM>) associated with the same logical channel identity value as the released configured SRB4, UE <NUM> validates the Handover Command message or the RRC Reconfiguration message because the logical channel identity value associated with the DRB configuration or new SRB4 configuration is not associated with the released SRB4 configuration.

Turning now to <FIG>, at the beginning of a scenario <NUM>, UE <NUM> and base stations <NUM>, <NUM> proceed to events <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

After successful completion of the handover scenario, base station <NUM> determines <NUM> to omit an SRB4 support for UE <NUM> in some embodiments. Base station <NUM> omits an SRB4 support indication when broadcasting <NUM> system information to UE <NUM> and other UEs in the wireless communication system <NUM>. In response, UE <NUM> and base station <NUM> proceed to events <NUM>, <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, <NUM>, and <NUM>.

In other embodiments, in response to the Handover Request message, base station <NUM> determines <NUM> to include the SRB4 support indication for UE <NUM>. Base station <NUM> includes an SRB4 support indication when broadcasting <NUM> system information to UE <NUM> and other UEs in the wireless communication system <NUM>. In response, UE <NUM> and base station <NUM> proceed to events <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, and <NUM>.

Although base station <NUM> is illustrated as transmitting a Handover Request (events <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and receiving a Handover Request Acknowledge message (events <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) in <FIG> and <FIG>, base station <NUM> may alternatively transmit a Handover Required message and receive a Handover Confirm message. Specifically, base station <NUM> may transmit a Handover Required message to CN <NUM> (e.g., Access Management Function (AMF) and/or Mobility Management Entity (MME)) instead of sending the Handover Request message to base station <NUM>. In response, CN <NUM> may send a Handover Request message to base station <NUM>, which in turn may include the Handover Command message in a Handover Request Acknowledge message and send the Handover Request Acknowledge message to CN <NUM>. CN <NUM> in turn may include the Handover Command message in a Handover Confirm message and send the Handover Confirm message to base station <NUM>.

<FIG> generally illustrate example message flow diagrams of the re-establishment scenario between UE <NUM> and base stations <NUM>, <NUM> of wireless communication system <NUM>.

Turning now to <FIG>, at the beginning of a scenario <NUM>, UE <NUM> and base station <NUM> perform <NUM> a measurement procedure, similar to event <NUM> discussed above.

After a period of time, UE <NUM> detects <NUM> radio link failure (RLF) over the established connection with the base station <NUM>, or other failure (e.g., failure of a handover procedure between base stations <NUM>, <NUM>, failure to reconfigure SRB4), by receiving a message from either base station <NUM> or base station <NUM>. After detecting failure, UE <NUM> subsequently selects base station <NUM> for servicing by performing <NUM> an RRC connection re-establishment procedure with base station <NUM>. Base station <NUM> does not support SRB4 in scenario <NUM>. After performing the RRC connection re-establishment procedure successfully, UE <NUM> operates <NUM> in a connected state with base station <NUM>. Subsequently, base station <NUM> performs <NUM> a reconfiguration procedure, similar to event <NUM>, and therefore causes UE <NUM> to release a previously configured SRB4 maintained by base station <NUM> and apply a DRB configuration provided by base station <NUM>. Accordingly, UE <NUM> operates in a connected state with base station <NUM>, and therefore UE <NUM> and base station <NUM> can exchange data via the logical channel identity mapped to the DRB.

In some embodiments, base station <NUM> may perform <NUM> the reconfiguration procedure before UE <NUM> completes <NUM> the RRC connection re-establishment procedure (i.e., base station <NUM> transmits an RRC reconfiguration message to UE <NUM> after transmitting the RRC connection reestablishment message to UE <NUM> and before receiving the RRC connection reestablishment complete message from UE <NUM>).

Turning now to <FIG>, at the beginning of a scenario <NUM>, UE <NUM> and base stations <NUM>, <NUM> proceed to events <NUM>, <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, <NUM>, and <NUM>.

In some embodiments, base station <NUM> proceeds to event <NUM>, similar to event <NUM>, and subsequently transmits <NUM> an RRC Reconfiguration message including a full configuration or delta configuration and omitting an SRB4 configuration to UE <NUM>, similar to event <NUM>. In response, UE <NUM> proceeds to events <NUM> and <NUM>, similar to events <NUM>, <NUM>.

In other embodiments, base station <NUM> proceeds to event <NUM>, similar to event <NUM>, and subsequently transmits <NUM> an RRC Reconfiguration message including a full configuration or delta configuration and including an SRB4 configuration to UE <NUM>, similar to event <NUM>. In response, UE <NUM> proceeds to event <NUM>, similar to event <NUM>.

In response to either applying <NUM> the DRB configuration or reconfiguring <NUM> the SRB, UE <NUM> transmits <NUM> an RRC connection reconfiguration complete to base station <NUM>, similar to event <NUM>. Accordingly, UE <NUM> operates <NUM> in a connected state with base station <NUM> via the DRB or the SRB, and therefore UE <NUM> and base station <NUM> can communicate <NUM> via the DRB or the SRB, similar to events <NUM> and <NUM>.

In some embodiments, base station <NUM> proceeds to event <NUM>, similar to event <NUM>, and subsequently transmits <NUM> an RRC Reconfiguration message omitting an SRB4 configuration indication to UE <NUM>, similar to event <NUM>. In response, UE <NUM> proceeds to events <NUM> and <NUM>, similar to events <NUM> and <NUM>.

In other embodiments, base station <NUM> determines <NUM> to include the SRB4 configuration for UE <NUM>. Base station <NUM> includes an SRB4 configuration in an RRC Reconfiguration message, and subsequently transmits <NUM> the RRC Reconfiguration message to UE <NUM>, similar to event <NUM>. In response, UE <NUM> reconfigures <NUM> the SRB4.

In some embodiments, base station <NUM> proceeds to event <NUM>, similar to event <NUM>, and subsequently transmits <NUM> an RRC Reconfiguration message including an SRB4 release indication or omitting an SRB4 kept indication to UE <NUM>, similar to event <NUM>. In response, UE <NUM> proceeds to events <NUM> and <NUM>, similar to events <NUM>, <NUM>.

In other embodiments, base station <NUM> proceeds to event <NUM>, similar to event <NUM>, and subsequently transmits <NUM> an RRC Reconfiguration message omitting an SRB4 release indication or including an SRB4 kept indication to UE <NUM>, similar to event <NUM>. In response, UE <NUM> proceeds to event <NUM>, similar to event <NUM>.

Turning now to <FIG>, at the beginning of a scenario <NUM>, UE <NUM> and base stations <NUM>, <NUM> proceed to events <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, and <NUM>. After performing the RRC connection re-establishment procedure successfully, UE <NUM> proceeds to events <NUM>, <NUM>, and <NUM> similar to events <NUM>, <NUM>, and <NUM>. As such, UE <NUM> releases SRB4 automatically in response to the RRC connection re-establishment procedure or after the re-establishment scenario is complete.

<FIG> and <FIG> generally illustrate example message flow diagrams of the re-selection scenario between UE <NUM> and base stations <NUM>, <NUM> of wireless communication system <NUM>.

Turning now to <FIG>, at the beginning of a scenario <NUM>, UE <NUM> and base station <NUM> perform <NUM> the measurement procedure, similar to event <NUM>. After a period of time, base station <NUM> may detect that below-threshold or no-data activity for UE <NUM> has occurred over some interval of time over the established connection. Upon this detection, base station <NUM> instructs UE <NUM> to enter into an inactive state of the RAT protocol (e.g., EUTRA-RRC INACTIVE, NR-RRC INACTIVE) by transmitting <NUM> an RRC Inactive message (e.g., an RRCConnectionRelease message or an RRCRelease message) to UE <NUM>. In some embodiments, the RRCConnectionRelease message includes an rrc-InactiveConfig field and the RRCRelease message includes a suspendConfig field.

In response to the RRC Inactive message, UE <NUM> enters <NUM> the inactive state.

At some point in time thereafter, such as when UE <NUM> has moved into a different coverage area and has payload data to transmit to the wireless communication system <NUM>, UE <NUM> (which is in the inactive state) selects or reselects base station <NUM> for servicing by performing <NUM> a (re)selection procedure. After UE <NUM> selects or reselects base station <NUM>, UE <NUM> determines to perform <NUM> an RRC connection resume procedure with base station <NUM>, such as by transmitting a NAS message to base station <NUM> or performing a RAN Notification Area (RNA) update. UE <NUM> transmits <NUM> an RRC Resume Request message (e.g., an RRCConnectionResumeRequest message or an RRCResumeRequest message) to base station <NUM>.

In response, base station <NUM> determines <NUM> to configure UE <NUM> with a DRB configuration associated with the same logical channel identity value as the configured SRB4, similar to event <NUM>, either because base station <NUM> does not support or is otherwise unaware of the configured SRB, or because base station <NUM> supports the configured SRB4 yet intends to release the configured SRB4 (i.e., hence the logical channel identity value that was assigned to the configured SRB4 is available for proper use by base station <NUM>). Base station <NUM> includes a configuration for a DRB in an RRC Resume message (e.g., an RRCConnectionResume message or an RRCResume message), and subsequently transmits <NUM> the RRC Resume message to UE <NUM>.

The RRC Resume message causes UE <NUM> to release <NUM> the SRB4 and apply <NUM> the DRB configuration indicated in the RRC Resume message, similar to events <NUM> and <NUM>. Accordingly, and advantageously, UE <NUM> validates the RRC Resume message because the logical channel identity value associated with the DRB configuration is only associated with the DRB configuration and not the SRB4 configuration. In some embodiments, UE <NUM> can also release the measurement configuration provided by base station <NUM> at event <NUM>.

In turn, UE <NUM> transmits <NUM> an RRC Resume Complete message (e.g., an RRCConnectionResumeComplete message, an RRCResumeComplete message) to base station <NUM>, thereby successfully completing the re-selection scenario. Accordingly, UE <NUM> operates <NUM> in a connected state with base station <NUM>, and therefore UE <NUM> and base station <NUM> can exchange <NUM> data via the logical channel identity mapped to the DRB, similar to events <NUM> and <NUM>.

Although <FIG> illustrates that event <NUM> occurs before UE <NUM> completes the RRC connection resume procedure, in some embodiments, base station <NUM> may determine <NUM> to configure UE <NUM> with a DRB configuration associated with the same logical channel identity value as the configured SRB4 after UE <NUM> completes the RRC Resume procedure (i.e., after base station <NUM> transmits <NUM> the RRC Resume message or receives <NUM> the RRC Resume Complete message), similar to event <NUM> of the reconfiguration procedure illustrated in <FIG>. Subsequently, base station <NUM> may perform the remainder of the reconfiguration procedure, to cause UE <NUM> to release a previously configured SRB4 maintained by base station <NUM> and apply a DRB configuration provided by base station <NUM>.

Turning now to <FIG>, at the beginning of a scenario <NUM>, UE <NUM> and base stations <NUM>, <NUM> proceed to events <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

In some embodiments, base station <NUM> proceeds to event <NUM>, similar to event <NUM>, and subsequently transmits <NUM> an RRC Resume message including a full configuration or delta configuration and omitting an SRB4 configuration to UE <NUM>, similar to event <NUM>. In response, UE <NUM> proceeds to events <NUM> and <NUM>, similar to events <NUM> and <NUM>.

In yet other embodiments, base station <NUM> proceeds to event <NUM>, similar to event <NUM>, and subsequently transmits <NUM> an RRC Resume message including a full configuration or delta configuration and including an SRB4 configuration to UE <NUM>, similar to event <NUM>. In response, UE <NUM> proceeds to event <NUM>, similar to event <NUM>.

Although <FIG> illustrates that event <NUM> (or <NUM>) may occur before UE <NUM> completes the RRC connection resume procedure, in other embodiments, base station <NUM> may determine <NUM>, <NUM> to configure UE <NUM> with a full configuration or delta configuration and omit (or include) an SRB4 configuration after UE <NUM> completes the RRC Resume procedure (i.e., after base station <NUM> transmits <NUM> (or <NUM>) the RRC Resume message or receives <NUM> the RRC Resume Complete message from UE <NUM>), similar to event <NUM> (or <NUM>), and subsequently transmit an RRC Reconfiguration message, including a full configuration or delta configuration and omitting (or including) an SRB4 configuration, to UE <NUM>, similar to event <NUM> (or <NUM>) after UE <NUM> completes the RRC resume procedure. In response, UE <NUM> proceeds to event <NUM> (or <NUM>).

In response to either applying <NUM> the DRB configuration or reconfiguring <NUM> the SRB, UE <NUM> transmits <NUM> an RRC Resume Complete message to base station <NUM>, similar to event <NUM>. Accordingly, UE <NUM> operates <NUM> in a connected state with base station <NUM> via the DRB or the SRB, and therefore UE <NUM> and base station <NUM> can communicate <NUM> via the DRB or the SRB, similar to events <NUM> and <NUM>.

In some embodiments, base station <NUM> proceeds to event <NUM>, similar to event <NUM>, and subsequently transmits <NUM> an RRC Resume message omitting an SRB4 configuration to UE <NUM>, similar to event <NUM>. In response, UE <NUM> proceeds to events <NUM> and <NUM>, similar to events <NUM> and <NUM>.

In other embodiments, base station <NUM> proceeds to event <NUM>, similar to event <NUM>, and subsequently transmits <NUM> an RRC Resume message including an SRB4 configuration to UE <NUM>, similar to event <NUM>. In response, UE <NUM> proceeds to event <NUM>, similar to event <NUM>.

Although <FIG> illustrates that event <NUM> (or <NUM>) may occur before UE <NUM> completes the RRC connection resume procedure, in other embodiments, base station <NUM> may determine <NUM>, <NUM> to omit (or include) an SRB4 configuration after UE <NUM> completes the RRC Resume procedure (i.e., after base station <NUM> transmits <NUM> (or <NUM>) the RRC Resume message or receives <NUM> the RRC Resume Complete message from UE <NUM>), similar to event <NUM> (or <NUM>), and subsequently transmit an RRC Reconfiguration message, omitting (or including) an SRB4 configuration, to UE <NUM>, similar to event <NUM> (or <NUM>) after UE <NUM> completes the RRC resume procedure. In response, UE <NUM> proceeds to event <NUM> (or <NUM>).

In some embodiments, base station <NUM> proceeds to event <NUM>, similar to event <NUM>, and subsequently transmits <NUM> an RRC Resume message including an SRB4 release indication or omitting an SRB4 kept indication to UE <NUM>, similar to event <NUM>. In response, UE <NUM> proceeds to events <NUM> and <NUM>, similar to events <NUM> and <NUM>.

In other embodiments, base station <NUM> proceeds to event <NUM>, similar to event <NUM>, and subsequently transmits <NUM> an RRC Resume message omitting an SRB4 release indication or including an SRB4 kept indication to UE <NUM>, similar to event <NUM>. In response, UE <NUM> proceeds to event <NUM>, similar to event <NUM>.

Although <FIG> illustrates that event <NUM> (or <NUM>) may occur before UE <NUM> completes the RRC connection resume procedure, in other embodiments, base station <NUM> may determine <NUM>, <NUM> to include (or omit) an SRB4 release indication or omit (or include) an SRB4 kept indication after UE <NUM> completes the RRC Resume procedure (i.e., after base station <NUM> transmits <NUM> (or <NUM>) the RRC Resume message or receives <NUM> the RRC Resume Complete message from UE <NUM>), similar to event <NUM> (or <NUM>), and subsequently transmit an RRC Reconfiguration message, including (or omitting) an SRB4 release indication or omitting (or including) an SRB4 kept indication, to UE <NUM>, similar to event <NUM> (or <NUM>) after UE <NUM> completes the RRC resume procedure. In response, UE <NUM> proceeds to event <NUM> (or <NUM>).

Turning now to <FIG>, at the beginning of a scenario <NUM>, UE <NUM> and base stations <NUM>, <NUM> proceed to events <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In other embodiments, UE <NUM> may determine <NUM> to perform the RRC connection resume procedure after transmitting <NUM> the RRC resume request message to base station <NUM>.

After performing the RRC connection resume procedure successfully, UE <NUM> proceeds to events <NUM> and <NUM>, similar to events <NUM> and <NUM>. In turn, UE <NUM> and base station <NUM> proceed to events <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. As such, UE <NUM> releases SRB4 automatically after the re-selection scenario is complete.

In other embodiments, UE <NUM> releases SRB4 in response to the RRC connection resume procedure (e.g., after UE <NUM> receives <NUM> the RRC resume message from base station <NUM> or after UE <NUM> transmits <NUM> the RRC Resume complete message to base station <NUM>).

Turning now to <FIG>, at the beginning of a scenario <NUM>, UE <NUM> and base station <NUM> perform <NUM> the measurement procedure, similar to event <NUM>. After a period of time, base station <NUM> may determine <NUM> to not only instruct UE <NUM> to enter into an inactive state of the RAT protocol, but also release SRB4. In other words, base station <NUM> may determine that it should release SRB4 if an SRB4 release condition is the same as an inactive condition. For example, when base station <NUM> detects that data activity for UE <NUM> is below a first threshold over a first interval of time over the established connection, the data activity satisfies the inactive condition (and also the SRB4 release condition), and accordingly base station <NUM> sends <NUM> the RRC Reconfiguration message (e.g., an RRCConnectionReconfiguration message or an RRCReconfiguration message) to UE <NUM>, similar to event <NUM>, to cause UE <NUM> to release <NUM> SRB4. After releasing SRB4, UE <NUM> transmits <NUM> an RRC Reconfiguration Complete message (e.g., an RRCConnectionReconfigurationComplete message, an RRCReconfigurationComplete message) to base station <NUM>, similar to event <NUM>, thereby completing the SRB4 release. In addition, base station <NUM> sends <NUM> the RRC Inactive message to UE <NUM> to instruct UE <NUM> to enter into an inactive state of the RAT protocol (e.g., EUTRA-RRC INACTIVE, NR-RRC INACTIVE), similar to event <NUM>.

In other implementations, base station <NUM> determines to release SRB4 if the SRB4 release condition is similar but not identical to the inactive condition. For example, with reference to <FIG>, when base station <NUM> detects that data activity for UE <NUM> is below the first threshold over the first interval of time and above a second threshold over a second interval of time (where the second interval of time may be shorter than the first interval of time) over the established connection, base station <NUM> determines <NUM> that the data activity satisfies the SRB4 release condition, but does not satisfy the inactive condition, and accordingly base station <NUM> sends <NUM> the RRC reconfiguration message to UE <NUM>, similar to event <NUM>, to cause UE <NUM> to release <NUM> SRB4. After releasing SRB4, UE <NUM> transmits <NUM> an RRC Reconfiguration Complete message (e.g., an RRCConnectionReconfigurationComplete message, an RRCReconfigurationComplete message) to base station <NUM>, similar to event <NUM>, thereby successfully completing the SRB4 release. If the base station <NUM> subsequently detects that data activity for UE <NUM> is below the second threshold over the second interval of time over the established connection, the base station <NUM> determines <NUM> that the data activity satisfies the inactive condition, and accordingly, base station <NUM> sends <NUM> the RRC Inactive message to UE <NUM>, similar to event <NUM>, to instruct UE <NUM> to enter into an inactive state of the RAT protocol (e.g., EUTRA-RRC INACTIVE, NR-RRC INACTIVE).

Now referring to the scenario of <FIG>, when base station <NUM> in another implementation determines that the data activity satisfies the inactive condition (and also the SRB4 release condition), base station <NUM> may send <NUM> an RRC Inactive message (e.g., an RRCConnectionRelease message or an RRCRelease message) to UE <NUM>, in contrast to event <NUM> of <FIG> and similar to event <NUM> in <FIG>, to cause UE <NUM> to release <NUM> SRB4. Base station <NUM> may include a dedicated field (e.g., a SRB4 release indicator, a srb-ToReleaseListExt-r15 or a SRB4 configuration) in the RRC Inactive message to instruct UE <NUM> to enter into an inactive state of the RAT protocol (e.g., EUTRA-RRC INACTIVE, NR-RRC INACTIVE). After releasing SRB4, UE <NUM> may optionally transmit a confirmation message to base station <NUM>.

Referring now to <FIG>, <FIG>, and <FIG>, after UE <NUM> receives the RRC Inactive message, UE <NUM> and base stations <NUM>, <NUM> proceed to events <NUM>, <NUM>, <NUM>, and <NUM>, similar to events <NUM>, <NUM>, <NUM>, and <NUM>.

In response to the RRC Resume Request message, base station <NUM> sends <NUM> a Retrieve UE Context Request message to base station <NUM> to retrieve a UE context of UE <NUM>. In response, base station <NUM> sends <NUM> a Retrieve UE Context Response message including the UE context. In response to the Retrieve UE Context Response message, base station <NUM> sends <NUM> an RRC Resume message to UE <NUM>, similar to event <NUM>. In response, UE <NUM> operates <NUM> in a connected state with base station <NUM> and transmits <NUM> an RRC Resume Complete message (e.g., an RRCConnectionResumeComplete message or an RRCResumeComplete message) to base station <NUM>, thereby successfully completing the re-selection scenario.

Because base station <NUM> causes UE <NUM> to release SRB4, which base station <NUM> may not support, base station <NUM> does not receive the SRB4 configuration from base station <NUM> in event <NUM>, and further avoids providing a configuration to UE <NUM> that could have conflicted with the released SRB4. That is, if base station <NUM> determines to configure UE <NUM> with a DRB configuration or new SRB4 configuration (included in the RRC Resume message at event <NUM>, or separately in an RRC Reconfiguration message, similar to event <NUM>) associated with the same logical channel identity value as the released SRB4, UE <NUM> validates the RRC Resume message or the RRC Reconfiguration message because the logical channel identity value associated with the DRB configuration or new SRB4 configuration is not associated with the released SRB4 configuration.

<FIG> generally illustrate example message flow diagrams for managing radio bearers in view of a particular triggering event.

Turning now to <FIG>, method <NUM> releases or reconfigures an SRB4 in view of inclusion and/or exclusion of a particular type of configuration indication, which can be implemented in base stations <NUM>, <NUM> of <FIG>.

The method <NUM> begins at block <NUM>, where a first base station (e.g., base station <NUM>) transmits a first message (e.g., RRC Reconfiguration message) that includes an SRB4 configuration to the UE (e.g., UE <NUM>) (event <NUM> of <FIG>).

At block <NUM>, a second base station (e.g., base station <NUM>) determines to send a second message (e.g., Handover Command message, RRC Reconfiguration message, RRC Resume message) to configure the UE (events <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> of <FIG>, <FIG>, <FIG>, and <FIG>).

At block <NUM>, if the second base station determines to request the UE to release the SRB, the second base station at block <NUM> can (i) include indication of a DRB configuration associated with same logical identity as the SRB4 configuration in the second message (events <NUM>, <NUM>, and <NUM> of <FIG>, <FIG>, and <FIG>); and/or (ii) include a full configuration or delta configuration and omit an SRB4 configuration in the second message (events <NUM>, <NUM>, and <NUM> of <FIG>, <FIG>, and <FIG>); and/or (iii) omit an SRB4 configuration in the second message (events <NUM>, <NUM>, and <NUM> of <FIG>, <FIG>, and <FIG>); and/or (iv) include an SRB4 release indication in the second message (events <NUM>, <NUM>, and <NUM> of <FIG>, <FIG>, and <FIG>); and/or (v) omit an SRB4 kept indication in the second message (events <NUM>, <NUM>, and <NUM> of <FIG>, <FIG>, and <FIG>).

If the second base station determines to request the UE to reconfigure the SRB4, the second base station at block <NUM> can (i) include a full configuration or delta configuration and an SRB4 configuration in the second message (events <NUM>, <NUM>, and <NUM> of <FIG>, <FIG>, and <FIG>); and/or (ii) include an SRB4 configuration in the second message (events <NUM> and <NUM> of <FIG> and <FIG>); and/or (iii) omit an SRB4 release indication in the second message (events <NUM>, <NUM>, and <NUM> of <FIG>, <FIG>, and <FIG>); and/or (iv) include an SRB4 kept indication in the second message (events <NUM>, <NUM>, and <NUM> of <FIG>, <FIG>, and <FIG>).

Turning now to <FIG>, method <NUM> automatically releases an SRB4 in view of a type of procedure, which can be implemented in either UE <NUM> or base station <NUM> of <FIG>.

The method <NUM> begins at block <NUM>, where a first base station (e.g., base station <NUM>) transmits a first message (e.g., RRC Reconfiguration message) that includes an SRB4 configuration, and the UE (e.g., UE <NUM>) receives the first message (event <NUM> of <FIG>).

At block <NUM>, either the first base station or UE performs a procedure. For example, as illustrated in <FIG>, base station <NUM> performs a handover procedure at event <NUM>. As illustrated in <FIG>, UE <NUM> performs an RRC connection re-establishment procedure at event <NUM>. As illustrated in <FIG>, UE <NUM> performs an RRC connection resume procedure.

At block <NUM>, if the first base station or UE performs at least one of the handover procedure, RRC connection re-establishment procedure, or RRC connection resume procedure, the UE at block <NUM> automatically releases SRB4 (events <NUM>, <NUM>, and <NUM> of <FIG>, <FIG>, and <FIG>). Otherwise, the method <NUM> ends or proceeds back to block <NUM>.

Turning now to <FIG>, method <NUM> releases or reconfigures an SRB4 in view of inclusion and/or exclusion of a particular type of indication in system information, which can be implemented in either UE <NUM> or base stations <NUM>, <NUM> of <FIG>.

At block <NUM>, after the first base station successfully performs a handover procedure, so that the UE establishes a connection with a second base station (e.g., base station <NUM>), the second base station transmits or broadcasts system information, and the UE receives the system information (events <NUM>, <NUM> of <FIG>).

At block <NUM>, if the second base station determines to omit an SRB4 support indication in the system information, the UE at block <NUM> releases SRB4 (event <NUM> of <FIG>). At block <NUM>, if the second base station determines to include an SRB4 support indication in the system information, the UE at block <NUM> reconfigures the SRB4 (event <NUM> of <FIG>).

Turning now to <FIG>, method <NUM> releases an SRB4 in view of whether an SRB4 release condition is satisfied, which can be implemented in base station <NUM> of <FIG>.

The method <NUM> begins at block <NUM>, where a first base station (e.g., base station <NUM>) transmits a first message (e.g., RRC Reconfiguration message) that includes an SRB4 configuration, similar to blocks <NUM>, <NUM>, and <NUM> (events <NUM>, <NUM>, <NUM> of <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>).

At block <NUM>, the first base station detects that an SRB4 release condition is satisfied (and optionally, at block <NUM>, detect whether a handover condition or inactive condition is also satisfied) (events <NUM>, <NUM>, <NUM>, <NUM> of <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>). The first base station may continue to perform the detection at block <NUM> until the first base station detects that either the handover condition or inactive condition is satisfied.

In response, the first base station at block <NUM> sends a message (e.g., an RRC Reconfiguration message, an RRC Inactive message) to a UE (e.g., UE <NUM>) to cause the UE to release SRB4 (events <NUM>, <NUM>, <NUM> of <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>).

In some embodiments, when the first base station at block <NUM> optionally detects whether the handover condition or inactive condition is satisfied, the first base station at block <NUM> may determine that a handover condition is satisfied after block <NUM>, and proceed to determine at block <NUM> to handover the UE to a second base station (e.g., base station <NUM>) (event <NUM> of <FIG>). The first base station may continue to perform the detection at block <NUM> until the first base station detects that a handover condition is satisfied.

Alternatively, the first base station at block <NUM> may instead determine that an inactive condition is satisfied after block <NUM>, and proceed to determine at block <NUM> to instruct the UE to enter into an inactive state (event <NUM> of <FIG>). The first base station may continue to perform the detection at block <NUM> until the first base station detects that an inactive condition is satisfied.

<FIG> depicts an example method <NUM> for managing radio bearers, which can be implemented in RAN <NUM> of <FIG>, which includes first base station <NUM> that supports radio bearers of a first type and second base station <NUM> that does not support radio bearers of the first type.

The method <NUM> begins at block <NUM>, where a RAN determines that a UE (e.g., UE <NUM>) configured with a first radio bearer of the first type, the radio bearer terminated at the first base station, is to obtain a radio connection to the second base station (events <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> of <FIG> and <FIG>). Subsequently, the RAN at block <NUM> sends a message to cause the UE to release the first radio bearer and establish a second radio bearer of a second type, terminated at the second base station (events <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> of <FIG> and <FIG>).

<FIG> depicts an example method <NUM> for managing radio bearers, which can be implemented in UE <NUM> of <FIG>.

The method <NUM> begins at block <NUM>, where a UE communicates with a first base station over a first radio bearer associated with a dedicated control channel and configured to carry at least application-layer measurement reporting information, the radio bearer associated with a logical channel identity (events <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> of <FIG> and <FIG>, <FIG>). Subsequently, the UE at block <NUM> receives, from a RAN including the first base station and a second base station, a message related to (i) the first radio bearer or (ii) a second radio bearer having the logical channel identity and terminated at the second base station (events <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, <NUM>, and <NUM> of <FIG> and <FIG>, <FIG>). In response to the message, the UE at block <NUM> releases or reconfigures the first radio bearer (events <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, and <NUM> of <FIG> and <FIG>, <FIG>).

The following additional considerations apply to the foregoing discussion.

A user device in which the techniques of this disclosure can be implemented (e.g., the UE <NUM>) can be any suitable device capable of wireless communications such as a smartphone, a tablet computer, a laptop computer, a mobile gaming console, a point-of-sale (POS) terminal, a health monitoring device, a drone, a camera, a media-streaming dongle or another personal media device, a wearable device such as a smartwatch, a wireless hotspot, a femtocell, or a broadband router. Further, the user device in some cases may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device can operate as an internet-of-things (IoT) device or a mobile-internet device (MID). Depending on the type, the user device can include one or more general-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc..

Certain embodiments are described in this disclosure as including logic or a number of components or modules. Modules may can be software modules (e.g., code, or machine-readable instructions stored on non-transitory machine-readable medium) or hardware modules. A hardware module is a tangible unit capable of performing certain operations and may be configured or arranged in a certain manner. A hardware module can include dedicated circuitry or logic that is permanently configured (e.g., as a special-purpose processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP)) to perform certain operations. A hardware module may also include programmable logic or circuitry (e.g., as encompassed within a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. The decision to implement a hardware module in dedicated and permanently configured circuitry, or in temporarily configured circuitry (e.g., configured by software) may be driven by cost and time considerations.

Claim 1:
A method in a User Equipment (UE) for managing radio bearers, the method comprising:
communicating (<NUM>), by the UE, with a first base station over a signaling radio bearer <NUM> (SRB4), associated with a logical channel identity;
receiving (<NUM>), by the UE from a radio access network (RAN) including the first base station and a second base station, a message related to a data radio bearer (DRB) having the logical channel identity and terminated at the second base station; and
releasing (<NUM>), by the UE, the SRB4 in response to the message.